U.S. patent number 3,920,509 [Application Number 05/340,140] was granted by the patent office on 1975-11-18 for process of making polyolefin fibers.
Invention is credited to Hayato Yonemori.
United States Patent |
3,920,509 |
Yonemori |
November 18, 1975 |
Process of making polyolefin fibers
Abstract
An improved process of manufacturing fibers by the technique of
forming a mixture of polymer, solvent for such polymer and,
optionally, water or other flashing aids, at a temperature (flash
temperature) which is high enough to bring the polymer to a plastic
state and which will permit substantially complete vaporization of
the solvent when the mixture is flashed and flashing the mixture
into a flash zone to produce a fibrous product. In the improved
process (a) the flash zone is established at a pressure of 600 mm
Hg or below and, advantageously, between 50 and 500 mm Hg, and (b)
the flash temperature, the components of the mixture and the
concentration of each in the mixture (with respect to the heat
capacity of said components and with respect to the heat of
vaporization of those components in the mixture which will be
volatilized in flashing) are all chosen relative to each other so
as to produce in the flashed product a temperature which is less
than 94.degree. C., and, advantageously, below 80.degree. C. when
the mixture is flashed into said flash zone and substantially all
of the solvent vaporized. In an additional feature of the
invention, said flash zone pressure and the solvent in the mixture
are selected so as to produce a vapor condensation point in the
flash zone when the mixture is flashed thereinto which is at or
below 60.degree. C., an aqueous mixture of the flashed product is
produced in the flash zone by introduction thereinto of dilution
water at a temperature below 70.degree. C. and, advantageously,
within the range of 10.degree. C. to 60.degree. C., which
temperature is at or above said condensation point in said flash
zone, and refining the aqueous mixture at a temperature below
70.degree. C. and, advantageously, between 10.degree. C. and
60.degree. C. Advantageously, at least a part of the refining may
be carried out while the aqueous mixture is in pressure
communication with the flash zone and subjected to the ambient
pressure condition in the flash zone.
Inventors: |
Yonemori; Hayato (Iwakuni,
JA) |
Family
ID: |
26969063 |
Appl.
No.: |
05/340,140 |
Filed: |
March 12, 1973 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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295339 |
Oct 5, 1972 |
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Current U.S.
Class: |
162/157.5;
162/164.1 |
Current CPC
Class: |
D21H
5/202 (20130101); D01D 5/11 (20130101); D21H
13/14 (20130101) |
Current International
Class: |
D01D
5/00 (20060101); D01D 5/11 (20060101); D21F
011/00 () |
Field of
Search: |
;162/157R,146,164
;264/5,13,14,121,205,209 ;260/94.94 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Bashore; S. Leon
Assistant Examiner: Chin; Peter
Attorney, Agent or Firm: Tiegland; Stanley M. Horton; Corwin
R. Howard; Robert E.
Parent Case Text
CROSS-REFERENCE TO of APPLICATION
This is a continuation-in-part of Ser. No. 295,339 filed Oct. 5,
1972.
Claims
What I claim is:
1. A process for manufacturing papermaking pulp of synthetic fibers
comprising forming a mixture of a polymer and a solvent for such a
polymer, flashing said mixture at a temperature which is high
enough to bring said polymer to a plastic state and which will
permit substantially complete vaporization of the solvent when the
mixture is flashed, flashing said mixture into into a flash zone to
produce a fibrous product, and refining the fibrous product,
characterized in that
a. said flash zone is maintained at or below 600 mm Hg
pressure,
b. said flashing temperature, the components of said mixture and
the concentration of each in the mixture, with respect to their
heat capacity and with respect to the heat of vaporization of the
components vaporized during flashing, are all selected relative to
each other to produce a temperature of less than 94.degree.C in the
flashed fibrous product upon evaporation of substantially all of
said solvent,
c. the solvent has a vapor condensation point in the flash zone
below 60.degree.C,
d. dilution water is introduced into the flash zone at a
temperature above the vapor condensation point of the solvent but
below 70.degree.C to form an aqueous mixture,
e. the aqueous mixture is passed directly to a refiner which is in
direct pressure communication with the flash zone, and
f. the aqueous mixture is refined in the refiner at a temperature
below 70.degree.C to produce the papermaking pulp.
2. A process as in claim 1 and wherein the flash zone pressure is
maintained between 50 and 500 mm Hg pressure.
3. A process as in claim 1 and wherein said flashing temperature,
the components of said mixture and the concentration of each in the
mixture, with respect to their heat capacity and with respect to
the heat of vaporization of the components vaporized during
flashing, are all selected relative to each other to produce a
temperature less than 80.degree.C in the flashed fibrous product
upon evaporation of substantially all of said solvent.
4. A process as in claim 1 and wherein said flash mixture
contains
a. water as a flashing aid in an amount between about 30 and 70% by
volume of the mixture,
b. a saturated hydrocarbon solvent having a boiling point between
20.degree.C and 130.degree.C at atmospheric pressure, and
c. a crystallizable polyolefin in an amount between 2 and 30% of
the combined weight of the solvent and polymer.
5. A process as in claim 4 and wherein said mixture contains
between about 1 and 5% by weight of the polymer therein of a
polyvinyl alcohol having a degree of hydrolysis greater than 77
mols. % and a degree of polymerization between 200 and 4000.
6. A process as in claim 4 and wherein said solvent has a boiling
point at atmospheric pressure which is between 50.degree.C and
100.degree.C.
7. A process as in claim 6 and wherein said polymer is high density
polyethylene.
8. A process as in claim 6 and wherein said polymer is
polypropylene which is predominently isotactic.
9. A process as in claim 1 and wherein said dilution water is at
least 5.degree.C above said vapor condensation point.
10. A process as in claim 1 and wherein said aqueous mixture is
refined in the presence of between about 1 and 5% of an at least
partly water soluble polyvinyl alcohol having a degree of
hydrolysis greater than 77% and a degree of polymerization of
between 200 and 4000.
11. A process as in claim 1 and wherein said flash zone is
maintained at a pressure between 50 and 500 mm Hg, said dilution
water added to the flash zone is at a temperature between
10.degree.C and 60.degree.C and said refining is conducted at a
temperature between 10.degree.C and 60.degree.C.
Description
BACKGROUND OF THE INVENTION
Numerous processes have been proposed for preparing synthetic
fibrous materials by flashing polymer solutions or dispersions held
at high temperature and pressure into a zone of reduced pressure.
In various patent literature, such as German Offenlegungsschrift
No. 1,958,609 and Japanese patent applicaton having publication No.
71-34921, processes are proposed in which a polymer is dissolved in
a solvent therefor and heated under at least autogenous pressure
and then flashed into a zone of lower pressure to thereby vaporize
the solvent and form fibrous materials. In the latter mentioned
patent, the fibrous material thus formed is quenched with a water
spray at a temperature between 60.degree. C, and 80.degree. C.
Similar processes are presented in U.S. patent application Ser. No.
295,339, filed Oct. 5, 1972, (assigned to the assignee of the
present application) and as well in German OLS No. 2,121,512 and
German OLS No. 2,144,409. In these processes a polymer dissolved in
a solvent is mixed with water or other liquid non-solvents for the
polymer to form an emulsion of the polymer solution in a continuous
water phase and this emulsion is heated and flashed to a reduced
pressure zone to produce fibers.
Another approach is described in U.S. patent application Ser. No.
285,386 and now abandoned, filed Aug. 30, 1972, (assigned to the
assignee of the present application) wherein a polymer solution in
which water is dispersed as a discontinuous phase is flashed to
form fibers. In this process, the water concentration is held
between 30 and 70% of the entire mixture and in forming the mixture
it is preferable to add the water to the preformed polymer solution
to insure that the water forms the discontinuous phase.
