JP2021187039A - Method for molding foam resin sheet - Google Patents

Abstract

To provide a method for molding a foam resin sheet that enables thick wall molding even when, for example, polyethylene is used as a material for a foam resin sheet, and can improve flexural rigidity by thickening and improve performance by continuous foam layers generated inside.SOLUTION: A method for manufacturing a foam resin sheet has a step for molding a foam resin sheet in a molten state by using a mold. After the foam resin sheet in a molten state is sandwiched by a pair of molds, and each mold is brought into contact with each foam resin sheet, each mold is retracted while being vacuum sucked after a predetermined time elapses. Alternatively, after the foam resin sheet in a molten state is sandwiched by the pair of molds, and each mold is brought into contact with each foam resin sheet, each mold is retracted while being vacuum sucked after a surface of the foam resin sheet is hardened. The predetermined time is 1 second or more, or 2 seconds to 6 seconds when the foam resin sheet includes polyethylene, for example.SELECTED DRAWING: Figure 6

Description

The present invention relates to, for example, a method for molding a foamed resin sheet used for interior members for automobiles and industrial members.

Since the foam molded body obtained by molding the foam resin sheet is lightweight, it is used for automobile interiors such as door trims, cargo floor panels, and rear parcel shelves, and architectural interiors such as interior wall partitions and doors.

As a method for molding such a foamed molded product, there is known a method in which a foamed resin sheet is heated and melted, placed between split dies, and molded (see, for example, Patent Document 1). Patent Document 1 discloses a method for molding a foamed resin sheet using a matched mold type compressed air vacuum mold.

Japanese Unexamined Patent Publication No. 4-59223

By the way, as a material of this kind of foamed resin sheet, for example, high melt tension polypropylene suitable for foam molding is often used, but the use of high melt tension polypropylene leads to high cost. As an alternative, it is possible to maintain moldability by blending low-density polyethylene (LDPE) with strain curability, but there is a problem that the foaming ratio does not increase and it is difficult to reproduce the wall thickness with respect to the mold. ..

The present invention has been proposed in view of such conventional circumstances. For example, even when polyethylene is used as the material of the foamed resin sheet, it is possible to form a thick wall, and the bending rigidity due to the thickening can be achieved. It is an object of the present invention to provide a method for molding a foamed resin sheet, which can be improved and the performance can be improved by the open cell layer generated inside.

In order to achieve the above-mentioned object, the method for molding a foamed resin sheet of the present invention is a method for molding a foamed resin sheet including a step of molding a molten foam resin sheet using a mold, and is a method for molding a foamed resin sheet in a molten state. It is characterized in that the foamed resin sheet is sandwiched between a pair of molds, each mold is brought into contact with the foamed resin sheet, and then each mold is retracted while vacuum suctioning after a lapse of a predetermined time. Alternatively, the foamed resin sheet in a molten state is sandwiched between a pair of molds, each mold is brought into contact with the foamed resin sheet, and then the surface of the foamed resin sheet is cured, and then each mold is retracted while vacuum suctioning. Characterized by letting

In the present invention, core back molding is adopted in which the mold is retracted after shaping to expand the mold space, the foaming ratio is increased, and thick wall molding is realized. However, immediately after the mold comes into contact with the foamed resin sheet during core backing, the temperature of the foamed resin sheet is high and the fluidity is high, so it is difficult to retract the foamed resin sheet while keeping it in close contact with the mold by vacuum suction. .. Therefore, even if the mold space is expanded immediately after shaping, a gap is created between the foamed resin sheet and the mold, the bubbles in the foamed resin sheet do not expand completely, and the wall thickness does not sufficiently expand.

Therefore, in the present invention, the molten foam resin sheet is sandwiched between a pair of molds, and after each mold is brought into contact with the foam resin sheet, the core back is not immediately performed, but the core back is performed after a lapse of a predetermined time. I try to do it. After the mold is brought into contact with the foamed resin sheet, the temperature of the surface of the foamed resin sheet decreases with the passage of time, and the surface is hardened to form a so-called skin layer. In this state, the vacuum suction keeps the foamed resin sheet in close contact with the mold, and the core back sufficiently expands the bubbles in the foamed resin sheet and sufficiently expands the wall thickness.

