KR20150091493A - Multilayer film - Google Patents

Abstract

(Problem) Even when a thin PVA film is used, even when a laminated film for polarizing film production which can hardly cause stretching and cutting during stretching and which can easily produce a polarizing film excellent in polarization performance and a thin PVA film are used To provide a laminated film which can hardly cause stretching and cutting at the time of stretching and further can easily produce a polarizing film or the like having excellent polarization performance.
A laminated film for producing a polarizing film in which a PVA film and a thermoplastic resin film are adjacent to each other, the laminated film having an adhesive strength of 200 mN / 15 mm or less between both films; And a laminated film in which a PVA film and a thermoplastic resin film are adjacent to each other, wherein an adhesive strength between both films is less than 1.5 mN / 15 mm.

Description

[0001] MULTILAYER FILM [0002]

The present invention relates to a laminated film useful as a polarizing film production raw material film or the like, a film roll on which the polarizing film is wound, and a polarizing film producing method using the laminated film.

A polarizing plate having light transmission and shielding functions is a fundamental 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 cellulose acylate (TAC) film is stuck to the surface of a polarizing film. As the polarizing film constituting the polarizing plate, a polyvinyl alcohol film (hereinafter referred to as " polyvinyl alcohol " (I ₃ ^- , I ₅ ^-, etc.) and dichroic organic dyes are adsorbed on a stretched film obtained by uniaxially stretching and orienting a polylactic acid (hereinafter also referred to as " PVA " . Such a polarizing film can be obtained by uniaxially stretching a PVA film containing a dichroic dye in advance or by adsorbing a dichroic dye simultaneously with uniaxial stretching of the PVA film or by uniaxially stretching a PVA film and then adsorbing the dichroic dye Or the like.

The LCD is intended to be used in a wide range of small-sized devices such as an electronic desk calculator and a wrist watch, a notebook computer, a liquid crystal monitor, a liquid crystal color projector, a liquid crystal television, a car navigation system, a mobile phone, and a measurement device used indoors and outdoors. Particularly, it is often used in mobile applications such as a small-sized notebook computer and a mobile phone, and the demand for thinning of the polarizing plate is getting stronger.

One of the methods of making the polarizing plate thin is to thin the polarizing film. For this purpose, it is conceivable to thin the PVA film as a raw material of the polarizing film. However, a thin PVA film tends to cause stretching and cutting at the time of stretching, and the productivity and yield of the polarizing film are lowered, which tends to lead to high costs.

As a technique for producing a thin polarizing film without causing stretching break at the time of stretching, there is known a method of forming a thin PVA layer on a thermoplastic resin film by a coating method and stretching the laminated body (see, for example, Patent 1 and 2, etc.).

Japanese Patent No. 4804588 Specification Japanese Patent No. 4815544 Specification

However, the method using a laminate comprising a thermoplastic resin film and a PVA layer formed by a coating method has the following problems.

(I) Coating operation or subsequent drying operation is troublesome.

(Ii) since the heat treatment for the insolubilization treatment of the PVA layer needs to be carried out in the state of a laminated chain, the thermoplastic resin film to be used is limited to be stretchable even after the heat treatment and becomes expensive.

(Iii) a laminate obtained by forming a PVA layer on a thermoplastic resin film by a coating method has a relatively high adhesive strength between the thermoplastic resin film and the PVA layer, and when the laminate having such high bonding strength is stretched, It is difficult to obtain a polarizing film having an excellent polarizing performance.

Even when a thin PVA film is used, even if a laminated film for producing a polarizing film, which can easily produce a polarizing film having excellent polarization performance, and a thin PVA film are used, A laminated film which can hardly cause stretching breakage during stretching and can easily produce a polarizing film or the like excellent in polarization performance, a film roll in which they are wound, and a method for producing a polarizing film using the laminated film .

As a result of diligent studies to achieve the above object, the present inventors have found that, in the case of producing a polarizing film using a thin monolayer PVA film, the polarizing film is subjected to a step of contacting with water such as a swelling step or a dyeing step, It is likely that curling occurs at both end portions in the width direction of the film after passing through the film, which causes the film to easily cause stretching and cutting in the subsequent stretching step, When the thermoplastic resin film is laminated on the PVA film with an adhesive strength of not more than a specific value, the occurrence of curling can be suppressed and the occurrence of stretch cutting can be reduced. Further, when the adhesive strength is not more than a specific value, It has been found that it is very easy to remove the thermoplastic resin film when the thermoplastic resin film is removed, Thereby completing the present invention.

That is,

[1] A laminated film for producing a polarizing film, wherein the PVA film and the thermoplastic resin film are adjacent to each other, wherein the laminated film has an adhesive strength of 200 mN / 15 mm or less between both films;

[2] A laminated film in which a PVA film and a thermoplastic resin film are adjacent to each other, the laminated film having an adhesion strength between both films of less than 1.5 mN / 15 mm;

[3] The laminated film according to the above [1] or [2], wherein the thickness of the PVA film is 45 탆 or less;

[4] A laminated film according to any one of [1] to [3], which is a long laminated film;

[5] The laminated film according to the above [4], wherein the width of the thermoplastic resin film is at least 1.1 times the width of the PVA film;

[6] A film roll comprising the laminated film of [4] or [5] wound thereon;

[7] A method for producing a polarizing film having a water contacting step of bringing the laminated film of any one of the above [1] to [5] into contact with water, and thereafter a drawing step of drawing the PVA film;

[8] The method according to [7], wherein the thermoplastic resin film and the PVA film are adjacent to each other in the stretching step;

[9] The method according to the above [7], wherein the thermoplastic resin film is removed before the stretching step;

.

