Head-mounted display

Abstract

To provide a resin lens for a head-mounted display that can obtain clear images even in an optical system using polarized light.SOLUTION: A lens for a head-mounted display has an average of absolute values of the phase difference within an effective diameter is 5 nm or less. The content of a fluorescent substance determined, for a 2.0 mass% solution obtained by dissolving in chloroform, from the fluorescence intensity at a wavelength of 530 nm measured at an excitation wavelength 436 nm, by using a concentration-intensity conversion formula of an ethanol solution of fluorescein, is 0.1-4.0×10-9 mol / L.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a resin lens for a head-mounted display.

Background Art

[0002] In recent years, various electronic technologies such as VR (Virtual Reality) and AR (Augmented Reality) have been rapidly developing, and head-mounted display (HMD) products as their image display devices have begun to spread. Since a head-mounted display is an image display device used by wearing it on the head, it is required to be small and lightweight and have little discomfort when worn.

[0003] As a means for miniaturizing a head-mounted display, a method has been proposed in which a quarter-wave plate, a reflective polarizing plate, etc. are combined with a lens, and the polarization state of light after passing through the lens is changed to switch between reflection and transmission, thereby causing an image to make a round trip and a half in one lens. (Patent Documents 1 and 2). This method has the following mechanism, for example: a quarter-wave plate and a reflective polarizing plate are arranged on the back surface of a lens with a partially reflective coating on the front surface, and light incident as circularly polarized light from the front surface of the lens is converted into linearly polarized light by the quarter-wave plate after passing through the lens; this linearly polarized light is reflected by the reflective polarizing plate and is converted again by the quarter-wave plate into circularly polarized light opposite to the original one, and enters the lens from the back surface and reaches the partially reflective coating portion on the front surface; the light reflected by the partially reflective coating portion and exiting from the back surface of the lens becomes linearly polarized light with a direction 90° different from the original one by the quarter-wave plate, passes through the reflective polarizing plate, and enters the eye as an image. In this way, a high magnification and a wide viewing field can be obtained even in a thin optical module.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

[0005] However, in the above-described head-mounted display, when the polarization state changes while passing through the lens, for example, some light passes through the reflective polarizing plate after passing through the lens for the first time, and an image with a low magnification and an image with a high magnification overlap, making it difficult to obtain a clear image. Although a clear image can be obtained by using a glass lens with low birefringence, it is not desirable because the weight increases. Therefore, there is an urgent need to obtain a clear image even with a resin lens that is lightweight but generally prone to birefringence.

[0006] Accordingly, an object of the present invention is to provide a resin lens for a head-mounted display that can obtain a clear image even in an optical system using polarization. [Means for Solving the Problems]

[0007] As a result of intensive studies to solve the above problems, the inventors of the present invention have found that the retardation within the effective diameter caused by the birefringence of the resin lens, and more surprisingly, the content of the fluorescent substance contained in the resin lens affect the sharpness of the image of the head-mounted display, and thus have arrived at the present invention.

[0008] That is, the present invention is as follows. [1] A head-mounted display including a resin lens, wherein the resin lens, The average of the absolute value of the retardation within the effective diameter is 5 nm or less, wherein the resin lens, For a 2.0 mass% solution obtained by dissolving in chloroform, the content of the fluorescent substance determined using the concentration-intensity conversion formula of the ethanol solution of fluorescein from the fluorescence intensity at a wavelength of 530 nm when measured at an excitation wavelength of 436 nm is 0.1 to 4.0 × 10-9 is mol / L and the head-mounted display utilizes polarization and repeats reflection to allow image light to pass through the resin lens a plurality of times. A head-mounted display characterized by and [2] The head-mounted display according to claim 1, wherein a ratio (T450 / T680) of a transmittance (T450) at a wavelength of 450 nm to a transmittance (T680) at a wavelength of 680 nm of the resin lens is 0.98 or more. 3 wherein the resin lens, having a glass transition temperature (Tg) of more than 120°C and 160°C or less, [1] or [2] the head-mounted display described in and 4 wherein the resin lens, The absolute value of the photoelastic coefficient is 3.0×10 -12 Pa -1 or less, [1] any one of ~[3] the head-mounted display described in and 5 wherein the resin lens, including a methacrylic resin, the head-mounted display described in any one of [1] to 4 and 6 wherein the resin lens, The methacrylic resin includes a methacrylic resin having a structural unit (X) having a ring structure in the main chain, 5 the head-mounted display described in and 7 wherein the resin lens, The structural unit (X) includes at least one structural unit selected from the group consisting of a structural unit derived from an N-substituted maleimide monomer, a glutarimide-based structural unit, and a lactone ring structural unit, 6 the head-mounted display described in and 8 wherein the resin lens, The structural unit (X) includes a structural unit derived from an N-substituted maleimide monomer, 7 the head-mounted display described in​​​​​​​​​​​​​and 9 wherein the resin lens, The structural unit (X) contains a glutarimide-based structural unit. 7 The head-mounted display described in and

Advantages of the Invention

[0009] According to the present invention, it is possible to provide a resin lens for a head-mounted display that can obtain a clear image even in an optical system using polarization.

Brief Description of the Drawings

[0010]

Figure 1

Modes for Carrying Out the Invention

[0011] Hereinafter, modes for carrying out the present invention (hereinafter referred to as "the present embodiment") will be described in detail. However, the present invention is not limited to the following description and can be variously modified and implemented within the scope of the gist.

[0012] [Resin Lens for Head-Mounted Display] The resin lens for a head-mounted display according to the present embodiment has an average absolute value of retardation within the effective diameter of 5 nm or less, and for a 2.0 mass% solution obtained by dissolving in chloroform, the content of the fluorescent substance determined using the concentration-intensity conversion formula of the ethanol solution of fluorescein from the fluorescence intensity at a wavelength of 530 nm when measured at an excitation wavelength of 436 nm is 0.1 to 4.0×10 -9 mol / L.

[0013] -Retardation within the effective diameter- ​​​The resin lens for a head-mounted display in this embodiment has an average absolute value of retardation within the effective diameter of the resin lens of 5 nm or less, preferably 4 nm or less, and more preferably 3 nm or less. By having the average absolute value of retardation be 5 nm or less, the image can be clearly viewed without being doubled. Here, the effective diameter of the resin lens represents the range within which an image can be viewed when the lens is incorporated into the housing of the head-mounted display, and is shown as the diameter of a circle centered on the optical axis of the lens. When the range within which the image can be viewed is not a perfect circle, the minor axis is taken as the effective diameter. The retardation within the effective diameter of the resin lens can be specifically measured by the method described in the examples below.

[0014] - Content of fluorescent substance - The resin lens for a head-mounted display in this embodiment has a content of fluorescent substance determined using the concentration-intensity conversion formula for an ethanol solution of fluorescein from the fluorescence intensity at a wavelength of 530 nm when measured at an excitation wavelength of 436 nm for a 2.0 mass% solution obtained by dissolving the resin lens in chloroform, which is 0.1 to 4.0×10 -9 mol / L, preferably 0.2 to 3.5×10 -9 mol / L, more preferably 0.3 to 3.0×10 -9 mol / L, and even more preferably 0.3 to 2.5×10 -9 mol / L. By having the content of the fluorescent substance be below the above upper limit, the image can be clearly viewed without blurring. Also, by having the content of the fluorescent substance be above the above lower limit, it is possible to suppress the entry of light of low wavelengths that are harmful to the eyes into the eyes more than necessary. When the fluorescence intensity is high (when the content of the fluorescent substance is large), the reason why the image appears blurred is not clear. However, when fluorescence is generated by the light passing through the lens, it is presumed that the image appears blurred because light travels not only in the original direction of the transmitted light but also in other directions. Furthermore, in the lens for a head-mounted display that repeatedly transmits light through reflection using polarization, it is presumed that the blurring of the image becomes more prominent due to the increase in the optical path length through the lens and the further deviation from the original direction of light by the reflective polarizing plate or the partial reflection coating. Note that the content of the fluorescent substance can be specifically measured by the method described in the examples below.

[0015] - Glass transition temperature - The glass transition temperature (Tg) of the resin lens for a head-mounted display in the present embodiment is preferably above 120°C and below 160°C. It is preferable that the glass transition temperature of the resin lens for a head-mounted display exceeds 120°C from the viewpoints of heat resistance against heat generation from the electronic devices of the head-mounted display and the occurrence of photoelastic birefringence due to dimensional changes. The glass transition temperature (Tg) is more preferably 125°C or higher, and even more preferably 130°C or higher, from the viewpoint of dimensional stability at the use environment temperature. On the other hand, when the glass transition temperature (Tg) is 160°C or lower, extreme high-temperature melt processing can be avoided, thermal decomposition of resins and the like can be suppressed, and good products can be obtained. The glass transition temperature (Tg) is preferably 150°C or lower, and more preferably 140°C or lower, from the viewpoint of obtaining the above-described effects more effectively. Note that the glass transition temperature (Tg) can be determined by measuring in accordance with JIS-K7121. Specifically, it can be obtained by the method described in the examples below.

[0016] - Photoelastic coefficient C R - The photoelastic coefficient C of the resin lens for a head-mounted display of the present embodiment R The absolute value |C R | is 3.0×10-12 Pa -1 It is preferably the following, more preferably 2.0×10 -12 Pa -1 or less, and even more preferably 1.5×10 -12 Pa -1 or less, and still more preferably 1.0×10 -12 Pa -1 or less. There are descriptions in various documents regarding the photoelastic coefficient (see, for example, Chemical Review, No. 39, 1998 (published by the Academic Publishing Center)), and it is defined by the following formulas (i-a) and (i-b). The photoelastic coefficient C R The closer the value of is to zero, the smaller the birefringence change due to the external force. |C R | = |Δn| / σ R ···(i-a) |Δn| = |nx - ny| ···(i-b) (In the formula, C R is the photoelastic coefficient, σ R is the tensile stress, |Δn| is the absolute value of birefringence, nx is the refractive index in the stretching direction, and ny is the refractive index in the direction perpendicular to the stretching direction in the plane, respectively.) The absolute value |C R | of the photoelastic coefficient C R of the resin lens of this embodiment is 3.0×10 -12 Pa -1 or less, then the photoelastic birefringence caused by the stress generated when fixing the lens and the dimensional temperature change is sufficiently small, and a resin lens capable of obtaining a clear image can be obtained. In addition, the measurement of the photoelastic coefficient C R is performed by cutting the resin lens into small pieces and making it into a press film using a vacuum compression molding machine. Specifically, it can be obtained by the method described in the examples below.

[0017] -Light transmittance- For the resin lens for a head-mounted display according to this embodiment, regarding the light transmittance at the thickest part measured with a spectrocolorimeter under a D65 light source and a 10° field of view, the ratio (T450 / T680) of the transmittance (T450) at a wavelength of 450 nm to the transmittance (T680) at a wavelength of 680 nm is preferably 0.95 to 1.03, more preferably 0.97 to 1.01, and even more preferably 0.98 to 1.00. When the ratio (T450 / T680) is within the above range, an image with good color tone can be obtained. Specifically, the light transmittance can be measured by the method described in the examples below.

[0018] -Molecular weight and molecular weight distribution- The resin lens for a head-mounted display according to this embodiment preferably has a weight average molecular weight (Mw) in terms of polymethyl methacrylate measured by gel permeation chromatography (GPC) in the range of 80,000 to 170,000, more preferably in the range of 100,000 to 170,000, even more preferably in the range of 100,000 to 150,000, and even more preferably in the range of 120,000 to 150,000. When the weight average molecular weight (Mw) is within the above range, the balance between mechanical strength and fluidity is also excellent.

[0019] The weight average molecular weight (Mw), number average molecular weight (Mn), and Z average molecular weight (Mz) of the resin lens can be measured with the following apparatus and conditions. · Measuring apparatus: Gel Permeation Chromatography (HLC-8320GPC) manufactured by Tosoh Corporation · Measuring conditions: Column: One TSKguardcolumn SuperH-H, two TSKgel SuperHM-M, and one TSKgel SuperH2500 are connected in series in this order for use. Column temperature: 40 °C Developing solvent: Tetrahydrofuran, flow rate: 0.6 mL / min. As an internal standard, 2,6-di-t-butyl-4-methylphenol (BHT) is added at 0.1 g / L. Detector: RI (Differential Refractometer) detector Detection sensitivity: 3.0 mV / min Sample: 20 mL solution of 0.02 g resin lens in tetrahydrofuran Injection volume: 10 μL Standard sample for calibration curve: Use the following 10 kinds of polymethyl methacrylate (manufactured by Polymer Laboratories; PMMA Calibration Kit M-M-10) with known weight-average peak molecular weights and different molecular weights and monodisperse. Weight-average peak molecular weight (Mp) Standard sample 1 1,916,000 Standard sample 2 625,500 Standard sample 3 298,900 Standard sample 4 138,600 Standard sample 5 60,150 Standard sample 6 27,600 Standard sample 7 10,290 Standard sample 8 5,000 Standard sample 9 2,810 Standard sample 10 850 Under the above conditions, measure the RI detection intensity with respect to the elution time of the resin lens. Based on each calibration curve obtained by measuring the above standard samples for the calibration curve, determine the weight-average molecular weight (Mw), number-average molecular weight (Mn), and Z-average molecular weight (Mz) of the resin lens, and use these values to determine the molecular weight distribution (Mw / Mn) and (Mz / Mw).

[0020] - Methanol-insoluble matter - In this embodiment, the ratio of the amount of methanol-insoluble matter in the resin lens for a head-mounted display to 100% by mass of the total amount of the amount of methanol-insoluble matter and the amount of methanol-soluble matter is preferably 95% by mass or more, more preferably 95.5% by mass or more, still more preferably 96% by mass or more, even more preferably 96.5% by mass or more, particularly preferably 97% by mass or more, and most preferably 97.5% by mass or more. By setting the ratio of the amount of methanol-insoluble matter to 95% by mass or more, it is possible to suppress molding troubles such as the occurrence of silver streaks during injection molding. The methanol-insoluble matter and the methanol-soluble matter are obtained by dissolving the resin lens for a head-mounted display in chloroform to form a chloroform solution, then performing reprecipitation by dropping the solution into a large excess amount of methanol, separating the filtrate and the precipitate, and then drying each of them.

[0021] Specifically, it can be determined as follows. After dissolving 5 g of the resin lens in 100 mL of chloroform, the solution is placed in a dropping funnel and dropped into 1 L of methanol being stirred with a stirrer over about 1 hour to perform reprecipitation. After dropping the entire amount and allowing it to stand for 1 hour, suction filtration is performed using a membrane filter (manufactured by Advantec Toyo Co., Ltd., T050A090C) as the filter. The precipitate is vacuum dried at 60°C for 16 hours to obtain methanol-insoluble matter. Also, for the filtrate, using a rotary evaporator with a bath temperature of 40°C and gradually reducing the vacuum degree from the initial setting of 390 Torr to 30 Torr finally, after removing the solvent, the soluble matter remaining in the eggplant-shaped flask is recovered to obtain methanol-soluble matter. Weigh each of the mass of the methanol-insoluble matter and the mass of the methanol-soluble matter, and calculate the ratio (% by mass) (methanol-soluble matter ratio) of the amount of methanol-soluble matter to the total amount (100% by mass) of the amount of methanol-soluble matter and the amount of methanol-insoluble matter.

[0022] [Resin Composition] The resin lens for a head-mounted display of this embodiment preferably comprises a resin composition containing a methacrylic resin.

[0023] [Methacrylic resin] The methacrylic resin contained in the resin lens for a head-mounted display according to this embodiment preferably contains a methacrylic resin having a structural unit (X) having a ring structure in the main chain and a structural unit derived from a methacrylic acid ester monomer. By including a methacrylic resin, particularly a methacrylic resin containing a structural unit (X) having a ring structure in the main chain and a methacrylic acid ester monomer unit, a resin lens can be obtained in which the retardation within the effective diameter of the lens is sufficiently small and the photoelastic coefficient is also sufficiently small.

[0024] Hereinafter, each structural unit will be described.

[0025] - Structural unit derived from methacrylic acid ester monomer - Examples of the structural unit derived from a methacrylic acid ester monomer include structural units derived from monomers selected from the following methacrylic acid esters. Examples of the methacrylic acid ester include methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, cyclopentyl methacrylate, cyclohexyl methacrylate, cyclooctyl methacrylate, tricyclodecyl methacrylate, dicyclooctyl methacrylate, tricyclododecyl methacrylate, isobornyl methacrylate, phenyl methacrylate, benzyl methacrylate, 1-phenylethyl methacrylate, 2-phenoxyethyl methacrylate, 3-phenylpropyl methacrylate, 2,4,6-tribromophenyl methacrylate, and the like. These monomers may be used alone or in combination of two or more. The structural unit derived from the methacrylic acid ester monomer is preferably a structural unit derived from methyl methacrylate and benzyl methacrylate in terms of excellent transparency and weather resistance of the resulting methacrylic resin. The structural unit derived from the methacrylic acid ester monomer may contain only one kind or two or more kinds.

[0026] By appropriately adjusting the ratio between the structural unit (X) having a ring structure in the main chain and the structural unit derived from the methacrylic acid ester monomer in the resin lens for a head-mounted display of the present embodiment, birefringence caused by orientation and residual stress during molding can be reduced, and a resin lens for a head-mounted display with an average absolute value of the retardation within the effective diameter of 5 nm or less can be obtained. Further, by appropriately adjusting the above ratio, sufficient heat resistance can be imparted to the methacrylic resin. From these viewpoints, the content of the structural unit derived from the methacrylic acid ester monomer is preferably 50 to 97% by mass, more preferably 55 to 97% by mass, still more preferably 55 to 95% by mass, even more preferably 60 to 93% by mass, particularly preferably 60 to 90% by mass, with the methacrylic resin being 100% by mass. Note that the content of the structural unit derived from the methacrylic acid ester monomer can be determined by 1 1H-NMR measurement and 13 13C-NMR measurement. 1 1H-NMR measurement and 13 13C-NMR measurement can be performed, for example, using CDCl3 or DMSO-d6 as the measurement solvent at a measurement temperature of 40°C.

[0027] Hereinafter, the structural unit (X) having a ring structure in the main chain will be described. The structural unit (X) having a ring structure in the main chain preferably contains at least one structural unit selected from the group consisting of a structural unit derived from an N-substituted maleimide monomer, a glutarimide-based structural unit, and a lactone ring structural unit, and more preferably consists of only at least one structural unit selected from the group consisting of a structural unit derived from an N-substituted maleimide monomer, a glutarimide-based structural unit, and a lactone ring structural unit. The structural unit (X) having a ring structure in the main chain may be one kind or a combination of plural kinds.

[0028] - Structural unit derived from N-substituted maleimide monomer - Next, the structural unit derived from the N-substituted maleimide monomer will be described. The structural unit derived from the N-substituted maleimide monomer is preferably at least one structural unit selected from the group consisting of the structural unit represented by the following formula (1) and the structural unit represented by the following formula (2), and more preferably, it is formed from both of the structural units represented by the following formula (1) and the following formula (2).

[0029]

Chemical formula

Chemical formula

[0030] Hereinafter, specific examples will be shown. Examples of the monomer (N-aryl maleimides, N-aromatic substituted maleimides, etc.) that forms the structural unit represented by formula (1) include N-phenyl maleimide, N-benzyl maleimide, N-(2-chlorophenyl) maleimide, N-(4-chlorophenyl) maleimide, N-(4-bromophenyl) maleimide, N-(2-methylphenyl) maleimide, N-(2,6-dimethylphenyl) maleimide, N-(2-ethylphenyl) maleimide, N-(2-methoxyphenyl) maleimide, N-(2-nitrophenyl) maleimide, N-(2,4,6-trimethylphenyl) maleimide, N-(4-benzylphenyl) maleimide, N-(2,4,6-tribromophenyl) maleimide, N-naphthyl maleimide, N-anthracenyl maleimide, 3-methyl-1-phenyl-1H-pyrrole-2,5-dione, 3,4-dimethyl-1-phenyl-1H-pyrrole-2,5-dione, 1,3-diphenyl-1H-pyrrole-2,5-dione, 1,3,4-triphenyl-1H-pyrrole-2,5-dione, and the like. Among these monomers, N-phenyl maleimide and N-benzyl maleimide are preferred because the resulting methacrylic resin has excellent heat resistance and optical properties such as birefringence. These monomers may be used alone or in combination of two or more.