In the present invention, "after a predetermined time" means that after each mold is brought into contact with the foamed resin sheet, the core back is not performed immediately, but the contact state is positively maintained and a certain period of time elapses. It means that the core back is performed (for example, after 1 second or more). For example, depending on the performance and specifications of the device, the mold may stop slightly from the contact with the foamed resin sheet to the retreat. Does not include cases.

According to the present invention, for example, even when polyethylene is used as the material of the foamed resin sheet, it is possible to form a thick wall, and the bending rigidity is improved by the thickening and the performance is improved by the open cell layer generated inside. It is possible.

It is a figure which shows an example of the molding machine for molding a foamed resin sheet. It is a schematic sectional drawing of a foamed resin sheet. It is a schematic cross-sectional view which shows the insertion state between the molds of a foamed resin sheet. It is a figure which shows the state which sandwiched the foamed resin sheet with a mold. It is a figure which shows the state which the surface of the foamed resin sheet is hardened, and the skin layer is formed. It is a figure which shows the core back process which retracts a mold. It is a figure which shows the state of the core back in the state which the surface of the foamed resin sheet is not hardened. It is a figure which shows the relationship between the core back molding timing and the wall thickness of the foamed resin sheet to be molded. It is a figure which shows the state of the bubble of the molded foam resin sheet. It is a figure which shows the foamed resin sheet which had the fine pores formed on one side surface.

Hereinafter, embodiments of a foamed resin sheet molding method to which the present invention is applied will be described in detail with reference to the drawings.

In the molding method of the present embodiment, a foamed resin sheet is core-back molded to form a thick-walled molded product.

Examples of the thermoplastic resin used for the foamed resin sheet include polyolefins, and examples of the polyolefins include low-density polyethylene, linear low-density polyethylene, high-density polyethylene, polypropylene, ethylene-propylene copolymer and the like. Examples thereof include the mixture.

For example, high melt tension polypropylene is suitable as a material for this type of foamed resin sheet, but the use of high melt tension polypropylene leads to high cost. As an alternative, it is conceivable to blend polyethylene such as low density polyethylene (LDPE) having strain curability, but the foaming ratio does not increase and it is difficult to reproduce the wall thickness with respect to the mold. As described above, the molding method of the present invention is effective in molding a foamed resin sheet containing, for example, 50% by mass or more of polyethylene [for example, low density polyethylene (LDPE)] which is disadvantageous in terms of foaming ratio and molding thickness.

The foamed resin sheet is a single-layer resin sheet, but the thickness is increased by vacuum suctioning the inside of the mold at the time of molding, so that the foamed resin sheet is molded in contact with the mold, and as a result, the vicinity of both the front and back surfaces is cooled. It is in a state of being denser (lower foaming ratio) than the central part (a state of having skin layers on the front and back). Therefore, the structure is similar to the so-called double wall structure, and even a single layer has high rigidity.

Hereinafter, a method for molding the foamed resin sheet of the present embodiment will be described.

FIG. 1 shows an example of a molding machine for molding a foamed resin sheet 1. As shown in FIG. 1, the molding machine 10 includes a resin supply device 20, a T-die 18, and molds 30 and 40. The resin supply device 20 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 T-die 18 are connected via a connecting pipe 27.

The hopper 12 is used to charge the raw material resin 11 into the cylinder 13a of the extruder 13. The form of the raw material resin 11 is not particularly limited, but is usually in the form of pellets. The raw material resin 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 cylinder 13a is provided with an injector 16 for injecting a foaming agent into the cylinder 13a. When the raw material resin 11 is not foamed, the injector 16 can be omitted. 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 make it using 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.

