JPH0479301B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a synthetic resin sheet used for agricultural and horticultural greenhouses, livestock houses, outdoor tents, etc., and more specifically, it has excellent dew condensation prevention, dehumidification, heat retention, and durability. Moreover, the present invention relates to a polyvinyl alcohol sheet that is used for greenhouses for greenhouse horticulture, livestock farms, outdoor tents, etc., and has excellent dimensional stability and strength. [Prior Art] Conventionally, for the above-mentioned houses and tents,
Sheets made of synthetic resins such as polyethylene, polyvinyl chloride, ethylene vinyl acetate copolymer, and polyester are widely used and have the advantages of being inexpensive and having excellent processability and workability. However, these have the following drawbacks. (1) Since it is made of hydrophobic synthetic resin, it has virtually no hygroscopicity or moisture permeability, and the inside of the coating becomes humid, and dew condenses and drops. For this reason, in greenhouses for greenhouse horticulture, the healthy growth of crops is hindered, resulting in a decrease in quality, and in addition, diseases are likely to occur. In livestock houses, the breeding environment for animals such as pigs and chickens deteriorates, resulting in disadvantages such as decreased appetite, poor growth, and decreased egg production. Furthermore, a humid environment is also unfavorable for people working within the coating. (2) Heat retention is not necessarily sufficient. In particular, sheets such as polyethylene and ethylene-vinyl acetate copolymers that have high transmittance to long-wave infrared rays (so-called heat rays) have poor heat retention, and in some cases, the temperature inside the coating may be lower than the outside temperature. Therefore, the growth of crops in greenhouses for greenhouse horticulture is poor, and in the worst case, the crops may be wiped out due to frost damage. Heating houses consume a large amount of energy such as heavy oil and electricity to maintain the temperature. In livestock greenhouses, the temperature environment is poor, which reduces animal activity and is not favorable for growth. (3) Insufficient heat resistance and weather resistance, and lacks durability. In particular, sheets made of polyethylene, polyvinyl chloride, or ethylene-vinyl acetate copolymers have poor heat resistance and are easily degraded by ultraviolet rays, resulting in poor durability and can usually withstand use for only one year. Similar problems arise in other applications, such as for tents. A sheet made of polyvinyl alcohol synthetic resin has been proposed as a sheet with dehumidification, anti-condensation, heat retention, and durability that does not have the above drawbacks, but it has the following drawbacks. , has become a major practical obstacle. It has extremely poor dimensional stability and poor water resistance. Polyvinyl alcohol synthetic resin is
Because it has high hygroscopicity and water absorption, it swells greatly with moisture, making it difficult for ordinary sheet films to
It expands and contracts by 150-200%. As a means to improve these points, there are methods to increase the degree of crystallinity by heat treatment, and methods to improve water resistance by biaxial stretching and heat treatment, but both are insufficient and the expansion and contraction ratio is reduced to 6 to 10%. It can only be reduced to a certain extent. If a sheet with this elasticity is stretched under tension when constructing it as a sheet for a house or a tent as described above, it will shrink during drying, knocking down the props, or tearing the sheet. On the other hand, if the house is stretched so that it is sagging, it will stretch when it absorbs moisture, making the sag even bigger, and the house may become flapping due to the wind, and the house may even collapse. Insufficient strength for practical use. When a polyvinyl alcohol sheet absorbs water, it blocks and its strength decreases. In addition, it easily becomes brittle at low temperatures and lacks practical strength. This drawback also
Although some improvements have been achieved by the above-mentioned heat treatment crystallization method, biaxial stretching, heat treatment method, etc., they are not suitable for practical use in greenhouses, tents, etc. [Problems to be Solved by the Invention] An object of the present invention is to provide a sheet that has excellent dehumidification properties, anti-condensation properties, heat retention properties, and durability, as well as excellent dimensional stability and strength. [Means for Solving the Problems] The object of the present invention is to provide (a) a polyvinyl alcohol-based biaxially stretched film body that has been subjected to a shrinkage treatment and is in a contracted state, and (b) a polyvinyl alcohol-based fiber structure pasted thereon. This is achieved by using an integrated polyvinyl alcohol sheet that has excellent dimensional stability and strength. The polyvinyl alcohol of the invention (hereinafter
In PVA (sometimes referred to as PVA) sheet,
