AU463544B2 - Electrophotographic copy paper - Google Patents

Description

This invention relates to an improved electro-

phctographic copy paper and to electrophotographic copying.

It is especially concerned with an improved electrophotographic

copy paper containing small resinous particles. Paper has many uses in packaging, printing, prepara-

tion of containers, and the like. One of the basic short-

comings of conventional paper is its weight. The relatively high

density of paper imposes a significant financial burden in

shipping, mailing, and the like. For example, magazines,

when printed on a paper which is sufficiently dense and thick

to give the reader the impression of quality, generally

weigh considerably more than is necessary if the minimum

thickness of paper were used which would permit readability.

Frequently among the thicker papers often referred to as

paper board or box board, a relatively high weight is

required to obtain the desired thickness and stiffness. In

many instances, such as in the preparation of paper cups,

conventional papers do not have a sufficient insulating value

for use as hot cups unless an excessive quantity of pulp is

employed.

In U.S. Patent 3,293,114 to Kenaga et al, there is

disclosed a product which overcomes the shortcomings of con-

ventional paper. More specifically the aforementioned patent

sets forth the preparation of a lightweight paper by incor-

porating a plurality of synthetic polymeric particles, having

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a generally spherical shape and defining a generally con-

centric spherical cavity, into paper fibers. The preparation

includes the addition of from about 0.05 to 60 percent by

weight of the weight of the paper of the spherical polymeric

particles, having a diameter of from about 0.5 to 200 microns

to a pulp slurry,

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The resulting paper product is characterized by its lightweight

and excellent stiffness characteristics. Another means of rendering paper lightweight is

described in U.S. Patent 3,210,239 issued to Eberl et al.

This patent describes a bulked paper product which contains

angulate fibrous fragments of foamed aminoplast resins as the

bulking material. The preparation of the lightweight paper

includes adding a

disintegrated aminoplast resin to a pulp slurry before

production of paper sheets. The paper product is

characterized by a low density compared to paper using wood

pulp alone.

In the art of electrophotography, paper is an

important consumable in that it is used in all electro-

photographic copiers. While the lightweight papers demonstrated

in U.S. Patents 3,293,114 and 3,210,239 obviate many of the

problems presented by conventional paper, more peculiar needs

exist in the use of a lightweight paper as a medium for

electrophotographic copying. Therefore, while there is a need

for a lightweight paper for use in electrophotography, certain

problems exist as to its physical and electrical properties with

regard to use in machines. For example, if such a paper has

too high a curl it will cause jamming as its proceeds from

the feeder through the electrophotographic machine. Likewise,

if the paper either has a high coefficient of friction or

accumulates electrostatic charges at its surface, sheets of

paper will stick and will not properly feed into the

electrophotographic machine.

It has been found that the difficulties as set

forth above, exist when utilizing a paper which has been A 463,5 44

50 171

rendered lightweight by the addition of bulking substances. For example, lightweight paper containing gas-containing thermoplas-

tic resin spheres exhibits tendencies to curl which property

causes the paper to wrap -about the roll feeders of the machine

and thereby jam it. In addition, the preparation of this

gas filled-resin sphere bulked paper results in the spheres being

located at or upon the surface of the paper fibers. Being in

such a position the polymeric spheres create a high coefficient of friction for the surface of the paper which high friction

property further ultimately results in a undesirable electrostatic

buildup. This type of lightweight paper, because of its undes-

irable electrostatic and frictional properties, is essentially non-functional in friction type paper feeders which are found in

conventional electrophotographtc equipment. Therefore, because of

the surface presence of the polymeric spheres the lightweight paper will retain such high electrostatic charges that it will

misspuffjin machines using photoreceptor drums; that is, the paper

will stick to the photoreceptor drum and fail to exit.

The same disadvantages encountered in using lightweight paper containing thermoplastic gas filled resin spheres in electrophotographic copying appear when the lightweight

paper contains other materials for bulking purposes. For example,

when using aminoplast thermosetting resins as a bulking material for paper, as taught in U.S. Patent 3,210,239, the paper has

too great a curl, surface friction, and discoloration for use in electrophotographic copying. And further, when using natural

polymeric substances such as cellulose cellulose derivatives,

and proteins as

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bulking substances, the lightweight paper is found inadequate

for electrophotographic purposes. The reason for the

shortcomings of these types of bulking materials appears

to be the same as that of the gasee fiefilled synthetic

resins in that the bulking substance appears at the surface

of the paper thereby rendering it unusable in electrophoto-

graphy.

These particular characteristics of bulked

lightweight paper are so serious that when used in an

electrophotographic machine malfunctions will occur as often

as one sheet in ten and sometimes even more often. In

addition, resulting copies are of poor quality due to a

slight discoloration. While it might be expected that

surface sizing would obviate the aforementioned difficulties,

the addition of conventional surface sizes having ordinary

salts in a concentration of from about 1 to 5 percent are

not generally found useful because the bulking substance is

still left exposed at the surface and will still cause the

problems outlined above. In addition, the use of ordinary

salts in surface sizings will cause increased tendency for

the paper to scorch or discolor when toner fusing is

accomplished by radiant or pressure fusing.

