JP2006212989A - Laminated film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coextrusion laminated film more excellent in production efficiency than before, enhanced in interlaminar strength, causing no crack in a resin layer and uniform in the thicknesses of respective layers. <P>SOLUTION: The laminated film is constituted by laminating films (B-layers) comprising a polynorbornene resin on both sides of a film (A-layer) comprising a polystyrenic resin through adhesive layers (C-layers). Each of the C-layers comprises a composition constituted of 40-98 wt.% of an unsaturated carboxylic acid modified polyethylene resin, 1-59 wt.% of a sticking agent and 1-59 wt.% of a specific thermoplastic elastomer and the melt flow rate of the composition [measured at 190°C under a load of 21.18 N (condition D) according to JIS K 7210] is 2.5 g/10 min or above. The laminated film is manufactured by a coextrusion method. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a laminated film having high adhesion strength between layers, no cracks in a resin layer, uniform film thickness of each layer, excellent transparency, and good surface smoothness and appearance. .

A retardation film plays an important role as a member for improving the display performance of a liquid crystal display (LCD). Various types of retardation films are known, such as a film in which liquid crystal is oriented, but since the production efficiency is particularly excellent, stretched films obtained by orienting resin films by stretching have been widely used.
Examples of the resin used for the stretched film include various polymers such as polycarbonate. Among them, a resin made of a styrene polymer that is excellent in transparency and has a large effect in viewing angle compensation for an LCD such as an STN type. Attention has been paid to a film using the film (Cited document 1).
However, since the styrenic polymer is inferior in mechanical strength when formed into a film, it has been pointed out that the styrene polymer resin film is easily broken when stretched, resulting in poor production efficiency.
Therefore, the present applicant has proposed a method of co-stretching a laminated film in which a transparent film is laminated on at least one surface of a styrene polymer film (Cited document 2). Here, a co-extrusion method is used to obtain a laminated film. Further, apart from this, the present applicant has proposed a laminated film obtained by a coextrusion method (Cited document 3).

JP-A-2-256603 JP 2004-133313 A JP 2004-058369 A

  However, the laminated film obtained by the co-extrusion method described in Patent Document 2 or Patent Document 3 has a problem that uneven thickness occurs in the inner layer, and needs to be improved. When used for optical applications such as retardation films, high-precision film thickness uniformity is required, and in laminated films, not only the film thickness as a whole is uniform, but the film thickness of all layers is uniform. It is required to be.

  Accordingly, an object of the present invention is to provide a coextruded laminated film having excellent production efficiency, high adhesion strength between layers, no cracks in the resin layer, and a uniform film thickness of each layer. is there.

  As a result of diligent research to solve the above-mentioned problems, the present inventors laminated a film made of a norbornene polymer via a specific adhesive layer on both sides of a film made of a styrene polymer resin by a coextrusion method. As a result, it has been found that the above object can be achieved, and the present invention has been completed.

Thus, according to the present invention,
(1) A laminated film in which a film (B layer) made of norbornene resin is laminated on both sides of a film (A layer) made of styrene resin via an adhesive layer (C layer),
Layer C comprises 40 to 98% by weight of unsaturated carboxylic acid-modified polyethylene resin, 1 to 59% by weight of an adhesive selected from aliphatic petroleum resins, aromatic petroleum resins, or hydrides thereof, and vinyl aromatic 1 to 59% by weight of a thermoplastic elastomer selected from a block copolymer having at least one polymer block containing a compound as a main component and at least one polymer block containing a conjugated diene compound as a main component or a hydride thereof. And a composition containing
The melt flow rate of the composition (measured at a temperature of 190 ° C. and a load of 21.18 N (condition D) according to JIS K7210) is 2.5 g / 10 min or more,
A laminated film formed by coextrusion,
(2) The laminated film according to (1), wherein the standard deviation of the thickness of the A layer / the average thickness of the A layer ≦ 0.025 is satisfied.
(3) The laminated film according to (2), which satisfies the standard deviation of the thickness of the laminated film / the average thickness of the laminated film ≦ 0.01,
(4) A retardation film obtained by stretching the laminated film according to (1) to (3),
(5) When the in-plane retardation of the A layer and the in-plane retardation of the B layer measured with light having a wavelength of 400 to 700 nm are Re (A) and Re (B), respectively, | Re (A) |> | Re (B) | and | Re (B) | is 20 nm or less, The retardation film according to (4),
(6) When the glass transition temperatures of the resin of the A layer and the resin of the B layer are Tg (A) (° C.) and Tg (B) (° C.), respectively, Tg (A)> Tg (B) + 20 ° C. (5) The retardation film according to the above,
Is to provide.

