Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Rod – strand – filament or fiber
Reexamination Certificate
1999-08-18
2001-08-28
Harris, Cynthia (Department: 1774)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Rod, strand, filament or fiber
C428S375000, C428S378000, C428S395000, C053S430000, C028S289000
Reexamination Certificate
active
06280841
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a package of polyurethane elastic yarn to be used for heat bonding. More particularly, the present invention relates to a package of polyurethane elastic yarn to be used to form the waist and leg parts of disposable diaper which need elastic properties. The polyurethane elastic yarn exhibits good bonding properties when disposable diapers undergo bonding such as hot-melt bonding, fusion bonding, and ultrasonic bonding during their production. The package keeps its good appearance in shape without slipping down of yarn layer and also permits good unwinding without mutual sticking of the polyurethane elastic yarn.
2. Description of the Prior Art
Owing to its good elastic properties, polyurethane elastic yarn is used in various fields where extensibility and fittability are required. Polyurethane elastic yarn is usually supplied in the form of package and hence it is given a finishing agent so that it does not stick mutually in the package and it is unwound without unnecessary resistance.
In addition, in the case where polyurethane elastic yarn is used continuously it is necessary to replace packages frequently. The less the amount of yarn in the package, the greater the frequency of replacement. In order to reduce the frequency of package replacement, it has become common practice to make packages larger. In the case of large packages, application of finishing agent is indispensable to prevent yarn sticking which occur particularly in the core layer of the package.
Unfortunately, a polyurethane elastic fiber treated with a finishing agent has the disadvantage of being very poor in bonding properties due to the finishing agent present on it. This is true in the case where the gather of a disposable diaper is formed by adhesion or heat bonding with another material.
One way to solve this problem is disclosed in Japanese Patent Publication No. 50429/1993. According to this disclosure, a polyurethane elastic yarn is given a finishing agent composed mainly of silicone oil in an amount less than 2 wt % and then wound up such that its apparent elongation in the package is within a certain range for the amount of the finishing agent applied. Such polyurethane elastic yarn exhibits good adhesion properties with adhesive in the production of disposable diapers. The advantage of this method is that the polyurethane elastic fiber is not so poor in adhesion properties because of the smaller amount less than 2 wt % of the finishing agent used. On the other hand, this method has the disadvantage that the package of the polyurethane elastic yarn gives a poor appearance in shape because it is wound up with a lower tension than usual so as to prevent mutual sticking of yarn. This is true in the case where the apparent elongation is low even though it is within the certain range for the amount of the finishing agent used. Conversely, with a great apparent elongation, the polyurethane elastic yarn is not unwound smoothly due to mutual sticking of the yarn in the package. Thus, it is substantially difficult to obtain the package of polyurethane elastic yarn which appearance has a good in shape and is unwound smoothly by simply reducing the amount of finishing agent and defining the apparent elongation.
Japanese Patent Laid-open No. 152264/1998 discloses a package of elastic yarn which is given 2-5 wt % of a finishing agent, for example silicone oil, having a surface tension of 25-30 dyn/cm. It is claimed that this package is unwound smoothly and keeps its adhesion properties when used to make a disposable diaper. However, it has been found that the finishing agent having a surface tension of 25-30 dyn/cm as specified above does not provide satisfactory adhesion properties even when it is used in an amount of 2-5 wt %.
BRIEF SUMMARY OF THE INVENTION
The present invention was completed in order to overcome the above-mentioned disadvantages. Thus, it is an object of the present invention to provide a package of polyurethane elastic yarn for heat bonding, said package keeping its good appearance in shape and being capable of unwinding adequately without mutual sticking of yarn. This object is achieved by giving polyurethane elastic yarn a finishing agent which exhibits excellent heat bonding properties and permits smooth unwinding while preventing mutual sticking of yarn in the package.
The present invention covers a package of polyurethane elastic yarn for heat bonding which is obtained from polyurethane elastic yarn by giving it 3.0-10.0 wt % of a finishing agent and then winding it, said finishing agent being composed of component (A) which is a polypropylene glycol-based polyol and component (B) which is a reaction product of a polypropylene glycol-based polyol and an organic diisocyanate compound. According to the present invention, the finishing agent should preferably contain component (B) in an amount less than 30 wt % or it may contain component (A) alone. According to the present invention, the finishing agent should have an apparent viscosity of 50-250 mPa·s at 30° C. and a surface tension of 30-45 dyn/cm. According to the present invention, the package of polyurethane elastic yarn for heat bonding weighs more than 1 kg and measures such that the ratio of winding thickness to winding width is greater than 0.5.
DETAILED DESCRIPTION OF THE INVENTION
The polyurethane elastic yarn in the present invention is not specifically restricted. It may be either one which is obtained by wet spinning or dry spinning or by melt spinning. The polyurethane elastic yarn may be incorporated with a light stabilizer, a UV light absorbent, an agent to prevent discoloration by gas, a dye, an activating agent, a delustering agent, etc.
Component (A) which is used as a finishing agent in the present invention is a polypropylene glycol-based polyol, which is a diol and/or triol obtained by polymerization of propylene oxide alone or with ethylene oxide and has a weight-average molecular weight of 200-1500. With the molecular weight lower than 200, it unfavorably contains a low-molecular weight fraction which hinders heat bonding. With the molecular weight higher than 1500, it has such a high viscosity as to cause mutual sticking of yarn, preventing smooth unwinding. Incidentally, the polyol may have its hydroxyl groups partly esterified or acylated.
Component (B) is a reaction product of a polypropylene glycol-based polyol and an organic diisocyanate compound. The polyol is a diol and/or triol obtained by polymerization of propylene oxide alone or with ethylene oxide. The organic diisocyanate compound is one or more members selected from 4,4′-diphenylmethane diisocyanate, 3,3′-dichloro-4,4′-diphenylmethane diisocyanate, m-xylylene diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, hexamethylene diisocyanate, etc.
The polypropylene glycol-based polyol should preferably have a weight-average molecular weight of 200-2000. With a molecular weight lower than 200, it would cause obtained component (B) to increase a content of hard segments which gives rise to undesirable gel. With the molecular weight higher than 2000, it would cause obtained component (B) to have a high apparent viscosity which results in mutual sticking of yarn and makes unwinding difficult.
The reaction to produce the component (B) should be carried out in such a way that the amount of isocyanate groups in an organic diisocyanate compound or the total amount of isocyanate groups in two or more organic diisocyanate compounds is 50-90 eq %, preferably 50-70 eq %, of the amount of hydroxyl groups in the polyol used. If the ratio of isocyanate groups is higher than this, obtained component (B) has such a high degree of polymerization that it is poor in compatibility with component (A) and hence the resulting finishing agent has an adverse effect on unwinding. Moreover, if the ratio of isocyanate groups is more higher, obtained component (B) contains residual isocyanate groups which react with component (A) and the resulting finishing agen
Miyazawa Fumio
Morishita Nobuya
Noda Keiko
Birch & Stewart Kolasch & Birch, LLP
Fuji Spinning Co., Ltd.
Gray J. M.
Harris Cynthia
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