WO2023228584A1

WO2023228584A1 - Method for producing polarizing plate

Info

Publication number: WO2023228584A1
Application number: PCT/JP2023/013788
Authority: WO
Inventors: 裕史太田; 慎也萩原
Original assignee: 住友化学株式会社
Priority date: 2022-05-26
Filing date: 2023-04-03
Publication date: 2023-11-30
Also published as: TW202346988A; JP2023173674A

Abstract

Provided is a method for producing a polarizing plate, whereby the occurrence of discoloration in the process of producing the polarizing plate can be suppressed even when the boron content of a polarizing element is high.

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 personal computers, mobile phones such as mobile phones, and in-vehicle applications such as car navigation systems. Generally, a liquid crystal display device has a liquid crystal panel member in which polarizing plates are bonded to both sides of a liquid crystal cell using an adhesive, and displays are performed by controlling light from a backlight member with the liquid crystal panel member. In recent years, organic EL display devices have also been widely used in mobile applications such as televisions, cell phones, and in-vehicle applications such as car navigation systems, similar to liquid crystal display devices. In an organic EL display device, in order to prevent external light from being reflected by a metal electrode (cathode) and viewed as a mirror surface, a circularly polarizing plate (a polarizing element and a λ/4 plate) is installed on the viewing side surface of the image display panel. laminate) may be arranged.

As mentioned above, polarizing plates are increasingly being installed in cars as components of liquid crystal display devices and organic EL display devices. Polarizing plates used in in-vehicle image display devices are often exposed to high temperature environments compared to other mobile applications such as televisions and mobile phones, and are required to have higher durability at high temperatures. It will be done.

As a manufacturing method for such a polarizing element with high high temperature durability, for example, Patent Documents 1 and 2 disclose that components such as metal salts containing zinc, copper, aluminum, etc. are added to a treatment bath, and these components are added to the polarizing element. It has been disclosed that the durability of a polarizing element can be improved by including a component therein. Further, Patent Documents 3 and 4 disclose a method for manufacturing a polarizing element in which a component such as an organic titanium compound is added to a treatment bath.

International Publication No. 2016/117659 Japanese Patent Application Publication No. 2006-047978 Japanese Patent Application Publication No. 2008-46257 Japanese Patent Application Publication No. 6-172554

The present inventors have discovered that the durability of the polarizing plate at high temperatures can be improved by increasing the boron content of the polarizing element. However, it has been discovered that discoloration may occur during the manufacturing process of the polarizing plate due to the large amount of boron contained in the polarizing element.
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 of the polarizing element is increased.

The present invention provides the following method for manufacturing a polarizing plate.
[1] A method for producing a polarizing plate comprising a polarizing element and a transparent protective film laminated on at least one surface of the polarizing element,
A polarizing element manufacturing process for obtaining a polarizing element from a polyvinyl alcohol resin film;
a bonding step of bonding the transparent protective film to the polarizing element via a water-based adhesive;
The polyvinyl alcohol resin film has a boron adsorption rate of 5.70% by mass or more,
The method for producing the aqueous adhesive has an ethanol concentration of 16% by mass or more and 50% by mass or less.
[2] The manufacturing method according to [1], wherein the polarizing element has a boron content of 4.0% by mass or more and 8.0% by mass or less.
[3] The manufacturing method according to [1] or [2], wherein the water-based adhesive contains a polyvinyl alcohol resin.
[4] The manufacturing method according to [3], wherein the water-based adhesive has a concentration of the polyvinyl alcohol resin of 2.85% by mass or more.
[5] In the polarizing plate, the adhesive layer formed of the water-based adhesive interposed between the polarizing element and the transparent protective film has a thickness of 0.01 μm or more and 7 μm or less, [1] to [4] ] The manufacturing method according to any one of the above.

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 of the polarizing element is increased.

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

[Manufacturing method of polarizing plate]
The present invention provides a method for manufacturing a polarizing plate having a polarizing element and a transparent protective film laminated on at least one surface of the polarizing element, the method comprising: a polyvinyl alcohol resin film (hereinafter referred to as "PVA resin film"). A polarizing element manufacturing process of obtaining a polarizing element from the polarizing element (also referred to as "polarizing element"), and a bonding process of bonding the transparent protective film to the polarizing element via a water-based adhesive. The PVA resin film has a boron adsorption rate of 5.70% by mass or more. The water-based adhesive has an ethanol concentration of 16% by mass or more and 50% by mass or less. Embodiments of the present invention will be described below, but the present invention is not limited to the following embodiments.

<Polarizing element manufacturing process>
In this embodiment, the polarizing element has a dichroic dye (iodine or dichroic dye) adsorbed and oriented on a uniaxially stretched polyvinyl alcohol resin film.

In this embodiment, a polarizing element is produced using a polyvinyl alcohol resin film with a boron adsorption rate of 5.70% by mass or more. By using such a PVA-based resin film, even if the polarizing plate is exposed to a high-temperature environment, for example, at a temperature of 105° C., the transmittance is less likely to decrease. Moreover, it is preferable that the boron adsorption rate of the PVA-based resin film is 10% by mass or less.

By using a PVA resin film with a boron adsorption rate as described above, it is possible to avoid increasing the concentration of boric acid in the crosslinking treatment bath in the polarizing element manufacturing process, and also to shorten the processing time for crosslinking treatment. Therefore, it becomes easier to obtain a desired polarizing element, and the productivity of the polarizing element can also be improved. When the boron adsorption rate of the PVA-based resin is 10% by mass or less, an appropriate amount of boron is incorporated into the PVA-based resin film, making it easy to reduce the shrinkage force of the polarizing element. As a result, when incorporated into an image display device, problems such as peeling between the polarizing plate and other members such as the front plate are less likely to occur. In addition, if the boron adsorption rate of the PVA resin film is less than 5.70% by mass, the transmittance tends 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 Examples below.

The boron adsorption rate of a PVA-based resin film is a characteristic that reflects the spacing between molecular chains and the crystal structure in the PVA-based resin film. A PVA resin film with a boron adsorption rate of 5.70% by mass or more has a wider spacing between molecular chains than a PVA resin film with a boron adsorption rate of less than 5.70% by mass. It is thought that there are few crystals. Therefore, it is presumed that boron easily enters the PVA-based resin film and that polyenization is easily prevented in a high-temperature environment.

The boron adsorption rate of the PVA-based resin film can be adjusted, for example, by pre-processing the PVA-based resin film at the raw material stage, such as hot water treatment, acidic solution treatment, ultrasonic irradiation treatment, radiation irradiation treatment, etc. I can do it. These treatments can widen the spacing between molecular chains and destroy the crystal structure in the PVA resin film. Examples of the hot water treatment include immersion in pure water at 30° C. to 100° C. for 1 second to 90 seconds and drying. Examples of the acidic solution treatment include immersion in a boric acid aqueous solution having a concentration of 10% by mass to 20% by mass for 1 second to 90 seconds and drying. 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 200 W to 500 W for 30 seconds to 10 minutes. Sonication can be performed in a solvent such as water.

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

These PVA-based resins may be modified; for example, polyvinyl formal, polyvinyl acetal, polyvinyl butyral, etc. modified with aldehydes may also be used.

In the present invention, as a starting material for producing a polarizing element, an unstretched polyvinyl alcohol resin film (original film) having 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 even more preferably 30 μm or less film). This makes it possible to obtain a thin film polarizing element, for which market demand is increasing. The width of the raw film is not particularly limited, and can be, for example, about 400 to 6000 mm. The raw film is prepared, for example, as a roll (original roll) of a long unstretched polyvinyl alcohol resin film. The original film may be a commercially available product or may be obtained by film forming, and the film forming method is not particularly limited, and known methods such as melt extrusion and solvent casting may be employed. can.

