Note: Descriptions are shown in the official language in which they were submitted.
39'~
ABRA:SION~RESIS~ANT LAMINATE
FIELD OF I~IENTION
The present invention relates to laminates and, more
particularly, decorative laminates of high abrasion resis-
tance.
BACKGROU~D
High pressure decorative laminates are conventionally
produced by stacking and curing undex heat and pressure a
plurality of layers of paper impregnated with various syn-
thetic thermosetting resins. In normal practice the assembly,
from the bottom up, consists of a plurality, e.g. three to
eight, core sheets made from phenolic resin impregnated
kraft paper, above which lies a pattern or print sheet
impregnated with melamine resin; on top of the print ~heet
is provided an overlay sheet which, in the laminate, is
almost transparent and provides protection for the pattern
sheet.
The core sheets are conventionally made from krat
paper of about 90-125 pound ream weight. Prior to stac}cing,
the kraft paper is impregnated with a water-alcohol solution
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,j .` ,
~3
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of phenol-formaldehyde reslle, dried and partially cured in
a hot air oven, and finally cut into sheets. The print
sheet is a high quality, 50-125 ream weight, pigment ~illed,
alpha cellulose paper that has been impregnated with a
water-alcohol solution of melamine-formaldehyde resin, dried
and partially cured, and finally cut into sheets. The print
sheet, prior to impregnation with the resin, usually has
been printed with a decorative design, or with a photogravure
reproduction of natural materials, such as wood, marble,
leather, etc.
The overlay shee~ is almost invariably used when the
print or pat~ern sheet has a surface printing in order to
protect the printing from abrasive wear. The overlay sheet
is a high quality alpha cellulose paper of about 20-30
pounds ream weight that i5 also lmpregnated with melamine-
formaldehyde resin in a manner similar to that used for the
print sheet, except that a greater amount of resin per unit
weight of paper is used. The indivldual sheets are stacked
in the manner indicated above and, if six sheets of impreg-
nated core paper are used, af~er lamination under heat andpressure there results a finished laminate having a thickness
of about 50 mils, it being understood that a different number
of sheets can be used to provide thicker or thinner laminates.
The stack of sheets as described above is placed
between polished steel plates and subjected to about
230-340F (e.g. 300F) at 800-1600 p.s.i. ~e.g. 1000 p.s.i.
for a time sufficient to consolidate the laminate and cure
the resins ~e.g. ~bout ~wen~y-~ive minu~es). This causes
the resin in the paper sheets to flow, cure and consolidate
the sheets into a unitary laminated mass referred to in the
art as a decorative high-pressure laminate. In actual
practice, two laminated stacks are often pressed back to
back, separated by a coated release sheet that allows the
two laminates to be peeled apart after pressing. Also, a
large proportion of the stacks are laminated with an aluminum
foil-kraft paper composi~e sheet inserted between the overlay
and the metal plate, with the aluminum facing the overlay,
in order to obtain a laminate having a lower gloss and a
slightly ~extured surface which is desirable for some
products.
At the comple~lon of the laminating operation, the
backs of the laminates are sanded to permit gluing to
particle board, plywood or other substrates. The glued,
laminate surfaced panel is then fabricated into furniture,
kitchen counter tops, table tops, store fixtures and other
end-use applications widely accepted for the combination
of appearance, durability and economy.
A number of variations of ~he above-described general
process are known, particularly those operations designed
to obtain special effects in appearance and texture. Also
other curing cycles are possible and, in fact, sometimes
other resin systems are used as well.
Besides decorative high-pressure laminates referred
to above, there are also a number of low-pressure products
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~ 3~'7
which have been developed in recent years, including
low-pressure laminates using either saturated polyester
resins, or melamine-formaldehyde resin. One of the astest
growing materials competing with high-pressure lamlnates
in recent years is a product referred to as low-pressure
melamine board whlch is normally pressed in a short cycle
at 175-225 p.s.i. at 325-350F. These low-pressure products
have the advantage of being normally less expensive, but
they cannot be given the title of "high pressure laminates"
because in order to be en~itled to that designation, a
product must meet a variety of rigid standards promuLgated
by the National Electric Manufacturers Association, NEMA
LD3-1975 which includes standards relating to abrasive wear,
stain resistance, heat resistance, lmpact resistance,
lS dimensional stability, etc. While various other decorative
printed,surfacing materials, such as some of the low-pressure
laminates, have certain of the desirable characteristics, no ;
products other than high-pressure lamlnates currently
available have all of these properties.
One of these properties in particular which is very
important is abrasion resistance. A high-pressure decorative
laminate must have sufficient abrasion res~stance to permit
use in high exposure areas such as dinette surface tops,
check-out counters, etc. The standard NEMA test for abrasion
reslstance is NEMA test LD-3.01. In this test a laminate
sample i5 clamped on a rotating disc, over which ride two
weighted rubber wheels, faced with calibrated sand-paper
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strlps. As the lamlna~e surface is rotated under the
wheels, ~he abrasive action of the sand-paper cuts through
the surface of the laminate and gradually through the
overlay until the prlnted pa~tern is exposed and destroyed.
The NEMA standard for TYPE I laminate requires that the
laminate, a~ter four hundred rotation cycles, has no more
than 50% of its pattern destroyed. The 50% end point is
estimated by averaging the number of cycles at which the
pattern shows initial wear, and the number of cycles at
which the pattern is completely destroyed.
If a high-pressure decorative laminate is prepared
in a conventional manner, with a normal 35-40% resin content
in the print or pattern sheet, but without an overlay sheet,
the abrasion resistance will be only about 50-75 cycles. If
specially formulated melamlne resins are used in the pattern
sheet with a resin content of 50~55%, abrasion resistance of
up to about 150-200 cycles are on occasion obtainable with-
out an overlay sheet, but in this latter case the laminates
have a tendency to develop surface craze and, furthermore,
they are quite difficult to prepare due to the difficulty
of impregnating the pr~nt sheet in a uniform manner; addition-
ally, they do not meet the 400 cycle minimum required by the
NEMA standard.
