WO2020184657A1

WO2020184657A1 - Adhesive and polarizing plate

Info

Publication number: WO2020184657A1
Application number: PCT/JP2020/010766
Authority: WO
Inventors: 絵美川崎; 孝徳磯崎
Original assignee: 株式会社クラレ
Priority date: 2019-03-14
Filing date: 2020-03-12
Publication date: 2020-09-17
Also published as: JP7394112B2; CN113544230B; TW202045668A; TWI836033B; CN113544230A; KR20210139232A; JPWO2020184657A1

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

Adhesives and polarizing plates

The present invention relates to an adhesive and a polarizing plate.

A polarizing plate having a function of transmitting and shielding light is a basic component of a liquid crystal display (LCD) together with a liquid crystal that changes the polarization state of light. Many polarizing plates have a structure in which a protective film such as a triacetyl cellulose (TAC) film is bonded to the surface of the polarizing film. The polarizing film constituting the polarizing plate, a polyvinyl alcohol film (hereinafter, "polyvinyl alcohol" and "PVA" and is sometimes abbreviated) uniaxially stretched iodine to stretched film was oriented dye (I ₃ ^- Ya I ₅ ^- etc.) And dichroic organic dyes that adsorb dichroic dyes are the mainstream. Such a polarizing film can be obtained by uniaxially stretching a PVA film containing a dichroic dye in advance, adsorbing a bicolor dye at the same time as uniaxially stretching the PVA film, or uniaxially stretching the PVA film and then dichroic. Manufactured by adsorbing dyes.

LCDs have come to be widely used in small devices such as calculators and wristwatches, notebook computers, LCD TVs, mobile phones, tablet terminals, and the like. In recent years, LCDs have also been used as in-vehicle image display devices such as car navigation devices and back monitors. Along with this, LCDs are required to have high durability in harsher environments than before.

An image display device configured by laminating a polarizing plate between an image display cell and a transparent plate such as a front plate or a touch panel via an adhesive layer is provided at a high temperature for a long time required for an in-vehicle display. It is known that the light transmittance of a polarizing plate decreases when it is subjected to a durability test. One of the causes is the polyene formation of PVA constituting the polarizing film, and the higher the temperature condition, the more remarkable the decrease in the light transmittance of the polarizing plate.

Regarding the problem of polyene formation of such a polarizing plate, Patent Document 1 describes that polyene formation can be suppressed by adopting a polarizing plate having a protective film having a high moisture permeability on the surface of the polarizing film. Patent Document 2 describes that polyene formation can be suppressed by adjusting the thickness of the pressure-sensitive adhesive used for bonding the polarizing plate to the image display cell or the transparent plate and the absorbance of the polarizing film.

Japanese Unexamined Patent Publication No. 2014-102353 JP-A-2018-25764

However, according to the studies by the inventors, although the methods described in Patent Documents 1 and 2 tend to suppress the decrease in the light transmittance of the polarizing plate, the temperature is 105 ° C. or higher, which has been required in recent years. In the durability test in a high temperature environment, a sufficient effect of suppressing polyene formation could not be confirmed.

The present invention has been made based on the above circumstances, and uses an adhesive capable of producing a polarizing plate capable of sufficiently suppressing a decrease in light transmittance in a high temperature durability test, and an adhesive using this adhesive. An object of the present invention is to provide a obtained polarizing plate.

As a result of diligent studies to achieve the above object, the present inventors have found that the polyene formation of PVA in the polarizing film provided on the polarizing plate is promoted by the acid generated from the protective film, and that the polarizing film and the protective film are promoted. It was found that polyene formation was suppressed by including an acid trapping agent in the adhesive used for adhering to and, and based on these findings, further studies were carried out to complete the present invention.

That is, the present invention
[1] An adhesive for producing a polarizing plate for adhering a polarizing film containing polyvinyl alcohol and a protective film containing a cellulose ester resin, which contains an acid trapping agent and a non-volatile component other than the acid trapping agent. , An adhesive in which the content of the acid trapping agent with respect to 100 parts by mass of the non-volatile component is 0.1 parts by mass or more;
[2] The adhesive according to [1], wherein the non-volatile component does not contain a urethane resin, or the non-volatile component contains a urethane resin, and the content of the urethane resin in the non-volatile component is 3% by mass or less.
[3] The adhesive according to [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 with respect to 100 parts by mass of the non-volatile component is 0.1 part by mass or more and 50 parts by mass or less.
[5] The adhesive according to any one of [1] to [4], wherein the non-volatile component contains polyvinyl alcohol;
[6] The adhesive according to any one of [1] to [5], wherein the acid scavenger is water-soluble;
[7] A polarizing plate including 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 adhesive layer is [7]. A polarizing plate formed from the adhesive according to any one of 1] to [6];
Regarding.

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 durability test, and a polarizing plate obtained by using this adhesive.

