TW202404818A - Method of manufacturing polarizer - Google Patents

Abstract

A polarizer with reduced wrinkles is obtained. The present invention provides a method of manufacturing polarizer having polyvinyl alcohol-based resin film, the method has a step of contacting the polyvinyl alcohol-based resin film with a treatment liquid and a drying step in this order, wherein the drying step includes contacting at least one widening roll with the polyvinyl alcohol-based resin film.

Description

Manufacturing method of polarizer

The present invention relates to a method for manufacturing a polarizer composed of a polyvinyl alcohol resin film.

In liquid crystal display devices, polarizers obtained by uniaxially stretching a polyvinyl alcohol-based resin film are widely used. Japanese Patent Laid-Open No. 2012-173544 (Patent Document 1) discloses a method for manufacturing a polarizer, which involves at least one of the steps of swelling treatment, dyeing treatment, and cross-linking treatment of a polyvinyl alcohol-based film. Among them, a widening roller is used as a guide roller in the treatment bath to stretch the film.

[Prior technical literature]

[Patent Document]

[Patent Document 1] Japanese Patent Application Laid-Open No. 2012-173544

Polarizers made of polyvinyl alcohol-based resin films may have longitudinal wrinkles along the conveyance direction of the film. The object of the present invention is to provide a polarizer that reduces wrinkles.

The present invention relates to the items illustrated below.

[1] A method of manufacturing a polarizer, which is a method of manufacturing a polarizer composed of a polyvinyl alcohol-based resin film, the manufacturing method sequentially including the steps of bringing the polyvinyl alcohol-based resin film into contact with a treatment liquid, and drying steps,

The aforementioned drying step includes bringing at least one widening roller into contact with the aforementioned polyvinyl alcohol-based resin film.

[2] The manufacturing method according to [1], wherein the drying step includes bringing a plurality of expanding rollers into contact with the polyvinyl alcohol-based resin film in a drying furnace.

[3] The manufacturing method according to [1] or [2], wherein the drying step includes upstream of the center of the entire length of the conveyance path of the polyvinyl alcohol-based resin film in a relatively dry furnace so that the expanding roller Contact with the aforementioned polyvinyl alcohol-based resin film.

[4] The manufacturing method according to any one of [1] to [3], wherein the treatment step includes at least one selected from the group consisting of a swelling step, a dyeing step, and a cross-linking step.

[5] The manufacturing method according to any one of [1] to [4], wherein the widening roller is an arcuate curved widening roller.

[6] A polarizing plate manufacturing device, which is a device for manufacturing a polarizing plate made of a polyvinyl alcohol-based resin film, the device having a processing section for bringing the polyvinyl alcohol-based resin film into contact with a processing liquid, and a drying oven,

The conveyance path of the polyvinyl alcohol-based resin film in the drying furnace is provided with at least one widening roller.

According to the present invention, a polarizer with reduced wrinkles can be obtained.

11: Guide roller

12: Expanding roller

100: Polyvinyl alcohol resin film

110: Polyvinyl alcohol-based resin embryonic membrane (polyvinyl alcohol-based resin film)

111: Take-out roller

113: Swelling tank

115:Dyeing tank

117: Cross-linking tank

119: Washing tank

123: Drying oven

127: Take-up roller

130:Polarizer

Figure 1 is a schematic diagram illustrating longitudinal wrinkles produced by polarizers.

FIG. 2 is a schematic diagram showing a drying oven used in a method for manufacturing a polarizer according to an embodiment of the present invention.

3 is a schematic top view of (a) the widening roller, (b) a schematic cross-sectional view of the widening roller, and (c) illustrating the widening roller used in the manufacturing method of the polarizer according to one embodiment of the present invention. Schematic diagram of the force exerted on the film by the expanding roller.

FIG. 4 is a schematic diagram showing a method of manufacturing a polarizer according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiments. In all the drawings below, the scale is appropriately adjusted to facilitate understanding of each component. However, the scale of each component shown in the drawing may not necessarily be consistent with the scale of the actual component.

[Polarizer]

The polarizer has the property of absorbing linearly polarized light having a vibration surface parallel to its absorption axis, and transmitting linearly polarized light having a vibration surface orthogonal to the absorption axis (parallel to the transmission axis). The polarizer may be, for example, one in which a dichroic dye such as iodine is adsorbed and oriented to a uniaxially stretched polyvinyl alcohol-based resin film.

The manufacturing method of the polarizer of the present invention sequentially includes a treatment step of contacting a polyvinyl alcohol-based resin film with a treatment liquid, and a drying step.

The drying step includes bringing at least one widening roller into contact with the polyvinyl alcohol-based resin film.

As shown in FIG. 1 , a polarizing plate containing a polyvinyl alcohol-based resin film may have longitudinal wrinkles along the conveyance direction of the film. By bringing the expansion roller into contact with the film during the drying step, longitudinal wrinkles can be reduced.

As an embodiment of the polarizing plate manufacturing method of the present invention, in the drying step, a plurality of expanding rollers may be brought into contact with the polyvinyl alcohol-based resin film in a drying furnace. In the first half of the drying furnace, the amount of moisture contained in the polyvinyl alcohol-based resin film decreases rapidly, so wrinkles are likely to occur. From the viewpoint of further suppressing the occurrence of wrinkles, in the drying step, it is preferable to position the expanding roller and the polyvinyl alcohol-based resin film at least upstream of the center of the entire conveyance path of the polyvinyl alcohol-based resin film in the drying furnace. Vinyl alcohol resin film contact. The area further upstream than the center of the entire length of the film conveyance path in the drying furnace may be one third of the upstream side area or one quarter of the upstream side area of the entire length of the film conveyance path. Figure 2 shows an example of a drying oven. A plurality of expanding rollers 12 are provided in the drying furnace 123 so as to be in contact with the film. The conveyance path in the drying furnace 123 may be provided with both the guide roller 11 and the widening roller 12 .

