Method for manufacturing an injection molded article

Abstract

To provide a method for manufacturing an injection molded article that contributes to global environmental preservation, sufficiently suppresses molding defects, and is useful for expanding a range of plant-derived polyethylene options used in combination with fossil fuel-derived polypropylene resin.SOLUTION: A method for manufacturing an injection molded article according to the present disclosure includes: a process of preparing a raw material containing plant-derived polyethylene resin and fossil fuel-derived polypropylene resin; and a process of supplying the raw material into a cavity through a gate. The gate has a flow path with a flatness f of cross section of 0.5 or more, as calculated by a following equation (1). The flatness f=(a-b) / a...(1) [In the equation, a represents a longitudinal width of the cross section of the flow path and b represents a short directional width of the cross section of the flow path.]SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing an injection molded article.

Background Art

[0002] From the perspective of global environmental conservation, the development of plastic materials using plant-derived raw materials has been underway. Patent Document 1 discloses a method for producing one or more olefins from residues of renewable natural raw materials (e.g., sugarcane) and also discloses polymers using these.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the field of injection molding using a plastic material as a raw material, using a plant-derived raw material as part of the raw material contributes to global environmental conservation. Therefore, the present inventors prepared a raw material by blending a plant-derived polyethylene resin and a fossil fuel-derived polypropylene resin, and supplied this to a mold of a cold runner system to manufacture an injection molded article. However, solidified resin remained at the gate portion of the molded article taken out from the mold. This is a type of molding defect and is called gate residue.

[0005] Referring to FIGS. 1(a) and 1(b), the gate residue will be described. FIG. 1(a) is a cross-sectional view schematically showing a state where a plastic material P is filled in a cavity C defined by a pair of molds 1a and 1b. The gate G1 shown in this figure is a flow path connecting a cold runner (not shown) and the cavity C. The plastic material P is supplied into the cavity C through the gate G1. In this state, the gate G1 is also filled with the plastic material P. FIG. 1(b) is a cross-sectional view schematically showing an injection molded body 10 recovered from the molds 1a and 1b. The injection molded body 10 has a protrusion 10a (gate residue) of the plastic material P at the gate portion.

[0006] According to the study by the present inventors, when a raw material obtained by blending a plant-derived polyethylene resin and a fossil fuel-derived polypropylene resin was supplied to a conventional mold to produce an injection molded body, when high-density polyethylene (HDPE) was used as the plant-derived polyethylene resin, gate residue was more likely to occur than when low-density polyethylene (LDPE) was used.

[0007] If the range in which a plant-derived polyethylene resin can be applied in the field of injection molded products can be further expanded, it can contribute to global environmental conservation. Therefore, the present inventors have proceeded with studies on a method for suppressing gate residue even when HDPE is used as the plant-derived polyethylene used in combination with a fossil fuel-derived polypropylene resin.

[0008] The present disclosure provides a method for manufacturing an injection molded body that contributes to global environmental conservation, sufficiently suppresses the occurrence of molding defects, and is useful for expanding the options of plant-derived polyethylene used in combination with a fossil fuel-derived polypropylene resin.

Means for Solving the Problems

[0009] The manufacturing method of an injection molded article according to one aspect of the present disclosure includes a step of preparing a raw material containing a plant-derived polyethylene resin and a fossil fuel-derived polypropylene resin, and a step of supplying the raw material into a cavity through a gate. The gate has a flow path with a flatness f of the cross section calculated by the following formula (1) being 0.5 or more. Flatness f = (a - b) / a…(1) [In the formula, a represents the longitudinal width of the cross section of the flow path, and b represents the lateral width of the cross section of the flow path.]

[0010] According to the above manufacturing method, since a plant-derived resin material is used as part of the raw material, it can contribute to global environmental conservation. Further, according to the above manufacturing method, not only when using LDPE but also when using HDPE as the plant-derived polyethylene resin used in combination with the fossil fuel-derived polypropylene resin, the occurrence of molding defects can be sufficiently suppressed. "The occurrence of molding defects can be sufficiently suppressed" in this specification means that the height of the gate residue of the injection molded article (the length from the product part to the tip of the gate residue) is 0.5 mm or less.

