CA1037713A

CA1037713A - Coated paper

Info

Publication number: CA1037713A
Application number: CA208,839A
Authority: CA
Inventors: Lawrence Westcott
Original assignee: Wiggins Teape Ltd
Current assignee: Arjo Wiggins Ltd
Priority date: 1973-09-13
Filing date: 1974-09-10
Publication date: 1978-09-05
Also published as: DE2443099C3; AU7319874A; JPS56159196A; JPS5711089A; FI57143B; JPS6133718B2; JPS5083117A; NL7412106A; AR204332A1; GB1433165A; ZA745812B; IN142448B; NL168762C; US4081188A; SE417587B; SE7411514L; ES430043A1; BE819851A; FR2243827A1; NL168762B

Abstract

ABSTRACT

Paper for use in pressure-sensitive copying systems consists of a base paper one surface of which is machine glazed and the oppo-site surface of which is left rough due to expulsion of moisture during manufacture. Those sheets which are provided with a colour reactant have the reactant applied to the glazed surfaces thereof and those sheets which are provided with a microcapsule coating have the microcapsule coating applied to the rough surfaces thereof.

Description

~Q377~3 ; This invention relates to coated paper for use in so-called "clean-to-handle" pressure-sensitive copying systems.
One known clean-to-handle pressure-sensitive copying system com-prises an upper sheet, known as a CB sheet, whi¢h is coated on its lower sur~ace with pressure-rupturable microcapsules containing a solution of a colour former material, and a lower sheet, known as a CF sheet, which i~ coated on its upper suriace with a colour reactant material, such ~s an acidic clay or a phenolic resin. For most application~, a number of intermediate sheets, known as CFB sheets, are also provided each of which is coated on its lower surface wlth microcapsules and on it8 upper surface wlth colour reactant material.
The pressure exerted on the sheets by writing or typing ruptures the microcapsules, thereby releasing the colour former solution onto the reactant material o~ the next lower sheet and giving rise to a chemi-cal reaction which develops the colour of the colour former. The mlcrocapsules are usually!applied in aqueous suspen~ion~
The above d~scribed pressure-sensitive copying system will here-ina~ter be called a "pressure-sensitive copying system of the kind referred to".
CF sheets in which the colour reactant material is an acidic clay have hitherto been manu~actured by coating, e.g. blade coating, a suitable base paper with an aqueous coating mix, and for this purpo~e it is desirable for the base p~per to have as smooth a surface as possible, ~lnce a smooth surface allows a low colour reQctant ~aterlal coat ~eight to be used, whilst still affording the desired C~ proper-- ties. The desired smoothness is normally obtained by calendering the base paper prior to coating thereof, and such calenderin~ also serves to make the surface of the base paper compact, which mlnimises migra-tion Or the subsequently applied coating into the base paper. The base paper is normally calendered again after coating ~n order to make the coating compact and give ~t a smooth surface. A ~mooth C~ sur-~ace is desirable since when a CB or CFB sheet overlies the CF sheet there will be a tendency for any roughnesses of the CF surface to

- 2 _ ; ' '' ' '; ' ' -:, 1037~13 snag the microcapsules on the CB surface, which may lead topremature rupture of the microcapsule, or "smudging" as it is usually known.
Similarly, base paper for the manufacture of CB
sheets has hitherto been calendered to provide a compact surface prior to application of an aqueous microcapsule dispersion thereto. The microcapsule dispersion may for ~ example be applied by means of an airknife coater. However, - the smoothness resulting from calendering fo the CB sheet base paper would lead to the microcapsules standing out from the surface of the base paper, in which position they would be very prone to accidental rupture, for example during handling operations. It has therefore become a normal practice to coat the microcapsules onto the surface together with a so-called stilt material, such as cellulose fibres or starch granules, the dimensions of which are such that the stilt material protrudes further from the base paper than the microcapsules. The stilt material therefore serves .
to protect the microcapsules against accidental rupture while still allowing rupture under typing or writing pressure.
The presence of stilt material adds to the expense of CB and CFB sheets, and may also lead to problems in coating the base paper with microcapsule suspension.

