Lategan, Gary (14 Maureen Street, Wilkoppies, 2571 Klerksdorp, ZA)
| 1. | A process for manufacturing a moulded polymeric plastics artefact or product by rotational moulding, from a particulate polymeric starting material, the process including the steps of: blending, a slip agent or lubricant and an antistatic agent together with the particulate polymeric starting material to form a particulate blend ; and moulding the artefact or product from the blend using a rotational moulding technique, the slip agent or lubricant and the antistatic agent each forming between 0.05% and 0.6% by mass of the particulate blend. |
| 2. | A process as claimed in Claim 1, in which the polymeric starting material is selected from the group consisting of polyolefins, ethyl vinyl acetates, polycarbonates, polyurethanes and suitable mixtures thereof. |
| 3. | A process as claimed in Claim 2, in which the polymeric starting material is a polyolefin. |
| 4. | A process as claimed in Claim 3, in which the polymeric starting material is selected from the group consisting of polyethylenes, polypropylenes and mixtures thereof. |
| 5. | A process as claimed in any one of the preceding claims, in which the polymeric starting material, the slip agent or lubricant and the antistatic agent each have a particle size of between 1 micrometre and 1000 micrometres. |
| 6. | A process as claimed in any one of the preceding claims, in which the slip agent or lubricant and the antistatic agent form, respectively, between 0.1 % and 0.3% and between 0.07 % and 0.2% by mass of the blend. |
| 7. | A process as claimed in any one of the preceding claims, in which the slip agent or lubricant is selected from the group consisting of hydrocarbon waxes, longchain alcohols, longchain carboxylic acids, long chain carboxylic acid amides, longchain carboxylic acid esters, and long chain substituted pyrrolidones. |
| 8. | A process as claimed in Claim 7, in which the slip agent or lubricant is selected from the group consisting of polyethylene, polypropylene, natural wax, stearyl alcohol, behenyl alcohol, tallow fatty alcohol, erucic acid, behenic acid, oleamide, erucamide, stearamide, ethylenebis stearamide, behenamide, stearyl stearate, cetyl palmitat, ethylene glycol monostearate, glyceroi monostearate, sorbitan monopalmitate, N octadecylpyrrolidone and suitable derivatives thereof. |
| 9. | A process as claimed in Claim 8, in which the slip agent or lubricant is erucamide. |
| 10. | A process as claimed in any one of the preceding claims, in which the antistatic agent is selected from the group consisting of polyethylene glycol esters, polyethylene glycol ethers, fatty acid esters, fatty acid ethanolamides, monoglycerides, diglycerides, and ethoxylated fatty amines. |
| 11. | A process as claimed in Claim 10, in which the antistatic agent is glycerol monostearate. |
| 12. | A process as claimed in any one of the preceding claims, in which the slip agent or lubricant and an antistatic agent are blended together with the particulate polymeric starting material by way of dryblending to provide a dry particulate mixture of the polymeric starting material and the slip agent or lubricant and the antistatic agent. |
| 13. | A process as claimed in Claim 12, which includes dry mixing the particulate polymeric starting material with the slip agent or lubricant and the antistatic agent to obtain a blend in the form of a homogeneous mixture, such that the slip agent or lubricant and the antistatic agent each form, separately, at least 0.05% and at most 0.6% by mass of the particulate blend. |
| 14. | A process as claimed in any one of Claims 1 to 11, inclusive, in which the slip agent or lubricant and the antistatic agent are blended together with the particulate polymeric starting material by compounding the polymeric starting material with the slip agent or lubricant and the antistatic agent to provide a homogeneous intimate solid blend thereof, followed by size reduction into particulate or powder form. |
| 15. | A process as claimed in Claim 14, which includes extruding the compounded solid blend into an extruded shape prior to size reduction into particulate or powdered form. |
| 16. | A process as claimed in any one of the preceding claims, in which the slip agent or lubricant and the antistatic agent respectively have a particle size smaller than that of the polymeric starting material. |
| 17. | A process as claimed in Claim 16, in which the slip agent or lubricant and the antistatic agent respectively have a particle size of at most 800 micrometres. |