The expansion roller can add external force to the film in the width direction. In the present invention, the external force applied in the width direction of the film is the stretching force from the inside to the outside in the width direction of the film. Expansion of The direction can be adjusted by the arrangement angle of the widening roller 12, etc. The size of the expansion can be adjusted by the arrangement angle of the expansion roller 12, the contact angle between the expansion roller 12 and the polyvinyl alcohol resin film 100, the bending degree (arc height) of the expansion roller 12 used, etc.

Examples of the expanding roller include arcuate curved expanding rollers (expanding rollers), pinch rollers, crown rollers, and reverse crown rollers. These can also be used together.

An example of the arrangement of the widening roller 12 when using an arcuate curved widening roller as the widening roller is shown in FIG. 3 . As shown in Figure 3(a), the arcuate curved expansion roller is equipped with a plurality of spooling rollers (spooling) with built-in ball bearings on the curved shaft 120. The expansion roller covered with a rubber tube on the roll is called a rubber expansion roller, and the expansion roller not covered with a rubber tube is called a metal expansion roller. In the present invention, the expansion roller 12 can be a rubber expansion roller or a metal expansion roller. Generally, the vertical section of the expanding roller 12 relative to the axis 120 is circular, and its area is equal in any vertical section. In the widening roller 12, the vertical section relative to the shaft 120 has a diameter of, for example, 50 mm to 400 mm, and may be about 100 mm.

The orthogonal cross section with respect to the axis 120 in the central portion of the widening roller 12 (a-a cross section in Fig. 3(a)) is represented by cross section 122 in Fig. 3(b), and its center is designated as C'. The orthogonal cross-section with respect to the axis 120 of the portion where the expansion roller 12 contacts the end of the polyvinyl alcohol-based resin film 100 is represented by cross-section 121 in FIG. 3(b) , and its center is designated as C. In the case where the center C' of the cross section 122 of the central portion is located further downstream in the conveyance direction than the center C of the cross section 121, that is, the center portion of the polyvinyl alcohol-based resin film 100 in the width direction is When the end portion is arranged in contact with the expanding roller 12 further back, a stretching force from the inside to the outside in the width direction can be added to the polyvinyl alcohol-based resin film 100 . Figure 3(c) shows the effect of the force exerted on the film by the expanding roller. The end portions in the width direction of the polyvinyl alcohol-based resin film 100 are expanded first than the central portion. When the roller 12 comes into contact (indicated by area A2), and then the expanding roller 12 is arranged so that the central portion contacts the expanding roller 12, an outward stretching force (indicated by arrow b2) can be added to the film to suppress The production of wrinkles.

In FIG. 3(b) , arrow x represents the incident direction of the end of the polyvinyl alcohol resin film 100 incident on the expanding roller 12 , and arrow y represents the direction from the center C toward the center C′ of the expanding roller 12 . In the case of the direction, from the perspective of appropriately expanding the polyvinyl alcohol-based resin film 100, the angle θ of the arrow y with respect to the arrow 90°. The arc height of the widening roller 12 is, for example, 1 mm to 20 mm, or about 10 mm. As used herein, the “arc height of the widening roller” means the distance between the center C and the center C’, and the “arrangement angle of the widening roller” means the angle θ of the arrow y relative to the arrow x.

According to the contact angle α of the polyvinyl alcohol-based resin film 100 in the expanding roller 12, the magnitude of the external force added to the film can also be adjusted. The contact angle α can be adjusted by moving the guide roller 11 and/or the widening roller 12 up and down. In order to easily adjust the amount of stretching force applied by the widening roller 12, the contact angle α is preferably 0° to 30°, and may be about 10°.

The width of the polyvinyl alcohol-based resin film 100 in contact with the expanding roller 12 is not particularly limited, and it is preferable that the film exists within the existing width of the expanding roller 12 .

By providing the film within the existing width of the widening roller 12, wrinkles in the entire film can be easily reduced. In addition, since the film does not contact the end of the expanding roller 12, occurrence of appearance abnormalities such as scratches and wrinkles can be suppressed. The length of the expanding roller 12 in the longitudinal direction is, for example, 500 mm to 3000 mm, and may be about 2000 mm.

The pinch rollers pinch the ends of the polyvinyl alcohol-based resin film in the width direction. The pinch rollers are preferably provided at both ends of the conveyance path of the polyvinyl alcohol-based resin film. The pinch roller can be a metal roller, Plastic roller or rubber roller. The roller diameter of the pinch roller is, for example, about 10 mm to 50 mm. The length of the side end of a pinch roller clamping the film can be about 2% to 10% relative to the full width of the film. The pinch roller may be inclined at an angle β in the film conveyance direction when the film is viewed from the upper surface. That is, in the plane of the film, the angle β between the axis of the pinch roller and the width direction orthogonal to the conveyance direction may be 0 to ±45°, 0 to ±30°, or 0 to ±15°. The pinch roller may also be inclined in the vertical direction with respect to the film conveyance direction. The inclination angle γ of the pinch roller may be 0 to ±45°, 0 to ±30°, or 0 to ±15° relative to the outer side of the film and the central side of the film.

