Molding material, method for manufacturing molded article, and molded article

Abstract

The present invention provides: a novel molding material, which enables a shorter cycle time as compared with conventional materials and improves surface properties of molded articles; a method for manufacturing a molded article; and the molded article. The molding material contains pulp and a water-soluble binder. The pulp includes dry-defibrated wood pulp.

Description

Molding material, manufacturing method of molded product, and molded product

[0001] The present invention relates to a molding material used in molding a biodegradable molded article, and to the molded article.

[0002] The applicant previously held, for example, Patent No. 2951933 (Patent Document 1), a molding material for injection molding that contains pulp and a starch-based binder as its main components.

[0003] Products (molded articles such as containers) made from the molding material disclosed in Patent Document 1 (hereinafter referred to as the "conventional material") have been well-received as being environmentally friendly.

[0004] In order to mass-produce the above molded products, there is a demand for shortening the cycle time (the time from one injection to the next) in injection molding.

[0005] Patent No. 2951933

[0006] The present invention has been made in consideration of the current situation as described above, and aims to provide a novel molding material, a method for manufacturing a molded product, and a molded product, which uses dry-defibrated wood pulp, thereby enabling a shorter cycle time compared to conventional materials and improving the surface properties of the molded product.

[0007] The gist of the present invention will be described.

[0008] A first aspect of the present invention relates to a molding material comprising pulp and a water-soluble binder, wherein the pulp comprises dry-defibrated wood pulp.

[0009] A second aspect of the present invention relates to a molding material according to the first aspect, characterized in that the dry-defibrated wood pulp has a fiber length of 0.3 mm or more and 1.2 mm or less, and contains 30 mass% or more of the dry-defibrated wood pulp among components other than water.

[0010] A third aspect of the present invention relates to the molding material of the second aspect, wherein the dry-defibrated wood pulp is softwood pulp having a fiber length of 0.5 mm or more and 1.2 mm or less and a fiber width of 25 μm or more and 32 μm or less, or hardwood pulp having a fiber length of 0.3 mm or more and 0.8 mm or less and a fiber width of 15 μm or more and 25 μm or less.

[0011] A fourth aspect of the present invention relates to the molding material of the second aspect, wherein the pulp contains undefibrated wood pulp, and the undefibrated wood pulp accounts for 40% by mass or less of the components other than water.

[0012] A fifth aspect of the present invention relates to the molding material of the third aspect, wherein the pulp contains undefibrated wood pulp, and the undefibrated wood pulp accounts for 40% by mass or less of the components other than water.

[0013] A sixth aspect of the present invention relates to a molding material according to the fourth aspect, characterized in that the molding material contains, as components other than water, 50% by mass or more and 80% by mass or less of pulp and 20% by mass or more and 50% by mass or less of a water-soluble binder.

[0014] A seventh aspect of the present invention relates to a molding material according to the fifth aspect, characterized in that the molding material contains, as components other than water, 50% by mass or more and 80% by mass or less of pulp and 20% by mass or more and 50% by mass or less of a water-soluble binder.

[0015] An eighth aspect of the present invention relates to the molding material of the sixth aspect, wherein the water-soluble binder contains starch and polyvinyl alcohol, and the molding material contains, among the components other than water, 5% by mass or more and 45% by mass or less of the starch and 5% by mass or more and 15% by mass or less of the polyvinyl alcohol.

[0016] A ninth aspect of the present invention relates to the molding material of the seventh aspect, wherein the water-soluble binder contains starch and polyvinyl alcohol, and the molding material contains, among the components other than water, 5% by mass or more and 45% by mass or less of the starch and 5% by mass or more and 15% by mass or less of the polyvinyl alcohol.

[0017] A tenth aspect of the present invention relates to a molding material according to any one of the first to ninth aspects, characterized in that the moisture content is 20% by mass or more and 60% by mass or less.

[0018] An eleventh aspect of the present invention relates to a method for producing a molded article, characterized in that the molding material according to the tenth aspect is injection molded or compression molded to obtain a molded article.

