JP2013218359A - Polarizing plate and dichroism pigment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarizing plate for which various dichroism pigment can be used, and which is excellent in durability, especially moisture resistance.SOLUTION: A method of manufacturing a polarizing plate comprises the steps of: (1) extending a resin sheet; and (2) coloring the extended resin sheet with dichroism pigment. Various resin such as polyester (for example, polyethylene terephthalate (PET)) or polyolefin (for example, norbornene resin) is used for manufacturing the polarizing plate.

Description

  The present invention relates to a polarizing plate and a method for producing the same. In this specification, the term “polarizing plate” includes a polarizing film.

In recent years, with the widespread use of liquid crystal displays, use in various applications has been promoted. However, from the viewpoint of durability, there is a growing demand for durability against humidity, heat, and light. Since conventional LCDs use iodine-based polarizing films, their durability against humidity is low, and future demand is expected by improving their wet and heat resistance. The establishment of the technology of the polarizing film using the dichroic dye which is excellent in is expected. Currently, research and development are being conducted in Japan and overseas to establish production technology for polarizing film parts using dichroic dyes with excellent durability.
Conventionally, a polarizing plate is produced by stretching a film of polyvinyl alcohol that is excellent in transparency, affinity for iodine, etc. and high orientation during stretching. By uniaxially stretching a polyvinyl alcohol film on which iodine is adsorbed, the polarizing element layer having polarizing performance is obtained by orienting iodine in the stretching direction.
Japanese Patent Application Laid-Open No. 2002-48918 discloses manufacturing a polarizing plate using a polyvinyl alcohol layer containing a dichroic dye.

JP 2002-48918 A

  However, conventionally, since polyvinyl alcohol is water-soluble, there have been a drawback that the polarizing plate is inferior in wet resistance, and a dichroic dye that can be used is limited.

  An object of the present invention is to provide a polarizing plate in which various dichroic dyes can be used and which is excellent in durability, particularly wet resistance.

The present invention
There is provided a method for producing a polarizing plate, comprising (1) a step of stretching a resin sheet, and (2) a step of dyeing the stretched resin sheet with a dichroic dye.

According to the present invention, polarizing plates are manufactured using various resins such as polyester (for example, polyethylene terephthalate (PET)) or polyolefin (for example, norbornene resin).
According to the present invention, a polarizing plate and a polarizing film excellent in wet resistance and heat resistance can be produced. Conventionally, since water-soluble polyvinyl alcohol (PVA) is used, the polarizing film cannot be used under high humidity conditions, but the polarizing plate can be used even under high humidity conditions.

Various types of dichroic dyes can be applied as long as they do not have a hydrophilic group. Conventionally, dichroic dyes are limited to hydrophilic dyes so as to be compatible with polyvinyl alcohol (PVA). However, according to the present invention, oil-soluble dichroic dyes can be used, and the options for dichroic dyes are expanded.
Resins such as polyester are easily plastically deformed, so that the polarizing plate can be easily processed.

In the method of the present invention, the resin sheet is made of a resin other than polyvinyl alcohol (PVA) and is preferably colorless and transparent. The resin is preferably thermoplastic and amorphous. The resin is not hydrophilic but hydrophobic. A resin sheet mainly composed of a linear polymer is preferred. The linear polymer may have a long main chain and a branched chain in a part of the main chain.
Examples of the resin for the resin sheet include cellulose polymers such as diacetyl cellulose and triacetyl cellulose; vinyl butyral polymers; vinyl halides such as vinyl chloride, and vinyl halide polymers such as polyvinylidene chloride such as vinylidene chloride. Polyester polymers such as polyethylene terephthalate and polyethylene naphthalate; carbonate polymers; acrylic polymers such as polymethyl methacrylate; styrene polymers such as polystyrene and acrylonitrile / styrene copolymers (AS resin); amide polymers such as nylon Olefin polymers such as polyethylene, polypropylene, polyolefins having a cyclo or norbornene structure, ethylene / propylene copolymers; It can be mentioned. These polymers may be cross-linked as necessary.
The colorless and transparent resin sheet refers to a sheet having a thickness of 100 micrometers having a light transmittance of 70% or more in visible light (wavelength: 450 nm to 650 nm).

The resin sheet is obtained by molding a resin (particularly, a thermoplastic resin) into a sheet. Various molding methods can be used as the molding method, but a press molding method is preferable. The thickness of the sheet is generally 0.1 to 2 mm.
About a sheet | seat, a polarizing plate is manufactured by performing the extending process (1) only before the dyeing process (2), only after the dyeing process (2), or before and after the dyeing process (2).
The stretching step (1) is preferably performed before and after the dyeing step (2). Therefore, it is preferable to obtain a polarizing plate or a polarizing film by performing (1) a step of stretching the sheet, (2) a step of dyeing the sheet, and (1 ′) a step of stretching the dyed sheet.