In the drying step, when the plurality of expanding rollers are brought into contact with the polyvinyl alcohol-based resin film in the drying furnace, the plurality of expanding rollers may be the same as each other or may be different from each other.

The treatment step of bringing the polyvinyl alcohol-based resin film into contact with the treatment liquid may include at least one selected from the group consisting of a swelling step, a dyeing step, and a cross-linking step.

Various processing steps that can be included in the manufacturing method of the present invention can be continuously implemented by continuously transporting the polyvinyl alcohol-based resin film as the embryonic film along the film transport path of the polarizer manufacturing device. The film transfer path is equipped with equipment (processing tanks, furnaces, etc.) for carrying out the various processing steps mentioned above according to the execution order.

In addition to the above-mentioned equipment, the film conveyance path can also be constructed by arranging guide rollers, nip rollers, etc. at appropriate positions. For example, guide rollers can be disposed before, after, and in each treatment tank, whereby the film can be introduced into the treatment tank, immersed in the film, and pulled out from the treatment tank. More specifically, two or more guide rollers are provided in each treatment tank, and the film can be immersed in each treatment tank by conveying the film along the guide rollers.

An example of a method of manufacturing a polarizer will be described with reference to FIG. 4 . The polyvinyl alcohol-based resin film 110 as the embryonic membrane rolled out from the unwinding roller 111 is immersed in a swelling tank using water as a swelling bath. In step 113, swelling treatment (swelling step) is performed. The membrane subjected to the swelling treatment is immersed in a dyeing tank 115 using an aqueous solution containing a dichroic dye as a dyeing bath to adsorb the dye (dyeing step). Thereafter, the dye is immersed in a crosslinking tank 117 using an aqueous solution containing a crosslinking agent as a treatment bath, and crosslinking treatment is performed to fix the pigment (crosslinking step). Next, the film is washed in the washing tank 119 (cleaning step), and dried in the drying furnace 123 (drying step), thereby obtaining the polarizing plate 130. The polarizing sheet 130 is wound on the winding roller 127 . The polyvinyl alcohol-based resin film is subjected to uniaxial stretching treatment (stretching step) at any one or more stages from the swelling step to the cross-linking step.

Examples of the polyvinyl alcohol-based resin constituting the polyvinyl alcohol-based resin film include those obtained by saponifying polyvinyl acetate-based resin. Examples of the polyvinyl acetate-based resin include, in addition to polyvinyl acetate, which is a homopolymer of vinyl acetate, copolymers of vinyl acetate and other monomers copolymerizable with the vinyl acetate. Examples of other monomers copolymerizable with vinyl acetate include: unsaturated carboxylic acid compounds, olefin compounds, vinyl ether compounds, unsaturated sulfonic acid compounds, and (meth)acrylamide having an ammonium group. Amine compounds. The saponification degree of the polyvinyl alcohol-based resin is usually about 85 mol% or more, preferably about 90 mol% or more, and more preferably about 99 mol% or more. In this specification, "(meth)acrylic acid" means at least one selected from acrylic acid and methacrylic acid. The same applies to "(meth)acrylyl".

Polyvinyl alcohol-based resins can also be modified. For example, aldehyde-modified polyvinyl formal, polyvinyl acetal, polyvinyl butyral, etc. can also be used.

The average degree of polymerization of the polyvinyl alcohol-based resin is preferably from 100 to 10,000, more preferably from 1,500 to 8,000, even more preferably from 2,000 to 5,000. The average degree of polymerization of polyvinyl alcohol-based resin can be determined based on JIS K6726 (1994). When the average degree of polymerization is within the aforementioned range, polarization performance and film processability tend to be excellent.

The thickness of the polyvinyl alcohol-based resin film as the embryonic membrane can be, for example, 10 μm or more and 150 μm or less, preferably 15 μm or more and 100 μm or less, and more preferably 20 μm or more and 80 μm or less. The length in the width direction of the polyvinyl alcohol-based resin film as the embryonic membrane can be, for example, 600 mm or more and 5000 mm or less.

The thickness of the polarizer is usually 65 μm or less, preferably 50 μm or less, more preferably 35 μm or less, more preferably 30 μm or less. The thickness of the polarizer is usually 2 μm or more, preferably 5 μm or more, more preferably 10 μm or more, more preferably 15 μm or more. The thickness of the polarizer can be controlled, for example, by selecting a polyvinyl alcohol-based resin film, adjusting the stretching ratio, and the like.

The polyvinyl alcohol-based resin film as the embryonic membrane can be prepared, for example, as a roll (rolled product) of a long unstretched or stretched polyvinyl alcohol-based resin film. In this case, the polarizer is also obtained in the form of a long object. Each step is explained in detail below.

(1) Swelling step

The swelling treatment in this step is a treatment performed as necessary for the purpose of removing foreign matter from the polyvinyl alcohol-based resin film that is the embryonic membrane, removing the plasticizer, imparting easy dyeing, and plasticizing the film. Specifically, the swelling treatment may be a treatment in which the polyvinyl alcohol-based resin film 110 is immersed in a swelling tank containing a treatment liquid containing water. The membrane can be immersed in one swelling tank or in two or more swelling tanks in sequence. Before the swelling treatment, during the swelling treatment, or before and during the swelling treatment, the film may also be subjected to uniaxial stretching treatment.

