Note: Descriptions are shown in the official language in which they were submitted.
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1 BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
This invention relates to a nitrile rubber-
polyvinyl chloride polyblend rubber composition used as
a material for rubber molded articles having a portion
for glass movement with rubbing, such as a glass run.
DESCRIPTION OF THE RELATED ART
As a material for molding glass runs, such as
the door mirror brackets, conventionally ethylene-
propylene rubber (EPR) has been used. EPR molded productsthemselves generally have a high coefficient of friction,
so that the frictional resistance is high when glass
movement causes rubbing of the glass (hereinafter referred
to merely as "frictional resistance") in the glass run of
the door mirror bracket. In order to reduce this
fractional resistance typically the glass run is
lubricated with a urethane coating or a silicone oil.
However, the use of such lubricants has its
drawbacks. For example, employment of a urethane coating
requires pretreatment (primer treatment, etc.), and thus
results in an increase in the number of production steps.
On the other hand, when a silicone oil is used the oil
adheres to the glass and stains the glass. In addition,
in both cases, the rubber surface is still exposed to
the glass as the coating film comes off the surface with
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1 the lapse of time. This results in increased frictional
resistance and glass stained black by adherence of rubber
line powder formed by abrasion.
Therefore, a nitrile rubber/polyvinyl chloride
(NBR/PVC) rubber composition for molding a door mirror
bracket which does not require surface treatment in order
to reduce the frictional resistance in the glass run
portion has been proposed [see Jap. Pat. Appln. Rokai
(Laid-Open) No. 60-234046]. The NBR/PVC composition of
the present invention differs from that of 60-234046 in
the polymerization degree (p), the presence of carbon
black and the amount of nitrile in the composition.
While the NBR/PVC rubber composition of
60-234046 is effective to a certain extent in reducing
the frictional resistance, it tends to cause an increase
of compression set. The reason for this may be that NBR
of a high-nitrile type (acrylonitrile (AN) content:
36-42%) is used in the composition. Such NBR is used
from the viewpoint of injection moldability and ozone
resistance.
Recently glass runs have been required to
possess better sealing properties and improved impact
resilience and resistance to compression set.
OBJECT AND SUMMARY OF THE INVENTION
In view of such conditions, it is an object of
the present invention to provide an NBR/PVC rubber
composition which makes it possible to improve the impact
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1 resilience and the resistance to compression set without
increasing the frictional resistance greatly and with
almost no deterioration of ozone resistance. The
NBR/PVC rubber composition of the present invention solves
the above-described problems.
Accordingly, in one embodiment, the present
invention relates to a nitrile rubber-polyvinyl chloride
polyblend rubber composition comprising a polyvinyl
chloride in an amount of 15 to 30% by weight baded on the
weight of nitrile rubber-polyvinyl chloride polyblend,
a nitrile rubber of a moderate-nitrile type or a moderate-
high-nitrile type, and carbon black having a particle size
of 30 to 80 ~m. The polymerization degree of the
polyvinyl chloride is such that the mean polymerization
degree (P) equals 1000 to 1500.
In another embodiment, the present invention
relates to a sulfur-vulcanizable composition comprising a
polyvinyl chloride in an amount of 15 to 30% by weight
based on the weight of nitrile rubber-polyvinyl chloride
polyblend, a nitrile rubber of a moderate-nitrile type
or a moderate-high-nitrile type, a carbon black having
a particle size of 30 to 80 ~m, and sulfur or a sulfur-
yielding compound. The polymerization degree of the
polyvinyl chloride is such that P = 1000 to 1500.
Various other objects and advantages of the
present invention will become apparent from the drawings
and the following description of the invention.
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1 BRIEF DESCRIPTION OF THE DRAWINGS
In the attached drawings:
FIG. 1 is a front view showing one example of
door mirror bracket to which the present invention is
applied;
FIG. 2 is an end view along the line 2-2 in
FIG. l;
FIG. 3 is a model diagram showing a method for
measuring frictional resistance; and
FIG. 4 depicts a door mirror bracket mounted
on a door.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
A list of abbreviations used in the present
specification is shown below.
NBR --- nitrile rubber
PVC -~- polyvinyl chloride
NsR/PvC --- nitrile rubber-polyvinyl chloride
polyblend
AN --- acrylonitrile
The blending amounts in the present specifica-
tion are all by weight unless otherwise specified.
