Note: Descriptions are shown in the official language in which they were submitted.
CA 02607647 2007-10-24
TEFLON COMPOSITION FOR COATING WIPER BLADE RUBBERS AND
COATING METHOD USING THE SAME
Detailed description of the invention
Technical field
The present invention relates to a coating composition for wiper blade
rubbers. More
specifically, the present invention relates to a Teflon composition for
coating wiper
blade rubbers to improve endurance and resistance to frictional forces of the
blade
rubbers and a coating method using the same.
Technical back_ground
For an automobile in general, strip rubbers for a wiper, that are attached to
a wiper
blade, are run by wiper arm of the vehicle. With such drive apparatus, strip
rubbers of
a wiper constantly slide over the windshield of a vehicle from side to side to
remove
any raindrops, snowflakes, and dust, etc., thus providing a car driver with a
good
visibility. Because the region of a wiper blade which contacts the windshield
is
generally strip-shaped, wiper blade rubbers are often called as strip rubbers
for wiper
blades, or more shortly wiper blade rubbers or wiper blades. Thus, said terms
are
used herein interchangeably.
Wiper rubbers which are attached to a frame of wiper blade are made of elastic
materials. Specifically, wiper rubbers are divided into a head part that is
joined to a
frame of wiper blade and a wedge part that contacts the windshield of a motor
vehicle
(i.e., wiper blade part). The wiper head part and wedge part are assembled in
a way
that they can fold in an opposite direction compared to the direction of
windshield
glass washing, based on frictional forces occurring between the windshield and
the
wiper rubbers. As a result, the wiper rubbers can maintain its uniform
cleaning
ability, possibly without any slipping.
Materials for preparing such wiper blade rubbers should have not only a good
mechanical property but also should satisfy other complex requirements that
are
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related to the safety of a vehicle against any external influences. Wiper
rubber
materials should have flexibility and slide smoothly over the car windshield.
Furthermore, they should have a resistance to external influences, especially
to
oxidation (ozone cleavage), mineral oil and chemicals that are contained, for
example,
in washing fluid.
Materials used for preparing a wiper blade are generally rubbers, i.e.,
vulcanized
natural rubbers or synthetic rubbers. However, in order to improve the sliding
properties of the rubbers, additional treatments including coating the surface
of the
wiper blade rubbers, chlorinating it, or coating it with a sliding powder
agent such as
molybdenum sulfide have been suggested.
The wiper rubber described in DE-C-35 27 093 is preponderantly consists of
EPDM
(Ethylene-Propylene-Dien-Monomer). Meanwhile, in EPDM, the unsaturation sites
are present outside the main ring of the polymer. As a result, EPDM has not
been
halogenated and has no endurance to mineral oil and chemicals contained in
washing
fluid. Therefore, according to DE-C-35 27 093, in order to improve the sliding
properties and the endurance of wiper blades consisting preponderantly of
EPDM,
chlorinated diene-type rubber segments were placed on a matrix that is
consisted of
EPDM, at least in the regions that slide over the car windshield during proper
use.
However, it is disadvantageous in that such wiper rubbers have a rather
complex
structure having layers of different rubber materials.
On the other hand, according to WO 1999/39948 (Corresponding Korean Laid-open
publication No. 10-2001-0015914), a wiper blade is disclosed in which
different kinds
of wiper rubber materials are used for a head part and a wedge, respectively.
In this
invention, since the head part made of a diene-type rubber can be halogenated,
favorable sliding properties and smooth running can be obtained. Further, an
easy
access to the regions in which the wiper blade cooperates with the supporting
strip
and the spring rail of the metallic support and a harder surface can be also
obtained.
In addition, for the flexing part and the wedge of the wiper blade,
chloroprene rubber
(CR) is used according to said invention. Meanwhile, chloroprene has excellent
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mechanical properties with high resistance to the influences of weather,
aging,
chemicals, and temperature. Therefore, a favorable wiper quality can be
achieved in a
simple and inexpensive manner according to said invention. However, although
chloroprene has a high resistance to the influences of weather, aging,
chemicals, and
temperature, it has a limitation including poor resistance to frictional
forces, which
occur between windshield glass and wiper rubbers, etc.
