Note: Descriptions are shown in the official language in which they were submitted.
- 2178~13 3657
INR JET PRINTING PAPER
This invention relates to a versatile ink-jet printing paper,
i.e. to paper which is specially adapted to give good imaging
performance when used with an ink jet printer, but which also
exhibits good toner adhesion when imaged by
electrophotographic processes as used in laser printers,
xerographic copiers and such like.
Ink-jet printers will produce an image on most papers, but the
print quality varies markedly in dependence on the nature of
the paper used. By "print quality" is meant factors such as
the sharpness, intensity and uniformity of the image produced
and its susceptibility to smudging immediately or shortly
after the ink has been applied. In the case of colour
printing, it is important also that the colours should not run
into one another and that they should be vivid, with good
brightness.
Print quality is influenced by a number of factors, but the
two most important are the extent to which the ink droplets
spread out ~fter contact with the paper and the rapldity with
which the ink droplets are absorbed into the paper. Excessive
droplet spreading resulting from, for example, flow of ink
along the length of the paper fibres, produces an image which
appears blurred, with fuzzy edges, spidery lines and a general
lack of resolution (this is often referred to as feathering or
wicking, and the effect is somewhat analogous to that obtained
by writing with a fountain pen on blotting paper). Slow
absorption of the ink into the paper can result in smudging of
the image and in merging of ink from different droplets,
giving ragged images and, if the ink droplets are of different
colours, running of the colours into one another, often termed
ink bleed.
Hitherto, it has generally been found necessary to apply a
pigment coating to the paper in order to achieve top quality
colour images, i.e. vivid bright colours which do not run into
one another. The pigment coating makes the paper highly
2178013
-
absorptive to the aqueous ink vehicle, so that the vehicle
drains away quickly into the body of the paper, leaving the
coloured dye at the surface and thereby giving bright intense
colours with minimal print bleed. Whilst pigment coating has
not been found essential for good quality black (monDchrome)
images, it does generally enhance the quality of those images
compared with those obtained on uncoated papers.
The use of a pigment coating is disadvantageous in certain
respects, in that it adds to raw material and process costs,
and tends to give rise to "dusting" problems in subsequent
conversion and printing operations, i.e. pigment particles can
become dislodged from the coating and deposit on reeling,
slitting and printing equipment.
For papers for general office use, the cost of pigment coating
is often not justified, and ordinary uncoated papers have been
used. These have generally been hard sized in order to give
good ink "hold-out", which produces bright colours and
minimises strike-through and feathering (regardless of whether
colour or monochrome inks are used). However, hard sizing can
adversely affect toner adhesion when the paper is imaged with
laser printers, xerographic copiers and such like. It is
important to appreciate in this regard that the commercial
need is for a versatile paper which offers good performance
not just with respect to ink-jet printers but also to laser
printers, xerographic copiers and such like. Many customers
utilise a variety of types of printer, and they seek to obtain
paper which works well on all these printers rather than being
forced to use a different paper for each type of printer.
Good performance with a laser printer or similar requires that
the paper should have a good affinity for the toners used to
effect imaging, so that the toner adheres well to the paper.
The adverse effect of hard sizing on toner adhesion can be
particularly pronounced when sizing is achieved by the use of
alkyl ketene dimer (AKD) sizing agents, possibly because AKD
sizes are waxy in nature and can produce a release effect.
Since AKD sizing offers the papermaker many benefits compared
~- 2178~13
with traditionally rosin-alum sizing, it is important that it
should be possible to utilise AKD sizing in the production of
papers for office use, and that a solution should be found to
the problem of achieving good ink-jet printing performance and
good toner adhesion in the same product.
Good toner adhesion is particularly difficult to achieve with
rough papers which carry a surface-profile texture, for
example a laid line, chain line or other pattern applied by
means of a dandy roll, or a pattern applied by felt marking or
wet or dry embossing. This is probably because toner adhesion
is normally achieved by heat- and/or pressure-fusion of the
toner to the paper. With rough or surface-textured papers, it
is difficult to achieve sufficiently good physical contact for
this fusion to be effective.
