This application is a continuation in part of U.S. application Serial No. 013,418, filed February 21, 1979.

This invention relates to radiation curable coating compositions which when cured form highly abrasion resistant coatings for most any susbtrate.

In the past, many curable or crosslinkable composi¬ tions have been developed in the art for use as coatings for clear plastics and the like which when cured offer varying degrees of abrasion and solvent resistance. Among such co - positions are fluorocarbon-vinyl ether copolymers cross- linked with polysilicic acid, melamine-f.or_maldehyde coatings, polyurethanes, pol siloxanes, polyak ls, polyall I icarbon¬ ates, and polyfunctional acrylics. Such coatings have been applied to a wide variety of polymeric substrates including acrylic sheeting, polycarbonates, polyesters and the like. These compositions are generally applied to the substrate by any known method such as dipping, brushing or spraying and are cured at either high temperature or at low temperature in the presence of a catalyst. Ultraviolet curable coatings based on unsaturated polyester resins, including polyacrylics, and containing a photoinitiator have also been described in the art.

The present invention deals with radiation curable coating compositions containing a specific class of polyacry- lates and cellulose esters which can be applied to a variety of substrates. The precured coatings are dust-free, level out extremely well on the substrates and are stable against air inhibition of cure such that they can be cured in air hours after application to the substrate. On curing, coatings are formed exhibiting extremely high abrasion resistance, flex¬ ibility, weatherability and resistance to thermal stress crack¬ ing. Such coatings are additionally scratch resistant and are not attacked by chemical or organic solvents.

SU MARY OF THE INVENTION

In one embodiment of the present invention a coating composition curable by actinic radiation is provided which can be applied to most any substrate and when cured forms an extremely abrasion-resistant coating on the substrate.

The curable composition comprises a pentaerythritol- based polyacrylate or polymethacrylate, a cellulose ester and a photoinitiator which can be applied to the substrate by any means known in the art such as by brushing, dipping, spraying or by roller, gravure, spin or flow coating techniques. Spraying is particularly preferred. Solvents such as lower alcohols, lower acetates, ketones and ethylenegylcol alkyl ethers may also be added to the composition to facilitate mix¬ ing of the components and to allow efficient and uniform application of the composition to the substrate.

In another embodiment of this invention a method of forming an abrasion resistant coating on a substrate is pro¬ vided comprising applying the above composition to the sub¬ strate to form a coating, removing any solvents from the com¬ position by evaporation and exposing the coating to ultra¬ violet radiation to effect curing thereof. Post-curing of the coating at elevated temperatures may be conducted to further enhance'abrasion resistance.

In other embodiments of the invention a composition comprising the cured product of the above curable composition and a substrate having a coating ^* of the curable composition and the cured product of the curable composition are also pro¬ vided.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The pentaerythritol-based polyacr lates and poly- methacrylates of the curable compositions of this invention include polyacrylates and polymethacrylatesof pentaerythritol such as the tri- and tetra-acrylates and methacrylates of pentaerythritol, polyacrylates and methacrylates of di- and tri-pentaerythritols such as dipentaer thritol penta- and

OM

hexa-acrylate and dipentaerythritol penta- and hexa- etha- crylate and tripentaer thritol octa_-acr late and methacrylate

5 as well as mixtures of the above polyacrylates and polymeth- acrylates. Pentaerythritol tetraacrylate is particularly

-•- p-referred due to its. high -performance in imparting abrasion resistance to the final, cured composition.

The cellulose esters of this invention comprise the

10 reaction product of cellulose with at least one organic carbo- xylic acid having from about 2 to 4 carbon atoms or nitric acid. The preferred cellulose esters are cellulose acetate butyrates containing on the average from about 15% to 50% butyrl groups, from about 1% to 30% acetyl groups and from

15 about 1% to 5% hydroxyl groups and preferably having a vis¬ cosity in Poises- of from about 50 to -200 at 25°C. in a solution comprising 20 wt. % cellulose ester, 72 wt. % acetone and 8 wt. % ethyl alcohol. Particularly preferred is a cellu¬ lose acetate butyrate containing on the average 37% butyryl

20 groups, 13% acetyl groups and 2% hydroxyl groups and having a viscosity in Poises of from about 64 to 124 at 25°C. in the above described solution. Nitrocellulose may also be employed as the cellulose ester.

