Note: Descriptions are shown in the official language in which they were submitted.
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ABRASIVE SHEETING HAVING INDIVIDU~LLY
POSITIONED ABRASIVE GRANULES
Background of the Invention
Field of the Invention
The invention concerns abrasive sheeting or
coated abrasives of the type having a backing which usually
is flexible and carries abrasive grains or granules
embedded in a binder layer and usually is flexible.
Description of the Related Art
At least as early as l90S, as taught in U.S.
Patent No.7~4,495 (Gorton), it was discovered that unbroken
"abrading surfaces soon become clogged and gummed by the
fine grit and minute particles worn from the abrading
surface and from the metal-work (or other work) being held
to the abrading-surface" and that these materials can be
carried away more effectively by applying the abrasive grit
in a dot pattern. In U.S. Patent No. 1,657,784
(8ergstrom), a dot pattern is obtained by applying a binder
to a backing, applying abrasive grains or granules to the
binder, and then scraping off portions of the binder and
adhered abrasive granules. More commonly, an adhesive is
applied in a dot pattern so that the abrasive granules
25 adhere only in that pattern. In U.S. Patent No. 4,317,660
(~ramis et al.), the adhesive dot pattern is obtained by
applying the adhesive through stencil holes. After
attracting a large number of abrasive granules to each dot,
the abrasive granules are covered with a size coat.
In abrasive sheeting that has appeared on the
market with such a dot pattern, there is a heap or a pile
of abrasive granules at each dot, and that heap of granules
is covered with a size coat. Because the height of each
heap is more or less random, the individual heaps and the
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individual granules of each heap are loaded differently and
hence produce uneven cutting. The size coat interferes
with the cutting action of the abrasive granules and also
results in uneven cutting due to variations in the extent
to which the size coat covers the abrasive granules.
Uneven cutting of prior abrasive sheetings also
emanates from irregular sizes and shapes of their abrasive
granules. This effect has been minimized by using
spherical granules of equal size. Another type of
spherical abrasive granule consists of a large number of
abrasive grains in either an organic or inorganic matrix.
Because of their uniformity, such composite granules renew
themselves as they wear away, thus maintaining relatively
uniform abrasive cutting action for longer periods of time
than has been possible when using abrasive sheeting coated
with irregular abrasive granules. Such composite abrasive
granules are disclosed in U.S. Pats. No. 3,916,584 ~Howard
et al.); No. 4,112,631 (Howard); and No. 4,541,842
tRostoker). U.S. Pat. No. Re. 29,808 (Wagner) shows hollow
balls consisting of abrasive grains bonded onto the outer
surface of a friable matrix. Even though Fig. 1 of the
Wagner patent shows those spheres uniformly po~itioned in a
binder layer, the patent says that the hollow balls "are
mixed with a bonding material and brought into the shape of
the grinding body, after which the bonding material is
allowed to harden out, and during the production of an
abrasive belt the hollow bodies are bonded in the usual
manner to a base material" (col. 6, lines 43-48). In
Example 1, ready-prepared abrasive grain balls are
uniformly strewn onto a layer of resin on a cotton twill
fabric.
Even when prior abrasive sheetings employ
composite spherical granules of equal size, sheetings made
at one time tend to have different cutting rates than do
those made at other times due to variables in their
manufacture. Accordingly, when prior abrasive sheetings
have been used under numerical or robotic contcol, it has
~29~9*0
been necessary to test the cutting rate of each jumbo roll
before putting it to use.
Abrasive sheeting ordinarily is manufactured in
great lengths that are wound into rolls for storage and
shipment. Eventually, the sheeting is die-cut into desired
sizes and shapes. For example, it may be cut to form daisy
pads that are used to polish lenses. In doing so, the die
contacts the abrasive particles which cause its cutting
edge to become dull and to require resharpening within a
short period of time.
Other Prior Art
Abrasive tools are often made by handsetting
abrasive granules such as diamonds, but such granules are
quite large. It is believed that handsetting has never
15 been employed in abrasive sheeting that has appeared in the
market.
