TW202125005A - Polarizing plate and manufacturing method thereof - Google Patents

Abstract

An object of the present invention is to provide a polarizing plate which does not cause discoloration even in a durability test at a high temperature (105℃) and for a long time (600 hours or more).

As a solution, provided is a polarizing plate having a single hue b value of 2.7 or more and an absorbance at a wavelength of 700 nm of 4.5 or less.

Description

Polarizing plate and manufacturing method thereof

The invention relates to a polarizing plate and a manufacturing method thereof.

Patent Documents 1 and 2 have proposed a polarizing film whose hue is still small after heating at 120°C for 100 hours.

Patent Document 3 discloses a polarizing plate that can obtain a polarizing plate having excellent durability against a thermal cycle test and having a polarizing film with a neutral gray in the cross hue.

Patent Document 4 has proposed an optical laminate that is excellent in yellowing resistance when exposed to a high-temperature environment.

[Prior Technical Literature]

[Patent Literature]

[Patent Document 1] JP 2004-226707 A

[Patent Document 2] JP 2007-304626 A

[Patent Document 3] JP 2013-148806 A

[Patent Document 4] JP 2018-025765 A

In the polarizing plates described in Patent Documents 1 to 4, even under more severe conditions, high temperature (for example, 105° C.) and long-term (for example, 600 hours or more) endurance tests, discoloration may still occur.

The object of the present invention is to provide a polarizing plate that does not cause discoloration even in high temperature (105°C) and long-term (600 hours or more) endurance tests.

The present invention provides the following polarizing plate and its manufacturing method.

[1] A polarizing plate having a monomer hue b value of 2.7 or more, and an absorbance at a wavelength of 700 nm of 4.5 or less.

[2] The polarizing plate according to [1], which is provided with a polarizer, and a first thermoplastic resin film bonded to one side via an adhesive.

[3] The polarizing plate according to [2], further comprising a second thermoplastic resin film that is bonded to the side of the polarizer and the first thermoplastic resin film via an adhesive. It is the opposite side.

[4] The polarizing plate according to [2] or [3], wherein the adhesive is a water-based adhesive.

[5] The polarizing plate according to any one of [1] to [4], wherein the content of the zinc element in the polarizing plate is 150 ppm or more.

[6] A display device for a vehicle, comprising the polarizing plate according to any one of [1] to [5].

[7] A method of manufacturing a polarizing plate, which is the method of manufacturing a polarizing plate described in [2], wherein the polarizer includes a polyvinyl alcohol-based resin film, and the method of manufacturing a polarizing plate includes a cleaning step. In the cleaning step, the aforementioned polyvinyl alcohol-based resin film is cleaned with a cleaning liquid, and the cleaning liquid at a temperature exceeding 22° C. is not used for cleaning.

[8] The method for manufacturing a polarizing plate as described in [7], which further includes a drying step in which the polyvinyl alcohol resin film is dried at a temperature of 96° C. or higher.

[9] The method for manufacturing a polarizing plate as described in [7] or [8], which further includes a bonding step in which the first thermoplastic resin film is bonded to the polarizer via an adhesive On one side, and the aforementioned adhesive is dried at a temperature above 85°C.

According to the present invention, it is possible to provide a polarizing plate that does not cause discoloration even in high temperature (105°C) and long-term (600 hours or more) endurance tests.

10: Polarizing plate

11: The first thermoplastic resin film

12: Polarizer

13: The second thermoplastic resin film

110: Embryo membrane of polyvinyl alcohol resin (polyvinyl alcohol resin)

111: delivery roller

113: swelling groove

115: dyeing tank

117: Cross-linking tank

119: washing tank

123: Drying furnace

127: take-up roller

130: Polarizer

Fig. 1 is a schematic cross-sectional view of a polarizing plate related to an embodiment of the present invention.

Fig. 2 is a schematic cross-sectional view of a polarizing plate related to an embodiment of the present invention.

3 is a schematic cross-sectional view showing an example of the arrangement of the device used in the manufacturing step of the polarizer.

Hereinafter, the 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 following drawings, in order to easily understand each component, the scale is appropriately adjusted and shown. The scale of each component shown in the drawing does not necessarily match the scale of the actual component.

<Polarizer>

According to one aspect of the present invention, the hue b value of the polarizing plate monomer is 2.7 or more, and the absorbance at a wavelength of 700 nm is 4.5 or less. When the hue b value of the polarizer system monomer is 2.7 or more, the endurance test at high temperature (105°C) and long time (600 hours or more) at high temperature (105°C) and long time (600 hours or more) by setting the absorbance at 700nm wavelength to 2.7 or more For endurance test), there is also a tendency not to change color easily. In this specification, the endurance test refers to an endurance test performed in accordance with the method described in the column of Examples described later. The term "non-discoloration" means that the yellowing cannot be recognized when observing the polarizing plate according to the method described in the column of Examples described later. The polarizing plate of the present invention preferably does not produce discoloration until 1000 hours in the durability test, and more preferably does not produce discoloration until 1400 hours.

Generally, the absorbance of the polarizer at a wavelength of 700nm tends to be less likely to produce red change, and the lower the monomer hue b value of the polarizer is, the less likely it is to produce yellow change. _{In the durability test, the collapse of polyiodide complex I 5} ^- in the polarizer and the polyolefinization of polyvinyl alcohol in the polarizer are produced by heating in the endurance test, and it is difficult to cause a decrease in absorbance at a wavelength of 700 nm and monomers. The tendency of the hue b value to rise. Therefore, Xian believes that in the endurance test of the polarizing plate, it is advantageous to suppress the color change of the polarizing plate at a wavelength of 700 nm, and have a low b value of the monomer hue. However, unexpectedly, according to the present inventors, in a more severe endurance test at high temperature (105°C) and long time (600 hours or more), it was found that by setting the individual hue b value of the polarizing plate to 2.7 or more, In addition, the absorbance at a wavelength of 700 nm is set to 4.5 or less to suppress discoloration. A polarizing plate having a monomer hue b value of 2.7 or more and an absorbance of 700 nm at a wavelength of 4.5 or less is a novelty that has not been disclosed in any of Patent Documents 1 to 4.

The monomer hue b value of the polarizing plate is preferably 2.9 or more, more preferably 3.1 or more, still more preferably 3.3 or more, particularly preferably 3.5 or more. The monomer hue b value of the polarizing plate is usually 4.1 or less, for example, it can be 3.9 or less.

The b value of the individual hue of the polarizer is the b value of the Lab color system of the individual polarizer. The b-value is the tristimulus value X, Y and Z specified in JIS Z 8722:2009 "Methods for Measuring Color-Reflected and Penetrated Object Color", calculated according to the following formula.

b value=7.0(Y-0.847Z)/Y ^1/2

The monomer hue b value of the polarizing plate can be measured according to the measurement method described in the column of the examples described later.

The absorbance of the polarizing plate at a wavelength of 700 nm is preferably 4.4 or less, more preferably 4.3 or less. The absorbance of the polarizing plate at a wavelength of 700 nm is usually 3.9 or higher, for example, it may be 4.1 or higher, or it may be 4.2 or higher.

The absorbance of the polarizing plate at a wavelength of 700 nm can be measured using an absorbance photometer such as an ultraviolet-visible spectrophotometer, and is calculated from the following formula.

Absorbance at 700nm wavelength=-log[{TD transmittance at 700nm wavelength(%)}/100]

The incident light is measured using polarized light parallel to the absorption axis direction of the polarizer. In this formula, the so-called TD transmittance is the transmittance when the direction of the polarized light from Glan-Thompson is orthogonal to the transmission axis of the polarizer.

The absorbance of the polarizing plate at a wavelength of 700 nm can be measured in accordance with the measurement method described in the column of Examples described later.

The monomer hue b value and the absorbance at 700 nm in the above range can be adjusted by the temperature of the cleaning solution in the cleaning step in the polarizer manufacturing step described later, the adjustment of the drying temperature in the drying step, and It is obtained by adjusting the drying temperature of the adhesive for bonding the polarizer and the thermoplastic resin film.

