KR20170113313A - Method for manufacturing a polarizing plate - Google Patents

Abstract

[PROBLEMS] To provide a polarizing film producing method capable of appropriately suppressing the breakage of the polarizer at the time of manufacture and facilitating stretching at a high magnification.
[MEANS FOR SOLVING THE PROBLEMS] The present invention provides a method for producing a stretched film, comprising the steps of stretching a strip-shaped resin film comprising a polyvinyl alcohol resin as a forming material to obtain a stretched film; A bonding step of obtaining a laminated film in which a stretched film and a base film are laminated, dyeing the stretched film with a dichroic dye, and stretching in the longitudinal direction of the entire laminated film to form a polarizer And the base film in the joining step has a method of producing a polarizing film in which the stretching magnification in the longitudinal direction is less than the stretching magnification in the longitudinal direction of the stretched film in the stretching step.

Description

METHOD FOR MANUFACTURING A POLARIZING PLATE [0002]

The present invention relates to a method for producing a polarizing film.

Conventionally, a liquid crystal display device is known as an image display device. The liquid crystal display device has a liquid crystal panel and a polarizer formed on both surfaces of the liquid crystal panel. As a polarizer, a polarizing film in which a dichroic dye such as iodine is adsorbed and oriented on a stretched film obtained by stretching a polyvinyl alcohol (PVA) based resin film is known.

As a method for producing a polarizing film, for example, a method described in Patent Document 1 is known. In the manufacturing method described in Patent Document 1, first, a coating film of a polyvinyl alcohol resin is formed on the surface of a base film to form a resin layer, and then a laminate film of the resin layer and the base film is stretched. Subsequently, the resin layer is dyed with iodine, which is a dichroic dye, and further stretched in one direction.

Thus, a polarizing film is produced using the resin layer as a polarizer.

As another method for producing a polarizing film, there is known a method in which a polyvinyl alcohol resin film and a base film are laminated and then stretched, followed by further iodine dyeing and stretching.

Patent Document 1: JP-A-2000-338329

In recent years, a liquid crystal display device has been required to be reduced in size and thickness in order to reduce weight. For this reason, thinner polarizers and polarizing films constituting the liquid crystal display device have been studied.

It is also known that when a resin layer dyed with a dichroic dye is stretched at the time of production, the polarizer has a tendency to improve the polarization characteristics of the polarizer when the stretching magnification is high. Therefore, in recent years, as a polarizing film used in a liquid crystal display device, it is required to have a thin polarizer stretched at a high stretching magnification.

However, when the polarizer is made thinner at the time of producing the polarizing film, the resin layer (polarizer) tends to break at the time of stretching the film. In addition, if a polarizing film having a higher draw ratio than that of the conventional one is produced, the load on the processing apparatus during stretching becomes high, so that the production efficiency tends to be lowered.

Therefore, there has been a demand for a manufacturing method capable of reducing the apparatus load during stretching while suppressing the breakage of the polarizer in the stretching process.

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and an object thereof is to provide a polarizing film production method which can appropriately inhibit the polarizer from being broken at the time of manufacture and is easy to stretch at a high magnification.

In order to solve the above problems, one aspect of the present invention is a method for producing a stretched film, comprising: a stretching step of stretching a strip-shaped resin film made of a polyvinyl alcohol resin as a forming material to obtain a stretched film; A step of bonding a strip-shaped base film to the base film, and a step of obtaining a laminated film in which the stretched film and the base film are laminated, a step of dying the stretched film by dichroic dye, Wherein the base film in the joining step has a stretching magnification in the machine direction in the longitudinal direction of the stretched film in the stretching step, Of the polarizing film.

In one embodiment of the present invention, in the joining step, the base film may be formed in a non-stretched state in the longitudinal direction.

In one embodiment of the present invention, in the polarizer forming step, the laminated film in which the stretched film is dyed may be immersed in an aqueous solution containing boric acid and stretched in the aqueous solution.

In one embodiment of the present invention, the stretching step may be a manufacturing method of stretching the resin film using a fixed end stretching method.

In one embodiment of the present invention, the resin film may have a thickness of 15 mu m or more and 75 mu m or less.

In one embodiment of the present invention, in the joining step, the stretched film and the base film may be bonded to each other through an aqueous adhesive.

In an embodiment of the present invention, after the polarizer-forming step, a polarizing film-forming step of cutting the polarizer into a plurality of polarizing films may be employed.

According to the present invention, it is possible to provide a method of manufacturing a polarizing film in which breakage of the polarizer is suitably suppressed at the time of manufacture, and stretching at a high magnification is easy.

1 is a schematic cross-sectional view showing a polarizing film produced using the polarizing film producing method according to the present embodiment.
2 is a schematic diagram showing an example of a drawing process.
3 is a schematic diagram showing an example of a bonding step.
Fig. 4 is a schematic diagram showing an example of the dyeing process in the polarizer forming process. Fig.
5 is a schematic diagram showing an example of the drawing process in the polarizer forming process.
Fig. 6 is a schematic view showing a state in which a test piece is stretched in the examples. Fig.

Hereinafter, a method of manufacturing a polarizing film according to this embodiment will be described with reference to Figs. 1 to 5. Fig. In all of the following drawings, dimensions, ratios, and the like of the respective components are appropriately made different for easy viewing of the drawings.

[Polarizing Film]

1 is a schematic cross-sectional view showing a polarizing film produced using the polarizing film producing method according to the present embodiment. As shown in the figure, the polarizing film 10 produced by the polarizing film producing method of the present embodiment has the polarizer 1. Further, the polarizing film 10 may have a protective film 2 formed on one surface of the polarizer 1.

As the polarizer 1, a monoaxially stretched polyvinyl alcohol resin film having a dichroic dye adsorbed and oriented can be used. Details of the material for forming the polarizer 1 will be described later.

The protective film (2) protects the surface of the polarizer (1). The protective film 2 is bonded to the surface of the polarizer 1 through, for example, an adhesive layer or a pressure-sensitive adhesive layer. The material for forming the protective film 2 will be described later in detail.

The polarizing film 10 may have a film having an optical function such as a retardation film or a brightness enhancement film on the surface of the polarizer 1, if necessary.

That is, in the polarizing film produced in the polarizing film producing method of the present embodiment, in the case of the minimum layer structure, only the polarizer 1 is used and a layer having various functions having desired optical characteristics and mechanical characteristics Layered structure.

