Note: Descriptions are shown in the official language in which they were submitted.
~;~5818~
60-SI~ 457
--1--
FOAMED ORGANOPOLYSILOXANE ABRASIVE MATERIALS
.. _ . .. .
This invention relates generally to abrasive
foam materials and a method of making foamed abrasive
S materials, and more particularly, relates to foamed
organopolyciloxane abrasive materials having abrasive
grit uniformly dispersed throughout the
organopolysiloxane.
A wide variety of materials is available for
use in abrading and polishing surfaces, for stock
removal and the like. The abrasive materials are
generally classified into two types, namely, coated or
bonded. A coated abrasive is one in which the particles
of abrasive material, or alternatively, a polishing
medium, identified herein as an abrasive material, are
present as a thin coating on the surface of a body
material which may be paper, cloth, netting, metal,
resin, and the like, and are bonded to the body material
by suitable adhesive or binder vehicle. A bonded
abrasive is one in which the abrasive is dispersed
within the bonding vehicle which is preformed into
various solid shapes and cured or otherwise solidified
for use in the solid form.
18~
60-SI-457
--2
While abrasive and polishing means of the
coated and bonded types have been used for many years,
they have not been entirely satisfactory for many
applications. For example, the coated abrasives often
wear of revealing the underlying body material, thereby
providing a non-uniform abrading and polishing surface.
The bonded abrasives are generally dense, hard solids
which become even harder in use. In many instances,
because of localized temperature elevation in the
vicinity of the working surface of the abrasive
material, many of the polymeric materials used as
binders and adhe~ives show some degree of thermal
degradation resulting in smearing of the substrate being
abraded or polished and in loss of cutting, abrasive or
polishing action. Furthermore, because of the method o
dispersing the abrasive in the binder in bonded
abrasives, or because of the adhesive or binder vehicle
used to adhere the abrasive to the surface of coated
abrasive materials, there is poor accessability of the
grit or grain surfaces to the surface undergoing
abrasion, cutting, polishing and the like. Because of
the foregoing, many of the prior art abrasive materials
have to be resurfaced or refaced or discarded resulting
in high costs due to downtime or due to the replacement
of the material.
To overcome many of the foregoing
deficiencies, it has been proposed to use abrasive foams
wherein an abrasive grain is incorporated in foamable
material prior to foaming with the resultant in situ
production of a foam containing abrasive grain or grit
substantially uniformly distributed throughout as
>8~8'~
60-SI-457
--3--
described in U.S. Patent No. 3,252,775, or wherein a
pre-formed foam material in which the cells or voids in
the foamed material, are impregnated with a slurry of
abrasive and binder adhesive, dried and cured so that
the voids or cells contain the abrasive substance bonded
by the binder to the foamed material as described in
U.S. Patent No. 3,653,859. By the latter method, the
dispersion of the abrasive grit material is only as
uniform as the distribution of voids or cells within the
foamed material, and the integrity of the abrasive
material is entirely dependent upon the binder adhesive
utilized in the voids or cells. In most cases, these
cellular or foamed grinding materials are made of
phenolic resins and epoxy resins which can be foamed;
In many instances, the foams have such little integrity
that they must be mounted or bound to more durable
substrates to be effective as abrasive materials.
One type of abrasive wheel made of a soft,
low-density polyurethane foam is described in U.S.
Patent No. 3,252,775, however, this type of abrasive
material has poor strength and poor wearing properties
and has not been successful commercially. It i5 for
this reason that the art generally recognizes the
necessity of employing highly dense and reinforced
materials, such as a dense polyurethane composition
cast around rein~orcing members as described in U.S.
Patent No. 4,150,955, to produce adequate abrasive and
polishing members. Furthermore, the prior art teaches
in U.S. ~atent No. 4,128,972 that the presence of foam
in the final polishing wheel is unwanted. It is stated
in U.S. Patent No. 4,128,972 that it is known that gas
l'~S8~8~
60-SI-4s7
--4--
cells assist in cooling abrasive wheels through better
heat ~ransfer, but void cells lessen the physical
integrlty of the wheel, and distortion and ballooning
are more often experienced, and the cohesive forces
holding the unit abrasive grains in the tool and
toqether are materially weakened. Thus, the prior art
generally teaches that the presence of foaming agents in
the adhesive elastomer bond are to be avoided.
