IE42102B1 - Moulding processes and material - Google Patents

Description

This invention concerns a moulding material, moulding processes and articles obtained by the processes.

Numerous injection moulding processes are already known. In one such process a fluid plastics material is injected into a mould and allowed to cool, the mould being topped up with further quantities of the plastics material as the mould cools and contracts in the mould. Articles produced by this process are expensive in view of the high cost of the raw plastics material. In order to reduce the cost of articles produced by this process, a relatively cheap inert filler is commonly mixed with the plastics material prior to moulding. Conventional fillers are in the form of solid particles and have a high specific gravity, usually in the range of 2.0 to 4.5. Accordingly, articles made by this modified process are relatively heavy. Attempts have been made to reduce the weight of articles produced in this process by using fillers in the form of hollow particles, which thus have a lower density. However, the high moulding pressures required in the prooess result in breakdown of the filler particles which can become abrasive when broken, both in the moulding machine and in the mould itself, and the benefits derived from the low density of the filler are reduced.

In a further process, a plastics material is moulded with the addition of a blowing agent to create what is known as a structural foam. The blowing agent may be a chemical agent mixed with the plastics material before injection and which creates gas within the plastics material at a predetermined temperature to form a cellular structure within the plastics material. Alternatively, the same effect may be obtained by blowing an inert gas such as nitrogen into the plastics material during the mould process. The resulting moulded article has cellular structure and is light in weight.

An object of the present invention is to provide a relatively inexpensive extrusion or injection moulding material, and an extrusion or injection process which can result in the extruded or injection moulded article having an intermediate weight and firm surface texture without sink, a uniform foam structure, increased rigidity, and a reduction of strain in the finished article.

According to a first aspect of the present invention there is provided a structural foam extrusion or injection mould material comprising a thermoplastic or thermosetting polymer mixed with an inorganic filler material in the form of hollow particles and with a blowing agent, the filler material comprising aluminium siliceite.

According to a second aspect of the present invention there is provided an extrusion or injection mould process comprising mixing a thermoplastic or thermosetting polymer with an inorganic filler material in the form of hollow particles and extruding or moulding the resultant mixture with the addition of a blowing agent to form a structural foam.

The particles of filler material may be in the form of hollow spheres of aluminium silicate, and prefer42102 - 4 ably mixed in a ratio of 5% to 70% by weight of the total mix.

The polymer material may be in the form of particles in which case the particles of filler material are pre5 ferably of substantially the same size as the polymer particles and may have a chemical composition of silica as Si02 between 46% and 68% by weight, and alumina as Al203 between 20% and 38% by weight, the remainder being made up of alkalides in the form Na20 and K20 and iron oxide as E^O^. Such hollow particles are commercially available from Fillite (Runcorn) Limited under the trade name Fillite.

However, the particles of filler material may be considerably smaller than the particles of polymer in which case a wetting agent is added during the mixing and before the mould operation to ensure a uniform mixture and avoid separation of the filler and plastics particles.

Mixing may be performed immediately before the ex20 trusion or injection moulding operation and at the point of feed to the extrusion or injection moulding machine by means of metering devices.

Preferably the filler material has a specific gravity in the range of from 0.5 to 1.5.

The blowing agent may be a chemical agent or an inert gas such as nitrogen.

At the present time, the cost per ton of aluminium silicate filler material in the form of hollow spheres is about 2 to 3 times as much as that of a conventional filler material. However, conventional filler material is between 4 and 5 times as dense as the - 5 aluminium silicate filler, and so the use of the aluminium silicate filler is cheaper on a volumetric basis. In view of this, the process of the present invention offers improved economics of material costs as compared with known extrusion or injection moulding processes.

There is a further significant cost saving, as compared with known injection moulding processes, as a result of a reduction in moulding production time cycles resulting from faster setting up in the mould of the mouldings enabling them to be ejected from the mould after a shorter period of time. This is a direct result of the inclusion of the filler.

