JP2000248101A - Polymer foam and method for producing the same - Google Patents

Abstract

(57) [Problem] To provide a polymer foam having a small cell shape deformation and shrinkage after foaming. SOLUTION: A polymer foam is produced by impregnating a shape memory polymer alone or a polymer mixture of a shape memory polymer and a thermoplastic elastomer with a high-pressure gas under a high pressure, and then foaming the polymer under reduced pressure. As the high-pressure gas, for example, carbon dioxide in a critical state can be used. The glass transition point of the shape memory polymer is, for example, 20 ° C. or higher. By this method, for example, a shape memory polymer foam having a relative density of 0.01 to 0.8 is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a polymer foam and a method for producing the same. More specifically, the present invention makes use of the excellent properties of a shape memory polymer such as shape fixability, mechanical properties, abrasion resistance, and high rebound resilience. The present invention relates to a polymer foam having uniform and fine cells and a low relative density, and a method for producing the same. The polymer foam of the present invention is useful, for example, as an internal insulator for electronic equipment, a cushioning material, a heat insulating material, a food packaging material, a clothing material, and a building material.

[0002]

2. Description of the Related Art Conventionally, chemical methods and physical methods have been known as methods for producing polymer foams. As a general physical method, a method of dispersing a low-boiling point liquid (blowing agent) such as chlorofluorocarbons or hydrocarbons in a polymer, and then heating to volatilize the blowing agent to form bubbles is used. ing. In the chemical method, a compound (foaming agent) added to a polymer base is used.
A foam is obtained by forming a cell with a gas generated by thermal decomposition of.

[0003] However, the former physical foaming technique has various environmental problems such as harmfulness of a substance used as a foaming agent and destruction of the ozone layer. In the latter foaming technique using a chemical technique, after foaming, a residue of a foaming agent that has generated gas remains in the foam. For this reason, in particular, in the use of electronic components for which low pollution is highly required, contamination by corrosive gas or impurities becomes a problem.

On the other hand, in recent years, as a method of obtaining a foam having a small cell diameter and a high cell density, a gas such as nitrogen or carbon dioxide is dissolved in a polymer at a high pressure, the pressure is released, and the glass transition of the polymer is started. A method has been proposed in which bubbles are formed by heating to a temperature or near the softening point. In this foaming method, a nucleus is formed from a thermodynamically unstable state, and the nucleus expands and grows to form cells, thereby obtaining a microporous foam. According to this method, there is an advantage that an unprecedented microporous foam can be obtained. Various attempts have been made to apply this foaming method to thermoplastic elastomers such as thermoplastic polyurethane. However, in these methods, when the pressure is released to, for example, the atmospheric pressure, the nucleus expands and grows to form bubbles, and once a foam having a high magnification is formed,
Gases such as nitrogen and carbon dioxide remaining in the bubbles gradually permeate through the polymer wall, thereby shrinking the polymer after foaming, gradually deforming the cell shape, and reducing the cell size, There was a problem that the expansion ratio could not be obtained.

[0005]

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a polymer foam having a small cell shape deformation and shrinkage after foaming and a method for producing the same.

[0006]

The present inventor has studied to solve the above-mentioned problems, and as a result, using a shape-memory polymer alone or a thermoplastic elastomer containing a shape-memory polymer as a thermoplastic polymer, the use of carbon dioxide, nitrogen, etc. It has been found that a polymer foam which can maintain a desired expansion ratio for a long period of time without significantly shrinking or deforming after firing can be obtained by using the high-pressure gas as a foaming agent, and have reached the present invention.

That is, the present invention provides a polymer foam characterized by impregnating a shape memory polymer alone or a polymer mixture of a shape memory polymer and a thermoplastic elastomer with a high-pressure gas under high pressure and then foaming the polymer under reduced pressure. And a method for producing the same. In this manufacturing method, carbon dioxide or the like can be used as the high-pressure gas. The carbon dioxide may be in a supercritical state. The glass transition point of the shape memory polymer is, for example, 20 ° C. or higher. The present invention also comprises a shape memory polymer alone or a polymer mixture of a shape memory polymer and a thermoplastic elastomer, and has a relative density of 0.0
A polymer foam is provided that ranges from 1 to 0.8.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, as a shape memory polymer used as a raw material of a polymer foam, any polymer can be used as long as its shape reversibly changes depending on temperature. is not. Examples of the polymer having a shape memory function with respect to temperature include a resin that exists in a glassy state at room temperature or a state similar thereto at room temperature, and is in a rubber state when the glass transition point is higher than room temperature. Can be Representative examples of such resins include polynorbornene, styrene-butadiene copolymer, polyurethane, polyvinyl chloride, polymethyl methacrylate, polycarbonate, crystalline polyolefin, crystalline trans polyisoprene, crystalline trans polybutadiene or These crosslinked products are included. The resins may be used alone or in combination of two or more.