U.S. Pat No. 4,536,195 (Ishikawa) concerns a
method of making grinding stones, the abrasive grains of
which are distributed in a controlled manner so that the
20 load working on each grain is even, making the stone more
efficient and of longer life. In a first variation of the
Ishikawa method, an electrically conductive pattern is
formed on a resinous binder sheet which is then immersed
into an electroplating path containing metallic ions mixed
25 with abrasive grains that are attracted to the pattern.
The electrically conductive pattern may be formed by
photoetch~ng or printing techniques. A number of the
abrasive-bearing sheets are placed in layers and molded
into a grinding stone by warm or hot pressure molding.
30 Another variation is the same as the first except that the
sheet is metallic and a surface is masked so that the
abrasive grains are attracted only to the unmasked areas.
An example of distribution of abrasive grains on the
surface of a grinding stone is shown in Fig. 15 wherein the
35 grains are located in rows and uniformly spaced from
adjacent grains.
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Summarv of the Invention
The invention provides abrasive sheeting or coated
abrasive that can produce finer finishes at faster cutting rates
than could be attained in the prior art. Furthermore, the novel
abrasive sheeting is believed to provide a more predictable
cutting rate, thus minimizing the need to test its cutting rate
before using it in robotic or numerically controlled machines.
Briefly, the abrasive sheeting of the invention has a
backing carrying a binder in which abrasive granules are strongly
bonded and lie substantially in a plane and at a predetermined
lateral spacing. The granules should be of substantially equal
size, i.e., the mean dimension of 90~ of the granules should
differ by less than 2:1. Each of the abrasive granules should
pass a screen with 300 ~m openings, because substantially larger
granules would not provide the fine flnishes desired in uses for
which the novel abrasive sheeting is intended.
According to one aspect of the present invention there
is provided abrasive sheeting comprising a backing carrying a
binder layer of substantially uniform thlckness in which abraslve
granules are strongly bonded and lie substantially in a plane and
at a predetermined lateral spacing, said granules being of
substantlally equal size and passing a screen with 300 ym
openings, and a portion of virtually every granule protruding from
the surface of the binder layer.
According to a further aspect of the present invention
there is provlded abrasive sheeting comprlsing a backing carrying
a binder layer in which abrasive granules are bonded and lie
substantially in a plane and at a predetermined lateral spacing,
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1298980
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said granules being of substantially equal size and passing a
screen with 300 ~m openings, a portion of virtually every granule
protruding from the surface of the binder layer, and a size coat
covering the granules and binder layer.
According to another aspect of the present invention
there is provided abrasive sheeting comprising a backing carrying
a binder layer of substantially uniform thickness in which
abrasive granules are strongly bonded and lie substantially in a
plane, said granules being of substantially equal slze to pass a
screen with 300 ~m openingx, the granules having individual
positions that are uniformly spaced laterally, there being only
one granule at almost every position.
According to a still further aspect of the presen~
lnvention there is provided method of making abrasive sheeting
comprising a backing carrying a binder layer in which abrasive
granules of sub6tantially uniform thicknesses are individually
embedded in a predetermined pattern, said method comprising the
steps of
1) coating one face of a metal foil with rubber and
the other face with a photoresist,
2) exposing the photoresist to light in a
predetermined pattern,
3~ removing areas of the photoresist corresponding to
said pattern,
4) removing areas of the metal foil, to expose the
rubber in said pattern,
5) attracting abrasive granules to the exposed rubber
areas,
12~81D
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6) while moving the tacky binder layer in synchronism
with the exposed rubber areas, pressing the attracted granules
into the binder layer in said pattern, and
7) rendering the binder nontacky, thereby producing
abrasive sheeting, the individual abrasive granules of which lie
in said pattern.
The granules preferably are in a predetermined pattern
~or patterns when using granules of differing sizes or types) that
provides spaces between the granules of sufficient width to carry
off detritus. In a preferred pattern, single granules are
uniformly spaced and aligned in rows extending both longitudinally
and transversely (i.e., ln the X and Y directions). In another
preferred pattern, abrasive sheeting having circular rows of
uniformly spaced granules can be cut into discs, the centers of
which are concentric with the circular rows.
