Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
2001-02-16
2002-08-20
Cooney, Jr., John M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C521S137000, C521S159000, C521S170000
Reexamination Certificate
active
06437013
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a microcellular polyurethane elastomer and a method of producing the same, more particularly to a microcellular polyurethane elastomer for a shoe sole and a method of producing the same.
2. Description of the Prior Art
A microcellular polyurethane elastomer has fine cells uniformly dispersed in a formed body, and is characterized by its forming density lower than that of a solid type polyurethane elastomer but higher than that of a flexible polyurethane foam. The microcellular polyurethane elastomer has been used for, e.g., shoe soles, gaskets, sealants and vibration insulators, and is still a very important material.
The representative microcellular polyurethane elastomer is produced by reacting a resin premix with an isocyanate component, wherein the resin premix is a mixture of a polyol component and one or more aids/additives, e.g., chain extender, catalyst, foam stabilizer and foaming agent.
It is known that polyester polyol and polyoxyalkylene polyol are used as the polyol component.
However, the microcellular polyurethane elastomer using a polyester polyol is insufficient in resistance to hydrolysis, although excellent in various physical properties, e.g., tensile strength, elongation and tear strength. Therefore, various attempts have been done to retard the hydrolysis, e.g., use of various types of additives and modification of chemical structures of polyester polyol. One of the methods proposed so far for improving resistance to the hydrolysis is to contain 0.001 to 0.007 mol of a compound having 3 active hydrogen atoms per 1000 g of the polyurethane resin produced, to cause a small quantity of branched structure. Such a compound, however, is still required to be further improved in resistance to hydrolysis.
On the other hand, use of polyoxypropylene polyol as the polyoxyalkylene polyol is known to improve resistance of the polyurethane to hydrolysis. However, a polyoxypropylene polyol has generally insufficient reactivity, and causes problems, e.g., extended demolding time and deterioration of green and final strength. These problems may be solved by increasing quantity of the catalyst, which, however, is accompanied by other problems, e.g., deterioration of processability and moldability resulting from shortened cream time or gel time.
Development of a polyoxyalkylene polyol exhibiting higher physical characteristics has been demanded even for the areas to which the conventional polyoxyalkylene polyol is sufficiently applicable with its resistance to hydrolysis, because of the problems associated with production of the polyol. One of the methods generally used for producing a polyoxyalkylene polyol is addition polymerization in which an active hydrogen compound is reacted with an alkylene oxide in the presence of potassium hydroxide (KOH) as the catalyst. However, it is known that, when propylene oxide as the common alkylene oxide is used for addition polymerization in the presence of a KOH catalyst, a mono-ol having an unsaturated group at the molecular chain piece terminal is produced increasingly as the by-product, as the polyoxypropylene polyol increases in molecular weight.
In general, mono-ol content corresponds to overall degree of unsaturation of polyoxypropylene polyol. The mono-ol has a lower molecular weight than the polyoxypropylene polyol produced by the main reaction, and greatly widens molecular weight distribution of the polyoxypropylene polyol and hence decreases average number of functional groups. It is also known that the mono-ol retards formation of the polymer networks for the urethane-forming reaction with polyisocyanate compound, resulting in deterioration of mechanical strength of polyurethane as the reaction product.
Attempts have been made to improve productivity of the polyoxyalkylene polyol synthesis, while inhibiting formation of mono-ol as the by-product. For example, a double metal cyanide complex (DMC) is proposed as the catalyst for addition polymerization of propylene oxide, as disclosed by publications of U.S. Pat. No. 3,829,505 and U.S. Pat. No. 4,472,560, which describe that DMC is an excellent catalyst for polymerization of propylene oxide.
A publication of U.S. Pat. No. 5,728,745 discloses a polyoxyalkylene polyol synthesized in the presence of an improved DMC as the catalyst, which gives a microporous elastomer showing a very high green strength and demolded in a short time, without causing deterioration of the final elastomer properties. Japanese Patent Publication No. 3-47202 describes, in its exmaples, that the polyoxyalkylene polyol synthesized in the presence of a DMC catalyst gives a polyurethane-based resin for shoe soles highly resistant to moist heat.
However, addition polymerization of ethylene oxide as the alkylene oxide in the presence of a DMC catalyst needs several steps, e.g., deactivation of the DMC catalyst by the reaction with an oxidant (e.g., an oxygen-containing gas, peroxide or sulfate), separation of the residual catalyst from the polyoxyalkylene polyol, and addition polymerization in the presence of a hydroxide of alkali metal (e.g., KOH), alkoxide of alkali metal or the like as the catalyst, as disclosed by U.S. Pat. No. 5,235,114. The inventors of the present invention have synthesized a polyoxyalkylene polyol in the presence of a DMC catalyst, and produced the microcellular polyurethane elastomer from the polyol, to find that the microcellular polyurethane elastomer fails to satisfy the desired characteristics they have pursued with respect to demolding time, durability-related characteristics (e.g., compression set), and cell shape in a specific range.
One of the catalysts other than the above-described ones for synthesizing polyoxyalkylene polyol is a phosphazene compound, disclosed by a publication of EPO 763,555, Macromol. Rapid Commun. Vol. 17, pp. 143 to 148, 1996, and Macromol. Symp. Vol. 107, pp. 331 to 340, 1996). When used as the catalyst for synthesizing polyoxyalkylene polyol, the phosphazene compound brings about advantages of controlled production of the mono-ol as the by-product and greatly improved productivity.
BRIEF SUMMARY OF THE INVENTION
Object of the Invention
It is an object of the present invention to provide a microcellular polyurethane elastomer which can solve the problems involved in the conventional techniques. It is another object of the present invention to provide a method of producing the same. More concretely, the present invention provides a microcellular polyurethane elastomer showing reduced demolding time, greatly reduced compression set and excellent mechanical properties, and, at the same time, excellent in appearances and coating characteristics, and also provides a method of producing the same.
SUMMARY OF THE INVENTION
The inventors of the present invention have found, after having extensively studied to develop a microcellular polyurethane elastomer of excellent characteristics and a method of efficiently producing the same, that the microcellular polyurethane elastomer can have excellent mechanical strength when it has an overall density (D) in a specific range and its compression set (CS2) and cell diameter on the skin surface satisfy specific correlations with its overall density (D), that the microcellular polyurethane elastomer can have excellent characteristics and its demolding time can be reduced to improve production efficiency by use of polyoxyalkylene polyol having a specific hydroxyl value (OHV), an overall degree of unsaturation and head-to-tail (H-T) linkage selectivity, and that the microcellular polyurethane elastomer can have reduced demolding time and excellent mechanical properties by use of a specific quantity of polyoxyalkylene polyol having a W
20
/W
80
ratio as an index representing molecular weight distribution in a specific range, reaching the present invention.
The present invention, which solves the above problems, provides the following items (1) to (21).
(1) A microcellular polyurethane elastomer, having
(a) an overall density (D) of 100 kg
Chikamoto Takuya
Kuwamura Goro
Nishiguchi Daisuke
Ueno Kaoru
Usaka Kazuto
Birch & Stewart Kolasch & Birch, LLP
Cooney Jr. John M.
Mitsui Chemicals Inc.
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