[0031] Examples of the monomer that forms the structural unit represented by the formula (2) include N-methylmaleimide, N-ethylmaleimide, N-n-propylmaleimide, N-isopropylmaleimide, N-n-butylmaleimide, N-isobutylmaleimide, N-s-butylmaleimide, N-t-butylmaleimide, N-n-pentylmaleimide, N-n-hexylmaleimide, N-n-heptylmaleimide, N-n-octylmaleimide, N-laurylmaleimide, N-cyclopentylmaleimide, N-cyclohexylmaleimide, 1-cyclohexyl-3-methyl-1H-pyrrole-2,5-dione, 1-cyclohexyl-3,4-dimethyl-1H-pyrrole-2,5-dione, 1-cyclohexyl-3-phenyl-1H-pyrrole-2,5-dione, 1-cyclohexyl-3,4-diphenyl-1H-pyrrole-2,5-dione, and the like. Among these monomers, N-methylmaleimide, N-ethylmaleimide, N-isopropylmaleimide, and N-cyclohexylmaleimide are preferable from the viewpoint of excellent weather resistance of the methacrylic resin. In particular, N-cyclohexylmaleimide is particularly preferable because it has excellent low hygroscopicity required for optical materials in recent years. These monomers can be used alone or in combination of two or more.

[0032] In the methacrylic resin of the present embodiment, using the structural unit represented by the formula (1) and the structural unit represented by the formula (2) in combination can exhibit highly controlled birefringence characteristics. This is particularly preferable above. The molar ratio (X1 / X2) of the content (X1) of the structural unit represented by the formula (1) to the content (X2) of the structural unit represented by the formula (2) is preferably more than 0 and 15 or less, more preferably more than 0 and 10 or less. When the molar ratio (X1 / X2) is within this range, the resin lens of the present embodiment maintains transparency, does not involve yellowing, and exhibits good heat resistance and good photoelastic characteristics without impairing environmental resistance.

[0033] The content of the structural unit derived from the N-substituted maleimide monomer is preferably in the range of 5 to 40% by mass, more preferably in the range of 5 to 35% by mass, based on 100% by mass of the methacrylic resin. When within this range, the methacrylic resin can obtain a more sufficient heat resistance improvement effect, and more preferable improvement effects can be obtained for weather resistance, low water absorption, and optical properties. Note that setting the content of the structural unit derived from the N-substituted maleimide monomer to 40% by mass or less is effective in preventing the deterioration of the physical properties of the methacrylic resin due to the decrease in the reactivity of the monomer components during the polymerization reaction and the increase in the amount of unreacted monomers remaining. In addition, by appropriately adjusting the content of the structural unit derived from the N-substituted maleimide monomer within this range, the birefringence caused by orientation and residual stress during molding can be reduced, and a resin lens for a head-mounted display with an average absolute value of the retardation within the effective diameter of 5 nm or less can be obtained. Although the optimal content of the structural unit derived from the N-substituted maleimide monomer varies depending on the type of N-substituted maleimide, for example, when using methyl methacrylate as the methacrylic acid ester monomer and N-phenylmaleimide and N-cyclohexylmaleimide as the N-substituted maleimide monomers, it is preferable to adjust within the range of 79 to 83% by mass of the structural unit derived from methyl methacrylate, 6 to 8% by mass of the structural unit derived from N-phenylmaleimide, and 11 to 13% by mass of the structural unit derived from N-cyclohexylmaleimide.

[0034] The methacrylic resin having a structural unit derived from the N-substituted maleimide monomer, which constitutes the resin lens for a head-mounted display of the present embodiment, may contain structural units derived from other monomers copolymerizable with the methacrylic acid ester monomer and the N-substituted maleimide monomer, as long as the object of the present invention is not impaired. For example, examples of the other copolymerizable monomers include aromatic vinyls; unsaturated nitriles; acrylic acid esters having a cyclohexyl group, a benzyl group, or an alkyl group having 1 to 18 carbon atoms; glycidyl compounds; unsaturated carboxylic acids; and the like. Examples of the aromatic vinyls include styrene, α-methylstyrene, divinylbenzene, and the like. Examples of the unsaturated nitrile include acrylonitrile, methacrylonitrile, ethacrylonitrile, and the like. Examples of the acrylic acid ester include methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, and the like. Examples of the glycidyl compound include glycidyl (meth)acrylate and the like. Examples of the unsaturated carboxylic acids include acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, and their semi-esterified products or anhydrides, and the like. The structural unit derived from another copolymerizable monomer may have only one kind, or may have two or more kinds.

[0035] As the content of the structural unit derived from these other copolymerizable monomers, when the methacrylic resin is 100% by mass, it is preferably 0 to 10% by mass, more preferably 0 to 9% by mass, and even more preferably 0 to 8% by mass. When the content of the structural unit derived from another monomer is within this range, it is preferable because the moldability and mechanical properties of the resin can be improved without impairing the original effect of introducing a ring structure into the main chain.

[0036] In addition, the content of the structural unit derived from the N-substituted maleimide monomer and the content of the structural unit derived from other copolymerizable monomers are 1 determinable by H-NMR measurement and 13 13C-NMR measurement. 1 H-NMR measurement and 13 13C-NMR measurement can be performed, for example, using CDCl3 or DMSO-d6 as a measurement solvent at a measurement temperature of 40°C.

[0037] -Glutarimide-based structural unit- Examples of the methacrylic resin having a glutarimide-based structural unit in the main chain include, for example, the methacrylic resins having a glutarimide-based structural unit described in JP-A-2006-249202, JP-A-2007-009182, JP-A-2007-009191, JP-A-2011-186482, and Re-Published Patent 2012 / 114718, and they can be formed by the methods described in these publications. The glutarimide-based structural unit constituting the methacrylic resin of this embodiment may be formed after resin polymerization. Specifically, the glutarimide-based structural unit may be represented by the following general formula (3).

[0038]

Chemical formula

[0039] In the methacrylic resin having a glutarimide-based structural unit, regarding the content of the glutarimide-based structural unit, with the methacrylic resin being 100% by mass, it is preferably in the range of 3 to 70% by mass, more preferably in the range of 3 to 60% by mass. When the content of the glutarimide-based structural unit is within the above range, it is preferable because a resin having good moldability, heat resistance, and optical properties can be obtained. Further, by appropriately adjusting the content of the glutarimide-based structural unit within this range, birefringence caused by orientation and residual stress during molding can be reduced, and a resin lens for a head-mounted display with an average absolute value of the retardation within the effective diameter of 5 nm or less can be obtained. R in the general formula (3) 7 ~R 9 The optimal content of the glutarimide-based structural unit varies depending on the type of the substituent, but for example, when R 7 and R 8 are hydrogen atoms and R 9 is a methyl group, when the content of the glutarimide-based structural unit is in the range of 3 to 10% by mass, birefringence caused by orientation and residual stress during molding can be reduced, and a resin lens for a head-mounted display with an average absolute value of the retardation within the effective diameter of 5 nm or less can be obtained. In addition, the content of the glutarimide-based structural unit in the methacrylic resin can be determined using the method described in the aforementioned patent document.

[0040] The methacrylic resin having a glutarimide-based structural unit may further contain an aromatic vinyl monomer unit as necessary. The aromatic vinyl monomer is not particularly limited, and examples thereof include styrene and α-methylstyrene, and styrene is preferred.

[0041] The content of the aromatic vinyl unit in the methacrylic resin having a glutarimide-based structural unit is not particularly limited, but it is preferably 0 to 20% by mass with the methacrylic resin having a glutarimide-based structural unit being 100% by mass. When the content of the aromatic vinyl unit is within the above range, it is preferable because both heat resistance and excellent photoelastic characteristics can be achieved. For example, when obtaining a resin by glutarylimidating a methyl methacrylate-styrene copolymer obtained by copolymerizing methyl methacrylate as a methacrylic acid ester monomer and styrene as an aromatic vinyl monomer, by adjusting within the range of 25 to 90% by mass of a structural unit derived from methyl methacrylate, 5 to 15% by mass of a structural unit derived from styrene, and 5 to 70% by mass of a glutarylimide-based structural unit, birefringence caused by orientation and residual stress during molding can be reduced, and a resin lens for a head-mounted display with an average absolute value of retardation within an effective diameter of 5 nm or less can be obtained.

[0042] -Lactone ring structural unit- The methacrylic resin having a lactone ring structural unit in the main chain can be formed by the methods described in, for example, JP-A-2001-151814, JP-A-2004-168882, JP-A-2005-146084, JP-A-2006-96960, JP-A-2006-171464, JP-A-2007-63541, JP-A-2007-297620, JP-A-2010-180305, etc.

[0043] The lactone ring structural unit constituting the methacrylic resin of the present embodiment may be formed after resin polymerization. As the lactone ring structural unit in the present embodiment, a 6-membered ring is preferable because of excellent stability of the ring structure. As the lactone ring structural unit that is a 6-membered ring, for example, the structure represented by the following general formula (4) is particularly preferable.

[0044]

Chemical formula

[0045] The lactone ring structure unit can be formed, for example, by copolymerizing an acrylic monomer having a hydroxy group and a methacrylic acid ester monomer such as methyl methacrylate, introducing a hydroxy group and an ester group or a carboxyl group into the molecular chain, and then causing dealcoholization (esterification) or dehydration condensation (hereinafter also referred to as "cyclization condensation reaction") between these hydroxy group and ester group or carboxyl group.

[0046] Examples of the acrylic monomer having a hydroxy group used in the polymerization include 2-(hydroxymethyl)acrylic acid, 2-(hydroxyethyl)acrylic acid, alkyl 2-(hydroxymethyl)acrylate (for example, methyl 2-(hydroxymethyl)acrylate, ethyl 2-(hydroxymethyl)acrylate, isopropyl 2-(hydroxymethyl)acrylate, n-butyl 2-(hydroxymethyl)acrylate, t-butyl 2-(hydroxymethyl)acrylate), alkyl 2-(hydroxyethyl)acrylate, etc. Preferably, they are 2-(hydroxymethyl)acrylic acid and alkyl 2-(hydroxymethyl)acrylate which are monomers having a hydroxyalkyl moiety, and particularly preferably methyl 2-(hydroxymethyl)acrylate and ethyl 2-(hydroxymethyl)acrylate.

[0047] In the methacrylic resin having a lactone ring structural unit in the main chain, the content of the lactone ring structural unit is preferably 5 to 40% by mass, more preferably 5 to 35% by mass, based on 100% by mass of the methacrylic resin. When the content of the lactone ring structural unit is within this range, the effects of introducing the ring structure such as improvement in solvent resistance and surface hardness can be exhibited while maintaining the moldability. Further, by appropriately adjusting the content of the lactone ring structural unit within this range, birefringence caused by orientation and residual stress during molding can be reduced, and a resin lens for a head-mounted display having an average absolute value of the retardation within the effective diameter of 5 nm or less can be obtained. In addition, the content of the lactone ring structure in the methacrylic resin can be determined using the method described in the aforementioned patent documents.

[0048] The methacrylic resin having a lactone ring structural unit in the main chain may have a structural unit derived from another monomer copolymerizable with the above-described methacrylic acid ester monomer and an acrylic acid-based monomer having a hydroxy group. Examples of such other copolymerizable monomers include monomers having a polymerizable double bond such as styrene, vinyltoluene, α-methylstyrene, α-hydroxymethylstyrene, α-hydroxyethylstyrene, acrylonitrile, methacrylonitrile, methallyl alcohol, ethylene, propylene, 4-methyl-1-pentene, vinyl acetate, 2-hydroxymethyl-1-butene, methyl vinyl ketone, N-vinylpyrrolidone, and N-vinylcarbazole. These other monomers (structural units) may have only one kind or two or more kinds.

[0049] The content of the structural unit derived from these other copolymerizable monomers is preferably 0 to 20% by mass, more preferably less than 10% by mass, and even more preferably less than 7% by mass, based on 100% by mass of the methacrylic resin, from the viewpoint of weather resistance. The methacrylic resin in the present embodiment may have only one kind or two or more kinds of the structural units derived from the above other copolymerizable monomers.

[0050] The methacrylic resin in this embodiment preferably has at least one structural unit selected from the group consisting of a structural unit derived from an N-substituted maleimide monomer, a glutarimide-based structural unit, and a lactone ring structural unit. Among them, in particular, from the viewpoint of easily controlling optical properties such as the photoelastic coefficient without blending other thermoplastic resins, it is particularly preferable to have a structural unit derived from an N-substituted maleimide monomer. Also, in particular, from the viewpoint of obtaining a high-strength resin lens, it is particularly preferable to have a glutarimide-based structural unit.

[0051] [Manufacturing method of methacrylic resin] Hereinafter, the manufacturing method of the methacrylic resin of this embodiment will be described.

[0052] [Manufacturing method of methacrylic resin containing a structural unit derived from an N-substituted maleimide monomer] As a manufacturing method of a methacrylic resin having a structural unit derived from an N-substituted maleimide monomer in the main chain (hereinafter, may be referred to as a "maleimide copolymer"), any of bulk polymerization method, solution polymerization method, suspension polymerization method, precipitation polymerization method, and emulsion polymerization method can be mentioned. From the viewpoint of reducing the amount of residual monomers and impurities contained in the resin lens, preferably suspension polymerization, bulk polymerization, or solution polymerization method, and more preferably solution polymerization method.

[0053] In the manufacturing method of this embodiment, as the polymerization form, for example, any of batch polymerization method, semi-batch method, and continuous polymerization method can be used. In this embodiment, a method in which a part of the monomer is charged into the reactor before the start of polymerization, polymerization is started by adding a polymerization initiator, and then the remainder of the monomer is supplied, so-called semi-batch polymerization method, is preferably used from the viewpoint of reducing the amount of residual maleimide at the end of polymerization and reducing the fluorescence intensity (reducing the content of the fluorescent substance).

[0054] In a methacrylic resin having a structural unit derived from an N-substituted maleimide monomer, as a method for controlling the resulting resin lens to exhibit a predetermined fluorescence intensity (the content of the fluorescent substance is within a predetermined range), examples include: (1) using an N-substituted maleimide monomer with a controlled content of specific impurities as a raw material; (2) applying a polymerization method for reducing the amount of unreacted N-substituted maleimide remaining after the polymerization; (3) applying a devolatilization method with reduced shear, etc. At least one of these methods is to be carried out. Among them, it is preferable to select a production method that combines (1) and (3), or a production method that combines all three.

[0055] (1) Control of impurities in N-substituted maleimide As one of the impurities in N-substituted maleimide that imparts fluorescence to the methacrylic resin, 2-amino-N-substituted succinimide formed by the reaction of N-substituted maleimide and a primary amine can be mentioned. Examples of 2-amino-N-substituted succinimide include 2-cyclohexylamino-N-cyclohexyl succinimide and 2-anilino-N-phenyl succinimide. 2-Amino-N-substituted succinimide not only has fluorescence itself, but although the detailed denaturation mechanism is unknown, it has been clarified by the inventors' studies that when it is heated to 300 °C or higher or subjected to a devolatilization device with shear, a thermally denatured product with fluorescence is generated. That is, reduction of 2-amino-N-substituted succinimide contained in N-substituted maleimide and performing devolatilization at 300 °C or lower using a devolatilization device without a rotating part in the production of methacrylic resin are preferable for controlling the fluorescence intensity of the methacrylic resin and the resulting resin lens.

[0056] As a method for controlling impurities in N-substituted maleimide, examples include providing a pretreatment step of washing with water (water washing step) and / or dehydrating (dehydration step) the N-substituted maleimide. The above pretreatment step may be only water washing, or may be a combination of water washing and dehydration. Further, water washing and dehydration may be performed once or may be performed a plurality of times. In the above pretreatment step, a concentration adjustment step for adjusting the concentration of the N-substituted maleimide solution obtained in the dehydration step may be further provided.

[0057] In the present embodiment, for example, 2-amino-N-substituted succinimide in N-substituted maleimide is removed by the following water washing step, and water is removed in the subsequent dehydration step, whereby the fluorescence intensity is controlled and a methacrylic resin having a good color tone can be obtained. An N-substituted maleimide solution suitable for preparation can be obtained. In the water washing step, for example, N-substituted maleimide is dissolved in a water-insoluble organic solvent, separated into an organic layer and an aqueous layer, and this organic layer is mixed and washed by a batch method, a continuous method, or both methods using one or more of an acidic aqueous solution, water, and an alkaline aqueous solution, and then, a method of separating the organic layer and the aqueous layer can be employed.

[0058] The amount of 2-amino-N-substituted succinimide in the organic layer after the water washing step is preferably 5 mass ppm or less, more preferably 0.1 mass ppm or more and 1 mass ppm or less when the amount of N-substituted maleimide in the organic layer is 100 mass%. When the amount of 2-amino-N-substituted succinimide in the organic layer is within this range, the concentration of the fluorescent substance in the methacrylic resin and the obtained resin lens can be controlled within the above range, and a resin lens for a head-mounted display capable of obtaining a clear image can be obtained, which is preferable. Further, it is also preferable from the viewpoint of the cost in washing. When the dehydration step is not provided, the organic layer containing N-substituted maleimide obtained in the water washing step may be used in the polymerization step as an N-substituted maleimide solution. Note that the amount of 2-amino-N-substituted succinimide in the organic layer can be measured by gas chromatography, liquid chromatography, etc. using isopropyl benzoate as an internal standard substance, for example, and specifically, it can be measured by the method described in the examples below.

[0059] The water-insoluble organic solvent to be used is not particularly limited as long as it can dissolve N-substituted maleimide and 2-amino-N-substituted succinimide, phase-separate from water, and has an azeotropic point with water. Specifically, for example, aromatic hydrocarbons such as toluene and xylene; aliphatic hydrocarbons such as normal hexane and cyclohexane; halogenated hydrocarbons such as chloroform and dichloroethane; etc. can be used. Any of sewage water, pure water, and tap water can be used as the water to be used. Also, the acidity of the acidic aqueous solution and the alkaline aqueous solution is not particularly limited.

[0060] The concentration of N-substituted maleimide in the organic layer before the water washing step is preferably 0.5% by mass or more and 30% by mass or less, more preferably 10% by mass or more and 25% by mass or less, and even more preferably 20% by mass or more and 25% by mass or less. The temperature when mixing and washing the organic layer and the aqueous layer may be 40°C or higher, preferably 40°C or higher and 80°C or lower, and more preferably 50°C or higher and 60°C or lower. The mass ratio of the aqueous layer to the organic layer is preferably 5% by mass or more and 300% by mass or less, more preferably 10% by mass or more and 200% by mass, and even more preferably 30% by mass or more and 100% by mass or less when the mass of the organic layer is 100% by mass. When the concentration of N-substituted maleimide in the organic layer, the liquid temperature during washing, and the mass ratio of the aqueous layer are within these ranges, the reaction between N-substituted maleimide and water hardly proceeds, and 2-amino-N-substituted succinimide is easily extracted to the aqueous layer side, which is preferable.

[0061] When washing in a batch system, the reaction vessel to be used may be made of stainless steel or glass lining, or other reaction vessels may also be used. Also, the shape of the stirring blade is not particularly limited. As specific stirring blades, for example, three retreat blades, four paddle blades, four inclined paddle blades, six turbine blades, and anchor blades can be used, and also twins and full zones manufactured by Shinko Environmental Solutions can be used. The stirring time is preferably 10 minutes or more and 120 minutes or less, more preferably 30 minutes or more and 60 minutes or less. Also, the stirring speed is appropriately selected such that the mixed solution is in a turbulent flow state and does not emulsify. When the stirring time and the stirring speed are within these ranges respectively, the stirring efficiency and the extraction efficiency of 2-amino-N-substituted succinimide into the aqueous layer are improved, and the 2-amino-N-substituted succinimide in N-substituted maleimide can be further reduced, which is preferable.

[0062] When performing continuous washing, a packed tower, a plate column, or an empty tower can be used, and a static mixer such as a static mixer or a rotary mixer such as a dynamic mixer can also be used. The contact time between the organic layer and the aqueous layer is preferably set to 1 second or more and 60 minutes or less, more preferably 30 seconds or more and 10 minutes or less. When the contact time is within this range, the reaction between N-substituted maleimide and water hardly proceeds, and 2-amino-N-substituted succinimide is easily extracted to the aqueous layer side, which is preferable.

[0063] In the dehydration step, the organic layer is fed into the reaction tank and heated under reduced pressure to remove moisture. The pressure and temperature are not particularly limited as long as the solvent and water used form an azeotropic composition. When the mass of the organic layer is taken as 100% by mass, the water content in the organic layer after the dehydration step is preferably 100 ppm by mass or less. When the water content after the dehydration step is within this range, the deterioration of the color tone due to water during the polymerization of the methacrylic resin can be suppressed, and the amount of the solvent distilled off together with water can be reduced, which is also preferable from the cost aspect. The organic layer containing N-substituted maleimide obtained in the dehydration step may be used in the polymerization step as an N-substituted maleimide solution, or an N-substituted maleimide solution with adjusted concentration in the concentration adjustment step may be used in the polymerization step.

[0064] In the concentration adjustment step, for example, the organic layer of the above N-substituted maleimide obtained in the dehydration step or the like may be diluted with the above water-insoluble organic solvent. The water-insoluble organic solvent used in the concentration adjustment step is preferably the same as the water-insoluble organic solvent used in the washing step.