According to the present invention, even when a thin PVA film is used, a laminated film for polarizing film production which can hardly cause stretching and cutting at the time of stretching and which can easily produce a polarizing film excellent in polarization performance, and a case in which a thin PVA film is used A laminated film which can hardly cause stretching breakage at the time of stretching and can easily produce a polarizing film or the like excellent in polarization performance, a film roll in which they are wound, and a method for producing a polarizing film using the laminated film are provided do.

Hereinafter, the present invention will be described in detail.

In the laminated film of the present invention, the PVA film and the thermoplastic resin film are adjacent to each other.

[PVA film]

Examples of the PVA constituting the PVA film include vinyl esters such as vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl versatate, vinyl laurate, vinyl stearate, vinyl benzoate and isopropenyl acetate Or a polyvinyl ester obtained by polymerizing two or more kinds of polyvinyl esters can be used. Of the above vinyl esters, compounds having vinyloxycarbonyl groups (H ₂ C = CH-O-CO-) in the molecule are preferable from the viewpoints of easiness in production of PVA, availability, cost and the like, and vinyl acetate is more preferable .

The above-mentioned polyvinyl ester is preferably obtained by using only one kind of vinyl ester or two or more kinds of vinyl esters as monomers, more preferably obtained by using only one kind of vinyl ester as a monomer, It may be a copolymer of one or more vinyl esters and other monomers copolymerizable therewith.

Examples of other monomers copolymerizable with the above vinyl ester include? -Olefins having 2 to 30 carbon atoms such as ethylene, propylene, 1-butene and isobutene; (Meth) acrylic acid or a salt thereof; (Meth) acrylate, n-butyl (meth) acrylate, i-butyl (meth) acrylate, t- (Meth) acrylic acid esters such as butyl, 2-ethylhexyl (meth) acrylate, dodecyl (meth) acrylate and octadecyl (meth) acrylate; (Meth) acrylamide; (Meth) acrylamide, N, N-dimethyl (meth) acrylamide, diacetone (meth) acrylamide, (meth) acrylamide propanesulfonic acid or a salt thereof, ) Acrylamidopropyldimethylamine or a salt thereof, (meth) acrylamide derivatives such as N-methylol (meth) acrylamide or derivatives thereof; N-vinyl amides such as N-vinyl formamide, N-vinylacetamide and N-vinyl pyrrolidone; Vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether and stearyl vinyl ether Ether; Vinyl cyanide such as (meth) acrylonitrile; Vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride and vinylidene fluoride; Allyl compounds such as allyl acetate and allyl chloride; Maleic acid or its salt, ester or acid anhydride; Itaconic acid or its salt, ester or acid anhydride; Vinylsilyl compounds such as vinyltrimethoxysilane; Unsaturated sulfonic acid or a salt thereof. The above-mentioned polyvinyl esters may have a structural unit derived from one or more of the above-mentioned other monomers.

The proportion of the structural unit derived from the other monomer in the polyvinyl ester is preferably 15 mol% or less, more preferably 10 mol% or less, based on the number of moles of the total structural units constituting the polyvinyl ester, More preferably 5 mol% or less.

As the above-mentioned PVA, those not graft-copolymerized can be preferably used. However, as far as the effect of the present invention is not impaired, the PVA may be one modified by one kind or two or more graft copolymerizable monomers. This graft copolymerization can be carried out on at least one of polyvinyl ester and PVA obtained by saponifying it. As the graft copolymerizable monomer, for example, unsaturated carboxylic acid or its derivative; Unsaturated sulfonic acid or a derivative thereof; And? -Olefins having 2 to 30 carbon atoms. The proportion of the structural unit 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 the total structural units constituting the polyvinyl ester or PVA.

In the PVA, a part of the hydroxyl groups may be crosslinked or not crosslinked. In the above-mentioned PVA, a part of the hydroxyl groups may react with an aldehyde compound such as acetaldehyde, butylaldehyde or the like to form an acetal structure, or may not react with these compounds and form an acetal structure.

The degree of polymerization of the PVA is not particularly limited, but is preferably 1,000 or more. When the degree of polymerization of PVA is 1000 or more, there is an advantage that the polarizing performance of the obtained polarizing film can be further improved. If the degree of polymerization of PVA is too high, the production cost of PVA tends to increase and the processability at the time of film formation tends to be poor. Therefore, the degree of polymerization of PVA is more preferably in the range of 1,000 to 10,000, more preferably in the range of 1,500 to 8,000 And particularly preferably within the range of 2000 to 5000. [0050] In the present specification, the degree of polymerization of PVA means the average polymerization degree measured in accordance with the description of JIS K 6726-1994.

The degree of saponification of PVA is preferably 99.0 mol% or more, more preferably 99.8 mol% or more, and even more preferably 99.9 mol% or more, from the standpoint of good heat and humidity resistance of the resulting polarizing film and the like. In the present specification, the degree of saponification of PVA refers to the mole number of a structural unit (typically a vinyl ester unit) that can be converted into a vinyl alcohol unit by saponification of PVA and the total number of moles of the vinyl alcohol unit, (Mol%) of the total amount of the components. The degree of saponification can be measured in accordance with the description of JIS K 6726-1994.

The PVA film may contain a plasticizer together with the above PVA. By containing the plasticizer in the PVA film, the handleability and the stretchability of the PVA film can be improved. As the plasticizer, a polyhydric alcohol is preferably used. Specific examples of the plasticizer include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, trimethylolpropane, And one or more plasticizers. Of these, glycerin is preferable in that the stretchability of the PVA film becomes better.

