JPH0420937B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for continuous pre-foaming of synthetic resin particles.

Synthetic resin foams are used in a variety of fields, such as packaging materials and cushioning materials, and 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. ing. The pre-expanded particles used here are manufactured, for example, by a method in which resin particles are dispersed in a dispersion medium together with a dispersant and a foaming agent in a closed container, heated, and then the resin particles are released into a low-pressure atmosphere from inside the container to cause foaming. The resin particles that are normally subjected to foaming are used as particles of a predetermined size depending on the size of the intended pre-expanded particles, expansion ratio, etc., and the resin particles are heated to make them spheroidal and/or crosslinked. Processing is in progress. However, in the past, the so-called repellet process and heat treatment process for turning the resin particles into particles of a predetermined size were not performed continuously, and therefore a storage space was required to temporarily store the repellet resin particles. In addition, when heat-treating the resin particles, the stored resin particles must be released again and weighed together with the dispersion medium, dispersant, etc., making the work complicated. There were drawbacks such as a decrease in work efficiency. In addition, conventionally, a heat treatment process,
Since the foaming step of foaming the heat-treated resin particles is not carried out continuously, there are problems in securing storage space for the resin particles and lowering work efficiency as well as in the above-mentioned case. Since it is once cooled, it is necessary to heat it again in the foaming process, which has the disadvantage of poor thermal efficiency and enormous energy consumption. Furthermore, since the foaming process has conventionally been carried out in batches, the foaming process has had many drawbacks, such as extremely poor production efficiency of pre-expanded particles.

As a result of intensive research by the present inventors in order to eliminate the above-mentioned drawbacks, we continuously carried out the repellet process of resin particles, the heat treatment process of the repellet resin particles, the foaming process of the heat treated resin particles, and By sequentially repeating the process of sequentially transferring the particles to multiple foaming tanks and foaming the resin particles in each foaming tank, it is possible to solve the problem of securing storage space for resin particles and improve work efficiency.
The present invention was completed based on the discovery that thermal efficiency can be significantly improved.

That is, in the present invention, immediately after extruding a synthetic resin, it is cut into resin particles of a predetermined size, and then the resin particles are transferred by an appropriate transfer means and continuously placed in a heating tank together with a predetermined amount of a dispersion medium and a dispersant. A predetermined amount of resin particles that have been introduced and heat-treated by passing through a heating zone continuously are introduced into any one of the plurality of foaming tanks, and the resin particles are heated in the presence of a predetermined amount of blowing agent. After heating and maintaining the temperature above the softening temperature, one end of the foaming tank is opened and the resin particles and dispersion medium are released into an atmosphere at a lower pressure than the inside of the foaming tank to foam the resin particles, while the foaming tank is heated to a temperature lower than that of the foaming tank. After the introduction of the resin particles, a predetermined amount of the resin particles that have been continuously heat-treated in the heating tank and transferred is introduced into another foaming tank, heated in the presence of a predetermined amount of foaming agent, and then heated in the foaming tank. The gist of this invention is a continuous pre-foaming method for synthetic resin particles, which is characterized in that the same foaming steps as described above are repeated in each foaming tank and are carried out continuously.

Examples of the base resin of the synthetic resin particles used in the present invention include low-density polyethylene, linear low-density polyethylene, high-density polyethylene (polyethylene resin), ethylene-propylene random copolymer, ethylene-propylene block copolymer, etc. Coalescence, propylene homopolymer, etc. (polypropylene resin), ethylene-α-olefin copolymer, propylene-α-olefin copolymer, various polyolefin resins such as polybutene, styrene homopolymer, acrylonitrile-styrene copolymer , styrene resins such as acrylonitrile-butadiene-styrene copolymers, etc., but polyolefin resins are particularly preferred. In addition, in the case of polyolefin resins, crosslinking may be performed, and examples of crosslinking agents such as 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
-Butylperoxyisopropyl carbonate, etc. can be used. In addition, a crosslinking aid may be used if necessary, and examples of the crosslinking aid include functional vinyl compounds such as divinylbenzene, polyethylene glycol dimethacrylate, triallyl cyanurate, diallyl phthalate, quinone dioxime, bisamide, etc. can be mentioned. The above crosslinking agent is 0.01 parts by weight per 100 parts by weight of resin particles.
~1.0 parts by weight, and 0.05 to 10 parts by weight of the crosslinking aid. These crosslinking agents and crosslinking aids are kneaded into the resin in the extruder, or added when the resin particles are introduced into the heating tank, and incorporated into the resin in the heating tank. The heating temperature within the extruder is the temperature that melts the resin, but in particular when a crosslinking agent is contained within the extruder, heating within the extruder will advance the crosslinking reaction and prevent the problem of making extrusion impossible. It is necessary to heat below the decomposition temperature of the crosslinking agent.

