TWI836033B - Adhesive and polarizing plate - Google Patents

Abstract

Provided are an adhesive for producing a polarizing plate that can sufficiently suppress the decrease in light transmittance in a high-temperature durability test, and a polarizing plate obtained using the adhesive. An adhesive for producing a polarizing plate for bonding a polarizing film containing polyvinyl alcohol and a protective film containing a cellulose ester resin, comprising an acid scavenger and a non-volatile component other than the acid scavenger, wherein 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.

Polarizing plates that have the functions of transmitting and shielding light, and liquid crystals that change the polarization state of light, are the basic components of liquid crystal displays (LCDs). Most polarizing plates have a structure in which a protective film such as a triacetate cellulose (TAC) film is bonded to the surface of the polarizing film. As for the polarizing film constituting the polarizing plate, the mainstream is a film obtained by uniaxially stretching a polyvinyl alcohol film (hereinafter referred to as "polyvinyl alcohol" for short as "PVA") and adsorbing dichroic pigments such as iodine-based pigments (I ₃ ^- , I ₅ ^- , etc.) and dichroic organic dyes on the stretched film to make it oriented. Such a polarizing film is produced by uniaxially stretching a PVA film that contains a dichroic pigment in advance, adsorbing the dichroic pigment while uniaxially stretching the PVA film, or adsorbing the dichroic pigment after uniaxially stretching the PVA film.

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 in-vehicle image display devices such as car navigation devices and backup monitors. Along with this, LCDs are required to have high durability in harsher environments than ever before.

It is known that it is necessary to provide an image display device composed of a polarizing plate bonded between an image display cell and a transparent plate such as a front panel or a touch panel through an adhesive layer for a vehicle-mounted display. During long-term high-temperature durability tests, the light transmittance of polarizing plates will decrease. One of the reasons for this is the polyolefinization of PVA constituting the polarizing film, and the decrease in the light transmittance of the polarizing plate becomes more significant under higher temperature conditions.

Regarding the problem of polyene formation in such a polarizing plate, Patent Document 1 describes that polyene formation can be suppressed by using a polarizing plate having a protective film with 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 adhesive used to bond the polarizing plate, the image display unit, and the transparent plate, and the absorbance of the polarizing film. [Prior technical literature] [Patent Document]

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

[Problems to be solved by the invention]

However, according to the examination of the inventors, although the method described in Patent Documents 1 and 2 tends to suppress the decrease in the light transmittance of the polarizing plate, in recent years, it is necessary to perform the method in a high temperature environment of 105° C. or above. In the durability test, sufficient polyene formation inhibitory effect could not be confirmed.

The present invention is accomplished based on the above circumstances, and aims to provide an adhesive for producing a polarizing plate that can sufficiently suppress the decrease in light transmittance in a high-temperature durability test, and a polarizing plate obtained using the adhesive. [Means for solving the problem]

As a result of repeated and careful studies to achieve the above-mentioned purpose, the inventors of the present invention have discovered that the polyeneization of PVA in the polarizing film of the polarizing plate is promoted by the acid generated from the protective film, and that the polyeneization can be suppressed by making the adhesive used to bond the polarizing film and the protective film contain an acid scavenger. Based on such knowledge and insights, the inventors of the present invention have completed further repeated studies.

That is, the present invention relates to [1] An adhesive for manufacturing a polarizing plate that is used to bond a polarizing film containing polyvinyl alcohol and a protective film containing a cellulose ester resin, which contains an acid capture agent and an agent other than the above-mentioned acid capture agent. Non-volatile components, and the content of the above-mentioned acid capture agent is 0.1 parts by mass or more relative to 100 parts by mass of the above-mentioned non-volatile components; [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 urethane resin is added to the non-volatile component The content of the ingredients is less than 3% by mass; [3] The adhesive according to [1] or [2], wherein the acid capture agent 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 above-mentioned acid trapping agent is 0.1 to 50 parts by mass relative to 100 parts by mass of the above-mentioned non-volatile components; [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 above-mentioned acid capturing agent 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 above The adhesive layer is formed of the adhesive according to any one of [1] to [6]. [Effects of the invention]

According to the present invention, it is possible to provide an adhesive that can produce a polarizing plate that can sufficiently suppress a decrease in light transmittance in a high-temperature durability test, and a polarizing plate obtained by using the adhesive.

