JPH024264B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an agricultural covering material used for tunnel cultivation, greenhouse cultivation, etc.

[Conventional technology]

Agricultural covering materials generally used for tunnel cultivation, greenhouse cultivation, etc. include synthetic resin films such as polyethylene, polyvinyl chloride, polyester, and ethylene-vinyl acetate copolymer. Although these synthetic resin films are highly translucent, they themselves do not have hygroscopicity or moisture permeability, so the inside of the coating tends to become humid or overhumidified. Also,
Since it does not have ventilation, it has the disadvantage of causing the internal temperature of the coating to rise (approximately 40°C or higher during the day) even in the final low temperature period. In particular, when the distance between the crop and the covering synthetic resin film is narrow or the two are in contact, as in tunnel cultivation, etc., the frost that falls on the covering synthetic resin film at the end of the season may damage the crop. It also has the disadvantage of being cooled and causing frost damage. Among these problems, high humidity and high temperatures inside the coating encourage the propagation of pathogenic bacteria in the crops, leading to the withering of the crops, and in some cases, even total extinction. Openings are provided in the cladding to ventilate the air inside the cladding at appropriate time intervals. However, performing ventilation at appropriate intervals in this manner is extremely complicated. Therefore, in order to solve such problems, it has been considered and partially implemented to use a nonwoven fabric made of synthetic resin fibers such as polyester or polyolefin instead of the above-mentioned covering synthetic resin film. Since the nonwoven fabric has voids, it has a certain degree of ventilation. Therefore, it is effective to some extent in preventing high temperature and high humidity inside the coating, but since this nonwoven fabric has voids, it is easy to release solar energy accumulated during the day at night, making it difficult to retain heat. It has the disadvantage of insufficient properties. Further, since no measures have been taken to prevent frost damage for both the synthetic resin film and the nonwoven fabric, the reality is that frost damage is prevented by using soft straw or the like.

[Problem to be solved by the invention]

In order to solve these drawbacks, we focused on the hygroscopic and water-swelling properties of polyvinyl alcohol (hereinafter abbreviated as "PVA") itself, and created a PVA sheet-like network by stretching, splitting, widening, and heat treating PVA film. On the surface of the body, strips of PVA film are placed side by side at predetermined intervals, and one side edge of each is lined up.
An agricultural covering material made by adhering to a PVA sheet-like mesh has been proposed (Japanese Patent Application Laid-open No. 89957/1989). However, although this agricultural covering material has excellent ventilation properties, it does not take heat retention in winter into consideration, and therefore there is a problem in terms of preventing frost damage in winter.

This invention was made in view of the above circumstances, and aims to prevent high temperature and humidity inside the coating during summer,
The purpose is to provide an agricultural covering material that can prevent frost damage in winter, prevent tearing during folding and unfolding, and can be stored in a small size.

[Means to solve the problem]

In order to achieve the above object, the agricultural covering material of the present invention stretches, splits, widens, and spreads a PVA film.
PVA-based sheet-like nets obtained by heat treatment are stacked and glued in a state perpendicular to the width expansion direction.
A pair of upper and lower flexible power supply lines is arranged between the above-mentioned sheet-like mesh bodies, and a plurality of linear heating elements without insulation coating are arranged at predetermined intervals in the lateral direction between the two power supply lines. Both ends thereof are connected to the pair of upper and lower flexible power supply lines, and flexible and insulating reinforcing threads are arranged orthogonally so as to form a lattice shape with these linear heating elements. It has a structure in which it is fixed using adhesive between both sheet-like net-like bodies.

[Effect]

That is, this agricultural covering material has a mesh structure and has sufficient ventilation, so it exhibits an excellent effect in preventing high temperature and high humidity inside the covering. Moreover, this agricultural covering material has linear heating elements distributed in a distributed manner, and by energizing the linear heating elements to generate heat during the low temperature period of winter, frost that has fallen on the surface of the covering material can be melted and removed. In addition to preventing the occurrence of frost damage, the generated heat also increases the temperature inside the coating, providing a sufficient heat-retaining effect.

Next, the present invention will be explained in detail based on examples.

FIG. 1 is an external perspective view of one embodiment of the present invention. That is, this agricultural covering material 1 consists of a plurality of flexible linear heating elements 2 arranged at predetermined intervals and a plurality of reinforcing cotton threads 3 arranged perpendicularly thereto. It is constructed by laminating and adhering two PVA-based sheet-like mesh bodies 4 in a sandwiched state in a warp-to-warp direction using a PVA-based binder. Reference numeral 5 denotes a flexible power supply line for energizing the linear heating element, and the end thereof is connected to a power source (not shown). here
The PVA-based sheet-like network 4 includes not only a network made of completely saponified polyvinyl acetate (hereinafter abbreviated as "PVAc"), but also a network made of partially saponified polyvinyl acetate (hereinafter abbreviated as "PVAc"). Also included are networks made of saponified copolymers of vinyl acetate and other monomers. In the case of partial saponification of PVAc or saponification of a copolymer of VAc and other monomers, components other than PVA are
% (mol%, the same applies hereafter) or less, and the network composed of things within this range is the above-mentioned
Included in the range of PVA-based sheet-like networks.

