JP2011232699A - Polypropylene polarizer and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarizer superior in durability, in particular moistening-proofness.SOLUTION: A method of manufacturing a polarizer has (1) a step for obtaining a dyeing sheet by (a) dyeing with a dichroism pigment after molding a polypropylene as a sheet or (b) kneading a polypropylene and a dichroism pigment under heating and subsequently molding them, and (2) a step for stretching the dyeing sheet. In this method of manufacturing a polarizer, the melt mass flow rate of the polypropylene is 0.1-50 g/10 min. There is also provided a polarizer obtained by the method.

Description

  The present invention relates to a polypropylene polarizing plate and a method for producing the same. In this specification, the term “polarizing plate” includes a polarizing sheet and 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, a polarizing element layer having polarization performance is obtained by arranging iodine in the stretching direction.

  Japanese Patent Application Laid-Open No. 2002-048918 discloses manufacturing a polarizing plate using a polyvinyl alcohol layer containing a dichroic dye.

  On the other hand, since polyvinyl alcohol is water-soluble, in order to improve the point that the polarizing plate is inferior in wet resistance and the dichroic dye that can be used is limited, it is replaced with hydrophobic alcohol. A polarizing plate using polypropylene as a polymer is also disclosed (Japanese Patent Laid-Open No. 2009-217012). Since this polarizing plate is hydrophobic, it has excellent wet resistance, and usable dyes have also extended to the range of dichroic dyes having no hydrophilic group such as a sulfonic acid group. However, further improvements are required in the dichroic ratio and polarization degree of the obtained polarizing plate.

JP 2002-049818 A JP 2009-217012 A

  An object of the present invention is to improve the above-mentioned problems of the prior art, and a method for producing a polarizing plate that is excellent in durability, particularly wet resistance, and at the same time has improved optical characteristics such as dichroic ratio and degree of polarization. Another object is to provide a polarizing plate obtained by the method.

The present invention
A method of manufacturing a polarizing plate,
(1) (a) a step of forming polypropylene into a sheet and then dyeing with a dichroic dye to obtain a dyed sheet, or (b) molding and dyeing after kneading polypropylene and dichroic dye under heating. A step of obtaining a sheet, and (2) a step of stretching a dyed sheet,
Provided are a method for producing a polarizing plate having a melt mass flow rate (hereinafter abbreviated as MFR) of polypropylene in the range of 0.1 to 50 g / 10 min, and a polarizing plate obtained by the method.

  According to the present invention, it is possible to produce a polarizing plate and a polarizing film that are excellent in wet resistance and improved in optical properties such as dichroic ratio and degree of polarization. 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.

  The polypropylene used in the present invention (hereinafter abbreviated as PP) includes a homopolymer of propylene and / or a copolymer of propylene and another olefin. The stereoregularity of polypropylene is not particularly limited. As the other olefin copolymerized with propylene, a chain or branched olefin having 2 to 8 carbon atoms may be used. For example, ethylene, 1-butene, 1-pentene, 1-hexene, 2-ethyl-1-hexene, 1-octene, 4-methyl-1-pentene, etc. may be used, preferably ethylene, 1-butene, 1-hexene, etc. It may be hexene. As a copolymer type, a random copolymer obtained by randomly copolymerizing propylene and another olefin can be preferably used. This is because the transparency is good.

  The PP used in the present invention is characterized in that the MFR is in the range of 0.1 to 50 g / 10 min. The MFR may preferably be in the range of 0.5-40 g / 10 min, more preferably 1-20 g / 10 min. If the MFR is less than 0.1 g / 10 min, the load on the extruder increases and it becomes difficult to extrude the PP sheet. This is because if the MFR is larger than 50 g / 10 min, the fluidity of PP is excessively increased and uniform stretching becomes difficult, and the dichroic ratio and the degree of polarization are likely to be reduced.

The polarizing plate manufacturing method of the present invention comprises a step (1) of obtaining a PP dyed sheet and a step (2) of stretching the obtained dyed sheet.

