Note: Descriptions are shown in the official language in which they were submitted.
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FLEXIBLE ABRASIVE ARTICLE RELEASING LOW AMOUNTS OF CONTAMINANTS
Background
This invention is related to abrasive articles, particularly abrasive articles
especially suited for use in critical or controlled environments.
An ever increasing number of industrial operations require isolation from
potential
ubiquitous physical and chemical contaminants. Conversely, other industrial
operations
may require quarantine from the general environment due to their toxic or
infectious
nature. Such needs are generally met by the design, fabrication, and use of so-
called
"clean rooms" (also known as "white rooms").
Such facilities have found widespread use in the manufacture of semiconductor
devices, where the presence of external contaminants such as unwanted
particles and ions
must be minimized. Operations such as, for example, crystal growth, ion
implantation,
metal deposition, and etching are typically carried out in low pressure
(vacuum) chambers
or reactors that are operated in clean room environments. Following use for a
time, these
chambers inevitably become soiled and therefore require cleaning. Depending on
the
nature of the contamination, abrasive articles may be required to remove
tenaciously-held
contaminants. Such abrasive operations by definition generate particulate
materials that
may contaminate the clean room environment. Further, the abrasive articles
themselves
may convey unwanted particles and/or ionic moieties into the chamber and/or
clean room.
There thus is a need for an abrasive article for use in critical, clean room
environments.
Such an abrasive article should efficaciously remove residue from reactor
surfaces,
minimize the release of particles into the clean room environment, and
minimize transfer
of ionic contaminants to the reactor andlor the clean room.
Summary of the Invention
One embodiment of this present invention provides a flexible abrasive article
comprising a foraminous substrate, at least one binder, and abrasive
particles, wherein the
abrasive article contains minimal amount of releaseable physical and chemical
contaminants and when used to clean a surface provides a clean workpiece with
minimal
amounts of physical and chemical contaminants and does not damage the
workpiece
surface.
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Another embodiment of this invention provides a method of making a flexible
abrasive article comprising the steps of
Providing a foraminous substrate;
Coating the foraminous substrate with a make coating;
Coating the coated substrate with abrasive granules;
Curing the granule coated substrate;
Coating the granule coated cured substrate with a size coating;
Curing the size-coated substrate;
Converting the cured, size-coated substrate into useful shaped abrasive
article;
Post-cleaning the abrasive articles to remove potential workpiece
contaminants;
and
Packaging the post-cleaned abrasive articles.
"Flexible abrasive article" refers to an abrasive article, which when folded
onto
itself with the abrasive surface exposed, that does result in knife-edging of
the abrasive
coating.
"Foraminous substrate" refers to a porous, organic substrate having openings
defined by interconnecting voids throughout at least one surface of the
substrate. For
example, either an open-celled foam substrate or lofty, fibrous, nonwoven web
or fabric
qualifies as a foraminous substrate.
"Make coat precursor" refers to the coatable resinous adhesive material
applied to
the coatable surfaces of the openings of the foraminous substrate to secure
abrasive
particles thereto.
"Make coat" refers to the layer of cured resin over the coatable surfaces of
the
openings of the foraminous substrate formed by hardening the make coat
precursor.
"Size coat precursor" refers to the coatable resinous adhesive material
applied to
the coatable surfaces of the openings of the foraminous substrate over the
make coat.
"Size coat" refers to the layer of cured resin over the coatable surfaces of
the
openings of the foraminous substrate formed by hardening the size coat
precursor.
"Cured" or "fully cured" means a hardened polymerized curable coatable resin.
"Fine abrasive particles" refers to abrasively effective particles comprising
any of
the materials set forth herein and having distribution of particle sizes
wherein a highly
preferred median particle diameter is about 60 microns or less. A spherical
particle shape
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is assumed in referring to the median particle diameter, based on standard
test methods
available for the determination of particle diameters such as, for example,
ANSI test
method B74.18-1884.
"Substantially uniform" refers to the distribution of fine abrasive particles
in the
finished articles that are distributed along coatable surfaces of the contours
and walls i.e.,
coatable surfaces, defined by interstices or voids without significant
agglomeration of the
resin and the particles, as may be visually observed by microscopic
examination of the
surfaces. In the finished article, the majority of the particles are
positioned along the
coatable surfaces of the openings to be abrasively effective in the initial
application of the
article.
The abrasive articles of this invention may be provided in the form of hand
pads,
endless belts, discs, densified or compressed wheels and the like.
Additionally, the articles
of the invention may be laminated to other articles such as nonwoven, closed
cell foam,
open cell foam, or rigid foam substrates and the like or the articles may be
provided a in a
roll form with or without perforations therein.
In the preparation of the foregoing articles, a foraminous substrate is
prepared or is
otherwise provided. A make coat precursor composition is applied to a surface
of the
foraminous substrate to form a first coating layer. A plurality of fine
abrasive panicles are
applied to the first coating layer, and the make coat precursor composition is
at least
partially cured. Optionally, a size coat precursor composition is applied over
the abrasive
particles and the first coating layer to form a second coating layer. The
first and second
coating layers are cured to affix the abrasive particles to the coatable
surfaces of the
openings of the foraminous substrate to provide the abrasive article wherein
the particles
are affixed to the surfaces in a substantially uniform distribution along
their contours.
The fine abrasive particles are deposited onto the make coat precursor,
preferably
by depositing the particles first on one major surface of the foraminous
substrate and then
over the second major surface of the foraminous substrate using the deposition
method
described in U.S. 5,863,305. Larger abrasive particles, i.e., greater than 60
micron
diameter, are preferably applied to the make coat precursor by known methods
such as
drop coating or electrostatic coating. Preferably, the make and size coat
precursors are
thermosetting, coatable, polyurethane resins. Likewise, the optional size
coat, when
applied to the article, is preferably applied over the at least partially
cured make coat. The
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make coat precursor and size coat precursor are then fully cured to provide
the flexible
abrasive articles of the invention, and the thus prepared articles may be
further processed
to provide hand pads, endless belts, discs, densified or compressed wheels and
the like.
Description of the Drawings
Figure 1 illustrates a known coating on a fibrous nonwoven substrate.
Figure 2 schematically illustrates a preferred coating process.
Figure 3 illustrates a preferred coating apparatus.
Figure 4 illustrates a preferred coating on a fibrous nonwoven substrate.
Figure 5 illustrates a particle coater of the invention.
Figures ti and 6a illustrate more detail of the particle coater of Figure 5.
Figure 7 illustrates an alternative embodiment of a particle coater.
Figures 8a, 8b, 8c, and 8d illustrate various multiple particle coater
arrangement
geometries.
Figure 9 is a copy of a photograph of a known foam abrasive article.
Figure 10 is a copy of a photograph of a preferred foam abrasive article.
Detailed Description of the Invention
The organic substrate used as the support material for the abrasive particles
may be
a fibrous substrate, such as woven, knitted, or nonwoven fabric. For example,
the fibrous
substrates include woven, knitted, or nonwoven fabrics such as air-laid,
carded, stitch
bonded, spunbonded, wet laid, or melt blown constructions. Alternatively,
thermoplastic,
thermosetting, or thermoplastic elastomeric foams can be used as the organic
substrate. In
the event that foam constructions are used, open-celled or reticulated foam
structures are
preferred.
In one embodiment, the organic substrate is an open, lofty, three-dimensional
nonwoven fabric, comprising a nonwoven web and fiber adhesive treatment
(generally
known as "prebond" adhesive). The nonwoven web suitable for use in the
articles of the
invention may be made of an air-laid, carded, stitch-bonded, spunbonded, wet
laid, or melt
blown construction. A preferred nonwoven web is the open, lofty, three-
dimensional
air-laid nonwoven fabric described in U.S. 2,958,593. The web may be made of
any
suitable fiber such as nylon, polyester, and the like, capable of withstanding
the curing
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temperatures to which the adhesives are heated without deterioration.
Polyester fibers are
preferred due to their compatibility with suitable adhesives and their
relatively low
moisture absorption and therefore commensurate low susceptibility to ionic
contamination. The fibers of the web are preferably tensilized and crimped but
may also
be continuous filaments formed by an extrusion process such as that described
in U.S.
4,227,350.
