Note: Descriptions are shown in the official language in which they were submitted.
--1--
FINING SHEET AND METHOD OF MAKING ~ND USIN(:; THE i~ME
This invention relates to finishing the su~face
of vitreous materials. In particular, this invention
relates to an abrasive Eining sheet, its method of
production and its method of use.
The grinding and polishing of glass sllrfaces are
important processes in produciLng acceptable surfaces on
optical components, such as lenses, prisms, mirrors, and
the like. Such processes are also useful for repairing
scratched or otherwise damaged surfaces of utility glass,
such as plate glass windows, windshields o automobilesj
windows in railroad cars, display cases, and observation
windows of instruments and various other types of
equipment. And, while glass may be-the primary material
which is ground and polished, the processes discussed
Aerein also relate to the grinding and polishing of other
vitreous materials such as gem stones and the like. Any
discussions hereinafter with respect to finishing glass
per_se are also intended to relate to such other
materials, if applicable.
The production of a smooth, finished vitreous
surface involves three basic operations. The first
operation involves rough grinding of the surface being
finished with a coarsa hard abrasive such as diamond to
produce the desired configuration, for example, either a
flat surface or the proper degree of curvature in the case
of a lens. The next step, called "finin~l', involves a
preliminary finishin~ of the coarse ground surface to
remove deep scratches, correcl: elliptical error in the
case o~ glass lenses, and otherwise provide a
substantially smooth although not polished sur~ace. The
last step, called the polishing step, involves fine
grinding to remove small scral:ches and provide a smooth,
finisned, or, in the case of an optical component, an
optically clear surface. This invention is concerned only
with the fining step or operation.
Prior to the present invention, it was
conventional to employ a slurry of the appropriate
abrasive particles in a liquid vehicle such as water in
the fining operation. It has been generally known, that
the loose abrasive grains of an abrasive fining slurry
will, when combined under a load at the grinding
interface, roll or rotate to "pit" or cut small portions
out of the surface being fined to form small craters of
well defined conchoidal shape and size. Blocky abrasive
granules are tnerefore employed for this purpose to obtain
a more uniform pattern of pits.
Such ining slurries are applied, for example,
at the interface between the iens being finished and the
curved metal lap being employed while at least one or both
of these are oscillated or rotated in force contact with
one another to produce a grinding action on the surface of
2~i7
--3--
the lens. This action not only abrades or fines the glass
lens but also wears away the surface of the curved metal
lap, requiring resurfacing after only a few lenses have
been processed. Nonabrasive protective lap covers have
been employed to retard such unwanted wear but their use
increases the lens' processing time.
There are m~ny disadvantages in grinding glass
surfaces with an abrasive slurry. These include the
inconvenience of handling the required large volume of the
slurry, the required agitation to prevent settling of the
abrasive granules and to assure a uniform concentration of
abrasive granules at the yrinding interface, and the need
for additional equipment to prepare, to handle and also to
recover and recycle the abrasive slurry. Additionally,
l$ the slurry itself must be analysed to assure its quality
and dispersion stability requiring aaditional costly man
hours. Furthermore, pump heads, valves, feed lines,
grinding laps, and other parts of the slurry supply
equipment which contact the slurry show undesirable
abrasive wear.
Understandably, attempts have been made,
generally without success, to use coated abrasive pads and
belts and bonded abrasive wheels to replace slurry fining
systems Decause of the obvious simplicity of use of such
abrasive elements. However, the fixed abrasive granules
of such abrasive elements do not rotate and thus do not
provide the necessary pattern of pits required in the
Z~17
fining step. Abrasive Eining slurries commonly used prior
to this invention remove more gJass per unit time than
fining with abrasive elements which have fixed abrasive
granules. Slurries also produce a more uniformly pitted
surface free of scratches, and, equally important, do not
create chatter marks or hairline cracks (stress crack
lines which often extend deep into the bulk of the surface
being fined) which are almost unavoidable when grinding
with bonded or coated abrasives. Such stress cracks are
generally not easily detected unless etching solutions are
applied because stress cracks may be polished over to form
an apparently perfect polished surface but thereafter
remain as sub-surface flaws. Such flaws provide sites
where cracks may easily be initiated and propagated in the
event of external or internal stresses, such as caused by
loads, vibrations, heat and by other sources. In a number
of ground glass products, in particular safety
eye-glasses, safety shieJds and windows, and the like,
where impact resistance is of prime importance,
2Q sub-surface flaws are particularly detrimental.
The peaks of such fixed abrasive granules wear
away quickly, leaving wear-flats which not only
drastically reduce the amount of stock removed but also
burnish and scratch the surface. The sub-surface flaws
discussed above are often the result of the scratching of
the glass by these wear-flats. Polishing such a surface
leaves a wleakened sub-surface containing numerous flaws,
,
. . .
