TWI617415B - Method for producing polarizing plate - Google Patents

Abstract

When the swelling process is performed by a plurality of swelling treatment tanks, the method of manufacturing the polarizing film of the present invention is such that the expansion rate in the width direction of the film in the first swelling treatment tank is the ratio of the saturation expansion rate at its processing temperature and composition 90% or less, and the absolute value of the difference between the expansion rate in the first swelling treatment tank and the expansion rate in the width direction of the film in the subsequent second swelling processing tank is adjusted within 2 points so that each processing temperature and processing time are adjusted. When the swelling treatment is applied through a swelling treatment tank, the expansion rate in the width direction of the film in the swelling treatment tank is set to be less than 90% of the saturation expansion rate at the processing temperature and composition, and the swelling rate in the swelling treatment tank The absolute value of the difference between the expansion rate in the width direction of the film in the subsequent dyeing treatment tank was adjusted to within 2 points, and each treatment temperature and the time to pass through the treatment tank were adjusted.

Description

Manufacturing method of polarizing film

The present invention relates to a method for manufacturing a polarizing film used in a liquid crystal display device.

Regarding polarizing films, those who have absorbed and aligned dichroic dyes to polyvinyl alcohol resin films have been used. That is, an iodine-based polarizing film using iodine as a dichroic dye and a dye-based polarizing film using dichroic dye as a dichroic dye are known. These polarizing films are usually on at least one side, preferably on both sides. A protective film such as triethyl cellulose is bonded with a protective film made of an aqueous solution of a polyvinyl alcohol resin to form a polarizing plate, and is used in LCD televisions. , LCD screens for personal computers and mobile phones.

The polarizing film is produced by subjecting a polyvinyl alcohol resin film to a swelling treatment, a dyeing treatment, an elongation treatment, a boric acid treatment (crosslinking treatment), and a washing treatment, and finally drying. This stretching process is generally performed by using a pair of rolls by changing the rotational peripheral speed of the rolls.

In recent years, in addition to the liquid crystal display devices In addition to enlargement and thinning, there is also a tendency to demand high display quality, followed by widening and thinning of polarizing films, and it is required to achieve excellent optical characteristics and in-plane uniformity across the area of large polarizing films. Manufacturing method of high-performance polarizing film. In order to manufacture a large-scale polarizing film, it is necessary to uniaxially stretch a wide-width blank film uniformly. However, when using a wide blank film, it is difficult to uniformly swell and uniaxially stretch compared with conventional blank films. Therefore, the light absorption axis of the obtained polarizing film cannot be uniform in a certain direction, and the optical properties such as polarization performance are made. Tendency to deteriorate performance. In addition, there is a tendency that the in-plane uniformity of optical characteristics such as non-uniform film thickness and transmittance deteriorates. An image display device using such a polarizing film has a problem that display unevenness occurs and the image quality is deteriorated. Therefore, development of a manufacturing method of a polarizing film having the above-mentioned requirements of a polarizing film and excellent productivity has been performed.

For example, Japanese Patent No. 4229932 (Patent Document 1) It is disclosed that by setting a plurality of swelling treatment tanks, the bath temperature of the swelling treatment tanks located at the front side of the middle is set higher than the bath temperature of the swelling treatment tanks located at the rear, so that the stain can be produced in a short time. Method for manufacturing polarizing film of suppressed high-quality polarizing film. According to this method, since the swelling amount of the resin film reaches saturation in a short time, it is not easy to swell the film in the subsequent dyeing treatment, and the stain of the polarizing film caused by this is suppressed. On the other hand, just increasing the bath temperature of the swelling treatment tank located at the front end as in Patent Document 1 may cause the film to rapidly swell due to the high processing temperature, the film thickness may become uneven, and the film may be further caused by the temperature of the subsequent swelling treatment bath. Swelling causes wrinkles of the film to deteriorate the appearance.

An object of the present invention is to provide an excellent A method for producing a polarizing film capable of suppressing unevenness in film thickness or occurrence of wrinkles, and excellent appearance in various processes of a green film made of a polyvinyl alcohol resin, particularly in a swelling process.

According to the present invention, a method for manufacturing a polarizing film is provided. Method, which is a method of manufacturing a polarizing film by sequentially applying a swelling treatment, a dyeing treatment, a boric acid treatment, and a cleaning treatment to a blank film made of a polyvinyl alcohol resin, wherein the thickness of the blank film is 10 to 60 μm. The swelling treatment is performed by a plurality of swelling treatment tanks including at least a first swelling processing tank and a second swelling processing tank sequentially arranged from the feeding side of the raw film. The film width in the first swelling processing tank is The expansion rate in the direction is less than 90% of the saturated expansion rate when immersed in the processing solution of the same temperature and composition, so that the expansion rate in the width direction of the film in the first swelling treatment tank and the film width in the second swelling processing tank The expansion rate in the direction is expressed as a percentage, and the absolute value of the difference is within 2 points. The processing temperature of the first swelling treatment tank and the second swelling processing tank and the time of passing through the processing tank are adjusted.

In this method, the processing temperature of the first swelling processing tank is preferably It is 35 ~ 45 ° C, and the processing temperature of the second swelling treatment tank is lower than that of the first swelling treatment, which is 25 ~ 35 ° C. In these methods, it is preferable to adjust the processing temperature of the first swelling processing tank and the time for passing through the processing tank so that the expansion ratio in the width direction of the film in the first swelling processing tank becomes 15 to 25%.

And, according to the present invention, the manufacture of a polarizing film is provided. Method, which is a method for manufacturing a polarizing film by sequentially applying a swelling treatment, a dyeing treatment, a boric acid treatment, and a washing treatment to a blank film made of a polyvinyl alcohol resin, and is characterized in that the thickness of the blank film is 10 to 60 μm. The above swelling treatment is performed by passing through a swelling treatment tank, and the expansion rate in the width direction of the film in the swelling treatment tank is less than 90% of the saturation expansion rate when immersed in the treatment solution of the same temperature and composition to make the swelling Adjust the processing temperature of the swelling treatment tank and the dyeing treatment tank in such a way that the absolute value of the difference between the expansion rate of the film width direction in the processing tank and the film width direction expansion rate in the dyeing processing tank is expressed as a percentage, respectively. And the time to pass through the treatment tank.

In the above method, the processing temperature of the preferred swelling treatment tank is 35 ~ 45 ℃, the processing temperature of dyeing treatment tank is lower than that of swelling treatment, which is 25 ~ 35 ℃. In these methods, it is preferable to adjust the processing temperature of the swelling treatment tank and the time to pass through the treatment tank so that the expansion ratio in the width direction of the polyvinyl alcohol-based resin film becomes 15 to 25%.

The method for manufacturing a polarizing film according to the present invention The various treatments performed in the polarizing film, especially in the swelling treatment, can suppress uneven swelling of the film, and can also suppress the occurrence of wrinkles or cracks in the film. Therefore, a polarizing film with excellent appearance can be efficiently obtained.