Nevertheless, it is desirable to produce a laminate
without an overlay sheet which is capable of attaining the
performance chatacteris~ics of a laminate using an overlay,
and, in particular, one that provides a 400 cycle abrasion
~ ~æ~
resistance. Furthermore, it is desirable to provide a
laminate ~hich, in addition to having the 400 cycle
~brasion resistance, has an inltial wear point at least
equal to the initial wear point of a conventional high-
pressure lamlnate having overlay, typically 175-200
cycles. This is desirable because in actual use the lami-
nate appearance becomes unsatisfactory not when 50% of the
pattern is destroyed, but ~he~ a much lower percentage is
destroyed. It is well known from many years of field
experience that conventional laminates with overlay, which
have 175-200 cycle initial wear point, when used in hard
use areas~ will have a satis~actory appearance, at least as
long as the normal replacement cycle, it being understood
that replacement of most laminates in commercial uses is
lS made for style reasons rather than because of pattern wear.
Therefore, a laminate without overlay should meet these
same criteria, namely it should have both a NEMA a~rasion
res1stance of at least 4~0 cycles and an initial wear point
in the same test of at least 175-200 cycles, even though
the latter requirement is not part of the ~EMA standard.
It is de~irable to be able to provide these charac-
terist~cs, but without using an overLay, for several
reasons:
l. Overlay adds substantial raw material costs to
the manufacturP of laminates, b~h the cost of the overlay
paper itself, the cost of the resin used to impregnate the
overlay paper and the in-process and handling 1QSSeS of
these materials.
3~7
2. l`he overlay, by imgQsing an intermediate layer
of substantial thickness between the print sheet and the
eyes of the viewer, detracts signlf~cantly from the
desired visual clarity of the pattern. The celluLose
fibers used to make overlay paper have a ref~active index
close to that of cured melamine-formaldehyde resin. The
fibers are therefore almost invislble in the cured lami-
nate~ and permit the printed pattern to be seen with very
little attenuation. However, modern printing techniques
are making available very accurate reproductions of
natural materials, particularly various wood veneer species.
As these prlnted reproductions approach in appearance the
natural veneer, even small amounts of haze or blur intro-
duced by the overlay paper are disturbing visually and
destroy much of the realism desired by the user.
3. Furthermore~ the overlay contributes to the rejec-
tion rate of the laminate products produced. The impreg-
nated, dry overlay sheet tends to attract small dirt
particles because it develops statlc electricity c~.arges
during drying. This dirt is hard to detect and remove before
laminating, and results in spoLled laminate sheets that
cannot be reprocessed. In addition, the impregnated dried
overlay is brittle and hard to handle without breakage.
Broken pieces are accidentally trapped on the surface of
the overlay and also result in visually defective sheets.
Additionally, overlay containing laminate ! particularly
those having a relatively high sur~ace gloss, have a ten-
dency to become dull very quickly when subjected even to
only moderate abrasive wearO This is understandably
unacceptable where glossy laminates are desired.
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The problem of prov~din~ improved abrasion reslstance
has been a long standing problem in ~he field. Many
solu~ions to the problem have been suggested and, in fact,
some of these have reached commercial development. Neverthe-
; ~ less, prior to the embodiments of the paren~ applications,it has no~ been possible to provide a laminate, without an
overlay sheet, but having a NEMA abrasion resistance of at
least 400 cycles and an initial wear point in the same test
of at least 175-200 cycles.
It is well known that small, hard mineral particles
dispersed in overlay paper, or in resin mixtures to coat the
impregnated pat~ern sheet, can enhance the abrasion resistance
of hlgh-pressure laminates (see, for example, the patents to
Michl, 3,135,643; Fuerst, 3,373,071 and Fuerst, 3,373,070).
Techniques such as these do not eliminate the overlay, but
either enhance its abrasion resistance, or provide an
alternate form of overlay and associated resin.
For example, in the Barna patent, 3,123,515, the over-
lay sheet is impregnated with a finely divided frit, the
impregnated sheet containing between 20 and 60% by weight of
resin and frit in which the proportion of frit is between
about 35 and 60% o the to~al solids added. ~he overlay is
used in the normal manner by placing it over the print or
pattern sheet.
In the Fuerst patent, 3,373,070, a process is disclosed
whereby silica is incorporated illtO the overlay structure
during the manufacture of the overlay paper itself, thereby
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providing a uniÇorm distribution of the silica throughout
the overlay sheet. This patent includes a discusslon near
the bottom of column 1 of the disadvantages of the Barna
type procedure of impregnating the overlay, Fuerst being
of the opinion that a silica rich resinous coating on the
top of the overlay is undesirable.
The Michl patent, 3,135,642 in essence shows the
casting of, or the in situ manufacture of, an overlay sheet
over ~he print sheet. The coating includes silica, ~inely
; 10 divided cellulose flock, carboxy methyl cellulose and
melamine resin solids. The weight of the dry coating is
said to be 0.022 to 0.033 pounds per square foot of print
sheet on the dry basis. This weight is equivalent to 66-99
pounds per ream, corresponding almost exactly to the weight range
of conventional impregnated overlay papers,and has a
thickness of about 2.5 mils (see Table D of Michl). At
best the Michl procedure provides only a minor raw material
cost advantage compared with the use of conventional overlay,
and does not solve the problem of impaired visual effects
due to haze or blur.
The Fuerst patent, 3,373,071 is very similar to the
Michl patent, except that the overlay cast in situ over the
print sheet contains micro crystalline cellulose. This coat-
lng is said to be applied, on a dry weight basis, of 0.022
to 0.33 pounds per square foot, again giving a thick coating
which weighs at least 66 pounds per ream, the same minimum weight
as the conventional impregnated overlay paper. Alumina in
significant amounts cannot be used in place of silica because
the resultant product contains so much alumina that the products
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~ 7
cannot be CUt without excessive tool wear. Even the silica,
far less abrasive than alumina, presents tool wear problems
in the Fuerst products when used in significant amounts.
One interesting technique which was briefly tested at
commercial scale, but has now been abandonecl, is ~hat disclosed
in the Lane et al patent 3,798,111 in which thereis disclosed
~he use of small mineral particles, preferably alumina, which
are incorporated within and near the upper layer of the base
paper during its manufacture. Thus, the abrasive-resistant
particles are incorporated in the paper during the paper-
maklng process as in Fuerst '070, but, more analogously to
Barna, they are incorporated after the base layer of paper
has been formed and is still in a wet state supported on
the forming wire.
