CA1116349A - Blowing agent concentrate having a thermoplastic plastics material as support - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE:

A blowing agent concentrate based on a chemical blowing agent and a thermoplastic plastics material as support.
The support is a saturated polyester and/or copolyester with a crystallite melting point of from 100°C to 220°C and with a reduced viscosity of from 0.4 dl/g to 1.6 dl/g. These blowing agent concentrate are particularly suitable for use as flowing-gas-releasing component in the production of structured foam moldings of high molecular weight polyalkylene terephtalates.

Description

This invention relates to a blowing agent concentrate based on a chemical blowing agent and a thermoplastic plastics material as support. The invention also relates to the use of blowing agent co~ncentrates as blowing-gas-releasing component in the production of structured foam mouldings of high molecular weight polyalkylene terephthalates.
~ here are various processes for working chemical blowing agents into the thermoplastic plastics material to be foamed.
For example, the generally pow~er-form blowing agent may be scattered onto the plastics granulate in the requisite concentra-; tion which generally amounts to between 0.1 and 5.0 % by weight;
depending upon the effectiveness of the blowing agent used.
Although this process is still frequently appliéd in practice, it is attended by ~ome serious disadvantages. Dust is given off, occasionally in considerable quantities, during the mixing process.
This dust soil~ the mixing units and pollutes the atmosphere and, in addition, is physiologically harmful to a certain extent.
~ In addition, disintegration phenomena can occur, especially in ; ; cases where the powder-form blowing agent is added in relatively large quantities. The fluctuations in the content of blowing agent which may occur as a result adversely affect the quality of the end products produced from mixtures such as these. In addition, deposits are formed and losses of blowing agent incurred during delivery processes. Pneumatic delivery over relatively long distances is almost impossible, In cases where powder-form chemical blowing agents are used, disintegration phenomena can occur and depo~its can be formed during processing in the storage container of the processing machine, giving rise to fluctuations in quality. In cases where powder-form blowing agents are used, blowing gas can be lost by escaping through the feed opening in the feed zone of the processing machines after the decomposition temperature of the blowing agent has been exceeded, with the result that the yield of blowing gas is reduced to a very considerable extent.
In order to obviate these disadvantages, it has also been proposed (cf for example DT-OS No. 2,~34,085) directly to work the blowing agent powder into the plastics material to be foamed. In this process, the blowing agent used is first worked into the melt of the polymer in suitable machines in a quantity which is in a fixed ratio to the polymer, and forms an integral part of the granulates produced. During processing into structured mouldings, the blowing agent present in the granulate is activated and enables the foam structure to be formed. One serious disadvantage of this method o incorporating blowing agents is that the blowing agent undergoes partial decomposition during the actual production o the blowing-agent-containing granulate because the processing temperature required to obtain a homogeneous melt is so close to the decomposition temperature of the blowing agent, depending upon the particular type of blowing agent used, that the blowing agent actually gives off gas before processing into structured foam mouldings and i therefore seriously limited in its further activity. This results in fluctuations in the density of the structured foam. In many cases, the blowing pressure reduced by the premature losses of gas is no longer sufficient for the formation of a satisfactory structured oam.
Another disadvantage of this process is that blowing-agent-containing plastic~ of the type in question have to be stored in relatively large quantities because it i~ necessary to prepare batches with different blowing agent contents which are adapted to the 10w properties of the plastics material to be foamed and to the dimensions of the mouldings to be produced.
In order to obviate these disadvantages, the blowing agent has already been worked in concentrated form into a pol~ner intended to be processed in plastic form below its decomposition temperature and the resulting mixture blended in the necessary ratio with the plastics material to be foamed. This obviates the disadvantages involved in handling powder-form blowing agents. There is no need to prepare and store several batches with different blowing agent contents because the required blowing agent contents can be adapted to meet particular requirements immediately before the actual foaming process by varying the ratios in which the blowing agent concentrate is mi~ed with the polymer to be foamed~
Blowing agent concentrates based on polystyrene and polyolefins are known. Unfortunately, blowing agent concentrates such as these are attended by the disadvantage that they are unsuitable for the production of structured foam mouldings of high molecular weight polyalkylene terephthalates. In cases where blowing agent concentrates such as these are used in conjunction ; with polyalkylene terephthalates, the mouldings obtained have inferior physical, mechanical and thermal properties. For this reason, it has hitherto been necessary to rely on the above-mentioned processes with all their disadvantages for working in blowing agents in the production of st~uctured foam mouldings of polyalkylene terephthalates.
The object of the present invention is to provide foamable blowing agent concentrates, in which the above-mentioned disadvantages are no longer encountered in the foaming of, in particular, polyal]cylene terephthalates by in-mould foaming techniques to form structured foam mouldings.
It has now been found that the disadvantages referred to above can be eliminated by using as support for the chemical blowing agent a saturated polyester or copolyester with a crystallite melting point of from 100C to 220C and with a reduced viscosity of from 0.4 dl/g to 1.6 dl/g.

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In particular the present invention provides a blowing agent concentrate hased on a chemical blowing agent and a thermoplastic plastics material as support, wherein the support is a satura-ted polyester and/or copolyester with a crystallite melting point of from 100C -to 220C and wi-th a reduced viscosity of from 0.4 dl/g to 1.6 dl/g and wherein said blowing agent concentrate has a blowing agent content of from

2 to 50% by weigh-t.
According to another aspect of the present invention, there is provided in a method for producing a s-tructured foam moulding by foaming polyalkylene terephthalate combined with a blowing-gas-releasing component, the improvement wherein .~said blowing-gas-releasing component is a blowing concentrate as defined above.
.The polyesters and copolyesters used as support for the : /

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f ~ f blowing agent according to the invention have glass transition temperatures of from -20 to ~50~C and preferably from -10 to +20C.
The glass transition temperatures are measured in accordance with DIN 53~45 as the maximum logarithmic decrement of mechanical damping according to tor~ional vibration analysis. The logarithmic decrement of mechanical damping amounts to between 0.2 and 1.3.
The crystallite melting points are measured as melting maximum by the differential thermoanalysis method. A Perkin-Elmer Differ-cntial Scanning Calorimether (DSC-l), was used for differential thermoanalysis, a heating rate of 16C per minute being applied~

The reduced viscosity ~ red is measured on a 1 % by weight solution in a mixture of 60 parts by weight of ph~enol and 40 parts by weight of 1,1,2,2-tetrachloroethane at a temperature of 25C and is calculated in accordance with the following formula :

tL - 1 _ ~

red = _ Lr _ dl/g where tL is the flowout time of the solution, t~m is the flowout time of the solvent and c is the concentration in g/100 ml.
According to the invention, it is preferred to used polyesters or copolyesters with crystallite melting points in the range from 160 to 200C. The preferred reduced viscosity is ; from 0.7 dl/g to 1~0 dl/g.
The entire acid component of the polyesters and co-polyesters used as support for the blowing agent in accordance with the invention, or more than ~0 mole % thereof,~y be derived from terephthalic acid or its polyester-forming derivatives. One or more other aromatic and/or saturated aliphatic dicarboxylic acids containing from 2 to 12 carbon atoms between the functional groups or their polyester-forming derivatives may be used as co-acids _ ~ _ .J ~ ~

