TW201728916A - Method for manufacturing polarizing film - Google Patents

Abstract

The present invention provides a method for manufacturing a polarizing film having high optical properties in spite of the boron content being suppressed and the shrinking force being reduced. The method is for manufacturing a polarizing film having a boron content of 1.5 to 3.0% by weight from a polyvinyl alcohol based resin film, and it comprises: a dyeing step of dyeing a polyvinyl alcohol based resin film with a dichroic dye; a crosslinking step of treating the film after the dyeing step with a crosslinking agent containing at least boric acid; a first stretching step of uniaxially stretching the polyvinyl alcohol based resin film during and/or before the crosslinking step; and a second stretching step of uniaxially stretching the polyvinyl alcohol based resin film after the crosslinking step.

Description

Method for manufacturing polarizing film

The present invention relates to a method of producing a polarizing film from a polyvinyl alcohol-based resin.

A polarizing plate has been widely used as a polarizing element or the like in an image display such as a liquid crystal display. The polarizing plate is usually a member in which a transparent resin film (protective film or the like) is bonded to one surface or both surfaces of the polarizing film by using an adhesive or the like.

The polarizing film is mainly applied to a germicidal film made of a polyvinyl alcohol-based resin, which is immersed in a dyeing bath containing a dichroic dye such as iodine, and then immersed in a crosslinking bath containing a crosslinking agent such as boric acid. At the same time, it is manufactured by uniaxially stretching the film at any stage. In the uniaxial stretching, there are a dry extension extending in the air and a wet extension extending in a liquid such as the dye bath or the crosslinking bath.

Since the polarizing film is crosslinked, if it is heated, it may shrink easily and the durability may be insufficient. Japanese Laid-Open Patent Publication No. 2013-148806 (Patent Document 1) discloses a polarizing film which is excellent in durability by providing a boron content as low as 1 to 3.5% by weight.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2013-148806

However, when the amount of boron is reduced in the polarizing film, a sufficient degree of crosslinking may not be obtained and the optical characteristics may be lowered. An object of the present invention is to provide a method for producing a polarizing film which is capable of producing a polarizing film having high optical characteristics despite suppressing the boron content and reducing the shrinkage force.

The present invention provides a method of producing a polarizing film shown below.

[1] A method for producing a polarizing film, which is a method for producing a polarizing film having a boron content of 1.5 to 3.0% by weight from a polyvinyl alcohol-based resin film, comprising: dyeing a polyvinyl alcohol-based resin film with a dichroic dye a step of treating the film after the dyeing step with a crosslinking agent containing at least boric acid; and first, uniaxially stretching the polyvinyl alcohol resin film in the crosslinking step and/or before the crosslinking step And an extension step; and a second stretching step of uniaxially stretching the polyvinyl alcohol resin film after the crosslinking step.

[2] The method for producing a polarizing film according to [1], wherein a magnification of the uniaxial stretching performed in the second extending step is 1.04 to 1.2 times.

The method for producing a polarizing film according to the above aspect, wherein the second stretching step is performed by uniaxially rotating the polyvinyl alcohol resin film in an environment having an absolute humidity of 100 g/m ³ or more. extend.

The method for producing a polarizing film according to any one of the above aspects, wherein the polyvinyl alcohol-based resin film is in contact with one or a plurality of rolls in the second extending step. At least 70% of the time between the initial contact with the roll and the final release from the roll is uniaxially extended in contact with either roll.

According to the production method of the present invention, a polarizing film having a low boron content and a polarizing film having excellent optical characteristics can be obtained.

S10, S20, S30, S40, S50, S60‧‧ steps

Fig. 1 is a flow chart showing an embodiment of a method for producing a polarizing film of the present invention.

<Method of Manufacturing Polarizing Film>

Referring to Fig. 1, a method for producing a polarizing film of the present invention is a method for producing a polarizing film having a boron content of 1.5 to 3.0% by weight from a polyethylene resin film, comprising the steps of: a dyeing step S20 for dyeing a coloring pigment; a crosslinking step S30 of treating the film after the dyeing step with a crosslinking agent containing at least boric acid; and a first stretching step S40 of uniaxially stretching the polyethylene resin film in the crosslinking step and/or before; After the crosslinking step, the polyethylene resin film is subjected to a second stretching step S60 of uniaxial stretching.

According to the present invention, a polarizing film having a boron-containing ratio as low as 1.5 to 3.0% by weight and capable of suppressing shrinkage force and having excellent optical characteristics can be produced. The boron content is preferably 2.0 to 2.8% by weight.

The method for producing a polarizing film of the present invention may further include a step other than the above, and specifically, for example, Fig. 1 shows a swelling step S10 before the dyeing step S20 and a cleaning step S50 after the crosslinking step S30.