[Production method of polarizing film]

Figs. 2 to 5 are explanatory diagrams showing a method for producing a polarizing film according to the present embodiment. Fig. In the method for producing a polarizing film of the present embodiment,

(1) a stretching process for stretching a strip-shaped resin film comprising a polyvinyl alcohol-based resin as a forming material to obtain a stretched film

(2) a joining step of joining a strip-shaped base film to at least one surface of the stretched film to obtain a laminated film in which a stretched film and a base film are laminated

(3) a step of dyeing a stretched film by a dichroic dye and stretching in the longitudinal direction of the entire laminated film to form a polarizer in which a stretched film is used as a polarizer

(4) Protective film bonding process for bonding a protective film to the surface of the polarizer

(5) Polarizing film forming process for forming a polarizing film by cutting a polarizer and a protective film into plural pieces

Lt; / RTI >

Hereinafter, description will be made in order.

<Stretching Step>

2 is a schematic diagram showing an example of a drawing process. In the stretching step, a strip-shaped resin film made of a polyvinyl alcohol-based resin is stretched to obtain a stretched film. 2 (a) shows a state in which the stretched resin film 11 is obtained by stretching the resin film 11 by a fixed-end transverse stretching method. Fig. 2 (b) And the stretched film 12 is obtained by stretching.

In the method shown in Fig. 2 (a), the resin film 11 wound from the unwinding roll 101 is introduced into a heating furnace (not shown). The resin film 11 in the heating furnace is sequentially transported in the longitudinal direction of the resin film 11 while both ends in the width direction of the resin film 11 are grasped by the plurality of grip portions 109. [ The gripping section 109 stretches the resin film 11 in the width direction (TD direction indicated by D1 in the figure) by applying a force to the resin film 11 in the width direction to form the stretched film 12A ).

Here, regarding the longitudinal direction of the stretched film 12A (the MD direction indicated by the symbol D2 in the figure), it is preferable that the rotational speed of the take-up roll 101 and the rolls such as the transport roll or the take- Or may be stretched or shrunk by difference, or may not be stretched.

2 (b), the resin film 11 wound from the unwinding roll 101 has a heating roll 102 and a pair of nip rolls 103 and 104 rotating at a higher speed than the heating roll, And is transported in the longitudinal direction. The resin film (11) is heated by the heating roll (102). The resin film 11 is formed between the heating roll 102 and the nip rolls 103 and 104 by a circumferential speed difference between the heating roll 102 and the nip rolls 103 and 104 in the longitudinal direction In the MD direction indicated by the symbol D3) to form the stretched film 12B.

(Resin film)

As the polyvinyl alcohol-based resin forming the resin film 11, saponified polyvinyl acetate-based resin can be used. As the polyvinyl acetate-based resin, a copolymer of vinyl acetate, which is a homopolymer of vinyl acetate, and other monomers copolymerizable with vinyl acetate can be used. 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 polyvinyl alcohol resin preferably has a saponification degree of 80.0 mol% or more. When the degree of saponification of the polyvinyl alcohol resin is 80.0 mol% or more, the water resistance after forming the polarizer tends to be high, and the property of enduring the wet environment and the high temperature environment tends to be high. The saponification degree is more preferably 90.0 mol% or more, still more preferably 94.0 mol% or more, and most preferably 100 mol% (completely saponified product).

Here, the &quot; degree of saponification &quot; refers to the ratio of units of acetic acid ester contained in a polyvinyl acetate-based resin as a raw material of a polyvinyl alcohol-based resin to a hydroxyl group in the saponification step as a unit ratio (mol% It is a defined value. The degree of saponification can be determined by a method prescribed by JIS K 6726 (1994).

Saponification degree (mol%) = (number of hydroxyl groups) / (number of hydroxyl groups + number of acetic acid groups) x 100

The polyvinyl alcohol resin may be a modified polyvinyl alcohol partially modified. Examples thereof include those obtained by modifying a polyvinyl alcohol resin with an olefin such as ethylene or propylene, an unsaturated carboxylic acid such as acrylic acid, methacrylic acid or crotonic acid, an alkyl ester of an unsaturated carboxylic acid, an acrylamide or the like . The ratio of denaturation is preferably less than 30 mol%, more preferably less than 10%. If the ratio of denaturation is less than 30 mol%, the adsorption of the dichroic dye is not well inhibited, and the degradation of polarization performance due to denaturation does not occur well.

As described above, the material for forming the resin film 11 used in the present embodiment may not be a pure polyvinyl alcohol resin, and may be various kinds of chemical structures depending on the degree of saponification, the kind of copolymerized monomer, . As described above, the polyvinyl alcohol resin is used as a basic skeleton and derivatives that can be employed are integrated to be referred to as &quot; polyvinyl alcohol resin &quot; in the present embodiment.

The average degree of polymerization of the polyvinyl alcohol resin is not particularly limited, but is preferably 100 to 10,000, more preferably 1,500 to 8,000, and further preferably 2,000 to 5,000. The average degree of polymerization of the polyvinyl alcohol resin can be determined by a method determined by JIS K 6726 (1994).

By forming the polyvinyl alcohol resin as described above, a resin film 11 is obtained. The film forming method of the resin film 11 is not particularly limited. For example, a solvent casting method in which a polyvinyl alcohol resin solution is coated on a support and dried, a melt extrusion method in which a polyvinyl alcohol resin containing water is melt-kneaded and extruded on a support by an extruder, a polyvinyl alcohol resin aqueous solution Is discharged into a poor solvent, and the like.

Of these, a solvent casting method or a melt extrusion method is preferable in that a more transparent film can be obtained.

Hereinafter, the solvent casting method will be described in more detail.

When the resin film 11 is formed by the solvent casting method, a polar organic solvent such as water, alcohols, ketones, and esters can be used as a solvent for dissolving the polyvinyl alcohol resin. However, . To the aqueous solution of the polyvinyl alcohol resin, a polar organic solvent may be appropriately added.

Further, a plasticizer may be added to the polyvinyl alcohol-based resin solution to be used.

Examples of the plasticizer include polyhydric alcohols such as ethylene glycol, glycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, and trimethylolpropane. The plasticizer may be used alone, or two or more plasticizers may be used in combination. In particular, ethylene glycol or glycerin is suitably used. If necessary, an antiblocking agent such as a surfactant may also be used in combination.

The polyvinyl alcohol resin solution used in these methods can be obtained, for example, by dissolving a polyvinyl alcohol resin in water heated to 80 to 90 占 폚.

The solid content concentration of the polyvinyl alcohol resin is preferably in the range of 6 wt% to 50 wt%. If the concentration of the solid content is less than 6% by weight, the viscosity becomes too low, and the fluidity at the time of forming the resin layer becomes excessively high, and it becomes difficult to obtain a uniform film. On the other hand, if the concentration of the solid content exceeds 50% by weight, the viscosity becomes too high and the fluidity at the time of forming the resin layer becomes low, so that the film formation becomes difficult.

