GB2185748A - Method of making particle boards - Google Patents

Abstract

In a method of making water-resistant particle boards by molding and adhering chips or flakes of wood or other vegetable fiber material together by the use of adhesive, the chips or flakes are first heated at a temperature of 100 DEG C to 200 DEG C at least for one hour in an atmosphere of 95% or more of incombustible gas while rotating said chips or flakes, whereby water and sap contained in said chips or flakes is substantially completely removed, prior to the adhering of said chips or flakes.

Description

SPECIFICATION Method of making particle boards Background of the invention Field of the invention: The present invention relates to a method of making water-resistant particle boards.

Description ofthepriorart: Particle boards are made of wood or other vegetable fiber chips orflakeswhich are molded into a desired board configuration and adhered together bythe use of any suitable adhesive material. Such particle boards have substantially no anisotropyand none of knars, warps and the like which have been found in the conventional woody products. The particle boards can be molded to have practically sufficient strengths and desired dimensions from valueless wood materials including logs of small diameters. The particle boards can be produced with increased yields. For such reasons, particle boards are currently used as furniture materials, building materials and others.

However, the wood chips or flakes molding particle boards have water or moisture absorption as in the conventional woody products. When the particle boards are subjected to water or moisture, therefore, they may swell to change their dimensions such as thickness, width and length.

Further, moisture or water penetrated into the chips or flakes do not easily evaporate. Thus, the swelled particle boards can hardly be restored into their original configurations and will be reduced in strength. Such phenomena provide problems in manufacturing and working products from the particle boards. To overcome such disadvantages, various proposals have been made, for example, to improve adhesive for adhering wood chips orflakes together orto resinify wood chips orflakes.

However, no proposal has still been madeto provide a particle board having a perfectwateror moisture resistance.

Summary of the invention It is therefore an object of the present invention to provide an improved a method of making particle boards by molding chips orflakes of wood or other vegetable fiber materials into a desired board configuration and adhering said chips orflakes together by adhesive. The improvement comprises the step of heating saidchipsorflakesuptoa temperature of 100 C to 200 0C at least for one hour while rotating in an atmosphere of 90% or more incombustible gas to completely remove moisture and sap from said chips orflakes, priorto said stepof adhering said chips orflakestogether.

Since the dried chips orflakes include only fibers without any water and sap, adhesive can penetrate sufficiently into the tissue of the chips or flakes to adhere orjoin them together with an increased strength. When a particle board is made of such adhered or joined chips orflakes, it cannot swell even if it is subjected to water or moisture. Thus, the method according to the present invention provides a particle board improved in water- and moisturn-rnsistances and strength.

Briefdescription ofthe drawing The accompanying single drawing is a graph showing test results of particle boards constructed according to the method of the present invention and samples constructed in accordance with the prior art.

Description of preferred embodiments In accordance with the present invention, an adhesive isfirstappliedto chips orflakes of any suitable wood or other vegetable fiber material. The chips orflakes are then molded into a desired board configuration. The novel and essential feature of the present invention resides in that the chips or flakes are treated to have water-resistance prior to the step of applying the adhesive to the chips or flakes. The process of the present invention will be described below in more detail.

Wood materials used to produce chips or flakes in the present invention are not limited to any particular kind of wood material. Forexample,anywood material used to produce conventional particle boards may be utilised in a similar manner. Wood materials containing more water and sap than usual may similarly be used in the method of the present invention since they can be dried to completely remove the water and sap.

The wood blanks are cut orworked into chips or flakes in any suitable manner as in the conventional processes. The shape and size of the chips orflakes are suitably determined depending on the quality and class of particle boards to be produced, as in the conventional processes. Chips or flakes may be obtained by breaking or cutting unseasoned woods of high water content. If wood materials of about 6% of water content are used, the process of the present invention can be shortened in time.

The chips orflakes so produced are then thrown in a drying container or autoclave which may be conventional. Subsequently, air is extracted from the interior of the drying container or autoclave. An incombustible gas selected from the group of inert gases such as argon, helium and krypton, carbon dioxide, ammonia, sulfur dioxide and nitrogen is then charged into the drying container or autoclave to provide an atmosphere of 95% or more of incombustible gas. The incombustible gas to be charged may include a combination oftwo or more incombustible gases mentioned above. In brief, it is desirable that the atmosphere in the interior ofthe drying container contains no or only a very small amount of oxygen.If an increased amount of oxygen exists in the drying container, the chips or flakes would be burned or carbonized to decrease their strength when they are heated up to a raised temperature as will be described.