The various processing steps included in the production method of the present invention are carried out continuously by continuously transporting the polyvinyl alcohol-based resin film of the germ film along the film transport route of the polarizing film production apparatus. The membrane transport route is provided with equipment (treatment bath, furnace, etc.) for carrying out the various processing steps described above in the order of implementation. The treatment bath, such as a swelling bath, a dye bath, a cross-linking bath, and a washing bath, is a bath containing a treatment liquid to which a polyvinyl alcohol-based resin film is treated.

The film transport path may be constructed by arranging a guide roll or a roll at an appropriate position in addition to the above-described equipment. For example, the guide rolls may be disposed in front of or after the respective treatment baths or in the treatment bath, whereby the introduction of the film to the treatment bath, the immersion, and the pulling out of the treatment bath may be performed by such equipment. More specifically, two or more guide rolls may be provided in each treatment bath to pass the film along These guide rolls are transported to immerse the film in each treatment bath.

As the polyvinyl alcohol-based resin of the polyvinyl alcohol-based resin film constituting the germ film, those obtained by saponifying a polyvinyl acetate-based resin can be used. The polyvinyl acetate-based resin is a copolymer of vinyl acetate and another monomer copolymerizable therewith, in addition to the polyvinyl acetate of a homopolymer of vinyl acetate. Examples of the other monomer copolymerizable with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and acrylamides having an ammonium group. The degree of saponification of the polyvinyl alcohol-based resin is usually about 85 mol% or more, more preferably about 90 mol% or more, and still more preferably about 99 mol% or more.

The polyvinyl alcohol-based resin may be modified, and for example, aldehyde-modified polyvinyl formal, polyvinyl acetal, polyvinyl butyral or the like may be used.

The average degree of polymerization of the polyvinyl alcohol-based resin film is preferably from 100 to 10,000, more preferably from 1,500 to 8,000, still more preferably from 2,000 to 5,000. The average degree of polymerization of the polyvinyl alcohol-based resin film can be determined in accordance with JIS K6726 (1994). When the average degree of polymerization is less than 100, it is difficult to obtain good polarizing performance, and when it exceeds 10,000, the workability may be poor.

The thickness of the polyvinyl alcohol-based resin film is, for example, about 10 to 150 μm, and is preferably 100 μm or less from the viewpoint of reducing the thickness of the polarizing film, more preferably 70 μm or less, and even more preferably 50 μm or less. It is more preferably 40 μm or less.

For the polyvinyl alcohol-based resin film of the germ film, for example, a roll (winding) of a long unstretched polyvinyl alcohol-based resin film can be prepared. At this time, the polarizing film It can also be obtained as a long strip. Hereinafter, each step will be described in detail.

(1) Swelling step S10

The swelling treatment in this step is a treatment carried out for the purpose of removing foreign matter, removing a plasticizer, imparting dyeability, plasticizing the film, etc., depending on the desired polyvinyl alcohol-based resin film of the germ film, and specifically, The treatment for immersing the polyvinyl alcohol-based resin film in a swelling bath containing water. The film may be immersed in one swelling bath or may be immersed in two or more swelling baths in this order. The film may also be subjected to uniaxial stretching treatment before swelling treatment, swelling treatment, or before swelling treatment and swelling treatment.

The swelling bath system may be, in addition to water (for example, pure water), an aqueous solution to which a water-soluble organic solvent such as an alcohol has been added.

The temperature of the swelling bath when immersing the film is usually about 10 to 70 ° C, preferably about 15 to 50 ° C, and the immersion time of the film is usually about 10 to 600 seconds, preferably about 20 to 300 seconds.

(2) Dyeing step S20

The dyeing treatment in this step is carried out for the purpose of adsorbing and orienting the dichroic dye to the polyvinyl alcohol-based resin film. Specifically, the polyvinyl alcohol-based resin film may be immersed in the dichroic dye. Treatment in the dye bath. The film system may be immersed in one dye bath or may be immersed in two or more dye baths in that order. In order to improve the dyeability of the dichroic dye, it is also possible to apply at least some degree of uniaxial stretching treatment to the film in the dyeing step. Replace the uniaxial stretching treatment before the dyeing treatment, or the uniaxial one before the dyeing treatment The stretching treatment can also be performed by uniaxial stretching treatment at the time of dyeing treatment.

