JP7048238B2 - Coating liquid manufacturing method, polarizing element manufacturing method, and coating liquid manufacturing equipment - Google Patents

Description

The present invention relates to a method for producing a coating liquid, a method for producing a polarizing element, and an apparatus for producing a coating liquid.

A PVA-based resin layer is formed on the thermoplastic resin film by applying a coating liquid containing polyvinyl alcohol (PVA) to the thermoplastic resin film and drying it, and by stretching and dyeing this laminate, the thickness is thin. A method for obtaining a stator has been proposed (for example, Patent Document 1). As the PVA coating liquid used for producing the above-mentioned polarizing element, PVA coating liquid having excellent transparency and uniformity is obtained by dissolving PVA in water and then quenching to a predetermined temperature of 10 ° C to 40 ° C. A method for obtaining it has been proposed (Patent Document 2).

Japanese Unexamined Patent Publication No. 2000-338329 Japanese Patent No. 5146091

When mass-producing a polarizing element using the above-mentioned PVA coating liquid, typically, the PVA coating liquid obtained by dissolving PVA at a high temperature is kept warm or slowly cooled in a tank, filtered through a filter, and then filtered. Apply from the coating die to the thermoplastic resin film. However, it may be necessary to intermittently stop the supply of PVA coating, for example when replacing the filter. As a result, the PVA coating liquid may stay inside the piping or the like, and the PVA coating liquid may gel and the transparency may decrease. When a stator is manufactured using a PVA coating liquid whose transparency is lowered due to gelation, the optical characteristics of the obtained polarizing element may be deteriorated. Further, when the PVA coating liquid stays in a pipe, a pump, a three-way valve or the like, PVA may precipitate to form nuclei and locally gel. Further, if the PVA coating liquid stays for a long time in a portion such as a joint portion in a pipe or a switching portion of a three-way valve where bubble accumulation is likely to occur, PVA may locally gel. When the locally gelled PVA coating liquid is applied onto a thermoplastic resin film to form a laminate, the above-mentioned local gel causes the surface of the PVA-based resin layer to have irregularities. May occur. When a polarizing element is manufactured using such a laminate, the obtained polarizing element may have a defect of unevenness and / or a defect of light leakage at the time of orthogonal display.

The present invention has been made to solve the above-mentioned conventional problems, and the main purpose thereof is a method for producing a polyvinyl alcohol coating liquid in which the decrease in transparency and the generation and precipitation of local gel are suppressed, such as. It is an object of the present invention to provide a method for producing a polarizing element using a polyvinyl alcohol coating liquid, and an apparatus for producing a polyvinyl alcohol coating liquid.

The method for producing a coating liquid of the present invention is a method for producing a coating liquid containing a polyvinyl alcohol-based resin, in which the solution containing the polyvinyl alcohol-based resin is kept warm at 80 ° C. or higher and the solution at 80 ° C. or higher is prepared. Cooling to 40 ° C. or lower, continuously supplying the cooled solution as a coating liquid, and heating the cooled solution to 80 ° C. or higher when the supply of the coating liquid is stopped. Including keeping warm.
In one embodiment, the cooling rate in the above cooling is 1 ° C./min or more.
According to another aspect of the present invention, there is provided a method for manufacturing a polarizing element. The method for producing a polarizing element includes forming a polyvinyl alcohol-based resin layer on the resin base material by applying the coating liquid to the resin base material and drying it.
According to another aspect of the present invention, an apparatus for producing a coating liquid is provided. The coating liquid manufacturing apparatus is a coating liquid manufacturing apparatus containing a polyvinyl alcohol-based resin, and has a heat insulating portion that keeps the solution containing the polyvinyl alcohol-based resin at 80 ° C. or higher and 40 of the above solution at 80 ° C. or higher. The cooling unit that cools to ℃ or less, the supply unit that continuously supplies the cooled solution as a coating liquid, and the above-mentioned cooling unit that is cooled by the cooling unit when the supply of the coating liquid by the supply unit is stopped. It has a heating circulation section that heats the solution to 80 ° C. or higher and returns it to the heat retaining section.

According to the present invention, when the supply of the coating liquid is stopped, the supply of the solution (coating liquid) is stopped by heating the cooled solution to 80 ° C. or higher to keep it warm, for example, by replacing the filter. Even so, it is possible to suppress the solution from staying in a pipe or the like and gelling, and as a result, it is possible to suppress a decrease in the transparency of the solution. In addition, it is possible to suppress the generation of local gel, and as a result, it is possible to suppress the defects of unevenness when such a polyvinyl alcohol coating liquid is formed.

It is a schematic diagram which shows the structure of the coating liquid manufacturing apparatus by one Embodiment of this invention.

Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to these embodiments.

