Plate-shaped molded product

Abstract

To provide a plate-like molded product with good appearance and suppressed warpage of the molded product, even when a surface having a fine convex-shaped portion and a surface being planar are provided as principal surfaces.SOLUTION: In order to achieve the above-mentioned purpose, the present invention provides a plate-like molded product having one principal surface 11 having a plurality of fine convex-shaped portions 14 having a height (a) of 50 to 600 μm and the other principal surface being planar. The plate-like molded product includes a methacrylic resin composition having a glass transition temperature (Tg) of 115 to 150°C. A flatness of the other principal surface 11 measured using a laser interferometer satisfies the following equation. (Flatness)=(PV value / the number of scan points)≤5.0×10-4 μm.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a plate-shaped molded product having a fine convex shape on one of its main surfaces. [Background technology]

[0002] Injection-molded products with fine convex shapes are widely used as optical components such as Fresnel lenses and light guide plates, and are often required to have a good appearance and excellent optical properties such as transmittance, haze, and yellowness index (YI). Furthermore, in the manufacture of injection-molded products having fine convex shapes, it is required that the concave parts of the mold that form the convex shapes are sufficiently filled with resin.

[0003] Conventionally, in the molding of injection-molded products having fine uneven surfaces, an injection molding method has been used in which the entire surface of the mold cavity in contact with the molded product is preheated to a set value above the resin softening temperature, this set value is controlled to be maintained during the injection process, and when the process switches to the cooling process, the heating is terminated and the mold is cooled. In such injection molding methods, techniques are known to improve the filling degree of the molded product, reduce residual stress, and suppress molding defects such as deformation, cracking, and deterioration of birefringence by heating the mold cavity surface to a set value above the resin softening temperature before the injection process begins (see, for example, Patent Documents 1 to 5). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 10-80940 [Patent Document 2] Japanese Patent Application Publication No. 10-80938 [Patent Document 3] Japanese Patent Application Publication No. 11-58476 [Patent Document 4] Japanese Patent Application Publication No. 63-95919 [Patent Document 5] Japanese Patent Publication No. 2010-264703 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] However, when molding a plate-shaped molded product having one main surface with fine convex shapes and the other main surface being flat, using the injection molding technology described above, there was a problem in that the surface area of ​​the main surface with fine convex shapes and the other main surface being flat differed, resulting in a difference in shrinkage during the cooling process of the molded product and causing warping. It has become clear that, especially when the height of the convex portion of the molded product is high (the concave portion of the mold that forms the convex portion of the molded product is deep), the difference in surface area between one main surface having the fine convex portion and the other main surface being flat becomes larger, and consequently, the warping of the plate-shaped molded product increases and the flatness of the flat side decreases. Furthermore, when the flatness of the flat surface of the plate-shaped molded product decreases, the performance when the molded product is used as an optical component deteriorates significantly, and improvement is desired.

[0006] The present invention has been made in view of the above-mentioned problems, and aims to provide a plate-shaped molded product that has good appearance and suppresses warping, even when the main surface includes a surface with a fine convex shape and a flat surface. [Means for solving the problem]

[0007] The inventors of the present invention have diligently studied a plate-shaped molded product having one main surface with a plurality of fine convex shapes having a height of 50 to 600 μm and the other main surface being flat, in order to solve the problems of the prior art described above. As a result, they have found that by constructing the plate-shaped molded product from a specific methacrylic resin composition and keeping the flatness of the other main surface, measured using a laser interferometer, within a specific range, it is possible to suppress warping of the plate-shaped molded product and achieve excellent appearance, thus completing the present invention.

[0008] This invention is based on the above findings, and its gist is as follows. [1] A plate-shaped molded product comprising one main surface having a plurality of fine convex shapes with a height of 50 to 600 μm, and the other main surface being flat, The aforementioned plate-shaped molded product contains a methacrylic resin composition having a glass transition temperature (Tg) of 115 to 150°C. A plate-shaped molded product characterized in that the flatness of the other main surface, measured using a laser interferometer, satisfies the following formula. (Flatness) = (PV value / number of scan points) ≤ 5.0 × 10 -4 μm [2] The plate-shaped molded product according to [1], characterized in that the ratio (b / a) of the arrangement pitch (b) of the fine convex shapes to the height (a) of the fine convex shapes on one main surface having the fine convex shapes is 0.1 to 2.0. [3] The plate-shaped molded product according to [1] or [2], characterized in that the in-plane phase difference of one main surface having the fine convex portion is 100 nm or less. [4] A plate-shaped molded product according to any one of [1] to [3] above, characterized in that it is an injection-molded product. [5] The plate-shaped molded product according to [4], characterized in that the surface temperature of the mold is heated to a temperature above the glass transition temperature (Tg) of the methacrylic resin composition, and then the methacrylic resin composition is injected and filled into the mold to obtain the injection-molded product. [Effects of the Invention]

[0009] According to the present invention, even when the main surface includes a surface having a fine convex shape and a flat surface, it is possible to provide a plate-shaped molded product with good appearance and suppressed warping. [Brief explanation of the drawing]

[0010] [Figure 1] This figure shows an example of a plate-shaped molded product according to this embodiment, where (A) is a top view and (B) is a side view. [Figure 2]It is a partial cross-sectional view schematically showing the shape (triangular pyramid shape) of the convex portion formed on one main surface of the plate-shaped molded product shown in FIG. 1. [Figure 3] It is a diagram showing another example of the plate-shaped molded product of the present embodiment, where (A) is a top view and (B) is a side view. [Figure 4] It is a partial cross-sectional view schematically showing the shape (frustum of a square pyramid shape) of the convex portion formed on one main surface of the plate-shaped molded product shown in FIG. 3. [Figure 5] It is a partial cross-sectional view for explaining the optical path when the plate-shaped molded products obtained in the examples and comparative examples are used as the light direction conversion element. [Figure 6] It is a diagram schematically showing the arrangement of the equipment used for the characteristic evaluation when the plate-shaped molded products obtained in the examples and comparative examples are used as the light direction conversion element. [Figure 7] It is a plan view schematically showing the state when the USAF Target 7 used in FIG. 6 is viewed from the X-axis direction.

Mode for Carrying Out the Invention

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

[0012] <Plate-shaped molded product> FIG. 1 is a diagram showing an example of the plate-shaped molded product of the present embodiment. Further, FIG. 2 is a cross-sectional view schematically showing the shape of the convex portion formed on one main surface of the plate-shaped molded product shown in FIG. 1. The plate-shaped molded product of the present embodiment (hereinafter sometimes simply referred to as "molded product") has a plurality of fine convex portions 14 with a height of 50 to 600 μm on one main surface 11 (hereinafter sometimes simply referred to as "one main surface") as shown in FIGS. 1(A) and (B), and a flat other main surface 12 (hereinafter sometimes simply referred to as "the other main surface"), and is a plate-shaped molded product 1. Furthermore, the plate-shaped molded product of the present invention is characterized in that the flatness of the other main surface 12, as measured using a laser interferometer, satisfies the following formula. (Flatness) = (PV value / number of scan points) ≤ 5.0 × 10 -4 μm The flatness of the other main surface 12 is 5.0 × 10 -4 By keeping the thickness to below μm, it is possible to reduce warping of plate-shaped molded products and appearance defects such as mold release marks.

[0013] From a similar viewpoint, the flatness of the other main surface 12 is preferably small, specifically preferably 4.0 × 10 -4 μm or less, more preferably 3.0 × 10 -4 μm or less, more preferably 2.0 × 10⁻¹⁶ -4 It is less than μm. The method for controlling the flatness of the other main surface 12 of the plate-shaped molded product 1 is not particularly limited. For example, as will be described later, one method is to set the maximum temperature during heating and the minimum temperature during cooling of the mold that forms the fine convex shape and the mold that forms the flat surface within a specific range during the process of heating and then cooling the mold during resin injection molding. If the maximum temperature during mold heating and the minimum temperature during cooling fall outside this specific range, molding defects such as warping and demolding marks occur, and the flatness of the molded product surface decreases. As a result, the PV value when measuring the molded product surface with a laser interferometer increases and the number of scan points decreases, so the flatness value expressed as (PV value / number of scan points) tends to increase. The flatness of the other main surface 12 can be measured by the method described in the embodiment described later.

[0014] As shown in Figure 2, the plate-shaped molded product of this embodiment has a plurality of fine convex-shaped portions 14 (hereinafter also referred to as "fine convex-shaped portions" or simply "convex-shaped portions") on one of the main surfaces 11. Here, the height a of the convex portion 14 is 50 to 600 μm. Good optical properties can be obtained while maintaining a good mold transfer rate. As the height a of the convex portion 14 increases, the difference in surface area with the other main surface 12 (flat surface) of the plate-shaped molded product increases, and the amount of warping also increases. However, if the height a of the convex portion is within the above range, it is possible to suppress the amount of warping to some extent. If the height a of the convex portion 14 is higher than 600 μm, poor mold release of the resin from the mold is likely to occur, so from the perspective of mass production, it is preferable that it be within the above range. From a similar viewpoint, the height a of the convex portion 14 is preferably 100 to 600 μm, more preferably 200 to 500 μm, and even more preferably 350 to 500 μm.

[0015] Furthermore, on one main surface 11 having the fine convex portion 14, the ratio of the arrangement pitch b of the convex portion 14 to the height a of the convex portion 14 (b / a) is preferably 0.1 to 2.0. By setting the ratio of the height a of the convex portion 14 to the arrangement pitch b within the above range, the molded product can be cleanly demolded while maintaining a good mold transfer rate. From a similar viewpoint, the ratio of the arrangement pitch b of the convex portion 14 to the height a of the convex portion 14 (b / a) is preferably 0.1 to 2.0, more preferably 0.2 to 1.5, and even more preferably 0.3 to 1.0.

[0016] Furthermore, the arrangement pitch b of the convex portion 14 is preferably 50 to 600 μm, more preferably in the range of 100 to 500 μm, even more preferably 150 to 350 μm, and particularly preferably 180 to 300 μm. When the pitch b of the convex portion 14 is within the above range, when the mold surface is treated with an external release agent, a release film can be formed to the depths of the concave portion of the mold that forms the convex portion, making it less likely for resin to be released from the mold, and resulting in a molded product with good appearance and optical properties.

