Paper mulch sheet

Abstract

To provide a paper-made mulching sheet that can be sufficiently applied even to crops with long growth periods.SOLUTION: A paper-made mulching sheet has base paper and a coating layer applied on at least one side of the base paper. The base paper comprises, as papermaking fibers, 40 wt.% or more of wood pulp. The coating layer comprises lignin and resin with a weight ratio (lignin:resin) of 30:70 to 99:1.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a paper mulch sheet 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. Plastic films such as polyethylene and polyvinyl chloride are typically used as mulch sheets. However, these plastic films are not biodegradable and must be collected and incinerated after use. Furthermore, collection and incineration requires special equipment, a great deal of effort, and time, and is problematic in terms of environmental pollution.

[0003] Against this background, the use of mulch sheets made of biodegradable materials that can be plowed into the soil after crop harvest while maintaining their shape during installation is becoming more widespread. 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 proposes 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, and which contains 0.05% to 10% by weight of a penetration aid relative to the pulp, and has a basis weight of 50 g / m 2 More than 120g / m 2 and water permeability is 30 ml / m or less 2 ·min or more 500ml / m 2 An agricultural mulch sheet characterized by a drying time of 1 minute or less has been proposed. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-68458 [Patent Document 2] Japanese Patent Application Laid-Open No. 2000-102329 Summary of the Invention [Problem to be solved by the invention]

[0005] Mulch sheets made from biodegradable resins or paper have the advantage of not requiring collection or disposal after use. However, biodegradable resin mulch sheets have problems such as deterioration during storage and getting tangled in rotary tillers when plowing. Paper mulch sheets are thick (heavy) to increase their strength, making them difficult to install. Furthermore, because they biodegrade quickly, they deteriorate before harvest and lose strength, and they have poor wind and rain resistance, making them unsuitable for use on crops with long growing periods. Chemical treatment of paper mulch sheets has been proposed as a method to extend the biodegradation period, but the treatment method is complicated, posing challenges to productivity, and the paper's strength is also reduced. An object of the present invention is to provide a paper mulch sheet that can be adequately applied to agricultural crops that have a long growing period. [Means for solving the problem]

[0006] The means for solving the problems of the present invention are as follows. 1. A paper sheet having a base paper and a coating layer on at least one side of the base paper; The base paper contains 40% by weight or more of wood pulp as papermaking fibers, A paper mulch sheet, wherein the coating layer contains lignin and resin in a weight ratio (lignin:resin) of 30:70 to 99:1. 2. The lignin content is 0.3 g / m 2 The paper multi-sheet according to 1. above, characterized in that: 3. The paper mulch sheet according to 1. or 2., wherein the resin comprises at least one of a polylactic acid resin and a polyvinyl alcohol resin. 4. The basis weight of the base paper is 20 g / m 2 More than 50g / m 2The paper multi-sheet according to 1. or 2., characterized in that: 5. A paper mulch 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. [Effects of the Invention]

[0007] The paper mulch sheet of the present invention is slow to biodegrade and can be applied to agricultural crops with long growing periods. The biodegradability of the paper mulch sheet of the present invention can be adjusted by adjusting the blending ratio of wood pulp. DETAILED DESCRIPTION OF THE INVENTION

[0008] The paper mulch sheet of the present invention comprises a base paper and a coating layer containing lignin coated on at least one surface of the base paper. (base paper) The base paper is a sheet made of papermaking fibers, fillers, various auxiliaries, and the like. The base paper of the present invention contains 40% by weight or more of wood pulp as papermaking fibers. The wood pulp may be one or more of the following: bleached hardwood kraft pulp (LBKP), bleached softwood kraft pulp (NBKP), unbleached hardwood kraft pulp (LUKP), unbleached softwood kraft pulp (NUKP), chemical pulp such as sulfite pulp, mechanical pulp such as stone-ground pulp and thermomechanical pulp, recycled paper pulp derived from wood pulp, dissolving pulp, mercerized pulp, etc. Among these, NBKP and NUKP are preferred because of their excellent strength, and NUKP is more preferred.