The polarizing plate system may contain zinc element. When the polarizing plate contains zinc element, the zinc element is preferably included in at least any one of the polarizer and the adhesive. When the polarizing plate contains zinc element, the content of zinc element in the polarizing plate may be 150 ppm or more, for example. When the content of zinc in the polarizing plate is 150 ppm or more, it tends to be easy to suppress discoloration in the durability test. The content of zinc in the polarizing plate is preferably 200 ppm or more, more preferably 250 ppm or more from the viewpoint of suppressing discoloration. On the other hand, the content of zinc in the polarizing plate is usually 1000 ppm or less. The content of zinc element is measured in accordance with the measurement method described in the column of Examples described later. The content of the zinc element in the polarizer can be, for example, within the above-mentioned range by adjusting the zinc concentration in the polarizer and/or the adhesive.

FIG. 1 shows a polarizing plate 10 related to an embodiment of the present invention. As shown in FIG. 1, the polarizing plate 10 may include a polarizer 12 and a first thermoplastic resin film 11 bonded to one side with an adhesive interposed therebetween. As shown in FIG. 2, the polarizing plate 10 may further include a second thermoplastic resin film 13 that is bonded to the polarizer 12 on the side opposite to the first thermoplastic resin film 11 side via an adhesive. Hereinafter, the first thermoplastic resin film and the second thermoplastic resin film may be collectively referred to as a thermoplastic resin film. The polarizer is on the opposite side of the thermoplastic resin film from the polarizer side, and can be further equipped with an adhesive layer, an optical function layer, and a protective film described later.

The polarizing plate can be used in image display devices. The image display device may be any of a liquid crystal display device, an organic EL display device, etc., but is preferably a liquid crystal display device. The liquid crystal display device includes a liquid crystal panel including a liquid crystal cell as an image display element, and a backlight. When constructing a liquid crystal display device, the polarizing plate can be used for the polarizing plate disposed on the recognition side, the polarizing plate disposed on the backlight side, and the polarizing plate for both the recognition side and the backlight side.

When the polarizing plate includes the first thermoplastic resin film and the second thermoplastic resin film, the polarizing plate can be bonded to the image display device so that the first thermoplastic resin film becomes the outer side of the image display device. Partial When the light plate is equipped with the first thermoplastic resin film and the second thermoplastic resin film, the polarizing plate is suitable for use in the following vehicle display device, which is sequentially provided with a transparent plate arranged on the side of the first thermoplastic resin film of the polarizing plate. The optical member and the display device arranged on the second thermoplastic resin film side of the polarizing plate. The light-transmitting member may be a glass plate or a resin film having light-transmitting properties.

[Polarizer]

The polarizer is an absorption type polarizer with the following properties: absorbs linearly polarized light with a vibration plane parallel to its absorption axis, and transmits linearly polarized light with a vibration plane orthogonal to the absorption axis (parallel to the penetration axis) through. The polarizer system may be, for example, a polarizer in which a dichroic dye such as iodine is adsorbed on a uniaxially stretched polyvinyl alcohol-based resin film.

The thickness of the polarizer is usually 65 μm or less, preferably 50 μm or less, more preferably 35 μm or less, and still 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, and still more preferably 15 μm or more. The thickness of the polarizer can be controlled by, for example, the selection of the polyvinyl alcohol-based resin film and the adjustment of the stretching ratio.

An example of the manufacturing process of the polarizer will be described with reference to FIG. 3. The polyvinyl alcohol resin film 110, which is the embryonic film, rolled out from the delivery roller 111 is then guided to a swelling tank 113 that uses water as a swelling bath, where it is immersed in a swelling bath (water), and Apply swelling treatment (swelling step). The film system subjected to swelling treatment is guided to the dyeing tank 115 in which an aqueous solution containing iodine is used as a dyeing bath, where it is dyed and iodine is adsorbed (dyeing step). Thereafter, it is guided to a cross-linking tank 117 that uses an aqueous solution containing boric acid as a treatment bath, where the polyvinyl alcohol resin adsorbed with iodine is cross-linked by boric acid to fix iodine (cross-linking step). Then, the film is washed in the washing tank 119 (washing step), and dried in the drying oven 123 (drying step), and the polarizer 130 is obtained. The polarizer 130 is taken up by the take-up roller 127. Polyvinyl alcohol resin film is in More specifically, any one or more stages of the polarizer manufacturing steps are subjected to uniaxial stretching treatment in any one or more stages from before the swelling step to the crosslinking step.

Each processing step can be continuously carried out by continuously conveying the polyvinyl alcohol-based resin film as the embryo film along the film conveying path of the polarizer manufacturing apparatus. The film transport path is equipped with equipment (processing tank, furnace, etc.) for implementing the above-mentioned various processing steps in the order of its implementation.

In addition to the above-mentioned equipment, guide rollers, nip rollers, etc. can be arranged in appropriate positions to construct a film transport path. For example, the guide roller system can be arranged before and after each treatment tank or in the treatment tank, whereby the film can be introduced/dipped into the treatment tank and pulled out from the treatment tank. More specifically, each treatment tank may be provided with two or more guide rollers, and the film may be immersed in each treatment tank by conveying the film along these guide rollers.

Examples of the polyvinyl alcohol-based resin system constituting the polyvinyl alcohol-based resin film include those obtained by saponifying a polyvinyl acetate-based resin. In addition to polyvinyl acetate, which is a homopolymer of vinyl acetate, polyvinyl acetate resins can also exemplify copolymers of vinyl acetate and other monomers copolymerizable with vinyl acetate. Other single systems that can be copolymerized with vinyl acetate include, for example, unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and (meth)acrylamides having an ammonium group. The degree of saponification of the polyvinyl alcohol 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)acryloyl".

The polyvinyl alcohol-based resin system can be modified. For example, polyvinyl formaldehyde, polyvinyl acetal, polyvinyl butyral and the like modified with aldehydes can also be used.

The average degree of polymerization of the polyvinyl alcohol resin is preferably 100 or more and 10,000 or less, more preferably 1,500 or more and 8,000 or less, and still more preferably 2,000 or more and 5,000 or less. Average of polyvinyl alcohol resin The degree of polymerization can be determined based on JIS K 6726 (1994). When the average degree of polymerization is within the above range, the polarization performance and film processability tend to be excellent.

The thickness of the polyvinyl alcohol-based resin film as the embryo film may 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 of the polyvinyl alcohol-based resin film as the embryo film in the width direction can be, for example, 600 mm or more and 5000 mm or less.

The polyvinyl alcohol-based resin film as the embryo film can be prepared, for example, as a long unstretched or stretched roll (winding product) of the polyvinyl alcohol-based resin film. At this time, the polarizer is also obtained as a long strip.

(1) Swelling step

The swelling treatment in this step is a treatment that is carried out as needed for the purpose of removing foreign matter of the polyvinyl alcohol resin film as the embryonic membrane, removing plasticizer, imparting easy dyeability, and plasticizing the film. Specifically, In other words, it may be a process of immersing the polyvinyl alcohol-based resin film 110 in a swelling tank containing a treatment liquid containing water. The film system can be immersed in one swelling tank or in two or more swelling tanks in sequence. Before swelling treatment, during swelling treatment, or before swelling treatment and during swelling treatment, the film may be subjected to uniaxial stretching treatment.

The treatment liquid contained in the swelling tank may be water (for example, pure water), or may be 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 solution 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. More than 300 seconds or less.

(2) Dyeing steps

The dyeing treatment in this step is performed for the purpose of adsorbing and orienting the dichroic pigment on the polyvinyl alcohol resin film. Specifically, it can be a dyeing tank containing a treatment solution containing the dichroic pigment. The treatment of impregnating polyvinyl alcohol resin film. 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 pigment, the film supplied to the dyeing step may be subjected to at least a certain degree of uniaxial stretching treatment. Instead of the uniaxial stretching treatment before the dyeing treatment, the uniaxial stretching treatment may be performed during the dyeing treatment, or the uniaxial stretching treatment may be performed during the dyeing treatment in addition to the uniaxial stretching treatment before the dyeing treatment.

