GB2125057A - Polyester moulding compositions - Google Patents

Abstract

A moulding composition is based on polyethyleneterephthalate (PET) and contains as additives polycaprolactone with a number average molecular weight greater than 20,500 and a nucleant for crystallisation of the PET. The composition can also contain a reinforcing fibre, such as glass, and a plasticising additive, which may be, for example, a polycaprolactone of low molecular weight, or a plasticiser such as dibenzyl adipate. The nucleant can be a metal salt of an organic acid, or a finely divided solid, and the amount is no more than 6 parts per 100 parts total polymer when reinforcing fibre is present and no more than 1.9 parts per 100 parts total polymer when no reinforcing fibres are present.

Description

SPECIFICATION Improvements in and relating to moulding compounds based on polyester The present invention relates to polyester compositions for moulding materials, and particularly to novel polyester compositions which exhibit good mouldability.

Polyethylene terephthalate is used for many products such as fibres and films because of its excellent resistance to heat, resistance to chemicals, mechanical and electrical properties. However, in the field of plastics moulding, when it is used to produce, for example, injection moulded articles, it has many short-comings which arise primarily from its particular crystallisation behaviour. Polyethylene terephthalate crystallises very slowly from the molten state, and has a relatively high second order transition temperature so that mouldings made from it exhibit poor dimensional stability, and have to be made at higher than normal mould temperatures.

It is therefore desirable, for moulding applications, to increase the rate of crystallisation of the polyethylene terephthalate and lower its second order transition temperature, and there is a substantial body of prior art concerned with various additives for achieving this purpose, for example, to UK Published Applications Nos. 2015031 Aand 2,015,014A (DuPont) UK Published Application No.

2 021 131 A (Toyobo) EP Published Application No. 0 021 648 (ICI) and US Patent No 3,368,995 (Teijin).

Thus a nucleating agent may be added to the polyethylene terephthalate to speed up its crystallisation, a plasticizer to encourage molecular movement within the composition and facilitate crystallisation at lower temperatures, and a polymeric additive may be used to enhance physical properties whilst preferably also improving crystallisation. It is also well-known that it is advantageous to include a fibrous reinforcement such as glass fibre in the composition.

Furthermore, it is known that polybutylene terephthalate (PBT), which is used in moulding applications, may have incorporated into its moulding compositions a polycaprolactone of molecular weight 5000 to 300,000 either in small quantities to act as a mould release agent for PBT (Jap Patent Publication No. 1 058 455) or in larger quantities to improve impact resistance in a filled composition (Jap Patent Publication No. 1 058 456). There is no suggestion in this however, that the polycaprolactone would affect the crystallisation rate of PBT or, indeed PET, since the crystallisation rate of PBT is very good, and impact modifiers or mould release agents are normally not concerned with polymer crystallisation rates.We have now found a novel combination of additives which gives a polyethylene terephthalate moulding composition of advantageous properties.

Thus according to the present invention a polyester moulding composition comprises polyethylene terephthalate or a polyester containing at least 80% of polyethylene terephthalate repeating units, polycaprolactone, a nucleant for crystallisation of the polyethylene terephthalate the polycaprolactone having a number average molecular weight of above 20,500 and the amount of nucleant being not greater than 6 parts by weight per 100 parts by weight total polymer when reinforcing fibres are present but not greater than 1.9 parts by weight per 100 parts by weight total polymer when no reinforcing fibres are present.

Preferably the composition contains reinforcing fibre, preferably short lengths of reinforcing fibre such as glass fibre, although other types of fibre which will stand up to the processing conditions to which the composition is subjected may be used.

The nucleant may be either a metal salt of an organic acid, for example a metal stearate, acetate or benzoate, or a finely divided material which does not melt at or below the melting point of polyethylene terephthalate, and is chemically inert in the composition, for example microtalc. The preferred nucleant is a group 1 metal stearate.

Preferably the group 1 metal stearate is sodium stearate, which is a known nucleant for polyethylene terephthalate and gives easier nucleation of the polyester. The nucleant is preferably used in an amount no more than 1% by weight of the composition, particularly in the range 0.1 to 0.7% by weight. However, if a finely divided solid nucleant is used it may be used in greater proportion, e.g.

when used alone, up to 6 parts by weight per 100 parts by weight total polymer, and may be used, if desired, in addition to a nucleant of the other type. When no fibrous reinforcement is employed however, the total amount of nucleant, including finely divided solid nucleant is preferably not more than 1.9 parts by weight per 100 parts by weight total polymer. It is to be noted that the maximum nucleation when using a finely divided solid type nucleant appears to be achieved at the same low levels as with the metal stearates, so that when more is used the excess functions as a filler.

