JP6835476B2 - Method for manufacturing stretched film roll - Google Patents

Description

The present invention relates to a method for producing a stretched film roll formed by winding a stretched film which is a stretched polyvinyl alcohol-based resin film.

As the polarizing film constituting the polarizing plate, a stretched polyvinyl alcohol-based resin film in which a dichroic dye such as iodine or a dichroic dye is adsorbed and oriented is conventionally used. A polyvinyl alcohol-based resin film, which is a raw material film for a polarizing film, is usually prepared as a film roll (original roll) formed by winding the film in a roll shape, and the polarizing film continuously unwinds the film from the film roll. However, it is continuously produced by subjecting it to a predetermined treatment such as immersion in a chemical solution [for example, paragraph [0002] of JP2013-109287A (Patent Document 1)].

Japanese Unexamined Patent Publication No. 2013-109287

In the production of a polarizing film, when the film is unwound from the film roll (original roll), the film may be broken immediately after being unwound from the film roll, for example.

An object of the present invention is to provide a film roll formed by winding a polyvinyl alcohol-based resin film, and to produce a film roll capable of suppressing film breakage when the film is unwound from the film roll. There is.

The present invention provides a method for producing a stretched film roll shown below, and a roll of a stretched polyvinyl alcohol-based resin film.

[1] A step of preparing a polyvinyl alcohol-based resin film having a maximum surface roughness Rz of 30 nm or more and a standard deviation σ of the thickness in the film width direction of 0.2 μm or more.
A step of stretching the polyvinyl alcohol-based resin film to obtain a stretched film,
The step of winding the stretched film and
A method for producing a stretched film roll, including.

[2] The production method according to [1], wherein the stretched film has a surface maximum height roughness Rz of 25 nm or more.

[3] The production method according to [1] or [2], wherein the step of preparing the polyvinyl alcohol-based resin film includes a step of bringing it into contact with a thermal roll having a maximum surface roughness Rz of 30 nm or more.

[4] The production method according to any one of [1] to [3], wherein the step of obtaining the stretched film includes a step of dry stretching the polyvinyl alcohol-based resin film.

[5] The polyvinyl alcohol-based resin film is stretched at a stretching ratio of 3 to 6 times using a thermal roll having a surface temperature of 90 to 150 ° C. in the dry stretching step, according to [4]. Production method.

[6] The production method according to any one of [1] to [5], wherein the winding tension in the step of winding the stretched film is 50 MPa or less.

[7] The production method according to any one of [1] to [6], wherein the standard deviation σ of the thickness in the film width direction is 1 μm or less.

[8] The production method according to any one of [1] to [7], wherein the polyvinyl alcohol-based resin film has an average thickness T of 35 μm or less.

[9] A roll of a stretched polyvinyl alcohol-based resin film having a maximum surface roughness Rz of 25 nm or more.

According to the present invention, it is possible to provide a method for producing a film roll capable of suppressing film breakage when the film is unwound.

It is a flowchart which shows an example of the manufacturing method of the stretch film roll which concerns on this invention. It is the schematic sectional drawing which shows an example of the longitudinal stretching process using a thermal roll. It is the schematic sectional drawing which shows another example of the longitudinal stretching process using a thermal roll.

<Manufacturing method of stretched film roll>
With reference to FIG. 1, the method for producing a stretched film roll according to the present invention includes the following steps:
Step S10 of preparing a polyvinyl alcohol-based resin film having a maximum surface roughness Rz of 30 nm or more and a standard deviation σ of the thickness in the film width direction of 0.2 μm or more.
Step S20 of stretching a polyvinyl alcohol-based resin film to obtain a stretched film, and step S30 of winding a stretched film.
including. Hereinafter, each step will be described in detail.

In the following, the polyvinyl alcohol-based resin film is also referred to as "PVA-based resin film". Further, the mechanical flow direction of the film is also referred to as "MD", and the direction orthogonal to the MD, that is, the width direction of the film is also referred to as "TD".

(1) Step of preparing PVA-based resin film S10
The PVA-based resin film prepared in this step is a film composed of a polyvinyl alcohol-based resin, and this film is usually long. As the polyvinyl alcohol-based resin, a saponified polyvinyl acetate-based resin can be used. Examples of the polyvinyl acetate-based resin include polyvinyl acetate, which is a homopolymer of vinyl acetate, and a copolymer of vinyl acetate and another monomer copolymerizable therewith. Examples of other monomers copolymerizable with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and (meth) acrylamides having an ammonium group. In addition, "(meth) acrylic" represents at least one selected from the group consisting of acrylic and methacrylic. The same applies to other terms with "(meta)".

The degree of saponification of the polyvinyl alcohol-based resin can be in the range of 80.0 to 100.0 mol%, but is preferably in the range of 90.0 to 100.0 mol%, more preferably 94.0. It is in the range of 100.0 mol%, more preferably in the range of 98.0-100.0 mol%. When the degree of saponification is less than 80.0 mol%, when a polarizing film is produced using the obtained stretched film roll and a polarizing plate is produced using the polarizing film, the water resistance and moisture heat resistance of the polarizing plate are lowered. obtain.

_{The degree of saponification is the ratio (mol%) of the acetic acid group (acetoxy group: -OCOCH 3} ) contained in the polyvinyl acetate-based resin, which is the raw material of the polyvinyl alcohol-based resin, changed to a hydroxyl group by the saponification step. It is expressed by the following formula:
Degree of saponification (mol%) = 100 x (number of hydroxyl groups) / (number of hydroxyl groups + number of acetic acid groups)
Defined in. The degree of saponification can be determined in accordance with JIS K 6726 (1994).

