JPH0464334B2 - - Google Patents

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 the polymer to a temperature above the softening temperature of the polymer while maintaining the pressure at the vapor pressure of the blowing agent or higher, one end below the water surface in the container is opened, and the polymer particles and water are poured into the container at the same time. from,
It is produced by discharging into an atmosphere with a lower pressure than the internal pressure of the container. In this case, volatile organic blowing agents include, for example, propane, butane, heptane,
Hexane, cyclobutane, cyclopentane, trichlorofluoromethane, dichlorodifluoromethane, etc. are used. However, these volatile organic blowing agents act as good solvents for the polymer and swell the polymer particles, so the suitable temperature range for foaming during pre-foaming is narrow, and the effect of foaming temperature on the expansion ratio is small. The problem was that it was difficult to control the foaming ratio. In addition, some of these volatile organic blowing agents are toxic and flammable and therefore dangerous, while others are expensive and difficult to use, even though they do not present much of a problem in terms of danger. Therefore, 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 environmental pollution problems such as destruction of the ozone layer. In any case, although the above-mentioned volatile organic blowing agents had various problems, they continued to be used because no effective blowing agent existed to replace them. [Objective] The object of the present invention is to provide a method for producing expanded polymer particles, which 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 inventors have discovered that various effects that could not be achieved with conventional methods, such as increased safety and prevention of environmental pollution problems, have been achieved, and have completed the present invention. [Structure] That is, according to the present invention, when foaming polymer particles, there are the following steps: () dispersing the polymer particles in a liquid dispersion medium; () heating the polymer particles to a temperature equal to or higher than their softening point; () A step of bringing the polymer particles into contact with a nitrogen-containing inorganic gas having an absolute pressure of 30 kg/cm ² or more, thereby impregnating the polymer particles with the nitrogen-containing inorganic gas, () containing the nitrogen-containing inorganic gas, and A method for producing expanded polymer particles is provided, which comprises the step of foaming polymer particles heated to a temperature equal to or higher than their softening point, together with a liquid dispersion medium, from a heating zone to a low-pressure zone. The method of the present invention includes a step of impregnating polymer particles with a nitrogen-containing inorganic gas (impregnation step), dispersing the polymer particles in a liquid dispersion medium (dispersion step), and heating the polymer particles to a temperature higher than their softening point. The method includes a heating step (heating step) and a step of foaming polymer particles impregnated with nitrogen-containing inorganic gas (foaming step). In the present invention, these steps are generally preferably carried out in the same container,
Each step can be performed 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, or the impregnation step, the dispersion step, or the impregnation step 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 the dispersion medium. As the dispersing agent, liquid substances such as water, ethylene glycol, glycerin, methanol, and ethanol are usually used.
Generally water is preferred. The amount of dispersion medium used is
The amount is 1.5 parts by weight or more, preferably 2 to 5 parts by weight, per 1 part by weight of the polymer particles. Further, in this dispersion step, an anti-fusing agent for the polymer particles is preferably used, and such agents include:
Preferred solid particles that do not melt in the heating step, such as aluminum oxide, titanium oxide, basic magnesium carbonate, basic zinc carbonate, and calcium carbonate, are of course not limited to these. For example, organic fine particles that are insoluble in urea-formaldehyde resin or other dispersion medium are also 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 usually preferably in the range of (melting point -30°C) to (melting point +40°C) for non-crosslinked crystalline polymer particles, and for crosslinked crystalline polymer particles. The temperature is usually from (melting point -20°C) to (melting point +120°C) preferably. In addition, for amorphous polymer particles (softening point +10
Temperatures in the range of (softening point + 120°C) are preferred. In addition, the softening point of the polymer particles in the present invention is
The value was determined according to ASTMD643 and a load of 4.6 kg/mm ² , and the melting point of the polymer particles was determined by differential scanning calorimetry (DSC). The melting point is determined by heating the sample at a rate of 10°C/min to 200 to 300°C in a nitrogen atmosphere, then increasing the temperature to 50°C at a rate of 10°C/min, and then increasing the temperature again at a rate of 10°C/min. This is the peak temperature of the melting peak when heated, and if there are multiple peaks, this is the highest temperature. This heating step is preferably carried out simultaneously with the above-described dispersion step in the same heating 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 nitrogen-containing inorganic gas by bringing the nitrogen-containing inorganic gas into contact with the polymer particles under pressure.
Conventionally, it has not been known that gaseous nitrogen is effective as a blowing agent for unfoamed polymer particles. Until now, gaseous 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 gaseous nitrogen is effective as a blowing agent for polymer particles. When bringing the nitrogen-containing inorganic gas into contact with the polymer particles, the nitrogen-containing inorganic gas may be brought into direct contact in a gaseous state, or may be brought into contact via a liquid. When the contact is made through a liquid, the nitrogen-containing inorganic gas comes into contact with the polymer particles in a form dissolved in the liquid. The pressure is 30Kg/cm ² or more as an absolute pressure. 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 nitrogen-containing inorganic gas, any gas containing gaseous nitrogen is usually used. For example, in addition to nitrogen gas, air is preferably used as the nitrogen-containing inorganic gas, and argon, xenon, Nitrogen gas or air enriched with an inert gas such as helium, neon, or 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 within a range that is not dangerous and does not impede the purpose of the present invention. In the present invention, generally,
Gaseous nitrogen at least 5% by volume, preferably 10% by volume
