Note: Descriptions are shown in the official language in which they were submitted.
` ` ~ ;2~5~36~
The present invention relates to laminates and, more particulnrly,
decorative laminates of high abrasion resistance.
High pressure decorative laminates are conventionally produced by stacking
and curlng under heat and pressure a plurality of layers Df paper lmpre~nated
with various synthetic thermosetting resins. In norm~l practice the assembly,
from the bottom up, consists of a plurality, e.~. three to eight, core shaets
made from phenolic resin impregnated kraft paper, above which lies a pattern
or print sheet impregnated with melnmine resin; on top of the print sheet is
provided an overlay sheet which, in the laminate, is almost trnnsparent and
provides protection for the pattern sheet.
The core sheets are conventionally made from kraft paper of about 90-125
pound ream weight. Ream weight ls the weight per ream (S00 sheets) of paper
having a sheet size of 24 x 36 inches; thus ream weight is pounds per 3000 sg.
ft. of paper.
Prior to stackin~, the kraft paper is impregnsted with a water-alcohol
solution of phenol-formaldehyde resole resin, dried and partially cured in a
hot air oven, Qnd finally cut into sheets. The print sheet is a high quallty,
50-125 lb. ream weight, pigment filled, alpha cellulose paper that has been
impregnated with a water-alcohol solution of melamine-formaldehyde resin,
drisd and partially cured, and finally cut into sheets. The print sheet,
prior to impregnstion with the resin, usually has been printed with a
deGorative design, or with a photogravure reproduction of natural materials,
such as wood, marble, leather, etc.
~ n overlay sheet is almost invariably used when the print or pattern sheet
has A surface printing in order to protect the printing from abrasive wear.
The overla~ sheet i6 a high quality alpha cellulose paper of about 20-30
pounds ream weight that is also impresnated with melamine-formaldehyde resin
in a manner similar to that used for tha print sheet, e~cept that a 8reater
amount of resin per unit waight of paper is used. The individual sheets are
stacked in the manner indicated above and, if si~ sheets of impragnated core
paper are used, there results a finished laminate having a thickness of about
S0 mils, it being understood that a dieferent number of sheets can be used to
provide thicker or thinner laminates.
The stack of sheets as described abova is placed between polished steel
plates and subjected to about 230-340 F (e.g. 300 F) at 800-1600 p.s.i.
9686-1
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5~
(~.g. 1000 p.s.i.) for a time sufficient to consolidate the l~inate and cure
the resins (e.g. about twenty-five minutes~. 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 pressed back to back, separated by a coated
release sheet that allows the two laminates to be peeled apart after
separation. Also, a large proportion of the stacks are laminated with an
aluminum foil-kraft paper composite shee~ inserted between the overlay and the
metal plate, with the sluminum facing the overlay, in order to obtain a
laminate having a lower gloss and a slightly textured surface which is
desirable for some products.
At the completion of the laminating oper~tion, the backs of the laminates
are sanded to permit gluing to particle board, plywood or other substrates.
The glued, l~minate surfaced panel is then fabricated into furniture, kitchen
counter tops, table tops, store fi~tures and other end-use applications widely
accepted for the combin~tion of appearance, durability and econ~my.
A number of VQriatiOnS of the above-described general process are ~nown,
particularly those operations designed to obtain special effects in appearance
and te2ture. Also other curing cycles are possible and, in fact, sometimeg
other resin systems are used as well.
Besides decorative high-pressure laminates referred to above, there are
also a number of low-pressure products which have been developed in recent
years, including low-pressure laminates using either sntur~ted polyester
resins, or melamine-formaldehyde resin. One of the fastest growing materials
competin~ with high-pressure laminates in recent years is a product referred
to as low-pressure melamine board which is normally pressed in a short cycle
at 175-225 p.s.i. at 325-350 F. These low-pressure products have the
advantage of bein~ normally less e~pensive, but they cannot be given the title
of "high pressure laminates" because in order to be entitled 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, impact
resistance, dimensional stability, etc. While various other decorative
printed, surfacing materials, such as some of the low-pressure laminates, have
certain of the desirable characteristicsl no products other than high-pressure
9686-1
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`\ ~ s
lamiaates currently available have all of these properties.
