JP2011150162A - Polarizing plate and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polarizing plate which is superior in durability, especially, in wetting resistance. <P>SOLUTION: A method for producing the polarizing plate includes a step (1) to obtain a sheet with a degree of molecular orientation of 100 or more, by stretching a polyethylene terephthalate sheet; and a step (2) to dye the stretched polyethylene terephthalate sheet with a dichroic dye mixture which constituting neutral gray. The polarizing plate obtained thereby is also disclosed. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a polarizing plate and a method for producing the same. The present invention relates to a yellow dichroic dye used for a polarizing plate. 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 molecular orientation during stretching. By uniaxially stretching a polyvinyl alcohol film on which iodine is adsorbed, iodine is molecularly oriented in the stretching direction, and a polarizing element layer having polarization performance is obtained.
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 excellent in durability, particularly wet resistance.

The present invention
(1) Stretching a polyethylene terephthalate sheet to obtain a sheet having a molecular orientation degree of 100 or more, and (2) Staining the stretched polyethylene terephthalate sheet with a dichroic dye mixture constituting neutral gray. And a polarizing plate having a molecular orientation of 100 or more obtained by the method.
The present invention also provides a yellow dichroic dye used for a polarizing plate.

  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.

  In the present invention, since a plurality of dichroic dyes are mixed and used so as to constitute a neutral gray, the entire visible light can be polarized. Therefore, since it can be used for a display, it is excellent in terms of practicality.

  The molecular orientation referred to in the present invention refers to a phenomenon in which linear molecules constituting PET are arranged in a certain direction. That is, it corresponds to the anisotropy of the PET sheet. It is known that the molecular orientation structure in PET affects various physical properties such as mechanical properties (film strength), heat shrinkage, electrical properties, and optical properties of sheets and films. This degree of molecular orientation is referred to as molecular orientation. In general, the degree of molecular orientation is measured by a microwave method, an X-ray diffraction method, an infrared dichroic method, a birefringence method, or the like.

  In the present invention, the degree of molecular orientation was measured by a microwave method. The instrument used is a microwave molecular orientation measuring instrument MOA-6015 manufactured by Oji Scientific Instruments. In the microwave method, a microwave cavity resonator is used for the measurement part, and the molecular orientation state is evaluated from the angular dependence of the microwave transmission intensity of the sample (Shigehiro Sugao, Chemistry and Industry, vol. 78, pp. 625 ( 2004)). The ratio of the major axis to the minor axis of the microwave resonance curve obtained by the measurement is referred to as molecular orientation and is abbreviated as MOR (Microwave Orientation Ratio). The molecular orientation after the thickness correction of the sample sheet is abbreviated as MOR-c. In the present invention, the value of molecular orientation (MOR-c) after thickness correction is used as the value of molecular orientation.

  To describe a more specific mode of measuring the degree of molecular orientation, a film to be measured is cut into a 3 cm square, set in a microwave molecular orientation degree measuring device, input the film thickness, and automatically measured. With the obtained data, the value of MOR-c is output and read.

In the present invention, the molecular orientation degree of the PET sheet may be 100 or more, preferably 130 or more, more preferably 150 or more. The upper limit of the degree of molecular orientation is not particularly limited, but is usually about 300, for example about 250.
A higher degree of molecular orientation of the PET sheet usually increases the orientation of the dichroic dye, and as a result, the degree of polarization of the PET sheet (or film) is expected to be improved.
On the other hand, if the molecular orientation of the PET sheet becomes extremely high, the crystallization rate may increase and the light transmission may decrease.
Moreover, when the degree of molecular orientation before dyeing is too high, the crystallinity of the PET sheet increases, so that it is difficult for the dichroic dye to permeate and the dyeability may deteriorate. In such a case, the degree of molecular orientation of the PET sheet before dyeing is suppressed to some extent, the degree of molecular orientation is further increased after dyeing, and as a result, the degree of molecular orientation of the finally obtained polarizing plate is 100 or more, preferably It can be 130 or more, more preferably 150 or more.

In the present invention, the molecular orientation degree of the PET sheet can be increased by the stretching step (1). The stretching step can be performed by a normal method using a normal stretching machine. As the stretching, uniaxial stretching and biaxial stretching are known, and any stretching method may be used as long as the desired degree of molecular orientation of the present invention can be obtained. From the viewpoint of obtaining a high degree of molecular orientation, uniaxial stretching is preferred. For example, a non-oriented PET sheet is uniaxially stretched at 65 ° C. with a uniaxial stretching machine.
The operating temperature (stretching temperature) in the stretching process may be arbitrarily selected from a range not exceeding the melting point of PET. The stretching temperature may usually be in the range of 50-100 ° C, for example 55-80 ° C.
The operation time of the stretching process (stretching time) can also vary depending on the stretching temperature. When the stretching temperature is low, a longer stretching time is required to obtain the desired molecular orientation, and when the stretching temperature is high, the stretching time for obtaining the desired molecular orientation may be shorter. Accordingly, the appropriate stretching time may vary depending on the stretching temperature, economic efficiency, and the like, but may usually be in the range of 1 minute to 60 minutes, for example, 5 minutes to 30 minutes.