[0065] The N-substituted maleimide solution obtained in the above pretreatment step is preferably a solution (organic layer) of the above water-insoluble organic solvent. In the N-substituted maleimide solution obtained in the above pretreatment step, the mass ratio of 2-amino-N-substituted succinimide contained in the N-substituted maleimide solution is preferably 5 mass ppm or less, more preferably 0.1 mass ppm or more and 1 mass ppm or less, based on 100 mass% of the N-substituted maleimide contained in the N-substituted maleimide solution. The amount of water contained in the N-substituted maleimide solution obtained in the above pretreatment step is preferably 200 mass ppm or less, more preferably 100 to 200 mass ppm, based on 100 mass% of the N-substituted maleimide solution. The mass ratio of the N-substituted maleimide contained in the N-substituted maleimide solution obtained in the above pretreatment step is preferably 5 to 30 mass%, more preferably 5 to 25 mass%, based on 100 mass% of the N-substituted maleimide solution. When in this range, it is preferable because the N-substituted maleimide is less likely to precipitate and can be transferred as a uniform solution.

[0066] When using a plurality of types of N-substituted maleimide solutions in the polymerization step, it is preferable that the mixture of the plurality of types of N-substituted maleimide solutions satisfies the mass ratio of the 2-amino-N-substituted succinimide, the amount of water, and / or the mass ratio of the N-substituted maleimide, and it is more preferable that each N-substituted maleimide solution satisfies the mass ratio of the 2-amino-N-substituted succinimide, the amount of water, and / or the mass ratio of the N-substituted maleimide. By adopting the water washing step and dehydration step of N-substituted maleimide as described above, it becomes possible to reduce 2-amino-N-substituted succinimide having fluorescence luminescence property and remove water that causes color deterioration of the methacrylic resin, and it is preferable because a methacrylic resin having a good color tone and a composition of the resin can be obtained even in a lens having a long optical path length. In the polymerization step, a methacrylic acid ester monomer, an optional other monomer, a polymerization initiator, a polymerization solvent, a chain transfer agent, etc. may be mixed with the N-substituted maleimide solution obtained in the above pretreatment step to obtain a monomer mixture solution and then used for polymerization.

[0067] (2) Reduction of unreacted N-substituted maleimide at the end of polymerization When unreacted N-substituted maleimide is present at the end of the polymerization of the methacrylic resin, although the detailed mechanism is unknown, the inventors have found that a low molecular weight reaction by-product having fluorescence and containing N-substituted maleimide as its structural unit may be generated in a heated devolatilization apparatus or the like.

[0068] In order to control the content of the fluorescent substance in the methacrylic resin and the resulting resin lens within the above range, it is preferable that the total mass of the unreacted N-substituted maleimide remaining after the end of polymerization is 1000 mass ppm or less based on 100 mass% of the polymerization solution at the end of polymerization, more preferably 10 mass ppm or more and 500 mass ppm or less. When N-aryl maleimides such as N-phenyl maleimide are used as the N-substituted maleimide, the total mass of the unreacted N-aryl maleimides remaining after the end of polymerization is preferably 500 mass ppm or less, more preferably 10 mass ppm or more and 500 mass ppm or less, and even more preferably 10 mass ppm or more and 50 mass ppm or less based on 100 mass% of the polymerization solution at the end of polymerization. When within these ranges, it is preferable because the content of the fluorescent substance in the methacrylic resin and the resulting resin lens can be suppressed within the above range. Also, in order to make the amount of unreacted N-substituted maleimide less than 10 mass ppm, it is necessary to increase the polymerization temperature or the amount of the polymerization initiator, which increases maleimide thermal denaturation products and active radicals and causes deterioration of the color tone of the methacrylic resin, so it is not preferable.

[0069] As a means for controlling the amount of unreacted N-substituted maleimide after the completion of coincidence within the above range, a semi-batch polymerization method can be mentioned. In the semi-batch polymerization method, in the polymerization step, after 30 minutes from the start of addition of the polymerization initiator, with the total mass of all monomers to be supplied to the polymerization (for example, methacrylic acid ester, N-substituted maleimide, and any other monomers) being 100% by mass, it is preferable to additionally add 5 to 35% by mass of the methacrylic acid ester monomer. In other words, 65 to 95% by mass of the total mass of 100% by mass of all monomers to be supplied to the polymerization is charged into the reactor before the addition of the polymerization initiator, and the remaining 5 to 35% by mass of the methacrylic acid ester monomer is additionally added after 30 minutes from the start of addition of the polymerization initiator. The amount of the methacrylic acid ester monomer to be additionally added is more preferably 10 to 30% by mass with the total mass of all monomers to be supplied to the polymerization being 100% by mass. When the amount of the methacrylic acid ester monomer to be additionally added is within the above range, the unreacted N-substituted maleimide reacts with the additionally added methacrylic acid ester monomer, and the amount of unreacted N-substituted maleimide after the completion of polymerization can be controlled within the above range, which is preferable.

[0070] The start time of the additional addition of the monomer, the speed of the additional addition, etc. may be appropriately selected according to the polymerization conversion rate. Also, within a range that does not inhibit the effects of the present invention and the reduction of the amount of unreacted N-substituted maleimide, in addition to the methacrylic acid ester monomer, a monomer mixture containing an N-substituted maleimide monomer and other monomers may be additionally added. By adopting the semi-batch polymerization method as described above, it becomes possible to reduce the amount of unreacted N-substituted maleimide monomer at the latter half of the polymerization and minimize the generation of the fluorescent substance in the devolatilization step, and it is preferable because a methacrylic resin having a good color tone and a composition of the resin can be obtained even in a lens having a long optical path length.

[0071] Hereinafter, as an example of a method for producing a methacrylic resin having a structural unit derived from an N-substituted maleimide monomer, the case of producing by radical polymerization in a semi-batch manner using a solution polymerization method will be specifically described.

[0072] In the semi-batch polymerization method, it is preferable to additionally add 5 to 35% by mass of a methacrylic acid ester monomer, with the total mass of all monomers (methacrylic acid ester, N-substituted maleimide, and any other monomers) contributed to the polymerization being 100% by mass, 30 minutes or more after the start of addition of the polymerization initiator. In other words, 65 to 95% by mass of the total mass of 100% by mass of all monomers contributed to the polymerization is charged into the reactor before the start of polymerization, and 5 to 35% by mass of the remainder of the methacrylic acid ester monomer is additionally added 30 minutes or more after the start of addition of the polymerization initiator. The amount of the methacrylic acid ester monomer to be additionally added is more preferably 10 to 30% by mass, with the total mass of all monomers contributed to the polymerization being 100% by mass.

[0073] The start time of the additional addition of the monomer, the speed of the additional addition, etc. may be appropriately selected according to the polymerization conversion rate. Also, within a range that does not inhibit the effects of the present invention and the conversion rate of the N-substituted maleimide monomer, in addition to the methacrylic acid ester monomer, a monomer mixture containing an N-substituted maleimide monomer and other monomers may be additionally added.

[0074] By adopting the semi-batch polymerization method as described above, it becomes possible to increase the conversion rate of the N-substituted maleimide monomer at the latter half of the polymerization, reduce the content of the fluorescent substance, have excellent light transmittance for a lens with a long optical path length, easily control the molecular weight distribution of the obtained polymer, and particularly obtain a resin having fluidity suitable for injection molding and a composition of the resin, which is preferable.

[0075] The polymerization solvent to be used is not particularly limited as long as it can increase the solubility of the maleimide copolymer obtained by polymerization and appropriately maintain the viscosity of the reaction solution for the purpose of preventing gelation. Specific examples of the polymerization solvent that can be used include aromatic hydrocarbons such as toluene, xylene, ethylbenzene, and isopropylbenzene; ketones such as methyl isobutyl ketone, butyl cellosolve, methyl ethyl ketone, and cyclohexanone; and polar solvents such as dimethylformamide and 2-methylpyrrolidone. These can be used alone or in combination of two or more. Also, within a range that does not inhibit the dissolution of the polymerization product during polymerization, alcohols such as methanol, ethanol, and isopropanol may be used in combination as a polymerization solvent.

[0076] The amount of the solvent during polymerization is not particularly limited as long as the polymerization proceeds, no precipitation of the copolymer or the monomer to be used occurs during production, and it can be easily removed. For example, when the total amount of the monomers to be blended is 100% by mass, it is preferably 10 to 200% by mass. More preferably, it is 25 to 150% by mass, still more preferably 40 to 100% by mass, and even more preferably 50 to 100% by mass. In this embodiment, a method of polymerizing while appropriately changing the solvent concentration during polymerization within a range of 100% by mass or less when the total amount of the monomers to be blended is 100% by mass is also preferably used. More specifically, 40 to 60% by mass is blended at the initial stage of polymerization, and during the polymerization process, the remaining 60 to 40% by mass is blended. Finally, when the total amount of the monomers to be blended is 100% by mass, a method of making the amount of the solvent fall within the range of 100% by mass or less can be exemplified. By adopting this method, the polymerization conversion rate can be increased, the molecular weight distribution can be further controlled, the resin and resin composition having excellent injection moldability, a reduced content of the fluorescent substance, and a good color tone even when a lens with a long optical path length is prepared can be obtained, which is preferable.

[0077] In solution polymerization, it is important to reduce the dissolved oxygen concentration in the polymerization solution as much as possible. For example, the dissolved oxygen concentration is preferably 10 ppm or less. The dissolved oxygen concentration can be measured, for example, using a dissolved oxygen meter DO meter B-505 (manufactured by Iijima Electronics Industry Co., Ltd.). As a method for reducing the dissolved oxygen concentration, a method of bubbling an inert gas into the polymerization solution, a method of repeating an operation of pressurizing the container containing the polymerization solution with an inert gas to about 0.2 MPa and then releasing the pressure before polymerization, a method of passing an inert gas through the container containing the polymerization solution, etc. can be appropriately selected.

[0078] The polymerization temperature is not particularly limited as long as the polymerization proceeds, but it is preferably 70 to 180°C, more preferably 80 to 160°C, still more preferably 90 to 150°C, and even more preferably 100 to 150°C. From the viewpoint of productivity, it is preferably 70°C or higher, and preferably 180°C or lower in order to suppress side reactions during polymerization and obtain a polymer with a desired molecular weight and quality.

[0079] Regarding the polymerization time, there is no particular limitation as long as it is a time that can obtain the required degree of polymerization at the required conversion rate. However, from the viewpoints of productivity and the like, it is preferably 2 to 15 hours, more preferably 3 to 12 hours, and still more preferably 4 to 10 hours.

[0080] As the polymerization initiator, any initiator generally used in radical polymerization can be used. For example, organic peroxides such as cumene hydroperoxide, diisopropylbenzene hydroperoxide, di-t-butyl peroxide, lauroyl peroxide, benzoyl peroxide, t-butyl peroxyisopropyl carbonate, t-amyl peroxy-2-ethylhexanoate, t-amyl peroxyisononanoate, 1,1-di(t-butylperoxy)cyclohexane; azo compounds such as 2,2'-azobis(isobutyronitrile), 1,1'-azobis(cyclohexanecarbonitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), dimethyl-2,2'-azobisisobutyrate; etc. can be mentioned. These may be used alone or in combination of two or more. The addition amount of the polymerization initiator is preferably 0.01 to 1% by mass, more preferably in the range of 0.05 to 0.5% by mass, when the total amount of the monomers used in the polymerization is 100% by mass. As a method for adding a polymerization initiator, there is no particular limitation as long as it is a variable addition according to the monomer concentration remaining in the polymerization solution instead of a constant addition rate, and it may be added continuously or intermittently. When adding the polymerization initiator intermittently, the addition amount per unit time is not considered for the time when it is not being added.

[0081] In this embodiment, it is preferable to appropriately select the type and addition amount of the polymerization initiator, the polymerization temperature, etc. so that the ratio of the total amount of radicals generated from the polymerization initiator to the total amount of unreacted monomers remaining in the reaction system is always below a certain value. By adopting these methods, it is also possible to suppress the generation amount of oligomers and low molecular weight substances in the latter stage of polymerization, or to suppress overheating during polymerization to achieve the stability of polymerization.

[0082] During the polymerization reaction, a chain transfer agent may be added and polymerized as necessary. As the chain transfer agent, chain transfer agents used in general radical polymerization can be used. For example, mercaptan compounds such as n-butyl mercaptan, n-octyl mercaptan, n-decyl mercaptan, n-dodecyl mercaptan, 2-ethylhexyl thioglycolate; halogen compounds such as carbon tetrachloride, methylene chloride, bromoform; unsaturated hydrocarbon compounds such as α-methylstyrene dimer, α-terpinene, dipentene, terpinolene; etc. can be mentioned. These may be used alone or in combination of two or more. These chain transfer agents may be added at any stage as long as the polymerization reaction is in progress, and are not particularly limited. As the addition amount of the chain transfer agent, when the total amount of monomers used in the polymerization is 100% by mass, it may be 0.01 to 1% by mass, preferably 0.05 to 0.5% by mass.

[0083] As a method for recovering a polymer from a polymerization solution obtained by solution polymerization, a method of separating a polymerization solvent and unreacted monomers through a process called a devolatilization step and recovering the polymerization product can be mentioned. Here, the devolatilization step refers to a step of removing volatile components such as a polymerization solvent, residual monomers, and reaction by-products under heating and reduced pressure conditions. In the present embodiment, it is preferable to control the content of unreacted N-substituted maleimide monomer contained in the polymerization solution containing a methacrylic resin to be subjected to the devolatilization step to a certain concentration or less. The details are as described in the above “(2) Reduction of unreacted N-substituted maleimide at the end of polymerization”. In addition to the above methods, for example, in order to increase the monomer conversion rate, the polymerization time is made as long as possible, or the polymerization is carried out by changing the addition rate of the polymerization initiator according to the concentration of unreacted monomers in the polymerization solution; a method of polymerizing while appropriately changing the solvent concentration during polymerization; a method of additionally adding other monomers having high reactivity with the N-substituted maleimide monomer remaining in the latter half of polymerization; a method of adding a compound having high reactivity with N-substituted maleimide, such as α-terpinene, at the end of polymerization, etc. can also be used.

[0084] - Residual amount of N-substituted maleimide monomer - As a method for determining the residual amount of N-substituted maleimide monomer remaining in the polymerization solution containing a methacrylic resin, for example, a part of the polymerization solution is sampled and weighed, this sample is dissolved in chloroform to prepare a 5 mass% solution, n-decane is added as an internal standard substance, and the concentration of the N-substituted maleimide monomer remaining in the sample is measured using gas chromatography (GC-2010 manufactured by Shimadzu Corporation), and it can be determined. As more specific measurement conditions, those described in the following examples can be used.

[0085] (3) Devolatilization method with reduced shear As the apparatus used in the above devolatilization step, it is preferable to use a devolatilization apparatus mainly composed of a heat exchanger and a reduced pressure vessel and having no rotating part in its structure. By not providing a rotating part, the shear during devolatilization can be reduced, and a resin with even lower fluorescence can be obtained. Specifically, a devolatilization device can be adopted, which is composed of a devolatilization tank with a pressure reduction unit attached to a pressure reduction vessel having a size capable of devolatilization with a heat exchanger arranged on its upper part, and a discharge device such as a gear pump for discharging the polymer after devolatilization. The above-mentioned devolatilization device preheats the polymerization solution by supplying it to a heat exchanger arranged at the upper part of the pressure reduction vessel and heated, for example, a multi-tube heat exchanger, a plate fin heat exchanger, a plate-type heat exchanger having a flat plate-type flow path and a heater, etc., and then supplies it to the devolatilization tank under heating and reduced pressure to separate and remove the polymerization solvent, unreacted raw material mixture, polymerization by-products, etc. from the polymer. By using a devolatilization device having no rotating part as described above, it is possible to suppress reaction by-products having a low molecular weight and fluorescence luminescence derived from unreacted N-substituted maleimide, and the fluorescence intensity (content of fluorescent luminescent substances) in the methacrylic resin and the obtained resin lens can be controlled within a predetermined range, which is preferable. Further, since a methacrylic resin having a good color tone can be obtained, it is preferable.

[0086] Examples of the device having the above-mentioned rotating part include thin film evaporators such as Wiperen and Exeva manufactured by Shinko Environmental Solutions Co., Ltd., Contrar and inclined blade Contrar manufactured by Hitachi, Ltd.; extruders with vents, etc.

[0087] In the devolatilization step in this embodiment, it is preferable that the shear rate applied to the polymerization solution is 20 s -1 or less, more preferably 10 s -1 or less, and even more preferably 0.1 s -1 or more and 10 s -1 or less. By setting the shear rate to 0.1 s -1 or more, the flow of the molten resin does not become too slow, and the deterioration of the color tone due to an increase in the residence time can be suppressed. Also, by setting it to 20 s -1 or less, the generation of reaction by-products having fluorescence luminescence due to shear can be suppressed. Here, for example, the shear rate γ in an extruder is calculated by the following formula. γ = (π × D × N) / H (In the formula, D represents the screw diameter (m), N represents the number of screw rotations per second, and H represents the screw groove depth (m).) Also, in the case of a flat plate type flow path, the shear rate γ is calculated by the following formula. γ=(6×Q) / (w×h 2 ) (In the formula, Q represents the volume flow rate (m 3 / s) passing through the flat plate type flow path, w represents the width (m) of the flat plate type flow path, and h represents the distance (m) between the flat plates.)

[0088] In the present embodiment, as the heat exchanger disposed above the pressure reducing vessel, it is preferable to use a flat plate type heat exchanger having a flat plate type flow path and a heater. More preferably, it is a flat plate type heat exchanger having a flat plate type flow path and a heater having a laminated structure having a plurality of slit-shaped flow paths with a rectangular cross section in the same plane.

[0089] The polymerization solution supplied to the devolatilization device is sent from the central part of the heat exchanger to the slit-shaped flow path and heated. The heated polymerization solution is supplied from the slit-shaped flow path into the pressure reducing vessel under reduced pressure integrated with the heat exchanger and flash-evaporated. Such a devolatilization method may also be referred to as flash devolatilization, and in the present invention, it will be hereinafter also referred to as flash devolatilization.

[0090] It is also possible to adopt a method of installing two or more of the above-described devolatilization devices in series and performing devolatilization in two or more stages.

[0091] The temperature range for heating with the heat exchanger attached to the devolatilization device may be 100°C or higher and 300°C or lower, preferably a temperature of the glass transition temperature (Tg) of the methacrylic resin + 100°C to Tg + 160°C, more preferably a temperature of Tg + 110°C to Tg + 150°C. The temperature range of the heated and heat-insulated devolatilization tank may be 100°C or higher and 300°C or lower, preferably a temperature of Tg + 100°C to Tg + 160°C, more preferably a temperature of Tg + 110°C to Tg + 150°C. When the temperatures of the heat exchanger and the devolatilization tank are within this range, thermal denaturation of the remaining 2-amino-N-substituted succinimide can be suppressed, and generation of the fluorescent substance can be suppressed, which is preferable. Also, it is effective for preventing an increase in the remaining volatile content, and is preferable because the thermal stability and product quality of the obtained methacrylic resin are improved.

[0092] The degree of vacuum in the devolatilization tank may be in the range of 5 to 300 Torr, and among them, the range of 10 to 200 Torr is preferable. When the degree of vacuum is 300 Torr or lower, unreacted monomers or a mixture of unreacted monomers and polymerization solvents can be efficiently separated and removed, and the thermal stability and quality of the obtained thermoplastic copolymer do not deteriorate. When the degree of vacuum is 5 Torr or higher, industrial implementation is easier.

[0093] The average residence time in the devolatilization tank is 5 to 60 minutes, preferably 5 to 45 minutes. When the average residence time is within this range, devolatilization can be carried out efficiently, and coloring and decomposition due to thermal denaturation of the polymer can be suppressed, which is preferable.

[0094] The polymer recovered through the devolatilization step is processed into pellets in a step called the pelletizing step. In the granulation process, the molten resin is extruded in a strand shape using at least one discharge granulation device selected from a gear pump, a single-screw extruder, a twin-screw extruder, etc. having a porous die as an accessory equipment, and processed into pellets by a cold cut method, an air hot cut method, an underwater strand cut method, or an under water cut method. From the viewpoint of suppressing the generation of fluorescent reaction by-products due to shear, it is preferable to select a conveying device with a low shear rate without using an extruder.

[0095] In this embodiment, in order to obtain a highly controlled resin composition, it is preferable to adopt a granulation method that can quickly cool and solidify the resin composition in a molten state at a high temperature so as to avoid contact with air as much as possible. In that case, it is more preferable to carry out granulation under conditions that can lower the molten resin temperature as much as possible, minimize the residence time from the porous die outlet to the cooling water surface, and set the temperature of the cooling water to a high temperature as much as possible within the possible range. For example, the molten resin temperature is preferably 220 to 280°C, more preferably 230 to 270°C. The residence time from the porous die outlet to the cooling water surface is preferably within 5 seconds, more preferably within 3 seconds. The temperature of the cooling water is preferably 30 to 80°C, more preferably in the range of 40 to 60°C.

[0096] By carrying out the process within the ranges of these molten resin temperature and cooling water temperature, it is preferable because a methacrylic resin and its composition with less coloring and a lower moisture content can be obtained.