Examples of the method for coating a polyvinyl alcohol resin solution on a support include a roll coating method such as a wire bar coating method, a reverse coating method and a gravure coating method, a die coating method, a comma coater method, a lip coating method, a spin coating method, Known methods such as a coating method, a fountain coating method, a dipping method, and a spraying method can be suitably selected and employed.

In the solvent casting method, a polyvinyl alcohol resin solution is applied on a support to form a resin layer, and then the resin layer formed on the support at low temperature is dried to such an extent that the resin layer can be peeled from the support, And drying the resin layer peeled off from the support.

Hereinafter, the step of drying to such an extent that it can be peeled from the support is referred to as a &quot; first drying step &quot;, and the step of drying the resin layer peeled off from the support is referred to as a &quot; second drying step &quot;.

Examples of the support include release films, stainless steel belts, chill rolls, and the like.

In the first drying step, the "degree of peeling from the support" means that the solvent is removed from the applied resin solution to form a film-like coating film (hereinafter simply referred to as film), and the film is peeled to be. Experience has shown that if the moisture content of the film is dried to 30 wt% or less, the film can be stably peeled off. Further, drying of the film to a moisture content of 20% by weight or less is preferable because it can be easily peeled off.

The term "moisture content" as used herein refers to a value obtained by a dry weight method, as a ratio of water contained in a film. The water content can be obtained by the following method.

First, the film after peeling is allowed to stand at room temperature (approximately 25 DEG C, 55% RH) for 30 minutes or more, and then the mass of the film is measured. Subsequently, the film is dried in an oven at 105 DEG C for 60 minutes. After taking out from the oven, the film is allowed to stand for several minutes until the temperature returns to room temperature. Subsequently, the mass of the film is re-measured.

The water content is obtained from the following formula by using the mass (mass before drying) of the obtained film before drying and the mass (mass after drying) of the film after drying.

Water content (%) = {(mass before drying) - (mass after drying)} / (mass before drying) × 100

In the production process, it is preferable to carry out preliminary experiments to set the drying conditions under which the film is in a peelable state, and to perform drying under the above conditions. For example, as the drying condition of the film, it is preferable to dry it at a temperature range of 40 to 60 캜 for 1 to 30 minutes, more preferably to dry at 50 캜 for 3 to 20 minutes.

In the first drying step, by drying at a low temperature, drying and shrinkage of the film does not occur easily, and curling of the end portion can be prevented. In addition, in the first drying step, the film is not completely dried but dried and peeled to such an extent that it can be peeled off from the support, so that drying and shrinkage of the film does not occur easily and curling of the end portion can be prevented.

After the first drying step, the film is peeled from the support. Subsequently, in the second drying step, the film is dried. In the second drying step, the conditions are changed from the first drying step, and the film is sufficiently dried. Specifically, in the second drying step, the film is dried at a higher drying temperature than the first drying step.

The drying temperature in the second drying step is preferably higher than the set temperature in the first drying step, and is preferably 150 ° C or lower. The drying temperature in the second drying step is more preferably 120 DEG C or lower, and more preferably 100 DEG C or lower. The drying temperature in the second drying step is more preferably 60 DEG C or higher, and more preferably 70 DEG C or higher.

As the drying method which can be employed in the second drying step, there are various methods such as a method of spraying hot air, a method of bringing into contact with a heat roll, a method of heating with an IR heater, all of which can be suitably used. The drying temperature referred to in the first drying step and the second drying step means a drying method in which a drying path is formed and drying is performed in a drying furnace such as a method of spraying hot air or a method of heating with an IR heater, Means the atmospheric temperature in the facility. In the case of contact type drying equipment such as a heat roll, it means the surface temperature of the heat roll.

As described above, a resin film can be produced by melt casting. The resin film produced by such a solvent casting method is good in that the resin film is not peeled off from the end portion and the film is prevented from being cut off when the resin film is stretched in the dyeing step or the crosslinking step after bonding the resin film to the base material .

The resin film (11) is preferably a single layer.

The thickness of the resin film 11 is preferably 15 m or more. The thickness of the resin film 11 is preferably 75 占 퐉 or less, more preferably 60 占 퐉 or less. The width of the resin film 11 is industrially practically 1500 mm or more and 6000 mm or less.

(Drawing method)

In the stretching process, the resin film 11 as described above is stretched to obtain the stretched film 12. As the stretching method, a free-end drawing method or a fixed-end drawing method may be used.

The term "free-end stretching" as used herein refers to stretching without restraining shrinkage of the film in a direction perpendicular to the stretching direction when the film is stretched in one direction. Examples of the free-end stretching method include a method of stretching an unstretched resin film by a difference in rotational speed of two or more rolls, and a method called a long span stretching method. The long span stretching method is a method of stretching an unstretched resin film in an oven by using a longitudinal stretching machine having two pairs of nip rolls and an oven disposed therebetween while applying a difference in rotational speed between two pairs of nip rolls to be.

The term &quot; fixed end stretching &quot; refers to stretching while suppressing shrinkage of the film in a direction perpendicular to the stretching direction when the film is stretched in one direction. Examples of the method for the fixed-end stretching include a method in which the distance between the rolls is shortened in the roll stretching performed using a conveying roll while heating with a heating furnace, and a method in which stretching is performed in the carrying direction, .

The drawing step may be performed in one step or in multiple steps. The stretching step may be uniaxial stretching or biaxial stretching. Or it may be oblique stretching.

In the present embodiment, it is preferable that the stretched resin film 11 is stretched by fixed end stretching to form the stretched film 12. In general, in the fixed-end stretching, it is easy to make the stretched film 12 thinner than the free-end stretching, so that the stretched film 12 can be suitably thin.

The draw ratio of the stretched film 12 obtained by the stretching process may be 1.5 times or more, for example, and preferably 4 times or more. Although the upper limit of the draw ratio is not particularly limited, it is usually 8 times or less, preferably 6 times or less.

The thickness of the stretched film 12 obtained by stretching is preferably 20 탆 or less, more preferably 10 탆 or less, and further preferably 7 탆 or less.

<Bonding Step>

3 is a schematic diagram showing an example of a bonding step. In the bonding step, a strip-like base film is bonded to at least one surface of the stretched film 12, and the laminated film 30 in which the stretched film 12 and the base film 21 are aligned in the longitudinal direction is laminated .

3, the stretched film 12 wound from the unwinding roll 111 is superimposed on the base film 21 wound from the unwinding roll 112 and the pair of rolls 113 and 114. (Not shown) or an adhesive is disposed on one or both of the opposite surfaces of the stretched film 12 and the base film 21. The stretched film 12 and the base film 21 are laminated via a pressure-sensitive adhesive or an adhesive, not shown, and are bonded by passing between a pair of rolls 113 and 114. Thus, the laminated film 30 is obtained.

