JP6920604B2 - Foam molded product and its manufacturing method - Google Patents

Description

The present invention relates to a foam molded product and a method for producing the same.

A foamed molded product using a foamed resin obtained by foaming a thermoplastic resin with a foaming agent is known (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2012-034998

Foam moldings are lightweight, but tend to be inferior in mechanical properties to non-foam moldings. A method of improving the mechanical properties of the foamed molded product by adding a filler such as talc to the foamed resin can be considered, but according to a preliminary experiment by the present inventor, even if 1.5% by mass of talc is added to the foamed resin, it is possible. It was found that the mechanical properties were hardly improved, and that the moldability deteriorated when the amount of talc added was increased.

The present invention has been made in view of such circumstances, and provides a method for producing a foamed molded product, which has good moldability and can significantly improve the mechanical properties of the foamed molded product.

According to the present invention, there is provided a method for producing a foamed molded article, which comprises a step of molding a foamed resin containing insoluble fibers, and the content of the insoluble fibers in the foamed resin is 0.3 to 3% by mass. Will be done.

As a result of diligent studies by the present inventor to improve the mechanical properties of the foamed molded product, the moldability is good when the content of the insoluble fiber in the foamed resin is 0.3 to 3% by mass. Moreover, they have found that the mechanical properties of the foam molded product are significantly improved, and have reached the completion of the present invention.

Hereinafter, various embodiments of the present invention will be illustrated. The embodiments shown below can be combined with each other.
Preferably, the content of the insoluble fiber is 0.6 to 2.1% by mass.
Preferably, the insoluble fiber is glass fiber or carbon fiber.
Preferably, the insoluble fiber has an average length of 50 to 500 μm in the foam molded product.
Preferably, the average length is 70-120 μm.
Preferably, the foam molded product has a tensile elastic modulus of 400 MPa or more.
According to another aspect of the present invention, there is provided a foam molded product containing insoluble fibers, wherein the content of the insoluble fibers is 0.3 to 3% by mass.

An example of an effervescent molding machine 1 that can be used in the method for producing an effervescent molded article according to an embodiment of the present invention is shown. It is a schematic diagram which shows the structure of the foam molded article of one Embodiment of this invention. It is a schematic diagram which shows the structure of the foam molded article which added the insoluble fiber excessively. It is a cross-sectional photograph of the foam molded product of Example 3.

Hereinafter, embodiments of the present invention will be described. The various features shown in the embodiments shown below can be combined with each other. In addition, the invention is independently established for each feature.

The method for producing a foamed molded article according to an embodiment of the present invention includes a step of molding a foamed resin containing insoluble fibers, and the content of the insoluble fibers in the foamed resin is 0.3 to 3% by mass. ..

Hereinafter, with reference to FIG. 1, a method for producing a foam molded product according to an embodiment of the present invention and a foam molding machine 1 that can be used for carrying out the method will be described. The foam molding machine 1 includes a resin supply device 2, a head 18, and a split mold 19. The resin supply device 2 includes a hopper 12, an extruder 13, an injector 16, and an accumulator 17. The extruder 13 and the accumulator 17 are connected via a connecting pipe 25. The accumulator 17 and the head 18 are connected via a connecting pipe 27.
Hereinafter, each configuration will be described in detail.

<Hopper 12, extruder 13>
The hopper 12 is used to charge the raw material composition 11 into the cylinder 13a of the extruder 13. The form of the raw material composition 11 is not particularly limited, but is usually in the form of pellets. The raw material resin contained in the raw material composition 11 is a thermoplastic resin such as polyolefin, and the polyolefin includes low density polyethylene, linear low density polyethylene, high density polyethylene, polypropylene, ethylene-propylene copolymer and the like. Examples include mixtures. The raw material composition 11 is charged into the cylinder 13a from the hopper 12 and then heated in the cylinder 13a to be melted into a molten resin. Further, it is conveyed toward the tip of the cylinder 13a by the rotation of the screw arranged in the cylinder 13a. The screw is arranged in the cylinder 13a, and the molten resin is kneaded and conveyed by its rotation. A gear device is provided at the base end of the screw, and the screw is rotationally driven by the gear device. The number of screws arranged in the cylinder 13a may be one or two or more.

