JPH0455216B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for making polymeric pre-expanded particles. 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, heated and foamed. These pre-expanded particles can be used, for example, in the
As described in Publication No. 56-1344, polymer particles containing a volatile blowing agent are dispersed in water in a closed container, and the pressure inside the container is maintained at the vapor pressure of the blowing agent or higher. After heating the polymer to a temperature higher than the softening temperature of the polymer, one end below the water surface in the container is opened, and the polymer particles and water are simultaneously released into an atmosphere having a lower pressure than the inside of the container. Manufactured by a pre-foaming method of coalescing particles. Volatile blowing agents are used in the production of pre-expanded particles, and examples of the blowing agents include propane, butane, hebutane, hexane, cyclobutane, cyclopentane, trichlorofluoromethane,
Dichlorodifluoromethane etc. are used. However, when these conventional volatile blowing agents are used, the suitable foaming temperature range during pre-foaming is narrow, the influence of foaming temperature on the expansion ratio is large, and the expansion ratio is difficult to control. Was. In addition, these volatile blowing agents are generally expensive, and in order to obtain highly expanded pre-expanded particles, a large amount of blowing agent must be used, which increases the production cost of polymer pre-expanded particles. It also had In any case, although the above-mentioned volatile blowing agents had various problems, they continued to be used because there were no effective blowing agents to replace them. On the other hand, as a result of intensive research in order to eliminate the drawbacks of the above-mentioned conventional technology, the present inventors have discovered that carbon dioxide, which has not been considered as a blowing agent in the past, has been used as a blowing agent to achieve a suitable foaming temperature during pre-foaming. By expanding the scope of the invention, we succeeded in developing a method to inexpensively produce pre-foamed particles that not only can be pre-foamed easily and stably, but also have a high closed cell ratio and excellent moldability, and we have previously filed an application for this patent. However, when carbon dioxide is used alone as a blowing agent, in order to obtain highly expanded pre-expanded particles, the pressure inside the container must be extremely high, and there are some problems such as the need for a container with high pressure resistance. It was left behind. Therefore, as a result of further intensive research, the present inventors found that by impregnating polymer particles with a blowing agent composition consisting of carbon dioxide and a volatile blowing agent, foaming can be easily carried out without raising the internal pressure of the container significantly. We have discovered that it is possible to obtain pre-expanded particles with a high degree of foaming, and that it is also possible to easily obtain pre-expanded particles with a higher degree of foaming than when conventional volatile blowing agents or carbon dioxide alone are used as the blowing agent. The present invention has now been completed. That is, the present invention impregnates polymer particles with a blowing agent composition consisting of carbon dioxide and a volatile blowing agent containing more than 30 mol% and less than 85 mol% of the total number of moles of carbon dioxide. a step of dispersing the polymer particles in a dispersion medium in a closed container; a step of heating the polymer particles above a temperature at which the particles soften; and a step of opening one end of the container to separate the polymer particles and the dispersion medium. The gist of the present invention is to provide a method for producing pre-expanded polymer particles, which comprises a step of simultaneously releasing the inside of the container into a low-pressure atmosphere. Materials for the polymer particles used in the present invention include polyethylene resins such as low-density polyethylene, high-density polyethylene, and linear low-density polyethylene, propylene homopolymers, ethylene-propylene random copolymers, and ethylene-propylene block copolymers. Examples include polypropylene resins such as polymers, polyolefin resins such as ethylene-vinyl acetate copolymers, and polyesters such as aromatic polyester/polyether glycol block copolymers. Furthermore, in addition to the above-mentioned polymers, polymers such as polystyrene, polyvinyl chloride, and polyamide elastomer can also be used. However, among these polymers, crystalline polyolefin resins are preferred. Further, these may be either crosslinked or non-crosslinked. The step of impregnating the polymer particles with a blowing agent composition consisting of a volatile blowing agent of carbon dioxide may be carried out before or after the step of dispersing the polymer particles in a dispersion medium, but usually involves dispersing or heating the polymer particles. Do it when you do it. Carbon dioxide can be used in either a gaseous, liquid, or solid state such as dry ice, and carbon dioxide and a volatile blowing agent can be mixed together and then impregnated into polymer particles. may be individually impregnated into polymer particles. The volatile blowing agents include propane, n-butane, i-butane, butylene, i-butene, pentane, neopentane, aliphatic hydrocarbons such as hexane, monochloromethane, monochloroethane, dichlorofluoromethane, dichlorodifluoromethane, etc. methane,
Examples include halogenated aliphatic hydrocarbons such as trifluoromethane, and cyclic aliphatic hydrocarbons such as cyclopentane and cyclohexane, and one or more of these may be appropriately selected and used. The content of the volatile blowing agent in the blowing agent composition consisting of carbon dioxide and the volatile blowing agent is more than 30% mole and not more than 85 mole% based on the total number of moles of carbon dioxide and the volatile blowing agent. be. If the amount of volatile blowing agent relative to carbon dioxide is less than or exceeds the above range, the resulting pre-expanded particles will have large deformation and shrinkage of the particle shape, and will have irregular sizes.
Moreover, the resulting particles are extremely rough with bubbles. The above blowing agent composition is 5 to 5 parts by weight per 100 parts by weight of the polymer particles.
