Polarizing plate and method for manufacturing the same, and method for manufacturing display device

Abstract

The polarizing plate of the present application is obtained by laminating a polarizer, a first protective film disposed on one side thereof, a second protective film disposed on the other side, and a release film disposed on the side of the first protective film opposite to the polarizer. The light absorption coefficient A2 of the second protective film for light having a wavelength of 9.4 μm is 1.0 x 10 2 ~ 4.5 x 10 2 / μm. In a cross section of the polarizing plate along the lamination direction, the inclination angle φ of a straight line connecting an end point P1 of the release film on the side opposite to the first protective film in the cut end surface and an end point P2 of the second protective film on the side of the polarizer with respect to the lamination direction is 0.5 ~ 10°.

Description

TECHNICAL FIELD

[0001] The present application relates to a polarizing plate and a manufacturing method thereof, and a manufacturing method of a display device. BACKGROUND

[0002] A display panel such as a liquid crystal panel or an organic EL panel generally includes a polarizing plate. The polarizing plate includes a polarizer and two protective films (optical films) sandwiching the polarizer. Such a polarizing plate is manufactured by joining the polarizer and the two protective films in a roll-to-roll manner, and then cutting (cutting process) the obtained laminate into a size suitable for a display panel.

[0003] In the cutting process of the laminate, a cutting method using a blade has been employed in the past. However, in the case of the cutting process using a blade, foreign matter such as film dust is easily generated at the time of cutting. The protective film to which such foreign matter adheres sometimes causes display defects in the display panel.

[0004] Therefore, in recent years, cutting of the polarizing plate using a laser is performed (for example, refer to Patent Documents 1 and 2). For example, as a cutting method of a laminate film of a plurality of resin layers having different materials, a method of cutting using lasers having different wavelengths is known according to the kind of the resin layer (for example, Patent Document 1). In addition, a method of cutting by physically tearing after cutting to a depth halfway through with a laser, and the like, is known (for example, Patent Document 2).

[0005] PRIOR ART DOCUMENTS

[0006] PATENT DOCUMENTS

[0007] Patent Document 1: Japanese Patent Application Laid-Open No. 2019-98400

[0008] Patent Document 2: Japanese Patent Application Laid-Open No. 2012-30243 SUMMARY

[0009] PROBLEMS TO BE SOLVED BY THE INVENTION

[0010] However, in the kind and combination of the two protective films for the polarizing plate, there are various cases, and sometimes the absorbance of the laser is also greatly different. For example, in Patent Documents 1 and 2, a laminate in which a cellulose triacetate film (TAC) is laminated on one face of a polarizer and a cyclic olefin resin film is laminated on the other face is cut with a laser to obtain. However, a display device manufactured using such a polarizing plate has a problem that display unevenness is easily generated at the end portion of the display screen.

[0011] In addition, in the method of Patent Document 1, it is necessary to use different kinds of lasers, and in the method of Patent Document 2, since the cutting method using a laser and the physical cutting method are used together, there is also a problem that the productivity is low.

[0012] The present application has been achieved in view of the above-described actual circumstances, and aims to provide a polarizing plate and a manufacturing method thereof, and a manufacturing method of a display device, in which cutting processing using a laser can be performed without reducing productivity, and display unevenness at the end portion of the display device can be suppressed.

[0013] Means for solving the problem

[0014] The present application relates to a polarizing plate and a manufacturing method thereof, and a manufacturing method of a display device.

[0015] The polarizing plate of the present application is a polarizing plate in which a polarizer, a first protective film disposed on one side of the polarizer, a second protective film disposed on the other side of the polarizer, and a release film disposed on the side of the first protective film opposite to the polarizer are laminated, the light absorption coefficient A2 of light of a wavelength of 9.4 μm measured by an ATR method of the second protective film is 1.0 x 10 2 ~ 4.5 x 10 2 / μm, and the polarizing plate has a cut end surface, in a cross section of the polarizing plate along the lamination direction, the inclination angle of a straight line connecting an end point P1 of the release film opposite to the first protective film and an end point P2 of the polarizer on the side of the second protective film in the cut end surface with respect to the lamination direction is 0.5 to 10°.

[0016] The manufacturing method of the polarizing plate of the present application includes a step of preparing a laminate including a polarizer, a first protective film disposed on one side of the polarizer, a second protective film disposed on the other side of the polarizer, and a release film disposed on the side of the first protective film opposite to the polarizer, the ratio A1 / A2 of the light absorption coefficient A1 of light of a wavelength of 9.4 μm measured by an ATR method of the first protective film to the light absorption coefficient A2 of light of a wavelength of 9.4 μm measured by an ATR method of the second protective film is 1 to 5; and a step of cutting the laminate along the lamination direction of the laminate by irradiating the laminate with a laser from the side of the release film.

[0017] The manufacturing method of the display device of the present application includes a step of adhering the polarizing plate of the present application to at least one side of a display element so that the second protective film is on the side of the display element.

[0018] Effects of the invention

[0019] According to the present application, an optical film, a polarizing plate, and a liquid crystal display device in which light leakage does not occur in a display device and the cutting property of a laser can be improved can be provided. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1A and B are cross-sectional views of a part of a manufacturing process of a display device using a conventional polarizing plate.

[0021] Figure 2 A and B are cross-sectional views of a part of a manufacturing process of a display device using another conventional polarizing plate.

[0022] Figure 3 A and B are cross-sectional views of a part of a manufacturing process of a display device using a polarizing plate according to the present embodiment.

[0023] Figure 4 A is a cross-sectional view showing a configuration of a polarizing plate according to the present embodiment, Figure 4 B is Figure 4 A is an enlarged view of a cross section.

[0024] Figure 5 A to C are cross-sectional views showing a manufacturing process of a polarizing plate according to the present embodiment.

[0025] Figure 6 is a cross-sectional view showing a configuration of a display device according to the present embodiment. DETAILED DESCRIPTION

[0026] The present inventors have studied a cause of display unevenness occurring at an end portion of a display screen in a display device using a conventional polarizing plate cut by laser (for example, the polarizing plate of Patent Documents 1 or 2), and found that an inclination angle of a cut end surface of the polarizing plate after cutting by laser is related. That is, although the mechanism of the display unevenness at the end portion is not clear, it is presumed as follows.

[0027] Figure 1 A to 2B are cross-sectional views of a part of a manufacturing process of a display device using a conventional polarizing plate. Figure 3 A and B are cross-sectional views of a part of a manufacturing process of a display device using a polarizing plate according to the present embodiment.

[0028] (Influence of inclination angle φ of cut end surface)

[0029] In manufacturing the display device, the polarizing plate P with a release film cut by laser is attached to the display element C while being pressed via a pressure-sensitive adhesive (not shown) or the like.

[0030] At this time, if the difference in laser absorbability of the two protective films 2 and 3 holding the polarizer 1 is too large as in Patent Documents 1 or 2 (specifically, if the laser absorbability of the protective film 3 is extremely low compared with the laser absorbability of the protective film 2), an inclination (an inclination (a positive direction inclination) that widens as it approaches the surface of the display element C) is easily formed at the cut end surface of the polarizing plate P (refer to FIG. 2B). Figure 1A). If the polarizing plate P having the cut end surface thus inclined is attached to the display element C while being pressed, the inclination after attachment also remains (see Figure 1 B), and thus display unevenness is easily generated at the end portion of the display screen due to refraction of light from the backlight or the like.

[0031] On the other hand, if the polarizing plate P having no inclination of the cut end surface is attached to the display element C while being pressed (see Figure 2 A), the cut end surface of the polarizing plate P is easily inclined in the direction opposite to the above (negative direction) after attachment (see Figure 2 B). Thus, as in the above, display unevenness is easily generated at the end portion of the display screen.

[0032] In contrast, in the present application, the inclination of the cut end surface of the polarizing plate 10 before attachment to the display element C is moderated (see Figure 3 A). Specifically, the inclination angle of the cut end surface of the polarizing plate 10 is adjusted to 0.5 to 10° at a cross section in the stacking direction of the respective films (see Figure 4 B) to be described later). Thereby, the inclination angle of the cut end surface of the polarizing plate after attachment to the display element C can be made close to substantially 0° (can be made substantially perpendicular with respect to the surface of the display element C) (see Figure 3 B), and thus display unevenness at the end portion of the display screen due to the inclination angle (shape) of the cut end surface can be suppressed.