Many prior art abras.ve and polishing
materials have been made by incorporating the abrasive
grit or polishing media in silicone resins or rubbers.
These are described, for example, in U.S. Patent No~
3,528,788, U.S. Patent No. 3,982,359, U.S. Patent No;
4 t 162,900 and U.S, Patent No. 4,307,544. In the
foregoing patents ~hich utilize silicone rubber or
elastomer as the binder medium, there is generally less
localized temperature elevation in the vicinity of the
working surface of the abrasive material at the
interface with the part being abraded or polished where
most organic polymers and even silicone resins show some
degree of thermal degradation resulting in smearing and
loss of cut or polishing action. The use of the
silicone rubber or elastomer generally results in a much
higher useable service temperature than the organic
polymers and thereby provides higher stability and
longer-lasting materials. However, there is still a
certain degree of surface friction which results in
localized temperature elevation and build up in the
solid silicone rubbers.
~81~
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Summary of the _nvention
In general, it is an object of ~he present
invention to provide improved abrading and polishing
materials which solve or substantially eliminate the
foregoing problems, yet which are essentially cellular
in structure.
It is another object of the present invention
to provide an abrasive material having improved surface
friction characteristics.
Another object of the present invention is to
provide a method of preparing an abrasive material
having improved surface friction characteristics.
Still another object of the present invention
is to provide an article made of an abrasive material
having improved surface friction characteristics.
Another object of the present invention is to
provide an ahrasive material and method of making an
abrasive material wherein there is improved
accessability of the abrasive or grain material in the
surface of the abrasive material.
These and other object of the invention are
achieved by providing an organopolysiloxane foam having
abrasive grit uniformly dispersed in the
organopolysiloxane. Improved surface friction
characteristics are realized by providing the voids or
cells in the organopolysiloxane without sacrifice to the
integrity of the material itself. Because of the
properties and characteristics of the silicone rubber or
lZS~3~8;~
60-SI_ 457
--6--
elastomer coupled with the void volume or cellular
nature tnereof, there is reduced surface friction as
well as improved heat dissipation resulting in reduced
thermal degradation. This, in turn, improves the
accessability of the abrasive or grain material at the
surface. Furthermore, the use of the organopolysiloxane
foam ha~ing abrasive grit uniformly dispersed in the
organopolysiloxane, can be used at much higher service
temperatures than the solid silicone rubbers or the
organic polymeric foams or solids. The solid silicone
rubbers or elastomers cause higher frictional heat
leading to lower service life. The foamed
organopolysiloxane elastomers of the present invention
should operate at lower temperatures than the solid
silicone elastomers. Thus, the foamed
organopolysiloxane elastomers of the present invention
having abrasive grit uniformly dispersed therein, will
have an extended service life when compared with the
service life of solid organopolysiloxane containing
abrasive grit.
In accordance with at least some of the
objects of the present invention, there is also provided
a method of preparing an abrasive material having
improved surface friction characteristics comprising
mixing an abrasive grit or polishing media in an
organopolysiloxane having an organopolysiloxane
foam-forming agent therein until the abrasive grit is
substantially uniformlv dispersed therein; allowing the
mixture to foam and curing the foam. Furthermore, in
accordance with at least some of the objects of the
present invention, the abrasive grit-containing
l'~S8;~8~
60-SI- 457
organopolysiloxane having an organopolysiloxane
foam forming agent and a catalyst therein are placed in
a mold and heated at an elevated temperature to foam and
cure the organopolysiloxane to produce a molded
article. Thus, in certain embodiments~ an article is
formed of abrasive foam material by heating the abrasive
yrit-containing organopolysiloxane having an
organopolysiloxane foam-forming agent therein at an
elevated temperature in the presence of a catalyst in a
mold, whereby gas formed in situ by the reaction of
components in the filler and the organopolysiloxane,
form cells in the organopolysiloxane while
simultaneously curing the organopolysiloxane in the mold
at the elevated temperature.
These and various other objects, features and
advantages of the invention can be best understood from
the following detailed description.
