TWI738636B - Method for manufacturing polyvinyl alcohol resin film and method for manufacturing polarizing film - Google Patents

Abstract

The present invention provides a method for manufacturing polyvinyl alcohol resin film and a method for manufacturing polarizing film. The method for manufacturing polyvinyl alcohol resin film includes a drying step of removing water from aqueous solution which contains polyvinal alcohol resin and has a water content of more than 30%, wherein a removal rate of water is 0.01 to 1.8 weight %/ second when the water content is 30% in the drying step. The method for manufacturing polarizing film uses a polyvinyl alcohol resin film resulting from the method for manufacturing polyvinyl alcohol resin film.

Description

Manufacturing method of polyvinyl alcohol resin film and manufacturing method of polarizing film

The present invention relates to a method for manufacturing a polyvinyl alcohol-based resin film and a method for manufacturing a polarizing film.

Polarizing plates are widely used in devices such as image display devices represented by liquid crystal display devices. The polarizing plate is generally formed by attaching a protective film on one side or both sides of a polarizing film, and the aforementioned polarizing film is formed by dyeing a stretched polyvinyl alcohol-based resin film with a dichroic dye. The polyvinyl alcohol-based resin film, which is the raw material of the polarizing film, can be produced by drying and removing water from a film-like aqueous solution containing polyvinyl alcohol-based resin [for example, Japanese Patent Laid-Open No. 2014-059564, Japanese Patent No. 5390053] .

Regarding the polyvinyl alcohol-based resin film for polarizing film, when a polarizing film is formed by stretching/dyeing, it is required to exhibit high polarizing performance. Although the polarization performance of the polarizing film can be improved by increasing the stretching ratio or neck-in ratio when the polyvinyl alcohol resin film is stretched, this method has the following problems: 1) The film is prone to cracks, 2) The resulting polarizing film The heat shrinkage rate of the polarizer becomes larger, the heat resistance of the polarizing plate becomes lower, and 3) the width efficiency (the ratio of the width of the obtained polarizing film relative to the width of the polyvinyl alcohol-based resin film) becomes lower.

The object of the present invention is to provide a method for producing a polyvinyl alcohol-based resin film that can exhibit high polarization performance when used as a polarizing film, and a method for producing a polarizing film using the polyvinyl alcohol-based resin film.

The present invention provides a method for producing a polyvinyl alcohol-based resin film and a method for producing a polarizing film as shown below.

[1] A method for producing a polyvinyl alcohol resin film, comprising a drying step of removing water from an aqueous solution containing polyvinyl alcohol resin and having a water content of more than 30% by weight, wherein, in the drying step, the water content is The water removal rate at 30% by weight is 0.01 to 1.8% by weight/sec.

[2] A method for producing a polyvinyl alcohol resin film, comprising a drying step of removing water from an aqueous solution containing polyvinyl alcohol resin and having a water content of more than 30% by weight, wherein, in the drying step, the water content is The average removal rate of water in the range of 30 to 10% by weight is 0.01 to 1.8% by weight/sec.

[3] The method for producing a polyvinyl alcohol-based resin film as described in [1], which further includes a step of forming a coating layer of the aqueous solution on the base film before the drying step.

[4] The method for producing a polyvinyl alcohol-based resin film as described in [2], which further includes a step of forming a coating layer of the aqueous solution on the base film before the drying step.

[5] A method of manufacturing a polarizing film, comprising the following steps: a step of obtaining a polyvinyl alcohol-based resin film by the method of manufacturing a polyvinyl alcohol-based resin film described in any one of [1] to [4], The step of stretching the polyvinyl alcohol-based resin film to obtain a stretched film, and the step of obtaining a polarizing film from the stretched film.

[6] The method for producing a polarizing film according to [5], wherein the thickness of the polarizing film is 10 μm or less.

According to the present invention, it is possible to provide a method for producing a polyvinyl alcohol-based resin film that can exhibit high polarization performance when used as a polarizing film, and a method for producing a polarizing film using the polyvinyl alcohol-based resin film.

1‧‧‧Polarizing plate with protective film on one side

2‧‧‧Polarizing plate with protective film on both sides

5‧‧‧Polarizing film

6‧‧‧Coating layer

7‧‧‧PVA series resin film (PVA series resin layer)

7’‧‧‧Extended PVA series resin film (PVA series resin layer)

10‧‧‧The first protective film

15‧‧‧The first adhesive layer

20‧‧‧Second protective film

25‧‧‧Second Adhesive Layer

30‧‧‧Base film

30’‧‧‧Stretched base film

100‧‧‧Coating film

200‧‧‧Laminated film

300‧‧‧Extended film

400‧‧‧Polarizing laminated film

500‧‧‧Polarizing laminated film with protective film

Fig. 1 is a flowchart showing a preferred example of the method for producing a polyvinyl alcohol resin film of the present invention.

Fig. 2 is a schematic cross-sectional view showing an example of the layer structure of the coating film obtained in the coating step.

Fig. 3 is a schematic cross-sectional view showing an example of the layer structure of the laminated film obtained by the drying step.

FIG. 4 is a flowchart showing a preferred example of the method of manufacturing the polarizing film and the polarizing plate of the present invention.

Fig. 5 is a schematic cross-sectional view showing an example of the layer structure of the stretched film obtained by the stretching step.

Fig. 6 is a schematic cross-sectional view showing an example of the layer structure of the polarizing laminated film obtained by the dyeing step.

Fig. 7 is a schematic cross-sectional view showing an example of the layer structure of the polarizing laminated film with a protective film obtained in the first bonding step.

Fig. 8 is a schematic cross-sectional view showing an example of the layer structure of a polarizer with a single-sided protective film obtained by the peeling step.

Fig. 9 is a schematic cross-sectional view showing an example of the layer structure of the double-sided protective film-attached polarizing plate obtained in the second bonding step.

Figure 10 is based on the relationship between the removal rate V(30) of the drying step in each embodiment and comparative example and the luminosity factor corrected polarization factor Py of the obtained single-sided protective film polarizer. chart.

Figure 11 is a graph based on the relationship between the average removal rate Vave (30-10) of the drying step in each embodiment and comparative example and the luminescence factor correction polarization factor Py of the obtained single-sided protective film polarizer .

Figure 12 is a graph based on the relationship between the luminescence factor correction monomer transmittance Ty and the luminescence factor correction polarization factor Py of the single-sided protective film polarizers obtained from each embodiment and comparative example.

<Manufacturing method of polyvinyl alcohol resin film>

The manufacturing method of the polyvinyl alcohol-based resin film of the present invention (hereinafter, the polyvinyl alcohol-based resin is also referred to as "PVA-based resin") includes a drying step by removing water from an aqueous solution containing the PVA-based resin, Then, a layer (film) containing the PVA-based resin is formed to obtain a PVA-based resin film.

Fig. 1 is a flowchart showing a preferred example of the manufacturing method of the PVA-based resin film of the present invention. The manufacturing method of the PVA-based resin film of the present invention preferably includes a step of making the aqueous solution into a film before the drying step. Typically, this step may be to coat the aqueous solution on the substrate film to form a coating layer的步。 The steps. At this time, the manufacturing method of the PVA-based resin film of the present invention, as shown in Figure 1, includes the following steps in sequence: (1) Coating step S10, which is to coat the above-mentioned aqueous solution on the substrate film to form a coating Layer, (2) Drying step S20 is to remove water from the coating layer (film-like aqueous solution) to obtain a PVA-based resin film.

The steps are explained below. In addition, in the coating step S10, a PVA-based resin film (also referred to as a "PVA-based resin layer") can be formed on both sides of the base film by forming a coating layer on both sides of the base film, but the following mainly explains When forming a PVA-based resin film on one side of the base film.

(1) Coating step S10

Referring to FIG. 2, this step is a step of forming the coating layer 6 by coating an aqueous solution containing a PVA-based resin on at least one side of the base film 30 to obtain the coating film 100. In terms of easily obtaining the PVA-based resin film of the thin film and the polarizing film of the thin film, the coating layer 6 is formed by coating the base film 30, and the PVA-based resin film ( The method of PVA-based resin layer) is advantageous.

