Note: Descriptions are shown in the official language in which they were submitted.
CA 02444936 2003-10-15
F~739 _
A METHOD OF PRODUCING A COATED SUBSTRATE
This invention relates to a method of producing coated substrates. In a
further embodiment
the present invention relates to a method of producing coated paper or
paperboard.
In the manufacturing of coated substrates, coming compositions usually are
applied to said
substrate by, for example, blade type, bar type, or reverse roll type coating
methods. The
line speed may exceed 1,000 m/min. Any or all of these methods are commonly
employed
to sequentially apply coatings to the moving substrates.
However, each of these application methods inherently has its own set of
problems that can
result in an inferior coated surface quality. In the case o:f the blade type
coating method, the
lodgment of particles under the blade can result in streaks in the coating
layer, which lowers
the quality of the coated paper or paperboard. In addition, the high pressure
that must be
applied to the blade to achieve the desired coating weight places a very high
stress on the
substrate and can result in breakage of the substrate web, resulting in
lowered production .
efficiency. Moreover, since the pigmented coatings are highly abrasive, the
blade must be
replaced regularly in order to maintain the evenness of the coated surface.
Also, the
distribution of the coating on the surface of the paper or paperboard
substrate is affected by
the surface irregularities of the substrate. An uneven distribution of coating
across the
paper or paperboard surface can result in a dappled or mottled surface
appearance that can
lead to an inferior printing result:
The bar (rod) type coating method is limited as to the solids content and
viscosity of the
pigmented coating color that is to be applied. Pigmented coatings applied by
the bar type
coating method are typically lower in solids content and viscosity than
pigmented coating
colors applied by the blade type method. Accordingly, for the bar type coating
method it is
not possible to freely change the amount of coating that can be applied to the
surface of the
paper or paperboard substrate. Undesirable reductions in the quality of the
surface of the
coated paper or paperboard can result when the parameters of coating solids
content,
viscosity and coatweight axe unbalanced. Moreover, abrasion of the bar by the
pigmented
-1-
CA 02444936 2003-12-03
64693-5708
coatings requires that the bar be replaced at regular intervals in order to
maintain the
evenness of the coated surface.
The roll type (film) coating method is a particularly complex process of
applying pigmented
S coatings to paper and paperboard in that there is a narrow range of
operating conditions
related to substrate surface charaderistias, substrate porosity, coating
solids content and
coating viscosity that must be observed for each operating speed and each
desired
coatweight to be achieved. An imbalance between these variables can lead to an
uneven
film-split pattern on the surface of the coated paper, which can lead to an
inferior printing
result, or the expulsion of small droplets of coating as the sheet exits the
coating nip. These
droplets, if re-deposited on the sheet surface, can lead to an infezior
printing result.
Moreover, the maximum amount of coating that can be applied to a paper or
paperboard
surFace in one pass using the roll type coating method is typically less than
that which can
be applied in one pass by the blade or bar type coating methods. This coating
weight
limitation is especially pronounced at high coating speeds.
A common feature of all these methods is that the amount of coating liquid
applied to a
paper web, which generally has an irregular surface with hills and valleys, is
different
depending on whether it is applied to a hill or a valley. Therefore, coating
thiclCncss, and
thus ink reception properties, will vary across the surface of the coated
paper. resulting in
irregularities in the printed image. Despite their drawbacks, these coating
methods are still
the dominant processes in the paper industry due to their economics,
especially since very
high line speeds can be achieved.
A feature common to all of the mentioned coating techniques is that an excess
of coating
liquid is applied to the substrate and then is metered off. In the case of a
reactive coating,
which is a coating comprising reagents capable of reacting with each other,
the reaction
occurring in the metered excess coating renders it useless. Furthermore, each
of these
coating methods have, as already mentioned, rheological constraints for
obtaining good
runnability so that the addition of a reactive additive may change the coating
rheology
profile so that it falls outside of the window of coatability. There are cases
where reactive
chemistries are used to impart functionality to the coated substrate; however,
these coatings
-2-
CA 02444936 2003-10-15
X739
are applied through the use of a subsequent coating or converting step that
adds complexity
and expense.
Curtain coating is a relatively new coating technique. EP-A 517 223, and
Japanese patent
applications JP-94-89437, JP-93-.31'1931, JP=93-177816, JP-93-131718; JP-92-
298683, JP-
92-51933, JP-91-298229, JP-90-217327, and JP-8-310110 disclose the use of
curtain
coating methods to apply one or more pigmented coating layers to a moving
paper surface.
More specifically, the prior art relates to:
(i) The curtain coating method being used to apply a single layer of pigmented
coating to a basepaper substrate to produce a single-layer-pigmented coating
on
paper.
(ii) The curtain coating method being used to apply a single priming layer of
pigmented coating to a basepaper substrate prior to the application of a
single
1 S layer of pigmented topcoat applied by a blade type coating process. Thus a
multiiayer-pigmented coating of paper was achieved by sequential applications
of
pigmented coating.
(iii) The curtain coating method being used to apply a single topcoaHng layer
of
pigmented coating to a basepaper substrate that has previously been primed
with
a single layer of pigmented precoat that was applied by a blade or a metering
roll
type coating process. Thus a multilayer-pigmented paper coating was achieved
by sequential applications of pigmented coating.
(iv) The curtain coating method being used to apply two single layers of
specialized
pigmented coating to a basepaper substrate such that the single layers were
applied in consecutive processes. Thus a multilayer-pigmented coating of paper
was achieved by sequential applications of pigmented coating.
The use of a curtain coating method to apply a single layer of pigmented
coating to the
surface of a moving web of paper, as disclosed in the prior art discussed
above, is stated to
offer the opportunity to produce a superior quality coated paper surface
compared to that
produced by conventional means. However, the sequential application of single
layers of
pigmented coating using curtain coating techniques is constrained by the
dynamics of the
-3-
CA 02444936 2003-10-15
(x273,9
curtain coating process. Specifically, lightweight coating applications can
only be made at
coating speeds below those currently employed by conventional coating
processes because
at high coating speeds the curtain becomes unstable, and this results in an
inferior coated
surface. Unfortunately, the application of consecutive single layers of
pigmented coatings
to paper or paperboard at successive coating stations, whether by any of the
above coating
methods, remains a capital-intensive process due to the number of coating
stations required,
the amount of ancillary hardware required, for example, drive units, dryers,
etc., and the
space that is required to house the machinery.
Coated papers and paperboards that have received a coating that contains an
additive
designed to impart functional properties, such as barrier properties,
printability properties,
adhesive properties, release properties, and optical properties such as color,
brightness,
opacity, gloss, etc., are described as functional products and their coatings
may be referred
to as functional coatings. The coating components that impart these properties
may also be
referred to as functional additives. Functional products include paper types
such as self
adhesive papers, stamp papers, wallpapers, silicone release papers, food
packaging, grease-
proof papers, moisture resistant papers, and saturated tape backing papers.
The curtain coating method for the simultaneous coating of multiple layers is
well known
and is described in U.S. Patents 3,508,947 and 3,632,374 for applying
photographic
compositions to paper and plastic web. However, photographic solutions or
emulsions have
a low viscosity and a low solids content, and are applied at low coating
speeds.
In addition to photographic applications, the simultaneous application of
multiple coatings
by curtain coating methods is known from the art of malting pressure sensitive
copying
paper. For example, U.S. Patent 4,230,743 discloses in one embodiment the
simultaneous
application of a base coating comprising microcapsules as a main component and
a second
layer comprising a color developer as a main component onto a travelling web.