After its manufacture, this paper of the Lane et al
paten~ is subsequently printed, impregnated and then used
in the laminating operation as the print sheet without the
necessity of using an overlay. In this process, the print-
ing occurs above or on top of the hard mineral particles
and, consequently, high-pressure laminates produced using a
print sheet made in accordance with the Lane patent, and
without an overlay, have unacceptably low inltial wear,
even though they do have a NEMA abraslon resistance of at
least 400 cycles. In tests, it has been shown that laminates
made with the print paper of Lane et al, without overlay, had
~nitial wear values of under 100 cycles, some as low as 35
cycles. Furthermore, in a rubbillg test to determine initial
wear, such laminates began to show pattern destruction after
only 3,000 rub cycles, far less than necessary.
Even if the Lane eq al paper is used as an overlay, the
three problems caused by overlay and mentioned abovc (pp. 7 and
8) still exis~, although abrasion resistance is excellent.
O~her prior art patents of some interest with regard
S to the background of the present invention are the patents
to Fuerst, 3,445,327; Gibbons, 3,928,706 which suggests the
use of a cast in situ overlay used together with a convention-
al overlay, and Merriam, 3,661,673. Of somewhat less interest
are the Battista patents 3,25~,537 and 3,157,518; Ando et al,
3,716,440; Power et al, 3,946,137 and Boenig, 3,318,760.
There are many end uses of laminates in which initial
pattern wear rather than NEMA wear value determine the accept-
able life of the surace. For example, supermar~et check-out
counters, food service counters, cafeterla tables, and other
commercial surfaces are exposed to abrasive rubbing and
sliding of unglazed dinnerwear, canned goods, fiberglas trays,
etc. If small areas of the pattern begin to disappear after a
relatively short period of use, particularly in an irregular
pattern, the surface wlll be unacceptable to the owner and
will result in an expensive replacement. If the surface wears
gradually and evenly over a long period o time, the wear out
time exceeds the normal replacement cycle due to style changes,
approximately 3-5 years.
Conventional high pressure laminates (see Fig. 1)
2S with initial wear values of 175~200 are known to be satis-
factory in commercial or institutional service, and show
perhaps lQ-20% pattern loss in 3-5 years on checkout counters.
~ 3-~ 7
To determine a predicted wear-out time for laminate (Fig. 2)
without overlay,made using the print paper of the Lane et al
patent No. 3,798,111, such lamlnates along with conventional
laminates and those made in accordance with embodiments of
the paren~ applications were subjected to an abrasive rub
test conslsting of sliding a simulated fiberglas tray surface
back-and-forth over the test laminate, th~ simulated fiber-
glas tray surface being bonded to the bottom of a No. 10 can
carrylng 5 lbs. of weight, and flexibly clamped in a cam
driven Jig that provided about 5 inches of oscillatory motion.
~n this test, the laminate according to patent No. 3,798,111
began to show pattern destruction after about 3000 rub cycles.
Conventional laminate with overlay and laminate prepared in
accordance with embodiments of the parent applications with-
out overlay did not show any pattern destruction after 30,000cycles,
The "rub test" or "sliding can test" was also used
to compare the embodiments of the parent applicationswith
conventional mirror-surfaced laminates having overlay. As
previously noted, both start initial pattern destruction at
about 30,000 rub cycles. The conventional laminate shows
gradual sur~ace dulling beginning almost with the first few hun-
dred rub cycles, and is completely dulled well before initial
pattern destruction. The abrasion-resistant embodiments of
the parent applications, however, showed negligible surface
dulling almost up to the point of pattern destruction.
These results suggest not only an important advantage of
these laminates compared wl~h conventional laminates
including overlay, but also similar advantages compared
with laminates produced by ~he casting of the overlay
in situ on the prln~ sheet, e.g. the Fuerst patent, 3,373,071.
Even after the considerable activity in the field in
order to solve the problems indicated above, these problems
have not been solved until the embodiments of the parent
applications. In the parent applications the technique
exemplified utilizes a single ultra-thin layer comprising
a mixture of binder and abrasion-resistant particles. While
the laminates so produced are far superior to all prior
attempts, it has now be~n found that in a minority of patterns,
i~e. heavily inked patterns, and some printed on smooth paper,
it is necessary - to achieve good initial wear - to provide
the single ultra-thin layer in undesirably heavy thicknesses,
i.e. as much as 8-12 lbs/ream or even as high as 16 lbs/ream,
whereas most patterns are provided with good initial wear in
accordance with the parent applications with ultra-thin
coatings of only 4-5 lbs/ream.
While the heavier coatings applied to the heavily inked
patterns, still ultra-thin in comparison with the prior art,
provide superior initial wear and sliding can values, these
laminates ~aving abrasive-resistant coatings much above
6 lbs/ream where the abrasive particles are alumina) are
difficult to handle in the sense that tools used to cut such
laminates are quickly worn out by the quantities of alumina
present, and chipping at a rapid rate during machine routing
operations sometimes occurs.
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SUMMARY
__
This invention is concerned with an improved decorative
laminate.
The high-pxessure decorative laminate does not contain an over-
lay sheet, but nevertheless meets the requirements of the NE~A
abrasion standard, and furthermore provides an initia7 wear point
of at least 175 200 cycles in this same test.
The high pressure laminate uses conventional base papers used
for the printing of the pattern or print sheet. The printed
pattern sheet is impregnated utilizing conventional impregnation
and drying equipment commonly used in the laminating field.
The improved decorative lamina~es do not require substantial
raw matexial costs and significantly enhance the economics of
laminate production by the elimination o~ the overlay sheet.
There is also described a process for making laminates which
involves significant cost reduction and results in a product having
improved appearance and which has the potential for previously
unavailable additional novel graphics development.
Thus there i5 described improved low-pressure laminates in-
cluding up-graded low-pressure melamine board.
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353~7
The quantity of abrasion-resistant material necessary to
achieve superior abrasion resistance is reduced, as described
hereinafter, without causing excessive tool wear in the cutting
of the product.
