Note: Descriptions are shown in the official language in which they were submitted.
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COATED ABRASIVE HAVING A
COEXTRUDED POLYESTER SUPPORT FILM BACKING
The invention relates to coated abrasive products
having a coextruded biaxially oriented, heat-set polyester
support film backing.
The backings employed typically for coated abrasive
products include paper, metal foil, cloth, film-forming plastic
material, and the like. Biaxially oriented and heat-set films
of highly crystalline polymeric materials such as polyethylene
terephthalate (PET), polycyclohexanedimethyl terephthalate
(PCDT) and polyethylene naphthalate (PEN) are particularly
attractive candidates for use as coated abrasive backings
because of their high tear-resistance, dimensional stability,
chemical resistance, wear resistance, strength, abrasion resis-
tance and temperature stability. Such films, however, typically
have a smooth, tough, abrasion-resistant, chemical-resistant,
dense surface to which conventional adhesive materials bond
only with difficulty. Numerous attempts have been made to
render the surface of such films more receptive to coatings.
While many of these attempts have some merit, none has produced
a film which is substantially universally receptive to a wide
variety of binder materials typically used for abrasive products.
One method employed to make such films more receptive
is to roughen their surfaces by mechanical or chemical means.
Mechanical roughening involves making minute cuts into the
surface of the film, tending to weaken it structurally.
Chemical treatments with strong acids or bases are generally
undesirable because they not only tend to degrade the polymer
and weaken the film but also are extremely toxic and hazardous
to use.
Ano-ther method of making the surface of oriented heat-set films
more receptive is to apply a primer layer of a chem:i.cally related but more
receptive ma-terial by solvent casting or lamina-tion. Because of the
unreceptive nature of the surface of biaxially oriented heat-set PET, PCDT
and PEN films, even these primer coatings tend to easily delam:inate,
producing products which have at best, a very short useful life.
According to the present invention, there is provided composite
coated abrasive sheet material, comprising, in combination:
(1) a biaxially oriented and heat-set coextruded support film
comprising (A) a base layer of highly dimensionally s-table crystalline
polyester having a surface which has a low receptivity to polymeric coatings,
(B) a thin adhesion-promoti.ng layer of polyester having a minor degree of
crystallinity and melting at a temperature less than about 230C; and
(2) a coating of binder material and abrasive granules firmly
adherently bonded to the face of said (B) layer, the base layer and adhesion-
promoting layer being conjoined at an interface, said interface being an
integral layer of intermingled base layer and adhesion-promoting layer
polyesters.
In the present invention, a coated abrasive is provided which
employs a novel support film backing which has at least two distinct but
firmly united coextruded layers. The support film is biaxially oriented and
heat-set and has a highly dimensionally stable base layer formed of a
crystalline thermoplastic polyester, especially PEN, PCDT or PET, and a thin
layer of a thermoplastic adhesion-promoting polyester. The coated abrasive
products of the invention are dimensionally stable, strong, resist delamination
under a wide variety of use conditions, and are economical to prepare, avoiding
mechanical surface treatment of films, solvent and hazardous chemical handling
steps.
Coextrusion is a process for forming composi.te layers of thermo-
plastic material, as exemplified by United States patent number 3,767,523,
and involves simultaneously extruding the constituent layers of a composite
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film through a di.e so that the layers meet under lam:inar flow cond;.tions,
intermingling at the interface and becoming :Eirmly united. Such a process,
although known for the production of laminated films, has not been known
for use in producing abrasive products of the type described herein.
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It has surprisingly been discovered that coextruded
biaxially oriented, heat-set polyester backings, where one
layer is crystalline PEN, PCDT or PET, and the layer which is
to be coated is oriented but less crystalline, are not only
flexible, tough, wear-resistant, chemical-resistant, strong,
and have the other desirable properties of heat-set, biaxially
oriented PET, PCDT or PEN film but also forms a tough,
adherent bond with a wide variety of binder materials typically
employed to bond abrasive yranules.