The dichroic dye can be an iodine or a dichroic organic dye. Specific examples of the dichroic organic dye include: red BR, red LR, red R, pink LB, rubin BL, Bordeaux GS, sky blue LG, lemon yellow, blue BR, blue 2R, Navy Blue RY, Green LG, Purple LB, Purple B, Black H, Black B, Black GSP, Yellow 3G, Yellow R, Orange LR, Orange 3R, Scarlet GL, Scarlet KGL, Congo Red, Bright Purple BK, Super Blue G , Super Blue GL, Super Orange GL, Direct Sky Blue, Direct Fast Orange S, Fast Black. The dichroic dye system may be used alone or in combination of two or more.

When iodine is used as the dichroic dye, an aqueous solution containing iodine and potassium iodide can be used in the dye bath. Instead of other iodides such as zinc iodide, potassium iodide may be used, and potassium iodide may be used in combination with other iodides. At the same time, compounds other than iodide, such as boric acid, zinc chloride, cobalt chloride, and the like, may be present. When boric acid is added, the point of containing iodine can be distinguished from the crosslinking treatment described later. The iodine content in the above aqueous solution is usually from about 0.003 to about 1 part by weight per 100 parts by weight of water. Meanwhile, the content of the iodide such as potassium iodide is usually from about 0.1 to 20 parts by weight per 100 parts by weight of water.

The temperature of the dye bath when immersing the film is usually about 10 to 45 ° C, preferably about 10 to 40 ° C, more preferably about 20 to 35 ° C, and the immersion time of the film is usually about 30 to 600 seconds. It is preferably about 60 to 300 seconds.

When a dichroic organic dye is used as the dichroic dye, an aqueous solution containing a dichroic organic dye can be used in the dye bath. The content of the dichroic organic dye in the aqueous solution is usually from about 1 × 10 ^-4 to 10 parts by weight per 100 parts by weight, preferably from about 1 × 10 ^-3 to about 1 part by weight. In the dye bath, a dyeing aid or the like may be allowed to coexist, and for example, an inorganic salt such as sodium sulfate or a surfactant may be contained. The dichroic organic dye may be used alone or in combination of two or more. The temperature of the dye bath at the time of immersing the film is, for example, about 20 to 80 ° C, preferably about 30 to 70 ° C, and the immersion time of the film is usually about 20 to 600 seconds, preferably about 30 to 300 seconds.

(3) Cross-linking step S30

The cross-linking treatment of treating the polyvinyl alcohol-based resin film after the dyeing step with a crosslinking agent is carried out by crosslinking for water resistance or adjusting color, and specifically, after the dyeing step The film is immersed in a crosslinking bath containing a crosslinking agent. The film system may be immersed in one crosslinking bath or may be immersed in two or more crosslinking baths in this order. Uniaxial stretching can also be performed during the cross-linking process.

The crosslinking agent contains boric acid, and may further be glyoxal or glutaraldehyde containing other crosslinking agents. The content of boric acid in the crosslinking bath is usually from about 0.1 to 15 parts by weight per 100 parts by weight of water, preferably from about 1 to 10 parts by weight. When the dichroic dye is iodine, the crosslinking bath preferably contains an iodide in addition to boric acid. The content of the iodide in the crosslinking bath is usually from about 0.1 to 20 parts by weight per 100 parts by weight of water, preferably from about 5 to 15 parts by weight. The iodide may, for example, be potassium iodide or zinc iodide. At the same time, compounds other than iodide such as zinc chloride, cobalt chloride, zirconium chloride, Sodium thiosulfate, potassium sulfite, sodium sulfate, etc. coexist in the crosslinking bath.

The temperature of the crosslinking bath when immersing the film is usually about 50 to 85 ° C, preferably about 50 to 70 ° C, and the immersion time of the film is usually about 10 to 600 seconds, preferably about 20 to 300 seconds.

(4) First extension step S40

As described above, when the polarizing film is produced, the polyvinyl alcohol-based resin film may be in the crosslinking step S30 and/or before, or may be 1 or 2 or more before any of the swelling step S10 to the crosslinking step S30. The stage is uniaxially stretched. In terms of improving the dyeability of the dichroic dye, the film supplied to the dyeing step is preferably a film which has been subjected to at least a certain degree of uniaxial stretching treatment, or is dyed in addition to the uniaxial stretching treatment before the dyeing treatment. The uniaxial stretching treatment is preferably performed in place of the uniaxial stretching treatment before the dyeing treatment.

The uniaxial stretching treatment in the first stretching step S40 may be either dry stretching in the air or wet stretching extending in the bath, or both. The uniaxial stretching treatment is performed by imparting a circumferential speed difference between the two rolls, and performing longitudinal uniaxial stretching between the rolls, stretching of the heat roll, stretching of the tenter, and the like, and preferably including stretching between rolls. The total stretching ratio of the first stretching step S40 based on the embryonic film (the cumulative stretching ratio when the stretching treatment is performed at a stage of 2 or more) is about 3 to 8 times. In order to impart good polarizing characteristics, the stretching ratio is preferably 4 times or more, more preferably 4.5 times or more. At the same time, since the manufacturing method of the present invention includes the second extending step S60, the total stretching ratio in the first extending step S40 can be It is 7 times or less, 6 times or less, and further 5 times or less.