The average degree of polymerization of the polyvinyl alcohol-based resin is preferably 100 to 10000, more preferably 1500 to 8000, and further preferably 2000 to 5000. The average degree of polymerization of the polyvinyl alcohol-based resin can also be determined in accordance with JIS K 6726 (1994). When the average degree of polymerization is less than 100, when the obtained stretched film roll is used as a raw material for a polarizing film, it is difficult to obtain a polarizing film having preferable polarizing performance, and when it exceeds 10,000, the solubility in a solvent deteriorates. , PVA-based resin film formation (film formation) can be difficult.

The PVA-based resin film prepared in this step may be a stretched one, but is usually an unstretched film formed by forming the above-mentioned polyvinyl alcohol-based resin. The film forming method is not particularly limited, and a known method such as a melt extrusion method or a solvent casting method can be adopted.

The PVA-based resin film can contain additives such as a plasticizer. Preferred examples of the plasticizer are polyhydric alcohols, and specific examples thereof include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, triglycerin, tetraethylene glycol, trimethylolpropane, polyethylene glycol and the like. .. The PVA-based resin film can contain one or more plasticizers. The content of the plasticizer is usually 5 to 20 parts by weight, preferably 7 to 15 parts by weight, based on 100 parts by weight of the polyvinyl alcohol-based resin constituting the PVA-based resin film.

The PVA-based resin film prepared in this step has a maximum surface height roughness Rz of 30 nm or more and a standard deviation σ of the thickness in the film width direction of 0.2 μm or more. By producing a stretched film roll using such a PVA-based resin film as a raw material, it is possible to effectively suppress film breakage when the stretched film is unwound from the stretched film roll. From the viewpoint of more effectively suppressing film breakage when the stretched film is unwound, Rz is preferably 32 nm or more, more preferably 35 nm or more, still more preferably 38 nm or more, and particularly preferably 40 nm. That is all. For the same reason, σ is preferably 0.25 μm or more, more preferably 0.3 μm or more, still more preferably 0.35 μm or more, and particularly preferably 0.4 μm or more.

If Rz is less than 30 nm and / or σ is less than 0.2 μm, the effect of suppressing film breakage cannot be obtained. Therefore, increasing either Rz or σ does not mean that the effect of suppressing film breakage can be obtained. In order to obtain the effect of suppressing film breakage, Rz is set to 30 nm or more and σ is set to 0.2 μm. It is necessary to do the above.

The larger the Rz and the larger the σ, the higher the effect of suppressing film breakage tends to be. However, even if either Rz or σ is relatively low within the above predetermined range, the other value tends to be high. If is relatively large, a sufficient effect of suppressing film breakage can be obtained.

However, if Rz and / or σ is too large, excessive unevenness may occur in the polarization performance of the obtained polarizing film when the polarizing film is manufactured using the stretched film roll. Therefore, Rz is preferably 100 nm or less, more preferably 80 nm or less, and further preferably 70 nm or less. For the same reason, σ is preferably 1 μm or less, more preferably 0.8 μm or less, still more preferably 0.7 μm or less.

In the present specification, the "maximum surface roughness Rz" of the PVA-based resin film means an average of the maximum height roughness Rz of both sides (both main surfaces) of the PVA-based resin film. The specific measurement method follows the description in the section of Examples described later. The "maximum height roughness Rz" means the maximum height roughness Rz described in 4.1.3 of JIS B 0601: 2013.

Further, the "standard deviation σ of the thickness in the film width direction" of the PVA-based resin film is T ₁ , T ₂ , ..., T, respectively, when the thickness is measured at n points of the PVA-based resin film. _{When n} is set and the average thickness of the PVA-based resin film is T, the following formula:

It is represented by. The n measurement points are measurement points along the width direction of the film (positioned so as to be parallel to the width direction), and are positioned at 100 mm intervals over the entire width of the film. Therefore, the specific numerical value of the integer n depends on the total width of the PVA-based resin film. The "average thickness T" of the PVA-based resin film is the average value of the thickness measurement values at n measurement points. More specific measurement methods of "standard deviation σ of thickness in the film width direction" and "average thickness T" follow the description in the section of Examples described later.

The average thickness T of the PVA-based resin film is usually 65 μm or less, preferably 50 μm or less, more preferably 35 μm or less, still more preferably 30 μm or less, and particularly preferably 25 μm or less. When a PVA-based resin film is used as a raw material for a polarizing film, the smaller the average thickness T of the PVA-based resin film, the more advantageous it is for thinning the polarizing film. However, in general, when the average thickness T of the PVA-based resin film is reduced, the film is likely to break when the stretched film is unwound from the stretched film roll. According to the present invention, it is possible to effectively suppress film breakage even when the average thickness T of the PVA-based resin film is small. The average thickness T of the PVA-based resin film is usually 5 μm or more, preferably 10 μm or more.

The PVA-based resin film prepared in this step may be a PVA-based resin film in which Rz and σ are set in the above-mentioned predetermined ranges by subjecting the film to a treatment. Examples of the above-mentioned treatment include a treatment for roughening the surface of the PVA-based resin film. Examples of the treatment for roughening the surface include a treatment in which a PVA-based resin film is brought into contact with a thermal roll having a maximum surface roughness Rz of 30 nm or more. The thermal roll is a roll capable of raising the surface temperature. By bringing the surface of the PVA-based resin film into contact with a thermal roll having a high surface temperature (for example, holding the PVA-based resin film in the thermal roll), the surface shape of the thermal roll is reflected (or transferred) on the surface of the PVA-based resin film. ) Can be made. The surface temperature of the heat roll when the PVA-based resin film is brought into contact with the heat roll is, for example, 90 to 150 ° C. Further, when forming a PVA-based resin film from a solution containing a PVA-based resin, the rate of volatilizing the solvent (the rate before leveling) can be increased, the content of the leveling agent can be adjusted, or the above solution can be used. It is possible to control σ within the above range by increasing the concentration or the like.