In the present invention, the stretching step (1) is either (i) only before the dyeing step (2), (b) only after the dyeing step (2), or (c) both before and after the dyeing step (2). Can be done.
In addition to the economic merit that the stretching operation only needs to be performed once in the method (a), since the molecular orientation of the PET sheet is increased before dyeing, the dye molecules can be easily arranged at the time of dyeing. This is a preferable method since it also increases and as a result good polarization is obtained.
The method (b) also has the economic advantage that only one stretching operation is required, but the dyeability may be insufficient because a sufficient arrangement of dye molecules cannot be obtained at the time of dyeing. Although the degree of molecular orientation of the PET molecules is increased by the stretching operation after dyeing, the alignment of the dye molecules is often not improved, and as a result, the desired polarization property may not be obtained.
The method (c) is accompanied by an increase in the number of steps that require two stretching operations and economic disadvantages, while the arrangement of the dye molecules can be adjusted by appropriately adjusting the molecular orientation of the PET before and after dyeing. The desired polarization property can be obtained while maintaining good dyeability.
Which method (a) to (c) is selected can be easily determined by those skilled in the art in consideration of the above-described elements, but the methods (a) and (c) are preferable.

In the method of the present invention, the PET sheet may be colorless and transparent. PET is thermoplastic and is preferably amorphous.
The colorless and transparent PET 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 PET sheet is obtained by molding PET into a sheet. Various molding methods can be used as the molding method. For example, an extrusion molding method can be used. The thickness of the sheet may generally be 0.1-5 mm, for example 0.2-1 mm.

In the step (1), the formed sheet is stretched. Regarding the stretching conditions, the temperature is usually in the range of 50 to 100 ° C., preferably 55 to 80 ° C. as described above, and the pressure may be 0.1 to 10 atm, for example 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, For example, it is 3 to 5 times, and the draw ratio after the dyeing step (2) may be usually 1.3 to 5 times, for example, 1.4 to 3 times. When the stretching step (1) is performed before and after the dyeing step (2), the crystallinity of the PET sheet (accordingly, Tg) with the increase in the degree of molecular orientation of the PET sheet by the stretching step before dyeing. The temperature after stretching (referred to as “re-stretching”) after the dyeing step (2) is 100 ° C. or higher, preferably 130 ° C. or higher, more preferably 160 ° C. to 200 °. The temperature may be about 0C. The stretching before and after the dyeing step (2) is preferably uniaxial stretching in the same direction.

  In step (2), the stretched sheet is dyed with a neutral gray color mixture composed of a mixture of dichroic dyes. That is, the dichroic dye is impregnated into the PET sheet. Dyeing can be performed by immersing PET in a dichroic dye dispersion. In dyeing, the pressure may be 1 to 100 atmospheres, such as 10 to 80 atmospheres, and the temperature may be 70 to 150 ° C., such as 100 to 140 ° C. The concentration of the neutral gray color mixture dispersion composed of a mixture of dichroic dyes (weight ratio of the dye to the dispersion) is generally 0.1 to 30% by weight, for example 1 to 20% by weight. It's okay. The concentration of the neutral gray mixture consisting of a mixture of dichroic dyes (on weight of fiber) (% by weight of the dye to the sheet) is generally 0.1 to 30% by weight, for example 2 to 10% by weight. It may be. 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 dye dispersion, a dispersant may be present to promote the dispersion of the dye. The dispersant may generally be a surfactant, such as a nonionic or ionic (cationic or anionic) surfactant.

  The PET sheet may contain a weather resistance 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.

  The dyeing step (2) of the present invention can be performed by immersing a PET sheet in a dispersion of a neutral gray color mixture composed of a mixture of dichroic dyes. The dyeing step (2) is preferably performed using a rotary high-pressure dyeing machine or a jigger dyeing machine.