[0017] In this specification, the height a of the convex portion 14 refers to the height of the highest part (vertex) of the convex shape, measured relative to a planar portion on one main surface 11 that is parallel to the other main surface, as shown in Figure 2. For example, in Figure 2, it is the height a to the vertex of the convex portion 14 of the cone. Furthermore, the height a of the convex portion 14 is the average value of the measured heights of five or more convex portions. Moreover, if there is no planar portion on one main surface 14 that is parallel to the other main surface, the height a of the convex portion may be the height a to the vertex of the convex portion 14 relative to the average thickness T of the molded product excluding the convex portion. Furthermore, in this specification, the arrangement pitch b of the convex shape portion 14 refers to the distance between the centers of two adjacent convex shape portions 14, as shown in Figure 2. In addition, the arrangement pitch b is the average value of the arrangement pitch measured for five or more convex shape portions 14. Furthermore, the height a and arrangement pitch b of the convex portion 114 can be visually measured from observation images obtained using an optical microscope, electron microscope, digital microscope, etc. For example, they can be measured by the method described in the embodiment described later.

[0018] Furthermore, the shape of the convex portion formed on one of the main surfaces is not particularly limited, and may include, for example, polygonal pyramids such as triangular pyramids, square pyramids, and pentagonal pyramids; curved pyramids such as cones, elliptical pyramids, semicones, semielliptical pyramids, and oval pyramids (pyramids having a cross-section in which both ends of a pair of parallel lines are connected by a semicircle); frustums of triangles, frustums of squares, and frustums of pentagons; frustums of cones, elliptical frustums, semicone frustums, semielliptical frustums, and oval frustums (where both ends of a pair of parallel lines are connected by a semicircle); Examples include curved frustums (frustums having a cross-section of the shape shown), polygonal prisms such as triangular prisms, quadrangular prisms (cubes, rectangular prisms, etc.), and pentagonal prisms, curved columns such as cylinders, elliptical prisms, semicylinders, semielliptical prisms, and oval cones (prisms having a cross-section of a pair of parallel lines connected at both ends by a semicircle), and dome shapes (structures such as hemispheres, quadrispheres, and aspherical structures in which the cross-sectional area when cut in the axial direction gradually decreases as the direction is directed upward in the axial direction). If the convex portion is a polygonal pyramid, a polygonal prism, or the like, the corners may be rounded. Also, the side surface of the convex portion may be flat or curved. These convex shapes may be of a single type or a combination of multiple types, but it is preferable to have only one type.

[0019] Here, Figure 2 is a partial cross-sectional view when the fine convex portion 14 formed on one of the main surfaces is triangular pyramidal, and Figure 4 is a partial cross-sectional view when the fine convex portion 24 formed on one of the main surfaces 21 is truncated square pyramidal.

[0020] The fine convex shapes formed on one of the main surfaces may be arranged in a linear, curved, dot-like pattern, or the like. Furthermore, the convex shapes may be arranged across the entire surface of one of the main surfaces, or only in a portion of that surface. For example, Figures 1(A) and 3(A) show plan views from the surface side of one of the main surfaces 11 and 21, illustrating an example where the convex portions 14 and 24 are arranged only in certain areas 13 and 23 of one of the main surfaces 11 and 21.

[0021] Furthermore, when one of the main surfaces having the convex portion is observed from above, the size of the planar shape of the convex portion is preferably 0.1 to 600 μm in diameter, more preferably 0.5 to 500 μm, and even more preferably 1 to 400 μm. For example, if the plan view shape of the convex portion is a line pattern, it shall be the length of the width in the direction perpendicular to the line direction; otherwise, if the plan view shape is not circular, it shall be the diameter of its circumscribed circle. The diameter of the plan view of the convex portion can be visually measured from observation images obtained using an optical microscope, electron microscope, digital microscope, etc. Furthermore, the size (height and diameter of the plan view) of the convex portion may be the same or different for all of them.

[0022] The overall shape of the molded product in this embodiment is not particularly limited, as long as one main surface has a plurality of fine convex shapes and the other main surface is a flat plate or substantially plate-shaped. When one of the main surfaces having the aforementioned fine convex shape is observed from above, its shape (plan view shape) can be, for example, a polygon such as a triangle, square, rectangle, parallelogram, trapezoid, or pentagon, or a circle, ellipse, semicircle, semiellipse, oblong (a shape formed by connecting the ends of a pair of parallel lines with a semicircle), or an annular shape. In the case of a polygon, the corners may be rounded. Furthermore, from the viewpoint of mold release during molding, a frame may be provided on the outer circumference of the molded product for ejection with an ejector pin.

[0023] Furthermore, as shown in Figure 2, for the plate-shaped molded product 1 of this embodiment, the thickness T of the flat portion excluding the fine convex shape portion 14 is preferably 1.5 mm or more and less than 6 mm, more preferably 2 mm or more and less than 5 mm, and even more preferably 2 mm or more and less than 4 mm. As the thickness T of the flat portion decreases, it becomes more difficult to control warping, and as the thickness T increases, it becomes advantageous for controlling warping, but it takes time to cool during molding, a temperature difference is created between the surface and the interior, the central part may become concave and the flatness of the plane may be impaired, which may adversely affect the optical properties of the molded product. The size of each main surface 11, 12 of the plate-shaped molded product 1 is not particularly limited and can be set appropriately according to the required performance.

[0024] In this embodiment, as shown in Figure 1, the plate-shaped molded product 1 has a fine convex shape formed only on one main surface 11, and the other main surface 12 is flat. In addition, the amount of warpage is preferably 0.4 mm or less, more preferably 0.35 mm or less, and even more preferably 0.3 mm or less. If the amount of warpage of the plate-shaped molded product 1 is 0.4 mm or less, it can be said to be a molded product with good dimensional accuracy. Furthermore, by calculating the square root of the area value when viewing the region 13 where the convex shape 14 is formed from a plan view with the main surface 11 on which the convex shape 14 is formed as the upper surface (in Figure 1, the shaped surface region is 80 mm square, so the square root is 80 mm), if the amount of warpage relative to the obtained value is 0.50% or less, it can be determined that the dimensional accuracy of the molded product is within an excellent range. From a similar viewpoint, the value of the amount of warpage relative to the square root of the area value is more preferably 0.44% or less, and even more preferably 0.38% or less. The amount of warpage of the plate-shaped molded product 1 is the value at the point with the largest gap when the outer circumference of the molded product 1 is evenly divided into four points (see, for example, 3a to 3d in Figure 1) and the gap between the molded product and the surface plate is measured at these four points, with the main surface 11 having the convex shape 14 facing upwards. Specifically, it can be measured by the method described in the embodiments below.

[0025] The plate-shaped molded product of this embodiment preferably has a filling degree of 0.92 or higher, more preferably 0.95 or higher, and even more preferably 0.99 or higher. A filling degree of 0.92 or higher indicates that the convex shape is well formed in the molded product. The degree of filling is calculated using the following formula based on the height of the convex portion and the depth of the concave portion in the mold used to form the convex portion 14, and is the average value measured at four locations. Specifically, it can be measured by the method described in the embodiment below. (Filling density) = (Height of the convex part of the plate-shaped molded product) / (Depth of the concave part of the mold)

[0026] In this embodiment, the birefringence of the plate-shaped molded product is preferably 100 nm or less as the in-plane phase difference of one main surface having the fine convex portion, more preferably less than 50 nm, and even more preferably less than 20 nm. When the in-plane phase difference of one main surface having the fine convex portion is within the above range, the polarization of light transmitted through the plate-shaped molded product of this embodiment tends to be kept constant, and adverse effects on optical properties are less likely to occur. When polarized light passes through the inside of the molded product, the phase difference changes in the field where total internal reflection occurs inside the molded product, but if it is confirmed that the phase difference is small by measuring the in-plane phase difference of the molded product, the phase difference imparted to the final transmitted light will be constant, and it will function like a phase difference plate. Since the polarization characteristics will be uniformly aligned, it will work particularly effectively when combined with optical equipment such as projectors, head-up displays, and headsets that utilize various types of polarization, and with video display equipment such as in-car displays that are expected to be viewed with polarized sunglasses. When combined with liquid crystal displays, optical elements using liquid crystals, and polarizing plates, it can help improve the efficiency of light utilization and reduce noise. Furthermore, it is advantageous when using circular polarizers or polarizers to block external light, or when improving visibility when wearing polarized sunglasses. The in-plane phase difference of one of the main surfaces of the plate-shaped molded product having the fine convex shape can be measured by the method described in the embodiment described later.

[0027] (Methacrylic resin composition) The methacrylic resin composition contained in the plate-shaped molded product of this embodiment contains a methacrylic resin and may optionally contain other additives. It may also contain other thermoplastic resins, rubbery polymers, etc., in addition to the methacrylic resin.

[0028] The methacrylic resin constituting the methacrylic resin composition is not particularly limited. For example, resins mainly composed of structural units derived from methyl methacrylate are included, and these include homopolymers of methyl methacrylate, or copolymers of methyl methacrylate with one or more copolymerizable monomers such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, butyl acrylate, acrylonitrile, acrylic acid, methacrylic acid, vinylpyridine, vinylmorpholine, vinylpyridone tetrahydrofurfuryl acrylate, N,N-dimethylaminoethyl acrylate, N,N-dimethylacrylamide, 2-hydroxyacrylate, 2-(hydroxymethyl)ethyl acrylate, ethylene glycol monoacrylate, glycerin monoacrylate, maleic anhydride, N-cyclohexyl maleimide, N-phenyl maleimide, styrene, or α-methylstyrene. In addition, the aforementioned methacrylic resins also include heat-resistant methacrylic resins having structural units derived from methyl methacrylate and lactone rings or glutarimide in their main chains, as well as methyl methacrylate and low-hygroscopic methacrylic resins. These can be used individually or blended together.

