WO2005023540A1

WO2005023540A1 - Laminate

Info

Publication number: WO2005023540A1
Application number: PCT/IB2004/002950
Authority: WO
Inventors: Peter James King; Nelson John Nortje
Original assignee: Peter James King; Nelson John Nortje
Priority date: 2003-09-10
Filing date: 2004-09-10
Publication date: 2005-03-17
Also published as: WO2005023540A8

Abstract

A panel (1) formed from at least one wood section (2) bonded to at least one optically transmissive section (3) formed from an inorganic material, preferably formed from a thermoplastic (3), characterised in that the bond is formed by a solvent applied to the surface of the thermoplastic transmissive section (3) and a waterproof wood adhesive applied to the surface of the wood section (2) prior to clamping the sections (2,3) together.

Description

LAMINATE

TECHNICAL FIELD

The present invention relates broadly to a laminate formed from rigid, non-porous sections and flexible, porous sections. In particular, the present invention relates to a laminate of timber and an optically transmissive substance such as acrylic.

BACKGROUND ART

Inorganic materials such as metals, concrete, glass, plastics, fibreglass in the production of furniture, displays, and support structures such as poles, beams, panels and so forth are in widespread use in modern building construction and interior fittings. However, despite this prevalence of inorganic materials, timber is still utilised worldwide and is often considered a desirable or even premier material. This is partly due to the appealing aesthetic properties of wood and partly due to its inherent properties, i.e. strength, flexibility, light weight and durability.

An unavoidable consideration of using timber building materials is the need to allow for the natural expansion and contraction caused by environmental fluctuations in temperature and humidity. Furthermore, to make a uniform finish and/or to provide an increased resistance to the detrimental effects such as weather, impacts, or staining, a protective coating or lacquer is often applied to the exterior of the wood. Such requirements pose some limitations on the composite structures that may be formed from wood and/or the inorganic materials.

These difficulties are particularly evident when seeking to form a structural element such as a panel from wood and a rigid, non-porous inorganic material such as glass or acrylic. Without a sufficiently flexible bonding means, any joins between the dissimilar materials are subjected to continual strain leading to possible failure. Consequently, such combinations have typically been restricted to applications where the bond between the wood and the inorganic material is not structurally critical.

It would therefore be desirable to produce a means of forming a composite building element, such as a panel from wood and other organic materials e.g. fibreboard, engineered wood or similar, bonded with an inorganic material such as acrylic, perspex, glass, or the like.

Wood has been used in an extremely wide number of applications, and with numerous treatments, to provide a range of aesthetic appearances. Nevertheless, there is an ongoing desire to provide yet further visually attractive, though useable and practical uses for timber. Despite the numerous advantages of timber, one obvious and hitherto intrinsic characteristic is its opacity except in extremely thin sections. Atmospheric and practical lighting forms an important consideration in modern building and decorative techniques and it is thus desirable to be able to combine the use of illumination techniques with the existing desirable properties of wood furniture and building elements.

All references, including any patents or patent applications cited in this specification are hereby incorporated by reference. No admission is made that any reference constitutes prior art. The discussion of the references states what their authors assert, and the applicants reserve the right to challenge the accuracy and pertinency of the cited documents. It will be clearly understood that, although a number of prior art publications are referred to herein, this reference does not constitute an admission that any of these documents form part of the common general knowledge in the art, in New Zealand or in any other country.

It is acknowledged that the term 'comprise' may, under varying jurisdictions, be attributed with either an exclusive or an inclusive meaning. For the purpose of this specification, and unless otherwise noted, the term 'comprise' shall have an inclusive meaning - i.e. that it will be taken to mean an inclusion of not only the listed components it directly references, but also other non-specified components or elements. This rationale will also be used when the term 'comprised' or 'comprising' is used in relation to one or more steps in a method or process.

It is an object of the present invention to address the foregoing problems or at least to provide the public with a useful choice.

Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.

DISCLOSURE OF INVENTION

According to one aspect of the present invention there is provided a laminate formed from at least one wood section bonded to at least one optically transmissive section formed from an inorganic material.

Preferably, said inorganic material is rigid (or semi-rigid) and non-porous, such as an acrylic thermoplastic. Alternative organic materials include other thermoplastics, glass, Perspex, clear polypropylene, and/or any other optically transmissive rigid, stable, non-porous material.

