JPS5837815B2 - Agricultural covering material with excellent heat retention, dehumidification, and drip-free properties - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an agricultural covering material, and more particularly to an agricultural covering material that is excellent in heat retention, dehumidification, and drip-free properties.

After the war, Japan's agriculture has achieved remarkable development based on the development of advanced agricultural production technology and the use of a wide variety of agricultural production materials, but in the recent harsh environment surrounding oil,
The abnormally high price of heavy oil has had an extremely large impact on the management of farmed farms, and it is no longer possible to operate farms with conventional facilities that rely on heavy oil.

In order to realize energy-saving agriculture under such severe conditions, effective use of solar energy such as solar heat exchangers and underground heat exchangers, oil-saving cultivation through variable temperature management, or the use of agricultural covering materials with higher heat retention are recommended. All kinds of countermeasures, including development and usage, are being considered by national and public testing institutes and cultivation farmers.

On the other hand, as a conventionally important problem in the facility cultivation of crops, there are measures to prevent excessive humidity, high humidity, and dew condensation within the covering.

In a closed environment where crops are flourishing, the humidity level tends to reach 80 to 90% or more, and this humid condition not only encourages the propagation of pathogenic bacteria in the crops, hindering the stable growth of the crops, but in some cases even leading to extinction due to withering. Sometimes even.

Particularly in the low-temperature season, conditions such as gray mold, which attacks various fruits and vegetables, as well as late blight of tomatoes, leaf mold, downy mildew of cucumbers, and sclerotinia, are induced by humid and overhumid conditions, and the crops themselves However, efforts are being made to lower the humidity as much as possible because the growth is soft and elongated, and in the future when the realization of energy-saving agriculture as described above is essential, prevention of high humidity, overhumidity, and dew condensation will become an increasingly important issue. It becomes.

In recent agricultural management environments as described above, nonwoven fabrics made of synthetic resin fibers such as polyester and polypropylene have been attracting attention as agricultural covering materials with heat retention and dehumidification properties to realize energy-saving agriculture and prevent high humidity and excessive humidity. However, such nonwoven fabrics have the following drawbacks and cannot be said to be satisfactory as agricultural covering materials that meet the above objectives.

First of all, the fatal drawback is that because it has voids and is breathable, it is easy to release the solar energy accumulated during the day through convection heat transfer or the transmission of infrared rays in the 6-17μ wavelength range. For example, if we take polyester synthetic fiber nonwoven fabric as an example, it lacks cooling blocking ability and has insufficient heat retention properties. Polyethylene synthetic fibers have low heat retention properties as agricultural covering materials when the humidity is 60 to 70%, depending on the humidity inside the coating. It is comparable to a resin film, and when it absorbs moisture at a humidity of 80 to 90% or higher, it has only a heat retaining property inferior to that of a polyethylene synthetic resin film.

However, on the other hand, if the voids are eliminated to make the material non-breathable, as will be discussed later, the dehumidification performance is completely impaired and the resulting material is not as effective in preventing high humidity, overhumidity, and dew condensation.

Another drawback is that conventionally, nonwoven fabrics have been designed to prevent moisture, overhumidity, and dew condensation within the coating by providing moisture permeability through air-permeable voids or water retention through capillary action, but the material itself Because it has no hygroscopic or water absorbing properties, its effects may not be completely satisfactory.

The present inventors completed the present invention as a result of intensive studies to eliminate the above-mentioned drawbacks of existing agricultural covering materials made of non-woven fabrics, and the purpose of the present invention is to improve the above-mentioned drawbacks. The purpose of the present invention is to provide a novel agricultural covering material that has excellent heat retention, moisture removal, and drip-free properties.

Therefore, the above purpose is to heat only the layer substantially exposed on the outer surface of the nonwoven fabric with a porosity of 0.01 to 0.
This is accomplished by an agricultural covering material with excellent heat retention, moisture removal, and drip-free properties, which is coated with a film layer mainly made of heat-treated polyvinyl alcohol synthetic resin and has a sandwich-like structure.

The nonwoven fabric used in the present invention is made of synthetic or resin fibers such as polyester, polyolefin, polyvinyl alcohol, polyamide, and polyacrylonitrile, chemical fibers such as rayon and acetate, or natural fibers such as cotton and linen, and has a fineness of 1 to 10 deniers. Preferably, the one having a denier of 2 to 6 denier is prepared by a known method such as a needle punch method, a stitch method,
It is obtained by cross-bonding by an adhesive method, a spunbond method, etc., but preferably has hygroscopicity, as will be described later.
In terms of water absorption, hydrophilic fibers such as polyvinyl alcohol,
Preferably, it is a nonwoven fabric made of fibers such as rayon and acetate.