| 18. | A process as claimed in Claim 17, in which the slip agent or lubricant and the antistatic agent respectively have a particle size of 50 micrometres. |
| 19. | A process as claimed in any one of the preceding claims, which includes the step of coating a rotational mould used in the moulding step with a mould release agent. |
| 20. | A particulate chemical composition for use in manufacturing a polymeric artefact or product by rotational moulding, the composition comprising a particulate blend which includes a particulate polymeric starting material for the polymeric artefact or product; a particulate slip agent or lubricant; and a particulate antistatic agent, the slip agent and the antistatic agent each forming between 0.05 % and 0.6% by mass of the blend. |
| 21. | A composition as claimed in Claim 20, in which the polymeric starting material is selected from the group consisting of polyolefins, ethyl vinyl acetates, polycarbonates, polyurethanes and suitable mixtures thereof. |
| 22. | A composition as claimed in Claim 21, in which the polymeric starting material is a polyolefin. |
| 23. | A composition as claimed in Claim 22, in which the polymeric starting material is selected from the group consisting of polyethylenes, polypropylenes and mixtures thereof. |
| 24. | A composition as claimed in any one of Claims 20 to 23, inclusive, in which the polymeric starting material, the slip agent or lubricant and the anti static agent each have a particle size of between 1 micrometre and 1000 micrometres. |
| 25. | A composition as claimed in any one of Claims 20 to 24, inclusive, in which the slip agent or lubricant and the antistatic agent form, respectively, between 0.1 % and 0.3% and between 0.07 % and 0.2% by mass of the blend. |
| 26. | A composition as claimed in any one of Claims 20 to 25, inclusive, in which the slip agent or lubricant is selected from the group consisting of hydrocarbon waxes, longchain alcohols, longchain carboxylic acids, long chain carboxylic acid amides, longchain carboxylic acid esters, and long chain substituted pyrrolidones. |
| 27. | A composition as claimed in Claim 26, in which the slip agent or lubricant is selected from the group consisting of polyethylene, polypropylene, natural wax, stearyl alcohol, behenyl alcohol, tallow fatty alcohol, erucic acid, behenic acid, oleamide, erucamide, stearamide, ethylenebis stearamide, behenamide, stearyl stearate, cetyl palmitate, ethylene glycol monostearate, glycerol monostearate, sorbitan monopalmitate, Noctadecylpyrrolidone and suitable derivatives thereof. |
| 28. | A composition as claimed in Claim 27, in which the slip agent or lubricant is erucamide. |
| 29. | A composition as claimed in any one of Claims 20 to 28, inclusive, in which the antistatic agent is selected from the group consisting of polyethylene glycol esters, polyethylene glycol ethers, fatty acid esters, fatty acid ethanolamides, monoglycerides, diglycerides, and ethoxylated fatty amines. |
| 30. | A composition as claimed in Claim 29, in which the antistatic agent is glycerol monostearate. |
| 31. | A composition as claimed in any one of Claims 20 to 30, inclusive, in which the slip agent or lubricant and the antistatic agent respectively have a particle size smaller than that of the polymeric starting material. |
| 32. | A composition as claimed in Claim 31, in which the slip agent or lubricant and the antistatic agent respectively have a particle size of at most 800 micrometres. |
| 33. | A composition as claimed in Claim 32, in which the slip agent or lubricant and the antistatic agent respectively have a particle size of 50 micrometres. |
| 34. | An additive blend for use in the manufacturing of a polymeric artefact or product by rotational moulding, which additive blend comprises a slip agent or lubricant; and an antistatic agent, the blend comprising the antistatic agent and the slip agent or lubricant in a mass ratio of antistatic agent to slip agent or lubricant in a range between 1: 12 and 12: 1. |
THIS INVENTION relates to moulding, and, in particular, to rotational moulding. More particularly, the invention relates to a process for manufacturing a moulded polymeric plastics artefact or product by rotational moulding, to a particulate chemical composition for manufacturing a polymeric artefact or product by rotational moulding, and to an additive blend for use in the. manufacturing of a polymeric artefact or product by rotational moulding.
