JPS6234338B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for continuous pre-foaming of polyolefin resin particles. Conventionally, polyolefin resin foam moldings have been used in a wide variety of applications, such as packaging materials and cushioning materials. One of the methods for manufacturing this type of foam is the so-called bead molding method, in which pre-expanded particles are filled into a mold and molded. , a volatile blowing agent is placed in a sealed container together with a crosslinking agent and/or a dispersing agent if necessary, and after heating and raising the temperature, the pressure inside the container is maintained at a pressure above or below the vapor pressure of the volatile blowing agent. However, it is manufactured by opening one end of the container and simultaneously releasing the resin particles and dispersion medium from the inside of the container into a low-pressure atmosphere. However, the pre-foamed particles obtained by such a batch method are those obtained after the amount of resin particles remaining in the container is reduced, that is, those obtained at the end of the pre-foaming process, and those obtained at the beginning. The expansion ratio etc. will be different compared to what is obtained, and in the end, with the batch method, it is difficult to control the quality of all the pre-expanded particles obtained in one operation so that they are uniform. It was hot. In addition, in the above method, when obtaining a large amount of pre-expanded particles, it is necessary to repeat the same operation repeatedly, and heating and cooling operations must be performed each time, resulting in very poor thermal efficiency and huge energy consumption. There was a drawback. In addition, in the above method, it is necessary to apply back pressure using nitrogen, air, etc. when releasing the resin particles and dispersion medium, and although butane is a cheap and useful blowing agent, there is a risk of explosion when it comes into contact with air. Therefore, it is difficult to use it as a volatile blowing agent, and the types of volatile blowing agents that can be used are limited. The present invention aims to provide a method for continuous pre-foaming of polyolefin resin particles that eliminates the drawbacks of the above-mentioned conventional techniques. By continuously supplying the particles and dispersion medium, heating, containing the volatile blowing agent, and releasing the resin particles and dispersion medium without interruption, uniform pre-expanded particles can be obtained, and productivity and thermal efficiency can be improved. The inventors discovered that it was possible to significantly improve the process, and also succeeded in developing a continuous pre-foaming method, thereby completing the present invention. That is, the present invention provides polyolefin resin particles, a dispersion medium, and, if necessary, a crosslinking agent and/or a dispersant, which are mixed in advance at a temperature below the boiling point of the dispersion medium under normal pressure, or while being mixed. The mixture is introduced into a pre-expanded particle manufacturing apparatus by an appropriate feeding means, and the resin particles are heated to a predetermined temperature by passing continuously through a heating zone under pressure, and then the mixture is continuously passed through a blowing agent-containing zone. continuous preparation of polyolefin resin particles, characterized in that the resin particles are made to contain a volatile blowing agent by passing through the device, and then the resin particles are continuously discharged from the inside of the device into a low-pressure atmosphere together with a dispersion medium. The gist is the foaming method. In the present invention, the base resin of the polyolefin resin particles is low density polyethylene (hereinafter referred to as
It is called LDPE. ), polyethylene resins such as linear low-density polyethylene and high-density polyethylene, polypropylene resins such as ethylene-propylene random copolymers, ethylene-propylene block copolymers, and propylene homopolymers, ethylene-α-olefin copolymers , propylene-α-olefin copolymer, polybutene, and the like. These polyolefin resins may or may not be crosslinked. In the present invention, volatile blowing agents include, for example, inorganic blowing agents such as carbon dioxide, aliphatic hydrocarbons such as propane, butane, pentane, hexane, heptane, etc., and cyclic blowing agents such as cyclobutane, cyclopentane, etc. Formula aliphatic hydrocarbons and halogenated hydrocarbons exemplified by trichlorofluoromethane, dichlorodifluoromethane, dichlorotetrafluoroethane, methyl chloride, ethyl chloride, methylene chloride, etc. are used. The amount of the blowing agent added is usually 5 to 30 parts by weight per 100 parts by weight of the resin particles. Furthermore, in the present invention, the resin particles are dispersed in a dispersion medium, and at this time, if necessary, a dispersant such as fine particles of aluminum oxide and titanium oxide, basic magnesium carbonate,
