GB2092192A - Internally honeycombed hardboard and method of making the same - Google Patents

Abstract

An internally honeycombed hardboard is composed of a planar sheet from at least one side of which an array of embossments projects (18), having a density lower than that of the surrounding planar areas (21). The invention also relates to a layered hardboard structure containing at least one of said internally honeycombed hardboards and to its manufacture by hot pressing a lignocellulosic fibrous mat. <IMAGE>

Description

SPECIFICATION Internally honeycombed hardboard and method of making the same It is known to make panels of interfelted lignocellulosic fibers (hardboards) adapted to be used, for example, as filling and building materials, starting from a mat of interfelted fibers, which generally have a certain moisture content.

To make such a panel, the starting fibrous mat is pressed in a hot press wherein also the removal of moisture is achieved. Thereafter, a treatment in an oven follows to improve the mechanical resistance properties of the panel and a moisturizing stage.

The pressing stage is usually carried out by introducing the fibrous mat, in a moist condition, between the plates of a hot press. Pressing can be effected by using different pressures from time to time to produce panels having a thickness, and thus a density, which are correspondingly different. When using higher pressures, consistently with the properties of the starting materials, panels are obtained which have improved physical and mechanical properties and a density in the neighborhood of about 1000 kg/cubic meter, whereas, if lower pressures are adopted, panels of a lesser density are obtained, the physical and mechanical properties of which decrease more than proportionally to the pressure decrease.

The ideally desirable properties for such a hardboard would be a low density, that is pieces which are substantially lightweight, but accompanied by good physical and mechanical properties, such as resistance to bending and resistance to soaking in water. Inasmuch as, as outlined above, the increase of the former property entails a decrease of the other, and vice versa, the conventional technology has been oriented towards a trade-off, so that the hardboard for which adequate physical and mechanical properties are required have, in general, a density of not less than 800 kg/cu.meter, whereas hardboards having a lesser density, due to their inadequate mechanical resistance, can be used for particular uses only, of a restricted extension, such as filling materials.

The principal object of this invention is to provide hardboard panels which are adapted to the use, principally if not exclusively, as structural materials and thus having satisfactory physical and mechanical properties but concurrently endowed with a substantial lightweight so as to facilitate their production, shipping and assemblage.

Another object of the invention is also to obtain hardboard panels of the kind referred to above with a manufacturing method which is easy to carry out and is cheap: in this connection, the invention aims at basically using the machinery which is already available according to the present state of the art by modifying them, at the most, with such changes as not to have a considerable bearing on the first costs. The foregoing and other objects are achieved, according to the present invention by providing an internally honeycombed hardboard panel which is more particularly suitable for composing multilayered panels and is composed of a planar sheet on at least one side of which there extends an array of projections having a density less than that of the surrounding planar zones.

A preferred internally honeycombed hardboard panel according to this invention provides to that said projections are marshalled along parallel but staggered lines.

A structure such as defined above is produced according to the invention by a manufacturing method which is characterized in that it comprises the steps of placing a fibrous mat of lignocellulosic fiber material between the two plates of a hot press spaced apart from one another, inserting between either hot plate and said fibrous mat a substantially planar die-plate of a stiff material having on its face confronting said fibrous mat an array of hollow spaces arranged according to the honeycombed structure array one desired to impart to said projections to obtain said honeycombed pattern, and hot pressing said fibrous mat.

The internally honeycombed structure thus obtained is particularly adapted, according to the invention, to compose multilayered hardboard panels for various uses, such as structural materials.

In order that the features and the advantages of the present invention may better be understood, an example of practical embodiment will be described hereinafter with reference to the figures of the accompanying drawings.

In the drawings: Figures 1 and 2 show the different shaping stages of an internally honeycombed structure made according to this invention.

Figure 3 is a plan view of the structure thus formed.

Figure 4 is a cross-sectional view, taken along the line IV-IV of the structure of Figure 3, matched to a second, identical structure so as to make up a multilayered panel, and Figure 5 is a cross-sectional view of the multilayered panel of Figure 4, taken along the line V-V of Figure 3.

Having now reference to Figure 1, a fibrous, compact and wet mat, 11, of a lignocellulosic material is inserted between the top plate 1 2 and the bottom plate 13, spaced apart from one another, of a hot press: the latter is quite conventional hydraulically controlled hot press of the kind used for producing the conventional hardboard panels, the top plate being movable and the bottom plate fixed.

On the bottom plate, a wire frame 14 is laid, which serves to encourage the evaporation of the water from the fibrous mat 11 while the latter is being hot pressed. Between the top plate 12 and the fibrous mat 11, a dieplate 1 5 is placed, which consists of a sheet metal piece, for example made of stainless steel. This dieplate is planar and smooth on its surface contacting the top pressing plate 12, while it is shaped, in its surface facing the fibrous mat, that is the bottom face of the dieplate, according to a honeycombed pattern which is defined by an array of hollow spaces 16 arranged according to parallel and staggered lines so that planar zones 1 7 are inserted between said hollow spaces: the outline of the hollow spaces in the example shown in Figure 1 is frustoconical.

Starting from the position shown in Figure 1, hot pressing is carried out as shown in Figure 2: once the press plates are properly heated, the press is actuated by depressing the top plate 12 under a preselected pressure magnitude: the latter coincides with the pressure magnitude which would be required for obtaining a solid hardboard panel of conventional make, having a thickness "h". The effect of the dieplate 15 inserted between the top plate and the fibrous mat is to distribute the pressure impressed by the top plate onto the fibrous mat in a differential way in correspondence with the hollow spaces 16 and the planar zones 1 7.The result, as can be best seen in Figure 2, is to form, starting from the fibrous mat in question, a honeycombed structure consisting of a planar slab from the top surface of which an array of projections 1 8 jut, which have a density substantially lower than that of the surrounding planar zones 21. The honeycombed hardboard panel structure as withdrawn from the press is shown in Figure 3, wherein the entire structure is indicated at 20 and the planar zones, which have been more intensely compacted and thus have a higher density, have been indicated at 21. The projections 1 8 are frustoconical bosses topped by the lesser bases 19.

