Note: Descriptions are shown in the official language in which they were submitted.
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INVENTOR
Michael J. Haun
TITLE
METHOD FOR MAKING PRODUCT FROM WASTE GLASS
BACKGROUND OF THE INVENTION
The invention is directed to ceramic products made from waste glass; raw batch
formulations
for making ceramic products from waste glass; and a method for making ceramic
products
from waste glass. Examples of ceramic products that can be made by the
invention are tile
and brick, but other ceramic products can also be made. The invention
addresses two current
problems: energy usage by the ceramic industry needs to be reduced; and new
recycled-glass
products are needed.
The ceramic industry consumes large amounts of energy, especially during the
Ering process.
Firing temperatures greater than 1200° C (2200° F) are required
to sinter typical ceramic raw
materials into dense products. Modifications of the raw material formulations
have led to
reductions in firing temperatures, but the improvements are limited because of
the types of
raw materials used. Most traditional ceramic products, such as tile and brick,
consist mainly
of clay-based raw materials, which inherently require high firing
temperatures. Other ceramic
manufacturing steps, such as the drying processes, are also very energy
intensive. Energy
costs are a major portion of the total manufacturing costs, and thus new
methods to reduce
the amount of energy required will be a great benefit to the ceramic industry.
New products utilizing recycled waste glass are needed to further promote
glass recycling,
because only a limited amount of glass can be remelted to make new containers
(currently the
primary use of recycled glass). New products are especially needed that are
less sensitive to
contaminants in the glass, and that can be made from green or mixed-color
waste glass.
Research has been conducted and products developed using recycled glass as a
ceramic raw
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material. However, processing problems have limited the developments, so that
only a
negligible amount of waste glass is currently utilized (excluding remelting to
form new glass
products). These problems occur because of inherent chemical and processing
incompatibilities with traditional ceramic raw materials and manufacturing
methods. These
incompatibilities have greatly hampered the development of ceramic products
from waste
glass.
Waste glass in the invention refers to any industrial or post-consumer glass
that is discarded.
A~iy form of glass, such as containers (bottles, jars, etc.), plate glass, or
fiber glass, can be
used. Waste glass can be obtained from recycling companies or glass
manufacturers. Most
waste glass consists mainly of silicon, sodium, and calcium oxides (referred
to as soda-lime
glass) with other minor components, such as aluminum and magnesium oxides.
Soda-lime
glass compositions typically soften from about 650° to about
750° C. This unique softening
behavior causes articles formed from fme powders of soda-lime glass to densify
by viscous-
phase sintering at temperatures much lower than usually required to fire
ceramic products.
The invention utilizes the low-temperature densification behavior of soda-lime
glass to
reduce manufacturing costs by conserving energy and lowering equipment and
maintenance
expenses.
Water, clay, and some other common ceramic raw materials are inherently
incompatible with
sintering of soda-lime glass powder at low temperatures. This is because
chemical species
resulting from reaction of glass with water, or from decomposition of clay,
volatilize in the
temperature range where soda-lime glass softens. The volatile species become
trapped in the
densifying glass, which causes foaming and porous defects in the final
product. Previous
waste-glass based ceramic products have been made with the addition of water
and clay. The
porous defects that resulted were minimized by optimizing the processing
parameters, but not
eliminated. The following paragraphs describe the previous processing problems
that have
occurred when trying to use waste glass as a ceramic raw material.
Brown and Mackenzie [J. of Materials Science, Vol. 17, pp. 2164-2193, 1982]
fabricated
ceramic tile from recycled glass combined with clay and water. The fired
properties were
found to be greatly affected by the amount of clay and water added, because of
variations in
the amount of porosity that occurred. Low [J. of Materials Science, Vol. 15,
pp. 1509-1517,
1980] demonstrated that special foaming agents, such as calcium carbonate,
were not
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necessary to foam glass. The volatile species from decomposition of mica,
similar to that in
clays, combined with the glass-water reaction was all that was necessary to
produce extreme
foaming.
Liu, Li, and Zhang [Glass Technology, Vol. 32, No. l, pp. 24-27, 1991]
investigated
processing recycled glass powder with organic binders and water. They reported
that the
binder (and water) content had to be kept low to prevent bubbling in the fired
samples and
"inferior chemical and physical properties.." Even with low water content, the
densities of the
fired samples indicate that some degree of foaming occurred. This work
demonstrates the
adverse effects that occur from reactions between glass powder and water, even
when only
small amounts of water are added without the addition of clay.