  The laminated film of the present invention is particularly useful as a film for optical applications because it is excellent in transparency, has high adhesion strength between layers, does not cause cracks in the resin layer, and has a uniform thickness in each layer. In addition, the stretched film obtained by stretching the laminated film of the present invention has a large effect on viewing angle compensation for various display devices, and is used as a retardation film that maintains good optical characteristics over a long period of time. It can be widely applied to devices and organic EL display devices.

  The laminated film of the present invention has a configuration in which a film (B layer) made of a polynorbornene resin is laminated on both surfaces of a film (A layer) made of polystyrene resin via an adhesive layer (C layer).

  Examples of the polystyrene resin used in the present invention include polystyrene, styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene, p-chlorostyrene, p-nitrostyrene, p-aminostyrene, and p-carboxy. Styrene monomers such as styrene and p-phenylstyrene, ethylene, propylene, butadiene, isoprene, (meth) acrylonitrile, α-chloroacrylonitrile, methyl (meth) acrylate, ethyl (meth) acrylate, (meth) Examples thereof include copolymers with other monomers such as acrylic acid, maleic anhydride and vinyl acetate. Among these, polystyrene or a copolymer of styrene and maleic anhydride can be suitably used.

  The molecular weight of the polystyrene resin used in the present invention is appropriately selected depending on the purpose of use, but polyisoprene measured by gel permeation chromatography using cyclohexane (toluene when the polymer resin is not dissolved) as a solvent. Or it is a weight average molecular weight (Mw) of polystyrene conversion, and is 10,000-300,000 normally, Preferably it is 15,000-250,000, More preferably, it is 20,000-200,000. The polystyrene resin used in the present invention preferably has a glass transition temperature of 120 ° C. or higher, more preferably 120 to 200 ° C., and still more preferably 120 to 140 ° C.

  In the present invention, the polystyrene-based resin may contain an antioxidant, a heat stabilizer, a light stabilizer, an ultraviolet absorber, an antistatic agent, a dispersant, a chlorine scavenger, a flame retardant, a crystallization nucleating agent, if necessary. Antiblocking agent, antifogging agent, release agent, pigment, organic or inorganic filler, neutralizing agent, lubricant, decomposition agent, metal deactivator, antifouling agent, antibacterial agent and other resins, thermoplastic elastomer Known additives such as these can be added as long as the effects of the invention are not impaired.

  The A layer of the laminated film of the present invention preferably satisfies the standard deviation of the thickness of the A layer / the average thickness of the A layer ≦ 0.025, and the standard deviation of the thickness of the A layer / the average thickness of the A layer. More preferably, ≦ 0.02 is satisfied. If the A layer does not satisfy the above range, uneven stretching tends to occur in the A layer when the laminated film of the present invention is stretched, and as a result, uneven thickness may occur in the stretched A layer. If thickness unevenness occurs in the stretched A layer, there is a risk that variation in retardation in the thickness direction of the stretched film obtained by stretching the laminated film of the present invention may increase, and the stretched film was applied to a display device. In some cases, the display performance (viewing angle performance) may be significantly reduced.

  Examples of the polynorbornene resin used in the present invention include a ring-opening polymer of a monomer having a norbornene structure, a ring-opening polymer of a monomer having a norbornene structure and another monomer, or a hydride thereof. And an addition polymer of a monomer having a norbornene structure, an addition polymer of a monomer having a norbornene structure and another monomer, or a hydride thereof. Among these, a ring-opening (co) polymer hydride of a monomer having a norbornene structure is particularly suitable from the viewpoints of transparency, moldability, heat resistance, low hygroscopicity, dimensional stability, lightness, and the like. Can be used.

Examples of the monomer having a norbornene structure include bicyclo [2.2.1] hept-2-ene (common name: norbornene), tricyclo [4.3.0.1 ^2,5 ] deca-3,8. -Diene (common name: dicyclopentadiene), 7,8-benzotricyclo [4.3.0.1 ^2,5 ] dec-3-ene (common name: methanotetrahydrofluorene), tetracyclo [4.4. 0.1 ^2,5 . 1 ^7,10 ] dodec-3-ene (common name: tetracyclododecene) and derivatives of these compounds (having substituents in the ring). Here, examples of the substituent include an alkyl group, an alkylene group, an alkoxycarbonyl group, and a carboxyl group. Moreover, these substituents may be the same or different and a plurality may be bonded to the ring. Norbornene monomers can be used alone or in combination of two or more.