A photoinitiator is added to the composition to

25 initiate crosslinking or curing upon irradiation. Such photo-.- initiators are well known in the art and include such com¬ pounds as benzoin, benzoin methylether, diphenyl disulfide, dibenzyl disulfide, benzil, benzophenone, xanth'ane, acetophe- none, anthraquinone, Michler's ketone and the like. A prefer-

30 red photoinitiator is alpha-chloroacetyldiphenyloxide. An accelerator such as a tertiary a ine may also be added.

It has also been found that small amounts of a per¬ oxide such as benzoyl peroxide may act- as a photoinitiator by initiating crosslinking or curing of the compositions. Such

35 peroxide has the added advantage that it can be used in smaller amounts than the photoinitiators described above and does not tend to discolor or yellow the cured coatings. A combination of photoinitiators may be employed in some cases.

The compositions of the present invention may be

40 applied to the substrate in any conventional manner such as

OMPI

spraying, dipping, brushing or by roller, gravure, spin or flow coating techniques. Spraying is preferred since i allows uniform application of thin cured coatings to the sub¬ strate, i.e. on the order of 0.1 to 1.5 mils.

In order to facilitate mixing of the elements of the composition and to allow for efficient spraying, one or mor solvents may be employed in the composition, which include lower alcohols having from 1 to 4 carbon atoms such as pro- panol and butanol; lower alkyl acetates having from 4 to 6 carbon atoms such as propyl and butyl acetate; alkyl ketones having from 3 to 7 carbon atoms such as methyl isoa yl ketone; and eth lene glycol lower alkyl ethers (Cellosolves) such as methyl and ethyl Cellosolve. Organic solvents other than those named above may also be employed provided they are good solvents for the pentaerythritol-based polyacrylate or poly- methacrylate and cellulose ester and do not attack the sub¬ strate on which the composition is coated. For example, quantity of an aromatic solvent such as xylol may also be employed with the above-described solvents to dissolve certain pentaerythritol-based poly ethacrylates such as penta¬ erythritol tetramethacr late.

The composition may also contain small amounts of flatting agents to lower the gloss of the coating and sili- cones to increase the flowabili'ty of the compositions.

The substrates which can be coated with the curable compositions of this invention are numerous and include any material to which the composition will adhere and coat such as wood, glass, metal, rubber and plastics. The compositions are particularly useful for coating polymeric substrates such as polycarbonates, polyvin ls including rigid polyvinyl chloride sheet substrate and substrates comprised of copolymers of polyvinyl chloride and polyvin lacetate, polyacrylics and polyesters. The compositions may be used for the coating of vinyl and polycarbonate substrates used to manufacture low reflection filters for cathode ray tubes (C.R.T. 's) and for acrylic substrates used as front panels for electronic equip¬ ment.

Upon curing in air by actinic radiation, the pres

compositions form a highly abrasion resistant coating even on contoured surfaces- which have ^• a lower point of contact with abrasive objects moved along its surface. Tests conducted on cured compositions of this invention coated on polymeric sub¬ strates have -prove their extremely -high -resistance to steel wool abrasion and Taber Abrasion. The compositions are also resistant to scratching as shown by tests with a weighted stylus according to the BTL Balanced Beam Mar Test (ASTM Method D-2197). The cured compositions of this invention are also characterized by their high resistance to organic sol¬ vents, acids and bases, to thermal stress cracking and are flexible and weatherable. Moreover, clear, cured coatings containing flatting agents made according to the invention are also characterized by their low gloss and high resolution mak¬ ing them ideally suitable for low reflection filters for C.R.T.'s. Clear coatings of this invention may also be ap¬ plied to clear plastic lenses, meter faces, formed plastic windshields and flat plastic windows used for optical applica¬ tions to provide abrasion and scratch resistance.

