JPS5910376B2 - Styrene polymer expandable into low density foam - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to foamable molding materials based on styrene polymers, aliphatic hydrocarbons, and plasticizers, which can be processed into low-density foam materials.

According to a method that has been put into practical use in industry, a molded article from a foamed styrene polymer is produced by expanding a fine particulate foaming agent-containing styrene polymer in a mold.

In this method, a finely divided styrene polymer is first foamed into a loose deposit by heating it with steam or hot gas to a temperature above its softening point.
This takes place in a continuously operating foaming device and is called "prefoaming". The pre-foamed particles were then heated to 24
After storage for a period of time, it is heated again in the mold for "finish foaming" and then fused to form a molded product. Blowing agents for expandable styrene polymers are generally low-boiling hydrocarbons, such as propane, butane, pentane, hexane, heptane, cyclohexane, or halogenated hydrocarbons, such as methyl chloride, dichlorodifluoromethane or Mixtures of these blowing agents are used.

It is also advantageous to process the expandable styrene polymer by homogeneously dispersing small amounts of solvent. This results in better welding of the foam particles in the mold during final foaming. Using conventional blowing agents or blowing agent-solvent mixtures, expandable styrene polymers can be pre-foamed within a relatively short period of time to obtain particles of low density, which are difficult to process into molded bodies. After removal from the mold, depressions occur.

Therefore, in the past, a foam-like molded product with stable shape could only be obtained by using a styrene polymer that was gradually pre-foamed. The addition of flame retardants also enhances this effect, so that in many cases self-extinguishing polymers could only be processed gradually and only with loss of material due to subsequent edging. In addition, the shape-stable molded bodies often had only a very small degree of welding. It is therefore an object of the present invention to be able to foam particles of low density in a relatively short time, in which case these prefoamed particles do not shrink or shrink only slightly after being removed from the mold. The objective was to produce a foamable molding material that could be processed into a molded body J2 with no foam.

This problem has been solved according to the invention by using an industrial mixture containing 50% by weight or more of isobutane, isobutene, isobutyne or a branched C4 fraction, respectively based on the styrene polymer, and 0.5% by weight of a plasticizer. The solution is to use molding compositions based on styrene polymers, aliphatic hydrocarbons and plasticizers containing 2 to 2% by weight.

In a particularly advantageous embodiment, the foamable molding composition further contains 2 to 4% by weight of n-pentane in addition to the blowing agent and plasticizer mentioned above.

The advantage is that 6% by weight of isobutane exhibits a pressure of 19 bar on polystyrene at a polymerization temperature of 115°C, compared to 3% by weight of isobutane and 3% by weight of n-pentane.
The problem lies in the fact that the mixture with has a pressure of only 12 bar. In the present invention, the styrene polymer refers to a copolymer of polystyrene and a polystyrene roll containing at least 50% styrene by weight.

As the copolymer component, for example, the following can be used. alpha-methylstyrene, acrylonitrile, methacrylnitrile, esters of acrylic or methacrylic acid with alcohols having 1 to 8 carbon atoms, esters of fumaric acid with alcohols having 1 to 8 carbon atoms,
vinylpyridine, N-vinyl compounds such as N-vinylcarbazole, butadiene or small amounts such as 0.001
~1.0% by weight, preferably 0.01-0.1% by weight of divinylbenzole. The molding materials for producing foam moldings also contain so-called impact-resistant styrene polymers.

Examples of the impact-tough styrene polymer include mixtures obtained by polymerizing styrene, optionally with other monomers, in the presence of finely divided rubber-like polymers. This type of polymer can also be produced by mixing a styrene-acrylonitrile copolymer with a butadiene polymer or an acrylic acid ester polymer. Is there 2 to 8 weight of isobutane per styrene polymer in the molding material? Preferably 4.5 to 6.
5 weight? The plasticizer is preferably 0.2 to 2% by weight in an amount of
5 is contained in an amount of 0.5 to 1.5 weight e.

By plasticizer in the present invention is meant a solvent or other organic liquid that is homogeneously dispersed in the styrene polymer. Preferably, an organic solvent having a molecular weight of 100 or more to about 300 is used. The boiling point of the plasticizer is preferably 90°C or higher. Furthermore, the plasticizer should be largely dissolved in the polystyrene under foaming conditions (100°C) and has a high degree of special plasticizing action (glass transition temperature per weight of plasticizer). Plasticizers must also be physiologically harmless, such as aliphatic hydrocarbons having 8 to 16 carbon atoms, such as n-octane, n-hexadecane, and aromatic hydrocarbons, such as monostyrene. Dimers or trimers of ethylbenzole and styrene are suitable.