However, it
is reported that the resulting paper has the same characteristics as the paper
made by
sequential application of the layers. Moreover, the coating composition
containing the color
developer is described as having a viscosity between 14 and 20 cps at
22°C.
_q._
CA 02444936 2003-10-15
02739 x
JP-A-10-328613 discloses the simultaneous application of two coating layers
onto a paper
web by curtain coating to make an inkjet paper. The coating compositions
applied
according to the teaching of that reference are aqueous solutions with an
extremely low
solids content of 8 percent by weight. Furthermore a thickener is added in
orderto obtain
non-Newtonian behavior of the coating solutions. The examples in JP-A-10-
328613 reveal
that acceptable coating quality is only achieved at line speeds below
404mlmin. The low
operation speed of the coating process is not suitable for economic production
of printing
paper, especially commodity printing paper
In view of the deficiencies of conventional commercial :paper coating
techniques, it would
be desirable to have a process capable of improving the properties of a coated
substrate,
such as printing quality of the resulting coated substrate.
The technical problem underlying the present invention is to overcome the
disadvantages of
the prior art and, thus, to provide a coating method capable of applying
coatings comprising
one or more reactive compounds. A further aspect of the present invention is
to provide a
coating method whereby the properties of the applied coating is not
detrimentally affected
by the presence of reagents in the coating capable of reacting with each
other. Moreover, a
further aim of the present invention is to provide coated substrates having
improved
properties and a method of producing the same.
The technical problem of the present invention is solved 'by a method of
producing a coated
substrate comprising the steps of
a) forming a free flowing curtain, the curtain having at least a first
component and a second
component capable of reacting with each other, and
b) contacting the curtain with a continuous web substrate.
In one embodiment, the present invention is a method of producing a coated
substrate
comprising the steps o~
a) forming a composite, multilayer free flowing curtain, the curtain having at
least two
layers, whereby one layer comprises at least a first component that is capable
of reacting
-5-
CA 02444936 2003-10-15
X739
with at least a second component comprised in the other layer, and
b) contacting the curtain with a continuous web substrate.
In a preferred embodiment there is at least one internal layer present between
the layer
S comprising the first component and the layer comprising the second
component.
In a further embodiment, the problem of the invention is solved by a process
for producing
a coated substrate comprising the steps of:
a) forming a free flowing curtain, the curtain having at least one component
capable of
reacting with itself or another compound, and
b) contacting the curtain with a continuous web substrate,
wherein at least one component of the curtain begins reacting during the
coating process
and is essentially completely reacted before the coating process is complete.
In another embodiment, the problem of the present invention is solved by a
method of
producing a coated substrate comprising the steps of
a) forming a free flowing curtain, the curtain having at least one layer
comprising a
composition capable of reacting, and
b) contacting the curtain with a continuous web substrate.
The composition forming the at least one layer of the free flowing curtain of
step a) may
comprise at least one first component and at least one second component
capable of reacting
with each other or may contain a reaction system wherein reaction of at least
one reactive
component can be induced by means of catalyst, initiator or activator present
in the
composition or by exposure to energy such as heat or radiation. As used
herein, the term
"reactive component" means a material that is capable of reacting andlor a
material that
initiates, catalyzes or is otherwise involved in a reaction. As used herein,
the term "coating
process" means a process comprising coating a substrate to a point such that
the coating is
immoblized and/or the coated substrate is finished and ready for sale.
Preferably, said free flowing curtain of step a) is a composite multilayer
free flowing
curtain.
-6-
CA 02444936 2003-10-15
X739
Preferably, there are three main means by which the curtain coating can be
used to apply
reactive coatings:
1) Precoat reaction - the first and second component capable of reacting with
each
other are added to the coating liquid just before or when said coating liquid
passes
through the curtain coating head, possibly through the use of inline mixing;
2) Coating reaction - vc~here two or more reactive layers are prepared and
brought
together in the falling curtain so that the reaction can begin during the
coating
application process; and
3) Postcoat reaction - where at least one reactive layer is introduced into
the coating
and the reaction takes place after said ec>ating is applied to the substrate
but before
the coated substrate is in its finished form.
Thus, preferably the reaction between the first component and the second
component of step
a) takes place within the coating die or head, in the free flowing curtain
and/or when applied
to the substrate, and/or when initiated by, for example,, pressure, heat, pH
change, radiation
and/or exposure to a gas or vapor, such as oxygen or ammonia.
The reaction type of which the first component and the second component of
step a) react
with each other is not limited, and may be, for example: an anionic-cationic
interaction; a
crosslinking reaction; a free radical reaction; a step growth reaction; a
addition reaction; a
curing reaction such as a UV induced curing reaction, an oxygen induced curing
reaction, a
catalyzed reaction or an electron beam induced curing reaction; an acid base
reaction; a
grafting reaction; a ring opening reaction; a precipitation; a phase change; a
floceulation/coagulation reaction or a combination thereof. Examples of
reactive first and
second component combinations include, for example, the following: a polyvinyl
alcoholA
and borax; a cationic starch and an anionic coating composition; a starch and
a dialdehyde;
an epoxy-functional polymer and an amine hardening agent; and a polyisocyanate
and a
polyol. In a preferred embodiment of the invention, the reaction involved in
the coating
_7_
CA 02444936 2003-10-15
~2~3a~ '~
process proceeds readily at room temperature in the substantial absence of
external energy
sources.
In a preferred embodiment it is excluded that a crosslinhing reaction takes
place between
the at least first component and at least second component if said components
are present in
the same layer. Preferably, the process of the invention is conducted in the
substantial
absence of electron beam radiation.
In a further preferred embodiment it is excluded that a flocculation can be
induced by
adding calcium chloride solution to a coating composition.
The term anionic-cationic interaction refers to the reaction of an anionic
compound with a
cationic compound in a coating liquid, whereby the properties of said coating
liquid change
due to said anionic-cationic interaction. The property change may be a
flocculation that
would make it impossible to apply said coating to substrates using blade, rod,
or airbrush
(air knife) coating techniques.
The substrate of the present invention preferably is a basepaper or paperboard
so that a
coated basepaper or paperboard is produced accordingly.
In a preferred embodiment, photographic papers and/or pressure sensitive
copying papers
are excluded from the scope of the present invention. The term "excluding
photographic
papers should be interpreted in the sense that none of the layers of the
curtain used in the
practice of the present invention comprise silver compounds. 'The term
"excluding pressure
sensitive copying papers" should be interpreted in the sense that the layers
of the curtain do
not contain a combination of a microencapsulated color former and a color
developer in a
single layer or in different layers.
The curtain layers can be simultaneously applied according to the present
invention by
using a curtain coating unit with a slide nozzle arrangement for delivering
multiple liquid
layers to form a continuous, multilayer curtain. Alternatively, an extrusion
type supplying
head, such as a slot die or nozzle having several adjacent extrusion nozzles,
can be
_g_
CA 02444936 2003-10-15
X273 g
employed in the practice of the present invention. In a preferred embodiment,
the entire
coating liquid that passes through the curtain coating unit is applied to the
substrate.
Preferably, on the edges of the formed curtain only a minor part of coating
liquid is
removed before said curtain is applied to the substrate. Coating liquids that
pass through
the curtain coating unit and that are not applied to the substrate may be
discarded.