The composiiton of the present invention is a
carbon black-containing NBR/PVC rubber composition useful
as a material for rubber molded articles having a
portion for glass movement with rubbing, such as a glass
run. The composition is characterized in that:
1) the PVC content of the NBR/PVC is 15 to 30%,
12) the NBR is of a moderate-nitrile type or a
moderate-high-nitrile type,
3) the particle size of carbon black is 30 to 80
~m, and
54) the polymerization degree of the polyvinyl
chloride is such that the mean polymerization degree (P)
equals 1000 - 1500.
Glass runs, in which the composition of the
present invention can be used are exemplified by, for
example, door mirror brackets, door glass weatherstrips,
and door glass runs.
A glass run made from the composition of the
present invention is explained in the following case of a
door mirror bracket. While a glass run is exemplified
here by a door mirror bracket, it is not limited
thereto.
The structure of a door mirror bracket used for
mounting a door mirror on a sash door is generally as
shown in Figures 1 and 2. The door mirror bracket is
shown mounted on a door in Figure 4. A mirror-mounting
portion 1 has an external shape in which it occupies the
included angle portion between the upper edge lla of the
body of a closed door 11 and a front pillar 12. It also
has a glass-accommodating groove 3 whose bottom is
2S on a side on which the bracket is brought into contact
with the front pillar. In addition, it has a glass run
portion 5 composed of a pair of long and narrow lips 4
which are close to each other at the end of the glass-
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1 accommodating groove 3, at the open end facing theaforesaid included angle portion. Numeral 6 shows a
mounting leg for fixing the bracket on the door body 11.
The mirror mounting portion 1 is composed of a U-shaped
insert 7 made of a metal plate and a coating portion 8
made of a polymer blend of the present invention. The
glass run portion 5 is formed by extending the coating
portion 8. Numeral 9 shows a mirror-mounting hole and
numeral 10 a hole for lead wire.
The base polymer of the composition of the
present invention is an NBR/PVC satisfying the following
conditions:
1) The PVC content is between 15 to 30%. When
the PVC content is less than 15%, the ozone resistance,
and the abrasion resistance, for example, tend to be
insufficient and the frictional resistance is increased.
Thus, such a content is not desirable. On the other
hand, when the PVC content exceeds 30%, improvement of
the impact resilience and the resistance to compression
set cannot be expected. Therefore, a content exceeding
30% is also not desirable.
2) The NBR is preferably of a moderate-nitrile
type (AN content: 25-30%) or a moderate-high-nitrile
type (AN content: 31-35%). This is desirable from the
viewpoint of balancing required physical properties such
as, for example, polyblending properties, low-temperature
resistance, and resistance to compression set. When the
AN content is too low, the blending properties with PVC
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l are not sufficient and the strength tends to be low.
Whereas, when the AN content is too high, the main object
of the present invention, that is, improvement of the
impact resilience and the resistance to compression
set, cannot be expected.
3) As the PVC, there is used a PVC having
such a polymerization degree that P = lO00 - 1500, from
the viewpoint of resistance to compression set. The
polymerization degree is preferably high. But when
it is too high, the viscosity of the polymer is increased,
so that the moldability is liable to be low.
With an NBR/PVC satisfying the above condition
is blended a carbon black together with other
supplementary materials usually blended with NBR, such
as for example, zinc oxide, vulcanizing agents, such as
sulfur and sulfur-yielding compounds, vulcanization
accelerators, plasticizers and antioxidants. The carbon
black should be one which has a particle size of 30 to
80 m~. When the particle size is less than 30 m~, the
dispersibility of carbon black is low and when it exceeds
80 m~, the impact resilience and the tensile strength are
apt to be low. Suitable carbon black for use in the
present invention includes, but is not limited to, high
abrasion furnance black (HAF), medium abrasion furnance
black (MAF), fast extruding furnance black (FEF) and
semireinforcing furnance black (SRF).
The bLending amount of the carbon black is
usually 30 to 80 parts per lO0 parts of the NBR/PVC.
