Injection-moldable thermoplastic polyester composition

#This invention relates to thermoplastic polyester compositions which are especially useful for injection molding operations conducted at relatively low mold temperatures.

#It has long been known that polyethylene terephthalate (PET) has superior physical properties, e.g., resistance to chemical attack, and desirable mechanical and electrical properties. Despite these superior physical properties, PET is not always the material of choice for injection molding usage because relatively high mold temperatures, e.g., 120.degree.-140.degree. C., must be utilized to insure good moldability. Any attempt to use a lower mold temperature, e.g., 100.degree. C. or lower, results in the injected material being unmoldable as, for one thing, the molded article sticks in the mold and often can only be removed with great difficulty. To circumvent this processing disadvantage, the molder is forced to select more expensive materials such as polybutylene terephthalate (PBT), inasmuch as this poly(alkylene terephthalate) is easily moldable even when using mold temperatures as low as 60.degree. C. By being able to use a lower mold temperature for PBT, the time necessary for cooling the injection molded article to a temperature at which it can be removed from the mold is considerably shorter than the cooling time necessary before the PET article can be removed from an initially hotter mold. Since this shorter cool-down period of PBT results in a shorter process cycle time and a higher rate of article production, economic justification exists for its use despite its higher unit cost.

#Numerous nucleating agents for use in PET compositions are recognized in the art. For example, the following nucleating agents are known: salts of montan wax or of esters of montan wax in which the cation is metals of main groups I-III of the Periodic System (see U.S. Pat. No. 3,619,166); alkaline earth metal carbonates, e.g., calcium magnesium carbonate [CaMg(CO.sub.3).sub.2 ] (see U.S. Pat. No. 3,619,266 and British Pat. No. 1,239,455); oxides, e.g. titanium oxide, aluminum oxide, magnesium oxide, zinc oxide, antimony trioxide and titanium dioxide (see U.S. Pat. No. 3,616,266, British Pat. No. 1,104,089, British Pat. No. 1,111,012, British Pat. No. 1,196,290, British Pat. No. 1,239,455, British Pat. No. 1,246,770 and translation of German Pat. No. 2,014,770); silicates, e.g. talc, sodium-aluminum silicate, CaSiO.sub.3, MgSiO.sub.3 (see U.S. Pat. No. 3,616,266 and British Pat. No. 1,111,012); lithium or sodium salts of polycarboxylic acids, e.g., succinic acid, adipic acid, suberic acid, 1,10-decanedicarboxylic acid, 1,4-cyclohexane-dicarboxylic acid, terephthalic acid, 1,2,3-propanetricarboxylic acid, 1,3,5-cyclohexanetricarboxylic acid, trimellitic acid, 1,2,3,4-cyclopentanetetracarboxylic acid and pyromellitic acid (see U.S. Pat. No. 3,761,450 and translation of German Pat. No. 2,014,770); carbon, e.g., graphite and carbon black (see British Pat. No. 1,104,089, British Pat. No. 1,111,012 and British Pat. No. 1,196,290); salts of alkaline earth metals, e.g., calcium carbonate and calcium sulphate (see British Pat. No. 1,104,089, British Pat. No. 1,196,290 and British Pat. No. 1,246,770); metals in a finely divided state, e.g., copper and antimony (see British Pat. No. 1,104,089 and British Pat. No. 1,196,290); sulphates, e.g., CaSO.sub.4, BaSO.sub.4 and calcined gypsum (see British Pat. No. 1,111,012, British Pat. No. 1,196,290 and translation of German Pat. No. 2,014,770); glass powder (see British Pat. No. 1,104,089 and British Pat. No. 1,196,290); phosphates, e.g., Ca.sub.3 (PO.sub.4).sub.2 (see British Pat. No 1,111,012 and translation of German Pat. No. 2,014,770); oxalates, e.g., calcium oxalate (see British Pat. No. 1,111,012); stearates, e.g., magnesium stearate (see British Pat. No. 1,111,012 and British Pat. No. 1,181,679); benzoates, e.g., calcium benzoate and potassium benzoate (British Pat. No. 1,111,012 and translation of German Pat. No. 2,014,770); salicylates, e.g., zinc salicylate (see Brtitish Pat. No. 1,111,012 and translation of German Pat. No. 2,014,770); tartrates, e.g., calcium tartrate (British Pat. No. 1,111,012 and translation of German Pat. No. 2,014,770); neutral clays, e.g., "HITDRON" (British Pat. No. 1,111,012 and translation of German Pat. No. 2,014,770 ); sodium, lithium or barium salts of monocarboxylic acids, e.g., formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, caprylic acid, stearic acid, cyclohexane carboxylic acid, benzoic acid, p-tert-butyl benzoic acid, and naphthalene-1-carboxylic acid (see British Pat. No. 1,282,679); the disclosure of the foregoing references are incorporated herein by reference.

#The present invention is further illustrated in the following examples, which are not to be construed as limiting.

#The various PET compositions of Examples 1-29 were prepared by mixing the components to form a premix, compounding the premix in a single screw extruder at temperatures of about 500.degree. F. (260.degree. C.), and molding the pellets into an article on a reciprocating screw injection molding machine. The injection mold was suitably shaped and dimensioned for providing an article having the configuration shown in the FIG.--which is a top plan view of the article. The mold utilized was a center gated mold having a nonmovable planar sprue side and a movable cavity side. As can be seen in the Figure the article formed by the mold has a plurality of runners, labeled "A", which terminate into various test pieces. Emanating from the center of the runner grid is a conventional tapered sprue. Two of the test pieces are rectangular bars and are labeled with the letter "B". These "B" bars are about six inches long, 1/2 inch wide and 1/4 inch thick. The test piece labeled "C" in the Figure is a rectangular bar which is 21/2 inches long, 1/2 inch wide and 150 inch thick. The two "dog bone" shaped test pieces are labeled "D" and are used for the testing of tensile properties. They measure about 61/2 inches long, 150 inch thick and 3/4 inch in width at each of their ends and 1/2 inch in width at their middles. The test piece labeled "E" is 4 inches long, 23/4 inches wide and 150 inch thick. The runners and sprue are approximately 154 inch in cross sectional width. This configuration for the test article was chosen for its complexity and for its yield of test specimens which are used in accordance with well recognized standard tests. The complexity of the article configuration was also thought sufficient to give a good prediction of moldability performance of the composition when used to form typical commercial articles.

#The PET, epoxidized plasticizer, glass and sodium stearate used in the Examples are identified as follows: