AU622633B2 - Improvements in or relating to the manufacture of particle board - Google Patents

Description

Uy 77'A 622 633

AUSTRALIA

PATENTS ACT 1952 COMPEETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE Application Number: Lodged: Complete Specification Lodged: Accepted: Published: *Priority: Related Art:

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o 6o .Name of Applicant: Address of Applica TO BE COMPLETED BY APPLICANT CSR LIMITED tnt: 1-7 O'Connell Street, New South Wales, 2000, 1 4- 1 1 1 Sydney, 9 r I 00 Actual Inventor: 00 :-Address for Service: 3 -0 U0 .Q .a.

Dietmar Torner Thomas Tisch ARTHUR S. CAVE CO.

Patent Trade Mark Attorneys Level Barrack Street SYDNEY N.S.W. 2000

AUSTRALIA

Complete Specification for the invention entitled IMPROVEMENTS IN OR RELATING TO THE MANUFACTURE OF PARTICLE BOARD The following statement is a full description of this invention including the best method of performing it known to me:- REPRINT OF RECEIPT soo4,34 1 19/12/00 1 4145F:AB This invention relates to the field of building and other materials which term includes within its ambit materials (for flooring, furniture manufacture et al) such as particle board, fibre board, shaped objects and the like. More specifically, the invention provides a process whereby particle board, fibre board and other reconstituted and otherwise formulated products based on ligno-cellulosic based materials and/or on other such materials as mineral-based materials, perlite, glass wool (and combinations thereof) may be manufactured more efficaceously than heretofore. For convenience, all-embracing :c reference, hereafter, will simply be to particlP board as E C C herein defined.

."or Manufacture of particle board from the raw material(s) thereof, as flake furnish, has normally been carried out by a c c c process which involves the steps of forming, pressing and curing the flake furnish. According to prior art procedures, C tt t'i" binding agents and curing agents are introduced to the flake *c furnish prior to forming and pressing. Introduction, either in single or multi-step applications, is effected in blenders 2. through which the furnish is fed.

A major problem with this prior art procedure, however, is that the rate of curing, which is critical to the successful performance of the process, is difficult to control. If reaction between the binding agent and curing agent is too rapid, curing will be effected prematurely; if it is too slow, the result will be totally unproductive or (at best) economically unviable. As a result, it has been necessary to employ various techniques and/or controlling agents, such as 2 1839E 0215s:AB -3retarders and accelerators, to govern the rate at which curing proceeds. Another disadvantage is that maximum advantage could not be taken of the extremely fast curing rates offered by some binding agent/curing agent combinations.

It is the principal object of the invention to provide a process whereby the foreqoing disadvantages are overcome or, at least, considerably alleviated. Tne process and apparatus whereby the aims of the invention are achieved will now be defined and detailedly described.

The invention is predicated on our finding that particle board (as above defined) can be more efficiently manufactured if the curing agent is introduced at a later stage in the overall manufacturing process. Accordingly, in one broad aspect, the invention provides a process of manufacturing particle board (as herein defined) from the raw material(s) therefor wherein a said raw material, as flake furnish, is formed into mats, the mats are pressed, and curing is carried out by in situ reaction between a binding agent and a curing agent, the said process being characterised in that introduction of the curing agent is delayed until the pressing step, the reaction between the curing agent and binding agent thus being initiated only during the pressing step. In the foregoing definition, and in corresponding claim 1, the expression "flake furnish" includes within its ambit both ligno-cellulosic based Sr materials (ligno-cellulose flake furnish) and o non-ligno-cellulosic based materials.

The invention has several other aspects which will appear hereafter. According to one aspect, the invention provides a process of manufacturing particle board (as herein j

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7i 0 'VTgc f 0215s:AB 4 defined) from ligno-cellulose flake furnish, by forming, pressing and curing the flake furnish, comprising the sequential steps of feeding the furnish through a blender, introducing a binding agent into the furnish therein, forming the furnish, and pressing the furnish, the said process being characterised in that introduction of a curing agent is delayed until the pressing step, the reaction between the binding agent and curing agent thus being initiated only during the pressing step.

