AU1847499A - Improvements relating to gaskets and their manufacture - Google Patents

Description

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AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION STANDARD PATENT "Improvements Relating to Gaskets and their Manufacture" The following statement is a full description of this invention, including the best method of performing it known to me: 2 Improvements Relating to Gaskets and their Manufacture This invention concerns the manufacture and use of gaskets. It has particular use for gaskets which may be used in the automobile manufacturing industry for sealing around plastic mouldings and sheet metal in bodywork, and especially around mouldings which form the frames for body glass where the frames fit to panels. The invention has wide potential for sealing applications in the bodies of a wide variety of transport vehicles such as cars, buses, trucks and trains.

"Many forms of gaskets have been proposed and used for sealing between the window frames and their mating surfaces in an automobile body. Traditionally these gaskets have been of solid moulded or extruded construction or die-cut from foam sheets, S: blocks or tapes. The foam versions have been of either closed cell or solid type in .15 order to prevent water penetration, or open cell type for improved sound absorption.

Sound absorption is an important feature as the NVH performance of automobiles gains greater attention. Closed cell foams are not as good at absorbing sound as open cell foams are, whereas open cell foams do not provide a water barrier.

S.i 20 A gasket's main purpose is to form a seal between surfaces. However there is a need for a gasket construction which provides the NVH performance advantages of the open cell type with the water barrier advantages of the closed cell type.

Skins may be put onto foamed materials and self skinning foamed materials are well known in the plastics moulding industry. These skins can be made impervious to water. They are produced when the foam at an open surface or, more commonly at a mould surface, collapses to produce a relatively hard skin. Modern soft-feel automobile steering wheels for example are commonly made by this technique. The restricted flexibility in such a skin, and the higher moulding densities required, make

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self skinning foams generally unsuitable as gasket materials of the type presently required.

It is well known to coat a relatively rigid foamed plastics material by pouring a thick layer of surfacing compound onto an inner surface of a mould and then filling the mould with a relatively rigid foam material. Many current automobile bumpers are made in this manner. But these are relatively dense and do not exhibit sufficient flexibility for use as the gaskets of the present invention.

The present invention has been developed to exhibit significant advantages in certain sealing functions compared with existing alternatives. Although developed particularly for use in automobile bodies, the gasket has much wider applicability.

In one aspect the present invention provides a gasket comprising a first portion formed of a waterproof or substantially waterproof plastics material and a second portion formed of a foam plastics material having an open cell structure moulded onto said first portion. The waterproof or substantially waterproof plastics material may be a membrane or a foam plastics material having a closed cell structure.

The gasket may carry a membrane on the whole of its outer surface, or just part of its surface, said membrane having a different chemical formulation to the first and second plastics and providing a barrier to moisture entering the open cell foam.

Preferably the membrane provides a waterproof or substantially waterproof barrier.

In another aspect the invention provides a method of manufacturing a gasket comprising covering the inside surface of a mould with a thin film of a first plastics material and then forming from a second plastics material within the mould a flexible open cell foam such that the foam and film cure to form a flexible foam with a skin integrally bonded thereon.

The use of such open cell foam gaskets with a skin has a number of advantages, including lower weight, increased noise and vibration absorption, and reduced noise transmission compared with closed cell foams. Compared with conventional gaskets cut from open cell foam, or moulded with a porous skin, those of the present invention exhibit better water repellency and lower surface friction for easier assembly onto the motor vehicle.

In another aspect the invention provides a seal arrangement between a window frame and the bodywork of a motor vehicle, the seal arrangement comprising a gasket of the form as described in the immediately preceding paragraph.

In another aspect the invention provides a method of manufacturing a gasket S"comprising placing in a mould one or more portions of waterproof or substantially waterproof plastics material and introducing into said mould a reacting plastics material which creates a foam to fill the remaining volume of the mould, allowing said reacting material to cure to a flexible open cell foam bonded to said waterproof or substantially waterproof plastics material and removing said gasket from the "mould.

