JP6458614B2 - Biodegradable industrial paper - Google Patents

Description

  The present invention relates to a biodegradable industrial paper that can be used in various industrial applications.

Since the paper base having biodegradability is naturally decomposed by being embedded in the soil at the time of disposal, it is attracting attention as an environmentally friendly material, and various products have been developed in various industrial fields.
For example, in the agricultural field, paper has conventionally been used for containers for raising seedlings and agricultural covering materials. When creating containers for raising seedlings, one of the major points in product development is to design them so that they are decomposed at an appropriate decomposition rate when buried in the soil while maintaining a moderate strength. Yes.

  Many studies have been made in response to such demands. For example, Patent Document 1 discloses a seedling transplanting pot base paper using kraft pulp with controlled resistance to cellulase. Patent Document 2 discloses a base paper for a seedling transplanting pot made of cellulose fiber added with carboxymethylcellulose. Patent Document 3 discloses a mixed paper obtained by mixing a cellulose-containing component and a polylactic acid-based composite short fiber having a low melting point of 150 ° C. or lower, and bonding the polylactic acid-based composite short fiber and the cellulose-containing component. Thus, the tear strength is improved.

Japanese Patent No. 5057319 JP 2003-23874 A JP 2003-82595 A

  Since the base papers described in Patent Document 1 and Patent Document 2 are base papers made only of pulp fibers, there is a limit to the control of the biodegradation speed, and the quality and operation are also improved in improving the wet tensile strength by the wet paper strength agent. It had a limit from the aspect. The mixed paper described in Patent Document 3 uses low-melting polylactic acid-based composite short fibers, so that the manufacturing apparatus is soiled in the manufacturing process of the mixed paper, or blocking occurs in the winding roll wound with the mixed paper. There was concern.

  The present invention has been made in view of such a situation, and is a biodegradable industrial paper that has less generation of dirt and blocking in the production process, has moderate biodegradability, and excellent wet tensile strength. The issue is to provide.

  By appropriately setting the content and melting point of the polylactic acid fiber, the present inventors can suppress the occurrence of dirt and blocking in the manufacturing process of industrial paper, it is possible to control the biodegradation rate, It has been found that the wet tensile strength can be improved.

  The present invention has been completed based on such knowledge. That is, the present invention has the following configuration.

(1) The biodegradable industrial paper of the present invention is a biodegradable industrial paper comprising a paper base material containing pulp fibers and polylactic acid fibers, and the content ratio of the polylactic acid fibers is the total fibers. a 3 to 60 wt%, the melting point of the polylactic acid fiber Ri der 160 ° C. or higher, the fiber length of the polylactic acid fibers is 3 to 10 mm, said paper substrate is by wet paper making process .

(4) In the biodegradable industrial paper of the present invention, it is preferable that the polylactic acid fiber is thermally deformed in the paper base material.

(5) The biodegradable industrial paper of the present invention preferably has a coating layer containing a water-soluble resin on at least one surface of the paper substrate.

(6) In the biodegradable industrial paper of the present invention, the water-soluble resin preferably contains one or more of polyvinyl alcohol, polyvinyl alcohol derivatives, starch and starch derivatives.

  The biodegradable industrial paper of the present invention is less likely to cause stains or blocking in the production process, has moderate biodegradability, and is excellent in wet tensile strength.

  An embodiment of the present invention will be described. However, embodiments of the present invention are not limited to the following embodiments.

  The biodegradable industrial paper of this embodiment is composed of a paper base material containing pulp fibers and polylactic acid fibers. Hereinafter, pulp fibers and polylactic acid fibers constituting the paper substrate will be described.

