US2931737A

US2931737A - Impregnation process

Info

Publication number: US2931737A
Application number: US726316A
Authority: US
Inventors: Thornton Jesse
Original assignee: HICKSON S TIMBER IMPREGNATION
Current assignee: HICKSON S TIMBER IMPREGNATION; HICKSON'S TIMBER IMPREGNATION CO (G B) Ltd
Priority date: 1957-07-30
Filing date: 1958-04-04
Publication date: 1960-04-05
Anticipated expiration: 1977-04-05

Description

United States Patent 1 2,931,737 IMPREGNATION PROCESS Jesse Thornton, Leeds, England, assignor to Hicksons Timber impregnation Co. (G.B.) Limited, Castleford,

England, a British company No Drawing. Application April 4, 1958 Serial No. 726,316 Claims priority, application Great Britain July 30, 1957 4 Claims. (Q1. 117- 116) This invention'is concerned withimprovements in or relating to impregnation processes, and is more particularly concerned with the. impregnation of fibreboard materials with liquids, such as aqueous solutions containing, for example, fire-retardants and/orpreservatives, and/or with aqueous solutions of resins capable of imparting dimensional stability.

' By the term fibre-board as used herein we means.

any board which has been manufactured by compression of comrninuted cellulose, such as insulation board and wall board and also includes such materials as cardboard which are made under light compresison as well as the more solid type of board. The term does not, however, include fibre-boards which are of such a solid nature that it is not feasible to impregnate them, for example such boards as have a hardness comparable to that of metal.

facturing process; furthermore the amount ofdmpregnant which is incorporated in'the fibre-board cannot be controlled accurately and, in addition, there is considerable waste of impregnant.

It is also virtually impossible to impregnate fibre-board by merely immersing the manufactured board in an impregnant solution as the board becomes virtually impossible to handle in the wet state because it becomes soft.

Various processes are now well-known for impregnation of timber with, for example, preservative solutions and examples of such processes include variouspressure/ vacuum impregnation processes. Timber, however, has a continuous cellular structure and consists substantially of a mass of inter-connected cells. Fibre-boards with which the present invention is concerned have, however, a discontinuous structure and thus the problem of their impregnation should differ radically from the impregnation of timber. We have, however, found that one of the impregnation processes developed for treating timber (and dependent on the continuous cellular structure thereof), namely the Rueping process, is capable of adaptation to the successful impregnation of fibre-board despite the discontinuous structure of the latter. 7

:The Rueping process for the treatment of timber consists basically in forcing air or other gas under pressure into the timber to be impregnated and then forcing the impregnant liquid into the timber at a higher pressure than that at which the air or other gas was introduced.

vAfter a certain time the pressure is released and, if desired, a vacuum is applied to the timber when a large quantity of the impregnant is forced out of the timber by the gas contained therein under pressure. By controlling theinitial gas pressure and the pressure at which the liquid is forced into the timber, and, if desired,'the'time 2,931,731 Patented Apr. 5, 19$!) 'ice 2 of impregnation, the amount of impregnant introduced into the timber can be controlled as well as the depth of impregnation.

According to the invention, therefore, we provide a process for the. impregnation of fibre-board with an impregnant liquid in which the fibre-board is subjected in a pressure vessel to an initial gas, preferably air, pressure, impregnant liquid is then introduced into the pressure vessel under a pressure greater than that of the initial gas pressure to force the impregnant liquid into the fibreboard against the initial gas pressure to the desired degree of impregnation after which the liquid pressure is released.

A further measure of control of the amount of impregnation'may be secured by variation of the time within which said liquid pressure is applied.

he pro ss a cording o the invent on is conveniently carried out for example using a conventional yacuuml pr ssu mpre ati p a t s us fo h mpr nation of timber. Other methods of operation can of course be used.

By the process according to the-invention it is possible to impregnate fibre-board to, any desired degree and to achieve any desired depth of impregnatiom- This represents a considerable advance in the art as fibre-board.

is very absorbent and immersion in liquid for very short periods results in a very high volumetric absorption. line, if reference is made to the table set out below it will be seen that the absorption in litres per cubic 'rnetre of fibre-board of impregnant is very high even after'only a few minutes immersion. i

Duration of Immersion Absorption in Litres/m3 Min s. Secs.

catamaran- 0 em- OOQOOOO! cording to the invention, however, it is possible to achieve to been possible.

Thus if reference is made to the table set out below it will be seen that the absorption of impregnant in litres per cubic metre of fibre-board can be controlled tea may fine degree. i v

control of the impregnation process which has not hither- TREATMENT CYCLE Initial Air Solution Vacuum Pressure 1 Pressure Absorption, Exlairmple l I g v H 'Litres/mz! 0. .3sam les Kg] Mins. KgJ Mins. mm! Mins. cm, cm. Hg

i "is. l 1.41 10 1. 41 3O 72. 3 10 2.82 30 ii) From the above table it will be apparent that it is possible to control accurately the absorption of the impregnant within the range of about 65-500 litres/m3", the latter quantity of impregnant being in general sufficient to impart substantially complete fire-retardancy to the fibre-board being treated Whilst a quantity of about 65 litres/m. would impart a considerable fire-retardancy to the surface of the fibre-board. It should be noted in this connection that it may often only be necessary to impart a fire-retardancy-to the surface of fibre-board and that by the process according to the invention it is possible to control the. depth of impregnation to a considerable degree. Thus, in Example 1 of the above table the fibreboard is impregnated to a depth of, approximately 3.2 mm., leaving the centre core of the board dry and free from fibre-retardant.

The process according to the invention gives the best results when operated within certain pressure and time limits which are set out in the table below.

achieve control of the impregnation process. The process according to the invention is, of course, not restricted to the use of aqueous solutions but could equally well be applied to non-aqueous solutions. In practice it is very often preferable to impregnate with aqueous solutions thus avoiding use of expensive solvents so that the present invention particularly includes the use of aqueous impregnant solutions.