The fibers used in the manufacture of the nonwoven web include both natural
and
synthetic fibers and mixtures thereof. Synthetic fibers are preferred such as
those made of
polyester (e.g., poly(ethylene terephthalate)), nylon (e.g.,
poly(hexamethylene adipamide),
polycaprolactam), polypropylene, acrylic (formed from a polymer of
acrylonitrile), rayon,
cellulose acetate, polyvinylidene chloride-vinyl chloride copolymers, vinyl
chloride-
acrylonitrile copolymers, and so forth. Natural fibers include those of
cotton, wool, jute,
and hemp. An important consideration in the selection of the fiber is that it
does not melt
or decompose at temperatures at or below the melting or curing temperature of
the
adhesive used as the fiber and abrasive bonding agent. The fiber used may be
virgin fibers
or waste fibers reclaimed from garment cuttings, carpet manufacturing, fiber
manufacturing, or textile processing, and so forth. The fiber material can be
a
homogenous fiber or a composite fiber, such as bicomponent fiber (e.g., a co-
spun sheath-
core fiber).
The fineness or linear density of the fiber used may vary widely, depending
upon
the results desired. Coarse fibers are generally more conducive to making pads
for rough
scouring jobs, while finer fibers are more appropriate for less aggressive
scouring
applications. Preferred fibers generally are those having a linear density
frorr~ about 1 to
denier, although finer or coarser fibers may be used depending, for example,
on the
25 application envisaged for the finished abrasive article. Those skilled in
the art will
understand that the invention is not limited by the nature of the fibers
employed or by their
respective lengths, denier and the like.
The nonwoven web may be formed by a commercially available
RANDO-WEBBER device, such as obtained from Rando Machine Co., Macedon, NY.
With such processing equipment, fiber length ordinarily should be maintained
within
about 1.25 cm to about 10 cm. However, with other types of conventional web
forming
equipment, fibers of different lengths, or combinations thereof also can be
utilized to form
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the nonwoven webs. The thickness of the fibers is not particularly limited
(apart from
processing considerations), as long as due regard is given to the resilience
and toughness
ultimately desired in the resulting web. With the RANDO-WEBBER equipment,
fiber
thickness is preferably within a range of about 25 to about 250 micrometers.
The fibers may be curled, crimped and/or straight. However, in the interest of
obtaining a three dimensional structure with maximum loft and openness, it is
preferable
that all or a substantial amount of the fibers be crimped. It will be
appreciated that
crimping may be unnecessary where the fibers readily interlace with one
another to form
and retain a highly open lofty relationship in the formed web.
The fibers may be used in the form of a web, a batt, or a tow. As used herein,
a
"batt" refers to a plurality of air laid webs or similar structures.
As an optional enhancement to a nonwoven abrasive article, it is desirable to
promote fiber bonding within the nonwoven web, so that the article will have
greater
structural strength. Such a fiber treatment may be imparted to the web,
preferably as a
separate treatment prior to or after the abrasive particles are adhesively
attached to the
fiber surfaces using the make adhesive. Adhesives known as "prebond" resins,
being
devoid of abrasive components may be used to further consolidate nonwoven
webs. The
resinous adhesive is applied to the fibers of the air-laid web as a liquid
coating using
known coating or spraying techniques followed by hardening of the adhesive
(e.g., by heat
curing) to thereby bond the fibers of the web to one another at their mutual
contact points.
Suitable adhesive materials that may be used in this regard are known and
include those
described in U.S. 2,958,593. Where melt bondable fibers are included within
the
construction of the nonwoven web, the fibers may be adhered to one another at
their
mutual contact points by an appropriate heat treatment of the web to melt at
least one of
the components of the fiber. The melted component performs the function of an
adhesive
so that, upon cooling, the melted component will re-solidify and thereby form
bonds at the
mutual contact points of the fibers of the web. The inclusion of melt bondable
fibers (such
as those described in U.S. 5,082,720) in a nonwoven web may or may not be
accompanied
by the application of a prebond resin, as known by those skilled in the art.
The selection
and use of melt bondable fibers, the selection and application of a prebond
resin and the
conditions required for bonding the fibers of a nonwoven to one another (e.g.,
by melt
bonding or by prebond resin) are typically within the skill of those
practicing in the field.
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As mentioned, the fibers are bonded together at their mutual contact points to
provide an open, low density, lofty web where the interstices between fibers
are left
substantially unfilled by resin or abrasive. For typical applications, the
void volume of the
finished nonwoven abrasive article preferably is in the range of about 75% to
about 95%.
At lower void volumes, a nonwoven article has a greater tendency to clog-up
which
reduces the abrasive rate and hinders cleaning of the web by flushing. If the
void volume
is too high, the web may lack adequate structural strength to withstand the
stresses
associated with cleaning or scouring operations.
It is also contemplated that the organic substrate may comprise an opened tow
of
substantially parallel-arranged filaments as the nonwoven flexible abrasive
article. In this
embodiment, a nonwoven abrasive pad, for example, may be formed by coating an
opened
tow of filaments with adhesive before or while depositing the abrasive
particles on the
tow. The adhesive is then subjected to heat treatment to fuse the abrasive
particles to the
filament surfaces, as described above.
The gas phase in a cellular polymer or foam is distributed in interstices or
voids
called cells. If these cells are interconnected in such a manner that gas can
pass from one
cell to another, the foam is termed open-celled. In contrast, if the cells are
discrete and the
gas phase of each is independent of that of the other cells, the foam is
termed closed-
celled. When the fraction of open cells in a foam is greater than the fraction
of closed
cells, the foam is an open-celled foam. The closed cell content of a foam may
be
measured by means of an airflow manometer described in ASTM method D3574
In general, any resilient and flexible foam substrate having open cells with
coatable
surfaces on at least one surface of the substrate may be used in the abrasive
articles of this
invention. Preferred foam substrates have between about 4 to about 100 pores
per inch
(ppi) (mean pore diameter of 6 to 0.25 mm). Foam substrates having greater
than about
100 ppi have surfaces that behave as solid surfaces. Such solid surfaces may
be coated by
the method of the invention however, such foam substrates may not maintain the
properties of the uncoated foam substrate due to non-uniform application of
the resin and
the particles. Useful foam substrates include those made from synthetic
polymer
materials, such as polyurethanes, foam rubbers, and silicones, and natural
sponge
materials.
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The thickness of the foam substrate is only limited by the desired end use of
the
flexible abrasive article. Preferred foam substrates have a thickness that
ranges from
about 1 mm to about 50 mm.
Preferred foam materials include those that are of polyester urethane, have
uniform
pores, and have an open, reticulated cell structure. Such preferred foams
provide the
needed product flexibility and abrasive performance and decrease the
propensity for
contamination.
As is described in more detail below, an adhesive layer is formed from the
application to the foraminous substrate of a resinous make coat precursor or
first resin and,
optionally, a size coat precursor or second resin applied over the make coat
precursor and
abrasive particles. Preferably, the adhesive layer is formed from the make
coat precursor
and the size coat precursor which have been applied to the foraminous
substrate at a
coating weight which, when hardened, provides the necessary adhesion to
strongly bond
abrasive particles to the substrate. Make coat and size coat precursors may
optionally be
frothed or foamed prior to application to the foraminous substrate. In the
finished articles
of the invention, the adhesive layer provides a thin coating of resin over the
abrasive
particles without burying the particles within the resin. When observed under
a
microscope, for example, the individual particles are observed to be anchored
to the
coatable surfaces of the substrate and to extend outwardly from the outer
surfaces of the
coatable surfaces. In this construction, the abrasive particles are positioned
in the article
to be immediately abrasively effective in the initial applications of the
finished article.
Moreover, the particles are strongly adhered to the coatable surfaces of the
interstices to
provide an abrasive article with a satisfactory work life.