[0029] Furthermore, from the viewpoint of transparency and heat resistance, the methacrylic resin is preferably a methacrylic resin having a ring structure in its main chain. In particular, it is preferable that the methacrylic resin has structural units derived from an N-substituted maleimide monomer, as this allows for a high degree of control over optical properties such as intrinsic birefringence and photoelastic coefficient without blending with other thermoplastic resins.

[0030] The method for producing the methacrylic resin is not particularly limited, but batch, semi-batch, and continuous polymerization methods can be used. A batch method is a process in which the entire amount of raw materials is added to the reactor, the reaction is started and carried out, and the product is recovered after completion. A semi-batch method is a process in which either the raw material is added or the product is recovered simultaneously while the reaction is in progress. A continuous method is a process in which both the raw material is added and the product is recovered simultaneously while the reaction is in progress. Among these processes, as a method for producing the methacrylic resin having a ring structure in the main chain, it is preferable to use a semi-batch method in which some of the raw materials are added after the reaction has started, from the viewpoint of precisely controlling the copolymer composition.

[0031] Furthermore, a continuous process is undesirable for the following reasons. While carrying out the polymerization reaction in a single complete mixing reactor has the advantage of minimizing the difference in monomer composition between fractions with different molecular weights in the methacrylic resin, a large amount of unreacted monomers remain after polymerization, which tends to negatively affect the color. On the other hand, when using a plug flow reactor, the amount of unreacted monomers can be reduced, but the difference in monomer composition between fractions with different molecular weights in the methacrylic resin tends to be large. When multiple complete mixing reactors or a complete mixing reactor and a plug flow reactor are combined in series, the amount of unreacted monomers can be reduced, but the difference in monomer composition between fractions tends to be large.

[0032] The polymerization solvent is not particularly limited, and for example, aromatic hydrocarbons such as toluene, xylene, ethylbenzene, and isopropylbenzene; esters such as methyl isobutyrate; ketones such as methyl isobutyl ketone, butyl cellosolve, methyl ethyl ketone, and cyclohexanone; and polar solvents such as dimethylformamide and 2-methylpyrrolidone can be used. Furthermore, alcohols such as methanol, ethanol, and isopropanol may be used as polymerization solvents in combination, provided that they do not inhibit the dissolution of the polymerization product during polymerization. The amount of solvent used during polymerization is not particularly limited as long as polymerization proceeds, and the copolymer or monomers used do not precipitate during production and can be easily removed. For example, if the total amount of monomers to be blended is 100 parts by mass, the amount of solvent is preferably 10 to 200 parts by mass, more preferably 25 to 200 parts by mass, even more preferably 50 to 200 parts by mass, and even more preferably 50 to 150 parts by mass.

[0033] As polymerization initiators, any initiator commonly used in radical polymerization can be used, such as organic peroxides including cumene hydroperoxide, diisopropylbenzene hydroperoxide, di-t-butyl peroxide, lauroyl peroxide, benzoyl peroxide, t-butyl peroxyisopropyl carbonate, t-amyl peroxy-2-ethylhexanoate, t-amyl peroxyisononanoate, and 1,1-di(t-butylperoxy)cyclohexane; and azo compounds such as 2,2'-azobis(isobutyronitrile), 1,1'-azobis(cyclohexanecarbonile), 2,2'-azobis(2,4-dimethylvaleronitrile), and dimethyl-2,2'-azobisisobutyrate. These may be used alone or in combination of two or more. These polymerization initiators may be added at any stage while the polymerization reaction is in progress. Furthermore, the amount of polymerization initiator added may be 0.01 to 1 part by mass, preferably 0.05 to 0.5 parts by mass, when the total amount of monomers used for polymerization is 100 parts by mass.

[0034] As chain transfer agents, those commonly used in radical polymerization can be used. Examples include mercaptan compounds such as n-butyl mercaptan, n-octyl mercaptan, n-decyl mercaptan, n-dodecyl mercaptan, and 2-ethylhexyl thioglycolate; halogen compounds such as carbon tetrachloride, methylene chloride, and bromoform; and unsaturated hydrocarbon compounds such as α-methylstyrene dimer, α-terpinene, dipentene, and terpinolene. These may be used individually or in combination of two or more. These chain transfer agents can be added at any stage while the polymerization reaction is in progress, and are not particularly limited to any specific stage. Furthermore, the amount of the chain transfer agent added may be 0.01 to 1 part by mass, preferably 0.05 to 0.5 parts by mass, when the total amount of monomers used for polymerization is 100 parts by mass.

[0035] There are no particular limitations on the method for recovering polymers from a polymerization solution obtained by solution polymerization. For example, one method involves adding the polymerization solution to a poor solvent, such as a hydrocarbon or alcohol-based solvent, in which the polymerization product obtained by polymerization does not dissolve, followed by homogenization (emulsification and dispersion), and then separating the unreacted monomers from the polymerization solution by pretreatment such as liquid-liquid extraction or solid-liquid extraction. Alternatively, one method involves separating the polymerization solvent and unreacted monomers via a process called defoliation and recovering the polymerization product. Here, the defoliation process refers to the process of removing volatile components such as polymerization solvent, residual monomers, and reaction by-products under heating and reduced pressure conditions.

[0036] Examples of equipment used in the devolatilization process include: a devolatilization apparatus consisting of a tubular heat exchanger and a devolatilization tank; thin film evaporators such as the Wibren and Excever manufactured by Kobe Steel Environmental Solutions Co., Ltd., and the Contra and Inclined-Blade Contra manufactured by Hitachi, Ltd.; and a vented extruder having sufficient residence time and surface area to exhibit devolatilization performance. A thawing process using a thawing apparatus that combines two or more of these devices can also be utilized.

[0037] From the standpoint of improving the color tone, it is preferable to use a davoltaic device that mainly consists of a heat exchanger and a vacuum vessel, and whose structure does not have a rotating part. Specifically, a devolatilization apparatus can be employed that consists of a devolatilization tank having a vacuum chamber with a heat exchanger positioned on top and a vacuum unit attached to a vacuum container large enough to perform devolatilization, and a discharge device such as a gear pump for discharging the polymer after devolatilization. The above-described devolatilization apparatus preheats the polymerization solution by subjecting it to a heated heat exchanger located at the top of a reduced-pressure vessel, such as a multi-tube heat exchanger, a plate-fin heat exchanger, or a plate-type heat exchanger having a plate-type channel and heater. After preheating, the solution is supplied to a devolatilization tank under heated and reduced pressure to separate and remove the polymerization solvent, unreacted raw material mixture, polymerization by-products, etc., from the copolymer. Using a devolatilization apparatus without a rotating part as described above is preferable because it allows for the acquisition of a methacrylic resin with a good color tone.

[0038] The processing temperature in the defoliation apparatus is preferably 150 to 350°C, more preferably 170 to 300°C, and even more preferably 200 to 280°C. Setting the temperature above the lower limit suppresses residual volatile components, while setting it below the upper limit suppresses discoloration and decomposition of the resulting acrylic resin.

[0039] Furthermore, the methacrylic resin composition may contain various additives, provided that they do not significantly impair the effects of the present invention. The aforementioned additives are not particularly limited, but examples include antioxidants, light stabilizers such as hindered amine-based light stabilizers, ultraviolet absorbers, mold release agents, thermoplastic resins other than methacrylic resins, paraffinic process oils, naphthenic process oils, aromatic process oils, paraffin, organic polysiloxanes, mineral oils and other softeners / plasticizers, flame retardants, antistatic agents, organic fibers, inorganic fillers such as pigments such as iron oxide, reinforcing agents such as glass fibers, carbon fibers, and metal whiskers, colorants, organophosphorus compounds such as phosphites, phosphonites, and phosphate esters, or mixtures thereof.

[0040] Furthermore, it is preferable that the methacrylic resin composition contains an antioxidant that suppresses deterioration and discoloration during molding or use. The aforementioned antioxidants are not limited to those listed below, but examples include hindered phenol antioxidants, phosphorus antioxidants, and sulfur antioxidants. In order to improve the transferability of the fine convex shapes formed on the mold and to highly control the distortion and warping of the molded product surface, it is essential to maintain the resin at a high temperature in the mold cavity and allow for an appropriate cooling time. When subjected to a long thermal history, it is necessary to increase the amount of heat stabilizer added to obtain the desired thermal stability. However, from the viewpoint of suppressing bleed-out of the heat stabilizer and preventing it from sticking to the mold, it is preferable to use multiple types of heat stabilizers in combination. For example, it is preferable to use at least one selected from phosphorus antioxidants and sulfur antioxidants in combination with a hindered phenol antioxidant. These antioxidants may be used individually or in combination of two or more.

[0041] The hindered phenol antioxidants mentioned above are not limited to the following, but include, for example, 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, ethylenebis(oxyethylene)bis[3-(5-tert-butyl-4-hydroxy-m-tolyl)propionate] [Pionate], Hexamethylenebis[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-xyline)methyl]-1,3,5-triazine-2,4,6(1H,3H,5 Examples include H)-trione, 2,6-di-tert-butyl-4-(4,6-bis(octylthio)-1,3,5-triazine-2-ylamine)phenol, 2-[1-(2-hydroxy-3,5-di-tert-pentylphenyl)ethyl]-4,6-di-tert-pentylphenyl acrylate, and 2-tert-butyl-4-methyl-6-(2-hydroxy-3-tert-butyl-5-methylbenzyl)phenyl acrylate. In particular, pentaerythritol terakis[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 are preferred.

