TW201817576A - Polyvinyl alcohol film and method for producing same, and polarizing film using said polyvinyl alcohol film - Google Patents

Abstract

Provided are: a polyvinyl alcohol film which exhibits excellent elongation properties when used to produce a polarizing film, and from which it is possible to obtain a polarizing film exhibiting a high degree of polarization and little color unevenness, and specifically, a polyvinyl alcohol film which does not break when used to produce a thin polarizing film; a method for producing this polyvinyl alcohol film; and a polarizing film which uses this polyvinyl alcohol film. This long polyvinyl alcohol film is characterized by having a thickness of 25-60[mu]m, and in that the thickness D ([mu]m) thereof and the tensile modulus of elasticity X(MPa) thereof in the lengthwise direction (MD direction) when the water content of the film is 9 wt% satisfy formula (1). 0.9 ≤ X/D ≤ 1.3 (1).

Description

Polyvinyl alcohol film and its manufacturing method and polarizing film using the polyvinyl alcohol film

The present invention relates to a polyvinyl alcohol-based film, and more particularly to a polyvinyl alcohol-based film having excellent elongation, a polarizing film capable of obtaining high polarization and few color spots, a method for manufacturing the same, and a method for using the polyvinyl alcohol-based film. Polarizing film.

In recent years, the development of liquid crystal display devices has been amazing, and they are widely used in smart phones, tablet computers, personal computers, LCD TVs, projectors, and car panels. A polarizing film is used in these liquid crystal display devices. As for the polarizing film, it is mainly used for polyvinyl alcohol-based films that adsorb and align with iodine or dichroic dye. In recent years, with the high definition, high brightness, large size, and thinness of the screen, a polarizing film having a wider polarization and a wider width than that of conventional products is required. In addition, the polarizing film in the present invention is also referred to as a polarizing film or a polarizing plate.

Generally, a polarizing film is drawn from a roll of a polyvinyl alcohol-based film from a roll, swelled with water (including warm water) while being transported in the flow direction (MD direction), and then uses dichroism such as iodine. Dyes are manufactured by dyeing and stretching. This stretching step is a step of stretching the dyed film in the flow direction (MD direction) to highly align the dichroic dye in the film. In order to improve the polarization of the polarizing film, it becomes a polyvinyl alcohol film of the original roll. It needs to have good extensibility in the flow direction (MD direction). For example, when the stretching tension is too large, it cannot stretch to a predetermined stretching ratio and the dichroic dye is not sufficiently aligned, so that the degree of polarization may not be improved. On the other hand, if the stretching tension is too small, the orientation of the dichroic dye is unstable even if it is stretched to a predetermined stretching magnification, and there is a tendency that the polarizing film generates color spots. In addition, in the order of polarizing film manufacturing, there are also cases where stretching and dyeing are reversed. That is, there are cases where the original polyvinyl alcohol film is swollen with water (including warm water), stretched, and dyed with a dichroic dye such as iodine. However, in this case, in order to improve the polarizing film Polyvinyl alcohol-based film also needs to have good extensibility in the flow direction (MD direction).

On the other hand, polyvinyl alcohol-based films that are raw rolls are generally produced from an aqueous solution of polyvinyl alcohol-based resins that are raw materials by a continuous casting method. Specifically, a film can be formed by casting an aqueous solution of a polyvinyl alcohol resin onto a casting mold such as a casting drum or an endless belt. After peeling the obtained film from the casting mold, the nip roller is used to equalize the flow direction (MD direction). It is transported and dried using a hot roll, and if necessary, heat-treated using a floating dryer or the like. In this conveying step, the film obtained through film formation is stretched in the flow direction (MD direction), so the polyvinyl alcohol polymer is easily aligned in the flow direction (MD direction). If the alignment is too large, the polyvinyl alcohol film The extensibility in the flow direction (MD direction) is reduced, and finally the polarization performance of the polarizing film is reduced.

Furthermore, due to the reduction in thickness of polarizing films in recent years, polyvinyl alcohol-based films have also become thinner. In the past, the thickness of polyvinyl alcohol-based films was about 60 μm, but now it is about 45 μm. It is expected to become 30 μm in the near future. This thin polyvinyl alcohol-based film has productivity problems such as breakage due to stretching during the production of a polarizing film.

As a method for improving the stretchability of polyvinyl alcohol-based films, for example, a method has been proposed in which the ratio of the speed of the casting drum during the film formation of the polyvinyl alcohol-based film to the final film winding speed is set to a specific ratio (for example, refer to Patent Document 1), a method of suspending and drying a film after forming a film using a casting drum (for example, refer to Patent Document 2), and a method for controlling a stretching state in a drying step of a polyvinyl alcohol-based film (for example, refer to Patent Document) 3). In addition, it has also been proposed that a polyvinyl alcohol-based film having a reduced in-plane retardation (for example, refer to Patent Document 4) should have the same tensile elongation in the flow direction (MD direction) and the width direction (TD direction). A polyvinyl alcohol-based film obtained (for example, refer to Patent Document 5), and a polyvinyl alcohol-based film obtained by reducing the Young's modulus (tensile elastic modulus) to 20 MPa or less by electromagnetic wave irradiation (for example, refer to Patent Document) 6) Wait. [Prior Art Literature] [Patent Literature]

[Patent Document 1] JP 2001-315141 [Patent Document 2] JP 2001-315142 [Patent Document 3] JP 2002-79531 [Patent Document 4] JP 2006-291173 [Patent Document 5] Japanese Patent Application Publication No. 2002-30164 [Patent Document 6] Japanese Patent Application Publication No. 2013-97232

[Problems to be Solved by the Invention] However, even with the method of the aforementioned patent document, the extensibility of the polyvinyl alcohol-based film at the time of manufacturing the polarizing film cannot be sufficiently improved.

The technique disclosed in the above Patent Document 1 specifies the degree of elongation (stretching condition) in the flow direction (MD direction) when manufacturing a polyvinyl alcohol-based film. If the drying conditions and heat treatment conditions are considered at the same time, the polyethylene The stretchability of the alcohol-based film is not sufficiently improved.

Although the technique disclosed in the aforementioned Patent Document 2 can uniformly dry the film after film formation, the tensile elastic modulus cannot be controlled, and the stretchability of the polyvinyl alcohol-based film during the production of the polarizing film has not been sufficiently improved.

