JP2024018990A - Polarizing film manufacturing method and manufacturing equipment - Google Patents

Abstract

An object of the present invention is to provide a novel method for producing a polarizing film that allows waste liquid to be recycled without going through complicated steps. A manufacturing method for manufacturing a polarizing film from a polyvinyl alcohol resin film, comprising: a chemical treatment step in which a chemical solution is brought into contact with the polyvinyl alcohol resin film to perform a chemical treatment; and after the chemical treatment step, the The chemical solution treatment step includes a cleaning step of washing the polyvinyl alcohol resin film with a cleaning solution, and a recycling step of adding at least a part of the waste solution generated in the cleaning step to the chemical solution, and the chemical solution treatment step includes the step of adding the chemical solution to the dyeing solution. A manufacturing method comprising at least one of a certain dyeing step and a crosslinking step in which the chemical solution is a crosslinking liquid. [Selection diagram] Figure 1

Description

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

Polarizing plates are widely used as polarizing elements in image display devices such as liquid crystal display devices. A polarizing plate generally has a structure in which a transparent resin film (protective film, etc.) is bonded to one or both sides of a polarizing film using an adhesive or the like.

Polarizing film is mainly produced by immersing a raw film made of polyvinyl alcohol-based resin in a dyeing bath containing a dichroic dye such as iodine, and then immersing it in a cross-linking bath containing a cross-linking agent such as boric acid. It is manufactured by subjecting the film to uniaxial stretching at some stage.

Conventionally, it has been known to wash a film immersed in a dyeing bath or a crosslinking bath with water in order to wash away chemicals such as boric acid adhering to the surface of the film. JP-A No. 10-160935 (Patent Document 1) describes that in the water washing step, the deterioration of polarization properties is suppressed by washing with water using an aqueous potassium iodide solution having a potassium iodide concentration of 1.5 to 5% by weight. ing. JP 2021-154214A (Patent Document 2) describes a waste liquid treatment method for recovering potassium iodide from the waste liquid.

Japanese Patent Application Publication No. 10-160935 JP 2021-154214 Publication

An object of the present invention is to provide a novel method for producing a polarizing film that allows waste liquid to be recycled without going through complicated steps.

The present invention provides a polarizing film manufacturing method and manufacturing apparatus shown below.
[1] A manufacturing method for manufacturing a polarizing film from a polyvinyl alcohol resin film, comprising:
a chemical solution treatment step of bringing a chemical solution into contact with the polyvinyl alcohol resin film to perform a chemical solution treatment;
a cleaning step of cleaning the polyvinyl alcohol resin film with a cleaning solution after the chemical treatment step;
a recycling step of adding at least a portion of the waste liquid generated in the cleaning step to the chemical solution,
In the manufacturing method, the chemical solution treatment step is at least one step selected from the group consisting of a dyeing step in which the chemical solution is a dyeing solution, and a crosslinking step in which the chemical solution is a crosslinking solution.
[2] The manufacturing method according to [1], wherein in the recycling step, at least a portion of the waste liquid is concentrated to 1/10 or less on a volume basis and added to the chemical solution.
[3] A manufacturing method for manufacturing a polarizing film from a polyvinyl alcohol resin film, comprising:
a chemical solution treatment step of bringing a chemical solution into contact with the polyvinyl alcohol resin film to perform a chemical solution treatment;
a recycling step of concentrating at least a portion of the waste liquid generated in the process of manufacturing the polarizing film from the polyvinyl alcohol resin film to 1/2 or less on a volume basis and adding it to the chemical solution;
In the manufacturing method, the chemical solution treatment step is at least one step selected from the group consisting of a dyeing step in which the chemical solution is a dyeing solution, and a crosslinking step in which the chemical solution is a crosslinking solution.
[4] Further comprising a cleaning step of cleaning the polyvinyl alcohol resin film with a cleaning liquid after the chemical treatment step,
The manufacturing method according to [3], wherein the waste liquid includes the cleaning liquid.
[5] The manufacturing method according to any one of [1] to [4], wherein in the chemical treatment step, the temperature of the chemical is 50° C. or higher.
[6] The production method according to any one of [1] to [5], wherein the waste liquid contains at least one of potassium iodide and boric acid.
[7] The method according to any one of [1] to [6], wherein in the recycling step, the boric acid concentration of the waste liquid added to the chemical solution is 0.01% by mass or more and 5.0% by mass or less. Production method.
[8] The manufacturing method according to any one of [1] to [7], wherein the chemical solution treatment step is a crosslinking step in which the chemical solution is a crosslinking solution.
[9] A manufacturing device for manufacturing a polarizing film from a polyvinyl alcohol resin film, comprising:
a chemical liquid processing unit that performs chemical liquid treatment by bringing a chemical liquid into contact with the polyvinyl alcohol resin film;
a recycling unit that concentrates at least a portion of the waste liquid generated in the process of manufacturing the polarizing film from the polyvinyl alcohol resin film to 1/2 or less on a volume basis and adds it to the chemical solution;
The chemical processing section is at least one selected from the group consisting of a dyeing section where the chemical solution is a staining solution, and a crosslinking section where the chemical solution is a crosslinking solution.
[10] A manufacturing device for manufacturing a polarizing film from a polyvinyl alcohol resin film, comprising:
a chemical liquid processing unit that performs chemical liquid treatment by bringing a chemical liquid into contact with the polyvinyl alcohol resin film;
a cleaning section that cleans the polyvinyl alcohol resin film with a cleaning solution after the chemical treatment section;
a recycling section that adds at least a portion of the waste liquid generated in the cleaning section to the chemical solution;
The chemical processing section is at least one selected from the group consisting of a dyeing section where the chemical solution is a staining solution, and a crosslinking section where the chemical solution is a crosslinking solution.

