JP2006145938A - Optical film, liquid crystal cell, liquid crystal display and image display unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical film in which a polarizer and a protective film that is less likely to cause delamination. <P>SOLUTION: The optical film comprises a polarizing plate formed by stacking at least one protective film on a polarizer via an adhesive, and a birefringent layer stacked on the polarizing plate, wherein the adhesive contains >30 to 46 pts.wt. of methylolmelamine with respect to 100 pts.wt. of a polyvinyl alcohol-based resin containing acetoacetyl groups. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical film including a birefringent layer and having a polarizer and a protective film laminated with a polyvinyl alcohol adhesive, and a liquid crystal cell, a liquid crystal display device, and an image display device using the optical film.

Conventionally, in various image display devices, an optical film having a polarizing plate in which a protective film is laminated on a polarizer and a birefringent layer is used.
A polarizer is generally obtained by dyeing with a polyvinyl alcohol film and a dichroic material such as iodine, followed by crosslinking using a crosslinking agent such as boric acid, and uniaxial stretching to form a film. Film is widely used. Such a PVA-based stretched film is easily shrunk and is very easily deformed particularly under humidified conditions. For this reason, the polarizing plate is comprised by bonding together protective films, such as a triacetyl cellulose, on the both sides or one side of a polarizer using an adhesive agent.
Furthermore, an optical film having a visual compensation effect and the like is formed by providing a birefringent layer on the polarizing plate.

  In the polarizing plate, a water-based adhesive is preferable as an adhesive for laminating the polarizer and the protective film, and for example, a polyvinyl alcohol-based adhesive is used. However, the polyvinyl alcohol-based adhesive may be peeled off at the interface between the polarizer and the protective film under humidified conditions. This is because the polyvinyl alcohol-based resin, which is the main component of the adhesive, is a water-soluble polymer, and therefore the adhesive may be dissolved under the dew condensation condition.

  In order to solve the above problems, JP-A-7-198945 proposes a polarizing plate using a polyvinyl alcohol resin containing an acetoacetyl group and an adhesive containing a crosslinking agent. However, the adhesive described in the publication does not have sufficient water resistance and cannot sufficiently solve the problem of delamination.

JP-A-7-198945

  Therefore, an object of the present invention is to provide an optical film in which the polarizer and the protective film hardly cause delamination and a liquid crystal cell using the optical film.

The first means for solving the above problems includes a polarizing plate in which at least one protective film is laminated on the polarizer via an adhesive, and a birefringent layer laminated on the polarizing plate, Provided is an optical film in which a cross-linking agent is contained in the range of more than 30 parts by weight and 46 parts by weight or less with respect to 100 parts by weight of a polyvinyl alcohol resin containing an acetoacetyl group.
In such an optical film, 100 parts by weight of a polyvinyl alcohol resin containing an acetoacetyl group as an adhesive contains a crosslinking agent in a range of more than 30 parts by weight and 46 parts by weight or less. Water resistance is dramatically improved. Thereby, delamination of a polarizer and a protective film can be prevented substantially.

In a preferred embodiment of the present invention, there is provided the above optical film wherein the crosslinking agent contains methylol melamine.
Moreover, in the preferable aspect of this invention, the polarizer is a polyvinyl alcohol-type polarizer and the said optical film whose protective film is a cellulose-type protective film is provided.
Furthermore, in a preferred aspect of the present invention, the birefringent layer has a structure in which nx> ny≈nz (nx is the refractive index in the slow axis direction in the plane of the birefringent layer, and ny is the fast axis direction in the same plane. The refractive index, nz, provides the above optical film exhibiting optical characteristics of the refractive index in the thickness direction of the birefringent layer.
In a preferred embodiment of the present invention, the optical film in which the birefringent layer has a single layer or a multilayer structure, and the thickness of the single layer or each layer constituting the multilayer is 10 μm to 40 μm, respectively. Provide film.
Furthermore, in a preferred embodiment of the present invention, there is provided the above optical film, wherein the birefringent layer contains at least one polymer selected from polycarbonate, polyvinyl alcohol, polystyrene, polymethyl methacrylate, polypropylene, polyarylate, norbornene, and polyamide.

The second means of the present invention provides a liquid crystal cell comprising any one of the above optical films.
The third means of the present invention provides a liquid crystal display device comprising the liquid crystal cell.
Furthermore, a fourth means of the present invention provides an image display device including any one of the above optical films.

In the optical film of the present invention, the adhesive layer for bonding between the polarizer and the protective film has extremely excellent water resistance.
Therefore, it is possible to provide an optical film that can be used satisfactorily even under high humidity such as in a dew condensation condition.
In addition, the optical film of the present invention can provide a film that is thinner and has an excellent visual compensation effect according to each preferred mode.

  The optical film of the present invention has at least a polarizing plate in which at least one protective film is laminated on a polarizer via an adhesive, and a birefringent layer laminated on the polarizing plate. A polyvinyl alcohol-based adhesive (hereinafter, polyvinyl alcohol is abbreviated as “PVA”) containing 100 parts by weight of a polyvinyl alcohol-based resin containing an acetyl group and a crosslinking agent of more than 30 parts by weight and 46 parts by weight or less. It is used.

(PVA adhesive)
The PVA adhesive used in the present invention contains at least a PVA resin containing an acetoacetyl group and a predetermined amount of a crosslinking agent.
The PVA resin containing an acetoacetyl group can be obtained by reacting a PVA resin and diketene by a known method. For example, a method in which a PVA resin is dispersed in a solvent such as acetic acid and diketene is added thereto, and a method in which a PVA resin is previously dissolved in a solvent such as dimethylformamide or dioxane and diketene is added thereto And a method in which diketene gas or liquid diketene is brought into direct contact with the PVA resin.

  Examples of PVA-based resins include PVA obtained by saponifying polyvinyl acetate and derivatives thereof, saponified products of copolymers with vinyl acetate and a copolymerizable monomer, PVA acetalization, urethanization, Examples thereof include modified PVA obtained by etherification, grafting or phosphoric esterification. These PVA resins can be used singly or in combination of two or more. Monomers copolymerizable with vinyl acetate include (anhydrous) maleic acid, fumaric acid, crotonic acid, itaconic acid, (meth) acrylic acid and other unsaturated carboxylic acids and esters thereof, ethylene and propylene, etc. α-olefin, (meth) allylsulfonic acid (soda), sulfonic acid soda (monoalkylmalate), disulfonic acid soda alkylmalate, N-methylolacrylamide, acrylamide alkylsulfonic acid alkali salt, N-vinylpyrrolidone, N- Examples include vinyl pyrrolidone derivatives.

