Post-press molding of man-made boards to produce contoured furniture parts

A method of molding a cellulosic fiber containing board at a temperature of at least 525.degree. F. to provide a relatively high density skin on at least one surface. A fibrous composition, including cellulosic fibers, is consolidated to form a blank having a density of less than 35 pounds/cubic foot. The blank is then cut to a shape larger in at least two of its three dimensions than corresponding dimensions of a mold cavity when said mold is in a closed position. Urea is then included in at least a surface layer of fibers of the blank in an amount of at least 5% based on the dry weight of the fibers contacted with urea, and thereafter the cut blank is molded to form a contoured product having a skin on at least one surface thereof, the skin defined by a thickness of material on said surface of said product having a density greater than the material on which the skin is formed.

FIELD OF THE INVENTION 
The present invention relates to a method of molding man-made boards to 
produce contoured furniture parts having relatively high density skins or 
surface portions thereon. More particularly, the present invention relates 
to a method of molding a man-made fiberboard to produce a contoured 
furniture part, such as a drawer front, having high density skins or 
surface portions as an integral part of a lower density core material. The 
high density skins are produced by contracting the surface fibers of a 
consolidated fiberboard with urea, and thereafter hot-pressing the 
fiberboard in a post-press or second press molding operation at a 
temperature of at least 525.degree. F. to form the fiberboard into its 
final shape and to densify the surface portions into stiff, hard skins. 
BACKGROUND OF THE INVENTION 
The process of the present invention relates to a "post-press" or second 
press molding operation for molding a fiberboard into a desired shape 
while, at the same time, creating thick, hard, integral surface portions 
on the surfaces of a man-made fiberboard substrate. The fiberboard 
substrate is formed by consolidating a mass of fibers. This may be done by 
either the dry process or the wet process method of manufacturing 
fiberboard. Typical products made by these systems are medium density 
fiberboard and insulation board. The board is thereafter "post-pressed" in 
a mold having a desired configuration, to form the consolidated fiberboard 
into a desired shape, to impart surface texture and to form dense surface 
layers while retaining a lower density core or central portion of the 
fiberboard. For the purpose of the present invention, a "post-press 
molding" operation refers to a molding step performed on a consolidated 
fiberboard which changes the dimensions of the consolidated fiberboard in 
at least two dimensions. 
It is necessary to form the furniture part of the present invention in two 
separate operations. The first operation forms a consolidated fiberboard 
common in the art of forming a fiberboard, such as insulation board. The 
second step comprises "post-press molding" which changes the dimensions of 
the consolidated fiberboard in at least two dimensions to correspond to 
the dimensions of the mold, and creates denser surface portions on the 
fiberboard. It is quite surprising that a "post-press molding" operation 
is effective in substantially altering the dimensions of the consolidated 
fiberboard and in densifying the surfaces of the consolidated fiberboard. 
It is very difficult to both densify and restructure the surfaces of a 
consolidated fiberboard without destroying the fiber-to-fiber surface 
welds referred to in our co-pending application Ser. No. 739,184, filed 
Nov. 5, 1976. In accordance with the present invention, it has been found 
that the configuration, surface density, and physical characteristics of a 
completely consolidated fiberboard mat can be altered in a post-press 
molding operation when at least the surface fibers of the mat are 
contacted with urea prior to the molding. During the post-press molding 
operation, at a temperature of at least 525.degree. F., the urea reacts to 
stiffen and strengthen the surface layers of a low density cellulosic 
fiberboard substrate, defined herein as fiberboard having a density in the 
range of 10-35 pounds/cubic foot, to provide the strength necessary for 
the product to be useful as a furniture part while, at the same time, 
restructuring the board to a desired configuration. The resulting 
lightweight product has a look, feel and sound equivalent to that of 
natural wood, while being produced at a much lower cost. 
PRIOR ART 
An article entitled "Wood Embossing Machines Cut Production Steps For 
`Carved` Parts" appearing in Furniture Design & Manufacturing, February 
1977, pages 30-33, relates to embossing materials, including fiberboard, 
in making furniture parts. The article does not suggest the use of urea, 
as disclosed herein. 
