JPS6355624B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a solar heat collector used for the purpose of domestic hot water supply, and more specifically, it is a plastic solar heat collector that has been subjected to selective absorption treatment on the surface of a base material whose main component is high-density polyethylene. It is related to heating devices. Conventional structure and its problems Conventional plastic solar collectors are made by filling high-density polyethylene with carbon black, etc.
It is manufactured by blow molding, but with this structure alone, the surface naturally does not have the ability to selectively absorb sunlight. Therefore, an inexpensive coating method is attracting attention as a means of achieving selective absorption on this surface, but in this case, sufficient adhesion cannot be obtained because the base material, high-density polyethylene, is highly non-adhesive. The problem was that it could not be done. Purpose of the Invention In view of the above conventional problems, an object of the present invention is to provide a solar heat collector in which a highly reliable and inexpensive selective absorption coating layer is realized on a base material mainly composed of high-density polyethylene. The purpose is to Composition of the Invention In order to achieve the above object, the present invention has a base material mainly composed of high-density polyethylene, and a thermoplastic acrylic resin, alkyd resin, chlorinated polyethylene, epoxy resin, and metallic powder as the main components. A first coating layer is formed, and a second coating layer having the ability to selectively absorb sunlight is further formed on the first coating layer. Since the high-density polyethylene itself, which is the base material, has a high infrared emissivity, it is first necessary to lower the infrared emissivity, and this is achieved by the metallic powder of the first coating layer. DESCRIPTION OF EMBODIMENTS The figure shows a conceptual diagram of the solar heat collector of the present invention, which consists of three layers. 1 in the layer is a base material made of high-density polyethylene, on which a first coating layer for suppressing infrared radiation is formed, and further on it a second coating layer having the ability to selectively absorb sunlight. is formed. The a side is the solar heat receiving surface side, and the b side is the medium side to which the converted heat is transferred. The first coating layer is mainly composed of thermoplastic acrylic resin, alkyd resin, chlorinated polyethylene, epoxy resin 2, and metallic powder 3. The metallic powder 3 reflects infrared rays well. The second coating layer is a coating layer that has a selective absorption ability for sunlight, and has good absorption ability in the sunlight wavelength region and sufficient transparency in the infrared wavelength region. Therefore, sunlight A is absorbed by this second coating layer and heat exchanged with the first coating layer.
The heat is conducted through the coating layer and the layer as shown by the arrow B, and the heat is transferred to the heating medium side b. On the other hand, since the second coating layer is sufficiently transparent to infrared rays, the radiation loss from the surface is dominated by the metallic powder 3 of the first coating layer, resulting in a low emissivity. sufficient selective absorption is achieved. Furthermore, with regard to adhesion to high-density polyethylene, which is a base material, it has been extremely difficult to adhere to it in the past, but in the present invention, by using chlorinated polyethylene, this difficulty in adhesion is solved. Attempts to use chlorinated polyethylene, focusing on its solubility parameters, for adhesion with difficult-to-adhere polyethylene substrates are not new. This type of technology has already been put to practical use in inks, etc., but most of them involve reducing the content of chlorine, which has a relatively low molecular weight (molecular weight in the thousands) and is produced using a solution method.
Highly chlorinated to 66% or more. Adhesion to low- and medium-pressure polyethylene was good, but adhesion to high-density polyethylene was problematic. Regarding the manufacturing method of chlorinated polyethylene, there is chlorinated polyethylene manufactured by an aqueous suspension method. In this case, chlorinated polyethylene with a molecular weight of tens of thousands to tens of thousands and a chlorine content of 30 to 50% is obtained. In the construction of the present invention, it is desirable to use chlorinated polyethylene produced by an aqueous suspension method. The reason is as follows. (1) Regarding the leafing property of metallic powder,
Since the chlorine content is low, the leafing properties of the metallic powder are less likely to be impaired. In other words, the polarity is low and the acid value is not low, so
Effective leafing of metallic powder can be achieved. (2) Since it has a large molecular weight and more structural similarities with high-density polyethylene, it can achieve good adhesion. However, these chlorinated polyethylenes have a large molecular weight and high solution viscosity, so there is a limit to their compatibility with other resins, but in order to achieve stable physical properties as a coating system, they can be used with other resins. It is best to use a mixture. A good resin base can be obtained by mixing the chlorinated polyethylene with an alkyd resin or an acrylic resin. When dispersing metallic powder into these resin bases to create a coating layer that provides good infrared reflection,
There is great difficulty. In order to obtain good infrared reflection, excessive dispersion of the metallic powder must be prohibited, but if the dispersion is limited to a range that improves leafing properties, the paint film will peel off the surface of the metallic leafing layer. It becomes unstable and unstable. Furthermore, if dispersion is performed to achieve sufficient adhesion, a problem arises in that leafing properties are difficult to achieve. To overcome this difficulty, the addition of epoxy resins is extremely effective. This epoxy resin achieves the function of stably adhering the metallic powder itself during coating while maintaining good leafing properties of the metallic powder. Further, as the metallic powder, a metallic powder having leafing properties such as copper or aluminum can be used, and it is preferable to use an aluminum powder with coarse particles. The blending ratio of metallic powder is preferably 5 to 40 wt%.
Desirably, a range of 10 to 25 wt% provides optimal leafing properties and adhesion. Once such a first coating layer has been formed, it provides a metal-like low emissivity surface, and therefore, on top of this first coating layer, conventionally applied on metals. Many paint-based coatings with the ability to selectively absorb sunlight can be applied. However, due to constraints regarding the adhesion of the first coating layer, curing conditions for application on plastic, or conditions regarding selective absorption, the second
The coating layer is Fe, Mn, Cu, Cr, Ni,
A coating with a thickness of 5 μm or less whose main components are one or more oxides and composite oxides 4 selected from the group of Co and one or more resins 5 selected from the group of acrylic resins, fluorocarbon resins, urethane resins, and alkyd resins. Preferably a layer. The metal oxide pigment has almost no infrared absorption and has good sunlight absorption ability. It is desirable to use these metal oxides having a particle size in the range of 0.01 to 0.5 μm. This is because it is thought that in the case of this particle size, the effect of scattering and absorbing sunlight favorably is remarkable. Furthermore, acrylic resin, fluorine resin, urethane resin, and alkyd resin all achieve good adhesion with the first coating layer. In addition, the film thickness was increased to 5 μm.
Since the settings are as follows, relatively good transparency of infrared rays is shown. The effects will be described below, focusing on Examples. Evaluation of selective absorption was performed by the following method. Absorption rate α was evaluated using Shimadzu MPS-5000.
Using a self-recording spectrophotometer (incident angle: 8 degrees, equipped with an integrating sphere reflector), the emissivity of atmospheric radiation AM=2 was calculated from the measured values at wavelengths of 0.3 to 2.0 μm. In addition, the evaluation of emissivity ε is provided by DEVICES & SERVICES.
Direct evaluation was performed using a DandSAERD type emissivity meter manufactured by COMPANY. Example A plate made of high-density polyethylene containing 1.5% carbon black and having dimensions of 70 mm x 150 mm x 1 mm was used as a test piece. The emissivity ε of this sample was 0.92. The undercoat paint was prepared by weighing the formulation shown in Table 1 and dispersing and mixing for 1 hour using a ball mill. Next, this paint was applied to the test piece with a film thickness of 10 to 20 μm and dried at 60° C. for about 1 hour.
Table 2 shows the results of evaluating the adhesion of each test piece by cellophane tape peeling test. This table 2
From the results, it was found that in a dispersed state that favors leafing of metallic powder and avoids excessive dispersion,
It can be seen that the metallic powder itself is extremely unstable without the coexistence of an epoxy resin and chlorinated polyethylene produced by a suspension method. Next, a top coat paint was prepared according to the formulation shown in Table 3.
Both were prepared by dispersing and mixing for 24 hours using a ball mill. This paint was applied to a dry film thickness of about 15 μm on a panel coated with paint P-12.