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to make up the balance to 100 mole %. The diol component of the polyesters and copolyesters may ke derived fr~m one or more saturated aliphatic glycols containing from 2 to 12 carbon atoms.
Suitable co-acidq are, for example, sebacic acid, azelaic acid, succinic acid, glutaric acid, adipic acid, isophthalic acid or cyclohexane dicarboxylic acid or their polyester-forming derivatives. In cases where the dicarboxylic acid component of the copolyesters consists solely of terephthalic acid or its polyester-forming derivatives, at least two diols are used for the diol component. q'he co-acids, together with terephthalic acid, are preferably used in quantities of from 10 to 40 mole %.
Preferred co-acids are isophthalic acid and/or adipic acid and, optionally, their dial]cyl esters. They may optionally be replaced either completely or in part by at least one aliphatic saturated dicarboxylic acid or a polyester-forming derivative thereof, such as for example sebacic acid, azelaic acid, succinic acid, glutaric acid or cyclohexane dicarboxylic acid or the like, preferably a~elaic or sebacic acid or mixtures thereof.
Polyester-forming derivatives of the dicarboxylic acids are, primarily, the monoalkyl esters or dialkyl esters, especially the dimethyl esters.
Suitable diols and co-diols are, for example, ethylene glycol, 1,2~propane diol, 1,3-propane diol, 1,3-butane diol, 1,4-butane diol, 1,5-pentane diol, neopentyl glycol, 1-6-hexane diol, 1,8-octane diol, cyclohexane dimethanol and the like or mixtures of the individual components. According to the invention, 1,4-butane diol ~r 1,6-hexane diol is preferably u~ed as diol or co-diol for the copolyesters.

In one preferredembodiment of the copolyesters used as support, their acid component is derived from 90 to 50 moles %

of terephthalic acid or its polyester-forming derivatives, preferably its dialkyl esters, more especially its dimethyl ester, :' """

and from 10 to 50 mole % of one or more of the above-mentioned co-acids. The diol component of this preferred copolyester is 1,4-butane diol. Up to 10 mole % of the 1,4-butane diol may optionally be replaced by another diol or by several other diols containing up to 12 carbon atoms. Suitable co-diols are, for example, ethylene glycol or 1,2-propane diol or 1,3-propane diol or 1,3-butane diol or 1,5-pentane diol or neo-pentyl glycol or 1,6-hexane diol or 1,8-octane diol or cyclo-hexane dimethanol or mi~tures of the individual components.
; 10 Ethylene glycol or 1,6-hexane diol is preferably used as co-diol for butane diol, In the case of 1,6-hexane diol, up to 50~ of the 1,4-butane diol can be replaced by 1,6-hexane diol.
In cases where 1,4-butane diol is used as the sole diol ! component, copolyesters of which the acid component is derived from 85 to 60 mole ~ of terephthalic acld or its polyester-forming derivatives and from 15 to 40 mole % of isophthalic acid or its polyester-forming derivatives have proved to be particularly suitable. The isophthalic acid may be completely or partly replaced by an aliphatic dicar-boxylic acid, such as a~elaic acid and/or adipic acid and/or :~ sebacic acid, preferably adipic acid.
Other copolyeste~s suitable for use in accordance with the invention are copolyesters of which the acld component is derived from 80 to 70 mole % of terephthalic acid or its poly-ester-forming derivati~es and from 20 to 30 mole % of one or more other aromatic co-acids and/or one or more aliphatic ~; saturated co-acids containing from 2 to 12 carbon atoms ~; between the two functional yroups, and of which the diol component is derived from ethylene glycol, up to 10 mole %
of the ethylene glycol optionally being replaced by one or ,~ more diols containing from 3 ~o 12 carbon atoms.
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A support which has proved to be particularly suitable for the purposes of the in~ention is a copolyester in which from ~ /

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-65 to 75 mole % of the acld c~mponent is derived from terephthalic acid or its dimethyl ester and 35 to 25 mole % from adipic acid, and of which the diol component i~ derived from 1,4-butane diol.
Another copolyester especially well suited for the purpose of the invention is one in which 85 mole % of the acid component i9 derived from terephthalic acid or it~ dimethyl ester and 15 mole % from isophthalic acid or it~ dimethyl e~ter, and in which 50 mole % of the diol component i~ derived from 1,4-butane diol and 50 mole % ~rom 1,6-hexane diol.
In addition to copolyesters, it is also possible in accordance with the invention to use ~pecial polyesters providing they have a crystallite melting point of 100 ~o 2209C and a recuded viscosity of 0.4 dl/g to 1.6 dl/g. One suitable polyester is, for example, a polyester of which the acid component is derived from terephthalic acid or it~ polye~ter forming derivative, preferably dimethyl ester, and of which the diol component is derived from 1,4-hexane diol.
The production of the polyesters and copolyesters used ~ as cupport for the blowing agents in accordance with the invention ,, f 20 does not form any part of the present invention. They may be produced by rnethod~ known per se, for example by methods similar to those used for the production of polyethylene terephthalate.
For example, dimethyl terephthalate a~d dimethyl i50-phthalata are transesterified in the above-mentioned molar ratio ~, with excess 1,4-butane diol in the presence of a transesterifica-tion catalyst, for example tetra-n-butyl titanate and, optionally, zinc acetate dihydrate, in a pre~ure vesqel equipped with a stirrer. At an internal temperature of from about 150 to 220~C, the methanol i~ distilled off, preferably under normal pressure, after which the co-acid, for example sebacic acid, ic added. To esterify the ~ebacic acid, the temperature is increased to 250C
and the reaction mixture left ~tanding at that temperature for - 7 _ "

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about 2 hours. The completeness of e~terification is monitored by measuring the quantity of water of reaction which distills over.
Following the introduction of triphenyl phosphite with a little diol (in order t~o inhibit the transe~terification catalyst, the pressure vessel is evacuated and the internal temperature increased to 260C. The internal temperature i9 then increased to 270C
over a period of 1 hour and, at the ~ame time, the pressure reduced to less than 1 Torr. After stirring for 3 to 4 hours under these conditions, the vacuum is broken by the introduction in nitrogen, the copolyester obtained is discharged through the bottom valve and granulated.
The blowing agent concentrates according to the inven-tion are produced by thoroughly mixing the granular or powder-form saturated polyester or copolyester used as support with the chemical blowing agent, for example a powder-form chemical blowing agent, and optionally other additives, inltially at room tempera-ture. This mixture is then homogenised in an extruder or kneader by way of the melt phase of the polyester or copolyester and dis-charged through a nozæle. The polyester of copolyester used as support and the blowing agent may also be separately introduced in the necessary ratio into the machine used for homogenisation by means of suitable metering system~. The blowing agent may even be added to the support already present in the form of a melt, Size reduction of the solidified concentrate mixture of a grain ~ize suitable for further processing i9 carried out in known manner, for example immediately after di~charge from the noz~la after adequate cooling by means of granulator~ or mills or even at a later stage. Basically, the grain size and shape of the blowing agent concentrate granulate may be selected as required, although i~ is best, in order to avoid disintegration phenomena, to adapt the shape and siæe of the blowing agent concentrate to those of the polyalkylene terephthalate to be foamed.

