CA1171742A - Self-supporting moldable fiber mat and process for producing the same - Google Patents

Abstract

ABSTRACT
A moldable fiber mat comprising cellulosic fibers and small percentage of textile fibers and binder is produced from ligno-cellulosic material which is abraded and heated to approximately 500 to 700°F. to melt the lignin in the material, rupture the lignin bonds in the cellulosic fibers and redistribute the lignin on the surface of the fibers. The ligno-cellulosic material has a 75 to 85 percent solids content before being heated. Blending of the various fibers and the binder is done batchwise. The mat is passed through a compactor to reduce its length and thickness and increase its density.

Description

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SELF-SUPPORTING MOLDABLE FIBER MAT
~ND PROCESS FOR PRODUCING SAME
TECHNICAL FIELD
. . _ The invention relates to a moldabIe fiber mat structure, to processes for forming fiber mats which subsequently can be shaped or molded into a variety of fiberboard products, and to processes for preparing cellulosic fibers which are used to form fiber mats. A fiber mat such as this is usually composed of a mixture of comminuted cellulosic fibers and binder which has been compressed into a mat having the desired thickness and mechanical properties. Such fiber mats are widely used in fabricating a variety of articles and products, including automotive parts, such as dashboards and interior door pane]s, and products made of flat hardboard, medium density fiberboard, cardboard (such as 9 point), and Kraft linerboard.
BACKGROUND ART
Many different processes have been and are now in use for ~orming flat or molded fiberboard products. Generally speaking, in the manufacture of fiberboard, ligno-cellulosic material such as wood, corn stalks, sugar cane waste (bagasse), straw and the like, and other materials such as waste paper and cardboard, are first reduced to their basic comminuted celluiosic fiber form in hammermills or refiners. The fibers are treated with the reguired resins and then air layed or felted into a predetermined shape or mat which then is consol~dated to the desired density by the application of heat and pressure. In this procedure, the quality and properties of the fiber mat produced from a given ligno-cellulosic material are most strongly determined by the physical and chemical treatment to which the ligno-cellulose fibers have been ~ !

11717~2 ubjected. These are the factors that the present invention addresses.
Some of the known fiberboard forming processes are referred to as "wet" slurry processes, wherein a slurry having a very small cellulosic solids constituent is applied directly to a porous chaffing surface until a sufficient thickness is built up to form the desired article. Basic examples of these "wet" processes are the old "Chapman Batch Process" which is obsolete and probably no longer in use, and the "Fibrit" process, which was developed in Germany.
In the Fibrit process, debarked wood is first cut to chip size to facilitate handling with material handling equipment. The chips are further reduced by mechanical grinding aided by saturated steam in a defibrator unit. The resultant coarse pulp passes through a cyclone that separates the steam. The next step involves a hydropulper where small amounts of cellulose fiber and ~ibrit scrap are added. Here the pulp is broken down to a uniform fiber length.
The mixture is then diluted to 5% consistency and stored in large tanks prior to pumping the resultant fluid through a secondary refiner which processes it to the correct molding conditions. At this point resins and water are added to reduce the consistency further.
The next stage of the process is a 3-stage molding sequence which starts by making a "felt" or pre-form. The diluted pulp mix is pumped into a closed, mold-like container that has on its surface a perforated screen shaped to the final component form. As water is forced through the perforations the individual fibers in the suspension interlock and build up to the required primary thickness. Pulp flow stops when this point is reached, and compressed air is introduced which further reduces the water content and densifies the mat.
The felt is now picked up by a rigid male tool which transfers it to a wet pressing station. Here the female tool in the form of the final component is a rubber diaphram that is expanded by fluid pressure to apply a uniform squeezing action over the entire working surface. This extracts most of the remaining liquid from the felt and at the same time reduces its thickness by about 50%. The felt is now in a "handleable" state. The last operation involves hot pressing with a matched pair of oil-heated steel dies. There the pre-formed work !

