Method for production of a coated substrate with controlled surface characteristics

A method for providing an abrasion-resistant, radiation-cured coating on a surface of a polymeric substrate is disclosed, as well as the article produced from the method. The uncured coating material is applied to the substrate, followed by the expulsion of air from the coating. The coating is then cured by directing the radiant energy through the substrate from the surface opposite the surface having the coating thereon to contact the radiation-curable coating.

BACKGROUND OF THE INVENTION 
This invention relates to a method for providing a coating on the surface 
of a polymeric substrate. More particularly, it relates to an improved 
method for providing an abrasion-resistant, radiation-cured coating on the 
surface of a polycarbonate substrate, and the article produced from the 
process. 
Polymeric substrates are often provided with protective coatings. When it 
is important that the substrate be transparent, it is generally also 
important that the coating exhibit high optical quality while also 
retaining its other physical attributes, such as abrasion resistance and 
high gloss. 
The coatings of the prior art are typically formed from various synthetic 
polymers and contain considerable amounts of volatile organic solvents 
which enhance the flow and leveling characteristics of the coating on the 
substrate. However, the inclusion of considerable amounts of volatile 
organic solvents creates several problems. First, the volatile material 
has to be eliminated from the cured coating so that it will not decrease 
the integrity of the coating. Therefore, expensive dryer systems have to 
be implemented to evaporate the solvents after the film is applied. 
Furthermore, other expensive equipment is required to remove the organic 
vapors from the work facility, and to comply with environmental 
requirements regarding atmospheric emissions and waste water disposal. 
Moreover, the presence of organic solvents creates-explosion and fire 
hazards which have to be eliminated through the use of additional safety 
equipment and explosion-proof facilities. Finally, the purchase of 
solvents as additional raw materials for the coatings represents a 
substantial expense which further increases the cost of the resulting 
products. 
One method for reducing the presence of organic solvents in coatings of 
this nature involves the use of radiation-curable coatings formed from 
various monomers and cross-linking oligomers, in which the monomer acts as 
a solvent by providing the necessary physical and theological properties 
for the uncured coating. Curing occurs when radiation is applied directly 
to the article surface having the coating thereon. The monomer enters the 
polymerization with the cross-linking oligomers and does not volatilize. 
The need for volatile solvents is thus eliminated or at least greatly 
reduced. However, several disadvantages exist with radiation-curable 
coatings. For instance, polymerizable monomers are not as effective as 
volatile solvent systems in the enhancement of flow and leveling of the 
coating on the substrate and therefore, the optical quality of the 
finished article is compromised. Moreover, oxygen which is present in the 
vicinity of the coating (and, to a lesser extent, within the coating 
material itself) often must be excluded during the curing process so that 
a coating having high optical clarity, abrasion resistance and chemical 
resistance may be formed. The elimination of oxygen is accomplished by 
continuously purging the cure chamber with nitrogen gas. However, a 
significant expense is required for the purchase of large volumes of 
nitrogen and for the maintenance of the purging equipment. Furthermore, 
safety equipment must be installed to protect operating personnel from 
accidental asphyxiation. 
OBJECTS OF THE INVENTION 
Accordingly, it is the primary object of the present invention to provide 
an improved process for coating the surface of a polymeric substrate which 
overcomes the foregoing disadvantages. 
It is another object of the present invention to provide an 
abrasion-resistant coating on a surface of a polymeric substrate without 
the use of volatile organic solvents. 
It is yet another object of the present invention to provide an 
abrasion-resistant, radiation-cured coating on a polymeric substrate 
surface without the use of a nitrogen blanket. 
Yet another object of the present invention is to provide a method of 
forming an abrasion-resistant coating having controlled surface 
characteristics. 
Still another object of the present invention is to provide an article 
comprising a polymeric substrate having an abrasion-resistant coating 
firmly adhered thereto. 
These and other objects and advantages of the present invention will become 
apparent to those skilled in the art as the description thereof proceeds. 
SUMMARY OF THE INVENTION 
The foregoing objects are generally achieved by a method for providing an 
abrasion-resistant, radiation-cured coating on a surface of a polymeric 
substrate capable of allowing the passage of radiant energy therethrough, 
comprising the steps of: 
(a) applying the uncured coating material to the substrate; 
(b) expelling air from the uncured material coating; and 
(c) contacting the coating with radiant energy by directing the radiant 
energy through the substrate from the surface opposite the surface having 
the radiation-curable coating thereon, thereby curing the coating. 
