Note: Descriptions are shown in the official language in which they were submitted.
1139'~66
il BACKGROUND OF THE INVENTION
I¦I. Field of the Invention: This invention is directed to a
~process for producing paper using water-insensitive starch fibers
to replace all or part of the cellulosic or other pulp convention-
l ally employed, and to the paper produced thereby. The invention
I ~ also relates to a novel method for the production of certain
specialty papers, as well as to methods for the incorporation of
functional additives into paper during the production thereof and
for binding fibers in non-woven webs.
II. Brief Description of the Prior Art: Various natural fibers
(other than cellulose) as well as a variety of synthetic fibers
have been employed in making paper, however, all these replace-
¦me~ts have failed to provide a commercially acceptable substitute I
¦for celluLose due to their cost, poor bonding properties, chemical¦
¦incompatibilities, difficulty in handling ln papermaking systems,
¦etc. While it has also been suggested to use starch fibers in
¦various aspects of the papermaking process, commercial attempt6 to¦
¦use such fibers have not resulted in any degree of success and
paper is still being manufactured almost completely from wood-base~
cellulosic ingredien~s - the supply of which is bein~ rapidly
Idepleted.
¦ It is apparent that the aqueous systems normally
¦employed in the paper making operations require pulp fibers
possessing sufici.ent water-insensitivity that they can be used
¦ in all aspects of the manufacturing process throughout a
relatively wlde pH range without losing their integrity. In this 1
¦I regard, the few references which suggest the replacement of starch
fibers for cellulose fibers (e.g. U.S. Patent 1,682,293) require
1~ chemical modification of the starch in order to radically change
11 its naturally occurring properties prior to forming the fiber
¦l so as to provide the degree of water-insensitivity required
l, l
466
in the paperma~ing process. Alternatively, other refer-
ences (e.g., U.S. Patent 2,570,4~9) require that the papermaking
process itself be modified as by replacing the conventionally
employed aqueous system with an alcohol solvent in which the
starch fibers are not soluble. It will be recognized that the
use o-f such ~echniques is both impractical and uneconomical
when employed on a commercial basis.
As another aspect of the papermaking operation, it
is often necessary to incorporate additives into the pulp in
order to achieve specific end properties. Thus, additives such
as pigments, latices, synthetic microspheres, fire retardants,
dyes, perfumes, etc. are often employed in the manufacture of
paper. The efficient retention of these additives at the wet
end of a paper machine presents difficulty to the manufacturer
since that portion which is not retained create~ not only an
economic loss, but also a significant pollution problem i~ it
becomes part of the plant effluent. Furthermore, such additives
are also added via coating or saturation processes commonly
known in the art. These processes usually require that ex~ess
heating energy be consumed to re-dry the paper after coating~
Moreover, in some instances the coating systems are required
to be solvent based which then creates extreme capital expense
and requires regulation to recover volatile materials.
It is therefore an object of the present invention
to provide a commercially viable process for the use of starch
fibers as a partial or complete replacement for cellulose in
conventional paperma~ing operations.
It is also an object to provide a process which effi-
ciently enables the retention and incorporation of additives
into paper during the manufacture thereof.
~ t is a further object to provide a process which
i I
enables water-insoluble additivcs to be introduced into the paper as fiber
encapsulated additives.
Another object is to provide ordinary and improved specialty papers
according to such process.
A further object of the invention is to provide an efficient and
economical process for binding synthetic and/or natural fibers in non-woven
web form.
These and other related objects will be apparent from the descrip-
tion which follows.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided in a
process for manufacturing paper and paperboard comprising the steps of in-
troducing an aqueous slurry of fibrous pulp material onto a screen in such a
manner that the water is removed thereby forming a sheet of consolidated
fibers which, upon pressing and drying, yields the final paper product, the
improvement comprising the step of employing starch in an amount of from 1
to 100% by weight of the pulp in the orm oE water-insensitive starch fibers
of 10 to 500 microns in diameter, said fibers being produced by extruding a
thread-like stream of a colloidal dispersion of starch, at 5-40% by weight
solids, into a moving coagulating bath comprising an aqueous solution of a
coagulating salt selected from the group consisting of ammonium sulfate,
ammonium sulfamate, mono-basic ammonium phosphate, di-basic ammonium phos-
phate and mixtures thereof, said solution containing said coagulating salt
in an amount at least sufficient to coagulate said starch.
In another aspect, there is provided paper and paperboard composi-
tions comprising a blend, on a weight basis, of 0-99% papermaking cellulose
pulp fibers and 1-100% water-insensitive starch fibers of 10 to 500 microns
in diameter produced by extruding a thread-like stream of a colloidal dis-
persion of starch, at 5-40% by weight solids, into a moving coagulating bath
comprising an aqueous solution of a coagulating salt selected from the group
; ~
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~ca74~6
consisting of a~nonium sulfate, ammonium sulfamate, mono-basic ammonium
phosphate, di-basic ammonium phosphate and mixtures thereof, said solution
containing said coagulating salt in an amount at least sufficient to coagu-
late said starch.
Furthermore, the invention provides a method for incorporating
wa~er-insoluble additives within the pulp of a conventional papermaking
system comprising the steps of thoroughly dispersing at least one water-
insoluble additive in a colloidal dispersion of starch, said starch being
present in an amount of 5-40% by weight solids, and precipitating said
dispersion by extruding a thread-like stream of said dispersion into a moving
coagulating bath comprising an aqueous solution of a coagulating salt selected
from the group consisting of ammonium sulfate, ammonium sulfamate, mono-basic
ammonium phosphate, di-basic ammonium phosphate and mixtures thereof, said
solution containing said coagulating salt in an amount at least sufficient
to coagulate said starch so as to form water-insensitive starch fibers en-
capsulating said additive; and subsequently using the resulting starch fibers
as components in a papermaking pulp system.
Thus, it has been found that water-insensitive starch fibers, pTO-
duced by the precipitation of a colloidal dispersion of starch in a coagula-
ting salt solution, may be employed as partial or complete replacements ~or
cellulose and similar fibers in conventional paper and paperboard manufac-
turing operations. The fibers may be used to extend the pulp, as a means
for incorporating additives into the paper product, as binder for the fibers
in non-woven webs or for any combination thereof.
As used herein, the term "paper and paperboard" includes sheet-
like masses and molded products made ~rom fibrous cellulosic materials as
well as such fibrous materials as may be derived from synthetics ~such as
polyamide, polyester, rayon and polyacrylic resin), mineral fibers ~such
as asbestos and glass), and the like.
As used herein, the expression "conventional papermaking operation"
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~97~66
means the process of introducing an aqueous slurry of wood cellulose fibers
~which have been beaten or refined to achieve a level of fiber hydration and
to which a variety of functional additives can be added) onto a screen or
-4b-
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7~6~i
similar device in such a manner that the water is removed, ~1
thereby forming a sheet of the consolidated fibers which, u~on
pressing and drying, can be processed into dry roll or sheet form.
Also included within the scope of this expression are the con
ventional processes for the production of wet and dry-laid
non-wovens.
Thus, in one aspect the present invention provides
a feasible, efficient and economical process for extending
¦ existing raw material sources. Further,it allows th~ paper
manufacturer a far greater degree of flexibility in his oper-
ations: he is able to obtain starch fibers in dry or wet-slab
form and store them for subsequent use or he may incorporate
the starch fiber manufacturing process into his plant as an
integrated step in his pulping ~md/or papermaking operations.
~oreover, the present invention offers the manufac-
turer a new means for incorporat:ing additives into paper prod-
ucts with increased retention and consequently less economic
loss and fewer pollution problems. As previously discussed,
it is common practice in the manufacture of paper to introduce
additives in conjunction with the fibers used in the pulp.
