TW202346988A - Fabrication method of polarizing plates - Google Patents

Abstract

Provided is a fabrication method of polarizing plates, which can have discoloration suppressed during the process of fabrication even if the polarizing element has an increased amount of boron.

Description

Manufacturing method of polarizing plate

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

Liquid crystal display devices (LCDs) are widely used not only in LCD televisions, but also in mobile applications such as personal computers and mobile phones, and in-vehicle applications such as car navigation. Generally, a liquid crystal display device has a liquid crystal panel member with polarizing plates bonded with an adhesive on both sides of a liquid crystal unit, and displays by controlling light from a backlight member using the liquid crystal panel member. In addition, in recent years, organic EL display devices, like liquid crystal display devices, have been widely used in mobile applications such as televisions and mobile phones, and in-vehicle applications such as car navigation. In organic EL display devices, in order to prevent external light from being reflected by the metal electrode (cathode) and being viewed like a mirror, a circular polarizing plate (a laminate including a polarizing element and a λ/4 plate) is disposed on the viewing side surface of the image display panel. body) situation.

As mentioned above, polarizing plates are increasingly likely to be installed in vehicles as components of liquid crystal display devices or organic EL display devices. Polarizing plates used in in-vehicle image display devices require more exposure to high-temperature environments than other mobile applications such as televisions and mobile phones, and require higher durability under high temperatures.

As a method of manufacturing such a polarizing element with high high-temperature durability, for example, Patent Documents 1 to 2 disclose a method of adding components such as metal salts containing zinc, copper, aluminum, etc. to a treatment bath. The polarizing element contains these components to improve the durability of the polarizing element. Furthermore, Patent Documents 3 to 4 disclose methods of manufacturing polarizing elements in which components such as organic titanium compounds are added to a treatment bath.

[Prior technical literature]

[Patent Document]

[Patent Document 1] International Publication No. 2016/117659

[Patent Document 2] Japanese Patent Application Publication No. 2006-047978

[Patent Document 3] Japanese Patent Application Publication No. 2008-46257

[Patent Document 4] Japanese Patent Application Laid-Open No. 6-172554

The inventors found that by increasing the boron content of the polarizing element, the durability of the polarizing plate at high temperatures can be improved. However, it was found that the problem of discoloration during the manufacturing process of the polarizing plate was caused by making the polarizing element contain more boron.

An object of the present invention is to provide a method for manufacturing a polarizing plate that can suppress discoloration during the manufacturing process of the polarizing plate even if the boron content rate of the polarizing element is increased.

The present invention provides the following method for manufacturing a polarizing plate.

[1] A method of manufacturing a polarizing plate having a polarizing element and a transparent protective film laminated on at least one side of the polarizing element. The manufacturing method has the following steps:

Polarizing element manufacturing steps for obtaining polarizing elements from polyvinyl alcohol-based resin films; and

The step of laminating the aforementioned transparent protective film to the aforementioned polarizing element via a water-based adhesive;

Among them, the boron adsorption rate of the aforementioned polyvinyl alcohol-based resin film is 5.70 mass% or more,

The ethanol concentration of the water-based adhesive is 16 mass% or more and 50 mass% or less.

[2] The manufacturing method according to [1], wherein the boron content rate of the polarizing element is 4.0 mass% or more and 8.0 mass% or less.

[3] The production method according to [1] or [2], wherein the water-based adhesive contains a polyvinyl alcohol-based resin.

[4] The production method according to [3], wherein the concentration of the polyvinyl alcohol-based resin in the water-based adhesive is 2.85% by mass or more.

[5] The manufacturing method according to any one of [1] to [4], wherein in the polarizing plate, a layer formed of the aqueous adhesive between the polarizing element and the transparent protective film is The thickness of the adhesive layer is 0.01 μm or more and 7 μm or less.

According to the present invention, it is possible to provide a method for manufacturing a polarizing plate that can suppress discoloration during the manufacturing process of the polarizing plate even if the boron content rate of the polarizing element is increased.

10: Embryonic membrane composed of polyvinyl alcohol resin

11: embryonic membrane roll

13: Swelling bath

15:Dyeing bath

17a: 1st cross-linking bath

17b: 2nd cross-linking bath

19:Cleaning bath

21: Drying oven

23:Polarizing element

30 to 48, 60, 61: guide roller

50 to 52, 53a, 53b, 54, 55: pinch roller

FIG. 1 is a cross-sectional view schematically showing an example of a method for manufacturing a polarizing element of the present invention.

[Manufacturing method of polarizing plate]

The present invention is a method for manufacturing a polarizing plate. The polarizing plate has a polarizing element and a transparent protective film laminated on at least one side of the polarizing element. The manufacturing method of the polarizing plate includes: a polarizing element manufacturing step, which is derived from a polyvinyl alcohol system. A resin film (hereinafter, also referred to as "PVA-based resin film") is used to obtain a polarizing element; and a bonding step includes bonding the transparent protective film to the polarizing element via a water-based adhesive. The boron adsorption rate of the PVA-based resin film is 5.70% by mass or more. The ethanol concentration of the water-based adhesive is 16 mass% or more and 50 mass% or less. Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments.

<Processes for manufacturing polarizing elements>

In this embodiment, the polarizing element has a dichroic dye (iodine or dichroic dye) adsorbed onto a uniaxially stretched polyvinyl alcohol-based resin film.

In this embodiment, a polyvinyl alcohol-based resin film with a boron adsorption rate of 5.70% by mass or more is used to produce a polarizing element. By using this kind of PVA-based resin film, even if the polarizing plate is exposed to a high temperature environment, such as an environment with a temperature of 105°C, the transmittance is not easily reduced. Furthermore, the boron adsorption rate of the PVA-based resin film is preferably 10% by mass or less.

By using a PVA-based resin film with a boron adsorption rate as mentioned above, the concentration of boric acid in the cross-linking treatment bath in the polarizing element manufacturing step will not become high, and the processing time of the cross-linking treatment can also be shortened, making it easy to obtain the required The required polarizing element can also improve the productivity of polarizing elements. If the boron adsorption rate of the PVA-based resin is 10% by mass or less, an appropriate amount of boron will be incorporated into the PVA-based resin film, and the shrinkage force of the polarizing element will be easily reduced. As a result, when incorporated into an image display device, problems such as peeling off between other components such as the front panel and the polarizing plate are less likely to occur. In addition, when the boron adsorption rate of the PVA-based resin film is less than 5.70% by mass, the transmittance is likely to decrease when exposed to a high temperature environment, and as mentioned above, productivity may decrease. The boron adsorption rate of the PVA-based resin film can be measured by the method described in the following examples.

The boron adsorption rate of the PVA resin film reflects the characteristics of the spacing between the molecular chains or the crystal structure of the PVA resin film. It is believed that a PVA-based resin film with a boron adsorption rate of 5.70 mass% or more has wider molecular chains and less crystallization of the PVA-based resin than a PVA-based resin film with a boron adsorption rate of less than 5.70 mass%. Therefore, it is estimated that boron is easily mixed into the PVA-based resin film and polyene formation is easily prevented in a high-temperature environment.

The boron adsorption rate of the PVA-based resin film can be adjusted, for example, by subjecting the PVA-based resin film in the raw material stage to pretreatment such as hot water treatment, acidic solution treatment, ultrasonic irradiation treatment, or radiation irradiation treatment. Through these treatments, the distance between molecular chains in the PVA-based resin film can be expanded or the crystal structure can be destroyed. Examples of hot water treatment include immersing in pure water at 30° C. to 100° C. for 1 second to 90 seconds and drying. Examples of the acidic solution treatment include treatment in which the material is immersed in a boric acid aqueous solution having a concentration of 10 to 20% by mass for 1 to 90 seconds and dried. Examples of the ultrasonic treatment include treatment in which ultrasonic waves with a frequency of 20 to 29 kc are irradiated with an output of 200W to 500W for 30 seconds to 10 minutes. Ultrasonic treatment can be performed in solvents such as water.

The polyvinyl alcohol-based resin (hereinafter also referred to as "PVA-based resin") constituting the PVA-based resin film is usually obtained by saponifying polyvinyl acetate-based resin. The degree of saponification is preferably 85 mol% or more, more preferably 90 mol% or more, and still more preferably 99 mol% or more. The polyvinyl acetate resin may be, for example, in addition to polyvinyl acetate, which is a homopolymer of vinyl acetate, or a copolymer of vinyl acetate and other monomers copolymerizable therewith. Examples of other copolymerizable monomers include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and the like. The degree of polymerization of polyvinyl alcohol-based resin is usually 1,000 to 10,000, preferably 1,500 to 5,000.

