Multilayer film and method of manufacturing polarizing plate using multilayer film

Abstract

To provide a multilayer film capable of carrying a very thin type of a polarizer protective film without difficulty and sticking to a polarizer without trouble.SOLUTION: A multilayer film is a coextruded film having a first layer containing a first thermoplastic resin and a second layer containing a second thermoplastic resin. A distance DHSP of a Hansen solubility parameter with the first thermoplastic resin and the second thermoplastic resin, and a radius R of the Hansen sphere of the first thermoplastic resin satisfy the relationship of DHSP / R≥1.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a multilayer film and a method for manufacturing a polarizing plate using the multilayer film.

Background Art

[0002] In an image display device (for example, a liquid crystal display device, an organic EL display device), in many cases, a polarizing plate is disposed on at least one side of an image display panel due to its image forming method. In recent years, the image display device has been becoming thinner and more flexible, and accordingly, thinning of the polarizing plate has been strongly demanded. Considering the current situation where the polarizer is being thinned, thinning of the polarizer protection film is demanded. However, when attempting to thin the polarizer protection film, there are problems such as difficulty in transporting the polarizer protection film in the polarizing plate manufacturing process, and breakage, wrinkles, etc. occurring during bonding to the polarizer, making it difficult to bond to the polarizer.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The present invention has been made to solve the above-described conventional problems, and its main object is to provide a multilayer film capable of transporting an extremely thin polarizer protection film without problems and bonding it to the polarizer without problems.

Means for Solving the Problems

[0005] The multilayer film according to an embodiment of the present invention is a coextruded film having a first layer containing a first thermoplastic resin and a second layer containing a second thermoplastic resin, and the distance D between the Hansen solubility parameters of the first thermoplastic resin and the second thermoplastic resin HSP and the radius R of the Hansen sphere of the first thermoplastic resin satisfy the relationship D HSP / R ≥ 1. In one embodiment, the difference in glass transition temperature between the first thermoplastic resin and the second thermoplastic resin is 50°C or less. In one embodiment, the thickness of the first layer is 7 μm or less, and the thickness of the second layer is 25 μm or more. In one embodiment, the first thermoplastic resin is a cyclic olefin resin, and the second thermoplastic resin is an acrylic resin. In one embodiment, the multilayer film has a light transmittance of 90% or more and a haze of 1.0% or less. In one embodiment, the first layer functions as a polarizer protection film, and the second layer functions as a support substrate. In one embodiment, the multilayer film further includes a third layer containing the first thermoplastic resin on the side opposite to the first layer of the second layer. In one embodiment, the third layer functions as a polarizer protection film. According to another aspect of the present invention, a method for manufacturing a polarizing plate is provided. This manufacturing method includes bonding the first layer of a multilayer film having the first layer and the second layer to a polarizer to obtain an intermediate laminate, and peeling the second layer from the intermediate laminate. Another manufacturing method of the present invention includes bonding the first layer of a multilayer film further including the third layer to a first polarizer to obtain a first intermediate laminate, peeling the laminate of the second layer and the third layer from the first intermediate laminate to obtain a first polarizing plate, bonding the third layer of the peeled laminate to a second polarizer to obtain a second intermediate laminate, and peeling the second layer from the second intermediate laminate to obtain a second polarizing plate. In one embodiment, the thickness of the polarizer is 20 μm or less.

Advantages of the Invention

[0006] According to the embodiments of the present invention, it is possible to realize a multilayer film that can convey an extremely thin polarizer protection film without defects and can be bonded to a polarizer without defects.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0008] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to these embodiments.

[0009] A. Multilayer Film A-1. Overall Configuration of the Multilayer Film FIG. 1(a) is a schematic cross-sectional view for explaining a multilayer film according to one embodiment of the present invention. The multilayer film 100 in the illustrated example is a coextruded film having a first layer 10 and a second layer 20. By forming the multilayer film by coextrusion molding, the peeling force between the first layer and the second layer can be made appropriate. The first layer 10 contains a first thermoplastic resin, and the second layer 20 contains a second thermoplastic resin. In the embodiments of the present invention, the distance D between the Hansen solubility parameters (hereinafter also referred to as HSP values) of the first thermoplastic resin and the second thermoplastic resin HSP and the radius R of the Hansen sphere of the first thermoplastic resin are D HSPSatisfies the relationship of / R ≧ 1. D HSP / R is preferably 1.1 or more, more preferably 1.3 or more, still more preferably 1.4 or more, and particularly preferably 1.5 or more. D HSP / R can be, for example, 3.0 or less, and can also be, for example, 2.7 or less. D HSP When / R is within such a range, due to the synergistic effect with the effect of forming the multilayer film by coextrusion molding, the first layer and the second layer do not peel off before the multilayer film is actually used, and when the first layer is peeled off from the multilayer film and used as various functional films, excellent peeling characteristics can be realized in that the first layer and the second layer peel off well.

[0010] The above Hansen solubility parameter divides the Hildebrand solubility parameter into three components: dispersion force (δD), permanent dipole intermolecular force (δP), and hydrogen bonding force (δH), and is represented by a vector plotted in three-dimensional space. It can be judged that those with similar vectors have high solubility. That is, the similarity of solubility can be judged from the distance between the HSP values of each other (HSP distance). The definition and calculation of the Hansen solubility parameter are described in Hansen Solubility Parameters: A Users Handbook (CRC Press, 2007) by Charles M. Hansen.