[0019] A twelfth aspect of the present invention relates to a molded article produced by the method for producing a molded article according to the eleventh aspect, characterized in that the molded article has a tensile stress of 20 MPa or more and a bending stress of 35 MPa or more.

[0020] Because the present invention is configured as described above, it is possible to shorten the cycle time compared to conventional materials and improve the surface properties of molded products, resulting in a molding material, a manufacturing method for a molded product, and a molded product that have never been seen before.

[0021] A preferred embodiment of the present invention will be briefly described below, showing the operation of the present invention.

[0022] The inventors conducted various experiments to find a formulation for shortening the cycle time of molding materials used in molding biodegradable molded articles, and as a result, they found that it is preferable to include dry-defibrated wood pulp.

[0023] In other words, by adding a certain amount of dry-defibrated wood pulp to a molding material containing pulp and a water-soluble binder, it was confirmed that the cycle time could be shortened (molding could be done in a short time) compared to conventional materials. This is presumably because the pulp and binder are easily mixed, and the voids between the pulp are equalized, making it easier for moisture to evaporate evenly.

[0024] Furthermore, it was confirmed that the surface properties improved when dry-defibrated wood pulp was added. This is presumably because the surface becomes denser as the number of fibers increases.

[0025] Therefore, according to the present invention, it is possible to realize a molding material that can shorten the cycle time and improve the surface properties compared to conventional materials.

[0026] A specific example of the present invention will now be described.

[0027] This example is a molding material to be molded into a storage container or the like, and contains pulp and a water-soluble binder.

[0028] Specifically, pulp, a water-soluble binder, and water are mixed and kneaded, and then molded into a predetermined shape (for example, pellets or tablets).

[0029] As the pulp, natural fibers can be used. Examples include wood pulps such as paper pulp, dissolving pulp, mercerized pulp, and fluff pulp; non-wood pulps obtained from cotton, linter, flax, Manila hemp, sisal, bagasse, kenaf, straw, and the like; waste paper pulp obtained from waste paper; and crushed plant materials such as rice husks and wood flour. In addition, lyocell fibers obtained by refining natural cellulose and rayon fibers obtained by regenerating natural cellulose can also be used as natural fibers.

[0030] The wood pulp can be softwood pulp, hardwood pulp, or a mixture of the two in a specific ratio. When hardwood pulp and softwood pulp are mixed, the ratio is set to 20:80 to 80:20, preferably 50:50.

[0031] Specifically, in this example, wood pulp that has been dry-type defibrated using a general dry type defibrator (e.g., one equipped with a defibrating section that applies mechanical shear force to cellulose fibers to defibrate them, and a screen with a large number of openings of a specified diameter through which the defibrated material passes) contains 30% by mass or more of components other than water.

[0032] Dry-type defibrated wood pulp refers to so-called cellulose fibers defibrated by a dry-type defibrator and has a fiber length of 0.3 mm to 1.2 mm. Specifically, in the case of softwood pulp, the fiber length is 0.5 mm to 1.2 mm (preferably 0.65 mm to 1.05 mm) and the fiber width is 25 μm to 32 μm, and in the case of hardwood pulp, the fiber length is 0.3 mm to 0.8 mm (preferably 0.49 mm to 0.64 mm) and the fiber width is 15 μm to 25 μm.

[0033] In the present examples, the fiber length refers to an average fiber length, and the fiber width refers to an average fiber width. The average fiber length and the average fiber width can be measured using a fiber length measuring device (for example, L&W Fiber Tester Plus manufactured by ABB).

[0034] In this embodiment, dry-defibrated softwood pulp is used.

[0035] More specifically, it is preferable that the composition contains both dry-defibrated wood pulp and undefibrated wood pulp. In this embodiment, the composition contains 40% by mass or less of undefibrated wood pulp among the components other than water. Specifically, the composition contains 30% by mass or more and 70% by mass or less of dry-defibrated wood pulp and 10% by mass or more and 40% by mass or less of undefibrated wood pulp among the components other than water.

[0036] Undefibrated wood pulp is wood chips that have been pulped by chemical reaction (for example, by the Kraft cooking method), and in the case of softwood pulp, the fiber length generally exceeds 2.0 mm, while in the case of hardwood pulp, the fiber length generally exceeds 0.8 mm.

