JP2001122999A - Method for producing thermoplastic resin foam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a thermoplastic resin form which enables the foam having a thin non-foaming layer and expanded in a high multiplying factor to be produced even when a resin composition comprises a filler. SOLUTION: The method for producing the thermoplastic resin foam features that a thermoplastic resin composition C impregnated with gas under a high pressure and comprising a thermoplastic resin A and a filler is fed from an extruder 1 into a die assembly 5 and then a thermoplastic resin B is fed from an extruder 4 into the die assembly 5 in such a way as to extrude the composition C and the resin B from the tip of the die assembly to release pressure under a condition where the resin B covers at least a part of the surface of the resin composition C along the die cavity surface in the die assembly 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a thermoplastic resin foam.

[0002]

2. Description of the Related Art As a conventional method for producing a thermoplastic resin foam, an inorganic gas such as carbon dioxide or an organic gas such as chlorofluorocarbon is supplied after a molten thermoplastic resin is supplied into an extruder, and a pressure is applied at a mold tip. A gas foaming method for foaming by releasing a gas is widely known. For example,
Japanese Patent Publication No. 506724 discloses that a thermoplastic resin foam having a cell diameter of about several μm can be obtained by using a fluid in a supercritical state.

However, in the conventional gas foaming method, a gas is mixed into a molten resin at a high pressure, and the pressure is released to the atmospheric pressure at the tip of a mold as it is. Thereafter, it grows rapidly and breaks bubbles, or diffuses in the resin without producing bubble nuclei and is released to the atmosphere. For this reason, a non-foamed layer of about 30 to 100 μm was inevitably generated on the foam surface.

Japanese Patent Laid-Open Publication No. Hei 10-176076 discloses a method in which a sheet-like resin immediately after being discharged from a mold is bonded to a gas-impermeable sheet and then foamed. If the non-foamed layer on the foam surface is 1
It is disclosed that the thickness can be reduced to about 0 μm or less.

However, according to the study by the present inventors, even if the method described in JP-A-10-176076 is adopted, depending on the type of the resin to be applied, for example, the resin does not sufficiently elongate at the time of melting and breaks. When a resin or a resin having a high gas diffusion rate is used, the gas impregnated in the resin is released to the atmosphere before the resin discharged from the mold is bonded to the gas-impermeable sheet. In some cases, it was released and the non-foamed layer could not be thinned.

This situation is remarkable when a filler, particularly a large amount of a filler, is blended. Compared with a case where no filler is blended, the resin composition discharged from the mold travels along the interface between the resin and the filler. Gas is released into the atmosphere at a remarkably fast rate, so no matter how much it is bonded to the gas-impermeable sheet immediately after the resin is discharged, the effect of thinning the non-foamed layer is hardly recognized. In some cases, a very low foaming ratio of about 1 to 1.5 times was obtained even at the center of the film.

That is, in the conventional gas foaming method, the gas in the surface layer is released at the moment when the resin containing the filler is discharged from the mold, so that the non-foamed layer becomes thicker. Magnification decreases, the flexibility of the foam decreases,
There is a problem that the texture is often impaired.

[0008]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems of the conventional gas foaming method, and a resin which easily releases gas immediately after being discharged from a mold, particularly a resin composition containing a filler. Even in this case, it is an object of the present invention to provide a method for producing a thermoplastic resin foam capable of producing a foam having a thin non-foamed layer and a high expansion ratio.

[0009]

According to a first aspect of the present invention, there is provided a method for producing a thermoplastic resin foam, comprising the steps of: The extruder supplies the thermoplastic resin B to the mold, and then supplies the thermoplastic resin B to the mold. In the mold, at least a part of the surface of the thermoplastic resin A is covered with the thermoplastic resin B along the mold surface. It is characterized in that the pressure is released by pushing out from the tip of the mold.

According to a second aspect of the present invention, there is provided a method for producing a thermoplastic resin foam according to the present invention, wherein a filler is added in an amount of 50 to 100 parts by weight per 100 parts by weight of the thermoplastic resin A instead of the thermoplastic resin A.
It is characterized by using a thermoplastic resin composition C containing 0 parts by weight. The method for producing a thermoplastic resin foam according to the present invention described in claim 3 is characterized in that the thermoplastic resin B is the same as the thermoplastic resin A. Hereinafter, the present invention will be described in more detail.