Preferably the abrasive granules are equiax, and the
dlameter of substantially every granule is within 10% of the mean
diameter so that the granules protrude from the surface of the
blnder layer to substantlally ~the same extent and so can be loaded
equally upon contactlng a workplece, thus providing an extra-
ordlnarlly unlform finish. By "equiax" is meant that each granule
has approximately the same thickness is every direction. An
., ,
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equiax granule can be considered to have a diameter,
whether or not it is spherical.
The abra ive granules can have various
populations at various areas of the novel abrasive sheeting
in order to remove material at differing rates from
selected faces of a workpiece. In one technique for
determining the populations required to accomplish this,
the wear of abrasive sheets of uniform density is studied,
and the novel abrasive sheeting is made to have increased
granule population at areas showing the most wear. The
predetermined granule pattern also can be selected to leave
the novel abrasive sheeting free from abrasive granules in
areas to be die-cut, thus allowing the die to remain sharp
much longer than has heretofore been possible. This also
minimizes waste.
The invention also concerns a novel method of
making abrasive sheeting by the sequential steps of
l) attracting small abrasive granules only to
dots in a predetermined pattern on a carrier,
2) while advancing a backing that carries a
tacky binder layer in synchronism with said carrier,
transferring the attracted granules into the binder
layer in said pattern, and
3) rendering the binder nontacky.
When the carrier is at the surface of a rotating cylinder,
this 3-step method can produce abrasive sheeting of almost
unlimited len~th which can be wound up in roll form for
convenient storage and shipment. In such a roll, the
predetermined pattern of abrasive granules repeats many
times. Such a roll can be converted into a variety of
articles such as discs, daisies, sheets, and belts.
When the abrasive granules have irregular shapes,
the 3-step method causes the major axis of each granule to
lie substantially in a plane parallel to the backing.
Hence, when irregular granules are of substantially the
same size, they tend to protrude from the binder to
substantially the same extent and to abrade uniformly to
afford uniform finishes.
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Preferably the binder is selected so that
subsequent to step 2) is an a~ditional step of softening
the binder, usually by being heated, to form a meniscus at
each granule, thus enhancing the bonding of each granule to
the backing. Doing so should make it unnecessary to
overcoat the granules, thus leaving the cutting surface of
each granule free from material that could otherwise
interfere with its abrasive function. When heat is used to
form menisci, the extent to which the abrasive granules
protrude from the binder can be controlled by adjusting the
time and temperature at which the menisci are formed. When
a meniscus is to be formed at each abrasive granule, the
pressure applied in step 2) can be very light, just enough
to tack the granules to the binder layer.
Instead of, or in addition to, forming a meniscus
15 at each granule, a size coat can be applied over the novel
abrasive sheeting to enhance the bonding of the abrasive
granules. Usually this is unnecessary, unless the abrasive
granules are rather large, e.g., are retained by a screen
with 100 ~m openings. When the abrasive granules are
20 expensive, e.g., diamonds, a size coat may be desirable to
ensure that they are not dislodged and lost.
Although the individual abrasive granules that
lie in a predetermined pattern should be of substantially
equal size, selected areas of the novel abrasive sheeting
can have abrasive granules of one size in one predetermined
pattern while other areas have granules of a different size
in another predetermined pattern, each to provide a desired
rate of cutting and degree of finish at a particular area
of a workpiece. For the same reason, the novel abrasive
30 sheeting may employ abrasive granules of two or more
different types, each type being individually positioned in
a peedetermined pattern. In order to make abrasive
sheeting having two sizes or two types of abrasive
granules, steps 1) and 2) are repeated with the second size
or type of granule prior to step 3).
