JP2000248230A - Metal oxide paste and infrared-radiating film obtained therefrom - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject paste low in viscosity, easy for coating and capable of obtaining infrared-radiating films excellent in mechanical characteristics and good in adhesiveness by making the paste contain a specific polyimide precursor varnish and a powdery infrared-radiating metal oxide. SOLUTION: This metal oxide paste contains (B) a powdery infrared radiating metal oxide in a polyimide precursor varnish in which (A) (i) a diamine expressed by formula I [R1 and R2 are each formula II, formula III, or the like; R3 to R8 are each H or a 1-5C alkyl; (m) is 0-20] and (ii) a tetracarboxylic acid and/or its ester are dissolved as a polyimide precursor in a solvent and the concentrations of the ingredient (i) and the ingredient (ii) are both 5-80 wt.%. It is preferable to blend 20-99 pts.wt. of the ingredient (i) per 100 pts.wt. of the total of the ingredients (i) and (ii) and 0.5-200 pts.wt. of the ingredient B per 100 pts.wt. of the ingredient A, and the ingredient B is an oxide of chromium, zirconium, or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal oxide paste containing an infrared-emitting metal oxide in a polyimide precursor varnish, and an infrared-emitting film obtained therefrom.

[0002]

2. Description of the Related Art Heretofore, as a material for increasing the infrared radiation efficiency of a heater, a heater made of ceramics containing a metal oxide as a main component or a heater coated with a metal tube has been used. It is also well-known that infrared radiation can be generated by forming an infrared-emitting film on the inner surface of an oven or a heat exchanger, thereby increasing the heat utilization efficiency. By the way, the characteristics required for the infrared radiation film include: 1) high emissivity over the entire region from the near infrared region to the far infrared region;
2) excellent heat resistance, water resistance, workability, flexibility, etc., 3) good adhesion to metal, and 4) excellent acid and alkali resistance. In recent years, the need for such infrared radiation materials has been increasing more and more from the viewpoint of energy saving.
Improvements are required in terms of processability (ease of coating), adhesion to metal, flexibility, and the like.

For the purpose of improving the above problems, there has been a demand for the development of a paint or paste type far-infrared radiation material using a polymer as a binder. By using a polymer as a binder, it is considered that processability, adhesion to metal, and flexibility can be improved. In this case, since the heater is generally used at a high temperature of 200 ° C. or higher, a resin having excellent heat resistance is required as a binder resin, and a high ratio is required to obtain a predetermined infrared radiation characteristic. It is necessary to contain a compound having infrared radiation. Potential examples of such a binder resin include a polyimide resin which is a resin having excellent properties and durability at high temperatures. Polyimide resin is
Since it has excellent heat resistance and chemical resistance, it is generally handled in the form of a polyimide precursor that is soluble in a solvent. As a polyimide precursor solution, a polyimide precursor solution (varnish) composed of a polyamic acid using dimethylformamide or N-methylpyrrolidone as a solvent has been well known. The dispersion of various fillers is also known from various documents. By applying this technique, it is possible to produce a paste in which infrared radiation fine particles are dispersed in a polyimide precursor varnish, and it is considered that an infrared radiation film can be formed from this paste.

However, it is difficult to increase the solid content ratio of a varnish prepared from a polyamic acid as a precursor due to its high degree of polymerization and low solubility. In the paste prepared using the method described above, a complicated operation such as repeated coating was required to obtain a film having a predetermined thickness. Furthermore, since the varnish using a polyamic acid as a precursor has a high viscosity even at a low solids concentration, the viscosity further increases when a paste is prepared by mixing metal oxide powder,
When the proportion of the metal oxide is increased to obtain a film having a predetermined infrared radiation characteristic, there is a problem that coating becomes difficult.

[0005]

In view of the above, the present invention has a low viscosity and is easy to apply even if a polyimide precursor and an infrared-emitting metal oxide are contained in an organic solvent at a high solid content ratio. It is an object of the present invention to provide a metal oxide paste which is excellent in mechanical properties obtained from the metal oxide paste and has good adhesion.

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have found that a polyimide precursor varnish consisting of a specific diamine and a carboxylic acid dissolved in an organic solvent and an infrared radiation A paste composed of a metal oxide powder has a low viscosity even if it has a high solid content ratio.Furthermore, a uniform paste composed of a polyimide and a metal oxide is obtained by coating and curing the paste. The inventors have found that a suitable infrared-emitting film can be obtained, and have reached the present invention. That is, the gist of the present invention is to
A diamine represented by the following formula (1) and a tetracarboxylic acid and / or an ester thereof represented by the following formula (2) are dissolved in an organic solvent as a polyimide precursor, and the diamine is mixed with a tetracarboxylic acid and / or an ester thereof. Concentration of 5-
A metal oxide paste comprising an infrared-emitting metal oxide powder in a polyimide precursor varnish of 80% by weight.

