CA1111984A - Polybutylene terephthalate/thermoplastic polyurethane molding compositions - Google Patents

Abstract

POLYBUTYLENE TEREPHTHALATE/THERMOPLASTIC
POLYURETHANE MOLDING COMPOSITIONS

ABSTRACT OF THE DISCLOSURE

The present invention pertains to molding compositions comprising intimate blends of polybutylene terephthalate and thermoplastic polyurethanes. Such molding compositions have been found to exhibit overall physical properties superior to the properties exhibited by either polymer individually.

Description

Mo-1843 POLYBUTYLENE TEREPHTHALATE/T~ERMOPLASTIC
POLYURETHANE MOLDING COMPOSITIONS
_ FIELD OP TH _ VENTIO

This invention relates to polymer blends and more particularly to molding compositions comprising intimate blends of polybutylene terephthalate and thermoplastic polyurethanes.

BACKGROUND OF THE INVENTION

Thermoplastic polyurethanes have found utility in many molding appllcations where good tensile strength, tensile modulus, good ductility and elongation properties are required. Molded articles of thermoplastic poly-urethanes have, therefore, found considerable use and success in the automobile industry, in the shoe industry, in the electrical industry and in the mechanical equipment industry, such as for pump stators, pump impellers and gasket materials. ~owever, it has been found that thermo-plastic polyurethanes may lack the requisite hardness properties required in various applications for parts or articles molded from these polymers.

Polybutylene terephthalate has been commercially available since about 1970 and has recently found extensive use in various molding applications due to its excellent processibility, excellent resistance to chemicals and solvents, excellent hardness, low coefficient of friction and wear resistance, high heat distortion temperature, low water absorptio~ and excellent electrical properties. The combination of these interesting mechànical, thermal, electrical and processibility properties make polybutylene Mo-1843 terephthalate an attractive polymer for mokling applications.
However, it has been found that po1ybutylene terephthalate may lack the necessary ductility properties (drop dart impact prope~ti(C;) re(luired in various app~ications ~or parts or articlcs molded fronl this polymer.

In accordance with tile present invention, molding compositions comprising intimate blends of polybutylene terephthalate and thermoplastic polyurethanes are provided which exhibit overall physical properties superior to the properties exhibited by either polymer individually.
Specifically, the ductility properties,of polybutylene terephthalate are improved by intimately blending with an effective amount of thermoplastic polyurethane, and the hardness properties of a thermoplastic polyurethane are improvecl by intimate blending with an effective a~ount of polybutylene terephthalate.

SU~RY OF THE INVENTION

The present invention is directed to molding compositions comprising intimate blends of polybutylene terephthalate and thermoplastic polyurethane.

DET~ILED DESCRI~TION OF THE INVENTION

The thermoplastic polyurethanes of the invention are those generally prepared from a diisocyanate, a polyester or polyether and a chain extender. These thermoplastic poly-urethanes are substantially linear and maintain thermoplastic processing characteris-tics.

The thermoplastic polyurethanes may be synthesized by methods disclosed in U. S. ~atent 3,214,411.

Mo-1843 - 2 -V

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A particularly useful polyester resin which may be used as a startincl material for the thermoplastic polyurethanes is produced from adipic acid and a glycol having at least one primary hydroxyl ~rou~. The aclipic acid is condensed with a suitable glycol or mixture of glycols which have at least one primary hydroxyl group. The condensation is stopped when an acid number of from about 0.5 to about 2.0 is reached. The water formed durin~ the reaction is removed simultaneously therewith or subsequently thereto so that the final water content is from about 0.01 to about 0.02~, preferably from about 0.01 to O.OS%.

~ny suitable glycol may be used in reaction with the adipic acid such as, for example, ethylene glycol, propylene glycol, butylene glycol, hexanediol, bis-(hydroxymethylcyclo-hexane), 1,4-butanediol, diethylene glycol, 2,2-dimethyl propylene glyco', l,3-propylene glycol and the like. In addition to the glycols, a small amQunt of trihydric alcohol, up to about l~,may be used along with the glycols such as, for example, trimethylolpropane, glycerine, hexanetriol and the like. The resulting hydroxyl polyester may have a molecular weight of at least about 600, a hydroxyl number of about 25 to about 190 and preferably between about 40 and about 60, an acid number of between about 0.5 and about 2 and a water content of about 0.01 to about 0.2~.