(Substrate film)

As the resin used for the base film 21, for example, a thermoplastic resin excellent in transparency, mechanical strength, thermal stability, stretchability and the like is used. The base film 21 is stretched together with the stretched film 12 in a polarizer forming step to be described later. Therefore, it is preferable to use the base film 21 which can be stretched in the same temperature range suitable for stretching the stretched film 12. At this time, an appropriate film may be selected based on the glass transition temperature (Tg) or melting point (Tm) of the thermoplastic resin forming the base film (21).

In the present embodiment, the base film 21 has a draw magnification factor in the longitudinal direction (MD direction indicated by symbol D4 in the figure) less than the draw ratio in the longitudinal direction of the drawn film 12 in the drawing step . The base film 21 is preferably not drawn in the longitudinal direction. The degree of orientation in the longitudinal direction of the base film is preferably 0.5 or less. Further, the base film 21 may be stretched in the short direction or may not be stretched in the short direction.

Here, the "stretching magnification" is a ratio of the length after stretching to the length before stretching in the stretching direction, and is a value obtained by dividing the length after stretching by the length before stretching.

The stretching magnification in the short direction (TD direction indicated by symbol D5 in the figure) of the base film 21 may be higher than the stretching magnification in the short direction of the stretching film 12 .

Specific examples of the thermoplastic resin as the material for forming the base film 21 include a polyolefin resin, a polyester resin, a cyclic polyolefin resin (norbornene resin), a (meth) acrylic resin, a cellulose ester resin, a poly Based resin, a polyvinyl alcohol-based resin, a polyvinyl alcohol-based resin, a polyarylate-based resin, a polystyrene-based resin, a polyether sulfone-based resin, a polysulfone-based resin, a polyamide- And copolymers thereof.

The base film 21 may be a film formed using only one kind of the above-mentioned resin, or a film formed using a mixture of two or more kinds of resins. The base film 21 may be a single layer film or a multilayer film.

Examples of the polyolefin-based resin include polyethylene and polypropylene. Polyethylene, polypropylene and the like are preferable because they can be stably drawn at a high magnification. An ethylene-polypropylene copolymer obtained by copolymerizing propylene with ethylene may also be used. The copolymerization can be made with other types of monomers, and examples of other types of monomers copolymerizable with propylene include ethylene and? -Olefin.

The stereoregularity of the propylene resin constituting the propylene-based resin film is preferably substantially isotactic or syndiotactic. A propylene resin film made of a propylene resin having substantially stereospecificity of isotacticity or syndiotacticity is relatively easy to handle and has excellent mechanical strength under a high temperature environment.

In addition to the above-mentioned thermoplastic resin, any suitable additives may be added to the base film 21. Examples of such an additive include 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, and a colorant.

The content of the above-mentioned thermoplastic resin in the base film 21 is preferably 50% by mass to 100% by mass, more preferably 50% by mass to 99% by mass, further preferably 60% by mass to 98% , And particularly preferably 70% by mass to 97% by mass. When the content of the thermoplastic resin in the base film 21 is less than 50% by mass, there is a possibility that the high transparency and the like inherently possessed by the thermoplastic resin may not be sufficiently expressed.

The thickness of the base film 21 before stretching can be suitably determined. In general, from the viewpoint of workability such as strength and handling property, the thickness is preferably 1 to 500 占 퐉, more preferably 1 to 300 占 퐉, more preferably 5 Mu] m to 200 [mu] m, and more preferably 5 [mu] m to 150 [mu] m.

The base film 21 may be subjected to a corona treatment, a plasma treatment, a flame treatment, or the like on at least the surface to which the stretched film 12 is bonded, in order to improve the adhesion with the stretched film 12. In order to improve the adhesion, a material exhibiting a strong adhesion to the base film 21 and the stretched film 12 to some extent on the surface facing the stretched film 12 in the base film 21 May be used to form the primer layer.

The material for forming the primer layer is not particularly limited as long as it can exert a strong adhesion to the base film 21 and the stretched film 12 to some extent. For example, a thermoplastic resin excellent in transparency, thermal stability, stretchability and the like is used. Specific examples include acrylic resins and polyvinyl alcohol resins, but are not limited thereto.

(Adhesive, adhesive)

In the bonding step, the stretched film 12 and the base film 21 are bonded to each other through an adhesive or an adhesive (pressure-sensitive adhesive).

In the present specification, &quot; adhesive &quot; means that when applied to a substrate, the substrate is wetted with a liquid and solidified to exhibit adhesiveness (i.e., the adhesive property is not exhibited until solidification).

In the present specification, the &quot; pressure-sensitive adhesive &quot; is a flexible rubber-like material, and the pressure-sensitive adhesive is instantly made to exhibit adhesiveness by attaching itself. When a pressure-sensitive adhesive is used, a solidification step is not required.

It is preferable to use an adhesive in view of the fact that, even when the stretching temperature is high, peeling does not easily occur at the time of stretching in the next step.

The pressure-sensitive adhesive is composed of, for example, an acrylic resin, a styrene-based resin, a silicone-based resin or the like as a base polymer and adding thereto a crosslinking agent such as an isocyanate compound, an epoxy compound or an aziridine compound.

A method of forming a layer of a pressure-sensitive adhesive on the base film (21) or the stretched film (12) is not particularly limited. For example, the base film 21 or the stretched film 12 can be formed by applying a solution containing each component including the base polymer described above and drying. Alternatively, a pressure-sensitive adhesive layer previously formed on the separator may be bonded to the base film 21 or the stretched film 12, and the separator may be removed and transferred.

The adhesive may be an aqueous adhesive using, for example, a polyvinyl alcohol resin aqueous solution, an aqueous urethane adhesive, a water-based polyester adhesive, a water-based vinyl acetate emulsion adhesive, or an aqueous acrylic adhesive. Among them, a polyvinyl alcohol resin aqueous solution is suitably used. As the water-based adhesive, polyaldehyde, a water-soluble epoxy compound, a melamine compound, a zirconia compound, a zinc compound or the like may be added as an additive.

The method of bonding the film using the water based adhesive is not particularly limited and the adhesive may be uniformly applied or introduced onto the surface of the base film 21 or the stretched film 12 and the other film may be superimposed on the coated surface, Followed by drying, and the like.

For example, the adhesive is applied at a temperature of 15 ° C to 40 ° C after its preparation, and the bonding temperature is in the range of 15 ° C to 30 ° C, for example.