A. Method for Producing Coating Liquid The method for producing a coating liquid according to one embodiment of the present invention is a method for producing a coating liquid containing a polyvinyl alcohol (PVA) -based resin, and keeps the solution containing the PVA-based resin warm at 80 ° C. or higher. When the solution of 80 ° C. or higher is cooled to 40 ° C. or lower, the cooled solution is continuously supplied as a coating liquid, and the supply of the coating liquid is stopped, the cooled solution is 80. Includes heating to above ° C to keep warm. The cooling rate in the above cooling is preferably 1 ° C./min or more. The coating liquid can be typically used for producing a polarizing element. As will be described later in Section B, the method for producing a polarizing element includes forming a polyvinyl alcohol-based resin layer on the resin base material by applying the coating liquid to the resin base material and drying it.

FIG. 1 is a schematic view showing the configuration of a coating liquid manufacturing apparatus according to one embodiment of the present invention. The coating liquid manufacturing apparatus 100 can be suitably used for a method for manufacturing a coating liquid. The coating liquid manufacturing apparatus 100 coats the heat-retaining unit 10 that keeps the solution containing the PVA-based resin at 80 ° C. or higher, the cooling unit 20 that cools the solution at 80 ° C. or higher to 40 ° C. or lower, and the cooled solution. When the supply unit 30 that continuously supplies the coating liquid as a liquid to the coating unit (not shown) and the supply unit 30 stop supplying the coating liquid, the solution cooled by the cooling unit is heated to 80 ° C. or higher. It has a heating circulation unit 40 that returns to the heat retaining unit 10. The heat insulating unit 10, the cooling unit 20, and the supply unit 30 are typically arranged in series via a pipe P. In one embodiment, the pipe P is branched between the cooling unit 20 and the supply unit 30, and a three-way valve 50 is arranged at the branch portion of the pipe. The pipe P branched from the branch portion is connected to the heat insulating portion 10 via the heating circulation portion 40. In one embodiment, a pump 60 for delivering a solution may be arranged between the heat insulating unit 10 and the cooling unit 20. The supply unit 30 may have a filter for filtering the solution. According to the above-mentioned manufacturing apparatus 100, even when the supply of the solution (coating liquid) from the supply unit 30 is stopped due to, for example, replacement of the filter, the solution is applied to the pipe between the heat insulating unit 10 and the branch portion. Retention can be suppressed and, as a result, solution gelation (including local gelation) can be suppressed.

A-1. Preparation of a solution containing a PVA-based resin As the PVA-based resin, any suitable resin can be adopted. For example, polyvinyl alcohol and ethylene-vinyl alcohol copolymers can be mentioned. Polyvinyl alcohol is obtained by saponifying polyvinyl acetate. The ethylene-vinyl alcohol copolymer is obtained by saponifying the ethylene-vinyl acetate copolymer. The saponification degree of the PVA-based resin is usually 85 mol% to 100 mol%, preferably 95.0 mol% to 99.95 mol%, and more preferably 99.0 mol% to 99.93 mol%. .. The degree of saponification can be determined according to JIS K 6726-1994. By using a PVA-based resin having such a degree of saponification, a polarizing element having excellent durability can be obtained. If the degree of saponification is too high, gelation may occur.

The average degree of polymerization of the PVA-based resin can be appropriately selected depending on the intended purpose. The average degree of polymerization is usually 1000 to 10000, preferably 1200 to 4500, and more preferably 1500 to 4300. The average degree of polymerization can be determined according to JIS K 6726-1994.

The solution containing the PVA-based resin is typically a solution in which the above-mentioned PVA-based resin is dissolved in a solvent. As the solvent, for example, water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide N-methylpyrrolidone, various glycols, polyhydric alcohols such as trimethylolpropane, and amines such as ethylenediamine and diethylenetriamine are used. These can be used alone or in combination of two or more. Among these, water is preferable. The PVA-based resin concentration of the solution is preferably 3 parts by weight to 20 parts by weight, more preferably 5 parts by weight to 15 parts by weight, and particularly preferably 7 parts by weight to 12 parts by weight with respect to 100 parts by weight of the solvent. It is a department. With such a resin concentration, when a PVA-based resin is applied to a resin base material and dried, a uniform coating film in close contact with the resin base material can be provided.

Additives may be added to the above solution. Examples of the additive include a plasticizer, a surfactant and the like. Examples of the plasticizer include polyhydric alcohols such as ethylene glycol and glycerin. Examples of the surfactant include nonionic surfactants. These are for the purpose of further improving the uniformity, dyeability, and stretchability of the PVA-based resin layer obtained when the PVA-based resin layer is prepared by applying the PVA-based resin to the resin base material and drying it. Can be used.

The viscosity of the solution is preferably 100 mPa · s to 10000 mPa · s, more preferably 300 mPa · s to 5000 mPa · s, and even more preferably 500 mPa · s to 3000 mPa · s.