The dichroic pigment system may be iodine or a dichroic organic dye. Specific examples of dichroic organic dyes include red BR, red LR, red R, pink LB, jade BL, claret GS, sky blue LG, lemon yellow, blue BR, blue 2R, navy blue RY , Green LG, Purple LB, Purple B, Black H, Black B, Black GSP, Yellow 3G, Yellow R, Orange LR, Orange 3R, Scarlet GL, Scarlet KGL, Congo Red, Bright Purple BK, Ultra Blue G , Super blue GL, super orange GL, direct sky blue, direct first orange S, first black. The dichroic dye system may be used individually by 1 type, and may use 2 or more types together.

When iodine is used as a dichroic pigment, the treatment liquid contained in the dyeing tank can be an aqueous solution containing iodine and potassium iodide. Other iodides such as zinc iodide can also be used instead of potassium iodide, and potassium iodide and other iodides can also be used in combination. In addition, compounds other than iodide, such as boric acid, zinc chloride, cobalt chloride, etc., can coexist. When boric acid is added, it is different from the cross-linking treatment described later in that it contains iodine. The content of iodine in the above-mentioned aqueous solution is usually 0.01 part by mass or more and 1 part by mass or less per 100 parts by mass of water. In addition, the content of iodide such as potassium iodide is usually 0.5 parts by mass or more and 20 parts by mass or less per 100 parts by mass of water.

The temperature of the treatment solution 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 may 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 the dichroic dye, an aqueous solution containing the dichroic organic dye can be used for 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 ^{per 100 parts by mass of water, preferably 1×10 -3} parts by mass and 1 part by mass or less. In the dyeing tank system, dyeing auxiliaries and the like may also coexist. For example, inorganic salts such as sodium sulfate or surfactants may be contained. The dichroic organic dye system may be used individually by 1 type, and may use 2 or more types together. When immersing the film, the temperature of the treatment solution in the dyeing tank 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. Less than 300 seconds.

(3) Cross-linking step

The cross-linking treatment of the polyvinyl alcohol resin film after the dyeing step with a cross-linking agent is a treatment for the purpose of water resistance or color adjustment due to cross-linking. Treatment of the film after the dyeing step by immersing the agent in the treatment solution in the cross-linking tank. The film can be immersed in one cross-linking tank or in two or more cross-linking tanks in sequence. During cross-linking treatment, uniaxial stretching treatment can be carried out.

Examples of the crosslinking agent system include boric acid, glyoxal, glutaraldehyde, etc., and boric acid is preferred. Two or more crosslinking agents can also be used in combination. 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 per 100 parts by mass of water, preferably 1 part by mass or more and 10 parts by mass or less. When the dichroic dye is iodine, the treatment solution contained in the cross-linking tank preferably contains iodide in addition to boric acid. The content of the iodide contained in the treatment liquid in the cross-linking tank is usually 0.1 parts by mass or more and 15 parts by mass or less per 100 parts by mass of water, preferably 5 parts by mass or more and 12 parts by mass or less. Iodide series can be listed Examples include potassium iodide and zinc iodide. In addition, for compounds other than iodide, for example, zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate, etc. can coexist in the cross-linking tank.

The temperature of the treatment solution contained in the crosslinking tank when the film 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. The best system is 2 seconds or more and 300 seconds or less.

In the cross-linking step, the number of cross-linking tanks may be 2 or more. At this time, 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 the 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 due to cross-linking and the cross-linking treatment for adjusting hue (complementary color) can be carried out in plural steps (for example, plural grooves).

Generally, when performing both cross-linking treatment for water resistance due to cross-linking and cross-linking treatment for adjusting hue (complementary color), the tank (complementary color tank) that performs cross-linking treatment for adjusting hue (complementary color) is Configured in the back section. The temperature of the treatment liquid contained in the color correction tank is, for example, 10°C or more and 55°C or less, preferably 20°C or more and 50°C or less. The content of the crosslinking agent contained in the treatment liquid in the color correction tank is per 100 parts by mass of water, for example, 1 part by mass or more and 5 parts by mass or less. The content of the iodide contained in the treatment liquid in the color correction tank is per 100 parts by mass of water, and is, for example, 3 parts by mass or more and 30 parts by mass or less.

As described above, when the polarizer is manufactured, the polyvinyl alcohol-based resin film is subjected to uniaxial stretching (stretching step) in any one or two or more stages from before the swelling step to the crosslinking step. From the viewpoint of improving the dyeability of the dichroic dye, the film supplied to the dyeing step is preferably a film subjected to at least a certain degree of uniaxial stretching treatment, and it is also preferred to replace the uniaxial stretching treatment before the dyeing treatment. During the dyeing process, the uniaxial stretching process is performed, or in addition to the uniaxial stretching process before the dyeing process, the uniaxial stretching process is also performed during the dyeing process.

The uniaxial stretching treatment may be either dry stretching in the air, wet stretching in the tank, or both. The uniaxial stretching treatment may provide a peripheral speed difference between two nip rollers to perform longitudinal uniaxial stretching between rolls, hot roll stretching, tensioner stretching, etc., but preferably includes inter-roll stretching. The stretch magnification based on the embryonic membrane (the cumulative stretch magnification when the stretch treatment is performed in two or more stages) is about 3 times or more and 8 times or less. In order to impart good polarization characteristics, the stretching ratio is preferably set to 4 times or more, and more preferably set to 5 times or more.

(4) Washing steps

The cleaning treatment in this step is to remove the excess crosslinking agent or dichroic pigment attached to the polyvinyl alcohol resin film, and is performed as needed, using a cleaning solution containing water And the treatment of the polyvinyl alcohol resin film after the washing and crosslinking step. Specifically, it may be the treatment of the polyvinyl alcohol-based resin film after the step of immersing and cross-linking the treatment liquid (cleaning liquid) contained in the washing tank. The film can be immersed in one washing tank or in two or more washing tanks in sequence. Or, the washing treatment may be a treatment of spraying a washing solution on the polyvinyl alcohol resin film to a shower after the crosslinking step, or a combination of the above-mentioned immersion treatment and spray treatment.

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

In the cleaning step, the temperature of the cleaning solution for cleaning the polyvinyl alcohol resin film after the crosslinking step can be, for example, 2°C or more and 40°C or less. From the above-mentioned range of monomer hue b value and From the standpoint of absorbance at a wavelength of 700 nm, it is preferable not to perform cleaning with a cleaning solution at a temperature exceeding 22°C.

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

After the cross-linking step, spray the cleaning solution on the polyvinyl alcohol resin film and turn it into a shower. The temperature of the cleaning solution is in the width direction of the polyvinyl alcohol resin film, and the temperature at the center and both ends can be the same. , May be different temperatures, but from the standpoint of monomer hue b value and absorbance at 700nm wavelength, different temperatures are preferred, and the temperature at the center is more preferably lower than the temperature at both ends . From the standpoint of monomer hue b value and absorbance at 700nm wavelength, the temperature of the cleaning solution is preferably 2°C or more and 10°C or less at the center and 10°C or more and 22°C or less at both ends, more preferably It is 3°C or more and 7°C or less at the center and 15°C or more and 22°C or less at both ends.

(5) Drying step

The drying step is a region for drying the polyvinyl alcohol-based resin film after the washing step. The polyvinyl alcohol-based resin film after the washing step can be continuously transported, and the film can be introduced in the drying step and subjected to a drying treatment, whereby a polarizer can be obtained.

The drying treatment is performed using the drying means (heating means) of the film. A suitable example of the drying means is a drying furnace. The drying furnace is preferably one that can control the temperature in the furnace. The drying furnace is, for example, a hot air oven that can increase the temperature in the furnace by supplying hot air. In addition, the drying treatment by drying means can be a treatment in which the polyvinyl alcohol resin film after the washing step is adhered to one or more heating bodies having a convex curved surface, or the film can be heated by using a heater.的处理。 The treatment.

