U.S. patent application number 10/668735 was filed with the patent office on 2005-03-24 for abrasive article and methods of making the same.
This patent application is currently assigned to 3M Innovative Properties Company. Invention is credited to Haas, John D., Provow, Ronald D..
Application Number | 20050060941 10/668735 |
Document ID | / |
Family ID | 34313558 |
Filed Date | 2005-03-24 |
United States Patent
Application |
20050060941 |
Kind Code |
A1 |
Provow, Ronald D. ; et
al. |
March 24, 2005 |
Abrasive article and methods of making the same
Abstract
An abrasive article and methods of making the same are
disclosed. The abrasive article includes a backing and an array of
features on the backing. Each feature includes a base and a body.
The body includes a face having an undercut. In one embodiment, the
feature also includes a planar top portion having abrasive
particles disposed thereon. In another embodiment, the feature also
includes a radiused portion on the undercut sidewall adjacent the
base.
Inventors: |
Provow, Ronald D.;
(Woodbury, MN) ; Haas, John D.; (Roseville,
MN) |
Correspondence
Address: |
3M INNOVATIVE PROPERTIES COMPANY
PO BOX 33427
ST. PAUL
MN
55133-3427
US
|
Assignee: |
3M Innovative Properties
Company
|
Family ID: |
34313558 |
Appl. No.: |
10/668735 |
Filed: |
September 23, 2003 |
Current U.S.
Class: |
51/293 ; 51/295;
51/298; 51/307; 51/308; 51/309 |
Current CPC
Class: |
B24D 11/00 20130101;
B24D 3/28 20130101; B24D 2203/00 20130101 |
Class at
Publication: |
051/293 ;
051/295; 051/298; 051/307; 051/308; 051/309 |
International
Class: |
B24D 003/00 |
Claims
What is claimed is:
1. An abrasive article comprising: a backing; and a plurality of
features, said features further comprising a binder and abrasive
particles, wherein said features have a base and at least three
sides, the angle between said base and one of said sides forming a
positive rake angle.
2. The abrasive article of claim 1 wherein at one of said abrasive
features further includes a planar top portion that is angled with
respect to said base.
3. The abrasive article of claim 2, further including abrasive
particles on the planar top portion of said abrasive features.
4. The article of claim 1, wherein the body includes a region or
point located most distally from the base, and further wherein the
region or point projects outside the base perimeter.
5. The abrasive article of claim 4 wherein at least one of said
abrasive features further includes a top planar section that is
angled with respect to said base.
6. A method of making an abrasive article comprising: providing a
tool including a pattern for forming abrasives features; placing
abrasive particles in the tool; filling the tool with a slurry;
contacting the slurry with a backing; and curing the slurry to form
abrasive features including a top portion bonded to said abrasive
particles and a bottom portion bonded to said backing.
7. The method of claim 6, wherein providing a tool includes
providing a tool for forming abrasives features including a planar
top.
8. The method of claim 7, wherein the planar top is angled with
respect to a reference plane defined by the backing.
9. The method of claim 7, wherein the abrasive particles are
aluminum oxide.
10. An abrasive article comprising: a backing; and a plurality of
abrasive features on the backing, each of the abrasive features
including a base and a body, wherein the body is defined by four
surfaces, and wherein at least one of the surfaces includes an
undercut portion.
11. The article of claim 10, further including a planar surface
opposite the base.
12. The article of claim 11, further including abrasive particles
disposed on the planar surface.
13. The article of claim 12, wherein the planar surface is angled
with respect to the base.
14. The article of claim 12, wherein the undercut portion includes
a radiused section adjacent the base.
15. The article of claim 10, wherein the undercut portion includes
a radiused section adjacent the base.
16. The abrasive article of claim 10, wherein the plurality of
features are arranged in an array wherein each undercut potion is
oriented in the same direction.
17. The abrasive article of claim 16, wherein the array is oriented
at a bias on the abrasive article.
18. A feature for an abrasive article comprising: a base and a
body, the body including four sidewalls, wherein at least one
sidewall forms a surface having a positive rake angle.
19. The feature of claim 18, further including a planar top section
disposed distally from the base.
20. The feature of claim 19, wherein the planar top section is
oriented substantially parallel to the base.
21. The feature of claim 19, wherein the planar top section is
oriented at an angle of more than about 2 degrees with respect to
the base, and further wherein the planar top section slopes away
from surface having a negative rake angle.
22. The feature of claim 19, further including abrasive particles
disposed on the planar top section.
23. The feature of claim 18, wherein the surface includes a
radiused portion adjacent the base.
24. The feature of claim 22, wherein the surface includes a
radiused portion adjacent the base.
25. A tool for making any of the abrasive articles in claims
1-17.
26. An belt for abrading material comprising: a backing defining a
belt shape; and a plurality of abrasive composites on the backing,
each of the abrasive composites including a base and a body,
wherein the body is defined by four surfaces, and wherein at least
one of the surfaces includes an undercut portion.
27. The belt of claim 26, further including a planar surface
opposite the base.
28. The belt of claim 27, further including abrasive particles
disposed on the planar surface.
29. The belt of claim 28, wherein the planar surface is angled with
respect to the base.
30. The belt of claim 28, wherein the undercut portion includes a
radiused section adjacent the base.
31. The belt of claim 26, wherein the undercut portion includes a
radiused section adjacent the base.
32. The belt of claim 26, wherein the plurality of composites are
arranged in an array wherein each undercut potion is oriented in
the same direction.
33. The belt of claim 32, wherein the array is oriented at a bias
on the abrasive article.
34. A method of abrading a wooden workpiece, the method comprising:
contacting an abrasive article to the workpiece, wherein the
abrasive article includes: a backing; a plurality of abrasive
composites on the backing, each of the abrasive composites
including a base and a body, wherein the body is defined by four
surfaces, and wherein at least one of the surfaces includes an
undercut portion, and wherein a section of the undercut portion
engages the workpiece before any other surface of the body.
35. The method of claim 34, wherein said contacting an abrasive
article further includes contacting the abrasive article including
a planar top section, and wherein abrasive particles are disposed
on the top section.
