JPH048733A - Transparent polyimide film - Google Patents

Abstract

PURPOSE:To provide the subject film comprising a polymide, polyimide copolymer or polyimide mixture as a main structural element, having excellent transparence and thermal resistance and useful for optical equipments, etc. CONSTITUTION:The objective film contains as a main structural element a polyimide, polyimide copolyimide or polyimide mixture having repeat units of the formula (R1 is a tetravalent organic group). The film is prepared by reacting a tetracarboxylic acid dianhydride (e.g. pyromellitic dianhydride) with a diamine [e.g. 2,2'-(bistrifluoromethyl)-4,4'-diaminobiphenyl] in a polar organic solvent such as N-methyl-2-pyrrolidone, casting the prepared polyamic acid on the surface of a flat plate such as a glass plate and subsequently heating the film at 250-350 deg.C.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a polyimide film with excellent transparency.

[Conventional technology]

With the development of new optical equipment, the applications for transparent plastic films are rapidly expanding. Simple ones are used for over-the-top projectors, plate making, and tracing. In addition, functional materials include transparent conductive films used in touch panels and the like, and heat ray reflective films.

Additionally, transparent films, which are characterized by their flexibility and easy formability, are increasingly replacing applications where hard plates such as glass plates and acrylic plates have been used up until now. Polyethylene terephthalate film is a transparent film that has been particularly widely used recently. However, polyethylene terephthalate has problems in terms of heat resistance depending on its use.

The future trend in transparent film development can be said to be to improve heat resistance.

As transparent films with improved heat resistance, transparent films made from super engineering plastics such as polysulfone and polyethersulfone are used as overlays. Polyetherimide films are examples of polyimide-based transparent films, and the heat resistance of these transparent films is about 150 to 200°C. Further improvement in heat resistance is expected.

[Problem to be solved by the invention]

As described in the section on conventional technology, the heat resistance of conventional transparent films is still not sufficient.

An object of the present invention is to provide a transparent film that has excellent heat resistance.

[Means to solve the problem]

To summarize the present invention, the present invention relates to a transparent polyimide film, which is a polyimide or a polyimide copolymer having a repeating unit represented by the following general formula: (wherein R1 represents a tetravalent organic group) Alternatively, the main component is a polyimide mixture.

The present inventors produced films using various polyimides and polyimide mixtures, and conducted extensive studies on transparent films that have both transparency and heat resistance. the result,
By producing polyimide using a specific diamine, the desired objective was achieved and a transparent polyimide film with excellent heat resistance could be obtained.

Examples of the tetracarboxylic dianhydride used in producing the polyimide, polyimide copolymer, and polyimide mixture used in the present invention include pyromellitic dianhydride, 3
．． 3', 4.4'-benzophenonetetracarboxylic dianhydride, 3.3', 4゜4'-biphenyltetracarboxylic dianhydride, 2゜2-bis(3,4-dicarboxyphenyl)hexafluoro Propane dianhydride, trifluoromethylpyromellitic dianhydride, 1,4-di(trifluoromethyl)pyromellitic dianhydride, 1゜4-di(pentafluoroethyl)pyromellitic dianhydride, hepta Examples include fluoropropylpyromellitic dianhydride. Among them, trifluoromethylpyromellitic dianhydride, 1,4-di(
trifluoromethyl)pyromellitic dianhydride, 1.4
Methods for producing -cy(pentafluoroethyl)pyromellitic dianhydride, heptafluoropropylpyromellitic dianhydride, etc. are described in Japanese Patent Application No. 165056/1983.

Further, as the diamine, it is preferable to use 2,2'-(bistrifluoromethyl)-4,4'-diaminobiphenyl alone, but other diamines may be used in combination. In that case, the diamines include 3.3'-(bistrifluoromethyl)-4゜4'-diaminobiphenyl, 2
．． 2'-dimethyl-4゜4'-diaminobiphenyl, 3
．． 3'-dimethyl-4゜4'-diaminobiphenyl, 4
．． Examples include 4'-diamino-p-terphenyl.

The method for producing 2,2'-(bistrifluoromethyl)-4,4'-diaminobiphenyl used in the present invention is described, for example, in Journal of the Chemical Society of Japan, Vol. 1972, No. 3, 675-6.
76 (1972).

The method for producing polyamic acid, which is a precursor of polyimide, polyimide copolymer, and polyimide mixture used in the present invention, may be the same as the production conditions of ordinary polyamic acid,
- For boat fishing, the reaction is carried out in a polar organic solvent such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide. In the present invention, not only diamino and tetracarboxylic dianhydride are used as a single compound, but also a mixture of a plurality of diamines and tetracarboxylic dianhydrides may be used. In that case, the total number of moles of multiple or single diamines and the total number of moles of multiple or single tetracarboxylic dianhydride are made to be equal or approximately equal.

