JPS58136631A - Production of expanded propylene resin particle - Google Patents

Abstract

PURPOSE:To obtain the titled highly expanded particles, by carrying out the blowing agent impregnation and heating of polypropylene particles in multiple stages and employing a mixed gas consisting of an inorganic gas and a low- boiling organic compound as blowing agents used in the second and subsequent stages. CONSTITUTION:The impregnation and heating of polypropylene resin particles, such as propylene/ethylene random copolymer particles or propylene/ethylene/ butene random terpolymer particles, with a blowing agent are carried out in multiple stages. Then, a mixed gas consisting of 1mol of an inorganic gas such as nitrogen, argon or helium and 0.01-3mol of a low-boiling (b.p. -50-50 deg.C) organic compound such as dichlorodifluoromethane, trichloromonofluoromethane or propane is used as the blowing agent in the second and subsequent stages. Thus, it becomes possible to obtain highly expanded resin particles by a synergistic effect of the inorganic gas and the low-boiling organic compound.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a polypropylene resin foaming method which is applied to molding etc. in order to obtain a molded article of a desired shape by incorporating a foaming agent into resin particles and heating them to obtain pre-expanded particles. This article relates to a method for producing particles, and a method for producing foamed polypropylene resin particles with a high expansion ratio in order to obtain molded articles having flexibility, cushioning properties, and toughness suitable for packaging materials and cushioning materials. .

Polystyrene and polyethylene are commonly used as base resins for foam molded products formed by in-mold molding.

When polystyrene is used as the base resin, foaming agent retention properties,
Although it has excellent workability and rigidity, it has brittleness, low temperature characteristics,
Poor chemical resistance. On the other hand, when polyethylene is used as the base resin, the foaming agent retention, processability, and rigidity are inferior, but it is flexible and strong, and has excellent low-temperature properties and chemical resistance. As described above, both have advantages and disadvantages, and at present they are used differently depending on the purpose.

The major disadvantages of polystyrene foam are its low heat resistance and its brittleness and easy breakage.The disadvantages of polyethylene foam are its low heat resistance and its expansion ratio, which has physical properties suitable for use as a cushioning material. The disadvantage is that the raw material cost is high due to the low magnification ratio.

Polypropylene resin has the same flexibility, toughness, low-temperature properties, and chemical resistance as polyethylene resin, which is also a polyolefin-based resin, and has a high heat resistance and high rigidity and strength, so it is the same as polyethylene foam. In the case of a foam having a cushioning performance of 1, the density can be lower than that of polyethylene, and the cost of raw materials is reduced, which is economically advantageous, so there is a great advantage in obtaining a molded product with a high expansion ratio. However, polypropylene resin particles contain a blowing agent consisting of a low-boiling organic compound that is normally used in the manufacture of polystyrene foam and polyethylene by the bead method, and are foamed by heating to form a preliminary material for in-mold molding. Even if one attempts to obtain expanded particles, only expanded particles with a low expansion ratio can be obtained.

The inventors of the present invention have conducted intensive research into a method for producing highly foamed foamed particles that overcomes the problems of polypropylene resins, and have found that when appropriate combinations of raw material resin type, foaming method, and foaming agent are used, the desired result can be obtained. The present invention was completed based on the discovery that foamed polypropylene resin particles having a high expansion ratio of 100% can be obtained.

That is, the present invention uses a mixed gas consisting of (a) an inorganic gas and (b) a low-boiling organic metal compound as a foaming agent in the second and subsequent stages in a method for foaming polypropylene resin particles in multiple stages. The present invention provides a method for producing expanded polypropylene resin particles characterized by the following.

In the case of polystyrene resins and polyethylene resins, it is possible to foam them to a predetermined ratio in a single foaming process by selecting the type and amount of foaming agent, heating conditions, etc.
When a polypropylene resin is used, it is difficult to foam to a high degree in a single foaming process, even if the type of foaming agent, amount of foaming agent, heating conditions, etc. are variously selected.