The blowing agent concentrates according to the inven-tion advantageously have a blowing agent content of from 2 to 5u % by weight, preferably from 2 to 3~ % by weight and morè
especially from 5 to 2u % by weight.
~ ccording to the invention, chemical blowing agents are used for the blowing agent. Chemical blowing agents are characterized by their spontaneou~ decomposition above a tempera-ture characteristic of the particular compound, the so-called activation temperature. The activation temperature i~ governed by ~ lû the chemical structure of the ~lowing agent used. The choice of the flowing agent for the blowing agent concentrate according to the invention i~ primarily determined by the meltlng or processing temperature of the support, i.e. the blowing agents should not be activated during production of the concentrate. In addition, the blowing agent must be compatible both with the support and also with the plastics material to be foamed and should have adequate activity~
Suitable blowing agent~ for foaming thermoplastic plastics are, Eor example, azo compounds, hydrazines semi-carbazides triazoles, tetrazoles and N-tritroso compounds containing decompo~able groups (cf. H. HurniX, "Treibmittel fur Kunststoffschaume", (Blowing Agents for Foam Plastics), Kunststoffe 62, 1972, No. 10, pages 687 - 689).
;~ The blowing agent concentrates according to the inven~ion are particularly suitable for use as blowing-gas-releasing compo-nent in the production of structured foam mouldings of high molecular weight polyalkylene terephthalates such as, for example, polyethylene terephthalate, poly-~1,3-propylene)-terephthalate and, in particular, poly-~1,4-butylene)-texephthalate. Polyalkyl-30 ene terephthalates with reduced viscosities of from about 0~7 to 2.3 are generally u~ed for the productio~ of structured foam mouldings with good mechanical, physical and thermal properties.

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In cases where the mechanical properties have to satisfy ~tringent requirement~, polytetramethylene terephthalate i~ generally processed with reduced visco~ities of from 0.7 to 2.0, preferably from 2.8 to 1.6; to form structured foam mouldings. Where the mechanical properties have to satisfy less stringent requirement~, it i9 possible to use polyalkylene terephthalates with lower reduced viscosities, for example from 0.4 to 0.7.
The production of the high molecular weight linear ~ polyalkylene-terephthalateq to be foamed does not form any i 10 part of the present invention. They may be produced by known methods, for example as described above. Conden~ation in the melt, for example in the production of high molecular weight polytetramethylene terephthalates, is optionally interrupted at reduced viscosities of from 0O9 to 1.0 and the conden~ation reaction continued inthe solid phase ~cf. for example DT-OS
- No. 2,315,272).
Polyalkylene terephthalates for which the blowing agent concentrates according to the invention are preferably used may be~foamed with basically any chemical ~ubstance ~hich is suitable for foaming thermopla~tic plastics providing it is not activated during production of the concentrate and providing it is compatibls !-both with the polyalkylene terephthalate~ to be foamed and with the blowing agent support used.

~ Blowing agents suitable for the purposes of the inven-; tion are blowing agents with decompo~ition temperatures in the ., ~- range from 120 to 260C and preferably in the range from 200 to - 260C, the blowing agent~upport combination being co-ordinated ~- in such a way that the blowing agent i~ not activated during production of the concentrate. Examples of blowing agents with decomposition temperature~ of from 120 to 260C are trihydrotri-azine, p-tolylene sulphonyl semicarba~ide, 4,4'-oxy-bis-(benzene sulphonyl semicarbazide), barium azodicarboxylate, various tetrazoles and hydrazine derivative3, modified azodicarbonamide, benzoxazine, for instance, i~atic acid anhydride, carboxylic acid-carbonic acid ester anhydride, for instance, isophthalic acid-carbonic acid ethyl e~ter anhydride or bi-benzoic acid-bi-carbonic acid 1,4-butanediol ester anhydride, mixtures of carboxylic acids and carbonate~, for instance, a mixture of citric acid and sodium carbonate.
The choice of the chemical blowing agent is also determined to a certain extent by the foaming proce3~ uqed, ~o hat it i~ best to use foaming agents which are adapted to the particular foaming process applied~
For example, for foaming the polyalkylene terephthalateq using the blowing agent concentrates according to the invention in conventional injection moulding maçhines, for example hydraulic screw injection extruders, which are also used for - lOa -o~

producing compact injection mouldinys, it is preferred to use blowing ayents of which tlle activation or decomposition tempera-ture is below, preferahly slightly below, the processing tempera-ture required for polyalkylene terephthalate moulding composi-tions. In the context of the invention, the processing tempera-ture is the melt temperature obtained where a temperature program specially adapted to the combination of polyalkylene terephthalate and blowing agent conventrate to be foamed is applied. For example, the foaming of polytetramethylene terephthalate (melting point 225C) is carried out according to a temperature program in which the temperature rises from the feed zone to the nozzle, for example zone 1 (~eed zone): 230C, zone 2 : 250C, zone 3 (barrel exit): 270C, nozzle 2~0C. ~n average melt temperature of approximately 2~0C is adjusted with this temperature program.
In this case, it i~ preferred to use a blowing agent activation temperatures in the range from more than 230 to 250C
and preferably in the range from 240 to 250C.
~ owever, the same blowing agents may also be used with equal effect in the foaming of other polyalkylene terephthalates, ~- 20 for example in the foaming of polyethylene terephthalate (melting point 260C), which is best processed according to a temperature program with which a melt temperature of approximately 280C
is adjusted. (For example zone 1 : 250C, zone 2: 270C, zone 3:
285~C, nozzle: 295C).
The blowing agents preferably used in the foaming of high molecular weight polyethylene terephthalate and, in particular, polytetramethylene terephthalate are 5-phenyl tetrazole and 5-phthalimido tetrazole.