Several patents involve the use of recycled glass as a ceramic raw material.
Shutt and
Campbell [US Patent 3,963,506] combined ground waste glass with clay, crushed
brick, and
water to produce building panels and bricks. The fired material had open
porosity, and
problems of warpage and bloating, indicating that adverse glass-water
reactions occurred.
Mackenzie [US Patent 3,963,503] patented a method of making glass products
from ground
waste glass combined with a treating agent. The work mainly concentrated on
foaming glass,
and is typical of how much of the research on recycled glass ended up focusing
on foamed
glass to take advantage of the problems that occurred.
Boyce [US Patent 4,271,109] received a patent for a method of manufacturing
ceramic
insulators for electric lamp bases from mixing 25-45% crushed scrap glass with
clay and
wollastonite. After firing at 1050° C, densities of 1.9 g/cc resulted,
which indicates that at
least 20% porosity still remained. Cihon [US Patent 5,028,569] patented a
batch formulation
and method of producing a ceramic article from 60-85% soda-lime glass Gullet
combined
with clay, flint, and a liquid (water was used in examples). He discussed
problems that
occurred because of reaction of glass with water.
Dutton [US Patent 5,244,850] patented a building material composed of 10-50%
recycled
glass combined with slate particles. Two processes were described. One
involved melting the
recycled glass, mixing in slate particles, and then pressing the molten
mixture in a mold. In
the second process, slate particles with or without recycled glass were mixed
with an alkali-
metal silicate water solution or suspension, such as sodium silicate (water
glass), pressed in a
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mold, dried, and fired at 920° and 1050° C. Lingart [US Patent
5,536,345] patented a process
for manufacturing natural stone-type, panel-shaped construction and decoration
materials
consisting of three layers; a bottom layer of sand, middle layer of a mixture
of sand and
crushed glass, and a top layer of crushed glass. The glass was crushed to 2-3
mm in size and
mixed with at least 5% water. The layers were deposited in a mold and fired in
the mold to
600-850° C, followed by an elaborate series of holds at different
temperatures and careful
cooling.
Golitz et al. [US Patent 5,583,079] patented a ceramic tile product composed
of 25-50% glass
mixed with fly ash, clay, and water. This work focused on lowering the cost of
the raw
materials by using fly ash. The pressed green tile was glazed and then fired
at 970-1025° C.
Greulich [US Patent 5,649,987] patented a process for producing tabular
building and
decorative materials similar to natural stone consisting of 85-98% glass mixed
with water and
various other components, such as sand and inorganic pigments. The mixture was
deposited
in a mold and fired in the mold at 720-1100° C. A closed glossy surface
resulted, however
polishing the surface revealed bubbles. Lingart and Tikhonova [US Patents
5,792,524 and
5,895,511] patented processes of producing ceramic tile from mixtures of
glass, sand, water,
and sodium silicate (water glass) solution. The materials were pressed in a
mold, and then
fired in the mold by a relatively complicated procedure. The authors stated
that air bubbles
formed, and were kept from rising to the surface by controlling the
temperature gradient
between the layers during firing.
The present invention eliminates the previous processing problems discuss
above. The
invention is novel, because a high-quality ceramic product can be manufactured
at low cost
from up to 100% waste glass without requiring the addition of water and clay.
The invention
also conserves energy and natural resources compared to traditional ceramic
processing
methods. It was unexpected that the addition of water and clay would not be
necessary to
manufacture a low-cost ceramic product, such as tile or brick, using waste
glass as a raw
material. It was also unexpected that a nonaqueous organic binder system could
be used to
process waste glass into ceramic products with the overall manufacturing costs
kept low. .
BRIEF SUMMARY OF THE INVENTION
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The invention provides a method to transform large quantities of waste glass
into useful
ceramic products by a low-cost highly-automated manufacturing process. The
major steps of
this method consist of dry preparation of glass powder, granulation with a non-
aqueous
organic binder system, dry pressing with adequate green strength, and firing
at low
temperatures. Up to 100 percent recycled waste glass can be used as the raw
material. Water
and clay are not required in the processing, which eliminates problems that
were encountered
in the past. An expensive spray drying step, which is traditionally needed to
produce
granulated powder for the pressing step, is not required. Molds to fire the
ceramic products in
are also not required. Only one firing step is needed with a low peak firing
temperature of
about 750° C. The method of the invention conserves energy and natural
resources compared
to clay-based traditional ceramic manufacturing.
