TW202045668A - Adhesive and polarizing plate - Google Patents

Abstract

Provided are: an adhesive with which it is possible to produce a polarizing plate in which it is possible to adequately suppress a reduction in light transmittance in a high temperature endurance test; and a polarizing plate obtained using this adhesive. This adhesive for producing a polarizing plate is used for bonding a polarizing film containing poly(vinyl alcohol) and a protective film containing a cellulose ester-based resin, and contains an acid scavenger and a non-volatile component other than the acid scavenger. The content of the acid scavenger is 0.1 parts by mass or more relative to 100 parts by mass of the non-volatile component.

Description

Adhesive and polarizing plate

The present invention relates to adhesives and polarizing plates.

The polarizing plate with light transmission and shielding function, and the liquid crystal that changes the polarization state of light, are the basic components of a liquid crystal display (LCD). Most polarizing plates have a structure in which a protective film such as a triacetate cellulose (TAC) film is attached to the surface of the polarizing film. Regarding the polarizing film constituting the polarizing plate, a polyvinyl alcohol film (hereinafter, "polyvinyl alcohol" is abbreviated as "PVA") is uniaxially stretched and aligned with iodine-based films. dye (I ₃ ^-, I ₅ ^-, etc.), organic dichroic dyes of dichroic dye donor line become mainstream. Such a polarizing film system uniaxially stretches a PVA film containing a dichroic dye in advance, or absorbs the dichroic dye at the same time as the uniaxial stretching of the PVA film, or makes the PVA film uniaxially stretched. Manufactured by adsorption of dichroic pigments, etc.

LCD can be used in a wide range of small machines such as calculators and watches, notebook computers, LCD TVs, mobile phones, and tablet terminals. In recent years, LCDs have also been used as video display devices for in-vehicle use such as car navigation devices and reversing monitors. Along with this, LCDs are required to have high durability in a harsher environment than before.

It is known that it is necessary to supply an image display device formed by bonding a polarizing plate through an adhesive layer between an image display cell and a transparent plate such as a front panel and a touch panel to a vehicle-mounted display. During the long-term high temperature durability test, the light transmittance of the polarizing plate will decrease. This is due to the polyolefinization of the PVA constituting the polarizing film as one of the reasons, and the lower the light transmittance of the polarizing plate becomes more pronounced under higher temperature conditions.

Regarding the problem of polyolefinization of such a polarizing plate, Patent Document 1 describes that polyolefinization can be suppressed by using a polarizing plate provided with a protective film with high moisture permeability on the surface of the polarizing film. Patent Document 2 describes that polyolefinization can be suppressed by adjusting the thickness of the adhesive for bonding the polarizing plate, the image display unit, and the transparent plate, and the absorbance of the polarizing film. [Prior Technical Literature] [Patent Literature]

[Patent Document 1] JP 2014-102353 A [Patent Document 2] Japanese Patent Application Publication No. 2018-25764

[The problem to be solved by the invention]

However, according to the research of the inventors, the methods described in Patent Documents 1 and 2 have a tendency to suppress the decrease in the light transmittance of the polarizing plate, but in recent years they are required to be used in a high temperature environment of 105°C or higher. In the endurance test, a sufficient polyolefinization inhibitory effect could not be confirmed.

The present invention was completed based on the above circumstances, and its object is to provide an adhesive capable of producing a polarizing plate capable of sufficiently suppressing a decrease in light transmittance in a high temperature endurance test, and a polarizing plate obtained by using the adhesive. [Means to solve the problem]

The inventors of the present invention repeated careful studies in order to achieve the above object, and found that the polyolefinization of PVA in the polarizing film of the polarizing plate is promoted by the acid generated from the protective film, and by making the polarizing film adhere to it. The adhesive used with the protective film contains an acid scavenger and can suppress polyolefination. Based on these knowledge and findings, the present invention was completed by repeating further studies.

That is, the present invention is about [1] An adhesive for the production of a polarizing plate for adhering a polarizing film containing polyvinyl alcohol and a protective film containing a cellulose ester resin, which contains an acid scavenger and other than the above acid scavenger Non-volatile components, and relative to 100 parts by mass of the non-volatile components, the content of the acid scavenger is 0.1 parts by mass or more; [2] The adhesive of [1], wherein the non-volatile component does not contain a urethane resin, or the non-volatile component contains a urethane resin, and the urethane resin is in the non-volatile The content of the ingredients is 3% by mass or less; [3] The adhesive of [1] or [2], wherein the acid scavenger is a carbodiimide compound having at least one carbodiimide group; [4] The adhesive according to any one of [1] to [3], wherein the content of the acid scavenger is 0.1 part by mass to 50 parts by mass relative to 100 parts by mass of the non-volatile component; [5] The adhesive according to any one of [1] to [4], wherein the non-volatile component includes polyvinyl alcohol; [6] The adhesive of any one of [1] to [5], wherein the acid scavenger is water-soluble; [7] A polarizing plate comprising a polarizing film containing polyvinyl alcohol, a protective film containing a cellulose ester resin, and an adhesive layer provided between the polarizing film and the protective film, wherein the The adhesive layer is formed of the adhesive as in any one of [1] to [6]. [Effects of Invention]

According to the present invention, it is possible to provide an adhesive capable of producing a polarizing plate capable of sufficiently suppressing a decrease in light transmittance in a high temperature endurance test, and a polarizing plate obtained by using the adhesive.

[Form to implement the invention]

The following is a detailed description of the embodiments of the present invention. ＜Adhesive agent＞ The adhesive of the present invention is used to bond a polarizing film containing PVA and an adhesive for manufacturing a polarizing plate to a protective film containing a cellulose ester resin. The adhesive agent of the present invention contains an acid scavenger and non-volatile components other than the acid scavenger, and the content of the acid scavenger is 0.1 parts by mass or more with respect to 100 parts by mass of the non-volatile components. In this specification, non-volatile components other than the acid scavenger are simply referred to as "non-volatile components". That is, the term "non-volatile components" refers to components other than acid scavengers and solvents.