The molten resin 11a to which the foaming agent is added or not added 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 molten resin 11a can be stored in the cylinder 17a. Then, by moving the piston 17b after the molten resin 11a is stored in the cylinder 17a in a predetermined amount, the molten resin 11a is pushed out from the slit provided in the T die 18 through the connecting pipe 27 and hung down to be a foamed resin sheet. Form 1.

The foamed resin sheet 1 is guided between the first and second dies 30 and 40 and is molded by the dies 30 and 40. The mold 30 has a convex portion 30a on a surface facing the mold 40. The mold 40 has a recess 40a on the surface facing the mold 30. The convex portion 30a and the concave portion 40a have substantially complementary shapes to each other. The mold 30 is preferably provided with a large number of vacuum suction holes, so that the foamed resin sheet 1 can be suctioned under reduced pressure to form a shape along the surface of the mold 30. The mold 40 is also provided with a decompression suction hole.

FIG. 2 is a diagram showing a cross section of the foamed resin sheet 1. The foamed resin sheet 1 is a sheet made of a resin material, and has a form in which bubbles 2 are dispersed and formed inside.

When molding the foamed resin sheet 1, in the molding machine shown in FIG. 1, the foamed resin sheet 1 is guided between the first and second molds 30 and 40 as shown in FIG. Next, as shown in FIG. 4, the first mold 30 or the second mold 40 is brought into contact with both sides of the foamed resin sheet 1, respectively. Vacuum suction holes 30A and 40A are formed in the first mold 30 and the second mold 40, respectively.

When the first mold 30 or the second mold 40 are brought into contact with both sides of the foamed resin sheet 1, the surface of the foamed resin sheet 1 is cooled, the surface begins to harden, and a so-called skin layer is formed. However, immediately after the first mold 30 or the second mold 40 is brought into contact with both sides of the foamed resin sheet 1, the temperature of the foamed resin sheet 1 is high and the fluidity is high. The formation of the skin layer is also insufficient.

Therefore, in the present embodiment, after the first mold 30 or the second mold 40 is brought into contact with both sides of the foamed resin sheet 1, the state is held for a certain period of time, and then the first and second molds 30 are held. , 40 core backs will be performed.

As shown in FIG. 5, the surface of the foamed resin sheet 1 is surfaced by abutting the first mold 30 or the second mold 40 on both sides of the foamed resin sheet 1 and then holding the state for a predetermined time. Curing progresses, and the skin layer S is sufficiently formed. Here, the predetermined time is, for example, 1 second or more. In the present embodiment, after the molds 30 and 40 are brought into contact with the foamed resin sheet 1, the core back is not performed immediately, but the contact state is positively maintained and after a certain period of time (for example, 1 second). After that, perform core back.

However, if the holding time is too long, the foamed resin sheet 1 may be cooled more than necessary and cured to the inside, making it difficult to stretch (increase the wall thickness) by the core back. From this point of view, the lower limit of the time (predetermined time) for holding the first mold 30 or the second mold 40 on both sides of the foamed resin sheet 1 and then holding the state is 1 second. It is preferably 2 seconds, more preferably 2.5 seconds, and even more preferably 3 seconds. On the other hand, the upper limit of the predetermined time is, for example, 7 seconds, preferably 6 seconds or less, and more preferably 5 seconds or less.

As shown in FIG. 6, the core back retracts the first mold 30 and the second mold 40 while performing vacuum suction from the vacuum suction holes 30A and 40A formed in the molds 30 and 40, respectively. This is an operation of increasing the distance between the 1st mold 30 and the 2nd mold 40. The core back stretches the bubbles 2 and increases the thickness of the foamed resin sheet 1. That is, a thick foamed resin sheet molded body having a high foaming ratio is formed.

As described above, the skin layer S is sufficiently obtained by abutting the first mold 30 or the second mold 40 on both sides of the foamed resin sheet 1 and then holding the state for a predetermined time and then performing core backing. The core back can be performed in a state where the surface of the foamed resin sheet 1 is surely brought into close contact with the first and second dies 30 and 40, and the resin of the foamed layer is stretched. The bubbles expand so as to satisfy the spread thickness, and the thickness of the foamed resin sheet 1 is sufficiently expanded.

