JPS6158132B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an agricultural film that has excellent visible light transmittance (herein referred to as "light transmittance") and heat retention. For example, agricultural films used in greenhouse cultivation, tunnel cultivation, etc. of agricultural products are required to have not only translucency but also heat retention properties. That is, daytime sunlight passes through the film and warms the ground and crops inside the greenhouse and tunnel, while at the same time the heat passes through the film and escapes to the outside, suppressing the rise in temperature. Therefore, the transmission of sunlight energy is large,
Films that do not allow heat to escape easily, that is, films that have a higher heat retention ability, can raise the temperature inside the house or tunnel. Even at night, the higher the heat retention capacity of the film, the slower the cooling inside the house and tunnel, keeping the minimum temperature high, and the faster the temperature rises after sunrise. In practical terms, these factors manifest as differences in the growth speed of agricultural crops, yield, and heating energy consumption, and heat retention is one of the most important properties for agricultural films. By the way, cooling in agricultural greenhouses and tunnels is mainly caused by infrared rays emitted from the ground passing through the film and dissipating to the outside.To prevent such cooling, it is necessary to block the transmission of infrared rays. It is already well known that this is a good thing. For example, the infrared spectrum emitted from the ground at a temperature of 10°C is approximated by the infrared spectrum emitted from a blackbody at the same temperature, and can be approximately expressed as shown in the figure using Planck's formula for blackbody radiation. As is clear from the figure, the wavelength range is 5 μ (wave number
Most of the energy is contained in the range of 2000) to 50μ (wavenumber 200). In addition, conventionally, it has been possible to prevent the transmission and dissipation of infrared rays by adding a substance that absorbs and reflects infrared rays to an agricultural film made of a thermoplastic synthetic resin, thereby improving the film's heat retention properties, and such substances include silicic anhydride, Phosphate, aluminosilicate anhydride, polyacetal, etc. are known. The additives used for this purpose must have the following properties: absorb infrared rays over a wide range of 5μ to 50μ, have a refractive index that matches that of the base resin so as not to reduce the transparency of the film, and be suitable for outdoor use. In order to use it, it must satisfy three conditions: it must be water resistant. However, there is no known infrared absorbing material that satisfies these three requirements at the same time. For example, silicic anhydride has a satisfactory refractive index and water resistance, but has a narrow infrared absorption wavelength range and poor heat retention. Calcium phosphate has a refractive index different from that of synthetic resins, so it becomes cloudy, and potassium phosphate has a defect of poor water resistance and whitening during use. The present inventors have conducted various studies on heat retention improving additives that satisfy the above three requirements, and have arrived at the present invention. That is, in the present invention, 1 to 60 mol% of one or more of alkali metal oxides and alkaline earth metal oxides are added to a transparent thermoplastic synthetic resin.
This is an agricultural film with excellent translucency and heat retention, characterized by being made of a composition to which phosphate glass powder is added. The thermoplastic synthetic resin having transparency in the present invention refers to a synthetic resin that can be formed into a transparent film when molded into a film, and examples thereof include:
For example, polyolefins such as low density polyethylene, medium density polyethylene, high density polyethylene, ethylene vinyl acetate copolymer, polypropylene,
Examples include polyvinyl chloride, polyester, polyamide, polymethyl methacrylate, and the like. The phosphate glass used in the present invention is
A glassy substance containing P ₂ O ₅ as a main component, which contains 1 to 60 mol% of one or more of alkali metal oxides and alkaline earth metal oxides. Further, it is preferable that the composition further contains 1 to 40 mol% of one or two of aluminum oxide, boron oxide, and titanium oxide. In the present invention, mol% is calculated by expressing the phosphoric acid component, which is the main component, as P ₂ O ₅ and the components added to it as basic oxides, such as K ₂ O, BaO, Al ₂ O ₃ , TiO ₂ . It is what was done. The addition of alkali metals and alkaline earth metals has the effect of adjusting the melting point and refractive index, and aluminum oxide and the like have the effect of strengthening the glass and further broadening the absorption range of infrared rays. This phosphate glass is desirably finely powdered from the viewpoint of miscibility with the thermoplastic synthetic resin, and its particle size is 50 μm or less, preferably 10 μm or less. In addition, fine powder of phosphate glass can be used in some cases to contain paraffin, fatty acids, polyhydric alcohols, etc.
It can be treated with a surface treatment agent such as a silane coupling agent. Powders subjected to such treatment have improved dispersibility in synthetic resins, as well as improved interfacial adhesion with synthetic resins, and can improve the tensile strength of the film. The agricultural film according to the present invention has broad absorption in the infrared wavelength range of 5μ to 50μ, has excellent heat retention, and has excellent translucency because the refractive index of the added glass can be matched to the base synthetic resin. It also has excellent water resistance. The amount of phosphate glass powder added is adjusted depending on the type of synthetic resin, the thickness of the film, etc. Naturally, the thinner the film, the greater the amount of addition needs to be. For example, when molding a low-density polyethylene film with a thickness of 100 μm, adding 10% by weight of phosphate glass powder can provide good infrared absorption and therefore good heat retention. Furthermore, for example, polyvinyl chloride itself has a higher infrared absorbing property than polyolefin, so the amount of phosphate glass powder added can be reduced. Generally, 1.0% by weight or more is used, and 2.0 to 25
