WO1996034047A1

WO1996034047A1 - Halogen-free flame-retardant thermoplastic polymer composition

Info

Publication number: WO1996034047A1
Application number: PCT/NL1996/000171
Authority: WO
Inventors: Richerdes Johanna Mathilda Hulskotte; Martinus Louis Maria Bos
Original assignee: Dsm N.V.
Priority date: 1995-04-28
Filing date: 1996-04-18
Publication date: 1996-10-31
Also published as: AU5409096A; BE1009351A3

Abstract

The invention relates to a flame-retardant polyester composition comprising a poylester derived from alkylene glycol that consists largely of ethylene glycol, 2-50 wt.%, relative to the polyester, of a complex oxalate and 5-100 wt.%, relative to the oxalate, of a synergist chosen from the group comprising oxides of metals of groups 8-10 and group 15, compounds derived therefrom, borates and silicates. Preferably use is made of antimony trioxide. The invention is particularly suitable for glass-fibre-reinforced polyester compositions which then meet the UL-94 V-0 qualification.

Description

HALOGEN-FREE FLAME-RETARDANT THERMOPLASTIC POLYMER COMPOSITION

The invention relates to a flame-retardant thermoplastic polymer composition comprising (a) a polyester derived from alkylene glycol and an aromatic dicarboxylic acid and (b) an oxalate complex.

Such a composition is known from GB-A- 1541296, which discloses a composition that consists of polyalkylene terephthalate and an oxalate complex with a complex anion [Z(C₂0₄)_n]^~β, where Z is chosen from the group comprising 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 is an integer and -e indicates the anion's negative charge. One or more alkali ions serve as the cation. The use of the complex oxalate results in an increase in the 'Limiting Oxygen Index' (the LOI). The LOI is the oxygen concentration of a nitrogen/oxygen mixture at which the combustion of a vertically attached test specimen whose top end has been ignited is just sustained, ASTM D 2863. In practice it is however very important that, when a source of ignition is present, the plastic composition spontaneously stops burning and does not generate burning droplets which could further propagate the fire. A test that is representative of this is the UL-94 test method, according to which a test specimen is vertically suspended and a flame is held beneath it for 10 seconds. This procedure is repeated as soon as the test specimen has stopped burning. The different classifications V-0 and V-l and V-2 are based on the observed burning and after-glowing times and on whether or not burning droplets are formed. The test's execution is laid down in UL-94. Another test is the glow-wire test, in which a glow wire is pressed against a vertically placed test specimen at a prescribed pressure for 30 seconds. The glow wire's temperature can be varied between 550 and 960°C. According to IEC 695-2-1, the highest temperature at which the test specimen still stops burning within 60 seconds from the beginning of the test, without afterglowing, is the glow-wire temperature. The compositions known from GB-A-1541296 do not meet these stringent reguirements and in the presence of for example 30 wt.% glass fibre the flame does not extinguish at all in the UL 94 test.

EP-A-0026956 yields improved dripping behaviour due to the use of 0.1-0.5 wt.% polytetrafluoroethylene with a molecular weight of over IO⁵. However, a V-0 classification again reguires the absence of fibrous fillers.

In view of the increasing importance of flame-retardant (glass-)fibre-reinforced thermoplastic polyester compositions for for example electrical and electronic applications and the increasingly greater need, for environmental reasons, for halogen-free flame retardants, the aim of the invention is a halogen-free flame-retardant polyester composition which, also in the presence of fibre reinforcement, meets the highest flame-retardancy reguirements.

