Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1998-05-11
2001-05-15
Michl, Paul R. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S207000
Reexamination Certificate
active
06232371
ABSTRACT:
FIELD OF INVENTION
The present invention relates generally to the field of thermoplastic polymeric materials containing one or more additives. In preferred exemplary embodiments, the present invention relates to synthetic filament additives (e.g., colorants) and to methods for incorporating such additives in melt flows of filament-forming thermoplastic polymeric materials prior to melt-spinning to form synthetic filaments therefrom.
BACKGROUND AND SUMMARY OF THE INVENTION
The incorporation of additives in so-called “neat” thermoplastic polymeric host materials (that is, polymeric materials containing no additives) so as to achieve desired physical properties is well known. Thus, the art has conventionally incorporated colorants, stabilizers, delusterants, flame retardants, fillers, antimicrobial agents, antistatic agents, optical brighteners, extenders, processing aids and other functional additives into polymeric host materials in an effort to “engineer” desired properties of the resulting additive-containing polymeric host material. Such additives are typically added any time prior to shaping of the polymeric material, for example, by spinning or molding (e.g., extrusion, injection, or blow-molding) operations.
The incorporation of colorant additives in filaments formed by melt-spinning a polymeric material has presented unique challenges. For example, the amount of particulate pigment dispersed in a concentrate which is added to the polymeric material must be sufficiently high to impart satisfactory color density, but must not be so high as to interrupt the spinning process. One prior proposal for incorporating colorant additives in thermoplastic polymeric materials is disclosed in U.S. Pat. No. 5,236,645 to Frank R. Jones on Aug. 17, 1993 (the entire content of which is expressly incorporated hereinto by reference).
According to the Jones '645 patent, additives are introduced into a thermoplastic melt by feeding at least one additive in an aqueous vehicle containing a dispersant to form an aqueous additive stream to a vented extruder which is extruding a thermoplastic. The aqueous portion of the aqueous additive stream is thereby volatilized within the extruder and is removed therefrom via an extruder vent. As a result, a substantially homogeneous system containing the thermoplastic, dispersant and the additive is obtained which may thereafter be spun into a filament by melt-extrusion through filament-forming orifices in a spinneret associated with a spin pack assembly.
Although the techniques disclosed in the Jones '645 patent are entirely satisfactory, some further improvements to incorporating additives in a melt flow of thermoplastic polymeric materials would be desirable. For example, it would especially be desirable if the additive stream was non-aqueous as this would obviate the need for a vented extruder (i.e., since a volatilized aqueous portion of the additive stream would not then need to escape prior to melt-spinning). Furthermore, it is entirely possible that a non-aqueous additive stream could be introduced physically near or into the spin pack assembly where it can be mixed with a melt flow of the polymeric material immediately upstream of the spinneret orifices (and preferably downstream of the polymer filter section of the spin pack assembly) thereby bypassing the extruder. Such a possibility would then allow additive concentration and/or types to be changed on a continuous basis to produce sequential lengths of melt-spun filaments having desired, but different, properties and/or characteristics. That is, the upstream processing equipment, for example, the extruders and process piping, which supply the polymeric host material to the spin pack assembly would not necessarily need to be shut down for purposes of cleaning. Furthermore, by introducing a non-aqueous additive stream directly into the spin pack assembly, the flushing time would be relatively short thereby allowing, for example, quick color changes to occur from one filament production batch to another. It is towards providing such improvements that the present invention is directed.
Broadly, the present invention is embodied in a nonaqueous additive concentrate system for thermoplastic polymeric host materials which may be added directly to a melt flow of the polymeric material in metered amounts. More specifically, the additive concentrate system according to the present invention includes an additive which is dispersed in a liquid or liquefied nonaqueous carrier. The additive is most preferably in the form of a solid particulate pigment which is coated with a normally solid dispersant. The dispersant is preferably polymeric and substantially soluble in the carrier so as to form a solid pigment phase dispersed throughout a liquid or liquefied carrier phase. The additive concentrate system according to this invention is most preferably in the form of a flowable paste which can be added in metered amounts (dosed) to a melt flow of the polymeric material prior to being spun into filaments, for example near or into the spin pack assembly upstream of the assembly's filament-forming spinneret orifices.
In such a manner, therefore, synthetic filament batches having different additives may be produced sequentially on a continuous basis without costly equipment downtime. That is, the same spin pack assembly may be used to produce a first batch of filaments containing one type of additive during one production interval, and then used to produce a second batch of filaments containing a second type of additive during a succeeding production interval by changing the additive which is introduced into the filament-forming melt. Moreover, the time interval needed to change between different additives is relatively short since the additive system is most preferably introduced into the melt flow near or into the spin pack assembly which in turn reduces significantly the time needed to flush residual additive incorporated into the first batch of filaments. Production of different additive-containing filaments (e.g., filaments containing different colorants) is now possible in a relatively short period of time without stopping filament winding.
Thus, another aspect of this invention involves a method of continuously producing sequential lengths of different additive-containing filaments by continuously supplying a melt-spinnable polymeric host material to orifices of a spinneret and, during a first time interval, controllably dosing a concentrate system having one additive into the polymeric material to form a first polymeric mixture which is extruded through the spinneret orifices. Subsequently, during a second time interval, another concentrate system containing a different additive is controllably dosed into the polymeric material without disrupting the continuous supply of polymeric material to the spinneret orifices to form a second polymeric mixture which is extruded through the spinneret orifices.
During the change of additive concentrate, an intermediate time interval will be needed in order to flush the spinneret of residual amounts of the first additive concentrate. Thus, during the intermediate time intervals, an intermediate length of filaments will be produced which will change over the filament length from containing all of the first additive concentrate to containing all of the second additive concentrate. This intermediate length of filaments produced according to the present invention will be handled separately from the first and second lengths of production filaments. However, the amount of such intermediate length of filaments will be relatively small since, as noted above, the time interval needed to flush the spinneret of residual amounts of the first additive concentrate is relatively short.
Other advantages ensue from introducing the additive concentrate system to the polymeric host material within the spin pack assembly. For example, the spin pack assembly and its associated spinneret orifices may be so designed to form melt-spun multicomponent filaments (e.g., filaments havin
Buchanan Karl H.
Caswell Donald
Gasperson G. Daniel
Helms, Jr. Charles F.
Jones Frank R.
BASF Corporation
Michl Paul R.
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