U.S. patent application number 10/765365 was filed with the patent office on 2005-07-28 for thermoplastic sheet abrasives and methods of making the same.
Invention is credited to Agarwal, Amit Ramesh, Kruegler, Gerald F., Mainer, Raymond George, Soelch, Richard Robert.
Application Number | 20050164619 10/765365 |
Document ID | / |
Family ID | 34795462 |
Filed Date | 2005-07-28 |
United States Patent
Application |
20050164619 |
Kind Code |
A1 |
Soelch, Richard Robert ; et
al. |
July 28, 2005 |
Thermoplastic sheet abrasives and methods of making the same
Abstract
The present invention provides sheet abrasives that include a
plurality of abrasive particles dispersed within a thermoplastic
polymer. The present invention also provides methods for producing
sheet abrasives.
Inventors: |
Soelch, Richard Robert;
(Essex Junction, VT) ; Kruegler, Gerald F.;
(Clifton Park, NY) ; Agarwal, Amit Ramesh;
(Vergennes, VT) ; Mainer, Raymond George;
(Hinesburg, VT) |
Correspondence
Address: |
TESTA, HURWITZ & THIBEAULT, LLP
HIGH STREET TOWER
125 HIGH STREET
BOSTON
MA
02110
US
|
Family ID: |
34795462 |
Appl. No.: |
10/765365 |
Filed: |
January 27, 2004 |
Current U.S.
Class: |
451/538 ;
451/298; 451/522; 51/298 |
Current CPC
Class: |
B24D 11/001 20130101;
B24D 3/002 20130101; B24D 3/20 20130101 |
Class at
Publication: |
451/538 ;
451/522; 451/298; 051/298 |
International
Class: |
B24B 021/00; B24D
017/00; B24D 011/00 |
Claims
What is claimed is:
1. A sheet abrasive comprising: a thermoplastic polymer layer; and
a plurality of abrasive particles dispersed therein.
2. The sheet abrasive of claim 1, wherein the thermoplastic polymer
layer is selected from the group consisting of polyamides,
polyurethanes, acetals, thermoplastic polyimides, liquid crystal
polymers, polyphenylene sulfides, polyetheramides, polyetheresters,
and polyethylene.
3. The sheet abrasive of claim 1, wherein the plurality of abrasive
particles is selected from the group consisting of silicon carbide,
aluminum oxide, diamond, ceramic aluminum oxide, ceramic, zirconia
aluminum, garnet, cubic boron nitride, and talc.
4. The sheet abrasive of claim 1, wherein the polymer layer has a
thickness from about 0.001 inch to about 0.25 inch.
5. The sheet abrasive of claim 1, wherein the plurality of abrasive
particles is dispersed substantially uniformly within the
thermoplastic polymer layer.
6. The sheet abrasive of claim 1, wherein the thermoplastic polymer
layer is an extruded thermoplastic polymer layer.
7. The sheet abrasive of claim 6, wherein the extruded
thermoplastic polymer layer is uni-axially oriented.
8. The sheet abrasive of claim 6, wherein the extruded
thermoplastic polymer layer is bi-axially oriented.
9. The sheet abrasive of claim 1, wherein the thermoplastic polymer
layer is an injection-molded thermoplastic polymer layer.
10. The sheet abrasive of claim 1, wherein the thermoplastic
polymer layer comprises a foamed thermoplastic polymer.
11. The sheet abrasive of claim 1, wherein the abrasive particles
comprise from about 1% to about 30% by volume of the sheet
abrasive.
12. The sheet abrasive of claim 1, wherein the abrasive sheet is
adapted to form a continuous belt.
13. The sheet abrasive of claim 1, wherein the abrasive sheet is
adapted to form a flap wheel.
14. The sheet abrasive of claim 1, further comprising a second
layer adjacent to the thermoplastic polymer layer.
15. The sheet abrasive of claim 14, wherein the second layer
comprises a polymer.
16. The sheet abrasive of claim 14, wherein the second layer
further comprises a plurality of abrasive particles.
17. The sheet abrasive of claim 14, further comprising an adhesive
layer disposed between the thermoplastic polymer layer and the
second layer.
18. The sheet abrasive of claim 14, wherein the abrasive sheet is
adapted to form a continuous belt.
19. The sheet abrasive of claim 14, wherein the abrasive sheet is
adapted to form a flap wheel.
20. A method of forming a sheet abrasive comprising the steps of:
dispersing a plurality of abrasive particles in a molten
thermoplastic polymer; and extruding the molten thermoplastic
polymer to form a sheet abrasive, wherein the sheet abrasive
comprises an extruded thermoplastic polymer layer and the plurality
of abrasive particles dispersed therein.