OLS No. 2,147,461 describes a process in which molten polymer is
emulsified with water (optionally, with a minor amount of solvent
in the polymer phase) and then heated and flashed to a reduced
pressure zone to form fibers.
While many variations are evident, it is seen that the common
feature of all these fiber-making processes is the flashing into a
zone of reduced pressure of a heated mixture containing a polymer
and a solvent for such polymer. Various conditions of flashing are
suggested in the referenced processes including temperature and
pressure ranges for the mixture to be flashed and various solvents,
flashing aids, etc. Most of the references contemplate flashing
into a zone held at atmospheric pressure. Others suggest the
possibility of flashing into a zone which is above or below
atmospheric pressure, in some cases with the application of heat in
such zone. All of these processes may lead to the production of
fibrous material. However, each suffers from the shortcoming that a
specific set of conditions of flashing, particularly with regard to
temperature and pressure, and interrelationship of such conditions
are not provided which will permit manufacture, in a practical
manner, of fibers having the optimum properties desirable for their
use as a synthetic pulp in the manufacture of paper by conventional
techniques.
Fibrous materials produced under the general process conditions
described in these references tend to be interconnected or bundled
together to an undesirable degree and the paper produced therefrom
is undesirably low in strength (e.g., tensile strength). Such
fibrous material is more difficult to separate, cut or refine in
preparation for paper making and contains a high content of gels
and chunks of polymer which cause undesirable "fish eyes" or
transparent spots in paper manufactured therefrom.
BRIEF DESCRIPTION OF THE PRESENT INVENTION
The purpose of the present invention is to provide an economical
technique involving a specific interrelated set of flashing
conditions, applicable to all of the foregoing described processes,
which will produce a product capable of being readily separated and
refined for paper making and which, upon refining in accordance
with the invention, will yield a pulp useful for producing
synthetic paper by conventional paper making techniques whic has
surprisingly improved properties and a low content of gels and
chunks.
Briefly, the present process comprises establishing a flash zone at
a pressure of 600 mm Hg or below and, advantageously, between 50
and 500 mm Hg, forming a mixture of polymer, solvent for such
polymer and, optionally, water and/or other flashing aids, at a
temperature which is high enough to bring the polymer to a plastic
state and which will result in substantially complete vaporization
of the solvent upon flashing of the mixture into the flash zone
held at between 50 and 600 mm Hg pressure, flashing the mixture at
such temperature through a nozzle to the flash zone to form a
fibrous product.
In this process, the flash temperature, the components of the
mixture and the concentration of each in the mixture (with respect
to the heat capacity of the components and with respect to the heat
of vaporization of those components in the mixture which will be
volatilized in flashing) are all chosen so as to produce in the
flashed product a temperature which is less than 94.degree. C., and
advantageously, below 80.degree. C when the mixture is flashed into
said flash zone. Desirably, the solvent or solvents selected have a
normal boiling point at one atmosphere pressure between 20.degree.
and 130.degree. C. and, preferably, between 50.degree. C. and
100.degree. C. The polymer may be any polymer capable of forming
fiber, preferably, a crystalline or partially crystalline polymer.
The preferred polymers are crystalline or partially crystalline
polyolefins, especially polyethylene and polypropylene.
In an additional feature of the invention, said flash zone pressure
and the solvent (or solvents) in the mixture are selected so as to
produce a vapor condensation point in the flash zone when the
mixture is flashed thereinto which is at or below 60.degree. C., an
aqueous mixture of the flashed product is produced in the flash
zone by introduction thereinto of dilution water at a temperature
below 70.degree. C. and, advantageously, within the range of
10.degree. C. to 60.degree. C., which temperature is at or above
said solvent boiling point in said flash zone, and refining the
aqueous mixture in a continuous manner at a temperature below
70.degree. C. and, advantageously, between 10.degree. C and
60.degree. C. Advantageously, at least a part of the refining may
be carried out while the aqueous mixture is in pressure
communication with the flash zone and subjected to the ambient
pressure condition in the flash zone.
DESCRIPTION OF PREFERRED EMBODIMENTS
In practicing the process of the present invention, any polymer or
copolymer may be employed which is capable of forming fibers by
conventional spinning techniques. It is preferred to employ
crystalline or partially crystalline polyolefins such as low
pressure polyethylene, isotactic or partially isotactic
polypropylene, and ethylene-propylene copolymers. Additionally,
polybutenes and polymethyl pentenes may be employed in the practice
of this invention. Crystalline or partially crystalline polyamides
and polyesters may also be used. Noncrystalline polymers such as
polycarbonates, polysulfones, polyvinyl chloride,
polymethyl-methacrylate, polyacrylonitrile and polystyrene may be
used. Mixtures of the foregoing with each other or other polymers
may also be employed.
The preferred polyolefins employed are those having an intrinsic
viscosity above about 0.7 dl/g., which for polyethylene corresponds
to a viscosity average molecular weight of about 30,000 to
40,000.
The polymers employed in practicing the present process may be in
the form of dried powder or pellets or, preferably, as a wet cake,
slurry or solution of polyolefin in the reaction solvent as
obtained after polymerization.
Generally, any substituted or unsubstituted aliphatic, aromatic or
cyclic hydrocarbon which is a solvent for the polymer at elevated
temperatures and pressures, which is relatively inert under the
conditions of operation and which has a boiling point at
atmospheric pressure that is between 20.degree. C and 130.degree.
C, preferably between 50.degree. C and 100.degree. C, and at the
flash zone pressure that is less than the softening point of the
polymer may be employed in practicing the present process.
Illustrative of the solvents which may be utilized are aromatic
hydrocarbons, e.g., benzene and toluene; aliphatic hydrocarbons,
e.g., pentane, hexane, heptane, octane and their isomers and
homologues; alicyclic hydrocarbons, e.g., cyclohexane; chlorinated
hydrocarbons, e.g., methylene chloride, carbon tetrachloride and
chloroform; higher alcohols; esters; ethers; ketones; nitriles;
amides; fluorinated compounds, e.g., fluoro-hydrocarbons;
nitromethane; and mixtures of the above solvents and other solvents
having a boiling point between 20.degree. C and 130.degree. C at
one atmosphere pressure.
The polymer-solvent mixture may be formed by any one of several
methods. One may start with a solution of polymer in solvent as it
comes from a solution polymerization process, either at the same
concentration, diluted or concentrated. Alternatively, one may
start with a slurry of polymer particles in the solvent such as is
produced by a slurry polymerization procedure and the appropriate
amount of water is added to the slurry or vice versa. A further
alternative would be to start with a dry polymer powder, or
granules, or a wet cake such as might be produced at some stage of
solvent removal in the polymer plant, and the appropriate amounts
of solvent is admixed therewith.
The polymer concentration relative to the solvent is not critical,
the solvent being present in an amount that is greater than 100
percent by weight of the polymer and sufficient to give a viscosity
at the flash temperature employed that can be easily handled.
Frequently, this viscosity will be between 500 and 3,500
centipoises. Generally, the polymer concentration will vary from
about 2 to about 30% by weight of the solvent plus polymer, and
preferably is in the range of about 5 to about 15%.