DETAILED DESCRIPTION OF THE INVENTION
High-quality impervious ceramic products can be produced by the invention with
low
manufacturing costs. A ceramic microstructure with only a small amount of
porosity can also
be achieved. Impervious refers to ceramic products with very low water
absorptions of less
than 0.5%. An impervious ceramic microstructure with a small amount of
porosity is critical
to achieve high-quality properties. Ceramic products can be produced by the
invention with a
wide range of colors with smooth glossy glaze-like surfaces. The surface
texture and other
fired properties can also be adjusted by the addition of fillers, and/or by
partial crystallization
of the glass.
The raw batch formulations of the invention consist of 70-99% waste glass, 0-
20% filler, and
1-10% organic binder. Preferred raw batch formulations consist of 84-99% waste
glass, 0-
10% filler, and 1-6% organic binder. All percentages are based on weight. It
is also
understood that other common ceramic processing additives, such as wetting
agents,
surfactants, deflocculants, coagulants, flocculants, plasticizers, antifoaming
agents,
lubricants, preservatives, etc. can be added to the raw batch formulation to
further optimize
the processing without changing the scope of the invention.
The organic binder and other organic additives (if included) will burn out
during firing, and
thus are not part of the final product. The waste glass and filler are
inorganic components that
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remain after firing, and make up the final product composition. The initial
raw batch
formulation (given above) therefore transforms during firing to the final
product composition
consisting of 80-100% waste glass and 0-20% filler. The preferred final
product composition
consists of 90-100% waste glass and 0-10% filler. The final product
composition is
determined by subtracting the organic binder amount from the raw batch
formulation, and
then renormallizing the remaining composition to 100%.
The filler in the invention is a ceramic raw material added to modify the
color, surface
texture, or any other property of the final product. The addition of a filler
is not necessary to
make a high quality ceramic product, but may be desired to produce a specific
set of
properties in the final product. A wide range of filler additives can be used
in the invention
individually or in combination. A filler added to control the color is
referred to as a colorant.
A wide range of common ceramic colorants can be used to produce ceramic
products by the
invention with any color desired. Examples of individual oxide colorants are
cobalt oxide to
produce blue colors, chromium oxide for greens, and iron oxide for reds. Many
commercial
colorants are available based on complicated combinations of oxides which are
often melted
to form glass frits. In addition to the color, other properties, such as
surface texture and
mechanical properties, can be modified by the .addition of fillers. Other
examples of fillers are
aluminum and zirconium oxides.
The waste glass and fillers must be in powder form to be used in the raw batch
formulations.
The powder particle size required depends on the final properties desired. For
the invention
the waste glass and filler powders have particle sizes <30 mesh (<0.6 mm). The
preferred size
is <100 mesh (<0.1 mm). Coarser particle size fillers can also be included in
the raw batch
formulations to adjust the properties of the final product. For example,
coarser fillers can be
added to produce a rougher surface texture to increase the coefficient of
friction and slip
resistance.
The organic binder in the invention consists of any organic material that can
be added to bond
the inorganic waste glass and filler particles together. The organic binder is
initially mixed
with waste glass and filler particles to form a granulated free-flowing
powder. This powder
is then formed into the ceramic articles. After the forming step, the organic
binder provides
enough strength in the unfired article for handling and transport to the
firing step.
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Examples of organic binders are natural gums, cellulose ethers, polymerized
alcohols, acrylic-
resins, glycols, and waxes. Polyethylene glycol was used as the organic binder
in the
examples of the invention given below. Other organic binders can be used
without changing
the scope of the invention. To be effective the organic binder needs to be in
liquid form, so
that the inorganic waste glass and filler particles cari be wetted and coated
by the organic
binder. Organic binders at room temperature (~20° C) are in either
liquid or solid states. A
solid organic binder can be dissolved in specific liquids, mixed with the
inorganic powders,
and then dried to remove the liquid to produce an inorganic powder coated with
the organic
binder. In the invention nonaqueous liquids, such as alcohols, are used to
dissolve the solid
organic binders. If the organic binder is in a liquid form, then an additional
nonaqueous liquid
is not required.
