Note: Descriptions are shown in the official language in which they were submitted.
10468ZS
BACKGROUND OF THE INVENTION
Field of the Invention
; The present invention relates generally to electro-
graphic recording elements. More particularly, the invention --
relates to an electrographic recording element comprising a
base support having coated thereon a layer comprising a poly-
ester resin prepared from a dicarboxylic acid and a polyol,
said polyol having the following general formula
10Il-EO-C-C~ o~( R) a~ O~ C-C-O}H
H m A A A H H n
wherein a is 0 or 1, R is selected from the group consisting of
Cl to C5 alkylene, oxygen, sulfur, or a divalent radical having
one of the following formulas
~j,. . . .
~ O = S = O, C = O or S = O
,. . . .
. A
,, A is halogen or hydrogen, m and n are integers each of which is
equal to at least 1 and the sum of which is equal to from 2 to
, ,
~ 20 less than 7 and X and Y are methyl, phenyl, or hydrogen provided
., that, in any X and Y pair on adjacent carbon atoms, either X or
Y is hydrogen.
Description of the Prior Art
Electrographic recording elements are well known in
the art. These recording elements generally comprise a base
support having coated thereon a layer of a dielectric-i.e.,
insulating-material. Resins suitable for use in the dielectric
layers are also known in the prior art. See, in this regard,
.:
U.S. patent 3,639,640 issued to Gager; U.S. patent 3,385,730
30issued to Relph; U.S. patent 3,634,135 issued to Akiyama; and
.
- 2 - ~
`:~' qF
lV4t;825
U.S. patent 3,653,894 issued to Levy et al.
The electrographic recording elements are useful in
what is generally referred to as an electrographic or electro-
static printing process to provide a permanent record of the
information generated by such a process. Although the de-
tails of the recording processes involved are not necessary
to a complete understanding of the present invention which is
related only to electrographic elements which may be used in
such processes, a basic explanation of the process is useful
in understanding the invention. Basically, electrostatic re-
cording is accomplished by depositing a pattern of electrical
charge upon the surface of the dielectric layer of the recording
element, which charge pattern is made visible by bringing the
element into contact with a suitable, usually powdered, electri-
cally conductive ink or toner which adheres to the charged
areas, and then, if desired, fixing the ink by subjecting the
; developed recording element to heat and/or pressure.
Electrographic printing processes are generally cate-
gorized in one of two ways. In the first or direct electro-
graphic recording process, the information to be recorded isgenerated by way of an electrically energized stylus or an
; electrostatic writing tube, commonly referred to as a CRT pin
tube, which is in close proximity to the electrographic record-
ing element. Energization of the stylus or the electrostatic
writing tube results in the deposition of a charge pattern on
the surface of the electrographic recording element which charge
pattern is commonly referred to as a "latent image". This
charge pattern is then developed by any of the well-known
electrostatic developing techniques to form a permanent and
visible image or print. In the direct process, the charge
1046825
pattern is developed or imaged directly upon the surface on
which it is formed. Alternatively, in a transfer electrogra-
phic recording process, the charge pattern or latent image is
originally formed on a surface other than the surface of the
electrographic recording element, for example, on the surface
' of a photoconductive element, and the charge pattern is then
transferred to the electrographic recording element in order
'; to enable a permanent visible record to be made of the thus
formed latent image. After transfer of the latent image to
the electrographic recording element, development of the image
is achieved in a manner similar to that employed in a direct
process.
In either process, it is important that the dielectric
layer in the electrographic recording element be able to accept
and retain a high level of charge. If the material either does
' not initially accept a high level of charge or if the accepted
' charge is substantially dissipated or lost before a visible
image is formed, the recording element is of limited utility
in commercial applications.