As described above, the step (1) of obtaining a dyed sheet is (a) a step of obtaining a dyed sheet by dyeing with a dichroic dye after forming PP into a sheet, or (b) dichroism with PP. Any of the steps of kneading the dye under heating and then forming it to obtain a dyed sheet may be used. From the viewpoint of the dyeability of the dyed sheet, the step (a) in which PP is formed into a sheet and then dyed with a dichroic dye to obtain a dyed sheet is preferable. This is because, according to this step, the dichroic dye easily penetrates into the sheet. On the other hand, in the step (b) of obtaining a dyed sheet by heating and kneading the PP pellet with the dichroic dye, the dye is brought into the pellet by appropriately selecting the kneading conditions at a heating temperature equal to or higher than the melting point of PP. A dyed sheet that can be infiltrated and inferior to the step (a) can be obtained. The melting point of PP is determined by the molecular structure of PP, for example, homopolymer, copolymer, stereoregularity, crystallinity, molecular weight, molecular weight distribution.

  The operation of molding PP in the step (1) (a) of the present invention to form a PP sheet, and the operation of molding after heating and kneading with the dichroic dye in (1) (b) to form a dyed sheet are usually performed. This method can be used. For example, an extrusion method can be used. The thickness of the sheet may generally be 1000 μm to 1 μm, for example 800 μm to 5 μm, preferably 600 μm to 10 μm. The PP sheet in step (1) (a) may be colorless and transparent. The colorless and transparent PP 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 PP or PP sheet used in the present invention includes a weathering agent, a light-proofing agent, an antistatic agent, an antifogging agent, a lubricant, a light-shielding agent, an antioxidant, a fluorescent whitening agent, a matting agent, a heat stabilizer, a crystal nucleus. Agents, chlorine scavengers, antiblocking agents, flame retardants and the like. Moreover, in the range which does not impair the effect of invention, other resins, such as polyolefin resin other than the said polypropylene, rosin resin, polyterpene resin, petroleum resin, may be included as needed.

In the present invention, the dyeing operation is a method of dyeing a PP sheet with a dichroic dye (step (1) (a)), or a PP pellet (or powder) and a dichroic dye are kneaded under heating. The dyeing method (dying operation in the steps (1) and (b)) is performed.

  In the step (1) (a) of obtaining a dyed sheet by dyeing a PP sheet with a dichroic dye, the PP sheet is immersed in a dispersion of the dichroic dye (hereinafter referred to as “dye dispersion”). Can be done by. The dyeing temperature may be 110-150 ° C, for example 120-140 ° C. The concentration of the dichroic dye dispersion (weight ratio of the dye to the dispersion) may generally be 0.1 to 30% by weight, for example 1 to 20% by weight. Dyeing is preferably performed while vibrating the dispersion.

The dyeing operation performed by immersing the PP sheet in the dichroic dye dispersion can be performed using a normal dyeing machine. For example, it can be performed using a rotary high-pressure dyeing machine and a roll-type high-pressure dyeing machine (a jigger dyeing machine). In the dichroic dye dispersion, the medium (solvent) is not limited as long as it is water or an organic solvent in which the dye is dispersed. The medium to be used may dissolve the pigment, but does not cause changes in the sheet such as dissolving 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.
In the dye dispersion, a dispersant may be present so as to promote the dispersion of the dye. The dispersant may generally be a surfactant, such as a nonionic or ionic (cationic or anionic) surfactant.

On the other hand, the operation of kneading and dyeing PP pellets (or powder) and a dichroic dye under heating (dyeing operation in steps (1) and (b)) is performed at a temperature above the melting point of PP pellets (for example, 160 to 240 ° C., preferably 180 to 220 ° C., and kneading appropriately for several minutes to several tens of minutes (for example, 1 to 30 minutes, preferably 2 to 10 minutes, particularly 3 to 6 minutes). The dichroic dye powder is added to the mixture, and kneading is continued for several minutes to several tens of minutes (for example, 1 to 60 minutes, preferably 2 to 30 minutes, particularly 5 to 20 minutes) to obtain a dyed PP. it can. The amount of dichroic dye may generally be from 0.1 to 10% by weight, for example from 0.5 to 5% by weight, based on PP. This dyed PP can be made into a dyed PP sheet by the aforementioned extrusion molding method or the like.