The curable compositions of this invention are pre¬ pared by first forming a heavy solution of the cellulose ester in one or more solvents, i.e. about 10 to 15% of cellulose ester by weight. A portion of this solution and the penta¬ erythritol-based polyacrylate or methacrylate is added to a further solvent system to provide a coating composition which, if applied separately to a substrate and dried, would form a slightly tacky but dust free coating on the substrate. For example such a coating composition can be formed using penta¬ erythritol tetraacrylate and cellulose acetate butyrate by adding a portion of a heavy solution of cellulose acetate butyrate in propyl acetate and propanol and pentaerythritol tetraacrylate to a further solvent system comprising propyl acetate, propyl alcohol and methyl Cellosolve to form a solu¬ tion containing the following weight percentages of each com¬ ponent:

- URE3

O PI

-6-

pentaerythritol tetraacrylate 30 wt. % cellulose acetate butyrate 3 t. % propyl acetate 34 wt. % propyl alcohol 28 wt. % methyl cellosolve 5 wt. %

100 wt. %

This composition provides a weight ratio of pentaerythrito tetraacrylate to cellulose acetate butyrate of about 10 to 1. In the case of pentaerythritol-based poly ethacr lates such a pentaerythritol tetramethacrylate, an aromatic solvent suc as xylol may also be employed in forming the coating composi tion.

The weight ratio of pentaerythritol-based polyacry late or methacrylate to cellulose ester is an important facto in determining the abrasion resistance of the finally cure coatings. Coatings containing too low a ratio of penta erythritol-based polyacrylate or methacrylate to cellulos ester i.e., excessive cellulose ester, tend to lose abrasio resistance in the cured state because of the lack of suf ficient amounts of crosslinked polyacrylate or methacrylate. Coatings containing too high a ratio, i.e. insufficient cell ulose ester, tend to lose abrasion resistance in the cure state because of the non-uniform or irregular distribution o the polyacrylate or methacrylate and the inability of th cellulose ester to prevent air inhibition of the polyacrylat or methacrylate cure which will be discussed further below. Coatings containing no cellulose ester for example, are no appreciably abrasion resistant, especially as thin films. Therefore there exists a set of ratio ranges for each type o polyacrylate or polymethacrylate and cellulose ester above an below which abrasion resistance in the finally cured coat- ings may decrease significantly or completely.

In the case of compositions containing penta¬ erythritol-based polyacrylates or methacrylates an the preferred cellulose acetate butyrates, this ratio shoul be between about 6 to 1 and about 100 to 1 t achieve abrasion resistance in the cured coatings. High ab

sion resistance is achieved at ratios of from about 8 to-1 to about 20 to 1 and optimum abrasion resistance is achieved using a ratio of about 10 to 1. At ratios greater than about 20 to 1 thermal stress cracking begins to occur in the cured composition if- the temperature—-is .elevated- during curing. This also depends on the type of substrate coated and the film thickness of the coating. Below ratios of about 5 to 1 and above ratios of about 100 to 1, abrasion resistance decreases significantly. Although it is important that the ratio of pentaerythritol-based polyacrylate or methacrylate to cellu¬ lose ester be maintained in the above ranges, the solvent com¬ positions and amounts may be altered to provide pre-cured coatings or varying consistency as required or desired by those skilled in the art.

Next, a clear sprayable solution is prepared by dis¬ solving a portion of the above coating composition in one or more solvents which are mutually compatible and which will not attack the substrate onto which the composition is to be applied. It has been found that a sprayable solution compris¬ ing about 50% by weight of the above coating composition in equal parts by weight of butyl acetate, butanol, methyl iso- amyl ketone, and methyl Cellosolve is useful and has the advantage that such a mixture will not attack most polymeric substrates including polycarbonate substrates. However, such solvents may be varied by those skilled in the art depending on the substrate or the method of application. To this solu¬ tion is added the photoinitiator in a ratio of about 1 p.b.w. of photoinitiator to 150 p.b.w. of sprayable solution. The amount of photoinitiator based on the amount of pentaerythri¬ tol tetraacrylate in the solution is from about 2 to 5 weight per cent but may be varied by those skilled in the art. If a peroxide such as benzoyl peroxide is employed as a photo- initiator the amount used is generally about 1 weight percent.

