JP3167184B2 - Method for producing polycarbonate resin foam - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a high expansion ratio polycarbonate resin foam using clean and safe carbon dioxide gas as a foaming agent.

[0002]

2. Description of the Related Art Conventionally, as a method for producing a polycarbonate resin foam, a thermal decomposition type chemical foaming agent is kneaded into a resin in the same manner as in the method for producing other thermoplastic resin foams. And a boiling point below the melting point of a polycarbonate resin such as an aliphatic hydrocarbon such as pentane, hexane or octane, or a fluorinated aliphatic hydrocarbon such as dichlorodifluoromethane. A gas foaming method is known in which an organic gas or a volatile liquid is injected into a molten resin and then released into a low-pressure region to cause foaming (Japanese Patent Laid-Open No. 2-261636).

[0003] A foam having uniform and fine closed cells can be obtained by applying a chemical foaming agent method to a polycarbonate resin. Decomposes, discolors the foam, generates odors, and causes food hygiene problems.

On the other hand, in the gas foaming method, when the foaming agent used is an aliphatic hydrocarbon, an explosive gas is generated during the production of the foam, so that there is a danger of explosion. When the blowing agent to be used is a fluorinated aliphatic hydrocarbon, there is little danger of explosion, but it is progressing toward total elimination due to environmental problems such as destruction of the ozone layer. In order to solve such problems of the conventional method, a gas foaming method using an inert gas such as nitrogen gas or argon, or carbon dioxide gas or water as a foaming agent has been proposed.

[0005] Water is clean and does not cause the above-mentioned problems. However, if water is present when the polycarbonate resin is heated, the disadvantage that the carbonate bond in the polycarbonate resin is decomposed tends to occur. JP-A-53-9
No. 2874 discloses a method in which an epoxy compound is added and foaming is performed with water adsorbed on the polycarbonate in order to suppress the decomposition of the polycarbonate resin by water, but the moisture absorption of the polycarbonate is 0.15 to 0.3.
%, It is possible to obtain only a foam having a low expansion ratio of at most 2-3 times the expansion ratio.

An inert gas such as nitrogen gas or argon is clean, and there is no concern about decomposition of the polycarbonate resin upon heating such as water. However, since the solubility in the polycarbonate resin is extremely low, foaming with a high expansion ratio is performed. It is difficult to get a body.

On the other hand, carbon dioxide gas is not only clean but also acts as a plasticizer when dissolved in a polycarbonate resin, so that it can be foamed at a temperature about 90 ° C. lower than the glass transition point of the polycarbonate resin. . However, although the solubility of carbon dioxide gas in a polycarbonate resin is remarkably higher than that of an inert gas at around room temperature, the solubility is extremely reduced near the melting point of the polycarbonate resin, so that the gas is injected into the resin in a molten state. In a normal extrusion foaming method, the solubility is not so high, and it is difficult to obtain a foam having a high expansion ratio.

A batch type normal pressure foaming method has been reported in which a polycarbonate resin is placed in a pressure vessel, carbon dioxide gas is injected at around room temperature, the pressure is returned to normal pressure, and the resin is immersed in a glycerin bath and foamed by heating. Associate professor of Kumar, Faculty of Mechanical Engineering, the University of Washington) Because of foaming under normal pressure (normal pressure method), gas escape during foaming is severe, and carbon dioxide dissolved in polycarbonate resin does not contribute to foaming effectively, and foaming with high foaming ratio It is difficult to get a body.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to overcome the drawbacks of the prior art and to provide a method for producing a surface smooth, high expansion ratio polycarbonate resin foam using a clean and safe foaming agent. Is to provide.

The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems. As a result, carbon dioxide gas was injected into a pressure vessel containing a polycarbonate resin to reduce the temperature to 50 ° C. or lower than the glass transition temperature of the polycarbonate resin. Then, the carbon dioxide gas is sufficiently dissolved in the polycarbonate resin, and then the inside of the pressure vessel is rapidly heated to 100 ° C. or more to bring it to a high temperature / high pressure state. It has been found that a polycarbonate resin foam having a high expansion ratio can be manufactured. The present inventors have completed the present invention based on these findings.

[0011]

According to the present invention, carbon dioxide gas is press-fitted into a pressure vessel containing a polycarbonate resin, and the temperature in the pressure vessel is set at 50 ° C. or lower than the glass transition temperature of the polycarbonate resin. Hold at temperature,
Dissolve carbon dioxide in polycarbonate resin, then
A method for producing a polycarbonate resin foam, characterized in that after the temperature in the pressure vessel is heated to 100 ° C. or more, the pressure is released to a low pressure range and foaming is performed.