The dichroic dye used in the present invention is not particularly limited, but is preferably a hydrophobic dichroic dye that does not contain a hydrophilic group such as a carboxyl group or a sulfonic acid group.
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. A benzothiazole or thienothiazole is preferably present at one end, and a thienothiazole group is particularly preferably present. 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.

  Among the preferable dichroic dyes used in the present invention, as a magenta or red dichroic dye having an absorption maximum wavelength (λmax) in the vicinity of 500 nm to 600 nm, for example, a bisazo type having a thienothiazole group at one end R-02 is exemplified.

（式中、式中、Ｒ^１〜Ｒ^３はそれぞれ独立に、炭素数１〜６のアルキル基またはシアノ置換アルキル基を表す。）

(In formula, R < ¹ > -R < ³ > represents a C1-C6 alkyl group or a cyano substituted alkyl group each independently.)

  More specifically, R-1, R-2 and R-3 are exemplified.

  Examples of cyan or blue dichroic dyes having an absorption maximum wavelength (λmax) in the vicinity of 600 nm to 650 nm include, for example, a bisazo or triazo type dichroic having a thienothiazole group or a benzothiazole group between one end or a diazo group Sex pigments. Examples thereof include B-4, B-5, and B-07.

（式中、Ｒ⁴は炭素数１〜６のアルキル基またはシアノ基を表し、Ｒ^５およびＲ⁶はそれぞれ独立に、炭素数１〜６のアルキル基を表す。）

(In the formula, R ⁴ represents an alkyl group having 1 to 6 carbon atoms or a cyano group, and R ⁵ and R ⁶ each independently represents an alkyl group having 1 to 6 carbon atoms.)

  Furthermore, B-7 is mentioned as a preferable specific example of B-07.

  Examples of the yellow dichroic dye having an absorption maximum wavelength (λmax) in the vicinity of 450 nm to 4000 nm include Y-08 having a bisazostilbene structure.

（式中、Ｒ^７およびＲ^８はそれぞれ独立に、水素原子または炭素数１〜６のアルキル基を表す。）

(Wherein R ⁷ and R ⁸ each independently represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms.)

  A more preferred example of Y-08 includes double-terminal hydroxy type Y-8.

  A thienothiazole dye can be produced according to a conventional method, for example, according to the following synthetic reaction scheme.

  Among the yellow dichroic dyes, for example, the Y-8 yellow dye can be synthesized according to the following reaction formula.

  That is, diazotization with sodium 4,4'-diaminostilbene nitrite, diazo coupling with phenol Na salt, and neutralization with acid to obtain hydroxy-terminal Y-8. Can do.

  Further, by reacting the Na salt of Y-8 with a dialkyl sulfuric acid or an alkyl chloride, a double-terminal alkoxy type Y-08 can be obtained.

In the stretching step (2) in the present invention, both uniaxial stretching and biaxial stretching can be adopted, but uniaxial stretching is preferred from the viewpoint of increasing the dichroic ratio and the degree of polarization. This is because the dichroic dye is easily oriented in the uniaxial stretching direction. The draw ratio may be usually in the range of 2 to 20 times, for example, 3 to 15 times, or 4 to 10 times. Usually, the higher the draw ratio, the more the orientation of the dichroic dye increases. As a result, it is expected that the degree of polarization of the polypropylene sheet (or film) is also improved.

