JPS60229936A - Production of expanded polymer particle - Google Patents

Abstract

PURPOSE:To produce easily and stably expanded polymer particles having high content of closed cells and improved moldability, by using an inorganic gas containing molecular nitrogen as a foaming agent. CONSTITUTION:1pts.wt. polymer particles, preferably polyolefin based resin and >=1.5pts.wt. liquid dispersing agent, e.g. water or ethylene glycol, and preferably a fusion inhibitor, e.g. aluminum oxide, for the polymer particles, are put into a pressurized vessel under >=20atm, preferably >=30atm pressure, and mixed, and the resultant mixture is then heated at a softening temperature of the polymer particles or above. An inorganic gas containing molecular nitrogen, preferably nitrogen gas or air is brought into contact with the mixture at the above-mentioned temperature preferably in the presence of a volatile impregnation assistant, e.g. acetone, and the resultant polymer particles and the liquid dispersing agent are released to the outside of the pressurized vessel and expanded to afford the aimed expanded particles. In case the above-mentioned expanded particles are used as a preliminarily expanded particles for hot molding, the expansion ratio is preferably 5-50 times.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a novel method for producing expanded polymer particles.

[Prior art]

Conventionally, in producing synthetic resin foams, a so-called bead molding method has been used in which pre-expanded particles are filled into a mold and heated and foamed. These pre-expanded particles are produced by dispersing polymer particles containing a volatile organic blowing agent in water in a closed container, as described in Japanese Patent Publication No. 56-1344, and reducing the pressure inside the container. After heating to a temperature above the softening temperature of the polymer while maintaining the pressure at the vapor pressure of the blowing agent or higher, the 1@ below the water surface in the container is opened, and the polymer particles and water are poured into the container at the same time. It is manufactured by discharging force into an atmosphere at a pressure lower than the internal pressure of the container. In this case, examples of volatile organic blowing agents used include propane, butane, heptane, hexane, cyclobutane, cyclopentane, trichlorofluoromethane, dichlorodifluoromethane, and the like.

However, these volatile organic blowing agents act as good solvents for single polymers and swell the polymer particles, so the suitable temperature range for foaming during pre-foaming is narrow, and the influence of foaming temperature on the expansion ratio is limited. There was a problem in that it was difficult to control the foaming ratio. In addition, some of these volatile organic blowing agents are toxic or flammable and therefore dangerous, while others are expensive and therefore do not pose much of a problem in terms of danger. ,
When using these volatile organic blowing agents, the volatile organic blowing agent within the pre-expanded particles needed to be replaced with air and recovered. Furthermore, when such volatile organic blowing agents are released into the atmosphere, they cause problems of environmental pollution such as destruction of the ozone layer.

In any case, although the volatile organic blowing agents described above have various problems, they have continued to be used because there is no effective blowing agent to replace them.

〔the purpose〕

The object of the present invention is to provide a method for producing foamed polymer particles that overcomes the above-mentioned drawbacks found in the prior art.

As a result of extensive research to achieve the above object, the present inventors have discovered that by using a specific inorganic gas as a blowing agent, which has not been considered as a blowing agent for non-foamed polymer particles, The suitable temperature range for foaming during pre-foaming has been expanded, making it possible to carry out the pre-foaming operation easily and stably.Furthermore, foamed particles with a high closed cell ratio and excellent moldability can be obtained. The present invention has been completed based on the discovery that various effects that could not be achieved with conventional methods, such as increased safety and prevention of environmental pollution, have been achieved.

〔composition〕

That is, according to the present invention, when foaming polymer particles, (i) dispersing the polymer particles in a liquid dispersion medium, (1)
1) heating the polymer particles to a temperature equal to or higher than their softening point; (ii, i) impregnating the polymer particles with an inorganic gas containing molecular nitrogen; (1v) containing an inorganic gas containing molecular nitrogen; and a step of foaming the polymer particles heated to a temperature equal to or higher than the softening point by releasing them together with a liquid dispersion medium from a pressure zone into a low pressure zone. .