36. The method of claim 34, wherein said contacting an abrasive
article further includes contacting the abrasive article including
a radiused portion adjacent the base on the undercut portion.
37. The method of claim 36, further including removing swarf via
the radiused portion.
38. The method of claim 34, wherein the backing is a belt.
Description
FIELD
[0001] This disclosure is directed to an abrasive article,
particularly a structured abrasive article, methods of making, and
methods of using.
BACKGROUND
[0002] Abrasive articles have been utilized to abrade and finish
workpiece surfaces for well over a hundred years. These
applications have ranged from high stock removal, high pressure
metal grinding processes to fine polishing, such as of ophthalmic
lenses. In general, abrasive articles are made of a plurality of
abrasive particles bonded either together (e.g., a bonded abrasive
or grinding wheel) or to a backing (e.g., a coated abrasive). For a
coated abrasive there is typically a single layer, or sometimes two
layers, of abrasive particles. Once these abrasive particles are
worn, the coated abrasive is essentially worn out and is typically
discarded.
[0003] A more recent development in three-dimensional coatings of
abrasive particles has provided abrasive articles often referred to
as "structured abrasives". Various constructions of structured
abrasive articles are disclosed, for example, in U.S. Pat. No.
5,152,917 (Pieper et al.), which is herein incorporated by
reference. Pieper teaches a structured abrasive that results in a
relatively high rate of cut and a relatively fine surface finish on
the workpiece surface. The structured abrasive comprises
non-random, precisely shaped abrasive composites that are bonded to
a backing.
[0004] Other references directed to structured abrasive articles
and methods of making them include U.S. Pat. No. 5,855,632
(Stoetzel et al.), U.S. Pat. No. 5,681,217 (Hoopman et al.), U.S.
Pat. No. 5,435,816 (Spurgeon et al.), U.S. Pat. No. 5,378,251
(Culler et al.), U.S. Pat. No. 5,304,223 (Pieper et al.), and U.S.
Pat. No. 5,014,468 (Ravipati et al.), all of which are herein
incorporated by reference.
[0005] Pieper, and the other structured abrasive patents, are a
significant advancement in the abrasives art, however there is
always room for improvement.
SUMMARY
[0006] One aspect of the present disclosure is directed to a
feature for an abrasive article. The feature includes a base and a
body. The body is a polyhedron, in one embodiment being a pyramidal
polyhedron having four sidewalls defining the body. One sidewall
has an undercut forming rake angle. In one embodiment, the undercut
sidewall includes a radiused portion adjacent the base. In another
embodiment, the body also includes a planar top portion including
abrasive particles.
[0007] Another aspect of the present disclosure is directed to an
abrasive article having an array of features on a backing. The
array includes a plurality of features each including a base and a
body. Each body is a polyhedron, in one embodiment being a
pyramidal polyhedron having four sidewalls defining the body. One
sidewall has an undercut forming rake angle. In one embodiment, the
undercut sidewall includes a radiused portion adjacent the base. In
another embodiment, the body also includes a planar top portion
including abrasive particles.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a perspective view of section of an example
embodiment of an abrasive article according to the present
disclosure;
[0009] FIG. 1A is a side view of the article of FIG. 1 along line
A-A;
[0010] FIG. 1B is a front view of the article of FIG. 1 along line
B-B;
[0011] FIG. 2 is an example embodiment of a system for making
abrasive articles according to the present disclosure; and
[0012] FIG. 3 is another example embodiment of a system for making
abrasive articles according to the present disclosure.
DETAILED DESCRIPTION
[0013] Generally, the present disclosure is related to an abrasive
article and methods of making and using the same. In one example
embodiment, the abrasive article includes a plurality of
microreplicated features. In the context of this disclosure, the
terms feature and composite are used interchangeable.
[0014] The feature includes a base and a body. The body includes a
face having an undercut portion. The face can also include an
arcuate portion adjacent to the base. The feature can also include
a planar top portion. The planar portion can be angled with respect
to the base.
[0015] In another example embodiment, the abrasive article is a
belt. The belt includes a backing and a plurality of features
arranged on the belt. In one example embodiment, the features are
arranged such that all the undercut faces are similarly oriented.
In another example embodiment, the planar top portions are angled
with respect to the backing. Other embodiments can include one or a
combination of the characteristics described above.
[0016] Referring to FIG. 1, the abrasive article 100 comprises
abrasive composites 120 separated by a gap or boundary. The
abrasive composites are bonded to a surface of a backing 130. The
boundary or boundaries associated with the composite shape result
in one abrasive composite being separated to some degree from
another adjacent abrasive composite. To form an individual abrasive
composite, a portion of the boundaries forming the base shape of
the abrasive composite must be separated from one another. In some
embodiments, the base or a portion of the abrasive composite
closest to the backing can abut with its neighboring abrasive
composite. Abrasive composites 120 comprise a plurality of abrasive
particles that are dispersed in a binder and a grinding aid. It is
also within the scope of this invention to have a combination of
abrasive composites bonded to a backing in which some of the
abrasive composites abut, while other abrasive composites have open
spaces between them.
[0017] Backing
[0018] The backing of this invention has a front and back surface
and can be any conventional abrasive backing. Examples of useful
backings include polymeric film, primed polymeric film, cloth,
paper, vulcanized fiber, nonwovens, and combinations thereof. Other
useful backings include a fibrous reinforced thermoplastic backing
as disclosed in U.S. Pat. No. 5,316,812 and an endless seamless
backing as disclosed in published World Patent Application No. WO
93/12911. The backing may also contain a treatment or treatments to
seal the backing and/or modify some physical properties of the
backing. These treatments are well known in the art.
[0019] The backing may also have an attachment means on its back
surface to enable securing the resulting coated abrasive to a
support pad or back-up pad. This attachment means can be a pressure
sensitive adhesive, one surface of a hook and loop attachment
system, or a threaded projection as disclosed in the
above-mentioned U.S. Pat. No. 5,316,812. Alternatively, there may
be an intermeshing attachment system as described in the assignee's
U.S. Pat. No. 5,201,101, all of which are incorporated hereinafter
by reference.