PET is prepared by reaction of terephthalic acid
with ethylene glycol. In this reaction, the acid may be
converted to the dimethyl ester which is allowed to react with
the glycol by ester interchange. Typica11y, equimolar amounts
of the glycol and the acid are reacted, generally in the
presence of an excess of glycol. Minor amounts of another
dicarboxylic acid such as isophthalic, phthalic, 2,5- or 2,7-
naphthalene-dicarboxylic, succinic, sebacic, adipic, azelaic,
suberic, pimelic, glutaric, etc., or a diester thereof, e.g.,
up to 10 mole percent, may be substituted for the terephthalic
acid without deleteriously affecting the properties of the
resultant composite film. Additionally, minor amounts of
another glycol such as l,3-propanediol, 1,4-butanediol, neo-
pentyl glycol, l,4-cyclohexanedimethanol, etc., e.g., up to
10 mole percent, may be substituted for the ethylene glycol
without deleterious effects.
The preparation of PEN is analogous to the preparation
of PET, except that the terephthalic acid is replaced by a
free dibasic acid or lower alkyl diester of 2,6-naphthalene
dicarboxylic acid. The same minor amounts and types of other
dibasic acids or glycols may also be included. The preparation
of PCDT is analogous to the preparation of PET except the
ethylene glycol is replaced by l,4-cyclohexane dimethanol and
minor amounts of another dibasic acid not terephthalic acid
should be present to produce a film which can be biaxially
oriented without substantial degradation. For this purpose,
the other dibasic acid is present, on a molar basis, typically
at least about 10% (preferably at least about 15%).
The thermoplastic adhesion-promoting layer is a
polyester which melts below 230C., does not crystallize
rapidly, and is substantially non-crystalline between about
20C. and 230C. "Substantially non-crystalline" means not
more than a minor amount of crystallinity between about 20C.
and 230C.
Preferred polyesters for use in the invention,
having the properties defined above, may be produced by the
condensation reaction of a dicarboxylic acid component
consisting of ~rom about 10 to about 100 mole percent of a
dicarboxylic acid such as isophthalic acid, hexahydroterephthalic
acid, sebacic acid, succinic acid, adipic acid, azelaic acid,
suberic acid, pimelic acid, glutaric acid, or mixtures thereof,
or the diesters of such acids and correspondingly from 90 to
zero more percent of terephthalic acid, and a glycol component,
in substantially equimolar proportions with the dicarboxylic
acid component. The glycol is preferably polymethylene glycol
having the formula HO(CH2)nOH, wherein n is an integer of
2-10, e.g., ethylene glycol, 1,3-propanediol and 1,4-butanediol,
with ethylene glycol being preferred. Other useful glycols
include neopentyl glycol, l,4-cyclohexane dimethanol and
aromatic glycols such as bisphenol A.
As previously stated, the support film backing is
formed by a coextrusion process, wherein the individual layers
meet under laminar flow conditions and are expelled from the
die as an integral, mul ti-layer film structure. Coextruded
films prepared in this manner look much like monolayer films.
Such coextrusion processes are well known as exemplified by
aforementioned U.S. Pat. No. 3,767,523 and by U.S. Pat. No.
3,486,196 and No. 3,476,627. Canadian Pat. No. 929,455
discloses the preparation oF coextruded films which may be
useful in the present invention. The patentee does not,
however, suggest that such films be coated with another poly-
meric layer to provide improved composite articles such as a
coated abrasive but rather that it be overlapped and heat-
sealed to itself to enclose a comestible.
The freshly coextruded support film, formed as
described above, is amorphous. It is thereafter endowed
with improved physical properties by biaxial orientation and
heat-setting. Biaxial orientation involves stretching the
film in two directions normal to each other, generally in the
machine direction and at right angles thereto. In a typical
operation, the freshly extruded molten film is fed onto a
cooling drum to produce a quenched amorphous film which is
briefly heated and stretched in the machine direction, and
then conducted through a tenter frame where it is stretched
transversely with moderate heating. Machine direction stretch-
ing may be accomplished by passing between two sets oF nip
rolls, the second set rotating at a higher speed than the
first. Stretching typically increases the Film area by a
factor of at least 6, the stretching usually being equal in
30 each direction. For applications requiring a higher tensile
support film, this factor will be larger, e.g., above 14, and
the stretching may be greater in one direction than the other.
Heat-setting, or heat-stabilization of the stretched
coextruded film is accomplished by restraining the film in
its stretched dimension and heating briefly, then quenching.
Such heating is typically in the range of 175C. - 230C.
Tentering of plastic films or sheet material is
illustrated in U.S. Pat. No. 2,823,421.