[0042] The aforementioned hindered phenol antioxidant may be a commercially available phenol antioxidant, and such commercially available phenol antioxidants are not limited to the following, but include, for example, Irganox 1010 (pentaerythritol tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], manufactured by BASF) and Irganox 1076 (Irganox 1076: Octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate (BASF), Irganox 1330 (3,3',3'',5,5',5''-hexa-t-butyl-a,a',a''-(mesitylene-2,4,6-triyl)tri-p-cresol (BASF), Irganox 3114 (1,3,5-tris(3,5-di-t-butyl-4-hydroxybenzyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, B (Manufactured by ASF), Irganox 3125 (Manufactured by BASF), Adekastab AO-60 (Pentaerythritol tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], Adekastab AO-80 (3,9-bis{2-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionylxyoxy]-1,1-dimethylethyl}-2,4,8,10-tetraoxaspiro[5.5]undecane, ADEKA), Sumilizer BHT Examples include BHT (manufactured by Sumitomo Chemical), Cyanox 1790 (manufactured by Cytec), Sumilizer GA-80 (manufactured by Sumitomo Chemical), Sumilizer GS (2-[1-(2-hydroxy-3,5-di-tert-pentylphenyl)ethyl acrylate]-4,6-di-tert-pentylphenyl acrylate, manufactured by Sumitomo Chemical), Sumilizer GM (2-tert-butyl-4-methyl-6-(2-hydroxy-3-tert-butyl-5-methylbenzyl)phenyl acrylate, manufactured by Sumitomo Chemical), and Vitamin E (manufactured by Eisai). Among these commercially available phenolic antioxidants, Irganox 1010, Adeka Stab AO-60, Adeka Stab AO-80, Irganox 1076, and Smirizer GS are preferred from the viewpoint of providing thermal stability to the resin. These can be used individually or in combination of two or more types.

[0043] Furthermore, the phosphorus-based antioxidants used as antioxidants are not limited to the following, but include, for example, tris(2,4-di-t-butylphenyl) phosphite, bis(2,4-bis(1,1-dimethylethyl)-6-methylphenyl) ethyl ester phosphorous acid, tetrakis(2,4-di-t-butylphenyl)(1,1-biphenyl)-4,4'-diylbisphosphonate, bis(2,4-di-t-butylphenyl) pentaerythritol diphosphite, and bis(2,6-di-t-butyl-4-methyl Examples include phenyl)pentaerythritol diphosphite, bis(2,4-dicumylphenyl)pentaerythritol-diphosphite, tetrakis(2,4-t-butylphenyl)(1,1-biphenyl)-4,4'-diylbisphosphonate, di-t-butyl-m-cresyl-phosphonate, and 4-[3-[(2,4,8,10-tetra-tert-butyldibenzo[d,f][1,3,2]dioxaphosfepin)-6-yloxy]propyl]-2-methyl-6-tert-butylphenol. Furthermore, a commercially available phosphorus-based antioxidant may be used as the phosphorus-based antioxidant. Examples of commercially available phosphorus-based antioxidants include, but are not limited to, Irgafos 168 (tris(2,4-di-t-butylphenyl) phosphite, manufactured by BASF), Irgafos 12 (tris[2-[[2,4,8,10-tetra-t-butyldibenzo[d,f][1,3,2]dioxaphosphephine-6-yl]oxy]ethyl]amine, manufactured by BASF), Irgafos 38 (bis(2,4-bis(1,1-dimethylethyl)-6-methylphenyl) ethyl ester phosphorous acid, manufactured by BASF), ADK STAB 329K (ADEKA), ADK STAB PEP-36 (ADEKA), ADK STAB PEP-36A (ADEKA) Sandstab P-EP-36A (made by ADEKA), ADK STAB PEP-8 (made by ADEKA), ADK STAB HP-10 (made by ADEKA), ADK STAB 2112 (made by ADEKA), ADK STAB 1178 (made by ADEKA), ADK STAB 1500 (made by ADEKA), Sandstab P-EPQ (made by Clariant), Weston 618 (made by GE), Weston 619G (made by GE), Ultranox 626 (made by GE), Sumilizer GP (made by GE) Examples include GP:4-[3-[(2,4,8,10-tetra-tert-butyldibenzo[d,f][1,3,2]dioxaphosfepine)-6-yloxy]propyl]-2-methyl-6-tert-butylphenol (manufactured by Sumitomo Chemical Co., Ltd.) and HCA (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (manufactured by Sanko Co., Ltd.)). Among these commercially available phosphorus-based antioxidants, Irgaphos 168, Adekastab PEP-36, Adekastab PEP-36A, Adekastab HP-10, and Adekastab 1178 are preferred from the viewpoint of their effect in providing thermal stability to the resin and their combined effect with various antioxidants, with Adekastab PEP-36A and Adekastab PEP-36 being particularly preferred. These phosphorus-based antioxidants may be used individually or in combination of two or more.

[0044] Furthermore, the sulfur-based antioxidants used as antioxidants are not limited to the following, but examples include 2,4-bis(dodecylthiomethyl)-6-methylphenol (Irganox 1726, manufactured by BASF), 2,4-bis(octylthiomethyl)-6-methylphenol (Irganox 1520L, manufactured by BASF), and 2,2-bis{[3-(dodecylthio)-1-oxopolopoxy]methyl}propane-1 Examples include ,3-diirbis[3-dodecylthio]propionate (ADEKA AO-412S), 2,2-bis{[3-(dodecylthio)-1-oxopolopoxy]methyl}propane-1,3-diirbis[3-dodecylthio]propionate (CHEMINOX PLS, CHEMIPRO KASEI Co., Ltd.), and di(tridecyl)3,3'-thiodipropionate (AO-503, ADEKA). Among these commercially available sulfur antioxidants, Adeka Stab AO-412S and Cheminox PLS are preferred from the viewpoint of their effect in providing thermal stability to the resin, their effectiveness in combination with various antioxidants, and their ease of handling. These sulfur-based antioxidants may be used individually or in combination of two or more.

[0045] The amount of the antioxidant should be such that an effect of improving thermal stability can be obtained. If the amount is excessive, problems such as bleed-out may occur during processing. Therefore, it is preferable that the amount is 5 parts by mass or less, more preferably 3 parts by mass or less, even more preferably 1 part by mass or less, even more preferably 0.8 parts by mass or less, even more preferably 0.01 to 0.8 parts by mass, and particularly preferably 0.01 to 0.5 parts by mass per 100 parts by mass of methacrylic resin.

[0046] Furthermore, the methacrylic resin composition may also contain an ultraviolet absorber. While the ultraviolet absorber is not particularly limited, it is preferably an ultraviolet absorber having a maximum absorption wavelength of 280 to 380 nm. Examples include benzotriazole compounds, benzotriazine compounds, benzophenone compounds, oxybenzophenone compounds, benzoate compounds, phenol compounds, oxazole compounds, cyanoacrylate compounds, and benzoxazinon compounds. These UV absorbers may be used individually or in combination of two or more.

[0047] Of the aforementioned ultraviolet absorbers, benzotriazole compounds and benzotriazine compounds with a molecular weight of 400 or more are particularly preferred from the viewpoint of compatibility with the resin and volatility when heated, and benzotriazine compounds are particularly preferred from the viewpoint of suppressing decomposition of the ultraviolet absorber itself due to heating during extrusion processing.

[0048] The amount of the UV absorber is not particularly limited as long as it does not impair heat resistance, heat and humidity resistance, thermal stability, and moldability, and exhibits the effects of the present invention. For example, it is preferably 0.1 to 5 parts by mass, more preferably 0.2 to 4 parts by mass, more preferably 0.25 to 3 parts by mass, and even more preferably 0.3 to 3 parts by mass, per 100 parts by mass of the methacrylic resin. Within this range, an excellent balance of UV absorption performance, moldability, etc., is achieved.

[0049] The methacrylic resin composition may also contain a mold release agent. The mold release agent is not limited to the following, but examples include fatty acid esters, fatty acid amides, fatty acid metal salts, hydrocarbon lubricants, alcohol lubricants, polyalkylene glycols, carboxylic acid esters, and hydrocarbon paraffinic mineral oils. These release agents may be used individually or in combination of two or more.

[0050] There are no particular restrictions on the fatty acid ester that can be used as the mold release agent; conventionally known ones can be used. Examples of the fatty acid esters that can be used 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, and behenic acid, and monohydric aliphatic alcohols such as palmityl alcohol, stearyl alcohol, and behenyl alcohol, or polyhydric aliphatic alcohols such as glycerin, pentaerythritol, dipentaerythritol, and sorbitan; and complex ester compounds of fatty acids, polybasic organic acids, and monohydric or polyhydric aliphatic alcohols. Examples of such fatty acid ester-based lubricants 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, and glycerin monolinoleate. Examples include glycerin monobehenate, glycerin mono-12-hydroxystearate, glycerin di-12-hydroxystearate, glycerin tri-12-hydroxystearate, glycerin diacetomostearate, glycerin triceto fatty acid ester, pentaerythritol adipate stearate, montanic acid partially saponified ester, pentaerythritol tetrastearate, dipentaerythritol hexastearate, sorbitan tristearate, etc. These fatty acid ester lubricants can be used individually or in combination of two or more. Examples of commercially available fatty acid ester-based lubricants include the Rikemar series, Poem series, Rikestar series, and Rikemaster series from Riken Vitamin Co., Ltd., and the Excel series, Leodor series, Excelpearl series, and Coconard series from Kao Corporation. More specifically, examples include Rikemar S-100, Rikemar H-100, Poem V-100, Rikemar B-100, Rikemar HC-100, Rikemar S-200, Poem B-200, Rikestar EW-200, Rikestar EW-400, Excel S-95, and Leodor MS-50.

[0051] The amount of the mold release agent should be such that it is effective as a mold release agent. If the amount is excessive, problems such as bleed-out during processing and extrusion defects due to screw slippage may occur. Therefore, the amount is preferably 5 parts by mass or less, more preferably 3 parts by mass or less, even more preferably 1 part by mass or less, even more preferably 0.8 parts by mass or less, even more preferably 0.01 to 0.8 parts by mass, and particularly preferably 0.01 to 0.5 parts by mass per 100 parts by mass of the methacrylic resin. Adding the agent in the above range tends to suppress the decrease in transparency due to the addition of the mold release agent and to suppress mold release defects during injection molding.

[0052] The methacrylic resin composition may also contain other thermoplastic resins other than methacrylic resins for the purpose of adjusting birefringence or improving flexibility, without impairing the objectives of the present invention. Other thermoplastic resins include, for example, polyacrylates such as polybutyl acrylate; styrene-based polymers such as polystyrene, styrene-methyl methacrylate copolymer, styrene-butyl acrylate copolymer, styrene-acrylonitrile copolymer, and acrylonitrile-butadiene-styrene block copolymer; and, for example, acrylic rubber particles with a 3-4 layer structure as described in Japanese Patent Publication No. 59-202213, Japanese Patent Publication No. 63-27516, Japanese Patent Publication No. 51-129449, Japanese Patent Publication No. 52-56150, etc.; rubbery polymers disclosed in Japanese Patent Publication No. 60-17406 and Japanese Patent Publication No. 8-245854; and methacrylic rubber-containing graphite copolymer particles obtained by multi-stage polymerization as described in International Publication No. 2014-002491.