The temperature ofthe drying container or autoclave is subsequently increased within the range of 100 "C to 200 "C. This temperature may suitably be selected depending on the property of the chips or flakes placed within the drying container. In most cases, it is desirable to heatthe chips orflakes to a temperature of 200 'C since they can be dried into the most desirable state in the concept of the present invention, underwhich state water and sap are completely removed from the chips orflakes. If the chips orflakes are heated to a temperature of 100 "C or less, water and sap are insufficiently removed.On the contrary, if the chips or flakes are heated up to a temperature of more than 200 'C, they would be burned or carbonized to be become unsuitable for particle board materials.

Preferably, such atmosphere and temperature conditions are maintained at least for one hour at a normal pressure. At the same time, the chips or flakes are rotated, for example, by rolling the drying container or autoclave. This improves the removal of the water and sap from the chips or flakes. Time for which the chips or flakes are heated at a selected temperature is determined depending on the property, size and other factors ofthe chips orflakes.

In any event, the time should be at least one hourfor the intended purpose. Normally, the chips or flakes are heated ata selected temperatureforfourto eight hours.

Afterthechipsorflakeshavebeen heated art a selected temperature for a selected time, water and sap are completely removed from the chips or flakes with only fibers remaining in their tissues. The weight ofthe chips or flakes so treated is smaller than those of chips orflakes used to produce the conventional particle boards. The chips or flakes so treated are not burned or carbonized since they are heated in the above atmosphere of incombustible gas. In addition, the chips flakes are uniformly treated since they are rotated during heating.

Asynthetic resin adhesive,forexample, urea resin adhesive is applied to the dried chips orflakes in the conventional manner. The quality and amountofthe synthetic resin adhesive are similar to those ofthe synthetic resin adhesive used in the conventional process. In otherwords, they are determined within an appropriate range depending on various factors required in the finished products, such as quality, class, workability, manufacturing cost and others. In this step, the adhesive can penetrate sufficiently into the interior of each ofthe chips orflakes since it includesonlyfiberswithoutanywaterandsap.

Thereafter, the chips orflakes are molded into a desired board configuration and also adhered together by the use of a conventional molding apparatus. The molded board isthen subjected to the conventional treating steps such as hot-pressing, size finishing, surface abrading and others to provide afinished product.

The particle board so obtained will not swell if subjected to water or moisture since it is made of the water-resistant chips or flakes adhered together. The particle board has increased strength and decreased weight since the chips or flakes therein are more firmly adhered together. The workability of the particle board is similar two that of the conventional particle board. The particle board can resist rot and insects since the water and sap are completely removed therefrom.

An examplewill now be described below.

Chips werefirst placed within an autoclave. Air in the autoclave was then replaced byan atmosphere containing 95% or more of inert gas. The chips in the autoclave were heated at a temperature of 100 'Cto 200 Cfor a time between one hourandtwo hours.

Thereafter, the water content in the chips was controlled upto4%.

A conventional adhesive and water repellent material were applied to the dried chips. The chips were then formed into a desired board configuration in the conventional mannerwithout any particular and additional instrumentortool.

The formed boards were hot-pressed under a pressure of 15 to 20 kg/cm2 at a temperature of 170 to 180 'C for five minutes. The resulting particle boards fulfilled the requirements of JIS 5908 Quality Standard under which a particle board should have a density of 0.72-0.75, a water content of 5-8%, a flexural strength of 180 kg/cm2 or more, a peeling strength of 3 kg/cm2, a force for holding wood screws of 50 kg/cm2 or more, an amount of discharged formaldehyde equal to or less than 5 mg/l and soon.

Water-resistant particle boards produced according to the method of the present invention and particle board samples produced according to the prior art methods were subjected to comparison testsforexpansivity on the basis of JIS 5908 standards. The results are shown in the accompanying drawing in which lettersA and B indicatethepriorartparticleboardswhilea IetterC indicates particle boards of the present invention. It is apparent from this graph thatthe expansivity of the water-resistant particle boards according to the present invention are smaller than those of the prior art boards.

Claims (6)

1. A method of making water-resistant particle boards by molding and adhering chips orflakes of wood or other vegetable fiber material together by the use of adhesive, said method comprising the step of heating said chips or flakes at a temperature of 100 'Cto 200 "C at least for one hour in an atmosphere of 95% or more of incombustible gas while rotating said chips or flakes, whereby water and sap contained in said chips orflakes can be substantially completely removed, prior to the adhering of said chips orflakes.

2. A method as defined in claim 1 wherein said chips or flakes are heated in a rotary autoclave.

3. A method as defined in claim 1 further comprising a step of hot-pressing the resulting particle boards.

4. A method as defined in claim 1 wherein said incombustible gas is selected from the group consisting of inert gases including argon, helium, krypton and others, carbon dioxide, ammonia, sulfur dioxide, nitrogen and a combination of two or more of said gases.

5. A method of making water-resistant particle boards substantially as herein described.

6. A water-resistant particle board produced buy a method as claimed in any one of Claims 1 to 5.