Although the technique disclosed in the above Patent Document 3 can make the film thickness uniform, the tensile elastic modulus cannot be controlled, and the stretchability of the polyvinyl alcohol-based film during the production of the polarizing film is not sufficiently improved.

Although the technique disclosed in the above Patent Document 4 can reduce the in-plane retardation of the film, there is still room for improvement in terms of controlling the tensile elastic modulus and improving the stretchability of the polyvinyl alcohol-based film during the production of the polarizing film. The manufacturing method of this disclosed technology is characterized in that the film after being dried (70 ° C) and heat-treated (120 ° C) is temporarily cooled to 50 ° C or lower, and then heated again at 50 to 100 ° C before being wound into a film roll. ; But the heating steps are complicated, and there is still room for improvement in terms of productivity.

Although the technique disclosed in the above Patent Document 5 can stabilize the tensile elongation of the polyvinyl alcohol-based film, the tensile elastic modulus itself is not controlled, and the extensibility of the polyvinyl alcohol-based film during the manufacture of the polarizing film is not sufficiently improved. . Moreover, the example of the said patent document 5 only described the polyvinyl-alcohol-type film of 75 micrometers, and it cannot respond to the demand for thickness reduction in recent years.

Although the technique disclosed in the aforementioned Patent Document 6 can reduce the extension tension, the polarization degree cannot be improved and stabilized without an appropriate tensile elastic modulus, so it is difficult to say that the extensibility at the time of manufacturing the polarizing film has been improved. Generally, a polarizing film obtained from a low molecular weight polyvinyl alcohol resin and a low saponification degree polyvinyl alcohol resin has a low degree of polarization. The reason is that the polyvinyl alcohol-based film formed of the polyvinyl alcohol-based resin does not generate a moderate stretching tension, and therefore cannot maintain a stable alignment state of iodine and dichroic pigments. Elongation alone cannot improve the extensibility when manufacturing polarizing films. In order to meet the needs of high polarization in recent years, it is necessary to obtain a polyvinyl alcohol resin with a high molecular weight and a high saponification degree and a moderate tensile elastic modulus. Polyvinyl alcohol based film. The comparative example of the aforementioned Patent Document 6 describes the tensile elastic modulus (27 MPa) of the polyvinyl alcohol-based film when no electromagnetic wave irradiation is performed, but even this tensile elastic modulus cannot obtain a sufficient degree of polarization, and there is no The tendency of stabilization, especially in reliability tests such as high temperature and high humidity, tends to reduce the degree of polarization. Moreover, the example of the said patent document 6 only described the polyvinyl-alcohol-type film of 60 micrometers, and in order to respond to the demand for thickness reduction in recent years, it is desired to improve further.

Therefore, the present invention aims to provide a polyvinyl alcohol-based film having excellent stretchability during the manufacture of a polarizing film, a polarizing film having a high degree of polarization and few color spots, and particularly a thin polarizing film. A polyvinyl alcohol-based film that does not break at any time, a manufacturing method thereof, and a polarizing film using the polyvinyl alcohol-based film. [Means for solving problems]

As a result of intensive research in view of these circumstances, the inventors of the present case focused on the relationship between the thickness and the tensile elastic modulus in the flow direction (length direction, MD direction), and found out that the ratio was controlled within a specific range. Vinyl alcohol-based films have excellent elongation during the manufacture of polarizing films, and can produce thin polarizing films with good productivity. In addition, it has been found that the polarizing film obtained by using this polyvinyl alcohol-based film is a polarizing film having a high degree of polarization and less color spots.

That is, the first gist of the present invention is a polyvinyl alcohol-based film, which is a long polyvinyl alcohol-based film having a thickness of 25 to 60 μm, which is characterized by a thickness D (μm) and a moisture content of the film of 9 weight. The tensile elastic modulus X (MPa) in the longitudinal direction (MD direction) of the% state satisfies the following formula (1). 0.9 ≦ X / D ≦ 1.3 (1) The tensile elastic modulus is also referred to as the Young's modulus and the tensile elastic modulus.

In addition, the second gist of the present invention is a method for producing a polyvinyl alcohol-based film, which is a method for manufacturing the polyvinyl alcohol-based film of the first gist, and includes the following steps: a film-forming step, which is an aqueous solution of a polyvinyl alcohol-based resin The continuous casting method is used to form a film; a drying step is performed to dry the film obtained by the film formation; and a heat treatment step is performed to perform heat treatment on the dried film; The drying temperature is 100 ° C or higher. The heat treatment step is to cool the dried film to 50 ° C or lower, and then heat the film at 60 to 99 ° C.

The third gist of the present invention is a polarizing film using the polyvinyl alcohol-based film of the first gist. [Effect of the invention]

The polyvinyl alcohol-based film according to the first aspect of the present invention has a tensile elastic modulus X (MPa) in a longitudinal direction (MD direction) in a state where the thickness D (25 to 60 μm) and the moisture content of the film are 9% by weight. It satisfies the above formula (1), so it has the effect of being excellent in stretchability at the time of manufacturing a polarizing film, and preventing breakage when manufacturing a thin polarizing film.

In particular, the tensile elastic modulus X (MPa) in the longitudinal direction (MD direction) and the tensile elastic modulus Y (MPa) in the width direction (TD direction) in a state where the moisture content of the film is 9% by weight are satisfied. In the formula (2), there is an effect that the extensibility can be improved when manufacturing a polarizing film. 0.9 ≦ Y / X ≦ 1.1 ・ ・ ・ (2)

Further, when the tensile strength F in the longitudinal direction (MD direction) is 80 MPa or more, it has the effect of preventing breakage during the production of a thin polarizing film.

Further, let the refractive index in the longitudinal direction (MD direction) be nx, the refractive index in the width direction (TD direction) be ny, the refractive index in the thickness direction be nz, and the thickness be D (μm). Calculate according to the following formula (3) When the phase difference Rth (nm) in the thickness direction is 80 to 140 nm, there is an effect that the swelling property in the thickness direction can be optimized and the extensibility in the production of a polarizing film can be optimized. Rth = {(nx ＋ ny) / 2-nz} × 1000 × D ・ ・ ・ (3)

In addition, when the width is 4 m or more and the length is 4 km or more, there is an effect that productivity can be improved.