When the PVA-based resin is dissolved in a solvent, the PVA-based resin and the solvent are typically mixed at a temperature of 80 ° C. or higher. The temperature at the time of melting is preferably 80 ° C. or higher, and more preferably 85 ° C. to 95 ° C. If the melting temperature is lower than 80 ° C., the PVA-based resin may not be sufficiently melted and a uniform solution may not be obtained.

In one embodiment, a PVA-based resin is gradually added to a solvent at room temperature, stirred to disperse well, swelled, and then heated to a temperature of 80 ° C. or higher while continuing stirring, and further determined at that temperature. Continue stirring for hours.

After preparing the solution containing the PVA-based resin, the solution can be kept warm in the heat insulating part.

A-2. Insulation of the solution containing the PVA-based resin The solution containing the PVA-based resin is kept warm at 80 ° C. or higher as described above. In one embodiment, the solution is kept at 80 ° C. or higher in a heat insulating section. The temperature at which the solution is kept warm is preferably 80 ° C. to 95 ° C., more preferably 85 ° C. to 90 ° C. By keeping the temperature at 80 ° C. or higher, precipitation and gelation of the PVA-based resin can be suppressed. The heat retention time is preferably 1 hour to 48 hours, more preferably 3 hours to 24 hours. Preferably, the solution is kept warm with stirring. As a result, a solution having excellent transparency and uniformity can be obtained. The solution kept warm in the heat insulating part can be continuously supplied to the cooling part by a pump. The capacity of the heat insulating unit is not particularly limited and can be appropriately set according to the intended use.

A-3. Cooling of the solution containing the PVA-based resin As described above, the solution containing the PVA-based resin is kept warm at 80 ° C. or higher and then cooled to 40 ° C. or lower. In one embodiment, the solution is cooled to 40 ° C. or lower in the cooling section. The cooling temperature (temperature of the above solution after cooling) is preferably 10 ° C to 40 ° C, more preferably 20 ° C to 30 ° C. If the cooling temperature exceeds 40 ° C., the mixture is slowly cooled to room temperature, which may cause gelation and reprecipitation. On the other hand, when the cooling temperature is lower than 10 ° C., the solubility of the PVA-based resin in water becomes insufficient, and reprecipitation of the PVA-based resin may occur.

As described above, the cooling rate is preferably 1 ° C./min or higher. The cooling rate is more preferably 1 ° C./min to 10 ° C./min, and even more preferably 1 ° C./min to 5 ° C./min. As a result, precipitation and gelation of the PVA-based resin can be suppressed. The cooling rate is expressed by the following equation.
Cooling rate = (Temperature of solution at the start of cooling-Temperature of solution at the end of cooling) / Cooling time

The cooling rate may be constant or may change from the start of cooling to the end of cooling, but preferably, there is no state in which the temperature is kept almost constant or the temperature temporarily rises in the middle. To cool down. That is, preferably, the cooling is performed so that the temperature continuously decreases with time.

Any suitable configuration may be adopted as the cooling unit. A heat exchanger can be typically adopted. For example, a cooling pipe is laid around the tank containing the solution, and the cooling pipe is forcibly cooled while flowing the refrigerant through the pipe. A cooling pipe is arranged in the tank, and the refrigerant flows there. However, there is a configuration in which it is forcibly cooled. Examples of the refrigerant include ice water and brine (salt water).

A-4. Supply of coating liquid As described above, the solution containing the PVA-based resin is continuously supplied as the coating liquid after being cooled to 40 ° C. or lower. In one embodiment, the solution is continuously supplied from the supply section to the coating section. The supply speed is not particularly limited and may be appropriately set according to the coating width and the line speed (coating speed).

As the coating portion, a coating machine capable of coating by any appropriate coating method can be adopted. Examples of the coating method include a roll coating method, a spin coating method, a wire bar coating method, a dip coating method, a die coating method, a curtain coating method, a spray coating method, and a knife coating method (comma coating method, etc.). As the coating machine, a coating machine capable of coating by the above coating method can be adopted, and is typically a coating die. The amount of coating by the coating portion is not particularly limited, and can be appropriately set according to the coating width and the line speed (coating speed).

In one embodiment, the supply unit has a filter, and the solution is filtered using the filter and then supplied as a coating liquid. This can remove air bubbles and foreign matter from the solution. As the filter, any suitable filter may be adopted. Preferably, a depth type filter can be used. Specific examples of the depth type filter include a thread winding type in which a thread is wound around a cylindrical core, a non-woven fabric laminated type in which a non-woven fabric is wound around a cylindrical core, and a resin molding type using a resin molded product such as a sponge, depending on the form of the filter medium. ..

