Adhesive composition and method for producing polarizing plate

Abstract

The invention provides an adhesive composition and a method for manufacturing a polarizing plate. The adhesive composition can be used for manufacturing a polarizing plate which can inhibit the reduction of transmittance in a high-temperature environment and the reduction of polarization degree in a high-temperature environment. The adhesive composition contains a polyvinyl alcohol resin and an amide compound represented by formula (1). (In formula (1), R1, R2, and R3 each independently represent a hydrogen atom, a hydroxyl group, an alkyl group having 1-5 carbon atoms, or an alkyl group having 1-5 carbon atoms in which one or more hydrogen atoms are substituted by a hydroxyl group. ] # imgabs0 #.

Description

Technical Field

[0001] The present invention relates to an adhesive composition and a method for producing a polarizing plate. Background Art

[0002] Liquid crystal display devices (LCDs) are widely used not only in LCD televisions but also in personal computers, mobile devices such as cell phones, and in-vehicle applications such as car navigation systems. Typically, an LCD display has a liquid crystal panel component in which polarizing plates are bonded to both sides of a liquid crystal cell using an adhesive. This component controls light from a backlight component to produce a display. Similarly to LCDs, organic EL displays have also recently become widely used in televisions, mobile devices such as cell phones, and in-vehicle applications such as car navigation systems. In organic EL displays, a circular polarizing plate (a laminate consisting of a polarizing element and a λ / 4 plate) is sometimes placed on the viewing side of the image display panel to prevent external light from being reflected by the metal electrode (cathode) and observed as a mirror surface.

[0003] As mentioned above, polarizing plates are increasingly being installed in vehicles as components of liquid crystal displays and organic EL displays. Compared to other mobile applications such as televisions and mobile phones, polarizing plates used in automotive image displays are often exposed to high-temperature environments and are therefore required to exhibit minimal changes in properties under high temperatures (high-temperature durability).

[0004] On the other hand, to prevent damage to the image display panel caused by impacts from the external surface, configurations in which a front panel (also referred to as a "window layer") such as a transparent resin plate or glass plate is provided on the viewing side of the image display panel, closer to the polarizing plate, are becoming increasingly common. Furthermore, in display devices equipped with a touch panel, a configuration in which the touch panel is provided on the viewing side of the image display panel, closer to the polarizing plate, and a front transparent plate is provided on the viewing side of the touch panel is also widely adopted.

[0005] In such a configuration, if an air layer exists between the image display panel and transparent components such as the front transparent plate and touch panel, reflection glare from external light will occur due to light reflection at the interface of the air layer, which tends to reduce the visibility of the screen. Therefore, a configuration in which the space between the polarizing plate disposed on the viewing side surface of the image display panel and the front transparent component is filled with a material having a refractive index close to that of these materials (hereinafter sometimes referred to as an "interlayer filling configuration") is becoming popular. As the interlayer filling material, adhesives and UV-curing adhesives are used to suppress the reduction in visibility caused by reflection at the interface and to bond and secure the components together (for example, see Patent Document 1).

[0006] This interlayer filler structure is widely adopted in mobile devices, such as mobile phones, which are often used outdoors. Furthermore, due to the recent increase in visibility requirements, research has also been conducted in automotive applications such as car navigation systems, using a structure in which a front transparent plate is placed on the surface of the image display panel and an interlayer filler is formed between the panel and the front transparent plate using an adhesive layer or the like. However, reports indicate that when using this structure, a significant decrease in transmittance is observed in the center of the polarizing plate's surface during a heat durability test (e.g., at 95°C for 200 hours). Meanwhile, no significant decrease in transmittance is observed for the polarizing plate alone even after 1000 hours at 95°C. These results also indicate that a significant decrease in the transmittance of the polarizing plate in high-temperature environments is a particular problem associated with image display devices using an interlayer filler structure, in which one side of the polarizing plate is bonded to the image display unit and the other side is bonded to a transparent component such as a touch panel or front transparent plate, when exposed to high-temperature environments (Patent Document 2).

[0007] Furthermore, in Patent Document 2, the polarizing plate having a significantly reduced transmittance due to the interlayer filling structure has a Raman spectroscopic measurement at 1100 cm -1 Nearby (from =CC= bond) and 1500cm -1 There is a peak near (from the -C=C- bond), so it is believed that a polyene structure (-C=C) is formed. n -, which is presumed to be generated by polyeneization of the polyvinyl alcohol constituting the polarizing element through dehydration (Patent Document 2, paragraph

[0012] ).

[0008] Patent Document 2 proposes, as a solution to the above problem, a method of suppressing transmittance reduction by reducing the moisture content per unit area of ​​the polarizing plate to a predetermined amount or less and reducing the saturated water absorption of the transparent protective film adjacent to the polarizing element to a predetermined amount or less.

[0009] Patent Document 3 proposes a method for suppressing a decrease in transmittance of a polarizing plate under a high-temperature environment by adding at least one urea-based compound selected from urea, urea derivatives, thiourea, and thiourea derivatives to a polarizing film.

[0010] Prior art literature

[0011] Patent Literature

[0012] Patent Document 1: Japanese Patent Application Laid-Open No. 11-174417

[0013] Patent Document 2: Japanese Patent Application Laid-Open No. 2014-102353

[0014] Patent Document 3: Japanese Patent Application Laid-Open No. 2020-204641 Summary of the Invention

[0015] Problems to be solved by the invention

[0016] However, the present inventors have discovered that, while the method described in Patent Document 3 can suppress a decrease in the transmittance of the polarizing plate in a high-temperature environment, it does not sufficiently suppress a decrease in the degree of polarization in such a high-temperature environment. In particular, the present inventors have discovered that, when the polarizing plate described in Patent Document 3 is exposed to a high-temperature environment for an extended period of time (e.g., 500 hours at 105°C), the degree of polarization tends to decrease, and light leakage in the crossed Nicol state (cross leakage) is more likely to occur.

