U.S. patent application number 11/652232 was filed with the patent office on 2008-07-10 for surface sizing with sizing agents and glycol ethers.
Invention is credited to Daniel F. Varnell.
Application Number | 20080163993 11/652232 |
Document ID | / |
Family ID | 39512577 |
Filed Date | 2008-07-10 |
United States Patent
Application |
20080163993 |
Kind Code |
A1 |
Varnell; Daniel F. |
July 10, 2008 |
Surface sizing with sizing agents and glycol ethers
Abstract
In this invention a composition is applied to the surface of
paper comprising a glycol ether based polymer that provides
enhanced ink-jet print quality. The advantage of using the
composition is that it improves ink-jet printing on the paper
without significant loss of water hold-out. More specifically, the
paper is uncoated and has been treated on the surface with the
following materials and dried to the point of usefulness. These
materials are: 1) one or more compounds that increase water
hold-out. These are known as sizing agents, 2) starch, 3) A glycol
ether based polymer.
Inventors: |
Varnell; Daniel F.;
(Wilmington, DE) |
Correspondence
Address: |
Joanne Mary Fobare Rossi;Hercules Incorporated
Hercules Plaza, 1313 North Market Street
Wilmington
DE
19894-0001
US
|
Family ID: |
39512577 |
Appl. No.: |
11/652232 |
Filed: |
January 10, 2007 |
Current U.S.
Class: |
162/135 ;
162/164.3 |
Current CPC
Class: |
D21H 21/16 20130101;
D21H 19/54 20130101; D21H 17/16 20130101; D21H 19/60 20130101; D21H
17/17 20130101 |
Class at
Publication: |
162/135 ;
162/164.3 |
International
Class: |
D21H 21/16 20060101
D21H021/16 |
Claims
1. An uncoated cellulosic paper having a front and a back surface,
having been treated on at least one surface with: a) at least one
sizing agent present in an amount of between 0.01 to 0.3% based on
dry weight of paper; b) starch present in an amount of between 1 to
8% based on dry weight of paper c) a glycol ether based polymer
present in an amount less than 0.025% based on dry weight of paper
and optionally, a divalent metal salt.
2. The cellulosic paper of claim 1 wherein the glycol ether based
polymers primary backbone is selected from polyethylene glycol, or
polypropylene glycol.
3. The cellulosic paper of claim 1 wherein the glycol ether based
polymers have glycidyether functional groups.
4. The cellulosic paper of claim 1 wherein the glycol ether based
polymers primary backbone is selected from polyethyleneglycol
diglycidyl ether or polypropylene glycol diglycidyl ether.
5. The cellulosic paper of claim 1 wherein the sizing agent is
selected from alkyl succinic anhydride, ketene dimers, or alkenyl
ketene dimers.
6. An aqueous composition for surface treating paper through a size
press, which composition contains: a) Sizing agent in an amount of
0.03-1.0%, b) starch present in an amount of 1.5-12% c) a glycol
ether based polymer present in an amount of less than 0.25% of the
composition.
7. The composition of claim 6 wherein the glycol ether polymers
primary backbone is either polyethylene glycol or polypropylene
glycol.
8. The composition of claim 6 wherein the glycol ether polymers
primary backbone Is selected from polyethyleneglycol diglycidyl
ether or polypropylene glycol diglycidyl ether.
9. The composition of claim 6 wherein the glycol ether based
polymers have glycidyl ether based functional groups.
10. The composition of claim 6 wherein the sizing agent is selected
from alkyl succinic anhydride, ketene dimers, or alkenyl ketene
dimers.
11. Process for improving ink-jet printing properties of paper
which comprises treating paper with a composition of claim 6.
12. Process of claim 11 wherein the glycol ether based polymer is
selected from polyethylene glycol, polypropylene glycol,
polyethyleneglycol diglycidyl ether, or polypropylene glycol
diglycidyl ether.
13. Process of claim 11 wherein the glycol ether based polymers
have glycidyl ether functionality.
14. The process of claim 12 wherein the sizing agent is a reactive
sizing agent.
15. Process of claim 11 wherein the sizing agent is selected from
alkyl succinic anhydride, ketene dimers, or alkenyl ketene
dimers.
16. The cellulosic paper of claim 1 wherein the sizing agent is a
combination of a reactive dimer sizing agent and a polymeric latex
sizing agent.
17. The process of claim 12 wherein the sizing agent is a
combination of a reactive dimer sizing agent and a polymeric latex
sizing agent.
18. Aqueous composition containing a glycol ether based polymer and
an emulsified sizing agent where the glycol ether based polymer is
present in an amount of 3-50% based on amount of sizing agent.
19. The cellulosic paper of claim 1 wherein the starch is present
in an amount of between 2 to 7%, and the glycol ether based polymer
is present in an amount less than 0.02%.
Description
FIELD OF THE INVENTION
[0001] This invention describes the improvement of uncoated fine
paper by treatment of the surface of the paper with polymers based
on glycol ethers used in combination with starch and paper sizing
agents. The invention results in paper with enhanced ink-jet print
quality. The enhanced qualities include less mottle on the printed
images, less strike-through to the back side of the paper when
printed, and enhanced optical density of printed images.
BACKGROUND OF THE INVENTION
[0002] Glycol ether based polymers including those end capped with
epoxy groups have been added to paper for many years. As far back
as at least 1972, U.S. Pat. No. 3,873,354A (1972) describes the
addition of humectants along with salts, such as sodium chloride
and calcium chloride, to paper to be used for electroreprographic
(or electrostatic) printing, that is copy paper. The humectants
named included "polyethylene glycols and polymers . . . ". The
humectant must be water soluble or water miscible. The size press
is mentioned as a means of application and "another additive which
will typically be added to the size press solution is a
conventional binder such as a starch, gum, casein, polyvinyl
alcohol or acetate, animal glue, etc.". The goal was to reduce the
static build-up on the paper. The level of addition of salts was
recited but not the level of humectant. However, in an example,
about 0.05% of the paper weight of polyethylene glycol was added.
