JP6682760B2 - Multilayer film and its manufacturing method, polarizing plate and its manufacturing method, and liquid crystal display device and its manufacturing method - Google Patents

Description

  The present invention relates to a multilayer film and a manufacturing method thereof, a polarizing plate and a manufacturing method thereof, a liquid crystal display device and a manufacturing method thereof.

  An image display device such as a liquid crystal display device may be provided with a retardation film in order to ensure a retardation due to the refractive index of the liquid crystal cell. Examples of such a retardation film include a stretched film obtained by stretching a resin film. Further, as such a stretched film, a film formed of a resin containing a polymer having an alicyclic structure has attracted attention.

  When a film is produced using a resin containing a polymer having an alicyclic structure, a resin containing a polymer having an alicyclic structure may be used in addition to the technique of using a resin containing a polymer having an alicyclic structure alone. There is known a technique in which is used in combination with any other resin. For example, a multilayer film including a resin layer containing a polymer having an alicyclic structure and an arbitrary resin layer is known (see Patent Documents 1 and 2).

JP, 2014-123059, A JP, 2010-091646, A

  Due to the increasing demands for downsizing and weight reduction, it is required for recent films to reduce the thickness of the film. The demand for thinning is also demanded for a film using a resin containing a polymer having an alicyclic structure. Therefore, the present inventor has tried to manufacture a thin film by molding a resin containing a polymer having an alicyclic structure into a single-layer film. However, when a resin containing a polymer having an alicyclic structure is formed into a thin film, there is a possibility of film breakage. Further, in particular, when an unstretched film is stretched to produce a thin stretched film, film breakage is likely to occur in the stretching step, and production of the stretched film may be difficult.

  The present invention was devised in view of the above problems, and is a multilayer film capable of producing a thin film made of a resin containing a polymer having an alicyclic structure; a method for producing the multilayer film. A polarizing plate having a thin film obtained from the multilayer film and a method for producing the same; and a liquid crystal display device having a thin film obtained from the multilayer film and a method for producing the same. With the goal.

The inventor of the present invention has diligently studied to solve the above problems. As a result, a layer made of a resin containing a polymer having an alicyclic structure, a layer made of a thermoplastic resin, and a layer made of a resin containing a polymer having an alicyclic structure in this order, and, The present invention found that a thin film made of a resin containing a polymer having an alicyclic structure can be produced by using a multilayer film in which the glass transition temperature of the resin forming each layer satisfies a predetermined relationship. Was completed.
That is, the present invention is as follows.

[1] B layer made of a resin (B) containing a polymer having an alicyclic structure, B'layer made of a resin (B ') containing a polymer having an alicyclic structure, and the resin (B) And an A layer made of a thermoplastic resin (A) different from the resin (B ′), in the order of the B layer, the A layer and the B ′ layer,
Glass transition temperature TgB of the resin (B), glass transition temperature TgB ′ of the resin (B ′), glass transition temperature TgA of the thermoplastic resin (A), thickness tb of the B layer, thickness of the B ′ layer. tb ′ and the thickness ta of the A layer are
15 ° C ≤ TgB-TgA ≤ 70 ° C
15 ° C ≤ TgB'-TgA ≤ 70 ° C
4 μm ≦ tb ≦ 15 μm
4 μm ≦ tb ′ ≦ 15 μm
5 μm ≦ ta ≦ 40 μm
A multi-layer film that satisfies the requirements.
[2] The polymer having an alicyclic structure contained in the resin (B) and the polymer having an alicyclic structure contained in the resin (B ′) are cycloolefin polymers. ] The multilayer film described.
[3] The multilayer film according to [1] or [2], wherein the thermoplastic resin (A) contains an acrylic polymer.
[4] The multilayer film according to any one of [1] to [3], wherein the thermoplastic resin (A) contains rubber particles.
[5] At least one layer selected from the group consisting of the A layer, the B layer, and the B ′ layer obtained by peeling from the multilayer film according to any one of [1] to [4]. And a polarizing film.
[6] The polarizing plate according to [5], wherein the polarizing film contains polyvinyl alcohol.
[7] A step of peeling at least one layer selected from the group consisting of the A layer, the B layer and the B ′ layer from the multilayer film according to any one of [1] to [4],
A polarizing plate, comprising a step of laminating a polarizing film with at least one layer selected from the group consisting of the A layer, the B layer and the B ′ layer obtained by peeling from the multilayer film. Method of manufacturing a plate.
[8] B layer formed of a resin (B) containing a polymer having an alicyclic structure, B ′ layer formed of a resin (B ′) containing a polymer having an alicyclic structure, the resin B and the above A method for producing a multilayer film, which comprises an A layer made of a thermoplastic resin (A) different from the resin B ', in the order of the B layer, the A layer and the B'layer,
Including a step of co-extruding the thermoplastic resin (A), the resin (B) and the resin (B ′),
Glass transition temperature TgB of the resin (B), glass transition temperature TgB ′ of the resin (B ′), glass transition temperature TgA of the thermoplastic resin (A), thickness tb of the B layer, thickness of the B ′ layer. tb ′ and the thickness ta of the A layer are
15 ° C ≤ TgB-TgA ≤ 70 ° C
15 ° C ≤ TgB'-TgA ≤ 70 ° C
4 μm ≦ tb ≦ 15 μm
4 μm ≦ tb ′ ≦ 15 μm
5 μm ≦ ta ≦ 40 μm
A method for producing a multilayer film, which satisfies the above conditions.
[9] The pre-stretch film obtained in the step of coextruding the thermoplastic resin (A), the resin (B) and the resin (B ′),
TgA + 26 ° C <Ts
Ts <TgB + 30 ° C
Ts <TgB '+ 30 ° C
The method for producing a multilayer film according to [8], including a step of stretching at a stretching temperature Ts satisfying the above conditions.
[10] At least one layer selected from the group consisting of the A layer, the B layer, and the B ′ layer, which is obtained by peeling from the multilayer film according to any one of [1] to [4]. A liquid crystal display device.
[11] A method for manufacturing a liquid crystal display device including a liquid crystal panel,
A step of peeling at least one layer selected from the group consisting of the A layer, the B layer and the B ′ layer from the multilayer film according to any one of [1] to [4],
Providing a liquid crystal panel with at least one layer selected from the group consisting of the layer A, the layer B, and the layer B'obtained by peeling from the multilayer film.

  According to the present invention, a multilayer film capable of producing a thin film made of a resin containing a polymer having an alicyclic structure; a method for producing the multilayer film; a thin film obtained from the multilayer film. It is possible to provide a polarizing plate provided with a film and a manufacturing method thereof; and a liquid crystal display device provided with a thin film obtained from the multilayer film and a manufacturing method thereof.

  Hereinafter, the present invention will be described in detail with reference to embodiments and examples. However, the present invention is not limited to the embodiments and exemplifications shown below, and may be implemented by being arbitrarily modified within the scope of the claims of the present invention and the scope of equivalents thereof.

  In the following description, “(meth) acrylic acid” includes both “acrylic acid” and “methacrylic acid”, and “(meth) acrylamide” includes both “acrylamide” and “methacrylamide”. , "(Meth) acrylonitrile" includes both "acrylonitrile" and "methacrylonitrile".

  In the following description, the in-plane retardation Re of a layer is a value represented by Re = (nx−ny) × d unless otherwise specified. Here, nx represents the refractive index in the direction perpendicular to the thickness direction of the layer (in-plane direction) and giving the maximum refractive index. ny represents the refractive index in the in-plane direction of the layer and in the direction perpendicular to the nx direction. d represents the thickness of the layer. The measurement wavelength is 590 nm unless otherwise specified.

  In the following description, the term “polarizing plate” includes not only a rigid member but also a flexible member such as a resin film unless otherwise specified.

  In the following description, the “long” film refers to a film having a length of usually 5 times or more, preferably 10 times, with respect to the width, and specifically, it is wound into a roll and stored or A film having a length that allows it to be transported.

[1. Multilayer film]
The multilayer film of the present invention comprises a B layer made of a resin (B) containing a polymer having an alicyclic structure, and a B'layer made of a resin (B ') containing a polymer having an alicyclic structure, An A layer made of a thermoplastic resin (A) different from the resin (B) and the resin (B ′) is provided in the order of a B layer, an A layer and a B ′ layer. Usually, the A layer and the B layer are in direct contact with each other, and another layer is not provided between the A layer and the B layer. Further, normally, the A layer and the B ′ layer are in direct contact with each other, and another layer is not provided between the A layer and the B ′ layer.

  From the multilayer film of the present invention, at least one layer selected from the group consisting of A layer, B layer and B'layer can be peeled off. The layer thus peeled off can be used as an independent thin film. Hereinafter, the film thus obtained by peeling from the multilayer film of the present invention may be appropriately referred to as "release film".

[1.1. Layer A]
The layer A is made of a thermoplastic resin (A) different from the resin (B) and the resin (B ′). Usually, the A layer is provided so as to be peelable from the B layer and the B ′ layer. Therefore, as the thermoplastic resin (A), an appropriate thermoplastic resin is used according to the resin (B) and the resin (B ′) so that the A layer can be separated from the B layer and the B ′ layer. preferable.

