Method for manufacturing shaped articles by moulding and shaped articles as obtained by this method

Abstract: A method for manufacturing shaped articles by moulding, said method comprising the steps of providing a mould conforming to a desired shape, introducing into the mould a fabric, which is dimensionally stable under first temperature conditions but is able to yield under second temperature conditions, said fabric containing or consisting at least partly of polyethylene and/or polypropylene and/or polystyrene, and expandable polyethylene and/or polypropylene and/or polystyrene, which will expand under said second temperature conditions, and heating the mould containing said fabric and said expandable polyethylene and/or polypropylene and/or polystyrene to said second temperature conditions.

Description: The present invention relates to a method for manufacturing shaped articles by moulding and to shaped articles as obtained by using said method. Shaped articles consisting of a moulded foam structure are well known in the art. Moulded foam structures are e.g. used in many applications where impact protection is desired, for example as inner liners of bicycle helmets and motorcycle helmets, in automotive trim pieces such as dashboards, door panels and headliners etc. Moulded foam structures are, however, not strong enough in itself for many applications and thus frequently need to be reinforced by other materials. In many fields of use, especially in the automotive industry, moulded foam parts do not have a surface which is suitable as a visible exterior surface for reasons of both wear and appearance. It is therefore common to apply a textile or other decorative layer to the foamed part after the foaming/moulding process has been completed. In order that such a textile or other layer is bonded to the foamed structure adhesives are used for fastening the layer to the foamed part. The closest prior art document JP-A-05 147 121 discloses a method for manufacturing shaped articles by stretching a fabric containing polyolefine between male and female mould parts, closing the mould, introducing thermoplastic beads into the mould cavity, and heating the mould for integrating the fabric with the form. The object of the present invention is to provide a new way of manufacturing shaped articles by moulding for obtaining moulded foam structures having superior mechanical properties, i.e. better strength and stability than conventional products of this kind, as well as - optionally - an exterior surface which has low wear and a desired appearance. The new method for manufacturing shaped articles by moulding shall also be able to comply with environmental aspects as e.g. reduced use of chemicals and good recyclability. The present invention also aims at providing shaped articles of various nature that can be manufactured by the afore-mentioned new method. The above objects are met according to the present invention by a method for manufacturing shaped articles by moulding, which method comprises the steps of providing a mould conforming to a desired shape, introducing into the mould a fabric, which is dimensionally stable under first temperature conditions but is able to yield under second temperature conditions, said fabric comprising polyethylene and/or polypropylene and/or polystyrene, and expandable polyethylene and/or polypropylene and/or polystyrene, which will expand under said second temperature conditions, and heating the mould containing said fabric and said expandable polyethylene and/or polypropylene and/or polystyrene to said second temperature conditions. The invention further provides shaped articles as defined in the independent claim 19. The fabric, if desired, reinforces the foamed core and may also provide a desired decorative appearance at its visible outer surface. The fabric may also act as a function layer, e.g. as an EMR-shielding fabric. No adhesives are necessary to fasten the fabric to the foam core, bonding is instead achieved during the foaming process in which both the expandable polyethylene and/or polypropylene and/or polystyrene as well as the polyethylene and/or polypropylene and/or polystyrene portion of the fabric assume an at least partly molten state resulting in an integral connection between the fabric and the foamed core after the shaped article thus produced has been cooled. In addition, the proposed method provides the opportunity to manufacture shaped articles consisting of just one material, e.g. polyethylene or polypropylene or polystyrene, thus facilitating future dismantling and recycling. Basically, any kind of fabric as defined in claim 1 may be used in the method according to the present invention. The fabric used must be dimensionally stable under said first temperature conditions in order to avoid distortion of the fabric upon insertion into the mould. During the moulding or shaping process, however, the fabric used shall be able to easily assume the desired shape which is why it must yield under said second temperature conditions. The fabric used thus has to have the ability to change its mechanical properties in situ, i.e. in the mould under said second temperature conditions, to allow easy shaping. This may e.g be achieved by using a fabric which comprises yarns that are not fully drawn or heat set. The fabric may be of the woven, knitted, laid, tufted, flocked, non-woven or any other known type of fabric or may also be a combination of such types of fabric. The fabric may also be a woven construction consisting of single or multiple layers (two-dimensional fabric or three-dimensional fabric). According to the present invention the expandable polyethylene and/or polypropylene and/or polystyrene which is introduced into the mould preferably is in the form of beads. Such beads can easily be introduced into the mould by blowing. Heating the mould containing said fabric and said expandable