Note: Descriptions are shown in the official language in which they were submitted.
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RADIATION CURED COATING CONTAINING GLITTER
PARTICLES AMD PROCESS THEREFOR
Background of the Invention
Radiation curable coatlngs for use on a variety of sub-
qtrate~ and curable by exposure to ionizing irradiation or ultra-
violet light are well known. The use of urethane type coatings
cured with ultraviolet light to provide protective wear layers
for wall or floor tile is for in~tance described in ~.S. Pat.
No. 4,180,615. U.S. PatO No. 3,918,393 describes a method for
obtaining a non-glossy coating on various substrates by curing
radiation sensitive material with ionizing irradiation or ultra-
violet light in two ~tage~. In this process the coating is
partially cured in an oxygen~containing atmosphere and the curing
is comple~ed in an inert a~osphere. U.S. Pat. NoO 4,122.225
discloses a ~ethod and apparatus for coating tile which in.volves
the application of one coat of radiation curable material to
an entire Yubstrate followed by partial curing and the subse-
quent application and curing of a second coat of radiation
curable ~aterial only on high areas of the substrate which are
subject to greater than average wear.
Use of pigment in radiation cured coatings on products
such a~ floor covering which are subject to wear during us~ has
presented substantial difficulties. Incorporation of pigment,
especially enough pigment to make the coating opaque, ~akes the
coating hard to cure ana s~bstantially reduces the thicknesses of
coating which can be cured relative to a clear coating cured
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under the same conditions.
Summary of the Invention
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The product of the invention is a coated article com-
prising a substrate with two layers of radiation cured coa~ing
material adhered thereto. The first layer, which may be pigmented
or unpigmented, contains glitter particles which may be metallic
particles or flakes of synthetic material such as mylar, and i5
preferably between 0.01 and about 0.1 millimeter (mm) thick. The
second layer i9 preferably between about 0.01 and about 0.15 rnm
thick, of the same or a different radiation cured coating
material. In a preferred embodiment the coating layers comprise
urethane compound photo-polymerized from a fluid coating composi-
tion comprising at least two photo-polymerizable ethylenically
unsaturated groups of the general structure
R 0
"
H2C-C-C-
Where R is either H or CH3.
The proces~ of the invention is a method of forming
a radiation cured coating on a substrate comprising:
(a) applying to the substrate a first layer between
about 0.01 and about 0.1 mm thick of radiation curable
material containing glitter particles, and
(b) applying to the surface of the first layer
a second layer bet~een about 0.01 and about 0.15 mm
thick, of the same or a different radiation curable
material, and
(c) curing ~he coating.
The curing may be conducted in one stage after both
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c~ating layers are applied to the qub~trate, or may be conducted
in two stage~ as diqclosed in u.s.P. 4,326,001 and u.s.P.
4,439,480.
According to a bxoad aspectj thP invention relates
to a method of forming a radiation cured coating on a
substrate comprising:
(a) applying by roll coating to the substrate a
first layer between about 0.01 and about 0.1 mm
th.ick o~ radiation curable material containing
glitter particles in an amount of ~rom about 4
to 33.3% by weight of said first layer;
(b) applying by curtain coating to the surface of
the first layer an unpigmented second layer
between about 0.01 and about 0.15 mm thick of
the same or a different radiation curable
material in a wet-on-wet process; and
(c3 sub~ecting the first and second layers to
ionizing irradiation or ultraviolet light in an
inert atmosphere containing less than about
1,000 ppm oxygen in a one stage curing process
after both layers have been applied to the
substrate, to thereby cure the coating.
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Detailed Description of the Invention
The invention contemplates the formation of pigmented
radiation cured coatings on a wide variety of substrates in-
cluding such diverse materials aq wood, glas3, plastics, metals,
paper, etc. The invention has particular applicability to tiles
and decorative sheet covering material suitable for use on walls
and floors, especially vinyl tiles and sheet vinyl.