A-5. Heating of the cooled solution When the supply of the coating liquid is stopped, the cooled solution is heated to 80 ° C. or higher and kept warm as described above. In one embodiment, the solution is heated by a heated circulation section. The temperature at which the solution is heated and kept warm is preferably 80 ° C. to 95 ° C., more preferably 85 ° C. to 90 ° C. The solution heated to 80 ° C. or higher can be kept warm again, cooled to 40 ° C. or lower, and then supplied as a coating liquid.

In one embodiment, the heating circulation section heats the solution cooled in the cooling section to 80 ° C. or higher and returns it to the heat insulating section. That is, when the supply of the solution is stopped, the solution is heated to 80 ° C. or higher again and circulated by piping. As a result, even when the supply of the coating liquid (solution) is stopped due to, for example, replacement of the filter, it is possible to suppress the solution from staying in the piping or the like, and as a result, the gelation of the solution can be suppressed. ..

Typically, the pipe that supplies the cooled solution to the supply section is branched, and a three-way valve is arranged at the branch section. By switching the opening of the three-way valve, the solution is sent to the supply section. Or, it is used for heating.

Any suitable configuration may be adopted for the heat circulation unit. A heat exchanger can be typically adopted.

B. Use of Coating Liquid The coating liquid obtained by the production method according to Item A can be used for producing a polarizing element. The method for producing a polarizing element is to apply the coating liquid to a resin base material and dry it to form a polyvinyl alcohol-based resin layer on the resin base material to form a laminate, and to form a laminate on the laminate. It may include subjecting the resin layer to a predetermined treatment for forming a polarizing element. Examples of the predetermined treatment include dyeing treatment, stretching treatment, insolubilization treatment, cross-linking treatment, cleaning treatment, and drying treatment. These processes may be appropriately selected depending on the purpose. Further, the processing order, the processing timing, the number of processing times, and the like can be appropriately set. Hereinafter, each process will be described.

B-1. Preparation of Resin Base Material The resin base material is typically formed of a thermoplastic resin. As the thermoplastic resin, any suitable resin is used. For example, (meth) acrylic resin, olefin resin, norbornene resin, polyester resin and the like can be mentioned. Preferably, a polyester resin is used. Of these, an amorphous (non-crystallized) polyethylene terephthalate resin is preferably used. In particular, an amorphous (difficult to crystallize) polyethylene terephthalate resin is particularly preferably used. Specific examples of the amorphous polyethylene terephthalate resin include a copolymer further containing isophthalic acid as a dicarboxylic acid and a copolymer further containing cyclohexanedimethanol as a glycol.

The glass transition temperature (Tg) of the resin substrate is preferably 170 ° C. or lower. By using such a resin base material, it is possible to sufficiently secure the stretchability of the laminated body while suppressing the crystallization of the PVA-based resin layer. Further, considering that the resin base material is plasticized with water and well stretched in water, the temperature is more preferably 120 ° C. or lower. In one embodiment, the glass transition temperature of the resin substrate is preferably 60 ° C. or higher. By using such a resin base material, problems such as deformation of the resin base material (for example, unevenness, tarmi, wrinkles, etc.) when the coating liquid containing the PVA-based resin is applied and dried are prevented. Therefore, the laminated body can be satisfactorily produced. Further, the PVA-based resin layer can be well stretched at a suitable temperature (for example, about 60 ° C. to 70 ° C.). In another embodiment, the glass transition temperature may be lower than 60 ° C. as long as the resin base material is not deformed when the coating liquid containing the PVA-based resin is applied and dried. The glass transition temperature of the resin base material can be adjusted, for example, by heating with a crystallization material that introduces a modifying group into the constituent material. The glass transition temperature (Tg) is a value obtained according to JIS K 7121.

In one embodiment, the resin base material preferably has a water absorption rate of 0.2% or more, more preferably 0.3% or more. Such a resin base material absorbs water, and the water can act as a plasticizer to be plasticized. As a result, the stretching stress can be significantly reduced in the stretching in water, and the stretchability can be excellent. On the other hand, the water absorption rate of the resin base material is preferably 3.0% or less, more preferably 1.0% or less. By using such a resin base material, it is possible to prevent problems such as deterioration of the appearance of the obtained laminate due to a significant decrease in dimensional stability of the resin base material during manufacturing. Further, it is possible to prevent the PVA-based resin layer from being broken or peeled from the resin base material during stretching in water. The water absorption rate is a value obtained according to JIS K 7209.

The thickness of the resin base material is preferably 20 μm to 300 μm, more preferably 30 μm to 200 μm.

The resin base material may be surface-treated (for example, corona treatment or the like) in advance. This is because the adhesion between the resin base material and the PVA-based resin layer can be improved.

B-2. Formation of PVA-based Resin Layer Any suitable method can be adopted as a method for forming the PVA-based resin layer on the resin base material. Preferably, the coating liquid obtained by the method according to Item A is applied onto a resin base material and dried to form a PVA-based resin layer.