The treatment liquid contained in the swelling tank may be water (for example, pure water) or an aqueous solution added with a water-soluble organic solvent such as alcohol. As mentioned above, the treatment liquid contained in the swelling tank may contain zinc salt.

The temperature of the treatment liquid contained in the swelling tank when the film is immersed is usually 10°C or more and 70°C or less, preferably 15°C or more and 50°C or less. The immersion time of the film is usually 10 seconds or more and 600 seconds or less, preferably 20 seconds or more and 300 seconds or less.

(2) Dyeing steps

The dyeing treatment in this step is performed for the purpose of adsorbing and aligning the dichroic pigment to the polyvinyl alcohol-based resin film. Specifically, the dyeing treatment may be a treatment in which the polyvinyl alcohol-based resin film is immersed in a dyeing tank containing a treatment liquid containing a dichroic dye. The film can be immersed in one dyeing tank or in two or more dyeing tanks in sequence. In order to improve the dyeability of the dichroic dye, the film used in the dyeing step may also be subjected to at least a certain degree of uniaxial stretching treatment. The uniaxial stretching treatment can also be performed during the dyeing treatment to replace the uniaxial stretching treatment before the dyeing treatment, or at the same time as the uniaxial stretching treatment before the dyeing treatment, the uniaxial stretching treatment can also be performed during the dyeing treatment.

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

When iodine is used as the dichroic dye, an aqueous solution containing iodine and potassium iodide can be used as the treatment liquid contained in the dyeing tank. Other iodides such as zinc iodide may be used instead of potassium iodide, or potassium iodide and other iodides may be used in combination. Compounds other than iodide can also coexist in the treatment liquid. substances, such as boric acid, zinc chloride, cobalt chloride, etc. When boric acid is added, it differs from the cross-linking treatment described below in that it contains iodine. The content of iodine in the aqueous solution is usually from 0.01 parts by mass to 1 part by mass relative to 100 parts by mass of water. In addition, the content of iodides such as potassium iodide is usually 0.5 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of water.

The temperature of the treatment liquid contained in the dyeing tank when the film is immersed is usually 10°C or more and 45°C or less, preferably 10°C or more and 40°C or less, more preferably 20°C or more and 35°C or less. The immersion time of the film can be, for example, 20 seconds or more and 600 seconds or less, preferably 20 seconds or more and 300 seconds or less.

When a dichroic organic dye is used as a dichroic pigment, an aqueous solution containing a dichroic organic dye can be used as the treatment liquid contained in the dyeing tank. The content of the dichroic organic dye in the aqueous solution is usually 1×10-4 parts by mass or more and 10 parts by mass or less, preferably 1×10-3 parts by mass or more and 1 part by mass or less based on 100 parts by mass of water. Dyeing auxiliaries can also coexist in the dyeing tank. For example, inorganic salts such as sodium sulfate or surfactants can also be included. Only one type of dichroic organic dye may be used alone, or two or more types may be used in combination. The temperature of the treatment liquid contained in the dyeing tank when the film is immersed is, for example, 20°C or more and 80°C or less, preferably 25°C or more and 50°C or less. The immersion time of the film is usually 30 seconds or more and 600 seconds or less, preferably 60 seconds or more and 300 seconds or less.

(3) Cross-linking step

The cross-linking treatment of the polyvinyl alcohol-based resin film after the dyeing step is treated with a cross-linking agent for the purpose of water resistance or hue adjustment by cross-linking. Specifically, the cross-linking treatment may be performed by immersing the membrane after the dyeing step in a cross-linking tank containing a treatment liquid containing a cross-linking agent. handle. The film can be immersed in one cross-linking tank or in two or more cross-linking tanks in sequence. Uniaxial stretching processing can also be performed during cross-linking processing.

Examples of the cross-linking agent include boric acid, glyoxal, glutaraldehyde, etc., and boric acid is preferably used. It is also possible to use two or more cross-linking agents together. The content of boric acid in the treatment liquid contained in the cross-linking tank is usually 0.1 parts by mass or more and 15 parts by mass or less, preferably 1 part by mass or more and 10 parts by mass or less based on 100 parts by mass of water. When the dichroic dye is iodine, the treatment liquid contained in the cross-linking tank preferably contains iodide in addition to boric acid. The content of the iodide in the treatment liquid contained in the cross-linking tank is usually 0.1 parts by mass or more and 15 parts by mass or less, preferably 5 parts by mass or more and 12 parts by mass or less based on 100 parts by mass of water. Examples of the iodide include potassium iodide, zinc iodide, and the like. In addition, compounds other than iodide, such as zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate, etc., may coexist in the crosslinking tank.

The temperature of the treatment liquid contained in the crosslinking tank when the membrane is immersed can be, for example, 30°C or more and 85°C or less, preferably 30°C or more and 60°C or less. The immersion time of the film can be, for example, 2 seconds or more and 600 seconds or less, preferably 2 seconds or more and 300 seconds or less.

In the cross-linking step, the number of cross-linking tanks may be two or more. In this case, the composition and temperature of the treatment liquid contained in each cross-linking tank may be the same or different. The treatment liquid contained in the cross-linking tank may have a concentration or temperature of the cross-linking agent, iodide, etc. according to the purpose of impregnating the polyvinyl alcohol-based resin film. The cross-linking treatment for water resistance through cross-linking and the cross-linking treatment for adjusting the hue (complementary color) can also be performed in a plurality of steps (for example, a plurality of tanks).