The method for producing a polyvinyl alcohol-based film according to the second aspect of the present invention includes a specific drying step and a heat treatment step, so that it has polyethylene having the above-mentioned first aspect, which is excellent in elongation and fracture resistance when manufacturing a polarizing film. Effect of alcohol-based film.

Since the polarizing film of the third aspect of the present invention uses the polyvinyl alcohol-based film of the first aspect described above, it has the effect that it can be made into a polarizing film that exhibits high polarization and has few color spots.

The present invention is described in detail below. The polyvinyl alcohol-based film of the present invention is a strip having a thickness D of 25 to 60 μm, and is characterized by a thickness D (μm) and a length direction (MD) measured in a state where the moisture content of the film is 9% by weight. Direction) The tensile elastic modulus X (MPa) satisfies the following formula (1). 0.9 ≦ X / D ≦ 1.3 ・ ・ ・ (1)

In addition, while the polyvinyl alcohol-based film is being transported in its longitudinal direction (flow direction, MD direction), a polarizing film is formed through a swelling step, an extending step, and the like. Here, the polyvinyl alcohol-based film has a specific thickness D (25 to 60 μm) and satisfies the above formula (1). Therefore, the polyvinyl alcohol-based film has excellent elongation at the time of manufacturing a polarizing film, even if a thin The polarizing film does not break. In addition, the obtained polarizing film is one having a high degree of polarization and few color spots.

With regard to the above polyvinyl alcohol-based film, in terms of improving the extensibility when manufacturing a polarizing film, it is preferable to satisfy the following formula (1 '), and in terms of further improving the extensibility, it is particularly preferable to satisfy the following formula (1' '). 1.0 ≦ X / D ≦ 1.2 ・ ・ ・ (1 ') 1.0 ≦ X / D ≦ 1.1 ・ ・ ・ (1' ')

The tensile elastic modulus in the present invention is a value measured under an environment of 20 ° C and 65% RH in accordance with JIS K7127: 1999. As described above, in the production of a polarizing film, a polyvinyl alcohol-based film is stretched after swelling, and it is difficult to accurately and stably measure the tensile elastic modulus after swelling. In the present invention, in view of the fact that the moisture content of a polyvinyl alcohol-based film generally supplied to a polarizing film is several%, the tensile elastic modulus when the moisture content is 9% by weight, which is easily controlled by humidity adjustment, is used as an index. The method for controlling humidity is not particularly limited. For example, the moisture content can be stabilized by adjusting the humidity of a relatively dry polyvinyl alcohol-based film that has just been prepared in an environment of 20 ° C and 65% RH for several hours to several tens of hours. It is close to 9% by weight of the equilibrium moisture content of the above environment.

In addition, in the present invention, the above-mentioned "moisture content of 9% by weight" means that "the moisture content is within a range of 9.0% by weight ± 0.5% by weight", and the tensile elastic modulus is almost unchanged within this range. Moreover, in the present invention, since the turbulance factor is large due to the crystalline state and the alignment state of the polymer, the calculation of the tensile elastic modulus is not performed based on the measured moisture content.

The moisture content in the present invention is a value calculated from the weight before and after drying a polyvinyl alcohol-based film at an ambient temperature of 105 ° C. for 16 hours. Let the weight before drying be A and the weight after drying be B. It is calculated by the following formula. Moisture content (wt%) = 100 × (AB) / A In addition, the moisture content in the polyvinyl alcohol-based film changes to an equilibrium moisture content that depends on the ambient humidity. Therefore, the test has been adjusted to a moisture content of 9 wt%. The sheet shall be provided in time for the determination of the tensile elastic modulus.

In the present invention, the in-plane shift ΔX (MPa) of the tensile elastic modulus X in the longitudinal direction (MD direction) in a state where the moisture content is 9% by weight, and the width direction (TD) in a state where the moisture content is 9% by weight. Direction), the in-plane deviation ΔY (MPa) of the tensile elastic modulus Y (MPa) is preferably 10 MPa or less, particularly preferably 5 MPa or less, and more preferably 3 MPa or less. If the in-plane offset ΔX and the in-plane offset ΔY are too large, uneven stretching may occur during the manufacture of the polarizing film, and the polarizing film tends to have stains.

Here, the manufacturing method of the polyvinyl-alcohol-type film of this invention is demonstrated. That is, the method for producing a polyvinyl alcohol-based film of the present invention includes the following steps: a film-forming step (A), which forms a solution of a polyvinyl alcohol-based resin solution by a continuous casting method; and a drying step (B), The film obtained through film formation is dried; and the heat treatment step (C) is performed to heat-treat the dried film; characterized in that in the drying step (B), the temperature at which the film obtained through film formation is dried is 100 ° C; As mentioned above, the heat treatment step (C) is cooling the dried film to 50 ° C or lower, and then heating at 60 to 99 ° C.

[Film-forming step (A)] First, the film-forming step (A) will be described in detail.

As the polyvinyl alcohol-based resin used in the present invention, an unmodified polyvinyl alcohol-based resin is generally used, that is, a resin obtained by saponifying a polyvinyl acetate obtained by polymerizing vinyl acetate. When necessary, a resin obtained by saponifying a copolymer of vinyl acetate and a small amount (usually 10 mol% or less, preferably 5 mol% or less) of a copolymerizable component with vinyl acetate may also be used. Components that can be copolymerized with vinyl acetate include, for example, unsaturated carboxylic acids (for example, salts, esters, amidines, nitriles, etc.), and olefins having 2 to 30 carbon atoms (for example, ethylene, propylene, n-butene, and isobutylene). Etc.), vinyl ethers, unsaturated sulfonates, etc. Alternatively, a modified polyvinyl alcohol-based resin obtained by chemically modifying the saponified hydroxyl group may be used.

In addition, as the polyvinyl alcohol-based resin, a polyvinyl alcohol-based resin having a 1,2-diol structure in a side chain can also be used. The polyvinyl alcohol-based resin having a 1,2-diol structure in a side chain can be obtained by, for example, (i) a copolymer of vinyl acetate and 3,4-diethoxyl-1-butene. Saponification method, (ii) saponification and decarboxylation of a copolymer of vinyl acetate and vinyl ethylene carbonate, and (iii) vinyl acetate and 2,2-dialkyl-4-vinyl-1 A method of saponifying and deketalizing a copolymer of 3,3-dioxolane, (iv) a method of saponifying a copolymer of vinyl acetate and glycerol monoallyl ether, and the like.