  Other monomers capable of ring-opening copolymerization with a monomer having a norbornene structure include, for example, monocyclic olefins such as cyclohexene, cycloheptene, and cyclooctene and derivatives thereof; and cyclic conjugates such as cyclohexadiene and cycloheptadiene. Dienes and derivatives thereof; and the like.

  Ring-opening polymers of norbornene monomers and ring-opening copolymers of norbornene monomers and other monomers capable of ring-opening copolymerization are used in the presence of a ring-opening polymerization catalyst. Can be obtained by polymerization.

  As the ring-opening polymerization catalyst to be used, for example, a catalyst comprising a metal halide such as ruthenium or osmium and a sulfate or acetylacetone compound and a reducing agent; or a metal halide such as titanium, zirconium, tungsten or molybdenum Or a catalyst comprising an acetylacetone compound and an organoaluminum compound;

An addition polymer of a monomer having a norbornene structure and an addition copolymer of a monomer having a norbornene structure and another monomer capable of addition copolymerization in the presence of an addition polymerization catalyst. Can be obtained by polymerization.
As the addition polymerization catalyst, for example, a catalyst composed of a metal compound such as titanium, zirconium, vanadium and an organoaluminum compound can be used.

  Other monomers that can be copolymerized with a monomer having a norbornene structure include, for example, ethylene, propylene, 1-butene, 1-pentene, 1-octene, 1-decene, 1-dodecene, and 1-tetradecene. , 1-hexadecene, 1-octadecene, 1-eicosene and the like α-olefins having 2 to 20 carbon atoms and derivatives thereof; cyclobutene, cyclopentene, cyclohexene, cyclooctene, 3a, 5,6,7a-tetrahydro-4,7 -Cycloolefins such as methano-1H-indene and derivatives thereof; non-conjugated such as 1,4-hexadiene, 4-methyl-1,4-hexadiene, 5-methyl-1,4-hexadiene, 1,7-octadiene Examples include dienes. These monomers can be used alone or in combination of two or more. Among these, α-olefin is preferable and ethylene is more preferable.

  The molecular weight of the polynorbornene-based resin used in the present invention is appropriately selected depending on the purpose of use, but it is determined by gel permeation chromatography using cyclohexane (toluene when the polymer resin does not dissolve) as a solvent. The weight average molecular weight (Mw) in terms of isoprene or polystyrene is usually 5,000 to 500,000, preferably 10,000 to 100,000, more preferably 18,000 to 55,000. The polynorbornene-based resin used in the present invention preferably has a glass transition temperature of 70 to 120 ° C, more preferably 80 to 120 ° C, and further preferably 100 to 110 ° C.

  In the present invention, to the polynorbornene resin, additives described in the description of the polystyrene resin can be added to the polynorbornene resin as necessary as long as the effects of the invention are not impaired.

  The layer B of the laminated film of the present invention preferably satisfies the standard deviation of the thickness of the B layer / the average thickness of the B layer ≦ 0.025, and the standard deviation of the thickness of the B layer / the average thickness of the B layer. More preferably, ≦ 0.02 is satisfied. If the B layer does not satisfy the above range, there is a risk that uneven stretching tends to occur in the A layer when the laminated film of the present invention is stretched, and as a result, uneven thickness may occur in the stretched A layer.

  The layer B of the laminated film of the present invention preferably has a tensile elongation at break of 30% or more, and more preferably 50% or more. By laminating the A layer and the B layer having a tensile breaking elongation of 30% or more via the C layer, the laminated film of the present invention can be stably stretched. Here, the tensile elongation at break is a value measured according to JIS K6251.

  The C layer used in the present invention comprises a composition containing 40 to 98% by weight of an unsaturated carboxylic acid-modified polyethylene resin, 1 to 59% by weight of an adhesive, and 1 to 59% by weight of a thermoplastic elastomer, preferably The composition comprises 40 to 70% by weight of an unsaturated carboxylic acid-modified polyethylene resin, 15 to 35% by weight of an adhesive, and 10 to 40% by weight of a thermoplastic elastomer. If the content ratio of the unsaturated carboxylic acid-modified polyethylene resin is less than 40% by weight, the extrusion moldability may be deteriorated. If the content ratio of the unsaturated carboxylic acid-modified polyethylene resin exceeds 98% by weight, the delamination strength may decrease. If the content of the pressure-sensitive adhesive is less than 1% by weight, the delamination strength may be reduced. When the content ratio of the pressure-sensitive adhesive exceeds 59% by weight, the extrusion moldability may be deteriorated. When the content of the thermoplastic elastomer is less than 1% by weight, the delamination strength may be reduced. If the content of the thermoplastic elastomer exceeds 59% by weight, the adhesive resin may become cloudy.