In one preferred embodiment water is employed as a flashing aid. In
this embodiment the water may be in a continuous phase or
discontinuous phase, depending upon the amount of water added to
the polymer-solvent mixture and the manner of addition. If the
water is to form the discontinuous phase it should be present in an
amount less than 70%. To form a continuous water phase the water
should be present in an amount greater than 30% by volume of the
mixture and preferably between 50 and 70%. The particular method of
mixing is not critical, but if it is desired to have the water form
a discontinuous phase it has been found to be advantageous to have
the solvent present prior to water addition since the solvent or
polymer solution will form the continuous phase of the mixture to
be formed. This latter approach is particularly desirable when one
employs an amount of water which is near the borderline of an
inversion occurring, i.e., at the point where the amount of water
is approaching that level where it would form the continuous phase.
Conversely, if the water is added with or before ths solvent, it
will tend to form the continuous phase.
A primary function of the water is to provide energy to aid the
vaporization of the solvent during flashing since it is not
desirable to have the temperature so high that there is sufficient
energy imparted to the solvent alone to effect its complete
vaporization. However, the amount of water should not be so great
as to require the expenditure of unnecessary heat values in
attaining the desired flashing temperature, i.e., once that amount
of water required to form an aqueous solution or dispersion of the
agent having a suitable viscosity is determined, additional water
may be employed to a certain extent since it helps to lower the
mixture viscosity and aids solvent vaporization but the additional
amount need not be great.
Another function of the water is to reduce the temperature of the
fibrous mass in the zone immediately following the nozzle (flash
zone). The addition of water increases the total vapor pressure of
the system at the moment of flashing, thus reducing the boiling
point of the flashing mixture. This is independent of the amount of
water employed, and very small quantities may thus be employed for
this purpose. As a practical matter, however, water would be
employed in the amount of at least about 1% by volume of the
solvent-water mixture. Lowering the boiling point of the mixture in
this fashion will assist in establishing proper temperature
conditions in the fibrous mass formed upon flashing in accordance
with this invention, as discussed in detail at a later point.
Another function of the water is to act as the carrier for a
hydrophilic water-dispersing agent for the fibers to be formed. It
has been found that it is most advantageous to have the
water-dispersing agent present during flashing and precipitation of
the fibrous polymer. An equivalent amount of the same agent added
at a later stage to the already formed fibers does not give the
same degree of dispersibility and the presence of the agent
enhances the refinability of the fibers. Therefore, the water
should be present in an amount sufficient to carry that amount of
the hydrophilic agent employed to impart to the fibrous polymer the
desired level of water dispersibility, preferably as a solution
thereof. Additional water above such minimum amount required to
carry the agent may be employed to impart a suitable viscosity to
the aqueous solution or dispersion agent, i.e., the aqueous
solution of the water-dispersion agent should not be so viscous as
to present problems of handling or incorporation into the polymer
solution as a dispersed phase. Also, the water can aid in reducing
the viscosity of the mixture to a level less than that of the
polymer solution alone, thus permitting higher polymer
concentrations.
The agents which may be added to the mixture to impart water
dispersibility to the fibrous polymer are preferably watersoluble
or partially water-soluble high molecular weight materials.
However, they may also be materials which are soluble or partially
soluble in the solvent so long as they are somewhat hydrophilic and
impart water dispersibility to the fibers. The amount of
water-dispersing agent employed may range from about 0.1% to about
15% by weight of the polymer, preferably from about 0.1% to about
5% by weight. The preferred water-dispersing agent is an at least
partially water-soluble polyvinyl alcohol (PVA) having a degree of
hydrolysis greater than about 77% and, preferably, greater than
about 85 mol. % and having a viscosity (in a 4% aqueous solution at
20.degree. C.) greater than about 2 centipoises. Desirably the PVA
has a degree of polymerization in the range of 200 to 4000 and
preferably between 300 and 1500. If desired, the PVA may be
chemically modified to enhance its adhesion to the polymer,
dispersion and other properties. The polyvinyl alcohol is
preferably added with the water at the time the mixture is formed.
Illustrative of other water-dispersing agents that may be employed
are cationic guar, cationic starch, potato starch, methyl cellulose
and Lytron 820 (a styrene-maleic acid copolymer).
Such water dispersing agents are also advantageous in developing
the fiber properties during refining of the flashed product in
accordance with this invention as described at a later point.
Alternatively for this purpose, such agents may be added subsequent
to flashing, such as with the dilution water for refining. It is
particularly advantageous to add at least 1% and preferably between
11/2% and 5% by weight of the flashed polymer of polyvinyl alcohol,
either before and/or after flashing (but prior to refining).
The ingredients of the mixture can be placed in any suitable vessel
which is capable of being heated to an elevated temperature and
pressure. Generally, an autoclave is employed. However, when water
is added as a flashing aid it is important that the vessel employed
be equipped with a mixing or stirring device capable of keeping the
mixture in a constant state of agitation since a stable emulsion is
not formed and upon standing the mixture will quickly separate into
two distinct and separate phases.
The ingredients are then heated to a suitable temperature and
preferably agitated if water is present to form a uniform mixture
wherein water is present as a discontinuous or dispersed phase
within a continuous phase of polymer solution or as a continuous
phase with polymer solution dispersed uniformly therein, depending
upon the water concentration and mode of addition as previously
discussed. The temperature employed is preferably above the melt
dissolution temperature of the polymer in the solvent employed. The
melt dissolution temperature of any particular solvent is
determined by placing low concentrations of the polymer (e.g., 0.1
and 1.0% by weight) into the solvent in a vial which is then sealed
and placed in an oil bath. The temperature of the oil bath is
raised slowly (e.g., 10.degree. C/hour) until the last trace of
polymer disappears. This temperature is the melt dissolution
temperature. In some instances, it may be desirable to operate at a
temperature below the melt dissolution temperature. In this case
the temperature should be high enough under the operating
conditions so that the polymer is dissolved in the solvent or at
least is in a swollen state with sufficient fluidity to be
discharged from nozzle, i.e., in a plastic state.
Flashing is preferably carried out substantially adiabatically,
utilizing the heat (enthalpy) in the heated mixture to provide the
heat of vaporization for vaporizing substantially all of the
solvent when the mixture is discharged to the flash zone held at a
suitable lower pressure. Accordingly, for adiabatic flashing the
temperature of mixture prior to flashing should be high enough to
provide sufficient heat content or enthalpy for vaporization
adiabatically of substantially all solvent upon flashing to the
flash zone. However, the maximum temperature employed should be
less than the critical temperature of the solvent and/or the
decomposition temperature of the polymer.
It is also possible to carry out the flashing to some extent in a
non-adiabatic fashion, for example, by the addition of heat to the
material as it is flashed from the nozzle. For instance, low
pressure steam (e.g., below 20 psi) or water at 100.degree. C. may
be added to the fibrous noodle in the flashing zone as by injection
thereof in a conduit immediately following the flash nozzle into
which the flashed noodle is also injected. In this case, the
flashing temperature should be chosen so the heat content in the
mixture to be flashed plus the heat added to the flashed material
is sufficient to vaporize substantially all of the solvent in the
flash zone.
The pressure employed in the vessel containing the heated mixture
is preferably substantially autogenous. While pressures
substantially higher than autogenous may be employed, they are not
preferred as in some cases poor fiber formation may result. It may
be desirable, particularly in batch operations, to employ an inert
gas such as nitrogen during the flashing operation to maintain
substantially autogenous pressure in the vessel and thus maintain
the velocity of the mixture through the nozzle at a fairly constant
level.
Flashing is preferably effected through a nozzle which has a
substantial longitudinal dimension in order to efficiently impart
shear to the mixture (particularly the polymer component thereof)
immediately prior to flashing. Such shearing action aids fiber
formation and enhances fiber properties for paper making purposes.
The nozzle may be circular or noncircular in crosssection and may
be an annulus.