The weight average molecular weight of the polyvinyl alcohol resin is preferably 100,000 to 300,000, particularly preferably 110,000 to 280,000, and more preferably 120,000 to 260,000. If the weight average molecular weight is too small, the degree of polarization of the polarizing film tends to decrease, and if it is too large, the stretching of the polyvinyl alcohol-based film during the production of the polarizing film tends to be difficult. The weight average molecular weight of the polyvinyl alcohol resin is a weight average molecular weight measured by a GPC-MALS method.

The average saponification degree of the polyvinyl alcohol resin used in the present invention is usually preferably 98 mol% or more, particularly preferably 99 mol% or more, more preferably 99.5 mol% or more, and even more preferably 99.8 moles %the above. If the average saponification degree is too small, the degree of polarization of the polarizing film tends to decrease. Here, the average saponification degree in the present invention is measured in accordance with JIS K 6726.

As for the polyvinyl alcohol-based resin used in the present invention, two or more types of polyvinyl alcohol-based resins having different modified substances, modified amounts, weight average molecular weight, average saponification degree, and the like may be used.

In addition, the polyvinyl alcohol-based resin is preferably washed with a solvent such as water and dehydrated using a centrifugal separator or the like, and a polyvinyl alcohol-based resin wet cake having a moisture content of 50% by weight or less is preferable. When the water content is too large, it tends to be difficult to form a desired aqueous solution concentration. This polyvinyl alcohol resin wet cake is dissolved in warm water or hot water to prepare a polyvinyl alcohol resin aqueous solution.

The method for preparing the polyvinyl alcohol-based resin aqueous solution is not particularly limited. For example, the polyvinyl alcohol-based resin can be prepared by using a heated multiaxial extruder. Alternatively, the polyethylene can be added to a dissolution tank provided with an up-and-down circulation flow type stirring blade. The alcohol-based resin was wet cake, and water vapor was blown into the tank to dissolve and prepare an aqueous solution of a desired concentration.

The polyvinyl alcohol resin aqueous solution contains glycerin, diglycerol, triglycerol, ethylene glycol, triethylene glycol, polyethylene glycol, trimethylolpropane, etc. in addition to the polyvinyl alcohol resin. A plasticizer; at least one of a nonionic, anionic, and cationic surfactant is preferred in terms of film forming properties of a polyvinyl alcohol-based film.

The plasticizer is preferably glycerin, and the content of the plasticizer in the polyvinyl alcohol resin aqueous solution is preferably 1 to 20% by weight. As the above-mentioned surfactant, polyoxyethylene alkylamine and higher fatty acid alkanolamine are preferred, and the content of the surfactant in the polyvinyl alcohol resin aqueous solution is preferably 0.01 to 1% by weight.

The resin concentration of the polyvinyl alcohol-based resin aqueous solution obtained in this manner is preferably 15 to 60% by weight, particularly preferably 17 to 55% by weight, and more preferably 20 to 50% by weight. If the resin concentration of this aqueous solution is too low, the productivity tends to decrease due to an increase in drying load, and if it is too high, the viscosity tends to become too high and it becomes difficult to dissolve uniformly.

Then, the obtained polyvinyl alcohol-based resin aqueous solution is subjected to a defoaming treatment. As the defoaming method, there are methods such as standing defoaming and defoaming by using a multi-axis extruder having a vent hole. As a multi-axis extruder having a vent hole, a biaxial extruder having a vent hole is generally used.

After the defoaming treatment, a polyvinyl alcohol-based resin aqueous solution was sequentially and quantitatively introduced into a T-slot die, and was discharged and cast onto a rotating casting drum, and film formation was performed by a continuous casting method.

The temperature of the polyvinyl alcohol-based resin aqueous solution at the exit of the T-slot die is preferably 80 to 100 ° C, particularly preferably 85 to 98 ° C. If the temperature of the polyvinyl alcohol-based resin aqueous solution is too low, the fluid tends to flow poorly, and if it is too high, the fluid tends to foam.

The viscosity of the polyvinyl alcohol-based resin aqueous solution is preferably 50 to 200 Pa · s, and particularly preferably 70 to 150 Pa · s at the time of discharge. If the viscosity of the aqueous solution is too low, the flow tends to be poor, and if it is too high, the casting tends to be difficult.

The discharge speed of the polyvinyl alcohol-based resin aqueous solution discharged from the T-slot die to the casting drum is preferably 0.5 to 5 m / min, particularly preferably 0.6 to 4 m / min, and more preferably 0.7 to 3 m / min. If the discharge speed is too slow, productivity tends to decrease, and if it is too fast, casting tends to become difficult.

The diameter of the casting drum is preferably 2 to 5 m, particularly preferably 2.4 to 4.5 m, and even more preferably 2.8 to 4 m. If the diameter is too small, the drying length tends to be insufficient and it is difficult to increase the speed. If it is too large, the transportability tends to decrease.

The width of the casting drum is preferably 4 m or more, particularly preferably 4.5 m or more, more preferably 5 m or more, and even more preferably 5 to 6 m. If the width of the casting drum is too small, productivity tends to decrease.

The rotation speed of the casting drum is preferably 3 to 50 m / min, particularly preferably 4 to 40 m / min, and more preferably 5 to 35 m / min. If the rotation speed is too slow, productivity tends to decrease, and if it is too fast, dehydration tends to be insufficient.

The surface temperature of the casting drum is preferably 40 to 99 ° C, and particularly preferably 50 to 95 ° C. If the surface temperature is too low, dehydration tends to be poor, and if it is too high, foaming tends to occur.

The film forming step (A) is performed in this manner, and the film obtained by the film formation is peeled from the casting drum.

[Drying Step (B)] Next, the drying step (B) will be described in detail. This drying step (B) is a step of heating and drying the thin film obtained through the film formation.

The film peeled from the casting drum (the film obtained by the above-mentioned film formation) is conveyed by a nip roller in a flow direction (MD direction), and the surface and the back surface of the film are alternately brought into contact with a plurality of heat rollers and dried. As for the heat roller, for example, a roller having a diameter of 0.2 to 2 m which has been hard-chrome plated or mirror-finished on the surface is preferred, and usually 2 to 30, preferably 10 to 25, are preferably used for drying.

