JP3218049B2 - Method for producing transparent film having birefringence - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transparent film having birefringence, and more particularly, to the production of a transparent film mainly composed of an amorphous aromatic polyester having little change over time and a uniform birefringence. It is about the method.

[0002]

2. Description of the Related Art In recent years, as an optical film used in the field of optoelectronics, a film having birefringence and extremely high transparency has been required. There is a phase difference plate or the like used for an STN liquid crystal display device.

[0003]

Problems to be Solved by the Invention
FIG. 4 shows a birefringent film using an aromatic polyester as a base film. However, such a film is not always sufficient in terms of uniform birefringence in the same plane, and has problems in terms of stable productivity.

[0004]

Means for Solving the Problems In view of such circumstances, the present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have found that deformation due to heating and change in birefringence are small and uniform birefringence in the same plane. The present inventors have found that a film having properties can be stably provided, and arrived at the present invention.

That is, the present invention provides an amorphous aromatic polyester film in a temperature range of 30 ° C. higher than Tg (glass transition temperature) of the amorphous aromatic polyester to 60 ° C. higher than Tg by 10 to 1000% / The birefringence is 0.0001 to 0.1 and the variation of the birefringence in the same plane is 5% or less by uniaxially stretching to a stretching ratio of 1.05 to 5.00 at a stretching speed of min. A method for producing a transparent film having a birefringence, characterized by obtaining a transparent film.

The aromatic polyester used in the present invention is not particularly limited. However, from the viewpoint of obtaining raw materials, terephthalic acid alone or isophthalic acid alone, or a mixture of terephthalic acid and isophthalic acid and a divalent compound represented by the following general formula: An aromatic polyester comprising a phenol component is desirable.

[0007]

Embedded image

Wherein R ¹ and R ² are an alkyl group having 1 to 4 carbon atoms, a halogen group, a halogenated hydrocarbon group, p and q are integers of 1 to 4, X is a direct bond, an alkylene group, an alkylidene group. Groups (one or more of the hydrogen atoms in the alkylene group or alkylidene group may be substituted with a hydrocarbon group, a halogen group, or a halogenated hydrocarbon group), -O-,-
S -, - SO -, - SO 2 -, - shows a CO-. ]

Specific examples of the dihydric phenol used in the present invention include 2,2'-bis (4-hydroxyphenyl) propane and 4,4 '-(α-methylbenzylidene).
Bisphenol, bis (4-hydroxyphenyl) methane, 2,2'-bis (4-hydroxyphenyl) butane, 3,3'-bis (4-hydroxyphenyl) pentane, 4,4'-bis (4-hydroxyphenyl ) Heptane, 4,4'-bis (4-hydroxyphenyl) 2,5
-Dimethylheptane, bis (4-hydroxyphenyl)
Methylphenylmethane, bis (4-hydroxyphenyl) diphenylmethane, 2,2′-bis (4-hydroxyphenyl) octane, bis (4-hydroxyphenyl) -4-fluorophenylmethane, bis (3,5-dimethyl-4) (Hydroxyphenyl) methane, 2,2'-bis (3,5-dimethyl-4-hydroxyphenyl) propane, bis (3,5-dimethyl-4-hydroxyphenyl) phenylethane, bis (3-methyl-4-hydroxyphenyl) ) Diphenylmethane, bis (3,5-dimethyl-4hydroxyphenyl) sulfone and the like, and these can be used alone or as a mixture, but are not limited thereto.

[0010] Transparent films having birefringence may be processed at high temperatures in the processing process when applied. Aromatic polyesters are suitable because they have excellent transparency, high heat resistance, little change in heating, and little change in birefringence with time after birefringence is imparted by stretching.

Films made of these polymers can be obtained by extrusion molding or casting from a solution in which the polymer is dissolved in a solvent. However, since film thickness unevenness and poor surface properties cause stretching unevenness, a film formed by casting is preferable. It is. The thickness of the film is usually several μm to several hundred μm, more preferably 10 to 30 μm.
0 μm.

These films rarely show birefringence as they are, especially when obtained by casting. Even in the case of extrusion molding, the birefringence is not so high unless strong tension is applied in the machine direction in the film forming process. As a means for imparting higher birefringence to these films, there is a method of stretching in a uniaxial direction, a method of stretching in a biaxial direction, and giving a difference in the degree of biaxial stretching.

In order to obtain a transparent film having a uniform birefringence in the same plane according to the present invention, the film is uniaxially stretched at a temperature 30 ° C. higher than Tg to 60 ° C. higher than Tg. As the stretching temperature increases, the birefringence decreases. The birefringence increases as the stretching magnification increases, and stretching immediately before the film breaks gives the largest birefringence. Another important factor in the stretching conditions is the stretching speed. In the case of the same stretching temperature, the birefringence increases as the stretching speed increases. The stretching ratio for obtaining a uniform birefringence is 1.05 to 5.0.
0 times, preferably 1.10 to 3.00 times, and the stretching speed is 10 to 1000% / min, preferably 10 to 300% / min.
min.