Any appropriate method can be adopted as the coating method of the coating liquid. For example, a roll coating method, a spin coating method, a wire bar coating method, a dip coating method, a die coating method, a curtain coating method, a spray coating method, a knife coating method (comma coating method, etc.) and the like can be mentioned.

The coating liquid is applied so that the thickness of the PVA-based resin layer after drying is preferably 3 μm to 40 μm, more preferably 3 μm to 20 μm. The coating / drying temperature of the coating liquid is preferably 50 ° C. or higher.

B-3. Air stretching treatment The stretching method of the aerial auxiliary stretching may be fixed-end stretching (for example, a method of stretching using a tenter stretching machine) or free-end stretching (for example, uniaxial stretching through a laminate between rolls having different peripheral speeds). Method) may be used. In one embodiment, the aerial stretching treatment includes a thermal roll stretching step of stretching the laminate by the difference in peripheral speed between the thermal rolls while transporting the laminated body in the longitudinal direction thereof. The aerial stretching treatment typically includes a zone stretching step and a thermal roll stretching step. The order of the zone stretching step and the thermal roll stretching step is not limited, and the zone stretching step may be performed first, or the thermal roll stretching step may be performed first. The zone stretching step may be omitted. In one embodiment, the zone stretching step and the thermal roll stretching step are performed in this order.

The stretching temperature of the laminate can be set to an arbitrary appropriate value depending on the material for forming the resin base material and the like. The stretching temperature in the air stretching treatment is preferably the glass transition temperature (Tg) or higher of the resin base material, more preferably the glass transition temperature (Tg) of the resin base material (Tg) + 10 ° C. or higher, and particularly preferably Tg + 15 ° C. or higher. On the other hand, the upper limit of the stretching temperature of the laminated body is preferably 170 ° C. By stretching at such a temperature, it is possible to suppress the rapid progress of crystallization of the PVA-based resin and suppress defects due to the crystallization (for example, hindering the orientation of the PVA-based resin layer due to stretching). can.

The draw ratio of the laminated body can be set to an arbitrary appropriate value depending on the material for forming the resin base material and the like. The stretching ratio in the aerial stretching treatment is preferably 1.5 times or more and 3.0 times or less.

B-4. Insolubilization treatment The insolubilization treatment is typically performed by immersing a PVA-based resin layer in a boric acid aqueous solution. By applying the insolubilization treatment, water resistance can be imparted to the PVA-based resin layer. The concentration of the boric acid aqueous solution is preferably 1 part by weight to 4 parts by weight with respect to 100 parts by weight of water. The liquid temperature of the insolubilizing bath (boric acid aqueous solution) is preferably 20 ° C to 50 ° C. Preferably, the insolubilization treatment is performed before stretching in water or dyeing treatment.

B-5. Dyeing treatment The dyeing treatment is typically performed by dyeing a PVA-based resin layer with a dichroic substance. It is preferably carried out by adsorbing a dichroic substance on the PVA-based resin layer. Examples of the adsorption method include a method of immersing a PVA-based resin layer (laminate) in a dyeing solution containing a dichroic substance, a method of applying the dyeing solution to the PVA-based resin layer, and a method of applying the dyeing solution to the PVA-based. Examples thereof include a method of spraying on the resin layer. A method of immersing the laminate in the dyeing solution is preferable. This is because the dichroic substance can be adsorbed well.

Examples of the dichroic substance include iodine and organic dyes. These can be used alone or in combination of two or more. The dichroic substance is preferably iodine. When iodine is used as the dichroic substance, the staining solution is preferably an aqueous iodine solution. The blending amount of iodine is preferably 0.05 parts by weight to 5.0 parts by weight with respect to 100 parts by weight of water. In order to increase the solubility of iodine in water, it is preferable to add iodide to the aqueous iodine solution. Examples of iodide include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. And so on. Among these, potassium iodide is preferable. The blending amount of iodide is preferably 0.3 parts by weight to 15 parts by weight with respect to 100 parts by weight of water.

The liquid temperature at the time of dyeing the dyeing liquid is preferably 20 ° C. to 40 ° C. When the PVA-based resin layer is immersed in the dyeing solution, the immersion time is preferably 10 seconds to 300 seconds. Under such conditions, the dichroic substance can be sufficiently adsorbed on the PVA-based resin layer. Further, the dyeing conditions (concentration, liquid temperature, immersion time) can be set so that the degree of polarization or the single transmittance of the finally obtained polarizing element is within a predetermined range. In one embodiment, the immersion time is set so that the degree of polarization of the obtained polarizing element is 99.98% or more. In another embodiment, the immersion time is set so that the single transmittance of the obtained polarizing element is about 40%.