In the polymerization solution such as the above-mentioned polyamic acid and the polymer solution for film formation, the concentration of the solution is appropriately 5 to 40 wt%, and preferably 10 to 25 wt%.

Further, the rotational viscosity (25°C) of the polymer solution is 50 to
Preferably it is 5000 poise.

The method for producing the polyimide film of the present invention includes, for example, casting a polyamic acid solution onto the surface of a support such as a smooth flat plate such as a glass plate, copper plate, or aluminum plate, a metal rotating drum, or a metal belt. , forming a polyamic acid thin film of uniform thickness. The thin film is 70 to 20
The solution is heated stepwise to 0° C., and the solvent is gradually removed to form a solidified film. After that, this solidified film was peeled off from the support 2
Processed at temperature between 50-350℃, thickness 1-150μ
A transparent polyimide film of m is obtained.

〔Example〕

Hereinafter, the present invention will be explained in more detail using some examples, but the present invention is not limited only to these examples.

Light transmittance is determined by transmitting He-Ne laser beam light with a wavelength of 633 nm into a polyimide film through a Kabra prism, and measuring the intensity of the scattered light generated at this time from a direction perpendicular to the film surface. Light transmission loss was calculated and determined from changes in light intensity. The thermal decomposition temperature was expressed as the temperature at which the weight decreased by 1Qwt% when the temperature was increased at a rate of 10° C./min under a nitrogen stream.

Example 1 43.6 g of pyromellitic dianhydride in an Erlenmeyer flask
(0.2 mol) and 64.0 g of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (
0.2 mol), and N,N-dimethylacetamide (
DMA) 1000g was added. This mixture was stirred at room temperature under a nitrogen atmosphere for 3 days, and the polyamic acid DM
Solution A was obtained. The viscosity of this solution was approximately 80 poise.

The above polyamic acid solution was spin-coated on an aluminum plate, and the solution was spin-coated on an aluminum plate for 2 hours at 70°C under a nitrogen atmosphere.
60℃ for 1 hour, 250℃ for 30 minutes, and 350℃ for 1 hour.
Heat cured for hours. This aluminum plate is 10%IIcI
The aluminum plate was immersed in an aqueous solution and dissolved to obtain a polyimide film with a thickness of 30 μm. The thermal decomposition temperature of this polyimide film is 610°C, and the light transmittance at a wavelength of 633 nm is 0.
It was 85 dB/cm.

Examples 2 to 6 Polyimide films were obtained in the same manner as in Example 1 except that the acid anhydrides shown in Table 1 below were used instead of the pyromellitic dianhydride used in Example 1. Their thermal decomposition temperatures and light transmittances are shown in Table 1 below together with other examples.

Examples 7 to 15 Polyimide films were obtained in the same manner as in Example 1 except that the mixture of acid anhydrides shown in Table 1 was used instead of the pyromellitic dianhydride used in Example 1. Table 1 shows their thermal decomposition temperatures and light transmittances.

Example 16 17 g of the polyamic acid solution prepared in Example 1 and 33 g of the polyamic acid solution prepared in Example 4 were mixed, and a polyimide film was obtained by the method shown in Example 1. The thermal decomposition temperature of this polyimide film is 546℃, wavelength 6
The light transmittance at 33 nm was 0.59 dB/cm.

Examples 17 to 20 In Example 16, the weight ratio of the polyamic acid solution prepared in Example 1 and the polyamic acid solution prepared in Example 4 was replaced with the weight ratio shown in Examples 17 to 20 in Table 1, and Example 16 A polyimide film was produced in the same manner as described above. Table 1 shows their thermal decomposition temperatures and light transmittances.

Comparative Example 1 Instead of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl used in Example 1,
A polyimide film was obtained in the same manner as in Example 1 using 2.2'-dimethyl-4,4'-diaminobiphenyl. The thermal decomposition temperature of this polyimide film is 569℃,
The light transmittance at a wavelength of 633 nm is 36 dB/C[I+
Met.

Comparative Example 2 Instead of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl used in Example 4,
A polyimide film was obtained in the same manner as in Example 4 using 2.2'-dimethyl-4,4'-diaminobiphenyl. The thermal decomposition temperature of this polyimide film is 533℃,
The light transmittance at a wavelength of 633 nm was 5.6 dB/cm.

〔Effect of the invention〕

As described above, the polyimide film of the present invention has excellent heat resistance and transparency, and therefore, by using it, it is possible to improve the reliability of various optical-related parts and devices.

Patent applicant: Nippon Telegraph and Telephone Corporation

Claims (1)

[Claims] 1. The following general formula I: ▲There are mathematical formulas, chemical formulas, tables, etc.▼...[I] (In the formula, R_1 represents a tetravalent organic group) Having a repeating unit represented by A transparent polyimide film characterized in that its main component is polyimide, a polyimide copolymer, or a polyimide mixture.