According to a first aspect of the invention, there is provided a process for manufacturing a moulded polymeric plastics artefact or product by rotational moulding, from a particulate polymeric starting material, the process including the steps of: blending a slip agent or lubricant and an anti-static agent together with the particulate polymeric starting material to form a particulate blend, and moulding the artefact or product from the blend using a rotational moulding technique, the slip agent or lubricant and the anti-static agent each forming between about 0.05% and about 0.6% by mass of the particulate blend.
The polymeric starting material may be selected from the group consisting of polyolefins, ethyl vinyl acetates, polycarbonates, polyurethanes, and suitable mixtures thereof. Preferably, the polymeric starting material is a polyolefin. More particularly, the polymeric starting material may be selected from the group consisting of polyethylenes, polypropylenes, and mixtures thereof.
The polymeric starting material, the slip agent or lubricant and the anti-static agent may each have a particle size of between about 1 micrometre and about 1000 micrometres, preferably between about 200 micrometres and about 800 micrometres, and more preferably between about 400 micrometres and about 600 micrometres.
Preferably, the slip agent or lubricant and the anti-static agent typically form, respectively, between about 0. 1% and about 0.3%, for example about 0. 2%, and between about 0.07% and about 0.2%, for example about 0. 1%, by mass of the blend.
The slip agent or lubricant may be selected from the group consisting of hydrocarbon waxes, long-chain alcohols, long-chain carboxylic acids, long-chain carboxylic acid amides, long-chain carboxylic acid esters, and long-chain substituted pyrrolidones. More particularly, the slip agent or
lubricant may be selected from the group consisting of polyethylene wax, polypropylene wax, natural wax (ie. animal or vegetable wax), stearyi alcohol, behenyl alcohol, tallow fatty alcohol, erucic acid, behenic acid, oleamide, erucamide, stearamide, ethylene-bis stearamide, behenamide, stearyl stearate, cetyl palmitate, ethylene glycol monostearate, glycerol monostearate, sorbitan monopalmitate, N-octadecylpyrrolidone, and suitable derivatives thereof. In a preferred embodiment, the slip agent or lubricant is erucamide, which has the chemical formula [CH3 (CH2) 7CH=CH (CH2) 11CONH2]. The erucamide may be that commercially available from CIBA CHEMICALS INC. in South Africa under the trade name Atmer SA1753FD.
The anti-static agent may be selected from the group consisting of polyethylene glycol esters, polyethylene glycol ethers, fatty acid esters, fatty acid ethanolamides, mono-glycerides, di-glycerides, and ethoxylated fatty amines. More particularly, the anti-static agent may be glycerol monostearate, which has the chemical formula [CH3 (CH2) 16COOCH2CHOHCH2OH]. The glycerol monostearate may be that commercially available from CIBA CHEMICALS INC. in South Africa under the trade name Atmer 129.
The slip agent or lubricant and the anti-static agent may be blended together with the particulate polymeric starting material by way of dry-blending to provide a dry particulate mixture of the polymeric starting
material and the slip agent or lubricant and the anti-static agent. Thus, the process may include the step of dry mixing the particulate polymeric starting material with the slip agent or lubricant and the anti-static agent to obtain a blend in the form of a homogeneous mixture, such that the slip agent or lubricant and the anti-static agent each form, separately, at least 0. 05% and at most 0.6% by mass of the particulate blend.
Instead, the slip agent or lubricant and the anti-static agent may be blended together with the particulate polymeric starting material by compounding the polymeric starting material with the slip agent or lubricant and the anti-static agent to provide a homogeneous intimate solid blend thereof, followed by size reduction into particulate or powder form. Thus, the process may include the step of blending by compounding the starting materials, for example by extrusion or by means of a kneader or masticator or other high intensity mixer in the proportions mentioned above.