Generally speaking, when both the cross-linking treatment for making water resistance by cross-linking and the cross-linking treatment for adjusting the hue (complementary color) are carried out, the tank for carrying out the cross-linking treatment for adjusting the hue (complementary color) (Complementary color tank) is arranged in the rear stage. The temperature of the processing liquid contained in the color correction tank is, for example, 10°C or above. and 55°C or lower, preferably 20°C or higher and 50°C or lower. The content of the crosslinking agent in the processing liquid contained in the color correction tank is, for example, 1 to 5 parts by mass relative to 100 parts by mass of water. The content of the iodide in the processing liquid contained in the color correction tank is, for example, 3 parts by mass or more and 30 parts by mass or less based on 100 parts by mass of water.

As described above, during the production of polarizers, the polyvinyl alcohol-based resin film is subjected to uniaxial stretching treatment (stretching step) at any one or two or more stages from before the swelling step to the cross-linking step. From the viewpoint of improving the dyeability of the dichroic dye, the film used in the dyeing step is preferably a film that has been subjected to at least a certain degree of uniaxial stretching treatment, or it is preferable that the film is subjected to a uniaxial stretching treatment during the dyeing treatment. To replace the uniaxial stretching treatment before the dyeing treatment, or at the same time as the uniaxial stretching treatment before the dyeing treatment, the uniaxial stretching treatment is also performed during the dyeing treatment.

The uniaxial stretching process may be either dry stretching in which stretching is performed in the air, wet stretching in a tank, or both of them may be performed. The uniaxial stretching treatment may include roller-to-roll stretching, hot roll stretching, tenter stretching, etc., in which circumferential speed differences are provided between two nip rollers to perform longitudinal uniaxial stretching, and preferably includes roller-to-roll stretching. The stretching magnification based on the embryonic membrane (when stretching is performed in two or more stages, the cumulative stretching magnification) is approximately 3 times or more and 8 times or less. In order to provide good polarization characteristics, the stretching ratio is preferably 4 times or more, more preferably 5 times or more.

(4) Washing steps

The cleaning treatment in this step is carried out as necessary in order to remove excess cross-linking agents, dichroic pigments and other chemicals attached to the polyvinyl alcohol-based resin film, and is washed with a cleaning solution containing water. The treatment of the polyvinyl alcohol-based resin film after the linking step. Specifically, it may be a process in which the polyvinyl alcohol-based resin film after the cross-linking step is immersed in a treatment liquid (cleaning liquid) contained in a cleaning tank. the The membrane can be immersed in one washing tank, or in two or more washing tanks in sequence. Alternatively, the cleaning treatment may be a treatment in which a cleaning solution is sprayed onto the polyvinyl alcohol-based resin film after the cross-linking step, or the aforementioned immersion treatment and spray treatment may be combined.

The cleaning solution may be water (for example, pure water), or an aqueous solution added with a water-soluble organic solvent such as alcohol.

When the polyvinyl alcohol-based resin film after the cross-linking step is immersed in a cleaning tank, the temperature of the cleaning liquid in the cleaning tank is, for example, 2°C or more and 40°C or less, preferably 2°C or more and 22°C. ℃ or less, more preferably 2 ℃ or more and 10 ℃ or less. The time of immersion in the washing tank can be, for example, 10 seconds or more and 100 seconds or less, preferably 20 seconds or more and 80 seconds or less.

When the polyvinyl alcohol-based resin film after the cross-linking step is sprayed with a cleaning solution, the temperature of the cleaning solution can be the same temperature at the center and both ends of the polyvinyl alcohol-based resin film in the width direction. , can also be different temperatures, preferably different temperatures, more preferably the temperature at the center is lower than the temperature at both ends. The temperature of the cleaning fluid is preferably 2°C or more and 10°C or less in the center, 10°C or more and 22°C or less at both ends, and more preferably 3°C or more and 7°C or less in the center, and 10°C or more and 22°C or less at both ends. The end portion is 15°C or more and 22°C or less.

(5) Drying step

The drying step is to dry the polyvinyl alcohol-based resin film after the treatment step. The polyvinyl alcohol-based resin film after the washing step can be introduced into the drying step while continuing to be conveyed, thereby performing a drying process, thereby obtaining a polarizing plate.

The drying process is performed using a thin film drying means (heating means). A preferred example of drying means is a drying oven. The drying furnace is preferably one that can control the temperature inside the furnace. The drying furnace is, for example, a hot air oven that can increase the temperature in the furnace by supplying hot air or the like. Also, use the drying place of the drying mechanism The treatment may also be a treatment in which the polyvinyl alcohol-based resin film after the cleaning step is brought into close contact with one or more heating bodies having a convex curved surface, or a treatment in which the film is heated using a heater.

Examples of the heating element include a roller (for example, a guide roller that also serves as a heat roller) that has a heat source inside (for example, a heat medium such as warm water or an infrared heater) and can increase the surface temperature. Examples of the heater include infrared heaters, halogen heaters, panel heaters, and the like.

In the drying step, the temperature of the drying treatment (such as the temperature in the drying furnace, the surface temperature of the hot roller, etc.) is usually 30°C or more and 100°C or less, preferably 50°C or more and 90°C or less. The drying time is not particularly limited, but is, for example, 30 seconds or more and 600 seconds or less, preferably 30 seconds or more and 60 seconds or less.