The process may either take place "on-line" by coating
and curing a sheet of conventional tile base which optionally may
have been embossed and/or printed, and then cutting the sheet
into tiles, or the process may be "off-line", the optionally em-
bossed and/or printed tile base being precut into tiles and then
coated and cured.
Radiation curable coatings suitable for use in the in-
vention may in general be selected from any of the coating
materials known to be suitable for curing with ionizing irradia-
tion or ultraviolet light. In this respect, ultraviolet light is
generally considered to be light having wavelengths in the range
from about 2500A to about 4000A. The term "ionizing irradia-
tion" is generally considered to include high energy radiation
and/or secondary energies resulting from conversion of electrons
or other particle energy to x-rays or gamma radiation. While
various types of ionizing irradiation are suitable, for instance
x-rays or gamma rays, the radiation produced by accelerated hiqh
energy electrons generally known as electron beam radiation, has
been found to be con~enient and economical and to give satisfac-
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tory results. Ionizing irradiation equivalent to at least about100,000 electron volts is generally satisfactory. Ultraviolet
light is, however, an especially preferred form of radiation for
use in the invention.
The first layer of coating, which is preferably ~etween
about 0.01 and about 0.1 mm thick, may be pigmented or unpig-
mented, in addition to containing glitter particles which may be
metallic flakes or synthetic glitter flakes, for example, mylar
flakes. Use of pigment in radiation cured coatings has, in
the past, presented substantial difficulties in curing, and has
limited the t:hickness of pigmented coatings which may be cured
with radiation compared with unpigmented coatings cured under the
same conditions. The use of metallic or synthetic glitter flakes
unexpectedly does not encounter the same problems, and the amount
of glitter flakes which may be added is limited by aesthetic and
aconomic factors, and not by curing ability. The second layer,
which is a clear wear layer, may be of the same or a different
composition from the first layer, but preferably does not contain
glitter particles.
The overail thickness of the two layers used is gener-
ally between about 0.01 and about 0.25 millimeters. With coatings
of such thickness, the total dosage of ionizing irradiation or
ultra-violet light is frequently between about 0.2 and about 30
megarads or more. In this respect a rad is defined as that amount
of radiation required to supply 100 ergs of energy per gram of
material treated, and a "megarad" is 106 rads.
In general, any radiation curable coatings may be used
in the invention, including tho~e disclosed in the above mentioned
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U.S. Pat. No. 3,918,393. Preferred coatings are, however, the
urethane coatings described in U.S. Pat. No. 4,180,615 wherein
the cured coating is formed from a fluid coating composition
comprising at least two photo-polymerizable ethylenically un-
saturated groups of the general structure:
R 0
"
H2C=C--C
Where R is either H or CH3
Any conventional coating method may be used to apply
coatings for use in the invention. Such conventional methods as
roll coating, spraying, dip coating, curtain coating, and the
like are, fo~ instance, suitable for both coatings with roll
coating being preferred for the first coating.
In one method of practicing the process of the inven-
tion, a first layer of radiation curable coating material con-
taining glitter flakes is coated onto the substrate, for example,
by roll coating, and partially cured by exposure to ionizing ir-
radiation or preferably ultraviolet light in an oxygen containing
atmosphere containing at least 5,000 ppm of oxygen. Air is, for
instance, a suitable atmosphere for only a partial cure in`the
sense that the curing is carried out only to the point where the
layer is at least gelled and optionally completely cured through-
out a portion of its thickness, but in any event only to the point
where at least the surface of the first layer remains partially
uncured and at least somewhat tacky. Curing of the surface of the
! first layer is completed at the same time as curing of the second
layer.
Following the application and partial curing of the
first layer of radiation curable coating ~aterial in an oxygen
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containing at~osphere, a second layer of the same or a different
coating is applied, fo~ example, by roll coating, to -the at least
partially uncured first layer and the entire coating, i.e., both
layers, is then subjected to complete curing in an inert atmos-
phere containing less than about 1,000 ppm oxygen and frequently
less than about 250 ppm oxygen. Gases such as nitrogen, helium,
etc. are for instance suitable for providing the inert atmosphere.