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[Table] Table 4 below shows the performance evaluation test results for each coating system.

[Table] From the above results, when comparing metal oxide pigments and carbon black, carbon black has 1.5μ
Even with a film thickness of m, selective absorption has not been achieved. It is also found that silicone resins have difficulty in adhesion with primers, and epoxy resins are inferior in terms of infrared transparency. The best results have also been obtained with fluorocarbon resins. Although not mentioned in the explanation of the coating, the coating may contain fillers, additives, surfactants, and others to maintain paint workability in order to realize the coating. . Effects of the Invention As described above, according to the present invention, a thermoplastic acrylic resin, an alkyd resin, a chlorinated polyethylene, an epoxy resin, and a metallic powder are used as main components on a base material that is a high-density polyethylene as a main component. A first coating layer is formed, and a second coating layer having the ability to selectively absorb sunlight is formed on the first coating layer. A material that can achieve highly reliable selective absorption on the material, is lightweight, has excellent workability, and is free from corrosion, making it possible to obtain an extremely inexpensive and high-performance solar collector. It is.

[Brief explanation of drawings]

The figure is a conceptual diagram of the solar heat collector of the present invention. DESCRIPTION OF SYMBOLS 1... High-density polyethylene base material, 2... Resin of the first coating layer, 3... Metallic powder, 4...
1 selected from the group of Fe, Mn, Cu, Cr, Co, Ni
5. Resin of the second coating layer.

Claims (1)

[Claims] 1. Thermoplastic acrylic resin, alkyd resin, chlorinated polyethylene, or epoxy resin on a base material mainly composed of high-density polyethylene,
A solar heat collector in which a first coating layer mainly composed of metallic powder is formed, and a second coating layer having a selective absorption ability of sunlight is further formed on the first coating layer. 2 The second coating layer contains Fe, Mn, Cu, Cr,
A coating layer with a thickness of 5 μm or less whose main components are one or more oxides or composite oxides selected from the group of Ni and Co, and one or more resins selected from the group of acrylic resins, fluorocarbon resins, urethane resins, and alkyd resins. A solar heat collector according to claim 1.