Detailed Description of the Invention
.
In the present invention, the abrasive
materials having improved surface friction
characteristics must have a binder or matrix material of
a sponged or foamed silicone elastomer or rubber, that
is, an organopolysiloxane foam or sponge rubber having
an abrasive or polishing ~aterial substantially
uniformly dispersed therein. In order to achieve at
least some of the objects of the present invention, the
organopolysiloxane foam or sponge rubber having the
abrasive or polishing material dispersed in the
:~ZS8~8'~
60-SI-457
--8--
organopolysiloxane material itself must be one which
results in reduced surface friction, thereby leading to
lower stock temperatures with improved accessability of
the abrasive or polishing surfaces to the body being
5 worked. The composite formed by the present invention
must contain substantially.uniformly dispersed abrasive
grit or polishing material in the organopolysiloxane
foam such that the resultant cured composite abrasive
material exhibits hoth cellular and abrasive
characteristics.
The organopolysiloxane foams are especially
adaptable to molding to zny shape, without great heat or
pressure and can be simply and inexpensively handled
during molding. In preferred embodiments, the
organopolys:iloxane foams are those which are curable at
elevated temperatures so that the organopolysiloxane
having an organopolysiloxane foam-forming agent therein
can be easily handled, for example, so that the abrasive
material or polishing material and other additives can
be substantially uniformly dispersed therein, prior to
placing in a mold and curing.
The Eormulation of the organopolysiloxane
foams of the present invention can be carefully
controlled to provide foamed binder or matrix material
of desired essential characteristics, including
desired cell sizes, that is, cells ranqing from about
0.001 cm. to about 0.30 cm.; a desired proportion of
void or cell space to the total volume of the body, that
is, a void space ranging from about 15% to about 85~ of
the organopolysiloxane in the foam material and more
l'~S8~8~
60-SI-457
_g_
preferably, from about 15~ to about 25~ of th2
organopolysiloxane in the foam material; essential
toughness or hardness for use in particular operations;
and adaptability to receive inert fillers to increase
S heat resistance, lubricating characteristics and the
like, as well as to receive the abrasive or polishing
materials, and the like.
Any organopolysiloxane material can be
suitably ~oamed to provide the organopolysiloxane foam
which may be used to form the abrasive material of the
pres~nt invention. Typical organopolysiloxane
foam-forming materials and methods and typical foamable
organopolysiloxanes are well-known in the art. One
typical organopolysiloxane foam-forming material is
described and claimed in U.S. Patent No- 3,379,659,
issued April 23,-1968. In United States Patent No.
3,379r659t there is disclosed and claimed a room
temperature vulcanizing organopolysiloxane foam-forming
composition and a method for making organopolysiloxane
foams which utilize a silicon hydride and an
aminoxy-substituted organosilicon material. Foaming in
U.S. Patent No. 3,3?9,659 is achieved by the liberation
of hydrogen gas from the silicon when the foam-forming
composition is contacted with hydroxylated material,
such as, atmospheric moisture. In one preferred
embodiment o the present invention, a hydrated filler
material, such as hydrated silica is incorporated in the
organopolysiloxane rubber or elastomer to provide the
moisture which is liberated from the hydrated silica
upon heating at an appropriate elevated temperature
which also simultaneously cures the composition in the
:~'Z58~8~
60-SI-457
--1 0--
presence of a catalyst, to form a cured material. The
moisture reacts with a foam-forming agent in the
organopolysiloxane elastomer to form a gas which foams
the organopolysiloxane rubber or elastomer. This can be
carried out in any mold to form a desired molded
article. In one molding technique known in the art, a
layer of fabric or cloth is placed between the platen
and side retaining wall of the mold. This aids in the
dissipation of the sponging gas or gases and is readily
adaptable to molding techniques which utilize low
molding pressures.
Another typical foamable organopolysiloxane
composition is described and claimed in U.S. Patent. No.