21. The method of claim 20, wherein the thermoplastic polymer is
extruded to form an extruded thermoplastic layer having a thickness
from about 0.001 inch to about 0.25 inch.
22. The method of claim 20, comprising orienting the extruded
thermoplastic polymer layer in a uni-axial or bi-axial
direction.
23. The method of claim 22, wherein the orienting step comprises
stretching the extruded thermoplastic polymer layer.
24. The method of claim 20, further comprising the step of
providing a second layer adjacent to the extruded thermoplastic
polymer layer.
25. The method of claim 24, wherein the second layer further
comprises a plurality of abrasive particles.
26. The method of claim 24, wherein the second layer comprises a
polymer.
27. The method of claim 26, wherein providing the second layer
comprises co-extruding the extruded thermoplastic polymer layer and
the second layer.
28. The method of claim 24, wherein providing the second layer
comprises adhering the second layer to the extruded thermoplastic
polymer layer with an adhesive.
29. A method of forming a sheet abrasive comprising the steps of:
dispersing a plurality of abrasive particles in a thermoplastic
polymer; and injecting the thermoplastic polymer into a mold to
form a sheet abrasive, wherein the sheet abrasive comprises an
injection-molded thermoplastic polymer layer and the plurality of
abrasive particles dispersed therein.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to the field of
sheet abrasives. More particularly, the invention relates to sheet
abrasives comprising abrasive particles dispersed within a
thermoplastic polymer and methods for making the same.
BACKGROUND
[0002] Conventional sheet abrasives generally consist of abrasive
particles bonded to the surface of a paper or cloth base material.
These types of coated sheet abrasives, however, suffer from several
disadvantages. Typically, a coated sheet abrasive contains a single
layer of abrasive particles coated on the base material, which
itself is non-abrasive. During use, the abrasive particles are
either worn down or become detached from the surface of the base
material, leaving only bare base material in contact with the work
surface. Thus, the useful life of these types of sheet abrasives is
limited by the thickness of the abrasive particle layer and by the
strength of the bond between the abrasive particles and the base
material. In addition, the flexibility of conventional coated sheet
abrasives is limited because bending or stretching the sheets can
dislodge the abrasive particles from the base material and crack,
crease, or otherwise damage the sheet.
[0003] Abrasive sheets made of abrasive particles dispersed within
a polymer are known. In some cases, these sheets are formed by
mixing the abrasive particles and the polymer in an organic
solvent, and subsequently evaporating the solvent. Storing,
handling, and transporting the organic solvents used in this
process pose a significant inconvenience and health hazard to
operators. Furthermore, evaporating the organic solvents can make
the process more costly and time consuming.
[0004] In other cases, abrasive particles are mixed with a polymer
in solid form, and the mixture is compression molded to form a pad
with a plurality of abrasive protrusions. The compression molding
process is time consuming because the process in non-continuous,
i.e., each mold can only produce one abrasive pad at a time.
[0005] Therefore, there is a need for flexible sheet abrasives
having increased durability and mechanical strength that can be
produced in an efficient, cost-effective manner.
SUMMARY OF THE INVENTION
[0006] The present invention provides a sheet abrasive that
includes a plurality of abrasive particles dispersed within a
thermoplastic polymer layer. The thermoplastic polymer layer
preferably is an extruded thermoplastic polymer layer or an
injection-molded thermoplastic polymer layer. The thermoplastic
polymer layer makes the sheet abrasive strong yet flexible, and the
abrasive particles are held firmly in place within the polymer
layer without the need for an additional bonding material.
Furthermore, because the abrasive particles are dispersed
throughout the thickness of the thermoplastic polymer layer, not
just on its surface, the sheet abrasive maintains its abrasive
qualities even after its topmost layer has been worn away.
[0007] The thermoplastic polymer layer can include, but is not
limited to, polyamides, polyurethanes, acetals, thermoplastic
polyimides, liquid crystal polymers, polyphenylene sulfides,
polyetheramides, polyetheresters, polyethylene, or combinations
thereof. In addition, the thermoplastic polymer layer may be a
foamed polymer. The thermoplastic polymer may be an extruded
thermoplastic polymer or an injection-molded thermoplastic polymer.
The extruded thermoplastic polymer layer can be uni-axially or
bi-axially oriented. The sheet abrasive preferably has a thickness
ranging from about 0.001 inch to 0.25 inch.
[0008] The abrasive particles can include, but are not limited to,
silicon carbide, aluminum oxide, diamond, ceramic aluminum oxide,
ceramic, zirconia aluminum, garnet, cubic boron nitride, talc, and
combinations thereof. The abrasive particles can be dispersed
substantially uniformly within the thermoplastic polymer layer. The
abrasive particles can comprise from about 1% to about 30% by
volume of the sheet abrasive.