Furthermore, as an important property of the above-mentioned nonwoven fabric used in the present invention, the porosity is about 0.01-0.7, preferably 0.03.
It is important that it be about 0.5.

The porosity referred to here is the apparent specific gravity divided by the true specific gravity, and it indicates the bulkiness, so to speak, but this value is also related to the thickness, so it is difficult to define it unambiguously, but the porosity is If it is smaller than 0.01, it is insufficient as a skeleton;
Although it is not preferable in terms of strength properties and has a porosity greater than 0.7, which will be discussed later, the structure is obtained by forming a film layer mainly composed of heat-treated polyvinyl alcohol synthetic resin into a sandwich-like structure. It is preferable in terms of heat retention because the amount of fiber voids, that is, the amount of air space contained therein is small.
do not have.

In the present invention, the film layer mainly composed of polyvinyl alcohol synthetic resin is preferably composed of a polyvinyl alcohol synthetic resin having an average degree of polymerization of 1000 or more and a saponification degree of 98% or more from the viewpoint of water resistance. It refers to a film layer containing inorganic or organic colorants, fungicides, fiber powder, etc.

This film layer mainly composed of polyvinyl alcohol synthetic resin has excellent hygroscopicity, moisture permeability, and water absorption, and has a thickness of 6 to 17 μm.
It also has excellent ability to block infrared transmission in the wavelength range, and this specific film layer covers only the outer layers of substantially both the front and back surfaces of the nonwoven fabric used in the present invention, which will be described in detail later, but the present invention This is the most important requirement, and the same effect as the present invention cannot be achieved by using a film layer made of other materials.

Furthermore, an important requirement of the present invention is that the film layer containing the polyvinyl alcohol synthetic resin as a main component is heat-treated at a temperature of 140 to 220°C.

That is, polyvinyl alcohol synthetic resin has excellent hygroscopicity, moisture permeability, water absorption, and ability to block infrared transmission in the 6 to 17 micron wavelength range, but it has poor water resistance and is prone to elution and blocking due to moisture absorption and water absorption. Simply using a film layer containing polyvinyl alcohol synthetic resin as the main component has practical problems, and it is important to heat-treat it at a temperature of at least 140°C to impart practical water resistance. If the temperature is lower than 220°C, the crystallization will be insufficient, which is undesirable from the point of view of practical water resistance.On the other hand, if the temperature exceeds 220°C, the polyhinyl alcohol synthetic resin will easily decompose, which is also undesirable.

In addition, as a method for making polyvinyl alcohol composites or resins water resistant, there is a method of acetalizing them in the presence of a melting medium such as sulfuric acid or phosphoric acid using aldehydes such as formaldehyde or acetaldehyde, but although this method can impart water resistance, it is difficult to synthesize polyvinyl alcohol. Since the OH groups of the resin are reduced, the hygroscopicity, moisture permeability, and water absorption properties are significantly impaired, so it cannot be said to be preferable.

The agricultural covering material according to the present invention is obtained by coating substantially only the outer layer of the nonwoven fabric with a film layer mainly composed of polyvinyl alcohol synthetic resin that has been heat-treated at 140 to 220°C to form a sandwich-like structure. However, one aspect and effect thereof will be explained based on the attached diagrams as follows.

The attached drawing is an explanatory diagram showing one example of the agricultural covering material of the present invention, and 1 is a film layer (hereinafter abbreviated as the film layer) whose main component is polyvinyl alcohol resin heat-treated at 140 to 220"C. , 2 indicate fibers constituting the nonwoven fabric, and 3 indicate voids in the nonwoven fabric.

The agricultural covering material shown in this figure is one in which only both surface layers of a nonwoven fabric are covered with a film layer 1 to form a sandwich-like structure. may be infiltrated into the nonwoven fabric and combined with the fibers 2 constituting the nonwoven fabric.In short, only substantially both surface areas of the nonwoven fabric are coated with a film layer so that the voids 30 between the constituent fibers of the nonwoven fabric remain. It is sufficient if the structure is sealed and covered in a sandwich-like structure.

As explained above, the agricultural covering material of the present invention is made by sealingly covering both outer surfaces of a non-woven fabric with the film layer 1 and is non-breathable, so it not only prevents heat radiation due to convective heat transfer, which was a drawback of conventional non-woven fabrics, but also Since the film layer is mainly composed of polyvinyl alcohol synthetic resin with extremely low infrared transmittance in the 6 to 17μ wavelength range, it has excellent radiation cooling blocking ability, and most of the voids 3 of the nonwoven fabric remain. The air layer contained therein acts as an effective heat insulating layer, making it an agricultural covering material with extremely high heat retention properties.