It is advantageous to use gases containing the above. 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 the impregnation step is carried out with polymer particles dispersed in a dispersion medium, the polymer particles are brought into contact with a nitrogen-containing inorganic gas dissolved or dispersed in the dispersion medium, whereby nitrogen-containing The inorganic gas is impregnated into the polymer particles, or the nitrogen-containing inorganic gas is impregnated into the polymer particles at the moment the polymer particles are suspended at the boundary between the dispersion medium phase and the gas phase by stirring. Further, the impregnation of the polymer particles with the nitrogen-containing inorganic gas can also be carried out in the presence of a volatile impregnation aid, unless the purpose of the present invention is particularly impaired. By using this volatile impregnation aid in combination, the impregnation ratio of the nitrogen-containing inorganic gas to the polymer particles can be increased. Specific examples of this impregnation aid include acetone,
Examples include toluene, xylene, heptane, ethyl ether, dioxane, methyl acetate, ethyl acetate, tetrahydrofuran, styrene monomer, isoprene oligomer, dipentene, etc., and any one can be used as long as it has a plasticizing effect on polymer particles. be done. This volatile impregnation aid usually has a boiling point of -50 to 250°C, preferably -30 to 200°C, and for the impregnation process, it can be supplied together with a nitrogen-containing organic gas, or it can be supplied in advance as a dispersion medium. It can be supplied in the form of a mixture of The proportion of volatile impregnating aid used is 0.5 to 30% of the polymer particles.
% by weight, preferably 2-20% by weight. In the foaming step, a homogeneous mixture of softened polymer particles containing 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 (pressurized (inside the pressurized container) into a low pressure zone (outside the pressurized container).
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 process, foamed polymer particles are obtained, and in this case, the foaming ratio of the resulting foamed particles is generally 1.5.
The foamed particles can be used as they are for various purposes, but it is especially suitable to use them as pre-expanded particles for heat molding.In this case, the expansion ratio is 5 to 50 times. It is best to specify a range. In the present invention, by using a 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 foaming agent used in this case is nonflammable and highly safe, and even if the foamed particles are released into the atmosphere after foaming, they will not destroy the ozone layer and cause air pollution. do not have. 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, which makes it possible to increase the impregnation rate of the 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 nitrogen-containing inorganic gas as a blowing agent for the polymer particles, but in this case, a volatile organic blowing agent, which has conventionally been generally used as a blowing agent, may be used in combination. You can also do it. When a nitrogen-containing inorganic gas and a volatile blowing agent are used together for polymer particles, the polymer particles may be impregnated with the nitrogen-containing inorganic gas and the volatile blowing agent at the same time, or the nitrogen-containing inorganic gas and the volatile blowing agent may be impregnated into the polymer particles at the same time. The volatile blowing agent can also be impregnated into the polymer particles in separate steps. Volatile organic blowing agents include propane, n-butane, iso-butane, butylene, iso-butene, pentane, neopentane,
Aliphatic hydrocarbons such as hexane; halogenated aliphatic hydrocarbons such as monochloromethane, monochloroethane, dichlorofluoromethane, dichlorodifluoromethane, trifluoromethane, trichlorotrifluoroethane, etc.; cyclopentane, cyclohexane, etc. Examples include cycloaliphatic hydrocarbons. In the present invention, these volatile organic blowing agents are used alone or in the form of a mixture. The proportion of volatile organic blowing agents used is nitrogen-containing inorganic gas.
The proportion of the volatile organic blowing agent to 100 parts by weight is preferably 2 to 200 parts by weight, particularly 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. Moreover, in the case of the present invention, when the amount of the volatile organic blowing agent used is less than 5 parts by weight based on 100 parts by weight of the polymer, the effects of the present invention are even more effectively exhibited. In other words, 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, there will be almost no foaming, or even if foaming occurs, the expansion ratio will be extremely low. However, by combining it with an inorganic gas, the amount of volatile organic blowing agent used was reduced to 100%.
Even if the amount is less than 5 parts by weight, it not only acts effectively as a blowing agent, but also produces a synergistic effect, and can eliminate various disadvantages that can be seen when using a volatile organic blowing agent alone. In the present invention, the use of a nitrogen-containing inorganic gas and a volatile organic blowing agent together as a blowing agent as described above has a synergistic effect on the foaming effect. Compared to the conventional method, highly expanded particles can be easily obtained even if the total amount of blowing agent used is small. Moreover, in this case as well, there is an advantage that the appropriate foaming temperature range during foaming is wide, similar to the case where a nitrogen-containing inorganic gas is used alone. [Effect] According to the present invention, in any case where a nitrogen-containing inorganic gas is used as a blowing agent alone or in combination with a volatile organic blowing agent, the foamed particles usually have an apparent expansion ratio of 1.5 to 80 times. 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 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 and heated and foamed using a heating medium such as water vapor to form foamed particles according to the mold. You can get a body. [Example] Next, the present invention will be explained in more detail with reference to Examples. Examples 1 to 3 300g of polymer particles shown in Table 1 were added to a container with an internal volume of 2100
cc autoclave with 1350 c.c. of water and 1 g of particulate aluminum oxide. under stirring, 5
The mixture was heated at a rate of 0.degree. 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 autoclave was held for 1 hour, and then one end of the autoclave was opened while maintaining the same pressure.
Pre-expanded particles having the apparent expansion ratio shown in Table 1 were obtained by discharging into the atmosphere at an average discharge rate of 1.5 Kg/min/mm ² . The obtained pre-expanded particles had a high closed cell ratio. Comparative Examples 1 to 3 Examples 1 to 3 except that the blowing agents shown in Table 1 were used.
Pre-expanded particles were obtained in the same manner as in case 3. 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. (1) Apparent foaming ratio Sampling is performed at regular intervals during pre-foaming, and the maximum and minimum values of the measured values are shown. (2) Particle condition Particle condition refers to the quality of the spherical shape of the pre-expanded particles;
The presence or absence of shrinkage, particle size, etc. were observed and judged as follows. There is no deformation or shrinkage in the spherical shape, and the particles are uniform in size...good There are some deformed or shrunk particles, and the sizes are uneven...slightly poor: there are an extremely large number of deformed or shrunk particles. , irregular size...Poor (3) Cell condition Cell 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 bubble sizes are even.Good.There are some rough bubbles and the bubble sizes are slightly uneven.Slightly good.There are a lot of rough bubbles and the bubble sizes are uneven.Poor.