The process of the invention also makes it easier to produce mouldings on both structural foam injection moulding machines and more conventional moulding machines. Mouldings hithereto not considered suitable as structural foam mouldings are now suitable for and benefit from this process because of increased rigidity, freedom from sinkage and faster time cycles.

The process of injection moulding in accordance with the invention facilitates the production of mouldings without the use of injection hold-on or back-up pressure in the material after injection into the mould in order to fill the mould during cooling and contraction of the material. It is normally necessary to force more material into the mould in order to compensate for .such contraction, but resulting movement of the material in a semi-molten state introduces strain into the moulding which can result in distortion of the moulding after injection from the mould. Inclusion of - 6 the blowing agent and filler material ensures filling of the mould without further material injection and therefore the introduction of strain into the material is substantially reduced. It is thus only necessary to introduce a metered volume of material into the mould . The production of mouldings of a high quality is thus made more consistent.

A further use of the process of the invention involves the addition of the filler material to a twocomponent mixture of a thermosetting foam such as polyurethane. The foam is created by chemical reaction, and combination and the two components such as polyol and isocyanate will produce the foam with the filler dispersed therein. The resulting foam has similar advantages to those obtained for the plastics material foam.

It will be appreciated that the process may include other additives, for example reinforcements such as glass fibre which are mixed with the moulding material at the same time as the filler. The combination of the filler and glass fibre produces a combination of improved physical properties which include increased tensile strength, increased rigidity’ and heat distortion whilst still retaining the advantages of a more uniform foam structure and good surface finish which result from the use of the filler.

A further improvement in the adhesion between the filler and the polymer can be obtained, with the use of a coupling agent such as silane. This will result in further improvement in physical properties such as tensile and impact strengths and resistance to creep under - 7 43102 load.

A further use of the process is in the extrusion of these material mixtures into profiled shapes. Advantages derived are similar to those of the injection moulded parts and include cost savings in raw material resulting from reduced weight of the extrusion and reduced material costs and increased extrudate output, increased rigidity, freedom from sinkages and dimensional stability. The extrusion of sections of 5 mm or more in thickness is made more feasible. The cost of extrusion as a result becomes more competitive with timber.

The moulded material obtained by the process of the invention has the following advantages as compared with conventional injection moulding processes :(a) Raw material costs are reduced by the inclusion of the filler material at a very much lower cost than that of the plastics material; (b) Reduced mould time as a result of reduced cooling time in the mould before the moulding reaches a rigidity sufficient for the moulding to be ejected from the mould, resulting in lower costs of production; (c) A weight and surface texture similar to that of wood can be obtained by appropriate proportioning of the plastics material and the filler material; (d) The surface texture obtained by inclusion of the filler material facilitates painting or similar post-moulding operations such as printing and metallising. It has been found that printing can be undertaken almost immediately after moulding whereas conventional mouldings have to be stored for several days before - 8 25 printing. The only surface preparation normally needed after this process is the application of the primer (in the case of polypropylene). Surface imperfections such as tear” marks normally evident in polypropylene foam mouldings are eliminated; I l (e) The inclusion of the filler material reduces the thermal conductivity of the moulding; (f) The rigid'ity, flexural strength, dimensional stability and temperature distortion point of the plastics are increased as a result of inclusion of the filler; (g) The mouldings are free from sinkage so that mouldings of varying thickness can be easily made by this process; (h) The abrasion resistance of mouldings is improved; (i) The foam structure is much more uniform throughout the moulding as a result of the filler acting as a nucleating agent during flow of material into the mould. The occurrence of large voids in the foam is reduced; and (j) The residual strain in the moulding is reduced so forming a more dimensionally stable mouldings conform ing more accurately to the shape of the mould.