According to the present invention, in the method for manufacturing a polarizing film, waste liquid can be recycled without going through complicated steps.

BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing which shows typically an example of the manufacturing method of the polarizing film based on this invention, and the polarizing film manufacturing apparatus used for it.

<Manufacturing method of polarizing film>
In the present invention, the polarizing film is a uniaxially stretched polyvinyl alcohol resin film on which a dichroic dye (iodine or dichroic dye) is adsorbed and oriented. The polyvinyl alcohol resin constituting the polyvinyl alcohol resin film is usually obtained by saponifying polyvinyl acetate resin. The degree of saponification is preferably 85 mol% or more, more preferably 90 mol% or more, even more preferably 99 mol% or more. The polyvinyl acetate resin may be, for example, a polyvinyl acetate homopolymer of vinyl acetate, or a copolymer of vinyl acetate and another monomer copolymerizable therewith. 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 1,000 to 10,000, preferably 1,500 to 5,000.

These polyvinyl alcohol resins may be modified; for example, polyvinyl formal, polyvinyl acetal, polyvinyl butyral, etc. modified with aldehydes may also be used.

In the present invention, as a starting material for producing a polarizing film, an unstretched polyvinyl alcohol resin film (original film) having a thickness of 65 μm or less (for example, 60 μm or less), preferably 50 μm or less, more preferably 35 μm or less, and even more preferably 30 μm or less is used. film). This makes it possible to obtain thin polarizing films for which market demand is increasing. The width of the raw film is not particularly limited, and can be, for example, about 400 to 6000 mm. The raw film is prepared, for example, as a roll (original roll) of a long unstretched polyvinyl alcohol resin film.

Further, the polyvinyl alcohol resin film used in the present invention may be laminated on a base film that supports the polyvinyl alcohol resin film. It may also be prepared as a laminated film with a polyvinyl alcohol resin film. In this case, the polyvinyl alcohol resin film can be produced, for example, by applying a coating liquid containing a polyvinyl alcohol resin to at least one surface of the base film and then drying the coating solution.

As the base film, for example, a film made of thermoplastic resin can be used. A specific example is a film made of a translucent thermoplastic resin, preferably an optically transparent thermoplastic resin, such as a chain polyolefin resin (polypropylene resin, etc.), a cyclic polyolefin resin, etc. Polyolefin resins such as (norbornene resins, etc.); Cellulose resins such as triacetylcellulose and diacetylcellulose; Polyester resins such as polyethylene terephthalate and polybutylene terephthalate; Polycarbonate resins; Methyl methacrylate resins, etc. (meth)acrylic resin; polystyrene resin; polyvinyl chloride resin; acrylonitrile/butadiene/styrene resin; acrylonitrile/styrene resin; polyvinyl acetate resin; polyvinylidene chloride resin; polyamide resin; polyacetal resin Resin; modified polyphenylene ether resin; polysulfone resin; polyether sulfone resin; polyarylate resin; polyamideimide resin; polyimide resin and the like.

The polarizing film is manufactured by unwinding the long original film from the original roll and continuously conveying it along the film transport path of the polarizing film manufacturing equipment, thereby combining the long original film and the processing liquid. By carrying out a drying process after carrying out a predetermined contacting process, a long polarizing film can be continuously manufactured. Note that the treatment process is not limited as long as it is a method of treating the film by bringing it into contact with the treatment liquid, and a method of treating the film by attaching the treatment liquid to the film surface by spraying, flowing down, dropping, dipping, etc. It may be. When the treatment step is performed by immersing the film in a treatment solution, the number of treatment solutions used in one treatment step is not limited to one, and the film can be immersed in two or more treatment solutions in sequence. One processing step may be completed.

Examples of the treatment liquid include a swelling liquid, a staining liquid, a crosslinking liquid, and a washing liquid. The above-mentioned processing steps include a swelling step in which a swelling solution is brought into contact with the original film to perform a swelling treatment, a dyeing step in which a dyeing solution is brought into contact with the film after the swelling treatment, and a dyeing step in which a dyeing solution is brought into contact with the film after the swelling treatment; Examples include a crosslinking process in which a crosslinking liquid is brought into contact with the film to perform a crosslinking process, and a cleaning process in which a cleaning liquid is brought into contact with the film after the crosslinking process and a cleaning process is performed. Further, between a series of these processing steps (that is, before or after any one or more processing steps and/or during any one or more processing steps), a wet or dry uniaxial stretching process can be performed. Other processing steps may be added as necessary.