The method of the present invention includes a step of impregnating polymer particles with an inorganic gas containing molecular nitrogen (impregnation step), a step of dispersing the polymer particles in a liquid dispersion medium (dispersion step), and a step of impregnating polymer particles with an inorganic gas containing molecular nitrogen. The method includes a step of heating to a certain temperature (heating step) and a step of foaming the polymer particles impregnated with molecular nitrogen-containing inorganic gas (foaming step). In the present invention, these steps are generally preferably carried out in the same container, and each step can be carried out sequentially or substantially simultaneously. For example, the impregnation step, the dispersion step, and the heating step can be performed in the same or different containers in that order, or in the order of the dispersion step, the heating step, and the impregnation step,
Further, the impregnation step and the dispersion step, or the impregnation step and the heating step can be performed simultaneously, and furthermore, the dispersion step and the heating step can also be performed simultaneously.

In the present invention, the dispersion step is a step of stirring and mixing polymer particles with a liquid dispersion medium and dispersing them in one dispersion medium. As the dispersant, those in liquid form, such as water, ethylene glycol, glycerin, methanol, and ethanol, are usually used.

Generally water is preferred. The amount of dispersion medium used is 1.5 parts by weight or more, preferably 2 parts by weight, per 1 part by weight of the polymer particles.
~5 parts by weight. In addition, in this dispersion step, preferably an anti-fusing agent for monopolymer particles is used,
Preferred examples of such materials include solid fine particles that do not melt in the heating process, such as aluminum oxide, titanium oxide, basic magnesium carbonate, basic zinc carbonate, and calcium carbonate. For example, organic fine particles insoluble in urea-formaldehyde resin or other dispersion medium may also be used.

The heating step is carried out by heating the polymer particles to a temperature above their softening point. In this case, the heating temperature is
For non-crosslinked crystalline polymer particles, (melting point -
30°C) to (melting point +40°C), and for crosslinked crystalline polymer particles usually (
Temperatures from (melting point -20°C) to (melting point +120°C) are preferred. For amorphous polymer particles, the temperature is preferably in the range of (softening point +10°C) to (softening point +120°C). Note that the softening point of the polymer particles in the present invention is a value determined according to ASTM D643 and a load of 4.6 kg/mm2, and the melting point of the polymer particles is a value determined by differential scanning calorimetry (DSC). The melting point is 200-300°C at a rate of 10°C/min in a nitrogen atmosphere.
℃, then lowered to 50℃ at a rate of 10℃/min, and then raised again at a rate of 10℃/min. This is the apex temperature of the melting peak, and if there are multiple peaks. is its maximum temperature. This heating step is preferably carried out simultaneously with the above-described dispersion step in the same pressurized container. That is, first, a dispersion medium and polymer particles are placed in a pressurized container, and the polymer particles and dispersion medium are mixed using a stirrer provided in the container. Next, in this state, the contents of the container are heated.

In the present invention, the polymer particles are impregnated with the molecular nitrogen-containing inorganic gas by bringing the molecular nitrogen-containing inorganic gas into contact with the polymer particles under pressure. Hitherto, it has not been known that molecular nitrogen is effective as a blowing agent for unfoamed polymer particles. Until now, molecular nitrogen has been known as a typical inert gas, and blowing agents that have been used conventionally are all volatile organic compounds that have a good affinity for polymers. It is completely unexpected that molecular nitrogen is effective as a blowing agent for polymer particles.