This is greater than the level use by applicant herein. In addition
the use of adducts of polyethylene glycol are not mentioned nor is
the use of polypropylene glycol or adducts of polypropylene glycol
mentioned. The latter two are not water soluble. There is no
mention of the use of sizing agents in the paper.
[0003] U.S. Pat. No. 4,210,412 describes the use of "polyhydric
alcohol" in cellulose based textiles. The additive is used to swell
the cellulose so it will accept dyes during a transfer printing
operation. What is called polyhydric alcohol includes "polyalkylene
glycols such as polyethylene glycol of average molecular weight of
200 to 4000, polypropylene glycol of average molecular weight of
400 to 5000, polyethylene glycol/polypropylene glycol block
copolymers of average molecular weight of 400 to 5000 . . . mono-
and diethers . . . and diesters . . . " The addition levels were
not given; but, the addition levels used in the examples were
higher than the current invention. For example, the level used in
Example 2 had polyethylene glycol added at 7.5% of the substrate.
This is far greater than used in the current invention
[0004] US Patent application 20050104947 A1 describes treatments
for paper to reduce the amount of cockle and curl and also to
provide an ink-jet image recording method. The treated paper is
defined by its level of water absorption and a ratio of wet to dry
tensile strength. The cockle and curl tendencies are lowered by
decreasing the hydrogen bonds between fibers in the paper. The
desired paper is obtained by two methods. One method deals with the
treatment of the pulp fibers before the sheet is formed such that
the treatment compounds are located between fibers. Among the
compounds that can be used are polyethylene glycol polypropylene
glycol block copolymers, polyoxyethylene fatty acid esters, and
other nonionic surfactant type materials. Also materials such as
monoglycidyl ethers can be used. A second method is to add to the
paper a heat-curable material or a thermoplastic material. Again
the material must be located between fibers and in this case adhere
fibers together. Epoxy resins are given as one class of suitable
additives. Thus, there is no surface treatment of a paper sheet.
The application expands on what can be done by saying that the
sheet can be treated by surface sizing to apply a nonionic
surfactant. Furthermore, the treatment is also said to preferably
include polyvalent metal salts such as calcium chloride or a
cationic polymer such as cationic starch. Either material can be
added at levels that provide 0.1 to 2 g/m.sup.2 of material to the
sheet. The sheet weights of interest are 60 to 128 g/m.sup.2.
Therefore, the range of percentage addition is from 0.08 to
3.3%.
[0005] The addition of polyethylene glycol and polypropylene glycol
to the wet end of a paper machine is described in U.S. Pat. No.
5,240,562 (issued in 1993 to Procter and Gamble). The patent points
out that polyhyroxy compounds like polyethylene glycols and
polypropylene glycols having weight average molecular weights from
about 200 to 4000 can be used with quatemary ammonium compounds to
give tissue paper a good combination of softness and absorbency.
This patent only covers the wet-end addition of the polyhydroxy
compounds before the paper is dried. There is no mention of the
impact on ink-jet printing. The quatemary ammonium compound and the
polyhydroxy compound were premixed.
[0006] There are numerous patents concerning coated paper where a
reactive polymer hardener is added to the ink absorptive layer. A
wide variety of materials to crosslink the absorptive layer are
known and they include diglycidyl ethers of glycol ether based
polymers, such as polyethylene glycol digylcidyl ether (PEGDGE). In
US Patent 20050202188A1 PEGDGE is used in a ink-jet absorptive
coating layer to crosslink polyvinyl alcohol.
[0007] However, coated papers are very different from the paper of
the current invention. A coated paper has one or more relatively
thick layers of treatment on one or both sides of a preformed
paper. Such papers find use in high-end printing application
including high-end ink-jet printing applications such as
photographic paper. For ink-jet applications, coated grades have an
absorbent layer composed of either a polymer that absorbs a high
volume of liquid ink or a high level of filler that can adsorb a
high volume of liquid ink. There are two uses of glycol ether based
polymers used in such coatings. First they may be added as an
absorbent material and secondly, diglycidyl ethers of glycol based
polymers may be added to improve surface strength. European Patent
0634284 discusses both such uses. The instant invention does not
cover coated papers.
[0008] There are also other uses for polyglycol ethers in paper
coatings. U.S. Pat. No. 5,746,814 describes the addition of the
following compounds as desizing agents in a more complex
composition for coating of paper: poly(alkylene glycol);
poly(propylene oxide)-poly(ethylene oxide) copolymers; fatty ester
modified compounds of glycerol and poly(ethylene glycol); and
poly(oxyalkyene)modified compounds of sorbitan esters, fatty
amines, alkanol amides, castor oil, fatty acid, fatty alcohol. The
overall composition contains solvent, binder, desizing agent,
anticurl agent, defoamer, biocide, antistatic agent, lighffastness
promoting agent, and a filler. All of the coating applications fall
into a different class of paper from the current invention and the
coating compositions are significantly different as noted
above.
[0009] US application, 20050013949 A1 concerns a coated paper.
However, its description of the base paper on which an ink
absorbing layer would be applied is described as. "Base paper
employed for the paper support of the present invention is made
employing wood pulp as a main raw material . . . It is possible to
incorporate into base paper sizing agents such as . . .
strengthening agents such as starch . . . moisture retention agents
such as polyethylene glycol, dispersing agents and softening agents
. . . "
[0010] U.S. Pat. No. 6,203,899B1 describes a printing medium
comprising a liquid absorbent base material, an ink-receiving layer
provided on the base material, which comprises a pigment, a binder
and a cationic substance, and a surface layer provided on the ink
receiving layer. Here again the concern is a coated paper. It is
described as fibrous pulp and a filler impregnated with a
crosslinking substance. The crosslinking substance is crosslinked
to form nonswelling paper. The crosslinking substance can be an
epoxy. PPGDGE is specifically described. Along with the
crosslinking substance can be a polymer having a reactive group.
Starch is one example of the polymer. The amount of starch is in
the range that can be applied by a size press. The ratio of
crosslinking substance, starch, to crosslinking agent, PPGDGE, is
from 100:1 to 1:1 by weight. The range is different from the
current invention where our ratio under preferred conditions is
about 400 to 1 or less. A polyvalent metal salt is mentioned as an
option for crosslinking certain materials. The divalent metal ions
that are optional additives of the invention of this disclosure do
not crosslink starch.
