IE43644B1 - Flame retardant and self-extinguishing polyesters - Google Patents

Abstract

Flame-retardant and optionally self-extinguishing polyester compositions which contain, as flame-inhibiting additive, one or more oxalato complexes, which preferably have the formula I Me@Me@ [Z(C2O4)m] (I> in which Me is Li, Na, K, Rb, Cs or NH4, Me is one of the abovementioned cations or Ba, Z is one of the central atoms Mg, Ba, Zr, Fe, Co, Cu, Zn, Al, Sn, Cr and Sb, and k APPROX 0, 1, 2, 3 or 4, l APPROX 0 or 1 and m APPROX 2, 3 or 4. The polyester compositions are prepared by grinding preferably alkali metal/aluminium/oxalic acid complex salts in the polyhydric alcohol or alcohols participating in the polycondensation of the polyester, and by adding the resultant suspension of the complex salt directly to the polycondensation mixture.

Description

This invention relates to flame retardant and selfextinguishing polyesters; more particularly, it relates to such polyesters which are suitable for the production of fibres, sheeting, films, panels, injection-moulded articles and other shaped articles and also for the production of lacquers and coatings.

Several processes for the production of substantially, non-inflammable polyesters are know. ' Reviews of developments in this field are provided, for example, by the following works Hans Vogel, Flammfestmachen von Kunststoffen (Flameproofing of Plastics), Dr. Alfred Huthig Verlag Heidelberg, 1966; John W. Lyons, The Chemistry and Uses of Fire Retardants, WileyInterscience, New York . London . Toronto, 1970; Allec Williams, Flame Resistant Fabrics, Noyes Data Corporation, Park Ridge, New Jersey. London, 1974. Reference is also made to the Supplement Flammhemrnende Textilien (Flame-Resistant Textiles) from the Journal Textilveredlung, V01. 10, No. 5, May, 1975.

Known commercial flameproofing agents largely contain phosphorus, halogens and nitrogen. In many cases, antimony, for example in the form of Sb^^, is also added to the flameproofing agents to improve the flameproofing effect thereof, 1 so that, in general, the flameproofed polymers contain relatively high percentages of additives. The incorporation of flameproofing agents of this quality and in this quantity into polymers is accompanied by a number of unfavourable secondary effects. 3 6 5 4 - 3 When added in effective quantities, flameproofing agents, of the above type generally have an undesirable adverse effect upon the physical properties and service properties of the polyesters. Thus, they generally produce a considerable deterioration in breaking strength, elongation, initial modulus, elasticity and adversely affect the colour. In addition, despite the relatively large amount of flameproofing agents in the polymer, the flameproofing effect obtained is in many cases inadequate, especially in the case of filaments, so that only a few of the polyesters flameproofed in this way are also self-extinguishing.

In many cases, conventional flameproofing agents are also largely incompatible with skin and are often physiologically harmful substances. Thus, numerous bromine-containing compounds cause irritation of the skin. Moreover numerous phosphorus compounds, especially halogenated phosphoric acid esters, are highly toxic.

In addition, the conventional flameproofing agents which decompose during the burning process give off toxic and, in some cases, aggressive gases, such as hydrohalic acids, elemental halogen, halogen-oxygen compounds, oxides of nitrogen, nitrogen-hydrogen compounds and, in some cases, even hydrogen cyanide and dicyanogen. Moreover, numerous conventional flameproofing agents cause accelerated degradation of the polymer melt during the burning process, thereby producing an increased dripping rate of, in some cases, burning polymer melt.

In cases where flameproofing agents are used in filaments and fibres, most conventional products produce only a temporary flameproofing effect because they may be washed out by repeated washing or dry cleaning.

Conventional flameproofing agents, especially those containing bromine are relatively expensive. In addition, specialized techniques have to be developed for many of these flameproofing agents to enable them to be incorporated into the polymer, for example specific dosage through mixers, metering pumps, the chemical aggressiveness of bromine compounds often giving rise to corrosion problems.

It has now surprisingly been found that, in contrast bo the simple salts of oxalic acid, complex compounds of oxalic acid represent excellent flameproofing agents for polyesters. Hitherto, the use of oxalato complexes has only ever been . mentioned in individual cases solely in conjunction with the flameproofing of natural and synthetic polyamides.

In a process described in German Offenlegungsschrift No. 1,941,189 for the flameproofing of filler-containing polyamide moulding compositions or block graft polymers, mixtures of heavily brominated polyethers and antimony trioxide or antimonyl compounds are used as flameproofing agents. Antimony compounds are usually used as synergistic additives to halogen compounds, the effectiveness being ascribed to the antimony rather than to the remainder of the molecule. In addition to antimony-(III) hydroxide, sodium antimonite,antimonyl chloride and antimony-potassium tartrate, complex antimony oxalates, such as NaSblC^O^z» are also mentioned as an example of an antimonyl compound, in this case, the oxalato complex represents only one of the possible antimony carriers. An independent flameproofing effect of the oxalic acid complexes, especially in the case of polyesters, is neither disclosed nor suggested in this Offenlegungsschrift.

A process for improving the flame resistance of natural and synthetic polyamide fibres using complex titanium compounds is known from German Offenlegungsschrift No. 2,152,196, 3 614 - 5 the complex being formed with an organic chelate-forming agent or with fluorine ions. In this case, too, the oxalato complex is mentioned as only one of the possible heavy metal carriers although citric acid and tartaric acid complexes are preferred. The flameproofing agent is generally applied to the textile material to be flameproofed from an aqueous solution. The process is said to be particularly suitable for wool and mixtures of wool and synthetic fibres, the flameproofing agent again being applied in the form of a treatment liquid. It is not surprising that this process is unsuitable for the flameproofing of completely synthetic fibres, especially hydrophobic polyesters. In the case of mixtures of wool and fully synthetic fibres, it is of course, only the wool component which is flameproofed. Accordingly, the use of oxalato complexes as flameproofing agents for polyesters is not suggested in this publication either.