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

In the drying step, the temperature of the drying process (for example, the temperature in the drying furnace, the surface temperature of the hot roller, etc.) can be, for example, 30°C or more, and the monomer hue b value within the above range is obtained and the wavelength is 700nm From the standpoint of absorbance, it is preferably 96°C or higher. The temperature of the drying treatment is usually below 100°C. The drying time is not particularly limited, but for example, it can be 30 seconds or more and 900 seconds or less, and preferably 30 seconds or more and 60 seconds or less.

The drying step can be one stage or multiple stages, preferably two stages or more and four stages or less. When the drying step is divided into multiple stages, from the viewpoint of the monomer hue b value and the absorbance at a wavelength of 700 nm, it is preferable that the drying temperature in at least one stage is 96° C. or higher. When the drying step is divided into multiple stages, the temperature of the drying treatment is preferably set so that the temperature of the later stage 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 to which the polyvinyl alcohol-based resin film is treated may contain a zinc salt. The treatment tank system that contains the treatment liquid includes, for example, a swelling tank, a dyeing tank, a cross-linking tank, a washing tank, and a color supplement tank. The treatment tank containing the treatment solution containing zinc salt is preferably a treatment tank after the dyeing tank and before the washing tank, more preferably at least one selected from the group consisting of a cross-linking tank and a complementary color tank, and even more preferably a cross-linking tank is When there are two or more, at least one selected from the last cross-linking groove and complementary color groove. 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 set by adjusting the concentration of the zinc salt in the treatment solution, the immersion time of the polyvinyl alcohol resin film in the treatment solution containing the zinc salt, and the temperature of the treatment solution. The content of zinc element in the range.

The zinc salt system contained in the treatment liquid includes, for example, zinc halides such as zinc chloride and zinc iodide, or zinc sulfate, zinc acetate, and zinc nitrate. Among them, zinc nitrate is preferred because of small changes in tension. The zinc salt system can be formed as a zinc salt solution and added to the treatment liquid.

The concentration of zinc salt in the treatment solution can be different in each treatment tank, but relative to 100 parts by mass of the treatment solution contained in the treatment tank, it can be, for example, 1 part by mass or more and 10 parts by mass or less, or 2 parts by mass or more and 7 parts by mass. Parts below are preferred.

After the above steps, a polarizer with dichroic dyes oriented on the uniaxially stretched polyvinyl alcohol resin film can be obtained.

The obtained polarizer is, for example, can be directly transported to the next polarizing plate manufacturing step (a step of laminating a thermoplastic resin film on one side or both sides of the polarizer).

[Thermoplastic resin film]

The thermoplastic resin film may be, for example, polyolefin resins such as chain polyolefin resins (polypropylene resins, etc.), cyclic polyolefin resins (norbornene resins, etc.); such as triacetyl cellulose or Cellulose ester resins of diacetyl cellulose; such as polyester resins of polyethylene terephthalate, polyethylene naphthalate, and polybutylene terephthalate; polycarbonate resins ; (Meth) acrylic resins such as polymethyl methacrylate resins; or light-transmitting resin films composed of such mixtures and copolymers. The thermoplastic resin film may have a single-layer structure composed of one resin layer composed of one or more than two types of thermoplastic resins, or a resin layer composed of one or more than two types of thermoplastic resins. Multi-layered structure. The first thermoplastic resin film and the second thermoplastic resin film may be the same or different types of thermoplastic resin films.

In addition to homopolymers of chain olefins such as chain polyolefin resins such as polyethylene resins and polypropylene resins, copolymers composed of two or more chain olefins can be cited.

Cyclic polyolefin-based resins include norbornene, tetracyclododecene (alias: dimethanooctahydronaphthalene) or derivatives thereof as representative examples. Cyclic olefins are a general term for resins that are polymerized units. Cyclic polyolefin resins include ring-opening (co)polymers of cyclic olefins. And its hydrogenated products, addition polymers of cyclic olefins, copolymers of cyclic olefins with chain olefins such as ethylene and propylene or aromatic compounds with vinyl groups, and the use of unsaturated carboxylic acids or their derivatives Modified (co)polymers made from modified materials.

Among them, it is preferable to use a norbornene-based resin, which uses a norbornene-based monomer such as a norbornene or a polycyclic norbornene-based monomer as a cyclic olefin.

The cellulose ester resin is a resin in which at least a part of the hydroxyl groups in cellulose is esterified with acetic acid, and may be a mixed ester in which a part is esterified with acetic acid and a part is esterified with other acids. The cellulose ester resin is preferably an acetyl cellulose resin.

Examples of the acetyl cellulose resin system include triacetyl cellulose, diacetyl cellulose, cellulose acetate propionate, and cellulose acetate butyrate.

The polyester resin is generally a resin other than the above-mentioned cellulose ester resin having an ester bond, and is composed of a polycondensate of a polyvalent carboxylic acid or a derivative thereof and a polyhydric alcohol.

Polyester resin series include polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, and polytrimethylene terephthalate. Esters, polytrimethylene naphthalate, polycyclohexane dimethyl terephthalate, polycyclohexane dimethyl naphthalate, etc.

Among them, from the viewpoints of mechanical properties, solvent resistance, scratch resistance, cost, etc., it is preferable to use polyethylene terephthalate. The so-called polyethylene terephthalate refers to a resin composed of ethylene terephthalate with 80 mol% or more of the repeating unit, and it may also contain structural units derived from other copolymerization components.

Examples of other copolymerization components include dicarboxylic acid components and glycol components.

The dicarboxylic acid component system can include isophthalic acid, 4,4'-dicarboxydiphenyl, 4,4'-dicarboxybenzophenone, bis(4-carboxyphenyl)ethane, adipic acid, decane Diacid, 5-sodium sulfoisophthalic acid, 1,4-dicarboxycyclohexane, etc.

The glycol component system can include propylene glycol, butylene glycol, neopentyl glycol, diethylene glycol, cyclohexanediol, ethylene oxide adducts of bisphenol A, polyethylene glycol, polypropylene glycol, and polytetrafluoroethylene. Methylene glycol and so on.

A dicarboxylic acid component or a glycol component can also be used in combination of two or more types, respectively, as needed.

In addition, the above-mentioned dicarboxylic acid component or glycol component, and hydroxycarboxylic acids such as p-hydroxybenzoic acid, p-hydroxyethoxybenzoic acid, β-hydroxyethoxybenzoic acid, and the like may be used in combination.

For other copolymerization components, a small amount of dicarboxylic acid components and/or glycol components having amide bonds, urethane bonds, ether bonds, carbonate bonds, etc. can be used.

Polycarbonate resin is a polyester formed by carbonic acid and glycol or bisphenol. Among them, from the viewpoint of heat resistance, weather resistance, and acid resistance, it is preferable to use an aromatic polycarbonate having diphenylalkane in the molecular chain.

The polycarbonate system includes 2,2-bis(4-hydroxyphenyl)propane (alias bisphenol A), 2,2-bis(4-hydroxyphenyl)butane, 1,1-bis(4- Polycarbonate derived from bisphenols such as hydroxyphenyl)cyclohexane, 1,1-bis(4-hydroxyphenyl)isobutane, and 1,1-bis(4-hydroxyphenyl)ethane.

The (meth)acrylic resin is a polymer containing a structural unit derived from a (meth)acrylic monomer, and the (meth)acrylic monosystem includes methacrylate and acrylate.

The methacrylate series can include methyl methacrylate, ethyl methacrylate, n-, iso- or tertiary butyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate, and benzene methacrylate. Methyl ester, 2-ethylhexyl methacrylate, 2-hydroxyethyl methacrylate, etc.

Acrylate series include ethyl acrylate, n-, iso- or tertiary butyl acrylate, cyclohexyl acrylate, phenyl acrylate, benzyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, etc. .

The thermoplastic resin film is preferably a cellulose ester resin film or a cyclic polyolefin resin film.