It is an object of the present invention to overcome or at
least reduce the problems described above and to provide an
improved ink jet printing paper which gives good colour and
monochrome images without the need for a full pigment coating
of the conventional kind, and which, particularly when the
paper has a surface-relief texture, is also capable of good
quality imaging by electrophotographic processes as used in
laser printers, xerographic copiers and such like.
We have now found that the above-stated object can be achieved
by treating a suitable base paper with a composition
comprising an admixture of: -
(a) a cooked and/or chemically modified starch;(b) a hydrophilic polymer other than a starch; and
(c) a hydrophobic polymer.
Accordingly, the present invention provides, in a first
aspect, an ink-jet printing paper of which the print-receiving
surface comprises a base paper treated with a composition
comprising an admixture of:
- 217801~
(a) a cooked and/or chemically modified starch;
tb) a hydrophilic polymer other than a starch; and
(c) a hydrophobic polymer.
In a second aspect, the present invention provides a method of
producing ink-jet printing paper, comprising the step of
treating at least the print-receiving surface of a base paper
with a composition comprising an admixture of:
(a) a cooked and/or chemically modified starch;
(b) a hydrophilic polymer other than a starch; and
(c) a hydrophobic polymer.
The treatment composition is conveniently applied to the paper
by means of a size press, but other techniques can be used,
for example spraying or coating. The expression "size press"
in this context includes modified size presses or coating
heads as supplled, for example, by Voith under the name
"Speedsizer", Valmet under the name "Sym-sizer", Jagenberg
under the name "Filmpress" and BSG under the name "Twin HSM".
Cooked and/or chemically modified starches are widely used in
the paper industry and are thus very well-known. They are to
be distinguished from particulate starches as found in plants
(such particulate starches are the raw material from which
cooked and/or chemically modified starches are produced).
Dextrins, although derived from starches, are not considered
to be "cooked and/or chemically modified starches" in this
context, since the hydrolysis processes involved in their
production result in loss of essential starch character.
Suitable starches for use in the treatment composition are
generally those used in the paper industry as surface sizes,
as coating binders, or as wet-end additives. Surface-sizing
starches are currently preferred. The starches can be
anionic, cationic, amphoteric or non-ionic in character. A
preferred surface sizing starch for use in the present
invention is an anionic oxidised potato-based starch. Other
suitable surface sizing starches are oxidised maize or wheat
- 2l7snl3
starches.
The hydrophilic polymer for use in the treatment composition
is preferably a polyvinyl alcohol, more preferably a
relatively low molecular weight partially-hydrolysed polyvinyl
alcohol with a degree of hydrolysation of around 88%, or 87-
89% as it is often expressed in manufacturer's product
information sheets. Other hydrophilic polymers which can be
used include dextrin, cellulose derivatives such as
carboxymethyl- cellulose (CMC) and hydroxyethyl cellulose
(HEC); gelatin; vegetable gums such as gum arabic;
polyvinylpyrrolidones; and maleic anhydride copolymers, for
example copolymers of maleic anhydride with ethylene (EMA), or
vinyl methyl ether (PVMMA).
The hydrophobic polymer for use in the treatment composition
is preferably a latex, typically a latex of the kind supplied
for use as a paper coating binder or as a surface sizing
additive. Suitable latexes include styrene-acrylic copolymer
latexes of various kinds (including acrylonitrile/n-
butylacrylate/styrene copolymer latex); styrene-butadiene
copolymer latexes; and polyurethane latexes.