The make coat precursor suitable for use in the invention is a coatable,
hardenable
adhesive binder and may comprise one or more thermoplastic or, preferably,
thermosetting
resinous adhesives. The preferred adhesive binder is that comprising
polyurethane due to
its flexibility, toughness, and minimal contribution of contaminants and
color. Other
resinous adhesives suitable for use in the present invention include phenolic
resins,
aminoplast resins having pendant a,(3-unsaturated carbonyl groups, epoxy
resins,
ethylenically unsaturated resins, acrylated isocyanurate resins, urea-
formaldehyde resins,
isocyanurate resins, acrylated urethane resins, acrylated epoxy resins,
bismaleimide resins,
fluorene-modified epoxy resins, and combinations thereof. Selection of such
resins,
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however, should be made with great care to avoid the introduction of
undesirable amounts
of contaminants or the production of friable coatings which tend to produce
undesired
particulates. Catalysts and/or curing agents may likewise add to the
contamination
potential of the adhesive binder and should therefore be chosen with care. The
make coat
dry add-on will typically be between 50 g/m2 and 170 g/mz.
Epoxy resins have an oxirane ring and are polymerized by the ring opening.
Such
epoxide resins include monomeric epoxy resins and polymeric epoxy reins. These
resins
may vary greatly in the nature of their backbones and substituent groups. For
example, the
backbone may be of any type normally associated with epoxy resins and
substituent
groups thereon may be any group free of an active hydrogen atom that is
reactive with an
oxirane ring at room temperature. Representative examples of acceptable
substituent
groups include halogens, ester groups, ether groups, sulfonate groups,
siloxane groups,
nitro groups and phosphate groups. Examples of some preferred epoxy resins
include
2,2-bis[4-(2,3-epoxypropoxy)-phenyl)propane (diglycidyl ether of bisphenol a)]
and
commercially available materials under the trade designation EPON 828, EPON
1004 and
EPON 1001 F 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-431 and DEN-428 available from Dow
Chemical Co.
Examples of ethylenically unsaturated binder precursors include aminoplast
monomer or oligomer having pendant alpha, beta unsaturated carbonyl groups,
ethylenically unsaturated monomers or oligomers, acrylated isocyanurate
monomers,
acrylated urethane oligomers, acrylated epoxy monomers or oligomers,
ethylenically
unsaturated monomers or diluents, acrylate dispersions or mixtures thereof.
The aminoplast binder precursors have at least one pendant alpha, beta-
unsaturated
carbonyl group per molecule or oligomer. These materials are further described
in U.S.
4,903,440 and U.S. 5,236,472.
The ethylenically unsaturated monomers or oligomers may be monofunctional,
difunctional, trifunctional or tetrafunctional or even higher functionality.
The term
acrylate includes both acrylates and methacrylates. Ethylenically unsaturated
binder
precursors include both monomeric and polymeric compounds that contain atoms
of
carbon, hydrogen and oxygen, and optionally, nitrogen and the halogens. Oxygen
or
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nitrogen atoms or both are generally present in ether, ester, urethane, amide,
and urea
groups. 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, malefic acid, and the like. Representative examples of
ethylenically
unsaturated monomers include methyl methacrylate, ethyl methacrylate, styrene,
divinylbenzene, hydroxy ethyl acrylate, hydroxy ethyl methacrylate, hydroxy
propyl
acrylate, hydroxy propyl methacrylate, hydroxy butyl acrylate, hydroxy butyl
methacrylate, vinyl toluene, ethylene glycol diacrylate, polyethylene glycol
diacrylate,
ethylene glycol dimethacrylate, hexanediol diacrylate, triethylene glycol
diacrylate,
trimethylolpropane triacrylate, glycerol triacrylate, pentaerthyitol
triacrylate,
pentaerythritol trimethacrylate, pentaerythritol tetraacrylate and
pentaerythritol
tetramethacrylate. Other ethylenically unsaturated resins include monoallyl,
polyallyl, and
polymethallyl esters and amides of carboxylic acids, such as diallyl
phthalate, diallyl
adipate, and N,N-diallyladipamide. Still other nitrogen containing compounds
include
tris(2-acryloxyethyl)isocyanurate, 1,3,5-tri(2-methyacryloxyethyl)-s-triazine,
acrylamide,
methylacrylamide, N-methyl-acrylamide, N,N-dimethylacrylamide, N-
vinylpyrrolidone,
and N-vinyl-piperidone.
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.
4,652,274. The preferred isocyanurate material is a triacrylate of
tris(hydroxy ethyl)
isocyanurate.
Acrylated urethanes are diacrylate esters of hydroxy terminated isocyanate
extended polyesters or polyethers. Examples of commercially available
acrylated
urethanes include UVITHANE 782, available from Morton Chemical, and CMD 6600,
CMD 8400, and CMD 8805, available from UCB Radcure Specialties. 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 CMD 3500,
CMD
3600, and CMD 3700, available from UCB Radcure Specialties.
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Examples of ethylenically unsaturated diluents or monomers can be found in
U.S.
5,667,842 and U.S. 5,236,472. In some instances these ethylenically
unsaturated diluents
are useful because they tend to be compatible with water.
Additional details concerning acrylate dispersions can be found in U.S.
5,378,252.
It is also within the scope of this invention to use a partially polymerized
ethylenically unsaturated monomer in the make or size coat precursor. For
example, an
acrylate monomer can be partially polymerized and incorporated into the make
coat
precursor. The degree of partial polymerization should be controlled so that
the resulting
partially polymerized ethylenically unsaturated monomer does not have an
excessively
high viscosity so that the precursor is a coatable material. An example of an
acrylate
monomer that may be partially polymerized is isooctyl acrylate. Tt is also
within the scope
of this invention to use a combination of a partially polymerized
ethylenically unsaturated
monomer with another ethylenically unsaturated monomer and/or a condensation
curable
resin.
In the manufacture of hand pads for use in clean room applications mentioned
above, the adhesive materials used as the make coat precursor in the present
invention may
comprise thermosetting phenolic resins such as resole and novolac resins,
described in
Kirk-Othmer, Encyclopedia of Chemical Technology, 3d Ed. John Wiley & Sons,
1981,
New York, Vol. 17, pp. 384-399. Resole phenolic resins are made with an
alkaline
catalyst and a molar excess of formaldehyde, typically having a molar ratio of
formaldehyde to phenol between 1.0:1.0 and 3.0:1Ø NOVOLAC resins are
prepared
under acid catalysis and with a molar ratio of formaldehyde to phenol less
than 1.0:1Ø A
typical resole resin useful in the manufacture of articles of the present
invention contains
between about 0.75% (by weight) and about 1.4% free formaldehyde; between
about 6%
and about 8% free phenol; about 78% solids with the remainder being water. The
pH of
such a resin is about 8.5 and the viscosity is between about 2400 and about
2800
centipoise. Commercially available phenolic resins suitable for use in the
present
invention include those known under the trade designations DUREZ and VARCUM,
available from Occidental Chemicals Corporation, N. Tonawonda, NY; RESINOX,
available from Monsanto Corporation; and AROFENE and AROTAP, both available
from
Ashland Chemical Company; as well as the resole precondensate available under
the trade
designation BB077 from Neste Resins, a Division of Neste Canada, Inc.,
Mississauga,
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Ontario, Canada. Organic solvent may be added to the phenolic resin as needed
or
desired.
Preferred adhesive materials used in the flexible abrasive articles of the
present
invention preferably comprise polyurethanes, such as those available
commercially from
S Crompton & Knowles Corporation, Stamford, CT under the trade designation
ADIPRENE
BL 16 and ADIPRENE BL31.
The size coat precursor may be the same as the above discussed make coat
precursor, or it may be different than the make coat precursor. The size coat
precursor
may comprise any of the aforementioned resinous or glutinous adhesives such as
phenolic
resins, urea-formaldehyde resins, melamine resins, acrylate resins,
polyurethane resins,
epoxy resins, polyester resins, aminoplast resins, and combinations and
mixtures of the
foregoing. Preferably, the size coat precursor will comprise a resinous
adhesive similar or
identical to the adhesive used in the make coat precursor. More preferably,
the size coat
precursor will comprise either a thermosetting resin or a radiation curable
resin. The size
coat precursor may be foamed prior to its application to the make coat in
order to reduce
the wet add-on weight of the resin so that the abrasive particles are not
buried within the
resin coating and rendered unavailable for use in the initial applications of
the finished
article. The size coat precursor is preferably applied to the foraminous
substrate to
provide an add-on weight which covers the abrasive particles with a thin and
substantially
uniform coating without burying the particles under the resin, and is
typically within the
range from about 50 g/m2 to about 200 g/mz. However, the specific add-on
weights will
depend on several factors such as the nature of the foraminous substrate as
well as the
nature of the resin being used. The determination of appropriate size coat add-
on weights
is well within the skill of those practicing in the field. A preferred size
coat is
polyurethane.