Further, the PVA resin film used in the present invention may be laminated on a base film that supports the PVA resin film. It may also be prepared as a laminated film with a resin film. In this case, the PVA-based resin film can be produced, for example, by applying a coating solution containing a PVA-based resin to at least one surface of the base film and then drying the coating solution.

As the base film, for example, a film made of thermoplastic resin can be used. A specific example is a film made of a translucent thermoplastic resin, preferably an optically transparent thermoplastic resin, such as a chain polyolefin resin (polypropylene resin, etc.), a cyclic polyolefin resin, etc. Polyolefin resins such as (norbornene resins, etc.); Cellulose resins such as triacetylcellulose and diacetylcellulose; Polyester resins such as polyethylene terephthalate and polybutylene terephthalate; Polycarbonate resins; Methyl methacrylate resins, etc. (meth)acrylic resin; polystyrene resin; polyvinyl chloride resin; acrylonitrile/butadiene/styrene resin; acrylonitrile/styrene resin; polyvinyl acetate resin; polyvinylidene chloride resin; polyamide resin; polyacetal resin Resin; modified polyphenylene ether resin; polysulfone resin; polyether sulfone resin; polyarylate resin; polyamideimide resin; polyimide resin and the like.

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

The polarizing element is manufactured by unwinding the above-mentioned long original film from the original film roll and continuously transporting it along the film transport path of the polarizing element manufacturing apparatus, and then applying the processing liquid (hereinafter referred to as A long polarizing element can be continuously manufactured by performing a drying process after performing a predetermined treatment process after immersing the polarizing element in a "processing bath" and then pulling it out. Note that the treatment process is not limited to the method of immersing the film in a treatment bath as long as the treatment is carried out by bringing the treatment liquid into contact with the film, and the treatment liquid can be applied to the film surface by spraying, flowing, dropping, etc. The method may be one in which the film is processed by When the treatment step is performed by dipping the film in a treatment bath, the number of treatment baths used in one treatment step is not limited to one, and the film can be immersed in two or more treatment baths in sequence. One processing step may be completed.

Examples of the treatment liquid include a swelling liquid, a staining liquid, a crosslinking liquid, a washing liquid, and the like. The above-mentioned processing steps include a swelling step in which a swelling solution is brought into contact with the original film to perform a swelling treatment, a dyeing step in which a dyeing solution is brought into contact with the film after the swelling treatment, and a dyeing step in which a dyeing solution is brought into contact with the film after the swelling treatment; Examples include a crosslinking process in which a crosslinking liquid is brought into contact with the film to perform a crosslinking process, and a cleaning process in which a cleaning liquid is brought into contact with the film after the crosslinking process and a cleaning process is performed. Further, between a series of these processing steps (that is, before or after any one or more processing steps and/or during any one or more processing steps), a wet or dry uniaxial stretching process can be performed. Other processing steps may be added as necessary.

Hereinafter, an example of a method for manufacturing a polarizing element according to the present invention will be described in detail with reference to FIG. FIG. 1 is a cross-sectional view schematically showing an example of a polarizing element manufacturing method and a polarizing element manufacturing apparatus used therein according to the present invention. The polarizing element manufacturing apparatus shown in FIG. 1 transports an original (unstretched) film 10 made of polyvinyl alcohol resin along a film transport path while continuously unwinding it from an original roll 11. A swelling bath (swelling liquid contained in the swelling tank) 13, a dyeing bath (staining liquid contained in the dyeing tank) 15, and a first crosslinking bath (a first crosslinking bath contained in the crosslinking tank) are provided on the conveyance path. Cross-linking liquid) 17a, second cross-linking bath (second cross-linking liquid stored in a cross-linking tank) 17b, and cleaning bath (cleaning liquid stored in a cleaning tank) 19 are passed in sequence, and finally passed through a drying oven 21. It is configured to allow The obtained polarizing element 23 can be transported as it is, for example, to the next polarizing plate production process (a process 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 FIG. 1 indicate the transport direction of the film.

In the description of FIG. 1, "processing tank" is a generic term including a swelling tank, dyeing tank, crosslinking tank, and washing tank, and "processing liquid" is a generic term including a swelling solution, dyeing solution, crosslinking solution, and washing solution, "Processing bath" is a general term that includes swelling baths, dyeing baths, crosslinking baths, and cleaning baths. The swelling bath, dyeing bath, crosslinking bath, and washing bath respectively constitute a swelling section, a dyeing section, a crosslinking section, and a washing section in the manufacturing apparatus of the present invention.

In addition to the above-mentioned processing bath, the film conveyance path of the polarizing element manufacturing apparatus includes guide rolls 30 to 48, 60, and 61 that support the conveyed film or can further change the film conveyance direction, and the conveyed film. It can be constructed by arranging nip rolls 50 to 55 at appropriate positions, which can press and nip and apply driving force to the film by rotation, or can further change the film transport direction. Guide rolls and nip rolls can be placed before and after each treatment bath or in the treatment bath, thereby allowing the film to be introduced into and immersed in the treatment bath and pulled out from the treatment bath (see FIG. 1). For example, the film can be immersed in each treatment bath by providing one or more guide rolls in each treatment bath and transporting the film along these guide rolls.

In the polarizing element manufacturing apparatus shown in FIG. 1, nip rolls are arranged before and after each processing bath (nip rolls 50 to 54), and thereby, nip rolls arranged before and after each of the processing baths are arranged in one or more processing baths. It is now possible to perform inter-roll stretching in which longitudinal uniaxial stretching is performed with a peripheral speed difference between the rolls. Each step will be explained below.

(swelling process)
The swelling step is performed for the purposes of removing foreign matter from the surface of the raw film 10, removing plasticizers in the raw film 10, imparting dyeability, plasticizing the raw film 10, and the like. The processing conditions are determined within a range in which the objective can be achieved and in which problems such as extreme dissolution and devitrification of the original film 10 do not occur.

Referring to FIG. 1, in the swelling step, the raw film 10 is continuously unwound from the raw roll 11 and conveyed along the film transport path, and the raw film 10 is immersed in a swelling bath 13 for a predetermined time. , and then by retrieving. In the example of FIG. 1, the raw film 10 is conveyed along the film conveyance path constructed by the guide rolls 60, 61 and the nip roll 50 from when the raw film 10 is unwound until it is immersed in the swelling bath 13. be done. In the swelling process, the film is transported along a film transport path constructed by guide rolls 30 to 32 and nip rolls 51.

Swelling liquids in the swelling bath 13 include, in addition to pure water, boric acid (Japanese Unexamined Patent Publication No. 10-153709), chlorides (Japanese Unexamined Patent Publication No. 06-281816), inorganic acids, inorganic salts, water-soluble organic solvents, and alcohol. It is also possible to use an aqueous solution to which 0.01 to 10% by mass of the following compounds are added.

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 raw film 10 is preferably about 10 to 300 seconds, more preferably about 20 to 200 seconds. Further, when the raw film 10 is a polyvinyl alcohol resin film stretched in advance in gas, 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 raw film 10 is preferably about 30 to 300 seconds, more preferably about 60 to 240 seconds.

In the swelling process, the problem that the raw film 10 swells in the width direction and wrinkles are likely to occur in the film tends to occur. As one means for conveying the film while removing wrinkles, it is possible to use a roll having a width-expanding function such as an expander roll, spiral roll, or crown roll as the guide rolls 30, 31, and/or 32, or use a cross guider or a bend bar. , or using other widening devices such as tenter clips. Another means for suppressing the occurrence of wrinkles is to perform a stretching process. For example, the uniaxial stretching process can be performed in the swelling bath 13 using the difference in circumferential speed between the nip rolls 50 and 51.