Thee substrate may be any conventional polymeric film or sheet material 
which is flexible and is capable of receiving a coating material as it 
passes through a coating means. The radiation-curable coating must be 
capable of adhering to the substrate, and is generally a nonvolatile 
coating comprising a cross-linkable resin and a photoinitiator. 
In a preferred embodiment of the present invention, air is expelled from 
the uncured coating by passing the substrate having; the uncured coating 
thereon through an adjustable air expulsion nip defined by the interface 
between a rotating nip roll and the surface of a rotating casting drum 
contacting the nip roll, such that the compression formed within the air 
expulsion nip upon the coating is sufficient to eliminate air from the 
coating and from the interface between the coating and the surface of the 
casting drum. 
Many of the typical forms of radiant energy may be used in the process of 
the present invention. Moreover, a plurality of layers of cross-linkable 
coatings may be applied to the surface of the substrate by this method. 
The radiation-curable coatings used in the present invention may also be 
applied on the surface of conventionally applied coatings, or they may 
serve as preliminary coatings for subsequently-deposited conventional 
coatings. 
The use of the improved process of the present invention results in an 
article having an abrasion-resistant coating thereon with excellent 
physical characteristics, such as hardness and chemical resistance, as 
well as a high degree of optical clarity. Furthermore, the process 
eliminates the need for organic solvent-based coatings, as well as 
eliminating the need for a nitrogen blanket in radiation-curable systems.

DESCRIPTION OF THE INVENTION 
The method of the present invention is suitable for providing an 
abrasion-resistant, radiation-cured coating on the surface of a wide range 
of polymeric substrates which may be in the form of sheets, films, 
laminates, etc. While the particular apparatus depicted in the FIGURE is 
intended for the application and cure of a coating material on a 
continuous film of the substrate, the apparatus may be easily modified to 
apply and cure such a coating material on individual sheets of the 
substrate. The composition of the substrate is not critical and may 
include acrylics, polyesters, polycarbonates, phenolics, urethanes, etc., 
or mixtures thereof. The only restriction on the choice of the substrate 
is that it be flexible and capable of allowing the passage of at least one 
form of radiant energy therethrough, and that its properties not be 
unacceptably affected by such passage of radiant energy. The radiant 
energy source is selected to operate at a frequency at which there is 
little or no absorption of the energy by the substrate. A preferred 
substrate for the method of the present invention is one formed from a 
thermoplastic polycarbonate material, such as Lexan.RTM. resin, a product 
of General Electric Company. Typical examples of polycarbonate resins are 
described in U.S. Pat. No. 4,351,920, and are obtained by the reaction of 
aromatic dihydroxy compounds with phosgene, as well as those obtained by 
the reaction of aromatic dihydroxy compounds with carbonate precursors 
such as diaryl carbonates. U.S. Pat. No. 4,351,920 also describes various 
methods for the preparation of polycarbonate resins which may be used as 
substrates in the present invention. Polycarbonate film may be made by 
well-known methods. Typically, the molten polycarbonate is cast onto an 
extrusion roll stack, and both sides of the material are polished and 
pressed to a uniform thickness. After cooling, the film is ready for 
having a coating applied thereon. Polycarbonate materials generally have 
known absorption spectra and, therefore, the most appropriate form of 
radiant energy used in the method of the present invention may be easily 
selected. Generally, ultraviolet (UV) radiation is used as the energy 
source when curing coatings on polycarbonate substrates. If another type 
of substrate is desired, an appropriate radiant energy source may be 
selected (as described below), based upon the particular absorption 
spectra of the material and upon the amenability of the material to 
radiant energy passing therethrough. The thickness of the substrate is not 
critical and may range from about 0.5 mil to about 30 mils, depending in 
part on both the end use contemplated for the article and upon the ability 
of the substrate to remain flexible. 
