GB2025989A - Process for preparing wood chip board - Google Patents

Abstract

A process for the preparation of a wood chip board wherein a particulate wood chip furnish is admixed with a binding agent and thereafter formed into a board, which process includes the steps of: (a) optionally adjusting the water content of the particulate wood chip furnish to a first desired level; (b) coating the particles of the wood chip furnish over a substantial portion of their surface area with a binder by contacting the wood chip furnish with a solution, suspension or dispersion of a binding agent in a solvent, whereby less than 15% by weight of binder, based on the dry weight of the wood chip furnish, is coated onto the furnish; (c) adjusting the water and/or other volatile solvent content of the coated particulate furnish to a second desired level; and (d) forming the thus treated furnish into a wood chip board under the influence of heat and pressure. This process is capable of providing a wood chip board having the same strength, etc., properties as a plywood, and is thus useful in construction application. p

Description

SPECIFICATION Process for preparing wood chip boards and a wood chip board product This invention relates to wood chip boards made by combining together wood chips, and an amount of a hardenable glue or resin as binding agent, and thereafter forming the combination of chips and binding agent under the influence of heat and pressure into a composite board.

Wood chip boards of various types are known, which may be broadly classified into two basic categories. This classification is primarily based on the size of the wood chips used in making the board.

In a first category can be placed those boards fabricated from smali-size chips, or even sawdust. These boards are generally termed "particle boards". In a secondary category can be placed those boards fabricated from relatively large, thin, chips, which are generally described as "flakes". These boards are generally termed "flake board" or "waferboard": in this specification the latter of these two terms will be used.

The boards themselves can also be further sub-ciassified. In one type of board, a relatively homogeneous mass of chips is used to produce what is called a "single layer board". It is also possible to produce what is called "multiple layer boards" wherein generally three layers are present. The two outer layers in such a multiple board are generally high quality chips selected for their aesthetic appearance and surface finish properties, whereas the central layer is generally of coarser, less regular, and frequently larger chips. This central layer may also contain a higher proportion of fine materials than the surface layers. These multiple layer boards are obtained by using a plurality of wood chip finishes, either randomly or in oriented layers wherein the wood chips are laid among the fibre by suitable means.

Further, as yet another variant, it is possible to produce wood chip boards of a laminate nature, wherein a continuous skin is used for the outer surface, and a wood chip board comprises the centre. In this form of board, the outer skin is bonded to the wood chip furnish by the same binding agent as is used to bond the furnished together in the board making step. A suitable continuous skin is a veneer, a thin plywood, or even a plastics layer if a more durable finish still is required.

Wood chip boards are produced, in broad outline, by feeding wood, logs, lumber, or the like through a chipping machine, adding to the chips a desired quantity of glue, resin, or other binding agent, forming a suitable quantity of this mixture of chips and binder into a composite mat, and thereafter compressing and heating the composite mat to provide a chip board. In order to obtain the various different types of board mentioned above, these steps are varied in obvious fashions. Thus, to produce a multiple layer board the mat is obtained by feeding in sequence the first outer layer of chips, then the centre layer and then the second outer layer of chips.Where a laminate-type of board is required, the composite mat is usually laid onto the outer skin in question and then, if desired, a second outer skin (which need not be the same as the first one) is laid on top of the mat before the whole is passed to the press for curing.

The process of this invention is equally applicable to all of these categories of boards. It is addressed to the manner in which the particulate wood furnish is bonded together to produce the particulate board, and therefore for simplicity will be discussed largely in the context of a single layer board prepared from a relatively homogeneous mass of chips.

It has been known for some time that the key features which will determine the quality of the wood chip board produced are as follows: the nature of the wood taken (for example hard wood as against soft wood); the nature of the glue or binding agent chosen (for example a water-degradable binder cannot be used for boards intended for outdoor use); and the relative distribution of the glue or binding agent into and onto the mass of wood chips at the composite mat stage before the board is pressed. It stands to reason that the better this distribution of the binding agent onto and into the mass of wood chips before the composite mat is passed to the press, then the better the bond which will be obtained between the chips, and the better the quality of board finally obtained.