The base film 30 may be composed of a thermoplastic resin, and among them, it is preferably composed of a thermoplastic resin having excellent transparency, mechanical strength, thermal stability, extensibility, and the like. Specific examples of such thermoplastic resins Including, for example: polyolefin resins such as chain polyolefin resins and cyclic polyolefin resins (norbornene resins, etc.); polyester resins; (meth)acrylic resins; such as cellulose triacetic acid Cellulose ester resins such as cellurose triacetate and cellurose diacetate; polycarbonate resins; polyvinyl alcohol resins; polyvinyl acetate resins; polyarylate resins; polyphenylene Ethylene resin; polyether chrysene resin; poly chrysene resin; polyamide resin; polyimide resin; and mixtures and copolymers of these.

The base film 30 may have a single-layer structure composed of a single resin layer containing one or more than two types of thermoplastic resins, or may be a resin composed of one or more types of thermoplastic resins laminated with multiple layers. Layered multilayer structure. In the stretching step of the method of manufacturing a polarizing film described later, the base film 30 is preferably made of a resin that can be stretched at a stretching temperature suitable for stretching a PVA-based resin film (PVA-based resin layer).

The base film 30 may contain additives. Specific examples of additives include ultraviolet absorbers, antioxidants, smoothing agents, plasticizers, release agents, anti-coloring agents, flame retardants, nucleating agents, antistatic agents, pigments, and coloring agents.

From the viewpoint of strength, handling properties, etc., the thickness of the base film 30 is usually 1 to 500 μm, preferably 1 to 300 μm, more preferably 5 to 200 μm, and still more preferably 5 to 150 μm.

The aqueous solution (coating liquid) applied to the base film 30 is an aqueous solution of a PVA-based resin containing a PVA-based resin and water. The aqueous solution may also contain solvents other than water, plasticizers, surfactants and other additives as needed. Examples of solvents other than water include organic solvents that are compatible with water such as alcohols represented by methanol, ethanol, propanol, and polyols (preferably glycerin).

PVA-based resins can be saponified with polyvinyl acetate-based resins. In addition to polyvinyl acetate, which is a homopolymer of vinyl acetate, polyvinyl acetate resins can also list copolymers of vinyl acetate and other monomers that can be copolymerized with vinyl acetate. Other monomers that can be copolymerized with vinyl acetate include, for example, unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and (meth)acrylamides having an ammonium group.

The saponification degree of the PVA-based resin may be in the range of 80.0 to 100.0 mol%, but is preferably in the range of 90.0 to 99.5 mol%, more preferably in the range of 94.0 to 99.0 mol%. When the degree of saponification is less than 80.0 mol%, the water resistance of the polarizing film obtained from the PVA-based resin film is likely to decrease. When using a PVA-based resin with a degree of saponification exceeding 99.5 mol%, the dyeing speed in the dyeing step of the polarizing film manufacturing method described later may slow down, the productivity may decrease, and it may be difficult to obtain a polarizing film with sufficient polarizing performance. .

The so-called saponification degree is expressed by the unit ratio (mole%) that the acetate group (acetoxy group: -OCOCH ₃ ) contained in the polyvinyl acetate resin, which is the raw material of the PVA resin, is changed to a hydroxyl group by the saponification step The ratio is defined by the following formula: Degree of saponification (mole%)=100×(number of hydroxyl groups)÷(number of hydroxyl groups+number of acetate groups)

The degree of saponification can be determined in accordance with JIS K 6726 (1994). The higher the degree of saponification, the higher the ratio of hydroxyl groups, and therefore the lower the ratio of acetate groups that hinder crystallization.

The PVA-based resin may be partially modified polyvinyl alcohol. For example, PVA-based resins can be used: olefins such as ethylene and propylene; Unsaturated carboxylic acids such as acrylic acid, methacrylic acid and crotonic acid; modified ones such as alkyl esters of unsaturated carboxylic acids and (meth)acrylamide. The ratio of modification is preferably less than 30 mol%, more preferably less than 10%. When the modification exceeds 30 mol%, it will become difficult to absorb the dichroic pigment, and it will tend to be difficult to obtain a polarizing film with sufficient polarization performance. In addition, in this specification, "(meth)acrylic acid" means at least one selected from the group consisting of acrylic acid and methacrylic acid. The same applies to "(meth)acrylic acid base" and so on.

The average degree of polymerization of the PVA-based resin is preferably 100 to 10,000, more preferably 1,500 to 8,000, and still more preferably 2,000 to 5,000. The average degree of polymerization of the PVA-based resin can also be determined in accordance with JIS K 6726 (1994).

As described in detail later, the water content of the aqueous solution containing the PVA-based resin exceeds 30% by weight.

The method of applying the above-mentioned coating liquid to the substrate film 30 can be appropriately selected from the following methods: wire bar coating method; roll coating method such as reverse coating method and gravure coating method; die coating method; dot type Coating method; lip coating method; spin coating method; screen coating method; spray method; impregnation method; spray method, etc. The coating layer 6 may be formed only on one side of the base film 30, or may be formed on both sides.

Before applying the coating liquid, in order to improve the adhesion between the base film 30 and the PVA-based resin film, at least the surface of the base film 30 on the side where the coating layer 6 is formed may be subjected to corona treatment, plasma treatment, Flame treatment etc. Furthermore, for the same reason, the coating layer 6 may be formed on the base film 30 via the primer layer.

The undercoat layer can be formed by applying a coating liquid for forming an undercoat layer on the surface of the base film 30 and then drying it. The coating liquid contains Both the base film 30 and the PVA-based resin film have components that exert a certain degree of adhesion, and usually contain a resin component and a solvent that impart such adhesion. As the resin component, it is preferable to use thermoplastic resins excellent in transparency, thermal stability, extensibility, etc., and examples thereof include (meth)acrylic resins and polyvinyl alcohol resins. Among them, it is preferable to use polyvinyl alcohol-based resins that impart good adhesion. More preferably, it is polyvinyl alcohol resin. As the solvent, a general organic solvent or water-based solvent that can dissolve the above-mentioned resin components is generally used, but it is preferable to form the primer layer from a coating liquid using water as a solvent.

In order to increase the strength of the undercoat layer, a crosslinking agent may be added to the coating liquid for forming the undercoat layer. Specific examples of crosslinking agents include epoxy-based, isocyanate-based, dialdehyde-based, metal-based (for example, metal salts, metal oxides, metal hydroxides, and organometallic compounds), and polymer-based crosslinking agents. When using polyvinyl alcohol-based resin as the resin component for forming the primer layer, polyamide epoxy resin, methylolated melamine resin, dialdehyde-based crosslinking agent, metal chelate compound-based crosslinking agent, etc. can be suitably used .

The thickness of the undercoat layer is preferably about 0.05 to 1 μm, more preferably 0.1 to 0.4 μm. When it is thinner than 0.05 μm, the effect of improving the adhesion between the base film 30 and the PVA-based resin film tends to decrease.

The method of applying the coating liquid for forming an undercoat layer to the base film 30 may be the same as the above-mentioned aqueous solution for the PVA-based resin film. The drying temperature of the coating layer formed from the coating liquid for forming an undercoat layer is, for example, 50 to 200°C, preferably 60 to 150°C. When the solvent contains water, the drying temperature is preferably 80°C or higher.

(2) Drying step S20

Referring to Figure 3, this step is to remove water from the coating layer 6 with a moisture content of more than 30% by weight of the coating film 100 and form a PVA-based resin film (PVA-based resin layer) 7 to obtain a laminated film 200 step. The drying (removal of water) of the coating layer 6 can be performed by heating the coating film 100, but drying by reduced pressure or the like can also be used in combination. The method of heating the coating film 100 includes a method of bringing the coating film 100 into contact with (surrounding) a heated roller (heat roller), a method of blowing hot air to the coating film 100, or a combination of these methods. The drying temperature in the drying step S20 is, for example, in the range of 50 to 200°C, preferably in the range of 60 to 150°C.