In the swelling treatment, the film swells and expands in the film transport direction, so if the film is not actively stretched, the film is placed before and after the swelling bath 13, for example, in order to eliminate sagging of the film in the transport direction. It is preferable to take measures such as controlling the speed of the nip rolls 50, 51. In addition, in order to stabilize the transport of the film in the swelling bath 13, the water flow in the swelling bath 13 is controlled by an underwater shower, and an EPC device (Edge Position
It is also useful to use a control device: a device that detects the edge of the film and prevents the film from meandering.

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

(dying process)
The dyeing step is performed for the purpose of adsorbing and orienting the dichroic dye to the polyvinyl alcohol resin film after the swelling treatment. The processing conditions are determined within a range in which the objective can be achieved and in which problems such as extreme dissolution and devitrification of the film do not occur. Referring to FIG. 1, the dyeing process involves transporting the film along a film transport path constructed by nip rolls 51, guide rolls 33 to 36, and nip rolls 52, and transporting the film after swelling treatment in a dyeing bath 15 (accommodated in a dyeing tank). This can be carried out by immersing the sample in a treatment liquid for a predetermined period of time and then pulling it out. In order to improve the dyeability of the dichroic dye, the film subjected to the dyeing process is preferably a film that has been subjected to at least some uniaxial stretching treatment, or instead of the uniaxial stretching treatment before the dyeing treatment, or In addition to the uniaxial stretching process before the dyeing process, it is preferable to perform the uniaxial stretching process during the dyeing process.

When using iodine as a dichroic dye, the dyeing solution in the dyeing bath 15 has a concentration of, for example, iodine/potassium iodide/water in a weight ratio of 0.003 to 0.3/0.1 to 10/100. An aqueous solution can be used. Instead of potassium iodide, other iodides such as zinc iodide may be used, or potassium iodide and other iodides may be used together. Further, compounds other than iodide, such as boric acid, zinc chloride, cobalt chloride, etc., may be coexisting. When adding boric acid, it is distinguished from the crosslinking treatment described below in that it contains iodine, and if the aqueous solution contains 0.003 parts by weight or more of iodine per 100 parts by weight of water, it can be used as dyeing bath 15. It can be considered. The temperature of the dyeing bath 15 when dipping the film is usually about 10 to 45°C, preferably 10 to 40°C, more preferably 20 to 35°C, and the immersion time of the film is usually 30 to 600 seconds. about 60 to 300 seconds, preferably 60 to 300 seconds.

When using a water-soluble dichroic dye as the dichroic pigment, the dyeing solution in the dyeing bath 15 is, for example, an aqueous solution having a concentration of dichroic dye/water = 0.001 to 0.1/100 in weight ratio. can be used. This dyeing bath 15 may contain a dyeing aid, for example, an inorganic salt such as sodium sulfate, a surfactant, and the like. 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 dipping the film is, for example, about 20 to 80°C, preferably 30 to 70°C, and the immersion time of the film is usually about 30 to 600 seconds, preferably about 60 to 300 seconds. be.

As mentioned above, in the dyeing process, the film can be uniaxially stretched in the dyeing bath 15. The uniaxial stretching of the film can be carried out by a method such as creating a difference in peripheral speed between the nip rolls 51 and 52 placed before and after the dyeing bath 15.

In the dyeing process, guide rolls 33, 34, 35 and/or 36 are equipped with expander rolls, spiral rolls, crown rolls, etc. in order to transport the polyvinyl alcohol resin film while removing wrinkles from the film, as in the swelling process. Rolls with a width-spreading function can be used, or other width-spreading devices such as cross guiders, bend bars, tenter clips, etc. can be used. Another means for suppressing the occurrence of wrinkles is to perform a stretching treatment, similar to the swelling treatment.

In the example shown in FIG. 1, the film pulled out from the dyeing bath 15 passes through a guide roll 36, a nip roll 52, and a guide roll 37 in order and is introduced into the crosslinking bath 17.

(Crosslinking process)
The crosslinking step is a process performed for the purpose of making the film water resistant and adjusting the hue (preventing the film from becoming bluish, etc.). In the example shown in FIG. 1, two crosslinking baths are arranged as crosslinking baths for performing the crosslinking process, the first crosslinking process for the purpose of water resistance is performed in the first crosslinking bath 17a, and the second crosslinking bath is for the purpose of hue adjustment. The crosslinking step is performed in the second crosslinking bath 17b. Referring to FIG. 1, in the first crosslinking step, the film is conveyed along a film conveyance path constructed by nip rolls 52, guide rolls 37 to 40, and nip rolls 53a. This can be carried out by immersing the dyed film in (1) crosslinking solution for a predetermined period of time and then pulling it out. In the second crosslinking step, the film is transported along a film transport path constructed by the nip rolls 53a, guide rolls 41 to 44, and nip rolls 53b, and the first This can be carried out by immersing the film after the crosslinking process for a predetermined period of time and then pulling it out. Hereinafter, the term crosslinking bath includes both the first crosslinking bath 17a and the second crosslinking bath 17b, and the term crosslinking liquid includes both the first crosslinking liquid and the second crosslinking liquid.

As the crosslinking liquid, a solution in which a crosslinking agent is dissolved in a solvent can be used. Examples of the crosslinking agent include boron compounds such as boric acid and borax, glyoxal, and glutaraldehyde. These may be used alone or in combination of two or more. As the solvent, for example, water can be used, but it may also contain an organic solvent that is compatible with water. Although the concentration of the crosslinking agent in the crosslinking solution is not limited thereto, it is preferably in the range of 1 to 20% by weight, more preferably 6 to 15% by weight.

The crosslinking liquid may be an aqueous solution containing, for example, 1 to 10 parts by weight of boric acid per 100 parts by weight of water. When the dichroic dye used in the dyeing treatment is iodine, the crosslinking liquid preferably contains iodide in addition to boric acid, and the amount thereof is, for example, 1 to 30 parts by weight per 100 parts by weight of water. It can be done. Examples of iodides include potassium iodide and zinc iodide. Further, compounds other than iodide, such as zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, and sodium sulfate, may be present.

In the crosslinking treatment, the concentrations of boric acid and iodide and the temperature of the crosslinking bath 17 can be changed as appropriate depending on the purpose. For example, in the case of the first crosslinking solution whose purpose in crosslinking treatment is water resistance through crosslinking, it can be an aqueous solution having a concentration of boric acid/iodide/water in a weight ratio of 3 to 10/1 to 20/100. If necessary, other crosslinking agents may be used in place of boric acid, or boric acid and other crosslinking agents may be used in combination. The temperature of the first crosslinking bath 17a when dipping the film is usually about 50 to 70°C, preferably 53 to 65°C, and the immersion time of the film is usually about 10 to 600 seconds, preferably 20 to 300 seconds. , more preferably 20 to 200 seconds. Further, when dyeing treatment and first crosslinking treatment are performed in this order on a pre-stretched polyvinyl alcohol resin film before swelling treatment, the temperature of the first crosslinking bath 17a is usually about 50 to 85°C, preferably about 55 to 85°C. The temperature is 80°C.

In the second crosslinking liquid for the purpose of hue adjustment, for example, when iodine is used as a dichroic dye, a concentration by weight of boric acid/iodide/water = 1 to 5/3 to 30/100 is used. can do. The temperature of the second crosslinking bath 17b during immersion of the film 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 crosslinking treatment may be performed multiple times, and is usually performed 2 to 5 times. In this case, the composition and temperature of each crosslinking bath used may be the same or different within the above range. The crosslinking treatment for water resistance and the crosslinking treatment for hue adjustment may be performed in multiple steps.

