Note: Descriptions are shown in the official language in which they were submitted.
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FILLERS FOR USE IN CASTING l~ARBLE PRODUCTS
Field of the Invention
This invention relates to filler compositions for
mixing with resins to form a castable product which may
simulate marble.
Background of the Invention
Shaped marble products are used widely for a variety
of purposes, such as plumbing products which include
sinks, toilets, bathtubs, shower stall bases and the like;
decorative mouldings; wall panels; and shelving systems to
name only a few. To form these products out of solid
marble is usually expensive and unsanitary. Cast marble
products have become a viable substitute for natural
marble where the desired article may be formed by casting
and setting a marble-like composition in a mold. By
casting the product, greater flexibility in design is
permitted and the surfaces are finished in a manner which
provides sanitary surfaces. Commonly, various types of
granulates especially of calcium carbonate admixed with an
20~ appropriate setting resin have been used in forming molded
products particularly in the plumbing industry. The
problem, however, in casting marble-like compositions to
form these products is that the resultant product is very
heavy. For example, a bathtub formed in this manner may
weight in excess of 500 pounds, therefore, resulting in
difficult installation procedures.
In an attempt to reduce the weight of the cast marble
product, attempts have been made to incorporate in the
marble product various types of glass spheres. However,
the glass spheres tend to break up or dissolve during
mixing of the mineral filler such as calcium carbonate
with the resin. Hence there is very little reduction in
weight of the product and furthermore the product tends to
loose structural strength due to the break-up of the glass
spheres.
According to this invention, a filler composition has
been developed which results in a cast marble product
weighing considerably less than existing types of cast
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marble products, yet maintaining desired s-tructural
characteristics.
Summary of the Invention
According to an aspect of the invention, a filler
composition for mixing with a resin to form a castable
product comprises an inorganic filler material in powder
form admixed with essentially hollow ceramic spheres and
essentially hollow plastic spheres. The plastic spheres
have an average diameter significantly less than an
average diameter of the ceramic spheres.
According to another aspect of the invention,
sufficient plastic spheres are present in the composition
to cushion the ceramic spheres and thereby minimize
break-up of the ceramic spheres during handling, mixing
and casting of the filler composition.
According to another aspect of the invention, a cast
product comprises a filler composition of the above
admixed with a color pigment and set with a resin such as
an unsaturated polyester resin. The inorganic filler
material may be calcium carbonate having granular elongate
crystals. The elongate crystals of calcium carbonate as
bonded by the resin increases tensile strength of the cast
product.
Detailed Description of the Preferred Embodiment
Cast products formed by mixing a mineral filler with
a resin has a variety of applications. The selection of
the particular mineral to be mixed with the resin depends
upon the type of product to be cast. The preferred
embodiment of this invention will be described with
respect to casting of marble-like products commonly used
in bathroom and other types of plumbing fixtures. In this
field of application, calcium carbonate is the principal
source of the inorganic filler. The calcium carbonate is
used in powder form and has a crystalline structure which
tends to be granular and elongate in shape. Normally the
mixing of such mineral fillers with a suitable resin
results in a very heavy product. This may be acceptable
in products such as short countertops; however,
37~
considerable weight is added when the material is cast in
the shape of bathtubs.
It has been found that the combined use of ceramic
spheres with plastic spheres of considerably smaller
diameter can be mixed with the mineral filler to provide
the preblend. When the preblend is mixed with a suitable
resin and cast into the desired shape, it has been found
that there is considerable weight reduction and in some
instances may be in the range of 50%. This reduces
shipping and handling costs substantially as well enabling
people working with the products to handle them in a more
careful manner with ease. For example, a bathtub which
may weigh normally in the range of 500 to 600 pounds, with
this composition may only weigh in the range of 250
pounds. This considerably facilitates the installation of
the tub in the bathroom.
The ceramic spheres are available in a variety of
configurations. The preferred source of ceramic spheres
is that sold under the trade mark SG by P.A. Industries of
Tennessee. The ceramic spheres tend to be hollow spheres
in structure where the shell thickness is approximately
10~ of the sphere diameter. The diameter of the spheres
range from approximately 10 microns up to 350 microns.
The average sphere diameter is approximately 100 microns.
The spheres have a specific gravity of 0.70 and a bulk
density of 25 pounds per cubic foot. The melting point of
the spheres is in the range of 1200C. The spheres will
withstand external pressures of up to 5000 psi before
break-up. The hardness of the spheres is in the range of
5 on the Mohn scale. The spheres consist principally of
silicon dioxide, aluminum oxide and ferrous oxide. It is
appreciated, of course, that not all types of ceramic
spheres, which are usable with this invention, are hollow
in nature and may instead be of a porous type having
similar specific gravity and bulk density.
The plastic spheres, which are used in combination
with the ceramic spheres, are preferably very light and
may have a specific gravity in the range of 0.014. It is
appreciated that the spheres are formed from a plastic
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which maintains integrity in the size range of
approximately 3 to 5 microns in diameter. The preferred
type of plastic spheres are that sold under the trade mark
EXPANCEL and are available from Expancel which is a Kema
Noble company of Sundsval, Sweden. The microspheres are
formed with a polymeric shell with enclosed blowing agent.