The invention also includes within its ambit, products produced in accordance with the foregoing processes, and apparatus for carrying out the foregoing processes. In its broadest latter aspect, the apparatus comprises, in sequential combination, blending means to which flake furnish is fed and wherein a binding agent, and other additives as required, are blended into the furnish; forming means to which the thus-treated furnish is fed and wherein it is formed into shape; and pressing means wherein the i formed furnish is pressed and to which a curing agent is S fed, initiation of curing of the furnish thus being delayed until the pressing operation.

i I The invention will now be specifically described with Sreference to preferred performance features, a particular 1: example, and the accompanying illustrative schematic drawing. It is therefore to be understood that such ensuing description should not be limitatively construed.

In one preferred process, ligno-cellulose flake furnish, of dimension employed in the art, is initially dried to a pre-determined moisture content 3 to and fed through a conventional blender wherein a binding agent is introduced. The binding agent can be any such .agent which is known to be 1 R -o~t 2\§LQY- :I cz/r A ri-i

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suitable for the purpose. A typical such binding agent is tannin which is a polymeric substance extracted from the bark of trees, such as acacia and pinus species. Tannin derived from pinus radiata is particularly suitable (as mentioned further hereafter). More specifically the commercially available forms of tannin such as the tannin available under the names 'Tanaphen" and "Mimosa" can be satisfactorily utilised. Other types of binding agents include mineral-type binders having a cement or sodium silicate basis.

The binding agent may be in liquid form, or in the form of a dry powder or a watery suspension with a proportion t to 50%) of dry powder. It is added in the requisite amount between 5 to 20% dry solids/dry fibre) and at a predetermined pH (typically 6 to 8 but allowably higher or lower depending upon specific requirements). The pH may be adjusted by any reagent suitable for the purpose, for example sodium hydroxide.

t e tc c The powdered (proportion of) binding agent operates to 'ec t C absorb some of the moisture from the watery suspension which C t C,0 increases viscosity and leads to good tack in the formed furnish. The powder is itself dissolved as the process proceeds. Other conventional additives in predetermined amounts, such as hydrophobic agents up to may be incorporated at this stage. Wax industrial wax/ 25 microcrystalline wax) is a typical hydrophobic agent. It may be used in cold emulsified form or heated.

If non-ligno-cellulose based materials are employed, they are also introduced, in proportions as required 50-60% by

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aI 4^1 5 1839E weight) at this stage. Materials such as glass wool and/or perlite are useful for the manufacture of specialty end-products fire-rated products). As foreshadowed heretofor, ligno-celluose flake furnish can in fact be entirely substituted by non-ligno-cellulose based materials.

The flake furnish is formed to shape in conventional forming equipment. At this stage curing has not commenced.

The step of curing, with simultaneous pressing, may be carried out in a single or multi "daylight" press fitted with both conventional plattens and additional perforated plattens connected to a high pressure gas (air and/or steam) system. By c i virtue of pressurised injection, a curing agent or a mixture j of such agents, in a predetermined amount as required (e.g.

c 8-17 parts to 100 parts in the case of aldehyde and tannin c C 4 respectively) is introduced into the stream of air and/or steam and conveyed thereby, under predetermined controlled conditions of time 1-50 seconds), temperature 100-200°C) and pressure 6-8 bars) to the furnish. Reaction between :C curing agent and binding agent will take place over the cross IZ?.0, section of the formed furnish.

Following curing, a vacuum may be applied, for example for a period of 0-60 seconds, to get rid of excess gases (where vacuum is not applied, such gases are removed by natural venting). In certain circumstances, an excess of curing agent S may be specifically removed by introducing appropriate agents, such as ammonia, to react therewith. Conversion to harmless by-products can thus be safely achieved.

The curing agent can also be selected from any agent known S-6- 1839E i i to be suitable for the purpose. Typical such agents are aldehydes, such as formaldehyde, and carbon dioxide. The latter will react with the mineral-type binders mentioned heretofore, the former with tannin binding agents. When formaldehyde is used as curing agent, and tannin derived from pinus radiata as bonding agent, a particularly fast reaction takes place. The present invention enables full advantage to be taken of such fast reactions.

A specific example of the process will now be described.

It is reiterated that the details thereof are merely by way of C c example.

Conventional ligno-cellulose flake furnish is dried to a moisture content of 4-6% and introduced into the blender. A Strr jcc measured amount of binding agent the tannin commercially available under the name "Minosa" is added in an amount between 8 to 15% dry solids/dry powder. The binding agent is a watery suspension with 25%, dry powder, the dry component being of value as indicated heretofore. The binding agent is adjusted to pH in the range 6-8, with sodium hydroxide, before 2,20.4 addition.