[0017] The present invention has been made in view of the above-mentioned problems of the prior art, and an object of the present invention is to provide an adhesive composition and a method for producing a polarizing plate capable of producing a polarizing plate capable of suppressing both a decrease in transmittance and a decrease in polarization degree in a high-temperature environment.

[0018] Means for solving problems

[0019] In order to solve the above-mentioned problems, the present invention provides the following adhesive composition and method for producing a polarizing plate.

[0020] [1] An adhesive composition comprising a polyvinyl alcohol-based resin and an amide compound represented by the following formula (1).

[0021] [Chemical Formula 1]

[0022]

[0023] [In formula (1), R 1 、R 2 and R 3 Each independently represents a hydrogen atom, a hydroxyl group, an alkyl group having 1 to 5 carbon atoms, or an alkyl group having 1 to 5 carbon atoms in which one or more hydrogen atoms are substituted with a hydroxyl group.]

[0024] [2] The adhesive composition according to [1], which is used for a polarizing plate.

[0025] [3] The adhesive composition according to [1] or [2], wherein the polyvinyl alcohol-based resin and the amide compound are dissolved in water.

[0026] [4] The adhesive composition according to any one of [1] to [3] above, further comprising a crosslinking agent.

[0027] [5] The adhesive composition according to any one of [1] to [4], wherein the proportion of the polyvinyl alcohol-based resin in the resins contained in the adhesive composition is 80% by mass or more.

[0028] [6] The adhesive composition according to any one of [1] to [5], wherein the content of the amide compound is 5% by mass to 90% by mass based on the total solid content of the adhesive composition.

[0029] [7] The adhesive composition according to any one of [1] to [6], wherein in the formula (1), R 3 A hydrogen atom.

[0030] [8] The adhesive composition according to any one of [1] to [7] above, wherein the liquid turbidity is 10% or less.

[0031] [9] A method for manufacturing a polarizing plate, wherein the polarizing plate comprises a polyvinyl alcohol-based resin polarizing film formed by iodine adsorption and orientation and a protective film, the method comprising the step of laminating the polarizing film and the protective film via the adhesive composition described in any one of [1] to [8].

[0032] Effects of the Invention

[0033] According to the present invention, there can be provided an adhesive composition and a method for producing a polarizing plate capable of producing a polarizing plate capable of suppressing both a decrease in transmittance and a decrease in polarization degree in a high-temperature environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a schematic cross-sectional view showing an example of a polarizing plate produced using the adhesive composition of the present invention.

[0035] Figure 2 This is a schematic cross-sectional view showing an example of a display device produced using the adhesive composition of the present invention.

[0036] Description of Reference Numerals

[0037] 1... first protective film, 2... first adhesive layer, 3... polarizing film, 4... second adhesive layer, 5... second protective film, 6... adhesive layer, 7... optical adhesive layer, 8... transparent member, 9... image display unit, 100... polarizing plate, 200... display device. DETAILED DESCRIPTION

[0038] Hereinafter, one embodiment of the present invention will be described in detail with reference to the accompanying drawings as appropriate.

[0039] [Adhesive composition]

[0040] The adhesive composition of the present invention (hereinafter also simply referred to as "adhesive") contains a polyvinyl alcohol-based resin and an amide compound represented by the following formula (1). This adhesive composition can be used for polarizing plates.

[0041] [Chemical Formula 2]

[0042]

[0043] [In formula (1), R 1 、R 2 and R 3 Each independently represents a hydrogen atom, a hydroxyl group, an alkyl group having 1 to 5 carbon atoms, or an alkyl group having 1 to 5 carbon atoms in which one or more hydrogen atoms are substituted with a hydroxyl group.]

[0044] According to the above-mentioned adhesive, by containing the above-mentioned specific amide compound, a polarizing plate can be produced that can suppress both the reduction in transmittance under high temperature environment and the reduction in polarization degree under high temperature environment. The present inventors speculate as follows about the reason for obtaining this effect. The reduction in transmittance of the polarizing plate is caused by the yellowing of the polyvinyl alcohol-based resin in the polarizing film. In addition, the yellowing of the polyvinyl alcohol-based resin is caused by the decomposition of the iodine complex in the polarizing film to produce I2, and this I2 acts as a catalyst to dehydrate the polyvinyl alcohol-based resin (polyene). In view of this, the above-mentioned specific amide compound can decompose I2. Therefore, by using an adhesive containing the above-mentioned amide compound to produce a polarizing plate, the dehydration of the polyvinyl alcohol-based resin in the polarizing film and the resulting yellowing can be suppressed, and the reduction in transmittance of the polarizing plate under high temperature environment can be suppressed. On the other hand, the reduction in polarization degree is caused by the reduction of the iodine complex in the polarizing film. Under high temperature environment, ammonia is generated by urea and the above-mentioned specific amide compound. When urea or the like is used to suppress a decrease in transmittance, ammonia generated by the urea or the like reacts with iodine complexes, accelerating their decomposition, thereby reducing the amount of iodine complexes and causing a decrease in polarization degree. In contrast, when the aforementioned specific amide compound is used, the amount of ammonia generated is less than when urea or the like is used, thereby suppressing the decomposition of iodine complexes. By using an adhesive containing the aforementioned amide compound to manufacture a polarizing plate, a decrease in the polarization degree of the polarizing plate under high-temperature environments can be suppressed.

[0045] When the above adhesive is used to make a polarizing plate, the adhesive can be used to attach a protective film to the polarizing film. As the adhesive, water-based adhesives, solvent-based adhesives, etc. can be used, preferably water-based adhesives. The adhesive may contain a crosslinking agent.

