Note: Descriptions are shown in the official language in which they were submitted.
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IIVIPROVED PAPER MAKlING PROCESS
Field of the Invention
The present invention is directed to the papermaking arts, more particularly
to a process
for the manufacture of a paper having improved grease and water resistance,
yet facilitating
recycling of the paper. Such papers (throughout the specification and claims
"papers" includes
virgin or recycled paper, kraft stock and similar materials) find particular
application in the
container maldng art wherein such iinproved properties are desirable. The
container making art, -
particularly, in the field of corrugated containers, folding cartons, and the
tray and box
industries, consumes much of the natural timber resources. Thus, it would be
beneficial to
formulate new processes of forining papers of improved grease and water
resistance properties
which would be recyclable.
Description of the related art
The art of "paperinaking" is an ancient one, being attributable to invention
by the
Chinese before the birth of Christ.
More modern developments resultecf in the widely accepted Fourdrinier process
(See Kirk-OtTtmer= ErrchclupGdicr c?f Chcniicul Techltology, 3rd ed_, Voi_ 9,
pp. 846-7,
John Wiley & Sons, New York 1980) in which a"furnisli" (a "ftirnish" is
predonlinantly water,
e.g., 99.5% by weight and 0.5% "stock" ('stock" being virgin, recycled or
mixed virgin and
recycled pulp of wood fibers, fillers, sizing atidlor dyes) is deposited from
a headbox on a
"wire" (a fast-moving foraminous conveyor belt or screen) which serves as a
table to fortn the
paper. As the furnish moves alona, gravity and suction boxes under the wire
draw the water
out. The volume and density of the material and the speed at which it flows
onto the wire
determine the paper's final weight.
Typically, after the paper leaves the -wet end" of the papermaking machine, it
still
contains a predominant amount of water. Therefore, the paper enters a press
section, which can
be a series of heavy rotating cylinders, which press the water from the paper,
further compacting.
it and reducing its water content, typically to 70% by weiglit.
Subsequent to pressing the paper enters a drying section. Typically, a drying
section is
the longest part of the paper machine. Hot air or stearn heated cylinders
contact both sides of
the paper, evaporating the water to a low level, e.g., 5% by weight of the
paper.
The paper optionally passes through a sizing liquid to inake it less porous
and to help
printing inks remain on the surface instead of penetrating the paper. The
paper can go through
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additional dryers that evaporate the liquid in the sizing and coating.
Calenders or polished steel
rolls make the paper even smoother and more compact. Wliile most calenders add
gloss, some
calenders are used to create a dull or inatte finish.
The paper is wound onto a "parent" reel and taken off the paper inaking
machine.
The paper on the parent reel can be further processed, such as on a
slitter/winder, into
rolls of smaller size or fed into sheeters, such as folio or cut-size sheeteA-
L. for printing end uses
or even office application.
In order to inake containers, rolls fornied by slitter/winder (e.g., of paper
and kraft
grades of liner) are unwound and coated with a wax, Waxes impart water
resistance and wet
strength to the liner btit inhibits recycling the ttsed containers
incorporating them. Additionally,
the prior art wax coated liners niust be adhered to the other components of
the container with
hot melt adhesives. These hot tnelt adhesives are a further impediinent to
recycling of forined
containers employing wax coated components. Thus, there still exists a need
for manufacturing
paper possessing superior wet strength and water and grease resistance
properties but facilitating
recycling thereof.
Stimmary of the Invention
In one embodiment the invention is directed to a process for mal:ing paper
wherein a
furnish is deposited on a wire and dewatered, characterized in:
adding to the fumish a recyclable plastic coating.
In another embodirnent, the invention is directed to a process for making
paper wherein
a furnish is deposited on a wire and dewatered to form a paper, and the
dewatered paper is
subsequently pressed a number of times to further reduce the water content of
the paper,
characterized in adding a recyclable plastic coating to at least one side of
the dewatered paper
subsequent to a first pressing step.
In a still further etnbodiment, the invention is directed to a process for_
making paper
wherein a furnish is deposited on a wire and dewatered, the dewatered paper is
subsequently
pressed to further reduce the water content of the paper and subsequently
calendered,
characterized in introducing to at least one side of the paper a recyclable
plastic coating
between the pressing and calendering steps.
A further embodiment discloses a process for inaking paper characterized in
the following
steps:
(a) applying a ftirnish to a wire,
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(b) dewatering the furnish and obtaining a water containing paper,
(e) pressing the water containing paper to reduce the water content,
(d) calendering the pressed paper,
(e) recovering a finished paper, and
(f) adding a recyclable plastic coating during the paper making process.
Brief Descri2tion of the 12f~wintrs
Fig. I is a perspective, schematic view of a typical paper-making tnachine.
Fig. 2 is a schematic, side view of an alternative coating iiiethod.
Detailed Descripticm of the InvCntion
A typical paper making machine is illtistrated generally at 10 in Fig. -1.
