DE102005026356A1 - Foamable moldings without chemical crosslinking agents - Google Patents

Abstract

The invention relates to a process for the production of thermally expandable shaped articles based on thermoplastic homopolymers and / or copolymers and blowing agents, in which the form-retaining crosslinking of the binder base without "chemical" crosslinking agents is effected by beta or gamma radiation. In a subsequent step, the preformed shaped bodies are expanded by heating to temperatures between 90 ° C. and 250 ° C. without collapsing during foaming of the shaped body.

Description

The The present invention relates to a process for the preparation of thermally expandable moldings based on thermoplastic homopolymers and / or copolymers and blowing agents without "chemical" crosslinking agents as well as their use.

modern Vehicle concepts and vehicle designs have a variety of cavities on, which must be sealed to prevent the entry of moisture and dirt, because these corrosion on the corresponding body parts of lead in inside can. This applies in particular to modern self-supporting body structures in which a heavy frame construction is replaced by so-called "space frames". The latter is a lightweight, structurally stable frame made of prefabricated Hollow profiles used. Such constructions are systemic a series of cavities on that against the ingress of moisture and dirt must be sealed. Because these cavities Furthermore Forward airborne sound in the form of unpleasant vehicle running and wind noise, serve such sealing measures also to reduce the noise and thus to increase the ride comfort in the vehicle. In conventional construction, these are Contain cavities Frame and body parts made of semi-skinned components prefabricated, at a later date by welding and / or gluing are joined to the closed hollow profile. With such a construction, the cavity is in the early construction state of a vehicle body so easily accessible, so that sealing and acoustically damping bulkhead parts in these early Phase of the shell by mechanical hooking, by plugging into appropriate Holding devices, holes or fixed by welding can be.

at the use of prefabricated hollow profiles for space frame technology as a sealing and acoustically damping Shaped parts ("bulkhead parts") as suggested WO 2004/024540 molded article used, the outer edge area a thermally expandable material comprising a high coefficient of friction across from Metal and plastic. This shaped body has in its interior an opening and / or recess for receiving a mounting aid, with their help the molded part by a cross-sectional end of the hollow profile in the hollow profile is used and under the action of force to the predetermined point pushed or pulled.

All Currently used expandable moldings for sealing and acoustically damping Effect of the aforementioned type usually contain polymeric binder based on ethylene-vinyl acetate copolymers, copolymers of the Ethylene with (meth) acrylic esters, which may also contain proportionate (meth) acrylic acid in copolymerized form, random or block copolymers of styrene with butadiene or isoprene or their hydrogenation products. In addition, the binders contain still crosslinking substances or groups ("crosslinkers"). Such crosslinkers can added low molecular weight compounds, the unsaturated double bonds hold such as (Meth) acrylate monomers or oligomers or others chemically reactive groups such as acid anhydrides, Hydroxyl compounds, amines, epoxides or the like, but it can also in the base binder copolymerized functional groups such as carboxyl groups, epoxy groups or olefinically unsaturated double bonds. The networking over the double bonds of the backbone the binder systems or the added crosslinker takes place by addition of radical crosslinkers. The remaining networking mechanisms include reactions between functional groups such as e.g. carboxyl and epoxy groups or hydroxyl groups and carboxyl groups or carboxylic anhydride groups.

So describes EP 0383498 A2 foamable molded parts containing a base polymer based on ethylene and olefinically unsaturated methyl acrylates having a melt index of 0.1 to 6 and containing from 10 to 40% by weight of methyl acrylate; and a crosslinking agent and a blowing agent such that the molded part is at temperatures between 110 and 190 ° C at the same time foamable and crosslinkable (curable) and gives a closed-cell foam. As the crosslinking agent peroxide compounds are proposed.