[0046] (Water-based adhesive)

[0047] The aqueous adhesive is an aqueous adhesive (PVA adhesive) containing a polyvinyl alcohol (PVA) resin. The aqueous adhesive may be an adhesive obtained by dissolving a PVA resin and an amide compound represented by formula (1) in water (e.g., pure water). From the perspective of adhesiveness, the average degree of polymerization of the PVA resin contained in the aqueous adhesive is preferably approximately 100 to 5500, more preferably 1000 to 4500. From the perspective of adhesiveness, the average degree of saponification is preferably approximately 85 mol% to 100 mol%, more preferably 90 mol% to 100 mol%.

[0048] The PVA resin contained in the water-based adhesive preferably contains acetoacetyl groups because this provides excellent adhesion between the PVA resin layer and the protective film and provides excellent durability. Acetoacetyl-containing PVA resins can be obtained, for example, by reacting a PVA resin with diketene using any method. The degree of acetoacetyl modification in acetoacetyl-containing PVA resins is typically 0.1 mol% or greater, and preferably approximately 0.1 mol% to 20 mol%.

[0049] The resin concentration of the aqueous adhesive is preferably 0.1% by mass to 15% by mass, and more preferably 0.5% by mass to 10% by mass.

[0050] The content of the PVA resin in the water-based adhesive (the proportion of the PVA resin in the resin contained in the adhesive) is preferably 80% by mass or more, more preferably 90% by mass or more, and can be 100% by mass, based on the total amount of resin in the water-based adhesive.

[0051] (cross-linking agent, solvent)

[0052] The water-soluble PVA-based adhesive that can be preferably used in the present invention may further contain a cross-linking agent as needed in addition to the above-mentioned PVA-based resin. As the cross-linking agent, a known cross-linking agent can be used. Examples of the cross-linking agent include water-soluble epoxy compounds, dialdehydes, isocyanates, and the like.

[0053] When the PVA resin is an acetoacetyl group-containing PVA-based resin, the crosslinking agent is preferably any one of glyoxal, glyoxylate, and methylolmelamine, more preferably any one of glyoxal and glyoxylate, and particularly preferably glyoxal.

[0054] The water-soluble PVA-based adhesive may contain an organic solvent. In this case, alcohols are preferred from the perspective of miscibility with water, and methanol or ethanol is more preferred among alcohols.

[0055] (Amide compound)

[0056] The amide compound is an amide compound represented by the above formula (1). In formula (1), R1 、R 2 and R 3 Each independently represents a hydrogen atom, a hydroxyl group, an alkyl group having 1 to 5 carbon atoms, or an alkyl group having 1 to 5 carbon atoms in which one or more hydrogen atoms are substituted with a hydroxyl group. 1 、R 2 and R 3 Preferably, it is a hydrogen atom, a hydroxyl group, or an alkyl group having 1 to 5 carbon atoms, and R 1 、R 2 and R 3 The total number of carbon atoms is 1 to 5, more preferably a hydrogen atom, a hydroxyl group, or an alkyl group with 1 to 3 carbon atoms, and R 1 、R 2 and R 3 The total number of carbon atoms of is 1 to 3. In addition, from the viewpoint of being able to further suppress the decrease in transmittance and polarization degree of the polarizing plate under high temperature environment, R 3 Preferably it is a hydrogen atom, more preferably R 1 is an alkyl group with 1 to 5 carbon atoms, R 2 is a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, and R 3 is a hydrogen atom, more preferably R 1 is an alkyl group with 1 to 3 carbon atoms, R 2 is a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and R 3 is a hydrogen atom, and R is particularly preferred 1 is methyl or ethyl, R 2 is a hydrogen atom, a methyl group or an ethyl group, and R 3 A hydrogen atom.

[0057] Specific examples of the amide compound include acetamide, propionamide, butanamide, valeramide, hexanoamide, heptanoamide, isobutyramide, 2-methylbutanamide, isovaleramide, pivalamide, 2-methylvaleramide, 2-ethylvaleramide, 3-methylvaleramide, 2-ethylbutanamide, 2,2-dimethylbutanamide, hydroxyacetamide, lactamide, glucamide, glyceramide, 2-hydroxybutanamide, 3-hydroxybutanamide, γ-hydroxybutanamide, mevalonamide, and pantothenic acid amide. The amide compound may be used alone or in combination of two or more.

[0058] When the adhesive contains an amide compound, its content is preferably 5 to 90% by mass, more preferably 10 to 80% by mass, and even more preferably 30 to 80% by mass, based on the total solid content of the adhesive. When the amide compound content is 5% by mass or greater, a decrease in the transmittance and polarization degree of the resulting polarizing plate under high-temperature conditions can be further suppressed. When the amide compound content is 90% by mass or less, sufficient adhesion between the polarizing film and the protective film can be achieved.

[0059] From the viewpoint of suppressing the deterioration of the polarization performance of the polarizing plate caused by the suspension of the adhesive layer, the liquid turbidity of the adhesive is preferably 10% or less, more preferably 5% or less, and even more preferably 3% or less. The lower limit of the liquid turbidity of the adhesive is not particularly limited, and for example, it may be 0.1% or more. The liquid turbidity of the adhesive can be measured as a turbidity value obtained by measuring a quartz cuvette filled with an adhesive and having an optical path length of 10 mm using a turbidimeter according to the method described in JIS K 7136.

[0060] [Polarizing plate and method for manufacturing the same]

[0061] A polarizing plate produced using the adhesive composition of the present invention will be described. The polarizing plate comprises a polyvinyl alcohol-based resin polarizing film formed by iodine adsorption and orientation, and a protective film. In the polarizing plate, the polarizing film and the protective film are bonded together via the adhesive composition of the present invention. Specifically, the polarizing plate is produced using a manufacturing method comprising bonding the polarizing film and the protective film together via the adhesive composition of the present invention.