  The degree of polymerization of the PVA-based resin is not particularly limited, but since the adhesiveness and the like are improved, the average degree of polymerization is about 100 to 3000, preferably 500 to 3000, and the average saponification degree is about 85 to 100 mol%, preferably It is preferable to use about 90-100 mol%.

  The acetoacetyl group content in the PVA-based resin containing an acetoacetyl group is not particularly limited as long as it is 0.1 mol% or more. If it is less than 0.1 mol%, the water resistance of the adhesive layer becomes insufficient, and the polarizer and the protective film may be peeled off. However, if the acetoacetyl group content is too large, the number of reaction points with the cross-linking agent decreases and no improvement in water resistance is observed. Therefore, the acetoacetyl group content is preferably 40 mol% or less. And the more preferable range of acetoacetyl group content is about 2-7 mol%.

As the crosslinking agent, for example, a compound having two or more reactive functional groups capable of reacting with the PVA resin having the acetoacetyl group can be used. Examples of the crosslinking agent include alkylene diamines having two alkylene groups and two amino groups, such as ethylene diamine, triethylene diamine, and hexamethylene diamine, tolylene diisocyanate, hydrogenated tolylene diisocyanate, trimethylolpropane tolylene diisocyanate adduct, tolyl. Phenylmethane triisocyanate, methylenebis (4-phenylmethane triisocyanate, isophorone diisocyanate and isocyanates such as ketoxime block product or phenol block product, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin Triglycidyl ether, 1,6-hexanediol diglycidyl ether, tri Epoxys such as tyrolpropane triglycidyl ether, diglycidyl aniline, diglycidyl amine, monoaldehydes such as formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, glyoxal, malondialdehyde, succindialdehyde, glutardialdehyde, maleindialdehyde , Dialdehydes such as phthaldialdehyde, methylol urea, methylol melamine, alkylated methylol urea, alkylated methylolated melamine, acetoguanamine, amino-formaldehyde resins such as condensates of benzoguanamine and formaldehyde, sodium, potassium, magnesium, Examples thereof include divalent or trivalent metal salts such as calcium, aluminum, iron and nickel, and oxides thereof.
Among these, it is preferable to use, for example, amino-formaldehyde resin or dialdehydes. As the amino-formaldehyde resin, a compound having a methylol group, particularly methylol melamine is preferably used, and as the dialdehyde, glyoxal is suitable.

  In the present invention, the cross-linking agent is contained in a range of more than 30 parts by weight and 46 parts by weight or less with respect to 100 parts by weight of the PVA resin containing an acetoacetyl group. Thereby, the water resistance of a PVA-type adhesive agent can be improved. In particular, in order to drastically improve the water resistance, the crosslinking agent is 31 parts by weight or more, preferably 32 parts by weight or more, more preferably 35 parts by weight with respect to 100 parts by weight of the PVA resin containing an acetoacetyl group. It is good to be included above. On the other hand, the upper limit of the crosslinking agent is 46 parts by weight or less, preferably 45 parts by weight or less, more preferably 40 parts by weight or less, with respect to 100 parts by weight of the PVA resin containing an acetoacetyl group. . If too much crosslinking agent is contained, the PVA-based resin gels early, and the time (pot life) that can be used as an adhesive becomes extremely short.

  Although the thickness of an adhesive bond layer is not specifically limited, Usually, it is about 1-1000 nm. This is because if the adhesive layer is thinner than 1 nm, adhesive force may not be obtained. Preferably, the thickness of the adhesive layer is designed to be 30 nm or more, further 40 nm or more, more preferably 50 nm or more. On the other hand, when the adhesive layer exceeds 1000 nm, it is difficult to obtain a polarizing plate having a substantially uniform in-plane thickness, and there is a possibility that a defect occurs in the appearance of the polarizing plate. Therefore, the thickness of the adhesive layer is preferably 300 nm or less, more preferably 120 nm or less, more preferably about 95 nm or less.

  A PVA adhesive is applied to the main surface of a polarizer or / and protective film by a known method such as a roll method, a spray method, or an impregnation method, for example, with an adhesive aqueous solution in which at least a PVA resin and a crosslinking agent are dissolved. can do.

  The concentration of the PVA resin in the adhesive aqueous solution is not particularly limited, but is preferably about 0.1 to 15% by weight, more preferably 0.5 to 10% by weight, more preferably 2 to 5% by weight. It is good to make it weight%.

  Examples of the adhesive include coupling agents such as silane coupling agents and titanium coupling agents, various tackifiers, ultraviolet absorbers, antioxidants, heat stabilizers, and hydrolysis stabilizers. You may add well-known additives, such as.

(Polarizer)
The polarizer is not particularly limited, and various types can be used. As a polarizer, for example, a dichroic material such as iodine or a dichroic dye is applied to a hydrophilic polymer film such as a PVA film, a partially formalized PVA film, or an ethylene / vinyl acetate copolymer partially saponified film. Examples thereof include a polyene-based oriented film such as an adsorbed and uniaxially stretched product, a dehydrated PVA product and a dehydrochlorinated product of polyvinyl chloride. Among these, it is preferable to use a film obtained by uniaxially or biaxially stretching a PVA film on which iodine or the like is adsorbed. The thickness of the polarizer is not particularly limited, but is generally about 5 μm to 80 μm.

  Such a suitable PVA-based dyed film can be prepared, for example, by dyeing a PVA-based film by immersing it in an aqueous solution of a dichroic material such as iodine and stretching it in a predetermined direction 3 to 7 times the original length. it can. If necessary, it can be immersed in an aqueous solution of boric acid or potassium iodide. If necessary, the PVA film may be immersed in water and washed before dyeing. Washing the PVA film with water can clean the surface of the PVA film and the anti-blocking agent. In addition, swelling the PVA film has the effect of preventing unevenness such as uneven dyeing. Stretching may be performed after dyeing with iodine or the like, or may be performed while dyeing. Moreover, you may dye | stain with an iodine etc. after extending | stretching. The film can be stretched in an aqueous solution of boric acid or potassium iodide or in a water bath.