The radiation-curable coating used in the method of the present invention 
may comprise a wide variety of compositions. The choice of a particular 
coating will depend on several factors, such as the type of substrate 
used, the particular type of radiant energy applied, and the particular 
physical properties desired for the coating. Typical radiation-curable 
coatings are described in the Kirk-Othmer Encyclopedia of Chemical 
Technology, Third Edition, Volume 19, 1982, pp. 607-622. The 
radiation-curable coating systems are generally comprised of polymers 
containing acrylic, methacrylic or fumaric vinyl unsaturation along or 
attached to the polymer backbone. The coating systems generally also 
comprise monomers having a molecular weight of from about 100 to 500, and 
having single unsaturation sites. Typical of these are high boiling 
acrylate esters, although styrene may also be used as a monomer in 
selected formulations. A cross-linking oligomer containing di-, tri-, or 
multifunctional unsaturation sites is generally also a part of the 
radiation-curable coating system. Typical coating formulation ingredients 
are listed on page 617 of the Kirk-Othmer reference cited above. It is 
preferred in the practice of the present invention that the coating be 
nonvolatile, although a coating material containing volatile components 
may also be used if certain modifications are made, as described below. 
In those instances in which the substrate is a polycarbonate material, 
ultraviolet (UV) radiation is the preferred radiant energy media, and 
therefore, a UV-curable coating material is required. Any of the 
well-known UV-curable coating compositions are suitable for the present 
invention. One typical UV-curable coating composition is described in U.S. 
Pat. No. 4,477,529, incorporated herein by reference, and comprises 
azobisisobutyronitrile, at least one UV-curable cross-linkable 
polyfunctional acrylate monomer, and a polysiloxane-polyether block 
copolymer. Another suitable coating composition for the present invention 
is described in U.S. Pat. No. 4,198,465, incorporated herein by reference, 
and comprises a photoinitiator, a UV light curable cross-linkable 
polyfunctional acrylate monomer, and resorcinol monobenzoate. Methods of 
preparing UV-curable compositions are also well-known in the art; one such 
method is described in U.S. Pat. No. 4,198,465. 
A typical apparatus for applying and curing a coating on the surface of a 
polymeric substrate in accordance with the method of the present invention 
is depicted in the drawing, although it is to be understood that any 
conventional system or device may be used for metering or doctoring the 
coating material on the surface of the substrate. In the FIGURE, 
radiation-curable coating material 10 in reservoir 8 is continuously taken 
up by gravure roll 12. The use of a gravure roll coating system is 
well-known in the art and is described, for example, in U.S. Pat. No. 
4,302,486. Typically, the gravure roll has a ridged surface (not shown), 
with steel bars or a pattern of ridged dikes protruding from the roll 
surface, the depressions formed from such an array being capable of 
picking up and retaining the coating material 10 within reservoir 8. This 
arrangement allows coating material 10, while riding on the surface of 
gravure roll 12 which revolves in a clockwise direction, to be transferred 
to transfer roll 14, which is in circumferential contact with roll 12, and 
which revolves in a counterclockwise direction. Transfer roll 14 is driven 
by an outside power source (not shown) and will thereby coordinate the 
movement of gravure roll 12 (which may also be driven by an outside power 
source, not shown), and impression roll 16, described below. 
Substrate roll 4 is formed from a roll of uncoated substrate 6 surrounding 
a core 5. Substrate 6 is unwound pursuant to the movement of casting drum 
22 (described below), and is passed through a nip defined by the junction 
of transfer roll 14 and impression roll 16. Impression roll 16, rotating 
in a clockwise direction (i.e. in a direction opposite that of transfer 
roll 14), compresses- substrate 6 against transfer roll 14, the latter 
having coating material 10 on its surface. In this manner, coating 
material 10 may be uniformly applied to the surface of substrate 6. It 
will be apparent to those skilled in the art that adjustments may be made 
in the coating system in order to apply the coating to the substrate 
efficiently. Typical adjustments involve roll speed, coating material 
viscosities, and nip spacings. Furthermore, it is not critical in the 
method of the present invention to apply coating material 10 by gravure 
roll means, as described above. Coating material 10 may also be applied to 
substrate 6 by any of a number of well-known coating methods, such as 
spraying, brushing, electrodeposition, curtain coating, and dipping, as 
well as other well-known roll coating methods, such as reverse roll 
coating, etc. The thickness of radiation-curable coating 10 is dependent 
upon the end use of the article and the physical properties desired, and 
may range from about 0.05 mil to about 5.0 mils for a nonvolatile coating. 
The preferred nonvolatile thickness is from about 0.2 mil to about 1.0 
mil. 
