Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof
Reexamination Certificate
2001-12-21
2003-10-07
Acquah, Samuel A (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carboxylic acid or derivative thereof
C528S295000, C528S298000, C528S300000, C528S302000, C528S308000, C528S308600, C528S275000, C528S296000, C524S710000, C524S711000, C524S713000, C428S035700
Reexamination Certificate
active
06630564
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to copolyester with improved extrusion processing and color for extrusion blow molding.
1. Background of the Invention
Polyethylene terephthalate (PET) is excellent in various features such as transparency, gas barrier properties, low toxicity of additives, and causing little worries about hygiene and safety with respect to being filled with foodstuff as compared with PVC containers, when molded into hollow shaped articles. The PET has therefore become widely used in food packaging materials.
Two representative processes for producing hollow shaped articles are extrusion blow molding and injection blow molding; in which, the extrusion blow molding process comprises extruding a melt resin with a screw or piston through a die-orifice into a cylindrical hollow parison and, while closing the left mold and the right mold to hold the parison in the mold cavity as it is still softened, quickly blowing the air into the parison; and the injection blow molding process comprises injecting a melted resin into a die to mold a closed parison (preforms) once and, after inserting it into a blow die, blowing the air into the preforms.
Of the above processes, the extrusion blow molding process has the advantage of simple technology, less expensive processing equipment, low cost of die, requiring no complex techniques to replace the die and being capable of producing large and complex-shaped articles, but suffers the disadvantage of slow processing speed; therefore is suitable for multiple-product-small-quantity production. The injection blow molding process is more suitable for large-quantity production, with the features of simple-shaped articles, requiring complex processing techniques, high cost of die and equipment, therefore meeting the requirement of large orders. From the viewpoint of practical application, the above two processes have advantages and disadvantages respectively, therefore the two processing equipment are widely used in present plastic processing industry.
General-purpose polyethylene terephthalate (PET) is molded into various hollow containers by injection blow molding process; when it is molded by extrusion blow molding process, the parisons melt extruded markedly sag (drawdown) and become difficult to be shaped which is caused by low melt viscosity. In addition, crystallization tends to occur on general-purpose PET, with whitening frequently being accompanied, thereby it is incapable of producing acceptable shaped articles especially on producing shaped articles in larger length. Furthermore, shaped articles by extrusion blow molding process has a rather lower draw ratio than the shaped articles by injection blow molding process, therefore having a bad impact resistance.
Taiwan Patent Application No. 88113151 discloses a copolyester suitable for extrusion blow molding processing. The patent application discloses that no severe drawdown of melted parisons occurs on melt extrusion processing, the shaped articles have the advantage of good transparency with excellent color hue, no crystallization whitening occurring and being capable of directly molding into bottle having a capacity of 2.0 liters and amounted with a handle, which features in shock resistance. However, the copolyester produced in this method undergoes a long period of time of solid phase polymerization to reach a sufficiently high degree of viscosity, thus leading to the copolyester being imparted an undesirable yellowish color hue.
The present invention relates to an improved process to the Taiwan Patent Application No. 88113151 which provides a copolyester suitable for extrusion processing with a high productivity and gives the copolyester chip obtained therefrom a better color, therefore leading to improvement to the color of molded articles; furthermore, the improved copolyester can reduce the decline degree of the viscosity of processing residue, ensuring the quality of processing residue even after re-processing.
2. Description of the Prior Art
Prior arts related to the copolyester suitable for extrusion processing are described as following:
1. U.S. Pat. No. 5,182,359, EP-A-0532943, JP-A-5-125165/1993 disclose process for producing polyesters suitable for extrusion processing, which comprises adding, on reacting a dicarboxylic acid component or ester-forming derivatives thereof with a diol component containing 2 to 8 carbon atoms, an ethylene oxide adduct of bisphenol A. However, polyesters obtained by the process gives extrusion blow molded articles having insufficient melt viscosity, severe drawdown on melt parisions and failure in molding articles under a stable state; further, surface roughness occurs when molded at a low temperature.
2. U.S. Pat. Nos. 4,161,579, 4,219,527, 4,234,708 disclose process for producing polyester suitable for extrusion blow molding, which comprises adding, on reacting terephthalic acid with ethylene glycol, a crosslinking agent such as trimethylol propane, or pentaerythritol or trimellitic acid, and further adding a chain terminating agent such as benzoic acid or stearic acid. However, crosslinking agent and chain terminating agent employed in the process improve the melt viscosity, but cause quicker crystallization rate as compared with the unmodified polyester, and crystallization whitening occurs on producing shaped articles in larger length. Furthermore, shaped articles produced from said copolyester also exhibits surface roughness as described in above process 1.
3. U.S. Pat. No. 4,182,841, JP-A-55-92730/1980 disclose process for producing polyester suitable for extrusion blow molding, which comprises reacting the terephthalic acid with ethylene glycol to prepare a prepolymer, adding trimethylol propane, or pentaerythritol or trimellitic acid to form copolyester chip and subjecting the copolyester chip to solid phase polymerization. However, the process also displays quicker crystallization rate as described in above process; furthermore, adding isophthalic acid or neopentyl glycol to the process suppresses the crystallization rate, but fails to modify the state of surface roughness due to gel generation resulting from over-crosslinkage.
4. U.S. Pat. No. 4,554,329 discloses a process for producing copolyester suitable for extrusion blow molding, which comprises reacting terephthalic acid, isophthalic acid and ethylene glycol, adding a crosslinking agent such as pentaerythritol, and further adding m-anisic acid. Adding pentaerythritol and m-anisic acid in the process can lead to a sufficient high degree of melt viscosity and rather less gel generation, and adding isophthalic acid can suppress the crystallization rate. However, the slight surface roughness and crystallization whitening still occur on producing shaped articles having a length of at least 30 cm.
5. U.S. Pat. Nos. 3,558,557, 4,188,357, 4,196,275 disclose a process for producing copolyester suitable for extrusion blow molding, which comprises reacting terephthalic acid, ethylene glycol and disphenol A diglycol ether with small amount of multifunctional groups crosslinking agent. However, in this method, the bisphenol A structural modification agent used causes non-crystal phase, therefore increase of molecular weight only depends on melt phase polymerization, thus leading to insufficient high degree of melt viscosity and severe drawdown of melted parisons on producing shaped articles. In order to solve the problem, several methods are proposed which comprise adding substantially disphenol A diglycol ether, which causes extremely long period of time experienced by the polyester subjecting to melt phase polymerization, therefore leading to heat splitting, yellowish color of polyester and failure in proper control to the melt viscosity.
6. EP 0774 477A2 discloses a process for producing copolyester, which comprises adding, on reacting terephthalic acid with ethylene glycol, 1 to 4 mole % of aliphatic or alicyclic bifunctional group component (called a1 unit, such as cyclohexane dimethanol and cyclohexane dicarboxylic acid) or 0.5 to 7 mole % of aromatic
Acquah Samuel A
Bacon & Thomas PLLC
Nan Ya Plastics Corporation
LandOfFree
Copolyester with improved extrusion processing and color for... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Copolyester with improved extrusion processing and color for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Copolyester with improved extrusion processing and color for... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3171856