WO1994005480A1

WO1994005480A1 - A method of producing veneer-faced items

Info

Publication number: WO1994005480A1
Application number: PCT/GB1993/001661
Authority: WO
Inventors: Alan Fraser Sawyer
Original assignee: Automotive Fascia Systems Limited
Priority date: 1992-08-26
Filing date: 1993-08-05
Publication date: 1994-03-17
Also published as: AU4721893A; GB9218148D0

Abstract

A method of producing wood veneer-faced moulded items, comprising the steps of placing between a pair of heated profile forming dies, a sheet of a decorative wood veneer, and a quantity of a hot curing catalysed resin-based moulding compound containing a mixture of fillers and reinforcing fibres, with a slip sheet between the wood veneer and the adjacent die surface, and closing the dies together under a predetermined pressure and temperature and for a predetermined time. The dies interact to form an edgewise pinch line whereby excess material is trimmed in the moulding process, and further excess material is released remote from the pinch line. A wood veneer-faced moulded article is produced without the use of adhesives but with sufficient inherent integrity for use without additional reinforcement. Prior to closure of the dies, a further polymeric component may be combined with the veneer sheet which in the finished product will enhance the surface texture thereof.

Description

A METHOD OF PRODUCING VENEER-FACED ITEMS

This invention relates to a method of producing veneer-faced items. Such items are used particularly, though by no means exclusively, in the automotive industry for the interior trim of vehicles.

Veneer-faced items have traditionally been produced by a lamination process in which a decorative wood veneer is bonded to a foundation. One traditional process involves the application of a liquid or impregnated sheet adhesive between a number of laminae, including an outer veneer layer, which are built up to form the completed article. In another known process, in which the foundation is moulded, either the foundation is preformed and the decorative veneer then added, usually by membrane or compression moulding, or the formation of the foundation and attachment of the veneer is carried out simultaneously. In either case, generally adhesive is employed to attach the veneer to the foundation. With both known processes, there then follows a machining operation to remove excess material. Thus the process can be lengthy and expensive, and the surface finish of the article is dependent largely upon the combining force which can be applied and the characteristics of the materials used.

It is amongst the objects of the present invention to provide a method of producing veneer-faced moulded items, which is performed using less materials in a shorter time and without specially skilled personnel, and does not involve the use of adhesives.

According to one aspect of the present invention, there is provided a method of producing wood veneer-faced moulded items comprising the steps of providing a quantity of an uncured thermosetting resin-based moulding compound and a sheet of a decorative wood veneer, placing said two components in superimposed relationship between a pair of forming dies at least one of which is heated, closing the dies together with a predetermined pressure and temperature, and for a predetermined time, the dies interacting to form a pinch line such that excess moulding compound is at least partially trimmed as the dies close together, further excess moulding compound being released at a position remote from said pinch line, and subsequently opening the dies to remove the so-formed veneered item therefrom.

The advantages of this method include the fact that no adhesive need be provided, giving a saving in terms of material costs and process time. Furthermore, the at least partial trimming of excess moulding compound means that the further finishing trimming steps necessary can be reduced. The cooperation of the dies at the pinch line can also be employed to trim excess wood veneer so that a pre-shaped sheet does not have to be provided, nor does a veneer trimming finishing step have to be performed.

Release of further excess moulding compound at a position remote from the pinch line will further reduce the finishing necessary, particularly if, as in a preferred embodiment, the further excess moulding compound is removed at the release position by a powered shear before opening of the dies. Moreover, release of the further excess moulding compound ensures avoidance of excess pressure on the veneer which could cause it to shatter.

According to another aspect of the present invention, there is provided a method of producing wood veneer-faced moulded items comprising the steps of providing a quantity of an uncured thermosetting resin- based moulding compound and a sheet of a decorative wood veneer, placing said two components in superimposed relationship between a pair of forming dies at least one of which is heated, combining with the wood veneer a further polymeric component of a type which, in the finished product, will enhance the surface texture thereof, closing the dies together with a predetermined pressure and temperature, and for a predetermined time, and subsequently opening the dies to remove the so-formed veneered item therefrom.