【table】

[Table] Examples 4 to 7 100 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 mixed together with the volatile impregnating aid shown in the same table in an internal volume of 4950 c. .c. was placed in an autoclave. While stirring, the temperature was raised to a predetermined temperature (Table 2) at a rate of 5° C./min, and then maintained at the same temperature for 60 minutes. Next, one end of the autoclave was opened while pressurizing with 45 kg/cm ² of nitrogen, and the polymer particles and water were released into the atmosphere at the same time, thereby obtaining pre-expanded particles having the apparent expansion ratio shown in Table 2. . The obtained pre-expanded particles had closed cells and were highly foamed.

【table】

Claims (1)

[Claims] 1. When foaming polymer particles, () a step of dispersing the polymer particles in a liquid dispersion medium, () a step of heating the polymer particles to a temperature equal to or higher than their softening point, () an absolute pressure A step of contacting the polymer particles with a nitrogen-containing inorganic gas having a nitrogen-containing inorganic gas of 30 kg/cm ² or more, thereby impregnating the polymer particles with the nitrogen-containing inorganic gas, 1. A method for producing foamed polymer particles, comprising the step of foaming the heated polymer particles together with a liquid dispersion medium from a heating zone into a low pressure zone. 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. 4. The method according to any one of claims 1 to 2, wherein the nitrogen-containing inorganic gas is air.