JP3370383B2 - Heat-resistant transparent film and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a heat-resistant transparent film which is made of an amorphous polymer having an aromatic group in its main chain and which is suitable for optical use and has excellent thickness accuracy.

[0002]

2. Description of the Related Art With the rapid progress of electronics technology, a large area called so-called giant microelectronics has been rapidly expanded centering on liquid crystal display devices, and it is possible to easily increase the area. Taking advantage of this, the expansion of optical applications of polymer films such as polarizing films, retardation films and transparent conductive films is remarkable. Polymer materials used for these purposes are selected from the viewpoint of long-term reliability such as heat resistance or humidity resistance when incorporated in equipment, and are widely known to polyester, polycarbonate, polysulfone, polyether sulfone, etc. The heat-resistant polymer material is used. However, since films made of these materials are formed by the melt extrusion method, defects such as die lines inevitably occur, and optical anisotropy due to molecular orientation is likely to occur, and film formation accuracy with respect to the film thickness. Has the drawback of being large.

On the other hand, when used for optical purposes, the optical properties of the film include the properties of the film itself,
Since the thickness has a great influence, the demands for not only the transparency of the film but also the uniformity of the thickness are becoming more severe. Therefore, the film that was initially supplied by the melt extrusion method has the characteristics that it is easy to obtain a film with little optical anisotropy and that the variation in thickness can be suppressed to a low level. Is being replaced by the film When a polymer material having high heat resistance is used, the solvent casting method is preferable also from the viewpoint of heat deterioration of the material, and a polymer having a glass transition point of 180 ° C. or higher such as polyarylate can be suitably used.

Further, in recent years, a large-sized display element using a super twisted twisted nematic (STN) type liquid crystal has attracted attention,
Widely used as a display element for personal computers and word processors. In order to correct undesired coloring due to the birefringence of the display element, the use of a retardation plate has spread, and in particular, a polymer film has been widely used. The polymer film is
It is a transparent film having birefringence obtained by uniaxially stretching an optically isotropic polymer film formed by a solvent casting method, and plays a role of compensating for retardation in a liquid crystal element. However, as the required display quality becomes higher, in-plane dispersion of the retardation due to minute unevenness of birefringence of the film and minute unevenness of the thickness of the film causes unevenness in the compensation performance. It has been pointed out that the image quality of the display element is deteriorated, and a retardation film with more improved retardation unevenness is required.

[0005]

However, in the case of a casting film made of a heat-resistant polymer for optical use, the average height between adjacent ridges and valleys (thickness in the vicinity depends on the casting method and conditions). Change) is about 1% of the average film thickness. On the other hand, the thickness accuracy required from the optical characteristics is required to be higher, and it is the current situation that it has not reached a sufficient level. In addition, in particular, at present, there is no retardation film which can sufficiently satisfy the demand for reducing the retardation unevenness due to colorization. The present invention provides a method for producing a heat-resistant transparent film having excellent thickness accuracy and a method for producing a retardation film having improved retardation unevenness.

[0006]

The inventors of the present invention have conducted extensive studies in order to achieve the above-mentioned object in view of the above-mentioned circumstances, and as a result, a surface conditioner comprising a silicon compound in a dope for casting comprising an amorphous polymer. It was found that the heat-resistant transparent film for optics having a significantly improved thickness accuracy can be obtained by adding in advance. That is, the first aspect of the present invention is that when a heat-resistant transparent film made of an amorphous polymer having an aromatic group in its main chain is formed by a solution casting method, a surface conditioner made of a silicon compound is added to a dope for casting. A second method of the present invention is to uniaxially stretch the heat-resistant transparent film obtained above, which is characterized by adding a heat-resistant transparent film for optics (excluding the film for electrophotographic photoreceptors). The content of each of the methods of producing the characteristic retardation film is described. In the present invention, the “change in thickness in the vicinity” refers to peaks and valleys (concavities and convexities) having a height difference of 0.04 μm or more, and refers to the average height between adjacent peaks and valleys.

The polymer material used in the present invention is a substantially amorphous heat-resistant polymer having an aromatic group in the main chain, such as polycarbonate, polyarylate, polyester, polysulfone, and polyethersulfone. Further, it may be a blend or alloy of the polymer materials having high compatibility.

In particular, the following general formula

[0009]

[Chemical 2]

(In the formula, X is a substituted or unsubstituted divalent hydrocarbon group having 1 to 10 carbon atoms, and R ₁ and R ₂ are ₁ to ₂ carbon atoms.
A monovalent group selected from the group consisting of 0, alkyl, allyl, aralkyl, alkoxyl, aryloxyl and allylalkoxyl groups, substituents thereof, halogen and mixtures thereof, p,
q is an integer of p + q = 1 to 8, m, n, r, and s are 0 or 1, provided that n ≠ 0 when m = 1, s ≠ 0 when r = 1, and (I) and (II) The molar ratio is (I) / (I) + (II) =
Polyarylate represented by 1 to 0) is preferable. The details are described in JP-A No. 50-13491.