The thermoplastic resin A is not particularly restricted but includes, for example, polyolefin resins such as polyethylene, polypropylene, ethylene-vinyl acetate copolymer (EVA), polyvinyl chloride, polyvinylidene chloride, acrylonitrile-styrene copolymer. (AS resin), acrylonitrile-butadiene-styrene copolymer (ABS resin),
Examples include polystyrene, methacrylic resin, polyamide, polycarbonate, polyacetal, polyester, acrylic resin, thermoplastic elastomer, and powdered rubber.

Preferably, it has a melt tension and an extensional viscosity characteristic suitable for foaming. For example, in addition to polyolefin resins such as polyethylene, polypropylene and EVA, polystyrene resins, acrylonitrile-butadiene-styrene ( ABS) resin, vinyl chloride resin and the like.

Among these resins, EVA, polyethylene and polypropylene are particularly preferable in view of recyclability and physical properties. These may be used alone or in combination. In addition, a modified or cross-linked resin may be used as long as the object of the present invention is not impaired.

In the present invention, the thermoplastic resin A
If necessary, additives such as a filler, a lubricant, a stabilizer, a flame retardant, an antiblocking agent, an antifoaming agent, a pigment, and a dye may be added to such an extent that the object of the present invention is not impaired. In some cases, it is possible to mix a plasticizer and a solvent in the same manner. However, it is desirable that these are not used as much as possible from the viewpoint of environment and safety.

The filler is not particularly limited. For example, silica, mica, talc, stone powder, diatomaceous earth, clay, graphite, carbon black, calcium carbonate, titanium oxide, alumina, aluminum powder, iron powder, molybdenum disulfide, barium sulfate, Lithium soap, wood powder, glass,
Inorganic or organic fillers such as pulp. These may be used alone or in combination.

The amount of the filler is preferably 50 to 1000 parts by weight based on 100 parts by weight of the thermoplastic resin A. That is, as described in claim 2, instead of the thermoplastic resin A, 50 parts by weight of the filler is added to 100 parts by weight of the thermoplastic resin A.
It is preferable to use the thermoplastic resin composition C containing up to 1000 parts by weight. If the amount is less than 50 parts by weight, it is difficult to exhibit the properties of the filler, and it is often possible to carry out ordinary extrusion, so that it is not necessary to apply the present invention. On the other hand, if it is attempted to mix the thermoplastic resin A in an amount exceeding 1000 parts by weight, the viscosity of A may be remarkably increased, or the obtained foamed molded article may be so brittle that the shape cannot be maintained.

The gas used in the present invention is not particularly limited as long as it is an organic or inorganic substance which is in a gaseous state at normal temperature and normal pressure and has good impregnating property at high temperature and high pressure and does not deteriorate the resin. Although it can be used without any risk, it is desirable to use a gas that is safe for the environment and worker's health and has no danger of fire or explosion and is easy to collect. Since it is in a gaseous state at normal temperature and normal pressure, it can be easily removed from the resin after use.

Examples of such a gas include inorganic gases such as carbon dioxide, nitrogen, argon, neon, helium and oxygen, and organic gases such as chlorofluorocarbon and low molecular weight hydrocarbons. Are preferably selected.

The gas is preferably in a supercritical state where the impregnation rate is high. The supercritical state refers to a state at a critical temperature or higher and a critical pressure or higher. For example, when the gas is carbon dioxide, the critical temperature is 30.9 ° C. and the critical pressure is 7.
In the case of 4 MPa and nitrogen, the critical temperature is −146.9 ° C., and the critical pressure is 3.4 MPa.

The pressure at the time of impregnation of the gas, that is, the pressure at the time of supply to the extruder, is preferably not less than (critical pressure of gas-3 MPa) and not more than (critical pressure of gas + 100 MPa).
The pressure is more preferably (critical pressure of gas + 3 MPa) or more and (critical pressure of gas + 60 MPa), and it is particularly preferable that the gas is in a supercritical state in order to efficiently impregnate the thermoplastic resin with the gas.

