JPH0561300B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for pre-foaming expandable polyolefin resin particles (hereinafter abbreviated as resin particles) containing talc as an inorganic nucleating agent.
More specifically, foamable resin particles containing a volatile foaming agent are heated to a temperature higher than the softening temperature of the resin under pressure higher than the vapor pressure of the volatile foaming agent, and then the resin particles are released into a low pressure region. The present invention relates to a method for pre-foaming expandable resin particles, characterized in that the pre-foaming method uses resin particles obtained by adding a specific amount of talc as an inorganic nucleating agent to a resin. Pre-expanded particles with fine bubbles and extremely uniformity are obtained. The cell diameter of the pre-expanded particles used in in-mold foam molding depends on the flexibility, cushioning properties, and
Considering the appearance etc., the maximum diameter is 500μm,
It is said that a thickness of 300 μm or less is particularly preferable. Conventionally, there is a known method of pre-foaming resin particles by dispersing resin particles, a blowing agent, and water in a pressurized container such as an autoclave, bringing the container to a high temperature and high pressure state, and then opening the container to a low pressure region. This is described, for example, in West German Published Patent Publication No. 2107683, Japanese Patent Publication No. 1344/1983, and the like. When pre-foaming is carried out by these methods, for example, the method disclosed in Japanese Patent Publication No. 1344/1983, the cell diameter of the pre-foamed particles is
Only those with a diameter of 500 μm or more could be obtained, and only those with irregular bubble diameters within and between particles were obtained, so they had no commercial value. The present inventors have conventionally proposed a method of adding ethylene bis fatty acid amide, organic amide, etc., known as a nucleating agent, to the resin for the purpose of uniformly making the cell diameter finer in the pre-foaming of resin particles. However, the cell diameter of the pre-expanded particles was about the same as that without additives, and there was almost no effect of making the cell diameter uniform and fine. The present inventors have conducted intensive research to overcome such problems and to industrially utilize a process that can accomplish the inclusion of a blowing agent into resin particles and pre-foaming in one step, and have finally completed the present invention. Ivy. That is, the present invention involves heating expandable polyolefin resin particles containing a volatile blowing agent dispersed in water in a pressure-resistant container to a temperature higher than the softening temperature of the resin under pressure higher than the vapor pressure of the volatile blowing agent. In a pre-foaming method for resin particles in which a mixture of the particles and water is released into a low pressure region after heating, resin particles containing 0.01 to 1 part by weight of talc as an inorganic nucleating agent per 100 parts by weight of resin. The present invention provides a method for pre-foaming expandable thermoplastic resin particles, which is characterized by using the following methods. According to the method of the present invention, pre-expanded particles with fine bubbles and extremely homogeneous cells can be obtained, and easily have a diameter of 500 μm.
Cell diameters of ~300 μm or less, even 100 μm or less, are achieved. Furthermore, the present invention has significant advantages in terms of foaming technology, such as making the surface appearance of the foamed particles more beautiful due to the miniaturization of the cells, and further improving the foaming ratio. The inorganic nucleating agent used in the present invention is talc, and the amount added is 0.01 to 100 parts by weight of the resin.
1 part by weight, preferably 0.01 to 0.5 part by weight.
When forming foamed particles with a foaming ratio of 30 times using a combination of low-density polyethylene and dichlorodifluoromethane, the amount of talc added is 0.01 to 0.1 part, and when a combination of ethylene-propylene random copolymer and butane is used, the foaming ratio is 30 times. When forming expanded particles, the preferred amount of talc added is 0.05 to 1 part. When forming foamed particles with a foaming ratio of 40 times using a combination of ethylene-propylene random copolymer and dichlorodifluoromethane, the amount of talc added is
0.01 to 0.5 part is preferred. In general, if the amount added is less than 0.01 part by weight, it is difficult to obtain the desired effect of making the bubbles uniform and fine, and even if it is added in excess of 1 part by weight, the remarkable effect of adding a large amount may not be obtained, or the desired effect may not be achieved. This tends to cause the effect to be lost. In the present invention, the inorganic nucleating agent may be added using any commonly used method, but
For example, there are the dry blend method and the master batch method. Any method may be used as long as the inorganic nucleating agent of the present invention is uniformly added to the resin particles before foaming. The type of resin particles used in the present invention is not particularly limited as long as it is a thermoplastic resin that can contain a volatile foaming agent and can exhibit a viscoelastic state suitable for foaming when heated, but may include low-density polyethylene, medium-density polyethylene, Density polyethylene and high-density polyethylene are preferred, and ethylene-propylene random copolymers are particularly preferred. The particle size of the resin particles is preferably in the range of 300 to 5000 μm, but there is no particular restriction on the particle size. Volatile blowing agents used in the present invention include those having a boiling point in the range of -60 to 120°C under atmospheric pressure, such as aliphatic hydrocarbons such as propane, butane, pentane, hexane, and heptane. ; Aliphatic cyclic hydrocarbons such as cyclobutane and cyclopentane, and trichloromonofluoromethane, dichloromonofluoromethane, dichlorodifluoromethane, dichlorotetrafluoroethane, trichlorotrifluoroethane, perfluorocyclobutane , methyl chloride, methylene chloride, ethyl chloride, halogenated hydrocarbons such as trichloroethylene, etc., and these volatile blowing agents are used singly or as a mixture of two or more. In the present invention, when dispersing resin particles in water, it is desirable to use a small amount of a dispersant to prevent agglomeration of the resin particles during heating. Dispersants include water-soluble polymers such as polyvinyl alcohol, carboxymethylcellulose, and N-polyvinylpyrrolidone; inorganic substances that are poorly soluble in water such as calcium phosphate and magnesium pyrophosphate, or these inorganic substances and a small amount of dodecylbenzenesulfonic acid. A combination of anionic surfactants such as sodium and sodium α-olefin sulfonate is used. The heating temperature in the method of the present invention is equal to or higher than the softening temperature of the resin containing the foaming agent, or the softening temperature + 50°C.