  Usually, the thermoplastic resin (A) contains a polymer having thermoplasticity and, if necessary, an arbitrary component. Examples of the polymer contained in the thermoplastic resin (A) include an acrylic polymer, a styrene polymer, a maleimide polymer and the like. Further, the polymer contained in the thermoplastic resin (A) may be used alone or in combination of two or more kinds at an arbitrary ratio.

  As the polymer contained in the thermoplastic resin (A), an acrylic polymer is preferable among the above-mentioned polymers. The acrylic polymer means a polymer of (meth) acrylic acid or a (meth) acrylic acid derivative. Acrylic polymers usually have low affinity with polymers having an alicyclic structure. Therefore, by using the thermoplastic resin (A) containing an acrylic polymer, it is possible to obtain the A layer which is easily separated from the B layer and the B'layer. Further, since the acrylic polymer has high mechanical strength and is hard, the mechanical strength of the multilayer film can be increased to prevent breakage, and the handling property of the multilayer film can be improved.

  Examples of the (meth) acrylic acid derivative include (meth) acrylic acid ester, (meth) acrylamide, and (meth) acrylonitrile. Further, the above-mentioned monomers such as (meth) acrylic acid and (meth) acrylic acid derivative may be used alone or in combination of two or more kinds at an arbitrary ratio. Therefore, the acrylic polymer may be a homopolymer or a copolymer of the above monomers.

  Usually, the acrylic polymer contains a structural unit having a structure formed by polymerizing monomers such as (meth) acrylic acid and a (meth) acrylic acid derivative. Above all, the acrylic polymer preferably contains a structural unit having a structure formed by polymerizing a (meth) acrylic acid ester.

  Examples of the (meth) acrylic acid ester include alkyl esters of (meth) acrylic acid. Above all, as the (meth) acrylic acid ester, those having a structure derived from (meth) acrylic acid and an alkanol or cycloalkanol having 1 to 15 carbon atoms are preferable. Further, as the (meth) acrylic acid ester, one having a structure derived from (meth) acrylic acid and an alkanol having 1 to 8 carbon atoms is more preferable. By reducing the number of carbon atoms as described above, the elongation at break of the multilayer film can be increased.

  Specific examples of the acrylate ester include methyl acrylate, ethyl acrylate, n-propyl acrylate, i-propyl acrylate, n-butyl acrylate, i-butyl acrylate, sec-butyl acrylate, t-acrylate. -Butyl, n-hexyl acrylate, cyclohexyl acrylate, n-octyl acrylate, 2-ethylhexyl acrylate, n-decyl acrylate, n-dodecyl acrylate and the like.

  Specific examples of the methacrylic acid ester include methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, sec-butyl methacrylate, t-methacrylic acid. -Butyl, n-hexyl methacrylate, n-octyl methacrylate, 2-ethylhexyl methacrylate, n-decyl methacrylate, n-dodecyl methacrylate and the like.

  The (meth) acrylic acid ester may have a substituent such as a hydroxyl group or a halogen atom, as long as the effects of the present invention are not significantly impaired. The (meth) acrylic acid ester may have a plurality of the same or different substituents. Examples of the (meth) acrylic acid ester having a substituent include 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 4-hydroxybutyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 4-hydroxybutyl methacrylate, 3-chloro-2-hydroxypropyl methacrylate, glycidyl methacrylate and the like can be mentioned.

  The total amount of (meth) acrylic acid and (meth) acrylic acid derivative is preferably 50 parts by weight, more preferably 85 parts by weight, and particularly preferably 90 parts by weight with respect to 100 parts by weight of all monomers of the acrylic polymer. Is. Therefore, in the acrylic polymer, the proportion of structural units having a structure formed by polymerizing (meth) acrylic acid or a (meth) acrylic acid derivative is preferably 50% by weight or more, more preferably 85% by weight or more, It is particularly preferably 90% by weight or more. As a result, the characteristics of the acrylic polymer are effectively utilized to effectively enhance the peelability between the A layer and the B layer and the peelability between the A layer and the B ′ layer, and the mechanical strength of the multilayer film. Can be effectively increased.

  The acrylic polymer may be a polymer of only (meth) acrylic acid or a (meth) acrylic acid derivative, and (meth) acrylic acid or a (meth) acrylic acid derivative and the above (meth) acrylic acid and (meth) It may be a copolymer with any monomer other than the acrylic acid derivative. Examples of the optional monomer include, for example, α, β-ethylenically unsaturated carboxylic acid ester monomers other than (meth) acrylic acid ester, α, β-ethylenically unsaturated carboxylic acid monomer, and alkenyl. Examples thereof include aromatic monomers, conjugated diene monomers, non-conjugated diene monomers, carboxylic acid unsaturated alcohol esters, and olefin monomers. As the arbitrary monomer, one type may be used alone, or two or more types may be used in combination at any ratio.

  Specific examples of the α, β-ethylenically unsaturated carboxylic acid ester monomer include dimethyl fumarate, diethyl fumarate, dimethyl maleate, diethyl maleate, dimethyl itaconate and the like.

  The α, β-ethylenically unsaturated carboxylic acid monomer may be any of monocarboxylic acid, polyvalent carboxylic acid, partial ester of polyvalent carboxylic acid, and polyvalent carboxylic acid anhydride. Specific examples of the α, β-ethylenically unsaturated carboxylic acid monomer include crotonic acid, maleic acid, fumaric acid, itaconic acid, monoethyl maleate, mono-n-butyl fumarate, maleic anhydride, and itaconic anhydride. Is mentioned.

  Specific examples of the alkenyl aromatic monomer include styrene, α-methylstyrene, methyl α-methylstyrene, vinyltoluene and divinylbenzene.

  Specific examples of the conjugated diene monomer include 1,3-butadiene, 2-methyl-1,3-butadiene, 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene and 2-chloro-1. , 3-butadiene, cyclopentadiene and the like.

  Specific examples of the non-conjugated diene monomer include 1,4-hexadiene, dicyclopentadiene, ethylidene norbornene and the like.

  Specific examples of the carboxylic acid unsaturated alcohol ester monomer include vinyl acetate and the like.

  Specific examples of the olefin monomer include ethylene, propylene, butene, pentene and the like.

  Among the above-mentioned acrylic polymers, polymethacrylate is preferable, and polymethylmethacrylate is more preferable.

  The amount of the polymer in the thermoplastic resin (A) is preferably 50% by weight to 100% by weight, more preferably 70% by weight to 100% by weight. By setting the amount of the polymer within the above range, the A layer having desired characteristics can be easily realized.

  Examples of the optional component that the thermoplastic resin (A) may include include rubber particles. By including the rubber particles, the flexibility of the thermoplastic resin (A) can be increased and the impact resistance of the multilayer film can be improved. Further, since the rubber particles form irregularities on the surface of the layer A, when the layer A is separated from the multilayer film to separate the layer A as an independent release film, the slipperiness of the release film can be enhanced.

  Examples of the rubber forming the rubber particles include acrylic acid ester polymer rubber, polymer rubber containing butadiene as a main component, ethylene-vinyl acetate copolymer rubber, and the like. Examples of the acrylic ester polymer rubber include those containing butyl acrylate, 2-ethylhexyl acrylate, etc. as the main component of the monomer. Among these, an acrylic ester polymer rubber containing butyl acrylate as a main component and a polymer rubber containing butadiene as a main component are preferable.

  Further, the rubber particles may contain two or more types of rubber. Further, those rubbers may be mixed uniformly, but may be layered. Examples of the rubber particles in which the rubber is layered include particles having a core layer formed inside the rubber particles and a shell layer covering the core layer. Specific examples include a core layer made of a rubber elastic component obtained by grafting an alkyl acrylate such as butyl acrylate and styrene, and a shell layer made of a copolymer of one or both of polymethyl methacrylate and methyl methacrylate and an alkyl acrylate. And rubber particles having

  The number average particle diameter of the rubber particles is preferably 0.05 μm or more, more preferably 0.1 μm or more, preferably 0.3 μm or less, more preferably 0.25 μm or less. By setting the number average particle diameter within the above range, aggregation of rubber particles in the A layer can be prevented, so that the effect of improving the impact resistance of the A layer single layer film by including the rubber particles is maintained. At the same time, the rise of the internal haze in the A layer can be suppressed. Further, since the unevenness can be appropriately formed on the surface of the layer A, when the layer A is separated from the multilayer film to separate the layer A as an independent release film, the slipperiness of the release film can be effectively enhanced.

  The amount of rubber particles is preferably 5 parts by weight or more and preferably 50 parts by weight or less with respect to 100 parts by weight of the polymer contained in the thermoplastic resin (A). By setting the amount of the rubber particles within the above range, the impact resistance of the A-layer single-layer film can be enhanced, and the impact resistance of the multilayer film can be enhanced to improve the handling property.

  Examples of optional components that the thermoplastic resin (A) may include include colorants such as pigments and dyes; plasticizers; fluorescent whitening agents; dispersants; heat stabilizers; light stabilizers; ultraviolet absorbers; Agents; antioxidants; compounding agents such as surfactants. One of these may be used alone, or two or more may be used in combination at an arbitrary ratio.

