GB2395921A

GB2395921A - Production of flame-retardent panels

Info

Publication number: GB2395921A
Application number: GB0228193A
Authority: GB
Inventors: John Joseph Burke
Original assignee: Individual
Current assignee: Individual
Priority date: 2002-12-03
Filing date: 2002-12-03
Publication date: 2004-06-09
Anticipated expiration: 2022-12-03
Also published as: GB0228193D0; GB2395921B

Abstract

A panel (P) is produced which has required flame-retardant properties and the appearance of a solid wood or laminated core (41). Defects arising from bubbling of air from small pockets in the wood grain are avoided by cross and longitudinal sanding in each of two stages (2/3, 16/17, 22/22), and by spray washing immediately before application of flame-retardant coats. The coats are applied while the panel surface is still wet, and the panel is then dried (15, 20, 31) for 24 hours under room temperature and humidity conditions.

Description

239592 1

- 1 "Production of flame-retardant panels" Introduction

5 The invention relates to production of flame-retardant panels for purposes such as cladding of walls or for doors, for example.

Heretofore many methods have been employed for producing flame-retardant panels.

For example, United States Patent Specification No. US6271156B1 (Gleason ef at)

10 describes a method in which a composite having an inorganic non-woven fibrous web is bonded to a wood core. While this type of approach is appropriate in some situations, it is often preferred to retain the natural appearance of the wood. Thus, flame-retardant paints and varnishes have been developed to allow the grain and general appearance of the wood core (either solid wood or laminated) to be visible, 15 flame- retardant properties being provided by the coating.

However, it has been found in practice that application of such liquid coatings has an adverse impact on the panel finish quality. The major problem is that of the coating being rough at some parts of the surface. This is caused by the fact that the wood 20 surface is not perfectly flat irrespective of the extent of sanding, and because of the nature of the coatings. Thus, this problem is particular to natural wood cores and not to man-made core materials. While the defect may appear to be minor, for high-

quality wood panels a defect may require the panel to be re-worked. In many cases re-work involves sanding down to remove the coating. This is very costly because 25 such defects arise close to the end of production. Also, it is extremely difficult to achieve a consistent level of sanding which only removes the coating and not any of the wood (either core or veneer). Thus, a small blemish can be very costly.

It is therefore an object of the invention to provide a method of producing coated 30 wood panels to achieve improved consistency in quality of finish together with meeting flame retardant specification requirements.

À À e. e c e À a À e - 2 Statements of Invention

According to the invention, there is provided a method of producing a flame S retardant wood panel, the method comprising the steps of: providing a solid wood or laminated wood core; washing the panel by application of water to completely wet at least one 10 surface of the panel; while the panel surface is still wet, applying a flame-retardant liquid coating to said surface; and 15 allowing the coating to cure.

In one embodiment, the method comprises the further step of sanding the surface before washing.

20 In one embodiment, the sanding is performed in a sanding stage with a cross belt across the wood grain and a longitudinal belt in the direction of the wood grain.

In one embodiment, the cross belt sands with rougher paper than the longitudinal belt. In another embodiment, the cross belt paper gauge is in the range of 180 to 200, and the longitudinal belt paper gauge is in the range of 240 to 400.

In one embodiment, the surface is sanded in two stages before washing, each stage 30 sanding with a cross belt and a longitudinal belt.

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À a À - 3 In one embodiment, a first stage is performed with rougher paper than a second stage. 5 In a further embodiment, the panel is dried for at least 20 hours after application of the liquid coating.

In one embodiment, the method comprises the further steps of applying at least one subsequent flame-retardant coat, the panel surface being sanded and washed before 10 application of each subsequent coat.

In one embodiment, the method comprises the further steps of, after a final flame-

retardant coat has been applied and cured, sanding the surface and applying a top coat of lacquer.

Detailed Description of the Invention

The invention will be more clearly understood from the following description of

20 some embodiments thereof, given by way of example only with reference to the accompanying drawings in which: Figs. l(a), l(b), and l(c) are together a flow diagram illustrating a coating method of the invention; and Fig. 2 is a diagrammatic cross-sectional view of an end-product panel.

Referring to Figs. l(a) to l(c) a method of producing a flame-retardant wood panel is illustrated. In step 1 the panel is prepared by sawing, planing, and possibly 30 veneering.

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À À À À e - 4 This is performed in a conventional manner as the subsequent treatment provides a substantially transparent coat allowing the wood surface to be visible.

In step 2 the panel (P) is sanded in a pass in which the panel is fed under firstly a 5 cross belt 3 across the grain and then a soft belt 4 in the line of the grain. The sandpaper for the cross belt is 180 gauge and that of the soft belt in a finer 240 gauge.

This provides a first, relatively rough, sanding of the wood.

The panel P is then sanded in a second pass 5 using the belts 3 and 4 in the same 10 layout as the first pass. However, in this case the belt 3 has 320 gauge and the belt 4 has 400 gauge sandpaper. These, as will be appreciated by those skilled in the art, are much finer than the paper used for the first pass. The panel P therefore has excellent level surfaces at this stage of production.