'
Oi7
--5--
as explained above, resu].ting in unacceptabl.e i.mpact
resistance.
wnile diamond abrasive granules contained in
~onded a~rasive sheets or wheel under higher loads may
remove an amount o~ stock comparable to that removed by
slurry grinding, the flawed sub-surface would still result
since the fixed granule mechanism of stock removal is
based on cutting the surface and not on the formation of
desired conchoidal pits. Moreover diamond coated a~rasive
lo tools are very costly and therefore not economically
practical for many applications.
Several means of incorporating fining abrasive
- material into a cohesive layer which will release the
abrasive in use have been attempted for glass grinding
operations without much success. Such attempts were
directed to cause the binder material to disintegrate,
dissolve or soften, and thereby free the abrasive granules
which may then roll and rotate to generate the desired
pitted surface in substantially the same manner as
2Q obtained in slurry fining processes. For example, it has
been known to employ for this purpose lubrican~s such as
stearic acid, tallow, paraffin wax and similar materials
as a bonding agent and lubricant. Such materials
generally disintegrate too rapidly because they have poor
dimensional stability under -the load and ~riction forces
encountered and the generally uncontrolled frictionally
2~17
generated heat.
The present invention provides a fining sheet or
pad which .is particularly suited for finishing rough
ground vitreous surfaces and for repairing scratched
vitreous surface.s to provide a uniformly pitted surface
better than or comparable to that provided by slurry
fining, which surface may thereafter be readily polished
in a subsequent polishing operation. The abrasive fi.ning
sheet of the present invention eliminates liquid handling
steps and measuring and analytical operations normally
associated with the use of conventional fining slurries.
A small amount of water supplied to the fining
sheet of the invention permits the sheet or pad of the
invention to create its own slurry`in situ during the
fining operation, while allowing the user to start with a
clean, easily handled dry sheet or pad. The sheet of the
invention includes a coating which constitutes a dry
slurry concentrate which will be gradually dispersed under
use conditions to form an effective mineral slurry capable
of fining glass surfaces at least as well as conventional
fining slurries.
The abrasive fining sheet according to the
present invention is particularly suited for finishing
rough ground glass lenses when employed with conventional
glass lens fining or polishing machines. The undesirable
abrasion of feed lines, valves, pump heads, and other
equipment, usually associated with the use of conventional
abrasive fining slurries, is eliminated. The fining sheet
o~ the invention also protects tne texture and curvature
of the lap surface, virtually eliminating resurfacing
operations normally associated with the use of
conventional slurries.
The abrasive fin~nc~ sheet of the invention
comprises a microcellular layer formed of water-insoluble
modified phenol formaldehyae or urea formaldehyde resinous
~inding material which bonds therein fining abrasive
granules on a flexible conformable backing sheet. The
aDrasive sheet of the present invention is made by coating
the backing sheet with a composition comprising liquid
binder, fining abrasive granules and sufficient compatible
solvent, if needed, to provide a foamed, homogeneous,
coatable composition. The coating composition is
prepared, coated, dried and cured to yield a uniform
microcellular, handlable, somewhat brittle coating which
will erode or disintegrate and release its loading of
fining abrasive granules at a uniform controlled rate
under use conditions. The gradually released abrasive
granules are capable of rotating freely and thereby
generate a uniformly pitted surface, leaving as flawless a
sub-surface as conventional fining slurries as may be
verified by etching the subsequently polished surface.
Specifically, the fining sheet of the present
Z~l~
invention comprises a f]exible, conformable backing sheet
covered on one side thereof with a microcellular,
abrasive-containing, resinous layer having a weight of at
least 450 grams per m2, a thickness of at least 250
microns (10 mils), and the capability of being uniformly
eroded in use. Tne resinous binder material is a
thermosetting polymer which is selected from the group
consisting of urea formaldehyde and phenol formaldehyde
and which is modified by the addition of about 1% to about
40% (preferably 3~ to 15~) by weight of a thermoplastic
polymeric modifier. The thermoplastic modifier may be
selected from the group consisting of polyamide,
polyacrylate, polyacrylonitrile, polyvinyl ester,
polyvinyl alcohol, copolymers comprising such
1~ thermoplastic polymeric materials and combinations
thereof. The abrasive fining granules have a Knoop
hardness of at least about 1000 and an average particle
size of about 15 to 60 microns and are contained in the
microcellular layer to provide a volume ratio of abrasive
granules to binder in the range of about 0.75:1 to 1.75:1.
The rate of abrasive granule release under use
conditions is controllable because release of the abrasive
granules does not depend on binder solubility parameters
as in the prior art. Rather, granule release from the pad
of the invention depends upon the gradual mechanically
induced failure of the coating. The coating binder is a
fragile microcellular matrix containing fining granules
20~7
g
throughout, which, under load and frictional surface
contact in the presence of an aqueous flow, readily
releases its surface abrasive granules at a useful rate
for effectiYe fining without undesirable clustering or
agglomeration.