WO 92/02574 A1 describes a process for producing shaped foamable parts from a polymer composition containing a polymer preferably based on ethylene-methyl acrylate copolymers, a curing agent and a foaming agent. The manufacturing process involves dry blending the propellant with a wax powder to produce a dry blend of these ingredients, followed by blending this dry blend and all remaining portions of the total composition in the melt at a temperature between the melting point and not more than 5 to 10 ° C above the melting point of the polymer. Subsequently, the melt mixture is molded under low shear by extrusion or press molding into a shaped article. As a crosslinking agent peroxide compounds are disclosed in turn, so that the foamable moldings are foamed and crosslinked simultaneously in a subsequent step under heating.

US 2004/0101651 A1 describes a foamable copolymer composition for mounting a light-emitting glass lamp in a metal frame. The foamable or expandable copolymer based on ethylene vinyl acetate copolymers, Ethylmethyl acrylate copolymers or their combination. Farther This paper teaches that these compositions in addition to propellants for foaming should contain a chemical crosslinking agent, it is preferred chemical crosslinkers called peroxides. The foamable and networkable Compositions are first produced in granular form, then the expandable moldings produced by injection molding. According to the teaching of this document should the foaming and curing by thermal activation to temperatures between 120 ° C and 200 ° C. This document further discloses that it may be advantageous additionally to the thermally activatable crosslinking agent, a crosslinking agent To add, by radiation curing, a crosslinking of the polymeric Binder causes, by way of example be mentioned for this triallyl cyanurate, triallyl isocyanurate, Triallyl trimellitate and other allyl compounds.

US 6,124,370 describes foamed articles which are to be cured in a two-stage process according to a dual curing mechanism, thereby having improved tensile strengths, elastic recovery and improved creep and fatigue resistance. This document proposes to cure the binder system based on an olefinic polymer and blowing agents in a first stage by heat or radiation curing, followed by a moisture-activated second curing stage. As the heat-activatable curing step, the compositions should contain peroxides, sulfur or similar crosslinking agents. It can also be seen from the document that initiators which generate free radicals should also be used for radiation crosslinking. To activate the moisture-curing post-crosslinking, the incorporation of silane-functional groups or sulfonyl groups and similar moisture-reactive groups is proposed. As an application for such foamed moldings, this document proposes the production of foamed insoles in sports shoes. Foamed floor coverings are proposed as a further application, in both fields of application dynamic fatigue resistance and static creep resistance are critical properties for the permanent use of such foamed moldings.

WHERE 03/051601 A2 describes a process for the treatment of a foamable Plastic, in which the plastic from a starting state of higher density by means of a blowing agent in a foaming process in a foamed state low density is transferred, the plastic before the foaming process by at least a first crosslinking agent and during the foaming is crosslinked by at least one second crosslinking agent. It will be as crosslinking agents, physical and chemical crosslinking agents proposed, as a physical crosslinking agent is intended in particular high energy radiation, e.g. electron beam or gamma radiation. As a chemical crosslinking agent Peroxides, in particular organic peroxides proposed. According to the teaching This document is a partially crosslinked at the first level of crosslinking Molding. Preferably, the injection-molded part before the foaming process pre-crosslinked with a high-energy radiation in partial areas and then For example, be used in the cavity of the body of an automobile in a second step, the foaming process and the second chemical Crosslinking agent to activate the polymer chains of the plastic molding continue with foaming to crosslink, causing the cavities be sealed in the body.

A disadvantage of the foamable and crosslinked moldings of the aforementioned prior art is that organic peroxides may have to be added in conjunction with unsaturated crosslinkers. Such organic peroxides are known to be very sensitive to temperature, so that the choice of peroxide is crucial for the crosslinking and for the achievable degree of expansion of the molding. Particularly good results are achieved when crosslinking peroxides are used at low temperatures. However, these have a very low half-life, because they crosslink the plastic even at low temperatures, before it is foamed with a blowing agent. This results in unsatisfactory storage stability of the unfoamed shaped body. A further disadvantage of such moldings of the prior art is that foaming process and crosslinking process take place in one stage, so that at the beginning of the heating of the moldings is not sufficiently crosslinked and loses its originally given shape by flow processes during reflow, thereby the foaming process proceeds not isotropic. The structure or shape given to the shaped body prior to the foaming process consequently goes into the Re Gel lost because the melt is not sufficiently dimensionally stable.