The organic diisocyanate to be used in the preparation of the elastomer is preferably 4,4'-diphenyl-methane diisocyanate. It is desired that the 4,4'-diphenyl-methane diisocyanate contain less than about 5% of 2,4'-diphenylmethane diisocyanate and less than about 2% of the dimer of diphenylmethane diisocyanate. It is furthe- desired Mo-1843 ~ 3 B
... ...... ........ . ..

that the acidity calculated as HCl be ~rom about 0.~001 to ~.2%. The acidity calculated as percent HCl is determined by extracting the chloride from the isocyanate in a hot a~ueous meth.anol solution or by liberating the chloride on hydrolysis with water and titrating the extract with a standard silver nitrate solution to obtain the chloride ion concentration present.

Other diisocyanates may be used in preparing the thermoplastic polyurethanes such as ethylene diisocyanate, ethylidene diisocyanate, propylene diisocyanate, butylene diisocyanate, cyclopentylene-1,3-diisocyanate, cyclohexylene- :
1,4-diisocyanate, cyclohexylene-1.,2-diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 2,2-diphenylpropane-4,4'-diisocyanate, p-phenylene diisocyanate, m-phenylene diisocyanate, xylylene diisocyanate, 1,4-napthylene diisocyan-ate, l,S-naphthylene diisocyanate, diphenyl-4,4'-diisocyanate, azobenzene-4,4'-diisocyanate, diphenyl sulfone-4,4'-diisocyan-ate, dichlorohexamethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, 1-ahlorobenzene-2,4-diisocyanate, furfurylidene diisocyanate and the like.

Any suitable chain extending agent having active hydrogen containing groups reactive with isocyanate groups may be used such as, for example, diols including ethylene glycol, propylene glycol, butylene glycol, 1,4-butanediol, butenediol, bytynediol, xylylene glycols, amylene glycols, 1,4-phenylene-bis-~-hydroxy ethyl ether, 1,3-phenylene-bis-~-hydroxy ethyl ether, bis-(hydroxy-methyl-cyclohexane), hexanediol, thiodiglycol and the like; diamines including ethylene diamine, propylene diamine, butylene diamine, Mo-1843 ~ 4 ~

hexametllyl~ne diamine, cyclohexalene diamine, phenylene diamine, tolylene diamine, xylylene diamine, 3,3'-dichloro-benzidine, 3,3'-dinitrobenzidine and the like; alkanol amines such as, for example, ethanol amine, aminopropyl alcohol,

2,2-dimethyl propanol amine, 3-aminocyclohexyl alcohol, p-aminobenzyl alcohol and the like. The difunctional chain extenders mentioned in U. S. Patents 2,620,516, 2,621,166 and 2,729,618 may be used. If desirable, a small amount of polyfunctional material may be utilized. This polyfunctional chain extender, however, should not be present in an amount grea~ter than about 1~ by weight. Any suitable polyfunctional compound may be used in this application such as, for example, glycerine, trimethylol-propane, hexanetriol, pentaerythritol and the like.

The polyester, the organic diisocyanate and the chain extender may be individually heated preferably to a temperature of from about 60C. to about 135 and then the polyester and chain extender may be substantially simultaneously mixed with the diisocyanate. Preferably, the chain extender and the polyester, each of which has been previously heated, are first mixed and the resulting mixture is mixed with the heated diisocyanate. This method is preferred for the reason that the extender and the polyester will not react prior to the introduction of diisocyanate and rapid mixing with the diisocyanate is thus facilitated.

The mixing of the polyester, the chain extender and diisocyanate may be suitably carried out by using any mechanical mixer such as one equipped with a stirrer which results in intimate mixing of the three ingredients in a short period of time. If the material begins to become too Mo-1843 - 5 --I

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thick, either the temperature may be lowere(l or a small amount of citric acid or the like of from about 0.00l to 0.050 parts by weight based on 100 parts of the polyester may be added to slow down the reaction. Of course, to increase the rate of reaction, any suitable catalyst may be added to the reaction mixture such as tertiary amines and the like as set forth in U. S. Patent Nos. 2,620,516, 2,621,166 and 2,729,618.

