CN112946806A

CN112946806A - Polarizing plate and method for manufacturing same

Info

Publication number: CN112946806A
Application number: CN202011405164.4A
Authority: CN
Inventors: 邱怡欣; 黄怡菱
Original assignee: Sumitomo Chemical Co Ltd
Current assignee: Sumitomo Chemical Co Ltd
Priority date: 2019-12-11
Filing date: 2020-12-04
Publication date: 2021-06-11
Also published as: JP2022105721A; JP2021092676A; TW202125005A; KR20210074200A; JP7430745B2

Abstract

The invention provides a polarizing plate which does not generate color change even in a high-temperature (105 ℃) and long-time (more than 600 hours) endurance test. The polarizing plate of the present invention has a single-component color b value of 2.7 or more and an absorbance at a wavelength of 700nm of 4.5 or less.

Description

Polarizing plate and method for manufacturing same

Technical Field

The present invention relates to a polarizing plate and a method for manufacturing the same.

Background

Patent documents 1 and 2 propose polarizing films that show little change in color tone even after heating at 120 ℃ for 100 hours.

Patent document 3 discloses a polarizing film which can provide a polarizing plate excellent in durability to a heat cycle test and has a neutral gray color in an orthogonal color tone.

Patent document 4 proposes an optical laminate having an excellent yellowing-inhibiting effect even when exposed to a high-temperature environment.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2004-226707

Patent document 2: japanese laid-open patent publication No. 2007-304626

Patent document 3: japanese patent laid-open publication No. 2013-148806

Patent document 4: japanese patent laid-open publication No. 2018-025765

Disclosure of Invention

Problems to be solved by the invention

The polarizing plates described in patent documents 1 to 4 may be discolored in a high-temperature (for example, 105 ℃) and long-time (for example, 600 hours or more) durability test under more severe conditions.

The invention aims to provide a polarizing plate which does not generate color change in a high-temperature (105 ℃) and long-time (more than 600 hours) endurance test.

Means for solving the problems

The present invention provides the following polarizing plate and a method for manufacturing the same.

[1] A polarizing plate having a single-component color b value of 2.7 or more and an absorbance at a wavelength of 700nm of 4.5 or less.

[2] The polarizing plate according to [1], which comprises a polarizing plate and a 1 st thermoplastic resin film bonded to one side of the polarizing plate via an adhesive.

[3] The polarizing plate according to [2], further comprising a 2 nd thermoplastic resin film, wherein the 2 nd thermoplastic resin film is bonded to the polarizer on a side opposite to the 1 st thermoplastic resin film side via an adhesive.

[4] The polarizing plate according to any one of [2] and [3], wherein the adhesive is an aqueous adhesive.

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

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

[7] A method for producing a polarizing plate according to [2],

the polarizer comprises a polyvinyl alcohol resin film,

the production method comprises a cleaning step of cleaning the polyvinyl alcohol resin film with a cleaning liquid without cleaning with a cleaning liquid having a temperature higher than 22 ℃.

[8] The method for producing a polarizing plate according to [7], further comprising a drying step of drying the polyvinyl alcohol resin film at a temperature of 96 ℃ or higher.

[9] The method for producing a polarizing plate according to [7] or [8], further comprising a bonding step of bonding the 1 st thermoplastic resin film to one side of the polarizer via an adhesive, and drying the adhesive at a temperature of 85 ℃ or higher.

Effects of the invention

According to the present invention, a polarizing plate can be provided which does not suffer from discoloration even in a high-temperature (105 ℃) and long-term (600 hours or longer) durability test.

Drawings

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

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

Fig. 3 is a schematic cross-sectional view showing an example of arrangement of devices used in a polarizing plate manufacturing process.

Description of the reference numerals

A polarizing plate 10, a thermoplastic resin film 1, a polarizing plate 12, a thermoplastic resin film 2 13, a raw material film of a polyvinyl alcohol resin 110, a take-out roll 111, a swelling bath 113, a dyeing bath 115, a crosslinking bath 117, a washing bath 119, a drying furnace 123, a take-up roll 127, and a polarizing plate 130.

Detailed Description

Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the embodiments below. In all the drawings below, the scale of each component shown in the drawings is appropriately adjusted to be displayed in order to facilitate understanding of each component, and the scale of each component does not necessarily coincide with the scale of the actual component.

< polarizing plate >

The polarizing plate according to one embodiment of the present invention has a single-component color b value of 2.7 or more and an absorbance at a wavelength of 700nm of 4.5 or less. In the polarizing plate, when the b value of the monomer color tone is 2.7 or more, the absorbance at a wavelength of 700nm is 4.5 or less, and thus the polarizing plate tends to be less likely to be discolored even in a long-term (600 hours or more) durability test (hereinafter, also simply referred to as a durability test) at a high temperature (105 ℃ C.). In the present specification, the durability test refers to a durability test performed according to the method described in the section of examples described later. The term "no discoloration" means that no yellowing is observed when the polarizing plate is observed by the method described in the first column of examples described below. The polarizing plate of the present invention does not change color in the durability test preferably for 1000 hours, more preferably for 1400 hours.

In general, a polarizing plate tends to be less likely to be reddish when the absorbance at a wavelength of 700nm is high, and tends to be less likely to be yellowed when the monomer color tone b value of the polarizing plate is low. In the durability test, polyiodide complex I in the polarizing plate was generated by heating₅ ^－The decomposition of (2) and the polyene formation of polyvinyl alcohol in the polarizing plate tend to easily cause a decrease in absorbance at a wavelength of 700nm and an increase in the monomer color tone b value. Therefore, it is considered that, in order to suppress discoloration in the durability test of the polarizing plate, it is advantageous that the polarizing plate has a high absorbance at a wavelength of 700nm and a low b value of the monomer color tone. However, unexpectedly, the present inventors found that discoloration can be suppressed by setting the b value of the monomer color tone of the polarizing plate to 2.7 or more and the absorbance at a wavelength of 700nm to 4.5 or less in a more severe durability test at a high temperature (105 ℃) and a long time (600 hours or more). Polarizing plates having a monomer hue b value of 2.7 or more and an absorbance at a wavelength of 700nm of 4.5 or less are novel polarizing plates which are not disclosed in any of patent documents 1 to 4.

The b value of the single-component color tone of the polarizing plate is preferably 2.9 or more, more preferably 3.1 or more, still more preferably 3.3 or more, and particularly preferably 3.5 or more. The polarizing plate may have a b value of 4.1 or less, for example, 3.9 or less.

The b value of the monomer color tone of the polarizing plate is the b value of the polarizing plate monomer in the Lab color system. According to JIS Z8722: in 2009 "color sensing method", reflection およ allows the tristimulus values X, Y and Z specified in the heat emission body color "(color measurement method — reflection and transmission body color), and the value b is calculated by the following equation.

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

The b value of the single-component color tone of the polarizing plate can be measured by the measurement method described in the column of examples described later.

The polarizing plate preferably has an absorbance at a wavelength of 700nm of 4.4 or less, more preferably 4.3 or less. The polarizing plate has an absorbance at a wavelength of 700nm of usually 3.9 or more, for example, 4.1 or more, or 4.2 or more.

The absorbance of the polarizing plate at a wavelength of 700nm can be measured using an absorption spectrophotometer such as an ultraviolet-visible spectrophotometer and calculated according to the following formula.

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

The incident light was measured using polarized light parallel to the absorption axis direction of the polarizing plate. In this formula, TD transmittance is a transmittance when the direction of polarized light emitted from the grazing thomson prism is perpendicular to the transmission axis of the polarizing plate.

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

The monomer hue b value and the absorbance at a wavelength of 700nm in the above ranges can be obtained by, for example, adjusting the temperature of a cleaning liquid in a cleaning step in a polarizing plate production step, a drying temperature in a drying step, and a temperature for drying an adhesive for bonding a polarizing plate and a thermoplastic resin film, which will be described later.