[0053] Among the above, from the viewpoint of obtaining good optical and mechanical properties, it is preferable that the other thermoplastic resin is a rubber-containing graft copolymer particle having a graft portion on its surface layer that has a composition compatible with styrene-acrylonitrile copolymer or methacrylic resin containing a structural unit (X) having a ring structure in the main chain. Furthermore, the average particle size of the acrylic rubber particles, methacrylic rubber-containing graphite copolymer particles, and rubbery polymer is preferably 0.03 to 1 μm, and more preferably 0.05 to 0.5 μm, from the viewpoint of improving the impact strength and optical properties of the molded article obtained from the composition of this embodiment. Furthermore, the content of the other thermoplastic resin is preferably 0 to 50 parts by mass, and more preferably 0 to 25 parts by mass, when the methacrylic resin is 100 parts by mass.

[0054] The aforementioned methacrylic resin composition has a glass transition temperature (Tg) of 115 to 150°C, as measured by the midpoint method in accordance with JIS-K7121. When the Tg of the methacrylic resin composition is 115°C or higher, it is higher than the boiling point of the solvent component used to prepare the mold release agent commonly used during molding, allowing the mold temperature to be set above the boiling point to volatilize the preparation solvent. Furthermore, if the molded product does not have heat resistance of 115°C or higher, warping and deformation of convex shapes may occur in reliability tests such as high-temperature aging tests, adversely affecting the optical properties. On the other hand, when the glass transition temperature (Tg) exceeds 150°C, there are fewer types of equipment that can raise the maximum temperature of the mold to an appropriate temperature, and it takes time to raise and lower the mold temperature, resulting in a longer cycle time, which is undesirable. The glass transition temperature (Tg) is preferably 120 to 145°C, and particularly preferably 125 to 140°C. The glass transition temperature of the methacrylic resin composition can be specifically measured by the method described in the examples below.

[0055] Furthermore, the methacrylic resin composition is preferably characterized by a low viscosity and high fluidity during injection molding in order to enhance the transferability of fine convex shapes. Therefore, the melt viscosity is preferably 270°C, 1000 sec. -1 In this case, the melt viscosity is preferably 20 to 235 Pa·sec, more preferably 20 to 230 Pa·sec, even more preferably 30 to 180 Pa·sec, and particularly preferably 50 to 150 Pa·sec. If the melt viscosity is less than 20 Pa·sec, it becomes difficult to control the flow of the resin during injection, and the transferability of fine convex shapes tends to deteriorate due to air entrapment. If the melt viscosity is greater than 235 Pa·sec, the fluidity of the resin decreases, which tends to deteriorate the transferability of convex shapes in the molded product. The melt viscosity of the methacrylic resin composition is a value measured in accordance with JIS-K7199, and specifically, it can be measured by the method described in the examples below.

[0056] The methacrylic resin composition is preferably characterized by a high tensile elongation at break to avoid cracking during demolding and resin residue in the mold. Specifically, the tensile elongation at break of the methacrylic resin composition is 1.5% or more, preferably 2.0% or more, and more preferably 2.5% or more. The tensile elongation at break is a value measured in accordance with ISO 527, and specifically, it can be measured by the method described in the examples below.

[0057] The method for producing the methacrylic resin composition is not particularly limited, but examples include kneading using a kneader such as an extruder, heated roll, kneader, roller mixer, or Banbury mixer. Among these, kneading by extruder is preferred in terms of productivity. The mixing temperature should follow the preferred processing temperature of the polymer constituting the methacrylic resin and the other resins being mixed, and is generally in the range of 140 to 300°C, preferably 180 to 280°C. Furthermore, it is preferable to provide a vent in the extruder to reduce volatile components.

[0058] <Method for manufacturing sheet-shaped molded products> The method for manufacturing the plate-shaped molded product of this embodiment is described below. In this embodiment, the plate-shaped molded product is molded in a state where the molten resin flows sufficiently and degradation due to thermal decomposition of the resin is suppressed, by setting the temperature from the nozzle tip to the center of the injection molding machine cylinder to 120 to 180°C higher than the glass transition temperature (Tg) of the methacrylic resin composition used. Thermal decomposition of the resin adversely affects the color tone, transmittance, and haze, and also generates gas during injection molding. This gas fills the mold, and the gas that is pushed into the uneven parts during resin filling is not released, hindering resin filling and resulting in a poor mold transfer rate. Therefore, more preferably, the temperature is 130 to 170°C higher than the glass transition temperature (Tg) of the methacrylic resin composition used.

[0059] In this embodiment, in order to improve the transferability of the molded product, it is preferable to heat and maintain the mold temperature to above the Tg of the methacrylic resin composition before injecting the methacrylic resin composition into the mold. For example, when molding a molded product having one main surface with a plurality of fine convex shapes and the other main surface being flat, if the mold forming the main surface with fine convex shapes is called the first mold and the mold forming the flat main surface is called the second mold, then when the maximum temperature of the first mold when the methacrylic resin composition is injected into the mold is Tmax1, it is preferable that the maximum temperature Tmax2 of the second mold be (Tmax1-30)°C to (Tmax1-5)°C. More preferably it is (Tmax1-30)°C to (Tmax1-10)°C, and particularly preferably (Tmax1-30)°C to (Tmax1-20)°C. When the temperature of the second mold is (Tmax1-30)°C or higher, the amount of warpage of the molded product tends to decrease. On the other hand, if the temperature is below (Tmax 1-5)℃, deterioration of the flatness of the second main surface of the molded product due to the effects of thermal shrinkage of the resin and adhesion to the mold is suppressed, so a plate-shaped molded product with a good appearance and a small flatness value defined as (PV value / number of scan points) can be obtained.

[0060] Furthermore, in this embodiment, it is preferable to heat and then cool the first mold and the second mold. The maximum temperature Tmax1 of the mold when the first mold, which forms the main surface having fine convex shapes, is heated is preferably controlled to a temperature range of (Tg+15)°C to (Tg+40)°C, with Tg being the glass transition temperature of the methacrylic resin composition, more preferably (Tg+15)°C to (Tg+35)°C, and even more preferably (Tg+20)°C to (Tg+35)°C, in order to improve the transferability (moldability) of the fine convex shapes. If the temperature is set above (Tg+40)°C, the fluidity of the resin becomes too high, which tends to cause molding defects due to the entrapment of air or gas. On the other hand, if the temperature is below (Tg+15)°C, the transferability decreases, and the appearance of the molded product tends to deteriorate. The minimum temperature Tmin1 of the first mold when cooled is preferably controlled within the temperature range of (Tg-75)°C to (Tg-45)°C, more preferably (Tg-70)°C to (Tg-50)°C, and even more preferably (Tg-65)°C to (Tg-55)°C, with Tg being the glass transition temperature of the methacrylate resin composition. Lowering Tmin to a temperature below (Tg-75)°C increases the cycle time. If it is above (Tg-45)°C, the amount of warping of the molded product increases, and the appearance of the molded product tends to deteriorate and the flatness increases. On the other hand, the minimum temperature Tmin2 of the second mold when cooled is preferably controlled within the temperature range of (Tmin1+10) to (Tmin1+30)°C, more preferably (Tmin1+10)°C to (Tmin1+20)°C, and even more preferably (Tmin1+10)°C to (Tmin1+15)°C. When Tmin2 is lowered to a temperature below (Tmin1+10), the amount of warping of the molded product increases, the flatness of the molded product's surface decreases, and the flatness tends to increase. On the other hand, when it is above (Tmin1+30), demolding marks appear on the surface of the molded product, the flatness of the molded product's surface decreases, and the flatness tends to increase.

[0061] In this embodiment, the method of heating the mold is not particularly limited and any method may be used. For example, a method in which a water or oil channel is placed inside the mold and the mold temperature is adjusted to a temperature above the Tg of the methacrylic resin composition used by the medium such as water or oil; a method in which a heater is embedded inside the mold and the mold is heated; a method in which an electrically conductive layer that can conduct electricity is provided on the surface of the mold and heat is generated by passing an electric current through it; a method in which the mold is heated from the outside or inside using an induction heating device; and a method in which the mold is heated from the outside by radiation from a halogen lamp or ceramic heater using far-infrared rays. Furthermore, in this embodiment, the method of cooling the mold is not particularly limited and any method may be used. For example, one method is to arrange water or oil channels inside the mold and cool it using a medium such as water or oil.

[0062] In this embodiment, for a mold forming a main surface having fine convex shapes, the heating rate of the surface temperature during heating is preferably 1 to 10°C / second, more preferably 1.5 to 10°C / second, and even more preferably 2 to 10°C / second. A faster heating rate is effective in shortening the cycle time, but it is acceptable to deviate from this range as long as there are no constraints on the cycle time and resin degradation due to heat retention in the cylinder is not a problem. Furthermore, the cooling rate of the surface temperature during cooling of the mold is preferably 0.5 to 10°C / second, more preferably 1 to 10°C / second, and even more preferably 2 to 10°C / second. A faster cooling rate is effective in shortening the cycle time, but as described later, maintaining the mold temperature at a high temperature is effective in improving transferability. However, if the cooling rate deviates from this range, it tends to lead to redundant cycle times and deterioration of molded product warpage, which is undesirable. In this embodiment, temperature control can be set as appropriate while observing the state of the molded product, such as raising or lowering the temperature at a constant rate, slowing down the rate of heating or cooling, or holding the product at a predetermined temperature for a certain period of time. To improve the transfer of the convex shape, it is preferable to maintain a long holding time at the temperature at which the resin flows (preferably above the glass transition temperature). Furthermore, since birefringence occurs due to the formation of a skin layer if the holding time is short, it is preferable to slow down the cooling rate in order to suppress this.