That is, (critical pressure of gas -3 MPa)
If it is less than this, the impregnation amount will be small and the foaming ratio will be low. If it exceeds (critical pressure of gas + 100 MPa), the pressure will be too high and the equipment will be large, which is not preferable.

Means for impregnating the thermoplastic resin A with gas at a high pressure is described in, for example, Japanese Patent Application Laid-Open No. H10-230541.
As disclosed in Japanese Patent Application Laid-Open Publication No. H10-107, an extruder equipped with a pressure-resistant hopper that can perform in a closed high-pressure space from gas impregnation to supply of the extruder may be used. Alternatively, after supplying the thermoplastic resin A to the extruder under normal pressure, the supercritical gas and the resin A may be sealed and kneaded in the extruder.

Means for realizing this content include a method of supplying a gas to a connection portion by using a tandem type extruder, and a method of forming a resin by using a screw capable of forming two molten resin seals in the extruder. A method of supplying a gas between the seals may be used. The extruder is an extruder that is one screw or two or more screws or a combination thereof. In the case of two screws, the rotation direction of the screw may be opposite or the same in each shaft, and the shaft type may be parallel. Type or conical type may be used. Further, a tandem system in which extruders are combined in multiple stages may be used.

The amount of gas impregnated in the thermoplastic resin A can be appropriately selected depending on the type of gas.
It is desirable to impregnate 3 to 50 parts by weight of gas with respect to 0 parts by weight. Most preferably, gas impregnation is in a saturated state, but need not necessarily be achieved.

The mold for shaping is not particularly limited as long as it can exhibit "a state where at least a part of the surface of the thermoplastic resin A is covered with the thermoplastic resin B along the mold surface". . For example, as a sheet die, if it is a T die, a multi-manifold die, a stack plate die,
If the feed block die is a circular die, a multilayer spiral die may be used. In addition to the sheet mold, a mold having a multi-layered mechanism may be used for a mold having a round shape or an irregular shape.

The thermoplastic resin B is not particularly limited.
All those exemplified as the thermoplastic resin A can be used, and may be the same or different from the resin A,
Preferably, a resin whose melting point or melting temperature is about the same as or slightly higher than that of the thermoplastic resin A is used.

The means for supplying the thermoplastic resin B to the mold is not particularly limited as long as the thermoplastic resin B can be supplied stably, but it is desirable to use an extruder. When the thermoplastic resin B is supplied to the mold, continuous production of the thermoplastic resin foam according to the present invention is started, and when the thermoplastic resins A and B are constantly supplied, It can be said that the thermoplastic resins A and B are simultaneously supplied to the mold.

The above-mentioned “state in which at least a part of the surface of the thermoplastic resin A is covered with the thermoplastic resin B along the mold surface”.
The term “state” refers to a state where at least a part of the thermoplastic resin A, which is a foamed material impregnated with a high-pressure gas, has the thermoplastic resin B adhered along the mold surface in the mold. Of course, both sides of the sheet-like thermoplastic resin A may be covered with the thermoplastic resin B.

It is necessary that the material discharged from the tip of the mold is extruded and discharged from the mold in a state where the thermoplastic resin A and the thermoplastic resin B are integrated, and that state must be maintained. This is because if the gas is spontaneously separated after the discharge, the release of the gas into the atmosphere cannot be suppressed. Further, after being discharged in an integrated state, they may be tightly adhered so that they cannot be separated by applying a force, or they may be so closely adhered that they can be separated.

The possibility of separation after ejection largely depends on the properties of the thermoplastic resin A and the thermoplastic resin B as materials, and cannot be said unconditionally. However, in order to realize a tightly adhered state, The thermoplastic resin A and the thermoplastic resin B may be combined at a high pressure and a high melting point or higher than the melting temperature at a relatively upstream portion in the mold.
On the other hand, in order to enable separation, the thermoplastic resin A and the thermoplastic resin B are merged at a relatively low pressure in the mold and at a low temperature near the melting point or the melting temperature. I just need.