The raw material composition 11 contains an insoluble fiber in an amount such that the content of the insoluble fiber in the foamed resin 11a described later is 0.3 to 3% by mass. The raw material composition 11 usually contains baking soda, talc, or the like as a nucleating agent for foaming, but in the present embodiment, since the insoluble fiber functions as a nucleating agent, it is not necessary to add the nucleating agent separately. Further, as shown in FIG. 2, the foamed molded product 31 is configured by dispersing a large number of bubbles 33 in the resin portion 32, but since the insoluble fiber functions as a nucleating agent, it corresponds to each bubble 33. The insoluble fiber 34 is arranged as described above. Since the insoluble fiber 34 has a certain length, each bubble is reinforced by the insoluble fiber 34. When a granular filler such as talc is added, the air bubbles are not strengthened, so that the mechanical properties of the foamed molded product are hardly improved. Further, as shown in FIG. 2, the bubbles 33 generated by using the insoluble fibers 34 as a nucleating agent tend to have an elongated shape, and the insoluble fibers 34 tend to be oriented along the longitudinal direction of the bubbles 33. When a force in the bending direction of the elongated bubble 33 is applied, the bubble 33 is easily destroyed. However, since the insoluble fiber 34 is oriented along the longitudinal direction of the bubble 33, the strength of the elongated bubble 33 against the bending force is applied. Is particularly strengthened to improve the mechanical properties of the foam molded body 31.

By containing 0.3% by mass or more of insoluble fibers in the foamed resin 11a, the mechanical properties of the foamed molded product are improved. Further, if the content of the insoluble fiber exceeds 3% by mass, the moldability of the foamed resin 11a may deteriorate, but by setting this content to 3% by mass or less, the moldability of the foamed resin 11a becomes good. .. Further, when the content of the insoluble fiber exceeds 3% by mass, as shown in FIG. 3, the excessively formed bubbles 33 are arranged continuously or close to each other in the thickness direction of the foamed molded product 31. Although the strength of the foamed molded product 31 is significantly reduced, the occurrence of such a problem is suppressed by reducing the content to 3% by mass or less.

By the way, the effect of containing a filler such as insoluble fiber or talc is significantly different between the foamed molded product and the solid (non-foamed) molded product. In the foam molded product, the mechanical properties increase as the content of the insoluble fibers increases up to 0.9% by mass of the insoluble fibers, but even if the content of the insoluble fibers is further increased, the mechanical properties are further increased. No improvement is seen, and when the content of the insoluble fiber exceeds 3% by mass, the mechanical properties deteriorate. On the other hand, in the solid molded product, when the content of the insoluble fiber is 0.9% by mass, the mechanical properties are not significantly improved, and when the content of the insoluble fiber is 3% by mass, the foamed molded product is the insoluble fiber. The same improvement in mechanical properties as in the case of containing 3% by mass is observed. Further, when the content of the insoluble fiber is set to 6 to 9% by mass, the mechanical properties are further significantly improved as compared with the case of 3% by mass. Therefore, in a solid molded product, 6 to 9% by mass of insoluble fiber is usually added, and the content of insoluble fiber of 0.3 to 3% by mass in the present embodiment is usually added in a solid molded product. Is the content not adopted. Further, talc is a typical filler for improving the mechanical properties of a solid molded product, but even if talc is contained in the foam molded product, the mechanical properties are hardly improved. For this reason, no attempt has been made so far to improve the mechanical properties of the foam molded product by adding a filler. In such a situation, the present inventor has found that the addition of a small amount of insoluble fiber has the effect of significantly improving the mechanical properties of the foamed molded product, but such an effect cannot be predicted from the prior art. rice field.

