U.S. patent application number 09/466974 was filed with the patent office on 2001-06-21 for production of layered engineered abrasive surfaces.
This patent application is currently assigned to Paul Wei. Invention is credited to SWEI, GWO SHIN, WEI, PAUL, YANG, WENLIANG PATRICK.
Application Number | 20010003884 09/466974 |
Document ID | / |
Family ID | 23853812 |
Filed Date | 2001-06-21 |
United States Patent
Application |
20010003884 |
Kind Code |
A1 |
WEI, PAUL ; et al. |
June 21, 2001 |
PRODUCTION OF LAYERED ENGINEERED ABRASIVE SURFACES
Abstract
Coated abrasives comprising shaped structures deposited on a
backing can be given increased versatility by varying the
composition comprising the structure such that different
characteristics are revealed as the structure is eroded during
use.
Inventors: |
WEI, PAUL; (LATHAM, NY)
; SWEI, GWO SHIN; (EAST AMHERST, NY) ; YANG,
WENLIANG PATRICK; (BALLSTON LAKE, NY) |
Correspondence
Address: |
DAVID BENNETT
NORTON COMPANY
1 NEW BOND STREET
BOX 15138
WORCESTER
MA
016150138
|
Assignee: |
Paul Wei
|
Family ID: |
23853812 |
Appl. No.: |
09/466974 |
Filed: |
December 20, 1999 |
Current U.S.
Class: |
51/298 ; 51/295;
51/307; 51/309 |
Current CPC
Class: |
B24D 3/28 20130101; B24D
11/04 20130101; B24D 3/34 20130101 |
Class at
Publication: |
51/298 ; 51/295;
51/307; 51/309 |
International
Class: |
B24D 003/00; B24D
011/00; B24D 011/04 |
Claims
What is claimed is:
1. A coated abrasive having a patterned surface comprising a
plurality of shaped structures wherein each such structure
comprises a curable binder with abrasive particles dispersed
therein wherein the improvement comprises providing that the
structures are layered such that, as the structure is eroded during
use, different properties are revealed.
2. A coated abrasive according to claim 1 in which the abrading
properties change as the structures are eroded.
3. A coated abrasive according to claim 1 in which the size of the
abrasive particles in the portions of the structures closer to the
backing are finer than those in the portions more remote from the
backing.
4. A coated abrasive according to claim 1 in which the size of the
abrasive particles in the portions of the structures closer to the
backing are coarser than those in the portions more remote from the
backing.
5. A coated abrasive according to claim 1 in which the portions of
the structures closer to the backing are provided with a color that
is different from that of the portions of the structure more
distant from the surface.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to the production of coated abrasives
engineered to have patterned surfaces with properties specific to
the desired application.
[0002] The proposal to deposit isolated structures such as islands
of a mixture of a binder and abrasive material on a backing
material has been known for many years. If the islands have very
similar heights above the backing and are adequately separated
then, (perhaps after a minor dressing operation), use of the
product will result in reduced surface scratching and improved
surface smoothness. In addition the spaces between the islands
provide a route by which swarf generated by the abrasion can be
dispersed from the work area.
[0003] In a conventional coated abrasive, investigation of the
grinding surface reveals that a comparatively small number of the
surface abrasive grits in an active abrading zone are in contact
with the workpiece at the same time. As the surface wears, this
number increases but equally the utility of some of those abrasive
grits may be reduced by dulling. The use of abrasive surfaces
comprising a uniform array of isolated islands has the advantage
that the uniform islands wear at essentially the same rate such
that a uniform rate of abrasion can be maintained for longer
periods. In a sense the abrading work is more evenly shared among a
larger number of grinding points. Moreover since the islands
comprise many smaller particles of abrasive, erosion of an island
uncovers new, unused abrasive particles which are as yet
undulled.
[0004] One technique for forming such an array of isolated islands
or dots that has been described is that of the rotogravure
printing. The technique of rotogravure printing employs a roll into
the surface of which a pattern of cells has been engraved. The
cells are filled with the formulation and the roll is pressed
against a surface and the formulation in the cells is transferred
to the surface. Normally the formulation would then flow until
there was no separation between the formulations deposited from any
individual cell. Ultimately a layer of essentially uniform
thickness would be obtained. By way of illustration, comparative
Examples C and D of U.S. Pat. No. 5,152,917 describe a process in
which the pattern obtained by a rotogravure process quickly lost
all separation of the individual amounts deposited from the
cells.