One of these properties in particular which i5 Yery important is abrasion
r~sistance. A high-pressure decorative laminate must have sufficient abraslon
resistanee to permit use in high exposure areas such as dinette surface tops,
check-out counters~ etc. The standard NEMA test for abrasion resistance is
NEMA test LD-3.01. In this test a laminate sample is clamped on a rotating
disc, over which ride two weighted rubber wheels, faced with calibrated
sandpaper strips. As the laminate surface is rotated under the wheels, the
abrssive action of the sandpaper cuts through the surface of the laminate and
gradually throu&h the overlay until the printed pattern is exposed and
destroyed. The NEHA standard for Class I laminate requires that the laminate,
after 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 os pattern sheet, but
without an overlay sheet, the abrasion resistance will be only about 50-75
cycles. If speciall~ formulated melamine resins are used in the pattern sheet
with a resin content of 50-55%, abrasion resistance of up to abo~t 150-200
cycles are on occssion obtainable without ~n overlay sheet, but in this latter
case tha laminates have a tendency to develop surface craze and, furthsrmore,
they ~re quite difficult to prepare due to the difficulty of impregnating the
print sheet in a uniform manner; additionally, 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 characteristics of a
laminate using an overlay, and, in particular, one that provides a 400 cycle
abrasion resistance. Further~ore, it is desirable to provide a laminate
which, in addition to having the 400 cycle abrasion resistance, has an initial
wear point at least equal to the initial wear point of a conventional
high-pressure laminate having overlay, typically 175-200 cycles. This is
desirable because in actual use the laminate appearance becomes unsatisfactory
not when 50~ of the pattern is destroyed, but when a much lower psrcentage is
destroy~d. It is well known from many years of field experience that
96~6-1
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~2~ 5
conventional laminates with overlay, which have 175-200 cycle initial wear
point, when used in hard use areas, will have a ~atisfactory appearance, at
lea~t as long as the norm~l replacement cycle, it being understood that
replacement of most lam;nQtes in commercial uses is made for style reasons
rather thnn because of pattern wear. Therefore, a laminate ~ithout overlay
should meet these same criteria, namely it should have both a NEMA abraslon
resistance of at least 400 cycles and an initial wear point in the same tast
of at least 175-200 cycles, even though the latter requirement is not part of
the NEHA standard.
It is desirable to be able to provide these characteristics, but without
using an ovarlay, for several reasons:
1. Overlay adds substantial raw material costs to the manufacture of
laminates, both the cost of the overlay paper itself, the cost of tha resin
used to impregnate the overlay paper and the in-process and handling losses oP
these materials.
2. The overlay, by imposing an intermediate layer of substantial
thickness between the print sheet and the eyes of the viewer, detracts
significQntly from the desired visual clarity of the pattern. The cellslose
fibers used to make overlay paper have a refractive inde~ close to that of
cured melamine-formaldehyde resin. The fibers are therefore almost invi3ibl~
in the cured l~minate, and permit the printed pattern to be seen with vary
little attenuation. However, modern printing techniques are making available
vsrg accurate reproductions of natural materials, particularly various wood
veneer species. As these printed reproductions approach in appearance the
natural veneer, even small amounts of haze or blur introduced by the overlay
pRper are disturbing visually and destroy much of the realism desired by the
user .
3. Furthermore, the overlay contributes to the rejection rate of tha
laminate products produced. The impregnated, dry overlay sheet tends to
attract small dirt particles because it develops static electricity charges
during drying. This dirt is hard to detect and remove before laminating, and
results in spoiled laminate sheets that cannot be reprocessed. In addition,
the impregnated dried overlay is brittle and hQrd to handle without breakage.
Broken pieces are accidentally trapped on the surface of the overlay and also
result in visually defective sheets.
9686-1
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.$
Additionally, overlay containing laminate, particularly those having A
relatively high surf~ce gloss, have a tendency to become dull very quickly
when subjected even to only moderate abrasive wear. This is understandably
unacceptable where glossy laminates are desired.
The problem of providing improved abrasion resistance has been a
long-standing problem in the field. Many solutions to the problem have been
su~gested and, in fact, some of these have reached commercial development.
Nevertheless, it has not heretofore been possible to provide a laminate, not
having an overlay sheet, but h~ving 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 i8 well known that small, hard mineral particles dispersed in overlay
paper, or in resin mixtures to cost the impregnated pattern sheet, csn enhance
the nbrasion resistance of hi~h-pressure laminates (see, for example, the
patents to ~ichl, 3,135,643; Fuerst 3,373,071 and Fuerst 3,373,070).
Techniques such ~s these do not eliminate the ovarlay, but either enhance its
abrasion resistance, or provide an alternate form of overlay and associated
resin.
For e~ample in the Barna patent 3,123,515, the overlay sheet is
impregnated with a finely divided frit. The overlay is used in the normal
manner by placing it over the print or pattern sheet.
Another technique is that disclosed in the L~ne et al paten~ 3,798,111 in
which there is disclosed the use of smA11 mineral particles, preferably
alumina, which are incorpor~ted within and near the upper layer of the base
paper during its m~nufacture. In tests, it has been shown thst laminates made
with the print paper of Lane et al, without overlay, hnd initial wear values
of under 100 cycles, some as low as 35 cycles. Furthermore in a rubbing test
to determine initial wear, such laminates be~an to show pattern destruction
after only 3~000 rub cycleE, far less than necessary.
Oth~r prior art patents of some interest with regard to the background of
the present invention are the patents to Fuerst 3,445,327; Gibbons 3,928,706
~nd Merriam 3,661,673. Of somewhat less interest are the Battista patents
3,259,537 and 3,157,518; Ando et al 3,716,440; Power et al 3,946,137 and
soeni~ 3,318,760.
