AU2006100019A4 - Moulding Thermoplastic Materials - Google Patents
Moulding Thermoplastic Materials Download PDFInfo
- Publication number
- AU2006100019A4 AU2006100019A4 AU2006100019A AU2006100019A AU2006100019A4 AU 2006100019 A4 AU2006100019 A4 AU 2006100019A4 AU 2006100019 A AU2006100019 A AU 2006100019A AU 2006100019 A AU2006100019 A AU 2006100019A AU 2006100019 A4 AU2006100019 A4 AU 2006100019A4
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- AU
- Australia
- Prior art keywords
- sheet
- thermoplastic
- solid
- mould
- region
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Links
- 238000000465 moulding Methods 0.000 title claims description 29
- 239000012815 thermoplastic material Substances 0.000 title claims description 29
- 238000000034 method Methods 0.000 claims description 39
- 239000000463 material Substances 0.000 claims description 36
- 229920001169 thermoplastic Polymers 0.000 claims description 34
- 239000004416 thermosoftening plastic Substances 0.000 claims description 34
- 239000006260 foam Substances 0.000 claims description 29
- 239000007787 solid Substances 0.000 claims description 24
- 238000010438 heat treatment Methods 0.000 claims description 21
- 239000006261 foam material Substances 0.000 claims description 8
- 239000002131 composite material Substances 0.000 claims description 6
- 230000006835 compression Effects 0.000 claims description 4
- 238000007906 compression Methods 0.000 claims description 4
- 230000015572 biosynthetic process Effects 0.000 claims description 2
- 238000004519 manufacturing process Methods 0.000 claims description 2
- 230000003014 reinforcing effect Effects 0.000 claims description 2
- 239000010410 layer Substances 0.000 description 12
- 239000000853 adhesive Substances 0.000 description 7
- 230000001070 adhesive effect Effects 0.000 description 7
- 238000007666 vacuum forming Methods 0.000 description 5
- 239000004800 polyvinyl chloride Substances 0.000 description 4
- 229920002943 EPDM rubber Polymers 0.000 description 3
- 239000004698 Polyethylene Substances 0.000 description 3
- 239000004743 Polypropylene Substances 0.000 description 3
- 238000007792 addition Methods 0.000 description 3
- 238000003475 lamination Methods 0.000 description 3
- 239000005038 ethylene vinyl acetate Substances 0.000 description 2
- 230000004927 fusion Effects 0.000 description 2
- 238000013023 gasketing Methods 0.000 description 2
- 229920001903 high density polyethylene Polymers 0.000 description 2
- 229920005669 high impact polystyrene Polymers 0.000 description 2
- 239000004700 high-density polyethylene Substances 0.000 description 2
- 239000004797 high-impact polystyrene Substances 0.000 description 2
- 238000002844 melting Methods 0.000 description 2
- 230000008018 melting Effects 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 239000004033 plastic Substances 0.000 description 2
- 229920003023 plastic Polymers 0.000 description 2
- 239000011343 solid material Substances 0.000 description 2
- 238000003856 thermoforming Methods 0.000 description 2
- 239000012790 adhesive layer Substances 0.000 description 1
- 238000007664 blowing Methods 0.000 description 1
- 239000007795 chemical reaction product Substances 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000007499 fusion processing Methods 0.000 description 1
- 238000010030 laminating Methods 0.000 description 1
- 239000004816 latex Substances 0.000 description 1
- 229920000126 latex Polymers 0.000 description 1
- 239000002985 plastic film Substances 0.000 description 1
- 229920001084 poly(chloroprene) Polymers 0.000 description 1
- 229920002635 polyurethane Polymers 0.000 description 1
- 239000004814 polyurethane Substances 0.000 description 1
- 239000000047 product Substances 0.000 description 1
- 230000000717 retained effect Effects 0.000 description 1
- 238000007789 sealing Methods 0.000 description 1
Landscapes
- Blow-Moulding Or Thermoforming Of Plastics Or The Like (AREA)
Description
AUSTRALIA
PATENTS ACT 1990 COMPLETE SPECIFICATION INNOVATION PATENT for the invention entitled: "Moulding Thermoplastic Materials" The following statement is a full description of this invention, including the best method of performing it known to me: MOULDING THERMOPLASTIC MATERIALS Field of the Invention This invention relates to processes for moulding thermoplastic materials and to materials formed by such processes. In one aspect it relates to the moulding of foamed thermoplastic sheet. In another aspect it relates to the moulding of composite materials which are formed from a moulded solid plastic sheet in combination with a foam plastic.