The manner in which l:he microcellular layer
erodes, disintegrates or wears away is a critical factor
in determining whether or not :it will complete the fining
operation in a satisfactory and in a commercially
acceptable period of time. For commercial purposes, it is
high]y desirable for one fining sheet to be employed to
complete an entire fining operation. The fining sheet
should erode at a sufficiently rapid rate to provide the
necessary concentration of abrasive granules at the
interface with the stock being fined, yet the sheet should
not wear away so fast as to exhaust its supply of abrasive
before the fining operation is completed. The rate at
which the sheet or pad of the invention erodes or wears
away may be determined by an erodability test which is a
measure of the average volume of product coating lost
during a controlled simulated use test. The test involves
abrading a weighed 11.4 cm diameter disc of the sheet
being tested in a standard Taber abrader. The coating is
wetted with water and two 5 cm diameter, 1.3 cm wide
standard type H-22 "Calibrade" abrasive wheels are mounted
each under a load of 1000 gram against the coating surface
of ~he test pad, and the disc rotated for 100 revolutions
z~
--10--
with the addition of small amounts of water at the surface
of the test disc. The test disc is then removed, the
loose abraded coating washed away, and the disc is dried
and weighed. The coating volume lost, referred to
hereinafter as the "erodability index", is obtained by
dividing weight lost by the specific density of the
coating. It has been observed that useful fining sheets
according to the present invention have an erodability
index between about 0.15 to about 0.30 cm3.
When used, the sheet of the invention may be
interposed between a lap or other pad holding device and a
vitreous surface being fined while applying conventional
motion and pressure with a sufficient aqueous flow to
generate a fining slurry and remove surface stock.
In the accompanying drawing:
FIG. 1 is a plan view of the glass fining sheet
illustrative of the present invention made in the form of
a slotted disc suited for usè in a conventional lens
fining apparatus;
FIG. 2 is a fragmentary cross-sectional view of
the pad of FIG. 1 taken at line 2-2; and
FIG. 3 is an exploded side elevation view
partially in cross-section of a lens fining apparatus
including a lap having tbe pad of FIG. 1 mounted on its
working faceO
~Z2017
--11--
Reference is now made to the drawing and to
FIG. 1 and ~IG. 2 in particular, wherein a glass lens
fining sheet in the form of a circular pad 10 which has
~een cut to provide a plurality of equally spaced radially
aligned slots 11 is depicted. The sheet comprises an
abrasive layer 12 which comprises glass fining abrasive
granules contained in a microcellular matrix of cured
water-insoluble resinous binder material. This layer is
adherently bonded to a conformable, flexible backing sheet
13.
A layer 14 of pressure-sensitive adhesive
material may also ~e included on the opposite side of
sheet 13 to adhere the pad 10 to the working face of a
lens lap. A suitable release liner 15 may also be
provided to protect the pressure-sensitive adhesive layer
from beiny contaminated in storage prior to use.
In use, the sheet material of the present
invention is attached to the working face 30 of a curved
lens fining lap 31 as depicted in FIG. 3. The lens 32 is
then urged against the lap 31 under conventional pressure
against appropriate holding block 33 which has a
depression 34 for receiving the lens. It should be noted
that some apparatus provide for urging the lap against the
lens, this being well known in the ]ens finishing art. In
operation, lap 31 and block 33 are moved with respect to
one another with rotational or oscillatory movement while
2~7
-12-
fresh water or other aqueous solution from a suitable
source 35 is continuously supplied a~ a relatively slow
rate at the lens~sheet material interface.
The fining abrasive granules and limited amounts
of water are maintained at the interface to provide an
abrasive slurry which fines the lens surface. The
mineral-resin matrix will gradually erode under the
effects of load and surface friction, in the presence of
an aqueous flow, and will release the abrasive granules
over a period of time sufficient to fine the lens.
As fining occurs, tne abrasive action causes
removal of additional binder material and release of
additional abrasive granules, replenishing the supply of
abrasive granules at a relatively uniform controlled rate.
The loose abrasive granules are carried to the periphery
of the interface between the lens and pad and removed with
the assistance of the aqueous flow, providing a supply of
fresh abrasive granules at the interface during the entire
operation.
2Q The form of the fining sheet may be any
convenient form presently used for lens grinding or
polishing operations such as the disc shape depicted in
FIG. 1 or any modification thereof. A disc may be slit or
slotted, as shown in FIG. 1, to make it more easily
2~ conform to a curved lap or may be provided with other
perforations. The pad may also be in other shapes such as
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-13-
rectangular, oval, and the like, depending upon the shape
of the lap being employed. The sheet material may be
formed into an endless belt ~y conventional methods by
splicing the abutted ends of an elongate strip of the
sheet material. The preferrled fining pad made in
accordance with the present invention is that depicted by
FIG. 1 having a plurality of radially aligned equally
spaced slots extending from the edge of the pad toward its
center.
he fining abrasive granules employed in the
present invention have a particle size on the order of 10
to 80 microns and have a Knoop hardness of at least 1000
to provide the necessary degree of abrasion on the surface
of the glass heing fined. Granules smaller than 10
microns are generally insufficiently abrasive to remove
deep scratches in a commercially acceptable amount of
time, while granules larger than 90 microns leave deep
scratches which generally cannot be removed by
conventional polishing operations.