Even after the considerable activity in the field in order to solve the
problems indicated ~bove, these problems have not been solved until the
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present time.
The prasent invention provides d method of producing an abrasion resistant
decorative laminate from at least one backing layer and a thermo~etting resln
impregnated decorntive facing sheet, said laminate having enhanced abrasion
resistance without an overlay layer, the method comprising:
coating a decorative facing sheet with an ultra-thin wet layer of a
mixture of ~l) an abrasion resistant mineral of fine particle size in a
quantity sufficien~ to provide an abrasion resistant layes without interferinB
with visibility and (2) a stabilizine binder material for the mineral having
the properties of withstanding the subsequent laminating conditions and being
compatible with the thermcsetting resin, the binder beine present in an amount
sufficient to bind said abrasion resistant mineral to the surface of said
decorative facing sheet, and the binder-mineral layer in the dry state bein~
permeable to said thermosetting resin;
drying said coated binder-mineral mixture at a temperature sufficient to
enhance the bonding of said abrasion resistant mineral by said binder material
to said decorative facing sheet, to provide an ultra-thin dry porous layer of
said binder-mineral mixture thereon;
impreenating said coated facing sheet with said thermosetting resin;
assembling said resin impregnated and coated facing sheet over said
backin~ layer; and
subjecting said assembly to heat and pressure sufficient to effect
consolidation of said backing layer aDd s~id facing sheet to thereby provide
said abrasion resistant decorative laminate.
Also provided is an abrasion resistant decorative laminate meeting NEHA
abrasion resistance standards and also capable of withstanding 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, the decorative facing sheet having an
ultra-thin, abrasion resistant coating over the upper surace thereof, sald
ultra-thin, abrasion resistant coating comprising a mi~ture of (1) an abrasion
resistant mineral in fine particle size and quantity sufficient to provide for
abrasion resistance without int~rferinB with visibility and (2) a stabilizin~
binder material for the mineral which binder is compatible with the thermoset
resin impregnated throughout said facing sheet, the binder not interferinB
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with visibility, and wlth the ultra-thin, abrasion resistant co~ting forming
the uppermost layer of the laminate.
These products of the invention nre attained by coatin~ conventional
printed or otherwise decorated pattern paper with an ultra-thin coating
containing small mineral particles immobilized in place on the paper shest by
a suitable binder, and wherein such sheet is then impregnated ln the normal
manner with a suitable thermosetting resin such as melamine resin, and then
using the sheet in the production of decorative laminates without an overlay
sheet. It should be noted that both solid coloured and patterned decorative
sheets or print sheets are envisaged for use in the present invention.
In another aspect, the invention provides a decorative sheet for use in
the preparation of decorative laminates of high abrasion resistance comprisin~
a decorative paper sheet, the surface of which has an ultra-thin, abrasion
resistant porous coating which comprises (1) an abrasion resistant hard
mineral of fine particle size in a quantity sufficient to provide abrasion
resistance without interfering with visibility snd (2) a binder material for
said mineral compatible with a thermosettable laminating resin selected from
melamine-formaldehyde resin and polyester resin; the coated substrate being
impregnable with said laminatin~ resin and the binder material being present
in an amount sufficient to bind and stabilize said abrasion reslstant mineral
to the surface of said decorative paper sheet substrQte.
Also provided is a method of producing a decorative sheet comprising:
praviding a tecorative sheet havin~ a decorative fncin~ and formed of B
porous material;
coatinS said decorative sheet with an ultra-thin wet layer of a mixture of
(1) an abrasion resistant hard mineral of particle si~e 20-50 microns in
quantities sufficient to provide an abrasion resistant layer without
interferlng w;th visibility, and (2) binder material for said mineral, which
binder material has the properties of beine capable of withstanding heat and
pressure, and being compatible with a thermosettable resin, said binder being
present in an amount sufficient to bind said abrasion resistant mineral to the
surface of said decorative sheet, and the binder-mineral layer in the dry
state being permeable to said thermosettable resin;
drying said coated binder-mineral material mixture at a temperature
sufficient to enhance the bonding of said abrasion resistant nineral by said
9686-1
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binder material to s~id decorative sheet, to provide a porous, ultra-thin, dry
layer of said binder-mineral mixture thereon.
In one of its most preferred for~s, the invention provides an abrasion
resistant ds~orative laminate having superior NEMA abrhsion resistance,
superior initial wear resistance in the same test, and superior wear
resistance in the Sliding Can Test comprising:
a backine layer and laminated thereto a thermoset laminating resin
impregnated decorative facin~ sheet, said decorative facing sheet having an
ultra-thin abrasion resistant coating thereo~er, said ultra-thin abrasion
resistant coating having a thickness of up to about 0.3 mils comprising a
mi~ture of (1) an abrasion resistant hard mineral of particle size 20-50
microns in high concentration sufficient to provide for abrasion resistance
without interering with visibility, and (2~ stabilizing binder materi~l for
said mineral, said thermoget resin being impregnated throu~hout said
decorative sheet and said coating, said binder material not interfering with
visibility, and with said ultra-thin abrasion resistant coating forming the
uppermost layer of said laminate.