  Examples of the unsaturated carboxylic acid-modified polyethylene resin used in the C layer of the present invention include those obtained by graft polymerization of an unsaturated carboxylic acid or a derivative thereof to an ethylene polymer. For example, there are Admer (trade name, manufactured by Mitsui Chemicals Co., Ltd.), Orebak G (trade name, manufactured by Arkema Co., Ltd.) Of these, an ethylene polymer obtained by graft polymerization of maleic anhydride is preferable.

  The pressure-sensitive adhesive used in the C layer of the present invention is selected from aliphatic petroleum resins, aromatic petroleum resins, or hydrides thereof. Examples of the aliphatic petroleum resin include Hilets (trade name, manufactured by Mitsui Chemicals), Escorez (trade name, manufactured by Esso Chemical Co., Ltd.), and the like. Examples of the aromatic petroleum resin include Alcon P, Alcon M (trade name, manufactured by Arakawa Chemical Co., Ltd.) and Quinton (trade name, manufactured by Nippon Zeon Co., Ltd.). Among them, hydrides of aliphatic petroleum resins or aromatic petroleum resins are preferable. The pressure-sensitive adhesive has a softening point of preferably 70 to 150 ° C., particularly preferably 90 to 150 ° C. When the softening point is less than 70 ° C., extrusion processability may be reduced. If the softening point exceeds 150 ° C, the delamination strength may be reduced.

  The thermoplastic elastomer used for the C layer of the present invention is a block copolymer having at least one polymer block mainly composed of a vinyl aromatic compound and at least one polymer block mainly composed of a conjugated diene compound. Or it is chosen from the hydride. The content of the polymer block containing a vinyl aromatic compound as a main component is preferably 10 to 80% by weight, and more preferably 10 to 70% by weight. If the content of the polymer block containing a vinyl aromatic compound as a main component is less than 10% by weight, the moldability may be lowered. When the content rate of an adhesive exceeds 80 weight%, there exists a possibility that delamination strength may fall. Here, the block structure of the monomer of the vinyl aromatic compound and the monomer of the conjugated diene compound is not particularly limited, and the copolymer includes, for example, a general formula: MN; MN— Block copolymer represented by M; NMMNM; MNMMM, etc. (wherein M represents a polymer block composed of a vinyl aromatic compound, and N is a conjugate) A polymer block composed of a diene compound, and the double bond of the polymer block N may be partially or completely hydrogenated).

  Examples of the vinyl aromatic compound include styrene, α-methylstyrene, and vinyl toluene. Of these, styrene can be particularly preferably used. Commercially available products of vinyl aromatic compounds include Quintac (trade name, manufactured by Nippon Zeon Co., Ltd.), Clayton (trade name, manufactured by Kraton Polymer Japan Co., Ltd.), Tuftec (trade name, manufactured by Asahi Kasei Corporation), Septon (( Kuraray brand name). Examples of the conjugated diene compound include butadiene, isoprene, and 1,3-pentadiene. Of these, butadiene, isoprene, and combinations thereof can be particularly preferably used.

  The composition constituting the C layer has a melt flow rate of 2.5 g / 10 min or more, preferably 2.5 when measured at a temperature of 190 ° C. and a load of 21.18 N (condition D) according to JIS K7210. -10 g / 10 min. When the melt flow rate of the copolymer is less than 2.5 g / 10 min, when the laminated film of the present invention is formed by coextrusion, the interface between the C layer and the A layer, and the C layer The interface with the B layer is disturbed, and as a result, the film thickness of the A layer may be particularly nonuniform, and in addition, wrinkles may occur on the film surface.

  The composition constituting the C layer preferably has a tensile strength of 2 MPa or more, and more preferably 4 MPa or more. If the tensile strength is less than 2 MPa, the film may crack when the laminated film of the present invention is stretched. Here, the tensile strength is a value measured according to JIS K6251.

  The composition constituting the C layer preferably has a tensile elongation at break of 400% or more, and more preferably 600% or more. If the tensile elongation at break is less than 400%, the film may crack when the laminated film of the present invention is stretched. Here, the tensile elongation at break is a value measured according to JIS K6251.

  The composition constituting the C layer preferably has a JIS A hardness of 30 to 100, and more preferably 60 to 90. If the JIS A hardness is less than 30, the mechanical strength of the laminated film of the present invention may be insufficient. If the JIS A hardness exceeds 100, the film may crack when the laminated film of the present invention is stretched. Here, the JIS A hardness is a value measured according to JIS K6253 (durometer hardness test type A).

  If necessary, an additive described in the description of the polystyrene-based resin can be added to the copolymer constituting the C layer as long as the effects of the invention are not impaired.