Abrasive materials having adequate hardness may
be formed of any conventional abrasive minerals, such as
garnet, emery, aluminum oxide, silicon carbide, zirconium
oxide and the like. As known from slurry grinding
processes, a uniform particle size dlstribution will
provide a uniformly fined (or pitted), scratch-free
surface. Since the mechanism of grinding with slurries
.
,, . . : :,
Z2~17
-14-
and with the abrasive sheets of the present invention is
primarily based on the rolling action of the abrasive
granules, shape ratios close to unity (ratio of the axes
of the mineral granules) are~ preferred. The preferred
fining abrasive granules of the present invention are
formed of "wheel grade" (or blocky) silicon carbide
carefully screened to have a uniform particle size
distribution. Particles much larger than the mean should
be avoided since they generally will damage or scratch the
surface beinq fined.
The binder which provides the cohesive
microcellular matrix which bonds tne fining abrasive
- granule therein and adheres the abrasive layer to the
conformable sheet is formed of a water-insoluble resinous
material. The cured granule-free, modified binder should
have a Knoop hardness value within the range of 15 to S0,
preferably 20 to 40, to provide the necessary support to
the abrasive granules.
The mineral-resin layer may be described as a
rigid microcellular matrix containlng minute cells or
voids which have average void diameters in a size range
which typically dves not exceed by more than 50~ the size
of the abrasive granules, with the average void diameter
most typically being approximately the same as or smaller
than the average diameter of the abrasive granules. The
void fraction of the abrasive layer for useful product
.
~Z;~7
-15-
according to the present invention have been found to be
typically on the order of 0.35 to 0.60. ~ product having
a void fraction less than 0.2 has been found to not fine
or grind at a commercially acceptable rate.
A suitable binder composition is provided by
urea- or phenol-formaldenyde type thermosetting polymeric
materials which are preferably modified by the addition of
from about 1% to about 40% (most preferably 3% to about
15~) ~y weight thermoplastic polymeric modifier to provide
increased cohesive strength. Such resins provide good
adhesion to the backing substrate and only a minimum
adhesion to the surface of the abrasive mineral granules.
~hile unmodified phenol-formaldehyde type resins may be
used, some will produce a very brittle mineral-resin
matrix which may easily break off when handled.
The thermoplastic polymeric modifier may be
selected from a variety of polymers, such as polyamides,
polyacrylates, polyacrylonitriles, polyvinyl esters,
polyvinyl alcohol, copolymers thereof and combinations
thereof. The preferred modifier is nitrile rubber latex
available from B. F. Goodrich Chemical Company under the
trade designation Hycar~ 1571.
The modifier materials preferably are added to
the coating composition as a solution in a suitable
compatible solvent or as a latex or other particulate
dispersion in a liquid vehicle such as water.
; ~ ;'' ' . '''; '
-
17
-16-
Such resin coatings may be cured by heating at
an appropriate temperature for an appropriate time to
remove solvent and affect a complete resin cure, e.~.,
about 115C for approximately 8 hours. Shorter heating
times are of course possible at higher temperatures, if
tolerated by the backing. The preferred temperature for
curing is 100C to 130C.
The weight ratio of fining abrasive granules to
binder resin in the abrasive coating should be in the
range of about 6:1 to about 2:1, preferably 4:1 to 3:1, if
SiC is the abrasive, to obtain the necessary loading of
abrasive granules to provide an effective slurry for
fining as the binder is worn away. The mineral:resin
ratio may be better defined as a volume ratio varying from
0.75:1 to 1.75:1 regardless of the type of abrasive used.
Preparation of the microporous mineral-binder
layer requires the preparation of a coated composition
which will provide for the`formation of minute closed
cells or voids wnich will be retained during coating and
curing. Fortunately, most abrasive granules used will by
their nature provide such min~te cells with one or more
cells being associated with each granule and the size of
each cell typically not greatly exceeding the size of the
granule. ~'are should be taken to select granules and
binder to assure such cell formation and to avoid use of
materials which interfere with this effect. In some
Z~17
-17-
cases, since adjustment in the coating composition is
required to optimize the cell formation effect, the
addition of solvents, viscosity aids and fillers may be
desirable. Coating techniques shoul~ be controlled to
prevent binder enrichment at the top surface oE the
microcellular layer. For example, the viscosity of the
mineral-resin coating composition may be adjusted
depending on the capability of the particular coating
equipment, with compatible solvents, such as water or
ethylene glycol monoethyl ether (sold under the trade
designation "Ethyl Cellosolve" by Union Carbide Company)
or combinations thereof which may be added to obtain the
desired coating consistency. The preferred coating
composition has a viscosity in excess of 60,000 Cp5.