In the present invention, a method of manufacturing a polarizing film by sequentially applying a swelling treatment, a dyeing treatment, a boric acid treatment, and a cleaning treatment to a green film made of a polyvinyl alcohol resin is sequentially performed. After the washing process, a drying process is performed. The obtained polarizing film becomes suppressed by wrinkles and the like, so it can be suitably used for polarizing plates. Hereinafter, the present invention will be described in detail.

[Manufacturing method of polarizing film]

The polarizing film is specifically one that adsorbs and aligns a dichroic dye to a polyvinyl alcohol-based resin film. The polyvinyl alcohol-based resin used as a raw material is usually obtained by saponifying polyvinyl acetate. The saponification degree is usually 85 mol% or more, preferably 90 mol% or more, and more preferably 99 mol% or more. Examples of the polyvinyl acetate-based resin include, in addition to polyvinyl acetate, a homopolymer of vinyl acetate, and copolymers of vinyl acetate and other monomers copolymerizable therewith. Other monomers copolymerizable with vinyl acetate include, for example, unsaturated carboxylic acids, olefins, unsaturated sulfonic acids, vinyl ethers, and the like. The degree of polymerization of the polyvinyl alcohol resin is usually about 1,000 to 10,000, preferably about 1500 to 5,000.

These polyvinyl alcohol-based resins may also be modified. For example, polyvinyl aldehyde, polyvinyl acetal, and polyvinyl butyral modified with aldehydes may be used. As a material for manufacturing a polarizing film, an unstretched film (blank film) of a polyvinyl alcohol-based resin film having a thickness of about 10 to 60 μm, preferably about 12 to 55 μm is used. Industrially, it is more practical to use a film width of 1500 ~ 6000mm. The blank film is sequentially subjected to swelling treatment, dyeing treatment, boric acid treatment (cross-linking treatment), and washing treatment. The thickness of the polarizing film obtained after drying is about 5 to 25 μm.

The polarizing film is sequentially subjected to a swelling treatment, a dyeing treatment, a boric acid treatment, and a cleaning treatment to a green film made of the polyvinyl alcohol-based resin described above. It is manufactured by a physical treatment, and the film is uniaxially stretched during the boric acid treatment and, if necessary, before the boric acid treatment. Uniaxial stretching can be either wet or dry stretching. It is wet stretching when performed in boric acid treatment, swelling treatment or dyeing treatment before boric acid treatment, and dry stretching before swelling treatment. The uniaxial extension may be performed in one step or in two or more steps, but it is preferably performed in plural steps. The uniaxial stretching of the present invention can be performed by a known stretching method. As for the stretching method, there are roll-to-roll stretching in which a peripheral speed difference is generated between two rolls conveying the film, hot-roll stretching as described in Japanese Patent No. 2731813, and tenter stretching.

(Swelling treatment)

The swelling treatment swells the polyvinyl alcohol resin film in the width direction, which easily causes problems such as wrinkles on the film. Therefore, it is preferable to use a stretch roll (expanding roll), a spiral roll, and a convex continuous change roll (crown). A conventional widening device such as a roll, a bend bar, or the like, transports the film while processing the film crease. For example, it is preferable to use this in a swelling treatment tank with a high film expansion rate, as in the first swelling treatment tank when performing a swelling treatment with a plurality of processing tanks and when the swelling processing is performed with one processing tank, as described later Amplifier.

In addition, for the purpose of stabilizing the transfer of the film in the bath, an EPC device (Edge position control device) that can control the flow of water in the swelling treatment tank with water rinse, detect the end of the film, and prevent meandering, etc. Also useful.

The swelling process will cause the film to swell due to the film's transport direction. In order to prevent the film from being loosened in the conveying direction when the film is not actively stretched, it is better to adjust the speed of the conveying roller such as a roll or a guide roller. In addition, when the blank film is sequentially subjected to the swelling treatment, the dyeing treatment, and the boric acid treatment, uniaxial stretching can also be performed in the swelling treatment. In this case, the stretching ratio is about 1.2 to 3 times, preferably 1.3 to 2.5 times.

In the swelling treatment bath, in addition to pure water, In the range of 0.01 to 10% by weight, an aqueous solution of boric acid (Japanese Patent Application Laid-Open No. 10-153709), chloride (Japanese Patent Application Laid-Open No. 06-281816), inorganic salts, inorganic acids, alcohols, etc. are added.

As an embodiment of the present invention, a plural number may be used as an example. Each swelling treatment tank is swelled. In this case, the swelling treatment is performed by a plurality of swelling treatment tanks including at least a first swelling processing tank and a second swelling processing tank, which are sequentially arranged from the feeding side of the raw film. The processing temperature of the first swelling processing tank and the second swelling processing tank and the time for the film to pass are adjusted so that the expansion rate in the width direction of the film in each processing tank is within a specific range.

Here, for the expansion rate in the width direction of the film, Take note. The so-called expansion ratio of the film width refers to the percentage expansion in the width direction of the polyvinyl alcohol-based resin film generated by the swelling treatment as a percentage. Specifically, first, a long blank film made of a polyvinyl alcohol-based resin is cut into pieces having a length of 50 mm × width 50 mm, and the thin film pieces are subjected to a swelling treatment under the same processing conditions as the swelling treatment tank. Divide the change in the width direction of the film section before and after the treatment (the length in the width direction after the swelling treatment-the length in the width direction before the swelling treatment) divided by the width at the time of cutting The length in the direction of direction (50mm) and expressed as a percentage is the aforementioned expansion rate.

Film width in the first swelling treatment tank referred to in the present invention The degree of expansion in the direction of direction refers to the expansion rate when the above-mentioned film fragment is subjected to swelling treatment under the same processing conditions as those applied to the first swelling treatment tank. This expansion ratio is set by immersing the above-mentioned film fragments in the same composition as the first swelling treatment bath at the same time as when the film passes through the first swelling treatment tank in the manufacturing apparatus without applying tension to the film fragments. The amount of change in the width direction of the film fragments generated at this time in the aqueous solution at the same temperature is calculated by dividing the width direction length (50 mm) at the time of cutting, and it is expressed as a percentage.

Similarly, in the second swelling treatment tank referred to in the present invention, The expansion rate in the width direction of the film refers to the expansion when the film section subjected to the swelling treatment under the same conditions as the first swelling treatment tank is further subjected to the swelling treatment under the same processing conditions as those applied to the second swelling processing tank. rate. This expansion ratio is a film that is subjected to a swelling treatment equivalent to the first swelling treatment tank in the state that the film passes through the second swelling treatment tank at the same time in the manufacturing device without applying tension to the film fragment. The amount of change in the width direction of the film after cutting after immersion in the aqueous solution of the same composition and at the same temperature as the second swelling treatment bath (the length in the width direction after the second swelling treatment-when cutting) The length in the width direction) is calculated by dividing the length in the width direction (50 mm) at the time of cutting, and it is expressed as a percentage.