The relative proportions of the starch, hydrophilic polymer
and hydrophobic polymer can vary quite widely, although the
starch is normally the major component of the composition,
usually making up at least 50% of its total weight on a dry
basis. The amount of hydrophobic polymer present can vary
quite widely, depending on the degree of hydrophobicity of the
polymer. For example, the amount of hydrophobic polymer
required when the polymer is a polyurethane is much less than
when the polymer is a styrene-acrylic or carboxylated styrene-
butadiene material. Detailed guidance as to suitable relative
proportions of the various mix components can be gained from
the specific examples given hereafter, but in general terms,
the treatment composition should contain from about 50 to
about 90% by weight starch, from about 5 to about 50%, more
preferably 5 to 25%, by weight of a hydrophilic polymer such
as polyvinyl alcohol, and from about 2 to about 40% of
2178013
hydrophobic polymer, all these percentages being on a dry
basis. Whilst the amount of polyvinyl alcohol used can vary
quite widely, as indicated, cost factors would normally lead
to usage in the lower part of the range quoted. The amount of
hydrophobic polymer used will depend in part on its degree of
hydrophobicity. In general the amount used will be in the
range 2 to 30% by weight. Typically the treatment composition
is made up at a solids content of about 5 to about 15% by
weight, although this is not believed to be critical.
If desired, the treatment composition can include a small
proportion of pigment such that the weight of pigment in the
composition is less, normally much less, than the aggregate
dry weight of the starch, the hydrophilic polymer and the
hydrophobic polymer. The weight ratio of pigment : aggregate
dry weight of starch, hydrophilic and hydrophobic polymer may
be, for example, about 1:20, although the precise ratio is not
thought to be critical. The inclusion of a minor proportion
of pigment in this way can in some cases enhance the ink-jet
printing performance of the paper still further. The use of
a minor proportion of pigments to enhance the effect of the
present composition is to be contrasted with the use of
conventional pigment coatings, in which the pigment normally
predominates (a typical pigment : binder ratio for such
coatings might be of the order of 4:1 to 8:1).
The present treatment composition can be used to enhance the
ink-jet printing performance of a wide variety of papers for
office or other business use. Typically however, the base
paper is an around 80 to 100 g m~2 woodfree base which has been
conventionally internally sized, for example with alkyl-ketene
dimer or a rosin/alum sizing system. Hard sizing is
preferable, for example to a Cobb value (60 seconds) in the
range 15 to 30. The pulps used and their relative proportions
can vary widely, but a typical furnish would comprise 80%
hardwood pulp and 20% softwood pulp. Usual papermaking
fillers and other additives can be present.
2l7snl3
The treatment composition is preferably present in an amount
of 1 to 5%, more preferably 2 to 4%, by weight of the base
paper on a dry basis. Thus for a 100 g m~2 base paper to which
the treatment composition is applied by means of a size press,
the dry pick-up should preferably be from about 2 g m~2 to
4 g m~2, on a dry basis (i.e. 1 or 2 g m~2 per side). Higher
pick-up levels are technically acceptable but may be
economically disadvantageous.
The paper can be preferably calendered after treatment and
subsequent drying, for example to a Bendsten roughness value
of 500 ml min~~ or less. Alternatively the paper can be one
which carries a surface-profile texture as referred to
earlier.
The reasons why the use of the present treating composition
gives good results are not yet fully understood. However, we
believe the presence of the hydrophobic polymer causes the
ink, which is normally aqueous in nature, to be better "held
out" on the surface of the paper - if hydrophobic polymer is
omitted, the ink penetrates the paper structure too rapidly
and dull and ragged print images are obtained.
The polyvinyl alcohol or other hydrophilic polymer on the
other hand promotes a controlled penetration of the ink but
without much lateral spreading. If hydrophilic polymer is
omitted, penetration is poor and the ink drying time is too
long and an undesirable degree of mottle results. Thus
although bright colours may be obtained, differently-coloured
inks remain on the paper surface for sufficient time to run
into and merge with one another, i.e. print bleed occurs.
This is not a problem with monochrome inks, but the tendency
of the ink to stay at the paper surface may give rise to
smudging of the image.
Thus in summary, the benefits of the present invention are
thought to accrue from the presence of a complementary
balanced combination of hydrophilic and hydrophobic elements.
The starch component of the composition is thought to
2l7~nl3
-
contribute primarily the normal benefits of a starch sizing
agent, i.e. it fills in pores and voids at the sheet surface
and thereby provides a physical impediment to liquid
penetration, sticks down loose fibres, and enhances the
strength of the final paper.