Basic zinc carbonate, calcium carbonate, etc. can be used. The amount of the dispersant added is 0.01 to 10 parts by weight per 100 parts by weight of the resin particles. Further, the dispersion medium may be any solvent that does not dissolve the resin particles, and examples thereof include water, ethylene glycol, glycerin, methanol, ethanol, etc., or a mixture of two or more thereof, but water is usually preferred. . The mixing ratio of resin particles and dispersion medium is 1:1 ~
The ratio is 1:30, preferably 1:2 to 1:10. In the present invention, crosslinking may be carried out especially in the case of polyethylene resin, but as a crosslinking agent,
For example, di-t-butyl peroxide, t-butyl-cumyl-peroxide, dicumyl peroxide, α,α-bis(t-butylperoxy)
p-diisopropylbenzene, 2,5-dimethyl-2,5-di-(t-butylperoxy)-hexyne-3, 2,5-dimethyl-2,5-di-(benzoylperoxy)hexane, t- Butyl peroxyisopropyl carbonate and the like can be used. In addition, a crosslinking aid may be used if necessary, and examples of the crosslinking aid include divinylbenzene,
Examples include functional vinyl compounds such as polyethylene glycol dimethacrylate, triallyl cyanurate, and diallyl phthalate, as well as quinone dioximes and bisamides. The above-mentioned crosslinking agent is used in an amount of 0.01 to 1.0 parts by weight, and the crosslinking aid is used in an amount of 0.05 to 10 parts by weight, based on 100 parts by weight of the resin particles. Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 schematically shows the manufacturing process of a continuous pre-foaming method for polyolefin resin particles, which is an embodiment of the present invention. In FIG. 1, 1 is a pre-expanded particle manufacturing device, 2 is a raw material supply tank, 3 to 6 are heating tanks,
7 and 8 are foaming agent containing tanks, 9 is a pump, 11 is a foaming agent introduction pipe, 12 is a conduit, and 13 is a discharge pipe. When manufacturing pre-expanded particles using the manufacturing apparatus 1 described above, the case of polypropylene resin will be explained. First, the raw material polypropylene resin, the dispersion medium,
and, if necessary, a dispersant is introduced into the raw material supply tank 2, and after or while mixing at a temperature below the boiling point of the dispersion medium under normal pressure, the mixture is pumped from the raw material supply tank 2 to the pump 9.
The material is sequentially sent to heating tanks 3 to 6 and heated. The pump 9 determines the flow rate in the manufacturing apparatus 1, and the flow rate is normally 0.02 to 1.2 m ³ /hr, but it can be adjusted outside this range by changing the residence time of the mixture in the container, the volume of the container, etc. The flow rate can also be selected as appropriate. The mixture is heated to a predetermined temperature, e.g. 50-180°C, preferably 120-180°C.
Although it is heated to 180°C, it is preferably heated to a temperature higher than the temperature at which the resin particles soften. The heating tanks 3 to 6 adjust and maintain the temperature in each tank so that it increases successively in the feeding direction. Next, the mixture is transferred to the blowing agent containing tank 7.
8, and the volatile foaming agent supplied from the foaming agent introduction pipe 11 by an appropriate pump (not shown) is incorporated into the resin particles. The temperature of the containing tanks 7 and 8 is the same as the above-mentioned heating temperature, and is usually preferably higher than the temperature at which the resin particles soften. Thereafter, the resin particles and dispersion medium are simultaneously and continuously discharged from the foaming agent-containing tank 8 into a low-pressure atmosphere to foam the particles, thereby obtaining pre-expanded polypropylene resin particles. Next, a case will be described in which pre-expanded polyethylene resin particles are manufactured using the manufacturing apparatus 1 as shown in FIG. The manufacturing process for polyethylene resin is almost the same as that for polypropylene resin, but differs in that the resin particles are usually crosslinked. The crosslinking agent is introduced into the raw material supply tank 2 together with the resin particles, dispersion medium, etc., and is uniformly stirred and mixed under normal pressure at a temperature below the boiling point of the dispersion medium, usually below 30°C. Next, it is sent to heating tanks 3 and 4, where it is heated and crosslinked, and this temperature is, for example, 100 to 180°C.