The stretching step (2) can be performed by a normal method using a normal stretching machine. Here, examples of the stretching method include a roll stretching method in which a sheet is stretched due to a difference in rotational speed between two or more rolls, and a tenter stretching method in which a sheet having both ends fixed with a chuck or the like is stretched in an oven to widen the chuck interval. It is done. The operation temperature (stretching temperature) in the uniaxial stretching step may be arbitrarily selected from a range not exceeding the melting point of PP. The stretching temperature is usually in the range of 50 ° C. to 5 ° C. or lower (melting point−5 ° C.), preferably 60 ° C. to melting point−10 ° C.
The operation time (stretching time) of the stretching process can vary depending on the structure of the stretching machine, the stretching temperature, and the stretching ratio. When the stretching temperature is low, a longer stretching time is required to obtain the desired stretching property, and when the stretching temperature is high, the stretching time for obtaining the desired stretching property may be shorter. Accordingly, the appropriate stretching time can vary depending on the stretching temperature, economy, and the like.

  The polarizing plate obtained by the present invention can provide a relatively high degree of polarization as a hydrophobic PP polarizing plate while maintaining an excellent dichroic ratio. For example, a dichroic ratio of 2 or more, 4 or more, or 6 or more, and a degree of polarization of, for example, 70% or more, or 80% or more, or about 90% can be obtained. The PP polarizing plate obtained in the present invention exhibits excellent characteristics in terms of durability (wet resistance and heat resistance).

EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.
Various evaluations in the examples were performed by the following methods.
(1) Melt mass flow rate (MFR)
The MFR of PP was measured based on JIS K7210 using MELT INDEXER L242 manufactured by Takara Thermistor Co., Ltd. The measurement temperature was 230 ° C., and the load was 2.16 Kg / cm ² .
(2) A sample with a melting point of 5 mg was precisely weighed and then enclosed in an aluminum pan, which was then mounted on a differential thermal scanning calorimeter (model “SSC / 5200” manufactured by Seiko Instruments Inc.) and in a nitrogen stream of 20 mL / min. The temperature is raised to 230 ° C., held at this temperature for 10 minutes, cooled to −10 ° C. at a temperature lowering rate of 10 ° C./min, and then heated to 210 ° C. at a temperature rising rate of 10 ° C./min. In the endothermic curve, the peak temperature showing the maximum endotherm was taken as the melting point.
(3) Dichroism measurement The visible part maximum absorption wavelength (λmax (nm)) and its absorbance were measured with reference to a PP sheet containing the dichroic dye treated in the same manner as the dyed sheet.
Dichroism was measured using a spectrophotometer CM-3600d manufactured by Konica Minolta.
The measurement procedure is as follows. 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 sheet is inserted on the detector side at a wavelength of 600 nm so that the vibration direction of the incident polarized light is perpendicular to the stretch axis, and the range of 800 nm to 400 nm is measured. Were inserted so as to be vertical, the absorbance (Ay, Az) of each was measured, and the dichroic ratio was calculated.
Next, another sample sheet is inserted into the sample side so that the vibration direction and the stretching axis are parallel, and the range of 800 nm to 400 nm is measured. Next, the second sample sheet is inserted with the vibration direction and the stretching axis. It inserted so that it might become parallel, and the transmittance | permeability was measured similarly. The dichroic ratio and the degree of polarization were calculated by the following equations.
Formula for calculating the dichroic ratio:
Dichroic ratio (D) = Ay / Az
Formula for calculating degree of polarization A = −log (T)
A: Absorbance T: Transmittance T = 10 ^(−A)
p: Degree of polarization (%)
p = [(Ty−Tz) / (Ty + Tz)] ^1/2 × 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

Example 1
[Create PP sheet]
The PP used was in the form of pellets, and was random with homo PP [1] (melting point = 160 ° C., MFR = 3 g / 10 min), homo PP [2] (melting point = 163 ° C., MFR = 8 g / 10 min), and ethylene. Copolypropylene (random PP [3]) (ethylene content = 4 mol%, melting point = 139 ° C., MFR = 7 g / 10 min).
Each of the above PP [1] to [3] was supplied to an extruder (90 mmφ extruder), heated and melted at 260 ° C., extruded from a T-shaped die, and each PP sheet was obtained while being cooled and solidified on a cooling roll. . The obtained PP sheet was colorless and transparent, and the thickness of the sheet was 300 μm.
[Dyeing PP sheet]
Each of the PP sheets [1] to [3] obtained above was dyed at 130 ° C. for 2 hours using a high-temperature and high-pressure dyeing machine (HCC-BS-1 manufactured by Sakurai Dyeing Machine Co., Ltd.). A dyed sheet was obtained. The staining solution was a thienothiazole group-containing azo dichroic dye R-1.