Preferably the open cell foam is produced by a reaction injection moulding process, preferably a cold cured low pressure process. Preferably the open cell foam is a flexible polyurethane foam. Preferably the closed cell foam is a flexible polyethylene, EVA or PVC foam, more preferably a low density foam, and more preferably a polyethylene foam.

Before the blank or blanks of closed cell foam are placed in the mould, an inside surface of the mould may be covered or partially covered with a thin film of a plastics material so that upon curing of said reacting material, the film forms a skin integrally bonded to part or all of the outside of the foam gasket. This technique of applying a thin film of plastics material may be used to cover the outside part of the gasket where the open cell foam shows, while leaving the closed cell foam uncovered. Optionally the open cell foam may be covered in only those areas where protection from water entry is needed. Preferably such a membrane skin is less than 100pm thick, more preferably between 25 tm and 75[m thick. Instead of using a thin film of plastics material, a thin sheet or blanket of closed cell foam material less than 3mm thick may be used whereby, upon curing of said reacting material, the blanket forms a skin integrally bonded to the outside of the foam gasket.

The use of such gaskets, which are a composite of foam materials, has a number of advantages, including improved noise and vibration absorption, and reduced noise transmission compared with closed cell foams. Compared with conventional gaskets cut or moulded from open cell foam, and having a porous skin, those of the present invention exhibit less water absorption. In the case of the embodiments having the outer membrane skin, there is an increased water repellency and lower surface friction for easier assembly of the gasket onto the motor vehicle.

An example of the invention involves a gasket intended to seal between the frame of a fixed side window in a rear door of an automobile, near the C-pillar, and the adjacent metal bodywork of the door onto which the window frame is located. In modem automobiles, such a window frame is generally a hard plastic moulding and is designed to mate to the metal bodywork by way of the bodywork locating into a peripheral channel on the window frame.

Prior to the present invention, the sealing between a window frame and bodywork engaged generally in this general manner would conventionally be accomplished by a series of rubber or rubber-like strips and closed cell tapes or foam pads. A gasket according to the present invention can achieve superior sealing and a much less complicated installation procedure and therefore substantial cost savings in the automobile assembly operation.

Before the bodywork and window frame are mated together, a gasket according to the present invention is placed within the channel such that at least part of it is compressed as the bodywork and window frame are mated together. The gasket substantially fills the cavity between the window frame and bodywork. It is desired that such a gasket performs a role as a moisture barrier and also as a sound absorber.

But in such an application, the whole of the gasket need not be water repellent. Only those parts of the gasket which are in contact with wet areas and/or closure lines and the like where water may enter need to have a water repellent outer surface. The remaining parts of the gasket can be either closed or open cell foam. In some circumstances it could be an advantage to have a large proportion of open cell foam in order to improve sound absorption. In other circumstances it could be an advantage to have a large proportion of closed cell foam. A single gasket may also provide a moisture barrier in different directions at different parts of the gasket.

The shape of the gasket may vary with the application, the types including sausageo like shapes, as well as flatter profiled shapes. For example in the case of the above described gasket for a window frame, there may be indentations and protrusions in the •gasket to locate into the window frame and bodywork.

Examples of the invention will now be described with reference to the attached drawings where: Figure 1 is a cross section view through portion of the frame of a fixed side •window fitted in a door near the C-pillar of an automobile and showing a gasket according to the present invention in use; Figure 2 is an isometric view of one embodiment of a gasket, according to the present invention, with a portion cut from it to expose the structure; Figure 3 is a further illustration of the view in Figure 2 indicating the location of cross section views shown in Figure 4; Figure 4 shows five cross section views through the gasket which are shown as sections A, B, C, D and E in Figure 3; Figure 5 is an isometric view of another embodiment of a gasket according to the present invention, with a portion cut from it to expose the structure; Figure 6 is an isometric view of a foam block used to form a blank in the manufacture of the gasket of Figure 5; and Figure 7 is a top view of the block of Figure 6 stretched to the shape of the gasket blank.

