Plastic and nonmetallic article shaping or treating: processes – Forming continuous or indefinite length work – Shaping by extrusion
Reexamination Certificate
1999-12-03
2002-09-24
Eashoo, Mark (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Forming continuous or indefinite length work
Shaping by extrusion
C264S211210, C264S331180, C264S331210
Reexamination Certificate
active
06454983
ABSTRACT:
FIELD OF THE INVENTION
This invention is concerned with compositions and masterbatches of selected antistatic agents in polymers, preferably certain copolyesters based on terephthalic acid, naphthalenedicarboxylic acid, and/or 1,4-cyclohexanedicarboxylic acid and on the blending of these masterbatches with the same or other homo- or copolyesters to provide films, sheeting, and thermoformed articles having antistatic properties. Specifically, antistat additives for polymers, preferably certain copolyesters are disclosed which provide the required antistat performance in the final film, sheet, or molded article. However, these additives cause feeding problems during single screw extrusion processing for some polymers, including the preferred copolyester compositions, e.g., Eastar PETG 6763. It has now been found that certain extrusion processing conditions result in improved processing and therefore allow these antistat additives to be used.
BACKGROUND OF THE INVENTION
Polyesters are widely used as extrusion and injection molding resins for applications such as fibers, films, sheeting, food and beverage containers and the like. Commonly used polyesters include polyethylene terephthalate (PET), poly-1,4-butylene terephthalate (PBT), and poly-1,4-cyclohexanedimethylene terephthalate (PCT). Copolyesters are frequently used when special properties such as lower processing temperatures, clarity, or inhibited crystallization are needed. Polyesters like most other synthetic polymers are poor conductors of electricity. Thus, during extrusion, processing, or handling of such polymers, static charges may accumulate. This is especially true under conditions of low relative humidity. Static charge is highly undesirable in that it can cause material handling problems during processing, lead to shocks when molded parts are handled, lead to the collection of dust on packages, and cause damage to sensitive electronic parts that are stored in plastic packaging due to dissipation of static charge. Therefore, it would be advantageous if thermoplastic polyesters could be provided which had good antistatic properties.
There are many antistat additives available for use in thermoplastic polymers including polyesters. Often these additives are blended with the same or other thermoplastic polymer in higher concentration to form a masterbatch that is subsequently let down for film or sheet extrusion or injection molding. Some antistat additives can cause processing problems such as poor feeding during extrusion that can prohibit their use.
SUMMARY OF THE INVENTION
In accordance with this invention, antistat additives for polymers, preferably polyesters and copolyesters are disclosed which provide the required antistat performance in the final film, sheet, or molded article. However, these additives do cause pellet conveying problems in the extruder feed zone during single screw extrusion processing, such as poor feeding, for some polymers, including preferred copolyester compositions, e.g. Eastar PETG 6763. The antistatic agent is present in an amount of greater than 0.5 weight percent to about 10 weight percent based on the final composition. It has now been found unexpectedly that the control of certain extrusion processing conditions results in improved processing and therefore, allows these antistat additives to be used in the polymers. More particularly, it has been found that the temperature of the feed zone during the single screw extrusion process must be maintained at no greater than 385° F. Preferably the temperature of the feed zone should be maintained within a range of about 200° F. to no greater than 385° F.; more preferably the temperature should be maintained within a range of about 300° F. to about 365° F.; and still more preferably within a range of about 340° F. to about 365° F.
DETAILED DESCRIPTION OF THE INVENTION
The novel extrusion process of the present invention involves a conventional single screw extrusion process having a feed zone, a compression zone, a metering zone, and a zone in which material is passed to a die. The temperatures in all zones are maintained in the conventional range of about 392° F. to about 572° F., except for the temperature in the feeding zone. In the feeding zone it has been found essential to maintain the temperature at no greater than 385° F. in order that the antistat-containing polymer composition or masterbatch may be processed. Preferably the temperature of the feed zone should be maintained within a range of about 200° F. to no greater than 385° F.; more preferably the temperature should be maintained within a range of about 300° F. to about 365° F.; and still more preferably within a range of about 340° F. to about 365° F. As indicated, the antistatic agent is present in amounts of from greater than 0.5 weight percent to about 10 weight percent, based on the final composition, preferably from about 3 to about 7 weight percent, and still more preferably in amounts ranging from about 0.6 to about 1.5 weight percent.
The process of the present invention is suitable for use with any composition or masterbatch of a polymer and the antistatic agent. Suitable for use herein are any polymers such as polyesters, copolyesters, polyolefins, styrene resins such as polystryene, styrene-acrylonitrile copolymers, poly (styrene-acrylonitrile-butadiene) terpolymers, high impact polystyrene, poly (methylacrylate), poly (methylmethacrylate) and poly (vinyl acetate), polycarbonates, polyamides, polyacetals, phenol-formaldehyde resins, vinyl resins, polyvinyl chloride, copolymers of vinyl chloride with vinyl acetate, vinylidene chloride, acrylonitrile, polyurethanes, poly (phenylene ether) and the like.
Preferred for use herein are polyesters and copolyesters and mixtures thereof. Preferred polyesters nonexclusively include linear, thermoplastic, crystalline, or amorphous polyesters produced by conventional polymerization techniques from one or more diol(s) with one or more dicarboxylic acids.
Copolyesters by definition comprise one or more diol(s) with two or more dicarboxylic acids, or one or more dicarboxylic acid(s) with two or more diols. Exemplary diol components of the described polyesters and copolyesters may be selected from ethylene glycol, neopentyl glycol, 1,4-cyclohexanedimethanol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, 1,2-cyclohexanediol, 1,4-cyclohexanediol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, Z,8-bis(hydroxymethyl)-tricyclo-[5.2.1.0]-decane wherein Z represents 3, 4, or 5; and diols containing one or more oxygen atoms in the chain, e.g. diethylene glycol, triethylene glycol, dipropylene glycol, tripropylene glycol, and the like. In general, these diols contain 2 to 18, preferably 2 to 8 carbon atoms. Cycloaliphatic diols can be employed in their cis or trans configuration or as mixtures of both forms.
Exemplary acid components (aliphatic, alicyclic, or aromatic dicarboxylic acids) of the linear copolyester are selected, for example, from terephthalic acid, isophthalic acid, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, succinic acid, glutaric acid, adipic acid, sebacic acid, 1,12-dodecanedioic acid, 2,6-naphthalenedicarboxylic acid and the like. In polymer preparation, it is often preferable to use a functional acid derivative thereof such as the dimethyl, diethyl, or dipropyl ester of the dicarboxylic acid. The anhydrides or acid halides of these acids also may be employed where practical. The linear polyesters or copolyesters may be prepared according to polyester of copolyester forming conditions well known in the art. For example, a mixture of one or more dicarboxylic acids, preferably aromatic dicarboxylic acids, or ester forming derivatives thereof, and one or more diols may be heated in the presence of esterification and/or polyesterification catalysts at temperatures in the range of about 150° C. to about 300° C., and pressures of atmospheric to about 0.2 mm Hg. Normally, the dicarboxylic acid(s) or derivative thereof is esterified or transesterified with the dio
Bell Emily Tedrow
Dobbs Harold Eugene
Hanson Scott Arnold
McWilliams Douglas Stephens
Boshears, Esq. Betty J.
Eashoo Mark
Eastman Chemical Company
Graves, Jr. Esq. Bernard J.
LandOfFree
Single screw extrusion of polymers does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Single screw extrusion of polymers, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Single screw extrusion of polymers will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2885657