[0011] U.S. Pat. No. 6,706,320B2 describes modifying a surface
containing a polymeric material. In one claim, it is said the
substrate can be cellulosic and in another claim it is said the
modifying agent can be a crosslinker. The crosslinker can be an
epoxy compound such as diglycidyl ethers of polyols. However, the
process of the patent requires the presence of a polyamine as a
surface modifying agent and that the polyamine vaporize in the
process. The epoxy compound reacts with the amine.
[0012] U.S. Pat. No. 5,746,814A includes polyethyleneglycol
diglycidyl ether as one of the compounds that can be added to
prevent paper from curling. An elaborate composition for treating
paper is described with a wide range of levels of each component.
There are nine components in the composition and they can include
water, starch as a binder, and PEGDGE as an anticurl or a desizing
agent. Taking the maximum of starch in the composition and the
minimum of PEGDGE one gets a ratio of 150:1. This is different from
that of the current invention. Furthermore the current invention
does not require many of the other components listed such as
antistatic agent or desizing agent or lightfastness promoting
agent. The composition is for treating paper that has already been
imaged.
[0013] Hercules Incorporated has a patent (U.S. Pat. No. 6,207,258
B1) on the use of divalent metal salts with sizing agents. It also
had a patent (U.S. Pat. No. 6,051,107A) on mixtures of reactive and
nonreactive sizing agents as pre-mixes and in paper treatment
compositions. The later patent was not maintained.
SUMMARY OF THE INVENTION
[0014] In general one embodiment of the invention involves a paper
composition having applied to its surface a composition comprising
a glycol ether based polymer that provides enhanced ink-jet print
quality. The advantage of the paper composition is improved ink-jet
printing without significant loss of water hold-out.
[0015] More specifically, this first embodiment of the invention is
an uncoated paper (based on wood pulp or other cellulose product
based) that has been treated on the surface with at least the
following materials and dried to the point of usefulness. These
materials are:
[0016] 1) one or more compounds that increase water hold-out. These
are known as sizing agents,
[0017] 2) starch,
[0018] 3) a glycol ether based polymer.
[0019] The sizing agent will be present in an amount of 0.01% to
0.3% based on dry weight of paper.
[0020] The starch will be present in an amount of 1 to 8% based on
dry weight of paper.
[0021] The glycol ether based polymer will be present in an amount
of less than 0.025% based on dry weight of paper.
[0022] One preferred composition is paper surface-treated with
starch, sizing material, a glycol ether based polymer and a
divalent metal salt. The sizing materials and glycol ether based
polymers are defined below along with the addition levels.
[0023] The paper of the invention has improved ink-jet print
qualities of less mottle of printed areas, less strike-through of
ink, and possibly increased optical density over paper not treated
with all the components of the invention.
[0024] The sizing agents, as defined below, provide water hold-out.
They may also improve the sharpness and optical density of ink-jet
printed images. The addition of sizing agents to paper is common.
Likewise starch is a standard additive to paper and thus, the
invention in one embodiment is the addition of sizing agent and
starch with glycol ether based polymers, such as polypropylene
glycol diglycidyl ether. Another option is that the paper as
described above also contains a divalent metal salt as described in
Hercules patent U.S. Pat. No. 6,207,258 B1, incorporated by
reference.
[0025] Any uncoated paper can be used, but a preferred paper is
uncoated "fine" paper for printing and writing applications. Such
paper typically contains bleached wood pulp, precipitated calcium
carbonate, and starch along with other materials deemed beneficial
for preparing the paper or enhancing paper properties or reducing
the cost of the paper. A typical uncoated fine paper has a basis
weight of 70 to 80 grams per square meter.
[0026] For the present invention, the three or four components of
the invention, listed above, may be added either separately or
together to the surface of the paper. Fine paper for printing and
writing is usually treated before it leaves the paper machine on
which it was made.
[0027] A clear distinction should be made between surface
treatments and coatings. Both are applied to paper that is already
formed. Both can be used to enhance printing properties. A
treatment is meant to modify the surface of the paper but the
general structure remains mostly unchanged. A coating creates a new
surface. More material is applied with a coating than a treatment.
Coatings are usually made up of a large percentage of inorganic
filler or pigment such as silica or clay or calcium carbonate. A
coating covers the entire surface of the paper substrate blocking
the porous nature of the paper and leveling the surface. With a
"treatment", the composition of the base sheet still has a large
influence on final properties. For example, more wet-end sizing
leads to a higher surface tension in the final paper versus a low
level of sizing. With a "coating", the internal chemistry may
affect the application of the coating but does not have a direct
effect on the final properties of the paper. For example, internal
sizing is covered up by a coating and will not directly change the
surface tension of the final coating unless it migrates through the
coating.
[0028] The method of applying the materials used in this invention
is not crucial as long as the application method for the materials
is controllable and leads to the desired results. The most
preferred method of addition is for the starch to be dissolved in
water by cooking and for the other components to be added to the
starch solution and then for the resulting composition (the
treatment composition) to be applied to the paper with a paper
machine size press.
[0029] A second embodiment of the invention is the composition used
to treat the paper. It is defined as a starch based solution
containing at least one paper sizing agent and at least one glycol
ether based polymer and optionally a soluble divalent metal salt
such as calcium chloride and optionally other additives common to
the treatment of paper. The treatment composition allows for all of
the additives to be applied simultaneously to the paper. This is an
aqueous composition that contains:
[0030] sizing agent in an amount of 0.03-1%,
[0031] starch present in an amount of 1.5-12%,
[0032] glycol present in an amount of less than 0.25%.
[0033] The treatment composition consists predominantly of water in
which a binder is dissolved. The binder is the predominant
component aside from the water. The binder for this invention is
predominantly starch. Other binders such a polyvinyl alcohol can be
used in combination with the starch. With the binder, other
additives are typically added such as sizing agents that hold out
water and improve printing properties; optical brightening agents;
dyes; and antistatic agents. Sometimes materials such as inorganic
fillers are added. When fillers are added they do not constitute
more than about 40% of the composition on a dry weight percent
basis of the non-water components.
