JPS601269A - Coating composition having selective light absorption - Google Patents

Abstract

PURPOSE:To provide the titled coating compsn. consisting of a fluorine-contg. polymer having OH groups in the molecule, a hardener, a specified metal oxide and a coupling agent, which absorbs a maximal amount of solar radiation energy and minimizes loss of heat radiation from the absorbing surface. CONSTITUTION:The coating compsn. is prepd. by dispersing in an organic solvent (A) a fluorine-contg. polymer with a hydroxyl value of 20-300 having OH groups in the molecule, (B) a hardener for (A) (e.g. butylated melamine resin), (C) 10-60pts.wt. metal oxide having a high absorptivity of light with a wave length of 0.3-2.5mum and a low radiation ratio of light with a wave length of 5-10.6mum (e.g. CuO), (D) a coupling agent used in an amt. of 0.5-2.0pts.wt. per 100pts.wt. (C), and (E) a dispersant. The compsn. is applied to the surface of a heat collecting plate in a film thickness of 1-10mum.

Description

[Detailed description of the invention] The present invention relates to photoselective 1-absorbing coating compositions.

For more details, the heat collecting plate (collector) surface is coated with n1
The present invention relates to a photoselective absorptive coating composition that maximizes solar radiant energy absorption (absorption rate α) and minimizes thermal radiation loss (emissivity ε) from the absorbing portion.

In recent years, with the spread of solar water heaters and the like, demands on heat collecting plates in terms of performance, price, etc. have become stricter. Essentially, the following properties are required for heat collecting plates.

That is, the energy H99.9% radiated from the high temperature sun, whose surface temperature is said to be 6000°, is 0.8 to 2.9%.
It is in the short wavelength range of 5 am, and it is desirable to absorb as much of this radiation as possible.
The peak wavelength of thermal radiation is approximately 10.6 μm at 0°C.
100℃・approx. 7.8μm, 200℃・approx. 6.1μm, 8
Since the target temperature is 1 μm at 00° C., it is desirable to avoid emitting thermal radiation with a wavelength of 5.1 to 1016 μm at 0 to 800° C. as much as possible.

On the other hand, the following method is used to conventionally form a film on the surface of a heat collecting plate, and its general performance is as follows.

(1) Chemical treatment (copper oxide, iron oxide, etc.).

α〉0.9, ε〈0.1゜ Excellent corrosion resistance and workability,
It has shortcomings in heat resistance and moisture resistance.

(2) Electroplating (black nickel, black chrome, etc.).

a'=0.9~0.96, t=0.05~0.11
．． Although tL is the best in terms of photoselective absorption, it is difficult to form a uniform film, and it is also expensive.

Black Nickel 1-Lliw has poor wettability.

(3) Aluminum electrolytic color coating Q! > 0.9, ε (0,10 heat resistant temperature is 850'
C and the best commercially available ones, but they are expensive.

(4) Stainless steel oxidized wave film (chromic acid treatment).

a! =0.91~0.94゜t =0.09~0.1
2゜Poor heat resistance.

(5) Black paint Most of the paints are so-called carbon paints, and these paints do not have light selective absorption ability, and α and ε are both 0.9 or more. Recently, paints with light selective absorption ability (acrylic resin, silicone polyester m II,
Although silicon alkyd materials (based on M11, etc.) are commercially available, they do not have sufficient weather resistance or durability.

The present research provides a coating composition that solves these problems. (1) A fluorine-containing polymer having a hydroxyl group in the molecule, a curing agent, and a wavelength of 0.8 to 2.5
High absorption rate of light in μm and wavelength of 5 to 10.6 μm
(2) A coating composition containing a coupling agent as an essential component in addition to the essential components in (1) above. be.

The fluorine-containing polymer having a hydroxyl group in the molecule used in the present invention is typically disclosed in JP-A-57-84107, etc., and has a hydroxyl value of 20 to 20.
200 is desirable for purposes of this invention. This type of fluorine-containing polymer is commercially available from Asahi Glass Co., Ltd. under the trade name "Lumiflon".