The glass transition temperature TgA of the thermoplastic resin (A) usually satisfies a predetermined relationship with the glass transition temperature TgB of the resin (B) and the glass transition temperature TgB ′ of the resin (B ′). Specifically, "TgB-TgA" and "TgB'-TgA" satisfy the relationships represented by the following formulas (i) and (ii).
15 ° C ≤ TgB-TgA ≤ 70 ° C (i)
15 ° C ≤ TgB'-TgA ≤ 70 ° C (ii)

  The formulas (i) and (ii) will be described in more detail. “TgB-TgA” is usually 15 ° C. or higher, preferably 16 ° C. or higher, more preferably 17 ° C. or higher, usually 70 ° C. or lower, preferably 60 ° C. or lower, more preferably 40 ° C. or lower. Further, "TgB'-TgA" is usually 15 ° C or higher, preferably 16 ° C or higher, more preferably 17 ° C or higher, and usually 70 ° C or lower, preferably 60 ° C or lower, more preferably 40 ° C or lower.

That "TgB-TgA" and "TgB'-TgA" are more than the lower limit of the said range means that TgB and TgB 'are higher than TgA by a predetermined degree. As a result, when the resin (A), the resin (B) and the resin (B ′) are extruded through the lip of the die in the coextrusion method, even if the resin (A) is temporarily decomposed, the resin (A) is usually separated from the resin (A). The decomposition of the resin (B) and the resin (B ′) having a high glass transition temperature TgB and TgB ′ can be suppressed. In the multilayer film of the present invention, since the A layer is provided between the B layer and the B'layer composed of the resin (B) and the resin (B ') which are hardly decomposed as described above, decomposition products that may be generated in the A layer Can be suppressed from adhering to the lip. Therefore, it is possible to suppress the occurrence of die lines due to the deposits on the lip. Here, the die line refers to irregularly-formed linear concave portions and linear convex portions extending in the longitudinal direction of the multilayer film.
Further, since TgB and TgB ′ are higher than TgA by a predetermined degree, sticking of the stretched film to the stretching device can be suppressed when a multilayer film is manufactured as the stretched film. For example, it is possible to prevent the stretched film from being unintentionally pulled by sticking the stretched film to a portion that can come into contact with the stretched film, such as a roll and a clip of a stretching device. Therefore, damage to the stretched film can be suppressed.
Further, since TgB and TgB ′ are higher than TgA by a predetermined degree, when stretching is carried out at a temperature higher than TgA, the B layer and the B ′ layer do not align the polymer molecules contained in the A layer. The polymer molecules contained in can be oriented. Therefore, in the stretching step, the retardation can be selectively expressed in the B layer and the B ′ layer while suppressing the expression of the retardation in the A layer.
On the other hand, by setting "TgB-TgA" and "TgB'-TgA" to be not more than the upper limit value of the above range, the mechanical strength of the A layer can be increased or the flexibility of the B layer and the B'layer can be increased. .

  The range of the glass transition temperature TgA of the thermoplastic resin (A) can be appropriately set within the range satisfying the above formulas (i) and (ii). Specifically, the glass transition temperature TgA of the thermoplastic resin (A) is preferably 80 ° C or higher, more preferably 90 ° C or higher, particularly preferably 100 ° C or higher, preferably 150 ° C or lower, more preferably 140 ° C or higher. C. or lower, particularly preferably 130.degree. C. or lower. When the glass transition temperature TgA of the thermoplastic resin (A) is at least the lower limit value of the above range, the heat resistance of the layer A can be increased, and when it is at most the upper limit value, the processing can be facilitated.

  The layer A is preferably an optically isotropic layer. Therefore, the in-plane retardation ReA of the A layer is preferably substantially zero. Here, the in-plane retardation ReA of the A layer being substantially zero means that the in-plane retardation ReA of the A layer is preferably 0 nm to 4 nm, more preferably 0 nm to 3 nm, and particularly preferably 0 nm to 2 nm. Indicates the following. By setting the in-plane retardation ReA of the A layer to substantially zero, the in-plane retardation ReB of the B layer and the in-plane retardation ReB 'of the B'layer can be easily measured.

  The total light transmittance of the layer A is preferably 80% or more, more preferably 90% or more. The total light transmittance can be measured using a spectrophotometer (manufactured by JASCO Corporation, UV-visible near-infrared spectrophotometer "V-570") in accordance with JIS K0115.

  The internal haze of the A layer is preferably 0.3% or less, more preferably 0.2% or less. The internal haze can be measured in an aqueous zinc bromide solution according to the refractive index of the A layer according to JIS K7136-. As a measuring device for this internal haze, "turbidity meter NDH-300A" manufactured by Nippon Denshoku Industries Co., Ltd. can be used.

  The amount of the volatile component in the layer A is preferably 0.1% by weight or less, more preferably 0.05% by weight or less, still more preferably 0.02% by weight or less. By setting the amount of the volatile component within the above range, the dimensional stability of the A layer can be improved. Here, the volatile component is a substance having a molecular weight of 200 or less. Examples of volatile components include residual monomers and solvents. The amount of volatile components can be quantified by analysis by gas chromatography as the sum of substances with a molecular weight of 200 or less.

  Since the multilayer film of the present invention includes a plurality of layers, ie, A layer, B layer, and B'layer, the thickness of the multilayer film as a whole becomes large even if the thickness of each layer is small. Therefore, even if the thickness of each layer is thin, the mechanical strength of the multilayer film as a whole can be increased, so that damage to each layer can be suppressed. Therefore, according to the multilayer film of the present invention, the thickness of the A layer can be reduced. Specifically, the thickness ta of the A layer is usually 40 μm or less, and is preferably 38 μm or less, and more preferably 30 μm or less from the viewpoint that the winding diameter can be reduced and a long length can be wound. The lower limit of the thickness ta of the A layer is usually 5 μm or more, preferably 6 μm or more, more preferably 7 μm or more. By setting the thickness ta of the A layer to be the above lower limit value or more, it is possible to suppress damage to the A layer when the A layer is peeled from the B layer and the B ′ layer.

[1.2. B layer]
The B layer is made of a resin (B) containing a polymer having an alicyclic structure. The polymer having an alicyclic structure is a polymer in which the structural unit of the polymer has an alicyclic structure. The polymer having an alicyclic structure may have an alicyclic structure in its main chain, or may have an alicyclic structure in its side chain. Among them, a polymer having an alicyclic structure in the main chain is preferable from the viewpoint of mechanical strength and heat resistance.

  Examples of the alicyclic structure include a saturated alicyclic hydrocarbon (cycloalkane) structure and an unsaturated alicyclic hydrocarbon (cycloalkene, cycloalkyne) structure. Of these, a cycloalkane structure and a cycloalkene structure are preferable, and a cycloalkane structure is particularly preferable, from the viewpoint of mechanical strength and heat resistance.

  The number of carbon atoms constituting the alicyclic structure is preferably 4 or more, more preferably 5 or more, preferably 30 or less, more preferably 20 or less, and particularly preferably, per alicyclic structure. Is a range of 15 or less. By setting the number of carbon atoms constituting the alicyclic structure within this range, the mechanical strength, heat resistance, and moldability of the resin (B) containing the polymer having the alicyclic structure are highly balanced.

  In the polymer having an alicyclic structure, the proportion of structural units having an alicyclic structure can be appropriately selected according to the purpose of use. The proportion of structural units having an alicyclic structure in the polymer having an alicyclic structure is preferably 55% by weight or more, more preferably 70% by weight or more, and particularly preferably 90% by weight or more. When the ratio of the structural unit having an alicyclic structure in the polymer having an alicyclic structure is within this range, the resin (B) containing the polymer having the alicyclic structure has good transparency and heat resistance. Become.

Among the polymers having an alicyclic structure, cycloolefin polymers are preferable. The cycloolefin polymer is a polymer having a structure obtained by polymerizing a cycloolefin monomer. The cycloolefin monomer is a compound having a ring structure formed of carbon atoms and having a polymerizable carbon-carbon double bond in the ring structure. Examples of the polymerizable carbon-carbon double bond include a polymerizable carbon-carbon double bond such as ring-opening polymerization. Moreover, examples of the ring structure of the cycloolefin monomer include a monocycle, a polycycle, a condensed polycycle, a bridged ring, and a polycycle combining these. Among them, a polycyclic cycloolefin monomer is preferable from the viewpoint of highly balancing the dielectric properties and heat resistance of the polymer.
When a cycloolefin polymer is used as the polymer having an alicyclic structure and an acrylic polymer is used as the polymer contained in the thermoplastic resin (A), the cycloolefin polymer has high flexibility. The layer A containing the acrylic polymer can be protected by the layer B to increase the mechanical strength of the multilayer film to suppress breakage, or to improve the handling property of the multilayer film.

  Among the cycloolefin polymers, preferred are norbornene-based polymers, monocyclic cycloolefin-based polymers, cyclic conjugated diene-based polymers, and hydrogenated products thereof. Among these, the norbornene-based polymer is particularly preferable because it has good moldability.

  Examples of norbornene-based polymers include ring-opening polymers of monomers having a norbornene structure and hydrogenated products thereof; addition polymers of monomers having a norbornene structure and hydrogenated products thereof. Further, examples of the ring-opening polymer of a monomer having a norbornene structure include ring-opening homopolymers of one kind of monomer having a norbornene structure and ring-opening of two or more kinds of monomers having a norbornene structure. Examples thereof include a copolymer, a monomer having a norbornene structure, and a ring-opening copolymer with an arbitrary monomer copolymerizable therewith. Further, examples of addition polymers of monomers having a norbornene structure include addition homopolymers of one kind of monomer having a norbornene structure and addition copolymers of two or more kinds of monomers having a norbornene structure. And an addition copolymer with a monomer having a norbornene structure and an arbitrary monomer copolymerizable therewith. Among these, the hydrogenated product of a ring-opening polymer of a monomer having a norbornene structure is particularly preferable from the viewpoint of moldability, heat resistance, low hygroscopicity, dimensional stability, light weight and the like.