(Pulp fiber)
The pulp fiber of this embodiment has cellulose pulp as a main component. As a pulp fiber used for a paper base material, the following various pulp can be used 1 type or in mixture of 2 or more types. For example, chemical pulp such as kraft pulp (KP), sulfite pulp (SP), soda pulp (AP); semi-chemical pulp such as semi-chemical pulp (SCP), chemi-ground wood pulp (CGP); groundwood pulp (GP) , Thermo-mechanical pulp (TMP, BCTMP), refiner grandwood pulp (RGP) and other mechanical pulp; non-wood fiber pulp made from cocoon, sardine, hemp, kenaf, etc .; deinked pulp made from waste paper Can do. In addition to these, synthetic pulp, rayon fiber, and the like may be included. The wood used as the raw material for the pulp fiber may be a softwood material or a hardwood material, or may be used as a mixture. When used as a raw material pulp, it is preferable to select a pulp fiber having a low mineral content. The pulp fiber used in the present embodiment is preferably softwood kraft pulp (NBKP) or hardwood kraft pulp (LBKP) from the viewpoints of supply amount, quality stability, cost, and the like.

  The pulp fiber used in the present embodiment preferably has a freeness (Canadian standard freeness) measured according to JIS P 8121-2012 of 200 to 600 ml, more preferably 300 to 500 ml. The freeness of the pulp fibers may be adjusted to the above range by beating at least one kind of pulp to be used. When two or more kinds of pulp are used, the pulp beaten separately may be mixed to the above range, or the previously mixed pulp may be beaten and adjusted to the above range. When the freeness of the pulp fiber is 200 ml or more, the wire is excellent in dewaterability. On the other hand, when the freeness of the pulp fiber is 600 ml or less, paper strength is increased, wet strength is improved, and fluffing of the paper base material can be suppressed.

(Polylactic acid fiber)
Polylactic acid is a polyester formed by condensation polymerization of carboxyl groups and hydroxyl groups in lactic acid, and is a biodegradable polymer. Lactic acid has two isomers, D and L. The melting point of polylactic acid can be controlled by the copolymerization ratio and arrangement of these isomers. For example, the melting point of poly-L-lactic acid is 170 ° C. In addition, there are polylactic acid having a melting point of 160 to 170 ° C. and polylactic acid having a melting point of 200 to 230 ° C. Furthermore, polylactic acid having a melting point of less than 160 ° C. is also present by copolymerization with other monomers. The melting point of polylactic acid is measured as the temperature of the melting point peak by DSC. In the present embodiment, polylactic acid is defined as including polylactic acid having such characteristics as polylactic acid and modified by copolymerization or the like. Let the fiber manufactured using the polylactic acid-type resin be a polylactic acid-type fiber.

  As will be described later, when a paper substrate is produced by a papermaking method, a drying step is provided to remove moisture after papermaking. Moreover, also when forming a coating layer, the drying process for drying a coating layer after application | coating is provided. In a drying process, it is normally heated at 100 degreeC or more and about 120-140 degreeC. For this reason, if the paper-made sheet contains fibers that are melted or largely thermally deformed at a temperature of about 120 to 140 ° C., there is a concern that it adheres to a manufacturing apparatus such as a dryer and causes stains. Moreover, there exists a concern which a manufacturing apparatus, a paper base material, or paper base materials adhere | attach and cause blocking. Therefore, the melting point of the polylactic acid fiber of this embodiment is set to 160 ° C. or higher. The range of the melting point of the polylactic acid fiber is preferably about 160 to 230 ° C, more preferably about 160 to 190 ° C, and still more preferably about 165 to 190 ° C.

  The polylactic acid fiber in the present invention is preferably a fiber made of the same kind of polymer. Thereby, the biodegradation rate can be controlled effectively. For example, polylactic acid fibers having a core-sheath structure have different polymers in the core and the sheath and have different biodegradation rates, which may make it difficult to control the biodegradation rate.

  The fiber length of the polylactic acid fiber is preferably 3 to 10 mm. When the fiber length is 3 mm or more, the paper strength of the paper substrate is increased, and damage or the like is less likely to occur during use. On the other hand, if the fiber length is 10 mm or less, fiber dispersion failure and fiber entanglement are suppressed, and it becomes difficult for foreign matter to be generated on the paper surface, and the amount of fluffing is reduced. Furthermore, during the preparation process such as fiber disaggregation and dispersion, in the piping, pulp storage tank, paper machine stock inlet, dewatering wire, etc., polylactic acid fibers or polylactic acid fibers and pulp fibers are entangled to form a flock. It is suppressed. As a result, deterioration of formation and paper breakage hardly occur, and papermaking suitability can be improved. A more preferable range of the fiber length is 4 to 7 mm. The fiber length in this embodiment is a value obtained by measuring the weight-weighted average fiber length using FIBER LAB manufactured by METSO, which is an optical fiber length measuring device.