[0009] The higher the ratio of wood pulp to the total papermaking fibers of the base paper, the faster the biodegradation will be. However, the paper mulch sheet of the present invention has a coating layer containing lignin, which allows it to suppress biodegradation even when it contains a high amount of wood pulp. In the paper mulch sheet of the present invention, from the viewpoints of biodegradation rate and cost, the wood pulp content relative to the total papermaking fibers is preferably 50% by weight or more, more preferably 60% by weight or more. The base paper can be made of 100% by weight of wood pulp, but if the wood pulp content is too high, biodegradation may become rapid, so the wood pulp content is preferably 95% by weight or less, more preferably 90% by weight or less.

[0010] The papermaking fibers used in combination with wood pulp are not particularly limited and may include, for example, non-wood pulps such as bast fibers (e.g., flax, kenaf, paper mulberry, and mitsumata), hard fibers (e.g., bagasse, bamboo, and esparto), seed fibers (e.g., cotton pulp), and leaf sheath and leaf fibers (e.g., Manila hemp pulp and sisal pulp); and synthetic fibers such as polylactic acid fibers, regenerated cellulose fibers, polybutylene succinate fibers, polyethylene succinate fibers, polybutylene succinate-adipate fibers, polybutylene succinate-carbonate fibers, polycaprolactone fibers, and polyvinyl alcohol fibers. Synthetic fibers may be either single-material fibers or composite fibers with a core and sheath. Biodegradable synthetic fibers are preferred, with polylactic acid fibers and composite fibers with a polylactic acid core and polybutylene succinate sheath fibers being more preferred. When polylactic acid fibers are used, the fineness is preferably 0.01 dtex or more and 3.0 dtex or less, more preferably 0.05 dtex or more and 1.5 dtex or less, and the fiber length is preferably 2 mm or more and 10 mm or less, more preferably 3 mm or more and 8 mm or less.

[0011] The base paper may contain known internal additives. Because the paper mulch sheet is laid on the ground, the base paper preferably contains a wet strength agent. The wet strength agent is preferably contained in an amount of 0.5 to 3 parts by weight per 100 parts by weight of papermaking fibers.

[0012] The method for producing the base paper (papermaking) is not particularly limited, and the paper base material can be produced by acidic papermaking, neutral papermaking, or alkaline papermaking using a known Fourdrinier former, on-top hybrid former, gap former machine, etc. The base paper may be composed of one layer or two or more layers.

[0013] The basis weight of the base paper of the present invention is not particularly limited, but is, for example, 15 g / m 2 More than 80g / m 2 From the viewpoint of strength, the basis weight of the base paper is 18 g / m 2 More than 20g / m is preferable. 2 From the viewpoint of weight reduction, the basis weight of the base paper is 60 g / m 2 Less than 50 g / m 2 Less than 45 g / m is more preferable. 2 More preferably, 35 g / m 2 Even more preferred are the following:

[0014] (coating layer) The coating layer is formed on at least one surface of the base paper by coating. The coating layer may contain lignin and resin in a weight ratio (lignin:resin) of 30:70 to 99:1, and may contain additives such as external papermaking chemicals such as surface strength agents and sizing agents, colorants, surfactants, dispersants, thickeners, water retention agents, antifoaming agents, and water repellents. It may also contain one or more chemicals such as insecticides, miticides, nematicides, fungicides, plant growth regulators, and fertilizers. Lignin, along with cellulose and hemicellulose, is a major component of woody plants. Although lignin is decomposed by white-rot fungi, the decomposition is slow. Therefore, the formation of a coating layer on paper mulch sheets can slow down the decomposition of the sheets. The lignin is not particularly limited as long as it can be dissolved and applied, but lignin sulfonic acid or its salts are preferred because they facilitate the preparation of coating materials. Examples of lignin sulfonic acid salts include calcium salts, magnesium salts, and sodium salts. Commercially available lignin sulfonic acid or its salts include Sunex M-100, Sunex P321, Sunex 252, Sunex P252, Sunex SCL, Sunex SCP, Sunex FDL, Vanilex N, Pearlex NP, and Pearlex DP (all manufactured by Nippon Paper Industries Co., Ltd.).