The polycaprolactone is an aliphatic polyester which has a repeat unit of %CO-(CH2)5-O4, the end groups depending upon the initiator used to start polymerisation of the caprolactone. In the present invention, the caprolactone polymers have a number average molecular weight above 20,500, for example in the range 20,500 to 300,000 however, lower molecular weight polycaprolactones may additionally be included, e.g. those corresponding to n being in the range of 2 to 35, which gives material in the range of a liquid pre-polymer type to a waxy solid at room temperature.

Preferably the higher molecular weight polycaprolactones have a number average (N A) Molecular weight not greater than 100,000.

The amount of the higher molecular weight polycaprolactone in the composition will generally be at least 2.5 parts by weight per 100 parts by weight total polymer and may, if desired, be substantial e.g. up to 25 parts by weight per 100 parts by weight total polymer, but the amount of the lower molecular weight material, if used, is lower, e.g. up to 6 parts by weight per 100 parts by weight total polymer. (By 'total polymer' in this specification we mean the total of polyethylene terephthalate based polyester plus the higher molecular weight polycaprolactone).

The lower molecular weight polycaprolactone, when used in the composition, can be considered to be a plasticiser for the polyethylene terephthalate and can be replaced wholly or partially by other plasticisers. Such plasticisers include esters of aromatic acids or aromatic alcohols, such as dibenzyl adipate and neopentyl glycol dibenzoate, and polyethers such as polyethylene glycols. The total amount of plasticizer will be as indicated for the lower molecular weight polycaprolactone above, and preferably is in the range 1 to 4 parts by weight per 100 parts by weight of total polymer.

In examining the crystallisation behaviour of polyethylene terephthalate Differential Thermal Analysis (DTA) is used to measure (a) Recrystallisation temperature (Tr) (b) Second order glass transition temperature (Tg) and (c) Cold crystallisation temperature (Tc).

In DTA the sample and an inert reference sample are heated according to a predetermined temperature programme. Their difference in temperature (AT) and the sample temperature (T) are recorded as a function of time. Endothermic and exothermic changes in the sample such as melting and recrystallisation, give rise to peaks in the AT trace, and second order transitions, such as the glass transition, to shifts in the baseline.

Thus, (a) is measured by heating the polymer until it is molten and then cooling at a constant rate until recrystallisation occurs.

(b) and (c) are measured by melting the sample, quenching to a low temperature and then carrying out DTA with a constant heating rate.

For pure polyethylene terephthalate the Tr is about 1900 C, Tg is about 900C and Tc is about 1 600 C. In adding a nucleant and plasticizer etc. to the polyethylene terephthalate an objective is to raise Tr and to lower Tg and Tc, as well as to increase the rate of recrystallisation.

The invention will now be described more particularly by means of examples.

Examples Experimental procedures Compositions were prepared by melt processing, in a twin-screw extruder, all the ingredients being dry blended and compounded together. The glass was added to the molten polymer/additive mixture at a second port in the extruder. The polymer and other additives require careful drying to a very low moisture content (generally less than 0.02%).

The extruded material was cut and the granules dried to less than 0.02% moisture prior to injection moulding. In evaluating the moulding performance, the mould temperature is important. In the small-scale screening tests reported below, the mould temperature was varied and the ease of mould release and surface appearance of the moulding noted at each temperature. If the moulding stuck or its surface appearance was poor, the mould temperature was raised until these properties were satisfactory.

The molecular weight of the material was determined by dilution viscometry in o-chlorophenol at 250C using the relationship reported by Ward (Trans Faraday Soc. 1957, 53, 1406): [g]=1.7x10-4 Moo.83 Thermoanalytical measurements were made on extruded materials which had been remeltedat2900C and quenched by dropping into liquid nitrogen. The sample was examined by Differential Thermal Analysis (DTA) in a Stanton-Redcroft STA 780 simultaneous thermal analysis system: reference material-alumina; programme-heat at 1 00C/min to 3500 C, cool at 1 00C/min or the natural rate, whichever is the lower, to room temperature.