(2) Step S20 for obtaining a stretched film
This step is a step of stretching the PVA-based resin film prepared in step S10 to obtain a stretched film. This stretched film is usually a long film. Providing this step of applying the stretching treatment to the PVA-based resin film is advantageous in suppressing the film breakage when the film is unwound from the film roll. From this point of view, it is preferable that the PVA-based resin film is stretched before the film is wound to produce a film roll.

The stretching treatment for the PVA-based resin film may be a dry stretching performed in the air, or a wet stretching performed in a liquid such as water, an aqueous solution, or an organic solvent, but is preferably a dry stretching. That is, the step S20 for obtaining the stretched film preferably includes a step of dry-stretching the PVA-based resin film. One of the reasons why dry stretching is preferable is that it is relatively easy to maintain the surface characteristics (Rz and σ) of the PVA-based resin film before stretching, which makes it easy to obtain the effect of suppressing film breakage. Further, in the case of dry stretching, the film can be wound without being dried. In the case of wet stretching, the film may be easily broken when the film is unwound from the stretched film roll, depending on the drying treatment conditions of the film.

The stretching treatment for the PVA-based resin film is usually uniaxial stretching, preferably longitudinal uniaxial stretching. The longitudinal stretching refers to the MD of the film, that is, the stretching of the film in the longitudinal direction.

In the dry stretching, a film is passed between a heat roll whose surface is heated and a guide roll (or a heat roll) having a peripheral speed different from that of the heat roll, and heating is performed using the heat roll. Thermal roll stretching that performs longitudinal stretching underneath; between rolls that perform longitudinal stretching due to the difference in peripheral speed between these two nip rolls while passing through a heating means (oven, etc.) between two nip rolls installed at a distance. Stretching; tenter stretching; compression stretching and the like can be mentioned.

Among the above, the dry stretching is preferably a thermal roll stretching using a thermal roll because the surface characteristics (Rz and σ) of the PVA-based resin film before stretching are relatively easy to maintain. Therefore, in this step, for example, a long PVA-based resin film is continuously conveyed and introduced into a hot roll stretching apparatus including a hot roll to continuously manufacture the stretched film as a long product. There can be. Thermal roll stretching is usually longitudinal uniaxial stretching, more typically free-end longitudinal uniaxial stretching.

The thermal roll stretching apparatus may include at least one thermal roll and may include two or more thermal rolls. FIG. 2 shows an example of the thermal roll stretching treatment and the thermal roll stretching apparatus used for the thermal roll stretching treatment. The thermal roll stretching apparatus shown in FIG. 2 includes a first nip roll 10, a thermal roll 5, and a second nip roll 20 in this order from the upstream side of film transport. The PVA-based resin film 1 introduced into the thermal roll stretching apparatus is conveyed along a transfer path including the first nip roll 10, the thermal roll 5, and the second nip roll 20 in this order. That is, the PVA-based resin film 1 first passes between the first nip rolls 10 and 10, then runs while being wound around the thermal roll 5 while contacting the surface thereof, and then runs between the second nip rolls 20 and 20. It passes through and the stretched film 2 is obtained. The first nip roll 10, the second nip roll 20, and the thermal roll 5 are all drive rolls. The drive roll refers to a roll such as a roll to which a roll drive source such as a motor is directly or indirectly connected, which can give a driving force for film transfer to a film in contact with the roll. A guide roll may be provided between the first nip roll 10 and the heat roll 5 and / or between the heat roll 5 and the second nip roll 20.

In the thermal roll stretching apparatus shown in FIG. 2, the tension (tensile force) on the PVA-based resin film 1 required for longitudinal stretching is between the first nip roll 10 or the second nip roll 20 and the thermal roll 5. It is given by the peripheral speed difference. For example, when the peripheral speed of the heat roll 5 is made larger than the peripheral speed of the first nip roll 10, PVA is applied under heating by the heat roll 5 while applying tension (backward tension) in the direction from the heat roll 5 to the first nip roll 10. The based resin film 1 is vertically stretched. On the other hand, when the peripheral speed of the second nip roll 20 is made larger than the peripheral speed of the thermal roll 5, tension (forward tension) in the direction from the second nip roll 20 toward the thermal roll 5 is applied, and the heat roll 5 heats the film. The PVA-based resin film 1 is vertically stretched.

The longitudinal stretching occurs when the PVA-based resin film 1 is heated to a extent that it can be stretched by the heat roll 5 and a sufficient tension is applied. When the back tension is applied, the longitudinal stretching may occur at the moment when the PVA-based resin film 1 comes into contact with the surface of the thermal roll 5 and / or before and after (for example, before). When forward tension is applied, longitudinal stretching can occur during and / or shortly after contact with the surface of the thermal roll 5.

The preferred range of tension applied to the PVA-based resin film 1 required for longitudinal stretching is 10 to 25 MPa, more preferably 13 to 22 MPa. If the tension is less than 10 MPa, the transportability of the film is lowered, and wrinkles and the like may occur. Further, when the tension exceeds 25 MPa, it becomes difficult to perform uniform longitudinal stretching. The transport speed of the film is not particularly limited, and is, for example, 2 to 20 m / min.

