THE USE OF SURFACE-TREATED REINFORCEMENT MATERIAL FOR USE IN EXTRUSION AND INJECTION MOULDING OF THERMOPLASTICS

Abstract: Experience has shown that when fiberglass is added to plastic granulate in an extruder, the abrasive action of the fiberglass against the extruder walls and the screw will gradually cause wear damage in the extruder. According to the invention, such wear will be eliminated by the use of fibreglass which has been pre-coated with a suitable thermoplastic material. This is achieved by pre-heating chopped strand fibreglass, having a length of approx. 3 mm to 50-300<o>C. A thermoplastic granulate, with a grain size of between 5-100 mu m is thereafter blended with the hot coated fibreglass under agitation of the components. The thermoplastic granulate is thereby sintered to the surface of the fibreglass forming a coating which later acts as an efficient self-lubricating barrier between the fibreglass and the metal components in the extruder.

Description: The Use of surface-treated Reinforcement Material for Use in extrusion and injection moulding of Thermoplastics The present ivention relates to the use of pre-treated, chop¬ ped strand fibreglass made from-monofilament roving, and/or monofi . _nts, suitable for the reinforcement of thermo¬ plastic oducts to eliminate mechanical wear in processing machine- . and to result in a cleaner end product. It is well-known that the blending of solid additives with plastics results in a high rate of wear in the processing machinery. An article by H. Hermann: "Schneckenmaschinen fiir das Auf- bereiten von Kunststoffen", Kunststoffe 71 (1981), page 623 et seq. , describes how mechanical wear in processing machinery can be reduced by adding the fibreglass to.the plastic molt in the extruder. This practice reduces the rate of wear but does not eliminate it. The extruder will even¬ tually have to be replaced. To- avoid the high cost of com¬ plete extruder replacement, some extruders have replaceable units allowing wear-prone parts to be replaced individually. European patent application No. 0036097 describes a process in which fibreglass (monofilaments) , after leaving the spin¬ nerets, is fed into a tank containing a watery solution of polyolefine, silan and bis-maleic acid, whereby the surface of the fibreglass strands are coated, ensuring affinity between the fibreglass and plastic material in the finished product. After this pre-treatment of the fibreglass, and OMPI after it has been dried and is moisture free. It must be cut into chopped strand, and then dry-blended with the plastic compound in a known manner, at room temperature. This is a normal and well-known procedure in the plastics industry. The innovation concerns the use of bis-maleic plastic compound. West German patent No. 2,202,860 describes a method of pro¬ ducing fibreglass reinforced plastic sheeting in which the top layer consists of a special extruded blend of- 10 weight percent chopped strand and 90 percent plastic. This fibre- glass/plastic blend is produced by the usual process of dry blending before it is poured into the extruder hopper. U.S. patent No. 3,396,142 relates to a process in which fibreglass is blended with a solid thermoplasticpolymer in order to obtain certain properties in the finished product. The above patens have in common that they are based on the usual, known methods of dry blending fibreglass and plastic at room temperature. In these inventions the intention is to increase the affinity between fibreglass and plastic thereby increasing the mechanical strength of the finished products. This is an interesting approach in relation to the end pro¬ perties of the fibreglass reinforced plastic. However, the dry-blends described in the processes do not reduce the problem of wear in processing machinery. EPO patent application No. 0022165 describes a procedure for chopped strand fibreglass coating which is equivalent to the type of fibre used in this invention. Norwegian patent application No. 2042/72 describes a process for plastic coating of endless fibreglass monofilaments which are subsequently collected into endless ribbons of plastic coated fibreglass. The ribbons are then drawn through a heated tube where the plastic strand ' coating melts, and the strands are fused together. It is mentioned in the applica¬ tion that there is no apparent wear in the heated tube which per se is not surprising since the drawings indicate that the ribbon does not actually come into contact with the tube surface. Reference is also made to the fact that the use of fibreglass causes wear in extruders. It should be noted in this connection that only chopped strand fibreglass is used in extruders and injection moulding equipment, not roving as described in the above Norwegian patent. There is also a considerable difference between the tube described in the said patent application and an extruder. In an extruder, plastic and additives are subjected to high pressure and temperature when being screw-fed through the extruder and the material is in intensive contac ' t with the cylinder walls and the extruder screw. In the above mentioned tube process, the plastic/fibreglass mass is not screw-fed through the tube, but is drawn freely through by means of an external device. Neither is there any pressure in the tube when fibreglass roving is drawn through it, in contrast to an extruder or injection moulder. The intention, which is consistent with the present inven¬ tion, is to obtain a product either with wear-reducing pro¬ perties, or which will eliminate wear altogether, in proces¬ sing machinery. - . _ The term processing machinery is used above. This is mechani¬ cal equipment for the compression and melting of plastic com¬ pounds suitable for extruding or injection moulding. Tnus, in this context, processing machinery means extrusion and injec¬ tion moulding ' equipment for plastics. It now