Adhesion promoters containing optical brightener

A composition comprising a chlorinated polyolefin and an optical brightener is disclosed. The compositions are useful as detectable adhesion promoters for polyolefin substrates. The compositions are applied as a coating to the polyolefin substrate and the coated substrate exposed to an ultraviolet light source to determine uniformity of the coating over the substrate. Uniform coverage is necessary to develop optimum adhesion between the substrate and a subsequently applied paint layer.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to compositions for use as adhesion promoters 
on polyolefin substrates and to a method of applying such compositions to 
the polyolefin substrate. More particularly, the present invention relates 
to compositions containing chlorinated polyolefins for use as adhesion 
promoters and to a method of applying such compositions to polyolefin 
substrates. 
2. Brief Description of the Prior Art 
Polyolefins such as ethylene and propylene as well as copolymers thereof 
are being used in increasing amounts in the fabrication of automobile 
bodies and trim such as front end fascia and filler panels located between 
the bumper and the chassis. These materials are light weight and have 
excellent impact resistance. They can withstand low speed collisions much 
better than metal counterparts. However, to be aesthetically acceptable, 
the polyolefin must be painted to match the paint on the rest of the 
automobile. Because of the low surface tension of polyolefins, it is very 
difficult to adhere paint directly to the surface of the polyolefin. 
It is known in the industry that the adhesion of a paint layer to a 
polyolefin substrate can be improved if the substrate is first treated 
with an adhesion promoter. Typical adhesion promoters are solutions of 
chlorinated polyolefins which when applied as a coating to the polyolefin 
substrate act as a tie layer between the polyolefin and the subsequently 
applied paint. However, if the adhesion promoter is not applied uniformly 
to the polyolefin substrate, the adhesion of the subsequently applied 
coating will fail. 
It is an object of the present invention to provide a detectable adhesion 
promoting composition, that is, one which when applied to the polyolefin 
substrate can be determined if it has been applied uniformly to the 
substrate. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, a composition which when applied 
as a coating to a polyolefin substrate improves the adhesion of the 
polyolefin to other materials is provided. The composition comprises a 
chlorinated polyolefin and an optical brightener. When the applied coating 
is exposed to an ultraviolet (UV) light, the optical brightener fluoresces 
and it can readily be determined if the coating has been applied uniformly 
across the substrate. 
The invention also provides for a method of treating the polyolefin 
substrate by applying to the polyolefin the composition described above, 
forming a substantially continuous film on the substrate and then exposing 
the coated substrate to an ultraviolet light source to detect the coverage 
of the composition over the substrate. 
In practicing the method of the present invention, one can determine before 
a subsequent painting operation whether the adhesion promoter is uniformly 
distributed over the surface of the substrate. This will significantly 
reduce rejected parts caused by adhesion failure of the paint to the 
substrate resulting in a considerable savings of time, labor and money. 
DETAILED DESCRIPTION 
The essential components in the composition of the present invention are a 
chlorinated polyolefin and an optical brightener. 
The chlorinated polyolefin may be a chlorinated copolymer of ethylene, 
propylene and copolymers thereof with homopolymers of polypropylene being 
preferred. Typically, the chlorine content of the chlorinated polyolefin 
will be about 15 to 75 percent by weight based on total weight of the 
monomer. The chlorinated polyolefins are available industrially as high 
chlorinated products, that is, 55 to 75 percent by weight chlorine, and as 
low as chlorinated products, that is, 15 to 50 percent by weight chlorine, 
with the low chlorinated products, particularly those of polypropylene, 
being preferred. 
The chlorinated polyolefins are usually prepared by polymerizing the olefin 
or mixture of olefins in an inert organic diluent in the presence of a low 
pressure polymerization catalyst. After polymerization, the catalyst is 
deactivated and the resultant polyolefin reaction mixture is treated with 
a chlorinating agent to produce the chlorinated polyolefin product. 
Chlorinated polyolefins are available industrially from Eastman Kodak 
Company as CP-343-1 and CP-515-2 and from Toyo Kasei Kogyo Co., Ltd. under 
the trademark HARDLEN. 
The chlorinated polyolefin is usually present in amounts of at least 10, 
preferably 20 to 80 percent by weight based on total solids weight of the 
composition. Amounts less than 10 percent by weight are undesirable 
because of insufficient adhesion promotion. 
The optical brighteners are compounds that absorb ultraviolet light and 
convert the energy taken up into the longer wavelength visible portions of 
the spectrum. This is evidenced by a fluorescence. Any optical brightener 
can be used in the practice of the invention as long as it can be 
formulated along with the chlorinated polyolefin into a composition which 
can be applied to the polyolefin substrate as a substantially continuous 
film. 
Typically, the optical brighteners are aromatic or heterocyclic compounds 
often with condensed ring structures and with an uninterrupted chain of 
conjugated double bonds. Examples of optical brighteners are derivatives 
of diaminostilbenedisulfonic acid such as the bistriazinyl derivatives, 
i.e., those compounds of the structure: 
##STR1## 
where X, X' and Y and Y' can be the same or different and include amino, 
substituted hydroxyl and chloro. 