  The laminated film of the present invention preferably satisfies the standard deviation of the thickness of the laminated film / the average thickness of the laminated film ≦ 0.01, and the standard deviation of the thickness of the laminated film / the average thickness of the laminated film ≦ 0. It is more preferable to satisfy 007. If the laminated film does not satisfy the above range, for example, when the laminated film is used as a polarizing plate protective film, there is a risk that air bubbles may be involved between the polarizer and the protective film in the laminating process by roll-toe-roll. There is.

  In the laminated film of the present invention, the delamination strength between the A layer and the C layer and between the C layer and the B layer is preferably 0.5 N / 25 mm or more, and 0.7 N / 25 mm or more. More preferably. When the delamination strength between the A layer and the C layer and between the C layer and the B layer is less than 0.5 N / 25 mm, delamination may occur when the laminated film is stretched. Here, the delamination strength is a value measured by 180 ° peeling at a tensile speed of 100 mm / min in accordance with JIS K-6854-2.

  The laminated film of the present invention is preferably long. The long shape means one having a length of at least about 5 times or more with respect to the width direction of the film or laminate, preferably 10 times or more, and specifically in a roll shape. It has a length that is wound and stored or transported.

  The laminated film of the present invention is formed by a coextrusion method. The coextrusion molding method includes a flat die coextrusion molding method using a flat die and a coinflation molding method using a cylindrical die, and the flat die coextrusion molding method is preferable. The flat die coextrusion molding method is a method in which a resin is heated and melted by an extruder and then coextruded from a flat die to continuously obtain a film-shaped molded product. Examples of the flat die include a T die, a coat hanger die, and a fish tail die according to the structure of the resin distribution flow path. The extruder heats and kneads the resin and extrudes the melt in the form of a film from the die with a constant extrusion amount. Usually, it is preferable to remove a gel or a foreign substance by inserting a screen or a filter between the extruder and the die. The resin used is preferably dried before being introduced into the extruder, and the content of water and volatile solvents is reduced in order to prevent the generation of fish eyes and bubbles.

  The co-extrusion temperature is preferably 80 to 180 ° C. higher than the glass transition temperature of the polystyrene resin, and more preferably 100 to 150 ° C. higher than the glass transition temperature of the polystyrene resin. If the melting temperature in the extruder is excessively low, the fluidity of the resin may be insufficient. Conversely, if the melting temperature is excessively high, the resin may be deteriorated.

  The laminated film of the present invention can be further stretched to obtain a retardation film. The stretching method is not particularly limited, and conventionally known methods such as longitudinal uniaxial stretching, transverse uniaxial stretching, longitudinal and transverse simultaneous stretching, and longitudinal and transverse sequential stretching can be applied.

  The retardation film formed by stretching the laminated film of the present invention has a retardation in the front direction of the A layer and a retardation in the front direction of the B layer measured with light having a wavelength of 400 to 700 nm, respectively. B), it is preferable that | Re (A) |> | Re (B) | and | Re (B) | be 40 nm or less, and | Re (A) |> | Re (B) More preferably, | Re (B) | is 30 nm or less, | Re (A) |> | Re (B) |, and | Re (B) | is 20 nm or less. Is more preferable. When | Re (A) |> | Re (B) | and | Re (B) | is 40 nm or less, the optical characteristics of the optically adjusted A layer can be effectively used. Can do. In addition, the coefficient NZ described below can be efficiently reduced to 0.4 or less. If | Re (A) | ≦ | Re (B) |, the optical compensation function of the retardation film may not be sufficiently exhibited. Further, if | Re (B) | exceeds 40 nm, the optical compensation function of the retardation film may not be sufficiently exhibited. Note that | Re (B) | is the sum of absolute values of the retardation in the front direction of each B layer.

The retardation film formed by stretching the laminated film of the present invention has a variation in retardation (Re) in the front direction within 10 nm, preferably within 5 nm, and more preferably within 2 nm. By setting the variation of Re within the above range, it is possible to improve the display quality when used in various display devices. Here, the variation in Re is a difference between the maximum value and the minimum value of Re when the retardation in the front direction is measured in the width direction of the film. Note that Re in the present invention is the refractive index nx in the slow axis direction of the film, the refractive index ny in the direction perpendicular to the slow axis in the plane, the refractive index nz in the thickness direction, and the average thickness Tw of the film. to a value defined by _{(nx-ny) × T w} .