[0097] Regarding the content of the monomer remaining in the methacrylic resin after the devolatilization process, the lower the content, the more preferable from the viewpoints of thermal stability and product quality. Specifically, the content of the methacrylic acid ester monomer is preferably 3000 mass ppm or less, more preferably 2000 mass ppm or less. The total content of the N-substituted maleimide monomer is preferably 200 mass ppm or less, more preferably 100 mass ppm or less. Also, the content of the remaining polymerization solvent is preferably 500 mass ppm or less, more preferably 300 mass ppm or less.

[0098] - Method for Producing Methacrylic Resin Containing Glutarimide-Based Structural Unit - As a method for producing a methacrylic resin having a glutarimide-based structural unit in the main chain, examples of the polymerization method include bulk polymerization, solution polymerization, suspension polymerization, precipitation polymerization, and emulsion polymerization methods. Preferably, suspension polymerization, bulk polymerization, and solution polymerization methods are used, and more preferably, the solution polymerization method is used. In the production method of the present embodiment, as the polymerization form, for example, any of batch polymerization method, semi-batch method, and continuous polymerization method can be used. In the production method of the present embodiment, it is preferable to polymerize the monomer by radical polymerization.

[0099] The methacrylic resin having a glutarimide-based structural unit in the main chain is, for example, a methacrylic resin having a glutarimide-based structural unit described in JP-A-2006-249202, JP-A-2007-009182, JP-A-2007-009191, JP-A-2011-186482, WO2012 / 114718, etc., and can be formed by the method described in the publication. Hereinafter, as an example of the production method of the methacrylic resin having a glutarimide-based structural unit, the case of producing by batch radical polymerization using the solution polymerization method will be specifically described.

[0100] First, a (meth)acrylic acid ester polymer is produced by polymerizing a (meth)acrylic acid ester such as methyl methacrylate. When an aromatic vinyl unit is included in the methacrylic resin having a glutarimide-based structural unit, a (meth)acrylic acid ester and an aromatic vinyl (for example, styrene) are copolymerized to produce a (meth)acrylic acid ester-aromatic vinyl copolymer.

[0101] Examples of the solvent used for the polymerization include aromatic hydrocarbons such as toluene, xylene, and ethylbenzene; ketones such as methyl ethyl ketone and methyl isobutyl ketone; and the like. These solvents may be used alone or in combination of two or more. The amount of the solvent during the polymerization is not particularly limited as long as the polymerization proceeds, no precipitation of the copolymer or the monomer used in production occurs, and it can be easily removed. For example, when the total amount of the monomers to be blended is 100% by mass, it is preferably 10 to 200% by mass. More preferably, it is 25 to 200% by mass, still more preferably 50 to 200% by mass, and even more preferably 50 to 150% by mass.

[0102] The polymerization temperature is not particularly limited as long as the polymerization proceeds, but it is preferably 50 to 200°C, more preferably 80 to 200°C. Still more preferably, it is 90 to 150°C, even more preferably 100 to 140°C, and even more preferably 100 to 130°C. From the viewpoint of productivity, it is preferably 70°C or higher, and from the viewpoint of suppressing side reactions during the polymerization and obtaining a polymer with a desired molecular weight and quality, it is preferably 180°C or lower. The polymerization time is not particularly limited as long as the target conversion rate is satisfied, but from the viewpoints of productivity and the like it is preferably 0.5 to 15 hours, more preferably 2 to 12 hours, and still more preferably 4 to 10 hours.

[0103] During the polymerization reaction, a polymerization initiator or a chain transfer agent may be added and polymerized as necessary.

[0104] The polymerization initiator is not particularly limited, and for example, the polymerization initiators disclosed in the method for preparing a methacrylic resin having a structural unit derived from the above N-substituted maleimide monomer can be used. These polymerization initiators may be used alone or in combination of two or more. These polymerization initiators may be added at any stage as long as the polymerization reaction is in progress. The addition amount of the polymerization initiator may be appropriately set according to the monomer combination, reaction conditions, etc., and is not particularly limited. However, when the total amount of the monomers used in the polymerization is 100% by mass, it may be 0.01 to 1% by mass, preferably 0.05 to 0.5% by mass.

[0105] As the chain transfer agent, a chain transfer agent used in general radical polymerization can be used. For example, the chain transfer agent disclosed in the method for preparing a methacrylic resin having a structural unit derived from the above N-substituted maleimide monomer can be used. These may be used alone or in combination of two or more. These chain transfer agents may be added at any stage as long as the polymerization reaction is in progress, and are not particularly limited. Regarding the addition amount of the chain transfer agent, it is not particularly limited as long as the desired degree of polymerization can be obtained under the polymerization conditions used. However, preferably, when the total amount of the monomers used in the polymerization is 100% by mass, it may be 0.01 to 1% by mass, preferably 0.05 to 0.5% by mass.

[0106] A suitable method for adding the polymerization initiator and the chain transfer agent in the polymerization step may be, for example, the method described in the method for preparing a methacrylic resin having a structural unit derived from the above N-substituted maleimide monomer. The dissolved oxygen concentration in the polymerization solution may be, for example, the value disclosed in the method for preparing a methacrylic resin having a structural unit derived from the above N-substituted maleimide monomer.

[0107] Next, an imidization reaction is carried out by reacting the above (meth)acrylic acid ester polymer or the above methacrylic acid ester-aromatic vinyl copolymer with an imidizing agent (imidization step). Thereby, a methacrylic resin having a glutarimide-based structural unit can be produced.

[0108] The imidizing agent is not particularly limited as long as it can generate the glutarimide-based structural unit represented by the above general formula (3). As the imidizing agent, specifically, ammonia or a primary amine can be used. Examples of the primary amine include aliphatic hydrocarbon group-containing primary amines such as methylamine, ethylamine, n-propylamine, i-propylamine, n-butylamine, i-butylamine, tert-butylamine, n-hexylamine; alicyclic hydrocarbon group-containing primary amines such as cyclohexylamine; and the like. Among the above imidizing agents, from the viewpoints of cost and physical properties, it is preferable to use ammonia, methylamine, or cyclohexylamine, and it is particularly preferable to use methylamine.

[0109] In this imidization step, by adjusting the addition ratio of the imidizing agent, the content of the glutarimide-based structural unit in the methacrylic resin having the glutarimide-based structural unit obtained can be adjusted.

[0110] The method for carrying out the above imidization reaction is not particularly limited, but a conventionally known method can be used. For example, the imidization reaction can be advanced by using an extruder or a batch reactor.

[0111] The extruder is not particularly limited. For example, a single-screw extruder, a twin-screw extruder, a multi-screw extruder, etc. can be used. Among them, it is preferable to use a twin-screw extruder. According to the twin-screw extruder, the mixing of the raw material polymer and the imidizing agent can be promoted. Examples of the twin-screw extruder include a non-intermeshing co-rotating type, an intermeshing co-rotating type, a non-intermeshing counter-rotating type, an intermeshing counter-rotating type, and the like. The above-exemplified extruders may be used alone or a plurality of them may be connected in series and used. In addition, it is particularly preferable to attach a vent port capable of reducing the pressure to below atmospheric pressure to the extruder used, because by-products such as the imidizing agent, methanol, or monomers can be removed.

[0112] In the production of a methacrylic resin having a glutarimide-based structural unit, in addition to the imidization step, an esterification step of treating the carboxyl groups of the resin with an esterifying agent such as dimethyl carbonate can be included. At that time, a catalyst such as trimethylamine, triethylamine, or tributylamine can also be used in combination for the treatment. The esterification step can proceed in the same manner as the above imidization step, for example, by using an extruder or a batch reactor. Also, for the purpose of removing excess esterifying agent, by-products such as methanol, or monomers, it is preferable to attach a vent port to the apparatus that can reduce the pressure below atmospheric pressure.

[0113] The methacrylic resin that has undergone the imidization step and, if necessary, the esterification step is melted and extruded in a strand form from an extruder equipped with a porous die, and processed into pellets by a cold cut method, an air hot cut method, an underwater strand cut method, an under water cut method, etc. Also, in order to reduce the number of foreign substances in the resin, it is also preferable to use a method in which the methacrylic resin is dissolved in an organic solvent such as toluene, methyl ethyl ketone, or methylene chloride, the obtained methacrylic resin solution is filtered, and then the organic solvent is devolatilized.

[0114] From the viewpoint of reducing the fluorescence intensity (content of the fluorescent substance), it is preferable not to use a twin-screw extruder that is subjected to shear force and imidize the polymerization solution after the polymerization is completed in a batch reactor. The imidization reaction is preferably carried out at 130 to 250 °C, more preferably at 150 to 230 °C, and even more preferably at 170 to 190 °C. The reaction time is preferably 10 minutes to 5 hours, and more preferably 30 minutes to 2 hours. After the imidization step, if necessary, after passing through the esterification step, it is preferable from the viewpoint of reducing the fluorescence intensity to carry out devolatilization by the devolatilization method with reduced shear described in (3) in the method for preparing a methacrylic resin having a structural unit derived from the N-substituted maleimide monomer, and then pelletize.

[0115] -Method for Producing Methacrylic Resin Containing Lactone Ring Structure Unit- As a method for producing a methacrylic resin having a lactone ring structure unit in the main chain, a method of forming a lactone ring structure by a cyclization reaction after polymerization is used. However, in order to promote the cyclization reaction, it is preferable to polymerize monomers by radical polymerization by a solution polymerization method using a solvent. In the production method of the present embodiment, as the polymerization method, for example, any of a batch polymerization method, a semi-batch method, and a continuous polymerization method can be used. The methacrylic resin having a lactone ring structure unit in the main chain can be formed by the methods described in, for example, JP-A-2001-151814, JP-A-2004-168882, JP-A-2005-146084, JP-A-2006-96960, JP-A-2006-171464, JP-A-2007-63541, JP-A-2007-297620, JP-A-2010-180305, etc.

[0116] Hereinafter, as an example of the method for producing a methacrylic resin having a lactone ring structure unit, the case of producing by batch radical polymerization using a solution polymerization method will be specifically described. As a method for producing a methacrylic resin having a lactone ring structure unit, a method of forming a lactone ring structure by a cyclization reaction after polymerization is used. However, in order to promote the cyclization reaction, solution polymerization using a solvent is preferable.

[0117] Examples of the solvent used for polymerization include aromatic hydrocarbons such as toluene, xylene, and ethylbenzene; ketones such as methyl ethyl ketone and methyl isobutyl ketone; and the like. These solvents may be used alone or in combination of two or more.

[0118] The amount of the solvent during polymerization is not particularly limited as long as the polymerization proceeds and gelation can be suppressed. For example, when the total amount of the monomers to be blended is 100% by mass, it is preferably 50 to 200% by mass, more preferably 100 to 200% by mass.

[0119] In order to sufficiently suppress the gelation of the polymerization solution and promote the cyclization reaction after polymerization, it is preferable to carry out the polymerization so that the concentration of the produced polymer in the reaction mixture obtained after polymerization is 50% by mass or less. Further, it is preferable to appropriately add a polymerization solvent to the reaction mixture and control the concentration to 50% by mass or less.

[0120] The method of appropriately adding the polymerization solvent to the reaction mixture is not particularly limited. For example, the polymerization solvent may be added continuously or intermittently. The polymerization solvent to be added may be a single solvent of only one kind or a mixed solvent of two or more kinds. The polymerization temperature is not particularly limited as long as the polymerization proceeds, but from the viewpoint of productivity, it is preferably 50 to 200°C, more preferably 80 to 180°C. The polymerization time is not particularly limited as long as the target conversion rate is satisfied, but from the viewpoints of productivity and the like, it is preferably 0.5 to 10 hours, more preferably 1 to 8 hours.

[0121] During the polymerization reaction, if necessary, a polymerization initiator or a chain transfer agent may be added for polymerization. The polymerization initiator is not particularly limited. For example, the polymerization initiators disclosed in the method for preparing a methacrylic resin having a structural unit derived from the above N-substituted maleimide monomer can be used. These polymerization initiators may be used alone or in combination of two or more. These polymerization initiators may be added at any stage as long as the polymerization reaction is in progress. The addition amount of the polymerization initiator may be appropriately set according to the monomer combination, reaction conditions, etc., and is not particularly limited. However, when the total amount of the monomers used for polymerization is 100% by mass, it may be 0.05 to 1% by mass.

[0122] As the chain transfer agent, a chain transfer agent used in general radical polymerization can be used. For example, the chain transfer agent disclosed in the method for preparing a methacrylic resin having a structural unit derived from the above N-substituted maleimide monomer can be utilized. These may be used alone or in combination of two or more. These chain transfer agents may be added at any stage as long as the polymerization reaction is in progress, and are not particularly limited. Regarding the addition amount of the chain transfer agent, it is not particularly limited as long as the desired degree of polymerization can be obtained under the polymerization conditions used. Preferably, when the total amount of the monomers used for polymerization is 100% by mass, it may be 0.05 to 1% by mass.

[0123] A suitable method for adding the polymerization initiator and the chain transfer agent in the polymerization step may be, for example, the method described in the method for preparing a methacrylic resin having a structural unit derived from the above N-substituted maleimide monomer.

[0124] The dissolved oxygen concentration in the polymerization solution may be, for example, the value disclosed in the method for preparing a methacrylic resin having a structural unit derived from the above N-substituted maleimide monomer.

[0125] The methacrylic resin having a lactone ring structural unit in the present embodiment can be obtained by performing a cyclization reaction after the above polymerization reaction. Therefore, it is preferable to subject it to the lactone cyclization reaction in a state containing the solvent without removing the polymerization solvent from the polymerization reaction solution. The copolymer obtained by polymerization undergoes a cyclization condensation reaction between the hydroxyl group (hydroxyl group) and the ester group present in the molecular chain of the copolymer by heat treatment to form a lactone ring structure. During the heat treatment for forming the lactone ring structure, a reaction apparatus equipped with a vacuum apparatus or a devolatilization apparatus for removing the alcohol that may be by-produced by cyclization condensation, an extruder equipped with a devolatilization apparatus, etc. can also be used.

[0126] When forming a lactone ring structure, if necessary, heat treatment may be performed using a cyclocondensation catalyst to promote the cyclocondensation reaction. Specific examples of the cyclocondensation catalyst include, for example, monoalkyl esters, dialkyl esters or triesters of phosphorous acid such as methyl phosphite, ethyl phosphite, phenyl phosphite, dimethyl phosphite, diethyl phosphite, diphenyl phosphite, trimethyl phosphite, triethyl phosphite; monoalkyl esters, dialkyl esters or trialkyl esters of phosphoric acid such as methyl phosphate, ethyl phosphate, 2-ethylhexyl phosphate, octyl phosphate, isodecyl phosphate, lauryl phosphate, stearyl phosphate, isostearyl phosphate, dimethyl phosphate, diethyl phosphate, di-2-ethylhexyl phosphate, diisodecyl phosphate, dilauryl phosphate, distearyl phosphate, diisostearyl phosphate, trimethyl phosphate, triethyl phosphate, triisodecyl phosphate, trilauryl phosphate, tristearyl phosphate, triisostearyl phosphate; organic zinc compounds such as zinc acetate, zinc propionate, zinc octyl; etc. These may be used alone or in combination of two or more.

[0127] The amount of the cyclocondensation catalyst used is not particularly limited. For example, it is preferably 0.01 to 3% by mass, more preferably 0.05 to 1% by mass, based on 100% by mass of the methacrylic resin. When the amount of the catalyst used is 0.01% by mass or more, it is effective for improving the reaction rate of the cyclocondensation reaction. When the amount of the catalyst used is 3% by mass or less, it is effective for preventing the resulting polymer from coloring or the polymer from crosslinking and making melt molding difficult.

[0128] The timing of adding the cyclocondensation catalyst is not particularly limited. For example, it may be added at the initial stage of the cyclocondensation reaction, during the reaction, or both. When performing the cyclocondensation reaction in the presence of a solvent, devolatilization can also be carried out simultaneously.

[0129] The apparatus used when simultaneously performing the cyclization condensation reaction and the devolatilization step is not particularly limited, but a devolatilization apparatus composed of a heat exchanger and a devolatilization tank, an extruder with a vent, or an apparatus in which the devolatilization apparatus and the extruder are arranged in series is preferable, and a twin-screw extruder with a vent is more preferable. As the twin-screw extruder with a vent to be used, an extruder with a vent having a plurality of vent ports is preferable.

[0130] When using an extruder with a vent, the reaction treatment temperature is preferably 150 to 350 °C, more preferably 200 to 300 °C. If the reaction treatment temperature is less than 150 °C, the cyclization condensation reaction may be insufficient and the residual volatile matter may increase. Conversely, if the reaction treatment temperature exceeds 350 °C, the obtained polymer may be colored or decomposed. When using an extruder with a vent, the degree of vacuum is preferably 10 to 500 Torr, more preferably 10 to 300 Torr. If the degree of vacuum exceeds 500 Torr, volatile matter may easily remain. Conversely, if the degree of vacuum is less than 10 Torr, industrial implementation may become difficult.

[0131] When performing the above cyclization condensation reaction, it is also preferable to add an alkaline earth metal and / or an amphoteric metal salt of an organic acid during granulation for the purpose of deactivating the remaining cyclization condensation catalyst. Examples of the alkaline earth metal and / or amphoteric metal salt of an organic acid that can be used include calcium acetylacetate, calcium stearate, zinc acetate, zinc octylate, zinc 2-ethylhexanoate, and the like.

[0132] After passing through the cyclization condensation reaction step, the methacrylic resin is melted and extruded in a strand shape from an extruder equipped with a porous die, and processed into pellets by a cold cut method, an air hot cut method, an underwater strand cut method, and an under water cut method. In addition, the lactonization for forming the aforementioned lactone ring structural unit may be performed after the production of the resin and before the production of the resin composition (described later), or may be performed in combination with the melt kneading of the resin and components other than the resin during the production of the resin composition.

[0133] From the viewpoint of reducing the fluorescence intensity (content of the fluorescent substance), it is preferable not to use a twin-screw extruder that is subjected to shear force and to perform lactone cyclization of the polymerization solution after the polymerization is completed in a batch reactor. After the lactone cyclization step, devolatilization is performed by the devolatilization method with reduced shear described in (3) in the method for preparing a methacrylic resin having a structural unit derived from the above N-substituted maleimide monomer, and then pelletization is preferably performed from the viewpoint of reducing the fluorescence intensity.

[0134] [Additive] The resin composition constituting the resin lens for a head-mounted display of the present embodiment may contain various additives as long as the effects of the present invention are not significantly impaired as described above. The additives are not particularly limited, and examples thereof include antioxidants, light stabilizers such as hindered amine-based light stabilizers, ultraviolet absorbers, mold release agents, other thermoplastic resins, paraffinic process oils, naphthenic process oils, aromatic process oils, paraffin, organopolysiloxanes, softening agents / plasticizers such as mineral oils, flame retardants, antistatic agents, inorganic fillers such as pigments such as organic fibers and iron oxide, reinforcing agents such as glass fibers, carbon fibers, and metal whiskers, colorants; organic phosphorus compounds such as phosphites, phosphonites, and phosphates, other additives, or mixtures thereof.

[0135] -Antioxidant- The resin composition constituting the resin lens for a head-mounted display of the present embodiment preferably contains an antioxidant that suppresses deterioration and coloring during molding or use. Examples of the antioxidant include, but are not limited to, hindered phenol-based antioxidants, phosphorus-based antioxidants, sulfur-based antioxidants, and the like. These antioxidants may be used alone or in combination of two or more. Also, from the viewpoints of improving thermal stability and suppressing molding defects, it is preferable to use a plurality of types of heat stabilizers in combination. For example, it is preferable to use in combination at least one selected from phosphorus-based antioxidants and sulfur-based antioxidants and a hindered phenol-based antioxidant.

[0136] Examples of the hindered phenol-based antioxidant include, but are not limited to, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, 3,3’,3’’,5,5’,5’’-hexa-tert-butyl-a,a’,a’’-(mesitylene-2,4,6-triyl)tri-p-cresol, 4,6-bis(octylthiomethyl)-o-cresol, 4,6-bis(dodecylthiomethyl)-o-cresol, ethylene bis(oxyethylene) bis[3-(5-tert-butyl-4-hydroxy-m-tolyl)propionate], hexamethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, 1,3,5-tris[(4-tert-butyl-3-hydroxy-2,6-xylyl)methyl]-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, 2,6-di-tert-butyl-4-(4,6-bis(octylthio)-1,3,5-triazin-2-ylamine)phenol, 2-[1-(2-hydroxy-3,5-di-tert-pentylphenyl)ethyl]-4,6-di-tert-pentylphenyl acrylate, 2-tert-butyl-4-methyl-6-(2-hydroxy-3-tert-butyl-5-methylbenzyl) phenyl acrylate, and the like. Particularly preferred are pentaerythritol tetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl 3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, and 2-[1-(2-hydroxy-3,5-di-tert-pentylphenyl)ethyl]-4,6-di-tert-pentylphenyl acrylate.