[0011] HSP values are known for various resins and solvents, and these can be used as they are, or values calculated using the computer software HSPiP (Hansen Solubility Parameters in Practice) can be used. Note that this HSPiP also has a database of resins and solvents. In this specification, the HSP value of the first thermoplastic resin is calculated using HSPiP by the following procedure using the Hansen sphere method. First, the solubility of the first thermoplastic resin to be evaluated is evaluated using a solvent with a known solubility parameter. Here, methyl ethyl ketone (MEK) is used as a good solvent, and n-hexane, methanol, trichlorobenzene, and γ-butyrolactone are used as poor solvents, and the solubility in a mixed solvent of these good and poor solvents is evaluated. Details of the evaluation method are as described in the examples below. Next, δD, δP, and δH are calculated using HSPiP from the obtained solubility evaluation results and plotted in three dimensions, and a Hansen sphere is obtained from these coordinates. The center coordinates of this Hansen sphere are the HSP value of the first thermoplastic resin, and the radius of the Hansen sphere is the interaction radius R of the first thermoplastic resin. Furthermore, in the same manner as for the first thermoplastic resin, the HSP value of the second thermoplastic resin can be obtained. The distance on the coordinates between the HSP value of the first thermoplastic resin and the HSP value of the second thermoplastic resin is D HSP becomes. D HSP is represented by the following formula. The subscript "1" in the formula means the first thermoplastic resin, and "2" means the second thermoplastic resin. D HSP = √{4 × (δD1 - δD2) 2 + 2 × (δP1 - δP2) 2 + 2 × (δH1 - δH2) 2}

[0012] The difference in glass transition temperature (Tg) between the first thermoplastic resin and the second thermoplastic resin is preferably 50°C or less, more preferably 40°C or less, still more preferably 30°C or less, and particularly preferably 20°C or less. The difference in Tg can be, for example, 3°C or more. If the difference in Tg is within such a range, excellent stretchability can be achieved while ensuring the excellent peel characteristics as described above. Specifically, stretching unevenness and breakage can be favorably suppressed. When forming a multilayer film by coextrusion, stretching for the purpose of thinning is included, and if the difference in Tg is too large, thickness unevenness may occur. Such thickness unevenness may cause wrinkles, breaks, and / or meandering, or breakage during conveyance. As a result, the bonding between the polarizer and the first layer may not be performed well. If the difference in Tg is within the above range, such problems can be suppressed.

[0013] The multilayer film preferably has a light transmittance of 90% or more, more preferably 92% or more, and still more preferably 95% or more. The higher the light transmittance, the more preferable it is, and it may be, for example, 100% or less, or may be, for example, 99% or less. Further, the multilayer film preferably has a haze of 1.0% or less, more preferably 0.8% or less, and still more preferably 0.5% or less. The lower the haze, the more preferable it is, and it may be, for example, 0.1% or more. If the light transmittance and / or haze is within such a range, when the first layer functions as a polarizer protection film as described later, very good characteristics can be exhibited. The light transmittance can be measured, for example, by a method according to ASTM-D-1003. The haze can be measured, for example, by a method according to JIS K 7136.

[0014] In one embodiment, the first layer functions as a polarizer protection film, and the second layer can function as a support substrate for the first layer. By configuring the multilayer film as described above, even if the first layer is made very thin (for example, the thickness is 7 μm or less, or for example, 1 μm), the first layer can function as a polarizer protection film. That is, even if the first layer is made very thin, it can be transported well as a multilayer film in the polarizer manufacturing process, and as described above, the first layer can be peeled well from the second layer. Therefore, when bonding the polarizer and the first layer (when transferring the first layer to the polarizer), breakage, wrinkles, etc. can be suppressed, and good bonding (transfer) can be achieved. As a result, a very thin polarizer protection film in the polarizer can function well. That is, the multilayer film can be suitably used for the manufacture of polarizers.

[0015] In another embodiment of the present invention, as shown in FIG. 1(b), the multilayer film 101 may further include a third layer 30 on the side opposite to the first layer 10 of the second layer 20. The third layer 30 typically includes a first thermoplastic resin. Therefore, the third layer can preferably function as a polarizer protection film.

[0016] Hereinafter, the first layer to the third layer will be specifically described in Items A-2 to A-4, respectively. Further, the method of using the multilayer film in which the first layer (and the third layer if present) can function as a polarizer protection film will be described in Item B as a method for manufacturing a polarizer.

[0017] A-2. The first layer The first layer contains the first thermoplastic resin as described above. As the first thermoplastic resin, any suitable thermoplastic resin can be used as long as the multilayer film satisfies the above characteristics. Examples of the first thermoplastic resin include cyclic olefin resins, polyester resins, and (meth)acrylic resins. These resins may be used alone or in combination. Preferably, they are cyclic olefin resins or polyester resins, and more preferably cyclic olefin resins. This is because it is easy to adjust D HSP / R to an appropriate range with the second thermoplastic resin. Representative examples of cyclic olefin resins include norbornene resins. Representative examples of polyester resins include polyethylene terephthalate (PET); polyesters containing terephthalic acid, isophthalic acid, ethylene glycol, and neopentyl glycol as monomer units; The (meth)acrylic resin will be described later with respect to the second thermoplastic resin in item A-3.