The invention will now be illustrated by the following
Examples, in which an asterisk indicates the first occurrence
of a proprietary trade mark, all parts and percentages are by
weight unless~otherwise stated, and which provide details of
additional specific benefits which have been achieved by the
invention with particular types of paper:
- EXAMPLE 1
55 parts of anionic oxidised potato starch ("Perfectamyl P 255
SH" supplied by Tunnel Avebe, of Ulceby, South Humberside,
United Kingdom) and 15 parts of an 88 Mol% hydrolysed
relatively low molecular weight polyvinyl alcohol ("Mowiol
8-88" supplied by Harlow Chemical Company Limited of Harlow,
Essex, United Kingdom) were blended as dry powders. The blend
was then made up in~o an approximately 10% solids content
aqueous solution/dispersion and cooked at about 90C for
30 minutes. After allowing the mixture to cool to about 50C,
parts of 50% solids content (i.e. 30 dry parts) of
acrylonitrile/n-butylacrylate/styrene copolymer latex
("Acronal S 360 D" supplied by BASF) were added with stirring,
to give a treatment composition of a little under 15% solids
content and a viscosity of about 80 cps (measured at 20C,
Brookfield viscometer, Spindle No. 2, speed 100 rpm).
This treatment composition was then applied to a sheet of
100 g m~2 white uncoated woodfree general office base paper
using a laboratory size press. The base paper was internally
sized with alkyl ketene dimer, but had not previously been
surface sized. The treated sheet was then dried using a
laboratory rotary dryer. The dry pick-up was found to be
about 5% (i.e. about 2.5 g m-~ per side), based on the dry
weight of the base paper before treatment. The treated paper
217~013
~ g
had a 60 second Cobb value of 18. The treated sheet was then
laboratory calendered. After calendering the sheet had a
Bendsten roughness of 150 ml min'.
The sheet and a control sheet which had been treated with a
conventional starch sizing composition were then printed by
means of a Hewlett Packard' Deskjet 560C ink jet printer. The
printed images were of a standard test card giving both colour
and monochrome (black) images and specifically designed to
evaluate print quality and reveal failings in intensity,
sharpness, wicking, print bleed and such like.
The paper according to the invention was found to give rapid
ink drying--(i.e. penetration into the paper), good colour
intensity, low ink bleed, and sharply defined colour and
monochrome characters, with little wicking and low mottle,
i.e. non-uniformity in print intensity in different areas of
the paper. There was little or no strike-through of the ink
to the reverse (unprinted) surface of the sheet.
By comparison, the control sheet showed more print bleed and
less bright colours on colour-printed areas. The monochrome
image quality was quite good (probably a consequence of the
internal sizing of the paper) but had a longer "drying time".
This would be likely to give rise to smudging in everyday use.
EXAMPLE 2
This illustrates the use of three alternative hydrophobic
polymers to that used in Example l. These were as follows:
Mix I - polyurethane latex supplied at 20% solids
content by Akzo Nobel under the name
"Cyclopal AP"
Mix II - styrene/acrylic copolymer latex supplied
at 27% solids content by Akzo Nobel under
the name "Bewopress AE 27"
- 2178013
Mix III - carboxylated styrene/butadiene copolymer
latex supplied at 50% solids content by
Dow Chemical under the name "Dow DL 950"
The other mix components were the same starch and polyvinyl
alcohol as used in Example 1. The treatment compositions were
prepared by the same general procedure as described in Example
1, but the final solids content was a little lower (about
12%). The % dry composition of the compositions was as
follows: ~
Component Mix I Mix II Mix III
Starch 77.5 55 55
Polyvinyl alcohol 20.0 15 15
Latex 2.5 30 30
The polyurethane has a higher degree of hydrophobicity than
the other two polymers, and so it was used in a much smaller
quantity.