[0009] The sheet abrasive can contain a second layer, such as a
polymer layer, adjacent to the thermoplastic polymer layer. The
second layer also may contain a plurality of abrasive particles. An
adhesive layer may be disposed between the thermoplastic polymer
layer and the second layer. Sheet abrasives of the invention can be
adapted to form a continuous belt or a flap wheel.
[0010] The present invention also provides methods of forming sheet
abrasives of the invention that include the steps of dispersing a
plurality of abrasive particles in a thermoplastic polymer and
either extruding the thermoplastic polymer to form an extruded
thermoplastic polymer layer or injecting the thermoplastic polymer
into a mold to form an injection-molded thermoplastic polymer
layer. The thermoplastic polymer layer preferably is extruded or
molded to a thickness ranging from about 0.001 inch to 0.25 inch.
An extruded thermoplastic polymer layer can be oriented either
uni-axially or bi-axially, for example, by stretching.
[0011] A second layer can be provided adjacent to the thermoplastic
polymer layer. The second layer can be a polymer and/or contain a
plurality of abrasive particles. The second layer can be
co-extruded with an extruded thermoplastic polymer layer, or the
second layer can be adhered to the extruded thermoplastic polymer
layer with an adhesive. The second layer can be co-molded with an
injection-molded thermoplastic polymer layer, or the second layer
can be present within the mold prior to injecting the molten
thermoplastic polymer, or the second layer can be adhered to the
injection-molded thermoplastic polymer layer with or without an
adhesive.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The invention is pointed out with particularity in the
appended claims. The advantages of the invention can be better
understood by reference to the description taken in conjunction
with the accompanying drawings.
[0013] The drawings are not necessarily to scale, emphasis instead
generally being placed upon illustrating the principles of the
invention. In the drawings, like reference characters generally
refer to the same parts throughout the different views.
[0014] FIG. 1A is a schematic cross-sectional views of an
embodiment of a sheet abrasive.
[0015] FIG. 1B is a schematic cross-sectional view of the sheet
abrasive of FIG. 1A after use.
[0016] FIG. 2 is a schematic cross-sectional view of another
embodiment of a sheet abrasive.
[0017] FIG. 3 is a schematic cross-sectional view of an embodiment
of a sheet abrasive that includes a thermoplastic polymer layer and
a second layer.
[0018] FIG. 4 is a schematic representation of an embodiment of an
extruder for producing sheet abrasives.
DETAILED DESCRIPTION
[0019] Throughout the description, where compositions are described
as having, including, or comprising specific components, or where
processes are described as having, including, or comprising
specific steps, it is contemplated that compositions of the
invention also consist essentially of, or consist of, the recited
components, and that the processes of the invention also consist
essentially of, or consist of, the recited steps.
[0020] As illustrated by FIG. 1A, a sheet abrasive 2 according to
one embodiment of the invention includes a plurality of abrasive
particles 4A, 4B dispersed within a thermoplastic polymer layer 6.
The abrasive particles can be dispersed substantially uniformly
throughout the thickness of the thermoplastic polymer layer, or
they can be dispersed in a non-uniform fashion. For example, the
concentration of abrasive particles may be greater near one or more
surfaces of the thermoplastic polymer layer.
[0021] Wither reference to FIG. 1A, a portion of the abrasive
particles may be located at or near a surface 8 of the
thermoplastic polymer layer 6 (e.g., abrasive particle 4A in FIG.
1A) with other abrasive particles located in the interior 10 of the
thermoplastic polymer layer 6 (e.g., abrasive particle 4B in FIG.
1A). During use, friction between the surface of the sheet abrasive
and a work surface wears away portions of the thermoplastic polymer
layer and any abrasive particles embedded therein. As the
thermoplastic polymer layer 6 is worn away, an abrasive particle 4B
that was previously in the interior 10 of the thermoplastic polymer
layer 6 is exposed, as illustrated by FIG. 1B. Thus, unlike
conventional coated sheet abrasives, which are no longer useful
once their topmost abrasive layers have worn away, a sheet abrasive
of the invention maintains its abrasive qualities after portions of
the thermoplastic polymer layer are worn away, thereby increasing
the useful life of the sheet abrasive.
[0022] In some embodiments of a sheet abrasive, a portion of the
abrasive particles are located at more than one surface of the
thermoplastic polymer layer. For example, in the illustrative
embodiment shown in FIG. 2, the abrasive particle 4A is located at
one surface 8 of the thermoplastic polymer layer 6, and the
abrasive particle 4C is located at the other surface 12. The
remaining abrasive particle 4B is located in the interior 10 of the
thermoplastic polymer layer 6. In this embodiment, both surfaces 8,
12 of the sheet abrasive 2 can perform work on one or more work
surfaces.