Examples of the monomer having a norbornene structure include bicyclo [2.2.1] hept-2-ene (conventional name: norbornene), tricyclo [4.3.0.1 ^2,5 ] deca-3,7. - diene (common name: dicyclopentadiene), 7,8-tricyclo [4.3.0.1 ^{2, 5]} dec-3-ene (common name: methanolate tetrahydrofluorene), tetracyclo [4.4. 0.1 ^2,5 . 1 ^7,10 ] dodec-3-ene (conventional name: tetracyclododecene), and derivatives of these compounds (for example, those having a substituent on the ring) and the like. Here, examples of the substituent include an alkyl group, an alkylene group, and a polar group. A plurality of these substituents may be the same or different and may be bonded to the ring. As the monomer having a norbornene structure, one kind may be used alone, or two kinds or more may be used in combination at an arbitrary ratio.

  Examples of the type of polar group include a hetero atom or an atomic group having a hetero atom. Examples of the hetero atom include oxygen atom, nitrogen atom, sulfur atom, silicon atom and halogen atom. Specific examples of the polar group include a carboxyl group, a carbonyloxycarbonyl group, an epoxy group, a hydroxyl group, an oxy group, an ester group, a silanol group, a silyl group, an amino group, a nitrile group, and a sulfonic acid group.

  Examples of the monomer having a norbornene structure and a monomer capable of ring-opening copolymerization include, for example, monocyclic olefins such as cyclohexene, cycloheptene, cyclooctene and derivatives thereof; cyclic conjugated dienes such as cyclohexadiene and cycloheptadiene, and Its derivative; and the like. As the monomer having a norbornene structure and the monomer capable of ring-opening copolymerization, one type may be used alone, or two or more types may be used in combination at an arbitrary ratio.

  The ring-opening polymer of a monomer having a norbornene structure can be produced, for example, by polymerizing or copolymerizing the monomer in the presence of a ring-opening polymerization catalyst.

  Examples of the monomer capable of addition copolymerization with the monomer having a norbornene structure include ethylene, propylene, 1-butene, and other α-olefins having 2 to 20 carbon atoms and their derivatives; cyclobutene, cyclopentene, cyclohexene. And the like; and non-conjugated dienes such as 1,4-hexadiene, 4-methyl-1,4-hexadiene, and 5-methyl-1,4-hexadiene; and the like. Of these, α-olefins are preferable, and ethylene is more preferable. Moreover, the monomer having a norbornene structure and the monomer capable of addition copolymerization may be used alone or in combination of two or more kinds at an arbitrary ratio.

  The addition polymer of a monomer having a norbornene structure can be produced, for example, by polymerizing or copolymerizing the monomer in the presence of an addition polymerization catalyst.

  The hydrogenated product of the ring-opening polymer and addition polymer described above is, for example, carbon-carbon in a solution of the ring-opening polymer and addition polymer in the presence of a hydrogenation catalyst containing a transition metal such as nickel or palladium. Unsaturated bonds can be produced by hydrogenating, preferably 90% or more.

Among the norbornene-based polymers, X: bicyclo [3.3.0] octane-2,4-diyl-ethylene structure and Y: tricyclo [4.3.0.1 ^2,5 ] decane-as structural units. 7,9-diyl-ethylene structure, the amount of these structural units is 90% by weight or more based on the total structural units of the norbornene-based polymer, and the proportion of X and the proportion of Y It is preferable that the ratio is 100: 0 to 40:60 by weight ratio of X: Y. By using such a polymer, the B layer containing the norbornene-based polymer can be made to have excellent dimensional stability without dimensional change in the long term.

  Examples of the monocyclic cycloolefin-based polymer include addition polymers of monocyclic cycloolefin-based monomers such as cyclohexene, cycloheptene, and cyclooctene.

  Examples of the cyclic conjugated diene-based polymer include a polymer obtained by cyclizing an addition polymer of a conjugated diene-based monomer such as 1,3-butadiene, isoprene, chloroprene; cyclopentadiene, cyclohexadiene, and the like. Examples thereof include 1,2- or 1,4-addition polymers of diene-based monomers; and hydrogenated products thereof.

  The weight average molecular weight (Mw) of the polymer having an alicyclic structure is preferably 10,000 or more, more preferably 15,000 or more, particularly preferably 20,000 or more, preferably 100,000 or less, It is preferably 80,000 or less, particularly preferably 50,000 or less. When the weight average molecular weight is in such a range, the mechanical strength and moldability of the B layer are highly balanced. The weight average molecular weight (Mw) is calculated by gel permeation chromatography using cyclohexane as a solvent (however, toluene may be used when the sample does not dissolve in cyclohexane), and is converted into polyisoprene or polystyrene. It can be measured as a weight average molecular weight.

  The molecular weight distribution (weight average molecular weight (Mw) / number average molecular weight (Mn)) of the polymer having an alicyclic structure is preferably 1.2 or more, more preferably 1.5 or more, and particularly preferably 1.8 or more. And is preferably 3.5 or less, more preferably 3.0 or less, and particularly preferably 2.7 or less. When the molecular weight distribution is not less than the lower limit of the above range, the productivity of the polymer can be increased and the production cost can be suppressed. Further, when the amount is less than or equal to the upper limit, the amount of the low molecular weight component becomes small, so that relaxation at the time of high temperature exposure can be suppressed and the stability of the B layer can be increased.

  The saturated water absorption of the polymer having an alicyclic structure is preferably 0.03% by weight or less, more preferably 0.02% by weight or less, and particularly preferably 0.01% by weight or less. When the saturated water absorption is within the above range, it is possible to reduce a change with time in optical characteristics such as retardation of the B layer. Further, it is possible to suppress deterioration of the polarizing plate and the liquid crystal display device provided with the multilayer film, and it is possible to maintain stable and good display of the image display device for a long period of time.

  The saturated water absorption is a value in which the mass increased by immersing the test piece in water at a constant temperature for a certain time is expressed as a percentage with respect to the mass of the test piece before the immersion. Usually, it is measured by immersing it in water at 23 ° C. for 24 hours. The saturated water absorption in the polymer can be adjusted to the above range by, for example, decreasing the amount of polar groups in the polymer. Therefore, from the viewpoint of further lowering the saturated water absorption, the polymer having an alicyclic structure preferably does not have a polar group.

  The amount of the polymer having an alicyclic structure in the resin (B) is preferably 50% by weight to 100% by weight, more preferably 70% by weight to 100% by weight. By controlling the amount of the polymer having an alicyclic structure within the above range, the B layer having desired characteristics can be easily realized.

  The resin (B) may contain any component other than the above-mentioned polymer unless the effects of the present invention are significantly impaired. As an example of the optional component, the same component as the optional component that can be contained in the resin (A) can be mentioned. One kind of these components may be used alone, or two or more kinds thereof may be used in combination at an arbitrary ratio.

  The glass transition temperature TgB of the resin (B) can be appropriately set within the range that satisfies the above formula (i). Specifically, the glass transition temperature TgB of the resin (B) is preferably 100 ° C. or higher, more preferably 110 ° C. or higher, particularly preferably 120 ° C. or higher, preferably 160 ° C. or lower, more preferably 150 ° C. or lower. And particularly preferably 140 ° C or lower. By setting the glass transition temperature TgB of the resin (B) to the lower limit value of the above range or higher, the durability of the B layer in a high temperature environment can be increased, and by setting it to the upper limit value or lower, the stretching treatment becomes easy. You can do it.

The absolute value of the photoelastic coefficient of the resin (B) is preferably 10 × 10 ⁻¹² Pa ⁻¹ or less, more preferably 7 × 10 ⁻¹² Pa ⁻¹ or less, particularly preferably 4 × 10 ⁻¹² Pa ⁻¹ or less. Is. This makes it possible to reduce variations in retardation of the B layer. Here, the photoelastic coefficient C is a value represented by C = Δn / σ when birefringence is Δn and stress is σ.

  It is preferable that the layer B exhibits retardation by being stretched. The retardation range of the B layer can be appropriately set according to the use of the release film when the B layer is peeled from the A layer and handled as an independent release film. Specifically, the in-plane retardation ReB of the B layer is preferably 1 nm or more, more preferably 10 nm or more, particularly preferably 20 nm or more, preferably 500 nm or less, more preferably 400 nm or less, particularly preferably 300 nm or less. Is.

  The total light transmittance of the layer B is preferably 80% or more, more preferably 90% or more. The haze of the B layer is preferably 0.3% or less, more preferably 0.2% or less.

  The amount of the volatile component in the B layer is preferably 0.1% by weight or less, more preferably 0.05% by weight or less, still more preferably 0.02% by weight or less. By setting the amount of the volatile component within the above range, the dimensional stability of the B layer can be improved and the change with time of the optical characteristics such as retardation can be reduced. Furthermore, when the B layer is used as an independent release film, deterioration of the polarizing plate and the liquid crystal display device provided with the release film can be suppressed, and stable and favorable display of the liquid crystal display device can be maintained for a long period of time.

