Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From silicon reactant having at least one...
Reexamination Certificate
2001-07-17
2002-06-18
Acquah, Samuel A. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From silicon reactant having at least one...
C528S027000, C528S038000, C528S272000, C528S288000, C528S297000, C528S300000, C528S302000, C528S306000, C528S308000, C528S308600, C524S188000, C524S196000
Reexamination Certificate
active
06407194
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to polyester polymers. More specifically, this invention relates to polyester polymers having temporarily crosslinked polyester molecules.
BACKGROUND OF THE INVENTION
Polyesters are widely used to manufacture textile fibers and can be manufactured by combining a glycol, such as ethylene glycol, and a carbonyl compound, such as dimethyl terephthalate (DMT) or terephthalic acid (TPA). In the DMT process, DMT reacts with a glycol, such as ethylene glycol, to form a bis-glycolate ester of terephthalate (“monomer”) and a byproduct methanol in an ester exchanger column. The monomer is then polymerized by condensation reactions in one or two prepolymerizers and then a final polymerizer or finisher.
In the TPA process, TPA is combined with a glycol, such as ethylene glycol, to form a slurry at 60° C. to 100° C. followed by injecting the slurry into an esterifier. A linear oligomer with a degree of polymerization less than 10 is formed in one or two esterifiers (first and second in series, if two) at temperatures from 240° C. to 290° C. The oligomer is then polymerized in one or two prepolymerizers and then in a final polymerizer or finisher at temperatures from 250° C. to 300° C. Water is a byproduct of the TPA esterification and polycondensation process.
A problem associated with polyester fibers is their tendency to pill. Pilling is a defect in fabric caused when fibers are rubbed or pulled out of yarns and entangled with intact fibers, forming soft, fuzzy balls on the fabric surface. One of the most common commercial practices to produce pilling resistant fibers is to make lower molecular weight polyester fibers with an intrinsic viscosity of 0.30 to 0.55, which have lower strength and are pill resistant. Unfortunately, spinning is more difficult with lower molecular weight and lower strength polyester fibers.
A temporary crosslinker, brancher, or melt viscosity booster can be used to increase melt viscosity and polymer strength temporarily for better spinning performance. Tetraethoxysilane (TEOS) has been used commercially for many years as a temporary brancher for pilling resistant polyesters made from DMT process. TEOS temporarily crosslinks or branches polyester molecules and increases melt viscosity and strength for spinning. After spinning, the crosslinks break down by hydrolysis in drawing and other processes, thereby obtaining lower molecular weight fibers and offering pilling resistant properties.
Unfortunately, the use of TEOS as a temporary brancher for pilling resistant polyesters is not compatible with the TPA process. A major problem with TEOS is that TEOS forms sands and solids when it reacts with water. Although TEOS is suitable for the DMT process, where there is no water byproduct, the TPA process produces a water byproduct. Therefore, TEOS is not suitable for the TPA process due to the formation of sands and solids by the reaction of TEOS with the water byproduct.
There have been many studies to use permanent crosslinkers such as trimethylolpropane (TMP) and trimellitic acid or its ester to produce pilling resistant fibers. Unfortunately, the permanent crosslinks do not break down after spinning and their pilling resistant properties are only from the increased brittleness from crosslinking. Polymer molecular weight must be high enough for good spinning, but the high molecular weight polymers have poor pilling resistance. Therefore, permanent crosslinkers are fundamentally inferior compared with temporary crosslinkers or branchers such as TEOS.
The TPA process has gradually become a preferred process for manufacturing of polyethylene terephthalate, polypropylene terephthalate, and polybutylene terephthalate, where water is a byproduct. Therefore, there is an increased need to develop a process to produce lower molecular weight polyesters with temporary crosslinks or branches to increase melt viscosity and strength for spinning, which does not form a solid in the presence of water.