Useful abrasive particles suitable for inclusion in the abrasive articles of
the
present invention include all known fine, and larger, abrasive particles
having a median
particle diameter of from 1 micron to about 600 microns with median particle
diameters
from about 10 microns to about 100 microns being preferred. More preferably,
such fine
abrasive particles are provided in a distribution of particle sizes with a
median particle
diameter of between about 30 microns to about 60 microns. Included among the
various
types of abrasive materials useful in the present invention are particles of
aluminum oxide
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including ceramic aluminum oxide, heat-treated aluminum oxide and white-fused
aluminum oxide; as well as silicon carbide, alumina zirconia, diamond, ceria,
cubic boron
nitride, garnet, ground glass, quartz, and combinations of the foregoing.
Useful abrasive
particles may also include softer, less aggressive materials such as
thermosetting or
S thermoplastic polymer particles as well as crushed natural products such as
nut shells, for
example. Chemically active particles may also be included in the abrasive
articles,
provided that such chemically active particles do not add objectionable levels
of
contaminants.
Those skilled in the art will appreciate that the selection of particle
composition
and particle size will depend on the contemplated end use of the finished
abrasive article,
taking into account the nature of the workpiece surface to be treated by the
article and the
abrasive effect desired. Preferably, the fine abrasive particles for inclusion
in the articles
of the invention comprise materials having a Mohs hardness of at least about
5, although
softer particles may be suitable in some applications, and the invention is
not to be
construed as limited to particles having any particular hardness value. The
particles are
added to at least one of the first or second major surfaces of the foraminous
substrate to
provide a particle loading which is adequate for the contemplated end use of
the finished
article. Abrasive particles may be applied to the foraminous substrate to
provide an add-
on weight within the range from about 209 to 628 g/mz (about 50 to 150
grains/24 inz).
Preferred abrasive particles are those of fused white alumina because of its
relatively low
cost and low amounts of contaminants. More preferred abrasive particles are
fused white
alumina that contains low amounts of sodium, sodium oxides or other sodium
derivatives.
The make coat precursor or the size coat precursor or both may contain
optional
additives, such as fillers, fibers, lubricants, grinding aids, wetting agents,
surfactants,
pigments, dyes, coupling agents, photoinitiators, plasticizers, suspending
agents, antistatic
agents and the like. Such types and amounts of additives that have a potential
to increase
the presence of contaminants must, however, be strictly avoided. The types and
amounts
of additives are selected to provide the properties desired, as known to those
skilled in the
art.
Organic solvent and/or water may be added to the precursor compositions to
alter
viscosity prior to coating with the caveat that such solvents need to be
selected to avoid
adding to the contaminant level of the resulting product. The selection of the
particular
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organic solvent and/or water is believed to be within the skill of those
practicing in the
field and depends upon the thermosetting resin utilized in the make or size
precursor and
the amounts of these resins utilized.
As seen in FIG. 2, in the preparation of the articles of the invention the
foraminous
substrate 100 having first side 104 and second side 106 is fed into apparatus
14. The
foraminous substrate 100 is first passed through coater 20 which applies first
adhesive or
make coat precursor to the foraminous substrate 100. The coater 20 can
comprise any
suitable coater known in the art, such as a spray coater, roll coater, dip
coater, knife over
roll coater, or the like. When applying make coat precursor described below,
the preferred
coater 20 comprises a double roll coater with the foraminous substrate 100
passing
through the nip formed by the two opposed rollers. Preferably, the pressure of
the rollers
is controlled so as to control the penetration of the make coat precursor into
the thickness
of the foraminous substrate. Suitable coaters are well known in the art. The
make coat
precursor is applied to the bottom roller from a pan as is known in the art.
Other suitable
arrangements for applying the make coat precursor to the foraminous substrate
include but
are not limited to applying the make coat precursor with a slot die to the
bottom roll or to
both rolls of a double roll coater, applying the make coat precursor with a
slot die directly
to the foraminous substrate prior to entering the nip of a double roll coater,
applying the
make coat precursor with a slot die without a roll coater and optionally by
drawing a
ZO vacuum across the foraminous substrate opposite the slot die, applying the
make coat
precursor to both sides of the foraminous substrate with opposed slot dies
with or without
subsequently passing the foraminous substrate through a roll coater, and
applying the
make coat precursor with a hose or duct transversing across the foraminous
substrate.
After exiting the first adhesive coater 20, foraminous substrate 100 passes
through
first particle coater 22. First particle coater 22 is preferably configured to
apply fine
abrasive particles to the first surface 104 of the foraminous substrate. As
explained further
below, the abrasive grains will penetrate from surface 104 to some depth into
the
foraminous substrate 100 depending on the properties of the cells of the
foraminous
substrate. When it is desired to apply abrasive grains to second side 106 of
the foraminous
substrate 100, the foraminous substrate passes over rollers 24a and 24b so as
to re-orient
the foraminous substrate to have second side 106 facing up. The foraminous
substrate 100
then passes through an optional second particle coater 26 configured to apply
abrasive
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particles to the second side 106 of foraminous substrate 100. Preferably,
second particle
coater 26 is of like construction as first particle coater 22. However, for
certain
applications, it may be preferable to use second coater 26 of a different type
or
configuration from first particle coater 22. Also, the second abrasive
particle coater 26
may apply abrasive particles having either the same or different composition
and/or size as
the abrasive particles applied by the first abrasive particle coater 22. The
particles may
also be coated onto the foraminous substrate using electrostatic coating
techniques.
After applying fine abrasive particles to at least the first surface 104 of
foraminous
substrate 100, and optionally to second surface 106, the foraminous substrate
100 is
preferably exposed to a heat source (not illustrated), such as infrared lamps
or an oven, to
heat the make coat precursor to the extent necessary to at least partially
cure the resin. In
some applications, it may be preferable to fully cure the make coat precursor
at this step.
Heating can be done with any source giving sufficient heat distribution and
air flow.
Examples of suitable heat sources include forced air oven, convection oven,
infrared heat
and the like. It is also within the scope of the invention to use radiation or
actinic energy.
For heat-activatable thermosetting resins, it is preferred that heating be for
a sufficient
amount of time to drive off residual solvent and initiate at least partial
curing of the resin.
In a preferred embodiment, the foraminous substrate 100 optionally passes
through
second adhesive or size precursor coater 28 to apply an optional but preferred
size coat
precursor to the foraminous substrate 100 after it exits the second abrasive
particle coater
26. Preferably, the size precursor coater is of the same configuration as the
make
precursor coater 20. For some applications, it may instead be desired to use a
coater 28 of
a different configuration from that of the first coater 20. In some
applications, it may be
preferred not to add the size coat.
A preferred embodiment of first particle coater 22 is illustrated in greater
detail in
FIG. 3. Foraminous substrate 100 is conveyed through the coater 22 by a earner
belt 30
which passes around rollers 32a and 32b, at least one of which is a drive
roller. The
foraminous substrate 100 passes through particle spray booth 34. Booth 34
includes first
side 36, second side 38, top 40, and bottom 42. Booth 40 also includes front
and back
sides not illustrated. First side 36 includes entry slot 44a sized and
configured to allow
foraminous substrate 100 and carrier belt 30 to enter the booth 34. Second
side 38 includes
exit slot 44b sized and configured to allow foraminous substrate 100 and belt
30 to exit the
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booth 34. Slots 44a, 44b are located near the bottom of sides 36, 38
respectively.
Mounted through an opening in the top 40 of the booth 34 is particle sprayer
46, having
deflector 48 mounted at the exit 4? of the sprayer. The foraminous substrate
100, which at
this point includes a make coat precursor thereon, is carried by belt 30
through the booth
34. As the foraminous substrate passes from entry slot 44a to exit slot 44b,
particle
sprayer 46 introduces particles 102 into the booth so as to coat the first
side 104 of the
foraminous substrate with abrasive particles. As described below, the
particles 102 will
penetrate to some depth into the foraminous substrate 100. The foraminous
substrate 100,
now comprising abrasive particles adhered to the foraminous substrate by the
make coat
precursor, then exits the booth 34.