The drying temperature (the temperature at which the film obtained through the film formation is dried) is preferably 100 ° C or higher, particularly preferably 100 to 120 ° C, more preferably 100 to 115 ° C, and even more preferably 100 to 110 ° C. If the drying temperature is too low, poor drying tends to occur, and if it is too high, poor appearance such as undulations tends to occur. In addition, the drying temperature in the present invention means the surface temperature of the hot roller having the highest temperature among the plurality of hot rollers used.

The drying time is not particularly limited, but is usually 1 to 60 seconds, preferably 2 to 50 seconds, particularly preferably 3 to 40 seconds, and more preferably 4 to 30 seconds. If the drying time is too short, poor drying tends to occur, and if it is too long, poor appearance such as undulations tends to occur. In addition, the drying time in the present invention refers to the contact time between the hot roller with the highest temperature and the film obtained through the above-mentioned film formation. When there are multiple hot rollers with the highest temperature, it is the accumulation of the contact time with these hot rollers. value.

The moisture content of the dried film is preferably 10% by weight or less, particularly preferably 1 to 9% by weight, more preferably 2 to 8% by weight, even more preferably 3 to 7% by weight, and still more preferably 4 to 6%. weight%. If the moisture content is too high, the finally obtained polyvinyl alcohol-based film tends to have poor drying.

[Heat Treatment Step (C)] Next, the heat treatment step (C) will be described in detail. This heat treatment step (C) is a step of heat-treating the dried film. This heat treatment step is generally an arbitrary step performed as needed, but in the present invention, it is a necessary step for controlling the tensile elastic modulus. That is, the heat treatment step (C) is performed by temporarily cooling the film dried at a temperature of 100 ° C or higher in the drying step (B) to 50 ° C or lower (the temperature of the dried film itself), and then again at It is heated at 60 to 99 ° C so that the tensile elastic modulus becomes a desired range, and the extensibility at the time of manufacturing the polarizing film is improved.

Examples of the above-mentioned cooling method include natural cooling in which the natural cooling is performed, and a method of blowing cold air.

Examples of the heating method include a method of blowing hot air using a floating dryer and a method of contacting it with a hot roller. In the present invention, a method using a floating dryer is considered in consideration of stabilization of tensile elastic modulus. The method is better.

The heating temperature is preferably 65 to 95 ° C, particularly preferably 70 to 90 ° C, and more preferably 70 to 80 ° C. If the heating temperature is too low, the tensile elastic modulus tends to decrease, and if it is too high, the tensile elastic modulus tends to increase. In addition, regarding the heating temperature in the present invention, when the heating method is a method of blowing hot air using the floating dryer, it means the temperature of the hot air, and when the heating method is a method of bringing it into contact with the hot roller, it means The surface temperature of the heat roller.

The heating time is not particularly limited. When a floating dryer is used, it is preferably 10 to 120 seconds, particularly preferably 20 to 90 seconds, and more preferably 30 to 60 seconds. If the heating time is too short, the shift in tensile elastic modulus tends to increase, and if it is too long, the productivity tends to decrease.

The moisture content of the film after heating is preferably 5% by weight or less, particularly preferably 0.1 to 4% by weight, more preferably 0.2 to 3% by weight, and even more preferably 0.3 to 2.5% by weight. If the moisture content is too high, the finally obtained polyvinyl alcohol-based film tends to have poor drying.

As described above for the drying step (B) and the heat treatment step (C), the temperature balance between the two is important for the manufacturing method of the present invention. The drying temperature in the drying step (B) should be the boiling point of water The above is preferably 100 ° C or higher, and a relatively lower temperature in this temperature range should be selected. Further, the heating temperature in the heat treatment step (C) should be below 100 ° C, which is particularly preferred.

[Polyvinyl alcohol-based film] Through the drying step (B) and the heat treatment step (C), a polyvinyl alcohol-based film of the present invention having a longer flow direction (MD direction) can be obtained. This polyvinyl alcohol-based film can be cut at both ends and wound around a core tube to form a roll.

The width of the polyvinyl alcohol-based film of the present invention thus obtained is preferably 4 m or more in terms of improving productivity, and 4 to 6 m in terms of avoiding breakage.

In addition, the length of the polyvinyl alcohol-based film of the present invention is preferably 4 km or more in view of improvement in productivity, and it is more preferably 5 km or more in consideration of corresponding to a polarizing film and corresponding to an increase in area of a liquid crystal screen. In terms of weight, it is particularly preferably 5 to 50 km.

The thickness D of the polyvinyl alcohol-based film of the present invention is 25 to 60 μm as described above. In consideration of the thickness reduction of the polarizing film, it is preferably 30 to 55 μm, and particularly preferably 35 to 50 μm. The thickness of the polyvinyl alcohol-based film can be adjusted based on the resin concentration in the polyvinyl alcohol-based resin aqueous solution, which is the raw material, the amount of the raw material to be poured into the casting mold (discharging speed), the stretching ratio of the film obtained through film formation, and the like. .

With regard to the polyvinyl alcohol-based film of the present invention, in terms of improving the extensibility when manufacturing a polarizing film, the tensile elastic modulus X (MPa) in the longitudinal direction (MD direction) and the moisture content of the polyvinyl alcohol-based film are considered. It is preferable that the tensile elastic modulus Y (MPa) in the width direction (TD direction) in a state of 9% by weight satisfies the following formula (2). 0.9 ≦ Y / X ≦ 1.1 ・ ・ ・ (2)

In consideration of the improvement of the extensibility at the time of manufacturing the polarizing film, it is more preferable to satisfy the following formula (2 '), and in consideration of the further improvement of the extensibility, it is particularly preferable to satisfy the following formula (2' '). 0.95 ≦ Y / X ≦ 1.09 ・ ・ ・ (2 ') 1.0 ≦ Y / X ≦ 1.08 ・ ・ ・ (2' ')

If the value of Y / X is too small, the extensibility in the flow direction (MD direction) during the production of the polarizing film tends to decrease, and if it is too large, the extensibility tends to be unstable.

In the polyvinyl alcohol-based film of the present invention, the tensile strength F (MPa) in the longitudinal direction (MD direction) in a state where the moisture content is 9% by weight is preferably 80 MPa or more, particularly preferably 90 MPa or more, and more preferably 100 MPa or more. . If the tensile strength F (MPa) is too small, the thin polarizing film tends to be easily broken during production. The upper limit of the tensile strength F (MPa) is usually 200 MPa.

