JP2003089727A - Method for producing thermoplastic resin foam and thermoplastic resin foam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a thermoplastic resin foam in which fine bubbles are formed by impregnating a thermoplastic resin with an inert gas or a supercritical fluid thereof, to produce an inert gas or a supercritical fluid thereof. To reduce the time required for impregnation and increase productivity. SOLUTION: An inert gas or a supercritical fluid thereof is impregnated in a thermoplastic resin under a high pressure and a heating condition, and then the pressure is released to produce a thermoplastic resin foam having fine cells by releasing the pressure. The condition is a temperature lower than the glass transition temperature or the melting point of the thermoplastic resin and higher than the glass transition temperature or the melting point of the thermoplastic resin impregnated with the inert gas or its supercritical fluid.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a thermoplastic resin foam in which fine cells are formed, and a thermoplastic resin foam.

[0002]

2. Description of the Related Art Thermoplastic resin foams are used in various structural materials for the purpose of reducing weight, improving heat insulating properties, or imparting soundproofing properties. In terms of weight reduction and improvement of functionality, it is desirable to increase the expansion ratio of the thermoplastic resin foam to make it a foam having a small specific gravity, but as the expansion ratio increases, the foam expands. Since the strength of No. 1 decreases, the expansion ratio was restricted from the viewpoint of strength in industrial applications.

On the other hand, there has been proposed a technique for suppressing the decrease in strength or increasing the strength as the expansion ratio increases by making the bubbles of the foam extremely fine. For example, Shimbo et al., Polymer Engineering Science, 3
5, 1387 (1995) describes that rigidity is slightly improved by forming foamed bubbles having a diameter of 3.5 to 9.5 μm. This technology is called Microcellular Plastics, USP4,473,665 (1984), USP5,158,986 (1992)
The details are described in. In this method, specifically, a thermoplastic resin is impregnated in a high-pressure container under high pressure with an inert gas such as nitrogen or carbon dioxide at a high pressure or in a supercritical state, and then the thermoplastic resin impregnated with the gas is injected into the high-pressure container. Further, it is taken out and heated to a temperature not lower than the glass transition temperature Tg of the thermoplastic resin in an oil bath or the like to induce nucleation to cause bubble growth to obtain a fine bubble foam.

[0004]

However, in this method, the time spent for gas impregnation is enormous, and it is usually 24 to 48.
Since it is foamed after being kept under high pressure gas for a long time, the production efficiency is remarkably poor and it is not suitable for industrialization.

It is well known that the glass transition temperature Tg or the melting point Tm is lowered by impregnating a thermoplastic resin with an inert gas. For example, Japanese Patent Laid-Open No. 11-2
No. 63858 discloses polyphenylene ether (PP
E) is impregnated with supercritical carbon dioxide to obtain a glass transition temperature T
A method of realizing low temperature moldability by changing g is disclosed. Also, Handa et al., Journal of
Polymer Science: Part B: Polymer Physics, 32, 254
9 (1994), a differential scanning calorimeter (DS
C) TPE of PPE is 61.2 atm by measurement.
It has been reported that it was confirmed that the temperature was lowered by 31.6 ° C. by impregnating with O ₂ .

[0006] However, a technique which links the change of Tg or Tm caused by an inert gas with foam molding has not been proposed or even suggested.

The present invention is a method for solving the above conventional problems and producing a thermoplastic resin foam in which fine cells are formed by impregnating a thermoplastic resin with an inert gas or its supercritical fluid. And a method for producing a thermoplastic resin foam, which requires a short time for impregnation with an inert gas or a supercritical fluid thereof and can sufficiently secure industrial productivity, and a thermoplastic resin produced by such a method. It is intended to provide a foam.

[0008]

According to the method for producing an amorphous thermoplastic resin foam of the present invention, an amorphous thermoplastic resin is impregnated with an inert gas or a supercritical fluid thereof under high pressure and heating conditions. Then, a method for producing a thermoplastic resin foam having fine cells by releasing pressure, wherein the heating condition is a temperature lower than the glass transition temperature of the amorphous thermoplastic resin, The temperature is higher than the glass transition temperature of the amorphous thermoplastic resin impregnated with the active gas or its supercritical fluid.