Thus, there is provided by coating conventional printed or
otherwise decorated pattern paper first with an ultra thin coating
of suitable binder and then with an ultra thin coating containing
small mineral particles immobilized by preferably the same binder,
and wherein ~uch print sheet is then impregnated in the normal
manner with a suitable thermo-setting resin such as melamine resin,
and then using the print sheet in the production of decorative
laminates without an overlay sheet. The abrasion-resistant
particles are, therefore, used in lesser quantities and are more
concentrated on the uppermost surfaces of the laminates compared
with examples of the parent applications giving equivalent wear
resistance.
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~ .3~'~
CONSISTORY CLAUSE
In a method of producing an abrasion~resistant
decorative laminate from at least one backing layer and a
thermosetting resin impregnated decorative facing sheet, said
laminate having enhanced abrasion resistance without an
overlay layer, the method compris;ng:
coating a decorative facing sheet with an ultra thin
wet layer of a mixture of (1) an abrasion-resistant hard
mineral of particle size 20-50 microns and quantity-sufficient
to provide an abrasion-resistant layer without interfering
with visibility and (2) binder material for said mineral which
binder material has the properties of withstanding the subse-
quent laminating conditions, being compatible with said
thermosetting resin, together with said resin being substan-
tially transparent after lamination, said binder material
being present in an amount suficient to bind said abrasion-
resistant mineral to the surface of said decorative facing
sheet, and the binder/mineral layer in the dry state being
permeable to said thermosetting resin;
drying said mixture on said facing sheet at a temper-
ature suficient to enchance ~he bonding of said abrasion-
resistant mineral by said binder to the sur~ace of said
decorative facing sheet, to provide an ultra-thin dry layer
of said mixture thereon;
impregnating said coated facing sheet with said
thermosetting resin;
assembling said resin impregnated and coated facing
sheet over said backing layer;
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subjecting said assembly ~o heat and pressure sufficient
to effect consolidation of said backing layer and said facing
sheet to thereby provide said abrasion-resistant decorative
laminate, the improvement compris.ing
prior to said impregnating step coating either directly
said decorative facing sheet or said ultra-thin dry layer
of mixture with an ultra-thin wet layer of binder materi.al
having, the properties of withstanding the subsequent laminating
conditions, being compatible with said thermnsetting resin,
being in the dry state permeable tc. said therm~setting.resin
and together with said resin being substantially transparent.
after lamination; and
drying said wet ultra-thin binder material layer to
provide an ultra-thin .dry binder materiàl layer i~mediately
below or above said ultra-thin dry layer of binder material/
mineral mixture.
In a print sheet for use in the preparation o:E
decorative laminates of high abrasion-resistance, comprising:
a paper sheet substrate having a print design thereon, and
an ultra-thin abrasion-resistant coating over said print design,
said ultra-thin abrasion-resistant coating comprising a mix
ture of ~1) an abrasion-resistant hard mineral of particle
size 20-50 microns and quantity sufficient to provide an
abrasion-resistant layer without interfering with visibility
and (2~ binder material for said mineral compatible with a
thermosetting laminating resin selected from the group con-
sisting of melamine-formaldehyde. resin and polyester resin,
said coating being impregnable, said laminating resin and
substantially transparent together with said resin after curing
of said resin, said binder material being present in an amount
16b-
.
~ ~ ~2 ~
sufficient to bind and stabili~e sai~ abrasion-resistant
mineral to the surface of said paper sheet, the improvement
comprising
an ultra-thin layer of binder material located either
directly over the surface of said print sheet and beneath
said ultra thin abrasion-resistant coating, or above said
abrasion-resistant coating.
In an abrasion-resistant decorative laminate meeting
NEMA abrasion-resi'stance standards and also capable of with-
standing 175-200 cycles of initial wear in the same test,
comprising:
a backing layer and laminated thereto a thermoset
laminating resin impregnated decorative facing sheet, said
decorative facing sheek having a print design thereon and an
ultra-thin abrasion-resistant coating over said prin~ design,
said ultra-thin abrasion-resistant coating comprising a
mixture of (1) an abrasion-resistant hard mineral of particle
size 20-50 microns and quantity sufficient to provide for
'abrasion resistance without interfering with visibility and
(2) a stabilizing binder material for said mineral which binder
is compati'ble with said thermoset resin impregnated throughout
said print sheet, said binder not interfering with visibiLity,
and with said ultra-~hin abrasion-resistant coating being at
or near the surface of said laminate, the improvement comprising
an ultra-thin layer of binder material impregnated with
said thermoset resin and located either directly over the
print design surface of said decorative facing sheet beneath
said ultra-thin abrasion-resistant coating, or a'bove said
abrasion-resistant coating.
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BRIEF; DES'C`R'IPT'ION OF THE DRAWINGS
The above and other objects and the nature and
advantages of the instant invention will be more apparent
from the following detailed description of embodiments taken
in conjunction with the drawing (not to scale) wherein:
Figs. 1-3 are schematic sectional views of laminates
in accordance with the prior art;
Fig. 4 is a laminate developed by the present
inventors,
Fig. 5 is a flow-diagram showing a method of prepar-
ing a print layer in accordance with the present lnvention;
Fi~. 6 is a schematic sectional view, not in scale,
showing an embodiment of the print sheet in accordance with
the present inventlon; and
Fig. 7 ls a schematic sectional view, not ln scale,
showing a laminate in accordance with the present invention.
Unless paper is hLghly calandered or otherwise
pressed to a very smooth surface, its surface is fairly
rough. When paper is printed the ink sinks partly into the
upper surface of the paper and partly projects above its
upper surface thereby making the upper surface even more
rough and irregular. This is the nature of the print paper
used in the manufacture of laminates. Some heavily printed
patterns in particular have rough surfaces and, accordingly,
when an ultra-thin abrasion-resistant coating in accordance
with embodiments of the parent applications are applied
thereto, the valleys between
i!~ r
~ 3~7
the pe~ks where ~he printing occurs are only partly filled
with the result that the abrasion-resistant coating over
such peaks is thinner and the surface is still somewhat
irregular as schematically illustrated in Fig. 4. The
S tendency of the coating to level and provide a thinner
layer over the peaks is accentuated when the inks are
composed of hydrophobic thermoplastics, as is common.