In one preferred embodiment, the particle sprayer 46 receives an abrasive
particle/air mixture from fluidizing bed 52. Abrasive particles 102 are
fluidized in the bed
52 by fluidizing air (from a suitable source, not illustrated), introduced
into the bed via
fluidizing air inlet 53.
Atop the fluidizing bed 52 is a venturi inlet 56 as is well known in the art.
In the
illustrated embodiment, venturi 56 receives primary air from a suitable source
via primary
air inlet 58. The primary air passes through the venturi 56 drawing the
mixture of
fluidized particles and air through the draw tube 54 which extends from the
venturi 56 into
the fluidizing bed 52. Secondary air optionally can be added to the venturi
inlet 56 via
secondary air inlet 60. The secondary air is added to the flow of fluidized
abrasive
particles after the particles are drawn into the venturi to aid in delivering
the fluidized
abrasive particle/air mixture to the sprayer 46 via particle hose 64 which
extends from the
venturi exit 62 to the inlet of the particle sprayer 46.
The deflector 48 mounted in the exit 47 of the particle sprayer 46 redirects
the
fluidized abrasive particle/air mixture. Deflector 48 includes deflector top
49 (illustrated in
FIGS. 5 and 6), deflector bottom 50, and deflector wall 51. In one preferred
arrangement,
the deflector bottom 50 has a diameter of 32 mm (1.26 inches), the bottom edge
of the
deflector extends 20 mm (0.79 inches) from the exit of the spray gun, and is
held at a
height of 155 mm (6.1 inches) above the foraminous substrate 100. Of course,
other
arrangements fall within the scope of the present invention. For example, the
size of the
deflector, the shape of the deflector, the contour of wall 51, the number and
location of
particle sprayers 46, the height of the deflectors above the foraminous
substrate, the speed
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of the foraminous substrate 100, and the air pressure and ratio of abrasive
particles in the
particle/air mixture may each be varied. Such parameters may be varied to
achieve the
desired add-on weight of abrasive particles, the desired penetration into the
foraminous
substrate 100 of the abrasive particles, or the desired uniformity of the
abrasive particles
102 on the foraminous substrate 100.
In one preferred embodiment, sprayer 46, fluidizing bed 52, and controller
(not
illustrated) is a commercially available system known as MPS 1-L Manual Powder
System, including model PG 1-E Manual Enamel Powder Gun, available from Gema,
an
Illinois Tool Works Company, of Indianapolis, Ind., with a round deflector 48
substantially as illustrated in FIG. 5.
In another preferred embodiment, the abrasive particle spray apparatus is of
the
type commercially available from Binks Manufacturing Company (Sames), of
Franklin
Park, IL, and includes a 50 1b. fluidized bed, a GCM-200 Gun Control Module, a
SCM-110 Safety control Module, a STAJET SRV Type 414 gun, with a standard
powder
pump.
Another preferred embodiment of particle sprayer 46 is illustrated in FIGS. 5
and
6. In this embodiment, the sprayer comprises an elongate tube 66 having an
exit 47 at one
end and an inlet 68 at the opposite end of the tube. In use, this embodiment
of the sprayer
46 has the abrasive particlelair mixture hose attached to the inlet 68 as is
illustrated with
respect to the earlier described embodiment of FIG. 5. The embodiment of the
sprayer 46
illustrated in FIGS. ~ and 6 is mounted in spray booth 34 and operates as
described with
respect to the embodiment of particle coater 22 illustrated in FIG. 3.
Returning to FIGS. 5 and 6, sprayer 46 includes particle deflector 48 mounted
at
exit 47 of tube 66. Deflector 48 is mounted to the tube 66 by any suitable
mounting means.
In one preferred embodiment, deflector mount 70 includes a base 72 comprising
a
generally rectangular plate having a first end 74 and a second end 76. Base 72
is sized and
configured to fit in slot 69 in the end of tube 66 proximate the exit 47.
Mount 70 can be
permanently or removably mounted to the tube 66. In the illustrated
embodiment, base 72
is releasably held in slots 69 by a spring, clip, or other suitable fastener
(not illustrated)
affixed to holes 78 in the first and second ends of base 72. Extending from
base 72 is a
threaded rod 80 having a first end 82 aW xed to the base (such as by brazing,
for example)
and second end 84 extending beyond the exit 47 of tube 66. Threaded rod 82 is
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configured to engage with a like-threaded hole in the top 49 of deflector 48.
This allows
the position of deflector 48 to be conveniently adjusted with respect to the
exit 47 of the
tube 66 by rotating the deflector 48. This allows for varying the direction of
motion of the
particles 102 leaving the sprayer 46 as described above. Deflector 48 also
includes bottom
SO opposite top 49, and deflector wall 51 extending between top 49 and bottom
50.
An alternate embodiment of sprayer 46 is illustrated in FIG. 6A. In this
embodiment, threaded rod 80 is elongated, and includes a tapered end 82 to
help direct the
flow of abrasive particles through tube 66. Pins 73 extend through holes 75 in
the wall of
the tube 66, and extend through holes in the rod 80, to mount the rod 80 in
the sprayer 46.
In one embodiment, the tapered end 82 of rod 80 ends at the inlet 68. In other
embodiments, the end 82 can extend beyond the inlet 68, or the inlet may
extend beyond
the end 82 of the rod. Deflector 48 is mounted on threaded end 84 as described
above.
The tube 66 and deflector 48 should be sized and configured to provide the
desired
uniform spray pattern of abrasive particles 102. In one preferred embodiment,
tube 66 is
approximately 61 cm (24 inches) long, has an inside diameter of 1.08 cm (0.425
inches),
and an outside diameter of 1.27 cm (0.5 inches), and is constructed of
stainless steel. It is
understood that other sizes and materials of tube 66 fall within the scope of
the present
invention.
Another preferred embodiment of the abrasive particle sprayer 46 is
illustrated in
FIG. 7. In this embodiment, the sprayer 46 comprises rotating first and second
circular
discs 90 and 91, respectively, joined by studs 93. Second disc 91 has a hole
92 in the
center thereof. Second disc is joined to rotating shaft 94 which is concentric
with the
center hole 92. Rotating shaft 94 is rotatably mounted on the outside of
stationary feed
tube 95 by means of bearings 98, such that rotating shaft 94 is concentric
with stationary
feed tube 95. In this manner, rotating shaft 94, first plate 90, and second
plate 91 are able
to rotate together as a unit about stationary feed tube 95. The rotating shaft
94 can be
driven by any suitable power means, such as an air motor (not illustrated).
Feed tube 95
includes inlet 96 and outlet 97. In one preferred embodiment, inlet 96 of the
feed tube 95
is attached to abrasive particle/air mixture hose 64, and the particle sprayer
46 is mounted
on the top 40 of particle booth 34 as explained with regard to the embodiment
of FIG. 4.
In such an arrangement, the particle sprayer 46 receives fluidized abrasive
particles from
the fluidizing bed 52. In a variation of this embodiment, a vibratory feeder
can be used in
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place of the fluidizing bed 52. The vibratory feeder is connected to feed
abrasive particles
into the inlet 96 of feed tube 95.
In operation, the rotating shaft 94 is driven so as to cause plates 90 and 91
to rotate.
Fine abrasive particles pass through feed tube 95 and exit from outlet 97.
Tube outlet 97
is positioned through hole 92 in second plate 91 such that the abrasive
particles enter the
space between first and second plates 90, 91. The abrasive particles strike
the top surface
of rotating plate 90, and will be dispersed through exit 47 in a direction
generally parallel
to the plane of first and second plates 90, 91. The particles preferably form
a cloud that
deposits, preferably by settling due to gravity onto the surface of foraminous
substrate 100
as explained with regard to the embodiments described above. In one preferred
embodiment, particle sprayer 46 comprises a Binks EPB-2000, commercially
available
from Binks Manufacturing Company (Sames), of Franklin Park, IL, and the
abrasive
particles are fed to the particle sprayer by a vibratory pre-feeder
commercially available as
"Type 151" from Cleveland Vibratory Company, Cleveland, OH. The plates 90, 91
of the
particle sprayer are preferably driven at 6,000 to 9000 RPM, however slower
and faster
speeds are within the scope of the present invention. The abrasive particle
feed rate, type
of particle feeder, or rotational speed of the plates may be selected to
provide the desired
abrasive particle spray pattern, desired abrasive particle add-on weight, or
desired degree
of penetration into foraminous substrate 100 of the abrasive particles.
