JPH11291318A - Manufacture of thermoplastic resin foam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable stable forcing of a foaming agent into a molten resin by filling the interior of piping from a storage tank for the foaming agent containing carbon dioxide to the forcing part of an extruder, with a liquid or a specific pressure gas, and/or pressurizing the storage tank to a specific pressure level and/or cooling a liquid feed pump below an atmospheric temperature. SOLUTION: (A) Prior to feeding a foaming agent containing a carbon dioxide, the interior of piping from a storage tank to a point right before the foaming agent forcing part of an extruder is filled with a liquid. Alternatively the interior of the piping is filled with a gas at a pressure above 10 kgf/cm<2> . (B) A storage tank for the foaming agent containing the carbon dioxide is pressurized above a steam pressure at the temperature of the storage tank for the carbon dioxide. (C) It is preferable to make the temperature of a liquid feed pump lower than an atmospheric temperature so that the former is cooled below 0 deg.C. The steps (A) and/or (B) and/or (C) are put into practice. The liquid is preferably a material such as hydrocarbons, hydrofluorocarbons, an ether, alcohol or the like which become easily a liquid even at a normal temperature, for example, by pressurizing. The gas is preferably the carbon dioxide, nitrogen, air, helium or argon.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention has high environmental compatibility and is desired to be used as a foaming agent, but it is difficult to ensure production stability, and it is difficult to use it industrially. The present invention relates to a method for producing a thermoplastic resin foam while ensuring high production stability by using a hindered blowing agent containing carbon dioxide.

[0002]

2. Description of the Related Art In the extrusion foaming of a thermoplastic resin, substances such as chlorofluorocarbons, hydrocarbons, and alkyl chlorides, which are generally called physical foaming agents, are used. In order to achieve the magnification, it is common to use a liquid sending pump to feed the liquid from a foaming agent storage tank to an extruder.

Carbon dioxide is considered to be superior in safety, ozone destruction and global warming performance as compared with conventional blowing agents such as fluorocarbons, hydrocarbons and alkyl chlorides, and has been studied as a blowing agent for thermoplastic resins. Has been made. However, carbon dioxide has a lower boiling point and critical temperature than these conventional blowing agents, and tends to solidify when exposed to a low pressure from a high-pressure liquid state (which generally means a state called dry ice). doing. For this reason, cavitation occurs in the liquid feed pump to disable liquid transfer, or the liquid becomes a compressible gas in the piping, making liquid transfer impossible,
Due to the generation of dry ice, the piping may be clogged and the liquid may not be sent. From this, the blowing agent containing carbon dioxide until now can not be used stably in the liquid state,
Actually, industrial use has not been realized, and there are many industrial problems to stably feed the liquid and press-fit it into the extruder.

On the other hand, Japanese Patent Application Laid-Open No. 3-81346 discloses a method for producing a thin sheet-like foam, in which a pump head is cooled to -17.8 ° C. using liquid nitrogen, and a steam lock is applied to the sheet. (Discussed to be in a liquid-disabled state). However, the problem that occurs when the blowing agent containing carbon dioxide is transported while being pressurized from the storage tank to the extruder press-fitting section is not only the vapor lock in the pump head as described above, but also becomes dry ice before being sent to the pump head and becomes a pipe. May be clogged and the transport itself may not be possible, or the state of liquid carbon dioxide at the time of being sent to the pump head may be already unstable, and may not be sufficiently stabilized by cooling at the pump head alone, Further improvements were required.

[0005]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and is capable of industrially utilizing a blowing agent containing carbon dioxide by stably injecting a blowing agent into a molten resin in an extruder. Aims to realize stable production of foam.

[0006]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies in view of the above-mentioned problems. As a result, when the blowing agent containing carbon dioxide was injected into the molten resin in the extrusion foaming method, the inside of the piping was not filled before the blowing agent was sent out from the storage tank. Is filled with a liquid or a pressurized gas, cooling the liquid feeding pump during liquid feeding, and pressurizing the storage tank, it is found that the foaming agent can be stably injected. The present invention has been made.

That is, the present invention provides: 1) a method of melting a thermoplastic resin at a high temperature and a high pressure, sending a foaming agent from a foaming agent storage tank to the extruder using a liquid feed pump, and pressing the extruder into the extruder; In kneading and cooling the molten thermoplastic resin and the blowing agent to form a foamable gel, and extruding the gel into a low-pressure region through a die to obtain a foam by extrusion foaming, the blowing agent contains carbon dioxide,
The present invention relates to a method for producing a thermoplastic resin foam, which comprises carrying out the following (A) and / or (B) and / or (C). (A) (A) Before starting the delivery of the blowing agent from the storage tank, fill the pipe from the storage tank to the extruder press-fitting section with a liquid, or (B) Before starting the delivery of the blowing agent from the storage tank The pressure in the pipe from the storage tank to the press-fitting section of the extruder is 10 kgf / cm ^2.
Fill with the above gas. (B) The storage tank of the blowing agent containing carbon dioxide is pressurized to a pressure exceeding the vapor pressure of carbon dioxide at the temperature in the storage tank. (C) The liquid sending pump is at a temperature lower than the air temperature, preferably 0 ° C.
Cool below.