The agricultural covering material 1 as described above is manufactured, for example, as follows. That is, first, to PVA with an average degree of polymerization of 1400 or more and a degree of saponification of 98.5% or more, a plasticizer such as glycerin or polyalkyl ether, or a splitting accelerator such as water-soluble or thermoplastic resin is added as necessary. A PVA film is produced by liquefying it into an aqueous solution and forming it into a film using a known film forming method such as a casting method or a coagulation method. In this way, PVA with an average polymerization degree of 1400 or more and a saponification degree of 98.5% or more
When using PVA film made using
This is preferable in terms of practical strength and dimensional stability of the PVA sheet-like network obtained. Next, this PVA
As shown in Figure 2, the film is stretched at least 5.5 times, preferably 6 to 6.5 times, at a temperature of 180°C or higher in the same direction as the molecular orientation direction (direction of arrow A), and then multi-circumferentially stretched. The fibers are split using a splitting roll 7 having a large number of cutting blades 6, and a large number of streak-like cuts 9 of a predetermined length are made in the stretched film 8 in the same direction as its running direction (direction of arrow B). If the stretching temperature of the PVA film is set to 180℃ or higher (the upper limit is 220 to 230℃, which is the temperature at which thermal decomposition does not occur) as described above,
It is preferable in terms of stretchability, and in this case, setting the stretching ratio to 5.5 times or more improves the splitting properties of the stretched film 8 and the practical strength of the resulting PVA sheet-like network 4.
Preferable in terms of dimensional stability. Next, the striped cut 9
The stretched film 8a to which the film is attached is heat-treated at a temperature of 180° C. or higher to set it in a stretched state. When the heat treatment is performed at a temperature of 180°C or higher (the upper limit is 220 to 230°C, which is the temperature at which thermal decomposition does not occur), a sufficient heat setting effect can be obtained, and the dimensions of the resulting PVA sheet-like network 4 can be reduced. Good stability. Next, the stretched film 8a with the linear cuts thus set in the stretched state is stretched in a direction perpendicular to the direction in which the linear cuts 9 are formed to widen it. The width is widened by a known cross guider method, spring method, or the like. As a result, as shown in FIG.
is obtained. Next, as shown in FIG. 4, on top of this PVA-based net-like body 4, a plurality of flexible wires made of cotton thread as a core material and coated with strip-shaped copper foil spirally wound are placed. The heating elements 2 are arranged side by side at a predetermined interval, and both ends of each are connected to a flexible power supply line 5 for energization extending in a direction perpendicular to the linear heating elements 2, and a plurality of reinforcing cotton threads 3 are connected to the plurality of reinforcing cotton threads 3. are arranged at a predetermined interval so as to be orthogonal to the flexible linear heating elements 2. Next, in this state, another PVA network 4a is placed on top of the other and bonded together using a PVA binder. In this case, since the PVA network 4 has a weak tensile strength in the same direction as the width expansion direction, the two PVA network bodies 4, 4a are stacked and bonded together so that the width expansion directions are perpendicular to each other. In this way, an agricultural covering material 1 as shown in FIG. 1 is obtained.

This agricultural covering material 1 has a mesh structure and has sufficient ventilation, so it can prevent the inside of the covering from becoming hot and humid, and it also generates heat by passing electricity through the linear heating element 2 (for example, 50~ near the heating element
By generating heat to a temperature of 60 degrees Celsius), it exhibits a frost-proofing effect in the winter, and also exhibits a sufficient heat-retaining effect inside the coating. In order to maximize such effects, it is preferable to set the porosity of the mesh within a range of 5 to 50%. In other words, if the porosity is less than 5%, the ventilation will be poor and it may be necessary to create an opening for ventilation, whereas if it exceeds 50%, the ventilation will be too large and the inside of the coating will be damaged. This is because heat retention becomes worse.
The porosity can be easily adjusted by adjusting the width expansion ratio and the number of laminated sheet-like mesh bodies. In particular, as in this example, as a material for covering materials.
When a PVA-based sheet-like network is used, the properties of PVA are that deterioration due to heat resistance does not occur for a long time, and infrared transmittance in the 6-17μ wavelength range is low.
Because it has excellent moisture absorption and moisture permeability, it exerts a kind of humidity regulating effect.
The coating material has a long lifespan, and the emission (radiative cooling) of the solar energy accumulated during the day is suppressed at night, which, together with the heat generated by the linear heating element, significantly increases the heat retention of the coating material. It is possible to prevent high temperature, excessive humidity, and dew condensation within the coating, and also to prevent insufficient humidity. Furthermore, the covering material of the above-mentioned embodiments does not use a PVA-based sheet-like mesh body made by simply weaving or knitting PVA fibers in warp and warp directions;
Because it uses a PVA sheet-like network made by stretching, splitting, widening, and heat treating a PVA-based film, in addition to the effects listed above due to the general properties of PVA, it also has the following advantages: It has a great effect. In other words, when the PVA-based sheet-like network absorbs moisture caused by frost during frost, if heat is generated by the linear heating element, the PVA-based sheet-like network will shrink, and as a result, As the mesh size becomes smaller and the porosity automatically becomes smaller, heat retention is significantly improved and extremely effective in preventing frost damage.

