Login| Sign Up| Help| Contact|

Patent Searching and Data


Title:
METHOD OF MANUFACTURING A COMPOSITE PANEL AND COMPOSITE PANEL OBTAINED THEREBY
Document Type and Number:
WIPO Patent Application WO/2001/028760
Kind Code:
A1
Abstract:
A method of manufacturing a composite panel (30), e.g. for use as an acoustic radiator of a loudspeaker. The panel (30) comprising a core (32) sandwiched between two skins (34, 36), each skin being bonded to the core by a combination of a layer (38, 40) of thermoplastic adhesive between each skin and the core and thermosetting resin comprised in each skin. The thermoplastic adhesive and thermosetting resin being chosen so they are compatible and may be processed under the same conditions.

Inventors:
Bream, Charles (41 Whitehall Gardens Duxford Cambridgeshire CB2 4QL, GB)
Application Number:
PCT/GB2000/003958
Publication Date:
April 26, 2001
Filing Date:
October 16, 2000
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
NEW TRANSDUCERS LIMITED (37 Ixworth Place London SW3 3QH, GB)
Bream, Charles (41 Whitehall Gardens Duxford Cambridgeshire CB2 4QL, GB)
International Classes:
B29C70/08; B29C70/34; H04R31/00; H04R7/04; (IPC1-7): B29C70/08; B32B31/00
Foreign References:
US5449425A
US5338238A
EP0786330A2
Attorney, Agent or Firm:
Maguire, Boss (5 Crown Street St. Ives Cambridgeshire PE27 5EB, GB)
Download PDF:
Claims:
CLAIMS
1. A method of manufacturing a composite panel (30) comprising the steps of: providing a core (32), a skin (34) comprising un cured thermosetting resin and a layer (38) of a thermoplastic adhesive, arranging the skin (34) adjacent a first face (42) of the core (32), such that the layer (38) of the thermoplastic adhesive is between the core (32) and the skin (34), bringing the core (32), the skin (34) and the adhesive layer (38) into facetoface contact, and curing the thermosetting resin and activating the thermoplastic adhesive simultaneously to form a composite panel (30).
2. A method according to claim 1, further comprising the steps of providing a second skin (36) comprising un cured thermosetting resin and a second layer (40) of a thermoplastic adhesive and arranging the second skin (36) adjacent a second face (44) of the core (32), such the second layer (40) of the thermoplastic adhesive is between the core (32) and the second skin (36) before curing.
3. A method according to claim 1 or claim 2, wherein the parameters of the or each layer (38,40) of thermoplastic adhesive are used individually or in combination to control the level of damping in a panel.
4. A method according to any one of claims 1 to 3, wherein at least one layer (38,40) of thermoplastic adhesive is in the form of a continuous film so that a continuous thermoplastic bonding layer is formed between the or each skin (34,36) and the core (32) on curing.
5. A method according to any one of claims 1 to 3, wherein at least one layer (38,40) of thermoplastic adhesive is adapted so that a hybrid bondline which includes both thermoplastic and thermoset bonding between the or each skin (34,36) and the core (32) is formed on curing.
6. A method according to claim 5, wherein at least one layer (38,40) of thermoplastic adhesive is in the form of a slit film.
7. A method according to claim 5, wherein at least one layer (38,40) of thermoplastic adhesive is in the form of a web.
8. A method according to any one of the preceding claims, wherein the or each skin (34,36), the or each adhesive layer (38,40) and the core (32) are substantially coextensive.
9. A method according to claim 3, wherein the polymer type is selected from the group consisting of polyester, polyamide, polyurethane or polyolefin.
10. A composite panel comprising a core (32) sandwiched between two skins (34,36), each skin being bonded to the core (32) by cocuring thermoset resin comprised in each skin and a layer (38,40) of thermoplastic adhesive arranged between a face (42,44) of the core (32) and each skin (34,36).
11. A loudspeaker comprising an acoustic radiator in the form of a composite panel (30) made according to any one of claims 1 to 10 and an exciter for exciting the panel to produce an acoustic output.
Description:
METHOD OF MANUFACTURING A COMPOSITE PANEL AND COMPOSITE PANEL OBTAINED THEREBY

DESCRIPTION TECHNICAL FIELD The invention relates to a method of making panels, and more particularly to a method of making so-called sandwich'panels comprising a core sandwiched between opposed skins or facing layers of thermosetting materials.