As defined herein, the terms wood includes wood products such chipboard, particleboard, plywood, hardboard, engineered wood, fibreboard, veneers, wood laminates, composites and the like. According to one embodiment, the present invention provides a panel, composed of alternate sections of wood and an optically transmissive material. The panel may used as both a structural component and as a decorative feature, wherein natural or artificial light may filter though the transmissive sections to create an aesthetically pleasing effect. Varying the wood and transmissive section dimensions enables panels of varying stiffness, weight and structural integrity to be produced.

It will be appreciated however that alternative laminate shapes are possible, such as beams, blocks, spheres or any other geometric configuration of interest.

Where the panels are used in conjunction with an artificial light source, the exterior surface of both wood and transmissive sections may be affected by the heat from the light source. Thus, according to one embodiment the panel is provided with a heat-resistant coating. In an alternative embodiment, the wood sections and/or transmissive sections are formed from heat-resistant materials. It will be appreciated that the thickness of the panels will also contribute to the response of the panel to heat and the consequent effect on any coating applied to the panel such as varnish, staining or the like.

Whilst a variety of wood types may be used, it has been found Rimu, Tawa, Saligna, Blackwood, Jarrah and Ash provide the necessary stability and a suitable range of colour and grain figuring. To ensure the necessary stability, seasoning of the wood is a key factor, with a moisture content of 12% (+/- 5%) (by oven weight in typical New Zealand conditions) being found to give optimum results.

As seasoned timber retains a degree of flexibility, it is necessary for the bond with the transmissive section to also be flexible. The primary means of forming the bond is by way of an adhesive capable of bonding two such dissimilar materials with sufficient strength and longevity when subjected to the flexing forces of the wood during the lifetime of the laminate.

Known wood glues or adhesives are primarily effective for bonding wood to other pieces of wood. These adhesives operate by penetrating and surrounding the wood cell clusters whilst still in the liquid phase before curing.

Wood adhesives may be derived from several general groups including PVA (water-based), Urea (water), urea formaldehydes, melamine, resorcinol (all phenol based), polyurethane, epoxy resins, silicones and other forms of contact adhesive.

Thermoplastics such as acrylic exhibit several properties that enhance their suitability of the present invention in comparison to alternatives such as glass and other plastics.

Glass is well known for its desirable qualities in terms of optical transmission properties and rigidity. However, it is not possible to easily machine sections of the laminate to different sizes once the glass and wood is bonded together into a panel for example. This increases costs as each laminate must be custom assembled to the specific size required for the application, instead of being manufactured in extended lengths and cut to size as required.

An encapsulating pouring resin is a further alternative. This would involve pouring the resin (without foaming or entraining bubbles) into a mould containing the timber sections. The mould would also need to be absolutely level - particularly for large panels. The finished panel would also be difficult to polish to the desired degree of gloss. These factors reduce the attractiveness of this method.

Consequently, the availability of rigid, non-porous thermoplastic sheet material offers the most desirable combination of features for use in the present invention. Nevertheless, ensuring an appropriate bond between the wood and the transmissive thermoplastic section is still paramount. Furthermore, acrylic possesses a high degree of surface tension which must be overcome to ensure a good bond with the wood.

A transmissive thermoplastic section such as solid acrylic may be bonded to itself using known spirit-based contact adhesives which partially melt the surface of the acrylic before bonding. However, initial tests using such known species of adhesives yielded excessive failure rates in comparison to conventional wood- wood adhesive bonding. Some improvements were observed in the tests where the timber was bonded to abraded acrylic and even greater improvement when the acrylic was both abraded and primed with thinners. Nevertheless, the strength of the resultant panels was still 30% less than a conventional wood/wood bond.

Further testing identified the following characteristics of an ideal adhesive;

1. Applicable to a variety of timber species including the aforementioned Rimu, Tawa, Saligna, Blackwood, Jarrah and Ash.

2. May be applied without expensive and/or complex equipment, e.g. by roller.

3. Provides sufficient open time to allow arrangement of the wood and acrylic pieces before initial set occurs.

4. Is able to withstand the temperature range of commercial glue-bays used in commercial joinery manufacture.

5. Is coloured (preferably darkly) to create an even coloured glue line.

6. Retains its flexibility and adhesion during the entire life of the laminate product.

7. Has a reliable and proven use history in comparable application.

8. Provides a water-proof finish.

9. Adaptable to provide satisfactory bonding with an acrylic thermoplastic.

The above criteria were met by Resorcinol formaldehyde, a widely used adhesive in the timber, aeronautic and marine industries, particularly due to its waterproof properties. It is possible that alternative formaldehyde adhesives may also be suitable.

