Paper mulch sheet

Abstract

To provide paper-based mulch sheets that use minimal materials derived from fossil resources. [Solution] The base paper and the coated layers formed on both sides of the base paper by coating, The aforementioned base paper contains biomass-derived fibers, The aforementioned coating layer contains shellac, A paper-based mulch sheet in which the proportion of materials derived from fossil resources to the total is 1% by weight or less.

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 weeds. Generally, plastic films such as polyethylene and polyvinyl chloride are used as mulch sheets. However, mulch sheets made of plastic film are generally not biodegradable, so they must be collected and incinerated after use. This collection and incineration process requires special equipment, considerable labor, and time. Furthermore, if they are torn during use or collection, or if they are dislodged from farmland due to wind or flood damage, they are released into the environment without decomposing, posing a problem in terms of environmental pollution.

[0003] From the perspective of reducing environmental impact, mulch sheets made of biodegradable resin film or paper have been proposed. Mulch sheets made from biodegradable resins will biodegrade and eventually break down. However, biodegradable resin films may contain trace amounts of non-biodegradable chemicals as additives, and there are concerns that these non-biodegradable chemicals in the mulch sheets may be transferred into the soil as the mulch sheets biodegrade. Traditional paper mulch sheets have problems such as low water resistance, making them prone to tearing due to wind and rain, and their rapid biodegradation, making them unsuitable for cultivating crops with long growing seasons. In Patent Document 1, the applicant has proposed a paper mulch sheet that has a base paper and a coated layer on at least one surface of the base paper, wherein the base paper contains 40% by weight or more of wood pulp as papermaking fibers, and the coated layer contains lignin and resin in a weight ratio of 30:70 to 99:1 (lignin:resin), and is suitable for crops with slow biodegradation and long growing seasons. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2024-81432 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] The paper mulch sheet described in Patent Document 1 allows for adjustment of the biodegradation rate by combining wood fibers and synthetic fibers made of biodegradable resin as papermaking fibers. In Patent Document 1, the example uses a composite type synthetic fiber in which polylactic acid is used as the core and polybutylene succinate as the sheath. The polylactic acid and polybutylene succinate contained in this synthetic fiber can be derived from either plants or fossil resources, but plant-derived materials are expensive, and currently, the process of manufacturing synthetic fibers from raw materials derived from plants and microorganisms consumes energy for transportation and chemical processing, resulting in the generation of large amounts of carbon dioxide. On the other hand, the use of materials derived from fossil resources is low-cost, but is undesirable from the standpoint of reducing environmental impact. The present invention aims to provide a paper-based mulch sheet that uses less material derived from fossil resources. [Means for solving the problem]

[0006] The means for solving the problems of the present invention are as follows. 1. It comprises a base paper and a coating layer formed on both sides of the base paper by coating, The aforementioned base paper contains biomass-derived fibers, The aforementioned coating layer contains shellac, A paper-based mulch sheet characterized by having a proportion of fossil resource-derived materials of 1% by weight or less of the total material. 2. The paper mulch sheet according to 1, characterized in that the fiber is wood pulp. 3. The amount of shellac adhering to the surface is 0.8 g / m² by oven-dry weight.2 More than 20g / m 2 The paper mulch sheet according to 1. or 2., characterized in that it is as follows: 4. The basis weight of the base paper is 15 g / m². 2 More than 80g / m 2 A paper mulch sheet according to any one of 1. to 3., characterized in that it is one of the following: 5. A paper mulch sheet according to any of 1 to 4, 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. [Effects of the Invention]

[0007] The paper mulch sheet of the present invention contains biomass-derived fibers as papermaking fibers, and the coating layer contains shellac made from the secretions of scale insects, thus significantly reducing the use of materials derived from fossil resources. The paper mulch sheet of the present invention is biodegradable, and even if fragments etc. are released into the environment, the impact on the environment is very small. [Modes for carrying out the invention]

[0008] The paper mulch sheet of the present invention comprises a base paper and a coating layer formed on both sides of the base paper by coating, wherein the base paper contains biomass-derived fibers, the coating layer contains shellac, and the proportion of materials derived from fossil resources to the whole is 1% by weight or less.

[0009] (base paper) The base paper is a sheet consisting of papermaking fibers, fillers, various auxiliary agents, etc. As papermaking fibers, natural fibers derived from biomass (plants, microorganisms, animals) can be used without particular limitation. Specifically, wood pulps such as softwood pulp and hardwood pulp; bast fibers such as flax, ramie, jute, kenaf, hemp, paper mulberry, and Mitsumata; hard fibers such as bagasse, bamboo, and esparto; seed hair fibers such as cotton pulp; non-wood pulps such as leaf sheath and leaf fibers such as abaca and sisal; microbial cellulose fibers using cellulose produced by microorganisms such as acetic acid bacteria; and animal hairs such as silk, wool, and goat hair can be exemplified, and one or more of these can be mixed and used.