A DTA curve for a quenched specimen shows the glass transition (Tg), an exothermic secondary (or 'cold') crystallisation (Tc) and the melting endotherm (Tm) on heating, and recrystallisation from the melt (Tr) on cooling. The size of the secondary crystallisation peak and the temperature at which it occurs shows the effectiveness of the additives in promoting crystallisation: a small Tc peak (measured relative to the size of Tm), and low Tc and Tg temperatures indicate efficient crystallisation. Similarly, a high Tr indicates rapid crystallisation from the melt.

Example 1 Table 1 gives thermoanalytical data on samples of extruded polyethylene terephthalate containing varying amounts of the polycaprolactone CAPA 601 M (polycaprolactone with a NA molecular weight of 45,000-50,000 suppiied by Interox Chemicals Ltd).

Table 1 O/o Capa 601M 0 5 10 20 Te (OC) 137 131/118* 124/110* 110/103* Relative crystallinity (%) 30 37 26 29 *Double peak The relative crystallinity is an approximate guide to the amount of crystallinity present in the quenched sample before it is heated above the cold crystallisation temperature Tc.

(AmAc) Relative crystallinity (%)=1 00 Am Where Am=Area of melting endotherm A -Area of cold crystallisation exotherm The results in Table 1 show that addition of the polycaprolactone aione produced a marked fall in Tc of the polyethylene terephthalate, without any separate nucleant, such as sodium stearate, being present.

Examples 2 to 5 To further explore the effect of polycaprolactone with other additives on the Tc of the polyethylene terephthalate as used in Example 1 a series of compositions was made as described above to the following basic formulation: Polyethylene terephthalate (PET) 70 parts 3 mm glass fibre 30 parts Polycaprolactone as specified Sodium stearate The PET was a dull fibre-grade polymer with a limiting viscosity number of 0.54, i.e., molecular weight approximately 1 6,600, containing titanium dioxide as a delustrant.

Results Table II shows the temperature of the cold crystallisation peak (Tc) for a series of materials containing varying amounts of a polycaprolactone (CAPA 601 M ex Interox Chemicals Ltd) 0.5% by weight of sodium stearate, and 3.0% by weight of a polycaprolactone (CAPA 200 ex Interox Chemicals Ltd.) of N.A. molecular weight 550.

Table II %HigherM.W polycaprolactone Example No. by weight Tc 2 0 107 3 5 104 4 10 97 5 20 72 eft 84 (double peak) It will be appreciated from this that the presence of sodium stearate and the two polycaprolactones in the material has further lowered the temperature Tc to a considerable extent relative to Example 1.

Examples 6 to 8 Table Ill shows the compositions and physical properties of small scale test mouldings made from PET of the same type as before but containing orie or both of two grades of polycaprolactone namely CAPA 240 having a N.A. molecular weight of 4000 (ex. Interox Chemicals Ltd.) and CAPA 601 M as in Example 1 above. In the compositions the amounts of all the ingredients except the glass fibres are given as parts by weight, a composition containing no caprolactone is included for comparison. The content of glass fibres is given as a percentage by weight of the total composition in each case.

Table Ill Example No. 6 7 8 9 PET 100 90 90 100 CAPA601M 0 10 10 0 CAPA240 3 3 0 0 Sodium stearate 0.5 0.5 0.5 0.5 Percentage of glass fibres 37 26 29 29 Tensile strength MPa 132 127 119 122 Tensile modulus GPa 12.4 10.9 9.0 9.7 Elongation percentage 2.7 3.3 3.3 4.0 Table Ill (contd.) Flexural strength MPa 199 205 194 195 Flexural modulus GPa 10.4 10.3 8.6 8.4 Charpy notched Impact KJ/m2 8.2 1 1.8 12.5 6.8 Charpy unnotched Impact KJ/m2 22.0 32.0 31.0 22.6 Moulding performance All three materials of Examples 6, 7 and 8 respectively released from the mould at 1 000C, although with a poor surface.

At 1 050C mould temperature Example 6 gave one side of a Water absorption (WA) disc completely dull with considerable dullness on the other side. Example 7 at 101 OC mould temperature gave much less dullness but there were additional flow marks.

At 11 60C mould temperature Example 7 produced a glossy surfaced moulding and Examples 6 and 8 had 10% surface dullness at 1 50C mould temperature. In contrast Example 9 gave mouldings with 50% surface dullness at 11 9 C mould temperature.