Further, the present invention relates to a method for producing a thermoplastic resin foam, wherein the parts to be cooled by the liquid sending pump in 2) and 1) (C) above are at least a suction part and a pump head. .

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention uses a foaming apparatus using a conventional extruder, and performs a well-known extrusion foaming method. The present invention provides a method for producing a stable thermoplastic resin foam.

[0010] The thermoplastic resin used in the present invention is not particularly limited as long as carbon dioxide can be dispersed in an extruder and a foam can be obtained by the extrusion method using a blowing agent containing carbon dioxide. However, alkenyl aromatic resins, particularly thermoplastic resins mainly containing polystyrene, are preferred. The amount of carbon dioxide in the blowing agent may be changed according to the properties of the foam to be obtained, and is not particularly limited. However, since the injection tends to be difficult as the amount of carbon dioxide increases, it is preferable to carry out several elements of the present invention at the same time.

When another blowing agent is used together with carbon dioxide, it is a blowing agent that does not solidify at the cooling temperature, flow rate, and pressure of the liquid sending pump when cooling by the method of the present invention, and is pressed into the extruder. The foaming agent is a liquid foaming agent until it is formed, and a known foaming agent capable of obtaining a foam in the thermoplastic resin to be used can be used. When using an alkenyl aromatic resin, these blowing agents include:
Hydrocarbons, hydrofluorocarbons, ethers and alcohols are preferred. Among them, propane, n-butane, i-
Butane, n-pentane, i-pentane, neopentane,
1,1,1,2-tetrafluoroethane, 1,1-difluoroethane, difluoromethane, 1,1,1,2,2
3,3-hexafluoropropane, 1,1,1,3,3
-Pentafluoropropane, dimethyl ether, methyl alcohol, ethyl alcohol are preferred, propane,
n-butane, i-butane, n-pentane, i-pentane, 1,1-difluoroethane and dimethyl ether are particularly preferred.

The liquid feed pump used in the present invention is a pump used for pressurizing a foaming agent and injecting a foaming agent into an extruder. Any known pump can be used. The storage tank of the present invention is a part having a function of storing carbon dioxide or a blowing agent containing carbon dioxide, and a known tank or a cylinder generally having a function equivalent thereto can be used.

Next, description will be made below along symbols ((A) to (C)) attached to the technical requirements of the present invention used in the claims. (A) When starting to supply the blowing agent containing carbon dioxide from the storage tank to the liquid sending pump, (a) before sending, filling the pipe immediately before the extruder foaming agent press-fitting section from the tank with a liquid; B) High pressure of 5 kgf / cm ² or more,
Preferably, the gas is filled with a gas having a high pressure of 10 kgf / cm ² or more.

In this case, the liquid used is a hydrocarbon,
Preferred are substances such as hydrofluorocarbons, ethers, and alcohols that can easily exhibit a liquid state even at normal temperature, for example, under pressure. As the gas, carbon dioxide or nitrogen, air, helium, and argon are preferable. The gas or liquid previously filled in these pipes is installed in a part close to the extruder, preferably immediately before the foaming agent press-fitting part of the extruder, in the process of pressurizing the blowing agent containing carbon dioxide and starting press-fitting. It is preferable from the viewpoint of production yield that the obtained branch pipe is used to sequentially discharge the pipe from the branch pipe to the outside and that the gas or liquid is not left as much as possible in the pipe at the stage of starting to press the foaming agent into the extruder.

[0015] In discharging, depending on the degree to which the blowing agent containing carbon dioxide is pressurized, when the substance previously filled in the pipe is a gas, the pressure in the pipe is at least 5 kgf / c.
It is preferable that the pressure does not become less than m ² , preferably less than 10 kgf / cm ^2. For example, it is preferable that the gas is discharged intermittently every time a constant value pressure is increased by pressurization. If the gas is continuously discharged at random, the pressure in the pipe becomes low, and the effect of pressurizing and sealing the gas in advance tends to decrease.

