Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to an improved method and product
for surfacing and/or polishing lenses and the like. More
particularly, this invention relates to a novel gel producing
fining or polishing pad which considerably simplifies the
process of fining and/or polishing lenses.
In general, the process for producing fine ground or
polished surfaces on optical materials, such as for example
on optical lenses, is much the same regardless of the type of
fining or polishing medium employed, or the type of material
being processed. In typical such operations, a fining or
polishing pad is moved across the surface of the material to
be processed, while either a slurry containing abrasive
particles, or plain water, is directed in a stream between
the pad and the surface to be processed.
one such prior art process is disclosed in U.S. Patent
No. 4,138,228, which teaches the use of a polishing pad
having a water soluble, hydrophilic matrix containing
unencapsulated abrasive particles that are rather weakly
bonded to the matrix. This pad is used in conjunction with a
constant stream of water, which assists in the release of
polishing particles which are leached or torn from the pad
matrix as the latter breaks down during use. In practice
this pad has been found to be unsatisfactory because of the
lack of contact between the released abrasive particles and
the work.
U.S. patent No. 4,255,164 discloses a glass fining pad
or sheet having a water insoluble, microcellular matrix
containing abrasive fining particles. When the pad is used
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with an aqueous ~low or stream its matrix breaks down and
allegedly releases the ~ining particles at a controlled rate.
While being effective for tlle grinding or fining stages of
surfacing, this type of pad is not effective for polishing,
5 even when using a polishing grade abrasive.
U.S. patent No. 4,576,612 discloses a polishing pad
having a water soluble matrix containing polishing particles.
A stream of water which is directed onto the interface
between the pad and the work causes the exposed surface of
the matrix slowly to dissolve thus slowly releasing polishing
particles.
U.S. patent No. 3,042,509 also discloses a wax-like,
polyethylene based polishing compound containing polishing
particles, and adapted to be rubbed onto the surface o~ a
buffing wheel or lap to provide both lubricating and
polishing properties for the wheel or lap surface. The
compound is water-soluble so that it can be washed off of the
wheel after the buffing operation.
Still other such prior art processes showing
desirability of directing a slurry or other liquid in a
stream to the interface between the work and a grinding or
polishing pad are disclosed in U.S. patents No. 3,921,344;
3,959,935; 3,522,680; 3,225,497; 3,128,580 and 2,886,923.
None of the above-noted patents, however, discloses a
25 pad designed to produce an abrasive gel upon being wetted.
Moreover these prior art processes involve several problems,
including the following:
A. It is difficult to keep the abrasive particles
suspended in the liquid slurry or stream; or in other words,
to prevent the settling out of the particles.
B. Large amounts of abrasive particles tend to stick to
and to dry upon the processing equipment.
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C. Frequent repair and replacement of pumps, which are
used to circulate the abrasive slurry, are necessary.
D. It is extremely difficult to mix and control the
concentration of the abrasive slurry.
This invention provides an improved fining or polishing
process which eliminates the need for directing a stream of
water or liquid slurry onto the workj thereby circumventing
many of the problems associated with the previously mentioned
processes.
To this end it also provides a novel fining or polishing
pad which in the presence of a small amount of water forms a
very viscous gel, which adheres to both the object being
polished and to the pad substrate.
The invention provides a novel water absorbent or
adsorbent pad which, when wetted, makes all of its abrasive
material instantly available for fining or polishing.
Further, this invention provides a novel pad of the type
described having an abrasive-containing matrix made from a
polymer which can absorb and retain large amounts of water to
enable formation of a long lasting gel.
The hereinafter described pad provides a disposable,
self-~ontained article for fining or polishing the surfaces
of various materials (plastics, metals, glass, ceramics,
etc.) using only a small amount of a liquid agent to produce
between the pad and the work a gel which contains abrasive
particles (fining or polishing). The abrasive particles
(aluminum oxide, cerium oxide, etc.) are dispersed in a water
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absorbent or adsorbent, gel-producing carrier or matrix,
which is coated uniformly onto a fLexible reinforcing
substrate, such as for example a fabric of the type used for
conventional polishing or finishing pads. An adhesive is
applied to the back of the substrate, and the entire
structure is cut to form a conventionally shaped, multi-petàl
pad. The pad i9 attached to a surfacing lap and its matrix
and substrate are wetted with a small amount of liquid. The
motion of the lap forms on the pad a gel, which acts like a
viscous slurry to surface the associated workpiece.
The optimum abrasive carrier or matrix provides rapid
gelation, uniform dispersion of surfacing agent, lubrication
between the lap or other surfacing substrate and the object
being fined or polished, and produces a viscous ma~rix which
retains or prevents loss of the abrasive. The preferred,
matrix-supporting substrate is a fabric capable of absorbing
water to function as a reservoir for the gel produced during
use. The replacement of a slurry with a gel producing matrix
eliminates the need for preparing, storing, and disposing of
liquid slurries. It also reduces machine maintenance and
cleanup-time.