In the step (1), the formed sheet is stretched. Regarding the stretching conditions, the temperature may be 0-100 ° C., for example 50-80 ° C., in particular 60-70 ° C., and the pressure may be 0.1-10 atm, in particular 1 atm. It is preferable to perform stretching in a uniaxial direction.
The draw ratio is generally 2 to 20 times, for example 3 to 10 times. When the stretching step (1) is performed before and after the dyeing step (2), the total stretching is preferably 2 to 20 times, and the stretching ratio before the dyeing step (2) is 2 to 6 times, It is especially 3-5 times, and it is preferable that the draw ratio after dyeing process (2) is 1.3-5 times, for example, especially 1.4-3 times. The stretching before and after the dyeing step (2) is preferably uniaxial stretching in the same direction.
Since the stretched sheet obtained by the step (1) has high heat resistance, it is preferable to stretch before the dyeing step (2).

  In step (2), the stretched sheet is dyed with a dichroic dye. That is, the resin sheet is impregnated with a dichroic dye. Dyeing can be performed by immersing the resin in a dichroic dye dispersion. In dyeing, the pressure is preferably 1 to 100 atm, and the temperature is preferably 70 to 150 ° C. (particularly 80 to 120 ° C.). The concentration of the dichroic dye dispersion (weight ratio of the dye to the dispersion) is generally 0.1 to 30% by weight, and particularly preferably 1 to 20% by weight. The concentration of the dichroic dye dispersion (on weight of fiber) (weight% of the dye sheet) is generally 0.1 to 30% by weight, particularly preferably 2 to 10% by weight. Dyeing is preferably performed while vibrating the dispersion.

In the dispersion, the medium (solvent) is not limited as long as it is water or an organic solvent in which the pigment is dispersed. The medium may dissolve the dye. The medium does not cause changes in the sheet, such as dissolving the sheet. The medium does not dissolve the sheet. Examples of the medium include hydrocarbons such as water, toluene, xylene, pentane, hexane, heptane and cyclohexane; halogenated hydrocarbons such as dichloromethane and chloroform; methanol, ethanol, isopropanol, 2,2,3,3- Alcohols such as tetrafluoropropanol; ethers such as tetrahydrofuran, diethyl ether, 1,4-dioxane and 1,3-dioxolane; cellosolves such as methyl cellosolve and ethyl cellosolve; esters such as ethyl acetate, propyl acetate and butyl acetate Ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclopentanone and cyclohexanone; amides such as dimethylformamide and N-methylpyrrolidone; sulfoxides such as dimethyl sulfoxide and the like That.
The mixture of dye and medium is generally a dispersion of the dye. In the pigment dispersion, a dispersant is preferably present so as to promote the pigment dispersion. The dispersant is generally a surfactant, such as a nonionic or ionic (cationic or anionic) surfactant.

  In the present invention, a resin sheet is subjected to steps (1) and (2). The resin is preferably polyester or polyolefin. The dyeing step (2) is preferably performed using a rotary high-pressure dyeing machine.

  Polyester is obtained by polycondensation of an aromatic dicarboxylic acid and an aliphatic glycol. Specific examples of the aromatic dicarboxylic acid include terephthalic acid and 2,6-naphthalenedicarboxylic acid. Specific examples of the aliphatic glycol include ethylene glycol, diethylene glycol, and 1,4-cyclohexanedimethanol. Representative polyesters include polyethylene terephthalate (PET), polyethylene-2,6-naphthalenedicarboxylate (PEN), and the like. The polyester may be a homopolyester or a copolyester. In the case of a copolyester, the amount of the third component other than the aromatic dicarboxylic acid and the aliphatic glycol is generally 50 mol% or less, for example, 0.1 to 30 mol%, based on the total of these components. Examples of the third component in the copolyester are dicarboxylic acids other than aromatic dicarboxylic acids and glycols other than aliphatic glycols. In the copolyester, other dicarboxylic acid components include isophthalic acid, phthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, and oxycarboxylic acid (for example, p-oxybenzoic acid). One or two or more selected from the above can be mentioned, and the other glycol components include one or more selected from ethylene glycol, diethylene glycol, propylene glycol, butanediol, 1,4-cyclohexanedimethanol, neopentyl glycol, etc. Is mentioned.

  Examples of polyolefins are polyethylene, polypropylene, cyclo- or polyolefins having a norbornene structure.

  The resin sheet may contain a weathering agent, a light resistance agent, an antistatic agent, a lubricant, a light shielding agent, an antioxidant, a fluorescent whitening agent, a matting agent, a heat stabilizer, and the like.