It is an object of the present invention to provide
an electrostatic recording element which both accepts a high
level of charge-i.e. has a high charge acceptance - and which
retains a high percentage of that charge for a period of time
sufficient to allow development of the charge pattern to form
a visible image - i.e. has a high charge retention~
~UMMARY OF THE INVENTION
In accordance with the present invention electro-
graphic recording elements having improved properties such as
increased charge acceptance and improved charge retention are
prepared comprising a base support having coated thereon a
;
-- 4
1046825
layer of a polyester resin prepared by reacting a dicarboxylic
acid selected from the group consisting of alpha-unsaturated
dicarboxylic acids and aromatic dicarboxylic acids with a
polyol having the following general formula
X Y A A A A _ _
H- -O-C-C -O ~ (R) ~ O- C-C-O I H -
H H m A A A A H H n
wherein a is 0 or 1, R is selected from the group consisting
; of Cl to C5 aIkylene, oxygen, sulfur, or a divalent radical
having one of the following formulas
O = S = O, C = O or S = O
A is halogen or hydrogen, m and n are integers each of which is
equal to at least 1 and the sum of which is equal to from 2 to
less than 7 and X and Y are methyl, phenyl or hydrogen provided
that, in any X and Y pair on adjacent carbon atoms, either X or
Y is hydrogen.
- DESCRIPTION OF THE PREFERRED EMBODIMæNTS
.
As mentioned above, the electrographic recording
elements of the present invention comprise a base support
having coated thereon a layer comprising a polyester resin
prepared by reacting a polyol with a dicarboxylic acid. Each
of these components is described in detail below.
Base Support
The base support used to prepare the electrographic
recording elements of the present invention may be any one of
a number of base supports conventionally employed in electro-
graphic recording elements. Representative base supports which
may be employed include, for example, metal foil, an electri-
- 5 -
,
- - '
~0468ZS
cally conductive paper, an electrically conductive film and
an electrically conductive cloth. Of these, it is preferred to
employ an electrically conductive paper.
When a base support other than a metal foil is em-
ployed, electrical conductivity can be imparted to the base by
impregnating or coating the base with any of the compositions
or materials which have previously been employed to impart
electrical conductivity to such bases. Illustrative of such
materials are materials such as carbon black; inorganic electro-
lytes such as sodium chloride, calcium chloride, and lithiumchloride; and electrically conductive resinous polymers such as
resinous polymers of quaternary ammonium salts. Since materials
such as carbon black impart a color to the base which might
~ be considered to be objectionable and materials such as inorganic
;j electrolytes are somewhat dependent on the ambient relative
humidity for their effectiveness as conductive agents, the use
of electrically conductive resinous polymers to impart electrical
conductivity to the base supports is preferred. Examples of
- such polymers can be found, for example, in U.S. patent 3,011,918
which relates to homopolymers and copolymers of vinylbenzyl
quaternary ammonium compounds and papers coated with such com-
pounds. Other compounds which are useful for this purpose in-
clude, for example, polymers of vinyl pyridine quaternized with
aliphatic esters, such as a polymer of vinyl pyridine which has
been quaternized with diethyl sulfate.
Polyester Resin
The polyester resins which have been found to be
especially useful in the preparation of electrographic recording
elements in accordance with the present invention are prepared
; 30 by reacting a dicarboxylic acid with a polyol. The polyols
,,
. .,
-- 6
,.~
.
1046825
which may be employed in the preparation of the polyester
resins may be represented by the following general formula
~ ~O-C-C} o ~ (R)a ~ O ~C-C-O~ H
; H H m A A A H H n
wherein a is 0 or 1, R is selected from the group consisting
of Cl to C5 alkylene, oxygen, sulfur, or a divalent radical
;having one of the following formulas
, . . .
:'- ' ' '
O = S = O, C = O or S = O
''- ' ' ' ' ' .
A is halogen or hydrogen, m and n are integers each of which
"; .
is equal to at least 1 and the sum of which is equal to from
2 to less than 7 and X and Y are methyl, phenyl, or hydrogen
provided that, in any X and Y pair on adjacent carbon atoms,
either X or Y is hydrogen.
;
j~These polyols are prepared by reacting an alkylene
oxide, such as ethylene oxide or propylene oxide, or styrene
oxide, with a dihydric phenol having the following general
~.,
formula
~ A A A A
,~HO ~ (R)a ~ OH
,,;, .
-wherein R, A, and a are as defined above. The sum of m and n
in the previous formula is determined by the number of mols of
alkylene oxide or styrene oxide added per mol of the dihydric
phenol. Thus, in preparing the polyols useful in the present
invention, an average of from about 2 to about 7 mols of
alkylene oxide or styrene oxide should be reacted with each mol
.
'30 of the dihydric phenol.