Generally, when a polarizing film provided with a stretched PVA film and a protective film containing a cellulose ester is exposed to a high temperature for a long period of time, acid is generated by hydrolysis of the cellulose ester constituting the protective film. It is estimated that this acid becomes a catalyst for the dehydration reaction of PVA, and the PVA in the polarizing film will be polyalkylenized. When the polarizing film and the protective film are bonded by the adhesive of the present invention to produce a polarizing plate, a sufficient amount of acid scavenger may be present in the adhesive layer formed by the adhesive. Therefore, the acid generated from the protective film is captured by the acid scavenger existing in the adhesive layer, and the acid becomes difficult to reach the polarizing film, and the polyolefinization of PVA in the polarizing film in the polarizing plate can be suppressed. That is, according to this adhesive, it is possible to manufacture a polarizing plate capable of sufficiently suppressing a decrease in light transmittance in a high temperature endurance test. Below, each component etc. are demonstrated in detail.

唑啉基的化合物、烷基磷酸金屬鹽、強鹼性胺基化合物、萜烯系化合物、

化合物等之有機系化合物、及水滑石石群等之無機化合物等。所謂有機化合物，係指包含碳的化合物，所謂無機化合物，係指有機化合物以外的化合物。此外，酸捕捉劑亦有被稱為酸去除劑、酸捕獲劑、酸捕集劑等的情況，但在本發明中，並無因此等稱呼所致的差異而皆可使用。酸捕捉劑可1種單獨使用，亦可將2種以上組合而使用。(Acid scavenger) The acid scavenger is a compound that reacts with an acid to inactivate the acid. The acid scavenger includes, for example, a compound having a carbodiimide group (–N=C=N–), a compound having an epoxy group, and

Oxazoline-based compounds, alkyl phosphate metal salts, strongly basic amino-based compounds, terpene-based compounds,

Organic compounds such as chemical compounds, and inorganic compounds such as hydrotalcite group. The organic compound refers to a compound containing carbon, and the inorganic compound refers to a compound other than an organic compound. In addition, acid scavengers are sometimes called acid removers, acid scavengers, acid scavengers, etc., but in the present invention, they can be used without any difference due to such names. An acid scavenger may be used individually by 1 type, and may be used in combination of 2 or more types.

The acid scavenger is preferably an organic compound, and more preferably a carbodiimide compound having at least one carbodiimide group. The carbodiimide compound has a large polyolefination inhibitory effect, and is also preferable from the viewpoint of handling properties and safety.

With regard to the mass (molecular formula weight) of the group capable of capturing an acid per 1 mol of the acid scavenger, for example, it is preferably 200 g/mol or more and 1,000 g/mol or less, and more preferably 400 g/mol or less. When the acid scavenger is a carbodiimide compound, the mass (molecular formula weight) of the group capable of capturing an acid per 1 mol is also referred to as the carbodiimide group equivalent, and is the mass per 1 mol of the carbodiimide group.

When the non-volatile component of the adhesive of the present invention contains a water-soluble resin such as PVA described later, the acid scavenger is preferably water-soluble. By using a water-soluble acid scavenger that is easily compatible with water-soluble resins, the adhesive layer formed by the adhesive of the present invention tends to have low haze, so a polarizing plate with good light transmittance and polarization performance can be obtained . In addition, the term "water-soluble" means that the solubility in water is 1 g/100 g or more of water. The so-called solubility in water refers to the limit amount (mass) of 100 g of water dissolved at 20°C. The lower limit of the solubility of the acid scavenger in water is preferably 2 g/100 g of water, and more preferably 3 g/100 g of water. On the other hand, the upper limit of the solubility may be 200 g/100 g of water, 100 g/100 g of water or 50 g/100 g of water, for example.

The molecular weight of the acid scavenger is not particularly limited, and for example, an acid scavenger having a molecular weight of 100 or more or 200 or more is used. The acid scavenger may be a polymer. The term "polymer" refers to a molecule having a weight average molecular weight of 300 or more. The weight average molecular weight is preferably 1,000 or more, more preferably 3,000 or more. On the other hand, the upper limit of the weight average molecular weight of the polymer acid scavenger may be, for example, 100,000 or 10,000.

Commercial products of acid scavengers include 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride manufactured by FUJIFILM Wako Pure Chemical Corporation and manufactured by Nippon Shokubai Co., Ltd. EPOCROS SERIES, water-soluble polycarbodiimide resin CARBODILITE SERIES manufactured by Nisshinbo Chemical Co., Ltd., etc.

In the adhesive, the lower limit of the content of the acid scavenger relative to 100 parts by mass of non-volatile components is 0.1 parts by mass, preferably 1 part by mass, more preferably 3 parts by mass, still more preferably 10 parts by mass, and more It is more preferably 20 parts by mass, and still more preferably 30 parts by mass. By setting the content of the acid scavenger to be greater than or equal to the above lower limit, it is possible to produce a polarizing plate that has an improved ability to capture acid, exhibits a sufficient function of suppressing polyolefination in a high-temperature endurance test, and can more sufficiently suppress a decrease in light transmittance. On the other hand, the upper limit of this content may be 100 parts by mass, for example, but is preferably 50 parts by mass, and more preferably 40 parts by mass. By setting the content of the acid scavenger to be equal to or less than the above upper limit, the adhesive performance can be improved, and the haze of the formed adhesive layer can be suppressed, and the light transmittance and polarization performance can be improved.

The content of the acid scavenger in the adhesive of the present invention can be obtained by analyzing the polarizing plate manufactured using the adhesive of the present invention. The analysis method is not particularly limited. For example, after removing the protective film of the polarizing plate by using a solvent or the like, the polarizing film of the adhesive layer is subjected to Soxhlet extraction with a solvent such as methanol to capture the acid contained in the film The agent is extracted into the solvent for analysis.

(Non-volatile ingredients) The type of the adhesive of the present invention is not particularly limited, but generally, an aqueous adhesive containing a PVA aqueous solution in which PVA or the like is dissolved as a main component, or a solvent-free active energy ray hardening adhesive is used. That is, the main component of the non-volatile component in the adhesive of the present invention is usually resin such as PVA, other water-soluble resins, and active energy ray curable resins.