When an aqueous adhesive is used, the film is bonded and then dried to remove water contained in the aqueous adhesive. The temperature of the drying furnace is preferably 30 占 폚 to 90 占 폚. If it is less than 30 ° C, the adhesive surface tends to be easily peeled off. If the temperature exceeds 90 ° C, the stretched film 12 may be deformed by heat and the optical performance of the polarizer may deteriorate. The drying time can be from 10 seconds to 1000 seconds.

As the non-aqueous adhesive, a photo-curable adhesive may be used. Examples of the photo-curable adhesive include a mixture of an epoxy resin and a photo cationic polymerization initiator. Also, a mixture of a component containing a (meth) acryloyl group and a photo radical polymerization initiator may be mentioned.

As a method of bonding the films to each other with the photo-curable adhesive, conventionally known methods can be used. For example, an adhesive is applied to the bonding surface of the film by a flexible method, a Meyer bar coating method, a gravure coating method, a comma coater method, a doctor blade method, a die coating method, a spraying method, . The flexible method is a method in which the two films as the object to be coated are moved in a substantially vertical direction, a substantially horizontal direction, or an inclined direction therebetween, and an adhesive is flowed down on the surface to spread the adhesive.

An adhesive is applied to the surface of the film, and then the film is bonded by nip roll or the like, and the film is bonded, dried, or irradiated with light. Further, a method of pressing the laminate with a roll or the like and uniformly widening it may also be suitably used.

The adhesive surface of the film may be appropriately subjected to surface treatment such as plasma treatment, corona treatment, ultraviolet ray irradiation treatment, flame treatment, saponification treatment and the like in order to improve the adhesiveness.

As the saponification treatment, there may be mentioned a method of immersing in an aqueous solution of an alkali such as sodium hydroxide or potassium hydroxide.

When a photo-curable resin is used as the adhesive, the photo-curable adhesive is cured by laminating the film and irradiating with an active energy ray. A light source of an active energy ray is not particularly limited, but an active energy ray having a light emission distribution at a wavelength of 400 nm or less is preferable. Specifically, a low energy mercury lamp, a medium pressure mercury lamp, a high pressure mercury lamp, Mercury lamp, metal halide lamp and the like are preferably used.

In the case of curing the photo-curing adhesive on the base film 21 or the stretched film 12 by irradiation of an active energy ray, the activity of the polarizing plate after various steps such as transmittance, hue and transparency of the film, It is preferable to perform the curing under the energy ray irradiation condition.

&Lt; Polarizer forming step &

4 and 5 are schematic diagrams showing an example of a polarizer forming step. In the polarizer forming step, the stretched film 12 is dyed (hereinafter referred to as a dyeing process) with the dichroic dye and the entire length of the laminated film 30 is stretched (hereinafter, stretched) ) As a polarizer. Fig. 4 is a schematic diagram showing an example of the dyeing treatment in the polarizer forming step, and Fig. 5 is a schematic diagram showing an example of the stretching treatment in the polarizer forming step.

(Dyeing treatment)

As shown in Fig. 4, the laminated film 30 is conveyed in the longitudinal direction by conveying rolls 141 to 144. Fig. The laminated film 30 is transported while dyed in the dyeing solution 151 in which the dichroic dye is dissolved in the dyeing bath 150 formed in the transport path, and is dyed. Thus, the stretched film 12 of the laminated film 30 is dyed, and the laminated film 31 having the stretched film 13 dyed is obtained.

In the present embodiment, the stretched film 12 constituting the laminated film 30 is dyed with a dichroic dye. Examples of the dichroic dye include iodine and organic dyes.

The dyeing treatment is performed, for example, by immersing the entire laminated film 30 in a solution (dyeing solution) in which a dichroic dye is dissolved in a solvent. As the solvent of the dyeing solution, generally water is used, but an organic solvent compatible with water may be further added.

The concentration of the dichroic dye is preferably 0.01% by mass to 10% by mass, more preferably 0.02% by mass to 7% by mass, and particularly preferably 0.025% by mass to 5% by mass.

When iodine is used as the dichroic dye, it is preferable to add iodide in order to further improve the dyeing efficiency. Examples of the iodide include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide and titanium iodide. The addition rate of these iodides is preferably 0.01% by mass to 20% by mass in the dyeing solution.

Among iodides, it is preferable to add potassium iodide. 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, more preferably in the range of 1: 7 to 1: 70.

The immersion time of the stretched film 12 with respect to the dyeing solution is not particularly limited, but is preferably in the range of 15 seconds to 15 minutes, more preferably 1 to 3 minutes. The temperature of the dyeing solution is preferably in the range of 10 캜 to 60 캜, and more preferably in the range of 20 캜 to 40 캜.

(Crosslinking treatment)

After the dyeing treatment, the crosslinking treatment can be carried out. The crosslinking treatment is carried out, for example, by immersing the laminated film 31 having the dyed stretched film 13 in a solution (crosslinking solution) containing a crosslinking agent. As the crosslinking agent, conventionally known materials can be used. Examples thereof include boron compounds such as boric acid and borax, and glyoxal and glutaraldehyde. The crosslinking agent may be used alone or in combination of two or more.

As the crosslinking solution, a solution in which a crosslinking agent is dissolved in a solvent can be used. As the solvent, for example, water may be used, but an organic solvent compatible with water may also be contained. The concentration of the crosslinking agent in the crosslinking solution is not limited thereto, but is preferably in the range of 1% by mass to 20% by mass, more preferably 6% by mass to 15% by mass.

Iodide may be added to the crosslinking solution. By adding iodide, the polarization characteristics in the plane of the resin layer can be more uniform. Examples of the iodide include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide and titanium iodide. The content of iodide is 0.05% by mass to 15% by mass, and more preferably 0.5% by mass to 8% by mass.

The immersion time of the laminated film 30 in the crosslinking solution is preferably 15 seconds to 20 minutes, more preferably 30 seconds to 15 minutes. The temperature of the cross-linking solution is preferably in the range of 10 占 폚 to 80 占 폚.

(Drawing process)

Subsequently, as shown in Fig. 5, the laminated film 31 is transported in the longitudinal direction by the transport rolls 161 to 164. The laminated film 31 is transported while immersed in, for example, an aqueous boric acid solution 171 in a drawing bath 170 formed in the transport path. In the drawing bath 170, the entire laminated film 31 is stretched between the conveying roll 162 and the conveying roll 163. As a result, the stretched film 13 is stretched to become the long polarizer 14. Thus, the laminated film 31 having the polarizer 14 and the base film 22 stretched is obtained.