[0018] The above norbornene-based resin is a resin polymerized with norbornene-based monomers as polymerization units. Examples of the norbornene-based monomers include norbornene, and its alkyl and / or alkylidene substitution products, such as 5-methyl-2-norbornene, 5-dimethyl-2-norbornene, 5-ethyl-2-norbornene, 5-butyl-2-norbornene, 5-ethylidene-2-norbornene, etc., and their polar group substitution products such as halogen, ester, etc.; dicyclopentadiene, 2,3-dihydrodicyclopentadiene, etc.; dimethanooctahydronaphthalene, its alkyl and / or alkylidene substitution products, and polar group substitution products such as halogen, ester, etc., such as 6-methyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, 6-ethyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, 6-ethylidene-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, 6-chloro-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, 6-cyano-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, 6-pyridyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, 5-methyl-5-methoxycarbonylbicyclo[2.2.1]hept-2-ene, 6-methoxycarbonyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, etc.; trimers to tetramers of cyclopentadiene, such as 4,9:5,8-dimethano-3a,4,4a,5,8,8a,9,9a-octahydro-1H-benzindene, 4,11:5,10:6,9-trimethano-3a,4,4a,5,5a,6,9,9a,10,10a,11,11a-dodecahydro-1H-cyclopentaanthracene, tetracyclo[4.4.0.1 2,5 .1 7,10 dodeca-3-ene, tetracyclo[9.2.1.0 2,10 .0 3,8Examples include tetradeca-3,5,7,12-tetraene. The norbornene resin may be a copolymer of a norbornene monomer and another monomer.

[0019] In one embodiment, the norbornene resin can be a copolymer containing a polar norbornene monomer (polar skeleton) and a non-polar norbornene monomer (non-polar skeleton). Specific examples of the polar norbornene monomer include 5-methyl-5-methoxycarbonylbicyclo[2.2.1]hept-2-ene and 6-methoxycarbonyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene. Specific examples of the non-polar norbornene monomer include norbornene, 2,3-dihydrodicyclopentadiene, tetracyclo[4.4.0.1 2,5 .1 7,10 dodeca-3-ene, tetracyclo[9.2.1.0 2,10 .0 3,8 tetradeca-3,5,7,`12-tetraene. In this case, the content ratio of the polar skeleton in the norbornene resin is preferably 35 mol% to 95 mol%, more preferably 40 mol% to 90 mol%, and even more preferably 42 mol% to 88 mol%. Also, the content ratio of the non-polar skeleton in the norbornene resin is preferably 5 mol% to 65 mol%, more preferably 10 mol% to 60 mol%, and even more preferably 12 mol% to 58 mol%. If the content ratios of the polar skeleton and the non-polar skeleton in the norbornene resin are within such ranges, excellent peelability can be achieved. Note that if the content ratios of the polar skeleton and the non-polar skeleton in the norbornene resin are within the above ranges, the norbornene resin may contain other monomer units (skeletons).

[0020] The Tg of the first thermoplastic resin can be, for example, 100°C to 130°C, or can be, for example, 140°C to 160°C. If the Tg of the first thermoplastic resin is within such a range, the difference from the Tg of the second thermoplastic resin can be made within the above desired range.

[0021] The thickness of the first layer is preferably 10 μm or less, more preferably 7 μm or less, still more preferably 5 μm or less, and particularly preferably 3 μm or less. The thickness of the first layer can be, for example, 0.7 μm or more. According to an embodiment of the present invention, even if the thickness of the first layer is made extremely thin in this way, the first layer can be conveyed without problems and bonded to the object without problems. Therefore, when the object to be bonded is, for example, a polarizer, an extremely thin polarizing plate can be produced favorably.

[0022] The light transmittance of the first layer is preferably 88% or more, more preferably 92% or more, and still more preferably 95% or more. If the light transmittance is in such a range, the desired transparency can be ensured. The higher the light transmittance of the first layer, the more preferable it is, and it may be, for example, 100% or less, or may be, for example, 99% or less. The haze of the first layer is preferably 1.0% or less, more preferably 0.8% or less, and still more preferably 0.5% or less. If the haze is in such a range, when the first layer is used as, for example, a polarizer protection film, a good clear feeling can be given to the polarizing plate. Further, even when it is used for the viewing-side polarizing plate of the image display device, the display content can be viewed favorably. The lower the haze, the more preferable it is, and it may be, for example, 0.1% or more.

