Process for producing an ultraviolet radiation stabilized polymeric article

A process for producing an ultraviolet radiation stabilized polymeric, particularly polycarbonate, article comprising impregnation of the surface of said article with an ultraviolet radiation absorber by heating said polymeric article and applying onto the surface of said heated article an ultraviolet radiation stabilizing composition containing an ultraviolet radiation absorbing compound and a nonaggressive carrier.

This invention relates to polycarbonate resin and more particularly to a 
process for producing shaped polycarbonate articles exhibiting superior 
resistance to ultraviolet radiation. 
BACKGROUND OF THE INVENTION 
The vast majority of all organic polymeric materials undergo some mode of 
degradation when exposed to the high energy photons of ultraviolet 
radiation. The degradation manifests itself depending on the polymeric 
material in yellowing, discoloration, embrittlement and other loss of 
physical properties. Polycarbonate resin is no exception and it is, 
therefore, an object of this invention to provide a method of producing a 
polycarbonate resin article which is highly resistant to ultraviolet 
radiation degradation. 
The use of ultraviolet radiation absorbers with various resins, such as 
polyesters, polyolefins, vinyls, and polystyrene to provide protection 
against attack by ultraviolet radiation is known in the art. The 
ultraviolet radiation absorber functions by reason of its ability to 
screen out the damaging ultraviolet portion of light due to its very high 
absorptivity relative to that of the polymer. In order to qualify as a 
successful ultraviolet light absorber for a polymer, particularly for 
polycarbonate, there are several requirements which the absorber must 
fulfill. The absorber must have a high specific absorptivity in the range 
of wave lengths that are most deleterious to the polymer and that are 
present in the source of the exposure. The absorber must be compatible 
with the polymer such as polycarbonate and must not degrade the polymer 
with loss of properties and increase in color. The absorber must not 
significantly absorb in the visible region of the spectrum or a color will 
be imparted to the polymer to which it has been added. The absorber must 
also have a sufficiently low volatility to permit its continued residence 
in the polymer. 
Several methods are known in the prior art utilizing these ultraviolet 
radiation absorbers to stabilize various polymers, including 
polycarbonate, against ultraviolet radiation. These methods include 
blending the ultraviolet radiation absorbers with the polymer prior to 
processing; incorporating the absorbers in surface laminating or coating 
materials which are applied onto the surface of the processed polymer; and 
impregnating the absorbers in the polymer surface. The surface 
impregnation techniques known in the prior art include (i) using 
aggressive solvents to swell or soften the polymer surface thereby 
allowing the absorber to diffuse into the softened surface of the polymer; 
(ii) melting the absorber and the polymer surface in order to diffuse the 
molten absorber into the molten polymer surface; and (iii) partitioning of 
the absorber between a polymeric surface and a relatively poor solvent for 
the absorber held at high temperatures whereby the absorber, which is more 
soluble in the polymer than in the solvent, diffuses into the polymer 
surface. 
While each of these methods can be utilized to impart improved ultraviolet 
stability to a polymer system, each of them has certain disadvantages. 
Blending the absorber with the bulk polymer results in the absorber being 
distributed throughout the entire polymer system. This procedure is both 
uneconomical, as these absorbers are usually quite expensive, and not 
completely successful. Since most of the absorber resides in the polymer's 
interior instead of at the surface where it is most needed, much of the 
harmful ultraviolet radiation penetrates and deteriorates the surface of 
the polymer structure before reaching the majority of the interiorly 
distributed absorber. Furthermore, since the concentration of the absorber 
in the resin is limited by the degree of compatibility of the absorber 
with the polymer, using sufficiently high concentrations of absorber 
effective to provide surface protection generally tends to adversely 
affect the physical properties of the polymer. Incorporating the absorbers 
in surface laminating or coating materials suffers from the disadvantage 
of being difficult and expensive to use since an extra complicated 
processing step is required. Furthermore, difficulties are sometimes 
encountered in adhering the coating or laminating material to the surface 
of the polymer, or in maintaining continued adequate adhesion, especially 
after exposure to weathering. Even when the coating or laminating material 
adheres well, they often cannot be applied without forming unsightly 
streaks on the polymer surface. An additional drawback to this method is 
that often the physical properties of the polymer, such as impact 
strength, are adversely affected by these coating or laminating materials. 
