TW201539065A - Method for fabricating polarizing plate - Google Patents

Abstract

This invention provides a method for fabricating a polarizing plate, the method comprising the steps of: through an adhesive layer, attaching a protective film having a balanced water ratio adjusted to be higher than 55% RH at 25 DEG C in a polarizer layer of the polarizing laminated film, the polarizing laminated film having the polarizer layer on at least one side of a substrate film; and then removing the substrate film subsequently.

Description

Method for manufacturing polarizing plate

The present invention relates to a method of manufacturing a polarizing plate.

The polarizing plate is widely used in display devices such as liquid crystal display devices, and has been widely used in thin televisions and various mobile devices in recent years. As the polarizing plate, generally, a member in which a protective film is bonded to one surface or both surfaces of a polarizer using an adhesive is used.

The polarizing plate can be produced by a method of bonding a protective film (hereinafter also referred to as a "single film method" to a polarizer (polarizing film) including a monomer film (separate film) via an adhesive layer. The method includes the steps of: forming a resin layer on a substrate film by coating; and forming, by extending and dyeing, the resin layer becomes a polarizer layer to obtain a polarizing laminated film; and on the polarizing layer of the polarizing laminated film The step of bonding the protective film via the adhesive layer; after the protective film is bonded, the step of peeling off the substrate film; and the method (hereinafter also referred to as "coating method"). The latter method is advantageous in that the operability of the film is good in the step, and the point of the polarizer layer of the film is easily obtained.

In JP-A-2009-098653 (Patent Document 1) and JP-A-2009-093074 (Patent Document 2), it is described that a polarizing plate is produced by a method similar to the coating method.

Prior technical literature Patent literature

Patent Document 1: JP-A-2009-098653

Patent Document 2: JP-A-2009-093074

With the spread of thin-type televisions and mobile devices, the demand for thinner polarizing plates has been increasing in recent years. However, if the polarizing plate is made thin, there is a problem that curling tends to occur. When the polarizing plate is improperly curled, when the polarizing plate is bonded to a display cell such as a liquid crystal cell by the adhesive layer to form a display device, air bubbles are easily caught. When such a bubble exists in a display device such as a liquid crystal display device, light is scattered by light bubbles during lighting, and a display defect occurs in a black display state (light bubbles become bright spots).

Patent Document 1 and Patent Document 2 describe that curling of a polarizing plate can be suppressed according to a method similar to the above-described coating method. However, the polarizing plate for suppressing curling in the above-mentioned documents refers to a polarizing plate which does not peel off the base film of the coating method and uses a protective film as a polarizing plate layer as it is, but does not mention peeling off the substrate. The curl of the polarizing plate comprising the polarizer layer and the protective film obtained by the film.

An object of the present invention is to provide a method for producing a polarizing plate by peeling off a base film after bonding a protective film to a polarizing layer of a polarizing laminated film, for example, and to suppress the obtained polarizing plate. The manufacturing method of curling.

The present invention provides a method of producing a polarizing plate shown below.

[1] A method of producing a polarizing plate, comprising: adjusting a moisture content of a polarizing layer having a polarizing film layer on a surface of at least one side of a base film; A step of a protective film having a higher equilibrium moisture ratio than 25 ° C and 55% RH; and a step of peeling off the substrate film.

[2] The method for producing a polarizing plate according to the above aspect, wherein, in the step of bonding the protective film, the moisture content of the protective film is 70% or less of the saturated moisture content.

The method for producing a polarizing plate according to the above aspect, wherein the polarizing laminated film is produced by a method comprising the steps of: coating on at least one side of the base film; After the coating liquid containing the polyvinyl alcohol-based resin is dried, the coating liquid is dried to form a polyvinyl alcohol-based resin layer to obtain a laminated film, and the step of stretching the laminated film to obtain a stretched film; The polyvinyl alcohol-based resin layer of the stretched film is dyed with a dichroic dye to form the polarizing plate layer, whereby a polarizing laminated film is obtained.

[4] The method for producing a polarizing plate according to any one of the above aspects, wherein the protective film comprises a cellulose ester resin or a (meth)acrylic resin.

[5] The method for producing a polarizing plate according to any one of [1] to [4] wherein the thickness of the polarizing plate layer is 10 μm or less.

According to the present invention, a method of producing a polarizing plate comprising a polarizing film layer and a protective film attached to one surface of the polarizing film layer after the protective film is bonded to the polarizing layer of the polarizing laminate film is removed. The curl of the resulting polarizing plate can be suppressed.

1‧‧‧ polarizing plate with protective film on one side

2‧‧‧ polarizing plates with protective film on both sides

5‧‧‧Polarized film

6‧‧‧Polyvinyl alcohol resin layer

6'‧‧‧Extended polyvinyl alcohol resin layer

10‧‧‧1st protective film

15, 25‧‧‧ adhesive layer

20‧‧‧2nd protective film

30‧‧‧Base film

30'‧‧‧Extended substrate film

100‧‧‧ laminated film

200‧‧‧Extension film

300‧‧‧Polarized laminated film

400‧‧‧Polarized laminated film with protective film

Fig. 1 is a flow chart showing a preferred example of the method for producing a polarizing plate of the present invention.

Fig. 2 is a flow chart showing a preferred example of a method for producing a polarizing laminated film.

Fig. 3 is a flow chart showing another preferred example of the method for producing a polarizing plate of the present invention.

Fig. 4 is a schematic cross-sectional view showing an example of a layer configuration of a laminated film obtained by the resin layer forming step.

Fig. 5 is a schematic cross-sectional view showing an example of a layer configuration of a stretched film obtained by the stretching step.

Fig. 6 is a schematic cross-sectional view showing an example of a layer configuration of a polarizing laminate film obtained by the dyeing step.

Fig. 7 is a schematic cross-sectional view showing an example of a layer configuration of a polarizing plate with a protective film obtained by the first protective film bonding step.

Fig. 8 is a schematic cross-sectional view showing the layer constitution of a polarizing plate having a protective film on one side obtained by the peeling step.

Figure 9 shows the two sides of the second protective film bonding step. A schematic cross-sectional view of the layer structure of the polarizing plate of the film.

Fig. 1 is a flow chart showing a preferred example of the method for producing a polarizing plate of the present invention. The manufacturing method of the present invention as shown in Fig. 1 includes the following steps: (1) a polarizing layer of a polarizing laminated film having a polarizing plate layer on at least one surface of a base film, followed by The first protective film bonding step S10 of the first protective film having a bonding water ratio higher than the equilibrium moisture ratio of 25° C. and 55% RH is adjusted, and (2) the first protective film bonding step is followed by peeling off. Step S20 of the aforementioned substrate film.

Further, as shown in Fig. 2, the polarizing laminated film is produced by the above-described coating method, and is preferably produced by a method comprising the following steps: [a] on at least one side of the substrate film, After coating a coating liquid containing a polyvinyl alcohol-based resin and drying it, a polyvinyl alcohol-based resin layer is formed to obtain a resin layer forming step S1-1 of the laminated film; [b] the extended laminated film is extended Film extending step S1-2; and [c] dyeing the polyvinyl alcohol-based resin layer of the stretched film with a dichroic dye to form the polarizing layer, thereby obtaining a dyeing step S1-3 of the polarizing laminated film .