[0005] In U.S. Pat. No. 5,014,468 a binder/abrasive formulation was
deposited from rotogravure cells on a roller in such a way that the
formulation was laid down in a series of structures surrounding an
area devoid of abrasive. This is believed to be the result of
depositing less than the full volume of the cell and only from the
perimeter of each cell, which would leave the ring formations
described.
[0006] The problem with the rotogravure approach has therefore
always been the retention of a useful shape to the island. To
formulate an abrasive/binder mixture that is sufficiently flowable
to be deposited and yet sufficiently non-flowable such that it does
not slump to an essentially uniform layer coating when deposited on
a substrate has proved very difficult.
[0007] Chasman et al., in U.S. Pat. No. 4,773,920 disclosed that
using a rotogravure coater, it is possible to apply a uniform
pattern of ridges and valleys to the binder composition which, when
cured, can serve as channels for the removal of lubricant and
swarf. However beyond the bare statement of possibility, no details
are given that might teach how this might be carried out.
[0008] In U.S. Pat. No. 4,644,703 Kaczmarek et al. used a
rotogravure roll in a more conventional fashion to deposit an
abrasive/binder formulation to deposit a layer that is then
smoothed out before a second layer is deposited by a rotogravure
process on top of the smoothed-out first layer. There is no
teaching of the nature of the final cured surface.
[0009] Another approach has been to deposit the abrasive/binder
mixture on a substrate surface and then impose a pattern comprising
an array of isolated islands on the mixture by curing the binder
while in contact with a mold having the inverse of the desired
patterned surface. This approach is described in U.S. Pat. Nos.
5,437,754; 5,378,251; 5,304,223 and 5,152,917. There are several
variations on this theme but all have the common feature that each
island in the pattern is set by curing the binder in contact with a
molding surface.
[0010] Yet another approach is described in U.S. Pat. No. 5,863,306
in which a pattern is embossed on a surface of a layer comprising a
radiation-curable binder having abrasive particles dispersed
therein after the surface of the layer has been modified to
increase its viscosity but before curing of the binder has been
initiated.
[0011] The present invention presents a technique for tailoring the
formulation formed into patterns to generate grinding properties
that vary with the degree of wear the coated abrasive has
experienced.
[0012] The present invention therefore provides a flexible and
effective route for the production of products uniquely suited to a
specific task such that multiple abrading/fining/polishing
operations can be avoided.
General Description of the Invention
[0013] The present invention provides a coated abrasive having a
patterned surface comprising a plurality of shaped structures
wherein each such structure comprises a curable binder with
abrasive particles dispersed therein wherein the improvement
comprises providing that the structures are layered such that, as
the structure is eroded during use, different properties are
revealed.
[0014] The term "shaped structure" is intended to convey a
structure having a defined contoured shape that is raised above a
backing surface upon which the structure is located. A "patterned
surface" is a surface comprising a plurality of such shaped
structures disposed on a backing surface in a repeating pattern
with each shaped structure having a height dimension above the
backing surface such that an initial contact plane is defined
parallel to the backing surface and passing through only the tops
of shaped structures. In preferred patterned surfaces at least 50%
of the tops of the shaped structures lie in the initial contact
plane. The shape of each "shaped structure" can be exactly
replicated either across the whole of the patterned surface or in a
number of groups of different repeating shaped structures, each
structure within a group being identical, in defined or randomized
patterns. Alternatively the shapes may be less exactly replicated
as would be the case if an instrumentality imposing the shape were
to be removed before the material shaped had completely lost the
ability to flow.
[0015] The layers which make up the shaped structures comprise a
curable binder and, dispersed therein, a particulate material. The
nature and/or the amount of the particulate material varies within
the shaped structure so as to achieve different properties at
different layers of the structure as indicated above.