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piece is reduced to its final thickness and density under heat and pressure.
In contrast to the above described "wet" process, Weyerhaeuser had developed a "dry" process called "Press-Tock", which is described in U.S. Patent Nos. 3,230,287 and 3,261,898. In such a process the fiber-resin mixture is dried under carefully controlled conditions to form a pre-form or mat which later can be molded to form an article of desired shape.
A known fiberboard forming process which is closely related to that of the invention is disclosed in U.S. Patent No. 3,741,863. In this process ligno-cellulosic material in the form of wood chips is pulverized in a hammermill and then dried to remove excess moisture.
The material then is heated in the presence of steam and is abraded under steam pressure to raise its temperture sufficiently to rupture the hydrogen bonds in the fibers and cause softening of the lignin present in the material, thereby separating the fibers from one another. After separating the fibers from the steam, a resin binder is mixed with the fibers. The mixture is then formed into a mat which is compressed under heat and pressure to form a fiberboard product.
In connection with the above described process it was believed that the temperature of the fibers undergoing abrasion should not be permitted to exceed approximately 500 F. for fear that the fibers would be scorched and darkened or otherwi~e damaged. Quite unexpectedly, however, it has been discovered in connection with the process of the invention that temperatures on the order of 500 to 700F. do not have such a detrimental effect on the fibers, and in fact actually contribute to producing a superior product because the lignin present in the fibers is actually melted and redistributed over the surface of the fibers. These high temperatures are attained according to the invention by using steam at a pressure of 50 to 150 p.s.i.g. in the defibering or refining stage. The steam and the heat of attrition contribute to raise the temperature of the fibers to 500 to 700 F.
range, also causing the steam to become superheated. This is accomplished with a relatively small expenditure of energy because of the fact that the material is first dried before being heated. The 117i7 energy normally expended to generate steam in wet chips is now expended to superheat the steam atmosphere.
It also has been found, quite surprisingly, that superior fiber mat characteristics can be obtained by mixing the refined fibers with a binder in a batch blender, instead of in a conventionally used continuous blender. It also has been discovered, quite surprisingly, that a superior fiberboard product could be obtained by mixing relatively wet refined fibers (solids content of 90 to 80 percent) with a very small amount of dry powdered binder. This represents a three to twenty-five fold reduction in the amount of binder needed as compared to so-called wet processes. Also unexpected is the successful use of textile or organic fibers in the process according to the invention, wherein a small percentage of relatively long textile fibers, or long organic fibers, are intermixed with the cellulosic fibers and the binder prior to formation of the fiber mat.
Most fiber mat preforms produced by known processes present difficult handling problems due to their relatively low tensile strength. These prior art mats therefore require special handling equipment to transfer them without breakage from the mat forming machines to the presses which press and heat the mats to form rigid fiberboard end products. It has been found, quite surprisingly, that superior fiber mat characteristics can be obtained by compacting the fiber web longitudinally (that is, in the direction of its travel) while compressing it to reduce its thickness. Such compaction results in much more intimate fiber-to-fiber contact. In a preferred embodiment this is accomplished by passing the web through a special two-roll compactor having web retarding surfaces. Conventionally a single-roll compactor similar to this piece of equipment is used to crepe much thinner web products such as paper and textiles. In using this machine in the process of the invention, however, a creping action does not occur. Rather, a retarding of the web parallel to the flow of the web occurs. This retarding effect tends to densify the web, reduce its thickness and surprisingly makes the final web structure extremely flexible and gives it a high mechanical and tensile strength, enabling it to be wound into rolls.

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DISCLOSURE OF THE INVENTION
In accordance with the present invention, a method of producing cellulosic fibers, suitable for use in moldable fiber mats, from small pieces of ligno-cellulosic material comprises the steps of drying the small pieces to a 75 to 85 percent solids content to remove excess moisture therefrom, heating the dried pieces with a non-flammable heating medium, and abrading the pieces in the heating medium to elevate the temperature of the pieces to approximately 500 to 700 F.
to melt to lignin in the pieces, rupture the lignin bonds in the cellulosic fibers and redistribute the lignin on the surface of the fibers.
The invention also encompasses a method of making a fiber mat from small pieces of ligno-cellulosic material which comprises the additional steps of separating the fibers from the heating medium, intermixing a binder with the fibers, forming the mixed fibers and binder into a mat, and pressing the fibers and binder in the mat together.
The invention further comprises a method of making a fiber mat from small pieces of ligno cellulosic material having a 75 to 85 percent solids content comprising the steps of heating the pieces with a non-Mammable heating medium, abrading the pieces in the heating medium to elevate the temperature of the pieces sufficiently to melt the lignin in the pieces, rupture the lignin bonds in the cellulosic fibers and redistribute the lignin on the surface of the fibers, separating the fibers from the heating medium, intermixing a measured amount of binder into a discrete batch of fibers, forming the mixed batch of fibers and binder into a mat and pressing the fibers and binder in the mat together.
The invention also includes a method of making a fiber mat from small pieces of ligno-cellulosic material having a 75 to 85 percent sdids content, comprising the steps of heating the pieces with a non-flammable heating medium, abrading the pieces in the heating medium to elevate the temperature of the pieces sufficiently to rF elt the lignin in the pieces, rupture the lignin bonds in the cellulosic fibers and redistribute the lignin on the surface of the fibers, separating the fibers from the heating medium, the separated fibers having an 80 to 90 precent solids content, intermixing 1 to 5 percent dry binder with 1~ ~717~