When bringing the molecular nitrogen-containing inorganic gas into contact with the polymer particles, the molecular nitrogen-containing inorganic gas can be brought into direct contact in a gaseous state, or can be brought into contact via a liquid. When the contact is made through a liquid, the molecular nitrogen-containing inorganic gas comes into contact with the polymer particles in a form dissolved in the liquid. The pressure is usually 20 atmospheres (absolute pressure) or higher, preferably 30 atmospheres or higher. The contact time depends on the pressurizing conditions, but is usually 10 minutes or more, preferably 20 minutes or more. Further, in this impregnation step, it is advantageous to employ heating conditions, and generally heating at a temperature equal to or higher than the softening point of the polymer particles is employed. As the molecular nitrogen-containing inorganic gas, any gas containing molecular nitrogen is usually used. For example, in addition to nitrogen gas, air is preferably used as the molecular nitrogen-containing inorganic gas, and further, argon, xenon, helium, neon,
Alternatively, nitrogen gas or air enriched with an inert gas such as krypton may also be used. Furthermore, other gases such as oxygen, hydrogen, ozone, or water vapor can also be present in appropriate amounts in the nitrogen gas or air as long as they are not dangerous or do not impede the purpose of the present invention. In the present invention, it is generally advantageous to use a gas containing 5% by volume or more, preferably 10% by volume or more of molecular nitrogen.

The impregnation step is usually carried out in a pressurized container, but in this case, the polymer particles can be present alone in the container, or can be present in a state dispersed in a liquid dispersion medium. can. When performing the impregnation step with polymer particles dispersed in a dispersion medium, the polymer particles are
Contact with molecular nitrogen-containing inorganic gas dissolved or dispersed in the dispersion medium.

As a result, the molecular nitrogen-containing inorganic gas is impregnated into the polymer particles, or the molecular nitrogen-containing inorganic gas is impregnated into the polymer particles at the moment when the polymer particles are suspended at the boundary between the dispersion medium phase and the gas phase due to stirring. Furthermore, the impregnation of the polymer particles with the molecular nitrogen-containing inorganic gas can also be carried out in the presence of a volatile impregnation aid, as long as it does not particularly impede the purpose of the present invention. By using this volatile impregnation aid in combination, the impregnation ratio of the molecular nitrogen-containing inorganic gas to the polymer particles can be increased. Specific examples of this impregnation aid include acetone, toluene, xylene, heptane, ethyl ether, dioxane, methyl acetate, ethyl acetate, tetrahydrofuran, styrene monomer, isoprene oligomer, dipentene, etc. Any material can be used as long as it has a plasticizing effect.

This volatile impregnation aid usually has a boiling point of -50 to 250°C,
It is preferably -30 to 200°C, and can be supplied together with the monomolecular nitrogen-containing inorganic gas to the impregnation step, or can be supplied in advance in the form of a mixture with a dispersion medium. The proportion of the volatile impregnation aid used is 0.5 to 30% by weight, preferably 2 to 20% by weight, based on the polymer particles.

In the foaming step, a homogeneous mixture of softened polymer particles containing molecular nitrogen-containing inorganic gas and a dispersion medium obtained through the above-described impregnation step, dispersion step, and heating step is heated in a pressurized zone ( It consists of discharging from a pressurized vessel (inside the pressurized vessel) to a low pressure zone (outside the pressurized vessel).

The pressure in the pressurized zone is usually at least 20 atmospheres, in particular at least 30 atmospheres, while the pressure in the low pressure zone is lower than that in the pressurized zone, usually normal pressure. Through this foaming step, foamed polymer particles are obtained. In this case, the expansion ratio of the foamed particles obtained is generally 1.5 to 80 times, and these foamed particles can be used as they are for various purposes. In particular, it is suitable for use as pre-expanded particles for heat molding, and in this case, the expansion ratio is preferably set within a range of 5 to 50 times.

In the present invention, by using a molecular nitrogen-containing inorganic gas as a blowing agent, it is possible to stably obtain foamed particles having a wide range of suitable temperature for foaming and having a high closed cell ratio. Moreover, the blowing agent used in this case is
It is nonflammable and has excellent safety, and after foaming,
Even if the expanded particles are released into the atmosphere, the ozone layer will not be destroyed and air pollution will not occur. Also. The blowing agent used in the present invention has the advantage of being significantly cheaper than conventional volatile organic compounds.