  As described above, the multilayer film of the present invention can suppress damage to each layer even if each layer included in the multilayer film is thin. Therefore, according to the multilayer film of the present invention, it is possible to reduce the thickness tb of the B layer. Specifically, the thickness tb of the B layer is usually 15 μm or less, and preferably 14 μm or less, and more preferably 13 μm or less from the viewpoint that the winding diameter can be reduced and a long length can be wound. The lower limit of the thickness tb of the B layer is usually 4 μm or more, preferably 5 μm or more, more preferably 6 μm or more. By setting the thickness tb of the B layer to be equal to or more than the lower limit value, it is possible to suppress damage to the B layer when the B layer is peeled from the A layer.

[1.3. B'layer]
The B'layer is made of a resin (B ') containing a polymer having an alicyclic structure. As the resin (B ′), any resin selected from the range of the resins described as the resin (B) can be used. Therefore, the content and properties of the resin (B ′) can be selected and applied from the ranges described as the content and properties of the resin (B). As a result, the B ′ layer can obtain the same advantages as the B layer.

  As the resin (B ′), a resin different from the resin (B) may be used, or the same resin as the resin (B) may be used. Among them, the in-plane retardation ReB of the B layer and the in-plane retardation ReB ′ of the B ′ layer are measured by making the photoelastic coefficient of the resin (B) and the photoelastic coefficient of the resin (B ′) the same. It is preferable to use the same resin as the resin (B) and the resin (B ′) because they can be easily performed. Further, by using the same resin as the resin (B) and the resin (B ′), curling of the multilayer film can be effectively suppressed.

  It is preferable that the B'layer exhibits retardation by being stretched. The retardation range of the B'layer can be appropriately set according to the application of the release film when the B'layer is peeled from the A layer and handled as an independent release film. Specifically, the in-plane retardation ReB 'of the B'layer can be selected from the same range as the range of the in-plane retardation ReB of the B layer.

  There is no limitation on the total light transmittance of the B'layer, the haze, and the amount of the volatile component, and it can be selected from the same range as the total light transmittance, the haze, and the amount of the volatile component of the B layer. As a result, the B'layer can obtain the same advantages as the B layer.

  As described above, the multilayer film of the present invention can suppress damage to each layer even if each layer included in the multilayer film is thin. Therefore, according to the multilayer film of the present invention, it is possible to reduce the thickness tb 'of the B'layer. Specifically, the thickness tb 'of the B'layer is usually 15 μm or less, and is preferably 14 μm or less, more preferably 13 μm or less from the viewpoint that a long diameter can be wound by reducing the winding diameter. The lower limit of the thickness tb 'of the B'layer is usually 4 µm or more, preferably 5 µm or more, more preferably 6 µm or more. By setting the thickness tb 'of the B'layer to be the lower limit value or more, it is possible to suppress damage to the B'layer when the B'layer is peeled from the A layer.

[1.4. Optional layer]
The multilayer film of the present invention may further include an optional layer in addition to the A layer, the B layer and the B'layer. For example, an arbitrary layer may be provided on the surface of the B layer on the opposite side of the A layer and on the surface of the B ′ layer on the opposite side of the A layer. However, from the viewpoint of reducing the thickness of the release film obtained by peeling A layer, B layer and B ′ layer from the multilayer film, the multilayer film has only three layers of A layer, B layer and B ′ layer. It is preferable.

[1.5. Method for producing multilayer film]
There is no limitation on the method for producing the multilayer film of the present invention. The multilayer film can be manufactured by a manufacturing method including a molding method such as a co-extrusion method and a co-casting method. Among the molding methods, the coextrusion method is preferable because it is excellent in production efficiency and it is difficult for volatile components to remain in the multilayer film.

  The co-extrusion method includes an extrusion step of co-extruding the thermoplastic resin (A), the resin (B) and the resin (B '). In the extrusion step, the thermoplastic resin (A), the resin (B) and the resin (B ') are extruded in layers in a molten state. At this time, examples of the resin extrusion method include a co-extrusion T-die method, a co-extrusion inflation method, and a co-extrusion lamination method. Of these, the co-extrusion T-die method is preferable. The co-extrusion T-die method includes a feed block method and a multi-manifold method, and the multi-manifold method is particularly preferable from the viewpoint that thickness variation can be reduced.

  In the extrusion step, the melting temperature of the extruded thermoplastic resin (A), resin (B) and resin (B ′) is preferably Tg + 80 ° C. or higher, more preferably Tg + 100 ° C. or higher, preferably Tg + 180 ° C. or lower, It is preferably Tg + 150 ° C. or lower. Here, "Tg" represents the highest temperature of the glass transition temperature TgA of the thermoplastic resin (A), the glass transition temperature TgB of the resin (B), and the glass transition temperature TgB 'of the resin (B'). By setting the melting temperature of the extruded resin to the lower limit value of the above range or more, the fluidity of the thermoplastic resin (A), the resin (B) and the resin (B ′) can be sufficiently enhanced to improve the moldability, Further, by setting the upper limit value or less, deterioration of the thermoplastic resin (A), the resin (B) and the resin (B ′) can be suppressed.

  In the coextrusion method, usually, a film-shaped molten resin extruded from a lip of a die is brought into close contact with a cooling roll to be cooled and cured. At this time, examples of the method for bringing the molten resin into close contact with the cooling roll include an air knife method, a vacuum box method, and an electrostatic contact method.

  The number of cooling rolls is not particularly limited and is usually two or more. Examples of the arrangement method of the cooling rolls include linear type, Z type, and L type. At this time, the method for passing the molten resin extruded from the lip of the die through the cooling roll is not particularly limited.

  By forming the thermoplastic resin (A), the resin (B) and the resin (B ′) into layers in the extrusion step, the thermoplastic resin (A) layer, the resin (B) layer and the resin (B ′) are formed. A long raw film having the following layers is obtained. In the method for producing a multilayer film, the multilayer film of the present invention may be produced as the raw film. Further, in the method for producing a multilayer film, the multilayer film may be produced as a stretched film by using the raw film as a pre-stretch film and performing a stretching step of stretching the pre-stretch film.

  Examples of the stretching method include a method of uniaxially stretching in the longitudinal direction by utilizing the difference in peripheral speed between rolls (longitudinal uniaxial stretching method); a method of uniaxially stretching in the width direction using a tenter (horizontal uniaxial stretching method); Method of sequentially performing longitudinal uniaxial stretching and transverse uniaxial stretching (sequential biaxial stretching method); Method of simultaneously performing longitudinal stretching and transverse stretching (simultaneous biaxial stretching method); Method of stretching film before stretching in oblique direction (oblique stretching) Method); and the like. Here, the “oblique direction” means a direction that is neither parallel nor perpendicular to the longitudinal direction of the film.

  The stretching temperature Ts in the stretching step is preferably higher than TgA + 26 ° C, more preferably higher than TgA + 30 ° C, and particularly preferably higher than TgA + 35 ° C. By setting the stretching temperature Ts to such a temperature, the desired retardation can be stably expressed in the B layer and the B'layer while suppressing the expression of the retardation in the A layer. The stretching temperature Ts is preferably lower than TgB + 30 ° C, more preferably lower than TgB + 27 ° C, particularly preferably lower than TgB + 25 ° C, and preferably lower than TgB ′ + 30 ° C, more preferably lower than TgB ′ + 27 ° C, particularly preferably lower than TgB ′ + 27 ° C. Is less than TgB ′ + 25 ° C. By setting the stretching temperature to such a temperature, sticking of the stretched film to the stretching device can be suppressed, and thus damage to the stretched film can be effectively suppressed.

  The stretch ratio of the stretched film is preferably 1.05 times or more, more preferably 1.1 times or more, particularly preferably 1.15 times or more, preferably 10 times or less, more preferably 7 times or less, particularly preferably Is 5 times or less. Here, when the stretching treatment is performed in two or more steps, the product of the stretching ratios in each step is preferably within the above range. By setting the stretching ratio within the above range, desired retardation can be expressed in the B layer and the B'layer.

  By stretching the unstretched film as described above, a multilayer film having A layer, B layer and B'layer having a desired thickness can be produced as a stretched film. At this time, in the stretched film produced by stretching at the stretching temperature Ts described above, the retardation does not usually appear in the A layer, and the retardation stably appears in the B layer. Therefore, when the photoelastic coefficient of the resin (B) and the photoelastic coefficient of the resin (B ′) are the same, for example, when the same resin is used as the resin (B) and the resin (B ′), The in-plane retardation ReB of the B layer and the in-plane retardation ReB ′ of the B ′ layer of the stretched film are calculated from the in-plane retardation ReO of the stretched film as a whole, the thickness tb of the B layer and the thickness Tb ′ of the B ′ layer, It can be easily measured.