The coating weight of the abrasive layer should
be at least 450 grams per square meter with a minimum
coating thickness of at least 250 microns (10 mils) (dry)
to provide sufficient abrasive granules and sufficient
thickness to complete a conventional lens fining
operation
Conventional mixing and coating techniques and
equipment may be employed to produce the article of the
present invention. The preferred mixing equipment is a
low speed agitator or kneader, and knife coating is the
preferred c:oating method.
A glass lens fining operation using the abrasive
Z~17
-18-
fining pads of the invention is completed in less than 10
minutes, typically in 3 to 6 minu~es, if fining a
conventional 65 millimeter diameter eyeglass lens having a
moderate degree of curvature ~6 diopter curve) under a 20
pound load. Under these circumstances, sheet material of
the present invention will typically remove at least 0.5
gram of glass, usually about 0.75 to about 1.30 gram of
glass.
The conformable, flexible backing sheet may be
any suitable material which is compatible with the coating
components and maintains its integrity under the curin~
conditions, including permeable and impermeable materials.
However, when impermeable backing materials are used,
coating viscosity and drying techniques may require
1~ adjustment to prevent the formation of large blisters
during drying and loss of cells to such an extent to
change the erodability index to an unacceptable level.
The preferred backing sheet material is a spun bonded
polyester web such as that available from the West Point
Pepperell Company of Palatine, Illinois under the trade
designation "~anapress~" No. 00-4219-02 or E. I. duPont
Company under the trade designation "Reemay~", but any
other web of similar construction may also be used.
~rhe aqueous flow applied in using the fining
sheet or pad of the invention is preferably predominately
water but Tnay also include other ingredients as typically
Z~l~
--19--
used in solutions employed in slurry fining or in
conventional coated a~rasive finishing. Such additives
may include water-soluble oils, emu]sifiable oils, wetting
agents, and the like.
The water flow supply at the interface of the
fining pad and lens being fined should be relatively
small, on the order o~ about 1,~ to 50 ml, per minute,
preferably 2 to 20 ml, per minute, Too li~tle or too much
water will reduce the grinding efficiency. The water flow
rate should be adjusted to maximize the amount of glass
being cut from the lens surface,
The fining sheet of the invention is attached to
the working face o~ the lap by conventional means. In
some instances, it may be desirable to apply a layer of
conventional pressure-sensitive adhesive to the back side
to facilitate holding the fining sheet to the working
face. Useful pressure-sensitive adhesive compositions
include those of the rubber-resin type and the acrylate.
The rubber:resin pressure-sensitive adhesives are
preferred, When a pressure-sensitive adhesive layer is
applied to the fining sheet, it may be desirable to also
add a release liner to protect the adhesive surface of the
pressure-sensitive adhesive layer from contamination
during storage and handling prior to use. Such release
liners may be silicone treated paper, nonadherent plastic
films or any suitable material known for this purpose,
'.
, . ,. ~
~Z~17
-20-
EXA~PLES
The invention is f~lrther illustrated by the
following examples:
Example 1
Coating C:omposition
Ingredient Parts by_Weight
1. Alkaline catalyzed resole phenol-
formaldehyde resin having 53-57%
solids, a viscosity of 200-400 cps
at 25C, gel time of 29-36 minutes
at lOQC and a pH of 9.0-9.4 (avail-
able from Ashland Chemical Company
under the trade aesignation
"Arofene"~72155) 54
2. Reacti~e, low melting polyamide resin
having 100% solids, a specific gravity
of 0.97, amine value of 275-325, amine
equivalent weight of 180, viscosity of
31,000-48,000 cps at 25C (available
from the General Mills Chemical Compan~
under the trade designation "Versamid"~
125) 23
3. Alkaline catalyzed resole phenol-
formaldehyde resin having 75-77% solids
a viscosity of 1600-2500 cps at 25C, a
gel time of 50-58 minutes at lOQC, a
formaldehyde to phenol ratio of
1.75:1.00, number average molecular
weight of 168 and specific gravity
of 1.2. 23
Finin~ Abrasives Granule
400 mesh wheel grade silicon carbide
having a specific gravity of 3.18 and
Knoop hardness of 2480 (average particle
size 20 microns) 275
The coating ingredients described above were
~2~3~7
-21-
mix~d in the proportions shown to form a homogeneous
mixture into which were blended the abrasive granules and
about 20 parts by weight ethy]ene glycol monoethyl ether
to form a coatable composition. The resulting (dry)
mineral:resin ratio is 4:1 by weight or 1.5:1 by volume.