In particular, when the coating layer contains aluminum powder, the light reflectivity, which is a characteristic of aluminum, shields infrared rays in the 6 to 17 micron wavelength range, and the reflectivity is added to the above-mentioned characteristics of the present invention to prevent extremely high radiation cooling at night. It can be used as an agricultural covering material that exhibits its ability and has excellent heat retention.

Furthermore, the agricultural covering material of the present invention is of a sealed type because the film layer that covers the nonwoven fabric is mainly composed of polyvinyl alcohol composite or resin that has excellent hygroscopicity, moisture permeability, and water absorption. It exhibits an extremely excellent affinity for moisture, absorbing and permeating water vapor inside the coating, exhibiting high dehumidification properties, and exhibiting high drop-free properties by absorbing and retaining moisture that would otherwise condense during nighttime cooling. .

If a coating layer whose main component is a synthetic resin such as polyethylene, polyvinyl chloride, polyvinyl acetate, etc. other than polyvinyl alcohol resin is used instead of the coating layer of the present invention, the moisture absorption and moisture permeability Not only is it impossible to provide dehumidification and drip-free properties due to lack of water absorption, but also 6-
Since the transmittance of infrared rays in the 17μ wavelength range is high, the heat retention property is also insufficient, and the effects as the agricultural covering material of the present invention cannot be expected.

Therefore, as explained above, the fiber material of the nonwoven fabric used in the present invention is not particularly limited, but from the viewpoint of hygroscopicity and water absorption, hydrophilic fibers such as polyvinyl alcohol, rayon, acetate, etc. are preferred. It is preferable that the

A method for coating substantially only both surface layers of a nonwoven fabric with a film layer in the form of a sandwich is, for example, when producing a polyvinyl alcohol synthetic resin film by a known method such as a casting method or a melt extrusion method. A method in which the above-mentioned film is simultaneously laminated and then heat-treated at a temperature of 140 to 220°C, or a method in which a polyvinyl alcohol synthetic resin film that has been previously heat-treated at a temperature of 140 to 220°C is bonded to both sides of the nonwoven fabric using a binder, etc. However, in the latter method using a binder, it is particularly preferable to use polyvinyl alcohol synthetic resin as the binder from the viewpoints of hygroscopicity, moisture permeability, and water absorption.

The thickness of the coated film layer is not particularly limited, but is usually 5 to 40μ, more preferably 10 to 2μ.
A value of 0μ is preferable, and if it is smaller than 5μ, the strength of the coated film will be poor, and if it is larger than 40μ, the coating will be more than necessary, resulting in a high price and lack of flexibility, making it difficult to handle, so it is not practical. Both are unfavorable.

Further, the thickness of the agricultural covering material of the present invention is 5 thick or less, usually around 3 thick.

Next, the present invention will be explained with reference to examples.

In addition, the various physical property values in the examples were measured by the following methods.

(Moisture absorption rate) The weight (W1) when the sample was left for 24 hours at 20°C and 65% RH, and the absolute dry weight (WO) when the same sample was vacuum-dried at 50°C for 10 hours were measured. It was calculated from the formula.

(Maximum water retention vehicle) Weight (W1) when a sample is immersed in water at 20°C for 10 hours and the falling interval of water droplets is 10 seconds or more, and the absolute dryness when the same sample is vacuum-dried at 70°C for 24 hours. The weight (Wo) was measured and calculated from the following formula.

(Temperature retention) A tunnel-type tunnel with a width of approximately 1.2 m, a height of approximately 0.6 m, and a total length of approximately 20 rrL, the minimum nighttime temperature under the cover (t1) and the minimum nighttime temperature under the uncovered condition (t2) at a height of about 10 m above the ground. Each was measured and calculated using the following formula.

(Usability) Samples were distributed to 30 people, and practical tests were carried out using tunnel coverings and interior curtains, and the results were categorized based on questionnaires regarding expansibility, opening/closing properties, etc.

** (Durability) This is the result of conducting a 3-month extension test using the same tunnel slag coating as the one used for keeping the temperature, and examining the state of damage caused by rain and wind.

Example 1 Completely saponified PV with average polymerization degree of 1700 and saponification degree of 99.9%
Film A (thickness: 20 μm) was heat-treated for 30 seconds using a cylinder heated with Etsotherm to produce a heat-treated PVA film.

Two sheets of the heat-treated PVA film were fed out at the same time, and a binder consisting of a 9% aqueous solution of completely saponified PVA with an average degree of polymerization of 1400 and a degree of saponification of 99.9% was applied using a roll coater method, and the fiber length was 501ILrIL, the fineness was 3 denier, and the porosity was 0.1. 1 on both sides as if sanding the rayon non-woven fabric.
After polymerization and pressure bonding, the products of the present invention were manufactured by drying and bonding using a Teflon-coated steam heating cylinder at a surface temperature of 100°C.