The present invention further includes a recycling step in which at least a portion of the waste liquid generated in the process of manufacturing the polarizing film is added to the chemical solution. Examples of the chemical solution include a staining solution, a crosslinking solution, and the like. Examples of the waste liquid include swelling liquid surplus in the swelling process, dyeing liquid surplus in the dyeing process, crosslinking liquid surplus in the crosslinking process, and cleaning liquid surplus in the washing process. The waste liquid may be a mixture of multiple types of treatment liquids. The waste liquid may or may not be concentrated at the time it is added to the drug solution. When the waste liquid is concentrated, it can be concentrated to, for example, 1/2 or less on a volume basis. By concentrating the waste liquid, the volume of the waste liquid can be reduced. The waste liquid may be concentrated to 1/5 or less, or may be concentrated to 1/10 or less. Even when the waste liquid is concentrated, it is preferable to concentrate it to 1/50 or more from the viewpoint of energy load.

The cleaning process is performed for the purpose of removing dirt attached to the polarizing film, adjusting the concentration of chemicals remaining in the polarizing film, etc., and requires a larger amount of processing liquid (here, cleaning liquid) than other processing processes. May be used. When using cleaning liquid as waste liquid, it does not need to be concentrated at the time it is added to the chemical solution, but if it is concentrated, the amount is larger than the waste liquid discharged from other treatment processes, so it should be stored and stored. In order to reduce the amount of waste liquid to be transferred, it may be concentrated to, for example, 1/10 or less on a volume basis.

If the waste liquid contains drugs originally contained in the added chemical solution, such drugs can be recycled. Such agents include potassium iodide, boric acid, zinc chloride, and the like. Preferably, the recycled waste liquid contains at least one of potassium iodide and boric acid. In the recycling step of the present invention, such chemicals can be recycled, and costs can be reduced.

Hereinafter, an example of the method for manufacturing a polarizing film according to the present invention will be described in detail with reference to FIG. FIG. 1 is a sectional view schematically showing an example of a polarizing film manufacturing method and a polarizing film manufacturing apparatus used therein according to the present invention. The polarizing film manufacturing apparatus shown in FIG. 1 transports an original (unstretched) film 10 made of polyvinyl alcohol resin along a film transport path while continuously unwinding it from an original roll 11. The swelling liquid 13, the staining liquid 15, the first crosslinking liquid 17a, the second crosslinking liquid 17b, and the cleaning liquid 19 provided on the conveyance path are sequentially passed through, and finally passed through the drying oven 21. The obtained polarizing film 23 can be transported as it is, for example, to the next polarizing plate production process (a process of laminating a protective film on one or both sides of the polarizing film 23). The arrows shown on the films 10 and 23 in FIG. 1 indicate the transport direction of the film. The polarizing film manufacturing device shown in FIG. and a crosslinking liquid.

In the description of FIG. 1, the "processing tank" is a general term including a swelling tank, a dyeing tank, a crosslinking tank, and a washing tank. The swelling tank is a tank that stores a swelling liquid, the dyeing tank is a tank that stores a dyeing liquid, the crosslinking liquid is a tank that stores a crosslinking liquid, and the washing tank is a tank that stores a cleaning liquid. "Chemical solution tank" is a general term that includes a dyeing tank and a crosslinking tank. "Processing solution" is a generic term that includes a swelling solution, a staining solution, a crosslinking solution, and a cleaning solution. It is a generic term that includes The swelling tank containing the swelling solution and the swelling solution, the dyeing solution and the dyeing tank containing the dyeing solution, the crosslinking solution and the crosslinking tank containing the crosslinking solution, and the cleaning solution and the cleaning tank containing the cleaning solution are It constitutes a swelling section, a dyeing section, a crosslinking section, and a washing section in the manufacturing apparatus of the invention. Further, the system for supplying the waste liquid to the chemical solution, including the waste liquid recovery tank 71, constitutes a recycling section in the manufacturing apparatus of the present invention.

In addition to the above-mentioned processing liquid, the film transport path of the polarizing film manufacturing apparatus includes guide rolls 30 to 48, 60, and 61 that support the film to be transported or can further change the film transport direction, and the film to be transported. It can be constructed by arranging nip rolls 50 to 55 at appropriate positions, which can press and nip and apply driving force to the film by rotation, or can further change the film transport direction. Guide rolls and nip rolls can be placed before and after each treatment liquid, or in the treatment liquid, thereby allowing the film to be introduced into, immersed in, and pulled out from the treatment liquid (see FIG. 1). For example, the film can be immersed in each treatment liquid by providing one or more guide rolls in each treatment liquid and transporting the film along these guide rolls.