Similar foaming methods for foaming polyethylene in multiple stages (JP-A-54-81475, JP-A-54-52169, JP-A-55-2)
780) is known, but in the case of polyethylene, it is possible to foam to a desired expansion ratio even with one foaming, and the main purpose of this foaming method is to reduce the variation in expansion ratio. . Furthermore, as a blowing agent for the second stage of foaming, it is preferable to use an inert gas such as air, nitrogen, carbon dioxide, or heritum, but foaming cannot be achieved even if an organic volatile substance such as propane or pentane is used. has been shown to be achievable. In addition, a similar method for foaming polyethylene in multiple stages is shown in Japanese Patent Publication No. 48-84891, but according to this, the blowing agent used for the second and subsequent stages of foaming is one of gases or easily volatile substances under normal conditions. Among the fluorocarbon-based gaseous compounds, dichlorotrifluoroethane has been shown to be the most suitable. In this way, when polyethylene resin is subjected to a multi-stage foaming process, the foaming agent used for the second and subsequent stages of foaming can be either an inert gas, an organic volatile substance, or a mixture of these. It can be achieved. On the other hand, in the case of polypropylene resin, due to the characteristics of the resin, it is difficult to achieve a high expansion ratio if only an inert gas such as air or nitrogen is used as a blowing agent in the second and subsequent stages. This is thought to be due to the fact that polypropylene resin has a slower gas permeation rate than polyethylene resin. In addition, when only organic volatile substances are used as the blowing agent in the second and subsequent stages, even if heated, the foaming ratio is still high, probably because the foamed particles shrink during the process of incorporating the blowing agent. It is difficult to obtain expanded particles.

When foaming polypropylene resin, which behaves differently from polyethylene resin, a mixture of inorganic gas and low-boiling point organic compound is used as a blowing agent for the second and subsequent stages of foaming in multi-stage foaming. It has been found that foamed particles with a desired high expansion ratio can only be obtained by using gas.

The polypropylene resin particles used in the present invention are preferably random copolymers of propylene and ethylene or random terpolymers of propylene, ethylene, and butene. Foaming is possible using a polypropylene homopolymer or a block copolymer of propylene and ethylene, but a uniform cell structure cannot be obtained and the expansion ratio is difficult to increase. On the other hand, when a random copolymer of propylene and ethylene or a random terpolymer of propylene, ethylene, and butene is used, foamed particles having a uniform cell structure and a high expansion ratio can be obtained. The reason for this has not yet been elucidated, but it is believed that random copolymerization of monomers such as ethylene and butene reduces the crystallinity of polypropylene and improves its viscoelasticity in the foaming temperature range. It will be done. In addition, the polypropylene resin may contain other polymers such as polyethylene and polystyrene, ultraviolet absorbers, antistatic agents, heat stabilizers, coloring agents, inorganic fine powders, and bubble control agents, as long as they do not impede the purpose of the present invention. A compound may also be included.

The method for producing the single-stage expanded particles used in the present invention includes:
Polypropylene resin particles contain organic compounds with low boiling points, such as aliphatic hydrocarbons such as propane, butane, and penkune, and halogenated hydrocarbons such as methylene chloride, dichlorodifluoromethane, trichloromonofluoromethane, and monochlorodifluoromethane. Generally, a method is carried out in which one selected from the following or a mixture of two or more thereof is contained and foamed by heating. Inorganic gases used in the present invention include air, nitrogen, argon, neon, helium, etc., and these can be used alone or in combination. It is economically advantageous to use The low boiling point organic compounds to be mixed with these inorganic gases have boiling points of 150 to
50°C halogenated hydrocarbons such as dichlorodifluoromethane, dichlorotetrafluoroethane, trichloromonofluoromethane, aliphatic hydrocarbons such as propane, butane, pentane, or a mixture of two or more of these. can be given. The composition of the mixed gas consisting of these inorganic gases and low-boiling organic compounds used as the blowing agent in the second and subsequent stages of the present invention is determined by the type of resin, the expansion ratio of the particles, the type of inorganic gas, and the type of low-boiling organic compound. Although it cannot be determined unambiguously because the preferred composition changes depending on factors such as
Generally, it is preferable that the amount of the low-boiling organic compound mixed per mole of the inorganic gas ranges from 0.01 to 8 moles because a high expansion ratio can be obtained. If the amount of the low-boiling organic compound mixed per mole of inorganic gas is less than 0.01 mole, the mixing effect of the low-boiling organic compound will not be significant, the foaming ratio will not be high, and the low-boiling organic compound will not be mixed per mole of the inorganic gas. If the amount exceeds 8 moles, the foamed particles will shrink during the process of containing the mixed gas, which is not preferable.