In addition to the foregoing more general parameters for the
flashing operation, an important feature of this invention is the
maintenance of certain pressure and temperature conditions in the
flash zone and the interrelationship of these conditions with the
temperature and other conditions of the mixture prior to flashing.
In accordance with this invention the flash zone is maintained at a
pressure of between 50 mm Hg and 600 mm Hg and the other conditions
of flashing are selected so that the temperature of the flashed
product is almost immediately lowered in the flash zone, by
evaporation of substantially all of the solvent (and a portion of
the flashing aids, if employed), to a temperature below 94.degree.
C. and, preferably, below 80.degree. C. It will be appreciated that
a portion of the solvent may still be unvaporized in the close
vicinity of the flash nozzle so in this case the appropriate point
at which the temperature of the flash product should be below
94.degree. C is that point downstream of the nozzle where
substantially all (above 95%) of the solvent has vaporized. In a
typical flashing procedure in accordance with this invention
vaporization may be substantially complete 10 to 100 cm downstream
of the nozzle. However, this can vary widely depending upon the
flow velocity, flash zone pressure, flash temperature, solvent,
etc.
Importantly, in the mixture to be flashed, all of the components of
the mixture and the concentration of each in the mixture are chosen
with respect to the heat capacity of each, with respect to the heat
of vaporization of each component which will be volatilized in
flashing, and with respect to the flash temperature chosen so as to
produce in the flashed product a temperature below 94.degree. C.
and, preferably, below 80.degree. C. upon flashing of the mixture
into the flash zone held at 50-600 mm Hg pressure. Expressed in
another way, the heat content of the mixture to be flashed and the
heat to be removed through vaporization of the vaporizable
components (solvent and any flashing aids vaporized, if employed)
should be adjusted so that the residual heat in the flashed
product, after removal of the heat of vaporization of the vaporized
components, will impart a temperature in the flashed product which
is below 94.degree. C. and, preferably, below 80.degree. C.
Selection of the appropriate flashing temperature and of the
components of the mixture and their concentrations for this purpose
will depend upon the pressure within the range of 50 -600 mm Hg
selected for the flash zone and the amount of heat added to the
flash material during flashing if the flashing is performed
non-adiabatically. If the flash temperature is too high or if the
components of the flash mixture and their concentrations with
respect to their heat capacity and heat of vaporization (for the
vaporizable components) are improperly chosen, the temperature of
the flashed product, upon substantially complete evaporation of the
solvent, will remain above 94.degree. C. If the flash temperature
is too low or, again, the components are improperly chosen with
respect to heat capacity and heat of vaporization, there will be
incomplete evaporation of the solvent. For the purposes of this
invention, appropriate selection of these variable parameters,
namely, the flash temperature, components and concentrations
thereof in the flash mixture, may be determined for a given
pressure condition in the flash zone by making a heat balance for
the flashing operation which will produce the desired noodle
temperature below 94.degree. C. Advantageously, these variable
parameters may be selected so as to satisfy the following equation:
##EQU1## where Q.sub.p = Enthalpy of polymer(s) in flash
mixture
Q.sub.s = Enthalpy of solvent(s) in flash mixture
Q.sub.f = Enthalpy of flashing aid(s) in flash mixture
Q.sub.na = Heat added to flashing mixture (if non-adiabatic)
V.sub.s = Enthalpy of vaporization of solvent vaporized
V.sub.f = Enthalpy of vaporization of flashing aids vaporized (if
any)
W.sub.p = Weight of polymer in the flashed product
C'.sub.p = Heat capacity of polymer in the flashed product
W'.sub.f = Weight of the flashing aids, adjuvants, and/or
nonvolatile components other than polymer in the flashed product
(if any)
C'.sub.f = Heat capacity of the flashing aids in the flashed
product (if any)
and where such enthalpy values are based on the same temperature
datum plane and the heat capacities are those applicable between
such datum plane and the temperature of the flashed product.
In using this formula, the heat capacity values and weights of the
flash components may be substituted into this formula, for example,
as follows for the specific case where a single polymer, solvent
and flashing aid are present in the flash mixture: ##EQU2## where
the additional terms are: W.sub.s = Weight of the solvent in the
flash mixture
C.sub.s = Heat capacity of the solvent in the flash mixture
W.sub.f = Weight of the flashing aid in the flash mixture
C.sub.f = Heat capacity of the flashing aid in the flash
mixture
C.sub.p = Heat capacity of the polymer in the flash mixture
.DELTA.H.sub.s = Enthalpy of vaporization of solvent under flash
conditions
.DELTA.H.sub.f = Enthalpy of vaporization of flashing aid under
flash conditions
T.sub.f = Flash temperature, .degree. C.
and where the indicated heat capacities are those applicable
between the flash temperature and the previously mentioned
temperature datum plane.
In practice, the heat capacity and enthalpy of vaporization values
for the desired components can be substituted into this equation.
Then, a flash temperature and the concentrations of the flash
mixture components may be selected relative to each other to
satisfy the equation for a desired flashed product temperature. For
ease of calculation it can be useful to program these variables for
computer analysis to select the desired components and flash
temperature.
It may not be necessary to actually measure the noodle temperature
(which is a cumbersome procedure under the flash zone conditions).
All that is necessary for control purposes is to maintain the
indicated parameters for the flash procedure at values that satisfy
this equation for the noodle temperature below 94.degree. C. which
is desired. Of course, the various parameters should also satisfy
the other conditions for proper flashing as previously discussed,
e.g., the flash temperature should be above the melt dissolution
temperature, substantially all of the solvent should be vaporized,
etc.
During flashing, the polymer is precipitated as a fibrous "noodle,"
which is a loose aggregation of fibers which is sometimes
continuous. The fibrous noodle is collected in a suitable receiving
vessel, preferably one which permits the vaporized solvent to be
separated therefrom.
Fibrous material may be formed in accordance with the foregoing
procedures which has improved properties, which will be discussed
at a later point. The mechanisms by which the combined parameters
of the pressure conditions in the flash zone and the flash
conditions which produce a noodle temperature below 94.degree. C.
can result in improved fiber formation have not been fully
elucidated. However, in addition to other possible mechanisms, it
is believed that the more rapid and pronounced cooling of the
precipitating polymer combined with the relatively violent flashing
caused by the prescribed pressure conditions in the flash zone are
at least, in part, responsible.
The fibrous noodle formed in accordance with this invention may be
processed, by the various conventional procedures, for use such as
for paper making. However, it is an additional advantageous feature
of this invention to process the noodle in a manner which is
interrelated with the conditions of flashing and wherein water is
introduced into the flash zone for processing of the flashed
product. In this procedure the solvent and flashing aid if employed
in the flash mixture and the pressure in the flash zone at the
location where the introduced water is in contact with the flashed
product (between 50-600 mm Hg) are appropriately selected so that
the temperature at which vapor condensation would occur
(condensation point) in the flash zone during flashing is
maintained at or below 60.degree. and, advantageously, below
55.degree. C. For this reason, the solvent and flashing aid (if
employed) selected should have a combined vapor pressure at
60.degree. C. which is at least 600 mm Hg, or higher.
Correspondingly, the pressure in the flash zone at and following
the location of introduction of the processing water should be
maintained at least as low as the combined vapor pressure at or
below 60.degree. C of the solvent and any flashing aid employed.
For convenience, reference may be made to easily available vapor
pressure tables for solvents and flashing aids to make appropriate
selection of solvents and flash zone pressures in accordance with
the foregoing.