[0033] (Influence of internal stress due to laser cutting)

[0034] Further, in the conventional polarizing plate (inclination angle φ = 0°) of Figure 2 A, almost no internal stress due to cutting remains in the protective film. Thus, due to moisture absorption or the like, almost no force for shrinking of the protective film occurs when the polarizer expands, and thus the inclination angle φ of the cut end surface of the polarizing plate easily becomes large in the above negative direction (the amount of change in the inclination angle φ due to humidity change is large) from the tangent point with the display element C (cut end surface). On the other hand, in the polarizing plate (φ is too large) of Figure 1 A, large internal stress due to laser cutting remains in the protective film. Thus, due to moisture absorption or the like, the force for shrinking of the protective film becomes excessively large with respect to the force for expansion of the polarizer, and the inclination angle φ easily changes in the above positive direction.

[0035] In contrast, in the polarizing plate (φ = 0.5 to 10°) of Figure 3In the polarizer of the present invention, such as A, the internal stress caused by laser cutting in the protective film is moderately retained. Therefore, due to moisture absorption, the force that needs to contract in the direction that eliminates the force that causes the polarizer to expand is easily and moderately generated, and it is difficult to increase in either the negative or positive direction centered on the tangent point with the display element C (the change in tilt angle φ caused by humidity change is small). As a result, optical non-uniformity after damp heat durability can also be further reduced.

[0036] The tilt angle of the cut end face of the polarizer 10 can be adjusted by any method. Preferably, the tilt angle of the cut end face of the polarizer 10 is adjusted according to the light absorption properties of the first protective film 12 and the second protective film 13, and their ratio. Specifically, it is preferable that the ratio of the light absorption properties of the first protective film 12 and the second protective film 13 is moderately small; that is, that the light absorption coefficient of the second protective film 13 at a wavelength of 9.4 μm is moderately large (1.0 × 10⁻⁶). 2 ~4.5×10 2 The light absorption coefficient A1 of the first protective film 12 and the light absorption coefficient A2 of the second protective film 13 are made to be appropriately small (A1 / A2). The configuration of the present invention will be described below.

[0037] 1. Polarizing filter

[0038] Figure 4 A is a cross-sectional view showing the configuration of the polarizer 10 according to this embodiment. Figure 4 B is Figure 4 An enlarged view of section A. It should be noted that... Figure 4 The diagrams of the adhesive layer are omitted in A and B.

[0039] like Figure 4 As shown in A and B, the polarizer 10 of this embodiment includes: a polarizer 11, a first protective film 12 disposed on one side thereon, a second protective film 13 disposed on the other side thereon, and a release film 14 disposed on the side opposite to the polarizer 11 via the first protective film 12. It should be noted that an adhesive layer (not shown) is disposed between the polarizer 11 and either the first protective film 12 or the second protective film 13.

[0040] 1-1. Polarizer 11

[0041] The polarizer 11 is a component that allows light with a polarization plane in only a certain direction to pass through, and is a polyvinyl alcohol-based polarizing film. Among polyvinyl alcohol-based polarizing films, there are polarizing films that dye polyvinyl alcohol films with iodine and polarizing films that dye dichroic dyes.

[0042] The polyvinyl alcohol (PVA) polarizing film can be a film that has been uniaxially stretched and then dyed with iodine or dichroic dyes (preferably a film that has undergone a durability treatment with boron compounds); or it can be a film that has been uniaxially stretched after being dyed with iodine or dichroic dyes (preferably a film that has undergone a durability treatment with boron compounds). The absorption axis of the polarizer is parallel to the direction of maximum stretching.

[0043] The thickness of the polarizer 11 is preferably 5 to 40 μm, and more preferably 5 to 30 μm in order to make the polarizer thinner.

[0044] 1-2. First protective film 12

[0045] The first protective film 12 is disposed on one side of the polarizer 11, specifically, between the polarizer 11 and the release film 14. When the display device is manufactured, the first protective film 12 is disposed on the opposite side (the side away from the display element) of the display element via the polarizer 11.

[0046] There are no particular limitations on the resin constituting the first protective film 12, as long as it is transparent and the ratio of the light absorption coefficients of the first protective film 12 to the second protective film 13, A1 / A2, is a certain value or less. Examples of such resins include polyester resins, (meth)acrylic resins, cellulose ester resins (TAC films, etc.), and cyclic olefin resins. Preferably, the first protective film contains a (meth)acrylic resin or a cyclic olefin resin.

[0047] ((meth)acrylic resin)

[0048] (Meth)acrylic resins are preferably polymers containing structural units derived from methyl methacrylate. The polymer may further contain structural units derived from monomers that can copolymerize with methyl methacrylate. Examples of other monomers that can copolymerize with methyl methacrylate include alkyl methacrylates with 1 to 18 carbon atoms other than methyl methacrylate, such as 2-ethylhexyl methacrylate; α,β-unsaturated acids such as (meth)acrylic acid; unsaturated dicarboxylic acids such as maleic acid, fumaric acid, and itaconic acid; styrene derivatives such as styrene and α-methylstyrene; maleic anhydride; maleimide derivatives such as maleimide and N-phenylmaleimide; and glutaric anhydride.

[0049] The proportion of structural units derived from methyl methacrylate relative to all structural units constituting the above copolymer is preferably 50% by mass or more, more preferably 70% by mass or more.

[0050] (Cyclic olefin resin)

[0051] The cyclic olefin resin can be the same as the cyclic olefin resin contained in the second protective film 13 described later. That is, the composition of the cyclic olefin resin contained in the first protective film can be the same as or different from the composition of the cyclic olefin resin contained in the second protective film.

[0052] The weight-average molecular weight of (meth)acrylic resins and cyclic olefin resins can be in the same range as that of cyclic olefin resins described later.

[0053] (thickness)

[0054] There is no particular limitation on the thickness of the first protective film 12, which is preferably 20 to 70 μm, and more preferably 30 to 60 μm.

[0055] 1-3. Second protective film 13

[0056] The second protective film 13 is disposed on the other side of the polarizer 11. Specifically, the second protective film 13 is disposed between the display element and the polarizer 11 (on the side closer to the display element than the polarizer 11) when the display device is manufactured.

[0057] The material of the second protective film 13 preferably has an absorption coefficient ratio A1 / A2 of 1 to 5 between the first protective film 12 and the second protective film 13. If A1 / A2 is 1 or more, it is easier to cut the polarizer in a shorter time. On the other hand, if A1 / A2 is 5 or less, the second protective film 13 has moderate laser absorption (since the laser absorption of the second protective film 13 is not too low compared to the first protective film 12), which can reduce the shrinkage caused by cutting. As a result, the tilt angle of the cut end face 10a of the obtained polarizer 10 can also be made smaller. From the same point of view, the absorption coefficient ratio A1 / A2 is preferably 1.5 to 5.0, more preferably 2.0 to 4.5.

[0058] Regarding the absorption coefficient A2 of light with a wavelength of 9.4 μm for the second protective film 13, as described above, it is preferably 1.0 × 10⁻⁶. 2 ~4.5×10 2 / μm. If the absorption coefficient A2 is 1.0×10 2 A light absorption coefficient of A2 of the second protective film 13 is greater than / μm, which allows for moderate laser absorption and thus improves the laser-generated cutoff capability. From the viewpoint of minimizing damage to transparency and reducing the likelihood of light leakage in the display device, a coefficient of 1.5 × 10⁻⁶ is more preferable for the second protective film 13. 2 ~4.0×10 2 / μm, further preferably 2.0×10 2 ~3.5×10 2 / μm.

[0059] The absorption coefficients A1 of the first protective film 12 and A2 of the second protective film 13 can be determined by the following methods.

[0060] Microscopic FTIR (Agilent "UMA600" and "FTS3000") was used, employing the ATR method (Attenuated Total Reflection), with an incident light diameter of 100 μm, a Ge prism (incident angle 45°), an MCT-A detector, and a resolution of 4.0 cm⁻¹. -1 The infrared absorption spectrum was measured under the condition of 64 cumulative measurements. From the obtained infrared absorption spectrum, the portion corresponding to a wavelength of 9.4 μm (wavenumber 1041 cm⁻¹) was read. -1 The absorbance of the film is then calculated using the following formula.

[0061] Absorption coefficient ( / μm) = Absorbance × loge10 / Film thickness (μm)

[0062] The light absorption coefficient of a membrane can be adjusted primarily by the membrane's composition.

[0063] The composition of the second protective film 13 is not particularly limited as long as it satisfies the above-mentioned absorption characteristics. Preferably, it contains a cyclic olefin resin, and more preferably, it also contains a light-absorbing material. That is, the second protective film 13 preferably contains a cyclic olefin resin and a light-absorbing material.