To overcome this problem various solutions are
proposed:
~1) the incorporation in the printing inks used
on the print paper of silanes to better bond the abrasion-
resistant particles o the coating thereto, and/or the
incorporation of wetting agents in the inks to better permit
wetting of the otherwise hydrophobic ink peaks;
(2) the provision of a second ultra-thin binder
Layer over the main ultra-thin layer of binder/abrasion-
resistant particles to increase the quantity of melamine
resin at the surface of the laminate; and
(3) the provision of such a second ultra-thin
binder layer below the maln ultra-thin abrasion-resistant
layer.
While all three alternatives give improved results,
the third alternative gives by far the most superior results.
Therefor, in accordance with the present invention, there is
first applied to the print or pattern paper an ultra-thin
coating of binder, preferably microcrystalline cellulose of
average thickness about 0.05 to 0.3 mils (dry), i.e. applied
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3~
at a rate of about 1/2 to 3 pounds per ream. This coating,
which tends to level the roughness of the upper surface of
the print sheet and also to coat the peaks sufficiently to
form a better anchor base for the abrasion-resistant layer
than does the ink peaks, is then dried. The ultra-thin
abrasion-resistant coating is ~hen applied at a much lower
rate without being wasted in the valleys compared with the
embodiments of the parent applications, e.g. the abrasion-
resistant layer is appli~d at the rate of only 1-6 pounds per
ream to provide a dry upper layer thickness of 0.02-0.2 mils
(usually less than 0.15 mils thick) over the first coating
which serves as a substrate.
The abrasion-resistant composition, containiny small
mineral particles, when coated without resin over unimpreg-
nated printed pattern paper having a sub-coating thereon,
provides surprising and unexpected properties by permitting
such paper to be used in the preparation of decorative
laminates without an overlay sheet and wherein the resultant
laminates are highly abrasion-resistant, using only small
amounts of mineral particles and without causing the heavily-
inked product to be unduly hard on cutting tools.
In its preferred form, the coating CompQ~i~ion is
composed of a mixture of small particles of alumina or other
abrasion-resistant particles of average 20-50 micron particle
size, and a lesser amount of micro-crystalline cellulose
particles, both dispersed in a stable, aqueous slurry. The
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~ 3~t~
particles of alumina~ of small slze such that they do not
lnterfere with the visual effects in the final product,
serve as the abrasion resistant material and the micro-
crystalline cellulose particles serve as the preferred
temporary binder. It will be understood that the binder
must be compatible wi~h the resin system later utillzed in
the laminating procedure, usually a melamine resin or in
the case of certain low-pressure laminates a polyester resin
system, and the micro-crystalline cellulose serves this
function as well as stabilizing the small particles of
alumina on the surface of the print sheet.
The sub-layer is also formed of a temporary binder
havlng the same properties as the binder of the abrasion-
resistant layer. Preferably the binder is the same binder,
most preferably micro-crystalline cellulose.
With reference to Fig. 5, in the preferred operation
a conventional unimpregnated print or pattern paper is coated
first with the binder material at a rate of about l/2 to 3,
preferably about 1-l/2 to 2-lt2, lbs./ream and the coating is
leveled and dried. As seen schematically in Fig. 6, the
binder layer tends to level and fill in the holes ln the
surface, e.g. between the ink peaks while providing a
coating thereover as well; therefore, while the average
thickness of the binder layer may be as great as 0.3 mil,
its thickness over the peaks will always be much less,
normally less than 0.1 mil. The dried layer is then coated
with the mixture of hard mineral particles and binder, prefer-
ably alumina and micro-crystalline cellulose particles in a
-20-
stable aqueous slurry,normally at a rate of about 1-~ lbs.
per ream, and the coa~ing is drled a~ an elevated ~emperature
of at least 140~. and preferably 180F., such as in a hot-
air oven, to produce a thin over-coating only 0.02 to 0.2
mils thick, usually less than 0.15 mils thick.
The resultant abrasion-resistant coated paper (Fig. 6)
is then impregnated with the melamine or polyester resin and
dried in a conventional way, at which point it ls ready for
the laminating procedure. Based on the comparative weights
of the print sheet and the micro-crystalline cellulose in
the ultra-thin coatings thereon, and the to~al amount of
melamine resin impregnated thereinto, it is calculated that
only 2 - 13 parts of micro-crystalline cellulose are
used per 100 parts of resin.
With reference to Fig. 7, it is seen that the abrasion-
resistant resin impregnated print sheet, having an ultra-thin
abrasive-resistant coating on its upper surface, is assembled
for the laminating step in the conventional way, except that
no overlay sheet is used. The lamlnate is then cured under
heat and pressure in the conventional manner. A surprising
characteristic of the ultra-thin coating is that even though
its total thickness (both layers) is so thin, it can provide
abrasion resistance in the finlshed laminate not only meeting
40V cycles NEMA Standard, but also providing an initial wear
point in excess of 175-200 cycles.
It is also surprising that the coatings forming the
total ultra-thin layer tightly adhere to th~ surface of the
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~ 3~'7
printed paper when the paper is later impregnated with
melamine resin, without significant amounts of the mlneral
particles either being lost in the impregnating solution
or migrating away from the surface of the paper. A further
surprising characteris~ic of these coatings is that they
do not appear ~o hinder the penetration of the melarnine-
formaldehyde resin solution into the interior of the paper,
during the impregnation step; such penetration is essential,
or the pattern sheet will be irregularly starved such as at
its center, and could possibly delaminate after pressing.
A further desirable characteristic of the coatings is that
they do not significantly scatter or attenuate light,
resulting in very clear, crisp appearance of the pattern in
the finished laminate. Also, because of the very ultra-thin
nature of the mineral particle containing layer, there is no
tool wear problem during the subsequent processing of the
resultant laminates.
Without being bound to the following theory, it is
believed that the improved characteristics of the invention
can be accounted for as follows. Microcrystalline cellulose
particles contain very large external forces that bind to
other polar substances, such as cellulose and alumina.