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Detailed Description
Each of the abrasive granules of the novel
sheeting preferably is an eql-iax composite of a large
number of abrasive grains in an inorganic or organic binder
matrix. For example, abrasive grains having a mean
dimension of about 4 ~m can be bonded together to form
spheres of virtually identical diameters, preferably within
a ranqe of from 25 to 100 ~m. secause of their uniform
diameter, each equiax granule can be positioned to protrude
to the same extent from the binder layer. By individually
positioning the e~uiax granules to be spaced equally from
adjacent granules, the granules each bear the same load and
hence wear at substantially identical rates and tend to
continue to be equally effective as long as uncoated
portions protrude from the binder layer. Consequently,
workpieces continue to be polished uniformly, in contrast
to the tendency of prior abrasive sheeting to provide
uneven polishing upon becoming worn.
Preferably the thickness of the binder layer of
the novel abrasive sheeting is from 25 to 150 ~m.
Thicknesses above that range may be uneconomical, while
thicknesses below that range may not bind the abrasive
granules as strongly as desired. When the binder layer is
coated from solution or emulsion, it may be difficult to
obtain uniform layers much greater than 50 ~m.
A carrier that can be used in the above-outlined
3-step process is a printing plate marketed by Toray
Industries as "Toray Waterless Plate." It has a flexible
sheet of aluminum bearing a layer of photosensitive
material covered with a layer of silicone rubber. Upon
exposure to light through a half-tone screen, the silicone
rubber of a positive-acting plate causes the photosensitive
material to bind itself firmly to the silicone rubber in
areas where the light strikes, after which the silicone
rubber in unexposed areas can be brushed off, leaving
silicone rubber dots in the predetermined pattern provided
by the light exposure. The printing plate is then wrapped
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onto a cylinder, and the cylinder is rotated through a
fluidized bed of abrasive granules. The granules are
attracted to the printing plate only where the silicone
rubber remains and not to the ink-receptive areas. Upon
moving a binder-carrying backing in synchronism with the
rotating printing plate, the granules are picked up by and
become embedded into the binder layer in the pattern of the
printing plate. That pattern repeats many times when the
backing is long.
When a "Toray Waterless Plate" is used in the
above-outlined 3-step process and the tacky binder layer
would stick to the silicone rubber of the printing plate, a
transfer roll can be positioned between the binder layer
and the printing plate. The surface of the transfer roll
should be selected to cause the abrasive granules to
transfer from the silicone rubber of the printing plate,
while acting as a release surface in relation to the tacky
binder.
For most applications of the novel sheet, the
breadth of the dots formed in step 1) of the above 3-step
20 process should be small enough that only one abrasive
granule is attracted to each position, but when each dot is
large enough to make it fairly certain that there will be a
granule at every dot, it can be expected two or possibly
three granules will be deposited side by side at a few
positions. When only one abrasive granule per dot is
desired, each dot preferably is roughly circular and has a
diameter within the range of 30 to 90% of the mean
dimension of the abrasive granules. When using spherical
abrasive granules 80 ~m in diameter, good results have been
3 attained with dots 62 ~m in diameter. When the diameter of
each dot substantially exceeds the diameter of an abrasive
granule, a monolayer of several granules may be attracted
to each dot.
The use of a printing plate mounted on a cylinder
in the above-outlined 3-step process may result in a seam
that may produce discontinuities in the pattern of abrasive
9 ~ 9~0
granules. Abrasive sheeting of the invention, that has no
seam in its pattern, can be made by sequentially coating
onto a cylinder formulations that provide a cylindlical
printing plate, preferably including a silicone rubber
layer. Preferred sequential coating formulations are those
of U.S. Pat. No. 3,511,178 (Curtin).
If a seam in the pattern is not objectionable,
step 1) of the above-outlined 3-step process for making
abrasive sheeting of the invention can use a carrier
prepared by the steps of
1) coating one face of a sheet of metal foil
with rubber and the other face with a photoresist,
2) exposing the photoresist to light in a
predetermined pattern,
3) removing areas of the photoresist
corresponding to said pattern, and
4) etching away the metal foil in said areas to
expose the rubber in said predetermined pattern.
It is also preferred, particularly if the abrasive granules
would be attracted to the remaining photoresist, to include
2 after the etching step the step
5) removing the remaining photoresist.