The invention will be described further by way of example, with reference to the following typical mixes wherein the material proportions are all by weight. 42103 - 9 EXAMPLE 1: Polypropylene 57.0% Fillite filler 32.5% Chemical blowing agent 0.5% EXAMPLE 2: Polystyrene 57.0% Fillite filler 32.5% Chemical blowing agent 0.5% EXAMPLE 3: Polyacetol 75.0% Fillite filler 24.5% Chemical blowing agent 0.5% EXAMPLE 4: Nylon 80.0% Fillite filler 19.8% Chemical blowing agent 0.2% EXAMPLE 5: Polypropylene 80.0% Fillite filler 20.0% In this example an inert gas such as nitrogen is used as a blowing agent.

EXAMPLE 6: Polypropylene 80.0% Fillite filler 19.5% Chemical blowing agent 0.5% This mixture is particularly suitable for extrusion into foam sheet. - 10 EXAMPLE 7: Polypropylene 94.5% Pillite filler 5.0% Chemical blowing agent 0.5% EXAMPLE 8: Polys tyrene 29.5% Finite filler 70.0% Chemical blowing agent 0.5% It will be appreciated that the chemical blowing 10 agents may be replaced by an inert gas blowing agent such as nitrogen, resultant with minor modification of the proportions of the plastics and filler materials. However, where a chemical blowing agent is used, that marketed by Fisons Limited under the trade name Genitron has been found to be particularly suitable.

Claims (17)

1. CLAIMS: 1. A structural foam extrusion or injection moulding material comprising a thermoplastic or thermosetting polymer mixed with an inorganic filler material in the form of hollow particles and with a blowing agent, the filler material comprising aluminium silicate.

2. A mould material as claimed in Claim 1, in which the hollow particles are spherical.

3. A mould material as claimed in Claim 1 or 2 in which the filler material is mixed in a ratio of 5% to 70% by weight of the total mix.

4. A moulding material as claimed in any preceding claim, in which the thermoplastic or thermosetting polymer is in the form of particles which are of substantially the same size as the particles of filler material.

5. A moulding material as claimed in any of Claims 1 to 3, in which the thermoplastic or thermosetting polymer is in the form of particles, and in which the particles of filler material are smaller than particles of the plastics material, the material also including a wetting agent added during mixing.

6. A moulding material as claimed in any preceding claim, in which the filler material has a chemical composition comprising silica as SiO^ between 46% and 68% by weight, and alumina as Al„0 between 20% and 38% 4 3 by weight, the remainder being alkalies in the form Na 2 0 and K^O and iron oxide as Pe 2 O 3 ·

7. A moulding material as claimed in any preceding claim, in which the filler material has a specific gravity in the range of from 0.5 to 1.5. - 12

8. A moulding material as claimed in Claim 1, and substantially as herein described.

9. An extrusion or injection moulding process comprising mixing a thermoplastic or thermosetting polymer 5 with an inorganic filler material in the form of hollow particles, and extruding or moulding the resultant mixture with the addition of a blowing agent to form a structural foam.

10. A process as claimed in Claim 9, in which the 10 hollow particles are Spherical.

11. A process as claimed in Claim 9, or 10 in which the filler material is aluminium silicate.

12. A process as claimed, in Claim 9, IO or 11, in which the filler material is mixed in a ratio of 5% to 15 70% by weight of the total mix.

13. A process as claimed in any of claims 9 to 12, in which the thermoplastic or thermosetting polymer material is in the form of particles and in whieh the particles of filler material are of substantially the 20 same size as particles of the polymer.

14. A process as claimed in any of Claims 9 to 12, in which the thermoplastic or thermosetting polymer material is in the form of particles and in which the particles of filler material are smaller than particles 25 of the plastics material, the process also including the addition of a wetting agent during mixing.

15. A process as claimed in any of Claims 9 to 14, in which the filler material has a chemical composition comprising silica as SiO 2 between 46% and 68% by 30 weight, and alumina as A l 2 °3 between 20% and 38% by - 13 weight, the remainder being alkalies in the form Ν & 2 θ 3 and Κ,,Ο and iron oxide as Fe^O^. 1.6. A process as claimed in any of Claims 9 to 15, in which the filler material has a specific gravity 5 in the range of from 0.5 to 1.5.

16.

17. A process as claimed in Claim 9 substantially as herein described.