Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
Xerographic drums of a conductive substrate such
as aluminum with a layer of a photoconductive material such as
vitreous or amorphous selenium on its surface have been in use
for many years. More recently, the endless xerographic belt
has come into use in xerographic duplicators due to its greater
flexibility. Xerographic belts must be flexible and in addition
must have a conductive band. These belts are preferably seamless.
Suitable belts generally are quite thin and have a surface with
a high degree of smoothness due to the need for the production
of high quality images on the image retention side of the belt.
A further requirement is that the belt have a relatively high
tensile strength. Satisfactory belts can be prepared by electro-
plating a ductile metal, e.g. stainless steel, brass, aluminum
or nickel, onto a mandrel to form a thin, uniform layer of the
metal. Removal of the metal layer from the mandrel provides the
substrate upon which the photoconductive material can be deposited
to form the xerographic belt.
The belts prepared by the above-described process
are of necessity quite thin and have sharp edges. These edges
present a possible safety hazard to those who must handle the
belts durin~ the servicing which is periodically required. In
order to solve this problem, the edge must be blunted in some
manner.
Blunting of the belt edge has proven problematical
due to the rigors the belt is subjected to during use. Since
the belt revolves around rollers at very high speeds in operation,
a great deal of flexing stress is encountered. In addition,
the belt must pass a rigorous thermal cycle test and a cold shock
test before being marketed in order to provide quality control
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in o~der to ensure its integrity during the loyi~tics of
handling and storage under environmental extremes.
Various methods for blunting the belt's edge have
been considered and tried. One such method involves the
application of high strength plastic tape over the edge of the
belt so that approximately 1/4 inch adheres to both the top
and bottom along the belt edge. The problem with this method
lies in the fact that the tape is not sufficiently flexible
to pass over the rollers without bunching and wrinkling. In
addition, the 1/4 inch width needed for adhesion is sufficiently
wide so as to interfere with machine components. An alternative
method involves rolling up the edge of the belt and flattening
the rolled-up edge back down on the belt proper. This method
offers more than the sought after personnel protection but
suffers from the disadvantage of the bead cracking during the
flexing the belt undergoes in use.
An alternative method is to apply a hot thermoplastic
organic resin to the belt edge which upon hardening forms a
protective coating along the edge. Thermoplastic adhesives
are well-known in the art. These materials are usually hard
and non-tacky at room temperature and are softened or melted
by application of heat to bring them to a condition in which
they will wet or stick to surfaces with which they are brought
into contact. When contact is established, they are allowed
to cool and harden to bond to the surface. Many the~moplastic
resins are sufficiently flexible to withstand the flexing of the
belt; however~ only a limited group of such resins which are
insoluble in the c~eaning solutions used on the belt during
operation will adhere to the helt during the aforementioned
thermal cycle and cold shock tests.
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There exists a need for a system whereby the sharp
edge of a xerographic belt can be blunted so as to reduce or
eliminate the danger to personnel during handling of such a
belt, and it is an object of the present invention to provide such
a system.
A further object is to provide such a system in which
the blunted edge does not crack or bunch up as the belt revolves
around a set of rollers.
An additional object is to provide such a system in
which the blunted edge comprises a protective coating of a
thermoplastic resin around the sharp side of the belt which
adheres to the belt during the thermal stress to which the belt
is subjected during operation.
SUMMARY OF THE INVENTION
The present invention is an improvement to an endless,
flexible, smooth xerographic belt made up of a ductile metal
having a photoconductive material on the outer surface thereof.
The improvement comprises a protective coating of an adhesive
polyester thermoplastic resin along at least one edge of the
belt.
DETAILED DESCRIPTION
The xerographic belt to which the edge protective
material is applied can be made up of any ferrous or non-ferrous
metal provided it has sufficient ductility and tensile strength
to be useful for the purpose intended. In addition, the belt can
be made of a laminate of a flexible non-metal with a metallic
coating on its surface. Exemplary of metals from which the
belt may be prepared are stainless steel, brass, copper, aluminum,
iron and steel. Nickel is the preferred metal.
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The photoconductive material can consist of any
substance which i5 useful as a photoconductor in xerographic
copying. Homogeneous organic or inorganic photoconductors may
be applied to the surface of the belt as well as the binder
type photoreceptor described in U.S. Patent 3,121,006. Preferably,
the photoconductive material is selenium or a selenium alloy
deposited on the belt by vacuum deposition.
The thickness of the xerographic belt can vary widely
since the only requirements are that it be sufficiently flexible
to revolve about a system of rollers without cracking and that
it have sufficient tensile strength to retain its physical
integrity. A belt thickness of from 0.003 to 0.010 inch is
preferred. Obviously, belts in this range of thickness will
have extremely sharp edges.
The sharp edges are blunted by the application of a
coating of an adhesive, thermoplastic, polyester resin so as to
coat and overlap the belt edge. The thickness of the coating
and degree of overlap are not critical provided sufficient overlap
is provided to ensure a fast bond between the belt and the resin.
Preferably, the resin is applied in an amount sufficient to
provide a coating having a thickness of from 0.005 to 0.05 inch
and an overlap on both the top and bottom of the belt of from
0.020 to 0.125 inch.
