US3120466A - Method of producing hardboard in prdetermined shapes and a mat used in such method - Google Patents

Description

Feb. 4, 1964 c. BOJANOWSKI 3,120,466

METHOD OF PRODUCING HARDBOARD IN PREDETERMINED SHAPES AND A MAT USED IN SUCH METHOD Filed March 21, 1960 FEED DIRECTION I IIIIIIIIIIIIIIII/ IIIIIIIIIIIIII A W M m 02%" Attorney United States Patent 3,12ll,466 METHGD 0F PRGDUCENG HARDBUARD IN PRE- DETERl /HNED SHAPES AND A MAT USED IN SUCH METHQD Carl Bojanowsld, Alpena, Mich, assignor to Abitibi Power 3: Paper tlompany, Limited, Iroquois Falls, @utar-lo, Qanada Filed Mar. 21, 19%, Ser. No. 16,346 (Zlaims. (ill. 162-164) This invention relates to a method for making hardboard in predetermined shapes and to a mat used in such method.

The utilization of hardboard has been limited by the fact that when conventional manufacturing techniques are used the product is in the form at a flat sheet or can be slightly curved. While there are several methods of obtaining irregular three dimensional shaped hardboard, none appear to be totally satisfactory. For example if the conventional wet process is used comprising the delibration and refining of wood chips followed by forming and dewater-in g the wet lap on a Fourdrinier machine and the consolidation of the dewatered Wet lap under heat and pressure, it is possible to impart a slight curvature or minor indentations to the hardboard by using suitably shaped platens in the hot press, but if an attempt is made to use platens shaped to give a severe draw, the hardbourd will be severely weakened or rupture.

The methods which have previously been considered for making shaped hardboard have mainly been based on the idea of preforming the met. In accordance with one technique a wet slurry is deposited on a form approximating the end shape and dried on this form. The ast mentioned method suffers from the disadvantage that the shaped mat does not retain its preformed shaped unless handled with extreme care with the consequence that it is impractical to ship the preformed mat to a fabricator. The preformed mat must be specially made to suit the contemplated end product, consequently the method is both costly and subject to handling problems. Some shapes have been made by a centrifugal forming technique in accordance with which a sluary is forced against a screen having the desired shape by centrifugal action, following which heat and pressure are applied undcr conditions which produce some hardening though not sufiicient to compare to usual hardboard standards. The latter tecimique is costly and the product is re only for limited applications.

it is believed that air felting and also a semi dry Pour- .dririier type formation have been tried in an attempt to produce a mat having greater draw than conventional techniques, but without being able to provide a mat which can readily be handled and which at the same time provides satisfactory elongation when pressed in forming dies.

An object of this invention is to provide amat which has superior elongation compared with the mat made by conventional techniques so as to be suitable for making a wider range of shaped products than is possible using conventional hardboard techniques A further object of this invention is to provide amat which can readily be shaped to conform with dies in which the mat is to be moulded into hardboard.

Anotherobjeotof this invention is to provide a mat which can conveniently be shipped.

in accordance with this invention a dry mat is formed and this in its broadest aspect is fiexibilized by a crushing operation, to break down the fibre bond in the mat. This crushing operation makes the mat more flexible and improves the elongation of the board in a die to a modest extent to provide a mat suitable for pressing shapes which vary to a minor extent from the flat plane. The crushing ice operation can be localized if desired to the portion or portions of the mat which will be elongated in the die.

Greatly improved results are obtained by both crush ing and bendin the dry mat so as not only partially to break down the fibre bond in the mat but also to provide cleavage planes extending primarily parallel to the surface of the mat, thus forming laminae extending substantially parallel to the surface of the mat and being adhered together suffioiently loosely at the cleavage planes to perrnit relative sliding movement between the laminae.

The crushing and bending operations can be performed simultaneously or the bending operation can follow the crushin g operation.