Uniaxial stretching can also be performed in the first crosslinking bath 17a by utilizing the difference in peripheral speed between the nip rolls 52 and 53a. Furthermore, the uniaxial stretching process can be performed in the second crosslinking bath 17b by utilizing the difference in circumferential speed between the nip rolls 53a and 53b.

In the crosslinking treatment, in order to convey the polyvinyl alcohol resin film while removing wrinkles from the film as in the swelling treatment, an expander roll and a spiral roll are used in the guide rolls 38, 39, 40, 41, 42, 43 and/or 44. , a roll having a width-expanding function such as a crown roll, or other width-expanding devices such as a cross guider, a bend bar, or a tenter clip may be used. Another means for suppressing the occurrence of wrinkles is to perform a stretching treatment, similar to the swelling treatment.

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

(Washing process)
The example shown in FIG. 1 includes a washing step after the crosslinking step. The cleaning treatment is performed for the purpose of removing excess chemicals such as boric acid and iodine that have adhered to the polyvinyl alcohol resin film. The cleaning step is performed, for example, by immersing the crosslinked polyvinyl alcohol resin film in the cleaning bath 19. Note that the cleaning process is performed by spraying a cleaning liquid onto the film as a shower, or by using a combination of immersion in the cleaning bath 19 and spraying of the cleaning liquid, instead of immersing the film in the cleaning bath 19. You can also do that.

FIG. 1 shows an example in which a polyvinyl alcohol resin film is immersed in a cleaning bath 19 to perform 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 film is usually about 2 to 120 seconds.

In addition, in the cleaning process, for the purpose of transporting the polyvinyl alcohol resin film while removing wrinkles, the guide rolls 45, 46, 47 and/or 48 are rolls having a width-expanding function such as expander rolls, spiral rolls, and crown rolls. or other widening devices such as cross guiders, bend bars, and tenter clips. Furthermore, in the film cleaning process, a stretching process may be performed to suppress the occurrence of wrinkles.

(Stretching process)
As mentioned above, the raw film 10 is subjected to uniaxial stretching in a wet or dry manner during the series of processing steps (that is, before and/or during any one or more processing steps). It is processed. A specific method for the uniaxial stretching process is, for example, to perform longitudinal uniaxial stretching with a peripheral speed difference between two nip rolls (for example, two nip rolls placed before and after the processing bath) that constitute the film transport path. Stretching, hot roll stretching as described in Japanese Patent No. 2731813, tenter stretching, etc. may be used, and inter-roll stretching is preferable. The uniaxial stretching step can be performed multiple times until the polarizing element 23 is obtained from the original film 10. As mentioned above, the stretching treatment is also advantageous in suppressing the occurrence of wrinkles in the film.

The final cumulative stretching ratio of the polarizing element 23 based on the original film 10 is usually about 4.5 to 7 times, preferably 5 to 6.5 times. The stretching process may be performed in any process, and even when the stretching process is performed in two or more processes, the stretching process may be performed in any process.

(drying process)
After the washing step, it is preferable to perform a process of drying the PVA resin film. Drying of the film is not particularly limited, but can be performed using a drying oven 21 as in the example shown in FIG. The drying oven 21 may include, for example, a hot air dryer. 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 resin film can also be performed using a far-infrared heater.

(Other processing steps for PVA resin film)
Processes other than those described above can also be added. Examples of treatments that may be added include immersion treatment in an iodide aqueous solution that does not contain boric acid (complementary color treatment), and immersion treatment in an aqueous solution that does not contain boric acid and contains zinc chloride etc. (zinc processing).

(Polarizing element)
The thickness of the polarizing element 23 obtained as described above is preferably 5 to 50 μm, more preferably 8 to 28 μm, even more preferably 12 to 22 μm, and most preferably 12 to 15 μm. When the thickness of the polarizing element is 50 μm or less, it is possible to suppress the influence of polyenization of PVA-based resin on deterioration of optical properties in a high-temperature environment, and when the thickness of the polarizing element is 5 μm or more, it is possible to suppress the effect of polyene conversion on optical properties in a high-temperature environment. This makes it easy to create a configuration that achieves the optical characteristics of.

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 such a range, the in-plane retardation distribution that occurs due to contraction of the polarizing element in a high-temperature environment becomes small, and the display quality of the display device becomes good. Further, by setting the thickness of the polarizing element to 12 μm or more, it becomes easier to maintain polarization characteristics in a high humidity environment.

The content of boron in the polarizing element is preferably 4.0% by mass or more and 8.0% by mass or less, more preferably 4.2% by mass or more and 7.0% by mass or less, and even more preferably 4.4% by mass or less. It is not less than 6.0% by mass and not more than 6.0% by mass. When the boron content of the polarizing element is 4.0% by mass or more, the transmittance of the polarizing element is unlikely to decrease even when exposed to a high temperature environment, for example, a high temperature environment of 105°C. It is presumed that this is because when the boron content is 4.0% by mass or more, polyenization is less likely to occur even in a high-temperature environment, and a decrease in transmittance is suppressed. On the other hand, if the boron content of the polarizing element exceeds 8.0% by mass, the shrinkage force of the polarizing element becomes large, and the shrinkage force of the polarizing element becomes large, causing damage to other members such as the front plate to be bonded together when incorporated into an image display device. Problems such as peeling between the two may occur. The boron content in the polarizing element can be calculated as the mass fraction (mass %) of boron relative to the mass of the polarizing element, for example, by high frequency inductively coupled plasma (ICP) emission spectrometry. Boron is thought to exist in the polarizing element in the form of boric acid or a crosslinked structure formed with the constituent elements of the polyvinyl alcohol resin, but the boron content here refers to the boron content as boron atoms (B). It is a value.

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

The visibility correction single transmittance Ty of the polarizing element is preferably 40 to 47%, more preferably 41 to 45%, taking into consideration the balance with the visibility correction polarization degree Py. The visibility correction polarization degree Py is preferably 99.9% or more, more preferably 99.95% or more, and the larger the value is, the more preferable it is.

The obtained polarizing element is subjected to the subsequent lamination step. After the polarizing element manufacturing process, the polarizing element may be sequentially wound onto a take-up roll to form a roll form, or may be directly subjected to the bonding process without being wound up.

<Lamination process>
The bonding step is a step of bonding a transparent protective film (hereinafter also simply referred to as "protective film") to at least one side of the polarizing element manufactured as described above via a water-based adhesive. A polarizing plate is produced through a bonding process.

As a method of laminating a protective film to a polarizing element using a water-based adhesive, an adhesive is applied to one or both of the laminating surfaces of two films to be laminated, and the two films are bonded together through the adhesive layer. One example is a method of overlapping sheets of film. For coating the adhesive, for example, a casting method, a Meyer bar coating method, a gravure coating method, a comma coater method, a doctor blade method, a die coating method, a dip coating method, a spraying method, etc. can be adopted. The casting method is a method in which the film to be laminated is moved approximately vertically, approximately horizontally, or in a diagonal direction between the two, and an adhesive is flowed down and spread on the surface of the film. A film laminate formed by laminating the films with an adhesive layer interposed therebetween is usually pressed from above and below through nip rolls (lamination rolls) or the like.