Such additives are incorporated in order to achieve specific
paper properties other than what is contributed by the fiber
itself. Such additives include materials which f~mction as 1l
pigments (titanium dioxide, for example) as ~ell as other materials
introduced into paper to achieve such properties as improved
¦¦brightness, opacity, smoothness, ink receptivity, fire retard-
l¦ance, water resistance, increased bulk, etc. As an additional
¦lembodimen~ of the present invention, it has been found that
l¦when starch fibers are produced so as to contain various func-
ii tional additives, and such fibers are then utilized in the
llaqueous paper ~aking process, retention of the additives is
_ 5
1C\~74~6
1~ ~
greatly increased when compared with that achieved using current
methods. In addition to the increased retention, a further
advantage of the addition of additives in this manner is the fact¦
that there is no necessity for relying upon the sensitive
charge balance relationship between the cellulose fiber additive
and the flocculant (e.g., alum) or other retention aids.
Indeed, it is unnecessary to use a flocculant or retention aid
with the starch fibers used in the present invention.
It has also been found that non-woven webs can be
produced in wet or dry-laid form in accordance with the present
invention wherein starch fibers are incorporated within the
web to serve as binders therefor. The starch fibers may be
retained in the final web or,if the base fiber employed in the
web is non-combustible, may be removed, depending upon the de- ¦
sire.d end use.
Specifically, the present invention is directed to an
improvement in a process for manufacturing paper and paperboard
co~prising the steps of introducing an aqueous slurry of a
~ fibrous pulp material onto a screen in such a mannar that the water
- 20 j is removed thereby forming a sheet of consolidated fibers which,
upon pressing and drying,yields the final paper product. The
I reD/~ci~ ~
improvement comprises the step of cm~l~i~g~ from 1 to 100~/o by
k)i~ ~r-i~?S~S~ e
weight of the pulp ~ e~ starch fibers of 10 to 500
microns in diameter produce~ by extruding a thread-like stream
of a colloidal dispersion of the starch,at 5 to ~0% by weight
solids, into a moving coagulating bath comprising an aqueous
solution of a coagulating salt selected from the group consisting I
of ammonium sulfate, ammonium sulfamate, mono-basic ammonium ~ -
¦phosphate, di-basic ammonium phosphate and mixtures thereof, ~h~ ¦
¦ solution containing the coagualting salt in an amount at least
sufficient to coagulate the starch.
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~0~466
I DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
ii The process of the present invention may readily be
; adapted to be used on any conventional paper making equipment
i using the procedures commonly used in the specific plant, with
i the only difference residing in the substitution of starch fibers
for all or part of the cellulose pulp.
The starch fibers employed may be produced using a
number of variations, the only requirement being that the water-
insensitive fibers have a diameter of 10 ~o 500 microns and that
they be precipitated by the extrusion of a thread-like stream of ¦
a colloidal dispersion of starch at 5 - ~0%, by weight solids,
into a suitable moving coagulating salt solution.
Fibers may be employed which are produced from any
naturally occurring or fractionated starch. Thus, corn starch,
waxy tnaize, rice, tapioca, wheat, potato, high amylose corn starch
commercial amylose powder, etc. may be employed with naturally
occurring corn starch, tapioca and waxy maize being preferred due
to their economy and availability.
The concentration of the starch solids in the dispersio~
should be about 5 to 40% by weight. While higher concentrations
of starch solids may be used, the resuLting dispersions become
very viscous and special equipment is required to handle them.
The particular concentrations employed in the dispersions will
however, affect the properties of the final fiber and the desired~
¦~ end use. As an example, starch fibers prepared from 5V/o solids
¦¦ dispersions have been found to be particularly useful in the
production of glassine or greaseproof papers while starch fibers
prepared from 15V/C solids dispersions have been found better
suited for use in rore porous papers ~such as ~ilter peper.
1-~7466
j The particular starch employed must be used in the form
Il¦of a colloidal dispersion. For the purposes of this invention,
¦Ithe term "colloidal dispersion" means dispersion of starch which
,lis substantially free of granules and which exhibits, on standing
~lat the temperature at which it is to be used9 little evidence of
¦igelation or precipitation. This state of dispersion may be
obtained using a variety of techniques depending upon the particu-l
lar starch base employed, the desired end use and the equipment
available.
¦ When native starches that are very high in amylopectin i
content, such as waxy maize, are employed, a suitable colloidal
dispersion may be prepared merely by thoroughly cooking the starch
in water with no chemical additives or modifications required.
In most cases where starches whi.ch contain less than about 95%
; amylopectin are employed, it will be desirable to chemically
derivatize or modify the starch to ensure its colloidal dispersion
before adding it to the aqueous system. The derivatization or
I ¦ modification is carried out to an extent which will insure the
production of the desired colloidal dispersion without affecting
the ability of the starch to subsequently precipitate. Alterna- ¦
¦tively, if there is no objection to the presence of caustic in
¦the system, the latter starches may be dispersed in aqueous
sodium hydroxide, potassium hydroxide or other common alkali. As
further alternatives, the starch bases may also be dispersed in
a minor amount of an organic solvent such as dimethylsulfoxide
and then added to water, or the starch base may be dispersed in
conjunction with chemical additives such as urea and/or para-
¦formaldehyde. In the cases where causticizing is employed, the
~¦amount of alkali used must be sufficient to adequately disperse
!¦the starch. Typical amounts of alkali used when sodium hydroxide ¦
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10''7466
¦lis employed are from 15 to ~0%, by weight, based on the weight of
the starch.
In preparing the starch dispersion, the starch is added I
~¦to the dispersing medium and vigorously agitated until a state of i
colloidal dispersion is achieved. In the case of dilute
dispersions of starch (i.e. about 5-10% starch solids by weight),
this will require about 45 minutes, with longer periods and/or
moderate heat required for more concentrated starch dispersions
lor for certain chemically modified starch bases.
¦ Most of the starch dispersions, including those of waxy
¦maize and most of the chemically modified starches, may be
cooled to room temperature prior to introduction into the coagulatT
ing bath. In the case of a few of the less chemically modified
starches, it will be preferred ~o employ the dispersions at
approximately the elevated temperatures at which they are prepared
so as to maintain the necessary colloidal dispersion and to
insure efficient fiber production.
The coagulating bath used in preparing the starch fi~ers
employed in the present invention comprises an aqueous solution
containing specific ammonium salts selected from the group con-
` sisting of ammonium sulfate, ammonium sùlfamate, mono- and di-
¦¦basic ammonium phosphate and mixtures thereof. It is also
¦¦possible to combine the above-mentioned functional salts with
other compatible salts which will form a starch precipitate so as
~to obtain satisfactory coagulation and a fibrous product. Suit-
able salts for this purpose include ammonium persulfate, ammonium
carbonate, ammonium bromide, ammonium bisulfite, ammonium nitrite
ammonium nitrate, ammonium bicarbonate, ammonium oxalate, sodium
l and potassium chloride, sodium and potassium sulfate, among
l~others. Generally, no ad~antaee is seen in using these additional
l ~,
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~l;)C~74~
salts since the ammonium sulfate, sulfamate or phosphate salts
must still be present in their respective minimum amount in order
i to effect coagulation. The only instances where the presence
of substantial amounts of other salts may be desirable is in the ¦
use of the recycled coagulation bath wherein salts are present
which have been generated in situ, as will be discussed herein-
below.
The minimum concentration of the salt required to
~ effect coagulation as well as the preferred salt or salt blend
will vary depending upon the particular starch base employed.
