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

Abstract

To provide a molding material, a manufacturing method for a molded product, and a molded product that can shorten the cycle time compared with conventional materials and improve the surface properties of the molded product. The molding material includes pulp and a water-soluble binder, and the pulp includes dry-defibrated wood pulp.

Description

[Technical Field]

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

[0002] The applicant previously held patents such as Patent No. 2951933 (Patent Document 1) for molding materials for injection molding that consist primarily of pulp and starch-based binders.

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

[0004] Incidentally, for the mass production of the above molded products, there is a demand for shortening the cycle time (the time from one injection to the next injection) in injection molding. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 2951933 Summary of the Invention [Problem to be solved by the invention]

[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. [Means for solving the problem]

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

[0008] The present invention relates to a molding material containing pulp and a water-soluble binder, characterized in that the pulp contains dry-defibrated wood pulp.

[0009] Furthermore, in the molding material described in claim 1, the dry-defibrated wood pulp has a fiber length of 0.3 mm or more and 1.2 mm or less, and the molding material is characterized in that it contains 30 mass% or more of the dry-defibrated wood pulp among the components other than water.

[0010] In addition, in the molding material described in claim 2, 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.

[0011] Furthermore, in the molding material described in claim 2, the pulp contains undefibrated wood pulp, and the molding material is characterized in that the undefibrated wood pulp is contained in an amount of 40 mass% or less of the components other than water.

[0012] Furthermore, in the molding material described in claim 3, the pulp contains undefibrated wood pulp, and the molding material is characterized in that the undefibrated wood pulp accounts for 40 mass% or less of the components other than water.

[0013] The molding material according to claim 4 is characterized in that it 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] The molding material according to claim 5 is characterized in that it 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] In addition, in the molding material described in claim 6, the water-soluble binder contains starch and polyvinyl alcohol, and the molding material is characterized in that, among the components other than water, the starch is contained in an amount of 5% by mass to 45% by mass and the polyvinyl alcohol is contained in an amount of 5% by mass to 15% by mass.

[0016] In addition, in the molding material described in claim 7, the water-soluble binder contains starch and polyvinyl alcohol, and the molding material is characterized in that, among the components other than water, the starch is contained in an amount of 5% by mass to 45% by mass and the polyvinyl alcohol is contained in an amount of 5% by mass to 15% by mass.

[0017] The present invention also relates to 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.

[0018] The present invention also relates to a method for producing a molded article, characterized in that the molding material according to claim 10 is injection molded or compression molded to obtain a molded article.

[0019] The present invention also relates to a molded article produced by the method for producing a molded article according to claim 11, characterized in that the molded article has a tensile stress of 20 MPa or more and a bending stress of 35 MPa or more. [Effects of the Invention]

[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. DETAILED DESCRIPTION OF THE INVENTION

[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 the molding material used in molding biodegradable molded products, and as a result, they found that it is preferable to include dry-defibrated wood pulp.

[0023] In other words, it was confirmed that by adding a certain amount of dry-defibrated wood pulp to a molding material containing pulp and a water-soluble binder, the cycle time can be shortened (molding can 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 the water 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. [Example]

[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 may be softwood pulp, hardwood pulp, or a mixture of the two in a predetermined 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-defibrated using a general dry 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 the components other than water.

[0032] Dry-type defibrated wood pulp is so-called cellulose fiber 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 the average fiber length, and the fiber width refers to the 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 through a 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 contains 30 mass% dry-type defibrated softwood pulp and 30 mass% undefibrated softwood pulp among the components other than water (Experimental Example 6 described below). Note that softwood pulp and hardwood pulp can be combined appropriately, and may contain dry-type defibrated softwood pulp and undefibrated hardwood pulp, or may contain dry-type defibrated hardwood pulp and undefibrated softwood pulp.

[0038] Examples of water-soluble binders that can be used include starch and polyvinyl alcohol (PVA). Examples of starch that can be used include corn starch, potato starch, and rice flour. In this example, corn starch is used. In addition, in this example, polyvinyl alcohol is further included to smooth the surface.

[0039] In this example, the components other than water (total solid content being 100% by mass) are 50% to 80% by mass of pulp, 20% to 50% by mass of a water-soluble binder, etc. Specifically, the components are 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 example, 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 (including pellets and tablets) after kneading is less than 20% by mass, the fluidity of the molding material will be significantly reduced, making molding difficult, which is undesirable. 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 undesirable.

[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] As shown in Tables 1 and 2, molding materials were prepared by blending predetermined amounts of pulp, starch, and PVA and adjusting the moisture content (approximately 40%), and the materials 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 test pieces. 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 tension speed 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] [Table 1]

[0050] [Table 2]

[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) compared to undefibrated pulp.

[0052] [Table 3]

[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 not measurable).

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

3. 3. The molding material according to claim 2, 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.

4. 3. The molding material according to claim 2, wherein the pulp contains undefibrated wood pulp, and the molding material contains 40% by mass or less of the undefibrated wood pulp among components other than water.

5. 4. The molding material according to claim 3, wherein the pulp contains undefibrated wood pulp, and the molding material contains 40% by mass or less of the undefibrated wood pulp among components other than water.

6. 5. The molding material according to claim 4, comprising, 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.

7. 6. The molding material according to claim 5, further comprising, 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. 7. 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 more and 15% by mass or less of the polyvinyl alcohol.

9. 8. The molding material according to claim 7, wherein the water-soluble binder contains starch and polyvinyl alcohol, and the molding material contains, among 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.

10. The molding material according to any one of claims 1 to 9, wherein 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 a molded product.

12. A molded product produced by the method for producing a molded product according to 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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