The sprayable solution is then preferably sprayed on the substrate using a conventional low pressure spray gun at a wet film thickness of from about 0.9 to 3.0 mils. Thereafter, the solvents are allowed to evaporate either at room temper- ature for about 10 minutes or at 100° F. to 120°F. for abo

inutes. Coatings so applied level out well on the substrate that is form a smooth contiguous film. The dry coating i essentially non-tacky and dust-free. Finally, the dry coatin is exposed to actinic radiation to provide a cured coating o from about 0.1 to about 1.5 mil. in dry film thickness.

Actinic radiation as used herein is electromagneti radiation having a wavelength of 700 nanometers or less whic is capable of producing, either directly or indirectly, fre radicals in the photoinitiator which in turn cause cross-link ing addition polymerization of the compositions. The mos commonly used form of actinic light and the preferred for herein is ultraviolet light, that is, electromagnetic radia tion having a wavelength in the range of from about 180 nano meters to about 460 nanometers, although actinic light o greater or shorter wavelengths may also be used. Generally, exposures of from about 1 to 5 sec. are sufficient to effec curing of pentaerythritol-based polyacrylate composition while somewhat longer exposure times are required for th pentaerythritol-based polymethacr late compositions.

Any suitable source which emits ultraviolet ligh may be used in curing the compositions of this invention. Particularly preferred are ultraviolet emitting lamps of th medium mercury vapor type having a power rating of 20 watts/inch.

It has been found that the use of cellulose acetat butyrate as the cellulose ester, particularly the preferre cellulose acetate butyrates described above, solve many prob lems associated with coating substrates with thin films, ie. on the order of 2 to 20 microns, of compositions comprised o radiation curable pentaerythritol-based polyacrylates o methacrylates. Pentaerythritol-based polyacrylates such as pentaerythritol tetraacrylate are low viscosity liquids whic when deposited on a substrate do not form uniform coatings, nor do they level out well on the substrate. Pentaerythritol- based polymethacr lates such as pentaerythritol tetrameth- acrylate are soft, tacky solids and tend to crystallize whe coated in solution on the substrate after solvent removal. Moreover, coatings of pentaerythritol-based polyacrylates £p

wet, tacky and dust attractive. It is also necessary to cure pentaerythritol-based polyacrylate or methacrylate films in an inert atmosphere since the presence of air inhibits their cure. The exclusion of air to enable curing of the poly¬ acrylates or. me.thacr lates is_-impractical for.mo.s_t- commercial coating applications and costly as well. Cured coatings of such polyacrylates are characterized by being brittle, inflex- ible and subject to cracking in response to heat or stress.

The use of a cellulose ester such as the cellulose acetate butyrates described -above increases the viscosity of the pentaerythritol-based polyacrylate thereby allowing the coating to be uniformly deposited and to level out well on the substrate. Cellulose acetate butyrate inhibits crystalliza¬ tion of the - pentaerythritol-based polymethacrylates. Secondly, thin films on the order of 2 to 20 microns contain¬ ing the ester can be deposited on the substrate and dry quickly to a substantially dust free coating. Thirdly, and probably most importantly, is the ability of the cellulose ester to substantially eliminate the air inhibition of the polyacrylate or methacrylate cure. Fourthly, cured films con¬ taining the cellulose ester are characterized by being thermal stress crack resistant, flexible, and resistant to weathering. Thus, compositions according to the present inven¬ tion can be applied as thin films which readily flow and level out on the substrate, dry rapidly to a dust-free and stable condition such that the films can be cured either immediately or hours later in a few seconds without concern for the elimi- nation of air at any time and form flexible, thermal stress crack-resistant, weatherable, and highly abrasion resistant coatings.

It has also been found that by post-curing the irra¬ diated coating at temperatures of from about 100°F. to 200°F. at from 2 to 5 hrs. , abrasion resistance is even further enhanced.

In order to more completely describe the present invention, the following Examples are given:

EXAMPLE 1

This example illustrates the preparation, applica tion to a substrate and curing of the preferred composition o this invention. The cellulose acetate butyrate employed i this Example had on the average 37% butyryl groups, 13% acety groups and 2% hydroxyl groups and a viscosity in Poises o ^" . between about 64 and 124 at 25°C. in a solutio comprising 20 wt. % cellulose acetate butyrate, 72 wt. % aceton and 8 wt. % ethyl alcohol.