[0023] The thermoplastic polymer layer can be any thermoplastic
polymer known in the art. Suitable materials include, for example,
polyamides, polyesters, polyoxymethylenes, polyethylene, ethylene
copolymers, ethylene acrylic acid copolymers, ethylene acrylate
copolymers, ethylene methacrylic acid copolymers, ethylene vinyl
alcohol copolymer, ethylene vinyl acetate copolymers, polyphenylene
ether, polyphenylene oxide, polyphthalamide, polypropylene,
polystyrene, polyacrylonitrile, polyurethanes, rubbery polymers
(such as, for example, ethylene propylene rubbers and ethylene
propylene diene rubbers), polyvinyl chloride, styrene
acrylonitrile, acrylonitrile butadiene styrene, styrene butadiene,
styrene maleic anhydride, polycarbonate, polyurethanes, acetals,
acrylics, cellulosics, cellulose acetate butyrate, cellulose
acetate propionate, fluoropolymers (such as, for example,
polyvinylidene fluoride (PVDF), perfluoroalkoxy (PFA), ethylene
tetrafluoroethylene (ETFE), fluorinated ethylene propylene (FEP),
chlorotrifluoroethylene (CTFE), and polytetrafluoroethylene
(PTFE)), ionomers, liquid crystal polymers, polyphenylene sulfide,
polyamide imide, thermoplastic polyimides, polyarylate,
polybutylene, polyaryletherketone, polyetherether ketone,
polyetherketones, polyetherimides, polyethersulfone, polysulfone,
thermoplastic elastomers, polyetheramides, polyetheresters, diallyl
phthalate, melamine phenolic, phenolics, and unsaturated
polyesters.
[0024] Alternatively, the thermoplastic polymer layer can include a
combination, blend or alloy of one or more polymers as described
above. Polymer blends or alloys can include one or more polymers
suspended in another polymer, one or more polymers dissolved in
another polymer, or a mixture of suspended and dissolved polymers.
The blends or alloys can be miscible or immiscible. Sheet abrasives
can also be formulated such that the thermoplastic polymer layer
can be subsequently cross-linked or cured in a secondary operation,
if desired, in order to maximize certain properties such as heat
resistance, toughness or elasticity.
[0025] In some embodiments, the thermoplastic polymer layer is
foamed. Foaming makes the thermoplastic polymer lightweight and
shock-absorptive. One method for foaming a polymer is by the
addition of one or more blowing agents to the polymer prior to
forming an abrasive sheet. A blowing agent is a solid or a fluid
that causes bubbles, for example, gas bubbles, to form within the
polymer, which expand as the molten polymer cools. Examples of
blowing agents include foaming agents such as Foamazol.RTM. 72 and
Foamazol.RTM. XO-227 (Bergen International, Rochelle Park, N.J.).
Gaseous blowing agents include inert gases such as nitrogen and
argon.
[0026] The abrasive particles generally have a Knoop scale hardness
value that is greater than the thermoplastic polymer layer.
Suitable materials include, for example, aluminum oxide, silicon
carbide, zirconia aluminum, ceramic aluminum oxide, natural and
artificial diamond, glass beads, calcium oxide, talc, clay,
ceramic, fiberglass, silica, wood fillers, nut shells, apatite,
feldspar, tool steel, quartz, chromium, zirconium, beryllia, topaz,
garnet, zirconium boride, titanium nitride, tungsten carbide,
tantalum carbide, zirconium carbide, alumina, beryllium carbide,
titanium carbide, silicon carbide, aluminum boride, cubic boron
carbide, cubic boron nitride, emery, spinel, flint, and mixtures
thereof.
[0027] One example of a suitable mixture of abrasive particles is a
mixture of silicon carbide and aluminum oxide. In addition,
aggregates or multiple abrasive particles fused together by a
bonding agent can be used. The abrasive particles may be completely
or partially coated by an inorganic or metallic coating material.
Examples include nickel-coated diamond and copper-coated diamond.
The abrasive particles may be coated with a coupling agent, such as
a silane coupling agent (e.g., 3-aminopropyl-triethoxysilane) to
increase the adhesion of the abrasive particles to the
thermoplastic polymer layer. The abrasive particles can have any
size or shape, although preferably the abrasive particles are small
enough to be contained entirely within the thickness of the
thermoplastic polymer layer. Mixtures of different sized of
abrasive particles can be used, such as, for example, a mixture of
46 mesh and 120 mesh silicon carbide.
[0028] The abrasive particles can comprise from about 1% to about
50% by volume of the thermoplastic sheet abrasive, from about 1% to
about 40% by volume of the thermoplastic sheet abrasive, or from
about 1% to about 30% by volume of the thermoplastic sheet
abrasive. In some embodiments, the abrasive particles comprise up
to 25% by volume, or up to 35% by volume, or up to 45% by volume of
the thermoplastic sheet abrasive. The amount of abrasive particles
found in sheet may be higher than 50% by volume depending on the
particular characteristics of the abrasive particles and/or the
thermoplastic polymer used to form the thermoplastic sheet
abrasive.