Certain other practical difficulties also have to be taken into account when producing wood chip boards.

It is desirable to minimize the number of handling stages through which the chips are passed, especially in producing boards from flakes. The flakes are fragile, tending to break along the line of grain.

Since any handling system inherently involves a level of attrition, each handling step reduces a proportion of the flakes to smaller particles, even to fine powder. Such fine particles tend to absorb, relative to the larger particles and the flakes, excessive amounts of binder. Thus generally steps have to be taken to separate out such particles of an undesired size.

It is also desirable to be able to control the amount of water (and other volatile liquids) in the system. Such materials will be evaporated when the composite mat is heated and pressed in the board making press, at which time the binding agent is also cured. The need to vent large volumes of steam or other vapour from the press is undesirable, and also the presence in the composite mat in the press of such large volumes of vapour can lead to imperfections in the board produced.

But probably the most important problem which must be considered in making wood chip boards is the relative distribution of the glue or other binding agent onto and into the wood chip furnish. For this one factor, more than any other, probably has more effect on the properties of the finished board, once the nature of the wood taken to provide the wood chip furnish and the binding agents have been decided upon.

It is usual to use a dry particulate binder, for example the commonly used phenol-formaldehyde resins, and thus it becomes necessary to distribute this binder evenly throughout the wood chip mass.

But in practice this is extremely difficult. First, one is attempting to blend together two particulate materials both of quite different sizes and quite different properties. Under these circumstances achieving a uniform blend is either difficult, or effectively impossible. Second, any blending process must be carried on for some time if efficient blending of the two materials together is to be achieved.

But such a blending process must involve attrition, and therefore its continuance for any long period of time is quite undesirable. As a final disadvantage, the commonly used binding agent systems do not flow, or spread, very much whilst the wood chip furnish is under conditions of both heat and pressure in the board making press, even though comparatively high press pressures can be used. Consequently, in most boards this lack of flow or spread of a particulate binder results in what can be regarded as a random spot-bond between the wood chips making up the board. From this it follows that the strength of the board obtained is in large part determined both by the number of such random spot-bonds, and, to an extent, by their distribution.

Similarly, where binding agent systems comprising a binding agent dissolved, suspended, or -dispersed in a solvent are used, adequate binder distribution is still very difficult. If a relatively concentrated binding agent system is used, then again poor distribution results, since such systems tend to be highly viscous. It is also not desirable to use a relatively weak solution, even though such solutions have usable viscosities, as this requires the removal, somehow, of the solvent used in the solution. It has been pointed out above that the presence in the press of large volumes of vapour is quit( undesirable. Further, when solutions are used any fine particles present tend to take up far more than their fair share of the binding agent, which only exacerbates the binding agent distribution difficulties.

This invention seeks to provide a process for making a wood chip board whereby these difficulties are mitigated, and a far more even distribution of the binding .agent onto the wood chips can be obtained, and without the use of excessive quantities of the binding agent. This invention also provides novel wood chip boards, which result from the process of this invention, wherein each particle of the wood chip furnish used to make the board is bonded to its neighbouring particles over a substantial proportion of its surface area.

Particularly, this invention seeks to provide a wafer board which meets the requirements laid down by the C.S.A., for a construction board, which standards have hitherto only been met by various grades of plywood.

Thus in one aspect this invention provides a process for the preparation of a wood chip board wherein a particulate wood chip furnish is admixed with a binding agent and thereafter formed into a board, which process includes the steps of: (a) optionally adjusting the water content of the particulate wood chip furnish to a first desired level; (b) coating the particles of the wood chip furnish over a substantial portion of their surface area with a binder by contacting the wood chip furnish with a solution, suspension or dispersion of a binding agent in a solvent, whereby less than 15% by weight of binder, based on the dry weight of the wood chip furnish, is coated onto the furnish; (c) adjusting the water and/or other volatile solvent content of the coated particulate furnish to a second desired level; and (d) forming the thus treated furnish into random or oriented mat to form a wood chip board under the influence of heat and pressure.