In the polarizing film manufacturing apparatus shown in FIG. 1, nip rolls are placed before and after each processing liquid (nip rolls 50 to 54), and thereby the nip rolls placed before and after each processing liquid are placed in one or more of the processing liquids. It is now possible to perform inter-roll stretching in which longitudinal uniaxial stretching is performed with a peripheral speed difference between the rolls. Each step will be explained below.

(swelling process)
The swelling step is performed for the purposes of removing foreign matter from the surface of the raw film 10, removing plasticizers in the raw film 10, imparting dyeability, plasticizing the raw film 10, and the like. The processing conditions are determined within a range in which the objective can be achieved and in which problems such as extreme dissolution and devitrification of the original film 10 do not occur.

Referring to FIG. 1, in the swelling step, the raw film 10 is continuously unwound from the raw roll 11 and conveyed along the film transport path, and the raw film 10 is immersed in the swelling liquid 13 for a predetermined time. , and then by retrieving. In the example of FIG. 1, from when the raw film 10 is unwound until it is immersed in the swelling liquid 13, the raw film 10 is transported along the film transport path constructed by the guide rolls 60, 61 and the nip roll 50. be done. In the swelling process, the film is transported along a film transport path constructed by guide rolls 30 to 32 and nip rolls 51.

In addition to pure water, the swelling liquid may include boric acid (Japanese Unexamined Patent Publication No. 10-153709), chlorides (Japanese Unexamined Patent Publication No. 06-281816), inorganic acids, inorganic salts, water-soluble organic solvents, alcohols, etc. It is also possible to use aqueous solutions with additions in the range of 0.01 to 10% by weight.

The temperature of the swelling liquid 13 is, for example, about 10 to 50°C, preferably about 10 to 40°C, more preferably about 15 to 30°C. The immersion time of the raw film 10 is preferably about 10 to 300 seconds, more preferably about 20 to 200 seconds. Further, when the raw film 10 is a polyvinyl alcohol resin film stretched in advance in gas, the temperature of the swelling liquid 13 is, for example, about 20 to 70°C, preferably about 30 to 60°C. The immersion time of the raw film 10 is preferably about 30 to 300 seconds, more preferably about 60 to 240 seconds.

In the swelling process, the problem that the raw film 10 swells in the width direction and wrinkles are likely to occur in the film tends to occur. As one means for transporting the film while removing wrinkles, it is possible to use a roll having a width-expanding function such as an expander roll, spiral roll, or crown roll for the guide rolls 30, 31, and/or 32, or use a cross guider or a bend bar. , or using other widening devices such as tenter clips. Another means for suppressing the occurrence of wrinkles is to perform a stretching process. For example, the uniaxial stretching process can be performed in the swelling liquid 13 using the difference in circumferential speed between the nip rolls 50 and 51.

In the swelling treatment, the film swells and expands in the film transport direction, so if the film is not actively stretched, the film is placed before and after the swelling liquid 13, for example, in order to eliminate sagging of the film in the transport direction. It is preferable to take measures such as controlling the speed of the nip rolls 50, 51. In addition, for the purpose of stabilizing the transport of the film in the swelling liquid 13, the water flow in the swelling liquid 13 is controlled by an underwater shower, and an EPC device (Edge Position
It is also useful to use a control device: a device that detects the edge of the film and prevents the film from meandering.

In the example shown in FIG. 1, the film pulled out from the swelling liquid 13 passes through the guide roll 32, the nip roll 51, and the guide roll 33 in this order and is introduced into the dyeing liquid 15.

(dying process)
The dyeing step is performed for the purpose of adsorbing and orienting the dichroic dye to the polyvinyl alcohol resin film after the swelling treatment. The processing conditions are determined within a range in which the objective can be achieved and in which problems such as extreme dissolution and devitrification of the film do not occur. Referring to FIG. 1, the dyeing process includes transporting the film along a film transport path constructed by nip rolls 51, guide rolls 33 to 36, and nip rolls 52, and immersing the film after swelling treatment in dyeing solution 15 for a predetermined time. This can then be carried out by withdrawal. In order to improve the dyeability of the dichroic dye, the film subjected to the dyeing process is preferably a film that has been subjected to at least some uniaxial stretching treatment, or instead of the uniaxial stretching treatment before the dyeing treatment, or In addition to the uniaxial stretching process before the dyeing process, it is preferable to perform the uniaxial stretching process during the dyeing process.

When using iodine as a dichroic dye, the staining solution 15 has a concentration of, for example, iodine/potassium iodide/water in a weight ratio of 0.003 to 0.3/0.1 to 10/100. An aqueous solution can be used. Instead of potassium iodide, other iodides such as zinc iodide may be used, or potassium iodide and other iodides may be used together. Further, compounds other than iodide, such as boric acid, zinc chloride, cobalt chloride, etc., may be coexisting. When the dyeing solution contains boric acid, it is distinguished from the crosslinking solution in the crosslinking step described below in that it contains iodine, and the aqueous solution contains 0.003 parts by weight or more of iodine per 100 parts by weight of water. For example, it can be regarded as a staining solution 15. The temperature of the dyeing liquid 15 when dipping the film is usually about 10 to 45°C, preferably 10 to 40°C, more preferably 20 to 35°C, and the immersion time of the film is usually 30 to 600 seconds. about 60 to 300 seconds, preferably 60 to 300 seconds.