A suitable range is selected within this range depending on the type of resin and the type and amount of the volatile blowing agent contained. For example, a combination of ethylene-propylene random copolymer and dichlorodifluoromethane allows foaming in the range of 120 to 160°C. The pressure inside the container during foaming in the method of the present invention is the vapor pressure of the foaming agent to the vapor pressure + 30Kg/cm ²
It is appropriate to hold it at G. The vapor pressure of the blowing agent referred to here is the pressure of the system when resin particles and the blowing agent are dispersed in water and heated. If you want to obtain a pressure higher than this vapor pressure, use an inert gas such as _N2 . It is also possible to pressurize the system with gas. As the mixture of resin particles and water inside the container is released, the mixture of resin particles and water inside the container decreases, so the blowing agent or an inert gas such as N ₂ is added to the upper space of the container from outside the container. It is preferable to maintain the pressure inside the pressure vessel by introducing In addition, in the present invention, a small orifice is inserted before or after the discharge valve, or the discharge port from the discharge valve is throttled to control the discharge amount and make it easier to maintain the pressure inside the container. Particles can be easily obtained as single particles. The low-pressure zone in the present invention may be any atmosphere having a lower pressure than the inside of the pressurized container, but is usually preferably at atmospheric pressure or reduced pressure. In the present invention, by containing talc, the pre-expanded particles have a uniform and fine cell diameter, have a good surface appearance, and have an improved expansion ratio. The pre-expanded particles obtained in the present invention can be used directly or after being re-foamed with an inert gas, filled into a mold and fused by steam heating etc. to produce a foamed molded article. However, in this case, if the pre-expanded particles of the present invention having uniform fine cells are used, the properties of the obtained molded product, especially flexibility, cushioning properties, surface appearance, etc., will be extremely excellent, and therefore it will be a good product. It has the advantage of increasing in value. Conventionally, one of the technical challenges has been to make the cell diameter of pre-expanded thermoplastic resin particles small and uniform. For example, in the case of polystyrene resin, an organic substance such as ethylene bis fatty acid amide or organic amide is added as a nucleating agent, or a preform with uniform fine bubbles is formed by steam foaming after impregnation with a blowing agent and aging etc. after impregnation with a blowing agent. Foamed particles are obtained. In the pre-foaming of polyethylene resin, pre-foamed particles having uniform fine cells are obtained by cross-linking the resin, setting the temperature during impregnation with a blowing agent, etc. Furthermore, in the pre-foaming of polypropylene resin, the purpose is achieved by adding compounds such as fatty acid amides and glycerin esters of fatty acids; This method is applied to a method in which particles are foamed by contacting them with a heating medium such as steam in a container to form pre-expanded particles.
On the other hand, as a method for foaming synthetic resins, an extrusion foaming method is known, in which foaming is carried out under high temperature and high pressure using an extruder, etc., and the mixture is extruded from a die to a low pressure region. Its use is known. However, the reserve obtained by the foaming method of the present invention, that is, the foaming method in which resin particles containing a blowing agent are dispersed in water in a container and the mixture of resin particles and water is discharged from a high temperature and high pressure to a low pressure zone. There is no method disclosed for solving the technical problem of making the cell diameter of expanded particles fine and uniform, and the present invention is the first to solve this problem. Furthermore,
In addition, in the extrusion foaming method, the amount of the cell regulator used to make the cell size of the foam uniform and fine is at least 0.5 parts, and adding a small amount as in the present invention will not produce any effect. In addition, in the extrusion foaming method, as mentioned above, the cell diameter obtained by using a cell control agent is about 300 μm at the most, and it is difficult to achieve a cell size of 300 μm or less, or even 100 μm or less, as in the present invention. It is difficult. Next, the present invention will be explained with reference to Examples and Comparative Examples. The evaluation scales shown in the following Examples and Comparative Examples are classified as follows. Cell diameter of pre-expanded particles (measured in accordance with JIS-K6402) Code Evaluation A Average cell diameter is less than 200 μm B 〃 200 μm or more and less than 500 μm C Average cell diameter is 500 μm or more The compounds used in Examples and Comparative Examples are as follows. It is written in Talc (manufactured by Hayashi Kasei Co., Ltd.; Talcan Powder P.
K) Ethylene bisstearamide (manufactured by Kao Sekiken Co., Ltd.; Wax EB-P) Stearic acid amide (manufactured by Kao Sekiken Co., Ltd.; Amide T) Examples 1 to 4, Comparative Example 1 Ethylene-propylene random copolymer (density 0.90, MI = 9, ethylene content 4.5% by weight), talc listed in Table 1 was added, dry blended, and extruded under normal conditions to make pellets with a particle size of approximately 2 μm Φ. parts by weight of powdered basic tribasic calcium phosphate as a dispersant.
0.5 parts by weight and 0.025 parts by weight of sodium dodecylbenzenesulfonate were dispersed in 300 parts by weight of water, and while stirring, 55 parts by weight of dichlorodifluoromethane was added and the temperature was raised to 135°C. Subsequently, while maintaining the pressure inside the container at 30Kg/cm ² G with N ₂ , a hole with a diameter of 3 mm was made in a cylindrical plate attached after the release valve.
The pellets and water were released into atmospheric pressure through the holes to obtain pre-expanded particles. The results of evaluating the obtained pre-expanded particles are shown in Table 1, and the foamed particles of Examples were beautiful with uniform cells and fine cell diameters. On the other hand, when no talc was added, as shown in Comparative Example 1, the foamed particles had large cell diameters and were non-uniform, and had no commercial value.