[0011] Based on the total mass of the above plant-derived polyethylene resin and the above fossil fuel-derived polypropylene resin, the content of the plant-derived polyethylene resin may be 10 to 50% by mass, and the content of the fossil fuel-derived polypropylene resin may be 50 to 90% by mass. If the ratio of the plant-derived polyethylene resin contained in the injection molded article is within the above range, it can contribute to global environmental conservation in terms of carbon neutrality, and if the ratio of the fossil fuel-derived polypropylene resin is within the above range, physical properties such as excellent moldability due to the fossil fuel-derived polypropylene resin are likely to be exhibited in the injection molded article.

[0012] The above plant-derived polyethylene resin may be HDPE. The above manufacturing method is useful in that it can stably suppress the occurrence of molding defects not only when using LDPE but also when using HDPE as the plant-derived polyethylene resin. The above fossil fuel-derived polypropylene resin may be a random copolymer.

Advantages of the Invention

[0013] According to the present disclosure, there is provided a method for manufacturing an injection molded article that contributes to global environmental conservation, can sufficiently suppress the occurrence of molding defects, and is useful for expanding the options of plant-derived polyethylene used in combination with fossil fuel-derived polypropylene resin.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0015] Hereinafter, embodiments of the present disclosure will be described in detail. Note that the present invention is not limited to the following embodiments.

[0016] <Method for Manufacturing an Injection Molded Article> The method for manufacturing an injection molded article according to the present embodiment includes the following steps. (A) A step of preparing a raw material containing a plant-derived polyethylene resin and a fossil fuel-derived polypropylene resin. (B) A step of supplying the raw material into the cavity through a gate.

[0017] (Raw Material for Manufacturing an Injection Molded Article) First, the raw materials for manufacturing the injection molded article will be described. As described above, this raw material contains a plant-derived polyethylene resin and a fossil fuel-derived polypropylene resin. Examples of the plant-derived polyethylene resin include those manufactured by Braskem. Braskem manufactures linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE), and low-density polyethylene (LDPE) from renewable natural raw materials and sells them. For example, plant-derived LLDPE has a C4 or C6 α-olefin having 4 or 6 carbon atoms in the side chain, which is denoted as C4-LLDPE or C6-LLDPE.

[0018] The melt flow rate of the plant-derived polyethylene resin at 190°C is not particularly limited. For example, it is 25 g / 10 min or less, preferably 20 g / 10 min or less. When this value is 20 g / 10 min or less, even when the plant-derived polyethylene resin is used in combination with the fossil fuel-derived polypropylene resin, the occurrence of molding defects can be sufficiently suppressed. This value is, for example, 5 g / 10 min or more, preferably 7 g / 10 min or more. When this value is 7 g / 10 min or more, even if the proportion of the plant-derived polyethylene resin in the raw material is relatively large, the fluidity of the raw material can be sufficiently maintained. Also, even when the plant-derived polyethylene resin and the fossil fuel-derived polypropylene are blended, basic functions such as the drop strength of the injection molded product can be satisfied. The value of the melt flow rate in the present disclosure means a value measured under the conditions of a predetermined temperature (190°C or 230°C described later) and a load of 2.16 kg in accordance with the method described in JIS K7210-1:2014.

[0019] The density of the plant-derived polyethylene resin is, for example, 0.910 to 0.960 g / cm 3 and may be 0.915 to 0.918 g / cm 3 or 0.953 to 0.959 g / cm 3 When the density of the plant-derived polyethylene resin is within this range, even when the plant-derived polyethylene resin is used in combination with the fossil fuel-derived polypropylene resin, the occurrence of molding defects can be sufficiently suppressed.

[0020] Examples of the fossil fuel-derived polypropylene resin include a homopolymer of propylene, a block copolymer, and a random copolymer. From the viewpoint of moldability, it is preferable to use a random copolymer of propylene.

[0021] The melt flow rate of the fossil fuel-derived polypropylene resin at 230 °C may be, for example, 30 g / 10 min or less, and more preferably 25 g / 10 min or less. When this value is 25 g / 10 min or less, even if the proportion of the plant-derived polyethylene resin in the raw material is relatively large, the occurrence of molding defects can be sufficiently suppressed. This value is preferably 3 g / 10 min or more, more preferably 5 g / 10 min or more, and still more preferably 7 g / 10 min or more. When this value is 3 g / 10 min or more, even if the proportion of the fossil fuel-derived polypropylene resin in the raw material is large, the fluidity of the raw material can be sufficiently maintained.