Hereinafter, embodiments of the present invention will be described in detail.
<Adhesive>
The adhesive of the present invention is an adhesive for producing a polarizing plate for adhering a polarizing film containing PVA and a protective film containing a cellulose ester resin. The adhesive of the present invention contains an acid scavenger and a non-volatile component other than the acid scavenger, and the content of the acid scavenger with respect to 100 parts by mass of the non-volatile component is 0.1 part by mass or more. In the present specification, non-volatile components other than the acid scavenger are simply referred to as “non-volatile components”. That is, the non-volatile component means a component other than the acid scavenger and the solvent.

Normally, when a polarizing plate including a polarizing film which is a stretched PVA film and a protective film containing a cellulose ester is exposed to a high temperature for a long period of time, the cellulose ester constituting the protective film is hydrolyzed to cause acid. Generate. It is presumed that this acid acts as a catalyst for the dehydration reaction of PVA and the PVA in the polarizing film is polyeneified. When a polarizing film and a protective film are adhered to each other by the adhesive of the present invention to produce a polarizing plate, a sufficient amount of acid trapping agent is present in the adhesive layer formed by the adhesive. Therefore, the acid generated from the protective film is captured by the acid scavenger present in the adhesive layer, making it difficult for the acid to reach the polarizing film, and suppresses polyene formation of PVA in the polarizing film in the polarizing plate. be able to. That is, according to the adhesive, it is possible to manufacture a polarizing plate capable of sufficiently suppressing a decrease in light transmittance in a high temperature durability test. Hereinafter, each component and the like will be described in detail.

(Acid scavenger)
An acid scavenger is a compound that reacts with an acid to inactivate the acid. Examples of the acid trapping agent include compounds having a carbodiimide group (-N = C = N-), compounds having an epoxy group, compounds having an oxazoline group, alkyl phosphate metal salts, strongly basic amino compounds, and terpene compounds. Examples thereof include organic compounds such as oxazine compounds and inorganic compounds such as hydrotalcite stones. The organic compound means a compound containing carbon, and the inorganic compound means a compound other than the organic compound. The acid scavenger may be referred to as an acid scavenger, an acid scavenger, an acid catcher, etc., but in the present invention, it can be used without any difference depending on these names. The acid scavenger may be used alone or in combination of two or more.

The acid scavenger is preferably an organic compound, more preferably a carbodiimide compound having at least one carbodiimide group. The carbodiimide compound has a large effect of suppressing polyene formation, and is also preferable from the viewpoint of handleability and safety.

The mass (molecular formula amount) per 1 mol of the group capable of trapping the acid in the acid scavenger is, for example, 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 amount) per 1 mol of the group capable of capturing the acid 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 trapping agent that is easily compatible with the water-soluble resin, the haze of the adhesive layer formed from the adhesive of the present invention tends to be low, so that the polarizing plate has good light transmittance and polarization performance. Can be obtained. In addition, "water-soluble" means that the solubility in water is 1 g / 100 g or more of water. Solubility in water refers to the limit amount (mass) of dissolution in 100 g of water at 20 ° C. As the lower limit of the solubility of the acid scavenger in water, 2 g / 100 g of water is preferable, and 3 g / 100 g of water is more preferable. On the other hand, the upper limit of this solubility may be, for example, 200 g / 100 g of water, 100 g / 100 g of water, or 50 g / 100 g of water.

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 “polymer” refers to a molecule having a weight average molecular weight of 300 or more, and the weight average molecular weight is preferably 1,000 or more, and more preferably 3,000 or more. On the other hand, the upper limit of the weight average molecular weight of the high molecular weight acid scavenger may be, for example, 100,000 or 10,000.

Commercially available acid scavengers include 1-ethyl-3- (3-dimethylaminopropyl) carbodiimide hydrochloride manufactured by Fuji Film Wako Pure Chemical Industries, Ltd., Epocross series manufactured by Nippon Catalyst Co., Ltd., and water-soluble polycarbodiimide resin. One day, the Carbodilite series manufactured by Seibo Chemical Industries Co., Ltd. can be mentioned.

The lower limit of the content of the acid scavenger with respect to 100 parts by mass of the non-volatile component in the adhesive is 0.1 parts by mass, preferably 1 part by mass, more preferably 3 parts by mass, further preferably 10 parts by mass, and 20 parts by mass. Is even more preferable, and 30 parts by mass is even more preferable. By setting the content of the acid scavenger to the above lower limit or higher, a polarizing plate capable of enhancing the acid scavenging ability, exhibiting a sufficient polyene formation suppressing function in a high temperature durability test, and further suppressing a decrease in light transmittance is manufactured. can do. On the other hand, the upper limit of this content may be, for example, 100 parts by mass, but 50 parts by mass is preferable, and 40 parts by mass is more preferable. By setting the content of the acid scavenger to the above upper limit or less, the adhesive performance can be improved, the haze of the formed adhesive layer can be suppressed, and the light transmittance and the polarization performance can be improved.

The content of the acid scavenger in the adhesive of the present invention can also be determined by analyzing a 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 with a solvent or the like, the polarizing film with an adhesive layer is soxley-extracted with a solvent such as methanol to obtain an acid contained in the film. Analysis can be performed by extracting the trapping agent in a solvent.