surprisingly appears that chopped strand fibreglass of suitable length, surface coated in accordance with the afore- OMPI IPO mentioned EPO patent application, can be used to advantage to prevent wear in plastic processing machinery. According to the said patent, such coated fibreglass is pro¬ duced by heating the chopped strand to 320°C and then blen¬ ding with PVC compound in a slow mixer, whereby the plastic is sintered to. the fibreglass strands. Reference is made to Example 1 in which this production sequence is described. The raw material used must be thermoplastic. Of such materials, polyamide, polycarbonate, polyacetates, polypropylene, poly¬ styrene, polyacrylnitrile-butadiene-styrene and polyvinyl- chloride are the most suitable for the purpose, but the inven¬ tion does not impose limits on choice of thermoplastic mate¬ rial. The only condition is that it must be thermoplastic. The fibreglass used is of the kind used for plastic reinforce¬ ment. It is usual to employ a type of fibreglass whose surface is specially treated by the supplier. Fibreglass is either supplied as roving (endless strands) or as chopped strand. For the production of reinforced plastic, 3 mm is usually con¬ sidered to be an acceptable length, but the fibre length may be shorter or longer than this. Such chopped strands will usually vary between 1-5 mm. The present invention is not dependent on the type of fibre¬ glass used being either pure monofilament or roving, since a mixture of both types is normally present in the finished product sold. For preference collected monofilaments in the form of chopped strand fibreglass should be used. This product is normally sur¬ face treated by the manufacturer. Alternatively, the plastics manufacturer may specially treat the fibreglass for his own purposes. OMPI It i-s of the utmost importance for the coating of the fibre¬ glass that the plastic, or plastic compound, is of the cor¬ rect granular size. Normal granular distribution for this type of operation is between 5 and 100 ,um. If the granules are too large it will not be possible to achieve an even coating of the fibreglass strands. The cost of beating limits the use of very small size granules. Grain size 5-50 ,um is therefore considered to be best suited for the sintering, but larger or smaller grains may be used, as efficient coating is not only dependent on grain size, but also in the length and thickness of the fibres. When the coated product was used in production it was shown that mechanical wear in the processing machinery was reduced to a minimum and is directly comparable with expected wear when processing pure plastic without the addition of a rein¬ forcing medium. Reference is made to tables 1 and 2 which illustrate this point. The invention is pursuant to the patent claim. Example 1 Chopped strand fibreglass with an average strand length of 3 mm is pre-heated in a known manner by means of hot air in a suitable apparatur to approx. 160°C. When the fibres reach the correct temperature, they are sprinkled into a tank con¬ taining E-PVC compound having a granular distribution of 5-50 /u . The blending ratio is one part fibreglass to one part PVC compound. The compound must be agitated constantly during the sprinkling and sintering process. When the sin¬ tering process is completed, the coated fibreglass is separa¬ ted from the unused E-PVC compound. FS ETTT OMPI Example 2 Coated fibreglass, produced in accordance with Example 1 is blended with pure thermoplastic granulate in a Gδttfert twin screw extruder and the melt is extruded through nozzles in the usual manner. In order to measure the rate of wear in the processing machinery, samples are taken of the extruded material and expressed in iron content in ,ug Fe per gram material, i.e. pp . Blind tests were made using pure PVC granulate (Test No. 1) and granulate containing untreated fibreglass (Test No. 2) and fibreglass coated with titanium tristearin (TTS) (Test No. 3). In relation to the invention, E-PVC sintered to the fibre¬ glass was used (Test No. 4), E-PVC being a polyvinylchloride produced on the emulsion principle. - ~ U_U- OMPI Table 1 Test No. PVC-compound Fibreglass Remarks quantity in % quantity in % 1 100 0 2 92 8- 3 mm fibreglass uncoated 3 92 8 3 mm fibreglass TTS-coated 4 92 8 3 mm fibreglass E-PVC-coat Table 2 Test No. Fe in ppm Fe content after ekstruding 23 320 265 160 Fe content in fibreglass 0 1770 1770 1770 Theoretical Fe content according to formula 25 165 165 165 Fe content related to mechanical wear 0 155 100 Table 2 shows that mechanical wear in processing machinery is eliminated when plastic coated fibreglass is used relative to the invention (Test No. 4).

Claims: Patent claim 1. The use of pre-treated chopped strand fibreglass to - prevent wear in processing machinery (extruders and injection moulders in the plastics industry), and to achieve a cleaner end product, c h a r a c t e r i z e d i n t h a t the pre-treated chopped strand fibreglass takes the form of collected monofilaments and/or glassfibres as monofilaments, having a length of between 1 and 5 mm, for preference approx. 3 mm, and that these fibres are coated in a manner known per se with a plastic having a granular size of between 5 and 100 Aim, preferably between 5 and 50 /u , the chopped strand fibreglass being heated to a temperature of between 50 and 300°C, depending on the melting point of the plastic, and thereafter being blended with the plas¬ tic under agitation whereby the plastic is sintered to the surface of the fibreglass, the coated fibre¬ glass thereafter being blended with the correct volume of plastic for use in processing machinery. OMPI

Inventors: DAAE-JOHANSEN FINN, HAGEN OLE KRISTIAN, DAAE-JOHANSEN, FINN, HAGEN, OLE, KRISTIAN
Applicants: NORSK HYDRO AS, NORSK HYDRO A.S.
Application year: 1984
Main classification: B29F3
IPC codes: B05D1, B05D7, B29B15, B29C47, C03C25, C08K9