the fibers, forming the mixed fibers and binder into a mat and pressing the fibers and binder in the mat together.
The invention also comprises a method of making a fiber mat from small pieces of ligno-cellulosic material having a 75 to 85 percent solids content, comprising the steps of heating the pieces with a non-flammable heating medium, abrading the pieces in the heating medium to elevate the temperature of the pieces sufficiently to melt the lignin in the pieces, rupture the lignin bonds in the cellulosic fibers and redistribute the lignin on the surface of the fibers, separating the fibers from the heating medium, intermixing a binder with the fibers, forming the mixed fibers and binder into a mat, and retarding longitudinal movement of the pressed mat to reduce its length and increase its density.
Other aspects of this invention are as follows:
A method of making a formable, superior strength, self-supporting and easily handled fiber mat preform of substantially uniform thickness which is an intermediate preform formable by the application of heat and pressure into a superior strength, rigid fiberboard end product, comprising the steps of:
intermixing fibers with a small percentage of binder by dry weight of fibers;
forming the mixture of fibers and binder into a mat; and moving the mat longitudinally through pressing and retarding means to reduce the thickness of the mat substantially uniformly by at least 60 percent, and to compress the mat lengthwise by at least 10 percent, thereby increasing the density of the mat by at least 175 percent.
A formable, superior strength, self-supporting and easily handled fiber mat of substantially uniform thickness which is an intermediate preform formable by D

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- 6a -the application of heat and pressure into a superior strength, rigid fiberboard end product, the mat comprising a weblike mixture of fibers and a small percentage of binder by dry weight of fibers, which has been compressed in the direction of its thickness by at least 60 percent and in the direction of its length by at least 10 percent to increase its density by at least 175 percent.
Finally, the invention comprises fiber mats produced by the above described methods, and fiberboard products produced by compressing and heating these mats.
BRIEF DESCRIPTION OF THE DRAWINGS
The details of the invention will be described in connection with the accompanying drawings, in which Figures la through ld, and 2a and 2b are schematic rep-resentations of various portions of the process, the figures being interrated as indicated therein, and Figure 3 is a schematic illustration of a compactor used in connection with the process~
BEST MODE FOR CARRYING OUT THE INVENTION
Referring to Figure la, the process is designed to utilize ligno-cellulosic material from any available source, such as green logs delivered to a log deck 2, or chips from a local mill 4. Logs are fed through a debarker 6, the bark removed and stored in a fuel silo 8 (Figure lb). The debarked logs are then reduced to chips in a chipper 10. Metering bin 12 combines these chips with the chips delivered from mill 4.
Referring to Figure lb, a feeder and blower 14 delivers the chips selectively to fuel silo 8 through a collector filter 16, to a chip silo 18 for further pro-cessing through a collector 20, or to yard storage 22.
Chips delivered from chip silo 18 are reduced in size in hog 24 to a maximum 3/4 inch mesh. Magnet 26 extxacts ferrous metal pieces.