The thermoplastic resin film may contain additives as needed. The additive system includes, for example, slip agents, anti-compressive agents, heat stabilizers, antioxidants, ultraviolet absorbers, antistatic agents, lightfast agents, impact resistance modifiers, surfactants, and the like.

Examples of the ultraviolet absorber system include hydrocationic acid ester-based compounds, benzophenone-based compounds, benzotriazole-based compounds, cyanoacrylate-based compounds, nickel complex-based compounds, and the like.

Either or both of the first thermoplastic resin film and the second thermoplastic resin film may be a protective film that has an optical function such as a retardation film and a brightness enhancement film together. For example, by stretching a transparent resin film made of the above-mentioned material (uniaxial stretching, biaxial stretching, etc.), or forming a liquid crystal layer on the film, it can be a retardation film that gives an arbitrary retardation value.

The surface of the thermoplastic resin film on the opposite side of the polarized light side can also be formed with a surface treatment layer (coating layer) such as a hard coat layer, an anti-glare layer, an anti-reflection layer, an anti-static layer, and an anti-fouling layer.

From the viewpoint of thinning of the polarizing plate, the thickness of the thermoplastic resin film is better, but if it is too thin, the strength will decrease and the workability tends to deteriorate. Therefore, it is preferably 5 μm or more and 150 μm or less, and more preferably 5 μm or more and 100 μm or less, more preferably 10 μm or more and 60 μm or less.

[Adhesive]

In order to bond the polarizer and the thermal hypothetical resin film, an adhesive can be used. Adhesives are only required to exhibit adhesion to polarizers and thermal imaginary resin films. For example, water-based adhesives in which the components of the adhesive are dissolved or dispersed in water, or curable adhesives containing active energy ray curable compounds Agent. If considering that the surface of the polarizing film is hydrophilic, the adhesive is preferably an aqueous adhesive that dissolves or disperses the components of the adhesive in water. From the viewpoint of reducing the thickness of the adhesive after curing, a water-based adhesive is also preferable. The adhesive component that becomes the main component of the water-based adhesive includes polyvinyl alcohol-based resin, urethane resin, and the like.

When a polyvinyl alcohol-based resin is used as the main component of the water-based adhesive, the polyvinyl alcohol-based resin is obtained by saponifying a polyvinyl acetate-based resin. In addition to polyvinyl acetate, which is a homopolymer of vinyl acetate, the polyvinyl acetate resin is a copolymer of vinyl acetate and other monomers copolymerizable with vinyl acetate. Examples of other single systems copolymerized by vinyl acetate include unsaturated carboxylic acids, unsaturated sulfonic acids, olefins, vinyl ethers, and acrylamides having an ammonium group. The polyvinyl alcohol resin used in the adhesive preferably has a moderate degree of polymerization. For example, when it is set as a 4% by mass aqueous solution, the viscosity is within the range of 4mPa‧sec to 50mPa‧sec, more preferably 6mPa‧ Within the range of sec above 30mPa‧sec.

The degree of saponification of the polyvinyl alcohol resin used in the adhesive is not particularly limited, but generally 80 mol% or more is preferred, and 90 mol% or more is more preferred. If the degree of saponification of the polyvinyl alcohol resin used in the adhesive is low, the water resistance of the adhesive tends to become insufficient.

The adhesive is preferably a modified polyvinyl alcohol-based resin. Suitable modified polyvinyl alcohol-based resins include polyvinyl alcohol-based resins that have been modified by acetyl acetone groups, polyvinyl alcohol-based resins that have been modified by anions, and polyvinyl alcohol-based resins that have been modified by cations. If such a modified polyvinyl alcohol-based resin is used, it is easy to obtain the effect of improving the water resistance of the adhesive.

The polyvinyl alcohol-based resin modified by the acetyl acetyl group has an acetyl acetyl group (CH ₃ COCH ₂ CO-) in addition to the hydroxyl group constituting the polyvinyl alcohol skeleton, and other groups, such as With acetyl and so on. The acetylacetonyl group typically exists in a state of substituting the hydrogen atom constituting the hydroxyl group of the polyvinyl alcohol. The polyvinyl alcohol-based resin system modified with an acetyl acetyl group can be produced, for example, by a method of reacting polyvinyl alcohol with diketene. The polyvinyl alcohol-based resin modified with the acetyl acetyl group has an acetyl acetyl group with a highly reactive functional group, so it is preferable to improve the durability of the adhesive.

The content of the acetyl acetyl group in the polyvinyl alcohol-based resin modified with the acetyl acetyl group is not particularly limited as long as it is 0.1 mol% or more. The content of the so-called acetyl acetyl group is relative to the total amount of the hydroxyl group, acetyl acetyl group, and other ester groups (acetyl group, etc.) in the polyvinyl alcohol resin, and it is expressed in %. The value of the molar fraction of acetyl acetyl is sometimes referred to as the "degree of acetyl acetylation". If the degree of acetylation of the polyvinyl alcohol resin is less than 0.1 mol%, the effect of improving the water resistance of the adhesive may not be sufficient. The degree of acetylation in the polyvinyl alcohol resin is about 0.1 to 40 mol%, preferably 1 to 20 mol%, and particularly preferably 2 to 7 mol%. If the degree of acetylation of acetone exceeds 40 mol%, the effect of improving water resistance becomes smaller.

The anion-modified polyvinyl alcohol resin contains anionic groups in addition to the hydroxyl groups constituting the polyvinyl alcohol skeleton, and typically contains carboxyl groups (-COOH) or salts thereof. Other groups, for example, may have Acetyl and so on. The anionic modified polyvinyl alcohol resin system can be produced by, for example, copolymerizing an unsaturated monomer having an anionic group (typically a carboxyl group) with vinyl acetate, and then performing saponification. On the other hand, cationic modified polyvinyl alcohol-based resins, in addition to the hydroxyl groups constituting the polyvinyl alcohol skeleton, contain cationic groups, typically those containing tertiary amine groups or quaternary ammonium groups, which may have Other bases, such as acetyl and so on. Cationic modified polyvinyl alcohol-based resins, for example, can be prepared by copolymerizing unsaturated monomers with cationic groups (typically tertiary amine groups or quaternary ammonium groups) with vinyl acetate, and then Manufactured by saponification method.

The adhesive system may contain two or more of the above-mentioned modified polyvinyl alcohol-based resins, and may also contain unmodified polyvinyl alcohol-based resins (specifically, fully or partially saponified products of polyvinyl acetate) And both of the above-mentioned modified polyvinyl alcohol-based resins.

The polyvinyl alcohol-based resin system constituting the adhesive can be appropriately selected from commercially available products and used. Specifically, for example, polyvinyl alcohol with a high degree of saponification can be cited, and it is made of KURARAY stock "PVA-117H" sold by Nippon Synthetic Chemical Industry Co., Ltd., or "GOHSENOL NH-20" sold by Nippon Synthetic Chemical Industry Co., Ltd., polyvinyl alcohol modified with acetyl acetone, and manufactured by Nippon Synthetic Chemical Industry Co., Ltd. "GOHSEFIMER Z" series, anion-modified polyvinyl alcohol sold by Co., Ltd., and "KL-318" and "KM-118" sold by KURARAY Co., Ltd., or by Nippon Synthetic Chemical Industry Co., Ltd. The company sells "GOHSENOL T-330", cationic modified polyvinyl alcohol, and "CM-318" sold by KURARAY Co., Ltd., or "GOHSEFIMER K" sold by Nippon Synthetic Chemical Industry Co., Ltd. -210" etc.