(PVA(A)) The non-volatile component preferably contains PVA. Hereinafter, the PVA contained in the adhesive of the present invention is referred to as "PVA(A)". By including PVA (A) in the non-volatile component, the adhesion between the polarizing film and the protective film can be improved.

PVA(A) is a polymer with vinyl alcohol unit (-CH ₂ -CH(OH)-) as the main structural unit. For PVA(A), unmodified PVA and modified PVA can be used. The so-called unmodified PVA is PVA obtained by saponifying a vinyl ester polymer, which is obtained by polymerizing only vinyl ester monomers such as vinyl acetate. An example of the modified PVA is a saponified product of a copolymer of a vinyl ester-based monomer and a monomer having copolymerizability with the vinyl ester-based monomer. The modified PVA can also be modified PVA after acetyl acetyl modified PVA. Acetyl Acetyl-modified PVA is, for example, unmodified PVA, its derivatives, or modified PVA acetalization, carbamateization, etherification, grafting, phosphate esterification, etc. Modified PVA introduced by acetyl. In order to obtain sufficient water resistance, the acetyl acetyl content of the acetyl acetyl modified PVA is preferably 0.1 mol to 40 mol%.

With regard to monomers having copolymerizability with vinyl ester monomers, unsaturated carboxylic acids such as maleic acid (anhydride), fumaric acid, crotonic acid, itaconic acid, (meth)acrylic acid, etc., and Its esters, ethylene, propylene and other α-olefins, (meth) allyl sulfonic acid (sodium), sodium sulfonate (monoalkyl maleate), sodium disulfonate alkyl maleate, N- Hydroxymethacrylamide, acrylamide alkyl sulfonic acid alkali salt, N-vinylpyrrolidone, N-vinylpyrrolidone derivatives, etc. One or two or more of these are used in combination.

According to the number of moles of all structural units constituting PVA(A), the upper limit of the ratio of the structural units derived from monomers having copolymerization with vinyl ester monomers is preferably 15 mole%, more preferably 10 moles. Ear% is more preferably 5 mol%, still more preferably 1 mol%.

As far as PVA (A) is concerned, it is better to use one that has not been grafted copolymerized. However, PVA (A) can be modified by one or more monomers that can be grafted and copolymerized. The graft copolymerization can be performed on at least one of polyvinyl ester and PVA obtained by saponifying it. Examples of monomers that can be grafted and copolymerized include unsaturated carboxylic acids or derivatives thereof; unsaturated sulfonic acids or derivatives thereof; α-olefins having 2 to 30 carbon atoms and the like. According to the number of moles of all the structural units constituting the polyvinyl ester or PVA, the ratio of the structural units derived from the graft-copolymerizable monomer in the polyvinyl ester or PVA is preferably 5 mole% or less.

PVA (A) has a part of hydroxyl groups that may be crosslinked or uncrosslinked. In addition, PVA (A) has a part of its hydroxyl groups that can react with aldehyde compounds such as acetaldehyde and butyraldehyde to form an acetal structure.

The lower limit of the degree of polymerization of PVA (A) is preferably 100, more preferably 500, still more preferably 1,000, and still more preferably 1,500. On the other hand, the upper limit of the degree of polymerization is preferably 4,000, more preferably 3,000. When the degree of polymerization of PVA (A) is within the above-mentioned range, adhesiveness and the like can be improved. In addition, the degree of polymerization of PVA means the average degree of polymerization measured in accordance with the description of JIS K6726-1994.

The lower limit of the degree of saponification of PVA(A) is preferably 85 mol%, more preferably 90 mol%, further preferably 95 mol%, still more preferably 99 mol%, particularly preferably 99.5 mol% %. The upper limit of the degree of saponification is not particularly limited, and it may be 100 mol% or 99.99 mol%. When the degree of saponification of PVA (A) is within the above range, adhesiveness and the like can be improved. The so-called saponification degree of PVA refers to the ratio of the molar number of vinyl alcohol units to the total molar number of structural units (typically vinyl ester units) that can be converted into vinyl alcohol units by saponification and vinyl alcohol units (Mole%). The degree of saponification can be measured in accordance with the description of JIS K6726-1994.

The lower limit of the content of PVA (A) in the adhesive of the present invention is preferably 0.1% by mass, more preferably 0.5% by mass, and still more preferably 2% by mass. On the other hand, the upper limit of the content rate is preferably 15% by mass, more preferably 10% by mass, and still more preferably 6% by mass. In addition, the lower limit of the content of PVA (A) in the non-volatile components in the adhesive of the present invention is preferably 50% by mass, more preferably 70% by mass, and still more preferably 90% by mass, 95% by mass. Mass% or 99% by mass. On the other hand, the upper limit of the content rate of PVA (A) in non-volatile components may be 100% by mass or 90% by mass. When the content of PVA (A) is in the above-mentioned range, adhesiveness and the like can be improved.

(Urethane resin) It is preferable that the non-volatile component of the adhesive agent of this invention does not contain a urethane resin. In addition, even in the case where the non-volatile component contains a urethane resin, the upper limit of the content of the urethane resin in the non-volatile component is preferably 3% by mass, more preferably 2% by mass, and more It is preferably 1% by mass, more preferably 0.5% by mass, and still more preferably 0.1% by mass. The urethane resin may react with the acid scavenger. Therefore, by reducing the content of the urethane resin in the adhesive, the acid trapping ability of the acid scavenger can be fully utilized, and a polarizing plate can be manufactured that can more fully suppress the decrease in light transmittance in the high temperature durability test .

Examples of the urethane resin include commercially available products such as ADEKA BONTIGHTER SERIES manufactured by ADEKA Co., Ltd., OLESTER SERIES manufactured by Mitsui Chemicals Co., Ltd., HYDRAN SERIES manufactured by DIC Co., Ltd., and SANPRENE manufactured by Sanyo Chemical Co., Ltd. SERIES etc.

