JP5763367B2 - Method for producing acrylic resin film, acrylic resin film produced by the method, and polarizing plate - Google Patents

Description

  The present invention relates to a method for producing an acrylic resin film, an acrylic resin film produced by the method, and a polarizing plate, and in particular, a method for producing an acrylic resin film containing rubber elastic particles and the method. The present invention relates to an acrylic resin film and a polarizing plate.

  The polarizing plate is used as a constituent member of a liquid crystal display device, and the demand for the polarizing plate is rapidly increasing with the spread of the liquid crystal display device. With the application of a liquid crystal display device to a large-sized television or the like, the polarizing plate is also required to be thinner and cheaper while maintaining or improving its performance.

  In general, a polarizing plate has a structure in which a transparent protective film is bonded to at least one side, usually both sides, of a polarizing film made of a polyvinyl alcohol-based resin in which a dichroic dye is adsorbed and oriented. As the protective film for the polarizing plate, a film of cellulose acetate resin typified by triacetyl cellulose is often used, and the thickness is usually about 40 to 120 μm. For bonding such a cellulose acetate resin film to a polarizing film, an adhesive made of an aqueous solution of a polyvinyl alcohol resin is often used. However, a polarizing plate in which a protective film is laminated on a polarizing film through a water-soluble adhesive has a problem that the polarizing performance is deteriorated or the protective film is peeled off from the polarizing film when used for a long time under wet heat conditions. was there.

  Therefore, there is an attempt to configure the protective film bonded to the polarizing film with a resin other than the cellulose acetate resin. As such a resin, a technique using an acrylic resin which is a relatively inexpensive resin material is known. As such a technique, for example, a protective film (see Patent Document 1) using a (meth) acrylic resin containing a lactone ring is known. Furthermore, a protective film (see Patent Document 2) is also developed in which an acrylic resin is uniaxially or biaxially stretched within a stretch ratio of 50 to 200%. By using such a stretched acrylic resin, an optical film having excellent mechanical strength and heat shrinkability can be obtained.

  However, the conventional outer resin film made of an acrylic resin has a problem that it is inferior in flexibility and easily broken. Therefore, research is being carried out to increase the flexibility of acrylic resin films and make them difficult to break. The inventors have so far developed a technique for increasing the flexibility of an acrylic resin film by blending rubber elastic particles with an acrylic resin.

JP 2009-122663 A JP 2008-216586 A

  An acrylic resin film containing rubber elastic particles in an acrylic resin is more flexible, but when an impact is applied to the film surface, irregularities such as dents (dents) and pyramids (convex parts) are formed on the film surface. It was found that the shape tends to occur and the uneven shape once generated tends to be difficult to disappear. This is presumably because the stress applied to the periphery of the irregularities on the film surface was likely to remain in the film as a result of blending the elastic rubber particles with the acrylic resin. Generally, acrylic resin films are stored, transported, etc. as raw materials wound into a roll after being formed into a sheet, but such irregularities on the film surface are films that overlap in a roll It is likely to occur when foreign matter such as dust is caught between each other. Such unevenness on the surface of the film becomes a defect when an acrylic resin film is used for a polarizing plate or the like, and causes deterioration of visibility.

  An object of the present invention is to provide a method for producing a smooth acrylic resin film with few irregularities such as dents and pyramids on the film surface, and an acrylic resin film produced by the method. Another object of the present invention is to provide a polarizing plate with few defects and good visibility, using such a smooth acrylic resin film.

  That is, according to the method for producing an acrylic resin film of the present invention, the above-described problem is a method for producing an acrylic resin film comprising an acrylic resin composition in which rubber elastic particles are blended with an acrylic resin, It is solved by pressing a pressing member having a smooth surface and heated to a predetermined heating temperature against the film surface.

  In this case, the rubber elastic body particles preferably have a number average particle diameter in the range of 10 to 300 nm and are blended in an amount of 25 to 45% by weight with respect to the acrylic resin.

  Moreover, it is preferable that the said heating temperature exists in the range of Tg-50 degreeC or more and Tg + 5 degrees C or less, when the glass transition temperature of the said acrylic resin composition is set to Tg.

  Furthermore, it is preferable that the pressing member is a heat roll or a heat iron.

  Moreover, according to the acrylic resin film of this invention, the said subject is solved by being manufactured by the method in any one of said.

  The said subject is solved by laminating | stacking the acrylic resin film as described above and a polarizing film according to the polarizing plate of this invention.

  According to the method for producing an acrylic resin film of the present invention, a pressing member having a smooth surface and heated to a predetermined heating temperature is pressed against the film surface. The stress that generates the light is relaxed by heat, and the film surface can be smoothed.

  In addition, according to the acrylic resin film of the present invention, it is possible to provide an acrylic resin film with less irregularities on the film surface, a smooth surface and less defects. Furthermore, according to the polarizing plate of the present invention, by using the acrylic resin film having a smooth surface and few defects as described above, it is possible to provide a polarizing plate having few problems due to unevenness and having good visibility. It becomes possible.

It is the schematic diagram which showed the manufacturing method of the acrylic resin film in 1st Embodiment. It is the cross-sectional schematic diagram which showed an example of the polarizing plate. It is the cross-sectional schematic diagram which showed an example of the liquid crystal display device which uses a polarizing plate. It is the schematic diagram which showed the manufacturing method of the acrylic resin film in 2nd Embodiment. It is the top view which showed embodiment of the evaluation test by the heat iron process of an Example. It is a photograph of the dent and its peripheral region before and after the thermal ironing process.

  Hereinafter, some embodiments of the present invention will be described with reference to the drawings. In addition, this invention is not limited by the member, arrangement | positioning, etc. which are demonstrated below, These members etc. can be suitably changed in accordance with the meaning of this invention.

  Hereinafter, the acrylic resin film will be described. The acrylic resin film of the present invention is a sheet-like film made of an acrylic resin composition in which rubber elastic body particles are blended with an acrylic resin.

(First embodiment)
Drawing 1 is a mimetic diagram showing the manufacturing method of the acrylic resin film in a 1st embodiment, and shows the example which used the heat roll as a press member in this embodiment. As shown in this figure, the method for producing an acrylic resin film includes a step of feeding a sheet-like acrylic resin film 25 from an acrylic resin film raw fabric 11 wound in a roll shape, and a roll on the acrylic resin film 25. A smoothing step for smoothing the surface irregularities by pressing the hot roll, and a winding step for winding the acrylic resin film 25 whose surface is smoothed by the smoothing step into a roll shape. .

  The acrylic resin film 25 can be manufactured by forming a sheet of an acrylic resin composition in which rubber elastic particles are blended with an acrylic resin, as will be described later. The manufactured acrylic resin film 25 is usually wound into a roll and stored and transported as a raw material. The acrylic resin film 25 is unwound from a raw material into a sheet as needed.

  The acrylic resin film 25 is more likely to have surface irregularities such as dents and pyramids due to external impacts compared to films formed from other resin materials such as polypropylene resins, and even if time passes. The uneven shape is difficult to disappear. This is because the acrylic resin film 25 has a property that when the surface is subjected to an impact or the like, the stress is likely to remain on the film, and thus the uneven shape formed by the impact is difficult to disappear. Conceivable. In particular, when the acrylic resin film 25 is wound into a roll and made into a raw material, if foreign matter such as dust is sandwiched between the laminated acrylic resin film 25, the portion becomes a dent (concave portion). Or a pyramid (convex portion) when viewed from the opposite side.

  In the present invention, by pressing a pressing member (heat roll 14 in this embodiment) having a smooth surface and heated to a predetermined heating temperature against the surface of the acrylic resin film 25, the above-described stress is relieved and a dent is formed. It is characterized in that the surface of the film is smoothed by reducing the uneven shape such as a ridge and a pyramid.