  The fineness of the polylactic acid fiber is preferably 0.1 to 6.0 dtex. When the fineness is 0.1 dtex or more, the paper strength of the paper base material is increased, and paper breakage is less likely to occur. On the other hand, when the fineness is 6.0 dtex or less, the amount of fluffing can be reduced. A more preferable range of fineness is 0.5 to 5.0 dtex, and further preferably 1.0 to 5.0 dtex. In addition, 1 dtex is the mass (gram number) per 10,000 m.

(Paper substrate)
The biodegradable industrial paper of this embodiment is composed of a paper base material in which the content of polylactic acid fibers is 3 to 60% by mass in the solid content of at least pulp fibers and polylactic acid fibers. The content ratio of the polylactic acid fiber is preferably 4 to 60% by mass, more preferably 5 to 50% by mass, and still more preferably 10 to 40% by mass. When the content of the polylactic acid fiber is within the above range, it is possible to control the biodegradation of the entire paper substrate within 3 months, and the form as the paper substrate is collapsed in a short period of time. be able to. In addition, when the content of the polylactic acid fiber exceeds 60% by mass, the wet strength as a paper base material is not given, and it takes time for biodegradation. .

In this embodiment, the paper base is manufactured by a wet papermaking method. By using the papermaking method, a plurality of types of fibers can be easily mixed.
The papermaking method is generally a method of forming a sheet after mixing the short fibers as raw materials. The papermaking method is roughly classified into a dry method and a wet method. Specifically, the dry method is a method of forming a sheet by dry blending short fibers and then accumulating on a net using an air stream. A water stream or the like can be used for forming the sheet. On the other hand, the wet method is a method in which short fibers are dispersed and mixed in a liquid medium and then accumulated on a net to form a sheet. Among these, a wet papermaking method using water as a medium is preferably selected.

  In the wet papermaking method, an aqueous slurry containing short fibers is generally sent to a paper machine to disperse the short fibers, and then dehydrated, squeezed and dried, and then wound up as a sheet. As the paper machine, a long paper machine, a circular paper machine, a slanted paper machine, and a combination paper machine combining these are used.

  When a paper base material is produced by the papermaking method, the pulp fiber contains moisture, and thus a drying step is required. Drying in the drying step is usually performed at a temperature of about 100 ° C or higher and about 120 to 140 ° C. In the drying process, dryers such as a multi-cylinder dryer, a Yankee dryer, an after dryer, a band dryer, and an infrared dryer are used.

  Use wet paper strength agents, sizing agents, fillers, yield improvers, fixing agents, dry paper strength agents, dyes, pigments, etc. as internal additives to the paper base as long as they do not affect biodegradability. Can do.

  When adding a wet paper strength agent, it is preferable to contain in the ratio of 0.5-3.0 mass parts in conversion of solid content with respect to 100 mass parts of all the fibers of a paper base material. The content ratio of the wet paper strength agent is more preferably 0.7 to 2.5 parts by mass, and still more preferably 0.8 to 2.0 parts by mass. When the content ratio of the wet paper strength agent is 0.5 parts by mass or more, the wet strength can be maintained. On the other hand, when the content ratio of the wet paper strength agent exceeds 3.0 parts by mass, the effect of maintaining the wet strength reaches a peak, and therefore, the content is preferably 3.0 parts by mass or less. Moreover, if the content rate of a wet paper strength agent is 3.0 mass parts or less, while suppressing cost, the effect of improving the disaggregation property of a waste paper is also acquired.