The insoluble fiber may be added as it is, but from the viewpoint of ease of handling, it is preferable to add the insoluble fiber in the form of a master batch containing the insoluble fiber. The insoluble fiber is a fiber that does not melt and disappear in the foam molding step, and is preferably an inorganic fiber, more preferably a glass fiber or a carbon fiber. The content of the insoluble fiber is preferably 0.5% by mass or more, more preferably 0.6% by mass or more. In this case, the mechanical properties of the foam molded product are significantly improved. The content of the insoluble fiber is preferably 2.5% by mass or less, more preferably 2.1% by mass or less. In this case, the moldability of the foamed resin 11a is further improved. Specifically, the content of the insoluble fiber is, for example, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2. , 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5 It is 2.6, 2.7, 2.8, 2.9, and 3% by mass, and may be within the range between any two of the numerical values exemplified here.

The average length of the insoluble fiber in the foam molded product is, for example, 50 to 500 μm, preferably 70 to 120 μm, and specifically, for example, 50, 70, 100, 120, 150, 200, 250, 300, 350. , 400, 450, 500 μm, and may be within the range between any two of the numerical values exemplified here. The average diameter of the insoluble fiber in the foam molded product is, for example, 1 to 30 μm, and specifically, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, ... It is 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30 μm, and is between any two of the numerical values exemplified here. It may be within the range. The average aspect ratio of the insoluble fiber in the foam molded product is, for example, 3 to 100, preferably 5 to 25, and specifically, for example, 3, 5, 10, 15, 20, 25, 30, 35, 40. , 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, and may be within the range between any two of the numerical values exemplified here.

The average length, average diameter, and average aspect ratio of the insoluble fiber in the foamed molded body are (thickness of the foamed molded body) × (twice the thickness of the foamed molded body) in the cross section of the foamed molded body. The constituent image is cut out, all the fibers having a length of 30 to 1000 μm that can be visually recognized in the image are picked up, and the length, diameter, and aspect ratio (length / diameter) of each fiber are measured, and the measured value is measured. Can be calculated by averaging.

The average length of the insoluble fiber in the pellet state is, for example, 1 to 10 mm, preferably 2 to 5 mm, specifically, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, and so on. It is 10 mm and may be within the range between any two of the numerical values exemplified here. The average diameter of the insoluble fiber in the pellet state is the same as the average diameter of the insoluble fiber in the foam molded product. The average aspect ratio of the insoluble fiber in the pellet state is, for example, 100 to 2000, specifically, for example, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1100, 1200, It is 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000, and may be within the range between any two of the numerical values exemplified here. For the average length, average diameter, and average aspect ratio of insoluble fibers in the pellet state, 10 insoluble fibers observed on the surface of the pellet were randomly extracted, and the length, diameter, and aspect ratio of each fiber were measured. Then, it can be calculated by calculating and averaging the measured values.

<Injector 16>
The cylinder 13a is provided with an injector 16 for injecting a foaming agent into the cylinder 13a. Examples of the foaming agent injected from the injector 16 include a physical foaming agent, a chemical foaming agent, and a mixture thereof, and a physical foaming agent is preferable. As the physical foaming agent, inorganic physical foaming agents such as air, carbon dioxide, nitrogen gas, and water, organic physical foaming agents such as butane, pentane, hexane, dichloromethane, and dichloroethane, and their supercritical fluids are used. be able to. As the supercritical fluid, it is preferable to use carbon dioxide, nitrogen, etc., for nitrogen, the critical temperature is -149.1 ° C, the critical pressure is 3.4 MPa or more, and for carbon dioxide, the critical temperature is 31 ° C, the critical pressure. It is obtained by setting the pressure to 7.4 MPa or more. Examples of the chemical foaming agent include those that generate carbon dioxide gas by a chemical reaction between an acid (eg, citric acid or a salt thereof) and a base (eg, baking soda). The chemical foaming agent may be injected from the hopper 12 instead of being injected from the injector 16.