[0137] In addition, as the antioxidant, a hindered phenol-based antioxidant may be a commercially available phenol-based antioxidant. Such commercially available phenol-based antioxidants include, but are not limited to, for example, Irganox 1010 (Irganox 1010: pentaerythritol tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], manufactured by BASF), Irganox 1076 (Irganox 1076: octadecyl 3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, manufactured by BASF), Irganox 1330 (Irganox 1330: 3,3’,3’’,5,5’,5’’-hexa-t-butyl-a,a’,a’’-(mesitylene-2,4,6-triyl)tri-p-cresol, manufactured by BASF), Irganox 3114 (Irganox3114: 1,3,5-tris(3,5-di-t-butyl-4-hydroxybenzyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, manufactured by BASF), Irganox 3125 (Irganox 3125, manufactured by BASF), Adeka Stab AO-60 (pentaerythritol tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], manufactured by ADEKA), Adeka Stab AO-80 (3,9-bis{2-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxyoxy]-1,1-dimethylethyl}-2,4,8,10-tetraoxaspiro[5.5]undecane, manufactured by ADEKA), Sumilizer BHT (Sumilizer BHT, manufactured by Sumitomo Chemical), Cyanox 1790 (Cyanox 1790, manufactured by Cytec), Sumilizer GA-80 (Sumilizer GA-80, manufactured by Sumitomo Chemical), Sumilizer GS (Sumilizer GS: 2-[1-(2-hydroxy-3,5-di-tert-pentylphenyl)ethyl]-4,6-di-tert-pentylphenyl acrylate, manufactured by Sumitomo Chemical), Sumilizer GM (Sumilizer GM: 2-tert-butyl-4-methyl-6-(2-hydroxy-3-tert-butyl-5-methylbenzyl)phenyl acrylate, manufactured by Sumitomo Chemical), vitamin E (manufactured by Eisai), and the like. Among these commercially available phenolic antioxidants, from the perspective of the effect of imparting thermal stability to the resin, Irganox 1010, Adeka Stab AO-60, Adeka Stab AO-80, Irganox 1076, Sumilizer GS, etc. are preferred. These may be used alone or in combination of two or more.

[0138] In addition, the phosphorus-based antioxidants as the above antioxidants are not limited to the following, but for example, tris(2,4-di-t-butylphenyl) phosphite, bis(2,4-bis(1,1-dimethylethyl)-6-methylphenyl) ethyl ester phosphite, tetrakis(2,4-di-t-butylphenyl)(1,1-biphenyl)-4,4'-diylbisphosphonite, bis(2,4-di-t-butylphenyl)pentaerythritol diphosphite, bis(2,6-di-t-butyl-4-methylphenyl)pentaerythritol diphosphite, bis(2,4-dicumylphenyl)pentaerythritol-diphosphite, tetrakis(2,4-t-butylphenyl)(1,1-biphenyl)-4,4'-diylbisphosphonite, di-t-butyl-m-cresyl-phosphonite, 4-[3-[(2,4,8,10-tetra-tert-butyldibenzo[d,f][1,3,2]dioxaphosphepin)-6-yloxy]propyl]-2-methyl-6-tert-butylphenol, etc. may be mentioned.

[0139] Furthermore, a commercially available phosphorus-based antioxidant may be used as the phosphorus-based antioxidant. Examples of such commercially available phosphorus-based antioxidants include, but are not limited to, Irgafos 168 (Irgafos 168: tris(2,4-di-t-butylphenyl) phosphite, manufactured by BASF), Irgafos 12 (Irgafos 12: tris[2-[[2,4,8,10-tetra-t-butyldibenzo[d,f][1,3,2]dioxaphosphepin-6-yl]oxy]ethyl]amine, manufactured by BASF), Irgafos 38 (Irgafos 38: bis(2,4-bis(1,1-dimethylethyl)-6-methylphenyl)ethyl ester phosphite, manufactured by BASF), ADK STAB 329K (manufactured by ADEKA), ADK STAB PEP-36 (manufactured by ADEKA), ADK STAB PEP-36A (manufactured by ADEKA), ADK STAB PEP-8 (manufactured by ADEKA), ADK STAB HP-10 (manufactured by ADEKA), ADK STAB 2112 (manufactured by ADEKA), ADK STAB 1178 (manufactured by ADEKA), ADK STAB 1500 (manufactured by ADEKA), Sandstab P-EPQ (manufactured by Clariant), Weston 618 (manufactured by GE), Weston 619G (manufactured by GE), Ultranox 626 (manufactured by GE), Sumilizer GP (Sumilizer GP: 4-[3-[(2,4,8,10-tetra-tert-butyldibenzo[d,f][1,3,2]dioxaphosphepin)-6-yloxy]propyl]-2-methyl-6-tert-butylphenol, manufactured by Sumitomo Chemical), HCA (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, manufactured by Mitsuho Corporation), and the like. Among these commercially available phosphorus-based antioxidants, from the viewpoints of the effect of imparting thermal stability to the resin and the combined effect with various antioxidants, Irgafos 168, AdekaStab PEP-36, AdekaStab PEP-36A, AdekaStab HP-10, and AdekaStab 1178 are preferred, and AdekaStab PEP-36A and AdekaStab PEP-36 are particularly preferred. These phosphorus-based antioxidants may be used alone or in combination of two or more.

[0140] In addition, examples of the sulfur-based antioxidants as the above antioxidants include, but are not limited to, 2,4-bis(dodecylthiomethyl)-6-methylphenol (Irganoox 1726, manufactured by BASF), 2,4-bis(octylthiomethyl)-6-methylphenol (Irganoox 1520L, manufactured by BASF), 2,2-bis{[3-(dodecylthio)-1-oxopropoxy]methyl}propane-1,3-diylbis[3-dodecylthio]propionate (AdekaStab AO-412S, manufactured by ADEKA), 2,2-bis{[3-(dodecylthio)-1-oxopropoxy]methyl}propane-1,3-diylbis[3-dodecylthio]propionate (Cheminox PLS, manufactured by Chemipro Kasei Co., Ltd.), di(tridecyl) 3,3'-thiodipropionate (AO-503, manufactured by ADEKA), and the like. Among these commercially available sulfur antioxidants, from the viewpoints of the effect of imparting thermal stability to the resin, the combined effect with various antioxidants, and the handleability, AdekaStab AO-412S and Cheminox PLS are preferred. These sulfur-based antioxidants may be used alone or in combination of two or more.

[0141] The content of the antioxidant only needs to be an amount that can achieve the effect of improving thermal stability. If the content is excessive, problems such as bleeding out during processing may occur. Therefore, based on 100% by mass of the methacrylic resin, it is preferably 5% by mass or less, more preferably 3% by mass or less, still more preferably 1% by mass or less, even more preferably 0.8% by mass or less, even more preferably 0.01 - 0.8% by mass, and particularly preferably 0.01 - 0.5% by mass.

[0142] There is no particular limitation on the timing of adding the antioxidant. Examples include a method of starting polymerization after adding it to the monomer solution before polymerization, a method of subjecting it to a devolatilization step after adding and mixing it into the polymer solution after polymerization, a method of pelletizing after adding and mixing it into the molten polymer after devolatilization, and a method of adding and mixing it when remelting and extruding the pellets after devolatilization and pelletizing. Among these, from the perspective of preventing thermal degradation and coloring in the devolatilization step, it is preferable to add the antioxidant after adding and mixing it into the polymer solution after polymerization and then subject it to the devolatilization step before the devolatilization step.

[0143] - Hindered amine light stabilizer - The resin composition constituting the resin lens for a head-mounted display of this embodiment can contain a hindered amine light stabilizer. The hindered amine light stabilizer is not particularly limited, but is preferably a compound containing three or more ring structures. Here, the ring structure is preferably at least one selected from the group consisting of an aromatic ring, an aliphatic ring, an aromatic heterocyclic ring, and a non-aromatic heterocyclic ring. When one compound has two or more ring structures, they may be the same or different from each other. Examples of hindered amine light stabilizers include, but are not limited to, for example, specifically, bis(1,2,2,6,6-pentamethyl-4-piperidyl) [[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]methyl]butyl malonate, a mixture of bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate and methyl 1,2,2,6,6-pentamethyl-4-piperidyl sebacate, bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate, N,N'-bis(2,2,6,6-tetramethyl-4-piperidyl)-N,N'-diformylhexamethylenediamine, a polycondensate of dibutylamine·1,3,5-triazine·N,N'-bis(2,2,6,6-tetramethyl-4-piperidyl)-1,6-hexamethylenediamine and N-(2,2,6,6-tetramethyl-4-piperidyl)butylamine, poly[{6-(1,1,3,3-tetramethylbutyl)amino-1,3,5-triazine-2,4-diyl}{(2,2,6,6-tetramethyl-4-piperidyl)imino}hexamethylene{(2,2,6,6-tetramethyl-4-piperidyl)imino}], tetrakis(1,2,2,6,6-pentamethyl-4-piperidyl) butane-1,2,3,4-tetracarboxylate, tetrakis(2,2,6,6-tetramethyl-4-piperidyl) butane-1,2,3,4-tetracarboxylate, a reaction product of 1,2,2,6,6-pentamethyl-4-piperidol and β,β,β',β'-tetramethyl-2,4,8,10-tetraoxaspiro[5.5]undecane-3,9-diol, a reaction product of 2,2,6,6-tetramethyl-4-piperidol and β,β,β',β'-tetramethyl-2,4,8,10-tetraoxaspiro[5.5]undecane-3,9-diol, bis(1-undecanoxy-2,2,6,6-tetramethylpiperidin-4-yl) carbonate, 1,2,2,6,6-pentamethyl-4-piperidyl methacrylate, 2,2,6,6-tetramethyl-4-piperidyl methacrylate, and the like. Among them, bis(1,2,2,6,6-pentamethyl-4-piperidyl) [[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]methyl]butyl malonate, the polycondensate of dibutylamine, 1,3,5-triazine, N,N'-bis(2,2,6,6-tetramethyl-4-piperidyl)-1,6-hexamethylenediamine and N-(2,2,6,6-tetramethyl-4-piperidyl)butylamine, poly[{6-(1,1,3,3-tetramethylbutyl)amino-1,3,5-triazine-2,4-diyl}{(2,2,6,6-tetramethyl-4-piperidyl)imino}hexamethylene{(2,2,6,6-tetramethyl-4-piperidyl)imino}], the reaction product of 1,2,2,6,6-pentamethyl-4-piperidol and β,β,β',β'-tetramethyl-2,4,8,10-tetraoxaspiro[5.5]undecane-3,9-diol, and the reaction product of 2,2,6,6-tetramethyl-4-piperidol and β,β,β',β'-tetramethyl-2,4,8,10-tetraoxaspiro[5.5]undecane-3,9-diol are preferred. The content of the hindered amine light stabilizer may be an amount that can obtain the effect of improving the light stability. If the content is excessive, problems such as bleeding out during processing may occur. Therefore, based on 100% by mass of the methacrylic resin, it is preferably 5% by mass or less, more preferably 3% by mass or less, still more preferably 1% by mass or less, even more preferably 0.8% by mass or less, even more preferably 0.01 to 0.8% by mass, and particularly preferably 0.01 to 0.5% by mass.

[0144] --Ultraviolet Absorber-- The resin composition constituting the resin lens for a head-mounted display of the present embodiment can contain an ultraviolet absorber. The ultraviolet absorber is not particularly limited, but it is preferably an ultraviolet absorber having a maximum absorption wavelength of 280 to 380 nm. For example, benzotriazole compounds, benzotriazine compounds, benzophenone compounds, oxybenzophenone compounds, benzoate compounds, phenol compounds, oxazole compounds, cyanoacrylate compounds, benzoxazinone compounds, etc. can be mentioned. Examples of the benzotriazole compound include 2,2'-methylenebis[4-(1,1,3,3-tetramethylbutyl)-6-(2H-benzotriazol-2-yl)phenol], 2-(3,5-di-tert-butyl-2-hydroxyphenyl)-5-chlorobenzotriazole, 2-(2H-benzotriazol-2-yl)-p-cresol, 2-(2H-benzotriazol-2-yl)-4,6-bis(1-methyl-1-phenylethyl)phenol, 2-benzotriazol-2-yl-4,6-di-tert-butylphenol, 2-[5-chloro(2H)-benzotriazol-2-yl]-4-methyl-6-t-butylphenol, 2-(2H-benzotriazol-2-yl)-4,6-di-t-butylphenol, 2-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol, 2-(2H-benzotriazol-2-yl)-4-methyl-6-(3,4,5,6-tetrahydrophthalimidylmethyl)phenol, the reaction product of methyl 3-(3-(2H-benzotriazol-2-yl)-5-t-butyl-4-hydroxyphenyl)propionate / polyethylene glycol 300, 2-(2H-benzotriazol-2-yl)-6-(linear and branched dodecyl)-4-methylphenol, 2-(5-methyl-2-hydroxyphenyl)benzotriazole, 2-[2-hydroxy-3,5-bis(α,α-dimethylbenzyl)phenyl]-2H-benzotriazole, 3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-C7-9 side chain and linear alkyl ester. Among these, benzotriazole compounds having a molecular weight of 400 or more are preferred. For example, in the case of commercially available products, Kemisorb (registered trademark) 2792 (manufactured by Chemipro Kasei Co., Ltd.), Adeka Stab (registered trademark) LA31 (manufactured by ADEKA CORPORATION), Tinuvin (registered trademark) 234 (manufactured by BASF), etc. can be mentioned. Examples of benzotriazine compounds include 2 - mono(hydroxyphenyl)-1,3,5 - triazine compounds, 2,4 - bis(hydroxyphenyl)-1,3,5 - triazine compounds, and 2,4,6 - tris(hydroxyphenyl)-1,3,5 - triazine compounds. Specifically, 2,4 - diphenyl - 6-(2 - hydroxy - 4 - methoxyphenyl)-1,3,5 - triazine, 2,4 - diphenyl - 6-(2 - hydroxy - 4 - ethoxyphenyl)-1,3,5 - triazine, 2,4 - diphenyl-(2 - hydroxy - 4 - propoxyphenyl)-1,3,5 - triazine, 2,4 - diphenyl-(2 - hydroxy - 4 - butoxyphenyl)-1,3,5 - triazine, 2,4 - diphenyl - 6-(2 - hydroxy - 4 - butoxyphenyl)-1,3,5 - triazine, 2,4 - diphenyl - 6-(2 - hydroxy - 4 - hexyloxyphenyl)-1,3,5 - triazine, 2,4 - diphenyl - 6-(2 - hydroxy - 4 - octyloxyphenyl)-1,3,5 - triazine, 2,4 - diphenyl - 6-(2 - hydroxy - 4 - dodecyloxyphenyl)-1,3,5 - triazine, 2,4 - diphenyl - 6-(2 - hydroxy - 4 - benzyloxyphenyl)-1,3,5 - triazine, 2,4 - diphenyl - 6-(2 - hydroxy - 4 - butoxyethoxy)-1,3,5 - triazine, 2,4 - bis(2 - hydroxy - 4 - butoxyphenyl)-6-(2,4 - dibutoxyphenyl)-1,3 - 5 - triazine, 2,4,6 - tris(2 - hydroxy - 4 - methoxyphenyl)-1,3,5 - triazine, 2,4,6 - tris(2 - hydroxy - 4 - ethoxyphenyl)-1,3,5 - triazine, 2,4,6 - tris(2 - hydroxy - 4 - propoxyphenyl)-1,3,5 - triazine, 2,4,6 - tris(2 - hydroxy - 4 - butoxyphenyl)-1,3,5 - triazine, 2,4,6 - tris(2 - hydroxy - 4 - butoxyphenyl)-1,3,5 - triazine, 2,4,6 - tris(2 - hydroxy - 4 - hexyloxyphenyl)-1,3,5 - triazine, 2,4,6 - tris(2 - hydroxy - 4 - octyloxyphenyl)-1,3,5 - triazine, 2,4,6 - tris(2 - hydroxy - 4 - dodecyloxyphenyl)-1,3,5 - triazine, 2,4,6-Tris(2-hydroxy-4-benzyloxyphenyl)-1,3,5-triazine, 2,4,6-tris(2-hydroxy-4-ethoxyethoxyphenyl)-1,3,5-triazine, 2,4,6-tris(2-hydroxy-4-butoxyethoxyphenyl)-1,3,5-triazine, 2,4,6-tris(2-hydroxy-4-propoxyethoxyphenyl)-1,3,5-triazine, 2,4,6-tris(2-hydroxy-4-methoxycarbonylpropyloxyphenyl)-1,3,5-triazine, 2,4,6-tris(2-hydroxy-4-ethoxycarbonylethyloxyphenyl)-1,3,5-triazine, 2,4,6-tris(2-hydroxy-4-(1-(2-ethoxyhexyloxy)-1-oxopropan-2-yloxy)phenyl)-1,3,5-triazine, 2,4,6-tris(2-hydroxy-3-methyl-4-methoxyphenyl)-1,3,5-triazine, 2,4,6-tris(2-hydroxy-3-methyl-4-ethoxyphenyl)-1,3,5-triazine, 2,4,6-tris(2-hydroxy-3-methyl-4-propoxyphenyl)-1,3,5-triazine, 2,4,6-tris(2-hydroxy-3-methyl-4-butoxyphenyl)-1,3,5-triazine, 2,4,6-tris(2-hydroxy-3-methyl-4-butoxyphenyl)-1,3,5-triazine, 2,4,6-tris(2-hydroxy-3-methyl-4-hexyloxyphenyl)-1,3,5-triazine, 2,4,6-tris(2-hydroxy-3-methyl-4-octyloxyphenyl)-1,3,5-triazine, 2,4,6-tris(2-hydroxy-3-methyl-4-dodecyloxyphenyl)-1,3,5-triazine, 2,4,6-tris(2-hydroxy-3-methyl-4-benzyloxyphenyl)-1,3,5-triazine, 2,4,6-tris(2-hydroxy-3-methyl-4-ethoxyethoxyphenyl)-1,3,5-triazine, 2,4,6-tris(2-hydroxy-3-methyl-4-butoxyethoxyphenyl)-1,3,5-triazine, 2,4,6-tris(2-hydroxy-3-methyl-4-propoxyethoxyphenyl)-1,3,5-triazine, 2,4,Examples include 6-tris(2-hydroxy-3-methyl-4-methoxycarbonylpropyloxyphenyl)-1,3,5-triazine, 2,4,6-tris(2-hydroxy-3-methyl-4-ethoxycarbonylethyloxyphenyl)-1,3,5-triazine, 2,4,6-tris(2-hydroxy-3-methyl-4-(1-(2-ethoxyhexyloxy)-1-oxopropan-2-yloxy)phenyl)-1,3,5-triazine, etc. As the benzotriazine compound, commercially available products may be used. For example, Kemisorb 102 (manufactured by Chemipro Kasei Co., Ltd.), LA-F70 (manufactured by ADEKA Corporation), LA-46 (manufactured by ADEKA Corporation), Tinuvin 405 (manufactured by BASF), Tinuvin 460 (manufactured by BASF), Tinuvin 479 (manufactured by BASF), Tinuvin 1577FF (manufactured by BASF), etc. can be used. Among them, from the viewpoints of high compatibility with acrylic resins and excellent ultraviolet absorption characteristics, an ultraviolet absorber having a 2,4-bis(2,4-dimethylphenyl)-6-[2-hydroxy-4-(3-alkyloxy-2-hydroxypropyloxy)-5-α-cumylphenyl]-s-triazine skeleton (where "alkyloxy" means a long-chain alkyloxy group such as octyloxy, nonyloxy, decyloxy, etc.) can be more preferably used. As the ultraviolet absorber, particularly from the viewpoints of compatibility with resins and volatility during heating, benzotriazole compounds and benzotriazine compounds having a molecular weight of 400 or more are preferable. Also, from the viewpoint of suppressing decomposition of the ultraviolet absorber itself during heating in extrusion processing, benzotriazine compounds are particularly preferable. In addition, the melting point (Tm) of the above ultraviolet absorber is preferably 80°C or higher, more preferably 100°C or higher, further preferably 130°C or higher, and even more preferably 160°C or higher. When the above ultraviolet absorber is heated at a rate of 20°C / min from 23°C to 260°C, the weight loss rate is preferably 50% or less, more preferably 30% or less, further preferably 15% or less, even more preferably 10% or less, and even more preferably 5% or less. These ultraviolet absorbers may be used alone, or two or more of them may be used in combination. By using two ultraviolet absorbers having different structures in combination, ultraviolet rays in a wide wavelength range can be absorbed. The content of the above ultraviolet absorber is not particularly limited as long as it does not inhibit heat resistance, heat and humidity resistance, thermal stability, and molding processability and exhibits the effects of the present invention. However, it is preferably 0.1 to 5% by mass, preferably 0.2 to 4% by mass or less, more preferably 0.25 to 3% by mass, and even more preferably 0.3 to 3% by mass with respect to 100% by mass of the methacrylic resin. When it is within this range, the balance between ultraviolet absorption performance, moldability, etc. is excellent.