B-6. Crosslinking Treatment The crosslinking treatment is typically performed by immersing a PVA-based resin layer (laminate) in an aqueous boric acid solution. By applying the cross-linking treatment, water resistance can be imparted to the PVA-based resin layer. The concentration of the boric acid aqueous solution is preferably 1 part by weight to 5 parts by weight with respect to 100 parts by weight of water. Further, when the cross-linking treatment is performed after the dyeing treatment, it is preferable to further add iodide. By blending iodide, the elution of iodine adsorbed on the PVA-based resin layer can be suppressed. The blending amount of iodide is preferably 1 part by weight to 5 parts by weight with respect to 100 parts by weight of water. Specific examples of iodide are as described above. The liquid temperature of the cross-linked bath (boric acid aqueous solution) is preferably 20 ° C to 60 ° C. Preferably, the crosslinking treatment is performed before the underwater stretching treatment. In a preferred embodiment, the air stretching treatment, the dyeing treatment, and the cross-linking treatment are performed in this order.

B-7. Underwater Stretching Treatment Any suitable method can be adopted as the stretching method in the underwater stretching treatment. Specifically, it may be fixed-end stretching (for example, a method using a tenter stretching machine) or free-end stretching (for example, a method of uniaxial stretching through a laminate between rolls having different peripheral speeds). Further, simultaneous biaxial stretching (for example, a method using a simultaneous biaxial stretching machine) may be used, or sequential biaxial stretching may be used. The stretching of the laminate may be carried out in one step or in multiple steps. When performed in multiple stages, the draw ratio (maximum draw ratio) of the laminated body is the product of the draw ratios of each stage.

Any appropriate direction can be selected as the stretching direction of the laminated body. In one embodiment, the elongated laminate is stretched in the longitudinal direction. Specifically, the laminated body is transported in the longitudinal direction, and the transport direction (MD) thereof. In another embodiment, the elongated laminate is stretched in the width direction. Specifically, the laminated body is transported in the longitudinal direction, and the direction is orthogonal to the transport direction (MD) (TD).

The stretching temperature of the laminate can be set to an arbitrary appropriate value depending on the forming material of the resin base material, the stretching method, and the like. The stretching temperature is preferably 40 ° C. to 85 ° C., more preferably 50 ° C. to 85 ° C. At such a temperature, the PVA-based resin layer can be stretched at a high magnification while suppressing dissolution. Specifically, as described above, the glass transition temperature (Tg) of the resin base material is preferably 60 ° C. or higher in relation to the formation of the PVA-based resin layer. In this case, if the stretching temperature is lower than 40 ° C., there is a possibility that the resin substrate cannot be stretched satisfactorily even if the plasticization of the resin base material by water is taken into consideration. On the other hand, the higher the temperature of the stretching bath, the higher the solubility of the PVA-based resin layer, and there is a possibility that excellent optical characteristics cannot be obtained.

The underwater stretching is preferably carried out by immersing the laminate in a boric acid aqueous solution (boric acid water stretching). By using the boric acid aqueous solution as the stretching bath, it is possible to impart rigidity to withstand the tension applied during stretching and water resistance that does not dissolve in water to the PVA-based resin layer. Specifically, boric acid can generate a tetrahydroxyboric acid anion in an aqueous solution and crosslink with a PVA-based resin by hydrogen bonding. As a result, it is possible to impart rigidity and water resistance to the PVA-based resin layer, to stretch it satisfactorily, and to produce a polarizing element having excellent optical characteristics (for example, degree of polarization).

The boric acid aqueous solution is preferably obtained by dissolving boric acid and / or borate in water as a solvent. The boric acid concentration is preferably 1 part by weight to 10 parts by weight with respect to 100 parts by weight of water. By setting the boric acid concentration to 1 part by weight or more, the dissolution of the PVA-based resin layer can be effectively suppressed, and a polarizing element having higher characteristics can be produced. In addition to boric acid or borate, an aqueous solution obtained by dissolving a boron compound such as borax, glioxal, glutaraldehyde or the like in a solvent can also be used.

When a dichroic substance (typically iodine) is adsorbed on the PVA-based resin layer in advance by the dyeing treatment, iodide is preferably added to the stretching bath (boric acid aqueous solution). By blending iodide, the elution of iodine adsorbed on the PVA-based resin layer can be suppressed. Examples of iodide include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. And so on. Among these, potassium iodide is preferable. The concentration of iodide is preferably 0.05 parts by weight to 15 parts by weight, and more preferably 0.5 parts by weight to 8 parts by weight with respect to 100 parts by weight of water.

The draw ratio (maximum draw ratio) of the laminated body is typically 4.0 times or more, preferably 5.0 times or more, with respect to the original length of the laminated body. Such a high draw ratio can be achieved, for example, by adopting an underwater stretching method (boric acid underwater stretching). In the present specification, the "maximum draw ratio" means the draw ratio immediately before the laminate breaks, and separately confirms the draw ratio at which the laminate breaks and means a value 0.2 lower than that value. ..