In a preferred aspect of this invention we provide a process which includes the steps of: (1) converting a bulk wood feed into a particulate wood chip furnish of primarily the desired size; (2) separating from the particulate wood chip furnish particles of an undesired size; (3) adjusting the water content of the particulate wood chip furnish to a first desired level; (4) coating the particulate wood chip furnish with a binding agent by contacting the particulate wood chip furnish with a solution, suspension or dispersion of the binding agent in a solvent; (5) separating the wood chip furnish from the solution, suspension or dispersion of the binding agent to provide a wood chip furnish having a coating of binding agent over a substantial proportion of its surface area;; (6) adjusting the water, and other volatile solvent, content of the coated particulate wood chip furnish to a second desired level to provide a storable coated particulate wood chip furnish; (7) forming a desired quantity of the coated particulate wood chip furnish into a composite mat in random or oriented fashion; and (8) converting the composite mat of coated particulate wood chip furnish into a wood chip board under the influence of heat and of pressure.

In a further aspect this invention provides a wood chip board obtained by bonding together by means of a binding agent a particulate wood chip furnish wherein the separate chips making up the furnish are bonded together over a major proportion of their surface area and containing less than 1 5% by weight of binding agent, based on the dry weight of the particulate wood chip furnish.

Preferably, the solvent used in the binding agent system is water, and, conveniently, the binding agent system contains from about 1% to about 10% by weight, more preferably about 5% by weight, of binding agent. A preferred binding agent is a phenolformaldehyde resin, especially the water dispersible solid resins described in United States Patent 4,098,770. Conveniently, the weight of binder coated onto the furnish, based on the dry weight of furnish, can range as low as 0.1% by weight.

By utilizing the process of this invention various advantages result. An important one is that a wood chip board, especially a waferboard, can be made which has equivalent strength properties of plywood of equivalent thickness, and thus can be used as a constructional board suitable for use as a sub-floor, or as a roofing board onto which shingles of the like may be laid. Alternatively, a board can be made having the properties of known boards, particularly waferboards, but utilizing far less binding agent. Each of these advantages follows as a consequence of both the improved distribution of the binding agent onto the furnish that this process allows, and also from the capability of this'process allows to control the amount of binding agent taken up by the furnish.A third advantage is that far lower levels of binding agent can be utilized to produce a useful board by this process than is possible with conventional wood chip board processes. For example, it is virtually impossible to fabricate a wood chip board by the conventional processes which does not have highly variable properties, due to imperfect bonding, if less than about 3% by weight of binding agent is used: by the process of this invention waferboards have been successfully made with as little as 0.16% binding agent by weight.

Thus, an attractive feature of this invention is that it permits significant economies in the amount of binding agent used in the fabrication of particle boards.

These, and other, advantageous features of this invention can best be explained by comparing the process of this invention with the conventional process, by way of reference to the attached Figures, in which: Figure 1 represents, in block format, a flow-diagram for the conventional process; and Figure 2 represents, in a similar fashion to Figure 1, the process of this invention.

In the conventional process, as is shown diagrammatically in Figure 1, round wood is drawn from the wet pond, or other storage, and passed first to a debarker. The removed bark is separated and the rounded logs then pass to a chipper. The chipper reduces the wood to chips, and the chips then pass to the screen. The type of chip, and hence the type of screen, depends upon the board being made.

For waferboard, large, thin, chips are needed which are typically several centimeters wide and long, and but a few millimeters thick; In this case, the screen separates as reject material, undersize particles.

For particle board, the chips required are small, even down to the size of sawdust, and hence the screen functions to remove oversize material. In this case also, the oversize material may be recycled and reduced in size, rather than discarded as is the case with waferboards.

The screened chips then pass to one, or more, storage bins. From the storage bins, the chips are passed through a drier, which removes substantially all of~the water in the chips. Routinely, a moisture content of from about 1% to about 4% (based on the amount of water normally present in the wood chips) will be left in the chips.