  The hot roll 14 is a roll-shaped member having a smooth surface and capable of being heated at a predetermined temperature. The surface of the heat roll 14 is formed of a material such as a metal having high thermal conductivity and high rigidity. Examples of the metal material constituting the surface of the hot roll 14 include chrome and stainless steel.

  The surface of the heat roll 14 is characterized by being smooth. As such a heat roll 14, a surface whose surface is mirror-finished is preferably used. As for the roughness of the surface of the hot roll 14, for example, the maximum height (Ry) is preferably 5 μm or less, more preferably 2 μm or less, and further preferably 1 μm or less. Moreover, although the minimum of the maximum height (Ry) of the heat roll 14 is not specifically limited, For example, it is 0.01 micrometer or more.

  A heating element is provided inside the heat roll 14 of the present embodiment. As the heating element, known heating means such as an electric resistance heating element or a dielectric heating coil can be employed. The heat generated by the heating element is transmitted to the surface of the heat roll 14 and heats the acrylic resin film 25 pressed against it. The heating temperature can be appropriately set depending on the composition of the acrylic resin composition constituting the acrylic resin film 25, and the closer to Tg, the better the glass transition temperature of the acrylic resin composition as Tg. . Moreover, it is preferable to set as the range of heating temperature so that it may become in the range of Tg-50 degreeC or more and Tg + 5 degreeC or less. When the temperature is lower than Tg-50 ° C., the heating temperature is not sufficient to relieve the residual stress of the acrylic resin film 25, and it is difficult to smooth the unevenness of the film surface. On the other hand, if it exceeds Tg + 5 ° C., the acrylic resin film 25 contracts, making it difficult to use it for an optical film or the like.

  The heating time can be appropriately set according to the glass transition temperature (Tg) of the acrylic resin film 25 and the heating temperature of the hot roll 14, but is usually in the range of 1 to 60 seconds. When the heating time is less than 1 second, the acrylic resin film 25 cannot be sufficiently heated, and the unevenness tends to remain on the surface. On the other hand, when the heating time exceeds 60 seconds, the heating time becomes too long and the acrylic resin film 25 is likely to suffer from heat shrinkage. It is preferable to set the heating time shorter as the heating temperature of the hot roll 14 is closer to the glass transition temperature (Tg). On the contrary, it is preferable to set the heating temperature longer as the heating temperature becomes lower than the glass transition temperature (Tg).

  The acrylic resin film 25 fed out from the acrylic resin film original 11 into a sheet shape is guided by the guide rolls 12 and 13 and is finally wound up in a roll shape by the winding roll 15. The heat roll 14 of the present embodiment is located between the guide roll 12 and the guide roll 13. Tension is generated along the machine flow direction of the acrylic resin film 25 between the acrylic resin film original fabric 11 and the take-up roll 15, and the acrylic resin film 25 is pulled in the machine flow direction. It has become. The heat roll 14 presses the acrylic resin film 25 against this tension. The acrylic resin film 25 is wound around the outer periphery of the heat roll 14, and the heat roll 14 can apply heat while rotating while pressing the acrylic resin film 25. By such press heat treatment, the uneven shape of the acrylic resin film 25 and the stress remaining in the periphery thereof are alleviated, the uneven shape becomes small, and the film surface becomes smooth.

(1) Acrylic resin film 25;
Next, the acrylic resin film 25 will be described. The acrylic resin film 25 is a film made of an acrylic resin composition in which rubber elastic particles are blended with an acrylic resin, and used for a protective film of the polarizing plate 20 as shown in FIG. Can do. Here, acrylic resin means (meth) acrylic resin and is a concept including both acrylic resin and methacrylic resin. Hereinafter, the acrylic resin will be described.

(1-1) Acrylic resin;
As described above, the acrylic resin is a (meth) acrylic resin and means a polymer of acrylic acid ester or methacrylic acid ester. As the polymer of the methacrylic acid ester, for example, a polymer composed mainly of an alkyl methacrylate is preferable. The monomer composition of the alkyl methacrylate is preferably 70% by weight or more, more preferably 80% by weight or more, and still more preferably 90% by weight or more, based on the total 100% by weight of all monomers. And alkyl methacrylate is 99% by weight or less. The acrylic resin may be a homopolymer of alkyl methacrylate, or a copolymer of 50% by weight or more of alkyl methacrylate and 50% by weight or less of a monomer other than alkyl methacrylate. Also good. As the alkyl methacrylate, those having 1 to 4 carbon atoms of the alkyl group are usually used, and among them, methyl methacrylate is preferably used.

  The monomer other than alkyl methacrylate may be a monofunctional monomer having one polymerizable carbon-carbon double bond in the molecule, or two or more polymerizable carbons in the molecule. -A polyfunctional monomer having a carbon double bond may be used. In particular, monofunctional monomers are preferably used. Examples thereof include alkyl acrylates such as methyl acrylate and ethyl acrylate, styrene monomers such as styrene and alkyl styrene, acrylonitrile and methacrylonitrile. Such unsaturated nitriles. When using alkyl acrylate as a copolymerization component, the carbon number is 1-8 normally.

  The acrylic resin preferably does not have a glutarimide derivative, a glutaric anhydride derivative, a lactone ring structure, or the like. These acrylic resins may not have sufficient mechanical strength and heat-and-moisture resistance as the acrylic resin film 25 in some cases.

(1-2) Rubber elastic particles;
In order to improve flexibility and handleability, rubber-based elastic particles are blended in the acrylic resin. The rubber elastic particles are particles containing a rubber elastic body, and may be particles composed only of a rubber elastic body, or may be particles having a multilayer structure having a rubber elastic body layer. Examples of rubber elastic bodies include olefin-based elastic polymers, diene-based elastic polymers, styrene-diene-based elastic copolymers, and acrylic-based elastic polymers. Among these, an acrylic elastic polymer is preferable from the viewpoint of the surface hardness, light resistance, and transparency of the acrylic resin film 25.

  The acrylic elastic polymer is preferably a polymer mainly composed of alkyl acrylate, and may be a homopolymer of alkyl acrylate, or may be a single polymer other than alkyl acrylate of 50% by weight or more and alkyl acrylate. A copolymer with 50% by weight or less of the monomer may be used. As the alkyl acrylate, those having 4 to 8 carbon atoms in the alkyl group are usually used. Examples of monomers other than alkyl acrylate include alkyl methacrylates such as methyl methacrylate and ethyl methacrylate, styrene monomers such as styrene and alkyl styrene, acrylonitrile and methacrylonitrile. Monofunctional monomers such as unsaturated nitriles, alkenyl esters of unsaturated carboxylic acids such as allyl (meth) acrylate and methallyl (meth) acrylate, dialkenyl esters of dibasic acids such as diallyl maleate, And polyfunctional monomers such as unsaturated carboxylic acid diesters of glycols such as alkylene glycol di (meth) acrylate.

  The rubber elastic particle containing the acrylic elastic polymer is preferably a particle having a multilayer structure having an acrylic elastic polymer layer, and a polymer mainly composed of alkyl methacrylate outside the acrylic elastic polymer. It may be a two-layer structure having the above-mentioned layer, or a three-layer structure having a polymer layer mainly composed of alkyl methacrylate inside the acrylic elastic polymer. In addition, the example of the monomer composition of the polymer mainly composed of alkyl methacrylate constituting the layer formed on the outside or inside of the acrylic elastic polymer is the alkyl methacrylate mentioned above as an example of the acrylic resin. It is the same as that of the example of the monomer composition of the polymer which has as a main component. Such acrylic rubber elastic particles having a multilayer structure can be produced, for example, by the method described in Japanese Patent Publication No. 55-27576.