[Form used to implement the invention]

The embodiments of the present invention will be described in detail below. ＜Adhesive＞ The adhesive of the present invention is an adhesive for manufacturing polarizing plates that is used to bond a polarizing film containing PVA and a protective film containing a cellulose ester resin. The adhesive of the present invention contains an acid trapping agent and non-volatile components other than the acid trapping agent, and the content of the acid trapping agent is 0.1 parts by mass or more relative 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 non-volatile components refer to components other than the acid capture agent and the solvent.

Generally, when a polarizing film having a stretched PVA film and a polarizing plate having a protective film containing cellulose ester are exposed to high temperature for a long time, acid is generated by hydrolysis of cellulose ester constituting the protective film. It is estimated that this acid serves as a catalyst for the dehydration reaction of PVA, and the PVA in the polarizing film is polyene-formed. When a polarizing plate is manufactured by bonding the polarizing film and the protective film with the bonding agent of the present invention, a sufficient amount of acid scavenger exists in the bonding agent layer formed by the bonding agent. Therefore, the acid generated from the protective film is captured by the acid scavenger in the bonding agent layer, and it becomes difficult for the acid to reach the polarizing film, thereby suppressing the polyene-formation of the PVA in the polarizing film in the polarizing plate. That is, according to this adhesive, a polarizing plate can be manufactured that can sufficiently suppress the decrease in light transmittance in a high-temperature durability test.

(Acid scavenger) The acid scavenger is a compound that reacts with an acid to inactivate the acid. Examples of the acid capture agent include compounds having a carbodiimide group (–N=C=N–), compounds having an epoxy group, compounds having Zozoline compounds, alkyl phosphate metal salts, strongly basic amine compounds, terpene compounds, Organic compounds such as chemical compounds, and inorganic compounds such as hydrotalcite groups, etc. The organic compound refers to a compound containing carbon, and the inorganic compound refers to a compound other than an organic compound. In addition, the acid trapping agent may also be called an acid remover, an acid trapping agent, an acid trapping agent, etc. However, in the present invention, there is no difference due to these names and all can be used. One type of acid trapping agent may be used alone, or two or more types may be used in combination.

The acid scavenger is preferably an organic compound, and more preferably a carbodiimide compound having at least one carbodiimide group. Carbodiimide compounds are preferred from the viewpoints of high polyene-inhibiting effect, ease of handling, and safety.

The mass (molecular formula weight) of the group capable of capturing acid per mole in the acid scavenger is, for example, preferably 200 g/mol or more and 1,000 g/mol or less, more preferably 400 g/mol or less. When the acid capturing agent is a carbodiimide compound, the mass (molecular formula weight) of the group that can capture the acid per 1 mol is also called 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 includes 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 miscible with the water-soluble resin, the haze of the adhesive layer formed by the adhesive of the present invention is easily reduced, so that a polarizing plate with good light transmittance and polarization performance can be obtained. In addition, the so-called "water-soluble" refers to a solubility in water of 1g/100g water or more. The so-called solubility in water refers to the maximum amount (mass) that is dissolved in 100g of water at 20°C. As for the lower limit of the solubility of the acid scavenger in water, it is preferably 2g/100g water, and more preferably 3g/100g water. On the other hand, the upper limit of the 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, but for example, an acid scavenger having a molecular weight of 100 or more or 200 or more is used. The acid capture agent can be a polymer. "Polymer" refers to a molecule with a weight average molecular weight of 300 or more. 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 polymer acid scavenger may be, for example, 100,000 or 10,000.

Commercially available products of the acid scavenger include 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride manufactured by FUJIFILM Wako Pure Chemical Corporation, EPOCROS SERIES manufactured by Nippon Catalyst Co., Ltd., and CARBODILITE SERIES manufactured by Nisshin Chemical Co., Ltd., which are water-soluble polycarbodiimide resins.

In the adhesive, the lower limit of the content of the acid scavenger relative to 100 parts by mass of the non-volatile components is 0.1 parts by mass, preferably 1 part by mass, more preferably 3 parts by mass, further preferably 10 parts by mass, further preferably 20 parts by mass, further preferably 30 parts by mass. By setting the content of the acid scavenger to be above the above lower limit, a polarizing plate can be manufactured that has an improved ability to capture acid, fully exerts a polyene inhibition function in a high-temperature durability test, and can more fully inhibit the reduction in light transmittance. On the other hand, as for the upper limit of this content, for example, it can be 100 parts by mass, but is preferably 50 parts by mass, and more preferably 40 parts by mass. By setting the content of the acid scavenger to be below the upper limit, the adhesive performance can be improved, and the haze of the formed adhesive layer can be suppressed, thereby improving the light transmittance and polarization performance.