According to a preferred embodiment of the present invention at least one
curtain layer of
the free falling curtain comprises at least one pigment. Preferably, in making
a paper for
printing purposes at least two of the coating layers comprise at least one
pigment.
Preferably, a top layer ensuring printability is present. ~' aid layer
improves surface
properties like gloss or smoothness and optionally is not pigmented. For the
manufacture of
commodity printing paper; coating with two pigmented layers is su~cient for
most
purposes.
The present inventors have surprisingly discovered that coated substrates,
such as -paper and
paperboard, with improved properties can be readily prepared using coating
formulations
comprising reactive components via the process of the invention.
The curtain employed in the invention has a bottom, or interface, layer, and
optionally a top
layer, and/or optionally one or more internal layers. Each layer comprises a
liquid,
emulsion, suspension; dispersion or solution. The coating curtain of the
present invention
suitably includes at least one layer, and also includes embodiments having at
least 2, at least
3, at least 4, at least 5, or at least 6 or more layers. The layers of the
curtain can include one
or more printing layers, one or more functional layers, one or more spacing
layers, one or
more coating layers, and one or more layers imparting reactive
functionalities, and the like,
or any combination thereof. A spacing layer is a layer that separates at least
two other
layers. For example, a spacing layer can be employed between layers having
reactive
components in order to delay the initiation of a reaction between the
components.
A coating layer of the invention preferably comprises at least one pigment
and/or binder,
and can be formulated to be the same or different than conventional paper
coating
formulations. The primary function of a coating layer is to cover the surface
of the
_g_
CA 02444936 2003-10-15
0273.9 y
substrate as is well known in the paper-coating art. Conventional coating
formulations,
referred to in the industry as coating colors, can be employed as the coating
layer.
Examples of pigments useful in the process of the present invention include
clay, kaolin,
talc, calcium carbonate, titanium dioxide, satin white, synthetic polymer
pigment, zinc
oxide, barium sulphate, gypsum, silica, alumina trihydrate, mica, and
diatomaceous earth.
Kaolin, talc, calcium carbonate, titanium dioxide, satin white and synthetic
polymer
pigments, including hollow polymer pigments, are particularly preferred.
Binders useful in the practice of the present invention include, for example,
styrene-
butadiene latex, styrene-acrylate latex, styrene-aerylate-acrylonitrile latex,
styrene-
butadiene-acrylate-acrylonitrile latex, styrene-butadiene-acrylonitrile latex,
styrene-malefic
anhydride latex, styrene-aerylate-malefic anhydride latex, polysaccharides,
proteins,
polyvinyl pyrrolidone, polyvinyl alcohol, polyvinyl acetate, epoxy resin,
cellulose
derivatives, and polyurethane. Examples of preferred binders include
carboxylated styrene-
butadiene latex; carboxylat~i styrene-acrylate latex, carboxylated styrene-
butadiene-
acrylonitrile latex, carboxylated styrene-malefic anhydride latex,
carboxyiated
polysaccharides, proteins, polyvinyl alcohol, and carboxylated polyvinyl
acetate latex.
Examples of polysaccharides include agar, sodium alginate, and starch,
including modified
starches such as thermally modified starch, carboxymethylated starch;
hydroxyethylated
starch, and oxidized starch: Examples of proteins that can be employed in the
process of the
present invention include albumin, soy protein, and casein. A wide variety of
suitable
binders are commercially available.
When a multilayer curtain is employed, the coatweight of. each layer of the
curtain can be
adjusted to obtain the desired coated substrate properties. At least one of
the layers of the
multilayer curtain desirably has a dry coatweight of less than 30 g/m2,
preferably less than
20 g/m2, more preferably less than 10 g/m2, even more preferably less than 5
g/m2, and most
preferably less than 3 g/m2.
'The curtain of the invention comprises an interface layer, that is the layer
that comes in
contact with the substrate to be coated. One important function of the
interface layer may
be to promote wetting of the substrate paper. The interface layer can have
more than one
-10-
CA 02444936 2003-10-15
6~273Q
function. For example, in addition to wetting it may provide coverage of the
substrate and
improved functional performance such as adhesion, sizing, stiffness or a
combination of
functions. The interface layer can include a reactive component or can be free
of reactive
compounds. This layer is preferably a relatively thin layer when employed in a
multilayer
curtain. The coatweight of the interface layer when employed in a multilayer
curtain
preferably is from 0.01 to 5 g/m2, and more preferably is from 1 to 3 glm2.
In a preferred embodiment of the invention, the interface layer includes one
or more of the
following: a dispersion such as a latex, including an alkali swellable latex,
a blend of starch
and polyethylene acrylic acid) copolymer, and the like, or a water soluble
polymer, such as,
for example, polyvinyl alcohol, a starch, an alkali soluble latex, a
polyethylene. oxide, or a
polyacrylamide. 'The interface layer can optionally be pigmented, and this is
preferred for
certain applications.
The curtain of the invention can include one or more functional layers. The
purpose of a
functional layer is to impart a desired functionality to the coated paper.
Functional layers
can be selected to provide, for example, at least one of the following:
printability; burner
properties, such as moisture barrier, aroma barrier, water andlor water vapor
barrier; solvent
barrier, oil burner, grease barrier and oxygen barrier properties; sheet
stiffness; fold crack
resistance; paper sizing properties; release properties; adhesive properties;
and optical
properties, such as, color, brightness, opacity and gloss; etc. In one
embodiment of the
invention, the first and second reactive components can react to impart
functionality to a
layer in the coating. Functional coatings that are very tacky in character
would not
normally be coated by conventional consecutive coating processes because of
the tendency
of the tacky coating material to adhere the substrate to guiding rolls or
other coating
equipment. The simultaneous multilayer coating method of the invention, on the
other
hand, allows such functional coatings to be placed underneath a topcoat that
shields the
functional coating from contact with the coating machinery.
The solids content of a functional layer can vary widely depending on the
desired function.
A functional layer of the present invention preferably has a solids content of
up to 75
percent by weight based on the total weight of the functional layer and a
viscosity of up to
-11-
CA 02444936 2003-10-15
~27~9 r
10,000 cps (Brookfield, spindle 5, 100 rpm, 25°C), more preferably 50
to 3,000 cps.
Preferably, the coatweight of a functional layer is from 0.1 to 30 g/m2, more
preferably 0.5
to 10 g/m2, and most preferably from 1 to 3 g/m2. In certain situations, such
as, for
example, when a dye layer is employed or in the case of certain reactants such
as borax, the
coatweight of the functional layer can be less than 0.1 glm2.
The functional layer of the present invention can contain, for example, at
least one of the
following: a polymer of ethylene acrylic acid; a polyethylene; other
polyolefins; a
polyurethane; an epoxy resin; a polyester; an adhesive such as a styrene
butadiene latex, a
styrene acrylate latex, a caxboxylated latex, a starch, a protein, or the
like; a sizing agent
such as a starch, a styrene-acrylic copolymer, a styrene-malefic anhydride, a
polyvinyl
alcohol, a polyvinyl acetate, a carboxymethyl cellulose or the like; and a
barrier such as
silicone, a wax or the like.
Each functional layer can include, but is not limited to include, at least one
pigment and/or
binder as previously described for the coating layer, and/or one or more
reactive
components.