3,425,967, issued February 4, 1969. In United States
Patent No. 3,425,967, the foamable composition comprises
a vinyl chain~stoped polysiloxane having a specified
formula, an organopolysiloxane copolymer comprising
(R")3SiOo 5 units and SiO2 units in which from
about 2.5 to about 10 mole percent of the silicon atoms
contain silicon-bonded vinyl groups; an inorganic
fibrous material; a finely divided filler; an amount of
a liquid organohydrogenpolysiloxane having a specified
formula; and a blowing agent.
Still another typical silicone foam is
described and claimed in United States P~tent Number
3,62~i,010, issued November 30, 1971, wherein
organopolysiloxane foam is made by mixing a
carboxyalkylpolysiloxane, a diisocyanate and a tertiary
amine; allowing the composition to foam; then curing the
foamed composition. Carbon dioxide generated during the
125~8~8'~
60-SI-457
reaction of the components in U.S. Patent No. 3,524,010,
causes foaming of the product during the curing
reaction, and, thus, causes foam formation. Heating o
the product in U.S. Patent No. 3,S24,010 at a
temperature of from about 100C to about 120C results
in a cured, foamed organopolysiloxane product.
Still other typical organopolysiloxane foams
well known in the art may be used in the present
invention. For example, other typical
organopolysiloxane foams which may be used in the
present invention, are the peroxide-cured
organopolysiloxanes containing a conventional blowing
agent, such as, benæenesulfonyl hydrazide (BSH). Other
conventional blowing agents include, for example,
toluenesulfonyl hydrazide (TSH),
4,4'-oxybis(benzenesulfonyl hydrazide) (OBSH) and
azobisformamide (ABFA) also known as azodicarbonamide.
A sufficient amount of heat is applied to cause the
formation of gas from the blowing agent while
simultaneously curing the rubber or elastomer undergoing
"foaming" by the action of the gas. Other typical
organopolysiloxane foams are the addition-cured
organopolysiloxane rubbers or elastomers, such as, those
containing a silicon hydride which releases hydrogen gas
(the foaming agent) in the presence of moisture, such
as, the water contained in a water-containing filler
dispersed in the organopolysiloxane material, the water
in the water-containing filler being released when the
organopolysiloxane containing the water-containing
filler is heated at an elevated temperature. As
indicated above, in this preferred embodiment, the
1~58~
60-SI-457
-12-
heating of the organopolysiloxane rubber or elastomer to
release the water in the hydrated filler, such as
hydrated silica, also simultaneously cures the
organopolysiloxane while the hydrogen gas is released
during the heating to form the cells or voids in the
organopolysiloxane rubber or elastomer. Thus, in
preferred embodiments of the present invention, the
organopolysiloxane foam is one which is curable at
elevated temperatures because it not only affects the
cure by forming crosslinks between vinyl groups on the
polymer with hydrogen on the methyl hydrogen on the
silicon hydride (methyl silicon hydride) crosslinking
a~ent which is catalyzed by platinum, but because it
also affects the foaming by releasing the water of
hydration contained in the filler in the
organopolysiloxane material. The water reacts with
silicon hydride also incorporated in the
organopolysiloxane rubber or elastomer to release
hydrogen gas and cause the void formation in the
organopolysiloxane material. Thus, when the
organopolysiloxane foam is an addition cured
organopolysiloxane and contains a typical
addition-curing or crosslinklng agent, such as, a
silicon hydride tfor example, methyl silicon hydride),
it is cured at an elevated temperature in the presence
of an addition catalyst, preferably, a class of typical
platinum derivative catalysts well-known in the art,
while hydrogen gas is simultaneously released to form
the voids or cells in the organopolysiloxane foam which
also contains the abrasive material or polishing
material uniformly dispersed therein.