(Non-volatile component)
The type of the adhesive of the present invention is not particularly limited, but generally, a water-based 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-curing adhesive is used. .. That is, the main component of the non-volatile component in the adhesive of the present invention is usually a resin such as PVA, other water-soluble resin, or active energy ray-curable resin.

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

PVA (A) is a polymer having a vinyl alcohol unit (-CH _2- CH (OH)-) as a main structural unit. As PVA (A), unmodified PVA or modified PVA can be used. The unmodified PVA is a PVA obtained by saponifying a vinyl ester polymer obtained by polymerizing only a vinyl ester-based monomer such as vinyl acetate. An example of the modified PVA is a saponification of a copolymer of a vinyl ester-based monomer and a monomer having copolymerizability with the vinyl ester-based monomer. The modified PVA may be a post-modified PVA such as an acetoacetyl group modified PVA. The acetoacetyl group-modified PVA is, for example, an unmodified PVA, a derivative thereof, or a modified PVA in which an acetoacetyl group is introduced by acetalization, urethanization, etherification, grafting, phosphate esterification, or the like. is there. The acetoacetyl group content of the acetoacetyl group-modified PVA is preferably 0.1 mol to 40 mol% in order to obtain sufficient water resistance.

Examples of the monomer having copolymerizability with the vinyl ester-based monomer include unsaturated carboxylic acids such as (anhydrous) maleic acid, fumaric acid, crotonic acid, itaconic acid, and (meth) acrylic acid, and esters thereof, ethylene, propylene, and the like. Α-Olefin, (meth) allylsulfonic acid (soda), sodium sulfonic acid (monoalkylmalate), sodium disulfonic acid alkylmalate, N-methylolacrylamide, acrylamidealkylsulfonic acid alkali salt, N-vinylpyrrolidone, N -A vinylpyrrolidone derivative and the like can be mentioned. One or two or more of these are used in combination.

The upper limit of the proportion of structural units derived from a monomer copolymerizable with a vinyl ester-based monomer is preferably 15 mol%, preferably 10 mol%, based on the number of moles of all structural units constituting PVA (A). More preferably, 5 mol% is even more preferable, and 1 mol% is even more preferable.

As PVA (A), one that has not been graft-copolymerized can be preferably used. However, PVA (A) may be modified with one or more graft-copolymerizable monomers. Graft copolymerization can be carried out on at least one of the polyvinyl ester and the PVA obtained by saponifying it. Examples of the graft copolymerizable monomer include unsaturated carboxylic acids or derivatives thereof; unsaturated sulfonic acids or derivatives thereof; α-olefins having 2 to 30 carbon atoms, and the like. The proportion of structural units derived from the graft copolymerizable monomer in the polyvinyl ester or PVA is preferably 5 mol% or less based on the number of moles of all structural units constituting the polyvinyl ester or PVA.

Part of the hydroxy group of PVA (A) may or may not be crosslinked. Further, PVA (A) may form an acetal structure in which a part of its hydroxy group reacts with an aldehyde compound such as acetaldehyde or butyraldehyde.

The lower limit of the degree of polymerization of PVA (A) is preferably 100, more preferably 500, even more preferably 1,000, and even 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 range, the adhesiveness and the like can be improved. The degree of polymerization of PVA means the average degree of polymerization measured according to the description of JIS K6726-1994.

The lower limit of the saponification degree of PVA (A) is preferably 85 mol%, more preferably 90 mol%, further preferably 95 mol%, further preferably 99 mol%, and particularly preferably 99.5 mol%. The upper limit of the saponification degree is not particularly limited, and may be 100 mol% or 99.99 mol%. When the degree of saponification of PVA (A) is within the above range, the adhesiveness and the like can be improved. The degree of saponification of PVA is the ratio (mol%) of the number of moles of vinyl alcohol units to the total number of moles of structural units (typically vinyl ester units) that can be converted to vinyl alcohol units by saponification. Say. The degree of saponification can be measured according to 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 even more preferably 2% by mass. On the other hand, the upper limit of this content is preferably 15% by mass, more preferably 10% by mass, and even more preferably 6% by mass. Further, the lower limit of the content of PVA (A) in the non-volatile component in the adhesive of the present invention is preferably 50% by mass, more preferably 70% by mass, still more preferably 90% by mass, 95% by mass or 99% by mass. There is also. On the other hand, the upper limit of the content of PVA (A) contained in the non-volatile component may be 100% by mass or 90% by mass. When the content of PVA (A) is in the above range, the adhesiveness and the like can be improved.

(Urethane resin)
The non-volatile component of the adhesive of the present invention preferably does not contain urethane resin. Even when 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, further preferably 1% by mass, and 0.5. Mass% is even more preferred, and 0.1% by mass is even more preferred. Urethane resins may react with acid scavengers. Therefore, by reducing the content of the urethane resin in the adhesive, the acid scavenging ability of the acid scavenger can be sufficiently exhibited, and the decrease in light transmittance can be more sufficiently suppressed in the high temperature durability test. Plates can be manufactured.