What is common to the preferred embodiments described herein is that the
particle
sprayer includes means to change the direction of flow of particles 102
exiting the sprayer
from perpendicular to the foraminous substrate 100, to a direction
approaching, or
exceeding, a plane parallel to foraminous substrate 100. Such directions are
described
with reference to the area immediately surrounding the exit 47 of particle
sprayer 46.
Thereafter, the fine particles 102 preferably disperse into a cloud of
particles in the booth
34. The particles then settle from the cloud onto the foraminous substrate
under the
influences of gravity. Thus in one preferred embodiment of the inventive
method,
immediately before the particles adhere to foraminous substrate 100, gravity
has a greater
effect on the motion of the abrasive particles than does the momentum imparted
by the
particle sprayer 46. In some applications, the momentum imparted by the
particle sprayer
46 will have little or no effect on the motion of the particles 102
immediately before the
particles adhere to foraminous substrate 100. In other applications, for
example where
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greater penetration of abrasive particles 102 into the foraminous substrate
100 is desired,
the above apparatus parameters and configuration may be selected such that the
downward
momentum imparted to the particles 102 by the sprayer 46 will have a greater
effect on the
motion of the particles immediately before the particles adhere to the
foraminous
S substrate.
In the embodiments described with respect to FIGS. 3, 5, and 6, the means for
directing the flow of particles 102 exiting the particle sprayer 46 is the
deflector wall 51 of
deflector 48. Preferably, the location of the deflector 48 relative to the
exit 47 of the
particle sprayer may be varied to obtain the desired redirection of flow of
abrasive
particles 102 exiting the particle sprayer. It will be appreciated that
without the deflector
48, the abrasive particles exiting the particle sprayer 46 will travel
generally parallel to the
longitudinal axis of the sprayer, which is generally perpendicular to the
foraminous
substrate 100. Generally, the closer the wall 51 and bottom 50 of the
deflector are to the
exit 47, the greater the change in direction of motion of particles 102 from
perpendicular
to the foraminous substrate 100 will be. Moving the wall 51 and bottom 50 of
the
deflector further from the exit 47 will reduce the amount the direction of
motion of the
particles is varied from perpendicular to the foraminous substrate 100. In the
embodiment
described with respect to FIG. 7, the structure for directing the flow of
abrasive particles is
the rotating plates 90, 91.
In some applications, it may be desirable to place hard inserts, such as
ceramic
inserts, into those components of the apparatus 14 that are prone to wear
under prolonged
flow of abrasive particles through the components. This may be desirable, for
example, in
the particle sprayer 46, the venturi inlet 56, and the deflector 48. Such
inserts would
prolong the useful life of certain components of apparatus 14, but would not
be expected
ZS to have a significant effect on the performance of the apparatus.
For some applications, it is preferable to use a plurality of particle
sprayers 46 in a
single spray booth 34. Preferably, each of the particle sprayers are of like
configuration,
however it is understood that different types of particle sprayers could be
used in a single
booth. The particle sprayers 46 should be arranged in a pattern that provides
a uniform
coating of abrasive particles 102 to the foraminous substrate 100 as the
foraminous
substrate passes through the booth 34. This may be accomplished by arranging
the
plurality of particle sprayers 46 such that each location across the width of
the foraminous
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substrate 100 traverses through an equal number of spray patterns caused by
each of the
particle sprayers 46. Exemplary particle sprayer arrangements are illustrated
schematically in FIGS. 8A through 8D. These figures are schematic top views of
the
foraminous substrate 100 passing under the spray patterns 45 created by
particle sprayers
46 mounted in the top 40 of the booth 34 (not shown). It is possible to vary
the flow rates
of each of the plurality of sprayers 46, or to use different configurations of
sprayers 46 to
obtain a desired coating pattern of abrasive particles 102 on foraminous
substrate 100. It
is also possible to oscillate or reciprocate the particle sprayers 46 to
achieve a desired
spray pattern as is known in the art.
When using a plurality of particle sprayers 46, it is possible to use a like
number of
particle coaters 22 as illustrated in FIG. 3, where each particle'sprayer
receives abrasive
particles 102 for a respective fluidizing bed 52. In some applications, it is
preferable to
feed a plurality of particle sprayers 46 from a single fluidizing bed 50. In
one such
arrangement, a plurality of venturi injectors 56 are mounted on a single
fluidizing bed. In
an alternate arrangement, a plurality of volumetric control auger feeders are
mounted on
the side wall of a fluidizing bed to draw a desired rate of fluidized abrasive
particle/air
mixture from the fluidizing bed 50. The operation and design of such feeders
is well
known and need not be further discussed. Each auger feeder deposits the
abrasive
particles into a venturi injector 56 as described above. Each venturi injector
56 is
connected to an abrasive particle/air mixture hose 64 for conveying the
abrasive
particle/air mixture to a particle sprayer 46 as described above. In one
preferred
embodiment, the fluidizing bed 50 having a plurality of auger feeders mounted
thereon is
of the type commercially available as the POWDER DELIVERY CONTROL UNIT from
Gema, an Illinois Tool Works Company, of Indianapolis, IN. It is also within
the scope of
the invention for the auger feeder to feed abrasive particles from a
volumetric feeder of the
type commercially available as DRY MATERIAL FEEDER from AccuRate of
Whitewater, WI.
It is also within the scope of the present invention to include additional
particle
sprayers configured to spray abrasive particles onto the foraminous substrate
100 with
enough force to achieve greater penetration into the center portion of the
foraminous
substrate. Such additional particle sprayers can be included in the spray
booth 34 along
with the particle sprayers 46 described above, either in the arrangement of
particle
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sprayers 46, or arranged to spray the foraminous substrate 100 before or after
the
foraminous substrate passes under sprayers 46. Such additional sprayers could
also be
arranged in a second particle spray booth before or after the sprayers 22, 26,
described
above. Preferably, the additional sprayers are arranged to deposit abrasive
particles onto
S the foraminous substrate before the sprayers 46, so as not to disturb or
disrupt the
advantageous spray pattern achieved by the sprayers 46. Such a combination of
sprayers
may be used to provide a foraminous substrate 100 having the advantageous fine
particle
distribution at surfaces 104, 106 as described herein, along with particles in
the center
portion of the foraminous substrate for a longer-life abrasive article.
In one preferred embodiment, the foraminous substrate 100 has a width from
first
edge 107 to second edge 108 of 61 cm (24 inches) and is fed through apparatus
14 at a
foraminous substrate speed of from about 3 to 30 meters/minute (10 to 100
feet/minute),
more preferably 16 meters/minute (52.5 feet/minute). The first adhesive coater
20 is a
double roll coater with the foraminous substrate 100 passing through the nip
formed by the
two opposed rollers. The fine abrasive particles 102 are applied by eight
particle sprayers
46 generally as described with respect to FIGS. 5 and 6, fed by eight venturi
injectors 56
mounted on a fluidizing bed 52. The spray pattern of the injectors is
generally as
illustrated with respect to FIG. 8B. The parameters for the Gema particle
coater described
above are as follows: fluidizing air introduced through inlet 53 at a pressure
of from about
2 to 15 psi; primary air introduced into inlet 58 of venturi 56 at a pressure
of up to 90 psi,
preferably 30 to 60 psi; secondary air introduced into inlet 60 at a pressure
of from 0 to
about 90 psi, preferably from 0 to about 20 psi. A size coating precursor may
be applied
and cured in the same manner as the make coat precursor.
By applying the make coat precursor in the manner described herein, the
tendency
for the make coat precursor to migrate or concentrate and agglomerate is
reduced. In this
manner, the coatable surfaces of the substrate are uniformly coated with the
make coat
precursor, allowing the abrasive particles 102 to be coated onto and adhered
to the
coatable surfaces in a more uniform distribution. By coating the make coat
precursor and
abrasive particles in different steps, the abrasive particles are less likely
to be "buried"
Within the make coat as is prone to happen in the prior art method of applying
a make coat
precursor/abrasive particle slurry. In the finished articles made by the
methods and
apparatuses of the invention, the size coat provides a thin coating of resin
over the fine
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abrasive particles without burying the particles within the resin. When
observed under a
microscope, for example, the individual particles are observed to be anchored
to the
coatable surfaces of the openings and to extend outwardly from the coatable
surfaces of
the openings. In this construction, the fine abrasive particles are positioned
in the article
to be immediately abrasively effective in the initial applications of the
finished article.
