JPH04110380A - Ultraviolet absorber - Google Patents

Abstract

PURPOSE:To provide an ultraviolet absorber which can cut widely an ultraviolet light and provide a high haze by coating the surface of a fine zinc oxide particle having a specified particle diameter with titanium oxide. CONSTITUTION:An ultraviolet absorber is prepd. by coating the surface of a zinc oxide particle having a particle diameter of 0.1mum or smaller with titanium oxide. As the surface of the fine particle of zinc oxide with good transparency and ultraviolet insulating action is coated with titanium oxide, regardless of the thickness of the surface layer of titanium oxide, a part of the light is reflected and remaining light enters into the zinc oxide particle, where the visible light is passed while the ultraviolet light is absorbed. Then, the light reaches the next zinc oxide particle and repeats the reflection and ultraviolet absorption to obtain a large haze caused by light scattering and sufficient ultraviolet absorption. The obtd. ultraviolet absorber is suitably used as a filler for coatings and plastics.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an ultraviolet absorbent having excellent translucency and high haze (haze value).

[Conventional technology]

In general, light emitted from lighting lamps and sunlight contain ultraviolet rays, which adversely affect foods and other objects such as deterioration and discoloration. Therefore, it is necessary to cut out this ultraviolet ray as much as possible, and conventional methods have been to apply paint mixed with an ultraviolet absorber to the shade cover of the lighting lamp, or to mix in ultraviolet absorbing fiber and irradiate the lamp. However, there was nothing that could be put to practical use.

Conventionally, as transparent ultraviolet absorbers, benzophenone type and benzophenol type are known as organic types, and titanium oxide, zinc oxide, etc. are known as inorganic types.

[Problem to be solved by the invention]

However, while organic UV absorbers absorb UV rays, they themselves deteriorate and turn yellow or brown, eventually becoming saturated and no longer absorbing UV rays, and because they are organic, they pose hygiene and toxicity issues. There is.

On the other hand, titanium oxide (TiO3) does not deteriorate because it is an inorganic substance, but anatase has an ultraviolet absorption edge of 36
0 nm, and there is a gap up to 400 nm, which is the upper limit of ultraviolet rays, and the ultraviolet absorption ability is insufficient. Furthermore, although rutile has an absorption edge at 370 nm, it does not cut ultraviolet rays sharply, so the absorption tail reaches toward visible light, giving it a yellowish tinge. Furthermore, since titanium oxide is an excellent white pigment, it also absorbs a lot of light.

On the other hand, zinc oxide (Zn0) can block ultraviolet rays of 380 nm or less, and is known to be the material that can cut ultraviolet rays closest to 400 nm among inorganic ultraviolet absorbers. However, it lacks sufficient transparency and absorbs a considerable amount of visible light, unlike conventionally used white pigments.

In addition, in the case of lighting lamps, in order to absorb ultraviolet rays and reduce eye irritation, it is possible to increase the haze value (haze value = the proportion of light that does not travel in a straight line in the transmitted light) to obtain a vague and soft light. Although this is required, the conventional method is to corrode the surface of the lamp itself or the shade cover with chemicals, roughen the surface by sandblasting, etc., or create a rough surface with a satin pattern or textured surface to create diffused reflection. Met. For this reason, a surface treatment process is required, the cost is also high, and it cannot be applied to surfaces with complicated shapes. Furthermore, if oil or the like adheres to this rough surface, there are problems such as the diffused reflection decreases and the surface becomes transparent, and the rough surface easily attracts dust and becomes dirty.

By the way, when trying to solve the problem of ultraviolet rays and haze at the same time using the zinc oxide mentioned above, the commonly used zinc oxide is composed of a large number of crystallites, so reflection occurs at the boundaries of each particle, and therefore it becomes transparent. Although the haze increases as the properties worsen, light is absorbed by the impurity layer generated at the boundaries of each particle, and more than 40% of visible light is absorbed when passing through the zinc oxide layer IJLm. As a result, it could not be used as a fish that was transparent and had a high haze. In addition, ordinary zinc oxide pigments do not absorb short-wavelength ultraviolet rays, so they cannot provide sufficient UV protection.

Therefore, the technical object of the present invention is to provide an ultraviolet absorber that can sufficiently block ultraviolet rays and at the same time ensure a high haze by itself.

[Failure to solve the problem]

In order to solve the above-mentioned technical problem, the present invention uses an ultraviolet absorber in which titanium oxide is coated on the surface of zinc oxide particles having a particle size of 0.1 μm or less.

Fine particles of zinc oxide are durable and transparent, and are a substance that blocks ultraviolet rays with wavelengths close to 400 nm or less, but their haze is quite small. However, by coating titanium oxide on particles of zinc oxide, it is possible to approach the high refractive index n = 2.5 of titanium oxide,
As a result, the reflectance of the zinc oxide particles increases, resulting in high haze.

The physical property of zinc oxide itself is that it is inherently transparent. Zinc oxide for ordinary pigments has a particle size of 1 m or more and is a polycrystalline aggregate. Zinc oxide is a solid solution of various substances, and when it crystallizes, the solid solution precipitates on the crystal surface and light is easily absorbed there, so the light transmission of zinc oxide particles is very poor as it is made of polycrystals. Become.