According to the above production method, a polarizing plate having a protective film on one surface of the surface on which the first protective film is bonded to the polarizing plate layer is obtained. As shown in FIG. 3, after the peeling step S20, the surface of the polarizing plate layer on the side of the polarizing plate having the protective film provided on one side thereof is bonded to the surface of the second protective film via the adhesive layer. 2 The protective film bonding step S30 can also obtain a polarizing plate with a protective film on both sides.

In addition, the polarizing plate of the present invention (the polarizing plate obtained by the method for producing a polarizing plate of the present invention) refers to a protective film including a polarizing plate layer and a surface on which at least one layer is laminated via an adhesive layer ( That is, a polarizing plate having a protective film on one side or a polarizing plate having a protective film on both sides thereof, and a base film having no polarizing laminated film contained in the precursor thereof. However, the polarizing plate obtained by the production method of the present invention may be formed as a composite polarizing plate by laminating other optical members (peripheral members) such as other films and layers thereon, or may be used as a composite polarizing plate. The polarizer layer may be one in which a dichroic dye is adsorbed to a polyvinyl alcohol-based resin layer (or film) which is extended by one axis.

In addition, the polarizing laminate film of the present invention refers to a polarizer layer having a base film and a layer laminated on at least one side thereof, and is not bonded to a protective film. In the first protective film bonding step S10, the polarizing laminated film formed by bonding the first protective film to the polarizing plate layer is hereinafter referred to as "a polarizing laminated film with a protective film" for distinguishing it from the polarizing laminated film. "."

Hereinafter, each step will be described in detail. In the resin layer forming step S1-1, the polyvinyl alcohol-based resin layer can be formed on both surfaces of the base film, and the case where it is formed on one surface will be mainly described below.

<First protective film bonding step S10>

The polarizing laminate film as described above is preferably produced by the method of [a] resin forming step S1-1, [b] extending step S1-2, and [c] dyeing step S1-3.

[a] Resin formation step S1-1

Referring to Fig. 4, this step is a step of forming a polyvinyl alcohol-based resin layer 6 on at least one surface of the base film 30 to obtain a polarizing laminated film 100. This polyvinyl alcohol-based resin layer 6 becomes a layer of the polarizer layer 5 via the extending step S1-2 and the dyeing step S1-3. The polyvinyl alcohol-based resin layer 6 can be formed by applying a coating liquid containing a polyvinyl alcohol-based resin on one surface or both surfaces of the base film 30 to dry the coating layer.

The base film 30 may be composed of a thermoplastic resin, and is preferably made of a thermoplastic resin excellent in transparency, mechanical strength, thermal stability, and elongation. Specific examples of the thermoplastic resin include, for example, a polyolefin resin such as a chain polyolefin resin or a cyclic polyolefin resin (such as a decene-based resin); a polyester resin; and a (meth)acrylic resin. a cellulose resin such as cellulose triacetate or cellulose diacetate; a polycarbonate resin; a polyvinyl alcohol resin; a polyvinyl acetate resin; a polyarylate resin; Resin; polyether oxime resin; polyfluorene resin; polyamine resin; polyimine resin; and mixtures and copolymers thereof.

In the present specification, the term "(meth)acrylic acid" means at least one selected from the group consisting of acrylic acid and methacrylic acid. The same applies to "(meth)acrylonitrile" or the like.

The base film 30 may have a single layer structure including one resin layer containing one or two or more kinds of thermoplastic resins, or a multilayer structure in which a plurality of resin layers including one or two or more kinds of thermoplastic resins are laminated. . When the base film 30 is extended in the extending step S1-2 to be described later, the laminated film 100 is extended at an extension temperature at which the polyvinyl alcohol-based resin layer 6 can be suitably extended. The resin is preferably constructed.

The base film 30 may contain an additive. As the additive, for example, an ultraviolet absorber, an antioxidant, a lubricant, a plasticizer, a release agent, a coloring inhibitor, a flame retardant, a nucleating agent, an antistatic agent, a pigment, a coloring agent, and the like. The content of the thermoplastic resin in the base film 30 is preferably from 50 to 100% by weight, more preferably from 50 to 99% by weight, still more preferably from 60 to 98% by weight, particularly preferably from 70 to 97% by weight.

The thickness of the base film 30 is usually from 1 to 500 μm, preferably from 1 to 300 μm, more preferably from 5 to 200 μm, still more preferably from 5 to 150 μm, from the viewpoint of workability such as strength and workability.

The coating liquid applied to the base film 30 is preferably a polyvinyl alcohol-based resin solution obtained by dissolving a powder of a polyvinyl alcohol-based resin in a good solvent (for example, water). Examples of the polyvinyl alcohol-based resin include polyvinyl alcohol-based resins and derivatives thereof. Examples of the derivative of the polyvinyl alcohol-based resin include, in addition to polyvinyl formal, polyvinyl acetal, and the like, a polyvinyl alcohol-based resin modified with an olefin such as ethylene or propylene; and, for example, acrylic acid or methyl group. Modified by unsaturated carboxylic acid of acrylic acid or crotonic acid; modified by alkyl ester of unsaturated carboxylic acid; modified by (meth) acrylamide. The proportion of the modification is preferably less than 30 mol%, and more preferably less than 10 mol%. When the modification is more than 30 mol%, it is difficult to adsorb the dichroic dye, and the polarizing performance is lowered. Among the above polyvinyl alcohol-based resins, a polyvinyl alcohol resin is preferably used.

The polyvinyl alcohol-based resin preferably has an average polymerization degree of from 100 to 10,000, more preferably from 1,000 to 10,000, more preferably from 1,500 to 8,000, and most preferably from 2000 to 5,000. The average degree of polymerization can be based on JIS The method specified in K6726-1994 "Test Method for Polyvinyl Alcohol" is obtained. When the average degree of polymerization is less than 100, it is difficult to obtain a preferable polarizing performance, and when it exceeds 10,000, the solubility in a solvent is deteriorated, and formation of a polyvinyl alcohol-based resin layer becomes difficult.

The polyvinyl alcohol-based resin is preferably a saponified product of a polyvinyl acetate-based resin. The degree of saponification is in the range of 80 mol% or more, and more preferably 90 mol% or more, particularly preferably 94 mol% or more. When the degree of saponification is too low, durability and heat and humidity resistance in the case of a polarizing laminated film or a polarizing plate may become insufficient. Further, although it may be a completely saponified product (the degree of saponification is 100 mol%), if the degree of saponification is too high, the dyeing speed is slow, and in order to impart sufficient polarizing performance, the production time becomes long, and depending on the case, sometimes it may not be obtained. A polarizer layer having sufficient polarizing properties. Therefore, the degree of saponification is 99.5 mol% or less, and preferably 99.0 mol% or less.

The degree of saponification refers to the ratio of the acetic acid group (acetoxy group: -OCOCH ₃ ) of the polyvinyl acetate-based resin contained in the raw material of the polyvinyl alcohol-based resin to the hydroxyl group by saponification treatment, in units of ratio (mole The ratio is expressed by the following formula: degree of saponification (% by mole) = [(number of hydroxyl groups) ÷ (number of hydroxyl groups + number of acetate groups)]. The degree of saponification can be determined in accordance with JIS K 6726 (1994). The higher the degree of saponification, the higher the proportion of the hydroxyl group, and therefore the lower the proportion of the acetate group which hinders crystallization.