On leaving the drier, through, if desired, another screen which functions in the same fashion as the first screen, the chips pass to the blender. In the blender the chips are mixed with both the binding agent to be used, and also any other additives desired, for example waterproofing agents, waxes, pigments, fire retardants, and the like. If necessary, the chips can again be dried, depending on the manner in which the various materials are applied to the chips in the blender, before going to the spreader. In the spreader, a loose composite blanket of wood chips in random or oriented fashion is laid on a press platen.

This platen is then passed to the press for the final fabrication step. In the press the loose blanket is both heated and compressed to achieve two things: the heating effects final bonding of the binding agent to the wood chips, and the pressure compresses the composite mat to provide a board of the requisite final thickness. Clearly, the amount of wood chip furnish fed to the spreader is regulated dependent upon the density and final thickness of the wood chip board being made. The finished boards are then taken from the press for storage, sale, or other use.

The key feature in this old process we have discovered to be the drying of the chips. Hitherto, it has been thought that control of board quality can only be obtained if the blending steps are carried out on uniform materials. Since woods from different sources will have different levels of moisture present, it follows that drying of the chips is mandatory if a reproducible board is to be obtained. In the only process of which we are aware in which it is proposed that undried chips be used, a very high binding agent content is also required. The range given is from 15% to 30% by weight, of binding agent, based on the dry wood weight. We have now discovered that high quality wood chip board can be made without pre-drying the wood chips, and also using far less binding agent than 15%.

As is shown in Figure 2, the initial stages of the process of this invention, as far as the first screen, are the same as the conventional process. Following the screen is a drier, which is shown in the Figure in broken lines: this use of broken lines rather than solid lines is intended to convey that the presence, or use, of this drier is optional. Its use is described in detail further, below; suffice it to note here that when used, it would not be used to dry the wood chips to the level used in the conventional process, but only to remove a proportion of the water present in the wood chips.

From the screen, or drier (as the case may be), the chips pass into the coater. In the coater, which may be of any suitable construction, the wood chips are contacted with an excess of a solution, suspension, or dispersion of the binding agent in a solvent. Whilst nonaqueous systems can be used, aqueous ones are to be preferred, for which there are several reasons: not the least of the reasons is the fact that if a non-aqueous system is used, then the solvent must usually for both cost and pollution reasons be recovered. For simplicity, the remainder of this description is addressed to the situation where an aqueous binding agent system is used. In the coater, the aqueous binding agent and chips come into intimate and thorough contact.

Three factors appear to determine the amount of binding agent which the wood chips will take up whilst in the coater: all of these three factors are susceptible to being controlled. The first factor is the residence time of the chips in the coater. Increasing the residence time increases the amount of binding agent taken up, but only up to a maximum. The second factor is the relative concentration of the binding agent in the aqueous binding agent system. Whilst increasing the quantity of binding agent in the aqueous system will also increase the amount of binding agent taken up by the chips, it has to be borne in mind that increasing the quantity of binding agent in the binding agent system also increases the system viscosity. Systems s involving a highly viscous binding agent are clearly extremely difficult to handle.Consequently, as a matter of practice, a binding agent solution strength of from 5% to 10% binding agent solids by weight seems to be satisfactory but somewhat higher and, particularly, lower levels can be used. The third factor which can be controlled is the chip water content.

We have found that although the chip water content can be controlled, a dried chip taking up resin much faster than wet chip, somewhat surprisingly we have discovered that it is usually not necessary to dry the chips at all. It appears that leaving all of the water in the chips, and controlling binding agent takeup through control of contact time and of binding agent solution strength is both quite adequate, and eminently practicable. It would appear that some pre-drying before the coating stage is only necessary when the chips are very wet, indeed. Additionally, we have discovered that the process of this invention works well with chips that are either wet through extended contact with water, for example through being stored in a log pond, or still contain their natural sap (and are thus in the state normally described as "green").Chips made from "green" wood appear to function particularly well in the process according to this invention.

Exactly why wood chips containing so much water are so amenable to board formation by the process of this invention is not at all clear. A possible reason is that the water content of the wood chips inhibit absorption without in any way inhibiting adsorption of binding agent onto the surface of the wood chips. If this in fact is so, it is not at all clear why any binding agent take-up happens at all. But what does seem to be clear, is that the use of this coating technique substantially evenly coats all of the chip surface: as a consequence of this, when the board is finally formed a far better and more complete bond, in terms of bonded chip area, is obtained in the board press. In its turn, this has a fundamental effect on the strength properties of the formed board.