A stock solution containing 14.3 wt. % of cellulos acetate butyrate in propyl acetate and propanol was first pre pared by dissolving 50 parts by weight (p.b.w. ) of the cellu lose acetate butyrate in a solvent mixture of 200 p.b.w. o propyl acetate and 100 p.b.w. of propanol.

A coating formulation was prepared by dissolving portion of the so-formed stock solution and pentaerythrito > tetraacrylate in a further solvent system as shown below.

Additive p. b.w.

Stock Solution 126

Pentaerythritol Tetraacrylate 180

Solvents

Propyl acetate 132

Propanol 132

Methyl Cellosolve 30

600 This coating formulation contained the following total weight percentages of each component.

Total Component wt. %

Pentaerythritol Tetraacrylate 30

Cellulose Acetate Butyrate 3

Propyl Acetate 34

Propyl Alcohol 28

Methyl Cellosolve 5_

Total 100

OM

Such a coating formulation, if separately applied to a. substrate and dried .to remove, solvents, leaves a slightly tacky and dust free film on the substrate.

Next, a sprayable, clear solution was formed by add- ing a portion of the. above. coat ing formulation to a spray-able solvent system as set forth below.

Additive p. b. .

Coating Formulation 356 Solvents

Butyl Acetate 100

Butanol 100

Methyl Isoamyl Ketone 100

Methyl Cellosolve . 100

756

This sprayable solution contained the following total weight percentages of each component.

Total Component wt. %

Pentaerythritol Tetraacrylate 14.2

Cellulose Acetate Butyrate 1.4

Propyl Acetate 16.0

Propyl Alcohol 13.2

Methyl Cellosolve 15.6

Butanol 13.2

Butyl Acetate 13.2

Methyl Isoamyl Ketone 13.2

100.0

To this solution was added 0.8 p.b.w. of alpha chloroacetyldiphenyloxide to form a UV curable coating compo¬ sition. This curable composition was then sprayed under low pressure on a polyvinyl chloride substrate (TENNECO CHEM. CO.) at a wet film thickness of about 0.9 mil using a DeVilbiss- TYPΞ EGA spray gun and allowed to dry in air at room tempera¬ ture. The composition leveled out well on the substrai____-_____ f OMPI < _ W1PO .

ϋpon drying the film thickness was about 0. ^' 3 mil. and wa dust-free. The polyvinylchloride substrate coated with th curable mixture was then irradiated with high intensity U light for about 3 sec. to effect curing. It was found tha the curable composition could be left on the substrate fo hours before UV curing without air inhibition of cure.

EXAMPLE 2

This Example demonstrates the resistance to stee wool abrasion of a cured composition according to this inven tion on a polymeric substrate and its comparison to othe coated substrates and an uncoated substrate.

In this Example, a sample of the cured compositio of Example 1 on polyvinyl chloride (Ex. 1 COATING) was sub jected to abrasion by rubbing with a inch block of aluminu covered with 1/8 inch thick 0000 steel wool under a 1000 gm. load. After each double rub (1 back and forth stroke) th coating was observed for visible scratches. No more than 100 double rubs were made. As comparison samples, the followin were also tested:

A polyvinyl substrate coated with a vinyl urethan composition (VINYL URETHANE);

A vinyl substrate coated with a composition compris ing a vinyl chloride - vinyl acetate - vinyl alcohol terpoly mer and melamine (VINYL MΞLAMINE);

An acrylic substrate coated with a nitrocellulose aliphatic urethane coating (ALIPHATIC URETHANE); and

An uncoated polyvinyl chloride substrate (UNCOATE SUBSTRATE).

Table 1 below summarizes the results of all test.

^' BUR -fø fr,

Table 1

As the table shows, the Example 1 COATING resisted scratching by the steel wool up to 1000 double rubs. The re¬ maining samples did not endure more than 3 double rubs before severe scratching developed. In addition, the Example 1 COAT¬ ING was resistant to thermal stress cracking and flexible.

