Plastic and nonmetallic article shaping or treating: processes – Forming continuous or indefinite length work – Shaping by extrusion
Reexamination Certificate
1999-03-18
2001-07-10
Silbaugh, Jan H. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Forming continuous or indefinite length work
Shaping by extrusion
C264S171100, C264S209600, C264S211240, C525S131000
Reexamination Certificate
active
06258310
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a thermoplastic polyurethane product with improved high temperature softening point, hot oil fuel resistance, and improved compression set.
2. Description of the Prior Art
Processes for the continuous production of thermoplastic polyurethanes in double shaft screw extruders with self-cleaning screws by the reaction of relatively high molecular weight polyhydroxyl compounds, polyisocyanates and chain lengthening agents have been disclosed in U.S. Pat. No. 3,963,679. In these processes, the reaction mixture must be mixed vigorously inside the screw extruder with the aid of kneading elements at a stage in which the melt still has a low viscosity (about 20 to 70 Pascals) so as to produce homogeneity in the end product. According to one variation of these processes, aggregates such as thermoplasts may be mixed with the product in the screw extruder during or after the reaction but there is no indication in these publications that the mechanical properties of thermoplasts could be improved.
U.S. Pat. No. 4,261,946, issued to Goyert et al. describes a process for the addition of polyurethane forming components to a molten thermoplastic polymer to form so-called “hard elements” in situ. In this way, Goyert is able to form very rigid and highly elastic materials from inexpensive thermoplastic materials that would otherwise have only moderate hardness and strength. The Goyert reference does not disclose a method for producing a thermoplastic polyurethane material having a high temperature softening point, resistance to thermal attack and similar characteristics which would be useful in numerous applications such as tubes, hoses, cable jacketing, film, sheet or any other extrusion profile form.
SUMMARY OF THE INVENTION
The invention comprises modifying a preformed thermoplastic polyurethane product made from the reaction of a difunctional isocyanate with a polyester or a polyether diol, along with a monomeric, low molecular weight diol as a chain extender. The preformed thermoplastic polyurethane product is then cross-linked by the addition of an isocyanate prepolymer made from the reaction of an excess of a polyisocyanate with a polyester or polyether polyol.
The invention further comprises a process for forming the thermoplastic polyurethane product described above utilizing a single or twin-screw extruder to mix and react the ingredients.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The process of the invention comprises mixing, reacting and forming the finished product, which can be in the form of a tube, hose jacketing, cable jacketing, film, sheet or any other extrusion profile form in one step. Advantageously, the finished product provides improved thermal resistance. Further, the cross-linking that occurs during the extrusion process and forming the finished product is done in one step.
The invention relates to the modification of a preformed thermoplastic polyurethane comprising first introducing a preformed thermoplastic polyurethane into an extruder, preferably a multishaft extruder, most preferably a double shaft screw extruder with self-cleaning screws, at a first inlet, wherein the temperature in the extruder is such that said thermoplastic polyurethane melts. The second step comprises adding to said molten thermoplastic polyurethane through a second inlet, and optionally other inlets, a cross-linking composition comprised of an isocyanate prepolymer.
The isocyanate prepolymer is made from the reaction of an excess of a polyisocyanate with a polyester, a polyether polyol or combinations of the two. Once the thermoplastic polyurethane and the isocyanate prepolymer have reacted, the finished thermoplastic polyurethane product is discharged from the extruder.
Preferably, the isocyanate prepolymer is added in an amount of from about 0.5 to about 15.0% by weight of the preformed thermoplastic polyurethane.
Preferably, the isocyanate prepolymer of the invention comprises a prepolymer having free NCO in the range of from about 10 to about 30% by weight of the prepolymer, more preferably from about 15 to about 25% by weight of the prepolymer. NCO levels above the top of this range tend to also have high functionalities and result in prepolymers with poor flow characteristics. Similarly, NCO levels below the bottom of the range tend to bunch up and flow poorly.
The previously prepared thermoplastic polyurethanes that may be used according to the invention include in particular the known thermoplastic polyurethanes that may be obtained, for example, in accordance with U.S. Pat. No. 3,963,679 and U.S. Pat. No. 4,035,213, the disclosures of which are incorporated herein by reference, using the starting materials described therein.
The polyester polyols used in forming the isocyanate prepolymer advantageously have an average functionality of from about 2.0 to about 3.0. Their average hydroxyl number values generally fall within a range of from about 56 up to about 1200.
Suitable polyester polyols can be produced, for example, from organic dicarboxylic acids with 2 to 12 carbons, preferably aliphatic dicarboxylic acids with 4 to 6 carbons, and multivalent alcohols, preferably diols, with 2 to 12 carbons, preferably 2 to 6 carbons. Examples of dicarboxylic acids include succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, maleic acid, fumaric acid, phthalic acid, isophthalic acid, and terephthalic acid. The dicarboxylic acids can be used individually or in mixtures. Instead of the free dicarboxylic acids, the corresponding dicarboxylic acid derivatives may also be used such as dicarboxylic acid mono- or di-esters of alcohols with 1 to 4 carbons, or dicarboxylic acid anhydrides. Dicarboxylic acid mixtures of succinic acid, glutaric acid and adipic acid in quantity ratios of 20-35:35-50:20-32 parts by weight are preferred, especially adipic acid. Examples of divalent and multivalent alcohols, especially diols, include ethanediol, diethylene glycol, 1,2- and 1,3-propanediol, dipropylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,10-decanediol, glycerine and trimethylolpropanes, tripropylene glycol, tetraethylene glycol, tetrapropylene glycol, tetramethylene glycol, 1,4-cyclohexane-dimethanol, ethanediol, diethylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, or mixtures of at least two of these diols are preferred, especially mixtures of 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol. Further, preferred polyester polyols, including polyester polyols of lactones, e.g., &egr;-caprolactone or hydroxycarboxylic acids, e.g., (&ohgr;-hydroxycaproic acid, may be used.
The polyester polyols can be produced by polycondensation of organic polycarboxylic acids, e.g., aromatic or preferably aliphatic polycarboxylic acids and/or derivatives thereof and multivalent alcohols in the absence of catalysts or preferably in the presence of esterification catalysts, preferably in an atmosphere of inert gases, e.g., nitrogen, carbon dioxide, helium, argon, etc., in the melt at temperatures of 150° to 250° C., preferably 180° to 220° C., optionally under reduced pressure, up to the desired acid value which is preferably less than 10, especially less than 2. In a preferred embodiment, the esterification mixture is subjected to polycondensation at the temperatures mentioned above up to an acid value of 80 to 30, preferably 40 to 30, under normal pressure, and then under a pressure of less than 500 mbar, preferably 50 to 150 mbar. The reaction can be carried out as a batch process or continuously. When present, excess glycol can be distilled from the reaction mixture during and/or after the reaction, such as in the preparation of low free glycol-containing polyester polyols usable in the present invention. Examples of suitable esterification catalysts include iron, cadmium, cobalt, lead, zinc, antimony, magnesium, titanium and tin catalysts in the form of metals, metal oxides or metal salts. However, the polycondensation may also be preformed i
Sardanopoli Armando
Stonehouse J. Richard
BASF Corporation
Borrego Fernando A.
Eashoo Mark
Silbaugh Jan H.
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