[0001] The present invention relates to a process for finishing colour developer paper of
the type which is used in pressure-sensitive copying systems and particularly copying
systems of the transfer type.
[0002] In such a transfer system an upper sheet (hereinafter referred to as a CB sheet)
is coated on its lower surface with microcapsules containing an oily solution of at
least one colourless colour former and a lower sheet (hereinafter referred to as a
CF sheet) is coated on its upper surface with a colour developing co-reactant such
as an acidic clay, a phenolic resin or certain organic acid salts. If more than one
copy is required, one or more intermediate sheets (hereinafter referred to as CFB
sheets) are provided each of which is coated on its lower surface with microcapsules
and on its upper surface with colour developing co-reactant material. Pressure exerted
on the sheets by writing or typing ruptures the microcapsules thereby releasing colour
former solution on to the colour developing co-reactant material and giving rise to
a chemical reaction which develops the colour former and so produces an image.
[0003] One of the main uses of pressure sensitive copying systems is in business forms.
It is important that the coated paper which is to be used for the business forms should
be easily printable and should be of good handleability for ease of feeding into a
printing machine.
[0004] In particular colour developer paper should be smooth and of a certain stiffness
and bulk to provide the desired handleability.
[0005] 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 from the
drying section). However an acceptable smoothness is often only obtained at the expense
of stiffness and bulk.
[0006] It is an object of the present invention to produce colour developer paper which
is of excellent smoothness but is also of good handleability.
[0007] According to a first aspect of the present invention 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 web carrying a coating of inorganic colour
developing co-reactant material through a nip between two calendering rolls, characterized
in that the calendering rolls are both heated other than solely by contact with the
web such that their surfaces are at a temperature of at least 105°C.
[0008] In a second aspect the present invention provides colour developer paper which has
been finished according to said first aspect.
[0009] In a third aspect the present invention provides a pressure sensitive copying system
utilizing colour developer paper finished according to said first aspect.
[0010] Heating may be achieved by means of, for example, any one of the following 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 type of roll is known as a displacer roll and provides a more even
temperature across the roll).
[0011] In general suitable calendering rolls may be any of those conventionally used in
the paper industry for example chilled iron rolls.
[0012] The present process is suited for use with papers in which the colour developing
co-reactant material is an acidic clay or other inorganic material.
[0013] Preferably the colour developing co-reactant material is an acid washed dioctahedral
montmorillonite clay such as that sold by Mizusawa Industrial Chemicals of Japan under
the trade mark "Silton" or that sold by Sud-Chemie A.G. of West Germany under the
trade mark "Copisil".
[0014] Additionally the colour developer coating may incorporate a filler such as kaolin
or calcium carbonate. A binder such as latex may also be included in the coating.
[0015] As well as affording improved smoothness without the corresponding deterioration
in stiffness and bulk usually experienced, the present invention also affords the
benefit of considerable cost savings in so much as an increased amount of filler may
be added to the base paper, thus reducing the amount of expensive fibre needed without
affecting the stiffness and bulk of the resulting colour developer sheet for a given
smoothness.
[0016] In order that the present invention be more readily understood reference will now
be made to the accompanying drawing which illustrates diagrammatically and by way
of example an embodiment thereof, and which is a schematic side view of apparatus
for finishing colour developer paper.
[0017] 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 direction 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 chilled iron and are supplied with high pressure steam
such that their surface is at a temperature of the order of 105°C. The rolls 6 form
a pressure nip 9 at their point of contact. The nip 9 is protected by a nip guard
8.
[0018] The web 1 then passes around two further guide rolls 2 before being wound up into
a roll 5.
[0019] 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
rolls.
[0020] The invention will now be illustrated by the following example.
Example
[0021] A web of clay coated colour developer paper ("Idem" CF 57 supplied by Wiggins Teape)
was passed through a hot calendering nip as shown in the drawing with the coated side
down. The surfaces of the calendering rolls were maintained at a temperature of 105°C.
The nip pressure was varied as was the speed at which the web passed through the hot
calendering nip.
[0022] A control was also run by passing a similar web through a cold calendering nip, the
surfaces of the calendering rolls being at a temperature of 18°C.
[0023] The bulk and stiffness of the paper were then measured to give an indication of the
handleability of the resulting paper. Bendtsen and Parker roughness were also measured
to indicate the degree of smoothness of the colour developer coating. The stiffness
was measured in Taber units using the method according to International Standard (IS)
No. 2493 in both the machine direction (MD) and the cross section (CD) of the web.