The content of the acid scavenger in the adhesive of the present invention can be obtained by analyzing the polarizing plate produced 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 using a solvent, the polarizing film with the adhesive layer attached is subjected to Soxhlet extraction with a solvent such as methanol, so that the acid scavenger contained in the film can be extracted into the solvent, thereby performing analysis.

(Non-volatile components) The type of adhesive of the present invention is not particularly limited, but generally, a water-based adhesive having a PVA aqueous solution in which PVA or the like is dissolved as the main component, or a solvent-free active energy ray-curable 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 or other water-soluble resins, active energy ray-curable resins, etc.

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

PVA(A) is a polymer having vinyl alcohol units (–CH ₂ –CH(OH)–) as its main structural unit. As for PVA (A), unmodified PVA and modified PVA can be used. The so-called unmodified PVA refers to PVA obtained by saponifying a vinyl ester polymer obtained by polymerizing only a vinyl ester monomer such as vinyl acetate. An example of modified PVA is a saponified product of a copolymer of a vinyl ester monomer and a monomer copolymerizable with the vinyl ester monomer. Modified PVA can also be acetyl-acetyl modified PVA, etc. and then modified PVA. Acetyl acetyl-modified PVA is, for example, acetalization, urethanization, etherification, grafting, phosphorization, etc. of unmodified PVA, its derivatives, or modified PVA to acetate. Modified PVA with introduced acetyl groups. In order to obtain sufficient water resistance, the acetyl acetyl group content of the acetyl acetyl group-modified PVA is preferably 0.1 mole to 40 mole %.

As monomers copolymerizable with vinyl ester monomers, there can be mentioned maleic acid (anhydride), fumaric acid, crotonic acid, itaconic acid, unsaturated carboxylic acids such as (meth) acrylic acid and their esters, α-olefins such as ethylene and propylene, (meth)allylsulfonic acid (sodium), sodium sulfonate (monoalkyl maleate), sodium disulfonate maleate, N-hydroxymethylacrylamide, acrylamide alkylsulfonate base, N-vinylpyrrolidone, N-vinylpyrrolidone derivatives, etc. These can be used alone or in combination of two or more.

Based on the molar number of all structural units constituting PVA(A), the upper limit of the proportion of structural units derived from monomers copolymerizable with vinyl ester monomers is preferably 15 mol%, more preferably 10 mol%, further preferably 5 mol%, and further preferably 1 mol%.

As for PVA(A), it is preferable to use one that has not been graft copolymerized. However, PVA(A) may be modified by one or more graft copolymerizable monomers. Graft copolymerization may be performed on at least one of polyvinyl ester and PVA obtained by saponifying the polyvinyl ester. As for the graft copolymerizable monomers, for example: unsaturated carboxylic acid or its derivatives; unsaturated sulfonic acid or its derivatives; α-olefins having 2 to 30 carbon atoms, etc. may be listed. Based on the molar number of all structural units constituting polyvinyl ester or PVA, the proportion of structural units from graft copolymerizable monomers in polyvinyl ester or PVA is preferably less than 5 mol%.

A part of the hydroxyl groups of PVA(A) may be crosslinked or not crosslinked. In addition, a part of the hydroxyl groups of PVA(A) may react with an aldehyde compound such as acetaldehyde or butyraldehyde to form an acetal structure.

The lower limit of the degree of polymerization of PVA (A) is preferably 100, more preferably 500, further preferably 1,000, and further preferably 1,500. On the other hand, the upper limit of the degree of polymerization is preferably 4,000, and more preferably 3,000. When the degree of polymerization of PVA (A) is within the above range, adhesion and the like can be improved. In addition, 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 this saponification degree is not particularly limited, and can be 100 mol% or 99.99 mol. By having the saponification degree of PVA (A) within the above range, adhesion can be improved. The so-called saponification degree of PVA refers to the ratio (mol %) of the molar number of vinyl alcohol units to the total molar number of structural units (typically vinyl ester units) and vinyl alcohol units that can be converted into vinyl alcohol units by saponification. The saponification degree 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 further 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 further preferably 6% by mass. In addition, the lower limit of the content of PVA(A) in the adhesive of the present invention in the non-volatile components is preferably 50% by mass, more preferably 70% by mass, and further preferably 90% by mass, 95% by mass, or 99% by mass. On the other hand, the upper limit of the content of PVA(A) in the non-volatile components can be 100% by mass or 90% by mass. When the content of PVA(A) is within the above range, the adhesion can be improved.