[0023] In one embodiment, the first layer may be substantially optically isotropic. Such properties can be imparted to the first layer by co-extruding a multilayer film using a predetermined material. As used herein, "substantially optically isotropic" means that the in-plane retardation Re(550) is from 0 nm to 10 nm and the retardation in the thickness direction Rth(550) is from -20 nm to +10 nm. The in-plane retardation Re(550) is more preferably from 0 nm to 5 nm, still more preferably from 0 nm to 3 nm, and particularly preferably from 0 nm to 2 nm. The retardation in the thickness direction Rth(550) is more preferably from -5 nm to +5 nm, still more preferably from -3 nm to +3 nm, and particularly preferably from -2 nm to +2 nm. If the Re(550) and Rth(550) of the first layer are within such ranges, when the first layer is used as a polarizer protection film, applying a polarizing plate including the polarizer protection film to an image display device can suppress an adverse effect on display characteristics. Here, Re(550) is the in-plane retardation of the film measured with light having a wavelength of 550 nm at 23°C. Re(550) is obtained by the formula: Re(550) = (nx - ny) × d. Rth(550) is the retardation in the thickness direction of the film measured with light having a wavelength of 550 nm at 23°C. Rth(550) is obtained by the formula: Rth(550) = (nx - nz) × d. Here, nx is the refractive index in the direction in which the in-plane refractive index is maximum (i.e., the slow axis direction), ny is the refractive index in the direction orthogonal to the slow axis in the plane (i.e., the fast axis direction), nz is the refractive index in the thickness direction, and d is the thickness (nm) of the film.

[0024] A-3. The second layer As described above, the second layer contains a second thermoplastic resin. As the second thermoplastic resin, any suitable thermoplastic resin can be used as long as the multilayer film satisfies the above properties. Preferred examples of the second thermoplastic resin include (meth)acrylic resins. D with the first thermoplastic resin HSPThis is because it is easy to adjust / R within an appropriate range. The (meth)acrylic resin may be used alone or in combination with different (meth)acrylic resins. In this specification, “(meth)acrylic” means acrylic and / or methacrylic. Hereinafter, (meth)acrylic may sometimes be simply referred to as acrylic.

[0025] As the (meth)acrylic resin, any appropriate (meth)acrylic resin can be adopted. Typically, the (meth)acrylic resin contains an alkyl (meth)acrylate as a main component as a monomer unit. Examples of the alkyl (meth)acrylate constituting the main skeleton of the (meth)acrylic resin include those having 1 to 18 carbon atoms in a linear or branched alkyl group. These can be used alone or in combination. Further, any appropriate copolymerization monomer may be introduced into the (meth)acrylic resin by copolymerization. The type, number, copolymerization ratio, etc. of such a copolymerization monomer can be appropriately set according to the purpose.

[0026] The above alkyl (meth)acrylate is typically represented by the following general formula (1):

[0027]

Chemical formula

[0028] In general formula (1), R 4 represents a hydrogen atom or a methyl group, and R 5represents a hydrogen atom, or an optionally substituted aliphatic or alicyclic hydrocarbon group having 1 to 6 carbon atoms. Examples of the substituent include halogen and hydroxyl group. Specific examples of the alkyl (meth)acrylate include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate, n-hexyl (meth)acrylate, cyclohexyl (meth)acrylate, chloromethyl (meth)acrylate, 2-chloroethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2,3,4,5,6-pentahydroxyhexyl (meth)acrylate and 2,3,4,5-tetrahydroxypentyl (meth)acrylate. In General Formula (1), R 5 is preferably a hydrogen atom or a methyl group. Therefore, particularly preferred alkyl (meth)acrylates are methyl acrylate or methyl methacrylate.

[0029] The above (meth)acrylic resin may contain only a single alkyl (meth)acrylate unit, or may contain a plurality of alkyl (meth)acrylate units in which R 4 and R 5 are different.

[0030] The content ratio of the alkyl (meth)acrylate unit in the above (meth)acrylic resin is preferably 50 mol% to 98 mol%, more preferably 55 mol% to 98 mol%, still more preferably 60 mol% to 98 mol%, particularly preferably 65 mol% to 98 mol%, and most preferably 70 mol% to 97 mol%. If the content ratio is less than 50 mol%, the effects exhibited from the alkyl (meth)acrylate unit (for example, high heat resistance and high transparency) may not be fully exerted. If the above content ratio is more than 98 mol%, the resin becomes brittle and prone to cracking, and high mechanical strength cannot be fully exerted, and there is a risk of inferior productivity.

[0031] In one embodiment, the (meth)acrylic resin may further contain vinyl monomer units copolymerizable with the above alkyl (meth)acrylate (other vinyl monomer units). Examples of other vinyl monomers include acrylonitrile, methacrylonitrile, ethacrylonitrile, allyl glycidyl ether, maleic anhydride, itaconic anhydride, N-methylmaleimide, N-ethylmaleimide, N-cyclohexylmaleimide, aminoethyl acrylate, propylaminoethyl acrylate, dimethylaminoethyl methacrylate, ethylaminopropyl methacrylate, cyclohexylaminoethyl methacrylate, N-vinyldiethylamine, N-acetylvinylamine, allylamine, methallylamine, N-methylallylamine, 2-isopropenyl-oxazoline, 2-vinyl-oxazoline, 2-acroyl-oxazoline, N-phenylmaleimide, phenylaminoethyl methacrylate, styrene, α-methylstyrene, p-glycidylstyrene, p-aminostyrene, 2-styryl-oxazoline, and the like. These may be used alone or in combination. Preferably, they are styrene monomers such as styrene and α-methylstyrene. The content ratio of other vinyl monomer units is preferably 0 to 1% by weight, more preferably 0 to 0.1% by weight. Within such a range, the occurrence of an undesired phase difference and a decrease in transparency can be suppressed.