[0062] Figure 1 Schematic cross-sectional view showing an example of a polarizing plate. Figure 1 The polarizing plate 100 shown has a structure in which a first protective film 1, a first adhesive layer 2, a polarizing film 3, a second adhesive layer 4, and a second protective film 5 are stacked in this order. In the polarizing plate 100, at least one of the first adhesive layer 2 and the second adhesive layer 4 is formed using the adhesive composition of the present invention. From the viewpoint of more easily suppressing the decrease in transmittance and polarization degree of the polarizing plate under a high temperature environment, in the polarizing plate 100, it is preferred that both the first adhesive layer 2 and the second adhesive layer 4 are formed using the adhesive composition of the present invention. In the polarizing plate 100, the amide compound represented by formula (1) may be further contained in a layer other than the first adhesive layer 2 and the second adhesive layer 4. In the case where a plurality of layers constituting the polarizing plate contain the above-mentioned amide compound, the amide compounds contained in each layer may be the same or different. Below, each layer of the polarizing plate is described in detail.

[0063] Polarizing film 3

[0064] The polarizing film is formed by adsorbing and aligning iodine on a polyvinyl alcohol resin film. The polyvinyl alcohol resin film may be a uniaxially stretched film. The polyvinyl alcohol resin constituting the polyvinyl alcohol resin film is usually obtained by saponifying a polyvinyl acetate resin. The degree of saponification is usually about 85 mol% or more, preferably about 90 mol% or more, and more preferably about 99 mol% or more. For example, in addition to polyvinyl acetate which is a homopolymer of vinyl acetate, the polyvinyl acetate resin may also be a copolymer of vinyl acetate and other monomers copolymerizable therewith. As other monomers that can be copolymerized, for example, unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, etc. The degree of polymerization of the polyvinyl alcohol resin is usually about 1000 to 10000, preferably about 1500 to 5000.

[0065] These polyvinyl alcohol-based resins may be modified. For example, polyvinyl formal, polyvinyl acetal, polyvinyl butyral, etc. modified with aldehydes may be used.

[0066] When manufacturing polarizing films, an unstretched polyvinyl alcohol-based resin film (stock film) with a thickness of 65 μm or less (e.g., 60 μm or less), preferably 50 μm or less, more preferably 35 μm or less, and even more preferably 30 μm or less can be used as the raw material. This allows for the production of thin polarizing films, which are increasingly in demand in the market. The width of the stock film is not particularly limited and can be, for example, approximately 400 to 6000 mm. The stock film is prepared, for example, in the form of a long roll of unstretched polyvinyl alcohol-based resin film (stock roll).

[0067] Alternatively, the polyvinyl alcohol-based resin film may be laminated on a substrate film supporting the polyvinyl alcohol-based resin film, that is, the polyvinyl alcohol-based resin film may be prepared as a laminated film of the substrate film and the polyvinyl alcohol-based resin film laminated thereon. In this case, the polyvinyl alcohol-based resin film may be produced, for example, by applying a coating liquid containing a polyvinyl alcohol-based resin to at least one side of the substrate film and then drying the coating liquid.

[0068] The substrate film may be, for example, a film made of a thermoplastic resin. Specifically, a film made of a light-transmitting thermoplastic resin, preferably an optically transparent thermoplastic resin, may be a polyolefin resin such as a linear polyolefin resin (such as a polypropylene resin) or a cyclic polyolefin resin (such as a norbornene resin); a cellulose resin such as triacetyl cellulose or diacetyl cellulose; a polyester resin such as polyethylene terephthalate or polybutylene terephthalate; a polycarbonate resin; a (meth)acrylic resin such as methyl methacrylate; a polystyrene resin; a polyvinyl chloride resin; an acrylonitrile-butadiene-styrene resin; an acrylonitrile-styrene resin; a polyvinyl acetate resin; a polyvinylidene chloride resin; a polyamide resin; a polyacetal resin; a modified polyphenylene ether resin; a polysulfone resin; a polyethersulfone resin; a polyarylate resin; a polyamide-imide resin; or a polyimide resin.

[0069] The polarizing film can be produced continuously in the form of a long polarizing film by unwinding the above-mentioned long raw film from a raw material roll, continuously conveying it along the film conveying path of the polarizing film manufacturing device, immersing it in a treatment tank (hereinafter also referred to as a "treatment bath") containing a treatment liquid and then pulling it out. After implementing the prescribed treatment process, a drying process is carried out, thereby continuously producing the long polarizing film. It should be noted that the treatment process is not limited to the method of immersing the film in the treatment bath as long as it is a method of treating by bringing the treatment liquid into contact with the film. It can also be a method of treating the film by allowing the treatment liquid to adhere to the surface of the film by spraying, flowing, dripping, etc. In the case of performing the treatment process by immersing the film in a treatment bath, the treatment bath for one treatment process is not limited to one, and the film can also be immersed in two or more treatment baths in sequence to complete one treatment process.

[0070] Examples of the treatment liquid include swelling liquids, dyeing liquids, crosslinking liquids, and cleaning liquids. Furthermore, examples of the treatment steps include a swelling step in which the original film is brought into contact with a swelling liquid to swell it, a dyeing step in which the film after the swelling step is brought into contact with a dyeing liquid to dye it, a crosslinking step in which the film after the dyeing step is brought into contact with a crosslinking liquid to crosslink it, and a cleaning step in which the film after the crosslinking step is brought into contact with a cleaning liquid to clean it. Furthermore, between these treatment steps, a uniaxial stretching treatment may be performed in a wet or dry process. Other treatment steps may also be added as needed.

[0071] When the polarizing film contains the amide compound, the polarizing film can be treated by spraying, flowing, or dripping, as in the aforementioned treatment steps. Preferably, the polarizing film is treated by immersing the polarizing film in a treatment bath containing the amide compound. The treatment bath containing the amide compound can be provided separately from the treatment bath used in conventional manufacturing methods, or the amide compound can be added to the conventional treatment bath to provide an amide compound treatment function. From the perspective of productivity, the method of adding an amide compound treatment function to the conventional treatment bath is more preferred.