(Urethane resin) The non-volatile component of the adhesive of the present invention preferably does not contain urethane resin. Moreover, even if the non-volatile component contains urethane resin, the upper limit of the content of urethane resin in the non-volatile component is preferably 3 mass%, more preferably 2 mass%, further preferably 1 mass%, further preferably 0.5 mass%, further preferably 0.1 mass%. Urethane resin may react with acid scavengers. Therefore, by reducing the content of urethane resin in the adhesive, the acid scavenging ability of the acid scavenger can be fully exerted, and a polarizing plate can be manufactured that can more fully suppress the reduction of light transmittance in a high-temperature durability test.

Examples of commercially available urethane resins include 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 SERIES manufactured by Sanyo Chemical Industries, Ltd.

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

(cross-linking agent) In order to obtain sufficient adhesiveness, water resistance, etc., the non-volatile component of the adhesive agent of this invention may contain a crosslinking agent. It can also contain no cross-linking agent. Examples of cross-linking agents include alkylene diamines, isocyanates, epoxy compounds, aldehydes, and divalent or trivalent metals such as sodium, potassium, magnesium, calcium, aluminum, iron, and nickel. salts and their oxides. The content of the cross-linking agent in the non-volatile components is, for example, preferably 0.1 mass % or more and 30 mass % or less, more preferably 1 mass % or more and 20 mass % or less.

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

As a component other than the acid scavenger and the non-volatile component, the adhesive of the present invention may further include a solvent. When the adhesive of the present invention includes 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 can be, for example, 10 mass %, but it is preferably 30 mass %, more preferably 50 mass %, further preferably 70 mass %, and particularly preferably 90 mass %. By setting the water content to above the above lower limit, the acid scavenger, PVA (A), etc. can be fully dissolved. From the point of view of drying efficiency, etc., the upper limit of the water content in the adhesive of the present invention is, for example, preferably 99 mass %, and more preferably 97 mass %.

(Method for 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 more of any components such as acid scavenger, PVA (A), and cross-linking agent can be mixed in water and stirred until it becomes Made until uniform. The temperature, stirring method, time, etc. during production can be carried out under any conditions as long as the function as an adhesive is not lost.

<Polarizing plate> The polarizing plate of the present invention comprises 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 by the adhesive of the present invention. 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 following describes the PVA film that is the raw material film for the polarizing film. In addition, the PVA contained in the PVA film or polarizing film is referred to as "PVA (B)".

(PVA(B)) 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 equal to or higher 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-mentioned upper limit, an increase in the production cost of PVA (B) and the occurrence of defects during film production can be suppressed.

The saponification degree of PVA (B) is preferably 90 mol% or more, more preferably 95 mol% or more, and still more preferably 99 mol% or more, in view of the excellent moisture and heat resistance of the polarizing film obtained. , the best value is above 99.5 mol%. The upper limit of the saponification degree is not particularly limited, and may be 100 mol% or 99.99 mol%.

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

The lower limit of the content rate of PVA (B) in the PVA film is preferably 50 mass%, more preferably 80 mass%, and further preferably 85 mass%. By setting the content rate of PVA (B) to be not less than the above-mentioned lower limit, a good polarizing film can be obtained. On the other hand, the upper limit of the content rate of PVA (B) is preferably 99 mass%, more preferably 95 mass%.

(Plasticizer) The PVA film may contain a plasticizer. By containing a plasticizer in the PVA film, the handling properties and stretchability of the PVA film can be improved. As for the plasticizer, polyols are preferably used. Specific examples include ethylene glycol, glycerol, propylene glycol, diethylene glycol, diglycerol, triethylene glycol, tetraethylene glycol, trihydroxymethylpropane, etc. The PVA film may contain one or more of these plasticizers. Glycerol is preferred among these plasticizers in terms of improving the stretchability of the PVA film.

The lower limit of the plasticizer content in the PVA film is preferably 2 parts by mass, more preferably 3 parts by mass, and further preferably 4 parts by mass relative to 100 parts by mass of PVA (B). On the other hand, the upper limit of the content is preferably 20 parts by mass, more preferably 17 parts by mass, and still more preferably 14 parts by mass relative to 100 parts by mass of PVA (B). When the plasticizer content in the PVA film is more than 2 parts by mass, the stretchability of the PVA film will be improved. On the other hand, when the content of the plasticizer in the PVA film is 20 parts by mass or less, it can be suppressed that the plasticizer bleeds out to the surface of the PVA film and the handling properties of the PVA film are reduced.