For example, in the case of waxy maize starch, it is necessary
for ammonium sulfate to be present in amo~mts of at least 35%,
¦ by weight of the total solution, ammonium sulfamate 72% (satura-
tion), di-basic ammonium phosphate 37% and mono-basic ammonium
phosphate 40%. In the case of corn starch or similar starches
¦ containing about 64-80% amylopectin, lower concentrations of
¦ salt may be used with ammonium sulfate required in amounts of 20~/o~
' ammonium sulfamate 50%, mono-basic ammonium phosphate 25% and
di-basic ammonium phosphate 30%. In the case of hybrid corn
starches containing less than about 50% amylopectin, ammonium
sulfate must be present in amounts of at least 15%, ammonium
I sulfamate 40%, di-basic ammonium phosphate 25% and mono-basic
ammonium phosphate 20%.
~ It will be recognized that alkali salts are generated
¦¦ in the coagulating bath when causticized starch dispersions are
l employed, with satisfactory production of the desired starch
I fibers continuing until the level of the generated salt is
relatively high. The generated salt tolerance level above which
l~ production of the fibers becomes inefficient will vary depending
i~ upon such factors as the specific salt employed, the total salt
,1 - 10 -
1097466
solids employed, the starch solid concentration in the dispersion,~
the amount of amylopectin in the starch base, etc. Once this salt
¦tolerance level is determined a steady-state system may be achieved
¦at this maximum level (or less~ by the periodic addition of
ammonium sulfate on a continuous basis. As an example, when
sodium hydroxide is used as a dispersing medium and the starch
mixture is extruded into an ammonium sulfate coagulating bath,
sodium sulfate i.s generated. In this case, it has been found that
production of corn starch fibers (13% solids dispersion) will con-
tinue at a satisfactory level until a maximum of about 70 parts
: sodium sulfate per 30 parts ammonium sulfate (4.~% solids solution)is present in the bath. Above this level of sodium sulfate,
production of the starch fibers becomes less e~ficient and the
resulting fibers tend to lose thleir individual integrity. However,
by adding a small amount of an inorgan-lc acid to the initial
coagulating bath or to the bath during formation of the fibers, th
level of the generated sal~ in the system may be appreciably
raised before production of the :Eibers is seriously affected. Thus
~using the eæample discussed previously, the addition of as little
1 as 3 parts of sulfuric acid per hundred parts of the initially
charged coagulating bath salt results in a tolerance level of 90
¦parts sodium sulfate per 10 parts ammonium sulfate thereby increas-
I ¦ ing the longevity of the coagulating bath.
It is apparent that the salt solution used in the fiber~forming process may be recycled and used again once the fibers have
been removed. It is, however, important that the salt concentratio
e maintained, especially where the salt is being depleted through
a chemical reaction lnvolving the starch dispersion as it is
~ntroduced. In this regard, the starch dispersions which do not
lontain caustic present little diffic~lty in recycling other than
I . ,
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lVq7466
¦that the solids content of the salt be maintained. However~ in
I those cases where causticized starch dispersions are employed,
chemical reactions with the coagulating solution will occur. For
~exam2le, if ammonium sulfate is used, the reaction results in the
¦formation of ammonium gas and sodium sulfate. The recycling of
¦such a system can be extended by recovering the ammonia in an
¦acid scrubber and returning it to the system as ammonium sulfate.
¦The generated sodium sulfate can be used in the coagulating bath
¦as part o~ the salt blend until the tolerance levels discussed
¦previously are attained or can be used as a raw material in o~her
¦aspects of the pulp or papermaking operation, e.g. as a source of
I''salt cake" in the production of Kraft pulp.
¦ Starch fibers can be produced at any temperature at
¦which the starch dispersion can be handled. Generally, the
¦coagulation bath is maintained at about room temperature (20C.)
¦ during production of the fibers,, however, temperatures as high as
about 70C. may be used. These higher temperatures may be desired
¦under certain conditions since they increase the solubility of
i the salt in the coagulating bath resulting in more concentrated
1 solutions. Th~s, when it is desired to produce waxy maize fibers
using mono-basic ammonium phosphate as coagulant, it is desirable ¦
¦ to increase the temperature of the bath so as to obtain a concen-
¦ tration of salt of approximately 40% (saturation level for the
mono-basic ammonium phosphate at 20C. is 2 8~/o) .
¦ In preparing the starch fibers used in the invention,
the starch dispersion is introduced continuously or by drops in
¦ the form of a thread-like stream into the moving coagulating salt
, s~lution. This Lntroduction ma~ be accomplished either~a~ove or
below the salt solution using any conventional techniques. Thus,
1 the dispersion may be extruded through an apparatus containing at~
l least one aperture, such as a spinnerette, a syringe or a biure~
Il ~
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i6
feed tube. Alternatively, the dispersion may be discharged
under pressure from a pipe or tube containing a plurality of
¦ apertures into a surrounding enclosed area, e.g. a concentric
~ pipe, containing the moving coagulating solution. Various
¦ adaptations of the above and related techniques may be used and
the fibers may be thus produced using either batch or continuous
operations.
In accordance with either embodiment, the aqueous salt
coagulating solution should be moving when the starch dispersion
¦ is introduced and the directionality of the two flows can also
be utilized in controlling fiber lengths and diameters or widths.
Thus, if the salt solution is moving in a direction generally
concurrent with the flow of the starch dispersion, ~ounder
fiber lengths are formed; if thle starch dispersion is introduced
at an angle of about 90 to the flow of the salt soluti,on, '~
l ~er-~r~ !
B ~ relatively flatter fibers are formed. Generally a~erat~e~ of 10¦
to 500 microns in diameter are preferred, in order to produce
¦ fibers of the size required herein. Thus, the starch fi~ers used
¦ in the present invention have diameters (widths) of 10 to 500
microns and will generally have lengths of from about 0.1 to
I ~ 3.0 mm. i~ they are to be used as cellulose pulp replacements in
paper. For non-woven application, fibers of longer lengths may
be employed.
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~LC3''3~66
It will be recognized that the length, cross-sectional size and
configuration of the resultant fibers are dependent upon a number of inter-
related parameters in addition to those described hereinabove. Thus, the
YiSCosity, the solids content of the starch dispersion, as well as the
particular components used in the coagulating solution and/or starch dis-
persion and the relative flow viscosities thereof are additional factors
which can be used in conjunction with the parameters discussed previously
in order to control the dimensions of the resultant fiber.
This and similar coagulating processes producing starch fibers
use~ul herein are described in United States Patent No. 4,139,699 issued
February 13, 1979, National Starch and Chemical Corporation, as well as in
United States Patent 2,902,336 issued September 1, 1959, Pieter Hiemstra and
Johannes Muetgee~t~ Various modifications of the processes may also be
employed as long as the final fiber possesses sufficient water insensitivity
to be employed in the papermaking operation.
l`he resulting aqueous slurry or suspension of starch flbers may be
used directly by introducing it into the pulp stream thereby enabling pro-
duction of fibers and paper web "in-line" in the paper manufacturing plant.
If this embodiment is to be used, it is generally preferred to first wash
the fibers free of coagulating salt prior to introducing the slurry into the
paper manufacturing operation. Alternatively, the fibers may be recovered
in the dry state by collecting from water on a screen or similar device. It
is then preferable to reslurry the fibers into a non-aqueous solvent such
as methanol, ethanol, isopropanol, acetone or the like in which the fibers
are not soluble. The fibers are then reco~ered, as by filtration, from the
solvent and
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l~g7466
,~dried. Other methods such as centrifuging, flash-drying or
¦~spray~drying may also be used to remove the water. Once dried,
the fibers may be re-introduced into an aqueous medium and will
jexhibit excellent re-dispersibility maintaining their discrete,
~discontinuous structure. Alternatively, the fibers may be
recovered from the slurry, as by filtration, washed and placed in
water at levels of up to about 50% solids and formed into "wet-
slabs" for subsequent use.
l It is also to be noted that the starch employed may be
¦chemically treated to vary the properties of the fiber produced
¦ or to help effect formation of the colloidal dispersion. ~lter-
¦natively, the starch fibers may be treated after formation in
¦order to produce certain functional characteristics. Thus, the
starch may be chemically treated, as by aminoethylation, in order
to provide rapid dispersibility of the starch in the dispersion,
I which treatment will also result in the production of a fiber
which possesses a cationic charge when employed in an a~ue~us
Imedium. Similarly, a starch may be used which is modified to
¦contain anionic groups so as to be stable in a dispersion and
¦ which, after regeneration, will produce a fiber having anionic
properties. The fibers may also be modified after their formationl
~in order to achie~e specific functional properties. Thus, improv-¦
ed anionic functionality might be obtained by bleaching the
fibers af~er precipitation as long as the conditions are not so
severe as to destroy the fibers. The properties of the fibers
may also be controlled by using blends of modified and unmodified
starches or by the addition of other functional materials, such as
polyacrylic acid, to obtain the specifically desired properties.