It has now been found that this aim is achieved if the polyester is based on ethylene glycol and if, in addition to the complex oxalate, it also contains an inorganic compound chosen from the group comprising the oxides of the metals of groups 8-10 and 15 and compounds derived therefrom, borates and silicates. The halogen-free flame-retardant thermoplastic polyester composition containing a complex oxalate as the flame retardant comprises: (a) a polyester derived from alkylene glycol, at least 50 mol.% of which consists of ethylene glycol, and one or more aromatic dicarboxylic acids, (b) 2 to 50 wt.%, relative to (a), of a complex oxalate, (c) 5 to 100 wt.%, relative to (b), of an inorganic compound chosen from the group comprising oxides of metals of groups 8-10^1J and group 15^X) and compounds derived therefrom, borates and silicates. The thermoplastic polyester is derived from one or more alkylene glycols, at least 50 mol.% of which is ethylene glycol, preferably at least 75 mol.% and most preferably at least 95 mol.%, and one or more aromatic dicarboxylic acids. The aromatic dicarboxylic acids are preferably chosen from the group comprising phthalic acids, for example iso- and terephthalic acid, naphthalene dicarboxylic acids, for example 2,6- naphthalene dicarboxylic acid, and diphenyl dicarboxylic acids, for example 4,4 '-diphenyl dicarboxylic acid. Terephthalic acid is very suitable. Preferably the thermoplastic polyester is polyethylene terephthalate, PET. Other thermoplastic polyesters that are very suitable for use in the composition according to the invention are polyethylene naphthalate, PEN, copolyesters of ethylene glycol and terephthalic acid containing preferably at most about 20 mol.% isophthalic acid and copolyesters of ethylene glycol and 2,6-naphthalene dicarboxylic acid and 4,4 '-diphenyl dicarboxylic acid, the naphthalene dicarboxylic acid : diphenyl dicarboxylic acid molar ratio preferably lying between 0.6 : 0.4 and 0.4 : 0.6.

Also mixtures of polyesters, at least 50

^1} According to the new IUPAC notation of the periodic system as shown in the table printed in the cover of the Handbook of Chemistry and Physics, 70th edition, CRC-Press, 1989-90. - A -

mol.% of which being polyester based on ethylene glycol, form part of the invention.

These polyesters can be obtained through polycondensation of the monomers concerned. The preparation method is for example extensively described in Encyclopedia of Polymer Science and Engineering, Vol. 12, pp. 1-69 (1988), ISBN 0-471-80943-8 (v. 12) and the references mentioned therein. Some of the aforementioned polyesters are commercially available. The polyester 's molecular weight may vary over a wide range, expressed in the relative viscosity _rβl, measured in a 1 wt.% solution in m-cresol, for example between 1.2 and 2.2. Preferably between 1.5 and 1.9. The complex oxalate (b) is preferably an oxalate from the group described in the introduction to this application's description. With greater preference the complex oxalate is chosen from the group comprising double oxalates whose first metal is chosen from the group comprising alkali metals (group 1) and the other metal is chosen from the group comprising alkaline earth metals (group 2) or metals of group 13, for example potassium-aluminium oxalate, potassium- magnesium oxalate and rubidium-aluminium oxalate. The complex oxalates can for example be obtained with the aid of the method described in GB-A-1541296. The concentration of complex oxalate (b) in the composition may vary over a wide range, for example between 2 and 50 wt.%, relative to (a). Preferably the concentration of (b) is between 10 and 40 wt.%, relative to (a).

