DE1298274B - Production of foamable, finely divided styrene polymers - Google Patents

Description

It is known that moldings made from foam-like styrene polymers can be used obtained when finely divided styrene polymers, which are a gaseous or liquid Containing propellants in non-gastight forms at temperatures above the boiling point of the blowing agent and the softening point of the polymer.

In technology, one way of working has been introduced above all, at the foamable blowing agent-containing particles in a first working stage initially heated so far and so long that they foam incompletely. This process is known as "pre-expanding". The pre-expanded particles are then heated in a non-gastight mold so that they foam up completely and sintered to form a molded body. This process is called "foaming".

Foamable styrene polymers are generally in open or closed vessels prefoamed with the help of steam. The pre-expanded Particles, if they are e.g. B. heated to too high temperatures or too long, Sinter to form larger agglomerates, which can be recovered before further processing Must comminute, since the agglomerates are difficult to form into molded bodies with more homogeneous Let the structure foam up.

It is already known that the sintering of the particles when Can prevent pre-foaming if you use small amounts of wax or heavy metal soaps, such as zinc stearate, on the surface of the particles. It has shown, that in the production of moldings from particles treated in this way, i.e. when foaming, Difficulties arise because the particles sinter only incompletely. The so foam moldings obtained have only a low mechanical strength and unfavorable insulation properties.

Finally, it is also known to glue polystyrene during of prefoaming by coating with perfluorooctanoic acid (cf. USA. patent 3,056,752) or coating with polysiloxane emulsions (cf. USA patent 3 086 885). However, these methods have significant disadvantages. Perfluorooctanoic acid is difficult to process; there must be large amounts of water removed. In addition, foams coated with perfluorooctanoic acid are suitable expandable polystyrene particles because of their corrosive and toxic effects the acid not for the manufacture of packaging goods for z. B. Food and medical equipment. The coating of expandable styrene polymer with a Polysiloxane emulsion, on the other hand, leads to products that are essential when "foaming" are poorly weldable and therefore form bodies with reduced strength to lead.

It is also known, expandable polystyrene beads with vinyl polymers to be coated, whereby according to the Belgian patent specification 596 919 resp.

"Modern Plastics", Vol. 38, July 1961, p. 92 ff., 3 to 5 parts by weight expandable polystyrene are coated with one part by weight of vinyl polymer.

However, these products stick together to form agglomerates and during pre-expansion sinter only incompletely when foaming in molds.

The subject of the invention is a process for production during prefoaming non-sticking molding compounds made from blowing agent-containing styrene polymers Coating with thermoplastic fabrics, characterized in that one the blowing agent-containing molding compositions with 0.005 to 0.5 percent by weight, based on the molding compound of a finely powdered thermoplastic plastic, coated.

Styrene polymers are polystyrene and copolymers of styrene, which contain at least 50 percent by weight of styrene polymerized, Understood. As copolymerization components come, for. B. in question a-methylstyrene, Nuclear halogenated styrenes, acrylonitrile, esters of acrylic or methacrylic acid of Alcohols with 1 to 8 carbon atoms, N-vinyl compounds such as vinyl carbazole, vinyl esters of carboxylic acid with 1 to 6 carbon atoms or small amounts of butadiene or divinylbenzene.

Under propellants, which are contained in the plastic masses, understood gaseous or liquid hydrocarbons or halogenated hydrocarbons are used under normal conditions, which do not dissolve the styrene polymer and whose boiling points are below the softening point of the polymer. Suitable propellants are e.g. B. propane, butane, pentane, Hexane, cyclohexane, dichlorodifluoromethane and trifluorochloromethane. The propellants can be used in the foamable plastic masses in amounts of 2 to 20 percent by weight, based on the polymer contained in the plastic compounds.

The plastic compounds can also contain other components be e.g. B. flame retardants, such as tris-dibromopropyl phosphate or hexabromocyclododecane, or fillers, color pigments, antistatic agents and plasticizers.

The foamable molding compositions can be in the form of beads or granules or in the form of small chunks, as they are when grinding bulk polymers can be obtained.

The particles of the molding compound are fine-powdered thermoplastic Plastics in amounts of 0.005 to 0.5 percent by weight, preferably 0.01 to 0.1 percent by weight, based on the molding compound, coated.

Smaller amounts are ineffective; one uses larger amounts of finely powdered thermoplastics, the particles sinter when foaming only incomplete in forms.

The particle size of the plastic powder is preferably between 0.1 to 10.

The thermoplastics expediently have a softening point over 60 "C, advantageously over 800 C (determined using the Vicat method [DIN 57302]).

Of the thermoplastics, polystyrene is particularly suitable and copolymers of styrene. The same are used as comonomers for styrene in question, as it is also polymerized into the foamable styrene polymers could be. Homopolymers and copolymers of vinyl chloride are also suitable and vinylidene chloride as well as ethylene and propylene. There are also fine powdered ones Crosslinking products made from unsaturated polyester resins, d. H. Mixtures of unsaturated Polyesters and cz, fl-unsaturated compounds, such as styrene, are possible.

The plastic powder can, for. B. obtained by grinding large particles have been. It is also possible, for. B. to use plastic powder, which by Emulsion polymerization of the monomers are produced.