In the present invention, resin particles are introduced into a heating tank together with a dispersion medium and a dispersant to perform heat treatment, but the dispersion medium may be any solvent as long as it does not dissolve the resin particles.
Examples 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 in the heating tank and the foaming tank is 1:1 to 1:50, preferably 1:2 to 1:30. Further, as the dispersant, for example, fine particles of aluminum oxide and titanium oxide, basic magnesium carbonate, basic zinc carbonate, calcium carbonate, aluminum hydroxide, 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.

In the present invention, the heat-treated resin particles are heated in a foaming tank in the presence of a foaming agent, and then released and foamed. ,
Aliphatic hydrocarbons exemplified by pentane, hexane, heptane, etc., cycloaliphatic hydrocarbons exemplified by cyclobutane, cyclopentane, etc., trichlorofluoromethane, dichlorodifluoromethane,
Volatile blowing agents such as halogenated hydrocarbons exemplified by 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.

Embodiments of the present invention will be described below based on the drawings.

FIG. 1 schematically shows the steps of an embodiment of the present invention. In the figure, 1 is an extruder, and 2 is a resin particle manufacturing device that cuts the resin extruded from the extruder 1 into a predetermined size. , 3 are heating tanks, and 4, 5, and 6 are first, second, and third foaming tanks, respectively. The raw resin supplied from the raw resin supply hopper 7 is heated and melted in the extruder 1, and extruded into the resin particle manufacturing apparatus 2 by the screw 8. A dispersion medium such as water is constantly supplied into the resin particle manufacturing apparatus 2 from a dispersion medium tank 9 by a dispersion medium supply pump 10, and the extruded resin is cut into a predetermined size by a rotary blade 11 in the dispersion medium. It is repelleted into particles. The resin particles repelleted to a predetermined size are fed to a dispersion medium supply pump 1.
The dispersion medium is sent to the solid-liquid separation tank 12 provided as necessary together with the dispersion medium supplied by the dispersion medium 0, and after separating the excess dispersion medium and recovering it to the dispersion medium tank 9 via the dispersion medium flow rate control valve 19, It is transferred to the heating tank 3 together with a predetermined amount of dispersion medium and a predetermined amount of dispersant supplied from the dispersant tank 13 . Next, the resin particles are continuously passed through a heating zone in the heating tank 3 to undergo heat treatment such as spheroidization and/or crosslinking, but this temperature should normally be higher than the temperature at which the resin particles soften. is preferred. The heating of the resin particles in the heating tank 3 may be carried out by keeping the temperature of the heating zone constant. Alternatively, the heating zone may have a temperature gradient, for example, the temperature of the heating zone may gradually increase in temperature in the direction of transfer of the resin particles. You can do it as you see fit. The heat-treated resin particles sent out from the heating tank 3 are sent to the transfer switching device 14. The transfer switching device 14 uses a flow meter to detect the flow rate of the resin particle mixture (mixture of resin particles, dispersant, and dispersion medium) to be transferred, or detects the content in each of the foaming tanks 4, 5, and 6 using a float or the like. For example, when a predetermined amount of the resin particle mixture has been introduced into the first foaming tank 4, the mixture is transferred to the second foaming tank 5, and a predetermined amount of the resin particle mixture is transferred to the second foaming tank 5 in conjunction with a liquid level gauge. When the introduction of the mixture is completed, the mixture is transferred to the third foaming tank 6,
The foaming tank into which the resin particle mixture is sequentially introduced is changed over. On the other hand, for example, the resin particles introduced into the first foaming tank 4 are stirred within the foaming tank 4 to a temperature higher than the temperature at which the resin particles soften in the presence of a foaming agent, usually 50°C to
After being heated and maintained at 180°C, preferably 120°C to 180°C, it is discharged from the foaming tank 4 into a low pressure atmosphere (usually an atmospheric pressure atmosphere) through the discharge port 17 to cause foaming. The time required to foam the resin particles introduced into the first foaming tank 4 and obtain pre-expanded particles is usually 30 minutes to 240 minutes,
The resin particle mixture is sequentially transferred to the second and third foaming tanks 5 and 6, and by the time a predetermined amount of the resin particle mixture has been introduced into the third foaming tank 6, the resin particles in the first foaming tank 4 are After completing the foaming process, the resin particle mixture is again introduced into the first foaming tank 4 and foamed. The resin particles are foamed in the second foaming tank 5 and the third foaming tank 6 in the same manner as in the first foaming tank 4, and by repeating the above steps in each foaming tank 4, 5, and 6 in turn. Prefoaming is carried out continuously.