After coating material 10 is applied to substrate 6, substrate 6 is guided 
around idler roll 18 to nip roll 20. The choice of materials which form 
the rolls used in the present invention is not critical. The rolls may be 
made of plastic, metal (i.e. stainless steel, aluminum), rubber, ceramic 
materials, and the like. Furthermore, the surface of each roll should be 
smooth and resilient. Typically, each roll is provided with a sleeve or 
cover on its surface. Nip roll 20 may be provided with such a sleeve, 
preferably formed from a resilient material such as tetrafluoroethylene or 
polypropylene, or from one of the variety of currently available synthetic 
rubber compounds and blends thereof. The sleeve is snugly fitted over the 
roll surface to provide a smooth, friction-minimizing surface for 
contacting substrate 6. Nip roll 20 is adjustable relative to the position 
of casting drum 22, described below, and may optionally be independently 
driven. 
As shown in the FIGURE, casting drum 22 is situated in a position adjacent 
nip roll 20, such that the outer circumferences of nip roll 20 and drum 22 
are in contact with each other at an interface defining a nip 25 which is 
described below. For the purpose of clarity, this particular nip will 
hereinafter be referred to as the air expulsion nip. The applied pressure 
at the interface of nip roll 20 and drum 22 may be adjusted by well-known 
methods, such as a spring mechanism (not shown), attached to the axle of 
nip roll 20, which selectively urges the roll toward drum 22. Typically, 
the applied pressure at the interface is slight, i.e. less than 5 pounds 
per square inch, when the substrate is not passing through air expulsion 
nip 25. The applied pressure can be readjusted according to a variety of 
parameters when a substrate having a coating thereon is passing through 
nip 25, as described below. 
Drum 22 surrounds central axle 21, and may be made from a wide variety of 
materials, such as various plastics, ceramics or metals. Typically, the 
drum is comprised of stainless steel or chromium-plated steel. 
Furthermore, it is preferred that the drum be independently driven by an 
outside power source (not shown). 
Casting drum surface 23 may be provided with a wide variety of textures or 
patterns, depending upon the texture or pattern desired to be imparted to 
coating 10. For instance, surface 23 may be provided with a highly 
polished chrome-plated surface if a high degree of gloss is desired for 
coating 10. If a lower sheen is desired for the coating, surface 23 may be 
less polished, or may be rubberized so as to provide a matte texture to 
the coating. Similarly, a design pattern may be embossed on surface 23 to 
impart a mirror-image design pattern to coating 10. The cured coating 10 
will thus become a permanent mirror-image of casting drum surface 23. 
In order to ensure the exclusion of air from and adjacent to coating 10 
prior to curing, without the use of a nitrogen gas blanket, the pressure 
capable of being exerted at air expulsion nip 25 is carefully adjusted. 
The adjustment of applied pressure at air expulsion nip 25 may be 
accomplished as described above. The exact pressure that can be exerted at 
nip 25 will depend on many factors, e.g., the viscosity of coating 10, the 
degree of detail in the design pattern on surface 23 (if present), and the 
thickness of coating 10. Typically, for a substrate having a thickness of 
5 mils having applied thereon an acrylic-based coating having a thickness 
of 0.6 mil and a viscosity of 800 centipoises, an air expulsion nip 
pressure of 25 pounds/square inch applied to the coated substrate is 
sufficient to expel any air which is within coating 10 and which is 
between coating 10 and drum surface 23. Coating 10 is thereby pressed into 
full anaerobic contact with both substrate 6 and casting drum surface 23, 
thereby ensuring that the coating, when cured, will exhibit strong 
adherence to substrate 6 while also exhibiting a mirror image of the 
texture and/or pattern of casting drum surface 23. 