If desired, at least one additive such as, for example, at least one
dispersant, at least one
lubricant, at least one water retention agent, at least one surfactant, at
least one optical
brightening agent, at least one pigment dye or colorant, at least one
thickening agent, at
least one defoamer, at least one anti-foaming agent, at least one biocide, at
least one soluble
dye or colorant, including any combination of these or the like may be used in
at least one
layer of the curtain. Polyethylene oxide is an example of a preferred
additive, and can be
employed in any layer. In a preferred embodiment, polyethylene oxide is
employed as a
thickening agent, preferably at least in the interface layer. Advantageously,
the
polyethylene oxide has a weight average molecular weight of at least 50,000,
preferably at
least 100,000, more preferably at least 504,000, and most preferably at least
800,000.
Preferably, the amount of ~lyethylene oxide employed is sufficient to prevent
cratering,
and is preferably less than 2 weight percent, based on the weight of solids in
the layer in
which it is employed.
-12-
CA 02444936 2003-10-15
a
For the purposes of the present invention, in a multilayer curtain the layer
most distant from
the substrate paper is referred to as the top layer. This layer typically is
the layer that will
be printed upon, although it is possible that the coated paper of the present
invention could
also be further coated using conventional means, such as rod, blade; roll,
bar, or air knife
(airbrush) coating techniques, and the like. The top layer can be a coating
layer or a
functional layer, including a gloss layer, and can contain a reactive
component. In a
preferred embodiment of the invention, the top layer is very thin, having a
~coatweight of,
for example from 0.5 to 3 g/m2. This advantageously allows the use of less
expensive
materials under the top layer, while still producing a papex having good
printing properties.
In one embodiment, the top layer is free of mineral pigment.
According to a paxticularly preferred embodiment the top layer comprises a
glossing
formulation. The novel combination of glossing formulation and simultaneous
multilayer
curtain coating combines the advantages of curtain coating with good gloss.
The glossing formulations useful in the present invention comprise gloss
additives, such as
synthetic polymer pigments, including hollow or solid polymer pigments,
produced by
polymerization of, for example, styrene, acrylonitrile and/or acrylic
monomers. The
synthetic polymer pigments preferably have a glass transition temperature of
40 = 200°C,
more preferably 50 -130°C, and a particle size of 0.02 -10 Vim, more
preferably 0.05 - 2
gm. The glossing formulations contain 5 -100 weight percent, based on solids,
of gloss
additive, more preferably 60 -100 weight percent. Another type of glossing
formulation
comprises gloss varnishes, such as those based on epoxyacrylates, polyesters,
polyesteracrylates, polyurethanes, polyetheracrylates, oleoresins,
nitrocelluloses,
polyamides, vinyl copolymers and various forms of polya~crylates. According to
a preferred
embodiment of the present invention the viscosity of the top layer is greater
than 20 cps (at
25°C). A preferred viscosity range is from 90 cps to 2,000 cps, more
preferably from 200
cps to 1,000 cps.
When the curtain has at least 3 layers, then it has at least one internal
layer. The viscosity
and solids content of the internal layers) is not critical, pa~ovided a stable
curtain can be
maintained. The internal layer preferably is a functional layer or a coating
layer. When
-13-
CA 02444936 2003-10-15
6'273
more than one internal layer is present, combinations of functional and
coating layers can be
employed. For example, the internal layers can comprise a combination of
identical or
different functional layers, a combination of identical or different coating
layers, or a
combination of coating and functional layers. An internal layer may contain a
reactive
component.
The process of the invention expands the limits of paper coating technology,
gives the
coated paper producer unprecedented flexibility, and the ability to prepare
novel coated
papers.
Preferably, the free flowing curtain desirably has a solids content of at
least 10 weight
percent, preferably at least 40 weight percent, more preferably at least 45
weight percent,
and most preferably at least 50 weight percent. Advantageously, the free
flowing curtain
has a solids content of from 10 to 80 weight percent. At least one layer. of a
multilayer free
flowing curtain of the invention preferably has a solids content of at least
40 weight percent,
preferably at least 50 weight percent, and most preferably at least 65 weight
percent.
A particular advantage of one embodiment of the present invention is that, by
the
simultaneous application of at least two coating layers by curtain coating,
very thin layers or
in other words very low coatweights of the respective layers can be obtained
even at very
high application speeds. For example, the coatweight of each layer in the
composite curtain
can be from 0.01 to 10 g/m2, more preferably 0.1 to 3 g/m2. The coatweight of
each layer
can be the same as the others, or can vary widely from the other layers; thus,
many
combinations are possible.
The process of the invention can produce substrates having a wide range of
coatweights.
Preferably, the coatweight of the coating on the paper produced is from 3 to
60 g/m2, more
preferably from 5 to 25 g/rn2. The coating prepared from the curtain desirably
has a dry
coatweight of less than 60 g/mz, alternatively less than 30 g/m2,
alternatively less than 20
g/m2, alternatively less than 15 g/m2, alternatively less than 12 g/m2,
alternatively less than
10 g/m2, and most preferably less than S glm2.
-14-
CA 02444936 2003-10-15
~i27~9
In one embodiment of the present invention the coatweight of the top layer is
lower than the
coatweight of the layer contacting the basepaper or baseboard. Preferably, the
coatweight
of the top layer is less than 75 percent, more preferably less than 50
percent, of the
coatweight of the layer contacting the basepaper or baseboard. Thus, greater
coating raw
material efficiencies in the paper and paperboard coating operations is
achieved. In another
embodiment, the coatweight of the top layer is higher than the coatweight of
the layers)
below it. Unlike conventional coating processes, the simultaneous multilayer
coating
method of the present invention allows the use of much larger quantities of
relatively
inexpensive raw materials such as, for example, under are extremely thin top
layer of more
expensive raw materials or in combination with an expensive reactant, such as
a curing
agent, without compromising the quality of the finished <;oated product. In
addition, the
method of the invention allows the preparation of papers that have never been
produced
before. For example, a tacky functional internal layer can be included in the
curtain.
A pronounced advantage of the present invention irrespective of which
embodiment is used
is that the process of the present invention can be run at very high coating
speeds that
hitherto in the production of printing paper could only be achieved using
blade; bar or roll
application methods. Usual line speeds in the process of the invention are at
least 300
m/min, preferably at least 400 m/min, more preferably at least 500 m/min, such
as in a
range of 600 - 3200 m/min, and more preferably at least 800 mJmin, such as in
a range of
800 to 2500 m/min. In one embodiment of the invention, the line speed, or
speed of the
moving substrate, is at least 1000 m/min, preferably at least 1500 m/min.
Preferably, the continuous web substrate of step b) is neither precoated nor
precalendered.
In another embodiment, the continuous web substrate of step b) is not
precoated, and in a
further embodiment the continuous web substrate of step b) is not
precalendered. The
continuous web substrate of step b) preferably has a grammage, or basis
weight, of from 20-
400 g/m2.
Figure 1 is an explanatory cross-sectional view of a curtain coating unit 1
with a slide
nozzle arrangement 2 for delivering multiple streams 3 of curtain layer to
form a
continuous, multilayer curtain 4. When a dynamic equilibrium state is reached,
the flow
-15-
CA 02444936 2003-10-15
62739
amount of the curtain layers flowing into the slide nozzle arrangement 2 is
completely
balanced with the flow amount flowing out of the slide nozzle arrangement. The
free
falling multilayer curtain 4 comes into contact with web 5, which is running
continuously,
and thus the web 5 is coated with multiple layers of the curtain. The running
direction of
the web 5 is changed immediately before the coating area by means of a roller
6 to
minimize the effect of air flow accompanying the fast moving web 5.