[0072] The polarizing film should preferably contain an amide compound after dyeing with iodine and then treating it with a treatment solution containing the amide compound. Including the amide compound after dyeing minimizes color change and, in interlayer filling configurations, tends to more easily suppress decreases in transmittance and polarization degree in high-temperature environments.

[0073] Hereinafter, each step in producing the polarizing film will be described in more detail.

[0074] (Swelling process)

[0075] The swelling step can be carried out by continuously unwinding the raw film from a raw roll while conveying it along a film conveyance path, immersing the raw film in a swelling bath for a predetermined time, and then unwinding it. From the time the raw film is unwound until it is immersed in the swelling bath, the raw film can be conveyed along a film conveyance path constructed by guide rollers and nip rollers.

[0076] As the swelling liquid of the swelling bath, in addition to pure water, an aqueous solution to which boric acid (Japanese Patent Application Laid-Open No. 10-153709), a chloride (Japanese Patent Application Laid-Open No. 06-281816), an inorganic acid, an inorganic salt, a water-soluble organic solvent, an alcohol, or the like is added in a range of about 0.01 to 10 mass % can be used.

[0077] (Dyeing process)

[0078] The dyeing process is carried out for the purpose of adsorbing and orienting the dichroic dye on the polyvinyl alcohol-based resin film after the swelling treatment. The treatment conditions are determined within a range that can achieve this purpose and within a range that does not cause adverse conditions such as extreme dissolution and devitrification of the film. The dyeing process can be carried out as follows: the film after the swelling treatment is transported along a film transport path constructed by guide rollers and clamping rollers, immersed in a dye bath for a predetermined time, and then pulled out. In order to improve the dyeing properties of the dichroic dye, the film provided for the dyeing process is preferably a film that has been subjected to at least some degree of uniaxial stretching, or preferably a uniaxial stretching treatment is performed during the dyeing process instead of, or in addition to, the uniaxial stretching treatment before the dyeing process.

[0079] In the present invention, iodine is used as a dichroic pigment. The dyeing solution of the dye bath can be, for example, an aqueous solution having a concentration of iodine / potassium iodide / water = approximately 0.003 to 0.3 / approximately 0.1 to 10 / 100 by mass. Other iodides such as zinc iodide can be used instead of potassium iodide, or potassium iodide and other iodides can be used in combination. In addition, compounds other than iodides, such as boric acid, zinc chloride, and cobalt chloride, can also be coexisted. When boric acid is added, it is distinguished from the cross-linking treatment described later in that it contains iodine. If the aqueous solution contains approximately 0.003 parts by mass or more of iodine relative to 100 parts by mass of water, it can be considered a dye bath.

[0080] (Cross-linking process)

[0081] The cross-linking process is a treatment performed for the purpose of water resistance, color adjustment, etc. based on cross-linking. The cross-linking process can be configured with two cross-linking baths, and the first cross-linking process for the purpose of water resistance is performed in the first cross-linking bath, and the second cross-linking process for the purpose of color adjustment is performed in the second cross-linking bath. The first cross-linking process can be implemented as follows: the film is transported along a film transport path constructed by a guide roller and a clamping roller, and the dyed film is immersed in the first cross-linking bath for a predetermined time, and then pulled out. The second cross-linking process can be implemented as follows: the film is transported along a film transport path constructed by a guide roller and a clamping roller, and the film after the first cross-linking process is immersed in the second cross-linking bath for a predetermined time, and then pulled out. Hereinafter, when referred to as a cross-linking bath, it includes either the first cross-linking bath or the second cross-linking bath, and when referred to as a cross-linking liquid, it includes either the first cross-linking liquid or the second cross-linking liquid.

[0082] As a cross-linking liquid, a solution obtained by dissolving a cross-linking agent in a solvent can be used. Examples of cross-linking agents include boric acid, borax and other boron compounds, glyoxal, glutaraldehyde and the like. These can be one or more. As a solvent, for example, water can be used, and an organic solvent compatible with water can also be included. The concentration of the cross-linking agent in the cross-linking solution is preferably in the range of 1 to 20% by mass, but is not limited thereto.

[0083] From the viewpoint of promoting crosslinking of the polyvinyl alcohol resin film, the temperature of the crosslinking solution is preferably 30° C. or higher. From the viewpoint of preventing elution of the polyvinyl alcohol resin film, the temperature of the crosslinking solution is preferably 70° C. or lower, more preferably 65° C. or lower.

[0084] The crosslinking treatment can be performed multiple times, typically 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 above ranges. The crosslinking treatment for water resistance by crosslinking and the crosslinking treatment for color adjustment can be performed in multiple steps.

[0085] (Cleaning process)

[0086] The cleaning process is performed to remove excess boric acid, iodine, or other chemicals adhering to the polyvinyl alcohol resin film. The cleaning process is performed, for example, by immersing the cross-linked polyvinyl alcohol resin film in a cleaning bath. Depending on the circumstances, the cleaning process may be omitted.

[0087] (Stretching process)

[0088] The raw film is uniaxially stretched in a wet or dry process between the above-mentioned treatment steps. Specific methods of uniaxial stretching include, for example, inter-roll stretching, which applies a circumferential speed difference between two nip rollers forming the film transport path to perform longitudinal uniaxial stretching, hot roll stretching as described in Japanese Patent No. 2731813, or tenter stretching, with inter-roll stretching being preferred. The uniaxial stretching step can be performed multiple times from the raw film to the polarizing film. As described above, stretching also helps to prevent the formation of wrinkles in the film.

