Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-07-27
2003-07-22
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C528S085000, C528S059000, C544S180000, C544S193000, C525S458000, C556S414000
Reexamination Certificate
active
06596819
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a polyisocyanate curing agent for a laminate adhesive which can be aged in a short time without shortening the pot life and which has good adhesivity, as well as to a process for production of the polyisocyanate curing agent.
(2) Related Prior Art
Recently, as a packaging method, complex flexible packaging has been remarkably developed for reasons such as strength of package, protectability for goods packed, workability during packaging, propaganda effect of package, reduction of packaging cost caused by the use of a film supplied in a large amount at a low cost, and the like. In the complex flexible packaging, there is used a laminated film or sheet produced using an adhesive. The current main stream of such a laminate adhesive is a two-pack type polyurethane adhesive generally composed of a base resin having active hydrogen group and a curing agent having isocyanate group, because the two-pack type polyurethane adhesive is excellent in adhesivity, low-temperature resistance and heat resistance and further it can be widely applied to various adherends such as plastics, metal foils and the like.
As such a laminate adhesive, there is disclosed, in JP-A-5-51574, an adhesive composition comprising a polyester polyurethane polyol, a carboxyl group-terminated polyester resin mixture, orthophosphoric acid or an ester thereof, an organic isocyanate compound and, as necessary, a silane coupling agent. According to the literature, as the organic isocyanate compound, there can be used a urethane bond-containing polyisocyanate derived from tolylene diisocyanate or an isocyanurate bond-containing polyisocyanate derived from tolylene diisocyanate.
In JP-A-63-110272 is disclosed an adhesive composition for complex laminate composed of at least one kind of polyol selected from polyether polyols, polyester polyols, polyether-urethane polyols and polyester-urethane polyols, an isocyanate group-containing silane coupling agent and a polyisocyanate curing agent.
In laminate adhesives, the shortening of curing time has been required. In most of the curing agents used in conventional laminate adhesives, however, no consideration has been made on the reactivity with the base resin. As a result, the curing of adhesive after application is slow, making necessary a step of curing acceleration, i.e. aging. Specifically explaining, it is necessary to store a laminated film in a warm chamber of 35 to 60° C. for about 3 to 5 days to conduct aging and sufficiently cure the adhesive used in the laminated film. At that time, the curing degree of the adhesive differs depending upon the aging conditions, which may allow the laminated film to vary in adhesion strength; in case of insufficient aging, delamination due to the insufficient curing of the adhesive may take place. Particularly in aliphatic polyurethane adhesives, a fairly long time is needed for the curing reaction. Such an aging step is essential in a dry lamination process and makes it difficult to respond to a request for short delivery period. Also in the aging step, there have been necessary an investment for construction of a warm house for conducting aging and a cost for utilities for temperature maintenance. In the technique described in JP-A-63-110272, no consideration is made to the shortening of aging time although improvements are achieved in the adhesivity, chemical resistance and heat resistance of the laminate adhesive.
In order to achieve the shortening of aging time, it is generally effective to add an additive. As such a technique, there can be mentioned a technique described in JP-A-9-316422. In the technique described in JP-A-9-316422, a catalyst is added to a polyurethane resin (a solution); as a result, a shorter aging time is obtained but there is a problem that the pot life after mixing of the base resin and the curing agent is shortened as well. An adhesive of short pot life tends to be used in an excessive amount and, moreover, solidifies often and impairs the applicator.
In JP-A-60-15419 is described a polyisocyanate resin (as a curing agent) obtained by reacting an isocyanurate bond-containing polyisocyanate derived from tolylene diisocyanate, with a polyhydric alcohol having a number-average molecular weight of 5,000 or less. As the organic polyisocyanate (as a curing agent) described in JP-A-5-51574, there are mentioned low-molecular isocyanate compounds, polyurethane isocyanates obtained by reacting such a low-molecular isocyanate compound with water or a polyhydric alcohol, dimers or trimers of low-molecular isocyanate compound, etc.
According to the description of JP-A-60-15419, the polyisocyanate resin is useful as a curing agent for coatings but its use as a curing agent for laminate adhesive is not mentioned. According to the description of JP-A-5-51574, no mention is made on any isocyanate group-terminated prepolymer having urethane group and isocyanurate group, obtained by reacting a diisocyanate and a high-molecular polyol. With the polyisocyanate curing agent described in JP-A-5-51574, it is impossible to achieve a shorter aging time without shortening the pot life.
OBJECTS AND SUMMARY OF THE INVENTION
The objects of the present invention are to provide a polyisocyanate curing agent for use in a laminate adhesive which can be aged in a short time without shortening the pot life, which has good adhesivity and which can withstand a severe retort treatment; and a process for producing such a polyisocyanate curing agent.
The present inventors made a study and found out that the above objects could be achieved by a polyisocyanate curing agent having particular groups, obtained by a particular polyisocyanate and a particular polyol. The finding has led to the completion of the present invention.
The present invention lies in the following 1 to 10.
1. A polyisocyanate curing agent for laminate adhesive, comprising:
(A) an isocyanate group-terminated prepolymer having isocyanurate group and urethane group, obtained by reacting an organic polyisocyanate containing at least (a1) an aromatic diisocyanate, with an active hydrogen group-containing compound containing at least (a2) a diol compound having a number-average molecular weight of 100 to 2,000.
2. A polyisocyanate curing agent for laminate adhesive, comprising:
(A) an isocyanate group-terminated prepolymer having isocyanurate group and urethane group, obtained by reacting an organic polyisocyanate containing at least (a1) an aromatic diisocyanate, with an active hydrogen group-containing compound containing at least (a2) a diol compound having a number-average molecular weight of 100 to 2,000, and
(B) an isocyanate group-terminated prepolymer having urethane group.
3. A polyisocyanate curing agent for laminate adhesive, comprising:
(A) an isocyanate group-terminated prepolymer having isocyanurate gorup and urethane group, obtained by reacting an organic polyisocyanate containing at least (a1) an aromatic diisocyanate, with an active hydrogen group-containing compound containing at least (a2) a diol compound having a number-average molecular weight of 100 to 2,000, and
(C) a silane coupling agent represented by the following general formula (1):
OCN—(CH
2
)
m
—Si(OR)
3
(1)
(wherein R is a methyl group or an ethyl group, and m is an integer of 1 to 5).
4. A polyisocyanate curing agent for laminate adhesive, comprising:
(A) an isocyanate group-terminated prepolymer having isocyanurate group and urethane group, obtained by reacting an organic polyisocyanate containing at least (a1) an aromatic diisocyanate, with an active hydrogen group-containing compound containing at least (a2) a diol compound having a number-average molecular weight of 100 to 2,000,
(B) an isocyanate group-terminated prepolymer having urethane group, and
(C) a silane coupling agent represented by the following general formula (1):
OCN—(CH
2
)
m
—Si(OR)
3
(1)
(wherein R is a methyl group or an ethyl group, and m is an integer of 1 to 5).
5. A process for producing a polyisocyan
Higashikubo Ichiro
Morikawa Yukihiro
Sasahara Toshiaki
Yoshida Kouji
Browdy and Neimark , P.L.L.C.
Dawson Robert
Nippon Polyurethane Industry Co., Ltd.
Peng Kim-Liang
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