[0034] These compositions can also contain other common additives
such as sodium chloride and defoamer. The advantage offered by the
second embodiment of the invention (the treatment composition) is
the simultaneous treatment of the paper with a composition that
leads to the improvements listed above in the first embodiment of
the invention. The composition must be such that it is uniform and
it can be applied to the paper in a uniform manner.
[0035] Preferably, the glycol ether based polymers will be added to
the treatment composition so that they are applied to the paper
with the paper machine at the same time as the starch and sizing
agent.
[0036] A third aspect of the current invention is a pre-mixture of
the sizing agents and glycol ether based polymers and optionally a
divalent metal salt. The pre-mixture is then added to the starch
based solution just described. The pre-mixtures may be water based
solutions or emulsions or dispersions. The glycol ether polymer
will be 3-50% based on the amount of sizing agent.
[0037] A third embodiment of the invention comprises pre-mixtures
of some of the additives that go into the surface treatment
composition thus offering the convenience of adding several
materials simultaneously to the mixture used to treat the paper.
The pre-mixtures that are of interest for this disclosure will
contain the following materials: [0038] A water-based composition
(i.e. a solution, latex, and or dispersion) of one or more paper
sizing agents, and one or more glycol ether based polymers.
DETAILED DESCRIPTION OF THE INVENTION
[0039] The glycol ether based polymers used in this invention
include polymers with repeat units of ethylene glycol or propylene
glycol or combinations of them. There may be other functional
groups along the backbone provided they do not account for more
than approximately ten percent by weight of the final polymer
structure. There may be branching along the backbone. The polymers
can be end-capped with hydroxyl groups, ethers, gylcidyl ethers,
esters, carboxylic acid groups, and other functionality so long as
the end groups do not account for more than 25% of the weight of
the average polymer molecule.
[0040] The polymer compositions may have one, two, or more types of
functional end groups other than hydroxyl groups. There may also be
one of more types of functional groups within the polymer backbone
or grafted on to it.
[0041] Use of glycol ether based surfactants that fit the above
criteria are part of this invention provided they meet the
remaining conditions given below. Glycidyl ether end-capped
polymers such as polyethyleneglycol digycidyl ether and
polypropyleneglycol digycidyl ether are useful also.
[0042] The average molecular weight of the glycol ether based
polymers of this invention shall be from approximately 350 g/mole
to approximately 200,000. The polymer must be soluble or readily
dispersible in water. The preferable average molecular weight is
between 380 and 20,000 and most preferably between 500 and 2000
g/mole.
[0043] The addition level of the glycol ether based polymers of the
invention is defined by the impact on sizing as defined in this
invention and by concentration. The glycol ether based polymers of
the invention should not cause greater than a 25% reduction in the
level of sizing when utilized under at least some portion of the
conditions of this invention. For example, polypropylene glycol
(PPG) may be used at a low level but at a high level it interferes
with sizing. The level of addition of the glycol ether polymers to
the aqueous composition for surface treating the paper shall be
less than 0.25%. The level of addition in a premix with sizing
agent should be less than 50% of the active sizing agent by
weight.
[0044] The paper substrate which is treated in the current
invention can contain wood based pulp from ground wood to
chemically bleached wood or a non-wood based pulp or a combination
of pulps. The paper can also contain usual paper making inorganic
fillers such as calcium carbonate or clay and may also contain
organic fillers. The paper can also contain strength additives,
retention additives, internal sizing agents and other common paper
additives such as alum. The preferred grade of paper can be any
type suitable for ink-jet printing which can include fine paper to
white-top liner board. The basis weight of the paper can be
anywhere from 40 g/m.sup.2 to 350 g/m.sup.2. The preferred paper is
any type of printing and writing paper including roll fed to sheet
fed papers. The most preferred is uncoated fine paper with a basis
weight between 60 and 100 g/m.sup.2.
[0045] The starches that are suitable as part of the paper
treatment can be of any kind provided they can be dissolved in
water and applied to the paper. The starches can be from a variety
of sources including corn, potato, rice, cassava root, and others
used in paper making. Unmodified and modified starches can be used.
Modified starches include oxidized, ethylated, cationic, anionic,
amphoteric, hydrophobically modified, and others used in paper
making. The preferred starches have reduced viscosities such that
solutions of greater than 6% solids can be used on a paper machine
size press. The most preferred are those with reduced viscosity
that are also are oxidized, ethylated, cationic, or amphoteric. The
range of starch treatment based on the dry weight of the final
paper is 1% to 8.0%. More preferably from 2% to 7% and most
preferably from 3% to 6%. The range of starch concentration in the
treatment composition can be from 1.5% to 12% provided the
viscosity allows for application to the paper substrate. More
preferably the concentration will be between 3% and 11% and most
preferably between 5% and 10%.
[0046] The surface treatment sizing agents suitable for the current
invention include those that are termed reactive such as alkyl
ketene dimers, alkenyl ketene dimers, and alkyl succinic
anhydrides. Sizing agents termed unreactive are also suitable and
may be mixed or used with the reactive sizing agents as described
in a previous Hercules' patent (U.S. Pat. No. 6,051,107A).
Unreactive sizing agents may be used on their own. Unreactive
sizing agents include soluble polymers such as styrene-maleic
anhydride based polymers, styrene-esterified maleic anhydride based
polymers, styrene acrylic acid and styrene methacrylic acid based
polymers and insoluble polymers such as polymer latexes commonly
used in paper making such as poly(styrene/acrylic) resins,
acrylonitrile/acylic resins and urethane polymers and insoluble
polymer dispersions such as of ethylene/acrylic acid polymers.
[0047] The level of surface treatment sizing agent in the final dry
paper will range from 0.01% to 0.3% on a dry weight basis.
Preferably the level is 0.02 to 0.2% and most preferably it is 0.03
to 0.1%.