In an alternative method of practicing the invention,
the curing process takes place in one step only. According to
;this method, the first layer of glitter containing radiation
curable material is coated onto the tile by any suitable method,
e.g., roll coating. Then, without curing this layer, the second
layer of radiation curable material is coated on top of the first
layer in a wet-on-wet process, for example, by curtain coating,
and both layers of coating are cured together in an inert atmos-
phere containing less than about 1,000 ppm oxygen, as described
above.
If both layers are applied by roll coating, for example,
in an on-line process, then the material must be cured in two
steps, i.e., partially cured after the first layer is applied,
with the completion of the curing after the second layer is ap-
~plied. This is necessary because, if roll coating is used for
application of the second layer without having at least partially
cured the first layer, the second roll coating may contaminate
the surface of the first layer. If however, the second layer is
applied by curtain coating, or other method of coating which
allows a "wet-on-wet" second layer to be applied without contami-
nation of the surface of the first layer, then both layers may
be cured in a single curing step by subjecting the coating to
ionizing radiation or ultra-violet light in an inert atmosphere
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containing less than about 1000 ppm of oxygen until both layers
of the coating are completely cured.
This alternative method using a "wet-on-wet" coating
process may conveniently ~e carried out by coating pre-cut, op-
tionally printed and embossed, tiles in an "off-line" process
in which the production line, which may travel at speeds of 100-
120 ft/min for the roll coating step, is speeded up to 400-500
ft/min for the curtain coating, and then slowed again to 100-12
ft/min for the one-stage curing process.
For a better understanding of suitable substrates and
radiation curable coatings, as well as techniques for curing such
coatings and making the tiles having radiation cured coatings,
reference may be had to V.S. Pat. Nos. 3,91a,393, 4,122,225,
4,180,615 and 3,293,094.
Viscosity of radiation curable coatings used in the in-
vention may vary widely depending upon the particular coating
technique employed. In a preferred embodiment in which roll
coating is used, the viscosity is preferably between about 1,000
and about 5,000 centipoises (cp) at 77F. Increasing the percen-
tages of glitter particles in the coating materials incre~ses
the viscosity.
Variou~ conventional additives for radiation curable
coatings may of course be present in coatings of the invention.
These include such materials as fillers, dyes, thermoplastic
additives, plasticizers, synthetic resins, heat and light sta-
bilizers, photo-initiators, fillers such as carbon black, glass
fibers, silica, e!tc.
~ t has unexpectedly been found that flakes of glitter,
quch as meta~ or ~ylar, even up to 33.3~ by weight of the base
coating, may be incorporated into the polyurethane coating
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material without curing problems, though resin containing above
about 20% by weight of glitter flakes is harder to coat due to
its high viscosity. The flakes appear to reflect the ultra-
violet radiation, without substantially absorbing it, so that the
radiation is still available to function as a curing agent. Con-
ventional pigments and other additives may also be present in
coatings of the invention, as disclosed in U.S. Pats. 4,~39,~80
and 4,326,001, so that a floor tile of the invention may have
glitter fla~es embedded in a pigmented or unpigmented base layer,
without encountering curing problems. The second layer is pre-
;ferably a clear unpigmented wear layer either of the same or adifferent formulation as that used in the base coat, and prefer-
ably between about 0.01 and 0.15 mm thick.
The glitter flakes are preferably present in the first
layer only, the second layer of the coating acting as a protec~
tive wear layer.
Coating compositions for use in the invention are pre-
ferably substantially free of non-reactive solvent, i.e., contain
no more than about 5 wt% solvent. Total inactive ingredients,
such as the pigments, additives and non-reactive solvent mentioned
above, where used, are preferably present in amounts of no more
than 10 wt%, excluding the glitter flakes which may be present up
to 33.3% wt% of the first layer of coating but preferably up to
15 wt%.