These PVA-based resins can be modified, and polyethylene formaldehyde, polyvinyl acetal, polyvinyl butyraldehyde, etc. modified by aldehydes can also be used.

In the present invention, as the starting material for manufacturing the polarizing element, unstretched polyvinyl alcohol with a thickness of 65 μm or less (for example, 60 μm or less), preferably 50 μm or less, more preferably 35 μm or less, and more preferably 30 μm or less is used. Department of resin membrane (embryonic membrane). In this way, thin-film polarizing elements that are increasingly required by the market can be obtained. The width of the embryonic membrane is not particularly limited, and may be about 400 mm to 6000 mm, for example. The embryonic membrane is prepared as a film roll (embryonic membrane roll) of a long unstretched polyvinyl alcohol-based resin film, for example. The embryonic membrane may be a commercially available product, or may be obtained by film formation. The film formation method is not particularly limited, and known methods such as melt extrusion and solvent casting may be used.

In addition, the PVA-based resin film used in the present invention may be laminated on a base film that supports it. That is, the PVA-based resin film may also be prepared as a laminate of a base film and a PVA-based resin film laminated thereon. membrane. In this case, the PVA-based resin film can be produced by, for example, applying a coating liquid containing a PVA-based resin to at least one side of the base film and then drying it.

As the base film, for example, a film containing a thermoplastic resin can be used. As a specific example, it is a film composed of a translucent thermoplastic resin, preferably an optically transparent thermoplastic resin, such as a chain polyolefin-based resin (polypropylene-based resin, etc.), a cyclic polyolefin-based resin, etc. Polyolefin-based resins (norbornene-based resins, etc.); cellulose-based resins such as triacetyl cellulose and diacetyl cellulose; such as polyethylene terephthalate, polybutylene terephthalate Polyester resin; polycarbonate resin; (meth)acrylic resin such as methyl methacrylate resin; polystyrene resin; polyvinyl chloride resin; acrylonitrile-butadiene-benzene Vinyl resin; acrylonitrile/styrene resin; polyvinyl acetate resin; polyvinylidene chloride resin; polyamide resin; polyacetal resin; modified polyphenylene ether resin; polypropylene resin Resin; polyether resin; polyarylate resin; polyamide imine resin; polyimide resin, etc.

When a polarizing element is manufactured using a laminated film of a base film and a PVA resin film laminated thereon, the base film can be used as a protective layer for the polarizing element, and can also be peeled off and removed from the polarizing element if necessary.

The polarizing element can be continuously transported along the film conveying path of the polarizing element manufacturing device while unwinding the long strip of embryonic film from the embryonic film roll, and is immersed in the processing liquid (hereinafter also referred to as ("processing bath"), specific processing steps of extraction are performed, and then a drying step is performed to continuously manufacture long polarizing elements. In addition, the treatment step is not limited to the method of immersing the membrane in a treatment bath as long as the treatment liquid is brought into contact with the membrane, and the treatment liquid may be adhered by spraying, flowing down, dropping, etc. A method of membrane treatment on the membrane surface. When the treatment step is performed by immersing the membrane in a treatment bath, the treatment bath used to perform one treatment step is not limited to one, and the membrane may be immersed in two or more treatment baths in sequence. And complete a processing step.

Examples of the treatment liquid include a swelling liquid, a dyeing liquid, a cross-linking liquid, a cleaning liquid, and the like. Examples of the aforementioned processing steps include: a swelling step in which a swelling solution is brought into contact with the embryonic membrane to perform a swelling treatment; a dyeing step in which a dyeing solution is brought into contact with the swelling-treated membrane to perform a dyeing treatment; and a cross-linking solution is brought into contact with the dyeing treatment. A cross-linking step in which the cross-linked membrane is brought into contact to perform a cross-linking treatment; and a cleaning step in which a cleaning solution is brought into contact with the cross-linked membrane to perform a cleaning treatment. In addition, between the series of processing steps (that is, before and after any one or more processing steps and/or during any one or more processing steps), the uniaxial stretching treatment can be performed in a wet or dry method. Other processing steps can be added as needed.

Hereinafter, an example of the manufacturing method of the polarizing element of the present invention will be described in detail with reference to FIG. 1 . FIG. 1 is a cross-sectional view schematically showing an example of the manufacturing method of the polarizing element of the present invention and the polarizing element manufacturing apparatus used therein. The polarizing element manufacturing apparatus shown in FIG. 1 is configured by continuously unwinding the embryonic film (unstretched film) 10 containing polyvinyl alcohol-based resin from the embryonic film roll 11 along the The film conveying path transports it in order to pass through: the swelling bath (the swelling liquid contained in the swelling tank) 13 set on the film conveying path, the dyeing bath (the dyeing liquid contained in the dyeing tank) 15, 1 The cross-linking bath (the first cross-linking liquid contained in the cross-linking tank) 17a, the second cross-linking bath (the second cross-linking liquid contained in the cross-linking tank) 17b, and the cleaning bath (the washing tank contains the The stored cleaning fluid) 19, and finally passes through the drying oven 21. The obtained polarizing element 23 can, for example, be directly transported to the next polarizing plate manufacturing step (the step of laminating a protective film on one or both sides of the polarizing element 23). The arrows shown on the films 10 and 23 in Figure 1 indicate the conveying direction of the films.

In the description of Figure 1, the "processing tank" is a general term including swelling tank, dyeing tank, cross-linking tank and cleaning tank, and the "processing liquid" is a general term including swelling liquid, dyeing liquid, cross-linking liquid and cleaning liquid. , "Processing bath" is a general term including swelling bath, dyeing bath, cross-linking bath and cleaning bath. The swelling bath, dyeing bath, cross-linking bath and cleaning bath respectively constitute the swelling section, dyeing section, cross-linking section and cleaning section in the manufacturing device of the present invention.

In addition to the above-mentioned treatment bath, the film conveying path of the polarizing element manufacturing device can be guided by guide rollers 30 to 48, 60, 61 that can support the conveyed film or further change the film conveying direction, or by pressing/clamping the conveyed film. The nip rollers 50 to 55 are arranged at appropriate positions to impart driving force generated by the rotation of the film to the film, or to further change the conveying direction of the film. Guide rollers or nip rollers can be arranged before and after each treatment bath or in the treatment bath, whereby the film can be introduced/immersed into the treatment bath and pulled out from the treatment bath (see Figure 1). For example, the film can be immersed in each treatment bath by providing one or more guide rollers in each treatment bath and transporting the film along the guide rollers.

The polarizing element manufacturing apparatus shown in FIG. 1 has rollers (rollers 50 to 54) disposed before and after each treatment bath. This allows the application of circumference between the rollers arranged before and after any one or more of the treatment baths. The speed difference enables longitudinal uniaxial stretching between rollers. Each step is explained below.

(swelling step)

The swelling step is performed for the purpose of removing foreign matter on the surface of the embryonic membrane 10 , removing plasticizer in the embryonic membrane 10 , imparting dyeability, and plasticizing the embryonic membrane 10 . The treatment conditions are determined within a range that can achieve the purpose and within a range that does not cause adverse conditions such as excessive dissolution or devitrification of the embryonic membrane 10 .

Referring to Figure 1 , the swelling step can be implemented by continuously unwinding the embryonic membrane 10 from the embryonic membrane roll 11 while transporting it along the film transport path, immersing the embryonic membrane 10 in the swelling bath 13 for a predetermined time, and then pulling it out. . In the example of FIG. 1 , from unwinding the embryonic film 10 to being immersed in the swelling bath 13 , the embryonic film 10 is transported along the film transport path constructed by the guide rollers 60 and 61 and the nip roller 50 . In the swelling process, the film is transported along the film transport path constructed by the guide rollers 30 to 32 and the nip roller 51 .

As the swelling liquid of the swelling bath 13, in addition to pure water, boric acid (Japanese Patent Application Laid-Open No. 10-153709) or chloride (Japanese Patent Application Laid-Open No. 06-281816) may be used, in the range of about 0.01 to 10% by mass. , aqueous solutions of inorganic acids, inorganic salts, water-soluble organic solvents, alcohols, etc.

The temperature of the swelling bath 13 is, for example, about 10 to 50°C, preferably about 10 to 40°C, more preferably about 15 to 30°C. The immersion time of the embryonic membrane 10 is preferably about 10 to 300 seconds, more preferably about 20 to 200 seconds. In addition, when the embryonic membrane 10 is a polyvinyl alcohol-based resin film that has been stretched in gas in advance, the temperature of the swelling bath 13 is, for example, about 20 to 70°C, preferably about 30 to 60°C. The immersion time of the embryonic membrane 10 is preferably about 30 to 300 seconds, more preferably about 60 to 240 seconds.

During the swelling treatment, problems such as swelling of the embryonic membrane 10 in the width direction and wrinkles in the membrane are likely to occur. As a means for conveying the film while removing the wrinkles, the guide rollers 30, 31 and/or 32 can be used to use rollers with a widening function such as expansion rollers, spiral rollers, and crown rollers, or the use of Transverse guides, bending rods, tenter clamps and other expansion devices. Another method used to suppress wrinkles is to perform stretching. For example, the difference in peripheral speed between the nip roller 50 and the nip roller 51 can be used to perform the uniaxial stretching process in the swelling bath 13 .

During the swelling treatment, since the film also swells and expands in the direction of film conveyance, when the film is not actively stretched, in order to eliminate the slack of the film in the conveyance direction, for example, it is better to use nip rollers arranged before and after the swelling bath 13. 50, 51 speed and other methods. In addition, in order to stabilize the film transport in the swelling bath 13, water spraying is used to control the water flow in the swelling bath 13, or an EPC device (edge position control device: a device that detects the edge of the film and prevents the film from snaking) is also used. it works.

In the example shown in FIG. 1 , the film pulled out from the swelling bath 13 is introduced into the dyeing bath 15 through the guide roller 32 , the nip roller 51 , and the guide roller 33 in sequence.

(staining step)

The dyeing step is performed for the purpose of adsorbing and aligning the dichroic pigment to the polyvinyl alcohol-based resin film after the swelling process. The treatment conditions are determined within a range that can achieve the purpose and within a range that does not cause undesirable conditions such as excessive dissolution or devitrification of the membrane. Referring to Figure 1, the dyeing step can be implemented in the following manner: conveying along the film conveying path constructed by the nip roller 51, the guide rollers 33 to 36 and the nip roller 52, and placing the swollen film in the dyeing bath 15 (dyeing tank). The contained treatment liquid) is immersed for a specified time and then drawn out. In order to improve the dyeability of the dichroic pigment, the film used in the dyeing step is preferably a film that has been subjected to at least a certain degree of uniaxial stretching treatment, or it is preferable to replace the uniaxial stretching treatment before the dyeing treatment, or in addition to the dyeing In addition to the uniaxial stretching treatment before treatment, uniaxial stretching treatment is performed during the dyeing process.

When iodine is used as a dichroic pigment, the dyeing solution of the dyeing bath 15 may, for example, use an aqueous solution with a weight ratio of iodine/potassium iodide/water=0.003 to 0.3/0.1 to 10/100. Other iodides such as zinc iodide may be used instead of potassium iodide, or potassium iodide and other iodides may be used in combination. In addition, compounds other than iodide, such as boric acid, zinc chloride, cobalt chloride, etc., may also coexist. When boric acid is added, it is different from the cross-linking treatment described below in terms of iodine content. If the aqueous solution contains 0.003 parts by weight or more of iodine relative to 100 parts by weight of water, it can be regarded as the dyeing bath 15. The temperature of the dyeing bath 15 when dipping the film is usually The temperature is about 10 to 45°C, preferably 10 to 40°C, and more preferably 20 to 35°C. The immersion time of the film is usually about 30 to 600 seconds, preferably 60 to 300 seconds.

When a water-soluble dichroic dye is used as the dichroic pigment, the dyeing solution of the dyeing bath 15 may use, for example, an aqueous solution with a weight ratio of dichroic dye/water=0.001 to 0.1/100. In the dyeing bath 15, dyeing auxiliaries and the like may coexist, and for example, inorganic salts such as sodium sulfate or surfactants may be included. Only one type of dichroic dye may be used alone, or two or more types of dichroic dyes may be used in combination. The temperature of the dyeing bath 15 when the film is immersed is, for example, about 20 to 80°C, preferably 30 to 70°C. The immersion time of the film is usually about 30 to 600 seconds, preferably about 60 to 300 seconds.

As mentioned above, in the dyeing step, the dyeing bath 15 can be used to perform uniaxial stretching of the film. The uniaxial stretching of the film can be performed by a method such as providing a peripheral speed difference between the nip rollers 51 and 52 arranged before and after the dyeing bath 15 .

In the dyeing process, similarly to the swelling process, in order to transport the polyvinyl alcohol-based resin film while removing the wrinkles of the film, guide rollers 33, 34, 35 and/or 36 can be used, such as expansion rollers, spiral rollers, and crown rollers. Rollers with a widening function, or other widening devices using transverse guides, bending rods, and tenter clamps. Another means for suppressing the occurrence of wrinkles is to perform stretching treatment in the same manner as the swelling treatment.

In the example shown in FIG. 1 , the film pulled out from the dyeing bath 15 is introduced into the cross-linking bath 17 through the guide roller 36 , the nip roller 52 , and the guide roller 37 in sequence.

(cross-linking step)

The cross-linking step is a process performed for the purpose of making water resistant by cross-linking or adjusting the hue (preventing the film from becoming blue, etc.). In the example shown in Fig. 1, two cross-linking baths are arranged as the cross-linking bath for performing the cross-linking step. The first cross-linking bath 17a is used to perform the first cross-linking step for the purpose of making water resistance, and the second cross-linking bath 17a is used to perform the first cross-linking step. The joint bath 17b performs the second cross-linking step for the purpose of adjusting the hue. Referring to Figure 1, the first cross-linking step can be It is implemented in the following manner: conveying along the film conveying path constructed by the nip roller 52, the guide rollers 37 to 40 and the nip roller 53a, and placing the dyed film in the first cross-linking bath 17a (the film contained in the cross-linking tank). Immerse it in the first cross-linking liquid) for a specified time, and then pull it out. The second cross-linking step can be implemented in the following manner: conveying along the film conveying path constructed by the nip roller 53a, the guide rollers 41 to 44, and the nip roller 53b, and placing the film after the first cross-linking step in the second cross-linking step. The liquid is immersed in the bath 17b (the second cross-linking liquid contained in the cross-linking tank) for a predetermined time, and then pulled out. Hereinafter, when it is called a cross-linking bath, it also includes either the first cross-linking bath 17a or the second cross-linking bath 17b. When it is called a cross-linking liquid, it also includes the first cross-linking liquid. and any one of the second cross-linking liquid.

As the cross-linking liquid, a solution in which a cross-linking agent is dissolved in a solvent can be used. Examples of the cross-linking agent include boron compounds such as boric acid and borax, glyoxal, and glutaraldehyde. These may be one type, or two or more types may be used in combination. As the solvent, for example, water can be used, and an organic solvent that is compatible with water may also be included. The concentration of the cross-linking agent in the cross-linking solution is not limited to this, but is preferably in the range of 1 to 20 mass %, and more preferably 6 to 15 mass %.

The cross-linking liquid may be an aqueous solution containing, for example, 1 to 10 parts by weight of boric acid relative to 100 parts by weight of water. When the dichroic dye used in the dyeing process is iodine, the cross-linking liquid preferably contains iodide in addition to boric acid, and the amount thereof can be, for example, 1 to 30 parts by weight relative to 100 parts by weight of water. Examples of the iodide include potassium iodide, zinc iodide, and the like. In addition, compounds other than iodide, such as zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate, etc., may also coexist.

In the cross-linking treatment, the concentrations of boric acid and iodide and the temperature of the cross-linking bath 17 can be appropriately changed depending on the purpose. For example, when the purpose of the cross-linking treatment is to achieve water resistance through cross-linking, the first cross-linking liquid may have a concentration of boric acid/iodide/water=3 to 10/1 to 20/100 in weight ratio. aqueous solution. If necessary, other cross-linking agents can be used instead of boric acid, or boric acid and other cross-linking agents can be used in combination. The temperature of the first cross-linking bath 17a when the film is immersed is usually about 50 to 70°C, preferably 53 to 65°C. The immersion time is usually about 10 to 600 seconds, preferably 20 to 300 seconds, more preferably 20 to 200 seconds. In addition, when the dyeing treatment and the first cross-linking treatment are sequentially performed on the pre-stretched polyvinyl alcohol-based resin film before the swelling treatment, the temperature of the first cross-linking bath 17a is usually about 50 to 85°C, preferably 55 to 80℃.