  The dichroic dye used in the present invention may be any one as long as they are mixed to become neutral gray. A dichroic dye that does not contain a hydrophilic group such as a carboxyl group or a sulfonic acid group is preferred. For example, it may be an azo dye. The number of azo groups may be 2 (ie diazo) or 3 (ie triazo). An aryl group (for example, a benzene ring or a naphthalene ring) or a stilbene group may be present between the azo group and the azo group. A benzothiazole group or a thienothiazole group may be present at one end. A dialkylaminophenyl group having 1 to 6 carbon atoms, particularly a diethylaminophenyl group, anisole group, hydroxyphenyl group or phenyl group may be present at the other end. In the present invention, groups (for example, anisole group and benzene ring) may or may not be substituted.

  The dichroic dye mixture of the present invention is mixed so as to constitute a neutral gray by mixing them. Normally, neutral gray has three colors, magenta or red dichroic dye, cyan or blue dichroic dye, and yellow dichroic dye. It can be obtained by subtractive color mixing so that both are in the vicinity of 0.31.

  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 found by the present inventors.

（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.)

  That is, the present invention also provides a yellow dye of formula Y-08.

（式中、Ｒ^７およびＲ^８は前記と同義である。）。

(Wherein R ⁷ and R ⁸ are as defined above).

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

If the specific example of the combination of the preferable dichroic dye which comprises neutral gray in this invention is given, for example,
Magenta dye of formula R-02

（式中、Ｒ^１〜Ｒ^３は上記と同義。）、
式Ｂ−０７のブルー色素

(Wherein R ^{1 to} R ³ are as defined above),
Blue dye of formula B-07

（式中、Ｒ⁴〜Ｒ⁶は上記と同義。）および
式Ｙ−０８のイエロー色素

(Wherein R ^{4 to} R ⁶ are as defined above) and a yellow dye of formula Y-08

（式中、Ｒ^７およびＲ^８は上記と同義。）からなる混合物が挙げられる。

(Wherein, R ⁷ and R ⁸ are as defined above).

More preferable combinations constituting neutral gray are, for example,
Magenta dye of formula R-2

式Ｂ−７のブルー色素

Blue dye of formula B-7

および
式Ｙ−８のイエロー色素

And a yellow dye of formula Y-8

からなる混合物が挙げられる。

The mixture which consists of is mentioned.

The synthesis of the dichroic dye used in the present invention can be carried out by a usual method. For example, the method described in Japanese Patent Application Laid-Open No. 60-228568 can be used.
Among the yellow dichroic dyes, for example, the Y-8 yellow dye found by the present inventors 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.

  The polarizing plate obtained in the present invention may have a degree of molecular orientation of 100 or more, preferably 130 or more, more preferably 150 or more. The upper limit of the degree of molecular orientation is not particularly limited, but is usually about 300, for example about 250. Since the polarizing plate obtained by the present invention uses a neutral gray dye and can polarize the entire visible light, it can be used for, for example, a display. Moreover, a high degree of polarization, for example, 90% or more, and further 99% or more can be exhibited. The polarizing plate obtained by 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. In the examples, the following experimental methods were used.

Preparation of Sample Sheet The used PET sheet is a commercially available PET sheet having a thickness of 500 μm and a specific gravity of 1.27.

Stretching method The PET sheet was stretched at a predetermined temperature for a predetermined time using a stretching machine (SS-70 type machine manufactured by Shibayama Kagaku Kikai Seisakusho). Stretching was uniaxial stretching.

The dyeing method sheet was dyed at 130 ° C. for 2 hours using a high-temperature high-pressure dyeing machine (HCC-BS-1 manufactured by Sakurai Dyeing Machine Co., Ltd.). As the staining solution, a neutral gray pigment mixture 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%.

After the dichroic measurement , the same treatment as that of the dyed sheet was performed, and the maximum absorption wavelength of the visible region and the absorbance thereof were measured using a film containing no dichroic dye as a reference.
Dichroism was measured using a spectrophotometer CM-3600d manufactured by Konica Minolta.
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 800 nm to 400 nm is measured, and then the vibration direction of the incident polarized light is perpendicular to the stretch axis. And the absorbance of each was measured, and the dichroic ratio was calculated.
Next, insert another sample sheet into the sample side so that the vibration direction and the stretching axis are parallel, measure 800 nm to 400 nm, and then place the second sample sheet 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)] ^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
Using a commercially available amorphous PET sheet, the film was uniaxially stretched 6 times at 65 ° C. for 5 minutes. A PET sheet having a molecular orientation of 124 was obtained.
Using this PET sheet, the re-stretching effect on the degree of molecular orientation was examined with respect to the stretching temperature and time factors. The obtained results are shown in Table 1.

Example 2
B-7 as the blue dichroic dye, R-2 as the magenta dichroic dye, and Y-8 obtained in Example 4 as the yellow dichroic dye are selected as a chloroform solution, and the color mixture ratio to the neutral gray system Was confirmed. The obtained results are shown in Table 2.