The polarizing plate may contain zinc element. When the polarizing plate contains zinc element, the zinc element is preferably contained in at least one of the polarizing plate and the adhesive. When the polarizing plate contains a zinc element, the content of the zinc element in the polarizing plate may be 150ppm or more, for example. When the content of the zinc element in the polarizing plate is 150ppm or more, discoloration tends to be easily suppressed in the durability test. The content of the zinc element in the polarizing plate is preferably 200ppm or more, and more preferably 250ppm or more, from the viewpoint of suppressing discoloration. On the other hand, the content of zinc element in the polarizing plate is usually 1000ppm or less. The content of zinc element was measured according to the measurement method described in the column of the example described later. The content of the zinc element in the polarizing plate can be set within the above range by adjusting the zinc concentration in the polarizer and/or the adhesive, for example.

Fig. 1 shows a polarizing plate 10 according to an embodiment of the present invention. As shown in fig. 1, the polarizing plate 10 may include a polarizing plate 12 and a 1 st thermoplastic resin film 11 bonded to one side of the polarizing plate 12 via an adhesive. As shown in fig. 2, the polarizing plate 10 may further include a 2 nd thermoplastic resin film 13 bonded to the polarizer 12 on the side opposite to the 1 st thermoplastic resin film 11 side via an adhesive. Hereinafter, the 1 st thermoplastic resin film and the 2 nd thermoplastic resin film may be collectively referred to as a thermoplastic resin film. The polarizing plate may further include a pressure-sensitive adhesive layer, an optical functional layer, and a protective film, which will be described later, on the side of the thermoplastic resin film opposite to the polarizer side.

The polarizing plate may be used in an image display device. The image display device may be any image display device such as a liquid crystal display device or an organic EL display device, but is preferably a liquid crystal display device. The liquid crystal display device includes a liquid crystal panel having a liquid crystal cell as an image display element, and a backlight. In the case of constructing a liquid crystal display device, the polarizing plate may be used for a polarizing plate disposed on the viewing side, a polarizing plate disposed on the backlight side, or both the viewing side and the backlight side.

In the case where the polarizing plate includes the 1 st thermoplastic resin film and the 2 nd thermoplastic resin film, the polarizing plate can be bonded to the image display device so that the 1 st thermoplastic resin film is outside the image display device. When the polarizing plate includes the 1 st thermoplastic resin film and the 2 nd thermoplastic resin film, the polarizing plate is suitable for an in-vehicle display device including a light-transmitting member disposed on the 1 st thermoplastic resin film side of the polarizing plate and a display device disposed on the 2 nd thermoplastic resin film side of the polarizing plate in this order. The light-transmitting member may be a glass plate, a resin film having light-transmitting properties, or the like.

[ polarizing plate ]

The polarizing plate is an absorption-type polarizing plate having a property of absorbing linearly polarized light having a vibration plane parallel to an absorption axis thereof and transmitting linearly polarized light having a vibration plane orthogonal to the absorption axis (parallel to a transmission axis). The polarizing plate may be, for example, a polarizing plate in which a uniaxially stretched polyvinyl alcohol resin film is oriented by adsorbing a dichroic dye such as iodine.

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

An example of the polarizing plate manufacturing process will be described with reference to fig. 3. The polyvinyl alcohol resin film 110 as a raw material film wound from the take-up roll 111 is then guided to a swelling tank 113 using water as a swelling bath, and is immersed in the swelling bath (water) to be subjected to a swelling treatment (swelling step). The swollen membrane is guided to a dyeing bath 115 in which an aqueous solution containing iodine is used as a dyeing bath, and is dyed and iodine is adsorbed (dyeing step). Thereafter, the polyvinyl alcohol resin adsorbed with iodine is guided to a crosslinking tank 117 in which an aqueous solution containing boric acid is used as a treatment bath, and the iodine is fixed by crosslinking the polyvinyl alcohol resin with boric acid (crosslinking step). Then, the film is washed in a washing tank 119 (washing step), and dried in a drying oven 123 (drying step), thereby obtaining a polarizing plate 130. The polarizing plate 130 is wound around a winding roller 127. The polyvinyl alcohol resin film is uniaxially stretched in any 1 or more stages of the polarizing plate production process, more specifically, in any 1 or more stages from before the swelling process to before the crosslinking process.

Each treatment step can be continuously performed by continuously conveying a polyvinyl alcohol resin film as a raw material film along a film conveying path of a polarizing plate manufacturing apparatus. The film transport path includes devices (a processing tank, a furnace, and the like) for performing the above-described various processing steps in accordance with the respective execution order.

The film transport path may be constructed by arranging a guide roller, a nip roller, and the like at appropriate positions in addition to the above-described apparatuses. For example, guide rollers may be disposed before and after each treatment tank and in the treatment tank, whereby the film can be introduced into, immersed in, and pulled out of the treatment tank. More specifically, the film may be immersed in each of the processing tanks by providing 2 or more guide rollers in each of the processing tanks and conveying the film along the guide rollers.

Examples of the polyvinyl alcohol resin constituting the polyvinyl alcohol resin film include a polyvinyl acetate resin saponified with polyvinyl acetate. Examples of the polyvinyl acetate resin include polyvinyl acetate which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate and other monomers copolymerizable with vinyl acetate. Examples of the other monomer copolymerizable with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and (meth) acrylamides having an ammonium group. The saponification degree 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. The term "(meth) acrylic" as used herein means at least one member selected from the group consisting of acrylic and methacrylic. The same applies to "(meth) acryloyl group".

The polyvinyl alcohol resin may be modified, and for example, polyvinyl formal, polyvinyl acetal, polyvinyl butyral, or the like modified with aldehydes may be used.

The polyvinyl alcohol resin preferably has an average degree of polymerization of 100 or more and 10000 or less, more preferably 1500 or more and 8000 or less, and further preferably 2000 or more and 5000 or less. The average degree of polymerization of the polyvinyl alcohol resin can be determined in accordance with JIS K6726 (1994). When the average polymerization degree is within the above range, the polarizing performance and the film processability tend to be excellent.

The thickness of the polyvinyl alcohol resin film as the raw material 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 polyvinyl alcohol resin film as the raw material film may have a length in the width direction of, for example, 600mm to 5000 mm.

The polyvinyl alcohol resin film as the raw material film may be prepared, for example, in the form of a long roll (wound product) of unstretched or stretched polyvinyl alcohol resin film. In this case, the polarizing plate may be a long strip.

(1) Swelling step

The swelling treatment in this step is carried out as needed for the purpose of removing foreign matter from the polyvinyl alcohol resin film as a raw material film, removing a plasticizer, imparting easy dyeing properties, plasticizing the film, and the like, and specifically, may be a treatment in which the polyvinyl alcohol resin film 110 is immersed in a swelling tank containing a treatment liquid containing water. The film may be immersed in 1 swelling bath, or may be successively immersed in 2 or more swelling baths. The membrane may be uniaxially stretched before, during, or both the swelling treatment and the swelling treatment.

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

The temperature of the treatment liquid contained in the swelling bath at the time of immersing the film is usually 10 ℃ to 70 ℃, preferably 15 ℃ to 50 ℃, and the immersion time of the film is usually 10 seconds to 600 seconds, preferably 20 seconds to 300 seconds.

(2) Dyeing process

The dyeing treatment in this step is performed for the purpose of adsorbing and orienting the dichroic dye to the polyvinyl alcohol resin film, and specifically, may be a treatment of immersing the polyvinyl alcohol resin film in a dyeing bath containing a treatment liquid containing the dichroic dye. The membrane can be immersed in 1 staining tank, also can be sequentially immersed in more than 2 staining tanks. In order to improve the dyeability of the dichroic dye, the film provided to the dyeing step may be subjected to at least some uniaxial stretching treatment. Instead of the uniaxial stretching treatment before the dyeing treatment, the uniaxial stretching treatment may be performed at the dyeing treatment, or the uniaxial stretching treatment may be performed at the dyeing treatment in addition to the uniaxial stretching treatment before the dyeing treatment.

The dichroic pigment may be iodine or a dichroic organic dye. Specific examples of dichroic organic dyes include Red BR (Red BR), Red LR (Red LR), Red R (Red R), pink LB (Pink LB), ruby Red BL (Rubine BL), Red GS (Bordeaux GS), sky Blue LG (sky Blue LG), lemon Yellow, Blue BR (Blue BR), Blue 2R (Blue 2R), Tibetan Blue RY (Navy RY), green LG (Green), purple LB (Violet LB), purple B (Violet B), black H (Black H), black B (Blacket B), black GSP (Black GSP), Yellow 3G (Yellow 3G), Yellow R KG (Yellow R), Orange LR (Orange LR), Orange LG 3R (Orange GL 3R), scarlet (scarlet), scarlet L (scarlet), Red GL BK (Red), Blue GL (Red) Blue BK, Blue LG (Orange GL), Blue GL (Red GL), Blue LG (Red GL, Direct sky blue, direct Fast orange S, Fast Black (Fast Black). The dichroic dye may be used alone in 1 kind, or may be used in combination in 2 or more kinds.

