AU684320B2 - Foamable plastics material and method of manufacture - Google Patents

Description

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT Name of Applicant: Actual Inventor: Address for Service: Invention Title: The following statement is invention, including the best us J.R. COURTENAY (NZ) LIMITED DARIO MASUTTI CULLEN CO., Patent Trade Mark Attorneys, 240 Queen Street, Brisbane, Qld. 4000, Australia.

FOAMABLE PLASTICS MATERIAL AND METHOD OF MANUFACTURE a full description of this method of performing it known to ,b 06 *ft ft ft ft ft ft ft ft...

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ft ft ft la- FOAMABLE PLASTICS MATERIAL AND METHOD OF MANUFACTURE BACKGROUND OF THE INVENTION This invention relates to foamable plastics and their method of manufacture and, in particular, although not necessarily solely, a foamable plastics material suitable for use in the rotational moulding industry.

Foamable plastics are known and in use in the industry to provide a product of greater dimension than a normal quantity of plastics material would allow through the introduction of cells within the final plastics product to increase the volume of the finished plastic. This is of particular use in some articles where an article of greater thickness is required and the mechanical disadvantage of having a less dense plastic forming the wall material is not a factor.

The use of foamable plastics in the rotational "moulding industry has resulted in finished articles having an uneven cell structure throughout the finished product leading to irregularities on the surface of the plastic product such as bubbles or overly large cavities and overly large hollows I I I- 2 within the plastic materials which can lead to structural failure.

Therefore, it is an object of the present invention to provide a foamable plastic and method of manufacture which, particularly in use in the rotational moulding industry, provides a product having a relatively even cell-structure or at least provides the public with a useful choice.

SUMMARY OF THE INVENTION Accordingly, in the first aspect, the invention may broadly be said to consist in a foamable plastics material comprising a granulated or powdered raw plastics material and p.p'-oxybis (benzenesulfonyl hydrazide) substantially evenly 2 dispersed throughout.

*4 .Preferably said p.p'-oxybis (benzenesulfonyl hydrazide) comprises no more than five percent per t o9 volume of the overall foamable plastics material.

Preferably said p.p'-oxybis (benzenesulfonyl hydrazide) is provided in an amount of approximately 20% by volume in a mastermix added to the raw S• plastics material.

3 Accordingly, in the second aspect, the invention may broadly be said to consist in a method of manufacturing a granulated or powder form foamable plastics material adapted for use in rotational moulding comprising: providing or manufacturing a granulated or powdered plastics material; adding a quantity of p.p'-oxybis (benzenesulfonyl hydrazide) to the raw plastics material; and mixing the two ingredients to ensure a substantially even dispersion of p.p'-oxybis (benzenesulfonyl hydrazide) throughout the final product.

Preferably said plastics material comprises polyethylene beads ground such that the majority of the resultant powder passes through a thirty-five mesh screen.

Preferably said quantity of p.p'-oxybis (benzenesulfonyl hydrazide) is less than or equal to five percent by volume.

Preferably said quantity of p.p'-oxybis (benzenesulfonyl hydrazide) is in an amount of I I a 4 approximately 20% of p.p'-oxybis (benzenesulfonyl hydrazide) by volume in a mastermix added to the raw plastics material.

Preferably said mixing comprises a low intensity mixing.

Preferably said low intensity mixing comprises mixing said materials in a tumble mixer for approximately 30 minutes.

Alternatively, said mixing comprises a high intensity mixing for a period of less than thirty minutes.

Accordingly, in a third aspect, the invention may broadly be said to consist in a method of manufacturing a rotationally moulded product comprising rotationally moulding a product from a foamable plastics material, or by a method, as defined in the preceding paragraphs.

Other aspects of this invention which should be considered in all its novel aspects will become apparent from the following description.

i 5 BRIEF DESCRIPTION OF PREFERRED EMBODIMENTS The invention relates to the provision of a plastics material for use in the rotational moulding industry. Although many alternative plastic raw materials can be used in the industry, a typical plastics material is polyethylene.

The plastics raw material such as polyethylene may be provided in a number of alternative forms such as in the form of polyethylene beads. To be suitable for rotational moulding, the polyethylene beads are ground such that the majority of the resultant powder passes through a thirty-five mesh screen. The thirty-five mesh screen is a US standard screen for such powders.

Once the plastics material has been ground to

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a powder of suitable size, the foaming agent 2 comprising p.p'-oxybis (benzenesulfonyl hydrazide) may be added. This has the specific registry number CAS 80-51-3 and wherever reference is made to this foaming agent this registry number is deemed to be included. The quantity of p.p'-oxybis *(benzenesulfonyl hydrazide) added to the plastics material may vary according to the desired degree of o: expansion.