However, unmodified Resorcinal formaldehyde is not in itself able to provide an adequate bond onto acrylic.

Testing revealed optimum bonding is achieved by a combination of abrading the surface of the acrylic before coating with a solvent-based gel formulated from hydrocarbons and monomers with an acrylic suspension. The formulation has two functions; the hydrocarbons soften the acrylic surface, while the monomers hold the acrylic suspension in place during the open time, i.e. the length of time after application that the gel remains exposed before being sandwiched between the acrylic section and the wood section. This allows the hydrocarbons to remain active long enough before it evaporates or 'flash-off to break up the surface cellular structure of the acrylic without permanent deformation . The monomers also flash off, though at a slower rate and effectively leave an acrylic primer bonded to the acrylic sheet surface. This acrylic primer also locks the molecules of the formaldehyde glue to fuse the wood section to the acrylic section after they are clamped together. The steps of abrading and applying the gel overcome the high surface tension of the acrylic sheet enabling a strong, yet flexible bond to be formed.

The formaldehyde adhesive is modified before use by the addition of a methyl solution. This modification assists the wood bond by softening the cellulose composition of the wood cells thus enhancing the penetration of the glue into wood surface. The laminate is then clamped together for a prescribed period and temperature.

Although several variants may also prove suitable, the following formulations were found effective after comprehensive testing:

A hydrocarbon solution, with a flash point of -4°c, in the form of a colourless liquid derived from mixed N-Butylenes and sulphuric acid to cause hydrolysis followed by distillation to separate the sec-butyl alcohol by which is then hydrogenated.

- A monomer solution, in the form of a colourless volatile liquid, derived from ethylene cyanohydrin, methanol and dilute sulphuric acid and with a flash point of - 3.8°C.

A methyl solution, in the form of a clear colourless, mobile highly polar liquid with a flash point of 13°c, dderived by high pressure catalytic synthesis from carbon monoxide and hydrogen.

Thus, according to a further aspect of the present invention, there is provided a laminate formed from at least one wood section bonded to at least one optically transmissive section formed from a thermoplastic, characterised in that the bond is formed by a solvent applied to the surface of the thermoplastic transmissive section and a waterproof wood adhesive applied to the surface of the wood section prior to clamping the sections together.

Preferably, the said solvent is in the form of a gel, permitting the solvent to remain active for a sufficient period to erode the surface cellular structure of the acrylic without permanent deformation.

According to a further aspect, the present invention provides a method of constructing a laminate substantially as described above, characterised by the steps of • abrading the surface of the thermoplastic;

• coating the thermoplastic surface with a solvent-based gel;

• coating the surface of the wood with a waterproof wood glue;

• clamping the wood and thermoplastic sections to form a composite laminate.

Preferably, said wood adhesive is a formaldehyde (e.g. Resorcinol formaldehyde), modified by the addition of a methyl solution.

Preferably, the gel is applied to all the contact faces of the thermoplastic for a period of 15-30 minutes at a temperature of approximately 20 degrees Celsius.

Preferably, the composite laminate is clamped together for at least 24 hours at approximately 20 degrees Celsius.

After construction, the laminate structure may be machined and sanded using conventional equipment. Similarly, varnishing and other preparations may be applied to the exterior surface.

It will also be appreciated that coloured thermoplastics may be employed to give differing visual effects without departing from the scope of the invention.

The present invention thus provides a means for manufacturing a material suitable for building and joinery purposes which allows the transmission of illumination through the transmissive sections, whilst still retaining the structural capabilities and benefits of an imperforate structure.

BRIEF DESCRIPTION OF DRAWINGS

Further aspects of the present invention will become apparent from the following description which is given by way of example only and with reference to the accompanying drawings in which:

Figure 1 shows a perspective view of a laminate panel formed according to a preferred embodiment of the present invention

BEST MODES FOR CARRYING OUT THE INVENTION

The present invention, as shown with respect to figure 1 , is comprised generally of a laminate of wood sections bonded to inorganic sections for use as a building product. Figure 1 shows a the present invention in the form of a panel (1 ) composed of multiple elongated strips of wood (2) interposed by optically transmissive sections in the form of elongated thermoplastic strips (3).

It will be appreciated that the configuration of the illustrated panel (1 ) is not limiting and that the invention may be utilised to form a variety of shapes and configurations. Reference herein to a panel is merely for exemplary purposes to aid clarity and for ease of understanding.

