AU738958B2

AU738958B2 - Apparatus and method for producing wood fibres-plastic composite articles

Info

Publication number: AU738958B2
Application number: AU80865/98A
Authority: AU
Inventors: Martyn Evan Bowis; Mervyn Uprichard
Original assignee: New Zealand Forest Research Institute Ltd
Current assignee: New Zealand Forest Research Institute Ltd
Priority date: 1997-08-20
Filing date: 1998-08-20
Publication date: 2001-10-04
Anticipated expiration: 2018-08-20
Also published as: AU8086598A

Description

P/00/01i1 Regulation 3.2

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT S S

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S

4* S S S S

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Invention Title: Articles Apparatus and Method for Producing Wood Fibres-Plastic Composite The following statement is a full description of this invention, including the best method of performing it known to me/us: FHPMELC69823201 4.6 a PATENTS FORM 5 PATENTS ACT 1953 COMPLETE SPECIFICATION Number Dated 328575 21 August 1997 APPARATUS AND METHOD FOR PRODUCING WOOD FIBRES-PLASTIC COMPOSITE ARTICLES We, NEW ZEALAND FOREST RESEARCH INSTITUTE LIMITED, a New Zealand company, of Sala Street, Rotorua, New Zealand do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement.

BACKGROUND

The invention comprises a diaphragm thermoformer and method for thermoforming a wood fibres-thermoplastic composite material.

FIELD OF INVENTION Wood fibre-thermoplastic composites comprise a matrix of a thermoplastic material which surrounds and encloses wood fibres so that the fibres act as reinforcing elements in the matrix. High temperature mechanical pulp (HTMP) fibres mechanically refined at an elevated temperature and thermoplastic polymers may be used to make sheets known as "prepregs" or pre-impregnated sheets. These are manufacturing intermediates, usually produced as flat sheets, for future shaping by pressing or forming at temperatures which soften or plasticise the thermoplastic 15 polymer.

Typically such fibre-thermoplastic composites are moulded using a matched die press which can be internally heated and/or cooled but the dies required are expensive to manufacture and with HTMP-PP prepregs wood fibre rupture may occur.

SUMMARY OF INVENTION It is an object of the invention to provide an improved or at least alternative means 25 and method for forming shaped wood fibres-thermoplastic composite articles.

In broad terms in one aspect the invention comprises a diaphragm thermoformer for thermoforming a wood fibres-thermoplastic composite material, comprising at least one pair of flexible diaphragms mountable adjacent a mould on one side of the pair of diaphragms and an inlet into and outlet from a space between the diaphragms enabling hot fluid to be circulated between the diaphragms to heat a wood fibresthermoplastic composite material placed between the diaphragms and the mould, and a space on the other side of the pair of diaphragms into which a fluid under pressure may be introduced to force the diaphragms and the wood fibres- 62704 thermoplastic composite material against the mould after heating and removal of the hot fluid from between the diaphragms, to shape the wood fibres-thermoplastic composite material to a mould.

Preferably the diaphragm thermoformer includes a second pair of flexible diaphragms mounted between the first diaphragm pair and the mould and an inlet into and an outlet from a space between the second pair of diaphragms enabling hot fluid to be circulated between the second pair of diaphragms to heat the wood fibres-thermoplastic composite material when placed between the two diaphragm pairs.

In broad terms in another aspect the invention comprises a method for thermoforming a wood-fibres composite material comprising positioning a preformed wood fibres-thermoplastic composite sheet, or a mat of wood fibres containing a thermoplastic material in particulate form, between at least one pair of flexible diaphragms and a mould, circulating a hot fluid between the diaphragms to heat the wood fibres-thermoplastic composite material, and subsequently introducing a fluid under pressure into a space on the other side of the pair of diaphragms to force the diaphragms and the wood fibres-thermoplastic composite material against the mould after heating and removal of the hot fluid from between o* the diaphragms, to shape the wood fibres-thermoplastic composite material to the S- mould.

Preferably the method includes positioning either a performed wood fibres- "25 thermoplastic composite sheet, or a mat of wood fibres containing a thermoplastic material in particulate form, between a first pair and a second pair of flexible diaphragms mounted adjacent a mould, circulating a hot fluid between the two diaphragms of each pair of diaphragms to heat the wood fibres-thermoplastic composite material, and subsequently introducing a fluid under pressure into a space on the other side of the pairs of diaphragms from the mould to force the wood fibres-thermoplastic composite material against the mould after heating and removal of the hot fluid from between the diaphragms, to shape the wood fibresthermoplastic composite material to the mould.