Preferably, the underwater stretching treatment is performed after the dyeing treatment.

B-8. Cleaning treatment The cleaning treatment is typically performed by immersing a PVA-based resin layer in an aqueous potassium iodide solution.

B-9. Drying Treatment The drying temperature in the drying treatment is preferably 30 ° C. to 100 ° C.

The obtained polarizing element is substantially a PVA-based resin film in which a dichroic substance is adsorbed and oriented. The thickness of the splitter is preferably 10 μm or less, more preferably 7 μm or less, and particularly preferably 5 μm or less. The splitter preferably exhibits absorption dichroism at any wavelength of 380 nm to 780 nm. The substituent preferably has a degree of polarization of 99.9% or more at a simple substance transmittance of 42% or more. The transducer can be used as a polarizing plate having a protective film arranged on at least one side. As the protective film, the resin base material may be used as it is, or a film different from the resin base material may be used. Examples of the material for forming the protective film include (meth) acrylic resin, diacetyl cellulose, cellulose resin such as triacetyl cellulose, cycloolefin resin, olefin resin such as polypropylene, and ester resin such as polyethylene terephthalate resin. , Polyamide-based resin, polycarbonate-based resin, and copolymer resins thereof. The thickness of the protective film is preferably 10 μm to 100 μm.

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to these Examples.

<Manufacturing example 1>
1. 1. Preparation of Resin Substrate Amorphous polyethylene terephthalate resin (A-PET) was formed into a long film having a thickness of 200 μm to obtain an A-PET substrate.
Water-based urethane resin (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., product name: Superflex 210R, solid content: 35%), oxazoline-based cross-linking agent (manufactured by Nippon Catalyst Co., Ltd., product name: Epocross WS700, solid content: 25%) ), Conductive material (manufactured by Agfa, trade name: Olgacon LBS, solid content: 1.2%), ammonia water and water with a concentration of 1%, weight ratio 9.03: 1.00: 18.1: 0.060. : A mixed solution mixed at 39.5 was prepared.
The obtained mixed liquid was applied to one surface of the A-PET base material and dried to form an antistatic layer on the surface of the A-PET base material. The thickness of the antistatic layer was 1 μm.
Subsequently, the A-PET substrate on which the antistatic layer was formed was conveyed in the longitudinal direction thereof and stretched 2.3 times in the lateral direction at 115 ° C. After that, both ends were removed with slits to obtain a resin base material for coating.
2. 2. Preparation of solution containing PVA-based resin PVA (polymerization degree: 4200, saponification degree: 99.2 mol%) and pure water are mixed at room temperature, and the temperature is raised to 95 ° C. with stirring to maintain PVA. It was dissolved and a solution containing PVA was prepared.

<Reference example 1>
A PVA-based resin layer was formed by supplying the solution of Production Example 1 as a coating liquid and applying the solution to the surface of the resin substrate opposite to the surface provided with the antistatic layer. The coating liquid was supplied as follows using the apparatus having the configuration shown in FIG.
First, the above solution was sent to the heat insulating unit 10 and held at 90 ° C. in the heat insulating unit. Subsequently, the solution was cooled by the cooling unit 20 via the heat exchanger. The temperature of the cooled solution was 25 ° C. Subsequently, the cooled solution was sent to the supply unit 30 via the three-way valve 50. In the supply section, the solution was supplied to the slot die (coating section) as a coating solution via a filter, and coated on the resin substrate by the slot die. This was dried at 60 ° C. to obtain a laminated body 1 in which a PVA-based resin layer having a thickness of 10 μm was formed on a resin base material.

<Example 1>
After circulating the solution of Production Example 1, a laminate was obtained in the same manner as in Reference Example 1 except that the solution was supplied as a coating liquid. Specifically, it is as follows.
The three-way valve was switched so that the solution was sent to the heating circulation section 40 (at the same time, the supply of the coating liquid by the supply section was stopped). In the heat circulation section, the temperature of the solution at 25 ° C. is raised to 90 ° C. using a heat exchanger, and the solution is sent to the heat insulation section again. The solution was circulated continuously for 10 hours in the order of ... Then, the three-way valve was switched so that the solution was sent to the supply unit, the coating liquid was applied to the resin base material in the same manner as in Reference Example 1, and dried to obtain the laminated body 2. While the solution was circulated for 10 hours, the piping between the supply section and the slot die, the slot die, and the like were cleaned cleanly, and the filter was replaced with a new one.