The content of the plasticizer in the PVA film is preferably 3 to 20 parts by mass, more preferably 5 to 17 parts by mass, and further preferably 7 to 14 parts by mass with respect to 100 parts by mass of the PVA. The content of the plasticizer in the PVA film is 3 parts by mass or more based on 100 parts by mass of the PVA, so that the stretching property 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 based on 100 parts by mass of the PVA, the plasticizer is bleed-out on the surface of the PVA film to suppress deterioration of the handleability of the PVA film.

When the PVA film is produced by using a stock solution for forming a PVA film to be described later, the film-forming property is improved to suppress the occurrence of thickness irregularity of the film, and when a metal roll or a belt is used for film formation, It is preferable to incorporate a surfactant into the stock solution for easy peeling of the PVA film from these metal rolls or belts. When a PVA film is produced from a film forming stock solution containing a surfactant, the PVA film may contain a surfactant. The kind of the surfactant contained in the surfactant to be added to the PVA film-forming stock solution, that is, the surfactant contained in the PVA film is not particularly limited, but from the viewpoint of the releasability from the metal roll or the belt, the anionic surfactant or non- Surfactants are preferred, and nonionic surfactants are particularly preferred.

Examples of the anionic surfactant include carboxylic acid type such as potassium laurate; Sulfuric acid ester type such as octylsulfate; Sulfonic acid type such as dodecylbenzenesulfonate and the like are preferable.

Examples of the nonionic surfactant include alkyl ether types such as polyoxyethylene oleyl ether and the like; Alkyl phenyl ether type such as polyoxyethylene octyl phenyl ether; Alkyl ester types such as polyoxyethylene laurate; Alkylamine type such as polyoxyethylene lauryl amino ether; Alkyl amide types such as polyoxyethylene lauric acid amide; Polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether; Alkanolamide types such as diethanolamide laurate, and diethanolamide oleic acid; And allyl phenyl ether type such as polyoxyalkylene allyl phenyl ether.

These surfactants may be used singly or in combination of two or more kinds.

When the surfactant is mixed into the stock solution for producing a PVA film, the content of the surfactant in the stock solution of the film-forming composition and further the content of the surfactant in the PVA film is preferably 100 mass% Is preferably in the range of 0.01 to 0.5 part by mass, more preferably 0.02 to 0.3 part by mass. The content of the surfactant is 0.01 part by mass or more based on 100 parts by mass of the PVA, so that the film formability and the peelability can be improved. On the other hand, when the content of the surfactant is 0.5 parts by mass or less based on 100 parts by mass of the PVA, the surfactant bleeds out on the surface of the PVA film to prevent blocking due to deterioration in handling properties.

The PVA film may be made of PVA alone or may be composed of only PVA, the plasticizer and / or the surfactant described above. However, if necessary, the PVA film and the plasticizer, such as an antioxidant, a cryoprotectant, a pH adjuster, a masking agent, And other components other than the surfactant.

The content of PVA in the PVA film is preferably within a range of 50 to 100 mass%, more preferably within a range of 80 to 100 mass%, and still more preferably within a range of 85 to 100 mass%.

Though the thickness of the PVA film is not particularly limited, the thickness is preferably 45 탆 or less, more preferably 35 탆 or less, in view of the fact that the above-mentioned curling easily occurs in a thin PVA film and the effect of the present invention is more remarkable in a thin PVA film. Or less, more preferably 25 m or less. Although the lower limit of the thickness of the PVA film is not particularly limited, it is preferable that the thickness is 3 占 퐉 or more because the polarizing film or the like can be produced more smoothly.

The shape of the PVA film is not particularly limited, but a long film is preferable in that a polarizing film or the like can be continuously produced with good productivity. The length of the long film is not particularly limited and may be suitably set according to the use of the polarizing film to be produced and may be within a range of 5 to 20000 m, for example. There is no particular limitation on the width of the long film. For example, the width of the long film may be 50 cm or more. However, in recent years, a wide polarizing film is required, and more preferably 1 m or more, more preferably 2 m or more, More preferably 4 m or more. There is no particular limitation on the upper limit of the width of the long film. However, if the width is too wide, it tends to be difficult to uniformly stretch the film when a polarizing film is produced by a practical apparatus. Is preferably 7 m or less.

The production method of the PVA film is not particularly limited, and a production method in which the thickness and width of the film after film formation are more uniform can be preferably employed. For example, the above PVA constituting the PVA film, A film forming solution in which a plasticizer, a surfactant and other ingredients are dissolved in a liquid medium, PVA and, if necessary, a plasticizer, a surfactant, another component, and a liquid medium, Can be manufactured. When the stock solution for film formation contains at least one kind of plasticizer, surfactant and other components, it is preferable that the components are uniformly mixed.

Examples of the liquid medium used for the preparation of the film-forming stock solution include water, dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerin, propylene glycol, diethylene glycol, Triethylene glycol, tetraethylene glycol, trimethylol propane, ethylenediamine, diethylenetriamine, etc. One or more of these may be used. Among them, water is preferable in terms of a small environmental load and recoverability.

The volatile matter content of the stock film-forming solution (the content ratio of volatile components such as a liquid medium removed by volatilization or evaporation at the time of film-forming in the film-forming stock solution) varies depending on the film-forming method, film-forming conditions and the like, , More preferably within a range of 55 to 90 mass%, and still more preferably within a range of 60 to 85 mass%. Since the volatile fraction of the undiluted film forming solution is 50 mass% or more, the viscosity of the undiluted film forming solution does not become excessively high, and filtration and defoaming at the time of preparation of the film forming solution smoothly occur, facilitating the production of a PVA film with few foreign matters or defects. On the other hand, when the volatile fraction of the stock film-forming solution is 95 mass% or less, the concentration of the film-forming stock solution is not excessively low, and the production of an industrial PVA film becomes easy.