The method for producing a crystalline thermoplastic resin foam of the present invention comprises the steps of impregnating a crystalline thermoplastic resin with an inert gas or its supercritical fluid under high pressure and heating conditions, and then releasing the pressure. A method for producing a thermoplastic resin foam having fine cells, wherein the heating condition is a temperature lower than the melting point of the crystalline thermoplastic resin and a crystal impregnated with the inert gas or a supercritical fluid thereof. The temperature is higher than the melting point of the thermoplastic resin.

That is, the inventors of the present invention have determined that the time required for impregnating an inert gas or its supercritical fluid into a thermoplastic resin is a sufficiently short time to have industrial value, and that sufficiently small fine bubbles are formed. As a result of examining the method for producing the formed thermoplastic resin foam, the change in Tg or Tm of the thermoplastic resin depending on the presence or absence of impregnation with an inert gas is utilized, and the Tg or Tm of the thermoplastic resin before the impregnation is Low,
It was also found that by maintaining the temperature higher than the Tg or Tm of the thermoplastic resin after impregnation, it is possible to produce a foam having extremely fine cells with a significantly shorter impregnation time than the conventional method. The present invention has been completed.

The impregnation with the inert gas lowers Tg or Tm as compared with that before the impregnation. The degree of this decrease is greater as the impregnation concentration of the inert gas is higher. Therefore, by holding under the heating conditions of the present invention, the inert gas is impregnated in the thermoplastic resin foam in a state where the mobility of the molecular chains is high, that is, a state where the gas diffusion coefficient is high, and The holding time under high pressure can be dramatically shortened.

After this impregnation operation, the pressure is rapidly released and the pressure is rapidly reduced to obtain a foam. In this foaming step, the Tg or Tm of the thermoplastic resin impregnated with the inert gas rises and is retained. Since the temperature is exceeded, bubble growth is suppressed and fine bubbles are formed. That is, in the foaming step by releasing the pressure, the inert gas impregnated in the thermoplastic resin is rapidly released, so that the concentration of the inert gas in the thermoplastic resin is rapidly reduced, and accordingly, Tg or Tm is To rise. As a result, at the holding temperature, the movement of the molecular chain is restrained, and the thermoplastic resin foam having fine cells can be obtained by being fixed in the state where the cell growth is suppressed.

In the method of the present invention, a thermoplastic resin is impregnated with an inert gas or a supercritical fluid thereof under a high pressure so that the glass transition temperature of the amorphous thermoplastic resin is set to the temperature before impregnation. 10 than the glass transition temperature of the plastic resin
The temperature is lowered by ˜250 ° C., and then the pressure is released to cause foaming to reduce the concentration of the inert gas, and the glass transition temperature after the pressure release is 10% lower than the glass transition temperature before the pressure release.
It is preferable to increase the temperature by ˜250 ° C. to suppress the growth of bubbles and form fine bubbles.

When a crystalline thermoplastic resin is used, the melting point of the crystalline thermoplastic resin is set higher than that of the thermoplastic resin before the impregnation by impregnating the thermoplastic resin with an inert gas or its supercritical fluid under high pressure. Is also 0 to 50 ° C, preferably 0.5
˜50 ° C., then pressure is released to foam to reduce the concentration of the inert gas, and the melting point after pressure release is 0 to 50 ° C., preferably 0.
It is preferable to increase the temperature by 5 to 50 ° C. to suppress the growth of bubbles and form fine bubbles.

In the present invention, suitable amorphous thermoplastic resins include polystyrene, syndiotactic polystyrene, polyphenylene ether, polymer alloys of polyphenylene ether and polystyrene, polymethylmethacrylate, polycarbonate, or norbornene resins. Moreover, polypropylene or polyethylene is mentioned as a suitable crystalline thermoplastic resin.

In the present invention, nitrogen and / or carbon dioxide is preferably used as the inert gas.

By such a method of the present invention, a thermoplastic resin foam having an average cell diameter of 0.01 to 10 μm and a cell number density of 10 ⁹ to 10 ¹⁵ cells / cm ³ can be produced. preferable.