As the polyvinyl acetate-based resin, in addition to the polyvinyl acetate of the homopolymer of vinyl acetate, a copolymer of another monomer copolymerizable with vinyl acetate or the like is exemplified. As a copolymerizable with vinyl acetate The monomers are, for example, unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, (meth) acrylamides having an ammonium group, and the like.

The coating liquid may contain an additive such as a plasticizer or a surfactant as needed. As the plasticizer, a polyol or a condensate thereof, or the like, for example, glycerin, diglycerin, triglycerin, ethylene glycol, propylene glycol, polyethylene glycol or the like can be used. The amount of the additive to be added is preferably 20% by weight or less based on the polyvinyl alcohol-based resin.

The method of applying the above coating liquid to the base film 30 can be carried out by a wire bar coating method; for example, a roll coating method by a reverse coating method or a gravure coating method; a slit coating method; a corner wheel coating method Method; lip coating method; spin coating method; screen coating method; fountain coating method; dip coating method; spraying method;

The drying temperature and drying time of the coating layer (polyvinyl alcohol-based resin layer before drying) are set depending on the kind of the solvent contained in the coating liquid. The drying temperature is, for example, 50 to 200 ° C, preferably 60 to 150 ° C. When the solvent contains water, the drying temperature is preferably 80 °C.

The polyvinyl alcohol-based resin layer 6 may be formed only on one side of the base film 30 or on both sides. When it is formed on both surfaces, since two polarizing plates can be obtained from one polarizing laminated film 300, it is advantageous in the production efficiency of the polarizing plate.

The thickness of the polyvinyl alcohol-based resin layer 6 of the laminated film 100 is preferably 3 to 30 μm, more preferably 5 to 20 μm. When the polyvinyl alcohol-based resin layer 6 having only the thickness in the range is subjected to the extending step S1-2 and the dyeing step S1-3 described later, the dyeability of the dichroic dye is good, and the polarizing performance is excellent. Further, a polarizing plate layer 5 sufficiently thin (for example, having a thickness of 10 μm or less) can be obtained. When the thickness of the polyvinyl alcohol-based resin layer 6 is less than 3 μm, it tends to be too thin after stretching, and the dyeability tends to be deteriorated.

Before the application of the coating liquid, in order to improve the adhesion between the base film 30 and the polyvinyl alcohol-based resin layer 6, the surface of the base film 30 on the side where at least the polyvinyl alcohol-based resin layer 6 is formed is also Corona treatment, plasma treatment, flame treatment, and the like can be performed.

Further, before the application of the coating liquid, in order to improve the adhesion between the base film 30 and the polyvinyl alcohol-based resin layer 6, a base layer 30 may be formed on the base film 30 via a primer layer or the like. A vinyl alcohol-based resin layer 6.

The undercoat layer can be formed by applying a coating liquid for forming an undercoat layer onto the surface of the base film 30 and then drying it. The coating liquid for forming an undercoat layer contains a component which can exhibit a certain strength of adhesion between the base film 30 and the polyvinyl alcohol-based resin layer 6. The coating liquid for forming an undercoat layer usually contains a resin component and a solvent which impart such an adhesive force. As the resin component, a thermoplastic resin excellent in transparency, heat stability, and elongation, for example, a (meth)acrylic resin, a polyvinyl alcohol-based resin, or the like is preferably used. Among them, a polyvinyl alcohol-based resin which imparts a good adhesion is preferable. More preferably, it is a polyvinyl alcohol resin. As the solvent, a general organic solvent or an aqueous solvent which can dissolve the above resin component is usually used, but an undercoat layer is preferably formed from a coating liquid containing water as a solvent.

In order to increase the strength of the undercoat layer, a crosslinking agent may be added to the coating liquid for forming an undercoat layer. The crosslinking agent can be selected from conventional ones such as an organic system and an inorganic system depending on the type of the thermoplastic resin to be used. Column Examples of the crosslinking agent include an epoxy-based, isocyanate-based, dialdehyde-based, metal-based (metal salt, metal oxide, metal hydroxide, or organometallic compound) and a polymer-based crosslinking agent. When a polyvinyl alcohol-based resin is used as the resin component for forming the undercoat layer, a polyamide solvent, a methylolated melamine resin, a dialdehyde-based crosslinking agent, a metal chelate-based crosslinking agent, or the like is preferably used.

The thickness of the undercoat layer is preferably about 0.05 to 1 μm. More preferably, it is 0.1 to 0.4 μm. When it is thinner than 0.05 μm, the effect of improving the adhesion between the base film 30 and the polyvinyl alcohol-based resin layer 6 is small, and if it is thicker than 1 μm, it is disadvantageous for thinning of the polarizing plate.

The method of applying the coating liquid for forming an undercoat layer to the base film 30 can be the same as the coating liquid for forming a polyvinyl alcohol-based resin layer. The undercoat layer is applied to a surface coated with a coating liquid for forming a polyvinyl alcohol-based resin layer. The drying temperature of the coating layer containing the coating liquid for forming an undercoat layer is, for example, 50 to 200 ° C, preferably 60 to 150 ° C. When the solvent contains water, the drying temperature is preferably 80 ° C or higher.

[b]Extension step S1-2

Referring to Fig. 5, in this step, the laminated film 100 including the base film 30 and the polyvinyl alcohol-based resin layer 6 is stretched to obtain an extended extension of the base film 30' and the polyvinyl alcohol-based resin layer 6'. The step of film 200. The extension process is typically a one-axis extension.

The stretching ratio of the laminated film 100 can be appropriately selected depending on the desired polarizing characteristics, and is preferably more than 5 times and 17 times or less, more preferably more than 5 times and 8 times or less with respect to the original length of the laminated film 100. Delay When the draw ratio is 5 or less, the polyvinyl alcohol-based resin layer 6' cannot be sufficiently aligned, and thus the degree of polarization of the polarizer layer 5 may not be sufficiently high. On the other hand, when the stretching ratio exceeds 17 times, the film is likely to be broken at the time of stretching, and the thickness of the stretching film 200 becomes thinner than necessary, and the workability and workability in the subsequent step may be lowered.

The extension processing is not limited to one-stage extension and can be performed in multiple stages. In this case, the multi-stage stretching treatment may be continuously performed before the dyeing step S1-3, or the stretching treatment after the second stage or the dyeing treatment and/or the crosslinking treatment of the dyeing step S1-3 may be simultaneously performed. When performing the multi-stage stretching process as described above, it is preferable to carry out the stretching treatment so that all the stages of the stretching process are combined to have a stretching ratio of more than 5 times.

The stretching treatment may be a longitudinal extension extending in the longitudinal direction of the film (the conveying direction of the film), or a lateral extension or oblique extension extending in the width direction of the film. As the longitudinal stretching method, for example, a roller extending extension between the rollers, a compression extension, a chuck (clip or clip) extension, or the like is used as a lateral stretching method, for example, a tenter method. The stretching treatment may be either a wet stretching method or a dry stretching method, but in the case of using a dry stretching method, it is preferred that the stretching temperature is selected from a wide range.

The elongation temperature is set to a temperature at which the polyvinyl alcohol-based resin layer 6 and the base film 30 all exhibit fluidity of a possible degree of elongation, and preferably -30 of the phase transition temperature (melting point or glass transition temperature) of the substrate film 30. The range of °C to +30 ° C, more preferably in the range of -30 ° C to +5 ° C, more preferably in the range of -25 ° C to +0 ° C. When the base film 30 is composed of a plurality of resin layers, The phase transition temperature refers to the highest phase transition temperature among the phase transition temperatures indicated by the plurality of resin layers.