The above and other advantages of the instant invention will be more
apparent from the following detailed description of embodiments taken in
conjunction with the drawin~ wherein:
~ ig. 1 is a ~low-diagram showing a method of preparing a print layer in
accordance with the present invention;
Fig. 2 is a ichematic sectional view showing an embodiment of the print
sheet in accordnnce with the present invention; and
Fig. 3 is a schematic sectional view showine a laminate in accordance with
the present invention.
There has now been discovered a novel composition, containing small
mineral p~rticles, which when coated without resin over unimpregnated printed
pattern psper, 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. In its preferred form, the conting composition is composed of a
mixture of small particles of alumina and a less0r amount of microcrystalline
cellulose particles, both dispersed in a stable, aqueous slurry. The
particles of alumina, of small size such that they do not interfere with the
9686-1
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~2~5~6~i
visual effects in the fin~l product, serve as the abr~sion resistant material
and the microcrystalline cellulose particles BerVe as the preferred binder.
It will be understood that th0 binder must be ~ompatible with the resin system
layer utilized in the laminsting procedure, usuQlly a melamine resin or in the
case of certain ~ow-pre~sure laminates a polyester resin system9 and the
microcrystalline cellulose serves this function as well as stabilizing the
small particles of alumina on the surface of the print sheet.
With reference to Fig. 1, in the pr~ferred operation a conventional
unimpregnated print or pattern pBper is coated with the mi~ture of h&rd
mineral particles and binder, preferably alumina and microcrystallin0
cellulose particles in a stable, aqueous slurry, and the coating is dried at
an elevated temperature, such ~s in a hot-air ovsn, to produce a thin coating
only 0.02 to 0.3 mils thick. The resultant abrasion resistant coated p~per
(Fig. 2) is then impregnated with the melamine or polyest~r resin and dried in
a conventional way, at which point it is ready for the laminating procedure.
With reference to Fig. 3, it is seen that the abrasion resistant rcsin
impregnated print sheet, having an ultra-thin abraeive resistant coating on
its upper surface, is ~ssembled for the laminating step in the conventional
w&y, except that no overlay sheet is used. The laminate is then cured under
heat and pressure in the conventional manner. A surprising characteristic of
the ultra-thin coating is that even thoueh it is so thin, it can provide
~brasion resistance in the finished laminate not only meeting 400 cycles NEMA
Standard, but also providing an initial wear point in sxcess of 175 200 cycles.
It is also surpriYing that this coating tightly adheres to the surf~ce of
the printed paper when the paper is later impregnated with melamine resin,
without significant amounts of the mineral particles either being lost in the
impregnating solution or migrating away from the surface of the paper. A
further surprising characteristic of this coating is that it does not appear
to hinder the penetration of the melamine-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 desirnble
characteristic of the coating is that it does not significantly scatter or
attenuate light, resulting in very clear, crisp appear~nce of the p~ttern in
the finished laminate.
9686-1
_ 9 _
Without being bound to the followin~ theory, it i5 believed that the
improved chPracteristics of the invention can be accounted for ns follows:
~icrocrystslline cellulose particles contain very large external forces that
bind to other polar substance , such as cellulose and alumina. Thus, an
aqueous slurry of microcrystQlline cellulose and alumina is stable ~nd does
not quickly settle out, even though alumina particles in water sre not
stable. Furthermore, when this slurry is coated on the paper, the
microcrystalline cellulose apparently binds the alumina partlcles to the
surface fibers of the paper, and to the top of the ink pattern, preventing
migration of the alumina particles to below the surface. This may account for
the good abrasion resistance developed by such small quantities of alumina.
Thus, all or substantially all of the alumina particles stay at the surface
where they do the most good, rather than becoming dispersed below the surface
where they would contribute relatively little initial wear resistance.
As indicated above, the preferred slurry composition contains a mixture of
~mall particles of alumina and a lesser amount of microcrystslline 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
abrnsion resistance as discussed above, and there must be an smount sufficient
20 of the binder to retain the mineral particles in place on the surface of the
print sheet. 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 rnnge but there is no ad~antage doing so and, furthermore, the
handling problems become quite complicated. The quantity of water in the
slurry is also dict~ted by practical considerations, since if there is too
little water the slurry becomes so thick that it is hard to apply; similarly,
if there i5 too much water the slurry becomas so thin that it is difficult to
maintain a consistent thlckness during the coating operation due to running of
the slurry. ~hus, a slurry containing about 2.0 wt.% microcrystalline
cellulose and about 24 wt.% alumina, based on the water, is stable, i.e. the
alumina does not settle out; but if more than about 3.5 wt.% microcrystalline
cellulose and about 24 wt.% alumina, based on the water, is used, the slurry
becomes ~ery thixotropic and difficult to apply.