[0064] 1-3-1. Cycloolefin resins

[0065] Cycloolefin resins are polymers containing structural units derived from norbornene monomers. Norbornene monomers are represented by the following formula (1).

[0066] [Chemistry 1]

[0067]

[0068] R in equation (1) 1 ~R 4 Each represents a hydrogen atom, a halogen atom, a hydrocarbon group, or a polar group.

[0069] Examples of halogen atoms include fluorine atoms, chlorine atoms, etc.

[0070] The hydrocarbon group is a hydrocarbon group having 1 to 10 carbon atoms, preferably 1 to 4, more preferably 1 or 2. Examples of hydrocarbon groups include alkyl groups such as methyl, ethyl, propyl, and butyl. The hydrocarbon group may further have a divalent linker containing an oxygen atom, nitrogen atom, sulfur atom, or silicon atom (e.g., carbonyl, imino, ether bond, silyl ether bond, thioether bond, etc.).

[0071] Examples of polar groups include carboxyl, hydroxyl, alkoxy, alkoxycarbonyl, allyloxycarbonyl, amino, amide, and those linked via methylene groups (-(CH2)). n - (n is an integer greater than or equal to 1) are groups formed by combining these groups. Among them, alkoxycarbonyl and aryloxycarbonyl are preferred, and alkoxycarbonyl is more preferred.

[0072] Among them, R is preferred. 1 ~R 4 At least one of the groups is a polar group. This is because cyclic olefin resins containing structural units from norbornene monomers with polar groups are readily soluble in solvents when film is formed, for example, using solution casting, and the glass transition temperature of the resulting film is also easily increased. On the other hand, in melt casting, cyclic olefin resins that do not contain structural units from norbornene monomers with polar groups can be used.

[0073] Additionally, in R 1 ~R 4 In the middle, R 1 and R 2 These two (or R) 3 and R 4 Both of these can be hydrogen atoms.

[0074] In equation (1), p represents an integer from 0 to 2. From the viewpoint of improving the heat resistance of the second protective film, p is preferably 1 to 2.

[0075] The following are specific examples of norbornene monomers represented by formula (1). Among them, the following examples are included in the examples of norbornene monomers having polar groups.

[0076] [Chemistry 2]

[0077]

[0078] Examples of norbornene monomers that do not have polar groups include the following.

[0079] [Chemistry 3]

[0080]

[0081] The content of structural units from norbornene monomers relative to the total number of structural units constituting cyclic olefin resins can be 50–100 mol%.

[0082] The cyclic olefin resin may further comprise structural units from other monomers that can copolymerize with structural units from norbornene monomers. Examples of other copolymerizable monomers include (in the case where the aforementioned norbornene monomers have polar groups) norbornene monomers without polar groups, cyclobutene, cyclopentene, cycloheptene, cyclooctene, dicyclopentadiene, and other cyclic olefin monomers that do not have a norbornene skeleton.

[0083] Commercially available products can be used as cyclic olefin resins. Examples of commercially available products include Arton (registered trademark) G, Arton F, Arton R, and Arton RX manufactured by JSR Corporation.

[0084] There are no particular limitations on the weight-average molecular weight (Mw) of the cyclic olefin resin, but it is preferably 20,000 to 300,000, more preferably 30,000 to 250,000, and even more preferably 40,000 to 200,000. If the weight-average molecular weight (Mw) of the cyclic olefin resin is within the above range, the molding processability will not be impaired, and the mechanical properties of the second protective film 13 can be improved.

[0085] The weight-average molecular weight (Mw) of cyclic olefin resins can be determined by gel permeation chromatography (GPC).

[0086] Specifically, a gel permeation chromatography (HLC8220GPC manufactured by Tosoo Corporation) was used as the measuring device, and a TSK-GEL G6000HXL-G5000HXL-G5000HXL-G4000HXL-G3000HXL manufactured by Tosoo Corporation was used in series as the column.

[0087] Then, 20 ± 0.5 mg of the sample was dissolved in 10 ml of tetrahydrofuran and filtered through a 0.45 mm filter. 100 ml of this solution was injected into the column (temperature 40 °C) and measured using a detector RI at 40 °C. The weight-average molecular weight was then converted to styrene and calculated.

[0088] The glass transition temperature (Tg) of cyclic olefin resins is preferably above 110°C, more preferably 110–350°C, and even more preferably 120–250°C. If the Tg of the cyclic olefin resin is above 110°C, deformation is unlikely to occur even under high-temperature conditions. If the Tg is below 350°C, molding processability is less likely to be impaired, and thermal degradation of the cyclic olefin resin during molding can be further suppressed.

[0089] The glass transition temperature can be determined using DSC (Differential Scanning Colorimetry) according to the method in JIS K 7121-2012.

[0090] There is no particular limitation on the content of cyclic olefin resin, but it is preferably 50% by mass or more, more preferably 70 to 99% by mass, relative to the second protective film 13.

[0091] 1-3-2. Light-absorbing materials

[0092] Light-absorbing materials are generally preferred to be compounds with carbonyl groups, more preferably ester compounds or (meth)acrylic acid polymer particles.

[0093] <Ester Compounds>

[0094] Ester compounds can be any of sugar ester compounds, polyester compounds, or polyol ester compounds.

[0095] (glycoester compounds)

[0096] Glycoester compounds are compounds in which all or part of the OH groups of a monosaccharide, disaccharide, or trisaccharide are esterified. Such glycolester compounds are preferably those represented by the formula (FA).

[0097] [Chemistry 4]

[0098]

[0099] In formula (FA), R1 to R8 represent substituted or unsubstituted alkyl carbonyl groups or substituted or unsubstituted aryl carbonyl groups. R1 to R8 may be the same as each other or different.

[0100] The substituted or unsubstituted alkyl carbonyl group is preferably a substituted or unsubstituted alkyl carbonyl group having 2 or more carbon atoms. Examples of substituted or unsubstituted alkyl carbonyl groups include methyl carbonyl (acetyl), ethyl carbonyl, etc. Examples of substituents in the alkyl group include aryl groups such as phenyl.

[0101] The substituted or unsubstituted aryl carbonyl group is preferably a substituted or unsubstituted aryl carbonyl group having 7 or more carbon atoms. Examples of aryl carbonyl groups include phenyl carbonyl groups. Examples of substituents in the aryl group include alkyl groups such as methyl groups.

[0102] The examples of R1 to R8 in equation (FA) include the following examples.

[0103] [Chemistry 5]

[0104]

[0105] The average degree of substitution of the sugar ester compound is preferably 3 to 6. The average degree of substitution of the sugar ester compound represents the average proportion of esterified OH groups out of the total number of sugars used as raw materials.

[0106] (Polyol ester compounds)

[0107] The polyol ester is an esterification of aliphatic polyols with 2 or more nucleotides (preferably aliphatic polyols with 2 to 20 nucleotides) and a monocarboxylic acid.

[0108] Examples of polyols include arbutin, arbutin, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,2-propanediol, 1,3-propanediol, dipropylene glycol, tripropylene glycol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, dibutylene glycol, 1,2,4-butanetriol, 1,5-pentanediol, 1,6-hexanediol, hexanetriol, galactitol, mannitol, 3-methylpentane-1,3,5-triol, pinacol, sorbitol, trimethylolpropane, trimethylolethane, xylitol, etc., preferably triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, sorbitol, trimethylolpropane, xylitol, etc.

[0109] There are no particular restrictions on monocarboxylic acids; aliphatic monocarboxylic acids such as acetic acid and propionic acid, alicyclic monocarboxylic acids such as cyclopentane carboxylic acid and cyclohexane carboxylic acid, and aromatic monocarboxylic acids such as benzoic acid and toluene carboxylic acid are all acceptable.

[0110] The carboxylic acid used in polyol ester compounds can be one type or a mixture of two or more types. Furthermore, all the OH groups in the polyol can be esterified, or some can remain as OH groups.

[0111] The molecular weight of the sugar ester compound and the polyol ester compound also depends on the manufacturing method of the second protective film. From the viewpoint of easily obtaining good compatibility with cyclic olefin resins, a moderately low molecular weight is preferred. Specifically, the molecular weight of the sugar ester compound and the ester compound can be, for example, 300 to 1500, preferably 600 to 1200.

[0112] (Polyester compound)

[0113] Polyester compounds are condensation polymers containing structural units obtained by reacting dicarboxylic acids with diols.

