Note: Descriptions are shown in the official language in which they were submitted.
~23~782
3431
PROCESS FOR FINISHING CO]LOUR DEVELOPER PAPER
The present invention relates to a process for finishing
colour developer paper of the t'ype ~hich is used in
pressure-sensitive copying systems and particularly
copying systems o~ the trans~er type.
In such a trans~er system an upper sheet (hereina~ter
referred to as a CB sheet) is coated on its lower surface
with microcapsules containing an oily solution o~ at least
one colourless colour ~ormer and a lower sheet
(hereina~ter referred to as a CF sheet) is coated on its
10 upper surface with a colour developing co-reactant such as
an acidic clay, a phenolic resin or certain organic acid
salts. If ~ore than one copy is required, one or more
intermediate sheets (hereinafter referred to as CFB
sheets) are provided each of ~hich is coated on its lower
15 surface with microcapsules and on its upper surface with
colour developing co-reactant material. Pressure e~erted
on the sheets by ~riting or typing ruptures the
microcapsules thereby releasing colour former solution on
to the colour developing co-reactant material and gi~ing
20 rise to a chemical reaction which develops the colour
former and so produces an image.
One of the main uses~o~ pressure sensitive copyin~
systems is in business forms~. It is important that the
coated paper which is to be used for the business ~orms
25 should be easily printable and should be of good
handleability for~eàse o~ ~eeding into a printing machine.
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In partlcular colour developer paper should be smoooth and
of a certain sti~ness and bulk to provide the desired
handleability.
Generally, in order to obtain the required smoothness,
colour developer paper is cold calendered (although the
calender rolls may become warm when a hot paper web passes
between them as may happen for example when the web passes
straight ~rom the drying section). Howe~er an acceptable
smoothness is often only obtained at the e~pense o~
10 stif$ness and bulk.
It is an object o~ the present invention to produce
colour developer paper which is of e~cellent smoothness
but is also o~ good handleability.
According to a first aspect of the present invention
15 there is provided a process for finishing colour developer
paper for use in a pressure sensitive copying system,
comprising the step of passing a paper ~eb carrying a
coating of inorganic colour developing co-reactant
material through a nip between two calendering rolls,
20 characterized in that the calendering rolls are both
heated to a temperature above that of the web.
In a second aspect the present invention provides colour
developer paper which has been finished according to said
first aspect.
25 In a third aspect the present invention provides a
pressure sensitive copying system utilizing colour
developer paper finished accordi~g to said ~irst aspect.
Preferably the calendering rolls are at a temperature o~
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1Z3~7~3Z
at least 50C, more pre~erably at least 80C and even more
pre~erably at least 110C. Heating may be achieved by
means o~, for example, any one of the ~ollowing media high
pressure steam, pressurised water or oil. The heating
media may pass through either a central reservoir in the
calendering roll or round an annular space within the roll
(this ~ype of roll is known as a displacer roll and
provides a more even temperature across the roll).
In general suitable calendering rolls may be any o~ those
10 conventionally used in the paper industry ~or e~ample
chilled iron rolls.
The present process is particularly suited ~or use with
papers in which the colour developing co-reactant material
is an acidic clay or other inorganic material, but in
15 principle, it could alternatively be a phenolic resin or
certain organic acid salts, both of ~hich alternative
co-reactant materials are well known in the pressure
sensitive copying art and so will not be described ~urther
herein.
~0 Pre~erably the colour developing co~reactant material is
an acid washed dioctahedral montmorillonite clay such as
that sold by ~izusawa Industrial Chemicals o~ Japan under
the trade mark "Sil~on" or that sold by Sud-Chemie A.G. o~
West Germany under tbe trade mark "Copisil".
25 Additionally the colour developer coating may incorporate
a filler such as kaolin or calcium carbonate. A binder
such as la*e~ may also be included in the coating.
As well as a~ording improved smoothness without the
corresponding deterioration in sti~ness and bulk usually
30 experienced, the present invention also af~ords the
bene~it o~ considerable cost savings in so much as an
increased amount o~ ~iller may be added to the base paper,
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387~2
thus reducing the amount of expensive fibre need~d
~ithout af~ecting the stiffness and bulk of ~he resulting
colour developer sheet for a given smoothness.
