GB2274084A

GB2274084A - Veneer board manufacturing process

Info

Publication number: GB2274084A
Application number: GB9227083A
Authority: GB
Inventors: Sean Ryan
Original assignee: DENLO PRECISION ENGINEERING LI
Current assignee: DENLO PRECISION ENGINEERING LI
Priority date: 1992-12-30
Filing date: 1992-12-30
Publication date: 1994-07-13
Anticipated expiration: 2012-12-30
Also published as: BE1005655A6; GB9227083D0; GB2274084B

Abstract

A veneer board manufacturing process involves bonding layers 11 of veneer to core material boards 13 by application of a bonding mixture at a station 3 and pressing at the station 6. The bonding mixture is created by mixing liquid hardener and liquid adhesive, the hardener being a solution of ammonium chloride, alkaline urea, hexamine and water, the adhesive being a urea/formaldehyde resin. A press 43 operates at approximately 7.25 x 10<6> M/n<2> for approximately 36 seconds at a temperature of approximately 150 DEG C. <IMAGE>

Description

WA Veneer Board Manufacturinq Process The invention relates to a manufacturing process for the production of veneer boards for use in furniture manufacture.

Such a manufacturing process involves equipment such as that described in German Patent Specification No. DE - Al -3,304,315 which joins veneer sheets together using a glass silk thread in a zig-zag pattern. Such equipment is also described in German Patent Specification No. DE - Al3,528,018, Other steps in the manufacturing process involve pressing layers of veneer onto both sides of a board of core material after adhesive has been applied to the surfaces of the board. In these process steps, it is very important that the adhesive be homogenous and be applied evenly over the board surfaces and that the correct parameters be adhered to in pressing of the veneer layer to the board. Otherwise, in time the veneer will become at least partially detached.

An object of the invention is to provide a veneer board manufacturing process which has a low discard rate and provides for high quality bonding of the veneer to the core material board on a consistent basis. It is a related object that the adhesives used for bonding of the veneer to the core material board have a more uniform consistency to achieve the above objective. A further related object is that the operating parameters for pressing of the veneer boards be related to the nature of the adhesives used to achieve a uniformly high quality.

These are the most important process steps, as the quality of the end product is very much dependent on them.

According to the invention, there is provided a veneer board manufacturing process comprising the steps of s- stripping veneer to create right-angled strips; stitching together a plurality of strips using glued thread which is pre-heated to form a veneer layer; mixing together a liquid adhesive and a liquid hardener, the adhesive being a urea / formaldehyde resin adhesive and the hardener being a solution of ammonium chloride, alkaline urea, hexamine and water, to create a bonding mixture; feeding the bonding mixture to upper and lower reservoirs of an application station; applying the bonding mixture to both surfaces of a board of core material fed to the application station;; pressing a pair of the veneer layers against the two surfaces of the board at a pressure in the range of 6.75 X 106 N/m2 to 7.75 X 1406 N/m2, at a temperature in the range of 140"C to 1600C for 35 to 40 seconds; and testing quality of the veneered board.

In one embodiment, the liquid hardener has a 20% solid content, has a specific gravity of approximately 1.0, and in which the liquid adhesive has a pH in the range of 7.5 to 8.5, has a specific gravity of approximately 1.3, and has a capacity in the range of 25 to 36 poise at 250C.

Preferably, veneer layers are manufactured to an excess size with respect to the board, and the board is of an excess size with respect to the desired veneered board end product, the excess of the veneer layer being used for testing of bonding quality, wherein the veneer layer and the board are trimmed after the processing operation.

In one embodiment, the bonding mixture is applied using upper and lower drive rollers, each of which is in contact with an auxiliary roller which supports the bonding mixture to achieve a uniform distribution.

The invention will be more clearly understood from the following description of some preferred embodiments thereof, given by way of example only with reference to the accompanying drawings in which: Fig. 1 is a diagrammatic view showing portion of a veneer board manufacturing plant of the invention; Fig. 2 is a diagrammatic perspective view showing strips of veneer and a veneer layer after stitching; Fig. 3 is a diagrammatic side view showing adhesive application and a core material board feeding station of the plant; and Fig. 4 is a diagrammatic plan view showing the production plant.

Referring to the drawings, there is shown a veneer board production plant for the carrying out of a manufacturing process of the invention. The plant is indicated generally by the reference numeral 1 and briefly it comprises a core material board feeding station 2, a bonding mixture application station 3, a veneer layer application station 5, and a pressing station 6. The bonding mixture application station 3 is fed by a mixing station 4 for the bonding mixture.

Materials which are supplied to the production plant 1 include uneven strips of veneer of a wood such as mahogany which are cut to even strips having right angles. Such strips are shown by the numeral 10 in Fig. 2. These strips are subsequently stitched together using a glue thread which is pre-heated by a tubular element surrounding the thread as it is being fed to the stitching head. This operation creates a layer 11 of veneer in which the thread 12 is shown in Fig. 2.

In addition, boards of core material such as chipboard or any other man-made raw material such as M.D.S. indicated by the numeral 13 are mounted on a platform 14 at the feeding station 2.