When using a water-soluble dichroic dye as the dichroic dye, the dyeing liquid 15 may be an aqueous solution having a concentration of dichroic dye/water = 0.001 to 0.1/100 in weight ratio, for example. can be used. This dyeing solution 15 may contain a dyeing aid or the like, for example, an inorganic salt such as sodium sulfate, a surfactant, or the like. One type of dichroic dye may be used alone, or two or more types of dichroic dyes may be used in combination. The temperature of the dyeing solution 15 when dipping the film is, for example, about 20 to 80°C, preferably 30 to 70°C, and the immersion time of the film is usually about 30 to 600 seconds, preferably about 60 to 300 seconds. be.

As described above, in the dyeing process, the film can be uniaxially stretched using the dyeing liquid 15. The uniaxial stretching of the film can be performed by a method such as creating a difference in peripheral speed between the nip rolls 51 and 52 placed before and after the dyeing liquid 15.

In the dyeing process, guide rolls 33, 34, 35 and/or 36 are equipped with expander rolls, spiral rolls, crown rolls, etc. in order to transport the polyvinyl alcohol resin film while removing wrinkles from the film, as in the swelling process. Rolls with a width-spreading function can be used, or other width-spreading devices such as cross guiders, bend bars, tenter clips, etc. can be used. Another means for suppressing the occurrence of wrinkles is to perform a stretching treatment, similar to the swelling treatment.

In the example shown in FIG. 1, the film pulled out from the dyeing liquid 15 passes through a guide roll 36, a nip roll 52, and a guide roll 37 in order and is introduced into the crosslinking liquid 17.

(Crosslinking process)
The crosslinking step is a treatment step carried out for the purpose of making the film water resistant and adjusting the hue (preventing the film from becoming bluish, etc.). In the example shown in FIG. 1, two crosslinking liquids are arranged as the crosslinking liquids for performing the crosslinking process. The crosslinking step is performed using the second crosslinking liquid 17b. Referring to FIG. 1, the first crosslinking step involves transporting the film along a film transport path constructed by nip rolls 52, guide rolls 37 to 40, and nip rolls 53a, and dyeing the film in first crosslinking liquid 17a. It can be carried out by soaking for a time and then withdrawing. In the second crosslinking step, the film is transported along the film transport path constructed by the nip rolls 53a, guide rolls 41 to 44, and nip rolls 53b, and the film after the first crosslinking step is immersed in the second crosslinking liquid 17b for a predetermined time. This can be done by pulling out. Hereinafter, the term crosslinking liquid includes both the first crosslinking liquid 17a and the second crosslinking liquid 17b, and the term crosslinking liquid includes both the first crosslinking liquid and the second crosslinking liquid.

As the crosslinking liquid, a solution in which a crosslinking agent is dissolved in a solvent can be used. Examples of the crosslinking agent include boron compounds such as boric acid and borax, glyoxal, and glutaraldehyde. These may be used alone or in combination of two or more. As the solvent, for example, water can be used, but it may also contain an organic solvent that is compatible with water. Although the concentration of the crosslinking agent in the crosslinking solution is not limited thereto, it is preferably in the range of 1 to 20% by weight, more preferably 6 to 15% by weight.

The crosslinking liquid may be an aqueous solution containing, for example, 1 to 10 parts by weight of boric acid per 100 parts by weight of water. When the dichroic dye used in the dyeing treatment is iodine, the crosslinking liquid preferably contains iodide in addition to boric acid, and the amount thereof is, for example, 1 to 30 parts by weight per 100 parts by weight of water. It can be done. Examples of iodides include potassium iodide and zinc iodide. Further, compounds other than iodide, such as zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, and sodium sulfate, may be present.

In the crosslinking treatment, the concentrations of boric acid and iodide and the temperature of the crosslinking liquid 17 can be changed as appropriate depending on the purpose. For example, in the case of the first crosslinking solution whose purpose in crosslinking treatment is water resistance through crosslinking, it can be an aqueous solution having a concentration of boric acid/iodide/water in a weight ratio of 3 to 10/1 to 20/100. If necessary, other crosslinking agents may be used in place of boric acid, or boric acid and other crosslinking agents may be used in combination. The temperature of the first crosslinking liquid 17a when dipping the film is usually about 50 to 70°C, preferably 53 to 65°C, and the immersion time of the film is usually about 10 to 600 seconds, preferably 20 to 300 seconds. , more preferably 20 to 200 seconds. Further, when dyeing treatment and first crosslinking treatment are performed in this order on a pre-stretched polyvinyl alcohol resin film before swelling treatment, the temperature of the first crosslinking liquid 17a is usually about 50 to 85°C, preferably about 55 to 85°C. The temperature is 80°C.