In the stretching treatment, the laminated film 30 is uniaxially stretched. As the stretching method, either fixed-end stretching or free-end stretching can be employed. The stretching process may be performed in one step or in multiple steps.

In the stretching treatment, the laminated film may be stretched in water. Examples of the water used in the underwater stretching include pure water, ion-exchanged water, distilled water, tap water and the like. In the case of performing the stretching treatment after the above-mentioned dyeing treatment, the elution of the dichroic dye adsorbed to the stretched film by the dyeing treatment can be suppressed by using an aqueous solution in which the dichroic dye is dissolved in water used for underwater stretching have. The crosslinking treatment may be carried out simultaneously with the stretching treatment by making an aqueous solution containing a borated compound dissolved in water used for underwater stretching.

The stretching treatment is performed, for example, by immersing the laminated film in an aqueous solution containing boric acid at 50 占 폚 or higher and stretching in the aqueous solution.

By the polarizer forming step described above, the dichroic dye is adsorbed to the stretched film of the laminated film and the dichroic dye is oriented in the stretching direction of the film in the stretching process (MD direction indicated by the symbol D6 in the figure) . Thus, the stretched film of the laminated film becomes the polarizer 14 having the absorption axis in the stretching direction of the film in the stretching treatment.

In this embodiment, the stretching process is performed after the dyeing process. However, the stretching process may be performed before the dyeing process, and the stretched laminated film may be subjected to the dyeing process. Further, the stretching treatment may be performed during the dyeing treatment.

The stretching magnification in the stretching treatment may be, for example, more than 1 time, preferably 1.1 times or more. Although the upper limit of the draw ratio is not particularly limited, it is usually 8 times or less, preferably 6 times or less, and more preferably 3 times or less.

The total stretching magnification of the polarizer after the stretching process and the polarizer forming process is preferably set to be more than 5 times. According to the production method of the present invention, the draw ratio can be set to 6 times or more, or 7 times or more. Normally, the total draw ratio of the polarizer is 10 times or less.

(Other processing)

When a plasticizer is used at the time of forming the resin film 11 as a raw material for the stretched film 12, the plasticizer is removed prior to the dyeing treatment and the stretching treatment.

The removal of the plasticizer is performed, for example, by immersing the laminated film 30 in water at about room temperature to about 50 캜, and swelling the water on the stretched film 12 to elute the plasticizer from the stretched film 12.

After the cross-linking treatment or in-water stretching treatment in an aqueous solution containing boric acid, the laminated film is immersed in water such as pure water, ion-exchanged water, distilled water, tap water, etc. to wash the laminated film. Thereafter, the laminated film is dried. As the drying treatment, known methods such as natural drying, heat drying, air drying, and vacuum drying may be employed.

&Lt; Protection film bonding step &

In the protective film bonding step, a protective film is bonded to the surface of the polarizer obtained in the polarizer forming step. The method of joining the polarizer and the protective film is not particularly limited. For example, a pressure-sensitive adhesive layer or an adhesive layer may be formed on the bonding surface of one or both of the polarizer and the protective film, and the two may be bonded through the pressure-sensitive adhesive layer or the adhesive layer. As the adhesive and the pressure-sensitive adhesive, those same as those used for bonding the base film and the resin film can be applied.

(Protective film)

The protective film may be a simple protective film having no optical function or a protective film having optical functions such as a retardation film and a brightness enhancement film.

Examples of the material of the protective film include, but are not limited to, a cyclic polyolefin resin film, acetic acid cellulose resin film made of a resin such as triacetylcellulose and diacetylcellulose, polyethylene terephthalate, polyethylene naphthalate, A polyester resin film, a polycarbonate resin film, an acrylic resin film, a polypropylene resin film, and the like, which have been conventionally widely used in the art, such as polyethylene terephthalate, polyethylene terephthalate,

The cyclic polyolefin-based resin film may be uniaxially or biaxially-stretched. By stretching, an arbitrary retardation value can be imparted to the cyclic polyolefin-based resin film.

The surface of the annular polyolefin-based resin film generally has poor surface activity. Therefore, the surface to be adhered to the polarizer is preferably subjected to surface treatment such as plasma treatment, corona treatment, ultraviolet ray irradiation treatment, flame (flame) treatment and saponification treatment Do. Of these, plasma treatment and corona treatment, which can be performed relatively easily, are suitable.

A liquid crystal layer or the like may be formed on the surface of the cellulose acetate-based resin film in order to improve the viewing angle characteristics. Further, in order to impart a phase difference, a cellulose acetate-based resin film may be stretched. The cellulose acetate-based resin film is usually subjected to saponification treatment in order to improve the adhesion with the polarizing film. As the saponification treatment, a method of immersing in an aqueous solution of an alkali such as sodium hydroxide or potassium hydroxide can be adopted.

On the surface of the protective film as described above, an optical layer such as a hard coat layer, an antiglare layer, and an antireflection layer may be formed. Methods for forming these optical layers on the surface of the protective film are not particularly limited, and known methods can be used.

The thickness of the protective film is preferably as small as possible, preferably 90 占 퐉 or less, more preferably 50 占 퐉 or less, because of the requirement for thinning. On the contrary, when the thickness is excessively thin, the strength is lowered and the workability is lowered, and therefore, it is preferably 5 m or more.

In the polarizing film producing method of the present embodiment, the protective film is bonded to one surface of the polarizer, and then the base film is peeled from the other surface of the polarizer. The method of peeling off the base film is not particularly limited, and a commonly known method can be employed. The base film may be peeled off immediately after bonding the protective film to the polarizer, or may be peeled off after the whole of the base film is rolled up once and then the peeling step may be separately provided.

&Lt; Pressure-sensitive adhesive forming process &

The layered product thus obtained may be provided with a layer of a pressure-sensitive adhesive for bonding to the glass cell.

Examples of the pressure-sensitive adhesive include a base polymer such as an acrylic resin, a styrene resin and a silicone resin, a crosslinking agent such as an isocyanate compound, an epoxy compound and an aziridine compound and an additive such as a silane coupling agent in consideration of adhesiveness to the glass Composition. The pressure-sensitive adhesive layer may further contain an ionic compound as an antistatic agent for imparting antistatic properties. The ionic compound is a compound having an inorganic or organic cation and an inorganic or organic anion.

The method of forming the pressure-sensitive adhesive layer on the laminate is not particularly limited. For example, the base film 21 or the stretched film 12 can be formed by applying a solution containing each component including the base polymer described above and drying. Alternatively, a pressure sensitive adhesive previously formed on the separator may be bonded to the base film 21 or the stretched film 12. By using the separator, the surface of the pressure-sensitive adhesive can be protected until the polarizing plate is bonded to the liquid crystal cell.

