JPS6217486B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to agricultural covering materials, and more particularly to agricultural covering materials that have excellent heat retention, frost resistance, transparency, and moisture absorption properties, and do not require ventilation operations.

The amount of light that affects the growth of vegetables, flower petals, fruit trees, etc.
The influence of environmental factors such as carbon dioxide concentration, temperature, and humidity is extremely important, and the use of a wide variety of agricultural production materials that are essential for modern agricultural management also artificially makes the growing environment suitable for these crops. This is what we are trying to cultivate. For example, light, carbon dioxide gas, and water are indispensable for photosynthesis, which is the basis of crop growth, and the values of the light saturation point and carbon dioxide gas compensation point differ depending on the type of crop, but in general, the more good. In addition, temperature is an important environmental factor involved in various physiological phenomena, including photosynthesis and absorption of nutrients and water by roots, and the relationship between crop growth and temperature depends on the type of crop or the stage of growth. Although it varies depending on the species, each species has its own suitable temperature for growth, with a high temperature limit for daytime temperatures and a low temperature limit for night temperatures during the low temperature period.

Furthermore, the relationship between crop growth and humidity is extremely important.
This leads to overhumidity, which promotes the growth of pathogenic bacteria in crops. Particularly in the low-temperature season, humid conditions induce gray mold, downy mildew of cucumbers, and sclerotium, which attack various fruits and vegetables, and the crops themselves grow weakly under humid conditions. Efforts are made to lower humidity as much as possible during the cold season.

Conventionally, synthetic resin films such as polyvinyl chloride, polyethylene, ethylene-vinyl acetate copolymers, polyethylene nets, and cheesecloth have been used as agricultural covering materials for accelerated cultivation, frost protection, and cold protection for vegetables, flowers, fruit trees, etc. in low-temperature seasons. , nonwoven fabrics, etc. have been used, but they have the following drawbacks in terms of regulating the growing environment of crops, and cannot be said to be truly satisfactory.

In other words, when synthetic resin films such as polyvinyl chloride, polyethylene, and ethylene-vinyl acetate copolymers are sealed, there is no exchange with the outside air, so there is a lack of carbon dioxide, which is essential for photosynthesis. Since it has no hygroscopicity, it is always under humid conditions, which causes various diseases as explained above. Furthermore, even in low-temperature periods, daytime temperature increases can be extremely large depending on the cropping season, exceeding the optimum temperature for crop growth, so ventilation operations, including the effects of carbon dioxide supply and humidity control, are required. Ventilation operations require a great deal of effort, but if they are neglected, not only will crops not be able to grow stably, but in some cases they may even be wiped out. Furthermore, materials such as polyethylene and ethylene-vinyl acetate copolymer have a high transmittance for infrared rays centered on the 6-17μ wavelength range, so even though the temperature rises significantly during the day, they do not transmit at night. Even within a covering, the air temperature, soil temperature, and crop body temperature decrease significantly due to radiation cooling, and in some cases may even be lower than that without a covering. Furthermore, dirt tends to adhere due to plasticizers or static electricity, and the light transmittance decreases during use, making it impossible to receive sufficient light necessary for crop growth.

Perforated polyvinyl chloride film, polyethylene film, etc. have a partial ventilation effect, but they also reduce heat retention at night, and the materials themselves have inherent drawbacks such as a decrease in light transmittance over time and moisture absorption. No improvement can be made regarding the lack of.

Polyethylene nets have exactly the same drawbacks, and exhibit virtually no effect on heat retention, especially at night.

Furthermore, vinylon cheesecloth has some hygroscopicity, but because it is light-blocking, it cannot supply enough light for crop growth, and because of its high porosity, it is also insufficient in terms of heat retention at night. If the porosity is decreased with the intention of increasing heat retention, the light transmittance will further decrease, making it impractical.

Furthermore, nonwoven fabrics also have a large degree of light shielding and cannot receive enough sunlight, and also have insufficient heat retention properties and do not have hygroscopicity or dehumidification properties.

The inventors of the present invention have completed the present invention as a result of intensive study to eliminate the above-mentioned drawbacks of existing agricultural covering materials for low-temperature seasons. The object of the present invention is to provide a new agricultural covering material that has excellent transparency and moisture absorption, and does not require complicated ventilation operations.

Other objects and effects of the present invention will become clear from the following description. However, the above purpose is to create a structure with a porosity of 10 to 70% by knitting or weaving a polyvinyl alcohol-based slit yarn with a crystal orientation of 0.92 or more and a crystallinity of 0.47 or more for at least one of the warp or weft. This is achieved by using agricultural covering materials.