Such panels may have widely different uses in industry but one particular use is as a resonant diaphragm in a loudspeaker e. g. of the kind described in W097/09842 of New Transducers.

BACKGROUND ART It is known to make panels by bonding uncured thermoset-based faceskins (prepregs) to core material, typically honeycomb or foam structure. As shown in the exploded edge view of Figure la, one method of bonding a core (10) to opposed prepregs or skins (12,14) is to use interposed layers (16,18) of thermoset film adhesive.

Alternatively, as in the exploded edge view of Figure lb,

the adhesive layers may be eliminated, to reduce processing and material costs, by sandwiching a core (20) between two resin-rich prepregs or skins (22,24) which bond direct to the core on curing.

The resins in the prepregs and adhesives are selected such that they are compatible, are cured under the same processing conditions and reticulate around the cell-walls to form fillets and a strong faceskin-core bond.

Such panels may be used as diaphragms for loudspeakers. The thermoset film adhesives used are frequently rubber-toughened grades, which impart damping in the panels. In contrast, a panel using resin-rich prepregs and no additional adhesive generally produces a much livelier panel with low self damping levels, characterised by'ringing'in the panel.

It is also known to make panels by bonding dry' faceskins e. g. polymer films, papers, unclad or copper- clad laminate, high-pressure laminates etc to a core using a dry'hot-melt thermoplastic film. In this process, the adhesive is softened/melted under moderate pressure to promote wetting and bonding to the faceskin and core.

It is an object of the present invention to provide an improved sandwich panel for use, for example, as a diaphragm of a loudspeaker.

DISCLOSURE OF INVENTION According to the present invention, there is provided a method of manufacturing a composite panel comprising the steps of: providing a core, a skin comprising un-cured thermosetting resin and a layer of a thermoplastic adhesive, arranging the skin adjacent a first face of the core, such that the layer of the thermoplastic adhesive is between the core and the skin, bringing the core, the skin and the adhesive layer into material contact, and curing the thermosetting resin and activating the thermoplastic adhesive simultaneously to form a composite panel.

The method may further comprise the steps of providing a second skin comprising un-cured thermosetting resin and a second layer of a thermoplastic adhesive and arranging the second skin adjacent a second face of the core, such the second layer of the thermoplastic adhesive is between the core and the second skin before curing. In this way, the two skins may be arranged such that there is a layer of the adhesive between the core and each skin before curing. The first skin may be arranged adjacent to an upper face of the core and the second skin adjacent a lower face of the core so as to form a'sandwich'panel on curing.

Thus the present invention provides a novel

combination of two known methods, in which thermoset- based prepregs or skins are cured with thermoplastic hotmelt adhesive layers to form a composite panel.

To ensure a panel with high mechanical integrity is achieved and to ensure the thermoplastic adhesive and thermoset resin may be processed under the same conditions, the thermoplastic adhesive preferably meets the following requirements: 1. The thermoplastic adhesive must be compatible with the curing thermosetting resin; 2. The bonding species in the layer of thermoplastic adhesive are activated at the thermoset processing temperature, and 3. The layer of thermoplastic adhesive forms a high- integrity bond with the core.

The thermoplastic adhesive may be used to control damping of the panel. Three parameters of the layer of thermoplastic adhesive, namely polymer type, weight of the layer and form of the layer may be used individually or in combination to control the level of damping in a panel. The polymer type may be polyester, polyamide, polyurethane, polyolefin, or other similar material.

Typically, a higher adhesive weight imparts a higher level damping in the panel.