In order that the present invention be more readily
understood reference will now ble made to the accompanying
drawing which illustrates diagr,ammatically and by way o~
example an embodiment thereoi, and which is a schematic
side view of apparatus for flnilshing colour developer
paper.
10 A paper web generally indicated 1 carrying a coating of
colour developer material on its surface 3 is unwound from
a reel 4 in the dlrection shown by the arrow and then
passes around guide rolls 2. The web then passes between
two calender rolls 6. The calender rolls 6 are of
15 chilled iron and are supplied with high pressure steam
such that their surface is at a temperature of the order
o~ 105C. The rolls 6 form a pressure nip 9 at their
point of contact. The nip 9 is protected by a nip guard
8.
20 The web 1 then passes around two further guide rolls 2
before being wound up into a roll 5.
Instead of being unwound from a reel 4, the paper web may
alternatively pass straight from a coating'section at
which it has just been coated and dried to the calender
25 rolls.
The invention will now be illustrated by the Pollowing
example.
Example
A web of clay coated colour developer paper ("Idem" CF 57
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~23~78~
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supplied by Wiggins Teape) was passed through a hot
calendering nip as shown in the drawing with the coated
side down. The sur~aces of the calendering rolls were
maintained at a temperature o~ 105C. The nip pressure
was varied as was the speed at which the web passed
through the hot calendering nip.
A control was also run by pass:Lng a similar web through a
cold calendering nip, the surfaces of the calendering
rolls being at a temperature O~e 18C.
10 The bulk and stl~fness oi' the paper were then measured to
give an indication of the handleability o~ the resulting
paper. Bendtsen and Parker roughness were also measured
to indicate the degree of smoothness of the colour
developer coating. The stiffness ~as measured in Taber
15 units using the method according to International Standard
(IS) No. 2493 in both the machine direction (MD) and the
cross direction (CD) of the web. The bulk was measured
according to British Standard BS3983. The Bendtsen
roughness was measured according to British Standard
20 BS4420:19~9 for both the colour developer coated side o~
the paper web and also the uncoated side.
The Parker roughness was measured in a similar manner to
that described in the British Paper and Board Industry
Federation (BPBIF) proposed procedure No. PP 59.
25 Parker roughness may be measured under a variety of
conditions. The Parker roughness in this case was
measured ~ith a standard so~t backing (Neoprene Litho
blanket 85 Shore) at a clamping pressure of
20 kgfcm~20 Thls is indicated as S-20 in the tables
30 of results.
lZ3~7~32
For both Bendtsen and Parker roughness a high value
indicates a rough surface therefore the lower the value
the smoother the surface. All the results quoted are
mean values of several readings. In order to illustrate
that hot calendering does not impair the functional
properties of the colour developer paper a calender
intensity test was also carried out. The calender
intensity (CI) test involved superimposing strips of paper
coated with encapsulated colour former solution onto a
10 strip of the coated paper under test, passing the
superimposed strips through a laboratory calender to
rupture the capsules and thereby produce a colour on the
tes$ strip, measuring the reflectance of the thus coloured
strip (I) and expressing the result (I/IO) as a
15 percentage of an unused control strip ( Io)~ Thus the
lower the calender intensity value (I/IO) the more
intense the developed colour. The CI values were
recorded after 2 minutes and again after 48 hours.
The results are shown in Table 1, in which nip pressures
20 are quoted as linear pressures since it is di~ficult to
quote an absolute value, as is well understood in the
art.
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~Z3~3'782
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~23~82
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The above procedure was then repeated but this time the
colour developer web was hot calendered ~ith the coated
side uppermost. Again a control was run at 18~C.
The results are shown in Table 2.
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It will be seen from the results that the general e~ect
of hot calendering was to reduce the bulk and increase the
smoothness for a given line pressure. Stif~ness also
increased ~or a given smoothness.
Hot calendering does not appear to have any significant
effects on the functional properties o~ the CF as
evidenced by the CI values obtained. The CI values
obtained for hot calendered paper are not substantially
different from those obtained ~or cold calendered paper.
10 Although it appears from the results that the absolute
values obtained when calendering at 105C as compared to
120C are different, the proportional benefits o~ hot
calendering are the same in each case. These differences
are likely to be due to variations in web moisture content
15 before calendering or slight basis weig&t variations.
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