, ':
2 ~
1 When the blending amount is less than 30 parts, it is
difficult to attain a predetermined strength of
vulcanized product. However, when the blending amount
exceeds 80 parts, the resistance to compression set and
S the impact resilience tend to be low.
Although not essential, blending one or more
lubricants with the NBR/PVC of the present invention
is preferable for reducing the frictional resistance.
The lubricants include but are not limited to paraffinic
process oils, silicone oils, and higher fatty acid
amides in addition to the paraffin wax, paraffinic
synthetic waxes, ester waxes, polyethylenic waxes and
hïgher alcohols, which are described in the above-
mentioned prior art references. These lubricants can be
used singly or as a mixture thereof.
Whether the lubricants are used singly or as a
mixture thereof, their blending amount is usually 2 to 10
parts per 100 parts of the NBR/PVC. This range is
preferable because when the blending amount of the
lubricants is less than 2 parts, it is difficult to
obtain an effect desired from addition of the lubricants
~that is, frictional-resistance-reducing effect) and when
the blending amount exceeds 10 parts, bloom of the
lubricants tends to be formed.
The NBR/PVC rubber composition of the present
invention is usually kneaded, formed into a sheet, and
then cut into suitable lengths to obtain materials for
various moldings. Rubber molded articles such as glass
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1 runs are obtained by vulcanization and molding of the
molding materials by molding methods such as, for example,
transfer molding, injection molding, and compression
molding.
As described in the examples herelnafter,
molded articles obtained by molding the NBR/PVC rubber
composition of the present invention possess improved
impact resilience and resistance to compression set
without a large increase in the frictional resistance and
with almost no deterioration of the ozone resistance.
The following non-limiting example is given
to further illustrate the preferred embodiment of the
present invention.
EXAMPLE
As test pieces used in the Examples and
Comparative Examples of Table 1, rubber sheets 2 mm
thick (mmt) were obtained by vulcanization and molding
under conditions of 100 kgf/cm2 x 160C x 15 min rubber
compositions prepared according to the fundamental recipe
shown below using each NBR/PVC and each carhon black
listed in Table 1 in the respective blending amounts
described in Table 1.
Fundamental recipe (unit: parts by weight):
NBR/PVC 100
25 Carbon black varied
Plasticizer (fatty acid ester) varied
Zinc oxide 5
_ g
2a~C~ 3
1 Stearic acid
Sulfur
Vulcanization accelerator 4
Paraffin wax 3
Test methods of characteristics were as follows.
(1) Dry physical properties:
Hardness (Hs), tensile strength (TB) and
elongation (EB) were individually measured in accordance
with JIS-K 6301.
(2) Impact resilience test:
Carried out in accordance with JIS-K 6301.
(3) Compression set (Cs) test:
Compression set (a) Cs was measured under
conditions of 70C x 70 h and then room temperature x 24 h
in accordance with JIS-K 6301. Compression set (b) Cs
was measured under conditions of 100C x 22 h and then
room temperature x 3 h in accordance with JIS-K 6301.
(4) Ozone deterioration test:
Carried out in accordance with JIS-K 6301 under
the following conditions: elongation 20%; 40C atmosphere;
ozone concentration 50 pphm; 210 h.
(5) Vulcanization curve:
Obtained at 160C by means of curelastmeter.
(6) Frictional resistance:
As shown in Figure 3, a glass dish (50 g) 24
loaded with a weight (200 g) 23 was pulled with a thread 25
on a 2-mmt sheet (test piece) 22 placed on a testing stand
21, and the initial load (static friction) and the average
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1 load in sliding state (dynamic friction) were measured by
means of a load cell.
From the results shown in Table 1, it can be
seen that molded articles obtained by molding the
NBR/PVC rubber composition of the present invention
possess greatly improved impact resilience and resistance
to compression set, as compared with those obtained by
molding a conventional NBR/PVC rubber composition. It can
also be seen, that in the case of the forrner rubber
molded articles, the increase of frictional resistance
is small and that the ozone resistance is high.
*****
All publications mentioned hereinabove are
hereby incorporated by reference.
While the foregoing invention has been described
in some detail for purposes of clarity and understanding,
it will be appreciated by one skilled in the art from a
reading of this disclosure that various changes in form
and detail can be made without departing from the true
scope of the i.nvention.
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TEST RESULTS