An advantage of the process of the present invention over the prior art is
that a coated
substrate having specific properties can be obtained by applying a curtain
comprising at
least two reactive compounds to a substrate. Said method allows one to prepare
a coated
substrate having specific layers imparting, due to the reaction of said
reactive compounds,
specific properties: As the methods known in the prior axt apply an excess of
coating color,
they cannot effectively apply coatings comprising reactive compounds to
substrates.
Preferably, the coated substrates can be printed using any printing method
known to a
person skilled in the art.
'The present invention is exemplified by the following examples. All parts and
percentages
are by weight unless otherwise specified.
Examples:
The following materials were used to make the layers in the reactive coating
structure:
~ Ameo: 3-aminopropyl-triethoxysilane (DYNASYLA.N AMEO available from Degussa
AG, Hanau, Germany).
~ Carbonate (A): dispersion of calcium carbonate with particle size of 90
percent < 2 wm
in water (HYDROCARB 90 ME available from Pluess-Stauffer), 77 percent solids.
~ Carbonate (B): dispersion of calcium carbonate with particle size of 60
percent < 2~txn
in water (HYDROCARB 60 ME available from Pluess-Stauffer, Oftringen,
Switzerland), 77 percent solids.
~ Catalyst: an organo tin complex of dibutyltin dilaurate (available from Air
Products,
Allentown, PA, USA).
-16-
CA 02444936 2003-10-15
6273 '
~ Clay: dispersion of No. 1 high brightness kaolin clay with particle size of
98 percent <
2 ~m in water (HYDRAGLOSS 90 available from J.M Huber Corp., Have de Grace,
Maryland, USA), 71 percent solids.
~ Epoxy: dispersion of a bisphenol A based epoxy resin with a 500 epoxy
equivalent
weight based on solids, 55 percent solids in water.
~ DSP: dispersion of an ethylene acrylic acid copolymer (DSP 70 available from
The
Dow Chemical Company) 15 percent solids in water.
~ Glyeo: 3-glycidyloxypropyl-triethoxysilane (DYNASILAN GLYEO available from
Degussa AG, Hanau, Germany).
~ Glyoxal: a reactive polyhydroxylated dialdehyde resin (Cartabound GH Liquid
available from Clariant AG Lorrach Germany).
~ Hardener: an amino based epoxy curing agent with an amino-epoxy equivalent
weight
of 240 based on solids, (XZ 92441.01 available from The Dow Chemical Company)
75
percent solids in water.
~ Isocyanate: aliphatic poly-isocyanate of hexamethylene-1,6-diisocyanate
(Bayhydur VP
LS 2319 available from Bayer AG, Leverkusen, Germany).
~ Latex (A): carboxylated styrene-butadiene latex (DL 966 available from The
Dow
Chemical Company), 50 percent solids in water.
~ Latex (B): carboxylated styrene-butadiene latex (DL 980 available from The
Dow
Chemical Company), 50 percent solids in water.
~ Latex (C): alkali swellable carboxylated acrylate latex (XZ 92338 available
from The
Dow Chemical Company), 27 percent solids in water.
~ Latex (D): carboxylated acrylate latex (XU 31215.5 available from The Dow
Chemical
Company), S 1 percent solids in water.
~ Latex E: carboxylated aerylate latex (UCAR Latex DT 211 available from The
Dow
Chemical Company) 50.5 percent solids in water.
~ Latex F: carboxylated styrene butadiene latex (DL 939 available from The Dow
Chemical Company) 50 percent solids in water.
~ Polyethylene oxide: a 300 molecular weight polyethylene oxide (PEG 300
available
from Fluka).
~ PVOH: solution of 1 S percent of low molecular weight synthetic polyvinyl
alcohol
(MOWIOL 6198 available from Clariant AG, Basel Switzerland).
_17_
CA 02444936 2003-10-15
62739
~ Surfactant (A): aqueous solution of sodium di-alkylsulphosuccinate (AEROSOL
OT
available from Cyanamid, Wayne, New Jersey, USA), 75 percent solids.
~ Surfactant (B): TERGITOL TMN 6 aqueous solution of trimethylnonanol
ethoxylate 6
EO (available from The Dow Chemical Company), 90 percent solids.
~ Thickening agent: a 900;000 molecular weight non-ionic water-soluble
polyethylene
oxide) polymer (POLYOX WSR-1105 available from The I?ow Chemical Company), 4
percent solids in water.
~ Whitener: fluorescent whitening agent derived from diamino-
stilbenedisulfonic acid
(TINEPOL ABP/Z, available from Ciba Specialty Chemicals Inc. Basel,
Switzerland).
~ Borax: sodium tetra borate purity >98 percent, available from FLUKA.
~ Starch (A): Cationic Starch (C Size SP 5855 available from Cerestar,
Krefeld,
Germany).
~ Starch (B): Anionic Starch (C Film 07311 available from Cerestar, Krefeld,
Germany).
Coating Method
The above ingredients were mixed in the amounts given in tables herein below,
where all
parts are based on dry weights unless otherwise indicated. The pH of the
pigmented coating
formulations was adjusted by adding NaOH solution (10 percent) as indicated in
Table 1.
Water was added as needed to adjust the solids content of the formulations.
The
formulations were coated onto paper according to one of the following
procedures.
Coatin Procedure 1: A multilayer slide die type curtain coater manufactured by
Troiler
Schweizer Engineering (TSE, Murgenthal, Switzerland) was used. The curtain
coating
apparatus was equipped with edge guides lubricated with a trickle of water and
with a
vacuum suction device to remove this edge lubrication water at the bottom of
the edge
guide just above the coated paper edge. Volumetric pumps were employed to
provide
precise volumes to the die in order to achieve the desired coatweights. In
addition, the
curtain coater was equipped with a vacuum suction device to remove interface
surface air
from the paper substrate upstream from the curtain impingement zone. The
height of the
curtain was 300 mm. Coating formulations were deaerated prior to use to remove
air
bubbles. After coating on the web the paper was dried with a hot air drier.
-18-
CA 02444936 2003-10-15
6273~9
Coating Procedure 2: This procedure is identical to Coating Procedure 1 except
for the
following differences. The formulations were coated onto paper using a
multilayer slide die
type curtain coater, manufactured by Leuthold AG. When volatile components
were present
in the formulation, the formulations were poured into the feed containers at
least 12 hours
before application, without stirring, so natural deaeration could take place.
When two
coating formulations needed to be reacted just before entr~ring the slide die
they were
pumped through a small closed vessel and agitated by a paddle at up to 600
rpm.
Test Methods
Brookfield Viscosity
The viscosity is measured using a Brookfield RVT viscometer (available from
Brookfield
Engineering Laboratories, Inc., Stoughton, Massachusetts, USA). For viscosity
determination, 600 ml of a sample are poured into a 1000 ml beaker and the
viscosity is
measured at 25°C at a spindle speed of 100 rpm.
Paber Gloss
Paper gloss is measured using a Zehntner ZLR-1050. instrument at an incident
angle of 75°.
Ink Gloss
The test is carried out on a Pruefbau Test Printing unit with Lorrilleux Red
Ink No. 8588.
An amount of 0.8 g/m2 (or 1.6 g/m2 respectively) of ink is applied to coated
paper test strips
mounted on a long rubber-backed platen with a steel printing disk. The
pressure of the ink
application is 1,000 N and the speed is 1 m/s. The printed strips are dried
for 12 hours at
20°C at 55 percent minimum room humidity. The gloss is then measured on
a Zehntner
ZLR-1050 instrument at an incident angle of 75°.