[0114] The dicarboxylic acid can be any one of aromatic dicarboxylic acids, aliphatic dicarboxylic acids, or alicyclic dicarboxylic acids, preferably an aromatic dicarboxylic acid. The dicarboxylic acid can be one type or a mixture of two or more types. Preferably, an aromatic dicarboxylic acid is mixed with an aliphatic dicarboxylic acid.

[0115] The diol can be any one of aromatic diols, aliphatic diols, or alicyclic diols, preferably an aliphatic diol, and more preferably a diol having 1 to 4 carbon atoms. The diol can be a single type or a mixture of two or more types.

[0116] That is, the polyester compound preferably contains structural units obtained by reacting a dicarboxylic acid containing an aromatic dicarboxylic acid with a diol having 1 to 8 carbon atoms, and more preferably contains structural units obtained by reacting a dicarboxylic acid containing both aromatic and aliphatic dicarboxylic acids with a diol having 1 to 8 carbon atoms. The two ends of the polyester molecule may or may not be closed.

[0117] Among these ester compounds, sugar ester compounds are particularly preferred in terms of moderately low molecular weight and excellent compatibility with cyclic olefin resins.

[0118] <(meth)acrylic acid polymer particles>

[0119] (Meth)acrylic polymer particles are particles of polymers containing structural units derived from (meth)acrylates, preferably particles of polymers containing structural units derived from methyl methacrylates.

[0120] Polymers containing structural units derived from methyl methacrylate may further contain structural units derived from other comonomers. Examples of other comonomers include alkyl (meth)acrylates with 1 to 18 carbon atoms other than methyl methacrylate; α,β-unsaturated acids such as (meth)acrylic acid; unsaturated dicarboxylic acids such as maleic acid, fumaric acid, and itaconic acid; styrene-based monomers such as styrene and α-methylstyrene; polyfunctional (meth)acrylates having two or more (meth)acryloyl groups such as (poly)ethylene glycol di(meth)acrylate, butanediol di(meth)acrylate, ethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, and tetraethylene glycol di(meth)acrylate; and polyfunctional monomers such as allyl alkyl (meth)acrylates and allyl alkyl (meth)acrylates.

[0121] The polymer is preferably a crosslinked polymer, i.e., a copolymer containing structural units from methyl methacrylate and structural units from polyfunctional monomers; more preferably, it is a copolymer containing structural units from methyl methacrylate, structural units from styrene, and structural units from polyfunctional monomers.

[0122] From the viewpoint of improving the laser absorption rate of the second protective film 13, it is preferable that the content of structural units from carbonyl (meth)acrylates is a certain amount or more. From this viewpoint, the total amount of structural units from methyl methacrylates relative to all structural units constituting the polymer is preferably 30 mol% or more, more preferably 50 to 80 mol%.

[0123] The content of structural units from multifunctional monomers relative to the total number of structural units constituting the polymer is preferably 3 to 50 mol%, more preferably 10 to 35 mol%.

[0124] The (meth)acrylic acid polymer particles are preferably polymers with a refractive index difference of 0.01 or less with the cyclic olefin resin. Such (meth)acrylic acid polymer particles are less likely to reduce the transparency of the obtained second protective film.

[0125] The refractive indices of cyclic olefin resins and (meth)acrylic acid polymer particles can each be the refractive index of light at a wavelength of 550 nm. The refractive index of light at a wavelength of 550 nm can be obtained, for example, by preparing a sample film containing each component separately and measuring the refractive index of the sample film at a wavelength of 550 nm using a Hochika spectrophotometer (UVSEL).

[0126] The Tg of (meth)acrylic acid polymer particles is preferably above 80°C. The Tg of (meth)acrylic acid polymer particles can be determined in accordance with JISK 7121-2012 or ASTMD 3418-82, as described above.

[0127] There is no particular limitation on the average particle size of the (meth)acrylic polymer particles, but it is preferably 50 to 500 nm. If the average particle size is within the above range, moderately sized irregularities can be formed on the surface of the film while improving the laser absorption rate, thus imparting slip properties. From the above viewpoint, the average particle size of the (meth)acrylic polymer particles is more preferably 0.07 to 0.28 μm.

[0128] The average particle size of the (meth)acrylic polymer particles in the second protective film 13 can be determined using the following method. First, the second protective film 13 is cut, and the resulting cut surface is observed using TEM. Then, for any 100 particles, the particle size is measured. The particle size is measured as the equivalent diameter of the circle of the 100 particles obtained by TEM imaging, as described above. The average value of the obtained particle sizes is then taken as the "average particle size". It should be noted that in the TEM image, portions with a brightness greater than 150% of the average brightness of the field of view are identified as particles.

[0129] The content of light-absorbing material can be set such that the ratio A1 / A2 of the light absorption coefficients of the second protective film 13 and the first protective film 12 satisfies the above range, and the light absorption coefficient A2 of the second protective film 13 satisfies the above range.

[0130] For example, the content of the light-absorbing material in the second protective film 13 is preferably greater than the content of the light-absorbing material in the first protective film 12.

[0131] Specifically, the content of the light-absorbing material relative to the resin is preferably 0.5% to 10% by mass. If the content of the light-absorbing material is within the above range, it is easy to make the light absorption coefficient A2 of the second protective film 13 fall within the above range, and simultaneously adjust the ratio of the light absorption coefficients A1 / A2 to the above range. This makes it easy to moderately improve the laser-dependent cut-off properties of the second protective film 13, while simultaneously adjusting the tilt angle of the cut end face 10a of the resulting polarizer 10 to the above range. From the same perspective, the content of the light-absorbing material relative to the resin is more preferably 1% to 6% by mass.

[0132] 1-3-3. Other ingredients

[0133] The second protective film 13 may, as needed, further contain other components such as inorganic particles.

[0134] Inorganic microparticles enhance the slip properties of the second protective film 13. Examples of inorganic materials constituting the microparticles include oxides such as silicon dioxide (SiO2), titanium dioxide, aluminum oxide, and zirconium oxide. Among these, silicon dioxide is preferred from the perspective of reducing the increase in film haze. Examples of commercially available silicon dioxide particles include AEROSIL R812, R972 (manufactured by AEROSIL Corporation of Japan), and NanoTek SiO2 (manufactured by CI Chemical Co., Ltd.).

[0135] The average primary particle size of the inorganic particles is preferably 5 to 50 nm. If the average primary particle size of the inorganic particles is 5 nm or more, the surface of the film can be roughened, thus easily imparting slip properties; if it is less than 50 nm, it is easy to suppress the increase of haze. The average primary particle size of the inorganic particles is more preferably 5 to 30 nm. The average primary particle size of the inorganic particles in the second protective film 13 can be measured using the same method as described above.

[0136] There is no particular limitation on the content of inorganic particles, which can be 0 to 5% by mass relative to the second protective film 13, and is preferably 0 to 2% by mass.

[0137] 1-3-4.Physical properties

[0138] (Total light transmittance)

[0139] Regarding the total light transmittance of the second protective film 13, there are no particular limitations as long as it has sufficient light transmittance; preferably, it is 80% or more, more preferably 85% or more, and even more preferably 88% or more. The total light transmittance of the second protective film 13 can be measured according to JIS K7361-1:1997.

[0140] The total light transmittance of the second protective film 13 can be adjusted, for example, by adjusting the content of the light-absorbing material. In order to improve the total light transmittance of the second protective film 13, it is preferable, for example, to set the content of the light-absorbing material to a certain level or below.

[0141] (Phase difference Ro and Rt)

[0142] The second protective film 13 may have phase difference values ​​Ro and Rt that are appropriate for its application. For example, the in-plane phase difference Ro of the second protective film 13, measured at a measurement wavelength of 590 nm, 23°C, and 55% RH, preferably satisfies 40 nm ≤ Ro ≤ 60 nm, and the phase difference Rt in the thickness direction preferably satisfies 115 nm ≤ Rt ≤ 145 nm. Such a second protective film 13 is suitable as a phase difference film, for example, in combination with a VA-type liquid crystal cell.

[0143] Ro and Rt are each defined by the following formula.

[0144] Equation (2a): Ro=(nx-ny)×d

[0145] Formula (2b): Rt=((nx+ny) / 2-nz)×d

[0146] (in the formula,

[0147] nx represents the refractive index in the in-plane hysteresis axis direction (the direction where the refractive index is at its maximum) of the second protective film 13.

[0148] ny represents the refractive index of the second protective film 13 in the direction orthogonal to the in-plane hysteresis axis.

[0149] nz represents the refractive index in the thickness direction of the second protective film 13.

[0150] d represents the thickness (nm) of the second protective film 13.

