JPS6155471B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a polyvinyl alcohol-based agricultural covering material, and more particularly to a polyvinyl alcohol-based agricultural covering material that has excellent mechanical strength, practical dimensional stability, heat retention, dehumidification, dew condensation prevention, and durability. 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 covering material to replace conventional synthetic resin coatings such as polyethylene, polyvinyl chloride, and ethylene-vinyl acetate copolymers. In other words, coatings made from polyvinyl alcohol synthetic resins have extremely excellent hygroscopicity, water absorption, and moisture permeability due to the large number of OH groups in the molecules, and when used as agricultural covering materials, they are 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 little loss of 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 through 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. Improved swelling degree upon water absorption by 10
It is difficult to keep it below ~15%, and as mentioned below, the strength at low temperatures and low humidity is low and it lacks practicality. In the latter method of acetalization, the intramolecular
There are problems in terms of manufacturing technology and cost, such as a decrease in OH groups and a marked drop in hygroscopicity, water absorbency, and moisture permeability, and a long time required for the acetalization reaction. 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. Glycerin as a way to improve flexibility,
There is a method of adding polyhydric alcohol such as polyethylene glycol as a plasticizer, but in these methods, the added plasticity is removed in a short time by rainwater, etc., and the effect is only temporary. The inventors of the present invention have solved the various drawbacks of the above-mentioned polyvinyl alcohol-based synthetic resin coating materials, and have developed a new agricultural coating material that has superior performance to agricultural coating materials made of existing synthetic resin coating materials. As a result of intensive research to find a practical material, the present invention was completed, and its purpose is to have practical mechanical strength, excellent dimensional stability, heat retention, dehumidification, and dew condensation. An object of the present invention is to provide a polyvinyl alcohol-based agricultural covering material having good preventive properties and durability. The above-mentioned purpose is to produce a polyvinyl alcohol-based synthetic resin film in which 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 are laminated and bonded together with their orientation axes crossed. This is achieved by a polyvinyl alcohol-based agricultural covering material which is made of a synthetic resin film laminate and is characterized by having slits of appropriate lengths formed at appropriate intervals in the direction of the orientation axis of the film. The film body made of polyvinyl alcohol synthetic resin (hereinafter referred to as PVA) according to the present invention has an average degree of polymerization of 1000 or more and a degree of saponification of 98%.
It is preferable to use PVA with a raw material of 30% or more.
A film body made of modified PVA such as a copolymer or a polymer mixture containing other monomers or polymers, such as olefins, in the following proportions (mol %, the same applies hereinafter) may also 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 to be modified here is preferably 30% or less, from the viewpoint of not impairing the original properties of PVA such as heat retention, dehumidification, dew condensation prevention, and durability. It is even more preferable. This film made from PVA-based synthetic resin has excellent hygroscopicity, 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. . In other words, 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 body made of PVA-based 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. Highly uniaxially stretched and heat treated, the degree of crystal orientation of the film is at least 0.92.
The above can be solved by setting the 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 the shrinkage be reduced 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 5.5, although this varies slightly depending on the conditions during film formation of the PVA-based film.
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 preferable, but in general, the stretching ratio is 6.5.
~ up to 7 times, the heat treatment temperature is 220-230 in terms of pyrolysis
It is best to keep it up to. The stretching method may be any known method, and can be easily carried out by using rollers or chambers, usually at a temperature of 180 to 200°C, and by utilizing the speed difference between two sets of pinch rolls. Depending on the situation, multi-stage stretching of two or more stages may be used. Further, the heat treatment may be performed by any known method, and is carried out using a chamber or cylinder heated to 200°C or higher, but the latter cylinder is preferable in order to increase the heat treatment effect. Further, the timing of the heat treatment is usually 20 to 60 seconds. Furthermore, what is important for the present invention is the above
A plurality of substantially straight fine slits are formed in the same direction as the molecular orientation axis of the PVA-based uniaxially highly stretched and heat-treated film. By having this structure, it is possible to impart flexibility to the membrane and solve the problems caused by the lack of flexibility that conventionally occurred during expansion, removal, opening/closing, storage, etc., and it can be used as a curtain inside a house. is also applicable.
If the interval between fine slits in the width direction of the PVA-based uniaxially stretched and heat-treated film is smaller than 0.5 mm, there will be some problems with the practical strength of the resulting agricultural covering material and the stability of the laminated adhesive. If the length of the fine slits is smaller than 5 mm, the resulting agricultural covering material will be hard and somewhat inflexible, so it is preferable that the length of the fine slits be in the range of 5 to 20 mm. Tends to be inflexible100
If it is larger than mm, there will be some problems with the production stability of warp/warp lamination bonding and the practical strength of the resulting agricultural covering material, so it is preferably in the range of 5 to 100 mm. In this case, preferable results can be obtained if the slits are cut in such a way that when cut in an arbitrary cross section in the direction in which the molecules of the film are arranged, that is, in the direction of the orientation axis, they intersect with a plurality of slits. Any known method may be used to cut the fine slits, for example, a method in which a roll cutter provided with a plurality of cutting blades is brought into contact with a rotating film body, or a method in which a plurality of cutting blades are cut by a punching method is used. This is carried out by a method such as pressing a cutting blade against a film body. At this time, the shape of the fine slits, such as length and spacing, can be freely and easily adjusted by combining the length and spacing of the cutting blades, the diameter of the roll cutter, the contact angle and speed ratio between the roll cutter and the coating body, etc. I can do it. At least two of the thus obtained film bodies, each having a plurality of substantially straight fine slits cut in the same direction as the molecular alignment, are laminated and bonded with their orientation axes intersecting each other. Lamination and adhesion may be carried out by selecting an appropriate known method. For example, roll coating, dipping,
