JP3223368B2 - Agricultural covering sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an agricultural covering sheet used for the purpose of preventing frost on crops such as tea and keeping the temperature at night, and more particularly, to increase the porosity of materials at high temperatures during the day. In addition, by reducing the porosity at low temperatures at night, it prevents high temperatures in the coating system during the day, has sufficient heat retention and frost protection at night, and has an appropriate size at the time of spreading. Therefore, the present invention relates to an agricultural covering sheet in which a tape-like material or a thread-like material does not come loose from a cut surface even when cut with a pair of scissors or a cutter in the width direction.

[0002]

2. Description of the Related Art Conventionally, various types of sheet materials such as films, nets, knitted fabrics and nonwoven fabrics have been used as coating materials for frost protection and heat retention. And vinyl chloride etc. is used as a material with high heat retention for the film,
Polyethylene, polypropylene, polyester and the like have been used for nets, knitted fabrics and nonwoven fabrics.

[0003]

For the purpose of preventing the damage of late frost which occurs in early spring, a frost-proof covering material is widely used. At this time, the temperature decreases during the night and frost damage sometimes occurs, but during the day there is a large amount of solar radiation and the temperature in the coating system increases, which may cause high temperature damage to the crop. Therefore, as a function required for the coating material used for the purpose of frost prevention and heat retention, it is important to prevent the temperature inside the coating system during the day as well as the frost prevention and heat retention effects at night. The latter is required to have air permeability, and the former is required to have good adhesion of frost to the material and low infrared transmittance.

[0004] When a film is used as a coating material for preventing frost and keeping heat as in the prior art, since there is no air permeability and the temperature in the coating system during the day becomes high, so-called ventilation work is required and a great deal of work is required. There was a problem that labor was required. When a net-like material, a knitted fabric, a non-woven fabric, or the like is used, the material itself has air permeability, and it is possible to save labor for ventilating work. The frost adhesion was poor due to the nature, and the infrared ray transmissivity was high, so that the nighttime heat retaining effect was not sufficient.

Therefore, a polyvinyl alcohol-based synthetic resin having a high hygroscopicity, a high frost resistance due to frost being adsorbed and adhered to the surface of the material, a low infrared transmittance and a high heat retention, is used as a material constituting the material. Was considered. As one of the known agricultural coating materials, a slit yarn made of a polyvinyl alcohol-based synthetic resin is used for one of a warp and a weft and knitted or woven to form a structure having a porosity of 10% to 70%. (No. 62-17486). This agricultural covering material is excellent in heat retention, frost resistance, and durability, and has ventilation, so that daytime ventilation operation can be saved.

However, polyvinyl alcohol is a highly crystalline synthetic polymer, has a high glass transition point, is in a glassy state at room temperature, and is hard and brittle. For this reason, the tape yarn made of a polyvinyl alcohol-based synthetic resin is cut by the tension applied to the tape yarn and the stress from the weft direction in the knitting and weaving processes, and there is a problem that the production efficiency is low. It is also possible to increase the denier of the yarn in order to increase the strength of the tape yarn, but it is possible to increase the film thickness at normal temperature as described above, as well as to increase the cost. There is a problem in that the material becomes rigid, and when the material is covered with a crop, the crop is damaged by abrasion between the crop and the material.

[0007] Further, there is known an agricultural covering material in which a plurality of strip-shaped films made of a heat-treated polyvinyl alcohol-based synthetic resin are joined to a polyvinyl alcohol-based synthetic resin network at the center of the strip-shaped film. (Sho 60-
44136). This agricultural covering material utilizes the fact that the band-shaped film body expands and contracts by absorbing and releasing moisture. During the daytime, the band-shaped film body shrinks due to drying, thereby increasing the material porosity. Since the porosity of the material is reduced by the elongation of the band-shaped film due to the wetting, the material becomes close to a closed state, so that it is possible to prevent both high temperature during the day and heat retention at night.

[0008] Here, polyvinyl alcohol repeatedly shrinks and expands due to moisture absorption and desorption. In the case of an unstretched film, it has the property that it has no direction of expansion and contraction and repeats expansion and contraction in all directions. Even when heat treatment is performed to improve dimensional stability, the non-directionality of expansion and contraction does not change, and expansion and contraction occurs in the warp direction as well as in the weft direction. In addition to reducing the dimensional stability of the resulting sheet when integrated with
When the difference in expansion and contraction between the base material and the polyvinyl alcohol-based synthetic resin film is large, there has been a problem that the adhesive may be peeled off between the base material and the polyvinyl alcohol-based synthetic resin film.

