JP2000045163A - Biodegradable lining sheet for plastic greenhouse - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a lining sheet for a plastic greenhouse having excellent translucency and weather resistance and easily disposable owing to its biodegradability by forming a specific polylactate-based filament to a sheet. SOLUTION: The objective biodegradable sheet for the lining of a plastic greenhouse has a single fiber fineness of 1-15 de, an areal density of the sheet of 20-100 g/m2, a translucency of >=40% and a strength retention [(S1/S0)×100(%) (S1 is a tensile product of specimen irradiated for 300 hr; S0 is a tensile product of specimen before irradiation)] of >=50% determined by weather resistance test using a weather meter. The sheet can be produced from a polylactate-based polymer having a number-average molecular weight of >=20,000, preferably >=40,000 and composed of poly(D-lactic acid), poly(L-lactic acid), a copolyme of D-lactic acid and L-lactic acid, a copolymer of D-lactic acid and a hydroxycarboxylic acid, a copolymer of L-lactic acid and a hydroxycarboxylic acid or their blended product by forming a sheet of the polymer by spun-bonding method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sheet which is decomposed almost completely by the action of microorganisms after use and is easy to dispose of, and has high light transmittance and excellent weather resistance.
In particular, the present invention relates to a sheet that can be suitably used for a curtain for lining an agricultural house.

[0002]

2. Description of the Related Art Conventionally, a lining curtain of an agricultural house has been provided with various kinds of light so as to prevent the sun rays necessary for crops from passing therethrough but to prevent the warm air inside from escaping to the outside and lowering the temperature inside the house. Has been devised. That is, it is a device for improving the heat retention by increasing the heat transmission effect in the house and the heat insulation effect of radiation while maintaining the translucency. For example,
A single-layer lining curtain generally used in a conventional house may be changed to a multilayer structure having two or more layers. In the two-layer structure, an air layer is created between the layers of the curtain, which has the effect of preventing air convection and improving the heat insulating effect. In the case of this two-layer structure, a long-fiber nonwoven fabric is employed as the lower layer.

[0003] In addition to the above-mentioned various properties such as translucency and heat retention, such a sheet is used after being directly or indirectly exposed to sunlight for a long period of time. In conventional sheets containing a long-fiber nonwoven fabric as a component, the thermoplastic polymer used for the long-fiber nonwoven fabric alone often does not have sufficient weather resistance, and it is necessary to add some weathering agent. Was. However, when the thermoplastic polymer is polyester or polyamide, the added weathering agent is often thermally decomposed during melt spinning,
It is difficult to exhibit sufficient weather resistance. Although it is conceivable to employ a weathering agent having high thermal decomposition resistance, a weathering agent having a sufficient effect has not been found yet.

On the other hand, in recent years, plastic films and non-woven fabrics have been widely used in the agricultural field. On the other hand, how to treat used ones without polluting the natural environment has become a major issue. I have.

[0005]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, has high light transmittance and excellent weather resistance, and is almost completely decomposed by the action of microorganisms after use to facilitate disposal. The present invention provides a sheet for lining an agricultural house.

[0006]

The gist of the present invention is as follows. It is made of a polylactic acid-based long-fiber nonwoven fabric, has a light transmittance of 40% or more, and has a strength retention of 50% or more determined by the following formula (A) in a weather resistance test using a weather meter. Degradable agricultural lining sheet. Strong retention (%) = (S1 / S0) × 100 (b) S1: Strain product of sample after irradiation for 300 hours S0: Strain product of sample before irradiation

[0007]

The sheet of the present invention is composed of a non-woven fabric made of biodegradable polylactic acid-based long fibers, and is constituted by such a biodegradable fiber for a certain period of time. After the elapse of the time, the sheet is almost completely decomposed by microorganisms, so that it is not necessary to collect and recover the spread sheet and dispose of it, and the natural environment is not polluted. The polylactic acid-based polymer constituting the long fiber in the present invention is a thermoplastic aliphatic polyester having biodegradability, for example, poly (α-hydroxy acid) or a copolymer containing the polymer element as a main repeating unit. Coalescence. Specifically, poly (D-lactic acid), poly (L-lactic acid), a copolymer of D-lactic acid and L-lactic acid, a copolymer of D-lactic acid and hydroxycarboxylic acid or L-lactic acid Among the copolymers of lactic acid and hydroxycarboxylic acid, the melting point is 80
Polymers having a temperature of at least ° C are preferred. Here, examples of the hydroxycarboxylic acid in the case of a copolymer of lactic acid and hydroxycarboxylic acid include glycolic acid, hydroxybutyric acid, hydroxyvaleric acid, hydroxycaproic acid, hydroxyheptanoic acid, and hydroxycaprylic acid. Such a polylactic acid-based polymer is preferable in terms of fiber properties that can provide a number average molecular weight of about 20,000 or more, preferably 40,000 or more, and in terms of the spinning property during production.