After substrate 6 having coating 10 applied thereon passes through air 
expulsion nip 25, the coating is cured by means of radiant energy. As 
shown in the FIGURE, radiant energy is transmitted from radiant energy 
means 24 into the surface of substrate 6 opposite the surface having 
coating 10 thereon, i.e., the bottom surface of substrate 6. The radiant 
energy passes through the transparent substrate and is absorbed by the 
coating, the latter being compressed between substrate 6 and drum surface 
23. As mentioned above, the choice of a radiant energy source will depend 
upon several factors, including the chemical nature of the substrate as 
well as the chemical nature of the coating material being cured. It is 
important to select a radiant energy source which will not adversely 
affect substrate 6, e.g. by causing discoloration of the substrate. In 
those instances in which acrylic-based coatings are applied to 
polycarbonate substrates, the most appropriate radiant energy source is UV 
radiation. The preferred wavelength of the UV radiation is from about 1800 
Angstroms to about 4000 Angstroms. The lamp system used to generate such 
UV radiation may consist of discharge lamps, e.g. xenon, metallic halide, 
metallic arc, or high, medium, or low pressure mercury vapor discharge 
lamps, etc., each having operating pressures of from as low as a few 
milli-torrs up to about 10 atmospheres. The radiation dose level applied 
to coating 10 through substrate 6 may range from about 2.0 J/cm.sup.2 to 
about 10.0 J/cm.sup.2. A typical UV curing system suitable for the present 
invention is a Linde medium pressure mercury lamp, as described in U.S. 
Pat. No. 4,477,529. The number of lamps directing UV light to the surface 
of the substrate is not critical; however, a greater number of lamps may 
allow a higher production rate for the substrate having coating 10 
thereon. Typically, two lamps, each producing 200 watts/linear inch of 
radiant energy, are sufficient for an acrylic-based coating having a 
thickness of about 0.5 mils, when the production line speed is about 50 
feet/minute. Such a curing procedure should result in both the 
polymerization of the polyfunctional acrylic monomers and the 
cross-linking of the polymers to form hard, abrasion-resistant, non-tacky 
coatings. It will be understood to those skilled in the art that different 
substrates and different coating systems may require the use of different 
forms of radiant energy, such as electron beam curing, gamma ray curing, 
infrared curing, and curing methods which use visible wavelengths of 
light. Many of these methods are described in detail, along with 
descriptions of polymeric coatings amenable to cure by such methods, in 
the Kirk-Othmer reference cited above. 
In certain instances it may be desirable to provide additional lamps 
adjacent lamps 24 to emit a form of radiant energy suitable for curing 
coatings on other types of substrates. These lamps would remain inactive 
until a new substrate having coating 10 applied thereon reaches a position 
along drum surface 23 directly aligned with these lamps. While the coating 
on the new substrate is being cured, lamps 24 would remain inactive. 
Furthermore, additional lamps may be selectively activated when a 
different type of coating is being cured. 
In certain embodiments within the scope of the present invention, it may be 
desirable to apply coating material 10 in two or more layers. For 
instance, if the coating is to include an additive that might easily be 
leached by weather or ageing conditions, it may be desirable to 
incorporate the additive into the first coating layer and omit it from a 
second protective layer applied to the first layer prior to curing both 
layers simultaneously by radiant energy means. As depicted in the FIGURE, 
a two-layer coating may be achieved by the addition of coating station 40. 
The particular means for applying the second layer is not critical to the 
invention; such means are well-known to those skilled in the art. In this 
embodiment of the present invention, a first layer of coating material may 
be applied by the gravure roll apparatus described above. After the 
coating material has been applied to substrate 6, the substrate is guided 
around idler roll 18 and nip roll 20. Simultaneously, a second layer of 
coating material from a reservoir (not shown) is applied to casting drum 
surface 23 by means of secondary gravure roll 42 and secondary transfer 
roll 44. In the presently-described embodiment, the second layer material 
is comprised of the same material as the first layer, and typically has a 
thickness (when cured) of about 0.2 mils to about 3.0 mils when the first 
layer has a thickness of about 0.05 mil to about 2.0 mils (when cured). 
Generally, the combined thickness of the first and second coating layers 
ranges from about 0.25 mils to about 5.0 mils. As in the case of the nips 
of the previously-described embodiment, the nip between secondary transfer 
roll 44 and casting drum 22 may be adjusted by well-known methods to suit 
the particular characteristics of the second layer. Thus, the second layer 
is applied to substrate 6 while the substrate, having the first layer 
thereon (uncured), passes through air expulsion nip 25. The elimination of 
air from between both layers is thus achieved simultaneously as the 
substrate passes through air expulsion nip. Both coatings may then be 
cured by means of the radiant energy lamps 24, as described above. 
It will be apparent to those well-skilled in the art that the first and 
second (or additional) layers may be comprised of different types of 
materials, depending upon the particular end use requirements for the 
coated substrate. In this instance, additional radiation lamps may be 
situated opposite the circumference of casting drum 22 and adjacent lamps 
24 to emit the particular type of radiant energy appropriate for curing 
each layer of coating material. 