(surfactant) PVA films can contain surfactants. When a PVA film is produced using a film-forming stock solution as described later, by blending a surfactant into the film-forming stock solution, the film-forming properties are improved and the occurrence of uneven thickness of the film is suppressed. When using a roller or a belt, the PVA film can be easily peeled off from the metal roller or belt. When producing a PVA film from a film-forming stock solution mixed with a surfactant, the PVA film may contain a surfactant. The types of surfactants blended in the film-forming stock solution used to produce the PVA film and the surfactants contained in the PVA film are not particularly limited. However, from the viewpoint of peelability from metal rollers and belts, Anionic surfactants and nonionic surfactants are preferred, and nonionic surfactants are particularly preferred. A surfactant can be used individually by 1 type or in combination of 2 or more types.

Examples of anionic surfactants include carboxylic acid types such as potassium laurate; sulfate ester types such as octyl sulfate; and sulfonic acid types such as dodecyl benzenesulfonate.

As for the non-ionic surfactants, there can be cited, for example, alkyl ether types such as polyoxyethylene oleyl ether; alkyl phenyl ether types such as polyoxyethylene octylphenyl ether; alkyl ester types such as polyoxyethylene laurate; alkyl amine types such as polyoxyethylene laurylamine ether; alkyl amide types such as polyoxyethylene lauryl amide; polypropylene glycol ether types such as polyoxyethylene polyoxypropylene ether; alkanolamide types such as lauric acid diethanolamide and oleic acid diethanolamide; allyl phenyl ether types such as polyoxyalkylene allyl phenyl ether, etc.

When a surfactant is mixed in a film-forming solution for producing a PVA film, the lower limit of the content of the surfactant in the film-forming solution and the content of the surfactant in the PVA film is preferably 0.01 parts by mass, and more preferably 0.02 parts by mass, relative to 100 parts by mass of the film-forming solution or the PVA contained in the PVA film. On the other hand, the upper limit of the content of the surfactant in the film-forming solution and the content of the surfactant in the PVA film is preferably 0.5 parts by mass, and more preferably 0.1 parts by mass, relative to 100 parts by mass of the film-forming solution or the PVA contained in the PVA film. When the content of the surfactant is 0.01 parts by mass or more relative to 100 parts by mass of the PVA, the film-forming property and the peeling property can be improved. On the other hand, by setting the content of the surfactant to 0.5 parts by mass or less based on 100 parts by mass of PVA, it is possible to suppress the surfactant from seeping out to the surface of the PVA film to cause blocking and reduce the handling properties.

(Other ingredients, etc.) PVA films may contain antioxidants, antifreezes, pH adjusters, protective agents, anti-coloring agents, oil agents and other ingredients in addition to the above-mentioned PVA, acid capture agents, plasticizers and surfactants as needed. 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 polarizing 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 further preferably 40 μm. On the other hand, the lower limit of the average thickness is preferably 5 μm, more preferably 10 μm, and further preferably 15 μm. When the average thickness of the PVA film is within the above range, the handling property can be improved.

The shape of the PVA film is not particularly limited, but from the perspective of good productivity and continuous production of polarizing films, a long strip of film is preferred. The length of the long strip of film is not particularly limited, and can be appropriately set according to the purpose of the polarizing film to be produced, for example, it can be set in the range of 5 to 20,000 m. The width of the long strip of film is not particularly limited, and can be set to, for example, 50 cm or more, but due to the demand for wide polarizing films in recent years, it is preferably 1 m or more, more preferably 2 m or more, and further preferably 4 m or more. The upper limit of the width of the long strip of film is not particularly limited, but if the width is too large, it tends to be difficult to stretch uniformly when producing polarizing films with practical equipment, so the width of the PVA film is preferably 7 m or less.

The shape of the PVA film is not particularly limited, and it can be a single-layer film or a multi-layer film (laminated body), but from the perspective of the 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.

(Manufacturing method of PVA film) The manufacturing method of PVA film is not particularly limited, and it is preferable to adopt a manufacturing method that makes the thickness and width of the film after film formation more uniform. For example, the film-forming stock solution can be made by dissolving the above-mentioned PVA (B) constituting the PVA film, and one or more of the plasticizer, surfactant and other components as needed in a liquid medium, or by using a film-forming stock solution containing PVA (B), and one or more of the plasticizer, surfactant, other components and liquid medium as needed, and PVA (B) is molten. When the film-forming stock solution contains at least one of the plasticizer, surfactant and other components, it is preferable that these components are uniformly mixed.

As for the liquid medium used in the preparation of the membrane stock solution, for example, water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trihydroxymethylpropane, ethylenediamine, diethylenetriamine, etc. Among them, water is preferred in terms of small load on the environment and good recyclability.