  Specific examples of the wet paper strength agent include polyamide-epichlorohydrin, polyamine-epichlorohydrin, epoxy resin, melamine resin, and the like. In particular, it is preferable to use polyamide-epichlorohydrin or polyamine-epichlorohydrin.

  If necessary, a sizing agent can be used for the paper substrate. The sizing agent may be added internally or externally. Examples of the sizing agent to be used include rosin sizing agent, rosin emulsion sizing agent, α-carboxymethyl saturated fatty acid, alkyl ketene dimer, alkenyl succinic anhydride, and cationic polymer sizing agent. Among these, rosin sizing agents are preferable. The content ratio of the sizing agent is not particularly limited, but from the viewpoint of reducing dirt in the papermaking system, it is preferably 0.5 parts by mass or less in terms of solid content with respect to 100 parts by mass of all fibers of the paper base material, 0.4 The amount is more preferably equal to or less than mass parts, and still more preferably equal to or less than 0.3 parts by mass. A sulfuric acid band (aluminum sulfate) can be used as a fixing agent for the rosin sizing agent.

  If necessary, the paper base material may contain a yield improver. Examples of the yield improver include polyacrylamide compounds, polyethylene glycol compounds, polyvinylamine compounds, and the like. Among these, cationic polyacrylamide compounds are particularly preferable. When kaolin is used as the filler, the overall yield is likely to decrease, so a yield agent may be selected as appropriate in order to improve productivity. Although the content rate of a yield improving agent is not specifically limited, 0.001-0.035 mass part is preferable in conversion of solid content with respect to 100 mass parts of all the fibers of a paper base material, 0.005-0.030 mass part Is more preferable, and 0.008-0.020 mass part is still more preferable.

(Coating layer)
The paper substrate preferably has a coating layer formed from a coating solution containing a water-soluble resin on at least one surface thereof. The coating layer in the present invention is formed by coating or impregnating a coating liquid on a paper substrate. Thereby, generation | occurrence | production of the stain | pollution | contamination of a dryer and fluff produced with a polylactic acid-type fiber can be suppressed notably. In addition, in the present invention, it is possible to suppress dryer stains that are practically problematic such that the operation is stopped and cleaning is required. Continuous stable operation is possible without fear of causing it. Here, the water-soluble resin includes not only a water-soluble resin in which the resin is dissolved in water but also a water-dispersible resin in which the resin is finely dispersed in water.

  Examples of the water-soluble resin include fully saponified or partially saponified polyvinyl alcohol and derivatives thereof, modified polyvinyl alcohols such as ethylene-modified polyvinyl alcohol, acetoacetyl-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, and silicon-modified polyvinyl alcohol; Derivatives thereof, starch and derivatives thereof, cellulose derivatives such as methoxycellulose, carboxymethylcellulose, hydroxypropylmethylcellulose, methylcellulose and ethylcellulose, sodium polyacrylate, polyvinylpyrrolidone, acrylic acid amide-acrylic acid ester copolymer, acrylic acid amide-acrylic Acid ester-methacrylic acid copolymer, styrene-maleic anhydride copolymer salt, styrene-a Acrylic acid copolymer salts, polyacrylamide, sodium alginate, gelatin, casein, and the like. Examples of the salt include sodium salt, potassium salt, ammonium salt, and those in which these salts coexist. In these, since it has biodegradability, what contains any 1 or more types of polyvinyl alcohol, a polyvinyl alcohol derivative, starch, and a starch derivative is preferable.

  Examples of water-dispersible resins include polyvinyl acetate, polyurethane, styrene-butadiene copolymer, styrene-acrylic copolymer, styrene-butadiene-acrylonitrile copolymer, acrylonitrile-butadiene copolymer, polyacrylic acid, poly Homopolymer or copolymer such as acrylic ester, vinyl chloride-vinyl acetate copolymer, polybutyl methacrylate, ethylene-vinyl acetate copolymer, silylated urethane, acrylic-silicon composite, acrylic-silicon-urethane composite A coalesced resin is mentioned. These may be used in the form of emulsion or latex.