When the stretching temperature is lower than -30 ° C of the phase transition temperature, it is difficult to achieve a high-magnification extension of more than 5 times, or the fluidity of the base film 30 is too low, and the elongation treatment tends to be difficult. When the stretching temperature exceeds +30 ° C of the phase transition temperature, the fluidity of the base film 30 is too high, and the elongation tends to be difficult. Since it is easier to achieve a high-magnification extension of more than 5 times, the stretching temperature is in the above range, more preferably 120 °C or more.

The heating method of the laminated film 100 for stretching treatment includes a zone heating method (for example, a method of heating in an extended region of a heating furnace in which hot air is adjusted to a predetermined temperature); a method of heating the roller body when the roller is extended; heater heating A method (a method in which an infrared heater, a halogen lamp heater, a plate heater, or the like is provided above and below the laminated film 100 to heat the radiant heat) or the like. In the method of extending between the rolls, from the viewpoint of the uniformity of the stretching temperature, the area heating method is preferred.

The preheating step of the preheating laminated film 100 may be provided before the extending step S1-2. As the preheating method, the same method as the heating method of the elongation treatment can be used. The preheating temperature is preferably in the range of -50 ° C to ± 0 ° C of the stretching temperature, and more preferably in the range of -40 ° C to -10 ° C in the stretching temperature.

Moreover, after extending the extension process of step S1-2, a heat fixation process step may be provided. In the state in which the end portion of the heat-fixing treatment film extension film 200 is held by the jig, the heat treatment is performed at a crystallization temperature or higher while maintaining the stretched state. The crystallization of the polyvinyl alcohol-based resin layer 6' is promoted by the heat setting treatment. The temperature of the heat setting treatment is the extension temperature The range of -0 ° C to -80 ° C is preferred, and the range of -0 ° C to -50 ° C of the extension temperature is better.

[c] Dyeing step S1-3

Referring to Fig. 6, this step is a step of dyeing the polyvinyl alcohol-based resin layer 6' of the stretched film 200 with a dichroic dye to adsorb and align it to form the polarizer layer 5. Through this step, the polarizing layer 5 is laminated on the single-sided or double-sided polarizing laminated film 300 of the base film 30'. As the dichroic dye, specifically, iodine or a dichroic organic dye can be used.

The dyeing step can be carried out by immersing the entire stretched film 200 in a solution containing a dichroic dye (dyeing solution). As the dyeing solution, a solution in which the above dichroic dye is dissolved in a solvent can be used. As the solvent of the dyeing solution, water is generally used, but an organic solvent compatible with water may be further added. The concentration of the dichroic dye of the dyeing solution is preferably 0.01 to 10% by weight, more preferably 0.02 to 7% by weight, particularly preferably 0.025 to 5% by weight.

When iodine is used as the dichroic dye, it is preferable to further add iodide to the dye solution containing iodine because the dyeing efficiency can be further improved. Examples of the iodide include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, cesium iodide, calcium iodide, tin iodide, and titanium iodide. The concentration of the iodide of the dyeing solution is preferably from 0.01 to 20% by weight. Among the iodides, potassium iodide is preferably added. When potassium iodide is added, the ratio of iodine to potassium iodide is preferably in the range of 1:5 to 1:100, more preferably in the range of 1:6 to 1:80, and particularly preferably 1:7 to 1 in terms of weight ratio. : 70 range. The temperature of the dyeing solution is preferably in the range of 10 to 60 ° C, more preferably 20 to 40 The range of °C.

Further, the dyeing step S1-3 may be performed before the extending step S1-2, and the steps may be performed simultaneously, but in order to properly align the dichroic dye adsorbed to the polyvinyl alcohol-based resin layer, the laminated film 100 After performing at least a certain degree of extension, it is preferred to carry out the dyeing treatment S1-3. In other words, the stretching film 200 obtained by the stretching process until the target magnification is extended in the step S1-2 can be supplied to the dyeing step S1-3, and after the stretching step S1-2 is performed at a magnification lower than the target. In the dyeing step S1-3, the extension processing in which the total stretching ratio becomes the target magnification can also be performed. As an embodiment of the latter, for example, 1) in the extending step S1-2, after the stretching process of the magnification lower than the target, the stretching process in the dyeing step S1-3 is performed in the dyeing process of the dyeing step S1-3. As will be described later, when the cross-linking treatment is performed after the dyeing treatment, 2) after the stretching step of the magnification lower than the target is performed in the extending step S1-2, the total stretching ratio is not reached to the target in the dyeing step of the dyeing step S1-3. The stretching treatment of the magnification is performed, and then the final total stretching ratio becomes the extension processing of the target magnification in the crosslinking treatment.

The dyeing step S1-3 may include a crosslinking treatment step that is continued after the dyeing treatment. The crosslinking treatment can be carried out by immersing the dyed film in a solution (crosslinking solution) containing a crosslinking agent. As the crosslinking agent, conventionally known materials such as a boron compound such as boric acid or borax, glyoxal, glutaraldehyde or the like can be used. The crosslinking agent may be used alone or in combination of two or more.

The crosslinking solution is specifically dissolved in a solvent by a crosslinking agent. liquid. As the solvent, for example, water can be used, but an organic solvent compatible with water can be further included. The concentration of the crosslinking agent in the crosslinking solution is preferably in the range of 1 to 20% by weight, more preferably in the range of 6 to 15% by weight.

The crosslinking solution can comprise an iodide. By the addition of iodide, the in-plane polarization characteristics of the polarizer layer 5 can be more uniform. Examples of the iodide include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, cesium iodide, calcium iodide, tin iodide, and titanium iodide. The concentration of the iodide in the crosslinking solution is preferably from 0.05 to 15% by weight, more preferably from 0.5 to 8% by weight. The temperature of the crosslinking solution is preferably in the range of 10 to 90 °C.

The crosslinking treatment can be carried out by mixing a crosslinking agent in the dyeing solution or simultaneously with the dyeing treatment. Moreover, the elongation treatment can also be performed in the crosslinking treatment. The specific aspect in which the elongation treatment is carried out in the crosslinking treatment is as described above. Further, two or more kinds of cross-linking solutions having different compositions can be used for the second or more immersion in the cross-linking solution.

After the dyeing step S1-3, it is preferred to perform a washing step and a drying step before bonding the first protective film. The washing step typically includes a water washing step. The water washing treatment can be carried out by immersing the film after the dyeing treatment or the crosslinking treatment in pure water such as ion-exchanged water or distilled water. The water washing temperature is usually from 3 to 50 ° C, preferably from 4 to 20 ° C. The washing step may also be a combination of a water washing step and a washing step by an iodide solution.

As the drying step performed after the washing step, any suitable method such as natural drying, air drying, heat drying, or the like can be employed. For example, when heated and dried, the drying temperature is usually 20 to 95 °C.

Thickness of the polarizer layer 5 of the polarizing laminated film 300 The degree is, for example, 30 μm or less, and may be 20 μm or less. From the viewpoint of reducing the thickness of the polarizing plate, it is preferably 10 μm or less, more preferably 8 μm or less. The thickness of the polarizer layer 5 is usually 2 μm or more.