The thermoplastic resin foam of the present invention is produced by such a method for producing a thermoplastic resin foam of the present invention, and since it has fine cells, it is sufficient even if the expansion ratio is high. It is a highly functional thermoplastic resin foam having strength.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below in detail according to the method for producing a thermoplastic resin foam of the present invention.

In the method of the present invention, specifically, a thermoplastic resin foam is manufactured by the following procedure. Charge a solid thermoplastic resin into a pressure vessel with a valve. A pressure vessel containing a solid thermoplastic resin is heated to a predetermined temperature using an external heat source. When the thermoplastic resin is an amorphous thermoplastic resin, this heating temperature is lower than the Tg of the amorphous thermoplastic resin used (hereinafter referred to as "Tg (max)"), and The temperature is higher than Tg of the inert gas-impregnated amorphous thermoplastic resin in the state where the amorphous thermoplastic resin is sufficiently impregnated with the inert gas in the step of, and the thermoplastic resin is a crystalline thermoplastic resin. In this case, it is lower than the Tm (hereinafter referred to as “Tm (max)”) of the crystalline thermoplastic resin used, and the crystalline thermoplastic resin is sufficiently impregnated with the inert gas in the following steps. The temperature is higher than the Tm of the inert gas-impregnated crystalline thermoplastic resin in. Hereinafter, a state in which the thermoplastic resin is sufficiently impregnated with an inert gas under high pressure conditions is referred to as a saturated impregnation state, and Tg of the inert gas-impregnated thermoplastic resin in the saturated impregnation state is referred to as Tg (min),
The same Tm is referred to as Tm (min).

If the heating temperature is too low in the above range, the effect of shortening the impregnation time of the inert gas due to the improvement of gas diffusibility cannot be sufficiently obtained, and if it is too high, bubble growth in the following foaming step. It is not possible to obtain a sufficient suppression effect. Therefore, the heating temperature varies depending on the average cell diameter and cell number density of the thermoplastic resin foam to be produced, the impregnation concentration of the inert gas in the saturated impregnation state, etc., but in the present invention, by impregnating the inert gas, In the case of a crystalline thermoplastic resin, Tg (min) is lowered from Tg (max) by 10 to 250 ° C., preferably 50 to 250 ° C.,
This heating temperature is lower than Tg (max) by 10 to 250 ° C., preferably 50 to 250 ° C., and lower than Tg (min).
It is preferable to set the temperature at ˜250 ° C., preferably 0˜200 ° C. higher.

In the case of a crystalline thermoplastic resin, Tm (mi
n) from Tm (max) to 0 to 50 ° C, preferably 0.
5 to 50 ° C., more preferably 10 to 50 ° C., and the heating temperature is 0 to 50 ° C., preferably 0.5 to 50 ° C., more preferably 10 to 50 ° C. lower than Tm (max).
0 to 50 ° C., preferably 0.5 to 4 than m (min)
It is preferable that the temperature is 0 ° C. higher.

While heating at the above temperature, an inert gas is charged into the pressure vessel at the same time. As this inert gas, nitrogen, carbon dioxide, or a mixed gas thereof can be used. The inert gas is often impregnated into the thermoplastic resin as a supercritical fluid under heating and pressurization. Equilibrate the pressure vessel, thermoplastic and inert gas with the heat source temperature. The pressure in the pressure vessel is adjusted by adding more inert gas in order to reach the final pressure at which the inert gas is sufficiently dissolved in the thermoplastic. This pressure varies depending on the thermoplastic resin used and the average cell diameter or cell number density of the desired thermoplastic resin foam, but as described above, Tg (min) or Tm (min)
Is 0 than Tg (max) or Tm (max), respectively.
In order to lower the temperature by ˜250 ° C., preferably by 0˜250 ° C., the pressure is preferably 13˜30 MPa, particularly 15˜30 MPa.

The heating temperature and pressure are maintained for a predetermined time. This holding time, that is, the impregnation time varies depending on the heating and pressurizing conditions, but in the present invention, by heating under the above heating conditions, this holding time can be dramatically shortened compared to the conventional case. Generally, a holding time of 1 to 12 hours, preferably 2 to 10 hours can produce a thermoplastic resin foam having a sufficient expansion ratio.