An extensive search was performed to determine the prior art use of urea in 
the manufacture of cellulose fiber-containing substrates. Various patents 
and abstracts were found relating to the use of urea for fire-retardance, 
plasticization, resistance to aging, and as a binder. None of these 
patents are abstracts found, however, relates to the use of urea as 
disclosed herein, in post-press molding of a man-made cellulose 
fiber-containing product to provide a relatively high density, hard, stiff 
skin on one or more surfaces of a relatively low density core or center 
material. The relevant patents and abstracts found in the search are as 
follows: 
______________________________________ 
A.B.I.P.C. Abstracts Patents 
______________________________________ 
Vol. 36, No. 4; 2483; 1965 
2,298,017 
Vol. 38, No. 6; 4917; 1967 
2,912,392 
Vol. 39, No. 9; 7630; 1969 
2,912,394 
Vol. 39, No. 11; 9657; 1969 
3,285,801 
Vol. 41, No. 5; 4311; 1970 
3,667,999 
Vol. 42, July-Dec; 5715; 1971 
3,676,389 
Vol. 43, No. 9; 9665; 1973 
3,779,861 
Vol. 44, No. 10, 10423, 1974 
3,790,442 
Vol. 44, No. 10; 10754; 1974 
3,881,992 
Vol. 45, July-Dec; 4724; 1974 
3,915,911 
Vol. 45, No. 2; 1479; 1974 
777,090 (Canada) 
Vol. 46, No. 3; 2233, 1975 
Vol. 46, No. 5; 4954; 1975 
______________________________________ 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a method for making 
furniture parts made from man-made fiberboard having the look, feel and 
sound of natural wood. 
Another object of the present invention is to provide a method for making 
lightweight cellulosic fiber-containing molded furniture part or 
decorative molding having a hard, dense skin on at least one surface 
thereof. 
Another object of the present invention is to provide a method for making 
lightweight decorative, molded fiberboard having a central core of 
material with a density in the range of 10-35 pounds/ft.sup.3. 
Another object of the present invention is to provide a method for making 
lightweight man-made molded board having design-fidelity and paint 
hold-out properties equal to or better than hardboards manufactured in 
accordance with existing technology. 
Another object of the present invention is to provide a method of forming 
an integral, structural skin on one or more surfaces of a cellulosic 
fiber-containing consolidated board by including urea within at least the 
surface fibers of the consolidated board, and, thereafter, molding the 
urea treated consolidated board in a second-pressing operation at a 
temperature of at least 525.degree. F. 
In accordance with an important feature of the present invention, it has 
been found that urea will provide hard, dense surface skins to a 
consolidated handleable mat when the surface fibers are contacted 
therewith and the mat is thereafter molded at a temperature of at least 
525.degree. F. 
In accordance with another important feature of the present invention, the 
technology disclosed herein has been developed to provide a low density, 
strong cellulosic fiber-containing molded product, for example, molded 
fiberboard which has sufficient strength for end uses such as furniture 
parts and decorative moldings. The low density product is produced by 
first manufacturing a low density substrate having strength sufficient to 
be handled in manufacture, including urea in at least the surface fibers 
of the substrate and thereafter molding the consolidated substrate to 
reshape the substrate and to develop dense outer layers or skins on one or 
more exterior surfaces. 
Surprisingly, it has been found that the skin created by molding a low 
density consolidated fiberboard having urea in at least the outer surface 
fibers thereof creates a hard, dense surface which, if desired, 
effectively and permanently reproduces the details of the mold cavity on 
the surfaces of the product, permanently reshapes the fiberboard and 
creates a hard outer surface having excellent holdout of coating 
materials, such as paint.

DETAILED DESCRIPTION OF THE INVENTION 
Low Density Handleable Mat 
In accordance with the present invention, a fiberboard product having hard, 
dense skins or surface portions thereon is manufactured in two steps. The 
first step comprises manufacturing a relatively low density consolidated, 
handleable mat, using either the wet or dry process as known in the 
manufacture of man-made boards; the second step comprises post-press 
molding the consolidated mat, after first treating at least the surface 
fibers of the mat with urea, to form a skin on the surfaces of the 
product. The handleable mat is produced in a desired thickness, depending 
upon the end use, such as a drawer front or cabinet door. 
The method of producing a consolidated mat is well known as presently used 
in producing man-made boards such as hardboard, chipboard, particle board, 
panelboard, acoustical board, insulation board, and the like. In the wet 
process, the raw material is uniformly blended in a head box with copious 
quantities of water to form a slurry. The slurry is deposited onto a 
water-pervious support member, generally a Fourdrinier wire, where much of 
the water is removed leaving a wet mat of cellulosic material. The wet mat 
is then dryed to consolidate the fibers together, as is done in the 
manufacture of insulation board; or can be transferred from the previous 
support member and consolidated under heat and pressure to form the board. 