V An amount of hydrophobic wax as above, in cold t emulsified form, is introduced at this stage. The furnish is then formed into mats in conventional fashion and is ready for pressing.

The mats are loaded into the press which, as indicated above, is equipped with conventional heating plattens and with additional plattens juxtaposed each heating platten. The additional plattens are connected to the source of pressurised 7 1839E gas. As also indicated heretofore, the gas may be hot air, steam or a combination of both. The curing agent, which is formaldehyde, can be introduced with the gas or separately.

The press is closed and pressure exerted resulting in compression of the mats to a point where steam/gas permeability is of the order of 1 to 6 Ltr/sec/100mm 2 at a gas pressure of bar. The gas stream, heated to 150-180C, is activated and within 5-10 seconds, the measured quantity of formaldehyde is injected. The gas stream can be maintained for another 5-10 seconds with the hydraulic pressure applied to maintain the required thickness of particle board. After 60 seconds have elapsed, or possibly shorter time depending upon board density and/or other desired board characteristics, the pressure is reduced to a point where little spring back or back pressure of the board is noted.

o Vacuum is applied for a period of 5 to 10 seconds to get o oo rid of excess gases, after which the valves are closed, the system is vented to atmosphere, the pressure is totally relieved and the press is opened. The excess gases may be 29 collected in a condensor in a water mixture) for further re-use or safe disposal. Also as mentioned heretofore, excess Scuring agent can be accommodated by the positive introduction of A appropriate reagents which effect conversion to harmless by-products. Thus formaldehyde can be effectively bound by the introduction of ammonia.

Hot stacking of the manufactured particle board is beneficial for moisture equalization. The board is desirably kept for 24 to 72 hours before sanding.

8 On testing, particle board, manufactured as above, satisfies all the prescribed standards. In the following tables marked A to C, we set forth the properties exhibited by particle board, manufactured as single layer, in accordance with the above described (and defined) process of the invention. In each case, the reagent was formaldehyde, and the binding agent was tannin (10% w/w of furnish) in, respectively, liquid, semi-liquid and powdered form. Curing time et al were within the parameters set forth above. The density profile was kept substantially uniform over the thickness of the board to t produce firm edges with good machinability.

t c, The boards were tested according to Australian Standard (AS) 1859-1860. The satisfactory bond durability figures will I be particularly noted.

A. BONDED MIMOSA TANNIN LIQUID: 45% S.C.

HCOH (litres) 3 4 6 4 t i c r Steam (seconds) 60 60 120 S Thickness (mm) 23 23 25 24 SDensity (kg/m3) 826 876 813 857 M.O.R. (MPa) 15 18.5 15.9 15.6 M.O.E. (GPa) 2.5 3.0 2.8 2.6 IB (KPa) 410 527 986 663 Swell 24 hrs 13.4 14.1 12.8 12.8 Bond durability 39 34 33 32 9 1839E 41. -7 B. MIMOSA TANNIN 50% LIQUID: 50% POWDER HCOCH (litres) 2 Steam (seconds) 20 Thickness (mm) 22 Density (kg/m3) 814 M.O.R. (MPa) 16.0 M.O.E. (GPa) 3.5 lB (KPa) 543 Swell 24 hrs ()17.4 Bond durability 22 2 3 60 23 26 845 838 17.8 18.1 3.6 3.7 871 951 18.5 15.6 29 31 11th I 6 @6 @0 @6 0 @000 0 @004 0@ 0 000 @0 0 0 6@ o @0 o 0@ 0 0 4 06 06 @0 0

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@6 0 60 @0 0 006(66 6 t Ce C C C It (6 C 6 666664 0 C. MIMOSA TANNIN POWDER ONLY HCOH (litres) Steam (seconds) Thickness (mm) Density (kg/m3) M.O.R. (D4Pa) M.O.E. (GPa) lB (KPa) Swell 24 hrs(% Bond durability M% 1.5 60 22 860 19.8 4 411 40 Nil 4 22 367 17. 9 4.2 665 23.4 29 M.O.R. modulus of rupture M.O.E. modulus of elasticity lB internal bond 10 1839E i ~i

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2c The invention will now be further briefly set forth with specific reference to the accompanying schematic illustrative drawing. As the various components of the apparatus have already been introduced in describing the instant process, detailed recapitulation will not be necessary. It is however particularly pointed out that the apparatus is an "all purpose" apparatus, designed to accommodate the various alternatives enumerated heretofore. Thus there is provision for the several alternative (solid, liquid et al) forms of binding agent to be introduced to the blender and for the supplementing (or ncd substituting non-ligno-cellulose based materials for possible t C incorporation therein. Likewise there is provision for CC C alternative curing agents and excess gas removal.