Brief description of the drawings
Figure 1 shows a cross-section of conventional wiper blade rubbers in which a
head
part having an internal spring rail is coupled to a wedge part contacting the
surface of
windshield glass via flexing bridge.
Figure 2 shows a cross-section of two wiper blade rubbers of the present
invention in
which two wiper blade rubbers, each comprising in one integrated body a head
part
with an external spring rail and a wedge part contacting the surface of the
windshield
glass, are loosely connected and facing each other via connection.
Technical problems to be solved
Object of the present invention is to provide a Teflon coating composition
which has a
high resistance to external influences such as bad weather, chemical agents,
and
temperature, etc. and can be used for coating wiper blade rubbers to improve
endurance and resistance to frictional forces occurring between windshield
glass and
wiper blade rubbers, and a coating method using the same.
Means to solve the technical problems
The above-described object of the present invention is achieved by providing a
Teflon
composition for coating wiper blade rubbers, in which 3.5 to 15 wt% of Teflon,
3.2 to
9.6 wt% of urethane, 1.6 to 6.0 wt% of silicone resin, and 5.0 to 25.0 wt% of
a water-
based resin are comprised.
According to one embodiment of the present invention, the coating composition
of the
present invention may comprise 4.0 wt% or less of silver component, or 3.0 to
20.0
wt% of silicone oil, or both of the silver component and the silicone oil.
According to
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another embodiment of the present invention, the coating composition of the
present
invention may further comprise 3.5 to 15 wt% of graphite or carbon black.
The wiper rubbers used in the present invention are general rubbers, i.e.,
vulcanized
natural rubbers or synthetic rubbers can be used. However, as it has been
exemplified
in said prior art invention, it is preferred to use diene-type rubber or
chloroprene
rubber. More preferably, said diene-type rubber is a natural rubber, butadiene
rubber
or styrene-butadiene rubber.
Meanwhile, said object of the present invention is also achieved by a method
of
coating wiper rubber blades with the above-described coating composition of
the
present invention. In particular, coating is preferably carried out by first
pre-treating
the wiper blade rubbers with an intermediate medium for their smooth coating,
and
then coating with said composition of the present invention by spray coating
method.
Teflon, which is used as an essential component for the composition of the
present
invention, is a commercial name referring to polytetrafluoroethylene (PTFE), a
typical
example of synthetic fluororesin. As a crystalline resin, it has a heat-
resistance
enduring long-term use at 260 C and is known as a special synthetic resin
having a
favorable chemical-resistance, electric insulting property, non-stickiness,
and low
frictional coefficient, etc. Especially, PTFE is a crystalline polymer having
melting
temperature of 327 Cand it has a continuous use temperature of 260 C.
Furthermore,
being stable from low (-268 C) to high temperature, it is known to be used in
wide
range of temperatures.
In addition, Teflon's resistance to a chemical is known to be the best among
many
organic materials. Especially, Teflon is not degraded at all by acid, alkali,
and various
solvents. It is only degraded under extreme conditions including special
chemicals
such as fluorine gas and molten alkaline metals, etc. Thus, it is widely used
as a
material for preparing gasket, packing and various sealants. The most
remarkable
CA 02607647 2007-10-24
mechanical property of Teflon is its low frictional coefficient. As such, it
is used as a
reinforce material for various fillers. With high non-stickiness, it is also
known as the
best synthetic resin for manufacturing frying pans and for coating various
steel pipes.
5 Inventor of the present invention found that, when a composition containing
Teflon is
coated onto wiper blade rubbers, not only a high endurance to external
influences
including bad weather, aging, chemical agents, and temperature can be given to
the
wiper blade rubbers but also a resistance to frictional forces occurring
between
windshield glass and wiper blade rubbers can be improved, by taking an
advantage of
the above-described favorable physicochemical and mechanical properties of
Teflon.
