DE19710442B4 - Expandable styrene polymers, process for their preparation and elastic foams produced therefrom - Google Patents

Abstract

Expandable styrene polymers containing
a) a polymer matrix
70-95 wt .-% polystyrene or a styrene copolymer with up to 50% copolymerized comonomers and
30-5 wt .-% of a styrene-butadiene block copolymer having the structure SB / SS, a proportion of polystyrene blocks S from 5 to 40 vol .-%, and a butadiene / styrene copolymer block B / S with random distribution of Monomers and a glass transition temperature between -50 ° C and + 5 ° C,
b) 1 to 15 wt .-%, based on the polymer matrix, of a low-boiling propellant, and optionally
c) conventional additives in effective amounts.

Description

The The invention relates to expandable styrene polymers which are suitable for the production of elastic foams are suitable methods of preparation expandable styrene polymer and the produced therefrom elastic foams.

foams based on expandable polystyrene particles have as thermal insulation and Packaging material a big one acquired technical importance. They are manufactured industrially by that he first expandable by suspension polymerization of styrene in the presence of a blowing agent Styrene polymers prepared, this by heating to foam particles foams and subsequently in forms to foam blocks or welded to form parts.

polystyrene foams are hard foams. Their low elasticity is for many applications, for example in the packaging area, disadvantageous, since the protection of the packaged Good against shock and impact stress only insufficiently possible is and used as packaging foam materials already break at low deformation.

It Therefore, in the past has already been experiments, the elasticity of polystyrene foams to increase.

In WO 94/25516 Elastic foams are described, which are made of a propellant-containing polymer matrix, consisting of a continuous polystyrene phase and incorporated therein butadiene polymer particles. To prepare the polymer matrix, preferably styrene is polymerized in the presence of the butadiene polymer, in a less preferred embodiment, polystyrene and butadiene polymer can also be mechanically mixed together. The butadiene polymer may, inter alia, also be a butadiene-styrene block copolymer, for example a diblock polymer of the structure polystyrene-polybutadiene.

In DE 44 16 862 A1 ( EP-A 682 077 ) and DE 44 16 852 A1 are described expandable styrene polymers for elastic foams containing polystyrene, polybutadiene and a butadiene-styrene block copolymer. The latter may also include areas with statistical distribution of the monomers. Cariflex 1101, a triblock copolymer of the structure polystyrene-polybutadiene-polystyrene, is described by way of example. For the preparation of styrene is polymerized only in the presence of polybutadiene, the resulting graft copolymers is then mixed mechanically with the block copolymer.

The DE 44 20 952 A1 describes elastomeric block copolymers of at least one copolymerized units of a vinylaromatic monomer having a hard phase forming block A and at least one polymerized units of both a vinyl aromatic monomer such as a diene containing 1 elastomeric, a soft phase-forming block B / A, wherein the glass transition temperature Tg of the block A on 25 ° C and that of the block B / A is below 25 ° C and the phase volume ratio of block A to block B / A is selected so that the proportion of the hard phase in the total block copolymer 1-40% by volume and the weight fraction of Diene is less than 50 wt .-% is.

It has been shown in the mechanical mixing of polystyrene with simple two- and three-block copolymers high shear forces on the extruder have to be expended a sufficiently homogeneous distribution of the elasticizing block copolymer phase in the polystyrene matrix. But this carries the danger thermal damage the polystyrene matrix in itself.

Of the The invention was therefore based on the object expandable styrene polymers for elastic foams to provide by simple mechanical mixing of a Polystyrene component with an elastifying block copolymer component can be produced under mild conditions.

It it was found that these Task solved can be achieved by using a styrene-butadiene block copolymer having the structure S-B / S-S, a portion of the polystyrene blocks S of 5 to 40 vol .-%, and a butadiene / styrene copolymer block B / S with statistical distribution of the monomers and a glass transition temperature between -50 ° C and + 5 ° C.

The expandable styrene polymers contained in the polymer matrix 70 to 95 wt .-%, preferably 85 to 93 wt .-% polystyrene or a styrene copolymer with up to 50 wt .-%, preferably up to 80% by weight of copolymerized comonomers. Come as comonomers e.g. in question α-methylstyrene, nuclear halogenated styrenes, nuclear alkylated styrenes, acrylonitrile, esters of acrylic or methacrylic acid of alcohols having 1 to 8 carbon atoms, N-substituted methacrylic acid amides, N-vinylcarbazole and maleic acid (anhydride). Advantageously contains the polystyrene polymerized in a small amount of a crosslinker, i. a compound having more than one, preferably 2 double bonds, such as divinylbenzene, butadiene or butanediol diacrylate. The crosslinker is generally in amounts of 0.005 to 0.05 mol%, based on styrene, used. In contrast to the block copolymers described below these are random copolymers.