Examples of the film forming method for forming the 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 law is preferable. These film-forming methods may employ only one type, or two or more types may be used in combination. Among these film forming methods, the extrusion film forming method is more preferable in that a PVA film having uniform thickness and width and good physical properties can be obtained. The PVA film can be dried or heat-treated as required.

[Thermoplastic resin film]

Examples of the thermoplastic resin constituting the thermoplastic resin film include various thermoplastic resins such as polyolefin (polyethylene, polypropylene, polymethylpentene and the like), polystyrene, polycarbonate, polyvinyl chloride, methacrylic resin, nylon and polyethylene terephthalate Resins, and copolymers having a plurality of monomer units constituting these thermoplastic resins. In the thermoplastic resin film, the thermoplastic resin may be either one type or two or more types. Of these, polyolefins are preferred because they have high stretchability. The method for producing the thermoplastic resin film is not particularly limited and can be produced by a known method such as melt molding or calender molding.

The thickness of the thermoplastic resin film is not particularly limited, but it is preferable that the thickness is 10 占 퐉 or more, more preferably 15 占 퐉 or more in view of effectively suppressing curling occurring at both ends in the width direction of the PVA film , And more preferably 20 mu m or more. There is no particular upper limit to the upper limit of the thickness of the thermoplastic resin film, but it is preferable that the thickness is 100 占 퐉 or less because a polarizing film or the like can be produced more smoothly.

The shape of the thermoplastic resin film is not particularly limited and may be suitably selected in accordance with the shape of the PVA film. When the PVA film is a long film, it is preferable that the thermoplastic resin film is also a long film, and the length thereof can be, for example, in the range of 5 to 20,000 m.

In the case where the thermoplastic resin film is a long film, the width thereof is preferably 1.1 times or more of the width of the PVA film. This is because in the water contact process, the width of the PVA film tends to expand by swelling, while the width of the thermoplastic resin film hardly changes. Thus, the width of the thermoplastic resin film satisfies the above relationship, It is possible to more effectively suppress the curl occurring at both end portions in the width direction even in the case of swelling. From this viewpoint, the width of the thermoplastic resin film is more preferably 1.15 times or more of the width of the PVA film, and more preferably 1.2 times or more. The upper limit of the width of the thermoplastic resin film is not particularly limited. However, the width of the thermoplastic resin film is preferably 1.8 times or less the width of the PVA film, and 1.6 Fold or less.

[Laminated film]

In the case of using the laminated film of the present invention as a raw film for polarizing film production, the adhesive strength between the PVA film and the thermoplastic resin film needs to be 200 mN / 15 mm or less. If the adhesive strength is more than 200 mN / 15 mm, it is difficult to remove the thermoplastic resin film. In addition, when the stretching process is performed in a state where the thermoplastic resin film and the PVA film are adjacent to each other as described later, It is possible to interfere with a suitable nepheline of the PVA film, and it becomes difficult to obtain a polarizing film excellent in polarization performance. From this viewpoint, the adhesive strength is preferably 100 mN / 15 mm or less, more preferably 10 mN / 15 mm or less, and further preferably 5 mN / 15 mm or less. Further, the laminated film of the present invention is not limited to the case of using as a polarizing film production film, and if the adhesive strength is less than 1.5 mN / 15 mm, removal of the thermoplastic resin film becomes easier. From this viewpoint, it is more preferable that the adhesive strength is less than 1.3 mN / 15 mm, and it is more preferable that the two films are merely adjacently but not substantially bonded (the adhesive strength is less than 1.0 mN / 15 mm) . The above adhesive strength can be measured by a T-type peel test described in JIS K 6854-3: 1999, and specifically, it can be measured by a method described later in Examples.

The method for preparing the laminated film of the present invention is not particularly limited, and for example, a method of preparing the PVA film and the thermoplastic resin film and then overlapping or adhering them to each other; A method in which the above-mentioned film forming stock solution is applied to a thermoplastic resin film and then dried to form a PVA film on the thermoplastic resin film; In the latter case, it is usually difficult to adjust the adhesive strength between the two films to within the range specified in the present invention. In this case, the PVA film and the thermoplastic resin film are prepared, It is more preferable that a method of preparing a PVA film and a thermoplastic resin film and then adjoining them so as not to substantially bond them together is more preferable. When a long film is used for both the PVA film and the thermoplastic resin film, it is preferable to overlap or adhere so that the center lines in the width direction of the two films substantially coincide with each other. It is preferable that a long laminated film formed by using a long film of both the PVA film and the thermoplastic resin film is rolled into a film roll from the viewpoint of handling property and the like.

[Production method of polarizing film]

The laminated film of the present invention having the adhesive strength of 200 mN / 15 mm or less is used as a raw material film for polarizing film production. On the other hand, the laminated film of the present invention having an adhesive strength of less than 1.5 mN / 15 mm can suppress the occurrence of curling even when passed through a process of contacting with water, and can reduce the occurrence of stretch cutting in the case of stretching, In addition, since it is very easy to remove the thermoplastic resin film at the time of finally removing the thermoplastic resin film, it can be suitably used for various applications conventionally known as general PVA films such as a raw material film for producing a retardation film. In this laminated film, It is preferable to utilize the effect of the present invention as a raw material film for polarizing film production.