The saturation expansion ratio referred to in the present invention is Calculation of the expansion ratio in the above swelling treatment tank The ratio is the expansion ratio when the film is cut from the length of 50 mm in the longitudinal direction and 50 mm in the width direction of the film, and it is immersed in the treatment bath for 10 minutes. The saturation expansion ratio is the change in the width direction of the film break (the length in the width direction after the immersion-the length in the width direction before the immersion) divided by the immersion in the processing bath for 10 minutes without applying tension to the film break. The length in the width direction (50 mm) at the time of cutting is calculated and expressed as a percentage. The treatment bath used here is used to obtain the saturated expansion coefficient in the first swelling treatment tank, which is an aqueous solution having the same composition and set to the same temperature as the first swelling treatment bath.

According to an embodiment of the present invention, the swelling is applied in a plurality of steps. In the embodiment of the method, the time of passing through the treatment tank is adjusted so that the expansion ratio in the width direction of the first swelling treatment tank becomes 90% or less of the saturation expansion rate when immersed in the treatment solution of the same temperature and composition. . By being 90% or less of the saturation expansion rate, it is not necessary to use a huge manufacturing device when accelerating the feeding speed of the film, and the swelling treatment can be effectively performed. The expansion rate in the width direction of the film in the first swelling treatment tank is preferably 70% or more. When the expansion ratio is less than 70%, it is difficult to swell uniformly in the film surface during swelling treatment, and it is easy to cause stains or wrinkles.

Moreover, the width of the film in the first swelling treatment tank described above When the expansion rate is too small, and the expansion rate in the width direction of the film of the second swelling treatment tank becomes large, the film swelling in the second swelling treatment tank may cause deviations in the expansion rate between the film end and the center. . As a result, when the above-mentioned widening device is used in the processing tank, wrinkles may occur due to the variation in the expansion ratio. On the other hand, the film in the first swelling treatment tank is wide When the expansion rate in the degree direction is too large, the film cannot be sufficiently widened by the expansion device used inside the processing tank, and wrinkles may occur. Therefore, it is important that the absolute value of the difference between the expansion rate in the film width direction in the first swelling treatment tank and the expansion rate in the film width direction in the second treatment tank be within 2 points, respectively, as a percentage. In this way, each processing temperature of the first swelling processing tank and the second swelling processing tank and the time of passing through the processing tank are adjusted.

By making the film in the first swelling treatment tank wide The expansion rate in the degree direction and the expansion rate in the width direction of the film in the second swelling treatment tank are expressed as percentages. The absolute value of the difference is within 2 points, so that the first swelling processing tank and the second swelling processing are adjusted. Each processing temperature of the tank and the time of passing through the processing tank can suppress insufficient treatment of the first swelling processing tank, and can suppress bad rapid swelling in the second swelling processing tank. In addition, by combining the processing temperature of the first swelling treatment tank and the second swelling treatment tank and the time of passing through the treatment tank, the uneven thickness of the film during swelling can be suppressed, so the occurrence of wrinkles caused by it can also be suppressed. , Can produce polarizing films with good optical characteristics and appearance.

When applying a swelling treatment using a plurality of swelling treatment tanks, From the viewpoint of shortening the swelling processing time, the processing temperature of the first swelling processing tank is preferably higher than the processing temperature of the second swelling processing tank, and is preferably 35 to 45 ° C. In addition, the processing temperature of the second swelling processing tank is preferably 25 to 35 ° C. Furthermore, it is preferable to adjust the processing temperature of the first swelling processing tank and the time for passing through the processing tank so that the expansion ratio in the width direction of the film in the first swelling processing tank becomes 15 to 25%.

The time for the film to pass through the first swelling treatment tank is 10 ~ 60 Seconds, preferably 15-50 seconds. In addition, the time for the film to pass through the second swelling treatment tank is also 10 to 60 seconds, preferably 15 to 50 seconds.

As another embodiment of the present invention, for example, only one Swelling treatment tanks. In this embodiment, the raw film is taken out of the swelling treatment tank, and is then transferred to the dyeing treatment tank. In this case, the processing temperature in the swelling processing tank and the dyeing processing tank and the time for the film to pass are appropriately adjusted so that the expansion ratio in the width direction of the film in each processing tank is within a specific range. Specifically, the dyeing process will be described in detail below, but the expansion rate in the width direction of the film in the swelling treatment tank is set to 90% or less of the saturation expansion rate when immersed in the treatment solution of the same temperature and composition, and the swelling treatment tank The expansion rate in the width direction of the film and the expansion rate in the width direction of the film in the dyeing treatment tank are expressed as percentages, and the absolute value of the difference becomes within 2 points. The processing temperature and the temperature of the swelling treatment tank and the dyeing treatment tank are adjusted. Time to pass through the treatment tank.

(Dyeing treatment)

The dyeing treatment is performed for the purpose of adsorbing a dichroic dye to a polyvinyl alcohol-based resin film. As a dichroic dye, iodine, a water-soluble dichroic dye, etc. can be used. The processing conditions are determined within a range in which these objects can be achieved, and in a range where defects such as dissolution and devitrification of the polyvinyl alcohol resin film do not occur.

When using iodine as a dichroic pigment, the treatment bath (dyeing treatment bath) may use, for example, a concentration in a weight ratio of iodine / potassium iodide / water = about 0.003 ~ 0.2 / about 0.1 ~ 10/100 aqueous solution. Instead of this potassium iodide, other iodides such as zinc iodide may be used, or potassium iodide and other iodides may be used in combination. In addition, compounds other than iodide, such as boric acid, zinc chloride, and cobalt chloride, may be coexisted. When the boric acid is added to the processing bath, it is distinguished from the boric acid treatment described later in terms of iodine content. If the iodine content is about 0.003 parts by weight or more with respect to 100 parts by weight of water, it can be regarded as a dyeing treatment bath. The temperature of the treatment bath when the film is dipped is about 10 to 45 ° C, preferably 25 to 35 ° C. The film immersion time is 30 to 600 seconds, preferably 30 to 300 seconds.

When using a water-soluble dichroic dye as a dichroic dye, The treatment bath may use an aqueous solution having a concentration of dichroic dye / water = about 0.001 to 0.1 / 100 in a weight ratio. The processing bath may also contain dyeing aids, and examples thereof include inorganic salts such as sodium sulfate and surfactants. The dichroic dye may be used alone or in combination of two or more kinds. The temperature of the treatment bath when the film is dipped is about 20 to 80 ° C, preferably 25 to 70 ° C, and the immersion time of the film is 30 to 600 seconds, preferably 30 to 300 seconds.

When the dyeing process is used to stretch the film, the stretching process is performed by This is performed by a method in which a pair of rolls has a peripheral speed difference or the like. The cumulative elongation before dyeing is usually 1.6 to 4.5 times, preferably about 1.8 to 4 times. When the cumulative stretching ratio before the dyeing treatment is less than 1.6 times, the film breakage frequency tends to increase and the yield tends to deteriorate.

In the dyeing treatment, it is also preferable to make the same as in the swelling treatment. A conventional widening device such as an extension roller, a spiral roller, a convex continuous change roller, a curved rod roller, etc. is used to convey the film while straightening the wrinkle edge of the film.

In addition, the swelling treatment in the present invention uses only one swelling treatment. When the tank is in progress, the processing temperature in the swelling processing tank and the dyeing processing tank and the passage time of the film are appropriately adjusted so that the expansion ratio in the width direction of the film in the swelling processing tank and the dyeing processing tank is within a specific range.