[0032] (Meth)acrylic resin, in one embodiment, has at least one selected from the group consisting of a glutarimide unit, a lactone ring unit, a maleic anhydride unit, a maleimide unit, and a glutaric anhydride unit. The acrylic resin having a lactone ring unit is described, for example, in JP-A-2008-181078, the disclosure of which is incorporated herein by reference. The glutarimide unit is preferably represented by the following general formula (2):

[0033]

Chemical formula

[0034] In general formula (2), R 1 and R 2 each independently represent hydrogen or an alkyl group having 1 to 8 carbon atoms, and R 3 represents an alkyl group having 1 to 18 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, or an aryl group having 6 to 10 carbon atoms. In general formula (2), preferably, R 1 and R 2 are each independently hydrogen or a methyl group, and R 3 is hydrogen, a methyl group, a butyl group, or a cyclohexyl group. More preferably, R 1 is a methyl group, R 2 is hydrogen, and R 3 is a methyl group.

[0035] The above acrylic resin may contain only a single glutarimide unit, or may contain a plurality of glutarimide units in which R 1 , R 2 and R 3 in the general formula (2) are different.

[0036] The content ratio of the glutarimide unit in the (meth)acrylic resin is preferably 2 mol% to 50 mol%, more preferably 2 mol% to 45 mol%, still more preferably 2 mol% to 40 mol%, particularly preferably 2 mol% to 35 mol%, and most preferably 3 mol% to 30 mol%. If the content ratio is less than 2 mol%, the effects exhibited by the glutarimide unit (for example, high optical properties and high mechanical strength) may not be fully exerted. If the content ratio exceeds 50 mol%, for example, the heat resistance and transparency may be insufficient.

[0037] In one embodiment, the (meth)acrylic resin can contain, for example, 0 to 10% by weight of an unsaturated carboxylic acid unit not involved in the intramolecular imidization reaction. The content ratio of the unsaturated carboxylic acid unit is preferably 0 to 5% by weight, and more preferably 0 to 1% by weight. If the content is within such a range, transparency, retention stability, and moisture resistance can be maintained.

[0038] (Meta)acrylic resin preferably has an imidization rate of 2.5% to 20.0%. If the imidization rate is within such a range, a resin excellent in heat resistance, transparency, and moldability can be obtained, and the generation of scorch and the decrease in mechanical strength during film forming can be prevented. In the above (meta)acrylic resin, the imidization rate is represented by the ratio of the glutarimide unit to the alkyl (meta)acrylate unit. This ratio can be obtained, for example, from the NMR spectrum, IR spectrum, etc. of the (meta)acrylic resin. In the present embodiment, the imidization rate is 1 determined by 1H-NMR measurement of the resin using HNMR BRUKER AvanceIII (400 MHz). 1 More specifically, with the peak area of the O-CH3 proton of the alkyl (meta)acrylate around 3.5 to 3.8 ppm as A and the peak area of the N-CH3 proton of the glutarimide around 3.0 to 3.3 ppm as B, it is determined by the following formula. Imidization rate Im(%) = {B / (A + B)} × 100

[0039] (Meta)acrylic resin preferably has an acid value of 0.10 mmol / g to 0.50 mmol / g. If the acid value is within such a range, a resin excellent in the balance of heat resistance, mechanical properties, and moldability can be obtained. If the acid value is too small, problems such as cost increase due to the use of a modifier to adjust to the desired acid value and the generation of gel-like substances due to the remaining modifier may occur. If the acid value is too large, foaming during film forming (for example, during melt extrusion) is likely to occur, and the productivity of the molded product tends to decrease. In the above (meta)acrylic resin, the acid value is the content of the carboxylic acid unit and carboxylic anhydride unit in the (meta)acrylic resin. In the present embodiment, the acid value can be calculated, for example, by the titration method described in WO2005 / 054311 or JP-A-2005-23272.

[0040] The weight average molecular weight of the above (meth)acrylic resin is preferably from 1,000 to 2,000,000, more preferably from 5,000 to 1,000,000, still more preferably from 10,000 to 500,000, particularly preferably from 50,000 to 500,000, and most preferably from 60,000 to 150,000. The weight average molecular weight can be determined, for example, in terms of polystyrene by using gel permeation chromatography (GPC system, manufactured by Tosoh Corporation). Note that tetrahydrofuran can be used as the solvent.

[0041] The Tg of the second thermoplastic resin can be, for example, from 100°C to 130°C. If the Tg of the second thermoplastic resin is within such a range, the difference from the Tg of the first thermoplastic resin can be made within the above desired range.

[0042] The thickness of the second layer is preferably 20 μm or more, more preferably 25 μm or more, still more preferably 30 μm or more, and particularly preferably 35 μm or more. The thickness of the second layer can be, for example, 250 μm or less. If the thickness of the second layer is within such a range, it can function well as a support substrate. As a result, even if the thickness of the first layer is made very thin, the first layer can be conveyed without problems and bonded to the object without problems. Therefore, when the first layer is a polarizer protection film, a polarizing plate having a very thin polarizer protection film can be produced, which can greatly contribute to the thinning of the polarizing plate.