[0037] That is, this example contains dry-type defibrated softwood pulp and undefibrated softwood pulp, and specifically, among the components other than water, it contains 30 mass% dry-type defibrated softwood pulp and 30 mass% undefibrated softwood pulp (Experimental Example 6 described below). Note that softwood pulp and hardwood pulp can be combined appropriately, and it may contain dry-type defibrated softwood pulp and undefibrated hardwood pulp, or it may contain dry-type defibrated hardwood pulp and undefibrated softwood pulp.

[0038] As the water-soluble binder, for example, starch or polyvinyl alcohol (PVA) can be used. As the starch, corn starch, potato starch, rice flour, etc. can be used. In this embodiment, corn starch is used. In addition, in this embodiment, polyvinyl alcohol is further contained to smooth the surface.

[0039] In this example, the components other than water (total solid content is 100% by mass) are 50% to 80% by mass of pulp, 20% to 50% by mass of a water-soluble binder, etc. Specifically, the composition contains 50% to 80% by mass of pulp, 5% to 45% by mass of starch, and 5% to 15% by mass of polyvinyl alcohol.

[0040] In this embodiment, the moisture content (the ratio of moisture to the entire molding material) is set to 20% by mass or more and 60% by mass or less.

[0041] The molding material of this example can be obtained by adding water to a mixture of wood pulp, starch, and polyvinyl alcohol and kneading (while heating) it until the moisture content is 20% by mass or more and 60% by mass or less.

[0042] If the moisture content of the molding material after kneading (including pellets and tablets) is less than 20% by mass, the fluidity of the molding material will be significantly reduced, making molding difficult, which is not preferred. On the other hand, if the moisture content exceeds 60% by mass, molding will be difficult due to the low viscosity, and degassing and releasing water vapor during injection molding will take a long time, which will result in a long molding time and a decrease in production efficiency, which is also not preferred.

[0043] The molding material is filled into a heated injection mold or compression mold, and the added water is evaporated to remove the material, which is then dried and solidified, and the material is then removed to produce a molded product.

[0044] Since this embodiment is configured as described above, it is possible to realize a molding material that can shorten the cycle time and improve the surface properties compared to conventional materials.

[0045] An experimental example that supports the effect of this embodiment will be described.

[0046] [Experimental Example] Molding materials containing predetermined amounts of pulp, starch, and PVA, as shown in Tables 1 and 2, and adjusted to a predetermined moisture content (approximately 40%), were placed in an injection molding machine (NEX5000, manufactured by Nissei Plastic Industrial Co., Ltd.) to produce 1 mm thick JIS No. 1 test pieces specified in JIS K7113. The tensile strength, bending strength, and surface properties were evaluated using these. Table 1 shows comparative examples, and Table 2 shows experimental examples. Comparative examples are examples that do not contain dry-defibrated wood pulp, and experimental examples are examples that contain dry-defibrated wood pulp.

[0047] The tensile strength was measured at a pulling rate of 50 mm / min in accordance with JIS K 7113. The flexural strength was measured according to JIS K 7171. The results of the tensile test are shown in the columns for tensile stress, elongation, and tensile modulus of elasticity in the table, and the results of the flexural test are shown in the columns for flexural stress, strain, and flexural modulus of elasticity in the table.

[0048] The surface properties were evaluated visually, with a rating of ◯ if the surface was smooth with minute irregularities, and × if it was not smooth.

[0049]

[0050]

[0051] As shown in Table 3, one or two of the following pulps were used: NBKP (softwood kraft pulp, undefibrated), LBKP (hardwood kraft pulp, undefibrated), powder pulp (Sanyo Chemical #4000 (pure pulp FP-150)), defibrated NBKP (dry-defibrated; Φ is the screen diameter of the dry defibrator; the smaller the screen diameter, the shorter the fiber length), and defibrated LBKP (dry-defibrated; screen diameter is the same as above). Fiber length is the average fiber length, fiber width is the average fiber width, and fine ratio is the proportion of fibers with a fiber length of less than 0.2 mm. Dry defibration results in a higher fine ratio (17% or more) than undefibrated material.