The curing agent for the hydroxyl group-containing fluorine-containing polymer is a melamine resin curing agent such as a gtylated melamine resin, a gtylated melamine resin, a urea resin curing agent such as a butylated resin or a methylsilver resin, Polybasic acid curing agents such as long-chain aliphatic dicarboxylic acids or aromatic polycarboxylic acids and their anhydrides, and adducts of non-yellowing polyvalent isocyanates such as long-chain methylene diisocyanate, isophorone diisocyanate, and lysine isocyanate. and their block polyvalent incyanates, etc., and in the case of curing agents containing active incyanate groups, so-called 2
A wavy composition results.

The ratio of the curing agent to the fluoropolymer used here is 97/3 to 5015 in the case of melamine resin, urea resin, and polybasic acid curing agents.
0 (weight ratio) is preferable, more preferably 9515~
It is 70/80.

In this case, heating at IOθ°C to 200°C is essential for curing. When using a crushed polyvalent incyanate, the hydroxyl group of the fluorine-containing polymer/NCO group of the curing agent = 0.5 to 2.0
(equivalent) is preferable, more preferably 0.7 to 1.3
It is. In this case, curing is possible even at room temperature or by heating. However, when using a blocked polyvalent incyanate, heating to a temperature necessary for dissociation of the blocking agent is required.

The metal oxide used in the present invention has a large absorption rate (α) for light with a wavelength of 03 to 2.5 μm and a small emissivity (ε) for light with a wavelength of 5 to 10.6 μm, for example, M n O*, CuO1C"), Ch, CuOCrx
OI Fe1. OI.

Cu0-Cr= 0--41'n01Cos Oa-
F'llI OI-IV'nO-Nip.

Cu0-CryOs, COI04-Cr+O
s -Few OI , CuO-yno 1'e*o+
, CuOCr*O+! InOFoIds etc.

The blending ratio of the gold M1 oxide is 10 to 10 in all coating components.
60 parts by weight is desirable. If it is less than 10 parts by weight, the absorption rate α will be low and the performance will be insufficient;
If the amount exceeds 11' parts, the physical performance and V and durability of the coating will deteriorate even if the campling agent of Claim 2 is used in combination, so it cannot be used. The method for producing the coating composition includes -d1ζ or all of the hydroxyl group-containing fluorine-containing polymer, and all of the metal oxide.
1 and an appropriate amount of an organic solvent (one that is effective for production and coating workability, such as aromatic hydrocarbon, ester type, ketone type, ether type, etc. can be selected), and a dispersant, etc. are mixed uniformly,
Normal coating f such as ball mill, sand mill, roll mill, etc.
Distribute using a 'l teaching machine. It is necessary to disperse the coating composition as finely and uniformly as possible.In order to further improve the light selective absorption ability of the coating composition, it is necessary to disperse it as finely and uniformly as possible. It is desirable to fill the coating with more metal oxide. However, if the proportion R of the heel metal oxide exceeds about 20% of the total coating components, the physical performance and surface durability of the coating will be significantly impaired.
It is difficult to blend the above ingredients using conventional methods.

As a result of intensive research to solve this problem, the creators of Zero-Start E-Month discovered an effective method. That is, a method of blending a coupling agent. By combining this,
The amount of metal oxide blended has been dramatically improved, accounting for 6% of the total coating components.
The coupling agent used in the present invention includes a titanium coupling agent and a silane coupling agent. It is sufficient to add 1 part of 2.0 to 1 part before dispersion.In addition, the use of a coupling agent not only improves the amount of metal oxide blended, but also improves the coating film even in areas where the amount of metal oxide blended is small. It also has the ability to improve gloss and physical properties.

The coating composition of the present invention can be applied by adding an appropriate amount of solvent to adjust the viscosity to an appropriate level, and using conventional coating methods such as air spray, air spray, brush coating, electrostatic coating, roll coater, and flow coater. Solvents suitable for each method are used. However, when polyvalent incyanates are used as a curing agent, the use of alcohols and the contamination of water must be avoided.

The thinner the coating composition of the present invention is, the more light is reflected on the metal part, which is desirable because the emissivity ε is low, but the inverse VC1 absorption rate α tends to be low and the coating film Since the durability is poor, the coating thickness is preferably in the range of 1 to 10 μm.

The coating composition for Misfire 1J11 uses a fluorine-containing polymer as Pine Gu, so it is characterized by excellent weather resistance, and it has a rating of 50 ( Even after testing for 30 hours, no deterioration of the coating film was observed.