The same also applies to the process described in German Auslegeschrift No. 2,212,718, according to which natural and synthetic polyamide fibres are said to be finished with anionic complexes of zirconium with an organic chelate former or fluoride ions from aqueous solutions at pH values of from 0.5 to 4. In this case, too, the oxalato complex is mentioned in addition to purely inorganic compounds as one of the possible carriers for zirconium; in this case, too, the process is unsuitable for fully synthetic fibres.

The present invention relates to the use of oxalato complexes as the sole flameproofing agents for polyesters.

Oxalato complexes are coordination compounds comprising one or more central atoms, one or more ammonium or metal ions and one or more oxalato ligands. 3 6 4 4 In the context of the present invention, oxalato complexes ars, in particular, complexes containing a complex anion of the type [ZtCjO^)^] —, Z representing one or more central atoms, n being the number of ligands and —e representing the negative charge of the complex anion. Oxalato complexes of this type are described in detail by Κ. V. Krishnamurty and G. M. Harris in Chemical Reviews, Vol. 61 (1961), pages 213 to 246. In general, the number of ligands is 1, 2, 3 or 4, the,charge of the complex anion is -1, -2, -3, ) -4 or -5 and the number of central atoms is 1, the number of ligands and the charge of the complex anion being determined by the co-ordination number and charge of the central atom.

In the context of the present invention, oxalato complexes containing complex anions of the type —e are not only compounds whose composition is exactly stoichiometric, but also compounds of the type in which the values for n and —e differ from integers in the upward or downward direction. This is the case, for example, when a small number of the oxalato ligands is replaced by other ligands. Compounds of this type may be formed by incorporating or exchanging foreign ligands in the complex anion during or after synthesis of the oxalato complexes. The same also applies accordingly to the central atom, in other words the present invention also covers oxalato complexes of the type whose cationic constituent is not strictly stoichiometric in composition. Accordingly, the value for the central atom may also differ from an integer in this case, too. This will be the case when some of the central atoms are replaced by other central ato ms having a different co-ordination number or a different valency. Such deviations from strict stoichiometry are encountered fairly frequently in complex chemistry and are well known to those skilled in the art.

The oxalato complexes used in accordance with the present invention also include mixed oxalato complexes which, instead of the stoichiometric quantity of a central atom, contain the corresponding quantity of different central atoms. It is, of course, also possible to use mixtures of different single or mixed oxalato complexes.

Central atoms of the oxalato complexes, especially in the preferred compounds containing a complex anion of the type [Z(c„O.) ] —, are the metals Mg, Ca, Sr, Ba, Zr, Hf, Ce, V, Cr, 4 n Mn, Fe, Co, Ni, Cu, Zn, Cd, B, Al, Ga, In, Sn, Pb and Sb. The cationic constituent of the oxalato complex preferably conΉ *f *i* *1* *i* Ί* tains at least one of the ions Li , Na , K , Rb , Cs or NH. or 2+ one of the above-mentioned ions and Ba Preferred oxalato complexes correspond to the following general formula: ' . II wherein Me represents Li, Na, K, Rb, Cs or NH4; Me (I) represents one of the ahovementioned cations or Ba,- Z represents one of the central atoms, Mg, Ba, Zr, Fe, co, Cu, Zn, Al, Sn, Cr and Sb; kxwQ, 1, 2, 3 or 4; or 1; and κι^2, 3 or 4.

(The symbolwmeaning approximately equal to is used here in order to make it clear once again that the values for k, JL and m may differ from integers; cf. also Example 1). Particularly preferred oxalato complexes are alkali-aluminium oxalato complexes corresponding to one of the following general formulae: Mej1 [A1(C2O4)3] or MeL [Al^O^] and the oxalato complexes - 8 KBa [A1(C2O4)3], Kg [Mg(C2O4)2], [FefCgOjg], Kg [ZnfCgO^], K2 [CU(C2O4)2], Ba [Mg(C204)2].

The above-mentioned oxalato complexes represent a new class of compounds which are particularly suitable for use as flameproofing agents for polyesters. In general, the cesium complexes are the most effective, followed by the rubidium, potassium and sodium complexes and, finally, by the lithium complexes having, comparatively speaking, the lowest activity. Mixed alkali metal/barium complexes and the barium/magnesium ) complex also show a very good flameproofing effect.

Complexes corresponding to general formula (1) above, wherein _1 represents 0 and Z represents Al, are complex lithium, sodium, potassium, rubidium, caseium, ammonium-aluminium dioxalato and aluminium-trioxalato salts with, co-ordinatively, a tetravalent or hexavalent aluminium atom. They are known and are readily obtained by precipitation from aqueous solutions of the components thereof, for example by reacting an aluminium sulphate solution with a lithium, sodium, potassium, rubidium, cesium or ammonium oxalate solution. So far as the processes used for the production of these complex salts and the properties thereof are concerned, reference is made to Gmelins Handbuch der Anorganischen Chemie, 8th Edition, Aluminium”, part B, Number 1, Verlag Chemie GmbH, Weinheim/ Bergstr. 1933. Another process which is suitable for producing the potassium-aluminium trioxalate salt, in which freshly precipitated aluminium hydroxide is treated with an aqueous solution of potassium hydrogen oxalate, is described in Inorganic Synthesis, Vol. I, McGraw-Hill Book Comp. Inc., New York and London 1935, page 36. Of the oxalato complexes having other central atoms, most of the compounds used in accordance with the present invention are also known and 43044 - 9 adequately described. They may be obtained by reacting a salt of the central atom with alkali metal oxalate. Suitable compounds of the central atom are, for example, sulphates, chlorides, hydroxides, acetates, carbonates and oxalates. Further information on the production of these complexes may be found in the following literature reference: D. P. Graddon. j. Inorg. and Nucl. chem. 1956, Vol. 3, pages 308—322.

D. P. Graddon, inorg. Syntheses, Vol. 1, page 36 K. V. Krishnamurty et al., Che Rev. 61 (1961) pages 213—246.

Oxalato complexes, whose production is not explicitly described in the cited publications, may be similarly produced (see also the following Examples). In this case too, the number of alkali metal and alkaline earth metal atoms, i.e. the value of k and .1 and the value of m is, of course, determined by the valency of the central atom. Accordingly, the present invention also covers the use of compounds whose composition is not strictly stoichiometric in the sense of formula (1) above, i.e. inter alia compounds of the type in which the values for k, 1. and m differ from integers in the upward or downward direction.