The polyvinyl alcohol-based slit yarn (hereinafter polyvinyl alcohol is abbreviated as PVA) in the present invention preferably has an average degree of polymerization of 1000 or more and a degree of saponification of 98.
% or more of PVA and, if necessary, a plasticizer such as glycerin or polyalkylene ether, is made into an aqueous dispersion or aqueous solution, and this is processed by known methods such as casting, coagulation, extrusion, etc. It is obtained by slitting, stretching, and heat treating a PVA-based film obtained by forming a film by the film method, and the degree of crystal orientation thereof is at least 0.92 or more, preferably 0.94.
It is important that the degree of crystallinity is at least 0.47 or more, preferably 0.50 or more. In other words, by stretching and heat-treating the PVA-based film, the disadvantages inherent to PVA-based materials such as moisture absorption, blocking properties when absorbing water, significant swelling properties, and poor mechanical strength at low temperatures and low humidity can be improved. However, on the contrary, when it absorbs moisture or water, or when it is subsequently dried, it is once stretched by stretching and becomes significantly susceptible to contraction due to the relaxation phenomenon of the aligned molecules. Such shrinkage is inversely proportional to the degree of crystal orientation and crystallinity of the PVA film after stretching and heat treatment, and the higher the degree of both, the lower the shrinkage becomes.
Only when the degree of crystallinity is at least 0.92, or at least 0.47, can the degree of shrinkage be reduced to a practically acceptable degree. The degree of crystal orientation and degree of crystallinity after stretching and heat treatment of a PVA film body are influenced to some extent by the temperature and time of stretching and the time of heat treatment, but are mainly determined by the stretching ratio and heat treatment temperature.

Therefore, in order to increase the degree of crystal orientation and crystallinity and prevent shrinkage, it is necessary to perform heat treatment at a higher temperature after stretching to a higher magnification. 0.92 or more, crystallinity 0.47
To achieve this, it varies slightly depending on the conditions during film formation, but usually the stretching ratio is 5.5 times or more and the heat treatment temperature is 200%.
This is achieved by keeping the temperature above ℃. Naturally, by further increasing the stretching ratio and heat treatment temperature, the degree of crystal orientation and crystallinity will increase and the shrinkage will decrease, making it even more desirable. The temperature is up to 220-230 °C at the point of pyrolysis.

Furthermore, any known method may be used to slit, stretch, and heat-treat the PVA-based coated material to form slit yarn. For example, average degree of polymerization
1750, a PVA film containing 10% by weight of glycerin as a plasticizer in PVA with a saponification degree of 99.5% is slit into an appropriate width using a Cameron cutter or a razor blade, and then stretched to 5.5 times or more at 180℃ or higher. 200
It can be obtained by heat-treating at a temperature of 0.degree. C. or higher and then winding it onto a bobbin or the like. The stretching method can be easily carried out, for example, by using a roller or a chamber under heating and utilizing the speed difference between two sets of pinch rolls, and if necessary, multistage stretching of two or more stages may be performed. .

Further, the heat treatment may be performed by any known method, and is easily carried out using a chamber or cylinder heated to 200°C or higher; however, to further enhance the heat treatment effect, it is preferable to use the latter cylinder. is preferred. Further, the timing of the heat treatment is usually 20 to 60 seconds. Furthermore, although it is common to stretch and heat-treat the PVA-based film after slitting, slitting may also be performed after stretching and heat-treating using a lenting method or the like.

However, the width of PVA slit yarn is 1~10mm.
It is preferable if it is less than 1 mm, and will be described later if it is smaller than 1 mm, but if it is made into a structure with a porosity of 10 to 70%, the practical strength is insufficient and the production technology is also difficult. or
If it is larger than 10 mm, it is difficult to obtain a PVA-based slit yarn, and it is difficult to use the slit yarn in the warp and/or weft to form a structure with a porosity of 10 to 70%, and it is also difficult to use it practically.

