Note: Descriptions are shown in the official language in which they were submitted.
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RUBBER COMPOSITION HAVING BLUE-TINTED GREY COLOR
Field
This invention relates to a r~bber composition
having a blue-tinted grey color.
Background
Rubber which contains carbon black reinforcement is
often used for various rubber products. Some rubber
products are prepared of other colors by using a
colorant and reducing or deleting the carbon black.
hile various colors are often considered, many times
the color is white.
For a white colored rubber, the rubber is typically
compounded with a white-colored pigment s~ch as, for
example, titanium dioxide. Carbon black is not used
for white colored rubbers because even very small
amounts would discolor the white rubber.
It is appreciated that the titanium dioxide
coloring pigment is not considered to be a r~bber
reinforcing ingredient for rubber but is more in a form
of a filler.
In contrast, the typically unwanted carbon black is
well recognized as being a reinforcing ingredient for
rubber, and not usually just a filler pigment or
material.
The inventor is not aware of a rubber composition
having a grey color which is blue tinted.
Disclosure and Practice of the Invention
In accordance with this invention, a rubber
composition is provided which is comprised of a sulf~r
cured r~bber containing as basic colorants, based on
100 parts by weight rubber, about 40 to about 50 parts
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by weight titani~m dioxide pigment about 0.5 to abo~t
1.0 part by weight carbon black wherein preferably, the
said carbon black is characterized by having an iodine
absorption number in the range of about 38 to about 48,
and a dib~tylphthalate value in the range of about 116
to about 126.
Such colorants are referred to as basic colorants
since it considered that the color of the rubber
composition is derived primarily from such colorants
and, thus, dominate its visible color, although it is
recognized that it is likely that the rubber itself and
other compounding ingredients contained in the rubber
may contribute to its color in a minor way.
In further accordance with this invention, a rubber
composition is provided having a blue tinted grey color
characterized by having a RD axis value of about 20 to
about 40, an (a) axis value of about zero to about -3
and a (b) axis value of about -3 to about -6.
Thus, in one aspect, a rubber compocition is
provided which i8 comprised of a s~lfur cured rubber
composit~on containing, as basic colorants, based on
100 parts by weight rubber; about 40 to abo~t 50 parts
by weight titanium dioxide pigment and about 0.5 to
about 1.0 part by weight carbon black and where said
rubber composition is further characterized by having a
blue tinted grey color characterized by having a RD
axis value of about 20 to about 40, an (a) axis val~e
of about zero to about -3 and a (b) axis value of abo~t
-3 to about -6.
The color values are determined according to a
Gardner XL Colorimeter with a tungsten-halogen lamp.
For such measurements, it was calibrated to a white
blank standard with an RD value of 85.1, an (a) val~e
: . of -0.9 and a (b) value of +1.2.
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It is important to appreciate that the color of the
rubber composition, absent the included very small
amount of carbon black, would typically be white~
By inclusion of the very small amount of carbon
black, a rubber composition is provided which has a
pleasing effect. It is also perceived that the added
small, bllt appreciable, amount of carbon black
contributes a very small amount of reinforcement to the
white sidewall rubber which would not otherwise be
present.
~ lhile the relatively light grey color imparted to
the titanium dioxide pigment loaded rubber by the small
amount of carbon black might be predictive, the blue
tint of the grey color apparently imparted by specific
carbon black(~) selection is not clearly understood.
It is possible that the observed blue tint of the grey
colored sidewall rubber is a result of one or more of
the carbon black's specific surface area, or structure.
S~ch carbon black characteristics are conventionally
measured as (A) an iodine absorption number: ASTM Test
No. D1510 and (B) a DBP (dibutylphthalate) value; ASTM
Test No. D2414, respectively.
Preparation of a rubber composition with the
observed blue tinted grey color was obtained with an
FEF, oil-derived, N550 carbon black with an iodine
absorption number (g/kg) specification of 43 +/- 5 and
a DBP absorption number (cc/lOOg) specification of 121
; +/- 5. Thus, it is perceived that a carbon black,
namely an oil-derived carbon black, particularly of the
FEF type having an iodine absorption number in the
range of about 35 to about 50 and a DBP value in the
range of about 115 to about 130 would be satisfactory
for the preparation of a blue-tinted grey colored
sulf~r cured, titanium dioxide pigment loaded rubber
composition.
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The term FEF means it is a furnace carbon black,
namely, fine, or fast, extrusion f~rnace black.
While it is acknowledged that the amount of carbon
black used is onLy in a small amount of about 1 to
about 2.5 weight percent of the titanium dioxide ~sed
in the white sidewall rubber, the presence of carbon
black is considered of interest because of the rubber
reinforcement quality of carbon black, even though such
reinforcement e fect would be very small due to the
small amount of carbon black used, significantly a grey
color imparted to the sidewall rubber would be expected
to be of good stability because of the resistance of
the carbon black to migrate within the cured rubber
composition.
This is considered to be a particularly significant
quality of the carbon black as a colorant.
It is, thus, considered significant that the blue
tinted grey color are apparently primarily obtained
with pigments instead of oil-based dyes, because the
dyes wo~ld be expected to migrate to the rubber s~rface
and diminish their colorant effect over time.
Therefore, it is anticipated that the utilization of
the reinforcement type of carbon black adds a degree of
stability to the colorant effect for the sulfur cured
rubber.
The color of the s~lf~r cured blue tinted grey
rubber has been characterized by measurement with a
Gardiner Colorimeter X~20 (1978 model) using a
tungsten-halogen lamp. For the purposes of the
description of the invention, such color determination
may be referred to as a ~ardner Color.
The color measurements are reported on a three axis
basis and, thus, represent a ~hree-diminsional
pro~ection of values.