In the context of the present invention, the term polyesters includes both homopolyesters and copolyesters.

Examples of such polyesters which may be obtained from one or more of the acids identified below or the ester-forming derivatives thereof and one or more dihydric or higher polyhydric aliphatic, alicyclic, aromatic or araliphatic alcohols or a bisphenol, are: adipic acid, pimellic acid; suberic acid; azelate acid; sebacic acid; nonane diearboxylic acid; decane diearboxylic acid; undecane diearboxylic acid; terephthalic acid; isophthalic acid; alkyl-substituted or halogenated - 10 terephthalic and isophthalic acid; nitroterephthalic acid; 4,41-diphenyl ether dicarboxylic acid; 4,4'-diphenyl thioether dicarboxylic acid; 4,4'-diphenyl sulphone dicarboxylic acid; 4,4'-diphenyl alkylene dicarboxylic acid; naphthalene2, 6-dicarboxylic acid; cyclohexane-1,4-dicarboxylio acid and cyclohexane-1,3-dioarboxylic acid.

Typical diols and phenols suitable for the production of these homopolyesters and copolyesters are: ethylene glycol; diethylene glycol; 1,3-propane diol; 1,4-butane diol; 1,6) hexane diol; 1,8-octane diol; 1,10-decane diol; 1.2-propane diol; 2,2-dimethyl-l,3-propane diol; 2,2,4-trimethyl hexane diol; £-xylene diol; 1,4-cyclohexane diol; 1,4-cyclohexane dimethanol and bisphenol A. In the context of the present invention, polyesters are also the conventional resins based on unsaturated esters and the conventional products reinforced, for example, by glass fibres, asbestos, carbon and graphite fibres. The oxalato complexes are preferably used in the case of polyethylene terephthalate, polypropylene terephthalate and polybutylene terephthalate.

The flameproofing agents used according to the present invention are also suitable for the conventional polyester compositions. The compositions may be in the form of granulate, chips or strands, in the form of shaped articles, such as panels, sheeting, films and fibres, or in the form of finished textile products, such as yarns, knitted fabrics, non-wovens, cloths and carpets.

Little is known of the mechanism behind the oxalato complexes used as flameproofing agents in accordance with the present invention or of the principle behind the way in which they act. However, it is assumed that these compounds do not just intervene at one stage of the - 11 combustion process, i.e. as halogenated flameproofing agents, for example, retard the combustion process by intervening in the radical chain,instead the flameproofing effect according to the present invention is the result of several flameinhibiting individual processes at various stages of the com5 bustion process. The flameproofing agents used in accordance with the present invention belong to the group of substances which give off inert gases. They have the advantage that they give off up to four moles of carbon dioxide per mole of starting substance. The most important principles behind the way in which they act are presumably the following: dissipation of thermal energy from the melt by dissociation of the flameproofing agent and heating of the inert gas, displacement and dilution of the oxygen at the surface of the burning polymer melt by the evolution of carbon dioxide, formation of oxide and salt layers during the combustion process and accelerated transport of radical acceptors, for example alkali metal atoms, into the gas phase.

It is clear that there is a connection between the decomposition temperature and the effectiveness of the flame20 proofing agents according to the present invention, on the one hand, and the polymers to be flameproofed, on the other hand, which must be taken into consideration in the choice of the oxalato complexes. Thus, an important condition for the effectiveness of the oxalato complexes is that the decomposition temperature thereof should be below the melting temperature of the burning polymer. On the other hand, the oxalato complexes must be completely chemically inert in the behaviour thereof up to the temperature at which moulding or shaping is carried out. Accordingly, oxalato complexes suitable for polyethylene terephthalate should have a decomposition temperature which is above the processing temperature for polyethylene terephthalate of about 300°q., but which does not exceed the temperature of - 12 the burning polyethylene terephthalate melt of about 560°C. Where they are not quoted in the literature, the decomposition temperatures of the oxalato complexes may readily be determined by thermogravimetric analysis (TGA). So far as the carrying out of TGA is concerned, reference is made to Ullmanns Encyklopadie der technischen Chemie, 3rd Edition (1961), Verlag Urban & Schwarzenberg, Munich-Berlin Vol. 2/1, page 657. Some examples of decomposition temperatures of various oxalato complexes are shown in the following Table: Oxalato complex Decomposition temperature ocRb3[Ai(c2o4)3] 430 430K31fFe(c2O4)3l 440 450 395k2[^(c2o4)2] 470 KBa(Al(C2O4)3] 425 The melt temperature of the burning polymer, i.e. the temperature in the melt of the polymer burning in air, may be determined, for example, using a thermocouple. The measurement is best carried out in such a way that the soldered joint of the thermocouple is continuously covered by dripping melt during the measurement A particularly preferred method of determining the decomposition temperatures is differential thermoanalysis (DTA) because, in the DTA-diagrams of the oxalato complexes, the position of the endothermal main effect is indicative of the decomposition temperature. So far as differential thermo4 3 6 4 4 analysis is concerned, reference is made to the relevant text books and hand books, for example to Ullmanns Encyklopadie der technischen Chemie, l,e. pages 656—657 and to Pranke, Lexikon der Physik, Pranchn'sche Verlagshandlung Stuttgart, 3rd Edition.

Accordingly, when selecting suitable oxalato complexes as flameproofing agents for polyesters, it is best for the decomposition temperature of the oxalato complex and the melt temperature of the burning polymer to be brought as optimally as possible into line with one another. If one is confronted by the problem of having to flameproof a very specalized polymer, if the DTA values are not known and if, moreover, the instruments required for measuring the melt temperatures of the burning polymers and for the DTA-measurement are not available to him, he may form for himself, by means of a few empirical tests, a reliable picture as to which oxalato complexes may in fact be used and which of them guarantee optimum flameproofing. Naturally this also applies to the case where, despite the suitable position of the decomposition temperature of the oxalate complex and the melt temperature of the polymer, it is not possible to obtain satisfactory flameproofing for . reasons which could not be foreseen.