The heat and pressure of the forming operation is in this method also employed to improve the surface appearance of the veneer so that, in some cases, further surface finishing of the veneer will not be required..

Preferably, a slip sheet of a material having a low coefficient of friction is placed between the decorative veneer and the adjacent die surface prior to closing the dies. The slip sheet helps prevent cracking of the veneer, particularly in the portions thereof adjacent the pinch line. Its presence also results in the wood veneer being pressed, during forming of the veneer-faced item, against a smooth surface which will improve the surface finish of the veneer.

The die surface which is to come into contact with the moulding compound may be pre-coated with a release agent, such as a zinc stearate wax.

The process parameters may suitably be as follows: a closing pressure of between 50 bar and 500 bar, a temperature of between 80°C and 160°C, and a closure time of between 30 seconds and 10 minutes. Very preferably, the method is carried out in a vacuum chamber. If the dies define one or more blind holes into which moulding compound is forced during the formation process to form one or more projections for use, for example, as fixing locations, the vacuum significantly improves the uniformity of the projections and formation thereof in the desired shape. A vacuum during formation will also improve the surface finish of the veneer in the case where a further polymeric component is combined with the veneer prior to closure of the die, particularly if that further polymeric component is in liquid form. The vacuum prevents formation of air bubbles at the edges of the item.

Any suitable thermosetting resin-based moulding compound may be employed. If the compound is polyester resin-based, steps are preferably taken to ensure that any water is removed therefrom prior to placement between the dies. If the compound is phenolic resin-based, water may be removed before beginning the process, or an opening step is introduced into the process to allow steam release from the region between the dies.

The invention will now be further described, by way of example only, with reference to the accompanying drawings in which:-

Figure 1 is an isometric view of a moulded item produced by a method of the invention;

Figure 2 is a schematic side view of a pair of dies in an open condition prior to closure to form a moulded item, in accordance with the method of the invention; and

Figure 3 is a schematic side view similar to Figure 2 but with the dies in a closed condition.

A moulded item of the kind illustrated in Figure 1 comprises a two-part lamination consisting of an inner layer 10 formed from a thermosetting resin-based moulding compound, and a sheet of wood veneer 11 moulded thereto. The item may be, for example, a decorative wooden strip forming part of a fascia rail for the interior of a motor car. Therefore the view illustrated in Figure 1 is of the rear or underside of such an item and there are included a number of attachment pegs 12 which are integrally formed with the compound layer 10, as will be described, during the process.

Referring now to Figure 2 which shows a pair of heated dies 13 and 15 ready to be closed together for the forming process, the upper die 15 contains a central recessed profile 14 which will determine the shape of the finished article. Initially, with the upper die 15 raised in an open condition with respect to the lower die 13, there is placed thereon a quantity of resin-based moulding compound 10. There is then superimposed on compound 10 a cut blank or sheet 11 of wood veneer. This is then covered with a slip sheet 16 of material with a low coefficient of friction.

The lower die 13 includes a pommel 19 with a profile which is related in shape to, and mates with, the profile 14 of die 15, except for a number of bores 20 which are spaced apart along the lower die 13 to receive sprues of the moulding compound for the formation of the location pegs 12, and which extend to provide a number of material evacuation holes 21 to enable excess moulding compound, see 22, to escape from the moulding cavity.

The bores of the holes 21 must be large enough to allow the correct pressure in the moulding cavity thus eliminating sinkage on the surface of the moulded component near to the pegs 12. On the other hand, they must be sized such that the pressure in the moulding cavity does not cause cracking of the veneer sheet 11 during the moulding process. The holes 21 may have a diameter of between 0.25 mm and 3.0 mm, dependent on the size of the item to be formed and on the degree to which excess moulding compound is released elsewhere. The holes 21 need not, and in some cases, preferably do not, form continuations of bores 20.

In the moulding process, the dies 13, 15 are moved together by movement of both or one relative the other. The dies 13, 15 are heated to a temperature which is adjustable, for example between 80°C and 160°C and the pressure under which the dies are closed may be selected between, for example, 50 bar and 500 bar. The temperature and pressure to which the dies are set and the period during which they are maintained in the closed condition, which may be between 30 seconds and 10 minutes, are all variable and selected according to the thicknesses and quantities of the materials, the complexity of configuration of the article to be produced, and the surface finishes to be afforded.