The process according to the invention can clearly be applied to the impregnation of fibre-board with any desired solution and is not restricted to imparting fireretardancy thereto. Thus the solution used for impregnation may contain preservatives as well as or in place of fire-retardants; they may also contain resins for imparting dimensional stability. In fact, it may often be desirable to incorporate both fire-retardants and preservatives into the fibre-board being treated as well as resins for imparting dimensional stability.

After the fibre-board has been subjected to the im As will be seen from the above table, it is preferred that the initial air pressure be within the range of 1-3 kg./cm. and that it should be maintained for 5-20 minutes. Preferably the pressure of the impregnant liquid introduced after the air has been introduced is within the range of 1.5-7 kglcm. and such pressure should first be maintained for 10-60 minutes. Finally, it is preferred that a vacuum of 250-740 mm./Hg be applied after the impregnant liquid has been introduced, such vacuum being maintained for a time within the range of from 5-60 minutes.

The process according to theinvention can be used for the impregnation of fibre-board with any desired liquids. In practice, such liquids will often be aqueous solutions containing for example fire-retardant salts or preservative salts or aqueous solutions of resins capable of producing dimensional stability in the fibre-board. Where aqueous salt solutions are used the concentrations employed canvary. as desired and in the case of fireretardant compositions may, for example, contain from .5-30, preferably 10-20% of fire-retardant substances.

tions. This is because no advantage would normally be gained by using the Rueping process for the impregnation of timber using aqueous solutions as other methods of'impregnation are equally applicable. It is only where it is desired to conserve the solvents containing the impregnant as much as possible that one applies the Rueping process because in this process a large quantity of the impregnant is forced out under pressure after impregnation has taken place. Thus, it is only in the case where recovery is important that the Rueping process has been applied.

In the process according to the invention, however, it is only by applying the Rueping process that one can Initial air pressure 2.12 kg./cm.=, 10 mins. Solution pressure 8.18 kg./cm., 30 mins. Vacuum 625 mm. Hg, 15 mins. Absorption 190 litres/n13.

Fire retardant solution M o n o ammonium dihydrogcn phosphate, ammonium sulphate and borax.

Solution strength 15%.

Net dry salt retention 40.0 kgJmP.

Example 2 1.89 CM. THICK FIBRE INSULATION BOARD TILES Treatment cycle:

, Initial air pressure- 2.82 k n/cm). 10 mins. Solution pressure 4.23 ken/cm). 35 mins. Initial vacuum 609 mm. Hg. 12 mins. Absorption 330 litres/m3. Fire retardant solution M o n o ammonium dihydrogen phosphate, ammonium sulphate and borax. Solution strength 15 Net dry salt retention--. 48.0 kg./m..

Example 3 1.27 CM. FIBRE INSULATION BOARD Treatment cycle:

, Initial air pressure"--. 2.12 Ira/cm}, 10 mins. Solution pressure 2.82 kgjcmfi. 30 mins. Absorption litres/m3.

SOlIltlOll Disodium arsenate, sodium fluoride, sodium chromate. Solution strength Net dry salt retention--. 8.0 kgJmfl.

I claim: 1. A process for the controlled impregnation with an impregnant liquid of a highly absorbent fibre-board of compressed comminuted cellulose having a density not exceeding 720 kg./m. comprising subjecting the fibreboard in a pressure vessel to an initial superatmospheric gas pressure not greater than 3 kg./cm. for from 5-20 minutes, introducing impregnant liquid into the pressure vessel under a pressure greater than that of the initial gas pressure but not greater than 7 kg./cm. for from 10-60 minutes to force the impregnant liquid into the fibre-board against the initial gas pressure to obtain a relatively high concentration of impregnant in the outer portions of said fibre-board while leaving the centre portion of said fibre-board substantially free of impregnant and releasing the liquid pressure.

2. A process as claimed in claim 1 in which a vacuum of from 254-735 mm. Hg is applied to remove excess impregnant liquid after release of the liquid pressure.

3. A process as claimed in claim 2 in which the vacuum is applied for a period of from 5-60 minutes.

4. A process as claimed in claim 1 in which said impregnant liquid is an aqueous solution.

Wheaton Ian. 20, 1925 Coolidge Oct. 6, 1925

Claims

1. A PROCESS FOR THE CONTROLLED IMPREGNATION WITH AN IMPREGNANT LIQUID OF A HIGHLY ABSORBENT FIBRE-BOARD OF COMPRESSED COMMINUTED CELLULOSE HAVING A DENSITY NOT EXCEEDING 720 KG./M.3, COMPRISING SUBJECTING THE FIBREBOARD IN A PRESSURE VESSEL TO AN INITIAL SUPERATMOSPHERIC GAS PRESSURE NOT GREATER THAN 3 KG./CM.2 FOR FROM 5-20 MINUTES, INTRODUCING IMPREGNANT LIQUID INTO THE PRESSURE VESSEL UNDER A PRESSURE GREATER THAN THAT OF THE INITIAL GAS PRESSURE BUT NOT GREATER THAN THAT OF THE INITIAL 10-60 MINUTES TO FORCE THE IMPREGNANT LIQUID INTO THE FIBRE-BOARD AGAINST THE INITIAL GAS PRESSURE TO OBTAIN A RELATIVELY HIGH CONCENTRATION OF IMPREGNANT IN THE OUTER PORTIONS OF SAID FIBRE-BOARD WHILE LEAVING THE CENTRE PORTION OF SAID FIBRE-BOARD SUBSTANTIALLY FREE OF IMPREGNANT AND RELEASING THE LIQUID PRESSURE.