[0016] U.S. Pat. No. 5,863,306 shows a form of this approach in
which the structures comprise abrasive particles dispersed in a
UV-curable binder and the concentration of the abrasive in the
surface layers of an abrasive structure is increased by comparison
with the rest of the structure by for example application to the
uncured binder/abrasive formulation surface a layer of a functional
powder which, during an embossing process to form the shaped
structures becomes at least partially incorporated into the surface
layer of the structure. The functional powder can be, for example,
abrasive particles or particles of a grinding aid or a mixture of
both. This approach is described generically in U.S. Pat. No.
5,833,724. In each case the size of the powder particles laid on
the surface was the same as or finer than or coarser than the
abrasive particles within the shaped structure.
[0017] It is also known to deposit layers of grinding adjuvants on
the surface of a patterned abrasive in the form of a supersize
layer or even a "diamond-like" layer. These are however layers
deposited on top of shaped structures rather than forming part of
the structures themselves as is the case in the present
invention.
[0018] The layers from which the shaped structures are built up
need not be separately identifiable in a cross-section but can in
fact merge into one another to give a gradual transition from one
to the next. This is in fact to be expected if the layers are laid
down sequentially while the layers below are still fluid. Each
layer preferably comprises a curable resin binder in which an
active component is dispersed. In this context an "active
component" is a component that fulfils a function such as an
abrasive, a grinding aid, a wear indicator, a filler, a cure agent
or an anti-static additive.
[0019] A major component of formulations from which the layers are
formed is the binder. This is a curable resin formulation
preferably selected from radiation curable resins, such as those
curable using electron beam, UV radiation or visible light, such as
acrylated oligomers of acrylated epoxy resins, acrylated urethanes
and polyester acrylates and acrylated monomers including
monoacrylated, multiacrylated monomers, and thermally curable
resins such as phenolic resins, urea/formaldehyde resins and epoxy
resins, moisture curable resins, as well as mixtures of such
resins. The preferred curing mechanism is through UV light with or
without the assistance of an additional thermal cure mechanism.
[0020] It is often convenient to have a radiation curable component
present in the formulation that can be cured relatively quickly
after the formulation has been shaped so as to add to the stability
of the shape. In the context of this application it is understood
that the term "radiation curable" embraces the use of visible
light, ultraviolet (UV) light and electron beam radiation as the
agent bringing about the cure. In some cases the thermal cure
functions and the radiation cure functions can be provided by
different functionalities in the same molecule. This is often a
desirable expedient.
[0021] The resin binder formulation can also comprise a
non-reactive thermoplastic resin which can enhance the
self-sharpening characteristics of the deposited abrasive
composites by enhancing the erodability. Examples of such
thermoplastic resin include polypropylene glycol, polyethylene
glycol, and polyoxypropylene-polyoxyethylene block copolymer,
etc.
[0022] Fillers can be incorporated into the abrasive formulation to
modify the rheology of formulation and the hardness and toughness
of the cured binders. Examples of useful fillers include: metal
carbonates such as calcium carbonate, sodium carbonate; silicas
such as quartz, glass beads, glass bubbles; silicates such as talc,
clays, calcium metasilicate; metal sulfate such as barium sulfate,
calcium sulfate, aluminum sulfate; metal oxides such as calcium
oxide and alumina bubbles; and aluminum trihydrate.
[0023] The abrasive particles can be selected from those typically
used is such products including fused alumina, sintered alumina,
alumina-zirconia, silicon carbide, diamond, CBN and for
applications such as polishing or buffing or the finishing of
optical or electronic surfaces, gamma alumina, silica or ceria.
Other additives that might be added included grinding aids which
usually contain components that, under grinding conditions,
liberate chemicals that render the surface more susceptible to
abrading. Typical compounds liberate halogens or halogen acids or
sulfur oxides. Other possible components include: 1)
fillers--calcium carbonate, clay, silica, wollastonite, aluminum
trihydrate, etc.; 2) grinding aids--KBF.sub.4, cryolite, halide
salt, halogenated hydrocarbons, etc.; 3) anti-loading agents--zinc
stearate, calcium stearate, etc., 4) anti-static agents--carbon
black, graphite, etc., 5) lubricants--waxes, PTFE powder,
polyethylene glycol, polypropylene glycol, polysiloxanes etc.