[0145] --Release agent-- The resin composition constituting the resin lens for a head-mounted display of the present embodiment may contain a release agent. Examples of the release agent include, but are not limited to, fatty acid esters, fatty acid amides, fatty acid metal salts, hydrocarbon lubricants, alcohol lubricants, polyalkylene glycols, carboxylic acid esters, paraffinic mineral oils of hydrocarbons, and the like.

[0146] There is no particular limitation on the fatty acid ester that can be used as the release agent, and conventionally known ones can be used. Examples of the fatty acid ester include ester compounds of fatty acids having 12 to 32 carbon atoms such as lauric acid, palmitic acid, heptadecanoic acid, stearic acid, oleic acid, arachidic acid, behenic acid, and monohydric aliphatic alcohols such as palmityl alcohol, stearyl alcohol, behenyl alcohol, and polyhydric aliphatic alcohols such as glycerin, pentaerythritol, dipentaerythritol, sorbitan; composite ester compounds of fatty acids, polybasic organic acids, and monohydric aliphatic alcohols or polyhydric aliphatic alcohols can be used.

[0147] Examples of such fatty acid esters include cetyl palmitate, butyl stearate, stearyl stearate, stearyl citrate, glycerin monocaprylate, glycerin monocaprate, glycerin monolaurate, glycerin monopalmitate, glycerin dipalmitate, glycerin monostearate, glycerin distearate, glycerin tristearate, glycerin monooleate, glycerin dioleate, glycerin trioleate, glycerin monolinoleate, glycerin monobehenate, glycerin mono-12-hydroxystearate, glycerin di-12-hydroxystearate, glycerin tri-12-hydroxystearate, glycerin diacetomonostearate, glycerin citrate fatty acid ester, pentaerythritol adipate stearate, partially saponified montanic acid ester, pentaerythritol tetrastearate, dipentaerythritol hexastearate, sorbitan tristearate, and the like. These fatty acid esters can be used alone or in combination of two or more. Examples of commercially available products include the Rikemal series, Pemu series, Rikester series, Rikemaster series manufactured by Riken Vitamin Co., Ltd., and the Excel series, Leodol series, Exepal series, Cocnard series manufactured by Kao Corporation. More specifically, Rikemal S-100, Rikemal H-100, Pemu V-100, Rikemal B-100, Rikemal HC-100, Rikemal S-200, Pemu B-200, Rikester EW-200, Rikester EW-400, Excel S-95, Leodol MS-50, and the like can be mentioned.

[0148] There are no particular restrictions on fatty acid amides, and conventionally known ones can be used. Examples of fatty acid amides include saturated fatty acid amides such as lauric acid amide, palmitic acid amide, stearic acid amide, behenic acid amide, hydroxystearic acid amide; unsaturated fatty acid amides such as oleic acid amide, erucic acid amide, ricinoleic acid amide; substituted amides such as N-stearyl stearic acid amide, N-oleyl oleic acid amide, N-stearyl oleic acid amide, N-oleyl stearic acid amide, N-stearyl erucic acid amide, N-oleyl palmitic acid amide; methylol amides such as methylol stearic acid amide, methylol behenic acid amide; saturated fatty acid bisamides such as methylene bisstearic acid amide, ethylene biscapric acid amide, ethylene bislauric acid amide, ethylene bisstearic acid amide (ethylene bisstearyl amide), ethylene bisisostearic acid amide, ethylene bishydroxystearic acid amide, ethylene bisbehenic acid amide, hexamethylene bisstearic acid amide, hexamethylene bisbehenic acid amide, hexamethylene bishydroxystearic acid amide, N,N'-distearyl adipic acid amide, N,N'-distearyl sebacic acid amide; unsaturated fatty acid bisamides such as ethylene bisoleic acid amide, hexamethylene bisoleic acid amide, N,N'-dioleyl adipic acid amide, N,N'-dioleyl sebacic acid amide; aromatic bisamides such as m-xylylene bisstearic acid amide, N,N'-distearyl isophthalic acid amide, etc. These fatty acid amides can be used alone or in combination of two or more. Examples of commercially available products include Diamond Series (manufactured by Nippon Kasei Co., Ltd.), Amide Series (manufactured by Nippon Kasei Co., Ltd.), Nikka Amide Series (manufactured by Nippon Kasei Co., Ltd.), Methylol Amide Series, Bisamide Series, Slipax Series (manufactured by Nippon Kasei Co., Ltd.), Kao Wax Series (manufactured by Kao Corporation), Fatty Acid Amide Series (manufactured by Kao Corporation), Ethylene Bisstearic Acid Amides (manufactured by Dainichi Chemical Industry Co., Ltd.), etc.

[0149] The fatty acid metal salt refers to the metal salt of a higher fatty acid. Examples include lithium stearate, magnesium stearate, calcium stearate, calcium laurate, calcium ricinoleate, strontium stearate, barium stearate, barium laurate, barium ricinoleate, zinc stearate, zinc laurate, zinc ricinoleate, zinc 2-ethylhexoate, lead stearate, dibasic lead stearate, lead naphthenate, calcium 12-hydroxystearate, lithium 12-hydroxystearate, etc. Among them, calcium stearate, magnesium stearate, and zinc stearate are particularly preferred because the resulting transparent resin composition has excellent processability and extremely excellent transparency. As commercial products, for example, the SZ series, SC series, SM series, SA series, etc. manufactured by Sakai Chemical Industry Co., Ltd. can be mentioned. When using the above fatty acid metal salt, the content is preferably 0.2% by mass or less based on 100% by mass of the resin composition from the viewpoint of maintaining transparency.

[0150] The above mold release agent may be used alone or in combination of two or more.

[0151] As the mold release agent to be used, those with a decomposition start temperature of 200 °C or higher are preferred. Here, the decomposition start temperature can be measured by the 1% mass loss temperature by TGA.

[0152] The content of the mold release agent may be an amount that can obtain the effect as a mold release agent. If the content is excessive, problems such as the occurrence of bleed-out during processing and extrusion defects due to screw slippage may occur. Therefore, based on 100% by mass of the methacrylic resin, it is preferably 5% by mass or less, more preferably 3% by mass or less, still more preferably 1% by mass or less, even more preferably 0.8% by mass or less, and even more preferably 0.01 - 0.8% by mass, particularly preferably 0.01 - 0.5% by mass. Adding in the amount within the above range is preferred because it can suppress the decrease in transparency due to the addition of the mold release agent and tends to suppress mold release failure during injection molding.

[0153] -Other thermoplastic resins- The resin composition constituting the resin lens for a head-mounted display according to the present embodiment may contain other thermoplastic resins other than methacrylic resins for the purpose of adjusting the birefringence and improving the flexibility without impairing the object of the present invention.

[0154] Examples of other thermoplastic resins include polyacrylates such as polybutyl acrylate; styrene-based polymers such as polystyrene, styrene-methyl methacrylate copolymer, styrene-butyl acrylate copolymer, styrene-acrylonitrile copolymer, acrylonitrile-butadiene-styrene block copolymer; and further, for example, acrylic rubber particles having a 3-4 layer structure described in JP-A-59-202213, JP-A-63-27516, JP-A-51-129449, JP-A-52-56150, etc.; rubbery polymers disclosed in JP-B-60-17406, JP-A-8-245854; methacrylic rubber-containing graft copolymer particles obtained by multi-stage polymerization described in International Publication No. 2014-002491; and the like. Among these, from the viewpoint of obtaining good optical properties and mechanical properties, styrene-acrylonitrile copolymer or rubber-containing graft copolymer particles having a graft part composed of a composition compatible with a methacrylic resin containing a structural unit (X) having a ring structure in the main chain on its surface layer are preferable.

[0155] The average particle diameter of the aforementioned acrylic rubber particles, methacrylic rubber-containing graft copolymer particles, and rubbery polymer is preferably 0.03 to 1 μm, more preferably 0.05 to 0.5 μm, from the viewpoint of enhancing the impact strength and optical properties of the film obtained from the composition of the present embodiment.

[0156] When the methacrylic resin is 100% by mass, the content of other thermoplastic resins is preferably 0 to 50% by mass, more preferably 0 to 25% by mass.

[0157] [Method for Producing Resin Composition] As a method for producing the resin composition constituting the resin lens for a head-mounted display according to the present embodiment, as long as a composition satisfying the requirements of the present invention can be obtained, it is not particularly limited. For example, a method of kneading using a kneader such as an extruder, a heating roll, a kneader, a roller mixer, a Banbury mixer, etc. can be mentioned. Among these, kneading by an extruder is preferable in terms of productivity. The kneading temperature may follow the preferable processing temperature of the polymer constituting the methacrylic resin and other resins to be mixed. As a guideline, it is in the range of 140 to 300°C, preferably in the range of 180 to 280°C. Further, it is preferable to provide a vent port in the extruder for the purpose of reducing volatile components.

[0158] Here, in the resin composition constituting the resin lens for a head-mounted display according to the present embodiment, the remaining amount of solvent (residual solvent amount) is preferably less than 1000 mass ppm, more preferably less than 800 mass ppm, and even more preferably less than 700 mass ppm. Here, the remaining solvent refers to the polymerization solvent used during polymerization (excluding alcohols), and the solvent used when the resin obtained by polymerization is dissolved again to form a solution. Specifically, examples of the polymerization solvent include aromatic hydrocarbons such as toluene, xylene, ethylbenzene, and isopropylbenzene; ketones such as methyl isobutyl ketone, butyl cellosolve, methyl ethyl ketone, and cyclohexanone; polar solvents such as dimethylformamide and 2-methylpyrrolidone; etc. Examples of the solvent used for re-dissolution include toluene, methyl ethyl ketone, methylene chloride, etc.

[0159] In the resin composition constituting the resin lens for a head-mounted display according to the present embodiment, the remaining amount of alcohol (residual alcohol amount) is preferably less than 500 mass ppm, more preferably less than 400 mass ppm, and even more preferably less than 350 mass ppm. Here, the remaining alcohol refers to the alcohol by-produced by the cyclocondensation reaction. Specifically, examples include aliphatic alcohols such as methanol, ethanol, and isopropanol.

[0160] The above residual solvent amount and the above residual alcohol amount can be measured by gas chromatography.

[0161] In any case of the selected method, it is preferable to prepare the composition after reducing oxygen and water as much as possible. For example, as the dissolved oxygen concentration in the polymerization solution in solution polymerization, less than 300 ppm is preferable in the polymerization step. In the preparation method using an extruder or the like, as the oxygen concentration in the extruder, it is preferably less than 1% by volume, and more preferably less than 0.8% by volume. The water content of the methacrylic resin is preferably adjusted to 1000 mass ppm or less, more preferably 500 mass ppm or less. Within these ranges, it becomes relatively easy and advantageous to prepare a composition that satisfies the requirements of the present invention.

[0162] [Method for manufacturing a resin lens for a head-mounted display] The resin lens for a head-mounted display of the present embodiment is formed by molding the above resin composition. As the method for manufacturing the resin lens for a head-mounted display of the present embodiment, molding methods such as injection molding, compression molding, and extrusion molding can be used. Among these, injection molding is preferable from the viewpoint of productivity.

[0163] Generally, the injection molding method includes: (1) an injection step of melting the resin and filling the molten resin into the cavity of a temperature-controlled mold; (2) a holding pressure step of applying pressure to the cavity until the gate is sealed and injecting resin corresponding to the amount by which the molten resin filled in the injection step contacts the mold and cools and shrinks; (3) a cooling step of holding the molded product until the resin is cooled after releasing the holding pressure; and (4) a step of opening the mold and taking out the cooled molded product.

[0164] At this time, as the molding temperature, based on the glass transition temperature (Tg) of the resin composition, it is preferably in the range of Tg + 100°C to Tg + 160°C, more preferably in the range of Tg + 110°C to Tg + 150°C. Here, the molding temperature refers to the controlled temperature of the band heater wound around the injection nozzle. Although a resin lens with a lower phase difference can be obtained as the molding temperature is higher, since coloring due to thermal degradation during residence in the molding machine is promoted under constant temperature, the molding temperature should be appropriately selected. Also, as the mold temperature, based on the glass transition temperature (Tg) of the resin composition, it is preferably in the range of Tg - 70°C to Tg, and more preferably in the range of Tg - 50°C to Tg - 20°C.

[0165] Also, the injection speed can be appropriately selected according to the thickness and dimensions of the resin lens to be obtained. For example, it can be appropriately selected from the range of 5 to 1000 mm / second. Also, the pressure for holding pressure can be appropriately selected according to the shape of the resin lens to be obtained. For example, it can be appropriately selected in the range of 30 to 120 MPa. Here, the pressure for holding pressure is the pressure held by the screw for further sending out the molten resin from the gate after filling the molten resin.

[0166] Also, in order to relieve the residual stress generated by injection molding and reduce the phase difference of the resin lens, an annealing process may be performed. The temperature during annealing is preferably in the range of Tg - 50°C to Tg, and more preferably in the range of Tg - 30°C to Tg - 10°C, based on the glass transition temperature (Tg) of the resin composition.

[0167] On the surface of the resin lens for a head-mounted display of this embodiment, for example, surface functionalization treatments such as hard coat treatment, antireflection treatment, transparent conductive treatment, electromagnetic wave shielding treatment, and gas barrier treatment can be further performed. The thickness of these functional layers is not particularly limited, but is usually in the range of 0.01 to 10 μm.

[0168] As the hard coat layer to be applied to the surface, for example, a coating solution in which an acrylate such as a silicone-based curable resin, an organic polymer composite inorganic fine particle-containing curable resin, urethane acrylate, epoxy acrylate, or polyfunctional acrylate and a photoinitiator are dissolved or dispersed in an organic solvent is applied onto a film or sheet obtained from the resin composition of the present embodiment by a conventionally known coating method, dried, and photocured to form it. Further, before applying the hard coat layer, in order to improve adhesiveness, for example, a method of forming a hard coat layer after previously providing an easy adhesion layer, a primer layer, an anchor layer, etc. containing inorganic fine particles in its composition can also be used. As the antiglare layer to be applied to the surface, fine particles such as silica, melamine resin, and acrylic resin are made into ink and applied onto other functional layers by a conventionally known coating method, and are formed by heat or photocuring. Examples of the antireflection layer to be applied to the surface include those composed of a thin film of an inorganic substance such as a metal oxide, fluoride, silicide, boride, nitride, or sulfide, those in which resins having different refractive indexes such as an acrylic resin and a fluororesin are laminated in a single layer or multiple layers, and those in which a thin layer containing composite fine particles of an inorganic compound and an organic compound is laminated.

Examples

[0169] Hereinafter, the content of the present invention will be specifically described with reference to examples and comparative examples. Note that the present invention is not limited to the following examples.

[0170] <1. Measurement of the amount of 2-cyclohexylamino-N-cyclohexylsuccinimide in N-cyclohexylmaleimide> N-cyclohexylmaleimide or an N-cyclohexylmaleimide / m-xylene solution was sampled and weighed to prepare a 25 mass% N-cyclohexylmaleimide m-xylene solution. Isopropyl benzoate was added as an internal standard substance, and measurement was performed under the following conditions using gas chromatography (GC-2014 manufactured by Shimadzu Corporation) and determined. Detector: FID Column used: HP-5ms Measurement conditions: Hold at 80°C for 5 minutes, then increase the temperature to 300°C at a rate of 10°C / min, and then hold for 5 minutes

[0171] <Measurement of the amount of 2-anilino-N-phenylsuccinimide in N-phenylmaleimide> Collect and weigh N-phenylmaleimide or N-phenylmaleimide / m-xylene solution, prepare a 10% by mass m-xylene solution of N-phenylmaleimide, add isopropyl benzoate as an internal standard substance, and use liquid chromatography (UPLC H-class manufactured by Waters Corporation) to measure and determine under the following conditions. Detector: PDA (detection wavelength: 210 nm - 300 nm) Column used: ACQUITY UPLC HSS T3 Column temperature: 40°C Mobile phase: 50% aqueous acetonitrile solution containing 0.1% formic acid Flow rate: 0.4 mL / min

[0172] <Determination of the remaining amount of N-substituted maleimide monomer> Collect and weigh a part of the analysis target (the polymerization solution after polymerization or methacrylic resin pellets), dissolve this sample in chloroform to prepare a 5% by mass solution, add n-decane as an internal standard substance, and use gas chromatography (GC-2010 manufactured by Shimadzu Corporation) to measure and determine under the following conditions. Detector: FID Column used: ZB-1 Measurement conditions: Hold at 45°C for 5 minutes, then increase the temperature to 300°C at a rate of 20°C / min, and then hold for 15 minutes

[0173] <Analysis of structural units> Each structural unit in the methacrylic resins produced in the production examples and comparative examples described below, unless otherwise specified 1 1H-NMR measurement and 13 13C-NMR measurement were used to identify each structural unit of the methacrylic resin and the methacrylic resin composition, and calculate its abundance.1 1H-NMR measurement and 13 The measurement conditions for 13C-NMR measurement are as follows. · Measuring instrument: JNM-ECZ400S manufactured by JEOL Ltd. · Measuring solvent: CDCl3 or d6-DMSO · Measuring temperature: 40 °C

[0174] <5. Molecular weight and molecular weight distribution> The weight average molecular weight (Mw), number average molecular weight (Mn), and Z average molecular weight (Mz) of the methacrylic resin compositions produced in the production examples and production comparative examples described below were measured under the following apparatus and conditions. · Measuring apparatus: Gel Permeation Chromatography (HLC-8320GPC) manufactured by Tosoh Corporation · Measuring conditions: Column: One TSKguardcolumn SuperH-H, two TSKgel SuperHM-M, and one TSKgel SuperH2500 were connected in series and used. Column temperature: 40 °C Developing solvent: Tetrahydrofuran, flow rate: 0.6 mL / min. As an internal standard, 2,6-di-t-butyl-4-methylphenol (BHT) was added at 0.1 g / L. Detector: RI (differential refractive index) detector Detection sensitivity: 3.0 mV / min Sample: 20 mL solution of 0.02 g of methacrylic resin composition in tetrahydrofuran Injection volume: 10 μL Calibration curve standard sample: The following 10 types of polymethyl methacrylate (manufactured by Polymer Laboratories; PMMA Calibration Kit M-M-10) with known weight peak molecular weights and different molecular weights were used. Weight peak molecular weight (Mp) Standard sample 1 1,916,000 Standard sample 2 625,500 Standard sample 3 298,900 Standard sample 4 138,600 Standard sample 5 60,150 Standard sample 6 27,600 Standard sample 7 10,290 Standard sample 8 5,000 Standard sample 9 2,810 Standard sample 10 850 Under the above conditions, the RI detection intensity with respect to the elution time of the methacrylic resin composition was measured. Based on each calibration curve obtained by measuring the above calibration curve standard samples, the weight average molecular weight (Mw), number average molecular weight (Mn), and Z average molecular weight (Mz) of the methacrylic resin composition were determined, and using these values, the molecular weight distributions (Mw / Mn) and (Mz / Mw) were determined.

[0175] <6. Phase difference within the effective diameter of the resin lens> The resin lenses obtained in the examples and comparative examples were measured for the surface distribution of the phase difference from the optical axis direction at a wavelength of 520 nm using a birefringence evaluation system PA-200-L manufactured by Photonic Lattice Co., Ltd., and the average value (nm) of the absolute value of the phase difference was determined by designating the area within the effective diameter (Φ41 mm) of the lens.

[0176] <7. Content of fluorescent substance in the resin lens> The resin lenses obtained in the examples and comparative examples were shredded, weighed into a glass sample bottle, chloroform was added, and shaken at a speed of 800 times per minute for 30 minutes with a shaker to prepare a 2.0 mass% chloroform solution of the resin lens, and the fluorescence intensity was measured using a fluorescence spectrophotometer (Fluorolog3-22 manufactured by Horiba Jobin Yvon). The measurement conditions were as follows: a xenon lamp was used as the light source, a PMT was used as the detector, the excitation wavelength was 436 nm, the slit width was 2 nm for both the excitation side and the observation side, the time constant was 0.2 s, the measurement mode was Sc / Rc which normalizes the emission intensity with the excitation light intensity at each wavelength, and the measurement was performed with a 90° observation using a 1 cm optical path length quartz cell. The fluorescence intensity at a wavelength of 530 nm obtained was normalized using the fluorescence intensity of a fluorescein / ethanol solution. Specifically, it was done as follows. Ethanol, and 5×10 -8 mol / L and 1×10-6 The fluorescence intensity at a wavelength of 530 nm when each of the fluorescein / ethanol solutions at a concentration of mol / L was spectroscopically analyzed at an excitation wavelength of 436 nm was determined. After subtracting the background of ethanol, a concentration-intensity conversion formula was created. The fluorescence emission spectrum of chloroform was measured, and the concentration was converted using the previously obtained concentration-intensity conversion formula for the fluorescein / ethanol solution from the emission intensity obtained by subtracting the emission intensity of chloroform at a wavelength of 530 nm from the emission intensity at a wavelength of 530 nm of the 2.0 mass% chloroform solution of the resin lens, and the content (mol / L) of the fluorescent substance was determined.

