Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2001-07-18
2004-03-30
Niland, Patrick D (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S507000, C524S589000, C524S590000, C524S591000, C524S839000, C524S840000, C525S054260, C525S123000, C525S124000, C525S131000, C525S404000, C525S455000
Reexamination Certificate
active
06713551
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a resin composition for coatings and to a coating composition for curing (curable coating composition).
PRIOR ART
Polyol-containing resin compositions for coatings are applied in curable coating compositions or the like which are applied to various substrates for protecting and decorating the surface thereof. Such curable coating compositions are required to give cured coating films having a high luster as well as a high surface hardness without brittleness, namely hardness and flexibility, so that when widely applied to such structures as buildings, plants, tanks and bridges, and to automobiles, ships, industrial equipment, various industrial products and so forth, they can perform improved protective and decorative and other functions, protecting the substrate surface from mechanical shocks and the like and maintaining the substrate appearance. Flexibility contributes to improvements in processability as well. It is also demanded that the coating films, when exposed to outdoor conditions, show a high level of weathering resistance, since the maintenance cost can be reduced if those functions can be maintained for a prolonged period of time.
In Japanese Kokai Publication Sho-64-75571, there is disclosed a resin composition for coatings which comprises, as a main component, a urethane-modified resin obtained by reacting at least one polymer polyol selected from among polyester polyols, acrylic polyols and polyether polyols with an organic diisocyanate. This resin composition for coatings can form coating films with or without using a crosslinking agent such as a melamine resin and give coating films balanced between hardness and flexibility. However, the viscosity of the composition increases due to urethane bonds occurring in the resin skeleton. Thus, there is room for improvement in applicability through viscosity reduction or for contrivance to prepare high solid compositions to meet the recent resources saving and/or environmental protection requirements.
In Japanese Kokai Publication Hei-09-221627, there is disclosed a resin composition for use in urethane coating compositions for concrete coating form plywood panel which comprises a polyol-modified acrylic resin and a polyisocyanate compound incorporated therein. This resin composition for coatings is a solventless one resulting from the use of the polyol-modified acrylic resin, hence is excellent in resources saving and environmental protection. However, for applying the composition in various fields, the coatings or coating films are not yet satisfactory in hardness. In addition, there is room for contrivance to further increase the hardness and thus attain hardness and flexibility simultaneously.
Therefore, with these polyol-containing compositions for coatings, it is not possible to provide coatings with both hardness and flexibility simultaneously while forming cured coating films high in luster and excellent in weathering resistance, thus further improving the performance and quality of the coating films, and, since the hardness and flexibility of coating films are properties incompatible with each other. It is also impossible to satisfy the resources saving and environmental protection requirements by providing high solid compositions while meeting the performance requirements mentioned above.
Meanwhile, among polyurethane resin-based coatings, there is a reaction curing type one capable of forming urethane bonds by reaction of hydroxyl groups with isocyanato groups in the process of drying and, for promoting this reaction, methods are known, for example the method comprising providing the resin with an internal pendant acid value and the method comprising adding an external catalyst such as a tin catalyst. However, if the reactivity for curing is increased to a sufficient extent by using these two techniques, problems may arise, for example the coating films obtained may be poor in appearance and, in the case of two component type coating compositions, the pot life (working life) may become short. Thus there is room for contrivance to sufficiently increase the reactivity of such resin-based coating in the step of curing and, at the same time, improve the appearance of coating films formed and maintain the pot life of the film.
In view of the above-mentioned state of the art, it is an object of the present invention to provide a resin composition for coatings and a curable coating composition which can give cured coating films having excellent basic properties, inclusive of high luster and high weathering resistance, as well as high hardness and good flexibility and which not only satisfy the above performance requirements but also have a high solid content and thus can meet the resources saving and environmental protection requirements. Another object of the invention is to provide a curable coating composition which shows high reactivity in the step of curing and can form coatings having a good appearance and can sufficiently maintain the pot life thereof.
SUMMARY OF THE INVENTION
The present inventors closely examined the problems with polyol-containing resin compositions for coatings such as curable coating compositions and made intensive, investigations accordingly and, as a result, found that a resin composition for coatings, when it contains a polyol (A1) having a specific proportion of a ring structure, it can give cured coating high in luster and hardness and, when it contains a polyether polyol (B) capable of providing flexibility, it can give cured coating films having high hardness and at the same time good flexibility and, further, that when the polyol (A1) has a cycloalkyl group, among others, as the ring structure, the weathering resistance can be further improved. Furthermore, they revealed the fact that when the polyether polyol (B) is used in a specific amount, a high solid content, which is a preferred mode of a resin composition for coatings, can dramatically be attained in addition to the above-mentioned physical properties of cured coating films. These findings have now led to completion of the present invention.
When a polyol formed by using a specific linear branched structure-containing polymerizable unsaturated monomer as an essential starting material is used in a resin composition for coatings, the viscosity of the resin composition can be reduced (hence the composition can have a high solid content) but the coating films obtained are inferior in hardness as compared with the case where a ring structure-containing polyol (A1) is used. It was found that when a polyol (A2) designed so as to have an increased hydroxyl group content is used, the crosslink density is improved and viscosity reduction (formation of high solid compound) and coating films hardness can both be attained simultaneously. From the luster viewpoint, the polyol (A1) is preferred owing to the ring structure thereof.
It was further found that when, in a curable coating composition comprising such a resin composition for coatings and a crosslinking agent, the crosslinking agent comprises a (blocked) polyisocyanate compound as an essential constituent, (1) the reactivity in the step of curing can be increased and coating films having a good appearance can be formed and, in addition, the pot life of the coating can sufficiently be maintained by using an organometallic compound and an acidic substance combinedly for promoting the curing of the composition and (2) the coating composition can be rendered quickly curable and can maintain a satisfactory pot life by using a temperature-sensitive catalyst showing catalytic activity at 60° C. or above and, further, a high level of appearance can also be produced since the curable coating composition is generally applied at room temperature, in this case its catalytic activity is shown, and the reaction between the hydroxyl and isocyanato groups will not proceed immediately after application, hence there is enough time for the leveling of the coating film.
Thus, the present invention provides a resin composition for coatings
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Kodama Naoki
Takahashi Kunio
Yoshida Masaya
Connolly Bove & Lodge & Hutz LLP
Niland Patrick D
Nippon Shokubai Co. , Ltd.
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