1 - 15 -
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~1
As one of the advantages of the method of the present 1,
i¦invention there is provided a means to improve paper products in
¦¦ a variety of manners due to the properties which are either
¦~inherent in or which may be im~rted to the starch fiber itsel~.
As an example of such improved properties, we may consider the
production of such diverse specialty papers as glassine paper and
filter paper which require special treatment when conventionally
produced.
Glassine paper is made from pulps in which the quality
of the fiber permits a high degree of hydration. It is the
mechanical treatment of the pulp while suspended in water that
causes the distinctive greaseproof properties. The fibers are
fibrillated and swollen to an a].most gelatinous condition. When
paper is m~de from hydrated fibers, a dense non-porous sheet is
ormed on the wire. The result~mt sheet is resistant to the
penetration of greases and oils because it is composed of nearly
continuous well hydrated cellulose. To get the cellulose in this
well hydrated form requires a considerable amount of energy.
Glassine manufacturers must subject their stock to refining -for
extended periods of time or increase the number of refiners
through which the stock must pass. Once the s~ock is hydrated and
introduced on the wi/re i~ ~rains very slowly. As a result,
machine speeds are ~m~ to between 1~0-500 fpm depending some- ¦
what upon the basis weight of the paper. The stock temperature
~may be elevated with steam to accelerate water removal on the wire¦
IAttempts by glassine manufacturers to use cationic polyelectro-
¦ lytes for improving drainage has met only limited success. The.
flocculation of the fibers may improve drainage but this
1~ disruption in formati.on can cause pinholes which reduce oil and
ill greaseproof properties of the product.
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il We have now found that when starch fibers are combined
¦~ with cellulose fibers which have been beaten to a degree less
than would be required in conventional glassine manufacture, the
¦ resultant mixture has a significantly higher freeness and will
drain at lower temperatures in about one-third the time usually
required at the elevated temperatures presently used,with higher
wet mat solids after pressing and improved drying efficiency
relative to the conventional glassine stock. Moreover, the
resultant sheet properties of this novel paper exhibits greater
internal strength (Z-directional strength), improved oil holdout ¦
properties and greater resistance to the passage of air relative
to conventional glassine paper. It is apparent that the
reduction of the cellulose refi~ing requirements can result in
significant energy savings since the fiber mix need not be
¦ elevated in temperature to achilPve acceptable water removal rates~
as is common practice in conventional glassine manufacture.
Starch fibers may also be employed to provide a more
porous sheet which is a property that can be desirable i~ such
papers as filter or saturating grades. In prior art methods,
reduced refining of cellulose has been found to aid the develop- ~
ment of this property, but does so only at the expense of weaker ¦
web strength~ The incorporation of starch fibers according to
the present invention, in conjunction with the cellulose,can
result in a more porous sheet structure while maintaining, and
¦ often improving, the required strength properties.
¦ As a further feature of the invention it is possible to
¦ incorporate certain hydrocolloids in the dispersing medium and to
extrude the hydrocolloids together with the starch in order to
produce a starch-hydrocolloid fiber which may be used in the pape~-
I making process of the present invention. In order to achieve
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~74~6 11
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il this fiber composition, it is only necessary that the hydrocolloid
¦~ (in minor amounts, i.e. less than 50% by total solids weight),
¦together with the starch portion, be placed in a state of
¦ colloldal dispersion prior ~o contact with the coagulating bath.
I¦Thus, in the case of water-dispersible hydrocolloids such as poly-
¦ vinyl alcohol, carboxymethylcellulose, hydrox~ethylcellulose, etc.
it is only necessary to add the hydrocolloid to ~he water in which
the starch is dispersed. In the case of other hydrocolloids,
such as casein, it will be necessary to causticize the dispersion
in order to form the colloidal dispersion required.
As an alternative embodiment of the present invention,
water-insoluble additives may be uniformly admixed throughout the
starch dispersion and subsequently encapsulated within the
resultant starch fiber. Thus, water-insoluble additives, includ- ¦
ing pigments, metallic powders, latices, oils, plasticizers, 'I
microspheres (glass beads, foamed silica or other low density
materials either in b~own or unblown fonm~, etc., may be encapsul-
¦ated within the s~arch fibers of the invention. In a ~imilarmanner, water-insoluble synthetic polymers or latices, such as
polyvinyl acetate, polyacrylonitrile, polystyrene, etc., may be
¦ incorporated within the fiber. It wil~ also be noted that the
density of the starch fibers may be varied by incorporating air
¦or other gases in the starch dispersion prior to passing it into
the coagulating bath.
It is to be further noted that certain water-soluble
solid additives may also be co-extruded with the starch fibers.
In such ~ases, the additive will be dissolved in the aqueous
starch dispersion and the coagulating bath which is employed in
I¦ forming the starch fibers will be ad~usted by the addition of a
,1 - 18 -
~74~6
sufficient quantity of a compatible salt capable of precipitating the additive.
As an exan~le, a commercial rosin size can be added to the starch dispersion
and extruded into a coagulating bath containing the functional starch-
coagulating salt together with sufficient aluminum sulfate to precipitate the
rosin, thereby forming a co-precipitated starch-aluminum rosinate fiber.
The water-insolubility of the starch fibers of the present invention
can be further enhanced by the incorporation of conventional cross-linking
agents, such as urea-formaldehyde, glyoxal, urea-melamine-formaldehyde,
Kymene (registered trademark of Hercules, Inc., Wilmington, Delaware), etc.
These cross-linking agents may be incorporated into the starch dispersion
prior to extrusion or may be post-added to the starch fiber.
Generally, any additives employed will be used in amounts less than
about 50% by weight of the total solids, however, certain additives including
clay and pigments may be incorporated at levels up to about 80% by weight. .
It will be realized that the specific additive selected for incorporation, as
well as the amount employed in any of the above-described embodiments, will
depend upon what properties are desired in the final fiber. Thus, pigmented
fibers show improved opacity and may be inco~)orated by convent~onal methods
into the fibrous web with overall improved pigment retention relative to that
ohtained by merely adding pigment to a paper stock system. Fire retardant
prope~ties may be conveyed to a substrate by incorporating polyvinyl chloride
powder and antimony trioxide or other fire retardant chemicals within the
starch fiber. Starch fibers containing microspheres may be incorporated into
paper webs at high levels of retention. The retention of such spheres enables
the production of sheets of high bulk and low weight as compared with
cellulose sheets of comparable weight. In conventional sheets containing
microspheres, the presence of the microspheres between the fibers has a
debonding effect on the fibers and this
~IL09~4~;6
results in a sheet of low strength. In contrast, the sheets of
~ the present invention possess e~cellent strength properties as
I the spheres are encapsulated within the starch fibers so that the !
debonding effect of the spheres is minimiæed. The density of the
starch fibers, and resultant paper, may also be varied by the
incorporation of air or other gases in the starch dispersion
prior to passage into the coagulating bath.