In the case of using iodine as the dichroic dye, an aqueous solution containing iodine and potassium iodide may be used as the treatment liquid to be contained in the dyeing bath. Instead of potassium iodide, other iodides such as zinc iodide may be used, or potassium iodide may be used in combination with other iodides. Further, a compound other than iodide, for example, boric acid, zinc chloride, cobalt chloride, or the like may be coexistent. The addition of boric acid is different from the crosslinking treatment described later in that iodine is contained. The content of iodine in the aqueous solution is usually 0.01 to 1 part by mass per 100 parts by mass of water. 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 liquid contained in the dyeing bath in the membrane immersion is usually 10 to 45 ℃, preferably 10 to 40 ℃, and more preferably 20 to 35 ℃, and the immersion time of the membrane may be, for example, 20 to 600 seconds, and preferably 20 to 300 seconds.

In the case of using a dichroic organic dye as the dichroic dye, an aqueous solution containing the dichroic organic dye may be used as the treatment liquid contained in the dyeing bath. The content of the dichroic organic dye in the aqueous solution is usually 1X 10 per 100 parts by mass of water^-4Not less than 10 parts by mass, preferably 1X 10^-3The amount of the organic solvent is not less than 1 part by mass. The dyeing vessel may contain a dyeing assistant or the like, and may contain, for example, an inorganic salt such as sodium sulfate, a surfactant, or the like. The dichroic organic dye may be used alone in 1 kind, or may be used in combination in 2 or more kinds. The temperature of the treatment liquid contained in the dyeing bath when the membrane is immersed is, for example, 20 to 80 ℃, preferably 25 to 50 ℃, and the immersion time of the membrane is usually 30 to 600 seconds, preferably 60 to 300 seconds.

(3) Crosslinking step

The crosslinking treatment for treating the polyvinyl alcohol resin film after the dyeing step with the crosslinking agent is a treatment for the purpose of utilizing the resistance to hydration of crosslinking, adjusting the color tone, and the like, and specifically, may be a treatment in which the film after the dyeing step is immersed in a treatment liquid contained in a crosslinking tank containing the crosslinking agent. The membrane may be immersed in 1 crosslinking bath, or may be successively immersed in 2 or more crosslinking baths. The uniaxial stretching treatment may be performed at the time of the crosslinking treatment.

Examples of the crosslinking agent include boric acid, glyoxal, and glutaraldehyde, and boric acid is preferably used. More than 2 kinds of crosslinking agents may be used in combination. The boric acid content in the treatment liquid contained in the crosslinking tank is usually 0.1 part 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, per 100 parts by mass of water. When the dichroic dye is iodine, the treatment liquid contained in the crosslinking tank preferably contains boric acid and an iodide. The content of the iodide in the treatment liquid contained in the crosslinking tank is usually 0.1 part 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 per 100 parts by mass of water. Examples of the iodide include potassium iodide and zinc iodide. In addition, compounds other than iodide, for example, zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate, and the like may be present in the crosslinking tank.

The temperature of the treatment liquid contained in the crosslinking tank when the film is immersed is, for example, 30 to 85 ℃, preferably 30 to 60 ℃, and the immersion time of the film is, for example, 2 to 600 seconds, preferably 2 to 300 seconds.

In the crosslinking step, there may be 2 or more crosslinking grooves. In this case, the composition and temperature of the treatment liquid contained in each crosslinking tank may be the same or different. The treatment liquid contained in the crosslinking tank may have a concentration and a temperature of a crosslinking agent, an iodide, or the like corresponding to the purpose of impregnating the polyvinyl alcohol resin film. The crosslinking treatment for water resistance by crosslinking and the crosslinking treatment for color tone adjustment (complementary color) may be performed in a plurality of steps (for example, a plurality of tanks).

In general, when both the crosslinking treatment for water resistance by crosslinking and the crosslinking treatment for color tone adjustment (color correction) are performed, a groove (color correction groove) for performing the crosslinking treatment for color tone adjustment (color correction) is disposed at the subsequent stage. The temperature of the treatment liquid stored in the color correction tank is, for example, 10 ℃ to 55 ℃, preferably 20 ℃ to 50 ℃. The content of the crosslinking agent in the treatment liquid contained in the color replenishment bath is, for example, 1 part by mass or more and 5 parts by mass or less per 100 parts by mass of water. The content of iodide in the treatment liquid contained in the color replenishment tank is, for example, 3 parts by mass or more and 30 parts by mass or less per 100 parts by mass of water.

As described above, in the production of the polarizing plate, the polyvinyl alcohol resin film is uniaxially stretched (stretched) in any 1 or 2 or more stages from the swelling step to the crosslinking step. From the viewpoint of improving the dyeability of the dichroic dye, the film to be subjected to the dyeing step is preferably a film subjected to at least some degree of uniaxial stretching treatment, or instead of the uniaxial stretching treatment before the dyeing treatment, the uniaxial stretching treatment is performed at the time of the dyeing treatment, or in addition to the uniaxial stretching treatment before the dyeing treatment, the uniaxial stretching treatment is performed at the time of the dyeing treatment.

The uniaxial stretching treatment may be either dry stretching in which stretching is performed in air or wet stretching in which stretching is performed in a tank, or both of them. The uniaxial stretching treatment may be inter-roll stretching, hot-roll stretching, tenter stretching or the like in which longitudinal uniaxial stretching is performed with a difference in peripheral speed applied between 2 nip rolls, but preferably includes inter-roll stretching. The stretching ratio based on the raw material film (cumulative stretching ratio in the case of stretching treatment in 2 or more stages) is about 3 to 8 times. In order to provide good polarization characteristics, the stretching magnification is preferably 4 times or more, and more preferably 5 times or more.

(4) Cleaning process

The cleaning treatment in this step is carried out as needed for the purpose of removing an excessive amount of chemicals such as a crosslinking agent and a dichroic dye attached to the polyvinyl alcohol resin film, and is a treatment of cleaning the polyvinyl alcohol resin film after the crosslinking step with a cleaning solution containing water. Specifically, the polyvinyl alcohol resin film after the crosslinking step may be immersed in a treatment liquid (cleaning liquid) contained in a cleaning tank. The membrane can be immersed in 1 cleaning tank, or can be sequentially immersed in more than 2 cleaning tanks. Alternatively, the cleaning treatment may be a treatment of spraying the polyvinyl alcohol resin film after the crosslinking step with a cleaning liquid as a spray liquid, or a combination of the above-described treatment of dipping and the treatment of spraying.

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

In the washing step, the temperature of the washing liquid for washing the polyvinyl alcohol resin film after the crosslinking step may be, for example, 2 ℃ to 40 ℃, and it is preferable not to wash with the washing liquid at a temperature higher than 22 ℃ from the viewpoint of obtaining the monomer hue b value and the absorbance at a wavelength of 700nm within the above ranges.

When the polyvinyl alcohol resin film after the crosslinking step is immersed in the cleaning tank, the temperature of the cleaning liquid in the cleaning tank is preferably 2 ℃ to 22 ℃, and more preferably 2 ℃ to 10 ℃. The time for immersing in the cleaning tank may be, for example, 10 seconds to 100 seconds, and preferably 20 seconds to 80 seconds.

In the case of spraying the cleaning liquid as a shower liquid onto the polyvinyl alcohol resin film after the crosslinking step, the temperature of the cleaning liquid may be the same or different at the central portion and both end portions in the width direction of the polyvinyl alcohol resin film, but is preferably different from the viewpoint of the monomer hue b value and the absorbance at a wavelength of 700nm, and more preferably the temperature at the central portion is lower than the temperature at both end portions. The temperature of the cleaning liquid is preferably 2 ℃ to 10 ℃ in the central portion and 10 ℃ to 22 ℃ at both end portions, more preferably 3 ℃ to 7 ℃ in the central portion and 15 ℃ to 22 ℃ at both end portions, from the viewpoint of the hue b value of the monomer and the absorbance at a wavelength of 700 nm.