Although the glass transition point of such a shape memory polymer varies depending on the use of the foam, it is preferably at least 20 ° C. in view of a normal use range. When the glass transition point is lower than 20 ° C., the shape is not easily fixed when used at room temperature, and may be deformed over time. The upper limit of the glass transition point of the shape memory polymer is not particularly limited, but is generally about 100 ° C., preferably about 80 ° C.

The shape memory polymer may be used alone as a foam material, or may be used as a mixture with a thermoplastic elastomer. In the present invention, the thermoplastic elastomer used as the material of the foam is not particularly limited as long as it has foaming properties. For example, ethylene-propylene copolymer, ethylene-propylene-diene copolymer, ethylene- Olefin-based elastomers such as vinyl acetate copolymer, polybutene, chlorinated polyethylene; styrene-based elastomers such as styrene-butadiene-styrene copolymer and styrene-isoprene-styrene copolymer; polyester-based elastomer; polyamide-based elastomer; polyurethane-based Various thermoplastic elastomers such as elastomers are exemplified. These thermoplastic elastomers can be used alone or in combination of two or more.

The ratio of the thermoplastic elastomer and the shape memory polymer is, for example, the former (thermoplastic elastomer) / the latter (shape memory polymer) (weight ratio) = 0/100 to 90 /
10, preferably about 0/100 to 60/40, and more preferably about 0/100 to 30/70. If the proportion of the thermoplastic elastomer is too large, the fixation of the shape tends to be poor.

In the present invention, the high-pressure gas used as a foaming agent is not particularly limited as long as it impregnates the above-mentioned shape memory polymer or thermoplastic elastomer under high pressure. For example, carbon dioxide, nitrogen gas, air, etc. Is mentioned. These high-pressure gases may be used as a mixture. Among these, it is preferable to use carbon dioxide which has a large amount of impregnation into a shape memory polymer or a thermoplastic elastomer used as a material of the foam and has a high impregnation rate. Further, from the viewpoint of increasing the rate of impregnation into the resin, it is preferable that the high-pressure gas (for example, carbon dioxide) is in a supercritical state. The critical temperature of carbon dioxide is 31 ° C., and the critical pressure is 7.4 MPa. When a gas in a supercritical state (supercritical fluid) is used, the solubility in the resin increases and high-concentration mixing is possible. In addition, when the pressure is rapidly reduced, the concentration of the bubbles increases due to the high concentration. Even if the density of the bubbles formed by growing the nucleus is the same, the porosity is higher than in the other states, so that fine bubbles can be obtained.

When producing the polymer foam, additives may be added to the shape memory polymer or the polymer mixture of the shape memory polymer and the thermoplastic elastomer, if necessary. The type of the additive is not particularly limited, and various additives commonly used for foam molding can be used. Examples of the additive include a bubble nucleating agent, a crystal nucleating agent, a plasticizer, a lubricant, a coloring agent, an ultraviolet absorber, an antioxidant, a filler, a reinforcing agent, a flame retardant, and an antistatic agent. The additive amount of the additive can be appropriately selected within a range that does not impair the formation of bubbles and the like, and an additive amount used for molding a normal thermoplastic resin can be employed.

[0014] The production method of the present invention comprises a gas impregnating step of impregnating the shape memory polymer or a polymer mixture of the shape memory polymer and the thermoplastic elastomer with a high pressure gas under high pressure;
A foaming step of reducing the pressure after the step to foam the resin. Each step may be performed by any of a batch system and a continuous system.