The long fibers constituting the nonwoven fabric of the present invention preferably have a crystallinity of 10 to 40%. The crystallinity in this range can be achieved by adding a crystal nucleating agent such as talc, boron nitride, calcium carbonate, magnesium carbonate, and titanium oxide to the polylactic acid-based polymer. Addition of a nucleating agent promotes fiber crystallization, and can improve the mechanical strength and heat resistance of the resulting agricultural sheet.
It is more preferable because it is possible to prevent the fusion (so-called blocking) between the spun yarns in the cooling step. The amount of such a crystal nucleating agent is desirably in the range of 0.1 to 3.0% by weight, preferably 0.5 to 2.0% by weight.
In the polylactic acid-based polymer of the present invention, other additives such as a matting agent, a pigment, and various additives such as a crystal nucleating agent may be added as needed within a range that does not impair the effects of the present invention. May be.

The long fibers constituting the nonwoven fabric according to the present invention may be those having a fiber form of a polylactic acid-based polymer alone or a composite of two or more polylactic acid-based polymers having different melting points. In addition, the cross-sectional shape is a hollow cross-section, a modified cross-section, a side-by-side composite cross-section in addition to a normal round cross-section,
Multi-layer composite cross section, core-sheath type composite cross section, split type composite cross section, etc.
An arbitrary fiber cross-sectional shape can be adopted depending on the purpose and application, but from the viewpoint of biodegradability, a hollow cross-section, a modified cross-section, a split composite cross-section, or the like is preferable.

[0010] The long fibers constituting the nonwoven fabric in the present invention must have a single yarn fineness of 1 to 15 denier. If the single-fiber fineness is less than 1 denier, the operability is impaired in the melt spinning process at the time of production, and the decomposition rate of the sheet is too high, so that the effect as a coating material is temporary. On the other hand, when the single yarn fineness exceeds 15 denier, not only the cooling property of the spun yarn in the melt spinning process is poor, but also the flexibility of the obtained nonwoven fabric is impaired, which impairs the workability. For these reasons, the single yarn fineness is 1 to
15 denier, preferably 2 to 10 denier, more preferably 3 to 7 denier. The sheet of the present invention preferably has a basis weight in the range of ²⁰ to 100 g / m ² . If the basis weight is less than 20 g / m ² , the nonwoven fabric has a low strength, is easily broken when it is spread inside the house, and cannot withstand the tension, although it is excellent in penetration of sunlight. Conversely, the basis weight is 100 g / m
^If it exceeds ² , the penetration of sunlight is poor, and when used as a movable lining sheet, it is heavy and the workability is poor. In addition, the basis weight and the above-mentioned single yarn fineness are particularly closely related.For example, when the single yarn fineness is small, the same non-woven fabric becomes a dense nonwoven fabric. When the mechanical strength of the fiber itself is low, it is necessary to increase the single yarn fineness and the basis weight in order to obtain a practically constant strength as a nonwoven fabric. These basis weight nonwoven fabrics may be obtained in one step, or may be obtained by laminating two or more nonwoven fabrics.

The sheet of the present invention is made of a nonwoven fabric having a basis weight in the above-mentioned range formed of polylactic acid-based filaments having the above-mentioned single-filament fineness, and further having a light transmittance of 40% or more. If the light transmittance is less than 40%, the solar light cannot be sufficiently transmitted, which has an adverse effect on crop cultivation.

