WO2013084974A1

WO2013084974A1 - Method for producing polarizing film

Info

Publication number: WO2013084974A1
Application number: PCT/JP2012/081603
Authority: WO
Inventors: 圭二網谷
Original assignee: 住友化学株式会社
Priority date: 2011-12-06
Filing date: 2012-12-06
Publication date: 2013-06-13
Also published as: KR101956414B1; KR20140105727A; JP2013140345A; CN103988102B; JP6228359B2; CN103988102A

Abstract

The present invention relates to a method for producing a polarizing film, the method comprising a dyeing step of dyeing a polyvinyl alcohol-based film, a boric acid treatment step of treating the film with boric acid, and a cleaning step of cleaning the film thereafter, the method also comprising, before or during one of said steps, a stretching step of uniaxially stretching the film, wherein: the cleaning step involves an operation of showering the film; and the showering operation is performed by distinguishing between both edge parts of the film, which amount to a total of 5-60% with respect to the entire width of the film, and the central part, which is on the inner side of said edge parts in the width direction, the showering operation being performed such that the degree of cleaning of said both edge parts becomes greater than that of said central part by setting the temperature of the shower to be given to said both edge parts to 55°C or lower and making the temperature of the shower to be given to said both edge parts at least 15°C higher than the temperature of the shower to be given to said central part, and/or by making the total amount of the shower to be given to said both edge parts greater than the total amount of the shower of said central part.

Description

Manufacturing method of polarizing film

This patent application claims priority under the Paris Convention based on Japanese Patent Application No. 2011-266742 (filed on Dec. 6, 2011), and is incorporated herein by reference. The entire contents of which are incorporated herein.
The present invention relates to a method for producing a polarizing film used for a polarizing plate such as a liquid crystal display device.

Conventionally, a polarizing film in which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol-based resin film has been used. That is, an iodine polarizing film using iodine as a dichroic dye, a dye polarizing film using a dichroic dye as a dichroic dye, and the like are known. These polarizing films are usually used as polarizing plates by laminating a protective film such as triacetyl cellulose via an adhesive made of an aqueous solution of a polyvinyl alcohol resin on at least one surface, preferably both surfaces of the polarizing film. (LCD) is used for, for example, a liquid crystal television, a monitor for a personal computer, a display screen of a mobile phone, and the like.

As a method for producing a polarizing film, a nip roll and a guide roll are used, and a polyvinyl alcohol resin film is immersed in water to swell, then dyed with the dichroic dye, stretched, and then iodine is filmed. In order to fix the resin film, a method of boric acid treatment (crosslinking treatment) of the polyvinyl alcohol resin film, washing with water, and drying is known (see, for example, Patent Document 1 (Japanese Patent Laid-Open No. 2005-227650)). At this time, the film is stretched by giving a peripheral speed difference to the nip rolls before and after the treatment bath, the film transport direction is changed by the guide rolls, and the film is introduced into and taken out of the treatment liquid.

In recent years, along with the increase in size, function and brightness of liquid crystal display devices, the polarizing film used in the liquid crystal display device is also required to increase in optical properties and in-plane uniformity. However, large polarizing films tend to cause variations in the surface such as hue, and tend to deteriorate optical characteristics.

On the other hand, in Patent Document 2 (Taiwan Published Patent No. 20112375), a polyvinyl alcohol resin film is subjected to dyeing, stretching and crosslinking treatments, and then washed with water to produce a polarizing film. The water washing temperature is 9 to 25 ° C., and the water washing temperature at the center in the film width direction is 5 to 14 ° C. An example is shown in which the difference in the washing temperature between both ends and the center in the film width direction is varied in the range of 4 to 11 ° C.

JP 2005-227650 A Taiwan Published Patent No. 20112375

An object of the present invention is to provide a method for producing a polarizing film having excellent optical property uniformity.

The present invention includes the following preferred embodiments.
(1) a dyeing process for dyeing a film composed of a polyvinyl alcohol resin;
A boric acid treatment step of treating the film with boric acid;
A cleaning step of cleaning the film,
Further, before or during any of the above steps, a method for producing a polarizing film comprising a stretching step of uniaxially stretching the film,
The washing step includes an operation of showering the film,
The operation of taking a shower is performed by dividing into both ends corresponding to a total of 5 to 60% and a central portion inside in the width direction based on the width of the entire film,
The temperature of the shower showered on both ends is 55 ° C. or lower, and the shower temperature showered on both ends is higher by 15 ° C. or more than the temperature of the shower bathed on the center, and / or the both ends The production of a polarizing film is characterized in that the total amount of shower to be bathed in is larger than the total amount of shower to be bathed in the central portion so that the degree of cleaning of both end portions is larger than that of the central portion. Method.
(2) In the operation of taking a shower, increasing the total amount of showers to be applied to both end portions to be greater than the total amount of showers to be applied to the central portion causes the flow rate of showers to be applied to both end portions to be applied to the central portion. The manufacturing method of the polarizing film as described in said (1) performed by making more than the flow volume of a shower.
(3) In the operation of taking a shower, increasing the total amount of showers to be applied to both end portions than the total amount of showers to be applied to the central portion means that the time for taking showers at the both end portions is taken into the center portion. The manufacturing method of the polarizing film as described in said (1) performed by making it longer than the time to bathe.
(4) The operation of showering is performed by increasing the total amount of showers showered at both ends than the total shower showering at the center, and the shower temperature bathed at both ends is at the center. The manufacturing method of the polarizing film as described in said (1) which is the same or higher than the temperature of the shower to shower.
(5) The operation of taking a shower is performed at a plurality of locations in the transport direction of the film,
In some of the plurality of locations, the degree of cleaning at both ends is greater than the central portion,
In other places, the degree of washing of the entire film is made uniform, or the degree of washing of the central part is made larger than that of the both end parts. The manufacturing method of the polarizing film of crab.

