The invention is concerned with plastics molding materials, and particularly moulding materials based on thermoplastics.
Certain thermoplastics materials such as polystyrene and styrene-acrylonitrile copolymer (SAN) have excellent moulding properties but are brittle so that the impact resistance of articles moulded from them is not good.
It is well known that brittle thermoplastics polymers such as polystyrene and SAN can be rendered less brittle by incorporation therein of rubber. This so called "toughening" can increase the impact strength over untreated polymer by a factor of from 2 to 6. However, it has been found that when the impact strength is increased in this way there is an accompanying undesirable decrease in strengths and moduli, which may be up to 50% lower than those of the unmodified polymer.
In German Offenlegungschriften Nos. 2,633,501 and 2,744,593 we described moulding compositions comprising thermoplastics materials, a reinforcing filler which is either glass fibres or mica, and a minor proportion of a polyimide prepolymer, which is capable of thermosetting. The polyimide prepolymers concerned are addition polymers and their preparation is described in UK Patent Nos. 1,190,718; 1,355,401; 1,355,402; 1,355,403; 1,355,405; 1,355,406 and 1,355,407.
The effect of the polyimide prepolymers in these compositions is to increase strength and impact resistance of mouldings produced therefrom.
US Patent No. 3,717,615 discloses polymer compositions based on a mixture of a mono-imide of specified general formula and a bis-imide of specified general formula. It also discloses that the mono-and bis-imides can be co-reacted with various thermoplastics during copolymerisation of the imides and that the resulting compositions may be compounded with fillers including glass fibres, and with synthetic rubbers. The polyimides prepared in this specification are, however, the basis of the compositions described, and the final product in each case is a thermoset material. Where thermosplastics materials are used, their proportion is less than that of the mixture of imides and they are co-reacted in the polymerisation of the imides.
US Patent No. 3,678,075 discloses reacting an organic diamine with an aliphatically unsaturated dicarbonyl reagent in a solvent system to produce a polyimide by a condensation reaction. The polyimide is said to be able to be employed in combination with various thermoplastics polymers and can be compounded with fillers including glass fibre. The compositions disclosed are thermosetting, and the polyimide is not an addition polymer, nor is the inclusion of rubbery polymers in the compositions disclosed.
According to the invention there is provided a thermoplastic moulding material comprising a styrene-acrylonitrile copolymer containing a ratio of styrene to acrylonitrile in the range 85:15 to 60:40 by weight, and having a melt flow index (MFI) of 2 to 25 g/10 mins at 230°C under a 5 Kg load, an elastomeric material having an elongation at break greater than the styrene-acrylonitrile copolymer, in an amount of 1 to 50% by weight of the moulding material, and a reinforcing filler comprising glass fibres or mica characterised in that the material also comprises a poly-imide pre-polymer being the reaction product of a polyamine and a bis-imide of an unsaturated carboxylic acid and being capable of reacting further to give a thermoset resin.
The test used for melt flow index of the styrene-acrylonitrile polymer as quoted above is BS2782-105C. Styrene-acrylonitrile copolymers of the description in the preceding paragraph are widely commercially available.
We have found that when an elastomeric material is incorporated into a reinforced styrene/acrylonitrile copolymer as toughening agent together with a polyimide prepolymer the impact strength of the composition is increased with less reduction of the strengths or moduli than would be expected in view of prior art methods of increasing the impact strength.
As previously stated the toughening agent is an elastomeric material having an elongation at break greater than the styrene/acrylonitrile copolymer. It is preferred that the elongation at break should be significantly greater than that of the styrene-acrylonitrile copolymer, for example at least 10 times as great. We have found that both sulphur vulcanisable rubbers and thermoplastic rubbers can be used, vulcanisable rubbers preferably being used in a substantially uncured or partially cured state. The toughening agent is included in an amount of from 1 to 50% by weight (based on the weight of the total composition) preferably from 1 to 30% and more preferably from 5 to 20%. The toughening agent preferably has a glass transition temperature below 20°C.