polyethylene and/or polypropylene and/or polystyrene to said second temperature conditions is preferably performed by steam heating as it is commonly applied in the art of manufacturing of foamed products. Heating may, however, be achieved using any known method. For example, heating may be achieved by using waves for which the polyethylene and/or polypropylene and/or polystyrene portion of the fabric as well as the expandable polyethylene and/or polypropylene and/or polystyrene is sensitive. Various methods of heating may also be combined. An important aspect of the present invention is that both the foamed structure and the fabric contain at least one of the materials polyethylene, polypropylene or polystyrene because it is these materials which provide for the integral connection between the fabric and the foamed core of the shaped article. There are, however, various ways to ensure that polyethylene and/or polypropylene and/or polystyrene is present on or in the fabric used. In a preferred embodiment of the method according to the present invention a bonded fabric is used, which bonded fabric comprises a mesh of filaments of the core-sheath type and whose bonding is capable of yielding under said second temperature conditions. Such a bonded fabric is explained in more detail in applicant's international patent application PCT/EP94/01546 Such a fabric has substantially no elasticity in the longitudinal direction under first conditions but yields under second conditions without affecting the relatively strong filament cores. The sheath material, which has a lower melting point than the core and provides for the bonding, may be a yarn or foil which is spun, core-textured, enveloped or twisted around a core yarn such as glass, aramid or carbon. The core yarn may be a composite itself. If a bonded fabric comprising a mesh of filaments of the core-sheath type is used in the method according to the present invention it is preferred that the sheath comprises polyethylene and/or polypropylene and/or polystyrene. Preferably the mesh is bonded together at the crossing points of the filaments. Another way of achieving a fabric that is dimensionally stable under first temperature conditions and yields under second temperature conditions is to provide longitudinally extending filaments consisting of polyethylene and/or polypropylene and/or polystyrene, which filaments thus act as carriers only under said first temperature conditions as they yield under said second temperature conditons. A still further way to provide for polyethylene and/or polypropylene and/or polystyrene on or in the fabric is to apply, at least to the side of said fabric facing the expandable polyethylene and/or polypropylene and/or polystyrene in the mould, a solution or emulsion containing polyethylene and/or polypropylene and/or polystyrene before heating the fabric and expandable polyethylene and/or polypropylene and/or polystyrene to said second temperature conditions. A solution or emulsion containing polyethylene and/or polypropylene and/or polystyrene may be applied to the fabric by e.g. spraying or by dipping the fabric into said solution or emulsion. In addition to the reinforcing effect which the fabric may provide for the foamed core of a shaped article obtained with the method according to the present invention it is also possible to employ a fabric having a top side which provides for a desired appearance and a bottom side which faces the expandable polyethylene and/or polypropylene and/or polystyrene in the mould and which is adapted to at least partly melt under said second temperature conditions. By adapting the side of the fabric facing the foam core such that this side at least partly melts under said second temperature conditions an integral connection between the fabric and the foam core will be obtained without adversely affecting the top side, e.g. the decorative surface of the fabric. Automotive seat cushions or interior door panels may thus be produced in a one-step process. Such a fabric could e.g. have a satin weaving top side providing for a durable and pleasantly looking and feeling outer surface. The advantage of a satin weave with respect to the present invention is that most of the polyolefine type of yarn may be at one side of the fabric thus facilitating and enhancing bonding with the foam and providing, if desired, for a nice colour effect. It is worth noting that the fabric employed in the method according to the present invention need not appear textile-like but may also have an e.g. leather-like appearance and may also be a metal fibre type of fabric. It is apparent from the foregoing that the method according to the present invention provides a very favourable way of producing shaped articles by moulding. A promising field of application is the automotive industry where the method according to the present invention can be used to produce a variety of trim pieces such as interior door panels, headliners, seat cushions ready with upholstery, dashboards or portions thereof, sun visors, consoles and so on. Even complete convertible tops are envisaged to replace conventional fabric/foam constructions. Other fields of application are the production of helmets, e.g. sport helmets and motorcycle helmets, body protectors such as knee protectors or leg protectors as e.g. used by football players, baby seats, suitcases and last but not least protective pieces for electronic equipment with or without EMR-shielding capability. Another interesting field of application is the carpet industry as according to the method of the present invention carpets also may be produced. Such a carpet may e.g. consist of a top layer consisting of dyeable polyethylene and/or polypropylene having a backing layer of e.g. PE or PP or a mix thereof followed by a foam layer which has been bonded to the backing layer using the method according to the present invention.