In the present invention, as described above, a film composed of a polyvinyl alcohol-based resin (hereinafter also referred to as a polyvinyl alcohol-based resin film) is subjected to dyeing and boric acid treatment, and then washed to produce a polarizing film. Includes at least an operation of showering the polyvinyl alcohol resin film after the boric acid treatment, and the showering operation is performed at both ends in the width direction of the film and at the center in the width direction inside the film. The difference in the degree of cleaning is such that the degree of cleaning at both ends is greater than that at the center. Therefore, in one form, the temperature of the shower showered at both ends is increased by 15 ° C. or more than the temperature of the shower bathed at the center, and the above-described showering operation is performed. In another embodiment, the total amount of showers at both ends is made larger than the total amount of showers at the center, and the above-described showering operation is performed. In addition, you may perform operation which takes a shower combining the above-mentioned two forms.

As in the latter case, the operation of changing the total amount of shower showered at both ends and the center of the film in the width direction is, for example, the flow rate of shower showered at both ends of the film is greater than the flow rate of shower showered at the center of the film. This can be achieved. For example, it can also be achieved by setting the time for showering at both ends of the film to be longer than the time for showering at the center of the film.

In these methods, the showering operation is performed at a plurality of locations in the film conveyance direction, and the degree of cleaning at both ends of the film is greater than the central portion of the film at some locations among the plurality of locations. In other places, the degree of washing of the entire film can be made uniform, or the degree of washing of the central part of the film can be made larger than both ends of the film.

According to the present invention, it is possible to produce a polarizing film having uniform optical characteristics in the width direction.

It is a perspective view for demonstrating an example of the two-step washing | cleaning process in the manufacturing method of this invention. It is the schematic for demonstrating an example of the two-step washing | cleaning process in the manufacturing method of this invention. (A) is a side view, (b) and (c) are top views. It is a perspective view for demonstrating an example of the three-step washing | cleaning process in the manufacturing method of this invention. It is the schematic for demonstrating an example of the 3-step washing | cleaning process in the manufacturing method of this invention. (A) is a side view, and (b) to (d) are top views.

(Polyvinyl alcohol resin film)
In the present invention, a saponified polyvinyl acetate resin is exemplified as the polyvinyl alcohol resin constituting the polyvinyl alcohol resin film (film composed of the polyvinyl alcohol resin). Polyvinyl acetate resins include polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate and other monomers copolymerizable therewith (for example, ethylene-vinyl acetate copolymer). For example). Examples of other copolymerizable monomers include unsaturated carboxylic acids, olefins, vinyl ethers, and unsaturated sulfonic acids. The degree of polymerization of the polyvinyl alcohol resin is usually about 1000 to 10,000, preferably about 1500 to 5,000. The degree of saponification is usually about 85 mol% or more, preferably about 90 mol% or more, more preferably about 99 to 100 mol%. These polyvinyl alcohol resins may be modified. For example, polyvinyl formal modified with aldehydes, polyvinyl acetal, polyvinyl butyral, and the like may be used.

Usually, as a starting material (raw film) for manufacturing a polarizing film, a film obtained by forming such a polyvinyl alcohol resin is used. The method for forming the polyvinyl alcohol-based resin is not particularly limited, and the film can be formed using a normal method as appropriate. The thickness of the raw film is preferably about 20 to 100 μm, more preferably about 30 to 80 μm. Also, industrially, the film width is practically about 1500 to 6000 mm, preferably 2000 mm or more. In particular, when the width of the raw film is 2000 mm or more, the optical properties such as the hue of the polarizing film are likely to vary, so the production method of the present invention is effective. The raw film is usually supplied as an unstretched roll film.

The polarizing film is produced by subjecting such a raw film to dyeing treatment, boric acid treatment (crosslinking treatment), and washing treatment, and the film is uniaxially stretched before or during any of the above treatment steps. Is done. For example, it is manufactured by treating the raw film in the order of swelling treatment, dyeing treatment, boric acid treatment (crosslinking treatment), washing treatment, and finally drying, and before or during any of the above treatment steps, The film is uniaxially stretched.

As a more specific method for producing the polarizing film, for example, the raw film is uniaxially stretched (dry stretch) in air or an inert gas, and then subjected to swelling treatment, dyeing treatment, boric acid treatment and washing treatment, and finally And a method of drying. In addition, the unstretched raw film is subjected to swelling treatment, dyeing treatment, boric acid treatment and washing treatment, uniaxial stretching is performed in the boric acid treatment step and / or the previous step, and then dried. Is mentioned.

(Swelling process)
In the method of the present invention, it is preferable to perform a swelling step before the dyeing step. The swelling step is performed for the purpose of removing foreign matter from the film surface, removing the plasticizer in the film, imparting easy dyeability in the next step, and plasticizing the film. The treatment conditions are determined within a range in which these objects can be achieved and within a range in which problems such as extreme dissolution and devitrification of the base film do not occur. When the film previously stretched in gas is swollen, the film is preferably immersed in an aqueous solution at about 20 to 70 ° C., more preferably about 30 to 60 ° C., and the swelling treatment is performed. The immersion time of the film is preferably about 30 to 300 seconds, more preferably about 60 to 240 seconds. When the unstretched original film is swollen, the swelling treatment is preferably performed by immersing the film in an aqueous solution of about 10 to 50 ° C., more preferably about 20 to 40 ° C. The immersion time of the film is preferably about 30 to 300 seconds, more preferably about 60 to 240 seconds.

In addition, when processing a polyvinyl alcohol-type resin film in order of a swelling process, a dyeing process, and a boric acid process, you may perform uniaxial stretching in a swelling process. In that case, the draw ratio is usually 1.2 to 3.0 times, preferably 1.3 to 2.5 times.

In the swelling process, problems such as the film swelling in the width direction and wrinkling into the film are likely to occur, so widening devices such as widening rolls (expander rolls), spiral rolls, crown rolls, cross guiders, bend bars, tenter clips, etc. It is preferable to transport the film while removing the wrinkles of the film.

In addition, to stabilize the film transport in the swelling bath, the water flow in the swelling bath is controlled with an underwater shower, and the EPC device (Edge Position Control device: detects the edge of the film to prevent film meandering. It is also useful to use a combination of such devices. In this process, since the film swells and expands in the film running direction, if the film is not actively stretched, for example, the speed of the transport roll before and after the treatment tank is set to eliminate sagging of the film in the transport direction. It is preferable to take measures such as control.

