Paper mulch sheet

Abstract

To provide a paper mulch sheet that can maintain its sheet shape during the cultivation period and decomposes immediately after being tilled into the soil. [Solution] The base paper comprises a colored layer containing a coloring agent formed by coating on at least one surface of the base paper. The aforementioned base paper is a paper mulch sheet containing at least wood pulp and polylactic acid-based fibers as papermaking fibers in a weight ratio of 20:80 to 85:15 (wood pulp: polylactic acid-based fibers).

Description

[Technical Field]

[0001] This invention relates to paper mulch sheets used in the agricultural and horticultural fields. [Background technology]

[0002] Mulch sheets are agricultural materials used to cover the ground around crops or flowers. They are used to improve the quality and yield of crops or flowers by regulating soil temperature and suppressing weed growth. Generally, plastic films such as polyethylene and polyvinyl chloride are used as mulch sheets. However, these plastic films are not biodegradable, so they must be collected and incinerated after use. Furthermore, this collection and incineration process requires special equipment, considerable labor and time, and also poses environmental pollution problems.

[0003] Against this backdrop, the use of mulch sheets made of biodegradable materials that can be plowed into the soil after crop harvesting, while maintaining their form during the laying period, is expanding. For example, Patent Document 1 proposes a mulch sheet made of a resin composition in which powdered activated carbon is dispersed in a biodegradable resin. Patent Document 2 describes a mulch sheet whose main component is wood pulp containing 30% to 70% by weight of mechanical pulp and 30% to 60% by weight of chemical pulp, with a penetration aid containing 0.05% to 10% by weight per unit of pulp, and a basis weight of 50 g / m². 2 More than 120g / m 2 The following conditions must be met, and the water permeability must be 30 ml / m². 2 ·min or more 500ml / m 2 An agricultural mulch sheet characterized by being less than 1 minute long has been proposed. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2007-68458 [Patent Document 2] Japanese Patent Publication No. 2000-102329 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] In mulching, mulching sheets made of biodegradable resin or paper have the advantage of not requiring collection or disposal after use. However, biodegradable resin mulching sheets have problems such as deterioration during product storage and entanglement with rotary tillers during plowing. Paper mulching sheets are thick (heavy) to increase strength, making them difficult to install, and they also have problems such as rapid biodegradation leading to deterioration and reduced strength before harvest, as well as poor resistance to wind and rain. Furthermore, these biodegradable mulching sheets are required to maintain their shape during the cultivation period suitable for the target crop, but to decompose immediately after being plowed into the soil, but it has been difficult to adjust the rate of decomposition. The present invention aims to provide a paper mulch sheet that can maintain its sheet shape during the cultivation period and decomposes immediately after being tilled into the soil. [Means for solving the problem]

[0006] The means for solving the problems of the present invention are as follows. 1. Having a base paper and a colored layer containing a coloring agent formed by coating on at least one surface of the base paper, A paper mulch sheet characterized in that the base paper contains at least wood pulp and polylactic acid fibers as papermaking fibers in a weight ratio of 20:80 to 85:15 (wood pulp: polylactic acid fibers). 2. The colored layer contains a colorant and a resin, The paper mulch sheet according to claim 1, characterized in that the resin contains one or more of a polylactic acid resin and a polyvinyl alcohol resin. 3. The content of the colorant is 0.4 g / m 2 The paper mulch sheet according to 1. or 2., characterized by being as described above. 4. The basis weight of the base paper is 20 g / m². 2 More than 50g / m2 The paper multi-sheet according to 1. or 2., characterized in that it is as follows. 5. The paper multi-sheet according to 1. or 2., characterized in that the tensile strength in the MD direction measured in accordance with JIS P8118 is 20 N / 15 mm or more, and the wet tensile strength in the MD direction is 5 N / 15 mm or more. 6. The paper multi-sheet according to 1. or 2., characterized in that the tear strength in the MD direction measured in accordance with JIS P8116 is 300 mN or more.

Effect of the Invention

[0007] The paper multi-sheet of the present invention has sufficient strength and can maintain its sheet shape during the cultivation period. The paper multi-sheet of the present invention is excellent in biodegradability and is decomposed immediately after being dug into the soil. The biodegradability of the paper multi-sheet of the present invention can be adjusted according to the ratio of wood pulp and polylactic acid-based fibers.