  As the rubber elastic particles, those having a number average particle diameter of 10 to 300 nm of the rubber elastic bodies contained therein can be used. Thereby, when the acrylic resin film 25 is laminated | stacked on the polarizing film 21 using an adhesive agent, the acrylic resin film 25 can be made hard to peel from an adhesive bond layer. The number average particle diameter of the rubber elastic body is preferably 50 nm or more and 250 nm or less.

  In the case of rubber elastic particles in which the outermost layer is a polymer mainly composed of methyl methacrylate and the acrylic elastic polymer is encapsulated therein, the rubber elastic particles are mixed with the base acrylic resin. The outermost layer is mixed with the base acrylic resin. Therefore, in the cross section, when the acrylic elastic polymer is dyed with ruthenium oxide and observed with an electron microscope, the rubber elastic particles can be observed as particles excluding the outermost layer. Specifically, in the case of using rubber elastic particles having a two-layer structure in which the inner layer is an acrylic elastic polymer and the outer layer is a polymer mainly composed of methyl methacrylate, the inner layer is an acrylic elastic polymer. The portion is dyed and observed as particles having a single layer structure. Further, the rubber elastic particles having a three-layer structure in which the innermost layer is a polymer mainly composed of methyl methacrylate, the intermediate layer is an acrylic elastic polymer, and the outermost layer is a polymer mainly composed of methyl methacrylate. When is used, the center part of the innermost layer particle is not dyed, and only the acrylic elastic polymer part of the intermediate layer is dyed and observed as a two-layered particle.

  In the present specification, the number average particle diameter of the rubber elastic particles is, as described above, when the rubber elastic particles are mixed with the base resin and the cross section is dyed with ruthenium oxide, and is dyed in a substantially circular shape. It is the number average value of the diameters of the parts observed in FIG.

  In the acrylic resin composition forming the acrylic resin film 25, the blending amount of the rubber elastic body particles is not particularly limited. For example, a rubber elastic body having a number average particle diameter of 10 to 300 nm is added to a transparent acrylic resin. Those containing 25 to 45% by weight of particles are preferred.

  The acrylic resin composition is produced, for example, by obtaining rubber elastic particles and then polymerizing a monomer as a raw material of the acrylic resin in the presence thereof to produce a base acrylic resin. Alternatively, after obtaining rubber elastic particles and an acrylic resin, they may be produced by mixing them by melt kneading or the like.

  As necessary, the acrylic resin composition includes a colorant such as a pigment or a dye, a fluorescent brightener, a dispersant, a heat stabilizer, a light stabilizer, an infrared absorber, an ultraviolet absorber, an antistatic agent, You may contain compounding agents, such as antioxidant, a lubricant, and a solvent.

  The ultraviolet absorber is added to improve durability by absorbing ultraviolet rays of 400 nm or less. As the ultraviolet absorber, known ones such as a benzophenone ultraviolet absorber, a benzotriazole ultraviolet absorber, and an acrylonitrile ultraviolet absorber can be used. Among them, 2,2'-methylenebis (4- (1,1,3,3-tetramethylbutyl) -6- (2H-benzotriazol-2-yl) phenol), 2- (2'-hydroxy-3 ' -Tert-butyl-5'-methylphenyl) -5-chlorobenzotriazole, 2,4-di-tert-butyl-6- (5-chlorobenzotriazol-2-yl) phenol, 2,2'-dihydroxy- 4,4′-dimethoxybenzophenone, 2,2 ′, 4,4′-tetrahydroxybenzophenone and the like are preferably used. Among these, 2,2′-methylenebis (4- (1,1,3,3-tetramethylbutyl) -6- (2H-benzotriazol-2-yl) phenol) is particularly preferable.

  The concentration of the ultraviolet absorber can be selected in such a range that the transmittance of the acrylic resin film 25 having a wavelength of 370 nm or less is preferably 10% or less, more preferably 5% or less, and further preferably 2% or less. Examples of the method of containing the ultraviolet absorber include a method of previously blending the ultraviolet absorber into the acrylic resin; a method of supplying it directly at the time of melt extrusion molding, and any method may be employed.

  Infrared absorbers include nitroso compounds, metal complexes thereof, cyanine compounds, squarylium compounds, thiol nickel complex compounds, phthalocyanine compounds, naphthalocyanine compounds, triallylmethane compounds, imonium compounds, diimonium compounds, Infrared absorption of naphthoquinone compounds, anthraquinone compounds, amino compounds, aminium salt compounds, carbon black, indium tin oxide, antimony tin oxide, metal oxides belonging to Group 4A, 5A or 6A, carbides, borides, etc. An agent etc. can be mentioned. These infrared absorbers are preferably selected so as to be able to absorb the entire infrared ray (light having a wavelength in the range of about 800 nm to 1100 nm), and two or more types may be used in combination. The amount of the infrared absorber can be appropriately adjusted so that, for example, the light transmittance at a wavelength of 800 nm or more of the acrylic resin film 25 is 10% or less.

  The glass transition temperature Tg of the acrylic resin composition is determined by the resin composition and the like, but is usually preferably in the range of 80 to 120 ° C. Furthermore, the acrylic resin composition preferably has a high surface hardness when formed into a film, specifically, a pencil hardness (with a load of 500 g, conforming to JIS K5600-5-4) of B or higher. .

  In addition, the acrylic resin composition preferably has a flexural modulus (JIS K7171) of 1500 MPa or less from the viewpoint of flexibility of the acrylic resin film 25. The flexural modulus is more preferably 1300 MPa or less, and still more preferably 1200 MPa or less. This flexural modulus varies depending on the type and amount of acrylic resin and rubber elastic particles in the acrylic resin composition. For example, as the content of rubber elastic particles increases, the flexural modulus generally decreases. . In addition, the use of a copolymer of an alkyl methacrylate and an alkyl acrylate as an acrylic resin generally has a lower flexural modulus than using an alkyl methacrylate homopolymer.

  In addition, the elastic elastic polymer particles having the two-layer structure are generally used as the elastic rubber particles, rather than the acrylic elastic polymer particles having the two-layer structure. In general, the flexural modulus is smaller when the acrylic elastic polymer particles having a layer structure are used. Further, in the rubber elastic body particles, as the average particle diameter of the rubber elastic body is smaller or the amount of the rubber elastic body is larger, the bending elastic modulus is generally smaller. Therefore, it is preferable to adjust the kind and amount of the acrylic resin and the rubber elastic body particles within the predetermined range so that the flexural modulus is 1500 MPa or less.

  In the case where the acrylic resin film 25 has a multilayer structure, the layer that can exist other than the layer of the acrylic resin composition is not particularly limited in its composition. For example, an acrylic resin that does not contain rubber elastic particles or a composition thereof Or a layer made of an acrylic resin composition in which the content of the rubber elastic particles and the average particle diameter of the rubber elastic bodies in the rubber elastic particles are outside the above-mentioned regulations. Good.

  Typically, it has a two-layer or three-layer structure, and may be a two-layer structure including, for example, an acrylic resin composition layer / an acrylic resin not containing rubber elastic particles or a layer of the composition. Further, it may have a three-layer structure comprising an acrylic resin composition layer / an acrylic resin not containing rubber elastic particles or a layer of the composition / an acrylic resin composition layer. In the case of the acrylic resin film 25 having a multilayer structure, the surface of the acrylic resin composition layer may be a bonding surface with the polarizing film 21.

  Moreover, when making the acrylic resin film 25 into a multilayer structure, you may mutually differ content of rubber elastic-body particle | grains or each layer of the said compounding agent. For example, a layer containing an ultraviolet absorber and / or an infrared absorber and a layer not containing an ultraviolet absorber and / or an infrared absorber may be laminated with this layer interposed therebetween. Further, the content of the ultraviolet absorber in the layer of the acrylic resin composition may be higher than the content of the ultraviolet absorber in the layer of the acrylic resin not containing rubber elastic particles or the composition thereof. Well, specifically, the former is preferably 0.5 to 10% by weight, more preferably 1 to 5% by weight, and the latter is preferably 0 to 1% by weight, more preferably 0 to 0.5% by weight. As a result, ultraviolet rays can be efficiently blocked without deteriorating the color tone of the polarizing plate 20, and a decrease in the degree of polarization during long-term use can be prevented.