Thus, the birefringence (difference Δn in the in-plane perpendicular direction measured by a polarization microscope or ellipsometry method) is 0.0001 to 1.0,
More preferably, a film of 0.0005 to 0.05 is obtained. Further, although the transparency varies depending on the thickness of the film, a film having a total light transmittance of 50% or more, more preferably 60% or more, and still more preferably 80% or more is obtained. Further, the transparent film of the present invention may have a normal transparent hard coat layer on one or both sides for the purpose of surface protection, or may have a gas barrier layer.

[0015]

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

Example 1 A: Synthesis of amorphous aromatic polyester 5 mmol of 2,2-bis (4-hydroxyphenyl) propane and 5 mmol of bis (3,5-dimethyl-4-hydroxyphenyl) methane 0.8 mmol of para-t-butylphenol was dissolved in 20 ml of 1.25N sodium hydroxide. Terephthalic acid chloride 1
A solution of 0.4 mmol and 0.1 mmol of trioctylmethylammonium chloride (phase transfer catalyst) in 20 ml of orthodichlorobenzene was added, and the mixture was reacted at room temperature for 3 hours while stirring. After decanting the aqueous layer of the reaction mixture, the same amount of water was added to the organic layer and neutralized with a small amount of hydrochloric acid. Further, the organic layer was washed with water five times and then poured into a large amount of methanol to precipitate a solid aromatic polyester. The yield of the obtained polyester is about 10
It was 0%. The Tg of the obtained polyester is 2
At 50 ° C., the molecular weight (reduced viscosity) is ηsp / c = 0.60
(32 ° C., 0.32 g / dl in chloroform).

B: Preparation of Film The polymer obtained as described above was dissolved in methylene chloride to a concentration of 15% by weight, and the solution was cast on a SUS plate and heated on a hot plate. Heating condition is 50 ° C
For 20 minutes, then 100 ° C. for 20 minutes, and 150 ° C. for 2 minutes.
Heat fix at 250 ° C. for 10 minutes for 0 minute, about 100 μm
A thick film was obtained. 11cm x 11cm from this film
Of the sample, using a biaxial stretching test apparatus (manufactured by Toyo Seiki Seisaku-sho, Ltd., X4HD-HT), gripping the four sides of the sample and stretching at a rate of 1.0 in one direction at 290 ° C. (= Tg + 40 ° C.).
The film was stretched at a stretching ratio of 1.75 times at cm / min (= 10% / min) and cooled to room temperature. When the birefringence at 64 points was measured at an interval of 1 cm for the central portion of 8 cm × 8 cm of the stretched film, the average value was 0.00614 (Re = 3).
50 nm, thickness 57 μm), and the variation R is 0.000.
31 (5%). The total light transmittance is 90% and the haze is 0.2% (ASTM D 100
3). The birefringence index was measured by measuring the retardation at a measurement wavelength of 550 nm by the Senarmont method using a polarizing microscope at each of the 64 measurement points, measuring the film thickness with a precision dial gauge, and measuring each of the measurement points. Is calculated by (retardation at each measurement point / thickness at each measurement point), and the birefringence variation R
Was determined from the measurement data at 64 points by [(maximum value of birefringence index−minimum value of birefringence index) / average value of birefringence index].
When this film was stored at 120 ° C. for one month, no change was observed in the above physical properties.

Examples 2-3, Comparative Examples 1-2 A: Synthesis of amorphous aromatic polyester 2,2-bis (4-hydroxyphenyl) propane 2
0.11 g, bis (3,5-dimethyl-4-hydroxyphenyl) methane 15.06 g, para-t-butylphenol 0.95 g, sodium hydrosulfite 0.26 g, 5N-NaOH aqueous solution 78.2 ml, water 17
6.8 ml of the mixture was mixed in a 300 ml eggplant type flask in a nitrogen atmosphere, and cooled to 5 ° C. to prepare an alkaline aqueous solution of a dihydric phenol. On the other hand, terephthalic acid chloride 21.
32 g of isophthalic acid chloride and 9.14 g of isophthalic acid chloride were dissolved in 255 ml of methylene chloride in another 300 ml eggplant type flask under a nitrogen atmosphere and cooled to 5 ° C. 137 ml of water and 0.16 g of benzyltributylammonium chloride as a catalyst were charged in a 1-liter separable flask under a nitrogen atmosphere, and cooled in the same manner. While stirring this vigorously, the above two liquids were simultaneously added continuously by a pump over 10 minutes. Two hours after the completion of the addition, 0.42 g of benzoyl chloride was dissolved in 5 ml of methylene chloride, and the solution was added thereto. After 20 minutes, stirring was stopped. After decanting the aqueous layer, the same amount of water was added and neutralized with a small amount of hydrochloric acid while stirring. After repeated decanting and desalting by water washing, 300 ml of methylene chloride was added for dilution, and this solution was heated to 40 to 50 ° C., and the water in the methylene chloride was removed by azeotropic dehydration with methylene chloride to remove the polymer. 1
The methylene chloride was distilled to 5% by weight. The Tg of the obtained polymer was 215 ° C., and the molecular weight (reduced viscosity) was η.
sp / c = 0.90 (0.32 in chloroform at 32 ° C.)
g / dl).