Claims: A method for manufacturing shaped articles by moulding, said method comprising the steps of: providing a mould conforming to a desired shape, introducing into the mould a fabric, which is dimensionally stable under first temperature conditions but is able to yield under second temperature conditions, said fabric comprising polyethylene and/or polypropylene and/or polystyrene, and expandable polyethylene and/or polypropylene and/or polystyrene, which will expand under said second temperature conditions, and heating the mould containing said fabric and said expandable polyethylene and/or polypropylene and/or polystyrene to said second temperature conditions. A method according to claim 1, wherein the expandable polyethylene and/or polypropylene and/or polystyrene is in the form of beads. A method according to claim 1 or 2, wherein heating the mould containing said fabric and said expandable polyethylene and/or polypropylene and/or polystyrene to said second temperature conditions is achieved by steam heating. A method according to claim 1, wherein said fabric is of the woven, knitted, laid, tufted, flocked, non-woven or any other known type of fabric or a combination thereof. A method according to claim 4, wherein said fabric comprises yarns that are not fully drawn or heat set. A method according to claim 1, wherein said fabric comprises co-spun yarns or core-sheath yarns. A method according to claim 6, wherein said fabric is a bonded fabric comprising a mesh of filaments of the core-sheath type, whose bonding is capable of yielding only under said second temperature conditions. A method according to claim 7, wherein the mesh is bonded together at the crossing points of the filaments. A method according to claim 7 or 8, wherein the sheath comprises polyethylene and/or polypropylene and/or polystyrene. A method according to any of the preceding claims, wherein said fabric comprises longitudinally-extending filaments consisting of polyethylene and/or polypropylene and/or polystyrene and acting as carriers only under said first temperature conditions. A method according to claim 1, wherein a solution or emulsion containing polyethylene and/or polypropylene and/or polystyrene has been applied to the side of said fabric facing the expandable polyethylene and/or polypropylene and/or polystyrene before heating it to said second temperature conditions in the mould. A method according to claim 1, wherein said fabric has a top side providing for a desired appearance and a bottom side, which bottom side faces the expandable polyethylene and/or polypropylene and/or polystyrene in the mould and is adapted to at least partly melt under said second temperature conditions. A method according to claim 1, wherein said fabric is an EMR-shielding fabric. A shaped article comprising a fabric bonded to foamed polyethylene and/or polypropylene and/or polystyrene, as obtained by a method according to any of the preceding claims. A shaped article according to claim 14, wherein said fabric is a reinforcing fabric. A shaped article according to claim 14, wherein said fabric is an EMR-shielding fabric. A shaped article according to claim 14, wherein the shaped article is an automotive trim piece, such as an interior door panel, a console, a headliner, a seat upholstery, a dashboard or portion thereof, a sun visor etc. A shaped article according to claim 14, wherein the shaped article is a cycle helmet. A shaped article according to claim 14, wherein the shaped article is a portion of a suitcase. A shaped article according to claim 14, wherein the shaped article is a baby seat. A shaped article according to claim 14, wherein the shaped article is a body protector, e.g. a knee protector. A shaped article according to claim 14, wherein the shaped article is a protective piece for electronic equipment. A shaped article according to claim 14, wherein the shaped article is a wall or ceiling covering. A shaped article according to claim 14, wherein the shaped article is a carpet.

Inventors: DE MEYER WILLY, LAHAYE RENE L J, DE MEYER, WILLY, LAHAYE, RENE L.J.
Applicants: MILLIKEN EUROP NV, MILLIKEN EUROPE N.V.
Application year: 1998
Main classification: B29C44
IPC codes: B29C44