Among classes of binders that can be used in the
novel abrasive sheeting are thermoplastic resins such as
25 ethylene/acrylic acid copolymer, polyethylene, and
poly(ethylmethylacrylic) acid, which is available from E.I.
du~ont Company under the trade designation "Surlyn".
Another useful class of binders is acrylic
pressure-sensitive adhesives which cure to a nontacky
30 state. Also useful are thermosetting binders which have a
tacky state such as epoxy resins, phenolics, and
polyurethanes.
The backing of the novel abrasive sheeting can be
f~bric (e.g., woven or non-woven fabric such as paper)
35 which may be saturated with a filled binder material, a
polymer film such as that formed of oriented heat-set
polypropylene or poly(ethylene terephthalate) which may be
-10- 12~?~39fi~
first primed, if needed, with a priming material, or any
other conventional backing material.
In the novel abrasive sheeting, the addition of a
grinding aid over the surface of the abrasive granules may
provide improved grinding performance. Grinding aids may
also be added to the size coat or as particulate material.
The preferred grinding aid is KBP4, although other grinding
aids are also believed to be useful. Other useful grinding
aides include NaCl, sulfur, K2TiF6, polyvinyl chloride,
polyvinylidene chloride, cryolite and combinations and
mixtures thereof. The preferred amount of grinding aid is
on the order of 50 to 300 g, preferably 80 to 160 g, per
square meter of coated abrasive product.
The Drawing
The invention may be more understandable by
reference to the drawing wherein:
Fig. 1 schematically shows a method of printing
abrasive granules onto a binder layer carried by a flexible
backing, thus providing preferred abrasive sheeting of the
20 invention;
Fig. 2 is an electronmicrograph showing abrasive
granules having been attracted to a tackified binder layer
using apparatus illustrated in Fig. 1;
Fig. 3 is an electronmicrograph showing a
25 fragment of abrasive sheeting of the invention made by
heating the intermediate product of ~ig. 2 to form a binder
meniscus at each granule; and
Fig. 4 schematically shows a fragment of an
abrasive sheeting of the invention after it has been cut to
form daisy pads.
I~ Fig. 1, attached to a rotatable, heated metal
cylinder 10 is a printing plate 12, the outer surface of
which has been developed to leave roughly circular rubber
dots 13. The cylinder is rotated through a fluidized bed
of spherical abrasive granules 14, each of uniform diameter
somewhat larger than the diameter of the rubber dots.
29~98()
After removing excess granules by suction at 15,
substantially one abrasive granule 14 adheres to each of
the rubber dots 13. Moving at the same speed as the
surface of the cylinder 10 is a flexible backing 16
carrying a heat-activatable binder layer 18 which is
pressed against the printing plate 12 by a heated nip roll
20. Heat from the cylinder 10 and rubber-covered nip roll
20 tackify the binder layer 18 to permit the attracted
granules 14 to be adhered superficially to the binder layer
18 in spaced rows extending in the X and Y directions as
seen in Fig. 2. In the upper left corner of Fig. 2, a few
abrasive granules have fallen out, leaving small craters in
the binder layer. The abrasive granules have been
deposited in the lower part of Fig. 2 at twice the density
of the upper part. At most positions, only one abrasive
granule has been deposited, but at a few dots, there are
two granules side by side.
Referring again to Fig. 1, the granule-bearing
backing 16 is passed across a bank of infrared lamps 22 by
which the binder is heated to wet the surfaces of the
abrasive granules, thus causing the binder layer to flow
and form a meniscus 23 around the base of each granule as
shown in the electronmicrograph of Fig. 3. This causes the
abrasive granule to become strongly bonded to the flexible
backing 16.
The resulting abrasive sheeting 24 of the
invention contains abrasive granules 14 individually
positioned to permit the sheeting to be die-cut into daisy
pads 26 as shown in Fig. 4. The abrasive granules have
been positioned in concentric rows such that their density
in areas 28 adjacent the outer edges of each petal is twice
the density at the central areas 30 of the daisy pad. The
abrasive sheeting from which the daisy pads 26 were cut was
left free from abrasive granules adjacent the phantom line
32 at the peripheries of the petals along which the
sheeting 24 is to be die-cut so that the die does not
contact any abrasive granules. ~y leaving the area 34
-12- 12Q ~ ~ ~O
between the daisy pads free from abrasive granules, no
granules have been wasted.