Hereinafter, the present invention will be described in detail. The solubility of carbon dioxide gas in a polycarbonate resin tends to increase from a high-temperature region to a low-temperature region (A.R.
Berens et al. ACSympos. Se
ries No. 406, 1989). FIG. 1 shows the temperature dependence of the solubility of carbon dioxide gas in the polycarbonate resin when carbon dioxide gas was injected at a pressure of 40 kg / cm ² . As can be seen from FIG. 1, the solubility significantly decreases from around 25 ° C. to around 75 ° C. Therefore, in order to obtain a polycarbonate resin foam having a high expansion ratio, it is advantageous to dissolve carbon dioxide in the polycarbonate resin at around room temperature.

However, even when carbon dioxide gas is injected into the polycarbonate resin at around room temperature to obtain a carbon dioxide gas-dissolved polycarbonate resin, the pressure is returned to normal pressure and the mixture is foamed by heating.
Outgassing from the surface of the polycarbonate resin is severe, and dissolved carbon dioxide does not effectively contribute to foaming.

The inventors of the present invention have studied various means for making a carbon dioxide gas dissolved in a polycarbonate resin effectively contribute to foaming and obtaining a polycarbonate resin foam having a high expansion ratio. After injecting carbon dioxide gas in the vicinity and dissolving it sufficiently, do not return to normal pressure, heat it to 100 ° C or more while maintaining the high pressure state to make it a high temperature and high pressure state, then release it to the low pressure area and foam it As a result, it has been found that foaming can be performed while suppressing outgassing, and as a result, a polycarbonate resin foam having a high expansion ratio can be produced.

The polycarbonate resin used in the present invention is a polymer having a carbonic acid ester bond in the molecular structure. In particular, an aromatic polycarbonate having diphenylalkane in the molecular chain is excellent in heat resistance, weather resistance and acid resistance. Is preferred. Examples of the aromatic polycarbonate include 2,2-bis (4-oxyphenyl) propane, 2,2-bis (4-oxyphenyl) butane,
1,1-bis (4-oxyphenyl) cyclohexane,
1,1-bis (4-oxyphenyl) butane, 1,1-
Examples include polycarbonate resins from bisphenols such as bis (4-oxyphenyl) isobutane and 1,1-bis (4-oxyphenyl) ethane.

In the present invention, various additives generally used for molding a polycarbonate resin may be added as required. Examples of these additives include fillers such as plasticizers, lubricants, antioxidants, pigments, and flame retardants, and foam control agents such as talc, clay, silica, kaolin, and calcium carbonate.

Carbon dioxide gas is injected into the pressure vessel containing the polycarbonate resin, and the shape of the polycarbonate resin at this time is arbitrary, such as a granular shape, a pellet shape, a sheet shape, and a rod shape. While or after pressurizing the carbon dioxide gas, the temperature in the pressure vessel is kept at 50 ° C. or lower than the glass transition temperature of the polycarbonate resin to dissolve the carbon dioxide gas in the polycarbonate resin.

In the present invention, the temperature at which carbon dioxide is dissolved in the polycarbonate resin is 50 ° C. or less, preferably 100 ° C., lower than the glass transition temperature of the polycarbonate resin.
Hereinafter, the temperature is more preferably around room temperature (15 to 30 ° C.). If this temperature is too high, the solubility of carbon dioxide gas in the polycarbonate resin is too low, and a foam having a high expansion ratio cannot be obtained. The holding time is a time sufficient for sufficiently dissolving the carbon dioxide gas in the polycarbonate resin, and is usually 5 hours or more, preferably 10 hours or more, more preferably 20 hours or more. It is preferable that the carbon dioxide gas be sufficiently dissolved in the polycarbonate resin at a predetermined temperature and pressure until the carbon dioxide gas is saturated.

After dissolving the carbon dioxide gas in the polycarbonate resin, the temperature in the pressure vessel is heated to 100 ° C. or higher. The heating is performed as quickly as possible, and when the desired temperature is reached, the holding time is set as short as possible. It is preferable that the resin be released to a low pressure range and foamed. The heating temperature is preferably 140 ° C. or higher.