The inorganic compound (c) is chosen from the group comprising oxides of metals of group 15, for example Sb, and groups 8-10, for example Fe, alkali antimonates, borates, for example zinc borate, and silicates. Examples of preferable silicates are calcined kaolin and wollastonite. Such silicates are commercially available under various trade names. These silicates are used in a finely dispersed form, preferably in a particle size smaller than 50 μm , more preferably 10 μm. Antimony trioxide is very suitable for use as component (c). It is very surprising that antimony trioxide shows a synergistic effect when combined with a complex oxalate. The use of Sb₂0₃ as a synergist with halogen- containing flame retardants is known and is allegedly based on the formation of volatile antimony trihalogenide. However, Sb₂0₃ combined with halogen-free flame retardants has either no effect or a negative effect. See for example; Flame Retardancy of Polymeric Materials, Vol. 3, pp. 198-207, Marcel Dekker NY (1975). The concentration of component (c) may vary over a wide range and is generally between 5 and 100 wt.%, relative to component (b), preferably between 10 and 60 wt.%, even more preferably between 10 and 40 wt.%, relative to component (b). Optionally the composition contains up to approx. 1 wt.% polytetrafluoroethylene, PTFE, relative to component (a). The best results are obtained if the number average molecular weight of the PTFE is higher than 10^s. The composition furthermore optionally contains the usual additives, including nucleating agents, such as sodium acetate, softeners, such as polyethylene glycol compounds, stabilisers, pigments and release agents. The invention is particularly suitable if the composition contains a fibrous reinforcement. The fibrous materials are organic, for example aramide, or inorganic, for example glass fibres. The fibre content may vary over a wide range, for example between 1 and 150 parts by weight, preferably between 2 and 100 parts by weight per 100 parts by weight of polyester (a). The composition according to the invention can be prepared in different ways. Preferably the different components are mixed in the melt. This can take place in various apparatuses suitable for that purpose, for example in a Brabender or Haake kneader, preferably in an extruder, a twin-screw extruder being the most preferable. The extrudate obtained is then granulated and processed into the desired end products by means of for example injection-moulding, (blow) extrusion, rolling and/or compression. Optionally, the granules of the composition after the melt-mixing are subjected to after-condensation in the solid state to obtain a relative viscosity desired for the further processing by means of for example extrusion.

The various components are preferably mixed in the melt in dry condition, with the exclusion of oxygen. They may be fed to the melt-mixing apparatus separately or premixed in dry condition. It is also possible to use the so-called masterbatch method, according to which the individual components (b) and/or (c) are first premixed in the melt. The polymer used in this method may differ from polymer (a).

The invention will now be explained with reference to the following examples and comparative examples, without however being limited thereto.

Materials:

(a) PET (1) polyethylene terephthalate h._rβl = 1.60,

PET (2) polyethylene terephthalate _rβl = 1.62,

(b) flame retardant K₃A1(C₂0₄)₃ prepared according to the method described in GB-A-1541296

(c) Sb₂0₃: antimony trioxide, Blue Star^R, regular, from Campine Sb₂0₃-MB-PBT: 80 wt.% Sb₂0₃ in polybutylene terephthalate (masterbatch) NaSb0₂: sodium antimonite, average particle size 2 μm, Pyrobloc SAP2, from ANZON.

CDP: cresyldiphenylphosphate, from FMC

Zn stann. : water-free zinc stannate. Flamtard

S^R, from BA Chemicals. Fe₂0₃: iron(III)oxide, Bayferrox^R 130 M, from

Bayer

Nyad 400^R: wollastonite with aspect ratio 5, from Nyco

Translink^R 445: calcined clay, average particle size 1.4 μm, from Engelhard

(d) additives

OCF 429 YZ; glass fibre, from Owens Corning,

USA, average length 4.5 mm, diameter 10 μm.

PTFE: polytetrafluoroethylene, Hostaflon^R 1750, from Hoechst.

Method:

If PTFE was present it was mixed with the KAloxalate in a Henschler mixer and optionally dried before extrusion. The glass-fibre-filled compositions were produced using a ZSK twin-screw extruder. Glass fibre was dosed to the melt; the other components to the extruder's throat. The temperature was set to 275-280°C, the screw speed to 200 rpm and the throughput to 90 kg/hour. The measured melt temperatures varied between 290 and 310°C and were partly dependent on the set temperature and the glass content. The granules obtained after drying were subjected to after-condensation at about 210°C for 4-16 hours. The relative viscosity was measured at 25°C in a 1 wt.% solution in m-cresol or a trichlorophenol/phenol mixture (72:100 parts by weight) and converted to m- cresol. The release agent was mixed with the granules before the injection-moulding.

The UL-94 test specimens and the specimens for mechanical testing were produced using an injection- moulding machine at a set temperature of 285-295°C. The mould temperature was 150°C.

The test specimens for the UL-94 test were 1.6 mm; the thickness of the test specimens for the glow-wire test was 1.0 mm.

The following tables specify the flame retardancy, UL-94 classification and/or the glow-wire temperature for the different compositions.