The composition also preferable contains a sm~ll amount of wetting agent,
9686-1
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5~
pLeferably a non-ionic wetting agent, snd a silane. The quantity of wetting
agent is not critical, but only Q very small amount i~ desirable and excess
quantlties provide no advanta~e. ~f a sllane is used, it acts R5 a ~ouplln~
agent which chemically binds alumina 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 ~ddition to being
mechanically bound thereto and therefore stay in place longer under abrasive
wear. The silane should be selected from among the group making it compatlble
with the particular thermosetting laminating resin used; in this r~gard
silanes having an amino group, such as gamm~-aminopropyl trimethoxy silane,
are particularly effective for use with melamine resins. The quantity of
silane used need not be grest and, in fact, as little as 0.5~ based on the
weight of the alumina is effective to enhance the abrasion resistanse of the
final laminate; a maximum quantity of about Z% by weight based on the weight
of the alumina is suggested since greater quantities do not lead to ~ny
significantly better results and merely increase the cost of the raw materials.
It is an important feature of the present invention that the coating using
microcrystalline cellulose as the binder must be dried at an elevated
tamperature before the print sheet is impregnated with the melamine resin.
Thus, a minimum drying temperature is about 180 F and th~ preferred drying
temperatures are from 240-270 F.
With regard to the abrasion resistant mineral particles, aluminQ is the
preferred material. Silica, which has been suggested in certain prior art
patents as an abrasion resistant material, provides considerably inferior
results in the present invention compared with alumina. Other minerals of
sufficient hardness such as zirconium oxide, cerium oxide, diamond dust, etc.
can work, but are either too expensive for practical 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 axcessive color shift.
An important feature i5 the size of the alumina particles. Beneath 20
micron particle size, abrasion resistance becomes poor, ~nd the pr~ferr~d
minimum particle size is about 25 microns. Maximum particle size is limited
by surface roughness in the article and interference with visual effects. The
preferred maximum size of the alumina particles is about 50 microns.
9686-1
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It should be understood that acceptable products and methods of the
invention which fall outside this particle size rangs can be obtained. It is
possible to employ particles which ~re below the 20 micron particle size.
Although particles as small as 9 microns have proven unsatisfactory, this is
particularly so when the decorative sheet substrate is a solid color as
opposed to one with a printed pattern. The major improvement in abrasion
resistance for such products is observed in the sliding can test. Abrasion
resistant mineral particles of size somewhat below 20 microns ~ill give
satisfactory results for this test.
1~ 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. ~he
binder must serve not only to maintain the mineral particles in position on
the surface of the print sheet, but should also act as a suspending agent in
the slurry (otherwise, it would be necessary to add an additional suspendin~
agent). The peculiar property of microcrystalline cellulsse is thst it acts
like a typical suspending binding agent 6nd film former, but unlike other
a~ents is not water soluble before 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 microcrystallin0
cellulose is compatible with both melamine resin and polyester resins.
Furthermore, lt must not scatter or attenuate light in the thicknesses applied
in the final laminate, and microcrystalline cellulose is s~tisfactory in this
regard as well.
Other binders whach may be used, but which provide inferior results
compared with microcrystalline cellulose, aLe various typical
su6pending-binding agents including anionic acrylic polymer, carboxymethyl-
cellulose and similar materials such as hydroxypropyl cellulose,
methylcellulose, polyvinyl alcohol, polyvinyl pyrrolidone, etc. However, as
indicated above, microcryst~lline cellulose is by far 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. ~icrocrystalline cellulose is
available under the trade mark "AVICEL", the preparation of which is disclosed
9686-1
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~L2~5~
in the Battists patent No. 3,275,580. AVICEL Type ~C 581 is a white, odorless
hy~roscropic powder. It is wQter dispersible and cont~ins about 11% sodi~
csrboxrmethyl-cellulose as a protective colloid. Its particle size is less
than 0.1% on a 60 mesb screen.
Features and Qdvantages of the instant invention which are considered to
be particularly significant are as follows:
~ 1) The mixture of alumina particles and microcrystalline cellulose is
deposited from a water slurry, rather than used as fillers in a resin solution.
(2) Such slurry is coated on an unimpregnated printed pattern sheet,
rather t~an on an impregnated pattern sheet.
(3) The coating is dried at an elevated temperature of at least about
180F .
(4) The coating thickness is 0.02-0.2 mil5, rather than 1-2 mils.
(5) After applying the coating and drying it, the pattern sheet is then
impregnated with the thermosetting resin, and this conventional impre~nation
of the pattern sheet is carried out on conventional eguipment, rather than
special, difficult to control, coating of a thick slurry.
(6) The ultra-thin layer provides une~pectedly high abrasion resistance.