The valve in the pressure vessel is fully opened to rapidly release the pressure in the pressure vessel. As a result, a thermoplastic resin foam having fine cells is obtained. It should be noted that the temperature lowering after the pressure release is preferably carried out using liquefied gas or water as quickly as possible in order to suppress the growth of bubbles.

The thermoplastic resin applied to the method for producing a thermoplastic resin foam of the present invention is not particularly limited, but polystyrene, syndiotactic polystyrene, polyphenylene ether, a polymer alloy of polyphenylene ether and polystyrene, Amorphous thermoplastic resins such as polymethylmethacrylate, polycarbonate and norbornene resins, and crystalline thermoplastic resins such as polypropylene and polyethylene are exemplified as suitable thermoplastic resins. One of these thermoplastic resins may be contained alone in the raw material, or two or more thereof may be mixed and contained.

In addition, these thermoplastic resins include additives used for foam molding of ordinary thermoplastic resins, such as colorants, heat stabilizers, release agents, preservatives, ultraviolet absorbers, plasticizers, hardeners, and additives. 1 type or 2 types of flame retardant, conductivity imparting agent, antistatic agent, etc.
It may contain more than one seed.

The thermoplastic resin foam produced by the method of the present invention has an average cell diameter of 0.01 to 10 μm.
The bubble number density is preferably 10 ⁹ to 10 ¹⁵ cells / cm ³ . It is difficult to produce a thermoplastic resin foam having an average cell diameter of less than 0.01 μm, even if the effect of suppressing cell growth in the foaming step according to the present invention is sufficiently exerted, and the average cell diameter exceeds 10 μm. In the thermoplastic resin foam, it is not possible to sufficiently increase the strength by the fine bubbles. Further, a suitable cell number density varies depending on the average cell diameter, but if it is less than 10 ⁹ cells / cm ³ , a sufficient porosity as a foam cannot be secured, and 10 ¹⁵ cells / cm ³ cannot be ensured.
If it exceeds ³ cm ³ , the strength tends to be impaired, so 1
It is preferably from 0 ⁹ to 10 ¹⁵ pieces / cm ³ .

The thermoplastic resin foam of the present invention produced by the method of the present invention as described above is useful as various lightweight structural materials, carriers, etc., and particularly has an average cell diameter of 0.0.
The thermoplastic resin foam having ultrafine bubbles of about 1 to 1 μm is expected to be used as a separation membrane, a purifying material, a light reflecting material, etc. using the ultrafine bubbles.

[0030]

EXAMPLES The present invention will be described in more detail below with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples unless it exceeds the gist.

In the following examples and comparative examples,
The measurement of Tg or Tm and the measurement of the average cell diameter or the cell number density of the foam were performed by the following methods.

[Measurement of Tg or Tm] The decrease in glass transition temperature Tg or melting point Tm due to impregnation with an inert gas was measured using a DSC equipped with a high pressure cell. That is, first
A cylinder containing an inert gas is connected to a high-pressure cell via a pressure pump, then a thermoplastic resin is charged in the high-pressure cell, and the cell is hermetically sealed after maintaining the inert gas atmosphere under high pressure for a certain period of time, This sample-containing cell was placed in a DSC. As DSC, D manufactured by Parkin-Elmer
Using SC "Pyris1", a sample of about 5mg is 10 ℃
The temperature was raised at a rate of / minute. Tg was defined as the inflection point when moving from the first baseline to the next baseline, and Tm was defined as the intersection of the baseline and the rising line of the endothermic peak.

The expected value of Tg or Tm was obtained by linear extrapolation from a plurality of measured values.

[Measurement of Average Bubble Diameter and Bubble Number Density] The average bubble diameter and bubble number density are measured by a scanning electron microscope (SEM).
The foam sample was photographed and then statistically processed with image processing software. That is, a SEM of a foam cross section taken by a scanning electron microscope "S-2400" manufactured by Hitachi, Ltd.
After reading the photos into the computer with a digital scanner, image analysis software (Win R manufactured by Mitani Corporation)
Statistical processing was carried out by OOF), and the average value D of the cell diameters of the foam cross section was obtained. Further, the bubble number density N was obtained from the following equation. N = (n / A) ^3/2 / (1-4 / 3π (D / 2) ³ ·
(N / A) ^3/2 ) In the formula, N is the number density of bubbles [number / cm ³ ], A is the area of the statistical processing region, n is the number of bubbles in A, and D is the average bubble diameter.