After one or more layers of coating material have been applied to and cured 
on substrate 6 according to the method of the present invention, the 
resulting product is guided around idler rolls 28 and 30 and then 
collected on take-up roll 32, the latter typically being independently 
driven and capable of separating cured coating 10 from drum surface- 23. 
In certain embodiments within the scope of the present invention, it may be 
desirable to apply a radiation-curable coating 10 which contains some 
volatile components. Since such volatile components may adversely affect 
the ability to eliminate air from the coating and surrounding region, they 
should be removed from the coating prior to cure. This may be accomplished 
by drying station 36, as depicted in the FIGURE. Drying station 36 is 
typically a forced hot-air oven system having vapor exhaust means, 
although any type of ventilated furnace will be suitable for this 
function. The drying station is typically situated at some point along the 
process pathway between impression roll 16 and nip roll 20, as shown in 
the FIGURE. The volatile components in the coating material are thereby 
eliminated prior to the radiation curing of the coating. 
In another embodiment of the present invention, a preliminary coating 
material may be applied to substrate 6 prior to the application of one or 
more of the radiation-curable coatings described above. The preliminary 
coating is generally a conventional coating, which is air-dried or cured 
by the application of heat, and not by radiant energy. Typical examples of 
conventional thermoplastic coating materials used as preliminary coatings 
for the present invention are acrylic-based lacquers. Typical examples of 
conventional heat-curable thermosetting coating materials which may be 
used as preliminary coatings for the present invention include those 
comprising phenolics, alkyds, polyesters, epoxides, silicones, etc. The 
only requirements for materials used as preliminary coatings for the 
present invention is that they be physically and chemically compatible 
with the subsequently applied radiation-curable coatings, and that they be 
somewhat transparent to and not unacceptably affected by the radiant 
energy media used in that particular curing system. Preliminary 
conventional coating material 50 may be applied to substrate 6 by various 
methods well-known in the art, e.g. spraying, brushing, roll-coating and 
the like. In the FIGURE, for example, preliminary coating material 50 is 
applied to substrate 6 by means of rotating coating roll 54. After the 
preliminary coating has been applied to the substrate, the Substrate 
passes through furnace 56, if necessary, to cure preliminary conventional 
coating 50. The substrate will then have the radiation-curable coating 
applied and cured thereon, as described in detail above. 
In another embodiment of the present invention, a topcoat may be applied to 
the substrate on top of the radiation-cured coating(s). The composition of 
the topcoat may be selected from any of the conventional thermoplastic or 
thermosetting coating materials described above as being suitable for the 
preliminary coating. Additionally, the topcoat may comprise materials 
which are not transparent to radiant energy, e.g. pigmented coating 
materials, etc. Furthermore, the coating material may include materials 
which might be adversely affected by radiant energy, since radiant energy 
is no longer utilized at this stage. The topcoat may be applied to the 
coated substrate 6 by any of the well-known methods described above. In 
the FIGURE, the topcoat material is stored in a reservoir (not shown) and 
is applied through the use of topcoat transfer roll 62 adjacent topcoat 
gravure roll 60. The topcoat may be cured through the use of furnace means 
66, if necessary. Furthermore, the scope of the present invention 
encompasses the use of both a preliminary coating and a topcoat in 
conjunction with one or more radiation-curable coatings. 
It will be understood by those skilled in the art that a nitrogen blanket 
may be used alone or in conjunction with the apparatus and preferred 
methods of the present invention. 
The following specific example describes the novel methods and article of 
the present invention. It is intended for illustrative purposes of 
specific embodiments only and should not be construed as a limitation upon 
the broadest aspects of the invention. 
EXAMPLE 
Twelve samples of various coating materials were used for several 
comparative tests. All of the coating materials were 100% reactive solids 
formulations with viscosities that ranged from 40 cps to 90 cps. The 
coating material for samples 1 and 2 was produced by the Sherwin Wililiams 
Company and was a commercially available 100% solids UV-curable 
formulation sold as V88 VC-1. The coating material for samples 3 and 4 was 
also made by Sherwin Williams and was a developmental UV-curable acrylic 
formulation which was designated as 94-B. Samples 5 and 6 were a 
composition from DeSoto Chemical Company, commercially available as 
Desolite 950.times.343. The composition of samples 7, 8 and 9 was from the 
General Electric Company and contained the following ingredients: 43.3% 
trimethylolpropane triacrylate; 43.3% hexanediol diacrylate; 4.4% 
resorcinol monobenzoate; 4.5% triethanolamine; 4.5% benzophenone. The 
composition of samples 10, 11 and 12 was also from General Electric and 
contained the following ingredients: 44.9% trimethylolpropane triacrylate; 
44.9% hexanediol diacrylate; 4.5% resorcinol monobenzoate; 3.8% 
triethanolamine; 1.9% benzophenone. 