The coextruded biaxially oriented support film back-
ing should have a total thickness of at least 1 mil with atleast 1/4 mil of this thickness being the polyester adhesion-
promoting layer. Film thicknesses up to about 10 mils are
contemplated for the coated abrasive articles herein described,
but thicknesses in excess of 10 mils may be desired for some
purposes. The adhesion-promoting layer should not be thicker
than 1/4 of the total thickness of the coextruded film and
preferably is no more than 1 mil thick even for film thick-
nesses up to 10 mils.
The coextruded support film backing described above
provides a unique backing layer for coated abrasive products.
The thermoplastic adhesion-promoting layer provides a surface
which will form an adherent bond with any of a variety of
natural or synthetic resinous binder materials typically used
as binders for coated abrasive products without the use of
prime coatings or surface treatments. The resinous binder
materials which have been found to adherently bond to this
adhesive surface include varnish, hide glue, polyurethane,
phenolic resins such as phenol formaldehyde, epoxy resins,
etc. Upon suitable formulation, each of these resinous
binder materials can be coated upon the surface adhesion-
promoting layer with abrasive granules to provide coated
abrasive products.
The invention will be better understood by referring
to the drawing wherein:
The Figure depicts an abrasive coated sheet product
according to the invention in a greatly enlarged fragmentary
cross-section view.
Abrasive granules 18 are adhered to the surface of
layer 13 of support film 11 formed of a layer 12 of tough,
flexible, dimensionally stable crystalline polyester and a
layer 13 of adhesion-promoting polyester by means of binder 16,
which may include a conventional "make" coat 17 and a sandsize
coat 21. The adhesive binder or "make coat", which may be any
suitable resin or varnish binder presently known or suited for
use in the manufacture of coated abrasives, optionally contains
calcium carbonate or other filler. The resins and varnishes
are basically initially liquid materials, but, depending on
their use, they may be modified in various ways to give shorter
or longer drying times, greater strength, more flexibility or
other desirable properties. A preferred binder is a thermo-
setting adhesive such as phenol-formaldehyde.
The abrasive particles 18 can be any of a wide
variety of such material known for this use. The abrasive
particles will typically vary in size from smaller than about
1 micron for extra fine polishing to larger than 30 mesh for
extra coarse abrading. Examples of useful abrasive mineral
which may be utilized include flint, emery, garnet, aluminum
oxide, diamond, alumina-zirconia and silicon carbide.
The invention is further illustrated by reference
to the following examples wherein all parts are by weight
unless otherwise specified.
Example 1
An abrasive sheet was prepared in accordance with
the invention by coating a 7-mil biaxially oriented heat-set
support film consisting of a 6.75-mil polyethylene terephtha-
late layer and a 0.25-mil copolyester layer having a terephthale/
isophthalate ratio of 80/20 with grade 150 aluminum oxide
abrasive particles at a particle density of 42 grains per 24
square inches. The abrasive sheet was prepared by first roll
coating the copolyester surface at 6.5 grains (dry weight)
per 24 square inches with a uniform make coating of phenol-
formaldehyde (1:1.95 mole ratio) base catalyzed resin, electro-
statically depositing the abrasive particles, precuring the
resin at 190F. for four hours, and roll coating the resultant
coated abrasive surface with the same resin to provide a 11.4
grains (dry weight) per 24 square inch size coating. The size
coating was then precured at 190F. for two hours and the
resultant coated abrasive sheet was drum cured for ten hours
at 212F.
The abrasive sheet hereinafter identified as
Example 1 was evaluated against Control Examples A-C which
were prepared of common commercial materials. For each of
Examples A-C, as for Example 1, the abrasive mineral was
grade 150 aluminum oxide, coated at the mineral weights shown
in Table VI. Control A had an "E" weight paper backing,a
glue make coating and phenolic resin size coating (same
phenolic resin as Example 1). Controls B and C had cloth
backings and a make and size resin coating of filled phenolic
resin.
A test belt, (3 inches wide by 84 inches long) was
prepared from each coated abrasive test Example described
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above. Each test belt was entrained around a smooth-surfaced
14 inch diameter 3 inch wide rubber-covered contact wheel,
the rubber having a hardness value of 80-85 (Shore A). The
belt was operated at a speed of 7300 surface feet per minute.
