JPS6178465A - Formation of low reflective surface - Google Patents

Abstract

PURPOSE:To markedly lower reflectivity by efficiently scattering and absorbing the electromagnetic wave incident to a surface between erected fibers, by applying stable carbon fibers to the surface of a material such as a metal or plastic by electrostatic flocking. CONSTITUTION:A carbon fiber to be used has a diameter of 3-15mum, a length of 20-500mum and the ratio of the length to the diameter of 3-50. This carbon fiber is applied to the surface of a metal such as aluminum or titanium or plastic such as vinyl chloride or FRP by electrostatic flocking under such a condition that the distance between electrodes is 2-30cm and the intensity of an electric field is 2-25kV/cm. The reflectivity of thus obtained surface to an electromagnetic wave from a near ultraviolet region to an infrared region is about 0.01-0.02 and is hardly dependent on an incident angle.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention uses electrostatic flocking method to fabricate short carbon fibers into metals,
The idea is to develop a method of forming a low-reflectivity surface that has an extremely low reflectance of electromagnetic waves in the near-ultraviolet to infrared region, and whose reflectance is almost independent of the angle of incidence, by implanting it on the surface of a material such as plastic.

(Conventional technology) Spacecraft for artificial sanitary purposes usually use paint, vapor deposition, oxidation, tape, etc. on the surface of spacecraft to maintain the permissible temperature/degree range in which on-board equipment can operate normally during the entire mission. Various thermal control coatings are applied. These thermal control coatings regulate the amount of heat input and radiation based on the radiation characteristics of the surface (solar absorption rate, emissivity) and control the temperature of the spacecraft, and generally fall within the temperature range required for spacecraft. An appropriate coating is selected by Among these thermal control coatings, when a surface with high solar absorption and high emissivity is required, that is, a surface with low reflectance to electromagnetic waves from the solar spectral range to the infrared range, black paint, Alternatively, anodic oxidation that produces a black color has been used.

However, these coatings have the following problems. First of all, it deteriorates when exposed to ultraviolet rays, electron beams, proton beams, etc. in space, and its radiation characteristics change.

Second, as the angle of incidence of electromagnetic waves increases, the reflectance of the surface increases. Due to changes in these characteristic values, the temperature range that the spacecraft experiences becomes wider, and the initially permissible temperature range is no longer satisfied.In addition, in optical equipment such as cameras and spectrometers, the surfaces of hoods, etc. are used to prevent stray light. We apply black paint with low reflectance or attach felt etc. to the surface. However, high-precision optical instruments require a considerably low reflectance, and the surfaces obtained by the methods described above are insufficient, and surfaces with even lower reflectances are desired.

As described above, a method for forming a satisfactory surface that can exhibit a significantly low reflectance to electromagnetic waves in the near-ultraviolet to infrared region has not yet been found.

(Problems to be Solved by the Invention) Therefore, the purpose of the present invention is to provide space equipment surfaces such as artificial satellites or optical equipment hood surfaces such as cameras that require extremely low reflectance to electromagnetic waves in the near-ultraviolet to infrared range. An object of the present invention is to provide a method for forming a low-reflectivity surface that can be applied to, etc.

(Means for Solving the Problems) As a result of intensive research into a method for eliminating the drawbacks of the conventional coating methods and forming a low-reflectivity surface, the present inventors found that By planting short carbon fibers using electrostatic flocking, electromagnetic waves incident on the surface are efficiently scattered and absorbed between these upright fibers, resulting in a significant decrease in reflectance, and the reflectance is almost dependent on the angle of incidence. I found out that it doesn't.

That is, the method for forming a low-reflectivity surface of the present invention applies to
~15. carbon fibers with a length of 20 to 5 oO, pm and a length to diameter ratio of 3 to 50, with a distance between electrodes of 2
~aocms electric field strength 2-25 KV/cm,
By electrostatic flocking metals such as aluminium, beryllium, titanium etc. or plastics such as polyvinyl chloride,
Teflon, glass fiber reinforced plastic (FRP),
It is characterized by being planted on the surface of plastics such as carbon fiber reinforced plastics (arRP), Kapton, etc.

The cardon fiber used in the present invention has advantages such as its own low reflectance, high strength and excellent abrasion resistance, and extremely low deterioration due to ultraviolet rays, etc. Because it has moderate conductivity, it does not require electrodeposition treatment during electrostatic flocking, which is required for synthetic fibers. However, simply coating the surface with carbon fibers does not provide the advantages of the surface obtained by the present invention; an excellent surface can only be obtained by making the short fibers stand upright on the surface using electrostatic flocking.