In the polyvinyl alcohol-based film of the present invention, the refractive index in the longitudinal direction (MD direction) is nx, the refractive index in the width direction (TD direction) is ny, the refractive index in the thickness direction is nz, and the thickness is D (μm). In this case, the phase difference Rth (nm) in the thickness direction calculated according to the following formula (3) is preferably 80 to 140 nm, particularly preferably 85 to 130 nm, more preferably 90 to 120 nm, and even more preferably 95 to 110 nm. When the phase difference Rth (nm) in the thickness direction is too small, the swelling property in the thickness direction tends to decrease. When the phase difference Rth (nm) is too large, the polymer chain surface orientation is strong, and the stretchability in the production of the polarizing film tends to decrease. Rth = {(nx ＋ ny) / 2-nz} × 1000 × D ・ ・ ・ (3)

In addition, in the above-mentioned embodiment, the case where a casting drum (drum-type roller) is used as a casting mold is described as an example, and the method of manufacturing a polyvinyl alcohol-type film was demonstrated, and a casting tape and a resin film can also be used as a casting mold. To make.

Since the polyvinyl alcohol-based film of the present invention has excellent extensibility, it can be particularly preferably used as an original roll for a polarizing film.

Here, the manufacturing method of the polarizing film obtained using the polyvinyl-alcohol-type film of this invention is demonstrated.

[Manufacturing method of polarizing film] The polarizing film of the present invention is produced by taking out the polyvinyl alcohol-based film from a roll and transporting it in a horizontal direction, and through steps such as swelling, dyeing, boric acid crosslinking, stretching, washing, and drying.

The swelling step is performed before the dyeing step. In the swelling step, in addition to cleaning the stains on the surface of the polyvinyl alcohol-based film, by swelling the polyvinyl alcohol-based film, it also has the effect of preventing uneven dyeing. In the swelling step, water is usually used as the treatment liquid. This treatment liquid only needs to be water as a main component, and a small amount of additives such as an iodine compound, a surfactant, and an alcohol may be added. The temperature of the swelling bath is usually about 10 to 45 ° C, and the immersion time in the swelling bath is usually about 0.1 to 10 minutes.

The dyeing step is performed by contacting a polyvinyl alcohol-based film with a liquid containing iodine or a dichroic dye. Generally, an aqueous solution of iodine-potassium iodide is used, and the concentration of iodine is 0.1 to 2 g / L, and the concentration of potassium iodide is preferably 1 to 100 g / L. A dyeing time of about 30 to 500 seconds is more practical. The temperature of the treatment bath is preferably 5 to 50 ° C. In addition to the aqueous solvent, the aqueous solution may contain a small amount of water-compatible organic solvents.

The boric acid crosslinking step is performed using a boron compound such as boric acid or borax. The boron compound is used in the form of an aqueous solution or a water-organic solvent mixed solution and a concentration of about 10 to 100 g / L. Coexisting potassium iodide in the liquid is preferable in terms of stabilization of polarizing performance. The temperature during the treatment is preferably about 30 to 70 ° C, and the processing time is preferably about 0.1 to 20 minutes. In addition, if necessary, the stretching operation can be performed during the processing.

The extending step is preferably extended 3 to 10 times in the uniaxial direction [flow direction (MD direction)], and preferably 3.5 to 6 times. At this time, it is possible to perform a slight stretch [a degree of preventing shrinkage in the width direction (TD direction), or an extension of the degree or more] in the right direction of the stretch direction. The temperature during stretching is preferably 30 to 170 ° C. Furthermore, as long as the stretching magnification is finally set within the aforementioned range, the stretching operation can be performed not only once, but also in the polarizing film manufacturing step multiple times.

In the present invention, the stretching tension in the stretching step described above needs to be in a proper range. That is, when the stretching tension is too large, the dichroic dye is not sufficiently aligned because it cannot be stretched to a predetermined stretching ratio, and there is a tendency that the polarization degree cannot be improved. On the other hand, if the stretching tension is too small, the orientation of the dichroic dye is unstable even if it is stretched to a predetermined stretching magnification, and there is a tendency that the polarizing film generates color spots. In addition, in general, in the manufacturing steps of the polarizing film, the stretching tension is set according to each thickness, so it is difficult to summarize the preferred range. In the comparison of the same thickness, it is better to reduce the stretching tension by more than 10%, especially to reduce it. 20% to 40%.

The washing step is performed by, for example, immersing a polyvinyl alcohol-based film in an aqueous iodide solution composed of water, potassium iodide, or the like, so that precipitates generated on the surface of the polyvinyl alcohol-based film can be removed. The potassium iodide concentration when using an aqueous potassium iodide solution is preferably about 1 to 80 g / L. The temperature during the washing treatment is usually 5 to 50 ° C, preferably 10 to 45 ° C. The processing time is usually 1 to 300 seconds, preferably 10 to 240 seconds. In addition, washing with water and washing with an aqueous potassium iodide solution may be appropriately combined.

The drying step is, for example, drying the polyvinyl alcohol-based film in the air at 40 to 80 ° C. for 1 to 10 minutes.

Thus, the polarizing film of the present invention can be obtained. The degree of polarization of the polarizing film of the present invention is preferably 99.5% or more, and more preferably 99.8% or more. If the degree of polarization is too low, the contrast of the liquid crystal display may not be secured. In addition, the degree of polarization generally consists of the light transmittance (H ₁₁ ) measured at a wavelength λ in a state where two polarizing films are superimposed so that their alignment directions are the same, and two polarizing films are superimposed. The light transmittance (H ₁ ) measured at the wavelength λ with the alignment directions being perpendicular to each other was calculated according to the following formula. Polarization = [(H ₁₁ -H ₁ ) / (H ₁₁ + H ₁ )] ^1/2

Further, the monomer transmittance of the polarizing film of the present invention is preferably 42% or more, and more preferably 43% or more. If the transmittance of the monomer is too low, there is a tendency that the high brightness of the liquid crystal display cannot be achieved. The unit transmittance is a value obtained by measuring the light transmittance of a polarizing film unit using a spectrophotometer.

The polarizing film of the present invention is suitable for manufacturing a polarizing plate having excellent polarization and no color spots. Here, the manufacturing method of the polarizing plate using the polarizing film of this invention is demonstrated.