In addition to pure water, boric acid (described in JP-A-10-153709), chloride (described in JP-A-06-281816), inorganic acid, inorganic salt, water solution can be used for the swelling treatment bath used. It is also possible to use an aqueous solution to which a basic organic solvent, alcohols and the like are added in an amount of about 0.01 to 10% by weight.

(Dyeing process)
In the dyeing process, the film is usually dyed by adsorbing and orienting the dichroic dye on the film.

The dyeing of the polyvinyl alcohol-based resin film with the dichroic dye in the dyeing step is performed, for example, by immersing the polyvinyl alcohol-based resin film in an aqueous solution containing the dichroic dye. As the dichroic dye, for example, iodine, a dichroic dye or the like is used. Examples of dichroic dyes include C.I. I. Dichroic direct dyes composed of disazo compounds such as DIRECT RED 39, and dichroic direct dyes composed of compounds such as trisazo and tetrakisazo are included. In addition, since the polyvinyl alcohol-type resin film performs the immersion process to water before a dyeing process, since the uniformity of a more favorable optical characteristic is obtained, it is preferable.

When iodine is used as the dichroic dye, it can usually be dyed by immersing the polyvinyl alcohol resin film in an aqueous solution containing iodine and potassium iodide. The iodine content in this aqueous solution is preferably 0.003 to 0.2 parts by weight per 100 parts by weight of water, and the potassium iodide content is preferably 0.1 to 100 parts by weight per water. 10 parts by weight. When iodine is used as the dichroic dye, the temperature of the aqueous solution used for dyeing is usually 10 to 45 ° C., preferably 20 to 35 ° C., and the immersion time (dyeing time) in this aqueous solution is usually 30 to 600 seconds. It is preferably 60 to 300 seconds.

Instead of potassium iodide, other iodides such as zinc iodide may be used. Other iodides may be used in combination with potassium iodide. Furthermore, compounds other than iodide, such as boric acid, zinc chloride, cobalt chloride, etc. may coexist. Even when boric acid is added for the dyeing process, this dyeing process is distinguished from the boric acid process described later in that it contains iodine. If it contains about 0.003 parts by weight or more of iodine with respect to 100 parts by weight of water, it can be regarded as a dyeing bath.

When a water-soluble dichroic dye is used as the dichroic dye, the polyvinyl alcohol-based resin film can usually be dyed in an aqueous solution containing the water-soluble dichroic dye. The content of the dichroic dye in this aqueous solution is preferably 1 × 10 ⁻³ to 1 part by weight, more preferably 1 part per 100 parts by weight of water, from the viewpoint of obtaining better optical property uniformity. × 10 ⁻³ to 1 × 10 ⁻² parts by weight. This aqueous solution may contain a dyeing assistant. Examples of the dyeing assistant include inorganic salts such as sodium sulfate, surfactants and the like. A dichroic dye may be used independently and may be used combining two or more types of dichroic dyes.

The temperature of the aqueous solution containing the water-soluble dichroic dye is usually 20 to 80 ° C., preferably 30 to 70 ° C. The immersion time (dyeing time) in this aqueous solution is usually 30 to 600 seconds, preferably 60 to 300 seconds.

(Boric acid treatment process)
The boric acid treatment step is usually performed by immersing the dyed polyvinyl alcohol resin film in an aqueous boric acid solution. The amount of boric acid in the boric acid aqueous solution is preferably 1 to 10 parts by weight per 100 parts by weight of water.

When iodine is used as the dichroic dye in the dyeing process described above, the boric acid aqueous solution used in this boric acid treatment process preferably contains iodide. Examples of iodide include potassium iodide and zinc iodide. In this case, the amount of iodide in the boric acid aqueous solution is preferably 1 to 30 parts by weight per 100 parts by weight of water. Further, in the aqueous boric acid solution, compounds other than iodide, such as zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, and sodium sulfate may coexist.

This boric acid treatment is carried out for water resistance and hue adjustment (to prevent bluishness, etc.) by crosslinking. For the purpose of water resistance by cross-linking, a cross-linking agent such as glyoxal or glutaraldehyde can be used together with boric acid in addition to boric acid.

In addition, the boric acid treatment aiming at water resistance may be referred to by names such as water resistance treatment, crosslinking treatment, and immobilization treatment. In addition, boric acid treatment for hue adjustment may be referred to as complementary color processing, re-dyeing processing, or the like.

This boric acid treatment is performed by appropriately changing the concentration of boric acid and iodide and the temperature of the treatment bath according to the purpose. The boric acid treatment for water resistance and the boric acid treatment for hue adjustment are not particularly distinguished, but are carried out under the following conditions.

When the raw film is swelled and then dyed and treated with boric acid. When boric acid treatment is intended to provide water resistance by crosslinking, boric acid is about 3 to 10 weights per 100 parts by weight of water. It is preferable to use an aqueous boric acid solution containing about 1 to 20 parts by weight of iodide. In this case, the temperature of the boric acid aqueous solution is usually controlled to about 50 ° C. to 70 ° C., preferably about 53 ° C. to 65 ° C. The immersion time is usually about 10 to 600 seconds, preferably 20 to 300 seconds, more preferably 20 to 200 seconds.

When the film uniaxially stretched in advance is dyed and subjected to boric acid treatment, the temperature of the boric acid aqueous solution is usually about 50 ° C. to 85 ° C., preferably about 55 ° C. to 80 ° C.

After boric acid treatment for water resistance, boric acid treatment may be performed for the purpose of adjusting the hue. For adjusting the hue, for example, when iodine is used as the dichroic dye, an aqueous boric acid solution containing about 1 to 5 parts by weight of boric acid and about 3 to 30 parts by weight of iodide with respect to 100 parts by weight of water. Is preferably used. In this case, the temperature of the boric acid aqueous solution is usually controlled to about 10 ° C. to 45 ° C., and the immersion time is usually about 1 to 300 seconds, preferably 2 to 100 seconds.