To achieve a particularly high expandability, it is expedient that the styrene polymer has an average molecular weight M _w (weight average), measured by the GPC method, between 100,000 and 200,000, in particular between 130,000 and 180,000. Improved processing properties, the foam when the high-molecular-weight edge of the molecular weight-division curve measured by the GPC method is so steep that the difference in the mean values (M _{Z + 1} -M _Z ) is less than 150,000. The GPC method is described in G. Glöckler, Polymer Characterization, Chromatographic Methods Volume 17, Hüthig-Verlag, Heidelberg 1982. The mean values mentioned are described in HG Elias, Makromoleküle, Hüthig-Verlag, Heidelberg 1971, pages 52-64.

styrene polymers, which have the above average molecular weights, can by With the use of regulators in the polymerization can be obtained. As a regulator is used advantageously 0.01 to 1.5 wt .-%, preferably 0.01 to 0.5 wt .-%, of a bromine-free organic compound having a chain transfer constant K between 0.1 and 50. It will be useful the controller during the Polymerization only at a conversion of 20 to 90% added to a steep high molecular edge of the molecular weight distribution curve to achieve.

One Advantageous high expansion capacity can also be achieved by that this Polystyrene 0.1 to 10 wt .-%, preferably 0.5 to 10 wt .-%, of a low molecular weight styrene polymers having an average molecular weight Weight average) between 500 and 5,000 contains.

styrene polymers, from 0.1 to 2 wt .-%, preferably 0.15 to 1.5 wt .-%, copolymerized Acrylonitrile contain lead to foams, which are characterized by extensive shrinkage-free. Also, a mixture of 95 to 99.5 wt .-% polystyrene and 0.5 to 5 Wt .-% of a styrene-soluble styrene-acrylonitrile copolymer shows these properties when the total content of acrylonitrile in the mixture 0.1 to 2 wt .-%, preferably 0.15 to 2 wt .-% is.

styrene polymers, the 3 to 20 wt .-%, preferably 5 to 15 wt .-% copolymerizable acrylonitrile contain, lead to foams with high oil resistance. Also a mixture of 50 to 85 wt .-% polystyrene and 15 to 50 wt .-% a styrenic Styrene-acrylonitrile copolymers show this advantageous property, if the total content of acrylonitrile in the mixture is 3 to 20% by weight, preferably 5 to 15 wt .-%, is. The production of such Mixtures takes place in a simple manner by vor the polymerization, the intended amount of the styrene-acrylonitrile copolymer dissolves in styrene.

styrene polymers, the 2 to 15 wt .-%, in particular 3 to 12 wt .-% maleic acid (anhydride) as Comonomer included, lead to foams, which are characterized by high heat resistance. Advantageous one goes from a mixture of poly styrene and a commercially available styrene-maleic anhydride copolymers with a maleic anhydride content from 15 to 49 wt .-%, by dissolving the copolymer in styrene and subsequent Polymerization can be easily prepared.

Suitable block copolymers of the structure SB / SS are in WO 95/35335 described. It is essential that in the B / S block, the monomers are randomly distributed. The structure within this block can be homogeneous or inhomogeneous along the chain on a statistical average. Such block copolymers can be prepared by anionic polymerization of the monomers in a non-polar solvent containing from 0.1 to 5% by weight of a polar cosolvent. Details of suitable initiators, coupling agents, solvents, cosolvents, and other conditions of multistage polymerization are disclosed in U.S. Patent Nos. 4,199,074; WO 95/35335 described in detail.

For the mechanical Properties is the volume fraction of the soft phase consisting of the B / S block in the solid state crucial. According to the invention, the volume fraction of Soft phase at 60-95, preferably at 70-90 and more preferably at 80-90 Vol .-%. The polystyrene blocks S form the hard phase, the volume fraction corresponding to 5-40, preferably 10-30 and more preferably 10-20 Vol .-% makes up.

It is measurable the volume fraction of the two phases by contrasted electron microscopy or Solid-state NMR spectroscopy. The proportion of polystyrene blocks let yourself after osmium degradation of the polybutadiene fraction by precipitation and precipitation. The future phase relationship a polymer can be also calculate from the amounts of monomer used, if every time Completely can polymerize. By doing The range considered here corresponds to the percentage by weight of styrene and butadiene Shares in about the volume percentages.

in the The invention clearly defines the block copolymer by the quotient of the percentage by volume of the B / S block formed soft phase and the proportion of butadiene units throughout Block copolymer used for the combination styrene / butadiene preferably between 25 and 70 % By weight.

By the static incorporation of styrene units in the soft block of the block copolymer and the use of cosolvents during the polymerization the glass transition temperature (Tg) is influenced. A Glass transition temperature between -50 and + 5 ° C is typical.

The Molecular weight of the block S is i.a. between 1000 to 200,000, preferably between 3,000 and 80,000 [g / mol]. Within of a molecule can S blocks have different molecular weight.