[Manufacturing method of polarizing plate] The above-mentioned polarizing plate can be produced by bonding an optically isotropic resin film as a protective film on one or both sides of the polarizing film of the present invention through an adhesive. Examples of the protective film include cellulose triacetate, cellulose diacetate, polycarbonate, polymethyl methacrylate, cyclic olefin polymer, cyclic olefin copolymer, polystyrene, polyether fluorene, and polystyrene. Film or sheet of methyl ester, poly-4-methylpentene, polyphenylene ether, and the like.

The bonding method can be performed by a known method. For example, a liquid adhesive composition is uniformly applied to a polarizing film, a protective film, or both, and then the two are bonded and pressure-bonded, and heated or irradiated. Active energy rays.

A polarizing film can also be produced by coating a hardening resin such as a urethane resin, an acrylic resin, or a urea resin on one or both sides of the polarizing film, and curing the hardening layer. In this way, the hardened layer can replace the above-mentioned protective film, and realize a thin film.

The polarizing film and polarizing plate using the polyvinyl alcohol-based film of the present invention have excellent polarizing performance, and can be ideally used in portable information terminals, personal computers, televisions, projectors, sign boards, electronic desktop computers, electronics Clocks, word processors, electronic papers, game consoles, video cameras, cameras, photo albums, thermometers, audio, automotive or mechanical measuring instruments, liquid crystal display devices, sunglasses, anti-glare glasses, stereo glasses, wearables Anti-reflective layers for displays and display elements (CRT, LCD, organic EL, electronic paper, etc.), optical communication equipment, medical equipment, building materials, toys, etc. [Example]

Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to the following examples as long as the gist is not exceeded.

In addition, the properties (moisture content, tensile elastic modulus, tensile strength, phase difference in the thickness direction, and elongation tension) of the polyvinyl alcohol-based films in the following examples and comparative examples and the properties of the polarizing film (polarization, single The measurement and evaluation of the volume transmittance and staining were performed as follows.

<Measurement conditions> [Moisture content (% by weight)] A test piece of 100 mm × 100 mm was cut out of the obtained polyvinyl alcohol-based film, and dried from an initial weight A (g) and a dryer at an ambient temperature of 105 ° C. 16 The weight B (g) after the hour was calculated from the moisture content (% by weight) according to the following formula. Water content (% by weight) = 100 × (A-B) / A

[Tensile elastic modulus (MPa), tensile strength F (MPa)] A 120 mm × 15 mm test piece was cut out of the obtained polyvinyl alcohol-based film, and the humidity was adjusted in a constant temperature and humidity chamber at 20 ° C and 65% RH. The moisture content was set to 9.0% by weight ± 0.5% by weight, and then a "precision universal testing machine, Autograph (AG-IS)" manufactured by Shimadzu Corporation was used according to JIS K7127: 1999 (tensile speed 1000mm / min, distance between chucks 50mm), the tensile elastic modulus X (MPa) in the longitudinal direction (MD direction) and the tensile elastic modulus Y (MPa) in the width direction (TD direction) were measured under an environment of 20 ° C and 65% RH. The tensile strength F (MPa) was measured in the longitudinal direction (MD direction).

[Phase difference in thickness direction Rth (nm)] A test of 4 cm in length x 4 cm in width was obtained from the central portion and the two end portions (inside 10 cm from the film end) of the width direction (TD direction) of the obtained polyvinyl alcohol film. The phase difference Rth (nm) in the thickness direction of 590 nm was measured using a phase difference measuring device ("KOBRA-WR" manufactured by Oji Measurement Co., Ltd.). <Measurement conditions of Rth> Incident angle: 50 ° Tilt central axis: Late phase axis Average refractive index: Value measured by Abbe refractometer

[Extension Tension (N)] A test piece having a length (MD direction) of 50 mm × width (TD direction) of 35 mm was cut out of the obtained polyvinyl alcohol-based film, and a chuck with a width of 35 mm was used so that the distance between the chucks was 20 mm. Hold both ends in the length direction (MD direction), and then immerse them in warm water at 30 ° C for 240 seconds, while extending in the length direction (MD direction) to 1.7 times (34mm), and then lengthen the length in the dyeing solution at 30 ° C. The direction (MD direction) was extended to 1.6 times (54.4mm). Finally, the spring tension was used to measure the tension (N) at 50 ° C in the boric acid solution in the length direction (MD direction) to 2.1 times (114.2mm). The composition of the dyeing solution and the boric acid solution used is as follows. Dyeing solution: 0.5g / L of iodine, 30g / L of potassium iodide Boric acid solution: 30g / L of potassium iodide, 40g / L of boric acid

[Polarity (%), monomer transmittance (%)] Cut from the central portion in the width direction (TD direction) of the obtained polarizing film and the end portions on both sides (inside 10 cm from each end of the both end portions of the polarizing film) A test piece having a length of 4 cm and a width of 4 cm was taken out, and an automatic polarizing film measuring device (manufactured by JASCO Corporation: VAP7070) was used to measure the degree of polarization (%) and the transmittance (%) of the monomer. This measurement was performed with respect to the central part and the front-end part / terminal part of the polarizing film in the flow direction (MD direction) (inside 10 m from the front end of the polarizing film and each end of the terminal).

[Color spots] A test piece having a length of 30 cm and a width of 30 cm was cut out from the central portion of the obtained polarizing film in the width direction (TD direction) and both end portions (inside 10 cm from each end of both end portions of the polarizing film), and At a 45-degree angle, hold between two polarizing plates in the crossed Nicols state (transmittance of 43.5% and polarization of 99.9%), then observe the optical color in transmission mode using a light box with a surface illumination of 14,000lx And evaluated according to the following criteria. (Evaluation criteria) ○ ・ ・ ・ No colored spots △ ・ ・ Vaguely colored spots × ・ ・ The colored spots are in the center and front / end portions (distance from the polarizing film) of the polarizing film in the flow direction (MD direction) The front end and the inside of each end of the terminal are within 10 m).

