The present invention is directed to chemically treated glass fibers, strands or yarn where the fibers impart improved strength in reinforcing thermoplastics and in particular polyolefins.
Glass fibers are produced by flowing molten glass via gravity through a multitude of small openings in a precious metal device, called a bushing. Typical formulations of glass fibers are disclosed in The Manufacturing Technology of Continuous Glass Fibres, Library of Congress Catalog Card Number 72-97429, by K. L. Loewenstein, Elsevier Scientific Publishing, 1973, at page 29. Glass fibers are, for example, those known as "E glass", "S glass", "D glass" and are typically between 3 and 30 microns in diameter.
After the fibers have cooled very shortly after their issuance from the bushing and usually in close proximity to the bushing, these fibers are treated with a chemical treating formulation usually referred to in the art as a sizing composition or size. The size serves to make the fibers more compatible with the material they will ultimately be used to reinforce and to make the fibers more easy to process. The aqueous size can be applied by sprayers, rollers, belts, metering devices or any similar application device. The sized glass fibers are gathered into bundles or strands comprising a plurality of individual fibers, generally from 200 to more than 3000. The sized glass fibers generally can have between about 0.01 and 5 percent of sizing composition based on the weight of the glass fiber.
After their formation and treatment, the strands can be wound into a spool or "forming package" and/or may be chopped. The forming packages or chopped strands are usually dried in either an oven or at room temperature to remove some of the moisture from the fibers.
The strands of treated fibers can be used to reinforce various materials such as thermoplastic polymers. Thermoplastics can be of different types, including chemically coupled and non-chemically coupled polyalkylenes such as polypropylenes and particular types of strands of sized fibers have generally been directed to reinforcement of either of these thermoplastics.
U.S. Pat. No. 5,130,197 to Temple teaches a sizing having 1) an amino-silane coupling agent, 2) a carboxylic modified polyolefin resin, 3) an epoxy, urethane, or polyester resin or copolymer thereof, and 4) a binder stabilizer. These sized fibers are preferably used to reinforce non-chemically coupled polypropylene homopolymer. Also U.S. Pat. No. 4,341,677 to Tamosauskas teaches a size having a film forming polymer, coupling agent and an oil-in-water emulsion of an antioxidant like hindered phenols and diarylamines.
The fiber reinforced plastic industry continues to search for improvements in mechanical properties both initially and upon heat aging.
It would be beneficial, therefore, to provide chemically treated or sized fibers, strands and bundles thereof resulting in improved initial mechanical strength and/or improved mechanical strength retention and/or color on heat aging when used to reinforce for example, chemically coupled polypropylene, non-chemically coupled polypropylene and mixtures of these.