In the second cross-linking liquid for the purpose of hue adjustment, for example, when using iodine as a dichroic dye, a concentration of boric acid/iodide/water=1 to 5/3 to 30/100 in weight ratio can be used. The temperature of the second cross-linking bath 17b when the film is immersed is usually about 10 to 45°C, and the immersion time of the film is usually about 1 to 300 seconds, preferably 2 to 100 seconds.

The cross-linking treatment can be carried out multiple times, usually 2 to 5 times. In this case, the composition and temperature of each crosslinking bath used may be the same or different as long as they are within the aforementioned ranges. The cross-linking treatment for making water resistant by cross-linking and the cross-linking treatment for adjusting the hue can be performed in a plurality of steps respectively.

It is also possible to perform uniaxial stretching in the first crosslinking bath 17a by utilizing the difference in circumferential speed between the nip roller 52 and the nip roller 53a. Furthermore, the uniaxial stretching process may be performed in the second crosslinking bath 17b by utilizing the difference in circumferential speed between the nip roller 53a and the nip roller 53b.

In the cross-linking treatment, similarly to the swelling treatment, in order to transport the polyvinyl alcohol-based resin film while removing wrinkles on the film, the guide rollers 38, 39, 40, 41, 42, 43 and/or 44 can be used as follows: Expanding rollers, spiral rollers, crown rollers, rollers with a widening function, or other widening devices using transverse guides, bending rods, and tenter clamps. Another means for suppressing the occurrence of wrinkles is to perform stretching treatment in the same manner as the swelling treatment.

In the example shown in FIG. 1 , the film pulled out from the second cross-linking bath 17 b is introduced into the cleaning bath 19 through the guide roller 44 and the nip roller 53 b in order.

(washing step)

The example shown in Figure 1 includes a cleaning step after the cross-linking step. The cleaning treatment is performed for the purpose of removing excess chemicals such as boric acid and iodine adhering to the polyvinyl alcohol-based resin film. The cleaning step is performed, for example, by immersing the cross-linked polyvinyl alcohol-based resin film in the cleaning bath 19 . Furthermore, the cleaning step can also be performed by spraying the membrane with the cleaning liquid as a spray, or using a combination of immersion in the cleaning bath 19 and spraying of the cleaning liquid to replace the step of immersing the membrane in the cleaning bath 19 . And proceed.

FIG. 1 shows an example in which a polyvinyl alcohol-based resin film is immersed in a cleaning bath 19 and subjected to cleaning treatment. The temperature of the cleaning bath 19 in the cleaning process is usually about 2 to 40°C, and the immersion time of the membrane is usually about 2 to 120 seconds.

Furthermore, in the cleaning process, in order to transport the polyvinyl alcohol resin film while removing wrinkles, the guide rollers 45, 46, 47 and/or 48 may also be equipped with an expansion roller, a spiral roller, or a crown roller. Rollers with widening function, or other widening devices using transverse guides, bending rods, and tenter clamps. In addition, during the film cleaning process, in order to suppress the occurrence of wrinkles, a stretching process may be performed.

(Extended steps)

As described above, the embryonic membrane 10 is uniaxially stretched in a wet or dry manner between the aforementioned series of processing steps (that is, before and/or during any one or more processing steps). Specific methods of the uniaxial stretching treatment include, for example, inter-roller stretching in which a circumferential speed difference is provided between two nip rollers (for example, two nip rollers arranged before and after the treatment bath) constituting the film conveyance path to perform longitudinal uniaxial stretching; For example, hot roll stretching, tenter stretching, etc. described in Japanese Patent No. 2731813, inter-roller stretching is preferred. The uniaxial stretching step can be performed multiple times from the embryonic membrane 10 to obtaining the polarizing element 23 . As mentioned above, stretching treatment is also helpful in suppressing the occurrence of wrinkles in the film.

The final cumulative extension magnification of the polarizing element 23 based on the embryonic membrane 10 is usually about 4.5 to 7 times, preferably 5 to 6.5 times. The extension step can be performed in any processing step. When the extension processing is performed in two or more processing steps, the extension processing can also be performed in any processing step.

(drying step)

After the washing step, it is advisable to dry the PVA-based resin film. Drying of the film is not particularly limited, and can be performed using a drying oven 21 as shown in FIG. 1 . The drying furnace 21 may be provided with a hot air dryer, for example. The drying temperature is, for example, about 30 to 100°C, and the drying time is, for example, about 30 to 600 seconds. The process of drying the polyvinyl alcohol-based resin film can also be performed using a far-infrared heater.

(Other processing steps for PVA resin film)

Processing other than the above-mentioned processing may also be added. Examples of additional treatments include immersion treatment in an aqueous iodide solution that does not contain boric acid (complementary color treatment) after the cross-linking step, and immersion treatment in an aqueous solution that does not contain boric acid and contains zinc chloride or the like (zinc handle).

(Polarizing element)

The thickness of the polarizing element 23 obtained by the above operation is preferably 5 to 50 μm, more preferably 8 to 28 μm, more preferably 12 to 22 μm, and most preferably 12 to 15 μm. By setting the thickness of the polarizing element to 50 μm or less, the effect of polyolefinization of the PVA-based resin on the decrease in optical properties in a high-temperature environment can be suppressed. In addition, by setting the thickness of the polarizing element to 5 μm or more, it is easy to achieve the desired results. The composition of optical properties.

When the polarizing plate has a retardation film, the thickness of the polarizing element is preferably 5 to 22 μm, more preferably 12 to 15 μm. By setting the thickness of the polarizing element within this range, the in-plane phase difference distribution caused by shrinkage of the polarizing element in a high-temperature environment becomes smaller, and the display quality of the display device becomes better. In addition, by setting the thickness of the polarizing element to 12 μm or more, the polarizing characteristics in a high-humidity environment can be easily maintained.

The boron content rate of the polarizing element is preferably 4.0 mass% or more and 8.0 mass% or less, more preferably 4.2 mass% or more and 7.0 mass% or less, and still more preferably 4.4 mass% or more and 6.0 mass% or less. Since the boron content of the polarizing element is 4.0% by mass or more, the transmittance of the polarizing element is not easily reduced even in a high temperature environment, such as when exposed to a high temperature environment of 105°C. The reason for this is presumed to be that when the boron content is 4.0% by mass or more, polyene formation is less likely to occur even in a high-temperature environment, thereby suppressing a decrease in transmittance. On the other hand, when the boron content of the polarizing element exceeds 8.0% by mass, the shrinkage force of the polarizing element becomes large, causing problems such as peeling from other components such as panels before lamination when integrating into an image display device. situation. The boron content in the polarizing element is, for example, high-frequency inductively coupled plasma (ICP) luminescence spectroscopy.

Through analysis, the boron mass fraction (mass %) relative to the mass of the polarizing element can be calculated. It is considered that boron exists in the polarizing element in the state of forming a cross-linked structure with boric acid or a component of the polyvinyl alcohol-based resin. The boron content here refers to the value of boron atoms (B).

The polarizing element may contain metal ions other than boron. For example, in terms of adjusting the color tone or imparting durability, at least one metal ion containing transition metals such as cobalt, nickel, zinc, chromium, aluminum, copper, manganese, and iron is preferred. Among these metal ions, zinc ions are preferred from the viewpoint of adjusting color tone or imparting heat resistance.

Considering the balance with the visibility correction polarization degree Py, the visibility correction monomer transmittance Ty of the polarizing element is preferably 40 to 47%, more preferably 41 to 45%. The visibility correction polarization degree Py is preferably 99.9% or more, more preferably 99.95% or more, and the larger the value, the better.

The obtained polarizing element is used for the subsequent laminating step. The polarizing element can be sequentially wound on a winding roller after the polarizing element manufacturing step to form a roll, or it can be directly used in the laminating step without being wound.

<Fitting steps>

The laminating step is a step of laminating a transparent protective film (hereinafter, also referred to as "protective film") via a water-based adhesive on at least one side of the polarizing element manufactured in the above manner. The polarizing plate is produced through the lamination step.

An example of a method for bonding a protective film to a polarizing element using a water-based adhesive is as follows: applying an adhesive to the bonding surface of one or both of the two films to be bonded, and interposing the adhesive layer Overlap the 2 pieces of film. The adhesive can be applied by, for example, pouring method, Meyer rod coating method, gravure coating method, notched wheel coating method, doctor blade method, die coating method, dip coating method, spray coating method, etc. The so-called pouring method refers to a method in which the adhesive agent flows down and spreads on the surface while moving the film to be bonded in a generally vertical direction, a generally horizontal direction, or an inclined direction between the two. The film laminate formed by overlapping the adhesive layer is usually pressed from top to bottom by a nip roller (laminating roller) or the like.