; It has now been found that the use of machine glazed paper as the base paper obviates the need for stilt materials, or at least renders their presence necessary in smaller amounts. and affords a number of other advantages. ~;
Accordingly, therefore, the invention s a coated paper for use in pressure sensitve copying systems of the

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` ~o37~13 . type which includes (A) a copying system comprising an upper sheet which is coated on its lower surface with pressure rupturable microcapsules containing a colour former material, and a lower sheet coated on its upper surface with a colour reactant material, and (B) a copying system as described in (A) which additionally comprises at least one intermediate sheet which is coated on its lower surface with microcapsules :
and on its upper surface with colour reactant material, and is the improvement which comprises the coated paper being a machine glazed base paper having a smooth glazed surface and a rough surface and having a colour reactant on the smooth glazed surface of the base paper when it functions as a ~: lower sheet and having a microcapsule coating on the rough surface of the base paper, when it functions as an upper sheet, and having a colour reactant on the smooth glazed surface of the base paper and a microcapsule coating on the rough surface of the base paper when the paper functions as an intermediate sheet.
The coated paper may be CF sheet, in which case 2~ colour reactant will be present and microcapsules will be ^ absent, or a CB sheet, in which case colour reactant will be absent and microcapsules will be present, or a CFB sheet in which case colour reactant and mircrocapsules will both be present.
In a further aspect, the invention provides a process for manufacturing a coated paper for use in pressure sensitive copying systems of the type which includes (A) a : copying system comprising an upper sheet which is coated on its lower surface with pressure rupturable microcapsules containing a colour former material, and a lower sheet -3a-iA

1Q37~13 coated on its upper surface with a colour reactant material, and (B) a copying system as described in (A) which addition-ally comprises at least one intermediate sheet which is coated on its lower surface with microcapsules and on its upper surface with colour reactant material, comprising the steps of drying a paper web which has been formed on a paper-making machine wire by means of a machine glazing cylinder to give a machine glazed base paper having a smooth glazed surface and a rough surface, and applying a coating of a colour reactant material to the smooth glazed surface : of the base paper when it functions as a lower sheet and applying a microcapsule coating to the rough surface of the base paper, when it functions as an upper sheet, and applying a coating of a colour reactant material to the smooth glazed surface of the base paper and a microcapsule coating : to the rough surface of the base paper when the paper functions as an intermediate sheet.
Apparatus for manufacturing coated paper for use in a pressure-sensitive copying system of the kind referred .
to can comprise a paper making wire or wires for formation ~

of a wet paper web, a machine-glazing cylinder for drying ~ -: the web and imparting to the web a high glaze on one surface, while leaving the other surface rough, a coater for coating the glazed surface of the web with colour reactant material, :
: 25 and/or a coater for coating the rough surface of the web with microcapsules. ~.
Machine-glazed paper, usually known as MG paper, is paper which has been dried, after formation on the wire of a paper-making machine, with one surface in contact with a highly polished, heated drying cylinder, known as an MG
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1037ql3 cylinder, with the result that the surface contacting the cylinder is given an extremely smooth finish, while the other surface of the web becomes rough owing to water being expelled from the web through said other surface.
; 5 Hitherto, MG paper has generally been made in poor quality grades only, where opposite surfaces of markedly different roughness can be tolerated, and its use has not ~; been considered where quality, i.e. surfaces of similar smoothness, is important. Base paper for the present purpose may, however, be made from furnishes which are ; conventional for base paper for use in a pressure-sensitive copying system of the kind referred to.
Whereas MG paper is dried by means of an MG cylinder, - base paper for CF, CB and CFG sheets conventionally been dried on drying " ~
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cylinders and then calendered, as has already been d~scribed.
An MG paper can have a glazea surface much smoother than the surface which can be obtained by calendering or super-calendering a conventionall~ manu~actured base paper, which~ as discussed previous-ly permits the use of a small coat weight of colour reactant material whilst still providing the desired properties in the coated product.
A further advantage of MG paper for the present purpose is that the glazed surface is virtually sealed, and thus there is a low loss of applied colour reactant material by migration into the MG paper.
There is also no need to calender the paper after coating since the smoothness of the glazed surface of the MG paper is such that the coating applied thereto inherently has a satisfactory smoothness and ; resistance to smudging. ~he colour reactant material, e.g. an aci-- dic clay, can be applied by blade GOating~ for example. Yet a - further advantage of MG paper is that it has a good dimensional sta-bility.
Although calendering is unnecessary for smoothing purposes, it -; may be desirable to employ slight calendering to provide a draw sta-tion for drawing the paper web through the machine, and to provide fine control of surface smoothness. A single-nip calender may, for example be used, and it will be appreciated that this does not com-pare in severity with conventional calendering.
It is thought that it is the roughness of the unglazed surface of an MG paper which allows microcapsules to be applied without the need for any stilt material to prevent accidental rupture of the cap-sules, since the high spots of the unglazed surface generally protru-de further from the body Or the base paper than do the microcapsules.
The high spots, therefore function in a similar manner to convent-ional stilt material. Since the microcapsules can be coated onto the basc paper by themselves, i.e. without any simultaneous coating of stilt material, a more uniform coating of the microcapsules can be obtained which reduces the coat weight necessary to obtain desi-red properties~ A further advantage of the use of MG paper is that ., .