The expansion rate of the film in the width direction can be the same as the first The expansion rate of the film in the swelling treatment tank in the width direction can be obtained in the same manner. The film breaks obtained by cutting the blank film can be treated in the same processing conditions as the processing tanks as described above, and the film breaks generated at this time The amount of change in the width direction and the length in the width direction at the time of cutting are calculated. The saturation expansion rate in the swelling treatment tank can also be determined by the same method as the saturation expansion rate in the first swelling treatment tank.

Swelling in the width direction of the film in the dyeing tank The expansion ratio refers to the expansion ratio of the film section subjected to the swelling treatment under the same processing conditions as the swelling processing tank, and then the treatment is performed under the same processing conditions as the dyeing processing tank, and it can be expanded with the aforementioned second swelling processing tank. The rate is obtained in the same way. Specifically, the swollen film was subjected to swelling treatment under the same conditions as the swelling treatment tank, and was immersed in the same state as the dyeing treatment bath for a period of time equal to the time when the film passed the dyeing treatment tank without applying tension to the film break. The amount of change in the width direction of the film after cutting in the aqueous solution of the same composition and temperature (the length in the width direction after the dyeing process-the width in the cutting direction) divided by the width in the cutting direction , Which is expressed as a percentage.

In the present invention, only one swelling treatment tank is used for swelling In the embodiment of the method, the width direction of the film in the swelling treatment tank is changed. The swelling rate is adjusted so that the time to pass through the treatment tank is 90% or less of the saturated swelling rate when immersed in a treatment liquid of the same temperature and composition. By being 90% or less of the saturation expansion ratio, even when the film feeding speed is accelerated, there is no need to use a huge device, and the swelling treatment can be effectively performed. The expansion rate in the width direction of the film in the swelling treatment tank is preferably 70% or more. When the swelling ratio is less than 70%, it is difficult to swell uniformly in the film surface during swelling treatment, and it is easy to cause stains or wrinkles.

And, the expansion rate in the width direction of the film in the swelling treatment tank When the expansion rate in the width direction of the film of the dyeing treatment tank is too small, the film of the dyeing treatment tank is swelled rapidly, so there may be a deviation in the expansion rate between the film end portion and the central portion. As a result, when the above-mentioned widening device is used inside the processing tank, wrinkles may occur due to the variation in the expansion ratio. On the other hand, when the expansion ratio in the width direction of the film in the swelling treatment tank is too large, the film cannot be sufficiently widened by the expansion device used inside the treatment tank, and wrinkles may occur. Therefore, it is important to adjust the swelling so that the absolute value of the difference between the expansion rate of the film width direction in the above-mentioned swelling treatment tank and the expansion rate of the film width direction in the dyeing treatment tank is less than 2 points, respectively. Each processing temperature of the processing tank and the dyeing processing tank and the time of passing through the processing tank.

In the present invention, the film in the swelling treatment tank is widened. The expansion rate in the degree direction and the expansion rate in the width direction of the film in the dyeing treatment tank are respectively expressed as percentages so that the difference is within the above range. Can suppress the insufficient treatment of the swelling treatment tank, can suppress the dyeing treatment tank Bad bad swelling. In addition, by combining the processing temperature of the swelling processing tank and the dyeing processing tank and the time of passing through the processing tank, the uneven thickness of the film at the time of swelling can be suppressed, so the occurrence of wrinkles caused by it can be suppressed, and optical characteristics and A good polarizing film.

In this case, it is preferable from the viewpoint of shortening the swelling treatment time. In order not to dissolve the film as high as possible, the processing temperature of the swelling treatment tank is preferably 35 to 45 ° C. The temperature of the dyeing treatment tank is preferably 25 to 35 ° C. Furthermore, it is preferable to adjust the processing temperature of the swelling processing tank and the time to pass through the processing tank so that the expansion ratio in the width direction of the film in the swelling processing tank becomes 15 to 25%.

(Boric acid treatment)

The boric acid treatment is performed for the purpose of water resistance or hue adjustment (to prevent blue or red tint of the film color) by crosslinking. The treatment bath uses an aqueous solution containing about 1 to 10 parts by weight with respect to 100 parts by weight of water. When the dichroic pigment used in the dyeing process is iodine, it is preferably contained 1 to 30 with respect to 100 parts by weight of water in addition to boric acid. Parts by weight of iodide. Examples of the iodide include potassium iodide, sodium iodide, and zinc iodide. In addition, compounds other than iodide, such as zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate, and the like may also coexist. In addition, the boric acid treatment for water resistance is sometimes referred to by the names of cross-linking treatment, water resistance treatment, and immobilization treatment, and the boric acid treatment for hue adjustment is sometimes referred to by the names of complementary color treatment and color correction treatment. call.

This boric acid treatment is appropriately adjusted according to its purpose. The concentration of iodide and the temperature of the treatment bath were used. The boric acid treatment for water resistance and the boric acid treatment for hue adjustment are not specifically distinguished, and are implemented under the following conditions.

Sequentially apply the blank film made of polyvinyl alcohol resin For swelling treatment, dyeing treatment, and boric acid treatment, when the purpose of boric acid treatment is to use crosslinked water resistance, the treatment bath can be a concentration of boric acid / iodide / water = 3 ~ 10/1 ~ 20/100 in weight ratio. Aqueous solution. If necessary, cross-linking agents such as glyoxal and glutaraldehyde can also be used instead of boric acid, or boric acid can be used in combination with the cross-linking agent. The processing bath temperature is usually about 50 to 70 ° C, more preferably 55 to 65 ° C, and the film immersion time is usually about 10 to 600 seconds, preferably 20 to 300 seconds, and more preferably 20 to 200 seconds. In addition, when the polyvinyl alcohol resin film stretched in advance is sequentially subjected to a dyeing treatment and a boric acid treatment, the temperature of the boric acid treatment bath is usually about 50 to 85 ° C, preferably 55 to 80 ° C.

After treatment with water-resistant boric acid, it can also be used for The hue is adjusted by boric acid. For example, when the dichroic pigment is iodine, the treatment bath may be an aqueous solution having a concentration of boric acid / iodide / water = 1 to 5/3 to 30/100 in terms of weight ratio. The temperature of the processing bath is usually about 10 to 45 ° C, and the time for immersion of the film is usually about 10 to 300 seconds, preferably 10 to 100 seconds.

These boric acid treatments can also be used in accordance with the hydration resistant boric acid treatment. Twice with the degree of boric acid treatment with hue adjustment. In this case, the composition and temperature of the aqueous solution of each boric acid treatment tank used may be the same or different within the above range. Moreover, the boric acid treatment with water resistance and the boric acid treatment with hue adjustment can also be performed in a plurality of steps, respectively.

(Washing treatment)

The purpose of the cleaning treatment is to remove excess boric acid or iodine from the polyvinyl alcohol resin film after boric acid treatment. This washing treatment can be performed by, for example, immersing a polarizing film subjected to boric acid treatment for water resistance and / or hue adjustment in water, spraying with shower water, or the like, or using both. The temperature of the water in the washing treatment is usually about 2 to 40 ° C, and the processing time is preferably about 5 to 120 seconds.