The flame retardant polyesters obtainable in accordance with the present invention may be processed into the conventional shaped articles, such as fibres, sheeting, films, panels or injection-moulded articles.

All the complex salts according to the present invention are excellent flameproofing agents. The two complex potassium salts K3 [A1(C2O4)3] and K2 [Mg (c2O4)21 and also the complex rubidium salt Rb3 [A1(C2O4)3], are particularly effective in polyethylene terephthalate. They are distinguished from the other complex salts by the fact that they provide the poly4 3 6 4 4 - 14 ester compositions not only with flameproof properties, but also with self-extinguishing properties. Dripping of the melt during burning is largely prevented. Of the abovementioned complex salts, K3 [Al(C2O^)3] is preferred.

The oxalic acid complex salts used in accordance with the present invention develop a considerable flameproofing effect even in relatively small quantities. They are preferably used in quantities of from 1 to 40%, by weight, more especially from 5 to 15%, by weight, based on the flame retardant and, optionally, self-extinguishing polyester composition. The complex salts are preferably used in anhydrous form.

According to the present invention, a flame retardant and optionally self-extinguishing polyester moulding composition is produced by introducing one or more of the oxalic acid complex salts used according to the present invention into the polymer composition in the conventional way. This may be done inter alia by processes in Which the flameproofing agent is actually added to the monomers during polycondensation and in this way is uniformly dispersed in the polymer formed. Another possible method of incorporation is to melt the polymer composition, to mix it with the flameproofing agent and then to process it into granulate or directly subject it to moulding or shaping. Another possible method is to scatter the finely divided flameproofing agent onto the polymer granulate and to process it with the polymer granulate. The particular procedure adopted will be determined by the particular field of application intended for the flame retardant and self-extinguishing moulding composition and may readily be selected by those skilled in the art.

In the case of relatively large or thick-walled mouldings. 3 6 4 4 distribution of the flameproofing agent is relatively straightforward and no difficulties are involved in producing the flameproofing agent in the suitable grain size for this purpose. By contrast, in the production of flame retardant and self-extinguishing fibres by the process according to the present invention, it is desirable to use the flameproofing agent in very finely divided form to allow the polymer to be spun and to guarantee favourable physical properties for the end product. In the case of fibres, the flameproofing agent is generally added in a quantity of no more than 20%, by weight. The suitable particle size is also governed by the particular field of application intended and may readily be selected by those skilled in the art. In the case of fibres, for example, it is determined by the denier of the fibres and by the required physical properties of the end product. In the case of textile fibres, the complex salts may be used in particle sizes of up to 2 |im.

No difficulties are involved in size-reducing the complex salts used in a ccordance with the present invention. For example, they may readily be ground, in which case the adhering water and the water of crystallisation should be removed beforehand. In addition, drying of the complex salts does not involve any difficulties and is carried out, for example, over a period of several hours at 150° c/10 mm Hg. The complex salts may be both dry-ground and also wet-ground. In the case of wet-grinding, the choice of the suitable dispersing liquid will also be determined by the particular sphere of application envisaged for the flameproofing agent and the manner in which it is applied. The oxalato complex is preferably ground in the polyhydric alcohol used for synthesis of the polyester and the suspension of the oxalato complex obtainable in this way is added directly to the polycondensation 6 4 4 - 16 mixture.

In a preferred embodiment of the present invention, a homo- or co-polyester of terephthalic acid is used as the moulding composition and one or more of the complex salts [A1(C2O4)3], K2 [Mg(C2O4)2] and Rb3 [A1(C2C>4)3] as the oxalic acid complex salt, the oxalic acid complex salt or salts actually being added to the monomers to be polycondensed. In this case, the complex salts are ground in the polyhydric alcohol(s) required for synthesis of the polyester, i.e. in ethylene glycol in the case of polyethylene terephthalate.

The suspension of the complex salt obtainable in this way is preferably directly added to the polycondensation mixture.

The process according to the present invention is preferably used for the production of self-extinguishing homopolyester and copolyester fibres, especially polyethylene terephthalate fibres, in which case K3 [Al(c2C>4)3] is preferably used as the oxalic acid complex salt in a quantity of from 5 to 15%, by weight, based on the self-extinguishing moulding composition.

In cases where polyesters are reinforced with glass fibres, it should be noted that, in the case of glasses containing alkaline earth metals, especially calcium, the flameproofing effect of the flameproofing agents used according to the present invention is slightly impaired. It is assumed that this reduction in effectiveness is attributable to the presence of the alkaline earth metal, for example calcium, introduced into the polymer by way of the glass fibres. The calcium obviously reacts in the form of its oxide with the oxalato complex under melt conditions to form calcium oxalate and a complex reduced by one oxalato ligand. This reaction thus possibly leads to a successive degradation of the flameproofing agent in the melt, so that the flameproofing agent may only be effective to a limited extent. It has been found 3 0 4 4 that additives which are capable of binding alkaline earth metal, especially calcium, under the given conditions through the formation of stable calcium compounds, prevent the flameproofing effect from being impaired. Suitable additives are primarily such compounds as MgCOg, MgSO^, ^2C2°4' K2C°3' A12 (SO^)3 and KgSO^. The additive is used in quantities of from 1 to 10%, by weight, preferably from 5 to 10%, by weight, based on the total weight of polymer, glass fibre, flameproofing agent and additive. However, even in the absence of the additional additives described above, the flameproofing effect obtained in cases where the above-mentioned glass fibres are used is still appreciable and sufficient for numerous applications .

The above-mentioned additives may, of course, also be used in the case of other reinforcing fillers containing alkaline earth metals and in cases where other additives containing alkaline earth metals are present.

The present invention relates to the flame retardant and optionally self-extinguishing polyester composition obtained by the processes described above using the abovementioned oxalato complexes, especially those containing the oxalato complex in quantities of from 1 to 40%, by weight, preferably from 5 to 15%, by weight. Homopolyester and copolyester fibres of terephthalic acid, in particular polyethylene terephthalate, containing from 5 to 15%, by weight, of the flameproofing agent, are preferred.