Background of the Invention Sheets of foamed thermoplastic materials are commonly moulded by thermoforming processes to produce formed articles useful as gaskets in the automotive industry and in many other applications as well.
There are several types of moulding processes currently used in the industry for moulding articles from thermoplastic foam sheet materials.
In one form of simple vacuum formed moulding, the thermoplastic sheet is heated by any suitable source such as a radiant heat source and is brought into registry with a bottom mould or tool through which vacuum is applied. Atmospheric pressure on the opposite side of the sheet causes the heated and softened thermoplastic sheet to deform to assume the contours of the mould. Whilst this type of process is cost effective in certain situations, it suffers from a number of limitations, namely: Definition of detail on the sheet is limited, being reasonable on the tool or mould side, but rounded on the opposite surface.
Deep or small features on the tool side are only partially filled as vacuum alone has difficulty in drawing the material into such spaces.
0 The maximum final thickness of the finished article is limited to that of the original foamed thermoplastic sheet material.
The thickness of the finished article varies considerably across the surface depending on the draught, and is largely uncontrolled.
Simple vacuum forming can be moderately enhanced by adding a mechanical plug to assist with the moulding process. The mechanical plug is a very basic "male" shape which is lowered on a ram to push the heated thermoplastic material down into the deeper draughts of the bottom tool. This enhances the tool side definition and also gives some very limited definition on the top side of the thermoplastic material.
However, it also suffers from a number of disadvantages:- The maximum final thickness of the finished article is limited to that of the original sheet material.
The thickness of the final article varies considerably across the surface depending on the draught, and is largely uncontrolled.
An alternative technique involving closed die pressure moulding is also used in some situations. In this method, a two-sided tool set (like a clam shell) is used to squeeze a preheated thermoplastic foamed sheet into a high definition shape. This generally overcomes the surface definition problems, but falls short in that:- The maximum final thickness of the finished part is limited to that of the original foam thermoplastic material.
Materials need to be quite thick in comparison to the vacuum forming process described earlier. This substantially increases material costs.
The density of the foam material of the finished article varies greatly as the cell structure is compressed and collapses as a result of the pressure which is applied.
In one aspect the present invention seeks to provide a process and products formed by the process which overcome or ameliorate one or more of the aforesaid difficulties.
Also whilst the various techniques are suitable for producing sheets of moulded foamed thermoplastic materials which can be useful for gaskets in situations where the areas where the gaskets are required to seal are fully supported, they are generally not sufficiently rigid as to provide an adequate seal in regions where the foamed gasketing material is not supported by the construction in which it is being used ie.
the foamed sheet is liable to bend out of shape if it is not supported, with the result that an adequate seal may not be achieved. In another aspect the present invention provides a gasketing material which has sufficient rigidity to allow it to be used in situations where it is not supported, whilst having sufficient sealing capability (as is provided by foamed plastic) to provide an adequate seal in certain situations.
Disclosure of the Invention The invention provides in one aspect a method of moulding thermoplastic sheet to produce a moulded article comprising, heating the thermoplastic sheet, compressing the heated thermoplastic sheet between opposed moulds defining therebetween a cavity having the dimensions of the moulded article, the cavity having at least one region where the thickness of the moulded article formed therein is at least 25% greater than the thickness of the portion of the thermoplastic sheet in the region, and expanding the sheet to substantially fill the region.
Suitably the thermoplastic sheet is a foamed thermoplastic sheet. It may be formed of any suitable foamed material. Examples of suitable materials include PE, EVA, PP, HDPE, TET, HIPS and ABS.
The thermoplastic sheet may comprise a laminate of two or more materials. Suitably at least one of the layers of the laminate is a foamed material. The other material may comprise a solid thermoplastic material and/or a foam.
Suitably the foamed material has a density in the range 15 to 40kgrn 3 More suitably it may have a density in the range 20 to 33 kgm 3 The heating of the sheet may be carried out for sufficient time to allow the thermoplastic material comprising the sheet to soften sufficiently for the moulding to be carried out readily. It may be preheated on one side prior to compression. Where the material comprises a laminate of different materials of different melting points, it is preferred that the material of higher melting point be on the side where preheating is applied.
Preheating can occur using any suitable heating techniques such as radiant heaters, microwave energy or RF energy. Typically, preheating will be to a temperature in the range 150 0 C to 250 0
C.
Secondary heating may be applied whilst the thermoplastic sheet is between the opposed moulds. It may be applied using any suitable heating technique as is known in the art such as microwave, RF or direct contact thermal heating. Heating may be applied through one or more of the opposed moulds. The moulds may be used as electrodes to supply microwave or RF heating.