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~037713 since separate stilt material is not essential, problems caused by loss of such material from manufactured sheets, known as dusting problems, do not arise~ Another advantage is that by control of the manufacturing operation the roughness of the unglazed surface of the MG paper can be controlled in dependence upon the size of the micro-capsules to be coated thereon. An air-knife coater, for example, can be used to coat the microcapsules (in aqueous suspension).
In conventional paper making it is normal to size the paper web internally, and also to apply starch by means of a size press, in order to prevent a subsequently applied aqueous coating mix, for example a microcapsule or colour reactant material coating mix,from penetrating too far into the paper web. Starch sizing is normally ` carried out using a size press apparatus. It has also been proposed to apply dyes to a paper web using a size press apparatus, which aifords the advantage that only white paper webs have to be produced at the wet end of the paper making machinery since any desired co-lours can be applied at the size press. A further advantage of this procedure i5 that the problems associated with dyeing and the dura-tion of dyeing are reduced.
It has been found that such size press sizing and dyeing can he carried out on MG paper ii desired, without unduly harming the above described advantageous surface characteristics of the MG pa-per, and thus coated paper according to the present invention which is coloured can readily be produced. Starch sizing can be dispensed with altogether, if desirsd.
In order to enable the invention to be more readil~ understood~
reference will now be made to the accompanying drawings, which il-lustrate diagrammatically and by way of example some embodiments thereof, and an embodiment of conventional apparatus for making coa-ted paper for a pressure-sensitive copying system of the kind refer-red to, ~nd in which:-Figure 1 is a cross-section through an uncoated MG paper;
Figure 2 is a cross-section through a CF sheet having an MG paper base;

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~037713 Figure 3 is a cross-section through a CB sheet having an MG paper base;
Figure 4 is a diagrammatic cros~-æection through a CFB
sheet having an MG paper base;
Figure 5 is a schematic diagram of a first embodiment of apparatus according to the invention for manufac-turing a CFB sheet as shown in Figure 4;
; Figure 6 i9 a schematic diagram of a second embodiment of apparatus according to the invention for manufac-turing a CFB sheet as shown in Figure 4; and Figure 7 is a schematic diagram, to a scale different from that of Figure 6, of conventional apparatus for manufacturing a C~B sheet of which the base paper is conventionally dried and calendered~
Referring first to Figure 1, a sheet of uncoated MG paper 1 has one rough surface 2, the roughness being due to the expulsion ; o~ moisture from the paper through this surface 2 during manufact~
ure, and one extremely smooth surface 3 which has been in contact with a highly polished, heated drying cylinder during ma~ufacture.
.. ~ , ~he rough surface 2 may, for example, have a Bendsten roughness of between 700 and 1000 ml/min, while the smooth surface may, for ex-ample, ha~e a Bendsten roughness of less than 100 ml/min, which i8 smoother than can readily be obtained by calendering or super-cal-endering a conventionally manufactured paper.
Referring now to Figure 2, there is sho~ a CF sheet which has been manufactured from the MG paper 1 shown in Figure 1 by apply-ing a coating 4 of a colour reactant material such as an acidic clay ; or a phenolic resin material to the glazed surface 3 of the MG paper 1, by blade coating or other coating technique. ~he smoothness of the coating which can be obtained i8 such that calendering of the paper after coating is unnecessary and that a low coat weight can be used.
Referring now to Figure 3, there is shown a CB sheet which has - _ 7 _ - , . . .