The PVA-based biaxially stretched film (a) has been subjected to a shrinkage treatment, so that it hardly shrinks further under the conditions of use of the sheet, and preferably shrinkage is substantially zero. Therefore, when the sheet is actually used, it stretches, but no stress is generated in the direction of contraction. On the other hand, the PVA-based fiber structure (b) was not subjected to shrinkage treatment. When (a) and (b) are bonded together, when the sheet is actually used, the stretching force of (a) and the contraction force of (b) are counterbalanced, and the entire sheet is dimensional stability is improved. However, even if the PVA fiber structure (b) has improved dimensional stability, it has a practical elasticity of 2 to 3%, so depending on the environmental conditions, stress in the direction of contraction of (b) may be applied. may not occur. Therefore, PVA
The fiber structure (b) is preferably one that has been subjected to a swelling treatment, and more preferably one that does not further swell under the conditions in which the sheet is used and generates stress only in the direction of shrinkage during practical use. It has been found that by bonding and integrating the above (b) and the above (a), the dimensional stability can be significantly improved. The sheet of the present invention has practically preferable strength by combining a fibrous structure with a membrane. Note that the shrinkage rate of the untreated biaxially stretched PVA film is much larger than that of the untreated PVA fiber structure, so in contrast to the above, the PVA biaxially stretched film was subjected to swelling treatment. However, even if the PVA-based fiber structure is subjected to shrinkage treatment, sufficient effects cannot be achieved. In other words, between the contraction force and the extension force, the contraction force acts more strongly in the bonded and integrated structure, so if the biaxially stretched film body is made to shrink only, the dimensional stability cannot be sufficiently improved. do not have. The PVA-based biaxially stretched film body used in the present invention is PVA
It is obtained by stretching the film body in the warp and weft directions and then subjecting it to heat treatment, and the method may be any known method. For example, average degree of polymerization 1400
As described above, a PVA film body with a saponification degree of 98.5% or more is stretched at least 2.5 times, preferably 2.8 to 3.5 times, in the warp and weft directions at 180°C or higher, and then heat-treated preferably at 200°C or higher. can be easily obtained by In this case, the method for stretching in the warp and weft directions may be a so-called sequential biaxial stretching method in which stretching is first performed in the warp direction and then in the warp direction;
A so-called simultaneous biaxial stretching method in which stretching is performed simultaneously in the warp and weft directions may also be used. In addition, the stretching magnification in the warp and weft directions is
A ratio of 2.5 times or more is preferable in terms of mechanical strength and dimensional stability of the resulting biaxially stretched film. Although the stretching ratios in the warp and weft directions may be different, it is preferable that the stretching ratios be approximately the same because the physical properties in the warp and weft directions are balanced. Furthermore, the heat treatment temperature is
If the temperature is lower than 200°C, the heat setting effect will be poor, so in terms of practical water resistance and dimensional stability, the temperature is preferably 200°C or higher. The upper limit of stretching and heat treatment temperature is
The temperature at which the PVA film does not undergo thermal decomposition is generally 220 to 230°C. Further, the thickness of the PVA biaxially stretched film body is preferably 15 to 50 μm. A thickness of 15μ or more is suitable for practical strength, and a thickness of 50μ or less is suitable for flexibility. Regarding shrinkage treatment of PVA biaxially stretched film,
PVA-based membranes have the property of swelling under moisture absorption (wet) conditions and shrinking when heated and dried; the higher the temperature, the greater the shrinkage. Therefore, the shrinkage is low (preferably zero) under the conditions of use of the sheet.
The PVA-based biaxially stretched film, which continues to stretch, is wetted and then continuously dried while overfeeding the film at the highest practical temperature for the sheet, for example 40 to 50°C. It can be obtained by Drying is preferably carried out at a temperature of about 100° C. or lower; it is inconvenient if a wet material is suddenly exposed to high temperatures because it will melt. The PVA-based fiber structures used in the present invention include, for example, woven fabrics, knitted fabrics, non-woven fabrics made of vinylon fibers,
These include a reticulated nonwoven fabric obtained by stretching, splitting, heat treating, and widening a PVA film, a laminate obtained by laminating and adhering this reticulated nonwoven fabric in warp and warp directions, and woven and knitted fabrics made of PVA slit yarn. The reticulated nonwoven fabric preferably used in the present invention is
It is obtained by stretching, splitting, heat-treating, and widening a PVA-based film, and any known method may be used. For example, when using a film made of 100% PVA, the average degree of polymerization is 1400.