(5) Drying step

The drying step is a region for drying the polyvinyl alcohol resin film after the washing step. The polyvinyl alcohol resin film after the washing step is continuously conveyed, and the film is introduced into a drying step to be dried, whereby a polarizing plate can be obtained.

The drying process is performed using a drying mechanism (heating mechanism) for the film. A suitable example of the drying means is a drying oven. The drying oven is preferably capable of controlling the temperature within the oven. The drying furnace is, for example, a hot air oven capable of raising the temperature in the furnace by supplying hot air or the like. The drying treatment by the drying means may be a treatment of adhering the polyvinyl alcohol resin film after the washing step to 1 or 2 or more heating bodies having a convex curved surface, or a treatment of heating the film by a heater.

Examples of the heating body include a roller (e.g., a guide roller serving also as a heat roller) which is provided with a heat source (e.g., a heat medium such as warm water or an infrared heater) therein and can increase the surface temperature. Examples of the heater include an infrared heater, a halogen heater, and a plate heater.

In the drying step, the temperature of the drying treatment (e.g., the temperature in the oven of the drying oven, the surface temperature of the heat roll, etc.) may be, for example, 30 ℃ or higher, and is preferably 96 ℃ or higher from the viewpoint of obtaining the monomer color tone b value and the absorbance at a wavelength of 700nm within the above-mentioned ranges. The temperature of the drying treatment is usually 100 ℃ or lower. The drying time is not particularly limited, and may be, for example, 30 seconds to 900 seconds, and preferably 30 seconds to 60 seconds.

The drying step may be performed in 1 stage or may be divided into a plurality of stages, preferably 2 stages or more and 4 stages or less. When the drying step is divided into a plurality of stages, the drying temperature in at least 1 stage is preferably 96 ℃ or higher from the viewpoint of the monomer hue b value and the absorbance at a wavelength of 700 nm. When the drying step is divided into a plurality of stages, the temperature of the drying treatment is preferably set so that the temperature in the subsequent stage is higher than that in the first stage. When the drying step is divided into a plurality of stages, the drying time in each stage may be, for example, 10 seconds to 300 seconds, preferably 10 seconds to 20 seconds.

In the polarizing plate production step, at least 1 of the treatment liquids for treating the polyvinyl alcohol resin film may contain a zinc salt. Examples of the treatment tank for storing the treatment liquid include a swelling tank, a dyeing tank, a crosslinking tank, a cleaning tank, and a color correction tank. The treatment tank for containing the treatment liquid containing the zinc salt is preferably a treatment tank located after the dyeing tank and before the washing tank, more preferably at least 1 selected from the crosslinking tank and the color correction tank, and even more preferably at least 1 selected from the last crosslinking tank and the color correction tank when 2 or more crosslinking tanks are present. The polyvinyl alcohol resin film can be impregnated with a treatment liquid containing a zinc salt to make the polarizing plate contain zinc. The content of the zinc element in the polarizing plate can be set to the content of the zinc element within the above range by adjusting the concentration of the zinc salt in the treatment liquid, the immersion time of the polyvinyl alcohol resin film in the treatment liquid containing the zinc salt, the temperature of the treatment liquid, and the like.

Examples of the zinc salt contained in the treatment solution include zinc halides such as zinc chloride and zinc iodide, zinc sulfate, zinc acetate, and zinc nitrate. Among them, zinc nitrate is preferable in terms of reducing the change in tension. The zinc salt can be added to the treatment fluid in the form of a zinc salt solution.

The concentration of the zinc salt in the treatment liquid differs between the treatment tanks, and may be, for example, 1 part by mass or more and 10 parts by mass or less, and preferably 2 parts by mass or more and 7 parts by mass or less, per 100 parts by mass of the treatment liquid contained in the treatment tanks.

Through the above steps, a polarizing plate in which a uniaxially stretched polyvinyl alcohol resin film is oriented while a dichroic dye is adsorbed thereon can be obtained.

The obtained polarizer can be directly transferred to, for example, the following polarizing plate production step (step of bonding a thermoplastic resin film to one side or both sides of the polarizer).

[ thermoplastic resin film ]

Examples of the thermoplastic resin film include polyolefin resins including chain polyolefin resins (such as polypropylene resins) and cyclic polyolefin resins (such as norbornene resins); cellulose ester resins such as triacetyl cellulose and diacetyl cellulose; polyester resins such as polyethylene terephthalate, polyethylene naphthalate and polybutylene terephthalate; a polycarbonate-based resin; (meth) acrylic resins such as polymethyl methacrylate resins; or a resin film having light-transmitting properties such as a mixture or a copolymer thereof. The thermoplastic resin film may have a single-layer structure formed of 1 resin layer containing 1 or 2 or more thermoplastic resins, or may have a multilayer structure in which a plurality of resin layers containing 1 or 2 or more thermoplastic resins are stacked.

The 1 st thermoplastic resin film and the 2 nd thermoplastic resin film may be the same or different kinds of thermoplastic resin films.

Examples of the chain polyolefin resin include homopolymers of chain olefins such as polyethylene resins and polypropylene resins, and copolymers containing 2 or more kinds of chain olefins.

The cyclic polyolefin resin is a generic name of resins containing, as a polymerization unit, a cyclic olefin typified by norbornene, tetracyclododecene (also known as dimethyloctahydronaphthalene) or a derivative thereof. Examples of the cyclic polyolefin-based resin include ring-opening (co) polymers of cyclic olefins and hydrogenated products thereof, addition polymers of cyclic olefins, copolymers of cyclic olefins with linear olefins such as ethylene and propylene, or aromatic compounds having a vinyl group, and modified (co) polymers thereof modified with unsaturated carboxylic acids or derivatives thereof.

Among them, norbornene-based resins using norbornene-based monomers such as norbornene and polycyclic norbornene-based monomers as cyclic olefins are preferably used.

The cellulose ester resin is a resin obtained by esterifying at least a part of hydroxyl groups in cellulose with acetic acid, and may be a mixed ester obtained by esterifying a part of hydroxyl groups with acetic acid and esterifying a part of hydroxyl groups with another acid. The cellulose ester resin is preferably an acetyl cellulose resin.

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

The polyester resin is a resin other than the cellulose ester resin having an ester bond, and generally includes a polycondensate of a polycarboxylic acid or a derivative thereof and a polyol.

Examples of the polyester resin include polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polypropylene terephthalate, polypropylene naphthalate, polycyclohexanedimethanol terephthalate, polycyclohexanedimethanol naphthalate and the like.

Among them, polyethylene terephthalate is preferably used from the viewpoint of mechanical properties, solvent resistance, scratch resistance, cost, and the like. The polyethylene terephthalate is a resin composed of ethylene terephthalate in which 80 mol% or more of the repeating units are contained, and may contain a constituent unit derived from another copolymerizable component.

Examples of the other copolymerizable component include a dicarboxylic acid component and a diol component.

Examples of the dicarboxylic acid component include isophthalic acid, 4 '-dicarboxybiphenyl, 4' -dicarboxybenzophenone, bis (4-carboxyphenyl) ethane, adipic acid, sebacic acid, sodium 5-sulfoisophthalate, and 1, 4-dicarboxycyclohexane.

Examples of the diol component include propylene glycol, butylene glycol, neopentyl glycol, diethylene glycol, cyclohexanediol, ethylene oxide adducts of bisphenol a, polyethylene glycol, polypropylene glycol, and poly-1, 4-butylene glycol.

The dicarboxylic acid component and the diol component may be used in combination of 2 or more, if necessary.

In addition, the two carboxylic acid components, glycol components and the use of p-hydroxy benzoic acid, hydroxy ethoxy benzoic acid, beta hydroxy ethoxy benzoic acid and other hydroxy carboxylic acid.

As the other copolymerizable component, a dicarboxylic acid component and/or diol component having an amide bond, a urethane bond, an ether bond, a carbonate bond, or the like may be used in a small amount.

The polycarbonate-series resin is a polyester formed from carbonic acid and a diol or bisphenol. Among them, from the viewpoint of heat resistance, weather resistance and acid resistance, an aromatic polycarbonate having diphenylalkane in the molecular chain is preferably used.