Figures 4 and 5 show a multilayered panel 22 as obtained by uniting together, for example, by glueing honeycombed units 20, the union being effected in correspondence with the top bases of the ernbossments 18.

A multilayered panel according to the invention is characterized by zones 21 having a high density, and alternatingly inserted between zones 18 of lesser density, between which there are orderly arranged hollow spaces 23: the overall density of such a multilayered panel is roughly halved relative to that of a solid hardboard panel having the same overall thickness as conventionally produced, but, in spite of this, its mechanical properties are substantially in the same order of magnitude as those of a solid hardboard panel having a density of at least 0.8.

By way of example, when starting from an initial lignocellulosic fibrous mat of about 2.5 kg/sq.meter and pressing it with a metal dieplate so as to obtain a honeycombed structure having a thickness of 2.5 mm in the planar zones which have been more intensely compacted and a thickness of 5 mm in correspondence with the projections, it is possible to make, by jointing two of said honeycombed structures a multilayered panel of the kind shown in Figures 4 and 5, the overall thickness of the panel being 10 mm, with a density of about 500 kg/cu.meter with a resistance to bending of about 200 to 230 kg/sq centimeter.

Such a hardboard panel, subjected to water immersion resistance tests, gives the following results: 7% after 2 hours, and 25% after 24 hours.

These data show that the physical and mechanical properties of a multilayered hardboard panel comprising a honeycombed structure according to the invention are entirely satisfactory, the thickness being the same, relative to conventional hardboard solid panels, while the density of the composite panel is much lighter than that of the conventional panels. By so doing, the main object of the invention has been achieved. It should also be noted that these properties can be obtained by using the hot presses used in the conventional procedures for making the customary solid hardboard panels, the only expedient which is required being that of inserting the embossed dieplate between the fibrous mat and the top press plate.This fact permits, even applying to the press working pressure values in the same order of magnitude as used conventionally to impart to the fibrous mat used as the starting material a uniform pressure, that differential pressure may be applied to the various spots of the fibrous mat so that the result is a final honeycombed structure having differential density areas.

An additional and quite surprising advantage of the invention is that which is obtained as explained in the following example.

A hardboard panel made of a couple of honeycombed structures such as shown herein and having the properties set forth above, has shown a thermal insulation coefficient, A, as low as 0.065 W/m C at 1000. A conventional solid hardboard panel has a A coefficient as high as 0.1 10.12 W/cm OC approximately, so that the heat insulating power of ther conventional solid panel is about one half that of a composite panel according to the invention.

Such a property makes the multilayered panel particularly interesting for those uses in which high heat insulating powers are required. If the substantial lightweight of the article is considered, it can be seen that it lends itself particularly as a structural material for prefabricated buildings.

The honeycombed composite structure provided by this invention, as well as the individual honeycombed component panels may be differently changed over those described hereinabove; for example, by using two embossed dieplates in the pressing stage, it becomes possible to obtain a honeycombed structure having its embossments distributed over both the surfaces of the fibrous mat used as the starting material. The honeycombed composite thus obtained can be combined with other honeycombed structures according to the invention to make up multilayered panels composed of a plurality of layers. It has been found, by field tests, that a honeycombed structural unit according to the invention has, in the thinnest areas, a bending resistance of about 440 kg/sq.centimeter.According to the invention; the honeycombed structure can also be made with a foraminous, rather than an embossed, dieplate.

The exposed surface of the multilayered hardboard panels may be smooth or it can directly be obtained with decorative patterns, by inserting between the press plates and the panel surface to be exposed, appropriate embossed dieplate.

In the case in which it is desired to improve the physical and mechanical properties of the articles further, each individual honeycombed panel unit may be impregnated by substances such as drying oils, synthetic resins and other materials such as conventionally used in the hardboard manufacture for making solid items. A honeycombed structure according to the invention can be used with advantage, alone and without coupling it to another like structure, for a few uses, such as linings and filling materials and it can also be coupled to conventional solid hardboard panels or panels of another material for form composite panels adapted to a variety of applications.

Claims (9)

1. A honeycombed structure of a fibrous lignocellulosic material composed of a slab which is substantially planar and from at least one surface whereof an array of projections protrudes, which have a density lighter than that of the surrounding zones.

2. Honeycombed structure according to claim 1, characterized in that said projections are arranged along parallel lines.

3. Honeycombed structure according to claim 2, characterized in that said lines are both parallel and staggered.

4. Honeycombed structure according to claim 1, characterized in that said projections are frustoconical.

5. A multilayered hardboard panel characterized in that it contains at least one honeycombed structure according to the preceding claims.

6. Multilayered hardboard panel according to claim 5, characterized in that it comprises at least one couple of honeycombed structures unit together in correspondence with said projections.

7. A method for producing a honeycombed structure as claimed in claim 1, characterized in that it comprises the steps of placing a fibrous mat of a lignocellulosic material between the hot plates of a press as they are spaced apart, inserting between either plate and said mat at least a dieplate of a rigid material of substantially planar configuration with its surface exposed towards said fibrous mat having an array of hollow spaces or holes formed thereon according to the honeycombed pattern which it is desired to impart to said projections in order to form said structure, and hot pressing said fibrous mat.

8. A honeycombed structure, a panel comprising same and a method for their manufacture, substantially as hereinbefore described and illustrated in the accompanying drawings.

9. Any novel feature or combination of features described herein.