In order to prevent the above-mentioned inconveniences, it is necessary to reduce the degree of expansion and contraction of the polyvinyl alcohol-based synthetic resin film, and for that purpose, it is necessary to increase the dimensional stability. There was a problem that the difference in porosity from nighttime could not be made large. For the reasons described above, in order to increase the porosity of materials during the day under such conditions, there is a method of installing a large number of narrow band-shaped coatings, etc. There has been a problem that the bonding process with the body is complicated, the processing cost is high, and the obtained material is expensive.

[0010] Further, the above-mentioned frost-preventing coating material, when cut in the width direction of the material in order to have an appropriate size at the time of spreading, causes the warp and the weft to be unraveled from the cut surface and grow. It was necessary to take some measures to prevent transmission, which was a problem in use.

The present invention has been made in view of the above-mentioned problems, and is excellent in daytime air permeability, nighttime frost protection, and heat retention.
In addition to providing an inexpensive agricultural covering sheet with high production efficiency and providing an agricultural covering sheet in which warp and weft are not unraveled even when cut in the width direction. And

[0012]

According to the first aspect of the present invention, there is provided a tape-shaped material, comprising: a weft;
Or, it is an agricultural covering sheet that is used for weft and warp and is raschel knitted, and the tape-like material causes curling during drying, and curling is released when absorbing moisture, so that the material porosity during drying and when absorbing moisture Is a coating sheet for agricultural use, characterized in that: Claim 2
The invention of the present invention is an agricultural covering sheet obtained by using a tape-like material composed of a composite film formed by laminating a hydrophilic film and a hydrophobic film on weft yarns or weft yarns and warp yarns and raschel knitting. According to a third aspect of the present invention, in the agricultural covering sheet according to the second aspect, the hydrophilic film is a polyvinyl alcohol film stretched in a weft direction.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the agricultural covering sheet according to the present invention will be described below.

As described above, the agricultural covering sheet according to the present invention is a film in which the weft or the weft and the warp are hydrophilic and have a large degree of shrinkage difference between moisture absorption and drying (hereinafter referred to as “film 1”). ) And a film that is hydrophobic and has a small degree of expansion / contraction difference between moisture absorption and drying (hereinafter, referred to as
"Film 2") is a tape-like material obtained from a laminated composite film. FIG. 1 shows the structure of the composite film. The tape-shaped material has a characteristic that curling occurs or curling is corrected due to a difference in contraction between materials due to a change in environmental humidity.

The curling occurs because one layer of the film shrinks during drying, while the dimensional change of the two layers of the film hardly occurs, so that the composite film as a whole is rounded inside the one layer of the film. Conversely, curling is corrected because when the environmental humidity shifts from dry to humid, the film 1 layer gradually absorbs, swells, and expands, while the film 2 layer hardly undergoes dimensional change. , In order to exhibit the opposite behavior to that described above.

Here, the film 1 is not less than 3% when dried,
Suitably, it has a shrinkage of 10% or less, preferably 3% or more and 8% or less. In addition, -2% or more when absorbing moisture, 2.5%
% Or less, preferably -1% or more and 2% or less. Here, the shrinkage ratio refers to a temperature of 23 ± 2.
The ratio of dimensional change is represented by + in the shrinkage direction and-in the elongation direction based on the length at the time of standing for 88 hours in an environment of 50 ° C. and a humidity of 50 ± 5% RH. The shrinkage is the ratio of the dimensional change when the amount of water absorbed by the material is approximately 0%, and the shrinkage at the time of moisture absorption is water absorption (moisture absorption).
It shows the ratio of the dimensional change at the time when the amount substantially reaches the constant amount.

If the shrinkage during drying is less than 3%, sufficient curling cannot be obtained, and if it is more than 10%, the adhesive tends to peel off due to the large difference in shrinkage between the materials. Absent. On the other hand, when the shrinkage ratio at the time of moisture absorption is smaller than -2%, curling occurs with the film 2 layer inside, and when it is larger than 2.5%, the curling is not sufficiently corrected and is not appropriate. .

As a material that can be used as the film 1,
A polyvinyl alcohol film is exemplified. However, in the unprocessed state, the polyvinyl alcohol film does not meet the above-mentioned purpose because the expansion and contraction due to the humidity change is too large in the unprocessed state, and therefore, the degree of crystallinity and orientation are improved by stretching in the weft direction, and the expansion and contraction is suppressed. There is a need.

As a method of reducing the dimensional change of PVA due to moisture absorption and release, crystallization by heat treatment or crystallization by stretching is performed, but the film strength is improved and the treatment can be performed in a short time. For this reason, stretching is common. Here, the dimensional change due to moisture absorption and desorption of PVA is greatly affected by the crystallinity of the film and the orientation of the polymer chains, and the effect on the stretched PVA film is particularly remarkable.
The value varies depending on the stretching ratio and the like. That is, by controlling the stretching method, stretching ratio, etc., the desired P
It is possible to obtain a dimensional change of the VA film due to proper moisture absorption and release, and it is also possible to control the direction.

