Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof
Reexamination Certificate
2001-05-14
2002-12-03
Acquah, Samuel A. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carboxylic acid or derivative thereof
C528S274000, C528S275000, C528S280000, C528S283000, C528S285000, C528S286000, C528S297000, C528S302000, C528S308000, C528S308600, C524S081000, C524S147000, C524S323000, C524S710000, C524S713000, C524S783000, C524S785000
Reexamination Certificate
active
06489434
ABSTRACT:
DESCRIPTION OF THE PRESENT INVENTION
Field of the Present Invention
The present invention is a manufacturing method of copolyester for low acetaldehyde content of PET bottles. The main skill is to add inorganic phosphorus compound stabilizer and hindered phenol primary antioxidant containing Ca
+2
into the PET polymer prepared by polyethylene terephthalate polymer and its copolymer in order to decrease the production of acetaldehyde which is caused by the side reaction of PET polymer pyrolysis at least 30% than those without the addition of said modifier.
BACKGROUND OF THE PRESENT INVENTION
While blow molded by the ejector, the polyethylene terephthalate (PET) granules are heated by the high temperature of ejector and are affected by the mechanical force of screw, which causes the pyrolysis of PET polymer. Consequently, the acetaldehyde is produced from side reaction. While the content of acetaldehyde is too high, the PET bottle can be rejected because of the spoiled smell of beverage such as mineral water and cola.
DESCRIPTION OF PRIOR ART
Owning characteristics of lightness, transparency, and safety, the polyethylene terephthalate (PET) bottle has greatly replaced traditional vessels such as glass, aluminum, iron. The PVC plastic bottle is also replaced gradually by the PET bottle owing to its being apt to produce environmental problems such as Dioxin and Acid Rain while treated by combustion.
The manufacturing process of the PET bottle for the prior art can be separated to three main steps:
(1). Melted state polycondensation operation
(2). Solid state polycondensation operation
(3). Blow molded manufacturing operation
The three main steps of the prior art are described respectively as follows:
Step (1) “Melted State Polycondensation Operation ” can be Further Splitted to two Processes
(A). Continuous melted state polycondensation operation
(B). Batch melted state polycondensation operation
In the continuous melted state polycondensation operation process, the terephthalic acid (PTA) and the ethylene glycol (EG) are blended to form thick liquid; the isophthalic acid (IPA) 0~10 mol % is added thereafter and blended together and then transmitted to esterification tank so as to perform direct esterification. The operation temperature of esterification is between 220~265.degree.C. The operation pressure of esterification is between normal pressure and 2.0 kg/cm
2
. The produced water and alcohols during said process should be distilled out. While the esterification has completed 95~98% of esterification conversion ratio, the esterification has been stopped and the polycondensation is initiated. A catalyst should be added before polycondensation in order to expedite the rate of polycondensation so as to shorten the polycondensation time. Antimony acetate or antimony trioxide or germanium dioxide or titanium, or their mixture can normally be used as catalyst to expedite the completion of polycondensation. In addition, the stabilizer such as phosphoric acid, phosphorous acid, trimethyl phosphate, triphenyl phosphate, triethyl phosphate is added.
The polycondensation of PET and its copolymer includes pre-polymerization and main-polymerization. The operating temperature for pre-polymerization is between 270~280.degree.C., and the operating vacuum intensity for pre-polymerization is between 250~15 mmHg. The operating temperature for main-polymerization is between 275~285.degree.C., and the operating pressure for main-polymerization is below 1 mmHg. The intrinsic viscosity of PET polymer is raised to 0.5~0.7 dl/g at the end of PET melted state polycondensation. Then, the polymer is unloaded to cooling water for quick cooling-down and further be cut to PET chip with column shape. The residual of acetaldehyde in PET chip at this stage is approximately higher than 50 ppm, which makes the PET chip unsuitable to be directly processed by the blow molder to manufacture PET bottles.
While in the batch melted state polycondensation operation process, the dimethyl terephthalate (DMT) and the ethylene glycol (EG) are blended; then, the transesterification catalyst such as manganese acetate, or zinc acetate, or titanium is added so as to perform transesterification reaction. The operating temperature for transesterification reaction is between 140~260.degree.C. The methyl alcohol should be distilled out during the said process. While the transesterification reaction has completed 95~98% of esterification conversion ratio, the isophthalic acid (IPA) 0~10 mol % is added thereafter and blended together to form copolymer and so as to end the transesterification reaction. A polycondensation type catalyst should be added before melted state polycondensation in order to expedite the rate of polycondensation so as to shorten the polycondensation reaction time. Antimony acetate or antimony trioxide or germanium dioxide or titanium, or their mixture can be used as catalyst to expedite the completion of polycondensation. In addition, the stabilizer such as phosphoric acid, phosphorous acid, trimethyl phosphate, triphenyl phosphate, triethyl phosphate is added.
The polycondensation of PET and its copolymer includes pre-polymerization and main-polymerization. The operating temperature for pre-polymerization is between 270~280.degree.C. and the operating vacuum intensity for pre-polymerization is between 250~15 mmHg. The operating temperature for main-polymerization is between 275~285.degree.C. and the operating pressure for main-polymerization is below 1 mmHg. The intrinsic viscosity of PET polymer is raised to 0.5~0.7 dl/g at the end of PET melted state polycondensation. Then, the polymer is unloaded to cooling water for quick cooling-down and further be cut to PET chip with column shape. The residual of acetaldehyde in PET chip at this stage is approximately higher than 50 ppm, which makes the PET chip unsuitable to be directly processed by the blow molder to manufacture PET bottles.
In order to resolve the problem of excess residual of acetaldehyde in the PET chip produced either by continuous melted state polycondensation or by batch melted state polycondensation mentioned in the said prior art, the present invention adds inorganic phosphorus compound as stabilizer before polycondensation stage; in addition, the present invention adds antioxidant such as hindered phenol containing Ca
+2
or phosphite or thioether or carbodiimide or dibutylthioamine zinc formate ; moreover, the present invention adds toner such as tetrahydrated cobaltous acetate, cobaltous chloride, and cobaltous nitrate.
The main skill of the present invention is to add inorganic phosphorus compound as stabilizer and hindered phenol primary antioxidant into PET polymer prepared by polyethylene terephthalate polymer and its copolymer in order to reduce the quantity of acetaldehyde produced by the side reaction caused by pyrolysis of PET polymer, which reduces the content of acetaldehyde in PET bottle at least 30% compared with those without the addition of said modifier.
The analysis method of the said intrinsic viscosity:
A Ubelohde viscosity measuring instrument is used to measure the solution prepared by phenol and tetrachloroethane in a 3:2 weight ratio.
Step (2) “Solid State Polycondensation Operation”
The intrinsic viscosity of the PET chip made from Step (
1
) “Melted state polycondensation operation” is somewhere between 0.5~0.7 dl/g; however, the molecular weight of the PET chip is too low for Step (3) “Blow molded manufacturing operation”. Besides, its strength is below enough. Moreover, the residual acetaldehyde in the PET chip is too high to manufacture PET bottles. Consequently, step (2) “solid state polycondensation” is a necessity to raise the intrinsic viscosity of PET chip up to somewhere between 0.72~1.2 dl/g so as to obtain enough molecular weight needed by the succeeding blow molding process and to reduce the residual acetaldehyde in PET chip to below 1 ppm. One of the solid state polycondensation process is the batch process, where the PET chip is heated in a vacuum revolving tank. The other one is the conti
Acquah Samuel A.
Nan Ya Plastics Corporation
Stevens Davis Miller & Mosher LLP
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