;:~
. - 7 -
- 1~46825
The polyester resins are prepared from the resulting
polyol by reacting the polyol with an approximately equimolar
amount of a dicarboxylic acid selected from the group consisting
of alpha-unsaturated dicarboxylic acids and aromatic dicarboxylic
acids. Representative alpha-unsaturated dicarboxylic acids
which may be used to carry out this esterification reaction
include, for example, maleic acid and fumaric acid. Represen-
tative aromatic dicarboxylic acids which may be employed in-
clude, for example, phthalic acid, isophthalic acid and tere-
phthalic acid. Anhydrides of these acids, such as maleic an-
hydride and phthalic anhydride, may also be employed. The acid
employed in the esterification reaction may also contain a
minor amount of a saturated acid, a second aromatic acid or
another unsaturated aliphatic acid. If a mixture of acids is
employed, it is preferred that at least about 80 mol percent
of the acid be an alpha-unsaturated dicarboxylic acid or an aro-
matic dicarboxylic acid as described above. The preferred poly-
ester resins for use in the present invention are those prepared
from alpha-unsaturated dicarboxylic acids.
The reaction of the polyol and the dicarboxylic acid
may be pe,rformed in an inert a~mosphere and at moderate tempera-
tures and substantially atmospheric pressures during the early
stage, thus minimizing the loss of dicarboxylic acid by volati-
lization. As the reaction proceeds the temperature may be in-
creased and the pressure reduced. An esterification catalyst
may be used although it is generally preferred to carry out the
reaction in the absence of excessive amounts of catalyst to
avoid contamination of the final resinous product. Where an
unsaturated dicarboxylic acid is used, it is usually desirable
to include a small amount of a polymerization inhibitor such as
-- 8 --
. .
~0468;25
hydroquinone or pyrogallol. The procedure employed to prepare
the polyesters useful in this invention generally include heating
to about 200C for a period of time during the course of the
reaction. The resulting polyesters generally have low acid
numbers - i.e. up to about 30. As used herein, and as is well
known to those skilled in the art, the acid number of the resin
is determined by measuring the number of milligrams of potassium
hydroxide required to neutralize one gram of resin. Also, as
mentioned above, the ratio of carboxyl groups to hydroxyl groups
in the reaction mixt~re employed in preparing the polyester resins
, of this invention is preferably about 1. However, ratios as low
as about 0.8 and as high as about 1.2 can also be employed. ~ -
The preferred polyester resins employed in carrying
out the present invention are the polyoxyalkylene bisphenol A
fumarates such as polyoxypropylene bisphenol A fumarate contain- -
ing an average of 2.2 oxypropylene groups per mol of the bispheol
A. As is well known in the art, bisphenol A refers to the
following compound
HO ~ CH3 OH
CH3
The electrographic recording elements of the present
invention are prepared by coating a layer comprising one of
`~, the above-described polyester resins on any of the above-men-
~` tioned base supports. This coating operation may be carried
out by techniques which are well known in the art. Additives
which are conventionally employed in the preparation of electro-
graphic recording elements may also be included in the dielec-
tric layer. These additives include, for example, whitening
agents and toothing agents.
..
:~ , . . . . : .
10468Z5
In preparing the recording elements, the polyester
resin and any additives are first dissolved in or dispersed in
a suitable solvent, such as toluene, and the resulting slurry
, or solution is then coated onto a suitable base support and
the material dried to remove the solvent. The amount of resin
employed in the preparation of said elements may be varied
over a wide range depending upon the desired properties and
intended application of the electrographic recording element.
However, for most applications it has been found that an amount
of resin which will result in a coating weight of from about
' 0.5 to about 10 pounds per ream (3,000 square feet) is preferred.
,,~ Especially preferred results are achieved at coating weights
equal to from about 1 to about 5 pounds per ream.
~' .
3 As compared to the previously available electrographic
recording elements, materials prepared in accordance with the
present invention have been found to have improved charge accept-
~, ance and improved charge retention properties.
,', Charge acceptance is measured by recording the amount
of voltag,e on the electrographic recording element immediately
after exposure to a source such as a corona discharge.
Charge retention is measured by recording the amount
of voltage remaining on the recording element after a predeter-
~, mined period of time. This property is generally defined in
terms of the percentage of charge retained over a period of
~ .
time.