[0089] The final cumulative stretch ratio of the polarizing film based on the original film is generally about 4.5 to 7 times, preferably 5 to 6.5 times. The stretching step can be performed in any treatment step. When the stretching treatment is performed in two or more treatment steps, the stretching treatment can also be performed in any treatment step.

[0090] (Drying process)

[0091] After the cleaning step, the polyvinyl alcohol resin film can be dried. The film drying method is not particularly limited. For example, a drying oven equipped with a hot air dryer can be used. The drying temperature is, for example, approximately 30 to 100°C, and the drying time is, for example, approximately 30 to 600 seconds. The polyvinyl alcohol resin film can also be dried using a far-infrared heater. The polarizing film 23 obtained in this manner has a thickness of, for example, approximately 5 to 30 μm.

[0092] <Adhesive Layers (First Adhesive Layer 2 and Second Adhesive Layer 4)>

[0093] At least one of the first adhesive layer and the second adhesive layer for laminating a protective film on a polarizing film is formed using the adhesive composition of the present invention. One of the first adhesive layer and the second adhesive layer can be formed using an adhesive composition other than the adhesive composition of the present invention, but it is preferred that both the first adhesive layer and the second adhesive layer are formed using the adhesive composition of the present invention. It should be noted that as other adhesive compositions, aqueous adhesives, solvent-based adhesives, active energy ray-curing adhesives, etc. that do not contain the above-mentioned amide compound can be used. The first adhesive layer and the second adhesive layer can be formed using the same adhesive or different adhesives.

[0094] The thickness of the adhesive during application can be set to any appropriate value. For example, it can be set so that an adhesive layer having the desired thickness is obtained after curing or heating (drying). The thickness of the adhesive layer is preferably 0.01 μm to 7 μm, more preferably 0.01 μm to 5 μm, even more preferably 0.01 μm to 2 μm, and most preferably 0.01 μm to 1 μm.

[0095] <Protective Films (First Protective Film 1 and Second Protective Film 5)>

[0096] The protective films (first and second protective films) used in the present invention are bonded to both surfaces of the polarizing film via adhesive layers. The protective films can be transparent. They can also have other optical functions or have a laminated structure consisting of multiple layers. The first and second protective films can have the same or different structures.

[0097] From the viewpoint of optical properties, the protective film is preferably thin, but if it is too thin, the strength decreases and the processability deteriorates. The appropriate film thickness is 5 to 100 μm, preferably 10 to 80 μm, and more preferably 15 to 70 μm.

[0098] As the protective film, films such as cellulose acylate films, films made of polycarbonate resins, films made of cycloolefin resins such as norbornene, (meth)acrylic polymer films, and polyester resin films such as polyethylene terephthalate can be used.

[0099] From the viewpoint of moisture permeability, at least one of the first protective film and the second protective film is preferably a cellulose acylate film or a (meth)acrylic polymer film, and among them, a cellulose acylate film is preferred.

[0100] At least one of the first protective film and the second protective film may have a phase difference function for purposes such as viewing angle compensation. In this case, the film itself may have a phase difference function, may have a phase difference layer, or may be a combination of the two. It should be noted that the film having a phase difference function may be directly attached to the polarizing film via an adhesive, or may be further attached to another protective film via an adhesive or a bonding agent, and the other protective film may be attached to the polarizing film.

[0101] [Display device]

[0102] These polarizing plates are used in various display devices (image display devices), such as liquid crystal displays and organic EL displays. In particular, they are suitable for image display devices having an interlayer filler structure, in which a transparent component, such as a front panel or touch panel, is placed on the viewing side of the image display device and the image display panel and the transparent component are bonded together using an adhesive layer or the like.

[0103] Figure 2 This is a schematic cross-sectional view showing an example of a display device. Figure 2 The display device 200 shown has Figure 1 The polarizing plate 100 shown has a structure in which a transparent member 8 is laminated on a first protective film 1 via an optical adhesive layer 7, and an image display unit 9 is laminated on a second protective film 5 via an adhesive layer 6. In the display device 200, the amide compound represented by formula (1) may be contained in one or both of the adhesive layer 6 and the optical adhesive layer 7.

[0104] (Adhesive layer 6)

[0105] An adhesive layer (adhesive sheet) is provided on the second protective film. The adhesive layer can be attached to the polarizing plate by any suitable method. Examples include preparing a 10-40% by mass adhesive solution by dissolving or dispersing the base polymer or a combination thereof in a suitable solvent, such as toluene or ethyl acetate, either alone or in a mixture, and directly attaching the solution to the polarizing plate using a suitable spreading method, such as casting or coating. Alternatively, the adhesive layer can be formed on a spacer as described above and then moved to attach the spacer to the polarizing plate.

[0106] Regarding the adhesive layer, for example, those described in paragraphs

[0103] to

[0143] of Japanese Patent Application Laid-Open No. 2018-025765 can be used in the present invention.

[0107] (Image display unit 9)

[0108] Examples of image display units include liquid crystal cells and organic EL cells. The liquid crystal cell can be 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 semi-transmissive, semi-reflective liquid crystal cell that utilizes both external and light sources. In the case where the liquid crystal cell utilizes light from a light source, the image display device (liquid crystal display device) also includes a polarizing plate on the side of the image display cell (liquid crystal cell) opposite to the viewing side, and further includes a light source. The polarizing plate on the light source side is preferably bonded to the liquid crystal cell via a suitable adhesive layer. The liquid crystal cell can be driven in any of the following ways, including VA mode, IPS mode, TN mode, STN mode, and bend alignment (π-type).

[0109] Suitable organic EL units include those formed by sequentially stacking a transparent electrode, an organic light-emitting layer, and a metal electrode on a transparent substrate to form a light-emitting body (organic electroluminescent body). The organic light-emitting layer is a laminate of various organic thin films. For example, it can be a laminate of a hole-injection layer containing a triphenylamine derivative or the like and a light-emitting layer containing a fluorescent organic solid such as anthracene; a laminate of these light-emitting layers and an electron-injection layer containing a perylene derivative or the like; or a laminate of a hole-injection layer, a light-emitting layer, and an electron-injection layer.