[0024] The shaped structures preferably used in the coated
abrasives forming part of this invention typically are widest at
the base and decrease in cross-section with distance from the
substrate upon which they are deposited. Thus as the structure
erodes, a larger grinding surface is exposed. In products according
to the prior art the size of the abrasive grits remains unchanged
and this means that the grits in the lower portion of the
structures will not work quite so efficiently as the individual
pressure on each grit will be reduced. This is inefficient and can
lead to variations in cut rate during use. The present invention
avoids this result by tailoring the composition of the lower levels
to ensure that the desired cut rate and the desired finish can be
obtained efficiently in a single operation.
[0025] The pattern in which the shaped structures are arranged can
comprise isolated islands of formulation, or a pattern of ridges
separated by valleys or a plurality of connected ridges. The
patterns are generally designed to provide an abrasive product with
a plurality of abrading surfaces, (that is portions of the pattern
that contact the surface of the workpiece when the abrasive product
is in use), that are more or less equidistant from the backing.
Obviously the total area of abrading surface increases with erosion
of the layer unless the formation has uniform width from the
backing to the abrading surface. Between the abrading surfaces,
channels allow circulation of grinding fluids and removal of swarf
generated by the abrasion. Channels also allow for momentary
cooling before the surface is contacted by the next abrading
surface.
[0026] The surface structures of the coated abrasive of the present
invention can be created by any process adapted to the shaping of a
structure whose composition varies with distance from the backing
surface. Thus a process in which a sequence of horizontal layers of
varying composition is deposited on a surface of a backing material
and thereafter a shape is imposed on the layers to give a patterned
surface, is in accordance with the present invention. Such
imposition could be by molding the deposited layers. The molding
process referred to above could also include a process in which the
consecutive layers are deposited through a mask on the surface of
the backing which remains in place until the binder components of
the layers have been cured.
[0027] The structures can also be formed by an embossing process
accomplished using an embossing tool such as a plate forced into
contact with the layer of formulation or, often more simply, the
tool can comprise a roller with the desired pattern engraved on its
surface which when contacted with the slurry formulation imposes
the reverse of the pattern engraved on the surface.
[0028] Another means of forming the structures includes the
technique known as "free-forming". In free-forming the final
structure is built up in a sequence of deposited layers with the
pattern of deposition being controlled to result in a structure
having the desired shape. By varying the composition of the
material deposited in sequential layers a product according to this
invention can be obtained.
[0029] Yet another forming mechanism employs a substrate that is
contoured, that is to say has a relief pattern formed on its
surface for example by an embossing process. Layers deposited on
this contoured surface would then adhere to the contours to give a
pattern of shaped structures. Such a process is extremely versatile
since the pattern on the substrate can be varied readily and the
need for a very hard, abrasion resistant tool to impose a shape in
a highly abrasive material would be avoided. To avoid the problem
of the formulation comprising the layer collecting in the spaces
between the shapes on the patterned backing, it is desirable to
deposit each layer in the form of an extruded film that adheres and
conforms to the surface of the patterned backing or the most recent
layer previously deposited thereon.
DESCRIPTION OF DRAWINGS
[0030] FIGS. 1-4 are SEM photographs, taken at 50x magnification,
of cross-sections of abrasive sheets made according to the
invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0031] The present invention differs from the prior art approaches
in which a shaped structure is given a surface coating of a
different composition. According to the present invention the
composition of the actual shaped structure is varied so as to yield
different characteristics as wear progresses. A preferred way in
which this can be done is by decreasing the size of the abrasive
particles in the lower portion of the structure. In this an initial
rapid aggressive cut as a result of the use of a relatively coarse
grit at the surface, (which would produce a relatively rough
finish), would be followed by a polishing action as a result of the
use of much finer abrasive particles in the layers exposed after
erosion of the upper layers of the structure.
[0032] Alternatively and sometimes preferably the grains closer to
the backing can be made coarser to make the cut rate at constant
applied pressure more uniform with the more aggressive cutting
larger grits compensating for the larger contact area as the
abrasive structure wears down.
[0033] Besides varying the abrasive characteristics of the coated
abrasive as erosion of the structure proceeds by changing the grit
size, it is also possible to include additives in the lower levels
having specific properties. For example it is possible to provide
that the lower layer comprise a conductive material such as carbon
black or graphite to inhibit the build up a static electricity
during abrading.