[0015] In the present invention, the coating layer contains lignin and resin in a weight ratio (lignin:resin) of 30:70 to 99:1. If the lignin content is less than this range, biodegradation may not be sufficiently slow. On the other hand, if the lignin content is greater than this range (less resin), the adhesion of the lignin to the base paper may be reduced, and despite the high lignin content, the base paper may biodegrade faster than when the resin content is within the above range. A weight ratio of lignin to resin of 35:65 to 95:5 is more preferred.

[0016] The resin serves to adjust the adhesion of lignin to the base paper. Resins generally used as binders in coating solutions can be used without any particular restrictions. For example, one or more of polylactic acid resins, polyvinyl alcohol resins, acrylic resins, starches, cellulose ethers, styrene-butadiene copolymers, methyl methacrylate-butadiene copolymers, and vinyl acetate resins can be used. Among these, one or more of polylactic acid resins and polyvinyl alcohol resins are preferred because they are biodegradable.

[0017] The method for applying the coating material for forming a coating layer to the base paper is not particularly limited, and coating can be performed using known coating equipment and coating systems. Examples of coating equipment 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. Examples of coating systems include aqueous coating using a solvent such as water, and solvent-based coating using a solvent such as an organic solvent, with aqueous coating being preferred.

[0018] In the present invention, the coating amount per one side of the coating layer is 0.8 g / m2 in dry weight. 2 More than 10g / m 2 The coating weight is preferably 0.8 g / m or less. 2 If the amount is less than 10 g / m, the biodegradation inhibiting effect may not be fully exerted. 2 If the amount is more than this, the drying load during coating increases and the paper mulch sheet becomes heavy. 2 More preferably, 1.1 g / m 2 More preferably, 8 g / m 2 Less than 5g / m is more preferable. 2 The following is even more preferred:

[0019] The paper mulch sheet of the present invention has a lignin content of 0.3 g / m2 in terms of dry weight. 2 The lignin content is preferably 0.35 g / m or more in terms of inhibiting biodegradation. 2 More than 0.4g / m is preferable. 2 The upper limit of the lignin content is not particularly limited, but for example, it is 5 g / m 2 Even if the lignin content is increased further, the biodegradation inhibitory effect saturates and there is almost no improvement, and the raw material cost increases, resulting in high costs.

[0020] (Paper multi-sheet) The paper mulch sheet has a base paper and a coating layer containing lignin formed by coating on at least one side of the base paper. The paper mulch sheet may have coating layers on both sides of the base paper, or may have layers other than the base paper and the coating layer. In order to prevent breakage during the cultivation period, it is preferable that the paper mulch sheet have a (dry) tensile strength in the MD direction measured in accordance with JIS P8118 of 15 N / 15 mm or more and a wet tensile strength in the MD direction of 5 N / 15 mm or more. This (dry) tensile strength is more preferably 16 N / 15 mm or more, and even more preferably 17 N / 15 mm or more. This wet tensile strength is more preferably 6 N / 15 mm or more, and even more preferably 7 N / 15 mm or more. The paper mulch sheet preferably has a tear strength in the MD direction measured in accordance with JIS P8116 of 300 mN or more to prevent tearing during installation, more preferably 400 mN or more, and even more preferably 500 mN or more.

[0021] From the viewpoint of suppressing the growth of weeds, it is preferable that the light transmittance of a paper mulch sheet be 4.5% or less for wavelengths of 660 nm and 450 nm. A paper mulch sheet whose transmittance satisfies this condition can suppress the germination of weeds, and even if they germinate, they cannot efficiently photosynthesize, thereby suppressing weed growth. The light transmittance for 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. [Example]

[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 to these examples. The obtained base paper and paper mulch sheet were evaluated by the following measurement methods. 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 at a pressure of 100 kPa between the pressure surfaces in accordance with JIS P8118. Lignin content The coating amount was calculated from the basis weight before and after coating. The lignin content was calculated from the coating amount and the weight ratio of lignin to the total solid content in the coating material.

[0024] Tensile strength The (dry) tensile strength was measured in accordance with JIS P8118. The wet tensile strength was measured in accordance with JIS P8118 after the test sample, which had been immersed in water, was sandwiched between filter papers to remove excess water adhering to the surface. Tear strength The tear strength was measured in accordance with JIS P8116. ·Light transmittance The light transmittance (%) of the test sample was measured using a spectrophotometer (UV-160A, Shimadzu Corporation) for red light (660 nm) and blue light (450 nm), which are absorbed in large amounts by plant photosynthesis.