While utilizing the foregoing flashing conditions to produce a
solvent boiling point in the flash zone at or below 60.degree. C.,
dilution water may be introduced into the flash zone at a
temperature which is (a) below 70.degree. C. and advantageously
within the range of 10.degree. and 60.degree. C., and (b) at or
above the condensation point of the vapor in the flash zone. It is
desirable, particulary in a large scale operation, for the dilution
water to be at a temperature at least 5.degree. and preferably
between 10.degree. and 20.degree. C. higher than the boiling point
of the solvent in the flash zone as a safety factor to prevent any
solvent condensation by the dilution water. The dilution water
forms an aqueous mixture with the noodle in the flash zone and this
mixture is then refined. Advantageously, at least the initial part
of this refining is carried out while the mixture is still in
direct flow communication with the flash zone and subjected to the
pressure condition of the flash zone. That is to say, the initial
refining is preferably conducted in a continuous fashion while the
aqueous mixture is subjected to the ambient pressure of the flash
zone (between 50 and 600 mm Hg) and immediately following such
refining.
Desirably, the dilution water added to the flash noodle in the
flash zone is at a temperature and in sufficient quantity so that
the aqueous mixture assumes a temperature below 70.degree. C. and
preferably between 10.degree. C. and 60.degree. C. In the case
where the noodle has a temperature prior to dilution which is
70.degree. C. or above, it is desirable to add dilution water at a
temperature below 70.degree. C. in a quantity sufficient to create
a temperature below 70.degree. C. in the aqueous mixture formed
therewith.
The total dilution water added is desirably sufficient to provide
an appropriate aqueous mixture or slurry for refining of the
flashed product. Typically, an aqueous mixture with a consistency
of 1 to 10%, or higher, by weight of the flashed product may be
formed for refining. Preferably, refining is conducted in a disc or
conical refiner and is, preferably, conducted in a fashion to place
the fibers in a form optimumly suitable for paper making. The
refining of the fibrous noodle separates discrete fibers and also
may be used to control the length of the fibers. Preferably,
refining is carried out in two or more stages with multiple passes
through the refiner in the latter stages. It may be desirable in
the latter stages of refining to conduct such refining outside the
flash zone. That is to say, the latter stages of refining may,
preferably, be conducted under atmospheric pressure.
Importantly, this refining is carried out at a temperature below
70.degree. C. and preferably between 10.degree. C. and 60.degree.
C., which has been found to cause an unexpected degree of
fibrillation or fiber development, particularly when conducted in
the presence of a dispersing agent such as polyvinyl alcohol,
thereby greatly enhancing the strength of the fibers for paper
making use.
The foregoing flashed noodle processing procedure provides a unique
and industrially practical mode of continuously producing a flashed
noodle and refining same at a temperature below 70.degree. C.
Establishing a vapor condensation point in the flash zone of
60.degree. C., or below, makes possible the addition of dilution
water in the flash zone at a temperature below 70.degree. C. If the
vapor condensation point were appreciably above 60.degree. C.,
addition of dilution water at these temperatures would cause
condensation of solvent on the flashed product resulting in
unacceptable agglomeration or flocculation of the fibers.
Additionally, by selecting a dilution water temperature and amount
which will lower the aqueous mixture to be refined to a temperature
below 70.degree. C., refining may be accomplished at the desired
temperatures on a practical, continuous basis even in the case
where the flashed noodle has a temperature of 70.degree. C., or
higher. Becuase of the difficulty of cooling the noodle, which has
low heat conductivity, to the desired refining temperature, other
than by use of dilution water and because of the difficulty of
extracting the semisolid flashed product (which tends to float in
water) from the reduced pressure flash zone other than in the form
of an aqueous, at least partially refined, slurry, the foregoing
procedures are particularly suitable for a practical continuous
operation. This procedure has additional advantages in that by
conducting at least the initial refining under ambient pressure of
50-600 mm Hg, removal of residual minor amounts of solvent, which
may be entrapped in the flashed noodle and cause fiber
flocculation, is facilitated.
As mentioned previously, a principal advantage of the process of
this invention is the ability to improve the properties of the
fibers produced as compared to those produced by conventional
techniques. In this respect, one indication of the improvement of
the fibers made by the process of the present invention is the
drainage factor of such fibers as compared to fibers of similar
clasified fiber length which are made using parameters outside the
present invention. The drainage factor is a measure of the drainage
characteristics of a fiber when a slurry thereof is placed on a
foraminous surface. For synthetic fibers of similar fiber length
made by the flashing process, important strength properties thereof
correlate generally with their drainage factor. For a fiber pulp
having the same classified fiber length, various strength
properties of paper made therefrom increase with the drainage
factor of such fibers.
Another indication of improvement of the fibers made in accordance
with this invention is their slenderness relative to fibers
prepared by typical conventional technique. It is desirable to
produce fibers which are relatively thin (or of low coarseness) as
these fibers will impart higher opacity, density and better
formation to the paper prepared therefrom.
Generally, the set of operating parameters of the present invention
will result in improved fiber properties such as thinness and
drainage factor compared with fibers prepared using typical
conventional parameters. Because other process variables in
addition to the specific parameters of this invention also
influence fiber properties (e.g., flash nozzle size and
configuration, polymer type and molecular weight, solvent, flashing
aids, dispersants, etc.), such resulting fiber comparisons are
appropriately made with the other process variables held
constant.
For the same reason, i.e., the influence of other process
conditions besides the parameters specific to this invention on the
resulting fiber properties, no absolute fiber property values can
be assigned to the fibers which may be prepared by the process of
this invention. However, with appropriate selection of all
parameters, it has been found that pulps can be produced in
accordance with this invention which have a drainage factor in
excess of 1 and as high as 50 to 100 seconds per gram and which
have an average coarseness below 15 decidrex (as measured by TAPPI
Test 234 SU 67) and frequently between 1 and 10 decidrex (m/100 m).
For paper making use, a drainage factor between 2 and 10 may be the
preferred range as an appropriate balance between increased
strength and ease of water removal from the fibers. Higher drainage
factors can be obtained and may be useful where the enhanced
strength is more important than rapid water removal.
In the accompanying drawing, the
FIG. 1 represents a schematic representation of apparatus suitable
for use in carrying out the process of this invention, and
FIG. 2 is a detailed representation of the flash nozzle
schematically shown in FIG. 1.
In FIG. 1, 1 is a steam jacketed vessel, provided with an agitator
1a, which may be charged with solvent, polymer (or polymer
solution) and, if desired, flashing aids such as water. Conduit 2
is provided at the bottom of vessel 1 in communication with flash
nozzle 3 through shut-off valve 2a (a ball valve). As seen in FIG.
2, flash nozzle 3 is a circular orifice of substantially smaller
diameter than conduit 2. After the mixture is heated to the desired
temperature and agitated, if necessary, to dissolve the polymer
and/or disperse the flashing aids, valve 2a is opened and the
mixture thus formed is forwarded from vessel 1 to flashing nozzle 3
under autogenous pressure of the heated mixture. As the mixture
discharges from vessel 1, nitrogen or other inert gas may be
introduced into the head space thereof through line 4 in order to
maintain the pressure in the vessel at autogenous or higher
pressure. The mixture flashed through nozzle 3 into the flash zone
which is comprised of a separation vessel, cyclone 6, and
connecting conduit 5. Conduit 5 is a pipe having an internal
cross-sectional area larger than that of flash nozzle 3 and of
sufficient internal diamter to permit rapid, unrestricted passage
of the flashed noodle to cyclone 6, preferably having an internal
cross-sectional area many times larger than that of the nozzle
3.