The bulk was measured according to British Standard BS3983. The Bendtsen roughness
was measured according to British Standard BS4420: 1969 for both the colour developer
coated side of the paper web and also the uncoated side.
[0024] 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.
[0025] Parker roughness may be measured under a variety of conditions. The Parker roughness
in this case was measured with a standard soft backing (Neoprene Litho blanket 85°
Shore) at a clamping pressure of 20 kgf cm
_2. This is indicated as S-20 in the tables of results.
[0026] 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 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 test strip, measuring the reflectance
of the thus coloured strip (I) and expressing the result (
I/
Io) as a percentage of an unused control strip (10). 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.
[0027] The results are shown in Table 1, in which nip pressures are quoted as linear pressures
since it is difficult to quote an absolute value, as is well understood in the art.
[0028] It will be seen from the results that the general effect of hot calendering was to
reduce the bulk and increase the smoothness for a given line pressure. Stiffness also
increased for a given smoothness.
[0029] Hot calendering does not appear to have any significant effects on the functional
properties of the CF as evidenced by the CI values obtained. The CI values obtained
for hot calendered paper are not substantially different from those obtained for cold
calendered paper.
[0030] Although it appears from the results that the absolute values obtained when calendering
at 105°C as compared to 120°C are different, the proportional benefits of hot calendering
are the same in each case. These differences are likely to be due to variations in
web moisture content before calendering or slight basis weight variations.
1. A process for finishing colour developer paper for use in a pressure sensitive
copying system comprising the step of passing a paper web carrying a coating of inorganic
colour developing co-reactant material through a nit between two calendering rolls
characterised in that the calendering rolls are both heated other than solely by contact
with the web such that their surfaces are at a temperature of at least 105°C.
2. A process as claimed in Claim 1 wherein the colour developing co-reactant material
is an acidic clay.
3. A process as claimed in any preceding claim wherein the colour developing co-reactant
material is an acid washed dioctahedral montmorillonite clay.
4. A pressure sensitive copying system utilising colour developer paper finished by
the process as claimed in Claim 1.
1. Verfahren zum Appretieren von Farbentwicklungspapier zur Verwendung in einem druckempfindlichen
Kopiersystem, umfassend den Schritt des Durchführens einer Papierbahn, die eine Beschichtung
eines anorganischen Farbentwicklungs-Coreaktantenmaterials trägt, durch einen Walzenspalt
zwischen zwei Kalandrierungsrollen, dadurch gekennzeichnet, daß beide Kalandrierungsrollen auf andere Weise als nur durch Kontakt mit der Bahn
derart aufgeheizt werden, daß ihre Oberflächen auf einer Temperatur von mindestens
105°C sind.
2. Verfahren nach Anspruch 1, worin das Farbentwicklungs-Coreaktantenmaterial ein
saurer Ton ist.
3. Verfahren nach einem der vorhergehenden Ansprüche, worin das Farbentwicklungs-Coreaktantenmaterial
ein mit Säure gewaschener dioktaedrischer Montmorillonit-Ton ist.
4. Druckempfindliches Kopiersystem unter Verwendung von Farbentwicklungspapiers, das
nach dem Verfahren nach Anspruch 1 appretiert wurde.
1. Procédé pour l'apprêtage de papier révélateur couleur destiné à l'utilisation dans
un système de reproduction sensible à la pression, comprenant l'étape dans laquelle
on fait passer une bande de papier portant un revêtement en un matériau minéral co-réactant
révélateur de couleur à travers une ligne de serrage entre deux cylindres de calandrage,
caractérisé en ce que les cylindres de calandrage sont chauffés tous les deux autrement
que par seul contact avec la bande de telle sorte que leurs surfaces sont à une température
d'au moins 105°C.
2. Procédé selon la revendication 1, dans lequel le matériau co-réactant révélateur
de couleur est une argile acide.
3. Procédé selon l'une quelconque des revendications précédentes, dans lequel le matériau
co-réactant révélateur de couleur est une argile montmorillonite dioctaédrique lavée
à l'acide.
4. Système de reproduction sensible à la pression utilisant un papier révélateur de
couleur apprêté par le procédé selon la revendication 1.