[0034] It is also possible to incorporate in the lower levels of
the structure an erodable filler to ensure that abrasive particles
in that part of the structure are part of a more open structure
that permits the particles to work more efficiently.
[0035] The use of conventional patterned coated abrasive structures
is rarely continued until the backing is exposed such that it is
often useful and economic to provide that the lowest levels, whose
function is merely support for the upper levels, comprises no
abrasive at all or alternatively a lower quality and/or less costly
abrasive or even only a filler.
[0036] It is also a useful variation to provide that the different
layers of the structure have a different color such that the state
of wear of the abrasive structure can be readily determined by
visual examination.
[0037] Where the finished structure comprises a cured binder
material, it is often convenient to include cure initiators or
catalysts in amounts that reflect the distance from the source of
the curing mechanism. For example if the binder is a UV-curable
resin and the overall thickness of the structure is significant, it
can be convenient to include in the lower levels a higher level of
initiator or perhaps an initiator that is responsive to the heat
generated during cure of the upper levels. The objective is to
ensure complete cure throughout the shaped structure and all
additive/initiator variations that promote this objective are
within the intended scope of this invention.
[0038] The invention is now described with particular reference to
the Drawings. Examples 1-4 below detail the production of the
products illustrated in FIGS. 1-4 respectively.
General Process Operations
[0039] A cloth substrate was prepared and a first layer of a slurry
comprising fused alumina abrasive grain dispersed in a UV-curable
binder formulation, (a resin mixture of 30% Ebecryl 3700 acrylated
epoxy oligomer and 70% TMPTA monomer with 4% Irgacure 819
photoinitiator based on the resin weight), was deposited on the
substrate using a knife blade coater with a gap of 10 mil, (0.25
mm). A second layer of slurry was then deposited over the first
layer. The second layer contained abrasive particles of a different
size from those in the first layer. The curable binder formulation
was however the same and the deposition technique was the same
except that a gap of 20 mil, (0.51 mm) was used.
[0040] A surface layer of abrasive particles was then deposited on
top of the second layer. The particle size in this layer can be the
same as one of the previous layers or different.
[0041] The surface was then embossed using a rotogravure roll
engraved with a 25 lines per inch trihelical pattern and the
embossed surface was immediately subjected to UV cure conditions
using a 400 W/inch "V" bulb and a 300 W/inch "D" bulb at a speed of
50 ft/minute.
[0042] The UV-cured, abrasive-containing layers of the samples were
then peeled from the substrate and a cross-section made and
polished for SEM photography. In some cases this resulted in minor
damage to the first layer, especially where the first or lower
layer comprised a very fine grit particulate material such as in
Examples 1 and 2 as shown in FIGS. 1 and 2.
EXAMPLE 1
[0043] First layer: 7 micron alumina in a 68% solids slurry.
[0044] Second layer: 97 micron alumina in a 70% solids slurry
[0045] Surface Powder layer: 97 micron alumina.
[0046] In FIG. 1 it is possible to distinguish clearly the first
layer from the second but the surface powder layer can not readily
be distinguished from the second layer except by the absence of
binder all round the grains on the surface.
EXAMPLE 2
[0047] First layer: 20 micron potassium fluoroborate in a 65%
solids slurry.
[0048] Second layer: 97 micron alumina in a 70% solids slurry
[0049] Surface Powder layer: 97 micron alumina.
[0050] In FIG. 2 it is possible to distinguish the KBF4 layer
wherein the particles are darker but again the second layer and the
powder layer, having the same abrasive particles included are
distinguished only by their location at the surface of the binder
layer.
EXAMPLE 3
[0051] First layer: 97 micron alumina in a 70% solids slurry.
[0052] Second layer: 7 micron alumina in a 68% solids slurry
[0053] Surface Powder layer: 7 micron alumina.
[0054] FIG. 3 shows the cross-section of this product.
EXAMPLE 4
[0055] First layer: 97 micron alumina in a 70% solids slurry.
[0056] Second layer: 7 micron alumina in a 68% solids slurry
[0057] Surface Powder layer: 97 micron alumina.
[0058] FIG. 4 shows the delineation of the various layers quite
clearly by virtue of the different sizes.
* * * * *