JPH0696682B2 - Heat control coating composition - Google Patents

Description

TECHNICAL FIELD The present invention is applied to the surfaces of antennas, towers, etc. used in artificial satellites, space stations, etc., and controls heat flow in and out of the antennas, towers, etc. The present invention relates to a heat control coating composition capable of maintaining a temperature within a predetermined temperature range.

2. Description of the Related Art Devices used in artificial satellites and the like are generally placed under harsh conditions and are therefore required to withstand harsh environmental conditions, be lightweight and have high reliability. For example, satellite antennas are exposed to a very large temperature difference between when they are exposed to sunlight and when they are in the shade.
In order to operate the antenna normally, set the antenna to 100
It is necessary to keep the temperature below ℃. Since the temperature of this antenna is determined by the balance between the thermal energy due to the absorption of sunlight and the radiant energy due to the radiation of the antenna itself, the radiant heat energy of the antenna is increased, especially at high temperatures, or the absorptivity of sunlight is increased. Some kind of ingenuity is required to reduce it.

Therefore, conventionally, in order to keep the temperature of the antenna at 100 ° C. or lower, a heat control paint having a function of suppressing absorption of solar energy incident on the antenna to radiate heat to outer space has been used. The performance of this heat control paint is
It is determined by the solar absorptivity (α _s ) indicating the degree of absorption of sunlight and the thermal emissivity (ε) indicating the degree of radiation of the absorbed antenna heat. That is, the antenna temperature
To keep the temperature below 100 ° C, a heat control paint having a small α _s and a large ε is required.

In addition, the antenna of the satellite is exposed to radiation such as electron rays and gamma rays, and at low temperatures near -180 ° C in the shade, the paint deteriorates due to radiation, and α _s does not increase. It is necessary that abnormalities such as cracks and peeling do not occur in the coating film in the temperature range of ° C.

As a conventional heat control coating material, a coating material in which a silicone alkyd resin or a silicone resin is used as a film forming component and titanium oxide and / or zinc oxide is added is known.
All of these paints have excellent radiation resistance, but silicone alkyd resin paints are -180 ° C to 100 ° C.
It has a drawback that the coating film is cracked by the temperature change of 1. On the other hand, in the silicone resin coating, in order to make α _s 0.3 or less, it is necessary to use a thick coating film of 80 to 100 μm. There was a problem in terms of weight reduction.

On the other hand, conventionally, many paints using silicate as a film forming component have been proposed for various applications requiring corrosion resistance and heat resistance, for example, alkyl silicate-based zinc rich paints are well known. . The curing reaction of this alkyl silicate-based zinc rich paint is based on the reaction between the zinc powder added as a pigment and the film-forming component. When a non-reactive general pigment is used in place of the zinc powder, it is 1 μm or more. It was impossible to form a coating film having the above thickness, and the coating film performance was extremely low and poor in practical use.

Problems to be Solved by the Invention As described above, in antennas used in artificial satellites, space stations, etc., these are placed under severe conditions,
Especially when the temperature exceeds 100 ° C, the function is not fully exhibited. Therefore, various heat control coating compositions have been used for the purpose of reducing the absorptivity of the antenna for sunlight and ensuring high heat dissipation. However, as already mentioned, in the conventionally proposed one, cracks are generated due to thermal strain based on a large temperature difference,
Further, in order to secure necessary physical properties (absorption rate of sunlight, etc.), another important property in the above field, that is, weight reduction, is sacrificed.

Under such circumstances, it is important to improve the thermal characteristics of the antenna and to develop a coating composition for thermal control, which is advantageous in terms of weight reduction, in order to advance future space development, satellite communication technology, etc. It is extremely important for this purpose, and the object of the present invention is also in this respect.

That is, the object of the present invention is to improve the thermal characteristics of equipment used under severe environmental conditions such as antennas and towers in space stations, artificial satellites, etc. It is to provide a coating composition for control.

That is, the object of the present invention is to improve the crack resistance due to heat cycle, which is a drawback of conventional heat control paints, and to have excellent radiation resistance and heat cycle resistance. When the rate (α _s ) is 0.3 or less, the thermal emissivity (ε) is
It is to provide a heat control paint having a heat control performance of 0.8 or more.

Means for Solving the Problems In view of the above-mentioned current state of the heat control coating composition, the present inventors have conducted various investigations and studies to solve the various drawbacks, and as a result, do not include a silanol group. The present inventors have found that combining a condensate of a specific organosilicon compound with titanium oxide and mica in a specific ratio is extremely effective in achieving the above object, and have completed the present invention.