lZS8~8'~
60-SI- 457
-13-
When the organopolysiloxane foam is one which
is formed from an addition cured organopolysiloxane, the
gas which forms the voids or cells in the
organopolysiloxane, is derived from a reaction from
5 $illers and materials incorporated in the
organopolysiloxane. For example, a water-bearing
filler, such as a hydrated filler, for example, hydrated
silica, can be dispersed or mixed in the
organopolysiloxane as is well-known in the art. An
agent compatible with the organopolysiloxane and which
releases a gas in the presence of water, can be
incorporated in the organopolysiloxane by mixing. When
the water in the filler is released, the gas forms from
the reaction wi~h the agent in the organopolysiloxane
rubber or elastomer which agent forms a gas in the
presence of water, and the cells or voids are formed in
the organopolysiloxane by the gas. For example, one
typical agent is a silicon hydride, such as, a
methyl silicon hydride which reacts with water to form
hydrogen gas. Thus, in one of the preferred embodiments
o the present invention, hydrated silica is
incorporated in the organopolysiloxane rubber as a
filler, and a silicon hydride is incorporated in the
organopolysiloxane rubber as a crosslinking agent, and
at an elevated temperature, the water of hydration is
released from the hydrated silica, reacts with the
silicon hydride and f~rms hydrogen gas. The elevated
temperature used in this instance is about 50C to about
300C, and more preferably, about 150C to about 200C.
When a typical catalyst is incorporated therein, such as
a platinum catalyst, the organopolysiloxane rubber
l'~S8~8'~
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-14-
simultaneously cures while the hydrogen gas foams the
organopol~siloxane rubber. Thus, the elevated
temperature must be sufficient to cause the liberation
of hydrogen when water in the hydrated silica reacts
with the silicon hydride, whereby the hydrogen causes
the formation of cells within the organopolysiloxane
rubber, as well as to cause the curing.
The abrasive grit or polishing material,
generally referred to herein as abrasive grit, may be
any well-known abrasive or polishing material, for
example, it can be silicon carbide, finely-divided
aluminum oxide, synthetic alumina, diamond, cubic
crystal boron nitride, synthetic mullites and other
natural and synthetic materials generally well-known in
the art for their abrasive character or their polishing
character or both.
As indicated above, in certain preferred
embodiments of the present invention, the abrasive
material comprising the organopolysiloxane foam having
abrasive grit uniformly dispersed in the
organopolysiloxane, may be treated with an organosilane
or equivalent agent to promote the bonding of the
abrasive or polishing material to the organopolysiloxane
foam binder or matrix. In accordance with the present
invention, the preferred organosilanes may be
vinyltriethoxy silane, 2-13,4-epoxycyclohexyl)ethyl-
trimethoxy silane, phenyltriethoxy silane,
methacryloxypropyltrimethoxy silane,
gamma-aminopropyltriethoxy silane and saliciaminde of
aminosilane. Methods and compositions for pre-treating
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60-SI- 4~7
-15-
the abrasive or polishing material prior to dispersing
the material in the organopolysiloxane is deseribed and
claimed in U.S. Patent No. 3,489,541, issued
January 13, 1970 and U.S. Patent No. 3,904,391, issued
September 9, 1975 In essence, these referen~e disclose at
least washing the abrasive or polishing material with
the specified organosilane, preferably after treating
the abrasive or polishing material with a suitable
agent, such as, an alkali metal hydroxide or other
etching agent. Methods and solutions for treating the
abrasive or polishing material are well defined in the
foregoing references.
The amount of abrasive grit or polishing
material incorporated in the organoplysiloxane foam is
generally critical in order to avoid large islands of
non-grit-containing areas in the organopolysiloxane
foam. Thus, the minimum amount is that amount which
must be incorporated into the organopolysiloxane foam in
order to provide a sufficient amount of abrasive or
polishing material substantially uniformly dispersed in
the organopolysiloxane. The maximum amount of abrasive
or polishing material is that amount which does not
destroy or compromise the integrity of the
oranopolysiloxane foam rubber or elastomer in which it
is uniformly dispersed. In most embodiments, the
minimum amount required to avoid areas or islands of
non-grit-containing material, is at least about 53% by
weight, based on the weight of the organopolysiloxane.
Generally, in most embodiments, the abrasive grit or
polishing material is incorporated in the
organopolysiloxane foam rubber in an amount ranging from
60-SI-457
-16-
about 53 percent ~o abou. 80 weight percent, based on
the weight of the organoQolysiloxane rubber.