When carrying out the invention, it is advantageous to carry out the impregnation step in the presence of a volatile impregnation aid, in which case it is possible to increase the impregnation rate of the molecular nitrogen-containing inorganic gas into the polymer particles. As a result, foamed polymer particles with a high expansion ratio can be easily obtained.

The foamed polymer particles obtained by the present invention do not require any special recovery process because the blowing agent contained therein is harmless and inexpensive, and the pre-expanded particles have excellent foam moldability as they are. It can be used as

As described above, the present invention is characterized by using a molecular nitrogen-containing inorganic gas as a blowing agent for polymer particles. You can also. When a molecular nitrogen-containing inorganic gas and a volatile blowing agent are used together for polymer particles, the polymer particles may be impregnated with the molecular nitrogen-containing inorganic gas and the volatile blowing agent at the same time, or the molecular It is also possible to impregnate the polymer particles with the nitrogen-containing inorganic gas and the volatile blowing agent in separate steps.

Volatile organic blowing agents include propane, n-butane, 1
so-butane, butylene, 1so-butene, pentane,
Aliphatic hydrocarbons such as neopentane, hexane, etc.; halogenated aliphatic hydrocarbons such as monochloromethane, monochloroethane, dichlorofluoromethane, dichlorofluoromethane, trifluoromethane, trichlorotrifluoroethane, etc.; cyclopentane, cyclohexane, etc. Examples include cycloaliphatic hydrocarbons such as. In the present invention, these five volatile organic blowing agents may be used alone or in the form of a mixture. The usage ratio of the volatile organic blowing agent is 2 parts by weight of the volatile organic blowing agent per 100 parts by weight of the molecular nitrogen-containing inorganic gas.
A proportion of from 5 to 100 parts by weight is preferred, particularly from 5 to 100 parts by weight. Further, it is preferably 20 parts by weight or less per 100 parts by weight of the polymer. If the proportion of the volatile organic blowing agent used exceeds the above range, the resulting expanded particles will undergo particle shape deformation and shrinkage, resulting in irregular sizes and significant bubble roughness. Depending on the type of organic blowing agent, danger may also arise. Therefore, in the case of the present invention, the proportion of the volatile organic blowing agent is preferably within the above range.

In the present invention, the combined use of a molecular nitrogen-containing inorganic gas and a volatile organic blowing agent as the blowing agent as described above
It has a synergistic effect on the foaming effect, and compared to the case where a molecular nitrogen-containing inorganic gas or a volatile foaming agent is used alone, highly expanded particles can be easily obtained even if the total amount of foaming agent used is small. Moreover.

In this case as well, there is an advantage that the appropriate temperature range for foaming during foaming is wide, similar to the case where molecular nitrogen-containing inorganic gas is used alone.

〔effect〕

According to the present invention, in any case where a molecular nitrogen-containing inorganic gas is used as a blowing agent alone or in combination with a volatile organic blowing agent, foaming usually has an apparent expansion ratio of 1.5 to 80 times. particles can be obtained. Moreover, in the case of the present invention, it is possible to prevent the adverse effects of the swelling effect of the blowing agent on the polymer particles, so that it is possible to stably obtain expanded particles with less variation in expansion ratio. Furthermore, the expanded particles obtained by the present invention also have the advantage of having a high closed cell ratio and excellent moldability.

The foamed polymer particles obtained according to the present invention are suitably used as pre-foamed particles, and are filled into a mold for molding.
By heating and foaming using a heating medium such as water vapor, a foam molded article according to the shape can be obtained.

〔Example〕

Next, the present invention will be explained in more detail with reference to Examples.