A particular version of the process may include the steps of compounding the polymeric starting material with the slip agent or lubricant and the anti-static agent, extruding the compounded solid blend into an extruded shape, such as a pellet, prior to size reduction, for example by pulverising, to form powder particles or granules, each comprising the compounded blend/mixture.
The slip agent or lubricant and the anti-static agent may respectively have a particle size smaller than that of the polymeric starting material. In particular, the slip agent or lubricant and the anti-static agent may respectively have a particle size of at most about 800 micrometres, preferably about 50 micrometres.
Although it is an important feature and advantage of the present invention that the rotational moulding can take place in an unlined or uncoated metal rotational mould, such as a steel or aluminium rotational mould, the process may, when necessary to obtain a desired surface, finish, include the step of coating a rotational mould used for the moulding step with a mould release agent.
According to another aspect of the invention, there is provided a particulate chemical composition for use in manufacturing a polymeric artefact or product by rotational moulding, the composition comprising a particulate blend which includes a particulate polymeric starting material for the polymeric artefact or product; a particulate slip agent or lubricant ; and a particulate anti-static agent, the slip agent and the anti-static agent each forming between 0.05 % and 0.6% by mass of the blend.
The polymeric starting material may be selected from the group consisting of polyolefins, ethyl vinyl acetates, polycarbonates, polyurethanes, and suitable mixtures thereof. Preferably, the polymeric starting material is a polyolefin. More particularly, the polymeric starting material may be selected from the group consisting of polyethylenes, polypropylenes, and mixtures thereof.
The polymeric starting material, the slip agent or lubricant and the anti-static agent may each have a particle size of between about 1 micrometre and about 1000 micrometres, preferably between about 200 micrometres and about 800 micrometres, and more preferably between about 400 micrometres and about 600 micrometres.
Preferably, the slip agent or lubricant and the anti-static agent typically form, respectiveiy, between about 0. 1% and about 0.3%, for example about 0.2%, and between about 0.07% and about 0.2%, for example about 0. 1%, by mass of the blend.
The slip agent or lubricant may be selected from the group consisting of hydrocarbon waxes, long-chain alcohols, long-chain carboxylic acids, long-chain carboxylic acid amides, long-chain carboxylic acid esters, and long-chain substituted pyrrolidones. More particularly, the slip agent or lubricant may be selected from the group consisting of polyethylene wax,
polypropylene wax, natural wax (ie. animal or vegetable wax), stearyl alcohol, behenyl alcohol, tallow fatty alcohol, erucic acid, behenic acid, oleamide, erucamide, stearamide, ethylene-bis stearamide, behenamide, stearyl stearate, cetyl palmitat, ethylene glycol monostearate, glycerol monostearate, sorbitan monopalmitate, N-octadecylpyrrolidone, and suitable derivatives thereof. In a preferred embodiment, the slip agent or lubricant is erucamide, which has the chemical formula [CH3(CH2)7CH=CH(CH2)11CONH2]. The erucamide may be that commercially available from CIBA CHEMICALS INC. in South Africa under the trade name Atmer SA1753FD.
The anti-static agent may be selected from the group consisting of polyethylene glycol esters, polyethylene glycol ethers, fatty acid esters, fatty acid ethanolamides, mono-glycerides, di-glycerides, and ethoxylated fatty amines. More particularly, the anti-static agent may be glycerol monostearate, which has the chemical formula [CH3 (CH2) 16COOCH2CHOHCH2OH]. The glycerol monostearate may be that commercially available from CIBA CHEMICALS INC. in South Africa under the trade name Atmer 129.
The slip agent or lubricant and the anti-static agent may respectively have a particle size smaller than that of the polymeric starting material. In particular, the slip agent or lubricant and the anti-static agent may respectively have a particle size of at most about 800 micrometres,
preferably about 50 micrometres.