CC C Ere In the drawings, the numeral designations are as follows: C C c 1 Source of ligno-cellulose flake furnish to be fed to the dryer C LtC c e 2 Dryer C C c'c 3 Non-ligno-cellulose based materials S 4 Blender C cc 2101C 5 Tannin powder (binding agent)

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6 Tannin liquid S 7 Other liquid and semi-liquid binders c 8 9 Other additives Forming means 11 Pre-pressing means 12 Heating plattens 13 Air and/or steam connected additional heating plattens 14 Formed flake furnish 11 1839E Aldehyde (formaldehyde) curing agent 16 Alternative curing agents carbon dioxide) 17 Conversion reagent ammonia) 18 Injection device 19 Source of compressed air/gas Steam generator 21 Source of heat (hot oil/water) for heating plattens 22 Vacuum 23 Chemical recovery of excess curing agent 24 Source of hydraulic pressure 25 Finished product Se oo The ligno-cellulose flake furnish is fed from source 1 to dryer 2 and thence to blender 3, where the binding agent in So whatever form selected, and the other additives (or i substitutes), are incorporated. These operations, and the ensuing steps, are performed in the manner previously described.

oo° In closing it is stressed that the foregoing details A (temperatures, pressures, time periods, specific agents and the r lik) are intended to be merely illustrative of the invention.

1.2: t 0 As long as the basic criteria are observed, all such matters, not being critical in themselves, can be varied in accordance c with situational requirements.

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Claims (11)

1. 2. A process of manufacturing particle board (as herein defined) from ligno-cellulose flake furnish, by forming, pressing and curing the flake furnish, comprising the sequential steps of feeding the furnish through a blender, introducing a binding agent into the furnish therein, forming the furnish, and pressing the furnish, the said process being characterised in that introduction of a curing agent is delayed until the pressing step, the reaction S between the binding agent and the curing agent thus being initiated only during the pressing step.
2. 3. A process as claimed in claim 2 wherein the ligno- cellulose flake furnish is dried prior to being fed through the blender.
3. 4. A process as claimed in any one of the preceding claims wherein the binding agent is tannin. A process as claimed in claim 4 wherein the tannin is derived from pinus radiata.
4. 6. A process as claimed in any one of the preceding claims wherein the curing agent is an aldehyde.
5. 7. A process as claimed in claim 6 wherein the aldehyde is formaldehyde. 0215s:AB 14
6. 8. A process as claimed in any one of the preceding claims wherein other conventional additives, such as wax, are introduced along with the binding agent.
7. 9. A process as claimed in claim 2, or in any one of claims 3 to 8 as appended to claim 2, characterised in that the ligno-cellulose flake furnish is supplemented with, or suibstituted by, non-ligno-cellulose based materials introduced into the blender. A process as claimed in any one of the preceding claims wherein excess gases are removed by vacuum.
8. 11. A process as claimed in claim 1 or 2 and substantially as herein described.
9. 12. Apparatus for carrying out the process of claim 2 comprising,- in sequential combination, blending means to which flake furnish is fed and wherein a binding agent, and other additives as required, are blended into the furnish; j forming means to which the thus-treated furnish is fed and wherein it is formed into shape; and pressing means wherein the formed furnish is pressed and to which a curing agent is fed, initiation of curing of the furnish thus being delayed until the pressing operation.
10. 13. Apparatus as claimed in claim 12 which additionally comprises means for drying ligno-cellulose flake furnish I: prior to the feeding of such flake furnish to the blending !I means. I 14. Apparatus as claimed in claims 12 to 13 wherein the pressing means comprises heating plattens and, juxtaposed in relation thereto, respective additional perforated plattens. i- 4 paau cam i li 1 1 hri h Apparatus as claimed in claim 12 and substantially as herein described with reference to the accompanying drawing.
11. 16. Particle board (as herein defined) whenever produced by the process of any one of claims 1 to 11 or by the apparatus of any one of claims 12 to DATED this 19th day of December, 1988. CSR LIMITED By Its Patent Attorneys, Stt ARTHUR S. CAVE CO. C C c c C t1 C C 61 [*it1 183 9