The crushing operation can be performed by compressing the entire mat or the entire portion of the mat to be ilexibilized at once, for example in a press or by pounding the mat, but it is best successively to apply pressure to areas of the board extending in one direction such as by the use of rollers as the latter technique gives better working of the mat than compressing the entire mat atoncc Where rollers or the like are used, it is best to pass the mat through the rollers first in one direction and then in a direction transverse to the first direction to provide a mat having uniform elongation in each direction.

The bending operation may be carried out in one direction particularly if the shape to be formed requires good elongation in one direction only but the best results and the most versatile mat is obtained by bending first in one direction and then in a direction transverse to the first direction. The bending operation or operations should be carried out so as to produce the desired cleavage planes without rupturing the mat transversely to the direction of bending.

Where rollers or the like are used to provide directional crushing in two directions, and the mat is also subjected to a bending operation in two directions, the sequence of operations can be crushing in one direction followed or accompanied by bending in that direction and then crushing in a direction transverse to the first direction followed or accompanied by bending in the transverse direction. An alternative sequence is crushing first in one direction and then transversely followed by bending in one of such directions, followed by bending in the other of such directions. Another alternative sequence is crushing in one direction followed by bending in each of transverse directions, and then crushing in a direction transverse to the first direction.

The method of this invention significantly increases the capacity of the mat to conform to the shape of a die and to elongate in the press Without rupturing so as to greatly increase the range of shaped products that cm be formed. The additional flexibility of the mat also is advantageous in that th mat will conform with a curved die.

Referring now to the drawings which illustrate a method in accordance with this invention.

FIGURE 1 is a diagrammatic elevation view showing an apparatus suitable for use in the process of the invention for providing a crushing operation and illustrating also the lines of force and the resultant cleavage planes.

FIGURE 2 is an elevation view similar to FEGU'RE 1 but illustrating the crushing and bending operation.

FIGURE 3 is a perspective view of a die formed sheet of hardboard.

FIGURE 4 is a section view on the line IVIV of FIGURE 3.

The mat which is to be fiexibilized may be prepared from afibrous wet lap produced by the defibration and refining of wood chips, followed by forming and dewatering on a forming machine such as a Fourdrinier, by conventional hardboard methods to provide a lignocellulosic fibre Wet lap. However, it is desirable that an integral binder be used. The amount and type f binder depends on the particular molding required. A suitable binder may be one or a combination of materials selected from a wide range of binders including thermosetting resins such as phenol formaldehyde and melamine formaldehyde, thermoplastic resins such as asphalt, the resin known under the trade name Vinsol and manufactured by Hercules Powder Co., which is a thermoplastic resin derived from pine wood and containing phenol, aldehyde and ether groups, and wood resins, petroleum hydrocarbons such as the material known under the trade name Piccopale, and manufactured by Pennsylvania industrial Chemical Co., drying oils of vegetable, animal, or pctroleurn origin such as linseed oi tung oil, safilower oil and latices such as styrene-butadiene and poly-vinylacetate. It is best to use a combination of binders to achieve good forming characteristics and also good physical properties in the finished board. Thermoplastic resins have an excellent plasticizing effect in the hot forming press and permit severe draws without rupture of the mat. Drying oils, thermosetting resins and most latices tend to produce the best strength and water resistance. The amount of binder used will vary according to the choice of binder and the particular molding required, but will normally be within the range of 1 to 25% by weight of the dry mat and is preferably within the range of 4% to 10%.

Overlays of paper, cloth, plastic or the like may be used provided that such overlays are suificiently extensible not to rupture in the die. Although it is preferred for most applications that an integral binder be employed, it is not essential for all purposes and some formed shapes may require high strength only in particular areas and the binder can be applied by a localized spraying of an aqueous or solvent solution of binder on the forming mat in the particular areas where greater strength is required. The binder could also be applied with a brush or in any other convenient manner. The spray application may be to the wet lap, the dried mat or the crushed mat prior to hot pressing.