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Referring to Figure 1, a window frame 102 has a general H-shaped cross section but with one channel 104 being substantially larger than the other channel 106. The frame 102 is a hard plastic moulding. The larger peripheral channel 104 fits around the metal bodywork 108 which forms part of a door frame adjacent the C-pillar of an automobile. The smaller channel 106 fits around the edge of the fixed glass 110 in a rear side window. In Figure 1 the outside of the vehicle is on the left side of the illustration. Between the frame 102 and the bodywork 108 is a gasket 112 which substantially fills a hollow cavity between the frame and bodywork. The gasket 112 has the general shape of a long sausage which is laid around the frame. However the gasket is moulded with protrusions, indentations, bends and the like to snugly fit the cavity, and has ribs 116 and 117 protruding from each side towards the outside and inside respectively of the vehicle. Rib 116 is clamped between metal edge 118 on the "bodywork and shoulder 120 on the window frame while rib 117 is similarly clamped between edge 119 and shoulder 121. The only significant region of water entry will be along the interface 122 between the frame and bodywork on the outside of the vehicle. Accordingly the gasket need be waterproof only around the area of the rib 116 which extends towards the outside of the vehicle. It is a gasket for this purpose to which the present invention is particularly directed.

S. Referring to Figure 2, the gasket 1 has the general shape of a ring with an almost square cross section. The gasket is shown in Figure 2 with a portion of the ring cut from it in order to expose the cross section. The gasket 1 has a U-shaped portion 2 composed of a closed cell foam and a T-shaped portion 3 of open cell foam tightly bonded to the U-shaped portion. Closed cell portion 2 occupies about 30% of the cross section.

At the section showing in Figure 2, the U-shaped closed cell foam portion 2 has a web 6 forming the base and a pair of flanges 8 and 9 as the sides. The web 6 forms a side face 12 of the gasket while the flanges 8 and 9 form part of the inner face 13 and outer face 14 respectively of the gasket.

8 But the position of the closed cell portion 2 varies within the gasket around the gasket's circumference. This will be described with reference to Figures 3 and 4.

Figure 3 indicates the positions labelled A to E of the cross section views labelled A to E in Figure 4. By way of explaining the reason for the variation in position of the closed cell portion, the gasket 1 is required to prevent water penetration from its side face 12 for a short length around position A and water penetration from its inner face 13 for a substantial length from position C to position D. The requirement is to provide this water barrier while at the same time providing maximum possible sound o10 absorption characteristics.

•At position A the web 6 is against side face 12 of the gasket while from positions C to ~D it is against the inner face 13. The positions B and E show the position of the closed cell portion during its transition from one face to the other, the web 6 having been pushed into the corner of the gasket.

The gasket described with reference to Figures 2 to 4 is manufactured by first preparing a blank from a flexible, closed cell low density polyethylene foam.

Although polyethylene is preferred for the closed cell foam, an EVA or PVC foam for example may alternatively be used. This blank has the form of a long length of the same channel section shown as portion 2 in Figure 2. The blank is placed into a mould, carefully positioning it to lay against the faces 12 and 13 where required. It is not necessary to press the blank into the corners of the mould at the transition portions around positions B and E.

The mould is then closed and the mixed reactants for the low temperature production of an open cell polyurethane foam are introduced to the mould. It is desirable that this reactant mixture is introduced only on the channel side of the U-shaped section. In this way, as the reacting foam expands it pushes the web of the blank hard against the wall of the mould opposite the position where the reacting foam was introduced. It is the pressure of the expanding foam which bends the web 6, pressing it into the corner 21 of the mould. The reacting mixture is allowed to cure, integrally bonding to the 0 blank, and the composite gasket is removed from the mould. The closed cell foam may be treated with a primer to assist bonding to the polyurethane.