Typically, pressures of from 400-500 psi and temperatures up to about 
400.degree. F. are encountered in hot-press consolidation of a man-made 
board manufactured by the wet process. The dry process is similar to the 
wet process except that the cellulosic fibers are first coated with a 
thermosetting resin binder, such as a phenol-formaldehyde resin, and are 
then randomly distributed into a mat by air blowing the resin-coated 
fibers onto a support member. In the dry process, the mat is pressed at 
temperatures up to about 450.degree. F. and pressures less than about 1000 
psi to cure the thermosetting resin and to compress the mat into an 
integral consolidated structure. 
The handleable mat produced in accordance with the first step of the 
present invention is manufactured in a conventional manner, using 
conventional cellulosic fiber stock. To achieve the full advantage of the 
present invention, the handleable mat should have a density, after 
consolidation, in the range of 10-35 pounds/cubic foot, preferably in the 
range of 15-30 pounds/cubic foot. Panels of varying thicknesses having 
densities within this range can be produced in accordance with known 
technology to provide lightweight core materials on which a surface skin 
can be developed in accordance with the following disclosure. 
Handleable mats have been produced having a density as low as ten 
pounds/cubic foot and a thickness of one and one-half inches. Mats having 
densities as low as ten pounds/cubic foot are useful as the handleable 
mats in producing products in accordance with the principles of the 
present invention. In fact, in accordance with the present invention, any 
low density mat (less than 35 pounds/cubic foot) is considered to be 
handleable if it can survive the trimming, cutting stacking, packing, 
shipping, and unloading operations necessary to produce fiberboard. All 
such handleable mats are useful in accordance with the principles of the 
present invention. 
Blank Shaping 
The low density fiberboard is cut into blanks, such as that shown in FIG. 
5, slightly larger than the finished product in the dimensions in which a 
surface skin and/or surface design is desired. If a surface skin is 
required on all six sides of the finished furniture part, the blank is cut 
slightly larger than the finished part in all dimensions. In this manner, 
the furniture part is compressed during molding along the dimensions in 
which the blank is larger than the dimensions of a mold cavity, when the 
mold is in a fully closed position, to shape the blank where the blank is 
not initially in exact conformity with the interior dimensions of the 
closed mold. This compression is necessary to form a thick dense skin on 
the surface of the furniture part. 
A consolidated fiberboard blank having a very low density on the order of 
10-25 pounds/cubic foot can be substantially reshaped in the molding 
process so that it is not necessary to shape the blank to conform to the 
general interior shape of the closed mold. For example, 10-25 pounds/cubic 
foot low density fiberboard blanks having a rectangular shape, as shown in 
FIG. 5, can be molded without shaping. 
With higher density consolidated fiberboard blanks having a density, for 
example, of 25-35 pounds/cubic foot, some material should be removed prior 
to molding. Consolidated fiberboard blanks having a density of about 25-35 
pounds/cubic foot should be cut or routed, as known in the art of shaping 
natural wood furniture parts, preferably to correspond generally to the 
shape of the closed mold cavity, with at least two of its three dimensions 
slightly larger. For example, all dimensions of a 30 pounds/cubic foot 
blank, used to mold a shaped 15".times.71/4".times.3/4" drawer front, can 
be larger than the corresponding dimension of the closed mold in all 
dimensions, as shown in Table VII, to apply a dense skin to all sides of 
the finished drawer front. The less dense the fiberboard blank, the less 
closely the shape of the pre-mold blank must conform in shape to the shape 
of the mold cavity. For example, a fiberboard blank having a density of 
25-30 pounds/cubic foot used to form a drawer front having the shape shown 
in FIGS. 1, 2 and 4 can be formed by first partially shaping a rectangular 
blank by beveling the side edges, leaving enough extra edge material for 
compression during molding. 
MOLDING 
The consolidated fiberboard blank containing urea is post-pressed in a mold 
at a temperature of at least 525.degree. F. to develop a surface layer 
herein called a "skin", defined as an outer layer having a higher density 
than a thickness of material over which it is formed. It was found in 
early investigations that heat and pressure alone would not form a thick 
skin on the surface of a low density fiberboard. Skin thickness was very 
thin, regardless of the temperature and degree of compression. Table I 
shows that post-pressing alone, without urea pre-treatment does not 
produce a skin. 