The following paragraphs describe details of each step of the method of the
invention. The
t
first step of the method consists of dry preparation of glass powder. Typical
container glass
bottles and jars found in municipal solid waste can be used as the starting
glass to prepare the
powder, but other foams of waste glass can also be used. Any color or
combination of colors
of waste glass can be used. The method of the present invention is not
sensitive to normal
levels of contaminants in the waste glass, and thus cleaning of the glass is
not required. The
labels on the glass do not need to be removed. The waste glass is ground into
powder by two
grinding steps.
The first grinding step consists of crushing the glass to <4 mesh (<5 mm)
pieces. Any type of
equipment commonly used to crush glass, rocks, ceramic raw materials, etc.,
such as a jaw or
cone crusher can be used. The crushed glass is screened through a 4 mesh sieve
to separate
the <5 mm pieces. The larger sized pieces (>5 mm) of glass that do not pass
through the sieve
are circulated back into the crusher to further crush the glass until it is
less than 5 mm in size.
During the crushing step a dust collector is used to separate the lighter
weight label particles
from the glass. The label particles are discarded.
The <5 mm crushed glass is then dried in an oven to remove any moisture that
may be
present. Any type of oven can be used. A preferred type is a rotary drier that
can be setup in a
continuous process. After drying, the glass is ground in the second grinding
step to reduce the
size down to <30 mesh (<0.6 mm). The preferred size is <100 mesh (<0.1 mm).
Several types
of milling equipment can be used for this grinding step, such as a ball mill,
hammer mill,
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vibratory mill, attrition mill, roller mill, etc. After milling, the ground
glass is screened
through a 30 mesh sieve (or 100 mesh for the preferred particle size). The
particles that do
not pass through the sieve are circulated back into the mill to be milled
again. During this
grinding step a dust collector is again used to separate the lighter weight
label particles from
the glass.
The fme glass powder (<30 or <100 mesh) that results from the two step
grinding method is
combined with the desired amounts of fillers and organic binder based on the
raw batch
formulation used. The amounts of each component are weighed on a balance,
combined, and
then mixed. The organic binder is added in liquid form, either because the
starting binder is a
liquid, or because the binder is dissolved in a nonaqueous liquid, such as an
alcohol. The
liquid organic binder is combined with the dry glass and filler powders
preferably by
spraying the liquid on the powders, but other common methods of combining the
raw batch
materials can also be used. The combined materials are mixed in any type of
mixer that will
produce a granulated free-flowing powder, such as a pan mixer, conical
blender, ribbon
mixer, rotating drum mixer, etc. Excess nonaqueous liquid can be removed by
drying in a
drier, such as a fluid bed drier, or by spray drying. However, it is preferred
to keep the liquid
content low enough, so that a drying step is not required.
The granulated free-flowing powder of the raw batch formulation is formed into
a green
ceramic article. Green here refers to the unfired ceramic. Any type of forming
method can be
used, but preferably dry pressing is used. For dry pressing the powder is
placed in a metal die
of the desired shape and pressed with rams to compact the powder. The pressed
article is then
removed from the die and fired in a kiln or furnace. If a nonaqueous liquid
was added to
dissolve the binder, then an additional drying step in an oven can be included
before firing to
remove any remaining liquid. Preferably, this drying step is not required,
because additional
liquid was either not included (a liquid binder was used), or was removed
during mixing
and/or forming.
The initial stage of the firing process consists of binder burnout to remove
the organic binder.
Preferably the binder burnout is conducted during the initial heating of the
ceramic articles
for firing. Separate processes of binder burnout and firing can also be used.
In either case the
organic binder must be completely removed prior to the softening and sintering
of the glass
powder to prevent defects from developing in the fired product. Organic
binders typically
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burnout from about 200-400° C. The specific firing profile of
temperature and time will
depend on the raw batch formulation used. Preferably the temperature and time
required are
minimized, while still resulting in nearly 0% porosity. The maximum firing
temperature
required ranges from about 700° C to about 800° C, and is
preferably about 750° C.