In the sheet of the present invention, the tensile strength of the sample after irradiation for 300 hours with respect to the tensile strength retention S0 of the sample before irradiation with light is determined in the weather resistance test using a weather meter. The ratio (%) of the product S1 is 50
% Or more. The weather resistance of a sheet is an index indicating whether the strength and elongation of the sheet do not decrease due to a change in climate or the like before the sheet collapses by biodegradation. If the water content is reduced, an abnormality such as breakage is likely to occur, and it cannot be used for a long time as a lining sheet for an agricultural house. Therefore, in the present invention, when the strength retention is set to 50% or more and the strength retention is less than 50%, the strength decreases over time when used as a lining sheet, and as a result,
The service life of the seat is shortened.

In the sheet of the present invention, the tensile strength of the nonwoven fabric is preferably not less than 3 kg / 5 cm in terms of basis weight of 100 g / m ² , more preferably 5 kg / 5 cm.
It is more than width. If the tensile strength based on a basis weight of 100 g / m ² is less than 3 kg / 5 cm width, the workability will be poor when it is spread as a lining sheet for an agricultural house, which is not preferable. The tensile strength of the non-woven fabric is determined by the type of polymer used for the fibers constituting the non-woven fabric, the fineness and strength of the single fibers of the constituent fibers, the basis weight of the non-woven fabric, the partial thermocompression conditions for forming the non-woven fabric, and the like. The above tensile strength can be provided to the nonwoven fabric by appropriately selecting the conditions described above.

The nonwoven fabric constituting the sheet of the present invention is such that the web made of such long fibers is partially thermocompression-bonded and the form of the nonwoven fabric is maintained. In other words, the nonwoven fabric is hot-press bonded only in a partially fused area formed partly, and the nonwoven fabric has improved shape retention and flexibility with such a structure. become. In such partial thermocompression bonding, a point-like fusion zone is formed on the nonwoven web by an embossing process or an ultrasonic fusion process. Specifically, the heated embossing roll and the surface A method of forming a point fusion area between fibers through a web between a smooth metal roll or a point fusion area between fibers corresponding to a pattern portion by applying high frequency by ultrasonic waves on a pattern roll. The method of forming is adopted.

Next, a method for producing the sheet of the present invention will be described. First, the long-fiber nonwoven fabric for forming the sheet of the present invention can be efficiently produced by a so-called spunbond method. That is, the above-mentioned polylactic acid-based polymer is heated and melted, discharged from the spinneret, and the obtained spun yarn is cooled using a conventionally known cooling device such as a horizontal spraying or an annular spraying. Using a suction device such as air satsuka or other known traction means, it is towed and thinned,
Subsequently, the yarn group discharged from the traction means is spread, and then spread and deposited on a moving deposition device such as a conveyor formed of a mesh screen to form a web. Next, the web formed on the moving deposition apparatus is partially heated using a partial thermocompression bonding device such as a heated embossing roll and a smooth surface metal roll or a partial thermocompression bonding device such as an ultrasonic fusion bonding device. A long-fiber nonwoven fabric is obtained by performing a thermocompression treatment.

In the present invention, when producing a long-fiber nonwoven fabric by a so-called spunbonding method, the drawing speed of the spun yarn is preferably set to 1000 to 6000 m / min.
When the drawing speed at the time of drawing and narrowing the spun yarn is less than 1000 m / min, the oriented crystallization of the polymer does not progress, the mechanical strength of the obtained nonwoven fabric does not improve, and the decomposition rate is high. Too much. Conversely, if the pulling speed exceeds 6000 m / min, the spinnability deteriorates sharply and yarn breakage occurs. In addition, it is more preferable to add the above-mentioned nucleating agent to the polymer because the cooling property of the spun yarn at the time of melt spinning is improved.

[0017]

The sheet for lining the biodegradable agricultural house of the present invention is composed of a non-woven fabric made of polylactic acid long fibers, so that after a certain period of use, the sheet is almost completely decomposed by biodegradation. This eliminates the need to collect and dispose of the sheets, and does not pollute the natural environment. Also, since the light transmittance is 40% or more,
It allows the light necessary for the crop to pass. Further, since the strength retention rate in a weather resistance test using a weather meter is 50% or more, a reduction in the strength of the sheet can be prevented, and the service life can be extended.