The results of Example 8 are included to demonstrate that the additional plasticization of the lower molecular weight polycaprolactone gave a betterfinish: the appearance in Example 8, without the lower MW polycaprolactone is worse than that of Example 7. In conclusion, it may be seen that the inclusion of the higher molecular weight polycaprolactone in the compositions lowers the cold crystallisation temperature and gives improvement in impact strength over the use of the lower molecular weight material.

In all the following Examples compositions are quoted in parts by weight except the glass fibre contents which, where quoted, are quoted as percentages by weight of total composition.

Examples lotto 12 Table IV shows the compositions and physical properties of small scale test mouldings made from PET of the same type as before but containing only higher molecular weight polycaprolactones. In Example 11 and 12 the polycaprolactone used was the CAPA 601M as in Example 1 above but in Example 10 that used was CAPA 600M which is a polycaprolactone of N A molecular weight 25,000--30,000 also from Interox Chemicals Limited.

Table IV Example No. 10 11 12 PET 90 90 95 CAPA 601 M 0 10 5 CAPA 600M 10 0 0 Sodium stearate 0.5 0.5 0.5 % Glass fibres 27 32 34 Tensile strength MPa 112 123 131 Tensile modulus GPa 1 1.2 9.6 10.6 Elongation O/o 3.1 3.5 3.2 Flexural strength MPa 177 189 198 Flexural modulus GPa 8.5 9.2 9.7 Charpy impact Notched KJ/m2 11.3 12.5 8.1 Unnotched KJ/m2 30 33 27 Drop weight energy J 0.63 0.59 0.59 Mould temperature No data 990C 1 000C Surface finish on moulded disc about 50% one side was of surface dull the other was dull 50% dull Example 10 gave test mouldings with 10% of surface dull at a mould temperature of 1 130C.

Examples 11 and 1 2 both gave test mouldings with about 20% of surface dull at a mould temperature of 1 140C.

Examples 13 and 14 These examples show the use of other plasticizers in place of lower molecular weight polycaprolactone in PET compositions containing higher molecular weight polycaprolactone and sodium stearate. Table V shows the compositions and physical properties of small scale test mouldings as before. The PET used was the same as before, and the polycaprolactone was the CAPA 601 M as in Example 1. The amounts of ingredients are given in parts by weight.

Table V Example No. 13 14 PET 90 90 CAPA601M 10 10 Neopentyl glycol dibenzoate 3 0 dibenzyl adipate 0 3 Sodium stearate 0.5 0.5 % Glass fibres 30 26 Tensile strength MPa 112 103 Tensile modulus GPa 9.6 8.2 Elongation % 3.0 3.3 Flexural strength MPa 183 163 Flexural modulus GPa 9.5 7.5 Charpy impact notched KJ/m2 8.9 9.4 unnotched KJ/m2 > 25.1 22.4 Drop weight energy J 0.31 0.55 Mould temperature 100 C 990C Surface finish on moulded one side dull about 10% disc other side 50% dull of area dull Both these examples gave test mouldings whose surface was glossy at 11 50C mould temperature.

Examples 15to 18 These examples illustrate the use of a polycaprolactone of lower number average (N A) molecular weight as primary additive, with dibenzyl adipate (DBA) as plasticizer and sodium stearate as nucleant.

Small scale test mouldings were made as before and details of the compositions and physical properties of the mouldings made from them are given below in Table VI. The PET used was fibre grade polymer of 16,600 molecular weight and the polycaprolactone was the CAPA 600M of N A molecular weight 25,300--30,000.

Table VI Example No 15 16 17 18 PET 90 90 90 90 CAPA 600M 10 10 10 10 DBA 0 1 3 3 Sodium stearate 0.5 0.5 0.5 1.0 % Glass fibres 27 22 22 26 Mould temperature deg. C 115 105 105 100 Tensile strength MPa 112 90 83 77 Tensile modulus GPa 8.8 7.3 7.0 7.7 Elongation (% at break) 3.1 2.7 2.9 2.5 Flexuralstrength MPa 177 159 144 129 Flexural modulus GPa 8.5 7.3 6.9 7.4 Charpy notched impact KJ/m2 ~ 113 6.7 6.1 6.4 Charpy notched impact KJ/m2 30 21 18 14 There was variation in glass content in these small scale experiments which was the cause of much of the drop in mechanical properties between Examples 15 and 16. The mould temperature quoted is that required to achieve a glossy-surfaced moulding.