Additional processing techniques for the production of thermoplastic polyurethanes useful in the present invention are disclosed in the text Polyurethanes: Chemistry and Technology, Vol. II, pages 299 - 452, by J. H. Saunders and K. C. Frisch, Interscience Publishers, New York 1964 and in the pamphlet ~ Processing Handbook for Texin Urethane Elasto-plastic Materials, Mobay Chemical Corporation, Pittsburgh, PA.

Although adipate polyesters are preferred in producing suitable thermoplastic polyurethanes, polyesters may be used which are based on succinic acid, suberic acid, sebacic acid, oxalic acidl methyl adipic acid, glutaric acid, pimelic acid, azelaic acid, phthalic acid, tereL)hthalic acid, iso-phthalic acid and the like.
Suitable po].yesters for the production of the thermo-plastic polyurethanes also include those based on polymeriza-tion products of lactones, for example caprolactones.
A polyether may be used instead of the polyester in the preparation~of the thermoplastic polyurethane, preferably polytetramethylene glycol, having an average molecular : welght between about 600 and 2000 and preferably about 1000.
Other polyethers such as polypropylene glycol, polyethylene glycol and thelike may be used providing their molecular weight is above about 600.

Mo-1843 ..
IJ:~- . , The above and other thermoplastic polyurethanes such as disclosed in U. S. Patents 2,621,166, 2,729,618,

3,214,411, 2,778,810; Canadian Patents 754,233, 733,577 and 842,325 may be used to produce thermoplastic polyurethanes which can be intimately blended with the polybutylene terephthalate.

"Thermoplastic polyurethane" as used herein means block polymers prepared from a diisocyanate, a polyester or polyether, and a chain extender and are processable by all the standard techniques of compression or injection molding or extrusion.

The polybutylene terephthalate polymers used in the practice of the invention are those characterized by the repeating structural formula:

H20C ~ CO ~

Generally, polybutylene terephthalate is produced by the transesterification of dimethylterephthalate and 1,4-butanediol or by the direct esterification of terephthalic ~ , acid and l,4-butanediol. Such processes are described in 2Q ~ U. S. Patent Nos. 2,647,885; 2,643,989; 2,534,028; 2,578,660;
2,742,494 and 2,901,466.

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Polybutylene terephthalates suitable in the invention also include modified polybu~ylene terephthalates wherein the diol component used to produce the polymer comprises at least abc,ut 75 mol ~ of 1,4-butanediol, based on the total mols of dic,l component used, and the dicarboxylic acid component or corresponding dialkyl (preferably Cl-C6) ester component used to produce the polymer comprises at least about 75 mol %
of terephthalic acid or dialkyl terephthalate, respectively, based on the total mols of dicarboxylic acid component or corresponding dialkyl ester component used. Thus, up to about 25 mol ~ of diols other than 1,4-butanediol and up to about 25 mol % of dicarboxylic acids or corresponding dialkyl esters other than terephthalic acid or the corresponding dialkyl terephthalates may be used.

E~amples of suitable diols other than 1,4-butanediol that may be used include ethylene glycol, 1,3-propanediol, 2,2-dimethyl-1,3-propanediol,1,5-pentanediol and 1,6-hexane-diol. Examples of suitable dicarboxylic acids-and corresponding dialkyl esters other than terephthalic acid and the corres-ponding dialkyl terephthalates that may be used include aliphatic, cycloaliphatic and aromatic dicarboxylic acids such as succinic acid, glutaric acid, adipic acid, pimetic acid, suberic acid, azelaic acid, sebacic acid, 1,4-cyclohexane-dicarboxylic acid, isophthalic acid, 1,5- and 1,6-naphthalene-dicarboxylic acid, 4,4'-, 4,3'- and 3,3'-diphenyl-dicarboxylic acid and 4,4'-, 4,3'- and 3,3'-diphenylsulphonedicarboxylic acid, and the corresponding dialkyl esters produced from such acids.

Preferably, the polybutylene terephthalates and modified polybutylene terephthalates have an intrinsic viscosity of about 0.5 to 1.5 and more preferably about 0.7 Mo-1843 - 8 -.