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been manufactured from the MG paper 1 shown in Figure 1 by apply-ing a coating of microcapsules 6 to the unglazed surface 2 of the MG paper 1, by air-knife coating or other coating technique. Va-rious suitable kinds of microcapsules and various suitable colour for~er materials are well known in the art and will not therefore be discussed in detail herein. Owing to the roughness of the un-glazed surface 2, and to the fact that the microcapsules 6 tend to lie in depressions 7 in the unglazed surface 2, the microcapsules 6 are protected against accidental rupture after coating by high spots 8 of the rough unglazed surface 2.
Referring now to Figure 4 there is shown a CFB sheet which has been manufactured from an MG paper 1 as shown in Figure 1 by coat-ing a colour reactant material coating 4 on its glazed surface 3, and a coating of microcapsules 6 on its unglazed surface 2. It will be appreciated that in ~igures 1 to 4, the rough surface is shown as being uppermost, whereas in use, the smooth surface will be upper- -most to provide the writing sur~ace, and the rough surface will be face down.
Referring now to Figure 5, a paper web 13 produced on a paper-making machine wire 11 is passed to a first MG c~linder 12 by meansof a felt and roller arrangement 14. After drying o~ the cylinder 12 the paper web 13 passes through a conventional size press appa-ratus 15 where it is sized and dyed as desired. After being sized and dyed the paper web 13 is passed around a second unfelted MG cy-linder 16 to dry the sized and dyed web.
From the cylinder 16 the paper web is passed to a convention-al coating apparatus, e.g. a BiIl-blade 17 or a trailing-blade, where a colour reactant material coating is applied to the now gla-zed surface of the paper web to produce a coated paper web 21. ~rom the coating apparatus 17 the coated paper web 21 is passed around a third MG cylinder 18 which dries the applied colour reactant ma-terial coating. ~he web 21 is then passed to an air-knife coating apparatus 19 by means of which a microcapsule coating is applied to 1037 ~13 the unglazed uncoated surface of the paper web 21 to produce a web 22 which is coated on both surfaces. ~rom the coating apparatus 19 the web 22 is passed through a drying apparatus 20, for example an air suspension drying apparatus, and is then reeled up at a reel-up station (not shown), in the form of CFB paper as sho~m in ~igure 4.
Instead of the third MG cylinder 18, an air-suspension-drying appa-ratus may be used if de~ired.
By omitting the coating apparatus 19 and the drying apparatus 20 the machinery described above can be used to manufacture CF pa-per as shown in ~igure 2, and by omitting the coating apparatus 17and the cylinder 18 the machinery can be used to manufacture CB pa-per as shown in Figure 3. The size press apparatus 15 and the cy-linder 16 may if desired be omitted in which case the paper web 13 may be sized and dyed as necessary by suitable additions to the stock from which the paper web 13 is manu~actured.
Referring now to Figure 6, there is shown apparatus comprising a twin-wire papermaking station generally designated 30, arranged to be supplied with pulp from a head box 31. A web produced at the station 30 is de-watered at a press-felt station generally design-ated 32, and passed to an MG cylinder drying station 33 for finaldrying. ~ C~ coating is applied at a CF coating station 34, which as shown is a Bill-blade coater, but may be another type of coater.
~he CF coating i9 dried by means of a float drying apparatus 35.
The web passes to a CB coating station 36, which as shown is a re-- verse-roll coater, but may be another type of coater. ~he CB coat-ing i~ dried initially by means of a float drying apparatus 37 and finally by means of a vacuum through-dr~ing cylinder 38. The dried coated web is then reeled up at a reeling-up station 39. ~wo sin-gle-nip calenders 29, 291 are provided to draw the web through the ~ -apparatus, and are located immediately after the drying stations 33 and 35 respectively.
It will be appreciated that the apparatus can be modif~ed to produce CB paper by omitting the C~ coating and drying station~, or . .
_ 9 _ ~ 37~3 produce CF paper by omltting the CB coating and drying stations.
~'igure 6 shows the apparatus in more detail than has aust been described, but this detail is not material to the inv~ntion, and so further description is unnecessary for present purposes. In any case, a papermaker will have no difficulty in identif~ing the addi-tional features shown.
Referring now to Figure 7, there is shown apparatus comprising - a single wire papermaking station generally designated 40, arranged to be supplied with pulp from a head box 41. A web produced at the station 40 is de-watered at a press felt station gene~ally designa-ted 42, and of which the felts are not shown, and finally is dried - by a bank of drying cylinders 43. ~tarch is applied by means of a size press 44, and the web is then dried by means of a bank of dry-ing cylinders 45. The web is then calendered at a calenderin~ sta-tion 46 and CF coated at a coating station 47. ~he CF coating is dried by means of drying cylinders 48, and calendered at a calen-dering station 49. A CB coating is applied by a forward-roll coater 50, and smoothed by air-knives (not shown) before being dried at a - drying station 51 and passed to a humidity conditioner 52.
As mentioned previously, Figures 6 and 7 are not on the same scale, and the present invention permits a considerable saving in space to be achieved. ~he apparatus shown in Figure 7 is in fact 215 metres long, whereas that shown in Figure 6 is only 68 metres long.
In exèmplary manufacturing operations using the apparatus shown in Figure 5 to produce CF, CB and CFB sheets according to the present invention 49, 38 and 30 g/m paper webs 13 were pro-duced on the wire ll from a fibre furnish of 70% softwood kraft pulp and ~/o sulphite wood pulp with an 11% addition of china clay (based on dry fibre weight). ~he paper was dried on the first MG
cylinder 12 to give a glazed surface having a Bendsten roughness of about 800 ml/min.
CF sheets were produced by blade coating an approximately 9 .~ .