Conventionally, as fluororesin paints, paints mainly composed of polyvinylidene fluoride and paints mainly composed of polytetrafluoroethylene have been known, but these are insoluble in organic solvents, and the formation of a film depends on polymers. Due to thermal melting, it is necessary to heat to a high temperature.
These paints have excellent weather resistance due to the following reasons: It is very difficult to achieve a uniform coverage. However, it is not appropriate to apply it to a photo-selective absorbing coating composition.However, the composition used in the present invention is not suitable for application to a photo-selective absorbing coating composition.
It is C6f and can be used not only for baking drying but also for curing and drying at room temperature. Therefore, it has the ability to be coated with a thin film and maintains excellent weather resistance, making it ideal for use as a material for optically selective coating.

The coating composition of the present invention can be applied to aluminum, stainless steel, copper, copper, plastics (ABS, acrylic, vinyl chloride, , FRP, etc.), Molcle boards, wood, etc., and because they are susceptible to contamination, they are not only suitable for solar hot water, but also for other solar related fields. For example, curtain fall,
The present invention can be applied to greenhouses, pipelines, etc. The fact that the life of the heat collecting plate, which is the heart of a solar water heater, can be significantly extended is confirmed by accelerated weathering tests and other tests. It is clear from the following that the tree 8 @ river will be explained in detail by way of examples, but the invention is not limited to the examples unless it goes beyond the gist.

Examples 1-9 Table @1 shows the components of Examples 1 to 9 of the compositions of the present invention.

Among these, component (1) is a hydroxyl-based fluoropolymer, metal oxide, and components that do not contain or contain a coupling agent, and component (1) is a curing agent component. As for the composition to be used, component J was dispersed in a ball mill in a conventional manner and mixed with component (2) before application. Note that Attack L1 in the table is the ratio of senior employees.

Comparative Examples 1 and 2 Typical general black paints that do not have special light-selective absorption properties are phosphoric acid resin paints (medium oil linseed oil alkyd resin, containing 3% carbon blank, flfi product name: Neo Glipton Black, Tokyoku Paint) (manufactured by ) was selected as Comparative Example 1.

Furthermore, Solar Paint manufactured by Company A was selected as Comparative Example 2 from among paints said to have light selection 1 absorption performance.

Example Compositions 1 to 9 Vi components I and ■ were mixed and Comparative Example 1
The viscosity was adjusted to an appropriate viscosity with a special thinner along with 2 and 2, and the thickness was adjusted to a dry thickness of 2±0.3 μm using SUS-3O4 VC air spray. Example 1.2.7.9 and Comparative Example 1.2 were left at room temperature for 14 days, and Example 3.4 was left at 180'
For Example 5.6.8, baking was carried out for 20 minutes at 140°C, and for each test piece obtained, the light selective absorption performance was evaluated. The test results are shown in Table 2, and the results of tests on weather resistance and other film performance are shown in Table 3.

(Left below) Next, Example 9 and @Table 4 show that the addition of a compensating agent improves the gloss, mechanical properties, moisture resistance, etc. of the coating even when the amount of metal oxide is small. .

Table 4 Effect of coupling agent Note: 1 piece of raw material, aluminum (5052P, Bonderite #71
3 processing). Film thickness 2±0.3μn1 Drying conditions 120℃
20 minutes or more From Examples 1 to 9vc, the performance of the photoselectively absorbing coating composition of the present invention was found to be higher than that of the black paint of Comparative Example 1 and the commercially available solar paint of Comparative Example 2.
Non-resistant and durable? ff is excellent, and it is recognized that there is a significant difference.

Claims (1)

[Scope of Claims] 1. A fluorine-containing polymer having a hydroxyl group in its molecule, a curing agent, and a high absorption rate of light with a wavelength of 0.3 to 2.5 μm and a low emissivity of light with a wavelength of 5 to 106 μm A coating composition containing a metal oxide as an essential component. 2 Fluorine-containing polymers having hydroxyl groups in their molecules, curing agents, and metal oxides that have a high absorption rate for light in the wavelength range of 0.3 to 2.5 μm and a low emissivity for light in the wavelength range of 5 to 10.6 μm. A coating composition containing a coupling agent as an essential ingredient.