[Table] Comparative Examples 2 to 5 Example 1 except that ethylene bisstearamide and stearamide were used as additives.
Polymer pre-expanded particles were obtained in the same manner as in 4.
The foaming results and evaluation results are shown in Table 2. These conventional foam control agents for so-called pre-expanded polymer particles were not found to have any effect of uniformly making the cells fine.

【table】

[Table] Example 5 Talc was added to linear low-density polyethylene (comonomer: 1-butene) with a resin density of 0.92 and an MI of 1.0.
0.02 part by weight was added to make pellets with each grain weighing 4.5 mg, the temperature inside the container was 117℃, and the pressure inside the container was 27Kg/cm ² G.
Pre-expanded particles were obtained in the same manner as in Example 1 except for the following. The expansion ratio of the obtained pre-expanded particles is 26
The average bubble diameter was 150 μm (rank A) and uniform. As a comparative example, pre-expanded particles were obtained in the same manner as in the example without adding talc.
The foaming ratio was 13 times, the average cell diameter was C to B, and the cells were very non-uniform. Examples 6 to 8, Comparative Example 6 Examples 1 to 4 except that 40 parts by weight of n-butane was used as the volatile blowing agent and the heating temperature was 115°C.
It was carried out under the same conditions. The foaming results and evaluation results are shown in Table 3, and it can be seen that the cells in each Example were more uniform and finer and the surface appearance was better than in the Comparative Example.

[Table] Examples 9 to 10, Comparative Example 7 Examples 1 to 1 except that an ethylene-propylene random copolymer with MI = 30 and ethylene content of 3.5% by weight was used, and the heating temperature was 141°C.
It was carried out under the same conditions as in 4. The foaming results and evaluation results are shown in Table 4, and the bubbles in each example were more uniform and finer than in the comparative example, and the surface appearance was excellent.

【table】 [Brief explanation of the drawing]

FIG. 1 and FIG. 2 are microscopic photographs of expanded particles obtained in Example 1 and Comparative Example 1, respectively.

Claims (1)

[Claims] 1. After heating expandable polyolefin resin particles containing a volatile blowing agent dispersed in water in a pressure-resistant container under pressure higher than the vapor pressure of the volatile blowing agent to a temperature higher than the softening temperature of the resin, In the pre-foaming method of resin particles in which the mixture of particles and water is discharged into a low pressure region, it is recommended to use resin particles containing 0.01 to 1 part by weight of talc as an inorganic nucleating agent per 100 parts by weight of resin. A method for pre-foaming expandable thermoplastic resin particles for molding in bead molds.