Examples 1 to 4 and Comparative Examples 1 to 3 ZEO which is a norbornene resin used for optical parts.
NEX (manufactured by Zeon Corporation) was placed in a pressure vessel and heated to a temperature shown in Table 2 using an external power source. After that, while maintaining the heating temperature, CO 2 was supplied as an inert gas in the pressure vessel.
₂ was charged and the pressure shown in Table 2 was maintained for 2 hours. Then, the valve of the pressure vessel was fully opened to suddenly release the pressure in the vessel. The temperature at the time of pressure release was the same as the temperature at pressurization.

The average cell diameter and cell number density of the obtained thermoplastic resin foam were examined, and the results are shown in Table 2.

Table 1 shows changes in Tg of each ZEONEX used under various CO ₂ impregnation conditions.

[0038]

[Table 1]

[0039]

[Table 2]

As is clear from Table 2, the ZEONEX
Tg 143.0 ° C and CO_TwoZEONEX T in impregnated state
Examples 1 to 4 in which the heating temperature condition was between 61.8 ° C.
Then, a foam having fine cells is obtained. On the other hand, Z
Heat at a temperature higher than EONEX's Tg of 143.0 ° C.
In Comparative Examples 1 and 2, bubble growth was suppressed in the foaming process.
Since it is not controlled, fine bubbles cannot be formed.
On the other hand, CO_TwoZEONEX Tg in impregnated state 61.8 ° C
In Comparative Example 3 heated at a temperature lower than _TwoImpregnation
Is not sufficient and CO_TwoFrom Tg of impregnated ZEONEX
It is unfoamed because it is low enough.

Examples 5 to 7 and Comparative Example 4 ART which is a norbornene resin used for optical parts.
ON (manufactured by JSR) was used to produce a thermoplastic resin foam in the same manner as in Example 1 except that the heating conditions and pressurizing conditions shown in Table 4 were used, and the average of the obtained thermoplastic resin foams was obtained. The bubble diameter and bubble number density were examined, and the results are shown in Table 4.

Table 3 shows the change in Tg under each CO ₂ impregnation condition of the used ARTON.

[0043]

[Table 3]

[0044]

[Table 4]

As is clear from Table 4, ARTON T
g of 167.0 ° C. and Tg of ARTON impregnated with CO _{2 −}
In Examples 5 to 7 in which the heating temperature condition was between 37.1 ° C, fine cell foams were obtained. On the other hand, AR
In Comparative Example 4 which was heated at a temperature higher than Tg of 167.0 ° C. of TON, the bubble growth was not suppressed in the foaming step, and therefore, fine bubbles could not be formed.

Example 8 Polyphenylene ether (PP) used for electronic parts and the like
E) (model polymerization sample by Mitsubishi Kagaku Co., Ltd.) was used to obtain a thermoplastic resin foam in the same manner as in Example 1 except that the heating conditions and pressurizing conditions shown in Table 6 were used. The average cell diameter and cell number density of the thermoplastic resin foam were examined, and the results are shown in Table 6.

The polyphenylene ether (P
The change of Tg under each CO ₂ impregnation condition of PE) is as shown in Table 5.

[0048]

[Table 5]

[0049]

[Table 6]

As is clear from Table 6, the Tg of the polyphenylene ether (PPE) was 216.0 ° C. and the Tg of the polyphenylene ether (PPE) impregnated with CO ₂ was 145.
In Example 8 in which the heating temperature condition was between 3 ° C., a foam having fine cells was obtained.

Example 9, Comparative Example 5 Using Novatec MA3 (manufactured by Japan Polychem), which is a general-purpose resin polypropylene (PP) used in various products such as home electric appliances, automobile parts, and films, the heating conditions shown in Table 8 were used. Further, a thermoplastic resin foam was produced in the same manner as in Example 1 except that the pressurizing condition was used, and the average cell diameter and the cell number density of the obtained thermoplastic resin foam were examined, and the results are shown in Table 8. It was

Each CO _{2 of} Novatec MA3 used
The change in Tm under the impregnation condition is as shown in Table 7.