As a result, the present invention was completed.
Teflon can be used within a range of 3.5 to 15 wt% based on the total weight
of the
composition. If Teflon is used in an amount outside said range, desired
coating effect
of the composition cannot be obtained. Preferably, constitutional ratio of
Teflon in
the composition is between 7 to 8 wt%.
Polyurethane used in the present invention is a synthetic polymer compound
having
urethane linkages inside main chains of the polymer, which is obtained by
polyaddition reaction by which urethane linkages are repeatedly formed between
diisocyante and dialcohol. Any kinds of commercially available, water-soluble
polyurethane can be used in the present invention.
Urethane can be used within a range of 5 to 25 wt% based on the total weight
of the
composition. If urethane is used in an amount outside said range, desired
coating
effect of the composition cannot be obtained. Preferably, constitutional ratio
of
urethane in the coating composition is between 10 to 15 wt%.
Silicone resin used in the present invention is a polymer of organic
derivatives of
silicone compound. It is also referred to as silicon resin. Molecular
structure of the
silicone resin includes a silicon skeleton having siloxane linkage (Si-O
linkage)
wherein silicon atom altemates with oxygen atom and functional groups such as
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methyl group, phenyl group, and hydroxy group are attached to the silicon
atom. The
silicone resin is a thermoplastic synthetic resin and has a defoaming activity
in most
of the solvents that are commonly used. It also has water-repellency (i.e.,
water-
resisting activity) when it is applied to inorganic or organic materials. As
such,
silicone resin is advantageously used for the composition of the present
invention. It
is believed that any kinds of commercially available silicone resins can be
used in the
present invention.
Silicone resin can be used within a range of 1.6 to 6.0 wt% based on the total
weight
of the composition. If silicone resin is used in an amount outside said range,
desired
water-repelling effect of the composition cannot be obtained. Preferably,
constitutional ratio of silicone resin in the coating composition is between 2
to 5 wt%.
Silicone oil is a silicone polymer product which has an oily appearance at
room
temperature. Generally, dimethyl chlorosilane polymer is a colorless, tra
nsparent and
tasteless liquid. Due to its structural characteristic, it is chemically inert
and stable.
Further, having a relatively low surface tension, it has water-repellency
(i.e., water-
resisting activity) and an excellent defoaming activity. As such, it is widely
used as a
defoming agent that is not soluble in water but can prevent the formation of
foams. It
is believed that any kinds of commercially available silicone oils can be used
in the
present invention.
Silicone oil can be used within a range of 3.0 to 20.0 wt% based on the total
weight of
the composition. If the silicone oil is used in an arnount outside said ra
nge, desired
water-repelling effect of the composition cannot be obtained. Preferably,
constitutional ratio of silicone oil in the coating composition is within
about 13 wt%.
Meanwhile, in addition to the silicone resin and the silicone oil that are
used to
enhance the water-repellency of the coating composition of the present
invention, a
commercially available water-based resin can be further added to the
composition of
the present invention in order to provide wiper blades with additional
favorable
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physicochemical properties other than water-repellency. In this regard, a
thermosetting water-based resin is preferable in the present invention.
Water-based resin can be used within a range of 5 to 25 wt% based on the total
weight
of the composition. If water-based resin is used in an amount outside said
range,
desired effect of the composition cannot be obtained. Preferably,
constitutional ratio
of water-based resin in the composition is within about 20 wt%.
Moreover, in addition to said favorable mechanical properties, in order to
give a high
endurance to the coating composition of the present invention against external
influences, commercially available graphite or carbon black can be added to
the
composition.
The reason for further adding graphite or carbon black in addition to silicone
oil to the
coating composition of the present invention is as follows. When a wiper
glides over
the windshield, water-repelling silicone component present in the coated wiper
blade
rubbers is first transferred to the windshield glass. As a result, the
windshield glass
can have a water-repellent activity. However, such water-repellent components
contribute to the increase in frictional coefficients so that noise and/or
shaking may
occur during wiping action of a wiper. Thus, in order to prevent such
undesirable
phenomena, graphite or carbon black, which can reduce frictional coefficient,
are
introduced for preparing the coating composition.