The drying step may be one stage or may be divided into multiple stages. It is preferably divided into two or more stages and four or less stages. When the drying step is divided into multiple stages, the temperature of the drying process is preferably set so that the temperature of subsequent stages becomes higher than that of the initial stage. When the drying step is divided into multiple stages, the drying time in each stage may be, for example, 10 seconds or more and 300 seconds or less, preferably 10 seconds or more and 20 seconds or less.

In the polarizer manufacturing step, at least one of the treatment liquids used to treat the polyvinyl alcohol-based resin film may contain a zinc salt. Examples of the treatment tank that accommodates the treatment liquid include a swelling tank, a dyeing tank, a cross-linking tank, a washing tank, a complementary color tank, and the like. The treatment tank containing the treatment solution containing zinc salt is preferably a treatment tank located between the dyeing tank and the washing tank, and is more preferably at least one selected from a cross-linking tank and a complementary color tank, and is further preferably located in the cross-linking tank. When there are two or more slots, at least one is selected from the last cross-linking slot and the complementary color slot.

By immersing the polyvinyl alcohol-based resin film in a treatment solution containing zinc salt, the obtained polarizer can contain zinc element. The content of zinc in the polarizer can be adjusted by adjusting the zinc salt in the treatment solution. The content of the zinc element is set to the aforementioned range based on the concentration of the polyvinyl alcohol-based resin film, the immersion time of the polyvinyl alcohol-based resin film in the treatment liquid containing zinc salt, the temperature of the treatment liquid, etc.

Examples of zinc salts contained in the treatment liquid include zinc halides such as zinc chloride and zinc iodide, zinc sulfate, zinc acetate, zinc nitrate, and the like. Among them, zinc nitrate is preferred because the change in tension is small. The zinc salt can be added to the treatment solution in the form of a zinc salt solution.

The concentration of the zinc salt in the treatment liquid may vary depending on each treatment tank. For example, it may be 1 part by mass or more and 10 parts by mass or less, preferably 2 parts by mass or more, based on 100 parts by mass of the treatment liquid contained in the treatment tank. And less than 7 parts by mass.

After the above steps, a polarizer composed of a polyvinyl alcohol resin film can be obtained. The polarizer has dichroic pigments adsorbed and aligned on a uniaxially stretched polyvinyl alcohol resin film.

[Manufacturing equipment]

The manufacturing device of the present invention is a manufacturing device for manufacturing a polarizer composed of a polyvinyl alcohol-based resin film.

This apparatus includes a processing section for bringing the polyvinyl alcohol-based resin film into contact with the processing liquid, and a drying furnace.

The conveyance path of the polyvinyl alcohol-based resin film in the drying furnace is provided with at least one widening roller.

The treated part may be a part that performs the aforementioned swelling treatment, dyeing treatment, cross-linking treatment or washing treatment. Using the manufacturing apparatus of the present invention, the aforementioned polarizing plate can be obtained.

A manufacturing device according to one embodiment includes at least one of a swelling tank, a dyeing tank, a cross-linking tank, a washing tank, and a drying furnace. The drying oven may contain a plurality of expanding rollers. In the drying furnace, it is preferable to have a widening roller located closer to the entrance than the center of the entire length of the film conveyance path.

[Polarizing plate]

The obtained polarizer can be directly transported to the polarizing plate production step. In the polarizing plate manufacturing step, for example, a thermoplastic resin film is bonded to one side or both sides of the polarizing plate. The manufacturing method of the polarizing plate may include the aforementioned manufacturing steps of the polarizing plate.

A polarizing plate according to one embodiment is a laminate having a thermoplastic resin film on one side or both sides of the polarizing plate via an adhesive. The polarizing plate may further include an adhesive layer, an optical functional layer and a protective film. The polarizing plate may be, for example, a linear polarizing plate, a circular polarizing plate, an elliptical polarizing plate, or the like. The circular polarizing plate has a linear polarizing plate and a phase difference layer.

The thickness of the polarizing plate is usually 5 μm or more, and may be 20 μm or more, 25 μm or more, or 30 μm or more. The thickness of the polarizing plate is preferably 80 μm or less, more preferably 60 μm or less.

[Thermoplastic resin film]

Examples of the thermoplastic resin film include translucent resin films including chain polyolefin resins (polypropylene resins, etc.) and cyclic polyolefin resins (norbornene resins, etc.) Polyolefin resins; cellulose ester resins such as triacetyl cellulose, diacetyl cellulose; polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate Such polyester resins; polycarbonate resins; (meth)acrylic resins such as polymethyl methacrylate resins; or mixtures, copolymers, etc. The thermoplastic resin film may have a single-layer structure composed of one resin layer composed of one or more thermoplastic resins, or may have a plurality of laminated layers composed of one or more thermoplastic resins. Multi-layer structure of layers. The first thermoplastic resin film and the second thermoplastic resin film may be the same or different types of thermoplastic resin films.

The thermoplastic resin film may contain additives as necessary. Examples of additives include lubricants, anti-caking agents, heat stabilizers, antioxidants, ultraviolet absorbers, antistatic agents, light fast agents, impact resistance improvers, surfactants, and the like. Examples of ultraviolet absorbers include salicylate compounds, benzophenone compounds, benzotriazole compounds, cyanoacrylate compounds, nickel azide salt compounds, and the like.

Either or both of the thermoplastic resin films may be a protective film having optical functions such as a retardation film or a brightness improvement film. For example, by stretching (uniaxial stretching or biaxial stretching, etc.) a transparent resin film containing the above-mentioned materials, or forming a liquid crystal layer on the film, a retardation film giving an arbitrary retardation value can be produced.