In this step (drying step S20), it is derived from the coating layer 6 in a state where the moisture content exceeds 30% by weight (hereinafter, the moisture content of the coating layer 6 just before the drying step S20 is also referred to as "initial moisture content". The water is removed from the ratio W1"), and the drying is performed until the desired moisture content (hereinafter also referred to as the "final moisture content W2") is reached, and the PVA-based resin film 7 is obtained. At this time, appropriately adjust the water removal rate when the water content is 30% by weight (meaning the decrease in the water content (weight%) per unit time, in units of weight%/sec) or the vicinity of the water content of 30% by weight (That is, the average water removal rate is between 30 and 10% by weight). In the present invention, one or both of these are set to 0.01 to 1.8% by weight/sec. Within range. In the following, the water removal rate at the time when the moisture content of the coating layer 6 is 30% by weight is also referred to as "removal rate V(30)". When the moisture content of the coating layer 6 is in the range of 30-10% by weight The average water removal rate is also called "average removal rate Vave (30-10)". By adjusting the drying conditions so that the removal rate V(30) and/or the average removal rate Vave(30-10) are within the above range, the When used as a polarizing film, a PVA-based resin film 7 exhibiting high polarizing performance can be obtained.

The following is not intended to limit the present invention in any way, but the reason why the high polarization performance can be exhibited by adjusting the removal speed V(30) and/or the average removal speed Vave(30-10) within the above-mentioned predetermined range is inferred as follows.

That is, it is believed that high polarizing performance will be exhibited because the crystal nucleus of PVA-based resin will start to form when the water content is 30% by weight or around 30% by weight (in the range of 30 to 10% by weight), and by Set the water removal rate V(30) and/or the average removal rate Vave(30-10) when the coating layer 6 has a moisture content around 30% by weight and/or 30% by weight within the above range, and slow Ground drying will cause the crystal nuclei to be formed in a sufficient amount. Moreover, by generating a large number of crystal nuclei in this way, the density of microcrystals can be increased, and a denser crystal structure can be formed. It is recognized that, when dyeing with dichroic dyes such as iodine, it becomes easier to form a more stable and highly directional dichroic dye near the densely existing microcrystals. -PVA-based resin complex, so it will improve the polarization performance.

On the other hand, it is believed that in a region with a water content of more than 30% by weight, the PVA-based resin is uniformly dissolved in water, and the molecular chain of the PVA-based resin is in a stable and uniform (solution) state. In fact, in the region where the moisture content exceeds 30% by weight, the formation of stable crystal nuclei above the critical size hardly occurs. When the water content is as low as about 30% by weight, the formation of crystal nuclei above the stable critical size will proceed. However, it is believed that this is because the formation of crystal nuclei and crystallization is more stable.

In this way, the crystal nucleus of the PVA-based resin It starts to produce when the water content is as low as about 30% by weight, and the formation of crystal nuclei occurs in the vicinity of the water content of 30% by weight, that is, the region with the water content of 30 to 10% by weight. In the region, it is difficult to generate stable crystal nuclei above the critical size. It is believed that this is because there is very little water as a good solvent and the mobility of the molecular chain of the PVA-based resin is excessively reduced.

The present invention does not focus on the regions where the water content exceeds 30% by weight and the water content is less than 10% by weight where no or almost no crystal nuclei is generated, but instead focuses on the water content of 30% by weight where the crystal nucleus actually occurs. The time point and/or the area with the water content of 30 to 10% by weight, and the water removal rate V(30) and/or the average removal rate Vave(30-10) of the time point and/or area are adjusted to the above The predetermined range is used as one of the features.

In this step (drying step S20), the removal rate V(30) at the time when the crystal nucleus of the PVA-based resin starts to generate a water content of 30% by weight can be adjusted to the range of 0.01 to 1.8% by weight/sec. And/or the average removal rate Vave (30-10) in the range of 30 to 10% by weight of the water content of the crystalline nucleus can also be adjusted to the range of 0.01 to 1.8% by weight/sec in the same manner. However, since the total water content range for the generation of crystal nuclei is reached, a large amount of crystal nuclei can be sufficiently produced, so it is preferable to adjust at least the average removal rate Vave (30-10) within the above range, and it is more preferable to adjust the removal rate Adjust both V(30) and the average removal rate Vave(30-10) to fall within the above range.

Make the removal rate V(30) and/or the average removal rate For the method of reducing Vave (30-10) to the upper limit of the above range, if the heat roller is used for drying, the method of lowering the surface temperature of the heat roller can be cited, and if the method is for drying by hot air, A method of reducing the temperature and/or wind speed of the hot air can be cited. Moreover, the humidity of the environment in which the drying is implemented can also be increased. From the viewpoint of productivity, it is better to increase the water removal rate as much as possible in order to intensify the drying in areas where the moisture content greatly exceeds 30% by weight. % Instantaneously reduces the removal rate, so it is easier to reduce the removal rate V(30) and/or the average removal rate Vave(30- 10) Adjust to within the above range.

In addition, when drying from the initial moisture content W1 to the final moisture content W2, if the drying is always performed under certain drying conditions, the temperature of the coating film 100 will gradually increase, and the water removal rate will tend to increase significantly from the middle of the drying process. . Therefore, in order to keep the removal rate V(30) and/or the average removal rate Vave(30-10) within the above range, during the drying step S20, the drying conditions are not always kept constant, but are slowed down midway. The drying conditions are better.

From the viewpoint of further increasing the density of the crystal nuclei of the PVA-based resin, the upper limit of the removal rate V(30) and the average removal rate Vave(30-10) is preferably 1.65 wt%/sec or less, more preferably 1.5 Weight %/sec or less. Moreover, the lower limit of the removal rate V(30) and the average removal rate Vave(30-10) is above 0.01% by weight/sec. This is because the density of crystal nuclei becomes too high when the water removal rate is too slow. Will make the polarizing film described later The dyeing efficiency in the dyeing step of the manufacturing method is reduced. From this viewpoint and the viewpoint of the productivity of the PVA-based resin film 7, the lower limit is preferably 0.15 wt%/sec or more, and more preferably 0.5 wt%/sec or more.

Next, the method of measuring the removal rate V(30) and the average removal rate Vave(30-10) will be explained. These can be obtained by plotting the water content of the coating layer 6 with respect to the elapsed time from the drying step S20. Rate reduction curve (fit curve). As long as the measurement data (measurement points) of the moisture content are sufficiently dense, the slope [removal rate V(30)] can be accurately obtained from the differential value at the time point of the moisture content 30% by weight. However, it is difficult to obtain continuous measurement data in actual measurement, and it is often impossible to obtain sufficiently dense measurement data. Therefore, in this case, the average value of the measurement data in the predetermined range including the time point of the water content of 30% by weight is obtained as the removal rate V(30). Specifically, in this case, according to the following formula [a], the water content reduction amount between 32 and 28% by weight calculated based on the above-mentioned fitting curve (that is, 4 [weight %]) is divided by the time required for the moisture content from 32% by weight to 28% by weight [seconds] to obtain the value obtained as the removal rate V(30): removal rate V(30)=4 [wt%]/( The time required for the moisture content from 32% by weight to 28% by weight (seconds)) [a].

When obtaining the above-mentioned fitting curve, in order to accurately calculate the removal rate, the measurement data of the moisture content is obtained at intervals of about 2% by weight.

The average removal rate Vave (30-10) is also obtained in the same way as the above formula [a]. That is, according to the following formula [b], it will be based on The reduction in the moisture content between 30 and 10% by weight calculated by the above-mentioned fit curve (that is, 20 (weight%)) divided by the time required for the moisture content to change from 30% by weight to 10% by weight (seconds) The value obtained later is used as the average removal rate Vave(30-10): Average removal rate Vave(30-10)=20 [wt%]/(the time required for the moisture content from 30 wt% to 10 wt% [sec 〕) [b].