The volatile content of the film-forming stock solution (the proportion of volatile components such as liquid media removed by volatilization and evaporation during film-forming) in the film-forming stock solution also varies depending on the film-forming method, film-making conditions, etc., but it is As for the lower limit, 50 mass % is preferable, 55 mass % is more preferable, and 60 mass % is further more preferable. On the other hand, as for this upper limit, 95 mass % is preferable, 90 mass % is more preferable, and 85 mass % is further more preferable. By having a volatile fraction of 50% by mass or more of the film-making stock solution, the viscosity of the film-making stock solution will not become too high, and the filtration and defoaming during preparation of the film-making stock solution will proceed smoothly, resulting in a PVA film with fewer impurities and defects. Manufacturing becomes easy. On the other hand, since 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 industrial production of PVA films becomes easy.

When using the above-mentioned film-forming solution to form a PVA film, the film-forming method includes, for example, casting film-forming method, extrusion film-forming method, wet film-forming method, gel film-forming method, etc. Casting film-forming method and extrusion film-forming method are preferred. Among them, extrusion film-forming method is more preferred because it can obtain a PVA film with uniform thickness and width and good physical properties. The PVA film can be dried or heat-treated as needed.

The heat treatment temperature is not particularly limited and can be appropriately adjusted according to the swelling degree of the PVA film in each range. The heat treatment temperature is preferably 200°C or lower, more preferably 180°C or lower, and still more preferably 150°C or lower because discoloration and deterioration of the PVA film are observed if it is too high. 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 can be adjusted appropriately according to the swelling degree of the PVA film, etc., but from the viewpoint of efficiently producing the PVA film of the present invention, it is preferably 1 to 60 minutes, and more preferably 2 to 40 minutes. , further preferably 3 to 30 minutes.

(Polarizing film) Polarizing film is a polarizing film formed by the above-mentioned PVA film. Polarizing film is usually a film formed by adsorbing dichroic pigments such as iodine pigments and dichroic organic dyes on a stretched film obtained by uniaxially stretching a non-stretched PVA film to make it oriented.

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 the average thickness can be 1 μm, and preferably 5 μm.

(Method for manufacturing polarizing film) The method for manufacturing the polarizing film is not particularly limited, and any conventional method can be used. For example, a polarizing film can be produced by subjecting a PVA film to swelling treatment, dyeing treatment, uniaxial stretching, and further cross-linking treatment, fixation treatment, drying treatment, heat treatment, etc. if necessary. At this time, the order of each treatment such as swelling treatment, dyeing treatment, uniaxial stretching, and fixation treatment is not particularly limited, and one or more treatments may be performed simultaneously. Moreover, you may perform 1 or more of each process twice or more.

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, the upper limit is preferably 40°C, more preferably 38°C, and still more preferably 35°C. Moreover, the time for immersing 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. The dyeing period may be any stage before uniaxial stretching, during uniaxial stretching, or after uniaxial stretching. Dyeing is usually performed by immersing a PVA film in a solution (especially an aqueous solution) containing iodine-potassium iodide 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. In addition, 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. If cross-linking treatment is performed, cross-linking can be introduced into the PVA film and uniaxial stretching can be performed at a higher temperature. As the cross-linking agent used, one or more types of boron compounds such as boric acid and borates such as 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 mass %, more preferably 2 to 7 mass %. The temperature of the aqueous solution containing the cross-linking agent is preferably 20 to 60°C.

Uniaxial stretching can be performed by either wet stretching or dry stretching. In the case of wet stretching, it can be performed in an aqueous solution containing boric acid, or in the above-mentioned dyeing bath or the fixing treatment bath described later. In the case of dry stretching, it can be performed in the air. Among these, wet stretching 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 aqueous boric acid solution is preferably 0.5 to 6.0 mass%, more preferably 1.0 to 5.0 mass%, and further preferably 1.5 to 4.0 mass%. In addition, the aqueous boric acid solution may contain potassium iodide, and its concentration is preferably 0.01 to 10 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 further preferably 50 to 70°C.

From the viewpoint of 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 on the PVA film, it is preferable to perform a fixing process. For the fixing treatment bath used in the fixing treatment, one or more aqueous solutions containing boron compounds such as boric acid and borax can be used. In addition, 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 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, preferably 25 to 40°C.