The abrasive grit or polishing material must
be su~stantially uniformly dispersed within the
organopolysiloxane prior to foaming the
organopolysiloxane in order to provide the improved
surface friction characteristics. This is generally
accomplished by thoroughly blending, mixing or otherwise
distributing the abrasive grit or polishing material in
the organopolysiloxane rubber or elastomer prior to
foaming, and it may be carried out simultaneously with
the dispersion of other materials therein, for example,
fillers, blowing agents, such as, organopolysiloxane
lS foam-forming agents, whether blowing agents or
gas forming agents, such as, silicon hydride. The
organopolysiloxane rubber or elastomer which is
- subjected to foaming is generally a gum, however, in
certain instances, the organopolysiloxane may be a
liquid. Liquids may be utilized, however, it is more
difficult to maintain the abrasive grit on polishing
material in uniform dispersion therein until the
organopolysiloxane liquid is cured. In any event, the
abrasive material or polishing material as well as the
other materials, such as, fillers and organopolysiloxane
foam-forming agents, are incorporated in the
organopolysiloxane rubber or elastomer by thoroughly
mixing with a suitable mixing device, such as, a Waring
blender, a ball mlll, a rubber mill, a ~anbury mixer, or
any other suitable stirring or mixing device.
Various reinforcing fillers can also be
incorporated in the organopolysiloxane foams of the
8'~
60-SI-~57
-17-
present invention. Reinforcing inorganic fillers, such
as, calcium carbonate, titanium dioxide, silica,
fumed silica, hydrated silica as indicated above to
provide water for the reaction with silicon hydride to
produce hydrogen gas for foaming, and the like.
Kaolinite clays, aluminum silicate clays and silica, as
well as carbon black, can be added to provide desirable
results by one skilled in the art. In general, the
reinforcing fillers or additives can be used singly or
in combination and serve to strengthen the
organopolysiloxane matrix and to increase the Shore
hardness of the finished products. The proportion of
the abrasive grit or polishing material can also be
employed to vary the hardness, making it possible to
proportion the respective amounts of abrasive or
polishiny material and reinforcing filler to achieve a
desired hardness as well-known in the art, as well as
the desired polishing or abrasive action. Generally, in
accordance with the present invention, the amount of
reinforcing and other fillers or fillers may be used up
to about 50% by weight of the organopolysiloxane.
Naturally, as discussed above, the
organopolypolysiloxanes of the present invention also
contain an organopolysiloxane foam-forming agent, which
may be a gas, or which may be an agent which forms a gas
in the presence of moisture, heat, chemical additives,
and the like, and combinations thereof. The amount of
foam-forming agent in the organopolysiloxane of the
present invention is that amount which forms the desired
degree of porosity or proportion of gas cells or voids
within the foam, more specifically, that amo~nt which
l~S8~8~
60-SI~57
-18-
provides void spaces within the cellular body up to
about 85~ of .he total volume of the organopolysiloxane
body. Generally, between about 15% and about 85% of the
total volume of the organopolysiloxane body is void
volume, and more preferably, about 15% to about 25~ of
the total volume of the organopolysiloxane constitutes
the gas célls or voids. Such void spaces can be in the
form of substantially individualized cells or in the
form of generally open or interconnecting cells. As
indicated above, the cells or voids are generally formed
by the realease of gases within the organopolysiloxane,
for example, the release of hydrogen gas when silicon
hydride or hydrazides react with water, or the release
of carbon dioxide when diisocyanates operating as
- 15 blowing agents release the carbon dioxide in the
presence of heat. In most instances, in preferred
embodiments of the present invention, the abrasive
material, that is, the organopolysiloxane foam
containing the abrasive grit or polishing material
uniformly dispersed therein, has a density of about 60
pounds per cubic foot to about 95 pounds per cubic foot.
The degree of porosity and cell size of the
organopolysiloxane foams of the present invention is
controlled by the amount of blowing agent or other
organopolysiloxane foam-forming agent incorporated in
the organopolysiloxane. Also, various types and amounts
of surfactants and non-ionic cell stabilizers well known
in the art, may be employed to control porosity and cell
size. In general, the greater the amount of surfactant
or cell stabilizer, the ~iner and more uniform the cell.