However, it is also possible in principle to use other blowing agents providing they satisfy the above-mentioned requirements both in regard to compatibility and also in regard to non-activation during production of the concentrate, and at ~,-the same time also guarantee satisfactory foam formation by the various methods used for the production of structured foam mouldings The blowing agent concentrates according to the invention may be used as blowing-gas-releasing component in all processes for producing structured foam mouldings from polyalkylene terephthalate moulding compositions. They may be produced both in the injection moulding machines and extruders used for the production of compact mouldings and also in special-purpose machines specifically adapted for processing thermoplasts containing blowing agents. Processing by injection moulding and extrusion and also the in-mould foaming of thermoplasts containing blowing agents is described in detail in the literature (cf. Integral-schaumstoffe (Integral Foams), ; Piechota/Rohr, Carl Hanser-Verlag 1975, pages 91, 1423.
The blowing agent concentrates according to the invention are preferably used in the production of structured foam mouldings by the PSG process (Thermoplast-Schaumspritz-Gie~en = Thermoplastic Foam Injection Moulding) which is described on pages 94 to 125 of the abo~e-mentioned literature reference. They may be used as blowing-gas-releasiny component both in the production of mouldings pf high specific gravity and in the production of mouldings of low specific gravity.
~ In the context of the invention, structured foam mouldings `~ are foam mouldings with a substantially compact outer skin and a foamed core. Structured foam mouldings such as these are formed by initially keeping the ga~es, generally nitrogen or C02,given off ., .
; when the decomposition temperature of the chemical blowing agent , .
is exceeded in ~olution under pre~ure in the plastics melt an( subRequently expanding the pla~tics melt and pressing it against the walls of the mould under the effect of the expansion pres3ure during the moulding cycle.

In the production of structured foam mouldings from polyalkylene terephthalate moulding compositions using the blowing ,~ ,

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agent concentrates according to the invention, the polyalkylene terephthalate granulate and the blowing agent concentrate granulate are mixed together in suitable mixers. The quantitative ratio is governed by the~quantity of blowing agent required for the moulding to be produced and by the effectiveness of the blowlny agent used.
In general, the ~lowing agent concentrate is added in such a quantl-ty that the blowing agent content of the mixture as a whole amounts to between 0.05 and 10 % by weight, preferably between 0.1 and about 5.0 % by weight. Depending upon the concentration of the blowing agent in the concentrate, generally from 1 to 50 % by weight, prefer-: ably from 2 to 30 % by weight and, more especially, from 5 to 20 by weight of blowing agent concentrate is added to the plastics material to be foamed, based on the mixture as a whole. After mixing, the mixture i8 delivered to the storage vessel of the processing machine and processed into structured foam mouldings By means of the blowing agent concentr~tes according to .. the invention, it is possible to produce.structured foam mouldings of polyalkylene terephthalates, preferably polytetramethylene terephthalate, containing fillers and/or reinforcing ayents andJor flameproofing agents and, optionally, other additives such as, for example, light stabilisers, dyes, pigments, nucleating agents, forexample talcum, or pore regulators such as, for example, finely divided metal powders Reingorcing agents are, for example, glass powders, glass balls, glass fibres, asbestos fibres and the like which may optionally be treated with suitable sizes or adhesion promoters (cf. for example DT OS No. 2,426,656~.
Preerred reinforcing materials are glass fibres which - are best used in such a quantity that the foamed moulding has a glass fibre content of from 2 to 60 % by weight, preferab].y from 10 to 50 % by weight.`
Surprisingly, the addition of glass fibres provides the foamed mouldings with a particularly uniform, fine-cell pore structure and with a uniform, optically satisfactory surface~
In other advantageous embodiment of the invention, therefore, the blowing agent concentrates according to the invention are used as blowing-gas-releasing component in the production of glass-fibre-reinforced, optionally flameproofed structured foam mouldings of polyalkylene terephthalate, especially polytetramethylene terephthalates.
The above-mentioned additives, particularly the nucleating agents, pore regulators, dyes, pigments, light stabilisers and the liXe may optionally he present in the necessary quantity in the blowing agent concentrate used in accordance with the invention or in the polyalkylene terephthalate to be foamed.
Basically, however, the additives may also be mixed with the blowing agent concentrate and the polyalkylene terephtha-~- late to be foamed in the form o~ dye concentrates, filler or reinforcing agent concentrates, stabiliser concentrates, flame-`` proofing agent concentrates, nucleating agent and pore regulabor concentrates and the like in ~he necessary quantitative ratio, and the resulting granulate mixture introduced into the foaming machine. Suitable supports for the additives are thermoplasts of the type which are compatible both with the support for the flowing agent concentrate and also with the polyalkylene tereph-thalate to be foamed. The support used for the additives is ~ preferably the same support which is also used for the blowing ; agent concentrate.
;~ Suitable flameproofing agen-t~ are halogen-containing, especially bromine-containing compounds, of which the flame-` proofing effect may optionaLly be improved by additions of 3~ synergists, for example from the Fifth Group of the Periodic : ~ .
System, for example antimony trioxide.

It is preferred to use flameproofing agents with melting '''' points above the processing temperature of the thermoplasts used as support for the flameproofing agent concentrate. ~xamples of flameproofing agents of this type are octabromodiphenyl, decabromo-diphenyl, decab~omodiphenyl ether, crosslinked polytetrabromoxyly-lene glycol-bis-acrylate and the like.
Flameproofing agent concentrates containing more than 50 % by weight and preEerably from 70 to 90 % by weight of flame-~roofing agent are preferred.
The flameproofing agent concentrates may be produced in the same way as the blowing agent concentrates. For example, a mixture of 29 parts by weight of antimony trioxide, 58 parts by weight of octabromodiphenyl and 13 parts by weight of a suitable thermoplast, produced for example from 30 parts by weight of adipic acid, 70 parts by weight of terephthalic acid and 1,4-butane diol, is homogenised in a twin-screw extruder with a compression zone at its front end. A solid strand issues from the extrusion die and, immediately on leaving the die, may be chopped ; as "head granulate" into granulate particles of the required slze .
The flameproofing concentrates are best added to the polyalkylene terephthalate to be foamed or to the mixture to be foamed in such a quantity that the total mixture contains from about 4 to 10 % by weight of halogen, preferably BrO For example, 17 parts by weight of the above-mentioned flameproofing concentrate based on octabromodiphenyl, antimony trioxide and copolyester are mixed with 83 parts by weight of PTMT/blowing agent concentrate mlxture (ratio by weight 19:1, blowing agcnt content oE the concentrate 10 % by weight) and the resulting mixture subsequently foamed. The same procedure may be adopted for the production of glas~-fibre-reinforced flameproofed structured foam mouldings.
The processing of polyalkylene terephthalates into structured foam mouldings is considerably simplified and improved by using the blowing agent concentrates according to the invention.
The disadvantages involved in directly adding powder-form blowing agents are avoided, as are the disadvantages normally encountered during the processing of blowing-agent-containing polyallcylene terephthalate granulate. The blowiny agent concentrates according to the invention have distinct advantages over conventional blowing agent concentrates. By virtue of their compatibility with the polyalkylene terephthalate moulding compositions to be foamed, it is possible to produce mouldings with good physical, mechanical and thermal properties.
The polyesters and copolyesters used as supports in ~ accordance with the invention represent supports which are `~ particularly suitable for foaming polyalkylene terephthalate ;- moulding compositions in particular. By virtue of the favourable 10w properties of the mixture to be foamed, it is possible to produce compIicated mouldings with optically satisfactory and smooth surfaces.
One particular advantage is that there is har~ly any increase in the cycle time required for moulding the polyalkylene terephthalate moulding com~ositions into structured foam mouldings, especially in hydraulic screw injection extruders, as in the TSG
- process for example. Another advantage is that the molten support is thermally stable at the high processing temperatures re~uired - -for high molecular weight linear polyalkylene terephthalates.
In this way, the polyalkylene terephthalate moulding compositions are prevented from being discoloured through thermal decomposition of the support~
The invention will now be illustrated with reference to the following non restrictive examples.
Comparison Example 1 Cylindrical polytetramethylene terephthalate strand granulate, which was reinforced with 30 % by weight of glass 3 ~J