The reacting mixture may typically reach 90 0 C to 100 0 C and, with the forces pressing on the blank, thermoplastic deformation or thermoforming of the polyethylene blank would commonly occur. By careful selection of the points in a mould where the reactant mixture is introduced, considerable movement of the blank and control of that movement, may be gained by the operator. For example, a blank having a simple flat cross section may be caused to press on opposite faces of the mould at different places by introducing the reactant foam on one side of the blank at one place and on the other side elsewhere. Also, by appropriate positioning of slits and/or holes in a blank, reacting foam may be permitted to flow to both sides of a blank, so reducing othe blank's movement during the reaction.

As noted in the preceding paragraph, the temperature reached in the mould, and the pressure exerted by the reacting foam may be sufficient to thermoform the closed cell foam. The term thermoforming as used in this specification means applying sufficient heat and pressure to the closed cell foam in order to distort it from its original shape to the new shape required and provide a high enough temperature that the "memory" of the closed cell foam or membrane is lost and it retains the new shape when the composite gasket so formed is cooled to room temperature. Thermoforming of the closed cell foam and/or membrane is a preferred condition for the invention.

A gasket may also be produced with the general form and function described above, and having the cross sections identified as A, C and D with respect to Figures 3 and 4, but using a closed cell blank with a simpler shape than the U-shaped cross section blank described above. The blank may instead be a flat strip die cut from a flat sheet of closed cell foam, the width of the strip being the sum of the lengths of the web 6 plus the sides 8 and 9. The flat strip blank is laid in the mould much the same as the U-shaped blank and the pressure of the expanding reacting mixture presses it into the U-shaped configuration shown in sections A, C and D. However in contrast to the sections B and E at the transition portions described above, the flat preform produces an L-shaped portion of the gasket with its two legs extending from the corner 21 along faces 12 and 13.

We have found that it is common when producing gaskets according to the present invention to have the reaction mixture wet the wall of the mould over the area where the closed cell foam is in contact with the mould wall, resulting in a thin film of the reacting mixture adhering to the closed cell foam on the outer surface of the gasket.

This film can be extremely thin to the point where it shows only as a faint bloom on the surface of the closed cell foam. As it does not have the structure of a foam, such a 10 film does not affect the water barrier characteristics provided to the gasket by the underlying closed cell foam.

oooe **Referring to Figure 5, the gasket 41 has the same overall shape as that of gasket 1 in Figure 2. However its internal structure is different. Gasket 41 in the cross section shown has a rectangular portion 42 composed of a closed cell foam and an L-shaped portion 43 of open cell foam. The closed cell portion 42 occupies about 70% of the cross section.

The portion 42 is created from a rectangular block 45 of thermoformed low density polyethylene foam by die cutting the block through its thickness using a pattern of slits shown in Figure 3. One central slit 46 extends longitudinally along the block •o leaving only a narrow joining strip 48 of foam at each end face 62 and 63. Lateral slits 10 extend inwardly from side faces 58 and 59 stopping a short distance before the longitudinal slit 46. The block 45 may then be opened out into a ring shaped blank 52 as shown in Figure 7, with the longitudinal slit 46 opening to form the inner face 65 of the core and the lateral slits 50 opening to produce wedge shaped notches 67 in the perimeter face 69.

To then form a gasket, the blank 52 is laid in a mould and then into the mould is injected a reaction mixture for production of an open cell foam. In the present embodiment this is a cold cured RIM polyurethane. The reaction mixture reacts within the mould, filling all available space including the the notches 67. After curing, the composite so formed is removed from the mould.

The RIM polyurethane foaming reaction is sufficiently vigorous that it penetrates into any cut cells on the surface of the core, so producing a substantial keying of the two foams together. Any surface of the core which is not rough from, for example, cutting may be chemically treated (primed) to provide better adhesion between the polyurethane and the polyethylene.