Note that the flexible linear heating element is not limited to one in which a band-shaped copper foil is spirally wound around a cotton thread core, and flexible electric wire such as copper wire may also be used. good. Furthermore, the linear heating element may not be disposed between two sheet-like net-like bodies, but may be disposed on the inner surface (covered inward surface) of a laminated and integrated plurality of sheet-like net-like bodies. Furthermore, when three or more sheet-like mesh bodies are laminated and integrated, they may be inserted between appropriate layers. Further, in the above embodiments, reinforcing cotton threads are used, but threads made of other materials may also be used.

〔Effect of the invention〕

The agricultural covering material of the present invention is constructed as described above, and therefore has the effect of preventing high temperature and humidity inside the covering in the summer and frost damage in the winter, resistance to repeated folding, etc., and the effect of not being bulky when stored. play. That is, the agricultural covering material of the present invention has a mesh structure in which the PVA sheet-like mesh members are stacked with their width directions perpendicular to each other, allowing ventilation, and the PVA system itself has hygroscopic properties. This prevents the interior of the coating from becoming hot and humid during the summer. Therefore, the inside of the cover can be maintained in a suitable growing environment for crops and the outbreak of diseases can be effectively prevented, without having to perform the complicated work of opening and closing the openings at appropriate time intervals as in the past. sell. Since a pair of upper and lower flexible power supply lines and a bare linear heating element with no insulation coating are installed between the two sheets, the heat of the linear heating element is blocked by the insulation coating. Heat can be radiated directly from the mesh of the PVA-based sheet-like reticulated material without any heat generation, and frost damage can be prevented with minimal energy.
At the same time, the diameter of the linear heating element becomes smaller due to the lack of insulation coating, and the entire insulation coating becomes a flat structure, and the rigidity of the insulation coating is eliminated, making it possible to fold the entire body into a small size during transportation and storage. become. Furthermore, the cost is reduced by the omission of the insulation coating. In addition, the insulation of the linear heating element is performed by the PVA sheet-like mesh, and even if the sheet-like mesh has a mesh, the mesh becomes considerably smaller due to the superposition of the sheet-like mesh. Therefore, there is no problem of poor insulation. Moreover, the linear heating element can be made flexible and
By combining insulating reinforcement material in a grid pattern,
The linear heating element itself now functions as a reinforcing material, which saves on reinforcing material, which reduces costs.At the same time, its improved strength allows it to be repeatedly folded (agricultural covering materials can be easily folded when not in use). It has improved resistance to being folded and stored, and will not be damaged when folded.

[Brief explanation of drawings]

FIG. 1 is a perspective view of an embodiment of the present invention, FIG. 2 is an explanatory diagram for manufacturing a sheet-like net-like body, and FIG. 3 is a partially enlarged view of the sheet-like net-like body obtained thereby.
FIG. 4 is a manufacturing explanatory diagram of the one shown in FIG. 1. DESCRIPTION OF SYMBOLS 1... Agricultural covering material, 2... Flexible linear heating element, 3... Cotton thread, 4, 4a... PVA sheet-like mesh body, 5... Power supply line.

Claims (1)

[Scope of Claims] 1. A polyvinyl alcohol-based sheet-like network obtained by stretching, splitting, widening, and heat treating a polyvinyl alcohol-based film is overlapped and bonded with the widening direction orthogonal to each other, and both of the above-mentioned sheets are bonded together. A pair of upper and lower flexible feeder wires is arranged between the net-like bodies, and a plurality of linear heating elements without insulation coating are arranged laterally at predetermined intervals between the two feeder wires. Flexible and insulating reinforcing threads are connected to the above pair of upper and lower flexible power supply lines, and are orthogonally arranged so as to form a lattice shape with these linear heating elements, and these arranged bodies are connected to the above two sheet-shaped Agricultural covering material that is secured using mesh adhesive. 2. The agricultural covering material according to claim 1, wherein the flexible linear heating element is constructed by using thread as a core material and spirally winding a strip of copper foil around the thread. 3. The agricultural covering material according to claim 1 or 2, wherein the sheet-like network has a porosity of 5 to 50%.