[0177] <8. Glass transition temperature of the resin lens> In accordance with JIS-K7121, the glass transition temperature (Tg) (°C) of the resin lens was measured. First, four specimens (four locations), each approximately 10 mg, were cut out from the resin lens that had been conditioned (left to stand at 23 °C for one week) under standard conditions (23 °C, 50% RH) as test pieces. Next, a differential scanning calorimeter (Diamond DSC manufactured by PerkinElmer Japan Co., Ltd.) was used under the condition of a nitrogen gas flow rate of 25 mL / min. Here, the temperature was raised from room temperature (23 °C) to 200 °C at 10 °C / min (first temperature rise), held at 200 °C for 5 minutes to completely melt the sample, then cooled from 200 °C to 40 °C at 10 °C / min, held at 40 °C for 5 minutes, and further, among the DSC curves drawn during the second temperature rise under the above temperature rise conditions, the intersection point (midpoint glass transition temperature) between the stepped change portion curve during the second temperature rise and a straight line equidistant in the vertical axis direction from each baseline extension line was measured as the glass transition temperature (Tg) (°C). Four measurements were made for each sample, and the arithmetic mean (rounded to the nearest whole number after the decimal point) of the four points was taken as the measured value.

[0178] <9. Photoelastic coefficient of the resin lens> After cutting up the resin lenses obtained in the examples and comparative examples, they were made into press films using a vacuum compression molding machine to obtain samples for measurement. As specific sample preparation conditions, a vacuum compression molding machine (manufactured by Kando Metal Industry Co., Ltd., model SFV-30) was used. After preheating at 260°C under reduced pressure (about 10 kPa) for 10 minutes, the resin lens was compressed at 260°C and about 10 MPa for 5 minutes. After releasing the reduced pressure and the press pressure, it was transferred to a compression molding machine for cooling and solidification. The obtained press film was cured for 24 hours or more in a thermostatic and humidistatic chamber adjusted to 23°C and 60% humidity, and then a test piece for measurement (thickness about 150 μm, width 6 mm) was cut out. Using a birefringence measuring device described in detail in Polymer Engineering and Science 1999, 39, 2349-2357, the photoelastic coefficient C R (Pa -1 ) was measured. The film-shaped test piece was placed in a film tensile device (manufactured by Imoto Seisakusho) installed in the same thermostatic and humidistatic chamber so that the distance between the chucks was 50 mm. Next, the device was arranged so that the laser light path of the birefringence measuring device (manufactured by Otsuka Electronics Co., Ltd., RETS-100) was located at the center of the film, and the birefringence of the test piece was measured while applying an extensional stress at a strain rate of 50% / min (distance between chucks: 50 mm, chuck moving speed: 5 mm / min). From the relationship between the birefringence (Δn) obtained from the measurement and the extensional stress (σ R ), the slope of the straight line was obtained by the least squares approximation, and the photoelastic coefficient (C R )(Pa -1 ) was calculated. For the calculation, data between 2.5 MPa ≤ σ R ≤ 10 MPa were used. C R = Δn / σ R Here, the birefringence (Δn) is the value shown below. Δn = nx - ny (nx: refractive index in the stretching direction, ny: refractive index in the direction perpendicular to the stretching direction in the plane)

[0179] <10. Light transmittance of resin lens> The resin lenses obtained in the examples and comparative examples were measured for transmittance (%) every 5 nm in the wavelength range of 380 to 780 nm at a 10° field of view with a D65 light source using a spectrocolorimeter (SD-5000, manufactured by Nippon Denshoku Industries Co., Ltd.) with the light source passing through the thickest part of the lens in the thickness direction. Using the measured values, the ratio (T450 / T680) of the transmittance (T450) at a wavelength of 450 nm to the transmittance (T680) at a wavelength of 680 nm was determined.

[0180] <11. Sharpness of the image> Using the resin lenses obtained in the examples and comparative examples, a simulation device was fabricated in a dark room to reproduce the principle of the head-mounted display described in Japanese Patent Application Laid-Open No. 2017-21321 as shown in Fig. 1. In the simulation device, a liquid crystal display 1, a polarizing plate 2, a quarter-wave plate 3, a half mirror 4, a resin lens 5 obtained in the examples and comparative examples, a quarter-wave plate 6, and a reflective polarizing plate 7 are coaxially arranged in this order. The light along the optical axis from the liquid crystal display 1 passes through the polarizing plate 2, the quarter-wave plate 3, the half mirror 4, the resin lens 5, and the quarter-wave plate 6 and reaches the reflective polarizing plate 7, where it is reflected (the first reflection). Next, when it reaches the half mirror 4 through the quarter-wave plate 6 and the resin lens 5, it is reflected by the half mirror 4 (the second reflection), passes through the resin lens 5, the quarter-wave plate 6, and the reflective polarizing plate 7 again, and reaches the human eye. Note that the half mirror 4 enables some light to be reflected and the remaining light to be transmitted. The light increases its phase delay by 90 degrees each time it passes through a quarter-wave plate. The image is enlarged by the above two reflections and reaches the human eye. The still image displayed on the liquid crystal display 1 was observed through the above simulation device, and the sharpness of the image was evaluated according to the following evaluation criteria. [Evaluation criteria] 〇: The image is enlarged and there is no blurring or smearing. △: An image with a low magnification factor overlaps the enlarged image, and the image is slightly unclear. ×: An image with a low magnification factor is mainly seen and is unclear.

[0181] [Raw materials] The raw materials used in the following Examples and Comparative Examples are shown below. [Monomer] · Methyl methacrylate (MMA): manufactured by Asahi Kasei Corporation · N-cyclohexylmaleimide (chMI): manufactured by Nippon Shokubai Co., Ltd. (The mass ratio of 2-cyclohexylamino-N-cyclohexylsuccinimide (CCSI) to the mass of chMI is 80 ppm by mass) · N-phenylmaleimide (phMI): manufactured by Nippon Shokubai Co., Ltd. (The mass ratio of 2-anilino-N-phenylsuccinimide (APSI) to the mass of phMI is 60 ppm by mass)

[0182] -Pretreatment of N-substituted maleimide (chMI, phMI) (washing step with water and dehydration step)- For the above N-cyclohexylmaleimide (chMI) and N-phenylmaleimide (phMI), removal of 2-amino-N-substituted succinimide (CCSI, APSI) and removal of contained moisture were carried out by the following washing and dehydration steps.

[0183] --Washing and dehydration of N-cyclohexylmaleimide (chMI)-- ---Reducing CCSI in N-cyclohexylmaleimide to 5 ppm by mass or less--- Weighed 250.0 kg of chMI and 750.0 kg of metaxylene (hereinafter referred to as "mXy"), and added them to a 2.0 m glass-lined reactor equipped with a temperature control device by jacket and three retreating blades as stirring blades. Steam was blown into the jacket to raise the solution temperature in the reactor to 56°C, stirred to obtain an organic layer. Next, 350.0 kg of 2% by mass sulfuric acid water was weighed and added to the reactor, the solution temperature was maintained at 56°C, and stirred at 100 rpm for 10 minutes. Stirring was stopped, left standing for 10 minutes, and the aqueous layer was withdrawn into a drum can. 3 ​The same operation was repeated two more times, and the organic layer was washed with sulfuric acid water a total of three times. When the amount of CCSI in the organic layer was quantified by gas chromatography, it was 4.9 mass ppm with respect to chMI in the organic layer. Thereafter, 350.0 kg of ion-exchanged water was added to the reactor, the solution temperature was maintained at 55 °C, and it was stirred at 100 rpm for 10 minutes. Stirring was stopped, it was allowed to stand for 20 minutes, and the aqueous layer was withdrawn into a drum can. The same operation was repeated once more, and the organic layer was washed with ion-exchanged water a total of two times. When the amount of CCSI in the organic layer was quantified by gas chromatography, it was 4.6 mass ppm with respect to chMI in the organic layer. Next, while maintaining the solution temperature at 50 °C and stirring at 100 rpm, the pressure inside the reactor was gradually reduced, and the pressure inside the reactor was set to 5 kPa. Thereafter, the solution temperature was raised to 60 °C, and an azeotropic dehydration operation was performed. 131.6 kg of a water / mXy mixture was distilled off, and when the water concentration in the organic layer was quantified by a Karl Fischer moisture meter, it was 102 mass ppm with respect to the mass of the organic layer. Concentration-adjusting mXy was added to the organic layer to obtain 1034.3 kg of an organic layer with chMI at 24.0 mass%, a water concentration of 191 mass ppm, and CCSI at 4.6 mass ppm with respect to the mass of chMI.

[0184] ---Reduce CCSI in N-cyclohexylmaleimide to 1 mass ppm or less--- 80.0 kg of chMI and 240.0 kg of mXy were weighed and added to a 0.50 m glass-lined reactor equipped with a temperature control device by jacket and a full zone made by Kobe Steel Environmental Solutions as a stirring blade. 3 Steam was blown into the jacket to raise the solution temperature inside the reactor to 55 °C, stirred, and an organic layer was obtained. Next, 112.0 kg of 2 mass% sulfuric acid water was weighed and added to the reactor, the solution temperature was maintained at 55 °C, and it was stirred at 100 rpm for 30 minutes. Stirring was stopped, it was allowed to stand for 10 minutes, and the aqueous layer was withdrawn into a drum can. The same operation was repeated three more times, and the organic layer was washed with sulfuric acid water a total of four times. When the amount of CCSI in the organic layer was quantified by gas chromatography, it was 0.57 mass ppm with respect to chMI in the organic layer. Thereafter, 112.0 kg of ion-exchanged water was added to the reactor, the solution temperature was maintained at 55 °C, and the mixture was stirred at 100 rpm for 30 minutes. Stirring was stopped, and the mixture was allowed to stand for 10 minutes, after which the aqueous layer was withdrawn into a drum can. While maintaining the solution temperature at 50 °C and stirring at 100 rpm, the pressure inside the reactor was gradually reduced, and the pressure inside the reactor was set to 5 kPa. Thereafter, the solution temperature was raised to 60 °C, and an azeotropic dehydration operation was performed. 54 kg of a water / mXy mixture was distilled off, and when the water concentration in the organic layer was quantified using a Karl Fischer moisture meter, it was 46 mass ppm with respect to the mass of the organic layer. Concentration-adjusting mXy was added to the organic layer to obtain 384.0 kg of an organic layer having a chMI of 20.3 mass%, a water concentration of 125 mass ppm, and a CCSI of 0.60 mass ppm with respect to the mass of chMI.

[0185] --Washing and dehydration of N-phenylmaleimide (phMI)-- ---Reducing APSI in N-phenylmaleimide to 5 mass ppm or less--- 150.0 kg of phMI and 720.0 kg of mXy were weighed and added to a 2.0 m glass-lined reactor equipped with a temperature control device using a jacket and three retreating blades as stirring blades. Steam was blown into the jacket to raise the solution temperature inside the reactor to 55 °C, and the mixture was stirred to obtain an organic layer. Next, 336.0 kg of 7 mass% aqueous sodium bicarbonate solution was weighed and added to the reactor, the solution temperature was maintained at 55 °C, and the mixture was stirred at 100 rpm for 10 minutes. Stirring was stopped, and the mixture was allowed to stand for 10 minutes, after which the aqueous layer was withdrawn into a drum can. 3 Subsequently, 336.0 kg of ion-exchanged water was added to the reactor, the solution temperature was maintained at 55 °C, and the mixture was stirred at 100 rpm for 10 minutes. Stirring was stopped, and the mixture was allowed to stand for 10 minutes, after which the aqueous layer was withdrawn into a drum can. ​Subsequently, 336.0 kg of 2 mass% sulfuric acid solution was weighed and added to the reactor. The solution temperature was maintained at 55°C, and it was stirred at 100 rpm for 10 minutes. Stirring was stopped, and it was allowed to stand for 10 minutes. Then, the aqueous layer was withdrawn into a drum can. In the same manner as above, the operation of washing with ion-exchanged water was further performed twice. When the amount of APSI in the organic layer was quantified by liquid chromatography, it was 3.6 mass ppm with respect to phMI in the organic layer. Next, while maintaining the solution temperature at 50°C and stirring at 100 rpm, the pressure inside the reactor was gradually reduced, and the pressure inside the reactor was set to 5 kPa. Then, the solution temperature was raised to 55°C, and an azeotropic dehydration operation was performed. 190 kg of water / mXy mixture was distilled off. When the water concentration in the organic layer was quantified by a Karl Fischer moisture meter, it was 47 mass ppm with respect to the mass of the organic layer. Concentration-adjusting mXy was added to the organic layer, and 1340.7 kg of an organic layer with phMI of 10.8 mass%, water concentration of 170 mass ppm, and APSI of 3.4 mass ppm with respect to the mass of phMI was obtained.

[0186] ---Reduce APSI in N-phenylmaleimide to 1 mass ppm or less--- 50.0 kg of phMI and 240.0 kg of mXy were weighed and added to a 0.50 m glass-lined reactor equipped with a temperature control device using a jacket and a full zone made by Kobe Steel Environmental Solutions as a stirring blade. 3 Steam was blown into the jacket to raise the solution temperature inside the reactor to 55°C, and it was stirred to obtain an organic layer. Subsequently, 112.0 kg of 7 mass% sodium bicarbonate solution was weighed and added to the reactor. The solution temperature was maintained at 55°C, and it was stirred at 100 rpm for 15 minutes. Stirring was stopped, and it was allowed to stand for 10 minutes. Then, the aqueous layer was withdrawn into a drum can. The same operation was repeated once more, and the operation of washing the organic layer with sodium bicarbonate water was performed a total of 2 times. Next, 112.0 kg of ion-exchanged water was added to the reactor. The solution temperature was maintained at 55°C, and it was stirred at 100 rpm for 30 minutes. Stirring was stopped, and it was allowed to stand for 10 minutes. Then, the aqueous layer was withdrawn into a drum can. Subsequently, 112.0 kg of 2 mass% sulfuric acid water was weighed and added to the reactor. The solution temperature was maintained at 55°C, and it was stirred at 100 rpm for 30 minutes. Stirring was stopped, and it was allowed to stand for 10 minutes, and the aqueous layer was withdrawn into a drum can. The same operation was repeated 2 more times, and the operation of washing the organic layer with sulfuric acid water was performed a total of 3 times. In the same manner as above, the operation of washing with ion-exchanged water was further performed 2 times. When the amount of APSI in the organic layer was quantified by liquid chromatography, it was 0.37 mass ppm with respect to phMI in the organic layer. The solution temperature was maintained at 50°C, and while stirring at 100 rpm, the pressure inside the reactor was gradually reduced, and the pressure inside the reactor was set to 5 kPa. Subsequently, the solution temperature was raised to 55°C, and an azeotropic dehydration operation was performed. 72 kg of water / mXy mixture was distilled off, and when the water concentration in the organic layer was quantified by a Karl Fischer moisture meter, it was 60 mass ppm with respect to the mass of the organic layer. Concentration-adjusting mXy was added to the organic layer to obtain 432.8 kg of an organic layer with phMI of 10.3 mass%, water concentration of 180 mass ppm, and APSI of 0.42 mass ppm with respect to the mass of phMI.

[0187] [Polymerization initiator] · 1,1-Di(t-butylperoxy)cyclohexane: "Perhexa C" manufactured by NOF Corporation [Chain transfer agent] · n-Octyl mercaptan: manufactured by Kao Corporation [Hindered phenol antioxidant] · Irganox 1010: manufactured by BASF [Phosphorus antioxidant] · Irgafos 168 (melting point 180 - 190°C): manufactured by BASF

[0188] [Methacrylic resin composition] [Production Example 1] 374.8 kg of a 10.3 mass% mXy solution of phMI (APSI is 0.42 mass ppm with respect to the mass of phMI) that has undergone a water washing process and a dehydration process, and 323.6 kg of a 20.3 mass% mXy solution of chMI (CCSI is 0.60 mass ppm with respect to the mass of chMI) that has undergone a water washing process and a dehydration process were weighed, and added to a 1.25 m reactor equipped with a temperature control device by a jacket and a stirring blade. 3 While stirring at a solution temperature of 60 °C and a reactor internal pressure of 5 kPa, 160.8 kg of mXy was distilled off under reduced pressure. Next, the reactor was returned to normal pressure, and by adding 16.7 kg of mXy, a mixed solution of 38.6 kg of phMI, 65.7 kg of chMI, and 450.0 kg of mXy was prepared. 445.7 kg of MMA and 0.413 kg of n-octyl mercaptan, which is a chain transfer agent, were weighed, added, and stirred to obtain a monomer mixed solution. Regarding the content liquid in the reactor, nitrogen bubbling was carried out at a rate of 30 L / min for 1 hour to remove dissolved oxygen. Thereafter, steam was blown into the jacket to raise the solution temperature in the reactor to 125 °C, and while stirring at 50 rpm, a polymerization initiator solution in which 0.23 kg of 1,1-di(t-butylperoxy)cyclohexane was dissolved in 2.77 kg of mXy was added at a rate of 0.5 kg / hour to start polymerization, and the addition was stopped 6 hours after the start of polymerization. During polymerization, the solution temperature in the reactor was controlled to 125 ± 2 °C by temperature control with the jacket. After 8 hours had elapsed since the start of polymerization, a polymerization solution containing a methacrylic resin having a ring structure in the main chain was obtained. As a result of evaluating the amount of N-substituted maleimide contained in the obtained polymerization solution, it contained 1340 mass ppm of phMI and 4390 mass ppm of chMI. To this polymerization solution, 0.1 mass% of Irganox 1010 and 0.05 mass% of Irgafos 168 were added under stirring with respect to 100 mass% of the polymer contained in the solution. The polymerization solution containing this antioxidant was filtered through a filter with a filtration accuracy of 2 μm made of SUS316L metal fiber. To recover the polymer from the polymer solution, as the apparatus used in the devolatilization process, a plate heat exchanger having a flat plate slit type flow path and a heat transfer medium flow path and a vacuum vessel made of SUS with a heat transfer medium jacket having an internal volume of about 0.3 m 3 (hereinafter referred to as a devolatilization tank) were used to form a devolatilization apparatus. The solution containing the polymer obtained by polymerization was supplied to a heat exchanger installed at the upper part of the vacuum vessel at a rate of 30 liters / hour, heated to 260°C, and then supplied to a devolatilization tank heated and depressurized under the conditions of an internal temperature of 260°C and a vacuum degree of 30 Torr for devolatilization treatment. When the shear rate in the devolatilization apparatus was calculated from the apparatus shape and operating conditions, it was 5.3 s -1 . After devolatilization, the polymer was pressurized by a gear pump from the lower part of the devolatilization tank, extruded from a strand die, cooled with water, and pelletized to obtain a methacrylic resin composition A. When the composition of the methacrylic resin composition A was confirmed, the structural units derived from MMA, phMI, and chMI monomers were 81.2% by mass, 7.1% by mass, and 11.7% by mass, respectively. The weight average molecular weight Mw was 148,000, Mw / Mn was 2.12, Mz / Mw was 1.63, and the glass transition temperature was 133°C.