(5) Washing step S50

The washing treatment in this step is a treatment which is carried out as needed for the purpose of removing an agent such as an excess cross-linking agent or a dichroic dye attached to the polyvinyl alcohol-based resin film, and using a washing liquid containing water. The treatment of washing the polyvinyl alcohol-based resin film after the crosslinking step. Specifically, the treatment is performed by immersing the polyvinyl alcohol-based resin film after the crosslinking step in a washing bath (washing liquid). The film may be immersed in one washing bath or may be immersed in two or more washing baths in that order. Alternatively, the washing treatment may be such that the washing liquid is formed into a shower and the polyvinyl alcohol-based resin film after the crosslinking step is sprayed, and the immersion and the spray may be combined.

The washing liquid may be, in addition to water (for example, pure water), an aqueous solution to which a water-soluble organic solvent such as an alcohol has been added. The temperature of the washing liquid may be, for example, about 5 to 40 °C.

The washing step S50 is an optional step and may be omitted. Alternatively, as will be described later, the washing step is performed in the second extending step S60. Preferably, the film after the cleaning step S50 is subjected to the second stretching step S60.

(6) Second extension step S60

The second stretching treatment in this step is a treatment of uniaxially stretching the film after the crosslinking step S30. When the washing step S50 is carried out, it is preferred to carry out the second stretching treatment on the film after the washing step. After performing the drying treatment after the washing step S50, it is preferred to carry out the first step on the film after the drying treatment. 2 extension processing. The magnification of the uniaxial stretching in the second extending step S60 is preferably 1.01 to 1.3 times, more preferably 1.04 to 1.2 times. When the stretching ratio is 1.3 times or less, it is advantageous to suppress an increase in shrinkage force or film breakage.

The second stretching step S60 is preferably carried out in a high-humidity environment in which the film after the crosslinking step S30 is in an absolute humidity of 40 g/m ² or more. By performing the stretching treatment in the second extending step S60 in such a high-humidity environment, the contraction force of the polarizing film can be further suppressed. The reason for this is that the orientation of the molecular chain of the polyvinyl alcohol-based resin constituting the polarizing film can be lowered by the stretching treatment in a high-humidity environment, whereby the increase in residual stress in the film can be suppressed. By performing the second extension step S60 and performing the stretching treatment in a high-humidity environment, it is also advantageous to effectively increase the cumulative stretching ratio (total extension stretching ratio in the first stretching step S40) while preventing the film from being broken. It is advantageous to increase the use area of the polarizing film and the surface of the original unit which is reduced by the increase in the cumulative stretching ratio.

The absolute humidity of the environment in which the second stretching treatment is performed is more preferably 75 g/m ³ or more, and more preferably 100 g/m ³ or more, in order to more effectively suppress the increase in the shrinkage force. On the other hand, when the absolute humidity is too high, the film is contaminated by condensation or dew condensation in the treatment area, so the absolute humidity is preferably 550 g/m ³ or less, and more preferably 400 g/m ³ or less. It is more preferably 300 g/m ³ or less, and more preferably 180 m ³ or less.

In the second stretching process, the stretching method is not limited, and for example, uniaxial stretching can be performed by stretching between rolls or tenter stretching. In the second stretching treatment, it is preferred to prevent the shrinkage force from contacting the polyvinyl alcohol-based resin film with one or more rolls. In the second extension step, specifically, The polyvinyl alcohol-based resin film is in contact with one or more rolls, preferably at least 50% of the time between the initial contact roll and the last release from the roll for uniaxially extending in contact with either roll, to at least 70% The uniaxial stretching is preferably carried out in contact with either of the rolls, and it is more preferable to contact any of the rolls in at least 75% of the time. Even if the contact time of the polyvinyl alcohol-based resin film is made uniform, the number of rolls that can be brought into contact with the polyvinyl alcohol-based resin film in the second stretching step is preferably two or more. In the second stretching treatment, the surrounding gas atmosphere can be extended, and the film can be prevented from being broken. When the film is stretched at 40 ° C or higher, the absolute humidity is easily adjusted to the above preferred numerical range, and is good. In order to maintain the transportability of the film, it is more preferably 55 ° C or more, and still more preferably 60 ° C or more. Meanwhile, the ambient temperature is preferably 100 ° C or less, and in terms of obtaining excellent optical characteristics, it is preferably 90 ° C or less.