This composition was then kni~e coated at a
thickness of 0.~4 mm on a spun bonded non-woven polyester
web weighing approximately 85 grams per square meter and
having a thickness of about 10-11 mils (available form
~he ~est Point Pepperell Company of Palatine, Illinois
under the trade designation "Lanapress~" Style No.
0042-19-02). The coa~ed sheet was then placed in a
forced air oven heated at aproximately 115C and
- maintained in the oven for about 8 hours. A disc shaped
sample of this sheet was cut to thè configuration shown
in FIG. 1 with a diameter of 76 mm to provide a fining
pad
Fining pads made in accordance with the
procedure described in this~example were evaluated
against standard slurry compositions typical in the lens
finishing art and also against conventional coated
abrasive sheets. The grinding results of a laboratory
evaluation to compare the effective grinding rates of
slurries, coated abrasives, and the fining sheet of the
present invention are contained in Table 1. The standard
slurry containing 12 micron alumina abrasive as is
customary in the lens finishing art was evaluated at
2~
-22-
three concentrati.ons - 7.3 16.0 and 36.4 grams of
abrasive per 100 grams of slurry. The standard coated
abrasive sheet material contained 15 micron si.].icon
carbide abrasive granules in a 1 to 1 weight ratio with
the binder. Each of these was evaluated employi.ng a 65
millimeter rough ground glass lens with moderate
curvature and the amount of glass removed after each
minute of operation was determined by weighing the lens
before and after grinding. A flood of the slurry was
continuously applied to the interface of a smooth cast
iron lap and the glass lens by a recirculating pump. The
standard a~rasive sheet material was cut into a pad shape
to provide the same abrasive contact area as the pad of
- the present invention and a flood of water was applied at
~5 the interface of this sheet material and the lens being
finished Water was applied to the interface of the lens
pad according to the invention and the glass lens being
ground at a rate of approximately 2-1j2 cc per minute.
In each case the load between the lap and lens was
varied from 4.5 to 13.5 kg (10 to 30 pounds) as shown in
Table I. rrhe table also shows the amount of glass
removed during each time increment and the total amount
removed after 4 minutes.
. .
. . -- -
Z017
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TABLE I
Conventional Slurry
Load Time (conc. g/lOO cc ,?f slurry Coated
(kg) (min) 7.3 16.0 36.4 AbraslveExample
4.5 1 .150 ~163 .160 .022 .190
2 .130 .153 .138 .002 .142
3 .063 .130 .134 .001 .133
4 027 .133 .131 001 139
Total .390 .579 .563 .006 .604
9 1 .139 .213 .326 .008 .330
~ .087 .122 .271 .006 .232
3 .0~0 .099 .157 .003 .193
4 073 083 112 003 OllO
Total .359 .517 .866 .020 .865
1513.5 1 .108 .192 .286 .012 .325
2 .072 .085 .187 .008 .271
3 .031 .076 .131 .003 .348
~ 009 057 096 004 295
Total .220 .410 .700 .027 1.239
As can be seen, the pad of the invention
performed as well as or better than conventional slurry
under load conditions of 4.5 to 13.5 kg (10 to 30 lbs.).
Conventional coated abrasives were proven totally
unacceptable.
2$ The surface quality of the processed glass
i7
lenses was determined by measuring the roug~ness and
surface profile data on a Bendix Proficorder. The
recorded CLA-values (Center-Line-Average) - also referred
to as Arithmetrical Average (AA) Data - describe the
standard deviation of peak and valley from the mean. The
average Net Peak Height (NPH) describes the average
peak-valley height. The "Max NPH" describes the isolated
deep scratches.
A summary of the profile data for finished
lenses during various stages of the finishing includes
(1) the rough generated lens surfaces before fining, (2)
the resultant lens surface after being fined either with
a fining pad according to this invention as prepared in
Example 1 or with a commercial 12 micron aluminum oxide
slurry and (3) ~he finished lenses after having been
polished with conventional 1-3 micron cerium oxide
slurries, is given in Table 2.
TABLE 2
Evaluation of Glass Lens Surfaces
(microns)
(1) Generated: CLA - 5.0
(Before fining) AY. Net Peak H. - 10.0
Max. Net Peak H. - 25.0
(2) After Fining: Ex 1 Slurr~
CLA - 1.5 1.4
Av. NPH - 5.0 4.5
Max. NPH - 7.5 7.5
(3-) After Polishing Ex 1 Slurry
CLA. - 0.10 0.10
Av. NPH - 0.17 0.16
~ Z~7
-25-
Max. NPH - 0.22 0.23
The accuracy of the optical curvature of the
finished lenses processed by each method was determined
by measuring the diopter strength (focal length) and
optical axis on a lensometer commonly used in optical
la~oratories. The lenses processed by both methods
- ~exhi~itea the desired optical accuracy.