The content of the urethane resin in the non-volatile component of the adhesive of the present invention is the same as the acid scavenger, and it can also be obtained by analyzing the polarizing plate manufactured using the adhesive of the present invention. The analysis method is not particularly limited, but the analysis can be performed by extracting the urethane resin into the solvent by the same method as the acid trapping agent.

(Crosslinking agent) In order to obtain sufficient adhesiveness, water resistance, etc., a crosslinking agent may be included in the non-volatile component of the adhesive of the present invention. It may also contain no crosslinking agent. As for the crosslinking agent, alkylene diamines, isocyanates, epoxies, aldehydes, and further divalent or trivalent metals such as sodium, potassium, magnesium, calcium, aluminum, iron, nickel, etc. The salt and its oxides. The content of the crosslinking agent in the non-volatile components is, for example, preferably from 0.1% by mass to 30% by mass, and more preferably from 1% by mass to 20% by mass.

(Other ingredients) The adhesive of the present invention may further contain other components as non-volatile components. However, with regard to the upper limit of the content of components other than PVA (A) and the crosslinking agent in the non-volatile components, it is preferably 10% by mass, more preferably 1% by mass, and further Preferably it is the case of 0.1 mass %. By reducing the content of components other than PVA (A) and the crosslinking agent, it is possible to further improve adhesion and light transmittance.

As components other than the acid scavenger and non-volatile components, the adhesive of the present invention may further include a solvent. When the adhesive of the present invention contains a water-soluble resin such as PVA (A) as a non-volatile component, the solvent is usually water. However, a mixed solvent of water and other solvents can also be used. The lower limit of the water content in the adhesive of the present invention may be, for example, 10% by mass, but is preferably 30% by mass, more preferably 50% by mass, still more preferably 70% by mass, and particularly preferably 90% by mass. By setting the content of water at least the above lower limit, the acid scavenger, PVA (A), etc. can be sufficiently dissolved. From the viewpoint of drying efficiency and the like, the upper limit of the water content in the adhesive of the present invention is preferably, for example, 99% by mass, and more preferably 97% by mass.

(Method of manufacturing adhesive) The manufacturing method of the adhesive agent of this invention is not specifically limited. For example, when PVA (A) is included as a non-volatile component, one or two or more of any components such as acid scavenger, PVA (A), and crosslinking agent can be mixed in water and stirred until it becomes Manufactured until uniform. The temperature, stirring method, time, etc. at the time of production can be carried out under any conditions as long as the adhesive does not lose its function.

＜Polarizing plate＞ The polarizing plate of the present invention includes a polarizing film containing PVA, a protective film containing a cellulose ester resin, and an adhesive layer provided between the polarizing film and the protective film. The above-mentioned adhesive layer is a layer formed of the adhesive of the present invention. In addition, the polarizing film containing PVA is usually a stretched film produced using a non-stretched PVA film containing PVA as a raw film.

(PVA film) The PVA film used as the original film of the polarizing film will be described below. In addition, the PVA contained in the PVA film or the polarizing film is referred to as "PVA(B)".

(PVA(B)) The PVA film contains PVA (B). The lower limit of the degree of polymerization of PVA (B) is preferably 1,000, more preferably 1,500, and still more preferably 1,700. When the degree of polymerization of PVA (B) is more than the above lower limit, the flexibility of the PVA film can be improved. On the other hand, the upper limit of the degree of polymerization is preferably 10,000, more preferably 8,000, and still more preferably 5,000. When the degree of polymerization of PVA is equal to or less than the above upper limit, it is possible to suppress the increase in the production cost of PVA (B) and the occurrence of defects during film formation.

From the viewpoints that the humidity and heat resistance of the obtained polarizing film becomes good, the degree of saponification of PVA(B) is preferably 90 mol% or more, more preferably 95 mol% or more, and still more preferably 99 mol% or more , Particularly preferably above 99.5 mol%. The upper limit of the degree of saponification is not particularly limited, and it may be 100 mol% or 99.99 mol%.

The specific aspects of other PVA (B) can be the same as the above-mentioned PVA (A).

The lower limit of the content of PVA (B) in the PVA film is preferably 50% by mass, more preferably 80% by mass, and still more preferably 85% by mass. By setting the content of PVA (B) to be at least the above lower limit, a good polarizing film can be obtained. On the other hand, the upper limit of the content of this PVA (B) is preferably 99% by mass, and more preferably 95% by mass.

(Plasticizer) The PVA film may contain a plasticizer. Since the PVA film contains a plasticizer, the handling and stretchability of the PVA film can be improved. In terms of plasticizers, polyhydric alcohols are more suitable. Specific examples include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerol, triethylene glycol, tetraethylene glycol, and trimethylol The PVA film may contain one or two or more of these plasticizers. From the viewpoint that the stretchability of the PVA film becomes better, glycerin is preferred among these.

With respect to 100 parts by mass of PVA (B), the lower limit of the content of the plasticizer in the PVA film is preferably 2 parts by mass, more preferably 3 parts by mass, and still more preferably 4 parts by mass. On the other hand, with respect to 100 parts by mass of PVA (B), the upper limit of this content is preferably 20 parts by mass, more preferably 17 parts by mass, and still more preferably 14 parts by mass. When the content of the plasticizer in the PVA film is 2 parts by mass or more, the stretchability of the PVA film is improved. On the other hand, when the content of the plasticizer in the PVA film is 20 parts by mass or less, it is possible to suppress the bleed out of the plasticizer to the surface of the PVA film and reduce the handling properties of the PVA film.

(Surfactant) Surfactants may be contained in the PVA film. When a PVA film is produced using the film-forming stock solution described later, by blending the film-forming stock solution with a surfactant, the film forming properties are improved and the occurrence of film thickness unevenness is suppressed, and the metal is used for the film forming In the case of rollers and belts, peeling of the PVA film from these metal rollers and belts becomes easy. When a PVA film is manufactured from a film-forming stock solution blended with a surfactant, the PVA film may contain a surfactant. The types of surfactants blended in the film-forming stock solution used to manufacture the PVA film and the surfactants contained in the PVA film are not particularly limited, but from the viewpoint of peelability from metal rolls and belts, Anionic surfactants and nonionic surfactants are preferred, and nonionic surfactants are particularly preferred. Surfactant can be used individually by 1 type or in combination of 2 or more types.