The concentration of the polyvinyl alcohol resin in the adhesive is not particularly limited, but since it is used in the form of an aqueous solution, relative to 100 parts by mass of water, the polyvinyl alcohol resin is preferably 1 part by mass or more and 20 parts by mass or less Within the range, among them, it is 1 part by mass or more and 15 parts by mass or less, more preferably 1 part by mass or more and 10 parts by mass or less, and particularly preferably within the range of 2 parts by mass or more and 10 parts by mass or less. If the concentration of the polyvinyl alcohol-based resin in the aqueous solution is too small, the adhesiveness tends to be easily reduced. On the other hand, if the concentration is too large, the optical properties of the obtained polarizer tend to be easily reduced. The water system used in the adhesive can be pure water, ultra-pure water, tap water, etc., and there are no special restrictions, but from the viewpoint of the uniformity of the formed adhesive and the maintenance of transparency, pure water or ultra-pure Water is better. In addition, alcohol such as methanol or ethanol may be added to the adhesive aqueous solution.

The water-based adhesive system containing polyvinyl alcohol-based resin as a main component may contain a crosslinking agent. The crosslinking agent should just be a compound having a functional group reactive with polyvinyl alcohol-based resins, and it can be used without any particular limitation from users of polyvinyl alcohol-based adhesives. If the functional groups separately reveal compounds that can become crosslinking agents, there are: isocyanate compounds having at least two isocyanate groups (-NCO) in the molecule; and at least two epoxy groups in the molecule (bridging之-O-) epoxy compound; single-or Di-aldehydes; organic titanium compounds; inorganic salts of divalent or trivalent metals such as magnesium, calcium, iron, nickel, zinc, and aluminum; metal salts of glyoxylic acid; methylol melamine, etc.

Specific examples of isocyanate compounds used as crosslinking agents include toluene diisocyanate, hydrogenated toluene diisocyanate, adducts of trimethylolpropane and toluene diisocyanate, diphenylmethane diisocyanate, triphenylmethane triisocyanate, Isofluoroketone diisocyanate, these ketoxime blocks or phenol blocks, etc.

Specific examples of epoxy compounds that become crosslinking agents include ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol di- or tri-glycidyl ether, 1,6-hexane Alkyl glycol diglycidyl ether, trimethylolpropane triglycidyl ether, diglycidyl aniline, diglycidyl amine, polyamide in the reactant of polyalkylene polyamine and dicarboxylic acid Amine polyamine is a water-soluble polyamide epoxy resin obtained by reacting epichlorohydrin.

Specific examples of monoaldehydes used as crosslinking agents include formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, etc., and specific examples of dialdehydes include glyoxal, malondialdehyde, succinic dialdehyde, and glutaraldehyde. , Malealdehyde, phthalaldehyde, etc.

The organotitanium compounds used as crosslinking agents are sold by Matsumoto Fine Chemical Co., Ltd. From the homepage about the company’s organic titanium compounds (search Internet <URL: http://www.m-chem.co.jp/products/products1.html>, November 18, 2010), follow the indicative formula When the chemical name of the company and the product name of the company reveal the water-soluble organic titanium compound suitable for use in the present invention, it is as follows.

[(CH ₃ ) ₂ CHO] ₂ Ti[OCH ₂ CH ₂ N(CH ₂ CH ₂ OH) ₂ ] ₂ : The company’s chemical name "titanium diisopropoxy bis(triethanolaluminate)", The company’s trade name "Orgatix TC-400",

(HO) ₂ Ti[OCH(CH ₃ )COO-] ₂ (NH ₄ ⁺ ) ₂ : The company's chemical name "titanium ammonium lactate", the company's trade name "Orgatix TC-300",

(HO) ₂ Ti[OCH(CH ₃ )COOH] ₂ : The company's chemical name "titanium lactate", the company's trade name "Orgatix TC-310" and "Orgatix TC-315".

In addition, the metal salt of glyoxylic acid is preferably an alkali metal salt or alkaline earth metal salt, for example, sodium glyoxylate, potassium glyoxylate, magnesium glyoxylate, calcium glyoxylate, and the like are exemplified.

Among these crosslinking agents, it is suitable to use the above-mentioned water-soluble polyamide epoxy resins, or the alkali metal or alkaline earth metal salts of aldehydes, methylol melamine, and glyoxylic acid. Wait.

The crosslinking agent is preferably dissolved in water together with the polyvinyl alcohol-based resin to form an adhesive. However, as described below, the amount of the crosslinking agent in the aqueous solution can be a small amount. Therefore, for water, for example, those having a solubility of at least about 0.1% by mass can be used as a crosslinking agent. Of course, in addition to compounds having solubility in water, which is generally referred to as water solubility, they are suitable for use as the crosslinking agent in the present invention.

The blending amount of the crosslinking agent is appropriately designed according to the type of polyvinyl alcohol resin, etc., but relative to 100 parts by mass of the polyvinyl alcohol resin, it is usually 5 parts by mass or more and 60 parts by mass or less, preferably 10 parts by mass Above 50 parts by mass or less. If the crosslinking agent is blended in this range, good adhesiveness can be obtained. As mentioned above, in order to improve the durability of the adhesive, it is preferable to use a polyvinyl alcohol-based resin modified with an acetyl acetyl group. However, in this case, the crosslinking agent 5 is formulated relative to 100 parts by mass of the polyvinyl alcohol-based resin. To 60 parts by mass, more preferably, it is blended in a ratio of 10 parts by mass or more and 50 parts by mass or less. If the blending amount of the cross-linking agent is too large, the reaction of the cross-linking agent will proceed in a short time, and the adhesive tends to gel at an early stage. As a result, the operating time becomes extremely short and it is difficult to use it industrially.

Unlike a crosslinking agent, a water-based adhesive system having a polyvinyl alcohol-based resin as a main component may preferably contain a zinc salt from the viewpoint of suppressing discoloration. Examples of the zinc salt system include zinc halides such as zinc chloride and zinc iodide, or zinc sulfate, zinc acetate, and zinc nitrate. Among them, zinc nitrate is preferred. The zinc salt can be used as a zinc salt solution and added to an aqueous adhesive containing a polyvinyl alcohol resin as a main component.

When the water-based adhesive with polyvinyl alcohol-based resin as the main component contains zinc salt, the content of zinc salt is relative to 100 parts by mass of water. For example, it can be 0.01 parts by mass or more and 10 parts by mass or less. From a viewpoint, it is preferably not less than 0.1 part by mass and not more than 5 parts by mass, more preferably not less than 0.5 part by mass and not more than 2.5 parts by mass.

In the range that does not impair the effects of the present invention, in the adhesive system, for example, conventionally known suitable additives such as silane coupling agents, plasticizers, antistatic agents, and fine particles may be blended.

When a urethane resin is used as the main component of the water-based adhesive, a suitable example of the adhesive includes a mixture of a compound having a polyester-based ionomer type urethane resin and a glycidyloxy group. The so-called polyester-based ionomer urethane resin is a urethane resin having a polyester skeleton, and a small amount of ionic components (hydrophilic components) are introduced into it. Such an ionomer type urethane resin system does not use an emulsifier but is directly emulsified in water to become an emulsified liquid, so it is suitable for use in water-based adhesives. Adhesives that use polyester-based ionomer urethane resins for polarizing films and protective films are described in, for example, Japanese Patent Application Publication No. 2005-070140, Japanese Patent No. 4432487, and Japanese Patent Application Publication No. 2005-208456 No. Bulletin and known.

Examples of the active energy ray curable adhesive system include ultraviolet curable adhesives.

The ultraviolet curable adhesive system may be a mixture of a radical polymerizable (meth)acrylic compound and a photo-radical polymerization initiator, or a mixture of a cationic polymerizable epoxy compound and a photo-cationic polymerization initiator. In addition, cationic polymerizable epoxy compounds and radical polymerizable ones (A (Base) An acrylic compound, a photocationic polymerization initiator and a photoradical polymerization initiator may be used together as an initiator.

When laminating the thermoplastic resin film on both sides of the polarizer, the adhesive system may be the same or different. For example, when a thermoplastic resin film is attached to both sides of the polarizer, one can be attached using a water-based adhesive, and the other can be attached using an active energy ray curable adhesive.

The thickness of the adhesive in the polarizing plate can be, for example, 0.001 μm or more and 10 μm or less. From the viewpoint of adhesion and thinning, it is preferably 0.01 μm or more and 5 μm or less, more preferably 0.01 μm or more and 3 μm or less, and still more Preferably it is 0.02μm or more and 2μm or less.