, to 1.3 measured at 25C as a 0.1% solution in a 60/40 volume-tric mixture of phenol/tetrachloroethane.

The thermoplastic polyurethane may be homogeneously blended with the polybutylene terephthalate by melt homo-genlzation, extrusion or a like method for intimately mixingthermoplastic polymers.

After the thermoplastic polyurethane has been intimately blended with the polybutylene terephthalate, it can be molded by injection molding techniques or other techniques known to those skilled in the art.

During the blending process, it is also possible to admix additives such as pigments, stabilizers, flame retardants, flow agents, lubricants, antistatic agents and mold release agents in a known manner.

In a preferred embodiment of the present in~ention, the molding compositions comprise an intimate blend of 5-95% by weight of a polybutylene terephthalate with 95-5% by weight of a thermoplastic polyurethane, based on the total weight of the molding composition.

In a more preferred embodiment of the present invention, the molding compositions comprise an intimate blend of thermoplastic polyurethane with an effective amount of polybutylene terephthalate to improve the hardness properties of the thermoplastic polyurethane. In general, 5 to 30%
by weight of polybutylene terephthalate, based on the total weight of the molding composition, has been found to be an effective amount.

Mo-1843 ~ 9 ~

In a second more preferred embodiment of the present invention, the molding compositions comprise an intimate blend of polybutylene terephthalate with an effective amount of thexmoplastic polyurethane to improve the ductility properties of the polybutylene terephthalate. In general 5 to 30~ by weight of thermoplastic polyurethane, based on the total weight of the molding composition, has been found to be an effective amount.

The invention will be further illustrated by the following examples.

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EXAMPLES

The following thermoplastic polyurethanes were used in the examples:

POLYURETHANE A

This thermop~astic polyurethane was prepared by reacting butylene adipate (MW of 2000), 1,4-butanediol and methylene di-para-phenylene diisocyanate (MDI).

POLYURETHANE B

This thermoplastic polyurethane was prepared by reacting butylene adipate (MW of 2000), ethylene glycol and methylene di~para-phenylene diisocyanate (MDI).

POLYURETHANE C

This thermoplastic polyurethane was prepared by reacting butylene adipate (MW of 2000), para-phenylene-di (~-oxyethylether) and methylene di-para~phenylene diisocyanate.

- 100 parts by weight of thermoplastic Polyurethane A
were extruded and then cut into 1/8" X 1/8" granules. The granules were then molded into test specimens. The properties ~20 of this molding composition are reported in Tables 1 and 2.

85 parts by weight of thermoplastic Polyurethane A
were intimately blended with 15 parts by weight of a polybutylene terephthalate having an intrinsic visc06ity of about 0.80 in a single screw laboratory extruder. The intimately blended polymers were cut into 1/8" X 1/8" granules and molded into Mo-1843 - 11 -: . -test specimens. The properties of this molding composition are reported in Tables 1 and 2.

EX~PLES 3-26 These examples were conducted in a manner similar to that of Examples 1 and 2 except for the fact that various thermoplastic polyurethanes and polybutylene terephthalates of various intrinsic viscosities were used. The properties of these compositions are reported in Tables 1 and 2.

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ASTM D-412: Unless otherwise noted, ASTM "D" dumb-bells (.125" wide) die cut from 0.80" thick slabs were used and were tested at 20"/minute.

~ ASTM D-2240 -Drop dart impact strength was measured by dropping a 10.5 lb. weight with a contact surface of a 1"
diameter hemisphere upon a 0.10" thick, 4" diameter, securely clamped, molded specimen. The drop height corresponding to a 50% breakage of the specimen is proportional to the impact resistance of the test specimen.

~ ASTM D-256: With the notched samples struck on the unnotched (i.e.,"reverse") side.

These molding compositions were molded into dumbbells 0.263" wide and 0.127" thick due to their hardness.

These molding materials were tested at 2"/minute due to their plastic-like nature.

~ These molding materials were molded into dumbbells 0.500" wide and 0.125" thick and were tested at 2"/
minute.

B = break NB = no break ~ PBT = polybutylene terephthalate Mo-1843 - 17 -, ~ , : -.: ' . , ' . - , -,,': -. , ' ' ' '' ~ ' . . '. ~

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PU = thermoplastlc polyurethane RT - room temperature These samples yielded and necked like conventional plastic.