(Drying)

After the washing process, a polarizing film can be produced by drying the polyvinyl alcohol-based resin film. The drying process is performed in a drying furnace at a temperature of about 40 to 100 ° C for about 60 to 600 seconds.

The final cumulative stretch ratio of the polarizing film thus manufactured is usually about 4.5 to 7 times, preferably about 5 to 6.5 times.

(Other processing)

Furthermore, processes other than the above may be added for other purposes. Examples of treatment baths to be added include immersion treatment (iodide treatment) in an iodide aqueous solution containing no boric acid after the boric acid treatment, and immersion treatment (zinc treatment) in an aqueous solution containing zinc chloride and the like that does not include boric acid. Wait.

[Manufacturing method of polarizing plate]

Since at least one side of the polarizing film thus manufactured, the protective film is bonded with an adhesive to form a laminate of the polarizing film and the protective film. Polarizer. Examples of the protective film include, for example, ethyl acetate cellulose resin films such as triethyl cellulose, cycloolefin resin films, cycloolefin copolymer resin films, such as polyethylene terephthalate, and polyethylene naphthalate. Polyester resin films of ethylene or polybutylene terephthalate, polycarbonate resin films, acrylic resin films such as polymethyl methacrylate, non-cyclic olefins such as polypropylene and polyethylene Resin film.

In order to improve the adhesive and the polarizing film and / or the protection Adhesiveness of protective film, corona treatment, plasma treatment, flame treatment, ultraviolet treatment, primer treatment, saponification treatment, coating with solvent and drying can be applied to the bonding surface of polarizing film and / or protective film Surface treatment such as solvent treatment.

Alternatively, instead of these protective films, An extension film of a thermoplastic resin bonded to a polarizing film or an optical compensation film in which a liquid crystal compound is aligned in the thermoplastic resin. Such stretched films of thermoplastic resins or optical compensation films that align liquid crystal compounds in thermoplastic resins can be used as appropriate.

Adhesive for bonding polarizing film and protective film, etc. There is no particular limitation as long as the polarizing film can be bonded to a protective film or the like, but one that satisfies sufficient adhesion and transparency is selected. For these reasons, it is preferable to use an ultraviolet curing adhesive when bonding a polarizing film and a protective film. In addition, when bonding a polarizing film and an ethyl acetate cellulose resin film, in addition to the above-mentioned ultraviolet curable resin, an aqueous adhesive such as an aqueous solution of a polyvinyl alcohol resin, an aqueous solution in which a crosslinking agent is formulated, and an amine group can be used. Formate-based emulsion adhesives and the like.

The UV-curable adhesive may be an acrylic compound and A mixture of a photoradical polymerization initiator or a mixture of an epoxy compound and a photocationic polymerization initiator. In addition, a cationic polymerizable epoxy compound and a radical polymerizable acrylic compound may be used in combination, and a photocationic polymerization initiator and a photoradical polymerization initiator may be used in combination as an initiator.

When using a UV-curable adhesive, it is attached to the laminated film Then, the adhesive is hardened by irradiating ultraviolet rays. The ultraviolet light source is not particularly limited, but it is preferably used for persons with a light emission distribution below a wavelength of 400 nm. Specifically, low-pressure mercury lamps, medium-pressure mercury lamps, high-pressure mercury lamps, ultra-high-pressure mercury lamps, chemical lamps, black light lamps, microwave-excited mercury lamps, Metal halide lamps, etc.

The light irradiation intensity used to harden the UV-curable adhesive is appropriately determined depending on the composition of the adhesive, and is not particularly limited, but it is preferable that the irradiation intensity in the wavelength region where the polymerization initiator is activated is preferably 0.1 to 6000 mW / cm ² . By appropriately selecting the irradiation intensity within this range, the reaction time does not become too long, and the yellowing of the adhesive caused by the heat radiated from the light source and the heat generated when the adhesive is hardened, or the polarizing film can be suppressed. Degradation. The light irradiation time is also not particularly limited depending on the selection of the adhesive to be hardened, but it is preferable that the cumulative light amount expressed by the product of the above-mentioned irradiation intensity and irradiation time is set to 10 to 10,000 mJ / cm ² .

By appropriately selecting the amount of accumulated light from this range, charging can occur. The amount of the active species derived from the polymerization initiator allows the hardening reaction to proceed reliably, and the irradiation time can be shortened, so that good productivity can be maintained. In addition, a laminated film including a polarizing film or a protective film is irradiated with ultraviolet rays. When curing the UV-curable adhesive, it is preferred to perform the curing without reducing the polarizing film's polarization, transmittance, hue, and transparency of the protective film, and reducing the properties of the polarizing plate.

In addition, when using an aqueous adhesive, for example, a film can be used. The surface is uniformly coated with an adhesive or flows between two films, and the two films are overlapped via the coating layer, and the method is carried out by using a roller or the like and drying. After drying, it may be aged at room temperature or slightly higher temperature, for example, about 20 to 45 ° C.

The thickness of the above adhesive layer is from about 0.001 to 5 μm The range is appropriately selected according to the type of the adhesive or the composition of the two films to be bonded. Its thickness is preferably 0.01 μm or more, and more preferably 2 μm or less.

Examples

The following examples specifically illustrate the present invention, but the present invention is not limited to these examples. The widthwise expansion rate of the polyvinyl alcohol film in the following examples was measured by the following method.

<Measurement of expansion ratio>

The expansion coefficient of the film is calculated from the amount of change in the width direction of the film before and after immersion in the swelling treatment tank or dyeing treatment tank as the measurement target. First, the long polyvinyl alcohol film (blank film) used in each of the examples and comparative examples described below was cut into a length of 50 mm and a width of 50 mm to obtain a film fragment. Next, the film was processed with a method for measuring the swelling ratio. The treatment bath having the same composition as the bath was immersed in the treatment liquid at the same temperature as the actual treatment and at the same time as the time when the film passed the treatment tank. This impregnation is performed in a state where no tension is applied to the film. Subsequently, the film fragments were taken out from the treatment solution, and the change length of the film fragment width direction before and after the treatment with respect to the length in the width direction at the time of cutting (the length after the treatment-the length at the time of cutting at 50 mm) was obtained as a percentage. The length of the thin film after the treatment was measured by using a commercially available digital caliper [MITUTOYO Co., Ltd., "COOLANT DIGIMATIC CALIPER CD-15PSX"].