62704 BRIEF DESCRIPTION OF THE FIGURES The invention will be further described with reference to the accompanying drawings wherein: Figure 1 shows cross section a MDF-PP laminate undergoing consolidation to form a prepreg, Figure 2 is a schematic cross-section of a preferred form of an oil heated diaphragm thermoformer of the invention, Figure 3 is a schematic cross-section similar to Figure 1 showing insertion of a prepreg into the preferred form diaphragm thermoformer when open, Figure 4 shows the prepreg in place in the diaphragm thermoformer after closing, Figure 5 shows heating of the prepreg in the diaphragm thermoformer, Figure 6 shows the diaphragm thermoformer undergoing oil evacuation immediately prior to commencement of forming, Figure 7 shows moulding of the prepreg to shape with the application of pressure provided by the introduction of compressed air into the diaphragm thermoformer, Figure 8 shows the replacement of air with water to solidify the composite material, Figure 9 is a perspective view of the preferred form diaphragm thermoformer with mould cut away, Figure 10 is a schematic cross-section of the preferred form diaphragm thermoformer in a press, 62704 Figure 11 is an oil circulation diagram for the preferred form diaphragm thermoformer, Figures 12 and 13 are schematic longitudinal and transverse cross-sections of a CTP dynamic sheet former for forming a mat of wood fibres, Figure 14 is a schematic diagram of a dry mat former for forming a mat of wood fibres, and Figure 15 is a schematic longitudinal cross-section of the drum and fibre delivery head of the dry mat former of Figure DETAILED DESCRIPTION OF PREFERRED FORMS 15 Typically prepregs are prepared from wood fibres and powdered thermoplastic material such as polypropylene. The wood fibres are formed into a mat and the polymer'powder is enclosed between two layers of wood fibres. The uncompressed fibre mat-thermoplastic-fibre mat is hot pressed, and subsequently cooled, to form a prepreg comprising a flat wood fibres- thermoplastic composite sheet.

Manufacture of prepregs is shown in Figure 1. An uncompressed wood fibresthermoplastic-wood fibres laminate assembly 21 is placed between flexible diaphragms 22 mounted in frame 23 and a vacuum drawn between the diaphragms 22. The assembly is placed in a hot press between spacer plates 24 and then the 25 press platens 25 are closed. The thermoplastic material melts and flows to oo surround and enclose the wood fibres. Subsequently the laminate is allowed to cool and is removed from the press.

Figures 2-11 illustrate the oil heated diaphragm thermoformer of the invention and it's operation. The thermoformer comprises two pairs of diaphragms 26. The diaphragms of each pair are sealed at their perimeter by frame assembly 27. The diaphragms may be formed of silicone rubber or other elastic materials which can withstand heat and pressure and which have sufficient flexibility and-memory to allow adequate forming and then regain their shape. Hot oil may be circulated 62704 between each pair of diaphragms as indicated in Figure 2. A vacuum may be drawn between the two pairs of diaphragms as also shown in Figure 2. Air or cold water may be pumped into the space between the lower diaphragm pair as shown.

In use prepreg 27 previously formed as described above is placed between two pairs of oil filled diaphragms 26 as shown in Figure 3. The former is then closed as shown in Figure 4.

Hot oil, at 180'C for example, is pumped into the space between each pair of diaphragms 26 as shown in Figure 5, to heat the prepreg. Preferably a relatively high oil flow rate is used to ensure rapid heating of the prepreg. The prepreg is also under vacuum. A blank 28 is used above the diaphragms instead of a wooden mould 28 at this stage of the process. After sufficient time for the prepreg to soften, the oil flow rate is reduced and the blank 28 is replaced by a mould 29 of the 15 desired shape as shown in Figure 6.

The oil between the diaphragm pairs is then pumped out. To commence forming of the moulded article, air pressure is introduced below the diaphragms to push the diaphragms and the prepreg up into the cavity of the mould 29, as shown in Figure 7. Evacuation of the oil is necessary to ensure that the prepreg completely conforms to the mould.

Next cold water is introduced below the diaphragms to freeze the prepreg in its new shape, as shown in Figure 8. Alternatively cold oil or other fluid may be used 25 instead of water. The vacuum is maintained. When the prepreg has cooled the water is drained, the thermoformer assembly is opened and the moulded article is removed.

Fig 10 shows the preferred form diaphragm thermoformer in a press. The thermoformer is held between two press platens 30, separated by insulation layers 31. Pressure is exerted by ram 32.