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The (a) and (b) axes can be represented on a flat
plane with the RD axis being represented vertically
through the said plane. All three axes join at their
zero vaLue.
The (a) axis represents a red-green axis with (+a)
representing red and (-a) representing green.
The (b) axis, at right angles, or perpendicular, to
the (a) axis, represents a blue-yellow axis with (+b)
representing yellow and (-b) representing blue.
The RD axis, perpendicular to the plane of the (a)
and (b) axis; represents a white-black scale where a
zero value represents black and a +100 value represents
white. The RD axis might sometimes be referred to as a
grey scale.
Such color measurements and representations are
well known to those having skill in the color
characterization and color matching art.
Such rubber composition may be comprised of natural
rubber, butyl rubber, halobutyl r~bber, EPDM r~bber,
polyb~tadiene r~bber, synthetic polyisoprene rubber
and/or styrene/butadiene rubber. Preferably, the
rubber is natural rubber or a blend of natural rubber
with one or more of such other rubbers. For example,
such rubber may be comprised of at least one rubber
selected from natural rubber and halobutyl rubber may
contain EPDM rubber and/or styrene/butadiene copolymer
rubber.
As an example, such r~bber composition may be
comprised of a mixture of natural rubber and halobutyl
rubber or a mixture of natural rubber, halobutyl rubber
and EPDM rubber.
Preferably, the halobutyl rubber is selected from
at least one of chlorobutyl rubber and bromobutyl
rubber. EPDM rubber is an ethylene/propylene/
non-conjugated diene terpolymer rubber.
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The following example is intended to exemplify
features of ~he invention. The parts and percentages
are by weight ~nless otherwise indicated.
EXAMPLE I
Samples A and B were prepared and c~red to which,
for Sample A, titani~m dioxide had been added and for
Sample B, the titanium dioxide and a very small amo~nt
of carbon black had been added. Sample A is considered
a Control and is referred to herein as Exp. A and
Sample B, with the added carbon black, is referred to
herein as Exp. B. Its composition comprised the
ingredients shown in Table 1.
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Table 1
(Control)
Parts Parts
Ingredientsl Exp A Exp B
Chlorobutyl Rubber 20 20
Natural Rubber 40 40
EPDM Rubber2 20 20
Styrene/B~tadiene Rubber 20 20
Titanium Dioxide 30 30
Kaolin Clay 30 30
Stearic Acid
Microcrystalline Wax 1.5 1.5
Benzothiazole Type
Accelerator 0.75 0.75
Disulfide Type
Accelerator 1.25 1.25
Sulfur 0.5 0.5
Zlnc Oxide 10 10
Carbon Black (FEF,N550)3 0 0.7
Ultra Marine Blue4 0.2 0.2
1. White tire sidewall rubber, derived from Vanderbilt
Rubber Handbook (1978), page 651.
; 2. EPDM rubber, an ethylene/propylene/non-conjugated
diene terpolymer r~bber.
3. Obtainable from Cabot Corporation and reported as
having an iodine absorption number of 43 +/- 5 and
a DBP value of 121 ~/- 5.
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4. Ultramarine bl~e Pigment identified as #5005
Ultramarine Blue (R5-5) and obtainable from
Whittaker, Clark & Daniels, Inc.
The ultramarine bl~e pigment is often used in white
colored rubbers and is used in both Exp. A and Exp. B
rubbers. It is considered that it contrib~tes only in
a minor way, if at all, as a colorant, as compared to
the titanium dioxide and carbon black.
In the practice of this invention, the ingredients,
absent the carbon black, are first mixed together to
form a white colored compounded rubber composition.
Following such mixing step, the carbon black is then
mixed with the rubber composition to form the blue
tinted light grey colored compounded rubber.
The Exp. A (Control) and Exp. B sulfur c~red
rubbers were measured for their color characteristics
by a Gardner XL 20 Colorimeter. The colorimeter was a
1978 model with a tungsten halogen lamp (new lamp in
1990~ having a part No. lT41B, catalog No. CG-5875.
The colorimeter was t~rned on and warmed up for about
20-30 min~tes and calibrated to a white standard
(7900-202300).
The following results were obtained as shown in
Table 1.
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Table 2
Test
Object (RD) Axis (a) Axis (b) Axis
White
Standard 85.1 -0.9 +1.2
Exp. A 67.7 -1.7 -0.7
(Control)
Exp. B 33.3 -1.8 -4.2
The Exp. A (Control) rubber was white in color.
The Exp. B cured rubber had a visibly light grey
color with a definite blue tint.
Normally, absent the selection of the specified
carbon black, it would have been expected that the Exp.
B rubber composition would have simply exhibited a grey
color without the substantial blue tint.
The test values shown in Table 1 confirm the visual
inspection and show that there i8 a definite bl~e
presence in the Exp. B rubber indicated by the (b) axis
val~e of -4.2.
The test values reported in Table 1 show that the
Exp. A rubber was white in color with very little
(basically, insignificant) blue presence.
While various carbon blacks might be ~sed in the
practice of this invention for the rubber composition,
preferably the carbon black is of the N550 type, which
has an iodine absorption Number of 43 +/- 5 and a DBP
value of 121 +/- 5 and is apparently the cause of the
blue tint.
; While the creation of the blue tint in the rubber
composition might not be fully ~nderstood, it is
considered that the blue tint was caused by the
inclusion of the indicated FEF 550 carbon black.
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While certain representative embodiments and
details have been shown for the p~rpose of ill~strating
the invention, it will be apparent to those skilled in
this art that vario~s changes and modifications may be
made therein witho~t departing from the spirit or scope
of the invention.