The desirable characteristics of the alumina particle binding agent, which
characteristics are all ~et by microcrystalline cellulose, are: It acts as a
film former; it acts as a binding agent for the ~ineral pRrticles; it ~cts as
a ~uspending agent in the slurry for the mineral particles; it is not washed
off durin~ the subse~uent thermosetting resin impregnating process; it is
compatible with the subsequently applied thermosettin~ resin, such as melamlne
resin or polyester resin; it is permeable to the thermosetting impregnQting
resin (indeed microcrystalline cellulose forms a porous film); it is resistant
to the heat generated during the laminating procedure; Qnd it does not scatter
or attenuate li~ht in the laminate.
The following examples are offered illustratively:
FXA~PLE I
Microcrystalline cellulose (A~ICEL RC 581) was added to stlrred water in a
WaringX blender. After 2 to 3 minutes in the blender, the AVICEL was
completely dispersed and the aluminum oxide (Microgrit* WCA) WQS fiently
stirred in. Finally, three drops of TRITON~ X-100 (a non-ionic detergent) was
added to promote wetting.
9686-1
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Trade Mar~
L~ 59 ~ S
The resultant slurry was applied as a coating to a 65 lb./ream (3000
ft. ~ unimpregnated patterD sheet havin~ a wood~rain surf~ce print. The
coatin~ was dried at 265 F for 3 minutes. The paper was then satur~ted in
th0 normal way using melamine-formaldehyde resin and was dried in accordance
with normal procedures. The resin content w8s 45-48% and the volatile content
was 5~6%. The laminate was made up and pressed usin~ a conventional general
purpose cycle, viz. about 300 F, lOOO p.s.i., for about 25 minutes.
Formulations and abrasion results are listed below for a 1.5 mil wet
coating, which calculates to a 0.15 mil thick dry coat.
TA8LE 1
l 2 3 4 5 6 7
_
Water tml) - 250 250 250 250 250 250
AVICEL RC 581 - 6.5 7.5 7.5 7.5 7.5 7.5
~quantity in gms.)
~ICROGRIT WCA - - 30 30 30 60 60
~quantity in gms.)
MICROGRIT WCA - - 20 30 40 9 30
~particle size in
microns)
Abrasion cycles, 2540 lOO 400 475 75 500
Initial ~ear
Pattern Destruotion,
% Qt 500 cycles ~00% 100% 20% 5% 2% 95~ 0%
In the above Table, ~ICROGRIT WCA is sluminum 02ide lapping powder
manufactured by Micro Abrasives Corporation of Westeield, Hassachusetts.
From the above comparative trials, it is seen that the microcrystalline
cellulose by itself was not satisfactory (trial 2); and that the use of
alumina havin~ a particle size less than 20 microns did not give good rQsults
(trial 6). It is seen that MICROG~IT alumina above 20 micron average psrticle
size provided both satisfactory initial wear, and NEMA wear resistance. In
addition, the resulting laminates had clearer pattern appearance than
conventional laminates having overlay sheets, and such laminates also passed
the other NEMA durability tests.
EXAM_LE II
Four slurries were prepared as in Example I, trial #3. Each was used to
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5~5
coat 3 mils wet onto 65 lb. unimpregnated paper, and dried as in Example I to
provide 8 dry coating thickness of ~pproximately 0.3 mil. The dried paper wa~
impregnated with melamine resin and assembled in a laminate stack as shown in
Fig. 2. Lamination was carried out as described in Example I. The only
varistion in the four trials was the av~rage particle size of the al~mina.
Results were as follows:
TABLE 2
MICR0GRIT ~vera~,e Particle Size Pattern Destruction at 500 CVC1QS
10 30
9 70%
EXAMPLE III
Example II was repeated in three trials, in each case using alumina
particles having an average particle size of 40 microns. The only variation
wa5 in the wet coating thickness. Laminates were compared as in Example II.
The results were:
TABLE 3
Wet Coatin~ ThicknessPattern Destruction at 500 Cvcles
203 mils (0.3 mil dry) 1%
2 mils (0.2 mil dry) 10~
1 mil (~.1 mil dry) 30%
EXA~PLE IV
The procedure of Example I was repeated using as a coating slurry for the
print sheet the following composition:
250 ml. water;
7.5 gms. microcrystalline cellulose;
60 ~ms. of alumina of average particle size 40 microns; and
1 drop of TRITON X-100.
Two trials were carried out providing wet thicknesses of 1 and 2 mils,
respectively. After lamination, abrasion testing produced no initial pattern
destruction at 500 cycles.
EXANPLE V
The procedure of Example IV was repeated using the same coatin~
composition, except that 120 gms. of alumina having an average particle size
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of 30 microns wns used. Three trials were run with wet costings of 1/2, 1 and
1.5 mils, respectiuely. Abrasion resistancs of the final laminate after 500
cycles gave the following results:
TA~LE 4
1/2 mil (.05 mil dry) 10% pattern destruction
1 mil (.1 mil dry~ 1~ pattern destruction
1.5 mil ~.15 mil dry) 1~ pattern destr~ction
The three laminates were highly satisPsctory in all other respects.