Table I 
______________________________________ 
Effect of Heat, Pressure and Post-Pressing 
On Skin Development 
Final Caliper 
Density Skin Thickness 
Substrate (In.) lb/ft.sup.3 
(In.) 
______________________________________ 
fiberboard 
not post-pressed 
0.563 17 0 
post-pressed 
0.406 22 0 
fiberboard (no urea) 
fiberboard 
w/urea on all 
surfaces and post- 
pressed at 550.degree. F. 
0.406 22 0.030 
______________________________________ 
Various chemicals were evaluated on the surface of low density consolidated 
fiberboard blanks, and the skin thicknesses provided by each chemical were 
measured. Chemicals evaluated were phenol-formaldehyde resin, 
urea-formaldehyde resin, gelatin, mixtures of gelatin with 
phenol-formaldehyde, n-methylolacrylamide, and urea. The chemical was 
applied to the fiberboard blanks prior to molding. For example, urea was 
applied as an aqueous solution to all surfaces using a paint roller. Urea 
proved to be unexpectedly superior for skin development on the surface of 
a cellulosic fiber-containing substrate, particularly for low density 
(10-35 pounds/ft.sup.3) fiberboard blanks, as shown in Table II: 
Table II 
__________________________________________________________________________ 
EFFECT OF CHEMICAL SURFACE SPRAY 
23/42 Skin Thickness (In.) at Equivalent Cost Level 
$5/MFt.sup.2 $10/MFt.sup.2 
$20/MFt.sup.2 
Skin Skin Skin 
Chemical Pounds/MFt.sup.2 
Thickness 
Pounds/MFt.sup.2 
Thickness 
Pounds/MFt.sup.2 
Thickness 
REMARKS 
__________________________________________________________________________ 
urea 55 .026 111 .032 222 .033 Tough, smooth, but 
poor bond between 
skin and mat 
gelatin/ 
phenol-formaldehyde 
7 .015 15 .022 29 .030 Glossy surface film 
urea-formaldehyde 
42 .013 83 .019 167 .024 Hard surface but 
blistered in spots on 
all boards 
n-methylol- 
acrylamide 7 .014 14 .017 27 .018 Tough, smooth surface 
with good bond and 
mat 
gelatin 6 -- 12 -- 25 -- When exposed to hot 
platens the surface 
gummed up, charred, 
and stuck to platen 
phenol-formaldehyde 
24 .014 48 .014 95 .024 Reddish brown flat 
surface, tight bond 
to mat 
__________________________________________________________________________ 
In attempting to achieve thicker surface skins on the consolidated blanks 
during post-press molding it was found that urea should penetrate the 
surface fibers of the blank prior to post-press molding. Surface spraying 
therefore led to the impregnation method of incorporating urea into the 
blank. 
Impregnation Process 
It has been found that when urea is impregnated into the surface of a 10-35 
pound/cubic foot consolidated fiberboard blank, a much thicker skin can be 
produced by vacuum impregnating the urea to provide a skin thickness in 
the range of 0.060 inch. Surprisingly, urea is the only chemical 
impregnant able to achieve a skin thickness of 0.060 inch, regardless of 
the depth of penetration of the impregnant. 
In accordance with the results achieved as set forth in Table III, each 
material was applied to the surface of a 20 pounds/cubic foot consolidated 
fiberboard blank at an equivalent cost level and a vacuum box was utilized 
on the under surface of the blank to insure deep penetration of the 
impregnant. After impregnation, each blank was dried so that the moisture 
content in the mold did not exceed 10% (wet basis). The mold conditions 
were as follows: 
______________________________________ 
Mold Temperature 550.degree. F. 