According to the batch method, for example, a foam can be produced as follows. That is, by extruding a shape memory polymer or a polymer mixture of a shape memory polymer and a thermoplastic elastomer using an extruder such as a single screw extruder or a twin screw extruder, a sheet containing the shape memory polymer as a base resin is formed. It is formed. Alternatively, a shape memory polymer or a polymer mixture of a shape memory polymer and a thermoplastic elastomer is uniformly kneaded using a kneader provided with blades such as a roller, a cam, a kneader, and a Banbury type. By press molding to a predetermined thickness using a press of
A sheet including the shape memory polymer as the base resin is formed. The unfoamed sheet thus obtained is placed in a high-pressure vessel, and a high-pressure gas composed of carbon dioxide, nitrogen, air, or the like is injected, and the unfoamed sheet is impregnated with the high-pressure gas. When sufficient pressure gas is impregnated, the pressure is released (usually,
To atmospheric pressure) to generate bubble nuclei in the base resin. The bubble nuclei may be grown at room temperature as it is, or may be grown by heating in some cases. After the cells are grown in this manner, the foam is rapidly cooled to a temperature below the glass transition point of the shape memory polymer with cold water or the like, and the shape is fixed, whereby a shape memory polymer foam can be obtained.

On the other hand, according to the continuous method, for example, a foam can be produced as follows. That is, a high-pressure gas is injected while kneading a shape memory polymer or a polymer mixture of a shape memory polymer and a thermoplastic elastomer using an extruder such as a single-screw extruder or a twin-screw extruder. After impregnation, the pressure is released (typically to atmospheric pressure) by extrusion and, optionally, heating to grow the bubbles. After the cells are grown, they are rapidly cooled to below the glass transition point of the shape memory polymer with cold water or the like, and the shape is fixed, whereby a shape memory polymer foam can be obtained.

The pressure in the gas impregnation step is as follows:
It can be appropriately selected in consideration of the type of gas, operability, and the like.
a (preferably about 7.4 to 100 MPa). The temperature in the gas impregnation step varies depending on the type of gas used, the glass transition temperature of the polymer, and the like, and can be selected in a wide range. For example, when a foam is continuously obtained by an extruder, the temperature is generally about 180 to 260 ° C.

The foam made of the shape memory polymer or the polymer mixture of the shape memory polymer and the thermoplastic elastomer thus obtained has fine cells,
It is excellent in shape fixability, and a high expansion ratio is maintained for a long time without a large deformation and shrinkage of bubbles generated by releasing pressure of a high-pressure gas in a foaming process. For example,
The relative density of the foam (relative density after standing at 25 ° C. for 24 hours after foaming) is 0.01 to 0.8, preferably 0.04 to 0.5, more preferably 0.05 to 0.5.
It is in the range of about 0.25. The degree of change in relative density is, for example, about 1 to 6, preferably 1 to 4, and more preferably about 1 to 2. Further, the average cell diameter of the foam is, for example, 0.1 to 500 μm, preferably 0.1 to 5 μm.
0 μm, more preferably about 0.1 to 20 μm.

The relative density and the degree of change in the relative density are defined by the following equations. Relative density = density after foaming (density of foam) (g / cm
³ ) {Density before foaming (density of sheet or the like before foaming) (g / cm ³ )} Change in relative density = (relative density after standing at 25 ° C for 24 hours after foaming) ( (Relative density immediately after foaming) The polymer foam of the present invention can be used, for example, as internal insulators for electronic devices, cushioning materials, heat insulating materials, food packaging materials, clothing materials, building materials, and the like.

[0020]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. Note that the relative density and the degree of change in the relative density indicate values obtained by the above equations. The average bubble diameter is S
This is a value obtained by image processing from a foam observation image by EM (scanning electron microscope).

Example 1 A polyurethane-based shape memory polymer [manufactured by Mitsubishi Heavy Industries, Ltd.
Diary MM-3520, Tg 35 ° C] was kneaded at a temperature of 180 ° C with a kneader Labo Plastomill [manufactured by Toyo Seiki Co., Ltd.] equipped with roller type blades, and then heated to 180 ° C 0.5m thick using a press
m, formed into a sheet having a diameter of 80 mm. This sheet is 5
Carbon dioxide was impregnated in a pressure-resistant vessel of 00 cc and kept in a carbon dioxide atmosphere of 40 ° C. and 25 MPa for 1 hour. This sheet was continuously passed through hot water at 95 ° C. for 5 seconds to grow bubbles, and then rapidly cooled with water containing ice to obtain a foam made of a shape memory polymer. The relative density of the obtained foam immediately after foaming was 0.13.
8. After leaving the foam at room temperature (25 ° C.) for 24 hours, the relative density was 0.189, and the degree of change in the relative density was 1.37. The average bubble diameter determined from the SEM observation image was 1.9 μm.