In addition, in the method of the present invention, when pre-foaming is performed by impregnating a blowing agent in two or three stages, the blowing agent used in the second or third stage impregnation is a low boiling point organic compound per mole of inorganic gas. The mixing amount is preferably in the range of 0.1 to 8.0 moles.

In the present invention, a method of incorporating a mixed gas as a blowing agent in the second and subsequent stages is a gas phase impregnation method in which foamed particles are placed in a pressurized atmosphere of mixed gas and the mixed gas is permeated into the foamed particles. However, the total pressure of the mixed gas at this time is preferably in the range of 2 to 50 kg/cd. When the total pressure is less than 2 kg/c-, the foaming agent content is small and the expansion ratio is not high; when it exceeds 5 okti/d, the foamed particles tend to shrink, and it is difficult to obtain highly foamed particles. I can't. The treatment temperature for containing the mixed gas is lower than the temperature at which the expanded beads melt.

The reason why highly foamed polypropylene resin foam particles can be obtained by the present invention is that the low boiling point organic compound penetrates into the resin film of the foam particles, adjusts the viscoelasticity of the resin film to be suitable for foaming, and This is thought to be because the inorganic gas, which has a slow permeation rate, efficiently contributes to foaming, and it is thought that foamed particles with a high expansion ratio can be obtained due to the mutual stabilization effect between the inorganic gas and the low-boiling point organic compound.

When attempting to obtain expanded particles by foaming polypropylene resin particles in multiple stages using the method of the present invention, increasing the number of foaming stages is advantageous in obtaining a high expansion ratio, and the variation in expansion ratio is small. Become. When considering the foaming equipment required for foaming and the economic efficiency of production, the number of foaming stages is 2 to 5, preferably 2 to 8. Furthermore, it is particularly advantageous to obtain expanded particles with the desired high expansion ratio in two stages.

In the case of two stages, it is preferable that the expansion ratio of the expanded particles in the first stage of foaming is 3 to 20 times, and the expansion ratio of the foamed particles in the second stage of foaming is 10 to 60 times. When trying to obtain foamed particles with a high expansion ratio, it is advantageous to increase the expansion ratio of the first stage foamed particles, but it is recommended to increase the expansion ratio of the first stage foamed particles to more than 20 times. This is not preferable because it causes a decrease in the closed cell ratio of the expanded beads.

Furthermore, if the expansion ratio of the first stage foamed particles is less than 3 times, it becomes difficult to foam the second stage.

Furthermore, it is preferable that the first stage expanded particles have a high closed cell ratio. Closed cell ratio is the number of closed cells (cells that are flattened and sealed by cell partitions) to the total number of cells.
It can be measured as follows.

d: Density of the resin W: Weight of the foamed particle sample V: Apparent volume measured by submerging the foamed particle sample in water and thoroughly defoaming V: Air comparison type hydrometer (for example, air comparison type hydrometer 930 model manufactured by Toshiba Penkman Corporation) ) Volume of expanded particle sample measured using v-W/d Closed cell ratio (%) - . If the closed air compatibility in the first stage is less than 65%, the expansion of the foamed particles upon heating will be small and highly foamed foamed particles will not be obtained, and the expansion pressure of the foamed particles during molding will not be sufficient, resulting in fusion. good,
It is difficult to obtain a molded article with a beautiful appearance and excellent cushioning performance.

The expanded polypropylene resin particles obtained by the present invention are further imparted with foaming ability, and then filled into a mold and heated to obtain a molded product with good interparticle fusion and a smooth surface. be able to. When foaming ability is imparted by the method of containing a mixed gas consisting of an inorganic gas and a low-boiling organic compound as in the present invention, the foaming ability is large, so the amount of heat during molding heating is greater than when only an inorganic gas is contained. Even if the amount is small, the fusion between the particles is extremely good, and it is possible to obtain a molded article with a smooth surface. In the case of a method in which only an inorganic gas is contained, it is difficult to increase the expansion ratio, and a large amount of heat is required during secondary foaming and heating for molding.