There is no particular limitation on the method of producing the polarizing film using the laminated film of the present invention, but the method of contacting the laminated film with water (water contact step) Thereafter, a production method having a step of stretching the PVA film (stretching step) is preferred. When a polarizing film is produced through a water contact process and a subsequent stretching process using a thin PVA film as a single layer, curling is generated at both ends in the width direction of the film after the water contact process, and in the subsequent stretching process, Although the stretching and cutting of the film is likely to occur, the curl is inhibited by performing the water contact process on the laminated film of the present invention, whereby the stretching cutting of the PVA film in the stretching process can be prevented.

ㆍ Water contact process

Examples of the water contact process include a swelling treatment process, a dyeing treatment process, a crosslinking treatment process, and the like, and one or more of these processes can be employed. It is preferable that the swelling treatment step, the dyeing treatment step and the crosslinking treatment step are carried out in this order as a water contact step in that a polarizing film excellent in polarizing performance and the like can be easily produced. The contact between the laminated film and the water in the water contact process may be either a method of spraying water on the laminated film or a method of immersing the laminated film in water. From the viewpoints of ease of production of polarizing film and productivity, A method of immersing the film in water is preferable. The water to be used is not limited to pure water, but an aqueous solution as described later or an aqueous dispersion may be used depending on the purpose of each step.

The swelling treatment in the swelling treatment step can be carried out by immersing the laminated film in water. The temperature of the water to be immersed in water is preferably in the range of 20 to 40 캜, more preferably in the range of 22 to 38 캜, still more preferably in the range of 25 to 35 캜. The time for immersing in water is preferably in the range of, for example, 0.5 to 5 minutes, more preferably in the range of 1 to 3 minutes. Further, the water to be 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 in the dyeing treatment step can be carried out by immersing the laminated film in an aqueous solution containing a dichroic dye. The concentration of the dichroic dye in the aqueous solution containing the dichroic dye can be appropriately set according to the kind of the dichroic dye to be used and can be set within the range of, for example, 0.001 to 1% by mass, as the aqueous solution containing the iodine - when using a potassium iodide aqueous solution, to an iodine-based pigment efficiently in a range of from the point that can be adsorbed on a PVA film, 0.01 to 1.0 weight% in terms of the concentration of iodine (I ₂₎ to be used , And it is preferable that the concentration of potassium iodide (KI) used is in the range of 0.01 to 10 mass%. The temperature of the aqueous solution containing the dichroic dye is preferably in the range of 20 to 50 占 폚 and more preferably in the range of 25 to 40 占 폚 in that the dichroic dye can be efficiently adsorbed to the PVA film.

Examples of the dichroic dye include iodine dyes (I ₃ ^- and I ₅ ^- ) and dichroic organic dyes. The iodine dye can be obtained, for example, by contacting iodine (I ₂ ) with potassium iodide. The dichromatic organic dyes include Direct Black 17, 19, 154; Direct Brown 44, 106, 195, 210, 223; Direct Red 2, 23, 28, 31, 37, 39, 79, 81, 240, 242, 247; Direct Blue 1, 15, 22, 78, 90, 98, 151, 168, 202, 236, 249, 270; Direct Violet 9, 12, 51, 98; Direct Green 1, 85; Direct Yellow 8, 12, 44, 86, 87; Direct Orange 26, 39, 106, 107 and the like. Of these dichroic dyes, iodine dyes are preferable from the viewpoints of handleability, availability, and polarization performance. The dichroic dye may be either a single species or two or more species. For example, it may be an equilibrium mixture such as I ₃ ^- and I ₅ ^- .

When the crosslinking treatment is carried out, crosslinking is introduced into the PVA film, and the PVA is effectively prevented from being eluted into water when the stretching process is performed at a relatively high temperature and in a wet state. From such viewpoints and the like, it is preferable that the crosslinking treatment step is performed after the dyeing treatment step and before the stretching step. The crosslinking treatment can be carried out by immersing the laminated film in an aqueous solution containing a crosslinking agent. As the crosslinking agent, boron compounds such as boric acid salts such as boric acid and borax can be used. The concentration of the crosslinking agent in the aqueous solution containing the crosslinking agent is preferably within a range of 1 to 15 mass%, more preferably within a range of 2 to 7 mass%. The aqueous solution containing the crosslinking agent may contain an auxiliary agent such as potassium iodide. The temperature of the aqueous solution containing the crosslinking agent is preferably in the range of 20 to 50 캜, and more preferably in the range of 25 to 40 캜.

Apart from the later-described stretching step (the step of stretching the PVA film after the water contacting step), the laminated film is stretched during each water contacting step during the water contacting step and / or when the water contacting step is carried out for a plurality of steps . By such stretching (pre-stretching), wrinkles can be prevented from occurring in the PVA film. From the viewpoints of the polarizing performance and the like of the polarizing film to be obtained, the stretching magnification of the full-grain stretched film is preferably 4 times or less, more preferably 1.5 to 3.5 times, based on the original length of the laminated film before stretching. With respect to the draw ratio during each water contact step, for example, the draw ratio in the swelling treatment step is preferably in the range of 1.1 to 3 times, more preferably in the range of 1.2 to 2.5 times , More preferably in the range of 1.4 to 2.3 times; The stretching magnification in the dyeing treatment step is preferably 2 times or less, more preferably 1.8 times or less, still more preferably 1.1 to 1.5 times; The stretching ratio in the crosslinking treatment step is preferably not more than 2 times, more preferably not more than 1.5 times, and further preferably 1.05 to 1.3 times.