The moulding process is preferably carried out under vacuum conditions which may be achieved by positioning the dies 13, 15 in a vacuum chamber. The vacuum assists in ensuring that the moulding compound completely fills the bores 20 to ensure complete and even formation of the location pegs 12. It will be seen from Figure 3 that during the forming process excess veneer, slip sheet and moulding compound, are trimmed, see 23, at a pinch line 24 to produce the finished article shown in Figure 3. The trimming results from cooperation of the portion of the lower die 13 below the pommel 19 and the flared edge of the central recess of the upper die 15. These act together to cause cutting through of the moulding compound, veneer and slip sheets, commencing with the moulding compound which reduces the danger of cracking of the veneer at the edges of the item. The excess waste 23 is folded' down and away by the flared edge prior to final severance. The cooperation between the flared edge and the lower die 13 below the pommel 19 also causes the veneer to be bent around such that the edge of the item is completely covered by veneer.

Alternatively, the dies 13, 15 may be arranged such that a narrow gap remains therebetween at the pinch line 24 so that a release point for excess moulding compound is provided. Partial trimming will occur upon closure of the dies and removal will be completed by a subsequent minor trimming operation.

In all cases, excess moulding material is released at the pinch line 24 thus preventing excess pressure build¬ up in the moulding cavity. However the pinch line gap must not be such that there is insufficient pressure build-up within the cavity to properly set the moulding compound and attach the veneer thereto.

The pegs 12 are formed from the moulding compound as can be seen in Figure 3, and a powered shearing blade 25 is provided beneath the lower die 13 which moves linearly and automatically to remove excess moulding compound which has escaped through holes 21.

Upon completion of the forming process as described, the dies 13, 15 are separated and the thus formed item is removed from between the dies whereupon the slip sheet 16 may be discarded. The components of the moulded article will retain their moulded form, no post-moulding curing being required to achieve this stability.

The veneer is, in effect, bonded to the moulding compound by virtue of the heat and pressure applied in the forming process and the interfacial characteristics of the two materials. No additional adhesive substance is needed to bond the laminae together.

The material used for the moulding compound is a reinforced thermosetting plastics material in the form of an uncured, hot curing, catalysed resin. The resin which may be, for example, polyester resin or phenolic resin can be impregnated with glass or carbon fibres and/or fillers.

One suitable material is so-called "dough moulding compound" which has a dough-like texture, is somewhat tacky to the touch and is normally supplied in quantities which are commensurate with the expected period of use or shelf life. The required quantity of dough moulding compound is cut from the bulk supply and placed against the wood veneer prior to moulding. An alternative material is so-called "bulk moulding compound" which is very similar in appearance and texture to dough moulding compound but is formulated to produce mouldings of improved quality and finish.

As a further alternative, there is so-called "sheet moulding compound" which is supplied in sheet form usually some 3.0 mm thick and sandwiched between two polyethylene film layers to prevent contamination and adhesion during delivery and storage. This form of the compound is much easier to use since blanks equivalent in size to the wood veneer blanks may be cut from the sheet using a sharp knife.

The use of the slip sheet 16 reduces the incidence of veneer cracking by allowing it to be shaped more readily by sliding into the desired component profile.

The slip sheet 16 also provides a smooth surface against which the veneer 11 is pressed during the moulding process which improves the surface finish of the veneer. The slip sheet may comprise polyester film, particularly preferably, a film of the material sold under the name MJLAR.

The die which is to come into contact with the moulding compound is preferably pre-coated with a release agent such as a zinc stearate wax, particularly in cases where the compound is to fill the blind bores 20 to form the pegs 12. Alternatively a second slip sheet can be employed which is suitably apertured.