[0018]

The present invention will be described below in detail with reference to examples. The present invention is not limited by these examples. In the examples, each property value was obtained as follows. (1) Melting point (° C.): The temperature giving the extreme value of the melting endothermic curve obtained by measuring the temperature at a heating rate of 20 ° C./min using a differential scanning calorimeter DSC-7 manufactured by Perkin Elmer Co., Ltd. ° C). (2) Melt flow rate value (hereinafter abbreviated as MFR value) (g / 10 min): Measured according to the method described in ASTM D1238 (E). The melting temperature is set to 210
° C. (3) Intrinsic viscosity: a solution of an equal weight mixture of phenol and ethane tetrachloride as a solvent, a sample concentration of 0.5 g / dl, and a temperature of 2
It was measured at 0 ° C. (4) Cooling property: The spun yarn was visually observed and evaluated according to the following three grades. ；: No cohesive yarn was observed. Δ: A slight amount of cohesive yarn was observed. X: Mostly adhered, and opening was impossible. (5) Spreadability: The nonwoven web formed from the spun yarn discharged from the spreader was visually observed and evaluated according to the following three grades. ；: Most of the constituent fibers were separated, and no cohesive yarn or convergent yarn was observed. Δ: Cohesive yarn or convergent yarn was slightly observed. X: Most of the constituent fibers are in close contact with each other, and the spreadability is poor. (6) Single yarn fineness (denier): Fineness obtained by measuring the diameter of 50 fibers in a web state with a microscope and correcting the density. Was taken as the single yarn fineness (denier). (7) Crystallinity (%): Measured by wide-angle X-ray diffraction (powdering, Roland method). That is, in the wide-angle X-ray diffraction method, an interference intensity curve of a diffracted X-ray is measured in a reflection angle 2θ direction to obtain an interference intensity curve, and then, based on the obtained interference intensity curve, an interference peak based on a crystal part and an amorphous part By separating the halo based on
The crystallinity (%) was determined from the following equation (b). Crystallinity (%) = (integral intensity of crystal part / total integral intensity) × 100 (b) (8) Weight (g / m ² ): 10 samples from standard sample
After preparing 10 sample pieces of 10 cm × 10 cm and reaching equilibrium moisture, the weight (g) of each sample piece was weighed, and the average value of the obtained values was converted into a unit area to obtain a basis weight ( g /
m ² ). (9) Tensile strength (kg / 5cm width): JIS L19
The measurement was carried out according to the strip method described in No. 06. That is, ten sample pieces each having a sample length of 20 cm and a sample width of 5 cm were prepared, and each of the sample pieces was subjected to constant-speed extension type tensile tester (Tensilon UTM-4-1-100 manufactured by Toyo Baldwin Co., Ltd.). The film was stretched at a gripping interval of 10 cm and a pulling speed of 20 cm / min, the maximum tensile strength (kg / 5 cm width) was determined, and the average value of the obtained maximum tensile strength was defined as the tensile strength of the nonwoven fabric (kg / 5 cm width). (10) Tear strength (kg): Measured according to the Benziram method described in JIS L1096. That is, a sample piece having a sample length of 6.5 cm and a sample width of 10 cm is placed in a longitudinal direction (hereinafter, referred to as MD direction) and a lateral direction (hereinafter, referred to as MD direction) of the nonwoven fabric.
Called CD direction. ) Were prepared for each sample, and the tear strength of the nonwoven fabric in the MD and CD directions was determined for each sample piece, and the average of the obtained values was used as the tear strength (kg) of the nonwoven fabric.
And (11) Light transmittance (%): The illuminance (B) when the sample is placed between the light source (reflamp) and the illuminometer of the light receiving unit and the illuminance (A) when the sample is not placed are measured. , The following formula (c)
The light transmittance (%) was determined from. Light transmittance (%) = (B / A) × 100 (c) (12) Strong retention (%): The strong retention, which is an index of weather resistance, was determined as follows. That is, in a weather resistance test using a weather meter, the tensile product (Strength × Elongation) S0 of the sample before irradiation with light and the tensile product (Strength × Elongation) S1 of the sample after irradiation for 300 hours were measured by Tensilon. Using a mold tensile tester, the strength retention (%) was determined from the above equation (A). (13) Biodegradation performance: one year, two years
After 3 years and 3 years, take out and observe the form of the specimen,
The following three stages were used for evaluation. ：: The shape of the nonwoven fabric was retained until two years after the embedding of the sample, and it was broken after three years. Δ: The shape of the nonwoven fabric was disintegrated by two years after the sample piece was embedded. X: The nonwoven fabric was retained even after 3 years from the embedding of the sample.