℃, preferably 130-170℃. Next, the mixture is cooled by a cooler 10 to a temperature equal to or lower than the temperature of the heating tanks 5 to 6, and then passed through the heating tanks 5 to 6, preferably heated to a temperature higher than the temperature at which the resin particles soften, and then, After sending the resin particles to foaming agent containing tanks 7 and 8 and incorporating a volatile foaming agent into the resin particles in the same manner as in the case of polypropylene resin, the resin particles and dispersion medium are simultaneously released continuously from containing tank 8 into a low pressure atmosphere. to foam the particles, thus obtaining pre-expanded particles. In the above example, four heating tanks are used, but if the mixture reaches the desired temperature by appropriately changing the residence time of the mixture in the container, the capacity of the container, the flow rate, etc., any heating tank can be used in one tank. A tank may also be used. The apparatus used to carry out the continuous pre-foaming method of the present invention is not limited to the one used in the above embodiments, and for example, the diameter of a part of a long and thin pipe-shaped object may be enlarged to heat the apparatus. It is possible to use a structure in which a space corresponding to a tank, a foaming agent-containing tank, etc. is formed, and functions such as feeding, heating, and foaming agent containing are added. The polyolefin resin pre-expanded particles obtained by the present invention are uniform with little variation and usually have an expansion ratio of 3 to 60 times. The pre-expanded particles are aged, for example, at room temperature and pressure, and if necessary, pressure aged at a predetermined pressure for a predetermined time using an inorganic gas or a mixed gas of an inorganic gas and a volatile blowing agent. Next, the pre-expanded particles are filled into a mold and heated and foamed to obtain a foam molded article according to the mold. The foam molded product thus obtained can be used, for example, as a cushioning material, a packaging material, a heat insulating material, a food container, a building material, a flotation material, a toy, and the like. As explained above, according to the continuous pre-foaming method for polyolefin resin particles of the present invention, it is possible to obtain pre-foamed particles with uniform expansion ratio, shape, etc. compared to the conventional batch-type pre-foaming method, and Production efficiency is greatly improved because pre-expanded particles can be produced continuously, and there is no need to repeat heating and cooling operations every time a predetermined amount is produced, and it is only necessary to maintain a constant temperature at all times. It has various advantages such as high thermal efficiency and low energy consumption. Further, according to the present invention, since there is no need to apply back pressure using air or the like as in the case of the conventional batch type, inexpensive butane can be used as a volatile blowing agent, which is economically advantageous. Hereinafter, the present invention will be explained in more detail with reference to Examples. Examples 1 to 4 Base resin particles, dispersant, and dispersion medium of the types and amounts shown in Table 1 were continuously supplied to the raw material supply tank of the pre-expanded particle manufacturing device and mixed at 30°C under normal pressure. Meanwhile, the mixture is pumped from the raw material supply tank into four heating tanks each having an internal volume of 0.6 ^m3 at the flow rate shown in Table 1 (the temperatures of the four heating tanks A, B, C, and D are shown in Table 1). (shown in Figure 1). The mixture is then continuously fed into tanks containing blowing agents each having an internal volume of 0.6 m ³ maintained at the temperature and pressure shown in Table 1, and blowing agents of the type shown in Table 1 are introduced into the tanks by suitable pumps. and the amount used of a volatile blowing agent were included in the resin particles. Next, the resin particles and dispersion medium were continuously discharged from the exhaust pipe into the atmosphere to continuously obtain pre-expanded particles. The expansion ratio of the obtained pre-expanded particles is shown in Table 1.
The expansion ratio and shape were uniform. Note that when LDPE particles were used as the base resin, 0.5 parts by weight of dicumyl peroxide was used as a crosslinking agent.

【table】

【table】 [Brief explanation of the drawing]

The drawings show embodiments of the invention, and FIGS. 1 and 2 are schematic diagrams illustrating the foaming process of the method of the invention. 1... Pre-expanded particle manufacturing device, 2... Raw material supply tank,
3, 4, 5, 6... Heating tank, 7, 8... Foaming agent containing tank, 9... Pump, 10... Cooler, 11... Foaming agent introduction pipe, 12... Conduit, 13... Discharge pipe.

Claims (1)

[Claims] 1 After mixing the polyolefin resin particles, dispersion medium, and optionally a crosslinking agent and/or dispersant under normal pressure at a temperature below the boiling point of the dispersion medium, or while mixing, the mixture is heated to an appropriate temperature. The resin particles are introduced into a pre-expanded particle manufacturing apparatus by a feeding means, and are continuously passed through a heating zone under pressure to heat the resin particles to a predetermined temperature, and then the mixture is continuously passed through a blowing agent-containing zone. A method for continuous pre-foaming of polyolefin resin particles, characterized in that after the resin particles contain a volatile foaming agent, the resin particles are continuously discharged together with a dispersion medium into a low-pressure atmosphere from inside the apparatus.