Vaporized solvent and water leaving cyclone 6 pass through line 7
to scrubbing tower 8 in which water and any entrained polymer is
removed from the vapor stream. The solvent vapor leaving scrubbing
tower 8 passes to condenser 10 through condenser conduit 9, where
such vapor is condensed, and passes via conduit 11 to solvent
collection tank 12.
In order to provide reduced pressure throughout the system
downstream of nozzle 3, a vacuum generating device, steam ejector
14, is connected by conduit 15 to solvent collection tank 12. It
will be appreciated that there will be a pressure gradient between
the flash nozzle 3 and cyclone 6 due to the constricting effect of
conduit 5. Therefore, the vacuum generated by ejector 14 should be
adjusted so that the pressure condition in conduit 5 in the
vicinity of nozzle 3 is below 600 mm Hg.
The flashed fibrous noodle entering cyclone 6 through conduit 5,
together with the unvaporized portion of water or other flashing
aid present, passes downward through conduit 16 into disc refiner
17 where it is refined. Conduit 18 is provided in cyclone 6 for
introduction of nitrogen prior to start-up and to maintain an
oxygen-free atmosphere therein during operation. Nitrogen may also
be introduced during operation for the same purpose and also to
assist in regulating the pressure condition in the flash zone.
Conduit 19 is provided for introduction of water at an appropriate
low temperature to form a mixture of slurry with the fibrous
material having an appropriate consistency for disc refining.
The refined material leaving the refiner passes through conduit 20
to first receiving tank 21. To provide reduced pressure in
receiving tank 21 (and disc refiner 17) conduit 22 connects
receiving tank 21 with condenser conduit 9. Maintenance of the
reduced pressure throughout the refining operation in this manner
promotes removal from the flashed product any small residual amount
of solvent which may remain therein. It is thus seen that this
refining stage is in direct pressure communication with and a part
of the flash zone.
The water slurry of refined fibers may be withdrawn from receiving
tank 21 through line 23 utilizing pump 24, for a second refining
step in disc refiner 25 under atmospheric pressure conditions. The
fibrous slurry leaving refiner 25 passes through conduit 26 to
second receiving tank 27, which is maintained at atmospheric
pressure, where it is collected prior to further processing for
shipment or for paper making use. If desired, the fibrous slurry
leaving refiner 25 may be recycled through line 28 for one or more
additional passes through refiner 25.
The fibers after refining may be diluted to a suitable consistency
and made into synthetic paper webs either alone or blended with
normal cellulose paper making fibers. Alternatively, the fibers can
be dewatered, pressed into bales, stored and shipped to the
ultimate user.
The illustrated apparatus may be operated on a batch basis as
described or on a continuous basis by continuously feeding vessel 1
with polymer solution and any flashing aids desired as flow rates
to maintain the appropriate mixture in the vessel for flashing,
while heating the vessel to maintain the mixture at the appropriate
flash temperature. In order to insure uniform dispersion of
flashing aids, it may be desirable to place an inline mixing device
in line 2 between vessel 1 and flash nozzle 3.
Optionally, instead of using a stirred heated vessel such as vessel
1, it is also possible to prepare the mixture on a continuous basis
by blending a polymer solution with any flashing aids desired (as
by adding superheated water) continuously in an in-line mixing
device just prior to flashing through the nozzle. It is also
possible to utilize an in-line mixer.
An adiabatic operation has been described but for non-adiabatic
operation low pressure steam or water at 100.degree. C. may be
injected into conduit 5 immediately downstream of nozzle 3 through
a tee connection therein (not shown) in an appropriate amount to
add heat to the flashing mixture consistent with the prescribed
parameters of operation of the invention.
The following examples will illustrate the invention:
EXAMPLE 1
The apparatus employed in this example is that illustrated in the
drawing previously described, except that scrubbing tower 8 was
omitted. The dissolution vessel was a 250 liter, stainless steel,
baffled tank having a centrally disposed three h.p. rotating
stirrer having three blade back-swept impellers located therein,
each impeller being 50 cm. long. This stirrer was operated
throughout the run.
The vessel was charged with 9.6 kg of high density polyethylene
having an intrinsic viscosity of 1.4 dl/gm and a melt index of 5.58
(Mitsui 2,200 P) and 120 liters of water containing polyvinyl
alcohol (grade NL-05 from Nippon Gosei Chemical Industries,
viscosity 4.6-6 centipoise measured at 4% in water at 20.degree. C.
and having a degree of saponification of 98.5-100 mol.%) in the
amount of 3% by weight based on the polymer in the vessel. Then 120
liters of n-hexane were added and the vessel was sealed and heated
to 150.degree. C. and held with stirring for 2-3 hours to dissolve
the polyethylene and to form a dispersion of the polymer solution,
with the water assuming the continuous phase.
The water-to-hexane ratio in the mixture was 1:1 by volume and the
polyethylene concentration was 80 gm per liter of hexane. With the
mixture heated to 150.degree. C. and a pressure in the vessel of
175 p.s.i. the valve 2a at the bottom of the vessel was opened and
the mixture was flashed through nozzle 3 into conduit 5 (which has
an internal diameter of one inch and a length of ten meters) and
conveyed to cyclone 6. The flash nozzle consisted of a circular
orifice having an internal diameter of 3 mm and a length of 20 mm.
The mixture flowed through the nozzle at the rate of 10.4 kg of
polyethylene per hour. Steam ejector 14 was activated to provide a
flash zone pressure of 350 mm Hg measured immediately downstream of
flash nozzle 3. In cyclone 6 the pressure was about 200 mm Hg and
the condensation point of the vapor was about 27.degree. C. The
temperature of the flashed noodle in conduit 5 at the point where
substantially all of the solvent was vaporized was estimated to be
about 63.degree. C. Dilution water at 50.degree. C. was introduced
through line 19 at a rate to provide a consistency of between 1 and
5 gm of polyethylene per liter of water. The mixture of water and
fibrous noodle, at a temperature of 50.degree. C., was continuously
fed to refiner 17, a 12 in. diameter single disc refiner
manufactured by Kumagaya Riki Kogyo, for a single pass at a plate
clearance of 150 microns.
The plates of the refiner had brushing-type tackle consisting of
one-sixth inch wide, 1 to 2 inch long bars separated by
one-sixteenth inch wide, three-sixteenth inch deep grooves, the
grooves being offset about 10.degree. from the radial direction,
with no dams. The ambient pressure in refiner 17 and receiving tank
21 was about 300 mm Hg. The resulting slurry in receiving tank 21
was pumped into refiner 25 for a second stage of refining at
atmospheric pressure for a total of seven passes at a consistency
adjusted to 5.9 gm polyethylene per liter of water, and at the same
temperature and plate clearance and with the same type of refiner
plates as in refiner 17. The plate clearance of refiner 25 was then
adjusted to 80 microns and the slurry recycled therethrough for an
additional 8.5 (average) passes.
The resulting fibers had a classified fiber length of 1.35 mm and a
fiber fractionation, when tested according to TAPPI Standard
T233su64, as shown in Table I.
TABLE I ______________________________________ Mesh Weight %
______________________________________ On 20 17.70 On 35 38.96 On
65 23.50 On 150 13.70 Through 150 6.10
______________________________________
The fibers had a drainage factor (D.F.) of 15.59 sec/gram. From
microscopic examination the fibers were seen to be desirably thin
and there were few undesirable filmy fibers and chunks of
polymer.
Handsheets were prepared from the fibers and tested with the
results shown in Table II. These handsheets and those in subsequent
examples were prepared in accordance with TAPPI Standard T-205m-58
with modified web pressing (400 p.s.i.) and a heat-bonding step
(121.degree. C. at minimum pressure).