The laminated film to be provided in the water contact step may be one which has been taken out from a film roll in which a long laminated film as described above is rolled up in a roll form. However, a film roll of a single layer PVA film and a film roll of a single layer thermoplastic resin film And the films may be sequentially wound from these film rolls so that the two films are adjacent to each other and continuously provided in this state in the water contact process.

ㆍ Stretching process

After the water contact process, the polarizing film can be produced by carrying out a stretching process in which the PVA film is stretched and, if necessary, further performing fixing treatment and drying treatment. In the stretching process, the PVA film may be stretched in a state where the thermoplastic resin film and the PVA film are adjacent to each other, or the thermoplastic resin film may be removed before the stretching process, and then the PVA film may be stretched. In the case of the former, the thermoplastic resin film may be removed prior to the stretching step or the subsequent fixing treatment step and before the drying treatment step. In a case where the heat resistance of the thermoplastic resin film is high, the thermoplastic resin film may be removed after the drying treatment step.

The stretching method in the stretching step is not particularly limited, and the wet stretching method or the dry stretching method may be used. In the case of the wet stretching method, it may be carried out in an aqueous solution containing one or two or more kinds of boron compounds such as boric acid salts such as boric acid and borax. In the aqueous solution containing the dichroic dye or in a fixed treatment bath . In the case of the dry stretching method, the stretching may be performed at room temperature, or the stretching may be performed while heat is applied, or the stretching may be performed after absorption. Among them, the wet stretching method is preferable from the viewpoint of the thickness uniformity in the width direction in the polarizing film to be obtained, and it is more preferable to stretch in an aqueous solution of boric acid. The concentration of boric acid in the aqueous solution of boric acid is preferably within a range of 0.5 to 6.0 mass%, more preferably within a range of 1.0 to 5.0 mass%, and further preferably within a range of 1.5 to 4.0 mass%. The aqueous solution containing the boron compound may contain potassium iodide, and the concentration thereof is preferably in the range of 0.01 to 10 mass%.

The temperature at which the PVA film is stretched in the stretching process is preferably within the range of 30 to 90 占 폚, more preferably within the range of 40 to 80 占 폚, and still more preferably within the range of 50 to 70 占 폚.

The stretching magnification in the stretching step is preferably 1.2 times or more, more preferably 1.5 times or more, and more preferably 2 times or more, in view of obtaining a polarizing film having better polarizing performance. The total stretching magnification (magnification multiplied by the stretching magnification of each stretching) including the stretching magnification of the preceding stretch shrinkage is preferably 5.5 times or more, more preferably 5.7 times or more based on the original length of the laminated film to be used, More preferably 5.8 times or more, and particularly preferably 5.9 times or more. By setting each stretching magnification within the above range, a polarizing film having better polarizing performance can be obtained. The upper limit of the total draw ratio is not particularly limited, but is preferably 8 times or less.

The stretching of the PVA film in the stretching step is preferably uniaxial stretching in view of the performance of the resulting polarizing film. There is no particular restriction on the direction of uniaxial stretching, and uniaxial stretching or transverse uniaxial stretching in the longitudinal direction of a long film can be adopted. However, in view of obtaining a polarizing film superior in polarizing performance, Is preferred. The uniaxial stretching in the longitudinal direction can be carried out by using a stretching apparatus having a plurality of rolls parallel to each other and changing the peripheral velocity between the rolls. On the other hand, transverse uniaxial stretching can be carried out using a tenter-type stretching machine.

ㆍ Fixed treatment process

The fixing treatment in the fixed treatment step is mainly performed to strengthen the adsorption of the dichroic dye to the stretched PVA film. The fixing treatment can be carried out by immersing the stretched PVA film in a fixed treatment bath. As the fixed treatment bath, an aqueous solution containing one or two or more boron compounds such as boric acid salts such as boric acid and borax can be used. If necessary, an iodine compound or a metal compound may be added to the fixed treatment bath. The concentration of the boron compound in the aqueous solution containing the boron compound used as the fixed treatment bath is generally preferably in the range of 2 to 15 mass%, more preferably in the range of 3 to 10 mass%. The temperature of the fixed treatment bath is preferably in the range of 15 to 60 캜, more preferably in the range of 25 to 40 캜.

ㆍ Drying process

Conditions for the drying treatment in the drying treatment step are not particularly limited, but the drying temperature is preferably in the range of 30 to 150 占 폚, and more preferably in the range of 50 to 130 占 폚. By drying at a temperature within the above range, it is easy to obtain a polarizing film having excellent dimensional stability.

The polarizing film thus obtained is usually used as a polarizing plate by adhering a protective film optically transparent to both sides or one side thereof and having mechanical strength. As the protective film, a cellulose triacetate (TAC) film, a cellulose acetate (CAB) film, an acrylic film, a polyester film, or the like can be used. As the adhesive for bonding, PVA adhesive, urethane adhesive and the like can be mentioned, and among them, PVA adhesive is preferable.

Example

Hereinafter, the present invention will be described in detail by way of examples, but the present invention is not limited at all by these examples. In the following Examples and Comparative Examples, the methods of measuring the adhesive strength between the films and the polarization performance of the polarizing film are described below.

[Adhesive strength between films]

Short film pieces each having a size of 200 mm in the longitudinal direction and 15 mm in the width direction were cut out from the laminated film produced in the following examples or comparative examples and the film pieces were cut in accordance with JIS K 6854- 3: 1999, the T-type peeling test was conducted five times, and the average value was determined as the bonding strength. The measurement conditions in this test were as follows: temperature: 28 ° C, humidity: 50% RH, chucking interval of tensile testing machine: 50 mm, tensile speed: 250 mm / min (moving speed of the peeling point in the film piece was 125 mm / Min). Further, in the case where both the films are not bonded, the bonding strength between the films is evaluated to be less than 1.0 mN / 15 mm when the bonding strength is excessively low and both films are peeled off at the time of cutting the film pieces.