B: Preparation of Film A methylene chloride solution of the polymer obtained as described above was cast on a SUS plate and heated on a hot plate.
The heating conditions are 50 ° C. for 20 minutes, then 100 ° C. for 20 minutes.
Heat fixing at 150 ° C. for 20 minutes and 250 ° C. for 10 minutes to obtain a film having a thickness of about 100 μm. An 11 cm × 11 cm sample was prepared from this film and stretched in the same manner as in Example 1 under the four conditions shown in Table 1. The central portion of the obtained stretched film was 8 cm × 8 cm and was spaced at 1 cm intervals.
When the birefringence of a point was measured, the average value and the variation R
Was as shown in Table 1. The total light transmittance is 90
%, Haze is 0.2% (ASTM D 1
003). In addition, this film was heated at 120 ° C for 1 hour.
After storage for months, no change was observed in the above physical properties.

[0020]

[Table 1]

Example 4 A: Synthesis of amorphous aromatic polyester 30.45 g of 4,4 '-(α-methylbenzylidene) bisphenol, 1.58 of para-t-butylphenol
g, sodium hydrosulfite 0.53 g, 5N
-153 ml of an aqueous NaOH solution and 361 ml of water are mixed in a 1.5-liter separable flask in a nitrogen atmosphere,
By cooling to 5 ° C., an aqueous alkaline solution of dihydric phenol was prepared. On the other hand, 30.45 g of terephthalic acid chloride and 30.45 g of isophthalic acid chloride were mixed with 50 ml of methylene chloride.
0 ml was dissolved in another 1 liter flask under a nitrogen atmosphere and cooled to 5 ° C. 200 ml of water and 0.31 g of benzyltributylammonium chloride as a catalyst were charged in a 1-liter separable flask under a nitrogen atmosphere and cooled in the same manner. While stirring this vigorously, the above two liquids were simultaneously added continuously by a pump over 10 minutes. Two hours after the completion of the addition, 0.42 g of benzoyl chloride was dissolved in 5 ml of methylene chloride, and the solution was added thereto. After 20 minutes, stirring was stopped. After decanting the aqueous layer, the same amount of water was added and neutralized with a small amount of hydrochloric acid while stirring. After repeated desalting and desalting by washing with water, 300 ml of methylene chloride was added to dilute the solution, and this solution was diluted with 40 to 50 ml.
C. and water was removed from the polymer methylene chloride by azeotropic dehydration with methylene chloride, and methylene chloride was distilled until the polymer concentration became 15% by weight. The Tg of the obtained polymer was 240 ° C., and the molecular weight (reduced viscosity) was ηsp / c =
0.80 (32 C, 0.32 g / dl in chloroform).

B: Preparation of film A methylene chloride solution of the polymer obtained as described above was cast on a SUS plate and allowed to stand at room temperature for 1 hour and at 150 ° C. for 15 hours.
And heat-setting at 250 ° C. for 10 minutes to obtain a film having a thickness of about 100 μm. An 11 cm × 11 cm sample was prepared from this film, stretched under the following stretching conditions in the same manner as in Examples 1 and 2, and cooled to room temperature. Stretching temperature: 270 ° C. (= Tg + 30 ° C.) Stretching speed: 10 cm / min (= 100% / min) Stretching ratio: 2.25 times Birefringence index at 64 points at 1 cm intervals for the central portion 8 cm × 8 cm of the stretched film. Was measured, the average value was 0.1.
00720 (Re = 600 nm, thickness 83 μm),
The variation R was 0.00036 (5%). The total light transmittance is 90%, and the haze is 0.2%.
(ASTM D 1003). When this film was stored at 150 ° C. for one month, no change was observed in the above physical properties.

[0023]

As described above, according to the present invention, a plastic film having uniform birefringence in the same plane and high transparency can be provided.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-1-270004 (JP, A) JP-A-1-201607 (JP, A) JP-A-1-201608 (JP, A) JP-A-56- 130703 (JP, A) JP-A-1-127329 (JP, A) JP-A-3-122602 (JP, A) JP-A-3-155502 (JP, A) (58) Fields investigated (Int. ⁷ , DB name) G02B 5/30

Claims (1)

(57) [Claims] 1. A stretching rate of 10 to 1000% / min for an amorphous aromatic polyester film in a temperature range of 30 ° C. higher than Tg (glass transition temperature) of the amorphous aromatic polyester to 60 ° C. higher than Tg. Stretch ratio 1.
It is characterized in that a birefringent film having a birefringence of 0.0001 to 0.1 and a variation of the birefringence in the same plane of 5% or less is obtained by uniaxially stretching the film to a magnification of 05 to 5.00 times. A method for producing a transparent film having a birefringence.