NON-WOVEN FABRIC SHEET FOR AGRICULTURAL USE

Abstract: A non-woven fabric sheet for agricultural use, which has been rendered hydrophilic by applying a surfactant on at least part of the surface of a hydrophobic non-woven fabric. This treatment serves to provide the water passage through which water passes from the surface to the back side of the fabric, and imparts a water retentivity of 150 to 300 wt. %. The water passage permits rainwater to rapidly pass there-through from the surface to the back side, and the low water retenti­ tivity prevents an increase in weight of the fabric due to water retention. Abstract A nonwoven sheet for agricultural use made of a hydrophobic nonwoven fabric subjected to hydrophilic treatment in which a surfactant is applied to at least part of the surface of the hydrophobic nonwoven fabric, the sheet being characterized in that the hydrophilic treatment creates channels that allow water to pass from the obverse surface of the nonwoven fabric to the underside thereof and in that the percentage of water retention is within the range of 150 to 300 wt%. The provision of the channels enables water to rapidly pass from the obverse surface of the nonwoven sheet to the underside thereof, and the weight of the nonwoven fabric is not increased by water retention because of a small percentage of water retention.

Description: The present invention relates to a nonwoven sheet for agricultural use which may be used as a full-covering sheet for tunnel culture and outdoor culture. Examples of known applications of nonwoven fabrics include various types of agricultural covering materials such as full-covering sheets for tunnel culture and outdoor culture. Nonwoven fabrics composed of, for example, polyethylene terephthalate (PET) or polypropylene (PP) exhibit excellent heat retaining properties and permeability and their performance makes them suitable as nonwoven sheets for agricultural use. On the other hand, such nonwoven fabrics are basically composed of hydrophobic resins and thus have a tendency to allow rain water and so forth to collect on their surface because water does not easily pass therethrough. There is therefore a danger of the growing crops being crushed by the weight of drops of water that have collected on the nonwoven fabric used in a certain form. The inventors of the present invention developed a full-covering material for agricultural use made of a nonwoven fabric composed of hydrophobic fibers of 6 denier or more and having a METSUKE (weight /m²) amount of 10 to 30 g/m² and light transmittance of 85% or more as described in Japanese Patent Laid-Open No. 128955/1986. This material suffers from the same problem as that described above because it is composed of hydrophobic fibers. US-A-4 328 279 discloses a wettable nonwoven wiper which has been treated by a mixture of wetting agents. The wetting agent treatment includes a mixture of sodium dioctyl sulfosuccinate such as Aerosol OT and a non-ionic surfactant such as alkyl phenoxy ethanol (Triton X-100). FR-A-2 190 964 discloses a light-occluding and water-permeable nonwoven sheet, comprising continuous filaments and containing a solar ray-absorbing substance. An agricultural sheet composed of a nonwoven fabric which is subjected to hydrophilic treatment with a surfactant for the purpose of preventing water from collecting on its surface is known as a sheet that is capable of resolving the above-described problem. Such a hydrophilic-treated nonwoven fabric is subjected to hydrophilic treatment to a high degree so that any water in contact with the surface of the nonwoven fabric cart pass therethrough as fast as possible from the obverse surface of the nonwoven fabric to the underside thereof. As a result, the hydrophobic property of the fibers which form the nonwoven fabric deteriorates and thus waterdrops held in the voids of the nonwoven fabric do not easily escape therefrom. This leads to a situation of a significant increase occurs in the weight of the nonwoven fabric owing to the water retention phenomenon. Although the danger that growing crops will be crushed due to the increase in weight of the sheet due to water retention is not as great as with the above-described nonwoven sheet for agricultural use composed of a nonwoven fabric, it is not possible to completely avoid this problem. In the case of a hydrophobic nonwoven fabric, the water which collects on its surface can be easily removed by inclining the surface to allow it to run off, and thus any increase in the weight caused by this water can be ignored. On the other hand, since conventional hydrophilic-treated nonwoven fabrics exhibit a high percentage of water retention and the water held in the voids of the nonwoven fabric cannot be easily removed, the state of gradual increase in the weight continues for a long time. This leads to the problem that the increase in weight makes the work of removing the sheet very laborious. When the sheet is rolled up and stored for reuse after it has been used, there is also a great danger that, since the rolled up nonwoven fabric has a form in which both of the roll ends are fixed, the nonwoven fabric will be broken owing to shrinkage that occurs due to the drying that takes place during storage if the fabric has a high degree of water retention. The present invention seeks to solve the aforementioned problem of conventional nonwoven sheets for agricultural use, and seeks to provide a nonwoven sheet for agricultural use which permits rainwater and the like to pass therethrough without collecting on the surface, and which does not present the disadvantage