fibres and which had a specific gravity of 1.52 g/cc and an apparent density of 660 g/l for a reduced viscosity of the polymer of 1.0 dl/g, was mixed with 0.5 % by weight of powder-form 5-phenyl tetrazo~le as chemical blowing agent in a slowly rotating Papenmeier mixer. t~ considerable amount of dust was given off during the initial phase oE the mixing proces.s. The time required .:;
` to obtain uniform distribution of the blowing agent powder was 5 minutes. This mixture was discharged into a steel plate storage $~ vessel and introduced into the feed hopper of a compact inject~on 10 moulding machine. After emptying, the walls of the mixer and storage vessel were covered by thick residues of blowing agent ' powder.
~ The injection moulding machine used was a hydraulic i` screw machine (Krauss-Maffei type 150-600) with a screw diameter D of 40 mm and a screw length of 20 D~ Structured foam panels measuring 210 x 140 x 10 mm were injected at barrel temperatures (feed \ die) of 230, 250, 270, 280C, giving a melt temperature of 260C, and at a mould temperature of 50C. The cooling time up to mould release was 150 seconds. After processing, the feed 20 hopper of the injection moulding machine was covered by thick deposits of blowing agent. Disintegration phenomena occurred to i~ an extent in the feed hopper during processing, as reflected in separation of the blowing agent from the polytet:ramethylene terephthalate granulate. The panels have a specific gravity of 1.05 g/cc. The mechanical properties of Comparison Examples to 3 and Example 1 are set out in Table 2~ The quality features are as~e3~ed in Tal~le 1.

Comparison Example 2 A mixture of 69.5 % by weight of non-reinforced poly-30 tetramethylene terephthalate granulate, 30 % by weight of 6 mm short glass fibres and 0.5 % by weight of 5-phenyl tetrazole was digested and homogenised in the melt phase in a single screw ' - 17 -::
is extruder (Reifenhauser type R 30) with a screw diameter D of 30 mm and a screw len~th of 20 D, extruded in strand form through a mm round die and sizereduced into cylindrical granulate. The extruder barrel temperatures were in the range from 220C to 2~0C and the rotational speed of the screw amounted to 90 rpm.
The granulate had a~ apparent density of ~80 g/l and the PTMT had a reduced vlscosity of 1.0 dl/g. By comparison with the granulate of Comparison Example 1, the apparent density was reduced hy 180 g/l. This difference was attributable to partial decorn~osition of the blowing agent during production of the granulate which could not be avoided despite the relatively low barrel temperatures.
When the barrel was adjusted by way of experiment to lower tempera-ture the melt cooled below the meltiny point of 225C and solidifi-ed so that extrusion was impossible. ~s a result of this prelimi-nary decomposition, the effective ~uantity of blowing agent present in the granulate was reduced, with the result -that the effectiveness of the blowing agent was limited during the foaming process. The granulate was injected to form 10 mm thick structur-ed foam panels under the same conditions as in Comparison Example 1. The panels have a specific gravity of 1.1 g/cc~
Com~arison Example 3 The same glass-fibre-reinforced polytetramethylene terephthalate granulate as described in Comparison Example 1 was mixed with a standard granular blowing agent concentrate based on polystyrene, which contains 20 % by weight of a chemical blowing agent, in a ratio of 39:1 in a 510wly rotating mixer, so that the final concentration of the blowing agent in the mixture as whole amounted to 0.5 % by weight. The mixture was injection moulded into 10 mm thick structured foam panels with a specific gravity of 1.0 g/cc in the same way as described in Comparison ~3xamples 1 and 2. In this case, the cooling time had to be increased to 200 seconds because, with shorter cooling times, the panels show inadequate dimensional stability together with signs of post-expansion. During processing, an unpléasant odour was given off both from the feed hopper and from the die of the injection moulding machine. The panels had a rough, unevenly coloured and heavily streaked surface. These phenomena are indicative of incompatibility of -the concentrate support with polytetramethylene terephthalate.
EX~M~LE 1 granular crystalline copolyester based on 70 mole 'i' of terephthalic acid, 30 mole % of adipic acid and 1,4~butane diol, with a reduced viscosity of 0.~1 dl/g, a melting ma~imum as determined by differential thermoanalysis (DTA) of 173C and a maximum logarithmic damping decrement of 0~55 at a glass transition temperature Tgdyn of -1C (as determined by the torsional vibration test according to DIN 53445), was processed in the pres-- ~ence of lO % by weight of powderform 5-phenyl tetrazole in the single-screw e~truder described in Comparison Rxample 22 to form the blowing agent concentrate according to the invention. The material was fed into the feed hopper of the extruder by introduc-ing copolyester and blowing agent in a ratio of 90:10 by means of separate distributing belt weighing machines. These components were homogenised through the melt phase at a melt temperature of 195C and at a screw speed of 30 rpm, extruded in strandform through a 4 mm round die, cooled on an air-cooled conveyor belt and granulated in agranulator to form strand-form granulate.
The granulate had an apparent density of 600 g/l. The initial apparent den~ity of the copolyester granulate used as concentrate su~)port was al~o 600 g/1. The concentrate granulate did not undergo any prefoaming through partial decom~osition of the blowing agent because the melt temperature could be kept far below the melting and decomposition temperature of the blowing agent used during production of the concentrate. The blowing 3~3 agent concentrate produced in this way was mixed with the glas3-fibre-reinforced polytetramethylene terephthalate granulate of Comparison Examples 1 and 3 in a ratio by weight of 19:1 (final concentration of~the blowin~ agent in the mixture as a whole 0.5 %
by wei~ht) in a .slowly rotating mixer (see Comparison Example 1).
~ homogeneous mixture was formed after a mixing time of only 1.5 minutes. No residues were formed in the mixer.
This mixture was injection-moulded into 10 mm thic]~
structuréd foam panels under the same conditions and in the same 10 injection moulding machine as in Comparison Exarnples 1, to 3, and the cooling time of 150 seconds could be maintained. The panels had a specific gravity of 1.0 g/cc.
In contrast to the panels of Comparison Examples 1 to 3, the panels have a particularLy smooth, uniform ~urface, there was virtually no evidence of any structures, the natural colour was unchanged and corresponded in colour to the panels of Comparison Examples 1 and 2.
For an identica] starting quantity of 0.5 % by weight of the same blowing agent as in Comparison Examples 1 and 2, the blowing agent concentrate according to the invention was found to be considerably more effective. Whereas a minimum specific gravity of 0.8 g/cc is obtained with this concentrate in the ; production of the panels in the compact injection mouldlng machine used (the minimum specific gravlty is obtained when the mould is still just filled with the minimal possible quantity of melt), the mould could not be ade~uately filled with the melts according to Com~arison Examples 1 and 2 with the same machine setting and material input. The minirnum density which could be obtained amounted to 0.95 g/cc with the melts according to Comparison Example 1 and to 1.05 g/cc with the melts according to Comparison Exarnple 2. Due to the fixed bLowing agent content of the moulding composition of Comparison Example 2, it was not possible to obtain ,:

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lower densities by increasing the content of blowing agent.
In contrast to Comparison Exarnples 1 to 3, a part;cularly fine-cell uniform pore structure was obtained by using the blowing agent concentrate according to the invention. The nucleating effect already produced by the addition of glass fibres is thus effectively supported.
E,X~II'LE 2 A 19:1 mixture of glass-fibre-reinforced polytetramethylene terephthalate according to Comparison Example 1 and the copolyester blowing agent concentrate accordiny to Example 1 was prepared in a - standard cement mixer~ In contrast to the incorporation of powder-form blowing agents, the mixer could be left open during the mixing process so that the mixing process could be continuously monitored.
The mixing process was over after 2 minutes.
This mixture was processed in to panels with wall thicknesses of 6 to 10 mm in a thermoplastic foam injection mould-ing machine (so-called TSG machine) of the Structomat ST 6000-170 type manufactured by Schloemann-Siemag, with a quadruple panel die.
The screw diameter D of the plasticising unit was 80 mm and the screw diameter D of the plasticising unit was 80 mm and the screw length 20 D. The transfer plunger had a diameter of 130 mm for a stroke of 500 mm. The panels had a total weight of 1.5 kg for a specific gravity of 1.0 g/cc. The heating band temperatures along the screw barrel ~feed~ reversal~ were 200 - 260 - 260.C, the heating band temperature o~ the reversal collar was adjusted to 240C, the two control zones of the transfer cylinder had a control temperature of 240C. The die heating band had a tem~eratur og 250C~ This temperature program produced a melt temperature of ~, 255C. The speed of the screw during plasticisation was 50 rpm, the back pressure a,,pplied during plasticisation amounted to 30 kg/cm2. The injection pressure applied by the plunger of the ' transfer cylinder amounted to 185 kg/cm2, the injection time was "fi~ 9 3.5 seconds. The mould temperature was kept at 40C by means of a tempering device, and the cooling time was 120 seconds.
I)ust-free, odour-free and residue-free processing was possible with t~e blowiny agent concentrate according to the invention. The structured foam panels had a smooth uniform surface with the same natural colour as the moulding composition used.
By virtue of the effectiveness of the blowing agent concentrate according to the invention, it wa~ possible in this machine to obtain a-minimum moulding density of 0.75 g/cc, coupled with satisfactory filling of the mould, with an injection time of 1 second, corresponding to a reduction in density of about 51 %.

Non-reinforced polytetramethylene terephthalate granulate with a reduced viscosity of 1.3 dl~g and a specific gravity of 1.31 g/cc was mixed with the blowing agent concentrate of Example 1 in a ratio of 19:1~ Mixing was carried out in a ~- square tin plate canister which was turnbled and rotated by hand.
By virtue of the ready miscibility of the blowing agent concentrate, adequate mixing was obtained after only 20 turns. This mixture was processed into 10 mm thick structured foam panels under the same conditions and in the same compact injection moulding machine as described in Comparison Exam~le 1. The panels had a specific gravity of 0.85 g/cc, corresponding to a reduction in density of 35 %. The surfaces of the panels were smooth and uniform and ;~ there was no change in the natural colour of the granulate used.
' EX~PLE 4 ,,~
; Polytetramethylene terephthalate granulate which had been reinforced with 30 % by weight of glass fibres and which had a reduced viscosity of 1.5 dl/g was mixed with the blowing agent concentrate of Example 1 in the same way as in Example 3 and processed into 10 mm thick structured foam panels under the same conditions as in Comparison Example 1. Whereas in cases where the powder-form blowing agent according to Comparison ~ !

Example 1 was used it was only ~ossible to obtain ~anels with a rough unattractive surface on account of th~ poor fluidity of the melt attributable to i-ts high melt viscosity, the panels obtained in accordance with this Example had comparatively smooth surfaces.
EX~MPLE 5 Flameproofed polyethylene terephthalate granulate (flameproofing agent: 10 % by weight of crosslin]ced polytetra-bromoxylylene glycol-bis-acrylate, 4 % by weight of antimony trioxide-) which had heen reinforced with 33 % by weight of glass fibres was mixed with the blowing agent concentrate according to Example 1 in a ratiQ of 19:1 by the method described in Comparison Example 1. The resulting mixture had a specific gravity of 1.73 g/cc. It was injection-moulded into 10 mm thick structured foam ~-anels in the same way as in Com~arison Example 1~ The heating }~and temperatures (feed zone~ nozzle) were adjusted to 250 -270 - 285 - 295C. This temperature program gave a melt tempera-ture of 280C. The mould temperature was 120C and the cooling time 220 seconds. For a specific gravity of 1.04 g/cc, the reduction in density amounted to 40 %. The surfaces of the panels had only a slight structure.

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SUPPLEMENTAR~ DISCLOSURE

The following examples further illustrate blowing agentconcentrates in which the support is a saturated polyester and/or copolyester with a crys-tallite melting point of from 100C to <140C and, in particular, from 110 to 130C.
With such polyesters and/or copolyesters as supports, it is preferred to use blowing agents which begin to decompose at or below 170C. A product manufactured by the Boehringer company of Ingelheim under the trademark Hydrocerol-compound, and derivatives thereof, have proved to be a particularly suitable lQ blowing agent when using these copolyesters and/or polyesters as supports. The products in question are blowing agents based on hydrophobised mixtures of citric acid and sodium bicarbonate which, during thermal decomposition, primarily give off CO2 as the blowing gas.
The thermal decomposition of "Hydrocerol-Compound"
begins at 160C. Where products of this class are used as preferred blowing agents for polyalkylene terephthalates in conjunction with the above support in the form of a blowing agent concentrate, non-discoloured structured foam mouldings are 2~ formed with a uniform, fine-cell pore structure, even for low specific gravities.
The wide interval which is formed where blowing agents having decomposition temperatures below 170C are us~d between the beginning of decomposition of the blowing agents and the minimum melt temperature required for optimally processing the polyalkylene terephthalates is by no means critical because by virtue of the fact that the blowing agents are embedded in the concentrate support no decomposition occurs before the copoly-esters and/or polyesters have completely melted. The blowing 3Q agents are only activated during processing of the structured foam - when the process of delivery of the mixture of concentrate and pol~alkylene tereph-thalate to be foamed has advanced to such an extent in the processing machine that the material which, at this stage, has incipiently melted in -the feed zone of the machine prevents the blowing gas from escaping through the feed opening under the effect of its delivery back pressure. By contrast, in cases where the same blowing agents are directly used in the powder form in which they are usually supplied, considerable losses of blo~ing gas occur as a result of premature decomposition even in the feed zone of the processing machines, being reflected in a considerable reduction in the activity of the blowing agents.
Basically, however, it is possible to use the blowing agents described in the parent disclosure which begin to decompose at temperatures above 170 C.