[0048] All of the above levels are based on both sides of a base
paper being treated. However, the invention is applicable to
treatment of one or both sides. When only one side is being treated
all of the above levels relating to the paper will be one half of
the values listed.
[0049] The final paper may contain other additives that were
included in the formation of the paper or were applied along with
the surface treatment or separately from the surface treatment. The
additives applicable are those which are usually utilized in paper.
They include but are not limited to the following: inorganic and
organic fillers such as calcium carbonate or hollow sphere
pigments; optical brightening agents which are also known as
fluorescent whitening aids, pigments; dyes, strength additives such
as polyamidoamines, promoter resins such as
polydimethyldiallylammonium chloride; adhesion promoting polymers
such as styrene acrylic latexes and styrene maleic anhydride based
polymers; and inorganic salts such as sodium chloride and calcium
chloride. When the final paper contains a divalent metal salt it
should be less than 0.25% of the paper weight.
[0050] The methods of applying the paper treatment composition of
the current invention are not limited provided uniform controlled
application is obtained. The treatment may be made to paper formed
on a paper machine and then only partially dried or it can be made
on a paper machine to dried paper or the treatment can be done
separate from the paper machine to paper that was formed, dried,
and moved. The preferred process is for paper to be formed with a
paper machine, partially dried, and treated using a paper machine
size press, and then for the paper to be dried again. The paper may
be further modified by calendering.
[0051] The treatment composition, the second embodiment of the
invention described above, has the same components just described.
The starch solution in water must be of dissolved starch and the
viscosity must be such that the solution, containing other
components, can be applied to the paper. The viscosity and not the
solids of the starch solution is the most critical factor; however,
some starch materials can only be dissolved at very low
concentrations before they become too thick to use. A paper maker
will select a starch based on the properties it imparts to the
paper as well as its ease of use and the ability to apply the
desired level with the equipment being used. A preferred level of
starch in the treatment composition is 3 to 12% and a most
preferred level is 5 to 10%. Other materials such as polyvinyl
alcohol may be used with the starch, if desired. The additional
binder level will be less than the starch level.
[0052] Suitable sizing agents are described above. They are added
to the starch solution. The level of sizing agent in the
composition will depend on two factors: the level of the starch
composition applied to the paper and the desired level of sizing
treatment. Typically the level of starch addition is selected along
with the starch solution concentration and then the level of sizing
agent in the starch solution is adjusted to get the desired level
of treatment. The level of sizing agent in the starch composition
will be between 0.03 and 1% of the paper treatment composition
based on the active component of the sizing agent.
[0053] The level of glycol ether based polymer in the treatment
composition will be determined in the same manner as described for
the sizing agent level. The level of glycol ether based polymer
will be determined by the amount of starch solution applied and the
desired level of the polymer to be applied. The level of glycol
ether polymer in the paper treatment composition will be less than
0.25%.
[0054] The treatment composition may contain other materials as
noted above for the paper. When the treatment composition contains
a soluble divalent metal salt such as calcium chloride and
magnesium chloride the level of the salt will be less than 20% of
the starch level.
[0055] The sizing agents of interest were described above. One or
more sizing agents can be combined. The form of the sizing agent
will be as a solution emulsion or dispersion in water with suitable
additives used to obtain desired stability. One or more glycol
ether based polymers can be combined with the sizing agents. The
sizing agent formulation may also contain a water soluble divalent
metal salt such as calcium chloride or magnesium chloride.
[0056] The amount of glycol ether based polymer versus sizing
agents can be from 3% to 50% polymer to active sizing agent. More
preferably the level of glycol ether based polymer to active sizing
agent will be from 4% to 35%. When added the level of divalent
metal salt will be less than two times the total level of sizing
agents.
DEFINITIONS
[0057] Sizing
[0058] Paper sizing refers to the ability of a paper to hold out a
liquid or from preventing it from penetrating into or through the
paper. Generally the liquid held out is water. Sizing values are
specific to the test used. Compounds that are designed to increased
the hold-out of liquids are known as sizing agents. Sometimes a
specific type of sizing is referred to such as an oil sizing agent.
For the current work, the sizing and sizing agents are defined in
terms of the ability to hold out the water based ink solution used
in the Hercules Sizing Test. The test is defined below. For a
discussion on sizing, see Principles of Wet End Chemistry by
William E. Scott, Tappi Press 1996, Atlanta, ISBN 0-89852-286-2
[0059] Optical Density
[0060] Optical density is a measure of the inverse of the amount of
reflected light off a surface. Generally and for the purpose of
this invention, it is a measure of light reflecting off of a black
printed area on a sheet of paper. Optical Density (OD) equals
-log.sub.10(reflectance). The test method utilized was to use
commercial hand-held densitometer. It is further described below.
The concept of optical density is explained in detail in an article
by Allen Rushing found on the internet at
www.loglight.com/concepts&tools.htm.
[0061] Mottle
[0062] Mottle, or more accurately print mottle, refers to the
unevenness of a printed area. It can be blotchiness or variations
in optical density. They are visible to the eye. The method used to
measure the mottle will determine what value it has. The test
method used is provided below. An example of print mottle is shown
in FIG. 19.17 of Printing Fundamentals ed. Alex Glassman, Tappi
1985, Atlanta, ISBN 0-89852-045-2.
[0063] Strikethrough
[0064] Strike-through refers to the uneven penetration of ink
through to the back side of a printed paper. It is not show through
which is the ability to see the printed image from the back side of
the sheet but rather is penetration of the ink through or almost
through the sheet. The ink penetration is often uneven and the
strike-through will have a speckled appearance on the back side of
a large printed area. The method used to measure the mottle will
determine what value it has. The test method used in the current
invention is provided below.
TEST METHODS
[0065] Preparation of Samples
[0066] Paper samples for the examples below were prepared by either
a laboratory method or with a pilot paper machine. The general
procedures are described here. Specific details are listed with
each example.
[0067] For the laboratory test, base papers were prepared ahead of
time at Western Michigan University on their pilot paper machine.
The papers were made without any size press treatment, that is no
starch, sizing agent, or other additive was applied to the surface
of the formed paper. The pulp used to make the papers was a 75%/25%
by weight mixture of hardwood and softwood bleached craft pulp as
is typical of what would be used to produce commercial copy paper.