An adhesive is applied by a spray method or the like, and the film is fed out in the latitudinal direction with the orientation axis crossed, preferably directly supported, on the other longitudinal film, cut into a certain length, and then continuously supplied onto the longitudinal film. This is achieved by applying pressure with pinch rolls and drying using a chamber or cylinder.In order to use a multi-layer film, the same method may be used following the above steps. 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. At this time, moisture is added under sufficiently high temperature conditions to prevent the film from fibrillating after heat treatment, generally when the temperature of the film is 80°C or higher, so that the moisture content is 15% or more. It is preferable to absorb water and swell the material so that it becomes swollen. 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. An example of a polyvinyl alcohol-based agricultural covering material provided with fine slits according to the present invention will be explained with reference to the drawings. Figures 1 and 3 show a PVA-based uniaxially highly stretched and heat-treated film in which a plurality of substantially straight fine slits are cut in the same direction as the molecular arrangement, and Figures 2 and 4 respectively This is an explanatory diagram showing an example of the agricultural covering material of the present invention in which the coating bodies shown in Figures 1 and 2 are laminated and adhered to the warp and warp, and 1 is a PVA-based uniaxially highly stretched and heat-treated coating body, and 2 is a fine slit. represents. The agricultural covering material of the present invention shown in Fig. 2 is made by laminating and bonding one PVA-based uniaxially highly stretched and heat-treated film with fine slits cut in a staggered pattern as shown in Fig. 1 in the longitudinal direction. The agricultural covering material of the present invention shown in Fig. 4 is made by laminating and bonding PVA-based uniaxially highly stretched and heat-treated film bodies with fine slits cut at the same positions in the longitudinal direction as shown in Fig. 3 in the warp and warp directions. However, the fine slits may be provided in any other shape. However, it is better to have a plurality of fine slits in the zigzag pattern shown in Figure 1 in the width direction of the PVA-based uniaxially stretched and heat-treated film at any position in the longitudinal direction. It is more suitable in terms of the flexibility of the material and the prevention of fibrillation of the PVA-based uniaxially highly stretched and heat-treated film, ie, the stability of warp and warp lamination adhesion. Since the agricultural covering material of the present invention is made of PVA-based synthetic resin, it has excellent dehumidification, dew condensation prevention, heat retention, and durability, as well as extremely good dimensional stability, flexibility, and mechanical strength, making it an essential energy saver. It can be widely used for greenhouses and tunnels as a truly effective agricultural covering material for future agricultural management. 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 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 (Lw) 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 times at 190°C, then 6 rows at equal intervals in the circumferential direction and 2 rows in the width direction.
After making fine slits in the molecular alignment direction (stretching direction) using a roll cutter with cutting blades at mm intervals, heat treatment was performed at 205°C for 30 seconds to obtain a crystallinity of 0.49 and crystal orientation of 0.93. A polyvinyl alcohol uniaxially highly stretched and heat treated film body was obtained. In addition, by selecting the slitting conditions such as the speed ratio of the roll cutter and the coating body, the obtained coating body can have fine slits of 20 mm length at 2 mm intervals, and is stable without fibrillation. I was able to wind it up. Next, this film body was subjected to an average degree of polymerization of 1400 and a degree of saponification.
Product 1 of the present invention was manufactured by laminating and adhering each sheet to the warp and warp using a 99.9% polyvinyl alcohol 9% aqueous solution by a roll coater method. In this case, the production was extremely stable without any problems. As a comparative example, the stretching ratio was 4.5 times and the heat treatment temperature was
The crystallinity was determined in the same manner as the present invention except that the temperature was 190°C.
Comparative product 1 was produced, which consisted of a polyvinyl alcohol uniaxially stretched and heat-treated film having a crystal orientation of 0.46 and a crystal orientation of 0.90. 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] I tried laminating and adhering polyvinyl alcohol uniaxially highly stretched and heat-treated films without making fine slits in the film, but the result was large fibrillations, wrinkles, and
Due to occurrences of folding, partial cutting, etc., stable winding was not possible and production was impossible.

[Brief explanation of the drawing]

1 and 3 are explanatory diagrams showing an example of a PVA-based uniaxial high-stretch heat-treated film body provided with slits constituting the polyvinyl alcohol-based agricultural covering material according to the present invention, and FIGS. 2 and 4 are FIG. 3 is an explanatory diagram showing an example of a polyvinyl alcohol-based agricultural covering material according to the present invention in which the coating bodies shown in FIGS. 1 and 3 are laminated and bonded in the warp and warp directions. In the figure, 1 represents a PVA-based uniaxial high-stretch heat-treated film, and 2 represents a fine slit.

Claims (1)

[Scope of 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 and bonded together with their orientation axes intersecting. 1. A polyvinyl alcohol-based agricultural covering material comprising a laminate of polyvinyl alcohol-based synthetic resin films, characterized in that slits of appropriate lengths are provided at appropriate intervals in the direction of the orientation axis of the film. 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. The polyvinyl alcohol-based agricultural covering material according to claim 1, wherein the slits are provided so as to intersect with a plurality of slits when cut at an arbitrary cross section in the direction of the orientation axis.