The heat roll 5 is not particularly limited as long as it can raise the surface temperature thereof, and is provided with a heat source (for example, a heat medium such as hot water, an infrared heater, an induction heating coil, a dielectric heating circuit, etc.) inside. A roll whose surface is made of an alloy such as metal or stainless steel can be used.

As shown in FIG. 3, the thermal roll stretching apparatus may include two or more thermal rolls. FIG. 3 shows an example including three thermal rolls 6, 7, and 8. When including two or more thermal rolls, longitudinal stretching can occur between the two thermal rolls and / or while in contact with the surface of the thermal rolls.

The stretching ratio of the stretching treatment in this step is usually 1.1 to 8 times, preferably 2 to 6 times. From the viewpoint of the optical characteristics (particularly the polarizing characteristics) of the polarizing film when the stretched film 2 is used as a raw material for the polarizing film, the stretching ratio is more preferably 3.5 times or more, still more preferably 4 times or more. ..

The surface temperature of the thermal roll during stretching the thermal roll is, for example, 80 to 150 ° C. If the surface temperature is too high, the strength of the heated PVA-based resin film 1 decreases, and there is a possibility that the PVA-based resin film 1 will break during stretching. If the surface temperature is too low, stretching itself of the PVA-based resin film 1 can be difficult.

The stretched film 2 obtained by this step preferably has a surface maximum height roughness Rz of 25 nm or more. By producing a stretched film roll from such a stretched film, it is possible to effectively suppress film breakage when the stretched film is unwound from the stretched film roll. From the viewpoint of more effectively suppressing film breakage when the stretched film is unwound, the Rz of the stretched film 2 is more preferably 30 nm or more, further preferably 35 nm or more, still more preferably 38 nm or more. Yes, especially preferably 40 nm or more. For the same reason, the standard deviation σ of the thickness of the stretched film 2 in the film width direction is preferably 0.2 μm or more, more preferably 0.25 μm or more, still more preferably 0.3 μm or more. Particularly preferably, it is 0.35 μm or more.

In order to set the Rz of the stretched film 2 within the above-mentioned predetermined range, as the thermal roll used for thermal roll stretching, for example, a thermal roll having a maximum surface height roughness Rz of 25 nm or more can be used.

When the PVA-based resin film 1 is stretched by hot roll stretching, the surface characteristics (Rz and σ) of the PVA-based resin film before stretching are relatively easy to maintain. Therefore, the stretching ratio is set to 3 to 6 times, and the hot roll The surface temperature is preferably 90 to 150 ° C. The draw ratio is more preferably 3.5 to 6 times. The surface temperature of the heat roll is more preferably 100 to 135 ° C, still more preferably 100 to 125 ° C.

The average thickness of the stretched film 2 is usually 2 to 40 μm, and from the viewpoint of thinning the polarizing film produced using the stretched film 2, it is preferably 20 μm or less, more preferably 15 μm or less, still more preferably 10 μm. It is as follows. In general, when the average thickness of the stretched film is reduced, the film breaks easily when the stretched film 2 is unwound from the stretched film roll. According to the present invention, it is possible to effectively suppress film breakage even when the average thickness of the stretched film 2 is small.

The meanings of "maximum surface roughness Rz", "standard deviation σ of thickness in the film width direction" and "average thickness" of the stretched film 2 are the same as those of the PVA-based resin film.

(3) Step S30 for winding the stretched film
This step is a step of winding the stretched film 2 to obtain a stretched film roll. The film can be wound according to a conventional method.

The winding tension when winding the stretched film 2 is not particularly limited, but if it is too large, the film breaks easily when the stretched film 2 is unwound from the stretched film roll. Therefore, the winding tension is preferably 50 MPa or less, more preferably 40 MPa or less, and even more preferably 30 MPa or less. The take-up tension is usually 10 MPa or more.

The unwinding speed of the stretched film 2 is not particularly limited and may be a normal speed. The unwinding speed is, for example, 2 to 20 m / sec, preferably 4 to 15 m / sec.

As described above, from the viewpoint of suppressing film breakage when the stretched film is unwound, the stretched film 2 constituting the stretched film roll has a surface maximum height roughness Rz of preferably 25 nm or more, and more. It is preferably 30 nm or more, more preferably 35 nm or more, still more preferably 38 nm or more, and particularly preferably 40 nm or more. For the same reason, the standard deviation σ of the thickness of the stretched film 2 constituting the stretched film roll in the film width direction is preferably 0.2 μm or more, more preferably 0.25 μm or more, and further preferably 0. It is 0.3 μm or more, and particularly preferably 0.35 μm or more.

The length of the stretched film 2 constituting the stretched film roll is, for example, 1000 to 40,000 m, preferably 5,000 to 35,000 m. The width of the stretched film 2 is, for example, 1 to 3 m, preferably 1.5 to 2.5 m.

<Manufacturing of polarizing film and polarizing plate>
The stretched film roll obtained by the production method according to the present invention can be suitably used as a raw material for a polarizing film. The polarizing film is a step of adsorbing a dichroic dye by dyeing a stretched film unwound from a stretched film roll with a dichroic dye; a step of cross-linking a film on which the dichroic dye is adsorbed; It can be manufactured through a step of washing with water after a cross-linking treatment. The polarizing film produced in this manner is one in which the dichroic dye is adsorbed and oriented on the stretched PVA-based resin film. As the dichroic dye, iodine or a dichroic organic dye can be used.

