JPS6155470B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a polyvinyl alcohol-based agricultural covering material and a method for producing the same, and more particularly, it has excellent heat retention and dehumidification properties with mechanical strength and practical dimensional stability,
The present invention relates to a polyvinyl alcohol-based agricultural covering material with good anti-condensation properties and durability, and a method for producing the same. Agricultural technology in Japan has made remarkable progress through the use of agricultural covering materials, typified by synthetic resin coatings such as polyethylene, polyvinyl chloride, and ethylene-vinyl acetate copolymers. However, in the current severe situation surrounding oil, existing agricultural covering materials are not necessarily satisfactory, and there is a strong desire to develop agricultural covering materials with higher performance. Conventionally, coatings made from polyvinyl alcohol-based synthetic resins have not been used as agricultural covering materials, but as a unique synthetic resin coating with a large number of OH groups in the molecule, it has extremely excellent properties. It has great potential as a completely new agricultural coating material to replace conventional synthetic resin coatings such as polyethylene, polyvinyl chloride, and ethylene-vinyl acetate copolymers. In other words, coatings made of polyvinyl alcohol synthetic resin have extremely excellent hygroscopicity, water absorption, and moisture permeability due to the large number of OH groups in the molecule, and when used as agricultural covering materials, hydrophobic synthetic resin coatings It has excellent dehumidification and dew condensation prevention properties within the airtight covering, which were completely absent from the existing agricultural covering materials, and is extremely effective in controlling crop diseases that frequently occur under humid conditions. In addition, it has excellent transparency and is a hydrophilic synthetic resin film, so it does not generate static electricity, is less likely to get dirty over time, and has the advantage of being able to receive sufficient sunlight, which is essential for crop growth, that is, crop photosynthesis. Another important property is that it has excellent shielding properties for infrared rays in the 6-17μ wavelength range, that is, the so-called heat ray transmission, which is the main cause of radiation cooling at night, so it has good heat retention, and has a high oil-saving effect, which can be called abnormal. It is highly anticipated as an energy-saving agricultural covering material for future facility agriculture due to soaring prices. Furthermore, it has excellent weather resistance with almost no deterioration due to ultraviolet rays, and combined with the above-mentioned decrease in transparency over time, it is highly durable and can be used for a long period of time, making it easy to replace, which requires a lot of effort. In addition to being labor-saving, it also has the advantage of reducing costs. On the other hand, membrane bodies made of polyvinyl alcohol-based synthetic resins have not been put to practical use due to the following drawbacks. That is, first of all, since the coating material made of polyvinyl alcohol synthetic resin is hydrophilic, it inevitably has poor water resistance, absorbs moisture, causes blocking due to water absorption, and swells significantly, lacking practical dimensional stability. It cannot be used as a covering material for agricultural purposes such as houses or tunnels. In order to impart water resistance, there is a method of crystallization by heat treatment or a method of acetalization using an aldehyde such as formaldehyde or acetaldehyde in the presence of a catalyst such as sulfuric acid or phosphoric acid, but the former crystallization method does not have blocking properties. The swelling degree of the improved product upon water absorption
It is difficult to keep it below 10 to 15%, and as described below, the strength is low at low temperatures and low humidity, making it impractical.
In the latter acetalization method, the OH group in the molecule decreases, resulting in a significant decrease in hygroscopicity, water absorption, and moisture permeability, and the acetalization reaction takes a long time.
