Note: Descriptions are shown in the official language in which they were submitted.
~14~33~
TITLE
Process for Improving the Adhesion of
Paint to Pol olefin Surfaces
y
BACKG~OUND OF THE INVENTION
~his invention relates to a process for
modifying the surface of articles made of certain
polyolefins and polyolefin blends to improve adhesion
of paints and similar protective or decorative coat-
ings thereto.
Polyolefins such as polyethylene, poly-
propylene, and ethylene/propylene copolymers have
found many applications, for example, in household
~articles,~toys, appliances, furniture, and automobile
parts. It is often desirable to apply to the exterior
surface of a polyolefin article a protective or
decorative coating, especially paint, but it is nec-
essary to first prepare the surface either by mechani-
cal treatment or by use of a primer. It is known to
use as primers various ultraviolet sensitizers, for
example, benzophenone or trichloroethylene, then to
irradiate the surface with ultraviolet light. It is
also known to use primers which do not require ultra-
violet irradiation, for example, a chlorinated poly-
olefin sold by Eastman Kodak company and believed to
be a chlorinated polypropylene.
While most prior art methods of chemical
surface modification are adequate for certain poly-
olefin materials, they are not entirely satisfactory
for others. Thus, it is easier to prime the surface
of a vulcanized EPDM copolymer than of polypropylene
or polyethylene. EPDM copolymers are either copoly-
mers of ethylene, propylene, and a nonconjugated diene
having only one polymerizable double bond or copoly-
mers of ethylene, propylene, a diene having only one
polymerizable double bond, and a nonconjugated diene
in which both double bonds are polymerizable.
LC-2119
~.
~41330
Since it is frequently preferred to use a
polymer blend, rather than a single polymer, in
fabricating a polyolefin article, the selection of a
suitable primer will thus depend on the composition of
5 the blend. For example, blends of polypropylene with
EPDM copolymers have been found to be particularly
useful for automobile bumpers, bumper inserts, and
automobile trim. Because those automobile parts are
exposed to varying atmospheric conditions, to rain
10 water, and to hot water in automatic car wash instal-
lations, good adhesion of paint is particularly diffi-
cult to achieve. If the paint finish blisters or
peels, the part is unsatisfactory both to the car manu-
facturer and to the car owner. Accordingly, there is
15 great need in the industry for a primer that woul~
provide good dry and wet paint adhesion to surfaces or
articles made from a polyolefin or polyolefin blend in
which polyethylene or polypropylene is the only or the
predominating polymer.
SUMMARY OF THE INVENTION
According to the present invention, there is
now provided a process for improving the adhesion of
paint to a surface of an article made of polyolefin
selected from:
(1) polyethylene, polypropylene, and crystal-
line dipolymers of ethylene and propylene;
(2) blends of at least two members of the
group recited in (l) above; and
(3) blends of at least one member of the
30 group recited in (l) above with at least one elastomer
selected from the class of ethylene/propylene dipolymers
and EPDM copolymers in which the total amount of elas-
tomeric polymers is at most about 50 weight percent of
the final polymer blend;
said process comprising the steps of:
(a) cleaning said surface;
114133(1
~b~ applying to the cleaned surface a thin
layer of a chlorinated polypropylene, and
(c) exposing the chlorinated polypropylene
coated surface to ultraviolet radiation.
DETAILED DESCRIPTION OF THE INVENTION
The polyolefins to which the surface modi-
fication process of the present invention is appli-
cable are well known to the art and are readily avail-
able commercially from one or more sources. There is
10 abundant patent literature which discloses processes
for making both high and low density polyethylene;
isotactic and syndiotactic polypropylene; both crystal-
line and elastomeric ethylene/propylene dipolymers; and
EPDM copolymers, both tri- and tetrapolymers. These
15 patents are well known to a polymer chemist. The pre-
ferred crystalline ethylene/propylene dipolymers are
the hard, impact-resistant grades, which contain up to
22 weight percent ethylene. The preferred elastomeric
ethylene/propylene copolymers contain about 30-75%
20 ethylene, 60-90% propylene, and 0-10% nonconjugated
diene or dienes. These copolymers are rubbery and sub-
stantially amorphous. Nonconjugated dienes having only
one polymerizable double bond, which can be copolymer-
ized with ethylene and propylene to EPDM copolymers
25 have about 6-22 carbon atoms and include, for example,
acyclic dienes such as: 1,4-hexadiene, l,9-octadiene,
ll-ethyl-l,ll-tridecadiene, 9-ethyl-1,9-undecadiene,
8-ethyl-1,8-decadiene, 10-ethyl-1,9-dodecadiene,
12-ethyl-1,12-tetradecadiene, 13-butyl-1,12-heptadeca-
30 diene, and 15-ethyl-1,15-heptadecadiene; and cyclic
dienes such as: dicyclopentadiene, 5-butenyl-2-nor-
bornene, 5-ethylidene-2-norbornene, 5-methylene-2-nor-
bornene, 2-ethyl-2,5-norbornadiene, and 1,5-cyclo-
octadienes. The preferred diene in this category is
351,4-hexadiene, Representati~e nonconjugated dienes
in which both double bonds are polymerizable are
1,5-hexadiene, 1,4-pentadiene, and 2,5-norbornadiene.