Examples of the urethane resin include commercially available products such as ADEKA Corporation's Adeka Bontita series, Mitsui Chemicals' Co., Ltd. Orestar series, DIC Corporation's Hydran series, and Sanyo Kasei Kogyo Co., Ltd.'s Samplen series. ..

The content of the urethane resin in the non-volatile component of the adhesive of the present invention can also be determined by analyzing a polarizing plate manufactured using the adhesive of the present invention, as with the acid scavenger. 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 in the case of the acid scavenger.

(Crosslinking agent)
The non-volatile component of the adhesive of the present invention may contain a cross-linking agent in order to obtain sufficient adhesiveness, water resistance and the like. The cross-linking agent may not be contained. Examples of the cross-linking agent include alkylenediamines, isocyanates, epoxys, aldehydes, salts of divalent metals or trivalent metals such as sodium, potassium, magnesium, calcium, aluminum, iron and nickel, and oxides thereof. .. The content of the cross-linking agent in the non-volatile component is, for example, preferably 0.1% by mass or more and 30% by mass or less, and more preferably 1% by mass or more and 20% by mass or less.

(Other ingredients)
The adhesive of the present invention may further contain other components as non-volatile components. However, as the upper limit of the content of the components other than PVA (A) and the cross-linking agent in the non-volatile components, 10% by mass is preferable, 1% by mass is more preferable, and 0.1% by mass is further. It may be preferable. By reducing the content of components other than PVA (A) and the cross-linking agent, adhesiveness, light transmittance and the like may be further improved.

The adhesive of the present invention may further contain a solvent as a component other than the acid scavenger and the non-volatile component. 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 another solvent may 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, further preferably 70% by mass, and particularly preferably 90% by mass. preferable. By setting the water content to the above lower limit or more, the acid scavenger, PVA (A) and the like can be sufficiently dissolved. The upper limit of the water content in the adhesive of the present invention is preferably, for example, 99% by mass, more preferably 97% by mass, from the viewpoint of drying efficiency and the like.

(Adhesive manufacturing method)
The method for producing the adhesive of the present invention is not particularly limited. For example, when PVA (A) is contained as a non-volatile component, one or more of arbitrary components such as an acid scavenger, PVA (A), and a cross-linking agent are mixed in water and stirred until uniform. Can be manufactured by The temperature, stirring method, time, etc. at the time of production can be carried out under arbitrary conditions as long as the function as an adhesive is not lost.

<Polarizer>
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 adhesive layer is a layer formed from the adhesive of the present invention. Further, the polarizing film containing PVA is usually a stretched film produced by using a non-stretched PVA film containing PVA as a raw film.

(PVA film)
The PVA film which is the raw film of the polarizing film will be described below. 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 even more preferably 1,700. When the degree of polymerization of PVA (B) is at least 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 even more preferably 5,000. When the degree of polymerization of PVA is not more than the above upper limit, it is possible to suppress an increase in the production cost of PVA (B) and the occurrence of defects during film formation.

The degree of saponification of PVA (B) is preferably 90 mol% or more, more preferably 95 mol% or more, and 99 mol% or more, because the obtained polarizing film has good moisture and heat resistance. It is more preferably 99.5 mol% or more, and particularly preferably 99.5 mol% or more. The upper limit of the saponification degree is not particularly limited, and may be 100 mol% or 99.99 mol%.

Other specific aspects of PVA (B) can be the same as those of PVA (A) described above.

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

(Plasticizer)
The PVA film may contain a plasticizer. When the PVA film contains a plasticizer, the handleability and stretchability of the PVA film can be improved. Polyhydric alcohol is preferably used as the plasticizer, and specific examples thereof include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, trimethylolpropane, and the like, and PVA films. Can contain one or more of these plasticizers. Of these, glycerin is preferable because the stretchability of the PVA film becomes better.

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 even more preferably 4 parts by mass with respect to 100 parts by mass of PVA (B). On the other hand, the upper limit of this content is preferably 20 parts by mass, more preferably 17 parts by mass, and even more preferably 14 parts by mass with respect to 100 parts by mass of PVA (B). 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 prevent the plasticizer from bleeding out to the surface of the PVA film and deteriorating the handleability of the PVA film.

(Surfactant)
The PVA film may contain a surfactant. When a PVA film is produced using a film-forming stock solution as described later, by adding a surfactant to the film-forming stock solution, the film-forming property is improved and the occurrence of thickness unevenness of the film is suppressed. At the same time, when a metal roll or belt is used for film formation, the PVA film can be easily peeled off from the metal roll or belt. When a PVA film is produced from a film-forming stock solution containing a surfactant, the PVA film may contain the surfactant. The type of surfactant contained in the film-forming stock solution for producing PVA film, and thus the type of surfactant contained in PVA film, is not particularly limited, but from the viewpoint of peelability from metal rolls and belts, anions are used. Sexual surfactants and nonionic surfactants are preferable, and nonionic surfactants are particularly preferable. One type of surfactant may be used alone, or two or more types may be used in combination.