  The acrylic resin film 25 may be non-oriented or unstretched or may be stretched. When the stretching process is not performed, the thickness of the polarizing plate 20 is likely to increase because the thickness is increased. On the other hand, the handling property of the acrylic resin film 25 is improved because the thickness is increased. Such an acrylic resin film 25 can be obtained from an unstretched film (raw film) obtained by forming an acrylic resin composition. On the other hand, when stretched, the phase difference is easily developed, but stretching has the advantage that the thickness of the acrylic resin film 25 is reduced and the rigidity is improved. The stretched film can be produced by stretching an unstretched film by an arbitrary method.

  The acrylic resin can be formed into an unstretched film by any method. This unstretched film is preferably transparent and substantially free of in-plane retardation. Examples of the film forming method include an extrusion method in which a molten resin is extruded to form a film, and a solvent cast method in which a solvent dissolved in an organic solvent is cast on a flat plate and then the solvent is removed to form a film. Etc. can be adopted. As a specific example of the extrusion molding method, for example, there is a method of forming a film in a state where an acrylic resin composition is sandwiched between two rolls.

  In addition, when obtaining the thing of a multilayer structure as the acrylic resin film 25, what is necessary is just to film-form an acrylic resin composition after multilayer extrusion with another acrylic resin composition. The thickness of the unstretched film thus obtained is preferably 5 to 200 μm, more preferably 10 μm to 85 μm.

  The unstretched film made of an acrylic resin can be stretched by a known method such as uniaxial stretching or biaxial stretching as necessary. Examples of the stretching method include a tenter method using a tenter stretching machine. Biaxial stretching may be simultaneous biaxial stretching in which stretching is performed simultaneously in two stretching directions, or sequential biaxial stretching in which stretching is performed in a predetermined direction and then stretching in another direction.

  Next, the haze value of the acrylic resin film 25 will be described. The haze value is the ratio of the diffuse light transmittance to the total light transmittance when the film is irradiated with visible light. It is recognized that the smaller the haze value is, the better the film is. Moreover, an internal haze value shows the value which deducted the haze value (external haze value) resulting from the surface shape of a film from the haze value of a film.

  As described above, the haze value of the acrylic resin film 25 has an internal haze value of 1.0% or less, more preferably 0.5% or less, and an external haze value of 5% or less. If the internal haze value exceeds 1.0% and the external haze value exceeds 5%, the light transmitted through the film is scattered, and the display characteristics may be deteriorated when bonded to a liquid crystal display device.

  When the acrylic resin film 25 is used as the polarizing plate 20, it is preferable to provide a functional layer having various functions on the surface of the acrylic resin film 25. Examples of such a functional layer include a hard coat layer, an antiglare layer, an antireflection layer, a low reflection layer, an antifouling layer, and an antistatic layer.

(Polarizing plate 20)
Next, the polarizing plate 20 provided with the acrylic resin film 25 will be described. As shown in FIG. 2, the acrylic resin film 25 can be used as a film constituting the polarizing plate 20. In this figure, the example which used the acrylic resin film 25 as an outer side protective film of the polarizing film 21 is shown. The polarizing plate 20 has a layer structure in which an acrylic resin film 25, a polarizing film 21, an inner resin film 23, and an adhesive layer 27 are laminated in this order. Both the acrylic resin film 25 and the polarizing film 21 and the polarizing film 21 and the inner resin film 23 are bonded by an adhesive layer (not shown).

(2) Polarizing film 21;
Then, each layer which comprises the polarizing plate 20 is demonstrated. The polarizing film 21 is a member having a function of converting natural light into linearly polarized light. As the polarizing film 21, a film obtained by adsorbing and orienting a dichroic dye on a uniaxially stretched polyvinyl alcohol resin film can be used. As the polyvinyl alcohol resin, a saponified polyvinyl acetate resin can be used. As the polyvinyl acetate resin, in addition to polyvinyl acetate which is a homopolymer of vinyl acetate, polyvinyl acetate and Examples thereof include copolymers with other copolymerizable monomers. Examples of other monomers copolymerizable with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and acrylamides having an ammonium group.

  The saponification degree of the polyvinyl alcohol resin is usually about 85 to 100 mol%, preferably 98 mol% or more. The polyvinyl alcohol resin may be modified. For example, polyvinyl formal or polyvinyl acetal modified with aldehydes may be used. The degree of polymerization of the polyvinyl alcohol resin is usually about 1,000 to 10,000, preferably about 1,500 to 5,000.

  A film obtained by forming such a polyvinyl alcohol resin is used as a raw film of the polarizing film 21. The method for forming a polyvinyl alcohol-based resin is not particularly limited, and can be formed by a known method. Although the thickness of a polyvinyl alcohol-type raw film is not specifically limited, For example, it is about 5-150 micrometers.

  The polarizing film 21 usually has a step of uniaxially stretching such a polyvinyl alcohol resin film, a step of adsorbing a dichroic dye by dyeing the polyvinyl alcohol resin film with a dichroic dye, and a dichroic dye It is manufactured through a step of treating the adsorbed polyvinyl alcohol-based resin film with a boric acid aqueous solution and a step of washing with water after the treatment with the boric acid aqueous solution.

  Uniaxial stretching of the polyvinyl alcohol-based resin film can be performed before dyeing with the dichroic dye, simultaneously with dyeing, or after dyeing. When uniaxial stretching is performed after dyeing, this uniaxial stretching may be performed before boric acid treatment or during boric acid treatment. Of course, uniaxial stretching can also be performed in a plurality of stages shown here. For uniaxial stretching, a method of stretching uniaxially between rolls having different peripheral speeds, a method of stretching uniaxially using a hot roll, or the like can be adopted. The uniaxial stretching may be dry stretching in which stretching is performed in the air, or may be wet stretching in which a polyvinyl alcohol-based resin film is swollen using a solvent such as water. The draw ratio is usually about 3 to 8 times.

  The stretching direction of the polyvinyl alcohol-based resin film is a direction parallel to the longitudinal direction of the long polarizing film 21. For this reason, the absorption axis of the polarizing film 21 is a direction parallel to the stretching direction of the polyvinyl alcohol-based resin film, that is, the longitudinal direction of the long polarizing film 21.

  The polyvinyl alcohol resin film can be dyed with a dichroic dye by, for example, a method of immersing the polyvinyl alcohol resin film in an aqueous solution containing the dichroic dye. Specifically, iodine or a dichroic dye is used as the dichroic dye. In addition, it is preferable to perform the process which a polyvinyl alcohol-type resin film swells by immersing in water before a dyeing process.

  When iodine is used as the dichroic dye, a method of dyeing a polyvinyl alcohol-based resin film in an aqueous solution containing iodine and potassium iodide is usually employed. The content of iodine in this aqueous solution is usually about 0.01 to 1 part by weight per 100 parts by weight of water, and the content of potassium iodide is usually about 0.5 to 20 parts by weight per 100 parts by weight of water. It is. The temperature of the aqueous solution used for dyeing is usually about 20 to 40 ° C. Moreover, the immersion time (dyeing time) in this aqueous solution is usually about 20 to 1,800 seconds.