The following paragraphs provide 16 examples of the invention. Most of the
steps of the
method are the same for each of the examples. The differences are from
variations in the raw
batch formulations and organic binder system used.
Example 1: The raw batch formulation of Example 1 consisted of 94% clear glass
powder
and 6% organic binder (percentages based on weight). The glass powder was
prepared from
clear glass bottles and jars by a two step grinding process. In the first step
whole glass
containers were crushed in an in-house designed crushing system which involved
crushing
glass in a closed hard plastic chamber. The crushed glass was then sieved
through 6 mesh (<3
rrnn). In the second step the <3 mm glass particles were dry milled in an
alumina ball mill
with alumina media, and then sieved through 100 mesh (<0.1 mm). The glass
powder was
combined with an equal amount by weight of isopropyl alcohol (99%) and 6
weight % (of the
glass amount) organic binder polyethylene glycol (PEG-8000 from Union
Carbide). The
solution was mixed, dried in an oven at 60° C to remove the alcohol,
and sieved through 100
mesh (<0.1 mm). For each sample, approximately eight grams of the dried powder
was
pressed at 5,000 psi (pounds per square inch) in a one inch square metal die
using a hydraulic
press. The pressed articles were fired in a programmable box furnace to first
burnout the
organic binder, and then to sinter into dense ceramic tile. A maximum
temperature of 750° C
was held for one hour. The resulting tile samples had water absorptions of <
0.02%, apparent
porosities of < 0.04%, and densities of 2.47 g/cc (greater than 98% of the
theoretical density).
The samples were glossy white in color with smooth glaze-like surfaces.
Examples 2 and 3: The same procedure described above for Example 1 was also
used for
these examples, except that the clear glass containers used in Example 1 were
replaced by
green glass bottles in Example 2 and brown glass bottles in Example 3. High
quality tile
resulted similar to those of Example 1, except that the Example 2 tile were
green colored, and
the Example 3 tile brown colored.
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Examples 4-9: The same procedure described above for Example 1 was also used
for these
examples, except that 5% of the clear glass amount was replaced by a colorant
filler. Six
commercially available ceramic colorants were evaluated. Example 4 used a red
colorant
(Mason #6031); Example 5 an orange colorant (Mason #6121); Example 6 a green
colorant
(Mason #6224); Example 7 a blue colorant (Mason #6306); Example 8 a brown
colorant
(Mason #6109); and Example 9 a black colorant (Mason #6600). High quality tile
resulted
similar to those of Example 1, except that the colors of the tile corresponded
to the colorant
used. These examples demonstrate the ability of producing a wide range of
colors by the
invention.
Examples 10-15: The same procedures described above for Examples 2 and 3 were
also used
for these examples, except that 1% of the green or brown glass amounts was
replaced by a
colorant filler. The same red, green, and blue colorants were used as listed
in Examples 4, 6,
and 7. Example 10 combined green glass with red colorant; Example 11 green
glass with
green colorant; Example 12 green glass with blue colorant; Example 13 brown
glass with red
colorant; Example 14 brown glass with green colorant; and Example 15 brown
glass with
blue colorant. High quality tile resulted similar to those of the previous
examples, except that
additional color variations resulted. These examples further demonstrate the
ability of
producing a wide range of colors by the invention.
Example 16: The same procedure described above for Example 1 was also used for
this
example, except that the organic binder PEG-8000 was replaced with a different
polyethylene
glycol (PEG-300 from Union Carbide). PEG-8000 used in Examples 1-15 was
initially in a
solid form, and had to be dissolved in a liquid (isopropyl alcohol was used)
to wet and coat
the glass particles. PEG-300 was initially in a liquid form, and so a liquid
was not necessary.
Six weight % PEG-300 (based on the glass amount) was combined with the glass
powder
without any additional liquid added. The glass and PEG-300 were mixed, and
then pressed
without the drying and sieving steps that were previously used after the
binder addition. All
other steps of Example 1 were used. High quality tile resulted similar to
those of Example 1.
A detailed description of the invention with examples was described above. It
is understood
that various other changes and modifications can be made to the present
invention by those
skilled in the art without departing from the scope of the invention. For
example, a glaze can
also be applied to the ceramic product if desired, but is not necessary. A
glaze can be applied
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before firing, so that only one firing is required. A glaze can also be
applied after f ring, but
then a second firing is required.
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