After having been coated with the binder system, the chips and the binder system are separated.

The technique used to separate the chips from the binder is largely determined by the coating technique used to put the binder onto the wood chips.

If coating is achieved by spraying, then a simple strainer device is effective. But if spraying is used it is also to be borne in mind that steps must be taken to ensure that all surfaces of the wood chips are coated: this is particularly important when flakes are being coated.

We prefer to coat the wood chips by dipping them into the aqueous binder. In this case it is necessary to allow for the dipped wood chips to drain adequately.

In both cases, the separated binder system can be returned to the bulk of the coating solution, but it is also necessary to monitor the coating solution as both binder and water (or, where relevant, other solvent) are lost from the system, but not necessarily evenly. Both binder and possibly some water will be taken up by the wood chips. Since the quality of the final board is in large measure determined by control of this coating step, it is necessary that the strength of the binder solution used for the coating remain approximately constant if board quality is also to be maintained constant. From this it follows that some level of monitoring of the strength of the binder system is necessary.Continuous monitoring, by some suitable technique, is the ideal, but periodic monitoring will suffice provided that it is carried out sufficiently frequently to avoid wide fluctuations in the strength of the binder coating solution in the coater.

Returning now to Figure 2, after the dip coating stage the process largely follows conventional practice, but with one addition. The wet chips are stored temporarily, and then dried to about 15% maximum water content in the drier shown. They are then formed by a spreader into a composite mat on a platen, and the mat then passed to a suitable press for heating and pressing into final finished boards. Again, the finished boards are then stored, for later sale, or use for another purpose.

A further advantage of the process of this invention is that the coated, dried, chips can be stored and handled with the loss of binder: in the conventional process once the chips and binder are mixed storage is no longer feasible.

In the process of this invention it also follows that certain constraints are placed upon the binding agent system to be use. It is preferable, but not obligatory, that a single component system be used, so that the complete binding agent is taken up by the wood chips at the coating stage. For whilst resins such as urea-formaldehydes can be used as the binding agent, it is inconvenient to have to add to the coated wood chips at a later stage any hardener, or other second component, required in order to make the resin used as the binding agent cure when the composite mat is placed in the press.Distribution of such a hardener suffers all the disadvantages discussed earlier concerning distributing materials into the wood chip: clearly, bad, distribution of such a hardener over the wood chips would not be conducive to achieving good bonding between the chips and indeed would serve to vitiate the advantages gained by the process of this invention.

It is also preferable, but not necessary, that the binding aGent system used be water soluble or water dispersible. Although a solvent other than water can be used in the dip coating, its presence will complicate the drying steps since it will have to be recovered, for pollution reasons if not for cost reasons. In view of this we prefer to use phenol-formaldehyde binders, in particular the water dispersible spray dried solid binders described in our United States Patent 4,098,770.

The remaining unusual feature the binding agent must also meet is that it shall not cause difficulties in the drier following the coater. Thus if a heated drier is used, the binding agent must not be one that will result in premature bonding together of the chips. Thus there needs to be an adequate margin of safety between the curing temperature used in the press, at which the binding agent causes the wood chips to be bonded together, and the temperature used in the drier.

The invention will now be described by way of the following Examples.

EXAMPLES 1 and 2 A phenol-formaldehyde resin solution, containing approximately 5% solids, by weight, was prepared from the following ingredients: Liquid lB-286 resin (a Reichhold Chemicals Ltd. product) 1,000 gm.

Hexamethylene tetramine 50 gm.

Water: to 8,000 gm.

Two samples of waferboard were prepared using this resin.

Example 1. 4,000 gm. of dried wafers with a moisture content of approximately 6% were dipped into the resin solution for approximately 1 5 seconds, and then tumble dried to a moisture content of approximately 10%. Total resin solution pick-up was 5,660 gm., thus providing chips with about 7.1% resin solids content. Boards were then pressed from these chips as detailed below in Table 1.