In the first protective film bonding step S10, referring to Fig. 7, on the polarizing plate layer 5 of the polarizing laminated film 300, the adhesion ratio is adjusted to be 55% RH at 25 ° C via the adhesive layer 15 ( The first protective film 10 having a high moisture content and a high moisture content is obtained by a step of obtaining a polarizing laminated film 400 with a protective film.

The "25 ° C 55% RH equilibrium moisture content" of the protective film refers to the water content when placed in a 55% RH atmosphere at 25 ° C for 24 hours. The moisture content of the protective film is determined by the dry weight method. Specifically, when the weights of the protective films before and after the heat treatment at 105 ° C for 120 minutes are respectively set to W ₀ and W ₁ , the following formula: moisture ratio (wt/wt) %) = 100 × (W _{0 -} W ₁ ) / W _{0 is} obtained.

When the first protective film 10 having the specified moisture content is maintained in the predetermined moisture content, the polarizing layer 5 bonded to the polarizing laminate film 300 can be effectively prevented from being removed by peeling off. The polarizing plate produced by the peeling step S20 of the film 30' (as described above, the polarizing plate refers to a protective film including a polarizing plate layer and a surface on which at least one side of the adhesive layer is laminated) .

Here, the curling of the polarizing plate and the curl suppressing effect of the present invention are further explained. The term "curl" refers to a phenomenon in which a film (including a laminated film) such as a polarizing plate is bent into a bow shape (or a tubular shape in a remarkable case). If In the surface of one side of the polarizer layer 5, a polarizing plate having a protective film on one side of the first protective film 10 is bonded to the first protective film 10 via the adhesive layer 15, and the side of the first protective film 10 is curled inside. The state is referred to as positive curl, and the state in which the side of the polarizer layer 5 is set to the inside and curled is referred to as reverse curl.

In the case of a polarizing plate, curling is a problem in that when a display cell such as a liquid crystal cell is attached to a polarizing plate via an adhesive layer, the polarizing plate is curled. In other words, when the display cell is bonded to a display cell such as a liquid crystal cell, the polarizing plate is usually laminated with other peripheral members of various films and layers to form a composite polarizing plate. In the composite polarizing plate, it is necessary to suppress curling. As a peripheral member, for example, a protective film for scratch prevention attached to a protective film; laminated on a protective film (for example, when a polarizing plate having a protective film is attached) or a polarizing layer (for example, a protective film is attached to one side) The polarizing plate of the polarizing plate is bonded to the liquid crystal cell and the adhesive layer for other optical members; the release film laminated on the outer surface of the adhesive layer; and laminated on the protective film (for example, when the polarizing plate with the protective film is attached on both sides) Or an optical compensation film such as a retardation film, another optical functional film, a surface treatment layer laminated on the protective film, or the like on the polarizing plate layer (for example, when a polarizing plate having a protective film is provided on one side).

The composite polarizing plate is not curled and flat, or the side of the adhesive layer of the composite polarizing plate is set to the outer side (convex), and the curl is just right. As a result, when the composite polarizing plate is bonded to the display cell, air bubbles can be prevented from entering between the adhesive layer and the display cell, and defects in display on the display device and defects in the end portion of the bonding surface can be suppressed. On the other hand, when the side of the adhesive layer is set to the inner side (concave) and the composite polarizing plate is curled, it is easy to bite into the air during bonding, and the possibility of occurrence of the above-mentioned defects is high.

Attempting to suppress the composite polarizer when fitting the peripheral members Although the amount of curling and the direction of correcting the curl are possible, in the state where the protective film is bonded to the polarizing plate formed on at least one side of the polarizing plate layer, the curl must be small, and it is difficult to control the curl of the composite polarizing plate. Therefore, it is necessary to control the curl of the polarizing plate itself which is formed by bonding the protective film to the surface of at least one side of the polarizing plate layer.

In other words, the curl of the polarizing plate formed by bonding the protective film to at least one side of the polarizer layer is preferably reduced to a degree that can be corrected by the bonding of the peripheral members, regardless of the curl or the reverse curl. Better to be as flat as possible. This can be achieved according to the invention. In particular, in the conventional coating method, when the protective film is bonded to the polarizer layer and the base film is peeled off, the obtained polarizing plate tends to have a large curl in the direction of the reverse crimp, and is particularly effective according to the present invention. This reverse curl is suppressed.

In the conventional coating method, reverse curl is likely to occur, and it is considered that the binding force of the base film acts. In the polarizing laminate film formed by the coating method, the polarizer layer is in an uncontracted state due to the rigidity of the base film, and when the protective film is bonded, the base film is peeled off and the polarizing sheet is produced. shrink. In contrast, when a polarizing film (polarizing film) containing a monomer (separate) film is bonded to a single film method of a protective film via an adhesive layer, water is evaporated and dried before the protective film is bonded. Tension control, etc., because the polarizer is sufficiently shrunk, the polarizer does not cause so many dimensional changes after the protective film is bonded, and the problem of initial curling is less likely to occur.

The first protective film 10 having a water content ratio of 55% RH and an equilibrium moisture content is bonded to the polarizing layer 5 of the polarizing laminated film 300, and the base film 30' is peeled off. Method can be effective The reason for suppressing the reverse curl is presumed to be the following reason. In other words, the first protective film 10 having a moisture content higher than the above-described equilibrium moisture content has a slight expansion in size when bonded, and when the first protective film 10 in this state is bonded to the polarizer layer 5, After the normal environment (the environment of the manufacturing step after bonding, the storage environment of the obtained polarizing plate, and the environment when the polarizing plate is bonded to the display cell) is 25 ° C, 55% RH, the first protective film 10 is intended to shrink. The force (returns to the size of the environment at 25 ° C 55% RH), in other words, the force to be corrected in the direction of positive curl. This force suppresses the inverse curl.

When the moisture content of the first protective film 10 is too high, the curl in the positive crimping direction becomes strong, and the defects of air bubbles are likely to occur, and when it is placed in a severe environment, the curl is further promoted, and the end of the polarizing plate is feared. Will peel off from the display cells. Therefore, the moisture content of the first protective film 10 bonded to the polarizer layer 5 is preferably 70% or less, more preferably 60% or less. The saturated water content is a water content measured by immersing the first protective film 10 in water at 30° C. for 3 hours to remove adhering water on the surface, and the water content is defined as described above.

The method of preparing the first protective film 10 having a water content ratio higher than the equilibrium moisture ratio of 55% RH at 25° C. is not particularly limited. For example, a method in which the protective film is left for a predetermined period of time in a humidity control tank capable of adjusting temperature and humidity. As the humidity control tank, a commercially available humidity control box or an air conditioner can be used.

Further, as another method, a method in which the protective film is once passed through a water bath and the moisture content is too high may be suitably used. This method is suitable for continuous production and improves productivity because the moisture content can be adjusted to a desired value in a short time. By adjusting the residence time of the water bath, water In addition, the initial moisture content can be easily adjusted, and the final moisture content can be adjusted by drying time and drying temperature. The water bath may be, for example, a tank for storing warm water, and the temperature of the water bath may be adjusted to maintain the temperature at a certain level. Instead of the use of the water bath, a method of blowing steam to the protective film, a method of blowing water by a spray method or the like, or a method of applying water by a coater or the like may be employed.

The drying method may be any method such as blowing hot air, drying using a so-called hot air drying oven, drying by an infrared heater, or the like. It is preferable to suppress the rapid decrease in the moisture content and to adjust the humidity in the drying furnace in order to carry out the drying gently.

