PRESSURE-TUBE OF VINYLCHLORIDE PLASTIC

Abstract: Described is the use of a tube of plastics on the basis of a vinylchloride polymer whereby the tube has been given a ductile fracture behaviour in the test for establishing the fracture toughness thereof. The ductile fracture behaviour is provided by the addition to the plastic of 0,3-4 wt.% of an agent which influences the fracture behaviour which may be chosen from agents which are known per se and which improve the notched impact toughness. Also is described a pressure pipe from such plastic and a tube for use in such a pressure pipe.

Description: Pressure-tube of vinylchloride plastic, The invention relates primarily to a tube of thermoplastic material based on a vinyl chloride polymer. Such tubes are produced on a large scale by extruding polyvinyl chloride to which additives which have been extensively described in the relevant literature have been added in connection with processing and later use. The requirement that such tubes have a good fracture toughness in order to reduce the risk of a tube fracture when such a tube is used in the buried state as a transport pipe for, for example, pressurized water, is being imposed to an increasing extent in the use of such tubes manufactured from plastic material. British Standard Specification BS 3505: 1986 discloses an instruction for measuring the fracture toughness of a tube made of unplasticized polyvinyl chloride. In the measurement procedure described therein, a distinction is made between the fracture toughness as such ( Kc ) and the fracture toughness which has been corrected for dimensional effects of the sample (Kic). I n relation to the performance of the measurement , reference is made to the British Standards Institution document described above. The object of the present invention is to provide a tube of thermoplastic material based on vinyl chloride which has an increased fracture toughness, as a result of which such a tube becomes suitable for use as a pressure pipe without at the same time, however, making use of exceptionally large wall thicknesses. The applicant has carried out extensive experiments in order to establish the influence of the plastics composition and the process conditions in the maπufacturing of objects of PVC on the KiC value. It has been found that in general the KiC value of tubes which have been manufactured from a conventional PVC composition will be sufficiently high in order to meet the above mentioned British Standard. In the measurement of the KiC value according to this standard it appears, however, that the conventional PVC compositions show a substantially brittle fracture behaviour which puts the use of PVC tubes for transporting pressurised gaseous or liquid media at a disadvantage as this behaviour renders the use of high safety factors for determining the wall thickness necessary. The present invention therefore has as an objective to render possible the use of tubes out of thermoplastic material on the basis of a vinylchloride polymer for transporting pressurised media with an increased safety with respect to fracture. Surprisingly it has now appeared that such an application is possible if to the plastic from which the tube is manufactured, in addition to optional other conventional additives, 0,3-4 wt.% of a fracture behaviour influencing agent is added by which the fracture behaviour upon determination of the fracture toughness of the finished tube appears to be substantially ductile in comparison to the fracture behaviour of a tube of the same plastic to which said agent has not been added and whereby the finished tube shows a fracture behaviour which is substantially brittle. In the investigations carried out by applicant it appeared that the agents which influence the fracture behaviour belong inter alia to a group of agents which improve the notched impact strength which are known per se for example from EP-A-0 224 913. The use of such agents has however only a measurable effect with use of a content of at least about 5% as has been described in Polyvinylchlorid, Kunststoff Handbuch (2), 1985 (c) 1986, Carl Hanser Verlag p.p. 714, 715. As examples within the scope of the present application are mentioned chlorinated polythene, chlorinated polythene-vinyl chloride graft polymers, ethylene-viny1 acetate copolymers, ethylene-vinyl acetate/ vinyl chloride graft copolymers, polyacrylic acid ester/ vinyl chloride graft polymers, acrylic ester/methyl methacrylate graft polymers, methyl methacrylate-butadiene- styrene graft polymers, acrylonitrile - butadiene-styrene terpolymers etc; many other compounds are, however, known and may be applied within the scope of the present invention. Upon addition of an agent of the above described type which influences the fracture behaviour in the amount indicated to the PVC composition of which a tube is manufactured it appears that the fracture behaviour in the determination of the fracture toughness according to the earlier mentioned British Standard specification is changed from substantially brittle to substantially tough while at the same time no or only a very slight decrease in yield point stress occurs while the KiC value remains sufficiently high, i.e. greater than about 4. This implies that the use of such tubes for transportation of pressurised media in gaseous or liquid form is possible with an increased safety with respect to fracture. It may even be possible, by the occurrence of a trough fracture, to use lower safety coefficients such that PVC tubes may become available for pressure use having a smaller wall thickness than is now conventional under the same conditions. In respect of the amount of agent which influences the fracture behaviour it is observed that approximately two ranges of addition may be distinguished: Addition % Fracture Yield strength 0,5-1 wt.% substantially ductile about normal 1 -3 wt.% ductile slight decrease The invention is also embodied in a pressure pipe for transporting pressurised media which pipe is manufactured from plastics tube of thermoplastic material on the basis of a vinylchloride polymer which is characterised in that to the plastic, in addition to other conventional additives 0,3-4 wt.% of an agent which influences the fracture behaviour is added by which the fracture behaviour, upon determining the fracture toughness of the finished tube, is substantially ductile in comparison to the fracture behaviour of a tube from the same plastic to which said agent has not been added and whereby the finished tube shows a fracture behaviour which is substantially brittle. The amount of agent which influences the fracture behaviour amounts in particular to 0,5-1 wt.% with respect to the total amount of plastic for obtaining a substantially tough fracture and preferably 1-3 wt.% for obtaining a 100% tough fracture upon use of for example acrylate (PVC-A). The invention comprises also a tube for use in a pressure pipe as has been described hereinbefore. The tube is made from a vinylchloride polymer and this plastic comprises 0,3-4 wt.% of an agent which influences the fracture behaviour, such that a substantially tough fracture is observed, the agent being a notched impact strength influencing agent. The invention will now be illustrated with use of an example. Fracture toughness tests were carried out with tubes of PVC having a diameter of 160 mm and a wall thickness of 7,7 mm (160x7,7 mm). As agent which influences the fracture behaviour use was made of a graft polymer of vinylchloride and acrylate ( VC-A) . The results were as follows: 3/2 Acrylate wt.% KiC (N/mm ' ) Type of Yield strength 2 surface of N/mm fracture % ductile 0 0.5 1 1.5 2.5 In the above-mentioned table the percentages brittle and ductile have been determined visually. The brittle part shows a surface of fracture which is approximately undeformed, the ductile to the contrary shows a surface of fracture having flow phenomena. It is observed that upon addition of PVC-A to PVC the fracture behaviour changes from substantially brittle to ductile. In the table a 100% ductile fracture is observed at 2,5 wt.% acrylate; in dependence of the additive used and other circumstances such as process conditions also at lower amounts a 100% ductile behaviour may be observed. Also upon use of chlorinated polythene (CPE) as additive upon determination of the fracture behaviour results were obtained which are nearly identical to the results which have been shown in the table above.