Examples of the anionic surfactant include carboxylic acid type such as potassium laurate; sulfate type such as octyl sulfate; sulfonic acid type such as lauryl benzenesulfonate, and the like.

As for nonionic surfactants, for example, alkyl ether type such as polyoxyethylene oleyl ether; alkyl phenyl ether type such as polyoxyethylene octyl phenyl ether; polyoxyethylene laurate, etc. Alkyl ester type; polyoxyethylene lauryl amino ether and other alkyl amine type; polyoxyethylene lauramide and other alkyl amide type; polyoxyethylene polyoxypropylene ether and other polypropylene glycol ether type; laurel Alkanolamide type such as diethanolamide and oleic acid diethanolamide; allylphenyl ether type such as polyoxyallyl allyl phenyl ether.

When a surfactant is blended in the film-forming stock solution used to manufacture the PVA film, relative to the PVA contained in 100 parts by mass of the film-forming stock solution or the PVA film, the content of the surfactant in the film-forming stock solution and the PVA film The lower limit of the content of the surfactant is preferably 0.01 part by mass, more preferably 0.02 part by mass. On the other hand, relative to 100 parts by mass of the PVA contained in the film-forming stock solution or the PVA film, the upper limit of the content of the surfactant in the film-forming stock and the content of the surfactant in the PVA film is preferably 0.5 mass Parts, more preferably 0.1 parts by mass. When the content of the surfactant is 0.01 parts by mass or more with respect to 100 parts by mass of PVA, film forming properties and releasability can be improved. On the other hand, when the content of the surfactant is 0.5 parts by mass or less with respect to 100 parts by mass of PVA, it is possible to prevent the surfactant from oozing out to the surface of the PVA film, causing blocking and lowering of handling properties.

(Other ingredients, etc.) The PVA film may contain antioxidants, antifreeze agents, pH adjusters, masking agents, anti-coloring agents, oil agents, etc. in addition to the above-mentioned PVA, acid scavengers, plasticizers and surfactants. However, the content of other components other than PVA (B), plasticizer, and surfactant in the PVA film is preferably 1% by mass or less, and more preferably 0.1% by mass or less. In addition, the content of the inorganic compound in the PVA film is preferably 1% by mass or less, and more preferably 0.1% by mass or less. The above-mentioned other components and inorganic compounds may cause defects such as voids in the obtained polarizing film. Therefore, by reducing the content of the above-mentioned other components and inorganic compounds, the polarization performance of the obtained polarizing film tends to be improved.

The upper limit of the average thickness of the PVA film is not particularly limited, but is, for example, 100 μm, preferably 80 μm, more preferably 60 μm, and still more preferably 40 μm. On the other hand, in terms of the lower limit of the average thickness, it is preferably 5 μm, more preferably 10 μm, and still more preferably 15 μm. When the average thickness of the PVA film is in the above range, handling properties and the like can be improved.

The shape of the PVA film is not particularly limited, but from the viewpoint of producing a polarizing film with good productivity and continuous production, it is preferably a long film. The length of the elongated film is not particularly limited, and can be appropriately set in accordance with the use of the polarizing film to be produced, and for example, it can be set within the range of 5 to 20,000 m. The width of the elongated film is not particularly limited. For example, it can be 50 cm or more. However, since a polarizing film with a large width is required in recent years, it is preferably 1 m or more, more preferably 2 m or more, and still more preferably 4 m or more. The upper limit of the width of the long film is not particularly limited. However, if the width is too large, it tends to be difficult to uniformly stretch when manufacturing a polarizing film with a practical device. Therefore, the width of the PVA film is preferably Below 7m.

The shape of the PVA film is not particularly limited, and may be a single-layer film or a multilayer film (laminate), but from the viewpoint of complexity and cost of the lamination (coating, etc.) operation, a single-layer film is preferred. The PVA film that can be used as the raw material film of the polarizing film is usually a non-stretched film.

(Method of manufacturing PVA film) The manufacturing method of the PVA film is not particularly limited, and a manufacturing method in which the thickness and width of the film after film formation becomes more uniform can be preferably adopted. For example, it is possible to use the above-mentioned PVA (B) constituting the PVA film, as well as further plasticizers, surfactants, and other components as required, and a film formed by dissolving one or two or more of them in a liquid medium Stock solution, or one or more of PVA(B), and further plasticizers, surfactants, other ingredients, and liquid media as needed, and PVA(B) is a molten film-forming stock solution manufacture. When the film forming stock solution contains at least one of a plasticizer, a surfactant, and other components, it is preferable that these components are uniformly mixed.

The above-mentioned liquid medium used in the preparation of the film-forming stock solution includes, for example, water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, and ethylene glycol. , Glycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane, ethylenediamine, diethylenetriamine, etc. From the viewpoint of low load on the environment and recyclability, water is preferred among these.

The volatile fraction of the film-forming stock solution (the ratio of the volatile components in the film-forming stock solution of the liquid medium removed by volatilization and evaporation during film formation) also varies with the film forming method and film forming conditions. The lower limit is preferably 50% by mass, more preferably 55% by mass, and still more preferably 60% by mass. On the other hand, with respect to this upper limit, it is preferably 95% by mass, more preferably 90% by mass, and still more preferably 85% by mass. With the volatile fraction of the film-forming stock solution being 50% by mass or more, the viscosity of the film-forming stock solution will not become too high, and the filtration and defoaming during the preparation of the film-forming stock solution will proceed smoothly, and the PVA film with fewer impurities and defects Manufacturing becomes easy. On the other hand, since the volatile fraction of the film-forming stock solution is 95% by mass or less, the concentration of the film-forming stock solution does not become too low, and the industrial production of the PVA film becomes easy.