Examples 19 to 21 These examples investigate the effect upon mould temperature achieved by varying content of a plasticizer (dibenzyl adipate). The PET used was the fibre grade (M.W. 1 6,600), the polycaprolactone was CAPA 601 M (N.A Mol. Wt. 45.000--50.000) and small scale test mouldings were made as before. Table VII below gives details of the compositions and the physical properties of the mouldings made from them.

Table VII Example No. 19 20 21 PET 90. 90 90 CAPA601M 10 10 10 DBA 0 3 6 Sodium stearate 0.5 0.5 0.5 % Glass fibres 29 26 23 Mould temperature OC 115 110 105 Tensile strength MPa 119 102 89 Tensile modulus GPa 9.0 8.8 6.9 Elongation % 3.3 2.8 3.1 Flexural strength MPa 1 94 169 151 Flexural modulus GPa 8.6 8.6 6.8 Charpy notched impact KJ/m2 12.5 8.0 7.7 Charpy unnotched impact KJ/m2 > 25 20 16 It should be noted that in this series of Examples the variation in glass content is not sufficient to have appreciable effect on mould temperature, although it would affect the physical properties of the mouldings. Use of the plasticizer improves the mould temperature but reduces the physical properties of the mouldings.

Examples 22 and 23 These two Examples offer a direct comparison between two different grades of PET using the same amounts of polycaprolactone, (CAPA 601 M of N.A. Mol. Wt. 45,000-50,000) dibenzyl adipate, sodium stearate and glass. To ensure identical proportions of glass these compositions were pre-mixed and all fed into a small scale compounding extruder at one port. This, however, has a detrimental effect on physical properties of the mouldings so that the figures are not comparable with other examples.

Details of the compositions and physical properties of mouidings therefrom are included in Table VIII below.

Table Vlil Example No. 22 23 PET type Fibre Bottle Molecular weight 17,000 27,000 PET 90 90 CAPA601M 10 10 DBA 3 3 Sodium stearate 0.5 0.5 %Glassfibres 30 30 Mould temperature CC 110-115 110-115 Tensile strength MPa 95 106 Elongation % 5.1 5.7 Flexural strength MPa 162 188 Flexural modulus GPa 8.3 8.6 Charpy notched impact KJ/m2 6.4 8.3 Charpy unnotched impact KJ/m2 22 36 It will be noted that the minimum mould temperature for glossy surfaced mouldings is the same for both compositions but the physical properties of the mouldings are better when using the higher molecular weight PET.

Examples 24 to 26 In these Examples the PET is used in compositions without fibrous reinforcement and the effect of the high molecular weight polycaprolactone is illustrated.

The compositions were made up and tested on a small scale as before, details of composition and properties of mouldings being given in Table IX below.

Table IX Example No. 24 25 26 PET 100 90 80 CAPA 601 M 0 10 20 Sodium stearate 0.5 0.5 0.5 Tensile strength MPa B 32* 52 55 FlexuralstrengthMPa 97B 818 71cD Flexural modulus GPa 3.1 2.6 2.3 Charpy notched impact KJ/m2 3.3 5.1 8.1 Charpy unnotched impact KJ/m2 11 1 6 70 Mould temperature OC 120 103 105 Appearance dull glossy mottled Release sticking good poor B=at break CD=conventional deflection *=badly voided specimen At the addition level of 1 0 parts by weight per 1 00 of total polymer the polycaprolactone has dramatically improved the mouldability of the nucleated PET of Example 24.At the higher addition level the mouldability is still improved over Example 24 and impact strength is still further improved over Example 25 but the surface of the mouldings is mottled and the mould release is poor at this mould temperature.

Examples 27 to 29 In these Examples compositions were made up using PET of fibre grade (Mol. Wt. 16,600), glass fibre, sodium stearate and two different polycaprolactones, one example containing no polycaprolactone to act as control.

In previous examples the glass fibres have all been 3 mm chopped strand but in this case the glass was a continuous roving which was fed into a second (downstream) port on a twin screw Werner and Pfleiderer compounding extruder and broken up as the composition was being compounded.

The details of the compositions and properties of test mouldings are given below in Table X.

Table X Example No 27 28 29 PET 90 100 90 CAPA type 600M - 601 M Pts. weight of CAPA 10 0 10 Sodium stearate 0.5 0.5 0.5 % Glass fibres 27 26 26 Tensile strength MPa 114 87 117 Tensile modulus GPa 9.7 8.4 10.4 Charpy notched impact KJ/m2 7.5 5.2 7.6 CharpyunnotchedimpactKJ/m2 20 13 19 The mechanical properties are taken from materials all moulded at 1100. The compositions containing the polycaprolactones show greatly improved mechanical properties.