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~ . . , - - ~ - .-A review of the properties of the compositions of the above examples reveals that the intimate blends of the thermo-plastic polyurethanes and the various polybutylene terephtha-lates exhibit overall physical properties superior to the properties exhibited by either polymer individually.
Specifically, it is noted that the ductility (as represented by drop dart impact values) of polybutylene terephthalate i5 improved by intimately blending with thermoplastic poly-urethanes and the hardness (as measured by Shore hardness) of the thermoplastic polyurethanes are improved by intimately blending with polybutylene terephthalates. Such improved properties of the blends of the invention were unexpected because it was in no way predictable that the blends of these polymers would exhibit overall physical properties superior to those exhibited by either polymer alone.

Although the invention has been described in detail in the foregoing for the purpose of illustration, it is to be understood that such detail is solely for that purpose and that variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention except as it may be limited by the claims.

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Claims (14)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-

1. A molding composition comprising an intimate blend of a thermoplastic polyurethane and a polybutylene terephthalate.

2. The molding composition of Claim 1 wherein the polybutylene terephthalate is present in from about 5 to 95%
by weight and the thermoplastic polyurethane is present in from about 95 to 5% by weight, based on the total weight of the molding composition.

3. The molding composition of Claim 1 wherein the polybutylene terephthalate has an intrinsic viscosity of from about 0.5 to 1.5 as measured at 25°C as a 0.1% solution in a 60/40 volumetric mixture of phenol/tetrachloroethane.

4. A molding composition comprising an intimate blend of a polybutylene terephthalate with an effective amount of a thermoplastic polyurethane to improve the ductility of the polybutylene terephthalate.

5. The molding composition of Claim 4 wherein from about 5 to 30% by weight, based on the total weight of the molding composition, of the thermoplastic polyurethane is intimately blended with the polybutylene terephthalate.

6. A molding composition comprising an intimate blend of a thermoplastic polyurethane with an effective amount of a polybutylene terephthalate to improve the hardness of the thermoplastic polyurethane.

7. The molding composition of Claim 6 wherein from about 5 to 30% by weight, based on the total weight of the molding composition, of the polybutylene terephthalate is intimately blended with the thermoplastic polyurethane.

8. The molding compositions of Claims 1, 4 or 6 wherein the polybutylene terephthalate is produced using up to about 25 mol % of diols other than 1,4-butane-diol or up to about 25 mol % of dicarboxylic acids or corresponding dialkyl esters other than terephthalic acid or the corresponding dialkyl terephthalates.

9. The molding compositions of Claim 1, 4 or 6 wherein the polybutylene terephthalate has an intrinsic viscosity of from about 0.7 to 1.3 as measured at 25°C as a 0.1% solution in a 60/40 volumetric mixture of phenol/
tetrachloroethane.

10. A molding composition comprising an intimate blend of polyurethane and polybutylene terephthalate prepared from a homogeneous melt of about 60-95% by weight, based on the total weight of the molding composition, of a thermo-plastic polyurethane and about 5-40% by weight, based on the total weight of the molding composition, of a poly-butylene terephthalate.

11. The molding composition of Claim 10 wherein the polybutylene terephthalate has an intrinsic viscosity of from about 0.5 to 1.5 as measured at 25°C as a 0.1% solution in a 60/40 volumetric mixture of phenol/tetrachloroethane.

12. The molding composition of Claim 10 wherein from about 5 to 30% by weight, based on the total weight of the molding composition, of the polybutylene terephthalate is intimately blended with the thermoplastic polyurethane.

13. The molding composition of Claim 10 wherein the polybutylene terephthalate is produced using up to about 25 mol % of diols other than 1,4-butane-diol or up to about 25 mol % of dicarboxylic acids or corresponding dialkyl esters other than terephthalic acid or the corresponding dialkyl terephthalates.

14. The molding composition of Claim 10 wherein the polybutylene terephthalate has an intrinsic viscosity of from about 0.7 to 1.3 as measured at 25°C as a 0.1% solution in a 60/40 volumetric mixture of phenol/tetrachloroethane.