On the other hand, when a dichroic dye is used as the dichroic dye, a method of immersing and dyeing a polyvinyl alcohol-based resin film in an aqueous solution containing a water-soluble dichroic dye is usually employed. The content of the dichroic dye in this aqueous solution is usually about 1 × 10 ⁻⁴ to 10 parts by weight, preferably about 1 × 10 ⁻³ to 1 part by weight per 100 parts by weight of water. This aqueous solution may contain an inorganic salt such as sodium sulfate as a dyeing assistant. The temperature of the aqueous dichroic dye solution used for dyeing is usually about 20 to 80 ° C. Moreover, the immersion time (dyeing time) in this aqueous solution is usually about 10 to 1,800 seconds.

  The boric acid treatment after dyeing with a dichroic dye can be performed by immersing the dyed polyvinyl alcohol-based resin film in a boric acid-containing aqueous solution. The boric acid content in the boric acid-containing aqueous solution is usually about 2 to 15 parts by weight, preferably about 5 to 12 parts by weight per 100 parts by weight of water. When iodine is used as the dichroic dye, the boric acid-containing aqueous solution preferably contains potassium iodide. The content of potassium iodide in the boric acid-containing aqueous solution is usually about 0.1 to 15 parts by weight, preferably about 5 to 12 parts by weight per 100 parts by weight of water. The immersion time in the boric acid-containing aqueous solution is usually about 60 to 1,200 seconds, preferably about 150 to 600 seconds, and more preferably about 200 to 400 seconds. The temperature of the boric acid-containing aqueous solution is usually 50 ° C. or higher, preferably 50 to 85 ° C., more preferably 60 to 80 ° C.

  The polyvinyl alcohol resin film after the boric acid treatment is usually washed with water. The water washing treatment can be performed, for example, by immersing a boric acid-treated polyvinyl alcohol resin film in water. The temperature of water in the water washing treatment is usually about 5 to 40 ° C., and the immersion time is usually about 1 to 120 seconds.

  After washing with water, a drying process is performed to obtain the polarizing film 21. The drying process can be performed using a hot air dryer or a far infrared heater. The temperature of a drying process is about 30-100 degreeC normally, Preferably it is 50-80 degreeC. The drying time is usually about 60 to 600 seconds, preferably 120 to 600 seconds.

  In this way, the polyvinyl alcohol-based resin film is subjected to uniaxial stretching, dyeing with a dichroic dye, and boric acid treatment, and the polarizing film 21 is obtained. The thickness of the polarizing film 21 can be about 2-40 micrometers, for example.

  The polarizing film 21 is stored in a rolled state. At the time of use, it is used by extending from a state wound in a roll shape into a long shape. The absorption axis of the polarizing film 21 is a direction parallel to the longitudinal direction of the long polarizing plate 20, that is, the stretching direction of the polyvinyl alcohol resin film.

(3) Inner resin film 23;
The inner resin film 23 is a film that is bonded to the surface of the polarizing film 21, and films having various properties can be adopted depending on the characteristics required for a liquid crystal panel or a liquid crystal display device. As an example of the inner side resin film 23, when the polarizing plate 20 is used as an elliptically polarizing plate, a retardation layer provided with a quarter wavelength plate is mentioned, for example. Moreover, when the polarizing plate 20 is used as a linear polarizing plate, for example, a biaxial retardation film having an optical compensation function, a non-oriented film having a surface protection function, and the like can be given.

  The resin material which comprises the inner side resin film 23 is not specifically limited. Examples of such resin materials include (meth) acrylic resins such as methyl methacrylate resins ((meth) acrylic resins mean methacrylic resins or acrylic resins), olefin resins, poly Vinyl chloride resin, cellulose resin, styrene resin, acrylonitrile / butadiene / styrene copolymer resin, acrylonitrile / styrene copolymer resin, polyvinyl acetate resin, polyvinylidene chloride resin, polyamide resin, polyacetal resin Polycarbonate resin, modified polyphenylene ether resin, polyester resin (for example, polybutylene terephthalate resin, polyethylene terephthalate resin, etc.), polysulfone resin, polyethersulfone resin, polyarylate resin, polyamideimide resin, Polyimide resins, epoxy resins, and oxetane-based resin. These resins can contain additives as long as transparency and adhesiveness with the polarizing film 21 are not impaired.

  The resin material mentioned above can be made into the inner resin film 23 by forming a film by an arbitrary method and subjecting it to stretching treatment as necessary. Examples of the film forming method include an extrusion molding method from a molten resin, a solvent casting method in which a resin dissolved in an organic solvent is cast on a flat plate, and the solvent is removed to form a film.

  The obtained film may be used unstretched, but may be subjected to a stretching treatment as necessary. Examples of the stretching treatment include uniaxial stretching for stretching in the machine flow direction, biaxial stretching for stretching in a direction perpendicular to the machine flow direction in addition to uniaxial stretching, and oblique stretching for stretching in a direction oblique to the machine flow direction. . In the case of biaxial stretching, the order of stretching may be either sequential or simultaneous.

  The inner resin film 23 preferably has a Gurley bending resistance measured in accordance with JIS L 1096 of 350 mgf or less, more preferably 200 mgf or less, and even more preferably 150 mgf or less. Thus, since the rigidity of the polarizing plate 20 obtained is reduced by using the inner side resin film 23 with small bending resistance, the handleability at the time of bonding to a liquid crystal cell can be improved. In this specification, the Gurley bending resistance is a value measured according to JIS L 1096 as described above.

  The thickness of the inner resin film 23 is usually 20 to 200 μm, preferably 20 to 120 μm. When the thickness of the inner resin film 23 is less than 20 μm, the handling properties tend to be inferior, and even when the thickness exceeds 200 μm, the handling properties may be lowered due to the increased rigidity of the film.

  The resin material which comprises the inner side resin film 23 may use the resin material mentioned above independently, and may use it in combination of 2 or more types. Further, these resin materials can be used after any appropriate polymer modification. Examples of the polymer modification include modification such as copolymerization, cross-linking, molecular terminal modification, stereoregularity control, and mixing including a case involving reactions between different polymers.

(4) pressure-sensitive adhesive layer 27;
The pressure-sensitive adhesive layer 27 is used for bonding the polarizing plate 20 or the polarizing plate 20 cut into a predetermined shape from the polarizing plate 20 to a liquid crystal cell. Examples of the pressure-sensitive adhesive forming the pressure-sensitive adhesive layer 27 include those having an acrylic polymer, silicone-based polymer, polyester, polyurethane, polyether or the like as a base polymer. Among them, acrylic pressure-sensitive adhesives based on acrylic polymers are excellent in optical transparency, maintain appropriate wettability and cohesive strength, and are also excellent in weather resistance and heat resistance. It is preferably used because it does not easily cause separation problems such as floating and peeling even under conditions.

  In the acrylic base polymer constituting the acrylic pressure-sensitive adhesive, an acrylic acid alkyl ester having an ester group having an alkyl group having 20 or less carbon atoms such as a methyl group, an ethyl group, a butyl group, or a 2-ethylhexyl group; An acrylic copolymer with a functional group-containing (meth) acrylic monomer such as (meth) acrylic acid or 2-hydroxyethyl (meth) acrylate is preferably used. The pressure-sensitive adhesive layer 27 containing such an acrylic copolymer causes adhesive residue or the like on the glass substrate on the surface of the liquid crystal cell when it needs to be peeled off after being bonded to the liquid crystal cell. It can be peeled relatively easily without causing it. The acrylic copolymer used for the pressure-sensitive adhesive preferably has a glass transition temperature of 25 ° C. or lower, and more preferably 0 ° C. or lower. The acrylic copolymer usually has a weight average molecular weight of 100,000 or more.