Examples of other optical brighteners are bisazoles such as those of the 
structure: 
##STR2## 
where R is hydrogen, alkyl and alkoxy and X is an unsaturated radical such 
as: 
##STR3## 
Bisazoles are preferred in the practice of the invention because of their 
intense fluorescence upon exposure to UV light, and the compound 
2,2'-(2,5-thiophenediyl)bis(5-tert-butylbenzoxazole), that is, R equals 
tertiarybutyl and X equals 
##STR4## 
in the formula above, is especially preferred. 
The optical brightener is preferably present in the composition in amounts 
of at least 0.1, usually 0.1 to 2.5 percent by weight based on total 
solids weight of the composition. Amounts less than 0.1 percent by weight 
do not provide sufficient fluorescence upon exposure to UV light. The 
upper limit of optical brightener is not known with certainty, however, 
amounts greater than 2.5 percent by weight offer no particular advantage 
and increase the cost of the composition. However, amounts greater than 
2.5 percent can be used if desired. 
The compositions of the present invention also contain an organic diluent 
to reduce the viscosity of the compositions and to make them suitable for 
coating applications. The organic diluent should be a material which will 
disperse or preferably dissolve the chlorinated polyolefin and optical 
brightener. Non-polar solvents such as aromatic hydrocarbons, halogenated 
hydrocarbons and cycloaliphatic hydrocarbons can be used and are 
preferred. Polar solvents such as alcohols, ketones and esters may be used 
if used in minor amounts with non-polar solvents but their use is not 
preferred. Examples of suitable solvents include toluene, xylene, 
methylene chloride and cyclohexane. 
The organic solvent is usually present in the composition in amounts of 
about 50 to 98, preferably 70 to 95 percent by weight based on total 
weight of the composition. Amounts greater than 98 percent by weight are 
undesirable because of poor film build; whereas amounts less than 70 
percent by weight result in a composition which is very viscous and hard 
to handle. 
The composition can contain optional ingredients such as other resinous 
materials and pigments. Other resinous materials are often desirable to 
assist in the development of a continuous film and to provide for 
increased adhesion to the subsequent layer of paint. Examples of suitable 
adjuvant resins are vinyl acetate copolymers such as ethylene-vinyl 
acetate copolymers, alkyd resins, acrylic resins, and graft copolymers of 
vinyl monomers and alkyd resins. Vinyl acetate copolymer resins are 
preferred because in combination with chlorinated polyolefins, they 
provide a good combination of film-forming and adhesion-promoting 
properties. The co-resinous ingredients, if used, are preferably present 
in the compositions in amounts of up to 89, preferably 19 to 79 percent by 
weight based on total solids weight of the composition. 
The compositions of the invention can optionally be pigmented which 
provides color and conductivity to the coating. Examples of suitable 
pigments include titanium dioxide and carbon black. When used, the 
pigments are typically used in a pigment-to-resin weight ratio of about 
0.01 to 0.2:1. 
As mentioned above, the compositions of the present invention are applied 
to polyolefin substrates, particularly those substrates used in the 
fabrication of automobile bodies and trim such as bumpers, front end 
fascia and filler panels which are located between the bumper and the 
chassis. Usually, these flexible parts are made from thermoplastic 
polyolefin resins which are made by polymerizing olefins such as ethylene 
and propylene including copolymers thereof. The polyolefins most often 
used in the fabrication of automobile body parts and trim are 
ethylenepropylene copolymers which also contain a small amount of a 
non-conjugated diene such as dicyclopentadiene. Typical polymers are those 
containing from 50 to 75 percent by weight ethylene, 25 to 45 percent by 
weight propylene and 2 to 8 percent by weight non-conjugated diene. These 
polymers are available industrially from Republic Substrates Co. and 
Research Polymers Co. 
The compositions of the invention can be applied to the polyolefin 
substrate in any of the ways commonly used for applying coatings to 
substrates. The compositions can be applied by brushing, roll coating and 
spraying as long as a substantially continuous uniform film is formed on 
the substrate. Care should be taken that the correct amount of the 
composition is applied to the substrate. If the coating is too thick or 
too thin (non-uniform), adhesion failure of the substrate to the paint 
layer may result. Spraying is the preferred method of applying the 
composition to the substrate because it provides for the greatest control 
of coating thickness. Preferably, the coating thickness is controlled to 
levels of about 2 to 20 and more preferably from 3 to 15 microns. Air or 
airless spraying can be used. 
After the coating has been applied to the substrate, it is usually given an 
air flash to permit the solvents to volatilize. Preferably, the coating is 
then given an exposure to intense UV light such as from a medium pressure 
mercury arc lamp. Such lamps emit radiation over the range of 220 to 1400 
nanometers; emitting principally at 254, 313 and 365 nanometers. Exposure 
of this sort is not for the purpose of detecting coverage but seems to 
improve the adhesion promoting characteristics of the coating. Exposure 
need not be long but is usually at least 5 seconds, typically 5 seconds to 
2 minutes. 
The coated substrate is then exposed to UV light in the near, that is, 
about 360-370 nanometers, UV visible wavelength region to detect the 
uniformity of the coverage of the composition over the substrate. 