~141330
Curable homopol~ers and copolyme~-s are
normally cured before the surface modificat_on process
of the present invention is carried out. Curing
methods are well known in the art. Thus, amorphous
5 polyethylene, polypropylene, and ethylene/propylene
dipolymers are curable with conventional peroxide
systems. The EPDM copolymers, whether tripolymers or
tetrapolymers, can be cured either with a peroxide or
with sulfur by methods well known in the art. Crystal-
10 line polyethylene and polypropylene ordinarily are notcured.
The chlorinated polypropylene preferred in
the process of the present invention has a number aver-
age molecular weight of about 5,000-50,000 and con-
15 tains about 5-25% chlorine by weight. Commercially
available chlorinated polypropylenes, sold by
Eastman Chemical Products, Inc., Rochester, New York,
under the designation CP-343-1 and CP-515-2, are suit-
able in the instant process. The first of these two
20 commercial products is a chlorinated polypropylene
which is believed to contain cyclic anhydride groups in
the polymer backbone and has a number average molecular
weight of about 15,000. Its chlorine content is about
15 weight percent. The second commercial material has
25 about the same molecular weight and chlorine content
but contains no cyclic anhydride groups in its backbone.
Chlorinated polypropylene can be readily prepared by
solution, melt, or solid polymer chlorination at moder-
ate to high temperatures according to well-known tech-
30 niques as reviewed for example in Raff and Doak,"Crystalline Olefin Polymers II," p. 239. Interscience
Publishers, New York, N.Y., 1964.
For practical application of the chlorinated
polypropylene it is preferred to use a solution of the
35 chlorinated polypropylene in a suitable solvent,
for example, an aromatic hydrocarhon, a chlorinated
~1330
hydrocarbon, or a solvent blend. Alicyclic hydrocar-
bons can be used in solvent blends and are preferred
because of their low toxicity and ready availability at
a low cost. Tetrahydrofuran may also be used. Suitable
alicyclic hydrocarbon diluents include cyclohexane and
methylcyclohexane. While chlorinated hydrocarbons,
both aliphatic and aromatic, can be used, they are less
desirable on account of their greater toxicity. The
concentration of the chlorinated polypropylene in the
10 solution can be about 0.1 to 5.0~ by weight but 1.0-
2.5% is preferred.
The polyolefin surface to be treated accor-
ding to the process of this invention must be
thoroughly clean. Cleaning can be accomplished by
15 scrubbing with water and soap or detergent or by
solvent-cleaning with, for example, a hydrocarbon, a
chlorinated hydrocarbon, a ketone, or another suitable
solvent. The cleaned surface is then allowed to dry,
optionally at an elevated temperature. A solution of
20 chlorinated polypropylene is then applied to the clean
surface, and the solvent is allowed to evaporate, again
optionally at an elevated temperature. Finally, the
primed surface is exposed to ultraviolet radiation.
Most commercial sources of ultraviolet
25 radiation can be used in the process of the present
invention, although the most efficient radiation is
obtained within the wavelength range of about 200-
400 nm. It is preferred to adjust the radiation ex-
posure time so that the radiation energy received by
30 the surface is about 0.10-1.0 J/cm2. The optimum
radiation energy range is 0.2-0.5 J/cmZ. The surface
that has been primed with chlorinated polypropylene and
irradiated with UV is now ready for painting. ~he
quality of paint adhesion can be determined in both
35 dry and wet adhesion tests, as explained below in the
Examples.
The polyole~ins and polyolefin blends which
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can be advantageously treated according to the process
of this invention can be either uncompounded or com-
pounded in the usual manner, for example, with carbon
black and other fillers, process oils, plasticizers,
5 and similar ingredients. However, the proportions of
individual polyolefins in the blends recited in the
~ummary of the Invention and in the claims, are based
on the polyolefins themselves, not on the weight of a
compounded polyolefin composition.