Ink Set Off
The test is carried out on a Pruefbau Test Printing unit. 250 mm3 of ink
(Huber no 520068)
is distributed for 1 minute on the distributor. A metal printing disk is inked
by being placed
on the distributor for 15 seconds. The disk is placed on the first printing
station. At the
second printing station an uninked metal printing disk is placed, with a
pressure of 400N.
The coated paper strip, mounted on a rubber-backed platen, is printed with a
printing
_1g_
CA 02444936 2003-10-15
C27~9
pressure of 1000N at a speed of l.Sm/s. Time 0 is taken when printing happens.
After the
strip is printed at the first station, move the strip towards second printing
station, or Set off
station, by moving the hand lever. At the set off station, place a blank paper
strip between
the printed paper and the disk. At 15, 30 60 and 120 seconds, the blank paper
is pressed
against the printed sample in the set off station by moving the hand lever.
The amount of
non-immobilized ink from the printed paper transferred to the blank paper is
measured by
ink densities as given by optical density measurements.
Bri hotness
Brightness is measured on a Zeiss Elrepho 2000. Brightness is measured
according to ISO
standard 2469 on a pile of sheets. The result is given as 12457.
O acit
Opacity is measured on a Zeiss Elrepho 2000. Opacity is measured on a single
sheet
backed by black standard (Rfl) and on a pile of sheets (R«,). The result is
given as Ro/R~ x
100 (percentage).
Burn out test
The test is used to illustrate coating distributions and uniformity on
unprinted or printed
papers (exc. full-tone specimens).
Procedure:
1. Dip the 4 x 4 cm paper sample for 1 minute into a 10 percent
(weight/weight) aqueous
NH4C1 solution.
2. Dry the test paper for 3 minutes in an oven at 120 degrees Celsius.
3. Char the paper by moving it 5-10 cm over a hot plate until smoke has
disappeared (the
sample should not burn).
4. Measure Brightness. This procedure stains coating fibers, which appear
dark, so a higher
brightness value is indicative of improved coverage by the coating, which
appears bright
compared to the blackened fibers.
-20-
CA 02444936 2003-10-15
62739
Contact An~le
Contact angle is measured with a Fibro 1100 Dynamic Absorption Tester (Fibro
Systems
AB Sweden) according to method TAPPI T-558.
Dry Pick Resistance f IGTI
This test measures the ability of the paper surface to accept the transfer of
ink without
picking. The test is carried out on an AZ type printability tester,
commercially available
from IGT Reprotest BV. Coated paper strips (4 mm x 22 mm) are printed with
inked
aluminum disks at a printing pressure of 36 N with the pendulum drive system
and the high
viscosity test oil (red) from Reprotest BV. After the printing is completed,
the distance
where the coating begins to show picking is marked under a stereomicroscope.
The marked
distance is then transferred into the IGT velocity curve and the velocities in
cm/s are read
from the corresponding drive curve. High velocities mean high resistance to
dry pick.
Paler Roughness
The roughness of the coated paper surface is measured with a Parker PrintSurf
roughness
tester. A sample sheet of coated paper is clamped between a cork-melinex
platen and a
measuring head at a clamping pressure of 1,000 kPa. Compressed air is supplied
to the
instrument at 400 kPa and the leakage of air between the measuring head and
the coated
paper surface is measured. A higher number indicates a higher degree of
roughness of the
coated paper surface.
Pacer Stiffness
Paper stiffiiess is measured using the Kodak Stiffiiess method, TAPPI 535-PM-
79, or the
Gurely Stiffness method, TAPPI 543.
Coatwei t
The coatweight achieved in each coating experiment is calculated from the
known
volumetric flow rate of the pump delivering the coating to the curtain coating
head, the
speed at which the continuous web of paper is moving under the curtain coating
head, the
density and percent solids of the curtain, and the width of the curtain.
-21-
CA 02444936 2003-10-15
6273v
Water Resistance
The resistance of the coated paper to coating breakdown after it absorbs water
is tested with
the Adams Wet rub test. A strip of paper (24x2.5cm) is fixed onto a bronze
wheel, rolling
under constant speed and load over a. rubber roll, which dips into a pan
containing distilled
water for either 45 or 60 sec. The rolling makes the water in the pan turbid
if the coating
breaks down. After the rolling is completed, the light transmission of the
water form the
pan is measured with a turbidity meter: A love transmission reading indicates
significant
coating breakdown.
Comparative Experiment A and Examples 1 to 4
These examples used the reaction between borax in one layer and PVOH in
another layer.
This reaction led to a rapid increase in viscosity and the formation of a gel.
The details of
the formulations are shown in Table 1.
-22-
CA 02444936 2003-10-15
,9, O O. .-, V7 ~ N ~ ~ O O
~ M ~" cV O o0
d'
.~ 'd ~. M O O
iC
W
O ~ O O V1 ~ v~ M O O
N O O o0
~.
M ~ ~ O O ,-.. v7 ~ N v~ N O O
t~ M ~ cV O o0
~s,
M ~ O O
~O ~O M '"~ ~'
a
~1' O O .-, V7 N ~ M O O
N ~ ~ ~''~~' N '~ O o0
O ~,
a
C ~ O V1 Yi d' V~ ~ O 0
O 0 N
N 0 0 0 00 ~~.',~ ~
O O .~ V1 ~ N ~ ~ O
l~ M ~ N O oo N N
N
5, O O N ~ d' V7 N O O
O N CO O O O o0 ,-iCv
s..
~~, O O ,--i v~ ~ N v~ M O
~ Il M r. ~j O o0
O O v'~ d. ~ M O O
N O CO co
O
p U U t~
U err' ,.,,.t-~,'',~ "
~ ps ., ~ ~ ~ cN
v~ A o O
~.
a1
M
N
N
CA 02444936 2003-10-15
62739
The coatings were applied at 1000 m/min onto a wood-containing basepaper with
a
roughness of 4.3 microns using Coating Procedure 1. Two coating conditions
were used for
Examples 1, 2 and 3: Coating Condition 1 - where the bottom layer coatweight
was 1 g/m2
and top layer coatweight was 7 g/m2 and Coating Condition 2 - where the bottom
layer
coatweight was 2 g/m2 and top layer coatweight was 6 ~m2. These two coating
conditions
tested the effect of increasing the amount of the reactive bottom layer. The
comparative
experiment used the same two coating conditions but the reactive ingredient
(borax) was
left out. Example 4 used a three-layer coating having a thin middle layer
containing the
borax. For Example 4, the bottom layer coatweight was fixed at 1 g/m2 and the
top layer
coatweight wa.s 7 g/m2 while the coatweight of the middle layer was varied
from 0.018 gJm2
(Condition 1) to 0.036 gJm2 (Condition 2). The coated paper properties for
these examplos
are shown in Tables 2 and 3.