When attaching a protective film to a polarizing element, in order to improve the adhesion, plasma treatment, corona treatment, ultraviolet irradiation treatment, flame treatment, and saponification treatment can be performed on the bonding surface of the protective film or polarizing element to facilitate adhesion. Treatment, among which, plasma treatment, corona treatment or saponification treatment is preferred. For example, when the protective film is made of cyclic polyolefin-based resin, plasma treatment or corona treatment is usually performed on the bonding surface of the protective film. In addition, when the protective film is made of cellulose ester resin, saponification treatment is usually performed on the bonding surface of the protective film. Saponification treatment includes a method of immersing in an alkaline aqueous solution such as sodium hydroxide or potassium hydroxide.

After laminating the films, it is preferable to perform a drying step of drying the film laminate in order to remove water contained in the adhesive layer composed of a water-based adhesive. Drying can be performed, for example, by introducing the film laminate into a drying furnace. The drying temperature (temperature of the drying oven) is preferably 30 to 90°C. If the temperature is lower than 30°C, the protective film will tend to peel off from the polarizing element easily. Also, if the drying temperature exceeds 90°C, polarization will occur There is a risk that the polarizing performance of the element may be deteriorated by heat. The drying time can be set to about 10 to 1000 seconds. From the viewpoint of productivity, the drying time is preferably 60 to 750 seconds, and more preferably 150 to 600 seconds.

After the drying step, a curing step of about 12 to 600 hours can also be set at room temperature or a temperature slightly higher than room temperature, such as a temperature of about 20 to 45°C. The curing temperature is generally set lower than the drying temperature.

(water-based adhesive)

The polarizing element and the protective film are bonded using a water-based adhesive. A water-based adhesive is one in which the adhesive components are dissolved in water or dispersed in water. The ethanol concentration of the water-based adhesive used in this embodiment is 16 mass% or more and 50 mass% or less, preferably 18 mass% or more and 48 mass% or less, more preferably 20 mass% or more and 46 mass% or less, still more preferably It is 20 mass % or more and 35 mass % or less.

By containing ethanol in the aforesaid range in the water-based adhesive, discoloration during the manufacturing step of the polarizing plate can be suppressed. The discoloration here refers to the color unevenness observed when a polarizing plate is arranged in Cross Nicols and transmits high-brightness light. More specifically, it refers to overlapping in such a manner that it becomes a Cross Nicols state. When two polarizing plates were used to transmit white light, uneven color was observed in the brown part. This brown discoloration may be observed dispersed within the polarizing plate, and may be observed only in a specific portion. In addition, this brown discoloration may be observed at multiple locations within the polarizing plate, and may be observed at only one location. The size of the brown discolored area varies, but may be, for example, 100 to 4000 μm in diameter.

When a water-based adhesive is used to bond the polarizing element and the protective film, color unevenness is observed. When the boron content in the polarizing element is high and the water-based adhesive contains PVA-based resin, significant color unevenness is observed. , so it is believed that the mechanism that produces color unevenness is as follows. The boric acid in the polarizing element easily dissolves into the water in the water-based adhesive, and the dissolved boric acid reacts with the PVA-based resin contained in the water-based adhesive. Speculate This reactant produces unevenness in the water-based adhesive, and the unevenness becomes uneven as the water-based adhesive dries.

The mechanism by which the water-based adhesive can suppress discoloration by containing ethanol within the aforementioned range is not yet clear, but it is speculated that the ethanol present in the water-based adhesive helps inhibit the elution of boric acid in the polarizing element into the water-based adhesive, and inhibits the discoloration of the water-based adhesive. At least one of the reactions between boric acid and PVA resin in the agent proceeds.

The water-based adhesive is not particularly limited as long as it contains ethanol within the aforementioned range. Examples thereof include water-based adhesives containing PVA-based resin or urethane resin as a main component. When a water-based adhesive containing PVA-based resin is used, the effect of the present invention is remarkable, so it can be preferably used. The thickness of the adhesive layer formed of the water-based adhesive is usually 7 μm or less, and usually 0.01 μm or more. The thickness of the adhesive layer is preferably from 0.01 μm to 1.0 μm, more preferably from 0.02 μm to 0.8 μm.

When using polyvinyl alcohol-based resin as the main component of the adhesive, the polyvinyl alcohol-based resin can be, in addition to partially saponified polyvinyl alcohol or fully saponified polyvinyl alcohol, carboxyl-modified polyvinyl alcohol, ethanol, etc. Polyvinyl alcohol-based resin modified by acetyl-modified polyvinyl alcohol, hydroxymethyl-modified polyvinyl alcohol, and amine-modified polyvinyl alcohol. In addition to vinyl alcohol homopolymers obtained by saponifying polyvinyl acetate, which is a homopolymer of vinyl acetate, polyvinyl alcohol resins can also be copolymers of vinyl acetate and other monomers that can be copolymerized with it. A polyvinyl alcohol copolymer obtained by subjecting the material to saponification treatment.

A water-based adhesive containing PVA-based resin as an adhesive component is usually an aqueous solution of PVA-based resin. The concentration of the PVA-based resin in the adhesive is usually 1 to 10% by mass, preferably 1 to 5% by mass, and more preferably 2.85 to 5% by mass.

In order to improve the adhesiveness of the adhesive composed of an aqueous solution of PVA resin, it is preferable to add hardening components such as polyaldehydes, melamine compounds, zirconium oxide compounds, zinc compounds, glyoxal, and water-soluble epoxy resins. or cross-linking agent. As the water-soluble epoxy resin, for example, a polyamide polyamine epoxy resin obtained by reacting epichlorohydrin with a polyamide amine produced by diethylene triamine can be preferably used. It is obtained by the reaction of polyalkylene polyamines such as triethylenetetramine and dicarboxylic acids such as adipic acid. Commercially available products of the polyamide polyamine epoxy resin include "Sumirez Resin650" (manufactured by Taoka Chemical Industry Co., Ltd.), "Sumirez Resin675" (manufactured by Taoka Chemical Industry Co., Ltd.), and "WS-525" (Japan PMC (stock) system), etc. The amount of the curing component or cross-linking agent added (the total amount when the curing component and the cross-linking agent are added together) is usually 1 to 100 parts by weight relative to 100 parts by weight of the PVA resin, preferably 1 to 50 parts by weight. When the added amount of the aforementioned curing component or cross-linking agent is less than 1 part by weight relative to 100 parts by weight of the polyvinyl alcohol-based resin, the effect of improving adhesion tends to be smaller, and compared to the PVA-based resin When the added amount of the aforementioned curing component or cross-linking agent exceeds 100 parts by weight, the adhesive layer will tend to become brittle.

When the PVA-based resin is an acetyl acetyl-modified PVA-based resin, the cross-linking agent is preferably any one of glyoxal, glyoxylate, and methylol melamine, and more preferably ethylene glycol. Either aldehyde or glyoxylate, particularly preferably glyoxal.

When urethane resin is used as the main component of the adhesive, examples of suitable adhesive compositions include polyester-based ionomer-type urethane resin and glycidoxy group-containing urethane resin. Mixture of compounds. The so-called polyester ionomer type urethane resin is a urethane resin having a polyester skeleton into which a small amount of ionic components (hydrophilic components) are introduced. This ionomer type urethane resin is directly emulsified in water to form an emulsion without using an emulsifier, so it is suitable as a water-based adhesive.

The water-based adhesive contains ethanol and may contain organic solvents other than ethanol. In terms of miscibility with water, the organic solvent is preferably an alcohol, and may also include methanol, for example. From the viewpoint of improving heat resistance, the water-based adhesive may further contain: urea compounds such as urea, urea derivatives, thiourea, and thiourea derivatives; reducing agents such as ascorbic acid, isoascorbic acid, thiosulfuric acid, and sulfurous acid; cis Dicarboxylic acids such as butenedioic acid and phthalic acid; ammonium compounds such as ammonium sulfate, ammonium chloride, ammonium carbonate and ammonium fluoride; dextrins such as α-cyclodextrin, β-cyclodextrin and γ-cyclodextrin Semen; blocked isocyanate compounds obtained by blocking isocyanate compounds with blocking agents; nitroxyl groups of N-oxyl compounds; compounds with nitrogen oxide groups, etc. Some urea compounds have low solubility in water, but on the other hand, they have sufficient solubility in alcohol. At this time, it is also a preferred embodiment to dissolve the urea compound in alcohol to prepare an alcohol solution of the urea compound, and then add the alcohol solution of the urea compound to the PVA aqueous solution to prepare the adhesive.