In the present invention, when carbon dioxide gas is injected into the polycarbonate resin in a low temperature range and then the temperature is increased by heating, as can be seen from FIG. 1, the saturation solubility of the carbon dioxide gas in the polycarbonate resin decreases. However, the rate at which carbon dioxide escapes out of the polycarbonate resin system is slower than the rate of temperature rise by a normal heating method (heating with a heater or the like), so carbon dioxide exists in the polycarbonate resin in a supersaturated state at high temperatures. I do. 100
After the temperature is raised to a temperature of ℃ or more, when the carbon dioxide gas is rapidly released from the supersaturated dissolved state of the polycarbonate resin to a low pressure region, a small amount of gas is released, but the supersaturated carbon dioxide gas contributes to foaming. A foam having a higher expansion ratio than the foam obtained by the normal pressure method can be obtained.

[0021]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to Examples and Comparative Examples, but the present invention is not limited to only these Examples.

[Example 1] 100 parts by weight of a polycarbonate resin (manufactured by Mitsubishi Gas Chemical Company, Iupilon S-2000, medium viscosity type) and 1.0 part by weight of talc were kneaded with a mixing roll set at 250 ° C, and then kneaded for 250 minutes. The sheet was formed into a sheet having a thickness of 2 mm by a heating press set at a temperature of ° C. Next, the sheet-shaped molded body was placed in a pressure vessel, and carbon dioxide gas was injected at 25 ° C. at a pressure of 50 kg / cm ² . After being kept at 25 ° C. and left for 24 hours, it was rapidly heated to 150 ° C. by a band heater wound around a pressure vessel. 150 ° C
The moment it reaches, the pressure reducing valve is opened and the pressure is rapidly reduced to atmospheric pressure.
Upon cooling, a polycarbonate resin foam was obtained. The foam thus obtained was a foam having a foaming ratio of 10.5 and a smooth surface.

[Comparative Example 1] 100 parts by weight of a polycarbonate resin (manufactured by Mitsubishi Gas Chemical Company, Iupilon S-2000, medium viscosity type) and 1.0 part by weight of talc were kneaded with a mixing roll set at 250 ° C, and then kneaded for 250 minutes. The sheet was formed into a sheet having a thickness of 2 mm by a heating press set at a temperature of ° C. Next, the sheet-shaped molded body was placed in a pressure vessel, and after injecting carbon dioxide gas at 25 ° C. at a pressure of 50 kg / cm ² , immediately heated to 150 ° C. by a band heater wound around the pressure vessel. The moment the temperature reached 150 ° C., the pressure reducing valve was opened, the pressure was rapidly reduced to atmospheric pressure, and the mixture was cooled to obtain a polycarbonate resin foam. The foam thus obtained had a smooth surface, but had a low expansion ratio of 2.2 times.

Comparative Example 2 100 parts by weight of a polycarbonate resin (Iupilon S-2000, medium viscosity type, manufactured by Mitsubishi Gas Chemical Company) and 1.0 part by weight of talc were kneaded with a mixing roll set at 250 ° C., and then kneaded for 250 minutes. The sheet was formed into a sheet having a thickness of 2 mm by a heating press set at a temperature of ° C. Next, the sheet-shaped molded body was placed in a pressure vessel, and carbon dioxide gas was injected at 25 ° C. at a pressure of 50 kg / cm ² . After being kept at 25 ° C. and left for 24 hours, the pressure reducing valve was opened to return to the atmospheric pressure, and then the sheet-shaped molded product was taken out of the pressure vessel.
Thereafter, the sheet-like molded body was quickly immersed in an oil bath maintained at 150 ° C. for about 20 seconds to foam, thereby obtaining a polycarbonate resin foam. The foam thus obtained had a smooth surface, but had a low expansion ratio of 4.5 times.

[0025]

According to the production method of the present invention, since a clean carbon dioxide gas is used as a foaming agent, there is no problem in terms of safety and environment, and the surface of the polycarbonate resin foam is easily smooth and has a high expansion ratio. Can be provided. The polycarbonate resin foam according to the present invention is a heat insulating material,
It can be applied to various fields such as building materials and is very useful.

[Brief description of the drawings]

FIG. 1 shows carbon dioxide (40) for a polycarbonate resin.
FIG. 3 is a diagram showing the temperature dependence of the solubility in kg / cm ² ).

Claims (1)

(57) [Claims] 1. A carbon dioxide gas is press-fitted into a pressure vessel containing a polycarbonate resin, and the temperature in the pressure vessel is maintained at a temperature of 50 ° C. or less than the glass transition temperature of the polycarbonate resin, and the carbon dioxide is added to the polycarbonate resin. A method for producing a polycarbonate resin foam, comprising: dissolving a gas, heating the pressure in the pressure vessel to 100 ° C. or higher, and then releasing the gas to a low pressure range to cause foaming.