Example 2 Example 1 was repeated except that a dialy MM-2520 (Tg 25 ° C.) manufactured by Mitsubishi Heavy Industries, Ltd. was used as a polyurethane-based shape memory polymer, and the hot water temperature during foaming was 80 ° C. In the same manner as in the above, a shape memory polymer foam was obtained. The relative density of the obtained foam immediately after foaming was 0.13.
2. After leaving this foam at room temperature (25 ° C.) for 24 hours, the relative density was 0.242, and the degree of change in the relative density was 1.83. The average bubble diameter determined from the SEM observation image was 2.8 μm.

Example 3 As a polyurethane-based shape memory polymer, Hapler Freele # 2103 (Tg: 60 ° C.) manufactured by Polycis Co., Ltd. was used, and the hot water temperature during foaming was set to 40 ° C., the same as the temperature during impregnation. A shape memory polymer foam was obtained in the same manner as in Example 1. The relative density of the obtained foam immediately after foaming was 0.132, and the relative density of the foam after standing at room temperature (25 ° C.) for 24 hours was 0.132, and there was no change in the relative density. The average bubble diameter determined from the SEM observation image was 9.2 μm.

Example 4 Polyurethane-based shape memory polymer [manufactured by Mitsubishi Heavy Industries, Ltd.
100 parts by weight of diary MM-3520, Tg 35 ° C.] and a thermoplastic polyurethane [Nippon Milactran Co., Ltd.]
K.K., E-660), 30 parts by weight, and a kneader Labo Plastomill equipped with roller type blades [Toyo Seiki Co., Ltd.
And kneading at a temperature of 180 ° C.
0.5 mm thick using a hot plate press heated to ℃ 8
It was formed into a 0 mm sheet. 500cc of this sheet
And kept in a carbon dioxide atmosphere of 60 ° C. and 25 MPa for 1 hour to impregnate carbon dioxide. This sheet was continuously passed through hot water at 80 ° C. for 5 seconds to grow bubbles, and then rapidly cooled with water containing ice to obtain a foam made of a shape memory polymer. The relative density of the obtained foam immediately after foaming was 0.082, the relative density of the foam after standing at room temperature (25 ° C.) for 24 hours was 0.236, and the degree of change in the relative density was 2.9. Met. The average bubble diameter obtained from the SEM observation image was 2.0
μm.

Comparative Example A thermoplastic polyurethane foam was obtained in the same manner as in Example 1 except that a thermoplastic polyurethane [E-660, manufactured by Nippon Miractran Co., Ltd.] was used instead of the polyurethane-based shape memory polymer. . The relative density of the obtained foam immediately after foaming was 0.034, the relative density of the foam after standing at room temperature (25 ° C.) for 24 hours was 0.290, and the degree of change in the relative density was 8.5. Met. The average bubble diameter determined from the SEM observation image was 7.5 μm.

As described above, the polymer foam obtained in the examples had fine cells, a low relative density, and the relative density did not significantly change with time.

[0027]

The polymer foam of the present invention has excellent properties such as mechanical properties, abrasion resistance, and high rebound resilience of a shape memory polymer, has uniform and fine cells, and has a good shape after foaming. The temporal deformation and shrinkage of the cell shape are small. According to the production method of the present invention, such an excellent foam as described above can be produced simply and efficiently.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Norihide Baba 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation (72) Inventor Mitsuhiro Kaneda 1-2-1, Shimohozumi, Ibaraki-shi, Osaka No. Nitto Denko Corporation (72) Inventor Yoshihiro Minamizaki 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation F-term (reference) AA71 AA78 AB02 BA32 CA29 CC04Y CC05Z CC10X CC34X CC34Y CC45 DA02 DA32 DA33 DA38

Claims (5)

[Claims] 1. A method for producing a polymer foam, comprising impregnating a shape memory polymer alone or a polymer mixture of a shape memory polymer and a thermoplastic elastomer with a high-pressure gas at a high pressure and then foaming the polymer under reduced pressure. 2. The method according to claim 1, wherein the high-pressure gas is carbon dioxide. 3. The method for producing a polymer foam according to claim 2, wherein carbon dioxide in a supercritical state is used. 4. The glass transition point of the shape memory polymer is 20 ° C.
The method for producing a shape memory polymer foam according to claim 1, which is as described above. 5. A polymer foam comprising a shape memory polymer alone or a polymer mixture of a shape memory polymer and a thermoplastic elastomer, and having a relative density in a range of 0.01 to 0.8.