While, in principle, the surface impregnation techniques are the most 
desirable since the ultraviolet radiation absorbers are contained only in 
the surface regions of the polymer where they are needed, in practice the 
prior art surface impregnation techniques all suffer from certain 
disadvantages. Melting the polymer and the absorbers in order to diffuse 
the absorbers into the polymer surface suffers from the defect that the 
polymer, or at least its surface region, must be heated to the melting 
point. This may result in an uneven or wrinkled polymer surface being 
formed upon cooling and solidifying of the polymer. Furthermore, the 
physical properties of the polymer may sometimes be deleteriously affected 
by this melting of the polymer. In the aggressive solvent technique an 
ultraviolet radiation absorbing compound is dissolved in a solvent which 
is aggressive towards the polymer, such as polycarbonate. Typical 
aggressive solvents for polycarbonate include chlorinated hydrocarbons, 
esters, or aromatic hydrocarbons. When these solutions are applied onto 
the surface of a polycarbonate article the aggressive solvent functions as 
a softening or swelling agent for the polymer surface allowing the 
absorber to diffuse into the softened or swelled polymer surface regions. 
However, the aggressive nature of these solvents causes problems. Surface 
imperfections can occur during coating and prolonged contact between the 
polymer and the aggressive solvent can lead to etching, hazing and crazing 
of the polymer. Using ultraviolet radiation stabilizing solutions 
containing an ultraviolet radiation absorbing compound which is more 
soluble in the polymer than in the stabilizing solution rather sharply 
limits the number and type of ultraviolet radiation absorbing compounds 
which may be used. Also, a large volume of the stabilizing solution must 
be used. This requires the use of large amounts of ultraviolet radiation 
absorber which is a rather expensive proposition. 
Thus, there is a need for an economical and effective method for protecting 
polymeric, particularly polycarbonate, articles from the degradation 
caused by ultraviolet radiation. The instant invention provides such a 
method. 
DESCRIPTION OF THE INVENTION 
In accordance with the present invention there is provided a method of 
producing an ultraviolet radiation resistant polycarbonate article 
comprising impregnating the surface region of the polycarbonate article 
with an ultraviolet radiation absorber by heating the polycarbonate 
article and applying onto said heated article an ultraviolet radiation 
stabilizing composition containing an ultraviolet radiation absorbing 
compound and a nonaggressive liquid carrier for said compound. 
In accordance with the present invention an article comprised of 
polycarbonate resin is formed in a conventional manner, for example by 
injection molding, extrusion, cold forming, vacuum forming, blow molding, 
compression molding, transfer molding, and the like. The article may be in 
any shape and need not be a finished article of commerce, that is, it 
could be sheet material or film which would be cut or sized or 
mechanically shaped into a finished article. Therefore, as used herein, it 
will be understood that the term "article" refers to any shape or form of 
polycarbonate resin whether finished or stock material. 
The aromatic carbonate polymer used in the practice of the instant 
invention has recurring structural units of the formula 
##STR1## 
where A is a divalent aromatic radical of the dihydric phenol employed in 
the polymer producing reaction. These polycarbonate resins are high 
molecular weight aromatic carbonate polymers which may be prepared by 
reacting a dihydric phenol with a carbonate precursor such as phosgene, a 
haloformate or a carbonate ester. 
The aromatic carbonate polymers of this invention may be prepared by 
methods well known in the art and described in U.S. Pat. Nos. 3,161,615; 
3,220,973; 3,312,659; 3,312,660; 3,313,777; 3,666,614; and 3,989,672 all 
of which are incorporated herein by reference. 
Also included herein are branched polycarbonates wherein a polyfunctional 
aromatic compound is reacted with the dihydric phenol and the carbonate 
precursor to provide a thermoplastic randomly branched polycarbonate 
wherein the recurring units of formula I contain branching groups. 