The The inventors have therefore set themselves the task of such disadvantages the expandable molding overcome the aforementioned prior art. The inventive solution of Task is the claims refer to. It essentially consists in the provision a method for producing thermally expandable moldings the basis of thermoplastic homo- and copolymers and blowing agents, in which the expandable moldings in unexpanded form using beta or gamma radiation be crosslinked without the crosslinking by addition of crosslinking agents he follows. In a subsequent step, these moldings are under Heat foamed without further networking takes place.

The Crosslinking of the moldings without the addition of crosslinking agents takes place by acting of beta radiation or gamma radiation, preferably with an absorbed dose from 50 to 100 kGy, more preferably with an energy dose of 70 to 80 kGy. This radiation dose can be either with a Pass through the radiation source, but it can also be necessary that the moldings multiply have to go through the radiation source, this depends on the radiation power of the radiation source.

To the irradiation of the moldings with beta radiation or gamma radiation this is fully networked and becomes at the subsequent step of heating on Temperatures between 90 ° C and 250 ° C, preferably between 110 ° C and 180 ° C only with foaming expanded. This expansion step takes place in the preferred Use of the expandable moldings for sealing cavities or Hollow profiles in vehicles, especially motor vehicles in the Production line of the vehicle instead. Here is the process heat of the so-called KTL furnace exploited to the foaming process of the expandable molding trigger. The method according to the invention produced moldings are already fully networked at this time, so this is done foam Completely isotropic, i. the molded body has no tendency during of the expansion process to collapse but foams in all given directions evenly. The dimensional stability of the molding while of thermal frothing becomes decisive by the choice of thermoplastics used, especially in relation on their melt index, determined. For the inventive method for the preparation of the thermally expandable molded body, a Variety of thermoplastic binders used are essential is here that these thermoplastic polymers alone by the effect of beta or gamma radiation without the addition of "chemical" crosslinkers such as peroxides, or low molecular weight monomers or oligomers having reactive groups are networkable.

Specific examples of suitable thermoplastic polymers for use as binders for the process according to the invention are:
Polyethylene, polypropylene, copolymers of ethylene and propylene, ethylene vinyl acetate, copolymers of ethylene with (meth) acrylic acid and / or their C ₁ to C ₁₂ alkyl esters, random or block copolymers of styrene with butadiene and / or isoprene and their hydrogenation products, ethylene / Propylene-diene terpolymers (EPDM), polyether-ester block copolymers, polyether-amide block copolymers, thermoplastic polyurethanes or mixtures thereof.

When Polyethylene can Both high density polyethylene (HDPD) and low density (LDPE) can be used. The hydrogenation products of the block copolymers of styrene with butadiene or isoprene are also known as SEPS (Styrene-ethylene-propylene-styrene copolymer) or SEBS (styrene-ethylene-butylene-styrene copolymer). In addition to the aforementioned preferably used triblock copolymers can also the corresponding diblock copolymers with styrene-ethylene-propylene blocks or Styrene-ethylene-Butylenblöcken be used.

Very particular preference is given to copolymers of ethylene with (meth) acrylic acid and / or their C ₁ to C ₁₂ alkyl esters, for example ethylene-methyl acrylate copolymers having a methyl acrylate content of from 10 to 40% by weight (based on the copolymer) or ethylene vinyl acetate - Copolymers with a vinyl acetate content of 5 to 40 wt .-% (based on the copolymer).