On the other hand, when the core back is performed immediately after the first mold 30 or the second mold 40 is brought into contact with both sides of the foamed resin sheet 1, the skin layer is not formed as shown in FIG. Since the foamed resin sheet 1 is sufficiently thin and not uniform, the foamed resin sheet 1 is separated from the first and second molds 30 and 40, and the foamed resin sheet 1 cannot be sufficiently expanded (expanded).

In fact, a foamed resin sheet containing 30 parts by mass of polypropylene (manufactured by Japan Polypropylene Corporation, trade name BC4BSW) and 70 parts by mass of low-density polyethylene (LDPE) (manufactured by Asahi Kasei Co., Ltd., trade name M1820) is used to create a mold space. When the thickness is shaped to 3 mm and then increased to 6 mm (core back), the thickness of the foamed resin sheet most reproduces the thickness of the mold space when it is increased 4 seconds after shaping. found.

FIG. 8 shows the timing of core back molding (the time from when the first mold 30 or the second mold 40 is brought into contact with both sides of the foamed resin sheet 1 until the start of core back) and the foamed resin sheet to be molded. It is a figure which shows the relationship of the thickness of. As is clear from FIG. 8, the thickness of the foamed resin sheet increases by setting the time until the start of core back to 2 seconds or more, and reaches the maximum in 4 seconds. In the case of this example, the optimum value of the time until the start of core back after the first mold 30 or the second mold 40 is brought into contact with both sides of the foamed resin sheet 1 is 2 seconds to 6 seconds.

In the foamed resin sheet formed by the molding method of the present embodiment, as shown in FIG. 9, when the molten resin of the foamed layer is stretched, the wall surface of the bubble 2 is broken and the adjacent bubbles are continuous 1 It becomes one bubble. As a result, the water absorption performance and the sound absorption performance are improved. In FIG. 9, the orientation of the foamed resin sheet 1 is 90 ° different from that in FIGS. 2 to 6, and the core back direction is the vertical direction in the figure. Therefore, the bubble 2 has a shape that is stretched in the vertical direction. The same applies to FIG.

Further, for example, as shown in FIG. 10, when fine holes (micropores 50) having a diameter of 1 mm or less are formed in the skin layer on one side and the air is ventilated to open cells, the fine holes 50 are opened by the principle of Helmholtz resonance. A plate-shaped molded product exhibiting high sound absorption performance on the surface can be obtained.

Although the embodiments to which the present invention has been applied have been described above, it goes without saying that the present invention is not limited to the above-described embodiments, and various changes can be made without departing from the gist of the present invention. Is.

For example, the molding method of the present invention can be applied even in the case where a foamed resin sheet (parison) extruded into a cylindrical shape is crushed between dies and molded.

1 Foamed resin sheet 2 Bubbles 30, 40 Molds 30A, 40A Vacuum suction holes 50 Micro holes

Claims (5)

A method for molding a foamed resin sheet, which comprises a step of molding a molten foam resin sheet using a mold.
A foamed resin sheet characterized in that a molten foam resin sheet is sandwiched between a pair of molds, each mold is brought into contact with the foam resin sheet, and then each mold is retracted while vacuum suctioning after a lapse of a predetermined time. Molding method. The method for molding a foamed resin sheet according to claim 1, wherein the predetermined time is 1 second or longer. The method for molding a foamed resin sheet according to claim 2, wherein the predetermined time is 2 seconds to 6 seconds. The method for molding a foamed resin sheet according to any one of claims 1 to 3, wherein the foamed resin sheet contains polyethylene. A method for molding a foamed resin sheet, which comprises a step of molding a molten foam resin sheet using a mold.
The molten foam resin sheet is sandwiched between a pair of molds, each mold is brought into contact with the foam resin sheet, and after the surface of the foam resin sheet is cured, each mold is retracted while vacuum suctioning. A method for molding a foamed resin sheet.

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