The surface texture of the veneer in the finished product is enhanced by combining with it a further polymeric component. This may be effected by pre- impregnating or pre-coating the wood veneer with a polyester resin or by placing over the veneer, prior to pressing, a clear pre-catalysed thermosetting polymeric sheet material, thus produces a surface coating on the finished product. A further alternative is to spray polyester resin on to the die surface which is to come into contact with the veneer. The heat and pressure of the moulding process cures the polyester resin which is suitably thermosetting and forms a "lacquer" on the veneer in the finished item. Further lacquering steps may be necessary on completion of the moulding process if a particularly good finish is required. This may be achieved by coating or spraying the moulded item or by applying a sheet of coating material using a lower flowing temperature polymer.

Vacuum conditions enhance the effect of combining the veneer with a further polymeric component and, in particular, prevent formation of air bubbles at the edges of the veneer on the surface thereof.

A method of producing veneer-faced moulded items as described herein provides considerable advantage over the conventional vacuum/diaphragm forming system in requiring less material whilst ensuring lower manufacturing times and higher quality surface definition on the finished product. Further, the wood veneer will conform to more complex profiles with the increased temperature and pressure provided by the present process when•compared with vacuum forming. The dies 13, 15 therefore do not need to be symmetrical and the pinch trim line 24 does not need to be straight.

Only two laminae are required to produce complex shapes normally requiring a greater number of laminated materials. This aspect also ensures reduced preparation times and thus product costs.

Integral location or fixing means _' such as the pegs 12 of adequate strength may be formed with the process as a result of the increased pressure and temperature achieved therein.

Claims

1. A method of producing wood veneer-faced moulded items comprising the steps of providing a quantity of an uncured thermosetting resin-based moulding compound and a sheet of a decorative wood veneer, placing said two components in superimposed relationship between a pair of forming dies at least one of which is heated, closing the dies together with a predetermined pressure and temperature, and for a predetermined time, the dies interacting to form a pinch line such that excess moulding compound is at least partially trimmed as the dies close together, further excess moulding compound being released at a position remote from said pinch line, and subsequently opening the dies to remove the so-formed veneered item therefrom.

2. A method of producing wood veneer-faced moulded items comprising the steps of providing a quantity of an uncured thermosetting resin-based moulding compound and a sheet of a decorative wood veneer, placing said two components in superimposed relationship between a pair of forming dies at least one of which is heated, combining with the wood veneer a further polymeric component of a type which, in the finished product, will enhance the surface texture thereof, closing the dies together with a predetermined pressure and temperature, and for a predetermined time, and subsequently opening the dies to remove the so-formed veneered item therefrom.

3. A method according to Claim 2, wherein said further polymeric component is provided in the form of a thermosetting polymeric sheet of material which is placed over the veneer prior to pressing to produce a surface coating on the finished product.

4. A method according to Claim 3, wherein the polymeric sheet is of a clear pre-catalysed material.

5. A method according to Claim 2 , wherein said further polymeric component is provided by spraying, coating or impregnating the wood veneer with a polyester resin prior to use.

6. A method according to Claim 2, wherein the further polymeric component is provided by spraying the die surface which is to come into contact with the wood veneer with a polyester resin prior to closing the dies.

7. A method as claimed in any one of Claims 2 to 6, wherein the dies interact to form a pinch line such that excess moulding compound is at least partially trimmed as the dies close together, further excess moulding compound being released at a position remote from said pinch line.

8. A method according to either Claim 1 or Claim 7, wherein said further excess moulding compound is removed at said release position by a powered shear.

9. A method according to any preceding Claim, wherein a slip sheet of a material having a low coefficient of friction is placed between the wood veneer and the adjacent die surface prior to closing the dies.

10. A method according to any preceding Claim, wherein the die surface which is to come into contact with the moulding compound is pre-coated with a release agent such as a zinc stearate wax.

11. A method according to any preceding Claim, wherein the predetermined closing pressure of the dies is between 50 bar and 500 bar and/or the dies are heated to a temperature of between 80°C and 160°C and/or the predetermined time for which said dies are closed together is between 30 seconds and 10 minutes.

12. A method as claimed in any preceding Claim, wherein the closing together of the dies is carried out in a vacuum.

13. A method according to any preceding Claim, wherein the moulding compound is either so-called "dough moulding compound" or so-called "bulk moulding compound".

14. A method according to any preceding Claim, wherein the moulding compound is a hot curing catalysed polyester resin containing a mixture of' fillers and reinforcing fibres.