Where the preferred urethane type coating compositions
described above are used and cured by ultraviolet radiation,
photosenitizers are generally employed in amounts between about
0.5 to about 5% by weight of the composition. Such preferred
compositions also preferably include one or more mono or di-
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functional vinyl monomers, copolymerizable under ultravioletradiation with the above indicated urethane compounds used in the
coating composition. The monomer must also be sufficiently stable
to prevent premature gellation or reaction with the urethane com-
pounds prior to exposure to ultraviolet light for curing of the
coating. If desired, small amounts of polymerization inhibitors
may be added for this purpose. Suitable monofunctional monomers
include, for instance, acrylates or methacrylates having the
formula:
R
..
H2C=C--C--O--R2
Where Rlis H or C'~3 and R2 is an alkyl or cycloalkyl group
having 6 to 1~ carbon atoms, a phenozylalkyl group of 6 to 18
carbons or hydroxyalkyl group. Suitable monomers are described
;in greater detail in the above-mentioned U.S. Pat. No. 4,180,615.
The following examples are intended to illustrate the
invention without limiting the scope thereof.
EXAMPLE 1
A clear acrylo-urethane (Glidden 879-C-576) coating was
tinted with 1% of a'matched pigmented dispersion of three indi-
vidual pigmented diqpersions. The matched color concentrate was
dark brown.
The tinted coating was fed into a first direct roll
coater. An untinted coating of the same composition as the
; tinted coating was fed into a second direct roll coater.
The substrate used was conventional tile base about 80
mils thick printed and embossed to look like a red brick pattern.
This substrate was then coated with the first coating, so that
all of the sheet was covered by the tinted coating with enough
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pressure to leave puddles in the embossed valleys but wiped off
the tops. The substrate temperature at the first roll coater
was about 160-170F.
The coated sheet was then passed under a first source
of UV radiation in an air atmosphere which cured the lower layers
of the tinted coating and partially cured the exposed surface of
the tinted coating, leaving it tacky so that when the sheet was
now passed through the second direct roll coater (which applied
about 2 mils of untinted coating) this coating adhered to it.
The sheet was next passed under a second source of UV radiation,
~bUt in a nitrogen inerted atmosphere, where both coatings applied
were completely cured.
The coated sheet was cut into tiles.
EXAMPLE 2
4~ (by weight) of a "glitter" product from Atlantic
Powdered Metal, Inc. (Non-Tarnish Sparkles-M~lar 0.004 inches
x .0005 inches) was blended into a clear acrylic-urethane coating
(Glidden 879-C-602).
This coating was fed into a direct roll coater.
The substrate used was a conventional tile base ~bout
80 mils thick, printed and embossed, and cut into tiles. The
tiles were coated with the "glitter'i containing coating, so that
the tile was coated in all areas including the embossed valleys.
The substrate temperature at the roll coater was about 150F.
The coated tile was then passed through a curtain
~coater where about 4 mils of the same coating, without the
;"glitter"~ was applied. The sheet was next passed under a source
of UV radiation in a nitrogen inerted atmosphere, where both
~coatings applied were completely cured.
The finished tile showed mylar glitter particles ran-
domly scattered over the printed tile base.
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EXAMPLE 3
The method of Example 2 was repeated, but in addition
to the 4~ "glitter", an organic pigment concentrate (yellow
12341 from Penn Color Corp) was also added in a 1~ (by weight)
quantity. The processing of the tile was exactly like that in
Example 2. The finished tile was yellow with glitter particles
scattered through the coating.
XAMPLE 4
The method of Example 2 was repeated, but using 16.7%
"glitter". The finished tile was similar to that produced by
Example 2, but had a more pronounced glitter effect on its sur-
face.
While the invention has been described above with res-
pect to certain embodiments thereof, it will be appreciated that
;various changes and modifications may be made without departing
from the spirit and scope of the invention.
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