of crushing growing crops. The present invention provides a nonwoven sheet for agricultural use made of a hydrophobic nonwoven fabric, which sheet is obtainable by a hydrophilic treatment process which comprises applying a surfactant to at least part of the surface of the hydrophobic nonwoven fabric to create channels that allow water to pass from the obverse surface of said nonwoven fabric to the underside thereof, and has a percentage water retention of from 150 to 300 wt %. The invention further provides a hydrophilic treatment process for preparing a nonwoven sheet for agricultural use, which process comprises applying a surfactant to at least part of the surface of a hydrophobic nonwoven fabric to create channels in the fabric which allow water to pass from the obverse surface to the underside of the fabric, such that the percentage water retention of the fabric is from 150 to 300 wt %. In the nonwoven sheet for agricultural use of the present invention, since the hydrophilic treatment creates channels that allow water to pass from the obverse surface of the nonwoven fabric to the underside thereof, rainwater is able to rapidly pass through the channels from the obverse surface of the nonwoven fabric to the underside thereof even if it comes into contact with the surface of the nonwoven fabric during rain without collecting on the surface thereof. Furthermore, since the percentage of water retention is as low as from 150 to 300 wt% (the method of measuring the percentage of water retention being described below), there is no danger of crushing crops owing to an increase in weight of the nonwoven fabric caused by water retention. The nonwoven fabric used in the present invention is composed of hydrophobic fibers. One determines whether the fibers comprising a nonwoven fabric are hydrophobic by, for example, measuring the percentage water absorption. The percentage water absorption may be measured, for example, using a fiber having a given length, a fiber block having a given weight or a nonwoven fabric having a given area, in accordance with the Japanese Industrial Standard JIS K 7209. If the percentage of water absorption is 1% or less, the nonwoven fabric is regarded as being hydrophobic. In the present invention, any fiber may be used so long as it exhibits a percentage of water absorption of 1% or less. In the present invention, polyolefin fibers such as polyethylene fibers and polypropylene fibers, and polyester fibers such as polyethylene terephthalate fibers are preferably used, and particularly preferable are polyolefin fibers exhibiting low percentages of water absorption. In particular, polyolefin spun-bonded nonwoven fabrics are preferably used because of their productivity, bulk and strength. The above-described hydrophobic-treated nonwoven fabric is subjected to hydrophilic treatment by applying a surfactant to at least part of the surface thereof. This hydrophilic treatment creates channels which allow water to pass from the obverse surface of the nonwoven fabric to the underside thereof. These channels need not be formed over the whole of the portion subjected to hydrophilic treatment and it is sufficient to form the channels over part of the surface area at suitable intervals. For example, the nonwoven fabric may be formed into an elongated shape, and hydrophilic treatment may be carried out in the form of a band or line in the lengthwise direction thereof so as to form a plurality of channels arranged in parallel in the widthwise direction. Alternatively, hydrophilic treatment may be performed in the widthwise direction of the band-shaped nonwoven fabric so as to form a plurality of channels. Hydrophilic treatment may also be provided in the form of a plurality of treatment portions in the form of a band or line in the lengthwise and widthwise directions. In this way, when the hydrophilic treatment is imparted with a directional property, the water adhering to the nonwoven fabric can be guided in the direction of the hydrophilic treatment. The nonwoven sheet according to the present invention is made of a nonwoven fabric which is subjected to hydrophilic treatment and which has a percentage water retention of 150 to 300 wt%, preferably 150 to 200 wt%. If the percentage water retention is 150 wt% or less, the hydrophilic treatment is not sufficient, and water thus collects on the obverse surface of the nonwoven fabric and does not pass therethrough to the underside thereof. If the percentage water retention is 300 wt% or more, there is a danger of crushing crops owing to the significant increase in weight of the nonwoven fabric that is caused by water retention. Examples of surfactants that may be used in performing the hydrophilic treatment include surfactants of the polyethylene alkylphenol type, alkylsulfate type, aliphatic type, alkylethanolamine type and polyoxyethylene ether type. The polyoxyethylene ether type of surfactant is particularly preferable. It is also preferable to ensure that the surfactant is provided with functional permanence by incorporating 20 to 70 wt% of a binder exhibiting high adhesion properties. An example of such a binder is water-soluble acrylic resin. The following Examples illustrate the invention. Table 1 shows a comparison between a nonwoven fabric obtained by hydrophilic treatment of a span-bonded nonwoven fabric composed polypropylene fibers of 8 denier and having METSUKE of 20 g/m² so that the percentage water retention fell within the range of the present invention, a nonwoven fabric as a comparative example which was not subjected to hydrophilic treatment, and a conventional