The complex salts used in accordance with the present invention have several advantages over conventional flameproofing agents. Firstly, it is pointed out that they may readily be obtained from the starting materials oxalic acid, an inorganic metal salt or metal hydroxide and, optionally, a simple inorganic alkali salt, the production thereof being 43844 carried out in aqueous solution. Apart from the complex rubidium and caesium salts, they are considerably less expensive than the conventional products containing halogens, phosphorus, nitrogen and/or Sb_O . 2 3 Since the effectiveness of the complex salts used according to the present invention is greater than that of conventional flameproofing agents, they need only be added to the polymer in a quantity of a few percent, by weight, to obtain a comparable flameproofing effect. Accordingly, the > characteristic properties of the treated materials are only modified to a fairly limited extent.

The compounds used according to the present invention are extremely compatible with the skin Neither do they give off any toxic gases during the combustion process. Carbon dioxide is formed as the only gaseous combustion product of these substances. The polymer melt is largely prevented from dripping by the incorporation of the complex salts used according to the present invention.

There is no significant reduction in the flameproofing effect of the compounds used according to the present invention, as measured from the LOI values (Limiting Oxygen Index), either after repeated washing or even after the dry cleaning of textiles. Although soluble in water, the extent to which they may be washed out of textiles is surprisingly low and the flame resistance of these textiles remains fully intact, even after more than 20 washes.

The complex salts used according to the present invention are distinguished by the inert behaviour thereof with respect to melts of the above-mentioned polymers and with respect to the conventional vessel materials. Accordingly, they may be added without any problems to polymer melts or, with the i - 19 exception of the lithium complex, in the form of a suspension before the polycondensation reaction. In this case, the excess suspending agent may be directly reused because it is not contaminated by residues of the flameproofing agent or decomposition products thereof.

EXAMPLE 1.

Production of self-extinguishing polyethylene terephthalate fibres: (a) Production and grinding of the flameproofing agent Kg [A1(C2O4)3] was produced by the method described by J. C Bailar and Ε. M, Jones in Inorganic Synthesis 1, (1939), page 36. The complex salt obtained was then dried for 15 hours at 150° C./approx. 10 Torr, The analyses of samples taken from different batches lay between [AlCCjO^)^ an^ K „ [A1(C„O )^ ]. 200 g of the dried complex salt were ground for about 2 hours in a bead mill (the PMI model produced by Messrs. Draiswerke, Mannheim) with 410 g of quartz beads from 1 to 3 mm in diameter in 400 g of ethylene glycol. After grinding, the diameter of the largest complex salt particles in the dispersion was about 4 (im, whilst most of the particles had a particle size of 1 pm. The quartz beads were then separated off by filtration through a sieve, rinsed with 200 ml of ethylene glycol and the dispersion diluted with the rinsing solution. The particles having a particle size of more than 2 p,m were largely separated off by allowing the dispersion to stand for 72 hours in tall vessels (sedimentation). (b) Polycondensation 600 g of this dilute dispersion having a Kg [Al^O^pcontent of 150 g were transferred to the polycondensation vessel with the transesterification product of 1350 g of 43844 - 20 dimethyl terephthalate and 1200 g of ethylene glycol at a stirring speed of 30 rpm and at a temperature of about 245° C. Zinc acetate (150 ppm) was used as the transesterification catalyst and antimony trioxide (200 ppm) as the condensation catalyst.

The polycondensation reaction, which normally takes about 85 minutes, could be terminated after only 1 hour. The ethylene glycol distilled off could be reused without purification for further condensation reactions. The polycon) densate contained 10%, by weight, of K3 [Al(C2Oa)3] . (c) Forming The polycondensate obtained was processed into chip form in the conventional way and dried for 24 hours at 125° C./ 60 Torr. The chips were then spun at 296° C. (spinning head i temperature) into a filament yarn paving an individual denier of 3.0 dtex and an overall denier of 150 dtex 48. The filament yarn was drawn in a ratio of 1:4.2 and subsequently twisted.

The textile data of the material obtained (light stability, fastness to light and solution viscosity) largely correspond ) to those of conventional polyethylene terephthalate produced under the same conditions as above, but without the addition of a flameproofing agent. (d) Determining burning behaviour The filament yarn described above was knitted into a ; four-thread test specimen which was subjected to the vertical burning test according to DIN 53906 to determine burning behaviour. For comparison, a corresponding test specimen without any flameproofing agent added and a test specimen containing the same quantity of the conventional brominei containing flameproofing agent 2,2-bis-(4-ethoxy)-3,5-dibromophenylene propane, were also tested.

The following results were obtained: - 21 Non-flameproofed test specimen Test specimen containing 10% by weight, of conventional brominecontaining flameproofing agent Test specimen containing 10% by weight, of Κ3[Α1(Ο2Ο4)3] Plame exposure time (sec.) Burning time (sec.) Glow time (sec.) completely burnt LO 3 88 drips burning 3 0 12 Plame exposure time (sec) ίχ, 15 p-1 •P Φ 15 15 Burning time P-ί -P CM fi (sec) 39 0 U Λ Glow time (sec) drips burning 11 EXAMPLE 2.

The polyethylene terephthalate described in Example 1, made self-extinguishing using K3 [A1(C2O4)3], was processed into a 2 mm thick sheet. A corresponding sheet without any flameproofing agent added and a corresponding sheet containing the same quantity of a conventional bromine-containing flameproofing agent were produced for comparison. The flame resistance of the sample is characterised by the LOI-value.

IO .

The LOI-value was measured in accordance with ASTM—D 2863 by means of the measuring instrument produced by Messrs. Stanton Redcroft, Great Britain.

The LOI-value is defined as the oxygen content (in %) of an oxygen-nitrogen mixture, at which a vertically mounted test specimen ignited at its upper end just still burns. The LOI-value corresponds to the difference between the 433 44 measured LOI-value of the flameproofed test specimen and the LOI-value of the non-flameproofed test specimen.