Table 1

10

15

20

10

15

*) UL-94 test using 'dry as moulded' test specimens

In Experiment 2, according to the invention, antimony trioxide was mixed with the composition of (Comparative) Experiment 1, which immediately resulted in a V-0 classification and a glow-wire test temperature of 960°C. Comparative Experiments 3 and 11, in which a second known flame retardant was used besides the KAloxalate, did not result in improved burning behaviour.

Experiments 5 and 6, according to the invention, in which a wollastonite or a calcined clay was used besides KAloxalate, resulted in a glow-wire temperature of 960°C, while a considerable percentage of the test specimens already met the requirements of V-0. Further optimisation in this respect appears to be possible. Composition 1 , according to the invention, in which sodium antimonate was processed instead of antimony trioxide, met V-l, but the shortest burning times were obtained with antimony trioxide, which is preferred. From Experiments 9 and 10, according to the invention, it is apparent that in the case of the PET compositions according to the invention the presence of PTFE does not have a demonstrable positive influence on the classification.

Comparative Experiment 12 and Experiment 13, according to the invention, demonstrate the positive effect of antimony trioxide on the flame retardancy of the KAloxalate in unfilled PET.

Experiments 14-17 In these experiments the influence of antimony trioxide on the effect of the KAl-oxalate in a different polyester, polybutylene terephthalate, PBT, and a blend of PET and PBT was studied. The experiments clearly showed that the KAl-oxalate functions insufficiently as a flame retardant in PBT, even in the presence of antimony trioxide. In the blend antimony trioxide has a clear positive effect (experiment 17 according to the invention)

TABLE 2 compositions in wt.%

PBT = polybutylene terephthalate, h,_rβl = 2.0 (m-cresol)

The mechanical properties of the compositions obtained according to the invention are good.

Claims

C L A I M S

1. Flame-retardant thermoplastic polyester composition comprising

(a) a polyester derived from alkylene glycol, at least 50 mol.% of which consists of ethylene glycol, and one or more aromatic dicarboxylic acids (b) 2 to 50 wt.%, relative to (a), of an oxalate complex (c) 5 to 100 wt.%, relative to (b), of an inorganic compound, chosen from the group of oxides of metals of groups 8-10 and group 15 and compounds derived therefrom, borates and silicates.

2. Flame-retardant thermoplastic polyester composition according to Claim 1, characterised in that the polyester is derived from one or more aromatic dicarboxylic acids chosen from the group of tere- and isophthalic acid, naphthalene dicarboxylic acids and diphenyl dicarboxylic acids.

3. Flame-retardant thermoplastic polyester composition according to any one of the above claims, characterised in that the composition also contains reinforcing fibres chosen from the group of inorganic and organic fibrous materials.

4. Flame-retardant thermoplastic polyester composition according to Claim 3, characterised in that the reinforcing fibre is glass fibre.

5. Flame-retardant thermoplastic polyester composition according to Claim 3 or Claim 4, characterised in that the fibre content is between 1 and 150 parts by weight per 100 parts by weight of polyester.

6. Flame-retardant thermoplastic polyester composition according to Claim 5, characterised in that the fibre content is between 2 and 100 parts by weight per 100 parts by weight of polyester.

7. Flame-retardant thermoplastic polyester composition according to Claim 1, characterised in that the metal oxalate is chosen from the group of double oxalates whose first metal is chosen from the group comprising alkali metals and the other metal is chosen from the group of alkaline earth metals and metals of group 13.

8. Flame-retardant thermoplastic polyester composition according to Claim 7, characterised in that the oxalate is potassium-aluminium oxalate, potassium-magnesium oxalate or rubidium-aluminium oxalate.

9. Flame-retardant thermoplastic polyester composition according to any one of the above claims, characterised in that the inorganic compound is chosen from the group of oxides of iron and antimony.

10. Flame-retardant thermoplastic polyester composition according to Claim 9, characterised in that the oxide is antimony trioxide.

11. Flame-retardant thermoplastic polyester composition as described in the introduction and the examples.