As a method of dyeing the stretched film with a dichroic dye, for example, a method of immersing the stretched film in an aqueous solution (dyeing solution) containing the dichroic dye is adopted. It is preferable that the stretched film is immersed in water (swelling treatment) before the dyeing treatment.

When iodine is used as the dichroic dye, a method of immersing a stretched film in an aqueous solution containing iodine and potassium iodide and dyeing is usually adopted. The iodine content in this dyeing aqueous solution is usually 0.01 to 1 part by weight per 100 parts by weight of water. The content of potassium iodide is usually 0.5 to 20 parts by weight per 100 parts by weight of water. The temperature of the dyeing aqueous solution is usually about 20 to 40 ° C.

On the other hand, when a dichroic organic dye is used as the dichroic dye, a method of immersing a stretched film in a dyeing aqueous solution containing a water-soluble dichroic organic dye and dyeing is usually adopted. The content of the dichroic organic dye in the dyeing aqueous solution is usually 1 × 10 ^-4 to 10 parts by weight, preferably 1 × 10 ^-3 to 1 part by weight per 100 parts by weight of water. This dyeing aqueous solution may contain an inorganic salt such as sodium sulfate as a dyeing aid. The temperature of the dyeing aqueous solution is usually about 20 to 80 ° C.

The cross-linking treatment after dyeing with the dichroic dye can be performed by immersing the dyed film in an aqueous solution containing a cross-linking agent. A preferred example of the cross-linking agent is boric acid, but other cross-linking agents such as boron compounds such as borax, glyoxal and glutaraldehyde can also be used. Only one type of cross-linking agent may be used, or two or more types may be used in combination.

The amount of the cross-linking agent in the cross-linking agent-containing aqueous solution is usually 2 to 15 parts by weight, preferably 4 to 12 parts by weight, per 100 parts by weight of water. When iodine is used as the dichroic dye, the cross-linking agent-containing aqueous solution preferably contains potassium iodide. The amount of potassium iodide in the cross-linking agent-containing aqueous solution is usually 0.1 to 15 parts by weight, preferably 5 to 12 parts by weight, per 100 parts by weight of water. The temperature of the cross-linking agent-containing aqueous solution is usually 50 ° C. or higher, preferably 50 to 85 ° C.

The crosslinked film is usually washed with water. The water washing treatment can be performed, for example, by immersing the crosslinked polyvinyl alcohol-based resin film in water. The temperature of water in the washing treatment is usually about 1 to 40 ° C.

In any one or more of the swelling treatment, the dyeing treatment, the cross-linking treatment, and the washing treatment, the film may be wet-stretched if necessary.

After washing with water, it is dried to obtain a polarizing film. The drying treatment can be drying with a hot air dryer, drying by contacting with a hot roll, drying with a far-infrared heater, or the like. The temperature of the drying treatment is usually about 30 to 100 ° C, preferably 40 to 90 ° C. The average thickness of the polarizing film is usually 2 to 40 μm. From the viewpoint of thinning the polarizing plate, the average thickness of the polarizing film is preferably 20 μm or less, more preferably 15 μm or less, and further preferably 10 μm or less. The meaning of the average thickness here is the same as that of the PVA-based resin film.

The obtained polarizing film may be sequentially wound into a roll, or may be directly used in the polarizing plate manufacturing step without being wound.

A polarizing plate can be obtained by laminating a thermoplastic resin film on one or both sides of a polarizing film via an adhesive layer. The thermoplastic resin film is a film composed of a translucent thermoplastic resin, preferably an optically transparent thermoplastic resin. The thermoplastic resin constituting the thermoplastic resin film is, for example, a polyolefin resin such as a chain polyolefin resin (polypropylene resin or the like) or a cyclic polyolefin resin (norbornen resin or the like); triacetyl cellulose, diacetyl cellulose, etc. Cellular resin such as; polyester resin such as polyethylene terephthalate and polybutylene terephthalate; polycarbonate resin; (meth) acrylic resin such as methyl methacrylate resin; polystyrene resin; polyvinyl chloride resin; acrylonitrile. Butadiene / styrene resin; acrylonitrile / styrene resin; polyvinyl acetate resin; polyvinylidene chloride resin; polyamide resin; polyacetal resin; modified polyphenylene ether resin; polysulfone resin; polyether sulfone resin; polyallylate It can be a based resin; a polyamide imide resin; a polyimide resin or the like.

Examples of the chain polyolefin resin include homopolymers of chain olefins such as polyethylene resin and polypropylene resin, and copolymers composed of two or more kinds of chain olefins. More specific examples are polypropylene-based resins (polypropylene resin which is a homopolymer of propylene and copolymers mainly composed of propylene), polyethylene-based resins (polyethylene resin which is a homopolymer of ethylene, and ethylene as a main component). Copolymer).

Cyclic polyolefin resin is a general term for resins that are polymerized using cyclic olefin as a polymerization unit. Specific examples of the cyclic polyolefin resin include an open (co) polymer of a cyclic olefin, an addition polymer of a cyclic olefin, and a copolymer of a cyclic olefin and a chain olefin such as ethylene and propylene (typically). Is a random copolymer), a graft polymer obtained by modifying these with an unsaturated carboxylic acid or a derivative thereof, and a hydride thereof. Of these, a norbornene-based resin using a norbornene-based monomer such as norbornene or a polycyclic norbornene-based monomer is preferably used as the cyclic olefin.