As for the film forming method when forming a PVA film using the above-mentioned film forming stock solution, for example, cast film forming method, extrusion film forming method, wet film forming method, gel film forming method, etc. are mentioned, preferably Cast film method and extrusion film method. From the viewpoint of obtaining PVA films with uniform thickness and width and good physical properties, the extrusion film method is more preferable. PVA film can be dried and heat treated according to needs.

The heat treatment temperature is not particularly limited, and may be appropriately adjusted according to the swelling degree of the PVA film in each range. As for the heat treatment temperature, if it is too high, discoloration and deterioration of the PVA film will be observed, so it is preferably 200°C or less, more preferably 180°C or less, and still more preferably 150°C or less. The lower limit of the heat treatment temperature can be set to 80°C, for example.

The heat treatment time is not particularly limited, and may be appropriately adjusted according to the degree of swelling of the PVA film. However, from the viewpoint of efficiently producing the PVA film of the present invention, it is preferably 1 to 60 minutes, more preferably 2 to 40 minutes , More preferably 3 to 30 minutes.

(Polarizing film) The polarizing film is a polarizing film formed of the above-mentioned PVA film. The polarizing film is generally a film obtained by adsorbing dichroic dyes such as iodine-based dyes and dichroic organic dyes on a stretched film obtained by uniaxially stretching and aligning a non-stretched PVA film.

The upper limit of the average thickness of the polarizing film is, for example, 100 μm, preferably 50 μm, and more preferably 30 μm. On the other hand, in terms of the lower limit of the average thickness, it may be 1 μm, preferably 5 μm.

(Method of manufacturing polarizing film) The method for manufacturing the polarizing film is not particularly limited, and any method conventionally used can be adopted. For example, a polarizing film can be manufactured by subjecting the PVA film to swelling treatment, dyeing treatment, uniaxial stretching, and further cross-linking treatment, fixing treatment, drying treatment, heat treatment, etc. as needed. At this time, the order of each treatment such as swelling treatment, dyeing treatment, uniaxial stretching, and fixing treatment is not particularly limited, and one or two or more treatments may be performed simultaneously. In addition, one or two or more of each treatment may be performed twice or more.

The swelling treatment can be performed by immersing the PVA film in water. The lower limit of the temperature of water when immersed in water is preferably 20°C, more preferably 22°C, and still more preferably 25°C. On the other hand, with respect to this upper limit, it is preferably 40°C, more preferably 38°C, and still more preferably 35°C. Moreover, the time for immersion in water is preferably 0.1 to 5 minutes, for example. In addition, the water when immersed in water is not limited to pure water, and may be an aqueous solution in which various components are dissolved, or a mixture of water and an aqueous medium.

The dyeing treatment is performed using dichroic dyes such as iodine-based dyes and dyes, and the timing of dyeing may be any stage before uniaxial stretching, during uniaxial stretching, and after uniaxial stretching. Dyeing is usually performed by immersing the PVA film in a solution (especially an aqueous solution) containing iodine-potassium iodide as a dyeing bath. The concentration of iodine in the dye bath is preferably 0.01 to 0.5% by mass, and the concentration of potassium iodide is preferably 0.01 to 10% by mass. In addition, the temperature of the dyeing bath is preferably set to 20 to 60°C.

The crosslinking treatment can be performed by immersing the PVA film in an aqueous solution containing a crosslinking agent. If cross-linking treatment is performed, cross-linking can be introduced into the PVA film and uniaxially stretched at a higher temperature. As for the crosslinking agent to be used, one or two or more of boron compounds such as boric acid and borax salts can be used. The concentration of the crosslinking agent in the aqueous solution containing the crosslinking agent is preferably from 1 to 15% by mass, more preferably from 2 to 7% by mass. The temperature of the aqueous solution containing the crosslinking agent is preferably 20 to 60°C.

The uniaxial stretching can be performed by either a wet stretching method or a dry stretching method. In the case of the wet stretching method, it may be performed in an aqueous solution containing boric acid, or may be performed in the above-mentioned dyeing bath or a fixed treatment bath described later. In the case of the dry stretching method, it can be carried out in air. Among these, the wet stretching method is preferred, and it is more preferred to perform uniaxial stretching in an aqueous solution containing boric acid. The concentration of boric acid in the boric acid aqueous solution is preferably 0.5 to 6.0% by mass, more preferably 1.0 to 5.0% by mass, and still more preferably 1.5 to 4.0% by mass. Moreover, the boric acid aqueous solution may contain potassium iodide, and its concentration is preferably 0.01-10% by mass.

In the wet stretching method, the stretching temperature in the uniaxial stretching is preferably 30 to 90°C, more preferably 40 to 80°C, and still more preferably 50 to 70°C.

From the viewpoint of the polarization performance of the obtained polarizing film, the stretching ratio in uniaxial stretching is preferably 5 times or more, more preferably 5.5 times or more. The upper limit of the stretching ratio is not particularly limited, but the stretching ratio is preferably 8 times or less.

In the production of the polarizing film, in order to strengthen the adsorption of the dichroic pigment of the PVA film, it is preferable to perform a fixation treatment. Regarding the fixing treatment bath used in the fixing treatment, one or two or more aqueous solutions containing boron compounds such as boric acid and borax can be used. Moreover, if necessary, an iodine compound or a metal compound may be added to the fixed treatment bath. The concentration of the boron compound in the fixed treatment bath is generally 2 to 15% by mass, and particularly preferably about 3 to 10% by mass. The temperature of the fixed treatment bath is 15 to 60°C, particularly preferably 25 to 40°C.

The drying treatment is preferably carried out at 30 to 150°C, and more preferably at 50 to 130°C. By drying at a temperature within the above range, it is easy to obtain a polarizing film having excellent dimensional stability.

(Protective film) The protective film is usually a cellulose ester film containing a cellulose ester resin as a main component. As for the content of the cellulose ester resin in the protective film, it is preferably 70% by mass or more, and more preferably 90% by mass or more. Examples of cellulose ester resins include cellulose triacetate (cellulose triacetate: TAC), cellulose diacetate, cellulose acetate propionate, and cellulose acetate butyrate. , Cellulose acetate benzoate, cellulose acetate propionate benzoate, cellulose propionate, cellulose butyrate, cellulose acetate biphenylate, Cellulose acetate propionate biphenylate and the like, among which cellulose triacetate is preferred.