[0189] [Production Example 2] 352.4 kg of a 10.3% by mass mXy solution of phMI (APSI is 0.42 ppm by mass based on the mass of phMI) that had undergone a water washing process and a dehydration process and 310.3 kg of a 20.3% by mass mXy solution of chMI (CCSI is 0.60 ppm by mass based on the mass of chMI) that had undergone a water washing process and a dehydration process were weighed, and added to a 1.25 m 3 reactor equipped with a temperature control device by a jacket and a stirring blade. While stirring at a solution temperature of 60°C and a reactor internal pressure of 5 kPa, 335.4 kg of mXy was distilled off under reduced pressure. Next, the reactor was returned to normal pressure, and 8.9 kg of mXy was added to prepare a mixed solution of 36.3 kg of phMI, 63.0 kg of chMI, and 236.9 kg of mXy. 340.7 kg of MMA and 0.275 kg of n-octyl mercaptan as a chain transfer agent were weighed, charged, and stirred to obtain a monomer mixed solution. Next, 123.1 kg of mXy was weighed and added to Tank 1. Furthermore, 110.0 kg of MMA and 90.0 kg of mXy were weighed into tank 2, stirred, and used as a monomer solution for top-up. Regarding the content liquid in the reactor, nitrogen bubbling was carried out at a rate of 30 L / min for 1 hour, and for each of tank 1 and tank 2, nitrogen bubbling was carried out at a rate of 10 L / min for 30 minutes to remove dissolved oxygen. Thereafter, steam was blown into the jacket to raise the solution temperature in the reactor to 128 °C, and while stirring at 50 rpm, a polymerization initiator solution prepared by dissolving 0.37 kg of 1,1 - bis(t - butylperoxy)cyclohexane in 3.005 kg of mXy was added at a rate of 1 kg / hour to initiate polymerization. 0.5 hour after the start of polymerization, the addition rate of the initiator solution was decreased to 0.25 kg / hour, and mXy was added from tank 1 at a rate of 35.2 kg / hour for 3.5 hours. During polymerization, the solution temperature in the reactor was controlled at 128 ± 2 °C by temperature adjustment with the jacket. Next, 4 hours after the start of polymerization, the addition rate of the initiator solution was changed to 0.75 kg / hour, and a monomer solution containing MMA was added from tank 2 at a rate of 100.0 kg / hour for 2 hours. Furthermore, 6 hours after the start of polymerization, the addition rate of the initiator solution was decreased to 0.5 kg / hour, and the addition was stopped 7 hours after the start of polymerization. Polymerization was continued for another 1 hour to obtain a polymerization solution containing a methacrylic resin having a cyclic structure unit in the main chain. As a result of evaluating the amount of N - substituted maleimide contained in the obtained polymerization solution, it contained 220 mass ppm of phMI and 1070 mass ppm of chMI. To this polymerization solution, 0.1 mass% of Irganox 1010 and 0.05 mass% of Irgafos 168 were added under stirring with respect to 100 mass% of the polymer contained in the solution. The polymerization solution containing the antioxidant was filtered by passing it through a filter with a filtration accuracy of 2 μm made of SUS316L metal fiber. To recover the polymer from the polymerization solution, as an apparatus used in the devolatilization step, a plate - type heat exchanger having a flat - plate slit - type flow path and a heat - medium flow path and an internal volume of about 0.3 m 3A devolatilization apparatus without a rotating part, which is composed of a SUS heat medium jacketed vacuum vessel (hereinafter referred to as a devolatilization tank), was used. The solution containing the polymer obtained by polymerization was supplied to a heat exchanger installed at the upper part of the vacuum vessel at a rate of 30 liters / hour, heated to 260 °C, and then supplied to a devolatilization tank heated and depressurized under the conditions of an internal temperature of 260 °C and a vacuum degree of 30 Torr for devolatilization treatment. When the shear rate in the devolatilization apparatus was calculated from the apparatus shape and operating conditions, it was 5.3 s -1 It was. The polymer after devolatilization was pressurized by a gear pump from the lower part of the devolatilization tank, extruded from a strand die, cooled with water, and pelletized to obtain a methacrylic resin composition B. When the composition of the methacrylic resin composition B was confirmed, the structural units derived from each monomer of MMA, phMI, and chMI were 80.9% by mass, 7.0% by mass, and 12.1% by mass, respectively. Also, the weight average molecular weight Mw was 142,000, Mw / Mn was 2.32, Mz / Mw was 1.75, and the glass transition temperature was 134 °C.

[0190] [Production Example 3] A 10.8 mass% mXy solution of phMI (APSI was 3.4 mass ppm with respect to the mass of phMI) that had undergone a water washing step and a dehydration step, and a 24.0 mass% mXy solution of chMI (CCSI was 4.6 mass ppm with respect to the mass of chMI) that had undergone a water washing step and a dehydration step were used. A methacrylic resin composition C was obtained in the same manner as in Production Example 2, except that the composition of the mixed solution prepared in the reactor was made the same as in Production Example 2. In addition, as a result of evaluating the amount of N-substituted maleimide contained in the obtained polymerization solution, it contained 210 mass ppm of phMI and 1090 mass ppm of chMI. When the composition of the methacrylic resin composition C was confirmed, the structural units derived from each monomer of MMA, phMI, and chMI were 80.8% by mass, 7.1% by mass, and 12.1% by mass, respectively. Also, the weight average molecular weight Mw was 141,000, Mw / Mn was 2.31, Mz / Mw was 1.75, and the glass transition temperature was 134 °C.

[0191] [Production Example 4] Into a reactor equipped with a temperature control device using a jacket and a stirring blade, 40 parts by mass of MMA, 60 parts by mass of mXy, and 0.08 parts by mass of n-octyl mercaptan as a chain transfer agent were charged, and bubbling with nitrogen was carried out for 1 hour to remove dissolved oxygen. Then, steam was blown into the jacket to raise the solution temperature in the reactor to 120 °C, and while stirring at 50 rpm, a polymerization initiator solution prepared by dissolving 0.02 parts by mass of 1,1-di(t-butylperoxy)cyclohexane in 0.10 parts by mass of mXy was added at a constant rate over 5 hours to conduct polymerization, and further aging was carried out at 120 °C for 3 hours. Polymerization was terminated 8 hours after the start of polymerization to obtain an mXy solution of PMMA. After the polymerization was completed, the liquid temperature was lowered to 50 °C. Next, a mixed solution consisting of 12 parts by mass of monomethylamine and 12 parts by mass of methanol was dropped into the reactor at room temperature, the liquid temperature was raised to 170 °C, and stirring was carried out under pressure for 1 hour to advance the glutarimide cyclization reaction. The liquid temperature was lowered to 120 °C, the inside of the reactor was depressurized, and unreacted monomethylamine, methanol, and a part of mXy were distilled off to obtain a solution of about 50% by mass of glutarimide-cyclized methacrylic polymer in mXy. To this polymerization solution, 0.1% by mass of Irganox 1010 and 0.05% by mass of Irgafos 168 were added with stirring based on 100% by mass of the polymer contained in the solution. The polymerization solution containing the antioxidant was filtered by passing it through a filter with a filtration accuracy of 2 μm made of SUS316L metal fiber. In order to recover the polymer from the polymerization solution, as a device used in the devolatilization step, a devolatilization device having no rotating part, which is composed of a flat plate heat exchanger having a flat plate slit type flow path and a heat medium flow path and a decompression vessel with a SUS-made heat medium jacket with an internal volume of about 0.3 m 3 was used. The solution containing the polymer obtained by polymerization was supplied to a heat exchanger installed at the upper part of the decompression vessel at a rate of 30 liters / hour, heated to 260 °C, and then supplied to a devolatilization tank heated and depressurized under the conditions of an internal temperature of 260 °C and a vacuum degree of 30 Torr for devolatilization treatment. When the shear rate in the devolatilization device was calculated from the device shape and operating conditions, it was 5.3 s -1 It was. The polymer after devolatilization was pressurized with a gear pump from the lower part of the devolatilization tank, extruded from a strand die, cooled with water, and pelletized to obtain a methacrylic resin composition D. When the composition of the obtained methacrylic resin composition D was confirmed, the imidization rate was 3.2%, the amount of glutarimide structural units was 5.1% by mass. Further, the weight average molecular weight Mw was 93,000, Mw / Mn was 1.79, Mz / Mw was 1.51, and the glass transition temperature was 122°C.

[0192] [Production Example 5] A methacrylic resin composition E was obtained in the same manner as in Production Example 2, except that the amounts of each monomer in the solution prepared in the reactor were phMI 39.3 kg, chMI 46.5 kg, and MMA 354.2 kg. When the composition of the methacrylic resin composition E was confirmed, the structural units derived from each monomer of MMA, phMI, and chMI were 83.2% by mass, 7.6% by mass, and 9.2% by mass, respectively. Further, the weight average molecular weight Mw was 143,000, Mw / Mn was 2.35, Mz / Mw was 1.81, and the glass transition temperature was 132°C.

[0193] [Production Comparative Example 1] 352.4 kg of a 10.3% by mass mXy solution of phMI (APSI was 0.42 mass ppm with respect to the mass of phMI) that had undergone a water washing step and a dehydration step, and 310.3 kg of a 20.3% by mass mXy solution of chMI (CCSI was 0.60 mass ppm with respect to the mass of chMI) that had undergone a water washing step and a dehydration step were weighed, and added to a 1.25 m reactor equipped with a temperature control device by a jacket and a stirring blade. 3 While stirring at a solution temperature of 60°C and a reactor internal pressure of 5 kPa, 335.4 kg of mXy was distilled off under reduced pressure. Next, the reactor was returned to normal pressure, and 8.9 kg of mXy was added to prepare a mixed solution of phMI 36.3 kg, chMI 63.0 kg, and mXy 236.9 kg. 340.7 kg of MMA and 0.275 kg of n-octyl mercaptan as a chain transfer agent were weighed and added, and stirred to obtain a monomer mixed solution. Next, 123.1 kg of mXy was weighed and added to Tank 1. Furthermore, 110.0 kg of MMA and 90.0 kg of mXy were weighed into Tank 2, stirred, and used as a monomer solution for top-up. Regarding the content liquid in the reactor, nitrogen bubbling was carried out at a rate of 30 L / min for 1 hour, and for each of Tank 1 and Tank 2, nitrogen bubbling was carried out at a rate of 10 L / min for 30 minutes to remove dissolved oxygen. Thereafter, steam was blown into the jacket to raise the solution temperature in the reactor to 128°C, and while stirring at 50 rpm, a polymerization initiator solution prepared by dissolving 0.37 kg of 1,1-di(t-butylperoxy)cyclohexane in 3.005 kg of mXy was added at a rate of 1 kg / hour to initiate polymerization. 0.5 hour after the start of polymerization, the addition rate of the initiator solution was decreased to 0.25 kg / hour, and mXy was added from Tank 1 at a rate of 35.2 kg / hour for 3.5 hours. During polymerization, the solution temperature in the reactor was controlled at 128 ± 2°C by temperature adjustment with the jacket. Next, 4 hours after the start of polymerization, the addition rate of the initiator solution was changed to 0.75 kg / hour, and a monomer solution containing MMA was added from Tank 2 at a rate of 100.0 kg / hour for 2 hours. Furthermore, 6 hours after the start of polymerization, the addition rate of the initiator solution was decreased to 0.5 kg / hour, and the addition was stopped 7 hours after the start of polymerization. Polymerization was continued for another 1 hour to obtain a polymerization solution containing a methacrylic resin having a cyclic structure unit in the main chain. As a result of evaluating the amount of N-substituted maleimide contained in the obtained polymerization solution, it contained 220 mass ppm of phMI and 1070 mass ppm of chMI. To this polymerization solution, 0.1 mass% of Irganox 1010 and 0.05 mass% of Irgafos 168 were added under stirring with respect to 100 mass% of the polymer contained in the solution. The polymerization solution containing the antioxidant was filtered by passing it through a filter with a filtration accuracy of 2 μm made of SUS316L metal fiber. Next, the obtained polymerization solution was subjected to devolatilization by introducing it into a twin-screw extruder equipped with a plurality of vent ports for devolatilization. In the twin-screw extruder, the obtained polymerization solution was supplied so as to be 10 kg / h in terms of resin, and the conditions were set as a barrel temperature of 260°C, a screw rotation speed of 150 rpm, and a degree of vacuum of 10 to 40 Torr. The resin devolatilized by the twin-screw extruder was extruded from a strand die, pelletized after water cooling, and a methacrylic resin composition F was obtained. When the shear rate in the devolatilization apparatus was calculated from the apparatus shape and operating conditions, it was 80 s -1 It was. When the composition of the methacrylic resin composition F was confirmed, the structural units derived from each of the monomers MMA, phMI, and chMI were 80.9% by mass, 7.0% by mass, and 12.1% by mass, respectively. Further, the weight average molecular weight Mw was 136,000, Mw / Mn was 2.35, Mz / Mw was 1.81, and the glass transition temperature was 134°C.

[0194] [Production Comparative Example 2] A methacrylic resin composition G was obtained in the same manner as in Production Example 2, except that commercially available products of phMI and chMI were used as they were without purification to prepare a mixed solution of 36.3 kg of phMI, 63.0 kg of chMI, and 236.9 kg of mXy. When the shear rate in the devolatilization apparatus was calculated from the apparatus shape and operating conditions, it was 5.3 s -1 It was. Furthermore, as a result of evaluating the amount of N-substituted maleimide contained in the obtained polymerization solution, it contained 220 ppm by mass of phMI and 1070 ppm by mass of chMI. When the composition of the obtained pelletized polymer was confirmed, the structural units derived from each of the monomers MMA, phMI, and chMI were 80.9% by mass, 7.1% by mass, and 12.1% by mass, respectively. Further, the weight average molecular weight Mw was 142,000, Mw / Mn was 2.32, Mz / Mw was 1.75, and the glass transition temperature was 134°C.

[0195] [Production Comparative Example 3] Using commercially available products as phMI and chMI without purification, 38.6 kg of phMI, 65.7 kg of chMI, 450.0 kg of mXy, 445.7 kg of MMA, and 0.413 kg of n-octyl mercaptan as a chain transfer agent were weighed, and 1.25 m equipped with a temperature control device by a jacket and a stirring blade 3 was charged into a reactor and stirred to obtain a monomer mixed solution. Regarding the content liquid in the reactor, nitrogen bubbling was carried out at a rate of 30 L / min for 1 hour to remove dissolved oxygen. Thereafter, steam was blown into the jacket to raise the solution temperature in the reactor to 125 °C, and while stirring at 50 rpm, a polymerization initiator solution in which 0.23 kg of 1,1-di(t-butylperoxy)cyclohexane was dissolved in 2.77 kg of mXy was added at a rate of 0.5 kg / hour to start polymerization, and the addition was stopped 6 hours after the start of polymerization. During the polymerization, the solution temperature in the reactor was controlled to 125 ± 2 °C by temperature control with the jacket. After 8 hours from the start of polymerization, a polymerization solution containing a methacrylic resin having a ring structure in the main chain was obtained. As a result of evaluating the amount of N-substituted maleimide contained in the obtained polymerization solution, it contained 1340 mass ppm of phMI and 4390 mass ppm of chMI. To this polymerization solution, 0.1 mass% of Irganox 1010 and 0.05 mass% of Irgafos 168 were added under stirring with respect to 100 mass% of the polymer contained in the solution. The polymerization solution containing this antioxidant was filtered by passing it through a filter with a filtration accuracy of 2 μm made of SUS316L metal fiber. This polymerization solution added with the antioxidant was supplied to a concentration device composed of a tubular heat exchanger and a vaporization tank preheated to 170 °C to increase the concentration of the polymer contained in the solution to 70 mass%, and then the obtained polymerization solution was transferred to a thin film evaporator having a heat transfer area of 0.2 m 2 and having a rotating part, and devolatilization was carried out. The temperature inside the apparatus at this time was 280 °C, the supply rate was 30 L / hr, the rotation speed was 400 rpm, and the degree of vacuum was 30 Torr. The polymer after devolatilization was pressurized with a gear pump, extruded from a strand die, pelletized after water cooling, and methacrylic resin composition H was obtained. When the shear rate in the thin-film evaporator having a rotating part was calculated from the apparatus shape and operating conditions, it was 3200 s -1 It was. When the composition of the obtained pelletized polymer was confirmed, the structural units derived from each monomer of MMA, phMI, and chMI were 81.0% by mass, 7.2% by mass, and 11.8% by mass, respectively. Also, the weight-average molecular weight Mw was 136,000, Mw / Mn was 2.21, Mz / Mw was 1.71, and the glass transition temperature was 134 °C.

[0196] [Production Comparative Example 4] A methacrylic resin composition I was obtained in the same manner as in Production Example 2, except that the amounts of each monomer in the solution prepared in the reactor were 41.3 kg of phMI, 41.3 kg of chMI, and 357.5 kg of MMA. When the composition of the methacrylic resin composition I was confirmed, the structural units derived from each monomer of MMA, phMI, and chMI were 84.1% by mass, 8.0% by mass, and 7.9% by mass, respectively. Also, the weight-average molecular weight Mw was 145,000, Mw / Mn was 2.31, Mz / Mw was 1.77, and the glass transition temperature was 130 °C.

[0197] [Production Comparative Example 5] A methacrylic resin composition J having a glutarimide-based structural unit was obtained by imidizing polymethyl methacrylate with monomethylamine using a co-rotating twin-screw extruder. Specifically, a co-rotating twin-screw extruder with a screw diameter of 40 mm was used. The extruder cylinder temperature was set at 270 °C, the screw rotation speed was set at 150 rpm, and polymethyl methacrylate with a weight-average molecular weight Mw of 108,000 was supplied from the hopper at a rate of 20 kg / h. At the same time, nitrogen was flowed into the extruder at a flow rate of 200 mL / min. After the resin was melted and filled by the kneading block, 1.8 parts by mass of monomethylamine was injected from the nozzle with respect to 100 parts by mass of the raw resin, and an imidization reaction was carried out. A reverse flight was installed at the end of the reaction zone (in front of the vent port) to fill the resin. The by-products and excess methylamine after the reaction were removed by reducing the pressure at the vent port to 50 Torr. The resin that came out as a strand from the die provided at the extruder outlet was cooled in a water tank and then pelletized by a pelletizer to obtain an imide resin. Next, a co-rotating twin-screw extruder with a screw diameter of 40 mm was used. The extruder cylinder temperature was set at 250 °C, the screw rotation speed was set at 150 rpm, and the obtained imide resin was supplied at 20 kg / hr. After the resin was melted and filled by the kneading block, a mixed solution of dimethyl carbonate and triethylamine as an esterifying agent was injected from the nozzle to reduce the carboxylic acid groups in the resin. With respect to 100 parts by mass of the imide resin, dimethyl carbonate was 3.2 parts by mass and triethylamine was 0.8 parts by mass. A reverse flight was installed at the end of the reaction zone to fill the resin. The by-products and excess dimethyl carbonate after the reaction were removed by reducing the pressure at the vent port to 50 Torr. The resin that came out as a strand from the die provided at the extruder outlet was cooled in a water tank and then pelletized by a pelletizer to obtain a methacrylic resin composition J having a glutarimide structure. The imidization rate of this resin composition was 3.3%, and the content of the glutarimide-based structural unit was 5.2% by mass. When the shear rate in the twin-screw extruder was calculated from the apparatus shape and operating conditions, it was about 80 s -1 It was. Also, the weight-average molecular weight Mw was 96,000, Mw / Mn was 1.82, Mz / Mw was 1.48, and the glass transition temperature was 122 °C.

[0198] [Examples 1 to 5, Comparative Examples 1 to 5] Using the methacrylic resin compositions A to J obtained by Production Examples and Production Comparative Examples, resin lenses were injection-molded by the following method, and various properties were measured. The results are shown in Table 1. 〈Molding of Resin Lens〉 After drying the methacrylic resin compositions A to J in a forced-air circulation dryer at 100°C for 4 hours, a mold of a spherical plano-convex lens with a diameter of 41 mm and an R of 98 mm (the thickest part is 3.2 mm and has a side gate (0.95 mm thick, 5.0 mm wide)) was used, and an injection molding machine with a clamping force of 50 T was used. The cylinder temperature was 270°C, the mold temperature was 116°C, the injection speed was 10 mm / s, and pressure holding was performed in two stages. The first stage was 50 MPa for 4 seconds, and then the second stage was 30 MPa for 3 seconds, and injection molding was performed with a cooling time of 400 seconds. Furthermore, it was annealed for 3 hours in an oven set at a temperature 25°C lower than the glass transition temperature of the methacrylic resin composition.

[0199]

Table 1

Industrial Applicability

[0200] The resin lens for a head-mounted display of the present invention can contribute to the miniaturization and weight reduction of the head-mounted display because a clear image can be obtained even in an optical system using polarization.

Explanation of Signs

[0201] 1: Liquid crystal display 2: Polarizing plate 3: Quarter-wave plate 4: Half mirror 5: Resin lens 6: Quarter-wave plate 7: Reflective polarizing plate

Claims

1. A head mounted display including a resin lens, the resin lens has an average absolute value of retardation within an effective diameter of 5 nm or less; The resin lens has a content of a fluorescent substance of 0.1 to 4.0×10, calculated from the fluorescence intensity at a wavelength of 530 nm when a 2.0% by mass solution obtained by dissolving the resin in chloroform is measured at an excitation wavelength of 436 nm, using a concentration-intensity conversion formula for a fluorescein ethanol solution. －９ mol / L, The head mounted display uses polarized light and transmits image light through the resin lens multiple times by repeating reflection. A head mounted display comprising:

2. A head mounted display as described in claim 1, wherein the resin lens has a ratio (T450 / T680) of the transmittance (T450) at a wavelength of 450 nm to the transmittance (T680) at a wavelength of 680 nm of 0.98 or more.

3. A head-mounted display as described in claim 1 or 2, wherein the resin lens has a glass transition temperature (Tg) greater than 120°C and less than 160°C.

4. The head mounted display according to claim 1, wherein the resin lens has a photoelastic coefficient whose absolute value is 3.0×10 −12 Pa −1 or less.

5. A head-mounted display described in any one of claims 1 to 4, wherein the resin lens contains a methacrylic resin.

6. The head mounted display according to claim 5, wherein the resin lens includes a methacrylic resin having a structural unit (X) having a ring structure in its main chain.

7. The head mounted display according to claim 6, wherein the structural unit (X) of the resin lens includes at least one structural unit selected from the group consisting of a structural unit derived from an N-substituted maleimide monomer, a glutarimide structural unit, and a lactone ring structural unit.

8. The head mounted display according to claim 7, wherein the structural unit (X) of the resin lens includes a structural unit derived from an N-substituted maleimide monomer.

9. The head mounted display according to claim 7, wherein the structural unit (X) of the resin lens includes a glutarimide structural unit.

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