The total extension magnification of the stretching magnification in the first extension step S40 and the second extension step S60 is approximately 4 to 9 times. In order to impart good polarizing characteristics, the cumulative stretching ratio is preferably 4.5 times or more, more preferably 5.0 times or more, and more preferably 5.5 times or more.

By applying the second stretching step S60, even when the stretching ratio in the first stretching step S40 is lowered, a sufficient stretching ratio can be secured as the total stretching ratio, so that excellent optical characteristics of the polarizing film can be imparted. At the same time, even if the total stretching ratio is the same, the uniaxial stretching is performed by the first stretching step S40 and the second stretching step S60, and the optical characteristics of the polarizing film can be imparted as compared with the case where the second stretching step S60 is not provided. Further, by performing uniaxial stretching in the first stretching step S40 and the second stretching step S60, even if the boron content is as low as 1.5 to 3.0% by weight, the boron content is obtained. For example, a polarizing film having an optical property superior to 3.0% by weight. At the same time, since the polarizing film produced by the production method of the present invention has a boron content as low as 1.5 to 3.0% by weight, the shrinkage force can be suppressed, and the warpage of the polarizing plate or even the liquid crystal panel can be prevented.

Further, the second extending step S60 is not provided, and more excellent optical characteristics can be obtained only by the uniaxial stretching in the first extending step S40, and when the stretching ratio in the first extending step S40 is increased, the contraction force is increased. A problem arises in that a polarizing plate or even a liquid crystal panel is warped.

The uniaxial stretching treatment in the second stretching step S60 may be either extension of dry stretching or wet stretching, but is generally dry stretching when extending in a high-humidity environment. The uniaxial stretching treatment by dry stretching may be a roll-to-roll extension, a heat roll extension, a tenter extension, or the like which performs a longitudinal uniaxial extension between the two rolls.

The second stretching treatment in a high-humidity environment can be carried out, for example, by introducing a film after the crosslinking step S30 into a booth having a humidity (depending on the required temperature) while performing a high-humidity treatment. Extended processing. The second stretching treatment in a high-humidity environment is preferably 5 seconds or longer, and more preferably 10 seconds or longer. At the same time, although the time may vary depending on the temperature, if it is too long, the optical characteristics may be deteriorated, so it is preferably 60 minutes or less, more preferably 30 minutes or less, and more preferably 10 minutes or less. It is especially good for 5 minutes or less.

The second extending step S60 is preferably performed after the washing step S50. However, the washing liquid may be sprayed or the like while being extended in a high-humidity environment, and the stretching treatment and the washing place may be simultaneously performed in a high-humidity environment. At the same time, the second stretching step may be combined with the cleaning treatment by placing the film in a high-humidity environment to substantially clean the film.

In the second elongation treatment, the long polyvinyl alcohol-based resin film is transported along the film transport path, and the increase in the contraction force can be more effectively suppressed, and the tension is preferably 50 to 5,000 N/m. The film tension is preferably from 300 to 1,500 N/m in terms of suppressing occurrence of wrinkles of the film.

The second extension treatment can also be a treatment in which the polyvinyl alcohol-based resin film is dried, that is, a treatment in which the water content is lowered. Therefore, it is not always necessary to additionally perform the drying process before or after the second stretching process.

The moisture content of the film supplied to the second elongation treatment is usually about 13 to 50% by weight, and preferably about 30 to 50% by weight, depending on the thickness of the film. The degree of decrease in the water content by the second stretching treatment, that is, the difference between the moisture content before the second stretching treatment and the moisture content after the second stretching treatment (water content difference ΔS) depends on the thickness of the film, but is, for example, 5 to It is preferably 45 to 5% by weight and preferably 8 to 35% by weight. For example, when the thickness of the germ film is about 40 μm or less, the moisture content difference ΔS may be less than 15% by weight.

The moisture content of the film after the second stretching treatment (the polarizing film in the final step of the second stretching treatment) depends on the thickness of the film, but is preferably 5 to 30% by weight, and the subsequent film transportability is More preferably, it is 6 to 15% by weight. When the moisture content is too low, the film is liable to be broken during transportation, and when the moisture content is too high, curling may occur at the film end due to moisture release.

In general, the thinner the film, the more easily the water is dissipated. Therefore, the thinner the membrane, the easier the water content in the second stretching treatment and the second stretching treatment is lowered. When the moisture content is too low, the transportability of the film is easily lowered.