That is, the heat control coating composition of the present invention has the following general formula [I]: However, in the general formula [I], R may be the same or different and represents a hydrogen atom, a hydrocarbon group having 1 to 8 carbon atoms or a phenyl group, and the organosilicon compound represented by: A film-forming component comprising at least one compound selected from the group consisting of a high condensate containing no silal group, and the film-forming component 10
It is characterized by containing 100 to 300 parts by weight of mica having a particle size of 40 μm or less and 50 to 200 parts by weight of titanium oxide having a particle size of 1 μm or less per 0 parts by weight.

That is, according to the present invention, a high-condensation product of an inorganic silicone, which does not contain a silanol group and has a molecular chain consisting only of Si-O bonds, which is suitable for obtaining excellent radiation resistance, has been found, and has been conventionally used. In addition to titanium oxide, which is one of the white pigments that are used, the thermal cycle resistance is improved by adding mica to the highly-condensed product of inorganic silicone, and the particle size of titanium oxide and mica and the addition amount are optimized. A coating composition for heat control having a thin film and excellent heat control performance has been realized.

The present invention will be described in more detail below.

In the organic silicon compound represented by the general formula [I] used as a raw material in the present invention, R may be the same or different, and a hydrogen atom, a phenyl group or a carbon atom number 1
~ 8 hydrocarbon group, preferably a hydrogen atom or an alkyl group having 1 to 8 carbon atoms. Specific compounds include tetramethoxysilane, tetraethoxysilane,
Tetraphenoxysilane etc. can be illustrated. The low condensate means an oligomer having a polymerization degree of 10 or less.

An organosilicon compound represented by the general formula [I] or (and)
When the low-condensation product is condensed, the compound or / and the low-condensation product is added to a water-soluble solvent and bonded to Si in the presence or absence of an acid catalyst such as hydrochloric acid or acetic acid.
Add water at a ratio of 0.2 to 2 mol to 1 mol of RO group, and add 20 to 1
React with stirring at about 00 ℃ for about 30 minutes to 10 hours, then add inorganic salts such as sodium hydroxide and aliphatic amines such as triethylamine to raise the pH of the system to 7 or more to proceed the condensation reaction. . After the completion of the reaction, the residual water can be removed by distillation, azeotropic distillation, etc. to easily obtain the desired highly condensed product.

In the production of the high condensate useful in the composition of the present invention, by-products such as alcohol and water are formed during the condensation of the compound of the above formula [I] and / or its low condensate. Therefore, by using a combination of raw materials in which this by-product has a high vapor pressure at the condensation temperature, a high condensate containing no silanol group can be advantageously obtained.

The high condensate thus obtained is a three-dimensional condensate having a degree of condensation of at least 20 and a molecular weight of about 3000 or more, and has sufficient performance as an inorganic film-forming component of a paint, for example, clear coating as it is. Even then, a coating film having a film thickness of about 20 μm can be formed.

The titanium oxide used as a white pigment in the present invention has an average particle size of 1 μm or less, preferably 0.1 to 0.4 μm. Titanium oxide is used in a proportion of 50 to 200 parts by weight, preferably 100 to 150 parts by weight, per 100 parts by weight of the above inorganic film-forming component.

The mica used in the present invention has an average particle size of 40 μm or less, preferably 15 μm or less. Mica is used in a proportion of 100 to 300 parts by weight, preferably 150 to 250 parts by weight, per 100 parts by weight of the above-mentioned inorganic film-forming component.

When the composition of the present invention is applied to an antenna or the like, the above inorganic film forming component is added with the above titanium oxide and mica,
A solvent such as thinner or toluene is added, and the additives are dispersed in the film-forming components by a high-speed stirrer, and the additives are applied by various known coating methods, and then cured by water in the air in about 10 minutes to 10 hours.

The coating composition according to the present invention has excellent coating performance as compared with the conventional silicate-based coating film, can be formed into a thin film as compared with the conventional heat control coating, and can be exposed to sunlight with a coating thickness of 30 μm. It has excellent heat control performance with absorptance (α _s ) of 0.3 or less and thermal emissivity (ε) of 0.8 or more.

Action As described above, the thermal control coating composition useful for the conventionally proposed satellites, antennas used in space stations, etc. is particularly advantageous in terms of heat cycle resistance, radiation resistance, and light weight. Although it was a problem, the conventional problems can be almost solved by using the coating composition of the present invention.

This is a novel, radiation-resistant, inorganic silicone condensate having a silanol group-free molecular chain consisting only of Si-O bonds, is used as a film-forming component, and is oxidized with a specific particle size in a specific ratio. It is a result of using titanium and mica as additives.