When bonding a protective film to a polarizing element, the protective film or the bonding surface of the polarizing element is subjected to plasma treatment, corona treatment, ultraviolet irradiation treatment, flame treatment, and saponification treatment to improve adhesion. A treatment for facilitating adhesion such as the following can be performed, and among these, plasma treatment, corona treatment, or saponification treatment is preferably performed. For example, when the protective film is made of a cyclic polyolefin resin, the bonding surface of the protective film is usually subjected to plasma treatment or corona treatment. Further, when the protective film is made of cellulose ester resin, the bonding surface of the protective film is usually subjected to saponification treatment. Examples of the saponification treatment include a method of immersion in an alkaline aqueous solution such as sodium hydroxide or potassium hydroxide.

After carrying out the above film lamination, it is preferable to carry out a drying step of drying the film laminate in order to remove water contained in the adhesive layer made of a water-based adhesive. Drying can be performed, for example, by introducing the film laminate into a drying oven. The drying temperature (temperature of the drying oven) is preferably 30 to 90°C. When the temperature is lower than 30°C, the protective film tends to be easily peeled off from the polarizing element. Furthermore, if the drying temperature exceeds 90° C., the polarization performance of the polarizing element may deteriorate due to heat. The drying time can be about 10 to 1000 seconds, and from the viewpoint of productivity, it is preferably 60 to 750 seconds, more preferably 150 to 600 seconds.

After the drying step, a curing step may be performed in which the material is cured for about 12 to 600 hours at room temperature or a slightly higher temperature, for example, about 20 to 45°C. The curing temperature is generally set lower than the drying temperature.

(water-based adhesive)
A water-based adhesive is used to bond the polarizing element and the protective film. Water-based adhesives are those in which adhesive components are dissolved or dispersed in water. The water-based adhesive used in this embodiment has an ethanol concentration of 16% by mass or more and 50% by mass or less, preferably 18% by mass or more and 48% by mass or less, and more preferably 20% by mass or more and 46% by mass or less. It is more preferably 20% by mass or more and 35% by mass or less.

When the water-based adhesive contains ethanol within the above range, it is possible to suppress discoloration during the manufacturing process of the polarizing plate. The discoloration here refers to the color unevenness that is observed when polarizing plates are arranged in crossed nicols and high-intensity light is transmitted through them.More specifically, two polarizing plates are arranged in crossed nicols. This refers to color unevenness in which brownish areas are observed when white light is transmitted through stacked polarizing plates. Such brown discoloration may be observed scattered within the polarizing plate, or may be observed only in a specific portion. In addition, such brown discolored spots may be observed at multiple locations within the polarizing plate, or may be observed at only one location. Although the size of the brown discolored area varies, it may be, for example, 100 to 4000 μm in diameter.
Color unevenness is observed when a polarizing element and a protective film are bonded together using a water-based adhesive, and is observed noticeably when the polarizing element has a high boron content and the water-based adhesive contains a PVA-based resin. Therefore, the mechanism by which color unevenness occurs can be considered as follows. The boric acid in the polarizing element is easily eluted into the water in the water-based adhesive, and the eluted boric acid reacts with the PVA resin contained in the water-based adhesive. It is presumed that such reactants cause non-uniformity within the water-based adhesive, and such non-uniformity becomes apparent as unevenness as the water-based adhesive continues to dry.

Although the mechanism by which a water-based adhesive can suppress discoloration by containing ethanol within the above range is not clear, the ethanol present in the water-based adhesive causes the boric acid in the polarizing element to elute into the water-based adhesive. It is presumed that this contributes to at least one of the following: suppression of the reaction between boric acid and PVA resin within the water-based adhesive.

The water-based adhesive is not particularly limited as long as it contains ethanol within the above range, but examples include water-based adhesives containing PVA resin or urethane resin as a main component. A water-based adhesive containing a PVA-based resin is preferably used because the effects of the present invention are remarkable when it is used. The thickness of the adhesive layer formed from 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 0.01 μm or more and 1.0 μm or less, more preferably 0.02 μm or more and 0.8 μm or less.

When polyvinyl alcohol resin is used as the main component of the adhesive, the polyvinyl alcohol resin may include partially saponified polyvinyl alcohol, completely saponified polyvinyl alcohol, carboxyl group-modified polyvinyl alcohol, acetoacetyl group-modified polyvinyl alcohol, and methylol group-modified polyvinyl alcohol. Modified polyvinyl alcohol resins such as modified polyvinyl alcohol and amino group-modified polyvinyl alcohol may also be used. Polyvinyl alcohol-based resins include vinyl alcohol homopolymers obtained by saponifying polyvinyl acetate, which is a homopolymer of vinyl acetate, as well as vinyl alcohol homopolymers obtained by copolymerizing vinyl acetate with other monomers that can be copolymerized with it. A polyvinyl alcohol copolymer obtained by saponifying the polymer may also be used.

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 resin in the adhesive is usually 1 to 10% by weight, preferably 1 to 5% by weight, and more preferably 2.85 to 5% by weight.

Adhesives made of aqueous solutions of PVA resins contain curable components and crosslinking agents such as polyvalent aldehydes, melamine compounds, zirconia compounds, zinc compounds, glyoxal, and water-soluble epoxy resins to improve adhesive properties. It is preferable to add. Examples of water-soluble epoxy resins include polyamide polyamine epoxy resins obtained by reacting epichlorohydrin with polyamide amines obtained by reacting polyalkylene polyamines such as diethylene triamine and triethylene tetramine with dicarboxylic acids such as adipic acid. can be suitably used. Commercially available products of such polyamide polyamine epoxy resins include "SUMIREZ RESIN 650" (manufactured by Taoka Chemical Co., Ltd.), "SUMIRAZE RESIN 675" (manufactured by Taoka Chemical Co., Ltd.), and "WS-525" (Japan (manufactured by PMC Corporation), etc. The amount of these curable components and crosslinking agents added (when added together as a curable component and crosslinking agent, the total amount) is usually 1 to 100 parts by weight, preferably 1 part by weight, per 100 parts by weight of the PVA resin. ~50 parts by weight. If the amount of the curable component or crosslinking agent added is less than 1 part by weight per 100 parts by weight of the polyvinyl alcohol resin, the effect of improving adhesion tends to be small; If the amount of the crosslinking agent added exceeds 100 parts by weight based on 100 parts by weight of the PVA resin, the adhesive layer tends to become brittle.

When the PVA resin is an acetoacetyl group-modified PVA resin, the crosslinking agent is preferably glyoxal, glyoxylate, or methylolmelamine, and preferably glyoxal or glyoxylate. More preferred is glyoxal, particularly preferred.

Furthermore, when a urethane resin is used as the main component of the adhesive, an example of a suitable adhesive composition is a mixture of a polyester-based ionomer type urethane resin and a compound having a glycidyloxy group. A polyester-based ionomer type urethane resin is a urethane resin having a polyester skeleton into which a small amount of an ionic component (hydrophilic component) is introduced. Such an ionomer type urethane resin is suitable as a water-based adhesive because it emulsifies directly in water to form an emulsion without using an emulsifier.

The water-based adhesive contains ethanol and can also contain organic solvents other than ethanol. The organic solvent is preferably alcohol in terms of its miscibility with water, and may also include methanol, for example. From the viewpoint of improving heat resistance, water-based adhesives are recommended to use urea compounds such as urea, urea derivatives, thiourea, and thiourea derivatives; reducing agents such as ascorbic acid, erythorbic acid, thiosulfate, and sulfite; maleic acid, and phthalate. dicarboxylic acids such as acids; ammonium compounds such as ammonium sulfate, ammonium chloride, ammonium carbonate, and ammonium fluoride; dextrins such as α-cyclodextrin, β-cyclodextrin, and γ-cyclodextrin; may contain blocked isocyanate compounds having a nitroxide group; nitroxy radicals such as N-oxyl compounds; compounds having a nitroxide group, etc. While some urea compounds have low solubility in water, some have sufficient solubility in alcohol. In that case, one preferred embodiment is 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. be.