In this case, inventive product 1, in which the heat treatment temperature of the PVA film was 160°C, inventive product 2, 180°C, and inventive product 3, in which the heat treatment temperature was 200°C, were obtained.

Table 1 shows only the nonwoven fabrics used in Inventive Products 1 to 3 for comparison with the inventive products, and a polyester nonwoven fabric conventionally used as an agricultural covering material (manufactured by Unitika, trade name: Lovesheet).
, the results of investigating the hygroscopicity, water absorption, and heat retention properties of polyolefin nonwoven fabric i (manufactured by Mitsui Petrochemicals, trade name Syntex Sheet) are shown.

As can be seen from these results, it is clear that the product of the present invention has superior hygroscopicity, water absorption and heat retention properties compared to conventional products, and is an extremely suitable coating material for crop cultivation in the extremely cold season.

Although there seems to be little difference in absolute numerical values regarding temperature retention, it is not easy to maintain a temperature of 1℃ or higher all the time.
This is a big deal as an agricultural material.

Example 2 A product of the present invention was produced in the same manner as in Example 1, except that the heat treatment temperature of the PVA film was kept constant at 180° C. and the nonwoven fabric used was changed.

In this case, the nonwoven fabric used is a nonwoven fabric made of polyvinyl alcohol (vinylon) with a fiber length of 70 mm, a fineness of 5 denier, and a porosity of 0.1. Inventive product 4 has a fiber length of 50 mm, a fineness of 3 denier, and a porosity of 0.1. Inventive product 5, which is a polyester nonwoven fabric, and **Inventive product 6, which is a polypropylene nonwoven fabric with a fiber length of 501 ILm, a fineness of 3 denier, and a porosity of 0.1, were obtained.

The hygroscopicity, water absorption, and heat retention properties of products 2 and 4 to 6 of the present invention were examined and the results are shown in Table 2.

As shown in Table 2, in terms of temperature retention, they showed good performance without much difference, but in terms of hygroscopicity and water absorption, products 2 and 4 of the present invention, which used nonwoven fabrics made of hydrophilic fibers, compared to nonwoven fabrics made of hydrophobic fibers. It is clear that this is a more suitable agricultural covering material than Products 5 and 6 of the present invention using the following.

Example 3 A product of the present invention was manufactured in the same manner as in Example 1, but the heat treatment temperature was 180°C, and the PVA film used was mixed with 5% aluminum powder (average particle size 20 to 30μ). Product 7 was manufactured.

Inventive product 7 has hygroscopicity, and inventive products 1 to 3 have water absorbency.
As for the heat retention, as shown in the measurement results in Table 3, aluminum has a high infrared shielding property in the 6-17 μ wavelength range, so it has even better performance than the products 1 to 3 of the present invention. It is also a suitable agricultural covering material.

Example 4 Inventive products 8 to 10 and comparative products 1 to 2 were produced in the same manner as in Example 1, except that nonwoven fabrics having various porosities as shown in Table 4 were used, and the heat treatment temperature of the PVA film was 180°C.

The results of measuring the hygroscopicity, water absorption, heat retention, usability, and durability of the obtained product are shown in Table 4.
As is clear from the table, good results were obtained within a certain range of porosity of the nonwoven fabric.

[Brief explanation of the drawing]

The figure shows an agricultural covering material according to the invention. In an explanatory diagram showing one example, 1... a film layer mainly composed of heat-treated PVA,
...Nonwoven fabric structure fiber, 3...Void part of nonwoven fabric. 2

Claims (1)

[Scope of Claims] 1. Substantially only the outer surface layer of a nonwoven fabric having a porosity of 0.01 to 0.7 is coated with a film layer mainly composed of polyvinyl alcohol synthetic resin heat-treated at 140 to 220°C, An agricultural covering material with excellent heat retention, dehumidification, and drip-free properties, characterized by having a sandwich-like structure. 2. An agricultural covering material with excellent heat retention, dehumidification, and drip-free properties according to claim 1, wherein the nonwoven fabric is made of hydrophilic fibers. 3. Agricultural covering material with excellent heat retention, dehumidification, and drip-free properties according to claim 1 or 2, wherein the film layer mainly composed of polyvinyl alcohol composite or resin has a thickness of 5 to 40 μm. . 4. Agriculture with excellent heat retention, dehumidification, and drip-free properties according to claim 1, 2, or 3, wherein the film layer containing polyvinyl alcohol composite or resin as a main component contains aluminum powder. Covering material for use.