Furthermore, by using additive encapsulating fibers it
I will be possible, not only to provide a novel process of incorpor-~
¦ ating additives in paper, but also to produce novel effects in
¦ the paper itself. As an e~ample, there~are papermaking machines
¦ that produce a final web which i.s constr~cted of individual layersll
¦ compressed together. Such equipment may be described as cylinder ¦
¦ machines or Fourdriniers with a second down-line headbox or with ¦
multiple headboxes. Machines of this type normally use lower
quality fibers for the inner pli.es and quality pulp as the top
liner. By utilizing a pigmented starch fiber in the top liner,
production of paper web having the surface properties of coated
board is possible. In essence a coated board would be produced
via a wet-end application process due to the high concentration
I I of starch and pigment at the substrate surface. Alternatively,
special decorative or construction paper could be manufactured
~ having different colored sides. Dyed fiber could be prepared
i¦ at various colors and fed to two diff~rent headbo~es. Such two-
colored sided paper is prepared today but requlres the use of
surface applications during processing.
One of the ad~antages of the use of water-insoluble
synthetic polymers encapsulated within the starch fiber is that i~
permits a high retention in paper and paper-like webs of synthetic
- 20 -
10~7466
~fibers (such as rayon, acrylic, polyester, nylon or polypropylene)
Most of these fibers carry very low surface charge and therefore
their retention in commonly used latex binder sys~ems, which rely
upon precipitation and fiber deposition techniques, are poor.
Such poor retention can result in low binder efficiency and
problems with foam, sticking and accumulation of polymer in ~he
system. The resin encapsulating starch fiber insures efficient
retention and provides the desired end sheet properties.
An additional feature of the present invention is that
the starch fibers may also be employed in the production of dry
laid nonwovens of synthetic fibers. In such applications, a web
is produced using air as the medium for depositing the fibers on
a moving wire. Since the synthetic fibers are not hydrated, bond-
ing is inhibited and relatively weak and soft structures are
produced. Thus, in order to provide integrity to the web, it is
necessary to spray a binder on its surface. In accordance with
the present invention, it is possible to blend dry starch fibers
with the synthetic fibers. Such a method would be particularly
advantageous in the area of disposable nonwovens wherein the
biodegradable properties of the starch fiber would be superior to
those obtained with the presen~ly employed synthe~ic fiber binders .
¦ As binders those fibers particularly high in amylopectin content
are preferred. It is to be noted that the starch fiber may be
retained in the final non-woven web or removed therefrom if
¦ desired. If the starch fiber is to be removed, as for example,
¦ from a ceramic web, exposure to ashing conditions sufficient to
¦ burn off the starch fibers provides a suitable means for removal
thereof.
- 21 -
. ~1
,1 l
10 741~6
The starch fibers, filled or unfilled, may be success-
fully used alone in the formation of an all-starch paper product
or may be utilized in conjunction with all types of cellulosic or
non-cellulosic fibers. The hardwood or softwood cellulosic
fibers whic~ may be used include blff~ached and unbleached sulfate
(kraft), bleached and unbleached sulfite, bleached and unbleached
soda, neutral sulfite, semi-chemical groundwood, chemi-groundwood I
and any combination of these fibers. These dff~signations refer to ¦
wood pulp fibers which have been prepared by means of a variety
of processes which are conventionally used in the pulp and paper
industry. In addition, synthetic cellulosic ibers of the
viscose rayon or regenerated cel.lulose type can be used, as well
as recycled waste papers from va~rious sources. Similarly, ceramic
fibers, glass, asbestos or other inorganic ~ibrous materials may
be employed in conjunction with the starch fibers of the
invention.
~ue to the water-insensitive nature of the starch fibers
11 employed herein, the fibers disperse readily to form stable dis-
¦¦ persions which may be used in ordinary papermaking operations
20 1! without adding surfactants. This permits the use of the fibers i~
Il paper making operations and machinery without modification of the
¦¦ usual processing conditions. Thus, fibers may be added to the
beater or a blending chest into the head bo~ onto the screen of
a Fourdrinier machine and from there the sheet may be carried to
the wet press through drier rolls, calenders, and woundup as a
sheet without modifying substantially the normal operating
f characteristics of the machines as used for making cellulose ~ --
1I paper. It will bff~ appreciated that in the case of paper made
fll entirely from starch fibers, it may be desirable to place the web
1¦ between nylon mesh screens or to blot the web drier than is
common in conventional operations in order to prevent s~icking of~
- 22 -
f~
109, 46(i
the fibers in the drier.
~I Furthermore, the papermaking operations may be integrat-¦
11 ed with the starch fiber production operation by employing the
slurry containing the fibers as they are precipitated. It is
also possible to form shaped articles directly from thick fiber
slurries by slush-molding in patterns or molds.
l It will be obvious to those skilled in the art that the
¦ specific starch employed and the amount of starch fiber used
I will vary according to the desired quality paper. Thus, we have
¦ found that the choice of the proper type of starch makes it
1 possible to achieve selected sheet properties previously achieved
¦ only by hydrating and fibrillating wood pulp to various degrees
of freeness. Specifically, it has been necessary to lightly
refine pulp (650 ml. CSF) in unbleached kraft linerboard appli-
¦ cations to insure rapid water removal rates while maintai.ning
I ¦ high processing speeds. The degree of refining is controlled
also by the internal bond strength of the product being produced.
~he introduction of starch fiber enables rapid water removal and
maintenance of production speed but still insures ~he development
internal bond strength. Glassine papers are frequently processed
¦~ from pulp that has been refined extensively ~less than 50 ml. CSF)~
¦¦ We have now found that glassine type papers can be produced by
reducing the cellulose refining in half by adding as little as
1 15~/o starch fiber. Alternatively, for papers which require even
I ¦ lower opacity and porosity, it will be preferable to use starch
¦¦ fibers in larger quantities, i.e. about 50% or more.
The starch fiber containing papers of the present
¦ invention may be manufactured together with any commonly employed¦
internal additives such as sizes, wet and dry ~strength additives,
- 21 -
~g7~6
¦¦ etc. or may be surface treated by coating, spraying or saturating
~i as is conventional in the trade.
The starch fiber-containing paper of the present
invention can be repulped and recycled. The ability of the starch!
fiber itself to retain its fiber integrity during a repulping
process is influenced by the starch fibPr type (higher amylose ;~
starches repuLp more readily) and the repulping conditions to
; which it is subjected. Generally, the lower the usage of basic
chemicals and elevated temperatures during the repulping operation~,
the more avorable the recycling of the starch fiber. I
The following examples will serve to more fully explain !
the various aspects and embodiments of the present invention.
In the examples, all parts are by weight unless otherwise
indlcated.
EXAMPLE 1
A slurry was prepared by mixing a naturally occurring
unmodified starch composed of 70% amylose and 30% amylopectin in
water at a level of 5%, by weight, solid starch and then addin~
with agitation, a 25~/o solids solution of sodium hydroxide
sufficient to provide a level of 40% caustic on the starch on a
dry basis. This mixture was agitated until a dispersion of the
starch granules was obtained.
¦ The resultant dispersion was introduced at a pressure
¦ o~ 703 gms/sq. cm. into an agitated co~gulation bath consisting
of 28% solids ammonium suLfate through a spinnerette containing
100 apertures, each of which had a diameter of 70.2 microns, at
an angle of 90 to the moving salt solution. The resultant fibers
Il - 24 -
10~466
were collected on a wire mesh screen, washed free of salt and
r~ ~ recollected . The fibers possessed an average diameter of 65
i ~ ¦ microns, an average length of approximately 4 mm~.and a final
solids content of 23.5%, by weight.