4 6 3.5 44

506 /71 According to the present invention there is pro-

vided a lightweight electrophotographic copy paper compri-

sing paper making fibres having incorporated therein a

bulking material, of low apparent density relative to that

of the paper making fibers, bulking material in a proportion

of up to 10 percent by weight of the paper making fibers,

characterised in that said paper has a surface size thereon,

said size having a composition comprising a binder material,

a salt other than clay, in an amount of from 1 to 50 percent

by weight based on said binder, said salt being a salt which

in combination with the binder yields a surface sizing which

imparts to the paper the properties of increased scorch

resistance, conductivity and strength retention under condi-

tions of heating; and clay in an amount of from 38 to

percent by weight of the total composition, the combination

of salt and clay not exceeding 60 percent by weight of the

total composition, the percentages stated herein being on a

dry weight basis.

Electrophotographic copy papers in accordance with

the present invention are more readily prepared by the addi-

tion of the low density bulking material to the pulp slurry.

The resulting lightweight paper is then surface sized with

a size having the composition stated above.

The particular binder to be used in the surface

sizing composition is not critical to the electrophotographic

copy paper of the present invention. Therefore any

5n /71 commercially available binder products conventionally used

in surface sizing compositions may be used. Typical bin- ders include starch, starch derivatives, polyvinyl alcohol,

polystyrene, and mixtures thereof. Because of its anti-

scorch properties, polystyrene latex in a weight ratio of

at least 40 percent or more, on a dry weight basis, based

on the size, is a particularly useful binder in the sizing

of the present invention.

The particular salt other than the clay to be used

in combination with the binder in an amount of from 1 to

percent by weight based on the binder, on a dry weight basis,

can be any saltwhich in combination with the binder yields

a surface sizing which imparts to the lightweight paper the

properties of increased scorch resistance, conductivity,

and strength retention under conditions of heating. Pre- ferable salts within the purview of the present invention include the sulfate salts of any metal. Typical salts which give exceptional results are magnesium sulfate, zinc sulfate

and sodium sulfate and the hydrates thereof.

Any type of coating clay known to those skilled in

the art may be used within the purview of the present inven-

tion. The only requirement relating to the clay composition

is the amount present in the surface size. As mentioned above, the clay should be present in an amount of from 38 to

percent by weight based on the total composition, but such

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30506/7 that the combination of salt and clay does not exceed percent by weight, the percentages being on a dry weight basis. While the binder, salt and clay surface sizing of the present invention has been described with respect to the three major components, it is well understood to one skilled in the art that many additives can be used in the binder salt clay composition. For example, wetting agents can be added in order to improve the application of the surface coating.

As heretobefore mentioned, the lightweight electrophotographic copy paper of the present invention contains up to 10 percent of bulking material. For optimum

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properties for use in electrophotographic machines the

paper should comprise over 90 percent cellulose fiber to avoid

roughness in the paper surface. Therefore, the lightweight

paper of the instant invention preferably should contain

from 0.5 up to 5 percent bulking material. The particular material used for bulking the

paper is not critical within the purview of the present invention

and may be synthetic resins of the type described in U.S. Patents

3,293,114, 3,210, 239, 3,128,478, 2,929,106 and 2,797,201.

Natural bulking substances, such as foamed starch and foamed cellul

osic materials, can be used with similar results. In addition,

inorganic bulking substances such as hollow glass, ceramic and metal micros pheres can be used.

In the preparation of the lightweight electro-

photographic copy paper of the present invention, it is found that

bulking material accumulates on the surface of one side of the paper. In this condition the coefficient of friction of that

particular side of the paper is very high. Therefore, while not

a requirement in the preparation of the electrophotographic copy paper of the present invention, it is preferably to subject

the side 6f the paper having the bulking material on its surface

to a mechanical rubbing treatment for example with a cotton

fabric material before the step of surface sizing whereby flattenin

abrading, or breaking of the excess bulking material occurs

at the surface of the paper. By means of the mechanical treatment

of the paper those loose or protruding particles -of bulking material are removed or broken thereby rendering the subsequent surface size more effective.

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In one general embodiment of the instant invention, an aqueous pulp slurry is prepared and aboi:t 3 Percnt by

weight, based on the dry pulp, of Saran microspheres, which

are gas filled thermoplastic resin particles produced by the

Dow Chemical Company of Midland, Michigan, the resin com-

prising units derived from vinylidene chloride are added to

the slurry. The pulp-resin composition is then fed into a paper making machine which sequentially forms a paper sheet

of the pulp fibers and applies a surface size composition

comprising 12 percent sodium sulfate, 38 percent clay and

percent ethylated starch in an aqueous dispersion solution.