~achinability was goot with no chipping.
The physical properties of the third sample (prepared with 0.1 mil coated
paper) tested in accordance with NEMA Standard LD3-1975, after impregnation
and pres~ing, were as follows:
TABLE 5
Wear resistance 500 cycles
Stain resistance No effect
~oisture ~b~orption 6.5%
Center Swell 8.9%
Impact (unsupported) 36"
Radiant Heat (unsupported) 185 seconds
Hot Water No effect
~ot wax No effect
Dimensionnl stability ~.D. 0.24%
C.D. 0.56%
These are all satisfactory or superior -~alues.
EXAMPLE VI
Example IV was repeated in two trials using the same composition, except
that in the first trial 60 gms. of HICROGaIT SIC 400 (27 micron silicon
carbide) was substituted for the alumina and in the second trial 60 gms. of
MICROGRIT SIC 1000 (10 micron silicon carbide) was substituted for the
alumina. For each composition, coatings were deposited at 1/2, 1 and 1.5 mils
wet. The print sheet had a generally "gray" color due to the color of the
silicon carbide. Results were as follows:
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TABLE 6
Coat~n~~ Pattern De~truction at 500 Cycles
SIC 400 SIC 1000
1~2 ~0.5 mil dry) 20 85
1 (.1 mil dry) 5 80
1.5 (.15 mil dry) 5 70
As c~n be seen, while abrasion ~esistance was satisfactory, the 10 micron
silicon carbide gave poorer results than the 27 micron silicon carbide. The
poor color can be tolerated in only certain colors of print paper.
E~AMPLE YII
E~ample IV was again repeat0d with three compositions, this time
substituting 60 gms. of glass spheres (-3Z5 screen size) 9 240 gms. of such
glass sphares and 60 gms. of CABOSIL~ L-5 ~silica aerosil of millimicron
particle size), respectively, in place of the alumina particles. Each
composition was coated at lt2, 1 and 1.5 ~ils wet. The results were as
follows:
TABL~ 7
TYPE FULLY WOaN ON TABE:R*
~0 g glass 200 cycles
240 g glass 290 cycles
60 ~ Silica Aerosil 100 cycles
~The device ~or testing Rbrasion resistance described at pages 4 and 5 is
~nown as a Tabe~ abrader.
None of these samples gave sutisfactory abrasion resistance.
EXAMPLE VIII
The procedure of Example IV ~ras again repeated except that this time the
coating composition was modified in one sample by the substitution of 6 gms.
of an anionic acrylic polymer (aETENE* 420 - Hercules Powder Company) in place
of the microcrystalline cellulose, and in a second sample by 9 gms. of
carboxymethyl-cellulose in place of the microcrystalline cellulose. For both
samples, the Taber abrasion test showed about 5% wear at 500 cycles, a
satisfactory performance, however, the anionic acrylic polymer caused slight
milkiness in the laminate indicuting that the use of this material would be
satisfactory for only certain colors. The laminate in which
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Trade Mark
~2~
carboxymethyl-cellulose had been used as the binding sgent for the slumina
had A poor boiling water resistance and could not meet the NEMA Standard in
this re~ard; this material could only b0 used on certain lower grade low
pressure laminates.
E~A~PL~ I~
In order to investi~ate the effects of silanes, the following procedure
was carried out. One ~r~m of ~amma-amino propyltrimethoxy silane was mixed
with a 10% water-90~ methanol solution until dispersed; a minimum qusntity of
liquid is used sufficient to wet the al~mina powder. This dispersion was then
added to 100 gms. of alumina of 30 micron size (MICROGRIT WCA 30) and the
alumina was mixed with the solution until thoroughly wetted. The alumina was
then dried. E~ample IV was repeated e~cept that the coating was appli~d to
the print sheet in a 1/4 mil thick wet coatin~ (0.025 mils dried). The
resultant laminate was compared to laminates prepared in accordance with
e~ample IV (without the silane) also applied at a thickness of 1/4 mil wet.
All laminates were pressed to a mirror finish. The results of the abrasion
resistant tests are set forth in Table 8 below:
TABLE 8
No Silane Silane
Initial ~ear (cycles~ 300 525
Finsl Wear ~cycles) 1075 1250
Wear ~alue 687 8B7
It is seen from the above results that the silane improvad the efficiency
of the abrasion resistant coating.
EXAMPLE X
The present invention was tested to determine its efficacy in upgrading
the performance of low pressure board. A slurry was prepared as in Example I
with 250 gms. water, 6.5 gms. of microcrystalline cellulose, 30 gms. of
alumina of 30 micron size and 2 drops of TRITON X-100. The slurry was coated
in lt2 mil wet layer (.05 mil dry) onto unimpregnated printed pattern paper,
and dried for 3 minutes at 260F. The sheet was then impregnated and dried
twice to ensure complete impregnation. The impregnated sheet was then placed
over a wood particle panel and was pressed at 200 p.s.i. at 300F for 6
minutes. As a comparison, an otherwise identical low pressure laminnte was
made without providing the abrasion resistant coating on the top surface of
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~.2gL~
the print sheet. Both samples were subjected to the NEMA Rbrasion Test and
the results were as follows:
TA8LE 9
Abrasion Resistant Coatin~ No Coatin~
Initial Wear 200 Cycles nil
NEHA Abrasion1050 Cycles 150-200 cycles
From the above tests as tabulated in Table 9, it is seen that the present
invention vastly improves the abrasion resistance of low pressure laminates ns
w~ll.