[0010] Among these, chemical pulps such as hardwood bleached kraft pulp (LBKP), softwood bleached kraft pulp (NBKP), hardwood unbleached kraft pulp (LUKP), softwood unbleached kraft pulp (NUKP), and sulfite pulp, mechanical pulps such as stone ground pulp and thermomechanical pulp, waste paper pulp derived from wood pulp, wood pulp such as dissolving pulp and mercerized pulp are preferably used, and one or more of wood pulp can be used. From the viewpoint of strength, it is preferable to use NBKP and NUKP, and from the viewpoint of promoting recycling, it is preferable to use waste paper pulp.

[0011] As fillers, fillers known for papermaking such as inorganic fillers such as talc, kaolin, calcined kaolin, clay, heavy calcium carbonate, light calcium carbonate, white carbon, zeolite, magnesium carbonate, barium carbonate, titanium dioxide, zinc oxide, silicon oxide, amorphous silica, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide, barium sulfate, and calcium sulfate, and organic fillers such as urea-formaldehyde resin, polystyrene resin, phenolic resin, and micro hollow particles can be used. Note that the filler is not an essential material and may not be used.

[0012] Examples of various additives include sizing agents such as rosin, alkyl ketene dimer (AKD), and alkenyl succinic anhydride (ASA); dry strength enhancers such as polyacrylamide polymers, polyvinyl alcohol polymers, cationized starch, various modified starches, urea-formaldehyde resins, and melamine-formaldehyde resins; wet strength enhancers; yield enhancers; water drainage enhancers; coagulants; aluminum sulfate; bulk enhancers; dyes; fluorescent whitening agents; pH adjusters; defoamers; UV inhibitors; fade inhibitors; pitch control agents; and slime control agents. These can be selected and used as needed.

[0013] When using fillers or additives, it is preferable that they are not derived from fossil resources, and in the case of organic compounds, biodegradable materials are preferred. In this specification, biodegradable materials are those that are decomposed by microorganisms into at least water and carbon dioxide, and whose aerobic ultimate biodegradation rate in soil, measured using a plastic respiration meter in accordance with ISO-17556 (2003), is 50% or more in 6 months.

[0014] (Papermaking) Base paper can be manufactured by a wet papermaking method, in which paper fibers and other raw materials are dispersed and mixed in a liquid medium, and then formed into sheets by papermaking. The papermaking method for base paper is not particularly limited and can be carried out using a long screen papermaking machine, a cylinder screen papermaking machine, a short screen papermaking machine, a tilting short screen papermaking machine, etc. Among these, it is preferable to use a short screen papermaking machine that can control the fiber orientation. The drying process can be appropriately selected from a multi-cylinder dryer, a Yankee dryer, a hot air dryer, etc. Among these, the Yankee dryer is preferable because it allows for easy control of the paper surface temperature. There are no particular restrictions on the basis weight of the base paper, but for example, 15 g / m² 2 More than 80g / m 2 The following is possible. From the standpoint of strength, the basis weight of the base paper should be 18 g / m². 2 The above is preferable, 20 g / m 2 The above is preferable. From the standpoint of weight reduction, the basis weight of the base paper should be 60 g / m².2 The following is preferable, 45 g / m 2 The following is more preferable, 35 g / m 2 The following is even more preferable.

[0015] (Coating layer) The coating layer contains shellac. Shellac is a resinous substance obtained by purifying the body covering secreted by lac scale insects and several related scale insects. In addition to shellac, the coating layer can also contain external sizing chemicals for papermaking such as surface sizing agents and sizing agents; additives such as colorants, surfactants, dispersants, thickeners, water retention agents, defoaming agents, and water repellents; and one or more kinds of agents such as insecticides, acaricides, nematicides, fungicides, plant growth regulators, and fertilizers. However, it is preferable that these agents contained in the coating layer are not derived from fossil resources, that is, they are derived from biomass.

[0016] The coating layer is formed on both sides of the base paper. If the coating layer is only on one side of the base paper, the strength will be insufficient even if the total coating amount is the same. The method of coating the coating layer on the base paper is not particularly limited, and it can be coated with known coating devices and coating systems. For example, coating devices include blade coaters, bar coaters, nip coaters, roll coaters, air knife coaters, reverse roll coaters, curtain coaters, spray coaters, size press coaters, gate roll coaters, etc. Among them, coating methods used for impregnation coating such as size press coaters are preferable because they are suitable for double-sided coating. Also, coating systems include water-based coating using solvents such as water and solvent-based coating using solvents such as organic solvents, etc., but water-based coating is preferable.