<Example 1> (Production of polyvinyl alcohol-based film) 2,000 kg of a polyvinyl alcohol-based resin having a weight average molecular weight of 142,000 and a saponification degree of 99.8 mol%, 5,000 kg of water, and 220 kg of glycerin as a plasticizer were added while stirring. The temperature was raised to 140 ° C., and the concentration was adjusted to a resin concentration of 25% to obtain a uniformly dissolved polyvinyl alcohol-based resin aqueous solution. Then, the polyvinyl alcohol resin aqueous solution was supplied to a biaxial extruder having vent holes, and after defoaming, the temperature of the aqueous solution was set to 95 ° C, and the liquid was discharged from a T-slot die discharge port (discharge rate of 2.5 m / min). And cast to a rotating casting drum to form a film. The film obtained by the film formation was peeled from the casting drum, and the film was dried while the surface and the back surface of the film were alternately brought into contact with 20 hot rolls. The drying temperature (the surface temperature of the hot roller with the highest temperature) was 110 ° C, and the drying time (the cumulative time of the contact time between the hot roller with the film being the highest temperature) was 12 seconds. Thus, a film having a moisture content of 9% by weight was obtained. Then, by naturally cooling the dried film, the temperature of the film itself was temporarily set to 40 ° C, and then hot air of 95 ° C was blown from both sides of the film for 30 seconds by a floating dryer to obtain a moisture content of 2 weight. % Polyvinyl alcohol-based film (60 μm in thickness, 5 m in width, and 5 km in length). Finally, both ends of the polyvinyl alcohol-based film were cut and wound around a core tube to form a roll. The properties of the obtained polyvinyl alcohol-based film are shown in Table 1 below.

(Production of polarizing film) The obtained polyvinyl alcohol-based film was taken out from a roller and conveyed in a horizontal direction by a conveying roller. First, it was immersed in a water tank at a water temperature of 30 ° C and swelling in the flow direction (MD direction) ) To 1.7 times. Then, it was immersed in a 30 ° C aqueous solution consisting of 0.5 g / L of iodine and 30 g / L of potassium iodide, and was extended to 1.6 times in the flow direction (MD direction) while being dyed. Then, it was immersed in 40 g / L of boric acid and 30 g / potassium iodide. In an aqueous solution composed of L (50 ° C.), uniaxial extension was performed in the flow direction (MD direction) to 2.1 times while performing boric acid crosslinking. Finally, it was washed with an aqueous potassium iodide solution and dried at 50 ° C. for 2 minutes to obtain a polarizing film with a total stretching ratio of 5.8 times. No breakage occurred during this production. The characteristics of the obtained polarizing film are shown in Table 2 below.

<Examples 2 to 5, Comparative Examples 1 to 4> Except that the production was performed under the conditions shown in Table 1 below, the same procedure as in Example 1 was performed to obtain a polyvinyl alcohol-based film and a polarizing film. The characteristics of the obtained polyvinyl alcohol-based film are shown in Table 1 below, and the characteristics of the obtained polarizing film are shown in Table 2 below. In Comparative Example 3, an attempt was made to manufacture a polarizing film in the same manner as in Example 1. However, breakage occurred during the extension of the boric acid crosslinking step. The characteristics in Table 2 are characteristics of the leading end portion of the polarizing film which was barely obtained.

【Table 1】

【Table 2】

It can be seen that the values of the tensile elastic modulus / thickness (X / D) of the polyvinyl alcohol-based films of Examples 1 to 5 are within the specific range of the present invention. Therefore, a polarizing film with high polarization and no color spots can be obtained. With the polarizing films of the polyvinyl alcohol-based films of Comparative Examples 1 to 4, the tensile elastic modulus / thickness (X / D) fell outside the specific range of the present invention. As a result, the degree of polarization was poor, and colored spots were observed.

The above embodiments show specific forms of the present invention, but the above embodiments are for illustration only and are not to be construed in a limiting sense. Various changes obvious to those with ordinary knowledge in the technical field are still intended to be included in the scope of the present invention. [Industrial availability]

The polarizing film and polarizing plate using the polyvinyl alcohol-based film of the present invention have excellent polarizing performance, and can be ideally used in portable information terminals, personal computers, televisions, projectors, sign boards, electronic desktop computers, electronics Clocks, word processors, electronic papers, game consoles, video cameras, cameras, photo albums, thermometers, audio, automotive or mechanical measuring instruments, liquid crystal display devices, sunglasses, anti-glare glasses, stereo glasses, wearables Reflection reduction layers for displays and display elements (CRT, LCD, organic EL, electronic paper, etc.), optical communication equipment, medical equipment, building materials, toys, etc.

no

Claims (7)

A polyvinyl alcohol-based film is a long polyvinyl alcohol-based film with a thickness of 25 to 60 μm, and is characterized by a length direction (MD direction) in a state where the thickness D (μm) and the moisture content of the film are 9% by weight. The tensile elastic modulus X (MPa) satisfies the following formula (1); 0.9 ≦ X / D ≦ 1.3 (1). For example, the polyvinyl alcohol-based film according to item 1 of the patent application, the width direction (TD direction) of the tensile elastic modulus X (MPa) in the longitudinal direction (MD direction) and the moisture content of the film of 9% by weight The tensile elastic modulus Y (MPa) of) satisfies the following formula (2); 0.9 ≦ Y / X ≦ 1.1 (2). For example, the polyvinyl alcohol-based film according to item 1 or 2 of the patent application range has a tensile strength F in the longitudinal direction (MD direction) of 80 MPa or more. For example, the polyvinyl alcohol-based film in the first or second scope of the patent application, wherein the refractive index in the length direction (MD direction) is nx, the refractive index in the width direction (TD direction) is ny, and the refractive index in the thickness direction is nz. When the thickness is D (μm), the phase difference Rth (nm) in the thickness direction calculated according to the following formula (3) is 80 to 140 nm; Rth = {(nx ＋ ny) / 2-nz} × 1000 × D ・ ・ ・ ( 3). For example, the polyvinyl alcohol-based film in the first or second scope of the patent application has a width of 4m or more and a length of 4km or more. A method for manufacturing a polyvinyl alcohol-based film, which is a method for manufacturing a polyvinyl alcohol-based film according to any one of claims 1 to 5, including the following steps: a film-forming step, which is an aqueous solution of a polyvinyl alcohol-based resin Film formation by continuous casting method; drying step, drying the film obtained by the film formation; and heat treatment step, performing heat treatment of the dried film; characterized in that: the film obtained by the film formation step is used in the drying step; The drying temperature is above 100 ° C; the heat treatment step is a step of cooling the dried film to below 50 ° C and then heating at 60-99 ° C. A polarizing film is a polyvinyl alcohol film as described in any one of claims 1 to 5.