EXAMPLE 3

In this Example, the samples of Example 2 were test¬ ed on a Taber Abrader described in ASTM D 1004-56. To sum¬ marize this procedure, each sample was mounted on a turntable and was abraded by a pair of abrasive wheels (CS 10) weighing lOOOg each rotating in opposite directions. The abrasive wheels traveled on the sample about a horizontal axis displaced tangentially from the axis of rotation of the sample re¬ sulting in a wearing action. The abrasion was determined by the visual condition of each sample after 50, 100 and 200 revolutions of the Abrader. The weight loss of each sample was also determined after the test. Table 2 summarizes the results.

- 14- Table 2

As table 2 shows, hardly any abrasion of the Ex. COATING occurred even after 200 revolutions. The remainin samples, on the other hand, were all abraded after 50 revolu tions as indicated by their visible condition and weight loss.

EXAMPLE 4

This Example illustrates the high resistance t scratching of cured coatings according to the present inven tion on various polymeric substrates.

A sample of the curable coating composition as se forth in Example 1 was sprayed on an acrylic sheet substrate a vinyl sheet substrate and a polycarbonate sheet substrate a a wet film thickness of about 2 mil. and allowed to dry t remove solvents. The dry film thickness was about 0.4 mil and was dust-free. The dried coatings were then irradiate with high intensity UV light for 3 seconds in air to effec curing. Curing could be conducted hours after deposition o the composition without air inhibition of cure.

Each coated sheet was then subjected to a surfac

-15-

endurance test (BTL Balanced Beam Mar Test-ASTM Method D- 2197 ⁾ . In this test each sample was placed on a movable hori¬ zontal plastic plate beneath a stationary metal stylus pivoted at an angle of 45° with respect to the plate. The stylus carried a horizontal platform on "which were placed weights of different magnitudes. The weights used in this test were 50 g s. , 100 g s, , 150 g s. and 200 gms. After each weight was placed on the platform, the plate and sample were moved hori¬ zontally under the stylus and the visual condition of the sample observed thereafter.

Table 3 summarizes the results of the test.

Table 3

SAMPLE PLATFORM WEIGHT (GMS. ) 50 100 150 200

COATED ACRYLIC SHEET No effect No effect No effect No effect

COATED VINYL SHEET No effect No effect No effect No effect

COATED POLY¬ CARBONATE SHEET No effect No effect No effect No effect

UNCOATED VINYL Fineline Line Heavy Line Gouge

As the table shows all coated substrates were com¬ pletely resistant to scratching by the stylus, under all loads. The uncoated vinyl sheet developed scratches under the lowest load and the intensity of scratching increased with increasing loads.

Example 5

In this Example, the procedure of Example 1 was fo _l ¬ lowed except that the stock solution of cellulose acetate butyrate was eliminated and the curable composition formed after removal of solvents essentially comprised pentaerythri¬ tol tetraacrylate and the photoinitiator. After removal-fife— - _^ OMPI

solvents the coating was wet, tacky and easily picked up dust. After irradiating the composition with UV light ^" about 5 sec. in air the coating was hard and brittle and it was found tha stroking the coating with steel wool only a few times produce abrasion. This was attributed to air inhibition of the poly¬ acrylate cure which inhibition is substantially eliminated b the use of cellulose acetate butyrate as demonstrated in th

- foregoing Examples.

Example 6

In this Example, the procedure of Example 1 was fol¬ lowed except that nitrocellulose was substituted for cellulose acetate butyrate as the cellulose ester. The sprayable solu¬ tion formed using this procedure was applied to an acrylic substrate instead of the polyvinyl chloride substrate of Exam¬ ple 1. The resulting cured coating was subjected to the steel wool abrasion test as set forth in Example 2. It was found that after 6 double rubs with the steel wool pad faint lines began to appear on the coating thus indicating that the nitro¬ cellulose-containing coating, although abrasion resistant, is less abrasion resistant than the other samples tested in Ex. 2.

Example 7

This Example demonstrates the resistance of the Example 1 coating to boiling water, organic solvents, acids and alkalis. For ^' the boiling water and alcoholic potassium hydroxide tests, a sample of the Ex. 1 product was immersed in each reagent for ten minutes and the condition of the coating and substrate was observed for visual change. In the remain-

- ing tests the reagents were maintained on the product in a wet condition for ten minutes and examined for visual change. The remaining reagents were THF (tetrahydrofuran) which is a good solvent for PVC, MDC (methylene dichloride) a paint remover solvent, 50% hydrofluoric acid known for its glass etching

^• properties, 10% sodium hydroxide, 40% sulfuric

-17- ^'

nitric acid, an aromatic solvent mixture, ie. benzene, toluene and xylene, alcohol, esters and ketones, and gasoline and nitro ethene. Table 4 summarizes the results.