A series of handsheets were prepared on a ~oble and
Wood sheet mold, from varying levels of bleached softwood pulp
~BSWK) in com~ination with the above prepared fibers. The sheets
were dried on the Noble and Wood dryer at a drum tempera~ure of
1,?~1C. and then allowed to condition for a period of 24 hours
under constant 22C. temperature and 55% relative humidity.
Table I summarizes the pertinent sheet making conditions
and test data.
TABI,E I
Fiber Blend Basis Can~a~ Sheffield Z-direction-
~ Starch Weight Standarcl 2 al 3
BSWK Fiber gms7sq.m. Freeness (ml)(l) Porosity( )_Strength( )
100 0 78.~ 5~4 218 596
82.6 540 1~2 630
~` 75 25 80.4 475 7~ 846
77.9 367 28 1050~
77.1 250 16 1050+
(1) Measure of the drainage of water from the pulp
through a wire screen. Unbeaten pulps have a
high freeness relative to low freeness of well beaten
pulps. TAPPI test T227-M~58.
(2) This test measures the air resistance of paper. I
Sp~cifically, it measures the volume of air that can
be passed through a specific sample area at a given
pressure and time. The higher the test value, the
1 30 more porous the sheet (Used 7.62 cm. I.D. ring;
values are unitless).
(3~ The Scott Internal Bond Tester measures the Z-
directional strength of paper. This method is
designed to determine the average force in joules
per square meter required to separate a paper
¦ specimen. TAPPI RC-305.
- 25 -
~
i
~ 746~ 1
The results shown in the Table indicate that the presence
~of increasing amounts of this particular starch fiber prepared
at a 5% solids dispersion level extends the water holding
capabilities of the fiber blend and produces a sheet that is less
porous and of higher Z-directional strength than a lOOV/o cellulose
sheet.
EXAMPLE 2
Starch fibers were produced using the materials and
method employed in Example 1, however, after the final wash, ~he
fibers were dispersed in ethanol solution, collected and allowed
to dry. The fibers were then combined with cellulose and hand-
sheets prepared as in Example 1. Tests performed on these hand-
sheets show that the dried fiber provided performance character-
istics comparable to those obtained by the moist fibrous products
of Example 1.
EXAMPLE 3
¦ Starch fibers were produced using the materials and
¦methods employed in Example 1, however, the starch solids concen-
¦tration of the starch dispersion was 20% and the final solids
¦level in the fiber was 38%. Handsheets were prepared and tested
as in Example 1. The results are shown in Table II.
TABLE II
~Fiber Blend Basis Canadian
Starch Weight Standard Sheffield Z-directional I
BSWK Fiber _gms/sq~m. Freeness ~ml2 Porosity Strength _
100 0 86.2 505 158 538
82.9 545 333 527
82.9 595 1,215 565 l,
l~ 50 50 79.7 676 8,645 ~47 1,
11 25 75 79.7 81~50,496 1035+
- 2~ -
l~q74~6
~ As illustra~ed in Table II, the use of starch fibers
¦ prepared from a higher solids level dispersion resulted in an
¦ increase in the water releasing ability of the furnish ~i.e.,
¦ the freeness), and provided a more porous sheet of greater
porosity and Z-directional strength than a 100~/o cellulose sheet.
¦ It is to be noted that this starch solids level produced freeness
¦ and porosity values which distinctly contrast from the values
¦ obtained in Example 1 wherein a 5% starch solids level was used
¦ to produce fibers. This comparison illustrates the adaptability
¦ of the method of the present invention to the production of a
variety of properties in the final paper product (e.g., the level
¦ of porosity required in a glassine stock versus that required in
¦ filter paper). It is also to b~ noted that in both Example 1 and
¦ 3, the strength of the paper wa~ improved by the use of starch
I ¦ fibers.
I EXAMPLE ~
¦ Starch fibers were prepared using a 20~/~ solids starch
dispersion as in Example 3 except that after washing they were
reslurried in ethanol, recovered and dried. Handsheets were
¦ prepared and tested and showed that the dried fiber provided
¦ performance characteristics comparable to those obtained using
¦ the moist fibrous product of Example 3.
¦ E~AMPLE 5
This ex~mple illustrates the use of fibers formed from
I ~ a variety of starch bases in the production of paper according
~ to the present invention.
; I Starch fibers were prepared and combined with cellulose
i using the methods described in Example 1. The cellulose portion
- 27 -
74~i
, '
il was beaten to a Canadian Standard Freeness of 645 ml prior to
¦ being blended wi~h the starch fiber and the basis weight of the
,I handsheets was maintained at 97.5 gms/sq. m.
!~ !
TABLE III
Fiber Blend 1 2 direct- 4
Starch Starch Fiber Tensile Mullen ional3 MIT
BSWK Fiber Base gms/cm2 gms/cm2 Strength Fold
l 100 0 - - 10~0.55 4429.40 14~ 552
1 90 10 Aminoethyl- 1462.4 6679.26 903 1,210
ated corn
" " 1476.46 5624.641050+ 1,2~0
Waxy maize 1525.68 6679.26 853 1,670
" " 14:l3.19 5062.171050+ 1,125
Unmodified 1553.80 5484.02 567 1,340
corn
" " 1293.66 3445.091050+ 1,245
Hybrid corn 165~.26 5273.10 62~ 1,420
I containing
2n 1 70/O amylose
1 70 3~ " 1652.23 4148.171050~ 1,390
I ~ 90 10 Amylose 1545.99 5413.71 68~ 1,433
" 1652.23 4780.9~1050+ 1,395
TAPPI method T404-5s 66 - Determines the tensile breaking
strength in pounds per inch (converted to metric units).
TAPPI method T403-ts-63 The hydrostatic pressure in
pounds per sq. inch (converted) required to ruptur~ the
paper when the pressure is applied at a controlled
I increasing rate through a rubber diaphragm to a circular
area 3048 cm. in diameter.
3As deined in Example 1.
~ 4TAPPI method T423M-S0. The number of folds that the test
¦ specimen can endure prior to breaking using a fold tester
of the type developed at the Massachusetts Institute of
l Technology.
¦l As shown in Table III the addition of any of the variou~
! starch fibers may be used to improve particular strength
properties of the paper when compared with the 100% cellulose
fiber sheet.
- 28 -
l l
10~74$6
EXAMPLE 6
This example illustra~es two methods for the production
~¦of a 100% starch fiber sheet. I
¦Method A. Six grams of unmodified corn starch fibers were slurried
in 1 liter of water. The fibers were agitated with a paddle
stirrer until a uniform mixture was obtained. A handsheet was
formed on the Noble and Wood sheet former that had been fitted wi~
a 100 mesh wire screen. The resultant fibrous web was removed fro~
l the screen and blotters and subjected to a series of pressing
operations: 3 presses at 7030.~ gms/cm2 and 3 presses at 28123.2
gms/cm with changing of the blotters between pressing operations.
The resulting mat solids was 70%. The web was then placed between
blotters and dried on the Noble and ~ood dryer at 120.1C. The
resultant rigid self-supporting paper-like product had a basis
weight of 145 gms/sq.m.
Method B. Starch fibers were processed as described in Method A
and the resultant web mat was subjected to a pressing sequence of:
2 presses at 7030.8 gms/cm2 and 2 presses at 14061.6 gms/cm2 with
¦ changing of the blotters between pressing operations such that th~
l¦resultant wet mat solids was 50~/O. The web was placed between
two nylon wire screens and passed through the ~oble and Wood dryer
at 120.1~C. The resultant rigid self-supporting paper-like web
had a basis weight of 145 gms/sq.m.