Examples 1 to 3 300 g of polymer particles shown in Table 1 were added to a container with an internal volume of 2100 c.
The mixture was placed in an autoclave with 1350 cc of water and 1 g of finely divided aluminum oxide. The mixture was heated under stirring at a rate of 5°C/min to the foaming temperature shown in Table 1 and held at this temperature for 60 minutes. Next, air or nitrogen as a blowing agent was introduced until the pressure shown in Table 1 was reached, and the pressure was maintained for 1 hour. After that, one end of the autoclave was opened while maintaining the same pressure, and the pressure was 1.5 kg/min/mm2. By discharging into the atmosphere at an average discharge speed of , pre-expanded particles having the apparent expansion ratio shown in Table 1 were obtained. The obtained pre-expanded particles had a high closed cell ratio.

Comparative Examples 1 to 3 Pre-expanded particles were obtained in the same manner as in Examples 1 to 3, except that the blowing agents shown in Table 1 were used.

In this case, butane is inconvenient to handle because it is flammable and poses a risk of fire during preliminary foaming.

In addition, the apparent expansion ratio, particle state, and cell state shown for pre-expanded particles in the table below have the following meanings.

(]) Apparent foaming ratio Sampling is performed at regular intervals during preliminary foaming, and the maximum and minimum values of the measured values are shown.

(2) Particle condition The particle condition was determined as follows by observing the quality of the spherical shape of the pre-expanded particles, presence or absence of shrinkage, particle size, etc.

There is no deformation or shrinkage of the spherical shape, and the particles are of uniform size.
There are some particles with good deformation and shrinkage, and the sizes are uneven. Irregularity of the particles...................................................Poor (3) Cellular condition Cellular condition was determined as follows by observing the cross section of the pre-expanded particles with a microscope.

There are no rough bubbles and the bubbles are of a uniform size...
・・・・・・・・・・・・・・・・・・・・・・・・ Good There is some bubble-loving roughness, and the bubble sizes are slightly uneven.・・・・・・・・・・・・Slightly good There are many rough bubbles and the bubble sizes are uneven.
・・・・・・・・・・・・・・・・・・・・・・・・
...Poor Examples 4 to 7 1000 g of polymer particles shown in Table 2, 3000 g of water
, 3 g of finely divided aluminum oxide, and 100 g of air as a blowing agent were placed in an autoclave having an internal volume of 4950 cc together with the volatile impregnation aid shown in the same table. Under stirring,
After increasing the temperature to a predetermined temperature (Table 2) at a rate of 5° C./min, the temperature was maintained at the same temperature for 60 minutes. Then 45kg/cd
While pressurizing with nitrogen, one end of the autoclave is opened and the polymer particles and water are released into the atmosphere at the same time.
Pre-expanded particles with the apparent expansion ratio shown in Table 2 were obtained. The obtained pre-expanded particles had closed cells and were highly foamed.

Procedures Amendment Document June 6, 1980 1, Indication of the case Patent Application No. 86763 of 1987 2, Name of the invention Process for manufacturing expanded polymer particles 3, Person making the amendment Relationship with the case Patent applicant Address: 2-1-1 Uchisaiwai-cho, Chiyoda-ku, Tokyo Name:
Japan Styrene Paper Co., Ltd. Representative Kazuyoshi Nagano 4, Agent 151 Address 113 Nishiwaki Building, 1-58-10 Yoyogi, Shibuya-ku, Tokyo Name (7450) Patent Attorney Toshiaki Ikeura Telephone (370) 2533-5 , Date of amendment order Issue 1 6, Number of inventions increased by amendment O8, Contents of amendment Insert the following sentence between the 3rd and 2nd lines from the bottom of page 14 of the specification of the present application. .

"Moreover, in the case of the present invention, the effects of the present invention are even more effectively exhibited when the amount of the volatile organic blowing agent used is less than 5 parts by weight per 100 parts by weight of the polymer.