The diameter of the carbon fJti & used in the present invention is 3
~15 μm 1 preferably 5-12 μm, length 20-12 μm
500 μm 1 preferably so to aooPm, and the length to diameter ratio is 8 to 50. Preferably, a range of 10 to 30 is appropriate. When the length is longer and thinner than the above range, the entanglement of the short fibers becomes severe, and the flying condition of the short fibers during static 7IL flocking becomes extremely poor. Furthermore, when the hair is shorter and thicker than the above range, the reflectance of the flocked surface becomes high.

In addition, the distance between the electrodes during electrostatic flocking is 2 to 3 Qcm, preferably 8 to 20 C, Ill, and the electric field strength is 2 to 25 Kv/c.
rn1 is preferably 3 to 10 KV/c, and a range of 11 is suitable.

If the distance between the electrodes is less than 2 cm+, processing unevenness will be significant, and if it is greater than 30 cm, the applied τ pressure will be extremely large.
The application device becomes too large. On the other hand, %, electric field strength 2 KV/
If it is less than C1n, the ratio of carbon fibers flying up to the surface to be flocked becomes small, and if it is more than 2 5 Kv/cm, corona discharge tends to occur.

(Function) First, the surface obtained by the method of the present invention with the above configuration has a significantly low reflectance of about 0.01 to 0.02 for electromagnetic waves in the near-ultraviolet to infrared region. Second, its reflectance is almost independent of the angle of incidence. Thirdly, there is little deterioration due to ultraviolet rays, etc.

(Examples) The present invention will be described in more detail with reference to Examples below, but the present invention is not limited to these Examples and can be applied and implemented in various ways.

Example 1 Carbon short fibers with a diameter of about 6 μm, a length of 100 to 300 μm, 1 JL interpolar distance, 4 CTnSuU field strength, 3,5
Plants were planted with static tiLM bristles on aluminum plates coated with α-cyanoacrylate adhesive under KVAm conditions. As a result, 26.6% of the aluminum plate surface
An area equivalent to

The spectral reflectance of the surface of this sample for light at an incident angle of 5 is the first
Wavelength range 0.8~1.6 μ, as shown in song s1 in the figure.
m was extremely low at 0.012 to 0.023. Further, even when the incident angle of light was changed up to 60 degrees, the reflectance hardly changed.

Note that the spectral reflectance was measured using a monochromator and an integrating sphere.

Comparative Example 1 The same short carbon fibers as in Example 1 were dropped and scattered onto an aluminum plate coated with an α-cyanoacrylate adhesive. The spectral reflectance of the sample surface for light at an incident angle of 5° is within the wavelength range of 0.3 to 1.5°, as shown by curve 2 in FIG.
At 6 μm, the value was 0.035 to 0.090, which was a very high value because the fibers were not erect compared to Example 1.

Comparative Example 2 Low reflective black paint (3M Velvet Coatin)
gaextel) was spray-coated onto an aluminum plate to a film thickness of approximately 400 μm. The angle of incidence of this sample surface is 5.
The spectral reflectance of light is 0.038 to 0.03 in the wavelength range of 0.3 to 1.6 μm, as shown by curve 8 in FIG.
It was 039. Also, if the incident angle of light is set to 60 degrees,
The reflectance was higher than when the incident angle was 5.5, and the reflectance integrated over the above wavelength range increased by about 40%.

(Effects of the Invention) As explained above, according to the present invention, by applying electrostatic flocking of short carbon fibers to the surface of metals, plastics, etc., the reflectance of electromagnetic waves in the near-ultraviolet to infrared region is significantly reduced. It is possible to form a surface whose reflectance is almost independent of the angle of incidence, and is extremely useful as a technology that contributes to thermal control coatings in space equipment and adjustment of the reflective properties of optical equipment hood surfaces such as cameras. It is.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between wavelength and spectral reflectance of samples of Examples and Comparative Examples.

Claims (1)

[Claims] 1. Carbon fibers with a diameter of 3 to 15 μm, a length of 20 to 500 μm, and a length-to-diameter ratio of 3 to 50 are electrostatically flocked under an electrode distance of 2 to 30 cm and an electric field strength of 2 to 25 KV/cm. A method for forming a low-reflectivity surface, which is characterized by implanting it on the surface of a material such as metal or plastic.