  As the pressure-sensitive adhesive forming the pressure-sensitive adhesive layer 27, a diffusion pressure-sensitive adhesive in which a light diffusing agent is dispersed can be used. The light diffusing agent is for imparting light diffusibility to the pressure-sensitive adhesive layer 27. The light diffusing agent may be fine particles having a refractive index different from that of the base polymer constituting the pressure-sensitive adhesive layer 27, and fine particles made of an inorganic compound or fine particles made of an organic compound (polymer) can be used. Since the base polymer constituting the pressure-sensitive adhesive layer 27 including the acrylic base polymer as described above often has a refractive index of around 1.4, the light diffusing agent has a refractive index of about 1-2. What is necessary is just to select suitably from things. The difference in refractive index between the base polymer constituting the pressure-sensitive adhesive layer 27 and the light diffusing agent is usually 0.01 or more, and from the viewpoint of ensuring the brightness and visibility of the applied liquid crystal display device, 0.01 or more. It is preferable that it is 0.5 or less. The fine particles used as the light diffusing agent are preferably spherical and those close to monodisperse, and fine particles having an average particle diameter of about 2 to 6 μm are preferably used.

  Examples of the fine particles made of an inorganic compound include aluminum oxide (refractive index 1.76) and silicon oxide (refractive index 1.45). Examples of the fine particles composed of an organic compound (polymer) include melamine resin beads (refractive index 1.57), polymethyl methacrylate beads (refractive index 1.49), methyl methacrylate / styrene copolymer resin beads ( (Refractive index 1.50 to 1.59), polycarbonate beads (refractive index 1.55), polyethylene beads (refractive index 1.53), polystyrene beads (refractive index 1.6), polyvinyl chloride beads (refractive index 1. 46), silicone resin beads (refractive index 1.46), and the like.

  The amount of the light diffusing agent is appropriately determined in consideration of the haze value required for the pressure-sensitive adhesive layer 27 in which it is dispersed, the brightness of the liquid crystal display device to which it is applied, etc. The amount is about 3 to 30 parts by weight with respect to 100 parts by weight of the base polymer constituting the agent layer 27.

  The haze value measured according to JIS K 7361 of the pressure-sensitive adhesive layer 27 in which the light diffusing agent is dispersed is from the viewpoint of ensuring the brightness of the applied liquid crystal display device and making the display image less likely to bleed or blur. A range of 20 to 80% is preferable.

  Each component (base polymer, light diffusing agent, crosslinking agent, etc.) constituting the transparent pressure-sensitive adhesive or diffusion pressure-sensitive adhesive is dissolved in a suitable solvent such as ethyl acetate to form a pressure-sensitive adhesive composition. However, components that are not soluble in a solvent such as a light diffusing agent are dispersed. The pressure-sensitive adhesive layer 27 can be formed by applying this pressure-sensitive adhesive composition onto the inner resin film 23 and drying it.

  In order to remove static electricity charged in the polarizing plate 20, the pressure-sensitive adhesive layer 27 preferably has antistatic properties. In the polarizing plate 20, a separate film is laminated on the pressure-sensitive adhesive layer 27 as necessary. However, when the separate film is peeled off and bonded to a liquid crystal cell, it may be charged with static electricity. At this time, if the pressure-sensitive adhesive layer 27 has antistatic properties, the static electricity is quickly eliminated, and the display circuit of the liquid crystal cell is prevented from being broken and the liquid crystal molecules from being disturbed in alignment. .

  Examples of the method for imparting antistatic properties to the pressure-sensitive adhesive layer 27 include a method in which the pressure-sensitive adhesive composition contains metal fine particles, metal oxide fine particles, or fine particles coated with a metal, etc., electrolyte salt and organopolysiloxane And a method of incorporating an organic salt-based antistatic agent. The required antistatic holding time is at least about 6 months from the viewpoint of production, distribution, and storage period of a general polarizing plate 20.

  The adhesive layer 27 may pass active energy rays in order to cure the adhesive layer. Therefore, it is preferable to have a high transmittance in the corresponding spectral region of the active energy ray. In addition, it is preferable that various characteristics as an adhesive do not change by irradiation of an active energy ray.

  For example, the pressure-sensitive adhesive layer 27 is aged for about 3 to 20 days in an environment of a temperature of 23 ° C. and a relative humidity of 65%, and after sufficiently proceeding with the reaction of the crosslinking agent, is used for bonding to a liquid crystal cell. .

  The thickness of the pressure-sensitive adhesive layer 27 is appropriately determined according to the adhesive force and the like, but is usually about 1 to 40 μm. In order to obtain a thin polarizing plate 20 without impairing properties such as workability and durability, the thickness of the pressure-sensitive adhesive layer 27 is preferably about 3 to 25 μm. In addition, when the pressure-sensitive adhesive layer 27 in which the light diffusing agent is dispersed is used, the brightness when the liquid crystal display device is viewed from the front or obliquely is set by setting the thickness of the pressure-sensitive adhesive layer 27 within this range. It is possible to keep the display image from blurring and blurring.

(5) Adhesive layer (not shown);
The inner resin film 23 and the acrylic resin film 25 are usually bonded to the polarizing film 21 via an adhesive layer. The adhesive that forms the adhesive layer provided on both surfaces of the polarizing film 21 may be the same or different.

  As the adhesive, an adhesive having an epoxy resin, urethane resin, cyanoacrylate resin, acrylamide resin, or the like as an adhesive component can be used. One of the adhesives preferably used is a solventless type adhesive. Solventless adhesives do not contain a significant amount of solvent, and are curable compounds (monomers or oligomers) that are reactively cured by heating or irradiation with active energy rays (for example, ultraviolet rays, visible light, electron beams, X-rays, etc.) ), And an adhesive layer is formed by curing of the curable compound, and typically includes a curable compound that is reactively cured by heating or irradiation of active energy rays, and a polymerization initiator. In particular, when the inner resin film 23 and the acrylic resin film 25 are made of a polypropylene resin, the polypropylene resin film has a low moisture permeability, so that when water-based adhesive is used, water drainage is poor, and polarization is caused by moisture in the adhesive. The film 21 may be damaged or the polarization performance may be deteriorated. Therefore, when bonding such a resin film with low moisture permeability, a solventless adhesive is preferable.

  As an example of a preferable adhesive for forming the adhesive layer, an active energy ray-curable adhesive that is cured by irradiation with an active energy ray is used as an example of a preferable adhesive from the viewpoint of improving the productivity of the first polarizing plate 20 due to rapid curing. Can be mentioned. As an example of such an active energy ray-curable adhesive, for example, a photo-curable adhesive that is cured by light energy such as ultraviolet light and visible light can be cited. As the photocurable adhesive, those that are cured by cationic polymerization are preferable from the viewpoint of reactivity, and in particular, the solventless epoxy adhesive that uses an epoxy compound as a curable compound includes the polarizing film 21 and the inner resin film. 23 and the acrylic resin film 25 are more preferable because of excellent adhesion.

  Although it does not restrict | limit especially as an epoxy compound which is a sclerosing | hardenable compound contained in the said solventless type epoxy adhesive, The thing hardened | cured by cationic polymerization is preferable. In particular, from the viewpoint of weather resistance and refractive index, it is more preferable to use an epoxy compound that does not contain an aromatic ring in the molecule. Examples of such epoxy compounds that do not contain an aromatic ring in the molecule include hydrides of aromatic epoxy compounds, alicyclic epoxy compounds, and aliphatic epoxy compounds. In addition, the epoxy compound that is a curable compound usually has two or more epoxy groups in the molecule.

  After laminating the inner resin film 23 and the acrylic resin film 25 to the polarizing film 21 via an adhesive layer made of an uncured epoxy adhesive, by irradiating active energy rays or heating, The adhesive layer is cured, and the inner resin film 23 and the acrylic resin film 25 are fixed on the polarizing film 21. In the case of curing by irradiation with active energy rays, ultraviolet rays are preferably used. Specific examples of the ultraviolet light source include a low pressure mercury lamp, a medium pressure mercury lamp, a high pressure mercury lamp, a black light lamp, and a metal halide lamp. The irradiation intensity and irradiation amount of active energy rays such as ultraviolet rays are appropriately selected so as to sufficiently activate the cationic polymerization initiator and not adversely affect the cured adhesive layer, the polarizing film 21 and the like. . In addition, when cured by heating, it can be heated by a generally known method, and the temperature and time at that time can sufficiently activate the cationic polymerization initiator, and the cured adhesive layer or It is appropriately selected so as not to adversely affect the film such as the polarizing film 21.