Moreover, the particles are strongly adhered to the coatable surfaces of the
openings of the
foraminous substrate to provide an abrasive article with a satisfactory work
life.
Packaging
The abrasive articles are preferably packaged in a Class 100 envrionment
conforming to Fed. Std. 209 and Mil. Std. 1246C , Class 10'0 Particulate
Cleanliness
Levels.
All packaging materials are certified (e.g., according to Mil. Std. 1246C) for
use in
such facilities. First the articles are placed in a reduced pressure hood and
decontaminated
by using a blast of ionized air. The articles are then packaged in an inner
wrapping,
cleaned with another blast of ionized air, and then overpacked in an outer
wrapping.
Examples
Materials
Foam: polyester polyurethane reticulated foam, 50 cells per inch, 0.375-inch
(9.52 mm), illbruck, Inc., Minneapolis, MN
PM Ether: propylene glycol monomethyl ether, Lyondell Chemical Company,
Houston, Texas
PM Acetate: propylene glycol monomethyl ether acetate, Arco Chemical Company,
Houston, TX
BL-16: oxime-blocked isocyanate-terminated polyurethane prepolymer, Crompton
& Knowles Corporation, Stamford, CT
BL-31: oxime-blocked isocyanate-terminated polyurethane prepolymer, Crompton
& Knowles Corporation, Stamford, CT
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PACM-20: bis(para-aminocyclohexyl)methane, an aliphatic amine curative, Air
Products and Chemicals, Inc., Allentown, PA
Fiber: polyester staple 15 denier x 2", type 224, Hoechst Celanese, Salisbury,
NC
Mineral A: "P320" SWPL white aluminum oxide, Treibacher, Villach, Austria
Mineral B: "220 BM" white aluminum oxide, Graystar, Bluffton, SC
Mix l: 62% BL16, 8% PACM20, 30% PM ether (percent liquid weight)
Mix 2: 14% BL16, 39% BL31, 7% PACM20, 40% PM acetate (percent liquid
weight)
Mix 3: 50% BL31, 8% PACM20, 42% PM acetate (percent liquid weight)
Biaxial Shake Test
The Biaxial Shake Test was used to determine the propensity of the abrasive
articles of the present invention to produce particulate residues or
releaseable particles
when subjected to vigorous agitation. A 10 cm x 10 cm specimen from an
abrasive article
to be tested was placed in a sealable plastic bucket. 800 ml of COULTER ISOTON
solution was added to the bucket. The bucket was sealed and secured into a
biaxial motion
paint can shaker (Red Devil Inc., Union, NJ) and the shaker activated for 3
minutes. The
bucket was then opened and the specimen removed. A 250 ml aliquot of the
solution was
then transferred to a COULTER MULTISIZER II Discrete Particle Counter (Coulter
Corporation, Miami, FL) sample flask. The particle counter was set to perform
a 2 ml
volumetric particle analysis using a 100 micrometer orifice tube (for the
measurement of
2 micrometer to 100 micrometer particles). The total particle count was
determined and
normalized with respect to the specimen size to obtain releaseable particles
per square
meter of the abrasive article.
Elemental Analysis
Elemental Analysis was performed by various methods as shown in the following
chart:
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Sample DigestionAnalyte Analysis Reference
Lithium Borate ASTM D4503
Fusion
Silicon inductively coupled USEPA 6010B
plasma, mass spectrometry
Aluminum inductively coupled USEPA 6010B
plasma, mass spectrometry
Oxygen Bomb ASTM D808,
USEPA 5050
Halogens Ion chromatography ASTM D4327
Sulphur Ion chromatography ASTM D4327
Schoniger Flask ASTM E442
Combustion
Fluorine Ion selective electrodeASTM D3869-79
Wet Ash USEPA 3050
Digestion
Sodium inductively coupled USEPA 6010B
plasma, mass spectrometry
Potassium inductively coupled USEPA 6010B
plasma, mass spectrometry
Lithium inductively coupled USEPA 6010B
plasma, mass spectrometry
Silver inductively coupled USEPA 6010B
plasma, mass spectrometry
Metal Scaninductively coupled USEPA 6010B
plasma, mass spectrometry
Dry Schieffer Test
A scuffing test was used to simulate the abrasive qualities of abrasive
articles on
typical automotive painted surfaces. The test specimens are prepared from
poly(methyl)
S methacrylate sheet material 1/8 inch (3.2 mm) thick, Rockwell Ball Hardness
of 90-105,
available in 48 x 96-inch (1.22 x 2.44 m) sheets under the trade name ACRYLITE
from
American Cyanamid, Wayne, NJ. Following the removal of the protective covering
from
the top side of the acrylic sheet, a double coat of PPG BLACK UNIVERSAL BASE
COAT paint (PPG Industries Inc., Automotive Finishes Division, Cleveland, OH)
was
applied per the manufacturer's recommendations. The black base coat was
painted over
with three (3) double coats of PPG PAINT DAU-82, CLEAR (PPG Industries Inc.,
Automotive Finishes Division, Cleveland, OH) per the manufacturer's
recommendations,
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allowing about 30 minutes of "flash time" between each double coat
application. The
coated sheets were allowed to air-dry for approximately 72 hours. A number of
4-inch
(10.2 cm) diameter test specimens were cut from the coated sheet with care
taken to
minimize the scratching of the painted surface. The cut discs were then baked
at 150°F
(66°C) in an oven, avoiding any contact with the coated surface, for
about 16 hours to
fully cure the paint coatings. The test specimens were then ready for testing.
The tests were conducted on a Schieffer Abrasion Machine (available from
Frazier
Precision Company, Gaithersburg, MD) fitted with a spring clip retaining plate
to secure
the painted test specimen on the bottom turntable and a mechanical fastener
(SCOTCHMATE DUAL LOCK SJ3442 Type 170) to hold the abrasive composition on
the upper turntable. For each test, the counter was set to run 5'00
revolutions. A 4-inch
(10.2 cm) diameter disc of the abrasive article to be tested was cut and
mounted on the
upper turntable via the mechanical fastener. In the event that the abrasive
article had
contact surfaces significantly different from each other, notation was made as
to which
side was being tested. A previously-prepared 4-inch (10.2 cm) diameter painted
acrylic
disc was weighed to the nearest milligram (W(1)) and mounted via the-spring
clip to the
lower turntable with the painted surface facing up. A 10 1b. (4.55 kg) weight
was placed
on the load platform of the abrasion tester. If the abrasion tester is plumbed
for wet testing,
the water supply is shutoff. The upper turntable was lowered to contact the
painted acrylic
disc under the full force of the load weight, and the machine was started.
After 500
revolutions, the machine was turned off, the abrasive article removed from the
upper
turntable and discarded, and the painted acrylic disc was removed from the
lower
turntable. Any free dust or detritus was removed from the painted acrylic disc
by wiping
with a dry paper towel and the disc weighed again (W(2)). The difference W(1) -
W(2) is
reported to the nearest milligram as "cut".
The test should not abrade the painted acrylic disc to the extent that any of
the
underlying black paint is removed. In the event that the abrasion progressed
through the
black layer, the test was repeated. In the event that the abrasion passes
through the black
layer on the second attempt, new painted acrylic discs should be prepared with
additional
layers of the clear coating.
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Wet Schieffer Test
The Wet Schieffer Test was conducted identically to the Dry Schieffer Test
with
the exceptions of 1) no paint was applied to the acrylic disk; 2) 2500 cycles
were run per
test; and 3) a water drip was applied to the workpiece during the test at a
rate of about one
drop per second.
Examples A, B, and C
Foam Substrate
Examples A, B, and C were prepared using an open-cell polyurethane foam as the
substrate. The composition of Examples A, B and C are shown in Table 1. The
make coat
precursor was applied via a two-roll coater.