Mode for Carrying Out the Invention

[0008] The paper multi-sheet of the present invention has a base paper and a colored layer containing a coloring material formed by coating on at least one surface of the base paper. (Base paper) The base paper is a sheet made of papermaking fibers, fillers, various auxiliaries, etc. The base paper of the present invention contains wood pulp and polylactic acid-based fibers as papermaking fibers. As the wood pulp, one or more of chemical pulps such as hardwood bleached kraft pulp (LBKP), softwood bleached kraft pulp (NBKP), hardwood unbleached kraft pulp (LUKP), softwood unbleached kraft pulp (NUKP), sulfite pulp, mechanical pulps such as stone ground pulp and thermomechanical pulp, waste paper pulp derived from wood pulp, dissolving pulp, mercerized pulp, etc. can be used. Among these, NBKP and NUKP are preferable, and NUKP is more preferable because of their excellent strength.

[0009] The polylactic acid-based fiber can be used without particular limitation as long as it is a fiber mainly composed of polylactic acid used in the paper-making field. The polylactic acid-based fiber may be any of a single fiber of polylactic acid, a composite fiber having polylactic acid in either the core part or the sheath part, or both. When the polylactic acid-based fiber is a composite fiber, it may be made of two types of polylactic acid resins having different degrees of polymerization or the like, or may be made of other resins. When using other resins, as the other resins, polybutylene succinate, polyethylene succinate, polybutylene succinate adipate, polybutylene succinate carbonate, polycaprolactone, etc. can be used, and among these, polybutylene succinate, polyethylene succinate, and polybutylene succinate adipate, which are biodegradable resins, are preferable. The polylactic acid-based fiber preferably has a fineness of 0.01 dtex or more and 3.0 dtex or less, more preferably 0.05 dtex or more, and still more preferably 1.5 dtex or less. Also, the polylactic acid-based fiber preferably has a fiber length of 2 mm or more and 10 mm or less, more preferably 3 mm or more, and still more preferably 8 mm or less.

[0010] The base paper of the present invention contains wood pulp and polylactic acid-based fiber in a weight ratio of 20:80 to 85:15 (wood pulp: polylactic acid-based fiber). If the amount of polylactic acid-based fiber is more than this range, the liquid absorption property of the coating material will decrease, so stickiness is likely to occur when applying the coating material for forming the light-shielding layer, and the coating machine is likely to get dirty. On the other hand, if the amount of wood pulp is more than this range, biodegradation will be too fast, and decomposition may start during the cultivation period and the strength is likely to decrease. The ratio of wood pulp to polylactic acid-based fiber can be adjusted within the above range according to the required biodegradability, the strength of the base paper, etc. The less the wood pulp, the slower the decomposition and the higher the strength of the base paper. For example, when used for crops with a short cultivation period, the weight ratio of wood pulp to polylactic acid-based fiber is preferably 20:80 to 50:50, and when used for crops with a long cultivation period, the weight ratio of wood pulp to polylactic acid-based fiber is preferably 50:50 to 85:15.

[0011] The base paper of the present invention can also contain papermaking fibers other than wood pulp and polylactic acid fibers. For example, bast fibers such as flax, kenaf, paper mulberry, and Mitsumata; hard fibers such as bagasse, bamboo, and esparto; seed hair fibers such as cotton pulp; non-wood pulp such as Manila hemp pulp and sisal hemp pulp; regenerated cellulose fibers, polybutylene succinate fibers, polyethylene succinate fibers, polybutylene succinate adipate fibers, polybutylene succinate carbonate fibers, polycaprolactone fibers, polyvinyl alcohol, and other synthetic fibers can also be included. When other papermaking fibers are included, it is preferable to use biodegradable fibers. In the base paper, the total content rate of wood pulp and polylactic acid fibers with respect to the total papermaking fibers is preferably 80% by weight or more, more preferably 90% by weight or more, further preferably 95% by weight or more, still more preferably 98% by weight or more, and still more preferably 99% by weight or more.

[0012] The base paper can contain known internal additives. Since the paper multi-sheet is laid on the ground, it is preferable that the base paper contains a wet paper strength enhancer. The wet paper strength enhancer is preferably contained in an amount of 0.5 parts by weight or more and 3 parts by weight or less with respect to 100 parts by weight of the papermaking fibers.