The papers also contained precipitated calcium carbonate, cationic
starch, aluminum sulfate and a retention aid. Once made and dried
the papers were cut into sheets and stored. The paper was later
treated at the Hercules Research Center with a laboratory bench top
puddle size press. The size press consisted of a horizontal set of
ten inch pinched rollers, one rubber coated and one metal, through
which the paper was fed. A puddle of the size press treatment was
held by the rollers and dams on the top side of the rollers. The
rollers were held together with 14 pounds of air pressure. The
paper passed through the puddle as it was pulled by the rollers,
and through the rollers, to give a controlled and uniform level of
treatment. The level of treatment was controlled by the
concentration of the treatment chemicals in the treatment solution
which was generally a dissolved starch solution. The paper was
captured below the two rollers and immediately dried on a drum
drier set at about 100.degree. C. The paper was dried to about a
3-5% moisture level.
[0068] The size press formulations were prepared by dissolving
starch for 45 minutes at 95.degree. C., cooling, holding the starch
at 65.degree. C. Generally the starch pH was adjusted to 7.5. To
the starch was added other additives for this treatment such as
salt, sizing agents, and the glycol ether based polymers used in
this invention. Once the additives were in the starch solution the
solution pH was readjusted to a pH of 7.5. Then the starch
solution, still at 65.degree. C. was used to treat the paper. For
each base paper used the amount of solution picked up through the
rollers was determined and the additive levels set accordingly.
After drying, each sample was conditioned by aging at room
temperature for seven days. The samples were also conditioned for
at least 12 hours prior to being tested under the conditions they
would be tested.
[0069] Other samples used in the examples below were prepared on
Hercules' pilot paper machine. The paper was made with conditions
similar to those described above for Western Michigan University.
Again the goal was to make standard copy paper. On the Hercules
paper machine the first drier section was followed by a size press
and then another drier section and then a set of calendering rolls.
The treatments of the invention were applied to the paper at the
size press. A puddle size press mode was used. In the puddle mode,
the liquid treatment solution was held along the rolls as a puddle
through which the paper passed. The pilot machine process imitated
the process of a large paper machine. As with laboratory studies a
solution of cooked (dissolved) starch was used as the carrier for
treatment chemicals.
[0070] Sizing Test
[0071] Descriptions of various sizing tests can be found in The
Handbook of Pulping and Papermaking by Christopher J. Biermann
Acedemic Press 1996, San Diego, ISBN 0-12-097362-6. Properties of
Paper: An Introduction ed. William E. Scott and James C. Abbott
Tappi Press 1995, Atlanta, ISBN 0-89852-062-2. The Hercules Sizing
Test (HST) was used for the current work. It is described by Tappi
Method T530. For the test results presented in this disclosure a
solution containing 1% napthalene green dye and 1% formic acid was
used as the penetrant. The end point of the test was set at 80%
reflectance.
[0072] Ink-Jet Printing Conditions
[0073] Paper samples were printed with a Hewlett Packard HP6122
printer using HP45 black ink cartridges. The settings for the
printer were: plain paper, normal print quality, color, no color
enhancement. On each sample a solid black five inch by five inch
square was printed and allowed to dry before being stacked.
[0074] Image Analysis for Mottle and Strike-Through
[0075] Mottle and strike-through are both variations of uniformity,
mottle of black print and strike-through of the white back side of
paper that has been printed. An image analysis method was used to
quantify the variations. Images were captured by a dual light
scanner at a resolution of 600 dpi in bit-map format. The images
were then analyzed with a mottle analysis software package from
Verity IA 2004 Multifunction Version 1.4.1 designed by Roy R.
Rosenberger. The software does a stochastic analysis. Mottle values
can be obtained for various target sizes. A paper by Roy R.
Rosenberger of Appleton, Wis. explains the analysis. The paper
"Stochastic Frequency Distribution Analysis as Applied to Mottle
Measurement" can be obtained on the VerityIA web site
www.verityia.com. For the results presented in this disclosure
black printed samples were used and the luminance values of the
printed areas were evaluated on a grey scale. In the analysis,
three values are obtained: 1) the standard deviation of the
standard deviation of luminance values of each target on a grey
scale; 2) the mean of the standard deviation of the luminance
values; and 3) the standard deviation of the means of the standard
deviation of the luminance values. These values are multiplied
together to obtain what is called a Mottle Number.
[0076] For the examples presented in this disclosure, one target
size is reported. First the 600 dpi images were taken. Then each
image was analyzed as a collection of squares (a target size) of 16
dots by 16 dots (a 0.67 mm by 0.67 mm square) across approximately
a 55 mm by 55 mm area. Across the image, groups of four squares
were combined into a larger square. Each large square was a target
of 1.4 mm by 1.4 mm. The numbers for the analysis of the mottle was
determined for the collection of 1.4 by 1.4 mm squares across the
selected image area. The software provided a mottle number for the
1.4.times.1.4 mm targets. In the analysis, a higher value indicates
more mottle. A lower value represents a more uniform image and is
desirable.
[0077] The same procedure was used for quantifying
strike-through.
[0078] Measuring Optical Density
[0079] As noted above, optical density is a reflectance
measurement. For the values of the current disclosure, an optical
densitometer from Graphics Microsystems Inc. was used. The model
was a Cosar 200. Black optical densities were measured and
reported. Six readings were taken for each sample and averaged. A
higher optical density value represents less reflectance and thus a
darker looking print.
[0080] In all of the above tests, it is not so much the absolute
values that are of importance but rather the relative values versus
control samples that were included in all tests. The control
samples are described in each example.
EXAMPLES
Example 1
Demonstration of the Problem of Lowering Internal Sizing Levels
When No Glycol Based Polymer is Present
[0081] Using the pilot paper machine process described earlier and
the conditions listed here three different paper samples were
prepared with different levels of internal sizing and only starch
and sodium chloride applied at the size press. The sizing (liquid
hold-out property) of the final paper was determined by the
Hercules Sizing Test described above. The mottle and strike-through
were determined on ink-jet printed black squares as described
earlier.