&Lt; Polarizing Film Forming Step &

The polarizing film shown in Fig. 1 is formed by suitably cutting a laminate of the strip-shaped polarizer and the strip-shaped protective film thus obtained in a plurality of sheets as appropriate. In cutting, the strip-shaped polarizer may be cut into sheet pieces according to the size of the liquid crystal panel, and then the cut polarizer may be bonded to the liquid crystal panel.

In the polarizing film producing method of the present embodiment, the polarizing film can be produced by the process as described above.

In the polarizing film producing method of this embodiment as described above, the following effects can be obtained.

First, in the production method of the polarizing film of the present embodiment, the resin film is stretched to form a stretched film prior to the joining step, and the stretching ratio in the machine direction of the stretched film in the stretching process Direction stretch ratio of the base film. In the following description, the laminated film having such a constitution used in the production method of the present embodiment is referred to as &quot; laminated film A &quot;.

On the contrary, after the resin film which is made of the stretched film material of the laminated film A and which is not stretched and the same base film as the base film of the laminated film A are laminated and laminated, the laminated film thus obtained is laminated to the laminated film A The stretched film is stretched to a stretching ratio equal to the stretching ratio of the stretched film of the obtained laminated film. In the following description, the laminated film having such a constitution is referred to as &quot; laminated film B &quot;.

That is, in the laminated film A, a laminated film is formed by laminating a drawn film and a base film having a draw ratio smaller than that of the drawn film, whereas the laminated film B is a laminated film obtained by laminating a drawn film and a base film And laminated to form a laminated film.

Generally, the stress (shear yield stress) required for stretching the film tends to increase as the strain increases, that is, as the stretching magnification increases. Therefore, when two kinds of laminated films as described above are assumed, the base film in the laminated film A can be stretched at a stress smaller than that of the base film in the laminated film B.

On the other hand, the stretched film in the laminated film A and the stretched film in the laminated film B have the same stretching magnification. Therefore, it is conceivable that the respective stretched films have the same stress required for stretching.

Thereby, the laminated film A can be stretched with less stress than the laminated film B. Alternatively, when the laminated film is stretched at the same stress, the laminated film A can be stretched at a higher magnification than the laminated film B.

In the laminated film B, when the resin film is stretched, the base film is joined to form a laminated film. Therefore, in stretching the laminated film B, thermal roll stretching can not be employed, and there is a limitation in the stretching method of the resin film. On the other hand, in the laminated film A, the resin film is stretched to form a stretched film prior to the bonding step. Therefore, it is easy to form a thin stretched film by stretching the resin film in a favorable manner in the thinning of the polarizer. As a &quot; favorable method for thinning the polarizer, &quot; for example, thermal roll stretching can be mentioned.

Further, in the polarizing film producing method of the present embodiment, since the stretched film is laminated with the base film at the time of the stretching treatment in the polarizer forming step, the stretched film does not fracture well Do not. Therefore, the yield can be improved and the amount of waste can be reduced.

Thus, according to the polarizing film producing method of the present embodiment, it is possible to provide a polarizing film producing method which can appropriately inhibit the polarizer from being broken at the time of production and is easy to stretch at a high magnification.

In the present embodiment, the base film 21 is bonded to one side of the stretched film 12 in the bonding step, but in the bonding step, the base film 21 is bonded to both sides of the stretched film 12 Maybe. In this case, one base film is peeled off before the polarizer forming process.

For example, in the bonding step, two types of base films having different thicknesses are used. First, a relatively thick base film is bonded to one surface of the stretched film 12, and then, A thin base film may be bonded, and then the initially thick base film may be peeled off. In this method, for example, even if both the base film and the stretched film are thin and handling at the time of bonding is difficult, firstly, a relatively thick base film and a stretched film are laminated to form a laminate, , Workability can be improved.

While the preferred embodiments of the present invention have been described with reference to the accompanying drawings, it is needless to say that the present invention is not limited to these examples. Various shapes, combinations, and the like of the respective structural members shown in the above-described examples are merely examples, and various modifications can be made based on design requirements and the like without departing from the gist of the present invention.

[Example]

Hereinafter, the present invention will be described by way of examples, but the present invention is not limited to these examples.

In the present embodiment, a test piece of a model sample was produced by a method described later, and the stress required for stretching was measured and evaluated. In the production of the model sample, the resin film and the base film were bonded using an adhesive prepared by the following method.

(Adhesive adjustment)

Polyvinyl alcohol powder (Z-200, manufactured by Nippon Synthetic Chemical Industry Co., Ltd., average degree of polymerization: 1100, average saponification degree: 99.5 mol%) was dissolved in hot water at 95 캜 to prepare a 3% by mass polyvinyl alcohol aqueous solution.

A water-based adhesive was prepared by mixing a crosslinking agent (Sumirei Resin (registered trademark) 650 manufactured by Taoka Chemical Co., Ltd.) in an amount of 1 part by mass based on 2 parts by mass of the polyvinyl alcohol powder.

At the time of evaluation, the property values were measured by the following methods.

(In-plane retardation value measurement)

The in-plane retardation value (unit: nm) of the test piece was measured using KOBRA (registered trademark) -WPR manufactured by Oji Measurement Instruments Co., The in-plane retardation value was a value at a wavelength of 590 nm.

(Thickness measurement)

The thickness (unit: 占 퐉) of the test piece was measured by a contact type thickness meter (DIGITAL READ OUT TC-101, manufactured by Nikon Corporation).

(Degree of orientation)

The degree of orientation of the test piece was calculated as in-plane retardation ÷ thickness ÷ 10.

[Example 1]

The PVA original film (trade name: VF-PE6000, manufactured by Kuraray Co., Ltd., thickness 60 탆, average degree of polymerization 2400, degree of saponification 99.9 mol% or more, plasticizer content, degree of orientation 0.01) was continuously fed out from the rolls, And stretched in the width direction. The stretching conditions were a stretching temperature of 160 DEG C and a transverse stretching ratio of 4.5 times as a transverse stretching ratio to obtain a roll of a stretched monoaxially stretched stretched PVA film. The degree of orientation of the stretched PVA film was 2.76.

Subsequently, the aforementioned water-based adhesive was gravure-coated on the corona-treated surface of the substrate film while unwinding the base film (polypropylene film, 90 탆, degree of orientation: 0.13) subjected to the one side corona treatment from the roll. The coating was performed so that the film thickness immediately after coating was 4 占 퐉. The base film and the stretched PVA film were joined together by a nip roll and dried at 60 캜 for 4 minutes to obtain a single-side laminated film in which an unstretched base film was laminated on one surface of the stretched PVA film.