(urea compounds)

When the adhesive layer contains a urea compound, the urea compound is at least one selected from the group consisting of urea, urea derivatives, thiourea, and thiourea derivatives. As a method of making the adhesive layer contain a urea compound, it is preferable that the adhesive layer contains a urea compound. Furthermore, during the process of forming an adhesive layer from the adhesive through a drying step, etc., a part of the urea compound may also move from the adhesive layer to the polarizing element or the like. That is, the polarizing element may contain a urea compound. There are water-soluble and poorly water-soluble urea compounds, but any urea compound can be used for the adhesive of this embodiment. When a poorly water-soluble urea compound is used in a water-based adhesive, it is preferable to design a dispersion method so as not to cause an increase in haze after forming the adhesive layer.

When the adhesive is a water-based adhesive containing a PVA resin, the amount of the urea compound added is preferably 0.1 to 400 parts by mass, more preferably 1 to 200 parts by mass, and still more preferably 100 parts by mass of the PVA resin. 3 to 100 parts by mass.

(urea derivatives)

Urea derivatives are compounds in which at least one of the four hydrogen atoms of the urea molecule is substituted with a substituent. In this case, the substituent is not particularly limited, but is preferably a substituent composed of a carbon atom, a hydrogen atom and an oxygen atom.

Specific examples of urea derivatives include monosubstituted urea: methylurea, ethylurea, propylurea, butylurea, isobutylurea, N-octadecylurea, and 2-hydroxyethyl Urea, hydroxyurea, acetyl urea, allyl urea, 2-propynyl urea, cyclohexyl urea, phenylurea, 3-hydroxyphenylurea, (4-methoxyphenyl)urea, benzyl Urea, benzyl urea, o-tolylurea, p-tolylurea.

Examples of disubstituted ureas include: 1,1-dimethylurea, 1,3-dimethylurea, 1,1-diethylurea, 1,3-diethylurea, 1,3-bis( Hydroxymethyl)urea, 1,3-tert-butylurea, 1,3-dicyclohexylurea, 1,3-diphenylurea, 1,3-bis(4-methoxyphenyl)urea, 1-Acetyl-3-methylurea.

Examples of 4-substituted urea include: tetramethylurea, 1,1,3,3-tetraethylurea, 1,1,3,3-tetrabutylurea, 1,3-dimethoxy-1, 3-Dimethylurea.

(Thiocarbamide derivatives)

Thiourea derivatives are compounds in which at least one of the four hydrogen atoms of the thiourea molecule is substituted with a substituent. In this case, the substituent is not particularly limited, but is preferably a substituent composed of a carbon atom, a hydrogen atom and an oxygen atom.

Specific examples of thiourea derivatives include, as monosubstituted thioureas, N-methyl thiourea, ethyl thiourea, propyl thiourea, isopropyl thiourea, 1-butyl thiourea, and cyclohexyl thiourea. Thiourea, N-acetyl thiourea, N-allyl thiourea, (2-methoxyethyl) thiourea, N-phenyl thiourea, (4-methoxyphenyl) thiourea, N-(2-methoxyphenyl)thiourea, N-(1-naphthyl)thiourea, (2-pyridyl)thiourea, o-tolylthiourea, p-tolylthiourea.

2-substituted thioureas are 1,1-dimethylthiourea, 1,3-dimethylthiourea, 1,1-diethylthiourea, 1,3-diethylthiourea, 1,3-dimethylthiourea Butylthiourea, 1,3-diisopropylthiourea, 1,3-dicyclohexylthiourea, N,N-diphenylthiourea, N,N'-diphenylthiourea, 1,3 -Di(o-tolyl)thiourea, 1,3-bis(p-tolyl)thiourea, 1-benzyl-3-phenylthiourea, 1-methyl-3-phenylthiourea, N-ene Propyl-N'-(2-hydroxyethyl)thiourea.

Examples of 3-substituted thiourea include trimethylthiourea, and examples of 4-substituted thiourea include tetramethylthiourea and 1,1,3,3-tetraethylthiourea.

Among the urea compounds, a urea derivative or a thiourea derivative is preferred, and a urea derivative is more preferred. Among the urea derivatives, 1-substituted urea or 2-substituted urea is preferred, and 1-substituted urea is more preferred. 2-Substituted ureas include 1,1-substituted urea and 1,3-substituted urea, but 1,3-substituted urea is better.

(transparent protective film)

The protective film used in this embodiment is bonded to at least one side of the polarizing element via an adhesive. The protective film has the function of protecting the polarizing element.

The protective film may have an optical function, or may have a laminated structure in which a plurality of layers are laminated. From the viewpoint of optical properties, the thickness of the protective film is preferably thin. However, if it is too thin, the strength will be reduced and the processability will be deteriorated. An appropriate film thickness is 5 to 100 μm, preferably 10 to 80 μm, more preferably 15 to 70 μm.

Examples of the protective film include a chelated cellulose film, a film made of polycarbonate resin, a film made of cycloolefin resin such as norbornene, a (meth)acrylic polymer film, and a polyterephthalene film. Films such as polyester resin-based films such as ethylene formate. When the polarizing element has protective films on both sides and is bonded using a water-based adhesive such as PVA adhesive, in terms of moisture permeability, the protective film on at least one side is preferably a chelated cellulose-based film or (methyl) Any of acrylic polymer films, among which a chelated cellulose film is preferred.

At least one of the protective films may have a phase difference function for the purpose of viewing angle compensation, etc. In this case, the film itself may have a phase difference function, may additionally have a phase difference layer, or may be a combination of the two.

Furthermore, the structure in which the film having the phase difference function is directly bonded to the polarizing element via an adhesive is explained, but it can also be pasted via an adhesive or an adhesive via another protective film that is bonded to the polarizing element. The combined composition.

[Construction of image display device]

The polarizing plate of this embodiment is used in various image display devices such as liquid crystal display devices and organic EL display devices. In an image display device, when both sides of a polarizing plate are filled with interlayers in contact with a layer other than the air layer, specifically a solid layer such as an adhesive layer, the transmittance is likely to decrease in a high-temperature environment. In the image display device using the polarizing plate of this embodiment, even if the polarizing plate is formed with interlayer filling, the decrease in transmittance of the polarizing plate in a high-temperature environment can be suppressed. An example of the image display device may include a structure including an image display unit, a first adhesive layer laminated on the viewing side surface of the image display unit, and a polarizing plate laminated on the viewing side surface of the first adhesive layer. The image display device may further include a second adhesive layer laminated on the viewing side surface of the polarizing plate, and a transparent member laminated on the surface of the second adhesive layer. In particular, the polarizing plate of this embodiment can be preferably used in an image display device having an interlayer filling structure in which a transparent member is disposed on the viewing side of the image display device, and the polarizing plate and the image display unit are combined with each other. The polarizing plate and the transparent member are bonded together through the first adhesive layer, and the polarizing plate and the transparent member are bonded together through the second adhesive layer. In this specification, either or both of the first adhesive layer and the second adhesive layer may be simply referred to as "adhesive layer." Furthermore, the member used for bonding the polarizing plate and the image display unit, and the member used for bonding the polarizing plate and the transparent member are not limited to the adhesive layer, and may be an adhesive layer.

<Image display unit>

Examples of the image display unit include a liquid crystal unit or an organic EL unit. As the liquid crystal cell, any of a reflective liquid crystal cell that utilizes external light, a transmissive liquid crystal cell that utilizes light from a light source such as a backlight, or a transflective or semi-reflective liquid crystal cell that utilizes both external light and light from a light source can be used. One. When the liquid crystal unit uses light from a light source, the image display device (liquid crystal display device) also disposes a polarizing plate on the side opposite to the viewing side of the image display unit (liquid crystal unit), and then disposes the light source. The polarizing plate on the light source side and the liquid crystal unit are preferably bonded through an appropriate adhesive layer. As a driving method of the liquid crystal cell, any type such as VA mode, IPS mode, TN mode, STN mode or bend alignment (π type) can be used.