[0025] ·Soil degradability 250g of home gardening soil was placed in a 1.4L Tupperware container (soil moisture content: 20-30%). A sample piece for evaluation (16cm wide, 10cm long) was placed in a draining net, its weight was measured, and then it was placed on the soil surface. This was then covered with 250g of gardening soil and buried. The Tupperware container was then sealed with the lid and placed in an environmental testing chamber (Silvery Emperor, Kato Co., Ltd.) at 40°C to investigate its decomposition in the soil. After one week, the sample was removed, the surface soil was washed off under running water, and the sample was air-dried before being weighed. Soil decomposition was calculated as a reduction rate according to the following formula: Reduction rate (%) = weight after test / weight before test × 100

[0026] "Example 1" The raw fiber was prepared by blending 70 parts by weight of softwood unbleached kraft pulp (NUKP) with a Canadian Standard Freeness (CSF) of 400 ml with 30 parts by weight of polylactic acid fiber (Miracle Fiber KK-PL, manufactured by Daiwabo Co., Ltd., core polylactic acid, sheath polybutylene succinate, 2.4 dtex x 5 mm). A wet strength agent was added to the raw fiber at 2% by weight to prepare a paper stock with a target basis weight of 30 g / m. 2 The base paper was obtained by papermaking. The base paper was impregnated with a paint made by mixing lignin (Sunex P321, magnesium lignin sulfonate, manufactured by Nippon Paper Industries Co., Ltd.) and polylactic acid resin (Rezem W-990, manufactured by Chukyo Yushi Co., Ltd.) in a solids weight ratio of 70:30, and then dried at 110°C to form a coating layer, resulting in a paper mulch sheet.

[0027] "Example 2" A paper mulch sheet was obtained in the same manner as in Example 1, except that the blending ratio of lignin to polylactic acid resin was set to 53:47. "Example 3" A paper mulch sheet was obtained in the same manner as in Example 1, except that the blending ratio of lignin to polylactic acid resin was 40:60. Example 4 A paper mulch sheet was obtained in the same manner as in Example 1, except that the blending ratio of lignin to polylactic acid resin was 90:10. "Example 5" A paper mulch sheet was obtained in the same manner as in Example 1, except that a polyvinyl alcohol resin (Poval 25-88KL, manufactured by Kuraray Co., Ltd.) was used instead of the polylactic acid resin.

[0028] "Comparative Example 1" A paper mulch sheet was obtained in the same manner as in Example 1, except that only lignin was applied (the compounding ratio of lignin to polylactic acid resin was 100:0). "Comparative Example 2" A paper mulch sheet was obtained in the same manner as in Example 1, except that no coating layer was formed.

[0029] [Table 1]

[0030] The paper mulch sheets obtained in Examples 1 to 5 of the present invention are slow to decompose in soil, despite containing a high content of wood pulp, and can be applied to agricultural crops with long growing periods. The paper mulch sheet obtained in Comparative Example 1, in which the coating layer did not contain resin, biodegraded faster than, for example, the paper mulch sheet obtained in Example 3, which contained less lignin. This is presumably because the absence of resin meant that the lignin did not adhere well to the base paper, making it easier for the lignin to peel off from the base paper.

Claims

1. A base paper and a coating layer on at least one side of the base paper, The base paper contains 40% by weight or more of wood pulp as papermaking fibers, the coating layer contains lignin and resin in a weight ratio (lignin:resin) of 30:70 to 99:1, A paper mulch sheet, characterized in that the resin contains a polylactic acid-based resin.

2. The lignin content is 0.3 g / m ２ 2. The paper mulch sheet according to claim 1, wherein the paper mulch sheet is as described above.

3. The basis weight of the base paper is 20 g / m ２ 50g / m or more ２ 3. The paper mulch sheet according to claim 1, wherein the sheet is:

4. 3. The paper mulch sheet according to claim 1, wherein the tear strength in the machine direction measured in accordance with JIS P8116 is 300 mN or more.

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