[0052]

[0053] From Tables 1 and 2, it was confirmed that the cycle time was less than 60 seconds in all experimental examples, less than 50 seconds in experimental examples 2 to 5 and 8, and particularly less than 40 seconds in experimental example 3, which confirmed that the cycle time was shorter than in the comparative examples. In other words, it was confirmed that the cycle time can be shortened by using wood pulp dry-defibrated with a smaller screen diameter.

[0054] Furthermore, the tensile strength and bending strength of the experimental examples were comparable to those of the comparative examples, and it was confirmed that the tensile strength and bending strength were particularly good when dry-defibrated wood pulp and non-defibrated wood pulp were mixed in equal proportions. Note that there are no problems in use if the tensile stress is 20 MPa or more, the elongation is 2.5% or less, the tensile modulus is 2500 MPa or more, the bending stress is 35 MPa or more, the strain is 31% or less, and the bending modulus is 2500 MPa or more, but it is preferable that the tensile stress is 25 MPa or more and the bending stress is 40 MPa or more.

[0055] Furthermore, it was confirmed that the surface properties were not smooth in Comparative Examples 1 and 3 to 5, but were smooth in all of the experimental examples.

[0056] Although the pulp powder has a high fine ratio and a short average fiber length, the strength of the molded product is insufficient (the tensile strength and bending strength of Comparative Example 5 were unmeasurable).

[0057] From the above, it has been confirmed that by using dry-defibrated softwood pulp or hardwood pulp having a specified average fiber length and average fiber width, it is possible to shorten the cycle time and improve the surface quality while maintaining or improving the strength.

Claims

1. A molding material comprising pulp and a water-soluble binder, wherein the pulp comprises dry-defibrated wood pulp.

2. A molding material according to claim 1, characterized in that the dry-defibrated wood pulp has a fiber length of 0.3 mm or more and 1.2 mm or less, and contains 30 mass% or more of the dry-defibrated wood pulp among the components other than water.

3. A molding material according to claim 2, characterized in that the dry-defibrated wood pulp is softwood pulp with a fiber length of 0.5 mm or more and 1.2 mm or less and a fiber width of 25 μm or more and 32 μm or less, or hardwood pulp with a fiber length of 0.3 mm or more and 0.8 mm or less and a fiber width of 15 μm or more and 25 μm or less.

4. A molding material according to claim 2, characterized in that the pulp contains undefibrated wood pulp, and the undefibrated wood pulp accounts for 40% by mass or less of the components other than water.

5. A molding material according to claim 3, characterized in that the pulp contains undefibrated wood pulp, and the molding material contains 40% by mass or less of the undefibrated wood pulp among the components other than water.

6. The molding material according to claim 4, characterized in that the components other than water include 50% by mass to 80% by mass of pulp and 20% by mass to 50% by mass of a water-soluble binder.

7. The molding material according to claim 5, characterized in that it contains, as components other than water, 50% by mass to 80% by mass of pulp and 20% by mass to 50% by mass of a water-soluble binder.

8. The molding material according to claim 6, wherein the water-soluble binder contains starch and polyvinyl alcohol, and the molding material contains, among the components other than water, 5% by mass or more and 45% by mass or less of the starch and 5% by mass or less and 15% by mass or less of the polyvinyl alcohol.

9. The molding material according to claim 7, wherein the water-soluble binder contains starch and polyvinyl alcohol, and the molding material contains, among the components other than water, 5% by mass or more and 45% by mass or less of the starch and 5% by mass or less and 15% by mass or less of the polyvinyl alcohol.

10. The molding material according to any one of claims 1 to 9, characterized in that the moisture content is 20% by mass or more and 60% by mass or less.

11. A method for producing a molded product, comprising injection molding or compression molding the molding material according to claim 10 to obtain the molded product.

12. A molded product produced by the method of claim 11, characterized in that the molded product has a tensile stress of 20 MPa or more and a bending stress of 35 MPa or more.

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