In the second crosslinking liquid for the purpose of hue adjustment, for example, when iodine is used as a dichroic dye, an aqueous solution with a concentration of boric acid/iodide/water = 1 to 5/3 to 30/100 in weight ratio is used. can be used. The temperature of the second crosslinking liquid 17b when dipping the film is usually about 10 to 45°C, and the dipping time of the film is usually about 1 to 300 seconds, preferably 2 to 100 seconds.

The crosslinking treatment may be performed multiple times, and is usually performed 2 to 5 times. In this case, the composition and temperature of each crosslinking liquid used may be the same or different as long as they are within the above ranges. The crosslinking treatment for water resistance and the crosslinking treatment for hue adjustment may be performed in multiple steps.

Uniaxial stretching treatment can also be performed in the first crosslinking liquid 17a by utilizing the difference in peripheral speed between the nip rolls 52 and the nip rolls 53a. Further, the uniaxial stretching process can also be performed in the second crosslinking liquid 17b using the difference in circumferential speed between the nip rolls 53a and 53b.

In the crosslinking treatment, in order to convey the polyvinyl alcohol resin film while removing wrinkles from the film as in the swelling treatment, an expander roll and a spiral roll are used in the guide rolls 38, 39, 40, 41, 42, 43 and/or 44. , a roll having a width-expanding function such as a crown roll, or other width-expanding devices such as a cross guider, a bend bar, or a tenter clip may be used. Another means for suppressing the occurrence of wrinkles is to perform a stretching treatment, similar to the swelling treatment.

In the example shown in FIG. 1, the film pulled out from the second crosslinking liquid 17b passes through the guide roll 44 and the nip roll 53b in this order and is introduced into the cleaning liquid 19.

(Washing process)
The example shown in FIG. 1 includes a washing step after the crosslinking step. The cleaning treatment is performed for the purpose of removing excess chemicals such as boric acid and iodine that have adhered to the polyvinyl alcohol resin film, and for the purpose of adjusting the concentration of chemicals such as boric acid and iodine within the polyvinyl alcohol resin film. be exposed. The cleaning step is performed, for example, by immersing the crosslinked polyvinyl alcohol resin film in the cleaning liquid 19. Note that the cleaning process may be performed by spraying a cleaning liquid onto the film as a shower instead of immersing the film in the cleaning liquid 19, or by using a combination of immersion in the cleaning liquid 19 and spraying of the cleaning liquid. can.

FIG. 1 shows an example in which a polyvinyl alcohol resin film is immersed in a cleaning liquid 19 to perform a cleaning process. The temperature of the cleaning liquid 19 in the cleaning process is usually about 2 to 40°C, and the immersion time of the film is usually about 2 to 120 seconds.

In addition, in the cleaning process, for the purpose of transporting the polyvinyl alcohol resin film while removing wrinkles, the guide rolls 45, 46, 47 and/or 48 are rolls having a width-expanding function such as expander rolls, spiral rolls, and crown rolls. or other widening devices such as cross guiders, bend bars, and tenter clips. Furthermore, in the film cleaning process, a stretching process may be performed to suppress the occurrence of wrinkles.

(Stretching process)
As mentioned above, the raw film 10 is subjected to uniaxial stretching in a wet or dry manner during the series of processing steps (that is, before and/or during any one or more processing steps). It is processed. A specific method for the uniaxial stretching process is, for example, to perform longitudinal uniaxial stretching with a difference in circumferential speed between two nip rolls (for example, two nip rolls placed before and after the processing liquid) that make up the film transport path. Stretching, hot roll stretching as described in Japanese Patent No. 2731813, tenter stretching, etc. may be used, and inter-roll stretching is preferable. The uniaxial stretching step can be performed multiple times until the polarizing film 23 is obtained from the original film 10. As mentioned above, the stretching treatment is also advantageous in suppressing the occurrence of wrinkles in the film.

The final cumulative stretching ratio of the polarizing film 23 based on the original film 10 is usually about 4.5 to 7 times, preferably 5 to 6.5 times. The stretching process may be performed in any process, and even when the stretching process is performed in two or more processes, the stretching process may be performed in any process.

(drying process)
After the washing step, it is preferable to perform a process of drying the polyvinyl alcohol resin film. Drying of the film is not particularly limited, but can be performed using a drying oven 21 as in the example shown in FIG. The drying oven 21 may include, for example, a hot air dryer. The drying temperature is, for example, about 30 to 100°C, and the drying time is, for example, about 30 to 600 seconds. The process of drying the polyvinyl alcohol resin film can also be performed using a far-infrared heater. The thickness of the polarizing film 23 obtained as described above is, for example, about 5 to 30 μm.