Claims: Cl aims 1. Use of a tube out of thermoplastic material on the basis of a vinylchloride polymer for transport of a pressurised liquid or gaseous medium, whereby to the plastic, in addition to other conventional additives 0,3-4 wt.% of an agent which influences the fracture behaviour is added by which the fracture behaviour upon determination of the fracture toughness of the finished tube is substantially ductile in comparison to the fracture behaviour of an identical tube out of the same plastic to which said agent has not been added and whereby the finished tube shows a substantially brittle fracture behaviour. 2. Use according to claim 1, characterised in that the agent with which the fracture toughness has been increased has been chosen from the group of agents which improve notched impact strength, such as chlorinated polythene, chlorinated polythene-vinyl chloride graft polymers, ethylene-vinyl acetate copolymers, ethylene-vinyl acetate/vinyl chloride graft copolymers, polyacrylic acid ester/vinyl chloride graft polymers, acrylic ester/methyl methacrylate graft polymers, methyl methacrylate-butadiene-styrene graft polymers, acrylonitrile - butadiene-styrene terpolymers etc. 3. Use according to claim 1 and 2, characterised in that to the plastics 0,5-1 wt.% of an agent which influences the fracture behaviour is added. 4. Use according to claims 1 and 2, characterised in that to the plastics 1-3 wt.% of an agent which influences the fracture behaviour is added. 5. Pressure pipe for transporting pressurised media which pipe has been manufactured from thermoplastic material on the basis of a vinylchloride polymer, characterxsed in that to the plastic in addition to other conventional additives 0,3-4 wt.% of an agent which influences the fracture behaviour is added by which the fracture behaviour, upon determination of the fracture toughness of the finished tube, is substantially ductile in comparison to the fracture behaviour of an identical tube from the same plastic to which said agent has not been added and whereby the finished tube shows a substantially brittle fracture behaviour. 6. Pressure pipe according to claim 5, characterised in that to the plastic 0,5-1 wt.% of an agent which influences the fracture behaviour is added. 7. Pressure pipe according to claim 5, characterxsed in that to the plastic 1-3 wt.% of an agent which influences the fracture behaviour is added. 8. Tube of plastic on the basis of a vinylchloride polymer to be used in a pressure pipe according to any of the claims 5, 6 or 7.

Inventors: NAAKTGEBOREN AART JACOB, NAAKTGEBOREN, AART, JACOB
Applicants: WAVIN BV, WAVIN B.V.
Application year: 1989
Main classification: F16L9
IPC codes: B29D23, C08L23, C08L27, C08L29, C08L51, C08L55, F16L9