The mat to be fiexibilized in accordance with this invention should be dried to the state at which it stiffens and becomes relatively rigid, so that the crushing and bending operations will produce the desired partial break down of the fibre bond, preferably accompanied by the formation of cleavage planes. The density at this stage will vary between 12 and 40 lbs. per cubic foot, with a typical density being 20 lbs. per cubic foot. The moisture will be below 10% and preferably 0.1 to 2%. If a mat produced by the wet process of making hardboard, has I not been dried to a sufficient extent for the fibres to be bonded, the individual fibres will tend to conform with the crushing and bending without producing the desired breakdown of the fibre for the formation of cleavage planes. Furthermore, there may be a tendency of the mats to blow in the press if the moisture content is above 2%. Where an integral binder is used the wet mat should be dried under conditions of time and temperature varying with the binder such that the binding potential is not developed to an extent such as to prevent the desired partial breakdown of the fibre bond on formation of cleavage planes from occurring. Where the binder is thermosetting, premature loss of the binding potential during drying should be avoided.

The dried mat is then subjected to a crushing operation and preferably also to a bending operation. FIGURE 1 illustrates a method of accomplishing the crushing operation, and what are understood to be the main forces involved in the method illustrated. However, the forces and stresses which arise are complex. The predominant stresses may vary in methods in accordance with this invention. It is not desired therefore that this invention be taken as being limited by a particular theoretical explanation.

In FIGURE 1 guide rolls 1t) and 11 feed dry mat 12 through crushing rolls 13 and 14 which may, for example. have a nip pressure of 10 to 15 pounds per square inch, for a typical 20 lbs. per cubic foot mat. Rolls 13 and 14 may for example be 6" in diameter for treating a dry mat which is /2" in thickness. Guide rolls 15 and 16 support the crushed mat. Tension lengthwise of the mat will be created at the nip of rolls 13 and 14. This tension will be greater adjacent to the surface of the mat as indicated by arrows 17 than in the centre of the mat as indicated by arows 18 to create shear forces within the crushed mat 2t)". These shear forces break down the natural fibre bond in the mat.

In FIGURE 2 a bending roll 19 is located at the nip exit of rolls 13 and 14. This bending roll together with guide rolls 15a and 16.1 are offset from the plane of dry mat 12 to provide a reverse bend which causes the formation of cleavage planes. The tension at the nip close to that surface of the mat which is adjacent to roll 19, will be increased in comparison with FIGURE 1 as indicated by the arrow 17a and this will be accompanied by a decrease in the tension at the opposite surface as indicated by the arrow 17b. When the board is bent back by the action of bending roll 19 and guide rolls 15a and 16:1, there will be tension as indicated by arrows 21 at the surface of the mat which is close to guide rolls 15a and 16a accompanied by compression as shown by arrow 22 close to bending roll 19. Bending the mat thus gives rise to additional shear forces within the mat to form cleavage planes. The cleavage planes in crushed mat 20a in FIGURE 2 are designated 23a. Crushing rolls 13 and 14 may for example have a nip pressure of 10 to 15 pounds per square inch for a typical 20 lbs. per cubic foot mat. Rolls 13, 14 and 19 may for example be 6" in diameter for treating a dry mat which is /z" in thickness. Roll 19 is located so that the angle of bend will be sufficient to create the cleavage planes to the desired extent without however, being so great as to cause rupturing or tearing of the dry mat in a direction perpendicular to its surface. The angle of bend 0 in FIGURE 2 will be the angle subtended by a line 24 drawn parallel to the surfaces of the dry mat and a line 25 passing mid way between rolls 13 and 14 and rolls 19 and 15a respectively (where roll 15a is opposite to roll 19). The best angle of bend 0 will vary but will be about 5 to 20 for a mat of /2" thickness. The spacing between rolls 13 and 19 should be sufiicient for the bending not to be unduly abrupt so as to avoid rupturing the mat. Thus where the rolls are 6 in diameter an appropriate spacing of the centres of rolls 13 and 19 would be about 18".