Example 2. 4,000 gm. of dried wafers, as used in Example 1, were soaked overnight in water. The next day without any drying they were also dipped in the resin solution for 15 seconds. Total resin solution pick-up was 485 gm., thus providing chips with about 0.61% resin content After tumble drying to 89% moisture content, boards were pressed from these chips as detailed below in Table I.

TABLE I Example 1 Example 2 Board Thickness - nominal (inch) 5/16 7/16 5/16 7/16 - actual (inch) 0.285 0.406 0.288 0.406 Board Density (Ib/cu.ft) 39.1 39.27 42.88 42.28 Resin Solids Loading 7.1% 7.1% 0.61% 0.61% Press: Closing Time (sec) 80 80 80 80 Total Time (sec) 240 360 240 360 Test Results: M.O.R. (psi) 4591 3498 3257 2534 M.O. R. (aged) (psi)* 1667 1704 1172 1091 M.O.T. (psi) 643709 501730 479583 436959 i.B. (Average of 5 tests) % 85 86 55 56 Surface breaks nil nil nil nil *M.O.R. (aged): An accelerated aging procedure was used.

EXAMPLES 3-14 Using the procedure broadly outlined above, a number of board samples were prepared. In these experiments both the wood chips water content, the resin solution strength, and the resin solids pick-up by the chips were all varied. The resin used was a liquid phenol-formaldehyde type, supplied by Reichhold Chemicals Ltd. under number IB-305, as an aqueous system containing 40-42% solids. This base solution was further diluted with water to give the desired strength resin solution.

The results of these experiments are collected together in Table II.

The M.O.R. and l.B. tests were carried out according to the National Standards for waferboard, CSA3-01 -8S.2-M78.

TABLE II

Example No.

3 4 5 6 7 8 9 10 11 12 13 14 Wood Chip Moisture Cont. (%) 70.20 72.00 10.80 96.10 48.60 47.10 11.2 10.30 47.40 98.00 46.20 10.70 Resin Solution Solids (%) 5.00 10.00 2.20 5.00 5.00 5.00 5.00 5.00 10.00 10.00 10.00 10.00 Resin Solids Pick Up (%) 1.44 1.62 2.97 3.6 4.01 5.20 6.30 6.44 6.44 7.11 9.78 11.70 Dried Furnish Moisture Cont. (%) 13.90 13.60 8.90 4.6 12.6 10.24 10.86 12.22 10.40 9.05 10.84 9.72 Board Thickness, nominal (inch) 5/16 5/16 5/16 5/16 5/16 5/16 5/16 5/16 5/16 5/16 5/16 5/16 Board Thickness, actual. 0.288 0.286 0.288 0.287 0.283 0.287 0.284 0.286 0.285 0.284 0.282 0.285 Board Density (lbs./cu.ft.) 41.09 42.44 41.33 43.95 41.57 43.87 44.43 42.53 43.08 43.69 43.66 43.52 M.O.R. - (Dry) p.s.i. 2203 4058 2585 2221 3538 3531 3740 2711 3493 3576 4090 4185 M.O.R. - (Aged) p.s.i. 1378 2067 1194 1318 1333 1709 1677 1988 2016 1711 2058 2192 M.O.E. p.s.i. 391309 579388 424514 368622 534824 564923 606851 423775 524291 490680 599305 609772 Internal Bond p.s.i. 38 69 36 39 70 79 85 39 91 89 126 97

Claims (24)

CLAIMS:

1. A process for the preparation of a wood chip board wherein a particulate wood chip furnish is admixed with a binding agent and thereafter formed into a board, which process includes the steps of: (a) optionally adjusting the water content of the particulate wood chip furnish to a first desired level; (b) coating the particles of the wood chip furnish over a substantial portion of their surface area with a binder by contacting the wood chip furnish with a solution, suspension or dispersion of a binding agent in a solvent whereby less than 15% by weight of binder, based on the dry weight of the wood chip furnish, is coated onto the furnish; (c) adjusting the water and/or other volatile solvent content of the coated particulate furnish to a second desired level; and (d) forming the thus treated furnish into random or oriented mat to form a wood chip board under the influence of heat and pressure.