These boric acid treatments may be performed a plurality of times and are usually performed 2 to 5 times in many cases. In this case, the aqueous solution composition and temperature of each boric acid treatment tank to be used may be the same or different as long as they are within the above range. The boric acid treatment for the purpose of water resistance and the boric acid treatment for the purpose of adjusting the hue may be performed in a plurality of steps, respectively.

(Washing process)
The boric acid-treated polyvinyl alcohol-based resin film is washed in a subsequent process. The washing treatment is performed by, for example, a method of immersing the film in water or a method of spraying water on the film as a shower. In the present invention, at least the operation of spraying (showing) a shower of water on the film is performed in the cleaning step, and the degree of cleaning at both ends in the width direction of the film is made larger than the central portion in the width direction of the film. Of course, both the operation of immersing the film in water and the operation of showering the film may be performed.

In order to make the degree of washing at both ends in the width direction of the film larger than the central portion in the width direction of the film, both ends in the width direction of the film (parts having a predetermined width including both ends in the width direction of the film) The central portion (the portion other than the both end portions) is divided and the above showering operation is performed so that the degree of cleaning at both end portions is larger than that at the central portion. Of course, for example, even in the case where the degree of cleaning gradually increases from the center to the both ends in the width direction of the film, the relationship between the lengths of both ends and the center and the relationship of the degree of cleaning satisfy the following conditions. As long as it is satisfied, it is included in the method of the invention.

Here, the film end portions where the degree of cleaning is larger than the central portion is set to 5 to 60% in total based on the width of the entire film. Preferably, it is 5 to 50%. When the ratio of both end portions where the degree of washing is larger than the central portion is less than 5% or more than 60% with respect to the width of the entire film, the optical characteristics such as hue are made uniform in the width direction. It tends to be difficult to sufficiently obtain the effects of the present invention. It is preferable that both end portions here have the same length.

The first mode for making the degree of cleaning at both ends of the film larger than that at the central portion is that the temperature of the shower bathed at both ends of the film is higher by 15 ° C. or more than the temperature of the shower bathed at the central portion of the film. Is. In the second mode, the total amount of showers showered at both ends of the film is made larger than the total amount of showers bathed at the center of the film. In any case, the temperature of water used for the shower is 55 ° C. or lower. This is because if the shower temperature is too high, the optical performance of the resulting polarizing film, and thus the polarizing plate, tends to deteriorate. Moreover, it is also preferable to make the degree of washing | cleaning of the both ends of a film larger than a center part by using combining a 1st form and a 2nd form.

In the case of adopting the first form, the temperature of the shower exposed to the central part (or the whole) of the film is preferably 2 to 25 ° C., more preferably 3 ° C. or more, and more preferably 20 ° C. or less. . On the other hand, the temperature of the shower showered on both ends of the film is preferably 10 to 55 ° C., more preferably 20 ° C. or higher, especially 25 ° C. or higher, and more preferably 53 ° C. or lower, especially 51 ° C. or lower. . Within this range, the shower temperature applied to both ends of the film is set to be 15 ° C. or more higher than the temperature of the shower applied to the center (or the whole). The temperature difference between showers at both ends and the center, that is, (shower temperature at both ends−shower temperature at the center) is more preferably 18 ° C. or more, and more preferably 20 ° C. or more. Is more preferable, and it is particularly preferable to exceed 20 ° C. When this temperature difference is less than 15 ° C., the effect of hue adjustment tends to be hardly exhibited.

On the other hand, in the case of adopting the second form, specifically, a method of increasing the flow rate per unit time of the shower showered at both ends of the film more than the flow rate of the shower bathed at the center of the film, A method can be employed in which the time for showering at both ends is longer than the time for showering at the center of the film. When adopting the second form, the temperature of the shower bathed at both ends of the film should be the same or higher than the shower bath bathed at the center of the film. This is preferable because a polarizing film having uniform optical properties can be obtained.

The total amount of showers that can be bathed on the film (the total amount of water that can be bathed on the center and both ends of the film) is not particularly limited, but is 0.05 to 20 L / m ² per unit area of the film from the viewpoint of production efficiency. It is preferably 0.1 to 10 L / m ² . The total time for showering the film (the total time for showering at the center and both ends of the film) is not particularly limited, but if it is too short, the effect cannot be obtained sufficiently, and if it is too long, a large apparatus is required. Therefore, the time is preferably 0.1 to 5 seconds.

As a more specific cleaning method, for example, a shower is taken at a plurality of locations along the film conveyance direction, and the degree of cleaning at both ends of the film is determined at the central portion of the film at some of the plurality of locations. In other places, the degree of cleaning of the entire film is made uniform, or the degree of cleaning of the central part of the film is made larger than both ends of the film, and in the entire width direction of the film, There is a method in which the degree of cleaning at both ends is greater than that at the center.

In the present invention, from the viewpoint that it is easy to make a difference between the degree of washing at both ends of the film and the degree of washing at the center of the film, it is possible to use a method in which a shower is taken at a plurality of locations along the film transport direction. preferable. In this case, on the upstream side in the film conveyance direction, the degree of washing of the entire film is made uniform, or the degree of washing of the central part of the film is made larger than both ends, and the downstream side in the film conveyance direction Thus, it is preferable that the degree of washing at both ends of the film is larger than that at the center. This is because the boundary of the shower is less likely to cause color unevenness.

An example of such a two-stage cleaning process will be described with reference to FIGS. 2B and 2C are views seen from the upper surface side of FIGS. 1 and 2A, respectively. As shown in FIGS. 1 and 2 (a), the film 1 is conveyed in the direction of the arrow in the figure by a conveying guide roll 2. Thereby, after the film 1 is immersed in the pure water 32 in the washing tank 31, the film 1 sequentially passes through the first-stage shower 41 and the second-stage shower 42. In each of the

showers

41 and 42, a plurality of

shower nozzles

411 and 421 are arranged in the width direction of the film 1. After the film 1 passes through the

showers

41 and 42, it is sent to the draining roll 5 to remove water adhering to the surface.