There are problems in terms of manufacturing technology and cost. Furthermore, in addition to the above-mentioned drawbacks, coatings made of polyvinyl alcohol synthetic resins are flexible and have sufficient mechanical strength for practical use when absorbing moisture or at high temperatures, but they harden significantly and become brittle at low temperatures and low humidity. It does not have sufficient strength for practical use as an agricultural covering material that is used under harsh natural conditions due to the fact that it deteriorates and cannot withstand practical use. One way to improve flexibility is to add polyhydric alcohols such as glycerin and polyethylene glycol as plasticizers, but with these methods, the added plasticizers are removed in a short time by rainwater, etc., and the effect is only temporary. do not have. The present inventors have discovered that the present invention has superior performance to agricultural covering materials made of existing synthetic resin films, eliminates the inherent drawbacks of the above-mentioned films made of polyvinyl alcohol-based synthetic resins, and has developed a new agricultural covering material. As a result of intensive research to find a practical material, the present invention was completed, and the aim is to create a material that has practical mechanical strength, excellent dimensional stability, heat retention, and dehumidification properties. An object of the present invention is to provide a polyvinyl alcohol-based agricultural covering material having good dew condensation prevention properties and durability, and a method for producing the same. The above-mentioned purpose is to produce a polyvinyl resin film in which at least two or more uniaxially stretched polyvinyl alcohol-based synthetic resin films having an orientation degree of 0.92 or more and a crystallinity degree of 0.47 or more are laminated and bonded together with their orientation axes crossed. After swelling an alcohol-based agricultural coating material and at least two or more uniaxially highly oriented polyvinyl alcohol-based synthetic resin films having an orientation degree of 0.92 or more and a crystallinity degree of 0.47 or more to an extent that does not cause fibrillation, the This is achieved by a method for producing a polyvinyl alcohol-based agricultural covering material, which is characterized by laminating and adhering and integrating the coatings so that their orientation axes intersect. The film body made of polyvinyl alcohol-based synthetic resin (hereinafter referred to as PVA) according to the present invention has an average degree of polymerization of 1000 or more and a saponification degree of 98.
It is preferable that the raw material is PVA with a content of 30% or more.
% (mol %, hereinafter the same) or less of other monomers or polymers, such as olefins, or a copolymer or polymer mixture made of modified PVA may be used. Coatings made from these PVA-based synthetic resins can be easily obtained by known film-forming methods such as casting and melt-extrusion, and if necessary, plasticizers, ultraviolet absorbers, Various coloring agents, antifungal agents, etc. may be appropriately added to form a film. A film made of modified PVA can be obtained, for example, by melt-extruding a saponified ethylene-vinyl acetate copolymer or a blend of pelletized hydrous PVA and polyolefin synthetic resin into a film. The proportion of other monomers or polymers modified here is preferably 30% or less in order not to impair the original properties of PVA such as heat retention, dehumidification, dew condensation prevention, and durability. The following is more preferable. This film body made from PVA-based synthetic resin has excellent moisture absorption, water absorption, moisture permeability, and weather resistance.
It has excellent properties for shielding infrared rays, or heat rays, in the ~17μ wavelength range, making it extremely useful as an agricultural covering material, but as mentioned above, it has poor water resistance and is not practical due to blocking and significant swelling when absorbing moisture and water. Due to poor physical dimensional stability and poor mechanical strength due to embrittlement at low temperatures and low humidity, it is completely impractical as an agricultural covering material and requires specific treatment and specific structural form as described below. . That is, as a method for improving moisture absorption, blocking properties during water absorption, dimensional stability, and mechanical strength under low temperature and low humidity conditions of a film made of PVA synthetic resin, a method using stretching in addition to the above-mentioned heat treatment has been considered. However, although stretching does improve some mechanical strength and swelling properties during moisture absorption and water absorption, on the contrary, the strength against tearing is drastically reduced. Because the arranged molecules tend to relax and shrink significantly and lack dimensional stability, it is not practical as an agricultural covering material even if general heat treatment and stretching are used together. Among these problems, in order to prevent the shrinkage that occurs during moisture absorption and subsequent drying, PVA resin, which is obtained by highly stretching a film made of PVA synthetic resin in the uniaxial direction and then subjecting it to sufficient heat treatment, can be used. The degree of crystal orientation of the uniaxial high-stretch heat-treated film is at least 0.92.
The above can be solved by setting the degree of crystallinity to preferably 0.94 or more, and at least 0.47 or more, preferably 0.50 or more, which is one of the most important requirements of the present invention. As mentioned earlier, film bodies made of PVA-based synthetic resin can be stretched and heat treated to solve moisture absorption, blocking properties and swelling properties during water absorption, but conversely, during moisture absorption and water absorption, or during subsequent drying. It exhibits remarkable contractility due to molecular relaxation phenomena. This shrinkage is inversely proportional to the crystal orientation and crystallinity of the PVA film after stretching and heat treatment; the higher the shrinkage, the lower the shrinkage. Only in the above case can it be possible to reduce the shrinkage to a practically acceptable level. The degree of crystal orientation and crystallinity after uniaxial stretching heat treatment of a film made of PVA-based synthetic resin is influenced to some extent by the stretching temperature, time and heat treatment time, but mainly depends on 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. In order to achieve a crystal orientation of 0.92 or higher and a crystallinity of 0.47 or higher, the stretching ratio is usually adjusted, although this may vary slightly depending on the conditions during film formation of the PVA-based film.