Examples of the polycarbonate include polycarbonates derived from bisphenols such as 2, 2-bis (4-hydroxyphenyl) propane (also referred to as bisphenol a), 2-bis (4-hydroxyphenyl) butane, 1-bis (4-hydroxyphenyl) cyclohexane, 1-bis (4-hydroxyphenyl) isobutane, and 1, 1-bis (4-hydroxyphenyl) ethane.

The (meth) acrylic resin is a polymer containing a constituent unit derived from a (meth) acrylic monomer, and examples of the (meth) acrylic monomer include a methacrylic acid ester and an acrylic acid ester.

Examples of the methacrylic acid ester include methyl methacrylate, ethyl methacrylate, n-, iso-or tert-butyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate, benzyl methacrylate, 2-ethylhexyl methacrylate, and 2-hydroxyethyl methacrylate.

Examples of the acrylic ester include ethyl acrylate, n-, iso-or tert-butyl acrylate, cyclohexyl acrylate, phenyl acrylate, benzyl acrylate, 2-ethylhexyl acrylate, and 2-hydroxyethyl acrylate.

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 necessary. Examples of the additives include lubricants, antiblocking agents, heat stabilizers, antioxidants, ultraviolet absorbers, antistatic agents, light stabilizers, impact modifiers, and surfactants.

Examples of the ultraviolet absorber include salicylate-based compounds, benzophenone-based compounds, benzotriazole-based compounds, cyanoacrylate-based compounds, and nickel complex-based compounds.

Either or both of the 1 st thermoplastic resin film and the 2 nd thermoplastic resin film may be a protective film having an optical function such as a retardation film or a brightness enhancement film. For example, a transparent resin film containing the above-mentioned material is stretched (uniaxially stretched, biaxially stretched, or the like), or a liquid crystal layer or the like is formed on the film, whereby a retardation film to which an optional retardation value is applied can be produced.

A surface treatment layer (coating layer) such as a hard coat layer, an antiglare layer, an antireflection layer, an antistatic layer, and an antifouling layer may be formed on the surface of the thermoplastic resin film on the side opposite to the polarizer side.

From the viewpoint of thinning of the polarizing plate, the thickness of the thermoplastic resin film is preferably small, but if it is too thin, the strength tends to be lowered and the processability tends to be poor, and therefore, it is preferably 5 μm or more and 150 μm or less, more preferably 5 μm or more and 100 μm or less, and still more preferably 10 μm or more and 60 μm or less.

[ Adhesives ]

For bonding the polarizing plate to the thermoplastic resin film, an adhesive may be used. The adhesive may be any adhesive that exhibits adhesion to the polarizing plate and the thermoplastic resin film, and examples thereof include an aqueous adhesive obtained by dissolving or dispersing an adhesive component in water, and a curable adhesive containing an active energy ray-curable compound. Considering that the surface of the polarizing film is hydrophilic, the adhesive is preferably an aqueous adhesive in which an adhesive component is dissolved or dispersed in water. From the viewpoint of making it possible to reduce the thickness of the cured adhesive, an aqueous adhesive is also preferable. Examples of the adhesive component which is a main component of the aqueous adhesive include a polyvinyl alcohol resin and a urethane resin.

When a polyvinyl alcohol resin is used as the main component of the aqueous adhesive, the polyvinyl alcohol resin can be obtained by saponifying a polyvinyl acetate resin. Examples of the polyvinyl acetate resin include polyvinyl acetate which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate and other monomers copolymerizable with vinyl acetate. Examples of the other monomer copolymerizable with 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 an appropriate degree of polymerization, and for example, when the polyvinyl alcohol resin is an aqueous solution having a concentration of 4% by mass, the viscosity is more preferably in the range of 4mPa · sec to 50mPa · sec, and still more preferably in the range of 6mPa · sec to 30mPa · sec.

The saponification degree of the polyvinyl alcohol resin used in the adhesive is not particularly limited, but is generally preferably 80 mol% or more, and more preferably 90 mol% or more. When the polyvinyl alcohol resin used for the adhesive has a low saponification degree, the water resistance of the adhesive tends to be insufficient.

The adhesive is preferably a modified polyvinyl alcohol resin. Suitable examples of the modified polyvinyl alcohol resin include polyvinyl alcohol resins modified with an acetoacetyl group, polyvinyl alcohol resins modified with an anion, and polyvinyl alcohol resins modified with a cation. When such a modified polyvinyl alcohol resin is used, the effect of improving the water resistance of the adhesive can be easily obtained.

The acetoacetyl group-modified polyvinyl alcohol resin has an acetoacetyl group (CH) in addition to a hydroxyl group constituting a polyvinyl alcohol skeleton₃COCH₂CO-) may have other groups such as acetyl group. The acetoacetyl group is typically present in a state in which a hydrogen atom constituting a hydroxyl group of the polyvinyl alcohol is substituted. The acetoacetyl group-modified polyvinyl alcohol resin can be produced, for example, by a method of reacting polyvinyl alcohol with diketene. The acetoacetyl group-modified polyvinyl alcohol resin preferably has an acetoacetyl group as a functional group having high reactivity, and therefore, the durability of the adhesive is improved.

The acetoacetyl group content in the acetoacetyl group-modified polyvinyl alcohol resin is not particularly limited as long as it is 0.1 mol% or more. The acetoacetyl group content referred to herein is a value in which the mole percentage of acetoacetyl groups in the polyvinyl alcohol resin relative to the total amount of hydroxyl groups, acetoacetyl groups, and other ester groups (such as acetyl groups) is expressed as% and may be referred to as "degree of acetoacetylation". When the acetoacetylation degree of the polyvinyl alcohol resin is less than 0.1 mol%, the effect of improving the water resistance of the adhesive is not necessarily sufficient. The degree of acetoacetylation of the polyvinyl alcohol resin is preferably about 0.1 to 40 mol%, more preferably 1 to 20 mol%, and particularly preferably 2 to 7 mol%. When the acetoacetylation degree is more than 40 mol%, the effect of improving water resistance is small.

The anionically modified polyvinyl alcohol resin contains an anionic group, typically a carboxyl group (-COOH) or a salt thereof, in addition to a hydroxyl group constituting the polyvinyl alcohol skeleton, and may have another group such as an acetyl group. The anionically modified polyvinyl alcohol resin can be produced, for example, by a method in which an unsaturated monomer having an anionic group (typically, a carboxyl group) is copolymerized with vinyl acetate and then saponified. On the other hand, the cationically modified polyvinyl alcohol resin is a resin containing a cationic group, typically a tertiary amino group or a quaternary ammonium group, in addition to the hydroxyl group constituting the polyvinyl alcohol skeleton, and may have other groups such as an acetyl group or the like. The cationically modified polyvinyl alcohol resin can be produced, for example, by a method of copolymerizing an unsaturated monomer having a cationic group (typically, a tertiary amino group or a quaternary ammonium group) with vinyl acetate and then saponifying the copolymer.

The adhesive may contain 2 or more kinds of the above-mentioned modified polyvinyl alcohol resin, or may contain both an unmodified polyvinyl alcohol resin (specifically, a completely or partially saponified product of polyvinyl acetate) and the above-mentioned modified polyvinyl alcohol resin.

The polyvinyl alcohol resin constituting the adhesive can be appropriately selected from commercially available products. Specifically, there may be mentioned, for example, "PVA-117H" sold by Kuraray as a polyvinyl alcohol having a high degree of saponification, "GOHSENOL NH-20" sold by Nippon synthetic chemical industry, "GOHSEFIMER Z" series sold by Nippon synthetic chemical industry as a polyvinyl alcohol modified with an acetoacetyl group, "KL-318" and "KM-118" sold by Kuraray as a polyvinyl alcohol modified with an anion group, "GOHSENAL T-330" sold by Nippon synthetic chemical industry, "CM-318" sold by Kuraray as a polyvinyl alcohol modified with a cation group, and "GOHSEFIMER K-210" sold by Nippon synthetic chemical industry.