The moisture content of the coating layer 6 is based on the "IR moisture content meter: IRMA series" sold by CHINO (Co., Ltd.) and the "Fiber-type infrared moisture content meter: IM series" sold by Fujiwork (Co., Ltd.) Wait for IR moisture meter to measure. The IR moisture content meter is one that obtains the moisture content from the infrared absorption intensity derived from water. Therefore, in order to calculate the moisture content (moisture content) from this strength, it is necessary to create a standard curve that defines these correspondence relationships.

The moisture content of the film required to prepare the standard curve system is measured by the dry gravimetric method. The so-called dry weight method is to measure the weight of the PVA resin film (coating layer) [initial weight] for a film sample having a predetermined size during drying, and then perform a drying treatment at 105°C for 2 hours, and then measure The weight of the PVA-based resin film (coating layer) [weight after treatment], and the method for measuring the moisture content based on the following formula [c]: moisture content={(initial weight-weight after treatment)/initial weight}×100 [c].

The standard curve is obtained by the following method: prepare a plurality of film samples with different moisture content, measure the moisture content of these samples according to the above formula [c], and use an IR moisture content meter to measure the infrared absorption intensity derived from water , The corresponding relationship between the moisture content and infrared absorption intensity obtained Drawing. The moisture content range of the film sample used to prepare the standard curve is preferably set to be the same as or equal to or higher than the moisture content range of the coating layer 6 to be actually measured. This is because if the calibration curve is made in a range that is too narrow with respect to the measurement target range, it will cause a disadvantage that the moisture content does not match the actual moisture content due to the extrapolation approximation method. In addition, the standard curve is usually approximated by a linear expression, but a second-degree expression can also be used as necessary.

Pay attention to the following points when making a standard curve.

1) When the coating layer of the film sample used to prepare the calibration curve contains volatile components other than water (such as alcohol, etc.), the water content obtained from the above formula [c] includes the weight loss caused by the volatilization of the volatile components point. Therefore, at this time, in order to obtain the correct moisture content based on the above-mentioned formula [c], it is necessary to perform a correction after subtracting the weight loss point. It is preferable to use a film sample for preparing a calibration curve that does not contain volatile components other than water, or contains almost no volatile components other than water.

2) The film sample for preparing the calibration curve may have the same film structure as the coating film 100 which is formed on the base film to form a PVA-based resin film (coating layer) in the process of drying. At this time, the moisture content can also be measured together with the base film. However, at this time, in order to obtain the correct moisture content of the coating layer based on the above formula [c], the initial weight and the post-treatment weight must be corrected by subtracting the weight of the base film.

In addition, in the case of a film sample having the same film structure as the coating film 100, when the IR moisture content meter is used to obtain the infrared absorption intensity derived from water, the water contained in the base film can usually be ignored. It is divided into the infrared absorption that belongs to the infrared absorption of the base film, which is repeated in the infrared absorption region derived from water. This is because hydrophobic resins such as cyclic polyolefin resins, chain polyolefin resins, polyethylene terephthalate resins, etc. are usually used for the base film, so the water content is so small that it can be ignored. degree. Moreover, absorption bands other than water are inherent absorption bands in the resin, and are usually constant during the drying process, so absorption bands other than water can be ignored.

3) Since the IR moisture meter is one that obtains the moisture content from the infrared absorption intensity derived from water, for example, when the thickness of the manufactured PVA resin film is changed, even if the moisture content per unit volume is the same, only the thickness is different. , Will also change the infrared absorption intensity. Therefore, when changing the thickness of the manufactured PVA-based resin film, it is necessary to create a calibration curve every time. In addition, when the base film has scattering, absorption, etc., in the infrared absorption region derived from water, the infrared absorption intensity varies depending on the thickness of the base film. Therefore, when changing the thickness of the base film, it is also necessary to create a standard curve every time.

The initial moisture content W1 of the coating layer 6 (the moisture content of the coating layer 6 immediately before the drying step S20) is a value exceeding 30% by weight. When the initial moisture content W1 exceeds 30% by weight, the aqueous solution containing the PVA-based resin becomes a uniform solution, and it is possible to prevent unexpected crystallization before the drying step S20. Furthermore, in order to obtain the removal rate V(30) based on the above-mentioned formula [a], the initial moisture content W1 is preferably 32% by weight or more, and more preferably more than 32% by weight. On the other hand, from the viewpoint of handleability when applying an aqueous solution containing a PVA-based resin, the initial moisture content W1 is preferably 40% by weight or more, and more preferably 50% by weight or more.

In order to obtain the removal rate V(30) based on the above formula [a], the final moisture content W2 (the moisture content at the end of the drying step S20) of the coating layer 6 is preferably 28% by weight or less, more preferably less than 28% by weight. weight%. Furthermore, in order to obtain the average removal rate Vave (30-10) based on the above formula [b], the final moisture content W2 is more preferably 10% by weight or less, and particularly preferably less than 10% by weight. On the other hand, from the viewpoint of stability and strength of the PVA-based resin film (PVA-based resin layer) 7 obtained through the drying step S20, the final moisture content W2 is preferably 20% by weight or less, more preferably 10% by weight Hereinafter, it is more preferably 6% by weight or less.

The thickness of the PVA-based resin film (PVA-based resin layer) 7 in the laminated film 200 is preferably 3 to 30 μm, more preferably 5 to 20 μm. As long as it is a PVA-based resin film 7 having a thickness within this range, a polarizing film that has good dyeability of the dichroic dye and excellent polarization performance, and is sufficiently thin (for example, a thickness of 10 μm or less) can be obtained.

<The manufacturing method of polarizing film and polarizing plate>

The manufacturing method of the polarizing film of the present invention uses the PVA-based resin film obtained by the above-mentioned manufacturing method of the PVA-based resin film of the present invention as a raw film to manufacture a polarizing film. According to the manufacturing method of this polarizing film, a polarizing film with high polarization performance can be obtained.

The PVA-based resin film as the raw material film may be the PVA-based resin film 7 supported by the base film 30 (that is, the laminated film 200), or may be a separate PVA-based resin film 7 not supported by the base film 30.

If a method of manufacturing a polarizing film supported by a base film from the laminated film 200 is cited, referring to Figure 4, the manufacturing method may include the following steps: (1) Stretching the laminated film to obtain a stretched film S30; (2) ) Dyeing the PVA-based resin film (PVA-based resin layer) of the stretched film with a dichroic dye to form a polarizing film (polarizer layer), thereby obtaining a dyeing step S40 of a polarizing laminated film. The polarizing laminated film is a laminated film having a base film and a polarizing film laminated on the base film (that is, a polarizing film supported by the base film).

Referring to Figure 4, if the polarizing laminated film is supplied to the following steps, a polarizing laminated film with a protective film can be obtained: (3) The first protective film is laminated on the polarizing film of the polarizing laminated film to obtain The first bonding step S50 of the polarizing laminated film with a protective film.

Referring to Figure 4, if the polarizing laminated film with protective film is supplied to the following steps, a polarizing plate with a protective film on one side can be obtained: (4) The polarizing laminated film with protective film is peeled off to remove the base film , And obtain the peeling step S60 of a polarizing plate with a protective film on one side; if the aforementioned polarizing plate with a protective film on one side is further supplied to the following steps, a polarizing plate with a protective film on both sides can be obtained: (5) In The second bonding step S70 of bonding the second protection film on the polarizing film surface of the polarizing plate with a protective film on one side.

In addition, in this specification, a thin film laminate containing a polarizing film and not containing a base film is referred to as a "polarizing plate".

(1) Extension step S30

Referring to Fig. 5, in this step, the laminated film 200 including the base film 30 and the PVA-based resin film 7 is stretched to obtain the stretched base film 30' and the step of stretching the film 300 of the PVA-based resin film 7'. The stretching process is usually one-axis stretching. The laminated film 200 may be one in which the PVA-based resin film 7 is layered on the double area of the base film 30.