(Operation) In the present invention, according to the prior art, even if the thermoplastic resin A is of a type in which outgassing occurs immediately after the resin A is discharged from the mold, the resin A can be discharged at a high pressure in the mold. At least a part of the surface is covered with the thermoplastic resin B along the mold surface, and in this state, the pressure is released by extruding from the tip of the mold, so that the release of gas immediately after discharging the mold can be blocked. The thickness of the unfoamed layer of the thermoplastic resin A can be reduced. In particular, in the case of the thermoplastic resin composition C in which a large amount of filler is blended, outgassing occurs immediately after the mold unless the above-mentioned coating is performed, but the unfoamed layer is similarly thinned by the above-described action. It is possible.

[0032]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described specifically with reference to examples, but the present invention is not limited to these examples. (Example 1) A target substantially flat thermoplastic resin foam was obtained using the following equipment. Extruder a: For thermoplastic resin composition C: φ70 single screw extruder L / D = 30 Extruder b: For thermoplastic resin B: φ30 single screw extruder L / D = 22 Die: width 100mm two-layer, three-layer T-die (feed block die), lip thickness 1mm, temperature control by oil temperature adjustment.

[0033] Thermoplastic resin composition C: The following raw materials were premixed. 100 parts by weight of ethylene-vinyl acetate copolymer resin (thermoplastic resin A, pulverized from Novatech EVA LV660 manufactured by Nippon Polychem Co., Ltd.) Wood flour (manufactured by Sanwa Cellulosin, # 100 mesh, average particle size 2) 8 μm) 100 parts by weight Lubricant (Kaohax 220, manufactured by Kao Corporation) 5 parts by weight Thermoplastic resin B: Ethylene-vinyl acetate copolymer resin (thermoplastic resin A, “Novatech EVA LV660” manufactured by Nippon Polychem Co., Ltd.) Used) alone.

Gas: carbon dioxide, impregnation pressure of 20 MPa, average impregnation amount of 10 parts by weight (calculated from extrusion amount and gas supply amount), and provided at a set temperature of 130 ° C. in the middle of extruder a. Molding condition: Mold temperature setting: 60 to 70 ° C. Extrusion amount: Thermoplastic resin composition C: 5 kg / hour Thermoplastic resin B: 1 kg / hour

The thermoplastic resin composition C is supplied to a cylinder 2 from one hopper 6 as an extruder a shown in FIG. 1, and the carbon dioxide is supplied to a central portion of the cylinder 2 from a high-pressure gas supply device 3. The thermoplastic resin composition C was impregnated, and the gas-impregnated resin composition C was supplied from the cylinder 2 to the mold 5. Next, the resin B is used as the extruder 4 for the resin B
Is introduced into the multilayer mold 5, and in the mold 5, at least a part of the surface of the thermoplastic resin composition C is covered with the thermoplastic resin B along the substantially flat mold surface. To release a pressure to obtain a substantially flat thermoplastic resin foam.

The properties of this foam were evaluated as follows, and the results are shown in Table 1. -Thickness of portions corresponding to thermoplastic resin composition C and thermoplastic resin B The extruded and foamed sheet sample was frozen and broken with liquid nitrogen and observed with a scanning electron microscope (SEM). The thickness of each of the resin B as the coating layer and the resin composition C as the foamed layer was measured at 10 points, and the average value was taken as the thickness of the portion corresponding to the resin composition C and the resin B.

Bubble Diameter Along with the measurement of the thickness of the resin composition C and the resin B, 100 bubble diameters of a typical size of the resin composition C as the foamed layer were measured, and the average value was defined as the cell diameter.

-Thickness of non-foamed portion In addition to the measurement of the cell diameter, the thickness of the unfoamed portion of the resin composition C at the interface between the resin composition C and the resin B was measured at 10 points, and the average value was taken as the thickness of the unfoamed portion.

The expansion ratio (total) The density of the entire extruded and foamed sheet sample (multilayer sheet composed of a foamed layer formed of the resin composition C and a coating layer formed of the resin B) was measured, and the The expansion ratio (entire) was calculated from the measured density of the sheet sample (having a coating layer but not supplied with gas and not expanded). In the comparative example, the resin composition C
The calculation was made from the density of the foamed sheet sample alone and the density of the sheet made of the resin composition C.