The concentration of the polyvinyl alcohol resin in the adhesive is not particularly limited, but is preferably in the range of 1 part by mass or more and 20 parts by mass or less, more preferably 1 part by mass or more and 15 parts by mass or less, further preferably 1 part by mass or more and 10 parts by mass or less, and particularly preferably 2 parts by mass or more and 10 parts by mass or less, relative to 100 parts by mass of water, because the polyvinyl alcohol resin is used in the form of an aqueous solution. When the concentration of the polyvinyl alcohol resin in the aqueous solution is too small, the adhesiveness tends to be easily lowered, and when the concentration is too large, the optical properties of the obtained polarizing plate tend to be easily lowered. The water used in the adhesive may be pure water, ultrapure water, tap water, or the like, and is not particularly limited, but pure water or ultrapure water is preferable from the viewpoint of maintaining the uniformity and transparency of the formed adhesive. Alternatively, an alcohol such as methanol or ethanol may be added to the aqueous binder solution.

The aqueous adhesive containing a polyvinyl alcohol resin as a main component may contain a crosslinking agent. The crosslinking agent is not particularly limited as long as it is a compound having a functional group reactive with the polyvinyl alcohol resin, and any crosslinking agent conventionally used for polyvinyl alcohol adhesives can be used. If a compound capable of becoming a crosslinking agent is given in terms of a functional group, there are isocyanate compounds having at least 2 isocyanate groups (-NCO) in the molecule; an epoxy compound having at least 2 epoxy groups (bridged-O-) in the molecule; mono-or di-aldehydes; an organic titanium compound; inorganic salts of divalent or trivalent metals such as magnesium, calcium, iron, nickel, zinc, and aluminum; metal salts of glyoxylic acid; methylolmelamine, and the like.

Specific examples of the isocyanate compound to be the crosslinking agent include tolylene diisocyanate, hydrogenated tolylene diisocyanate, an adduct of trimethylolpropane and tolylene diisocyanate, diphenylmethane diisocyanate, triphenylmethane triisocyanate, isophorone diisocyanate, and a ketoxime-blocked product (Japanese text: ケトオキシムブロック product) or phenol-blocked product (Japanese text: フェノールブロック product) thereof.

Specific examples of the epoxy compound to be used as the crosslinking agent include ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, di-or triglycidyl ether of glycerol, 1, 6-hexanediol diglycidyl ether, trimethylolpropane triglycidyl ether, diglycidylaniline, diglycidylamine, water-soluble polyamide epoxy resins obtained by reacting epichlorohydrin with polyamide polyamine which is a reaction product of polyalkylene polyamine and dicarboxylic acid, and the like.

Specific examples of the monoaldehydes as the crosslinking agent include formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde and the like, and specific examples of the dialdehydes include glyoxal, malondialdehyde, succindialdehyde, glutaraldehyde, maledialdehyde, phthalaldehyde and the like.

Various organic titanium compounds are sold by Matsumoto Fine Chemical as a crosslinking agent. According to the homepage of the organic titanium compound of this company (Internet < URL: http:// www.m-chem. co. jp/products 1. html. >, search of 11 months and 18 days in 22 years), if the water-soluble organic titanium compound that can be suitably used in the present invention is given in accordance with its constitutional formula (Japanese text: illustrative formula), the chemical name called by this company, and the trade name of this company, there are the following organic titanium compounds.

[(CH₃)₂CHO]₂Ti[OCH₂CH₂N(CH₂CH₂OH)₂]₂: the chemical name "di (triethanolamine) diisopropyl titanate" called by the company, the trade name "Orgatix TC-400" of the company,

(HO)₂Ti[OCH(CH₃)COO-]₂(NH₄ ⁺)₂: the chemical name "titanium ammonium lactate" called by the company, the trade name "Orgatix TC-300" of the company,

(HO)₂Ti[OCH(CH₃)COOH]₂: the chemical name "titanium lactate" referred to by this company, the trade names "Orgatix TC-310" and "Orgatix TC-315" of this company.

The metal salt of glyoxylic acid is preferably an alkali metal salt or an alkaline earth metal salt, and examples thereof include sodium glyoxylate, potassium glyoxylate, magnesium glyoxylate, and calcium glyoxylate.

Among these crosslinking agents, epoxy compounds represented by the above-mentioned water-soluble polyamide epoxy resins, aldehydes, methylolmelamine, alkali metal or alkaline earth metal salts of glyoxylic acid, and the like can be suitably used.

The crosslinking agent is preferably dissolved in water together with the polyvinyl alcohol resin to form an adhesive. However, as described below, the amount of the crosslinking agent in the aqueous solution may be a trace amount, and therefore, any crosslinking agent having a solubility of, for example, at least about 0.1 mass% with respect to water may be used as the crosslinking agent. Of course, a crosslinking agent having a solubility in water to the extent generally referred to as water solubility is suitable as the crosslinking agent used in the present invention.

The blending amount of the crosslinking agent is appropriately designed according to the kind of the polyvinyl alcohol resin, and is usually 5 parts by mass or more and 60 parts by mass or less, and preferably 10 parts by mass or more and 50 parts by mass or less, with respect to 100 parts by mass of the polyvinyl alcohol resin. When the crosslinking agent is blended in this range, good adhesion can be obtained. As described above, in order to improve the durability of the adhesive, it is preferable to use a polyvinyl alcohol resin modified with an acetoacetyl group, and in this case, it is also preferable to add the crosslinking agent in a proportion of 5 to 60 parts by mass, more preferably 10 parts by mass or more and 50 parts by mass or less, to 100 parts by mass of the polyvinyl alcohol resin. If the amount of the crosslinking agent to be blended is too large, the reaction of the crosslinking agent proceeds in a short time, and the adhesive tends to gel in advance, and as a result, the pot life becomes extremely short, and the industrial use becomes difficult.

In the aqueous adhesive containing a polyvinyl alcohol resin as a main component, it is preferable that a zinc salt is contained in addition to the crosslinking agent from the viewpoint of suppressing discoloration. Examples of the zinc salt include zinc halides such as zinc chloride and zinc iodide, zinc sulfate, zinc acetate, and zinc nitrate. Among them, zinc nitrate is preferable. The zinc salt can be added to the aqueous adhesive containing the polyvinyl alcohol resin as a main component in the form of a zinc salt solution.

When the aqueous adhesive containing a polyvinyl alcohol resin as a main component contains a zinc salt, the content of the zinc salt may be, for example, 0.01 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of water, and is preferably 0.1 parts by mass or more and 5 parts by mass or less, and more preferably 0.5 parts by mass or more and 2.5 parts by mass or less, from the viewpoint of ensuring the durability of the adhesive.

The adhesive may contain conventionally known additives such as a silane coupling agent, a plasticizer, an antistatic agent, and fine particles, as long as the effects of the present invention are not impaired.

When a urethane resin is used as a main component of the aqueous adhesive, a mixture of a polyester ionomer urethane resin and a compound having a glycidyloxy group can be given as an example of a suitable adhesive. The polyester ionomer urethane resin as used herein is a urethane resin having a polyester skeleton and a small amount of an ionic component (hydrophilic component) introduced therein. The ionomer urethane resin is emulsified directly in water without using an emulsifier and is thus converted into an emulsion, and therefore can be suitably used in an aqueous adhesive. The use of a polyester ionomer urethane resin for an adhesive between a polarizing film and a protective film is known, for example, from jp 2005-070140 a, jp 4432487 a and jp 2005-208456 a.

Examples of the active energy ray-curable adhesive include an ultraviolet ray-curable adhesive and the like.

The ultraviolet-curable adhesive may be a mixture of a radical-polymerizable (meth) acrylic compound and a photo-radical polymerization initiator, a mixture of a cation-polymerizable epoxy compound and a photo-cation polymerization initiator, or the like. Further, a cationically polymerizable epoxy compound and a radically polymerizable (meth) acrylic compound may be used in combination, and a photocationic polymerization initiator and a photoradical polymerization initiator may be used in combination as an initiator.

When the thermoplastic resin films are bonded to both sides of the polarizing plate, the adhesives may be of the same type or different types. For example, when the thermoplastic resin films are bonded to both sides of the polarizing plate, one of the films may be bonded using an aqueous adhesive, and the other film may be bonded using an active energy ray-curable adhesive.

The thickness of the adhesive in the polarizing plate may be, for example, 0.001 μm or more and 10 μm or less, and 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 further preferably 0.02 μm or more and 2 μm or less, from the viewpoint of adhesion and reduction in thickness.