The stretching ratio of the laminated film 200 can be appropriately selected depending on the desired polarization characteristics, but it is preferably more than 5 times and 17 times or less, and more preferably more than 5 times and 8 times or less relative to the original length of the laminated film 200. When the stretching ratio is 5 times or less, since the PVA-based resin film 7'is not sufficiently oriented, the polarization factor of the polarizing film may not be sufficiently increased. On the other hand, when the stretching magnification exceeds 17 times, film breakage will easily occur during stretching, and the thickness of the stretched film 300 will become thinner than necessary, and the workability and handling properties in subsequent steps will be reduced. Yu.

The stretching process is not limited to one-stage stretching, and may be divided into multiple stages. At this time, all of the multi-stage stretching treatment can be continuously performed before the dyeing step S40, or the stretching treatment after the second stage and the dyeing treatment and/or cross-linking treatment in the dyeing step S40 can be performed simultaneously. In this manner, when the stretching treatment is performed in multiple stages, it is preferable to perform the stretching treatment so that the total of all stages of the stretching treatment becomes a stretching magnification of more than 5 times.

In addition to the longitudinal extension extending in the length direction of the film (film conveying direction), the stretching treatment may also be horizontal extension or diagonal extension extending in the width direction of the film. Examples of the longitudinal extension method include inter-roll extension using rollers, compression extension, and extension using a fixture (clamp), and the lateral extension method includes a tenter method. The extension treatment can be either wet extension method or dry extension method, but dry extension is used In the method, the extension temperature can be selected from a wide range, so it is better.

The stretching temperature is set to a temperature higher than the temperature at which fluidity is expressed to the extent that the entire PVA-based resin film 7 and the base film 30 can be stretched, and is preferably − The range of 30°C to +30°C, more preferably the range of -30°C to +5°C, and still more preferably the range of -25°C to +0°C. When the base film 30 includes a plurality of resin layers, the above-mentioned phase transition temperature means the highest phase transition temperature among the phase transition temperatures shown by the plurality of resin layers.

When the stretching temperature is lower than -30°C, which is the phase transition temperature, it may be difficult to achieve a high-magnification stretching of more than 5 times, or the fluidity of the base film 30 may be too low, and the stretching process tends to be difficult. When the stretching temperature exceeds +30° C. which is the phase transition temperature, the fluidity of the base film 30 may become too high and stretching tends to be difficult. Since it is easier to achieve a high stretching magnification of more than 5 times, the stretching temperature is within the above range, and more preferably 120°C or higher.

The heating method of the laminated film 200 in the stretching process includes: zone heating method (for example, heating in the stretching area of a heating furnace where hot air is blown in and adjusted to a predetermined temperature); when a roll is used for stretching, A method of heating the roller itself; a heater heating method (a method in which an infrared heater, a halogen heater, a flat heater, etc. are arranged above and below the laminated film 200 and heated by radiant heat), etc. In the stretching method between rolls, the zone heating method is preferred from the viewpoint of the uniformity of the stretching temperature.

In addition, the so-called elongation temperature refers to the ambient temperature of the gas in the area (for example, in the heating furnace) when the zone heating method is used. In the heater heating method, as long as the heating is performed in the furnace, it still means the temperature in the furnace. gas Ambient temperature. Moreover, when the method of heating the roll itself is used, it means the surface temperature of the roll.

Before the stretching step S30, a preheating step of preheating the laminated film 200 may be provided. The preheating method can use the same method as the heating method in the extension treatment. The preheating temperature is preferably in the range of -50°C to ±0°C of the extension temperature, more preferably in the range of -40°C to -10°C of the extension temperature.

Moreover, after the stretching process in the stretching step S30, a heat-fixing process step may be provided. The heat fixation process is a process of performing heat treatment at a temperature higher than the crystallization temperature while maintaining the tight state while holding the end of the stretched film 300 with a clamp. This heat fixing treatment promotes the crystallization of the PVA-based resin film 7'. The temperature of the heat fixing treatment is preferably in the range of -0°C to -80°C of the extension temperature, more preferably in the range of -0°C to -50°C of the extension temperature.

(2) Dyeing step S40

Referring to Fig. 6, this step is a step of dyeing the PVA-based resin film 7'of the stretched film 300 with a dichroic dye and adsorbing and aligning it to form a polarizing film (polarizer layer) 5. After this step, a polarizing laminated film 400 with a polarizing film 5 layered on one side or two areas of the base film 30' is obtained.

Specific examples of dichroic dyes include iodine or dichroic organic dyes. Specific examples of dichroic organic dyes include, for example: Red BR, Red LR, Red R, Pink LB, Rubin BL, Bordeaux GS, Sky Blue LG, Lemon Yellow, Blue BR, Blue 2R, Navy RY, Green LG, Violet LB , Violet B, Black H, Black B, Black GSP, Yellow 3G, Yellow R, Orange LR, Orange 3R, Scarlet GL, Scarlet KGL, Congo Red, Brilliant Violet BK, Supra Blue G, Supra Blue GL, Supra Orange GL, Direct Sky Blue, Direct Fast Orange S, Fast Black. The dichroic dye may be used alone or in combination of two or more.

The dyeing step S40 can usually be performed by immersing the stretched film 300 in a liquid (dyeing bath) containing a dichroic dye. For the dyeing bath, a solution in which the above-mentioned dichroic dye is dissolved in a solvent can be used. The solvent of the dyeing solution is generally water, but an organic solvent compatible with water can also be added. The concentration of the dichroic pigment in the dyeing bath is preferably 0.01 to 10% by weight, more preferably 0.02 to 7% by weight.

When iodine is used as a dichroic pigment, since the dyeing efficiency can be improved, it is preferable to add iodide to a dyeing bath containing iodine. Examples of iodides include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. The concentration of the iodide in the dyeing bath is preferably 0.01 to 20% by weight. Among the iodides, potassium iodide is preferably added. When potassium iodide is added, the ratio of iodine to potassium iodide is expressed by weight ratio, preferably 1:5 to 1:100, more preferably 1:6 to 1:80. The temperature of the dyeing bath is preferably 10 to 60°C, more preferably 20 to 40°C.

In addition, the dyeing step S40 may be carried out before the stretching step S30, or these steps may be carried out at the same time. However, it is preferable to perform at least the layered film 200 in such a way that the dichroic dye adsorbed to the PVA-based resin film can be well oriented. After a certain degree of extension treatment, the dyeing step S40 is performed.

The dyeing step S40 may include successive dyeing treatments. The cross-linking process steps. The cross-linking treatment can be performed by immersing the dyed stretched film in a liquid (cross-linking bath) containing a cross-linking agent. Examples of the crosslinking agent include boron compounds such as boric acid and borax; glyoxal and glutaraldehyde. The crosslinking agent may be used alone or in combination of two or more. As the crosslinking bath, a solution in which the crosslinking agent is dissolved in a solvent can be used. The solvent can be water, or it can contain an organic solvent compatible with water. The concentration of the crosslinking agent in the crosslinking bath is preferably 1 to 20% by weight, more preferably 6 to 15% by weight.

The cross-linking bath may further contain iodide. By adding iodide, the in-plane polarization characteristics of the polarizing film 5 can be made more uniform. Specific examples of iodide are the same as described above. The concentration of the iodide in the crosslinking bath is preferably 0.05 to 15% by weight, more preferably 0.5 to 8% by weight. The temperature of the crosslinking bath is preferably 10 to 90°C.

In addition, since the crosslinking agent is blended in the dyeing bath, the crosslinking treatment can also be performed simultaneously with the dyeing treatment. Furthermore, two or more types of crosslinking baths with different compositions may be used, and the treatment of immersing in the crosslinking bath may be performed twice or more.

After the dyeing step S40, a washing step and a drying step are preferably performed. The washing step usually includes a water washing step. The water washing treatment can be performed by immersing the film after dyeing treatment or crosslinking treatment in pure water such as ion exchange water or distilled water. The water washing temperature is usually 3 to 50°C, preferably 4 to 20°C. The washing step may be a combination of a water washing step and a washing step using an iodide solution. In the drying step performed after the washing step, any appropriate method such as natural drying, air blowing drying, and heat drying can be adopted. For example, during heating and drying, the drying temperature is usually 20 to 95°C.