(Protective film)
A protective film can be comprised, for example with the resin film which has a light transmittance, etc., and the film excellent in transparency is used. Moreover, since the protective film is for the purpose of protecting the polarizer, it is preferable to use a protective film having excellent mechanical strength, thermal stability, moisture barrier properties, and the like.
Examples of the material for the protective film include polyester polymers such as polyethylene terephthalate and polyethylene naphthalate, cellulose polymers such as diacetyl cellulose and triacetyl cellulose, acrylic polymers such as polymethyl methacrylate, polystyrene, acrylonitrile / styrene copolymer, and the like. Examples thereof include styrene polymers such as (AS resin), polycarbonate polymers, and the like. Other protective film materials include, for example, polyethylene, polypropylene, polyolefins having a cyclo or norbornene structure, polyolefin polymers such as ethylene / propylene copolymers, vinyl chloride polymers, amide polymers such as nylon and aromatic polyamides. , Imide polymer, sulfone polymer, polyether sulfone polymer, polyether ether ketone polymer, polyphenylene sulfide polymer, vinyl alcohol polymer, vinylidene chloride polymer, vinyl butyral polymer, arylate polymer, polyoxymethylene polymer Polymers, epoxy polymers, blends of these polymers, and the like are also included.
In addition, the protective film may be, for example, a cured layer such as an acrylic, urethane, acrylic urethane, epoxy, or silicone thermosetting or ultraviolet curable resin.

  Furthermore, as a protective film, a polymer film described in JP-A-2001-343529 (WO01 / 37007), for example, (A) a thermoplastic resin having a substituted and / or unsubstituted imide group in the side chain, and (B) A film made of a resin composition containing a thermoplastic resin having a substituted and / or unsubstituted phenyl and nitrile group in the side chain can also be used. Specific examples include a film of a resin composition containing an alternating copolymer composed of isobutylene and N-methylmaleimide and an acrylonitrile / styrene copolymer. As the film, a film made of a mixed extruded product of the resin composition or the like can be used. Since these films have a small retardation and photoelastic coefficient, problems such as unevenness due to distortion of the polarizing plate can be suppressed. Moreover, since moisture permeability can be made small, the humidification durability of a polarizing plate can be improved.

  The thickness of the protective film is appropriately designed. In general, from the viewpoints of workability such as strength and handleability and thin layer properties, the thickness is preferably about 1 μm to 500 μm, more preferably 1 μm to 300 μm, more preferably 5 μm. It is formed to ˜200 μm.

  Furthermore, the protective film is preferably one that is excellent in transparency and has as little color as possible. Specifically, for example, Rth = [(nx + ny) / 2−nz] · d (where nx and ny are main refractive indexes in the film plane (n-axis and y-axis are directions perpendicular to each other), nz Is a protective film having a retardation value in the film thickness direction represented by -90 nm to +75 nm. By using a film having a thickness direction retardation value (Rth) of −90 nm to +75 nm, the coloring (optical coloring) of the polarizing plate caused by the protective film can be almost eliminated. The thickness direction retardation value (Rth) is more preferably −80 nm to +60 nm, and particularly preferably −70 nm to +45 nm.

  As such a transparent protective film, a cellulose-based polymer such as triacetyl cellulose is preferable from the viewpoint of polarization characteristics and durability, and a triacetyl cellulose film is particularly preferable. In addition, when providing a protective film in the both sides of a polarizer, the protective film which consists of the same polymer material may be used by the front and back, and the protective film which consists of a different polymer material etc. may be used.

(Polarizer)
The polarizing plate is formed by laminating and bonding at least the polarizer and the protective film using the adhesive. That is, a polarizing plate consists of a laminated body by which the protective film was laminated | stacked through the adhesive bond layer formed with the said adhesive agent on the one side or both sides of a polarizer.

  When the polarizer and the protective film are bonded, an aqueous adhesive solution is prepared by dissolving the PVA resin and the crosslinking agent in water. It is preferable to prepare such an aqueous adhesive solution within 4 hours before coating. In order to perform the process from the preparation of the adhesive to the application in a short time within 4 hours, the adhesive preparation process is incorporated into a part of a series of steps of the polarizing plate manufacturing process, or an appropriate preparation device is arranged. This can be done.

  Such an adhesive is applied to the main surface of the polarizer or / and protective film by a known coating method. After apply | coating an adhesive agent, a polarizer and a protective film are bonded together by a roll laminator. Then, it dries and forms an adhesive bond layer. The drying temperature is, for example, about 5 ° C. to 150 ° C., preferably 30 ° C. to 120 ° C., and the time is, for example, 120 seconds or longer, preferably 300 seconds or longer.

  Moreover, when using an adhesive agent, it is preferable to control the temperature in the adhesive preparation step, coating step, and bonding step. Water resistance can be further improved by controlling the temperature of the adhesive. The management temperature of the adhesive is, for example, 0 to 50 ° C., preferably 20 to 40 ° C.

  In addition, you may give an easily bonding process to the adhesive surface of a polarizer and a protective film. Examples of the easy adhesion treatment include dry treatment such as plasma treatment and corona treatment, chemical treatment such as alkali treatment (saponification treatment), and coating treatment for forming an easy adhesive layer. Among these, a coating treatment or an alkali treatment for forming an easy-adhesive layer is preferable. For the formation of the easy-adhesive layer, various easy-adhesive materials such as polyol resin, polycarboxylic acid resin, and polyester resin can be used. The thickness of the easy-adhesive layer is usually about 0.01 μm to 10 μm, more preferably about 0.05 μm to 5 μm, and particularly preferably about 0.1 μm to 1 μm.

  Furthermore, on the main surface of the protective film (the main surface on the side where the polarizer is not bonded), for example, any one or more of treatments intended for hard coating, antireflection treatment, anti-sticking, diffusion, anti-glare, etc. May be applied.

  The hard coat treatment is applied for the purpose of preventing scratches on the surface of the polarizing plate. For example, it protects a cured film with excellent hardness and sliding properties by an appropriate UV curable resin such as acrylic or silicone. It can be applied by adding to the film. The antireflection treatment is performed for the purpose of preventing reflection of external light on the surface of the polarizing plate, and can be performed by adding an antireflection film or the like according to the related art to the protective film. In addition, the anti-sticking treatment is performed for the purpose of preventing adhesion between adjacent layers.

