Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From reactant having at least one -n=c=x group as well as...
Reexamination Certificate
2001-06-06
2004-04-13
Sergent, Rabon (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From reactant having at least one -n=c=x group as well as...
C428S423100, C528S061000, C528S065000, C528S077000, C528S904000
Reexamination Certificate
active
06720401
ABSTRACT:
The present invention relates to a novel coating composition to form a coating layer or film of a polyurethane resin which has a moisture permeability and is substantially non-porous.
It is known to form a layer of a hydrophilic polyurethane resin which is substantially non-porous, on a porous base material such as cloth, to produce a moisture permeable material suitable for application to clothing material. The layer of this hydrophilic polyurethane resin absorbs moisture from a high humidity side and discharges moisture to a low humidity side thereby to provide a moisture permeability.
As compared with a conventional polyurethane resin layer having numerous fine pores formed by a method such as a wet solidification method, a method by elution of fine soluble particles or a foaming method, the non-porous layer of the hydrophilic polyurethane resin is free from clogging of pores and is excellent also in the water-proofing property. The porous base material having such a non-porous hydrophilic polyurethane resin layer formed, is disclosed, for example, in JP-A-58-203172 or JP-A-58-222840.
To form a layer of a hydrophilic polyurethane resin, it is common to employ a method wherein a coating composition selected from a solution and a dispersion of a hydrophilic polyurethane resin, a mixture of raw materials for a hydrophilic polyurethane resin and a solution and dispersion thereof, is directly or indirectly coated on a porous base material to form a coating layer.
The above “indirectly” means a method wherein a coating layer not completely cured, is formed on a substrate having a release property, and then such a coating layer is laminated on the porous base material, and in some cases, an adhesive may be employed at the time of such lamination (see the above-mentioned JP-A-58-203172). Otherwise, a sufficiently cured hydrophilic polyurethane resin film may firstly be formed, and such a film may be laminated on the porous base material. Such a film is usually prepared by coating the above-mentioned coating composition on a substrate having a release property and curing it, and such a film peeled from the substrate having a release property is laminated on the porous base material, or such a film as supported on the substrate having a release property, may be laminated on the porous base material, and then the substrate having a release property is peeled to obtain the porous base material having the film laminated thereon.
For such lamination, the adhesive property or the fusing property of the hydrophilic polyurethane resin itself may be utilized, or an adhesive may be employed. The moisture permeability can be maintained by using, as the adhesive, an adhesive having moisture permeability (it is possible to increase the moisture permeability by adjusting the adhesive layer to be thin) or by applying the adhesive partially (for example, in a pattern of dots or lines).
The hydrophilic polyurethane resin is obtained usually from a highly hydrophilic polyol and a polyisocyanate compound as the main materials. In many cases, a two-pack coating composition consisting of a combination of an isocyanate group-containing prepolymer obtainable by reacting a highly hydrophilic polyol with a polyisocyanate compound, with a curing agent for the isocyanate group-containing prepolymer, is employed. As the curing agent, a polyfunctional active hydrogen compound having a low molecular weight, such as a diol or a diamine, is employed.
As mentioned above, the hydrophilic polyurethane resin is obtained from a highly hydrophilic polyol and a polyisocyanate compound as the main starting materials. As such a highly hydrophilic polyol, polyoxyethylene glycol has been commonly employed. However, use of such polyoxyethylene glycol brings about various problems.
Firstly, when a higher moisture permeability is desired, with a hydrophilic polyurethane resin employing polyoxyethylene glycol, the moisture permeability is inadequate in some cases. Namely, there is a limit in the moisture permeability of such a hydrophilic polyurethane resin, and it is difficult to accomplish a moisture permeability of a level higher than a predetermined level.
Secondly, when the isocyanate group-containing prepolymer is cured by a curing agent, the curing speed is very slow, and high speed coating and curing are difficult, whereby there is an operational or economical problem.
Thirdly, the isocyanate group-containing prepolymer employing polyoxyethylene glycol is solid or liquid having high viscosity at room temperature, and its handling is difficult. Usually, such an isocyanate group-containing prepolymer employing polyoxyethylene glycol is used as dissolved in a solvent in many cases, but use of such a solvent is likely to bring about an environmental or economical problem, and a coating composition having the amount of such a solvent reduced or containing substantially no solvent, is desired.
Fourthly, the mechanical properties used to be inadequate in some cases with the polyurethane resin obtained by using polyoxyethylene glycol.
An invention disclosing a coating composition to form a coating layer or film which maintains the flexibility or elongation of the above-mentioned polyurethane resin to some extent and which yet has high mechanical strength (JP-A-62-57467) or an invention disclosing a coating composition to form a coating layer or film having a high moisture permeability and elongation (JP-A-3-229773) has also been reported. However, with coating layers formed of such conventional coating compositions, mechanical strength such as durability or abrasion resistance has not been adequate. Further, the degree of swelling upon absorption of water tends to be high, and there has been a problem that the washing durability deteriorates.
The present invention is to solve the above problems and provides a coating composition to form a coating layer or film of a hydrophilic polyurethane resin having a moisture permeability and being substantially non-porous, which comprises, as an essential component, an isocyanate group-containing prepolymer obtainable by reacting diphenylmethane diisocyanate with the following polyoxyalkylene polyol:
A polyoxyalkylene polyol which contains at least 60 wt % of a polyoxyethylene polyol having at least three hydroxyl groups and having an oxyethylene group-content of at least 10 wt %, satisfies 3.0<n<3.5, where n is the average number of hydroxyl groups, and has an average oxyethylene group-content of from 60 to 90 wt %.
According to the present invention, it is possible to obtain a coating composition to form a coating layer or film which is excellent in mechanical properties such as tensile strength, elongation and abrasion resistance while maintaining an adequate moisture permeability and which has a low degree of swelling upon absorption of water and is excellent in washing durability. This can be accomplished for the first time by the reaction between the above-mentioned specific polyoxyalkylene polyol and the specific diisocyanate. It is particularly important that the average number n of hydroxyl groups in the polyoxyalkylene polyol satisfies 3.0<n<3.5, and diphenylmethane diisocyanate is used as the diisocyanate.
For example, the polyoxyalkylene polyol in the conventional coating composition has an average number n of hydroxyl groups, which is smaller than the above range, whereby no adequate mechanical properties can be obtained, and the swelling degree upon absorption of water tends to be high, whereby no adequate washing durability can be attained. On the other hand, if it is larger than the above range, the mechanical strength may be higher, but the flexibility or drape deteriorates substantially, whereby a coating composition having an excellent performance can hardly be obtainable.
Further, even if the average number n of hydroxyl groups satisfies the above range, if diphenylmethane diisocyanate is not used as the diisocyanate, and tolylene diisocyanate is, for example, used, no adequate mechanical properties can be obtained, the light resistance or NOx yellowing resi
Kashiwame Josho
Mori Satoru
Oguro Kaoru
Toyofuku Masanori
Asahi Glass Company Limited
Sergent Rabon
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