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In the preferred form of this invention, the quantity of p.p'-oxybis (benzenesulfonyl hydrazide) added to the plastic raw material is of the order of

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6 approximately 20% by volume in a mastermix added to the plastics raw material. The ratio in the final mixture may be of the order of up to 5 percent or preferably in a range of 0.5% to 2.0% by volume leading to a finished plastics product being perhaps 200% to 400% respectively greater in volume.

To ensure adequate mixing of the foaming agent throughout the plastics raw material, the foaming agent may be mixed in a low intensity mixer such as a tumble mixer until a suitable even consistency is obtained. It has been found that a mixing time of approximately thirty minutes is sufficient in a low intensity mixer to achieve the desired end result.

ooi Alternatively, a high intensity mixer can 0 achieve the necessary mixing in a shorter time.

However, the increased intensity of the mixing action leads to a greater generation of heat in the 2 mixing step itself. This can lead to the S" decomposition of the foaming agent and/or the plastics raw material either in total or in part which may lead to failures in the end product.

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Once suitably mixed, the mixture may be packaged and delivered as an end result of a process to rotational moulders for use in the moulding industry.

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-7- To produce the finished plastics product, the mixed plastics material may be placed in a rotational moulding machine and rotated while heated in accordance with conventional rotational moulding techniques. The finished product is provided having an increased wall thickness in accordance with the ratio of foaming agent used in the mixture through the creation of hollow cells within the finished product.

Thus it can be seen that by the use of the present invention a foamed plastic product can be provided having a relatively even cell structure and a decrease in large cavities or deformities in the Splastic product and, in particular, in the wall surfaces of the product.

.o Where in the foregoing description, reference •0 2 0 has been made to specific components or integers of the invention having knownequivalents, then such ooeee: equivalents are herein incorporated as if individually set forth.

Although this invention has been described by way of example and with reference to possible embodiments thereof, it is to be understood that modifications or improvements may be made thereto without departing from the scope of the invention as defined in the appended claims.

Claims (12)

1. A foamable plastics material comprising a granulated or powdered raw plastics material and p.p'-oxybis (benzenesulfonyl hydrazide) substantially evenly dispersed throughout.

2. A foamable plastics material as claimed in claim 1 wherein said p.p'-oxybis (benzenesulfonyl hydrazide) comprises no more than five percent per volume of the overall foamable plastics material.

3. A foamable plastics material as claimed in claim 2 wherein said p.p'-oxybis (benzenesulfonyl hydrazide) is provided in an amount of approximately 20 percent by volume in a mastermix added to the raw plastics material.

4. A foamable plastics material as claimed in claim 3 wherein said p.p'-oxybis (benzenesulfonyl hydrazide) comprises 0.5% to 2.0% by volume of the overall foamable S plastics material.

Al 9 A foamable plastics material as defined in claim 1 substantially as herein described with reference to Brief Description of Preferred Embodiments.

6. A method of manufacturing a granulated or powder form foamable plastics material adapted f:r use in rotational moulding comprising: providing or manufacturing a granulated or powdered plastics material; adding a quantity of p.p'-oxybis (benzenesulfonyl hydrazide) to the raw plastics material; and mixing the two ingredients to ensure a substantially even dispersion of p.p'-oxybis (benzenesulfonyl hydrazide) throughout the 2i final product.

7. A method as claimed in claim 6 wherein said plastics material comprises polyethylene beads *o 5* which are ground so that the majority of the resultant powder passes through a 35 mesh screen. *eoe 10

8. A method as claimed in claim 6 or claim 7 wherein said mixing comprises a low intensity mixing.

9. A method as claimed in claim 8 wherein said low intensity mixing comprises mixing said materials in a tumble mixer for thirty minutes.

A method as claimed in claim 6 or claim 7 in which said mixing comprises a high intensity mixing for a period of less than thirty minutes.

11. A method as claimed in any one of claims 6 to and substantially as herein described.

12. A method of manufacturing a rotationally moulded product comprising rotationally *.0 moulding a product from a foamable plastics material as defined in any one of claims 1 to DATED THIS 12TH DAY OF SEPTEMBER 1997 J R COURTENAY (NZ) LIMITED 5 BY THEIR PATENT ATTORNEYS CULLEN CO -u2~rrw -11- ABSTRACT FOAMABLE PLASTICS MATERIAL AND METHOD OF MANUFACTURE A foamable plastics material consists of a granulated or powdered raw plastics material such as ground polyethylene beads in which is evenly dispersed p.p'-oxybis (benzenesulfonyl hydrazide), registry No. CAS 80-51-3. Suitably the p.p'-oxybis (benzenesulfonyl hydrazide) is provided in an amount of approximately 20% by volume in a mastermix added to the raw plastics material to comprise suitably to 2% by volume of the overall foamable plastics material. A method of manufacturing the 0 foamable plastics material is also described including low intensity or high intensity mixing. r *0 0* S