[0151] The in-plane hysteresis axis of the second protective film 13 refers to the axis on the film surface where the refractive index is at its maximum. The in-plane hysteresis axis of the optical film can be confirmed using an automatic birefringence meter, AxoScan (AxoScan Mueller Matrix Polarimeter: manufactured by AxoScan).

[0152] The determination of Ro and Rt can be performed using the following methods.

[0153] 1) The second protective film 13 was conditioned at 23°C and 55% RH for 24 hours. The average refractive index of the optical film was measured using an Abbe refractometer, and the thickness d was measured using a commercially available micrometer.

[0154] 2) The phase difference Ro and Rt of the second protective film 13 after humidification were measured at a measurement wavelength of 590 nm using an automatic birefringence meter AxoScan (AxoScanMueller Matrix Polarimeter: manufactured by AxoScan Mueller Matrix Polarimeter) at an environment of 23°C and 55%RH.

[0155] The phase difference Ro and Rt of the second protective film 13 can be adjusted primarily by the stretching ratio. To improve the phase difference Ro and Rt of the second protective film 13, it is preferable to increase the stretching ratio.

[0156] (thickness)

[0157] There is no particular limitation on the thickness of the second protective film 13, which is preferably 20 to 70 μm, and more preferably 30 to 45 μm. In addition, there is no particular limitation on the ratio t1 / t2 of the thickness t2 of the second protective film 13 and the thickness t1 of the first protective film 12, which can be, for example, 1 to 5.

[0158] 1-3-5. Manufacturing Method

[0159] The first protective film 12 and the second protective film 13 can be manufactured by any method, such as melt casting or solution casting.

[0160] In the melt casting method, the hot melt stream of a thermoplastic resin composition is delayed and allowed to cool and solidify to obtain a cast film. Specifically, it can be obtained by a step of preparing the thermoplastic resin composition (A1), a step of delaying the cooling and solidification of the hot melt stream of the thermoplastic resin composition (A2), and a step of stretching the obtained film as needed (A3).

[0161] In process A1), the components of the protective film are dry-mixed and then melt-mixed using a twin-screw extruder or similar equipment to obtain granules.

[0162] In step A2), the granules of the prepared thermoplastic resin composition are melt-mixed using a twin-screw extruder or similar equipment, and then cast from a casting die. The hot melt temperature during melt casting can be (Tg+30)~(Tg+70)℃ when the glass transition temperature of the resin is set as Tg.

[0163] In the A3 process, stretching can be performed according to the desired optical properties, preferably in one or more of the following directions: width direction (TD direction), conveying direction (MD direction), and tilt direction.

[0164] The stretching ratio is set according to the required optical performance; for example, from the viewpoint of functioning as a film with low phase difference, it can be set to 1.01 to 1.3 times. The stretching ratio is defined as (the magnitude of the stretching direction of the film after stretching) / (the magnitude of the stretching direction of the film before stretching). The stretching temperature (the drying temperature during stretching) is preferably (Tg-20) to (Tg+30) °C.

[0165] (Solution casting method)

[0166] In solution casting, a solution (paste) in which the components of the protective film are dissolved in a solvent is cast and then dried to obtain a cast film. Specifically, it can be manufactured by the following steps: B1) preparing a paste containing a cyclic olefin resin, a light-absorbing material, and a solvent; B2) casting the obtained paste on a support, drying, and peeling it to obtain a cast film; and B3) stretching the obtained cast film as needed.

[0167] In step B1), the cyclic olefin resin and the light-absorbing material are dissolved or dispersed in a solvent to prepare a paste. The solvent used must contain at least an organic solvent (good solvent) capable of dissolving the cyclic olefin resin. Examples of good solvents include chlorinated organic solvents such as dichloromethane; and non-chlorinated organic solvents such as methyl acetate, ethyl acetate, acetone, and tetrahydrofuran, with dichloromethane being preferred. Regarding the solvent used, from the viewpoint of improving the peelability of the cast film from the support, a lean solvent such as methanol or ethanol (aliphatic alcohols with 1 to 4 carbon atoms) may be further included.

[0168] In step B2), the obtained resin is discharged from, for example, a casting die and cast onto a support. Next, the solvent is evaporated from the resin cast on the support, and the film is peeled off to obtain a cast film.

[0169] In step B3), the resulting cast film is stretched. The stretching ratio and stretching temperature can be the same as in step A3) above.

[0170] 1-4. Peel-off film 14

[0171] The peeling film 14 is a film that protects the first protective film 12 and is peeled off during use.

[0172] There are no particular limitations on the type of release film 14, as long as it can be peeled off during use. There are also no particular limitations on the light absorption coefficient of the release film 14 at a wavelength of 9.4 μm; it is generally higher than that of the second protective film 13 and to the same extent as, or higher than, that of the first protective film 12. The release film 14 is, for example, a release film that has undergone a demolding process; examples include plastic films such as acrylic films, polycarbonate films, polyester films, and fluoropolymer films.

[0173] (thickness)

[0174] The thickness of the release film 14 is only required to protect the first protective film 12 and is not particularly limited. For example, it is preferably 20 to 60 μm, and more preferably 30 to 50 μm.

[0175] 1-5. Adhesive layer

[0176] An adhesive layer (not shown) is disposed between the polarizer 11 and the first protective film 12, or between the polarizer 11 and the second protective film 13, to bond them together.

[0177] There are no particular limitations on the adhesive constituting the adhesive layer; it can be a product of drying a fully saponified aqueous solution of polyvinyl alcohol (water paste), or a cured product of an active energy radiation-cured adhesive. The active energy radiation-cured adhesive can be any one of a photoradical polymer composition utilizing photoradical polymerization, a photocationic polymer composition utilizing photocationic polymerization, or a combination thereof.

[0178] The thickness of the adhesive layer can be, for example, 0.01 to 10 μm, preferably about 0.03 to 5 μm.

[0179] 1-6.Physical properties

[0180] (Tilting angle)

[0181] The polarizer 10 having the above-described configuration has a cut end face 10a cut by laser (see reference). Figure 4 B). Then, at the cross-section of the polarizer 11 along the aforementioned lamination direction L0 (thickness direction of the polarizer 11) (specifically, the cross-section along the lamination direction L0 and orthogonal to the cut end face 10a), the tilt angle φ of the straight line L1 connecting the endpoint P1 of the release film 14 of the cut end face 10a of the polarizer 11 opposite to the first protective film 12 and the endpoint P2 of the polarizer 11 on the side of the second protective film 15 is 0.5 to 10° relative to the lamination direction L0. If the tilt angle φ is 0.5° or more, when the polarizer 11 is attached to the display element with the second protective film 13 side becoming the display element side and pressed, it is easy to make the tilt of the cut end face 10a approximately zero. As a result, when manufacturing the display device, even with changes in ambient humidity and temperature, light leakage caused by the shape of the cut end face 10a of the polarizer 10 can be suppressed. From the same viewpoint, the aforementioned tilt angle φ is more preferably 1 to 10°, and more preferably 6 to 8°.

[0182] The cut end face 10a of the polarizer 10 can be observed using an optical microscope. Specifically, the tilt angle is determined by observing the image obtained by using an optical microscope of the cut surface of a sample cut orthogonally to the cut end face 10a of the polarizer 10.

[0183] 2. Manufacturing method of polarizer

[0184] Figure 5 A to C are cross-sectional views showing the manufacturing method of the polarizer 10 according to this embodiment.

[0185] like Figure 5 As shown in A to C, the manufacturing method of the polarizer 10 according to this embodiment includes: 1) a step of preparing a laminate 20 comprising a polarizer 11, a first protective film 12, a second protective film 13, and a release film 14 (see reference). Figure 5 A) and 2) the process of irradiating the laminate 20 with a laser from the side of the release film 14 to cut the laminate 20 along the lamination direction (thickness direction) (refer to) Figure 5 (B and C).

[0186] Regarding the process in 1),

[0187] First, prepare a laminate 20 comprising a polarizer 11, a first protective film 12, a second protective film 13, and a release film 14 (see reference). Figure 5 A).

[0188] Regarding the bonding of the polarizer 11 to the first protective film 12 or the second protective film 13, the aforementioned adhesive can be used for roll-to-roll bonding.

[0189] Regarding process 2):

[0190] Next, a laser is irradiated onto the surface of the resulting laminate 20 (specifically, the surface of the release film 14) to cut the laminate 20 along the lamination direction (see reference). Figure 5 (B and C).