この結果より、色素B-7、R-2、Y-8の混合液を用いる混色で、x, y値がそれぞれ０．３１付近となるニュートラルグレー系色調が得られることが確認できた。

From this result, it was confirmed that a neutral gray color tone having x and y values of around 0.31 was obtained by color mixing using a mixture of the dyes B-7, R-2, and Y-8.

Example 3
Using the PET sheet having a molecular orientation of 124 obtained in Example 1 and referring to the result of Example 2, dyeing with a neutral gray dye by an aqueous dispersion of a dichroic dye mixture was performed. Dyeing was performed at 120 ° C. for 2 hours using a high-temperature high-pressure dyeing machine (HCC-BS-1 manufactured by Sakurai Dyeing Machine Co., Ltd.). After dyeing, it was dried in a desiccator for 24 hours to obtain a polarizing plate (polarizing sheet). The molecular orientation degree of the obtained polarizing plate was almost the same as that before dyeing. The optical properties of the obtained polarizing plate were measured, and the results shown in Table 3 were obtained. The degree of polarization is determined by polarizing the incident light with a commercially available polarizing film and setting the transmittance at that time as 100%, and the total light transmittance (Y / /) And the total light transmittance (Y⊥) in the vertical direction were measured and calculated from the following formula based on the measured values.
Polarization degree (%) = [(Y // − Y⊥) / (Y // + Y⊥)] ^1/2 * 100

  From Table 3, a high degree of polarization of 99% was obtained with the neutral gray polarizing sheet of No. G.

Example 4 (Synthesis of Yellow Dye Y-8)
In a 100 ml four-necked flask, 0.45 g (0.0016 mol) of 4,4-diaminostilbene, 1.40 g of concentrated hydrochloric acid and 1.48 g of water are stirred for 10 minutes at 0-5 ° C, and 0.23 g (0.0034 mol) of sodium nitrite is 30% An aqueous solution was added at once and stirred for 1 hour to obtain a tetrazo solution. In a solution of 0.03 g of sodium hydroxide and 0.23 g of sodium carbonate dissolved in 2.1 g of water, 0.33 g (0.035 mol) of phenol was dissolved while cooling, and tetrazo solution was added dropwise to the phenol solution over 10 minutes. g was added dropwise to a 40% aqueous solution over 1 hour, and the mixture was stirred overnight at room temperature.
Concentrated hydrochloric acid (0.38 g) was added, and the mixture was stirred at 70 ° C. for 1 hour, cooled to room temperature, and filtered. The solid obtained by washing the filtrate with water is dried, dissolved in 50 ml of methanol and filtered again. The filtrate is concentrated and vacuum dried at 90 ° C. to obtain 0.58 g (crude crude solid). Yield 86.9%).
This solid was purified by silica gel column chromatography using an acetone / toluene (20:80) mixed solvent as an eluent to obtain 120 mg of yellow crystals.
The results of IR absorption spectrum analysis of this crystal were as follows.
IR (KBr) / cm < ^-1 >; 3272,1591,1377,1248,968,849.
From this result, it was confirmed that the both-end hydroxyl group type yellow dye Y-8 was produced.

  According to the present invention, a polarizing plate (or a polarizing sheet or a polarizing film) having durability (wet resistance and heat resistance) is obtained using a neutral gray dye that is a mixture of a plurality of dichroic dyes. It is done. Since the present polarizing plate can polarize the entire visible light, it is useful for various applications, particularly for liquid crystal displays.

Claims (9)

(1) stretching a polyethylene terephthalate sheet to obtain a sheet having a molecular orientation degree of 100 or more, and (2) dyeing the polyethylene terephthalate sheet with a dichroic dye mixture constituting neutral gray. The manufacturing method of the polarizing plate characterized by the above-mentioned. The production method according to claim 1, wherein the stretching is uniaxial stretching. The production method 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 a polyethylene terephthalate sheet 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 production method according to any one of claims 1 to 5, wherein the dichroic dye mixture comprises an azo dye. The dichroic dye mixture is
Magenta dye of formula R-02

(Wherein R ^{1 to} R ³ each independently represents an alkyl group having 1 to 6 carbon atoms),
Blue dye of formula B-07

(Wherein R ^{4 to} R ⁶ each independently represents an alkyl group having 1 to 6 carbon atoms) and a yellow dye of the formula Y-08

(In formula, R < ⁷ > and R < ⁸ > represents a hydrogen atom or a C1-C6 alkyl group each independently.), The manufacturing method in any one of Claims 1-6. A polarizing plate having a molecular orientation degree of 100 or more produced by the production method according to claim 1. Formula Y-08

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