[0020] The backside of the abrasive article may also contain a slip
resistant or frictional coating. Examples of such coatings include
an inorganic particulate (e.g., calcium carbonate or quartz)
dispersed in an adhesive.
[0021] Abrasive Coating
[0022] Abrasive Particles
[0023] The abrasive particles typically have a particle size
ranging from about 0.1 to 1500 micrometers, usually between about
0.1 to 400 micrometers, preferably between 0.1 to 100 micrometers
and most preferably between 0.1 to 50 micrometers. In one
embodiment, the abrasive particles have a Mohs' hardness of at
least about 8, more preferably above 9. Examples of such abrasive
particles include fused aluminum oxide (which includes brown
aluminum oxide, heat treated aluminum oxide and white aluminum
oxide), ceramic aluminum oxide, green silicon carbide, silicon
carbide, chromia, alumina zirconia, diamond, iron oxide, ceria,
cubic boron nitride, boron carbide, garnet and combinations
thereof.
[0024] The term "abrasive particle" also encompasses when single
abrasive particles are bonded together to form an abrasive
agglomerate. Abrasive agglomerates are further described in U.S.
Pat. Nos. 4,311,489; 4,652,275 and 4,799,939 incorporated herein by
reference.
[0025] It is also within the scope of this invention to have a
surface coating on the abrasive particles. The surface coating may
have many different functions. In some instances the surface
coatings increase adhesion of abrasive particles to the binder,
alter the abrading characteristics of the abrasive particle, and
the like. Examples of surface coatings include coupling agents,
halide salts, metal oxides including silica, refractory metal
nitrides, refractory metal carbides and the like.
[0026] In the abrasive composite there may also be diluent
particles. The particle size of these diluent particles may be on
the same order of magnitude as the abrasive particles. Examples of
such diluent particles include gypsum, marble, limestone, flint,
silica, glass bubbles, glass beads, aluminum silicate, and the
like.
[0027] Binder
[0028] The abrasive particles are dispersed in an organic binder to
form the abrasive composite. The binder is derived from a binder
precursor which comprises an organic polymerizable resin. During
the manufacture of the inventive abrasive articles, the binder
precursor is exposed to an energy source which aids in the
initiation of the polymerization or curing process. Examples of
energy sources include thermal energy and radiation energy, the
latter including electron beam, ultraviolet light, and visible
light. During this polymerization process, the resin is polymerized
and the binder precursor is converted into a solidified binder.
Upon solidification of the binder precursor, the abrasive coating
is formed. The binder in the abrasive coating is also generally
responsible for adhering the abrasive coating to the backing.
[0029] There are two preferred classes of resins for use in the
present invention, condensation curable and addition polymerizable
resins. The preferred binder precursors comprise additional
polymerizable resins because these resins are readily cured by
exposure to radiation energy. Addition polymerizable resins can
polymerize through a cationic mechanism or a free radical
mechanism. Depending upon the energy source that is utilized and
the binder precursor chemistry, a curing agent, initiator, or
catalyst is sometimes preferred to help initiate the
polymerization.
[0030] Examples of typical and preferred organic resins include
phenolic resins, urea-formaldehyde resins, melamine formaldehyde
resins, acrylated urethanes, acrylated epoxies, ethylenically
unsaturated compounds, aminoplast derivatives having pendant
unsaturated carbonyl groups, isocyanurate derivatives having at
least one pendant acrylate group, isocyanate derivatives having at
least one pendant acrylate group, vinyl ethers, epoxy resins, and
mixtures and combinations thereof. The term "acrylate" encompasses
acrylates and methacrylates.
[0031] Phenolic resins are widely used in abrasive article binders
because of their thermal properties, availability, and cost. There
are two types of phenolic resins, resole and novolac. Resole
phenolic resins have a molar ratio of formaldehyde to phenol of
greater than or equal to one to one, typically between 1.5:1.0 to
3.0:1.0. Novolac resins have a molar ratio of formaldehyde to
phenol of less than one to one. Examples of commercially available
phenolic resins include those known by the trade names "Durez" and
"Varcum" from Occidental Chemicals Corp.; "Resinox" from Monsanto;
"Aerofene" from Ashland Chemical Co. and "Aerotap" from Ashland
Chemical Co.
[0032] Acrylated urethanes are diacrylate esters of
hydroxy-terminated, isocyanate NCO extended polyesters or
polyethers. Examples of commercially available acrylated urethanes
include those known under the trade designations "UVITHANE 782",
available from Morton Thiokol Chemical, and "CMD 6600", "CMD 8400",
and "CMD 8805", available from Radcure Specialties.
[0033] Acrylated epoxies are diacrylate esters of epoxy resins,
such as the diacrylate esters of bisphenol A epoxy resin. Examples
of commercially available acrylated epoxies include those known
under the trade designations "CMD 3500", "CMD 3600", and "CMD
3700", available from Radcure Specialities.
[0034] Ethylenically unsaturated resins include both monomeric and
polymeric compounds that contain atoms of carbon, hydrogen, and
oxygen, and optionally, nitrogen and the halogens. Oxygen or
nitrogen atoms or both are generally present in ether, ester,
urethane, amide, and urea groups.
[0035] Ethylenically unsaturated compounds preferably have a
molecular weight of less than about 4,000 and are preferably esters
made from the reaction of compounds containing aliphatic
monohydroxy groups or aliphatic polyhydroxy groups and unsaturated
carboxylic acids, such as acrylic acid, methacrylic acid, itaconic
acid, crotonic acid, isocrotonic acid, maleic acid, and the like.
Representative examples of acrylate resins include methyl
methacrylate, ethyl methacrylate styrene, divinylbenzene, vinyl
toluene, ethylene glycol diacrylate, ethylene glycol methacrylate,
hexanediol diacrylate, triethylene glycol diacrylate,
trimethylolpropane triacrylate, glycerol triacrylate,
pentaerythritol triacrylate, pentaerythritol methacrylate,
pentaerythritol tetraacrylate and pentaerythritol tetraacrylate.