The stretching ratio in the weft direction of the polyvinyl alcohol film used in the present invention is from 2.0 to 4.
It is 0 times, preferably 2.5 times to 3.5 times.
If the stretching ratio is less than 2.0 times, the stretching effect is not sufficient and an appropriate shrinkage cannot be obtained. When it is larger than 4.0 times, the stretching effect is large but the film is overstretched.
It is not appropriate because fibrillation occurs and stretching breakage occurs. However, as a matter of course, there is no particular limitation as long as the shrinkage rates during drying and moisture absorption are within the above-mentioned ranges.

Examples of the material that can be used as the film 2 include a polyethylene film and a polyester film. There is no particular limitation as long as the material has little or no dimensional change during drying and moisture absorption. Further, an agent such as an ultraviolet absorber for improving the weather resistance of the material may be added.

As a method of laminating the film 1 and the film 2 to obtain a composite film, any known method such as an extrusion lamination method and a dry lamination method may be used. Regarding the thickness, both the film 1 and the film 2 need to have a thickness of 10 μm or more in order to maintain the strength, and the thickness of the composite film needs to be set to 75 μm or less from the viewpoint of the flexibility of the material. The composite film by an appropriate method,
It can be processed into a tape-like material such as a slit tape, but the width of the obtained tape-like material must be high in manufacturing efficiency.
Because of the good effect of increasing the porosity by curling,
It is good to set in the range of 3 mm to 15 mm.

The above tape-shaped material is used for weft yarn, or weft yarn and warp yarn, and is subjected to Russell knitting to obtain the agricultural covering sheet of the present invention. FIG. 2 shows an example in which a tape-like material is used for the weft 4. The spacing between the wells formed by chain-knitting the warp yarns 5 during knitting may be appropriately set in consideration of the composite film configuration, the tape width, or the degree of curling. Than 10m
It is appropriate to set the range from m to 100 mm. As the warp, in addition to the above-mentioned tape-like material, monofilaments, multi-filaments, tape-like materials such as polyethylene, polyester, vinyl chloride, nylon and vinylon can be used.

The tape-like material is subjected to Russell knitting and is folded back in a loop formed in the well, so that when one layer of the film shrinks (dries), it curls firmly and becomes tubular. There is no occurrence, and when wet, one layer of the film quickly absorbs moisture and swells (elongates), so that curling can be completely corrected. For example, in the case of a structure in which wefts such as leno weaves are inserted without being folded, the tape-like material is strongly curled, and furthermore, the film becomes a tubular shape in which one layer of film is sandwiched by two layers of film. From the fact, when wet film 1
The layer cannot absorb moisture completely, and curling is not completely corrected, so that it is difficult to improve the heat retention and frost protection at night.

In the agricultural covering sheet obtained by the present invention, the tape yarn constituting the material is composed of a composite film of two or more layers of polyvinyl alcohol / polyethylene (PVA / PE) and has a glass transition point. Due to the presence of the PE layer that is low in plasticity at room temperature, even if the thickness of the tape yarn is small, the tape yarn is not cut during knitting, and production can be performed very easily.
Further, since the obtained material is flexible, even when the crop is covered with the crop, the crop is not damaged by the rubbing between the crop and the material.

The agricultural sheet obtained by the present invention has a material porosity that changes due to the tape yarn curling in the width direction due to the expansion and contraction difference between the PVA layer and the PE layer. It is possible to change the gap of the material, and even if the difference in expansion and contraction due to moisture absorption and desorption of the PVA layer is small, the rate of change of the porosity between day and night can be increased. Further, since the dimensional stability of the PVA layer can be sufficiently imparted, there is no inconvenience such as peeling off from the hydrophobic synthetic resin film.

Furthermore, in addition to improving the dimensional stability of the tape yarn itself constituting the weft, the agricultural covering sheet obtained according to the present invention is composed of Russell knitting, so that a slight dimensional change is caused by the material composition. Since it is absorbed into the inside, there is no problem even when, for example, the material is fixed to the cultivation facility and used. The agricultural covering sheet obtained by the present invention also has an advantage that the structure (configuration) is elastic as a material for Russell knitting in the weft direction and absorbs the displacement of the fixed shaft during expansion.

Further, the agricultural covering sheet obtained by the present invention can be easily implemented by a normal laminating machine and a Russell knitting machine, and does not require any special treatment. It is possible.