Table 4

Example 8

In this Example, Taber Abrasion tests as described in Example 3 were conducted to compare the substrates coated

in accordance with the procedure of Example 1 ie. , an acrylic polycarbonate, rigid PVC and polyester substrate, with severa uncoated substrates and substrates coated with other composi tions. The uncoated substrates included a polycarbonate sub strate sold under the trademark CR-39 (PPG-Industries, Inc. having abrasion resistant properties. The abrasive wheel used (CS-10F) έre of a more abrasive type than those used i Example 3 and weighed 500 gms. each. The change in visua appearance in the example after 100 cycles was measured a percent increase in haze, according to ASTM D-1003. "Measure ment of Haze and Luminance Transmit ance of Transparen Plastics" using a Gardner Haze meter. Table 5 summarizes th results.

Table 5

As Table 5 shows, the substrates coated with the Example 1 coating were from about 2 to 67 times more abrasion resistant than the comparison samples.

Example 9

In this Example, the sprayable composition of Example 1 was sprayed on an acrylic substrate, dried to remove solvents and irradiated with UV light to effect crosslinking according to Example 1. The dry film thickness of the cured coating was about 0.4 mil. " The cured, coated acrylic substrate was post- cured by heating it in an oven at 150°F. for about 4 hours. The post-cured coated substrate was then sub-jected to the steel wool abrasion- test of. Ex-ample.2_ using a more abrasive steel wool grade, #1 steel wool. After approximately 1000 double rubs there were no visible scratches on the coating, thus demonstrating that post-curing at elevated temp-eratures increases the abrasion resistance of cured coatings according to this invention.

Example 10 and 11

In these Examples, the procedure of Example 1 was repeat¬ ed except that in the coating formulation the weight ratio of pentaerythritol tetraacrylate to cellulose acetate butyrate was changed from 10 to 1 to 100 to 1 (Ex. 10) and to 6 to 1 (Ex. 11).

On testing for resistance to steel wool abrasion accord¬ ing to the procedure of Example 2 it was found that both the Example 10 and 11 coatings on a polyvinyl chloride substrate endured- about 20 double rubs without developing visible scratches which indicated that significant abrasion resist¬ ance of cured coatings according to the invention was still provided at the above ratios.

Example 12

In this Example, the procedure of Example 1 was fo

using di-pentaerythritol pentaacrylate instead of penta erythritol tetraacrylate. The cured coating on a polyviny chloride substrate was tested for steel wool abrasion i accordance with the procedure of Example 2. The results wer substantially the same in respect to abrasion resistance a the Ex. 1 coating.

Example 13

In the Example, the procedure of Example 1 was followe using benzoyl peroxide as a photoinitiator instead of alpha chloroacetyldiphenyloxide at a level of 1 weight percent base on the weight of pentaerythritol tetraacrylate. The composi tion was coated and cured on an acrylic substrate at a dr film thickness of about 0.3 mil. Steel wool abrasio resistance according to the procedure of Example 2 was as goo as the Ex. 1 coating.

Example 14

In this Example, the procedure of Example 1 was followe except that pentaerythritol tetramethacrylate was substitute for pentaerythritol tetraacrylate and about 150 p.b.w. o xylol was additionally used in preparing the coating formula¬ tion. About 1% benzoyl peroxide based on the weight of penta¬ erythritol tetramethacrylate was added as a co-photoinitiator with the alpha-chloroacetyldiphenyloxide. The sprayabl solution was sprayed on a polyvinyl chloride substrate at wet-film thickness of about 0.9 mil. After removal of sol¬ vents the dry film thickness was about 0.3 mil. The cure tim was about 15 sec. using high intensity UV light.

It was found that rubbing the coated surface with a #0000 steel wool pad according to the procedure of Example 2, pro¬ duced no scratches after 100 double rubs.