The invention will be further described by reference to
the accompanying drawings, in which:
Fig. 1 is a plan view of a gel producing fining or
polishing pad made according to one embodiment of this
invention;
Fig. 2 is an enlarged, fragmentary cross sectional view
taken generally along line 2-2 in Fig. 1 looking in the
direction of the arrows; and
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Fig. 3 is a side elevational view of a conventional
fining or polishing lap as it appears with the pad of Fig. 1
secured thereon.
Referring now to the drawing by numerals of reference,
10 denotes generally a gel producing surfacing pad having
therein the usual radial slots 11, which lend to the pad the
conventional appearance of a petal--shaped pad. Pad 10
comprises several parts, each of which is responsible for a
distinct function. For example, 12 denotes the attachment
layer - which, as noted hereinafter is used to attach the pad
10 to a lap or the like. This layer 12 may be any adhesive
well known to the industry, such as for example a PSA
adhesive.
Numeral 14 denotes the substrate layer. This layer has
several functions. It provides an intermediate supporting
layer between the attachment layer 12 and the hereinafter
described surfacing layer; it provides a pliable surface
which keeps the hereinafter described abrasive particles in
contact with the surface which is being polished or fined; it
retains a small amount of abrasive particles in its
structure; and in use it acts as a reservoir for the wetting
liquid. Any number of synthetic or natural pliable sheet
materials can be used for the substrate layer 14, including
but not limited to cotton, felt, paper, and woven or non-
woven synthetics. These materials can be in flocked form, or
may be altered in other ways (perforated, embossed,etc.) to
30 ` help them retain abrasivè particles and the surfacing layer
or particle carrier layer.
The surfacing or particle carrier layer is denoted at
15, and comprises, preferably, a water absorbent matrix 16
containing abrasive particles 17. Layer 15 is the key
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component of the gel producing abrasive pad, and as noted
hereinafter usually is coated as a paste onto substrate 14
in the range of approximately 10 milligrams to more than 250
milligrams of paste per square centimeter of the substrate
surface. When applied in this manner, part of the matrix 16
and its particles 17 penetrate to a certain extent into the
fabric substrate (Fig. 2), particularly in those cases where
layer 14 is flocked or felted. Layer 15 has multiple
functions which should be balanced to produce a good quality
surface in the shortest amount of time. ~or example, the
abrasive particles 17 preferably have a Knoop hardness of
greater than 1000, and are of a particle size distribution
which allows for rapid stock removal with the least amount of
scratches left on the surface. For use as a polishing pad
the p`articles 17 preferably should have an average particle
size of 0.1 to 10.0 micrometers or microns, and for fining
pads a range of from 10.0 to 50.0 micrometers is recommended.
Abrasives that can be used include, but are not limited to,
cerium oxide, aluminum oxide, silica, etc.
The gelling agent or matrix 16, which forms a gel on
contact with a liquid, provides a medium which holds the
abrasive particles 17 in the presence of a liquid between the
substrate 14 and the material being surfaced (not
illustrated). The matrix 16 is capable of holding relatively
large amounts of liquid, which takes on swarf from the
abraded surface, provides lubrication between the pad and the
object being surfaced, and can provide cooling to materials
which are heat sensitive. Materials suitable for creating
matrix 16 include cellulose based materials, clays,
alumina-silicates, polymer silicas, and similar materials.
Other additives can be used in conjunction with the gelling
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agent or matrix 16, such as chemical polishing accelerators,
coolants, oxidation inhibitors, etc.
Some typical examples of the invention are as follows:
EXAMPLE No. 1 - POLISHING PAD
Preparation of gel/abrasive matrix:
Part A) 20 grams of propylene glycol and 10 grams of a
sodium oarboxymethylcellulose carrier, such as for example
the type known as CMC 7L and sold by Aqualon of Wilmington,
Delaware, were mixed until well clispersed.
Part B) 160 gr. of water, plus 5 gr. of a dispersant
known as Darvan 7, which is sold by Vanderbuilt Co. of
Norwalk Conn., and 150 gr. of aluminum oxide, having an
average particle size of approximately 2.5 microns, were
mixed until well dispersed.
~art ~ was then mixed into Part A until the mixture was
a smooth paste. Ratio of abrasive (150 gr.) to dry carrier
(10 gr.) was 15:1.
The mixture of parts A and 8 was then coated as a layer
15 onto a pad substrate 14 which comprised of a commeroially
available flocked polyester fabric such as 0.0~0 inch rayon
flock sold by Tempo/Shane of Peabody Mass.
The layer 15 of paste was coated on substrate 14 to a
thickness of approximately .005 - .008 inches. The fabrio
substrate 14 was then placed in an oven at 300 F. for five
minutes. After cooling the fabric, a pressure sensitive
adhesive layer 12 was attached to the back of layer 14, and
pad 10 was cut to its desired shape using a steel rule die.