That is, conventionally, when only a volatile organic blowing agent is used as a blowing agent, if the amount used is less than 5 parts by weight per 100 parts by weight of the polymer, foaming hardly occurs or even if foaming occurs, foaming does not occur. You can only get things with extremely low magnification,
Although it did not function as a blowing agent, when used in combination with an inorganic gas, it became effective as a blowing agent even if the amount of volatile organic blowing agent used was less than 5 parts by weight per 100 parts by weight of the polymer. Not only that, but also a synergistic effect is produced, and the effect of eliminating various disadvantages seen when using a volatile organic blowing agent alone is exhibited. ” Procedural amendments January 30, 1985 Manabu Shiga, Commissioner of the Patent Office1, Indication of the case Patent Application No. 86763 of 19832, Name of the invention Process for manufacturing expanded polymer particles3, Amendments made Relationship with the Patent Case Patent Applicant Address 2-1-1 Uchisaiwai-cho, Chiyoda-ku, Tokyo Name
Japan Styrene Paper Co., Ltd. Representative Masaru Uchiyama 4, Agent 151 Address 113 Nishiwaki Building, 1-58-10 Yoyogi, Shibuya-ku, Tokyo Name (7450) Patent attorney Toshiaki Ikeura Telephone (370) 2533 5. Date of amendment order 6. Number of inventions increased by the amendment 0 7. Scope of claims and detailed explanation of the invention in the specification to be amended 8. Contents of the amendment In the specification of the present application, the following: Performs street correction.

(1) The scope of patent claims will be corrected as shown in the attached sheet.

(2) Page 5, line 4, page 5, line 6, page 5, line 12~
Line 13, page 5, line 16, page 8, lines 7-8, page 8, lines 8-9, page 8, line 18, page 8, line 19, line 9
Page 1st line to line 2, page 9 line 8 line to line 9, page 9 line 11, page 10 line 8, page 10 line 9.

Page 10, lines 11-12, page 10, lines 13-14.

Page 10, line 17, page 11, line 7, page 11, lines 13 to 14, page 12, lines 7 to 8, page 12, line 19,
Page 13, line 8, page 13, lines 11 to 12, page 13, line 13, page 13, line 15, page 14, lines 7 to 8,
"Molecular nitrogen-containing inorganic gas" on page 14, line 20, page 15, line 1-2, page 15, line 5, and page 15, line 9-10, is replaced with "nitrogen-containing inorganic gas". I will correct it.

(3) Page 8, line 11, page 8, line 12, page 8, line 16
line, page 9, line 9 and page 9, line 19, “Molecular chamber MJ
"Correct to gaseous nitrogen J.

(4) Correct "straight line" in line 19 of page 8 to "directly."

[Claims (1) When foaming the polymer particles, (i) dispersing the polymer particles in a liquid dispersion medium, (11) heating the polymer particles to a temperature equal to or higher than their softening point, (iii) a step of impregnating the polymer particles with a nitrogen-containing inorganic gas; (1v) moving the polymer particles containing the nitrogen-containing inorganic gas and heated to a temperature above the softening point from the heating zone to the low-pressure zone together with the liquid dispersion medium; 1. A method for producing foamed polymer particles, comprising the steps of: releasing the foam into foam.

(2) The method according to claim 1, wherein the polymer particles are a polyolefin resin.

(3) The method according to any one of claims 1 to 2, wherein the nitrogen-containing inorganic gas is nitrogen gas.

Claims (4)

[Claims] (1) When foaming the polymer particles, (i) dispersing the polymer particles in a liquid dispersion medium, (ii) heating the polymer particles to a temperature equal to or higher than their softening point, (iii,) polymer a step of impregnating the particles with an inorganic gas containing molecular nitrogen; (1v) transferring the polymer particles containing the inorganic gas containing molecular nitrogen and heated to a temperature above the softening point from a heating zone to a low pressure zone together with a liquid dispersion medium; A method for producing foamed polymer particles, comprising the steps of: releasing and foaming the particles. (2) The method according to claim 1, wherein the polymer particles are a polyolefin resin. (3) The method according to any one of claims 1 to 2, wherein the molecular nitrogen-containing inorganic gas is nitrogen gas. (4) The method according to any one of claims 1 to 2, wherein the molecular nitrogen-containing inorganic gas is air.