[Polarization performance of polarizing film]

(a) Measurement of transmittance Ts

Two samples having a square of 2 cm in width direction in the length direction of the polarizing film were collected from the central portion in the width direction of the polarizing film obtained in the following Examples or Comparative Examples, (V7100) manufactured by Mitsubishi Rayon Co., Ltd.) was used and the visual sensitivity of the C light source and the visible region of 2 ° field of view was corrected in accordance with JIS Z 8722: 2009 (measurement method of object color) And the transmittance of the light when tilted at -45 [deg.] Were measured, and the average value Ts1 (%) thereof was determined. In the same manner for the other one sample, the transmittance of light at an angle of 45 DEG and the transmittance of light at an angle of -45 DEG were measured, and the average value Ts2 (%) thereof was determined. Ts1 and Ts2 were averaged by the following formula (1) to obtain the transmittance Ts (%) of the polarizing film.

Ts = (Ts1 + Ts2) / 2 (1)

(b) Measurement of polarization degree V

The two samples taken from the measurement of the transmittance Ts, wherein the light transmittance T ∥ overlapping length of the case such that the direction is parallel to (%) transmittance of light in the case T⊥ longitudinal direction orthogonal to the overlapped (%) "( (a) Measurement of transmittance Ts ", and the degree of polarization V (%) was determined by the following formula (2).

V = {(T ∥ - T⊥ ) / (T ∥ + T⊥)} 1/2 × 100 (2)

[Example 1]

(PVA, glycerin and a surfactant, the content of glycerin being 12 parts by mass with respect to 100 parts by mass of PVA, and the content of the surfactant being 100 parts by mass of PVA) having a thickness of 30 占 퐉 and a width of 1 m 0.03 part by mass, PVA is a saponified product of a homopolymer of vinyl acetate, the degree of polymerization of PVA was 2400, and the degree of saponification of PVA was 99.9 mol%) was continuously withdrawn from the film roll. On the other hand, a long linear low density polyethylene film (LLDPE film, SE620N, manufactured by Tama Poly Co., Ltd.) having a thickness of 50 占 퐉 and a width of 1.2 m was continuously and continuously unwound from the film roll. The two films thus wound were superimposed so as to substantially coincide with the center line in the width direction (adhesion strength between both films was less than 1.0 mN / 15 mm), swelling treatment, dyeing treatment and crosslinking treatment were successively performed in this order, The laminated film was contacted with water.

Further, as the swelling treatment, the laminated film was immersed in distilled water (temperature: 30 ° C) for 1 minute, while being uniaxially stretched at a draw ratio of 2 in the longitudinal direction. As the dyeing treatment, the laminated film was immersed in an aqueous solution containing iodine dye (concentration of iodine being used: 0.05 mass%, concentration of potassium iodide used: 1.2 mass%, temperature: 30 占 폚) for 2 minutes, And then uniaxially stretched at a draw ratio of 1.2 times in the longitudinal direction. Further, as a crosslinking treatment, the laminated film was immersed in an aqueous boric acid solution (boric acid concentration: 2.6 mass%, temperature: 30 占 폚) for 2 minutes, while being uniaxially stretched in the longitudinal direction at a draw ratio of 1.1 times.

After the water contact step, the stretching step was continuously performed. In the stretching process, the stretching process was performed in a state where the thermoplastic resin film and the PVA film were adjacent to each other. Thereafter, the thermoplastic resin film was removed, and the stretched PVA film was dried to continuously produce a polarizing film.

As the stretching treatment, the PVA film adjacent to the thermoplastic resin film was stretched in the longitudinal direction in an aqueous solution of boric acid (boric acid concentration: 2.8 mass%, potassium iodide concentration: 5 mass%, temperature: 57 占 폚) (The total draw ratio including the draw ratio of the prior art in the water contact process is 6.3 times). As the drying treatment, the stretched PVA film was dried at 60 DEG C for 1 minute.

In the production of the above polarizing film, no curling was observed at both ends in the width direction of the PVA film even after passing through any water contact step, and no stretch breaking occurred in the stretching step. In addition, removal of the thermoplastic resin film was very easy. The polarization performance of the resulting polarizing film was measured according to the above-mentioned method. As a result, Ts = 43.5 (%) and V = 99.993 (%). Table 1 summarizes the above results.

[Example 2]

A polarizing film was continuously produced in the same manner as in Example 1 except that the thickness of the PVA film was changed to 15 탆. Further, in the laminated film, the bonding strength between both films was less than 1.0 mN / 15 mm.

In the production of the above polarizing film, no curling was observed at both ends in the width direction of the PVA film even after passing through any water contact step, and no stretch breaking occurred in the stretching step. In addition, removal of the thermoplastic resin film was very easy. The polarizing performance of the obtained polarizing film was measured according to the above-mentioned method. As a result, Ts = 43.7 (%) and V = 99.983 (%). Table 1 summarizes the above results.

[Example 3]

A polarizing film was produced in the same manner as in Example 1 except that a long, low-density polyethylene film (LDPE film, A-1 manufactured by Tama Poly Co., Ltd.) having a thickness of 50 탆 and a width of 1.2 m was used as the thermoplastic resin film . Further, in the laminated film, the bonding strength between both films was less than 1.0 mN / 15 mm.