(B) It is preferable to pressurize the storage tank of the blowing agent containing carbon dioxide at least exceeding the vapor pressure at the storage tank temperature of carbon dioxide. The degree of pressure may be determined by evaluating the breakdown voltage and the blowing agent press-stability of the blowing agent storage tank, it is preferable to pressurize 5 Kgf / cm ² or more with respect to vapor pressure, pressure 10 Kgf / cm ² or more pressurized Is more preferable. Pressurization can be easily achieved by sending an inert gas, such as nitrogen, pressurized to a desired pressure into the storage tank.

(C) When the blowing agent containing carbon dioxide is sent from the blowing agent storage tank to the extruder by using a pump, it is required that at least the liquid sending pump is lower than the air temperature.
It is preferable to cool to 0 ° C. or lower, more preferably to −5 ° C. or lower, and most preferably to −10 ° C. or lower. The cooling of the liquid sending pump is most preferably performed by cooling all parts that come into contact with the foaming agent, but it is preferable to cool at least the liquid suction part and the liquid pressurizing part to the pump, and more preferably the pump in addition to the cooling. Is to cool the outlet part. Further, it is more preferable to cool the piping from the storage tank to the liquid sending pump,
More preferably, the storage tank is also cooled. Since the increase and decrease of these cooling portions are also affected by the flow rate of the foaming agent, the determination is made while observing the pump condition according to the amount of carbon dioxide, and if the cavitation occurs, it may be performed.

In the present invention, the temperature measurement is preferably controlled not on the outer wall of the pump but on the inner wall in contact with the liquid. The temperature may be measured by a known or common means such as a thermocouple,
There is no particular limitation. The cooling in the present invention can be easily carried out by appropriately using a commonly available cooling means such as cooling water flowing through a chiller, for example, circulation of a common refrigerant such as chlorofluorocarbon, or winding of a solid cold / hot material such as dry ice. Achieved.

The cooling is above 0 ° C., in particular 10 ° C.
When the temperature exceeds ℃, carbon dioxide tends to be easily vaporized. The above requirements (A), (B) and (C)
Although each of them is effective alone, preferably (A)
And (B), (A) and (C), (B) and (C). Most preferably, all three requirements of (A), (B), and (C) are implemented.

Here, in the requirement (C), as described above, it is most preferable to cool the liquid-feeding pump by cooling all parts that come into contact with the foaming agent. It is preferable to cool the pressure part,
More preferably, in addition to the above cooling, the outlet of the pump is also cooled. ADVANTAGE OF THE INVENTION According to this invention, the favorable injection of the blowing agent containing carbon dioxide is attained, and a desired thermoplastic resin foam can be obtained. Therefore, the shape of the foam,
There are no particular restrictions on characteristics, expansion ratio, and the like. Although such an invention, since there is a tendency that it is difficult to stably inject a blowing agent containing carbon dioxide as the amount of carbon dioxide increases, the present invention has a relatively large expansion ratio,
Particularly, it is suitable for producing a thermoplastic resin foam of about 15 times or more, more preferably about 20 times or more. Similarly, the present invention can be suitably applied to the production of a thermoplastic resin foam having a relatively large thickness, particularly about 1/2 inch or more.

[0021]

The present invention will be described in detail below with reference to Examples and Comparative Examples for the method for producing a thermoplastic resin foam of the present invention. However, these are merely examples, and the present invention is not limited to these. However, the present invention is not limited to this. Unless otherwise specified, "parts" indicates parts by weight and "%" indicates% by weight.

(Example 1) A bromine-based resin was used for 100 parts of a polystyrene resin (trade name: Estyrene G17, manufactured by Nippon Steel Chemical Co., Ltd., melt index (MI): 3.1) and 100 parts of the polystyrene resin. 3.0 parts of hexabromocyclododecane as a flame retardant, and talc 0.1 as a nucleating agent
The resin mixture consisting of parts by weight was dry-blended, and the obtained resin mixture was supplied to an extruder in which two extruders having a diameter of 65 mm and a diameter of 90 mm were vertically connected.

The resin mixture supplied to the extruder having a diameter of 65 mm is heated to 200 ° C., melted or plasticized, kneaded, and the resin temperature is adjusted to 12 with a connected extruder having a diameter of 90 mm.
Cooled to 5 ° C, ambient temperature 15 ° C from a 50 mm width cross-section die provided at the tip of an extruder with a diameter of 90 mm.
Extruded into the atmosphere, the cross-sectional dimension is 46m thick
m, a width of 152 mm, and a rectangular foam having an expansion ratio of 26 times.

At this time, carbon dioxide is used as a foaming agent in an amount of 70%.
A 65 mm extruder tip (90 mm extruder) was supplied through separate foaming agent liquid supply lines such that the foaming agent composed of 30 wt% of n-butane and 30 wt% of n-butane was 6 parts by weight with respect to 100 parts by weight of the polythylene resin. Into the resin from the vicinity of the connection end with the resin). Before press fitting, liquefaction
-After filling with butane, the valve of the storage tank was opened and the pressurization of the blowing agent containing carbon dioxide was started.