The cellulosic resin is obtained by substituting a part or all of hydrogen atoms in the hydroxyl groups of cellulose obtained from raw material cellulose such as cotton linter and wood pulp (perforated tree pulp, coniferous tree pulp) with acetyl group, propionyl group and / or butyryl group. Also, it refers to a cellulose organic acid ester or a cellulose mixed organic acid ester. For example, those composed of acetic acid ester of cellulose, propionic acid ester, butyric acid ester, mixed ester thereof and the like can be mentioned. Of these, triacetyl cellulose, diacetyl cellulose, cellulose acetate propionate, and cellulose acetate butyrate are preferable.

The polyester-based resin is a resin other than the above-mentioned cellulosic resin having an ester bond, and is generally composed of a polyvalent carboxylic acid or a polycondensate of a derivative thereof and a polyhydric alcohol. As the polyvalent carboxylic acid or a derivative thereof, a divalent dicarboxylic acid or a derivative thereof can be used, and examples thereof include terephthalic acid, isophthalic acid, dimethyl terephthalate, and dimethyl naphthalenedicarboxylic acid. As the polyhydric alcohol, a divalent diol can be used, and examples thereof include ethylene glycol, propanediol, butanediol, neopentyl glycol, cyclohexanedimethanol and the like. Examples of suitable polyester resins include polyethylene terephthalate.

The polycarbonate-based resin is an engineering plastic made of a polymer in which monomer units are bonded via a carbonate group, and is a resin having high impact resistance, heat resistance, flame retardancy, and transparency. The polycarbonate-based resin may be a resin called modified polycarbonate in which the polymer skeleton is modified in order to lower the photoelastic coefficient, or a copolymerized polycarbonate having improved wavelength dependence.

The (meth) acrylic resin is a polymer containing a structural unit derived from a (meth) acrylic monomer. The polymer is typically a polymer containing a methacrylic acid ester. A polymer in which the proportion of structural units derived from methacrylic acid ester is 50% by weight or more based on all structural units. The (meth) acrylic resin may be a homopolymer of a methacrylic acid ester, or may be a copolymer containing a structural unit derived from another polymerizable monomer. In this case, the proportion of the structural units derived from other polymerizable monomers is preferably 50% by weight or less with respect to the total structural units.

As the methacrylic acid ester that can constitute the (meth) acrylic resin, an alkyl methacrylate ester is preferable. Examples of the alkyl methacrylate ester include methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, and cyclohexyl methacrylate. , Methacrylic acid alkyl ester having 1 to 8 carbon atoms in an alkyl group such as 2-hydroxyethyl methacrylate. The number of carbon atoms of the alkyl group contained in the methacrylic acid alkyl ester is preferably 1 to 4. In the (meth) acrylic resin, only one type of methacrylic acid ester may be used alone, or two or more types may be used in combination.

Examples of the other polymerizable monomer that can constitute the (meth) acrylic resin include acrylic acid esters and other compounds having a polymerizable carbon-carbon double bond in the molecule. As the other polymerizable monomer, only one type may be used alone, or two or more types may be used in combination. As the acrylic acid ester, an acrylic acid alkyl ester is preferable. Examples of the acrylic acid alkyl ester include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, and cyclohexyl acrylate. , Acrylic acid alkyl ester having 1 to 8 carbon atoms in an alkyl group such as 2-hydroxyethyl acrylate. The number of carbon atoms of the alkyl group contained in the acrylic acid alkyl ester is preferably 1 to 4. In the (meth) acrylic resin, only one type of acrylic acid ester may be used alone, or two or more types may be used in combination.

Examples of other compounds having a polymerizable carbon-carbon double bond in the molecule include vinyl compounds such as ethylene, propylene and styrene, and vinyl cyanide compounds such as acrylonitrile. As the other compounds having a polymerizable carbon-carbon double bond in the molecule, only one kind may be used alone, or two or more kinds may be used in combination.

The thermoplastic resin film can be a protective film for protecting the polarizing film. Further, the thermoplastic resin film can also be a protective film having an optical function such as a retardation film and a brightness improving film. For example, by stretching a thermoplastic resin film made of the above material (uniaxial stretching or biaxial stretching, etc.) or forming a liquid crystal layer or the like on the film, a phase difference to which an arbitrary retardation value is given is given. It can be a film. The thermoplastic resin film may have 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, which are laminated on the surface thereof.

The thickness of the thermoplastic resin film is usually 1 to 100 μm, but it is preferably 5 to 60 μm, more preferably 5 to 50 μm, from the viewpoints of strength, handleability, thinning of the polarizing plate, and the like.

As the adhesive used for bonding the polarizing film and the thermoplastic resin film, a water-based adhesive, an active energy ray-curable adhesive or a thermosetting adhesive can be used, preferably a water-based adhesive or an active energy ray. It is a curable adhesive.

The water-based adhesive is one in which the adhesive component is dissolved in water or one in which the adhesive component is dispersed in water. The water-based adhesive preferably used is, for example, an adhesive composition using a polyvinyl alcohol-based resin or a urethane resin as a main component.

When a polyvinyl alcohol-based resin is used as the main component of the adhesive, the polyvinyl alcohol-based resin can be a polyvinyl alcohol resin such as partially saponified polyvinyl alcohol and fully saponified polyvinyl alcohol, as well as carboxyl group-modified polyvinyl alcohol. , Acetacetyl group-modified polyvinyl alcohol, methylol group-modified polyvinyl alcohol, amino group-modified polyvinyl alcohol, and other modified polyvinyl alcohol-based resins may be used. The polyvinyl alcohol-based resin is a vinyl alcohol homopolymer obtained by saponifying polyvinyl acetate, which is a homopolymer of vinyl acetate, as well as the common weight of vinyl acetate and another monomer copolymerizable therewith. It may be a polyvinyl alcohol-based copolymer obtained by saponifying the coalescence.