(Adhesive layer) The adhesive layer is a layer formed of the adhesive of the present invention. The lower limit of the average thickness of the adhesive layer is preferably 0.01 μm, more preferably 0.1 μm. By setting the average thickness of the adhesive layer to be greater than or equal to the above lower limit, the adhesiveness and the effect of suppressing polyolefinization can be improved. On the other hand, the upper limit of the average thickness of the adhesive is preferably 20 μm, more preferably 10 μm. By setting the average thickness of the adhesive layer to be equal to or less than the above upper limit, the appearance and light transmittance can be improved.

The method of forming the adhesive layer, that is, the method of applying the adhesive is not particularly limited, and in addition to methods using a bar coater, a gravure roll, etc., a spray method, a dipping method, etc. may be used. For example, the adhesive of the present invention is applied to at least one surface of a polarizing film or a protective film, bonded to the other film, and heat-treated. Regarding the heat treatment conditions, the temperature can be set to 5 to 150°C, preferably 30 to 120°C, and the treatment time can be set to 10 seconds to 30 minutes. Thereby, the polarizing film surface and the protective film surface are bonded together to obtain a polarizing plate.

Generally, in a polarizing plate using a protective film containing a cellulose ester-based resin, when exposed to a high temperature for a long period of time, an acid that promotes the polyolefinization of the polarizing film is generated by hydrolysis of the cellulose ester of the protective film. In contrast, in this polarizing plate, since the acid trapping agent in the adhesive layer can trap acid, polyolefination is suppressed, and the decrease in light transmittance can be suppressed. [Example]

The present invention is specifically explained by the following examples, but the present invention is not limited to these examples at all. In addition, each evaluation method used in the following Examples and Comparative Examples is shown below.

[Measurement of swelling degree of PVA film] Take about 1.5g of PVA film and cut it into about 2mm×10cm. After that, the cut PVA film was covered with a mesh ("N-N0110S 115" manufactured by NBC Meshtec Co., Ltd.) and immersed in distilled water at 30°C for 15 minutes. Next, the PVA film coated with the screen was subjected to centrifugal dehydration at 3,000 rpm for 5 minutes, and the screen was removed to obtain the mass (W1) of the PVA film. Next, after drying the PVA film with a dryer at 105°C for 16 hours, the mass (W2) was determined. Then, the degree of swelling of the PVA film was calculated by the following formula. Swelling degree (%)=((W1)/(W2))×100

[High temperature durability test] (a) Sample making Cut the polarizing plate into 4cm square, use 10cm square glass plate (1mm thick) and cut 10cm square adhesive sheet (MeCan Imaging CO., LTD "MCS70"; thickness 25μm), according to glass plate/adhesive sheet /Polarizer/Adhesive sheet/Glass plate is laminated in order, and crimping is performed using a laminator. At this time, the polarizing plate is laminated on the center of the glass plate. Thereafter, using a vacuum laminator ("1522N" manufactured by Nisshinbo Mechatronics Inc.), a pressure of 10 kPa was applied at 50°C for 5 minutes to further perform pressure bonding. In addition, the obtained high-temperature durability test sample is one having a light transmittance in the range of 35 to 40% measured by the light transmittance measuring method described later.

(b) High temperature durability test The prepared high-temperature durability test sample was put into a dryer at 105°C for 250 hours. After that, the light transmittance of the sample was measured by the method described later.

(c) Measurement of light transmittance Using a spectrophotometer with integrating sphere ("U-4100" manufactured by Hitachi High-Tech Science Corporation) on the center of the sample for high temperature endurance test, the light transmittance when tilted 45° with respect to the absorption axis of the polarizing film was measured. And the light transmittance when tilted -45°, the average value T (%) of these is obtained. Use the following criteria to determine the high temperature durability. In addition, A, B, and C can be used because they have no practical problems, so they are judged as good, and D is judged as bad. A: The light transmittance after high temperature endurance test is more than 20% B: The light transmittance after the high temperature endurance test is 10% or more and less than 20% C: The light transmittance after high temperature durability test is 1% or more and less than 10% D: The light transmittance after high temperature durability test is less than 1%

The acid scavengers used in Examples and Comparative Examples are shown below. Acid scavenger A: "CARBODILITE V-04" (manufactured by Nisshinbo Chemical Co., Ltd., solubility 5g/water 100g, carbodiimide equivalent of 339g/ mol) Acid scavenger B: "CARBODILITE V-02" (manufactured by Nisshinbo Chemical Co., Ltd., solubility 100g/water 100g, carbodiimide equivalent 602g/ mol) Acid scavenger C: "CARBODILITE SV-02" (manufactured by Nisshinbo Chemical Co., Ltd., solubility 100g/water 100g, carbodiimide equivalent of 429g/ mol)

[Example 1] (1) Manufacturing of PVA film PVA (the saponified product of a homopolymer of vinyl acetate, the degree of polymerization of PVA is 2,400, and the degree of saponification of PVA is 99.95 mol%), glycerin (10 parts by mass relative to 100 parts by mass of PVA), interfacial activity The agent (0.03 parts by mass relative to 100 parts by mass of PVA) was mixed with water and dissolved at 90°C for 4 hours to obtain an aqueous PVA solution. Thereafter, in order to defoam the PVA aqueous solution, the PVA aqueous solution was kept at 85°C for 16 hours.

The obtained PVA aqueous solution was dried on a metal roll at 80°C, and the obtained film was heat-treated in a dryer at 110°C for 10 minutes to obtain a PVA film (average thickness 30 μm) with a swelling degree of 200%.