The heating conditions during foaming and molding are appropriately selected depending on the type of resin, the expansion ratio of the expanded particles, the composition of the mixed gas, the shape and size of the particles, etc., but when using water vapor as the heating medium,
Steam temperature 110-160°C 1 heating time 10 seconds-10
This can be done within a few minutes. The foaming machine and molding machine used in this case can be those normally used for foaming and molding polyethylene, as they are, or with some modifications.

The molded product obtained in this way has a higher heat resistance than a foamed polyethylene molded product due to the characteristics of the polypropylene resin, and has strength and cushioning properties that are comparable to those of a foamed polyethylene molded product even when the density is relatively low. flexibility, low temperature properties,
It has chemical resistance and is particularly suitable for use as cushioning materials, insulation materials, and packaging materials.

The present invention will be explained below with reference to Examples.

Examples, Comparative Example 1 Glopyrene-ethylene random copolymer (density 0.9
0g/d, MI=9, ethylene content 4.3%, Vicat softening point 119°C) 100 parts by weight of pellets were mixed with saturated steam of dichlorodifluoromethane at 60'C, pressure 15.6
9/C- for 4 hours to impregnate 27 parts by weight of ditaroldifluoromethane.

This foamable resin was heated and foamed with water vapor of L7kQ/c- for 40 seconds to obtain single-stage foamed beads with an expansion ratio of 10 times. After the single-stage foamed particles were left for 24 hours at room temperature and normal pressure, the mixed amount of dichlorodifluoromethane per mol of nitrogen was 0 mol (A), 0.1 mol (A), and 0.1 mol (A).
B), 0.8 mol (C), 1 mol (D), 8 mol (E)
, held in a mixed gas atmosphere of 5 mol (F) at a temperature of 80°C, a pressure of 20, and 9/cd for 4 hours to form (A) ~
(F) gas was contained.

Then, with water vapor of 1.5 to 2.5 kti/d-G,
Table 1 shows the results of foaming after heating for 0 seconds.

Table 1 Example, Comparative Example 2 The single-stage expanded particles obtained in Example 1 are used. These single-stage expanded particles were placed in a mixed gas atmosphere containing 0.1 mole of dichlorodifluoromethane per mole of nitrogen at a temperature of 8.
0'C1 pressure was held at 20 kg/cd for 4 hours to contain the mixed gas in the expanded particles, and then 2.8 kg/d -
The mixture was heated and foamed for 40 seconds with water vapor of G to obtain two-stage foamed particles with an expansion ratio of 84.8 times. After the two-stage expanded particles were left at room temperature and atmospheric pressure for 24 hours, they were placed in an In gas atmosphere containing 0 mole (A) and 0.8 mole (B) of dichlorodifluoromethane per mole of nitrogen at a temperature of 90 °C. (A), (B) inside the foamed particles by holding at 9/d for 4 hours at a pressure of 25°C and 25°C.
Fill a mold containing 50n of gas, vertically 3 Q Q jai11 horizontally, and 2.5#/d-
Table 2 shows the results of heating and molding with water vapor.

Table-2

Claims (5)

[Claims] (1) Impregnation of polypropylene resin particles with a blowing agent and heating are performed in multiple stages, and as a blowing agent in the second and subsequent stages (
A method for producing expanded polypropylene resin particles, characterized by using a mixed gas consisting of a) an inorganic gas and (b) a low-boiling point organic compound. (2) Production of foamed polypropylene resin particles according to claim 1, wherein the foamed polypropylene resin particles are a polymer whose main component is a random copolymer of propylene and ethylene, or a random terpolymer of propylene, ethylene, and phthene. Law. (3) The method for producing expanded polypropylene resin particles according to claim 1, wherein the inorganic gas is an inorganic gas containing nitrogen as a main component. (4) The method for producing expanded polypropylene resin particles according to claim 1, wherein the low-boiling organic compound is a hydrocarbon or halogenated hydrocarbon having a boiling point of -50 to 50°C, or a mixture thereof. (5) The polypropylene according to claim 1, wherein the composition of the mixed gas consisting of an inorganic gas and a low-boiling organic compound is such that the mixed amount of the low-boiling organic compound is 0.01 to 3 moles per mole of the inorganic gas. Method for producing foamed resin particles.