The coating amount of the coating layer is preferably 0.2 to 5.0 g / m ² per side with respect to industrial paper after drying. By setting it as 0.2 g / m < ² > or more, generation | occurrence | production of the dryer stain | pollution | contamination and fluff by a polylactic acid-type fiber can be suppressed effectively. On the other hand, when the coating amount is 5.0 g / m ² or less, it is possible to effectively suppress dryer stains in the drying process and the like. The coating amount of the coating layer is preferably about 0.5 to 3.5 g / m ² .

  As an apparatus for forming the coating layer, known coating or impregnation apparatuses such as a roll coater, a bar coater, a doctor coater, a blade coater, a curtain coater, a film transfer coater, and a size press can be used. In order to form the coating layer, the coating liquid is applied or impregnated and then dried in a drying step. A drying process is normally performed at the temperature of about 100 to 120 degreeC. In the drying step, a dryer similar to the dryer used in the drying step after papermaking is used.

(Biodegradable industrial paper)
Biodegradable industrial paper basis weight (hereinafter, sometimes abbreviated as "industrial Paper".) Is preferably 30 to 100 g / ^{m 2,} and more preferably 40~70g / ^{m 2.} By setting the basis weight to 30 g / m ² or more, it is possible to increase the tensile strength and reduce the frequency of occurrence of paper breaks during processing. For example, if industrial paper is laid on the slope of the soil, the collapse of the soil can be prevented until the undergrowth is rooted. On the other hand, when the basis weight of the industrial paper is 100 g / m ² or less, the processability as an industrial paper is improved and the biodegradability is excellent. In this embodiment, it is preferable to dry using a cylinder dryer from the viewpoint of adjusting the basis weight to a preferable range and fully exhibiting the effects of this embodiment.

  The tensile strength of the industrial paper is preferably 1.50 kN / m or more, and more preferably 2.00 kN / m or more. When the tensile strength is 1.50 kN / m or more, paper breakage is less likely to occur during winding during manufacturing or processing, and thus there is no risk of reducing productivity.

  The wet tensile strength of the industrial paper is preferably 0.5 kN / m or more, more preferably 1.5 kN / m or more in the state before use. When the wet tensile strength before use is 0.5 kN / m or more, breakage or the like is less likely to occur during use, and handling properties are improved. What is necessary is just to adjust the wet tensile strength of the state before use, for example by adjusting the kind and quantity of wet paper strength agent, and adjusting the freeness of a pulp fiber.

  The polylactic acid fiber is preferably thermally deformed in the paper base material. In order to impart tensile strength and wet tensile strength as industrial paper, not only the above-described means but also a method of appropriately heat-deforming polylactic acid fibers in the paper substrate can be employed. The thermal deformation of the polylactic acid fiber is carried out by heating in the drying step when manufacturing the paper substrate by the paper making method described above or in the drying step after applying the coating liquid. That is, in the drying step, the polylactic acid fiber is thermally deformed without causing dirt or blocking by being heated to a temperature lower than the melting point of the polylactic acid fiber and higher than the heat distortion temperature, As a result, the entanglement with the pulp fiber becomes denser, and the tensile strength and wet tensile strength of the industrial paper can be improved. The paper base material in the present invention can be used after further heat compression molding as long as the effects of the present invention are not impaired. Thereby, the shape and intensity | strength suitable for the use can be given.

  While industrial paper is excellent in biodegradability, it is used for purposes such as covering or storing moisture-containing soil, so the shape tailored to its use is maintained at a certain strength for a desired period of time. It is desirable to biodegrade quickly. The period required for biodegradation and almost disintegration is preferably at most one season, in other words, three months. On the other hand, it is desirable for industrial paper to maintain strength sufficient for handling during a period until seeds bud and become seedlings, that is, for at least two weeks. Therefore, for example, after the soil is immersed for 2 weeks under a constant temperature condition of 30 ° C., the wet tensile strength is preferably 0.15 kN / m or more, more preferably 0.35 kN / m or more. preferable. When the wet tensile strength is 0.15 kN / m or more, handling can endure, and the covered soil or the stored soil can be isolated or retained. In order to obtain the wet tensile strength after the burying treatment, for example, the wet paper strength agent can be adjusted, and the content ratio of the polylactic acid fiber can be adjusted to a desired period.