Other ethylenically unsaturated resins include monoallyl,
polyallyl, and polymethallyl esters and amides of carboxylic acids,
such as diallyl phthalate, diallyl adipate, and
N,N-diallyladkipamide. Still other nitrogen containing compounds
include tris(2-acryloyloxyethyl)isocyanurat- e,
1,3,5-tri(2-methyacryloxyethyl)-triazine, acrylamide,
methylacrylamide, N-methylacrylamide, N,N-dimethylacrylamide,
N-vinylpyrrolidone, and N-vinylpiperidone.
[0036] The aminoplast resins have at least one pendant alpha,
betaunsaturated carbonyl group per molecule or oligomer. These
unsaturated carbonyl groups can be acrylate, methacrylate, or
acrylamide type groups. Examples of such materials include
N-(hydroxymethyl)acrylami- de, N,N'-oxydimethylenebisacrylamide,
ortho and para acrylamidomethylated phenol, acrylamidomethylated
phenolic novolac, and combinations thereof. These materials are
further described in U.S. Pat. Nos. 4,903,440 and 5,236,472 both
incorporated herein by reference.
[0037] Isocyanurate derivatives having at least one pendant
acrylate group and isocyanate derivatives having at least one
pendant acrylate group are further described in U.S. Pat. No.
4,652,274 incorporated herein after by reference. The preferred
isocyanurate material is a triacrylate of tris(hydroxy ethyl)
isocyanurate.
[0038] Epoxy resins have an oxirane and are polymerized by the ring
opening. Such epoxide resins include monomeric epoxy resins and
oligomeric epoxy resins. Examples of some preferred epoxy resins
include 2,2-bis[4-(2,3-epoxypropoxy)-phenyl propane] (diglycidyl
ether of bisphenol) and commercially available materials under the
trade designations "Epon 828", "Epon 1004", and "Epon 1001F"
available from Shell Chemical Co., "DER-331", "DER-332", and
"DER-334" available from Dow Chemical Co. Other suitable epoxy
resins include glycidyl ethers of phenol formaldehyde novolac
(e.g., "DEN-43" and "DEN-428" available from Dow chemical Co.).
[0039] The epoxy resins of the invention can polymerize via a
cationic mechanism with the addition of an appropriate cationic
curing agent. Cationic curing agents generate an acid source to
initiate the polymerization of an epoxy resin. These cationic
curing agents can include a salt having an onium cation and a
halogen containing a complex anion of a metal or metalloid. Other
cationic curing agents include a salt having an organometallic
complex cation and a halogen containing complex anion of a metal or
metalloid which are further described in U.S. Pat. No. 4,751,138
incorporated here in after by reference (column 6, line 65 to
column 9, line 45). Another example is an organometallic salt and
an onium salt is described in U.S. Pat. No. 4,985,340 (column 4,
line 65 to column 14, line 50); and European Patent Application
Nos. 306,161 and 306,162, both published Mar. 8, 1989, all
incorporated by reference. Still other cationic curing agents
include an ionic salt of an organometallic complex in which the
metal is selected from the elements of Periodic Group IVB, VB,
VIIB, VIIB and VIIIB which is described in European Patent
Application No. 109,581, published Nov. 21, 1983, incorporated by
reference.
[0040] Regarding free radical curable resins, in some instances it
is preferred that the abrasive slurry further comprises a free
radical curing agent. However in the case of an electron beam
energy source, the curing agent is not always required because the
electron beam itself generates free radicals.
[0041] Examples of free radical thermal initiators include
peroxides, e.g., benzoyl peroxide, azo compounds, benzophenones,
and quinones. For either ultraviolet or visible light energy
source, this curing agent is sometimes referred to as a
photoinitiator. Examples of initiators, that when exposed to
ultraviolet light generate a free radical source, include but are
not limited to those selected from the group consisting of organic
peroxides, azo compounds, quinones, benzophenones, nitroso
compounds, acryl halides, hydrozones, mercapto compounds, pyrylium
compounds, triacrylimdazoles, bisimidazoles, chloroalkytriazines,
benzoin ethers, benzil ketals, thioxanthones, and acetophenone
derivatives, and mixtures thereof. Examples of initiators that when
exposed to visible radiation generate a free radical source, can be
found in U.S. Pat. No. 4,735,632, entitled Coated Abrasive Binder
Containing Ternary Photoinitiator System, incorporated herein by
reference. The preferred initiator for use with visible light is
"Irgacure 369" commercially available from Ciba Geigy
Corporation.
[0042] Grinding Aid
[0043] A grinding aid is defined as a material, preferably a
particulate material, the addition of which to an abrasive article
has a significant effect on the chemical and physical processes of
abrading which results in improved performance. Typically and
preferably the grinding aid is added to the slurry as a
particulate, however it may be added to the slurry as a liquid or
it may be added as an overcoat to reduce the loading of the
product. The presence of the grinding aid will increase the
grinding efficiency or cut rate (defined as weight of work piece
removed per weight of abrasive article lost) of the corresponding
abrasive article in comparison to an abrasive article that does not
contain a grinding aid. In particular, it is believed in the art
that the grinding aid will either 1) decrease the friction between
the abrasive grains and the workpiece being abraded, 2) prevent the
abrasive grain from "capping", i.e., prevent metal particles (in
the case of a metal workpiece) from becoming welded to the tops of
the abrasive grains, 3) decrease the interface temperature between
the abrasive grains the workpiece, 4) decreases the grinding force
required, or 5) prevents oxidation of the metal workpiece. In
general, the addition of a grinding aid increases the useful life
of the abrasive article.
[0044] Grinding aids useful in the invention encompass a wide
variety of different materials and can be inorganic or organic
based. Examples of chemical groups of grinding aids include waxes,
soaps, organic halide compounds, halide salts and metals and their
alloys. The organic halide compounds will typically break down
during abrading and release a halogen acid or a gaseous halide
compound. Examples of such materials include chlorinated waxes like
tetrachloronaphtalene, pentachloronaphthalene; and polyvinyl
chloride. Examples of soaps include lithium and zinc stearate.