Preferred sulphur vulcanisable elastomeric materials are rubbers such as nitrile rubbers, polyacrylate rubbers and polyurethanes.
Preferred thermoplastic rubbers are block copolymers containing styrene e.g. block copolymers of styrene and butadiene, which have been found particularly useful in the compositions of this invention although other thermoplastic rubbers such as polybutylene have also been found effective.
The elastomeric material used must be compatible with the styrene/acrylonitrile copolymer i.e. able to be compounded with the SAN in a satisfactory manner, and should be an elastomer which improves the impact resistance of the copolymer when so compounded, in the absence of other materials.
The polyimide prepolymer is preferably incorporated in an amount of from 0.1 to 10% by weight (based on the weight of the total composition) more preferably 0.5% to 5.0% by weight. Polyimides which can be used are described, inter alia, in British Patent Specifications Nos. 1,190,718; 1,355,401; 1,355,402; 1,355,403; 1,355,405; 1,355,406 and 1,355,407, and are believed to be formed by an addition reaction between the polyamine and the unsaturated bis-imide, rather than by a condensation reaction, the latter being the case with other polyimides.
It is preferred that the polyimide prepolymer is the reaction product of a primary diamine containing not more than 30 carbon atoms and an N,N' bis imide of general formula
Preferably the primary diamine is an aromatic compound, e.g. containing at least one phenylene group. A preferred compound is the compound of formula
Preferably the radical D in the N,N' bis imide is derived from an a;/3 unsaturated dicarboxylic acid such as maleic acid. The radical A is preferably an aromatic radical containing at least one phenylene group such as
The number average molecular weight of the prepolymer is preferably no more than 5000. In the polyimide the molar ratio of bis-imide to polyamine is preferably in the range 1.2 to 1 up to 50 to 1, more preferably in the range 1.2 to 1 up to 2.9 to 1.
The amount of filler present preferably does not exceed 50% by weight of the total composition and preferably is not less than 15 per cent. The particularly preferred range is 20 to 40 per cent by weight of the total composition.
The composition may optionally also include one or more other additives such as antioxidants, flame retardants, blowing agents, antistatic agents and pigments.
These should not be added in such quantities, however, that the proportion by weight of styrene/acrylonitrile copolymer in the total moulding material falls too low for the composition to have satisfactory thermoplastic flow properties. Preferably the composition contains at least 30% by weight of styrene/acrylonitrile copolymer.
The composition can be prepared by any suitable method such as by milling, extrusion, injection moulding all of which are known per se. The order in which the components of the composition are compounded together is not important. For example the polyimide prepolymer can be added to the base polymer and the resultant mixture combined with the toughening agent. Alternatively the polyimide prepolymer can be added to the toughening agent and the resultant mixture combined with the base polymer. When a filler is present the polyimide prepolymer can be applied as a dressing to the filler prior to incorporation of the filler into the composition i.e. when glass fibre is used the polyimide prepolymer may be used in a dressing for the glass fibres.
The following series of comparative Examples further illustrate the invention. In the Examples all percentages are by weight of total composition unless otherwise stated, and the words "Kerimid", "Krynac", "Flammex", "Perbunan", "Hycar", "Chemigum", "Paracril", "Elastothane", "Carifiex", "Solprene" and "Hytrel" used therein are Registered Trade Marks in the United Kingdom.
A composition consisting of styrene/acrylonitrile copolymer marketed by Monsanto as "QE 1044", 30% (based on the total composition) of glass fibre marketed by TBA Industrial Products, as "ECR 1346", 2% of a polyimide prepolymer derived from an aromatic diamine and a bis-maleimide marketed by Rhone Poulenc SA as "Kerimid 601" and 5% nitrile rubber marketed by Polysar as "Krynac 802" was produced by compounding the constituents in a twin screw extruder. The nitrile rubber has an acrylonitrile content of 28% and was added as uncured crumb.