The preferred polycarbonate resin is one which may be derived from the 
reaction of bisphenol-A with phosgene. These preferred polycarbonates have 
from about 10 to about 400 recurring structural units of the formula 
##STR2## 
The polycarbonate should preferably have an intrinsic viscosity between 0.3 
and 1.0, more preferably from 0.4 to 0.65 as measured at 25 degrees C. in 
methylene chloride. 
To the surface of this polycarbonate article, which has been heated, is 
applied an ultraviolet radiation stabilizing composition which contains at 
least one ultraviolet radiation absorbing compound and at least one 
nonaggressive liquid carrier for said absorbers. By nonaggressive is meant 
that the liquid carrier is nonaggressive towards the polycarbonate, i.e., 
it does not attack and deleteriously affect the resin. 
The ultraviolet radiation stabilizing composition of the instant invention 
may be in the form of a solution of the ultraviolet radiation absorber 
dissolved in the nonaggressive liquid carrier, a suspension or dispersion 
of the absorber suspended or dispersed in the liquid carrier, or part 
solution and part suspension or dispersion of the absorber in the carrier. 
Whether the stabilizing composition is in the form of a solution, a 
suspension or dispersion, or both a solution and a dispersion or 
suspension depends in part on the solubility of the particular absorber in 
the particular carrier with which it is combined. If the absorber is very 
soluble in the carrier then the stabilizing composition will be in the 
form of a solution. If the absorber is not very soluble in the carrier 
then the stabilizing composition will be in the form of a suspension or 
dispersion of the absorber in the carrier. If the absorber has medium 
solubility in the carrier then the stabilizing composition will have the 
character of both a solution and a suspension or dispersion with part of 
the amount of the absorber present being dissolved in the carrier and the 
remainder of the undissolved absorber being suspended or dispersed in the 
carrier. Also affecting the character of the stabilizing composition is 
the amount of the absorber present in the composition. Thus, if a small 
amount of an absorber having medium solubility in a particular carrier is 
used the stabilizing composition will tend to be in the form of a 
solution. If, however, a larger amount of the same absorber is used with 
the same carrier then the stabilizing composition will tend to be in the 
form of both a solution and a dispersion or suspension. Preferably the 
stabilizing composition should be in the form of a solution in order to 
achieve optimum results. 
The stabilizing composition contains a stabilizing amount of the 
ultraviolet radiation stabilizing or absorbing compound. By stabilizing 
amount is meant an amount of absorber effective to stabilize the 
polycarbonate article against degradation by ultraviolet radiation after 
the polycarbonate article has been treated with the stabilizing 
composition. Generally, a stabilizing amount of the ultraviolet radiation 
absorber is present when the stabilizing composition contains from about 
0.01 to about 15 weight percent of the ultraviolet radiation absorber, 
preferably from about 0.1 to about 10 weight percent of the ultraviolet 
radiation absorber, and more preferably from about 1 to about 8 weight 
percent of the absorber. The stabilizing composition may contain only one 
ultraviolet radiation absorbing compound or a combination of two or more 
ultraviolet radiation absorbing compounds. If two or more ultraviolet 
radiation absorbing compounds are present in the stabilizing composition 
their combined weight percentages should be from about 0.01 to about 15 
weight percent of the stabilizing composition. 
The ultraviolet radiation absorbers employed in the practice of this 
invention can be any of the known ultraviolet radiation absorbent 
compounds which function by reason of their ability to screen out the 
damaging ultraviolet portion of light due to their very high absorptivity 
in this region of the spectrum. These compounds include the benzophenones 
and benzophenone derivatives, benzotriazoles and benzotriazole 
derivatives, benzoate esters, phenyl salicylates, derivatives of crotonic 
acid, malonic acid esters, and cyanoacrylates. 
Ultraviolet radiation absorbers which fall into the benzophenone and 
benzotriazole derivatives include those compounds disclosed in U.S. Pat. 