The thickness of the polarizing film 5 of the polarizing laminated film 400 is, for example, 30 μm or less, and more preferably 20 μm or less, but from the viewpoint of thinning the polarizing plate, it is preferably 10 μm or less, more preferably 7 μm or less. By setting the thickness of the polarizing film 5 to 10 μm or less, a thin polarizing laminated film 400 can be formed. The thickness of the polarizing film 5 is usually 2 μm or more.

(3) The first bonding step S50

Referring to Fig. 7, this step is performed by applying the first adhesive layer 15 on the polarizing film 5 of the polarizing laminated film 400, that is, on the side opposite to the base film 30' side of the polarizing film 5 The first protective film 10 is combined to obtain a polarizing laminated film 500 with a protective film.

In addition, when the polarizing laminated film 400 has the polarizing film 5 on both sides of the base film 30', the first protective film 10 is usually attached to the polarizing film 5 on both sides, respectively. At this time, the first protective films 10 may be the same kind of protective films or different kinds of protective films.

The adhesive forming the first adhesive layer 15 may be an active energy ray-curable adhesive containing a curable compound that is cured by irradiating active energy rays such as ultraviolet rays, visible light, electron beams, X-rays, etc. (preferably, an ultraviolet curing agent). Adhesives), and water-based adhesives that dissolve or disperse adhesive components such as polyvinyl alcohol-based resins in water.

In terms of exhibiting good adhesiveness, the active energy ray-curable adhesive composition may preferably be an active energy ray-curable adhesive composition containing a cationically polymerizable curable compound and/or a radically polymerizable curable compound. The active energy ray-curable adhesive may further contain cationic polymerization to initiate the curing reaction of the above-mentioned curable compound. Initiator and/or radical polymerization initiator.

Examples of cationically polymerizable curable compounds include epoxy compounds (compounds with one or more epoxy groups in the molecule), oxetane compounds (with one or more epoxy groups in the molecule) Oxetane ring compound), or a combination of these. Examples of radically polymerizable curable compounds include (meth)acrylic compounds (compounds having one or more (meth)acryloyl groups or (meth)acryloyloxy groups in the molecule) , Other vinyl compounds with radically polymerizable double bonds, or a combination of these. A cationically polymerizable curable compound and a radically polymerizable curable compound can also be used in combination.

Active energy ray-curable adhesives may contain cationic polymerization accelerators, ion traps, antioxidants, chain transfer agents, tackifiers, thermoplastic resins, fillers, flow regulators, plasticizers, and defoamers as needed. , Antistatic agent, leveling agent, solvent and other additives.

When bonding the first protective film 10 using an active energy ray curable adhesive, the first protective film 10 is laminated on the polarizing film 5 through the active energy ray curable adhesive which becomes the first adhesive layer 15, and then irradiated with ultraviolet rays. , Visible light, electron beam, X-ray active energy rays to harden the adhesive layer. Among them, ultraviolet light is preferred. In this case, low-pressure mercury lamps, medium-pressure mercury lamps, high-pressure mercury lamps, ultra-high-pressure mercury lamps, fluorescent lamps, black light lamps, microwave-excited mercury lamps, metal halide lamps, etc. can be used as the light source. When using a water-based adhesive, after laminating the first protective film 10 on the polarizing film 5 via the water-based adhesive, it is only necessary to heat and dry it.

When bonding the first protective film 10 to the polarizing film 5, in order to improve To improve the adhesion with the polarizing film 5, the bonding surface of the first protective film 10 and/or the polarizing film 5 can be subjected to plasma treatment, corona treatment, ultraviolet radiation treatment, flame treatment, and saponification treatment. Treatment (easy to follow-up treatment), among which plasma treatment, corona treatment or saponification treatment is preferred.

The first protective film 10 may be a film containing a translucent (preferably optically transparent) thermoplastic resin, for example, a chain polyolefin resin (polypropylene resin, etc.), a cyclic polyolefin resin (Norbornene resins, etc.) polyolefin resins; cellulose ester resins such as cellulose triacetate and cellulose diacetate; polyester resins; polycarbonate resins; (methyl) Acrylic resin; polystyrene resin; or films such as mixtures and copolymers of these.

The first protective film 10 may also be a protective film having both optical functions such as a retardation film and a brightness enhancement film. For example, by stretching a film containing the above-mentioned thermoplastic resin (uniaxial stretching or biaxial stretching, etc.), forming a liquid crystal layer on the film, etc., a retardation film to which an arbitrary retardation value is given can be formed.

As the chain polyolefin resin, in addition to homopolymers of chain olefins such as polyethylene resins and polypropylene resins, copolymers containing two or more chain olefins can be cited.

Cyclic polyolefin resin is a general term for resins polymerized with cyclic olefin as a polymerization unit. Specific examples of cyclic polyolefin resins include: ring-opening (co)polymers of cyclic olefins, addition polymers of cyclic olefins, copolymers of cyclic olefins and chain olefins such as ethylene and propylene (Represented by random copolymers), and those modified by unsaturated carboxylic acids and their derivatives Graft polymers, and hydrogenated products of these, etc. Among them, it is preferable to use a norbornene-based resin using a norbornene-based monomer such as a norbornene-based monomer and a polycyclic norbornene-based monomer as a cyclic olefin.

Cellulose ester resin is an ester of cellulose and fatty acid. Specific examples of the cellulose ester resin include cellulose triacetate, cellulose diacetate, cellulose tripropionate, and cellulose dipropionate. Moreover, these copolymers and those in which a part of the hydroxyl group is modified by other substituents can also be used. Among them, cellulose triacetate (triacetyl cellulose: TAC) is particularly preferred.

The polyester resin is a resin other than the above-mentioned cellulose ester resin having an ester bond, and generally includes a polycondensate of a polycarboxylic acid or its derivative and a polyhydric alcohol. As the polycarboxylic acid or its derivative, dicarboxylic acid or its derivative can be used, and examples thereof include terephthalic acid, isophthalic acid, dimethyl terephthalate, and dimethyl naphthalene dicarboxylate. As the polyol, diols can be used, such as ethylene glycol, propylene glycol, butylene glycol, neopentyl glycol, cyclohexane dimethanol, and the like.

Specific examples of polyester resins include: polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, and polytrimethylene terephthalate Esters, poly(propylene naphthalate), poly(cyclohexane dimethyl terephthalate), poly(cyclohexane dimethyl naphthalate).

The polycarbonate resin contains a polymer in which monomer units are bonded via a carbonate group. The polycarbonate resin may also be a resin called modified polycarbonate, copolymerized polycarbonate, etc., with a modified polymer skeleton.

The (meth)acrylic resin is a resin whose main constituent monomer is a compound having a (meth)acryloyl group. Specific examples of (meth)acrylic resins include, for example, poly(meth)acrylate such as polymethyl methacrylate; methyl methacrylate-(meth)acrylic acid copolymer; methyl methacrylate-( Meth)acrylate copolymer; methyl methacrylate-acrylate-(meth)acrylic acid copolymer; methyl (meth)acrylate-styrene copolymer (MS resin, etc.); with methyl methacrylate Copolymers with alicyclic hydrocarbon-based compounds (for example, methyl methacrylate-cyclohexyl methacrylate copolymer, methyl methacrylate-norbornyl (meth)acrylate copolymer, etc.). It is preferable to use a polymer mainly composed of poly(meth)acrylic acid C _1-6 alkyl esters such as polymethyl (meth)acrylate, and it is more preferable to use a polymer mainly composed of methyl methacrylate (50 To 100% by weight, preferably 70 to 100% by weight) of methyl methacrylate resin.

In addition, the description of each of the thermoplastic resins shown above is also applicable to the thermoplastic resin constituting the base film 30.

On the surface of the first protective film 10 opposite to the polarizing film 5, a surface treatment layer (coating layer) such as a hardened coating, an anti-glare layer, an anti-reflection layer, an anti-static layer, and an anti-fouling layer can also be formed. In addition, the first protective film 10 may contain one or more additives such as a smoothing agent, a plasticizer, a dispersant, a heat stabilizer, an ultraviolet absorber, an infrared absorber, an antistatic agent, and an antioxidant.