The second stretching step S60 may be performed immediately after the crosslinking step S30 or the cleaning step S50, or may be performed after the step S30 or the cleaning step S50 is followed by the other steps. Other steps include drying treatment. However, in order to more effectively suppress the increase in the contraction force, it is preferable to directly supply the film of the crosslinking step S30 or the cleaning step S50 to the second stretching step S60.

Through the above steps, a polarizing film in which a dichroic dye is adsorbed and oriented on a uniaxially stretched polyvinyl alcohol resin film can be obtained. The boron-containing film of the polarizing film is from 1.5 to 3.0% by weight, and preferably from 2.0 to 2.8% by weight. The boron content in the polarizing film can be adjusted by the amount of boric acid in the crosslinking bath, the treatment temperature of the crosslinking step S30, and the treatment time. The thickness of the polarizing film is usually 5 to 40 μm, preferably 30 μm or less, and more preferably 20 μm or less. According to the polarizing film obtained by the present invention, even when the thickness is 30 μm or less and further thinner than 20 μm, excellent optical characteristics can be obtained, and an increase in shrinkage force can be suppressed.

For example, in order to adjust the water content, a drying treatment may be applied after the second stretching step S60. However, since the water content can be adjusted by the second extending step S60, the drying process can be performed as needed.

The obtained polarizing film can be directly transported, for example, to the subsequent polarizing plate producing step (step of swelling the protective film on one side or both sides of the polarizing film).

<Polarizing plate>

On at least one side of the polarizing film manufactured as described above, Then, a protective film was attached to the polarizing plate. The protective film may be a thermoplastic resin, for example, a polyolefin resin such as a chain polyolefin resin (such as a polypropylene resin) or a cyclic polyolefin resin (such as a decylene resin); for example, a triethylene fluorene fiber. a cellulose ester resin of a cellulose or a diacetyl cellulose; a polyester resin such as polyethylene terephthalate, polyethylene naphthalate or polybutylene terephthalate; polycarbonate A resin; a (meth)acrylic resin such as a polymethyl methacrylate resin; or a transparent resin film composed of such a mixture or a copolymer.

The protective film may also be a protective film having an optical function such as a retardation film or a brightness enhancement film. For example, a retardation film which imparts an arbitrary retardation value can be formed by stretching a transparent resin film made of the above material (uniaxial stretching or biaxial stretching or the like) or forming a liquid crystal layer or the like on the film.

A surface treatment layer (coating layer) such as a hard coat layer, an antiglare layer, an antireflection layer, an antistatic layer, and an antifouling layer may be formed on the surface opposite to the polarizing film in the protective film.

The thickness of the protective film is preferably thinner in terms of thinning of the polarizing plate, but when it is too thin, the strength is lowered and the workability is deteriorated, so it is preferably 5 to 150 μm, and more preferably 5 to 100 μm. Good, and even better with 10 to 50 μm.

The adhesive used for bonding the polarizing film and the protective film may, for example, be an active energy ray-curable adhesive such as an ultraviolet curable adhesive, or an aqueous solution of a polyhexenol-based resin, or a crosslinking agent may be formulated therein. An aqueous solution, such as an aqueous binder of a polyurethane emulsion adhesive. When a protective film is attached to both surfaces of the polarizing film, an adhesive for forming two adhesive layers may be used. For the same kind, it can also be different types. For example, when a protective film is bonded to both surfaces, an aqueous adhesive may be used for bonding on one side, and an active energy ray-curable adhesive may be used for bonding on the other side. The ultraviolet curable adhesive may be a mixture of a radically polymerizable acrylic compound and a photoradical polymerization initiator, or a mixture of a cationically polymerizable epoxy compound and a photocationic polymerization initiator. Meanwhile, a cationically polymerizable epoxy compound may be used in combination with a radically polymerizable acrylic compound, or a photocationic polymerization initiator may be used in combination with a photoradical polymerization initiator as a starter.

When an active energy ray-curable adhesive is used, after swelling, the adhesive is cured by irradiation of the active energy ray. Although the light source of the active energy ray is not particularly limited, it is preferably an active energy ray (ultraviolet light) having a luminescent distribution at a wavelength of 400 nm or less. Specifically, a low-pressure mercury lamp, a medium-pressure mercury lamp, a high-pressure mercury lamp, and an ultra-high pressure mercury lamp are used. Chemical lamps, black lamps, microwave-excited mercury lamps, metal halide lamps, etc. are preferred.

In order to improve the adhesion between the polarizing film and the protective film, before the bonding of the polarizing film and the protective film, corona treatment, flame treatment, plasma treatment, or the like may be applied to the swelling surface of the polarizing film and/or the protective film. Surface treatment such as ultraviolet irradiation treatment, primer coating treatment, and saponification treatment.