[0191] Regarding laser cutting, it is performed by irradiating the laminate 20 with laser L from the side of the release film 14. In this embodiment, the ratio A1 / A2 of the light absorption coefficients of the first protective film 12 and the second protective film 13 is appropriately adjusted (the light absorption coefficient A2 of the second protective film 13 is moderately increased compared to the conventional method). As a result, no excess energy is required during cutting, thus reducing the shrinkage of the film (especially the first protective film 12) on the irradiated side of laser L. Therefore, the tilt angle φ of the cut end face 10a of the polarizer 10 after cutting can be smaller than that of the conventional method (see reference). Figure 5 C).

[0192] 3. Display device and its manufacturing method

[0193] The display device according to this embodiment has a display element and a polarizer disposed on at least one of its surfaces.

[0194] There is no particular limitation on the type of display element; it can be an organic EL display element or a liquid crystal display element. In this embodiment, the display element is preferably a liquid crystal display element.

[0195] Figure 6 This is a cross-sectional view showing the configuration of the display device according to this embodiment.

[0196] like Figure 6 As shown, the display device 100 according to this embodiment includes a liquid crystal display element 30 (display element), a first polarizer 40 disposed on one side (e.g., the viewable side) of the liquid crystal display element 30, and a second polarizer 50 disposed on the other side (e.g., the backlight side) of the liquid crystal display element 30.

[0197] The liquid crystal display element 30 may have two transparent substrates 31 and 31, and a liquid crystal layer 32 disposed between them. There are no particular limitations on the display mode of the liquid crystal display element 30; for example, it may be STN (Super-Twisted Nematic), TN (Twisted Nematic), OCB (Optically Compensated Bend), HAN (Hybridaligned Nematic), VA (Vertical Alignment, MVA (Multi-domain Vertical Alignment), PVA (Patterned Vertical Alignment)), IPS (In-Plane-Switching), etc. Among these, the VA mode is preferred.

[0198] One or both of the first polarizer 40 and the second polarizer 50 are the polarizer 10 according to this embodiment. In this embodiment, both the first polarizer 40 and the second polarizer 50 are the polarizer 10 according to this embodiment. Preferably, the polarizer 10 according to this embodiment is arranged such that the second protective film 13 is on the side of the liquid crystal display element 30.

[0199] The display device thus configured is manufactured by a process of attaching the polarizer 10 according to this embodiment to at least one side of the display element. The attachment can be performed by pressing with the second protective film 13 of the polarizer 10 facing the display element side.

[0200] In the display device 100 of this embodiment, the cut end face 10a of the polarizer 10 adhered to the liquid crystal display element 30 is approximately parallel to the aforementioned lamination direction (approximately perpendicular to the surface of the liquid crystal display element 30) and is almost not tilted. Therefore, it is possible to suppress uneven display at the end caused by the tilt angle of the cut end face 10a of the polarizer 10. Furthermore, this polarizer 10 differs from existing polarizers where the tilt angle φ≒0° of the cut end face of the polarizer before adhesion is... Figure 2 A) Polarizing film with excessively large φ ( Figure 1Compared to A), the change in tilt angle φ caused by variations in the humid and hot conditions of the usage environment is also smaller. Therefore, it is possible to further suppress uneven display at the end after humid and hot storage.

[0201] Example

[0202] The present invention will be specifically described below through embodiments, but the present invention is not limited to these embodiments.

[0203] 1. Materials of the first protective film and the second protective film

[0204] (1) Resin

[0205] Cycloolefin resin A (COP-A, Tg: 162℃, Mw: 100000, Ethylene: Unit 1: Unit 2 = 50:28:22 molar ratio)

[0206] [Chemistry 6]

[0207]

[0208] Cycloolefin resin B (COP-B, Tg: 170℃, Mw: 100000)

[0209] [Chemistry 7]

[0210]

[0211] (Meth)acrylic resin (Acr): Polymethyl methacrylate (PMMA, Tg: 110℃, Mw: 300000)

[0212] The Tg and Mw of the resin were determined using the following method.

[0213] [Glass transition temperature (Tg)]

[0214] The glass transition temperature of the resin was determined using DSC (Differential Scanning Colorimetry) according to JIS K7121-2012.

[0215] [Weight-average molecular weight (Mw)]

[0216] The weight-average molecular weight (Mw) of the resin was determined using gel permeation chromatography (HLC8220GPC, Tosoo Corporation) and a column (TSK-GELG6000HXL-G5000HXL-G5000HXL-G4000HXL-G3000HXL, Tosoo Corporation). 20 ± 0.5 mg of the sample was dissolved in 10 mL of tetrahydrofuran and filtered through a 0.45 mm filter. 100 mL of this solution was injected into the column (40 °C), and the mass was measured using a RI detector at 40 °C. The mass was then converted to styrene to determine the weight-average molecular weight.

[0217] (2) Light-absorbing materials

[0218] Light-absorbing material A:

[0219] [Chemistry 8]

[0220]

[0221] Light-absorbing material B: Methyl methacrylate (MMA) / styrene (St) / ethylene glycol dimethacrylate (EGDMA) (70 / 10 / 20 molar ratio) copolymer particles (refractive index 1.51, average particle size 0.14 μm)

[0222] 2. Preparation or fabrication of the first protective film

[0223] <The Making of Membrane 101>

[0224] (Preparation of light-absorbing material additive solution)

[0225] 95 parts by mass of dichloromethane were added to a sealed container, and 4.5 parts by mass of light-absorbing material A were added while stirring. The mixture was then stirred in a dissolver for 50 minutes. 2000 g of the resulting mixture was passed through a high-pressure dispersion apparatus (trade name: M110-E / H ultra-high pressure homogenizer, manufactured by Microfluidics Corporation) and treated once at 175 MPa to prepare a light-absorbing material dispersion. This dispersion was then filtered using a Finemet NF filter manufactured by Nippon Seisen Corporation to prepare a light-absorbing material additive solution.

[0226] (Preparation of adhesive paste)

[0227] Prepare a paste with the following composition. First, add dichloromethane and ethanol to a pressurized dissolving vessel. While stirring, add dry acrylic resin and the above-mentioned light-absorbing material additive solution (light-absorbing material), heat, and stir until completely dissolved. Filter the mixture using Anji Filter Paper Co., Ltd. (Anji Filter Paper Co., Ltd.) to prepare the paste.

[0228] Dichloromethane: 300 parts by weight

[0229] Ethanol: 43 parts by weight

[0230] PMMA (polymethyl methacrylate): 60 parts by weight

[0231] Light-absorbing material additive solution (light-absorbing material A): 60 parts by weight

[0232] (Membrane fabrication)

[0233] Next, using a ring-belt casting apparatus, the adhesive paste is uniformly cast onto a stainless steel belt support at a temperature of 22°C and a width of 1500 mm. On the stainless steel belt support, the solvent is evaporated until the residual solvent content reaches 45%, and the film is peeled off from the stainless steel belt support while adjusting the peeling speed at a tension of 162 N / m. The resulting cast film is stretched using a longitudinal stretching device while the solvent is evaporated at 35°C. It is longitudinally cut to a width of 1.2 m, and then stretched 1.1 times its original width using a tenter frame while drying at 135°C. Finally, it is wound to obtain a film 101 with a thickness of 40 μm.

[0234] <Preparation of membranes 102-104>

[0235] Except for changing the type and content of the light-absorbing material as shown in Table 1, membranes 102 to 104 were obtained in the same manner as membrane 101.

[0236] <Membrane 105>

[0237] TOYOBO CO., LTD. (Registered Trademark)

[0238] <Membrane 106>

[0239] 100 parts by weight of cellulose triacetate (TAC) with a degree of acetyl substitution of 2.92 and a degree of uniform polymerization of 300, 2 parts by weight of ethyl phthaloyl ethyl glycolate, 10 parts by weight of triphenyl phosphate, 350 parts by weight of dichloromethane, and 50 parts by weight of ethanol were placed in a sealed container. The mixture was slowly stirred while the temperature was gradually increased to 45°C over 60 minutes to dissolve the slurry. The pressure inside the container was 1.2 atmospheres. The slurry was then filtered using Anji Filter Paper Co., Ltd. (Anji Filter Paper Co., Ltd.) No. 244 and allowed to stand for 24 hours to remove bubbles.