Here, as shown in FIG. 2C, in the first-stage shower 41, the shower is sprayed only from the shower nozzle 411a corresponding to the central portion of the film 1 in the shower nozzle 411. Next, as shown in FIG. 2 (b), in the second-stage shower 42, the shower is sprayed only from the shower nozzles 421 a corresponding to both ends of the film 1 in the shower nozzle 421, and the center of the film 1 is sprayed. The shower is not sprayed from the shower nozzle 421b corresponding to the portion.

Then, the shower temperature of the second-stage shower 42 is set to be 15 ° C. higher than the shower temperature of the first-stage shower 41 and / or the amount of water sprayed from the second-stage shower 42 is set to the first-stage shower 42. By increasing the number of showers 41, the degree of cleaning at both ends of the film can be made higher than that at the center.

Further, the present invention is not limited to such a form, and a shower may be applied only to both ends of the film. In this case, in the first stage along the film conveyance direction, the total width of both ends of the film to be showered is 5 to 60% of the entire film width, and in the second and subsequent stages, the shower is applied. The total width of both ends of the film is preferably 5 to 40% of the width of the entire film.

As shown in FIG. 1 and FIG. 2 (a) (the same applies to FIG. 3 and FIG. 4 (a) to be described later), in the cleaning process, it can be immersed in pure water 32 before taking a shower, and will be described later. As shown in the examples, the cleaning process can be configured only by an operation of taking a shower. In the present invention, as described above, it is possible to shower only at both ends of the film and not to shower at the center, but in this case, the film is immersed in pure water before showering. Is preferred. This is because it is preferable to clean the central portion of the film to some extent in order to adjust the optical characteristics of the polarizing film.

Furthermore, the shower may be taken in three or more locations along the film conveyance direction, that is, in three or more stages. In this case, when the showers at all locations are viewed comprehensively, the temperature of the shower that is applied to both ends of the film is set to be 15 ° C. higher than that of the shower that is applied to the center, and / or The total amount of showers showered at both ends is set to be larger than that at the center. In the case where there are two or more stages of showering only at both end portions of the film, the relationship between the both end portions and the central portion satisfies the provisions of the present invention at any stage.

An example of such a three-stage cleaning process will be described with reference to FIGS. 4B to 4D are views seen from the upper surface side of FIGS. 3 and 4A, respectively. As shown in FIG. 3 and FIG. 4A, the film 1 is conveyed in the direction of the arrow in the figure by the conveying guide roll 2. As a result, the film 1 is immersed in the pure water 32 in the cleaning tank 31 and then sequentially passes through the first-stage shower 41, the second-stage shower 42, and the third-stage shower 43. In each of the

showers

41, 42, 43, a plurality of

shower nozzles

411, 421, 431 are arranged in the width direction of the film 1. After the film 1 has passed through the

showers

41, 42, 43, it is sent to the draining roll 5 to remove the moisture adhering to the surface.

Here, as shown in FIG. 4 (d), in the first-stage shower 41, the shower is sprayed from the shower nozzle 411 corresponding to the entire width (or central portion) of the film 1. Next, as shown in FIG. 4 (c), in the second-stage shower 42, the shower is sprayed from only the shower nozzles 421 a corresponding to both ends of the film 1 of the shower nozzles 421, and the center of the film 1 is sprayed. The shower is not sprayed from the shower nozzle 421b in the portion corresponding to. Further, as shown in FIG. 4B, in the third-stage shower 43, the shower is sprayed only from the shower nozzles 431 a corresponding to the both ends of the film 1 in the shower nozzle 431, and the central portion of the film 1 is sprayed. The shower is not sprayed from the corresponding portion of the shower nozzle 431b. At this time, it is preferable that the width of the both ends where the shower in the third-stage shower 43 is sprayed is shorter than the width of both ends where the shower in the second-stage shower 42 is sprayed. For example, the total width of both ends of the film to be showered in the second stage is 5 to 60% of the width of the entire film, and the total width of both ends of the film to be showered in the third stage and after is The width is preferably 5 to 40%.

By performing such cleaning, the degree of cleaning at both ends of the film can be made larger than that at the center. However, the temperature of the second-stage shower 42 and / or the third-stage shower 43 is made higher than that of the first-stage shower 41 or the second-stage shower in order to further increase the effect of equalizing the optical characteristics. 42 and / or the flow rate of the third-stage shower 43 is preferably larger than that of the first-stage shower 41. However, even if the shower temperature and flow rate of each stage are not changed, showering only at both ends with the second-stage shower 42 and third-stage shower 43 increases the total amount of shower that can be showered at both ends of the film. In other words, since the degree of cleaning at both ends is greater than that at the center, it is possible to adopt this form as it is.

As described above, in the present invention, in the washing step after the dyeing step, boric acid treatment step (crosslinking step) and stretching step, the shower temperature bathed at both ends of the film is showered at the center portion of the film. The degree of washing at both ends becomes greater than that at the center by increasing the total amount of showers at both ends by increasing the temperature by 15 ° C. or higher than the temperature of the water. Like that. Here, the difference in shower temperature between the both ends and the center of the film and the difference in the total amount of shower are more likely to be different in the degree of cleaning, and the optical characteristics of the polarizing film to be obtained. , It is easy to make uniform in the width direction. Therefore, as long as the temperature difference between the showers at both ends and the center is 15 ° C. or more as described above, the total amount of showers that can be showered at both ends may be somewhat smaller than that at the center.

Therefore, when the temperature of the shower showered at both ends of the film is set to 15 ° C. or higher than the shower temperature bathed at the center of the film, the total amount of shower showered at both ends and the total shower showered at the center is not limited. It is preferable to make the total amount of showers showered at both ends larger than the total amount of showers bathed in the central part, because better uniformity can be obtained. Also, if the total amount of showers at both ends is greater than the total amount of showers at the center, the difference between the shower temperature at both ends of the film and the shower temperature at the center (from the former to the latter) The value obtained by subtracting the temperature may be less than 15 ° C. (including the case where both temperatures are the same), but the temperature of the shower bathed at both ends of the film is compared with the temperature of the shower bathed at the center portion. It is preferable that they are the same or higher because better uniformity can be obtained. In addition, the temperature of the shower bathed at both ends of the film should be 15 ° C. higher than the shower bath bathed at the center of the film, and the total amount of shower bathed at both ends should be greater than the total amount of shower bathed at the center. Is most preferred.