  The anti-glare treatment is performed for the purpose of, for example, preventing the external light from being reflected on the surface of the polarizing plate and obstructing the visibility of the light transmitted through the polarizing plate. Or by embossing the surface of the protective film with an appropriate method such as a roughening technique using an embossing method or blending transparent fine particles. As the fine particles to be included in the formation of this fine concavo-convex structure, for example, inorganic fine particles made of silica, alumina, titania, zirconia, tin oxide, indium oxide, cadmium oxide, antimony oxide or the like having an average particle diameter of 0.5 to 20 μm, Transparent fine particles such as organic fine particles made of a crosslinked or uncrosslinked polymer are used. In addition to the anti-glare, a diffusion function (viewing angle expansion function) for diffusing incident light to expand vision and the like may be provided.

  The antireflection, antisticking, antiglare and the like can be provided on the protective film itself, or can be laminated on the protective film as an optical layer separate from the transparent protective film.

Furthermore, for example, a reflective layer or a semi-transmissive layer can be added to the polarizing plate.
A polarizing plate provided with a reflective layer, a so-called reflective polarizing plate, is effective for use in, for example, a liquid crystal display device that reflects incident light from the viewing side (display side). In addition, the polarizing plate can be omitted from the built-in light source such as a backlight, and the liquid crystal display device can be made thinner and lighter. In addition, a polarizing plate provided with a reflective layer can be obtained, for example, by attaching a reflective layer made of a metal film or the like to one side of the polarizing plate via a protective film or the like as necessary.
Specific examples of the reflective polarizing plate include those in which a reflective layer is formed by attaching a foil or a vapor-deposited film made of a reflective metal such as aluminum on one side of a protective film matted as necessary.

  In addition, a polarizing plate including a semi-transmissive layer, a so-called semi-transmissive polarizing plate can be obtained by making the above-described reflective layer into a transmissive reflective layer such as a half mirror that reflects and transmits incident light. .

  The polarizing plate provided with the semi-transmissive layer is usually provided on the main surface opposite to the viewing side of the liquid crystal cell, that is, on the back side of the so-called liquid crystal cell. This polarizing plate displays an image by reflecting incident light from the viewing side when a liquid crystal display device or the like is used in a relatively bright atmosphere, while a built-in backlight or the like when used in a relatively dark atmosphere. It is effective for use in a liquid crystal display device of a type that displays an image using a light source. That is, the polarizing plate including the semi-transmissive layer can be applied to an energy saving type liquid crystal display device that does not use a backlight in a bright atmosphere.

(Birefringent layer)
The optical film of the present invention is one in which a birefringent layer is laminated on the polarizing plate described above. This birefringent layer is provided on the main surface of the protective film (the main surface on the side where the polarizer is not bonded).

The birefringent layer is not particularly limited as long as it has birefringence, but a so-called λ / 4 plate that can change linearly polarized light into circularly polarized light or circularly polarized light into linearly polarized light, or a linearly polarized light can be used. A so-called λ / 2 plate capable of changing the polarization direction is preferable.
When used as a λ / 4 plate, the in-plane retardation (Δnd) represented by the following formula is preferably 110 nm to 180 nm, more preferably 120 nm to 170 nm, and more preferably 130 nm to 160 nm. When used as a λ / 2 plate, the in-plane retardation (Δnd) is preferably 200 nm to 300 nm, more preferably 210 nm to 290 nm, more preferably 220 nm to 280 nm.
Δnd = (nx-ny) × d (n-axis and y-axis are directions orthogonal to each other in the plane, nx is the refractive index in the slow axis direction in the birefringent layer, and ny is the fast phase in the birefringent layer) The refractive index in the axial direction, d means the thickness of the birefringent layer).
In addition, the birefringent layer can be configured by using a λ / 4 plate, a λ / 2 plate, or the like alone or by appropriately combining these plates that function as a λ / 4 plate, a λ / 2 plate, or the like.

The birefringent layer preferably has optical characteristics of nx> ny≈nz. However, the n-axis and y-axis are directions orthogonal in the plane, nx is the refractive index in the slow axis direction in the birefringent layer, ny is the refractive index in the fast axis direction in the birefringent layer, and nz is the compound index. It means the refractive index in the thickness direction in the refractive layer. The reason why “ny≈nz” is set is that not only when both refractive indexes are exactly equal, but also the approximate value does not affect the effect. The approximate values are, for example, about the formula: | Rth−Δnd | ≦ 10 (Rth = (nx−nz) × d, Δnd = (nx−ny) × d).
By using a birefringent layer having such optical characteristics, good viewing angle characteristics can be obtained.

The birefringent layer can be composed of a retardation plate made of various films, for example. Examples of the retardation plate include polycarbonate, polyvinyl alcohol, polystyrene, polymethyl methacrylate, polypropylene, polyolefins other than polypropylene, cyclic polyolefins such as polyarylate and norbornene resins, and resin films made of appropriate polymers such as polyamide. Examples include a birefringent film subjected to stretching treatment, a liquid crystal polymer alignment film, and a liquid crystal polymer alignment layer supported by a synthetic resin film. The birefringent layer can be composed of a single layer of these films or a multilayer in which the same or different films are laminated.
The thickness of the birefringent layer is not particularly limited, but it is preferable that the birefringent layer is formed thinner in order to reduce the thickness and weight of the optical film. For example, in the case of a single birefringent layer, the thickness is preferably about 10 μm to 40 μm, and more preferably about 15 μm to 25 μm. When the birefringent layer is composed of a plurality of layers, the thickness of each layer constituting the multilayer is preferably about 10 μm to 40 μm, more preferably about 15 μm to 25 μm.

  Integration of the polarizing plate and the retardation plate (birefringent layer) is performed, for example, with an adhesive. As this adhesive, for example, an acrylic polymer, silicone polymer, polyester, polyurethane, polyamide, polyether, a resin having a base polymer such as a fluorine-based or rubber-based polymer, or the like can be used.