[0029] In addition to abrasive particles, one or more additives
known in the art can be included in a sheet abrasive. Examples of
additives include colorants, tougheners (including rubber
tougheners), plasticizers, fillers, reinforcements, lubricants,
anti-blocking compounds, process aids, stabilizers, and blowing
agents.
[0030] Sheet abrasives in accordance with the invention can be
produced by any conventional thermoplastic processing method,
including molding and extrusion. It should be understood that in
any of the methods described and claimed herein, the steps can be
performed in any order, or one or more steps can be performed
simultaneously, as long as the method remains operable.
[0031] In a preferred method, sheet abrasives are produced by an
extrusion method. Extrusion methods can produce sheet abrasives of
any length, and the sheets can conveniently be wound onto rolls.
The extrusion process generally involves adding one or more
thermoplastic polymers, abrasive particles, and any additional
polymers and/or additives into a thermoplastic melt-mixing device.
The components are transported through the device, for example,
using a screw, toward a die which is cut in the shape of the
desired product. As the thermoplastic polymer(s) move within the
device, they begin to melt into a softer flowing material and mix
with the other components. The molten thermoplastic polymer mixture
is forced through the die, yielding a polymer extrudate. The
extrudate then is quenched or solidified, typically using a
rollstack device. Alternatively, the extrudate may be quenched or
solidified using air or a water bath. Additional finishing steps
may include removing excess water using an air blower and/or
threading the extrudate through pinch rolls to control its width or
diameter. After quenching, the sheet abrasive can be cut to desired
lengths and/or wound onto rolls.
[0032] Examples of suitable extrusion devices include single-screw
extruders, twin-screw extruders, brabender type mixers, and
kneaders, some of which are commercially available from Battenfeld
Gloucester (Gloucester, Mass.) and Davis Standard (Pawcatuck,
Conn.). The surfaces of the extruder and other processing equipment
that come into contact with the sheet abrasives can be modified
with hardened surfaces or liners to prevent wear and increase the
useful life of the extruder.
[0033] In some embodiments, after the sheet abrasive has been
extruded and quenched or solidified, it is subjected to an
orientation process to increase the tensile strength of the sheet.
Orientation generally involves stretching or compressing the sheet
abrasive at a temperature above the polymer's glass transition
temperature, but below its crystalline melting temperature.
Orientation can be uni-axial, typically by stretching or
compressing the sheet along its length (i.e., in the casting
machine direction), or bi-axial, typically by also stretching or
compressing the sheet in a transverse direction (i.e., in a cross
machine direction). Bi-axial orientation is typically done using a
tenter frame or compression or nip rolls. In some embodiments, the
entire sheet abrasive can be oriented, while in other embodiments,
one or more portions of the sheet abrasive are oriented and other
portions are not. Suitable equipment for orienting sheet abrasives
is commercially available from Marshall and Williams Plastics
(Woonsocket, R. I.), Battenfeld Gloucester (Gloucester, Mass.), and
Davis Standard (Pawcatuck, Conn.).
[0034] Molded sheet abrasives preferably are prepared by
compression or injection molding. In compression molding, a
thermoplastic polymer is placed into a mold which is subsequently
closed and held at a high pressure. The mold is heated to fuse the
thermoplastic polymer, and after an appropriate time, the mold is
opened and the product removed. In contrast, injection molding
involves injecting a molten thermoplastic polymer into a closed
mold. The molten polymer cools and hardens into shape within the
mold, which then is opened to remove the product. Any materials and
methods used in compression or injection molding known in the art
may be used to form sheet abrasives in accordance with the
invention.
[0035] The cross-sectional shape of a sheet abrasive can be
tailored to suit its particular application. In some embodiments,
the sheet abrasive has the form of a film, strip, or tape, i.e.,
its width and length are greater than its thickness. However,
thermoplastic abrasives can be formed into any shape to adapt to
any particular application, for example, a block or o-ring shape.
For sheet abrasives produced by an extrusion process, the
cross-sectional shape is determined by the shape of the extrusion
die. For a molding process, the shape of the mold determines the
cross-sectional shape of sheet abrasives. In either process, the
cross-sectional shape can be further modified by thermal, chemical,
and/or mechanical means after the thermoplastic polymer has been
extruded or molded. A sheet abrasive can have any cross-sectional
shape, including, for example, quadrilateral, round, and oval.