TABLE II ______________________________________ Density 0.380
Breaking length 1.53 Stretch (%) 18.9 Zero span (Km) 2.10 Tear
strength (gm/sheet) 92 Porosity (Gurley secs) 180
______________________________________
In the foregoing example and subsequent examples, the density,
stretch and breaking length were determined by TAPPI Standard
T-220, tear strength by TAPPI Standard T-414 and zero span by TAPPI
Standard T-231. Porosity is reported in Gurley seconds.
The drainage factor in this and following examples was determined
substantially in accordance with TAPPI Test T221 OS-63 with a
slight modification in the method of calculation. Briefly,
approximately 10 grams of a fiber sample is weighed and dispersed
in water. The slurry is then added to the standard sheet mold and
water added to the mark. The slurry is stirred by four up-and-down
strokes of the standard stirrer, which is then removed. The water
temperature in the mold is measured and the drainage valve opened.
The time between the opening of the valve and the first sound of
suction is noted. The procedure is repeated with water only (no
fiber) in the sheet mold and the temperature and drainage time
noted. The drainage factor in seconds per gram is then calculated
as follows: ##EQU3## where DF = drainage factor, seconds/gram
D = drainage time with pulp in mold, seconds
d = drainage time without pulp in mold, seconds
V.sub.t = viscosity of water at temperature T
W = weight of fibers employed in test, grams
The quantity 1/V.sub.T - 1 is tabulated in the aforementioned TAPPI
Test T221 OS-63. This quantity is multiplied by 0.3 which has been
empirically determined for the present fibers.
EXAMPLE 2
To compare the effect of utilizing flash zone pressure of 600 mm Hg
the procedure described in Example 1 was repeated employing
identical apparatus, materials, concentrations and conditions,
except that the pressure in the flash zone was held at
approximately 600 mm Hg in the vicinity of the flash nozzle and 420
mm Hg in the cyclone. The resulting flash noodle temperature at the
point of substantially complete solvent vaporization was estimated
to be about 73.degree. C. The condensation point of the vapor in
the cyclone was about 46.degree. C., and the dilution water was
added at approximately 62.degree. C.
The flashed product was refined to produce a fibrous product with
fiber length characteristics substantially equivalent to those of
the product of Example 1. Specifically, following dilution with
water at 60.degree. C. to a consistency of between 1 to 5
gms/liter, the fibrous material was refined for one pass to refiner
17 with a plate clearance of 100 microns and of a temperature of
62.degree. C. and then with 10 passes through refiner 25 at a plate
clearance of 100 microns, at an average temperature of 60.degree.
C. and consistency of 8 vicinity complete
The resulting fiber had a classified fiber length of 1.33 mm and a
fiber fraction distribution as shown in Table III.
TABLE III ______________________________________ Mesh Weight %
______________________________________ On 20 16.57 On 35 39.29 On
65 24.80 On 150 13.10 Through 150 6.25
______________________________________
The fibers had a drainage factor of 6.85 sec/gm.
Handsheets were prepared and tested with the result shown in Table
IV.
TABLE IV ______________________________________ Density 0.366
Breaking length 1.12 Stretch (%) 14.6 Zero span 1.69 Tear strength
67 Porosity 110 ______________________________________
Comparison of the above results with Example 1 shows that the
drainage factor in this example is less than that for the product
in Example 1 and strength properties of the handsheets show a
similar decline. This example by way of comparison, illustrates the
advantages of more preferred range of 50-500 mm Hg pressure in the
flash zone.
EXAMPLE 3
The example which follows illustrates practice of the invention
with a flashing system employing water as a flashing aid and
wherein the water assumes the discontinuous phase. The same
materials, concentrations and flashing conditions were used as
described in Example 1, except as follows:
a. At start-up the dissolution vessel was charged by first adding
polymer solution followed by the PVA-containing water in order to
establish the water as the discontinuous phase;
b. The flashed noodle was adjusted to a slightly higher consistency
(6.7 gm/liter) prior to secondary refining.
The resulting fibers had a classified fiber length of 1.14 and a
fiber fractionation as shown in Table V.
TABLE V ______________________________________ Mesh Weight %
______________________________________ On 20 4.77 On 35 41.37 On 65
30.40 On 150 16.21 Through 150 7.31
______________________________________
The fibers had a drainage factor of 16.5 sec/gm. Handsheets
prepared from these fibers had the properties shown in Table
VI.
TABLE VI ______________________________________ Density 0.399
Breaking length (Km) 1.54 Stretch (%) 21.1 Zero span (Km) 2.05 Tear
strength (gm/sheet) 75 Porosity 170
______________________________________
EXAMPLE 4
To demonstrate the beneficial effects of the invention in
decreasing the degree of entanglement of the flashed fiber product,
the flashing procedures of Example 2 were repeated in a series of
three runs utilizing in each case the same flashing conditions,
concentrations, and materials, except for the pressure conditions
maintained in the flash zone. In each of these runs samples of the
flashed fibrous product were taken from cyclone 6 in the unrefined
state and these samples were tested as will be described. In run 1,
the flash zone was maintained at 360 mm Hg; in run 2, at 500 mm Hg;
and in run 3, for comparison, at 760 mm Hg.
Another series of three runs were made following the flashing
conditions, concentrations and materials of Example 3 but with the
flash zone maintained at 360 mm Hg for run 4, 500 mm Hg for run 5,
and at 760 mm Hg, for comparison, in run 6. In these three runs the
flashing nozzle was of the same length as that used in Example 3
but its internal diameter was 2 mm. Unrefined samples of the
flashed product were collected and tested as follows.
The fiber samples thus prepared were subjected to a screening test
to determine the percentage by weight of the sample which will pass
through a ten-mesh screen. The results were as shown in Table VII.
The screening test was made in accordance with TAPPI standard
T-233SC 64 except that only a 10 mesh screen was employed.
TABLE VII ______________________________________ % of Product Flash
Zone Passing Through Run No. (Pressure (mm Hg) 10-mesh Screen
______________________________________ 1 360 29.9 2 500 25.6 3
(comparison) 760 22.3 4 360 15.3 5 500 3.4 6 (comparison) 760 3.2
______________________________________
It can be seen that the percentage of fibers able to pass through a
10-mesh screen is markedly greater for the runs made in accordance
with this invention (runs 1, 2, 4 and 5). This demonstrates that by
utilizing the interrelated parameters of this invention the degree
of entanglement of the flashed fibrous product can be materially
decreased.
EXAMPLE 5
The procedure of Example 3 was repeated utilizing a higher
molecular weight polyethylene as the polymer, specifically Mitsui
Petrochemical Co grade 7000P which has a melt flow index of 0.04.
In this run the amount of polyethylene was adjusted to provide a
concentration of the polyethylene in the solvent in the dissolution
tank of 35 gm per liter. All the other conditions of flashing were
the same as in Example 3 except that the flash zone pressure in the
vicinity of the nozzle was held at 360 mm Hg. The flashed product
was refined at 50.degree. C at a slurry concentration of 1.1 gm per
liter as in Example 3 to a classified fiber length of 1.40 mm. The
resulting fibers had a drainage factor of 40.7 sec/gm. Handsheets
made therefrom had the properties listed in Table VIII.