In more detail, and referring specifically to Figs. 3 and 4, the feeding station 2 comprises a pneumatically driven feeding machine 20 having an arm 21 engaging the uppermost of a stack of boards 13 mounted on the platform 14. The board 13 which is fed to the application station 3 is driven by a pair of drive rollers 22 and 23 mounted underneath and above the board 13 respectively. There is an additional roller 25 driven by the drive roller 22, and an additional roller 24 driven by the drive roller 23 both of which are not in compact with the board 13. The purpose of these rollers is to maintain a reservoir of bonding mixture in contact with the drive rollers 22 and 23 or driving a board 13 through the station 3.The reservoir of bonding mixture between the rollers 23 and 24 is fed from a nozzle 26 and a tube 27 which is fed from a pump 31 at the bottom of a tank 28 of the mixing station 4. The tank 28 includes a mixing rotor 29 which is driven by a motor 30. The configuration of rollers 22, 23, 24 and 25 ensures that the bonding mixture is applied evenly to both surfaces of the board 13.

An important aspect of the invention is the manner in which the bonding mixture is prepared, the component of the mixture being a liquid adhesive and a liquid hardener.

The liquid adhesive is an aqueous solution of urea formaldehyde resin having a solid content in the range of 65.5% to 67.5%, and has a viscosity in the range of 25 to 36 poise at 250C. The specific gravity is 1.3, and the pH is in the range of 7.6 to 8.4. The free formaldehyde content is 3%. The liquid hardener is a solution having ammonium chloride which is slightly alkaline, has a specific gravity of 1.0 and a solids content of 20%. The chemical composition of the liquid hardener is a solution of ammonium chloride, alkaline urea and hexamine in water.

In the mixing station 28, the liquid hardener and liquid adhesive are mixed as 10 parts hardener to 100 parts resin and the life of the mixture in the pot is approximately 100 minutes. Mixing of the hardener and adhesive is achieved using the blade 29 which mixes the hardener and adhesive in a batch, the size of which is determined according to the production schedules, bearing in mind that the mixture has a pot life of less than 100 minutes.

After application of the bonding mixture, the board 13 is fed on a conveyor 40 between a pair of veneer layers 11, the upper layers being mounted on a stand 41. The board and veneer layers are then fed into the pressing station 6 where they are mounted on bed 42 and a pressing plate 43 is urged downwardly to press against the board and veneer layers. It has been found that a particularly good bonding is achieved where the operating parameters of the press station 6 are as follows: Pressure - in the range of 6.75 X 106 N/m2 to 7.75 X 106 N/m2; Temperature - in the range of 1400C to 1600C; Duration - 35 to 40 seconds.

The preferred operating parameters are 7.25 n/m2, at 1500C and 36 seconds.

It has been found that the combination of these operating parameters and the nature of the bonding mixture adhesive a particularly good bonding of the veneer to the board.

As shown on Fig. 4, the pressed board is drawn outwardly by delivery station 50 having rollers 51. Interleaved between the rollers 51 there is a set of conveyor belts 52 which deliver the board outwardly in a lateral direction onto a further set of conveyor belts 53. The boards are then stacked and delivered by a pallet to a trimming station and quality test station.

The veneer layers are made to have an excess length and width over and above the size of the board of 40 to 45 mm and indeed the board has an excess of approximately 25 mm over and above the desired end product size. The excess of the veneer layer allows it to be toted by pressing downwardly the part of the veneer layer which protrudes from the board and testing if it is sufficiently well bonded. After testing, the bonded board is trimmed at a cutting station. Finally, the board is sanded at a sanding station using a sanding belt of a 60 grit grade to provide a smooth finish of the end product.

It will be appreciated that the invention provides a production process which achieves a high quality end product with a low discard rate, and a high efficiency.

Another aspect by which high efficiency is achieved is control of the various operating parameters in combination with the bonding mixture to achieve a fast pressing time of 35 to 40 seconds so that a high throughput in the pressing station 6 is achieved.

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

Claims

1. A veneer board manufacturing process comprising the steps of stripping veneer to create right-angled strips; stitching together a plurality of strips using glued thread which is pre-heated to form a veneer layer; mixing together a liquid adhesive and a liquid hardener, the adhesive being a urea / formaldehyde resin adhesive and the hardener being a solution of ammonium chloride, alkaline urea, hexamine and water, to create a bonding mixture; feeding the bonding mixture to upper and lower reservoirs of an application station; applying the bonding mixture to both surfaces of a board of core material fed to the application station; pressing a pair of the veneer layers against the two surfaces of the board at a pressure in the range of 6.75 X 106 N/m2 to 7.75 X 1406 N/m2, at a temperature in the range of 140"C to 1600C for 35 to 40 seconds; and testing quality of the veneered board.

2. A process as claimed in claim 1, wherein the liquid hardener has a 20% solid content, has a specific gravity of approximately 1.0, and in which the liquid adhesive has a pH in the range of

7.5 to 8.5, has a specific gravity of approximately 1.3, and has a capacity in the range of 25 to 36 poise at 250C.

3. A process as claimed in claims 1 or 2, wherein veneer layers are manufactured to an excess size with respect to the board, and the board is of an excess size with respect to the desired veneered board end product, the excess of the veneer layer being used for testing of bonding quality, wherein the veneer layer and the board are trimmed after the processing operation.

4. A process as claimed in any of claims 1 to 3, wherein the bonding mixture is applied using upper and lower drive rollers, each of which is in contact with an auxiliary roller which supports the bonding mixture to achieve a uniform distribution.

5. A process substantially as hereinbefore described, with reference to and as described in the accompanied drawings.

6. A veneer board whenever produced by a process as claimed in any preceding claim.