<Accumulator 17, head 18>
A foamed resin 11a formed by melt-kneading the raw material composition 11 and the foaming agent is formed. The content of the insoluble fiber in the foamed resin 11a is 0.3 to 3% by mass. The foamed resin 11a is extruded from the resin extrusion port of the cylinder 13a and injected into the accumulator 17 through the connecting pipe 25. The accumulator 17 includes a cylinder 17a and a piston 17b slidable inside the cylinder 17a, and the foamed resin 11a can be stored in the cylinder 17a. Then, by moving the piston 17b after the foamed resin 11a is stored in the cylinder 17a in a predetermined amount, the foamed resin 11a is pushed out from the die slit provided in the head 18 through the connecting pipe 27 and hung down to form the foamed parison 23. To form. The shape of the foamed parison 23 is not particularly limited, and may be cylindrical or sheet-shaped.

<Split mold 19>
The foamed parison 23 is guided between a pair of split molds 19. A foamed molded product is obtained by molding the foamed parison 23 using the split mold 19. The molding method using the split mold 19 is not particularly limited, and may be blow molding in which air is blown into the foamed parison 23 after mold clamping to perform molding, from the inner surface of the cavity of the split mold 19 to the inside of the cavity. May be vacuum molding in which the foamed parison 23 is molded by reducing the pressure, or a combination thereof may be used. The foaming ratio of the foam molded product is, for example, 1.5 to 6 times, and specifically, for example, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5. It is 5 or 6 times, and may be within the range between any two of the numerical values exemplified here. The foaming ratio can be calculated based on the following mathematical formula (1).
Foaming ratio = (specific gravity of unexpanded raw material composition 11) / (specific gravity of foamed molded product) ... (1)

The tensile elastic modulus of the foam molded product is, for example, 250 MPa to 800 MPa, preferably 400 MPa or more. By including an appropriate amount of insoluble fiber in the foamed molded product, the tensile elastic modulus of the foamed molded product can be 400 MPa or more. Specifically, the tensile elastic modulus is, for example, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800 MPa, and is in the range between any two of the numerical values exemplified here. It may be inside.

A cylindrical foam molded product was produced using the foam molding machine 1 shown in FIG. The inner diameter of the cylinder 13a of the extruder 13 was 50 mm, and L / D = 34. The raw material composition contains polypropylene-based resin A (manufactured by Borealis AG, trade name "Daple WB140") and polypropylene-based resin B (manufactured by Japan Polypropylene Corporation, trade name "Novatec PP / BC4BSW") by mass. The mixture was mixed at a ratio of 60:40, and an inorganic filler of the type and parts by mass shown in Table 1 was added to 100 parts by mass of the resin. The insoluble fiber is added in the form of pellets containing the resin and the insoluble fiber, but the mass part of the insoluble fiber in Table 1 is not the mass part of the whole pellet but the mass part of only the insoluble fiber. The temperature of each part was controlled so that the temperature of the foamed parison 23 was 190 to 200 ° C. The rotation speed of the screw was 60 rmm, and the extrusion rate was 20 kg / hr. Blowing agent, using N ₂ gas was injected through the injector 16. N ₂ was injected in an amount such that the foaming ratio of the finally molded molded product was 2.8 to 3.0. The foamed parison 23 was formed so that the thickness of the molded product was about 2 mm.

The foamed parison 23 formed under the above conditions is placed between the split molds 19, and after molding, blow molding is performed by blowing air into the foamed parison 23 to obtain a foamed molded product having a thickness of about 2 mm. After forming, the foam molded product was subjected to a tensile test and evaluated according to the following criteria. The tensile test was performed in accordance with JIS K 7113. The tensile test speed was 50 mm / min, and the dumbbell shape for the test was No. 2.