EXAMPLE 7
Handsheets were prepared by the method of Examplel excep~
¦ that commercially unmodified refined glassine stock at two free-
ness levels was combined with corn starch fibers. The cellulose
pulp was obtained from two points in the refinery operation such
¦¦that one portion had a Schopper Reigler freeness of 350 ml. while
29 -
lOg~466
¦Ithe fully refined portion had a 160 ml. freeness. Starch fiber
~was substituted at the 20% level and all handsheets were prepared
¦'at a basis weight of 48.8 gms/m2. The sheets were then surface
~sized on a laboratory size press fitted with rubber rolls using
a 1% solids polyvinyl acetate solution.(available from Air Product
and Chemicals under the tradename Vinol 165) main~ained at 60C.
such that a 1% pick-up of polyvinyl acetate was obtained. The
¦sheets were then conditioned under constant temperature of 20C.
and room humidity 55% for 24 hours ~rior to being tested for
` kesl~stance using TAPPI standard T~54-ts-66. The results of the
terpentine testing are shown in Table IV.
TABLE IV
Cellulose
¦S.R. Starch Sheet Mold Stock Terpentine
¦Freeness* Parts Fiber Drain Time Temp. C. _Test _
350 ml 100 - 21.3 secs. 2~ 855 secs.
; 350 ml 8~ 20 19.9 secs. 24 1800+ secs.
160 ml 100 - - 62.1 secs. 60` 1~00+ secs.
Schopper-Riegler Freeness Tester supplied by
Testing Machines, Inc.
The use of starch fiber in combination with partially
¦ refined pulp increased the terpentine resistance of that pulp
alone and matched the resistance of a fully r~fined glassine stock~
In addition, the refining reduction enabled drain time reductions
by a factor of almost 3 fold at significantly lower temperatures.
Thus while it is necessary to elevate conventional stock to
l temperatures of about 60C. in order to obtain drainage in 62
! seconds, drainage in about 20 seconds can be achieved at temper-
atures of 24C. with no loss in desirable properties using the
30 1¦ method of the present invention. The improved drainage can result
~in faster machine speeds and efficiency of production while realiz~
¦¦ing considerable savings in energy due to reduced refining and
, - 30 -
Il l
~L0~7466
¦stock temperatures.
EX~MPLES g
¦ This example illustrates the improvement in properties
¦obtainable by the incorporation in cellulose pulp of starch fibers
¦containing polymeric m~crospheres.
¦ Starch fibers were prepared using the method of Example:
¦but also incorporating înto the starch dispersion, prior to fiber
¦formation, 8.5% microspheres (available from Dow Chemical
I as XD 6850). The fibers were then incorporated into handsheets
¦in combination with cellulose wood pulp using the method described
I ¦in Example 1. In all cases, the Canadian Standard Freeness value
l was 730 ml. for the cellulose componPnt. The results o testing
¦ are shown in Table V. As a means of comparison, samples were
also prepared in which the microspheres were added directly to the
paper pulp as is conventional practice in the industry.
TABLE ~ 2
Fiber Blend % Spheres Basis 1 Taber Z-dir~ct-
; I Starch In Weight Caliper Stiff- ional~
I BSWK Fiber Added Sheet ~ms/sq.m. lxlO~ cm. ness Stren~th
1 100 0 0 0 97.6 18.79 3.7 111
100 0 0 0 130.1 24.38 6.3 137
100 0 1.8 .86 97.~ 24.39 6.6 103
100 0 2.0 1.0 97.6 25.40 7.1 90
5 .43 .43 97.6 23.11 5.0 168
10 .86 .86 97.6 26.16 6.3 206
~5 151.29 1.29 97.6 28.45 7.5 237
Thickness of paper expressed in thousandths of a centimeter
TAPPI Method T451-M-60
3As defined in Example 1.
.. , ~ .... : . .
1 V~74~i6
As illustrated in Table V, the introduction of the
¦microspheres by either of the methods substantially improved both ¦
¦the caliper and stiffness of the paper product. In this regard,
it was possible by the addition of microspheres to achieve the
caliper and stiffness of 130g/sq.m. basis weight at a level of
only 97.6 g/sq.m. The weight saving, both in amount of fiber
required and in related costs recognized after produc~ion of the
paper (e.g. mailing), are readily recognizable.
When the o~her properties obtained from the microsphere ¦
containing sheets were compared, it was found that retention of
theexternally added spheres was approximately 50V/o of the amount
initially added while the retention was approximately 100% for
those added in the encapsulated fibers. Moreover, there was a
decrease in strength and evidence of non-uniform distribution of
the spheres (with a greater con~entration on the felt side) in
the case of the externally added spheres while these factors were
not presen~ in the case of the starch encapsu~ated spher~s. Thus,
the increase in~caliper and stiffness observed using the conventio~-
ally employed external addition of the spheres was obtained only
at the expense of decreasing internal bond strength of the paper,
¦while introducing the spheres within the starch fiber insured
their retention with the sheet while increasing the internal bond
strength in addition to providing the desired stiffness and calipe~ .
increases.
¦ E~AMPLE ~
This example illustrates the results obtained using
three methods for incorporating clay in paper production.
Handsheets were prepared using methods similar ~o those
- 32 -
l ll
-. :
1027466
described in Example 1. The handsheets were prepared so as to
incorporate a number two coating grade cl~ in the final sheet
¦ during the formation process. The incorporation of the clay into
¦ the handsheets was accomplished in three different manners:
1) by conventionally slurrying the pigment with the pulp fibers,
2) by incorporating starch fibers pr~pared according to Example 1
but containing 80% clay and 20% starch, and 3) using a combination
¦ of methods (1) and (2). In all cases the basis weight of the
l sheet was 97.6 g/sq.m.
¦ The physical and optical properties of the resulting
¦ paper sheets are shown in Table VI.
I ¦ TABLE VI
l Conventional
I Addition_ Starch Fiber Z-direction-
~/0 Cellu- % % ~~~~~~~~~~ Opaç- Ten~- al(3)
lose Clay TiO2 Starch Clay ity~l) ile~2) Strength
100 0 0 0 0 85.9991.34 302
87.2 12`.8 0 0 0 92.0625.74 113
1 75.2 0 0 5.0 19.8 88.91371.00 351
201 68.4 6.8 0 5.0 19.8 90.5864.79 256
; 1 72.1 0 4.5 4.7 18.7 94.1850.73 233
(l)TAPPI method T425-m-60.Expressed in percent and
defined as 100 times the ratio of the diffuse
reflectance of a specimen backed with a blank of
I no more than .005 reflectance of the same specimen
¦ backed with a white body having an absolute
reflectance of 0.89. The higher the value the more
opaque the paper.
l ( )Defined in Example 5.
(3~Defined in Example 1.
As illustrated in Table VI, incorporating the pigment
¦within the starch fiber enabled higher pigment loadings and
~¦strength properties when compared to conventional pigment loading
- 33 -
lOq~4~6
techniques. Thus, when 12.8% clay was added to cellulose pulp
~ using conventional techniques, the tensile and 7-directional
I strength decreased. In contrast, when 19.8% olay was added in
the form of encapsula~ed starch fibers (a total addition of
24~8~/o) ) the tensile and Z-directional strength improved. It is
~further shown that the reduction in opacity obtained by use of
¦~the clay-encapsulated fiber can be compensated for by the
¦external addition of a small amount of clay or of titanium dioxide
¦ EXAMPLE 10
l This example illustrates the superior retention ability
¦of the starch fibers as used in the method vf the present
¦invention.
¦ Bleached softwood kraEt was beaten to a freeness of 500
¦ml. Canadian Standard and divided into three portions. To one
¦portion, a No. 2 coating grade clay was added and the resultant
¦blend agitated until the pigment was uniformly distributed
throughout the pulp fibers. Another portion was treated in the
¦same manner except that Natron 86 (a trademark of ~ational Starch !
l and Chemical Corporation), a retention aid, was addedO To the
¦remaining portion of the pulp, starch fibers containing clay
encapsulated therein (50% starch and 50~/O clay~ were added and
¦the fiber blend was agitated until uniform distribution was
obtained. Handsheets were prepared by a method similar to
¦Example 1 and the sheets evaluated for clay content and percent
¦ retention. The results are shown in Teble VII.