The agricultural covering material of the present invention has a porosity of 10 to 70 using the PVA-based slit yarn warp and/or weft as described above.
% structure, but the method may be any known method. For example, it is similar to the method of manufacturing so-called Hessian cloth.
A method of weaving PVA-based slit yarn on a warp, or a method of feeding a large number of PVA-based slit yarns shaped at regular intervals onto a warp, cutting the weft, placing it on the warp, and then adhesively integrating it with a binder. Alternatively, it can be made by using a PVA-based slit yarn as the warp or weft yarn and knitting it with a binding yarn. In this case, any adhesive material may be used as the binder for the adhesive integration, but as will be discussed later, it is recommended to use a PVA binder, which is the same material, in terms of hygroscopicity, transparency, and weather resistance. Preferably,
Furthermore, as the binding yarn for yarn knitting, it is preferable to use PVA fiber, such as vinylon fiber, which is the same material in terms of moisture absorption and weather resistance.

Among the above-described embodiments of the agricultural covering material of the present invention, those knitted using binding threads are most suitable in terms of practical strength, ease of use, productivity, and cost. Fig. 1 shows an example of the agricultural covering material of the present invention knitted using binding yarn.
PVA slit yarn, 2 represents binding yarn. In this case, it is important to firmly weave the PVA-based slit yarn 1 with the binding yarn 2 so that the stitches do not shift.Especially, since the stitches are likely to shift at both ends of the resulting structure in the width direction, the binding yarns should be placed close together. It is preferable to use a method of using several pieces, or a method of fixing them using a binding agent if necessary.

Hereinafter, the characteristics and effects of the agricultural covering material of the present invention will be explained.

First of all, PVA-based materials have extremely excellent moisture absorption, moisture permeability, and water absorption properties that other synthetic resins do not have, so the agricultural covering material of the present invention has extremely excellent dehumidification properties, and can be used, for example, as tunnel covering or Directly covering the inside of the tunnel prevents excessive humidity and humidity inside the covering, and is extremely effective in controlling crop diseases.

In addition, PVA-based materials have extremely low transmittance to infrared rays, that is, heat rays, mainly in the 6 to 17 micron wavelength range, which is the cause of sudden temperature drops at night. Since only about 1/2 of vinyl chloride passes through, the agricultural covering material of the present invention has a high heat retention property even though it is a mesh material, and in combination with the preferential adsorption of frost due to the above-mentioned excellent hygroscopicity, it has excellent frost protection. Demonstrate your sexuality. However, in this case, if the porosity of the mesh body exceeds 70%, the heat retention and frost protection properties will be insufficient, so it is desirable that the porosity is 70% or less.

Furthermore, since the agricultural covering material of the present invention is a structure made of PVA-based slit yarn, no ventilation operation is required at all even when the entire surface is covered in the shape of a tunnel, for example. However, in this case, it is preferable that the porosity of the structure is 10% or more, although this will vary slightly depending on the type of crop and cropping type, in order to suppress the rise in daytime temperature and save labor for ventilation.

Furthermore, in addition to the fact that PVA-based materials are extremely resistant to UV deterioration and have excellent weather resistance, the agricultural covering material of the present invention stretches the PVA-based film body at a high magnification after slitting to improve molecular arrangement. Made of PVA-based slit yarn that has undergone sufficient heat treatment,
It has good durability because it has excellent practical strength without moisture absorption, blocking property when water is absorbed, or significant swelling property, which are the inherent disadvantages of PVA-based materials.

Furthermore, since it has high transparency and is difficult to attract stains due to static electricity or plasticity, there is little decrease in transparency over time, and it is also advantageous in terms of lighting performance.

As explained above in detail, the agricultural covering material of the present invention has heat retention, frost resistance, transparency, hygroscopicity, dehumidification,
It has excellent durability and can be widely used as an effective agricultural covering material that can save labor in laborious ventilation operations.

[Brief explanation of the drawing]

FIG. 1 is an explanatory view showing an example of the agricultural covering material according to the present invention, which is knitted using binding yarn. 1...PVA slit yarn, 2...binding thread.

Claims (1)

[Scope of Claims] 1. A structure in which a polyvinyl alcohol-based slit yarn with a degree of crystal orientation of 0.92 or more and a degree of crystallinity of 0.47 or more is used for at least one of the warp or weft, knitted or woven, and has a porosity of 10 to 70%. Agricultural covering material that can be used as a material. 2. The agricultural covering material according to claim 1, wherein the polyvinyl alcohol-based slit yarn is made of polyvinyl alcohol with an average degree of polymerization of 1000 or more and a saponification degree of 98% or more. 3. The agricultural covering material according to claim 1, wherein the polyvinyl alcohol-based slit yarn has a width of 1 to 10 mm. 4. The agricultural covering material according to claim 1, wherein the structure is knitted using polyvinyl alcohol-based slit yarn as the warp or weft and binding yarn.