In the embodiment shown in figures 1 , the transmissive sections (3) are formed from an acrylic thermoplastic. Alternative materials such as glass, Perspex, and the like may be employed, though these each have differing peculiarities in terms of bonding with the wood sections (2). The wood sections (2) may be chosen from a variety of woods though Rimu, Tawa, Saligna, Blackwood, Jarrah and Ash have been found to be effective. It is envisaged that Beech, Maple, and other timbers would be equally satisfactory.

Although the panel (1) permits an attractive aesthetic effect by allowing natural or artificial light to pass through the transmissive sections (3), the viability of the panel (1 ) in structural applications depends on the integrity of the bond between the panel sections (2, 3).

Acrylic is a man-made thermoplastic sheet readily available in a variety of thicknesses and is both rigid and non-porous. Acrylic may be produced in both transparent and coloured variants which may be readily polished to a visually acceptable finish whilst also being unaffected by ultra-violet radiation.

However, acrylic has a surface tension which requires overcoming in order to achieve a satisfactory adhesive bond. It is also necessary that the resultant laminate complies with any applicable building regulations in the jurisdiction of use. Following extensive testing, it was determined that existing bonding methods were unsuitable for use between the acrylic (3) and wood sections (2) and did not yield a comparable strength to existing wood/wood bonds. The tests did determine that using commercially available adhesives in combination with abrading and/or priming resulted in the following: 1. Applying the adhesive to the timber and bonding with un-primed acrylic resulted in a join of less than 50% strength compared to conventional wood/wood joins.

2. Applying the adhesive to timber together with abraded acrylic resulted in a slight improvement, though still only approximately 50% of the wood/wood bond strength.

3. Abrading the acrylic and applying a primer (e.g. Methyl ethyl ketone (MEK) -based fillers) resulted in significant improvement in all bonds, particularly for that of an epoxy and a polyurethane adhesive, though the resulting bond still yielded only 70% of the strength of the wood/wood bond.

Due to the unsuitability of the adhesives tested, it proved necessary to adapt an existing adhesive in combination with a custom-developed preparation for the acrylic surface.

The resultant bonding process is as follows:

1. The contact surfaces of the acrylic sections (3) are abraded with a belt sander using an 80 grit belt and then coated with a solvent-based gel using a formulation of hydrocarbons and monomers with an acrylic suspension, which essentially breaks up the surface cellular structure of the acrylic without permanent deformation. The gel is applied to both contact faces of the acrylic (3) and left for a period of between 15 minutes to 30 minutes at 20 degrees Celsius.

2. Resorcinol formaldehyde adhesive, modified by the addition of a methyl solution (to assist with the wood cell bond) is applied to the contact surface of the wood sections (2) in a double application via a standard glue roller.

3. The wood and acrylic pieces (2, 3) are clamped together for 24 hours at a temperature of 20 degrees Celsius.

The resultant panel (1 ) may still be cut (using a standard tungsten saw blade) and planed using a commercial panel planer. Due to the increased abrasive properties of the panel (1 ) in comparison to pure wood panels, tungsten blades should be substituted for standard steel blades in the planer to avoid excessive wear. The panel (1 ) may also be polished/sanded using conventional techniques to restore the desired surface finish of the acrylic sections (3).

A variety of surface finishes may be applied to the panel (1 ) as required according to the particular requirements of the panels (1 ) intended application.

Variations in panels (1 ) size may be readily achieved by using sections (2, 3) of different dimensions. Increasing the thickness (4) of the panel provides panels capable of use in horizontal (as well as vertical) applications with less support and/or bracing. Varying the respective widths (5, 6) of the wood and acrylic sections (2, 3) alters the proportion of optically transmissible panel area, to vary the amount of light transmitted through the panel (1 ).

Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope thereof.

Claims

1. A laminate formed from at least one wood section bonded to at least one optically transmissive section formed from an inorganic material.

2. A laminate as claimed in claim 1 wherein said inorganic material is rigid or semi-rigid.

3. A laminate as claimed in claim 1 wherein said inorganic material is non- porous.

4. A laminate as claimed in claim 2 or claim 3, wherein said inorganic material is acrylic thermoplastic.

5. A laminate as claimed in claim 4, wherein said inorganic material is selected from the group including other thermoplastics, glass, Perspex, clear polypropylene, and/or any other optically transmissive rigid, stable, non- porous material.