[0063] In this embodiment, a release coating or a spray-type release agent is preferably used for the mold surface release process. As a release coating, baked-on fluororesins or silicone resins can be used. As a spray-type release agent, for example, fluororesins, silicones, or waxes can be used. In particular, for spray-type external mold release agents used by spraying them onto the mold, for example, a fluorine-based mold release agent that has excellent mold release properties and forms a monomolecular film that does not significantly affect the transfer of the mold's fine shape can be used. Due to its low persistence on the mold, it is preferable to use a non-curing type mold release agent. Furthermore, regarding the highly volatile solvent component containing the active ingredient, it is preferable to use a solvent component that does not easily dissolve the methacrylic resin composition injected into the mold, and to use a solvent component whose boiling point is lower than or close to the Tg of the methacrylic resin composition. This makes it less likely for the solvent to remain in the concave parts of the mold that form the convex parts, and allows for the formation of a good release film. It is preferable to use a solvent component with a low boiling point for the release agent. Specifically, with Tg being the glass transition temperature of the methacrylic resin composition, it is preferable that the boiling point is in the range of (Tg-50)°C to (Tg+5)°C, more preferably (Tg-40)°C to (Tg+5)°C, and even more preferably in the range of (Tg-30)°C to (Tg+5)°C. By using a release agent in this range, a release film can be efficiently formed, and the transfer of the release component to the surface of the molded product is reduced, improving the transmittance of the molded product and making it easier to obtain a molded product with good optical properties and appearance.

[0064] <Products using sheet-shaped molded parts> As described above, the plate-shaped molded product of this embodiment has good appearance, suppresses warping, and exhibits excellent optical properties. Therefore, the plate-shaped molded product of this embodiment can be suitably used as an optical component such as a Fresnel lens, a light guide plate, a lenticular lens, or an anti-reflective sheet. [Examples]

[0065] The present invention will be described below with reference to specific examples and comparative examples, but the present invention is not limited to the following examples.

[0066] (Raw material for methacrylic resins) The following (a) to (e) were used as raw materials for the methacrylic resin.

[0067] (a) monomers that make up methacrylic resins • Methyl methacrylate (MMA): Manufactured by Asahi Kasei Corporation • N-phenylmaleimide (PMI): Manufactured by Nippon Shokubai Co., Ltd. • N-cyclohexylmaleimide (CMI): Manufactured by Nippon Shokubai Co., Ltd. • Styrene: Manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. • Methyl 2-(hydroxymethyl)acrylate (MHMA): Manufactured by Combi-Blocks.

[0068] (b) Organic solvents • Metaxylene (mXy): Manufactured by Mitsubishi Gas Chemical Company, Ltd. • Methyl isobutyrate: Manufactured by Kanto Chemical Co., Ltd. • Toluene: Manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.

[0069] (c) Polymerization initiator • 1,1-di(t-butylperoxy)cyclohexane: Manufactured by NOF Corporation • t-Amyl peroxy-2-ethylhexanoate: Luperox 575, manufactured by Arkema Yoshitomi Co., Ltd. t-Amil peroxyisononanoate: Manufactured by Arkema Yoshitomi Co., Ltd.

[0070] (d) Chain transfer agent n-Octyl mercaptan: Manufactured by Chevron Philips Chemicals. n-dodecyl mercaptan: Manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.

[0071] (e) Chain transfer agent • Pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]: BASF "Irganox 1010" • Tris(2,4-di-t-butylphenyl) phosphite: BASF "Irgafos168" • Rikemar H-100: Manufactured by Riken Vitamin Co., Ltd. • ADEKA Stub 2112: Manufactured by ADEKA Corporation • Stearyl phosphate / distearyl phosphate mixture: Manufactured by Sakai Chemical Industry Co., Ltd. • Monomethylamine: Manufactured by Mitsubishi Gas Chemical Company, Inc. • Dimethyl carbonate: Manufactured by Fujifilm Wako Pure Chemical Corporation Triethylamine: Manufactured by Fujifilm Wako Pure Chemical Corporation

[0072] <Methacrylic resin composition> Samples A to D of methacrylic resin compositions were prepared according to the following synthesis examples 1 to 4. For the methacrylic resin composition samples, the glass transition temperature, melt viscosity, and tensile elongation at break were measured under the following conditions.

[0073] ● Glass transition temperature The glass transition temperature of each sample of methacrylic resin composition was measured in accordance with JIS-K7121. A differential scanning calorimeter (DSC8000, manufactured by Perkin Lumer Japan Co., Ltd.) was used under nitrogen gas flow rate of 25 mL / min. The sample was heated from room temperature (23°C) to 200°C at 10°C / min (primary heating), 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 then heated again under the same heating conditions (secondary heating). The glass transition temperature (Tg) (°C) was measured at the intersection point (midpoint glass transition temperature) of the DSC curve drawn during this process, specifically between the step-like change portion of the curve during the secondary heating and a straight line equidistant in the vertical direction from each baseline extension.

[0074] ●Melting viscosity Under conditions conforming to JIS-K7199, a twin capillary rheometer (manufactured by ROSAND) was used, with a temperature of 270°C and a shear rate of 1000 sec. -1 The melt viscosity (Pa·sec) of each sample of methacrylic resin composition was measured using a capillary die with a diameter of 1 mm.

[0075] ●Tensile elongation at break Methacrylic resin pellets were dried at 80-100°C for 24 hours, and 4.0 mm thick ISO 3167 Type A dumbbell test specimens were prepared by injection molding using an injection molding machine (Toshiba Machine Co., Ltd., EX-100SX) in accordance with JIS-K6717. These specimens were subjected to tensile testing using a low-load universal material testing machine (Inslon Corporation) in accordance with ISO 527, at a measurement temperature of 23°C and a crosshead speed of 5 mm / min. Five measurements were taken, and the elongation between the chucks at tensile fracture was measured. The average value was calculated as the tensile fracture elongation (%).

[0076] (1) Synthesis Example 1 (Methacrylic resin composition A) 318.7 kg of methyl methacrylate (hereinafter referred to as MMA), 35.5 g of N-phenylmaleimide (hereinafter referred to as PMI), 63.7 kg of N-cyclohexylmaleimide (hereinafter referred to as CMI), 0.341 kg of n-octyl mercaptan (a chain transfer agent), and 225.1 kg of metaxylene (hereinafter referred to as mXy) ​​were weighed out and added to a 1.25 m³ reactor equipped with a jacketed temperature control device and stirring blades, and stirred to obtain a mixed monomer solution. Next, 116.9 kg of mXy was weighed and added to tank 1 to prepare the additional solvent. Then, 104.5 kg of MMA and 85.5 kg of mXy were weighed into tank 2 and stirred to obtain the additional MMA solution. The contents of the reactor were bubbling with nitrogen at a rate of 30 L / min for 1 hour, and the dissolved oxygen was removed from both Tank 1 and Tank 2 by bubbling with nitrogen at a rate of 10 L / min for 30 minutes. Subsequently, steam was blown into the jacket to raise the solution temperature in the reactor to 125°C, and polymerization was started by adding a polymerization initiator solution (0.457 kg of 1,1-di(t-butylperoxy)cyclohexane dissolved in 2.67 kg of mXy) ​​at a rate of 1 kg / hour while stirring at 50 rpm. During polymerization, the solution temperature in the reactor was controlled to 125 ± 2°C by temperature regulation using the jacket. Thirty minutes after the start of polymerization, the rate of addition of the polymerization initiator solution was reduced to 0.25 kg / hour, and mXy was further added from tank 1 at a rate of 29.24 kg / hour for 3.5 hours. Next, four hours after the start of polymerization, the addition rate of the polymerization initiator solution was increased to 0.75 kg / hour, and the additional MMA solution was added from tank 2 at a rate of 95 kg / hour for two hours. Furthermore, six hours after the start of polymerization, the rate of addition of the polymerization initiator solution was reduced to 0.25 kg / hour, and the addition was stopped seven hours after the start of polymerization. Eight hours after the start of polymerization, a polymerization solution containing a methacrylic resin was obtained. To this solution, 0.261 kg of Irganox 1010 and 0.784 kg of Irgafos 168 were added as antioxidants, and 0.784 kg of Rikemar H-100 was added as a release agent. Next, the obtained polymerization solution was supplied to a concentration apparatus consisting of a tubular heat exchanger and a vaporization tank, which had been preheated to 250°C, for defoliation. The vacuum level in the vaporization tank was set to 10-15 Torr. The resin flowing down the vaporization tank was discharged with a screw pump, extruded from a strand die, water-cooled, and pelletized to obtain methacrylic resin composition A having N-substituted maleimide structural units. The obtained pellets (methacrylic resin composition) had a Tg of 133°C, a melt viscosity of 131 Pa·sec, and a tensile elongation at break of 1.7%.

[0077] (2) Synthesis Example 2 (Methacrylic Resin Composition B) A monomer composition consisting of 60.000 mol% methyl methacrylate, 39.998 mol% styrene, and 0.002 mol% t-amyl peroxy-2-ethylhexanoate as a polymerization initiator was continuously supplied at 1 kg / h to a 10 L complete mixing tank equipped with helical ribbon blades, and continuous polymerization was carried out at an average residence time of 2.5 hours and a polymerization temperature of 150°C. The liquid was continuously withdrawn from the bottom of the polymerization tank to maintain a constant liquid level and supplied to a concentration device consisting of a tubular heat exchanger and a vaporization tank for defoliation. The vacuum level in the vaporization tank was set to 10-15 Torr. The resin flowing down the vaporization tank was discharged with a screw pump, extruded from a strand die, water-cooled, pelletized, and introduced into a solvent removal device to obtain pelletized methyl methacrylate-styrene copolymer. This copolymer was dissolved in methyl isobutyrate to prepare a 10% by mass methyl isobutyrate solution. 500 parts by mass of this copolymer 10% by mass methyl isobutyrate solution and 1 part by mass of 10% by mass Pd / C (manufactured by NE Chemcat) as a hydrogenation catalyst were charged into a 1000 mL autoclave. The mixture was maintained at a hydrogen pressure of 9 MPa and 200°C for 15 hours to hydrogenate the aromatic double bonds of the styrene moiety of the copolymer. The hydrogenation catalyst was removed by filtration, and 0.05 parts by mass of Rikemar H-100 was added and mixed to the polymer solution. The solution was then supplied to a concentration apparatus consisting of a tubular heat exchanger and a vaporization tank for defoliation. The vacuum level in the vaporization tank was set to 10-15 Torr. The resin flowing down the vaporization tank was discharged with a gear pump, extruded from a strand die, water-cooled, and pelletized to obtain methacrylic resin composition B. The obtained pellets (methacrylic resin composition) had a Tg of 118°C, a melt viscosity of 67 Pa·sec, and a tensile elongation at break of 2.2%.