[0013] The method for manufacturing (papermaking) the base paper is not particularly limited, and an acidic papermaking, neutral papermaking, or alkaline papermaking method can be used to manufacture a paper base material using a known fourdrinier former, on-top hybrid former, gap former machine, etc. The base paper may be a single layer or may be composed of two or more layers.

[0014] The basis weight of the base paper of the present invention is not particularly limited. For example, it can be 15 g / m 2 or more and 80 g / m 2 or less. From the viewpoint of strength, the basis weight of the base paper is preferably 18 g / m 2 or more, and more preferably 20 g / m 2 or more. From the viewpoint of weight reduction, the basis weight of the base paper is preferably 60 g / m 2 or less, and preferably 50 g / m 2The following is more preferable: 45 g / m 2 The following is even more preferable: 35 g / m 2 The following are even more preferable.

[0015] (colored layer) The colored layer contains a colorant and is formed by coating on at least one surface of the base paper. Preferably, the colored layer contains a colorant and a resin. It may also contain external papermaking chemicals such as surface paper strength agents and sizing agents, as well as additives such as surfactants, dispersants, thickeners, water-retaining agents, defoamers, and water-repellent agents. Furthermore, it may contain one or more chemicals such as insecticides, acaricides, nematicides, fungicides, plant growth regulators, and fertilizers. There are no particular restrictions on the colorants used; both inorganic and organic pigments can be used. The color of the colorant is not particularly limited, but for example, if a black colorant is used, the colored layer absorbs light, which helps maintain a high soil temperature, and if a white colorant is used, the colored layer reflects light, which helps suppress the rise in soil temperature. From the viewpoint of suppressing photosynthesis of weeds under the paper mulch sheet by reducing light transmittance, it is preferable to use phthalocyanine-based, diazo-based, natural pigments, carbon black, calcium phosphate, or iron(II,III) oxide as colorants. Furthermore, inorganic pigments are preferred because they are derived from natural minerals.

[0016] The resin acts as a binder to fix the colorant. The resin used as a binder is not particularly limited and can be one or more of the following: polylactic acid resins, polyvinyl alcohol resins, acrylic resins, starches, cellulose ethers, styrene-butadiene copolymers, methyl methacrylate-butadiene copolymers, vinyl acetate resins, etc. Among these, polylactic acid resins and polyvinyl alcohol resins (one or more) are preferred because they are biodegradable but do not decompose too quickly. While there are no particular restrictions on the ratio of colorant to resin in the colored layer, it is preferable to include the colorant and resin in a weight ratio of 50:50 to 95:5 (colorant:fiber) in order to enhance light absorption or light reflectivity.

[0017] The method for coating the base paper with the colored layer coating is not particularly limited and can be done using known coating equipment and coating systems. For example, coating equipment can include blade coaters, bar coaters, nip coaters, roll coaters, air knife coaters, reverse roll coaters, curtain coaters, spray coaters, size press coaters, and gate roll coaters. As for coating systems, there can be water-based coating using solvents such as water, and solvent-based coating using solvents such as organic solvents, but water-based coating is preferred.

[0018] In this invention, the amount of colored layer applied is 0.8 g / m² by dry weight. 2 More than 10g / m 2 The following is preferable: Coating amount of 0.8 g / m 2 If the amount is less than 10 g / m², the desired effect of the colored layer may not be fully achieved. 2 If the amount is too high, the drying load during coating increases, and the paper mulch sheet becomes heavier. The amount of colored layer to be applied is 1.0 g / m². 2 The above is more preferable, 1.1 g / m 2 The above is even more preferable, and also 8 g / m 2 The following is more preferable: 3 g / m 2 The following are even more preferable.

[0019] The paper mulch sheet of the present invention has a colorant content of 0.4 g / m² by dry weight. 2 The above is preferable in terms of increasing light absorption or light reflectivity. The colorant content is 0.6 g / m² by dry weight. 2 The above is preferable, 0.7 g / m 2 The above is preferable. There is no particular upper limit on the colorant content, but for example, 5 g / m 2 This is the extent of the problem. Increasing the amount of colorant further will not improve light absorption or light reflectivity beyond a certain point, as it will saturate and increase raw material costs, resulting in high overall costs.