Surface treatment layers (coatings) such as hard coat layers, anti-glare layers, anti-reflective layers, anti-static layers, and anti-fouling layers can also be formed on the surface of the thermoplastic resin film. The surface treatment layer may be formed on one side of the thermoplastic resin film or on both sides. The surface treatment layer may be formed on the surface of the thermoplastic resin film opposite to the polarizing plate side.

From the viewpoint of thinning the polarizing plate, the thickness of the thermoplastic resin film is preferably thin. However, if it is too thin, the strength tends to be reduced and the processability is deteriorated. Therefore, it is preferably 5 μm or more and 150 μm or less, and more preferably 5 μm or more and 150 μm or less. It is preferably 5 μm or more and 100 μm or less, and further preferably 10 μm or more and 60 μm or less.

[adhesive]

In order to bond the polarizer and the thermoplastic resin film, an adhesive can be used. Examples of the adhesive include a water-based adhesive containing a water-based composition and an active energy ray-curable adhesive containing an active energy ray-curable composition.

Examples of the resin component contained in the aqueous composition include polyvinyl alcohol resin, urethane resin, and the like. In order to improve the adhesiveness or adhesion, the aqueous composition containing polyvinyl alcohol-based resin may further contain polyhydric aldehydes, melamine-based compounds, zirconium oxide compounds, zinc compounds, glyoxal, glyoxal derivatives, and water-soluble epoxy resins. Hardening ingredients or cross-linking agents. Examples of the aqueous composition containing a urethane resin include a water-based composition containing a polyester-based ionomer-type urethane resin and a compound having a glycidoxy group.

The active energy ray curable composition is a composition that is cured by irradiation with active energy rays such as ultraviolet rays, visible light, electron beams, and X-rays. The ultraviolet curable adhesive may be a mixture of a radically polymerizable (meth)acrylic compound and a photoradical polymerization initiator, or a mixture of a cationically polymerizable epoxy compound and a photocationic polymerization initiator. Alternatively, a cationically polymerizable epoxy compound and a radically polymerizable (meth)acrylic compound may be used together, and a photocationic polymerization initiator and a photoradical polymerization initiator may be used together as initiators.

The thickness of the adhesive layer may be, for example, 1 μm or more and 25 μm or less. The thickness of the adhesive layer is preferably 2 μm or more, preferably 15 μm or less, and more preferably 5 μm or less. If the thickness of the adhesive layer is small, the impact resistance tends to decrease. If the thickness of the adhesive layer is large, the bending resilience tends to increase.

In order to improve the adhesion between the polarizer and the resin film, corona treatment, flame treatment, plasma treatment, or ultraviolet irradiation can be performed on the bonding surface of the polarizer and/or the resin film before the polarizer and the resin film are bonded together. Treatment, primer coating treatment, saponification treatment and other surface treatments.

[Adhesive layer]

The polarizing plate may have an adhesive layer for bonding the layers constituting the polarizing plate to each other, or for bonding the polarizing plate to a translucent member or an image display element. The adhesive layer may be made of (meth)acrylic It is an adhesive composition composed of acid-based, rubber-based, urethane-based, ester-based, polysiloxane-based, and polyvinyl ether-based resins as the main component. In terms of excellent transparency, weather resistance, heat resistance, etc., an adhesive composition using a (meth)acrylic resin as a base polymer is preferred. The adhesive composition may be an active energy ray hardening type or a heat hardening type.

As the (meth)acrylic resin (base polymer) used in the adhesive composition, butyl (meth)acrylate, ethyl (meth)acrylate, isopropyl (meth)acrylate can be preferably used. A polymer or copolymer of one or more (meth)acrylic acid esters such as octyl ester and 2-ethylhexyl (meth)acrylate as monomers. Among the base polymers, copolymerization with polar monomers is preferred. Examples of the polar monomer include: (meth)acrylic acid compound, (meth)acrylic acid 2-hydroxypropyl compound, (meth)acrylic acid hydroxyethyl compound, (meth)acrylamide compound, (meth)acrylic acid compound Monomers having carboxyl groups, hydroxyl groups, amide groups, amine groups, epoxy groups, etc., such as N,N-dimethylaminoethyl acrylate compounds and glycidyl (meth)acrylate compounds.

The adhesive composition may contain only the aforementioned base polymer, but usually further contains a cross-linking agent. Examples of the cross-linking agent include: a divalent or higher metal ion that forms a carboxylic acid metal salt with the carboxyl group; a polyamine compound that forms an amide bond with the carboxyl group; and a polyepoxy compound that forms an ester bond with the carboxyl group. Or polyol; an example is a polyisocyanate compound that forms an amide bond with a carboxyl group. Among them, polyisocyanate compounds are preferred.

The so-called active energy ray curing type adhesive composition has the property of being hardened by irradiation with active energy rays such as ultraviolet rays or electron beams. It can have adhesiveness even before irradiation with active energy rays and adhere closely to films and other objects to be adhered. An adhesive composition that has physical properties and can be hardened by irradiation with active energy rays and adjust the adhesion force. The active energy ray curing adhesive composition is preferably an ultraviolet curing type. Active energy ray curable adhesive composition In addition to the base polymer and cross-linking agent, it further contains an active energy ray polymerizable compound. Furthermore, a photopolymerization initiator, a photosensitizer, etc. may be contained as needed.