In principle, all common blowing agents can be used to achieve the foaming during the expansion or foaming process, but preferably organic blowing agents from the class of the azo compounds, N-nitroso compounds, sulfonyl hydrazides or sulfonyl semicarbazides are used puts. For the azo compounds to be used according to the invention, the azobisisobutyronitrile and in particular the azodicarbonamide are mentioned by way of example; from the class of the nitroso compounds, the di-nitrosopentamethylenetetramine is exemplified, from the class of the sulfohydrazides the 4,4'-oxybis (benzenesulfonic acid) hydrazide, the diphenylsulfone-3, 3'-disulfohydrazide or the benzene-1,3-disulfohydrazide and from the class of semicarbazides called p-Toluolsulfonylsemicarbazid. It is also possible to use propellants based purely on inorganic substances, for example azides, carbonates or bicarbonates in combination with solid acids, and in particular the alkali metal silicate-based expandable propellants known from WO 95/07809 or US Pat. No. 5,612,386. The aforementioned blowing agents may also be replaced by the so-called expandable microspheres, ie non-expanded thermoplastic polymer powders impregnated or filled with low-boiling organic liquids. As matrix material or shell, these expandable hollow microspheres contain a copolymer of acrylonitrile with vinylidene chloride and / or methyl methacrylate and / or methacrylonitrile. Such "microspheres" are described for example in EP-A-559254, EP-A-586541 or EP-A-594598. Although not preferred, already expanded hollow microspheres can be used or used. Optionally, these expandable / expanded hollow microspheres can be combined in any proportion with the above-mentioned "chemical" blowing agents. The chemical blowing agents are in foamable / expandable moldings in amounts between 0.1 and 10 wt .-%, preferably between 0.5 and 7 wt .-%, the hollow microspheres between 0.1 and 4 wt .-%, preferably between 0 , 2 and 2 wt .-% used.

Possibly can for the organic blowing agents or so-called activators such. zinc oxide used in amounts of up to 5 wt .-%, preferably up to 3 wt .-% become.

In addition, the Binders, if necessary, adhesion promoters, plasticizers and others Auxiliaries and additives contain, in particular fillers such as chalk, natural ground or precipitated calcium carbonates, Calcium magnesium carbonates, Silicates, heavy particles, graphite and possibly soot.

Versus the thermal, thermo-oxidative or ozone degradation of the shaped body according to the invention can conventional Stabilizers, e.g. sterically hindered phenols or amine derivatives be used. Typical quantity ranges for such stabilizers are 0.1 to 5 wt .-%.

The expandable moldings produced by the process according to the invention are preferably packaged by extrusion or injection molding as molded body for the final application and then irradiated by radiation with beta or gamma radiation with an absorbed dose of 50 to 100 kGy, preferably 70 to 80 kGy and thus completely crosslinked. In this case, preferably also on the otherwise necessary carrier materials, as described in WO 2004/024540, WO99 / 32328 or the EP 1031496 A1 be omitted, since the inventively produced expandable moldings during thermal expansion have excellent shape stability. These crosslinked moldings are then then, preferably in the shell of the vehicle manufacturing, fixed in the corresponding - still open in this stage of production - cavities and then foamed during the further manufacturing process of vehicle production in cathodic kiln (KTL = cathodic dip paint) by the prevailing process heat there , Temperatures between 110 ° C and 180 ° C prevail in the KTL furnaces of vehicle production, but peak values of up to 250 ° C are reached. The average residence time of the vehicles in this oven is between 10 min. and 30 minutes, typically between 15 minutes. and 20 min.

In the following embodiments the invention should be closer explained The selection of examples is not limited to the Invention object should represent, they should only in exemplary Way concrete examples illustrate. Unless otherwise stated, compositions are all quantities are parts by weight.

example 1

In an evacuable laboratory kneader in the melt, a mixture of 10 parts of ethylene vinyl acetate copolymer (vinyl acetate content 28 wt .-%, melt index ASTM D12386 g / min), 34 parts of ethylene vinyl acetate copolymer (vinyl acetate content 5 wt .-%, melt index 0.5 g / min) and 46 parts of ethylene vinyl acetate (vinyl acetate content 33% by weight, melt index 400 g / min), 2 parts of zinc oxide, 6 parts of azodicarbonamide, one part of 2,2-methylenebis (4-methyl-6-tert. -butylphenol), and a part N, N-ninitroso-pentamethylenetetramine up to Homogeneity mixed. Subsequently, a plate-shaped molded article having dimensions of 30 × 50 × 3 mm was formed by extrusion.