(2) Manufacturing of polarizing film A test piece of 9 cm in the length direction×10 cm in the width direction was taken from the obtained PVA film. The both ends of the test piece in the longitudinal direction were fixed to a stretching jig so that the size of the stretched part became 5 cm in the length direction × 10 cm in the width direction, and was immersed in water at a temperature of 30°C for 38 seconds. The stretching speed per minute is uniaxially stretched in the length direction (first stage stretching) to 2.2 times the original length. Thereafter, the test piece was immersed in an iodine/potassium iodide aqueous solution at a temperature of 30°C containing iodine at a concentration of 0.03% by mass and potassium iodide at a concentration of 3% by mass for 60 seconds, and stretched at 24 cm/min. The speed is uniaxially stretched in the longitudinal direction (second-stage stretch) to 3.3 times the original length. Next, while immersing the test piece in a boric acid/potassium iodide aqueous solution containing boric acid at a concentration of 3% by mass and potassium iodide at a concentration of 3% by mass for about 20 seconds, a stretching speed of 24 cm/min was applied. It is uniaxially stretched in the longitudinal direction (third-stage stretch) to 3.6 times the original length. Next, the test piece was immersed in a boric acid/potassium iodide aqueous solution at a temperature of 58°C at a concentration of 4% by mass and potassium iodide at a concentration of about 5% by mass, and stretched at a length of 24 cm/min. Uniaxial stretching (4th stage stretching) to 5.5 times the original length. After that, the test piece was immersed in a potassium iodide aqueous solution containing boric acid at a concentration of 1.5% by mass and potassium iodide at a concentration of 3% by mass for 10 seconds for fixing treatment, and then dried with a dryer at 60°C for 4 minutes. A polarizing film (average thickness of 13 μm) was obtained.

(3) Manufacturing of adhesive PVA (which is a saponified product of a homopolymer of vinyl acetate, the degree of polymerization of PVA is 2,400, and the degree of saponification of PVA is 99.95 mol%), and acid scavenger A as an acid scavenger (relative to 100 parts by mass (PVA (40 parts by mass)) was added to water and then dissolved at 90°C for 2 hours. In this way, an aqueous solution with a PVA concentration of 3.5% by mass was obtained. Use this PVA aqueous solution as an adhesive.

(4) Manufacturing of polarizing plate A test piece of 10 cm in the length direction and 5 cm in the width direction was taken from the obtained polarizing film. On both sides of this test piece (polarizing film), a cellulose triacetate film was bonded using the adhesive obtained above, and dried at 60°C for 10 minutes to produce a polarizing plate. In addition, the coating amount was adjusted so that the average thickness of the adhesive layer became about 1 μm.

Using a polarizing plate, according to the above-mentioned method, a high-temperature endurance test was performed and the light transmittance was evaluated. The results are shown in Table 1.

[Example 2] Except having used acid scavenger B as an acid scavenger, it carried out similarly to Example 1, and produced an adhesive agent and a polarizing plate. Evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

[Example 3] Except having used acid scavenger C as an acid scavenger, it carried out similarly to Example 1, and produced an adhesive agent and a polarizing plate. Evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

[Example 4] Except that the content (addition amount) of the acid scavenger A was set to 5 parts by mass with respect to 100 parts by mass of PVA, the same procedure as in Example 1 was carried out to produce an adhesive and a polarizing plate. Evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

[Example 5] In the production of the adhesive agent, except that 90 parts by mass of PVA, 10 parts by mass of urethane resin, and 40 parts by mass of acid scavenger A were added to water, the same procedure as in Example 1 was carried out to produce an adhesive agent And polarizer. Each evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

[Comparative Example 1] Except not adding an acid trapping agent, it carried out similarly to Example 1, and produced an adhesive agent and a polarizing plate. Each evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

[Comparative Example 2] Except that the content (addition amount) of the acid scavenger A was 0.01 parts by mass with respect to 100 parts by mass of PVA, it was carried out in the same manner as in Example 1, and an adhesive and a polarizing plate were produced. Evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

[Table 1] Acid scavenger Non-volatile ingredients High temperature durability test results PVA Urethane resin 105℃、250h species Add amount Add amount Add amount Light transmittance (%) determination (Parts by mass) (Parts by mass) (Parts by mass) Example 1 A 40 100 0 40 A Example 2 B 40 100 0 31 A Example 3 C 40 100 0 twenty four A Example 4 A 5 100 0 twenty three A Example 5 A 40 90 10 12 B Comparative example 1 - 0 100 0 0.4 D Comparative example 2 A 0.01 100 0 0.4 D

As shown in Table 1, the polarizing plates obtained by using the adhesives of Examples 1 to 5 with a content of 0.1 parts by mass or more of the non-volatile acid scavenger relative to 100 parts by mass of the non-volatile components sufficiently suppressed light in the high temperature durability test. Decrease in transmittance. In addition, the polarizing plate obtained by using the adhesive of Example 5 containing a urethane resin has a slightly inferior effect. [Possibility of Industrial Use]

The adhesive of the present invention can be suitably used for the production of polarizing plates.

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Claims (7)

An adhesive for the production of a polarizing plate for adhering a polarizing film containing polyvinyl alcohol and a protective film containing cellulose ester resin, which contains an acid scavenger and non-volatile components other than the acid scavenger And the content of the acid scavenger is 0.1 parts by mass or more with respect to 100 parts by mass of the non-volatile components. Such as the adhesive of claim 1, wherein the non-volatile component does not contain urethane resin, or The non-volatile component includes a urethane resin, and the content of the urethane resin in the non-volatile component is 3% by mass or less. The adhesive of claim 1 or 2, wherein the acid scavenger is a carbodiimide compound having at least one carbodiimide group. The adhesive according to any one of claims 1 to 3, wherein the content of the acid scavenger is 0.1 part by mass or more and 50 parts by mass or less relative to 100 parts by mass of the non-volatile component. The adhesive according to any one of claims 1 to 4, wherein the non-volatile component comprises polyvinyl alcohol. The adhesive according to any one of claims 1 to 5, wherein the acid scavenger is water-soluble. A polarizing plate comprising a polarizing film containing polyvinyl alcohol, a protective film containing cellulose ester resin, and an adhesive layer provided between the polarizing film and the protective film, wherein the adhesive layer It is formed by the adhesive of any one of claims 1 to 6.