The vigor of the foaming reaction is also sufficient that it can help push the blank 52 *too into its position in the mould. In producing the structure shown in cross section in S.Figure 5, the reaction mixture has been injected into the mould from the direction of a a*a the side face 83 and outer face 86, so that the blank 52 has been pressed into the opposite corner of the mould and thus forms corner 88 as part of the side face 84 and the inner face 85 of the gasket.

The gasket 41 may have the same cross sectional structure throughout, but it may alternatively be varied. For example the cross section illustrated in Figure 5 would 99 provide good resistance to water penetration from around corner 88 and nearby portions of faces 84 and 85, but not elsewhere where it might be required at some 0 •part. The blank 52 may be positioned up to side face 83 at some part of the gasket in order to provide a water barrier there. This would be accomplished by introducing reacting foam mixture in the mould at side face 84 and outer face 86.

Optionally the gasket may be provided with an outer skin or membrane to prevent or resist entry of water into the open cell foam. The skin may be created by first covering the inside of one or both of the halves of the mould with a thin layer of polymeric material, injecting the open cell foam reaction material into the mould, fitting the halves together with the core inside, allowing it to cure and then opening the mould to remove the gasket with the thin layer of polymeric material forming a skin on all or part of the outside of the gasket.

The thin layer can be placed on the mould surface by applying a pre-existing solid polymer film, such as a polyurethane sheet of 10tm to 1 00tm thick, to the surface or by spraying it as a liquid onto the surface. The choice of the particular polymer will depend on the end application and may be readily chosen by the skilled addressee.

Conventional release agents may be used on the moulds to facilitate separation of the formed gasket from the mould. The solid film placed against the mould, or the sprayed on liquid may themselves contain the releasing agents.

Such an outer skin or membrane may be made to cover only selected portions of the outer surface of the gasket.

o S. -The open cell foam used in this specific example of the invention is a conventional °open cell polyurethane foam produced by conventional low pressure reaction injection moulding techniques. The skin and the foam of this embodiment will have different chemistries because of their different sources. In this regard a gasket of the present invention which has a skin as described above is different from a gasket produced in a S* self skinning process as, in the latter, the skin has essentially the same chemistry as the underlying foam. A skin in other embodiments of the invention may be a polymeric material other than polyurethane, EVA or PVC.

The present invention involves the production of a composite construction, with the open cell and closed cell portions having quite distinct and different characteristics.

The gaskets of the present invention may also have incorporated into them stiffening ribs to provide resistance to sag in some applications. These ribs may be transverse or longitudinal to the sausage-like shapes described in this specification and can be made from any relatively inert material which can survive the heat and pressure of the foaming reaction with a suitable stiffness.

It will be appreciated that gaskets incorporating the structure described above are not restricted to sealing window frames in motor vehicle bodies. They also have 13 application in conjunction with other mouldings in a vehicle such as around console panels and dashboards or between the bodywork and external mirrors. Neither are the gaskets limited to automotive applications. The characteristics which make them desirable for that purpose make them similarly useful in architectural fitment applications for example.

It is to be understood that various alterations, modifications and/or additions may be introduced into the constructions and arrangements of parts previously described without departing from the spirit or ambit of the invention.

Throughout this specification, unless the context requires otherwise, the word oboe L"comprise", and variations such as "comprises" and "comprising", will be understood 0:.0 oo. &to imply the inclusion of a stated integer or group of integers but not the exclusion of b be any other integer or group of integers.

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Claims (23)

1. A gasket comprising a first portion formed of a waterproof or substantially waterproof plastics material and a second portion formed of a foam plastics material having an open cell structure moulded onto said first portion.

2. A gasket according to claim 1 wherein the waterproof or substantially waterproof plastics material is a membrane on at least part of the gasket's outer surface, said membrane having a different chemical formulation to the open cell foam and providing a waterproof or substantially waterproof barrier to moisture entering •the open cell foam. oo*. A gasket according to claim 1 wherein the waterproof or substantially waterproof plastics material is a foam plastics material having a closed cell structure.