The method for measuring the in-plane retardation of the B layer and the B ′ layer can be performed as follows.
When the in-plane retardation ReA of the A layer is substantially zero, the in-plane retardation ReO of the entire multilayer film is the in-plane retardation ReB of the B layer and the in-plane retardation ReB of the B ′ layer. Is the sum of Further, the in-plane retardation ReB of the B layer and the in-plane retardation ReB ′ of the B ′ layer are respectively proportional to the thickness tb of the B layer and the thickness tb ′ of the B ′ layer. Therefore, when the thickness tb of the B layer and the thickness tb ′ of the B ′ layer are known, the in-plane retardation ReB and the B ′ layer of the B layer are measured by measuring the in-plane retardation ReO of the entire multilayer film. The in-plane retardation ReB ′ is calculated by the following formula.
ReB = ReO × {tb / (tb + tb ′)}
ReB ′ = ReO × {tb ′ / (tb + tb ′)}
With such a measuring method, the in-plane retardation ReB of the B layer and the in-plane retardation ReB ′ of the B ′ layer can be measured without peeling the B layer and the B ′ layer from the A layer.

The method for producing a multilayer film of the present invention may further include any step in addition to the above-mentioned extrusion step and stretching step.
For example, the method for producing a multilayer film may include a step of subjecting the surface of the multilayer film to a surface treatment. Examples of the surface treatment include plasma treatment, corona treatment, alkali treatment, coating treatment and the like.

[2. Peeling of layers from multi-layer film]
As described above, the multilayer film of the present invention includes the thin A layer, B layer and B ′ layer. Further, since the adhesiveness between the A layer and the B layer is low, the A layer and the B layer can be easily peeled off. Furthermore, since the adhesiveness between the A layer and the B ′ layer is low, the A layer and the B ′ layer can be easily peeled off. Therefore, by performing the step of peeling at least one layer selected from the group consisting of A layer, B layer and B ′ layer from the multilayer film of the present invention, A layer, B layer and B ′ layer have independent thicknesses. Can be taken out as a thin release film. The release film thus taken out may have a thin thickness which is difficult to realize by the conventional manufacturing method.

  The method of peeling each layer from the multilayer film is not particularly limited. For example, there may be mentioned a method in which a multilayer film is wound into a roll and a desired layer is peeled off using a winder provided after this roll. In this method, when the multi-layer film is unwound by rotating the roll, the winding machine is rotated in the opposite direction of the roll to wind the desired layer while unwinding the multi-layer film. Then, the layer can be peeled off.

  The release film taken out from the multilayer film can be applied to any application by utilizing its thin thickness. Among them, the release film is preferably used as an optical film, for example, as a protective film for a polarizing plate; a retardation film and an optical compensation film for a liquid crystal display device;

[3. Polarizer]
The polarizing plate usually includes a polarizing film and a protective film provided on at least one side of the polarizing film. The A layer, B layer or B ′ layer obtained as an independent release film by peeling from the multilayer film of the present invention may be used as the protective film for the polarizing plate. Such a polarizing plate usually comprises a polarizing film and a peeling film as at least one layer selected from the group consisting of A layer, B layer and B ′ layer obtained by peeling from the multilayer film.

  The polarizing plate as described above is obtained, for example, by a step of peeling at least one layer selected from the group consisting of A layer, B layer and B ′ layer from the multilayer film of the present invention; It is possible to produce a polarizing plate by laminating a polarizing film and a release film as at least one layer selected from the group consisting of A layer, B layer and B ′ layer.

  As the polarizing film, a film capable of transmitting one of two linearly polarized lights intersecting at right angles and absorbing or reflecting the other can be used. Specific examples of the polarizing film include polyvinyl alcohol, a film of a vinyl alcohol-based polymer such as partially formalized polyvinyl alcohol, iodine, a dyeing treatment with a dichroic substance such as a dichroic dye, a stretching treatment, a crosslinking treatment, etc. Which has been subjected to an appropriate treatment in an appropriate order and manner. In particular, a polarizing film containing polyvinyl alcohol is preferable. The thickness of the polarizing film is usually 5 μm to 80 μm.

  The release film obtained by release from the multilayer film of the present invention may be provided on one side or both sides of the polarizing film. In addition, when the release film and the polarizing film are attached to each other, an adhesive may be used if necessary.

  The polarizing plate may further include an arbitrary layer in combination with the above-mentioned polarizing film and release film. For example, the polarizing plate may be provided with any film layer other than the release film obtained by peeling from the multilayer film of the present invention for protecting the polarizing film.

[4. Liquid crystal display]
The A layer, B layer or B ′ layer, which is obtained as an independent peeling film by peeling from the multilayer film of the present invention, may be provided in the liquid crystal display device. Such a liquid crystal display device can be provided with a release film as at least one layer selected from the group consisting of A layer, B layer and B ′ layer obtained by peeling from the multilayer film at any position.

  A liquid crystal display device usually includes a liquid crystal panel including a light incident side polarization film, a liquid crystal cell, and a light emission side polarization film in this order. The release film can be provided on this liquid crystal panel, for example. As a specific example, the release film can be provided between the liquid crystal cell and the light incident side polarizing plate, between the liquid crystal cell and the light emitting side polarizing plate, and the like. Such a liquid crystal display device includes, for example, a step of peeling at least one layer selected from the group consisting of A layer, B layer and B ′ layer from the multilayer film of the present invention; And a release film as at least one layer selected from the group consisting of the A layer, the B layer, and the B ′ layer thus obtained is provided on the liquid crystal panel.

  Liquid crystal cell driving methods include, for example, in-plane switching (IPS) mode, vertical alignment (VA) mode, multi-domain vertical alignment (MVA) mode, continuous spin wheel alignment (CPA) mode, and hybrid alignment nematic (HAN). Mode, twisted nematic (TN) mode, super twisted nematic (STN) mode, optical compensated bend (OCB) mode and the like.

Hereinafter, the present invention will be described specifically with reference to examples. However, the present invention is not limited to the examples shown below, and may be implemented by being arbitrarily modified within the scope of the claims of the present invention and the scope of equivalents thereof.
In the following description, "%" and "parts" representing amounts are by weight unless otherwise specified. In addition, the operations described below were performed in a normal temperature and normal pressure atmosphere unless otherwise specified.

[Evaluation methods]
(Measuring method of glass transition temperature of resin)
A resin pellet as a sample was prepared, and the glass transition temperature of the resin pellet was measured using a differential scanning calorimeter (“DSC6220” manufactured by Seiko Instruments Inc.). The conditions were a sample weight of 10 mg and a heating rate of 20 ° C./min.

(Method of measuring the thickness of each layer)
A test piece was prepared by embedding the multilayer film in an epoxy resin, and the test piece was sliced using a microtome (“RV-240” manufactured by Daiwa Koki Co., Ltd.). The cut surface of the sliced test piece was observed with a polarization microscope (“BX51” manufactured by Olympus Corporation) to measure the thickness of each layer included in the multilayer film.

(Measurement method of retardation of each layer)
Each layer was peeled from the stretched film. The in-plane retardation Re of each layer after peeling was measured with an automatic birefringence meter (“KOBRA-21ADH” manufactured by Oji Scientific Instruments) at a measurement wavelength of 590 nm.

(Evaluation method of releasability of each layer)
The multilayer film was cut into 100 mm × 100 mm, and cellophane tape (“CT24” manufactured by Nichiban) was attached to the corners of the B layer and the B ′ layer, respectively. By pulling the cellophane tapes in opposite directions, the layers B and B ′ were slowly peeled vertically, and the layers were separated to obtain a release film. At this time, when each of the layers A, B and B ′ could be separated without breaking, it was determined that the peelability was good. Further, when any one of the A layer, the B layer and the B ′ layer was broken, the peelability was determined to be poor.

(Evaluation method of releasability from stretched clip)
After the stretching, the stretching clip was opened to visually observe how the stretched film was removed from the stretching clip, and it was examined whether the stretched film was attached to the stretching clip. When the stretched clip was opened, the multi-layer film did not stick to the stretched clip, and when the layers of the stretched film remained in close contact with each other, it was determined that the releasability was good. Further, when the stretched film was attached to the stretched clip when the stretched clip was opened and the stretched film was pulled in the thickness direction, and peeling of the layer or breakage of the layer occurred, it was determined that the releasability was poor.

[Example 1]
A film forming apparatus for coextrusion molding of three kinds of three layers (of a type capable of producing a multilayer film composed of three layers by three kinds of resins) was prepared.

  As the thermoplastic resin (A), pellets of an acrylic resin containing an acrylic polymer and rubber particles (glass transition temperature 108 ° C .; “SUMIPEX” manufactured by Sumitomo Chemical Co., Ltd.) are charged into a single-screw extruder equipped with a double flight type screw. And melted.

  As the resin (B), pellets of a resin containing a cycloolefin polymer (glass transition temperature 136 ° C .; “ZEONOR 1420R” manufactured by Nippon Zeon Co., Ltd.) were charged into a single-screw extruder equipped with a double flight type screw and melted. It was

  As the resin (B '), pellets of a resin containing a cycloolefin polymer (glass transition temperature 136 ° C; "ZEONOR 1420R" manufactured by Nippon Zeon Co., Ltd.) were charged into a single-screw extruder equipped with a double flight type screw and melted. Let

  The molten resin (A), resin (B), and resin (B ') were supplied to each manifold of a T-die having a multi-manifold through a leaf disk-shaped polymer filter. And these resin (A), resin (B), and resin (B ') were simultaneously extruded into a film form from the T die. The molten resin thus extruded in a film shape was cast on a cooling roll to obtain a multilayer film having a three-layer structure and a width of 1350 mm. This multilayer film comprises a B layer made of a resin (B), an A layer made of a thermoplastic resin (A), and a B ′ layer made of a resin (B ′) in this order, and the thickness of the A layer is 28 μm. The thickness of the B layer was 9 μm, and the thickness of the B ′ layer was 9 μm.