  In particular, the adhesive layer is preferably optically transparent, such as acrylic, has adhesive properties such as moderate wettability, pseudo-collectability, and adhesiveness, and is excellent in weather resistance and the like. Furthermore, it is preferable to have a low moisture absorption rate and excellent heat resistance, such as prevention of foaming phenomenon and peeling phenomenon due to moisture absorption, deterioration of optical characteristics due to difference in thermal expansion, and prevention of warping of the liquid crystal cell.

  Examples of the pressure-sensitive adhesive include resins made of natural products and synthetic materials, in particular, tackifier resins, glass fibers, glass beads, metal powder, fillers made of other inorganic powders, colorants, antioxidants, etc. A conventionally well-known additive etc. which can be added to an adhesion layer may be added.

  Moreover, in order to improve adhesiveness with an adhesive, for example, an anchor layer etc. can also be provided in the main surface provided with the adhesive mentioned above in a polarizing plate or a birefringent layer.

  The anchor layer is made of, for example, a polyamine compound, and the thickness thereof is 5 nm to 500 nm. Further, from the viewpoint of improving adhesiveness and controlling peeling charging, the anchor layer is preferably 5 nm or more, more preferably 10 nm or more. On the other hand, the upper limit of the thickness of the anchor layer is preferably 500 nm or less, more preferably 500 nm or less, more preferably 300 nm or less, and an optimum range of 200 nm or less because optical characteristics and the like may be deteriorated. In the anchor layer, if the thickness is too thick, the film itself of the polyamine compound or the like has a low film strength, so there is a risk of destruction in the layer, and the adhesion strength between the layers may decrease. It is designed appropriately considering the points.

  In addition, as the anchor layer, for example, an ethyleneimine adduct of polyacrylic acid ester is proposed in Japanese Patent Laid-Open No. 10-20118. However, the anchor layer proposed in this publication has a small proportion of primary amine (secondary amino group) contained in the molecule, and the polyacrylate portion acts on the adhesion to the substrate. Since it is difficult, it is difficult to sufficiently improve interlayer adhesion.

  In this respect, in order to obtain an anchor layer capable of obtaining sufficient interlayer adhesion, for example, an allylamine compound is preferably used as the polyamine compound, and polyallylamine is particularly preferably used. Specific examples include polyethyleneimine.

The optical film of the present invention is obtained by laminating the above-mentioned various polarizing plates and a birefringent layer in an appropriate combination.
An optical film obtained by appropriately combining a polarizing plate and a birefringent layer can be used as a so-called elliptically polarizing plate or circularly polarizing plate. The elliptically polarizing plate is effectively used for black and white display without coloring by compensating (preventing) coloring (blue or yellow) caused by birefringence in the liquid crystal layer of a super twist nematic (STN) type liquid crystal display device. It is done. Furthermore, the one in which the three-dimensional refractive index is controlled is preferable because it can compensate (prevent) coloring that occurs when the screen of the liquid crystal display device is viewed from an oblique direction. The circularly polarizing plate is effectively used, for example, when adjusting the color tone of an image of a reflective liquid crystal display device in which the image is displayed in color, and also has an antireflection function.

Further, by providing a viewing angle compensation function to the optical film of the present invention, the viewing angle can be widened so that the image can be seen relatively clearly even when the screen of the liquid crystal display device is viewed from a slightly oblique direction. Such an optical film can be achieved by including, for example, a birefringent film biaxially stretched in the plane direction as the birefringent layer. That is, as a normal birefringent layer (retardation plate), a polymer film having birefringence stretched uniaxially in the plane direction is used, whereas a birefringent layer having a viewing angle compensation function has a plane direction. Biaxially stretched biaxially, birefringent films such as birefringent films with a controlled refractive index in the thickness direction, uniaxially stretched in the plane direction and stretched in the thickness direction, and tilted orientation films A stretched film or the like is used. Examples of the inclined alignment film include a film obtained by bonding a heat shrink film to a polymer film and stretching or / and shrinking the polymer film under the action of the contraction force by heating, and a film obtained by obliquely aligning a liquid crystal polymer. Can be mentioned. As the raw material polymer for the birefringent layer having a viewing angle compensation function, the same polymer as that described in the film example of the retardation plate is used.
In addition, a liquid crystal polymer alignment layer, particularly an optically anisotropic layer composed of a discotic liquid crystal polymer gradient alignment layer, supported by a triacetyl cellulose film is preferable from the viewpoint of achieving a wide viewing angle with good visibility. .

Furthermore, a brightness enhancement film can be bonded to the optical film of the present invention. Such an optical film is usually provided on the back side of a liquid crystal cell, and light such as a backlight can be efficiently used for displaying an image on a liquid crystal display device, and the screen can be brightened.
The principle will be briefly described. The brightness enhancement film reflects a linearly polarized light with a predetermined polarization axis or a circularly polarized light in a predetermined direction when natural light is incident due to a backlight such as a liquid crystal display device or reflection from the back side, and transmits other light. is there. Then, the light reflected by the brightness enhancement film surface is further reversed through a reflective layer or the like provided on the back side of the backlight and re-incident on the brightness enhancement film, and part or all of the light is reflected in a predetermined polarization state. Luminance can be improved by increasing the amount of light transmitted through the brightness enhancement film and increasing the amount of light by supplying polarized light that is difficult to be absorbed by the polarizer to the polarizer. That is, when light is incident through the polarizer from the back side of the liquid crystal cell without using a brightness enhancement film, the light having a polarization direction that does not coincide with the polarization axis of the polarizer is hardly polarized. And is not transmitted through the polarizer. Depending on the characteristics of the polarizer used, approximately 50% of the light is absorbed by the polarizer. Therefore, the amount of absorption and the amount of light that can be used for liquid crystal image display are reduced, and the image becomes dark. On the other hand, the brightness enhancement film is reflected once by the brightness enhancement film without entering the polarizer with light having a polarization direction that is absorbed by the polarizer. The reflected light is further inverted through a reflective layer or the like provided on the rear side thereof, and reenters the brightness enhancement film. While repeating this, the brightness enhancement film transmits only the polarized light whose polarization direction is such that the polarization direction of the light can pass through the polarizer, and supplies it to the polarizer. It can be efficiently used for displaying images on a liquid crystal display device, and the screen can be brightened.