Closing Speed Fast as possible 
Holding Time at Caliper 
30 Seconds 
Caliper 5/8" 
Pressure 500 psi 
Opening Speed Fast as possible 
______________________________________ 
Table III 
______________________________________ 
Effect of Impregnation 
% Increase in 
Skin Skin Thickness 
Caliper Density Thickness 
Open Surface 
Treatment 
(In.) (#/ft.sup.3) 
(In.) Spray System 
______________________________________ 
phenol- 
formaldehyde 
.615 26.5 0.47 136 
gelatin/ 
phenol- 
formaldehyde 
.611 28.8 .033 50 
n-methylol- 
acrylamide 
.612 24.7 .031 82 
urea formal- 
dehyde .633 25.0 .036 89 
urea -- -- .060 88 
______________________________________ 
The surface characteristics of the low density furniture parts are superior 
with respect to hardness, design fidelity, and paint holdout. "Design 
fidelity" or simply "fidelity" as used herein is a measure of the accuracy 
of reproduction of the mold design onto the surface of a consolidated 
blank during molding. "Paint holdout" is the ability of a panel to keep 
paint on its surface without a significant amount striking into the panel. 
Some caliper reduction of the blank on at least two of the three dimensions 
of the blank must result during molding to apply both heat and pressure 
necessary for thick skin development on each surface where such a skin is 
desirable. Contact (unregistrable) pressure is sufficient for slight 
caliper reduction. It has been found that as the fibers are compressed 
during the molding operation, the density increases in the outer material 
and, to some extent, in the core material. Thereafter, the core begins to 
resist compression. Accordingly, the face of the blank will compress more 
than the core of the oversized blank. 
Closing the mold will result in varied mold pressure readings depending 
upon the degree that the blank is oversized and the shape of the furniture 
part, and the density of the blank. Consolidated blanks having a density 
less than about 25 pounds/cubic foot can be oversized in thickness as much 
as 50% while achieving sharp crisp transferrence of mold details. As the 
density of the blank is increased, the oversizing of the blank should be 
reduced to provide good design fidelity. For example, to achieve the full 
advantage of the present invention, blanks having a density in the range 
of about 25-30 pounds/cubic foot should not be oversized more than about 
30% in thickness. 
Table VII relates the consolidated blank size and density to the resulting 
mold pressure reading in molding a drawer front having the shape of the 
furniture part of FIG. 1. The 30-35 pounds/cubic foot blanks were each 
shaped as shown in FIG. 3 prior to urea impregnation and prior to molding; 
the blanks having a density of 24-29 pounds/cubic foot were each beveled 
along the edges to partially shape the blank prior to urea impregnation 
and prior to molding; the blanks having a density in the range of 10-23 
pounds/cubic foot were not shaped prior to molding, as shown in FIG. 5. 
Table VII 
______________________________________ 
SIZE OF BLANK AND PRESSURE 
REQUIRED TO MAKE A DRAWER FRONT 
Final Product Dimensions 0.750" .times. 7.250" .times. 15.0" 
Pressure to 
Density Thickness Width Length 
Close Mold 
Substrate 
lbs/ft.sup.3 
(In.) (In.) (In.) (psi) 
______________________________________ 
Fiberboard 
30-35 0.850 7.281 15.031 
250-400 
Fiberboard 
24-29 0.950 7.328 15.078 
200-300 
Insulation 
Board 10-23 1.125 7.328 15.078 
150-250 
______________________________________ 
The time of molding is not critical and preferably is in the range of 5 to 
60 seconds. However, with higher temperatures in the range of 
575.degree.-650.degree. F., it is desirable to remove the product from the 
mold within about 30 seconds to avoid charring or decomposition of the 
surface skins. 
Amount of Urea 
The amount of urea necessary to form a sufficient skin thickness for the 
purpose of the present invention is at least about 5% by weight of the 
fibers contacted. That is, when combined by the impregnation process, the 
weight percent of urea needed is at least 5% based upon the dry weight of 
the surface material in which the chemical has penetrated. Accordingly, 
the urea needed is at least 5% based on the weight of fibers penetrated in 
forming the skin. When combined by the overlay process, the weight percent 
of urea needed is at least 5% based upon the dry weight of overlay 
material. 
The maximum amount of urea which can be incorporated into the handleable 
mat is dependent upon the method used to make the handleable mat. Mats 
made by the wet process can tolerate more urea than mats made by the dry 
process. The type of resin used in the dry process also has an influence. 
Phenol-formaldehyde resin bonded blanks can be treated with higher levels 
of urea than blanks bonded with urea-formaldehyde resins. As the urea 
content of the surface layers increases, the skins become more distinct 
and the embossing fidelity and coating holdout improve. 