hydrophilic-treated polyethylene terephthalate nonwoven fabric. Example 1 is a nonwoven fabric to which an aqueous solution of 2 wt% surfactant was applied with a spray discharge of 15 g/m², and Examples 2 and 3 are nonwoven fabrics to which an aqueous solution of 3 wt% surfactant was applied in ratios of 4.2 g/m² and 5 g/m², respectively. The percentage water retention of each of the fabrics was measured as the absolute value obtained by dipping each nonwoven fabric in water at 23°C for 5 minutes, naturally dewatering each nonwoven fabric for 1 minute by allowing it to stand on a wire mesh inclined at 45°, forcibly dewatering each nonwoven fabric by lifting and shaking it several times, and then calculating the percentage water retention using the following equation: Example Comparative Example 1 2 3 1 2 3 Material PP PP PP PP PET PET Thickness of fiber (denier) 8 8 8 8 3 2 METSUKE (g/m²) 20 20 20 20 15 15 Presence of hydrophilic treatment Treated Treated Treated Not treated Treated Treated Passage of water collecting on the surface Passing Passing Passing Not passing Passing Passing Percentage of water retention (%) 170 180 190 100 500 500 Each of the agricultural nonwoven sheets of Example 2 and Comparative Examples 1 to 3 shown in Table 1 were used in a tunnel culture application, and water was intentionally sprayed on each of the nonwoven sheets using a shower. In the case of Comparative Example 1, most of the water collected on the surface, and thus the nonwoven sheet used sagged under the weight of the water, leading to crushing of the crops being grown in the tunnel at certain portions. On the other hand, in Examples 2 and Comparative Examples 2 and 3, the water passed from the obverse surface of the nonwoven to the underside thereof, so no crushing of the crops being grown occurred. When each of these sheets was then removed, the ease of removal was poor in the case of Comparative Examples 2 and 3 owing to the increase in weight of the sheets caused by water retention while the sheet of Example 2 could be removed easily because substantially no increase in weight occurred. As described above, when the nonwoven sheet of the present invention is used as a tunnel for agricultural growing in a greenhouse or is used for full covering of crops, drops of water are able to pass through the hydrophilic channels and escape, so there is no danger of the crops growing underneath being crushed owing to the weight of rainwater collecting on the sheet. In addition, since the percentage water retention is within the range of 150 to 300 wt%, the weight of the sheet is never greatly increased, and there is therefore no danger at all of growing crops crushed by the sheet breaking. Although the nonwoven sheet of the present invention is suitable as a tunnel for agricultural growing in a greenhouse or for full covering of crops, the agricultural applications of the sheet are not limited to these purposes, and the sheet can also, for example, be used for providing heat insulation for growing crops.

Claims: A nonwoven sheet for agricultural use made of a hydrophobic nonwoven fabric, which sheet is obtainable by a hydrophilic treatment process which comprises applying a surfactant to at least part of the surface of the hydrophobic nonwoven fabric to create channels that allow water to pass from the obverse surface of said nonwoven fabric to the underside thereof, and has a percentage water retention of from 150 to 300 wt %. A nonwoven sheet according to claim 1, wherein the said hydrophobic nonwoven fabric is a polyolefin spun-bonded nonwoven fabric. A nonwoven sheet for agricultural use according to claim 1 or 2 wherein the hydrophobic nonwoven fabric is formed into an elongated shape and is provided with a plurality of hydrophilic treatment portions in the form of a band or line in the widthwise direction thereof. A nonwoven sheet according to claim 1 or 2, wherein the hydrophobic nonwoven fabric is formed into an elongated shape is provided with a plurality of hydrophilic treatment portions in the form of a band or line in the lengthwise and widthwise directions thereof. A nonwoven sheet according to any one of claims 1 to 4 wherein the surfactant contains from 20 to 70 wt % of a binder. A hydrophilic treatment process for preparing a nonwoven sheet for agricultural use, which process comprises applying a surfactant to at least part of the surface of a hydrophobic nonwoven fabric to create channels in the fabric which allow water to pass from the obverse surface to the underside of the fabric, such that the percentage water retention of the fabric is from 150 to 300 wt %. A process according to claim 6 wherein the hydrophobic nonwoven fabric is a polyolefin spun-bonded nonwoven fabric. A process according to claim 6 or 7 which comprises forming the hydrophobic nonwoven fabric into an elongated shape and providing the fabric with a plurality of hydrophilic treatment portions in the form of a band or line in the widthwise direction of the fabric. A process according to claim 6 or 7 which comprises forming the hydrophobic nonwoven fabric into an elongated shape and providing the fabric with a plurality of hydrophilic treatment portion in the form of a band or line in the lengthwise and widthwise directions of the fabric. A process according to any one of claims 6 to 9 wherein the surfactant contains from 20 to 70 wt % of the binder.

Inventors: FUJIMURA MITSUAKI, OHE TATSUYA, FUJIMURA, MITSUAKI, OHE, TATSUYA
Applicants: MITSUI PETROCHEMICAL IND, MITSUI PETROCHEMICAL INDUSTRIES, LTD.
Application year: 1988
Main classification: A01G13
IPC codes: A01G13