The obtained polarizing film may be sequentially wound onto a take-up roll to form a roll, or it may be directly subjected to a polarizing plate production process (a process of laminating a protective film, etc. on one or both sides of the polarizing film) without being wound. You can also do it.

(Other processing steps for polyvinyl alcohol resin film)
Processes other than those described above can also be added. Examples of treatments that may be added include immersion treatment in an iodide aqueous solution that does not contain boric acid (complementary color treatment), and immersion treatment in an aqueous solution that does not contain boric acid and contains zinc chloride etc. (zinc processing).

(Recycling process)
In the recycling process of the example shown in FIG. , the dyeing liquid 15, the first crosslinking liquid 17a, and the second crosslinking liquid 17b, and are recycled. In the dyeing liquid 15, the first crosslinking liquid 17a, and the second crosslinking liquid 17b, the amount of the chemical solution may decrease and the concentration of the drug may decrease due to being carried out by the immersed film or due to evaporation of the chemical solution. be. According to the present invention, in at least one of the treatment liquids, which are the staining liquid 15, the first crosslinking liquid 17a, and the second crosslinking liquid 17b, the waste liquid is added to the chemical liquid, so that the amount of the chemical liquid in the treatment liquid is reduced. A sufficient amount can be maintained, or the concentration of the drug solution can be maintained constant.

The waste liquid may be added when the amount of the chemical in the treatment tank is detected and the amount is below a predetermined amount, or when the concentration of a specific chemical in the treatment liquid is detected and it is above a predetermined value. It may be added at any time, it may be added constantly, or it may be added at predetermined intervals. When the temperature of the chemical solution is 50° C. or higher, the amount of evaporation increases and the amount of decrease increases. Since the temperature of the first crosslinking liquid 17a and the second crosslinking liquid 17b is preferably 50°C or higher, the waste liquid is not added to the chemical solution in at least one of the first crosslinking liquid 17a and the second crosslinking liquid 17b. It is preferable that

The waste liquid may or may not be concentrated at the time it is added to the drug solution. When concentrating the waste liquid, concentration can be performed by providing a concentration step during the recycling process. The concentration step may be performed, for example, between the cleaning liquid 19 and the waste liquid recovery tank 71, between the waste liquid recovery tank 71 and the dyeing liquid 15, or between the waste liquid recovery tank 71 and the first crosslinking liquid 17a. It may be between the waste liquid recovery tank 71 and the second crosslinking liquid 17b. Concentration methods for concentrating waste liquid in the recycling process include methods in which the waste liquid is forced into contact with a reverse osmosis membrane, and only water is passed through the reverse osmosis membrane and removed, concentrated by blowing hot air, and heated in an evaporation kiln. Examples include a method in which water is evaporated by evaporation, a method in which the pressure is reduced in an evaporation kiln, and the water is heated to evaporate water. A method using a reverse osmosis membrane is preferable from the viewpoint that water can be removed without heating the waste liquid and oxidation of potassium iodide can be suppressed. In the method using a reverse osmosis membrane, the method of pumping the waste liquid is not particularly limited, and examples include a volute pump, a diffuser pump, a vortex mixed flow pump, a piston pump, a plunger pump, a diaphragm pump, a gear pump, a screw pump, a vane pump, This can be done using a cascade pump or jet pump. The reverse osmosis membrane is not particularly limited as long as it can separate water from waste liquid, and conventionally known membranes can be used. It is preferable to use a reverse osmosis membrane through which active ingredients such as boric acid, potassium iodide, iodine, etc. do not pass. Examples include spiral type membrane elements, hollow fiber type membrane elements, tubular type membrane elements, frame and plate type membrane elements, and the like. A reverse osmosis membrane having one or more membrane elements can be used. The material constituting the membrane element is not particularly limited, and various polymeric materials such as cellulose acetate, polyvinyl alcohol, polyamide, and polyester can be used, for example.

The degree of concentration of the waste liquid may be adjusted by the amount of reduction on a volume basis as described above, or may be adjusted by the concentration of the drug contained in the waste liquid, or may be adjusted by a combination of both. Boric acid, potassium iodide, iodine, zinc chloride, etc. can be mentioned as the target drug for checking the degree of concentration of waste liquid. The waste liquid is concentrated, for example, so that the boric acid concentration is 5.0% by mass or less, preferably 4.0% by mass or less, more preferably 3.0% by mass or less. can be recycled from The boric acid concentration of the waste liquid at the time of addition to the chemical solution may be 0.01% by mass or more, or may be 0.1% by mass or more.

According to the above-mentioned recycling process, waste liquid can be recycled without going through complicated steps.

<Polarizing plate>
A polarizing plate can be obtained by bonding a protective film to at least one side of the polarizing film produced as described above via an adhesive. As a protective film, for example, a film made of acetyl cellulose resin such as triacetyl cellulose or diacetyl cellulose; a film made of polyester resin such as polyethylene terephthalate, polyethylene naphthalate, and polybutylene terephthalate; a polycarbonate resin film, cyclo Examples include olefin resin films; acrylic resin films; and films made of chain olefin resins such as polypropylene resins.