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11'7~'7'~' The chips then pass into dryer surge bin 28, thence to dryer 30 (Figure lc).
Dryer 30 produces hot gases by wood combustion in burner 32. The fuel for this burner is the chips or bark stored in fuel silo 8 delivered through metering bin 34 (Figure lb). This fuel may also be used to power one or more wood burning boilers 36.
In dryer 30 the solids content of the chips is increased from 50 percent to 75 to 85 percent. The chips are then blown by fan 38 into a cyclone separator 40 which separates air and gases from the chips. After passing through a rotary air lock 42 the chips are again exposed to a magnet 44 to extract any ferrous metal which may have adhered to the moist chips prior to drying. The dried chips are then screened at 46, the unacceptably small chips (those smaller than 1/8" diameter) being returned to fuel silo 8 through collector filter 16 by fan 48. Small fan 50 propels the chips through collector filter 52 and rotary air lock 54 into metering bin 56 (Figure ld).
Referring to Figure ld, items 61 through 68 all relate to the refining stage of the process. Chips flow from hopper 61 through refiner preheater 62 into preheater 65. A proper proportion of water from pump 63 is mixed with the chips through ratio meter 64 as the chips enter preheater 65. This added water cools the chips and adjusts their moisture content to an appropriate level. Feed screw 66 delivers the chips to pressurized refiner 67. The chips are exposed to high pressure steam in the range of 50 to 150 p.s.i.g. while being abraded in the single disc or double disc pressurized refiner 67. Refined fibers are then delivered to collector 68.
Because the chips are pre-dried, very little water is left to be driven off. Hence, most of the heat of the steam and the heat of attrition applied to the chips elevates their temperature to approximately 500 to 700 F. This represents a substantial savings in energy. For example, the conventional refiner ground wood system used as much as 80 to 100 horsepower days per ton of finished fiber. The process of high temperature refining according to the invention requires only 4 to io horsepower days per ton of fiber. The process according to the invention is therefore highly energy effieient, a major consideration 71'7~ ' in contemporary manufacturing processes. A minimum of 0.5 lbs. of steam is required for each pound of dried fiber produced. In the refiner the high temperatures literally melt the lignin contained in the fibers.
During refining the lignin is redistributed over the surface of the fibers.
Lignin redistribution is important in order to obtain an effective reaction with the surface resin subsequently to be applied, to produce the superior product formed in accordance with the present invention.
After, refining the fibers are classified at 70, rejects being blown by fan 72 back to collector filter 52. The final fibers are gathered in collector 74. If the fibers are to be shipped to another location for further processing, they are baled in baler 76, weighed in scale 78 and shipped.
Referring to Figures 2a and 2b, the refined fibers are now processed to form a fiber mat. If the fibers arrive in baled form, a bale opener 80 liberates the fibers, while fan 82 delivers them to collector 84, thence to doffing roll bin 86.
l:~offing roll bin 86 meters the fibers by holding a few minutes of processed fiber to reduce surges. The fibers are then delivered to a batch blender 88. Blender 88 also receives resin binder and, if desired, wax through pump 90, and any other auxiliary chemicals through feeder 92. Textile fibers are also introduced into blender 88 from collector 94, which receives a supply of textile fibers through fan 96, opener blender 98, prefeeder 100 and bale opener 102.
A phenolic dry powdered resin binder finely ground to a mesh of 200 may be used, in the range of 1 to S percent of dry phenolic resin to dry weight of wood fiber. The wood fiber entering blender 88 has a solids content of approximately 90 to 80 percent. Surprising, only l to 5 percent resin is required to produce a highly satisfactory product.
Other resins which may be used are urea-formaldehyde, isocynate or lignin based resins, to name just a few.
The binder employed may be virtually any organic binder of the type conventionally used to produce medium density fiberboard, hardboard and particle board products. The binder can be either thermoplastic, thermosetting or a two-polymer type, the only real requirement is that the binder be capable of bonding the fiber in such il~71'~
g a way that the end product produced is capable of passing end product use specifications. Animal, vegetable and other adhesives meeting such requirements are also acceptable.
Additional additives used, if any, may comprise such compositions as wax for water resistance, copper salts for preservation, borax compounds for fire prevention, etc., as desired, each in a manner and amount well-known to the art.
The following is a list of a Iew of the binders which may be used. The list is not exhaustive.
From Plastic Engineering Company (Plenco), Sheboygen, Wisconsin 53601:
B Plenco 374 and 675 dry powdered penol ground to a minus 200 mesh.
Prom Richhold Limited, Northbay, Ontario:
lB936 PF and RD-019 dry powdered phenol ground to a minus 200 mesh.
From Richhold Limited, Charlotte, North Carolina:
One part urea-formaldehyde resin rich-450 low viscosity M
D F resin.
From Pacific Resins and Chemicals, Inc., Atlanta, Georgia:
Resorcinol-phenol-formaldehyde resin S-3409 - Catalyst ~3409-E - Resin Fast curing phenol-formaldehyde resin N-2212 at 40 percent N V (non-volatiles) From Borden Chemical, Ontario, Canada:
Cascamite 1513~white powdered urea-formaldehyde resin.
From Upjohn Polymer Chemicals Div., LaPort, Texas:
ISO bind 100 ~ isocyanate-binder.
The textile fibers ~e for admixture in blender 88 are relatively long, having a fineness of 3 to 4 denier and a length of 1/2 ~ tr~e rna rk5 1~7~7'~