CO~IPARISON EX~MPLE 4 . . _ . . .
A granular crystalline copolyester based on 70 mole %
of terephthalic acid, 30 mole % of adipic acid and 1,4-butane diol and having a reduced viscosity of 0.81 dl/g and a melting point of 183C was mixed in a tumble mixer with 10% of "Hydrocerol-Compound" as blowing agent. The initial apparent density of the copolyester was 600 g/l. In a single screw extruder of the Reifenhauser R 30 type having a screw diameter of ~0 mm and a screw length of 20 D, this mixture was homogenised via the melt phase at a melt temperature of 195C and at a screw speed of 30 rpm, extruded in strand form through around die, cooled on an air-cooled conveyor belt and granulated in a granulator to form strand-form granulate.
During production of the blowing agent concentrate, it could be seen that the mixture behaved very poorly in the feed zone of the extruder. This was due to the fact that the blowing agent was actually decomposed in the feed zone of the extruder and the blowing gas given off escaped through the feed opening.

The extruded strand emerged from the round die in highly expanded form. The uncontrolled decomposition of blowing agent gave rise to a highly pulsating discharge of the strand. The release of the blowing agent was reflected in a crackling noise at-the output end of the die. The apparent density of the blowing agent concentrate amounted to only 280 g/l. The product was unsuitable for further use as a blowing agent concentrate for -the production of polyalkylene terephthalate structured foam mouldings.

A granular crystalline copolyester based on 57.5 mole %
of terephthalic acid, 42.5 mole % of adipic acid and 1,4-butane diol and having a reduced viscosity of 0.93 dl/g and a melting point of 150C was premixed in a tumble mixer with 10% of - "Hydrocerol-Compound" as blowing agent. A temperature interval of 10C separated the melting point of the copolyester from the beginning of decomposition at the blowing agent. The copolyester had an initial apparent density of 630 g/l.
- In the single-screw extruder described in Comparison Example 4, the mixture was homogenised via the melt phase ~;~ ' ' at a melt temperature of 160 - 165C, extruded in strand form and 2~ granulated. The behaviour of the mixture in the feed zone of the extruder, although considerable better than in Comparison Example

4, was still not completely satisfactory. Externally the extruded ; strand was relatively smooth but was permeated to an extent by bubbles. The blowing agent concentrate had an apparent den'sity of 480 g/l. Although a considerable improvement over the blowing agent concentrate of Comparison Example 4 was obtained in this case, premature decomposition of the blowing agent was again reflected in the reduced apparent density. Accordingly, the interval of 10C between the melting point of the copoly-3Q ester and the beginning of decomposition of the blowing agent was inadequate.

Cylindrical polytetramethylene terephthalate strand - ~8 -~ f~

granulate which had been reinforced with 30~ by weight of glass fibres and which had a specific gravity of 1.52 g/cc and an apparent density of 660 g/l for a reduced viscosity of the polymer of l.0 dl/g, was mixed with 0.5% by weight of powder-form "Hydrocerol-Compound" as chemical blowing agent in a slowly rotating Papenmeier mixer. The time required to obtain uniform distribution oE the blowing agent powder was 5 minutes. This mixture was introduced into the feed hopper of a compact injection moulding machine.
The injection moulding machine used was a hydraulic screw extruder of the Krauss-Maffei 150-600 type having a screw diameter D of 40 mm and a screw length of 20 D. Structured foam panels measuring 210 x 140 x 10 mm were injected at barrel temperatures (feed--~ die) of 230, 250, 270, 280C, giving a melt temperature of 260C, and at a mould temperature of 50C.
Serious decomposition of the blowing agent occurred as early as in the feed zone of the injection moulding machine, being reflected in extremely poor behaviour of the mixture in the feed zone. The spécific gravity of the structured foam panels fluctuated very considerably for the same machine setting. It was not possible to obtain specific gravities below 1.3 g/cc on account of the heavy premature losses of blowing gas.

A granular crystalline copolyester based on 85 mole %
of terephthalic acid and 15 mole ~ of isophthalic acid and diol components (50 le % of 1,6-hexane diol and 50 mole %
of 1,4-butane diol) and having a reduced viscosity of 0.9 dl/g and a melting point of 110C was premixed in a tumble mixer with 10% of "Hydrocerol-Compound" as blowing agent. ~he copolyester had an initial apparent density of 720 g/l.
In the single screw extruder described in Comparison Example 4, this mixture was homogenised via the melt phase at a melt ., .

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temperature of 125C, extruded in strand form through a round die, cooled on an air-cooled conveyor belt and granulated in a granulator into strand-form granulate. The interval between the melting point of the copolyester and the beginning of decomposition of the blowing agent was 50C. The mixture behaved satisfactorily and above all uniformly in the feed zone of the e~truder. The extruded strand emerged from the die completely smoothly and free from pulsation. The apparent density of the blowing agent concen-~; trate produce~ in this way amounted to 725 g/l. From this it can be seen that the blowing agent was completely incorporated into `~ the support without any decomposition. It could be seen from the fracture surfaces of the granulate particles that the blowing agent was uniformly distributed in the support and was surrounded on all sides by the solidified melt of the support.

The glass fibre reinforced polytetramethylene strandgranulate of Comparison Example 6 was mixed with the blowing agent concentrate of Example 6 for 1.5 minutes in a concrete mixer in a ratio by weight of lg:l. The final concentration of the blowing agent in the mixture as a whole amounted to 0.5% by weight.
In the injection moulding machine and under the processing conditions described in Comparison Example 6, the mixture thus obtained was injection moulded into structured foam panels measuring 210 x 140 x 10 mm.
The granulate mixture behaved satisfactorily and uniformly during the feed phase ofthe injection moulding cycle.
There was no premature decomposition of blowing agent. Structured , foam panels having a specific gravity of 1.0 g/cc were produced ,~ for a cooling time of 150 seconds. In this test series, there were no density variations in the panels. The surfaces of the panels were smooth and uniform.

.

,:

,, ~' .