As a liquid feed pump for press-fitting, a Nikkiso mill flow control displacement pump was used. While performing the above operations, the pressure in the extruder was adjusted to 65 kg by a pressure gauge attached to the tip of the extruder to a value of 110 kgf / cm ^2.
The screw rotation speeds of the m and 90 mm extruders were adjusted.

When the pressure in the pipe reached 150 kgf / cm ² , the foaming agent press-in valve was opened to start press-in of the foaming agent, and a foam was obtained. 12 hours after the start of the injection of the blowing agent, stable and good continuous operation was possible. However, after that, a phenomenon that the pressure fluctuated in a range of +5 kgf / cm ² to −5 kgf / cm ² occurred. Rotation speed of liquid pump,
48 hours of continuous operation was achieved by finely adjusting the number of revolutions of the extruder screw. As a result, the feasibility of industrial production was confirmed, and the experiment was terminated.

Subsequently, Examples 2 to 4 and Comparative Example 1 were carried out under the following conditions. (Example 2) The substance to be filled in the pipe beforehand in Example 1 was changed to gaseous carbon dioxide pressurized to 30 kgf / cm ² . (Example 3) In addition to Example 1, dry ice was wrapped around the pressurizing part and the suction part outer shell of the liquid sending pump, and the temperature was adjusted to -15 ° C by measuring with a thermocouple installed on the inner wall of the suction part.

Example 4 In addition to Example 1, the storage tank was pressurized with nitrogen to 80 kgf / cm ² . (Comparative Example 1) The charge of n-butane was eliminated from Example 1. The results are as follows. Example 2 Although good continuous operation was able to be performed stably for about 20 hours after the start of the press-fitting, the pressure was +5 kgf / cm ² thereafter.
Since the phenomenon that varies with a width of ~-5Kgf / cm ² was observed, the rotation speed of the liquid feed pump for each thereof was corrected by finely adjusting the rotational speed of the extruder screw, could 48 hours of continuous operation . As a result, the feasibility of industrial production was confirmed, and the experiment was terminated. Example 3 About 48 hours after the start of the press-in, stable and good continuous operation was performed. After the elapse of 40 hours, the amount of liquid sent tended to decrease, so the number of revolutions of the liquid sending pump was slightly increased. Thereafter, continuous operation was possible for up to 48 hours. As a result, the feasibility of industrial production was confirmed, and the experiment was terminated. Example 4 For about 48 hours, stable feeding of the blowing agent containing carbon dioxide was possible, and good continuous operation was possible without any adjustment of the liquid sending pump, the rotation speed of the extruder, and the like. As a result, the feasibility of industrial production was confirmed, and the experiment was terminated. Comparative Example 1 Immediately after the delivery valve from the storage tank to the liquid sending pump was opened, the pipe was clogged with dry ice, the flow of liquid stopped, the pressurization of the blowing agent containing carbon dioxide became impossible, and the press-fitting into the extruder was completely stopped. Because it was not possible, a foam could not be produced.

[0029]

Industrial Applicability According to the present invention, a foaming agent containing carbon dioxide can be stably injected into a molten thermoplastic resin in an extruder, and an excellent thermoplastic resin foam having high environmental compatibility can be obtained. Can be manufactured well.

Claims (2)

[Claims] 1. A thermoplastic resin is melted under high temperature and high pressure,
The foaming agent is sent from the foaming agent storage tank to the extruder using a liquid feed pump to the extruder, and after being press-fitted into the extruder, a foamable gel is formed while kneading and cooling the molten thermoplastic resin and the foaming agent. In extrusion foaming, in which a foam is obtained by extruding a gel into a low-pressure region through a die, the blowing agent contains carbon dioxide, and the following (A) and / or (B) and / or (C) is performed. A method for producing a thermoplastic resin foam. (A) (A) Before starting the delivery of the blowing agent from the storage tank, fill the pipe from the storage tank to the extruder press-fitting section with a liquid, or (B) Before starting the delivery of the blowing agent from the storage tank The pressure in the pipe from the storage tank to the press-fitting section of the extruder is 10 kgf / cm ^2.
Fill with the above gas. (B) The storage tank of the blowing agent containing carbon dioxide is pressurized to a pressure exceeding the vapor pressure of carbon dioxide at the temperature in the storage tank. (C) The liquid sending pump is at a temperature lower than the air temperature, preferably 0 ° C.
Cool below. 2. The method for producing a thermoplastic resin foam according to claim 1, wherein in (C), the parts to be cooled by the liquid sending pump are at least a suction part and a pump head.