Furthermore, silver is known for its antibacterial, germ-killing and endurance-
increasing activity as well as the activity of enhancing favorable properties
of
chemicals. Since such properties of silver is also desirable for the wiper
blades of the
present invention, silver can be advantageously used for the coating
composition of
the present invention. Being effective even in a small amount, silver can be
used
within a range of 4.0 wt% or less based on the total weight of the coating
composition. If silver is used in an amount outside said range, desired effect
of the
composition cannot be obtained and/or it becomes economically unfavorable.
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Preferably, constitutional ratio of silver in the coating composition is about
2 wt% or
less.
Lastly, the coating composition of the present invention may further comprise
additives such as a stabilizer, a drying agent, a thickening agent, and a
defoaming
agent for enhancing coating property as well as a dispersant which can
actively
promote the drying of the coating composition. Just a small amount of such
additives
and dispersants, etc. would be effective to obtain the desired effect. As
such, they can
be used in an amount of about 0.5 wt% or less, respectively, compared to the
total
weight of the coating composition.
The wiper blade rubbers of the present invention can be produced in accordance
with
any conventional methods. Still, as it has been described in the above-
described prior
art invention, it is advantageously produced by means of coextrusion of diene-
elastic
rubber and chloroprene-elastic rubber. In such case, an unvulcanized strip
having a
pre-determined cross-sectional form is produced first. The wiper blade rubbers
are
then preferably subjected to a vulcanization treatment and, if necessary, to a
chloride
treatment using hypochlorite salt or trichlorocyanuric acid.
The coating composition prepared according to the above-described method of
the
present invention can be coated onto wiper blades using any conventional
methods
that are used in the pertinent art, including graphite coating or silicone
coating.
However, as a pre-treatment step, it is preferable to treat the wiper blade
with an
intermediate medium which can promote smooth coating of the composition. Then,
the coating composition can be sprayed onto the wiper blade rubbers by spray
method.
Because the coating composition of the present invention comprises
simultaneously
graphite or carbon black and silicone components, a single step of coating can
be
sufficient to obtain dual effects of a graphite coating and a subsequent
silicone
coating.
Herein below, the preparation of the coating composition and the coating
method
using the same are briefly explained in view of specific examples.
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Specific embodiments for carrvin_g out the invention
Example I
Each component indicated in the following table is purchased as a material in
powder
form, and dispersed in a dispersing chamber (i.e., stirring chamber). After
adding
them to a blender to which resins and solvent are further added, the coating
composition of the present invention is obtained.
Component Constitutional ratio (wt%)
Carbon black 6.0
Water-based resin 20.0
Urethane 8.0
Silicone resin 5.0
PTFE 10.0
Dispersant 0.5
Silver 2
Coating additives 2
Water 48.5
Total 100.0
Figure 1 shows a cross-section of conventional wiper blade rubbers in which a
head
part (13) having an internal spring rail (10) is coupled to a wedge part (15)
contacting
the surface of windshield glass via flexing bridge (17). On the other hand,
Figure 2
shows a cross-section of two wiper blade rubbers of the present invention in
which
two wiper blade rubbers, comprising in one integrated body a head part (33)
with an
external spring rail (30) and a wedge part (35) contacting the surface of the
windshield glass, are loosely connected and facing each other via connection
(40).
According to the present invention, conventional wiper blade rubbers of Figure
1 can
be coated with the coating composition of the present invention as prepared
above.
Although it is not illustrated, the coating composition of the present
invention can be
applied similarly to wiper strips for the conventional wiper blades in which a
head
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part having an external spring rail is coupled with a wedge part contacting
the surface
of the windshield glass via flexing bridge or for other conventional wiper
blades in
which a head part having an external spring rail is coupled with a wedge part
in an
integrated body.