  Further, a diffusion plate can be provided between the brightness enhancement film and the reflective layer. The polarized light reflected by the brightness enhancement film is directed to the reflection layer or the like, but the installed diffuser plate uniformly diffuses the light passing therethrough, and at the same time cancels the polarization state and becomes a non-polarized state. That is, the diffusion plate has a function of returning polarized light to the original natural light state. The light in the non-polarized state, that is, the natural light state is directed toward the reflection layer and the like, reflected through the reflection layer and the like, and again passes through the diffusion plate and reenters the brightness enhancement film. In this way, by providing a diffuser plate that returns polarized light to its original natural light state between the brightness enhancement film and the reflective layer, etc., while maintaining the brightness of the display screen, at the same time, the brightness unevenness of the display screen is reduced and uniform. Can provide a bright screen. By providing such a diffusion plate, it is considered that the first incident light has a moderate increase in the number of repetitions of reflection, and can provide a uniform bright display screen coupled with the diffusion function of the diffusion plate.

  The brightness enhancement film has a characteristic of transmitting linearly polarized light having a predetermined polarization axis and reflecting other light, such as a multilayer thin film of dielectric material or a multilayer laminate of thin film films having different refractive index anisotropies. Such as a cholesteric liquid crystal polymer alignment film or a film substrate whose alignment liquid crystal layer is supported on a film substrate, reflecting either left-handed or right-handed circularly polarized light and transmitting other light Appropriate things such as can be used.

Therefore, in the brightness enhancement film of the type that transmits linearly polarized light having the predetermined polarization axis as described above, the transmitted light is incident on the polarizing plate with the polarization axis aligned as it is, thereby efficiently transmitting while suppressing absorption loss due to the polarizing plate. Can be made. On the other hand, in a brightness enhancement film of a type that transmits circularly polarized light such as a cholesteric liquid crystal layer, it can be directly incident on a polarizer, but from the point of suppressing absorption loss, the circularly polarized light is linearly polarized through a birefringent layer. It is preferable to make it enter into a polarizing plate. Note that circularly polarized light can be converted to linearly polarized light by using a λ / 4 plate as the birefringent layer.
A birefringent layer that functions as a λ / 4 plate in a wide wavelength range such as a visible light region is, for example, a layer that functions as a λ / 4 plate with respect to light-color light having a wavelength of 550 nm and a layer that exhibits other retardation characteristics, such as λ / 2 It can be obtained by a method of superimposing a layer functioning as a plate.

  The cholesteric liquid crystal layer also has a structure in which two or three or more layers are overlapped with a combination of those having different reflection wavelengths to obtain one that reflects circularly polarized light in a wide wavelength range such as the visible light region. And transmission circularly polarized light in a wide wavelength range can be obtained based on this.

  The optical film of the present invention can be formed by a method in which all or a part of each layer is sequentially and separately laminated in the manufacturing process of a liquid crystal display device or the like. This has the advantage of improving the manufacturing process of the liquid crystal display device and the like.

(Liquid crystal cell, image display device, etc.)
The optical film is used by being bonded to, for example, a liquid crystal cell.
FIG. 1 shows a configuration example of a liquid crystal cell having an optical film.
In FIG. 1, 1 indicates a liquid crystal cell. Examples of the liquid crystal cell 1 include an active matrix drive type typified by a thin film transistor type and a simple matrix drive type typified by a twist nematic type and a super twist nematic type.
On this liquid crystal cell 1, the optical film 2 is laminated | stacked through the adhesive layer (not shown. The following is the same). Specifically, a retardation film 21 is laminated on the liquid crystal cell 1 via an adhesive layer, and a polarizing plate 22 is laminated thereon via an adhesive layer. The polarizing plate 22 has a polarizer 221 at the center, and a protective film 223 is laminated on the main surfaces on both sides of the polarizing plate 22 with an adhesive layer 222 interposed therebetween.
When laminating the optical film and the liquid crystal cell, an adhesive layer may be provided on the optical film in advance.
The pressure-sensitive adhesive for laminating the optical film and the liquid crystal cell is not particularly limited. For example, an acrylic polymer, silicone polymer, polyester, polyurethane, polyamide, polyether, fluorine-based or rubber-based polymer is used as a base polymer. Can be appropriately selected and used. In particular, an acrylic pressure-sensitive adhesive having excellent optical transparency, moderate wettability, cohesiveness, and adhesive pressure-sensitive adhesive properties, and excellent weather resistance and heat resistance is preferable.

  Furthermore, in addition to the above, points such as prevention of foaming and peeling phenomenon due to moisture absorption, deterioration of optical characteristics and liquid crystal cell warpage due to differences in thermal expansion, etc., and formation of a liquid crystal display device with high quality and excellent durability More preferred is a pressure-sensitive adhesive layer having a low moisture absorption rate and excellent heat resistance.

  Examples of the pressure-sensitive adhesive include natural and synthetic resins, in particular, tackifier resins, fillers and pigments made of glass fibers, glass beads, metal powders, other inorganic powders, colorants, antioxidants, and the like. It may contain an additive to be added to the adhesive layer. Moreover, the adhesive layer etc. which contain microparticles | fine-particles and show light diffusibility may be sufficient.

  The application of the pressure-sensitive adhesive to one side or both sides of the optical film is not particularly limited, and can be performed by an appropriate method. For example, a pressure-sensitive adhesive solution of about 10 to 40% by weight in which a base polymer or a composition thereof is dissolved or dispersed in a solvent composed of a single solvent or a mixture of appropriate solvents such as toluene and ethyl acetate is prepared. A method of directly coating on an optical film by an appropriate development method such as a rolling method or a coating method, or a method of forming an adhesive layer on a separator according to this method and transferring it onto the optical film. Can be mentioned.

  The pressure-sensitive adhesive layer can be provided on one side or both sides of the optical film as a superposed layer of different compositions or types. Moreover, when providing in both surfaces, it can also be set as adhesive layers, such as a different composition, a kind, and thickness, in the front and back of an optical film. The thickness of the pressure-sensitive adhesive layer can be appropriately determined according to the purpose of use and adhesive force, and is generally 1 μm to 500 μm, preferably 5 μm to 200 μm, and particularly preferably 10 μm to 100 μm.