Examples of halide salts include sodium chloride, potassium
cryolite, sodium cryolite, ammonium cryolite, potassium
tetrafluoroborate, sodium tetrafluoroborate, silicon fluorides,
potassium chloride, magnesium chloride. Examples of metals include,
tin, lead, bismuth, cobalt, antimony, cadmium, iron titanium, other
miscellaneous grinding aids include sulfur, organic sulfur
compounds, graphite and metallic sulfides. It is also within the
scope of this invention to use a combination of different grinding
aids and in some instances this may produce a synergistic
effect.
[0045] The above-mentioned examples of grinding aids are meant to
be representative only. A preferred grinding aid for use in the
invention is cryolite, and the most preferred is potassium
tetrafluoroborate (KBF.sub.4).
[0046] The grinding aid is considered to be non-abrasive, that is,
the Moh hardness of the grinding aid is less than 8. The grinding
aid may also contain impurities; these impurities should not
significantly adversely affect performance of the abrasive
article.
[0047] The grinding aid particle size preferably ranges from about
0.1 to 100 micrometers, more preferably between 10 to 70
micrometers. In general the particle size of the grinding aid is
preferably equal to or less than the size of the abrasive
particles.
[0048] The abrasive coating comprises generally at least about 1%
by weight, typically at least about 2.5% by weight, preferably at
least about 5% by weight, more preferably at least about 10% by
weight grinding aid and most preferably at least about 20% by
weight grinding aid. More than about 50 weight % grinding aid may
be detrimental since it is theorized that grinding performance
would decrease (since there are less abrasive particles present).
It was surprising that as the amount of grinding aid was increased,
the relative grinding performance as measured by cut rate is also
increased. This was unexpected since as the amount of grinding aid
in the abrasive coating is increased, the relative amount of
abrasive particles is decreased. The abrasive particles are
responsible for cutting the workpiece surface, not the grinding
aid. In general, the abrasive coating comprises from 5 to 90% by
weight, preferably from 20 to 80% by weight abrasive particles,
from 5 to 80% by weight, preferably from 5 to 40% by weight binder,
and from 5 to 60% by weight, preferably from 10 to 40% by weight
grinding aid.
[0049] Optional Additives
[0050] Slurries useful in the invention may further comprise
optional additives, such as, for example, fillers, fibers,
lubricants, wetting agents, thixotropic materials, surfactants,
pigments, dyes, antistatic agents, coupling agents, plasticizers,
and suspending agents. The amounts of these materials are selected
to provide the properties desired. The use of these can affect the
erodability of the abrasive composite. In some instances an
additive is purposely added to make the abrasive composite more
erodable, thereby expelling dulled abrasive particles and exposing
new abrasive particles.
[0051] Examples of antistatic agents useful in the invention
include graphite, carbon black, vanadium oxide, humectants, and the
like. These antistatic agents are disclosed in U.S. Pat. Nos.
5,061,294; 5,137,542, and 5,203,884, all of which are incorporated
hereinafter by reference.
[0052] A coupling agent can provide an association bridge between
the binder precursor and the filler particles or abrasive
particles. Examples of useful coupling agents include silanes,
titanates, and zircoaluminates. Useful slurries preferably contain
from about 0.01 to 3% by weight coupling agent.
[0053] An example of a suspending agent useful in the invention is
an amorphous silica particle having a surface area less than 150
meters square/gram that is commercially available from DeGussa
Corp., under the trade name "OX-50".
[0054] Abrasive Coating Comprising Abrasive Composites
[0055] In one preferred aspect of the invention, the abrasive
coating is in the form of a plurality of abrasive composites bonded
to the backing. It is generally preferred that each abrasive
composites have a precise shape. The precise shape of each
composite is determined by distinct and discernible boundaries.
These distinct and discernible boundaries are readily visible and
clear when a cross section of the abrasive article is examined
under a microscope such as a scanning electron microscope. In
comparison, in an abrasive coating comprising composites that do
not have precise shapes, the boundaries are not definitive and may
be illegible. These distinct and discernible boundaries form the
outline or contour of the precise shape. These boundaries separate
to some degree one abrasive composite from another and also
distinguish one abrasive composite from another.
[0056] Referring to FIGS. 1-1B, an example embodiment of an
abrasive article 100 according to the present disclosure is
illustrated. The abrasive article 100 comprises abrasive composites
122. In some embodiments, the boundary or boundaries associated
with the composite shape result in one abrasive composite being
separated to some degree from another adjacent abrasive composite.
To form an individual abrasive composite, a portion of the
boundaries forming the shape of the abrasive composite must be
separated from one another. Note that in FIG. 1A, the base or a
portion of the abrasive composite closest to the backing can abut
with its neighboring abrasive composite. Abrasive composites 122
comprise a plurality of abrasive particles that are dispersed in a
binder and a grinding aid. It is also within the scope of this
invention to have a combination of abrasive composites bonded to a
backing in which some of the abrasive composites abut, while other
abrasive composites have open spaces between them.
[0057] In some instances the boundaries forming the shape are
planar. For shapes that have planes, there are at least three
planes. The number of planes for a given shape can vary depending
upon the desired geometry, for instance the number of planes can
range from three to over 20. Generally, there are between three to
ten planes, preferably between three to six planes. These planes
intersect to form the desired shape and the angles at which these
planes intersect will determine the shape dimensions.
[0058] In another aspect of this invention, a portion of the
abrasive composites have a neighboring abrasive composite of a
different dimension. In this aspect of the invention, at least 10%,
preferably at least 30%, more preferably at least 50% and most
preferably at least 60% of the abrasive composites have an adjacent
abrasive composite that has a different dimension. These different
dimensions can pertain to the abrasive composite shape, angle
between planar boundaries or dimensions of the abrasive composite.
The result of these different dimensions for neighboring abrasive
composites results in an abrasive article that produces a
relatively finer surface finish on the workpiece being abraded or
refined.
[0059] The abrasive composite shape can be any shape, but it is
preferably a geometric shape such as a rectangle, cone, semicircle,
circle, triangle, square, hexagon, pyramid, octagon and the like.