<Comparative Example 1>
A laminate was obtained in the same manner as in Reference Example 1 except that the solution of Production Example 1 was retained and then supplied as a coating liquid. Specifically, it is as follows.
The three-way valve was closed, the pump was stopped, and the solution was prevented from being sent to either the heating circulation section or the supply section (that is, the solution was retained), and the solution was left in this state for 10 hours. After that, the pump is started again, the three-way valve is opened so that the solution is sent to the supply section, the coating liquid is applied to the resin base material in the same manner as in Reference Example 1, and the laminate 3 is dried. Obtained. While the solution was allowed to stay for 10 hours, the piping between the supply section and the slot die, the slot die, and the like were cleaned cleanly, and the filter was replaced with a new one.

<Evaluation>
For each of the laminates of Reference Example, Example, and Comparative Example, the number of uneven defects derived from the gel of PVA was evaluated as follows.
First, the uneven defects of the laminated body were visually confirmed, and the defects were marked. The defect confirmed by visual inspection is referred to as defect A.
Subsequently, the defect A was observed under a microscope, and the defect A was classified into those in which bubbles or foreign substances could be confirmed in the PVA-based resin layer and those in which no foreign matter could be confirmed. Among the defects A, those in which no bubbles or foreign matter could be confirmed in the PVA-based resin layer were designated as defect B.
The PVA-based resin layer was peeled off and the surface of the resin base material was visually confirmed, and defects B were confirmed on the surface of the resin base material at positions corresponding to the markings, and those that could not be confirmed. It was classified as. Among the defects B, the defect C was defined as the defect B in which the uneven defect could not be confirmed at the position corresponding to the marking on the surface of the resin base material.
The defect C is a defect of the surface shape of the resin base material and an uneven shape not derived from bubbles or foreign substances in the PVA-based resin layer, and is considered to be a defect due to the local gel of PVA. The number of defects C was defined as the number of uneven defects derived from the gel of PVA.
The number of uneven defects derived from PVA gel in each laminate was as follows.
Laminated body 1 (Reference example 1) ・ ・ ・ 2 pieces / m ²
Laminated body 2 (Example 1) ... 3 pieces / m ²
Laminated body 3 (Comparative example 1) ... 16 pieces / m ²

As can be seen from the above results, in the laminate of Comparative Example 1 produced by supplying the solution as a coating liquid after retaining it, the laminate of Reference Example 1 produced by supplying the solution as a coating liquid without circulating and retaining the solution. Compared to the laminated body, a large number of gel-derived uneven defects occurred. On the other hand, the number of uneven defects of the laminate of Example 1 produced by circulating the solution and then supplying it as a coating liquid was not much different from the number of uneven defects of the laminate of Reference Example 1. ..

The coating liquid obtained by the production method and the production apparatus of the present invention is suitably used for producing a polarizing element, and the above-mentioned polarizing element is preferably used, for example, in an image display device.

10 Insulation unit 20 Cooling unit 30 Supply unit 40 Heating circulation unit 100 Coating liquid manufacturing equipment

Claims (5)

A method for producing a coating liquid containing a polyvinyl alcohol-based resin.
Insulating the solution containing the polyvinyl alcohol-based resin at 80 ° C. or higher and 95 ° C. or lower , and
Cooling the solution at 80 ° C. or higher and 95 ° C. or lower to 10 ° C. or higher and 40 ° C. or lower
Continuously supplying the cooled solution as a coating liquid and
When the supply of the coating liquid is stopped, the cooled solution is heated to 80 ° C. or higher and 95 ° C. or lower to keep it warm.
A method for producing a coating liquid , which comprises circulating the solution when the supply of the coating liquid is stopped . The method for producing a coating liquid according to claim 1, wherein the cooling rate in the cooling is 1 ° C./min or more. When the supply of the coating liquid is stopped, the step of heating the solution to 80 ° C. or higher and 95 ° C. or lower to keep it warm and the step of cooling the solution of 80 ° C. or higher and 95 ° C. or lower to 10 ° C. or higher and 40 ° C. or lower are repeated in order. The method for producing a coating liquid according to claim 1 or 2, which comprises the above. The present invention comprises forming a polyvinyl alcohol-based resin layer on the resin base material by applying the coating liquid obtained by the production method according to any one of claims 1 to 3 to a resin base material and drying it. A method for manufacturing a extruder. A device for producing a coating liquid containing a polyvinyl alcohol-based resin.
A heat insulating unit that keeps the solution containing the polyvinyl alcohol resin at 80 ° C. or higher and 95 ° C. or lower ,
A cooling unit that cools the solution at 80 ° C. or higher and 95 ° C. or lower to 10 ° C. or higher and 40 ° C. or lower.
A supply unit that continuously supplies the cooled solution as a coating liquid,
A coating liquid having a heating circulation unit that heats the solution cooled by the cooling unit to 80 ° C. or higher and 95 ° C. or lower and returns it to the heat insulating unit when the supply of the coating liquid by the supply unit is stopped. manufacturing device.

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