This invention is now illustrated by the
following examples of certain preferred embodiments
thereof, where all parts, proportions and percentages
are by weight unless otherwise indicated.
Polymer melt flow rate was determined
15 according to ASTM D-1238-73 (Condition L).
I. EXAMPLES
EXAMPLE 1
A filled polyolefin composition was prepared
by mixing the following ingredients in an internal
20 mixer for two minutes at 150C.
Parts
EPDM Rubber(l) 31.7
Polypropylene(2) 38.7
HAF Black 29.6
(1) Medium viscosity, non-crystalline copolymer of 35.5
mol % propylene/63 mol ~ ethylene/1.5 mol % 1,4-
hexadiene having a Mooney viscosity (~114)= 39
at 121C.
30 (2) 10-12 melt flow rate homopolypropylene.
Plaques of the above thermoplastic
composition were injection-molded at 232C. Two
plaques were cleaned in a power wash cycle and primed
as follows: On both plaques the primer consisted of a
35 lisht spray coat of a 1% solution in toluene of chlo-
rinated polypropylene (CP-343-1, Eastman Chemical
l330
Products Inc.) The dry weight of the chlorinated poly-
propylene deposited on each plaque was 0.095 mg/cm2.
After the primer had been applied and the plaques
allowed to dry, one of the two plaques was additionally
5 exposed to UV radiation from a medium pressure quartz-
jacketed mercury vapor lamp, radiating power at the
rate of about 80 watts per cm of lamp length. The
exposure was adjusted so that the plaque recei-Jed all
the radiation accompanying an irradiation of 0.33 J/cm2
10 at the wavelength of 3~5 nm. The other plaque received
no UV radiation. Both plaques were then painted with
a flexible alkyd enamel (~urethane~ 100, PPG Industries)
to give a dry film thickness of 22 ~m. The enamel was
baked for 40 minutes at 120C.
The plaques were tested as follows:
(i) Dry adhesion. A lattice pattern of cuts
was made through the paint over a small test area of
the sample. The lattice consisted of a series of
parallel cuts about 1.5 mm apart containing two sets
20 of cuts at right angles to each other and a third set
diagonally to the first two. Reinforced adhesive tape
was then pressed into the paint over the area of the
lattice cuts, then quickly ripped off. Adhesion was
rated from 100% to 0~ according to the area of paint
25 left adherent to the substrate.
(ii) Wet adhesion. The center of the plaque
was scribed with an "X". The plaque was then placed
about 5 cm below and at an angle of 45 to the nozzle
of a steam generator, so that the nozzle, capable of
30 delivering wet steam at about 0.4 MPa gauge pressure,
was aimed at the center of the "X". The test consisted
of measuring the time taken for the steam blast to
initiate a paint ~dhesion failure at the center of the
"X" and was run for a maximum of 180 seconds. This
35 test is particularly useful for evaluating the ability
of painted parts on the outside of cars to withstand
13;3~
exposure to an automatic car wash. The following
results were obtained:
No W With W
Dry Adhesion: 90% 100%
Wet Adhesion: 10 s >180 s
EXAMPLE 2
Plaques were prepared and tested as in
Example 1, except that the following thermoplastic com-
position was used:
Parts
EPDM Rubber(l) 50
Polypropylene(2) 50
(1) Partially crystalline copolymer of 18 mol % propyl-
ene/81 mol % ethylene/l mol % 1,4-hexadiene having
a Mooney viscosity (ML2+10)= 60 at 121C.
(2) Same as in Example 1.
Results:
-~ No UV With UV
Dry Adhesion: 95% 100~
Wet Adhesion: 50 s ~180 s
EXAMPLE 3
Plaques were prepared and tested as in
Example 1, except that the following thermoplastic com-
25 pOSition was used:
Parts
Propylene ~omopolymer(l) 99
HAF Black
30 (1) 4 melt flow rate
Test results were as follo.ws:
No W With W
Dry Adhesion: 10% 10~
Wet Adhesion: 10 s 20 s
~ . ~,
1330
EXAMPLE 4
Plaques were prepared and tested as inExample 1, except that the plaques were baked for 3
hours at 105C. and that the following composition was
5 used:
Parts
EPDM Rubber of Example 2 20
High Density Polyethylene80
(melt index 2.8)
Test results were as follows:
No WWith W
Dry adhesion: 0 99~
Wet adhesion: <5 s >180 s
EXAMPLE 5
This example compares the use of two
different commercial chlorinated polypropylenes:
CP-343-1, and CP-515-2, both supplied by Eastman
Chemical Products, Inc. Plaques having the same
composition as described in Example 1, were cleaned
20 in a power wash cycle and then lightly spray-coated
with one or the other of the two chlorinated poly-
propylenes as 1% solutions in toluene. After drying,
the plaques were exposed to UV radiation as described
in Example 1. Two coats of flexible alkyd paint were
25 applied: about 18 ~m of a neutral grey base coat,
which was baked for 20 minutes at 115C., and about
45 ~m of a white top coat, which was baked for 40
minutes at 115C.