The Molecular weight of the block B / S is usually between 2,000 up to 250,000 [g / mol], values between 5,000 and 150,000 [g / mol] are preferred.

The expandable styrene polymers contained in a homogeneous distribution as component b) 2 to 15% by weight, preferably 3 to 10% by weight a low boiling propellant. The propellants are the Do not dissolve polystyrene, but be soluble in polystyrene. The boiling point should be below the softening point of the polystyrene. Suitable propellants are, for example, propane, butane, pentane, Hexane, cyclopentane, cyclohexane, octane, dichlorodifluoromethane, trifluorochloromethane and 1,1,1-difluorochloroethane. Preferably, pentane is used.

The expandable styrene polymers may also conventional additives in effective amounts, such as dyes, fillers, stabilizers, flame retardants, Synergists, nucleating agents, lubricants, antistatic agents, anti-adhesive during foaming acting substances, means of shortening the demolding time during foaming, as well as carbon black or graphite to reduce the thermal conductivity the foams.

When Additives are also poly (2,6-dimethyl) -1,4-phenylene ether and Poly-1,4-phenylene sulfide suitable. In amounts of from 1 to 20% by weight, based on the component a), these additives cause an increase in the Heat resistance of the foam.

The expandable styrene polymers are generally in the form of particles, i. in pearl or granular form and have advantageously an average diameter of 0.1 to 6 mm, in particular 0.4 to 3 mm.

The Production of the expandable invention Styrene polymers are preferably carried out by mechanical mixing of the polystyrene or styrene copolymer with the block copolymer in the melt, preferably on an extruder, and impregnating with the propellant. You can already on the propellant Press the extruder into the melt, then extruded the strands and subsequently be granulated. But is preferred, the blowing agent in a separate step in aqueous suspension impregnated in granulated polymer mixture.

there the granules are in water, in the presence of the usual auxiliaries and additives in a pressure vessel suspended, rendered inert and brought to a temperature which is preferably just above the softening point of the polymer. At this temperature, the blowing agent is pressed. To cooling and relax is the impregnated Granules separated, cleaned and dried, with drying preferably at room temperature or slightly elevated temperature, to about 50 ° C, for example in a stream of air.

Further Information about the usual Manufacturing processes can be found, for example, in the Plastics Handbook, Volume 5, polystyrene, edited by R. Vieweg and G. Daumiller, Carl-Hauser-Verlag Munich, 1969th

For the production foams are the expandable styrene polymers in known manner by heating to temperatures above its softening point, for example with hot air or preferably with steam. The resulting foam particles can after cooling and optionally an intermediate storage by reheating further foamed become. You can finally in a known manner in non-gastight forms closing to moldings welded become.

The resulting foams have densities of 5 to 150 g / cm ³ , in particular 10 to 100 g / cm ³ , on.

The from the styrene polymers according to the invention produced foams are characterized by a high elasticity. So do they have a resilience that up to 90% with four compressions, measured according to DIN 53 777, is. So they are conventional, rubber-free styrene polymers clearly superior.

The prefoamed Pearls are of a uniform cell structure and weld in the molding process without Formation of voids. The moldings produced in this way have sufficient heat resistance on.

Furthermore own the foams of the invention a surprise good thermal insulation, the up to 10% better than the conventional polystyrenes same Density. The foams and shaped bodies are easily recyclable.

Claims (6)

Expandable styrene polymers containing a) a polymer matrix 70-95 % By weight polystyrene or a styrene copolymer with up to 50% copolymerized comonomers and 30-5 wt .-% of a styrene-butadiene block copolymer having the structure S-B / S-S, a portion of the polystyrene blocks S of 5 to 40 vol .-%, and a butadiene / styrene copolymer block B / S with statistical distribution of the monomers and a glass transition temperature between -50 ° C and + 5 ° C, b) 1 to 15 wt .-%, based on the polymer matrix, of a low-boiling Propellant, and optionally c) conventional additives in effective Amounts. Expandable styrene polymers according to claim 1, characterized in that the Block copolymer was prepared by anionic polymerization in a nonpolar solvent, which contained from 0.1 to 5% by volume of a polar cosolvent. Process for the preparation of expandable styrene polymers according to claim 1, characterized in that polystyrene or the styrene copolymer in the melt mixed with the block copolymer and during or impregnated after mixing with the blowing agent. Method according to claim 3, characterized that he the mixing takes place on an extruder, the mixture is squeezed and granulated and the granules in aqueous suspension impregnated with the blowing agent. Method according to claim 3, characterized that he mixed on an extruder, the polymer components, the blowing agent injects, that impregnated Extruded polymer mixture in water and granulated the strands. Elastic foams of density 5 to 150 g / cm ³ based on the expandable styrene polymers according to claim 1.