  On the exposed surface of the adhesive layer, a separator is temporarily attached and covered for the purpose of preventing contamination until it is put to practical use. Thereby, it can prevent contacting an adhesive layer in the usual handling state. As the separator, except for the above thickness conditions, for example, a suitable thin leaf body such as a plastic film, rubber sheet, paper, cloth, non-woven fabric, net, foam sheet, metal foil, laminate thereof, and the like, silicone type or Conventionally known materials such as those coated with an appropriate release agent such as long-chain alkyl, fluorine-based, or molybdenum sulfide can be used.

  In the present invention, each layer such as the polarizer, the protective film, and the pressure-sensitive adhesive layer includes, for example, an ultraviolet ray such as a salicylic acid ester compound, a benzophenol compound, a benzotriazole compound, a cyanoacrylate compound, or a nickel complex compound. Ultraviolet absorbing ability may be imparted by a method of treating with an absorbent.

  The optical film of the present invention can be preferably used for forming various devices such as a liquid crystal display device. In general, a liquid crystal display device is formed by appropriately assembling components such as a liquid crystal cell, an optical film, and an illumination system as necessary, and incorporating a driving circuit. There is no particular limitation on the structure of the liquid crystal display device except that it is used. For example, an appropriate liquid crystal display device such as a liquid crystal display device in which a polarizing plate or an optical film is disposed on one side or both sides of a liquid crystal cell, and a backlight or a reflecting plate as an illumination system is exemplified. As the liquid crystal cell, any type such as a TN type, an STN type, or a π type can be used. When configuring a liquid crystal display device, for example, a single layer of appropriate parts such as a diffusion plate, an antiglare layer, an antireflection film, a protective plate, a prism array, a lens array sheet, a light diffusion plate, and a backlight are provided at appropriate positions. Alternatively, two or more layers can be arranged.

  Next, an organic electroluminescence device (organic EL display device) will be described. Generally, in an organic EL display device, a transparent electrode, an organic light emitting layer, and a metal electrode are sequentially laminated on a transparent substrate to form a light emitter (organic electroluminescent light emitter). Here, the organic light emitting layer is a laminate of various organic thin films, for example, a laminate of a hole injection layer made of a triphenylamine derivative and the like and a light emitting layer made of a fluorescent organic solid such as anthracene, Or, a structure having various combinations such as a stacked body of an electron injection layer composed of such a light emitting layer and a perylene derivative, a stacked body of these hole injection layer, light emitting layer, and electron injection layer is known. Yes.

  In organic EL display devices, holes and electrons are injected into the organic light-emitting layer by applying a voltage to the transparent electrode and the metal electrode, and the energy generated by recombination of these holes and electrons excites the phosphor material. Then, light is emitted on the principle that the excited fluorescent material emits light when returning to the ground state. The mechanism of recombination in the middle is the same as that of a general diode, and as can be predicted from this, the current and the emission intensity show strong nonlinearity with rectification with respect to the applied voltage.

  In an organic EL display device, in order to extract light emitted from the organic light emitting layer, at least one of the electrodes must be transparent, and a transparent electrode usually formed of a transparent conductor such as indium tin oxide (ITO) is used as an anode. It is used as. On the other hand, in order to facilitate electron injection and increase luminous efficiency, it is important to use a material having a small work function for the cathode, and usually metal electrodes such as Mg—Ag and Al—Li are used.

  In the organic EL display device having such a configuration, the organic light emitting layer is formed of a very thin film having a thickness of about 10 nm. For this reason, the organic light emitting layer transmits light almost completely like the transparent electrode. As a result, light that is incident from the surface of the transparent substrate at the time of non-light emission, passes through the transparent electrode and the organic light emitting layer, and is reflected by the metal electrode is again emitted to the surface side of the transparent substrate. The display surface of the organic EL display device looks like a mirror surface.

  In an organic EL display device comprising an organic electroluminescent light emitting device comprising a transparent electrode on the surface side of an organic light emitting layer that emits light upon application of a voltage and a metal electrode on the back side of the organic light emitting layer, the surface of the transparent electrode The polarizing plate may be provided on the side, and the birefringent layer may be provided between the transparent electrode and the polarizing plate.

  Since the optical film has a function of polarizing light incident from the outside and reflected by the metal electrode, there is an effect that the mirror surface of the metal electrode is not visually recognized by the polarization function. In particular, if the birefringent layer is composed of a λ / 4 plate and the angle between the polarizing direction of the polarizing plate and the birefringent layer is adjusted to π / 4, the mirror surface of the metal electrode can be completely shielded. .

  That is, only the linearly polarized light component of the external light incident on the organic EL display device is transmitted by the polarizing plate. This linearly polarized light generally becomes elliptically polarized light by the birefringent layer, but becomes circularly polarized light when the birefringent layer is a λ / 4 plate and the angle formed by the polarization direction with the polarizing plate is π / 4 as described above. . This circularly polarized light is transmitted through the transparent substrate, the transparent electrode, and the organic thin film, is reflected by the metal electrode, is again transmitted through the organic thin film, the transparent electrode, and the transparent substrate, and becomes linearly polarized light again at the birefringent layer. And since this linearly polarized light is orthogonal to the polarization direction of a polarizing plate, it cannot permeate | transmit a polarizing plate. As a result, the mirror surface of the metal electrode can be completely shielded.

Examples of the present invention will be described below. However, the present invention is not limited to the following examples.
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Example 1
(Production of polarizer)
A PVA film having an average polymerization degree of 2400, a saponification degree of 99.9 mol%, and a thickness of 75 μm was immersed in water at 30 ° C. for 60 seconds to swell. Next, this film was immersed in an aqueous solution of 0.3% by weight of iodine / potassium iodide (weight ratio = 0.5 / 8), and the film was dyed while being stretched up to 3.5 times. Thereafter, the film was stretched in a boric acid ester aqueous solution at 65 ° C. so that the total length (relative to the initial length) was 6 times. After stretching, the film was dried for 3 minutes in a high-temperature bath at 40 ° C. In this way, a polarizer having a thickness of 25 μm was produced.

(Preparation of adhesive)
To 100 parts by weight of PVA-based resin containing acetoacetyl groups (average polymerization degree: 1200, saponification degree: 98.5 mol%, acetoacetylation degree: 5 mol%), 31 parts by weight of methylolmelamine serving as a crosslinking agent And dissolved in pure water at 30 ° C., and the solid content concentration was adjusted to 4% by weight.