[0043] The light transmittance of the second layer can be, for example, 90% or more, and can also be, for example, 92% or more. The haze of the second layer can be, for example, 1.0% or less, and can also be, for example, 0.8% or less. Although strict optical properties are not required because the second layer can function as a support substrate, if the light transmittance and haze of the first layer are within the above ranges by coextrusion molding of the multilayer film, the light transmittance and haze of the second layer can also be within such ranges.

[0044] The tensile modulus of the second layer is preferably 0.5 GPa or more, more preferably 1 GPa or more, and even more preferably 2 GPa or more. The upper limit of the tensile modulus may be, for example, 20 GPa. If the tensile modulus is less than 0.5 GPa, sufficient mechanical strength may not be exhibited. The tensile modulus may be measured, for example, in accordance with ASTM-D-882-61T.

[0045] The tensile strength of the second layer is preferably 10 MPa or more and less than 100 MPa, more preferably 30 MPa or more and less than 100 MPa. If the tensile strength is less than 10 MPa, sufficient mechanical strength may not be exhibited. If the tensile strength exceeds 100 MPa, processability may be insufficient. The tensile strength may be measured, for example, in accordance with ASTM-D-882-61T.

[0046] The tensile elongation of the second layer is preferably 1.0% or more, more preferably 3.0% or more, and even more preferably 5.0% or more. The upper limit of the tensile elongation can be, for example, 100%. If the tensile elongation is less than 1%, the toughness may be insufficient. The tensile elongation can be measured, for example, in accordance with ASTM-D-882-61T.

[0047] A-4.Third layer The specific configuration of the third layer is as explained in Section A-2 regarding the first layer. The third layer may have the same configuration as the first layer or a different configuration.

[0048] B. Polarizing Plate Manufacturing Method As described above, the multilayer film according to the embodiment of the present invention can be suitably used for manufacturing a polarizing plate. Therefore, a method for manufacturing a polarizing plate using such a multilayer film is also included in the embodiment of the present invention. The method for manufacturing a polarizing plate according to one embodiment of the present invention uses a multilayer film having a first layer and a second layer as shown in FIG. 1(a). FIGS. 2(a) to 2(c) are schematic diagrams for explaining such a method for manufacturing a polarizing plate. First, as shown in FIG. 2(a), the first layer 10 of the multilayer film 100 having the first layer 10 and the second layer 20 is bonded to the polarizer 200 to obtain an intermediate laminate. The bonding can be performed via any suitable adhesive layer (typically, an adhesive layer, a pressure-sensitive adhesive layer). Examples of the adhesive constituting the adhesive layer include aqueous adhesives (typically, polyvinyl alcohol (PVA)-based adhesives) and active energy ray-curable adhesives. Examples of the pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer include acrylic pressure-sensitive adhesives. The bonding is typically performed by so-called roll-to-roll. The polarizer 200 may be a single resin film or a laminate of a substrate and a resin layer (polarizer). The polarizer is typically a polyvinyl alcohol (PVA)-based resin film or resin layer containing a dichroic substance (e.g., iodine). Since a polarizer having any suitable configuration can be used as the polarizer, detailed description thereof is omitted. Next, as shown in FIG. 2(b), the second layer is peeled off from the intermediate laminate. As a result, as shown in FIG. 2(c), a polarizing plate 300 having the polarizer 200 and the first layer (polarizer protection film) 10 can be obtained. By using the multilayer film according to the embodiment of the present invention, an extremely thin polarizer protection film can be conveyed without problems and bonded to the polarizer without problems. As a result, an extremely thin polarizing plate can be produced favorably. For example, a polarizer obtained by using a laminate of a resin substrate and a PVA-based resin layer formed by coating on the resin substrate, as described in JP-A-2012-73580 and Japanese Patent No. 6470455, can have an extremely thin thickness of 5 μm or less (e.g., 3 μm). As a result, the thinning of the polarizer protection film becomes a dominant factor in the thinning of the entire polarizing plate.In other words, the difficulty in transporting and bonding a thin polarizer protection film to a polarizer has become an obstacle to thinning the entire polarizing plate. According to an embodiment of the present invention, as described above, a very thin (for example, 1 μm thick) polarizer protection film can be transported without problems and bonded to a polarizer without problems, so that a very thin polarizing plate can be manufactured well. According to an embodiment of the present invention, specifically, a first layer (polarizer protection film) with a thickness of 1 μm can be bonded to a polarizer with a thickness of 5 μm via a PVA-based adhesive layer with a thickness of 1 μm. As a result, a very thin polarizing plate with a thickness of 7 μm can be manufactured.