The spheres have a plastic shell predominantly of the
polymer polyvinyldichloride (C2H2C12)n. The blowing agent
is normally isobutene. When the mixture is heated, the
spheres are formed, all of approximately 3 to 5 microns in
diameter. It is appreciated, of course, that other
diameter of plastic spheres are usable. The main criteria
is that the plastic spheres should be significantly
smaller in diameter compared to the ceramic spheres.
The presence of the combined use of ceramic and
plastic spheres increases resistance in the cast product
to thermal shock. This is particularly important with
products exposed to extremes in hot and cold temperatures;
i.e. bathtubs. At the same time, the presence of the
spheres adds to the thermal insulative aspect of the
product so that heat loss from the product, when
containing hot liquids, is decreased. The presence of the
ceramic and plastic spheres also decreases effort required
in not only handling the product but also drilling,
trimming and finishing of the product.
A sufficient amount of plastic spheres is used in the
filler composition to act as shock absorbers in
surrounding and being adjacent the ceramic spheres. By
virtue of the plastic spheres being considerably smaller
in diameter than the ceramic spheres, many plastic spheres
can envelope or at least cover a major percentage of the
ceramic sphere surface and cushion the spheres as the
preblended combination of mineral and synthetic
ingredients is mixed with resin and cast into the desired
product. By preventing break up of the ceramic spheres,
the structural integrity of the cast product is maintained
while significantly reducing the weight of the product.
It has been experienced by the combined use of this type
of ceramic sphere with plastic sphere, a weight reduction
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of approximately 50% compared to existing types of cast
marble products using resin with mineral filler can be
achieved.
The plastic spheres, particularly when made of
polyvinyldichloride, carry an electric charge which
results in an electrical attraction of the plastic spheres
to the surface of the ceramic spheres. This ensures that
the plastic spheres remain about or on the surface of the
ceramic spheres during blending of the materials, handling
and mixing with resin. As a result, the plastic spheres
do not float away from the product mix.
The preblended composition for the filler comprises
by weight:
1) approximately 70% to 80% of calcium carbonate;
2) approximately 17% to 27.5% of ceramic spheres;
3) approximately 2.5% to 3.0~ of plastic spheres;
The preferred composition, according to this embodiment of
this invention, comprises 75% by weight of calcium
carbonate; 22% by weight of ceramic spheres and 3~ by
weight of plastic spheres. The calcium carbonate powder,
as used in the preferred composition, has the following
screen analysis on a percent retained cumulative basis:
40 mesh - 0.13%
50 mesh - 3.08%
60 mesh - 8.95%
70 mesh - 16.30%
100 mesh - 13.67%
200 mesh - 54.42%
325 mesh - 74.30~
The resultant filler composition, according to a preferred
embodiment of this invention, has the following screen
analysis on a percent retained cumulative basis:
30 mesh - 0.039%
40 mesh - 0.43%
50 mesh - 5.80%
60 mesh - 14.76
70 mesh - 24.50%
100 mesh - 33.94
200 mesh - 66.16%
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325 mesh - 90.71%
This prehlended combination of mineral and synthetic
ingredients may be blended with a suitable resin on a
batch basis to obtain optimum strength per weight ratio or
in combination with other fillers to produce unique blenas
if required. The materials may be blended in any size of
mixer to allow flexibility in manufacturing without change
in existing casting methods. Suitable resins are those
already commonly used in the field of cast marble
products, such as the unsaturated polyester resins to
which a catalyst is added to set the resin in forming the
solid cast product.
It is appreciated that depending upon the end use for
the castable composition, various consistencies will be
desired. Generally however, the preblended filler
material can be mixed with the resin for use as follows.
A known amount of resin is placed in the mixer. A
weighted amount of preblend is then added slowly to the
resin while mixing until the consistency is suitable for
the particular casting application. The left-over
preblend is then weighed to determine the weight of
preblend added to the mix. While continuing mixing,
catalyst is added to the mixture to commence reaction in
the resin to set the composition. The amount of catalyst
added is based on the original amount of resin placed in
the mixture. Once catalyst is distributed throughout the
resin, the thick mixture is removed from the mixer and
cast in a mold in the usual way. When desired, a gel coat
may be applied to the surface of the mold before the
mixture is added to the mold to provide the desired
surface finish on the product.
The preblended composition, according to this
invention, does not require any special equipment for
handling or mixing nor any special resins for setting.
The process to be followed in mixing the resin is
essentially the same as that already used. Hence without
any special requirements, the preblended combination of
mineral and synthetic ingredients of this invention for
cast marble products provides the significant advantage in
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weight reduction which may be as much as 50~ or more. In
addition, the overall structural, tensile and thermal
strength of the product is enhanced by the combined use of
the ceramic and plastic spheres with granular elongate
type crystals of calcium carbonate which, when set with
the resin, is provided.
Although preferred embodiments of the invention have
been described herein in detail, it will be understood by
those skilled in the art that variations may be made
thereto without departing from the spirit of the invention
or the scope of the appended claims.