Nos. 3,309,220; 3,049,443; and 2,976,259 all of which are incorporated 
herein by reference, Some non-limiting examples of these compounds 
include: 
2,2'-dihydroxybenzophenone; 
2,2',4,4'-tetrahydroxybenzophenone; 
2,2'-dihydroxy-4,4'-dimethoxybenzophenone; 
2,2'-dihydroxy-4,4'-diethoxybenzophenone; 
2,2'-dihydroxy-4,4'-dipropoxybenzophenone; 
2,2'-dihydroxy-4,4'-dibutoxybenzophenone; 
2,2'-dihydroxy-4-methoxy-4'-ethoxybenzophenone; 
2,2'-dihydroxy-4-methoxy-4'-propoxybenzophenone; 
2,2'-dihydroxy-4-methoxy-4'-butoxybenzophenone; 
2,2'-dihydroxy-4-ethoxy-4'-propoxybenzophenone; 
2,2'-dihydroxy-4-ethoxy-4'-butoxybenzophenone; 
2,3'-dihydroxy-4,4'-dimethoxybenzophenone; 
2,3'-dihydroxy-4-methoxy-4'-butoxybenzophenone; 
2-hydroxy-4,4',5'-trimethoxybenzophenone; 
2-hydroxy-4,4',6'-tributoxybenzophenone; 
2-hydroxy-4-butoxy-4',5'-dimethoxybenzophenone; 
2-hydroxy-4-ethoxy-2',4'-dibutylbenzophenone; 
2-hydroxy-4-propoxy-4',6'-dichlorobenzophenone; 
2-hydroxy-4-propoxy-4',6'-dibromobenzophenone; 
2,4-dihydroxybenzophenone; 
2-hydroxy-4-methoxybenzophenone; 
2-hydroxy-4-ethoxybenzophenone; 
2-hydroxy-4-propoxybenzophenone; 
2-hydroxy-4-butoxybenzophenone; 
2-hydroxy-4-methoxy-4'-methylbenzophenone; 
2-hydroxy-4-methoxy-4'-ethylbenzophenone; 
2-hydroxy-4-methoxy-4'-propylbenzophenone; 
2-hydroxy-4-methoxy-4'-butylbenzophenone; 
2-hydroxy-4-methoxy-4'-tertiary butylbenzophenone; 
2-hydroxy-4-methoxy-4'-chlorobenzophenone; 
2-hydroxy-4-methoxy-2'-chlorobenzophenone; 
2-hydroxy-4-methoxy-4'-bromobenzophenone; 
2-hydroxy-4,4'-dimethoxybenzophenone; 
2-hydroxy-4,4'-dimethoxy-3-methylbenzophenone; 
2-hydroxy-4,4'-dimethoxy-2'-ethylbenzophenone; 
2-hydroxy-4,4',5'-trimethoxybenzophenone; 
2-hydroxy-4-ethoxy-4'-methylbenzophenone; 
2-hydroxy-4-ethoxy-4'-ethylbenzophenone; 
2-hydroxy-4-ethoxy-4'-propylbenzophenone; 
2-hydroxy-4-ethoxy-4'-butylbenzophenone; 
2-hydroxy-4-ethoxy-4'-methoxybenzophenone; 
2-hydroxy-4,4'-diethoxybenzophenone; 
2-hydroxy-4-ethoxy-4'-propoxybenzophenone; 
2-hydroxy-4-ethoxy-4'-butoxybenzophenone; 
2-hydroxy-4-ethoxy-4'-chlorobenzophenone; 
2-hydroxy-4-ethoxy-4'-bromobenzophenone; 
2-(2'-hydroxy-5'-methylphenyl)-benzotriazole; 
2-(2'-hydroxy-5'-tert-butylphenyl)benzotriazole; 
2-(2'-hydroxy-3'-methyl-5'-tert-butylphenyl)-benzotriazole; 
2-(2'-hydroxy-5'-cyclohexylphenyl)-benzotriazole; 
2-(2'-hydroxy-3',5'-dimethylphenyl)-benzotriazole; 
2-(2'-hydroxy-5'-tert-butylphenyl)-5-chloro-benzotriazole: and 
2-(2'-hydroxy-3'-di-tert-butylphenyl)-benzotriazole. 