Light from this source, i.e., black light, is absorbed by the optical 
brightener and converted to energy in the visible portion of the spectrum 
where it appears as a fluorescence. 
By exposure of the coated substrate to the black UV light source and the 
resultant fluorescence, one can readily see whether the composition has 
been applied uniformly across the surface of the substrate. If different 
portions of the substrate fluoresce with different intensities or do not 
fluoresce at all, then the composition has not been applied uniformly and 
adhesion of the substrate to the layer of paint is uncertain. The 
polyolefin substrate can then be cleaned, recoated with the composition 
and evaluated again. Cleaning is easily accomplished by treating the 
coated substrate with an aromatic solvent. This is preferable to painting 
the substrate and finding out that the adhesion is unacceptable. The paint 
must then be stripped from the substrate or the painted part scrapped, 
both of which are costly. 
The layer of paint which is applied to the primed substrate described above 
is typically an elastomeric paint which is industrially available from 
many companies supplying the automotive industry. A typical paint is that 
provided by PPG Industries, Inc. under the trademark DURETHANE. Specific 
paint products are DURETHANE 700 and DURETHANE 800. The paint is typically 
cured at a temperature of 70.degree.-120.degree. C. for 15 to 40 minutes.

The present invention will be more fully understood from the following 
illustrated examples wherein all quantities, percentages and ratios are on 
a weight basis unless otherwise indicated. 
EXAMPLES 
A coating composition containing a chlorinated polyolefin and an optical 
brightener was prepared by first preparing a pigment paste followed by 
incorporation of the optical brightener into the pigment paste. The 
pigment paste was prepared from the following mixture of ingredients: 
______________________________________ 
Ingredient Parts by Weight (in grams) 
______________________________________ 
V + P Naphtha 41.20 
Cyclohexane 32.96 
Toluene 90.64 
ELVAX 260.sup.1 20 
Chlorinated polyolefin.sup.2 
20 
TiO.sub.2 1.2 
______________________________________ 
.sup.1 Ethylenevinyl acetate copolymer available from E. I. duPont de 
Nemours and Company. 
.sup.2 Chlorinated polypropylene (25 percent chlorine) available from 
Eastman Kodak Company as CP 3431. 
The V+P naphtha, cyclohexane and toluene were mixed together and heated to 
about 50.degree. C. The ELVAX 260 and CP 343-1 were first dissolved in the 
heated solvent mixture followed by the addition of the TiO.sub.2. The 
mixture was then ground in a Zircoa mill to a Hegman No. 7 grind. 
The optical brightener was incorporated into this pigment paste to form a 
sprayable coating composition as follows: 
______________________________________ 
Ingredient Parts by Weight (in grams) 
______________________________________ 
Pigment paste 206 
Optical brightener.sup.1 
2 
Cyclohexane 309 
Toluene 309 
______________________________________ 
.sup.1 UVITEX OB available from CibaGeigy used as a 5 percent by weight 
solution in toluene. 
The ingredients were mixed together in the order indicated with low shear 
mixing to form the coating composition containing 0.1 percent optical 
brightener based on weight of total solids. 
The coating composition was sprayed onto a thermoplastic polyolefin 
substrate (ETA 3131 available from Republic Substrates) to form a 
substantially continuous film having a thickness of about 10 microns. The 
film was then given an air flash at ambient temperature and then directly 
exposed to black UV light which showed a uniform fluorescence over the 
surface of the substrate indicating uniform coverage of the chlorinated 
polyolefin. 
When the substrate was topcoated with a coating composition available from 
PPG Industries, Inc. as DURETHANE 700 and heated at 120.degree. C. for 30 
minutes, excellent adhesion of the topcoat to the substrate was obtained. 
Additional compositions of the adhesion promoters were prepared as 
generally described above but with the exception that the compositions 
contained 0.5, 1.5 and 2.5 percent by weight optical brighteners. In each 
instance, it was found that when the adhesion promoting compositions were 
spray applied in a uniform manner over the thermoplastic polyolefin 
substrate (as evidenced by a uniform fluorescence when exposed to black UV 
light), excellent adhesion of the subsequently applied topcoat (DURETHANE 
700) was obtained. In each instance, the film thickness was about 10 
microns. 
A further experiment was conducted with a coating composition as generally 
described above containing 0.1 percent by weight optical brightener but in 
which the adhesion promoting composition was applied in a non-uniform 
manner to the thermoplastic polyolefin substrate. The composition was 
applied heavily in one area and lightly in another. Film thickness varied 
from 0 to 10 microns across the substrate. Upon exposure of the coated 
substrate to black UV light, a non-uniform fluorescence resulted. 
Application and curing of the topcoat DURETHANE 700 as generally described 
above resulted in very poor adhesion of the topcoat to the substrate. 
The above examples show that the adhesion promoting compositions containing 
a chlorinated polyolefin and the optical brighteners of the present 
invention provide a convenient way to determine whether the adhesion 
promoter is evenly distributed over a substrate, thereby insuring for good 
adhesion of the subsequently applied topcoat to the substrate.