Normally it
comprises a "wet end" 1 I including a headbox 12, a wire 13 and a press
section 15, a drying
section 16, a size press 18, calender section 20 and parent reel 22.
Optionally, a dandy roll 14
is positioned about two thirds of the way down the wire to level the fibers
and make the sheet
more uniform. Gravity and suction boxes (not sliowri) are positioned
underneatti the wire to
remove water from the furnish.
The stock fed to the headbox 12 can be virgin, recycled or a mixture of virgin
and
recycled pulp. In the headbox 12, the stock is mixed with water to for.m a
furnish for deposit
onto the wire.
In the invention, a recyclable plastic coating (RPC) is incorporated during
the
papermaking process. It should be understood that in this invention and
throughout the
specification and clainls, "coating" means "coating" or "impregnation" unless
otherwise
indicated.
For example, a typical (RPC) eonlposition is an aqueous acrylic resin based
composition.
A preferred three-coiiiponent cornposition according to the following formula
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COMPONEPiT A
TYPICAL CHARACTERISTICS Appearance Amber clear solution
Non-voladle 34.0 0.5% resins solids
pH
Viscosity, 2500 500 cps (Brookfield)
Lbs./gal. 8.7 0.1
Density 1.07
Acid Number 70
Tg. 95"C
Flash point 115 P
Freeze/Thaw Stability Yes
COMPONENT B
Appearance Translucent Bmulsion
Non-volatiles 40%
pH 2.5 - 3.5
Viscosity 25 - 35 cps
Weight per gallon 8.7 lbs.
M.F.T. 8 C.
Tg 00C
Acid number 58 (@ 100% NV)
COMPONENT C
A 35 % solids polyethylene wax emulsion having the following typical
properties:
Non-volatiles 34.7 -35_3%
pH 9.0-9.5
Weight per gallon 8.27 lbs.
is supplied to the headbox 12. Conlponents A. B and C are mixed in approximate
parts by
weight of 15:65:6 in admixture with 5.5 HOH, 0.5 NHaOH. 3 zinc oxide
~solution" (actually
a dispersion), under strong agitation. All of the f'oregoing proportions can
be varied plus or
minus 10% and still display the performance of the. RPC. In fact, Component A
and B can be
varied plus or minus 20% and Component C can be conipletely removed froin the
forniulation
or be substituted by otiier synthetic polyethylene waxes whiie still
acliieving tlie desired results of the invention. The percent solids of the
coEnposition supplied to lieadbox 12 or used at other
coating locations according to the inventioil can typically be varied frotn
abottt 3.0% to about
20% by weight.
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Components A, B and C are mixed in approximate parts (by weight) of 15:65:6 in
admixture with 5.5 HOH, 0.5 NH4OH, 3 zinc oxide solution, under strong
agitation.
The Components A, B and C, to be used in formulating the composition of the
invention,
are commercially availabie from S.C. Johnson & Sons, Inc., U.S. Specialty
Chemicals, 1525
5 Howe Street, Racine, ''Wisconsin under the trademarks JONCRYL 6I i.V,
JONCRYL 82 and
7ONCRYL.28, respectively.
JONCRYL 82 is a polyn-eric composition compatible with various solvents
including
methanol, 3A ethanol, isopropanol, n-propanol, ethylene glycol monobutyl
ether, diethylene
glycol rnonoethyl ether, acetone, methylene ketone and methyl isobutyl ketone.
Heat resistance
of JONCRYL 82 can be further increased by crosslinking the polymer with a zinc
oxide solution
which produces stable viscosities at higher pH. The maximuni workable pH of
JONCRYL 82
can be increased from 7 to 9 by incorporating a zinc oxide solution.
JONCRYL 61LV can be formulated in a ball-mill or high shear dispersion of up
to 40%
organic and 70% inorganic pigment. Unlike other acrylic polymer dispersions,
JONCRYL
61LV does not becon}e thixotropic at high pH. JONCRYL 61LV is compatible with
caseins,
shellacs and resin ester nialeics, as well as otlier acrylic resins.
However, more or less than 3.0-20% by weight of the aqueous composition can be
incorporated in the stock or finished paper. The following Examples will
demonstrate the wide
variation in RPC content.
Example 1 _
Within the laboratory environment, liner board was repulped to conform with
the
consistency of pulped fiber processed in an average paper mill machine. At
tliis point, the fiber
was separated into foar separate beakers each with 100 grams of fiber. To
beaker number 1,
5.0 grams of RPC was added. In beaker number 2, 10.0 grams of RPC was added.
In beaker
number 3, 20.0 grams of RPC was added. In beaker number 4, 30.0 grams of RPC
was added.
After stirring the fiber mixed with RPC at variotis levels, the fiber from
each beaker was
applied to a wire mesh which would simulate the wire tnesh of a paper machine
which allows
the fiber to drain by gravity or assisted through a particle vacuum action
that starts the renioval
of fluids on the paper machine. Through gravity and compTession in the
laboratory
environment, excess fluids were driven out of the fiber of each test sample,
one through four.