[0240] In addition, separately, 5 parts by weight of cellulose triacetate, 3 parts by weight of chinubin 326 (manufactured by BASF Japan Co., Ltd.), 7 parts by weight of chinubin 109 (manufactured by BASF Japan Co., Ltd.), 5 parts by weight of chinubin 171 (manufactured by BASF Japan Co., Ltd.), and 1 part by weight of AEROSIL 200V (manufactured by AEROSIL Japan Co., Ltd.) were mixed with 90 parts by weight of dichloromethane and 10 parts by weight of ethanol, and stirred to dissolve, to prepare a UV absorber solution. The UV absorber solution was added at a ratio of 2 parts by weight to 100 parts by weight of the above-mentioned adhesive paste, and after thorough mixing using a static mixer, it was cast from the die onto a stainless steel belt at an adhesive paste temperature of 35°C. After drying the stainless steel strip on the back side with warm water at 35°C for 1 minute under temperature control, the back side of the stainless steel strip is then exposed to cold water at 15°C for 15 seconds before being peeled off.

[0241] The residual solvent content in the mesh during peeling was 70% by mass. Next, while fixing both ends of the peeled mesh, it was dried at 120°C for 10 minutes to obtain a film 106 with a thickness of 80 μm.

[0242] The absorption coefficients A1 of the obtained films 101–106 were determined using the following method.

[0243] [Absorption coefficient]

[0244] The obtained film was analyzed using micro-FTIR (Agilent "UMA600" and "FTS3000") with the ATR method, at an incident light diameter of 100 μm, a Ge prism (incident angle 45°), an MCT-A detector, and a resolution of 4.0 cm⁻¹. -1 The infrared absorption spectrum was measured under cumulative conditions of 64 measurements. From the obtained infrared absorption spectrum, the portion corresponding to a wavelength of 9.4 μm (wavenumber 1041 cm⁻¹) was read. -1 The absorbance of the film is then calculated. The absorption coefficient of the film is then determined based on the following formula.

[0245] Absorption coefficient ( / μm) = Absorbance × log10 / Film thickness (μm)

[0246] The composition and physical properties of the obtained membranes 101 to 106 are shown in Table 1.

[0247]

[0248] 3. Fabrication of the second protective film

[0249] <The Making of Membrane 201>

[0250] (Preparation of granules)

[0251] COP-A and light-absorbing material A were mixed in a vacuum conical mixer (Nauta Mixer) with the content of light-absorbing material A being 2.8% by mass relative to COP-A. After drying, the mixture was melted using a twin-screw extruder to obtain granules of the resin mixture.

[0252] (cast)

[0253] The obtained granules were fed to an extruder under a nitrogen atmosphere and melt-cast. Then, the melt-extruded film was cooled with a cooling roller, stretched at 160°C and 140%, and peeled off with a peeling roller to obtain a film 201 with a thickness of 40 μm.

[0254] <The Making of Membrane 202>

[0255] Except for changing the content of the light-absorbing material as shown in Table 2, membrane 202 is obtained in the same way as membrane 201.

[0256] <Fabrication of Membranes 203 and 207>

[0257] Except for changing COP-A: 100 parts by mass to a mixture of COP-A: 50 parts by mass and COP-B: 50 parts by mass, and changing the content of light-absorbing material as shown in Table 2, membranes 203 and 207 are obtained in the same manner as membrane 201.

[0258] <The Making of Membrane 204>

[0259] Except for changing the stretching temperature to 180°C and the stretching ratio to 200%, membrane 204 is obtained in the same way as membrane 201.

[0260] <Membrane 205>

[0261] Except for changing the type and content of the light-absorbing material as shown in Table 2, membrane 205 was obtained in the same manner as membrane 201.

[0262] <Fabrication of Membranes 206 and 208>

[0263] Except for the absence of added light-absorbing material and the adjustment of stretching conditions to change the film thickness as shown in Table 2, films 206 and 208 were obtained in the same manner as film 201.

[0264] <The Making of Membrane 209>

[0265] (Preparation of light-absorbing material additive solution)

[0266] 95 parts by mass of dichloromethane were added to a sealed container, and 2.8 parts by mass of light-absorbing material A were added while stirring. The mixture was then stirred in a dissolver for 50 minutes. 2000 g of the resulting mixture was passed through a high-pressure dispersion apparatus (trade name: M110-E / H ultra-high pressure homogenizer, manufactured by Microfluidics Corporation) and treated once at 175 MPa to prepare a light-absorbing material dispersion. This dispersion was then filtered using a Finemet NF filter manufactured by Nippon Seisen Corporation to prepare a light-absorbing material additive solution.

[0267] (Preparation of adhesive paste)

[0268] The following paste was prepared. First, dichloromethane and ethanol were added to a pressurized dissolving vessel. While stirring, COP-A (cyclic olefin resin) and the aforementioned light-absorbing material additive solution (light-absorbing material) were added, and the mixture was heated while stirring until completely dissolved. The paste was then filtered using Anji Filter Paper No. 244 manufactured by Anji Filter Paper Co., Ltd.

[0269] Dichloromethane: 300 parts by weight

[0270] Ethanol: 19 parts by weight

[0271] COP-B (cycloolefin resin): 100 parts by weight

[0272] Light-absorbing material additive liquid (light-absorbing material A): 98 parts by weight

[0273] (Membrane fabrication)

[0274] Next, using a ring-shaped tape casting device, the adhesive is uniformly cast onto a stainless steel tape support at a temperature of 33°C and a width of 1500 mm. The temperature of the stainless steel tape is controlled at 30°C. After the solvent evaporates until the residual solvent content in the adhesive cast on the stainless steel tape support reaches 30% by mass, it is peeled off from the stainless steel tape support with a peel tension of 130 N / m.

[0275] The cast film obtained by peeling was stretched at a stretch rate of 50% in the width direction (TD direction) at 160°C (Tg of the resin -10°C). The residual solvent at the start of stretching was 10% by mass. Next, it was dried at 130°C while being transported by multiple rollers in a drying zone. Then, it was wound to obtain a film 209 with a thickness of 40 μm.

[0276] The absorbance coefficients A2 of the obtained films 201-209 were determined using the same method as described above. Furthermore, the average absorbance of the obtained films 201-209 was determined using the following method.

[0277] [Average Absorption Rate]

[0278] The absorbance of the membrane was measured using the above method.

[0279] Absorbance = Absorption coefficient (μm) × Film thickness (μm) / log10

[0280] The obtained values ​​were substituted into the following formula to determine the average absorption rate.

[0281] Average absorbance (%) = 100 - 10^(2 - absorbance)

[0282] The composition and physical properties of the obtained membranes 201-209 are shown in Table 2.

[0283]

[0284] 3. Fabrication of Polarizing Films

[0285] <Examples 1-9 and Comparative Examples 1-6>

[0286] (Making of a polarizing device)

[0287] A polyvinyl alcohol (PVA) resin film with a degree of polymerization of 2400 and a saponification degree of 99.7 mol% was prepared. While dyeing the film in an iodine aqueous solution at 30°C, it was stretched three times in the film transport direction. Next, it was stretched to six times its original length in a 4 wt% boric acid and 5 wt% potassium iodide aqueous solution at 60°C. Then, the stretched film was cleaned by immersing it in a 2 wt% potassium iodide aqueous solution at 30°C for several seconds. The resulting stretched film was dried at 90°C to obtain a polarizer with a thickness of 25 μm.

[0288] (Creating a layered body)

[0289] On one side of the first protective film in Table 3, a 40 μm thick polyethylene terephthalate (PET) film is adhered as a release liner using an adhesive. On the other side of the first protective film, the second protective film in Table 3 is laminated using an acrylic UV-curable adhesive laminator to create a laminate. The adhesive layer is 1 μm thick.

[0290] (Cut off a layered structure)

[0291] The surface of the release film of the obtained laminate was irradiated with a carbon dioxide laser with a wavelength of 9.4 μm to cut the laminate, thus obtaining a polarizer. The cutting conditions were: frequency 20 kHz, output power: 59 W, and speed: 60 m / min.

[0292] (evaluate)

[0293] The following methods were used to evaluate the cross-sectional shape, productivity, and display characteristics of the cut portion of the obtained polarizer.

[0294] 1) Shape of the cut end face of the polarizer

[0295] The polarizer is cut perpendicular to the cut end face and along the film's stacking direction (the thickness direction of the polarizer) using a cutting machine. The tilt angle φ of the laser-cut end face of the polarizer on the cut surface is observed using an optical microscope (refer to...). Figure 4 B). Then, in the above cross section, the angle φ formed by the straight line L1 of the laser cutting section, the end point P1 of the peeling film opposite to the first protective film, and the end point P2 of the polarizer on the second protective film side, relative to the lamination direction L0, is measured.