'', As mentioned above, in an electrographic recording or
" printing process it is important that the recording element
accept and retain a high charge. In this regard, it should be
noted that both the charge acceptance and charge retention are
frequently related to the amount of dielectric or insulating
:
-- 10
~.ID4682S
resin employed in the layer of the recording element. Thus,
in addition to having high charge acceptance and charge re-
tention properties it is desirable to achieve these properties
at a relatively low coating weight as is possible with the
resins which have been found to be useful for this purpose in
accordance with the present invention.
In order to describe the present invention so that
it may be more clearly understood, the following examples are
set forth. These examples are set forth primarily for the
10 purpose of illustration and any enumeration of detail contained
therein should not be interpreted as a limitation on the con-
cept of the present invention.
In the examples the following standard tests were
employed.
Charge acceptance was measured by a Most Stati-Tester
available from M. K. Associates, Bosto~" Ma~s. and is expressed
f in terms of volts. ~ -
Charge retention was also measured on the Most Stati-
Tester and is also given in volts. An important characteristic
20 of the materials prepared with the resins of the present inven-
tion is the ability to retain a high charge during the period
of from about 1 to about 4 minutes after termination of
charging. The percent charge retention in the examples refers
to the percent of the charge on the recording element after one
minute which is retained by the material after 4 minutes. This
is determined as follows:
., .
charge remaining
% charge retention = after 4 minutes
charge remaining
after 1 minute
Coating weight was determined by weighing a sample of
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\
` 1046825
the electrographic recording element, subtracting the weight
- of the base support and calculating the weight of the coating
in pounds per ream.
The following resins were used in the examples:
Resin A refers to a polyester resin, having an acid
. number of 10 - 20, prepared by condensing 580 grams of fumaric
acid with 1833 grams of polyoxypropylene(2.2)bisphenol A.
Resin B refers to a polyester resin, having an acid
number of 21.7, comprising the reaction product of
, 10 1810 grams of polyoxypropylene(2.2) bisphenol A,
15 grams of glycerine, and
,1' 6~3 grams of fumaric acid.
.:. ~
:' /
~ ' /
~1 /
~! /
il /
.~ /
., /
. /
' / '
,
': '
;
- 12 -
,,
;~ '
10468Z5
Resin C refers to a polyester resin, having an acid
number of 32.9, comprising the reaction product of
1737 grams of polyoxypropylene (2 2)bisphenol A,
86.3 grams of polyoxypropylene(6)sorbitol, and
676 grams of fumaric acid.
Resin D refers to a polyester resin, having an acid
number of 21.25, comprising the reaction product of
423 grams of polyoxypropylene(2.2)bisphenol A, and
177 grams of phthalic anhydride.
EXAMPLE 1
r~A
A coating composition was prepared comprising
50 grams of Resin A
50 grams of toluene.
The composition was coated using a wire wound rod on
Fletcher Tek (Registered Trade Mark) conductive papers and dried.
The properties of the resulting electrographic recording element
are given below.
Coating Charge Charge Retention % Charge
weightAcceptance after after Retention
20(lbs/ream) (volts) 1 min. 4 min.
2.7 588 197 177 90
8.1 718 580 515 89
EXAMPLE 2
Employing the procedure described in Example 1,
several additional compositions were prepared, used to prepare
electrographic recording elements and tested. The compositions
and test results are given in the following Table:
:-,
';
- 13
'
':
1046825
, ~
. . ~ ~ ., ., W ~ U~,
.. ,p~ ~ W W ~ ~ ~ ~ g
;~ O O ~ ~ ~
" U~.
,, o'
a~ J ~I ~ ~--
o o ~ ~ ~
'.~, ~g
co 1~ ~ ~ ~ ~
i . w w co ~ w w ~2
. . ~
:~
00 ~ J Q ~ n
.~ ao O O N~11 0 1--ID
CO O t~ ~ (Q
,,-,, , . U~ ID
;;, i ~D
' __
:. ~ n ~ .
~ o ~ _~ ~h
' . O ~ 0 00 0 0
,,i . .
., . ~ W Ul ~ ~ ~n ~p) rD
'.' O X ~n W ~n Ul ~, ~t ~
~ ~ O-
;' CO CO ~ CO ~D ~I ~D
',.............. ~ ~ O ~I ~S
., , . ul ~n Ul ~
.,~,, _ _
~,;.,,