Use 30 parts by weight. The heating temperature and heating time in the step of impregnating the polymer particles with the blowing agent composition vary depending on the type of volatile blowing agent in the blowing agent composition, the type of resin in the polymer particles, etc. For polymer particles consisting of the following, the melting point is usually -50°C to +50°C for 20 to 120 minutes. The heating temperature in the step of heating the polymer particles to a temperature higher than the temperature at which the particles soften is preferably from melting point -10°C to melting point +50°C for crystalline polymers. Further, in the case of an amorphous polymer, the heating temperature is preferably from the softening temperature +10°C to the softening temperature +70°C. In the present invention, it is not necessary to carry out the impregnation step and the step of heating above the softening temperature separately, but it is possible and preferable to carry out them simultaneously. In the present invention, the melting point of the above polymer is determined by differential scanning calorimetry (DSC) by heating a sample to 200 to 300°C at a rate of 10°C/min in a nitrogen atmosphere.
After that, the temperature was lowered to 50℃ at a rate of 10℃/min, and then 10℃/min again.
The melting point is determined by the apex of the melting peak when the temperature is raised at a rate of 100 min. If there are multiple peaks, the average temperature is taken as the melting point, and the softening temperature of the polymer is determined by the ASTM
These melting points are determined by D648 and a load of 4.6Kg/ ^cm2 ,
The heating temperature of the polymer particles is set based on the softening temperature. When dispersing polymer particles in a dispersion medium, a dispersant is used to prevent the polymer particles from fusing together.
Examples of the above-mentioned dispersants include finely divided aluminum oxide and titanium oxide, basic magnesium carbonate, basic zinc carbonate, calcium carbonate, etc., and the amount used is usually 0.01 to 10 parts by weight per 100 parts by weight of the polymer particles.
Parts by weight. Water, ethylene glycol, glycerin, methanol, ethanol, or a mixture thereof can be used as a dispersion medium, but water is usually preferred. In the present invention, one end of the container is opened and the polymer particles and dispersion medium are released into an atmosphere with a lower pressure than the inside of the container.
80Kg/cm ² , and a normal pressure atmosphere is usually selected as the low pressure atmosphere. The polymer pre-expanded particles obtained by the present invention usually have an apparent expansion ratio of 5 to 40 times. Further, according to the present invention, it is possible to stably obtain pre-expanded particles with little variation in expansion ratio, and the obtained pre-expanded particles have a high closed cell ratio and are excellent in moldability. Moreover, a foam molded article according to the mold can be obtained by filling a mold with the pre-expanded particles obtained by the present invention and heating and foaming the particles using a heating medium such as water vapor. As explained above, the present invention utilizes carbon dioxide by using a blowing agent composition consisting of carbon dioxide and a volatile blowing agent as a blowing agent to be impregnated into polymer particles when producing pre-expanded polymer particles. Due to the synergistic effect of the foaming effect of the foaming agent and the foaming effect of the volatile foaming agent, it is possible to obtain pre-expanded particles with a higher degree of foaming than when foaming is performed using carbon dioxide or a volatile foaming agent alone as the foaming agent. Furthermore, unlike when carbon dioxide is used as a blowing agent, there is no need to increase the pressure inside the container to obtain a highly foamed product, and it is extremely easy to use even if the amount of blowing agent composition used is small. Highly foamed pre-expanded particles can be obtained, and the blowing agent composition contains more than 30 mol% and 85 mol% or less of a volatile blowing agent based on the total number of moles with carbon dioxide. Because of the shrinkage of particles,
It is possible to obtain excellent pre-expanded particles that are not deformed, have a uniform size, and do not have rough bubbles. Further, according to the present invention, the appropriate foaming temperature range during pre-foaming is wide;
It is possible to stably obtain pre-expanded particles with little variation in expansion ratio and a high closed cell ratio. Furthermore, as mentioned above, highly foamed pre-expanded particles can be obtained even if the amount of the blowing agent composition used is small, and the carbon dioxide constituting the blowing agent composition can be supplied at low cost, making it easy to produce pre-expanded particles. It has various effects such as lower cost. EXAMPLES The present invention will be explained in more detail below with reference to Examples. Examples 1 to 5, Comparative Examples 1 to 6 1000 g of polymer particles shown in Table 1 and 5 g of finely divided aluminum oxide were mixed with carbon dioxide (dry ice),
It was placed in an autoclave with an internal volume of 5000 c.c. together with a volatile blowing agent. Table 1 shows the amount of carbon dioxide and the type and amount of volatile blowing agent. Next, these were stirred in an autoclave,
After heating to the foaming temperature shown in Table 1 at a temperature increase rate of 5°C/min and holding at the same temperature for 60 minutes, one end of the autoclave was opened while pressurizing with 55 kg/cm ² of nitrogen to separate the polymer particles and water. were simultaneously discharged into the atmosphere at a discharge rate of 1000 g/min/mm ² to foam the polymer particles to obtain pre-expanded particles. As shown in the table, the pre-expanded particles of Examples had a larger apparent expansion ratio than the pre-expanded particles of Comparative Examples, had no particle shrinkage or deformation, had a uniform particle shape, and had no rough or irregular bubbles. It was in good condition with no defects. 【table】

Claims (1)

[Claims] 1 The polymer particles contain more than 30 mol% and 85 mol% of the total number of moles of carbon dioxide and the carbon dioxide.
A step of impregnating a blowing agent composition consisting of a volatile blowing agent containing the following, a step of dispersing polymer particles in a dispersion medium in a closed container, and heating the polymer particles to a temperature higher than the temperature at which the particles soften. 1. A method for producing pre-expanded polymer particles, which comprises the steps of: opening one end of the container and simultaneously releasing the polymer particles and dispersion medium from inside the container into a low-pressure atmosphere.