Thus, an aqueous slurry of microcrystalline cellulose and
alumina is stable and does not ~uickly settle out, even
though alumina particles in water are not stable. Further-
more, when this slurry is coated onto the paper or the sub-
ultra-thin binder layer, the mlcrocrystalline cellulose
apparently binds the alumina particles to the surface fibers
to
of the paper or/the binder sub-layer, preventing migration
of the alumina particles to below the surface. This may
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~ 9~7
account for the good abrasion resistance developed by such very
small quanti~ies of alumina. Thus, all or substantially
all of the alumina partlcles stay at the surface where they
do the most good, rather than becoming dispersed below the
surface where they would contribute relatlvely little initial
wear resistance.
As lndicated above, the preferred slurry composition
for the abrasion-resistant ultra-thin upper layer contains a
mixture of small particles of alumina and a lesser amount of
microcrystalline cellulose particles, both dispersed in water.
There must be an amount sufficient of the small mineral
particles to provide the resultant product with the desired
abrasion resistance as discussed above, and there must be
an amount sufficient of the binder to retain the mineral
particles in place on the surface of the ultra-thin-sub-
layer.
In general, it has been found that satisfactory
results are attained with about 5 to 10 parts by weight of
the microcrystalline cellulose for about 20-120 parts by
weight of the alumina; it is possible to work outside this
range but there ls no advantage doing so and, furthermore,
the handling problems become complicated. The quantity of
water in the slurry is also dictated by practlcal consider-
ations, since if there is too little water the slurry becomes
so thick that it ls hard to apply; similarly, if there is too
much water the slurry becomes so thln that it is difficult
to maintain a consistent thickness durlng the coating operation
-23-
z~
due to running of ~he slur~y. Thus, a slurry containing
about 2.5 wt % microcrystalline cellulose and about 28 wt %
alumina, based on the water, is stable, i.e. the alumina
does not settle out; but if more than about 3.5 wt % micro-
crystalline cellulose and about 28 wt % alumina, based onthe water, is used, the slurry becomes very thixotropic
and difficult to apply. A preferred slurry contains about
3.2% microcrystalline cellulose and about 9% alumina.
The composition also preferably contains a small
amount of wetting agent, preferably a non-ionic wett:Lng
agent~ a small amount of a subsidiary suspending-binding
agent such as carboxy-methyl cellulose, and a small amount
of silane. The quantity of wetting agent is not critical,
but only a very small amount is desirable and excess
quantities provlde no advantage. If a subsidiary suspending-
binding agent, such as carboxy methyl cellulose is used to
help keep the mineral particles in suspension, it may be
used in amounts up to about 50% by weight of the amount of
the microcrystalline cellulose.
If a silane is used, it acts as a coupling agent*
which chemically blnds the alumina or other inorganic
particles to the melamine matrix after impregnation and
cure, and this provides better initial wear since the alumina
particles are chemically bound to the melamine in addition
to being mechanically bound thereto and therefore stay inplace longer under abrasive wear. The silane should be
/*Silanes as coupling agents in other arts are known, e.g.
in the manufacture of fiberglass tires, grinding wheels
and fiberglass reinforced polyester bodies. See the 1976-77
Edition of Modern Plastics Encyclopedia, Page 160, whlch
lists some silanes useful wlth melamine and polyester systems.
~Z4-
~ 3~t7
selected from atnong the group making i~ compatible withthe partlcular thermosetting lamina~ing resin used; in
this regard silanes having an amino ~roup, such as gamma-
aminopropyl trimethoxy sllane (Silane A-lllO) or ga~ma-
aminopropyl triethoxy silane (Silane A-lllO) are particularly
~fective for use with melamlne resins. The quantity of
silane used need not be great and, in fact, as little as
0.5% based on the weight of the alumina 1s effective to
enhance the abrasion resistance of the final laminate;
a maximum quantity of about 2% by weight based on the weight
of the alumina or other hard particles is suggested since
greater quantities do not lead to any signiflcantly better
results and merely increase the cost of the raw materials.
It is an important feature of the present invention
that the coating using micro-crystalline cellulose as the
binder must be dried at an clevated temperature before the
print sheet is impregnated with the melamine resln. Thus,
a minimum drying temperature is about 140F. web temperature
and the preferred drying temperatures are from 160-180F
web temperature, or even higher.
With regard to the abrasion-resi.stant mlneral
particles, alumina is the preferred material. Silica,
which has been suggested in certain prior art patents as
an abraslon-resistant material, provldes considerably
inferior results in the present invention compared with
alumina, but can be used. Other minerals of sufficient
hardness such as zirconium oxide, cerium oxide, diamond dust~
etc. can work, but are either too expensive for prac~ical
25-
~ 3~ 7
usage or under certain circumstances produce excessive
color shift. Glass beads have been tried unsuccessfully.
Silicon carbide also was tried, and while providing good
abrasion resistance, produced excessive colur shit.
Mixtures of silica and alumina give good results.
An important feature is the size of the alumina or
other hard particles. Beneath 20 micron particle size,
abrasion resis~ance becomes poor, and the preferre~ minimum
average particle size is about 25 microns. Maximum average
particle size is limited by surface roughness in the article
and interference with visual effects. The preEerred maximum
average size of the abrasive resistant particles is about 50
microns.
The nature of the binder for the mineral particles
is a very important feature in the present invention. Of
all the materials tried, microcrystalline cellulose is by
far the most satisfactory material. The binder must serve
not only to maintain the mineral particles in position on
the surface of the sub-layer on the print sheet, but should
also act as a suspending agent in the slurry (otherwise, it
would be necessary tv add an additional suspending agent).
The peculiar property of microcrystalline cellulose is that
it acts like a typical suspending binding agent and film
former, but unlike other agents is not water soluble before
~5 or after suspension and forms a highly porous film throu~h
which the thermosetting resin can penetrate. In addition,
the binder must be compatible with the laminating resin and
-26-
microc~ystc~ c cel.lulose is compatible with both melamine
resin and polvester resins. Furthermore, i.t must not
scat~.er or attenua~e light i.n thc thicknesses applied in
~he final laminate, and microcrysta].llne cellulose is
satisfac~ory in this regard as well.
Other binders which may be used, but which provide
inferior results compared with microcrys~alline cellulose,
are various typical suspending-binding agents including
anionic acrylic polymer, carboxy methylcellulose and similar
materials such as hydroxypropyl cellulose, methylcellulose,
polyvinyl alcohol, polyvinyl pyrrolidone, etc. These
materials provide somewhat better results when mixed with
alpha-cellulose floc. However, as indicated above,
microcrystalline cellulose is the preferred binder.