On the other hand, as the particle size of zinc oxide gradually decreases, particularly in the wavelength range of light, transparency improves. This is because when the particle size becomes 0.1 μm or less, the composition of each particle becomes a single crystal or single particle, and there is no boundary line between particles, which is a major cause of light absorption, and the particle size does not match the wavelength range of light. This is because the transparency itself will be improved if it becomes the same level or lower.

For this reason, in the present invention, the particle size of zinc oxide is 0.1
Although the particle size is set to be JLm or less, a particle size of 0.037 pm or less is preferable in order to obtain nearly perfect transparency.

When titanium oxide is coated on the surface of such fine particles of zinc oxide, part of the light is reflected regardless of the thickness of the titanium oxide surface layer, and the remaining light enters the zinc oxide particles and emits ultraviolet rays. It passes through the visible light range while absorbing
When it hits the next zinc oxide, reflection and ultraviolet absorption are repeated again, resulting in a large haze due to light scattering and sufficient ultraviolet absorption. This effect is not affected by the coating thickness of titanium oxide, so there is no limit to the coating thickness in normal cases, but if it becomes too thick, the amount of zinc oxide will be relatively reduced, so from that point of view Coating up to 0.2 diameter (40% of total volume)
) is preferred.

In this way, in the present invention, a unique effect is obtained by coating the surface of zinc oxide with titanium oxide, utilizing the characteristics of zinc oxide for transparency and ultraviolet absorption ability, and utilizing the reflection of titanium oxide for haze. It was done.

Therefore, if the zinc oxide particles coated with titanium oxide are mixed and dispersed in a normal binder (refractive index of 1.7 or less), a paint with good ultraviolet absorption and high haze can be obtained. For example, it can be applied or kneaded into the shade cover of a lighting lamp, it can be kneaded into plastic, and it can also be kneaded into the vinyl cover of an agricultural greenhouse. When used as a shade cover for lighting lamps, it can effectively prevent discoloration and deterioration of foods, other objects, paintings, furniture, etc. that are exposed to the lighting lamps as it absorbs ultraviolet rays, and at the same time prevents high haze. This reduces irritation to the eyes. On the other hand, transparent vinyl sheets used in agricultural greenhouses are generally not treated to block ultraviolet rays. Therefore, by coating or kneading paint containing the above-mentioned ultraviolet absorber into this vinyl sheet, it is possible to cut ultraviolet rays from entering the agricultural greenhouse and prevent the occurrence of pests, as well as to prevent the growth of nitrifying bacteria in the soil. It promotes the growth of plants and produces favorable results for plant growth. Furthermore, since the haze is increased by applying the above-mentioned paint, sunlight is scattered and hits the plants from multiple directions, resulting in even better growth.

Conventionally, increasing the haze required additional processing steps such as roughening the surface by sandblasting or providing a pear pattern, but the present invention eliminates the need for such processing steps at all. In addition, with the conventional method, dust and oil tend to stick to the surface, and when water or oil gets on the surface, especially with sandblasting and satin-like patterns, diffuse reflection occurs and haze disappears, but with the present invention, haze is caused by fissure, so this This will not cause any trouble.

(Example-1) Fine particles of zinc oxide (manufactured by Sumitomo Cement Hayashi Co., Ltd.) of 0.01 to 0.02 m are dispersed in ethanol by ultrasonication to obtain a suspension containing 54% by weight of zinc oxide. Next, 1 part of tetraethoxytitanium was added to 100 parts by weight of this suspension.
parts by weight, 2 parts by weight of water, and 0.03 parts by weight of hydrochloric acid, and dried by introducing hot air with an inlet temperature of 400°C using a spray dryer to obtain a particle size of 0.06 m coated with a thin film of titanium oxide. The following zinc oxide was obtained. Furthermore, 60 parts by weight of an acrylic resin (Dainippon Ink's Autasol 5744) and 120 parts by weight of isopropyl alcohol were mixed with 40 parts by weight of this zinc oxide and uniformly dispersed to obtain a paint. The paint thus obtained was applied to a glass plate and heated at 110°C for 15 minutes to obtain a coating film with a thickness of 5 m.

The total light transmittance of the above coating film is 96%, and the haze is 35%.
It cuts 98% of ultraviolet rays of 300 to 400 nm.

[Example-2] Polystyrene was dissolved in acetone, and 5% by weight of zinc oxide with a particle size of 0.06 μm obtained in Example-1 was added to the polystyrene, and the mixture was uniformly dispersed and mixed. After evaporating the acetone, this was pressure-molded at 200°C to produce a 1 mm thick sheet.

As a result of measurement using this sheet haze meter, the total light transmittance was 93% and the haze was 29%.

〔effect〕

As explained above, according to the ultraviolet absorber according to the present invention, it is possible to broadly block ultraviolet rays and at the same time obtain a high haze, so that it can be effectively used as a filler for paints and plastics. Further, since a high haze can be obtained by itself, there is an effect that the conventional surface treatment process for anti-glare can be omitted.

Claims (1)

[Claims] An ultraviolet absorber characterized by coating the surface of zinc oxide particles with a particle size of 0.1 μm or less with titanium oxide.