A single fiexibilizing operation consisting of crushing and bending as described above in one direction only, will improve the capacity of the dry mat to elongate in a die press. However, a considerable improvement in the results obtained and greatly increased flexibility in the shapes which can be produced is obtained by subjecting the dry mat to a second fiexibilizing operation in a direction transverse to that of the first operation. Thus, if the first crushing and bending operation is along the length, the second crushing and bending operation will be across the length. It is preferred that the first operation be along the grain and that the second operation be across the grain as the sequence is less likely to cause rupturing than if the reverse sequence were followed, but either sequence may be used. Alternatively each of the bending operations may be in other directions. Repeated rolling with increased nip pressure and increased flexing angles may be desired for some products.

In the subsequent bending operations, the angle of bending should be chosen which will give increased cleavage planes without causing tearing or rupturing.

The flexible product resulting from the second bending operation is flexible in each direction and resembles a thick floor carpeting. It differs from the initial dry mat in that it has cleavage planes generally parallel to the surfaces of the mat. In addition, it is capable of elongation in a die press to the extent of about 30% to 60%. The normal range of thickness for the mat will be about inch to 2 inches.

The fiexibilized dry mat is placed in a die press and subjected to press cycles, such as at temperatures 300 to 500 F., and a pressure of about 400 to 2,000 p.s.i., and cycle times of seconds to 10 minutes. A typical press cycle for mat containing 2% drying oil and 2% Vinsol is 450 F., 1,200 p.s.i. pressure for 1 minute.

Another typical press cycle for mat containing 2 /2% phenolic resin and 2 /2 petroleum resin is 400 F., 600 p.s.i. and 3 minutes.

At high temperatures moisture in the mat may cause blistering and it may be necessary to dry the mat to a low moisture content or to insert a flexible wire screen into the die on one side of the mat to allow moisture to escape.

If desired the properties of the board can be enhanced in a conventional manner by post baking in an oven or by hot stacking.

FIGURES 3 and 4 are illustrative of the shapes that can be produced in accordance with this invention. In FIGURES 3 and 4'there is illustrated a hardboard sheet 26 shaped'in a die press to have an indentation 27. The production of the shape illustrated in FIGURES 3 and 4 involve the use of a heated platen forming die with a 30% draw.

The process of this invention is further exemplified by the following example:

Example A dry mat having a density of lbs. per cubic foot, a thickness of inch and a moisture content of about 5% is made with the inclusion of 2%% of linseed oil and 2 /2% petroleum hydrocarbon. The mat is rolled along its length between crushing rolls having a nip pressure of about 12 lbs. per square inch using the apparatus illustrated in FIGURE 2, with 6" diameter bending and crushing rolls, at an angle of bend of 10 and with the bending roll and closet crushing rolls spaced 18". The mat is rolled transverse to its length using the same apparatus and nip pressure. The mat is then dried to below 1% in moisture. The mat is then molded at 450 F., and 1,200 p.s.i. using a press cycle of 45 seconds to form an automotive door panel.

I claim:

1. A method of making a shaped sheet of hardboard comprising crushing a mat of wood fibres bonded together and having a moisture content of below 10% to provide a partial breakdown of the fibrous bond and provide a mat having increased flexibility and elongation, and then die forming the mat with heat and pressure to make a shaped sheet of hardboard.

2. A method of making a shaped sheet of hardboard comprising subjecting a mat of wood fibres bonded together and having a moisture content of below 10% to a crushing operation involving the successive application of pressure to areas of the surface of the mat extending in one direction followed by a second crushing operation involving the successive application of pressure to areas of the surface of the mat extending in a direction transverse to said one direction to provide a partial breakdown of the fibrous bond and provide a mat having increased flexibility and elongation and then die forming the mat with heat and pressure to make a shaped sheet of hardboard.