Examples of the anionic surfactant include a carboxylic acid type such as potassium laurate; a sulfate ester type such as octyl sulfate; and a sulfonic acid type such as dodecylbenzene sulfonate.

Examples of the nonionic surfactant include an alkyl ether type such as polyoxyethylene oleyl ether; an alkylphenyl ether type such as polyoxyethylene octylphenyl ether; an alkyl ester type such as polyoxyethylene laurate; and polyoxyethylene lauryl amino ether. Alkylamine type such as; alkylamide type such as polyoxyethylene lauric acid amide; polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether; alkanolamide type such as lauric acid diethanolamide and oleic acid diethanolamide; polyoxyalkylene Examples thereof include allylphenyl ether type such as allylphenyl ether.

When a surfactant is mixed in the film-forming stock solution for producing a PVA film, the lower limit of the surfactant content in the film-forming stock solution, and by extension, the surfactant content in the PVA film is the film-forming stock solution or 0.01 parts by mass is preferable, and 0.02 parts by mass is more preferable with respect to 100 parts by mass of PVA contained in the PVA film. On the other hand, the upper limit of the content of the surfactant in the film-forming stock solution and the content of the surfactant in the PVA film is 0.5 parts by mass with respect to 100 parts by mass of PVA contained in the film-forming stock solution or the PVA film. Preferably, 0.1 part by mass is more preferable. When the content of the surfactant is 0.01 part by mass or more with respect to 100 parts by mass of PVA, the film-forming property and the peelability 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, the surfactant bleeds out on the surface of the PVA film, causing blocking and lowering the handleability. It can be suppressed.

(Other ingredients, etc.)
The PVA film contains other components other than the above-mentioned PVA, acid scavenger, plasticizer and surfactant, such as antioxidant, antifreeze agent, pH adjuster, concealing agent, anticoloring agent and oil agent, if necessary. May be contained. However, the content of the components other than PVA (B), the plasticizer and the surfactant in the PVA film may be preferably 1% by mass or less, and more preferably 0.1% by mass or less. Further, the content of the inorganic compound in the PVA film may be preferably 1% by mass or less, and more preferably 0.1% by mass or less. The other components and inorganic compounds may cause defects such as voids in the obtained polarizing film. Therefore, by reducing the content of the 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 even more preferably 40 μm. On the other hand, the lower limit of this average thickness is preferably 5 μm, more preferably 10 μm, and even more preferably 15 μm. When the average thickness of the PVA film is within the above range, handleability and the like can be improved.

The shape of the PVA film is not particularly limited, but a long film is preferable because the polarizing film can be continuously produced with good productivity. The length of the long film is not particularly limited, and can be appropriately set according to the intended use of the polarizing film to be manufactured, and can be, for example, in the range of 5 to 20,000 m. The width of the long film is not particularly limited and may be, for example, 50 cm or more. However, since a wide polarizing film has been demanded in recent years, it is preferably 1 m or more, and more preferably 2 m or more. It is preferably 4 m or more, and more preferably 4 m or more. There is no particular limitation on the upper limit of the width of the long film, but if the width is too wide, it tends to be difficult to uniformly stretch the polarizing film when manufacturing the polarizing film with a practical device. Therefore, the width of the PVA film is preferably 7 m or less.

The shape of the PVA film is not particularly limited and may be a single-layer film or a multilayer film (laminated body), but from the viewpoint of complexity and cost of laminating (coating, etc.) work, a single-layer film may be used. It is preferably a film. The PVA film used as the raw film of the polarizing film is usually a non-stretched film.

(Manufacturing method of PVA film)
The method for producing the PVA film is not particularly limited, and a production method in which the thickness and width of the film after film formation become more uniform can be preferably adopted. For example, the above-mentioned PVA (B) constituting the PVA film, and if necessary, a film-forming stock solution in which one or more of plasticizers, surfactants and other components are dissolved in a liquid medium. , PVA (B), and optionally one or more of plasticizers, surfactants, other components and liquid media, and a film-forming stock solution in which PVA (B) is melted. Can be manufactured using. When the film-forming stock solution contains at least one of a plasticizer, a surfactant and other components, it is preferable that those components are uniformly mixed.

Examples of the liquid medium used for preparing the membrane-forming stock solution include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, and the like. Examples include trimethylolpropane, ethylenediamine and diethylenetriamine. Of these, water is preferable because it has a small impact on the environment and is recoverable.

The volatile content of the membrane-forming stock solution (the content ratio of volatile components such as liquid media removed by volatilization or evaporation during membrane-forming in the membrane-forming stock solution) varies depending on the membrane-forming method, membrane-forming conditions, etc. 50% by mass is preferable, 55% by mass is more preferable, and 60% by mass is further preferable. On the other hand, as the upper limit, 95% by mass is preferable, 90% by mass is more preferable, and 85% by mass is further preferable. When the volatile content of the membrane-forming stock solution is 50% by mass or more, the viscosity of the membrane-forming stock solution does not become too high, filtration and defoaming during preparation of the film-forming stock solution are smoothly performed, and PVA with few foreign substances and defects. Film production becomes easier. On the other hand, when the volatile content 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 production of an industrial PVA film becomes easy.