Embodiments of preferred shapes are presented below in a section
entitled "GEOMETRIES." An individual abrasive composite shape may
be referred to herein as "protruding unit." The preferred shape is
a pyramid and the base of this pyramid can be a three or four
sided. It is also preferred that the abrasive composite cross
sectional surface area decreases away from the backing or decreases
along its height. This variable surface area results in a
non-uniform pressure as the abrasive composite wears during use.
Additionally, during manufacture of the abrasive article, this
variable surface area results in easier release of the abrasive
composite from the production tool. In general there are at least 5
individual abrasive composites per square cm. In some instances,
there may be at least 500 individual abrasive composites/square
cm.
[0060] Method of Making the Abrasive Article
[0061] An essential step to make any of the inventive abrasive
articles is to prepare the slurry. The slurry is made by combining
together by any suitable mixing technique the binder precursor, the
grinding aid, the abrasive particles and the optional additives.
Examples of mixing techniques include low shear and high shear
mixing, with high shear mixing being preferred. Ultrasonic energy
may also be utilized in combination with the mixing step to lower
the abrasive slurry viscosity. Typically, the abrasive particles
and grinding aid are gradually added into the binder precursor. The
amount of air bubbles in the slurry can be minimized by pulling a
vacuum during the mixing step. In some instances it is preferred to
heat, generally in the range of 30.degree. to 70.degree. C., the
slurry to lower the viscosity. It is important the slurry have
theological properties that allow the slurry to coat well and in
which the abrasive particles and grinding aid do not settle out of
the slurry.
[0062] Energy Source
[0063] After the slurry is coated onto the backing, such as via
transfer from a production tool (discussed below), the slurry may
be exposed to an energy source to initiate the polymerization of
the resin in the binder precursor. Examples of energy sources
include thermal energy and radiation energy. The amount of energy
depends upon several factors such as the binder precursor
chemistry, the dimensions of the abrasive slurry, the amount and
type of abrasive particles and the amount and type of the optional
additives. For thermal energy, the temperature can range from about
30.degree. to 150.degree. C., generally from 40.degree. to
120.degree. C. The exposure time can range from about 5 minutes to
over 24 hours.
[0064] Suitable radiation energy sources include electron beam,
ultraviolet light, or visible light. Electron beam radiation, which
is also known as ionizing radiation, can be used at an energy level
of about 0.1 to about 10 Mrad, preferably at an energy level of
about 1 to about 10 Mrad. Ultraviolet radiation refers to
non-particulate radiation having a wavelength within the range of
about 200 to about 400 nanometers, preferably within the range of
about 250 to 400 nanometers. Visible radiation refers to
non-particulate radiation having a wavelength within the range of
about 400 to about 800 nanometers, preferably in the range of about
400 to about 550 nanometers. It is preferred that 300 to 600
Watt/inch visible lights are used.
[0065] After this polymerization process is complete, the binder
precursor is converted into a binder and the slurry is converted
into an abrasive coating. The resulting abrasive article is
generally ready for use. However, in some instances other processes
may still be necessary such as humidification or flexing. The
abrasive article can be converted into any desired form such as a
cone, endless belt, sheet, disc, and the like, before the abrasive
article is used.
[0066] Production Tool
[0067] Regarding the third and fourth aspects of the invention, in
some instances it is preferred that the abrasive coating be present
as precisely shaped abrasive composites. In order to make this type
of abrasive article, a production tool is generally required.
[0068] The production tool contains a plurality of cavities. These
cavities are essentially the inverse shape of the abrasive
composite and are responsible for generating the shape of the
abrasive composites. The dimensions of the cavities are selected to
provide the desired shape and dimensions of the abrasive
composites. If the shape or dimensions of the cavities are not
properly fabricated, the resulting production tool will not provide
the desired dimensions for the abrasive composites.
[0069] The cavities can be present in a dot like pattern with
spaces between adjacent cavities or the cavities can butt up
against one another. It is preferred that the cavities butt up
against one another. Additionally, the shape of the cavities is
selected such that the cross-sectional area of the abrasive
composite decreases away from the backing.
[0070] The production tool can be a belt, a sheet, a continuous
sheet or web, a coating roll such as a rotogravure roll, a sleeve
mounted on a coating roll, or die. The production tool can be
composed of metal, (e.g., nickel), metal alloys, or plastic. The
metal production tool can be fabricated by any conventional
technique such as engraving, bobbing, electroforming, diamond
turning, and the like. One preferred technique for a metal
production tool is diamond turning.
[0071] A thermoplastic tool can be replicated off a metal master
tool. The master tool will have the inverse pattern desired for the
production tool. The master tool can be made in the same manner as
the production tool. The master tool is preferably made out of
metal, e.g., nickel and is diamond turned. The thermoplastic sheet
material can be heated and optionally along with the master tool
such that the thermoplastic material is embossed with the master
tool pattern by pressing the two together. The thermoplastic can
also be extruded or cast onto the master tool and then pressed. The
thermoplastic material is cooled to solidify and produce the
production tool. Examples of preferred thermoplastic production
tool materials include polyester, polycarbonates, polyvinyl
chloride, polypropylene, polyethylene and combinations thereof. If
a thermoplastic production tool is utilized, then care must be
taken not to generate excessive heat that may distort the
thermoplastic production tool.
[0072] The production tool may also contain a release coating to
permit easier release of the abrasive article from the production
tool. Examples of such release coatings for metals include hard
carbide, nitrides or borides coatings. Examples of release coatings
for thermoplastics include silicones and fluorochemicals.
[0073] One method to make the abrasive article of the invention
illustrated in FIG. 2 is illustrated in FIG. 2. Backing 41 leaves
an unwind station 42 and at the same time the production tool 46
leaves an unwind station 45. Production tool 46 is coated with
slurry by means of coating station 44. It is possible to heat the
slurry and/or subject the slurry to ultrasonics prior to coating to
lower the viscosity. The coating station can be any conventional
coating means such as drop die coater, knife coater, curtain
coater, vacuum die coater or a die coater. During coating the
formation of air bubbles should be minimized. The preferred coating
technique is a vacuum fluid bearing die, such as disclosed in U.S.