E~AMPLE XI
The procedure of Example IX was repPated and the coatings were applied at
a thickness of 1-1/2 mils wet (0.15 mil dry). Four trials were run with the
quantity of silane being varied, and the resultant laminate subjected to the
NEHA Abrasion Test. The initial wear was recorded, results being ~iven in
Table 10 below.
TABLE 10
Quantity of Silane-
~ms./100 ~ms. alumina Initial Wear, CYcles
0 175
~ 475
3 510
6 400
The above tests show the effect of the silane is not substantially
enhanced after reaching a quantity of about 2 wt.~ based on the weight of the
alumina; and, in fact, in this particular test at 6~ silane, the results were
poorer than at 2~, although significantly better than the layer containing no
silane at Qll.
E~AMPLE XII
. _ _
The proccdure of Example IX was repeated to determine initial wear
resistance of the ~inal laminate as a function of the temperature used to dry
the coating applied over the print sheet. Thus, the pattern sheet was coated
with the coatinG composition of Example IV at a rate of 8-10 pounds per ream
(0.2 mils dry), except that the coating composition contained silane in
accordance with Example IX. The coatin~ was dried for 3 minutes in each
sample at the various temperatures given in Table 11 below. After drying the
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coated sheets were allowed to come to moisture equilibrium with room air at
50~ relative humidity at 70 F; the sheets were then impregnated as u~ual
with ~elamine-formaldehyde resin, and were then laminated i~ the usual way
n~sinst a satin finished plate. The results ~ere as follows:
TABLE 11
Oven TemPerature. Initial Wear, Crclss
160 225
180 550
200 550
240 575
2~5 575
EXAMPLE XIII
A slurry of in~redients was prepared as disclosed in ~xample I using 6.5
parts by weight of A~ICEL microcrystalline cellulose, 2 parts by weizht of
carbo~ymethyl-cellulose, 30 parts of 30-micron alu~ina, and 250 parts by
weight of water. A trace quantity of TRITON X-100 was added.
The resultant slurry WAS applied to print sheet using a ~eyer rod coating
machine at the rate of 5.5 pounds per ream (0.15 mil dry thic~ness). The
print paper was then impregnated with mel~mine-formaldehyde resin to pr~vide n
resin content of 41.7~, and drying was effected to provide a volatil2 content
of 4.2%. A l~minate was then pressed with the coated print paper using a
standard laminatin~ cycle and a mirror-finished laminating plate so that the
inal laminate had a gloss surface.
The laminate so produced was compared with another mirror-finished
laminate made in a conventional way usin~ a 20-pound overlay, both laminates
bein~ subjected to the "sliding can test", described infra. The laminate in
accordance with the present invention had an initial wear of 325 cycles and a
NEMA wear value of 1021 cycles. In the sliding csn rub test, the comparative
results were as follows:
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TABLE 1, ?
SURFACE DULLING
La~inate Made With
CYCLESConventional Overlay Laminate Coated Print Sheet
1500 slight no effect
3000 slight no effect
6000(~,radually worse) no effect
12000 slight
1018000
24000 extreme wear slight w0ar
Pattern destruction began at about 30,000 cycles on both samples, but it
i8 seen that the conventional laminate shows gradual surface dulling even at
only 1500 rub cycles and, in fact, ~radual surface dullin~ began almost with
the first few hundred rub cycles. Furthermore, the conventional laminate is
completely dulled w011 before initial pattern destruction t30,000 rub cycles).
Compared with the prior attempts, the present invention provides vnstly
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 the first time n laminate without an
overlay sheet has been made which is capable of meeting both the NEM~ Abrasion
~esistance Standard of at least 400 cycles, and an initial wear point in this
same test of at least 175-200 cycles.
There are many uses of laminates in which initial pattern wear rather than
NEMA wear value deter~ine the acceptable life of the surface. For example,
supermar~et check-out counters, food service counters, cafeteria tables, and
other commercial surfaces are exposed to abrasive rubbing and sliding o
un~lazed dinnerwear, canned goods, fiberglas tray~, etc. If small areas of
the pattern be~in to disnppear after a relatively short period of use,
particularly in an irregular pattern, the surface will be unacceptable to the
owner and will result in an expensive replacement. If the surface wears
gradually and evenly over a lon~, period of time, the wear out time exceeds the
normal replacement cycle duc to style chan~,es, approximately 3-5 years.
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