This moldings was then exposed to a gamma ray dose of 75 kGy. Subsequently was this shaped body 30 min. to 180 ° C heated, with an expansion rate of 1200% was measured, without that it collapses and loses its shape during the molding Expansion came.

For the determination of the storage stability some moldings were stored for 12 weeks at -20 ° C, room temperature (RT) and + 40 ° C and thermally expanded after the expiration of this storage time. -40 ° C stored specimens 1200% expansion RT stored test specimens 1200% expansion + 40 ° C stored specimens 1200% expansion

Example 2 (comparison)

In An evacuable laboratory kneader was melted in a mixture from 10 parts of ethylene vinyl acetate copolymer (vinyl acetate fraction 28 % By weight, melt index according to ASTM D12386 g / min), 34 parts of ethylene vinyl acetate copolymer (vinyl acetate content 5% by weight, melt index 0.5 g / min) and 46 parts of ethylene vinyl acetate (Vinyl acetate content 33% by weight, melt index 400 g / min), 2 parts zinc oxide, 6 parts of azodicarbonamide, one part of 2,2-methylenebis (4-methyl-6-tert-butylphenol), and one part N, N-ninitroso-pentamethylenetetramine and additionally 2 Dicumyl peroxide parts mixed until homogeneous. Subsequently was by extrusion a plate-shaped moldings shaped with the dimensions 30 × 50 × 3mm.

Subsequently was this shaped body 30 min. to 180 ° C heated, with an expansion rate of 600% was measured. Of the lower degree of expansion is probably explained by the fact that a part of the peroxide in the production or molding (extrusion) of the molding (Temperature range 120-160 ° C) already has fallen apart and thus it is a part of the loss of shape of the molding during the Expansion came.

For the determination of the storage stability as in Example 1 some moldings were stored for 12 weeks at -20 ° C, room temperature (RT) and + 40 ° C and thermally expanded after the expiry of this storage time. Initial degree of expansion on the day of manufacture -600% -40 ° C stored specimens 300% expansion RT stored test specimens 100% expansion + 40 ° C stored specimens 0% expansion

The Storage experiments with the moldings of the comparative experiment according to the state the technique showed during the storage time a significant, undesirable drop in the degree of expansion in comparison to the moldings produced according to the invention.

Claims (8)

Process for the preparation of thermally expandable moldings based on thermoplastic homo- and copolymers and blowing agents, characterized in that the moldings are crosslinked in unexpanded form with beta or gamma radiation and are foamed in a subsequent step under heating. Method according to claim 1, characterized in that that is the crosslinking of the moldings with an absorbed dose of 50 to 100 kGy, preferably 70 to 80 kGy takes place. Method according to at least one of the preceding Claims, characterized in that the crosslinking without the addition of crosslinking agents he follows. Method according to claim 1, 2 or 3, characterized that the foaming of the molding at temperatures between 90 ° C and 250 ° C, preferably between 110 ° C and 180 ° C he follows. Process according to at least one or preceding claims, characterized in that the thermoplastic homo or copolymer is selected from polyethylene, polypropylene, copolymers of ethylene and propylene, ethylene vinyl acetate, copolymers of ethylene with (meth) acrylic acid and / or their C ₁ to C ₁₂ -Alkyl esters, random or block copolymers of styrene with butadiene and / or isoprene, as well as their hydrogenation products, ethylene / propylene-diene terpolymers (EPDM), polyether-ester block copolymers, polyether-amide block copolymers, thermoplastic polyurethanes or mixtures thereof. Method according to at least one of the preceding Claims, characterized in that the propellant is selected from azo compounds, sulfonic acid hydrazides, Semicarbazides, nitroso compounds, expandable hollow microspheres based on polyvinylidene chloride copolymers or acrylonitrile / (meth) acrylate copolymers or mixtures of the aforementioned blowing agents. Thermally expandable molded body, producible according to a Method according to claim 1 to 3 or 5 to 6. Use of the expandable moldings according to at least one of the claims 1 to 3 and / or 5 to 6 for sealing cavities or hollow profiles in vehicles, especially motor vehicles.