The porosity and cell size within the organopolysiloxane
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60-SI-457
_1 9--
foam can ~lso be cor.trolled to some extent by the degree
of loading of the material in a mold, with respect
either to the amount of organopolysiloxane employed or
the amount of various fillers and additives. For
example, the mold can be filled to any level, and when
closed, can expand only to the extent of the mold left
un-filled. Thus the control of the degree of porosity
and cell size can be dependent upon mold filling, that
is, the amount of organopolysiloxane material placed in
the mold.
Generally, in preparing the abrasive materials
having improved surface friction characteristics in
accordance with the present invention, the abrasive or
polishing material is mixed with the organopolysiloxane
having an organopolysiloxane foam-forming agent therein
until the abrasive or polishing material is
substantially unîformly ~ispersed therein. After the
mixing is complete and all of the ingredients are
uniformly dispersed therein, including any fillers,
catalysts, foam-forming agents, polishing or abrasive
materials, and the like, are uniformly dispersed
therein, the mixture is allowed to foam and cure. As
discussed above, the curing may be accomplished
simultaneously with ~he foaming. The order in which the
fillers, foam-forming agents catalysts and any other
materials are incorporated in the organopolysiloxane, is
not critical as long as they are uniformly dispersed in
the organopolysiloxane by appropriate mixing.
8'~
60-SI-457
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Appropriate catalysts, such as
organoperoxides, platinum or platinum derivatives and
any of the other well-known catalysts for
organopolysiloxanes, may also be mixed in an effective
catalytic amount into the organopolysiloxane along wi~h
the organopolysiloxane foam-forming agent, crosslinking
agent or agents~ such as, silicon hydride, fillers,
abrasive or polishing materials and the like.
Generally, the amount of catalyst can be easily adjusted
by one skilled in the art without undue experimentation.
Curing time can also be easily controlled, depending
upon the desired amount of cure, by one skilled in the
art.
After the mixing of the ingredients is
complete, and the abrasive grit or polishing material
are substantially uniformly dispersed throughout the
organopolysiloxane gum or fluidr the mixture is foamed
and cured by heating the abrasive grit-containing
organopolysiloxane having the organopolysiloxane
foam-forming agent therein at an elevated temperature in
the presence of an effective catalytic amount of
catalyst to cure the organopolysiloxane. In most
instances, the elevated temperature is a temperature of
about 50C to abouto 300C, and more preferably from
about 150C to about 200C. The length of time of
heating may be that amount of time required to effect
the desired cure~ such as, for example, from less than
about 1 minute up to 5 hours or more. After curing is
complete, generally in a mold, the cured foam containing
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the abrasive grit or ~olishing material is cooled to
room temperature and removed from the mold.
In general, the organopolysiloxane foams
having abrasive qrit or polishing material uniformly
dispersed in the organopolysiloxane, can be molded or
formed in virtually any shape and size desired.
Well-known molded and shaped abrasive and polishing
articles are known, such as abrasive wheels and
polishing wheels. Belts and sheets of the
organopolysiloxane foams having abrasive grit or
polishing material uniformly dispersed therein can also
be made or formed from the materials of the present
invention, and they can be formed onto a backing or
reinforcing material which may be fibrous or
non-fibrous. The organopolysiloxane foams having the
abrasive grit uniformly dispersed therein in accordance
with the present invention can be formed into continuous
belts or sheets following standard practices. The
flexible, cellular organopolysiloxane foams of the
present invention, when formed into abrasive or
polishing articles as described above, can be suitably
reinforced with fibers, fabrics, and the like.
Generally, there is also improved accessability of grain
surfaces yielding more aggressive cuts or greater
polishing ability and shorter grinding or polishing
times.
In one preferred embodiment of the present
invention, molded articles are formed by mixing the
abrasive grit or polishing material in an
organopolysiloxane gum or liquid having an
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organopolysiloxane foam-forming agent therein, until the
abrasive grit is substantially uniformly dispersed
therein; placing the mixture in a mold, the mixture
containing a crosslinking agent and a catalyst to
promote cross-linking or curing of the mixture; allowing
the mixture to foam; and curing the foam. The mixture
may be heated as desired at an elevated temperature in
the mold to promote the foaming and/or curing of the
organopolysiloxane rubber or elastomer. Naturally, when
the organopolysiloxane foam-forming agent is silicon
hydride which reacts with water from water-containing
filler or fillers in the organopolysiloxane, the cells
in the organopolysiloxane rubber or elastomer are formed
by the release of hydrogen gas when the mixture is
heated at an elevated temperature, generally, between
about 150~C. to about 200C.