The materials were compounded on a twin-screw extruder at barrel temperatures of 200°C, 125°C, 125°C and 190°C (die) and the extruded composition was chopped into pellets.
The resultant material was formed into test bars by injection moulding using conventional moulding conditions for reinforced styrene/acrylonitrile copolymer (220/250°C barrel temperatures). The test bars were tested for tensile strength, tensile modulus, flexural strength, flexural modulus and impact strength. The results are shown in the following Table 1.
The same procedure was followed as in Example 1 save that the amount of nitrile rubber was increased to 10% (Example 2) and 15% (Example 3). The products were tested and the results are set out in the Table 1.
A composition was made in the same manner as in Example 1 except that both "Kerimid 601" and the nitrile rubber "Krynac 802" were omitted. Test bars formed from the composition by injection moulding were tested for the same properties as in Example 1. The results are set out in Table 2.
A composition was made in the same manner as in Example 1 except that the nitrile rubber "Krynac 802" was omitted.
Test bars formed from the composition by injection moulding were tested. The results are shown in Table 2.
A composition was made in the same way as in Example 1 but "Kerimid 601" was omitted. The results of tests made on test bars formed from the composition are shown in the Table 2.
A series of compositions of increasing glass fibre content were prepared each containing the styrene/acrylonitrile copolymer of Example 1. For comparison, compositions of corresponding glass content were prepared in which 2 parts SAN by weight per 100 of composition were replaced by the polyimide prepolymer KERIMID 601; further compositions of corresponding glass content were prepared in which 15 parts of SAN per 100 of composition were replaced by the nitrile rubber KRYNAC 802; and further compositions of corresponding glass content were prepared in which 17 parts of SAN by weight per 100 of composition were replaced by 2 parts by weight of the polyimide prepolymer KERIMID 601 and 15 parts by weight of the nitrile rubber KRYNAC 802.
Compounding was carried out as in Example 1 and then test samples were injection moulded and tested as before.
The physical properties of the samples so obtained are tabulated in Tables 3, 4, 5 and 6 each Table representing comparative results at a particular glass content. In these Tables, for brevity, the polyimide prepolymer is represented by "PI" and the nitrile rubber by "R".
It will be noted that at each glass content the addition of the polyimide prepolymer alone gives some improvement in tensile, flexural and impact strengths. The addition of the nitrile rubber alone has a beneficial effect on impact strength but is detrimental to flexural strength in particular. The addition of both the polyimide prepolymer and the nitrile rubber gives a massive improvement in impact strength but also has very little effect on tensile or flexural strength despite the massive loss of flexural strength caused by addition of rubber alone (see particularly Tables 5 and 6).
These examples show that the invention can be used in a composition in which another filler and flame retardants are present in addition to glass fibres.
A composition was prepared by compounding together the following ingredients in a twin-screw extruder in the same manner as described in Example 1. The ingredients were 60 parts by weight of styrene/acrylonitrile copolymer (Monsanto QE 1044 as in Example 1), 15 parts by weight of glass fibres, (ECR 1346 as in Example 1) 15 parts by weight of talc and 10 parts by weight of fire retardants. The fire retardants consisted of a 3:1 w/w mixture of decabromobiphenyl (Flammex B10 commercially available from Berk Ltd.) and Antimony Trioxide.
Three comparable compositions were prepared by respectively replacing (i) 2 parts of the styrene/acrylonitrile copolymer (SAN) by 2 parts of the polyimide prepolymer KERIMID 601, (ii) 15 parts of the SAN by 15 parts of PERBUNAN N2810 (a nitrile rubber containing 28% by weight of acrylonitrile and commercially available from Farbenfabriken Bayer AG) and (iii) 7 parts of SAN by 2 parts of the KERIMID 601 and 5 parts of the PERBUNAN N2810.
Test mouldings were made from these compositions as before and the results of physical testing and fire testing of the mouldings are given below in Table 7. In this table the polyimide prepolymer is referred to as "Pl" and the nitrile rubber as "R".
These examples investigate the effect of curing the rubber before it is compounded into the composition.