Coating the particles of the foamable Plastic compound can, for example, by intensive mixing of the particles with the finely powdered Plastic can be made at room temperature.

The finely divided foamable plastics coated according to the invention do not sinter together to form larger agglomerates during prefoaming. When foaming of the pre-expanded particles sintered in molds that do not close in a gas-tight manner Particles largely complete.

The parts mentioned in the examples are parts by weight.

Example 1 1000 parts of bead-shaped foamable are made in a mixer Polystyrene with a content of 6% pentane as blowing agent, which has a grain diameter from 0.4 to 2.5 mm, with 1 part of a powdery copolymer of 80 Parts of styrene and 20 parts of acrylonitrile mixed for 40 seconds. The powdered copolymer has a softening point according to V i c a t of 102 "C and an average grain diameter of 0.5 µ.

100 parts of the coated, expandable, bead-shaped styrene polymer are in a discontinuously working pre-expander with flowing steam treated from 100 to 105 ° C for 5 minutes. The pre-expansion device consists of one Sheet metal box with steam inlet and outlet and contains one with a fine-meshed fabric covered grate on which the pre-foaming particles are spread out in a thin layer will. The steam supply is designed in such a way that the steam evenly touches the grate surface heated.

The pre-expanded material is placed in an air-permeable container Stored for 24 hours and then in a perforated shape measuring 100 x 100 30 cm and foamed to a foam block with steam of 1.0 atm.

After drying, the foam block is heated electrically Wires divided into sheets of 2 cm thick.

In the same way, untreated and 0.1 percent by weight Zinc stearate-coated foamable polystyrene, pre-expanded into a foam block foamed and the block divided into plates.

The foam sheets are broken in the middle and at the break points the percentage of pearls that are sintered is determined. Sintered pearls tear through when the plates break, pearls that have not been sintered separate along the way of the grain interfaces.

The following table shows the properties of the coated and the untreated expandable styrene bead polymers during prefoaming and foaming: Table 1 Proportion of Expandable prefoams sintered partial Molding compound of 100 ° c foam plate With mixed styrene polymer loading layers ...... unglued 10001o share in Expandable prefoams sintered partial Molding compound of 100 "C foam plate With zinc stearate coated. . . . . unglued 60% Untreated ........ 1000/0 of 100% Particle too Agglomerates glued Example 2 As described in Example 1, 1000 parts of granules of a molding composition composed of 91 parts of polystyrene, 5.5 parts of pentane and 3.5 parts of hexabromocyclododecane are mixed with 1 part of finely powdered polystyrene. The granulate particles have an average diameter of 0.8 mm and a length of about 1.5 mm. The polystyrene powder used for coating was produced in an aqueous emulsion; it has a softening point (according to Vi cat) of 94 ° C, the mean grain size is 0.2 2.

The properties of the expandable coated with polystyrene powder The table below shows dimensions for pre-foaming and foaming. The crowd was like Described in Example 1 pre-expanded and foamed to form a foam block.

Table 2 .. Proportion of Expandable pre-foaming on sintered Molding compound in steam particles of 100 "C in the plate With polystyrene powder coated unglued 90% Untreated ............ 100% of the 90% Particles are to agglo- merates sticks Example 3 Each 1000 parts of an expandable molding compound with an average grain diameter of about 1.5 mm made from a copolymer of 95 parts of styrene and 5 parts of methyl methacrylate and 6 parts of pentane are coated with 1 part of a plastic powder each as described in Example 1.

Plastic powder A: polyvinyl chloride with an average molecular weight of 40,000 and an average grain diameter of about 0.3 µ.

Plastic powder B: Finely ground - hardened polyester resin 65 parts of maleic acid-propylene glycol-1,2-polyester and 35 parts of styrene. Medium Particle size 0.5 u.

Plastic powder C: polyethylene powder with a softening point after Vi c a t of 1080C and an average grain diameter of 0.5 p.

Plastic powder D: copolymer of 90 parts of styrene, 5 parts Acrylonitrile and 5 parts of acrylic acid with an average grain diameter of 0.4 p.

Plastic powder E: Powdered polytetrafluoroethylene. Medium Particle size 10.

Plastic powder F: Finely ground polyoxymethylene. Mean particle size 8th.

Plastic powder G: Finely ground cellulose triacetate. Mean particle size 5 p.

The properties of the expandable with the plastic powders A, B and C, respectively Molding compositions for pre-foaming and foaming are shown in Table 3. The beads were as in the example 1 described pre-expanded and foamed to form a foam block.

Table 3 proportion of Expandable pre-foaming on sintered Molding compound 4 minutes in steam particles coated with from 100 "C in the plate Plastic powder A pearls are 95% not glued Plastic powder B beads are 95% not glued Plastic powder C beads are 90% not glued Plastic powder D beads are 1000/0 not glued Untreated ...... $ 80% of pearls 90% are to agglomerate merates sticks Plastic powder E pearls are 85% not glued Plastic powder F beads are 90% not glued Plastic powder G beads are 90% not glued

Claims (1)

Claim: Process for the production of non-sticking materials during prefoaming Molding compounds made from styrene polymers containing blowing agents by coating with thermoplastic Plastics, d u r c h it is not noted that the propellant-containing Molding compositions with 0.005 to 0.5 percent by weight, based on the molding composition of a fine powder thermoplastic plastic, coated.