5.5 times or more, and the heat treatment temperature is 200℃ or more. Naturally, when the stretching ratio and heat treatment temperature are increased, the degree of crystal orientation and crystallinity also increases, and the shrinkage property decreases, making it more desirable.
Up to 6.5~7 times, heat treatment temperature is 220~220 in terms of thermal decomposition
It is best to keep the temperature up to 230℃. The stretching method may be any known method, for example, by using a roller or a chamber, usually at a temperature of 180 to 200°C.
This can be easily carried out by utilizing the speed difference between pairs of pinch rolls, and if necessary, multi-stage stretching of two or more stages may be used. Furthermore, the method of applying the heat treatment may be any known method.
Although it is carried out using a chamber or cylinder heated to a temperature above .degree. C., the latter cylinder is preferable in order to increase the heat treatment effect, and the timing of the heat treatment is usually sufficient for 20 to 60 seconds. Next, in order to solve the problem of the above-mentioned PVA-based uniaxially highly stretched and heat-treated film, the molecular arrangement and tear strength in the parallel direction due to stretching are drastically reduced, making it unusable for practical use. Two or more film bodies are laminated and bonded with their orientation axes intersecting. This is the second most important requirement of the present invention. With this structure, the tear strength mutually compensates for each other, resulting in an agricultural covering material with excellent tear strength and good practical strength. Next, what is important in manufacturing these coating materials is that the above-mentioned PVA-based uniaxially highly stretched and heat-treated film is generally moistened and swelled at a temperature sufficiently high to prevent fibrillation after heat treatment. The purpose is to laminated and bond the materials so that their orientation axes intersect while preventing fibrillation. That is, film bodies made of PVA-based synthetic resins become extremely susceptible to fibrillation when highly stretched, so it is virtually impossible to laminate and bond them as they are. The ease of fibrillation of a PVA-based uniaxially highly stretched and heat-treated film is closely related to the temperature and moisture content of the film; the higher the temperature and the higher the moisture content, the more difficult it is to fibrillate. Therefore, the temperature after heat treatment of the coated body is maintained at a temperature sufficiently high to prevent fibrillation, and the coated body is laminated and bonded in a state in which, for example, water is added to the coated body to swell it and prevent fibrillation. The temperature of the film after heat treatment to prevent fibrillation is generally 80°C or higher, and while it is possible to maintain this temperature by laminating and bonding the film across the orientation axis, it is extremely difficult to manufacture. This is practically impossible, and a method of adding water to absorb water and cause swelling to prevent fibrillation is extremely effective. When producing a film body, first, a film body made of PVA-based synthetic resin is stretched at least 5.5 times by the above-mentioned known method under a temperature condition of usually 180 to 200°C, and then stretched at a temperature of at least 200°C or higher. Heat treatment is applied for 20 to 60 seconds by a known method to improve the degree of crystal orientation.
A PVA-based uniaxially highly stretched and heat-treated film body (hereinafter abbreviated as film body) with a crystallinity of 0.92 or higher and a crystallinity of 0.47 or higher.
In this case, the moisture content is increased to 15% or more by adding moisture under a sufficiently high temperature condition to prevent the film from fibrillating after heat treatment, generally at a temperature of 80°C or higher. It absorbs water and swells. Various methods can be used to add water to the heat-treated film to cause it to absorb water and swell. Examples include an underwater immersion method, a water spray method, and a live steam method. The applied water may be left as is, but if necessary, excess water adhering to the squeezing surface may be removed using pinch rolls. There is no problem if the next layer is bonded in succession, but if it is done over time, it should be wrapped tightly with a synthetic resin film such as polypropylene or polyethylene to prevent moisture from escaping15.
It is preferable to maintain the moisture content at % or more. The membrane bodies thus obtained may be laminated and bonded by any suitable known method. For example, a film body is fed out in the warp direction, an adhesive is applied thereto by a roll coater method, a dipping method, a spray method, etc., and then the film body is fed out in the weft direction with the orientation axis intersecting, preferably orthogonal to, the warp direction film body to a certain length. This is achieved by continuously supplying the film onto the film body in the warp direction after cutting, pressurizing it with a pinch roll, and drying it using a chamber or cylinder. It may be carried out in a similar manner. The adhesive for lamination bonding is preferably a PVA-based synthetic resin made of the same material as the film body from the viewpoints of hygroscopicity, water absorption, moisture permeability, and weather resistance. Since the agricultural covering material of the present invention uses PVA-based synthetic resin as a material, it has excellent dehumidification, dew condensation prevention, heat retention, and durability, as well as extremely good dimensional stability and mechanical strength, making energy saving essential for future agriculture. It is a very effective agricultural covering material for management and can be widely used for greenhouses and tunnels. The present invention will be specifically explained below with reference to Examples. . In addition, the various physical property values in the examples were measured by the following methods. (1) Crystal orientation: Crystal lattice (001) determined by wide-angle X-ray diffraction method
It was obtained by measuring the half width of the (100) plane. (2) Crystallinity The density was determined by measuring the density using the density gradient tube method. (3) Shrinkage rate A sample with a length of 100cm and a width of 2cm is placed in water at 20℃.