Example 2
Coatiny Composition
Parts by
Weight
Ingredient (wet)
1. Phenol-formaldehyde resin naving50
53-57~ solids, trade designation
"Arofene'~72155 (as described in
Example 1)
2. Phenol-formaldehyde resin having41
75-77% solids (as described in
~xample 1)
3. A nitrile rubber latex having
42-44% solids available from B.F.
Goodrich Chemical Corp. un~er the
trade designation "Hycar" ~ 1571 9
Fining Abrasive Granule
2S 400 mesh, wheel grade silieon carbide 218
(as described in Example 1)
The coating ingredients described above were
mixed in the proportions shown to form a homogeneous
~ .
-~6-
mixture into which were blended the abrasive granules and
about 20 parts by weight water to form a coatable
composition. The resulting (dry) mineral:resin ratio is
3.5:1 by weight or 1.4:1 by volume. The composition was
knife-coated on the non-woven web, cured and converted
into fining pads as described in Example 1. The grinding
results are summarized in Table 3.
z(3~7
-27-
Example 3
Coating Composition
Parts by
~eigh~
5 Ingredient (wet)
1. Phenol-formaldehyde resin having 37.5
53-57~ so~ids, trade designation
"Arofene~Y72155 (as described in
Example 1)
10 2. Phenol-formaldehyde resin having 58
75-77% solids (as described in
Example 1)
3. An acrylic latex having 48-52% 4.5
solids avilable from B.F. Goodrich
Chemical Corp. under the trade
designation "Hycar" ~ 2679
Fining Abrasive Granule
400 mesh, wheel grade silicon carbide
(as described in Example 1) 270
~0 Tne coating ingredients and the mineral were
mixed and the viscosity adjusted with water as described
in Example 2. The resulting (dry) mineral:resin ratio is
4:1 by weight or 1.6:1 by volume.
The composition was knife-coated on an
impermeable non-woven web, cured and converted into
fining pads as described in ~xample 1. The saturated
non-woven ~web was the spun bonded polyester web described
in Example 1 saturated with 3.7 mg per cm2 of a 1:1
Z~i~
-28
mixture on a solids basis of the 75-77% solids
phenol-formaldehyde resin and the acrylic latex described
above.
The grinding results are summarized in Table 3.
Example 4
Coating Composition
Parts by
Weight
lQ Inyredient (wet)
1. Phenol-formaldehyde resin having
53-57~ solids, trade designation
"Arofene'~2155 (as described
in Example 1) 26
2. Phenol-formaldehyde resin having
75-77% solids (as described in
Example 1) 41
3. A nitrile rubber latex having
42-44%~solids, trade designation
"~ycar~" 1571 (as described
in Example 2) 11
4. An aqueous polyvinyl alcohol solution
5% solids, made from a polyvinyl
alcohol powder available from E. I.
duPont Corp. under th~e trade
designation "Elvanol~", fully
hydrolyzed 22
Fining Abrasive Granule
400 mesh, wheel-grade silicon
carbide (as described in Example 1) 204
The coating ingredients and the mineral were
-29-
mixed and subsequently coated as described in the
previous ~xamples 1-3 to provide a mineral:resin weight
ratio of 4:1 (vol.ume ratio of 1.56:1).
Ihe fining pads made therefrom were tested and
results are summarized in Table 3.
2~i7
--30--
E xample_5
oating Cc>mposition
Parts by
~eiyht
5 Ingredient (wet)
1. Phenol-formaldehyde resin having
53-57% solids, trade clesignation
"Arofene'~72155 (as described in
Example 1) 50
2. Pnenol-formaldehyde resin having
75-77% solids ~as described in
Example 1) 41.5
3. A nitrile rubber latex having
42-44% ~olids, trade designation
"Hycar'~1571 (as described in
Exa;nple 2~ 8.5
Finin~ Abrasive Granule
400 mesh, wheel grade aluminum oxide
having a specific density of 3.95 and
a Knoop hardness of about 2100 269
The coating ingredients and the mineral were
mixed and subsequently coated as described in the
previous ~xamples 1-4. The (dry) mineral:resin ratio is
4.3:1 (1.37:1 volume ratio) which is comparable to a
3.5:1 ratio of tAe less dense silicon carbide mineral.
The fining pads made therefrom were tested and
results are summarized in Table 3.
Z~7
Examele 6
Parts by
In~redient wt. (wet)
1. Urea-formaldehyde resin having 63-
66% solids, a ph cf 7.6 and a
specific density of 1.296 available
from the Borden Chemical Co. under
the trade designation "Durite~" AL-8401 86
2. Nitrile rubber latex having 42-44
solids available under the trade
designation "Hycar~" 1571 14
3. 25% aqueous solution of ammonium
chloride (NH4Cl) as a catalyst for
the urea-formaldehyae resin 8
4. Fining abrasive granules, 400 mesh,
wheel grade silicon carbide (as
described in Example 1) 186
The coating ingredients and the abrasive granules
were mixed and subsequently coated as described in the
previous Examples 1-5.