(Drying process)
In the method of the present invention, after the washing step, it is usually preferable to perform a drying treatment to obtain a polarizing film. For the drying process, for example, a hot air dryer, a far infrared heater, or the like is preferably used. The temperature of the drying process is preferably about 40 to 100 ° C., and the time of the drying process is preferably 60 to 600 seconds.

(Stretching process)
The film is uniaxially stretched before or during any of the dyeing step, boric acid treatment step and washing step described above. Uniaxial stretching may be performed in only one stretching process, or may be performed in a plurality of processes.

For the uniaxial stretching, a normal stretching method can be adopted. Examples of a normal stretching method include inter-roll stretching in which stretching is performed with a difference in peripheral speed between two nip rolls that transport the film. Specifically, for example, the peripheral speed of the downstream nip roll in the film transport direction is made larger than the peripheral speed of the upstream nip roll, and the film is stretched with tension. Further, a hot roll stretching method, a tenter stretching method, or the like as described in Japanese Patent No. 2731813 can also be used.

The uniaxial stretching may be dry stretching performed in the air, or may be wet stretching performed in a state where the film is swollen with a solvent.

When wet stretching is adopted, the general process is performed on an unstretched raw film in the order of swelling treatment, dyeing treatment, boric acid treatment, washing treatment, and drying treatment. Uniaxial stretching is performed in the previous step. There are no restrictions on the number of treatment baths or treatment conditions.

The final integrated draw ratio of the film stretching (the length of the polarizing film with respect to the length of the original film) is not particularly limited, but is preferably 4.5 to 7 times, more preferably about 5 to 6.5 times. It is.

(Other processes)
Moreover, the process which is not described in the said process can be inserted suitably for another purpose. Examples of such steps include immersion treatment in an aqueous iodide solution not containing boric acid (iodide treatment) after boric acid treatment, and immersion treatment in an aqueous solution containing no boric acid and containing zinc chloride or the like. (Zinc treatment).

A polarizing film is manufactured as described above. The thickness of the obtained polarizing film is preferably in the range of 5 to 50 μm.

(Polarizer)
A polarizing plate can be obtained by pasting a protective film with an adhesive on at least one surface of the polarizing film thus produced.

As the protective film, for example, a film made of an acetyl cellulose resin such as triacetyl cellulose or diacetyl cellulose, a film made of a polyester resin such as polyethylene terephthalate, polyethylene naphthalate or polybutylene terephthalate, or a film made of a polycarbonate resin And a film made of a cycloolefin resin, an acrylic resin film, a polypropylene resin film, and the like. In order to improve the adhesiveness between the adhesive and the polarizing film and / or protective film, the polarizing film and / or protective film may be subjected to corona treatment, flame treatment, plasma treatment, ultraviolet irradiation, primer coating treatment, saponification treatment, etc. A surface treatment may be applied.

Examples of the method of bonding the polarizing film and the protective film include a method of bonding the polarizing film and the protective film via an adhesive or an adhesive. Examples of the adhesive include a composition in which an acrylic resin, a styrene resin, a silicone resin, or the like is used as a base polymer and a crosslinking agent such as an isocyanate compound, an epoxy compound, or an aziridine compound is added thereto. Examples of the adhesive include a water-based adhesive using a polyvinyl alcohol-based resin aqueous solution, a water-based two-component urethane emulsion adhesive, and the like, and an active energy ray-curable adhesive as a non-water-based adhesive. The active energy ray-curable adhesive includes, for example, an adhesive made of an epoxy resin composition containing an epoxy resin that is cured by irradiation with active energy rays from the viewpoint of weather resistance, refractive index, cationic polymerization, and the like. Can be mentioned. However, it is not limited to these, and it is possible to use various adhesives (organic solvent adhesives, hot melt adhesives, solventless adhesives, etc.) that are usually used in the manufacture of polarizing plates. it can.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.

In the following examples and comparative examples, the obtained polarizing films were obtained by obtaining orthogonal hue b values for 5 points in the width direction, and the difference between the obtained maximum value (MAX) and minimum value (MIN). Δ (MAX−MIN) was used as an index of uniformity of optical characteristics. For the orthogonal hue b value, a polarizing film was set on an ultraviolet-visible spectrophotometer V-7100 manufactured by JASCO Corporation, and linearly polarized light in the transmission axis direction was incident on the polarizing film, and linearly polarized light in the absorption axis direction was incident thereon. In each case, an ultraviolet-visible transmission spectrum was measured, and based on the spectrum, it was obtained by software incorporated in the ultraviolet-visible spectrophotometer V-7100 used here. The b value here means the b value in Hunter's Lab color system, and the orthogonal hue b value means that two polarizing films are stacked so that their absorption axes are orthogonal to each other, and natural light is emitted from one surface thereof. This corresponds to the b value of the hue of light transmitted to the opposite surface when incident. Hereinafter, the orthogonal hue b value is abbreviated as “orthogonal b”.

Also, in each of the following examples, the single transmittance of the obtained polarizing film was adjusted to 42.8% ± 0.1% by adjusting the chemical concentration of the dyeing tank.

Example 1
A polyvinyl alcohol film (Kurarevinylon VF-PS # 7500, polymerization degree 2400, saponification degree 99.9 mol% or more) having a thickness of 75 μm and a width of 3000 mm is placed in tension so that the film does not loosen in 30 ° C. pure water. The film was immersed while keeping it, and the film was sufficiently swollen. Next, uniaxial stretching was performed while being immersed and dyed in an aqueous solution containing iodine and potassium iodide.