Alkali metal salts of 5-sulfoisophthalic acids or their esters such as sodium sulfoisophthalic acid (Na-SIPA), sodium dimethylsulfoisophthalate (Na-DMSIP), and bis(2-hydroxyethyl) sodium 5-sulfoisophthalate (Na-SIPEG) have been studied to produce pilling resistant fibers. Unfortunately, to obtain desired pilling resistant properties, Na-SIPA or Na-SIPEG must be added at 3 to 10% by weight of polymer. Since Na-SIPA and Na-SIPEG cost about ten times more than TPA or DMT, the copolymer is much more expensive. In addition, this copolymer can only be hydrolyzed in acidic solution. A further problem with this copolymer is that melt viscosity is increased by the self association of the sodium sulfoisophthalate (Na-SIP) chain, not by molecular bonds. Therefore, even though the melt viscosity is high, the polymer strength is low and spinning performance is poor.
An additional consideration for producing polyester polymers is the rate of crystallization of the partially oriented polyester polymer during spinning. Normal spinning speeds for partially oriented polyester polymers are typically on the order of about 3000-3500 m/min. At higher spinning speeds, however, crystallization of the partially oriented polyester polymer occurs too fast, which results in low orientation in fibers and deteriorates physical properties such as tenacity, elongation, and shrinkage.
To increase productivity and spin at higher speeds, such as speeds of 4000-5000 m/min., additives are injected to decrease the crystallization rate of the polyester polymer. These additives include, for example, (i) a permanent crosslinker such as trimellitic acid that is added during the polymerization process or (ii) a liquid crystal polymer that is added to the polyester transfer line. Unfortunately, the permanent crosslinker and liquid crystal polymer often introduce undesirable changes to the physical properties of the polyester polymer fiber, such as higher brittleness and lower tenacity and elongation.
Accordingly, there is also a desire to decrease the crystallization rate of the polyester polymer during spinning without adversely altering the physical properties of the polyester polymer fiber.
SUMMARY OF THE INVENTION
The present invention provides a process for increasing the pill resistance of a polyester polymer, wherein the polyester polymer is produced by polymerizing a polymerization mixture comprising (a) a carbonyl compound or an oligomer of the carbonyl compound and (b) a glycol. The process comprises contacting the polymerization mixture with a cross-linker comprising (RO)
m
Si(X)
n
Z
p
, wherein:
R is hydrogen, a hydrocarbon, or a hydrocarbon oxygen;
X is a hydrocarbon or a hydrocarbon oxygen;
Z is a hydrophilic group;
m is 1 to 3;
n is 1 to 3; and
p is 1 to 30.
The invention also provides a process for decreasing the crystallization rate of a polyester polymer during a spinning, wherein said polyester polymer is produced by polymerizing a polymerization mixture that comprises (a) a carbonyl compound or an oligomer of said carbonyl compound and (b) a glycol, said process comprising contacting said polymerization mixture with a cross-linker comprising (RO)
m
Si(X)
n
Z
p
, wherein:
R is hydrogen, a hydrocarbon or a hydrocarbon oxygen;
X is a hydrocarbon or a hydrocarbon oxygen;
Z is a hydrophilic group;
m is 1 to 3;
n is 1 to 3; and
p is 1 to 30.
In another embodiment of the invention, the polyester polymer is produced by polymerizing a polymerization mixture that comprises a carbonyl compound or an oligomer of the carbonyl compound, wherein the carbonyl compound is HO—R
2
—COOH, wherein R
2
is (i) hydrogen, (ii) a hydrocarbon having 1 to 30 carbon atoms, or (iii) a hydrocarbon oxygen group having 1 to 30 carbon atoms and 1 to 20 oxygen atoms.
The invention also includes a pill resistant polyester polymer produced by the aforementioned process. The process of the invention increases the melt viscosity and strength of the polyester polymer temporarily. In addition, the process of the invention decreases the crystallization rate of the polyester polymer during spinning.
In on
Acquah Samuel A.
E. I. du Pont de Nemours and Company
Krukiel Charles E.
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