Example 1 Polylactic acid having a melting point of 171 ° C., a number average molecular weight of 59000 and an MFR value of 40 g / 10 min (D-form / L-form = 1.3 / 9)
8.7) (hereinafter abbreviated as PLA) chip and titanium oxide (hereinafter abbreviated as TO) for this chip
Using a masterbatch mixed with 20% by weight of lactic acid and having a titanium oxide content of 0.5% by weight with respect to polylactic acid
After metering and blending so as to obtain a spinning temperature of 200
The mixture was melt-spun from a spinneret under the conditions of ° C and a single hole discharge rate of 1.7 g / min. After the spun yarn is cooled by a cooling device, it is subsequently drawn and thinned at a drawing speed of 5100 m / min by an air sucker provided below the spinneret, and is spread using a known spreader and moved. It was collected and deposited as a web on a screen conveyor. Then, the web was heated to a temperature of 1
Partial thermocompression treatment is performed by passing through a partial thermocompression bonding device composed of an embossing roll heated to 23 ° C. and a metal roll having a smooth surface, and the basis weight of a single fiber with a denier of 3.0 denier is 50 g /. It was obtained composed sheet by long-fiber nonwoven fabric of m ^2. Table 1 shows various properties of the obtained sheet.

Example 2 Polylactic acid having a melting point of 169 ° C., a number average molecular weight of 71200 and an MFR value of 26 g / 10 min (D-form / L-form = 1.1 / 9)
8.9), and the spinning temperature was 220 ° C., the single-hole discharge amount was 1.6 g / min, and the drawing speed was 4700 m / min. 1
A sheet having a basis weight of denier long fibers and a nonwoven fabric of long fibers of 50 g / m ² was obtained. Table 1 shows various properties of the obtained sheet.

Example 3 A sheet made of a long-fiber nonwoven fabric was obtained in the same manner as in Example 1 except that the single hole discharge rate was 4.0 g / min and the single yarn fineness was 7.0 denier. Table 1 shows various properties of the obtained sheet.

Example 4 A sheet constituted of a long-fiber nonwoven fabric was obtained in the same manner as in Example 1, except that the basis weight of the long-fiber nonwoven fabric was changed to 75 g / m ² . Table 1 shows various properties of the obtained sheet.

Example 5 A sheet composed of a long-fiber nonwoven fabric was obtained in the same manner as in Example 1, except that the basis weight of the long-fiber nonwoven fabric was 30 g / m ² . Table 1 shows various properties of the obtained sheet.

Example 6 Polylactic acid having a melting point of 120 ° C. and an MFR value of 50 g / 10 min (D-form / L-form = 7.7 / 92.3) was used as a sheath component.
The core-sheath type composite continuous fiber having a core component of polylactic acid (D-form / L-form = 1.3 / 98.7) having a melting point of 171 ° C. and an MFR value of 40 g / 10 min used in the above was melt-spun, and A nonwoven fabric made of a core-sheath composite long fiber was prepared. Specifically, using a master batch containing 20% by weight of titanium oxide mixed therein, the titanium oxide content relative to polylactic acid was 0.5% by weight.
The above-mentioned low-melting polylactic acid, which was weighed and blended such that the titanium oxide content was 0.5% by weight, and the high-melting polylactic acid were melted using separate extruder-type melt extruders, and then the spinning temperature was adjusted. Under the condition of 200 ° C. and a single-hole discharge rate of 1.6 g / min, the core-sheath type is such that the low-melting-point polylactic acid has a sheath portion and the high-melting-point polylactic acid has a core portion (composite ratio (weight ratio) = 1/1). It was melt spun from a composite spinneret. After the spun yarn is cooled by the cooling device, it is subsequently drawn and thinned at a drawing speed of 4800 m / min by an air sucker provided below the spinneret, and is spread using a known spreader and moved. It was collected and deposited as a web on a screen conveyor. Next, the web is passed through a partial thermocompression bonding device consisting of an embossing roll heated to a temperature of 95 ° C. and a metal roll having a smooth surface, and subjected to a partial thermocompression bonding process, and has a single fiber fineness of 3.0 denier long fiber. The basis weight of 50 g / m ²
Was obtained. Table 1 shows various properties of the obtained sheet.