PVA film with saponification degree of 98.5% or more, 180
Stretched at least 5.5 times, preferably 6 to 6.5 times at temperatures above ℃, heat treated at 200 degrees C or above after splitting,
The width is then widened using a cross guider method, a spring method, or the like. in this case,
Average degree of polymerization is 1400 or less, saponification degree is 98.5% or less
A PVA coated body is not preferred in terms of practical dimensional stability and strength of the resulting reticulated nonwoven fabric. or,
If the stretching temperature is below 180°C, there will be a problem in terms of stretchability, and if the stretching ratio is lower than 5.5 times, the splitting properties and the strength and practical dimensional stability of the obtained reticulated nonwoven fabric will be poor, which is not preferable. Furthermore, if the heat treatment temperature is lower than 200°C, the heat setting effect will be poor and the practical dimensional stability will be poor, which is also not preferred. The upper limit of the stretching and heat treatment temperature is a temperature that does not cause thermal decomposition, generally 220 to 230°C.
When using an olefin-modified PVA coating as a PVA-based coating, the melting point and thermal decomposition temperature decrease in proportion to the olefin content, and the practical dimensional stability improves, compared to the case of the 100% PVA coating. Practical dimensional stability and sufficient mechanical strength can be imparted by stretching, splitting and heat treatment at low temperatures in the same manner as in the above methods. However, at least 80% of the split fibers constituting the reticulated nonwoven fabric used in the present invention are generally
It is preferable to have a width of 0.5 mm or more, more preferably 1.0 mm or more, and such a reticulated nonwoven fabric can be easily obtained by appropriately selecting the above-mentioned splitting conditions. If the width of the split fiber is smaller than 0.5 mm, the reinforcing effect against the embrittlement of the PVA film at low temperature and low humidity will be insufficient, which is not preferable. When high strength is required, such as when expanding a house, it is more preferable to use a width of 1 mm or more. Further, it is preferable that one sheet of the reticulated nonwoven fabric of the present invention is laminated on each side, or in some cases, more sheets are laminated and bonded by a known method. Furthermore, materials that adhere to the net-like laminate, such as vinylon-based or PVA-based stretched tape, may be inserted at appropriate intervals for reinforcement, but in either case, the porosity is usually 70% or less. is preferable. The swelling treatment of the PVA-based fiber structure can be easily performed by immersing it in water or spraying it with water. PVA biaxially stretched film (a) and PVA fiber structure
The adhesive integration in (b) is easily carried out by adhering with a binder. Paste one each of (a) and (b), or paste (a) with (b) in a sandwich pattern, or conversely, paste (b) with (a) in a sandwich pattern. It is possible to select an appropriate mode such as pasting with a sandwich. As the binder for bonding, it is preferable to use the same PVA-based polymer as in the production of the reticulated nonwoven fabric, such as a vinyl alcohol homopolymer, in terms of adhesion, weather resistance, hygroscopicity, and transparency. The adhesion may be done by any known method. For example, a PVA-based biaxially stretched film is obtained by immersing a PVA-based fiber structure in water at room temperature to undergo swelling treatment, then immersing it in an aqueous PVA-based binder solution to apply a PVA-based binder, and then shrinking it in advance. It is temporarily attached to the body at a temperature of 50 to 60 degrees Celsius,
Next, it is dried at a temperature of about 100°C to completely bond and integrate. At this time, it is not preferable to suddenly expose it to high temperatures because the PVA will melt. In order to improve the water resistance of the PVA binder, it is preferable to heat it next at 140°C or higher. "Polyvinyl alcohol" as used in the present invention refers to a polymer made of 100% PVA or, for example,
It is a modified PVA such as a copolymer or blend containing other monomers or polymers, preferably olefins or their polymers, in a proportion of 30% (mol %, the same hereinafter) or less. Karu PVA
The system coating has excellent hygroscopicity, transparency, and weather resistance, and has extremely low infrared transmittance in the 6 to 17μ wavelength range and good heat retention, and when used as a coating material,
There is little risk of disease outbreaks due to dew condensation, frost damage, and frost damage, and there is sufficient transparency for a long period of time.