The relative moulding performance of the three compositions was investigated using varying mould temperatures on the injection moulding machine. Gloss of the mouldings was also measured using an Eel Varispec Gloss Head with a 450 angle of incidence and reflectance. The monitoring Oialvanometer was set at 100% for the glass base plate and 2" disc mouldings examined on both sides.

Fibre discs were measured for each composition and the average taken to give the percentage figures shown in Table XI below.

Table XI Example Mould temperature (OCI No. 700--105 110--115 120-125 130-135 27 dull glossy sticking easy release 21% 31% 28 dull 8 rough dull 8 rough dull glossy not sticking sticking sticking sticking 7% 13% 26% 35% 29 dull glossy sticking easy release 16% 29% Examples 31 to 35 These Examples illustrate the use of an alternative nucleant, the nucleant chosen being a finally divided solid-microtalc of mean particle diameter 0.75 microns, 99% being less than 10 microns in diameter. The compositions were made up and test mouldings produced on a small scale using 3 mm chopped glass strand as before.Examples were made up using two different grades of PET, fibre grade of Mol. Wt. 16,600 and bottle grade of Mol. Wt. 24,000 with and without a polycaprolactone CAPA 601 P (ex. Interox Chemicals Ltd.) of N.A. molecular weight 45,000-50,000.

Details of the compositions and of test mouldings made therefrom are given below in Table XII.

Table XII Example No. 31 32 33 34 35 PET grade Fibre Bottle Fibre Bottle Bottle PET 100 100 90 90 95 CAPA 601 P 10 10 10 5 Talc 5 5 5 5 5 % Glass fibres 30 30 30 30 30 Tensile strength MPa 107 115 97 107 113 Tensile modulus GPa 10.5 10.2 10.4 10.2 10.5 Elongation (%) 1.9 2.1 1.7 2.2 2.9 Flexural strength MPa 180 197 166 181 173 Flexural modulusGPa 10.0 9.8 8.7 9.1 9.7 Charpy notched Impact strength KJ/m2 6.4 7.6 9.5 12.7 11.7 Charpy unnotched Impact strength KJ/m2 25 38 35 41 41 Temperature for gloss > 130"0 > 130"0 1200C 120"0 1300C Release very poor very poor excellent excellent excellent All materials were made by 'combined feeding' as used in Examples 22 and 23.

Examples 36 to 41 These-Examples illustrate the effect on moulding performance and impact strength of varying the amount of high molecular weight-polycaprolactone (CAPA 601 M) in PET compositions. The PET was the fibre grade and the combined feeding method was used to ensure consistent glass fibre content (as in Examples 22 and 23).

Details of the compositions and impact strengths and moulding performance are given below in Table XI II.

Table Xlil Example No 36 37 38 39 40 PET 100 95 90 80 70 Capa 601M 5 5 10 20 30 Sodium stearate 0.5 0.5 0.5 0.5 0.5 % Glass fibres 20 20 20 20 20 Charpy notched Impact strength KJ/m2 4.3 4.3 6.9 8.1 5.2 Charpy unnotched ImpactstrengthKJ/m2 12 14 25 23 14 Temperature for gloss OC 130 124 119 ca 108 - Release very poor excellent excellent acceptable very poor It will be noted that the moulding performance is greatly improved by the 5 and 10 parts additions of polycaprolactone but then the mould release characteristics begin to deteriorate again.

Gloss measurements were carried out on Examples 36 to 38 using the Eel Varispec Gloss Head as before.

The results of these measurements are given below in Table XIV.

Table XIV Example No. Mould temperature Gloss 36 1200C 30% 37 1200C 39% 38 1100C 31% Examples 41 to 43 These examples illustrate the improvement in moulding characteristics obtainable with low molecular weight plasticizers, although with some deterioration in physical properties. The combined feeding was used for the glass fibres as in Examples 22 and 23. Details of the compositions and the properties of the test mouldings made therefrom are given in Table XV below.