In the following examples, all parts are given by
weight.
5Example 1
Used to make abrasive sheeting of this example
were:
1) a negative-acting "Toray Waterless Plate" which
had been exposed to a half-tone screen to produce roughly
circular dots, each about 63 ~m in diameter and arranged in
rows extending parallel to both the lengthwise and
widthwise edges of the plate, 20 rows per inch (7.9 per cm)
in both directions;
2) spherical abrasive granules, each 80 ~m in
diameter and made of 77 parts Al203 grains having a mean
particle size of 4 ~m in 23 parts of a matrix based on
phenol-formaldehyde resin;
3) a long roll of biaxially oriented
poly(ethyleneterephthalate) polyester film 0.05 mm in
thickness bearing a 0.05 mm binder layer of
ethylene/acrylic acid copolymer.
The dot-containing plate was mounted on the metal
cylinder 10 of the apparatus shown in Fig. 1, and spherical
5 abrasive granules 14 were fluidized by a mechanical
v~brator and became attached to the silicone dots 13.
Excess granules were removed by suction at 15. The binder
layer 18 was heated by the rubber-covered nip roll 20 to
about 70C to become tacky so that the abrasive granules
transferred to it, with a force of 79 N applied to the nip
roll per c~ of width. Additional heating by infrared lamps
22 caused the binder to form a meniscus around the base of
each of the granules.
The exposed face of the polyester film backing of
35 the resulting abrasive sheeting was laminated with a
double-coated pressure-sensitive adhesive tape and this
composite was die-cut into daisy pads 7.6 cm in diameter
-13- lZ~8~8~
and similar in shape to the daisy pads 26 of Fig. 4 except
having six petals. The pads were used as a second fining
pad in the polishing of lenses formed of polycarbonate of
the type commercially available from PPG under the trade
designation CR39. A "Coburn" #506 cylinder machine was
used at a load of 20 pounds (89 N) with a water flood on
the high speed spindle setting. The test was conducted
using two types of lapping tools, a 6.25/8.25 dioptral and
a 2.12 dioptral. In both cases the amount of lens removed
after two minutes was measured. The results are in Table
I.
_xamples 2-6
Abrasive sheetings of Examples 2-6 were made as
in Example 1 except having different spacings of their rows
in both directions as indicated in Table I. Also in Table
I are results from using a "Control" daisy pad made with
the same spherical abrasive granules coated from slurry in
a manner used for current commercial production and having
about 870 granules/cm2. This granule density had been
20 selected based upon extensive experimentation for general
purpose use and was intermediate the granule densities of
the abrasive sheetings of Examples 3 and 4.
TABLE I
Rows Rows mm of lens removed in 2 mins
Ex. per inchper cm 2.12 d. lens 6.25/8.25 d. lens
1 20 7.9 0.001 0.000
30 2 40 15.7 0.091 0.058
3 65 25.6 0.025 0.07B
4 85 33.5 0.026 0.124
S 150 59.0 0.012 0.032
6 200 78.7 0.009 0.025
35 Control 0.026 0.056
-14- ~ Z9 ~ 9 ~O
Example 7
A negative-acting "Toray Waterless Plate" was
exposed to produce 63 ~m silicone rubber dots in rows
extending in the X and Y directions at a density of 65 rows
per inch (25.6 rows/cm). The plate was covered with the
spherical abrasive granules of Example 1, and excess
granules were then removed by turning the plate over and
tapping it. Examination of the plate showed that there was
at least one granule at each of the silicone dots. Against
those granules was laid the binder layer of the polyester
film backing of Example 1, and the composite was put
through the nip of a heated two-roll laminator at about
73C while a force of 79 N was applied to the nip roll per
cm of width. The composite was then placed in an oven at
112C for 10 minutes to cause the binder to form a meniscus
15 around the base of each granule, resulting in abrasive
sheeting of the invention.