As the solvent used in the present invention, any solvent can be used without limitation as long as it can uniformly dissolve the polymer material and the surface conditioner. Generally, ketones such as acetone, esters such as ethyl acetate, halogenated olefins such as trichloromethane and dichloromethane,
Amides such as dimethylacetamide and dimethylformamide are used. Further, a plurality of mixed solvents may be used as the solvent. Casting dope may require the addition of stabilizers to increase the thermal stability during drying, and as used in solvent casting methods such as cellulose acetate, phthalates, phosphates and glycols may be used. It may contain a plasticizer such as ester.

In the present invention, it is necessary to allow the surface modifier to be present in the dope obtained by dissolving the polymer material in the solvent. Surface modifiers are widely used for adjusting the coating surface when applying various coating agents.Acrylic, fluorine, and silicon surface modifiers are used as well as olefinic surfactants. It is used according to the purpose. In addition to the effect of improving the thickness accuracy, from the viewpoint of dope and dispersibility in the obtained film, the surface modifier is preferably a silicon compound, more preferably a compound having a dimethylpolysiloxane skeleton, and modified with a polyester residue. The polydimethylsiloxane-based surface conditioner is particularly effective. The polyester residue may have an aromatic residue such as a benzene ring or a polar group such as a hydroxyl group or a carboxyl group. The general formulas of typical polydimethylsiloxane surface conditioners are shown below.

[0013]

[Chemical 3]

However, R ₃ = -R ₄ -O-CO-R ₅ -C
O—O—R ₆ —O—R ₇ —Y, and R ₄ , R ₅ ,
R ₆ and R ₇ are selected from substituted or unsubstituted alkylene groups, arylene groups and araalkylene groups, and Y is selected from hydrogen or polar groups such as hydroxyl groups, carboxyl groups and amino groups. V is an integer of 0 to 100 and W is an integer of 1 to 100. When the surface modifier is used, a remarkable improving effect is obtained particularly for a film of polycarbonate and polyarylate. Excessive use of the surface conditioner does not improve the thickness accuracy, while excessive use causes cloudiness of the dope depending on the solvent used and also reduces the haze of the obtained film. Generally, it is selected from the range of 0.1 to 5 parts by weight with respect to 100 parts by weight of the polymer material, but the surface conditioner may be present on the surface immediately after the casting of the dope and the saturation of the surface conditioner. It is preferably used near the surface adsorption amount. The surface conditioner added to the dope may be used alone or in combination of two or more, or may contain a solvent.

In order to maintain good thickness accuracy, it is important to optimize the casting conditions according to the equipment used.
Optimum values for the dope concentration, viscosity, line speed, etc. are determined according to the type and molecular weight of the material. As the industrial solvent casting method, a known method such as casting on an endless belt or a drum type film forming apparatus can be applied. The film cast and dried until it is self-supporting is peeled off and post-dried in the vicinity of the glass transition point in order to completely dry the residual solvent and finely adjust the optical properties.

The heat-resistant transparent film for optics obtained by the production method of the present invention has an average thickness of preferably 20 to 200 μm, more preferably 40 to 120 μm. The optimum thickness is determined by the application used. Further, the average height (change in thickness in the vicinity) between adjacent peaks and valleys of the thickness pattern of the film is preferably 0.5% or less of the average thickness of the film. The heat-resistant transparent film for optics obtained by the production method of the present invention can be subjected to general film secondary processing such as adhesion processing and hard coating processing, if necessary. In particular, when used as a retardation film having optical anisotropy by heat drawing, the thickness accuracy of the film obtained by the production method of the present invention is extremely useful because it improves birefringence unevenness after drawing. . That is, the birefringence unevenness appears as color unevenness when it is used as a retardation film, but a sharp birefringence unevenness particularly in an adjacent portion has a high visibility and becomes a problem. The heat-resistant transparent film for optics obtained by the production method of the present invention has a particularly improved average height between adjacent ridges and valleys (change in thickness in the vicinity) of the thickness pattern. The improvement effect is extremely large.

[0017]

The present invention will be described in more detail below with reference to examples, but the present invention is not limited thereto.
The "change in thickness in the vicinity", which represents the film thickness and the thickness accuracy in the examples, was analyzed by loading a measurement signal of a stylus-type continuous film thickness meter into a computer. In addition, “change in thickness in the vicinity” is 0.04 based on the measured thickness pattern.
The peaks and valleys (unevenness) having a height difference of not less than μm were targeted, and the average height between adjacent peaks and valleys was expressed.