[0007]

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In the formula, R ₁ and R ₂ are each selected from structural formula groups 1 and 2, and R _{3 to} R ₈ are a hydrogen atom or a carbon atom having 1 to 5 carbon atoms.
And m represents an integer of 0 to 20.

Secondly, there is provided an infrared-emitting film characterized in that a polyimide comprising a repeating unit represented by the following formula (3) obtained by applying this metal oxide paste to a substrate and heating is used as a binder.

[0010]

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In the formula, R ₁ and R ₂ each represent the above structural formula group 1
And n is an integer of 10 to 5000.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The metal oxide paste of the present invention comprises a varnish obtained by dissolving a polyimide precursor in an organic solvent and containing a powder of an infrared-emitting metal oxide. The diamine represented by the above formula (1) is used as the polyimide precursor. And a tetracarboxylic acid and / or an ester thereof represented by the above formula (2).

The concentration (solid content) of the polyimide precursor in the polyimide precursor varnish is 5 to 80% by weight. If the concentration is lower than 5% by weight, it may be difficult to obtain a predetermined infrared-emitting film thickness only by adjusting the coating device, and therefore, it is necessary to repeatedly apply the film.
Advantages are easily lost in terms of productivity. On the other hand, when the concentration is higher than 80% by weight, it is difficult to stably dissolve the polyimide precursor, and even if the dissolution can be performed by selecting an organic solvent, the viscosity of the paste becomes high and the coating property becomes high. And the productivity of the film may be reduced. Considering productivity, the preferred concentration range is from 20% by weight to 55% by weight.
% By weight. Within this range, a paste suitable for conventionally known coating methods such as screen printing used for forming a fine pattern and other spin coating, bar coating, spray coating, and dip coating can be obtained.

The ratio of the diamine represented by the above formula (1) to the tetracarboxylic acid and / or ester thereof represented by the above formula (2) is determined by the ratio of the diamine represented by the above formula (1) to the tetracarboxylic acid represented by the above formula (2). It is preferable that the compounding amount of the diamine represented by the above formula (1) is in the range of 20 to 99 parts by weight based on 100 parts by weight of the sum of the acid and / or its ester.

The organic solvent used in the paste of the present invention includes N-methylpyrrolidone, dimethylformamide, dimethylacetamide, dimethylsulfoxide, hexamethylphosphoryltriamide, sulfolane, N, N
Polar solvents containing N, S, P atoms in molecules such as' -dimethylimidazolidinone, N-methylcaprolactam, etc., cellsolves such as cellsolve and phenylcellsolve, and cellsolve acetate such as ethylacetsolve and butylacetatesolve. Carbitols such as methyl carbitol and ethyl carbitol; carbitol acetates such as ethyl carbitol and butyl carbitol; carbitol diethers such as dimethyl carbitol (diglyme) and diethyl carbitol; Organic solvents having a boiling point of 150 ° C. or more, such as alcohols such as hexanol and benzyl alcohol, ketones such as cyclohexanone and isophorone, and esters such as γ-butyrolactone, are preferred. This is because, when performing continuous production, using an organic solvent having a boiling point of less than 150 ° C.
The organic solvent is remarkably volatilized, and the viscosity of the paste is hardly stabilized.

The type of the solvent can be appropriately selected depending on the desired evaporation rate and the viscosity of the paste, but the use of a highly polar organic solvent containing N, S or P atoms in the molecule makes it possible to use a polyimide precursor. When the thickness is desired to be increased, it is preferable to use a highly polar organic solvent in order to obtain a higher concentration of the polyimide precursor varnish.

Next, as the infrared-emitting metal oxide used in the present invention, an oxide of chromium, zirconium, copper, aluminum, iron, silicon, manganese, tin, antimony, cobalt or two or more of these metals Can be exemplified. Examples of composite oxides include:
_{Fe 2 O 3 -MnO 2 -CoO,} MnO 2 -CoO-C
_{uO, MnO 2 -Cr 2 O 3} -Fe 2 O 3, SnO 2 -
Sb ₂ O _{5 and the} like. The particle size of the metal oxide powder is not particularly limited, but is preferably in the range of 0.01 to 20 μm in consideration of the uniformity of the film. In addition, for the purpose of adjusting infrared radiation characteristics, aluminum nitride, silicon nitride, silicon carbide, boron nitride, or the like can be used. The paste of the present invention can be prepared by preparing the above-mentioned polyimide precursor solution, adding a metal oxide powder, and using a known dispersion method such as a ball mill, a bead mill, and a homogenizer.

After applying the paste of the present invention to the surface of glass, ceramics, metal, etc.,
, The polyimide precursor is imidized to form an infrared-emitting film using polyimide as a binder.