to 2 1/2 inches. Only a very small percentage of textile fibers is required (1 to 3 percent) in order to achieve a high quality end product.
Typical fibers which may be used comprise nylon, polypropylene, rayon, vinyon (waster polypropylene) cotton linters and cotton shoddy, to name just a few.
The mixture is then metered through doffing roll bin 104 into feeder 106A, webber 106B and slitter 106C. Items 106A, B and C
B are par~ of a web or mat forming mechanism such as the "Rando-Webber manufactured by Rando Machine Corporation of Macedon, New York. This machine forms the fiber into a very well consolidated mat.
The mat emerging from the webber and slitter is compacted in a compactor 108 (see Figure 3). Compactor 108 has a pair of counterrotating cooperating driven rolls 120 which compress the mat 109 in their nip and propel it forward into a retarding cavity 122. The retarding cavity has opposed stationary flexible retarding surfaces or platens 124 which frictionally engage the advancing mat and tend to retard its forward motion. This results in a lengthwise compression of the mat and an increase in its density, with much more intimate fiber-- to-fiber contact. Platens 124 are supported in holders 125 which are pivoted at 126. The positions of platens 124 are maintained by pneumatic or hydraulic cylinders 128. Pressure exerted on the mat by platens 124 snay be selected in accordance with the positions of the pistons in cylinders 128.
Cornpactors exist which utilize a single roll fo~ advancing material toward the retarding cavity. The basic principles of operation of such compactors, and of the two-roll compactor used in connection with the invention, are disclosed in Walton, U.S. Patent No. 3,260,778.
Single roll compactors are ordinarily used to crepe paper and laminated webs. However, a single roll cannot adequately thrust a thicker mat forward into the retarding cavity to obtain the desired longitudinal compaction. The two rolls of compactor 108 overcome this deficiency by cooperating as calender rolls to compress the mat and positively drive it forward.
The fiber mat according to the invention is not visibly creped by the two roll compactor. Instead, compactor 108 reduces the de m~k l7'~

thickness of the mat by at least 60 percent from up to 3 or 4 inches to approximately 1/4 inch or less. Upon emerging from the nip of the two rolls the mate is compressed lengthwise to reduce its length by about 10 to 15 percent and desirably increase its density by at least 175 percent. The mat has a density of approximately 3 to 5 lbs. per cubic foot before entering the compactor, and a density of 10 to 20 lbs. per cubic foot upon emerging. The mat emergir.g from the compactor is self-supporting and strong enough to be wound into a roll on mat wind up stand 110. In tests run on the two roll compactor 108 various mats were produced in accordance with the invention using Aspen wood fibers from Bemiji, Wisconsin. The results are as follows:

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Because compactor 108 develops such an intimate fiber-to-fiber contact in the mat, a satisfactory mat may contain a relatively high percentage of fibers which contain little or no lignin. For example, satisfactory mats have been produced according to the invention using up to 50% comminuted municipal refuse fiber, added to refined ligno-cellulosic fibers before blending with the required resin. In fact, it has been possible to produce certain fiberboard products from mats made in accordance with the invention exclusively of municpal refuse fiber and resin. Of course, such "all-refuse" products are not as strong as those formed from mats containing a relatively high percentage of ligno-cellulosic fibers, but they do find useful application in certain areas.
One use for such a mat is a core in a fiberboard product, sandwiched betweeh and laminated to two stronger mats made in accordance with the invention containing a relatively high percentage of ligno-cellulosic fibers.
Referring to Pigure 2b, the wound mat may be installed in a mat unwind stand 112, from which it is unwound and delivered to a molding press 114,` a continuous press 116, a calender stack or other machinery for subsequent formation into a finished fiberboard product.
Example: A sample fiberboard product was form ed (having a density of 46 lbs. per cubic foot) from a mat produced by the process of the invention. The resultant modulus of rupture of the fiberboard product was 5,000 p.s.i. The resultant modulus of elasticity of this sample was 350,000 p.s.i. Its internal bond was 150 p.s.i.
In contrast to this, a fiberboard sample having the same density was made from a mat produced by a process wherein the refining of the cellulosic fibers took place at atmospheric pressure and relatively low temperature. The resultant modulus of rupture of this sample was 2500 p.s.i., only half of that of the preceding sample. It modulus of elasticity was only 250,000 p.s.i, and its internal bond strength was 70 p.s.i.
It is flpparent from the foregoing description that the process according to the invention successfully accomplishes its objectives. The process forms a self-supporting mat structure of uniform thickness and density. The mat could contain as much as 98% dry refined comminuted 1'7'~

cellul-osic fibers, thermosetting or thermoplastic resins as well as long organic (over 1/2") or inorganic textile fibers, depending on end product requirements. The basic cellulosic fibers can be treated with fire retardants as required.
The mat structure that is described is very unique in that the mat has been compacted or densified in a direction parallel to the mat surface. This quite unexpectedly produces a mat structure that has high tensile, as well as mechanical strength and is extremely flexible.
These factors allow the mat to be rolled up in much the same way as sheet metal or aluminum is coiled.
The mats as described have also been pre-treated with their required resins. The mats can now be stacked to form several layers depending on the thickness and density rquirements for the finished product. The stacked mats when put under heat and pressure in a final compaction stage, either in a stationary press, continuous press or heated calender roll, will become one unified mass. There is no need for additional resins to be applied between the layers of fiber mats.
It is also possible to produce a 3-dimensional molded product that has varying cross sectional thickness with a constant density. This is made possible by the capability of stacking mats, and the fact that the second and other mats stacked can be pre-punched with voids that will match up with die sections in a molding press to yield a part with varying thicknesses, etc.
The self-supporting mat structure, due to its inherently good tensile and mechanical strength, allows the mat to be automatically unrolled and fed to multi-opening or single-opening presses, without the need for caulless loaders, caul plates or press conveyors to transport the mat into or out of such presses. Due to the unique parallel compaction or densification of the fiber mat, a much more intimate fiber to fiber contact is developed. This is not achievable through the use of conventional formers and other devices. This more intimate fiber to fiber contact increases final product strength, and allows products such as typical nine point (chipboard) liner board, corrugating medium, dry felt for asphalt impregnation, as well as medium density fiberboard products to be produced.

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The self-supporting mat structure produced by this process can be compressed, shaped or formed into either a flat board such as medium density fiberboard, cardboard such as 9 point, or a Kraft-like product such as linerboard corrugating medium. This unique new self-supporting mat structure can also be used to produce at least the following deep draw molded 3-dimensional contoured articles:
a) Building Industry 1. Exterior and interior decorative wall panels.

2. Exterior and interior window sills, as well as window frames and door jambs.

3. Concrete forms.

4. Crated suspended ceilings.

5. Embossed panels.
b) Automobile Industry 1. Dashboards.
2. Seats.
3. Body parts, such as ienders, doors, and interior door panels.
c) Furniture Industry 1. Table tops for indoor and outdoor use.
2. Frames for upholstered furniture.
3. Fronts for kitchen and living room furniture.
d) Electronics Industry 1. Cabinets for television sets.
2. Cases for record players.
3. Loudspeaker fronts.
e) Packaging Industry 1. Pallets and containers.
2. Fruit cases.
3. Crates and vegetables.
It will be obivous to one of ordinary skill that numerous modifications may be made without departing from the true spirit and scope of the invention, which is to be limited only by the appended claims.

