JPS597731B2 - expandable thermoplastic polymer particles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to expandable thermoplastic polymer particles, and more particularly to a method for preventing blocking of thermoplastic particles, particularly expandable polystyrene or styrene copolymer particles, during pre-foaming. The present invention further relates to expandable thermoplastic polymer particles that exhibit excellent interparticle fusion when formed into a foam molded product.

The production of foamed molded articles has conventionally been carried out using the following process.

That is, a polymer is prepared by suspension polymerization or the like, and is impregnated with a blowing agent to form expandable polymer particles, and then,
The pre-foamed particles are pre-foamed using steam or the like in a pre-foaming machine to form foamed particles, and the pre-foamed particles are left in a silo for curing and air drying for several days. Then, a large number of '' for steam heating.
The pre-expanded particles are filled into the inside of the mold of the molding machine equipped with the child L, and the foamed particles are heated above the softening point of the pre-expanded particles by injecting pressurized steam through the small hole. A molded body is obtained by fusing and integrating the two.
The properties required of thermoplastic particles, particularly expandable polystyrene or styrene copolymer particles, used for this purpose are that they do not cause a blocking phenomenon in which the particles fuse together during the pre-foaming process; Furthermore, when the pre-expanded particles are used for molding, the particles fuse together.

In other words, to obtain pre-expanded particles, steam is used while stirring in a pre-expanding machine.
At this time, blocking causes problems such as foamed particles adhering to the stirrer or, in extreme cases, stirring of the foaming machine being stopped. The pre-expanded particles obtained in this way are temporarily stored in a silo for curing and air drying, but the transfer to the silo is carried out using a blower using a pipe or the like.
At this time, if blocked particles are included, the pipe will become clogged and sufficient transfer will not take place. In addition, filling of the pre-expanded particles into the molding machine is carried out using air through the feeder, but if there are head-knocking particles at that time, they may clog in the pipes of the feeder, etc., or the filling inside the mold may become clogged. is also not done enough. Because of this inconvenience, it is necessary to prevent blocking. Further, when molding is performed using pre-expanded particles, it is required that the expanded particles are fused to each other, and this is required in order for the molded article to have sufficient mechanical strength.

However, conventional means for preventing locking tend to have an adverse effect on fusion during molding.

Examples of various methods for preventing these blockings include metal salts of higher fatty acids such as zinc stearate, calcium stearate, lithium stearate,
A method is known in which the surface of expandable particles is coated with sodium stearate or the like, or in which they are added during polymerization.
Also known are methods in which higher fatty acid amides or esters are coated or added during polymerization. Similarly, a method of coating the surface of expandable polymer particles with an inorganic substance has also been reported, and inorganic substances used for such purposes include calcium carbonate, magnesium carbonate, talc, and hydrated calcium silicate. It has been known. However, in the above-mentioned conventional method, there are disadvantages such as insufficient blocking prevention effect, and inter-particle fusion of the molded product being inhibited if the coating is applied in an amount necessary to have a sufficient blocking prevention effect. c occurred, and the performance required for the above-mentioned expandable thermoplastic polymer particles was not fully satisfied.

Furthermore, even in the case of inorganic materials, the particle size has traditionally been on the order of microns, and this has been difficult to achieve with sufficient performance in terms of anti-blocking effect and fusion properties during molding. I didn't give it. The present invention provides a composition of thermoplastic particles, particularly expandable polystyrene particles or styrene copolymer particles, in which the amount of blocking during pre-foaming is extremely small and the fusion between pre-foamed particles during molding is not inhibited. It is. That is, 1 to 10% of a blowing agent such as a saturated or unsaturated aliphatic hydrocarbon having a boiling point lower than the softening point of the thermoplastic polymer particles, such as propane, n-butane, isobutane, or pentane, is added to the thermoplastic polymer particles.
The above-mentioned requirements can be met by coating the surface of a foamable styrene polymer containing 15% by weight with 0.01 to 0.5% by weight of an inorganic substance in the form of an ultrafine powder of less than a micron, based on the polymer particles. It gives the performance of Aluminum oxide and titanium oxide are employed as the ultrafine powder inorganic substance used in the present invention.

It goes without saying that the method according to the present invention may be used in combination with conventional blocking prevention techniques.

Examples will be described below.

Example 1 Expandable styrene polymer particles "Kanepal GB" manufactured by Kanebuchi Chemical Co., Ltd. whose surface additives were washed away by washing with methanol were used as expandable styrene polymer particles, and the blocking amount and molding fusion described below were obtained. I asked for

That is, the anti-blocking agent shown in Table 1 is applied to the surface of expandable styrene polymer particles having a particle size of 736 to 1000 μm, and 1 kg of expandable particles are expanded to an apparent magnification of 50 times using a small pre-expanding machine. The amount of blocking at that time was measured by separating the blocking particles using a sieve with an opening of 8 mm.

In addition, the pre-expanded particles obtained in this manner were used as BELMO-90.
The steam pressure is 0.6 kg/C using a molding machine (manufactured by Toyo Kikai Kinzoku Kk).
(d) Molding was performed for 255 seconds during tertiary heating, and the fusion during molding was evaluated. However, mold fusion refers to the rate of fusion between embedded particles on the fractured surface of a molded body, and refers to the fusion rate between particles separated at the boundary between expanded particles among the particles on the fractured surface when the molded body is torn. Rather, it refers to the percentage of particles torn inside the foamed particles relative to the total number of foamed particles. In addition, Aluminum Oxide C (5Titani), which is an anti-blocking agent of the present invention,
Both um0xidep-25 are manufactured by Nippon Aerosil Co., Ltd.
Zinc stearate was used as a comparative example.

Claims (1)

[Scope of Claims] 1. A foamable thermoplastic polymer containing 1 to 15% by weight of a saturated or unsaturated aliphatic hydrocarbon having a boiling point lower than the softening point of the polymer particles as a blowing agent in the thermoplastic polymer particles. Foaming properties characterized in that the surface of the combined particles is coated with ultrafine aluminum oxide or titanium oxide with a particle size of 2 mμ to 100 mμ in an amount of 0.01 to 0.5% by weight based on the weight of the polymer particles. Thermoplastic polymer particles. 2. The polymer particles according to claim 1, wherein the thermoplastic polymer particles are polystyrene particles.