The material constituting the first protective film 10 is preferably a translucent (preferably optically transparent) thermoplastic resin, and such a resin is, for example, a chain polyolefin resin (such as a polypropylene resin) or a cyclic polyolefin. a polyolefin resin such as a resin (northene-based resin); a cellulose ester resin such as cellulose triacetate or cellulose diacetate; a polyester resin; a polycarbonate resin; Acrylic resin; polystyrene resin; or such mixtures, copolymers, and the like.

In the method of the present invention, the method of adjusting the water content to a predetermined value based on the equilibrium moisture content of the protective film at 25 ° C and 55% RH is used, and the curl is suppressed. Therefore, the obtained polarized light can be suppressed regardless of the type of the protective film. The advantage of the curl of the board. Among them, when a protective film having a high moisture permeability of a cellulose ester resin (for example, cellulose triacetate) or a (meth)acrylic resin (for example, polymethyl methacrylate resin) is used, the moisture content changes. The difference in size is large, so that the positive curling direction and the correcting force are large, and the advantages of the present invention are large.

The first protective film 10 may also be a protective film incorporating an optical function such as a retardation film or a brightness enhancement film. For example, the film formed of the thermoplastic resin is stretched (one-axis stretching or biaxial stretching, etc.), and a liquid crystal layer or the like is formed on the film to form a retardation film which imparts an arbitrary retardation value.

In addition to a homopolymer of a chain olefin such as a polyethylene resin or a polypropylene resin, a copolymer of two or more kinds of chain olefins may be mentioned as the chain polyolefin resin.

The cyclic polyolefin resin is a general term for a resin obtained by polymerizing a cyclic olefin as a polymerization unit. Specific examples of the cyclic polyolefin-based resin include a ring-opened (co)polymer of a cyclic olefin, an addition polymer of a cyclic olefin, and a copolymer of a cyclic olefin and a chain olefin such as ethylene or propylene ( Representative of a random copolymer) and such graft copolymers modified with unsaturated carboxylic acids and derivatives thereof, and such hydrides and the like. Among them, a norbornene-based resin having a norbornene-based monomer such as a norbornene or a polycyclic norbornene-based monomer as a cyclic olefin is preferably used.

The cellulose ester resin is an ester of cellulose and a fatty acid. Specific examples of the cellulose ester-based resin include cellulose triacetate, cellulose diacetate, cellulose tripropionate, and cellulose dipropionate. Further, these copolymers may be used, and a part of the hydroxyl group may be modified with other substituents. Among these, cellulose triacetate (triethylenesulfonyl cellulose: TAC) is particularly preferred.

The polyester resin is a resin having an ester bond, and is generally a polycondensate of a polyvalent carboxylic acid or a derivative thereof and a polyhydric alcohol. As the polyvalent carboxylic acid or a derivative thereof, a divalent dicarboxylic acid or a derivative thereof can be used, for example Terephthalic acid, isophthalic acid, dimethyl terephthalate, dimethyl naphthalene dicarboxylate, and the like. As the polyol, a divalent diol such as ethylene glycol, propylene glycol, butanediol, neopentyl glycol, cyclohexanedimethanol or the like can be used.

Specific examples of the polyester resin include polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, dibutyl naphthalate, and dibutyl terephthalate. Ester, dipolyethylene naphthalate, cyclohexyl dimethyl terephthalate, cyclohexyl dimethyl naphthalate.

The polycarbonate resin is a polymer containing a monomer unit bonded via a carbonate group. The polycarbonate resin may be a resin called a modified polycarbonate or a copolymerized polycarbonate which modifies a polymer skeleton.

The (meth)acrylic resin is a resin having a (meth)acryloyl group as a main constituent monomer. Specific examples of the (meth)acrylic resin include, for example, poly(meth)acrylate such as polymethyl methacrylate; methyl methacrylate-(meth)acrylic acid copolymer; methyl methacrylate-( Methyl) acrylate copolymer; methyl methacrylate-acrylate-(meth)acrylic acid copolymer; methyl (meth) acrylate-styrene copolymer (MS resin, etc.); methyl methacrylate and A copolymer of an alicyclic hydrocarbon group-containing compound (for example, methyl methacrylate-cyclohexyl methacrylate copolymer, methyl methacrylate-methyl (meth) acrylate), and the like. It is preferably a polymer containing a poly(meth)acrylic acid C _1-6 alkyl ester such as poly(methyl) acrylate as a main component, and more preferably a methyl methacrylate as a main component (50 to 100 weight). %, preferably 70 to 100% by weight of a methyl methacrylate-based resin.

Further, the description of each of the thermoplastic resins shown above can also be applied to the thermoplastic resin constituting the base film 30.

The surface of the first protective film 10 on the side opposite to the polarizer layer 5 may be a surface treatment layer (coating layer) such as a hard coat layer, an antiglare layer, an antireflection layer, an antistatic layer, or an antifouling layer. The method of forming the surface treatment layer on the surface of the protective film is not particularly limited, and a conventional method can be used.

The thickness of the first protective film 10 is preferably thinner from the viewpoint of thinning of the polarizing plate, and when it is too thin, the strength is lowered and the workability is deteriorated. Therefore, the thickness of the first protective film 10 is preferably 5 to 90 μm, more preferably 5 to 60 μm, still more preferably 5 to 50 μm.

The first protective film 10 formed by the adjusted moisture content is laminated on the polarizer layer 5 of the polarizing laminate film 300 via the adhesive layer 15 (the surface of the polarizer layer 5 opposite to the base film 30') ). When the polarizing film layer 3 has the polarizing plate layer 5 on both surfaces of the base film 30', the protective film is bonded to the polarizing plate layer 5 on both surfaces. In this case, the protective films may be the same type of protective film or different types of protective films.

When the first protective film 10 is bonded to the polarizer layer 5, the bonding surface of the first protective film 10 can be subjected to plasma treatment, corona treatment, or ultraviolet irradiation treatment in order to improve adhesion to the polarizer layer 5. A surface treatment (easily followed by treatment) such as a flame treatment or a saponification treatment, wherein a plasma treatment, a corona treatment or a saponification treatment is preferred. For example, when the first protective film 10 contains a cyclic polyolefin resin, it is usually subjected to plasma treatment or corona treatment. Further, when a cellulose-based resin is contained, it is usually subjected to a saponification treatment. As the saponification treatment, for example, a method of immersing in an aqueous alkali solution such as sodium hydroxide or potassium hydroxide.

As a bonding agent used for bonding, water connection can be used. A coating agent and a photocurable adhesive. The water-based adhesive is, for example, an adhesive containing a polyvinyl alcohol-based resin aqueous solution, an aqueous two-liquid urethane-based emulsified adhesive, or the like. In particular, when a cellulose ester-based resin film which has been subjected to surface treatment (hydrophilization treatment) such as saponification treatment is used as the first protective film 10, a water-based adhesive containing a polyvinyl alcohol-based resin aqueous solution is preferably used.

As the polyvinyl alcohol-based resin, in addition to the vinyl alcohol homopolymer obtained by the polyvinyl acetate saponification treatment of the homopolymer of vinyl acetate, saponification of a copolymer of vinyl acetate and other monomers copolymerizable therewith can be used. The obtained polyvinyl alcohol copolymer or the modified hydroxy group-modified modified polyvinyl alcohol polymer or the like is treated. The aqueous binder may include an additive such as a polyvalent aldehyde, a water-soluble epoxy compound, a melamine-based compound, a zirconia compound, a zinc compound or the like.