[0022] The density of the fossil fuel-derived polypropylene resin is, for example, 0.900 to 0.910 g / cm 3 When the density of the fossil fuel-derived polypropylene resin is within this range, even if the plant-derived polyethylene resin is used in combination with the fossil fuel-derived polypropylene resin, the occurrence of molding defects can be sufficiently suppressed.

[0023] Based on the total mass of the plant-derived polyethylene resin and the fossil fuel-derived polypropylene resin, the content of the plant-derived polyethylene resin in the raw material is 10 to 50% by mass, preferably 10 to 30% by mass, and more preferably 10 to 20% by mass. When this value is 10% by mass or more, it can contribute to the conservation of the global environment in terms of carbon neutrality. On the other hand, based on the same standard, the content of the fossil fuel-derived polypropylene resin in the raw material is 50 to 90% by mass, preferably 70 to 90% by mass, and more preferably 80 to 90% by mass. When this value is 50% by mass or more, the effects attributable to the polypropylene resin (e.g., excellent moldability and physical properties) can be sufficiently exhibited.

[0024] The total amount of the plant-derived polyethylene resin and the fossil fuel-derived polypropylene resin with respect to the total mass of the raw materials is, for example, 90% by mass or more, and may be 95% by mass or more or 98% by mass or more. In addition to the plant-derived polyethylene resin and the fossil fuel-derived polypropylene resin, the raw materials may contain, for example, additives and the like compounded in the raw materials of the injection molded article.

[0025] The raw materials can be prepared by mixing or kneading a plant-derived polyethylene resin, a fossil fuel-derived polypropylene resin, and, if necessary, other components ((step A)). An injection molded article can be obtained through the step of supplying the melt of this raw material into the cavity of the mold through the gate ((step B)). The preparation of the raw materials and the supply of the raw materials to the mold may be carried out by a kneading extruder. For example, when using a kneading extruder having a screw, the screw temperature may be adjusted according to the melt flow rate (melt viscosity) of the raw materials. The screw temperature may be, for example, 190 to 220°C. The injection speed of the raw materials into the cavity of the mold may be, for example, 30 to 80 mm / second. In addition, when using raw materials with a relatively small melt flow rate value (relatively high melt viscosity), by bringing the V-P switching position in the kneading extruder closer to the nozzle (discharge port) side, the filling property of the raw materials into the cavity can be improved.

[0026] Fig. 2(a) is a cross-sectional view schematically showing a state where the cavity C and the gate G2 are filled with a plastic material, and Fig. 2(b) is a cross-sectional view taken along the line b-b shown in Fig. 2(a). The shape of the cross-section of the flow path of the gate G2 may be flat, and may be, for example, elliptical, rectangular, or rounded rectangular. The flatness f of the cross-section of the flow path of the gate G2 is calculated by the following formula (1). The value of the flatness f is 0.5 or more, preferably 0.6 or more, and more preferably 0.75 or more. By this value being 0.5 or more, the occurrence of molding defects during the production of the injection molded article can be sufficiently suppressed. The upper limit value of this value is, for example, 0.8. Flatness f = (a - b) / a …(1) In formula (1), a represents the longitudinal width of the flow path (width a shown in Fig. 2(b)), and b represents the lateral width of the flow path (width b shown in Fig. 2(b)).

[0027] Note that the entire flow path of gate G2 does not necessarily have to be flat. For example, it may be flat in a region of 5 mm in the direction of gate G2 from the connection part between cavity C and gate G2. The range of this region may be appropriately set according to the shape of the runner and the size of the gate diameter.

[0028] The mold may be of a cold runner type or a hot runner type. However, according to this embodiment, even when using a cold runner type mold that is more likely to have gate residue compared to the hot runner type, the occurrence of gate residue can be sufficiently suppressed. This has the advantage that an injection molded article considering the global environment can be manufactured by using an existing cold runner type mold and replacing the resin raw material derived from conventional fossil fuels with the raw material according to this embodiment. That is, for example, there is an advantage that it is not necessary to newly introduce a hot runner type mold.

[0029] According to the above embodiment, it is possible to efficiently manufacture an injection molded article that contributes to global environmental conservation and sufficiently suppresses the occurrence of molding defects. Specific examples of the injection molded article include plastic caps, containers, and stoppers.