[0082] The paper was made with 70:30 ratio of bleached craft
hardwood and softwood as suitable for fine paper. 15% of a medium
size precipitated calcium carbonate (Albacar 5970) was added based
on the pulp solids. Likewise 0.75% cationic starch, 0.25%
papermakers alum (Al2O3*14H20), 0.015% of an anionic polyacrylamide
retention aid, and three different levels of alkyl succinic
anhydride (ASA) sizing agent were added on the same basis. The ASA
was added as a stable emulsion typical for papermaking. At the size
press, each sample was treated with a water solution of 8% oxidized
starch and 0.5% sodium chloride to give an addition of 4% starch
and 0.25% sodium chloride to the final dry paper.
[0083] The following table lists the results. Less ASA sizing agent
resulted in less sizing and more mottle and strike-through when
printed.
TABLE-US-00001 Sample ASA level HST (sec) Mottle Strike-Through 1.
0.036% 3 5.84 12.0 2. 0.046% 69 5.15 11.2 3. 0.060% 131 2.68 2.61
HST = Hercules Sizing test
Example 2
Demonstration of the Problem of Increasing Surface Sizing Levels
with No Glycol Based Polymer.
[0084] The same conditions of Example 1 were used. At the size
press, Hercules imPress.RTM. ST900 sizing agent (ST900) was added
along with the starch. ST900 is an emulsion containing alkenyl
ketene dimer as a sizing agent. The levels of addition on a dry
basis of the dimer to the final paper were 0 and 0.05%.
[0085] The results for sizing mottle and strike-through are listed
in the following table. Adding some surface sizing increased the
sizing but the mottle and strike-through were worse.
TABLE-US-00002 Sample dimer level HST (sec) Mottle Strike-Through
1. 0 3 5.84 12.0 2. 0.050 189 27.0 18.3
Example 3
Addition of Premixed Polyethyleneglycol and Magnesium Chloride
[0086] Samples were prepared in the laboratory using a bench top
size press and pre-made base sheet by the process described above.
The base sheet contained 1.25#/ton of a solid AKD sizing agent
applied as an emulsion (Hercules' Hercon.RTM. 70 sizing emulsion).
It also contained 10% Albacar HO PCC filler. The compositions of
the paper treatments applied at the size press were based on a 9%
solution, in water, of a low viscosity oxidized starch (D-15F from
Grain Processing Corporation). The pick-up of the base sheet of the
starch solution was 54.0%. Therefore, the final paper contained
approximately (54.times.0.09)/(100+(54.times.0.09).times.100% or
4.64% starch. Addition levels of additives were based on this
pick-up. To each formulation enough NaCl was added to give a final
paper content of 0.25%. Enough reactive sizing agent, non-reactive
sizing agent, glycol ether polymer and MgCl.sub.2 was added to give
the desired levels of addition as listed in the following table.
The reactive sizing agent used was a stable emulsion of liquid
dimer based on a saturated alkyl fatty acid (AKD). The unreactive
sizing agent was a styrene acidic emulsion type (SAE) consisting of
a poly(styrene/butyl acrylate) emulsion (Hercules' Chromaset 800
product). The glycol ether polymer was a polyethylene glycol (PEG)
of 1000 g/mole average molecular weight. Both the MgCl2 and PEG
were pre-mixed with the dimer emulsion before being added to the
starch solution. The results for the final paper sizing, mottle,
strike-through and optical density (OD) are also listed in the
table.
[0087] Values listed for materials are percent of final paper
weight. The HST values are in seconds.
TABLE-US-00003 Dimer SAE PEG MgCl.sub.2 HST Mottle St. Thr. OD A.
0.035 0.018 0 0 496 16.2 8.29 1.23 B. 0.045 0.023 0 0 515 18.0 2.78
1.32 C. 0.035 0.018 0.007 0 449 10.2 2.24 1.37 D 0.045 0.023 0.009
0 477 2.1 0.60 1.42 E 0.035 0.018 0 0.053 477 22.9 4.58 1.29 F.
0.045 0.023 0 0.068 513 11.0 2.04 1.45 G 0.035 0.018 0.007 0.053
378 23.0 4.31 1.32 H 0.045 0.023 0.009 0.068 431 0.7 0.42 1.47
[0088] The addition of PEG improved mottle, strike-through, and
optical density. The sizing was not compromized. Addition of
MgCl.sub.2 lowered sizing a little but also improved mottle,
strike-through, and optical density. Addition of both materials had
a significant effect on sizing and at the lower level did not
improve mottle. However, at the higher level mottle,
strike-through, and optical density improved. The benefits of
MgCl.sub.2 were known from previous work but the benefit obtained
from PEG was surprising. Surprisingly, the benefits of divalent
metals salts and PEG were additive.
Example 4
Addition of Polypropylene Glycol
[0089] Using the pilot paper machine described earlier with wet-end
conditions consisting of 75/25 hard wood/soft wood, 16% PCC, 0.07%
dimer from an AKD emulsion, alum, cationic starch, and anionic
polyacrylamide retention aid the effect of the additions of starch
with NaCl, liquid dimer emulsion and polypropyleneglycol (PPG) were
tested. The level of starch, NaCl, and dimer in the final paper
samples were constant and were 4%, 0.25%, and 0.035%,
respectively.
[0090] The wet-end conditions were as follows: [0091] The cationic
starch used was Stalok 400 from Staley [0092] The level of cationic
starch was 0.75% of the final paper weight [0093] AKD stands for
Alkyl Ketene Dimer Sizing Agent. The commercial product used was
Hercules Hercon 70 sizing agent. [0094] The alum level was 0.25%
based on final paper weight [0095] The level of anionic
polyacrylamide retention aid was 0.015% based on final paper weight
[0096] The temperature was 50.degree. C. [0097] The pH was 7.0
[0098] The basis weight of the paper formed was 75 grams per square
meter of paper
[0099] The size press conditions were as follows: [0100] The starch
used was an oxidized corn starch called D15F from Grain Processing
Corporation [0101] The starch was cooked for 40 minutes at
95.degree. C. [0102] The starch solution concentration was 7.5%
[0103] The temperature of the size press solution was 65.degree. C.