The water-based adhesive is applied to the bonding surface of the polarizing plate layer 5 of the polarizing laminated film 300 and/or the first protective film 10, and the films are bonded to each other via the adhesive layer, and it is preferable to use a bonding roller or the like. The step of bonding by press-fitting. The coating method of the water-based adhesive (the same applies to the photocurable adhesive) is not particularly limited, and a cast molding method, a Meyer bar coating method, a gravure coating method, a notch wheel coating method, or a doctor blade coating method can be used. Traditionally known methods such as cloth coating, slit coating, dip coating, and spray coating.

When the water-based adhesive is used, after the above-mentioned bonding, in order to remove the water contained in the aqueous binder, the drying step of drying the film is preferred. The drying system can be carried out, for example, by introducing the film into a drying furnace. The drying temperature is preferably from 30 to 90 °C. When the temperature is less than 30 ° C, the first protective film 10 is easily peeled off from the polarizer layer 5 . When the drying temperature exceeds 90 ° C, due to heat, polarizer The polarizing performance of the layer 5 may be deteriorated.

After the drying step, a ripening step at room temperature or a slightly higher temperature, for example, a temperature of about 20 to 45 ° C may be provided. The curing temperature is generally set to be lower than the drying temperature.

The photocurable adhesive refers to an adhesive which is cured by irradiation with an active energy ray such as ultraviolet rays, for example, a polymerizable compound and a photopolymerization initiator, a photoreactive resin, a binder resin, and a photoreaction. Sex cross-linkers, etc. The polymerizable compound is, for example, a photocurable epoxy monomer, a photocurable acrylic monomer, a photocurable monomer of a photocurable urethane monomer, or an oligomer derived from a photopolymerizable monomer. Things. As the photopolymerization initiator, for example, a substance which generates an active species such as a neutral radical, an anionic radical, or a cationic radical by irradiation with an active energy ray such as ultraviolet rays is included. As the photocurable adhesive containing a polymerizable compound and a photopolymerization initiator, those containing a photocurable epoxy monomer and a photocationic polymerization initiator are preferably used.

When the photocurable adhesive is used, after the above-mentioned bonding, the drying step is carried out as needed (when the photocurable adhesive contains a solvent), and then the photocurable adhesive is applied by irradiation with an active energy ray. Hardening hardening step. The light source of the active energy ray is not particularly limited, and is preferably an active energy ray having a light-emitting distribution with a wavelength of 400 nm or less, specifically, a low-pressure mercury lamp, a medium-pressure mercury lamp, a high-pressure mercury lamp, an ultra-high pressure mercury lamp, a chemical lamp, a black lamp, and microwave excitation. Mercury lamps, metal halide lamps and the like are preferred.

<Peeling step S20>

Referring to Fig. 8, this step is a step of peeling off the base film 30' after the first protective film bonding step S10. In this step, a polarizing plate 1 having a protective film on one side is obtained. The polarizing laminate film 300 has a polarizer layer 5 on both surfaces of the base film 30', and when the protective film is bonded to the polarizer layer 5, the polarizing film 300 is removed from the polarizing film 300 by the peeling step S20. Two polarizing plates 1 with a protective film on one side are obtained.

The method of peeling off the base film 30' is not particularly limited, and it can be peeled off in the same manner as the peeling step of the separator (release film) by the polarizing plate to which the adhesive is usually applied. After the first protective film bonding step S10, the base film 30' may be directly peeled off immediately, or may be wound into a roll once after the first protective film bonding step S10, and rolled out in the subsequent steps. Stripped on one side.

<Second protective film bonding step S30>

Referring to FIGS. 3 and 9, the surface of the polarizing plate 1 on the side of the polarizing plate 1 having the protective film on one side thereof can be bonded to the surface of the second protective film 20 via the adhesive layer 25, A polarizing plate 2 having a protective film on both sides was obtained. The description of the first protective film 10 and the adhesive layer 25 is referred to as the second protective film 20 and the adhesive layer 25 to which the adhesive film 20 is bonded. The first protective film 10 and the second protective film 20 may be the same type of protective film, or may be different types of protective films. The adhesive layer 15 and the adhesive layer 25 may be formed of the same kind of adhesives, or may be formed of different kinds of adhesives.

In the same manner as the first protective film 10, if the second protective film 20 having a moisture content higher than the equilibrium moisture ratio of 25 ° C and 55% RH is used, the polarizing plate with the protective film on both sides can be further improved. 2 Curl.

As described above, the obtained polarizing plate 1 having a protective film on one side and the polarizing plate 2 having a protective film on both sides thereof can be bonded to the above-exemplified peripheral member to form a composite polarizing plate, or can be used as such a composite polarizing plate. .

When the adhesive layer of one example of the peripheral member is attached to the polarizing plate 2 having the protective film on both sides, it can be laminated on the outer surface of any of the protective films, and when the polarizing plate 1 having the protective film is provided on one side, for example, it can be laminated on the polarizing plate. The face of the sheet opposite the protective film. The adhesive for forming the adhesive layer is usually a matrix polymer composed of a (meth)acrylic resin, a styrene resin, a siloxane resin, or the like, to which an isocyanate compound, an epoxy compound, such as aziridine is added. Aziridine) is an adhesive composition of a crosslinking agent. Further, it may be an adhesive layer which exhibits light scattering properties by containing fine particles. The thickness of the adhesive layer is usually from 1 to 40 μm, preferably from 3 to 25 μm.

Further, as an optical functional film of another example of the peripheral member, for example, a light-reflecting polarizing film that transmits polarized light of a reverse polarity is transmitted through light of a certain polarized light, and a film having an anti-glare function having a concave-convex shape on the surface; A film with a surface anti-reflection function; a reflective film with a reflective function on the surface; a semi-transmissive reflective film with both a reflective function and a transmissive function; and a viewing angle compensation film.

Example

Hereinafter, the present invention will be more specifically described by showing examples and comparative examples, but the present invention is not limited to the examples.

<Example 1>

(1) Undercoat layer forming step

Polyvinyl alcohol powder ("Z-200" manufactured by Nippon Synthetic Chemical Industry Co., Ltd., average polymerization degree 1100, average saponification degree: 99.5 mol%) was dissolved in hot water at 95 ° C to prepare a 3 wt% aqueous solution of polyvinyl alcohol. . In the obtained aqueous solution, a crosslinking agent ("SUMIREZ RESIN 650" manufactured by Tajika Chemical Industry Co., Ltd.) was added in an amount of 5 parts by weight based on 6 parts by weight of the polyvinyl alcohol powder to obtain a coating liquid for forming an undercoat layer.

Then, an unstretched polypropylene (PP) film (melting point: 163 ° C) having a thickness of 110 μm was prepared as a base film, and after performing corona treatment on one side thereof, a micro gravure coater was applied to the corona-treated surface. The coating liquid for forming an undercoat layer was dried at 80 ° C for 10 minutes to form an undercoat layer having a thickness of 0.2 μm.