There results a lightweight paper which functions properly

as copy paper in electrophotographic machines and shows no

indication of discoloration.

In electrophotographic machines, the novel light-

weight copy paper is coordinated in the ordinary electro-

photographic process of charging an electrophotographic

plate, imaging the charged plate with activating radiation,

developing said image with electroscopic marking particles,

transferring said image to the lightweight copy paper of the

present invention and fixing the transferred developed image

to the paper, for example by heat fixing or by pressure

fixing. The conventional electrophotographic process is fully detailed in U.S. Patent 2,297,691 to C.F. Carlson.

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EXAMPLE 1

An electrophotographic copy paper according to

the present invention is prepared by the following technique: A surface sizing is prepared by adding 100 parts

by weight of Penford Gum 280, an ethylated starch manufactured

by the Penick Ford Company of-Cedar Rapids, Iowa,

parts by weight Vinol 125, a polyvinyl alcohol manufacturdd

by the Air Reduction Chemical Carbide Co., of New York,

New York, and 18 parts sodium sulfate to 1500 parts of water.

A 220 parts by weight pre-dispersed clay solution, made with

Nuclay, manufactured Freeport Kaolin Co., of New York, New York,

which was prepared by adding enough clay to water to obtain

a 60 percent solids mixture, is then added to the coating composit-

ion. A slurry is prepared by adding 1000 Ibs. of dry

soft wood kraft fiber, manufactured by the ST. Regis Paper

Company of New York, New York, 500 lbs. of hardwood kraft fiber mar

factured by the international Pulp Sales Co. of New York to 50,000

gallons of water in a hydrapulper. The fiber is refined to

a 350 Canadian Standard Freeness in a Jordan. Thereafter 90 lbs.

Of Experimental Resin CX 058-1 which are gas filled resinous

spheres manufactured by the Dow Chemical Comapn of Midland,

Michidgan, the resin companing units derived from vinylidone

chloride are added to the slurry. The slurry is diluted to 0.5 box of 1 percent by weight of fiber and then fed into the head

a Four drinier paper machine. The resulting paper passed through

the dryers and at the size press the above prepared sizing composition is applied to the paper. The sized sheet is

then dried and very lightly calendered.

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The resulting surface sized lightweight

electrophotographic copy paper is cut to fit a Xerox 720

machine. A stack of 200 sheets are then placed in a Xerox

720 machine and set to copy a standard pattern 200 times. of There is no jamming of the machine and all 200 copies are excellent quality demonstrating no discoloration. EXAMPLE 11

A urea-formaldehyde foam (0.8 lb/cubic foot, 150

micron cell diameter)manufactured by the DuPont Corporation

of Wilmington, Delaware is pulverized in an Abbe mill with

a 1/16 inch screen plate. Discrete amounts of the disintegrated

foam are then blended with a slurry of 1000 lbs. of dry

softweod kraft fiber, 500 lbs. of hardwood karft fiber, and

5000 gallons of water, the slurry being prepared in the same

manner as Example 1. A total of about 2 percent, based on the

dry weight of the wood fibers, of the distintegrated thermosetting resin material is added to the slurry. The slurry is then diluted

to about 1 percent by weight of fiber and a sized sheet

prepared in the same manner as Example 1. Using the same sizing

composition. The resulting lightweight paper is tested in a

Xerox 720 machine in the same manner as Example 1 with the same

advantageous results. The words "Saran" Penford" and "Xerox"

used herein are registered trade marks.

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Claims (3)

30.506 71 The claims defining the invention are as follows

1. A lightweight electrophotographic copy paper

comprising paper making fibers having incorporated therein

a bulking material of low apparent density relative to that

of the paper making fibres, in a proportion of up to

percent by weight of the paper making fibers, characterised

in that said paper has a surface size thereon, said size

having a composition comprising a binder material, a salt

other than clay, in an amount of from 1 to 50 percent by

weight based on said binder, said salt being a salt which in

combination with the binder yields a surface sizing which

imparts to the paper the properties of increased scorch

resistance, conductivity and strength retention under

conditions of heating, and clay in an amount of from 38 to

percent by weight of the total composition, the combina-

tion of salt and clay not exceeding 60 percent by weight of the total composition, the percentages stated herein being

on a dry weight basis.

2. The paper of claim 1 in which the binder material is selected from starch, starch derivatives, polyvinyl alcohol, polystyrene, and mixtures thereof.

3. The paper of claim 2 in which the binder contains polystyrene- latex in a concentration of at least 40 percent, on a dry weight basis, based on the size.

4. The paper of any preceding claim in which the salt is a metallic sulfate.

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11. The method of claim 10 wherein the fixing step takes place by heat fixing.

12. The method of claim 10 wherein the fixing step takes place by pressure fixi

Dated this 4th day of July 1975

XEROX CORPORATION By its Patent Attorneys, DAVIES COLLISON

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