Microcrystalline cellulose is a non-fibrous form of
cellulose in which the cell walls of cellulose fibers have
been broken into fragments ranging in length from a few
microns to a few tenths of a micron. It is not a chemical
derivative but a purified alpha cellulose. Microcrystalline
cellulose is available under the trademark "AVICEL", the
preparation of which is disclosed in the Battista patent
No. 3,275,580. AVICEI, Type RC 581 is a white, odorless
hygroscropic powder. It is water dispersible and contains
about 11% sodium carboxymethyl cellulose as a protective
colloid. Its particle size is less than 0.1% on a 60 mesh
screen.
The ultra-thin sub-layer is much like the ultra-
thin abrasion-resistant top layer, except that it preferably
3 ~'7
contains no abrasion-resistant particles. An aqueous
slurry containing about 3-6 wt % microcrystalline cellulose
can be satisfactorily coated over the print layer to form
a substrate for the ultra-thin abrasion-resistant layer.
A small amount of wetting agent may be used.
Features and advantages of the instant invention
which are considered to be particularly significant are as
~ollows:
(1) The mixture of mineral particles and micro-
lQ crystalline cellulose is deposited from a water slurry,rather ~han used as fillers in a resin solution.
(2) Such slurry is coated on an unimpregnated
printed pa~tern sheet, rather than on an impregnated
pattern sheet.
(3) The coating is dried at an elevated temperature
of at least 140F.
(4) The total average coating thickness of both
layers is only 0.07 to 0.5 mils, with the upper abrasion-
resistant layer being a maximum of 0.2 mils thick, rather
than requiring an overlay of 1-2 mils thickness.
(5) After applying the coatings and drying, the
pattern sheet is then impregnated with the thermosetting
resin, and this conventional impregnation of the pattern
sheet is carried out on conventional equipment, rather
~5 than special, difficult to control, coating of a thick
slurry.
(6) The ultra-thin upper layer provides unexpectedly
high abrasion resistance.
-28-
The desirable characteristics of the mineral
particle binding agen~ hich characteristics are all met
by microcrys~alline cellulosc, are: It acts as a film
former; it acts as a binding agent for the mineral
particles; it acts as a suspending agent in the slurry
for the mineral particles; it is not washed off during
the subsequent thermosetting resin impregnating process;
it is compatible with the subsequently applied thermo-
setting resin, such as melamine resin or polyester resin;
it is permeable to the thermosetting impregnating resin
(indeed microcrystalline cellulose forms a porous film);
lt is resistant to the heat generated during the laminating
procedure; and it does not scatter or attenuate light in
the laminate.
The following examples are offered illustratively:
EXAMPLE I
A--TOP COATING
A typical composition in accordance with the parent
applications was applied in an ultra-thin layer in accordance
with said applications at a coating weight as shown in Table I
to print sheets having a heavily inked pattern. After drying,
an Avicel coating was applied at 2 lbstream (dry) in an ultra-
thin layer over the ultra-thin abrasion-resistant layer, and
the top coating was dried; the sheets were then impregnated
with melamine resin, the top coating providing for increased
melamine coverage and the so-prepared print sheets were used
to form laminates without any overylay sheet.
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3~3t7
B--UNDER 0ATING
.
The process of E~AMPLE I-A was repeated except that
the 2 lbs/ream (dry3 ultra-thin Avicel coating was applied
directly to the upper surface of the print sheets and the
ul~ra-thin abrasion-resistant layer was applied over the
dried Avicel layer, By filling the depressions on the print
sheet surface first with Avicel, the paper surface was made
more level and all of the abrasion-resistant coating was
placed over the pattern where it does the most good. No
abrasion-resistant coating was wasted in the valleys.
As a comparative example,alaminate was made in
accordance with the parent application using only the ultra-
; thin abrasion-resistant layer. Results may be found in
TABLES I and II.
TABLE I -
Initial Wear Abrasion Resistance
HEAVILY DRY COAT WEIGHT A B
D~D OFAL~A SD~E TOP UNDER
PAT~S CO~I~ING LAYER CQAT CQATED COATED
~0 (N~ER) _(lbs/RE~(CYCLES) (CYCLES) (CYCLES)
AN-l-l 6 100 300 ---
AN-l 1 5.6 --- --- 500~-
W-8-104 5 50 400 ---
W-8-104 5.6 --- - - 500+
It should be noted that the initial wear shown here
for single coated laminate is lower than shown in examples
of the parent applications. This is characteristic of
certain heavily inked patterns, of which these two are
examples.
-30-
3~'7
TABLE II -
Slidin~ Can Test
DRY ~o~TI~IGHT A B
OF AL~nNA SINCLE TOP UNDER
5 PAT~N o~lNlNG LAYER CQ~T CQATED OQ~TED
N~ER (lbs/R~ (CYCLES) (C~ES) tCYCLES)
AN-l-l 6 4,627 6,057
AN-l-l 5.6 -~ 40,271
W-8-104 ~. 6,500 25,433 ----
~0 W-8-104 4.5 ----~ - 40,825~
From this it can be seen that although top coating improves
wear, base coating is more effective.
EXAMPLE II
A sample production run of base coated paper was made
on an air knife coater. Formulations were as follows:
UNDER COATING
Water 300 lbs.
Avicel RC 581 10 lbs.
ABRASION-RESISTANT COATING
Water 300 lbs.
Avicel RC 581 11.2 lbs.
CMC 7L 1.4 lbs.
Alumina of 30~ average diameter 30.0 lbs.
Silane A-1100 0.7 lbs.
A heavily printed woodgrain pattern, W-8-104, was coated
with 1.4 lbs/ream of Avicel under coating and dried. This was
followed with 4.2 lbs/ream of abrasion-resistant coating
which was then also dried. The so double coated paper
was treated with melamine-formaldehyde resin to a resin
content of 42-44% and volatile of 5-6%. Laminates with-
out overlay were pressed using this print sheet. Initialwear on laminate made from this paper was 510 cycles.