The polarizing plate of the present invention is produced by laminating a protective film on a polarizing film of a single layer film as described above, but is not limited thereto, and may be a method described in, for example, Japanese Laid-Open Patent Publication No. 2009-98653 Production. The latter method is advantageous for obtaining a polarizing plate having a polarizing film (polarizing sheet layer) of a film, and may include, for example, the following steps.

A step of forming a resin layer by applying a coating liquid containing a polyvinyl alcohol-based resin to at least one surface of the base film and then drying the mixture to form a polyvinyl alcohol-based resin layer to obtain a laminated film; and extending the laminated film to obtain an extension a step of extending the film; forming a polarizing layer (corresponding to a polarizing film) by dyeing the polyvinyl alcohol-based resin layer of the stretched film with a dichroic dye to obtain a dyeing step of the polarizing laminated film; and forming a polarizing layer A first bonding step of bonding a protective film to a polarizer layer of a film to obtain a bonding film, and a peeling step of removing a substrate film from the bonding film to obtain a polarizing plate having a single-sided protective film .

When a protective film is laminated on both surfaces of the polarizer layer (polarizing film), the second swelling step of bonding the protective film using an adhesive on the polarizing surface of the polarizing plate having the protective film on one side is further included.

[Examples]

Hereinafter, the present invention will be more specifically described by showing examples, but the present invention is not limited by these examples.

<Example 1>

A long-length polyvinyl alcohol (PVA) film having a thickness of 30 μm (trade name "Kuraray Poval Film VF-PE #3000" manufactured by Kuraray, average polymerization degree 2,400, saponification degree: 99.9 mol% or more] from a roll The coil was continuously conveyed and immersed in a swelling bath composed of pure water at 20 ° C (swelling step) for a residence time of 31 seconds. Then, the film will be pulled out from the swelling bath The staining time was 122 seconds (staining step) in a dye bath containing 30% of iodine at a potassium iodide/boric acid/water ratio of 2/3/100 (weight ratio). Then, the film pulled out from the dyeing bath was immersed in a first crosslinking bath of 56 ° C in a potassium iodide/boric acid/water ratio of 12/2/100 (weight ratio) for 70 seconds (crosslinking step); The residence time was 13 seconds (crosslinking step) in a second crosslinking bath of 40 ° C in which potassium iodide/boric acid/water was 9/2/100 (weight ratio). In the dyeing step and the crosslinking step, longitudinal uniaxial stretching is performed by stretching between rolls in the bath (first stretching step). The total stretch ratio based on the embryonic membrane was 5.81 times.

Next, the film pulled out from the crosslinking bath was immersed in a washing bath composed of pure water at 5 ° C for 3 seconds (washing step). Next, a longitudinal uniaxial stretching treatment (second stretching step) was applied to a high humidity environment by introducing a humidity-adjustable shed to obtain a polarizing film. The temperature in the shed in the second stretching step was set to 87 ° C, and the absolute humidity in the shed was set to 113 g/m ³ , and the time between the first contact of the polyvinyl alcohol-based resin film with the roll and the last release from the roll was 75%. Contact with any roller. In the second stretching step, the stretching ratio based on the film before introduction into the shed was 1.08 times. The thickness of the obtained polarizing film was 9.3 μm.

[Evaluation of polarizing film]

The characteristics of the polarizing film obtained in each of the examples and the comparative examples were measured for the following items.

(1) boron content of polarizing film

0.2 g of the polarizing film was added to 170 mL of pure water, and the mixture was allowed to stand at 95 ° C. After completely dissolving, 30 g of an aqueous mannitol solution (12.5 wt%) was added to prepare a sample solution for measurement. The sodium hydroxide aqueous solution (1 mol/L) was dropped until the measurement sample solution reached the neutralization point, and the boron content (% by weight) in the polyvinyl alcohol-based resin film was calculated from the dropwise amount by the following formula.

Boron content (% by weight) = 1.08 × sodium hydroxide aqueous solution (mL) / weight of polarizing film (g)

(2) MD contraction force

A sample for measurement having a width of 2 mm and a length of 10 mm in the axial direction (MD, extending direction) was taken out from the obtained polarizing film. The sample was mounted on a thermomechanical analyzer (TMA) "EXSTAR-6000" manufactured by SII Nanotech Co., Ltd., and maintained at a constant size to measure the long-side direction generated when the temperature was kept at 80 ° C for 4 hours ( The contraction force (MD contraction force) of the absorption axis direction, MD).

(3) Optical properties

The MD polarizing rate and the TD transmittance in the range of 380 to 780 nm are measured for the obtained polarizing film by a spectrophotometer with an integrating sphere ["V7100" manufactured by JASCO Corporation), according to the following formula : monomer penetration rate (%) = (MD + TD) / 2

The degree of polarization (%) = {(MD - TD) / (MD + TD)} × 100 calculates the monomer transmittance and the degree of polarization in each wavelength.