[0110] The image display unit and the polarizing plate are bonded together via an adhesive layer.

[0111] (Transparent part 8)

[0112] Examples of the transparent member (front transparent member) 8 include a front transparent plate (window layer) and a touch panel. The front transparent plate should be one with appropriate mechanical strength and thickness. Examples of such a transparent plate include a transparent resin plate such as an acrylic resin or polycarbonate resin, or a glass plate. A functional layer such as an antireflection layer may also be laminated on the viewing side of the transparent plate. If the transparent plate is a transparent resin plate, a hard coat layer may be laminated to enhance physical strength, and a low moisture permeability layer may be laminated to reduce moisture permeability.

[0113] As the touch panel, various touch panels such as resistive film, electrostatic capacitance, optical, and ultrasonic touch panels, as well as glass plates and transparent resin plates with touch sensor functions can be used. When a electrostatic capacitance touch panel is used as the front transparent member, it is preferable to place a front transparent plate formed of glass or a transparent resin plate closer to the viewing side than the touch panel.

[0114] (Optical Adhesive Layer 7)

[0115] An optical adhesive is used to bond the polarizing plate to the front transparent member. The optical adhesive is a material used to fill the space between the polarizing plate and the transparent member (an interlayer filler). Suitable optical adhesives include adhesives or UV-curable adhesives. When using an adhesive, it can be applied using any suitable method. Specific methods include the adhesive layer used to bond the image display unit to the polarizing plate.

[0116] When using a UV-curable adhesive, to prevent the adhesive solution from spreading before curing, a suitable method is to place a dam material around the edge of the image display panel, place a transparent front member on the dam material, and inject the adhesive solution. After injection, alignment and degassing are performed as needed, and then UV light is irradiated for curing.

[0117] Example

[0118] Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

[0119] [Examples 1 to 15 and Comparative Examples 1 to 6]

[0120] <Preparation of Adhesive Composition>

[0121] Z-200 (a trade name for acetoacetyl-modified PVA manufactured by Mitsubishi Chemical Co., Ltd.) was dissolved in pure water to obtain a 5.7% PVA aqueous solution. Pure water, a 5.7% PVA aqueous solution, a 40% glyoxal aqueous solution (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and the additives listed in Table 1 were mixed so that the mass ratio of water in the adhesive composition (the total amount of water in the PVA aqueous solution, water in the glyoxal aqueous solution, and additional pure water) / PVA (solids) / glyoxal (solids) / additives was 100 / 3.0 / 0.15 / X, thereby obtaining a water-based adhesive composition. The additive amounts were adjusted so that the mass ratio X reached the values ​​shown in Table 1 below. The concentration of the additives per kg of the resulting water-based adhesive composition was calculated using the following formula.

[0122] Additive concentration (mol / kg) = Additive input amount (kg) / Additive molecular weight (kg / mol) × 1 / Water-based adhesive composition preparation amount (kg)

[0123] Polarizing Plate (Polarizing Film) Production

[0124] A 30μm-thick long polyvinyl alcohol film (Kuraray Co., Ltd., trade name: VF-PE#3000) was continuously fed and immersed in a swelling bath of 20°C pure water for a residence time of 31 seconds (swelling step). The film, pulled from the swelling bath, was then immersed in a 30°C dyeing bath containing iodine / potassium iodide / water at a mass ratio of 0.05 / 2 / 100 for a residence time of 122 seconds (dyeing step). The film, pulled from the dyeing bath, was then immersed in a 56°C crosslinking bath containing potassium iodide / boric acid / water at a mass ratio of 12 / 4.1 / 100 for a residence time of 70 seconds. The film was then immersed in a 40°C crosslinking bath containing potassium iodide / boric acid / water at a mass ratio of 9 / 2.9 / 100 for a residence time of 13 seconds (crosslinking step). Uniaxial stretching in the machine direction was performed in the dyeing and crosslinking steps by roller stretching in the baths. The total stretch ratio based on the base film was set to 5.5 times. Next, the film pulled from the crosslinking bath was immersed in a rinsing bath of pure water at 5°C for a residence time of 3 seconds (rinsing step). It was then dried in an 80°C drying oven for a residence time of 190 seconds (drying step), yielding a polarizing plate (polarizing film). The resulting polarizing plate had a thickness of 12 μm. It should be noted that the MD direction of the polarizing plate (polarizing film) was the absorption axis, and the TD direction (orthogonal to the MD direction) was the transmission axis.

[0125] Polarizing Plate Production

[0126] A 40 μm thick saponified triacetyl cellulose film was laminated to both sides of the polarizer using a roll laminator with the aqueous adhesive composition interposed therebetween. The resulting laminate was dried at 80°C for 3 minutes to produce a polarizing plate having a laminated structure of protective film / adhesive layer / polarizer / adhesive layer / protective film. The adhesive layer had a thickness of 0.07 μm.

[0127] <Production of a Polarizing Plate with Adhesive>

[0128] One surface of the polarizing plate was corona-treated, and a 25 μm-thick acrylic adhesive was bonded to the corona-treated surface using a roll laminator to obtain a polarizing plate with an adhesive.

[0129] <Preparation of samples for durability evaluation>

[0130] The adhesive-attached polarizing plate was cut into a size of 30 mm in the MD x 30 mm in the TD. The adhesive layer was then bonded to the center of a 40 mm x 40 mm x 0.7 mm thick piece of alkali-free glass. Next, a 30 mm x 30 mm x 0.15 mm thick cover glass was bonded to the opposite side of the polarizing plate via a 25 μm thick acrylic adhesive to produce a double-sided glass-attached polarizing plate. This was used as a sample for durability evaluation.