From the viewpoint of making the polarizing plate thinner, the thickness of the first protective film 10 is preferably 90 μm or less, more preferably 50 μm or less, and still more preferably 30 μm or less. From the viewpoint of strength and handling properties, the thickness of the first protective film 10 is usually 5 μm or more.

(4) Peeling step S60

Referring to Fig. 8, this step is a step of peeling and removing the base film 30' from the polarizing laminated film 500 with a protective film to obtain a polarizing plate 1 with a protective film on one side. The polarizing laminated film 400 has the polarizing film 5 on both sides of the base film 30', and when the two polarizing films 5 are bonded to the first protective film 10, by the peeling step S60, one polarizing film can be obtained. The laminated film 400 obtained two polarizing plates 1 with a protective film on one side.

The method of peeling and removing the base film 30' is not particularly limited, and it can be peeled by the same method as the peeling step of the separator (peeling film) usually performed on the polarizing plate with adhesive. The base film 30' may be peeled immediately after the first bonding step S50, or may be temporarily wound into a reel shape after the first bonding step S50, and then peeled off while being rolled out in a subsequent step.

(5) The second bonding step S70

Referring to Figure 9, this step is on the polarizing film 5 of the polarizing plate 1 with a protective film on one side, that is, on the opposite side of the first protective film 10 bonded in the first bonding step S50, and then The step of bonding the second protective film 20 through the second adhesive layer 25 to obtain the polarizing plate 2 with a protective film on both sides. The bonding of the second protective film 20 via the second adhesive layer 25 can be performed in the same manner as the bonding of the first protective film 10. The configuration and material system of the second protective film 20 and the second adhesive layer 5 refer to the description of the first protective film 10 and the first adhesive layer 15, respectively.

Above, although the method of manufacturing polarizing film (polarizing laminated film, polarizing laminated film with protective film) and polarizing plate using the PVA-based resin film (laminated film) supported by the base film is described, the use is not subject to Substrate In the case of a separate PVA-based resin film supported by the film, a polarizing film can also be manufactured in the same manner by performing stretching treatment and dyeing treatment. Furthermore, by bonding the protective film on one side or both sides of the polarizing film through the adhesive layer in the same manner, a polarizing plate with a protective film on one side or a polarizing plate with a protective film on both sides can be manufactured.

On the polarizing film 5 in the polarizing plate 1 with a protective film on one side shown in Figure 1, or the first protective film 10 or the second protective film in the polarizing plate 2 with a protective film on both sides shown in Figure 2 On the film 20, an adhesive layer for attaching the polarizing plate to other components (for example, a liquid crystal cell when applied to a liquid crystal display device) can also be laminated. The adhesive that forms the adhesive layer usually contains (meth)acrylic resin, styrene resin, polysiloxane resin, etc. as a base polymer, and is added with isocyanate compounds, epoxy compounds, and aziridines. The adhesive composition of the crosslinking agent of the compound. It may also be an adhesive layer that contains fine particles and expresses light scattering properties. The thickness of the adhesive layer is usually 1 to 40 μm, preferably 3 to 25 μm.

The polarizing plate 1 with a protective film on one side and the polarizing plate 2 with a protective film on both sides may further include the first and/or second protective films 10 and 20 and other optical layers laminated on the polarizing film 5. Other optical layers include: reflective polarizing film that penetrates certain polarized light and reflects polarized light showing the opposite properties of the polarized light; film with anti-glare function with unevenness on the surface; surface resistance Reflective film; reflective film with reflective function on the surface; semi-transmissive reflective film with both reflective and penetrating functions; viewing angle compensation film, etc.

(Example)

Hereinafter, examples and comparative examples are listed to explain the present invention more specifically, but the present invention is not limited to these examples. The measurement methods of the water removal rate V (30) and the average removal rate Vave (30-10) in the drying step of each of the Examples and Comparative Examples are basically based on the above description, but are specifically as follows.

[Determination of removal speed V(30) and average removal speed Vave(30-10)]

The removal rate V(30) and the average removal rate Vave(30-10) can be obtained by plotting the moisture content of the coating layer with respect to the elapsed time from the beginning of the drying step (fitting curve), Calculated according to the above-mentioned formulas [a] and [b], respectively. The measurement data of the moisture content is obtained at intervals of 2% by weight. The moisture content of the coating layer was measured using an IR moisture meter (infrared multi-component meter) "IRMA-5162S" manufactured by CHINO (Co., Ltd.).

The standard curve is obtained by the following method: prepare 10 film samples with different moisture content, measure the moisture content of these samples according to the above formula [c] (dry weight method), and use the above IR moisture content meter "IRMA -5162S" is used to measure the infrared absorption intensity derived from water, and the corresponding relationship between the moisture content and the infrared absorption intensity is plotted, and the result is obtained by linear approximation. The acquisition range of the standard curve is set to a range of 40 to 3% by weight of water content. The film sample used a coating film having a coating layer formed by coating an aqueous solution containing polyvinyl alcohol (PVA) on the same base film as the user in each of the Examples and Comparative Examples. This aqueous solution contains only water as a volatile component.

Determine the moisture content according to the above formula [c] (dry weight method) At the time, the following measurements (1), (2) and (3) were carried out in sequence for 10 film samples, and the moisture content measured by the dry gravimetric method was calculated according to the following formula [c']: water content Rate={[Measured value of (1)-Measured value of (2)]/[Measured value of (1)-Measured value of (3)]}×100 [c']. This formula [c'] has the same meaning as the above formula [c].

(1) Measure the weight of the coating film of the thin film sample (before drying treatment), (2) Measure the weight of the coating film after drying treatment at 105℃×2 hours, (3) Peel off the coating layer, and measure the residual The weight of the base film.

In addition, the final moisture content W2 (the moisture content of the coating layer (PVA film) at the end of the drying step) in each of the examples and comparative examples is measured by the above-mentioned IR moisture content meter "IRMA-5162S" It is calculated by substituting the value into the linear expression of the above-mentioned standard curve.

<Example 1>

(1) Steps for forming the primer layer

PVA powder ("Z-200" manufactured by Nippon Synthetic Chemical Industry Co., Ltd., with an average degree of polymerization of 1100 and a degree of saponification of 99.5 mol%) was dissolved in hot water at 95°C to prepare a PVA with a concentration of 3% by weight Aqueous solution. In the resulting aqueous solution, a crosslinking agent ("Sumirez Resin 650" manufactured by Taoka Chemical Industry Co., Ltd.) was mixed at a ratio of 5 parts by weight to 6 parts by weight of the PVA powder to obtain a coating for forming an undercoat layer liquid.

Next, prepare a substrate film with a thickness of 90μm. Stretched polypropylene (PP) film (melting point: 163°C), and corona treatment is applied to one side of the corona treated surface, and then the corona treated surface is coated with a small-diameter gravure coater. The liquid was applied and dried at 80°C for 10 minutes, thereby forming a primer layer having a thickness of 0.2 μm.

(2) Production of laminated film (coating step, drying step)

PVA powder ("PVA124" manufactured by Kuraray (Co., Ltd.), average degree of polymerization of 2400, degree of saponification of 98.0 to 99.0 mol%) was dissolved in 95°C hot water to prepare a PVA aqueous solution with a concentration of 7.5% by weight. Use a die coater to coat the surface of the undercoat layer of the substrate film having the undercoat layer prepared in (1) above, and apply the above-mentioned concentration of 7.5% by weight PVA aqueous solution to form a coating layer with a thickness of 130 μm (coating step) .

Then, the coating layer was dried by blowing hot air at 70°C (drying step). At this time, while monitoring the moisture content during drying with the above IR moisture content meter "IRMA-5162S" (as described above, the measurement data is obtained at intervals of 2% by weight of moisture content), while changing the wind speed of the hot air to increase the removal rate V(30) is regulated so that it becomes 1.30 wt%/sec. Then, the drying is continued while adjusting the wind speed of the hot air so that the average removal rate Vave (30-10) becomes 1.35 wt%/sec, and the drying step is ended when the final moisture content W2 reaches 4.86 wt%, and the Laminated film composed of base film/undercoat/PVA film (PVA layer). The thickness of the PVA film is 9.2 μm.