The water-based adhesive containing a polyvinyl alcohol-based resin as an adhesive component is usually an aqueous solution of the polyvinyl alcohol-based resin. The concentration of the polyvinyl alcohol-based resin in the adhesive is usually 1 to 10 parts by weight, preferably 1 to 5 parts by weight, based on 100 parts by weight of water.

Adhesives consisting of aqueous solutions of polyvinyl alcohol-based resins have curable components such as polyhydric aldehydes, melamine-based compounds, zirconia compounds, zinc compounds, glyoxal, glyoxal derivatives, and water-soluble epoxy resins in order to improve adhesiveness. It preferably contains a cross-linking agent. The water-soluble epoxy resin is a polyamide polyamine epoxy resin obtained by reacting epichlorohydrin with a polyamide amine obtained by reacting a polyalkylene polyamine such as diethylenetriamine or triethylenetetramine with a dicarboxylic acid such as adipic acid. Can be preferably used. Commercially available products of such polyamide polyamine epoxy resin include "Smiley's Resin 650" (manufactured by Taoka Chemical Co., Ltd.), "Smilase Resin 675" (manufactured by Taoka Chemical Co., Ltd.), and "WS-525" (Japan). (Manufactured by PMC Co., Ltd.) and the like. The amount of these curable component and cross-linking agent added (the total amount when both the curable component and the cross-linking agent are added) is usually 1 to 100 parts by weight, preferably 1 to 100 parts by weight, based on 100 parts by weight of the polyvinyl alcohol-based resin. 1 to 50 parts by weight. When the amount of the curable component or the cross-linking agent added is less than 1 part by weight with respect to 100 parts by weight of the polyvinyl alcohol-based resin, the effect of improving the adhesiveness tends to be small, and the amount of the addition is polyvinyl. If it exceeds 100 parts by weight with respect to 100 parts by weight of the alcohol-based resin, the adhesive layer tends to be brittle.

Moreover, as a preferable example when the urethane resin is used as the main component of the adhesive, a mixture of a polyester ionomer type urethane resin and a compound having a glycidyloxy group can be mentioned. The polyester-based ionomer type urethane resin is a urethane resin having a polyester skeleton, in which a small amount of an ionic component (hydrophilic component) is introduced. Such an ionomer type urethane resin is suitable as a water-based adhesive because it is directly emulsified in water to form an emulsion without using an emulsifier.

The active energy ray-curable adhesive is an adhesive that is cured by irradiation with active energy rays such as ultraviolet rays, visible light, electron beams, and X-rays. When an active energy ray-curable adhesive is used, the adhesive layer of the polarizing plate is a cured product layer of the adhesive.

The active energy ray-curable adhesive can be an adhesive containing an epoxy-based compound that is cured by cationic polymerization as a curable component, and preferably an ultraviolet curable adhesive containing such an epoxy-based compound as a curable component. It is an agent. The epoxy compound referred to here means a compound having an average of 1 or more, preferably 2 or more epoxy groups in the molecule. Only one type of epoxy compound may be used, or two or more types may be used in combination.

Specific examples of an epoxy-based compound that can be preferably used are a hydride-based compound obtained by reacting an alicyclic polyol obtained by hydrogenating the aromatic ring of an aromatic polyol with epichlorohydrin (a hydride-based compound obtained by reacting with epichlorohydrin. Glycidyl ether of a polyol having an alicyclic ring); an aliphatic epoxy compound such as polyglycidyl ether of an aliphatic polyhydric alcohol or an alkylene oxide adduct thereof; an epoxy group bonded to the alicyclic ring is 1 in the molecule. Includes an alicyclic epoxy compound which is an epoxy compound having more than one.

The active energy ray-curable adhesive can contain, as a curable component, a (meth) acrylic compound which is radically polymerizable in place of or together with the epoxy compound. The (meth) acrylic compound is a (meth) acrylate monomer having at least one (meth) acryloyloxy group in the molecule; obtained by reacting two or more kinds of functional group-containing compounds, and at least two in the molecule. Examples thereof include (meth) acryloyloxy group-containing compounds such as (meth) acrylate oligomers having a (meth) acryloyloxy group.

When the active energy ray-curable adhesive contains an epoxy compound that is cured by cationic polymerization as a curable component, it preferably contains a photocationic polymerization initiator. Examples of the photocationic polymerization initiator include aromatic diazonium salts; onium salts such as aromatic iodonium salts and aromatic sulfonium salts; and iron-allene complexes. When the active energy ray-curable adhesive contains a radically polymerizable curable component such as a (meth) acrylic compound, it preferably contains a photoradical polymerization initiator. Examples of the photoradical polymerization initiator include an acetophenone-based initiator, a benzophenone-based initiator, a benzoin ether-based initiator, a thioxanthone-based initiator, xanthone, fluorenone, camphorquinone, benzaldehyde, anthraquinone and the like.

Prior to bonding the thermoplastic resin film to the polarizing film, the bonding surface of the polarizing film and / or the thermoplastic resin film is subjected to plasma treatment, corona treatment, ultraviolet irradiation treatment, frame (flame) treatment, and saponification treatment. Such surface activation treatment may be performed. By this surface activation treatment, the adhesiveness between the polarizing film and the thermoplastic resin film can be enhanced.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these examples. The measurement regarding the thickness and surface characteristics of the film was carried out according to the following method.