Il ~
1.
lOq74~
TABLE VII
Fiber Blend
BSWK Starch Fiber
(50/O Clay) Clay _ Retention Aid % Clay Retention
90 0 10 0 11
90 0 10 0.02% 35
8020 0 0 97
As illustrated in Table VII, the retention of clay was
highest when the clay was encapsulated in the starch fiber
pursuant to the present invention.
EXAMPLE 11
The following example illustrates the use of starch
fibers for their binding properties in the production of a
multi-ply sheet.
Two-ply handsheets were prepared on a Noble and Wood
sheet former from bleachedsoftwood kraft that had been beaten to
a 500 ml. Canadian Standard Freeness. To achieve a final basis
weight of 146 gms. per square meter, two plies (each approximately!
73 gms. per square meter) were prepared and wet pressed together
Iprior ~o drying on the Noble and Wood drier at 121C. The control
¦handsheet contained 100% cellulose in both plies, while the test
handsheet had 20~Jo of ~he cellulose in the top ply replaced by
starch fiber. The bond between the plies was tested using the
Scott Internal Bond tester and the results shown in Table VIII.
TABLE VIII
Fiber Blend Z-direct~onal
¦Bottom Ply - Top Ply _ _ _ Stren~th
j100% Cellulose - 100~/o cellulose 119.7
¦ 100% Cellulose - 80% cellulose and 20% Starch Fiber 197.4
¦ (l)Defined in Example 1.
_ ~5 _
9 ~ 79~j~
As shown in Table VIII the presence of the starch fiber
l increased the bond strength between the pliPs of the final shee~s.
; ¦ EXAMPLE 12
This example shows the production of paper containing a
variety of additives incorporated by the addition of starch fibers
containing the encapsulated additives.
l In a manner similar to that described in Example 8,
¦ additives were encapsulated within the starch fibers and used to
¦ form handsheets having a given percentage of the starch fibers as
¦ indicated in Table IX.
TABLE IX
Additive% A,dditive in % Addition of Starch
l Star~h Fiber _ Fibers in Pulp
I __
TiO2 25 20
¦ CaC03 25 20
j Al powder 25 20
Carbon black 25 20
Fibran 68 5 10
I (A trademark for a sizing agent available from
¦ National Starch and Chemical Corporation~
Pexol 200 5 10
(A trademark for a sizing agent available from
¦ Hercules Powder Co.)
A l:l blend of 50 50
I antimony trioxide
¦ and vinyl chloride
¦ homopolymer (fire
retardant)
I I r ;s ~ d ~ch l ~r c:~
57 ~0
I propyl phosphate
(fire retardant)
In all cases, the additives were retained at al
high level in the fînal paper product and imparted their
characteristic property thereto.
Il I
~l - 3~ -
1~97q~6
EXAMPLE 13
This example illustrates the use of the sta~h fibers
as a means to incorporate latex binders in a nonwoven web of
synthetic fibexs.
A dispersion of rayon fibers (0.635 cm, 1.5 denier) and
polyester fibers (0.635 cm, 1.5 denier) were prepaxed at 0.1%
solids in sepaxate containexs.
A 100% staxch fiber product as well as a starch fiber
that contained 20% on a weight basis of encapsulated latex,vinyl
acetate/butyl acrylate copolymer,were added as binders in amounts
such that the final fiber blend would contain 25% of the starch
fiber products. Handsheets were prepared on a Noble and Wood
sheet former at a basis weight of 65 gms. per square meter using
methods similar to those described in Example 1. The webs were
tested to determine tensile stren~th improvement and the results
summarized in Table X.
TABLE X
Synthetic Tensile(l)
i ¦ Starch Fiber Description Bindex Level Fiber (gms/cm2)
l None (control) - Ra~on *
¦ None (contxol) - Polyester *
¦100% Starch 25% Rayon 710.11
¦ 100% Starch 25% Polyester 217.95
80% Starch - 20% latex 25% Rayon 984.31
80% Starch - 20% latex 25% Polyester 135.69
¦ Sheet did not possess sufficient integrity to
measure tensile
(l)Defined in Example 5.
- 37 -
,:1 ,~ ,... .
10~7466
! As shown in Table X, webs prepared using both the
¦starch fibers and the starch-latex fibers as binders possessed
¦superior tensile strength. In contrast, control webs prepared
¦from 100% synthetic fiber did not possess sufficient integrity
¦to even be handled for testing. It is noted that the particular
latex employed increased the tensile strength of the rayon web
while decreasing the strength of the polyester web compared to
the 100% starch fiber. This illustrates the necessity of choos-
ing the proper latex for the synthetic fiber being treated.
EXAMPLE 14
This example illustrates the use of starch fibers as
binders with ceramic fibers. The example also shows that the
starch fiber binders may be removed after formation of the web
resulting in the production of a 100% ceramic ~iber sheet.
A 3% solids ce~ramic iber slurry was prepared in a
Waring Blender and agitated for 1 minute after 0. 2~/o NaOH (dry
basis based on the weight of the fiber) was added to serve as a
dispersing agent. The fiber mix was then transferred to a con-
tainer that was equipped with a paddle stirrer and a pre-determine~
amount of starch fiber added from a 1% solids mix. After mixing
I the blend for a period of 5 minutes, handsheets were prepared at
407 gms/square meter basis weight, on the Noble and Wood sheet
former. As a control, a ceramic sheet was made without the addi-
tion of any starch fibers. All sheets were subjected to strength
tests with the results shown in Table XI.
.` ~
r~d~ûrk
. I
~ - 38 -
.'
:; .. .. : ., , ~; .
1(3~7466
i! TABLE XI
ll i
i Basis Weight Tensil2e(l)
I Starch Fiber gms/sq. meter gms/cm
I 407.5 __*
,1 5% 407.5 3.52
~ 10% 407.5 20.39
I
l Sheet did not possess sufficient integrity to
I measure tensile
l (l)Defined in Example 5.
¦ The sheets containing the starch fibers were then
r~ placed in a kiln malntaintained at a ~ sufficient to
ash the starch fibers and fuse t:he ceramic fibers. A
well bonded ceramic web was thereby produced.
EXAMPLE 15
Two ply handsheets containing 10% TiO2 on the final
sheet weight of approximately 145 gms/sq.m. were prepared. In
the control ha~dshee~s, TiO2 was added in the conventional manner
by dispersing the pigment with those unbleached kraft fibers
which comprised the top liner. In the remaining handsheets,
20% TiO2 encapsulated starch fiber on a weight basis was added
in sufficient quantity to the top liner to provide 10% TiO2 on
the final sheet weight.
The final sheet was constructed from two plies, each
prepared separately on the Noble and Wood sheet mold at
¦ approximately 72.5 gms/sq.m., removed from the wire and pressed
¦ together in the wet mat state at 14061.6 gms/cm2. The sheets
¦were then drîed on the Noble and Wood drier at 121C. Brightness
readings were taken on the top liner side in accordance with
- 39 -
1097~
I,ITAPPI standard R452-M-58 wi~h the results indicated in Table XII.
I TABLE XII
I Sample Sheet Top Liner Brightness
i
Control 26.2
Starch Fiber 30.1
The results shown in Table XII indicate that the
handsheets prepared using the TiO2 encapsulated starch fibers had
¦superior properties to those prepared using conventional methods.
¦ The preferred embodiments of the present invention
¦having been described above, various modifications and improvement~ ,
thereon will now become readily apparent to those skilled in the
¦art. Accordingly, the spirit and scope of the present invention
¦is to be limited not by the foregoing disclosure, but only by the
appended claims.
- ~0 -
!