(Urea-based compounds)
When the adhesive layer contains a urea compound, the urea compound is at least one selected from urea, urea derivatives, thiourea, and thiourea derivatives. As a method for incorporating a urea-based compound into the adhesive layer, it is preferable to incorporate the urea-based compound into the above-mentioned adhesive. Note that during the process of forming an adhesive layer from the adhesive through a drying process, etc., a part of the urea-based compound may migrate from the adhesive layer to the polarizing element or the like. That is, the polarizing element may contain a urea-based compound. Urea compounds include water-soluble ones and poorly water-soluble ones, and either type of urea compound can be used in the adhesive of this embodiment. When a poorly water-soluble urea compound is used in a water-based adhesive, it is preferable to devise a dispersion method after forming the adhesive layer so as to prevent an increase in haze.

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, and preferably 1 to 200 parts by mass, based on 100 parts by mass of the PVA resin. It is more preferable that the amount is 3 to 100 parts by mass.

(urea derivative)
A urea derivative is a compound in which at least one of the four hydrogen atoms of a urea molecule is substituted with a substituent. In this case, the substituent is not particularly limited, but a substituent consisting of a carbon atom, a hydrogen atom, and an oxygen atom is preferable.

Specific examples of urea derivatives include monosubstituted ureas such as methylurea, ethylurea, propylurea, butylurea, isobutylurea, N-octadecylurea, 2-hydroxyethylurea, hydroxyurea, acetylurea, allylurea, and 2-propynyl. Examples include urea, cyclohexyl urea, phenyl urea, 3-hydroxyphenylurea, (4-methoxyphenyl) urea, benzyl urea, benzoyl urea, o-tolylurea, and p-tolylurea.
As the 2-substituted urea, 1,1-dimethylurea, 1,3-dimethylurea, 1,1-diethylurea, 1,3-diethylurea, 1,3-bis(hydroxymethyl)urea, 1,3-tert- Examples include butyl urea, 1,3-dicyclohexyl urea, 1,3-diphenylurea, 1,3-bis(4-methoxyphenyl) urea, and 1-acetyl-3-methyl urea.
Examples of the 4-substituted urea include tetramethylurea, 1,1,3,3-tetraethylurea, 1,1,3,3-tetrabutylurea, and 1,3-dimethoxy-1,3-dimethylurea.

(thiourea derivative)
A thiourea derivative is a compound in which at least one of the four hydrogen atoms of a thiourea molecule is substituted with a substituent. In this case, the substituent is not particularly limited, but a substituent consisting of a carbon atom, a hydrogen atom, and an oxygen atom is preferable.

Specific examples of thiourea derivatives include monosubstituted thiourea such as N-methylthiourea, ethylthiourea, propylthiourea, isopropylthiourea, 1-butylthiourea, cyclohexylthiourea, N-acetylthiourea, N-allylthiourea, (2 -methoxyethyl)thiourea, N-phenylthiourea, (4-methoxyphenyl)thiourea, N-(2-methoxyphenyl)thiourea, N-(1-naphthyl)thiourea, (2-pyridyl)thiourea, Examples include o-tolylthiourea and p-tolylthiourea.
As the 2-substituted thiourea, 1,1-dimethylthiourea, 1,3-dimethylthiourea, 1,1-diethylthiourea, 1,3-diethylthiourea, 1,3-dibutylthiourea, 1,3-diisopropylthiourea, 1 , 3-dicyclohexylthiourea, N,N-diphenylthiourea, N,N'-diphenylthiourea, 1,3-di(o-tolyl)thiourea, 1,3-di(p-tolyl)thiourea, Examples include 1-benzyl-3-phenylthiourea, 1-methyl-3-phenylthiourea, and N-allyl-N'-(2-hydroxyethyl)thiourea.
Examples of the 3-substituted thiourea include trimethylthiourea, and examples of the 4-substituted thiourea include tetramethylthiourea and 1,1,3,3-tetraethylthiourea.

Among the urea compounds, urea derivatives or thiourea derivatives are preferred, and urea derivatives are more preferred. Among the urea derivatives, monosubstituted urea or disubstituted urea is preferable, and monosubstituted urea is more preferable. Disubstituted ureas include 1,1-substituted ureas and 1,3-substituted ureas, with 1,3-substituted ureas being more preferred.

(Transparent protective film)
The protective film used in this embodiment is attached 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 and may be formed into a laminated structure in which a plurality of layers are laminated. The thickness of the protective film is preferably thin from the viewpoint of optical properties, but if it is too thin, the strength will decrease and the processability will be poor. A suitable film thickness is 5 to 100 μm, preferably 10 to 80 μm, and more preferably 15 to 70 μm.

The protective film may be a cellulose acylate film, a polycarbonate resin film, a cycloolefin resin film such as norbornene, a (meth)acrylic polymer film, or a polyester resin film such as polyethylene terephthalate. I can do it. In the case of a configuration in which the polarizing element has protective films on both sides, when bonding is performed using a water-based adhesive such as PVA adhesive, the protective film on at least one side should be a cellulose acylate film or (meth)acrylic film in terms of moisture permeability. Any type of polymer film is preferred, and cellulose acylate film is particularly preferred.

At least one of the protective films may have a retardation function for the purpose of viewing angle compensation, etc. In that case, the film itself may have a retardation function, or it may have a separate retardation layer. or a combination of both.
In addition, although we have described a configuration in which the film with a retardation function is bonded directly to the polarizing element via an adhesive, it may also be attached via an adhesive or an adhesive via another protective film bonded to the polarizing element. It is also possible to have a structure in which they are bonded together.

[Configuration 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. For image display devices, if the polarizing plate has an interlayer filling configuration in which both sides of the polarizing plate are in contact with a layer other than an air layer, specifically a solid layer such as an adhesive layer, the transmittance will decrease in a high-temperature environment. tends to decrease. In the image display device using the polarizing plate of this embodiment, even with the interlayer filling configuration, it is possible to suppress a decrease in the transmittance of the polarizing plate in a high-temperature environment. An example of an image display device is a configuration including an image display cell, a first adhesive layer laminated on the viewing side surface of the image display cell, and a polarizing plate laminated on the viewing side surface of the first adhesive layer. be done. Such an 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, in the polarizing plate of this embodiment, a transparent member is arranged on the viewing side of the image display device, the polarizing plate and the image display cell are bonded together by a first adhesive layer, and the polarizing plate and the transparent member are bonded together by a second adhesive layer. It is suitably used in an image display device having an interlayer filling structure in which the adhesive layers are bonded together. In this specification, either one or both of the first adhesive layer and the second adhesive layer may be simply referred to as "adhesive layer." Note that the members used for bonding the polarizing plate and the image display cell and the members used for bonding the polarizing plate and the transparent member are not limited to adhesive layers, but may be adhesive layers. Good too.

<Image display cell>
Examples of the image display cell include a liquid crystal cell and an organic EL cell. Liquid crystal cells include reflective liquid crystal cells that use external light, transmissive liquid crystal cells that use light from light sources such as backlights, and transflective liquid crystal cells that use both external light and light from the light source. Any liquid crystal cell may be used. If the liquid crystal cell uses light from a light source, the image display device (liquid crystal display device) has a polarizing plate placed on the side opposite to the viewing side of the image display cell (liquid crystal cell), and a light source is also placed. be done. It is preferable that the polarizing plate on the light source side and the liquid crystal cell are bonded together via a suitable adhesive layer. As a driving method for the liquid crystal cell, any type of driving method can be used, such as VA mode, IPS mode, TN mode, STN mode, or bend alignment (π type).