The "MD penetration rate" is a transmittance when the polarization direction of Glan Thomson is parallel to the transmission axis of the polarizing film sample, and is expressed as "MD" in the above formula. Meanwhile, the "TD penetration rate" refers to a transmittance when the polarization direction of Glan Thomson is perpendicular to the transmission axis of the polarizing film sample, and is expressed as "TD" in the above formula. The obtained monomer transmittance and degree of polarization were measured by a 2 degree angle of view (C light source) of JIS Z 8701:1999 "Color representation method - XYZ color system and X ₁₀ Y ₁₀ Z ₁₀ color system" The visual sensitivity correction was performed to obtain the visual sensitivity correction single transmittance (Ty) and the visual sensitivity correction polarization (Py). The results of each evaluation are shown in Table 1.

<Examples 2 to 7>

The total stretching ratio in the first stretching step, the stretching ratio in the second stretching step, and the temperature and absolute humidity in the shed in the second stretching step, and the contact time with the roller from the initial contact with the roller to the last release from the roller The ratio is shown in Table 1. The rest was subjected to the same operation as in Example 1 to obtain a polarizing film. The thicknesses of the polarizing films of Examples 2 to 7 were 9.6 μm, 11.4 μm, 11.4 μm, 12.4 μm, 12.7 μm, and 9.5 μm, respectively. With respect to the obtained polarizing film, each evaluation was performed in the same manner as in Example 1. The results of the evaluations are shown in Table 1.

<Comparative Examples 1 to 6>

In the crosslinking step, the composition of the first crosslinking bath and the second crosslinking bath (the amount of boric acid relative to 100 parts by weight of water), the temperature, and the immersion time were appropriately adjusted to obtain a boron-containing polarizing film shown in Table 1. In the second stretching step, in Comparative Examples 1 to 3, the longitudinal uniaxial stretching in the second stretching step similar to that in Example 1 was carried out, and in Comparative Examples 4 to 6, the second stretching step was not performed. For each of the examples, the total stretching ratio in the first stretching step, the stretching ratio in the second stretching step, and the temperature and absolute humidity in the shed in the second stretching step are between the first contact with the roller and the last release from the roller. The ratio of the contact time of the rolls is shown in Table 1. The thicknesses of the polarizing films of Comparative Examples 1 to 6 were 11.5 μm, 12.8 μm, 13.4 μm, 13.2 μm, 12.4 μm, and 11.9 μm, respectively. For the obtained polarizing film, the same evaluation as in Example 1 was carried out. The results of the evaluations are shown in Table 1. Further, in the second stretching step, the maximum diameter of the roller in contact with the polyvinyl alcohol-based resin film is 270 mm when the roll contact time is 70% or more, and 75 mm at 10%.

As shown in Table 1, the polarizing films of Comparative Examples 1 to 4 had a boron content of 3.3% by weight or more and a large shrinkage force. In the polarizing film of Comparative Example 5 in which the second stretching step was not performed, the boron content was 3.0% by weight or less, but a decrease in optical characteristics was observed. The polarizing film of Comparative Example 6 in which the second stretching step was not performed had a high stretching ratio in the first stretching step, and although excellent optical characteristics were obtained, the shrinkage force was large.

S10, S20, S30, S40, S50, S60‧‧ steps

Claims (4)

A method for producing a polarizing film, which is a method for producing a polarizing film having a boron content of 1.5 to 3.0% by weight from a polyvinyl alcohol-based resin film, comprising: a step of dyeing a polyvinyl alcohol-based resin film with a dichroic dye; a crosslinking step of treating the film after the dyeing step with a crosslinking agent containing at least boric acid; and a first stretching step of uniaxially stretching the polyvinyl alcohol-based resin film in the crosslinking step and/or before; And, after the crosslinking step, the polyvinyl alcohol-based resin film is subjected to a second stretching step of uniaxial stretching. The method for producing a polarizing film according to the first aspect of the invention, wherein the uniaxial stretching ratio in the second extending step is 1.04 to 1.2 times. The method for producing a polarizing film according to the first aspect of the invention, wherein the polyvinyl alcohol-based resin film is uniaxially stretched in an environment having an absolute humidity of 100 g/m ³ or more. The method for producing a polarizing film according to any one of claims 1 to 3, wherein, in the second extending step, the polyvinyl alcohol resin film is in contact with one or more rolls, and is initially At least 70% of the time between the roll contact and the last release from the roll is uniaxially extended in contact with either roll.