Each treatment composition was applied to a respective sheet
of 95 g m~2 white uncoated woodfree premium business stationery
base paper which had been internally hard sized with alkyl
ketene dimer, but which had not been surface sized. The dry
pick-up was found to be about 4% (i.e. about 2 g m~2 per side).
After drying, the sheets were each laboratory calendered to a
Bendsten roughness of around 150 ml min~'.
The various sheets, together with a control sheet which was
conventionally starch-sized, were then printed and evaluated
as described in Example 1. All three papers according to the
invention were found to give the same good performance as
described in detail in Example 1, and the same benefits over
the control paper.
2178~13
11
EXAMPLE 3
This illustrates the use of the present invention on a full-
size papermachine, using a treatment composition with the same
ingredients and relative proportions as set out in detail in
Example 1 (55 parts anionic oxidised potato starch, 15 parts
88 Mol% hydrolysed low molecular weight polyvinyl alcohol, and
30 parts latex, all on a dry basis). The solids content of
the composition was 12%.
-
An 80% hardwood/20% softwood furnish internally sized withalkyl ketene dimer and containing usual papermaking fibres and
additives was used to produce a good quality very smooth white
woodfree general office paper. The treatment composition
described above was applied at the size press and the paper
was conventionally calendered after drying. The final paper
had a basis weight of 105 g m~2, topside and wireside Bendsten
roughnesses of 66 and 44 ml min~' respectively, a 60 second
Cobb value of 25 and a filler content of about 15% (urea-
formaldehyde resin synthetic filler).
The paper, and a control paper of the same type sized only
with a conventional starch size press formulation were then
evaluated for ink jet performance generally as described in
previous Examples.
Toner adhesion was also evaluated. The toner adhesion test,
also known as the tape pull test, involved printing a solid
block of toner onto each sheet by means of a Hewlett-Packard
LASERJET IV laser printer; measuring the print density by
means of an image intensity measuring instrument; applying
adhesive tape to the sheet over the block-imaged area;
carefully removing the tape with the aid of an Instron peel
force tester to ensure an even and reproducible removal force;
and re-measuring the print density. The ratio of the print
density after removal of the tape to the print density before
application of the tape is then expressed as a percentage
value termed the "toner adhesion".
~ 217~013
12
The results of the tests were as follows:-
Pro~ert~ Invention Control
Colour appearance good mottled
Colour brightness (see note 1) 10.1 14.3
Colour intensity (see note 2) 1.1 0.8
Colour print bleed good poor
Monochrome wicking good acceptable
Monochrome optical density 1.6 1.6
(see note 4)
Monochrome ink drying time 39 sec 68 sec
(see note 3)
Toner adhesion (%) 93 74
NOTES
1. Measured according to an optical reflectance testmethod in which the lower the number obtained, the
better the brightness and for which any value higher
than 12 is deemed unacceptable.
2. Measured according to a Hewlett Packard standard
test in relation to a composite black image derived
by printing the same area with several different
coloured inks and for which the higher the number
obtained, the better the intensity, with a value of
0.8 being the threshold of acceptability.
3. Measured according to a Hewlett Packard standard
test.
4. Measured using a Gretag optical densitometer, with
a value of 1.2 being an approximate threshold of
acceptability.
It will be seen that the paper according to the invention was
markedly better in most respects than the control paper.
2l7~nl3
13
In a later repeat making of the same type of paper, the starch
used was a mill-cooked potato-based starch. The same product
benefits were obtained.
EXAMPLE 4
This illustrates the use of the present invention on a full-
size papermachine making a less smooth paper than in the case
of Example 3 above.
The procedure was generally as described in Example 3, except
that the refining conditions were different, the solids
content of the treatment composition was 10% and precipitated
calcium carbonate was used as the filler rather than urea-
formaldehyde resin synthetic pigment. The final paper had a
basis weight of 101 g m~2, topside and wireside roughnesses of
l9S and 132 ml min~l respectively, a 60 second Cobb value of 27
and a filler content of about 11%.