Examples of the film-forming method for forming a PVA film using the above-mentioned film-forming stock solution include a cast film-forming method, an extrusion film-forming method, a wet film-forming method, and a gel film-forming method. The method and the extrusion film forming method are preferable. Above all, the extrusion film forming method is more preferable because a PVA film having a uniform thickness and width and good physical properties can be obtained. The PVA film can be dried or heat treated as needed.

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

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

(Polarizing film)
The polarizing film is a polarizing film formed from the PVA film described above. The polarizing film is usually a film formed by adsorbing a dichroic dye such as an iodine dye or a dichroic organic dye on a stretched film obtained by uniaxially stretching and orienting 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, the lower limit of this average thickness may be 1 μm, preferably 5 μm.

(Manufacturing method of polarizing film)
The method for producing the polarizing film is not particularly limited, and any conventionally adopted method may be adopted. For example, a polarizing film can be produced by subjecting a PVA film to a swelling treatment, a dyeing treatment, a uniaxial stretching treatment, and if necessary, a cross-linking treatment, a fixing treatment, a drying treatment, a heat treatment, and the like. In this case, the order of each treatment such as swelling treatment, dyeing treatment, uniaxial stretching, and fixing treatment is not particularly limited, and one or more treatments can be performed at the same time. It is also possible to perform one or more of each process 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 even more preferably 25 ° C. On the other hand, the upper limit is preferably 40 ° C, more preferably 38 ° C, and even more preferably 35 ° C. The time for immersion in water is preferably 0.1 to 5 minutes, for example. 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 a dichroic dye such as an iodine dye or a dye, and the dyeing time may be any stage before uniaxial stretching, during uniaxial stretching, and after uniaxial stretching. Dyeing is generally carried out by immersing the PVA film in a solution containing iodine-potassium iodide (particularly an aqueous solution) as a dyeing bath. The concentration of iodine in the dyeing bath is preferably 0.01 to 0.5% by mass, and the concentration of potassium iodide is preferably 0.01 to 10% by mass. The temperature of the dyeing bath is preferably 20 to 60 ° C.

The cross-linking treatment can be performed by immersing the PVA film in an aqueous solution containing a cross-linking agent. When the cross-linking treatment is performed, cross-linking is introduced into the PVA film, and uniaxial stretching can be performed at a relatively high temperature. As the cross-linking agent used, one or more kinds of boron compounds such as borate such as boric acid and borax can be used. The concentration of the cross-linking agent in the aqueous solution containing the cross-linking agent is preferably 1 to 15% by mass, more preferably 2 to 7% by mass. The temperature of the aqueous solution containing the cross-linking agent is preferably 20 to 60 ° C.

Uniaxial stretching may be performed by either a wet stretching method or a dry stretching method. In the case of the wet stretching method, it can be carried out in an aqueous solution containing boric acid, in the above-mentioned dyeing bath or in the fixing treatment bath described later. Further, in the case of the dry stretching method, it can be carried out in air. Among these, the wet stretching method is preferable, and uniaxial stretching is more preferable 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, still more preferably 1.5 to 4.0% by mass. Further, the boric acid aqueous solution may contain potassium iodide, and the concentration thereof is preferably 0.01 to 10% by mass.

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

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

In the production of the polarizing film, it is preferable to carry out a fixing treatment in order to strengthen the adsorption of the dichroic dye on the PVA film. As the fixing treatment bath used for the fixing treatment, an aqueous solution containing one or more kinds of boron compounds such as boric acid and borax can be used. Further, if necessary, an iodine compound or a metal compound may be added to the fixing treatment bath. The concentration of the boron compound in the fixing treatment bath is generally preferably about 2 to 15% by mass, particularly preferably about 3 to 10% by mass. The temperature of the fixing treatment bath is preferably 15 to 60 ° C., particularly preferably 25 to 40 ° C.

The drying treatment is preferably performed at 30 to 150 ° C., and more preferably 50 to 130 ° C. By drying at a temperature within the above range, a polarizing film having excellent dimensional stability can be easily obtained.

(Protective film)
The protective film is usually a cellulose ester film containing a cellulose ester resin as a main component. The content of the cellulose ester resin in the protective film is preferably 70% by mass or more, more preferably 90% by mass or more. Examples of the cellulose ester resin include cellulose triacetate (triacetyl cellulose: TAC), cellulose diacetate, cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate benzoate, cellulose acetate propionate benzoate, cellulose propionate, and cellulose buty. Rate, cellulose acetate biphenylate, cellulose acetate propionate biphenylate and the like can be mentioned, and among these, cellulose triacetate is preferable.