The retardation film obtained by stretching the laminated film of the present invention has a variation in retardation (Rth) in the thickness direction within 10 nm, preferably within 5 nm, and more preferably within 2 nm. By setting the variation of Rth within the above range, it is possible to improve the display quality (viewing angle performance) when used in a liquid crystal display device. Here, the variation in Rth is the difference between the maximum value and the minimum value of Rth when the retardation in the thickness direction is measured in the width direction of the film. Incidentally, Rth in the present invention is a value defined by ((nx + ny) / 2 -nz) × T w.

  In the retardation film obtained by stretching the laminated film of the present invention, the coefficient NZ expressing the relationship between the retardation in the front direction and the retardation in the thickness direction is 0.4 or less, preferably 0.2 or less, more preferably 0. Hereinafter, it is particularly preferably −0.2 or less. When NZ is 0.4 or less, when used as a retardation film for various display devices, the effect on viewing angle compensation is particularly great. NZ is a value represented by (nx−nz) / (nx−ny).

  The retardation film formed by stretching the laminated film of the present invention has a Tg when the glass transition temperatures of the resin of the A layer and the resin of the B layer are Tg (A) (° C) and Tg (B) (° C), respectively. (A)> Tg (B) + 20 ° C. is preferable, and Tg (A)> Tg (B) + 24 ° C. is more preferable. When the laminated film of the present invention is stretched, the birefringence characteristics of the A layer can be expressed sufficiently and uniformly by stretching near the temperature Tg (A) (° C.). At this time, the layer B is stretched at a temperature higher by 20 ° C. or more than its glass transition temperature Tg (B), so that the polymer is hardly oriented and becomes substantially non-oriented. Polystyrene resin films are difficult to stretch on their own and may cause uneven stretching or breakage, but they can be stably co-stretched by laminating with other transparent resins with low glass transition temperatures. And the thickness nonuniformity of A layer can be made small. In particular, since the laminated film of the present invention has small thickness unevenness of each layer, the thickness of each layer of a retardation film formed by stretching the layer can be easily made uniform.

  The laminated film of the present invention can be formed by laminating a cured resin layer or a liquid crystal polymer layer by applying an ultraviolet curable resin, a liquid crystal polymer (including a liquid crystal monomer before curing), an antireflection agent, or the like.

  The retardation film formed by stretching the laminated film of the present invention can be widely applied to liquid crystal display devices, organic EL display devices, plasma display devices, FED (field emission) display devices, SED (surface electric field) display devices, and the like. is there. Examples of the liquid crystal display device include an in-plane switching (IPS) mode, a vertical alignment (VA) mode, a multi-domain vertical alignment (MVA) mode, a continuous spin wheel alignment (CPA) mode, a hybrid alignment nematic (HAN) mode, Examples include a twisted nematic (TN) mode, a super twisted nematic (STN) mode, and an optically compensated bend (OCB) mode. Among these, the viewing angle compensation effect is particularly large for an IPS mode liquid crystal display device.

The present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples. Parts and% are based on weight unless otherwise specified.
In Examples and Comparative Examples, measurement and evaluation were performed by the following methods.
(1) Melt flow rate Based on JIS K7210 (temperature 190 ° C., load 21.18 N (condition D)), it is measured with a melt indexer F-B01 manufactured by Toyo Seiki Seisakusho.
(2) Thickness unevenness The thickness of each layer of the laminated film is measured by scanning a reflection spectral film thickness meter [FE-3000 manufactured by Otsuka Electronics Co., Ltd.] at intervals of 50 mm in the width direction of the laminated film. This operation is performed over 1000 mm at intervals of 50 mm in the flow direction of the laminated film. From all the measurement results, an average value T _av of thickness and a standard deviation T _σ of thickness are derived for each layer, and thickness unevenness is calculated according to the following equation.
Unevenness of thickness = T _σ / T _av
(3) Interlaminar peel strength Based on JIS K-6854-2 (a 180 degree peel at a tensile speed of 100 mm / min), an autograph [AGS-J, manufactured by Shimadzu Corporation] is used for the delamination strength of a laminated film. To measure.
(4) Surface property The state of the surface of the laminated film was observed and judged according to the following criteria.
○: The surface is free from wrinkles and whitening and is good.
Δ: Some fine wrinkles or whitening are observed. ×: There are large and small wrinkles or irregularities on the entire surface.
(5) Heat resistance test After the laminated film was allowed to stand for 240 hours in an air atmosphere at a temperature of 80 ° C, the test piece was visually observed.
(6) Glass transition temperature Measured by differential scanning calorimetry (DSC) based on JIS K7121.
(7) Front-side retardation Re, thickness-direction retardation Rth
An automatic birefringence meter [Oji Scientific Instruments Co., Ltd.] for a layer made of polystyrene resin (A layer), a layer made of polynorbornene resin (B layer) and a laminated film separated from a retardation film obtained by stretching the laminated film ) Manufactured by KOBRA-21ADH].
(8) NZ coefficient It is measured using an automatic birefringence meter [manufactured by Oji Scientific Instruments, KOBRA-21ADH].
(9) Viewing angle characteristics of liquid crystal display device A film formed by stretching a laminated film is incorporated into an in-plane switching (IPS) mode liquid crystal display device, and then the display device is placed in an atmosphere at a temperature of 30 ° C and a humidity of 80%. The display characteristics during black display are visually observed.