In addition, carboxylic acid esters of long-chain alcohols and carboxylic acids, such as decyl 2-ethylhexanoate, isodecyl stearate, di-n-butyl phthalate and di-2-ethyl-n-hexyl phthalate, are also used. Particular preference is given to foamable molding compositions which, in addition to the abovementioned amounts of isobutane and plasticizer, contain 2 to 4% by weight of n-pentane.

Other additives such as lubricants, stabilizers, dyes, fillers or flame retardants can also be mixed into the molding composition.

The molding material has fine shapes, e.g. small spherical or cylindrical granules,
Alternatively, it is used in the form of fragments obtained when crushing bulk polymers. The particles are preferably between 0.1 and 6 ml, especially 0.1 to 6 ml.
It has a particle size of 4-3 mm. The molding materials are obtained by conventional methods of granular polymerization, for example by polymerizing styrene in aqueous suspension in the presence of blowing agents and plasticizers. It is also possible to mix the styrene polymer with blowing agents, plasticizers and optionally other additives in a continuously operating mixer and to grind the resulting homogeneous mixture into granules. The foamable molding composition according to the invention has the advantage that it can be foamed in a short time into a granular foam material of low specific gravity.

Particularly high throughputs are achieved, for example, in commonly available commercially available continuously operating prefoaming devices, such as those used for the prefoaming of expandable styrene polymers. That is, up to 65 kg per hour can be processed in the Lausiel prefoaming machine C69. The particles have a bulk density of 5 to 20 f1/t. In addition, the molding composition has the advantage that it can be processed from the prefoamed state into molded bodies that exhibit only a small amount of depression. Operating methods for the processing of expandable styrene polymers are described, for example, in Kunstschütsfüh, volume 44 (
1954), pp. 173-180, and in the report of F. Stastnyi, published in "Der Plastofuel Albaita I", 1954, pp. 260-271.

Other operating methods include Willi-ichi Interscience Inc. 1
It is also mentioned in the book ``Plastik Forms'' by Siichi Shu Benning published in 1969. Parts and ? in the examples below? is related to weight.

Example 20 parts of potable water and poly-N-
1 part vinylpyrrolidone, 0.008 parts sodium pyrophosphate
An aqueous phase containing 5 parts of sodium acetate and 0.0125 parts of sodium acetate is prepared.

Styrene 19 parts, tertiary butyl perbenzoate 0.0
42 parts of dibenzoyl peroxide and 0.026 parts of dibenzoyl peroxide and the amounts listed in the table below of isobutane, plasticizer or n-pentane (extended by the amount present in the gas space of the vessel). i.e. 4.5% n-pentane and 6.5% isobutane to achieve blowing agent levels of 3% isobutane and 3% n-pentane in the final product.
is used. Polymerization was carried out at 90°C for 2 hours and at 107°C.
It will be held in 15 hours. Spherical particles with a diameter of 0.5-1 mm are obtained.

This styrene polymer has an average K value of 62. optionally hexabromocyclododecane 0.1 as a flame retardant
2 parts and 0.04 part dicumyl peroxide are added.
The obtained polymer is foamed using steam at 100° C. in a discontinuously operated stirring prefoamer.

Bulk density is measured at 2 minute intervals starting after 5 minutes of foaming time;
A minimum bulk density (adjustable) is thus established. The results are shown in the table below. These pre-foamed particles are
Heat in a mold with dimensions 100 x 200 x 50 cm using steam at 0.8 gauge pressure for 20 seconds, during which time the particles are fully expanded and welded into a compact foam block.

The mold is then cooled and the molded body is removed from the mold after a minimum residence time in the mold. This requires waiting a minimum amount of time to ensure that the block does not break after removal. The welding rate of pre-expanded particles is measured by the following method.

That is, a foam sample is taken out from the middle of the block and broken. Of the particles torn upon rupture? The number is determined by counting per fracture surface. A poor weld results in particle separation along the contact surface. A welding rate of 10% is usually sufficient. The welding rate is given by the number of 70 particles broken when the compact is broken. The remainder of the particle separates at the particle surface. In addition, shrinkage in the longitudinal direction is measured by the method described below.

In other words, measure the length of the block taken out from the mold and shrink it using the following formula? Calculate. ? The number represents the amount of loss incurred due to the necessary trimming. Furthermore, the dented part on the side is
It is measured by the method below.

That is, a board is placed along the length of both sides of 1 m, and the deepest point on the surface of the block, which is often somewhat curved, is measured in ml length. The table below shows the side drop, length shrinkage and bulk density of the foam moldings.

Claims (1)

[Claims] 1 Containing 2-8% by weight of an industrial mixture containing 50% by weight or more of isobutane, isobutene, isobutyne or branched C_4 fraction and 0.2-2% by weight of a plasticizer, respectively, based on the styrene polymer. A foamable molding material based on styrene polymers, aliphatic hydrocarbons and plasticizers, characterized in that