Maintain daylight. Of course, it is not necessary that the composition of the PVA-based film for obtaining the reticulated non-woven fabric (b) and the PVA-based film applied to the reticulated non-woven fabric (a) be the same; rather, the composition of one of them is, for example, a copolymerization ratio of olefins. Alternatively, when the blend ratio is large, it is better to use the other composition as a copolymerization ratio of olefins or a composition with a lower blend ratio, preferably one made of 100% PVA, which improves hygroscopicity, transparency, and wavelength range from 6 to 17μ. It is preferable in terms of infrared transmission. The PVA sheet of the present invention has excellent dehumidification, dew condensation prevention, heat retention, and durability derived from the inherent properties of PVA polymer, and is also excellent in dimensional stability and strength, which are the characteristics of the present invention. . The present invention will be further explained below with reference to Examples. Example A PVA film with an average degree of polymerization of 1700 and a degree of saponification of 99.9% (thickness 60μ was first stretched 3 times in the warp direction and then 3 times in the weft direction at 190°C using a sequential biaxial stretching method, and then stretched at 210°C for 30 seconds. Heat treatment was performed to obtain a PVA biaxially stretched film.Then, the PVA biaxially stretched film was continuously immersed in water at room temperature for 15 seconds to moisten it, and then continuously heated in an oven room at 50°C while overfeeding. By drying, a shrinkage treatment of 7% was performed.On the other hand, PVA with an average degree of polymerization of 1700 and a degree of saponification of 99.9%
A film (thickness 70μ) was stretched 6 times at 190°C, split, heat treated at 210°C for 30 seconds, and expanded in the direction perpendicular to the stretching direction. Using a 10% PVA aqueous solution of
A reticular laminate was obtained. Next, the same average polymerization degree 1400 and saponification degree 99.9%
A product (1) of the present invention was obtained by bonding and integrating the PVA biaxially stretched film subjected to the shrinkage treatment using a 10% PVA aqueous solution and a PVA network laminate. Furthermore, the PVA biaxially stretched film body subjected to the shrinkage treatment and the PVA network laminate subjected to the swelling treatment by immersion in water at room temperature for 20 seconds are bonded and integrated to produce a product (2) of the present invention. I got it. Regarding the products (1) and (2) of the present invention and the conventional product, Table 1 shows the moisture absorption rate, Table 2 shows the infrared transmittance and heat retention properties in the 6-17μ wavelength range, and Table 3 shows the PVA 2 axis A comparison of physical properties with the stretched film alone is shown. From these results, it is clear that the product of the present invention is a PVA sheet that has superior hygroscopicity and heat retention, as well as superior mechanical strength and dimensional stability, compared to conventional products.

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Claims (1)

[Claims] 1. Dimensional stability obtained by bonding and integrating (a) a polyvinyl alcohol-based biaxially stretched film body that has been subjected to a shrinkage treatment and is in a contracted state; and (b) a polyvinyl alcohol-based fiber structure. and a polyvinyl alcohol sheet with excellent strength. 2. The sheet according to claim 1, wherein the polyvinyl alcohol-based fiber structure is adhered while being in a swollen state after being subjected to a swelling treatment. 3 Polyvinyl alcohol-based biaxially stretched membranes that are in a state of contraction greater than the maximum possible contraction under the conditions of use of the sheet, and polyvinyl alcohol-based tissue structures that have the maximum possible swelling under the conditions of use of the sheet. A sheet according to claim 2, which is formed by bonding and integrating the above-mentioned materials in a swollen state. 4 Claims 1 to 3, in which a polyvinyl alcohol biaxially stretched film body and a polyvinyl alcohol fiber structure are bonded and integrated via a polyvinyl alcohol synthetic resin.
A sheet listed in any one of the sections.