The thermoplastic resin is applied to the belt edge
by heating it to its softening point, applying the softened
resin to the edge in the desired amount and location, and
allowing the softened resin to set. One method of application
is simply to dip the belt edge in a vessel of the softened resin
to the desired depth. This method; however, suffers from a
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disadvantage caused by flagging of the resin upon withdrawl of
the belt. The trimming of the excess material requires an
extra process step. A preferred method of application involves
the use of a mechanical applicator which has an applicator "shoe"
or tool which accepts the molten resin and meters it onto the
belt in a predetermined amount.
Suitable thermoplastic polyesters include linear
polyesters such as the polyterphthalates of either ethylene
glycol or 1,4-bis (hydroxymethyl) hexane; the polyadipates
of ethylene, propylene or butylene glycols and the polyesters
prepared by the esterification of an anhydride ~e. g., phthalic ,
anhydride or maleic anhydride) and a glycol; and polycarbonates
of 2,2-bis (4-hydroxyphenyl) propane. In addition, network
polyesters, both saturated and unsaturated, may be employed.
Exemplary of a saturated network polyester is the polymer prepared
by the reaction of a trifunctional glycerol with difunctional
phthalic anhydride with the optional addition of a monobasic
acid or a long chain dibasic acid or glycol to produce a
more flexible polymer. Unsaturated network polyesters, crosslinked
by a vinyl copolymerization reaction between double bonds in the~
polyester chain and a vinyl monomer, are also useful. Examples
of such polyesters include the copolyester of maleic anhydride
and phthalic anhydride crosslinked with styrene or a maleic
anhydride-1-4-butanediol polyester, with or without an adipic
acid coreactant, crosslinked with styrene.
A preferred class of polyesters comprises those
crystallizable resinous linear copolyesters of linear glycol and
dibasic acid components in which the dibasic acid component
comprises a mixture of terephthalic and isophthalic acids in
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the range of mole ratios of from 12:1 to 1:1 and in which the
copolyester preferably contains a major proportion of terephthalic
acid and a minor proportion of isophthalic acid. The glycol has
a formula of HO-~CH2 ~ 0H wherein n is an integer of from 2 to
10. Copolyesters of the glycols corresponding to the above
formula, wherein n is an even number, are preferred and those
glycols in which n is an even number of from 2 to 6 are especially
useful.
These copolyesters possess the novel combination of
physical properties to provide the desired physical action
involved in the bonding process. A further desirable property
of the bond is that the terephthalate-isophthalate copolyester,
although a thermoplastic material, differs from most
thermoplastic materials in that it is insoluble in the ordinary
organic solvents such as ketones, esters, ethers and napthas
as well as the chlorinated organic solvents such as methyl
chloroform and 1,1,2-trichloroethane. Thus, the bond is
unaffected by solvents which must periodically be used to clean
the photoreceptive surface of the belt.
The following examples are given to aid in the
understanding of the invention but it is to be understood that
the invention is not restricted to the particular times,
temperatures, proportions, components or other details of
the examples.
EXAMPLE I
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A thin, flexible, nontacky coil of a thermoplastic,
linear, resinous copolyester of terephthalic acid and~isophthalic
acids and 1,4-butanediol is advanced through a heating device
which softens it by bringing it to a temperature of 475 F. The
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softened resin is applied to the edge of a continuous, flexible,
nicke~ ~elt, .0045 inch thick, approximately 16 1/2 inches wide
and 65 inches in circumference having on its ~urface an alloy
comprising greater than 99% selenium, less that l/2% arsenic
and a few parts per million chlorine, at a rate of 1.62 inches
per second. The resin is applied so as to form a bead width on
the top of 0.10 inch and a width of 0.050 inch on the bottom.
The bead thickness is 0.023 inch on the top and 0.015 inch on
the bottom.
EXAMPLE II
Xerographic belts prepared as described in Example I
are mounted on a tri-roller assembly which in operation rotates
them at a rate of 20 inches per second. The belt and assembly
is placed in a temperature controlled chamber in which the pressure
is reduced to 3 inches H2O. The belts are rotated on the
assembly for a total of 50,000 cycles at both 110+ 8F. and
55+ 8F. After testing, the belts are inspected. Inspection
reveals no cracking in the protective edge coating. No separation
of the protective edge from the xerographic belt is observed.
EXAMPLE III
Xerographic belts prepared as described in Example I
are stored in a freezer at -20+ 5F. for one hour and immediately
taken to a hot room at 111+ 8F. for another hour. The thermal
cycle is repeated three times. Upon inspection, the belt's
protective edges are observed to have resisted cracking and
to remain adherent to the belt.
EXAMPLE IV
Xerographic belts prepared as described in Example I
are taped to a standard box insert, boxed and stored in a freezer
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at -20+ 5F. for two ho~rs. At the end of this period, the
box is removed from the freezer and immediately dropped from
a height of 42 inches in such a manner that the bottom strikes
the floor. Inspection of the belts so tested indicates that the
protective edge remains adherent to the belt.
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