As an organic EL unit, a transparent electrode, an organic light-emitting layer, and a metal electrode are sequentially stacked on a transparent substrate to form a light-emitting body (organic electroluminescence light-emitting body). The organic light-emitting layer is a laminate of various organic thin films. For example, a laminate of a hole injection layer made of a triphenylamine derivative and a light-emitting layer made of a fluorescent organic solid such as anthracene, or these light-emitting layers can be used. It is composed of various layers such as a laminate of an electron injection layer composed of a perylene derivative or the like, or a laminate of a hole injection layer, a light emitting layer, and an electron injection layer.

<Lamination of image display unit and polarizing plate>

In the lamination of the image display unit and the polarizing plate, an adhesive layer (adhesive sheet) can be preferably used. Among them, from the viewpoint of workability and the like, a method of bonding a polarizing plate with an adhesive layer provided with an adhesive layer on one side of the polarizing plate and an image display unit is preferred. The adhesive layer of the polarizing plate can be attached by an appropriate method. Examples thereof include: preparing an adhesive in an amount of about 10 to 40 mass % in which a base polymer or a composition thereof is dissolved or dispersed in a solvent containing a suitable solvent alone or in a mixture such as toluene or ethyl acetate. Solution, attach it directly by appropriate expansion methods such as pouring or coating. The method is to place it on the polarizing plate, or to form an adhesive layer on the isolation film and transfer it to the polarizing plate, etc.

<Adhesive layer>

The adhesive layer may include one layer, or may include two or more layers, and preferably includes one layer. The adhesive layer may be composed of an adhesive composition mainly composed of (meth)acrylic resin, rubber resin, urethane resin, ester resin, polysiloxy resin, or polyvinyl ether resin. Among them, an adhesive composition using (meth)acrylic resin as a base polymer having excellent transparency, weather resistance, heat resistance, etc. is preferred. The adhesive composition may be an active energy ray hardening type or a heat hardening type.

As the (meth)acrylic resin (base polymer) used in the adhesive composition, butyl (meth)acrylate, ethyl (meth)acrylate, and isoacrylate (meth)acrylate are preferably used. A polymer or copolymer of one or more (meth)acrylate esters such as octyl ester and 2-ethylhexyl (meth)acrylate as monomers. Among the base polymers, those copolymerizing polar monomers are preferred. Examples of the polar monomer include: (meth)acrylic acid compound, (meth)acrylic acid 2-hydroxypropyl compound, (meth)acrylic acid hydroxyethyl compound, (meth)acrylamide compound, (meth)acrylic acid compound Monomers having carboxyl groups, hydroxyl groups, amide groups, amine groups, epoxy groups, etc., such as N,N-dimethylaminoethyl acrylate compounds and glycidyl (meth)acrylate compounds.

The adhesive composition may contain only the aforementioned base polymer, but usually further contains a cross-linking agent. Examples of the cross-linking agent include: a metal ion having a valence of more than 2 and forming a carboxylic acid metal salt with a carboxyl group; a polyamine compound that forms an amide bond with a carboxyl group; and a polyamine compound that forms an ester bond with a carboxyl group. Polyepoxy compounds or polyols, and polyisocyanate compounds that form amide bonds with carboxyl groups. Among them, polyisocyanate compounds are preferred.

The active energy ray curable adhesive composition has the property of being hardened by exposure to active energy rays such as ultraviolet rays or electron beams, and has adhesive properties even before the active energy rays are irradiated. It has the property of being able to adhere closely to adherends such as films, and it has the property of being hardened and adjusting the adhesion force by irradiation with active energy rays. The active energy ray curing adhesive composition is preferably an ultraviolet curing type. The active energy ray curable adhesive composition contains an active energy ray polymerizable compound in addition to the base polymer and cross-linking agent. If necessary, a photopolymerization initiator, a photosensitizer, etc. may also be included.

The adhesive composition may include fine particles, beads (resin beads, glass beads, etc.), glass fibers, resins other than the base polymer, tackifiers, and fillers (metal powder or other inorganic materials) used to impart light scattering properties. Powder, etc.), antioxidants, ultraviolet absorbers, dyes, pigments, colorants, defoaming agents, anti-corrosion agents, photopolymerization initiators and other additives.

The adhesive layer can be formed by applying an organic solvent dilution of the aforementioned adhesive composition onto the surface of a base film, an image display unit, or a polarizing plate and drying it. The base film is generally a thermoplastic resin film, and a typical example thereof is a release film that has been subjected to a mold release treatment. The separation membrane may be, for example, a surface of a membrane containing resin such as polyethylene terephthalate, polybutylene terephthalate, polycarbonate, polyarylate, etc., on which the adhesive layer is formed, and is subjected to silicone treatment or the like to remove the membrane. Made by mold processing.

For example, the adhesive composition can be directly coated on the release-processed surface of the release film to form an adhesive layer, and the adhesive layer with the release film can be laminated on the surface of the polarizer. The adhesive composition can also be directly coated on the surface of the polarizing plate to form an adhesive layer, and a separation film can be layered on the surface outside the adhesive layer.

When disposing the adhesive layer on the surface of the polarizing plate, it is preferable to perform surface activation treatment, such as plasma treatment, corona treatment, etc., on the laminating surface of the polarizing plate and/or the laminating surface of the adhesive layer, and more preferably Implement corona treatment.

Alternatively, an adhesive composition may be applied to the second separation film to form an adhesive layer, and an adhesive sheet formed by laminating a separation film on the formed adhesive layer may be prepared, and the second separation film may be peeled off from the adhesive sheet. 2 separation membrane Then the adhesive layer with the release film is laminated on the polarizing plate. The second separation membrane is used which has weaker adhesion with the adhesive layer than the separation membrane and is easier to peel off.

The thickness of the adhesive layer is not particularly limited. For example, it is preferably not less than 1 μm and not more than 100 μm, more preferably not less than 3 μm and not more than 50 μm, and may be not less than 20 μm.

<Transparent component>

Examples of the transparent member disposed on the viewing side of the image display device include a transparent plate (window layer), a touch panel, and the like. As the transparent plate, one having appropriate mechanical strength and thickness can be used. Examples of such a transparent plate include a transparent resin plate such as polyimide-based resin, acrylic resin, or polycarbonate-based resin, or a glass plate. Functional layers such as anti-reflective layers can also be laminated on the visible side of the transparent plate. In addition, when the transparent plate is a transparent resin plate, a hard coat layer for improving physical strength or a low moisture permeability layer for reducing moisture permeability may be laminated.

As the touch panel, various touch panels such as resistive film type, capacitive type, optical type, ultrasonic type, etc., or a glass plate or a transparent resin plate with a touch sensor function can be used. When a capacitive touch panel is used as a transparent member, it is preferable to provide a transparent plate made of glass or a transparent resin plate closer to the viewing side than the touch panel.

<Lamination of polarizing plates and transparent components>

In bonding the polarizing plate and the transparent member, an adhesive or an active energy ray-hardening adhesive can be preferably used. When using adhesive, the attachment of the adhesive can be done in an appropriate manner. As a specific attachment method, for example, the attachment method of the adhesive layer used in the bonding of the image display unit and the polarizing plate can be cited.

When using active energy ray curable adhesive, in order to prevent the spread of the adhesive solution before curing, the following method can be preferably used: surrounding the peripheral portion of the image display panel A cofferdam material is installed, a transparent member is placed on the cofferdam material, and an adhesive solution is injected. After the adhesive solution is injected, alignment and degassing are performed as necessary, and then active energy rays are irradiated for hardening.

[Example]

Hereinafter, the present invention will be described in detail based on examples. Materials, reagents, amounts of substances, ratios, operations, etc. shown in the following examples may be appropriately changed as long as they do not deviate from the gist of the present invention. Therefore, the present invention is not limited to the following examples.

(1) Determination of thickness of polarizing element:

Measurement was performed using a digital micrometer "MH-15M" manufactured by Nikon Co., Ltd.

(2) Determination of boron content of polarizing elements:

0.2 g of the polarizing element was dissolved in 200 g of a 1.9 mass% mannitol aqueous solution. Then, the obtained aqueous solution was titrated with a 1 mol/L sodium hydroxide aqueous solution, and the boron content rate of the polarizing element was calculated by comparing the amount of sodium hydroxide aqueous solution required for neutralization with the calibration curve.

(3) Determination of the zinc ion content of the polarizing element:

Nitric acid was added to the polarizing element of the precision scale, and the solution obtained by acid decomposition using a microwave sample pretreatment device (ETHOS D) manufactured by Milstone General Co., Ltd. was used as the measurement liquid. The zinc ion content rate was determined by quantitatively measuring the zinc concentration of the solution using an ICP optical emission spectrometer (5110 ICP-OES) manufactured by Agilent Technology and calculating it as the mass of zinc relative to the mass of the polarizing element.