Prior to compressing the heated themoplastic sheet between the opposed moulds, vacuum may be applied through one of the moulds to cause the heated sheet to conform to the shape of that mould. Alternatively, vacuum may be applied through one mould simultaneously with compression of the heated sheet between opposed moulds.
Subsequently or simultaneously, vacuum may be applied through the other of the opposed moulds. The vacuum may be used as the means by which the thermoplastic sheet is expanded to substantially fill the region where the thickness of the article is greater than the thickness of the thermoplastic sheet.
Following forming of the article in this manner, it may be cooled and unloaded from the moulds. Thus the invention also provides an article which has been moulded by a process as hereinbefore described, the article having at least one area of thickness greater than the thickness of the sheet from which it has been moulded.
In a preferred aspect of the invention, the sheet from which the article is to be moulded may be formed in line with the moulding process by laminating a foam thermoplastic material with a solid thermoplastic material. A heat activated adhesive may be used to adhere the two thermoplastic materials together thereby providing a three-layer composite comprising foam/adhesive/solid material. The method of moulding the thermoplastic material, by virtue of the fact that it involves heating the layers of the sheet, may itself comprise the in line method whereby the adhesive is activated by heat to join the layers together.
Preferred aspects of the invention will now be described with reference to the accompanying drawings.
The invention provides in another aspect a method of manufacturing a composite thermoplastic item comprising, heating a solid sheet of thermoplastic material, retaining at least one block of resilient foam material in a mould, and deforming the heated solid sheet of thermoplastic material with the mould whilst bringing it into compression contact with the block of resilient foam to fasten the solid sheet and resilient foam together, wherein the deformation of the heated solid sheet results in the formation of one or more reinforcing formed profile features in the solid sheet in the region of the sheet which is next to or in contact with the foam to increase the rigidity of the resulting item.
Suitably, the formed profile feature comprises one or more ribs.
The solid sheet of thermoplastic material may comprise any thermoplastic material which is thermo-formable and which has substantially greater stiffness than the block of resilient foam. Examples of materials which may be used for the solid sheet include PVC, HIPS, PP, EVA, and HDPE. The solid sheet may be a laminate of two or more materials. It may be laminated with one or more layers of foamed sheet material separate from the block of resilient foam material.
Suitably the solid sheet of thermoplastic material has a thickness in the range 2mm to 10mm, more preferably 3mm to 6mm.
The block of resilient foam material may comprise EPDM, neoprene, polyurethane, expanded latex or any combination thereof. The block of resilient foam material may comprise a closed cell foam. It may be fastened to the solid sheet by use of a transfer adhesive. Alternatively, it may be fastened via fusion. The adhesive or fusion fastening may be directly to the solid sheet of thermoplastic material. Alternatively, it may be to a secondary material such as the foam sheet described above which may itself be laminated to the solid sheet of thermoplastic material.
The process of deforming the heated solid sheet of thermoplastic material may comprise a simple vacuum forming process. Alternatively, it may comprise a closed die pressure moulding process or a combination of both.
The block of resilient foam material may be retained in a recess in the mould. It may be held in position in the mould by use of vacuum applied through the mould to suck against one surface of the foam material to thereby hold it in place.
Alternatively it may be secured sitting proud of the mould.
Where the solid sheet of thermoplastic material is laminated with one or more foamed sheets, the lamination may be carried out prior to carrying out the method of the invention or the lamination may occur as a result of the heating and deformation steps of the invention. The lamination may occur both before and during the heating and deformation steps.
In one particular embodiment, the composite thermoplastic item produced by the invention may comprise a solid core of PVC laminated on both sides to PE foam sheet and attached to at least one block of EPDM closed cell foam on one of the sides of the laminate.
The formed profile features may extend for at least 80% of the length of the longest dimension of the block of resilient foam. It may extend for greater than that of its longest dimension.
Preferred aspects of the invention will now be described with reference to the accompanying drawings.
Brief Description of the Drawings Figures 1 to 4 show a process according to one embodiment of the invention involving four stages; and Figure 5 shows a cross section concept drawing of a closed die pressure moulding process according to another embodiment of the invention.
Detailed Description of the Drawings Referring to Figure 1, the sheet 10 of thermoplastic material comprises a layer of foamed thermoplastic 12 such as PE, EVA or PP superimposed on a sheet of solid material 14 with a heat sensitive adhesive layer 16 applied therebetween.