(Preparation of polarizing plate)
The adhesive was applied to a main surface on one side of a 80 μm-thick triacetyl cellulose film so that the thickness after drying was 80 nm and dried. Application of the adhesive was performed in a temperature atmosphere of 30 ° C. 30 minutes after the preparation of the adhesive.
Next, the protective film with the adhesive was bonded to the main surfaces on both sides of the polarizer in a 30 ° C. atmosphere with a roll machine, and then dried in a 55 ° C. atmosphere for 6 minutes to obtain Example 1. The polarizing plate which concerns is produced.

(Production of optical film)
Next, as a birefringent layer, a 25 μm thick resin film made of polycarbonate was stretched to produce a 20 μm thick film having a retardation value of Δnd of 140 nm and Rth of 140 nm. This film was bonded to the main surface on one side of the polarizing plate with an adhesive made of an acrylic resin. In this manner, an optical film according to Example 1 (thickness: about 209 μm, length: 30 mm × width: 40 mm) was produced.

Example 2
An optical film according to Example 2 was produced in the same manner as in Example 1 except that 46 parts by weight of methylol melamine was added to 100 parts by weight of the PVA-based resin to produce an adhesive.
Example 3
An optical film according to Example 3 was produced in the same manner as in Example 1 except that 40 parts by weight of methylol melamine was added to 100 parts by weight of the PVA-based resin to produce an adhesive.

Example 4
(Preparation of polarizer, adhesive, polarizing plate)
A polarizing plate produced in the same manner as in Example 1 was used as the polarizing plate according to Example 4.

(Production of optical film)
A resin film made of polycarbonate having a thickness of 25 μm was stretched to produce a 20 μm-thick film having a retardation value of Δnd of 140 nm and Rth of 140 nm (referred to as birefringent layer 1). Furthermore, a 25 μm thick resin film made of polycarbonate was stretched to produce a 20 μm thick film having a retardation value of Δnd of 550 nm and Rth of 550 nm (referred to as birefringent layer 2). The two birefringent layers 1 and 2 are laminated on the main surface on one side of the polarizing plate in the order of the polarizing plate, the birefringent layer 1 and the birefringent layer 2, and each layer is made of an acrylic resin. It bonded together with the adhesive. In this manner, an optical film according to Example 4 (thickness: about 230 μm, length 30 mm × width 40 mm) was produced.

Comparative Example 1
An optical film according to Comparative Example 1 was produced in the same manner as in Example 1 described above except that 30 parts by weight of methylolmelamine was added to 100 parts by weight of the PVA resin.

Comparative Example 2
An adhesive was prepared in the same manner as in Example 1 except that 47 parts by weight of methylol melamine was added to 100 parts by weight of the PVA resin.
When this adhesive was used in the production of a polarizing plate in the same manner as in Example 1, gelation had progressed, and the adhesive could not be applied so as to have a substantially uniform thickness. It could not be produced.

Comparative Example 3
An optical film according to Comparative Example 3 was produced in the same manner as Example 1 described above except that 25 parts by weight of methylolmelamine was added to 100 parts by weight of the PVA resin.

Humidification test In order to confirm the water resistance in the adhesive layer of the optical film according to each example and comparative example, a humidification test was performed.
When performing a humidification test, the film of each Example and the comparative example was cut out so that it might become 25 mm in the absorption axis direction of the polarizer and 25 mm in the direction orthogonal to an absorption axis, and each test piece was produced. First, the thickness of these test pieces was measured with a caliper. Next, after each test piece was immersed in warm water at 60 ° C. for 300 minutes, the amount of peeling (mm) at the four ends of the test piece was measured with a caliper.
Table 1 shows the results of the total thickness of the birefringent layer of each example and each comparative example, the total thickness of the test piece before humidification, and the amount of peeling after the humidification test. Table 1 shows the average value of the amounts of peeling at the four ends.

  From the evaluation results shown in Table 1, Example 1 using a PVA adhesive containing 31 parts by weight, 40 parts by weight, or 46 parts by weight of a crosslinking agent for 100 parts by weight of a PVA resin having an acetoacetyl group, respectively. -4 are compared to Comparative Example 1 containing 30 parts by weight of a crosslinking agent with respect to 100 parts by weight of a PVA-based resin having an acetoacetyl group and Comparative Example 3 containing 25 parts by weight. It can be seen that there is no lifting or peeling. That is, it is apparent that sufficient water resistance cannot be obtained by adding about 30 parts by weight or less of the crosslinking agent to 100 parts by weight of the PVA resin.

The reference sectional view showing one embodiment of the liquid crystal cell in which the optical film was laminated.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Liquid crystal cell, 2 ... Optical film, 21 ... Phase difference plate (birefringent layer), 22 ... Polarizing plate, 221 ... Polarizer, 222 ... Adhesive layer, 223 ... Protective film

Claims (10)

A polarizing plate in which at least one protective film is laminated on the polarizer via an adhesive, and a birefringent layer laminated on the polarizing plate,
An optical film, wherein the adhesive contains a crosslinking agent in a range of more than 30 parts by weight and 46 parts by weight or less with respect to 100 parts by weight of a polyvinyl alcohol resin containing an acetoacetyl group.   The optical film according to claim 1, wherein the crosslinking agent contains methylol melamine.   The optical film according to claim 1, wherein the polarizer is a polyvinyl alcohol-based polarizer, and the protective film is a cellulose-based protective film. The optical film according to claim 1, wherein the birefringent layer exhibits optical characteristics of nx> ny≈nz.
Where nx is the refractive index in the slow axis direction of the birefringent layer, ny is the refractive index in the coherent phase axis direction, and nz is the refractive index in the same thickness direction.   The optical film according to claim 1, wherein the birefringent layer has a single layer or a multilayer structure.   The optical film according to claim 5, wherein the thickness of the single layer or the thickness of each layer constituting the multilayer is 10 μm to 40 μm.   The optical film according to claim 1, wherein the birefringent layer includes at least one polymer selected from polycarbonate, polyvinyl alcohol, polystyrene, polymethyl methacrylate, polypropylene, polyarylate, norbornene, and polyamide.   A liquid crystal cell comprising the optical film according to claim 1.   A liquid crystal display device comprising the liquid crystal cell according to claim 8. The image display apparatus containing the optical film in any one of Claims 1-7.

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