To simulate paper machine drying the fiber, still on the wire mesh, was dried
bv infra-red heat.
After all four test satnples were drsed. the stirfaces were tested for grease
resistance and water
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resistance. A fiftli saiiiple was repulped, screened and dried witliout any
RPC to be the control.
Samples one through four showed improved grease and water resistance when
compared to the
control. The final phase was to repulp samples orie through four, rescreen and
dry. The final =
step in the process to determine success is examining the dry reformed
papen.under a microscope
5= to determine the presence of undissolved foreign niatter that would
indicate a failure to repulp.
The examination revealed that no undissolved irlaterial were present,
indicating success in
...
creating a barrier and having the barrier, RPC, dissolve and allow no foreign
matter to be
present in any beaker marked one through fottr. The foregoing experitnent is
indicative of
addition of RPC to the stock or furnish prior to deposit on the wire of a
paper making machine.
The next step in taking the invention from the laboratory to a commercially
viable
process was to introduce the RPC at different locations in conventional paper
making machines.
A position on the paper machine downstreatn of the lieadhox 12 was selected -
for a
manual "pour on" of liduid RPC on an edge of the paper approximately 24 inches
(58.8 cm) of
the width of the paper machine, in the amount of 5 galloiis (18.92 1). This
section of treated
paper was tracked through the paper machine and rotrieved at the dry end of
the machine. This
retrieval section was tested for grease and water resistaiice and stiowed
itnprovement in both
areas.
RPC was next applied witli a spraybar, the application rate applied t'rom a
miniinum
value, but sufficient to create perceptible enhancements to liner or mediuni,
to
approximately 40% by weight of paper, pH varied from 5.5 to 8Ø
The RPC was applied at the wet end via spray application to tiie top side of
the slieet
during a run of 26# mediuni. The trial spray head was positioned at:
(1) the wet/dry line on the wire, and
(2) after the second press. before the dryer.
Subsequently, the RPC was applied via calender stock treatment to a 69#
special liner.
The purpose of this trial was to ascertain the viability of this application
technique utilizing two
water boxes on one side. The results of this latter trial is as follows:
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7 69# Special Liner
Reg 69#! Liner Treated One Side Ti-eated Two Sides
Basis Wgt MSF 69 69.1 69.8
Caliper - 19.0 20.0 19.5
Mullen Min 128 117 120
STFI MD 46-69 52 65
CD 32-47 23.75 28.4
Cobb 1-min T/B gms. --- .37/.17 .20/.06
Scott plybond --- 95 100
Porosity Sec 8 700+ 1200+
Alternatively, as shown in Fig_ 2, coating on both sides of a nioving paper
web 24
can be effected by passing web 24 between the nip of rollers 26, 28 in which a
bank 30 of RPC
is found thereby applying the RPC to one side of web 24. After passing over
idler roll 32, the
other side of the web 24 can be coated by bank 40 and rollers 36, 38.
Additional layers of
coating may be applied one or more tinies to either or both sides of web 24 by
additional
rollers 46, 48, 56, 58 and banks 50 and 60. Additional idler rolls 42, 52 may
be provided to
convey and tension web 24. The device of Fig. 2 can be: used prior to,
subsequent to or in place
of size press 18 of Fig. 1. It should be understood that additional rollers
(not shown), banks
(not shown) and even idler rolls (not shown) may be empioyed to apply as many
additional
layers of RPC as desired, Additionally, sizing agents may be incorporated into
one or niore of
the banks of RPC.
All of the foregoing tests prodticed a paper that was repulpable. In addition,
the addition
of RPC appears to dramatically increase fiber strengths. Using 100% recycled
fiber treated with
RPC increased fiber strengths, giving strengths of 90% of virgin fiber,
whereas normal recycled
fiber are approximately 60% of virgin fiber.
The process of paper inaking can be moditied to inciude [~"C addition at the
headbox (or
even upstream of the headbox when the stock is inixed with tiliers. si2ing or
dyes), in the press
section at any point subsequent to the first press, and subsequent to the
drying section, either
at or in piace of the size press but before the calenders.
The papers coated by the process find special use in the following industries,
the label
industry, especially the 60#13000 S.F. label industry, folding carton, tray
and box (all board
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weights) and liquid packs, stich as water, soda, and milk, ice cream, yogurt
and delicatessen
carry-out containers.
The fine paper industry for barrier containers and interleaves for between
sensitive paper
or metallized papers or photographic plates can also benefit from the
#nc+ention.
By using the invention to apply a coating formulation into aõ~aper making
machine the
following benefits are achzeved:
(1) the overall cost of the finished coated/impregnated liner or paper is
reduced, and
(2) incorporating the technology into the paper inaking inachine (process)
would allow
the technology to reach its maximum potential.
Although the present invention has been described in terms of specif'ic
embodiments, it
will be apparent to one skilled in the art that various inodifications may be
made according to
those embodiments without departing from the scope of the applied ciaims and
their equivalents.
Accordingly, the present invention should not be construed to be limited to
the specific
embodiments disclosed herein.