(1) Maximum height roughness Rz of polyvinyl alcohol (PVA) film surface
The elevation of the main surface (surface) of the PVA film was measured using a three-dimensional microscope "PLμ2300" manufactured by Sensofar. The magnification of the objective lens at the time of measurement was 20 times. The maximum height roughness Rz was obtained from the cross-sectional roughness curve having a length of 636 μm obtained from the measurement data. The measurement was carried out at three points along the film width direction on each of both sides of the PVA film (measurement points were selected at three points at equal intervals along the film width direction), and these measured values (total of 6 points). ) Was taken as the maximum height roughness Rz of the PVA film surface.

(2) Standard deviation σ and average thickness T of the thickness in the PVA film width direction
A strip-shaped test piece having an MD length of 50 mm and a TD length of the entire width was cut out from the PVA film. Next, the thickness of the film was measured at 100 mm intervals in the film width direction using a digital micrometer "MH-15M" manufactured by Nikon Corporation. From the obtained measured values, the average thickness T of the PVA film was obtained as the average value of these measured values, and the standard deviation σ of the thickness of the PVA film was obtained.

(3) Maximum height roughness Rz of the surface of the stretched film
The elevation of the main surface (surface) of the stretched film was measured using a three-dimensional microscope "PLμ2300" manufactured by Sensofar. The magnification of the objective lens at the time of measurement was 20 times. The maximum height roughness Rz was obtained from the cross-sectional roughness curve having a length of 636 μm obtained from the measurement data. The measurement was carried out at three points along the film width direction on each of both sides of the stretched film (measurement points were selected at three points at equal intervals along the film width direction), and these measured values (six points in total). ) Was taken as the maximum height roughness Rz of the surface of the stretched film.

<Example 1>
The average degree of polymerization is about 2400, the degree of saponification is 99.9 mol% or more, the maximum surface roughness Rz is 35 nm, the average thickness T is 19.9 μm, and the standard deviation σ of the thickness in the width direction is 0.3 μm. A long PVA film was dryly uniaxially stretched 4.1 times using a thermal roll having a surface temperature of 105 ° C., and then wound with a winding tension of 22 MPa to obtain a stretched film roll. Here, the take-up tension was measured by a tension meter installed immediately before the take-up portion. The maximum height roughness Rz of the surface of the obtained stretched film was 39 nm.

The stretched film was continuously unwound from the obtained stretched film roll with a tension of 50 MPa, immersed in pure water at 30 ° C. for a residence time of 1 minute, and then the weight ratio of iodine / potassium iodide / water was 0.1 /. It was immersed in an aqueous solution of 5/100 at 28 ° C. with a residence time of 45 seconds. Then, it was immersed in an aqueous solution at 67 ° C. having a weight ratio of potassium iodide / boric acid / water of 15 / 5.5 / 100 for a residence time of 200 seconds. Subsequently, the film was washed with pure water at 20 ° C. for 5 seconds and then dried at 40 ° C. for 60 seconds to continuously produce a polarizing film in which iodine was adsorbed and oriented on a uniaxially stretched PVA film. When the stretched film was unwound from the stretched film roll in order to produce a polarizing film, the breaking frequency was 0.0 times / km. The breaking frequency (unit: times / km) means the number of times the film is broken per 1 km of the length of the unwound stretched film.

<Examples 2 to 4, Comparative Examples 1 to 2>
A stretched film roll was produced in the same manner as in Example 1 except that a PVA film was used in which the maximum surface roughness Rz, the average thickness T, and the standard deviation σ of the thickness in the width direction were as shown in Table 1. Then, the obtained stretched film roll was subjected to a polarizing film manufacturing process.

Maximum height roughness Rz of the surface of the PVA film, average thickness T, and standard deviation σ of the thickness in the width direction in Examples and Comparative Examples, maximum height roughness Rz of the stretched film surface, and stretching from the stretched film roll. Table 1 summarizes the breaking frequencies when the film is unwound.

1 Polyvinyl alcohol-based resin film (PVA-based resin film), 2 Stretched film, 5, 6, 7, 8 thermal rolls, 10 1st nip roll, 20 2nd nip roll.

Claims (7)

A step of preparing a polyvinyl alcohol-based resin film having a maximum surface roughness Rz of 30 nm or more and 100 nm or less and a standard deviation σ of the thickness in the film width direction of 0.2 μm or more and 1 μm or less.
A step of stretching the polyvinyl alcohol-based resin film to obtain a stretched film having an average thickness of 2 μm or more and 40 μm or less.
A step of winding the stretched film with a winding tension of 50 MPa or less,
A method for producing a stretched film roll, including. The production method according to claim 1, wherein the stretched film has a maximum surface roughness Rz of 25 nm or more. The production method according to claim 1 or 2, wherein the step of preparing the polyvinyl alcohol-based resin film includes a step of bringing the film into contact with a thermal roll having a maximum surface height roughness Rz of 30 nm or more. The production method according to any one of claims 1 to 3, wherein the step of obtaining the stretched film includes a step of dry-stretching the polyvinyl alcohol-based resin film. The production method according to claim 4, wherein in the dry stretching step, the polyvinyl alcohol-based resin film is stretched at a stretching ratio of 3 to 6 times using a thermal roll having a surface temperature of 90 to 150 ° C. The production method according to any one of claims 1 to 5 , wherein the average thickness T of the polyvinyl alcohol-based resin film is 35 μm or less. A roll of a stretched polyvinyl alcohol-based resin film for a polarizing film having a maximum surface height roughness Rz of 25 nm or more.

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