[0036] In some embodiments, a sheet abrasive according to the
invention has a thickness ranging from about 0.0005 inch to about
0.25 inch. In other embodiments, a sheet abrasive has a thickness
ranging from about 0.001 inch to about 0.25 inch, or from about
0.001 inch to about 0.125 inch. In other embodiments, a sheet
abrasive has a thickness ranging from about 0.001 inch to about
0.05 inch. In still other embodiments, a sheet abrasive has a
thickness ranging from about 0.005 inch to about 0.03 inch.
[0037] In the illustrative embodiment shown in FIG. 3, a sheet
abrasive 20 includes a second layer 22 adjacent to a thermoplastic
polymer layer 24 which contains a plurality of abrasive particles
26. The second layer can serve to enhance various properties of the
abrasive sheet, including, for example, stiffness, toughness,
resilience, abrasion resistance, coefficient of friction, heat
stability, chemical resistance, hydrolysis resistance, oxidative
stability, heat conductivity, anti-static properties, electrical
conductivity, and/or thermal coefficient of expansion. The second
layer can be made of any material, including, for example, paper,
cloth, metal, polymer, or combinations thereof. The second layer
can have various forms, including, for example, a continuous sheet,
a fibrous woven or non-woven belt, a web or mesh, or a layer of
abrasive particles.
[0038] Suitable metals for use in a second layer include, for
example, aluminum, chromium, steel, and alloys thereof. Any of the
polymers or combination of polymers described above in connection
with the thermoplastic polymer layer can be used to form the second
layer. In addition, the second layer can include any of the
abrasive particles and/or additives described above. In some
embodiments, the second layer contains the same type and/or amount
of abrasive particles and/or additives as the thermoplastic polymer
layer. In other embodiments, the second layer and the thermoplastic
polymer layer contain different types and/or amounts of abrasive
particles and/or additives.
[0039] The second layer can be bonded to the thermoplastic polymer
layer using an adhesive, or the second layer can be coated or
sprayed onto to the thermoplastic polymer layer. In cases where the
second layer includes a polymer, the second layer can be extruded
onto the thermoplastic polymer layer, or the second layer and an
extruded thermoplastic polymer layer can be co-extruded. A
co-extrusion process involves extruding two or more layers
simultaneously by combining the extrudates from multiple extruders
into a manifold and extruding through a special multi-layer die.
Alternatively, the second layer can be present within a mold prior
to injecting a molten thermoplastic layer into the mold. Each layer
can have the same or different widths, and the layers may be
offset.
[0040] The second layer can have the same thickness as the
thermoplastic polymer layer, or the two layers can have different
thicknesses. That is, the thermoplastic polymer layer can have a
thickness greater than the thickness of the second layer, or the
thermoplastic layer can have a thickness less than the thickness of
the second layer. The second layer and the thermoplastic polymer
layer can have the same shape and/or size, or their shapes and/or
sizes may differ.
[0041] In some embodiments, the second layer and the thermoplastic
polymer layer are aligned so that the second layer is adjacent to
substantially all of a surface of the thermoplastic polymer layer.
In other embodiments, the second layer and the thermoplastic
polymer layer are offset, so that at least one portion of the
thermoplastic polymer layer is not adjacent to the second layer.
This embodiment is particularly useful for sheet abrasives that are
extruded and wound into rolls.
[0042] The present invention also contemplates sheet abrasives that
contain further layers in addition to a thermoplastic polymer layer
and a second layer. For example, a sheet abrasive may include a
third layer, a fourth layer, a fifth layer, a sixth layer, a
seventh layer, an eighth layer, and so on. The additional layers
can be disposed adjacent to any other layer. For example, in a
sheet abrasive that contains a thermoplastic polymer layer, a
second layer, and a third layer, the third layer can be adjacent to
either the thermoplastic polymer layer or the second layer. The
additional layers can have some or all of the characteristics and
properties described above for the second layer and can be made by
the same processes and techniques described above.
[0043] Sheet abrasives in accordance with the invention can be used
in a variety of ways similar to conventional coated abrasives, such
as emery cloth or sand paper. In addition, the sheet abrasives can
be thermoformed into a variety of shapes heretofore unobtainable
with conventional coated abrasives to create new tools engineered
to fit specific applications.
[0044] Thermoforming involves applying heat and/or pressure to a
sheet abrasive to form the sheet into a different three-dimensional
shape. For example, in one embodiment according to the invention, a
thermoplastic sheet abrasive is thermoformed to fit over the end of
a pipe (e.g., similar to the shape of a lid for a disposable
drinking cup). The resulting thermoformed abrasive then can be used
as a de-burring or polishing tool for the end of like-sized metal
pipes.