4. A gasket according to claim 3 wherein the closed cell foam material is a layer of foam over at least part of the outer surface of the gasket said layer being up to 3mm thick. 20 5. A gasket according to claim 3 wherein the closed cell foam material within the gasket adopts different orientations in separate parts of the gasket.

6. A gasket according to any one of claims 3 to 5 having a membrane on at least part of its outer surface, said membrane having a different chemical formulation to the open cell foam and the closed cell foam materials and said membrane providing a waterproof or substantially waterproof barrier to moisture entering the open cell foam.

7. A gasket according to any one of claims 3 to 6 wherein the closed cell foam is a low density flexible foam.

8. A gasket according to any one of claims 3 to 7 wherein the closed cell foam is a flexible polyethylene, EVA or PVC foam. I 0-

9. A gasket according to any one of claims 3, 5 or 6 wherein the closed cell foam is a rigid or semi rigid foam.

10. A gasket according to any one of claims 1 to 9 in which the open cell foam is a flexible polyurethane foam.

11. A seal arrangement between a window frame and the bodywork of a motor vehicle, the seal arrangement comprising a gasket according to any one of the preceding claims.

12. A method of manufacturing a gasket comprising placing in a mould one or more portions of waterproof or substantially waterproof plastics material and introducing into said mould a reacting plastics material which creates a foam to fill 15 the remaining volume of the mould, allowing said reacting material to cure to a flexible open cell foam bonded to said waterproof or substantially waterproof plastics *material and removing said gasket from the mould. ••go

13. A method according to claim 12 in which the one or more portions of 20 waterproof or substantially waterproof plastics material are one or more blanks of closed cell foam.

14. A method according to claim 13 in which the blank or blanks of closed cell foam are caused to press on different faces of the mould at different places in the mould by introducing the reactant foam on one side of the blank(s) at one place and on another side of the blank(s) elsewhere. A method according to claim 12 or 13 wherein the closed cell foam is a flexible polyethylene, EVA or PVC foam.

16. A method according to claim 12 or 13 wherein the closed cell foam is a low density flexible foam. M

17. A method according to claim 12 or 13 wherein the closed cell foam is a rigid or semi rigid foam.

18. A method according to any one of claims 12 to 17 wherein an inside surface of the mould is covered with a membrane of a plastics material so that upon curing of said reacting material, the film forms a skin integrally bonded to the outside of the foam gasket. 10 19. A method according to any one of claims 12 to 17 wherein an inside surface of the mould is covered or partly covered with a blanket of closed cell foam plastics material so that upon curing of said reacting material, the blanket forms a skin integrally bonded to the outside of the foam gasket. 15 20. A method according to claim 19 wherein the blanket is up to 3mm thick.

21. A method according to any one of claims 18 to 20 wherein the skin covers only part of the gasket and overlies open cell foam. 20 22. A method according to any one of claims 18 to 21 wherein the skin is thermoformed to the shape of the mould by the heat in the mould and the pressure from the reacting material.

23. A method according to claim 18 wherein the membrane is less than 100pm thick.

24. A method according to claim 23 wherein the membrane is less than thick.

25. A method according to claim 24 wherein the membrane is less than thick. 17

26. A method according to any one of claims 12 to 25 in which the open cell foam is produced by a reaction injection moulding process.

27. A method according to any one of claims 12 to 26 in which the open cell foam is produced by a cold cured low pressure process.

28. A method according to any one of claims 12 to 27 in which the open cell foam is a flexible polyurethane foam.

29. A gasket manufactured using a method according to any one of claims 12 to 28. Dated this 26th day of February 1999 Universal Forme Cutting Pty Ltd o and Ureform Pty Ltd by their patent attorney Norman B Morcom oo*