  Regarding the biodegradability of industrial paper, for example, after being immersed in soil at a constant temperature of 30 ° C. for 3 months, even if industrial paper remains in shape, it is brittle and deteriorates to such an extent that strength cannot be measured. It is preferable that the industrial paper is almost completely decomposed and does not retain its form. In order to advance biodegradation at such a biodegradation rate, it can be adjusted, for example, by adjusting the wet paper strength agent and adjusting the content ratio of the polylactic acid fiber.

The industrial paper of this embodiment can be used in various industrial fields such as agriculture, forestry, fishery, mining, civil engineering, manufacturing, transportation, and service industries.
In the field of agriculture and forestry, it can be used by a method of natural decomposition after being buried in soil as a partition or box for nursery beds, a partition or box for growing seedlings for transportation or transportation.
In the civil engineering field, it can be constructed on slopes such as river dikes, and the fall of soil can be prevented until the undergrowth is rooted. In the transportation industry, it can be used as a casing material for freight transportation, and after use, it can be buried in the soil and decomposed naturally.

  When the industrial paper of this embodiment is formed into a shape such as a housing in the above various industrial fields, the industrial paper is cut and bonded using a biodegradable polyvinyl alcohol-based adhesive or the like. It can be done by the method. Moreover, the industrial paper of this embodiment can also be made into a composite comprising a plurality of paper layers by integrating industrial papers having different content ratios by a combination papermaking method or the like.

  The present embodiment will be described in more detail with reference to examples, but the present embodiment is not limited thereto. Unless otherwise specified, “parts” and “%” represent “parts by mass” and “mass%”, respectively.

In the examples and comparative examples, the coating solutions used are as follows.
(I) Starch; 4% aqueous solution of oxidized starch (trade name: Oji Ace Y, manufactured by Oji Cornstarch) (ii) PVA; 4% aqueous solution of fully saponified polyvinyl alcohol (trade name: PVA-117, manufactured by Kuraray Co., Ltd.) iii) SBR: 4% water dilution of styrene-butadiene copolymer latex (trade name: A6160, manufactured by Asahi Kasei Chemicals Corporation, solid content concentration 48%)

Example 1
<Preparation of paper substrate>
50 parts of hardwood bleached kraft pulp (LBKP, Canadian standard freeness 400 ml), 20 parts of softwood bleached kraft pulp (NBKP, Canadian standard freeness 400 ml), and polylactic acid fiber (trade name: Terramac PL-01, 30 parts of melting point 170 ° C., fiber thickness 15 μm, fiber length 5 mm, manufactured by Unitika Co., Ltd.) were mixed and stirred and dispersed in water to obtain a fiber slurry having a concentration of 2.0%. In this fiber slurry, with respect to 100 parts by mass of all fibers in terms of solid content, 2.0 parts by mass of sulfuric acid band and rosin-based sizing agent (trade name: “Size Pine N775”, solid content concentration 50%, Arakawa Chemical Industries, Ltd. 0.3 parts), and polyamide-epichlorohydrin resin (trade name: “Arafix 255”, solid concentration 25%, manufactured by Arakawa Chemical Industries, Ltd.) 1.5 parts as a wet paper strength agent Was added. Using the mixture obtained by adding these, papermaking and drying were performed with a long paper machine and a cylinder dryer to obtain a paper substrate having a basis weight of 60 g / m ² .

<Formation of coating layer>
Impregnation and drying were performed on both sides of the paper substrate obtained above using the starch as a coating solution so that the coating amount after drying on one side was 1.0 g / m ² by a size press.

(Examples 2-6, Comparative Examples 1-3)
According to Table 1, an industrial paper was obtained in the same manner as in Example 1 except that the type and the number of blended parts of the polylactic acid fiber and the type of coating solution used were changed so that the desired content ratio was obtained.

  The following evaluation was performed on the obtained industrial paper (in Example 5 only, an industrial paper on which no coating layer was formed). The results are shown in Table 2.