The drying treatment is preferably performed at 30 to 150° C., and more preferably at 50 to 130° C. By performing 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 with a cellulose ester resin as the main component. The content of the cellulose ester resin in the protective film is preferably 70% by mass or more, and more preferably 90% by mass or more. Examples of the cellulose ester resin include cellulose triacetate (cellulose triacetate: TAC), cellulose diacetate, cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate benzoate, cellulose acetate propionate benzoate, cellulose propionate, cellulose butyrate, cellulose acetate biphenylate, cellulose acetate propionate biphenylate, etc. Among them, 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 not less than the above-mentioned lower limit, the adhesiveness and the polyolefinization inhibitory effect 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 not more than the above upper limit, 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. In addition to methods using a bar coater, a gravure roller, etc., a spray method, a dipping method, etc. can also 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 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 to obtain a polarizing plate.

Generally, when a polarizing plate using a protective film containing a cellulose ester-based resin is exposed to high temperature for a long period of time, an acid that promotes polyeneization of the polarizing film is generated by hydrolysis of the cellulose ester of the protective film. On the other hand, in this polarizing plate, since the acid scavenger in the adhesive layer can capture acid, polyene formation is suppressed and a decrease in light transmittance can be suppressed. [Example]

The present invention is specifically described by the following embodiments, but the present invention is not limited to these embodiments. In addition, each evaluation method adopted in the following embodiments and comparative examples is presented as follows.

[Measurement of swelling degree of PVA film] Take about 1.5g of PVA film and cut it into about 2mm×10cm. Thereafter, 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 a mesh was centrifuged at 3,000 rpm for 5 minutes, and the mass of the PVA film (W1) was determined after removing the mesh. Next, the PVA film was dried with a dryer at 105° C. for 16 hours, and then the mass (W2) was determined. Then, the swelling degree of the PVA film was calculated according to the following formula. Swelling degree (%)={(W1)/(W2)}×100

[High temperature durability test] (a) Sample production Cut the polarizing plate into 4cm squares, use a 10cm square glass plate (1mm thick) and an adhesive sheet ("MCS70" manufactured by MeCan Imaging CO., LTD; thickness 25μm) cut into 10cm squares, according to the glass plate/adhesive sheet /Polarizing plate/adhesive sheet/glass plate are laminated sequentially and pressed using a laminating machine. At this time, the polarizing plate is laminated on the center part of the glass plate. Thereafter, a vacuum laminator ("1522N" manufactured by Nisshinbo Mechatronics Inc.) was used to apply a pressure of 10 kPa at 50° C. for 5 minutes to further perform pressure bonding. In addition, the light transmittance of the obtained sample for the high-temperature durability test was in the range of 35 to 40% as measured by the light transmittance measurement method described below.

(b) High temperature durability test The prepared high temperature durability test sample was placed in a dryer at 105°C for 250 hours. Thereafter, the light transmittance of the sample was measured by the method described below.

(c) Measurement of light transmittance For the central part of the sample for high-temperature durability test, a spectrophotometer with an integrating sphere ("U-4100" manufactured by Hitachi High-Tech Science Corporation) was used to measure the light transmittance when tilted 45° and when tilted -45° relative to the absorption axis direction of the polarizing film, and the average value T (%) was calculated. The high-temperature durability was determined using the following criteria. In addition, A, B, and C were judged as good because they could be used without practical problems, and D was judged as poor. A: The light transmittance after the high-temperature durability test was 20% or more B: The light transmittance after the high-temperature durability test was 10% or more and less than 20% C: The light transmittance after the high-temperature durability test was 1% or more and less than 10% D: The light transmittance after the high-temperature durability test was less than 1%

The acid capture agents used in the embodiments and comparative examples are presented below. Acid scavenger A: "CARBODILITE V-04" (manufactured by Nisshin Chemical Co., Ltd., solubility 5g/100g water, carbodiimide equivalent 339g/mol) of a high molecular weight (molecular weight of about 1,000 to 5,000) carbodiimide compound Acid scavenger B: "CARBODILITE V-02" (manufactured by Nisshin Chemical Co., Ltd., solubility 100g/100g water, carbodiimide equivalent 602g/mol) of a high molecular weight (molecular weight of about 1,000 to 5,000) carbodiimide compound Acid scavenger C: "CARBODILITE SV-02" (manufactured by Nisshin Chemical Co., Ltd., solubility 100g/100g water, carbodiimide equivalent 429g/mol) of a high molecular weight (molecular weight of about 1,000 to 5,000) carbodiimide compound

[Example 1] (1) Manufacturing of PVA film 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%), glycerin (10 parts by mass relative to 100 parts by mass of PVA), and surface active 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 a PVA aqueous 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) having a swelling degree of 200%.