Table XV Example No. 41 42 43 PET 90 90 90 Capa 601M 10 10 10 Dibenzyl azelate - 3 PET6000 - - 3 Sodium stearate 0.5 0.5 0.5 % Glass fibres 20 20 20 Tensile strength MPa 91 63 66 Tensile modulus GPa 6.3 6.4 6.6 Elongation % 2.2 1.3 1.2 Flexural strength MPa 134 102 108 Flexural modulus GPa 6.5 6.5 6.3 Charpy notched Impact strength (KJ/m2) 6.9 4.5 4.9 Charpy unnotched Impact strength (KJ/m2) 25 10 11 Temperature for gloss (OC) 119 111 111 Release (excellent) (excellent) (excellent) PEG 6000=Polyethylene glycol, molecular weight 6000 Examples 44 to 46 These Examples illustrate the effect of increasing the amount of reinforcing fibre in the composition.The PET used as bottle grade of molecular weight 24,000, and glass was added by feeding rovings into a second port on a compounding extruder as in Examples 27 to 29. Details of the compositions are given in Table XVI below, together with the physical properties of test mouidings made therefrom. In Examples 44 and 45 an assessment of heat distortion temperature was also made using BS 2782 Part 1 Method 121 A as the test method. The results of this are also indicated in the Table XVI, the mouldings for this test being moulded at 850C.

Table XVI Example No. 44 45 46 PET 90 90 90 CAPA601M 10 10 10 Sodium stearate 0.5 0.5 0.5 Glass fibres (%) 15 30 45 Tensile strength MPa 88 128 182 Tensile modulus GPa 5.8 9.7 16.2 Elongation at break (%) 2.0 2.2 2.0 Flexural strength MPa 135 1 96 239 Flexural modulus GPa 5.7 9.2 12.9 Charpy notched Impact strength KJ/m2 7.5 9.9 12.3 Charpy unnotched Impact strenath KJ/m2 18 29

Mould temperature (OC) 1 All three materials had a Release t glossy surface molded at J 1200C and easy release Heat distortion temp (OC) > 182 > 182

Claims (17)

Claims

1. A polyester moulding composition comprising polyethylene terephthalate or a polyester containing at least 80% by weight of polyethylene terephthalate repeating units, polycaprolactone and a nucleant for crystallization of the polyethylene terephthalate and optionally reinforcing fibres, the polycaprolactone having a number average molecular weight of above 20,500, and the amount of nucleant being not greater than 6 parts by weight per 100 parts by weight total polymer when reinforcing fibres are present but not greater than 1.9 parts by weight per 1 00 parts by weight total polymer when no reinforcing fibres are present.

2. A composition according to claim 1 comprising reinforcing fibres in which the amount of reinforcing fibres is in the range 5% to 55% by weight of the composition.

3. A composition according to claim 2 or 3 in which the reinforcing fibre is glass fibre.

4. A composition according to any one of claims 1 to 4 in which the amount of said polycaprolactone of molecular weight above 20,500 is in the range 2.5 to 25 parts by weight per 100 parts by weight of total polymer.

5. A composition according to any one of claims 1 to 4 in which said polycaprolactone has a number average molecular weight of not more than 100,000.

6. A composition according to any one of claims 1 to 6 which includes also up to 10 parts by weight per 100 parts by weight total polymer of a plasticizer for the polyethylene terephthalate.

7. A composition according to claim 6 in which the plasticizer is selected from esters of aromatic acids or aromatic alcohols and polyethers.

8. A composition according to claim 7 in which the plasticizer is at least one of dibenzyl adipate, dibenzyl azelate, polyethylene glycol and neopentyl glycol dibenzoate.

9. A composition according to claim 6 in which the plasticizer is a polycaprolactone haying a number average molecular weight below 10,000.

10. A composition according to any one of the preceding claims in which the nucleant comprises metal salt of an organic acid or a finely divided material which does not melt at or below the melting point of polyethylene terephthalate.

11. A composition according to claim 10 in which the nucleant comprises a metal salt of an organic acid which is present in an amount not greater than 1% by weight of the composition.

12. A composition according to claim 12 in which the nucleant is a Group 1 metal stearate.

13. A composition according to claim 12 or 13 in which the amount of nucleant is in the range 0.1 to 0.7% by weight of the composition.

14. A composition according to claim 11, 12 or 13 in which the nucleant is sodium stearate.

1 5. A composition according to claim 10 in which the nucleant is a talc having a particle size below 20 microns.

16. A composition substantialiy as described herein in any one of Examples 3 to 5, 7, 8, and 11 to 14.

17. A composition substantially as described herein in any one Examples 15 to 23, 25 to 27, 29, 33to35,37to39and41 to 46.