An oil circulation diagram is shown in Figure 11 showing the use of two oil heaters 71 and 72 one at a lower temperature such as 130°C and one at a higher 62704 temperature such as 180 0 Oil from these heaters is pumped into the thermoformer via manifold 73 and then received by a further manifold 74 and returned for reheating.

Instead of reshaping a performed wood fibres-thermoplastic composite prepreg as described above, a mat of uncompressed wood fibres containing a thermoplastic material in particulate form may be placed in the thermofdrmer 'between the diaphragms an consolidated and shaped in a single step in the diaphragm thermoformer of the invention.

While in the prepared form diaphragm thermoformer shown in the drawings there are two pairs of diaphragms 26, in a simpler form there may be only a single pair of diaphragms which both heats the prepreg when oil is circulated between the diaphragms, and presses the composite material against the mould.

S* Figures 12 and 13 schematically show one form of wet sheet former for forming a :1 mat of wood fibres, which consists of a large container 41 housing a perforated drum 42 which may independently rotate at high speed like a centrifuge. Water is allowed to collect on the inside of the large container 41 and forms a wall of water due to the centrifugal forces applied to it by the rotating inner perforated drum 42.

The thickness of the water wall 43 is regulated by a movable exit or shoe 44. The water removal shoe 44 is movable along the base of the large container 41 as indicated by arrow R in Figure 12. A spray arm 45 is movable within the drum as it rotates, as indicated by arrows in Figure 12. In use, fibres suspended in water pass 25 through the spray arm 45, and are sprayed by a spray nozzle onto the interior of the drum 42. The arm 45 moves back and forth in the direction of arrows spraying the fibres suspension against the sides of the drum 42 along its length. A paper making wire 48, placed onto the inside of the perforated drum 42, filters fibre from water sprayed onto it by the moving spray arm 45. Once sufficient fibre has built up on the paper making wire, all the water is removed from within the container 41 using the shoe 44, the rotation of the perforated drum 42 is stopped, and the wires 48 supporting the newly formed fibre mat are removed together. Excess water is removed from the wire and fibre mat using blotters and then the fibre mat is removed from the paper-making wire and subsequently dried.

62704 Figures 14 and 15 illustrate one form of dry mat former for forming a mat of wood fibres. Dry fibre 51 is placed in a hopper 52 and fed by a rotating paddle 53 down a delivery pipe 54. A conveyor belt 55 at the bottom of the delivery pipe 54 scavenges a thin layer of fibre from the fibre column inside the pipe 54. The thin layer of fibre is sucked off the conveyor 55 and through a pair of separation processors 56 by an air turbine 57. The separation processors 56 use a rotating blade (not shown) to break up clumps of fibre. The air turbine 57 forces the fibres suspended in the airstream along a duct 58 and out through a fibre delivery head 59 onto a rotating drum 60, the surface of which is perforated or is formed by a fibre mesh or similar.

Figure 15 shows the drum 60 and fibre delivery head 59 in schematic cross-section.

Air is sucked into the rotating drum through its surface and out through axial suction pipe 61, as indicated by arrows X. Fibre is filtered from the airstream by the 15 surface of the drum 60 and flattened out by an external roller 62 (see Figure 14).

Successive layers of fibre are built up on the surface of the rotating drum to form a fibre mat 63. Once a mat 63 of sufficient thickness has been formed the delivery of fibre is ceased, the roller 62 is removed, and the drum is stopped. The suction is stopped and the dry fibre mat 63 is carefully removed from the drum surface. In use the fibre delivery head 59 moves back and forth along the length of the drum in the direction of arrows Y, between walls 64. Adjacent each wall 64 is a recycle collection pipe 65 with an opening 66 for collecting fibres falling just outside the boundary wall 64.

The foregoing describes the invention and modifications and alterations thereto may be made without departing from the scope of the invention as defined in the following claims.

It will be understood that the term "comprises" or its grammatical variants as used herein is equivalent to the term "includes" and is not to be taken as excluding the presence of other elements or features.

62704

Claims

1. A diaphragm thermoformer for thermoformig a wood fibres-thermoplastic composite material, comprising at least one pair of flexible diaphragms mountable adjacent a mould on one side of the pair of diaphragms and an inlet into and outlet from a space between the diaphragms enabling hot fluid to be circulated between the diaphragms to heat a wood fibres- thermoplastic composite material placed between the diaphragms and the mould, and a space on the other side of the pair of diaphragms into which a fluid under pressure may be introduced to force the diaphragms and the wood fibres-thermoplastic composite material against the mould after heating and removal of the hot fluid from between the diaphragms, to shape the wood fibres-thermoplastic composite material to a mould.