[0045] In one embodiment, an adhesive polymer layer is disposed
between a thermoplastic polymer layer containing a plurality of
abrasive particles and a second layer that provides reinforcement,
toughening or other attributes. In a variation of this embodiment,
the second layer is a removable backing or liner, which, when
removed, exposes the adhesive layer which remains disposed on the
thermoplastic polymer layer. The sheet abrasive can then be adhered
to another surface using the adhesive layer. In a related
embodiment, the second layer is a fastening system, for example, a
hook and loop device (e.g., Velcro.RTM.), which can be used to
fasten the sheet abrasive to another surface.
[0046] In other embodiments of a sheet abrasive, the thermoplastic
polymer layer includes a thermoplastic elastomer, such as, but not
limited to, soft polyurethanes, polyetheresters, or polyetheramide
esters. The sheet abrasive is very flexible and can be used on
curved surfaces (e.g., contours of molding, metal rods, etc.) that
cannot effectively be sanded by conventional coated abrasives.
[0047] In some embodiments, the second layer is foamed to provide
for shock absorption, insulation, or sound damping qualities. In
other embodiments, the second layer includes fiberglass or clay to
provide enhanced stiffness. The second layer may include a high
thermal conductivity filler to enhance cooling of the sheet
abrasive. In other embodiments, the second layer includes tungsten
or other high density fillers to provide a sheet abrasive with
increased weight for use in flapwheel-type applications. In yet
other embodiments, an intermediate layer is extruded between two
thermoplastic polymer layers containing a plurality of abrasive
particles to produce an abrasive sheet construction with abrasive
on the top and bottom with a reinforcing or toughening layer in
between. It is to be understood that, in addition to the
embodiments described above, a sheet abrasive in accordance with
the present invention can have any configuration of thermoplastic
polymer layer, second layer, and/or additional layers.
[0048] Sheet abrasives in accordance with the invention can be cut
to any desired length or shape and used directly, like conventional
sand paper, or they can be formed into implements or tools. For
example, a sheet abrasive can be cut and the ends joined using
conventional bonding or joining techniques to form belts.
Alternatively, a sheet abrasive can be cut into flaps and formed
into star pads, cross pads, square pads, flap wheels, flap discs,
cartridge rolls, spiral bands, overlap discs, overlap cones, and
other implements known in the art. Examples of implements that can
be formed using sheet abrasives according to the invention can be
found in the catalogue, "3M Grindline Express Coated Abrasive,
Surface Conditioning, and Superabrasive Products 1996" (3M Company,
Minneapolis, Minn.).
EXAMPLES
[0049] The following examples are meant to illustrate, not limit,
the scope of the present invention.
Example 1
[0050] All examples were produced using the extruder 30 illustrated
schematically in FIG. 4. The polymer starting materials were added
to the rear of the extruder 30 through primary feeder 32, and the
abrasive particles were added through secondary feeder 34. The
extrudate 36 exited the die 38 vertically downward into a water
quench bath 40 where the extrudate 36 was solidified. A standard 6
inch film type die 38 with an adjustable die gap (Extrusion Dies
Inc., Chippewa Falls, Wis.) was used. The die gap was set at 0.058
inch for all examples. The extrudate 36 was pulled by a set of slow
group orientation rolls 42, and was passed through an orientation
oven 44 and then onto a set of fast group orientation rolls 46.
Next, the extrudate 36 was passed through a relaxation oven 48, a
set of crimp rolls 50 to provide crimp, and then through a set of
lube rolls 52 coated with a lubricant. The extrudate 36 then was
passed onto a set of relaxation group rolls 54, which were set at
the same speed as the fast group orientation rolls 46. Finally, the
extrudate 36 was wound onto a collection reel 56.
[0051] The extrusion conditions are listed in Table 1. Samples A,
B, C, D and the control sample included nylon 6 (Ultramid.RTM. B3
Natural, BASF, Ludwigschafen, Germany), and samples E and F
included nylon 6/12 (Zytel.RTM. 158, DuPont, Wilmington, Del.). All
nylons were dried for four hours at 175.degree. F. for four hours
just prior to extrusion. All samples except for the control
included 120 mesh aluminum oxide abrasive particles (Norton
Abrasives, Worcester, Mass.). The compositions are listed in weight
percent as determined by pyrolysis and gravimetric analysis of the
residual aluminum oxide.
1 TABLE 1 Control Sample A Sample B Sample C Sample D Sample E
Sample F Polymer 100% 60% 60% 54% 54% 40% 40% Nylon 6 Nylon 6 Nylon
6 Nylon 6 Nylon 6 Nylon Nylon 6/12 6/12 Abrasive 0% 40% 40% 46% 46%
60% 60% Extruder Temp. Zone 1 514.degree. F. 514.degree. F.
514.degree. F. 514.degree. F. 514.degree. F. 514.degree. F.
514.degree. F. Zone 2 516.degree. F. 516.degree. F. 516.degree. F.