  The thickness of the adhesive layer comprising the cured epoxy adhesive obtained as described above is usually 50 μm or less, preferably 20 μm or less, more preferably 10 μm or less, and usually 1 μm or more.

  Further, from the viewpoint of thinning the adhesive layer, an aqueous adhesive, that is, an adhesive in which an adhesive component is dissolved in water or an adhesive component is dispersed in water can also be used as the adhesive. For example, an aqueous composition using a polyvinyl alcohol resin or a urethane resin as a main component can be mentioned as a preferred aqueous adhesive.

  A conventionally known method can be used as a method of laminating each film. For example, the polarizing film 21 and / or the film to be bonded to it by the casting method, Meyer bar coating method, gravure coating method, comma coater method, doctor blade method, die coating method, dip coating method, spraying method, etc. The method of apply | coating an adhesive agent to a surface and superimposing both is mentioned. The casting method is a method of spreading and spreading an adhesive on the surface of a film to be coated while moving the film in a substantially vertical direction, a substantially horizontal direction, or an oblique direction between the two.

  In order to improve adhesiveness, the surface of each film may be appropriately subjected to surface activation treatment such as plasma treatment, corona treatment, ultraviolet irradiation treatment, flame (flame) treatment, and saponification treatment. Examples of the saponification treatment include a method of immersing in an aqueous alkali solution such as sodium hydroxide or potassium hydroxide.

  The laminated body joined through the water-based adhesive is usually subjected to a drying treatment, and the adhesive layer is dried and cured. The drying process can be performed, for example, by blowing hot air. A drying temperature is normally selected from the range of about 40-100 degreeC, Preferably it is 60-100 degreeC. The drying time is, for example, about 20 to 1,200 seconds. The thickness of the adhesive layer after drying is usually about 0.001 to 5 μm, preferably 0.01 μm or more, preferably 2 μm or less, more preferably 1 μm or less. If the thickness of the adhesive layer becomes too large, the appearance of the first polarizing plate 20 tends to be poor.

<Liquid crystal panel and liquid crystal display device>
Next, a liquid crystal panel and a liquid crystal display device using the polarizing plate 20 will be described. FIG. 3 is a schematic cross-sectional view showing an example of a basic layer configuration of the liquid crystal panel 2 using the polarizing plate 20 and the liquid crystal display device 1 to which the liquid crystal panel 2 is applied. As shown in this figure, the polarizing plate 20 is bonded to the liquid crystal cell 40 and used as a component of the liquid crystal panel 2. The liquid crystal panel 2 is a constituent member of the liquid crystal display device 1. The liquid crystal panel 2 includes a liquid crystal cell 40, a polarizing plate 20 bonded to the back side of the liquid crystal cell 40, and a polarizing plate 30 bonded to the viewing side of the liquid crystal cell 40. The liquid crystal display device 1 includes a liquid crystal panel 2, a backlight 10, and a light diffusion plate 50. In the liquid crystal display device 1, the liquid crystal panel 2 is disposed such that the polarizing plate 20 is on the backlight 10 side. The polarizing plate 20 and the polarizing plate 30 are each bonded to the liquid crystal cell 40 via an adhesive layer. Here, the back side means the backlight 10 side when the liquid crystal panel 2 is mounted on the liquid crystal display device 1. The viewing side means the side opposite to the backlight 10 when the liquid crystal panel 2 is mounted on the liquid crystal display device 1.

  In this figure, the acrylic resin film 25 is disposed outside the polarizing film 21 (on the opposite side of the liquid crystal cell 40 with the polarizing film 21 in between). It is not limited. For example, you may arrange | position inside the polarizing film 21 (The same side as the liquid crystal cell 40 across the polarizing film 21: The position of the inner side resin film 23).

  The liquid crystal cell 40 is an element that displays an image by electrically controlling a cell in which a liquid crystal material is sealed between glass substrates. More specifically, the liquid crystal cell 40 has a back surface polarized by the polarizing plate 20 disposed on the back side of the liquid crystal cell 40 by changing the molecular orientation of the liquid crystal material by electrical control from a display control unit (not shown). An image is displayed by changing the polarization state of the light of the light 10 and controlling the amount of light transmitted through the polarizing plate 30 disposed on the viewing side of the liquid crystal cell 40. The mode of the liquid crystal cell 40 is not particularly limited. For example, a VA mode, an IPS mode, a TN mode, an STN mode, an OCB mode, an ASM mode, or the like can be used.

  The liquid crystal panel 2 and the liquid crystal display device 1 can be manufactured by a known method. As a manufacturing method of the liquid crystal panel 2, the long polarizing plate 20 and the polarizing plate 30 wound in a roll shape can be cut into pieces and bonded to the liquid crystal cell 40.

  The backlight 10 is a device for illuminating the liquid crystal cell 40. Examples of the type of the backlight 10 include an edge light type and a direct type. The edge-light type backlight 10 irradiates light to the liquid crystal cell 40 through a light guide plate from a light source such as a cold cathode tube or an LED arranged on a side surface. In the direct type backlight 10, a light source is disposed on the back side of the liquid crystal cell 40 to irradiate the liquid crystal cell 40 with light. As the type of the backlight 10, a backlight according to the application of the liquid crystal display device 1 can be appropriately adopted.

  The light diffusing plate 50 is an optical member having a function of diffusing light from the backlight 10, for example, a material in which particles as a light diffusing agent are dispersed in a thermoplastic resin to impart light diffusibility, thermoplasticity The surface of the resin film may be uneven to provide light diffusibility, or the resin film may be provided with a coating layer of a resin composition in which particles are dispersed on the surface of the thermoplastic resin film. . The thickness can be about 0.1-5 mm.

  Between the light diffusing plate 50 and the liquid crystal panel 2, a sheet or film exhibiting other optical functionality such as a brightness enhancement sheet (a reflective polarizing film (such as “DBEF”)) or a light diffusing sheet is disposed. You can also. Two or more sheets or films exhibiting other optical functionalities can be arranged as needed.

(Second Embodiment)
In 1st Embodiment mentioned above, although the form using the heat roll 14 was demonstrated as a press member, it is not limited to a heat roll as a press member of this invention, Other members may be sufficient. In this embodiment, an example in which a thermal iron is used as the pressing member will be described.

  FIG. 4 is a schematic view showing a method for producing an acrylic resin film in the second embodiment. As shown in this figure, in this embodiment, the thermal iron 16 is used as a pressing member. As the thermal iron 16, a commercially available general iron or a commercial iron can be used.

  When the heat treatment of the acrylic resin film 25 is performed using the thermal iron 16, it can be performed by a method such as normal ironing for clothes and the like. That is, in a state where tension is applied to the acrylic resin film 25, the heated iron 16 is pressed from above to move the film surface, whereby the surface of the acrylic resin film 25 can be smoothed. . About the heating temperature and heating time of the thermal iron 16, it can be set as the conditions substantially the same as the conditions of 1st Embodiment mentioned above.

  Thus, by using the heating iron 16, it becomes possible to smooth the unevenness | corrugation of a film surface manually. Therefore, when unevenness is partially found on the surface of the acrylic resin film 25, it is possible for the worker to manually smooth the film surface using the heating iron 16. Further, by performing the heat treatment manually, the heat treatment can be performed while an operator observes the state of the film, so that it is possible to prevent insufficient heating and excessive heating.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further more concretely, this invention is not limited by these examples. In the following examples, the part representing the amount used is based on weight unless otherwise specified.