  The produced multilayer film was evaluated by the method described above. When each layer was peeled off with cellophane tape, peeling was easy.

[Example 2]
A multilayer film having a three-layer structure with a width of 1350 mm was produced and evaluated in the same manner as in Example 1 except that the opening width of the T-die and the extrusion amount of each resin were changed.
The produced multilayer film includes a B layer made of the resin (B), an A layer made of the thermoplastic resin (A), and a B'layer made of the resin (B ') in this order, and the thickness of the A layer is The thickness of the B layer was 22 μm, the thickness of the B layer was 6 μm, and the thickness of the B ′ layer was 6 μm. When each layer was peeled off with cellophane tape, peeling was easy.

[Example 3]
As the resin (B), instead of the resin containing a cycloolefin polymer (glass transition temperature 136 ° C .; “ZEONOR1420R” manufactured by Nippon Zeon Co., Ltd.), a resin containing a cycloolefin polymer (glass transition temperature 160 ° C .; manufactured by Nippon Zeon Co., Ltd.) "ZEONOR 1600") was used. Further, as the resin (B ′), a resin containing a cycloolefin polymer (glass transition temperature 136 ° C .; “ZEONOR1420R” manufactured by Nippon Zeon Co., Ltd.) instead of a resin containing a cycloolefin polymer (glass transition temperature 160 ° C .; Japan “ZEONOR1600” manufactured by Zeon Co., Ltd. was used. Further, the opening width of the T die and the extrusion amount of each resin were changed. A multilayer film having a three-layer structure and a width of 1350 mm was manufactured and evaluated in the same manner as in Example 1 except for the above matters.
The produced multilayer film includes a B layer made of the resin (B), an A layer made of the thermoplastic resin (A), and a B'layer made of the resin (B ') in this order, and the thickness of the A layer is 22 μm, the thickness of the B layer was 9 μm, and the thickness of the B ′ layer was 9 μm. When each layer was peeled off with cellophane tape, peeling was easy.

[Example 4]
As the thermoplastic resin (A), an acrylic resin containing an acrylic polymer and rubber particles (glass transition temperature 108 ° C .; “SUMIPEX” manufactured by Sumitomo Chemical Co., Ltd.), but containing an acrylic polymer but not containing rubber particles (Glass transition temperature 102 ° C .; “Delpet” manufactured by Asahi Kasei Corp.) was used. Further, the opening width of the T die and the extrusion amount of each resin were changed. A multilayer film having a three-layer structure and a width of 1350 mm was manufactured and evaluated in the same manner as in Example 1 except for the above matters.
The produced multilayer film includes a B layer made of the resin (B), an A layer made of the thermoplastic resin (A), and a B'layer made of the resin (B ') in this order, and the thickness of the A layer is 38 μm, the thickness of the B layer was 9 μm, and the thickness of the B ′ layer was 9 μm. When each layer was peeled off with cellophane tape, peeling was easy.

[Example 5]
As the thermoplastic resin (A), instead of an acrylic resin containing an acrylic polymer and rubber particles (glass transition temperature 108 ° C .; “SUMIPEX” manufactured by Sumitomo Chemical Co., Ltd.), a resin containing a styrene-methyl methacrylate copolymer (glass transition A temperature of 100 ° C .; manufactured by Denki Kagaku) was used. Further, the opening width of the T die and the extrusion amount of each resin were changed. A multilayer film having a three-layer structure and a width of 1350 mm was manufactured and evaluated in the same manner as in Example 1 except for the above matters.
The produced multilayer film comprises an A layer made of a resin (B), an A layer made of a thermoplastic resin (A), and a B'layer made of a multilayer layer made of a resin (B ') in this order. The layer thickness was 38 μm, the B layer thickness was 9 μm, and the B ′ layer thickness was 9 μm. When each layer was peeled off with cellophane tape, peeling was easy.

[Example 6]
A pre-stretch film having a three-layer structure and a width of 1350 mm was produced in the same manner as in Example 1 except that the opening width of the T-die and the extrusion amount of each resin were changed. This unstretched film comprises a B layer made of a resin (B), an A layer made of a thermoplastic resin (A), and a B ′ layer made of a resin (B ′) in this order, and the A layer has a thickness of 32 μm. The thickness of the B layer was 46 μm, and the thickness of the B ′ layer was 46 μm.

  The unstretched film produced above was supplied to a transverse stretching machine equipped with a stretching clip capable of gripping both widthwise ends of the unstretched film, and stretched at a stretching temperature of 150 ° C. and a stretching ratio of 4.6 times. The film was stretched in the width direction by pulling to obtain a stretched film as a multilayer film. This stretched film is provided with a B layer made of a resin (B), an A layer made of a thermoplastic resin (A), and a B ′ layer made of a resin (B ′) in this order, and the thickness of the A layer is 7 μm, The thickness of the B layer was 10 μm, and the thickness of the B ′ layer was 10 μm.

  The produced stretched film was evaluated by the method described above. When each layer of the stretched film was peeled off with cellophane tape, peeling was easy. Further, the stretched film did not stick to the stretched clip, and the releasability was good. Furthermore, the in-plane retardation Re of the A layer of the stretched film was 0 nm, the in-plane retardation Re of the B layer was 118 nm, and the in-plane retardation Re of the B'layer was 118 nm.

[Example 7]
A pre-stretch film having a three-layer structure and a width of 1350 mm was produced in the same manner as in Example 1 except that the opening width of the T-die and the extrusion amount of each resin were changed. This unstretched film comprises a B layer made of a resin (B), an A layer made of a thermoplastic resin (A), and a B'layer made of a resin (B ') in this order, and the thickness of the A layer is 28 μm. The thickness of the B layer was 55 μm, and the thickness of the B ′ layer was 55 μm.

  The pre-stretched film produced above was supplied to a transverse stretching machine equipped with a stretch clip capable of gripping both widthwise ends of the pre-stretched film, and stretched at a stretching temperature of 152 ° C. and a stretching ratio of 4.6 times. The film was stretched in the width direction by pulling to obtain a stretched film as a multilayer film. This stretched film is provided with a B layer made of a resin (B), an A layer made of a thermoplastic resin (A), and a B'layer made of a resin (B ') in this order, and the thickness of the A layer is 6 μm, B The layer thickness was 12 μm, and the B ′ layer thickness was 12 μm.

  The produced stretched film was evaluated by the method described above. When each layer of the stretched film was peeled off with cellophane tape, peeling was easy. Further, the stretched film did not stick to the stretched clip, and the releasability was good. Furthermore, the in-plane retardation Re of the A layer of the stretched film was 0 nm, the in-plane retardation Re of the B layer was 118 nm, and the in-plane retardation Re of the B'layer was 118 nm.

[Example 8]
A pre-stretch film having a three-layer structure and a width of 1350 mm was produced in the same manner as in Example 1 except that the opening width of the T-die and the extrusion amount of each resin were changed. This unstretched film comprises a B layer made of a resin (B), an A layer made of a thermoplastic resin (A), and a B ′ layer made of a resin (B ′) in this order, and the A layer has a thickness of 11 μm. The B layer had a thickness of 19 μm, and the B ′ layer had a thickness of 19 μm.

  The unstretched film produced above was supplied to an oblique stretching machine equipped with a stretching clip capable of gripping both ends in the width direction of the unstretched film, and stretched with a stretching clip at a stretching temperature of 144 ° C. and a stretching ratio of 1.35. By pulling, the film was stretched in an oblique direction forming an angle of 45 ° with respect to the width direction to obtain a stretched film as a multilayer film. This stretched film comprises a B layer made of a resin (B), an A layer made of a thermoplastic resin (A), and a B'layer made of a resin (B ') in this order, and the thickness of the A layer is 8 μm, The layer thickness was 14 μm, and the B ′ layer thickness was 14 μm.

  The produced stretched film was evaluated by the method described above. When each layer of the stretched film was peeled off with cellophane tape, peeling was easy. Further, the stretched film did not stick to the stretched clip, and the releasability was good. Furthermore, the in-plane retardation Re of the A layer of the stretched film was 0.1 nm, the in-plane retardation Re of the B layer was 99 nm, and the in-plane retardation Re of the B'layer was 99 nm.

[Comparative Example 1]
A multilayer film having a three-layer structure with a width of 1350 mm was produced and evaluated in the same manner as in Example 1 except that the opening width of the T-die and the extrusion amount of each resin were changed.
The produced multilayer film includes a B layer made of the resin (B), an A layer made of the thermoplastic resin (A), and a B'layer made of the resin (B ') in this order, and the thickness of the A layer is The thickness of the layer B was 28 μm, the thickness of the layer B was 2 μm, and the thickness of the layer B ′ was 2 μm. Further, when each layer was peeled off with a cellophane tape, the B layer and the B ′ layer were broken, and peeling was difficult.