The results of the ink jet printing performance evaluation for
the product according to the invention and an approximate
control paper were as follows:
ProPert~ Invention Control
Colour appearance good mottled
Colour brightness 9.7 8.3
Colour intensity 1.3 1.7
Colour print bleed good very poor
Monochrome wicking good good
Monochrome optical density 1.8 1.8
Monochrome ink drying time 8 sec 23 sec
Toner adhesion 73% 28%
It will be seen that the paper according to the invention
performed better than the control paper in terms of colour
appearance, colour print bleed and ink drying time. The
control paper was slightly better in terms of colour
brightness and intensity, probably because the control paper
was very hard sized, but these marginal benefits are
2178013
14
completely outweighed by the severe print bleed, the mottled
appearance and the high drying time of the control paper.
EXAMPLE 5
This illustrates the use of a range of different hydrophilic
polymers in the treatment composition (these include an
88 Mol % hydrolysed polyvinyl alcohol as used in previous
Examples). In each case, the treatment composition on a dry
basis was as follows:
Starch ("Perfectamyl P 255 SH") 85%
Hydrophilic polymer (see below) 9%
Latex ("Bewopress AE 27") 6%
Four different treatment compositions were prepared, the
hydrophilic polymers used being as follows:
Mix I - 88 Mol % hydrolysed polyvinyl alcohol
("Mowiol 8-88")
Mix II - Polyvinylpyrrolidone ("Lumiten PR 8450")
supplied in 30% aqueous solution b~,~ BASF)
Mix II - Low molecular weight carboxymethyl
cellulose ("Finnfix- 5" supplied by
Metsa-Serla, Finland)
Mix IV - Fully hydrolysed polyvinyl alcohol
("Mowiol 10-98" supplied by Harlow
Chemical Company)
Each treatment composition was applied to respective sheets of
test paper as used in Example 2, and then dried and
calendered, also as described in Example 2. The various
sheets, together with a control sheet which was conventionally
starch-sized, were then printed and evaluated as described in
Example 3.
The results were as follows:
2l7snl~
-
ProPertY Control Mix I Mix II Mix III Mix rv
Monochrome A A A A A
wicking
Monochrome 1.5 1.6 1.7 1.7 1.8
optical density
Monochrome ink 15 15 22 15 25
drying time (sec)
Colour G G G G G
appearance
Colour ~ 6.6 6.2 6.6 7.1 6.7
brightness
Colour print A E E G G
bleed
Toner - 58 86 67 74 78
adhesion (%)
Key: A = Acceptable
G = Good
E = Excellent
It will be seen that papers according to the invention showed
improved colour print bleed and monochrome optical density
performance, and much better toner adhesion compared with the
control paper.
EXAMPLE 6
This illustrates the use of the present invention for treating
a 100 g m-2 laid premium business stationery paper during its
manufacture on a full-sized papermachine. The paper was
internally AKD-sized and incorporated a ca. 15% precipitated
calcium carbonate loading. The procedure was generally
described in Example 3, and the final paper had a 60 second
Cobb value of 24.
The results of the tests were as follows:
2178013
16
Pro~ertY Invention Control
Colour appearance good good
Colour brightness 6.6 7.2
Colour intensity 1.6 1.4
Colour print bleed good poo~
Monochrome wicking good good
Monochrome optical density 1.8 1.8
Monochrome ink drying time 13 sec 24 sec
Toner adhesion (%) 92 51
It will be seen that the paper according to the invention had
improved colour brightness and colour print bleed, a shorter
ink drying time and much improved toner adhesion, compared
with the control paper.
EXAMPLE 7
This illustrates the use of a different type of starch in the
treatment composition, namely a wheat (carbohydrate extract)
starch supplied as "Abrastarch~" (at 9% solids content) by
ABR Foods Limited, Corby, England, in place of the
"Perfectamyl P 255 SH" starch used in previous Examples.