According to still another aspect of the invention, there is provided an additive blend for use in the manufacturing of a polymeric artefact or product by rotational moulding, which additive blend comprises a slip agent or lubricant; and an anti-static agent, in a mass ratio of anti-static agent to slip agent, or lubricant, in a range between 1: 12 and 12: 1.
The invention will now be described, by way of a non-limiting illustration, with reference to-the following worked Example : EXAMPLE Polymeric starting material in the form of linear low density polyethylene, commercially available from Sasol Polymers South Africa under the trade name LM 3076 and supplied as a pellet having a diameter of 4-6 mm and a length of 4-6mm in 25kg bags, was pulverized to an approximate maximum particle size of 500 micrometres (35 Mesh).
The pulverized starting material was then tumble-blended with 0.2% by mass of white pigment additive, comprising titanium dioxide, 0. 1% by mass of an anti-static agent powder, comprising glycerol monostearate of the type commercially available from Ciba Chemicals South Africa under the trade name Atmer 129, and 0.3% by mass of a slip agent (or lubricant), namely Atmer SA 1573 FD supplied by Ciba Chemicals South Africa in pellet form.
The tumble-blending was carried out for 20 minutes in a medium intensity Kelley duplex mixer. The blend was then compounded by extrusion and thereafter pulverized to a 35 Mesh powder.
The compounded blend comprising the polymeric starting material, the white pigment additive, the slip agent and the anti-static agent was then run in a raw or untreated mild steel rotational mould with no release agent, in a carousel-type rotational moulding machine. Typical rotational moulding procedures known in the art were adhered to. Thus, a shot weight of 5kg of the pulverized compounded blend was placed in the mould in an oven, and the mould closed. The oven temperature was set at 300 °C and the cycle time set at 10 minutes. After 10 minutes the oven doors and the mould were opened and a second shot weight of 2kg of pulverized unblended polyethylene starting material (with no additives) was loaded into the mould and run for a cycle time of 6 minutes. On completing the full 16 minute cycle time, the oven doors were opened and the untreated mould was moved to a cooling station where it was cooled for 25 minutes. Using separate 5kg and
2kg shot weights in succession gave rise to a multi-layered product of double-skinned form, the outer layer or skin being formed from the 5kg shot weight in contact with the mould, and the 2kg shot weight forming an inner layer or skin deposited by rotational-moulding on the inner surface of the outer layer or skin.
After cooling, each mould was moved to a de-moulding station where the moulded product (which was a 1 80E roof water tank) was removed from the mould, and the whole process was started again. The process was repeated for 300 successive mouldings without any delays, downtime or problems being encountered in de-moulding the product from the mould. The moulded product rendered by the process and from the composition of the invention was more readily released from the mould on each occasion.
As a control, a mould with a good mould release agent, such as Freecote 700NC, available in South Africa from Advanced Chemicals (Proprietary) Limited, well applied to an internal surface thereof, gave between 150 and 250 mould releases with conventional polymeric starting material before the mould had to be replaced, causing downtime on the machine and loss of production. The mould then had to be sent for cleaning and application of a fresh coat of release agent, which entailed spraying it with a coating of release agent and curing thereof by baking the mould three times in the rotational moulding machine, for 15 minutes on each occasion, before the
mould was again ready for production. This resulted in machine downtime and loss of production, which can be reduced if not avoided entirely by using the process and composition in accordance with the present invention.
Furthermore, as moulding using the process and composition of the invention can take place in a untreated steel or aluminium mould without a release agent lining a better and more consistent product surface finish is obtainable, particularly for long production runs including several hundred or more mould releases.
It is believed that the process and composition of the invention render a . rotational moulded product that is more easily released from the mould, successive moulded products being of a consistent quality such that repeated high quality yields are made possible. Moreover, it is believed that the additives to the polymeric starting material migrate to a surface of the moulded product and lend to an anti-static effect at the surface.
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