In the production of the above polarizing film, no curling was observed at both ends in the width direction of the PVA film even after passing through any water contact step, and no stretch breaking occurred in the stretching step. In addition, removal of the thermoplastic resin film was very easy. The polarizing performance of the resulting polarizing film was measured according to the above-mentioned method. As a result, Ts = 43.4 (%) and V = 99.993 (%). Table 1 summarizes the above results.

[Example 4]

(HDPE film, PAC-4K-80, manufactured by SANEI PHARMACEUTICAL CO., LTD.) Having a thickness of 50 m and a width of 1.2 m as a thermoplastic resin film, , A polarizing film was continuously produced in the same manner as in Example 1. [ Further, in the laminated film, the bonding strength between both films was 150 mN / 15 mm.

In the production of the above polarizing film, no curling was observed at both ends in the width direction of the PVA film even after passing through any water contact step, and no stretch breaking occurred in the stretching step. However, removal of the thermoplastic resin film was not as easy as in Example 1. The polarizing performance of the obtained polarizing film was measured according to the above-mentioned method. As a result, Ts = 43.7 (%) and V = 99.948 (%). Table 1 summarizes the above results.

[Example 5]

Prior to the stretching process, a polarizing film was continuously produced in the same manner as in Example 1 except that the thermoplastic resin film was removed and the PVA film was stretched alone.

In the production of the above polarizing film, no curling was observed at both ends in the width direction of the PVA film even after passing through any water contact step, and no stretch breaking occurred in the stretching step. In addition, removal of the thermoplastic resin film was very easy. The polarization performance of the obtained polarizing film was measured according to the above-mentioned method, and as a result, Ts = 43.3 (%) and V = 99.994 (%). Table 1 summarizes the above results.

[Comparative Example 1]

A polarizing film was continuously produced in the same manner as in Example 1, except that the PVA film was used as a single layer without using a thermoplastic resin film, followed by a water contact step and a subsequent drawing step.

In the production of the above polarizing film, after passing through the swelling treatment process, curling was generated at both ends in the width direction of the PVA film, and the polarizing film could not be obtained due to the occurrence of stretching cutting in the stretching process. Therefore, the polarization performance of the polarizing film was not measured. Table 1 summarizes the above results.

[Comparative Example 2]

An aqueous solution (PVA, glycerin and a surfactant) having a PVA concentration of 10% by mass was added to an elongated amorphous polyethylene terephthalate film (A-PET film, "NOVA CLEAR" manufactured by Mitsubishi Plastics Corporation) having a thickness of 200 μm and a width of 1 m Wherein the content of glycerin is 12 parts by mass with respect to 100 parts by mass of PVA and the content of the surfactant is 0.03 parts by mass with respect to 100 parts by mass of PVA, PVA is a saponified product of a homopolymer of vinyl acetate, Was 2400 and the degree of saponification of PVA was 99.9 mol%) and dried at 60 캜 to produce a laminated film having a PVA film having a thickness of 30 탆 formed on a thermoplastic resin film (a thermoplastic resin film and a PVA film The adhesion strength between the substrates is 250 mN / 15 mm). The thus obtained laminated film was subjected to a water contact step in the same manner as in Example 1 by performing the swelling treatment, the dyeing treatment and the crosslinking treatment in this order, and in the same manner as in Example 1, The drying treatment was carried out in this order to continuously produce a polarizing film. In addition, since the bonding strength between the PVA film and the thermoplastic resin film is high and it is very difficult to remove the thermoplastic resin film before the drying treatment after the stretching treatment, the thermoplastic resin film is removed after the drying treatment to form a polarizing film. Removal was still difficult.

In the production of the above polarizing film, no curling was observed at both ends in the width direction of the PVA film even after passing through any water contact step, and no stretch breaking occurred in the stretching step. However, the polarizing performance of the obtained polarizing film was measured in accordance with the above-mentioned method. As a result, Ts = 43.5 (%) and V = 99.854 (%). Table 1 summarizes the above results.

Industrial availability

According to the present invention, even when a thin PVA film is used, it is possible to easily produce a polarizing film or the like which is hard to cause stretching and cutting at the time of stretching and has excellent polarization performance. For example, the laminated film of the present invention can be used A polarizing plate made of a polarizing film manufactured by the method of the present invention can be preferably used for a mobile application such as a small-sized notebook computer or a mobile phone.

Claims (9)

Wherein the polyvinyl alcohol film and the thermoplastic resin film are adjacent to each other and the adhesive strength between both films is 200 mN / 15 mm or less. A laminated film in which a polyvinyl alcohol film and a thermoplastic resin film are adjacent to each other, wherein an adhesive strength between both films is less than 1.5 mN / 15 mm. 3. The method according to claim 1 or 2,
Wherein the thickness of the polyvinyl alcohol film is 45 占 퐉 or less. 4. The method according to any one of claims 1 to 3,
A laminated film which is a long laminated film. 5. The method of claim 4,
Wherein the width of the thermoplastic resin film is at least 1.1 times the width of the polyvinyl alcohol film. A film roll comprising the laminated film according to claim 4 or 5 wound thereon. A process for producing a polarizing film, which comprises a water contacting step of bringing the laminated film according to any one of claims 1 to 5 into contact with water, and thereafter a stretching step of stretching the polyvinyl alcohol film. 8. The method of claim 7,
Wherein the thermoplastic resin film and the polyvinyl alcohol film are adjacent to each other in the stretching step. 8. The method of claim 7,
And a step of removing the thermoplastic resin film before the stretching step.