The following results were Non-flameproofed test specimen Test specimen containing standard flameproofing agent Test specimen containing K3 obtained: LOI : 20.1 LOI : 23.6,ALOI=3.5 LOI : 27 1, AL0I=7.0 EXAMPLE 3.

Following the procedure of Example 1, Na^ [A1(C20j) J was produced and ground in ethylene glycol, a polyethylene terephthalate containing 10%, by weight, of the complex salt was produced and finally processed into a 2 mm thick test sheet- TheΛLOI-value measured in accordance with ASTM D 2863 amounted to 4.0.

EXAMPLE 4 The rubidium-aluminium-trioxalato complex was synthesized as follows (cf. Chem. Rev. 61 (1961), pages 312—246): A solution of 3.46 g (0 0864 mole) of sodium hydroxide ) in 15 cc of water was introduced while stirring into a warm solution of 9.65 g (0.0144 mole) of Al^SO^)^. 18 HjO in 43 cc of water. The aluminium hydroxide precipitated was filtered off, washed out and introduced into a boiling solution of 10.88 g (0.0864 mole) of oxalic acid in 50 cc of water. A i clear solution was obtained. A solution of 10 g (0.0433 mole) of rubidium carbonate in 13 cc of water was added dropwise to this solution at 100° C., followed by heating for another 30 minutes. Thereafter, the solution was freed from a slight haze (unreacted aluminium hydroxide formed by neutralisation) ' by filtration and finally cooled. The oxalato complex was then precipitated by the addition of methanol, subsequently 3 3 4 4 - 23 filtered under suction and dried in vacuo at 150° C. The yield amounted to 13 g (82.5% of the theoretical yield).

The Rb [A1(C 0.),] produced in the manner described 3 2 4 3 above was ground in ethylene glycol in the same way as in Example 1 and processed into a polyethylene terephthalate containing 10%, by weight, of the complex salt. The A LOIvalue was measured on a 2 mm thick test sheet in accordance with ASTM D 2863. It amounted to 7,3.

EXAMPLE 5.

Production of self-extinguishing copolyester fibres (polyethylene terephthalate containing 7.8%, by weight, of azelaic acid' containing 9% of K, [AHc^O^)^] (a) Production and grinding of the flameproofing agent .

[AliCjO^)^] was produced by the method described by J. C. Bailar and Ε M. Jones in Inorganic Synthesis 1. (1939), page 36. The complex salt obtained was then dried for 15 hours at 150° C./approx. 10 Torr. After 15 minutes1 predispersion in an Ultra-Turax mixer, 200 g of the dried complex salt were ground for about 2 hours in a bead mill (type PMI manufactured by Messrs. Draiswerke, Mannheim) with 410 g of quartz beads from 1 to 3 mm in diameter in 400 g of ethylene glycol. After grinding, the largest complex salt particles in the dispersion had a diameter of about 4 |im, whilst most of the particles had a diameter of ^.1 nm. The quartz beads were then separated off by filtration through a sieve, rinsed with 200 ml of ethylene glycol and the dispersion diluted with the rinsing solution The particles which had a size of more than 2 nm were largely separated off by leaving the dispersion standing for 72 hours in tall vessels (sedimentation) . 43S44 - 24 (b) Polycondensation 600 g of this dilute dispersion having a [Al^O^)^]content of 150 g were transferred to the polycondensation vessel with the transesterification product of 1393 g of di5 methyl terephthalate and 1200 g of ethylene glycol, together with 107 g of azelaic acid, at a stirring speed of 30 rpm and at a temperature of about 245° C. Manganese acetate (240 ppm) was used as the transesterification catalyst, antimony trioxide (400 ppm) as the condensation catalyst .0 and triethyl phosphate (300 ppm) as stabiliser. The polycondensation reaction was terminated after 106 minutes. The ethylene glycol distilled off could be reused without purification for further condensation reactions. The polycondensate contained 9%, by weight of K_ [Al(Co0.) ]. 2 4 3 (c) Forming The polycondensate obtained was processed into chips in the conventional way and dried for 24 hours at 125° C./60 Torr. The chips were spun at 296° C (spinning head temperature) into a filament yarn with an individual denier of 3.0 dtex and an overall denier of 150 dtex 48. The filament yarn was drawn in a ratio of 1:4.2 and then twisted. The textile data of the material obtained (light stability, fastness to light and solution viscosity) largely correspond to those of conventional polyethylene terephthalate produced under the same conditions as above, but without the addition of a flameproofing agent. (d) Determining burning behaviour The filament yarn described above was knitted into a four-thread test specimen which was then subjected to the vertical burning test according to DIN 53906 in order to determine burning behaviour. A corresponding test specimen 3 3 4 4 - 25 without any flameproofing agent added and the test specimen containing the same quantity of tha conventional flameproofing agent, 2,2-his-(4-ethoxy)-3,5-dibromophenyl propane, were tested for compariso.i.

The following results were obtained: Non-flame proofed test specimen Test specimen containing 10% of Test conventiona1 brominecontaining flame proofing agent specimen containing 9% of Κ3^Α1(σ2°4,3] Plame exposure >, 3 3 3 time (sec) ι—1 Φ 4J Burning time 0) Η (sec) § 0 3 88 2 0 rb Glow time (sec) drips burning 12 Plame exposure S 15 15 15 time (sec.) r—i Φ « +J Burning time iH C & M (sec.) e a 8* 39 1 Glow time (sec.) drips burning 11 EXAMPLE 6. parts, by weight, of dry polyethylene terephthalate chips, produced in known manner having a solution viscosity of 1.61, were thoroughly mixed in a cross beater mill with 1 part, by weight, of Lig [A1(C2O4) ] which had been pulverised beforehand in a ball mill. The mixture was moulded under heat in known manner to form a 2 mm thick sheet. The LOI-value of a sheet was determined in accordance with ASTM D 2Θ63 and compared with the LOI-value of a sheet of pure polyethylene terephthalate: LOI : comparison 20.I LOI : sheet according to Example 6: 23.6 EXAMPLE 7.