The following examples further illustrate the
practice of the invention, and they are meant to be
exemplary only and are not to be construed as limiting
the invention in any way.
EXAMPLE I
Sponging was accomplished by combining a
hydrated silica reinforced silicone rubber compound with
methyl hydride oil and a platinum catalyst. The
~ilicone rubber was 68.8 parts by weight
polydimethylmethylvinyl siloxane and contained 29 parts
by weight hydrated silica, 1.9 parts by weight silanol
stopped polydimethylsiloxane fluid, 0.4 parts by weight
vinyl tris(2-ethoxymethoxy)silane and 0.1 part by weigh~
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of a typical heat age additive. The formulation
contained 47 parts by weight of the above reinforced
organopolysiloxane, 53 parts by weight of a 60 grit
silicon carbide abrasive material, 1 part by weight
methyl hydride oil and 1 part by weight platinum
catalyst. The ingredients were uniformly mixed in a
conventional rubber mill so that the abrasive grit was
uniformly dispersed throughout the mixture. The mixture
as prepared in the rubber mill, was placed in a mold
15.24 cm. (6 inches) x 15.24 cm. (6 inches) x 1.27 cm.
(0.5 inch). The mold was underfilled to allow room for
expansion during the release of the hydrogen gas. At
the elevated molding temperature, the hydride reacted
with the water contained in the hydrated silica filler,
and hydrogen gas was liberated to form the cells in the
rubber. An open weave fabric was placed in the mold
prior to placing the mixture therein to assist in the
sponging operation by promoting the distribution of the
hydrogen gas. The mold was heated at about 177C for
abou~ 20 minutes. The slab of foamed organopolysiloxane
having the silicon carbide abrasive therein, had a
specific gravity of 1.42 compared with a specific
gravity of 1.66 for the comparable non-foamed
organopolysiloxane containing the same size and amount
silicon carbide abrasive material. The blow ratio of
the foamed organopolysiloxane containing the silicon
carbide abrasive was 1.17. The abrasiveness of the
compound was good, and the wear resistance of the slab
compound as subjectively assessed, is good.
Abrasiveness was qualitatively determined by
mounting a 5.08 cm. (~ inch) diameter by 1.27 cm. (0.5
inch) thick disk of the sponged composite on a portable
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electric drill which was then used to qrind various
metal surfaces. The material displayed good abrasive
and wear resistance properties.
EXAMPLE II
Sponging was accomplished by combining a
fumed-silica reinforced silicone rubber compound with a
blowing agent, organic peroxide catalyst and abrasive
1 n grit. The silicone rubber was 70.5 parts by weight
polydimethylmethylvinyl siloxane and contained 1.0 part
by weight of typical heat age and compression set
additives, 5.4 parts by weight diatomaceous earth, 19.5
parts by weight of treated fumed silica, 0.2 parts by
weight of vinyltriethoxy silane and 3.4 parts by weight
methoxy stopp~d polydimethylsiloxane fluid. The
formulation contained 47 parts by weight of the above
fumed silica-reinforced silicone rubber, 53 parts by
weight of an 80 mesh silicon carbide abrasive material,
0.4 parts by weight of benzenesulfonyl hydrazide blowing
agent, 0.8 parts by weight of 2,4-dichlorobenzoyl
peroxide and 2 parts by weight Verox powder, a 50
2,5-dimethyl-2,5-bis(t-butylperoxy~ hexane. The
formulation was mixed and molded as described in Example
I. The slab of foamed, cured organopolysiloxane having
the silicon carbide abrasive therein, had a specific
gravity of 1.24 compared with a specific gravity of 1.66
for the comparable non-foamed organopolysiloxane. The
blow ratio of the foamed organopolysiloxane containing
the silicon carbide abrasive was 1.34. Abrasiveness of
the compound was excellent.
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While other modifications of the invention and
variations thereof which may be employed within the
scope of the invention have not been described, the
invention is intended to include such modifications as
may be embraced within the following claims.