(Adhesive layer)
The adhesive layer is a layer formed from 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 equal to or higher than the above lower limit, the adhesiveness and the effect of suppressing polyene formation can be enhanced. On the other hand, the upper limit of the average thickness of the adhesive layer 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 a spray method, a dipping method, or the like can be adopted in addition to a method using a bar coater or a gravure roll. For example, the adhesive of the present invention is applied to at least one surface of a polarizing film or a protective film, and the film is bonded to the other film to perform heat treatment. As the heat treatment conditions, the temperature can be 5 to 150 ° C., preferably 30 to 120 ° C., and the treatment time can be 10 seconds to 30 minutes. As a result, the polarizing film surface and the protective film surface are adhered to each other, and a polarizing plate is obtained.

Normally, in a polarizing plate in which a protective film containing a cellulose ester resin is used, when exposed to a high temperature for a long period of time, an acid that promotes polyene formation of the polarizing film is generated by hydrolysis of the cellulose ester of the protective film. Generate. On the other hand, in the polarizing plate, since the acid scavenger in the adhesive layer can capture the acid, polyene formation can be suppressed and a decrease in light transmittance can be suppressed.

The present invention will be specifically described with reference to the following examples, but the present invention is not limited to these examples. The evaluation methods adopted in the following examples and comparative examples are shown below.

[Measurement of swelling degree of PVA film]
About 1.5 g of PVA film was collected and cut into about 2 mm × 10 cm. Then, the cut PVA film was wrapped in a mesh (“N-N0110S 115” manufactured by NBC Meshtec Inc.) and immersed in distilled water at 30 ° C. for 15 minutes. Subsequently, the PVA film wrapped in the mesh was subjected to centrifugal dehydration at 3,000 rpm for 5 minutes to remove the mesh, and then the mass (W1) of the PVA film was determined. Subsequently, the PVA film was dried in a dryer at 105 ° C. for 16 hours, and then the mass (W2) was determined. Then, the degree of swelling of the PVA film was calculated by the following formula.
Swelling degree (%) = {(W1) / (W2)} x 100

[High temperature durability test]
(A) Sample preparation Using a polarizing plate cut into 4 cm squares, a 10 cm square glass plate (1 mm thick), and an adhesive sheet cut into 10 cm squares (“MCS70” manufactured by Mitate Imaging Co., Ltd .; thickness 25 μm). Then, the glass plate / adhesive sheet / polarizing plate / adhesive sheet / glass plate were laminated in this order and pressure-bonded using a laminator. At this time, the polarizing plate was laminated on the central portion of the glass plate. Then, using a vacuum laminator (“1522N” manufactured by Nisshinbo Mechatronics Co., Ltd.), a pressure of 10 kPa was applied at 50 ° C. for 5 minutes for further pressure bonding. The obtained sample for high temperature durability test had a light transmittance in the range of 35 to 40% measured by a method for measuring the light transmittance described later.

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

(C) Measurement of light transmittance About the central part of the sample for high temperature durability test, 45 with respect to the absorption axis direction of the polarizing film using a spectrophotometer with an integrating sphere (“U4100” manufactured by Hitachi High-Tech Science Co., Ltd.). The light transmittance when tilted by ° and the light transmittance when tilted by −45 ° were measured, and their average value T (%) was obtained.
High temperature durability was judged according to the following criteria. In addition, A, B, and C were judged to be good because they could be used without any problem in practical use, and D was judged to be defective.
A: Light transmittance after high temperature durability test is 20% or more B: Light transmittance after high temperature durability test is 10% or more and less than 20% C: Light transmittance after high temperature durability test is 1% or more and less than 10% D: Light transmittance after high temperature durability test is less than 1%

The acid scavengers used in Examples and Comparative Examples are shown below.
Acid trapping agent A: "Carbodilite V-04" (manufactured by Nisshinbo Chemical Co., Ltd., solubility 5 g / water 100 g, carbodiimide group equivalent 339 g / mol), which is a high molecular weight (molecular weight of about 1,000 to 5,000) carbodiimide compound.
Acid trapping agent B: "Carbodiimide V-02" (manufactured by Nisshinbo Chemical Co., Ltd., solubility 100 g / water 100 g, carbodiimide group equivalent 602 g / mol), which is a high molecular weight (molecular weight of about 1,000 to 5,000) carbodiimide compound.
Acid trapping agent C: "Carbodiimide SV-02" (manufactured by Nisshinbo Chemical Co., Ltd., solubility 100 g / water 100 g, carbodiimide group equivalent 429 g / mol), which is a high molecular weight (molecular weight of about 1,000 to 5,000) carbodiimide compound.

[Example 1]
(1) Production of PVA film PVA (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 glycerin (relative to 100 parts by mass of PVA). 10 parts by mass), a surfactant (0.03 parts by mass with respect to 100 parts by mass of PVA) and water were mixed and dissolved at 90 ° C. for 4 hours to obtain an aqueous PVA solution. Then, the PVA aqueous solution was kept warm at 85 ° C. for 16 hours for defoaming of the PVA aqueous solution.

