JPS6141379B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a solar heat collector equipped with a heat collecting plate subjected to surface treatment aimed at improving heat collecting efficiency.

Currently, regarding the material of the heat collecting plate of the solar heat collector, which can be said to be the central part of the solar heat utilization system,
There are both metal and plastic. Comparing the two, there are advantages and disadvantages, but plastic is attractive in that it is lightweight, does not have the problem of corrosion on the water circuit side, and is inexpensive. Conversely, metals are advantageous in terms of heat resistance, weather resistance, strength, etc.

When considering the characteristics of the heat collection surface of a solar heat collector, it is important to consider what is called selective absorption, since the wavelength distribution of sunlight and the wavelength distribution of radiation from a radiator at a low temperature of about 100°C, for example, are different. Imparting properties is advantageous in terms of heat collection efficiency.

Since metals are good reflectors of infrared rays, they can be relatively easily imparted with selective absorption properties through surface treatments, etc.; however, in the case of plastics, they absorb infrared rays. Because of this, it is difficult to impart selective absorption properties. Traditionally,
The problem of imparting selective absorbency on plastics has received little consideration.

The present invention aims to achieve this selective absorption by forming a coating layer on a plastic substrate by painting and using a special pigment dispersed in this coating layer.

The problem with achieving selective absorption is how to keep the infrared emissivity low.

One way to achieve this is to first form a metal layer on the plastic surface as a first layer, and then form a second layer on top of this for solar absorption. Since there are two adhesive surfaces, concerns regarding durability, reliability, etc. will increase.

The present invention uses only one adhesive surface to the plastic base material to further improve its reliability, and also uses special pigments to exhibit most of its selective absorption properties.

The figure shows a cross-sectional view of the heat collecting plate in the solar heat collector of the present invention, where 1 is a plastic base material;
A covering layer A is formed on this plastic substrate 1. This coating layer A mainly consists of a urethane binder 2 and a pigment 5, which is formed by applying a blackening treatment layer 4 to the surface of a fine metal powder 3.

In the above configuration, incident sunlight a is absorbed by the blackening treatment layer 4 applied to the surface of the metal fine powder 3 and converted into heat, and then passes from the coating layer A through the plastic base material 1 to water or Pipe line 6 through which the medium passes
Conducts heat and collects heat.

On the other hand, infrared radiation from this heat collecting surface is transmitted through the coating layer A.
The infrared emissivity is kept low, largely depending on the infrared emissivity of the surface of the fine metal powder 3 dispersed near the surface of the metal powder.

In this way, selective absorption on the plastic substrate 1 is achieved.

Most of the solar heat collectors using plastic base materials that are currently in practical use are blow-molded using high-density polyethylene, and some are made using polypropylene. In any case, these polyolefin plastics have poor wettability with paint and are somewhat difficult to adhere to.

Therefore, the binder forming the coating layer A in the solar heat collector of the present invention should have adhesion to polyolefin plastics, and since it is difficult to bake in terms of heat resistance, However, its application is extremely limited due to the requirements for surface properties such as weather resistance.

As a result of searching for a suitable binder under these conditions, it was found that a urethane-based binder was most suitable. Among urethane binders,
In particular, rather than using aromatic polyisocyanates,
It has become clear that it is desirable to use aliphatic polyisocyanates. This is because fine metal powder is
This is thought to be because the surface layer is not completely hidden and some parts of the binder are exposed, and this is because aliphatic compounds have relatively less infrared absorption than aromatic compounds.

Regarding the blackening treatment of fine metal powder, various methods conventionally known as blackening treatment of metals can be applied.

Most of the conventional metal blackening techniques are mainly used for decorative purposes and are techniques aimed at plates.

In the case of the present invention, since the target is powder, the processing conditions are more moderate. Applicable metal powders include aluminum, titanium, zinc,
Metals selected from the group iron, copper, brass, nickel, chrome, and stainless steel are applicable. In the case of metals that have a relatively large ionization tendency, such as aluminum and zinc, copper compounds etc. are precipitated on the surface,
Copper, nickel, chromium, stainless steel, etc. can be blackened by oxidizing or sulfurizing their surface layers.

It is desirable that the blackening treatment layer formed on the surface of these metal powders has the property of absorbing sunlight well and absorbing almost no infrared rays, even if it is only a small amount.From this point of view, chromium, Preferably, a thin film of one or more oxides or sulfides selected from the group of manganese, iron, cobalt, nickel, and copper is formed.

Furthermore, the shape and size of these metal powders are important. It is desirable that the particle size of the metal is usually 50 μm or less. Among them,
In particular, a particle size of 1 .mu.m or less to 0.05 .mu.m or more is desirable; however, a particle size close to 50 .mu.m may be used as long as it has a flat shape.

The effects will be described below, focusing on Examples.

In addition, evaluation of selective absorption was performed by the following method.

Absorption rate α was evaluated using Shimadzu MPS-5000.
It was calculated using a self-recording spectrophotometer (incident angle: 6°, equipped with an integrating sphere reflector) from measurements at a wavelength of 0.3 to 2.0 μm for solar radiation with an atmospheric mass of 2. In addition, the evaluation of emissivity ε is based on DEVICES
& SERVICES COMPANY D and S
This was done using an AERD type emissivity meter.

Example Using aluminum powder with an average particle size of 5 μm,
This was added to an aqueous solution containing cupric nitrate: 2.5 wt%, potassium permanganate: 1 wt%, and nitric acid: 2 wt%.
The sample was immersed at 30°C for 20 minutes, blackened, washed with water and dried.

Next, as a urethane binder, 200 parts by weight of "Sumijiur N" (trade name) manufactured by Sumitomo Bayer Urethane Co., Ltd., and "Desmofene 670"
Add 128 parts by weight of (trade name), 60 parts by weight of the previously treated metal powder, and 150 parts by weight as a solvent.
A weight part of xylene was added and dispersed using a high-speed disperser to form a paint.

A polypropylene plate having dimensions of 70 mm x 150 mm x 1 mm was used as a test piece.

The emissivity ε of the base material of this test piece was 0.94. After activating this test piece in a dichromic acid mixture and drying it,
The coating was applied to a film thickness of approximately 15 μm, and the coating was allowed to harden naturally. This coating showed good selective absorption with an absorption rate α=0.95 and an infrared emissivity ε=0.45.

As described above, according to the present invention, it is possible to impart selective absorbency to a plastic substrate very easily, and since it is a coating, it is highly productive and can be obtained at low cost. Furthermore, by introducing selective absorption into a solar heat collector using a plastic base material, it is necessary to take more countermeasures than conventional methods regarding dry heating. Significant effects can be expected on the surface.

[Brief explanation of the drawing]

The figure is a sectional view of a heat collecting plate in the solar heat collector of the present invention. 1... Plastic base material, A... Covering layer, 3...
...Metal fine powder, 4...Blackening treatment layer, 5...Pigment.

Claims (1)

[Scope of Claims] 1. A heat collecting plate in which a coating layer mainly composed of a pigment formed by applying a blackening treatment layer to the surface of fine metal powder and a urethane binder is formed on a plastic base material by painting. A solar heat collector. 2 As the metal fine powder, one or more selected from the group of aluminum, titanium, zinc, iron, steel, brass, nickel, chromium, and stainless steel is used, and the surface thereof is coated with chromium, manganese, iron, cobalt, nickel, and copper. The solar heat collector according to claim 1, which uses a pigment formed by forming a thin film of one or more oxides or sulfides selected from the group.