GB1598852A

GB1598852A - Particle board free of formaldehyde

Info

Publication number: GB1598852A
Application number: GB4064/78A
Authority: GB
Original assignee: RYAB
Current assignee: RYAB
Priority date: 1977-02-03
Filing date: 1978-02-01
Publication date: 1981-09-23
Also published as: DK48978A; DK153636C; SE7701189L; SE403893C; FR2379374A1; NO780374L; NO155482C; FI780328A; SE403893B; DE2804514A1; DK153636B; DE2804514C2; FI69269C; NO155482B; FR2379374B1; FI69269B

Description

(54) PARTICLE BOARD FREE OF FORMALDEHYDE (71) We, RY AB, a Swedish joint-stock company of Box 136, S-313 00 Oskarstram, Sweden, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: During recent years, as is known, the occurrence of formaldehyde in dwellings has been observed. Among the products used in modern house-building, particle boards are thought to be one of the sources of the occurrence of free formaldehyde in air.

The art known to-day of using condensation products of formaldehyde and urea, phenol or melamine as binding agent in particle boards requires in practice a certain excess of formaldehyde.

This formaldehyde excess amounts to 0.02 - 0.2 % of the weight of the completed product and is assumed to be in the gaseous phase in the particle boards. Three years after their erection. for example, formaldehyde has been proved still to occur in residential buildings.

For restoring dwellings with a high content of free formaldehyde in the air to an acceptable state, the known fact has been applied that formaldehyde reacts with ammonia and thereby forms hexamethylenetetramine, which at room temperature is a stable substance in the solid state.

It is the aim of the present invention to provide a method of manufacturing particle boards on an industrial scale, in which the free formaldehyde has been immobilized in the form of hexamethylenetetramine by treatment with ammonia gas, based on the discovery that a particle board with a surface layer primarily of relatively large particles has such a high permeability to gases that an ammonia/air mixture at atmospheric pressure can be sucked with vacuum through the particle board sufficiently rapidly for rendering it technically possible to incorporate the process into a normal particle board manufacturing line.

According to the present invention we provide a method of immobilizing formaldehyde in particle boards by treatment with ammonia and formation of hexamethylene tetramine wherein one side of the board, after its completed pressing, is subjected to ammonia gas or to a mixture of air and ammonia gas at the same time as the opposite side of the board is subjected to a gas pressure being from 10,000 to 60,000 Pascal lower than the pressure acting on the said one side. Preferably the board during treatment is at a temperature of 40-100"C.

By sucking the ammonia gas through the board, it is also ensured that the inner parts of the board are supplied with a sufficient amount of ammonia.

The method proposed replaces prolonged treatment under pressure in autoclaves, which involves great sealing problems and incurs considerable cost.

This treatment can in practice be carried out in a continuous or discontinuous process, depending on the board sizes being manufactured. Modern particle board factories often work with large-size presses of 2.5 x 5-7 m, and the possibility of treating the particle boards in a continuous manner, therefore, is extremely valuable.

Two different installations for immobilizing gaseous formaldehyde in particle boards are shown by way of example in a schematic manner in the accompanying drawings, in which Figure 1 shows an apparatus for intermittently treating one particle board at a time, and Figure 2 shows also in a schematic manner an apparatus for continuously treating long particle boards sequentially.

In the embodiment shown in Figure 1, a particle board 1 is enclosed by the upper hood 2, in which ammonia or a mixture of air and ammonia is supplied under atmospheric pressure (i.e. a pressure of about 100,000 Pascal). On the lower side of the particle board and carrying the same, a lower hood 3 is provided, in which a pressure of between 90,000 and 40,000 Pascal, or 10,000 - 60,000 Pascal below atmospheric pressure, prevails. Hereby the ammonia or the mixture of air and ammonia is sucked through the particle board and evacuated from the lower hood 3. When the treatment has been carried out for a sufficient time, the next particle board 5 is introduced by means of feed rollers 4 and at the same time the preceding particle board 1 is pushed out. At the supply feed the particle board 5 is supported on carrying rollers 7, and the particle board 1 pushed out is received on conveying rollers 6.

Figure 2 shows a similar apparatus for continuously treating particle boards of especially great length. Between an upper hood 2' and a lower hood 3' the same pressure differences exist as in the foregoing embodiment, i.e. between 10,000 and 60,000 Pascal. In this case, conveying rollers 8 provided at the opposite edges of the hoods are surrounded by a wire or a slotted, or perforated rubber belt 9. The evacuation from the lower hood 3' in this case takes place through a laterally directed outlet 10.

Drive and guide rollers are arranged in about the same way as according to Figure 1 and have been given corresponding reference numerals.

Owing to the supply of the ammonia gas or ammonia gas-air mixture being under atmospheric pressure, there is no risk that ammonia gas is released into the environment, and the vacuum prevailing in the hood 3 and, respectively 3' takes care of the gases passing through the particle board.

These gases then can be removed and neutralized or regenerated, possibly within a closed system, which does not involve any consequences detrimental to the environment.

When using the continuously operating apparatus according to Figure 2 the speed of the boards running to the left in the Figure must be adjusted so that the time between the hoods permits complete binding of the free formaldehyde to take place. In this way, and with apparatus of this kind it is possible to manufacture particle boards, which can be used immediatelv in the construction of residential buildings and the like without the great disadvantage which derives from the harmful properties of formaldehyde.