[0020] (Paper mulch sheet) A paper mulch sheet comprises a base paper and a colored layer formed by coating on at least one surface of the base paper. The paper mulch sheet may have colored layers on both sides of the base paper, or it may have layers other than the base paper and the colored layer. For paper mulch sheets, it is preferable that the (dry) tensile strength in the MD direction measured in accordance with JIS P8118 is 20 N / 15 mm or more, and the wet tensile strength in the MD direction is 5 N / 15 mm or more, in order to prevent tearing during installation and cultivation. A (dry) tensile strength of 21 N / 15 mm or more is more preferable, and 22 N / 15 mm or more is even more preferable. A wet tensile strength of 6 N / 15 mm or more is even more preferable, and 7 N / 15 mm or more is even more preferable. For paper mulch sheets, it is preferable that the tear strength in the MD direction, as measured in accordance with JIS P8116, is 300 mN or higher, in order to prevent tearing during installation. A tear strength of 400 mN or higher is more preferable, and 500 mN or higher is even more preferable.

[0021] For paper mulch sheets, it is preferable that the light transmittance at wavelengths of 660 nm and 450 nm is 4.5% or less, in order to suppress weed growth. Paper mulch sheets that satisfy this transmittance condition can suppress weed germination, and even if germination occurs, photosynthesis cannot be carried out efficiently, thus suppressing weed growth. The light transmittance at wavelengths of 660 nm and 450 nm is more preferably 4.0% or less, even more preferably 3.0% or less, even more preferably 2.5% or less, and even more preferably 2.0% or less. [Examples]

[0022] The present invention will be described in more detail below with reference to examples, but the configuration of the present invention is not limited thereto. The obtained base paper and paper-based mulch sheets were evaluated using the following measurement method. The results are shown in Table 1.

[0023] (Evaluation method) • Basis weight, thickness The basis weight was measured in accordance with JIS P8124. The thickness of one sheet was measured with a pressure of 100 kPa between the pressurized surfaces, in accordance with JIS P8118. • Coating amount, colorant content The amount of coating applied was calculated from the basis weight before and after coating. The amount of colorant was calculated from the amount of coating applied and the weight ratio of colorant to the total solid content in the coating. • Machine dirt After manufacturing the paper mulch sheets, a visual inspection was conducted to check for contamination between the colored layer coating section and the drying section of the coating machine, and the following criteria were used for determination. ○: The machine is free of paint and dirt. ×: Paint has adhered to the machine, causing it to become dirty.

[0024] • Tensile strength (Dry) tensile strength was measured in accordance with JIS P8118. The wet tensile strength was measured in accordance with JIS P8118 after removing excess moisture from the surface of the test sample by sandwiching it between filter paper after immersion in water. • Tear strength Tear strength was measured in accordance with JIS P8116. ·Light transmittance Light transmittance was measured using a spectrophotometer (UV-160A, Shimadzu Corporation) on the test samples, determining the percentage of red light (660nm) and blue light (450nm), which are heavily absorbed by plant photosynthesis.

[0025] ·Weed control Put potting soil for home gardening into a planter and add weed seeds (cogongrass, windgrass, crabgrass). ESPECMIC Co., Ltd. seeds were sown and covered with soil. An evaluation sample (20 cm wide, 15 cm long) was laid to cover the surface of the sown soil, and the four sides of the sample were covered with soil to secure it. The sample was placed in a location that received plenty of direct sunlight, where the minimum temperature did not fall below 10°C, and was not protected from rain or wind. Its condition was observed after one month. Weed control effectiveness was determined by visual observation according to the following criteria. ○: Germination has occurred, but growth has not occurred. △: The seed has germinated and is growing, but the sample is not torn. ×: The germination has occurred, and the sample has ruptured, indicating growth and elongation. ·Soil degradability 250g of potting soil for home gardening was placed in a 1.4L container (soil moisture content: 20-30%). A sample piece for evaluation (16cm wide, 10cm long) was placed in a drain net, weighed, and then placed on the soil surface. This was then covered with another 250g of potting soil. The sealed container was placed in a 40°C environmental testing chamber (Silvery Emperor, Kato Co., Ltd.) to investigate its decomposition in the soil. After one week, the sample was removed, the surface soil was washed off with running water, and the sample was air-dried before its weight was measured. Soil decomposition was calculated as a rate of decrease according to the following formula. Reduction rate (%) = Weight after test / Weight before test × 100