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g~m2 coating of an acidic clay onto the glazed surface of the pa-per web 13 by means of the apparatus 7. CB sheets were produced by air-knife coating an approximately 5 g/m2 coating of 7Jum dia-meter microcapsules onto the unglazed surface of the paper web 13 by means of the apparatus 19. CFB sheets were produced by apply-ing acidic clay and microcapsule coatings as just deiscribed to the appropriate surfaces of the paper web 13.
On testing, the paper thus produced was found to be satisfac-tor~.

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-

1. In a coated paper for use in pressure sensitive copying systems of the type which includes (A) a copying system comprising an upper sheet which is coated on its lower surface with pressure rupturable microcapsules contain-ing a colour former material, and a lower sheet coated on its upper surface with a colour reactant material, and (B) a copying system as described in (A) which additionally comprises at least one intermediate sheet which is coated on its lower surface with microcapsules and on its upper surface with colour reactant material, the improvement which comprises the coated paper being a machine glazed base paper having a smooth glazed surface and a rough surface and having a colour reactant on the smooth glazed surface of the base paper when it functions as a lower sheet and having a microcapsule coating on the rough surface of the base paper, when it functions as an upper sheet, and having a colour reactant on the smooth glazed surface of the base paper and a microcapsule coating on the rough surface of the base paper when the paper functions as an intermediate sheet.

2. A coated paper according to claim 1, wherein the rough surface has a Bendsten roughness of between 700 and 1000 ml/min.

3. A coated paper according to claim 1, wherein the glazed surface has a Bendsten roughness of less than 100 ml/min.

4. A process for manufacturing a coated paper for use in pressure sensitive copying systems of the type which includes (A) a copying system comprising an upper sheet which is coated on its lower surface with pressure rupturable microcapsules containing a colour former material, and a lower sheet coated on its upper surface with a colour reactant material, and (B) a copying system as described in (A) which additionally comprises at least one intermediate sheet which is coated on its lower surface with microcapsules and on its upper surface with colour reactant material, comprising the steps of drying a paper web which has been formed on a paper-making machine wire by means of a machine glazing cylinder to give a machine glazed base paper having a smooth glazed surface and a rough surface, and applying a coating of a colour reactant material to the smooth glazed surface of the base paper when it functions as a lower sheet and applying a microcapsule coating to the rough surface of the base paper, when it functions as an upper sheet, and applying a coating of colour reactant material to the smooth glazed surface of the base paper and a microcapsule coating to the rough surface of the base paper when the paper functions as an intermediate sheet.

5. A process according to claim 4, wherein the rough surface has a Bendsten roughness of between 700 and 1000 ml/min.

6. A process according to claim 4, wherein the glazed surface has a Bendsten roughness of less than 100 ml/min.