  Any dichroic dye may be used. The dichroic dye is preferably an azo dye. The number of azo groups is preferably 2 (ie diazo) or 3 (ie triazo). It is preferable that an aromatic group (for example, a benzene ring or a naphthalene ring) or a stilbene group exists between the azo group and the azo group. It is preferred that benzothiazole or thienothiazole is present at one end. A diethylaminobenzene group, anisole group, or benzene ring is preferably present at the other end. In the present invention, groups (for example, anisole group and benzene ring) may or may not be substituted.

ベンゾチアゾール系色素（２）：

上記スキーム中、Ｒ、Ｒ_１、Ｒ_２およびＲ_３のそれぞれは、同一または異なって、水素原子または炭素数１〜３０の炭化水素基であってよい。 Specific examples of the dichroic dye are as follows. In some cases, the synthesis scheme is also shown.
Benzothiazole dye (1):

Benzothiazole dye (2):

In the above scheme, each of R, R ₁ , R ₂ and R ₃ may be the same or different and each may be a hydrogen atom or a hydrocarbon group having 1 to 30 carbon atoms.

チエノチアゾール系色素（２）：

スキーム中、Ｅｔはエチル基である。 Thienothiazole pigment (1):

Thienothiazole dye (2):

In the scheme, Et is an ethyl group.

Stilbene dyes:

  Hereinafter, the present invention will be specifically described with reference to examples.

  The following experimental method was used.

Preparation of Sample Film The film used was an amorphous PET film having a thickness of 500 μm and a specific gravity of 1.27 manufactured by Acrysandy Co., Ltd.

Dyeing method and stretching method In stretching before dyeing, the film was stretched 4 or 3 times in water at 65 ° C. The stretched film was dried in a desiccator for 24 hours.
Subsequently, the film was dye | stained at 120 degreeC for 2 hours using the high temperature / high pressure dyeing machine (Sakurai dyeing machine industry Co., Ltd. product HCC-BS-1). As the staining solution, a pigment was dispersed in water at a concentration of 10% owf, and as a dispersant, Irgasol NA manufactured by CIBA was added to the staining solution so as to have a concentration of 1%.
After dyeing, the film was again stretched 1.6 times in water at 65 ° C. The film was then dried in a desiccator for 24 hours.

After the dichroic measurement , the same treatment as that of the dyed film was performed, and the maximum absorption wavelength of the visible region and the absorbance thereof were measured with reference to a film containing no dichroic dye. Thereafter, the film was stretched in water at 65 ° C. and dried in a desiccator for 24 hours.
A polarizer was inserted on the sample side so that the vibration direction was vertical, and a baseline measurement was performed.
Next, the sample stretched film was inserted into the detector side at a wavelength of 600 nm so that the vibration direction of the incident polarized light was perpendicular to the stretch axis, and 800 nm to 400 nm was measured. Next, the vibration direction of the incident polarized light was perpendicular to the stretch axis. And the absorbance of each was measured, and the dichroic ratio was calculated.
Next, insert another sample film into the sample side so that the vibration direction and the stretching axis are parallel, measure 800 nm to 400 nm, and then insert the second sample film in parallel with the vibration direction and the stretching axis. The transmittance was measured in the same manner. The degree of polarization was calculated according to the following formula.

Calculation formula of degree of polarization
A = -log (T)
A: Absorbance
T: Transmissivity
T = 10 ^ (-A)
p (%): degree of polarization p = [(Ty-Tz) / (Ty + Tz)] × 100
Ty: Transmittance when the vibration direction of the incident polarized light is parallel to the stretching axis
Tz: Transmittance when the vibration direction of the incident polarized light is perpendicular to the stretching axis

Examples 1-15
Using the resin sheet, stretching, dyeing and measurement were performed.
The following dyes were used.
The conditions and results are shown in Tables 1 and 2.

色素２

Dye 1

Dye 2

色素４

Dye 3

Dye 4

色素６

色素７

Dye 5

Dye 6

Dye 7

  According to the present invention, a polarizing plate or polarizing film having durability (wet resistance, heat resistance) can be obtained using various dichroic dyes. The polarizing plate is useful for various applications, particularly for liquid crystal displays.

Claims (8)

(1) A process for stretching a resin sheet; and (2) a process for dyeing a stretched resin sheet with a dichroic dye. The process according to claim 1, wherein the stretching is uniaxial stretching. The process according to claim 1 or 2, wherein the stretching step (1) is performed only before the dyeing step (1), only after the dyeing step (2), or before and after the dyeing step (2). The manufacturing method in any one of Claims 1-3 which perform a dyeing process (2) by immersing resin in the dispersion liquid of a dichroic dye. The manufacturing method in any one of Claims 1-4 which perform a dyeing process (2) using a rotary high-pressure dyeing machine. The method according to claim 1, wherein the resin is polyester or polyolefin. The process according to any one of claims 1 to 6, wherein the dichroic dye is an azo dye. The polarizing plate manufactured by the manufacturing method in any one of Claims 1-7.