Example 1
B layer composed of polynorbornene resin [made by Nippon Zeon Co., Ltd., trade name “ZEONOR1060”, glass transition temperature 100 ° C.], styrene-maleic anhydride copolymer [glass transition temperature 130 ° C., oligomer component content 3 wt. %] And a composition [maleic anhydride-modified polyethylene resin (trade name “Olevac G18380”) 98% by weight, aromatic petroleum resin (trade name “Arcon P-100”) 1% by weight, From a composition comprising 1% by weight of a block copolymer having a polymer block of a vinyl aromatic compound and a polymer block of a conjugated diene compound (trade name “Tuftec H1031”), a melt flow rate of 5 g / 10 min] B layer (30 μm) -c layer (10 μm) -a layer (70 μm) -c layer (10 μm) -b layer (30 μm) The Lum D1 was obtained by co-extrusion.
The laminated film D1 was stretched laterally by a tenter at a stretching temperature of 135 ° C., a stretching speed of 8 m / min, and a stretching ratio of 2.4 times to obtain a retardation film E1 having a thickness of 70 μm.
A test piece was cut out from the center of the obtained retardation film E1, and laminated so that the slow axis of the retardation film and the absorption axis of a polarizing plate [manufactured by Sanlitz, HLC2-5618] were perpendicular to each other. Was replaced with a polarizing plate on the viewing side of a commercially available liquid crystal display device in an in-plane switching (IPS) mode. At this time, the optical element F1 was incorporated so that the retardation axis of the retardation film and the absorption axis of the backlight side polarizing plate were parallel to each other and the retardation film was disposed on the liquid crystal cell side.
All evaluation results are shown in Tables 1-4.

Example 2
As layer C, the composition [maleic anhydride-modified polyethylene resin (trade name “Orebak G 18350”) 98% by weight, aromatic petroleum resin (trade name “Arcon P-90”) 1% by weight, vinyl aroma A composition comprising 1% by weight of a block copolymer having a polymer block of an aromatic compound and a polymer block of a conjugated diene compound (trade name “Tuftec H1031”), a melt flow rate of 4 g / 10 minutes] Was obtained in the same manner as in Example 1 by coextrusion molding of a laminated film D2 of b layer (30 μm) -c layer (10 μm) -a layer (70 μm) -c layer (10 μm) -b layer (30 μm). . Further, in the same manner as in Example 1, transverse stretching was performed to obtain a retardation film E2. In addition, in the same manner as in Example 1, a retardation film E2 and a polarizing plate were laminated to produce an optical element F2. Further, the optical element F2 was incorporated into an IPS mode liquid crystal display device for evaluation. All evaluation results are shown in Tables 1-4.

Comparative Example 1
Example except that ethylene-vinyl acetate copolymer [Mitsui / DuPont Polychemical Co., Ltd., trade name “Evaflex P2805”, vinyl acetate composition 28 wt%, melt flow rate 6 g / 10 min] was used as C layer. In the same manner as in Example 1, a laminated film D3 of layer b (30 μm) −c layer (10 μm) −a layer (70 μm) −c layer (10 μm) −b layer (30 μm) was obtained by coextrusion molding. Further, in the same manner as in Example 1, transverse stretching was performed to obtain a retardation film E3. In addition, in the same manner as in Example 1, a retardation film E3 and a polarizing plate were laminated to produce an optical element F3. Further, the optical element F3 was incorporated into an IPS mode liquid crystal display device for evaluation. All evaluation results are shown in Tables 1-4.

Comparative Example 2
Layer B is the same as in Example 1, except that a linear low density polyethylene polymer [manufactured by Nippon Polyethylene Co., Ltd., trade name “NOVATEC LL UL960”, melt flow rate 5 g / 10 min] is used as layer C. A laminated film D4 of (30 μm) -c layer (10 μm) -a layer (70 μm) -c layer (10 μm) -b layer (30 μm) was obtained by coextrusion molding. Further, in the same manner as in Example 1, transverse stretching was performed to obtain a retardation film E4. At this time, in the film E4, partial peeling was observed between the A layer and the C layer. In addition, in the same manner as in Example 1, a retardation film E4 and a polarizing plate were laminated to produce an optical element F4. Further, the optical element F4 was incorporated into an IPS mode liquid crystal display device for evaluation. All evaluation results are shown in Tables 1-4.