[0131] [evaluate]

[0132] <Initial Ty and Py Measurement>

[0133] The durability evaluation samples obtained in each Example and each Comparative Example were measured for MD transmittance and TD transmittance within a wavelength range of 380 to 780 nm using a spectrophotometer with an integrating sphere (manufactured by JASCO Corporation, trade name: V7100). The single-element transmittance and polarization degree at each wavelength were calculated based on the following formula:

[0134] Single transmittance (%) = (MD transmittance + TD transmittance) / 2

[0135] Polarization degree (%) = {(MD transmittance - TD transmittance) / (MD transmittance + TD transmittance)} × 100.

[0136] Here, the MD transmittance refers to the transmittance when the direction of polarized light emitted from the Glan-Thomson prism is parallel to the transmission axis of the durability evaluation sample. Furthermore, the TD transmittance refers to the transmittance when the direction of polarized light emitted from the Glan-Thomson prism is orthogonal to the transmission axis of the durability evaluation sample. The obtained single transmittance and polarization degree were analyzed using JIS Z8701:1999 "Methods of expressing colors - XYZ colorimetric system and XYZ colorimetric system." 10 Y 10 Z 10 Visibility correction was performed using a 2-degree field of view (light source C) using the "colorimetric system" to determine the visibility-corrected single transmittance (Ty) and the visibility-corrected polarization (Py). These values ​​were used as the initial Ty and Py. The results are shown in Table 1.

[0137] <Measurement of Ty and Py after high-temperature durability test>

[0138] A high-temperature durability test was conducted by storing the samples for durability evaluation in a heated environment at 105°C for 500 hours. After the high-temperature durability test, the single-unit transmittance and polarization degree of the samples were measured using the same methods as above to determine Ty and Py. Based on the Ty and Py values ​​obtained after the high-temperature durability test, the effect of suppressing the decrease in transmittance and polarization degree in a high-temperature environment was evaluated according to the following criteria. The results are shown in Table 1.

[0139] (Transmittance)

[0140] A: Ty after high temperature durability test is 41.5% or more

[0141] B: Ty after high temperature durability test is 5% or more and less than 41.5%

[0142] C: Ty after high temperature durability test is less than 5%

[0143] (Degree of polarization)

[0144] A: Py after high temperature durability test is 98.0% or more

[0145] B: Py after high temperature durability test is less than 98.0%

[0146] <Measurement of Liquid Turbidity>

[0147] The adhesive compositions prepared in Examples 1 to 15 and Comparative Example 1 were filled into a quartz cuvette with a 10 mm optical path length. The turbidity was measured at 23°C using a turbidimeter (trade name: HZ-2) manufactured by Suga Test Instruments Co., Ltd. according to the method described in JIS K7136. The results are shown in Table 1.

[0148] <Determination of amide content>

[0149] The polarizing plate with adhesive prepared in Example 1 was freeze-ground. 100 mg of the resulting ground material was weighed and added to 4.0 g of methanol. The mixture was ultrasonically treated for 10 minutes and then filtered through a 0.45 μm filter to obtain an acetamide extract. Separately, an acetamide standard solution of known concentration was prepared. The extract and standard solution were subjected to gas chromatography-mass spectrometry (GC-MS) analysis, and the acetamide concentration in the polarizing plate with adhesive was calculated based on the measured values ​​of the extract and standard solution. The resulting acetamide concentration in the polarizing plate with adhesive was 0.010% by mass.

[0150] (GC-MS measurement conditions)

[0151] Column: DB-WAX (30m×0.25mmφ, film thickness 0.25μm)

[0152] Column temperature: 40°C → 10°C / min → 240°C (hold for 15 minutes)

[0153] Inlet temperature: 240℃

[0154] Injection volume: 1μm

[0155] Carrier: He

[0156] Flow rate: 1mL / min

[0157] Ionization method: EI

[0158] Ionic polarity: Positive

[0159] Measurement mode: SIM mode

[0160] The same measurement as above was performed to calculate the acetamide concentration for the polarizing plate with a pressure-sensitive adhesive produced in Example 3. The acetamide concentration in the obtained polarizing plate with a pressure-sensitive adhesive was 0.037% by mass.

[0161] [Table 1]

[0162]

Claims

1. An adhesive composition comprising a polyvinyl alcohol-based resin and an amide compound represented by the following formula (1), In formula (1), R 1 、R 2 and R 3 Each independently represents a hydrogen atom, a hydroxyl group, an alkyl group having 1 to 5 carbon atoms, or an alkyl group having 1 to 5 carbon atoms in which one or more hydrogen atoms are substituted with a hydroxyl group. The adhesive composition according to claim 1 , which is used for a polarizing plate. 3 . The adhesive composition according to claim 1 , wherein the polyvinyl alcohol-based resin and the amide compound are dissolved in water. The adhesive composition according to claim 1 , further comprising a cross-linking agent.

5. The adhesive composition according to claim 1, wherein The polyvinyl alcohol-based resin accounts for 80% by mass or more of the resins contained in the adhesive composition.

6. The adhesive composition according to claim 1, wherein The content of the amide compound is 5% by mass to 90% by mass based on the total solid content of the adhesive composition.

7. The adhesive composition according to claim 1, wherein In the formula (1), R 3 A hydrogen atom.

8. The adhesive composition according to claim 1, wherein The liquid turbidity is less than 10%.

9. A method for manufacturing a polarizing plate, wherein: The polarizing plate includes a polyvinyl alcohol-based resin polarizing film formed by iodine adsorption and orientation, and a protective film. The method for producing the polarizing plate includes the step of bonding the polyvinyl alcohol-based resin polarizing film and the protective film together via the adhesive composition according to any one of claims 1 to 8.

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