Two non-limiting examples of derivatives of crotonic acid which function as 
ultraviolet radiation absorbers are 
alpha-cyano-beta-(p-methoxyphenyl)-crotonic acid methyl ester and 
alpha-cyano-beta-N-(2-methyl-indolinyl)-crotonic acid methyl ester. The 
benzoate ester ultraviolet radiation absorbers include the C.sub.8 
-C.sub.20 alkyl and aryl benzoates, alkyl and aryl hydroxybenzoates, 
alkaryl and aralkyl benzoates, and alkaryl and aralkyl hydroxybenzoates. 
The malonic acid esters which are effective ultraviolet radiation absorbers 
include the benzylidene malonates. These benzylidene malonates are 
represented by the general formula 
##STR3## 
wherein X is selected from hydrogen, hydroxyl, halogen, alkyl, preferably 
C.sub.1 -C.sub.10 alkyl, and alkoxy, preferably C.sub.1 -C.sub.10 alkoxy, 
radicals; and R and R.sup.1 are independently selected from alkyl 
radicals, preferably alkyl radicals containing from 1 to about 10 carbon 
atoms, substituted alkyl radicals, preferably those containing from 1 to 
about 10 carbon atoms and hydroxyl or halogen substituents, aryl radicals, 
preferably the phenyl radical, alkaryl radicals, preferably alkaryl 
radicals containing from 7 to about 12 carbon atoms, aralkyl radicals, 
preferably aralkyl radicals containing from 7 to about 12 carbon atoms, 
and substituted aryl radicals, preferably those phenyl radicals containing 
hydroxyl or halogen substituents. Preferred benzylidene malonates 
represented by formula III are those wherein X represents an alkoxy group 
and R and R.sup.1 are independently selected from alkyl radicals. Examples 
of such benzylidene malonates include diethyl paramethoxybenzylidene 
malonate and dimethyl paramethoxybenzylidene malonate. 
Among the cyano-acrylates which are useful ultraviolet radiation absorbers 
are those cyano acrylates represented by the general formula 
##STR4## 
wherein R.sup.2 is alkyl or hydroxyalkyl. These compounds are disclosed in 
U.S. Pat. No. 4,129,667 which is incorporated herein by reference. 
The preferred ultraviolet radiation absorbing compounds, for the purposes 
of the present invention, are benzophenone and the benzophenone 
derivatives, benzotriazole and the benzotriazole derivatives, the 
benzylidene malonates, and the cyano-acrylates. 
The stabilizing composition contains at least one nonaggressive liquid 
carrier for the ultraviolet radiation absorber. This liquid carrier is 
nonaggressive towards the polycarbonate, i.e., it does not attack the 
polycarbonate and does not cause the polycarbonate to swell or soften. The 
stabilizing composition can contain only one liquid carrier or it may 
contain two or more of the liquid carriers. If two or more of the liquid 
carriers are present in the stabilizing composition they must be miscible 
with each other. The preferred nonaggressive liquid carriers for the 
ultraviolet absorber include hydroxy ethers, alcohols, alcohol-water 
mixtures, liquid aliphatic hydrocarbons, liquid cycloaliphatic 
hydrocarbons, and chlorofluorocarbons such as those marketed by the E. I. 
duPont Company under the tradename Freon, e.g., dichlorodifluoromethane, 
trichloromonofluoromethane, and the like. Generally it is preferred that 
these liquid carriers be relatively volatile, i.e., that they volatilize 
at or below about 130.degree. C. 
The preferred alcohols are the aliphatic alcohols with the alkanols, 
particularly the C.sub.1 -C.sub.6 alkanols, being preferred. Some 
nonlimiting examples of these C.sub.1 -C.sub.6 alkanols include methanol, 
ethanol, propanol, isopropanol, tertiary butanol, and the like. 