Each sample was applied as one layer on a Lexan substrate having a 
thickness of about 10 mils by means of the apparatus depicted in the 
FIGURE and described above. The samples were radiation-cured by means of 
two Linde medium pressure mercury lamps as described in U.S. Pat. No. 
4,477,529, operating at a total dose level of 6.2 joules/cm.sup.2. Samples 
1, 3, 5, 7 and 10 were cured in an air atmosphere, i.e., without the use 
of the air expulsion nip of the present invention, by directing the 
radiant energy source directly upon the coating material. Samples 2, 4, 6, 
8 and 11 were cured in a nitrogen atmosphere, i.e., under a nitrogen 
blanket, without the use of the air expulsion nip of the present 
invention, by directing the radiant energy source directly upon the 
coating material. Samples 9 and 12 were cured according to the method of 
the present invention, i.e., air was expelled from the coating and from 
the interface between the coating and the casting drum surface by means of 
the air expulsion nip depicted in the FIGURE. The thickness of the cured 
coatings far each sample was about 0.2 mil to about 0.3 mil. 
Abrasion and adhesion tests were performed on each coated substrate. The 
abrasion test was performed with a Taber Abraset, using a CS-10-F abrasive 
wheel and a 500 gram load. A higher Taber value represents the increase in 
the percentage of haze on the cured coating after 100 abraser cycles. 
The adhesion test was performed by crosshatching the cured coating of each 
sample, followed by a tape pull. No removal of the coating from the 
substrate indicates excellent adhesion, while a larger amount of coating 
removed indicates poorer adhesion. 
The test results are displayed in Table 1: 
TABLE 1 
______________________________________ 
SAMPLE CURE ABRASION ADHESION 
NUMBER ATMOSPHERE.sup.a 
VALUE.sup.b 
RATING 
______________________________________ 
1 Air 3.5 Good 
2 N.sub.2 2.4 Excellent 
3 Air 11.0 Excellent 
4 N.sub.2 2.5 Excellent 
5 Air 4.8 Poor 
6 N.sub.2 2.8 Good 
7 Air 12.2 Poor 
8 N.sub.2 5.1 Good 
9 A.E.N. 4.4 Good 
10 Air 8.0 Good 
11 N.sub.2 3.4 Excellent 
12 A.E.N. 4.1 Excellent 
______________________________________ 
.sup.a) N.sub.2 = Nitrogen; A.E.N = Air Expulsion Nip 
.sup.b) Abrasion Value = Taber Value 
The abrasion and adhesion test results for samples 1-6 indicate that 
coatings cured in a nitrogen atmosphere have superior abrasion resistance 
(lower abrasion values) and adhesion as compared to coatings cured in an 
air atmosphere, 
The results of tests performed on samples 7-12 demonstrate that coatings 
applied and cured by the preferred method of the present invention 
(samples 9 and 12) exhibit adhesion and abrasion resistance 
characteristics which are generally as good as or better than those of the 
coatings cured in air or nitrogen, 
The article produced by all of the embodiments of the improved method of 
the present invention is characterized by excellent scratch resistance, 
abrasion resistance, solvent resistance, and high optical properties. 
Furthermore, the coated article resulting from the process of the present 
invention exhibits high physical integrity because defects which would 
normally result from the trapping of oxygen within cured coatings are not 
present. The process also results in the coating surface having any 
desired texture or pattern. The preferred process of the present invention 
results in shorter processing times and lower overall production costs for 
the article because of the elimination of a nitrogen atmosphere. 
While the invention has been described with respect to preferred 
embodiments, it will be apparent that certain modifications and changes 
can be made without departing from the spirit and scope of the invention. 
It is therefore intended that the foregoing disclosure be limited only by 
the claims appended hereto.