2. Process according to claim 1 comprising: (1) converting a bulk wood feed into a particulate wood chip furnish of primarily the desired size; (2) separating from the particulate wood chip furnish particles of an undesired size; (3) adjusting the water content of the particulate wood chip furnish to a first desired level; (4) coating the particulate wood chip furnish with a binding agent by contacting the particulate wood chip furnish with a solution, suspension or dispersion of the binding agent in a solvent; (5) separating the wood chip fumish from the solution, suspension or dispersion of the binding agent to provide a wood chip furnish having a coating of binding agent over a substantial proportion of its surface area;; (6) adjusting the water, and other volatile solvent, content of the coated particulate wood chip furnish to a second desired level to provide a storable coated particulate wood chip furnish; (7) forming a desired quantity of the coated particulate wood chip furnish into a random or oriented composite mat; and (8) converting the composite mat of coated particulate wood chip furnish into a wood chip board under the influence of heat and of pressure.

3. Process according to claim 1 or 2 wherein the solvent used for the binding agent in the coating step is water.

4. Process according to any of claims 1 to 3 wherein the solution, suspension or dispersion of binding agent used in the coating step contains from about 1% to about 109/0 of binding agent.

5. Process according to any one of claims 1 to 4 wherein the solution, suspension or dispersion of binding agent used in the coating step contains about 5% of binding agent.

6. Process according to any of claims 1 to 5 wherein the binding agent is a phenol-formaldehyde resin.

7. Process according to any one of claims 1 to 6 wherein a plurality of different particulate wood chip furnishes are combined together to provide the wood chip board.

8. Process according to any one of claims 1 to 7 wherein the coated particulate furnish is formed into a composite laminate wood chip board having at least one surface skin of other material capable of being bonded by the binding agent to the particulate furnish.

9. Process according to any one of claims 1 to 8 wherein the coated particulate furnish is formed into a composite laminate wood chip board having surface skins of wood veneer or plywood.

1 0. Process according to any one of claims 1 to 9 wherein the first desired level of water content is the natural water level of the wood.

11. Process according to any one of claims 1 to 1 0 wherein the first desired level of water content is the water level present in wood chips obtained by chipping wood taken from a log wet pond.

12. Process according to any one of claims 1 to 11 wherein the second desired level of water content is less than 1 5%.

13. Process according to any one of claims 1 to 12 wherein the particulate wood chip furnish is a wood flake, and the product is a waferboard.

14. Process according to any one of claims 1 to 13 wherein the particulate wood chip furnish is a small size chip furnish or sawdust, and the product is a particle board.

15. Process according to any one of claims 1 to 14 wherein the coated furnish contains from 0.10/o.

to less than 15% by weight.of binding agent, based on the dry weight of wood chip furnish.

16. Process according to any one of claims 1 to 1 5 wherein the coated furnish contains from about 0.1 5% to about 12% by weight of binding agent, based on the dry weight of wood chip furnish.

17. A wood chip board obtained by bonding together by means of a binding agent a particulate wood chip furnish wherein the separate chips making up the furnish are bonded together over a major proportion of their surface area and containing less than 1 5% by weight of binding agent, based on the dry weight of the particulate wood chip furnish.

1 8. Wood chip board according to claim 1 7 additionally having at least one surface skin of other material bonded to the particulate wood chip furnish by means of the binding agent used to bond the particulate wood chip furnish.

1 9. Wood chip board according to claims 1 7 or 18 wherein the surface skin is a veneer or plywood skin.

20. Wood chip board according to claims 1 7, 18, 19 or 20 wherein a plurality of different wood chip furnishes are combined together to provide the particle board.

21. Wood chip board according to claims 17, 18, 19. 20 or 21 which is a waferboard.

22. Wood chip board according to claims 17, 18, 19,20 or 21 which is a particle board.

23. Process for the preparation of a wood chip board substantially as described herein with reference to the Examples.

24. Wood chip boards substantially as hereinbefore described.