The preferred liquid aliphatic and cycloaliphatic hydrocarbons are the 
liquid saturated aliphatic and cycloaliphatic hydrocarbons containing from 
5 to about 20 carbon atoms. Some nonlimiting examples of these 
hydrocarbons include pentane, hexane, octane, nonane, decane, undecane, 
the various positional isomers of the foregoing, cyclohexane, 
cyclopentane, cyclooctane, and the like. 
The hydroxy-ethers which are useful as carriers in the stabilizing 
composition are compounds represented by the formula 
EQU R.sup.3 --O--R.sup.4 --OH V. 
wherein R.sup.3 is an alkyl or an alkoxy alkyl radical containing from 1 to 
about 6 carbon atoms, and R.sup.4 is a divalent saturated aliphatic 
hydrocarbon radical containing from 1 to about 6 carbons. 
In the practice of the process of the instant invention a stabilizing 
composition containing the ultraviolet radiation absorber and the 
nonaggressive liquid carrier therefore is applied onto the surface of a 
preheated polycarbonate article by any of several known methods such as 
spraying, flow coating, brushing, and the like. The stabilizing 
composition is kept in contact with the preheated polycarbonate article 
for a period of time sufficient for the ultraviolet radiation absorber to 
effectively impregnate the surface layers of the polycarbonate article, 
this is for the ultraviolet radiation absorber to diffuse throughout the 
surface layers of the polycarbonate article in concentrations sufficient 
to provide protection against the deleterious effects of ultraviolet 
radiation. Since the stabilizing composition is nonaggressive towards the 
polycarbonate there is no upper time limit that the composition can remain 
in contact with the polycarbonate. Rather, the upper time limit is 
governed by such secondary considerations as speed of processing of the 
polycarbonate article, rate of cooling of the polycarbonate--if the 
polycarbonate cools below the critical temperature no more ultraviolet 
radiation absorber will diffuse into the polycarbonate--, rate of 
evaporation of the liquid carrier, and the like. The minimum period of 
time that the stabilizing composition is kept in contact with the 
polycarbonate article is the period of time which is sufficient for the 
ultraviolet radiation absorber to impregnate the surface layers of the 
polycarbonate in concentrations effective to protect the polycarbonate 
against degradation by ultraviolet radiation. This minimum period 
generally depends to a certain degree upon the particular ultraviolet 
radiation absorber present in the stabilizing composition, the particular 
liquid carrier present in the stabilizing composition, and the temperature 
to which the polycarbonate article is preheated. Generally, the 
stabilizing composition is kept in contact with the polycarbonate article 
from about 5 seconds to about 30 minutes, and preferably from about 30 
seconds to about 15 minutes. 
It is critical to the practice of the present process that the 
polycarbonate article be at a temperature sufficiently high when the 
stabilizing composition is contacted therewith for the ultraviolet 
radiation absorber to impregnate the surface layers thereof in 
concentrations effective to provide protection against degradation of the 
polycarbonate by ultraviolet radiation. If the polycarbonate is not at a 
temperature effective for the impregnation of the absorber into the 
polycarbonate surface layers when the stabilizing composition is applied 
onto the polycarbonate the ultraviolet absorber will not diffuse into or 
impregnate the surface layers of the polycarbonate and, consequently, the 
polycarbonate will not be protected against degradation by ultraviolet 
radiation. Generally, the minimum temperature at which impregnation of the 
polycarbonate article by the ultraviolet radiation absorber takes place is 
about 65.degree. C. Preferably the polycarbonate should be at about at 
least 75.degree. C. as at this temperature and above the ultraviolet 
radiation absorber generally diffuses rapidly and in large amounts into 
the surface layers of the polycarbonate resin article. The maximum 
temperature of the polycarbonate during contact with the stabilizing 
composition is governed by the fact that the temperature of the 
polycarbonate resin be not sufficiently high so as to deleteriously affect 
the physical properties of the polycarbonate resin. Thus the upper 
temperature limit is below about 150.degree. C. which is the glass 
transition temperature of the polycarbonate resin. Preferably it should be 
below about 135.degree. C., the temperature at which bubbles and other 
imperfections begin to appear in the polycarbonate resin. 
