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
2002-11-12
2004-03-23
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...
C252S182200, C252S182210, C252S188220, C525S124000, C525S127000, C525S128000, C525S131000, C525S440030, C525S454000, C525S455000, C525S458000, C528S059000, C528S060000, C528S065000, C528S066000, C528S067000, C528S073000, C544S067000, C544S068000, C560S024000, C560S025000, C560S115000, C560S157000, C560S158000, C560S336000, C560S354000, C560S355000
Reexamination Certificate
active
06710151
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an end-blocked isocyanate prepolymer that is preferable for a surface coating material, especially a powder coating material, a composition containing the end-blocked isocyanate prepolymer, and a process for preparing the end-blocked isocyanate prepolymer. More particularly, the invention relates to a novel end-blocked isocyanate prepolymer having an oxadiazine ring, a composition for a surface coating material, which contains the prepolymer, and a process for preparing the prepolymer.
BACKGROUND OF THE INVENTION
Blocked polyisocyanates wherein the isocyanate groups are previously reacted with an active hydrogen compound in order to maintain the isocyanate groups in an inert state until the reaction is initiated are publicly known. For example, the conventional information is collected in “Progress in Organic Coatings” 36(1999), 148-172, etc. The blocked polyisocyanates mentioned above have been widely used as curing agents for powder coating materials.
Since the quantity of VOC (volatile organic compounds) released from such powder coating materials is small, use of the powder coating materials is recently extending all over the world as environmentally low-burdening coating materials instead of the conventional solvent type coating materials.
The conventional blocked polyisocyanates, however, use VOC such as &egr;-caprolactam as a blocking agent, and the blocking agent dissociated in the course of the reaction is released as VOC into the environment directly or indirectly, so that further decrease of the VOC has been desired. Moreover, there has been presented a problem that the blocking agent such as &egr;-caprolactam volatilizes in the curing stage to cause resinous stain on the inside of the curing oven and this causes yellowing of the resulting coating film.
In order to solve the above problems, many uretdione curing agents (internally blocked isocyanates) have been reported (e.g., Japanese Patent Publication No. 29705/1985, Japanese Patent Laid-Open Publication No. 70761/1976, Japanese Patent Laid-Open Publication No. 64676/1982, Japanese Patent Laid-Open Publication No. 16090/1989, Japanese Patent Laid-Open Publication No. 188737/1997). In order to form good coating films, however, the uretdione curing agents need higher curing temperatures than the conventional blocked polyisocyanates (e.g., Japanese Patent Laid-Open Publication No. 46055/1998, Japanese Patent Laid-Open Publication No. 279450/1999), so that the energy consumption becomes large, and hence it cannot be said that they are environmentally low-burdening. Although various means to solve such problems have been studied, there still remain many practical problems.
On the other hand, diisocyanates having oxadiazinetrione ring structure, high-molecular weight or low-molecular weight glycols, and oligomers prepared by the use of an end-blocking material are also known. Under the conventional reaction conditions (use of reaction catalyst such as dibutyltin dilaurate, see Japanese Patent Laid-Open Publication No. 193327/1988, Japanese Patent Laid-Open Publication No. 206820/1985, Japanese Patent Laid-Open Publication No. 115615/1985 and Japanese Patent Laid-Open Publication No. 9773/1982), however, ring-opening reaction of the oxadiazinetrione ring proceeds partially or wholly, and in either case, a three-dimensionally crosslinked urethane oligomer is formed. In this case, the resulting compound has no melting point, and its melt viscosity is extremely high, so that this compound cannot be used unless it is diluted with a solvent. The above-mentioned oligomers are also used in a dilute state with a solvent such as tetrahydrofuran, Cellosolve acetate or polyoxypropylene glycol, without being separated.
That is to say, such an isocyanate prepolymer having an oxadiazinetrione ring and exhibiting a melting point as described in this specification is a novel substance, and an example relating to use of the substance as a curing agent for a surface coating material, not to mention a curing agent for a powder coating material has been hitherto unknown.
It is known that the oxadiazinetrione ring readily reacts with a hydroxyl group-containing compound at room temperature in the presence of a catalyst (see Japanese Patent Laid-Open Publication No. 87600/1998). It is also known that the ring-opening reaction proceeds at a temperature of not lower than 120° C. (see Japanese Patent Publication No. 35314/1970, Japanese Patent Laid-Open Publication No. 96658/1983 and Japanese Patent Laid-Open Publication No. 193327/1988). According to the conventional information, therefore, it is difficult to carry out the control of the curing reaction within a narrow temperature region such that at the melt kneading temperature (100-140° C.) the oxadiazinetrione ring is maintained unreacted and at the curing temperature (160-200° C.) ring-opening reaction of the oxadiazinetrione ring is promoted.
It is an object of the present invention to provide a novel end-blocked isocyanate prepolymer which can remarkably decrease occurrence of a volatile component in the curing stage, has excellent film properties, shows excellent energy efficiency and is favorable for a surface coating material, and to provide a process for preparing the prepolymer. It is another object of the invention to provide a surface coating material using the end-blocked isocyanate prepolymer, such as a powder coating material, which is free from occurrence of a volatile component in the curing stage, has excellent film properties and shows excellent energy efficiency, and to provide a process for preparing the surface coating material.
DISCLOSURE OF THE INVENTION
The present inventors have focused attention that the oxadiazinetrione structure reacts with an active hydrogen compound such as a polyol similarly to a blocked polyisocyanate and releases only small amount of carbon dioxide that is non-VOC, and have earnestly studied to attain the above objects. As a result, the present inventors have found that a novel end-blocked isocyanate prepolymer having a specific structure can remarkably decrease the amount of the released VOC as compared with the conventional end-blocked polyisocyanates and exhibits excellent film properties. Based on the finding, the present invention has been accomplished.
The end-blocked isocyanate prepolymer having an oxadiazine ring according to the invention is a prepolymer wherein at least one of isocyanate groups of a NCO-terminated isocyanate prepolymer, which has NCO groups at the ends and comprises units derived from an oxadiazinetrione compound (A) represented by the following formula (1) and units derived from an active hydrogen compound (B) represented by the following formula (2), is blocked with a unit derived from an end-blocking agent (C) having at least one active hydrogen in one molecule, said end-blocked isocyanate prepolymer having a softening point of not lower than 50° C.,
wherein R
1
is a group selected from the group consisting of an aliphatic hydrocarbon group of 2 to 20 carbon atoms, an aliphatic hydrocarbon group having an aromatic group and an alicyclic hydrocarbon group, and n is an integer of 1 or greater,
H—A—R
2
—A—H (2)
wherein R
2
is a straight-chain, branched or cyclic alkylene group of 2 to 12 carbon atoms, and A is any one of an oxygen atom, a sulfur atom, a N—R′ group (R′ is a hydrogen atom, an alkyl group, an aryl group or an aralkyl group) and a COO group.
The end-blocked isocyanate prepolymer having an oxadiazine ring according to the invention is a prepolymer obtained by allowing a NCO-terminated isocyanate prepolymer having NCO groups at the ends to react with an end-blocking agent (C) having at least one active hydrogen in one molecule, said NCO-terminated isocyanate prepolymer being obtained by allowing an oxadiazinetrione compound (A) represented by the following formula (1) to react with an active hydrogen compound (B) represented by the following formula (2),
wherein at least one of isocyanate groups of the NCO-terminated isoc
Haseyama Ryuuji
Kuwatsuka Toshiaki
Mega Izumi
Ogata Hideaki
Shimoda Manabu
Burns Doane , Swecker, Mathis LLP
Sergent Rabon
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