<Wet tensile strength>
The industrial paper was buried in soil for 2 weeks under a constant temperature condition of 30 ° C., and the wet tensile strength of the industrial paper was measured before and after the embedding treatment. The wet tensile strength was measured according to JIS P 8135. The immersion time was 10 minutes. The interval between the grips was 180 mm, and the measurement was performed in the longitudinal direction of the paper. The paper substrate after the burying treatment was washed with water and then measured for wet tensile strength in accordance with JIS P 8135. All were quantified in units of kN / m. Each evaluation was performed according to the following criteria.
Initial (before processing)
(Double-circle): It is 1.5 kN / m or more, and there is no problem.
A: 0.5 kN / m or more and less than 1.5 kN / m, and there is no practical problem.
X: Less than 0.5 kN / m, which is problematic.
After embedment treatment A: 0.35 kN / m or more, no problem.
A: 0.15 kN / m or more and less than 0.35 kN / m, and there is no practical problem.
X: Less than 0.15 kN / m, which is problematic.

<Biodegradability>
The industrial paper was buried in soil for 3 months under a constant temperature condition of 30 ° C. After the treatment, the appearance was visually observed and evaluated according to the following criteria.
A: Industrial paper is disassembled.
○: Some industrial paper remains, but it is brittle and cannot measure its strength.
X: Industrial paper remains without being disassembled.

<Dryer dirt>
Dryer stains in the papermaking and drying processes were visually observed and evaluated according to the following criteria.
(Double-circle): There is no transition of fiber, resin, etc., and there is no dryer dirt.
○: There is almost no transfer of fibers, resin, etc., and there is no dryer stains that are a problem in continuous stable operation.
Δ: There is a slight transition of fibers, resin, etc., but there is almost no stain on the dryer, which is a practical problem.
X: There are many transitions of fibers, resins, etc., and the dryer is very dirty.

<Blocking>
Regarding the winding of the paper substrate after papermaking and drying, the paper substrate was peeled off, and the degree of sticking of the front and back was evaluated according to the following criteria.
○: Sticking is not recognized.
X: Sticking is recognized considerably, which causes a problem in practical use.

  The industrial papers of Examples 1 to 6 have a predetermined wet tensile strength before and after being buried in the soil for 2 weeks, biodegraded after the treatment to be buried in the soil for 3 months, and there is no occurrence of dryer dirt and blocking. It was. The industrial paper of Comparative Example 1 generates dryer stains and blocking because the polylactic acid fiber has a low melting point. The industrial paper of Comparative Example 2 had a low content of polylactic acid fiber, rapidly biodegraded after being immersed in soil for 2 weeks, and was inferior in wet tensile strength. Since the industrial paper of Comparative Example 3 has a high content of polylactic acid fiber, it is inferior in wet tensile strength, inferior in biodegradability after being immersed in soil for 3 months, and inferior in dryer stains. .

Claims (5)

A biodegradable industrial paper comprising a paper base material containing pulp fiber and polylactic acid fiber,
The content of the polylactic acid fiber is 3 to 60% by mass of the total fiber,
The polylactic acid fiber has a melting point of 160 ° C. or higher,
The fiber length of the polylactic acid fiber Ri 3~10mm der,
A biodegradable industrial paper characterized in that the paper substrate is obtained by a wet papermaking method . Biodegradable industrial sheet according to claim 1, wherein the polylactic acid-based fibers with said paper substrate in is thermally deformed. The biodegradable industrial paper according to claim 1 or 2 , further comprising a coating layer containing a water-soluble resin on at least one surface of the paper substrate. The biodegradable industrial paper according to claim 3 , wherein the water-soluble resin contains one or more of polyvinyl alcohol, polyvinyl alcohol derivatives, starch, and starch derivatives. The biodegradability according to any one of claims 1 to 4 , comprising 0.5 to 3.0 parts by mass of a wet paper strength agent in terms of solid content with respect to 100 parts by mass of all fibers of the paper base material. Industrial paper.