[0053]

[Table 7]

[0054]

[Table 8]

As is clear from Table 8, Novatec MA
3 with Tm of 164.0 ° C and CO ₂ impregnated Novatec M
In Example 9 in which the heating temperature was between A3 and Tm of 150 ° C., a foam having fine cells was obtained. On the contrary,
In Comparative Example 5 heated at a temperature higher than Tm164.0 ° C. of Novatec MA3, the bubble growth is not suppressed in the foaming step, so that the fine bubbles cannot be formed.

[0056]

As described in detail above, according to the present invention, in a method for producing a thermoplastic resin foam in which fine cells are formed by impregnating a thermoplastic resin with an inert gas or a supercritical fluid thereof. The time required for impregnation with the inert gas or its supercritical fluid can be shortened. For this reason, it is possible to provide a highly functional thermoplastic resin foam having fine cells with a high expansion ratio and high strength with high productivity, so that it can be provided at low cost.

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Claims (9)

[Claims] 1. A thermoplastic resin foam having fine cells is produced by impregnating an amorphous thermoplastic resin with an inert gas or a supercritical fluid thereof under high pressure and heating conditions, and then releasing the pressure. A method, wherein the heating condition is a temperature lower than the glass transition temperature of the amorphous thermoplastic resin, and the glass transition of the amorphous thermoplastic resin impregnated with the inert gas or a supercritical fluid thereof. A method for producing a thermoplastic resin foam, which is characterized in that the temperature is higher than the temperature. 2. The amorphous thermoplastic resin according to claim 1, wherein the amorphous thermoplastic resin is impregnated with an inert gas or its supercritical fluid to impregnate the inert gas or its supercritical fluid. Glass transition temperature of 10 to 250 ° C. lower than the glass transition temperature of the amorphous thermoplastic resin,
Thereafter, the pressure is released so that the glass transition temperature of the amorphous thermoplastic resin impregnated with the inert gas or the supercritical fluid thereof is 10 to 25 than the glass transition temperature before the pressure release.
A method for producing a thermoplastic resin foam, which comprises raising the temperature by 0 ° C. 3. The amorphous thermoplastic resin according to claim 1 or 2, wherein the amorphous thermoplastic resin is polystyrene, syndiotactic polystyrene, polyphenylene ether, a polymer alloy of polyphenylene ether and polystyrene, polymethylmethacrylate, polycarbonate, or norbornene resin. A method for producing a thermoplastic resin foam, comprising: 4. A method for producing a thermoplastic resin foam having fine cells by impregnating a crystalline thermoplastic resin with an inert gas or a supercritical fluid thereof under high pressure and heating conditions, and then releasing the pressure. The heating condition is a temperature lower than the melting point of the crystalline thermoplastic resin and a temperature higher than the melting point of the crystalline thermoplastic resin impregnated with the inert gas or the supercritical fluid thereof. A method for producing a thermoplastic resin foam, comprising: 5. The melting point of a crystalline thermoplastic resin impregnated with an inert gas or a supercritical fluid thereof according to claim 4, wherein the crystalline thermoplastic resin is impregnated with an inert gas or a supercritical fluid thereof. By 0 to 50 ° C. lower than the melting point of the crystalline thermoplastic resin, and then releasing the pressure to release the melting point of the crystalline thermoplastic resin impregnated with the inert gas or its supercritical fluid before pressure release. 0 than the melting point of
A method for producing a thermoplastic resin foam, which comprises raising the temperature by 50 ° C. 6. The method for producing a thermoplastic resin foam according to claim 1, wherein the crystalline thermoplastic resin is polypropylene or polyethylene. 7. The method for producing a thermoplastic resin foam according to claim 1, wherein the inert gas is nitrogen and / or carbon dioxide. 8. The average bubble diameter according to claim 1, which is in the range of 0.01 to 10 μm,
A method for producing a thermoplastic resin foam, which comprises producing a thermoplastic resin foam having a cell number density of 10 ⁹ to 10 ¹⁵ cells / cm ³ . 9. A thermoplastic resin foam produced by the method according to any one of claims 1 to 8.