The film after dyeing is immersed in a 55 ° C. boric acid aqueous solution in which potassium iodide / boric acid / water has a weight ratio of 12 / 4.4 / 100, and is further subjected to water resistance treatment. The above-mentioned polyvinyl alcohol film) was uniaxially stretched until the cumulative draw ratio was 5.5 times. Then, it was immersed in 40 degreeC boric acid aqueous solution of the same composition. The width of the film at this stage was 1750 mm.

In the subsequent washing process, as a first-stage shower, a range of 950 mm in width corresponding to the center of the film (a range from the center in the width direction of the film to 475 mm on both sides, corresponding to 54% of the width of the entire film) Washing was performed by pouring pure water at 10 ° C. at a flow rate of 1 m ³ / hr for 0.5 seconds.

Next, as a second-stage shower, a total width of 800 mm corresponding to both ends of the film (a range from both ends in the width direction of the film to 400 mm, corresponding to 46% of the entire film width) is 30. Washing was performed by pouring pure water at 0 ° C. at a flow rate of 1 m ³ / hr for 0.5 seconds. Then, it dried at 70 degreeC for 3 minutes, and obtained the polarizing film.

(Example 2)
In the washing step, a polarizing film was obtained in the same manner as in Example 1 except that the first-stage shower was taken over the entire width (1750 mm) of the film.

(Comparative Example 1)
In the washing step, a polarizing film was obtained in the same manner as in Example 2 except that only washing by the first-stage shower was performed (no washing by the second-stage shower was performed).

(Comparative Example 2)
In the washing step, the range where the first-stage shower is taken is a range of 550 mm in width corresponding to the center of the film (a range from the center in the width direction of the film to 275 mm on both sides, corresponding to 31% of the width of the entire film) ) And the range where the second-stage shower can be taken is a range of a total width of 1200 mm corresponding to both ends of the film (each range from both ends in the width direction of the film to 600 mm, corresponding to 69% of the width of the entire film) A polarizing film was obtained in the same manner as in Example 1 except that.

(Comparative Example 3)
In the washing step, the range where the first-stage shower is taken is a range of 1700 mm in width corresponding to the center of the film (a range from the center in the width direction of the film to 850 mm on both sides, which corresponds to 97% of the width of the entire film) ) And the range where the second-stage shower can be taken is a total width of 50 mm corresponding to both ends of the film (each range from both ends in the width direction of the film to 25 mm, corresponding to 3% of the width of the entire film) A polarizing film was obtained in the same manner as in Example 1 except that.

With respect to the polarizing films obtained in Examples 1 and 2 and Comparative Examples 1 to 3, the values of orthogonal b (maximum value (MAX), minimum value (MIN) and difference Δ between both) were determined by the above-described method. . Table 1 shows the measurement results of orthogonal b, together with the shower conditions in the washing step and the total amount of water sprayed in each stage of shower (per unit area of the film).

(Example 3)
A polyvinyl alcohol film (Kurarevinylon VF-PS # 7500, polymerization degree 2400, saponification degree of 99.9 mol% or more) having a thickness of 75 μm and a width of 4000 mm is placed in tension so that the film does not loosen in 30 ° C. pure water. The film was immersed while keeping it, and the film was sufficiently swollen. Next, uniaxial stretching was performed while being immersed and dyed in an aqueous solution containing iodine and potassium iodide.

The film after dyeing is immersed in a 55 ° C. boric acid aqueous solution in which potassium iodide / boric acid / water is 12 / 4.4 / 100 in weight ratio, and further integrated from the original fabric. Uniaxial stretching was performed until the draw ratio reached 5.5 times. Then, it was immersed in 40 degreeC boric acid aqueous solution of the same composition. The film width at this stage was 2300 mm.

In the subsequent washing step, as a first-stage shower, a range of 1300 mm in width hitting the center of the film (a range from the center in the width direction of the film to 650 mm on both sides, corresponding to 57% of the entire film width) Washing was performed by pouring pure water at 5 ° C. at a flow rate of 1 m ³ / hr for 0.5 seconds.

Next, as a second-stage shower, a total width of 800 mm corresponding to both ends of the film (a range of 400 mm from both ends in the width direction of the film, corresponding to 35% of the entire width of the film) is 45. Washing was performed by pouring pure water at 0 ° C. at a flow rate of 1 m ³ / hr for 0.5 seconds. Then, it dried at 70 degreeC for 3 minutes, and obtained the polarizing film.

(Example 4)
In the washing step, a polarizing film was obtained in the same manner as in Example 1 except that the temperature of the second-stage shower was 10 ° C. and the flow rate was 4 m ³ / hr.

(Example 5)
In the washing step, a polarizing film was obtained in the same manner as in Example 1 except that the temperature of the second-stage shower was 10 ° C. and the showering time was 3 seconds.

(Example 6)
In this example, only the cleaning by the first-stage shower was performed in the cleaning process. Pure water at 25 ° C. is supplied at a flow rate of 1 m ³ / hr in a range of a total width of 800 mm that corresponds to both ends of the film (a range from each end in the width direction of the film to 400 mm, corresponding to 46% of the width of the entire film). A polarizing film was obtained in the same manner as in Example 1 except that the film was soaked for 0.5 seconds.

(Comparative Example 4)
In the cleaning process, the shower area is a range of a total width of 1200 mm that hits both ends of the film (a range from both ends in the width direction of the film to 600 mm, corresponding to 69% of the width of the entire film) Obtained a polarizing film in the same manner as in Example 6.

With respect to the polarizing films obtained in Examples 3 to 6 and Comparative Example 4 described above, the value of orthogonal b (maximum value (MAX), minimum value (MIN) and difference Δ between both) was determined by the method described above. Table 2 shows the measurement results of orthogonal b, together with the shower conditions in the washing step and the total amount of water sprayed in each stage of shower (per unit area of the film).

(Example 7)
In this example, the shower in the washing process was made into two stages, and both the shower areas were the both ends of the film. That is, as a first-stage shower, 25 ° C. in a range of a total width of 1000 mm corresponding to both ends of the film (a range from both ends in the width direction of the film to 500 mm, which corresponds to 43% of the entire width of the film) Of pure water was washed for 0.5 seconds at a flow rate of 1 m ³ / hr. Moreover, as a shower of the second stage, a total width of 600 mm corresponding to both ends of the film (a range from both ends in the width direction of the film to 300 mm, corresponding to 26% of the entire width of the film) is 45 ° C. Pure water was bathed at a flow rate of 1 m ³ / hr for 0.5 seconds. Other than that was carried out similarly to Example 3, and obtained the polarizing film.

