MOLDING COMPOSITION AND PROCESS FOR MOLDING
Publication Date: 2002-Nov-21
The IP.com Prior Art Database
A molding resin blend comprises a polyester blend and a core shell rubber modifier, wherein the blend has a melt strength suitable for blow molding.
FIELD OF THE INVENTION
The present invention generally relates to blow-molding compositions and processes to form hollow articles.
BACKGROUND OF THE INVENTION
Crystalline thermoplastic polybutylene terephthalate (PBT) resins have been used extensively as an engineering plastic in various fields owing to their excellent mechanical and electrical properties, as well as their physical and chemical characteristics. PBT resins have typically not been employed as a feedstock for blow-molding operations since the intermediate hollow parison that is formed during the blow-molding process is undesirably "drawn-down" due to the poor melt tension that conventional PBT resin exhibits. Thus, hollow blow-molded articles have typically not been produced from PBT resins. Instead, PBT resins are conventionally thought of as an injection-moldable resin from which hollow injection-molded articles may be produced.
Blow molding techniques are widely used in industry to fabricate a variety of hollow shaped plastic articles such as milk and water bottles, auto windshield washer tanks, street light globes, arms and legs on toy dolls, to name a few. Extrusion blow molding generally involves extruding a tube of plastic into a water-cooled mold, inflating the tube by internally introducing air or another gas until the walls of the molten tube assume the shape of the mold, allowing the shaped tube to cool to structural rigidity, and removing the extrusion blow molded part from the mold. Since linear polyesters do not possess sufficient melt strength for such applications, these polymers are typically alloyed with branched resins, such as branched polycarbonate or branched poly alkylene terephthalates, to obtain suitably high melt viscosity and melt elasticity.
DETAILED DESCRIPTION OF THE INVENTION
Linear polyesters are unbranched polyesters derived from an aliphatic diol and an aromatic dicarboxylic acid. Typically they have repeating units of the following general formula:
wherein n is an integer of from 2 to 6. R is a C6-C20 aryl radical comprising a decarboxylated residue derived from an aromatic dicarboxylic acid.
Examples of aromatic dicarboxcylic acids represented by the decarboxylated residue R are isophthalic or terephthalic acid, 1,2-di(p-carboxyphenyl)ethane, 4,4'-dicarboxydiphenyl ether, 4,4' bisbenzoic acid and mixtures thereof. All of these acids contain at least one aromatic nucleus. Acids containing fused rings can also be present, such as in 1,4- 1,5- or 2,6- naphthalenedicarboxylic acids. The preferred dicarboxylic acids are terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid or mixtures thereof.
The most preferred polyesters are poly(ethylene terephthalate) ("PET"), and poly(1,4-butylene terephthalate), ("PBT"), poly(ethylene naphthanoate) ("PEN"), poly(butylene naphthanoate), ("PBN") and poly(propylene terephthalate) ("PPT").
Also contemplated herein are the above polyesters with minor amounts, e.g., from about 0.5 to about 5...