Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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ABRASIVE MATERIAL AND METHOD OF FORMING SAME
FIELD OF THE INVENTION
The present invention relates to an abrasive material produced by an etching
process and suitable for sanding or smoothing a variety of surfaces and to a
method
of forming the abrasive material.
BACKGROUND OF THE INVENTION
Various abrading surfaces have been suggested over the years. Such
surfaces include those wherein abrasive particles such as garnet, aluminum
oxide,
silicon carbide, grit of zirconia and alpha aluminum oxide monohydrate, single
crystals of diamond or cubic boron nitride are adhered to a substrate. Also
known
are abrasive surfaces which are scored to provide grooves or punched to
provide
holes or openings with projections or burs surrounding the holes. Where
grooves
have been formed in metal sheets such as steel sheets, coating the surface or
the
cutting edge formed by the goove are also known. Metal abrasive sheets are
known which are prepared by forming a cured polyvinylchloride negative master
using a sheet of sandpaper and, then, electroplating the master to form the
sheet.
Etching processes using a suitable resist to form a desired pattern in a metal
substrate are also known. In one such technique, a resist pattern is applied
to a thin
flat steel plate in a predetermined pattern such as equal sized spots which
can be
round, elongate or polygonal. The plate is etched which an etchant such as an
aqueous solution of ferric chloride to remove the desired amount of metal and
form
the pattern elements. It is reported that through variations of spraying mode,
composition and temperature of the etching solution, the angle between the
side of
the protruding cutting elements and the original plate surface, as will as how
far
under the edge of the protecting pattern elements the etching will reach. One
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improvement suggested is to provide parallel ridges on the etched side of the
plate
in the form of rhombic quadrangles either tangentially or helically to prevent
the
plate from curling.
Another improvement suggested is a resist pattern which is reported to give
an even intermixing of fast working sharp points with smooth planing edges.
The
cutting teeth are formed in the shape of triangles or squares which come out
of the
etch process still sharp and usable due to the resist pattern which
accentuates the
corner points and eliminates under cutting of the upper surfaces of the
cutting teeth.
Each tooth bears an upper flat surface and is amenable to hardening by heat
treating
without excessive brittleness due to the tooth configuration. The upper flat
surface
of each tooth is reported to be typically about 3 mils with the width of the
base and
the height of the tooth being about twice that of the upper flat surface.
A process for producing cutting dies, particularly for use such as, for
example, cutting adhesive tape to form labels, has been disclosed wherein
multiple
etching steps are used. A resist corresponding to the contour of a label to be
propertied is formed on a steel plate and a first etching step is carried out,
thereby
forming a convex portion of a prescribed height. A second etching step is
carned
out whereby the resist extending from both sides of the top off the convex
portion is
removed and the steel plate is subjected to further etching. This second
etching
step may be carried out multiple times. The resist remaining on the top of the
convex porrion is then removed.
SUMMARY OF THE INVENTION
The present invention, in one aspect, provides an abrasive material
comprising a base surface having a plurality of pyramidal shapes protruding
therefrom the base surface and the protrusions being formed of the same
material,
each protrusion having a substantially triangular, square, or polygonal base
and
triangular sides which meet at an apex which substantially forms a point, the
protrusions providing intermixing cutting and planing edges in a pattern such
that
the material is capable of abrading independent of direction of use and a
coating
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applied to the base surface and protrusions to improve abrasive performance
and
reduce surface porosity.
The coating applied to the base surface and protrusions to improve abrasive
performance and reduce surface porosity can vary widely. Typical coatings
include
nickel or chrome plating or a diamond coating or plating in combination with
diamond dust or boron nitride. The surface of the protrusions can optionally
be
heat treated to improve hardness as is well known to those skilled in the art.
Preferably, the triangular sides of the pyramidal protrusions have an inward
arctuate slope. Such a slope provides greater longevity of the abarsive
material due
to lack of loading of material being abraded. The present invention provides
rapid
material removal from a workpiece, yet leaves a smooth surface on workpiece.
The
abrasive material of the invention can be provided with protrusions on both
surfaces
of the base material to prevent curling when the material is thin.
The present invention, in a further aspect, provides a method of forming an
abrasive material comprising the steps of
(a) providing a base material;
(b) applying to at least one surface of the base material a photoresist
coating;
(c) placing over the photoresist a mask having a randomly directional
triangular, square or polygonal pattern thereon;
(d) applying an etchant suitable for etching the base material for a time
sui~cient to provide a plurality of pyramidal protrusions on the base surface
each protrusion having a substantially triangular, square or polygonal base
and triangular sides which meet at an apex which substantially forms a point;
(e) removing the mask and the unexposed photoresist from at least the
etched surface;
(fj applying a coating to the surface to reduce surface porosity and improve
abrasion performance.