TESTI NG
Each of a first set of polishing pads made according to
Example No. 1 was mounted on a lap 20 and saturated with
about 20 ml. of water, enough to wet the matrix 16 and to
saturate the reservoir layer or substrate 14. The lap was
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put on a Coburn 505 polishing machine set on low speed and at
a pressure of at 20 psi. A fined plastic lens (Supremacy 65
from Coburn Optical Industries, Muskogee, OK.) was mounted
and (polished) run for three minutes for each pad.
A second set of pads was prepared and run using the same
procedure, exoept that in preparing part A of Example No. 1,
the amount of propylene glycol was increased to 40 grams, and
each pad was not saturated with water.
A third set of pads was prepared and run using the same
gel/abrasive matrix and polyester fabric as in the first set,
but the uncoated pad fabric was first attached to the lap,
after which 4 grams of paste was smeared onto each pad.
RESULTS: First Set of Pads
Number of tests : 10
Range of removal : 15 mg. to 31 mg.
Average removal : 25 mg.
Surface quality : Equal to current
industry standards
Optical quality : Very Good
Second Set of Pad 5
Number of tests : 3
Range of removal : 10-21 mg.
Average removal : 14.3
Surface quality : Equal to low quality
commercial lens.
Optical quality : Passable
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Third Set of Pads
Number of tests : 1
Removal : 23 mg.
Surface quality : Equal to industry
standard
Optical quality : Very good
EXAM PLE No. 2 - FINING_
Preparation of gel/abrasive matrix:
Part A) 150 grams of Fine-Rite .025 Alumina, produced by
Ferro Corp., Penn Yan, N.Y., plus 100 grams of deionized
water, and 5 grams of Darvan 7, all of which were mixed until
well dispersed.
Part B) 15 grams of carboxymethylcellulose (CMC 7L) plus
23 grams of propylene glyool were~mixed until well dispersed.
Part B was then mixed into Part A under agitation. ~atio
of abrasive (150 gr.) to dry carrier t15 gr.) was 10.1.
This mixture was coated as a layer 15 onto a .005 inch
glass- polishing fabric substrate, which was the type sold by
Pellon of Chelmsford, Ma., at a thickness of .005 inches, and
placed in a 300 F. oven until dry. The cooled material was
laminated to a pressure sensitive adhesive layer 17 and a
multi-petal pad was die-cut from this material.
TESTING
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The fining pad of Example No. 2 was mounted on a lap 20
and saturated with about 20 milliliters of water. The lap
was put on a Coburn 505 polishing machine set on low speed at
a pressure of 20 psi. A plastic lens was mounted and run
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(fined) for two minutes by the pad of ~xample No . 2 .
RESULTS: Finishing Pad
A) Number of tests
Removal : 44 mg.
Surface quality : Very good.
EXAMPLE No. 3 - POLISHING
20 grams of alumina having an average particle size of
approximately 2.5 microns was mixed with 8 grams of Clay
Bentone SD-1 (NL Chemicals) and 25 grams of deionized water
until well dispersed. Ratio of abrasive `(20 gr.) to dry
carrier (8 gr.) was 2.5:1.
TESTI NG
The paste was coated on a flocked polyester pad or
substrate 14, which was then attached to a polishing lap.
The lap was attached to a Coburn 505 polishing machine and
run for three minutes on low speed at a pressure of 20 psi.
A plastic lens was used.
RESULTS: Polishing Pad
.
A) Number of tests : 1
Removal : 21 milligrams
Surface quality : Equal to current industry
standards
Optical quality : Very good
As used herein the term gel is intended to have its
common meaning such as for example of substance which is a
colloid in which the disbursed phase has combined with the
continuous phase to produce a semisolid material, such as
a jelly.
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From the foregoing, it will be apparent that the present
invention considerably simplifies the process and apparatus
heretofore required to fine grind and/or to polish rigid
surfaces, such as for example the surfaces of optical lenses.
By using a special gel-producing pad, it is possible to
eliminate the need for directing a stream of liquid slurry or
water onto the interface between a pad and lens, for example,
thus eliminating also the need for using recirculating pumps
and/or filters for directing a slurry continuously onto the
work during a surfacing operation. With the novel pad
disclosed herein it is necessary only to wet the surface of
the pad at the commencement of a surfacing operation, and
possibly to squirt a supplemental amount of liquid onto the
pad during prolonged surfacing operations. In any event, it
15 is not necessary continuoulsy to dlrect a stream of liquid
onto the pad because of the gel-like coating formed thereon
at the outset of the operation. To prevent the dry oarrier
or matrix forming material from diluting the cuttin~ effect
of the abrasive it is preferred that the ratio of abrasive to
dry carrier be kept as high as possible.
Obviously pads of the type disclosed herein can be
utilized to surface rigid products or work pieces other than
optical lenses, for example in the lapidary and gem making
art. Also, while other organic compounds could be used as
gel producing matrices, such as for example polyvinyl
alcohol, polyethelene glycol, alginates, gums, and
combinations thereof, they are not quite as effective as the
above-noted water absorbing or retaining materials such as
cellulose based materials and the like. Also, in addition to
fabric substrates such as denoted at 14, other flexible,
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water absorbing and retaining substrates could be employed
without departing from this invent:ion.
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