Polyethylene terephthalate moulding compositions were produced from 55%, by weight, of polyethylene terephthalate, %, by weight, of glass fibres of a calcium-containing glass, 10%, by weight, of Kg [AKCgO^Jg] and 5%, by weight, of magnesium carbonate. The test specimens were self-extinguishing A test specimen produced for comparison from 60%, by 3 weight, of polyethylene terephthalate, 30%, by weight, of glass fibres and 10%, by weight, of K3 [Al(C204)g] was flameresistant, but not self-extinguishing.

EXAMPLE 8.

A curtain of 100% of polyethylene terephthalate filament i yarn was immersed at room temperature in an aqueous solution of 100 g/1 of Kg [AKCgO^lg] subsequently dried at 120° C. and then heated for 60 seconds at 190° C.

The test specimen was tested in accordance with DIN 53906 and proved to be resistant. ι EXAMPLE 9. (a) Production of K2 [Zn(C204)2]/K4 [ZnfCgOjg] The complex salt was produced by the method (I) described by D. P. Graddon in J. Inorg. & Nucl. Chem. 1956, Vol. 3, page 321. (b) Production of the glycolic suspension of the complex salt The coarse-grained complex salt obtained by the process described above was initially size-reduced in a ball mill and then dried for about 6 hours at 130° C./approx. 50 Torr. 1 part, by weight, of the finely ground complex salt was then dispersed in 4 parts, by weight, of ethylene glycol by means of a high speed stirrer, followed by stirring for about 30 3 3 4 4 - 27 minutes. The suspension obtained in this way was then subjected to fine grinding, for example in a bead mill. The product of predispersion should be intensively stirred during grinding to prevent it from settling. In general, stirring periods of about 10 minutes at intervals of 1 hour are sufficient for this purpose.

In batch operation, the suspension has to be filtered 2 through a sieve (3600 meshes/cm ) on completion of grinding in order to separate off the grinding elements and, optionally, any glass dust formed. The glass beads may be reused for further grinding operations. In continuous operation, the suspension may be immediately collected and further processed. During the process as a whole, it is important to ensure that the suspension remains as dry as possible (atmospheric moisture) because the salt is moderately soluble in water.

The glycolic suspension of the complex salt remains stable for several days. Before use it should be vigorously stirred once more for at least 10 minutes. (c) Condensation of polyethylene terephthalate in the presence of the complex salt For producing flameproofed polyethylene terephthalate on a 20 kg scale, 18 kg of dimethyl terephthalate were initially transesterified with 13.5 1 of ethylene glycol and 150 ppm of zinc acetate as catalyst. After the elimination of methanol has stopped (about 1 hour 56 minutes), 2 kg of the complex salt in the form of a 20% suspension in glycol were introduced into the transesterification vessel over a period of 20 minutes. The temperature in the transesterification vessel amounted to about 210° C. The excess glycol was then distilled off from the transesterification vessel with stirring over a period of about 70 minutes. The total transesterification time was 3 hours 7 minutes. - 28 Antimony trioxide (200 ppm) was used as the condensation catalyst, being added to the transesterification product at a temperature of 250° C. The condensation reaction was carried out at from 280 to 284° C. and was over after about 95 minutes The autoclave was a stream of nitrogen at then emptied in about 30 minutes with from 4 to 5 atms gauge.

The polymer was found to have the following data: LO Solution viscosity: Melt viscosity: Softening point: 1.660—1.700 4800—6000 poises 263—264° C.

The polycondensate contained 10%, by weight, of the complex salt. (d) Forming The polycondensate obtained was processed into chips .5 in the conventional way and dried for 24 hours at 150° C./50 Torr. The chips were spun at 296° C. (spinning head temperature) into a filament yarn having an individual denier of 3.0 dtex and an overall denier of 150 dtex 48. The filament yarn was drawn in a ratio of 1:4.2 and subsequently twisted. The textile data (light stability, fastness to light and solution viscosity) of the material obtained substantially correspond to those of conventional polyethylene terephthalate produced in the same way as described above, but without the addition of a flameproofing agent. (e) Determining the Λ LOI-value The LOI-value was determined on hose having a weight 2 per unit area of about 400 g/m in accordance with ASTM D 2863 using the measuring instrument manufactured by Messrs. Stanton Redcroft of Great Britain. It amounted to 5.0.

EXAMPLES 10 to 16.

The oxalato complex salts described in detail below were 3 6 4 4 - 29 used for the production of flame-resistant polyethylene terephthalate. (a) K3 [Fe(C2O4)3j Produced by D. P. Graddon's method described in J.

Inorg. & Nucl. Chem. 1956, Vol. 3, 308—322 or Inorg.

Synthesis Vol. I, page 36. (b) K3 [Cr(C2O4)3] Produced by D. P. Graddon's method, loc. cit. (c) K2 [Mg(c204)2] Produced by D. P. Graddon's method described in J.

Inorg.& Nucl. Chem. 1956, Vol. 3, page 321, method I: g (0.206 mole) of potassium oxalate monohydrate were dissolved in 50 cc of water, the resulting solution heated to boiling point and a solution of 2o.3 g (0.1 mole) of magnesium chloride in 100 cc of water added to it. The solution was then boiled for about another hour. After cooling to room temperature, the deposit was filtered off under suction, washed with water until free from chloride and finally dried in vacuo at. 150° C. The yield amounted to 20 g (72% of the theoretical yield). (d) K2[Zn(C2O4)2]/K4 [Zn(C2O4)3] Produced by D. P. Graddon's method described in J.

Inorg. & Nucl. Chem 1956, Vol. 3, page 321, method I: A solution of 57.5 (0.2 mole) of zinc sulphate heptahydrate in 200 cc of water was introduced with stirring into a hot solution of 36.8 g (0.2 mole) of potassium oxalate monohydrate in 100 cc of water. The zinc oxalate formed was filtered off under suction while still hot and washed with - 30 43644 cold water. The zinc oxalate obtained in this way was then introduced into a boiling solution of 75 g (0.47 mole) of potassium oxalate mqnohydrate. The clear solution obtained was boiled for about 30 minutes, diluted with water to approximately 150 cc and cooled. A deposit was precipitated on rubbing with a glass rod. It was filtered off under suction and dried in vacuo first at 100° C. and finally at 150° C. The yield amounted to 54 g (55% of the theoretical yield).