3. A method of making a shaped sheet of hardboard comprising subjecting a mat of wood fibres bonded to ether and having a moisture content of below 10 to a crushing operation to provide a partial breakdown of the fibrous bond and bending said mat without rupturing the mat to provide a flexible mat of increased elongation and with cleavage planes generally parallel to the surface of the mat, and then die forming the mat with heat and pressure to make a shaped sheet of hardboard.

4. A method of making a shaped sheet of hardboard comprising forming a mat of wood fibres bonded together having a moisture content of about 0.1 to 2%,and including an integral binder in the amount of about 1 to 25%, said integral binder having binding potential, subjecting said mat to a crushing operation to provide a partial breakdown of the fibrous-bond and bending said mat without rupturing the mat to provide a flexible mat of mcreased elongation comprising lamellae separated by cleavage planes extending generally parallel to the surface of the mat and then die forming the mat with heat and pressure to make a shaped sheet of hardboard and develop the binding potential of said binder.

5. A method of making a shaped sheet of hardboard comprising the steps of forming a ligno-cellulosic fibre wet lap, de-wiatering and drying said wet lap to form a stiff mat having a moisture content of below 10%, crushing said mat by the successive application of pressure to areas of the mat extending in one direction to provide a flexible mat Without tearing said mat and then subjecting said mat to heat and pressure to form a shaped sheet of hardboard.

6. A method of making a shaped sheet of hardboard comprising the steps of forming a ligno cellulosic fibre wet lap containing an integral binder, dewatering and drying said wet lap to form a stiff mat having a moisture content of below 10% under conditions of time and temperature at which said binder retains binding potential for bonding said sheets, crushing by the successive application of pressure to areas of the mat extending in one direction without tearing said mat and then subjecting said mat to heat and pressure to form a shaped sheet of hard'ooard, and setting said binder at a stage not earlier than the application of said heat and pressure.

7. A method of making a shaped sheet of hardboard comprising the steps of forming a ligno-cellulosic fibre wet lap containing an integral binder, dewatering and drying said Wet lap to form a stiff mat having a moisture content of below 10% for a time and at a temperature at which said binder retains binding potential for bond ing said sheets, crush ng said mat by the successive application of pressure to areas Olf the board extending in one direction, crushing said mat by the successive application of pressure to areas of the board extending in a direction transverse to the direction of the first operation Without tearing said mat and then subjecting said mat to heat and pressure to form a shaped sheet of hardboard, and setting said binder at a stage not earlier than the application of said heat and pressure.

8. A method of making a shaped sheet of hardboard comprising the steps of forming a ligno-ceilulosic fibre wet lap containing an integnal lbinder, dewatering and drying said wet lap to form a stiff mat having a moisture content of below 10% for a time and at a temperature at which said binder retains binding potential for bonding said sheets, crushing by the successive application of pressure to areas of the mat extending in one direction of said mat and bending the crushed mat to provide cleavage planes generaliy parallel to the surface of said mat with out tearing said mat and then subjecting said mat to heat and pressure to form a shaped sheet of hardboard, and setting said binder at a stage not earlier than the application of said heat and pressure.

9. A method of making a shaped sheet of hardboard comprising the steps of forming a ligno-cellulosic fibre wet lap containing an integral binder, ,dewatering and drying said wet lap to form a stiff mat having a moisture content of below 10% for a time and at a temperature at which said binder retains binding potential for bonding said sheets, crushing said mat by the successive application of pressure to areas of the mat extending in one direction, and bending the crushed mat to provide cleavage planes generally parallel to the surface of said mat without tearing said mart, crushing said mat by the successive application of pressure to areas of the mat extending in a direction transverse to the direction of the first operation, and bending the crushed mat to provide additional cleavage planes generally parallel to the surface of said mat without tearing said mat and then subjecting said mat to heat and pressure to form a shaped sheet of hardboard, and setting said binder at a stage not earlier than the application of said heat and pressure.