In order to improve the adhesion between the polarizing film and the protective film, at least one bonding surface selected from the group consisting of the polarizing film and the protective film is subjected to corona treatment, flame treatment, plasma treatment, ultraviolet irradiation, primer coating treatment, Surface treatment such as saponification treatment may also be applied. The adhesive used for laminating the polarizing film and the protective film is an active energy ray-curable adhesive such as an ultraviolet curable adhesive, an aqueous solution of polyvinyl alcohol resin, or an aqueous solution containing a crosslinking agent. , water-based adhesives such as urethane emulsion adhesives. The ultraviolet curable adhesive may be a mixture of an acrylic compound and a radical photopolymerization initiator, a mixture of an epoxy compound and a cationic photopolymerization initiator, or the like. Furthermore, a cationic polymerizable epoxy compound and a radically polymerizable acrylic compound can be used together, and a photocationic polymerization initiator and a photoradical polymerization initiator can also be used together as an initiator.

10 Raw film made of polyvinyl alcohol resin, 11 Raw roll, 13 Swelling liquid, 15 Staining liquid, 17a First crosslinking liquid, 17b Second crosslinking liquid, 19 Cleaning liquid, 21 Drying oven, 23 Polarizing film, 30 to 48 , 60, 61 Guide roll, 50 to 52, 53a, 53b, 54, 55 Nip roll, 71 Waste liquid recovery tank.

Claims (10)

A manufacturing method for manufacturing a polarizing film from a polyvinyl alcohol resin film, comprising:
a chemical solution treatment step of bringing a chemical solution into contact with the polyvinyl alcohol resin film to perform a chemical solution treatment;
a cleaning step of cleaning the polyvinyl alcohol resin film with a cleaning solution after the chemical treatment step;
a recycling step of adding at least a portion of the waste liquid generated in the cleaning step to the chemical solution,
In the manufacturing method, the chemical solution treatment step is at least one step selected from the group consisting of a dyeing step in which the chemical solution is a dyeing solution, and a crosslinking step in which the chemical solution is a crosslinking solution. 2. The manufacturing method according to claim 1, wherein in the recycling step, at least a portion of the waste liquid is concentrated to 1/10 or less on a volume basis and added to the chemical solution. A manufacturing method for manufacturing a polarizing film from a polyvinyl alcohol resin film, comprising:
a chemical solution treatment step of bringing a chemical solution into contact with the polyvinyl alcohol resin film to perform a chemical solution treatment;
a recycling step of concentrating at least a portion of the waste liquid generated in the process of manufacturing the polarizing film from the polyvinyl alcohol resin film to 1/2 or less on a volume basis and adding it to the chemical solution;
In the manufacturing method, the chemical solution treatment step is at least one step selected from the group consisting of a dyeing step in which the chemical solution is a dyeing solution, and a crosslinking step in which the chemical solution is a crosslinking solution. After the chemical treatment step, the method further includes a cleaning step of cleaning the polyvinyl alcohol resin film with a cleaning solution,
The manufacturing method according to claim 3, wherein the waste liquid includes the cleaning liquid. The manufacturing method according to any one of claims 1 to 4, wherein in the chemical solution treatment step, the temperature of the chemical solution is 50° C. or higher. The manufacturing method according to any one of claims 1 to 4, wherein the waste liquid contains at least one of potassium iodide and boric acid. The manufacturing method according to any one of claims 1 to 4, wherein in the recycling step, the boric acid concentration of the waste liquid added to the chemical solution is 0.01% by mass or more and 5.0% by mass or less. The manufacturing method according to any one of claims 1 to 4, wherein the chemical solution treatment step is a crosslinking step in which the chemical solution is a crosslinking liquid. A manufacturing device for manufacturing a polarizing film from a polyvinyl alcohol resin film,
a chemical liquid processing unit that performs chemical liquid treatment by bringing a chemical liquid into contact with the polyvinyl alcohol resin film;
a recycling section that concentrates at least a portion of the waste liquid generated in the process of manufacturing the polarizing film from the polyvinyl alcohol resin film to 1/2 or less on a volume basis and adds it to the chemical solution;
The chemical processing section is at least one selected from the group consisting of a dyeing section where the chemical solution is a staining solution, and a crosslinking section where the chemical solution is a crosslinking solution. A manufacturing device for manufacturing a polarizing film from a polyvinyl alcohol resin film,
a chemical liquid processing unit that performs chemical liquid treatment by bringing a chemical liquid into contact with the polyvinyl alcohol resin film;
a cleaning section that cleans the polyvinyl alcohol resin film with a cleaning solution after the chemical treatment section;
a recycling section that adds at least a portion of the waste liquid generated in the cleaning section to the chemical solution;
The chemical processing section is at least one selected from the group consisting of a dyeing section where the chemical solution is a staining solution, and a crosslinking section where the chemical solution is a crosslinking solution.

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