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BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. la, lb, and Ic are perspective views of pyramidal protrusions useful
in the invention.
FIG. 2 is a perspective view of a preferred pyramidal protrusion of the
invention having inward arctuate triangular sides.
FIG. 3 is a top view showing a suitable pattern of pyramidal protrusions for
use in the abrasive material of the present invention.
FIG. 4a is a top view of a photoresist pattern suitable for use in producing
an abrasive material of the invention.
FIG. 4b is a top view of an enlarged portion of the photoresist pattern
shown in FIG. 4a.
FIG. 5 is side view of a pyramidal protrusion useful in the invention having a
hard coating thereon.
FIG. 6 is a fragmented cross-section of an abrasive material of the present
invention having pyramidal protrusions on each surface thereof.
DETAILED DESCRIPTION OF THE INVENTION
The abrasive material of the invention can be formed from any material
susceptible to etching including, for example, stainless steel, carbon steel,
aluminum
alloys, iron-nickel-chrome alloys, and titanium; boron-filled eiastomers,
silica
composites, fluorocarbon materials, graphite alloys, plastics, and the like.
The
thickness of the material is not particularly limited, but after etching
should be
suitably flexible where it will be used over a roller or suitably stiff when
used as a
flat abrasive. Of course, stiffness can be provided, if necessary, by
attachment to a
stiff substrate such as, for example, a metal plate or synthetic resin plate
having
suitable stiffness.
With respect to the drawings, like references rn~mber will be used with
reference to like parts. FIGS. la, Ib, and lc depict various possible
embodiments
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of the pyramidal protrusions of the abrading material of the invention with
the bases
of the pyramidal protrusions being triangular, square and pentagonal,
respectively.
Of course, other polygonal shapes can be used. In FIG. 1 a, protrusion l0a is
shown
having triangular base 12a, triangular side 14a, and apex 16a. In FIG. lb,
protrusion lOb is shown having square base 12b, triangular side 14b and apex
16 b.
In FIG. lc, protrusion lOc is shown having polygonal base 12c, triangular side
14c
and apex 16c.
The apex of each protrusion need not form a true point as shown in the
FIGS., although this is the preferred configuration. The apexes of the
protrusions
may be slightly rounded or flat. However, this portion of the apexes should
preferably be no greater in width than 20 percent of edges L, more preferably
no
more than 10 percent of edges L, edges L being shown in FIG. 5.
The depth of the inward arctuate slope on the triangular sides of the
pyramidal protrusions which are found in the preferred embodiments of the
invention can be from very slight, e.g., 1 Eun, to as great as about 175 pln.
Such
arctuate slopes can readily be seen in FIGS. 2 and 3 wherein protrusion 20 has
arctuate sloped surfaces 22. The greater the size of the protrusions, the
deeper the
inward arctuate slope can be formed.
Preferably, the height H of the pyramidal protrusions from the etched
surface can be in the range of about 25 ~m to 1.5 mm, with higher pyramidal
protrusions for normal coarse abrading, i.e., from about 125 N,m to 375 pm,
and
lower pyramidal protrusions for finer abrading, i. e., from about 75 pm to 125
p,m.
The length of the edges L of the base is dependent on the height of the
protrusions.
Preferably, the ratio of the height of the protrusions from the etched surface
to the
length of the edge of the base is in the range of about 1:1 to 1:5, more
preferably
about 1:2 to 1:4, most preferably about 1:3. The thickness of the remaining
base
material B can vary widely and is not critical, with thinner base materials
being used
for more flexible abrasive materials and thicker base materials being used for
stiffer
abrasive materials as is well known to those skilled in the art. Such
dimensions are
indicated in the enlarged view of a portion of a hard coated abrasive
material, seen
in cross-section in FIG. 5.
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The spacing S of the pyramidal protrusions can also vary widely, from about
0.75 mm to 30 mm apart, as measured from center to center of the circular
pattern,
with geater spacing for coarse abrading, i.e., 2 to 10 mm or more apart and
less
spacing for finer abrading, i.e., from about 0.75 to 1.5 mm apart. A resist
pattern
suitable for a medium abrasive grit is shown in FIG. 4a. An enlarged portion
of the
resist pattern is shown in FIG. 4b to demonstrate the detail of the pattern.
The fineness or coarseness of the abrasive material can also be adjusted by
maintaining the height of the protrusions and the length of the base of the
protrusions and adjusting the size of the resist pattern. Greater spacing
between the
protrusions provides coarser abrading material, while lesser spacing between
the
protrusions provides finer abrading material.