(2) Manufacturing of polarizing film A test piece measuring 9 cm in the length direction and 10 cm in the width direction was taken from the obtained PVA film. Both ends of the test piece in the length direction were fixed to a stretching jig so that the dimensions of the stretched portion became 5 cm in the length direction x 10 cm in the width direction, and were immersed in water at a temperature of 30° C. for 38 seconds. /min stretching uniaxially in the length direction (first stretch) to 2.2 times the original length. Thereafter, the test piece was immersed in a 30°C iodine/potassium iodide aqueous solution 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 uniaxial stretching in the length direction (the second stretch) until it is 3.3 times the original length. Next, the test piece was immersed in a boric acid/potassium iodide aqueous solution at a temperature of 30°C containing boric acid at a concentration of 3% by mass and potassium iodide at a concentration of 3% by mass for about 20 seconds, and stretched at a speed of 24cm/min. Uniaxially stretch in the length direction (third stretch) until 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 containing boric acid at a concentration of 4% by mass and potassium iodide at a concentration of approximately 5% by mass, and the length was stretched at a speed of 24cm/min. Stretch uniaxially (the fourth stretch) to 5.5 times the original length. Thereafter, 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 to perform a fixation process, and then dried in a dryer at 60° C. for 4 minutes. A polarizing film (average thickness: 13 μm) was obtained.

(3) Preparation of adhesive PVA (a saponified homopolymer of vinyl acetate, with a polymerization degree of 2,400 and a saponification degree of 99.95 mol%) and an acid scavenger A (40 parts by mass relative to 100 parts by mass of PVA) were added to water and dissolved at 90°C for 2 hours. Thus, an aqueous solution with a PVA concentration of 3.5% by mass was obtained. This PVA aqueous solution was used as an adhesive.

(4) Production of polarizing plate A test piece with a length of 10 cm and a width of 5 cm was taken from the obtained polarizing film. A cellulose triacetate film was bonded to both sides of the test piece (polarizing film) using the adhesive obtained above, and the film was dried at 60°C for 10 minutes to produce a polarizing plate. The amount of adhesive applied 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 according to the above-mentioned method and the light transmittance was evaluated. The results are presented in Table 1.

[Example 2] Except using acid scavenger B as the acid scavenger, 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 presented in Table 1.

[Example 3] Except using acid scavenger C as the acid scavenger, 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 presented in Table 1.

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

[Example 5] The adhesive was 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. and polarizing plates. Each evaluation was performed in the same manner as in Example 1. The results are presented in Table 1.

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

[Comparative Example 2] Except that the content (addition amount) of the acid scavenger A was set to 0.01 parts by mass relative to 100 parts by mass of PVA, the same procedure as in Example 1 was followed to produce an adhesive and a polarizing plate. The 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 Type Addition amount Addition amount Addition amount Light transmittance(%) determination (Weight) (Weight) (Weight) Embodiment 1 A 40 100 0 40 A Embodiment 2 B 40 100 0 31 A Embodiment 3 C 40 100 0 twenty four A Embodiment 4 A 5 100 0 twenty three A Embodiment 5 A 40 90 10 12 B Comparison Example 1 - 0 100 0 0.4 D Comparison Example 2 A 0.01 100 0 0.4 D

As shown in Table 1, the polarizing plates obtained using the adhesives of Examples 1 to 5 in which the acid scavenger content is 0.1 parts by mass or more relative to 100 parts by mass of non-volatile components fully suppress the decrease in light transmittance in the high-temperature durability test. In addition, the polarizing plates obtained using the adhesive of Example 5 containing a urethane resin have slightly poorer results. [Possibility of industrial use]

The adhesive of the present invention can be suitably used in the manufacture of polarizing plates.

without.

without.

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Claims (4)

An adhesive for manufacturing polarizing plates for bonding a polarizing film containing polyvinyl alcohol and a protective film containing a cellulose ester resin, comprising an acid scavenger and a non-volatile component other than the acid scavenger, wherein 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, the non-volatile component comprises polyvinyl alcohol, and the content of the polyvinyl alcohol in the non-volatile component is 50% by mass or more, and the acid scavenger is a carbodiimide compound having at least one carbodiimide group and is water-soluble. Such as the adhesive of claim 1, wherein the non-volatile component does not contain urethane resin, or the non-volatile component includes urethane resin, and the content of the urethane resin in the non-volatile component It is 3 mass% or less. The adhesive of claim 1 or 2, wherein the content of the acid capturing agent is 0.1 to 50 parts by mass relative to 100 parts by mass of the non-volatile component. A polarizing plate comprises a polarizing film comprising polyvinyl alcohol, a protective film comprising a cellulose ester resin, and an adhesive layer disposed between the polarizing film and the protective film, wherein the adhesive layer is formed by an adhesive as described in any one of claims 1 to 3.