The following test results were obtained:
30 Chlorinated Polypropylene: CP-343-1 CP-515-2
Weight deposited, mg/cm2: 0.09 0.10
Dry Aahesion (a), 100% 100%
Dry Adhesion (b) very good good
Wet Adhesion (c), >60 s >60 s
35 Wet Adhesion (d) Pass Pass
~a) As described in Example 1.
(b) A "~" shaped cut was made through the paint, ar.d
g
` :`
1`141330
the paint peeled back from the apex of the "V"
with a sharp knife. The results reflect a
qualitative assessment of the force re~uired to
peel the paint.
(c) As described in Example 1. The test was stopped
at 60 seconds.
(d) The painted plaque, with an "X" cut in the sur-
face of the paint, was immersed in distilled
water for 1~ days at 38C. On removal from the
water, the plaque was quickly dried and reinforced
pressure sensitive tape pressed over the center of
the "X" cut. The tape was then rapidly stripped
off. A "Pass" indicated that none of the paint
was remo~ed.
It is evident that both types of chlorinated
polypropylene gave satisfactory levels of adhesion.
II. COMPARISON EXAMPLES USING BENZOPHENONE AND
UV RADIATION AS TAUGHT BY
CANADIAN PATENT 974,928 TO G. A. BASEDEN
Examples 1-3 above were repeated, but
instead of using a chlorinated polypropylene primer,
the priming was effected by spraying the plaques with
a 5~ solution of benzophenone in petroleum naphtha
having a boiling range 120-140C. (dry deposition 0.056
25 mg/cm2); after the solvent had evaporated, the sprayed
surfaces were exposed 'o UV radiation (approximately
0.5 J/cm2 as measured at a wavelength of 365 nm)t
This was followed by paint application in which the
same paint type, dry film thickness, and paint bake
30 cycle was used as in the corresponding examples of
Section ~. The following results were obtained:
~olyolefin Composition ~ Type Dry Wet
As Example in Section I Adhesion,% Adhesion,s
1 30 >180
2 0 >180
3 0 <5
;~,, 10
33(~
By comparing the ~bove results with those of
Examples 1-3 in Section I, it can be seen that chlori-
nated polypropylene primer treatment followed by
ultraviolet radiation is more effective than benzo-
5 phenone treatment followed by ultraviolet radiation.While results are dramatic for polypropylene blends
with EPDM rubber, an i~prove~ent can also be seen
for polypropylene alone.
III. COMPARISON WITH TRICHLOROETH~LENE AND
UV RADIATION AS TAUGHT BY
U.S. PATENT 3,619,245, TO R. A. BRAGOLE
Additional plaques identical to those used
in Section I, Example 2 above, were primed with tri-
chloroethylene and exposed to UV, as described in U.S.
15 Patent 3,619,246. After the surface of a plaque had
been cleaned in a power wash and oven dried, tri-
chloroethylene was brushed onto the surface. A short
time afterward (e.g., 1-2 minutes), the surface was
exposed to UV radiation of 0.5 J~cm2 at a wavelength
20 of 365 nm. Data supplied by the UV lamp manufacturer
(Hanovia Lamp Division, Canrad Precision Industries)
indicate that 0.5 J/cm2 at 365 nm is equivalent to an
exposure of about 1.43 J/cm2 in the range of 240-400 nm.
This lies within the radiation range given in the
25 examples of U.S. 3,619,246. A coating of paint was ap-
plied and baked, as described in Example 3 in Section I.
The following test results were obtained:
Dry Adhesion Wet Adhesion
20% >180~
3~ It is apparent that the level of dry
adhesion obtained with this priming procedure was
considerably inferior to that obtained by the
chlorinated polypropylene/~V priming process of the
present invention.
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