[Adhesive layer]

The polarizing plate is for bonding the light-transmitting member and the image display element, and may have an adhesive layer on the outermost surface of any one of the first thermoplastic resin film side and the second thermoplastic resin film side. The adhesive layer can be made of (meth)acrylic resin, rubber polymer, urethane resin, ester resin, silicone resin, polyvinyl ether resin, etc. as the main component. Adhesive composition composition. Among them, it is suitable for an adhesive composition using a (meth)acrylic resin excellent in transparency, weather resistance, heat resistance, etc., as a base polymer. The adhesive composition system can be an active energy ray hardening type or a heat hardening type.

For the (meth)acrylic resin (base polymer) used in the adhesive composition, for example, butyl (meth)acrylate, ethyl (meth)acrylate, isooctyl (meth)acrylate, (Meth)acrylic acid 2-ethylhexyl ester, etc., are polymers or copolymers using one or more of (meth)acrylic acid esters as monomers. It is preferable to copolymerize a polar monomer in the base polymer. Polar monomers include (meth)acrylic acid, 2-hydroxypropyl (meth)acrylate, hydroxyethyl (meth)acrylate, (meth)acrylamide, (meth)acrylic acid N,N-dimethyl Monoaminoethyl, glycidyl (meth)acrylate and other monomers having a carboxyl group, a hydroxyl group, an amide group, an amino group, an epoxy group, etc.

The adhesive composition system may contain only the above-mentioned base polymer, but usually contains a crosslinking agent. The crosslinking agent is exemplified by a metal ion having a valence of 2 or more that forms a carboxylic acid metal salt with a carboxyl group; a polyamine compound that forms an amide bond with a carboxyl group; a polyepoxy compound that forms an ester bond with a carboxyl group Or polyol; a polyisocyanate compound that forms an amide bond with a carboxyl group.

Among them, polyisocyanate compounds are preferred.

The adhesive layer is formed by dissolving or dispersing the adhesive composition in an organic solvent such as toluene or ethyl acetate to prepare an adhesive liquid, and applying this directly on the target surface of the laminate to form an adhesive layer Or, it can be carried out by forming an adhesive layer in the form of a sheet in advance on the separation film subjected to the release treatment, and then moving it to the target surface of the polarizing plate.

The thickness of the adhesive layer is determined in accordance with its adhesive strength, etc., but may be, for example, 1 μm or more and 50 μm or less, preferably 2 μm or more and 40 μm or less, more preferably 3 μm or more and 30 μm or less, and still more preferably 3 μm or more and 25 μm or less.

The polarizing plate may contain the above-mentioned separation membrane. The separation film may be a film composed of a polyethylene resin such as polyethylene, a polypropylene resin such as polypropylene, and a polyester resin such as polyethylene terephthalate. Among them, a stretched film of polyethylene terephthalate is preferred.

The adhesive layer can contain optional ingredients, glass fibers, glass particles, resin particles, metal powders, or fillers composed of other inorganic powders; pigments; colorants; antioxidants; ultraviolet absorbers; antistatic agents, etc.

[Optical Function Layer]

The optical functional layer may be an optical functional film other than a polarizer for imparting a desired optical function. A suitable example of the optical functional film is a retardation film. Examples of the retardation film system include a λ/2 retardation film (λ/2 wavelength plate), a λ/4 retardation film (λ/4 wavelength plate), and a positive C plate. The optically functional film may include an alignment layer and a base material, and may have two or more liquid crystal layers, alignment layers, and base materials, respectively.

The thermoplastic resin film may also serve as a retardation film, but the retardation film may be laminated for different purposes with these films.

The retardation film may include a birefringent film composed of a stretched film of a light-transmitting thermoplastic resin; a film in which discotic liquid crystal or nematic liquid crystal is oriented and fixed; and the above-mentioned liquid crystal layer is formed on a substrate film Wait.

The base film is usually a film composed of a thermoplastic resin, and an example of the thermoplastic resin is a cellulose ester resin such as triacetyl cellulose.

Examples of other optically functional films (optical components) that can be included in the polarizing plate are light-concentrating plates, brightness enhancement films, reflective layers (reflective films), semi-transmissive reflective layers (semi-transmissive reflective films), and light diffusion layers (Light diffusion film) and so on. These are generally installed 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 for protecting its surface (typically the surface of the thermoplastic resin film of the polarizing plate). For example, after the polarizing plate is attached to the image display element or other optical components, the protective film is peeled off together with the adhesive layer it has.

The protective film is composed of, for example, a base film and an adhesive layer laminated thereon. Regarding the adhesive layer, the above-mentioned description is cited. The resin system constituting the base film can be, for example, a polyethylene resin such as polyethylene, a polypropylene resin such as polypropylene, and a polyester resin such as polyethylene terephthalate or polyethylene naphthalate. , Thermoplastic resins such as polycarbonate resins. Preferably, it is a polyester resin such as polyethylene terephthalate.

The thickness of the protective film is not particularly limited, but it is preferably set to a range of 20 μm or more and 200 μm or less. If the thickness of the base film is 20 μm or more, it tends to be easy to impart strength to the polarizing plate.

<Manufacturing method of polarizing plate>

The manufacturing method of the polarizing plate of another aspect of this invention is the manufacturing method of the polarizing plate provided with the following member: a polarizer, and the 1st thermoplastic resin film laminated|pasted by the adhesive agent on one side. The manufacturing method of the polarizer may include the above-mentioned polarizer manufacturing steps. From the viewpoint of obtaining the monomer hue b value within the above range and the absorbance at a wavelength of 700nm, the manufacturing method of the polarizing plate is preferably the washing step of washing the polyvinyl alcohol-based resin film with water, including not exceeding At least any one of a washing step of washing with a cleaning solution at a temperature of 22°C and a drying step of drying the polyvinyl alcohol-based resin film at a temperature of 96°C or higher.

The manufacturing method of the polarizer may further include a bonding step in which the first thermoplastic resin film is bonded to one side of the polarizer via an adhesive, and the adhesive is dried at a temperature of 85°C or higher . In the bonding step, the adhesive may be applied to either or both of the bonding surfaces of the polarizer and the first thermoplastic resin film, and the bonding surface of the other side may be laminated here, for example, using a bonding roll or the like. Press from up and down to fit together. For the coating system of the adhesive, for example, various coating methods such as a doctor blade, a wire bar, a die coater, a chipped wheel coater, and a gravure coater can be used. In addition, it may be a method in which the polarizer and the first thermoplastic resin film are continuously supplied so that the bonding surfaces of the two are on the inner side, and the adhesive is allowed to flow between them.

After bonding the polarizer and the first thermoplastic resin film, the laminate including the polarizer, the adhesive, and the first thermoplastic resin film can be heated to dry the adhesive. The evaporation, hardening, and cross-linking of the solvent react at different temperatures, so it is preferable to use continuous or multi-stage heating treatment to gradually increase the temperature. From the viewpoint of obtaining the monomer hue b value and the absorbance at a wavelength of 700 nm within the above-mentioned range, the temperature of the heat treatment preferably includes the treatment at 85°C or higher. The upper limit of the temperature of the heat treatment for drying the adhesive is usually 100°C or lower, preferably 90°C or lower. The solvent contained in the adhesive can be removed by heat treatment. In addition, when the adhesive is a curable adhesive, the curing/crosslinking reaction can proceed by the heat treatment.

When an active energy ray curable adhesive is used as the adhesive, after bonding, the adhesive can be cured by irradiating the active energy ray. The light source of the active energy ray is not particularly limited, but it is preferably an active energy ray (ultraviolet) with a luminous distribution below the wavelength of 400 nm. Specifically, it is preferable to use a low-pressure mercury lamp, a medium-pressure mercury lamp, a high-pressure mercury lamp, Ultra-high pressure mercury lamp, chemical lamp, black light lamp, microwave excited mercury lamp, metal halide lamp, etc.