[0026] "Example 1" The raw material fiber was prepared by blending 30 parts by weight of unbleached softwood kraft pulp (NUKP) with a Canadian standard water filtration capacity (CSF) of 400 ml with 70 parts by weight of polylactic acid fiber (Miracle Fiber KK-PL, manufactured by Yamato Spinning Co., Ltd., with a polylactic acid core and polybutylene succinate sheath, 2.4 dtex x 5 mm). A wet strength enhancer was added to the raw material fiber at a rate of 2% per fiber weight to create the follicular material, and paper was produced on a short-wire paper machine with a target basis weight of 25 g / m². 2 The papermaking process was used to obtain the base paper. A coloring layer-forming coating was obtained by size-press impregnation coating a base paper with a mixture of colorant (PSM Black 14522, manufactured by Mikuni Shikiso Co., Ltd., containing carbon black) and polylactic acid resin (Rezem W-990, manufactured by Chukyo Yushi Co., Ltd.) in a solid weight ratio of 70:30. The coating was then dried at 110°C to form a colored layer, thereby obtaining a paper mulch sheet.

[0027] Example 2 A paper mulch sheet was obtained in the same manner as in Example 1, except that the mixing ratio of NUKP and polylactic acid-based fibers was set to 50:50. "Example 3" The blending ratio of NUKP to polylactic acid-based fibers is set at 70:30, with a target basis weight of 30 g / m².2 A paper mulch sheet was obtained in the same manner as in Example 1, except for the aforementioned difference. "Example 4" The blending ratio of NUKP to polylactic acid-based fibers is set at 80:20, with a target basis weight of 20g / m². 2 A paper mulch sheet was obtained in the same manner as in Example 1, except for the aforementioned difference.

[0028] Example 5 A paper mulch sheet was obtained in the same manner as in Example 3, except that a polyvinyl alcohol-based resin (Poval 25-88KL, manufactured by Kuraray Co., Ltd.) was used as the resin for the colored layer-forming coating. "Example 6" A paper mulch sheet was obtained in the same manner as in Example 5, except that the base paper obtained in Example 4 was used.

[0029] "Comparative Example 1" A paper mulch sheet was obtained in the same manner as in Example 1, except that the blending ratio of NUKP to polylactic acid-based fibers was set to 90:10. "Comparative Example 2" A paper mulch sheet was obtained in the same manner as in Example 1, except that the blending ratio of NUKP to polylactic acid-based fibers was set to 10:90. "Comparative Example 3" A paper mulch sheet was obtained in the same manner as in Example 3, except that a colored layer was not applied.

[0030] [Table 1]

[0031] The paper mulch sheets obtained in Examples 1 to 6 of the present invention possess sufficient strength, maintain their sheet shape during the cultivation period, and are highly biodegradable, decomposing immediately after being tilled into the soil. The paper mulch sheets obtained in Examples 1 to 6 of the present invention are lightweight due to their low basis weight and are easy to handle. The paper mulch sheet obtained in Comparative Example 1 was found to have inferior strength, decompose rapidly, and fail to maintain the required performance during the cultivation period. The paper-based mulch sheet obtained in Comparative Example 2 had no problems with strength or biodegradation rate, but its poor absorption of the coating solution resulted in staining of the machine. Comparative Example 3 used the base paper as is, but it was suggested that it decomposed quickly and could not maintain the specified performance during the cultivation period. Furthermore, because it did not have a colored layer, it could not suppress weed growth.

Claims

1. The material comprises a base paper and a colored layer containing a colorant and resin formed by coating on at least one surface of the base paper. The aforementioned base paper contains at least wood pulp and polylactic acid-based fibers as papermaking fibers in a weight ratio of 20:80 to 85:15 (wood pulp: polylactic acid-based fibers), The aforementioned colorant is an inorganic pigment, The aforementioned resin is one or more of the following: polylactic acid resin, polyvinyl alcohol resin, acrylic resin, cellulose ethers, styrene-butadiene copolymer, methyl methacrylate-butadiene copolymer, and vinyl acetate resin. A paper-based mulch sheet characterized by having a light transmittance of 4.5% or less at wavelengths of 660 nm and 450 nm.

2. The paper mulch sheet according to claim 1, characterized in that the inorganic pigment is carbon black.

3. The paper mulch sheet according to claim 1 or 2, characterized in that it contains the colorant and the resin in a weight ratio of 50:50 to 95:5 (colorant:resin).

4. The paper mulch sheet according to claim 1 or 2, characterized in that the base paper contains 0.5 parts by weight or more and 3 parts by weight or less of a wet paper strength enhancer per 100 parts by weight of papermaking fibers.

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