(3) Fabrication of stretched film (stretching step)

For the laminated film produced in (2) above, a floating longitudinal uniaxial stretching device was used, and the free end uniaxial stretching was carried out at 160°C by 5.3 times, and the stretching was obtained. membrane. The thickness of the stretched PVA film was 5.1 μm.

(4) Production of polarizing laminated film (dyeing step)

The stretched film produced in (3) above is immersed in a 30°C dyeing aqueous solution containing iodine and potassium iodide (0.6 parts by weight of iodine and 10.0 parts by weight of potassium iodide per 100 parts by weight of water) for about 180 seconds, and the PVA film is dyed After that, the excess dye solution was washed away with pure water at 10°C.

Next, immerse in a 78°C first crosslinking aqueous solution containing boric acid (containing 10.4 parts by weight of boric acid per 100 parts by weight of water) for 120 seconds, and then immerse in a 70°C second crosslinking aqueous solution containing boric acid and potassium iodide (per 100 parts by weight of water). (5.0 parts by weight of boric acid and 12.0 parts by weight of potassium iodide) are contained in the water of parts by weight for 60 seconds, and the crosslinking treatment is performed. Then, it was immersed in pure water at 10°C for about 10 seconds, and immediately after that, the water adhering to the surface was removed with a blower to obtain a polarizing laminated film containing a polarizing film.

(5) Production of polarizing plate with protective film on one side (bonding step, peeling step)

On the polarizing film of the polarizing laminated film produced in (4) above, a protective film [including three Transparent protective film of acetyl cellulose (TAC) ("KC-2UAW" manufactured by Konica Minolta Opto (Co., Ltd.))]. Next, ultraviolet rays are irradiated with a high-pressure mercury lamp to harden the adhesive layer to obtain a polarizing laminated film with a protective film (first bonding step). Then, the base film is peeled and removed from the obtained polarizing laminated film with a protective film to obtain a polarizing plate with a protective film on one side (peeling step).

(6) Measurement of polarization factor

Using a spectroluminescence factor meter ("V7100" manufactured by JASCO Corporation) on the obtained polarizing plate with a protective film on one side, the luminescence factor correction monomer transmittance Ty and the luminescence factor correction polarization factor Py were measured. During the measurement, a polarizing plate sample with a protective film on one side was mounted so that incident light was irradiated on the side of the polarizing film. The measurement results of Ty and Py are shown in Table 1. Polarization performance is good.

<Examples 2 to 12>

Except that by adjusting the wind speed of the hot air, the removal speed V (30) and the average removal speed Vave (30-10) of the drying step are set as shown in Table 1, and the rest is made in the same manner as in Example 1 for single-sided attachment. Polarizing plate with protective film. The measurement results of Ty and Py are shown in Table 1. The polarization performance is good.

<Example 13>

The drying step was performed in the same manner as in Example 1 to obtain a laminate film having a final moisture content W2 of the PVA film of 4.86 wt%. After the laminated film was allowed to stand for several hours in an environment of 25° C. 55% RH, additional drying was performed while blowing hot air at 80° C. until the moisture content reached 1.05% by weight. Then, the stretching step, the dyeing step, the bonding step, and the peeling step were performed in the same manner as in Example 1, to obtain a polarizing plate with a protective film on one side.

The measurement results of Ty and Py are shown in Table 1. Even if additional drying is performed, the polarization performance remains the same as in Example 1, and the system remains good. It can be confirmed that the adjustment of the removal rate V(30) and/or the average removal rate Vave(30-10) is important for the improvement of the polarization performance, and the additional drying after the drying step and the decrease in the moisture content caused by the drying Does not affect the polarization performance.

<Comparative Examples 1 to 2>

By adjusting the wind speed of the hot air, the removal speed V (30) and the average removal speed Vave (30-10) of the drying step are set as shown in Table 1, and the rest is made in the same manner as in Example 1. Polarizing plate with protective film. The measurement results of Ty and Py are shown in Table 1. Compared with Example 1, the polarization performance is inferior.

<Comparative Example 3>

The drying step was performed in the same manner as in Comparative Example 2, and a laminated film having a final moisture content W2 of 4.05% by weight of the PVA film was obtained. After the laminated film was allowed to stand for several hours in an environment of 25° C. 55% RH, hot air at 80° C. was further blown while additional drying was performed until the moisture content reached 1.05% by weight. Then, the stretching step, the dyeing step, the bonding step, and the peeling step were performed in the same manner as in Comparative Example 2 to obtain a polarizing plate with a protective film on one side.

The measurement results of Ty and Py are shown in Table 1. Even if additional drying was performed, the polarization performance was the same as that of Comparative Example 2 without change. It can be confirmed that the adjustment of the removal rate V (30) and/or the average removal rate Vave (30-10) is important for improving the polarization performance, and the additional drying after the drying step and the moisture content caused by the drying The reduction does not affect the polarization performance.

<Comparative Example 4>

The drying step was performed in the same manner as in Comparative Example 3, followed by additional drying to obtain a laminated film with a moisture content of 1.05% by weight of the PVA film, and then the laminated film was placed in an environment of 25°C and 70%RH. Thereby, the moisture absorption treatment (re-humidity treatment) to increase the water content of the PVA film to 5.05% by weight is performed. Then, the extension step and dyeing were performed in the same manner as in Comparative Example 3. Steps, bonding steps and peeling steps to obtain a polarizing plate with a protective film on one side.

The measurement results of Ty and Py are shown in Table 1. Even if additional drying and moisture absorption treatments (re-moisture conditioning treatments) are implemented, the polarization performance remains the same as that of Comparative Example 2 without any change. It can be confirmed that the adjustment of the removal rate V (30) and/or the average removal rate Vave (30-10) is important for the improvement of polarization performance, and the additional drying and moisture absorption (humidity adjustment) after the drying step Does not affect the polarization performance.

In Table 1, when additional processing is performed after the drying step, the processing content is described in the "additional processing" column. The "final moisture content W2" column in Table 1 indicates the moisture content of the PVA film at the end of the drying step. When additional processing is performed, brackets indicate the additional processing in the "additional processing" column Moisture content.

Moreover, in each of the Examples and Comparative Examples, the relationship between the removal speed V (30) of the drying step and the lumjnosity factor corrected polarization factor Py of the obtained polarizing plate with a protective film on one side was plotted. The graph is shown in Figure 10, and the graph is drawn from the relationship between the average removal rate Vave (30-10) of the drying step and the luminescence factor correction polarization factor Py of the obtained single-sided protective film polarizer In Figure 11. In addition, Figure 12 is a graph obtained by plotting the relationship between the luminescence factor correction monomer transmittance Ty and the luminescence factor correction polarization factor Pv of the single-sided protective film polarizer obtained in each of the Examples and Comparative Examples.

Claims (3)

A method for manufacturing a polyvinyl alcohol-based resin film includes the following steps: forming a coating layer of an aqueous solution containing a polyvinyl alcohol-based resin with a water content of more than 30% by weight on a substrate film; and A drying step for removing water from the layer; wherein, in the aforementioned drying step, the water removal rate when the water content is 30% by weight is more than 0.5% by weight/sec and 1.8% by weight/sec or less, and the water content is 30 to 10 The average removal rate of water in the range of wt% is more than 0.5 wt%/sec and 1.8 wt%/sec or less. A method for manufacturing a polarizing film, which includes the following steps: a step of obtaining a polyvinyl alcohol-based resin film by the method for manufacturing a polyvinyl alcohol-based resin film described in item 1 of the scope of patent application, and extending the aforementioned polyvinyl alcohol-based resin film The step of obtaining a stretched film and the step of obtaining a polarizing film from the aforementioned stretched film. The method of manufacturing a polarizing film as described in the second item of the scope of patent application, wherein the thickness of the polarizing film is 10 μm or less.

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