Agitating – Rubber or heavy plastic working – With specified feed means
Reexamination Certificate
1997-10-30
2001-01-30
Soohoo, Tony G. (Department: 1723)
Agitating
Rubber or heavy plastic working
With specified feed means
C366S082000, C366S150100, C366S320000, C366S325700
Reexamination Certificate
active
06179458
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a process and system for mixing fluids and particularly to mixing fluids that are not readily dissolved together and fluids that have very substantial differences in their relative viscosities.
BACKGROUND OF THE INVENTION
many years, E.I. du Pont de Nemours and Company (DuPont) has been making TYVEK® spunbonded olefin. Commercial end uses for TYVEK® spunbonded olefin sheets have been developed for mailing envelopes, housewrap, apparel, medical packaging and many other uses. The process for making the spunbonded olefin has been the subject of numerous patents including U.S. Pat. No. 3,081,519 to Blades et al., U.S. Pat. No. 3,169,899 to Steuber, U.S. Pat. No. 3,227,794 to Anderson et al., U.S. Pat. No. 3,484,899 to Smith, U.S. Pat. No. 3,497,918 to Pollock et al., U.S. Pat. No. 3,860,369 to Brethauer et al., U.S. 4,352,650 to Marshall, U.S. Pat. No. 4,554,207 to Lee, and U.S. Pat. No. 5,123,983 to Marshall. The basic steps of this process are (1) forming a solution of polyolefin polymer with Freon® 11 spin agent, and (2) flash spinning the solution in a spin cell. Freon® is a registered trademark owned by DuPont. However, Freon® 11 spin agent is a chlorofluorocarbon (CFC) and is believed to be a cause of ozone depletion. The use of most CFC materials are targeted to be eventually banned.
DuPont has sought a substitute spin agent for use in the continued manufacturing of spunbonded olefins. Unfortunately, there is not a readily available spin agent that would be a simple substitute for the Freon® 11 spin agent. Although it has been found that spunbonded olefins may be made using one of a number of different spin agents, each potential alternative spin agent gives rise to numerous production process or product quality issues. Among the alternative spin agents that have been found for making TYVEK® spunbonded olefin are certain hydrocarbons, including pentane. An important issue for hydrocarbon spin agents is their flammability whereas Freon® 11 spin agent is not at all flammable. The issues of flammability and explosivity are substantial when one considers that the spin agents will be subjected to high pressure and high temperature during the flash spinning processes. The solution provided to the spin cell is approximately eighty percent spin agent by weight so the amount of hydrocarbon that may be subjected to the high pressures and temperatures associated with flash spinning is not minimal.
The solutioning system in the process for making spunbonded olefin is the portion of the system that mixes the polymer with the spin agent to form a homogenous solution suitable for spinning into plexifilaments. The solutioning system in current use is generally illustrated in FIG.
1
. As illustrated, the system comprises a very large drum
12
arranged to receive measured amounts of polyethylene pellets and spin agent. The polyethylene pellets are supplied from a hopper
14
and the spin agent is supplied from a tank
15
. The drum
12
is sized to hold the pellets and spin agent for an extended period of time (e.g. hours) and is approximately 5000 gallons. The drum is closed and maintained at approximately room temperature and pressure. The pellets are rapidly stirred by a rotating agitator
19
to form a uniform slurry. The pellets and spin agent are drawn from the drum
12
into a pressure pump
21
which pumps the polymer slurry so as to raise the slurry pressure while directing the slurry through a heat exchanger
22
to raise the slurry temperature. The high pressure, high temperature slurry is then provided to a dissolver tank
23
where the slurry is stirred and mixed by an agitator
24
until the mixture becomes a homogeneous solution suitable for flash spinning in a spin cell, schematically indicated at
25
.
With the conventional solutioning system described above, there had been concern about transient fluctuations in the ratio of spin agent to polymer which may significantly effect the quality and properties of the flash spun product. Thus, there has been considerable effort to blend the solution in the system in a manner that eliminates or substantially reduces such transient fluctuations in the solution. As such, the system provides for large amounts of the solution in both the dissolver tank
23
and the drum
12
at any given time. A plant may spin anywhere from 2000 to 10,000 pounds of polymer per hour and the solution from which this polymer is spun is ordinarily comprised of 75 to 90 percent spin agent by weight. Thus the conventional solutioning process of
FIG. 1
requires that tank
23
hold very large amounts of spin agent at high pressure and temperature for extended periods of time. When the non-flammable spin agent is replaced with a highly flammable spin agent, such a large volume of flammable spin agent at high pressure and temperature would raise serious safety concerns.
Accordingly, a solutioning system for a flash spinning process is needed that reduces or avoids the safety concerns described above.
A solutioning system for mixing the polymer with a solvent to form a spin solution is also needed wherein the overall solutioning system has a reduced volume of spin agent as compared to current and conventional solutioning systems.
SUMMARY OF THE INVENTION
The above and other objects of the invention are achieved by a mixer for mixing at least two fluid materials wherein the two fluid materials have substantially different viscosities. The apparatus includes a generally cylindrical elongate tube forming an outer shell and defined by a longitudinal axis and an inner wall spaced at a generally uniform distance from the axis. A shaft is arranged along the axis with a plurality of flights attached thereto. The flights are arranged to provide substantial shear forces on the polymer and fluid mixture while generally not differentially conveying one of the two phases, which have a viscosity ratio of more than 10,000 to 1, causing transient fluctuations in the ratio of spin agent to polymer.
The objects of the present invention may also be characterized as a solutioning system for mixing a polymer and a spin agent wherein the spin agent and polymer which may be chemically compatible but are not readily miscible. The solutioning system forms a high pressure and temperature spin solution suitable for flash spinning plexifilaments and includes a heating mechanism for melting the polymer and a pressure creating device for raising the pressure of the molten polymer. The system further includes a mechanical mixer having a longitudinal generally cylindrical housing having an inner wall and a shaft mounted for rotation in the housing. The mechanical mixer also includes flights which are arranged on said shaft to provide shear forces on the polymer and spin agent within the chamber while not causing differential conveying of the material in the housing.
Another aspect of the present invention relates to a process for mixing two fluid materials which have low miscibility and a viscosity ratio of at least 10,000 to 1, wherein the process comprises adding the highly viscous fluid to a mechanical mixer, adding a portion of the low viscosity fluid, and agitating the two materials in the mixer in a first mixer section wherein the fluids are not differentially conveyed.
A further aspect of the present invention is a mixing element for a mechanical mixing apparatus suited for being rotated within a generally cylindrical housing. The mixing element includes a mounting shaft and flights extending outwardly from the mounting shaft. The mixing element provides a pressure drop as fluid passes through the cylindrical housing but wherein the pressure drop is substantially the same regardless of the speed at which the mixing element rotates with the cylindrical housing.
REFERENCES:
patent: 1500061 (1924-07-01), Dimm
patent: 3081519 (1963-03-01), Blades et al.
patent: 3160688 (1964-12-01), Aykanian et al.
patent: 3169899 (1965-02-01), Steuber
patent: 3199147 (1965-08-01), Aykanian et al.
patent: 3227794 (1966-01-01), Anderson et al.
patent: 327
Albers Robert E
Etchells Arthur William
Gutmann, Jr. Joseph Daniel
Shah Ashok H.
Slocum Edgar W.
E. I. Du Pont de Nemours and Company
Soohoo Tony G.
LandOfFree
Forming a solution of fluids having low miscibility and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Forming a solution of fluids having low miscibility and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Forming a solution of fluids having low miscibility and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2462079