[0078] (3) Synthesis Example 3 (Methacrylic resin composition C) In a 30L reaction vessel equipped with a paddle blade agitator, temperature sensor, condenser, nitrogen inlet tube, and dropper pump, 2.25 kg of methyl methacrylate, 0.32 kg of methyl 2-(hydroxymethyl)acrylate, 0.024 kg of styrene, and as a chain transfer agent, 0.025 parts by mass of n-dodecyl mercaptan, 0.025 parts of Adekastab 2112, and 5.39 kg of toluene were charged per 100 parts by mass of the total monomers to be charged into the reaction vessel. The mixture was then heated to 105°C while nitrogen was passed through and the mixture was stirred. As an initial initiator, a solution consisting of 0.20 kg of toluene and 0.014 kg of t-amyl peroxyisononanoate was added dropwise to the polymerization tank over 10 minutes while polymerization was carried out at 105°C to 110°C. Ten minutes later, a solution consisting of 0.26 kg of toluene and 0.017 kg of t-amyl peroxyisononanoate was added dropwise over 3 hours. Simultaneously with the addition of this initiator solution, a solution consisting of 2.75 kg of methyl methacrylate, 0.40 kg of methyl 2-(hydroxymethyl)acrylate, and 0.24 kg of styrene was added dropwise over 3 hours while polymerization was carried out at a polymerization temperature of 105°C to 110°C, followed by a 2-hour maturation period. To the obtained polymer solution, a mixed solution of 4.5 g of stearyl phosphate / distearyl phosphate and 72 g of toluene was added, and a cyclization condensation reaction was carried out at 90-110°C for 1.5 hours. Subsequently, 0.10 parts by mass of Rikemar H-100 was added to 100 parts by mass of the total monomers to be charged into the final reaction vessel, and the mixture was stirred. The obtained polymerization solution was subjected to a cyclocondensation reaction and defoliation treatment using a φ42 mm defoliation extruder with 4 fore vents and 1 back vent at a barrel temperature of 220°C, 120 rpm, and a resin volume of 5 kg / hour to obtain pellets of methacrylic resin composition C. The obtained pellets (methacrylic resin composition) had a Tg of 127°C, a melt viscosity of 72 Pa·sec, and a tensile elongation at break of 2.2%.

[0079] (4) Synthesis Example 4 (Methacrylic resin composition D) A methacrylic resin composition having a glutarimide structure was obtained by imidizing polymethyl methacrylate with monomethylamine using a twin-screw extruder with co-rotating operation. A twin-screw extruder with a 40 mm screw diameter and rotating in the same direction was used. The extruder cylinder temperature was set to 275°C and the screw rotation speed to 150 rpm. Polymethyl methacrylate with a weight-average molecular weight of 108,000, including 0.1 parts by mass for every 100 parts by mass of the total polymer mass, was supplied from the hopper at a rate of 20 kg / hour, while nitrogen was flowed into the extruder at a flow rate of 200 mL / min. After the resin was melted and filled using a kneading block, 1.8 parts by mass of monomethylamine per 100 parts by mass of the raw resin was injected from the nozzle to carry out the imidation reaction. A reverse flight was placed at the end of the reaction zone (before the vent port) to fill it with resin. By-products and excess monomethylamine after the reaction were removed by reducing the pressure at the vent port to 50 Torr. The resin that came out as strands from the die provided at the extruder outlet was cooled in a water bath and then pelletized in a pelletizer to obtain imide resin. Next, using a twin-screw extruder with a screw diameter of 40 mm and rotating in the same direction, the extruder cylinder temperature was set to 255°C and the screw rotation speed to 150 rpm. The obtained imide resin was supplied at a rate of 20 kg / hr, and after the resin was melted and filled by a kneading block, a mixture of dimethyl carbonate and triethylamine was injected from the nozzle as an esterifying agent to reduce the carboxylic acid groups in the resin. The amount of dimethyl carbonate was 3.2 parts by mass and triethylamine was 0.8 parts by mass per 100 parts by mass of imide resin. 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 strands from the die provided at the extruder outlet was cooled in a water bath and then pelletized in a pelletizer to obtain methacrylic resin composition D having a glutarimide structure. The obtained pellets (methacrylic resin composition) had a Tg of 122°C, a melt viscosity of 158 Pa·sec, and a tensile elongation at break of 7.9%.

[0080] <Examples, Comparative Examples> Using the methacrylic resin compositions obtained from the synthesis examples described above, samples of plate-shaped molded bodies were prepared under the following conditions.

[0081] (Example 1) The methacrylic resin composition A obtained in Synthesis Example 1 was used for injection molding using an injection molding machine (Sumitomo Heavy Industries, Ltd., SE180EV-A). The mold consisted of a mold (first mold) that formed a main surface with a triangular pyramidal convex shape with a height a = 400 μm and a pitch b = 300 μm, and a mold (second mold) that formed a flat main surface. A nested mold was used, with heater wires embedded inside the mold near the surfaces forming each main surface, and it was mounted on the injection molding machine. The mold temperature Tmax1 of the first mold was heated to 165°C, and the mold temperature Tmax2 of the second mold was heated to 150°C at a heating rate of approximately 3°C / second. After heating, a fluorine-based release agent was sprayed onto the surface of the first mold to perform a release treatment. Then, the mold was closed and injection molding was performed. After filling the mold with the resin composition, the mold temperature Tmin1 of the first mold was set to 60°C and the mold temperature Tmin2 of the second mold was set to 75°C. Cooling was performed at a rate of approximately 1.2°C / second, and after reaching the set temperature, cooling was continued for 90 seconds to obtain a plate-shaped molded product (90 mm long, 90 mm wide, 2.5 mm thick, see Figure 1) with a convex shape on one main surface. The holding pressure was set high at 80 MPa for the first stage immediately after injection to obtain good transfer, and then lowered from the first stage to relieve stress strain inside the molded product, with the second stage set to 30 MPa.

[0082] (Example 2) Injection molding was performed under the same conditions as in Example 1, except that the methacrylic resin composition B obtained in Synthesis Example 2 was used, and the mold temperature Tmax1 of the first mold was set to 150°C and Tmin1 to 65°C, and the mold temperature Tmax2 of the second mold was set to 145°C and Tmin2 to 75°C.

[0083] (Example 3) Injection molding was performed under the same conditions as in Example 1, except that the methacrylic resin composition C obtained in Synthesis Example 3 was used, and the mold temperature Tmax1 of the first mold was set to 155°C and Tmin1 to 60°C, and the mold temperature Tmax2 of the second mold was set to 145°C and Tmin2 to 80°C.

[0084] (Example 4) Injection molding was performed under the same conditions as in Example 3, except that the methacrylic resin composition D obtained in Synthesis Example 4 was used.

[0085] (Example 5) Injection molding was performed under the same conditions as in Example 1, except that the mold used was a frustoconical mold with a convex shape of a truncated square pyramid (base surface 140 μm square, angle between base surface and side surface 85 degrees) on one main surface, and a flat main surface on the other, with heater wires embedded inside the mold near the surfaces forming each main surface.

[0086] (Example 6) Injection molding was performed under the same conditions as in Example 1, except that the mold used was a frustoconical mold with a convex shape of a truncated square pyramid (base surface 140 μm square, angle between base surface and side surface 85 degrees) on one main surface, with the other main surface being flat, and a nested mold with heater wires embedded inside the mold near the surfaces forming each main surface.

[0087] (Comparative Example 1) Injection molding was performed under the same conditions as in Example 1, except that the methacrylic resin composition A obtained in Synthesis Example 1 was used, and the mold temperature Tmax1 of the first mold was set to 165°C and Tmin1 to 60°C, and the mold temperature Tmax2 of the second mold was set to 165°C and Tmin2 to 60°C.

[0088] (Comparative Example 2) Injection molding was performed under the same conditions as in Example 1, except that the methacrylic resin composition A obtained in Synthesis Example 1 was used, and the mold temperature Tmax1 of the first mold was set to 180°C and Tmin1 to 80°C, and the mold temperature Tmax2 of the second mold was set to 165°C and Tmin2 to 90°C.

[0089] (Comparative Example 3) Injection molding was performed under the same conditions as in Example 1, except that the methacrylic resin composition A obtained in Synthesis Example 1 was used, and the mold temperature Tmax1 of the first mold was set to 165°C and Tmin1 to 110°C, and the mold temperature Tmax2 of the second mold was set to 155°C and Tmin2 to 120°C.

[0090] (Comparative Example 4) Injection molding was performed under the same conditions as in Example 1, except that heating by heater was not performed and the temperatures of the first and second molds were set to 110°C before injection.

[0091] (Comparative Example 5) Injection molding was performed under the same conditions as in Example 1, except that the mold temperature Tmax1 of the first mold was set to 155°C and Tmin1 to 80°C, and the mold temperature Tmax2 of the second mold was set to 95°C and Tmin2 to 95°C.

[0092] <Rating> The following evaluations were performed on the plate-shaped molded articles obtained in each example and comparative example. The evaluation results are shown in Table 1.

[0093] (1) Flatness of the planar main surface For each sample of the plate-shaped molded body, the flatness of the molded product was measured using a VERIFIRE ASPHERE laser interferometer manufactured by Zygo Corporation. Specifically, the PV value and the number of scan points of the measurement surface (flat side) of the molded product were measured, and the flatness was calculated using the following formula. In addition, when measuring the surface accuracy of the molded product's flat surface, black tape was applied to the convex surface to suppress reflections. (Flatness) = (PV value / Number of scan points) Here, the difference between the point with the largest shape error from the mold's design value (Peak) and the point with the smallest shape error from the mold's design value (Valley) is expressed as the PV value, taking the first letters of each. This measurement was performed at three locations: the center of the molded product, near the gate, and near the end of the flow, and the average value was taken as the flatness value of the molded product.