2. A diaphragm thermoformer according to claim 1 including a second pair of eo 5 .flexible diaphragms mounted between the first diaphragm pair and the 15 mould and an inlet into and-an outlet from a space between the second pair of diaphragms enabling hot fluid to be circulated between the second pair of oo diaphragms to heat the wood fibres-thermoplastic composite material when placed between the two diaphragm pairs. S:

3. A diaphragm thermoformer according to claim 2 including a port enabling 0*• air to be drawn from the space between the diaphragm pairs. *6

4. A diaphragm thermoformer according to claim 3 including a reservoir, a fluid heater, and a hot fluid circulation circuit including a pump connected oo to the inlet to and outlet from the space between each pair of diaphragms; an air evacuation path and a pump, connected to the port enabling air to be drawn from between the diaphragm pairs; and an air compressor and a coolant reservoir and coolant circulation circuit including a pump, connected to said space below the first pair of diaphragms; and an associated control system arranged to first cause the circulation of hot fluid between the diaphragms of each of the diaphragm pairs and simultaneously evacuation of air from the space between the diaphragm pairs, and subsequently evacuation of the hot fluid from between the diaphragm pairs 62704 and the introduction of fluid under pressure to the space below the first pair of diaphragms to force the diaphragm pairs and the wood fibres- thermoplastic composite material against the mould after heating, and subsequently the evacuation of fluid under pressure and the introduction of cooling fluid into said space below the first pair of diaphragms.

A method for thermoforming a wood-fibres composite material comprising positioning a pre-formed wood fibres-thermoplastic composite sheet, or a mat of wood fibres containing a thermoplastic material in particulate form, between at least one pair of flexible diaphragms and a mould, circulating a hot fluid between the diaphragms to heat the wood fibres-thermoplastic composite material, and subsequently introducing a fluid under pressure into a space on the other side of the pair of diaphragms to force the diaphragms and the wood fibres-thermoplastic composite material against 0the mould after heating and removal of the hot fluid from between the *0 15 diaphragms, to shape the wood fibres-thermoplastic composite material to the mould. o•

6. A method of thermoforming a wood fibres-composite material to a mould, comprising positioning either a performed wood fibres-thermoplastic composite sheet, or a mat of wood fibres containing a thermoplastic 20 material in particulate form, between a first pair and a second pair of flexible diaphragms mounted adjacent a mould, circulating a hot fluid space between the two diaphragms of each pair of diaphragms to heat the wood fibres-thermoplastic composite material, and subsequently introducing a fluid under pressure into a space on the other side of the pairs of diaphragms from the mould to force the wood fibres-thermoplastic composite material against the mould after heating and removal of the hot fluid from between the diaphragms, to shape the wood fibres-thermoplastic composite material to the mould.

7. A method according to claim 6 including evacuating air from the space between diaphragm pairs while circulating the hot fluid. 62704

8. A method according to any one of claims 5 to 7 including replacing said fluid under pressure with a cooling fluid while maintaining pressure on the diaphragms towards the mould to press the wood fibres-thermoplastic composite material against the mould, to cool and set the composite material prior to removal from the thermoformer.

9. A method according to any one of claims 5 to 8 wherein said mat of wood fibres, or a mat of wood fibres from which said preformed wood fibres- composite sheet has previously been formed, is formed by depositing free fibres onto the exterior of a perforated rotating drum from the interior of which air is continuously drawn during rotation of the drum so that a layer of fibres is drawn against the drum to form the fibres mat.

A method according to any one of claims 5 to 8 wherein said mat of wood fibres, or a mat of wood fibres from which the said preformed wood fibres- o1** 1 thermoplastic composite sheet has previously been formed, has been 15 formed by spraying a suspension of wood fibres in water onto the interior surface of a perforated rotating drum from which water may drain during .rotation of the drum so that a layer of fibres is deposited against the interior of the drum to form the fibres mat.

11. A diaphragm thermoformer for thermoforming a wood fibres-thermoplastic 20 composite material, substantially as shown in Fig 2 of the accompanying drawings and described herein with reference thereto.

12. A method for thermoforming a wood fibres-thermoplastic composite material, substantially as described herein with reference to Figs 2 to 8 of the accompanying drawings.

13. A shaped wood fibres-thermoplastic composite product formed to shape on a diaphragm thermoformer, or by a method of thermoforming, according to any one of claims 1 to 4 and 11, or 5 to 10 and 12. NEW ZEALAND FOREST RESEARCH INSTITUTE LIMITED By Freehills Patent Attorneys Registered Patent Attorneys for the Applicant 16 September 1998 62704