[0017] The adhesion amount of shellac in the paper multi-sheet is 0.8 g / m in absolute dry weight 2 The above and 20 g / m 2 It is preferably the following. If the adhesion amount of this shellac is less than 0.8 g / m 2 the effects required for the coating layer may not be fully exerted. On the other hand, 20 g / m 2If the amount is too high, the drying load during coating increases, and the paper mulch sheet becomes heavier. The amount of shellac to adhere is 1.0 g / m² by oven-dry weight. 2 The above is more preferable, 3.0 g / m 2 The above is even more preferable, and also 15 g / m 2 The following is more preferable: 10 g / m 2 The following is even more preferable: The amount of shellac applied per side should be 0.3 g / m² by oven-dry weight. 2 More than 15g / m 2 The following is preferable. The coating amount for the entire coating layer is 0.8 g / m² by dry weight. 2 More than 25g / m 2 The following is preferable. Furthermore, the coating amount per side of the coating layer should be 0.3 g / m² by dry weight. 2 More than 20g / m 2 The following is preferable.

[0018] (Paper mulch sheet) The paper mulch sheet of the present invention has a material content of 1% by weight or less that is derived from fossil resources. More preferably, this material content is 0.5% by weight or less, even more preferably 0.3% by weight or less, even more preferably 0.1% by weight or less, and most preferably 0% by weight. Note that "material derived from fossil resources" means that 90% by weight or more of the material is derived from fossil resources.

[0019] The paper-based mulch sheet of the present invention comprises a base paper and a coating layer formed on both sides of the base paper by coating. By forming the coating layer on both sides of the base paper, it becomes easy to achieve practical strength and wet strength as a paper-based mulch sheet. 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 and other damage during the cultivation period. The (dry) tensile strength is more preferably 21 N / 15 mm or higher, and even more preferably 22 N / 15 mm or higher. There is no particular upper limit to the (dry) tensile strength, but for example, it is about 40 N / 15 mm or less. A wet tensile strength of 6 N / 15 mm or higher is more preferable, and 7 N / 15 mm or higher is even more preferable. There is no particular upper limit to the wet tensile strength, but for example, it is about 15 N / 15 mm or less. [Examples]

[0020] The present invention will be described in more detail by reference to examples, but these examples are not limiting. Unless otherwise specified, "parts" and "%" refer to "parts by weight" and "% by weight," respectively. (Evaluation method) (1)Basic weight Measurements were taken in accordance with JIS P 8124. (2) Thickness Measurements were taken in accordance with JIS P 8118. (3) Density It was calculated from the basis weight and thickness values. (4) Tensile strength (Dry) tensile strength was measured in accordance with JIS P8113. The wet tensile strength was measured in accordance with JIS P8113 after removing excess moisture from the surface of the test sample by sandwiching it between filter paper after immersion in water.

[0021] (Example 1) Softwood pulp, adjusted to a Canadian standard water filtration (CSF) of 680 ml, was used as papermaking fiber. Using this slurry of 100 parts by weight of wood pulp, the target basis weight is 30 g / m². 2 The base paper was obtained by papermaking using a cylinder screen paper machine. The base paper is impregnated with shellac solution (CG-35-GS, manufactured by Gifu Cerac Manufacturing Co., Ltd.) using a size-pressing process to create a coating layer on both sides (absolutely dry coating amount: 7.2 g / m²). 2 (The amount of coating per side was equal) and a paper mulch sheet was obtained.

[0022] (Comparative Example 1) Shellac solution was applied to one side of the bar to create a coating layer (absolutely dry coating amount: 7.0 g / m²). 2 A paper mulch sheet was obtained by carrying out the same procedure as in Example 1, except that a ) was formed.

[0023] [Table 1]

[0024] The paper mulch sheet obtained in the embodiment of the present invention had a coating layer on both sides and possessed practical strength for agricultural and horticultural use. In contrast, the paper-based mulch sheet obtained in the comparative example had a coating layer formed on only one side, resulting in insufficient strength.

Claims

1. It comprises a base paper and a coating layer formed on both sides of the base paper by coating, The aforementioned base paper contains biomass-derived fibers, The aforementioned coating layer contains shellac, A paper-based mulch sheet characterized in that the proportion of materials derived from fossil resources to the total is 1% by weight or less.

2. The paper mulch sheet according to claim 1, characterized in that the aforementioned fibers are wood pulp.

3. The amount of shellac adhering to the surface is 0.8 g / m² by dry weight. ２ 20g / m or more ２ The paper mulch sheet according to claim 1 or 2, characterized in that it is as follows.

4. The basis weight of the aforementioned base paper is 15 g / m². ２ 80g / m or more ２ The paper mulch sheet according to claim 1 or 2, characterized in that it is as follows.

5. The paper mulch sheet according to claim 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.

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