(Moldability)
⊚: A foam molded product having a desired shape was obtained.
◯: A foamed molded product having a desired shape was obtained, but air bubbles were accumulated on the surface of the foamed molded product.
X: A foam molded product having a desired shape could not be obtained.

(Breaking point strength)
⊚: 7.5 MPa or more ○: 6.5 MPa or more and less than 7.5 MPa Δ: 5.5 MPa or more and less than 6.5 MPa ×: less than 5.5 MPa

(Tensile modulus)
⊚: 500 MPa or more ○: 400 MPa or more and less than 500 MPa Δ: 270 MPa or more and less than 400 MPa ×: less than 270 MPa

The following are used as the inorganic fillers in Table 1.
Carbon fiber (short fiber): Mitsubishi Rayon PYROFIL PP-C-30A, pellet length 3 mm, diameter 6 μm
Carbon fiber (long fiber): PPLCF30 manufactured by Chuo Kasei, length 7 mm in pellet state, diameter 6 μm
Glass fiber: Asahi Fiber Glass Co., Ltd., GF PP-MG60, length 3 mm in pellet state, diameter 17 μm
Talc: Made of Shiraishi Calcium, MAT-725TP

As shown in Comparative Examples 5 to 7, even if 0.3 to 1.5% by mass of talc was added, the mechanical properties (breaking point strength / tensile elastic modulus) were hardly improved. On the other hand, when 3% by mass of talc was added, the moldability was significantly deteriorated. On the other hand, as shown in Examples 1 to 10, when 0.3 to 3% by mass of insoluble fiber was added, the breaking point strength was remarkably improved. Further, when 0.6 to 3% by mass of insoluble fiber was added, the breaking point strength was further improved and the tensile elastic modulus was also remarkably improved. Further, when 3% by mass of insoluble fiber was added, the moldability was slightly deteriorated, but when the carbon fiber was a short fiber, the moldability was deteriorated when the addition amount of the insoluble fiber was 2.1% by mass or less. I couldn't. When the carbon fiber was a long fiber, the moldability was worse than that of the short fiber.

A cross-sectional photograph of the foam molded product of Example 3 is shown in FIG. It can be seen that elongated bubbles are formed and the insoluble fibers are oriented along the longitudinal direction of the bubbles. The average length of the carbon fibers (short fibers) contained in the foam molded product of Example 3 was 100 μm. The average length of the carbon fibers (long fibers) contained in the foam molded product of Example 7 was 150 μm. Since the insoluble fibers are broken during melt kneading or the like, the average length of the insoluble fibers contained in the foamed molded product is shorter than the length of the insoluble fibers in the pellet state.

1: Foam molding machine 2: Resin supply device 11: Raw material composition 11a: Foam resin 12: Hopper 13: Extruder 13a: Cylinder 16: Injector 17: Accumulator 17a: Cylinder 17b: Piston 18: Head 19: Split mold 23 : Foamed parison 25: Connecting pipe 27: Connecting pipe 31: Foamed molded product 32: Resin part 33: Bubbles 34: Insoluble fiber

Claims (6)

A step of blow molding a polyolefin foam resin containing insoluble fiber is provided.
A method for producing a foamed molded product, wherein the content of the insoluble fiber in the foamed resin is 0.3 to 3% by mass. The method according to claim 1, wherein the content of the insoluble fiber is 0.6 to 2.1% by mass. The method according to claim 1 or 2, wherein the insoluble fiber is glass fiber or carbon fiber. The method according to any one of claims 1 to 3, wherein the insoluble fiber has an average length of 50 to 500 μm in the foamed molded product. The method according to claim 4, wherein the average length is 70 to 120 μm. The method according to any one of claims 1 to 5, wherein the foamed molded product has a tensile elastic modulus of 400 MPa or more.

Images