[ adhesive layer ]

The polarizing plate may have an adhesive layer on the outermost surface of either the 1 st thermoplastic resin film side or the 2 nd thermoplastic resin film side in order to bond the light-transmitting member and the image display element. The pressure-sensitive adhesive layer may be formed from a pressure-sensitive adhesive composition containing a polymer such as a (meth) acrylic resin, a rubber-based polymer, a urethane-based resin, an ester-based resin, a silicone-based resin, or a polyvinyl ether-based resin as a main component. Among them, the pressure-sensitive adhesive composition is suitable for use as a base polymer of a (meth) acrylic resin which is excellent in transparency, weather resistance, heat resistance and the like. The adhesive composition may be an active energy ray-curable type or a heat-curable type.

As the (meth) acrylic resin (base polymer) used in the adhesive composition, for example, a polymer or copolymer of 1 or 2 or more kinds of (meth) acrylic esters such as butyl (meth) acrylate, ethyl (meth) acrylate, isooctyl (meth) acrylate, and 2-ethylhexyl (meth) acrylate can be suitably used. It is preferred to copolymerize the polar monomer with the base polymer. Examples of the polar monomer include monomers having a carboxyl group, a hydroxyl group, an amide group, an amino group, an epoxy group, and the like, such as (meth) acrylic acid, 2-hydroxypropyl (meth) acrylate, hydroxyethyl (meth) acrylate, meth (acrylamide), N-dimethylaminoethyl (meth) acrylate, and glycidyl (meth) acrylate.

The adhesive composition may comprise only the above-mentioned base polymer, but usually also contains a crosslinking agent. Examples of the crosslinking agent include metal ions having a valence of 2 or more, which form a metal carboxylate salt with a carboxyl group; a polyamine compound forming an amide bond with a carboxyl group; polyepoxy compounds, polyhydric alcohols, which form ester bonds with carboxyl groups; a polyisocyanate compound which forms an amide bond with a carboxyl group. Among them, polyisocyanate compounds are preferable.

The pressure-sensitive adhesive layer can be formed by, for example, dissolving or dispersing a pressure-sensitive adhesive composition in an organic solvent such as toluene or ethyl acetate to prepare a pressure-sensitive adhesive liquid, and directly applying the pressure-sensitive adhesive liquid to the target surface of the laminate to form a pressure-sensitive adhesive layer; an adhesive layer is formed in a sheet form on the release film subjected to the release treatment, and transferred to the target surface of the polarizing plate.

The thickness of the pressure-sensitive adhesive layer is determined by the adhesive strength and the like, and may be, for example, in the range of 1 μm to 50 μm, preferably 2 μm to 40 μm, more preferably 3 μm to 30 μm, and still more preferably 3 μm to 25 μm.

The polarizing plate may include the above-described separation film. The separator may be a film containing a polyethylene resin such as polyethylene, a polypropylene resin such as polypropylene, a polyester resin such as polyethylene terephthalate, or the like. Among them, stretched films of polyethylene terephthalate are preferable.

The adhesive layer may contain optional ingredients, glass fibers, glass beads, resin beads, fillers containing metal powders and/or other inorganic powders; a pigment; a colorant; an antioxidant; an ultraviolet absorber; antistatic agents, and the like.

[ optically functional layer ]

The optically functional layer may be an optically functional film other than a polarizing plate for imparting a desired optical function. A preferable example of the optical functional film is a retardation film. Examples of the retardation film include a film (λ/2 wavelength plate) giving a retardation of λ/2, a film (λ/4 wavelength plate) giving a retardation of λ/4, and a positive C plate. The optical functional film may include an alignment layer and a substrate, or may include 2 or more liquid crystal layers, alignment layers, and substrates, respectively.

The thermoplastic resin film may also serve as a retardation film, but a retardation film may be laminated in addition to these films.

Examples of the retardation film include a birefringent film formed of a stretched film of a thermoplastic resin having light transmittance; a film in which the orientation of discotic liquid crystal or nematic liquid crystal is fixed; a film in which the above-described liquid crystal layer is formed on the base film, and the like.

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

Examples of other optical functional films (optical members) that can be included in the polarizing plate include a light-collecting plate, a brightness enhancement film, a reflective layer (reflective film), a semi-transmissive reflective layer (semi-transmissive reflective film), a light-diffusing layer (light-diffusing film), and the like. They are generally provided when a polarizing plate is disposed on the back side (backlight side) of the liquid crystal cell.

[ protective film ]

The polarizing plate may include a protective film for protecting a surface thereof (typically, a surface of a thermoplastic resin film of the polarizing plate). The protective film is, for example, peeled off together with the pressure-sensitive adhesive layer included therein after the polarizing plate is bonded to the image display element or another optical member.

The pellicle film is formed, for example, from a base film and an adhesive layer laminated thereon. For the adhesive layer, the above description can be cited. Examples of the resin constituting the base film include polyethylene resins such as polyethylene, polypropylene resins such as polypropylene, polyester resins such as polyethylene terephthalate and polyethylene naphthalate, and thermoplastic resins such as polycarbonate resins. Polyester resins such as polyethylene terephthalate are preferred.

The thickness of the seed 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, the polarizing plate tends to be easily provided with strength.

< method for producing polarizing plate >

A method for producing a polarizing plate according to another aspect of the present invention is a method for producing a polarizing plate including a polarizing plate and a 1 st thermoplastic resin film bonded to one side of the polarizing plate with an adhesive interposed therebetween. The method for manufacturing a polarizing plate may include the above-described polarizer manufacturing step. From the viewpoint of obtaining the monomer hue b value and the absorbance at a wavelength of 700nm within the above ranges, the method for producing a polarizing plate preferably includes at least either a cleaning step of cleaning the polyvinyl alcohol resin film with water without cleaning with a cleaning liquid at a temperature higher than 22 ℃ or a drying step of drying the polyvinyl alcohol resin film at a temperature of 96 ℃ or higher.

The method for producing a polarizing plate may further include a bonding step of bonding the 1 st thermoplastic resin film to one side of the polarizing plate via an adhesive and drying the adhesive at a temperature of 85 ℃ or higher. In the bonding step, an adhesive may be applied to either or both of the bonding surfaces of the polarizing plate and the 1 st thermoplastic resin film, and the other bonding surface may be laminated thereon and bonded by pressing from above and below using, for example, a bonding roller. For the application of the adhesive, various application methods such as a blade, a wire bar, a die coater, a comma type blade coater, and a slot roll coater (japanese text: グラビアコーター) can be used. In addition, the polarizing plate and the 1 st thermoplastic resin film may be continuously supplied so that the contact surfaces thereof are on the inner side, and the adhesive may be cast therebetween.

After the polarizing plate and the 1 st thermoplastic resin film are bonded, the adhesive can be dried by applying a heat treatment to the laminate including the polarizing plate, the adhesive and the 1 st thermoplastic resin film. The evaporation, curing, and crosslinking of the solvent are preferably performed by heating continuously or in multiple stages so as to gradually increase the temperature, since the reaction proceeds at different temperatures. The temperature of the heat treatment is preferably a temperature of 85 ℃ or higher, from the viewpoint of obtaining the monomer hue b value and the absorbance at a wavelength of 700nm within the above ranges. The upper limit of the temperature of the heat treatment for drying the adhesive is usually 100 ℃ or lower, and preferably 90 ℃ or lower. The solvent contained in the adhesive can be removed by heat treatment. In the case where the adhesive is a curable adhesive, the curing and crosslinking reaction can be advanced by the heat treatment.

In the case of using an active energy ray-curable adhesive as the adhesive, the adhesive can be cured by irradiation with an active energy ray after bonding. The light source of the active energy ray is not particularly limited, but active energy rays (ultraviolet rays) having a light emission distribution at a wavelength of 400nm or less are preferable, and specifically, a low-pressure mercury lamp, a medium-pressure mercury lamp, a high-pressure mercury lamp, an ultrahigh-pressure mercury lamp, a chemical lamp, a black light lamp, a microwave-excited mercury lamp, a metal halide lamp, or the like is preferably used.

In order to improve the adhesiveness between the polarizing plate and the thermoplastic resin film, the surface of the polarizing plate and/or the thermoplastic resin film to be bonded may be subjected to surface treatment such as corona treatment, flame treatment, plasma treatment, ultraviolet irradiation treatment, primer coating treatment, or saponification treatment before the polarizing plate and the thermoplastic resin film are bonded.