Example A was cured at 177°C; 2 minutes for the make coating and 3
minutes for
the size coating. Example B was cured at 189°C; 4 minutes for the make
coating and 10
minutes for the size coating. Example C was cured at 175°C; 6 minutes
for the make
coating and 12 minutes for the size coating.
Table 1
Foam Make-MixMake-MixSize-MixSize-MixMineral Mineral
grains/241 2 1 3 A B
xampleinz grains/24grains/24grains/24grain~/24grains/24grains/24
(g/mz) in2 in2 in- in2 in2 inz
(~m2) (~mz) (~m2) (P~m2) (~mZ) (P~m2)
A 62 (259)44 (184)-- 64 (268)-- 84 (351)--
B 67 (280)-- 29 (121)-- 26 (109)-- 91 (380)
C 65 (272)30 (125)-- -- 35 (146)72 (301)
Total Elemental Content
The total elemental content of Example C and comparative commercially
available
hand pads was determined by a wet ash digestion followed by inductively
coupled plasma
analysis. The results are shown in Table 2. Appropriate limits are shown in
Table 3.
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Table 2
Comparative Comparative
Example C Example 1 (ppm)Example 2 (ppm)
(ppm)
Sodium 85 963 1300
Potassium 5 3900 1500
Calcium 2.3 Major 23 800
Lithium < 1 22 Not determined
Chlorine <47 135 2300
Copper < 1.4 22 206
Iron 4.8 1696 830
Magnesium 0.45 716 390
Titanium 0.46 1461 1.22
Sulfur 26 268 1500
Phosphorus <0.4 16 820
TOTAL 174 34199 32768
Table 3
Preferred Good (ppm)Maximum Allowable
(ppm) (ppm)
Sodium 0-50 50-200 <500
Potassium0-20 20-100 <500
Calcium 0-20 20-100 <500
Lithium 0-20 20-50 <500
Chlorine 0-50 50-100 <500
Copper 0-20 20-50 <500
Iron 0-20 20-50 <500
Magnesium0-20 20-50 <500
Titanium 0-20 20-SO <500
Sulfur 0-20 20-50 <500
Phosphorus0-20 20-50 <500
TOTAL 0-200 200-1000 <5000
Extractables
Extractable objectionable ionic materials were determined for Example B and
for
commercial hand pads by a one hour deionized water soak followed by ion
chromatography. The test methods are described in ASTM D4327 and USEPA 300.1
with
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the modification that suppression is electrolytic rather than chemical. The
results are
shown in Table 4 for selected anions and cations in parts per billion.
Acceptable limits are
shown in Table S.
Table 4
Anions Example B (ppb) Comparative Example
1 (ppb)
Fluoride
Chloride 7.2 11
Nitrite 0.6 2.3
Bromide
Nitrate 6.7 7.1
Phosphate * 2.7
Sulfate 1.6 1 SO
TOTAL 16.1 173.1
Cations Example B (ppb) Comparative Example
1 (ppb)
Li 0.43 0. 5
Na 96 270
Ammonium 1.7 14
K 2.1 1300
Mg * 62
Ca 26 4700
TOTAL 126.23 6346.5
* means "not detected"
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Table 5
Ranges Preferred (ppb)Good (ppb) Must be (ppb)
Anions
Fluoride 0-1.0 1.0-2.0 <3.0
Chloride 0-5.0 5.0-10.0 < 10.0
Nitrite 0-1.0 1.0-2.0 <3 . 0
Bromide 0-1.0 1.0-2.0 <3.0
Nitrate 0-5.0 5.0-10.0 < 10.0
Phosphate 0-1.0 1.0-2.0 <3.0
Sulfate 0-2.0 2.0-10.0 < 10.0
TOTAL 0-20.0 20.0-40.0 <50.0
Cations
Li 0-0.5 0.5-1.0 <5.0
Na 0-SO 50-100 <150
Ammonium 0-1. 0 1. 0-5 . 0 < 10. 0
K 0-10.0 10.0-30.0 <50.0
Mg 0-1.0 1.0-5.0 <10.0
Ca 0-10.0 10.0-30.0 <50.0
TOTAL 0-150 150-250 <300
Example A was evaluated for cut by the Dry Schieffer test which was conducted
for 500 cycles with a load of 10 pounds. The results are shown in Table 6,
wherein
S acceptable values are greater than or equal to 0.04 gram, preferred values
are greater than
0.1 gram, and more preferred values are greater than 0.125 gram.
Table 6
Example Cut (g)
Comparative Example 1 0.078
Comparative Example 2 0.039
Example A 0.159
Example B was evaluated for cut by the Wet Schieffer test which was conducted
with a water drip for 2500 cycles on an acrylic workpiece under a load of 10
pounds,
wherein acceptable values must be greater than 2.9 grams, preferred values are
greater
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than 3.2 grams, and more preferred values are greater than 3.6 grams. The test
results are
shown in Table 7.
Table 7
Example Cut (g)
Comparative Example 1 3.6
Comparative Example 2 3.2
Example B 3.0
S
Example A was evaluated for its propensity to produce free particles by the
Biaxial
Shake Test. The results are shown in Table 8, wherein acceptable values are
less than 500
x 106 particles per square meter, the preferred range is between 100 x 106 and
200 x 106
particles per square meter, and more preferred is 0 to 100 x 106 particles per
square meter.
Table 8
Example Particles/m2 (millions)
Comparative Example 1 1213
Comparative Example 2 1076
Example A 136
Comparative Example 1
Comparative Example 1 is a commercially-available nonwoven abrasive surface
conditioning material having the trade designation "SCOTCH-BRITE 7447+ General
Purpose Hand Pad" available from Minnesota Mining and Manufacturing Company,
St. Paul, MN.
Comparative Example 2
Comparative Example 2 is a commercially available nonwoven abrasive general
purpose
commercial scouring pad available as "SCOTCH-BRITE #96" from Minnesota Mining
and Manufacturing Company, St. Paul, MN.
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Examples D and E
Nonwoven Substrate
Examples D and E were prepared to demonstrate the invention when using a
fibrous nonwove substrate. Table 9 shows the composition of Examples D and E.
Examples D and E were cured at an oven temperature of 350°F; 2 minutes
for the make
coating and 3 minutes for the size coating.
Table 9
Fiber Prebond Make Mix Mineral Size Mix
Mix 1 1 A 1
grains/24 grains/24 grains/24grains/24 grains/24
in2 in2 in2 in2 in2
Example(g/m2) (g/m2) (g/m2) (g/m2) (g/m2)
D 18 (75) 27 (113) 25 (104) 57 (238) 45 (188)
E 18 (75) 27 (113) 35 (146) 76 (318) 53 (222)
Total Elemental Content
The total elemental content of Example D was determined by wet ash digestion
followed by ion chromatography. The results are shown as parts per million in
Table 10.
Acceptable levels of the various components are shown in Table 3 in parts per
million
parts.
Table 10
Example Comparative ExampleComparative Example
D 1 2
(PPm) (PPm) (PPm)
Sodium 87 963 1300
Potassium < 1 3900 1500
Calcium 4 Major 23800
Lithium < 1 22 (unknown)
Chlorine <37 135 2300
Copper < 1 22 206
Iron 11 1696 830
Magnesium < 1 716 390
Titanium < 1 1461 122
Sulfur 11 268 1500
Phosphorus<1 16 820
TOTAL 156 34199 32768
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Example E was evaluated for cut by the Dry Schieffer test procedure wherein
the
test was run for 500 cycles under a load of 10 pounds. The results are shown
in Table 11.
For acceptable articles, the dry cut must be more than 0.04 gram of material
removed.
Preferred articles cut more than 0.1 gram, and more preferred articles cut
more than
0.125 gram.
Table 11
Example Cut (g)
Comparative Example 1 0.078
Comparative Example 2 0.039
Example E 0.095
Example E was also evaluated for particulate residue using the Biaxial Shake
test.
The results are shown in Table 12, wherein acceptable values are less than S00
x 106
particles per square meter, preferred values are less than or equal to 200 x
106 particles per
square meter, and more preferred values are less than or equal to 100 x 106
particles per
square meter.
Table 12
Particles/m2 (millions)
Comparative Example 1213
1
Comparative Example 1076
2
Example E 165
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