The fining pad made therefrom was tested and the
results are summarized in Table 3.
~2Z0~7
-32-
TABLE 3
Summary of Grinding Tests Grams of Glass
Removed After Fining Cycle.
Machine: Coburn #506 cylinder lens
polisher
Conditions: 9 kg (20 lbs)/ 4 minutes
- Stock
~lineral:RIesin Removed
1o Example Mineral Weight Ratio Resin Type ~
1 SiC 4:1 Phenolic/Polyamide .865
2 SiC 3.5:1 Phenolic/Rubber 1.194
3 SiC 4:1 Phenolic/Acrylic 1.392
4 SiC 4:1 Phenolic/Rubber/PVA 1.036
A123 4.3:1 Phenolic/Rubber 0.935
6 SiC 3:1 ureaformaldehyde/
Rubber 0.864
Control
Slurry 2 3 .866
20 Control
Coated
Abrasive SiC 1:1 Phenolic .020
01~
-33-
Examples ?-13 and Control A-D
Examples 7-13 and Control Examples A-D were
prepared and evaluated according to the methods described
in Examples 1-6. The specific ingredients ~orming these
examples were as follows:
Identification of I_~redients
. . .
"Phenolic I" is obtained from an alkaline
catalyzed resole phenol-formaldehyde resin h~ving 75-77~
solids, a viscosity of 1600-2500 cps at 25C, a gel time
of 50-58 minutes at 100C, a formaldehyde to phenol ratio
of 1.75:1.00, number average molecular weight of 168 and
specific gravity of 1.2.
"Phenolic II" is obtained from an alkaline
catalyzed resole phenol-formaldehyde resin having 53-57
solids, a viscosity of 200-400 cps at 25C, gel time of
29-36 minutes at 100C and a pH of 9.0-9.4 (available
from Ashland Chemical Company under the trade designation
"Arofene~ 72155).
"Nitrile rubber" is obtained from a nitrile
rubber latex having 42-44% solids and is available under
the trade designation "Hycar~ 1571.
"Polyamide" is obtained from a reactive, low
melting polyamide resin having 100% solids, a specific
gravity of 0.97, amine value of 275-325, amine equivalent
weight of 180, viscosity of 31,000-48,000 cps at 25C
~l~æ~oAL7
-34-
(available from the General Mills Chemical Company under
the trade designation "Versamid~" 125~.
~pecific compositions (in earl:s by weiyht dry)
Example 7 Parts
Binder: Phenolic I 64
Phenolic II 30
Nitrile rubbex 6
Abrasive: 400 mesh SiC 400
Example 8
Binder: Phenolic I . 50
Phenolic II 44
Nitrile rubber
Abrasive: 400 mesh alumina:zirconia 500
Example 9
Binder: Phenolic I 50
Phenolic II 44
Nitrile rubber 6-
Abrasive: 400 mesh A12O3 400
Example 10
Binder: Phenolic I - 50
Phenolic II 44
Nitrile rubber 6
Abrasive: 400 mesh A12O3 450
z~
-35-
Example Il
Binder: Phenolic I 35
Phenolic II 32.5
Polyamide 32.5
Abrasive: 400 mesh SiC 400
Parts
~xam~le 12
Binder: Phenolic I 56.5
Phenolic II 11
Polyamide 32.5
A~rasive: 400 mesh SiC 400
Example 13
- Binder: Phenolic I 67
Phenolic II 32
1~ Nitrile rubber
Abrasive: 400 mesh SiC 400
Control A
8inder: Phenolic I 64
Phenolic II 30
Nitrile rubber 6
Abrasive: 400 mesh SiC 400
~Z~ 7
-36-
Control B
Binder: Phenolic I 54
Phenolic II 30
Nitrile rubber 6
Abrasive: 400 mesh alumina:zirconia 400
Control C
Binder: Phenolic I 50
Nitrile rubber 50
Abrasive: 400 mesh SiC 400
Control D
Binder: Phenolic I 100
Abrasive: 400 mesh SiC 150
In Table 4, both the Erodability Factor and the
Glass Stock Removal are reported. The method of
obtaining the Erodability Factor is described above while
the method of obtaining the Glass Stock Removal is the
same as in Esample 1 when a 9 kg (20 lb.) load is used.
-37-
TABLE 4
GLASS
EX. ERODABILITYSTOCK REMOVAL
NO MINERAL FACTOR (cc)GRAMS/4 MINUTES
.
5 1 SiC .189.865
2 SiC .2041.194
3 SiC .2201~392
4 SiC .1961.036
A12O3 .260~935
lQ6 SiC .177.864
7 SiC .2511.160
8 Alumina Zirconia .208 1.100
9 A123 .192.908
A123 .2141.140
1511 SiC .167.940
12 SiC .252.997
13 SiC .167.940
A SiC .115.407
B Alumina:Zirconia .090 .376
20C SiC .471 .173
D SiC .006 .020