The adhesive composition may include fine particles for imparting light scattering properties, beads (resin beads, glass beads, etc.), glass fibers, resins other than the base polymer, adhesiveness imparting agents, and fillers (metal powder or other Inorganic powder, etc.), antioxidants, ultraviolet absorbers, dyes, pigments, colorants, defoaming agents, anti-corrosion agents, photopolymerization initiators and other additives.

The adhesive layer can be formed by the following methods: dissolving or dispersing the adhesive composition in an organic solvent such as toluene or ethyl acetate to prepare an adhesive liquid, and directly applying it to the target surface of the laminated film to form an adhesive. Layer method; or form an adhesive layer into a sheet in advance on the release film that has been subjected to release treatment, and then transfer it to the opposite surface of the polarizing plate, etc. When an active energy ray-curable adhesive composition is used, the formed adhesive layer can be irradiated with active energy rays to produce a cured product having a required degree of hardening.

The thickness of the adhesive layer may be, for example, 1 μm or more and 100 μm or less. The thickness of the adhesive layer is preferably 3 μm or more, preferably 50 μm or less, and more preferably 30 μm or less.

The polarizing plate may include a separation film. The separation membrane may be a membrane containing polyethylene resin such as polyethylene, polypropylene resin such as polypropylene, polyester resin such as polyethylene terephthalate, etc., preferably polyethylene terephthalate. Stretch film.

[Optical functional layer]

The optically functional layer may be an optically functional film other than a polarizer used to impart required optical functions. A preferred example of the optically functional film is a retardation film. Examples of the retardation film include a film imparting a phase difference of λ/2 (λ/2 wavelength plate), a film imparting a phase difference of λ/4 (λ/4 wavelength plate), a positive C plate, and the like. The optically functional film may include an alignment layer and a substrate, or may have separate More than 2 liquid crystal layers, alignment layers and substrates. The thermoplastic resin film may also serve as a retardation film, but a retardation film different from these films may be laminated separately.

Examples of the retardation film include: a birefringent film made of an extended film of a translucent thermoplastic resin; a film in which disk-like liquid crystal or nematic liquid crystal is aligned and fixed; examples include those formed on a base film Those having the aforementioned liquid crystal layer, etc. The base film is usually a film containing a thermoplastic resin, and an example of the thermoplastic resin is cellulose ester resin such as triacetyl cellulose.

Examples of other optically functional films (optical members) that can be included in the polarizing plate are light condensing plates, brightness improvement films, reflective layers (reflective films), semi-transmissive reflective layers (semi-transmissive reflective films), and light diffusion layers (light diffusion films). )wait. These are usually provided when the polarizing plate is arranged on the back side (backlight side) of the liquid crystal cell.

[Protective film]

The polarizing plate may include a protective film to protect its surface (typically, the surface of the thermoplastic resin film of the polarizing plate). The protective film is peeled off and removed together with the adhesive layer of the protective film after, for example, the polarizing plate is bonded to an image display element or other optical component.

The protective film can be composed of a base film and an adhesive layer laminated on it. Regarding the adhesive layer, the aforementioned description is cited. The resin constituting the base film may be, for example, polyethylene resin such as polyethylene, polypropylene resin such as polypropylene, polyester resin such as polyethylene terephthalate or polyethylene naphthalate, or polycarbonate. Thermoplastic resins such as ester resins. Preferred are polyester-based resins such as polyethylene terephthalate.

The thickness of the protective film is not particularly limited, but is preferably in the range of 20 μm or more and 200 μm or less. When the thickness of the base film is 20 μm or more, strength tends to be easily imparted to the polarizing plate.

Polarizing plates can be used as components of image display devices. The image display device is not particularly limited, and examples thereof include organic electroluminescence (organic EL) display devices, inorganic electroluminescence (inorganic EL) display devices, liquid crystal display devices, and electroluminescence display devices. When assembled into a display device, the polarizing plate is preferably disposed on the front (viewing side) of the image display element. The circular polarizing plate can absorb external light reflected in the image display device, and therefore can function as an anti-reflective film.

Claims (6)

A method for manufacturing a polarizer, which is a method for manufacturing a polarizer composed of a polyvinyl alcohol-based resin film, the manufacturing method sequentially including a treatment step of bringing the polyvinyl alcohol-based resin film into contact with a treatment liquid, and a drying step , The drying step includes bringing at least one widening roller into contact with the polyvinyl alcohol-based resin film. The manufacturing method according to claim 1, wherein the drying step includes contacting a plurality of expanding rollers with the polyvinyl alcohol resin film in a drying furnace. The manufacturing method according to claim 1 or 2, wherein the drying step includes upstream of the center of the entire length of the conveyance path of the polyvinyl alcohol-based resin film in a relatively dry furnace, so that the expansion roller and the polyvinyl alcohol are Contact with resin film. The manufacturing method according to any one of claims 1 to 3, wherein the treatment step includes at least one selected from the group consisting of a swelling step, a dyeing step and a cross-linking step. The manufacturing method according to any one of claims 1 to 4, wherein the aforementioned widening roller is an arcuate curved widening roller. A polarizing plate manufacturing device is a device for manufacturing a polarizing plate composed of a polyvinyl alcohol resin film, and the device is provided with a processing section for bringing the polyvinyl alcohol resin film into contact with a processing liquid, and a drying furnace. The conveyance path of the polyvinyl alcohol-based resin film in the drying furnace is provided with at least one widening roller.

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