The substance consists of a mixture of [zn(c204)3] and K2 [Zn(C204)2] and has a decomposition point of 395—430° c. (e) K4 [Zr(C2O4)4] 23.3 g (0.1 mole) of zirconium chloride were dissolved in 150 cc of methanol. The solution was filtered and introduced with stirring at room temperature into a solution of g (0.22 mole) of anhydrous oxalic acid in 100 cc of methanol.

A deposit was precipitated. The reaction mixture was left standing at room temperature for about 20 hours and then filtered. The deposit was thoroughly washed with methanol, dissolved in 100 cc of water, filtered and, finally, introduced while stirring into a hot solution of 40 g (0.24 mole) of potassium oxalate monohydrate in 100 cc of water. The mixture was filtered while still hot and finally cooled. The deposit precipitated was filtered off under suction, washed with methanol and dried in vacuo at 150° C. The yield amounted to 43 g (72% of the theoretical yield). (f) KBa [A1(C2O4)3J 40.8 g (0.1 mole) of K3 [Al(C204)3] were dissolved in 200 cc of hot water. The solution was cooled to approximately 30° C., followed by the dropwise addition with stirring of a ) solution of 22.4 g (0.1 mole) of barium chloride dihydrate.

A deposit was precipitated The mixture was stirred for about 6 4 - 31 30 minutes and left standing for another 2 hours. Finally, the deposit was filtered off, washed with water until free from chloride and dried at 150° C. The yield amounted to 46.6g(46.7% of the theoretical yield). (g) cs3 [Al(C204)3] The complex salt was produced by a method similar to that used for the synthesis of the rubidium-aluminium trioxala to complex described in Example 4. In contrast to the preceding Examples, 5 and 10%, by weight, of the complex salt were added to the completed polyester in an extruder. The extrudate was further processed into 2 mm thick polyester films.

The δLOI-values obtained in this way are shown in Table 1.

TABLE 1 Example No. Complex salt Quantity of complex salt in %, by weight A. LOI-value 10K3 IPe^C2°4^3·) 10 5.1 11K3 10 6.3 12K2 WiU 10 5.9 13K4 10 5.0 14 K4 [Zr(C204)4] 10 5.2 15 KBa [Al(C2Oa)3] 10 3.0 16 cs3 [ai(c2o4)3] 5 6.5

Claims (17)

1. CLAIMS:1. A process for the production of a flame retardant polyester composition which comprises incorporating as the sole flame-proofing agent one or more oxalato complexes. 5

2. A process as claimed in claim 1 in which the oxalato complex contains a complex anion of the type: [S n r a wherein Z represents one or more central atoms selected from 10 Mg, Ca, Sr, Ba, Zr, Hf, Ce, V, Cr, Mn, Fe, Co Ni, Cu, Zn, Cd, B, Al, Ga, In, Sn, Pb and Sb; n represents the number of ligands; and -e represents the negative charge of the complex anion.

3. A process as claimed in claim 1 or claim 2 ih which L5 the cationic constituent of the oxalato complex contains at •J- ·φ· ·$least one of the ions Li , Na , K , Rb , Cs or NH. and may -| | also contain Ba

4. A process as claimed in any of claims 1 to 3 in v/hich the oxalato complex corresponds to the following !O general formula: Μ < Μθΐ 11 wherein Me 1 represents Li, Na, K, Hb, Cs or NH.; II 4 Me represents Li, Na, K, Rb, Cs ? NH 4 or Ba;

5. Z represents Mg, Ba, Zr, Fe, Co, Cu, Zn, Al, Sn, Cr and Sb; ]C20, 1, 2, 3 or 4; 1^ 0 or 1; and mr=2, 3 or 4. 4 3 ϋ 4 4 - 33 5. A process as claimed in claim 4 in which the oxalato complex corresponds to one of the following general formulae: Me^ [AliC^O^)^] or Me 1 [A1(C 2 O 4 ) 2 ] or the formula K^ZniC^]; K 4 [Zr(C 2 0 4 ) 4 ] ; K 3 [Cr(C 2 O 4 ) 3 ], K 3 [Fe(C 2 O 4 ) 3 ], Kg [Sb(C 2 O 4 ) 3 ], KBa [Fe^O^], KBa [A1(C 2 O 4 ) 3 ], K 2 [Mg(C 2 O 4 ) 2 ] , K 2 [Fe(C 2 O 4 ) 2 ], K 2 [Zn(C 2 0 4 ) 2 ], K 2 [Cu(C 2 O 4 ) 2 ], or Ba [MgiC^)^.

6. A process as claimed in any of claims 1 to 5 in which the polyester is polyethyleneterephthalate, polypropylene terephthalate or polybutylene terephthalate.

7. A process as claimed in ahy of claims 1 to 6 in which the oxalato complex is incorporated in the polyester in a quantity of from 1 to 40%, by weight, based on the polyester composition.

8. A process as claimed in claim 7 in which the oxalato complex is incorporated in the polyester in a quantity of from 5 to 15%, by weight, based on the polyester composition.

9. A process as claimed in any of claims 1 to 8 in which the oxalato complex is used in anhydrous form.

10. A process as claimed in any of claims 1 to 9 in which the oxalato complex is ground in the polyhydric alcohol required for synthesis of the polyester and the suspension of the complex obtainable in this way is directly added to the polycondensation mixture.

11. A process as claimed in claim 1 substantially as herein described.

12. A process as claimed in claim 1 substantially as herein described with reference to any one of the Examples.

13. A flame retardant polyester composition which 4 3 3 4 4 contains one or more oxalato complexes as the sole flameproofing additive.

14. A composition as claimed in claim 13 which is selfextinguishing.

15. A composition as claimed in claim 13 substantially as herein described.

16. A composition as claimed in claim 13 substantially as herein described with reference to any one of the Examples.

17. A polyester as claimed in any of claims 13 to 16 when produced by a process as claimed in any of claims 1 to 12.