As the organic EL cell, one in which a transparent electrode, an organic light-emitting layer, and a metal electrode are sequentially laminated on a transparent substrate to form a light-emitting body (organic electroluminescence light-emitting body) is preferably used. The organic light emitting layer is a laminate of various organic thin films, such as a laminate of a hole injection layer made of a triphenylamine derivative or the like and a light emitting layer made of a fluorescent organic solid such as anthracene, or a laminate of these. Various layer configurations can be adopted, such as a laminate of a light emitting layer and an electron injection layer made of a perylene derivative or the like, or a laminate of a hole injection layer, a light emitting layer, and an electron injection layer.

<Attachment of image display cell and polarizing plate>
An adhesive layer (adhesive sheet) is suitably used for bonding the image display cell and the polarizing plate. Among these, a method in which a polarizing plate with an adhesive layer, in which an adhesive layer is attached to one side of the polarizing plate, is bonded to an image display cell is preferable from the viewpoint of workability and the like. The adhesive layer can be attached to the polarizing plate by any suitable method. For example, an adhesive solution of about 10 to 40% by mass is prepared by dissolving or dispersing the base polymer or its composition in a solvent consisting of an appropriate solvent such as toluene or ethyl acetate alone or in a mixture. , a method in which it is attached directly onto a polarizing plate using an appropriate development method such as a casting method or a coating method, or a method in which an adhesive layer is formed on a separator and then transferred to the polarizing plate. .

<Adhesive layer>
The adhesive layer may be composed of one layer or two or more layers, but is preferably composed of one layer. The adhesive layer can be composed of an adhesive composition containing a (meth)acrylic resin, a rubber resin, a urethane resin, an ester resin, a silicone resin, or a polyvinyl ether resin as a main component. Among these, a pressure-sensitive adhesive composition whose base polymer is a (meth)acrylic resin having excellent transparency, weather resistance, heat resistance, etc. is suitable. The adhesive composition may be of an active energy ray-curable type or a thermosetting type.

Examples of the (meth)acrylic resin (base polymer) used in the adhesive composition include butyl (meth)acrylate, ethyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, etc. Polymers or copolymers containing one or more types of (meth)acrylic esters as monomers are preferably used. It is preferable to copolymerize a polar monomer with the base polymer. As polar monomers, (meth)acrylic acid compounds, 2-hydroxypropyl (meth)acrylate compounds, hydroxyethyl (meth)acrylate compounds, (meth)acrylamide compounds, N,N-dimethylaminoethyl (meth)acrylate compounds Examples include monomers having carboxyl groups, hydroxyl groups, amide groups, amino groups, epoxy groups, etc., such as glycidyl (meth)acrylate compounds.

The adhesive composition may contain only the above base polymer, but usually further contains a crosslinking agent. Examples of crosslinking agents include metal ions with a valence of two or more that form carboxylic acid metal salts with carboxyl groups, polyamine compounds that form amide bonds with carboxyl groups, and metal ions that form carboxylic acid metal salts with carboxyl groups. Examples include polyepoxy compounds or polyols that form ester bonds, and polyisocyanate compounds that form amide bonds with carboxyl groups. Among these, polyisocyanate compounds are preferred.

Active energy ray-curable adhesive compositions have the property of being cured by irradiation with active energy rays such as ultraviolet rays or electron beams, and have adhesive properties even before irradiation with active energy rays to form films, etc. It has the property that it can be brought into close contact with an adherend, and its adhesion can be adjusted by curing by irradiation with active energy rays. The active energy ray-curable adhesive composition is preferably an ultraviolet ray-curable adhesive composition. The active energy ray curable adhesive composition further contains an active energy ray polymerizable compound in addition to the base polymer and the crosslinking agent. If necessary, a photopolymerization initiator, a photosensitizer, etc. may be included.

The adhesive composition contains fine particles, beads (resin beads, glass beads, etc.), glass fibers, resins other than the base polymer, tackifiers, fillers (metal powders and other inorganic powders) to impart light scattering properties. etc.), antioxidants, ultraviolet absorbers, dyes, pigments, colorants, antifoaming agents, corrosion inhibitors, photopolymerization initiators, and other additives.

The adhesive layer can be formed by applying a diluted solution of the adhesive composition in an organic solvent onto the surface of a base film, image display cell, or polarizing plate and drying it. The base film is generally a thermoplastic resin film, and a typical example thereof is a separate film that has been subjected to a mold release treatment. The separate film can be, for example, a film made of a resin such as polyethylene terephthalate, polybutylene terephthalate, polycarbonate, polyalate, etc., and the surface on which the adhesive layer is formed has been subjected to a release treatment such as silicone treatment. .

For example, an adhesive layer may be formed by directly applying an adhesive composition to the release-treated surface of a separate film, and this adhesive layer with a separate film may be laminated on the surface of a polarizer. The adhesive composition may be applied directly to the surface of the polarizing plate to form an adhesive layer, and a separate film may be laminated on the outer surface of the adhesive layer.
When providing an adhesive layer on the surface of a polarizing plate, it is preferable to subject the bonding surface of the polarizing plate and/or the bonding surface of the adhesive layer to surface activation treatment, such as plasma treatment or corona treatment. It is more preferable to perform a treatment.
Further, a pressure-sensitive adhesive sheet is prepared by coating a pressure-sensitive adhesive composition on a second separate film to form a pressure-sensitive adhesive layer, and a separate film is laminated on the formed pressure-sensitive adhesive layer. The adhesive layer with a separate film after peeling off the separate film may be laminated on a polarizing plate. The second separate film used has weaker adhesion to the adhesive layer than the separate film and is easily peelable.

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

<Transparent member>
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, a transparent plate having appropriate mechanical strength and thickness is used. Examples of such a transparent plate include a transparent resin plate made of polyimide resin, acrylic resin, or polycarbonate resin, or a glass plate. A functional layer such as an antireflection layer may be laminated on the visible side of the transparent plate. Furthermore, when the transparent plate is a transparent resin plate, a hard coat layer may be laminated to increase physical strength, and a low moisture permeability layer may be laminated to reduce moisture permeability.
As the touch panel, various touch panels such as a resistive film type, a capacitive type, an optical type, an ultrasonic type, etc., a glass plate, a transparent resin plate, etc. having a touch sensor function are used. When a capacitive touch panel is used as the transparent member, it is preferable that a transparent plate made of glass or a transparent resin plate is provided further on the viewing side than the touch panel.

<Lamination of polarizing plate and transparent member>
An adhesive or an active energy ray-curable adhesive is suitably used for bonding the polarizing plate and the transparent member. When an adhesive is used, the adhesive can be applied in any suitable manner. A specific attachment method includes, for example, the method of attaching the adhesive layer used in bonding the image display cell and the polarizing plate described above.

When using an active energy ray-curable adhesive, a dam material is provided to surround the periphery of the image display panel in order to prevent the adhesive solution from spreading before curing, and a transparent member is placed on the dam material. A method is preferably used in which the adhesive solution is injected after the adhesive is placed. After the adhesive solution is injected, alignment and defoaming are performed as necessary, and then active energy rays are irradiated to cure the adhesive solution.

Hereinafter, the present invention will be specifically explained based on Examples. The materials, reagents, amounts of substances, their proportions, operations, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the present invention is not limited to or limited to the following examples.

(1) Measurement of the thickness of the polarizing element:
Measurement was performed using a digital micrometer "MH-15M" manufactured by Nikon Corporation.