Comparative Example 1 A polyethylene terephthalate (hereinafter abbreviated as PET) chip having a melting point of 260 ° C. and an intrinsic viscosity of 0.7 was melted, and then a spinning temperature of 290 ° C. and a single hole discharge rate of 2.3 g / min. After melt spinning under the conditions and cooling the spun yarn with a cooling device, the yarn is continuously drawn and thinned at a drawing speed of 5200 m / min with an air scater provided below the spinneret, and opened using a known opening machine. Then, it was collected and deposited as a web on a moving mesh screen conveyor. Next, the web is passed through a partial thermocompression bonding device consisting of an embossing roll heated to a temperature of 230 ° C. and a metal roll having a smooth surface, and is subjected to a partial thermocompression bonding process, and has a single fiber fineness of 4.0 denier long fiber. A sheet composed of a long-fiber nonwoven fabric having a basis weight of 50 g / m ² was obtained. Table 1 shows various properties of the obtained sheet.

Comparative Example 2 A sheet composed of a long-fiber nonwoven fabric was obtained in the same manner as in Example 1 except that the basis weight of the long-fiber nonwoven fabric was changed to 150 g / m ² . Table 1 shows various properties of the obtained sheet.

[0027]

[Table 1]

Since the sheets obtained in Examples 1 to 5 have a light transmittance of 40% or more, good crop growth can be expected when used as a lining sheet for an agricultural house, and weather resistance. Are all high at 50% or more, and the weather resistance is also good. And since it is formed of a non-woven fabric made of polylactic acid fiber having biodegradability, it is buried in the soil and completely decomposed after 3 years,
There was no need for disposal. Further, the sheet obtained in Example 6 is made of a core-sheath composite type long-fiber nonwoven fabric of low-melting-point polylactic acid and high-melting-point polylactic acid, but has the same light transmittance and strong retention as in the other examples. Therefore, good crop growth was expected when used as a lining sheet for an agricultural house. On the other hand, since the sheet obtained in Comparative Example 1 used polyethylene terephthalate as the polymer of the nonwoven fabric constituent fibers, it had excellent mechanical strength such as tensile strength and tear strength, but had a low strength retention rate,
The weather resistance was poor. Also, since polyethylene terephthalate, which is not biodegradable, is used, it is buried in the soil and does not decompose in the soil even after a certain period of time, and it is necessary to collect and incinerate the sheet after use, It also pollutes the natural environment. On the other hand, the sheet obtained in Comparative Example 2 had good weatherability because the basis weight of the nonwoven fabric was too high, but had low light transmittance and was not suitable as a lining sheet for an agricultural house.

[0029]

The sheet for lining the biodegradable agricultural house of the present invention is composed of a non-woven fabric made of polylactic acid-based long fibers. It is almost completely disassembled, eliminating the need to collect and dispose of sheets and disposing of them, and does not pollute the natural environment. Further, since the light transmittance is 40% or more, light necessary for crops can be transmitted, and the heat retention can be improved. Furthermore, as the strength retention rate in the weather resistance test is 50% or more, the weather resistance is excellent, the deterioration is small,
It can withstand long-term use.

Claims (3)

[Claims] 1. A polylactic acid-based long-fiber non-woven fabric having a light transmittance of 40% or more and a strength retention of 5 from the following formula (A) in a weather resistance test using a weather meter.
A biodegradable agricultural house lining sheet characterized by being at least 0%. Strong retention (%) = (S1 / S0) × 100 (b) S1: Strain product of sample after irradiation for 300 hours S0: Strain product of sample before irradiation 2. The polylactic acid comprises poly (D-lactic acid), poly (L-lactic acid), a copolymer of D-lactic acid and L-lactic acid,
A copolymer of D-lactic acid and hydroxycarboxylic acid, and L-
The biodegradable agricultural house lining sheet according to claim 1, which is any polymer selected from a copolymer of lactic acid and hydroxycarboxylic acid, or a blend thereof. 3. A filament having a single fiber fineness of 1 to 15 deniers,
The sheet for lining a biodegradable agricultural house according to claim 1 or ² , wherein the basis weight of the sheet is 20 to 100 g / m2.