Thus in the practice of the instant process the polycarbonate should be at 
a temperature between about 65 and about 149 degrees C. during contact 
with the stabilizing composition. For optimum results and optimum 
operating conditions the polycarbonate article should preferably be at a 
temperature between about 75 and about 135 degrees C. The polycarbonate 
article is preheated to this temperature before the stabilizing 
composition is contacted therewith. There is no active heating of the 
polycarbonate article during the period when the stabilizing composition 
is in contact with the surface thereof. The stabilizing composition is not 
heated but is at room temperature at the time of application onto the 
polycarbonate. An example of the application of the instant method is the 
application of the stabilizing composition onto the surface of a 
polycarbonate article coming out of an extruder. 
After the stabilizing composition has been in contact with the preheated 
polycarbonate article for a period of time sufficient for the ultraviolet 
radiation absorber to diffuse into the surface areas of the polycarbonate 
in concentrations effective to stabilize the polycarbonate against 
degradation by ultraviolet radiation the polycarbonate article is washed, 
for example with isopropanol, to remove any residue of the stabilizing 
composition from the surface of the polycarbonate article. This washing of 
the surface of the polycarbonate article is an optional procedure. 
It is to be understood that the polycarbonate resin used in the practice of 
the present invention may contain various known additives such as 
plasticizers, fillers, flame retardants and the like. 
DESCRIPTION OF THE PREFERRED EMBODIMENT 
In order to more fully and clearly illustrate the present invention, the 
following specific examples are presented. It is intended that the 
examples be considered as illustrative rather than limiting the invention 
disclosed and claimed herein. In the examples all parts and percentages 
are on a weight basis unless otherwise specified.

EXAMPLE 1 
A 10 mil thick film of polycarbonate resin was taped to a 1/4 inch thick 
panel of polycarbonate (to act as a heat body simulating extrusion line 
conditions for 1/4 inch thick polycarbonate panels), heated to 125 degrees 
C., and flow coated with a solution of 5% 
2,2',4,4'-tetrahydroxybenzophenone in 2-butoxyethanol. After cooling, the 
film was vigorously washed with isopropanol. This treatment did not 
visibly alter the optical quality of the film. The treated film was placed 
in the sample beam of a Perkin-Elmer Model Coleman 575 Spectrophotometer 
and an untreated film was placed in the reference beam. The absorbance of 
the treated film was greater than 2 in the 290-350 nm. Using the 
relationship A=log I.sub.o /I where A is the absorbance, I.sub.o is the 
intensity of incident light, and I is the intensity of transmitted light, 
it was determined that an absorbance greater than 2 corresponds to 
absorption of more than 99% of the incident light by the treated film at 
.lambda. maximum. 
EXAMPLE 2 
The procedure of Example 1 was substantially repeated except that the 
stabilizing composition contained 5% of Uvinul N-539 (a cyanoacrylate 
ultraviolet radiation absorber marketed by GAF Corp. and represented by 
general formula IV wherein R.sup.2 is a C.sub.8 H.sub.17 radical). The 
absorbance of the treated film was found to be 1.82, which corresponds to 
absorption of 98% of the incident ultraviolet light by the treated film. 
EXAMPLE 3 
The procedure of Example 1 was substantially repeated except that the 
stabilizing composition contained 5% of Cyasorb UV-1988 (a benzylidene 
malonate ultraviolet radiation absorber marketed by American Cyanimid Co. 
and represented by general formula III wherein X is the OCH.sub.3 radical 
and R and R.sup.1 are methyl radicals). The absorbance at .lambda. max. of 
the treated film was found to be greater than 3, which corresponds to 
absorption at .lambda. max. of more than 99% of the incident ultraviolet 
light by the treated film. 