(Example 8)
In this example, the processes up to iodine staining including uniaxial stretching of the polyvinyl alcohol film and boric acid treatment were performed in the same manner as in Example 3, and then three stages of showers were installed in the cleaning process. That is, as the first stage shower, similarly to the first stage of Example 3, the range of 1300 mm in width hitting the center of the film (the range from the center in the width direction of the film to 650 mm on both sides, the width of the entire film) (Corresponding to 57%) was washed by pouring pure water at 5 ° C. at a flow rate of 1 m ³ / hr for 0.5 seconds. Next, as a second-stage shower, 30 ° C. in a range of a total width of 1000 mm corresponding to both ends of the film (a range from both ends in the width direction of the film to 500 mm, corresponding to 43% of the entire width of the film) Of pure water was washed for 0.5 seconds at a flow rate of 1 m ³ / hr. In addition, as a third-stage shower, 50 ° C. in a range of a total width of 600 mm corresponding to both ends of the film (a range from both ends in the width direction of the film to 300 mm, corresponding to 26% of the entire width of the film) Of pure water was washed for 0.5 seconds at a flow rate of 1 m ³ / hr. Then, it dried similarly to Example 3 and obtained the polarizing film.

Example 9
In the washing step, a polarizing film was obtained in the same manner as in Example 8 except that the first-stage shower was applied to the full width of the film (2300 mm).

(Comparative Example 5)
In the washing step, the range where the second-stage shower is taken is a range of a total width of 1600 mm that hits both ends of the film (a range from each end in the width direction of the film to 800 mm, which corresponds to 70% of the width of the entire film. A polarizing film was obtained in the same manner as in Example 9 except that.

With respect to the polarizing films obtained in Examples 7 to 9 and Comparative Example 5 described above, the values of orthogonal b (maximum value (MAX), minimum value (MIN) and difference Δ between both) were determined by the method described above. Table 3 shows the measurement results of orthogonal b, together with the shower conditions in the washing step and the total amount of water sprayed in each stage of shower (per unit area of the film).

(Example 10)
In the washing step, the range in which the second-stage shower is taken is a range of a total width of 200 mm corresponding to both ends of the film (a range from each end in the width direction of the film to 100 mm, corresponding to 11% of the entire width of the film. In the same manner as in Example 2 except that the temperature of the second-stage shower was 25 ° C., a polarizing film was obtained.

(Example 11)
A polarizing film was obtained in the same manner as in Example 10 except that the temperature of the second-stage shower was 50 ° C. in the washing step.

(Comparative Example 6)
In the washing step, a polarizing film was obtained in the same manner as in Example 10 except that the temperature of the second-stage shower was 5 ° C.

(Comparative Example 7)
A polarizing film was obtained in the same manner as in Example 10 except that the temperature of the second-stage shower was 60 ° C. in the washing step.

For the polarizing films obtained in Examples 10 and 11 and Comparative Examples 6 and 7, the values of orthogonal b (maximum value (MAX), minimum value (MIN), and difference Δ between the two) were determined by the above-described method. . Table 4 shows the measurement results of the orthogonal b, together with the shower conditions in the washing step and the total amount of water sprayed in each stage of the shower (per unit area of the film).

As shown in Tables 1 to 4, according to the present invention, the polarizing film manufactured in such a manner that the degree of cleaning at both ends of the film is larger than that at the center of the film, the maximum value (MAX) and the minimum value ( The difference Δ from MIN) is small, and the uniformity is excellent.

The polarizing plate produced by the method of the present invention can be effectively applied to various display devices including liquid crystal display devices.

1 film, 2 transport guide roll, 31 washing tank, 32 pure water, 41, 42, 43 shower, 411, 411a, 411b, 421, 421a, 421b, 431, 431a, 431b shower nozzle, 5 draining roll.

Claims

A dyeing process for dyeing a film composed of a polyvinyl alcohol resin;
A boric acid treatment step of treating the film with boric acid;
A cleaning step of cleaning the film,
Further, before or during any of the above steps, a method for producing a polarizing film comprising a stretching step of uniaxially stretching the film,
The washing step includes an operation of showering the film,
The operation of taking a shower is performed by dividing into both ends corresponding to a total of 5 to 60% and a central portion inside in the width direction based on the width of the entire film,
The temperature of the shower showered on both ends is 55 ° C. or lower, and the shower temperature showered on both ends is higher by 15 ° C. or more than the temperature of the shower bathed on the center, and / or the both ends The production of a polarizing film is characterized in that the total amount of shower to be bathed is larger than the total amount of shower to be bathed in the central portion so that the degree of cleaning of both end portions is larger than that of the central portion. Method.
In the operation of taking a shower, increasing the total amount of showers to be applied to both ends than the total amount of showers to be applied to the center is that the flow rate of showers to be applied to both ends is the flow rate of showers to be applied to the center. The manufacturing method of the polarizing film of Claim 1 performed by making more than.
In the operation of taking a shower, increasing the total amount of showers to be applied to both ends than the total amount of showers to be applied to the center is that the time to take showers at the ends is the time to take showers at the center. The manufacturing method of the polarizing film of Claim 1 performed by making it longer than this.
The showering operation is performed by increasing the total amount of showers showered at both ends than the total amount of showers showered at the center, and the shower temperature bathed at both ends is the temperature of the shower bathed at the center. The manufacturing method of the polarizing film of Claim 1 which is the same or higher compared with temperature.
The operation of taking a shower is performed at a plurality of locations in the transport direction of the film,
In some of the plurality of locations, the degree of cleaning at both ends is greater than the central portion,
5. In other places, the degree of washing of the entire film is made uniform, or the degree of washing of the central part is made larger than that of the both end parts. Manufacturing method of the polarizing film.