The length (Iw) when immersed for a time and the length (L _D ) when left in a dryer at 40°C for 5 hours after immersion were measured and calculated from the following formula. Shrinkage rate in water at 20℃ (%) = (100-Lw/100) x 100 Shrinkage rate when dried at 40℃ (%) = (100-L _D /100) x 100 Example 1 Average degree of polymerization 1700, saponification A 99.9% polyvinyl alcohol film (thickness 60μ) was stretched 6.0 times at 190°C and then heat-treated at 205°C for 30 seconds.The temperature of the film was
It was immersed in hot water at 40°C for 30 seconds at 90°C and squeezed with pinch rolls to obtain a uniaxially highly stretched and heat-treated film of hydrous polyvinyl alcohol. The obtained film body is 25%
The crystallinity containing water is 0.49, and the crystal orientation is
0.93, and could be wound stably without fibrillation. Next, this water-containing polyvinyl alcohol uniaxially highly stretched and heat-treated film body was coated with an average degree of polymerization of 1400 and a degree of saponification of 99.9%.
Using a 9% aqueous solution of porvinyl alcohol, one sheet was laminated and adhered on each side by a roll coater method.
In this case, the production was extremely stable without any problems. For comparison, the stretching ratio was 4.5 times and the heat treatment temperature was 190.
The crystallinity was determined in the same manner as the product of the present invention except that the temperature was
0.46 and a crystal orientation degree of 0.90, a comparative product was produced consisting of a polyvinyl alcohol uniaxially stretched heat-treated film body. Table 1 shows the shrinkage rates of the inventive product and the comparative product in water and on drying. From these results, it is clear that the inventive product has better dimensional stability and is superior in practicality than the comparative product. be.

[Table] Example 2 A polyvinyl alcohol uniaxial high-stretch heat-treated film was produced in the same manner as in Example 1 except that the step of immersing it in water (warm water) after heat treatment was omitted, but it was stable with large fibrillation. It was difficult to wind it up. Further, an attempt was made to laminate and bond this film body in the same manner as in Example 1, but it could not be stabilized due to the occurrence of wrinkles, folds, partial cuts, etc., and lamination bonding was not possible.

Claims (1)

[Claims] 1. At least two or more uniaxially highly oriented polyvinyl alcohol-based synthetic resin films having an orientation degree of 0.92 or more and a crystallinity of 0.47 or more are laminated, bonded, and integrated with their orientation axes crossed. Polyvinyl alcohol-based agricultural covering material. 2. The polyvinyl alcohol-based agricultural coating material according to claim 1, wherein the polyvinyl alcohol-based synthetic resin coating body is made of a polyvinyl alcohol-based synthetic resin having an average degree of polymerization of 1000 or more and a saponification degree of 98% or more. 3. The polyvinyl alcohol agricultural covering material according to claim 1 or 2, wherein the orientation axes intersect at right angles. 4 After swelling at least two or more uniaxially highly stretched polyvinyl alcohol-based synthetic resin coatings having an orientation degree of 0.92 or more and a crystallinity of 0.47 or more to an extent that does not cause fibrillation, the orientation axis of the coating is A method for producing a polyvinyl alcohol-based agricultural covering material, which comprises laminating and bonding the polyvinyl alcohol-based agricultural materials in an integrated manner. 5. The method for producing a polyvinyl alcohol-based agricultural covering material according to claim 4, wherein water is applied at a temperature of 80° C. or higher to swell the uniaxially highly oriented polyvinyl alcohol-based synthetic resin film to an extent that it does not become fibrillated. 6. The method for producing a polyvinyl alcohol agricultural covering material according to claim 4 or 5, wherein the orientation axes are made to intersect at right angles.