[Example 1]
(A) Production of acrylic resin film;
(Acrylic resin and acrylic elastic polymer particles)
As the acrylic resin, a copolymer having a weight ratio of methyl methacrylate / methyl acrylate of 96/4 was used. Further, as the elastic rubber particles, acrylic elastic polymer particles having a three-layer structure including an innermost layer, an intermediate layer, and an outermost layer were used. In the acrylic elastic polymer particles, the innermost layer is a hard polymer obtained by polymerizing methyl methacrylate with a small amount of allyl methacrylate, the intermediate layer is mainly composed of butyl acrylate, styrene and a small amount of Soft elastic body polymerized using allyl methacrylate, outermost layer is made of a hard polymer polymerized with a small amount of ethyl acrylate in methyl methacrylate, and the average particle size up to the elastic body that is the intermediate layer The diameter is 240 nm.

(Preparation of acrylic resin film)
While melting and kneading a pellet in which the above acrylic resin and the above acrylic elastic polymer particles are blended in a weight ratio of the former / the latter = 70/30 with a twin screw extruder, did. The pellets were put into a 65 mmφ single screw extruder, extruded through a T die having a set temperature of 275 ° C., and both sides of the extruded film-like molten resin were polished rolls (cooling rolls) having mirror surfaces set at 45 ° C. Roll) and a polishing roll (elastic roll) whose surface is formed of a rubber elastic body, and cooled, to prepare an acrylic resin film. It was 106 degreeC when the glass transition temperature (Tg) of this acrylic resin film was measured with the differential scanning thermogravimetry (the SII nanotechnology company make, EXSTAR6000).

(B) sample preparation;
The tip of a commercially available plus screwdriver (diameter 5 mm, tip 2 mm) was pressed into an acrylic resin film on a cutting mat to artificially form a dent on the film surface. As shown in FIG. 5A, the dents were formed in two rows at different positions along the longitudinal direction of the acrylic resin film 25, and about four places along the width direction. The dent depth at this time was measured with a confocal microscope (manufactured by Nano System Solutions, Inc., PL μ2300), and was 6 μm.

(C) thermal ironing;
Thermal ironing was performed using a drawing jig and a thermal iron shown in FIG. First, as shown in FIG. 5A, the acrylic resin film 25 on which the dents D are formed is mounted on the stretching jig H, and tension is applied to the acrylic resin film 25 in the machine flow direction (MD). I applied. In this state, as shown in FIG.5 (b), glass was applied under the acrylic resin film 25, and only one row (right row in the figure) of the two rows of dents D was heated to 60 ° C. Heat iron 16 was applied to the film for 10 seconds to carry out heat iron treatment. It was 2 micrometers when the dent depth after the heat iron process was measured by the method similar to the above.

  The haze of the film after ironing was measured. The haze was measured using a haze meter “HM-150” manufactured by Murakami Color Research Laboratory Co., Ltd. based on JIS K 7136. As a result, the internal haze was 0.0% and the external haze was 1.7%. The above results are shown in Table 1.

[Example 2]
The experiment was performed under the same conditions as in Example 1 except that the heating temperature of the heating iron in the above (c) was set to 80 ° C. and the time applied to the film was set to 5 seconds. The results are shown in Table 1.

[Example 3]
In the thermal ironing process of (c) above, an experiment was performed under the same conditions as in Example 1 except that the heating temperature of the thermal iron was 60 ° C. and the time applied to the film was 5 seconds. The results are shown in Table 1.

[Comparative Example 1]
The experiment was performed under the same conditions as in Example 1 except that the heating temperature of the heating iron in the above (c) was set to 40 ° C. and the time applied to the film was set to 20 seconds. The results are shown in Table 1.

[Comparative Example 2]
In the thermal ironing process of (c) above, an experiment was performed under the same conditions as in Example 1 except that the heating temperature of the thermal iron was 115 ° C. and the time applied to the film was 5 seconds. The results are shown in Table 1.

  From Table 1, it can be seen that in Examples 1 and 2, the dent depth before ironing was significantly improved after ironing and almost no dents remained. Further, it can be seen that the dent depth after ironing is smaller under the conditions of 80 ° C. and 5 seconds of Example 2 than with the conditions of 60 ° C. and 10 seconds of Example 1. From this, it was found that as the glass transition temperature (Tg = 106 ° C.) of the acrylic resin composition is closer, the dent becomes smoother in a shorter heating time.

  On the other hand, in Example 3, the dent depth before ironing is 7 μm and after ironing is 5 μm, and although there is some improvement, the improvement width is small. In Example 3, heating was performed at 60 ° C. as in Example 1, but the heating time was 5 seconds, which was half the time of Example 1, and the heating time was not sufficient because of the small improvement. It is believed that there is.

  In Comparative Example 1, the dent depth is not improved at all before and after the ironing. The reason for this is considered that the heating temperature in Comparative Example 1 was 40 ° C., which was significantly lower than the glass transition temperature (Tg), so that a sufficient amount of heat was not added to the film.

  In Comparative Example 2, the dent depth decreased to 1 μm, but the film contracted. This is probably because the heat treatment temperature of Comparative Example 2 was 115 ° C. and exceeded the glass transition temperature (Tg) by 9 ° C., so that the amount of heat applied to the film was too much.

  In both Examples and Comparative Examples, it was found that the values of internal haze and external haze were small. Therefore, it was confirmed that any of these acrylic resin films could be used for optical purposes.

(D) Observation of the acrylic resin film surface;
Next, the surface of the acrylic resin film of Example 1 was observed using a confocal microscope. PLμ2300 manufactured by Nano System Solutions Co., Ltd. was used as a confocal microscope. FIG. 6 shows a photomicrograph of the surface of the acrylic resin film, (a) is a photograph of the dent before and after the thermal ironing process, and (b) is a photograph of the dent and the surrounding area after the thermal ironing process. It is a photograph.

  As shown in these photographs, the dent (the portion surrounded by the broken line in the figure) can be clearly seen before the thermal ironing process (FIG. 6A), but after the thermal ironing process (FIG. 6B). Shows almost no dent marks and a smooth surface. From this, it was found that the depth of the dent on the surface of the acrylic resin film was reduced by the thermal ironing process, and the surface approached smoothness.

DESCRIPTION OF SYMBOLS 1 Liquid crystal display device, 2 Liquid crystal panel, 10 Backlight, 11 Acrylic resin film original fabric, 12, 13 Guide roll, 14 Heat roll, 15 Winding roll, 16 Heat iron, 20 Polarizing plate, 21 Polarizing film, 23 Inside Resin film, 25 Acrylic resin film, 27 Adhesive layer, 30 Polarizing plate, 40 Liquid crystal cell, 50 Light diffusion plate, D dent, H Stretching jig

Claims (4)

A method for producing an acrylic resin film comprising an acrylic resin composition in which rubber elastic particles are blended with an acrylic resin,
In a state where tension is applied to the acrylic resin film, the pressing member having a smooth surface and heated to a predetermined heating temperature is pressed against one surface of the acrylic resin film ,
The heating temperature is, when the glass transition temperature of the acrylic resin composition and Tg, Tg-50 ° C. or higher, Tg + 5 method of manufacturing ° C. or less in the range in der Ru acrylic resin film.   2. The production of an acrylic resin film according to claim 1, wherein the rubber elastic particles have a number average particle diameter in a range of 10 to 300 nm and are blended in an amount of 25 to 45 wt% with respect to the acrylic resin. Method. The pressing member is a heat roll or heat irons, manufacturing method of the acrylic resin film according to claim 1 or 2. The manufacturing method of the polarizing plate which laminates | stacks the acrylic resin film manufactured with the manufacturing method in any one of Claims 1-3, and a polarizing film.

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