6. A panel, composed of alternate sections of wood and an optically transmissive material.

7. A panel as claimed in claim 4, formed as a beam, block, sphere and/or any other geometric configuration.

8. A panel as claimed in any one of claims 6 or 7, wherein said panel is provided with a heat-resistant coating.

9. A panel as claimed in any one of claims 6 or 7, wherein said wood sections and/or transmissive sections are formed from heat-resistant materials.

10. A panel as claimed in any one of claims 6 to 9, wherein said wood sections are selected from a group including Rimu, Tawa, Saligna, Blackwood, Jarrah and/or Ash.

11. A panel as claimed in any one of claims 6 to 10, wherein said alternate sections of wood and an optically transmissive material are joined by an adhesive

12. A panel as claimed in claims 11 , wherein said adhesive is a spirit-based contact adhesives.

13. A panel as claimed in any one of claims 6 to 12, wherein said adhesive possesses at least one of the following properties;

- being applied by roller;

- providing sufficient open time to allow arrangement of the wood and acrylic pieces before initial set occurs;

- being able to withstand the temperature range of commercial glue- bays used in commercial joinery manufacture;

- being at least partially opaque, or coloured;

- providing a water-proof finish; and/or

- being adaptable to provide bonding with an acrylic thermoplastic.

14. A panel as claimed in any one of claims 6 to 13, wherein said adhesive is a Formaldehyde adhesives.

15. A panel as claimed in claim 14, wherein said Formaldehyde adhesive is modified by the addition of a methyl solution.

16. A panel as claimed in any one of claims 6 to 15, wherein said adhesive is a hydrocarbon solution.

17. A panel as claimed in claim 16, wherein said hydrocarbon solution has a flash point of -4°c.

18. A panel as claimed in claim 16 or claim 17, wherein said hydrocarbon solution is in the form of a colourless liquid.

19. A panel as claimed in any one of claims 16-18, wherein said hydrocarbon solution is derived from mixed N-Butylenes and sulphuric acid.

20. A panel as claimed in any one of claims 16-19, wherein said adhesive causes hydrolysis followed by distillation to separate the sec-butyl alcohol by which is then hydrogenated.

21. A panel as claimed in any one of claims 6 to 15, wherein said adhesive is a monomer solution.

22. A panel as claimed in claim 21 , wherein said monomer solution is in the form of a colourless volatile liquid.

23. A panel as claimed in claim 21 or 22, wherein said adhesive is derived from ethylene cyanohydrin, methanol and dilute sulphuric acid.

24. A panel as claimed in any one of claims 21-23, wherein said monomer solution has a flash point of - 3.8°C.

25. A panel as claimed in any one of claims 6 to 15, wherein said adhesive is a methyl solution.

26. A panel as claimed in claim 25, wherein said methyl solution is in the form of a clear colourless, mobile highly polar liquid.

27. A panel as claimed in claim 25 or 26, wherein said methyl solution has a flash point of 13°c.

28. A panel as claimed in any one of claims 25-27, wherein said methyl solution is derived by high pressure catalytic synthesis from carbon monoxide and hydrogen.

29. A laminate formed from at least one wood section bonded to at least one optically transmissive section formed from a thermoplastic, characterised in that the bond is formed by a solvent applied to the surface of the thermoplastic transmissive section and a waterproof wood adhesive applied to the surface of the wood section prior to clamping the sections together.

30. A laminate as claimed in claim 29, wherein the said solvent is in the form of a gel, permitting the solvent to remain active for a sufficient period to erode the surface cellular structure of the acrylic without permanent deformation.

31. A method of constructing a laminate as claimed in any one of the preceding, characterised by the steps of;

• abrading the surface of the thermoplastic;

• coating the thermoplastic surface with a solvent-based gel;

• coating the surface of the wood with a waterproof wood glue;

• clamping the wood and thermoplastic sections to form a composite laminate.

32. A method as claimed in claim 31 , wherein said wood adhesive is a formaldehyde, modified by the addition of a methyl solution.

33. A method as claimed in claim 31 or claim 32, wherein the gel is applied to all the contact faces of the thermoplastic for a period of 15-30 minutes at a temperature of approximately 20 degrees Celsius.

34. A method as claimed in any one of claims 31 to claim 33, wherein the composite laminate is clamped together for at least 24 hours at approximately 20 degrees Celsius.

35. A laminate substantially as hereinbefore described and as shown in the attached drawing.

36. A panel substantially as hereinbefore described and as shown in the attached drawing.

37. A method of constructing a laminate substantially as hereinbefore described and as shown in the attached drawing.