Plastic and nonmetallic article shaping or treating: processes – Forming continuous or indefinite length work – Shaping by extrusion
Reexamination Certificate
1999-10-22
2002-06-04
Tentoni, Leo B. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Forming continuous or indefinite length work
Shaping by extrusion
C264S211170, C528S059000, C528S065000, C528S080000
Reexamination Certificate
active
06399003
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention concerns a method of melt-spinning polyurethanes into textile decitex spandex and, more particularly, a method using ethylene glycol chain extender in the preparation of the polyurethane.
2. Discussion of Background Art
Spandex based on polymeric glycols, diisocyanates, and aliphatic diols is known. Ethylene glycol has been disclosed as a chain extender for making thermoplastic polyurethane-based spandex, but its use in making melt-spun spandex leads to the difficulty in melt-spinning such polyurethanes. U.S. Pat. No. 3,649,600 discloses spandex based on poly(tetramethyleneether) glycol 1,1′-methylenebis(4-isocyanatobenzene) and 1,4-butane-diol, polymerized in a two-step melt-polymerization process in the presence of 0.06-0.3% by weight of water based on the polymeric glycol. Although fibers are prepared, the high softening point of the polyurethanes obtained is expected to give poor spinnability due to excessive cross-linking at the high temperature needed to melt-spin the polymers.
Japanese Published Patent Application 04-146915 and U.S. Pat. No. 5,391,682 disclose a two-step melt polymerization and melt spinning of high molecular weight, number average above 160,000, polyurethanes under special conditions of high shear and a total glycol to isocyanate ratio range of 0.95 to 1.05. The product polyurethane is said to contain up to 500 crystalline particles (clumps) per kilogram.
Japanese Published Patent Application 05-214062 discloses melt polymerization and melt spinning of 2G-extended polyurethanes under special conditions of high shear rates (at least 10,000 sec
−1
) and very short residence times (60-300 seconds), without providing any examples using 2G, which can be used for pelletizing the large diameter strands. There is no disclosure of small-diameter textile fibers, whose manufacture makes more stringent demands on polymer quality.
There remains a need to be able to prepare polyurethanes based on ethylene glycol chain extender which can be reliably melt-spun into textile decitex fibers having useful properties.
SUMMARY OF THE INVENTION
The process of this invention for preparing melt-spun spandex comprises the steps of:
a) contacting in a solvent
i) a polymeric glycol selected from the group consisting of poly(tetramethyleneether) glycol and poly(tetramethyleneether-co-3-methyltetramethylene-ether) glycol having a number average molecular weight of 2400-8000,
ii) 1,11′-methylenebis(4-isocyanatobenzene) at a molar addition ratio of polymeric glycol to isocyanate of 1.8-6.0:1 and
iii) a chain extender selected from the group consisting of ethylene glycol, 1,3-propanediol, and 1,4-butanediol, to form a polyurethane;
b) adding a monofunctional chain terminator in order to obtain a polyurethane having a number average molecular weight 40,000-150,000 and a softening point of not more than 230° C.;
c) removing the solvent; and
d) melt-spinning the polyurethane to form spandex.
DETAILED DESCRIPTION OF THE INVENTION
As used herein, the term “spandex” has its customary meaning, that is, a manufactured fiber in which the fiber-forming substance is a long chain synthetic elastomer comprised of at least 85% by weight of a segmented polyurethane. The segments in the polyurethane are classified into “soft” segments of polyether-urethane blocks and “hard” segments containing aromatic and urethane groups.
Suitable polymeric glycols include poly(1,4-tetramethyleneether glycol) (PO4G) and copolymers of tetrahydrofuran and 3-methyltetrahydrofuran (3MePO4G) having a number-average molecular weight of about 2400-8000. 3MePO4G having 4-20 mole percent 3-methyl moieties and a molecular weight of about 2400-4500 is preferred. When the molecular weight of polymeric glycol is less than 2400, the recovery properties of the resulting yarn tend to become low and it becomes difficult to obtain the desired elongation. When the molecular weight of the polymeric glycol exceeds 8000, the strength decreases and the resistance to chemicals declines. Use of the preferred 3MePO4G glycol gives spandex having a particularly good balance of mechanical properties.
The diisocyanate used in the process of this invention is 1,1′-methylenebis(4-isocyanatobenzene) (MDI). Other diisocyanates can be included in minor amounts, provided they do not compromise the advantageous effects of the invention.
The chain extender used in the method of the present invention is selected from the group consisting of ethylene glycol (abbreviated hereinafter as 2G), 1,3-propanediol (3G) and 1,4-butanediol (4G). 2G is preferred and presents the most demands on stable melt-spinning of polyurethanes prepared with it. This is because polyurethanes made with 2G have a high hard segment melting point (about 240° C.). The hard ratio (the molar ratio of 2G to polymeric glycol) is in the range of about 1.75 to 3.0. Other diol chain extenders can be included in minor amounts.
A monofunctional chain terminator is used in the process of the present invention to control the molecular weight of the polyurethane. For polyurethanes useful in melt-spinning spandex, this number average molecular weight is determined to be 40,000-150,000. Useful chain terminators include monoamines, monoalcohols and monoisocyanates. Aliphatic alcohols are preferred, and n-butanol is especially preferred. The chain terminator can be added at the beginning or the end of the polymerization. Addition at the end of the polymerization is preferred for more uniform molecular weight distribution.
Any suitable solvent can be used in the polymerization process of the present invention, such as dimethylacetamide (“DMAc”), dimethylformamide, dimethylsulfoxide, n-methylpyrrolidone, and mixtures thereof.
The ingredients for the solution polymerization can be added in one step or in two steps. In the one-step method, the polymeric glycol, MDI and diol chain extender are added substantially simultaneously. In the two-step method, the polymeric glycol and MDI are first mixed to allow the formation of an isocyanate-terminated prepolymer, after which the diol chain extender is added to form a polyurethane. The one-step method is preferred because of its simplicity and low cost. In the one-step method, good results can be obtained when the starting materials are added to the solution at a relatively low temperature (for example in the range of about 20° C.-30° C.), the temperature is raised to the reaction temperature (for example at least about 70° C.) and, once a preselected degree of polymerization has been reached, the chain terminator is added.
After the completion of the above steps, any suitable method can be used to remove the solvent from the polymer solution. Typically the solvent can be removed in a vacuum or with hot air, and, alternatively, the solution can be poured into steam or water. A devolatilizing extruder, such as that used in Canadian Patent 1,321,852, can also be used so that polyurethanes can be continuously polymerized and spun. Methods combining these approaches can also be used.
Polyurethane from which the solvent has been removed in this way can be generally processed into chips, flakes, particles and the like. Chips offer the advantage of being easy to transport, in addition to which any further required drying is easy. Because the resulting polyurethane is sometimes tacky, the addition of a suitable lubricant or antitack agent such as silicone oil, calcium stearate, sodium stearate, magnesium stearate, talc, barium sulfate, and the like can be useful. These lubricants and antitack agents can be added to the solution or during the course of solvent removal.
The polyurethane which has been desolvated in this way is optionally further dried as needed. Any conventional drying method can be employed without particular limitation as to either the drying conditions or the method. Particularly advantageous methods include vacuum drying and drying in heated dry nitrogen.
The solution polymerization process of the invention requires a molar ratio of diisocyanate to po
DuPont-Toray Co. Ltd.
Tentoni Leo B.
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