[0030] Although the embodiments of the present disclosure have been described in detail above, the present invention is not limited to the above embodiments. For example, in the above embodiments, the case of manufacturing an injection molded article using a cold runner type mold is exemplified, but an injection molded article may also be manufactured using a hot runner type mold.

[0031] In the above embodiment, the case of using a plant-derived polyethylene resin and a fossil fuel-derived polypropylene resin in combination was exemplified. However, an injection molded article may be manufactured using a fossil fuel-derived polyethylene resin instead of the plant-derived polyethylene resin. The physical properties of the fossil fuel-derived polyethylene resin (for example, melt flow rate and density at 190°C) are preferably in the same range as those of the above-described plant-derived polyethylene resin.

Examples

[0032] Hereinafter, the present disclosure will be described based on examples and comparative examples. Note that the present invention is not limited to the following examples.

[0033] Using the following materials, raw materials according to examples and comparative examples were prepared. <Fossil fuel-derived polypropylene resin (PP)> · PP1 manufactured by Sun Allomer Co., Ltd. (melt flow rate at 230°C: 25.0 g / 10 min) · PP2 manufactured by Sun Allomer Co., Ltd. (melt flow rate at 230°C: 14.0 g / 10 min) · PP3 manufactured by Sun Allomer Co., Ltd. (melt flow rate at 230°C: 9.5 g / 10 min) <Plant-derived polyethylene resin (Bio-PE)> · HDPE manufactured by Braskem (melt flow rate at 190°C: 20.0 g / 10 min) · LDPE1 manufactured by Braskem (melt flow rate at 190°C: 8.3 g / 10 min) · LDPE2 manufactured by Braskem (melt flow rate at 190°C: 7.2 g / 10 min)

[0034] The following injection molded articles according to examples and comparative examples were produced under the conditions shown in Tables 1 to 4. · Injection molded article: Cap with hinge (diameter: 68.4 mm, height: 22.2 mm) FIG. 3 is a cross-sectional view schematically showing the caps (injection molded articles) produced in the examples and comparative examples. As shown in this figure, the cap 20 includes an upper lid 20a, a cap body portion 20b, and a hinge 20c that enables the upper lid 20a to be opened and closed with respect to the cap body portion 20b. The "gate height" in Tables 1 to 4 means the remaining height of the gate (see FIG. 1(b)).

[0035] As the molding machine, an injection molding machine manufactured by Sumitomo Heavy Industries, Ltd. was used. A cold runner type mold was used for the mold. FIG. 4 is a perspective view schematically showing the molds used in the examples and comparative examples. As shown in this figure, the mold 5 includes three parts 5a, 5b, and 5c. According to the mold 5, a total of eight caps 20 can be manufactured simultaneously. The part 5a has an opening 6. Molten resin is supplied into the mold 5 through the opening 6. The part 5b has a cold runner 7. The part 5c, together with the part 5b, has a recess 8 that forms a cavity.

[0036]

Table 1

[0037]

Table 2

[0038]

Table 3

[0039]

Table 4

Explanation of Reference Numerals

[0040] 1a, 1b, 5... mold, 5a, 5b, 5c... parts, 6... opening, 7, G2... gate, 8... recess, 10... injection molded body, 10a... protrusion (gate residue), 20... cap (injection molded body), 20a... upper lid, 20b... cap main body part, 20c... hinge, C... cavity, P... plastic material

Claims

1. A step of preparing a raw material containing a plant-derived polyethylene resin and a fossil fuel-derived polypropylene resin; A step of supplying the raw material into a cavity through a gate; comprising: The gate has a flow path with a flatness f of the cross section calculated by the following formula (1) being 0.5 or more. A method for manufacturing an injection molded article. Flatness f = (a - b) / a... (1) [In the formula, a represents the width in the longitudinal direction of the cross section of the flow path, and b represents the width in the short direction of the cross section of the flow path.]

2. Based on the total mass of the plant-derived polyethylene resin and the fossil fuel-derived polypropylene resin, the content of the plant-derived polyethylene resin is 10 to 50% by mass, and the content of the fossil fuel-derived polypropylene resin is 50 to 90% by mass. The manufacturing method according to Claim 1.

3. The manufacturing method according to Claim 1 or 2, wherein the plant-derived polyethylene resin is high-density polyethylene.

4. The manufacturing method according to any one of Claims 1 to 3, wherein the fossil fuel-derived polypropylene resin is a random copolymer.

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