20
30
-24-
CA 02444936 2003-10-15
6z7~ .,
Table 2
Comparative
Example Example Example Example
1 2 3 4
A
Coating Coating Coating Coating Coating
Coated Paper
Property
Condition ConditionConditionConditionCondition
1 1 1 1 1
PAPER GLOSS 75
43 43 45 43 37
(percent)
INK GLOSS 75;
0
8
. 58 62 62 58 51
g/m2 INK (percent)
INK GLOSS 75;
1
6
. 65 69 68 71 63
g/m2 INK (percent)
ROUGHNESS PPS 1.8 1.7 1.7 1.6 1.8
(~)
ISO BRIGHTNESS
R
76.8 78.4 77.1 77.2 78.4
457 (percent)
OPACITY (percent)92.8 92.8 93.5 93.6 93.8
INK SET OFF AFTER
0.08 0.11 0.11 0.05 0.09
15 SEC. (Density)
INK SET OFF AFTER
0.00 0.00 0.01 0.00 0.00
30 SEC. (Density)
INK SET OFF AFTER
0.00 0.00 0.00 0.00 0.00
60 SEC. (Density)
INK SET OFF AFTER
0.00 0.00 0.00 0.00 0.00
120 SEC. (Density)
Burn Out Test
28.4 30.8 28.9 31.3 30.5
Brightness
Bending Stiffness
Machine Direction0.050 0.049 0.055 0.056 0.060
(mNm)
-25-
CA 02444936 2003-10-15
62739
Table 3
t Comparative
Example Example Example Example
1 2 3 4
A
Coating Coating Coating Coating Coating
Coated Paper Property
ConditionConditionConditionConditionCondition
2 2 2 2 2
PAPER GLOSS 75
37 39 41 41 32
(percent)
INK GLOSS 75; 0.8
52 58 56 54 47
g/m2 INK (percent)
INK GLOSS 75; 1.6
63 69 70 62 60
g/m2 INK (percent)
ROUGHNESS PPS (p.)2.0 1.8 1.7 1.4 1.9
ISO BRIGHTNESS
R
77.0 77.8 76.6 77.3 78.3
457 (percent)
OPACITY (percent) 92.6 93.3 92.9 92.3 93.7
INK SET OFF AFTER
0.06 0.12 0.19 0.24 0.22
15 SEC. (Density)
INK SET OFF AFTER
0.01 0.01 0.00 0.01 O.OS
30 SEC. (Density)
INK SET OFF AFTER
0.00 0.00 0.00 0.00 0.01
60 SEC. (Density)
INK SET OFF AFTER
0.00 0.00 0.00 0.00 0.00
120 SEC. (Density)
Burn Out Brightness27.4 27.9' 29.5 29.9 29.4
BENDING STIFFNESS
MACHINE DIRECTION 0.049 0.057 0.057 0.064 0.057
(Mnm)
These results show that reaction between the borax and PVOH had a minor effect
on paper
gloss, a minor effect on paper roughness, a significant improvement in ink
gloss, a slowing
effect on ink setting, a significant improvement in opacity, a significant
improvement in
stiffness, a significant improvement in coating coverage determined by the
burn out test,
-26-
CA 02444936 2003-10-15
27 ~9 "
and some effect on brightness depending on the thickness of the borax-
containing layer. In _
comparing Coating Condition 1 with Coating Condition 2, it was found that
doubling the
amount of borax significantly affects the ink set off and stiffness
properties.
Comparative Experiment B and Example 5
This example used a cationic starch in the bottom layer to react with a
conventional anionic
paper coating top layer. The comparative experiment replaced the cationic
starch with a
conventional anionic coating starch. The details of the coating formulations
are given in
Table 4.
Table 4
Comparative Example
B 5
Bottom Top LayerBottom Top Layer
Layer Layer
Carbonate (A) 70 70
Clay 30 30
Latex (A) 11 11
PVOH 2.5 2.5
Starch (A) 100
Starch (B) 100
Whitener (A) 1 0 1
Surfactant (B) 2 0.4 2 0.4
PH 8.5 8.5 8.5
Density 8.5 1.10
1.08 1.53
1.53
Brookfield Viscosity 920 580 120 580
Solids percent 20.0 62.0 20.4 62.0
The coatings were applied at 1000 m/min to a wood-containing basepaper with a
roughness
of 6.2 microns using Coating Procedure 1. The bottom layer coatweight was 0.5
g/m2 and
top layer coatweight was 6.5 g/m2. The coated paper properties are in Table 5.
-27-
CA 02444936 2003-10-15
6~73~
Table 5
Coated Paper Properties Comparative Example 5
B
PAPER GLOSS 75 (percent) 35 37
INK GLOSS 75; 0.8 g/m2 INK (percent)47 52
INK GLOSS 75; 1.6 g/m2 INK (percent)58 68
IGT DRY PICK (cm/s) 52 57
INK SET OFF AFTER 15 SEC: (Density)0.48 0.57
INK SET OFF AFTER 30 SEC. (Density)0.20 0:25
INK SET OFF AFTER 60 SEC. (Density)0.07 0.09
INK SET OFF AFTER 120 SEC. (Density)0.04 0.01
BENDING STIFFNESS MACHINE
0.042 0.050
DIRECTION (mNm)
The use of the cationic starch gave a significant improvement in stiffness and
coating
strength as measured by IGT dry pick. In addition, ink set off got lower.
Example 6
This example demonstrated an interfacial reaction of a starch-containing
formulation with a
dialdehyde solution (Glyoxal) capable of reacting with the starch. The starch
was
formulated into the bottom layer and the Glyoxal solution was the middle
layer. The total
Glyoxal used in the formulation was 1 S percent of the starch amount. The top
layer of the
coating was a conventional pigmented printing Iayer. A starch- containing two-
layer
reference without glyoxal was coated as a control. The details of the coating
formulations
are given in Table 6.
_~8_
CA 02444936 2003-10-15
6273'9
Table 6
Reactive rs Reference
laye
Starch GlyoxyalTop Starch Top
Layer Layer Layer Layer Layer
Clay 0 0 20 0 20
Carbonate 0 0 80 0 80
(A)
Latex A 0 0 11 0 11
Starch B 100 0 0 100 0
DSP 10 0 0 10 0
Glyoxal 0 100 0 0 0
PVOH 0 0 2.5 0 2.5
Surfactant 0.4 0 0.3 0.4 0.3
A
Solids (percent)30.0 10:0 63.0 24.1 63.0
Coatweight 1 0.14 12 1 12
The coatings were applied at 700 m/min to a wood-containing base paper at the
coatweights
shown in Table 6 using Coating Procedure 2. Both calendered and uncalendered
coated
papers were tested for IGT dry pick resistance. The results are shown in Table
7.
Table 7
Uncalendered IGT (cm/s).
Reference 95
Glyoxal Containing 108
Calendered
Reference 62
Glyoxal Containing 76
The use of the reactive starch/glyoxal system improved the coating strength as
measured by
IGT dry pick.
-29-
CA 02444936 2003-10-15
627?~9
The stiffness and the water resistance of the calendered papers were tested
with the Gurley
Stiffness test (in the cross machine direction) and the Adams Wet Rub test,
respectively.
Table 8
Sample Gurley Stiffness Wet Rub Result
(Gurley units) (percent transmittance)
Reference 375.5 4.7
Glyoxal Containing397.8 ~ 83.5
S
The samples with Glyoxal showed increased stiffness and excellent water
resistance.
Example 7
This example demonstrated the use of a quick-setting latex to improve
the.properties of a
coated paper. The trigger for the quick setting reaction was believed to be
the conversion of
a nitrogen containing polymer from a neutral to a cationic charged state as
the pH changes
upon the evaporation of ammonia from the formulation during coating and/or
drying of the
paper. The details of the formulations are shown in Table 9.