[0049] A method for manufacturing a polarizing plate according to another embodiment of the present invention uses a multilayer film having a first layer, a second layer, and a third layer as shown in FIG. 1(b). FIGS. 3(a) to 3(f) are schematic diagrams for explaining such a method for manufacturing a polarizing plate. First, as shown in FIG. 3(a), the first layer 10 of the multilayer film 101 having the first layer 10, the second layer 20, and the third layer 30 is bonded to the first polarizer 201 to obtain a first intermediate laminate. Next, as shown in FIG. 3(b), the laminate of the second layer and the third layer is peeled off from the first intermediate laminate. As a result, as shown in FIG. 3(c), a first polarizing plate 301 having a polarizer 201 and a first layer (polarizer protection film) 10 can be obtained. Further, as shown in FIG. 3(d), the third layer 30 of the laminate of the second layer and the third layer peeled off from the first intermediate laminate is bonded to the second polarizer 202 to obtain a second intermediate laminate. Next, as shown in FIG. 3(e), the second layer 20 is peeled off from the second intermediate laminate. As a result, as shown in FIG. 3(f), a second polarizing plate 302 having a polarizer 202 and a third layer (polarizer protection film) 30 can be obtained. According to the present embodiment, since two polarizing plates can be obtained from one multilayer film, excellent manufacturing efficiency can be realized. Note that the configuration of the polarizer, the bonding method, the adhesive layer, the effect, etc. are as described above with respect to the embodiment shown in FIGS. 2(a) to 2(c).

[0050] The thickness of the polarizer can be, for example, 20 μm or less, for example, 15 μm or less, for example, 12 μm or less, for example, 10 μm or less, for example, 8 μm or less, for example, 5 μm or less, and for example, 3 μm or less. On the other hand, the thickness of the polarizer can be, for example, 1 μm or more, for example, 2 μm or more, and for example, 3 μm or more. As described above, according to the embodiment of the present invention, a polarizing plate having a very thin polarizer protection film can be manufactured, so the thickness of the polarizer may be appropriately set according to the purpose. For example, when using a thin polarizer of 5 μm or less, a very thin polarizing plate can be realized.

Example

[0051] Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to these examples. The measurement methods for each property are as follows. Unless otherwise specified, "parts" and "%" in the examples are based on weight.

[0052] (1) Stretchability The multilayer films obtained in the examples and comparative examples were cut into a width of 150 mm × a length of 150 mm to obtain measurement samples. Using a batch stretching machine, stretching was performed 2 times in the MD direction and 2 times in the TD direction at a temperature 20 °C higher than the glass transition temperature of the first layer, and the presence or absence of film breakage was observed. Evaluation was made according to the following criteria. ○: No film breakage was observed △: Slight film breakage was observed ×: Significant film breakage was observed (2) Peelability For the multilayer films obtained in the examples and comparative examples, a peel test was performed to evaluate the peelability between the first layer and the second layer. Specifically, it is as follows. The multilayer film was cut into a size of 200 mm in width and 15 mm in length. A cut was made with a cutter knife between the first layer and the second layer, and this was bonded to a glass plate. Using a tensilon, the first layer and the second layer were peeled at a peeling speed of 300 mm / min in the 135-degree direction, and the state at that time was observed. Evaluation was made according to the following criteria. ○: The film could be peeled well without breaking △: Slight breakage was observed in the film, but it could be peeled off. ×: The film was broken and could not be peeled off, or the cutter knife did not cut in.

[0053] <Example 1> A cycloolefin resin (manufactured by JSR Corporation) was used as the material for forming the first layer, and an acrylic resin (manufactured by Kuraray Co., Ltd., product name "HRS") was used as the material for forming the second layer. The cycloolefin resin contains 85 mol% of a polar skeleton (monomer unit of 6-methoxycarbonyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene) and 15 mol% of a non-polar skeleton (monomer unit of 2,3-dihydrodicyclopentadiene), and its Tg was 132°C. This cycloolefin resin is referred to as "COP A". The acrylic resin is polymethyl methacrylate (PMMA), and its Tg was 112°C. This acrylic resin is referred to as "Acrylic A". These materials showed a relationship of D HSP / R = 1.6. These materials were coextrusion molded using an extruder having a predetermined die to obtain a multilayer film having a first layer with a thickness of 5 μm and a second layer with a thickness of 35 μm. The obtained multilayer film was subjected to the evaluations (1) and (2) above. The results are shown in Table 1.

[0054] Furthermore, a polarizing plate was fabricated using the obtained multilayer film. Specifically, it was as follows. A long roll of a polyvinyl alcohol (PVA)-based resin film with a thickness of 30 μm (manufactured by Kuraray, product name "PE3000") was uniaxially stretched in the longitudinal direction by a roll stretching machine to 5.9 times its original length in the longitudinal direction while simultaneously performing swelling, dyeing, cross-linking, and washing treatments, and finally a drying treatment was performed to fabricate a polarizer with a thickness of 12 μm. The multilayer film and the obtained polarizer were laminated roll-to-roll via a PVA-based adhesive (with a thickness of 1 μm) such that the first layer of the multilayer film was adjacent to the polarizer to produce an intermediate laminate. Further, the second layer was peeled off from the obtained intermediate laminate to obtain a polarizing plate having a configuration of a polarizer / first layer (polarizer protective film). The polarizing plate could be fabricated without any problems in any of the processes of conveyance (roll-to-roll) and lamination.

[0055] <Examples 2 to 10> Except for using the materials shown in Table 1 for the first layer and the second layer (therefore, the Tg and D HSP / R became the values shown in Table 1), and setting the thicknesses of the first layer and the second layer to the thicknesses shown in Table 1, a multilayer film was obtained in the same manner as in Example 1. The obtained multilayer film was subjected to the same evaluation as in Example 1. The results are shown in Table 1. Furthermore, a polarizing plate was fabricated in the same manner as in Example 1 except for using each of the obtained multilayer films. Each polarizing plate could be fabricated without any problems in any of the processes of conveyance (roll-to-roll) and lamination.