5
Meanwhile, according to the present invention, two wiper blade rubbers are
first
formed as a single molded piece in which they are joined to each other at the
middle
region, e.g., connection (40). After cutting along the middle region, two
separate
wiper blade rubbers are produced. Specifically, instead of making a thorough
cut, a
10 slight dent is first formed over the connection region (40) and then a pre-
treatment
using an intermediate medium is carried out to obtain smooth coating. Then,
the pre-
prepared coating composition is coated over the entire surface of the wiper
blade
rubbers using spray coating method. After cutting with a knife along the
connection
region (40), two separate wiper blade rubbers are produced and then can be
used,
respectively.
Example 2
Coating composition is prepared using the same method as described in above
Example 1, except that silicone oil is used instead of silver.
Component Constitutional ratio (wt%)
Carbon black 6.0
Water-based resin 20.0
Urethane 4.0
Silicone resin 2.0
PTFE 7.0
Dispersant 0.5
Silicone oil 13.0
Coating additives 0.5
Water 48.0
Total 100.0
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Method for coating the coating composition obtained from Example 2 to wiper
blade
rubbers can be applied similarly to those explained in above Example 1.
Example 3
The silver component is excluded while all other components described in the
following table having the same constitution and constitutional ratio as
Example 1 are
dispersed in a dispersing chamber (stirring chamber). After adding resins and
solvents to them, all the components are blended in a blender to give a
coating
composition.
Component Constitutional ratio (wt%)
Carbon black 6.0
Water-based resin 20.0
Urethane 8.0
Silicone resin 5.0
PTFE 8.0
Dispersant 0.5
Coating additives 2.5
Water 52.0
Total 100.0
Method for coating the coating composition obtained from Example 3 to wiper
blade
rubbers can be applied similarly to those explained in above Example 1.
Meanwhile, in order to determine an improvement in wiping quality of the wiper
blade rubbers that are produced according to the present invention, a wiping
ability
test was carried out. Specifically, the test method corresponds to a
sensitivity
measurement test in which water is poured over a car windshield and then
wipers are
run to evaluate the wiping quality of the wipers (e.g., 10 is the maximum
score). With
respect to frictional forces applied on the wipers, electric currents can be
monitored to
determine the motor load that is required to run the wipers in wiper test
bench.
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Although such experimental data do not represent actual forces to run the
wipers, they
can be used for comparing relative strength of the forces.
For carrying the test, the coating composition prepared in above Example 1 was
first
selected. Then, 'EF Sonata', which is one of the automobile models
manufactured by
Hyundai Motor Company, was chosen as a test vehicle. The selected coating
composition was applied to said test vehicle and wiping quality was evaluated
under
the weather conditions including temperature of 28.3 C and humidity of 74%
(score
was given to the standard highest wiping quality). For the non-coated wiper
blade
10 rubbers (1), experimental results are given in the following Table 1. For
the coated
wiper blade rubbers (2), experimental results are given in the following Table
2.
Table 1(Experimental results before rubber coating)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 Mean value
Up 6 6 7 6 5 7 5 4 6 6 5 7 6 6 5.9
Down 7 7 7 6 5 6 4 5 5 6 5 5 5 6 5.6
Table 2 (Experimental results after rubber coating)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 Mean value
Up 9 9 9 9 8 10 8 8 9 9 10 9 10 10 9.1
Down 9 9 9 9 9 9 8 8 9 9 10 8 9 10 8.9
Comparing the results given in the above Table 1 and Table 2, mean value of
the
wiping ability for the wiper blade rubbers before rubber coating was 5.9 and
5.6, for
the up and down motions of the wiper blades, respectively. On the other hand,
mean
value of the wiping ability for the wiper blade rubbers after rubber coating
was 9.1
and 9.8, for the up and down motions of the wiper blades, respectively.
Therefore,
according to the above-described sensitivity evaluation test, it is again
confirmed that
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the wiping ability of the wiper blade rubbers after rubber coating is about
two times
better than that of the wiper blade rubbers before rubber coating.
Moreover, similar results are obtained from the tests using the costing
composition
that have been prepared from Example 2 and Example 3. Detailed comparative
tables
are not shown.