When the polarizing plate includes the 2 nd thermoplastic resin film, the polarizing plate may be bonded to the 2 nd thermoplastic resin film in the same manner as the polarizing plate is bonded to the 1 st thermoplastic resin film. The lamination of the polarizing plate and the 2 nd thermoplastic resin film may be performed before or after the lamination of the polarizing plate and the 1 st thermoplastic resin film, or may be performed simultaneously with the lamination of the polarizing plate and the 1 st thermoplastic resin film.

< use of polarizing plate >

The polarizing plate can be used for mobile devices such as televisions, personal computers, mobile phones, and tablet terminals. Further, the polarizing plate can suppress discoloration even after a durability test at a high temperature (105 ℃) for a long time (600 hours or longer), and is therefore suitable for use in a vehicle, which is likely to be exposed to a more severe temperature condition. Examples of the in-vehicle applications include an image display device used in a navigation device, a speedometer, an air-conditioning touch panel, a back monitor (japanese text: バックモニター), a rear view monitor (japanese text: リアモニター), and the like.

Examples

The present invention will be described in further detail below with reference to examples. In the examples, "%" and "parts" are mass% and parts by mass unless otherwise specified.

Production example 1: preparation of aqueous adhesive (1)

An acetoacetyl-modified polyvinyl alcohol (trade name "GOHSEFIMER Z-200", manufactured by japan synthetic chemical industry, having a 4% aqueous solution viscosity of 12.4mPa · sec and a saponification degree of 99.1 mol%) was dissolved in pure water to prepare a 10% aqueous solution. The obtained acetoacetyl group-modified polyvinyl alcohol aqueous solution, and sodium glyoxylate as a crosslinking agent were mixed so that the aqueous solution: the mass ratio of solid components of sodium glyoxylate is 1: mixed in the manner of 0.1. Then, zinc nitrate and pure water were added so that zinc nitrate was 1.5 parts and acetoacetyl-modified polyvinyl alcohol was 2.5 parts per 100 parts of water, to prepare an aqueous adhesive composition (1).

< example 1 >

A long polyvinyl alcohol (PVA) base film (trade name "M6000" manufactured by Kuraray Co., Ltd., degree of saponification of 99.9 mol% or more) having a width of 3390mm and a thickness of 60 μ M was continuously conveyed while being wound out from a roll, and immersed in a swelling bath containing pure water at 28 ℃ for a retention time of 45 seconds (swelling step). Thereafter, the film drawn out of the swelling bath was immersed in a dyeing bath containing iodine at 30 ℃ and having a potassium iodide/water ratio of 1.5/100 (mass ratio) for a retention time of 120 seconds (dyeing step). Then, the film drawn out from the dyeing bath was immersed in a first crosslinking bath at 30 ℃ at a residence time of 70 seconds in which potassium iodide/boric acid/water was 0.5/0.6/100 (mass ratio), and then immersed in a second crosslinking bath at 60 ℃ at a residence time of 50 seconds in which potassium iodide/boric acid/water was 15/4.9/100 (mass ratio) (crosslinking step). Thereafter the membrane was immersed in a cleaning bath containing pure water at 7 ℃ with a residence time of 40 seconds. Then, the center portion was sprayed with water at a temperature of 5.3 ℃ and both end portions were sprayed with water at a temperature of 22 ℃ to perform cleaning (cleaning step). The PVA thus obtained was continuously dried under the following 3-stage drying conditions of temperature and time (stage 1: 75 ℃ C. for 15 seconds, stage 2: 85 ℃ C. for 15 seconds, and stage 3: 96 ℃ C. for 15 seconds) (drying step). In the dyeing step and the crosslinking step, longitudinal uniaxial stretching is performed by inter-roll stretching in a bath. The total stretching ratio based on the raw material film was set to 5.8 times. The thickness of the obtained polarizing plate was 25 μm.

The polarizing plate obtained as described above was bonded with a thermoplastic resin film (trade name "KC 4CT 1W", manufactured by Konica Minolta) containing triacetyl cellulose as a protective film at a bonding temperature of 70 ℃ via an aqueous adhesive composition (1), and then the aqueous adhesive was continuously dried under the following 3-stage drying conditions of temperature and time (stage 1: 60 ℃ for 25 seconds, stage 2: 85 ℃ for 25 seconds, stage 3: 90 ℃ for 25 seconds) (bonding step). The aqueous adhesive was applied to one surface of the thermoplastic resin film at a thickness of 200 nm. The obtained polarizing plate was measured for zinc content, and the result was 280 ppm. The results of measurement of the monomer hue b value and the absorbance at a wavelength of 700nm and the results of the durability test are shown in Table 1.

< comparative example 1 >

A polarizing plate of comparative example 1 was produced in the same manner as in example 1, except that the water temperature of the showers on both ends was set to 24 ℃ in the cleaning step of example 1 and the temperature of the 3 rd stage was set to 93 ℃ in the drying step. The obtained polarizing plate was measured for zinc content, and the result was 280 ppm. The results of measurement of the monomer hue b value and the absorbance at a wavelength of 700nm and the results of the durability test are shown in Table 1.

[ durability test ]

The polarizing plate thus obtained was cut to prepare a sample (size: 12 cm. times.30 cm) for durability test. The sample for the durability test was subjected to autoclave treatment [ temperature 50 ℃ C., pressure 5kg/cm ] for 1 hour²(490.3kPa)]Thereafter, the mixture was left at a temperature of 23 ℃ and a relative humidity of 55% for 24 hours. The heating test was performed in a heating environment at a temperature of 105 ℃, and the change in color before and after heating was visually confirmed. The time required until the color change was measured.

[ measurement of the b value of the monomer hue and the absorbance at a wavelength of 700nm ]

The b value of the monomer color tone of the polarizing plate before the durability test and the absorbance at a wavelength of 700nm were measured using a spectrophotometer ("V-7100" manufactured by Nippon Denshoku Co., Ltd.).

[ measurement of Zinc content ]

The measurement of the zinc content in the polarizing plate was performed as follows.

Nitric acid was added to a precisely weighed polarizing plate, and the solution obtained by acid decomposition using a microwave sample pretreatment apparatus (ETHOS D) manufactured by Milestone General was used as a measurement solution. The zinc concentration was determined by measuring the zinc concentration of the measurement solution by an ICP emission spectrometer (5110ICP-OES) manufactured by Agilent Technology, and the zinc mass was calculated based on the mass of the polarizing plate.

[ Table 1]

	Example 1	Comparative example 1
			Monomer tone b	4.1	2.7
Wavelength 700[ nm ]]Absorbance of (b) of	4.4	4.6
			Duration of endurance	1400	510

Claims

1. A polarizing plate having a single-component color b value of 2.7 or more and an absorbance at a wavelength of 700nm of 4.5 or less.

2. The polarizing plate according to claim 1, which comprises a polarizing plate and a 1 st thermoplastic resin film bonded to one side of the polarizing plate via an adhesive.

3. The polarizing plate according to claim 2, further comprising a 2 nd thermoplastic resin film, wherein the 2 nd thermoplastic resin film is bonded to the polarizer on a side opposite to the 1 st thermoplastic resin film side via an adhesive.

4. The polarizing plate according to claim 2 or 3,

the adhesive is a water-based adhesive.

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

6. A display device for vehicle use, comprising the polarizing plate according to any one of claims 1 to 5.

7. A method for manufacturing a polarizing plate according to claim 2,

the polarizer comprises a polyvinyl alcohol resin film,

the manufacturing method comprises a cleaning procedure and a cleaning procedure,

in the cleaning step, the polyvinyl alcohol resin film is cleaned with a cleaning liquid, and is not cleaned with a cleaning liquid having a temperature higher than 22 ℃.

8. The method for manufacturing a polarizing plate according to claim 7, further comprising a drying step,

in the drying step, the polyvinyl alcohol resin film is dried at a temperature of 96 ℃ or higher.

9. The method for manufacturing a polarizing plate according to claim 7 or 8, further comprising a bonding step,

in the bonding step, the 1 st thermoplastic resin film is bonded to one side of the polarizing plate via an adhesive, and the adhesive is dried at a temperature of 85 ℃ or higher.