Comparative Example 3
A laminated film D5 of b layer (30 μm) −a layer (70 μm) −b layer (30 μm) was obtained by coextrusion molding in the same manner as Example 1 except that the C layer was not provided. Further, in the same manner as in Example 1, transverse stretching was performed to obtain a retardation film E5. At this time, the film E5 was completely peeled between the A layer and the C layer. In addition, in the same manner as in Example 1, a retardation film E5 and a polarizing plate were laminated to produce an optical element F5. Furthermore, the optical element F5 was incorporated into an IPS mode liquid crystal display device for evaluation. All evaluation results are shown in Tables 1-4.

The following can be understood from the results shown in Tables 1 to 4.
From Example 1 and Example 2, it can be seen that the laminated film of the present invention has a small thickness unevenness of the A layer, a high delamination strength, and a good surface condition of the laminated film. Further, the retardation film formed by stretching the laminated film of the present invention does not show delamination, and it can be seen that the variation in Re and the variation in Rth of the film are small. In addition, when the retardation film is used in a liquid crystal display device to check the display performance, there is no partial hue change on the screen, and a good display is confirmed even when observed obliquely. Display characteristics are good.

  In contrast, the laminated film of Comparative Example 1 using an adhesive layer composed of an ethylene-vinylacetic acid copolymer different from the component of the C layer of the present invention cracks in the B layer when left in a high temperature range for a long time. Occurs. In addition, when the retardation film is used in a liquid crystal display device to confirm the display performance, many point-like hue changes are observed over the entire screen, resulting in poor display. In addition, when the screen is observed obliquely, the dot-like hue change is observed more conspicuously, and the display quality is further deteriorated.

  Although the laminated film of Comparative Example 2 using an adhesive layer composed of a linear polyethylene-based polymer different from the component of the C layer of the present invention has a good surface condition, the delamination strength is weak. Furthermore, in the retardation film formed by stretching the laminated film of Comparative Example 2, partial peeling is observed between the A layer and the C layer. In addition, when the retardation film is used in a liquid crystal display device and the display performance is confirmed, a hue change is observed in most of the peripheral portion of the screen, and display is poor. Further, when the screen is observed from an oblique direction, the hue change is observed more conspicuously, and the display quality is further deteriorated.

Although the laminated film of Comparative Example 3 having no adhesive layer (C layer) has a good surface condition, the delamination strength is extremely weak. Furthermore, the retardation film formed by stretching the laminated film of Comparative Example 3 shows complete peeling between the layers. In addition, when the retardation film is used in a liquid crystal display device to confirm display performance, a hue change is observed over the entire screen, resulting in poor display. Further, when the screen is observed obliquely, the hue change over the entire surface is observed more conspicuously, and the display quality is further deteriorated.

Claims (6)

A laminated film in which a film (B layer) made of norbornene resin is laminated on both sides of a film (A layer) made of styrene resin via an adhesive layer (C layer),
Layer C comprises 40 to 98% by weight of unsaturated carboxylic acid-modified polyethylene resin, 1 to 59% by weight of an adhesive selected from aliphatic petroleum resins, aromatic petroleum resins, or hydrides thereof, and vinyl aromatic 1 to 59% by weight of a thermoplastic elastomer selected from a block copolymer having at least one polymer block containing a compound as a main component and at least one polymer block containing a conjugated diene compound as a main component or a hydride thereof. And a composition containing
The melt flow rate of the composition (measured at a temperature of 190 ° C. and a load of 21.18 N (condition D) according to JIS K7210) is 2.5 g / 10 min or more,
A laminated film formed by coextrusion. 2. The laminated film according to claim 1, wherein the standard deviation of the thickness of the A layer / the average thickness of the A layer ≦ 0.025 is satisfied. The laminated film according to claim 2, wherein the standard deviation of the thickness of the laminated film / the average thickness of the laminated film ≦ 0.01 is satisfied. A retardation film obtained by stretching the laminated film according to claim 1. When the in-plane retardation of the A layer and the in-plane retardation of the B layer measured with light having a wavelength of 400 to 700 nm are Re (A) and Re (B), respectively, | Re (A) | >> | Re (B ) | And | Re (B) | is 40 nm or less. 6. Tg (A)> Tg (B) + 20 ° C. where Tg (A) (° C.) and Tg (B) (° C.) are the glass transition temperatures of the A layer resin and the B layer resin, respectively. The retardation film described.