That is, in order to ensure excellent heat controllability and heat cycle resistance between large temperature differences and to ensure excellent thermal controllability, the solar absorptivity of the coating composition is 0.3 or less, and the thermal emissivity is
The amount of titanium oxide should be within the range of 50 to 200 parts by weight per 100 parts by weight of the high condensate, and the amount of mica should be 100 to 100 parts by weight per 100 parts by weight of the high condensate. It should be 300 parts by weight. The lower limit of each additive cannot prevent the generation of cracks when subjected to a heat cycle, which has been a problem in the conventional heat control coating composition. On the other hand, the upper limit is not particularly limited in terms of physical properties (α _s , ε), but since it causes problems in workability, that is, coatability and mechanical strength, 200 parts by weight (titanium oxide) and 300 parts by weight, respectively. It is desirable to be a part (mica). Furthermore, by adjusting the amounts of these used to 100 to 150 parts by weight and 150 to 250 parts by weight, respectively, it is possible to advantageously obtain a coating composition for heat control having desired properties.

It is also important to adjust the particle size of titanium oxide or mica as an additive in order to satisfy the above various characteristics and the requirements for weight reduction, and the average particle size is 1 μm or less, preferably
It is necessary that the thickness is 0.1 to 0.4 μm and 40 μm or less, preferably 15 μm or less.

Thus, according to the present invention, a highly condensate of an inorganic silicone excellent in radiation resistance is used as a film forming component of the coating composition for heat control, and further titanium oxide and mica are used in a controlled particle size and an addition amount, An excellent thermal control coating composition is obtained, which has a coating film thickness less than half that of conventional products, long life and small sunlight under the environment of radiation exposure and temperature environment of -180 to 100 ° C. It gives an absorption rate (α _s ) and a large thermal emissivity (ε). Therefore, when it is applied to the surface of antennas, towers in space stations, artificial satellites, etc.,
These original functions can be fully exerted.

EXAMPLES The heat control coating composition of the present invention will be described in more detail with reference to the following examples, but the scope of the present invention is not limited to the following examples.

Example 1 62 g of tetraethoxysilane, 125 g of methyltriethoxysilane, and 187 g of ethyl alcohol were added to a reaction vessel,
After stirring the contents and heating to 80 ℃, 0.2N
30 g of hydrochloric acid was added and reacted at 80 ° C. for 10 hours. Then,
To this reaction product, 30 g of triethylamine was added, the pH was raised to 7 or higher, the condensation reaction was carried out at 80 ° C. for 2 hours, and then 100 g of benzene was added and the solvent was removed until the nonvolatile content became 40% by weight. The reaction product thus obtained was transparent, had a viscosity of 5.8 centipoise, and did not change after storage at 30 ° C. for 2 months, showing excellent storage stability. Hereinafter, this is referred to as "reaction product A".

Then, with respect to 100 parts by weight of the reaction product A, an average particle size of 0.
A total of 200 parts by weight of 3 μm (particle size distribution 0.05 to 0.5 μm) rutile titanium oxide and muscovite with an average particle size of 4 μm (particle size distribution 0.05 to 12 μm) were added, and diluted with thinner 4
3 kinds of thermal control coating composition with 3 kinds of composition on CFRP plate (1mm thickness, α _s : 0.916, ε: 0.79) which is antenna skin material.
After coating to 0 μm and setting at room temperature for 30 minutes, 180 ℃
It was heat treated for 20 minutes to cure.

About α _s and ε of the heat control paint obtained by the above method, which corresponds to the irradiation amount for 10 years in outer space (in geosynchronous orbit) by Cockcroft-Walton type electron beam irradiation device 30
Electron beam irradiation at 0 KeV, 10 ¹⁶ e / cm ² (Fluence rate 6.25 × 10
The values after ¹¹ e / cm ² · sec, temperature 15 ° C., and vacuum degree 5 × 10 ⁻⁵ Torr) are shown in Table 1 together with the initial values.

In the heat control coating material shown in this example, the increase in α _s when the electron beam was irradiated at 10 ¹⁶ e / cm ² was only 0.01. In addition,
α _s uses a Beckman UV5240 device and ε is
Guiller, Dunkel refractometer model (Gier
Dunkel Reflectometer Model) DB 100 was used for measurement. The same applies to the measurements in the following examples.

In addition, regarding the thermal cycle resistance of the four types of thermal control coatings obtained by the above method, the heat of −180 to 100 ℃ which corresponds to the temperature change in outer space (geostation orbit) by the Ransco 934D thermal cycle test equipment The cycle test was performed for 50 cycles. The paint containing 100 parts by weight or more of mica was good, but the paint containing no mica had cracks in the coating film.

From the above results, it was revealed that the heat control coating material shown in this example has excellent electron beam resistance and that the thermal cycle resistance can be improved by adding mica.