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) having a swelling degree of 200%.

(2) Production of Polarizing Film From the obtained PVA film, a test piece having a length direction of 9 cm and a width direction of 10 cm was collected. Both ends of the test piece in the length direction are fixed to a stretching jig so that the size of the stretched portion is 5 cm in the length direction × 10 cm in the width direction, and 24 cm while immersed in water at a temperature of 30 ° C. for 38 seconds. At a stretching rate of / min, uniaxial stretching (first step stretching) was performed in the length direction to 2.2 times the original length. Then, the test piece was immersed in an aqueous iodine / potassium iodide solution at a temperature of 30 ° C. containing 0.03% by mass of iodine and 3% by mass of potassium iodide for 60 seconds at 24 cm / min. In the length direction, uniaxial stretching (second-stage stretching) was performed up to 3.3 times the original length at the stretching rate of. The test piece was then immersed in a boric acid / potassium iodide aqueous solution containing 3% by mass of boric acid and 3% by mass of potassium iodide at a temperature of 30 ° C. for about 20 seconds at 24 cm / min. In the length direction, uniaxial stretching (third step stretching) was performed up to 3.6 times the original length at the stretching rate of. Subsequently, the test piece was immersed in an aqueous solution of boric acid / potassium iodide at a temperature of 58 ° C. containing a concentration of 4% by mass of boric acid and about 5% by mass of potassium iodide at 24 cm / min. In the length direction, uniaxial stretching (fourth step stretching) was performed up to 5.5 times the original length at the stretching rate of. Then, the test piece is immersed in an aqueous potassium iodide solution containing 1.5% by mass of boric acid and 3% by mass of potassium iodide for 10 seconds for fixing treatment, and then dried at 60 ° C. It was dried in a machine for 4 minutes to obtain a polarizing film (average thickness 13 μm).

(3) Production of adhesive PVA (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 as an acid scavenger. After adding the scavenger A (40 parts by mass with respect to 100 parts by mass of PVA) to water, it was dissolved at 90 ° C. for 2 hours. As a result, an aqueous solution having a PVA concentration of 3.5% by mass was obtained. This PVA aqueous solution was used as an adhesive.

(4) Production of Polarizing Plate From the obtained polarizing film, test pieces having a length direction of 10 cm and a width direction of 5 cm were collected. A triacetyl cellulose film was attached to both sides of this test piece (polarizing film) using the adhesive obtained above, and dried at 60 ° C. for 10 minutes to produce a polarizing plate. The coating amount was adjusted so that the average thickness of the adhesive layer was about 1 μm.

Using a polarizing plate, a high temperature durability test was performed based on the above method to evaluate the light transmittance. The results are shown in Table 1.

[Example 2]
An adhesive and a polarizing plate were produced in the same manner as in Example 1 except that the acid scavenger B was used as the acid scavenger. Evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

[Example 3]
An adhesive and a polarizing plate were produced in the same manner as in Example 1 except that the acid scavenger C was used as the acid scavenger. Evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

[Example 4]
An adhesive and a polarizing plate were produced in the same manner as in Example 1 except that the content (addition amount) of the acid scavenger A was 5 parts by mass with respect to 100 parts by mass of PVA. 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, the adhesive and the polarizing plate were produced in the same manner as in Example 1 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. Each evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

[Comparative Example 1]
An adhesive and a polarizing plate were produced in the same manner as in Example 1 except that no acid scavenger was added. Each evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

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

As shown in Table 1, the polarizing plates obtained by using the adhesives of Examples 1 to 5 in which the content of the acid scavenger with respect to 100 parts by mass of the non-volatile component is 0.1 parts by mass or more are subjected to a high temperature durability test. The decrease in light transmittance is sufficiently suppressed in. The polarizing plate obtained by using the adhesive of Example 5 containing a urethane resin had a slightly inferior effect.

The adhesive according to the present invention is suitably used for producing a polarizing plate.

Claims

An adhesive for producing a polarizing plate for adhering a polarizing film containing polyvinyl alcohol and a protective film containing a cellulose ester resin, which contains an acid trapping agent and a non-volatile component other than the acid trapping agent, and is non-volatile. An adhesive in which the content of the acid trapping agent with respect to 100 parts by mass of the component is 0.1 parts by mass or more.
The adhesive according to claim 1, wherein the non-volatile component does not contain a urethane resin, or the non-volatile component contains a urethane resin, and the content of the urethane resin in the non-volatile component is 3% by mass or less.
The adhesive according to 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 with respect to 100 parts by mass of the non-volatile component is 0.1 part by mass or more and 50 parts by mass or less.
The adhesive according to any one of claims 1 to 4, wherein the non-volatile component contains polyvinyl alcohol.
The adhesive according to any one of claims 1 to 5, wherein the acid scavenger is water-soluble.
A polarizing plate including 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 adhesive layer is claimed 1 to 1. A polarizing plate formed from the adhesive according to any one of 6.