EXAMPLE 4 
The procedure of Example 1 was substantially repeated except that the 
stabilizing composition contained 5% of Uvinul N-35 (a cyanoacrylate 
ultraviolet radiation absorber marketed by GAF Corp. and represented by 
general formula IV wherein R.sup.2 is the ethyl radical). The absorbance 
of the treated film was found to be 2.5, which corresponds to absorption 
of more than 99% of the incident ultraviolet light by the treated film. 
EXAMPLE 5 
The procedure of Example 1 was substantially repeated except that the 
stabilizing composition contained 5% of 
2-hydroxy-4-dodecyloxybenzophenone. The absorbance of the treated film was 
found to be 1.3, which corresponds to absorption of 95% of the incident 
ultraviolet light by the treated film. 
EXAMPLE 6 
The procedure of Example 1 was substantially repeated except that the 
stabilizing composition contained 5% of Cyasorb 5411 (a derivative of 
benzotriazole marketed by American Cyanimid Co.). The absorbance of the 
treated film was found to be 2.2, which corresponds to absorption of more 
than 99% of the incident ultraviolet light by the treated film. 
EXAMPLE 7 
A 10 mil thick polycarbonate film was taped to a 1/4 inch thick panel of 
polycarbonate, heated to 75 degrees C., and flow coated with a solution of 
3% Cyasorb uv-1988 in butoxyethanol. After cooling the film was washed 
with isopropanol. Treatment did not visibly alter the optical quality of 
the film. The treated film was placed in the sample beam of a Perkin-Elmer 
Model Coleman 575 Spectrophotometer and an untreated film was placed in 
the reference beam. The absorbance was 1.7 in the 290-350 nm. range. This 
absorbance corresponds to absorption of 97% of the incident ultraviolet 
light by the treated film. 
EXAMPLE 8 
This Example illustrates a method falling outside the scope of the present 
invention. This method, in which the polycarbonate is not heated before 
application of the stabilizing composition, is not effective in providing 
protection to polycarbonate resins against degradation by ultraviolet 
radiation. A 10 mil thick film of polycarbonate was flow coated with a 
solution of 3% Cyasorb uv-1988 in butoxyethanol. After standing at room 
temperature for 18 hours the film was washed with isopropanol. The 
absorbance of the film was obtained according to the procedure described 
in Example 1. The absorbance of this film was found to be 0 indicating 
that no ultraviolet radiation absorber had diffused into the polycarbonate 
film. 
EXAMPLE 9 
A treated film produced substantially in accordance with the procedure of 
Example 7 and an untreated film were placed 10 inches below two General 
Electric Company RS-sunlamps on a rotating table. After 4 days, the 
untreated film was yellow while the treated film was colorless. 
As can be seen from the foregoing Examples the present method is effective 
in surface impregnating a polycarbonate resin with an ultraviolet 
radiation absorbing compound while a similar method, which differs from 
the instant method only in the omission of preheating the polycarbonate, 
is not effective in impregnating the surface of polycarbonate with the 
absorber. 
The success of the instant process in providing protection for 
polycarbonate resins against degradation by ultraviolet radiation is 
surprising and rather unexpected. Those skilled in the art could have 
expected in view of the teachings of the prior art that applying a 
stabilizing composition containing an ultraviolet radiation absorber and a 
nonaggressive liquid carrier on a hot but unmolten polycarbonate resin 
would result only in volatilization of the carrier and/or the stabilizer 
and no surface interaction between the absorber and the polycarbonate. 
The present process does not deleteriously affect the advantageous physical 
properties of the polycarbonate resin. When the non-opaque films of the 
foregoing examples were treated according to the process of the instant 
invention the optical properties of these films were not altered by the 
treatment. 
In the practice of the present invention the liquid carrier must not only 
be nonaggressive towards the polycarbonate, but should also wet the 
polycarbonate. Thus, for example, while water is nonaggressive towards 
polycarbonate it is not an effective liquid carrier for the purposes of 
the present invention because it does not wet the polycarbonate. 
The foregoing disclosure of this invention is not to be considered as 
limiting, since many variations may be made by those skilled in the art 
without departing from the scope or spirit of the foregoing description.