To achieve the full advantage of the present invention, the urea content 
incorporated into the consolidated blank should be in the range of 8-35% 
based on the dry weight of the material contacted therewith, and 
preferably in the range of 10-30% by weight. When a binder other than 
urea-formaldehyde resin, such as phenol-formaldehyde resin, is used in 
forming the consolidated blank by the dry process or when a consolidated 
blank made by the wet process is used, the urea content has no maximum. 
However, no advantage is realized in terms of skin thickness or other 
properties by using more than about 35% urea, based on the dry weight of 
contacted blank material. Accordingly, a useful range of urea is 5-35% 
based on the dry weight of contacted blank material. When 
urea-formaldehyde is the sole binder used in forming the consolidated 
blank, urea can be incorporated by the overlay process in an amount not 
exceeding about 12% based on the dry weight of overlay material. 
MOLDING CONDITIONS 
A consolidated blank having a density of less than 35 pounds/cubic foot is 
"molded" at a temperature of at least 525.degree. F. To achieve the full 
advantage of the present invention, the temperature of "molding" should 
not exceed 650.degree. F. It is preferred to mold at a temperature in the 
range of 525.degree.-575.degree. F. As shown in the drawing, a molded 
contoured drawer front, indicated generally by reference numeral 10 is 
molded from a consolidated blank. The consolidated blank can be 
pre-shaped, as indicated generally by reference number 12 of FIG. 3, or 
for low density products on the order of 10-25 pounds/cubic foot, the 
blank can be unshaped, as designated by reference numeral 14 of FIG. 5. 
Each blank must be larger than the dimensions of the mold cavity in at 
least two of its three dimensions to provide surface skins. The blank 12 
of FIG. 3 has been shaped by routing along its opposing side edges 16 and 
18 to provide a width (x-dimension) which is larger than the x' dimension 
in the corresponding finished part 20 (FIG. 2). These side edge surfaces 
10 and 18 are then contacted with an aqueous urea solution such as by 
brushing on the urea solution or by application with an absorbent roller, 
or by any coating method known in the art. 
Both of the major surfaces, top surface 24 and bottom surface 26, must be 
oversized and contacted with urea to prevent the furniture part from 
buckling. If only one major surface were contacted with urea, stresses 
would result from the differences in opposing surface characteristics 
which would cause the part to buckle or warp, along its major surfaces. 
However, because of the distance of separation between side surfaces 16 
and 18 and because of the distance between end surfaces 28 and 30 (FIG. 
1), any one of these surfaces can be urea treated without treating the 
corresponding opposing surface without causing buckling or warping in the 
part. 
It is important that at least two dimensions of a three dimensional part is 
oversized prior to molding to achieve the compression and heat transfer in 
the oversized dimensions necessary to impart surface skin 22 to all 
surfaces which are both oversized and contacted with urea prior to 
molding. For example, blank 12 (FIG. 3) need only be oversized along the x 
and y dimensions to provide skins on top surface 24, bottom surface 26 and 
one or both of side surfaces 16 and 18. If desired, the end edges 28 and 
30 (FIG. 1) also can be provided with surface skins. 
As shown in FIG. 6, a shaped blank 12 is molded by compressing top mold 
portion 32 onto bottom mold portion 34 to force blank 12 into the mold and 
to form the shape of the molded part to correspond to the dimensions of 
the mold cavity. 
Blank 14 can be molded directly, without pre-shaping, as shown in FIG. 7, 
so long as the blank 14 has a density of less than about 25 pounds/cubic 
foot. For example, a urea-contacted blank 14 having a pre-mold density of 
19 pounds/cubic foot and a thickness of 1.125 inches, when molded at 
550.degree. F. for 40 seconds at 250 psi, has a post-molded density of 24 
pounds/cubic foot, has excellent transference of design details from the 
mold cavity, includes a 0.060" skin on all surfaces, and has a look, feel 
and sound of natural wood. 
The product formed by the process of the present invention includes a hard, 
dense skin having a density in the range of 40-55 pounds/ft.sup.3, 
generally about 50 pounds/ft.sup.3. The composition of the skin cannot be 
determined by analysis. The base layer or core material underlying the 
skin has a density of 10-35 pounds/cubic foot, so that lightweight 
products of varying density can be manufactured having hard skins thereon 
as thick as 0.070 inch. 
Although the present invention is described in terms of particular 
constituents, and ranges thereof, and manner of making and using the same, 
it is recognized that departures may be made therefrom within the scope of 
the invention as defined in the appended claims.