[Comparative Example 2]
A multilayer film having a three-layer structure with a width of 1350 mm was produced and evaluated in the same manner as in Example 1 except that the opening width of the T-die and the extrusion amount of each resin were changed.
The produced multilayer film includes a B layer made of the resin (B), an A layer made of the thermoplastic resin (A), and a B'layer made of the resin (B ') in this order, and the thickness of the A layer is The thickness of the B layer was 2 μm, the thickness of the B layer was 9 μm, and the thickness of the B ′ layer was 9 μm. When each layer was peeled off with cellophane tape, the layer A was broken and it was difficult to peel off.

[Comparative Example 3]
A pre-stretch film having a three-layer structure and a width of 1350 mm was produced in the same manner as in Example 1 except that the opening width of the T-die and the extrusion amount of each resin were changed. This unstretched film comprises a B layer made of a resin (B), an A layer made of a thermoplastic resin (A), and a B'layer made of a resin (B ') in this order, and the thickness of the A layer is 9 μm. The thickness of the B layer was 55 μm, and the thickness of the B ′ layer was 55 μm.

  The pre-stretched film produced above was supplied to a transverse stretching machine equipped with a stretch clip capable of gripping both widthwise ends of the pre-stretched film, and stretched at a stretching temperature of 152 ° C. and a stretching ratio of 4.6 times. The film was stretched in the width direction by pulling to obtain a stretched film as a multilayer film. This stretched film is provided with a B layer made of a resin (B), an A layer made of a thermoplastic resin (A), and a B ′ layer made of a resin (B ′) in this order, and the thickness of the A layer is 2 μm, B The layer thickness was 12 μm, and the B ′ layer thickness was 12 μm. When each layer was peeled off with cellophane tape, the layer A was broken and it was difficult to peel off.

[Comparative Example 4]
As the thermoplastic resin (A), a resin containing a cycloolefin polymer (glass transition temperature 136 ° C., instead of the acrylic resin containing the acrylic polymer and rubber particles (glass transition temperature 108 ° C .; “SUMIPEX” manufactured by Sumitomo Chemical Co., Ltd.) "ZEONOR 1420R" manufactured by Nippon Zeon Co., Ltd.) was used. Further, as the resin (B), an acrylic resin containing a cycloolefin polymer (glass transition temperature 136 ° C .; “ZEONOR 1420R” manufactured by Nippon Zeon Co., Ltd.) and an acrylic resin containing glass particles (glass transition temperature 108 ° C.). "Sumipex" manufactured by Sumitomo Chemical Co., Ltd.) was used. Further, as the resin (B ′), instead of the resin containing a cycloolefin polymer (glass transition temperature 136 ° C .; “ZEONOR1420R” manufactured by Nippon Zeon Co., Ltd.), an acrylic resin containing an acrylic polymer and rubber particles (glass transition temperature 108 ° C; "Sumitepex" manufactured by Sumitomo Chemical Co., Ltd.) was used. Further, the opening width of the T die and the extrusion amount of each resin were changed. A pre-stretch film having a three-layer structure having a width of 1350 mm was produced in the same manner as in Example 1 except for the above matters. This unstretched film comprises a B layer made of a resin (B), an A layer made of a thermoplastic resin (A), and a B ′ layer made of a resin (B ′) in this order, and the A layer has a thickness of 55 μm. The thickness of the B layer was 46 μm, and the thickness of the B ′ layer was 46 μm.

  The unstretched film produced above was supplied to a transverse stretching machine equipped with a stretching clip capable of gripping both widthwise ends of the unstretched film, and stretched at a stretching temperature of 150 ° C. and a stretching ratio of 4.6 times. The film was stretched in the width direction by pulling to obtain a stretched film as a multilayer film. This stretched film comprises a B layer made of a resin (B), an A layer made of a thermoplastic resin (A), and a B'layer made of a resin (B ') in this order, and the thickness of the A layer is 12 μm and B The layer thickness was 10 μm, and the B ′ layer thickness was 10 μm.

  The produced stretched film was evaluated by the method described above. When each layer of the stretched film was peeled off with cellophane tape, peeling was easy. However, when the stretched film was removed from the stretched clip, sticking of the stretched film to the stretched clip was observed, and the releasability was poor. The in-plane retardation Re of the A layer of the stretched film was 118 nm, the in-plane retardation Re of the B layer was 0 nm, and the in-plane retardation Re of the B'layer was 0 nm.

[result]
The results of the above Examples and Comparative Examples are shown in Tables 1 and 2 below. In the table below, the abbreviations have the following meanings.
B / A / B ': A three-layer structure including a B layer, an A layer, and a B'layer in this order.
TgA: Glass transition temperature of resin (A).
TgB: Glass transition temperature of resin (B).
TgB ': Glass transition temperature of resin (B').
ta: thickness of the A layer.
tb: B layer thickness.
tb ': Thickness of B'layer.
ReA: In-plane retardation of A layer.
ReB: In-plane retardation of layer B.
ReB ': In-plane retardation of B'layer.

[Consideration]
As can be seen from the above Examples and Comparative Examples, the B layer and the B ′ layer can be taken out as independent release films by peeling from the multilayer film of the present invention. Therefore, by using the multilayer film of the present invention, a thin release film composed of the resin (B) or (B ′) containing the polymer having a cyclic structure can be easily produced. Further, by peeling from the multilayer film of the present invention, not only the B layer and the B ′ layer but also the A layer can be taken out as an independent peeling film. Therefore, by using the multilayer film of the present invention, a thin release film made of the thermoplastic resin (A) can be easily manufactured. Furthermore, since the multilayer film of the present invention can suppress sticking to a stretching device during stretching, it is possible to suppress film damage in the stretching step.

Claims (10)

B layer made of a resin (B) containing a polymer having an alicyclic structure, B'layer made of a resin (B ') containing a polymer having an alicyclic structure, the resin (B) and the resin (B ') and the a layer made of the thermoplastic resin (a) and including the rubber particles varies, the B layer, the a layer and the B' provided in the order of layer, a double layer film as the stretched film There
Glass transition temperature TgB of the resin (B), glass transition temperature TgB ′ of the resin (B ′), glass transition temperature TgA of the thermoplastic resin (A), thickness tb of the B layer, thickness of the B ′ layer. tb ′ and the thickness ta of the A layer are
15 ° C ≤ TgB-TgA ≤ 70 ° C
15 ° C ≤ TgB'-TgA ≤ 70 ° C
4 μm ≦ tb ≦ 15 μm
4 μm ≦ tb ′ ≦ 15 μm
5 μm ≦ ta ≦ 40 μm
A multi-layer film that satisfies the requirements.   The polymer having an alicyclic structure contained in the resin (B) and the polymer having an alicyclic structure contained in the resin (B ′) are cycloolefin polymers. Multi-layer film.   The multilayer film according to claim 1 or 2, wherein the thermoplastic resin (A) contains an acrylic polymer. Claim 1 was obtained by peeling from the multilayer film of any one of 3, and at least one layer of the A layer, selected from the group consisting of the B layer and the B 'layer, and the polarizing film A polarizing plate. The polarizing plate according to claim 4 , wherein the polarizing film contains polyvinyl alcohol. A step of peeling at least one layer selected from the group consisting of the A layer, the B layer and the B ′ layer from the multilayer film according to any one of claims 1 to 5 ,
A polarizing plate by laminating a polarizing film with at least one layer selected from the group consisting of the A layer, the B layer and the B ′ layer obtained by peeling from the multilayer film. Method of manufacturing a plate. B layer made of a resin (B) containing a polymer having an alicyclic structure, B'layer made of a resin (B ') containing a polymer having an alicyclic structure, the resin (B) and the resin (B ') and the a layer made of the thermoplastic resin (a) and including the rubber particles varies, the B layer, the a layer and the B' producing a multilayer film as stretched film with the order of layers Method,
Including a step of co-extruding the thermoplastic resin (A), the resin (B) and the resin (B ′),
Glass transition temperature TgB of the resin (B), glass transition temperature TgB ′ of the resin (B ′), glass transition temperature TgA of the thermoplastic resin (A), thickness tb of the B layer, thickness of the B ′ layer. tb ′ and the thickness ta of the A layer are
15 ° C ≤ TgB-TgA ≤ 70 ° C
15 ° C ≤ TgB'-TgA ≤ 70 ° C
4 μm ≦ tb ≦ 15 μm
4 μm ≦ tb ′ ≦ 15 μm
5 μm ≦ ta ≦ 40 μm
A method for producing a multilayer film, which satisfies the above conditions. The unstretched film obtained in the step of coextruding the thermoplastic resin (A), the resin (B) and the resin (B ′),
TgA + 26 ° C <Ts
Ts <TgB + 30 ° C
Ts <TgB '+ 30 ° C
The method for producing a multilayer film according to claim 7 , comprising a step of stretching at a stretching temperature Ts that satisfies the above condition. Obtained by peeling from the multilayer film according to any one of claims 1 to 3, wherein the layer A comprises at least one layer selected from the group consisting of the B layer and the B 'layer, a liquid crystal display apparatus. A method of manufacturing a liquid crystal display device including a liquid crystal panel, comprising:
A step of peeling at least one layer selected from the group consisting of the A layer, the B layer and the B ′ layer from the multilayer film according to any one of claims 1 to 5 ,
Providing a liquid crystal panel with at least one layer selected from the group consisting of the layer A, the layer B, and the layer B ′ obtained by peeling from the multilayer film.