The various layers of the sheet may be continuously unrolled from large rolls provided at the side of the forming machinery and advanced in increments as each article is moulded from the sheet.
Initially, the sheet 10 is preheated using radiant heat 20 applied to the top of the sheet whilst it is held above the bottom mould 18.
After radiant heating (shown as arrows 20) has been carried out for sufficient time to raise the temperature to a level where it is softened (eg. 150'C to 250 0 C is typically the temperature range required) the source of radiant heat is moved aside and the top mould 22 is pushed downwardly onto the sheet 10 to bring it into contact with the moulding surface 24 of the bottom mould 18.
Both the bottom and top moulds may themselves apply further heating to the sheet as pressure is applied as shown in Figure 2. Suitably the pressure is at least 2 tonnes/m 2 Initially as the sheet is compressed between the top and bottom moulds, vacuum (shown by way of air flow arrow 25) is applied through the bottom mould 18 via the gallery 26 which connects through a number of very small conduits 28 in the bottom mould communicating with a number of points on the moulding surface 24 of the bottom mould. This has the effect of initially causing atmospheric pressure on top of the sheet 10 to cause the sheet to conform to the shape of the surface 24 of the bottom mould in the manner illustrated in Figure 2 which shows the "First Stage Pressure and Vacuum Form".
It can be seen in Figure 2 that in this section of the process, the mould cavity formed between the top and bottom moulds is so large in certain regions that the sheet is not thick enough to fill it when the top and bottom moulds are pressed together.
When the initial vacuum forming to conform the sheet 10 to the shape of the bottom mould 18 has been completed, a second stage vacuum (shown by way of air flow arrow 33) and heating stage is undertaken. In that stage, further heat is applied and a vacuum is applied through a gallery 32 in the top mould 22 and, as in the case of the bottom mould, a series of small conduits 34 connecting with the moulding surface 36 of the top mould 22 evacuate the upper part of the mould cavity 30. This has the result that the layer of foamed material 12 in the mould cavity expands to fill the cavity completely as shown in Figure 3. During this process, heating of the sheet material being moulded is continued and the heat sensitive adhesive 16 between the layers 12 and 14 causes those layers to adhere together.
After moulding is completed, the heating is stopped and the vacuum is discontinued from both the top and bottom moulds, after which the two moulds are separated in the manner shown in Figure 4. This is the "Cool and Unload" stage of the process. The process provides a moulded article 36 having regions of increased thickness 38 which are of greater thickness than the original foamed material 12 from which the article has been formed. Cooling of the moulded article may be applied by blowing air (shown as flow arrows 40) across the article as it is ready to be removed from the gap between the separated moulds.
The invention is particularly suitable for forming laminates of two different materials, particularly combinations of materials having low density and high density cell structures. Soft, low density, large cell-structures can more readily achieve the desired expansion but typically such materials lack strength. High density, fine cell-structures will give the strength (rigidity, tenacity, shape) but typically will not expand. A laminate combining the two types of materials provides a good combination of properties for the process and end product.
Referring to Figure 5, the sheet 64 of thermoplastic material may comprise an unfoamed thermoplastic such as PVC. It may be laminated with one or more additional thermoplastic sheets on one or both sides of the PVC. The additional sheets may comprise foamed or unfoamed material.
The various layers of the sheet may be continuously unrolled from large rolls provided at the side of the forming machinery and advanced in increments as each article is moulded from the sheet. The moulding process itself may be used to laminate the various layers together. Alternatively, they may be pre-laminated prior to being introduced into the forming machinery.
The bottom mould 68 which includes two recesses 71, which are each loaded with a foam block 73 formed of a material such as closed cell EPDM so that the blocks 73 locate in the recesses 71.
Initially the sheet 64 is preheated using radiant heat prior to being moulded. The top mould 72 may be moved out of position during heating.
Radiant heating is carried out for sufficient time to raise the temperature to where it is softened (eg. 150'C to 250'C is typically the temperature range required). The heated sheet 64 is then held between the top mould 72 and bottom mould 68 when the top mould is moved into place above the sheet.
The foam blocks 73 are held in place in the recesses 71 by vacuum applied through the vacuum lines 78 extending through the bottom mould 68.
The top mould 72 includes two regions of raised profile 81 opposite the foam blocks 73. Thus, when the two moulds 68 and 72 are brought together during the die pressure moulding process, the raised profiles 81 of the top mould forms a rib in the corresponding region of the thermoplastic sheet. This corresponds to the region where each foam block is attached to the sheet 64 on the opposite side of the top mould. Thus the rib extends into the foam block.