15 In step 6 the panel surfaces are dampened and cleaned using a wet fabric. The purpose of this step is to remove the dust particles arising from the sanding passes.

The panel P is then washed in a step 7 and coated with a first base coat in a step 8.

Base coat application occurs immediately after washing, the panel P being passed 20 under a nozzle 10 which sprays lukewarm water and then immediately under a nozzle 8 spraying the base coat. In this embodiment, the base coat is applied within 30 seconds of washing, however, it is envisaged that the duration may be longer ( up to c. 10 minutes) for some wood cores and/or ambient conditions. In this embodiment the base coat is that marketed under the name FRC Hardcoat SystemTM 25 by Mandoval Coatings Ltd. It will be appreciated from the illustration that the basecoat is applied while the panel P is still wet. While this is a very simple sequence of steps, it has been found to be particularly effective at ensuring that there are no small air pockets within the grain of the wood, thereby dramatically reducing the downstream defect rate. The base coat thickness is 150 microns.

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- 5 The panel P is then allowed to dry at room temperature conditions for approximately 24 hours in step 15. This ensures comprehensive drying without risk of warping.

When dry, the panel P is sanded again in a third pass in step 16. Again, the same 5 belt arrangement is used, and the cross belt has I80 gauge paper and the soft belt 4 has 240 gauge. In step 17 there is fourth pass sanding with the same belt arrangement] the belt 3 having 320 gauge paper and the belt 4 having 400 gauge paper. These steps prepare the surface for subsequent base coat application without adversely affecting the first 150 micron coat.

Steps 18 and 19 involve washing and application of a second 150 micron basecoat of the same composition in the same manner as illustrated for steps 7 and 8. The panel P is then dried under room temperature conditions for 24 hours in step 20.

15 At this stage the panel has dried with two basecoat layers which are effectively integrated to a total thickness of approximately 300 microns.

The panel P is then sanded in fifth and sixth passes in steps 21 and 22 using the same belt arrangement as is illustrated for steps 2 and 5. In this case the belt gauges are 20 cross 200/ soft 260 and cross 320 / soft 400 respectively. The purpose of these sanding stages is to prepare the surfaces for a final coating. They do not reduce the thickness of the two flame-retardant base coats to any significant extent.

In step 30 the panel is washed to remove any remaining or recent dust particles. The 25 panel is then dried in step 31, in this case for only 2 hours because the coatings prevent significant absorption of the washing water from step 30.

A lacquer top coat of the appropriate type for the required visual finish is then applied by spraying. The coating thickness is c.lOO microns. The top coat is then 30 cured under room temperature conditions for 24 hours in step 33.

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- 6 Referring to Fig. 2, the final panel 40 comprises: a wood core 41; a flame-retardant coating 43 integrated with a second base coat 44; and 5 a lacquer top coat 45.

It will be appreciated that the invention provides a method which is both very simple and very effective at achieving the requirements of excellent quality visual finish and meeting flame-retardant requirements. The fact that base coat application occurs 10 immediately after washing while the panel is still wet significantly reduces occurance of roughness. It appears that this is because the water prevents occurance of air pockets in the wood surface.

The invention therefore provides for production of panels having the appearance of 15 the natural wood core, while also having excellent flame retardant properties.

Because the final visual appearance arises from the wood core, the end customer can choose from the full conventional range of wood panelling available at present.

The invention is not limited to the embodiments described but may be varied in 20 construction and detail.

Claims

À À . À À À À. À À À À e - 7 Claims

1. A method of producing a flame-retardant wood panel, the method comprising the steps of: providing a solid wood or laminated wood core; washing the panel by application of water to completely wet at least one surface of the panel; while the panel surface is still wet, applying a flame-retardant liquid coating to said surface; and allowing the coating to cure.

2. A method as claimed in claim 1, comprising the further step of sanding the surface before washing.

3. A method as claimed in claim 2, wherein the sanding is performed in a 20 sanding stage with a cross belt across the wood grain and a longitudinal belt in the direction of the wood grain.

4. A method as claimed in claim 3, wherein the cross belt sands with rougher paper than the longitudinal belt.

5. A method as claimed in claim 4, wherein the cross belt paper gauge is in the range of 180 to 200, and the longitudinal belt paper gauge is in the range of 240 to 400.

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6. A method as claimed in claim 5, wherein the surface is sanded in two stages before washing, each stage sanding with a cross belt and a longitudinal belt.

7. A method as claimed in claim 6, wherein a first stage is performed with 5 rougher paper than a second stage.

8. A method as claimed in any preceding claim, wherein the panel is dried for at least 20 hours after application of the liquid coating.

10

9. A method as claimed in any of claims 2 to 8, comprising the further steps of applying at least one subsequent flame-retardant coat, the panel surface being sanded and washed before application of each subsequent coat.

10. A method as claimed in any preceding claim, comprising the further steps of, 15 after a final flame-retardant coat has been applied and cured, sanding the surface and applying a top coat of lacquer.

A method of producing a wood panel substantially as described with reference to the drawings.

12. A wood panel whenever produced by a method as claimed in any preceding claim.