Claims (26)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method of making a formable, superior strength, self-supporting and easily handled fiber mat preform of substantially uniform thickness which is an intermediate preform formable by the application of heat and pressure into a superior strength, rigid fiberboard end product, comprising the steps of:
intermixing fibers with a small percentage of binder by dry weight of fibers;
forming the mixture of fibers and binder into a mat; and moving the mat longitudinally through pressing and retarding means to reduce the thickness of the mat substantially uniformly by at least 60 percent, and to compress the mat lengthwise by at least 10 percent, thereby increasing the density of the mat by at least 175 percent.

2. A method according to claim 1 wherein said fibers include cellulosic fibers.

3. A method according to claim 2 wherein said fibers include ligno-cellulosic fibers.

4. A method according to any of claims 1, 2, or 3 wherein 1 to 5 percent binder by dry weight of fibers is mixed with the fibers.

5. A method according to claim 1 wherein said pressing and retarding means comprises a retarding cavity having relatively stationary surfaces which contact the surfaces of the moving mat.

6. A method according to claim 1 wherein the fibers are derived from small pieces of ligno-cellulosic material having a 75 to 85 percent solids content by heating the pieces with a nonflammable heating medium; abrading the pieces in the heating medium to elevate the temperature of the pieces sufficiently to melt the lignin in the pieces, rupture the lignin bonds in the cellulosic fibers and redistribute the lignin on the surface of the fibers, and separating the fibers from the heating medium prior to intermixing said fibers with said binder.

7. A method according to claim 6 wherein the step of pressing the mat and retarding its longitudinal movement comprises passing the mat through a retarding cavity having relatively stationary surfaces that contact the surfaces of the mat.

8. A method according to claim 6 further comprising the step of compressing and heating the mat to form a fiberboard end product.

9. A method according to claim 1 wherein the initial thickness of the mat is up to approximately 4 inches, and the final thickness of the mat after compaction is about 1/4 inch or less.

10. A formable, superior strength, self-supporting and easily handled fiber mat of substantially uniform thickness which is an intermediate preform formable by the application of heat and pressure into a superior strength, rigid fiberboard end product, the mat comprising a weblike mixture of fibers and a small percentage of binder by dry weight of fibers, which has been compressed in the direction of its thickness by at least 60 percent and in the direction of its length by at least 10 percent to increase its density by at least 175 percent.

11. A mat according to claim 10 wherein the initial thickness of the mat is up to approximately 4 inches.

12. A mat according to claim 10 wherein said fibers include cellulosic fibers.

13. A mat according to claim 12 wherein said fibers include ligno-cellulosic fibers.

14. A mat according to claim 12 or 13 having a density of approximately 10 to 20 lbs. per cubic foot and a thickness of up to approximately 1/4 inch.

15. A mat according to claim 12 or 13 wherein 1 to 5 percent binder by dry weight of fibers is mixed with the fibers.

16. A fiberboard end product produced by compressing and heating the mat of any of claims 10, 12, or 13.

17. A formable floor mat according to claim 10 wherein the fibers are cellulosic fibers derived from ligno-cellulosic material by abrading and heating the material to melt the lignin in the material, rupture the lignin bonds in the fibers, and redistribute the lignin on the surface of the fibers, the percentage of binder being from 1 to 5 percent.

18. A mat according to claim 17 further comprising one to three percent textile fibers to dry weight of cellulosic fiber.

19. A mat according to claim 18 wherein said textile fibers have a fineness of approximately 3 to 4 denier and a length of 1/2 to 2-1/2 inches.

20. A mat according to claim 19 wherein said textile fibers are chosen from the group comprising nylon, rayon, polypropylene, and cotton fibers.

21. A mat according to claim 20 wherein said binder is chosen from the group comprising phenolic, ureaformalde-hyde and isocyanate resins.

22. A mat according to claim 17 wherein said binder is chosen from the group comprising phenolic, ureaformalde-hyde, and isocyanate resins.

23. A mat according to claim 19 having a density of approximately 10 to 20 lbs. per cubic foot and a thick-ness of up to approximately 1/4 inch.

24. A mat according to claim 17 having a density of approximately 10 to 20 lbs. per cubic foot and a thickness of up to approximately 1/4 inch.

25. A fiberboard end product produced by compressing and heating the mat of claim 17.

26. A fiberboard end product produced by compressing and heating the mat of claim 18.