WHAT WE CLAIM IS: 1. A method of immobilising formaldehyde in particle boards by treatment with ammonia and formation of hexamethyllenetetramine, wherein one side of the boards after their completed pressing is subjected to ammonia gas or to a mixture of air and ammonia gas at approximately atmospheric pressure at the same time as the opposite side of the board is subjected to a gas pressure being from 10,000 to 60,000 Pascal lower than the pressure acting on the said one side.

2. A method according to claim 1, wherein the board during treatment is at a temperature of 40-100"C.

3. An apparatus for carrying out the method according to claim 1 or 2, said apparatus comprising two hoods, between which a board is positioned, and a source of ammonia gas wherein said ammonia gas or a mixture of air and said ammonia gas is supplied to one hood, the other hood sealingly abuts against the particle board and communicates with a suction pump, which produces in the said other hood a pressure being from 10,000 to 60,000 Pascal lower than atmospheric pressure and wherein said apparatus is provided with means continuously or intermittently to convey subsequent boards through the space between the two hoods.

4. An apparatus according to claim 3, wherein the one hood is located above the board and the other hood is located below the board.

5. An apparatus according to claim 3 or 4, wherein the hoods are designed with such dimensions as together to provide treatment to the whole board.

6. An apparatus according to any of claims 3, 4, and 5 wherein the means continuously or intermittently to convey subsequent boards through the space between the two hoods comprise a wire or perforated or slotted rubber belt on two or more rollers.

7. A particle board treated according to claim 1 or 2, wherein the formaldehyde has been converted by the action of the ammonia gas to hexamethylenetetramine, which at room temperature is a stable substance in solid state, and which remains in the press compound of the board.

8. A method of immobilizing formaldehyde in particle boards, substantially as hereinbefore described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

hood 2, in which ammonia or a mixture of air and ammonia is supplied under atmospheric pressure (i.e. a pressure of about 100,000 Pascal). On the lower side of the particle board and carrying the same, a lower hood 3 is provided, in which a pressure of between 90,000 and 40,000 Pascal, or 10,000 - 60,000 Pascal below atmospheric pressure, prevails. Hereby the ammonia or the mixture of air and ammonia is sucked through the particle board and evacuated from the lower hood 3. When the treatment has been carried out for a sufficient time, the next particle board 5 is introduced by means of feed rollers 4 and at the same time the preceding particle board 1 is pushed out. At the supply feed the particle board 5 is supported on carrying rollers 7, and the particle board 1 pushed out is received on conveying rollers 6.

Figure 2 shows a similar apparatus for continuously treating particle boards of especially great length. Between an upper hood 2' and a lower hood 3' the same pressure differences exist as in the foregoing embodiment, i.e. between 10,000 and 60,000 Pascal. In this case, conveying rollers 8 provided at the opposite edges of the hoods are surrounded by a wire or a slotted, or perforated rubber belt 9. The evacuation from the lower hood 3' in this case takes place through a laterally directed outlet 10.

Drive and guide rollers are arranged in about the same way as according to Figure 1 and have been given corresponding reference numerals.

Owing to the supply of the ammonia gas or ammonia gas-air mixture being under atmospheric pressure, there is no risk that ammonia gas is released into the environment, and the vacuum prevailing in the hood 3 and, respectively 3' takes care of the gases passing through the particle board.

These gases then can be removed and neutralized or regenerated, possibly within a closed system, which does not involve any consequences detrimental to the environment.

When using the continuously operating apparatus according to Figure 2 the speed of the boards running to the left in the Figure must be adjusted so that the time between the hoods permits complete binding of the free formaldehyde to take place. In this way, and with apparatus of this kind it is possible to manufacture particle boards, which can be used immediatelv in the construction of residential buildings and the like without the great disadvantage which derives from the harmful properties of formaldehyde.

WHAT WE CLAIM IS:

1. A method of immobilising formaldehyde in particle boards by treatment with ammonia and formation of hexamethyllenetetramine, wherein one side of the boards after their completed pressing is subjected to ammonia gas or to a mixture of air and ammonia gas at approximately atmospheric pressure at the same time as the opposite side of the board is subjected to a gas pressure being from 10,000 to 60,000 Pascal lower than the pressure acting on the said one side.

2. A method according to claim 1, wherein the board during treatment is at a temperature of 40-100"C.

3. An apparatus for carrying out the method according to claim 1 or 2, said apparatus comprising two hoods, between which a board is positioned, and a source of ammonia gas wherein said ammonia gas or a mixture of air and said ammonia gas is supplied to one hood, the other hood sealingly abuts against the particle board and communicates with a suction pump, which produces in the said other hood a pressure being from 10,000 to 60,000 Pascal lower than atmospheric pressure and wherein said apparatus is provided with means continuously or intermittently to convey subsequent boards through the space between the two hoods.

4. An apparatus according to claim 3, wherein the one hood is located above the board and the other hood is located below the board.

5. An apparatus according to claim 3 or 4, wherein the hoods are designed with such dimensions as together to provide treatment to the whole board.

6. An apparatus according to any of claims 3, 4, and 5 wherein the means continuously or intermittently to convey subsequent boards through the space between the two hoods comprise a wire or perforated or slotted rubber belt on two or more rollers.

7. A particle board treated according to claim 1 or 2, wherein the formaldehyde has been converted by the action of the ammonia gas to hexamethylenetetramine, which at room temperature is a stable substance in solid state, and which remains in the press compound of the board.

8. A method of immobilizing formaldehyde in particle boards, substantially as hereinbefore described with reference to the accompanying drawings.

10. An apparatus according to claim 3

for immobilizing formaldehyde in particle boards, substantially as hereinbefore described with reference to the accompanying drawings.