TABLE VIII ______________________________________ Density 0.396
Breaking length 1.31 Stretch 12.9 Zero span 2.26 Tear strength 115
Opacity (%) 96.3 G.E. Brightness 96.9
______________________________________
EXAMPLE 6
The procedures of Example 1 were repeated utilizing polypropylene
as the polymer, specifically a polypropylene having an intrinsic
viscosity of 1.90 centipoise, melt flow index of 14.5 gm/minute and
an isotacticity index of 94.7%. The amount of polypropylene added
to the dissolution vessel was adjusted to give a polymer
concentration in the hexane of 100 gm per liter. The volume ratio
of solvent to water was 1:1. The polyvinyl alcohol (added in an
amount equal to 3% of the weight of the polypropylene) had a degree
saponification of 95-100 ml percent and a viscosity (4% in water at
20.degree.C) of 25-29 c.p. Also added with the water, as a heat
stabilizer for the polypropylene, was 3,5 -ditertiary butyl -4-
hydroxytoluene in an amount equal to 0.2% of the polypropylene.
This mixture was heated to a temperature of approximately
140.degree.C and flashed to a flash nozzle which was a circular
orifice 5 mm in diameter and 1000 mm long into the flash zone which
was maintained at approximately 400 mm Hg pressure in conduit 5 in
the vicinity of the flash zone and at approximately 240 mm Hg in
cyclone 6. The vapor condensation point in cyclone 6 was
approximately 32.degree.C. Dilution water was added to the flashed
product in cyclone 6 at a temperature of 44.degree.C to provide a
consistency of between 1 and 5 gm per liter and this mixture was
refined by a single pass at 44.degree.C in refiner 17 utilizing
cutting type refining plates (plates having more widely spaced,
higher tackle than the brushing type plate) with a plate spacing of
100 microns. The mixture was then allowed to settle in receiving
tank 21 and the dilution water drawn off. Then lower temperature
water was added to bring the temperature of the slurry to
22.degree.C and the consistency thereof to 4.0 gm per liter. This
mixture was refined in refiner 25 using the brushing type plates of
Example 1 for two passes at a zero plate clearance and at a
temperature between 22.degree. and 30.degree.C and then for nine
passes at a plate clearance of 50 .mu. and at a temperature of
approximately 30.degree.C.
The resulting fibers had a classified fiber length of 1.66 sec/gm
and a drainage factor of 1.66.
Handsheets made from the fibrous product had the properties listed
in Table IX.
TABLE IX ______________________________________ Density 0.264
Breaking length 0.24 Stretch 2.8 Zero span 0.62 Tear strength 10
Opacity (%) 96.8 G.E. Brightness 90.8 Porosity (Gurley sec) 9
______________________________________
When it was attempted to produce polypropylene fibers under similar
conditions but utilizing flash zone pressures of 760 mm Hg and
above, the result was the formation of an endless unfibrilated
noodle or weak powder like fibers.
EXAMPLES 7 - 11
A series of four runs were carried out on a continuous basis in
equipment as described in Example 1.
During each run the dissolution vessel was continuously charged
with an n-hexane solution of high density polyethylene at
150.degree.C having a concentration of 59 gm of polyethylene per
liter of hexane. The polyethylene had a melt flow index of 5.5. An
equal amount of polyvinyl alcohol - containing water at
150.degree.C was also continuously metered into the vessel during
the run to provide a mixture in the vessel having a water to hexane
ratio by volume 1:1. The polyvinyl alcohol (grade AL-04 having a
degree of polymerization of 450-460, viscosity of approximately 4
centipoise measured at 4% in water at 20.degree.C and a degree of
saponification of 95-97 mol.%) was metered into the vessel with the
water to provide the desired percentage thereof to the weight of
the polymer supplied to the vessel.
At start up for each run, the dissolution vessel was initially
charged by first intorducing the polymer solution followed by
addition of the PVA - containing water, in order to establish a
dispersion with the polymer solution assuming the continuous phase.
When the vessel was fully charged and the mixture well dispersed at
a temperature of 150.degree.C, the valve at the bottom of the
vessel was opened and the mixture continuously fed to flash nozzle
3.
Flash nozzle 3 was an angle valve (Yamatake Honeywell Model No.
1010) which had internal dimensions as follows: Valve seat section
8mm in diameter and 10mm in length with a "V" cut shaped valve body
adapted to nest in the valve seat. During flashing the valve is
partially opened and adjusted for the desired rate of flow.
Conduit 5 had an internal diameter of 21 mm and a length of about
10 meters.
The flashed product in each run was refined in refiner 17 utilizing
the refining plates described in Example 1 and in refiner 25
utilizing similar brushing type plates but which had a minor number
of more widely spaced deeper cutting type tackle. In Example 10,
additional PVA was added to the flashed product. After primary
refining in refiner 17, the material was permitted to settle in
receiving tank 21 and dilution water drawn off. Then additional
dilution water was added prior to secondary refining in refiner 25,
in order to adjust the temperature and consistency as indicated.
The other flashing conditions and refining conditions and the
properties of the resulting products are shown in Table X.
TABLE X
__________________________________________________________________________
Flash Conditions Example : 7 8 9 10 11
__________________________________________________________________________
PVA in flash mixture (% by weight of polymer) 1.5 1.5 3 1.5 1.5
Flash zone pressure in proximity of flash nozzle (mm Hg) 590 560
585 560 570 Flash zone in cyclone (mm Hg) 320 320 360 350 310 Vapor
condensation point in cyclone (.degree.C) 39 39 42 41 38
Temperature of dilution water added in cyclone (.degree.C) 50 50 70
50 50 PVA added with dilution water (% by weight of polymer) 0 0 0
1.0 0 Calculated temp. of flashed product 1 m. from nozzle
(.degree.C) 73 72 73 73 72 Primary Refining Temperature (.degree.C)
50 50 70 50 50 Plate clearance (microns) 50 50 5 200 200 Passes 2.8
4 4 4 4 Consistency (gm/L) 5 5 5 5 5 Secondary Refining Temperature
(.degree.C) 46 46 62 48 44 Plate Clearance (microns) 50 50 50 100
100 Passes 6.8 8 10 10 8 Consistency (gm/L) 3.7 3.3 3.7 3.7 3.7
Product Characteristics Classified fiber length 1.15 1.15 0.99 1.39
1.30 Drainage factor (gm/sec) 3.0 3.0 6.1 4.6 3.1 Handsheet
Properties Density (gm/cc) 0.411 0.413 0.434 0.413 0.410 Tear
strength (gm/sheet) 18 25 30 34 23 Breaking length 0.75 0.84 1.30
1.01 0.74 Stretch (%) 2.2 2.7 5.7 4.1 2.9 TEA (%) 0.006 0.009 0.036
0.019 0.009 Internal Bond C Range (Scott units) 43 55 70 68 40
Brightness (%) 95.2 94.8 91.6 87.4 91.7 Opacity (%) 96.9 96.4 96.9
97.2 97.5
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As a comparison, fibers having a classified fiber length of 0.89 mm
prepared from 5.5 melt index polyethylene under essentially the
same conditions of flashing and refining, except that the flash
zone pressure was between 840-760 mm Hg and the dilution water
temperature and temperature of refining was approximately
80.degree.C., had a drainage factor of only 1.0 gm/sec, tear
strength of 10 gm/sheet and breaking length of 0.38 km.
To evaluate the fibers of the foregoing example with respect to the
amount of gels and chunks of polymer therein, samples were taken
from the fibers of Example 9, 10 and 11 and each was mixed with
bleached kraft hardwood fiber to form a mixture of 60% by weight
wood fiber and 40% polyethylene fiber. Handsheets were made of each
sample in the manner previously described and these handsheets were
subjected to calendering with linear pressures from 14 to 31.5
kg/gm. The handsheets were visually inspected for transparent spots
resulting from gels and chunks. In comparison with similar
handsheets made from the comparison fibers described above, these
handsheets had a much lower number of tansparent spots.
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