(4) Determination of boron adsorption rate of PVA resin film:

A PVA-based resin film cut into a 100 mm square was immersed in pure water at 30°C for 60 seconds, and then immersed in a 60°C aqueous solution containing 5 parts of boric acid for 120 seconds. The PVA-based resin film taken out from the boric acid aqueous solution was dried in an oven at 80°C for 11 minutes. Adjust the humidity for 24 hours in an environment of 23°C and 55%RH to obtain a boron-containing PVA film. Dissolve 0.2 g of the boron-containing PVA-based resin film obtained in 1.9 Mass% mannitol aqueous solution in 200g. Then, the obtained aqueous solution was titrated with a 1 mol/L sodium hydroxide aqueous solution, and the boron content rate of the PVA-based resin film was calculated by comparing the amount of sodium hydroxide aqueous solution required for neutralization with the calibration curve. The boron content rate of the PVA-based resin film thus obtained was used as the boron adsorption rate of the PVA-based resin film.

<Production of polarizing elements>

(Polarizing element 1)

A PVA-based resin film with a thickness of 30 μm and a boron adsorption rate of 5.71% by mass was immersed in pure water at 21.5° C. for 79 seconds (swelling treatment). The PVA-based resin film was immersed in a 23° C. aqueous solution containing 1.0 mM iodine at a mass ratio of potassium iodide/boric acid/water of 2/2/100 for 151 seconds (dyeing step). Thereafter, the PVA-based resin film was immersed in an aqueous solution at 68.5° C. with a mass ratio of potassium iodide/boric acid/water of 2.5/4/100 for 76 seconds (first cross-linking step). Next, the PVA-based resin film was immersed in a 45° C. aqueous solution with a mass ratio of potassium iodide/boric acid/zinc chloride/water of 3/5.5/0.6/100 for 11 seconds (second cross-linking step, metal ion treatment step). Thereafter, it was immersed in a cleaning bath to wash (washing step), and dried at 38° C. (drying step) to obtain a 12 μm-thick polarizing element with iodine adsorbed and aligned to polyvinyl alcohol. Extension is mainly performed in the dyeing step and the first cross-linking step, and the total extension ratio is 5.85 times. The obtained polarizing element had a zinc ion content of 0.17% by mass and a boron content of 4.62% by mass.

<Preparation of Adhesive>

(The adhesive is prepared with PVA solution A)

50 g of modified PVA-based resin containing acetyl acetyl groups ("GOHSENEX Z-410" manufactured by Mitsubishi Chemical Co., Ltd.) was dissolved in 950 g of pure water. The solution was heated at 90°C for 2 hours and then cooled to normal temperature to obtain PVA solution A for adhesive.

(Preparation of adhesives 1 to 5)

Next, the PVA solution A, maleic acid, glyoxal, ethanol, and pure water were prepared so that each component would have the concentration (mass %) in Table 1 to prepare a PVA-based adhesive (adhesives 1 to 5). .

[Table 1]

<Preparation of transparent protective film>

(Saponification of chelated cellulose membrane)

Commercially available chelated cellulose film TJ40UL (manufactured by Fuji Film Co., Ltd.: film thickness 40 μm) was immersed in a 1.5 mol/L NaOH aqueous solution (saponification solution) maintained at 55° C. for 2 minutes, and the film was washed with water. Thereafter, the membrane was immersed in a 0.05 mol/L sulfuric acid aqueous solution at 25° C. for 30 seconds, and then passed through a water bath under running water for 30 seconds to bring the membrane into a neutral state. Then, repeat draining with an air knife three times. After removing the water, the film was left in a drying zone at 70° C. for 15 seconds to dry, and a saponified film (transparent protective film 1) was produced.

<Production of Polarizing Plate>

(Production of polarizing plate 1)

The transparent protective film 1 prepared above is bonded to both surfaces of the polarizing element 1 via the adhesive 1 using a roller laminating machine. The coating thickness of adhesive 1 is based on the thickness of the adhesive layer after drying, which is 100 nm on both sides. way to adjust. Thereafter, it was dried at 80° C. for 3 minutes to obtain the polarizing plate 1 with transparent protective films on both sides.

(Production of polarizing plates 2 to 5)

Polarizing plates 2 to 5 are produced in the same manner as polarizing plate 1 except that adhesive 1 is replaced by adhesives 2 to 5 respectively.

<Evaluation of discoloration>

A linear polarizing plate for inspection is placed on the back side of the target polarizing plate so that it becomes a cross-polarized state, and a high-brightness LED pen light with a beam of 1000 lumens is irradiated from the surface side of the linear polarizing plate for inspection at a distance of about 10 to 50 mm. , placed in a dark room for visual observation. When brown discoloration is observed, it is judged as "presence" of discoloration, and when brown discoloration is not observed, it is judged as "no" discoloration. The judgment results are shown in Table 2.

The evaluation results are shown in Table 2.

<High Temperature Durability Test (105℃)>

(Preparation of samples for evaluation)

An acrylic adhesive (manufactured by LINTEC Co., Ltd.) was coated on one side of the polarizing plates 1 to 5 produced above to form an adhesive layer with a thickness of 25 μm. By cutting the polarizing plate with an adhesive layer on one side to a size of 40mm x 40mm, and attaching alkali-free glass [trade name "EAGLE XG", manufactured by Coming Company] to the surface of the adhesive layer, this is achieved. Make evaluation samples.

(High temperature durability test)

The evaluation sample obtained above was subjected to autoclave treatment at a temperature of 50°C and a pressure of 5kgf/cm2 (490.3kPa) for 1 hour, and then placed in an environment of a temperature of 23°C and an RH of 55% for 24 hours. Measure the polarization degree, single transmittance, and hue of the polarizing plate and use them as initial values. Then, the sample for evaluation was heated to a temperature of 105 Stored in a high temperature environment of ℃ for 500 hours. Measure the polarization degree, monomer transmittance, and hue of the polarizing plate after storage.

Calculate the change amount of each of the polarizing plate's visibility-corrected single transmittance, visibility-corrected polarization degree, and hue based on the initial values and the measured values after the high-temperature endurance test. The change amount ΔTy of the visibility correction monomer transmittance and the change amount ΔPy of the visibility correction polarization degree are calculated as the values obtained by subtracting the initial value from the measured value after the high-temperature durability test. In addition, the change amount Δab of the hue is calculated by the following formula.

Δab={(a ₁ -a ₂ ) ² (b ₁ -b ₂ ) ² } ^1/2

Here, a ₁ and b ₁ are the initial values of the hue, and a ₂ and b ₂ are the measured values of the hue after the high-temperature endurance test.

Table 2 presents the values of ΔTy, ΔPy, and Δab.

[Table 2]

10: Embryonic membrane composed of polyvinyl alcohol resin

11: embryonic membrane roll

13: Swelling bath

15:Dyeing bath

17a: 1st cross-linking bath

17b: 2nd cross-linking bath

19:Cleaning bath

21: Drying oven

23:Polarizing element

30 to 48, 60, 61: guide roller

50 to 52, 53a, 53b, 54, 55: pinch roller

Claims (5)

A method of manufacturing a polarizing plate, which has a polarizing element and a transparent protective film laminated on at least one side of the polarizing element. The manufacturing method has the following steps: Polarizing element manufacturing steps for obtaining polarizing elements from polyvinyl alcohol-based resin films; and The step of laminating the aforementioned transparent protective film to the aforementioned polarizing element via a water-based adhesive; Among them, the boron adsorption rate of the aforementioned polyvinyl alcohol-based resin film is 5.70 mass% or more, The ethanol concentration of the water-based adhesive is 16 mass% or more and 50 mass% or less. The manufacturing method according to claim 1, wherein the boron content of the polarizing element is 4.0 mass% or more and 8.0 mass% or less. The manufacturing method according to claim 1 or 2, wherein the water-based adhesive contains a polyvinyl alcohol-based resin. The manufacturing method according to claim 3, wherein the concentration of the water-based adhesive and the polyvinyl alcohol-based resin is 2.85% by mass or more. The manufacturing method according to claim 1 or 2, wherein in the polarizing plate, the thickness of the adhesive layer formed of the water-based adhesive between the polarizing element and the transparent protective film is 0.01 μm or more. Below 7μm.

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