Expansion ratio (foamed portion) The overall density D and thickness t of the extruded and foamed sheet sample (multilayer sheet composed of a foamed layer formed of the resin composition C and a coating layer formed of the resin B) Is measured, and the density D2 of the resin B, which is the coating layer, measured in advance, and
From the thickness t1 of the foam layer formed from the resin composition C and the thickness t2 of one side of the resin B, the density D1 of the resin composition C forming the foam layer was calculated.

The calculation formula is as follows. D = D1 × t1 / t + D2 × 2 × t2 / t, where t
= T1 + 2 × t2 When deformed, D1 = (t × D−2 × t2 × D2) / (t
−2 × t2) Thereafter, the expansion ratio was calculated from the density D1 of the resin composition C as the foamed layer and the density of the sheet composed of the resin composition C measured in advance. Example 2 Filler (Wood Flour) in Thermoplastic Resin Composition C
A thermoplastic resin foam was obtained and evaluated in the same manner as in Example 1 except that 200 parts by weight of a filler (wood flour) was used instead of 100 parts by weight.

(Comparative Example 1) A thermoplastic resin foam was obtained and evaluated in the same manner as in Example 1 except that no thermoplastic resin B was used, and thus the extruder b in Example 1 was not used. . Comparative Example 2 Example 2 was repeated except that no thermoplastic resin B was used, and thus no extruder b was used in Example 2.
In the same manner as in the above, a thermoplastic resin foam was obtained and evaluated.

[0043]

[Table 1]

As is clear from Table 1, in Comparative Examples 1 and 2 in which the resin B coating layer was not formed, the unfoamed layer was 10
Occurrence was 0 μm or more, and the expansion ratio was as low as 2.3 times at the maximum. In contrast, in Examples 1 and 2 in which the coating layer was formed, the unfoamed layer was as small as about 10 μm, and the foaming ratio (total)
Was 3.7 times at the maximum and the expansion ratio (foamed portion) was as high as 5.7 times. This indicates that the gas impregnated in the resin composition C by the formation of the coating layer functions sufficiently and the expansion ratio is improved.

According to the method for producing a thermoplastic resin foam of the present invention, even if it is difficult to form a thin unfoamed layer with the prior art, at least a part of the thermoplastic resin A In a state where the surface of the resin is covered with the thermoplastic resin B along the mold surface, the resin is extruded from the mold tip to release the pressure, thereby preventing the release of gas immediately after being discharged from the mold. A multi-layer sheet having a foamed layer and a partial or entire covering layer formed of resin B, and a thin or non-foamed layer formed of resin A is easily obtained. As a result, a high expansion ratio can be realized, and thereby a thermoplastic resin foam having flexibility and good texture can be provided. A thermoplastic resin A100 instead of the thermoplastic resin A as described in claim 2.
When using a thermoplastic resin composition C containing 50 to 1000 parts by weight of a filler with respect to parts by weight, a thermoplastic resin foam having a thin unfoamed layer, which is quite difficult with conventional techniques, can be produced. The present invention is effective. Further, when the thermoplastic resin B is the same as the thermoplastic resin A as described in claim 3, the above effects can be more reliably achieved.

[Brief description of the drawings]

FIG. 1 is a schematic view showing one embodiment of a manufacturing apparatus suitable for being applied to a manufacturing method of the present invention.

[Explanation of symbols]

 Reference Signs List 1 extruder a 4 extruder b 5 mold A thermoplastic resin B (for coating) thermoplastic resin C thermoplastic resin composition

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Claims (3)

[Claims] 1. A thermoplastic resin A impregnated with a gas at a high pressure is supplied from an extruder to a mold, and then a thermoplastic resin B is supplied to the mold, and at least the thermoplastic resin A in the mold is supplied to the mold. A method for producing a thermoplastic resin foam, wherein a part of the surface is covered with a thermoplastic resin B along a mold surface and the pressure is released by extruding from a die tip. 2. The thermoplastic resin composition C according to claim 1, wherein a thermoplastic resin composition C containing 50 to 1000 parts by weight of a filler with respect to 100 parts by weight of the thermoplastic resin A is used in place of the thermoplastic resin A. A method for producing a foam. 3. The method for producing a foam according to claim 1, wherein the thermoplastic resin B is the same as the thermoplastic resin A.