[0029]

EXAMPLES (Example 1) A biaxially stretched polyvinyl alcohol film having a thickness of 18 μm (stretching ratio = 3.0 times for both processes) was subjected to a corona treatment, and then uniaxially stretched to a thickness of 25 μm using a polyester-based adhesive. The composite film obtained by performing dry lamination with the high-density polyethylene film was cut into a 4.5 mm width to obtain a tape. Russell knitting was performed using the tape-shaped material as a weft and a polyethylene monofilament as a warp to obtain an intended material. At this time, the warp constitutes a chain knit, but two rows and one set of wells are installed in parallel at a pitch of 20 mm, and the warp passes through a loop of two rows and one set of wells to form a turn portion. did.

Comparative Example 1 After a corona treatment was applied to a biaxially stretched polyvinyl alcohol film having a thickness of 18 μm (stretching ratio = 3.0 times in both directions), a uniaxially stretched film having a thickness of 25 μm was formed using a polyester-based adhesive. The composite film obtained by performing dry lamination with the high density polyethylene film was cut into a 4.5 mm width to obtain a tape. The tape-shaped material was used as a weft and a polyethylene monofilament was used as a warp to perform leno weaving to obtain a target material. At this time, a set of two rows of wells was formed at a pitch of 20 mm at a well interval formed by warps.

The agricultural coated sheet obtained in Example 1 was observed in a dry state (25 ° C., 30% RH) and in a wet (humid) state (5 ° C., 95% RH). As shown in FIG. 3, the tape-like material, which is a weft, is appropriately curled between the wells, the tape-like material takes a shape as if it was squeezed, and the porosity rises. In the state, as shown in FIG. 4, the tape-like material as the weft became flat between the wells, and the porosity decreased.
The above-mentioned behavior was reproduced by repeating the dry state and the wet state. On the other hand, when the agricultural covering sheet obtained in Comparative Example 1 was observed in the same state, the tape-shaped material, which is a weft, was curled into a cylindrical shape by curling during drying, and further formed into a coil shape. Become. Then, since the central portion could not absorb moisture sufficiently in the wet state, the curling was not completely corrected, and the tape-like material as the weft maintained the cylindrical shape. In addition, by repeating the dry state and the wet state, curling was generated more strongly, and the desired performance could not be obtained.

Further, when the agricultural sheet obtained in Example 1 was cut in the width direction using scissors, the weft and warp were not unraveled from the cut surface, and the unstretched sheet was stretched. It was possible to use it without any problem, but in the case of the agricultural covering sheet obtained in Comparative Example 1, the warp unraveled and then the weft fell off, so that it was untreated. It was not possible to do the expansion.

[0033]

As described above in detail, according to the present invention, the rise in the material porosity during the day (at the time of drying) suppresses the temperature rise in the coating system, and the material porosity at night (when the material is wet) By reducing the rate, it becomes possible to provide an agricultural covering sheet capable of improving heat retention and frost resistance.
In addition, even if the length is shortened by cutting in the width direction to adjust the dimensions at the stretch site, there is no risk of the material being released from the cut surface and further leading to disassembly, and there is no need to repair the cut surface. Therefore, the extension work can be easily performed.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an embodiment of a composite film according to the present invention.

FIG. 2 is a schematic view showing one embodiment of an agricultural covering sheet according to the present invention.

FIG. 3 is a schematic view showing a state of curling the agricultural covering sheet according to the present invention.

FIG. 4 is a schematic view showing a state of curling release of the agricultural covering sheet according to the present invention.

[Explanation of symbols]

 1 film 1 2 film 2 3 composite film 4 weft 5 warp

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kiyoo Ishii 4-1 Nihonbashi Kobunacho, Chuo-ku, Tokyo Inside Seirika Polymer Co., Ltd. (72) Inventor Yoshihiro Sunayama 4-1 Nihonbashi Kobunacho, Chuo-ku, Tokyo Taira Examiner Makoto Sakata (56) Reference Mikai Sho 61-146152 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) A01G 13/02 A01G 9/14

Claims (3)

(57) [Claims] Claims: 1. An agricultural covering sheet obtained by using a tape-like material for a weft, or a weft and a warp, and knitting the same, wherein the tape-like material curls when dried.
An agricultural covering sheet characterized in that the curling is released at the time of moisture absorption, whereby the material porosity at the time of drying and at the time of moisture absorption changes. 2. An agricultural covering sheet obtained by using a tape formed of a composite film obtained by laminating a hydrophilic film and a hydrophobic film on a weft, or a weft and a warp, and raschel knitting. 3. The agricultural covering sheet according to claim 2, wherein the hydrophilic film is a polyvinyl alcohol film stretched in a weft direction.