[Example 1]

Prepare a long polyvinyl alcohol film with a thickness of 60 μm [KURARAY POVAL FILM VF-PE # 6000 ', a degree of polymerization of 2400, a degree of saponification of 99.9 mol% or more], as a swelling treatment. Into the first swelling treatment tank with pure water at 37 ° C, immerse for 40 seconds to keep the film in a tense state without slackening. Subsequently, the film was immersed in a second swelling treatment tank containing pure water at 30 ° C for 20 seconds. At this time, the film was conveyed in the first swelling treatment tank using a stretch roll. Next, as a dyeing treatment, a uniaxial extension of 2.2 times was performed in a dyeing treatment tank containing a 30 ° C aqueous solution containing iodine and potassium iodide while immersed for 60 seconds, and the weight ratio of potassium iodide / boric acid / water was set as 12 / 4.4 / 100 55 ° C aqueous solution in a boric acid treatment tank is immersed in the boric acid treatment tank for water resistance treatment and uniaxially stretched until the cumulative extension ratio from the original film becomes 5.5 times. Next, immerse it in a tank containing a boric acid aqueous solution at 40 ° C, and then immerse it in a washing place where pure water at 12 ° C is placed. Then, it was dried in a drying oven at 70 ° C. for 3 minutes to prepare a polarizing film. No wrinkles were seen in the swelling process, and no film breakage was seen.

(A) Saturation expansion rate in the first swelling treatment tank

The polyvinyl alcohol film "KURARAY POVAL FILM VF-PE # 6000" used in Example 1 was cut to a size of 50 mm in the lengthwise direction and 50 mm in the widthwise direction, and then placed in a water tank (corresponding to the first one) of pure water at 37 ° C. The swelling rate when immersed in the swelling treatment tank) for 10 minutes was set to the saturation swelling rate, and the saturation swelling rate was determined. After dipping, the length in the width direction of the film fragment was 62.70 mm. According to the change in the length of the dipping relative to the length in the width direction before dipping, the saturation expansion rate in the first swelling treatment tank was 25.4%.

(B) Width expansion rate of the film in the first swelling treatment tank

In addition, the same cut pieces as those of the film cut in (A) above were prepared and immersed in a water bath placed at 37 ° C for 40 seconds in the same manner as in the first swelling treatment tank of Example 1. The expansion ratio was set to the expansion ratio of the first swelling treatment tank, and the expansion ratio was obtained. After dipping, the length in the width direction of the film fragment was 61.00 mm. According to the amount of change in the length of the first swelling treatment tank relative to the length in the width direction before immersion, the width expansion rate of the film in the first swelling treatment tank was 22.0%. The expansion ratio is 86.6% relative to the saturation expansion ratio of the above (A). In Table 1 below, the expansion rate of the first swelling treatment tank is shown in the "Expansion rate 1" column, and the expansion rate of the first swelling processing tank is shown in "Expansion rate 1 / Saturation expansion rate" relative to the saturated expansion rate. In the bar.

(C) Swelling rate in the width direction of the film in the second swelling treatment tank

In order to apply the same treatment as in the second swelling treatment tank to the film fragment of the above (B), which was subjected to the same treatment as the first swelling treatment tank, it was further immersed in a water bath placed at 30 ° C for 20 seconds. . After the dipping, the length in the width direction of the film fragment was 60.60 mm. According to the amount of change in the length of the second swelling treatment tank with respect to the length of the film in the width direction at the time of cutting, the expansion rate in the width direction of the film in the second swelling treatment tank was 21.2%. And, the difference from the expansion ratio in the width direction of the film in the first swelling treatment tank (B) described above was -0.8 points. In Table 1 below, the expansion rate of the second swelling treatment tank is shown in the "Expansion rate 2" column, and the difference in expansion rate between the first swelling processing tank and the second swelling processing tank is shown in "Expansion rate difference" In the bar.

[Example 2]

In addition to using a long polyvinyl alcohol film with a thickness of 50 μm [trade name “KURARAY POVAL FILM VF-PE # 5000” manufactured by KURARAY Co., Ltd., a degree of polymerization of 2400, and a degree of saponification of 99.9 mol% or more] were used as the blank film, and The swelling treatment of each swelling treatment tank was changed to immersion in pure water at 35 ° C. for 30 seconds, and a polarizing film was produced in the same manner as in Example 1. No wrinkles were seen in the swelling process, and no film breakage was seen.

(A) Saturation expansion rate in the first swelling treatment tank

The polyvinyl alcohol film "KURARAY POVAL" used in Example 2 FILM VF-PE # 5000 "cut out the film fragments, and the pure water temperature in the water tank was changed to other than 35 ° C. The saturation expansion ratio in the first swelling treatment tank was obtained in the same manner as in Example 1 (A). After immersion The length of the film in the width direction is 62.10mm. According to the change in the length of the dipping relative to the length in the width before the dipping, the saturation expansion rate in the first swelling treatment tank is 24.2%.

(B) Width expansion rate of the film in the first swelling treatment tank

In addition, the same cut pieces as those of the film cut in Example 2 (A) were prepared, and immersed in a water bath placed at 35 ° C for 40 seconds in the same manner as in the first swelling treatment tank of Example 2. Find the expansion rate of the first swelling treatment tank. After dipping, the length in the width direction of the film fragment was 60.45 mm. The expansion rate in the width direction of the film in the first swelling treatment tank was determined in the same manner as in Example 1 (B), and the result was 20.9%. The expansion coefficient was 86.4% relative to the saturation expansion ratio of the above (A).

(C) Swelling rate in the width direction of the film in the second swelling treatment tank

In order to apply the same treatment as in the second swelling treatment tank to the film fragment of the above (B), which was subjected to the same treatment as the first swelling treatment tank, it was further immersed in a water bath placed at 30 ° C for 20 seconds. . After immersion, the length in the width direction of the film fragment was 60.50 mm. The expansion rate in the film width direction in the second swelling treatment tank was determined in the same manner as in Example 1 (C), and it was 21.0%. And the difference from the expansion ratio in the width direction of the film in the first swelling treatment tank of (B) above is +0.1 point.

[Example 3]

In addition to using a long polyvinyl alcohol film with a thickness of 60 μm [trade name “KURARAY POVAL FILM VF-PE # 6000” manufactured by KURARAY Co., Ltd., a degree of polymerization of 2400, and a degree of saponification of 99.9 mol% or more] were used as a raw film and a swelling treatment It is immersed in a swelling treatment tank with pure water at 37 ° C for 40 seconds so as not to loosen the film and maintain a tense state. At this time, the film was transported in a swelling processing tank using a spreading roller. Next, as a dyeing treatment, a uniaxial extension of 2.2 times was performed in a dyeing treatment tank containing a 30 ° C aqueous solution containing iodine and potassium iodide while immersed for 60 seconds, and the weight ratio of potassium iodide / boric acid / water was set as 12 / 4.4 / 100 55 ° C aqueous solution in a boric acid treatment tank is immersed in the boric acid treatment tank for water resistance treatment and uniaxially stretched until the cumulative extension ratio from the original film becomes 5.5 times. Next, it was immersed in a tank containing a boric acid aqueous solution at 40 ° C, then immersed in a washing treatment tank containing 12 ° C pure water, and dried in a drying oven at 70 ° C for 3 minutes to prepare a polarizing film. No wrinkles were seen in the swelling treatment and dyeing treatment, and no film breakage was seen.

(A) Saturation expansion rate in the first swelling treatment tank

The polyvinyl alcohol film "KURARAY POVAL FILM VF-PE # 6000" used in Example 3 was cut in the same manner as in Example 1 (A), except that the film was cut. The saturation expansion coefficient in the swelling treatment tank was determined. After dipping, the length in the width direction of the film fragment was 62.70 mm. Saturated swelling in the swelling treatment tank according to the change in the length of the immersion relative to the length in the width direction before immersion The expansion rate is 25.4%.