Approximately % by weight is appropriate. In the present invention, various additives can be added to the composition before molding. For example, in order to improve the dispersibility of the phosphate glass powder into the synthetic resin, a dispersant such as a fatty acid metal salt can be added. The dispersant may be added after being mixed with the phosphate glass powder, or may be added during kneading of the phosphate glass powder and the resin. Addition of a dispersant improves the dispersibility of the phosphate glass powder, thereby improving the translucency of the film. Furthermore, in the present invention, the thermoplastic synthetic resin and the phosphate glass powder can be kneaded by various methods, such as using a Banbury machine, an extruder, a roll, a kneader, etc. It is usually molded in the form of pellets. The composition thus obtained is molded into a film using T-die molding, extrusion molding such as inflation molding, calender molding, or the like. The agricultural film of the present invention has excellent translucency and allows sunlight to pass through it well, but it also absorbs infrared rays emitted from objects at room temperature over a wide wavelength range, so it has extremely excellent heat retention properties. . Furthermore, since it has excellent water resistance, it can be advantageously used in various applications that utilize these characteristics. For example, it can be used as a covering material for greenhouse cultivation or tunnel cultivation. Next, an explanation will be given by giving Examples and Comparative Examples. Example 1 Low density polyethylene (trade name Yucalon AF30 manufactured by Mitsubishi Yuka Co., Ltd.) 90% by weight and average particle size of 2
μ, a composition of 10% by weight of phosphate glass powder with a composition of 75 mol% P ₂ O ₅ % BaO 25 mol% was formed into a film by the inflation method at a temperature of 170°C to a thickness of 0.1 mm.
I got the film. Example 2 Low density polyethylene (product name Yucalon AF30 manufactured by Mitsubishi Yuka Co., Ltd.) 90% by weight and average particle size of 2
μ, composition is P ₂ O ₅ 75 mol% K ₂ O 15 mol%, Al ₂ O ₃ 10
A composition containing 10% by weight of phosphate glass powder (mol%) was formed into a film by an inflation method at a temperature of 170°C to obtain a film with a thickness of 0.1 mm. Example 3 Soft polyvinyl chloride (35% DOP as plasticizer)
(wt% content) 95 wt%, average particle size 2μ, composition:
P ₂ O ₅ 45 mol%, MgO 30 mol%, B ₂ O ₃ 20 mol%,
A composition containing 5% by weight of phosphate glass powder, which is 5% by mole of Al ₂ O ₃ , was formed into a film by an inflation method at a temperature of 150° C. to obtain a film having a thickness of 0.1 mm. Comparative Example 1 The same low-density polyethylene used in Example 1 was formed into a film by an inflation method at a temperature of 170° C. to obtain a regular agricultural polyethylene film having a thickness of 0.1 mm. Comparative Example 2 A film was formed in the same manner as in Example 1, except that 10% by weight of silicon oxide powder with a particle size of 2μ was used instead of the phosphate glass powder in Example 1, and the film was formed to a thickness of 0.1
A film of mm was obtained. Comparative Example 3 A film was formed in the same manner as in Example 1 except that 10% by weight of calcium phosphate powder with a particle size of 3 μm was used instead of the phosphate glass powder in Example 1.
A film with a thickness of 0.1 mm was obtained. Comparative Example 4 A film was formed in the same manner as in Example 1, except that 10% by weight of potassium phosphate powder with a particle size of 3μ was used instead of the phosphate glass powder in Example 1.
A film with a thickness of 0.1 mm was obtained. Comparative Example 5 A film was formed in the same manner as in Example 3 except that the soft polyvinyl chloride used in Example 3 was used alone to obtain a 0.1 mm thick ordinary agricultural polyvinyl chloride film. The average blackbody radiant energy transmittance at 283 mm of the films obtained in each of the Examples and Comparative Examples was measured, and the results were as shown in Table 1. In addition, agricultural tunnels were made using the films obtained in each of the Examples and Comparative Examples, and the minimum temperature inside the tunnel was measured under the same conditions at night under clear skies (the minimum outside temperature at that time was 1.4°C). It was hot.). The results were as shown in Table 1. Next, in order to examine the translucency and water resistance of the film, the natural light transmittance of the film was measured, and then the film was soaked in warm water at 60° C. for a period of time, and the natural light transmittance of the film was measured. The results were as shown in Table 2. As is clear from the results shown in Tables 1 and 2, the films of the Examples are excellent in heat retention, translucency, and water resistance, whereas the films of the Comparative Examples are At least one of heat retention, translucency, and water resistance is poor.

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【table】

【table】 [Brief explanation of the drawing]

The figure shows a curve showing the radiant energy of a black body at 283〓.

Claims (1)

[Claims] 1. Phosphate glass powder containing 1 to 60 mol% of one or more of alkali metal oxides and alkaline earth metal oxides is added to a transparent thermoplastic synthetic resin. An agricultural film with excellent translucency and heat retention, characterized by comprising an additive composition. 2 Phosphate glass contains one or more alkali metal oxides and alkaline earth metal oxides.
60 mol% and 1 to 40 mol% of one or more of aluminum oxide, boron oxide, and titanium oxide. An excellent agricultural film.