10. A method as in claim 9 in which said binder is a combination of thermo-plastic and thermosetting resins.

11. A method as in claim 9 in which the moisture of the dry mat is from 0.1 to 2%.

12. A method of making a shaped sheet of hardboard comprising the steps of forming a ligno-cellulosic fibre wet lap containing an integral binder, dewatering and drying said wet lap to form a stiff mat having a moisture content of below 10% for a time and at a temperature at which said binder retains binding potential for bonding said sheets, crushing said mat partially to rupture fibrous bonds in said mat, bending successive areas to the mat extending in one direction to provide cleavage planes generally parallel to the surface of the mat Without tearing said mat, bending successive areas of the mat extending in a direction transverse to said one direction to pro vide additional cleavage planes generally parallel to the surface of the mat without tearing the mat and subjecting the mat to heat and pressure to provide a shaped sheet of hardboard and setting said binder at a stage not earlier than the application of heat and pressure.

13. A mat adapted to be consolidated under heat and pressure in a forming die to provide shamd hardboard comprising a dry flexible fibrous mat of defibrated wood chips fc-rrned from laminae separated by cleavage planes generally parallel to the surface of the mat when made by a method comprising the stages of subjecting a mat of wood fibers bonded together and having a moisture content below 10% to a crushing operation to provide a partial breakdown of the fibrous bond and bending said mat without rupturing the mat.

14. A mat as in claim 13 comprising an integral binder having binding potential and being in an amount of l to 25%.

15. A mat as in claim 13 in which said mat has an elongation of at least in said forming die.

References Cited in the file of this patent UNITED STATES PATENTS 107,562 Taylor et a1. Sept. 20, 1870 216,108 Scott June 3, 1879 327,138 Churchill Sept. 29, 1885 860,696 Scherf July 23, 1907 1,900,698 Ellis Mar. 7, 1933 2,229,401 Worm Jan. 21, 1941 2,907,071 Meiler et al. Oct. 6, 1959

Claims (1)

1. 9. A METHOD OF MAKING A SHAPED SHEET OF HARDBOARD COMPRISING THE STEPS OF FORMING A LIGNO-CELLULOSIC FIBRE WET LAP CONTAINING AN INTEGRAL BINDER, DEWATERING AND DRYING SAID WET LAP TO FORM A SSTIFF MAT HAVING A MOISTURE CONTENT OF BELOW 10% FOR A TIME AND AT A TEMPERATURE AT WHICH SAID BINDER RETAINS BINDING POTENTIAL FOR BONDING SAID SHEETS, CRUSHING SAID MAT BY THE SUCCESSIVE APPLICATION OF PRESSURE TO AREAS OF THE MAT EXTENDING IN ONE DIRECTION, AND BENDING THE CRUSHED MAT TO PROVIDE CLEAVAGE PLANES GENERALLY PARALLEL TO THE SURFACE OF SAID MAT WITHOUT TEARING SAID MAT, CRUSHING SAID MAT BY THE SUCCESSSIVE APPLICATION OF PRESSURE TO AREAS OF THE MAT EXTENDING IN A DIRECTION TRNSVERSE TO THE DIRECTION OF THE FIRST OPERATION, AND BENDING THE CRUSHED MAT TO PROVIDE ADDITIONAL CLEVAGE PLANES GENERALLY PARALLEL TO THE SURFACE OF SAID MAT WITHOUT TEARING SAID MAT AND THEN SUBJECTING SAID MAT WITHOUT TEARING SAID MAT AND THEN SUBJECTING SAID MAT TO HEAT AND PRESSURE TO FORM A SHAPED SHEET OF HARDBOARD, AND SETTING SIAD BINDER AT A STAGE NOT EARLIER THAN THE APPLICATION OF SAID HEAT AND PRESSURE.

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