~1
A round-dot litho contact screen was exposed to
20 form a pattern of spots, each 61 ~m in diameter and equally
spaced in rows extending in the X and Y directions. The
number of rows of spots per unit distance within an inner
circle 6.0 cm in diameter differed from the number of rows
between that circle and an outer circle 15.24 cm in
diameter. In other words, the spot population changed at
the junction of the two circles as it does in Fig. 2.
Several different combinations of populations were prepared
in this manner as shown in Table II.
A negative-acting "Toray Waterless Plate" was
exposed using each contact screen and developed in the
usual manner. The developed plate was mounted on a metal
cylinder and employed in the same way as in Example 1 to
transfer spherical abrasive granules 83 ~m in diameter from
a fluidized bed to create 6-petal daisy pads, the centers
-15- ~ Zg 89 ~O
of which coincided with the centers of the circles. The
daisy pads were tested as in Example 1 with results in
Table II in comparison to the same "Control".
TABLE II
5Inner Circle Outer Circle mm of lens removed _
Ex. Rows/cm Rows/cm 212 lens625/825 lens
8 19.7 33.5 0.034 0.040
9 25.6 19.7 0.108 0.086
25.6 33.5 0.058 0.102
10 11 25.6 39.4 0.070 0.103
Control 0.025 0.056
Example 12
A round-dot litho contact screen was exposed to
15 form an opaque spiral pattern using the standard formula X
- k~ and X ~ k~ + 0.317 mm, starting from a circle 2.1 cm
in diameter and extending to a circle 15.2 cm in diameter.
This produced opaque and transparent spiral areas of equal
size between the two circles. Then using the developed
20 contact screen as a mask, a laser was used to expose a
negative-acting "Toray Waterless Plate" through the
transparent areas of the mask to produce a pattern of dots
63 ~m in diameter equally spaced in rows extending in the X
and Y directions. There were 100 rows of silicone dots per
2 inch (39.4 dots/cm) within a spiral pattern on the
developed plate.
The developed plate was used as in Example 7
(except using abrasive granules 83 ~m in diameter) to
provide abrasive sheeting of the invention which was cut
3 into a disc on which was centered the spiral pattern of
abrasive granules in spaced rows.
Example 13
Abrasive sheeting was prepared as in Example 7
except as follows:
-16- 1 2~ 8 ~ 80
a) the abrasive granules were Al2O3 grains of
irregular shape which had been screened to pass 100 mesh
(150 ~m openings) and retained on 120 mesh (125 ~Im
openings);
b) there were 65 rows/inch (25.6 rows/cm) of
silicone dots;
c) the abrasive sheeting, after being removed
from the oven, was overcoated with a size coat of phenol-
formaldehyde resin which after curing in an oven had a dry
weight of 80 g/m2.
The backing of this abrasive sheeting was
laminated with a double-coated pressure-sensitive adhesive
tape and then die-cut to 3-inch (7.5 cm) discs. Each disc
was adhered by its pressure-sen!-itive adhesive to a
"Coburn" No. 507 cylinder machine using the following
settings: spindle stroke set at 7, spindle speed 100%,
cross stroke 0, and a load of 30 pounds (133 N). The
workpiece was a 1018 mild steel ring 4.45 cm I.D. and 5.4
cm ~.D. The ring was abraded in an operation normally
called flat lapping after being mounted on a bracket that
20 fixed it~ axis perpendicular to the abrasive surface as the
machine oscillated the abrasive surface in a circular
motion. The test was run in one minute cycles at a rate
endpoint of 0.3 g/min. The total cut and surface finish at
endpoint are given in Table III in comparison to a
"Control" made in the same way except that the abrasive
granule6 were coated from slurry to provide a binder layer
containing approximately the same mass of granules (i.e.,
about 0.40g).
TABLE III
Example Total Cut R~ (~m) Rt (~m)
13 2.94 g 0.30 2.87
Control 1.44 g 0.45 3.45
R, ~ average surface roughness
Rt ~ maximum peak-to-valley height