Pat. Nos. 3,594,865, 4,959,265, and 5,077,870, all incorporated
herein by reference. After the production tool is coated, the
backing and the slurry are brought into contact by any means such
that the slurry wets the front surface of the backing. In FIG. 2,
the slurry is brought into contact with the backing by means of
contact nip roll 47. Next, contact nip roll 47 also forces the
resulting construction against support drum 43. A source of energy
48 (preferably a source of visible light) transmits a sufficient
amount of energy into the slurry to at least partially cure the
binder precursor. The term partial cure is meant that the binder
precursor is polymerized to such a state that the slurry does not
flow from an inverted test tube. The binder precursor can be fully
cured once it is removed from the production tool by any energy
source. Following this, the production tool is rewound on mandrel
49 so that the production tool can be reused again. Optionally, the
production tool may be removed from the binder precursor prior to
any curing of the precursor at all. After removal, the precursor
may be cured, and the production tool may be rewound on mandrel 49
for reuse. Additionally, abrasive article 120 is wound on mandrel
121. If the binder precursor is not fully cured, the binder
precursor can then be fully cured by either time and/or exposure to
an energy source. Additional steps to make abrasive articles
according to this first method are further described in U.S. Pat.
No. 5,152,917 (Pieper et al.) and U.S. Pat. No. 6,129,540 (Hoopman
et al.), both incorporated herein by reference. Randomly shaped
abrasives composites may be made by the tooling and procedures
described in U.S. Pat. No. 6,129,540, to Hoopman et al.
[0074] It is preferred that the binder precursor is cured by
radiation energy. The radiation energy can be transmitted through
the production tool so long as the production tool does not
appreciably absorb the radiation energy. Additionally, the
radiation energy source should not appreciably degrade the
production tool. It is preferred to use a thermoplastic production
tool and ultraviolet or visible light.
[0075] The slurry can be coated onto the backing and not into the
cavities of the production tool. The slurry coated backing is then
brought into contact with the production tool such that the slurry
flows into the cavities of the production tool. The remaining steps
to make the abrasive article are the same as detailed above.
[0076] Another method is illustrated in FIG. 3. Backing 51 leaves
an unwind station 52 and the slurry 54 is coated into the cavities
of the production tool 55 by means of the coating station 53. The
slurry can be coated onto the tool by any one of many techniques
such as drop die coating, roll coating, knife coating, curtain
coating, vacuum die coating, or die coating. Again, it is possible
to heat the slurry and/or subject the slurry to ultrasonics prior
to coating to lower the viscosity. During coating the formation of
air bubbles should be minimized. Then, the backing and the
production tool containing the abrasive slurry are brought into
contact by a nip roll 56 such that the slurry wets the front
surface of the backing. Next, the binder precursor in the slurry is
at least partially cured by exposure to an energy source 57. After
this at least partial cure, the slurry is converted to an abrasive
composite 59 that is bonded or adhered to the backing. The
resulting abrasive article is removed from the production tool by
means of nip rolls 58 and wound onto a rewind station 60.
Optionally, the production tool may be removed from the binder
precursor prior to any curing of the precursor at all. After
removal of the production tool, the precursor may be cured. In
either event, the energy source can be thermal energy or radiation
energy. If the energy source is either ultraviolet light or visible
light, it is preferred that the backing be transparent to
ultraviolet or visible light. An example of such a backing is
polyester backing.
[0077] The slurry can be coated directly onto the front surface of
the backing. The slurry coated backing is then brought into contact
with the production tool such that the slurry wets into the
cavities of the production tool. The remaining steps to make the
abrasive article are the same as detailed above.
[0078] Method of Refining a Workpiece Surface
[0079] Another aspect of this invention pertains to a method of
abrading a metal or wooden surface. This method involves bringing
into frictional contact the abrasive article of this invention with
a workpiece having a metal or wooden surface. The term "abrading"
means that a portion of the metal workpiece is cut or removed by
the abrasive article. Additionally, the surface finish associated
with the workpiece surface is typically reduced after this refining
process. One typical surface finish measurement is Ra; Ra is the
arithmetic surface finish generally measured in microinches or
micrometers. The surface finish can be measured by a profilometer,
such as a Perthometer or Surtronic.
[0080] Workpiece
[0081] The metal workpiece can be any type of metal such as mild
steel, stainless steel, titanium, metal alloys, exotic metal alloys
and the like. The workpiece may be flat or may have a shape or
contour associated with it.
[0082] Depending upon the application, the force at the abrading
interface can range from about 0.1 kg to over 1000 kg. Generally
this range is from 1 kg to 500 kg of force at the abrading
interface. Also depending upon the application, there may be a
liquid present during abrading. This liquid can be water and/or an
organic compound. Examples of typical organic compounds include
lubricants, oils, emulsified organic compounds, cutting fluids,
soaps, or the like. These liquids may also contain other additives
such as defoamers, degreasers, corrosion inhibitors, or the like.
The abrasive article may oscillate at the abrading interface during
use. In some instances, this oscillation may result in a finer
surface on the workpiece being abraded.
[0083] The abrasive articles of the invention can be used by hand
or used in combination with a machine. At least one or both of the
abrasive article and the workpiece is moved relative to the other
during grinding. The abrasive article can be converted into a belt,
tape roll, disc, sheet, and the like. For belt applications, the
two free ends of an abrasive sheet are joined together and a splice
is formed. It is also within the scope of this invention to use a
spliceless belt like that described in the assignee's co-pending
patent application U.S. Ser. No. 07/919,541, filed Jul. 24, 1992,
incorporated herein after by reference. Generally the endless
abrasive belt traverses over at least one idler roll and a platen
or contact wheel. The hardness of the platen or contact wheel is
adjusted to obtain the desired rate of cut and workpiece surface
finish. The abrasive belt speed depends upon the desired cut rate
and surface finish. The belt dimensions can range from about 5 mm
to 1,000 mm wide and from about 5 mm to 10,000 mm long. Abrasive
tapes are continuous lengths of the abrasive article. They can
range in width from about 1 mm to 1,000 mm, generally between 5 mm
to 250 mm. The abrasive tapes are usually unwound, traverse over a
support pad that forces the tape against the workpiece and then
rewound. The abrasive tapes can be continuously feed through the
abrading interface and can be indexed. The abrasive disc can range
from about 50 mm to 1,000 mm in diameter. Typically abrasive discs
are secured to a back-up pad by an attachment means. These abrasive
discs can rotate between 100 to 20,000 revolutions per minute,
typically between 1,000 to 15,000 revolutions per minute.