(B) Swelling rate in the width direction of the film in the swelling tank

In addition, the same cut pieces as those of the film cut in (A) above were prepared, and they were immersed in a water bath placed at 37 ° C for 40 seconds in the same manner as in the swelling treatment bath of Example 3 to obtain a swelling treatment tank Expansion rate. After dipping, the length in the width direction of the film fragment was 61.00 mm. The expansion ratio in the width direction of the film in the swelling treatment tank was determined in the same manner as in Example 1 (B), and it was 22.0%. The expansion ratio is 86.6% relative to the saturation expansion ratio of the above (A). In Table 1 below, the expansion rate of the swelling treatment tank is shown in the column of "Expansion rate 1", and the expansion rate of the swelling treatment tank is shown in the column of "Expansion rate 1 / Saturation expansion rate" with respect to the saturation expansion rate.

(C) Swelling rate in the width direction of the film in the dyeing tank

In order to apply the same treatment to the dyeing treatment tank to the film section of the above (B) applying the same treatment as the swelling treatment tank, put it in a water tank having the same composition and the same temperature (30 ° C) as the dyeing treatment bath. 60 second. After the dipping, the length in the width direction of the film fragment was 60.85 mm. According to the amount of change in the length of the dyeing treatment tank with respect to the length of the film in the width direction at the time of cutting, the expansion rate in the width direction of the film in the dyeing treatment tank was 21.7%. The difference from the expansion ratio in the width direction of the film in the swelling treatment tank (B) is -0.3. In Table 1 below, the expansion ratio of the dyeing treatment tank is shown in the column of "Expansion Ratio 2", and the difference in expansion ratio of the swelling treatment tank and the dyeing treatment tank is shown in the column of "Expansion ratio difference".

[Comparative Example 1]

A polarizing film was produced in the same manner as in Example 1 except that the immersion time of the film in the first swelling treatment tank was changed to 10 seconds. Wrinkles occurred in the first swelling treatment tank and the second swelling treatment tank, and most films were cut during stretching. When the appearance of the obtained polarizing film was confirmed, wrinkles were seen.

(A) Saturation expansion rate in the first swelling treatment tank

The saturation expansion ratio of the first swelling treatment tank was determined in the same manner as in Example 1 (A). The width direction length of the immersed film fragment was 62.70mm, and the saturation expansion rate was 25.4%.

(B) Width expansion rate of the film in the first swelling treatment tank

The expansion ratio of the first swelling treatment tank was determined in the same manner as in Example 1 (B), except that the immersion time was changed to 10 seconds. After dipping, the width direction length of the film fragment was 55.35 mm, and the expansion ratio was 10.7%. The expansion ratio is 42.1% relative to the saturation expansion ratio of the above (A).

(C) Swelling rate in the width direction of the film in the second swelling treatment tank

The same procedure as in Example 1 (C) was performed except that the film fragments used were changed to those in which the same treatment as in the first swelling treatment tank was performed in (B) above. After immersion, the width direction length of the film fragment was 58.20mm, and the expansion ratio in the width direction of the film in the second swelling treatment tank was 16.4%. And the expansion in the width direction of the film in the first swelling treatment tank of (B) above The difference in rates is +5.7 points.

[Comparative Example 2]

A polarizing film was produced in the same manner as in Example 2 except that the immersion time of the film in the first swelling treatment tank was changed to 10 seconds. In addition, wrinkles occurred in the first swelling treatment tank and the second swelling treatment tank, and most films were cut during stretching. Wrinkles were seen when the appearance of the obtained polarizing film was confirmed.

(A) Saturation expansion rate in the first swelling treatment tank

The saturation expansion coefficient of the first swelling treatment tank was determined in the same manner as in Example 2 (A). The width direction length of the immersed film fragment was 62.10 mm, and the saturation expansion rate was 24.2%.

(B) Width expansion rate of the film in the first swelling treatment tank

The expansion ratio of the first swelling treatment tank was determined in the same manner as in Example 2 (B), except that the immersion time was changed to 10 seconds. After dipping, the width-wise length of the film fragment was 56.60 mm, and the expansion ratio was 13.2%. In addition, the expansion ratio is 54.5% relative to the saturation expansion ratio of the above (A).

(C) Swelling rate in the width direction of the film in the second swelling treatment tank

The same procedure as in Example 1 (C) was performed except that the film fragments used were changed to those in which the same treatment as in the first swelling treatment tank was performed in (B) above. After dipping, the width direction length of the film fragment was 59.05mm, and the expansion rate in the width direction of the film in the second swelling treatment tank was 18.1%. And The difference from the expansion ratio in the width direction of the film in the first swelling treatment tank of (B) above was +4.9 points.

[Comparative Example 3]

A polarizing film was produced in the same manner as in Example 2 except that the immersion time of the film in the first swelling treatment tank was changed to 100 seconds. No wrinkles were observed in the first swelling treatment tank and the second swelling treatment tank.

(A) Saturation expansion rate in the first swelling treatment tank

The saturation expansion coefficient of the first swelling treatment tank was determined in the same manner as in Example 2 (A). The width direction length of the immersed film fragment was 62.10 mm, and the saturation expansion rate was 24.2%.

(B) Width expansion rate of the film in the first swelling treatment tank

The expansion ratio of the first swelling treatment tank was determined in the same manner as in Example 2 (B), except that the immersion time was changed to 100 seconds. After dipping, the width-wise length of the film fragment was 61.70 mm, and the expansion ratio was 23.4%. And this expansion ratio is 96.7% with respect to the saturation expansion ratio of the said (A).

(C) Swelling rate in the width direction of the film in the second swelling treatment tank

The same procedure as in Example 1 (C) was performed except that the film fragments used were changed to those in which the same treatment as in the first swelling treatment tank was performed in (B) above. After immersion, the width direction length of the film fragment was 61.75mm, and the expansion ratio of the film width direction in the second swelling treatment tank was 23.5%. And The difference from the expansion ratio in the width direction of the film in the first swelling treatment tank of (B) above is +0.1 point.

[Comparative Example 4]

A polarizing film was produced in the same manner as in Example 2 except that the treatment temperature in the first swelling treatment tank was changed to 50 ° C. Wrinkles occurred in the first swelling treatment tank and the second swelling treatment tank, and many film cuts occurred during stretching. Therefore, a polarizing film could not be produced.

(A) Saturation expansion rate in the first swelling treatment tank

The saturation expansion coefficient of the first swelling treatment tank was determined in the same manner as in Example 2 (A) except that the temperature of pure water was changed to 50 ° C. The width direction length of the thin film segment after the dipping was 73.10 mm, and the saturation expansion rate was 46.2%.

(B) Width expansion rate of the film in the first swelling treatment tank

The expansion ratio of the first swelling treatment tank was determined in the same manner as in Example 2 (B), except that the temperature of pure water was changed to 50 ° C. After dipping, the width-wise length of the film fragment was 69.30 mm, and the expansion ratio was 38.6%. In addition, the expansion ratio is 83.5% relative to the saturation expansion ratio of the above (A).