It is important that the pyramidal protrusions be oriented such that the
cutting edges of the individual protrusions are oriented in different
directions to
provide the capability of abrading independent of direction of use. The
pyramidal
protrusions can be randomly oriented in various directions such as by
designing the
etching mask through the use of a computer-based random generator or an
etching
mask can be patterned which ensures random orieiltation as is well known to
those
skilled in the art. An example of a randomly oriented pattern is shown in
FIGS. 4a
and 4b. In FIG. 4a, a portion of mask pattern 40a is shown with spacing S. In
FIG.
4b, an enlarged portion of a preferred mask pattern is shown in geater detail
with
cured resist portion 42 providing the desired protrusions after etching.
As previously described, a coating such as nickel or chrome plating; a
diamond coating; or nickel or chrome plating in combination with diamond dust
or
Teflon~, tungsten, carbide or boron nitride particles can be applied to the
surface of
the abrasive material such as is shown in FIG. 5, wherein a portion of
abrasive
material 59 has protrusion 52, remaining base material 54, and coating 56.
The etching process can be carried out using well-known resist and etching
materials. The resist can be applied using, for example, hot roll lamination,
screen
printing, gavure printing, dip coating and the like. For example, when the
substrate
is stainless steel, carbon steel, or the like, suitable etchants include
ferric chloride,
hydrochloric acid, nitric acid or mixtures thereof; for aluminum or aluminum
alloys,
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suitable etchants include sodium hydroxide; for titanium, suitable etchams
include
hydrofluoric acid; and plastics are generally etchabie using various acids.
The
degree of etching can be adjusted by altering the concentration and
temperature of
the etchant solution and the method of application as is known to those
skilled in
the art. For example, when the base material, or substrate, is stainless
steel, an
aqueous ferric chloride solution of about 42° to 50° Baume can
be used, the lower
the Baume of the solution, generally the more srctuate the slope of the sides
of the
protrusions.
After etching, the resist can be removed by techniques well known to those
skilled in the art. Alternatively, the resist can be retained on the surfaces
of the
sheet material, particularly on the non-abrasive side of the material when
only one
side is masked and pattern etched, which aids in prevention of curling. A
suitable
method of preventing curling involves etching both surfaces of the base
material as
shown in FiG. 6, wherein abrasive material 60 has protrusions 62 on each
surface
I S 61, 63 extending from the remaining base material 64.
Objects and advantages of this invention are further illustrated by the
following examples, but the particular materials and amounts thereof recited
in
these examples, as well as other conditions and details, should not be
construed to
unduly limit this invention. All parts and percentages are by weight unless
otherwise indicated.
EXAMPLES
Example 1
A stainless steel sheet about 250 lun thick was rinsed with dilute nitric acid
and rinsed with water to remove any oils present on the surface. A
photoresist,
AX15 available from Morton Co., was coated on the surface to produce a dried
coating about 39 Irm thick. A mask having a pattern similar to that of FIG.
4a, but
transparent in the areas shown as being dark, was placed over the photoresist.
This
composite was exposed to ultraviolet light to effect cure of the photoresist.
The
mask was removed and the unexposed photoresist was removed by rinsing with
Developer KB lA, available from Morton Co., leaving a mask pattern similar to
that
of FIG. 4a. An aqueous ferric chloride solution about 42° Baume was
applies to
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the surface by spraying for about 11 minutes at about 50°C to effect
etching of the
exposed steel surface. The etched sheet was rinsed with water to suspend
etching.
The pyramidal protrusions had a triangular base, each edge of which was
about 400 Nxrl. The height of the protrusions was about 150 p,ln with inward
arctuate faces with maximum indentations of about 25 Vim. The resulting sheet
had
only a slight tendency to curl due to the resist being allowed to remain on
the non-
etched surface. When restrained in a flat position, the resulting sheet
performed
excellently in a manner similar to 180 grit sandpaper, but without loading
problems
typical with sandpaper.
A portion of the sheet was plated with chrome to achieve a chrome
thickness of about 5 p,m. This product exhibited excellent abrasive
performance
with little loading and good longevity.
Example 2
An abrasive stainless steel sheet was prepared as in Example 1, except both
surfaces of the stainless steel sheet were treated to provide pyramidal
protrusions
therein. Abrasive performance was found to be excellent and the sheet
exhibited no
curling.
Various modifications and alterations of this invention will become apparem
to those skilled in the art without departing from the scope and spirit of
this
invention, and it should be understood that this im~e~ion is not to be unduly
limited
to the illustrative embodiments set forth herein.
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