[0084] Geometries
[0085] Referring to FIGS. 1-1B, a portion of an example embodiment
of an abrasive article 100 is illustrated. The abrasive article 100
includes a backing 130. The backing 130 is typically a belt, though
other shapes and forms are possible. When the backing 130 is a
belt, it typically includes a machine direction and a cross
direction, which are arranged orthogonally to one another.
[0086] The backing 130 is adjacent to and connected to an array 110
of microreplicated features 120. Typically, the features 120 are
arranged on the backing 130 in an array 110 including an offset.
The array 110 is typically oriented on an angle or bias with
respect to the machine direction of the article 100.
[0087] The array 110 includes a plurality of features 120. In the
example embodiment shown, each feature includes a base 122 and a
body 123. In one embodiment, the base 122 is a parallelogram, but
can be in other shapes, as the particular applications requires.
Base 122 is adjacent or near the backing 130, and is connected or
coupled to the same. In the example embodiment shown, each feature
includes four sidewalls 127 or surfaces projecting from the base
forming a polyhedron. While the example features shown include four
sidewalls, there can be more or less, depending on the particular
application. The polyhedron can be of any shape, but is typically
pyramidal or prismatic in shape.
[0088] Each feature 120 includes at least one sidewall 124 that
forms positive rake angle y with respect to the base 122. The rake
angle .gamma. on the sidewall 124 forms an undercut section 125 on
the sidewall 124. The undercut 125 functions particularly well in
applications where wood is the material to be abraded with the
abrasive article 100.
[0089] In woodworking applications, swarf or other debris tends to
build up on and clog the abrasive article 100. Removal of swarf or
other debris is facilitated by including a radiused portion R on
the sidewall 124 have the undercut 125. The radiused portion R is
located adjacent to the backing 130. Including a gap or land region
between adjacent features also facilitates removal of built up
material.
[0090] Typically, the undercut face 125 is the leading edge 124 of
the abrasive article as the abrasive article 100 engages a
workpiece to remove material. As previously discussed, the leading
edge 124 can engage the workpiece with the leading edge oriented to
either directly engage or engage at a bias. Including a slight bias
angle allows swarf or other debris to be pushed preferentially to
one edge of the abrasive article 100 for removal. Also, in one
embodiment, the point of the body 123 located most distally from
the base 122 does not project into the area defined by the
perimeter of the base 122. This is illustrated in FIG. 1A, wherein
the perpendicular line extending from the backing 130 shows the
most distal point on the body 123 of the left-most feature 120
projects outside of the area defined by the perimeter of the base
122.
[0091] Each feature 120 can also include a top planar portion 128
that is angled at an angle .theta. with respect to the base 122 of
the feature 120. In one embodiment, the top section 128 is coated
with abrasive particles 140. The abrasive particles 140 assist in
removing material from and further conditioning the workpiece.
[0092] The features 120 of the array 110 are typically arranged
having a pitch P in the machine direction (the direction that the
undercut surface engages a workpiece) and a gap M between adjacent
features 120 in a direction perpendicular (cross-direction) to the
machine direction. The pitch P between features 120 in the
engagement (or machine) direction can be varied so that the leading
edge of the undercut 125 sidewall overlaps the base 122 of the
feature directly adjacent or neighboring. The pitch P can be
constant or varied.
[0093] Also, in one embodiment, the trailing sidewall 127 (opposite
the undercut sidewall) is slanted at angle .alpha. less than 90
degrees from the base 122. Also, adding a radiused section R2 at
the base of each sidewall in the cross-direction will also aid in
material removal. Also, the opposed sidewalls in the
cross-direction can be angled out from being perpendicular at an
angle .beta..
EXAMPLE 1
[0094] An abrasive article according to the present disclosure was
made and tested. The article included an array of features arranged
on a backing material. The features were arranged so that the
features were offset in the cross-direction. Each feature had a
height at its point most distally from the backing of about 20 mils
(1 mil equals 0.001 inch), a machine direction pitch P of about 32
mils and a cross direction gap of about 2 mils. The radius in the
sidewall on the undercut sidewall was about 4 miles and the radius
of each sidewall in the cross-direction was about 1.3 mils. The
undercut sidewall had a positive rake angle of about 5 degrees. The
sidewall opposite the undercut sidewall was angled at about 45
degrees from the base and the planar top portion was angled at
about 10 degrees from parallel with respect to the base.
[0095] The abrasive article described-above has been found by the
inventors to be particularly well-suited to removing material from
wooden workpiece. The undercut sidewall performs the majority of
material removal. The abrasive particles on the planar top section
then lightly scratch the surface of the workpiece, allowing the
workpiece to be ready to take a stain without further
preparation.
[0096] The abrasive article described-above was made by first
creating a tool that was a negative of the image formed by the
array. The tooling was coated with a medium grade abrasive mineral,
aluminum oxide, available from Washington Mills. A slurry, made
with Tatheic/TMPTA acrylic resin, KBF4, Irgacure 369, OX-50 silica
and A174 silane and mineral was then coated onto the backing. A
tool was applied to the slurry while it was on the backing. The
backing used was polyester/cotton woven backing, available from
Milliken. The product was then cured and separated from the
tooling. One of ordinary skill in the art will appreciate that many
different combinations of abrasive mineral or particles, slurry,
backing materials, can be used, depending on the particular
application desired for the abrasive article. Also, the use of the
undercut sidewall, radiused sections in one or more of the
sidewalls adjacent the base, and a planar top portion with abrasive
particles can be combined in various ways, as the particular
application may benefit from any combination of characteristics
described above.
[0097] The above specification, examples and data provide a
complete description of the manufacture and use of the invention of
the present disclosure. Since many embodiments of the invention can
be made without departing from the spirit and scope of the
invention, the invention resides in the claims hereinafter
appended.
* * * * *