-31-
23~3~7
Sliding can ~est gave over!40,000 strokes. In comparison,
noting TABI.E I above, single coated laminates having only
the ultra-thin abrasion-resistant layer applied to the same
heavily coated print sheet, W-8-104, a~ the rate of 5 lbs/
ream, had an initial wear of only 50 cycles.
Sheets of W-8-104 in O.OS0" thickness were glued to
3/4" particleboard with PVA adhesive. Laminate with a single
coat, such as tested in TABLE I at 6 lbs/ream, was compared
for "machineability" with the dual coat at 4.2 lbs/ream
over 1.4 lbs/ream of base coating. The single coat formulation
contained 86.7% alumina; therefore, it contained 6 lbs~ream
x 0.867 = 5.2 lbs/ream of alumina. Dual coat contai.ned 69.2%
alumina or 4.2 lbs/ream x .692 + 2.9 lbs/ream of alumina.
Both panels were machined using carbide flat knives
on a shaper. Single coat laminate started slight chipping at
about 100 linear feet of machining. Dual coat took about 1000
linear feet to show similar chipping. From this it can be
seen that dual coat at a little more than 1/2 alumina weight
had more than 10 times the initial wear and about 1/10 tool
wear.
Compared with the prior attempts, the present inven-
tion provides vastly improved results such that the present
invention can be truly considered to be a revolutionary
development in the field of decorative laminates. Insofar
as is known, the present invention provides for the first
time, except for the embodiments of the parent applications,
a laminate without an overlay sheet has been made which is
capable of meeting both the NEMA Abrasion Resistance Standard
-32-
~ 7
of at least 400 cycles, and an initial wear polnt in this
same test of at leas~ 175-200 cycles.
The closest thin~ previously available (see Fig. 2)
has been the use of print paper made in accordance with
the I,ane et al patent No. 3,798,111. While laminates made
using this paper, without an overlay, have excellent
abrasion values according to the NEMA Standard, the initial
wear point in these products, however, is still very poor.
Tests conducted on such laminates show that many have
initial wear values of under lO0 cycles, some as low as 35
cycles, whereas conventional laminates made with convention-
al overlay have an initial wear point of 175-200 cycles.
In contrast, laminates made in accordance with the present
invention have initial wear points of no less than 175
cycles (usually a minimum of 200 cycles~ and up to about
500 cycles.
In addition to providing poorer initial wear values,
the laminates made without overlay using the print paper of
the Lane et al patent No. 3,798,111 provide other dis-
advantages as well. In the Lane et al patent, the aluminaparticles are lntroduced during the paper making process
and this results in a special grade paper for each base
paper color required, greatly incrPasi.ng inventory require-
ments; in contrast, in the present invention in which the
2S coatings are applied after printing, use is made of all
existing stocks of conventional print paper. Furthermore,
the present invention is more flexible than the Lane et al
-33-
3~t7
process in that i~ permits tailorlng of the abrasion
resistance to specific needs, withou~ the cumbersome re-
development of a paper base on a paper machine.
The present invention is also believed to constitute
other important improvements over the casting of an overlay
sheet (Michl, No. 3,135,643 and Fuerst, No. 3,373,071; and
other patents). Such patents show what is in essence the
casting in situ of a resin containing paper layer onto
resin impregnated pattern sheet, in which the upper resin
paper layer contains abrasion-resistant mineral particles
(see Fig. 3). In these techniques, the base paper already
contains the melamine resin and the thick coating applied
also contains melamine resin. The coating is applled at
the rate of, at the very least, 0.022 lbs. per sq. ft.
which is a quanti~y on the order of about 8 times or more
as great as that used in the present invention. The thick-
ness of the dry layer runs at least 2 mil and preferably
more compared with dry coatings in the present invention
runnlng from 0.07 to 0.5 mils, the abrasion layer being
preferably a maximum of only 0.15 mils.
The Michl patent essentially discloses how to deposit
an overlay layer onto the impregnated pattern sheet, rather
than how to eliminate the overlay. The finished laminate
(Fig. 3) is essentially the same as that of a conventional
laminate, containing cellulose fibers, resin, and differs
only by the mineral particles dispersed in this layer. The
Fuerst patent No. 3,373,071 states that the process taught
-34-
~'9 ~ ~3 ~'
~ g ~ 7
by Michl results in laminates that are blotchy when
satinized A significant percentage of laminates are
satini~ed with pumice and ro~ating brushes to reduc~ their
surface gloss. The Fuerst patent replaces the cellulose
S fiber of the Michl process with microcrystalllne cellulose
in order to provide blotch-free surfaces after satinizing.
Thus, the basic process of Fuerst is the same as that of
Michl, i.e. depositing a resin containing overlay layer
onto the wet, impregnated pattern sheet,i the thickness of
the Fuerst coating being at least four times as thick as
the maximum of those found useful ln the present invention,
and offering no significant savlngs of raw material compared
with conventional, overlay containing laminate. The most
significant advantage of the present invention campared to
such prior art is, however, the vastly improved abrasion
resistance as evidenced by improved initial wear, improved
NEMA abrasion resistance and reduced dulling during the
sliding can test. Tool wear is also a problem with the
Michl and Fuerst laminates, where large quantities of
mineral are used.
It will be obvious to those skilled in the art that
various changes may be made without departing from the
scope of the invention and the invention is not to be
considered limited to what is shown in the drawings and
described in the specification. For example, it will be
understood that certain additional variations in process-
lng will, ln certain instances, give somewhat different
results. For example, results are generally better when
the laminates in accordance with the present inven~ion
-35-
~ 3 ~17
are formed against a hard !surface. Thus, plate produced
finishes, such as mirror and satin, provide better initial
wear under given coating conditions than do foil (pr other
soft-backed pressing surfaces) produced finishes. Accord-
ingly, in some lnstances it is advantageous ~o calenderthe dried, coated pattern sheet prior to impregnation with
the thermosetting resin.
The oregoing description of the specific embodiments
will so fully reveal the general nature of ~he invention
lQ that others can, by applying current knowledge, readily
modify and/or adapt for various applications such sp1ecific
embodiments without departing from the engineering concept
and, therefore, such adaptations and modifications should
and are intended to be comprehended within the meaning and
range of equivalents of the disclosed embodiments. It is
to be understood that the phraseology or terminology
employed herein is for the purposes of description and not
of limitation.
-36-