Example 2 To 100 parts by weight of the reaction product A obtained in Example 1, 100 parts by weight of rutile titanium oxide having an average particle size of 0.3 μm and 50 to 300 parts by weight of muscovite having an average particle size of 4 μm were added. , 7 types of heat control coating compositions were obtained. These coating compositions were applied to a CFRP plate in a film thickness of 30 μm and cured in the same manner as in Example 1. The initial thermal control characteristics (α _s , ε) of the seven types of paints obtained by the above method are shown in FIG.

In all paints, α _s was 0.27 or less and ε was 0.85 or more, which was the target. Further, a thermal cycle test of the above coating material was conducted in the same manner as in Example 1. As a result, cracks occurred in the paints containing 50 and 75 parts by weight of mica. From the result of heat cycle resistance, the addition amount of mica should be 100 parts by weight or more. Also, among the thermal control performances, α _s
As for the above, it is preferable that the addition amount of mica is about 200 parts by weight for lowering α _s .

Example 3 To 100 parts by weight of the reaction product A obtained in Example 1, 200 parts by weight of muscovite having an average particle size of 4 μm and 50 to 200 parts by weight of methyl titanium oxide having an average particle size of 0.3 μm were added. , 6 types of heat control coating compositions were obtained. These coating compositions were applied to a CFRP plate in a film thickness of 30 μm and cured in the same manner as in Example 1.

FIG. 2 shows α _s and ε of the six kinds of paints obtained by the above method. In all paints, α _s was 0.27 or less and ε was 0.85 or more, which was the target. Further, it was found that the higher the added amount of titanium oxide is, the lower the α _s can be made, but when the added amount is 100 parts by weight or more, the α _s does not change so much.

Comparative Example Heat Control Silicone Resin Paint S13G-LO [IIT Research Ins
titute), and a heat control silicone alkyd resin coating APA-2474 (manufactured by Whittaker) on a CFRP plate in the same manner as in Example 1 to a film thickness of 40, 80, 130 μm, and at room temperature 48 Allowed to cure for hours. The α _s and ε of these paints are shown in Table 2. In the case of S13G-LO, a film thickness of 80 μm or more is required to reach the target of α _s of 0.3 or less, but the product of the present invention achieves 0.23 where α _s is far below the target value at a film thickness of 30 μm. is doing.

Further, as a result of performing a heat cycle test on these coating materials by the same method as in Example 1, as for APA-2474, cracks occurred within 50 cycles at any film thickness, and crack resistance was higher than that of the present invention. It turns out that

EFFECTS OF THE INVENTION As described above, the heat control coating material according to the present invention has a small solar absorptivity (α _s ) at a coating thickness (40 μm) of about 1/3 of the conventional product, and a thermal emissivity ( ε) has a large thermal control performance and good radiation resistance and heat cycle resistance. For example, if it is applied to the antenna surface of a satellite, the antenna temperature can be kept below a certain temperature for a long time. Moreover, it has an excellent advantage that the weight of the coating material can be reduced by reducing the thickness of the coating film.

[Brief description of drawings]

1 and 2 show the solar absorptivity (α _s ) and the thermal emissivity (ε) of the thermal control coating composition according to the present invention with changes in the added amount of mica and the added amount of titanium oxide, respectively. It is a graph which shows the change of.

Claims (6)

[Claims] 1. The following general formula [I]: However, in the general formula [I], R may be the same or different and represents a hydrogen atom, a hydrocarbon group having 1 to 8 carbon atoms or a phenyl group, and the organosilicon compound represented by: A film-forming component comprising at least one compound selected from the group consisting of a high condensate containing no silal group, and the film-forming component 10
A thermal control coating composition comprising 100 to 300 parts by weight of mica having a particle size of 40 μm or less and 50 to 200 parts by weight of titanium oxide having a particle size of 1 μm or less per 0 parts by weight. 2. The heat control coating composition according to claim 1, wherein R in the general formula [I] is a hydrogen atom or an alkyl group having 1 to 8 carbon atoms. 3. The heat control coating composition according to claim 1 or 2, wherein the degree of condensation of the low condensate is 10 or less. 4. The film-forming component hydrolyzes at least one selected from the compound of the general formula [I] and its low condensate in the presence or absence of an acid catalyst, and then the pH is 7 or more. The heat control coating composition according to any one of claims 1 to 3, wherein the heat control coating composition is obtained by adjusting to the above condition and condensing. 5. The particle size of the mica is 15 μm or less, and the addition amount thereof is in the range of 150 to 250 parts by weight, according to any one of claims 1 to 4. Item 5. A heat control coating composition according to item. 6. A titanium oxide having a particle size in the range of 0.1 to 0.4 .mu.m and an addition amount in the range of 100 to 150 parts by weight. Item 5. A coating composition for heat control according to any one of items 5.