[0056] <Example 11> "COP A" was used for the first and third layers, and "Acrylic A" was used for the second layer. These materials were co-extrusion molded using an extrusion molding machine having a predetermined die to obtain a multilayer film having a first layer with a thickness of 1 μm, a second layer with a thickness of 38 μm, and a third layer with a thickness of 1 μm. The obtained multilayer film was subjected to the same evaluation as in Example 1. The results are shown in Table 1. Furthermore, a polarizing plate was produced using the obtained multilayer film. First, the multilayer film and the polarizer (the first polarizer) used in Example 1 were laminated roll-to-roll via a PVA-based adhesive (thickness: 1 μm) such that the first layer of the multilayer film was adjacent to the first polarizer to produce a first intermediate laminate. Next, the laminate of the second layer and the third layer was peeled off from the obtained first intermediate laminate to obtain a first polarizing plate having a configuration of the first polarizer / the first layer (polarizer protection film). Furthermore, the laminate of the second layer and the third layer and the polarizer (the second polarizer) used in Example 1 were laminated roll-to-roll via a PVA-based adhesive (thickness: 1 μm) such that the third layer of the laminate was adjacent to the second polarizer to produce a second intermediate laminate. Furthermore, the second layer was peeled off from the obtained second intermediate laminate to obtain a second polarizing plate having a configuration of the second polarizer / the third layer (polarizer protection film). Both the first polarizing plate and the second polarizing plate could be produced without any problems in any of the processes of conveyance (roll-to-roll) and lamination.

[0057] <Comparative Examples 1 to 5> The materials shown in Table 1 were used for the first and second layers (therefore, Tg and D HSP / R became the values shown in Table 1), and a multilayer film was obtained in the same manner as in Example 1 except that the thicknesses of the first and second layers were the thicknesses shown in Table 1. The obtained multilayer film was subjected to the same evaluation as in Example 1. The results are shown in Table 1. Furthermore, an attempt was made to produce a polarizing plate in the same manner as in Example 1 except that each of the obtained multilayer films was used. However, in Comparative Examples 1 to 3, the first layer did not peel off well and could not be laminated to the polarizer. In Comparative Examples 4 to 5, due to insufficient stretchability, the thickness unevenness of the first layer was large and it could not be laminated well to the polarizer.

[0058] Note that the materials shown in Table 1 have the following meanings. Also, the "first layer" in Example 11 of Table 1 means "the first layer and the third layer". Further, the "※" in Comparative Examples 4 and 5 of Table 1 means that a solvent capable of dissolving the resin at room temperature was not available, and D HSP / R could not be calculated. COP B: Manufactured by JSR Corporation, containing 60 mol% of a polar skeleton (monomer unit of 6-methoxycarbonyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene) and 40 mol% of a non-polar skeleton (monomer unit of 2,3-dihydrodicyclopentadiene) COP C: Manufactured by JSR Corporation, containing 45 mol% of a polar skeleton (monomer unit of 6-methoxycarbonyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene), 8 mol% of a non-polar skeleton (monomer unit of norbornene), and 47 mol% of a non-polar skeleton (monomer unit of 2,3-dihydrodicyclopentadiene) COP D: Manufactured by JSR Corporation, containing 66 mol% of a polar skeleton (monomer unit of 6-methoxycarbonyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene), 3 mol% of a non-polar skeleton (monomer unit of norbornene), and 31 mol% of a non-polar skeleton (monomer unit of 2,3-dihydrodicyclopentadiene) Acrylic B: Acrylic resin with a Tg of 120 °C Polyester A: Polyester resin with a Tg of 151 °C Polyester B: Manufactured by Bell Polyester Products Co., Ltd., product name "E03", containing terephthalic acid, isophthalic acid, ethylene glycol, and neopentyl glycol as monomer units PP: Manufactured by Japan Polypropylene Corporation, product name "FY6C", polypropylene OP: Manufactured by Mitsui Chemicals, Inc., product name "TPX-M002", polymethylpentene

[0059]

Table 1

[0060] <Evaluation> As is clear from Table 1, it can be seen that the multilayer film of the example of the present invention is excellent in both stretchability and peelability.

Industrial Applicability

[0061] The multilayer film according to the embodiment of the present invention can be suitably used for the production of a polarizing plate.

Explanation of Signs

[0062] 10 First layer 20 Second layer 30 Third layer 100 Multilayer film 101 Multilayer film 200 Polarizer 201 First polarizer 202 Second polarizer 300 Polarizing plate 301 First polarizing plate 302 Second polarizing plate

Claims

【Claim 1】 A coextruded film having a first layer containing a first thermoplastic resin and a second layer containing a second thermoplastic resin, The distance D between the Hansen solubility parameters of the first thermoplastic resin and the second thermoplastic resin ＨＳＰ and the radius R of the Hansen sphere of the first thermoplastic resin satisfy the relationship that ＨＳＰ D / R ≥ 1 a multilayer film.

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