-30-
CA 02444936 2003-10-15
6'273
Table 9
Formulation Reactive Comparative
Bottom MiddleTop Bottom MiddleTop
Clay 100 100 70 100 100 70
Carbonate 3 0 3 0
A
Latex A 13 13 13 13
Latex E 20
Latex D 20
PVOH 1 1 0.8 1 1 0.8
Surfactant 0.4 0.4 0.2 0.4 0.4 0.2
A
PH 8.2 8.2 8.5 8.2 8.2 9.9
Solids (percent)65.2 65.2 56 65.2 65.2 47.7
Speed (m/min)1000 1000
Coatweight 6 6 5 6 6 5
(~m2)
The coatings were applied with a 3-layer configuration at 1000 m/min with the
coatweights
shown in Table 9 onto a wood free basepaper with a basis weight of 120 g/m2.
Coating
Procedure 2 was used. The top layer contained the reactive system. There was
no nitrogen-
containing polymer in the comparative example. The contact angle of the papers
containing
the quick set system was 74°, and 64° for the comparative paper.
The quick set polymer
apparently served to form a combination of hydrophobic linkages that render
the paper
more water resistant.
Example 8
This example demonstrated coating using an amino-ethoxysilane (Ameo) and a
glycidyl
functionalized ethoxysilane (Glyeo). Multiple reactions can occur. In addition
to the
reaction between the amino group and the glycidyl group, a
hydrolysis/condensation
reaction took place via the glycidyl-functionalized silane reacting with
itself to form a
siloxane linkage when the pH was sufficiently high to hydrolyze the
ethoxysilane. Three
approaches for coating the paper were demonstrated. First the self reaction of
the Glyeo
was demonstrated, then in addition to the self reaction, a simultaneous
interfacial reactian
-31-
CA 02444936 2003-10-15
f273~ 'a
was demonstrated with the reaction between Ameo and Glyeo occurring in a
layered
structure. Third, an in-line approach was used, where a blend of Ameo and
Glyeo was fed
to a single layer slot of the die. The details of the formulations are shown
in Table 10.
Table 10
FormulationControl Glyeo Multi In line
layer GlyeoiAmeo
Glyeo/AmeolGlyeo
Carbonate 100 100 100 100 100 1 ~0
(A)
Latex F 11 11 11 11 11 11
Ameo 1.5 1.5
Glyeo 1.5 3 3 3
Surfactant0.4 0.4 0.2 0.4 U.6
A
Solids 64.9 64 63.2 63.9 63.1 66.1
{percent)
Speed 700 700 700 700
(m/min)
Coatweight17 17 4.5 9 4.5 18
(~m2)
The coatings were applied to wood-containing base paper using Coating
Procedure 2.
Coatweight and coater speed were as shown in Table 10. Uncalendered and
calendered
paper gloss were as shown in Table 11, which also includes a comparison of the
ink gloss
results. Paper gloss was reduced with these reactive systems. The ink gloss
was
significantly improved. The improvement was greatest for the calendered
papers. The
reacted samples showed an improvement in the delta between the ink gloss and
sheet gloss
for two ink loads.
-32-
CA 02444936 2003-10-15
6~73~~ .
Table 11
Sample ControlGlyeo Glyeo GlyeoControlGlyeo GlyeoGlyeo
Ameo Ameo Ameo Ameo
Mufti-inline Mufti-inline
layer blend Layerblend
Calendered No No no no yes yes Yes yes
Paper Gloss 30 24 25 27 75 69 67 69
75
Ink Gloss 52 54 52 53 75 85 84 85
75
at 1.6 glm2
load
Ink Gloss 46 46 47 47 72 80 77 82
75
at 0.8 g/m2
load
Adams wet rub resistance of the paper surfaces was measured for both
uncalendered and
calendered samples. The resulting turbidity measurements for two rub times are
shown in
Table 12, which also shows the contact angle measurement. The results showed
the
increased water resistance of the coating compared to an unreacted control.
-33-
CA 02444936 2003-10-15
739
Table 12
Run Adams wet rub Adarns wet Contact Angle
Run time: 60s rub (degrees)
(percent Run time: 45s
transmittance)(percent
transmittance)
Control Uncalendered26.7 32.6 58.5
Glyeo 92.3 95 60.7
Mufti Layer 90.2 95 78
In Line 84.0 92.6 73.9
Blend
Control Calendered 49.3 61.6
Glyeo 87.9 63.4
Mufti Layer 93.8 77.5
In Line 91.8 73.6
Blend
Water resistance was increased for paper coated with the Glyeo, and for the
Glyeo plus
Ameo reactive systems. The highest contact angle was obtained when both
reactive
functionalities were present.
Example 9
This example demonstrated the reaction between an amino-based epoxy curing
agent and
an epoxide. This example used an in-line approach, where a blend of curing
agent and the
epoxide was fed to a single layer slot of the die. The reference sample does
not contain the
hardener or the epoxide. The details of the formulations are shown in Table
13.
-34-
CA 02444936 2003-10-15
02739 .,
Table 13
Reference Epoxy/Hardener
Formulation Layer Layer Layer Layer
1 2 l 2
In
Line
Blend
Carbonate (A) 100 100
Latex A 13 99.8 13
PVOH 1 1
Epoxy 99.8
Hardener 99.8
Surfactant A 0.4 0.2 0.4 0.2 0.2
Solids (percent) 65.2 49.4 65.2 36.7 53.7
Speed (m/min) 1000 1000
Coatweight(g/m 24 3 24 0.6 1.8
)
The formulations were applied to a wood-containing base paper at the water
speeds and
coatweights indicated in Table 13 using Coating Procedure 2. After drying the
papers on
the machine, the samples were further cured for 15 minutes at 120°C to
complete the
reaction. Contact angle and paper stiffness were measured. The results are
shown in Table
14.
Table 14
Reference Epoxy/Hardener
Contact Angle 60.5 78.2
(degree)
Paper Stiffness 0.778 0.993
(mNm)
The water resistance and stiffness of the coated paper increased with the
epoxy/hardener
reaction.
Example 10
This example demonstrated the reaction between an isocyanate and polyol to
form a
polyurethane layer in a multilayer structure. The example used an in-line
blend of the
-35-
CA 02444936 2003-10-15
6273
reactive chemicals before entering the die of the water. Details of the
formulations are
shown in Table 15.
Table 15
Formulation Reactive Comparative
BottomMiddle Top Bottom Middle Top
in
Line
Blend
Carbonate (A) 70 70 100 50 70
Clay 30 30 30
Carbonate (B) 50
Latex (A) 11 I 1 13 10 11
PVOH 0.8 0.8 1 0.8 0.8
Thickener 0.1 0.1 0.1 0.1 0.1
Isocyanate 23
Polyethylene Oxide 7
Catalyst 0.02
Whitener 1 1 1 1
Surfactant (A) 0.4 0.4 0.4 0.2
Solids (percent) 62 100 100 62 60 70 62
Speed (mlmin) 1000 1000
Coatweight (g/m 3 6 2 10 3 , 6 5
)
The coatings were applied to wood containing base paper using Coating
Procedure 2.
Resulting paper properties are shown in Table 16,
-36-
CA 02444936 2003-10-15
c~~273~
Table 16
Reactive Comparative
~
Adams Wet Rub 99.3 32.8
(percent transmittance)
Dry Pick Resistance No Pick 46
(cm/s)
Uncalendered Gloss 45 28
The paper containing the polyurethane showed good dry pick resistance and good
water
resistance. 'The polyurethane also enhanced the uncalendered gloss.
S
-37-