The procedure was generally as described in Example 3, except
that the treatment composition was as follows:
Starch 85%
Polyvinyl alcohol ("Mowiol 8-88") - 9%
Latex ("Bewopress AE 27") 6%
The total dry pick up of the composition was ca. 4 g m -2
(4%) and the 60 second Cobb value was 24. The Bendsten
roughness of both surfaces of the paper was in the range
50 - 60 ml min~'.
The test results were as follows (no colour intensity
measurements were made for this and subsequent Examples):
2178013
17
Property Invention Control
Colour appearance no mottle mottled
Colour brightness 13 13
Colour print bleed good poor
Monochrome wicking good go~d
Monochrome optical density 1.7 1.7
Monochrome ink drying time 17 sec 20 sec
Toner adhesion (%) 99 $7
It will be seen that the paper according to the invention had
improved colour appearance, improved colour print bleed and
much improved toner adhesion compared with the control paper.
EXAMPLE 8
This illustrates the effect of omitting the hydrophilic
polymer from the treatment composition. Three treatment
compositions were evaluated, as follows (dry basis):
Invention : Starch ("Abrastarch") 85%
Polyvinyl alcohol ("Mowiol 8-88") 9%
Latex ("Bewopress AE 27") 6%
Control I : Starch (as above) 94%
Polyvinyl alcohol (as above) 6%
Control II : Starch (as above) 100%
These compositions were each applied to a relatively rough
flecked 100 g m~2 decorative text and cover paper during its
production on a full-size papermachine. The resulting papers
were tested as in Example 7, and the results obtained were as
follows:
2178013
18
Pro~erty Invention Control I Control II
Colour appearance acceptable acceptable acceptable
Colour brightness 11 10 10
Colour print bleed excellent acceptable acceptable
Monochrome wicking acceptable acceptable acceptable
Monochrome optical 1.5 1.6 1.6
density
Monochrome ink 12 sec 14 sec 11 sec
drying time
Toner adhesion (%) 77 36 23
It will be seen that the paper according to the invention had
improved colour print bleed and much improved toner adhesion
compared with the control paper. Accurate comparison of
properties such as appearance (mottle) and colour brightness
was hindered by the decorative flecked appearance of the
paper.
EXAMPLE 9
This illustrates the use of a minor proportion of pigment in
the treatment composition. The pigment used was calcium
carbonate ("Hydrocarb~ 90", supplied by Croxton & Garry,
Dorking, England) and was present in the treatment composition
in an amount of 5% calculated as dry weight of pigment to
aggregate dry weight of starch, hydrophilic polymer and
hydrophobic polymer. This treatment composition and general
procedure were otherwise as in Example 3. Additionally, paper
was produced using the same treatment composition without
pigment and, separately, with a 100% starch treatment
composition.
~ 2178013
19
ProPerty Invention Invention Control
(without Piqment) twith Piqment)
Colour appearance no mottle no mottle slight
mottle
Colour brightness 11.2 12.0 11.6
Colour print bleed good acceptable poor
Monochrome wicking good good good
Monochrome optical 1.7 1.6 1.6
density
Monochrome ink 23 36 43
drying time (sec)
Toner adhesion (%) 90 90 60
It will be seen that both papers according to the invention
had improved colour appearance, improved colour print bleed,
shorter ink drying time and much improved toner adhesion
compared with the control paper.
EXAMPLE 10
This illustrates the use of the invention with an acid sized
(rosin/polyaluminium chloride) paper produced on a full-sized
papermachine. The paper was a very smooth high quality white
100 g m~2 woodfree business stationery paper containing a
ca. 15% precipitated calcium carbonate loading. The treatment
composition, made up at 8% solids content, was as follows:
Cationic etherified starch 82%
("Amylopak 15", supplied by
Tunnel Avebe Limited, England)
Polyvinyl alcohol ("Mowiol 8-88") 10%
Styrene-acrylic latex ("Bewopress AE 27") 8%
The final paper had a 60 second Cobb value of 26, and topside
and wireside smoothness values of 60 ml min~' and 50 ml min~'
respectively (Bendsten). The dry pick up of the treatment
composition was ca. 4%, i.e. ca. 2 g m~2 per side.