The form of at least one adhesive layer may be a plain film so that a continuous thermoplastic bonding/damping layer is formed between the or each skin and the core on curing. Alternatively, at least one layer

of thermoplastic adhesive may be adapted so that a hybrid bondline which includes both thermoplastic and thermoset bonding between the or each skin and the core is formed on curing. The form of each adhesive layer may be a slit film or a web. Thus, each adhesive layer may be continuous or discontinuous. If desired, different types of layers of thermoplastic adhesive may be used to bond each skin to the core.

The relative proportions of the bond types (hybrid or continuous) will be primarily dependent on the weight of the thermoplastic adhesive used and the openness of the web/film. The specification of a plain film will impart higher damping than an open web of the same weight. This leads to the ability to control the dispersion of damping medium in the panel, and hence control the amount of damping.

The skins, the adhesive layers and the core may be substantially co-extensive.

The skins may be impregnated or coated with a thermosetting resin. The skins may comprise a fibrous layer impregnated with thermosetting resin, e. g. standard resin content prepreg. Alternatively, the skin layers may comprise a resin-rich prepreg.

The panel may be cured in a static press, autoclave, belt-press or similar, and in which the temperature, time and pressure of the curing process are adjusted to ensure the correct conditions for curing the panel.

According to a second aspect of the invention, there

is provided a composite panel comprising a core sandwiched between two skins, each skin being bonded to the core by co-curing thermoset resin comprised in each skin and a layer of thermoplastic adhesive arranged between a face of the core and each skin.

According to another aspect of the invention, there is provided a loudspeaker comprising an acoustic radiator in the form of a composite panel made as described above and an exciter for exciting the panel to produce an acoustic output.

The present invention thus covers the manufacture of sandwich panels, where an uncured thermoset-based prepreg faceskin is cured and bonded with a thermoplastic hot- melt film/web to a core material. The main benefits of this technique are that: 1. the level of damping in a panel can be closely controlled, by varying the weight, form and type of polymer used in the thermoplastic adhesive layer.

2. thermoplastic films/webs are available in lower, and a wider range, of weights than thermoset films. The minimum weight of thermoplastic films is 16gsm compared to a minimum weight of 75gsm for thermoset films. This leads to the potential for a reduction in adhesive weight and panel area density, which can lead to an increase in sensitivity. Thus it may be possible to manufacture light-weight panels with high sensitivities when forming the diaphragms of resonant loudspeaker panels.

3. thermoplastic adhesive films are more cost effective than their thermoset counterparts.

BRIEF DESCRIPTION OF DRAWINGS The invention is diagrammatically illustrated, by way of example, in the accompanying drawings in which: Figure la is an exploded edge view of a prior art composite panel; Figure lb is an exploded edge view of an alternative prior art composite panel; and Figure 2 is an exploded edge view of a composite panel embodying the present invention.

Figure 3 is a flowchart of the method of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION Figure 2 shows a panel (30) comprising a core (32) sandwiched between two skins (34,36) each comprising a thermosetting resin. One skin (34) is bonded to the upper face (42) of the core (32) using a first layer (38) of a thermoplastic adhesive. Similarly, the second skin (36) is bonded to the lower face (44) of the core using a second layer (40) of the thermoplastic adhesive. The thermosetting skins (34,36) either comprise a fibrous layer impregnated with thermosetting resin, e. g. standard resin content prepreg or a resin-rich prepreg. Thus, the thermosetting skins are formed as in Figures la or lb.

Figure 3 outlines the steps in the method, namely a) Providing a core, one or more (usually two) thermoset- resin based skins and a layer of thermoplastic adhesive

for each skin; b) Arranging the or each skin adjacent a face of the core so that there is a layer of thermoplastic adhesive between the core and each skin. Usually a skin is arranged adjacent each of upper and lower faces of the core so that the core is sandwiched between two skins; c) Bringing the skin (s), the core, and the layer (s) of thermoplastic adhesive into material contact, and d) Simultaneously curing the thermoset resin and the thermoplastic adhesive to form a composite panel INDUSTRIAL APPLICABILITY The invention thus provides an improved method of manufacturing a composite panel, e. g. for use in a loudspeaker.