(C) Swelling rate in the width direction of the film in the second swelling treatment tank

The same procedure as in Example 1 (C) was performed except that the film fragments used were changed to those in which the same treatment as in the first swelling treatment tank was performed in (B) above. After dipping, the width direction length of the film fragment is 67.00mm. The expansion rate in the width direction of the film in the two swelling treatment tanks was 34.0%. And the difference from the expansion ratio in the width direction of the film in the first swelling treatment tank of (B) above is -4.6 points.

[Comparative Example 5]

A polarizing film was produced in the same manner as in Example 2 except that the treatment temperature in the first swelling treatment tank was changed to 20 ° C. Wrinkles occurred in the first swelling treatment tank and the second swelling treatment tank, and most films were cut during stretching. Wrinkles were seen when the appearance of the obtained polarizing film was confirmed.

(A) Saturation expansion rate in the first swelling treatment tank

The saturation expansion coefficient of the first swelling treatment tank was determined in the same manner as in Example 2 (A) except that the temperature of pure water was changed to 20 ° C. The width direction length of the immersed film fragment was 59.15 mm, and the saturation expansion ratio was 18.3%.

(B) Width expansion rate of the film in the first swelling treatment tank

The expansion ratio of the first swelling treatment tank was determined in the same manner as in Example 2 (B) except that the temperature of pure water was changed to 20 ° C. After dipping, the width-wise length of the film fragment was 54.45 mm, and the expansion ratio was 8.9%. And this expansion ratio is 48.6% with respect to the saturation expansion ratio of said (A).

(C) Swelling rate in the width direction of the film in the second swelling treatment tank

The same procedure as in Example 1 (C) was carried out except that the film fragment used was changed to the one in which the same treatment as in the first swelling treatment tank was performed in (B) above. deal with. After immersion, the width direction length of the film fragment was 58.05mm, and the expansion ratio in the width direction of the film in the second swelling treatment tank was 16.1%. And the difference from the expansion ratio in the width direction of the film in the first swelling treatment tank of (B) above was +7.2 points.

As can be seen from Table 1, the facts that satisfy all the requirements of the present invention are relatively In Example 1, and Comparative Example 1 in which the same blank film as in Example 1 was used but did not meet the requirements of the present invention, the result of Example 1 was that the film in the first swelling treatment tank was sufficiently swollen, and the second in the manufacturing process continued. In the swelling treatment tanks, no wrinkles due to the difference in expansion ratio occurred, and no wrinkles were observed in the obtained polarizing film and the appearance was good. In contrast, Comparative Example 1 was not sufficiently swollen due to the short treatment time. As a result, wrinkles or film breakage occurred during production, and wrinkles were also observed in the obtained polarizing film. And when comparing Example 2 using a thinner film that is thinner than Example 1 and using Comparative Examples 2, 4 and 5 which use the same blank film but do not meet the requirements of the present invention, Example 2 does not cause wrinkles or films during manufacturing. It is possible to produce a polarizing film with a good appearance by breaking, whereas the results of all comparative examples are wrinkles or film breakage during production. The polarizing film was cracked, and wrinkles were also seen in the obtained polarizing film, and most of them were broken, and a polarizing film could not be obtained.

In Comparative Example 3, no film wrinkles or cracks occurred during manufacture, and a polarizing film with good appearance could be manufactured. However, the processing time in the first swelling treatment tank was longer. Compared with Example 2, the manufacturing efficiency was lower.

Example 3 of another embodiment of the present invention, in which only one swelling treatment tank is used to perform swelling treatment, satisfies all the requirements of the present invention. The result is that the film in the swelling treatment tank is fully swollen. Wrinkles due to the difference in expansion rate did not occur, and no wrinkles were observed in the obtained polarizing film, which was a good appearance.

[Industrial availability]

According to the method for manufacturing a polarizing film of the present invention, the various treatments performed during the manufacture of the polarizing film, especially in the swelling treatment, can suppress the occurrence of wrinkles or fractures of the film due to the suppression of the swelling deviation of the film, which is effective. In order to produce a polarizing film with excellent appearance.

Claims (7)

A method for manufacturing a polarizing film, which is a method for manufacturing a polarizing film by sequentially applying a swelling treatment, a dyeing treatment, a boric acid treatment, and a washing treatment to a blank film made of a polyvinyl alcohol resin, which is characterized in that The thickness is 10 to 60 μm. The aforementioned swelling treatment is performed by sequentially disposing a plurality of swelling treatment tanks including at least a first swelling processing tank and a second swelling processing tank, which are sequentially arranged from the feeding side of the blank film. The expansion rate in the width direction of the film in the swelling treatment tank is 70% or more and 90% or less of the saturation expansion rate when immersed in the processing solution of the same temperature and composition, so that the expansion rate in the width direction of the film in the first swelling treatment tank Adjust the processing temperature of the first swelling processing tank and the second swelling processing tank and pass the processing tank in such a way that the absolute value of the difference between the expansion rate in the width direction of the film in the second swelling processing tank and the percentage is expressed as a percentage. Time. The method of claim 1, wherein the processing temperature of the first swelling treatment tank is 35 to 45 ° C, and the processing temperature of the second swelling processing tank is 25 to 35 ° C lower than the processing temperature of the first swelling processing. For example, the method of manufacturing a polarizing film according to claim 1 or 2, wherein the processing temperature of the first swelling processing tank and the temperature of passing through the processing tank are adjusted so that the expansion ratio in the width direction of the film in the first swelling processing tank becomes 15 to 25%. time. For example, the manufacturing method of the polarizing film of claim 1 or 2, wherein the time for passing through the first swelling treatment tank is 15-50 seconds, and passing through the second swelling place. The time for slot management is 15 ~ 50 seconds. A method for manufacturing a polarizing film, which is a method for manufacturing a polarizing film by sequentially applying a swelling treatment, a dyeing treatment, a boric acid treatment, and a washing treatment to a blank film made of a polyvinyl alcohol resin, which is characterized in that The thickness is 10 to 60 μm. The aforementioned swelling treatment is performed by passing through a swelling treatment tank. The expansion rate in the width direction of the film in the swelling treatment tank is 70% of the saturation expansion rate when the treatment liquid is immersed in the same temperature and composition. Above 90%, adjust the swelling treatment so that the absolute value of the difference between the expansion rate in the width direction of the film in the swelling treatment tank and the expansion rate in the width direction of the film in the dyeing treatment tank is less than 2 points. The processing temperature of the tank and the dyeing processing tank and the time for passing through the processing tank. For example, the manufacturing method of the polarizing film of claim 5, wherein the processing temperature of the swelling processing tank is 35 to 45 ° C, and the processing temperature of the dyeing processing tank is lower than that of the swelling processing tank, which is 25 to 35 ° C. For example, the manufacturing method of the polarizing film of claim 5 or 6, wherein the processing temperature of the swelling processing tank and the time of passing through the processing tank are adjusted so that the expansion ratio in the width direction of the film in the swelling processing tank becomes 15 to 25%.