[0296] 2) Productivity

[0297] The resulting laminate was laser-cut to prepare 100 polarizing films of 300×210×0.1mm each. For each polarizing film, the peelability of the PET film was determined by a 90° peel test using adhesive tape, and evaluated according to the following standards.

[0298] ◎: No peeling defects

[0299] ○: It can be peeled off, but there is very little peeling residue, which is not a problem level.

[0300] △: It can peel off, but sometimes peeling residue occurs, which is a slightly problematic level.

[0301] ×: It can be peeled off, but the peeling residue leaves a large amount of residue in the polarizer, which is a problematic level.

[0302] If the value is ○ or above, it is judged as good.

[0303] 3) Display characteristics

[0304] The polarizer pre-attached to a SONY KLV-40J3000 40-inch LCD display, designed as a VA-type liquid crystal display device, was carefully peeled off. Then, a laser-cut polarizer was attached in a manner consistent with the transmission axis of the pre-attached polarizer to fabricate the liquid crystal display device. Specifically, the laser-cut polarizer was placed on the glass substrate of the liquid crystal cell (liquid crystal display element) using pressure-sensitive adhesive, with its second protective film facing the glass substrate side, and then pressed and attached. This yielded the liquid crystal display device.

[0305] The resulting liquid crystal display devices were then stored at 60°C and 90% RH for 500 hours. Then, for each liquid crystal display device before (initial) storage and after (after damp heat durability) storage, the display unevenness (light leakage) at the edges of the screen was evaluated by visual observation in a dark room with the entire screen displayed in black. The following criteria were used to evaluate the unevenness at the edges before (initial) storage and after (after damp heat durability) storage.

[0306] (Initial)

[0307] ◎: No light leakage was observed during a visual evaluation from a 45° angle from the front.

[0308] ○: During a visual evaluation from the front at a 45° angle, very little light leakage was observed, indicating a non-problematic level.

[0309] △: Light leakage observed during visual evaluation from a 45° angle from the front indicates a problematic level.

[0310] ×: Significant light leakage was observed during a visual evaluation from a 45° angle from the front, indicating a problematic level.

[0311] If the value is ○ or above, it is judged as good.

[0312] (After saving)

[0313] ◎: As before preservation, no light leakage was observed during visual evaluation from a 45° angle from the front.

[0314] ○: Compared to before preservation, very little light leakage was observed in a visual evaluation from a 45° angle from the front, indicating a problem-free level.

[0315] △: Light leakage was observed during visual evaluation from a 45° angle, compared to before preservation, indicating a problematic level.

[0316] ×: Significant light leakage was observed in a visual evaluation from a 45° angle, compared to before preservation, indicating a problematic level.

[0317] If the value is ○ or above, it is judged as good.

[0318] The evaluation results of Examples 1-9 and Comparative Examples 1-6 are shown in Table 3.

[0319]

[0320] As shown in Table 3, it can be seen that in Examples 1 to 9, where the light absorption coefficient A2 of the second protective film is a certain value or less, and the ratio of the light absorption coefficients of the first protective film to the second protective film, A1 / A2, is a certain value or less, the polarizers all have a small tilt angle φ of 0.5 to 10° at the cutting end face of the laser cutting section. Furthermore, it can be seen that liquid crystal display devices using these polarizers suppress uneven display at the edges of the image, and the PET film of the polarizer also exhibits good peelability.

[0321] It can be seen that the polarizers in Comparative Examples 1 and 3, where the ratio of the light absorption coefficients of the first protective film to the second protective film (A1 / A2) is large, all have a tilt angle φ of 12° or more on the cut end face of the laser-cut portion. Furthermore, it can be seen that liquid crystal display devices using these polarizers exhibit initial display unevenness at the ends. Additionally, it can be seen that the light absorption coefficient A2 of the second protective film exceeds 1.0 × 10⁻⁶. 2 ~4.5×10 2 In the comparison example 2 of the polarizer in the range of / μm, the tilt angle φ of the cut end face of the laser cutting part is less than 0.5°. Therefore, when it is bonded to the liquid crystal display device, due to the effect of compression, the tilt angle of the cut end face after bonding is no longer a right angle relative to the bonding surface. As a result, the liquid crystal display device using this polarizer produces initial uneven display at the end.

[0322] Furthermore, it is known that in the liquid crystal display device of Comparative Example 2, where the initial tilt angle φ of the polarizer's cut end face is close to 0°, uneven display at the end after humid heat storage is the main issue (see [reference]). Figure 2 A); In the liquid crystal display device of Comparative Example 1, where the tilt angle φ of the initial cut end face of the polarizer exceeds 10°, uneven display at the initial end mainly occurs (refer to...). Figure 1 A).

[0323] Furthermore, it was found that in the liquid crystal display devices of Comparative Examples 3 and 4, where the initial tilt angle φ of the polarizer's cut end face was extremely large, display unevenness was not completely suppressed during the initial stage and after humid heat storage. This is believed to be because the initial tilt angle φ of the cut end face exceeded 10°, which is very large, thus resulting in a state of display unevenness, and the force of contraction of the protective film became excessively large relative to the force of expansion of the polarizer during moisture absorption.

[0324] This application claims priority based on Japanese Patent Application No. 2020-178173, filed on October 23, 2020. All contents described in that application are incorporated herein by reference.

[0325] Industrial availability

[0326] According to the present invention, a polarizer capable of laser-based cutting without reducing productivity and capable of suppressing display unevenness at the end of a display device, as well as a method for manufacturing the polarizer and a method for manufacturing a display device, are provided.

[0327] Explanation of reference numerals in the attached figures

[0328] 10 Polarizing filters

[0329] 10a Cut end face

[0330] 11. Polarizer

[0331] 12 First protective film

[0332] 13 Second protective film

[0333] 14. Peel-off film

[0334] 20-layer stack

[0335] 30 Liquid Crystal Display Components

[0336] 40 First polarizer

[0337] 50 First polarizer

[0338] 100 display devices

[0339] L laser

[0340] φ Inclination angle

Claims

1. A polarizer comprising laminating a polarizer, a first protective film disposed on one side of the polarizer, a second protective film disposed on the other side of the polarizer, and a release film holding the first protective film disposed on a side opposite to the polarizer, wherein, The absorption coefficient A2 of the second protective film, measured by the ATR method for light at a wavelength of 9.4 μm, is 1.0 × 10⁻⁶. 2 ~4.5×10 2 / μm, The ratio A1 / A2 of the light absorption coefficient A1 of the first protective film at a wavelength of 9.4 μm, measured by the ATR method, to the light absorption coefficient A2 of the second protective film at a wavelength of 9.4 μm, measured by the ATR method, is 1 to 5. The polarizer has a cut-off end face. In the cross-section of the polarizer along the stacking direction, The angle of inclination of the straight line connecting the endpoint P1 of the peeling film opposite to the first protective film and the endpoint P2 of the polarizer on the second protective film side of the cutting end face with respect to the stacking direction is 0.5 to 10°.

2. The polarizer according to claim 1, wherein, The first protective film comprises (meth)acrylic resin or cycloolefin resin.

3. The polarizer according to claim 1 or 2, wherein, The second protective film comprises a cyclic olefin resin.

4. The polarizer according to claim 3, wherein, The second protective film also contains light-absorbing materials selected from one or more of ester compounds and (meth)acrylic polymer particles.

5. The polarizer according to claim 4, wherein, The content of the light-absorbing material in the second protective film is greater than the content of the light-absorbing material in the first protective film.

6. A method for manufacturing a polarizer according to any one of claims 1 to 5, comprising: A process for preparing a laminate, the laminate comprising a polarizer, a first protective film disposed on one side of the polarizer, a second protective film disposed on the other side of the polarizer, and a release film disposed on the side of the first protective film opposite to the polarizer; and The process of irradiating the laminate with a laser from the side of the release film to cut the laminate along the lamination direction of the laminate.

7. The method for manufacturing a polarizer according to claim 6, wherein, The first protective film comprises (meth)acrylic resin or cycloolefin resin.

8. The method for manufacturing a polarizer according to claim 6 or 7, wherein, The second protective film comprises a cyclic olefin resin.

9. The method for manufacturing a polarizer according to claim 8, wherein, The second protective film also contains light-absorbing materials selected from one or more of ester compounds and (meth)acrylic polymer particles.

10. The method for manufacturing a polarizer according to claim 9, wherein, The content of the light-absorbing material in the second protective film is greater than the content of the light-absorbing material in the first protective film.

11. A method for manufacturing a display device, comprising: The process of attaching a polarizer according to any one of claims 1 to 5 to at least one side of a display element so that the second protective film is on the side of the display element.

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