,, EX~MPLE 8 Non-reinforced polytetramethylene terephthalate granulate having a reduced viscosity of 1.3 dl/g and a specific gravity of 1.31 g/cc was mixed with the blowing agent concentrate of Example 6 in a ratio of 19:1. The mixer used was a square tin can of which the contents were tumble~mixed by hand. By virtue of -the ready miscibility of the blowing agent concentrate, adequate admixture was obtained after only 20 turns. In the compact injection moulding machine described in Comparison Example 6, the mixture thus obtained was processed under the same conditions to form 10 mm thick structured foam panels.
The panels have a specific gravity of 0.85 g/cc, corresponding to a reduction in density of 35%.
The surfaces of the panels were smooth and uniform and there was no change in the natural colour of the granulate used.
Despite the low density, the cell structure was fine and uniform.

Claims (31)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A blowing agent concentrate based on a chemical blowing agent and a thermoplastic plastics material as support, wherein the support is a saturated polyester and/or copolyester with a crystallite melting point of from 100°C to 220°C and with a reduced viscosity of from 0.4 dl/g to 1.6 dl/g and wherein said blowing agent concentrate has a blowing agent content of from 2 to 50% by weight.

2. A blowing agent concentrate as claimed in Claim 1, wherein the crystallite melting point is of from 160° to 220°C.

3. A blowing agent concentrate as claimed in Claims 1 or 2, wherein the reduced viscosity is of from 0.7 dl/g to 1.0 dl/g.

4. A blowing agent concentrate as claimed in Claim 1, wherein either the entire acid component of said polyester and/or copolyester is derived from terephthalic acid or its polyester forming derivatives or at least 50 mole % of the acid component of said polyester and/or copolyester is derived from terephthalic acid or its polyester forming derivatives and one or more other aromatic and/or saturated aliphatic dicarboxylic acids having 2 to 12 carbon atoms between the functional groups or their polyester forming derivatives are used as co-acids to make up the balance to 100 mole %,whilst their diol component is derived from one or more aliphatic glycols having 2 to 12 carbon atoms.

5. A blowing agent concentrate as claimed in Claim 4, wherein the diol component of said polyester and/or copolyester is derived from ethylene glycol, 1,2-propane diol, 1,3-propane diol, 1,3-butane diol, 1,4-butane diol, 1,5-pentane diol, neopentyl-glycol, 1,6-hexane diol, 1,8-octane diol,cylohexane dimethanol, or mixtures thereof.

6. A blowing agent concentrate as claimed in Claim 4, wherein the co-acid of said copolyester is derived from isophthalic acid, sebacic acid, azelaic acid, succinic acid, glutaric acid, adipic acid, or cyclohexane dicarboxylic acid, their polyester-forming derivatives,or mixtures thereof.

7. A blowing agent concentrate as claimed in Claim 4, wherein from 90 to 50 mole % of the acid component of said copolyester is derived from terephthalic acid or its polyester-forming derivatives and 10 to 50 mole % from one or more co-acids.

8. A blowing agent concentrate as claimed in Claim 7, wherein the diol component of said copolyester is derived from 1,4-butane diol.

9. A blowing agent concentrate as claimed in Claim 8, wherein up to 10 mole % of the 1,4 butane diol is replaced by one or more other diols containing from 2 to 12 carbon atoms.

10.A blowing agent concentrate as claimed in Claim 7, wherein from 65 to 75 mole % of the acid component of said copolyester is derived from terephthalic acid or its polyester-forming derivatives, the co-acid component being derived from adipic acid and the diol component from 1,4-butane diol.

11.A blowing agent concentrate as claimed in Claim 7, wherein from 85 to 60 mole % of the acid component of said copolyester is derived from terephthalic acid or its polyester-forming derivatives and 15 to 40 mole % from isophthalic acid or its polyester-forming derivatives, whilst the diol component is derived from 1,4-butane diol.

12. A blowing agent concentrate as claimed in Claim 11, wherein the isophthalic acid is completely or partly replaced by azelaic, adipic or sebacic acid, or a mixture thereof.

13. A blowing agent concentrate as claimed in Claim 7, wherein from 80 to 70 mole % of the acid component of said copolyester is derived from terephthalic acid or its polyester-forming derivatives, 20 to 30 mole % from one or more other aromatic and/or one or more aliphatic saturated co-acids with 2 to 12 carbon atoms between the two carboxyl groups, whilst diol component is derived from ethylene glycol.

14. A blowing agent concentrate as claimed in Claim 13, wherein up to 10 mole % of the ethylene glycol is replaced by one or more diols containing from 3 to 12 carbon atoms.

15. A blowing agent concentrate as claimed in Claim 4, wherein the diol component of said polyester is derived from 1,6-hexane diol and the acid component from terephthalic acid.

16. A blowing agent concentrate as claimed in Claim 1, wherein the blowing agent content is of from 2 to 30 % by weight.

17. A blowing agent concentrate as claimed in Claim 16, wherein the blowing agent content is of from 5 to 20% by weight.

18. A blowing agent concentrate as claimed in Claim 1, wherein the blowing agent is 5-phenyl tetrazole or 5-phthalimi-dotetrazole.

19. A blowing agent concentrate as claimed in any one of Claims 1 and 18, wherein the blowing agent has a decomposi-tion temperature in the range of 120° to 260°C.

20. A blowing agent concentrate as claimed in any one of Claims 1 and 18, wherein the blowing agent has a decomposi-tion temperature in the range of 200° to 260°C.

21. In a method for producing a structured foam moulding by foaming polyalkylene terephthalate combined with a blowing-gas-releasing component, the improvement wherein said blowing-gas-releasing component is a blowing agent concentrate as claimed in Claim 1.

22. A method as claimed in Claim 21, wherein the poly-alkylene terephthalate is polytetramethylene terephthalate.

23. A method as claimed in Claim 22, wherein the blowing agent has a decomposition temperature in the range of 240° to 250° C.

24. A method as claimed in Claim 22, wherein the blowing agent is 5-phenyl tetrazole or 5-phthalimidotetrazole.

25. A method as claimed in Claim 21, wherein the poly-alkylene terephthalate moulding composition contains fillers, reinforcing agents or flame-proofing agents, or mixtures thereof.

26. A method as claimed in Claim 25, wherein the reinfor-cing agents are glass fibers.

27. A method as claimed in Claim 21, wherein the polyalkylene te-rephthalate is a high molecular weight polyalkylene terephthalate.

CLAIMS SUPPORTED BY THE SUPPLEMENTARY DISCLOSURE

28. A blowing agent concentrate as claimed in Claim 1, wherein the support is a saturated polyester and/or copolyester having a crystallite melting point of from 100 to 140°C.

29. A blowing agent concentrate as claimed in Claim 28, wherein the crystallite melting point is of from 110 to 130°C.

30. A blowing agent concentrate as claimed in Claims 28 or 29, wherein the blowing agent has a decomposition tempera-ture equal to or below 170°C.

31. A blowing agent concentrate as claimed in Claims 28 or 29, wherein the blowing agent is based on a hydrophobised mixture of citric acid and sodium bicarbonate which, during thermal decomposition, primarily gives off CO2 as blowing gas.