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

(3) Measurement of zinc ion content of polarizing element:
Nitric acid was added to a precisely weighed polarizing element, and the solution was acid-decomposed using a microwave sample pretreatment device (ETHOS D) manufactured by Milestone General Co., Ltd., and the resulting solution was used as a measurement solution. The zinc ion content was measured using an Agilent Technologies ICP emission spectrometer (5110 ICP-OES).
) was used to quantify the zinc concentration of the measurement solution, and calculated as the mass of zinc relative to the mass of the polarizing element.

(4) Measurement of boron adsorption rate of PVA resin film:
A PVA resin film cut into 100 mm squares was immersed in pure water at 30°C for 60 seconds, and then immersed in an aqueous solution at 60°C 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 80° C. oven for 11 minutes. The humidity was controlled in an environment of 23° C. and 55% RH for 24 hours to obtain a boron-containing PVA film. 0.2 g of the boron-containing PVA resin film thus obtained was dissolved in 200 g of a 1.9% by mass mannitol aqueous solution. Next, the obtained aqueous solution was titrated with a 1 mol/L sodium hydroxide aqueous solution, and the boron content of the PVA resin film was calculated by comparing the amount of sodium hydroxide aqueous solution required for neutralization with a calibration curve. . The boron content of the PVA resin film thus obtained was used as the boron adsorption rate of the PVA resin film.

<Preparation of polarizing element>
(Polarizing element 1)
A 30 μm thick PVA resin film with a boron adsorption rate of 5.71% by mass was immersed in pure water at 21.5° C. for 79 seconds (swelling treatment). A PVA resin film was immersed for 151 seconds in a 23° C. aqueous solution having a mass ratio of potassium iodide/boric acid/water of 2/2/100 and containing 1.0 mM of iodine (staining step). Thereafter, the PVA resin film was immersed for 76 seconds in a 68.5° C. aqueous solution having a mass ratio of potassium iodide/boric acid/water of 2.5/4/100 (first crosslinking step). Subsequently, the PVA resin film was immersed for 11 seconds in an aqueous solution at 45°C with a mass ratio of potassium iodide/boric acid/zinc chloride/water of 3/5.5/0.6/100 (second crosslinking). process, metal ion treatment process). Thereafter, it was immersed in a cleaning bath for cleaning (cleaning step) and dried at 38° C. (drying step) to obtain a polarizing element with a thickness of 12 μm in which iodine was adsorbed and oriented in polyvinyl alcohol. Stretching was mainly performed in the dyeing process and the first crosslinking process, and the total stretching ratio was 5.85 times. The zinc ion content of the obtained polarizing element was 0.17% by mass, and the boron content was 4.62% by mass.

<Preparation of adhesive>
(Preparation of PVA solution A for adhesive)
50 g of a modified PVA resin containing an acetoacetyl group ("Gosenex Z-410" manufactured by Mitsubishi Chemical Corporation) was dissolved in 950 g of pure water. This solution was heated at 90° C. for 2 hours and then cooled to room 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 blended so that each component had the concentration (mass%) shown in Table 1 to prepare PVA adhesives (Adhesives 1 to 5).

<Preparation of transparent protective film>
(Saponification of cellulose acylate film)
A commercially available cellulose acylate film TJ40UL (manufactured by Fuji Film Corporation, film thickness: 40 μm) was immersed in a 1.5 mol/L NaOH aqueous solution (saponification solution) kept at 55° C. for 2 minutes, and the film was washed with water. Thereafter, the film was immersed in a 0.05 mol/L sulfuric acid aqueous solution at 25° C. for 30 seconds, and then passed through a washing bath under running water for 30 seconds to make the film neutral. Then, draining with an air knife was repeated three times. After removing the water, the film was dried by staying in a drying zone at 70° C. for 15 seconds to produce a saponified film (transparent protective film 1).

<Preparation of polarizing plate>
(Preparation of polarizing plate 1)
The transparent protective film 1 prepared above was bonded to both sides of the polarizing element 1 via the adhesive 1 using a roll bonding machine. The coating thickness of Adhesive 1 was adjusted so that the thickness of the adhesive layer after drying was 100 nm on both sides. Thereafter, it was dried at 80° C. for 3 minutes to obtain a polarizing plate 1 with a double-sided transparent protective film.

(Preparation of polarizing plates 2 to 5)
Polarizing plates 2 to 5 were produced in the same manner as polarizing plate 1 except that adhesive 1 was replaced with adhesives 2 to 5, respectively.

<Evaluation of discoloration>
Place a linear polarizing plate for inspection so that it is in a crossed nicol state with respect to the back side of the polarizing plate to be inspected, and place it at a distance of about 10 to 50 mm from the front side of the linear polarizing plate for inspection, with a luminous flux of 1000 lumen. The specimen was placed in a dark room under illumination with a high-intensity LED penlight and visually observed. When brown discoloration was observed, it was determined that discoloration was "present," and when brown discoloration was not observed, it was determined that discoloration was "absent." Table 2 shows the determination results.
The evaluation results are shown in Table 2.

<High temperature durability test (105℃)>
(Preparation of evaluation sample)
An acrylic adhesive (manufactured by Lintec Corporation) was applied to one side of each of the polarizing plates 1 to 5 produced above to form an adhesive layer with a thickness of 25 μm. By cutting a polarizing plate with an adhesive layer formed on one side to a size of 40 mm x 40 mm and pasting it on the surface of the adhesive layer to alkali-free glass [trade name "EAGLE XG", manufactured by Corning Incorporated]. , an evaluation sample was prepared.

(High temperature durability test)
The evaluation sample obtained above was subjected to an autoclave treatment at a temperature of 50° C. and a pressure of 5 kgf/cm ² (490.3 kPa) for 1 hour, and then left for 24 hours in an environment of a temperature of 23° C. and a RH of 55%. The degree of polarization, single transmittance, and hue of the polarizing plate were measured, and these were used as initial values. Next, the evaluation sample was stored in a high-temperature environment at a temperature of 105° C. for 500 hours. The degree of polarization, single transmittance, and hue of the polarizing plate after storage were measured.

The amount of change was calculated from the initial values of the visibility-corrected single transmittance, visibility-corrected polarization degree, and hue of the polarizing plate and the measured values after the high-temperature durability test. The amount of change ΔTy in the visibility correction single transmittance and the amount of change ΔPy in the visibility correction polarization degree were calculated as values obtained by subtracting the initial value from the measured value after the high temperature durability test. Further, the amount of change in hue Δab was determined using 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 durability test.

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

10 raw film made of polyvinyl alcohol resin, 11 raw roll, 13 swelling bath, 15 dyeing bath, 17a first crosslinking bath, 17b second crosslinking bath, 19 cleaning bath, 21
Drying oven, 23 Polarizing element, 30 to 48, 60, 61 Guide roll, 50 to 52, 53a, 53b, 54, 55 Nip roll.

Claims

A method for producing a polarizing plate comprising a polarizing element and a transparent protective film laminated on at least one surface of the polarizing element, the method comprising:
A polarizing element manufacturing process for obtaining a polarizing element from a polyvinyl alcohol resin film;
a bonding step of bonding the transparent protective film to the polarizing element via a water-based adhesive;
The polyvinyl alcohol resin film has a boron adsorption rate of 5.70% by mass or more,
The method for producing the aqueous adhesive has an ethanol concentration of 16% by mass or more and 50% by mass or less.
The manufacturing method according to claim 1, wherein the polarizing element has a boron content of 4.0% by mass or more and 8.0% by 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 water-based adhesive has a concentration of the polyvinyl alcohol resin of 2.85% by mass or more.
The manufacturing method according to claim 1 or 2, wherein in the polarizing plate, an adhesive layer formed of the water-based adhesive interposed between the polarizing element and the transparent protective film has a thickness of 0.01 μm or more and 7 μm or less. Method.