Of course it is to be appreciated that more than one rib may be formed by using multiple raised profiles. Furthermore, the rib or ribs may be provided adjacent rather than extending directly into the foam block. Additional profiling on the top and bottom moulds may be used to form the sheet into any desired shape.
Depending upon the materials used for the thermoplastic sheet and foam block, the sheet and foam blocks may be joined by a simple fusion process given the elevated temperature at which the moulding takes place. Alternatively, an adhesive or physical means of attachment may be used.
Whilst the example shown involves thermo-forming using closed die pressure moulding, other moulding process known in the art such as vacuum forming moulding may also be used.
Furthermore, in some applications it may be desirable to use moulds not having recesses for holding the foam blocks. In such instances the foam blocks may be secured in place by mechanical means or vacuum. The deformation of the sheet material during the moulding process over the raised foam blocks will of itself form profile features in the sheet, the profile features acting to increase the rigidity of manufactured composite thermoplastic item.
It is to be understood that the word comprising as used throughout the specification is to be interpreted in its inclusive form ie. use of the word comprising does not exclude the addition of other elements.
It is to be understood that various modifications of and/or additions to the invention can be made without departing from the basic nature of the invention. These modifications and/or additions are therefore considered to fall within the scope of the invention.
Claims (5)
1. A method of moulding thermoplastic sheet to produce a moulded article, said method comprising: heating the thermoplastic sheet, compressing the heated thermoplastic sheet between opposed moulds defining therebetween a cavity having the dimensions of the moulded article, the cavity having at least one region where the thickness of the moulded article formed therein is at least 25% greater than the thickness of the portion of the thermoplastic sheet in the region, and expanding the sheet to substantially fill the region.
2. A method according to claim 1 wherein the thermoplastic sheet is a foamed thermoplastic sheet material.
3. A method according to claim 1 wherein the thermoplastic sheet is a laminate comprising at least two layers, one layer being a foamed material and a second layer being a solid thermoplastic material.
4. A method according to claim 2 or 3 wherein a vacuum is applied through each of the opposed moulds in order to expand the foamed thermoplastic sheet material to substantially fill the region where the thickness of the moulded article is greater than the thickness of the thermoplastic sheet.
5. A method of manufacturing a composite thermoplastic item comprising: heating a solid sheet of thermoplastic material, retaining at least one block of resilient foam material in a mould, and deforming the heated solid sheet of thermoplastic material with the mould whilst bringing it into compression contact with the block of resilient foam to fasten the solid sheet and resilient foam together, wherein the deformation of the heated solid sheet results in the formation of one or more reinforcing formed profile features in the solid sheet in the region of the sheet 14 which is next to or in contact with the foam to increase the rigidity of the resulting item. Dated this 9th day of January 2005 Universal Forme Pty Ltd by their patent attorneys Morcom Pernat
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| AU2006100019A AU2006100019A4 (en) | 2005-01-13 | 2006-01-10 | Moulding Thermoplastic Materials |
Applications Claiming Priority (5)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| AU2005900117 | 2005-01-13 | ||
| AU2005900117A AU2005900117A0 (en) | 2005-01-13 | Moulding Thermoplastic Materials | |
| AU2005901384A AU2005901384A0 (en) | 2005-03-22 | Composite Material | |
| AU2005901384 | 2005-03-22 | ||
| AU2006100019A AU2006100019A4 (en) | 2005-01-13 | 2006-01-10 | Moulding Thermoplastic Materials |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| AU2006100019A4 true AU2006100019A4 (en) | 2006-02-09 |
Family
ID=35976902
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| AU2006100019A Ceased AU2006100019A4 (en) | 2005-01-13 | 2006-01-10 | Moulding Thermoplastic Materials |
Country Status (1)
| Country | Link |
|---|---|
| AU (1) | AU2006100019A4 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114770849A (en) * | 2022-05-13 | 2022-07-22 | 东莞海博斯新材料科技有限公司 | Supercritical die pressing foaming equipment for preparing foaming elastomer |
-
2006
- 2006-01-10 AU AU2006100019A patent/AU2006100019A4/en not_active Ceased
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114770849A (en) * | 2022-05-13 | 2022-07-22 | 东莞海博斯新材料科技有限公司 | Supercritical die pressing foaming equipment for preparing foaming elastomer |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FGI | Letters patent sealed or granted (innovation patent) | ||
| MK22 | Patent ceased section 143a(d), or expired - non payment of renewal fee or expiry |