[0094] (2) Height and pitch of the convex shape For each sample of the plate-shaped molded body, the cross-section obtained by cutting in a direction perpendicular to the main surface (thickness direction) was observed using a digital microscope (Keyence Corporation, VHX-1000). From the obtained observation images, the height and arrangement pitch of the convex shapes formed on the main surface of the molded product were measured, and the average values ​​of the five convex shapes were defined as height a and arrangement pitch b, respectively.

[0095] (3) Measurement of the degree of filling of the convex shape For each sample of the plate-shaped molded body, the cross-section obtained by cutting in a direction perpendicular to the main surface (thickness direction) was observed using a digital microscope (Keyence Corporation, VHX-1000). The height 'a' of the convex shape formed on the main surface of the molded product was determined, and the degree of filling, defined as the ratio of the depth of the concave shape in the mold used to form the convex shape to the depth of the concave shape in the mold, was derived using the following calculation formula, and the average value of the four points is listed in Table 1 as the degree of filling. Specifically, if the filling degree is 0.92 or higher, it can be determined that the molded product is preferable as one on which a convex shape has been transferred. (Filling density) = (Height a of the convex part of the molded product) / (Depth of the concave part of the mold)

[0096] (4) Curvature For each sample of the plate-shaped molded body, the main surface with a convex shape was placed on a metal surface plate with the convex side facing upwards. The outer circumference of the molded product was evenly divided at four points, and the gap between the molded product and the surface plate at these four points (see 3a to 3d in Figure 1) was measured with a thickness gauge. The value at the location with the largest gap (amount of warpage) was taken as the amount of warpage (mm) of the molded product. Specifically, for plate-shaped molded products with the shapes shown in Figures 1 and 3, a warpage of 0.4 mm or less can be considered within a desirable range for the dimensional accuracy of the molded product.

[0097] (5) Appearance evaluation Each sample of the plate-shaped molded body was visually inspected to observe uneven gloss on the main surface with the convex shape due to insufficient resin filling on the fine convex shaping surface of the mold on the main surface side with the convex shape, and appearance defects due to waviness on the back surface of the main surface with the convex shape (the other main surface, which is flat). If there are areas where the resin filling is inadequate, this can be identified as a partially chipped area. On the other hand, the quality of the flatness of the main surface can be judged by, for example, checking whether the straight lines are distorted when a fluorescent light placed in a rectangular case with one long side is shone from above and the reflected image is observed. For one main surface with a convex shape, if no gloss unevenness or waviness on the other main surface was observed, it was evaluated as "○ (Good)". If at least one of the following was observed, it was evaluated as "× (Poor)".

[0098] (6) Measurement of in-plane phase difference For each sample of the plate-shaped molded product, it was placed in a petri dish on a PA-300-L measuring stand (manufactured by Photonic Lattice Co., Ltd.) with the main surface having a convex shape facing upwards. A low-viscosity liquid (contact fluid manufactured by Shimadzu Corporation) with a refractive index close to that of the methacrylic resin used and that does not corrode the methacrylic resin was added to the petri dish so that it filled up to the top of the convex shape of the molded product. The main surface of the molded product with the convex shape was immersed in the liquid, and the liquid surface was made flat without any height difference. In this state, the in-plane phase difference distribution was measured at a wavelength of 520 nm. The average value of the absolute value of the in-plane phase difference (Re) in the area where the convex shape is formed (see Figures 1(A) and 3(A)) was calculated and used as the measured phase difference (nm). The measured birefringence value is preferably less than 100 nm as an in-plane phase difference, in order to minimize adverse effects on the optical properties.

[0099] [Table 1]

[0100] From the results in Table 1, the following was found: For each sample in Examples 1 to 6, the flatness value fell within the range of the invention, indicating that molded articles with high flatness on the planar side were obtained. Furthermore, the degree of filling, warping, and appearance were also good. On the other hand, for the sample of Comparative Example 1, the flatness value was 9.8×10 -4 and since the warpage was large, the reflected image of the fluorescent lamp on the molded product plane appeared distorted. Also, for the sample of Comparative Example 2, when Tmax1 was set to a high temperature, the fluidity of the resin improved more than necessary, and due to the entrainment of air, the molded product had many defects in the convex-shaped part. Also, the warpage was large and the flatness was not sufficient. Furthermore, for the sample of Comparative Example 3, the molded product was stuck when the mold was opened, and a good molded product could not be obtained. Also, for the sample of Comparative Example 4, the warpage was large and the flatness was not sufficient. Moreover, for the sample of Comparative Example 5, the warpage was large, parting lines occurred on the flat side of the molded product, and the flatness of the plane was not sufficient.

[0101] <Evaluation as a light direction conversion element> The characteristics when the plate-shaped molded products with fine convex-shaped parts obtained in Example 1 and Comparative Example 1 were used as light direction conversion elements were evaluated. As shown in Fig. 6, the light that entered at an incident angle of 45 degrees with respect to the incident surface (the other main surface which is the back surface of one of the main surfaces having the fine convex-shaped part) 81 of the plate-shaped molded product 8 with fine convex-shaped parts was reflected by the inclined surface 83 whose angle with the bottom surface 82 was 85 degrees, and then refracted and emitted outside from the inclined surface 84 whose angle with the bottom surface 82 was 65 degrees. At this time, since the light is emitted from the inclined surface 84 at a refraction angle of 64 degrees, the light is emitted at an angle of approximately 90 degrees with respect to the incident surface 81. That is, it can be said that it is a light direction conversion element that bends the light incident at an incident angle of 45 degrees on the incident surface in a direction perpendicular to the incident surface. The molded part 8 was positioned as shown in Figure 6, and the clarity of the reflected and transmitted image was evaluated as an optical direction conversion element. An LED light source 5 with a collimating lens emitting 530nm light (Thorlabs, M530L4) and a frosted diffuser plate 6 (Sigma Koki, #240) were placed, and a USAF Target 7 (Edmund, USAF1951 target negative, target area approximately 12mm) was illuminated from the back. Light from the Target image formed by light passing through the transmission region 71 of the Target (see Figure 7) was incident on the incident surface 81 of the molded product 8 at an incident angle of 45°. The reflected image (the image formed by light that is reflected by the inclined surface 83 and then transmitted through the inclined surface 84) of the light emitted from the convex-shaped surface (main surface having a fine convex shape) of the molded product 6 was captured by a single-lens reflex camera 9 (Olympus E-PL5) positioned 350 mm away perpendicular to the incident surface 81. The reflected image observed when using the molded product obtained in Example 1 was a clear image, but the reflected image observed when using the molded product obtained in Comparative Example 1 showed strong distortion of the target image and low clarity. [Industrial applicability]

[0102] According to the present invention, even when the main surface includes a surface having a fine convex shape and a flat surface, it is possible to provide a plate-shaped molded product with good appearance and suppressed warping. [Explanation of Symbols]

[0103] 1,2: Plate-shaped molded products 11,21: One main surface having a fine convex shape 12,22: The other main surface where no fine convex shapes are formed. 13,23: Regions where fine convex shapes are formed. 14,24:Convex shape part 15a, 15b, 15c, 15d: Measurement points for warpage 5:LED light source 6: Frost diffuser 7: USAF Target 71:Transparent area 72: Shading area 8: Plate-shaped molded product 81:Incidence plane 82: Bottom 83, 84: Slope 9: SLR camera

Claims

1. A plate-shaped molded product comprising one main surface having a plurality of fine convex shapes with a height of 50 to 600 μm, and the other main surface being flat, The aforementioned plate-shaped molded product contains a methacrylic resin composition having a glass transition temperature (Tg) of 115 to 150°C. The methacrylic resin in the methacrylic resin composition is a thermoplastic resin. A plate-shaped molded product characterized in that the flatness of the other main surface, measured using a laser interferometer, satisfies the following formula. (Flatness) = (PV value / number of scan points) ≤ 5.0 × 10 －４ μm

2. The plate-shaped molded product according to claim 1, characterized in that the ratio (b / a) of the arrangement pitch (b) of the fine convex portions to the height (a) of the fine convex portions on one main surface having the fine convex portions is 0.1 to 2.

0.

3. The plate-shaped molded article according to claim 1 or 2, characterized in that the in-plane phase difference of one main surface having the fine convex portion is 100 nm or less.

4. A method for producing a plate-shaped molded article according to any one of claims 1 to 3, characterized in that an injection-molded article is obtained by injection filling the methacrylic resin composition.

5. A method for producing a plate-shaped molded product according to claim 4, characterized in that the surface temperature of the mold is heated to a temperature above the glass transition temperature (Tg) of the methacrylic resin composition, and then the methacrylic resin composition is injected and filled into the mold to obtain the injection-molded product.

6. When the mold that forms the main surface having a fine convex shape is called the first mold, and the mold that forms the main surface having a flat shape is called the second mold, A method for manufacturing a plate-shaped molded article according to claim 4 or 5, characterized in that when a methacrylic resin composition is injected into a mold, the maximum temperature Tmax2 of the second mold is set to (Tmax1-30)°C to (Tmax1-5)°C, when the maximum temperature of the first mold is set to Tmax1.

7. The step of injecting the methacrylic resin composition into the mold and then cooling the mold, The method for manufacturing a plate-shaped molded article according to claim 6, characterized in that, when the glass transition temperature of the methacrylic resin composition in the cooling step is Tg, the lowest temperature Tmin1 of the first mold is (Tg-75)°C to (Tg-45)°C, and the lowest temperature Tmin2 of the second mold is (Tmin1+10) to (Tmin1+30)°C.

8. An optical member characterized by being made of a plate-shaped molded product according to any one of Claims 1 to 4.

9. The optical component according to claim 8, characterized in that it is one selected from a Fresnel lens, a light guide plate, a lenticular lens, and an anti-reflective sheet.

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