The time required to sequentially transfer the resin particle mixture from the first foaming tank 4 to the third foaming tank 6: t ₁ and the time required to foam the resin particles in each foaming tank 4, 5, and 6: t ₂ It is necessary that ₁ ≧t ₂ , but
In particular, it is preferable that t ₁ =t ₂ . The relationship between t ₁ and t ₂ is set by mutual adjustment of the flow rate of the resin particle mixture to be transferred, the capacity and number of foaming tanks, the amount of thermal energy supplied, and the like.

In the present invention, the blowing agent is introduced into the foaming tank by
As in the embodiment shown in FIG. 1, the resin mixture may be introduced from the foaming agent tank 15 through the foaming agent injection valve 16 after or during the introduction process after introducing the resin mixture from the heating tank to the foaming tank, or as shown in FIG. As in the example shown,
A foaming agent may be press-fitted from a foaming agent tank into the resin mixture transferred from the heating tank and introduced into the foaming tank together with the resin mixture. Alternatively, it may be introduced into the foaming tank using other appropriate means.

In addition, when introducing the foaming agent, the foaming agent may be introduced after the resin mixture transferred from the heating tank is once cooled to a predetermined temperature during the transfer or after being transferred to the foaming tank. This may be preferable in terms of temperature control.

In the present invention, when adding a crosslinking agent as necessary, the crosslinking agent may be kneaded into the resin in the extruder 1, or the resin particles may be heated as in another embodiment shown in FIG. When introducing the resin particles into the tank 3, a crosslinking agent is supplied together with the dispersant from the crosslinking agent tank 18, and the crosslinking agent can be incorporated into the resin particles and crosslinked in the heating tank 3.

Further, the dispersant may be dispersed in the dispersion medium tank 9 in advance. In that case, the dispersant tank 13 is not necessarily required.

In each of the above embodiments, three foaming tanks are provided, but the number of foaming tanks may be two, four or more.

As explained above, the present invention includes a repellet process in which resin particles are made into particles of a predetermined size, a heat treatment process in which the repellet resin particles are spheroidized and/or crosslinked, and the heat-treated resin particles are foamed. Since the foaming process is carried out continuously, the problem of securing storage space for temporarily storing repellet resin particles and heat-treated resin particles can be solved, and the series of processes can be carried out continuously. This can greatly improve work efficiency. Furthermore, by performing the heat treatment process and the foaming process in succession, the thermal energy supplied to the resin particles in the heat treatment process can be effectively used in the foaming process, so that less thermal energy is required to heat the resin particles in the foaming process. This can improve thermal efficiency and contribute to energy savings. In addition, multiple foaming tanks are provided in the foaming process, and foaming is repeated in each foaming tank in sequence, resulting in a significant improvement in the production efficiency of pre-expanded particles compared to the conventional batch-type foaming. It has various effects such as ease of production.

[Brief explanation of drawings]

The drawings show embodiments of the present invention; FIG. 1 is a schematic diagram showing the steps of one embodiment of the invention, and FIG. 2 is a schematic diagram showing the steps of another embodiment. 1... Extruder, 2... Resin particle manufacturing device, 3...
...Heating tank, 4...First foaming tank, 5...Second foaming tank, 6...Third foaming tank, 10...Dispersion medium supply pump, 14...Transfer switching device.

Claims (1)

[Claims] 1 Immediately after extrusion, the synthetic resin is cut into resin particles of a predetermined size, and then the resin particles are transferred by an appropriate transfer means and continuously introduced into a heating tank together with a predetermined amount of dispersion medium and dispersant, and heated. A predetermined amount of heat-treated resin particles are introduced into any one of the plurality of foaming tanks, and the temperature at which the resin particles soften in the presence of a predetermined amount of a blowing agent is After heating and maintaining the temperature above, one end of the foaming tank is opened, and the resin particles and dispersion medium are released into an atmosphere at a lower pressure than the inside of the foaming tank to foam the resin particles. After the introduction is completed, a predetermined amount of resin particles that are continuously heat-treated and transferred in the heating tank is introduced into another foaming tank,
A method for continuous preliminary foaming of synthetic resin particles, characterized in that the process of heating in the presence of a predetermined amount of a foaming agent and performing foaming in the same manner as described above in the foaming tank is successively repeated in each foaming tank.