A previously weighed 2 inch by 2 inch by 7 inch mild steel
(1018) work piece was reciprocally urged against the abrasive
belt with 19 pounds force, the grinding occurring along its
2 inch by 7 inch face being abraded. The test was discontinued
after 3 minutes of abrasion, the bar cooled to room temperature,
cleaned and weighed. Abrading was continued for an additional
period of 3 and 6 minutes respectively and the cooling,
cleaning and weighing repeated. Results, which reveal the
abrasive sheet material prepared according to the invention
to be substantially as good as such sheets prepared of common
commercial materials, are shown below:
TABLE VI
Mineral Wt.~eight Loss (g)
per 4 x 6per cut time (min)
Example (qrains) 3 6 12
1 42 103 180 319
Control A 40 87 166 299
Control B 62 111 221 366
Control C 54 105 203 359
Example 2
Coextruded Support Film
A 3-mil coextruded support film was prepared as
follows:
Granular polyethylene terephthalate resin having
a solution intrinsic viscosity of 0.60 and melting point of
250C. was extruded at a barrel temperature ranging from
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240-290C., a die temperature of 300C. and a feed rate of
90 lbs. per hour. Simultaneously, a granular copolyester resin
having an intrinsic viscosity of 0.61, a melting point of
197C. and consisting of 80/20 poly(ethylene terephthalate/
isophthalate) was extruded at a barrel temperature ranging
from 200C. - 300C. and a feed rate of 25 - 30 lbs. per hour.
The resultant molten composite film was cast onto a 12-inch
diameter casting wheel maintained at 60C. and rotated at
8 feet per minute, producing a quenched film 30 mils in
thickness having a 22 mil thick polyethylene terephthalate layer
and an 8 mil thick copolyester layer. The quenched film was
then oriented in the machine direction by stretching between
a series of idler nip rolls having outlet nip rolls operated
at three times the speed of inlet nip rolls while heating the
film at 80C. The uniaxially oriented composite film was then
fed into a tenter oven heated at 95C. wherein it was stretched
3 times in the transverse direction. The biaxially oriented
composite film was heat-set by briefly heating under restraint
at 205C., producing a 3 mil coextruded film.
Twelve parts of a mixture consisting of one part
of 3 micron diamond particles and 1.4 part of the phenolic
resin described in Example 1 was blended with 88 parts of
ethyl cellosolve to make a slurry which was knife-coated
(1.5 mil knife opening) on the surface of the coextruded 3
mil polyester support film described above. The resultant
coating was cured for 1 hour at 250F. to provide a coated
abrasive layer which could not be stripped from the backing by
scraping with a sharp edge without destruction of the support
film.
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Example 3
A coated abrasive sheet having an epoxy resin
binder and 3 micron diamond abrasive particles was prepared
according to the invention. The epoxy resin was a 50:50
5 mixture of (1) a linear polyamide resin condensation product
of dimeric fatty acid with a polyamine having an amine value
of 290-320 (sold under the trade designation "Versamide 125"*)
and (2) an epoxy resin of the bisphenol A type having an epoxy
equivalent of 180-195 (sold under the trade designation
10 "Epon 828"*).
One part diamond particles was mixed with 1.4 parts
resin, as a slurry, which was knife coated (1.5 mil knife
opening) on a 3 mil coextruded polyester film of the type
described in Example 2. The resultant coating was cured by
15 heating at 125F in a forced air oven for 8 hours.
The resultant coated abrasiYe sheet material was
used to hand lap a tungsten carbide block.
Example 4
A coated abrasive sheet material was prepared
20 using, as a backing layer, the 3 mil coextruded support fjlm
described in Example 2. The make coat (3 grains per 4" x 6")
and the size coat (6 grains per 4" x 6!') were urea-formaldehyde
resin, with 12 grains per 4" x 6!' of 220 grade aluminum oxide
abrasive particles and a supersize of zinc stearate applied
25 as a 26% solids zinc stearate solution in glycol to a reflec-
tance of 1000 (as described in U.S. Pat. No. 3,043,673~.
The resultant coated abrasive sheet was utilized
for the removal of paint and primer with excellent results.
*Trademark
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Example 5
A coated abrasive sheet material was prepared,
using the 3 mil coextruded support film described in Example 2.
The film was coated with an epoxy varnish make coat, 12
grains per 4" x 6" grade 400 silicon carbide abrasive grains
and 8 grains per 4" x 6" alkyd varnish size coat. Enamel was
easily removed from a panel with the resultant coated abrasive
sheet.