In order to improve the adhesion between the polarizer and the thermoplastic resin film, before laminating the polarizer and the thermoplastic resin film, corona treatment, flame treatment, plasma treatment can be applied to the bonding surface of the polarizer and/or thermoplastic resin film , Surface treatment such as ultraviolet radiation treatment, prepolymer coating treatment, saponification treatment, etc.

When the polarizing plate includes the second thermoplastic resin film, the bonding system of the polarizer and the second thermoplastic resin film can be performed in the same manner as the bonding of the polarizer and the first thermoplastic resin film. The bonding of the polarizer and the second thermoplastic resin film may be performed before or after the bonding of the polarizer and the first thermoplastic resin film, or at the time of bonding the polarizer and the first thermoplastic resin film.

<Use of Polarizing Plate>

Polarizers can be used for mobile devices such as TVs, personal computers, mobile phones, or tablet terminals. In addition, the polarizing plate also inhibits discoloration after a high temperature (105°C) and long-term (600 hours or more) endurance test, so it is suitable for use in vehicles that are easily exposed to more severe temperature conditions. Examples of vehicle applications include image display devices used in car navigation devices, speedometers, touch panels for air conditioners, rear monitors, end monitors, and the like.

[Example]

Hereinafter, the present invention will be explained in more detail with examples. The "%" and "parts" in the examples are% by mass and parts by mass unless otherwise stated.

[Manufacturing Example 1: Preparation of Aqueous Adhesive (1)]

Dissolve acetyl acetyl modified polyvinyl alcohol [trade name "Gohsefimer Z-200", manufactured by Nippon Synthetic Chemical Industry Co., Ltd., 4% aqueous solution with viscosity=12.4mPa‧sec, saponification degree=99.1mol%] Prepare a 10% concentration aqueous solution in pure water. The obtained aqueous solution of polyvinyl alcohol modified with acetylacetal group and sodium glyoxylate used as a crosslinking agent are mixed so that the solid content ratio of the aqueous solution: sodium glyoxylate becomes 1:0.1. Furthermore, with respect to 100 parts of water, zinc nitrate and pure water were added so that 1.5 parts of zinc nitrate and 2.5 parts of acetylated modified polyvinyl alcohol were used to prepare an aqueous adhesive composition (1).

<Example 1>

A long strip of polyvinyl alcohol (PVA) embryo film with a width of 3390mm and a thickness of 60μm (trade name "M6000" manufactured by KURARAY, with a saponification degree of 99.9 mol% or more) is unrolled from the roller and conveyed continuously at the same time as the residence time It is immersed in a swelling bath composed of pure water at 28°C for 45 seconds (swelling step). After that, the film drawn from the swelling bath was immersed in a 30°C dyeing bath containing iodine with a potassium iodide/water ratio of 1.5/100 (mass ratio) for a residence time of 120 seconds (dyeing step). Then, the film pulled out of the dyeing bath was immersed in the first crosslinking bath at 30°C with a residence time of 70 seconds in potassium iodide/boric acid/water (mass ratio) of 0.5/0.6/100, and then immersed in a residence time of 50 seconds The second cross-linking bath (cross-linking step) at 60°C at a ratio of potassium iodide/boric acid/water of 15/4.9/100 (mass ratio). After that, the film was immersed in a washing bath composed of pure water at 7°C for a residence time of 40 seconds. Furthermore, the temperature of the center part was 5.3 degreeC, and the temperature of both ends were showered with the water temperature of 22 degreeC, and it wash|cleaned (washing process). The obtained PVA was continuously dried (drying) under the following three-stage temperature and time drying conditions (first stage: 75°C for 15 seconds, second stage: 85°C for 15 seconds, and third stage: 96°C for 15 seconds) step). exist In the dyeing step and the cross-linking step, longitudinal uniaxial stretching is performed by stretching between rolls in the bath. The total extension magnification based on the embryonic membrane is set to 5.8 times. The thickness of the obtained polarizer was 25 μm.

For the polarizer obtained in this way, a thermoplastic resin film (trade name "KC4CT1W", manufactured by Konica Minolta Co., Ltd.) composed of triacetyl cellulose as a protective film was interposed with the water-based adhesive composition (1). Laminate at a bonding temperature of 70°C, and then dry conditions at the following three stages of temperature and time (first stage: 60°C for 25 seconds, second stage: 85°C for 25 seconds, and third stage: 90°C for 25 seconds. ) Continuously drying the water-based adhesive (bonding step). In addition, the water-based adhesive system was applied to one surface of the thermoplastic resin film with a thickness of 200 nm. The zinc content of the obtained polarizing plate was measured, and the result was 280 ppm. Table 1 shows the measurement results of the monomer hue b value and the absorbance at a wavelength of 700 nm and the endurance test results.

<Comparative Example 1>

Except that in the washing step of Example 1, the water temperature of the shower on both ends was set to 24°C, and in the drying step, the temperature of the third stage was set to 93°C, and the rest was the same as in Example 1. And the polarizing plate of Comparative Example 1 was produced. The zinc content of the obtained polarizing plate was measured, and the result was 280 ppm. Table 1 shows the measurement results of the monomer hue b value and the absorbance at a wavelength of 700 nm and the endurance test results.

[Durability Test]

The obtained polarizing plate was cut to prepare a sample for durability test (size: 12 cm×30 cm). The endurance test sample was subjected to autoclave treatment [temperature 50°C, pressure 5kg/cm ² (490.3kPa)] for 1 hour, and then placed in an environment with a temperature of 23°C and a relative humidity of 55% for 24 hours. Perform a heating test in a heating environment at a temperature of 105°C to visually confirm the color change before and after heating. Measure the time required until the color changes.

[Measurement of monomer hue b value and absorbance at 700nm wavelength]

A spectrophotometer ("V-7100" manufactured by JASCO Corporation) was used to measure the monomer hue b value of the polarizing plate before the endurance test and the absorbance at a wavelength of 700 nm.

[Determination of zinc content]

The measurement of the zinc content in the polarizing plate is carried out in the following manner.

The nitric acid was added to the polarizing plate of the precision scale, and the solution obtained by acid decomposition with the microwave sample pretreatment device (ETHOS D) manufactured by Milestone-General was used as the measurement solution. The zinc concentration was calculated by quantitatively measuring the zinc concentration of the solution with an ICP emission spectrometer (5110 ICP-OES) manufactured by Agilent Technology, and calculating the mass of zinc to the mass of the polarizing plate.

[Table 1]

Claims (9)

A polarizing plate with a monomer hue b value of 2.7 or more, and an absorbance at a wavelength of 700 nm of 4.5 or less. The polarizing plate according to claim 1, which includes a polarizer and a first thermoplastic resin film bonded to one side of the polarizer through an adhesive. The polarizing plate according to claim 2, further comprising a second thermoplastic resin film, the second thermoplastic resin film being bonded to the polarizer on the opposite side of the first thermoplastic resin film via an adhesive side. The polarizing plate according to claim 2 or 3, wherein the adhesive is a water-based adhesive. The polarizing plate according to any one of claims 1 to 4, wherein the content of zinc element in the polarizing plate is 150 ppm or more. A display device for a vehicle is provided with the polarizing plate according to any one of claims 1 to 5. A method for manufacturing a polarizing plate, which is the method for manufacturing a polarizing plate according to claim 2, wherein the polarizer includes a polyvinyl alcohol-based resin film, and the method for manufacturing a polarizing plate includes a cleaning step. The cleaning step is The above-mentioned polyvinyl alcohol resin film is washed with a washing liquid, and the washing liquid at a temperature exceeding 22° C. is not used for washing. The method for manufacturing a polarizing plate according to claim 7, which further includes a drying step in which the polyvinyl alcohol-based resin film is dried at a temperature of 96°C or higher. The method for manufacturing a polarizing plate according to claim 7 or 8, further comprising a bonding step in which the first thermoplastic resin film is bonded to one side of the polarizer via an adhesive, and Dry the aforementioned adhesive at a temperature above 85°C.

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