[0019]

The present invention will be specifically described below with reference to examples. As Example 1 polyimide precursor, R ₁ in formula (1) is the following formula (4), R ₂ is represented by the following formula (5), R _3, R
₄ is a hydrogen atom and m is 9; R ₂ in the above formula (2) is represented by the following formula (5); R ₅ and R ₆ are each a hydrogen atom; R ₇ and R ₈ are each a hydrogen atom; Carboxylic acids each having a methyl group were used in a weight ratio of 94: 6, and dissolved in dimethylacetamide to prepare a varnish having a concentration of 30% by weight. 8.6 parts by weight of a chromium oxide powder (Cr ₂ O ₃ , manufactured by Kojundo Chemical Laboratory, particle size: 3 μm) as a metal oxide was added to 100 parts by weight of the varnish, and the mixture was dispersed by a bead mill to prepare a paste. . The paste had a green color and a viscosity of 90 poise.

[0020]

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[0021]

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Example 2 A paste was prepared in the same manner as in Example 1 except that 17 parts by weight of chromium oxide was used for 100 parts by weight of the varnish prepared in Example 1. This paste had a green color and a viscosity of 130 poise.

Example 3 A paste was prepared by adding 10 parts by weight of copper oxide (CuO, particle diameter 1-2 μm) as a metal oxide to 100 parts by weight of the same varnish as in Example 1. This paste had a blue color and had a viscosity of 88 poise.

Example 4 Ferric oxide (Fe ₂ O ₃ , particle diameter 1 μm) as a metal oxide with respect to 100 parts by weight of the same varnish as in Example 1
A paste was prepared by adding 8.6 parts by weight. This paste had a brown color and a viscosity of 110 poise.

The pastes obtained in Examples 1 to 4 were bar-coated on a glass substrate, dried and then heated at a temperature of 300 ° C. for 2 hours to form an infrared-emitting film. Obtained. Using this film, the mechanical properties of the film were evaluated based on JIS. Of the mechanical properties, the tensile strength, tensile modulus and elongation are JIS-K
Each was evaluated based on -7127. Next, in order to evaluate the adhesion between the film and the metal, the paste obtained in the example was applied on SUS304 under the same conditions as described above, heat-treated, and an infrared-emitting film was formed on SUS. . This film was subjected to a grid test based on JIS-K-5400 to evaluate the adhesion between the film and the metal.
Table 1 shows the evaluation results.

[0026]

[Table 1]

[0027]

As described above, the paste of the present invention has a low viscosity and can be easily applied even if the polyimide precursor and the metal oxide are contained in the organic solvent at a high solid content ratio.
Therefore, an infrared-emitting film can be produced from this paste with high productivity, and the obtained film has excellent mechanical properties and excellent adhesion to a substrate.

 ──────────────────────────────────────────────────の Continuing from the front page (72) Inventor Yoshiaki Echigo 23 Uji Kozakura, Uji-city, Kyoto Prefecture Unitika Central Research Laboratory F-term (reference) 4J002 CM041 DE096 DE116 DE126 DE146 EC037 ED027 ED037 EE037 EJ027 EL057 EL067 EP017 EU017 EU117 EV207 EV307 EW157 FD200 FD206 FD207 GH00 HA08 4J038 DJ031 HA216 KA06 KA20 NA19

Claims (5)

[Claims] A diamine represented by the following formula (1) and a tetracarboxylic acid and / or an ester thereof represented by the following formula (2) are dissolved in an organic solvent as a polyimide precursor, and the diamine and the tetracarboxylic acid And / or a polyimide precursor varnish having a concentration of 5 to 80% by weight of an ester thereof, containing a powder of an infrared-emitting metal oxide. Embedded image In the formula, R ₁ and R ₂ are each selected from Structural Formula Groups 1 and 2, R _{3 to} R ₈ represent a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, and m represents an integer of 0 to 20. 2. A sum of a diamine represented by the formula (1) and a tetracarboxylic acid and / or an ester thereof represented by the formula (2):
The metal oxide paste according to claim 1, wherein the amount of the diamine represented by the formula (1) is in the range of 20 to 99 parts by weight with respect to 0 parts by weight. 3. The amount of the powder of the infrared-emitting metal oxide is 0.1 to 100 parts by weight of the polyimide precursor varnish.
The metal oxide paste according to claim 1, wherein the amount is 5 to 200 parts by weight. 4. The method according to claim 1, wherein the infrared-emitting metal oxide is chromium, zirconium, copper, aluminum, iron, silicon, manganese,
The metal oxide paste according to claim 1, wherein the metal oxide paste is at least one oxide selected from oxides of tin, antimony, and cobalt, or a composite oxide composed of two or more of the above metals. 5. An infrared-emitting film comprising a polyimide comprising a repeating unit represented by the following formula (3) obtained by applying the metal oxide paste according to claim 1 on a substrate and heating the binder: Embedded image In the formula, R ₁ and R ₂ are each selected from Structural Formula Group 1 and Structural Formula Group 2, and n is an integer of 10 to 5000.