From the obtained single-sided laminated film, a rectangular test piece having an axis of absorption axis of 150 mm and a transmission axis direction of 30 mm was produced.

Fig. 6 is a schematic diagram showing a state in which the obtained test piece is stretched.

First, a jig 1100 for drawing was attached to both ends of the test piece 1000 in the long-side direction (MD direction) so that the distance between the chucks was 55 mm, and a dyeing bath at 30 DEG C containing 0.11 mass% Lt; / RTI &gt;

Subsequently, the test piece 1000 drawn out from the dyeing bath was placed in a crosslinking bath 1400 in which a bridging solution 1300 having a potassium iodide: boric acid: water ratio of 5: 8: 100 (mass ratio) was stored, Was attached to the load cell 1500 formed in the crosslinking bath 1400 through the capillary 1100.

The crosslinking solution was maintained at 70 캜.

Subsequently, while the test piece 1000 was immersed in the cross-linking solution 1300 for 90 seconds, the test piece 1000 was stretched to 1.18 times by pulling the jig on the other end side to obtain a total draw ratio of PVA of 5.31 times (4.5 占 1.18 = 5.31 times).

The tensile force required for stretching in the crosslinking bath was 6830 g, and the stress per unit cross-section was 2183 g / mm ² . The &quot; tensile force required for stretching &quot; employed the stress measured at 1.18 times stretching using the load cell 1500 in the stretching process.

[Example 2]

The PVA original film (trade name: VF-PE2000, manufactured by Kuraray Co., Ltd., thickness 20 μm, average degree of polymerization 2400, degree of saponification 99.9 mol% or more, plasticizer content, orientation degree 0.04) was continuously fed out from the rolls, And stretched in the width direction. The stretching conditions were a stretching temperature of 160 DEG C and a transverse stretching ratio of 4.5 times as a transverse stretching ratio to obtain a roll of a stretched monoaxially stretched stretched PVA film. At this time, the degree of orientation of the stretched PVA film was 2.90.

The test piece of Example 2 was dyed and stretched in the same manner as in Example 1 except that the stretched PVA film thus obtained and the crosslinked solution were kept at 73 캜, and the stress at the time of stretching was measured. The tensile force required for stretching in the crosslinking bath was 3058 g, and the stress per unit cross-sectional area was 1062 g / mm ² .

[Comparative Example 1]

The base film used in Example 1 was sequentially bonded to both surfaces of the PVA original film used in Example 1 in the same manner as in Example 1 and dried at 60 캜 for 4 minutes to form a base film on both surfaces of the PVA original film Whereby a double-side laminated film in which a film was laminated was obtained.

Subsequently, the obtained laminated film was stretched in the width direction by using a tenter stretching device. The stretching conditions were a stretching temperature of 160 占 폚, a stretching ratio of 4.5 times as a transverse axis, and a stretched monoaxially stretched stretched double-side laminated film was obtained.

Subsequently, one base film of the obtained stretched double-side laminated film was peeled off to obtain a single-side laminated film. At this time, the total thickness was 34.8 탆.

The test piece of Comparative Example 1 was dyed and stretched in the same manner as in Example 1 except that the single-side laminated film thus obtained was used, and the stress at the time of stretching was measured. The tensile force required for stretching in the crosslinking bath was 6556 g, and the stress per unit cross-section was 6280 g / mm ² .

[Comparative Example 2]

On both sides of the original PVA film used in Example 2, the base film used in Example 1 was sequentially bonded in the same manner as in Example 1. In the same manner as in Comparative Example 1, on both surfaces of the original film, Whereby a laminated double-side laminated film was obtained.

Subsequently, the obtained laminated film was stretched in the transverse direction using a tenter stretching device in the same manner as in Comparative Example 1 to obtain a stretched, uniaxially stretched stretched double-side laminated film.

Subsequently, one base film of the obtained stretched double-side laminated film was peeled off to obtain a single-side laminated film. At this time, the total thickness was 33.4 탆.

The test piece of Comparative Example 2 was dyed and stretched in the same manner as in Example 2 except that the single-side laminated film thus obtained was used, and the stress at the time of stretching was measured. The tensile force required for stretching in the crosslinking bath was 4413 g, and the stress per unit cross-sectional area was 4404 g / mm ² .

The results of Examples 1 and 2 and Comparative Examples 1 and 2 are shown in Table 1.

PVA thickness
(탆) Base film thickness
(탆) Tension required for stretching
(g) Stress at stretching per unit area
(g / mm ² ) Example 1 14.3 90 6830 2183 Example 2 6.0 90 3058 1062 Comparative Example 1 14.3 20.5 6556 6280 Comparative Example 2 6.0 27.4 4413 4404

As a result of the evaluation, the thickness of the base film before stretching in the polarizer forming step was thicker in Example 1, and the total thickness was the same as in Comparative Example 1, although the thickness of Example 1 was thick. In addition, the stress per unit cross-sectional area of Example 1 was lower than that of Comparative Example 1.

As a result, it was found that Example 1 exhibited less stress required for stretching and was easily stretchable, confirming the usefulness of the present invention.

1, 14: Polarizer
30, 31: laminated film
10: polarizing film
11: Resin film
12, 12A, 12B, 13: stretched film
21, 22: substrate film

Claims (7)

A stretching step of stretching a strip-shaped resin film comprising a polyvinyl alcohol-based resin as a forming material to obtain a stretched film,
A joining step of joining a strip-like base film to at least one surface of the stretched film to obtain a laminated film in which the stretched film and the base film are laminated,
A step of dyeing the stretched film with a dichroic dye and stretching the entire laminated film in the longitudinal direction to form the stretched film as a polarizer;
Wherein the base film in the joining step has a stretching magnification in the longitudinal direction is less than a stretching magnification in the longitudinal direction of the stretched film in the stretching step. The method of producing a polarizing film according to claim 1, wherein in the joining step, the base film is unstretched in the longitudinal direction. The method of producing a polarizing film according to claim 1 or 2, wherein in the polarizer forming step, the laminated film in which the stretched film is dyed is immersed in an aqueous solution containing boric acid and stretched in the aqueous solution. The method of producing a polarizing film according to claim 1 or 2, wherein the stretching step stretches the resin film using a fixed end stretching method. The method of producing a polarizing film according to claim 1 or 2, wherein the resin film has a thickness of 15 mu m or more and 75 mu m or less. The polarizing film producing method according to claim 1 or 2, wherein in the joining step, the stretched film and the base film are joined via an aqueous adhesive. The polarizing film producing method according to claim 1 or 2, wherein after the polarizer forming step, the polarizing film is formed by cutting the polarizer into a plurality of polarizing films.

Images