516.degree. F. 516.degree. F. 516.degree. F. 516.degree. F. Zone 3
511.degree. F. 511.degree. F. 511.degree. F. 511.degree. F.
511.degree. F. 511.degree. F. 511.degree. F. Zone 4 500.degree. F.
500.degree. F. 500.degree. F. 500.degree. F. 500.degree. F.
500.degree. F. 500.degree. F. Zone 5 511.degree. F. 511.degree. F.
511.degree. F. 511.degree. F. 511.degree. F. 511.degree. F.
511.degree. F. Zone 6 504.degree. F. 504.degree. F. 504.degree. F.
504.degree. F. 504.degree. F. 504.degree. F. 504.degree. F. Zone 7
518.degree. F. 518.degree. F. 518.degree. F. 518.degree. F.
518.degree. F. 518.degree. F. 518.degree. F. Zone 8 523.degree. F.
523.degree. F. 523.degree. F. 523.degree. F. 523.degree. F.
523.degree. F. 523.degree. F. Zone 9 511.degree. F. 511.degree. F.
511.degree. F. 511.degree. F. 511.degree. F. 511.degree. F.
511.degree. F. Zone 10 509.degree. F. 509.degree. F. 509.degree. F.
509.degree. F. 509.degree. F. 509.degree. F. 509.degree. F. Zone 11
500.degree. F. 500.degree. F. 500.degree. F. 500.degree. F.
500.degree. F. 500.degree. F. 500.degree. F. Zone 12 500.degree. F.
500.degree. F. 500.degree. F. 500.degree. F. 500.degree. F.
500.degree. F. 500.degree. F. Zone 13 510.degree. F. 510.degree. F.
510.degree. F. 510.degree. F. 510.degree. F. 510.degree. F.
510.degree. F. Die Temp. 520.degree. F. 520.degree. F. 520.degree.
F. 520.degree. F. 520.degree. F. 520.degree. F. 520.degree. F.
Extruder 38 38 38 38 38 38 38 RPM Roller Speed (RPM) Slow group 79
79 72 72 79 80 80 Fast group 104 104 144 144 104 80 88 Relaxation
104 104 144 144 104 80 88 group Orientation 1.3 1.3 2.0 2.0 1.3 1.0
1.1 Ratio Sheet 0.007 0.016 0.015 0.015 0.017 0.025 0.024 Thickness
(inches)
[0052] Test strips (1.0 inch wide by 12 inches long) of each sample
were prepared. For comparative purposes, a test strip made from a
commercial non-woven abrasive strip, Standard B/T Belt, SCF-FE
containing 120 mesh aluminum oxide (Standard Equipment Company,
Mobile, Ala.), was also prepared. Each test strip was rubbed for 6
strokes (3 in each direction) using light hand pressure (about 5
lbs. or off-hand application) over a 1.5 inch diameter copper pipe.
The contact length on the pipe was controlled at 2 inches, with 5
inches of each test strip contacting the pipe. The polishing
ability of each sample was ranked from 0 to 5, with 0 being poor or
no polish and 5 being high polish. The test results are shown in
Table 2.
[0053] Referring to Table 2, the control sheet which contained no
abrasive particles had no polishing affect on the copper pipe. The
commercial abrasive strip produced very modest polishing results,
while samples A-F produced good polishing results. The polishing
results appeared to improve in proportion to the percent of
abrasive particles in the strips. This experiment demonstrates that
sheet abrasives in accordance with the present invention can
produce polishing results comparable with or better than
commercially available non-woven abrasive materials.
2TABLE 2 Sample Polymer % Abrasive Polishing Rank Control Nylon 6
None 0 Standard B/T Belt SCF-FE Unknown 1 SCF-FE A Nylon 6 40% 3 B
Nylon 6 40% 2 C Nylon 6 46% 3 D Nylon 6 46% 3.5 E Nylon 6/12 60% 4
F Nylon 6/12 60% 4
Example 2
[0054] A two layer sheet abrasive sample was prepared by adhering a
control sheet made of nylon 6 onto sample F using hot melt glue.
The resulting two-layer sheet abrasive sample could not be torn by
hand, while Sample E, which did not contain a second layer, could
be torn with moderate effort. This experiment demonstrates sheet
abrasives that include two or more layers can exhibit improved
mechanical properties, such as improved tensile strength.
[0055] The invention may be embodied in other specific forms
without departing from the spirit or essential characteristics
thereof. The foregoing embodiments are therefore to be considered
in all respects illustrative rather than limiting on the invention
described herein. Scope of the invention is thus indicated by the
appended claims rather than by the foregoing description, and all
changes that come within the meaning and range of equivalency of
the claims are intended to be embraced therein.
* * * * *