The liquid dimer sizing agent used was Hercules imPress ST900
sizing agent.
[0104] The level of PPG added is listed below in the table of
results. The PPG had an average molecular weight of 700 g/mole.
TABLE-US-00004 Sample PPG (%) HST (sec) Mottle Str-Thr A. 0 268
16.4 51.6 B 0.01% 229 14.6 37.4 C 0.02% 70 12.0 17.2
[0105] PPG was only slightly effective at lowering mottle. It was
effective at reducing strike-through. However, at 0.01% and 0.02%
in the paper it reduced the level of sizing. Example 5 Addition of
polyethyleneglycol diglycidyl ether and polypropylene glycol
diglycidyl ether.
[0106] The pilot paper machine described above was used to test the
effectiveness of PEG and PPG with glycidyl ether (epoxide) end
groups. The conditions were the same as in example 4, except the
wet-end sizing was alkyl succinic anhydride (ASA). The pH was 7.8
instead of 7.0
[0107] Paper was made with two levels of ASA, 0.036 and 0.041%. A
75/25 hard wood/soft wood mixture was used with 16% PCC filler,
0.75% cationic starch, 0.5% paper makers alum, and 0.015% anionic
retention aid. The paper was then treated on the paper machine at
the size press.
[0108] Polyethyleneglycol diglycidyl ether (PEGDGE) with an average
molecular weight of about 350 g/mole and polypropylene glycol
diglycidyl ether (PPGDGE) with an average molecular weight of about
400 g/mole were mixed with an oxidized starch and a liquid ketene
dimer sizing agent made from an unsaturated alkyl fatty acid. The
sizing agent was added as an emulsion to the starch solution. The
glycol ether polymers were also added to the starch solution. The
level of starch added to the paper was 4%. As is typical in fine
paper manufacturing 0.25% NaCl was added to the paper by also
adding NaCl to the size press starch solution. The levels of dimer
and glycol ether polymers in the final papers are noted below.
[0109] (the levels of materials are listed in dry percent of the
final paper weight.)
I. 0.036% ASA in the Base Sheet
TABLE-US-00005 [0110] Sample Dimer Polymer HST Mottle Str. Th. OD A
0.05 none 181 8.38 3.18 1.27 B 0.065 none 195 13.6 3.35 1.32 C 0.05
0.01 PEGDGE 169 9.79 3.22 1.34 D 0.065 0.01 PEGDGE 181 2.80 0.735
1.41 E 0.05 0.02 PEGDGE 154 2.16 1.05 1.38 F 0.065 0.02 PEGDGE 192
2.24 0.814 1.39 G 0.05 0.01 PPGDGE 162 1.16 0.921 1.43 H 0.05 0.02
PPGDGE 126 1.51 0.722 1.43
II. 0.041% ASA in the Base Sheet
TABLE-US-00006 [0111] Sample Dimer Polymer HST Mottle Str. Th. OD A
0.04 none 174 2.39 1.36 1.41 B 0.055 none 185 1.13 0.57 1.43 C 0.04
0.0075 PEGDGE 158 1.17 0.62 1.42 D 0.055 0.0075 PEGDGE 180 0.905
0.53 1.43 E 0.04 0.015 PEGDGE 156 1.02 0.83 1.41 F 0.055 0.015
PEGDGE 148 0.88 0.54 1.42 G 0.04 0.0075 PPGDGE 164 0.82 0.71 1.43 H
0.055 0.0075 PPGDGE 201 0.94 0.65 1.43
[0112] Both PEGDGE and PPGDGE reduced mottle and strike-through.
The benefit depends on the amount of mottle and strike-through of
the paper without them. The samples with more internal ASA had less
mottle and strike-through and therefore the amount of improvement
was less. PPGDGE was more effective than PEGDGE. However, when
0.02% PPGDGE was used the sizing was reduced. At lower levels, it
may also have a negative effect on sizing when a low level of
sizing agent is used. As an added benefit, both epoxides enhanced
optical density. PPGDGE was again more effective than PEGDGE.
Example 6
Addition of Alternative Functionalized Glycol Ether Polymers
[0113] Using the same conditions as Example 3, except for use of an
8% rather than a 9% starch solution, poly(ethylene glycol) bis
(carboxymethyl) ether (PEGBCME) was evaluated. The polymer was
obtained from Alrich and had an average molecular weight of 600.
The results are displayed in the following table.
[0114] Values listed for materials are percent of final paper
weight. The HST values are in seconds.
TABLE-US-00007 Dimer PEGBCME Mottle St. Thr. A. 0.04 0 15.0 10.5 B.
0.04 0.0075 4.75 14.3 C. 0.04 0.015 1.13 5.25 PEGBCME reduced
mottle and strike-through.
Example 7
Use of a pre-mixture
[0115] Using the same conditions as Example 3, except for use of a
10% starch solution instead of a 9% starch solution, a pre-mixture
of sizing agent and glycol ether polymer was evaluated.
[0116] ImPress.RTM. ST900 sizing emulsion of Hercules was used as
the sizing agent on its own and in pre-mixtures with PPG. The PPG
was predispersed in water, 10% PPG and 90% water, with a sonicator.
The PPG dispersion was mixed with the dimer emulsion. The ratio of
dimer to PPG in the pre-mixtures was 10 to 1 and 5 to 1. The
results of the evaluation are summarized in the following
table.
TABLE-US-00008 Dimer PPG HST Mottle St.Thr. A. 0.035 0 384 28.9
8.56 C. 0.035 0.0035 392 29.4 5.56 E. 0.035 0.007 349 16.6 4.83
[0117] PPG was premixed with a dimer emulsion and the mottle and
strike-through performance of the treated paper was improved. With
the lowest level of PPG, 0.0035%, there was little or no
improvement of mottle but strikethrough improved. At a higher level
the mottle and strikethrough performance of the paper improved. As
noted in a previous example, the addition of too much PPG will
reduce the level of sizing.
* * * * *
References