を１０％o.w.f.の濃度で水中に分散し、分散剤として、CIBA社製Irgasol NA を1％濃度になるように染色液に加えたものを用いた。得られた染色シートは、所定の色に着色された光透過性の良好なシートであった。
［染色シートの延伸］
上記で得られた染色シートを、それぞれ、島津製作所製 恒温槽付引張試験機（ＡＤ−５００）用い、１１０℃の温度、２００ｍｍ／ｍｉｎの延伸速度、延伸倍率４．５倍の条件で一軸延伸（テンター延伸法）することによって偏光板を作成した。得られた偏光板の二色性特性を表１に示す。

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 to a concentration of 1%. The obtained dyed sheet was a light-transmitting sheet colored in a predetermined color.
[Stretching of dyed sheet]
Each of the dyed sheets obtained above was uniaxially stretched under the conditions of a temperature test at 110 ° C., a stretch rate of 200 mm / min, and a stretch ratio of 4.5 times using a constant temperature bath tensile tester (AD-500) manufactured by Shimadzu Corporation. A polarizing plate was prepared by (tenter stretching method). Table 1 shows the dichroic characteristics of the obtained polarizing plate.

Example 2
A polarizing plate was prepared according to Example 1 except that the draw ratio shown in Table 2 was used instead of the draw ratio of 4.5 in Example 1. Table 2 shows the dichroic characteristics of the obtained polarizing plate including the results of Example 1.

Example 3
[Melt kneading of PP and dichroic dye]
70 g of the homo PP [2] pellets were preheated and kneaded at 200 ° C. for 3 minutes, and 7 mg of the dichroic dye R-1 was added thereto and kneaded for 10 minutes to obtain a dyed PP.
[Creation of dyed sheet]
Next, the dyed PP obtained here is filled into a 300 μm-thick tetragonal metal frame, its upper and lower sides are sandwiched with PTFE (polytetrafluoroethylene) film, and its upper and lower sides are sandwiched with a stainless steel plate. A dyed sheet was obtained by hot pressing from above and below with a hot plate. The hot press was hot pressed at 190 ° C. for 2 minutes. The obtained dyed sheet had a thickness of 300 μm and was a light-transmitting sheet colored in a predetermined color.
[Stretching of dyed sheet]
The dyed sheet obtained above was uniaxially stretched according to the method of Example 1 except for the temperature, and the influence of the uniaxial stretching temperature was examined. Table 3 shows the stretching temperature and the dichroic characteristics of the obtained polarizing plate.

  Since the polarizing plate obtained by the present invention can provide a relatively high degree of polarization as a hydrophobic PP polarizing plate while maintaining an excellent dichroic ratio, it has excellent durability (wet resistance and heat resistance). A polarizing plate can be provided.

Claims (5)

A method of manufacturing a polarizing plate,
(1) (a) a step of obtaining a dyed sheet by molding polypropylene into a sheet and then dyeing with a dichroic dye, or (b) a dyed sheet formed by kneading polypropylene and dichroic dye under heating. And (2) a step of stretching the dyed sheet, and a method for producing a polarizing plate,
The manufacturing method of a polarizing plate whose melt mass flow rate of this polypropylene exists in the range of 0.1-50 g / 10min.   The production method according to claim 1, wherein the polypropylene is a homopolymer of propylene or a random copolymer of propylene and another olefin.   The production method according to claim 1, wherein the stretching is uniaxial stretching.   The manufacturing method according to any one of claims 1 to 3, wherein the stretching is performed in a range of a stretching ratio of 2 to 20 times. The polarizing plate manufactured by the manufacturing method as described in any one of Claims 1-4.