Four compositions were prepared using SAN and glass fibre as used in Example 1. Each composition contained 30% by weight of glass fibre.
Two compositions contained 5% by weight of a nitrile rubber (KRYNAC 802) one having uncured rubber incorporated into it and the other having cured rubber incorporated into it. The other two compositions also contained 5% of uncured and cured rubber respectively but additionally contained 2% by weight of the polyimide prepolymer KERIMID 601. In each case SAN made up the whole of the balance of the composition.
The compounding was carried out in a twin screw extruder under the same conditions as in Example 1, and test mouldings were injection moulded from each of the four compositions.
The cured rubber was a compounded rubber in which the following formulation was compounded on a mill and press cured for 10 minutes at 150°C in sheets 1.5 mm thick. Under these conditions the rubber was substantially fully vulcanised i.e. 95% of available cross linking sites used up.
The rubber formulation was:-
The physical properties of the mouldings from the four different compositions are given below in Table 8 in which cured rubber is signified by "CR", uncured rubber by "UR" and the polyimide prepolymer by "PI".
These results show that the same sort of advantage is obtained when the polyimide prepolymer and cured rubber are used as when the polyimide prepolymer and uncured rubber are used. However, the cured rubber is less effective than the uncured rubber in improving the impact strength of the glass filled SAN. (These Examples may be compared directly with Example 4 (Table 2) which gives the properties of the glass/SAN without additives).
The following examples illustrate the use of the invention with various kinds of commercially available synthetic rubbers. In every case the composition was compounded as in Example 1, using the same type of SAN, glass fibre and polyimide prepolymer as in Example 1, to the following formulation: Glass fibre 30 parts by weight, polyimide prepolymer 2 pbw, Rubber 5 pbw and SAN 63 pbw.
Test mouldings were made as before by injection moulding, and the properties of the mouldings were measured.
The rubbers used in the various examples were as follows:-
- Example 31 - "HYCAR 1411", a nitrile rubber containing 41% by weight of acrylonitrile, the remainder being butadiene, commercially available from B.F. Goodrich. Used uncured.
- Example 32 - "HYCAR 1422", another nitrile rubber, containing 33% by weight acrylonitrile, available from B.F. Goodrich and used uncured.
- Example 33 - "CHEMIGUM N8B" a nitrile rubber containing 32% by weight acrylonitrile, available from Goodyear, and used uncured.
- Example 34 - "PARACRIL D" a nitrile rubber containing 45% by weight acrylonitrile, available from Uniroyal and used uncured.
- Example 35 - "ELASTOTHANE 640" a polyurethane rubber, sulphur vulcanizable available from Thiokol Chemical Corporation. Used uncured.
- Example 36 - "CARIFLEX TR1 102" a thermoplastic rubber available from Shell. This is an S-B-S block copolymer of polystyrene and polybutadiene.
- Examples 37 - "SOLPRENE 415" and "SOLPRENE 416", both thermoplastic rubbers available from
- and 38 Philips Petroleum. Both are block copolymers of styrene and butadiene containing respectively 40% styrene and 60% butadiene and 30% styrene and 70% butadiene.
- Examples 39 - "Polybutylene Grade 20" and "Polybutylene Grade 0.5", both thermoplastic rubbery
- and 40 polybutylenes available from CdF Chemie.
- Example 41 - "HYTREL 6345" a thermoplastic polyester elastomer available from Du Pont de Nemours.
- Example 42 - "CYANACRYL R" a sulphur vulcanizable polyacrylate elastomer available from American Cyanamid Company.
The physical test results obtained on the mouldings from the various compositions are given below in Tables 9 and 10.
As can be seen from these results, both the sulphur vulcanizable rubbers and the thermoplastic rubbers gave results showing improvement in impact strength without the accompanying loss of flexural strength which results from use of rubbers alone.
This series of Examples is comparable with Examples 4 and 5 (Table 2) which show the properties of the glass/SAN alone and with 2% of the polyimide prepolymer.