(2) Production of laminated film (resin layer forming step)

Polyvinyl alcohol powder ("PVA124" manufactured by Kuraray Co., Ltd., average polymerization degree 2400, average saponification degree: 98.0 to 99.0 mol%) was dissolved in hot water at 95 ° C to prepare a polyvinyl alcohol aqueous solution having a concentration of 8 wt%. This is used as a coating liquid for forming a polyvinyl alcohol-based resin layer.

The surface of the undercoat layer of the base film having an undercoat layer produced in the above (1) was applied to the coating liquid for forming a polyvinyl alcohol-based resin layer using a lip coater, and then 80 ° C, 20 After drying for a minute, a polyvinyl alcohol-based resin layer was formed on the undercoat layer to obtain a laminated film including a base film/undercoat layer/polyvinyl alcohol-based resin layer.

(3) Production of stretch film (extension step)

The laminated film produced in the above (2) was stretched by a 5.3-fold free end at 160 ° C using a tenter to obtain a stretched film. Extended poly The thickness of the vinyl alcohol-based resin layer was 5.0 μm.

(4) Production of polarizing laminated film (dyeing step)

The stretched film prepared in the above (3) is immersed in a dyeing aqueous solution containing 26% by weight of iodine and potassium iodide (containing 0.35 parts by weight of iodine and 10 parts by weight of potassium iodide per 100 parts by weight of water), followed by dyeing treatment, and then immersed in boric acid and A crosslinked aqueous solution of 78 ° C of potassium iodide (9.5 parts by weight of boric acid and 5 parts by weight of potassium iodide per 100 parts by weight of water) was subjected to a crosslinking treatment for 300 seconds. Then, it was washed with pure water at 8 ° C for 10 seconds, and finally, dried at 40 to 50 ° C for 200 seconds to obtain a polarizing laminated film including a base film/undercoat layer/polarizing sheet layer.

(5) Production of polarizing plate (protective film bonding step and peeling step)

Polyvinyl alcohol powder ("KL-318" manufactured by Kuraray Co., Ltd., average polymerization degree 1800) was dissolved in hot water at 95 ° C to prepare a polyvinyl alcohol aqueous solution having a concentration of 3 % by weight, and the obtained aqueous solution was compared with the obtained aqueous solution. 2 parts by weight of a polyvinyl alcohol powder, a cross-linking agent (trade name "SUMIREZ RESIN 650", manufactured by Tajika Chemical Industry Co., Ltd.) was mixed in an amount of 1 part by weight to obtain an aqueous solution of an adhesive.

Then, the above-mentioned aqueous solution of the adhesive is applied to the outer surface (bonding surface) of the polarizer layer of the polarizing laminate film produced in the above (4), and then placed in an environment of 25° C. and 85% RH for 24 hours to adjust the water content. A transparent protective film ("KC4UY" manufactured by Konica Minolta Optical Co., Ltd., thickness 40 μm) containing a protective film [triacetyl cellulose (TAC)], which is pressed by a pair of bonding rollers Thereafter, the adhesive layer is dried to obtain a polarizing laminate with a protective film including a base film/undercoat/polarizer layer/adhesive layer/protective film. membrane. Further, as shown in the following Comparative Example 1, the equilibrium moisture content of the above protective film at 25 ° C and 55% RH was 1.08%. The saturated moisture content of the above protective film was 3.53%.

Finally, the base film is peeled off from the polarizing laminated film with a protective film. The base film can be easily peeled off to obtain a polarizing plate with a protective film on one side.

<Example 2>

A polarizing plate having a protective film on one side thereof was produced in the same manner as in Example 1 except that the moisture content of the protective film was allowed to stand in an environment of 25 ° C and 70% RH for 24 hours.

<Comparative Example 1>

A polarizing plate having a protective film on one side thereof was produced in the same manner as in Example 1 except that the moisture content of the protective film was allowed to stand in an environment of 25 ° C and 55% RH for 24 hours.

<Comparative Example 2>

A polarizing plate having a protective film on one side thereof was produced in the same manner as in Example 1 except that the moisture content of the protective film was allowed to stand in an environment of 40 ° C and 55% RH for 24 hours.

The moisture content (wt/wt%) of the protective film used in each of the examples and the comparative examples when they were bonded to the polarizer layer was shown in Table 1 together with the humidity-conditioning conditions of the protective film. The water content is obtained by the above calculation formula.

[Measurement and Evaluation of Curl Amount of Polarizing Plate]

From the obtained polarizing plate with a protective film on one side, a test piece having an absorption axis direction (MD) of 80 mm × a transmission axis direction (TD) of 80 mm was cut out at 25 ° C and 55% RH. Leave it in the environment for 24 hours. This test piece has a reverse curl in which the side of the polarizer layer is formed inside and curled, and when the concave surface faces upward on the reference surface (water platform surface), the four end sides are raised. In this state, the heights from the reference plane were measured for the four corners of the test piece, and the heights of the four corners were averaged to obtain the amount of curl, and the degree of suppression of the curl was evaluated based on the following evaluation criteria. The results are shown in Table 1.

A: The curl amount is less than 28 mm, and the curl of the polarizing plate is sufficiently suppressed

B: The amount of curl is 28 mm or more, and the curl of the polarizing plate is remarkable

The above evaluation criteria are based on the following reasons. When the amount of crimping is less than 28 mm, the outer surface of the protective film of the polarizing plate having the protective film on one side thereof is bonded to the protective film for preventing scratching (the polyethylene terephthalate film with the adhesive layer). A nearly flat composite polarizer is obtained. Further, on the outer surface of the polarizer layer of the composite polarizing plate, even if the adhesive layer for liquid crystal cell bonding is bonded, the composite polarizing plate can be maintained in a nearly flat state.

On the other hand, when the amount of curling is 28 mm or more, even if the protective film is bonded to the outside of the protective film, the obtained composite polarizing plate is curled in the reverse crimping direction. Further, on the outer surface of the polarizer layer of the composite polarizing plate, even if the adhesive layer for liquid crystal cell bonding is bonded, the state of the reverse curl is maintained. Further, after standing for several days in an environment of 23 ° C and 55% RH, when observed again, a defect in which the reverse curl became larger occurred.

S10‧‧‧1st protective film bonding step

S20‧‧‧ peeling step

Claims (5)

A method for producing a polarizing plate includes sequentially adjusting a moisture content of a polarizing laminated film having a polarizing plate layer on a surface of at least one side of a base film, and adjusting a moisture ratio of the bonding layer a step of protecting the film having a high equilibrium moisture ratio at 25 ° C and 55% RH; and a step of peeling off the substrate film. The method for producing a polarizing plate according to the first aspect of the invention, wherein, in the step of bonding the protective film, the moisture content of the protective film is 70% or less of the saturated moisture content. The method for producing a polarizing plate according to the first or second aspect, wherein the polarizing laminated film is produced by a method comprising the step of coating on at least one surface of the base film. After the coating liquid containing the polyvinyl alcohol-based resin is dried, the coating liquid is dried to form a polyvinyl alcohol-based resin layer to obtain a laminated film; the step of stretching the laminated film to obtain a stretched film; and the stretching The polyvinyl alcohol-based resin layer of the film is dyed with a dichroic dye to form the polarizing layer, whereby the polarizing laminated film is obtained. The method for producing a polarizing plate according to any one of claims 1 to 3, wherein the protective film comprises a cellulose ester resin or a (meth)acrylic resin. Polarization as described in any one of claims 1 to 4 In the method for producing a sheet, the thickness of the polarizer layer is 10 μm or less.