Example 1 Polyarylate (molecular weight of about 50,000) 100 consisting of a cocondensation product of bisphenol A with terephthalic acid and isophthalic acid
20 parts by weight and 0.01 parts by weight of a phosphoric acid heat stabilizer were dissolved.
A polyester modified dimethylpolysiloxane solution as a surface modifier [BYK (registered trademark)- Three
10: manufactured by Big Chemie Japan Co., Ltd.] 2 parts by weight were added, and a transparent film having a width of 1.5 m was obtained by a solvent casting method. The average thickness of the obtained transparent film is 65.
was μm. The thickness change in the vicinity of this film is 0.2
2 μm, which corresponds to 0.34% of the average thickness.

Comparative Example 1 A transparent film was obtained in the same manner as in Example 1 except that the surface modifier was not added. The average thickness of this transparent film is 67μ
In m, the change in thickness in the vicinity was 0.60 μm, which corresponds to 0.90% of the average thickness.

Example 2 A transparent film having an average thickness of 77 μm was obtained in the same manner as in Example 1. The thickness change in the vicinity of this film is 0.36μ
m was 0.47% of the average thickness.

Comparative Example 2 A transparent film was obtained in the same manner as in Example 2 except that the surface modifier was not added. The average thickness of this transparent film is 75μ
At m, the change in thickness in the vicinity was 0.82 μm, which was 1.09% of the average thickness.

Example 3 A dope made of a 20% by weight dichloromethane solution in which 100 parts by weight of a polycarbonate (molecular weight of about 50,000) made of a condensate of bisphenol A and terephthalic acid chloride was dissolved, and a polyester-modified dimethylpolysiloxane was used as a surface conditioner. 2 parts by weight of the solution was added and a transparent film having a width of 1.5 m was obtained by a solvent casting method. The average thickness of the obtained transparent film was 70 μm. The thickness change near this film is 0.16 μm, which is
It was equivalent to 0.23% of the average thickness.

Comparative Example 3 A transparent film was obtained in the same manner as in Example 3 except that the surface modifier was not added. The average thickness of this transparent film is 68μ
At m, the change in thickness in the vicinity was 0.36 μm, corresponding to 0.53% of the average thickness.

Example 4 The film obtained in Example 2 was heat-stretched to 570 nm.
A retardation film having a birefringence of was obtained. This was observed with a polarizing film for scissors color unevenness, but color unevenness could not be observed.

Comparative Example 4 A retardation film was obtained in the same manner as in Example 4 except that the film obtained in Comparative Example 2 was used, and color unevenness was observed, but color unevenness was observed in the stretching direction.

[0026]

According to the production method of the present invention, the average height between adjacent peaks and valleys, that is, the thickness in the vicinity, of the resulting heat-resistant transparent optical film for unevenness having a height difference of 0.04 μm or more is targeted. It is also possible to make the change 0.5% or less, more preferably 0.4% or less of the average film thickness. As described above, according to the present invention, a heat-resistant transparent film for optics having excellent thickness accuracy can be obtained, and for example, a retardation film with improved unevenness of retardation is provided.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI G02B 5/30 G02B 5/30 // B29K 67:00 B29K 67:00 105: 32 105: 32 B29L 11:00 B29L 11:00 C08L 67:00 C08L 67:00 (56) Reference JP-A-57-40556 (JP, A) JP-A-60-71004 (JP, A) JP-A-6-89038 (JP, A) JP-A-5 -86295 (JP, A) JP-A 1-270004 (JP, A) JP-A 3-115324 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C08J 5/18 B29C 55/02 C08L 67/00 G02B 5/30

Claims (5)

(57) [Claims] 1. When a heat-resistant transparent film made of an amorphous polymer having an aromatic group in its main chain is formed by a solution casting method, a surface conditioner made of a silicon compound is added to a dope for casting. A method for producing a heat resistant transparent film for optics (however, excluding a film for an electrophotographic photoreceptor). 2. The method according to claim 1, wherein the surface modifier is a silicon compound having a dimethylpolysiloxane skeleton. 3. The method according to claim 1, wherein the surface treatment agent is a polyester-modified polysiloxane compound represented by the following general formula. [Chemical 1] _{(Wherein, R 3 = -R 4 -O-} CO-R 5 -CO-O-R
₆ is _{-O-R 7 -Y, R 4} , R 5, R 6, R 7 is selected alkylene group, an arylene group, from aralkylene group, Y is hydrogen or a hydroxyl group, a carboxyl group, the polar group of the amino group Selected from. V is 0 to 100, W is 1
An integer up to 100. ) 4. An amorphous polymer 100 having a surface modifier made of a silicon compound and having an aromatic group in its main chain.
The manufacturing method according to claim 1, wherein 0.1 to 5 parts by weight is added to parts by weight. 5. A method for producing a retardation film, which comprises uniaxially stretching the heat-resistant transparent film obtained in any one of claims 1 to 4.