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
1999-04-30
2001-09-18
Yoon, Tae H. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S089000, C525S314000
Reexamination Certificate
active
06291583
ABSTRACT:
This application is the national phase number 35 U.S.C. §371 of PCT International Application No. PCT/JP97/03967 which has an International filing date of Oct. 30, 1997 which designated the United States of America.
1. Technical Field
This invention relates to an aromatic vinyl compound-isoprene block copolymer composition which is useful as a hot-melt adhesive and other adhesives, a process for producing the copolymer composition, and an adhesive or pressure sensitive adhesive composition-comprising the copolymer composition.
2. Background Art
A polystyrene-polyisoprene block copolymer and other block copolymers have widely been used as a base polymer for an adhesive or pressure sensitive adhesive composition. Especially a styrene-isoprene-styrene block copolymer is known as a base polymer for a hot-melt adhesive.
For the production of disposable diapers, sanitary napkins and the like, a hot-melt adhesive is applied to a thermoplastic sheet or a nonwoven fabric made of a thermoplastic fiber by spiral spraying or other means. As the hot-melt adhesive, those which are applicable at a low melt-viscosity and a low temperature are desired with a view to preventing discoloration of adherends such as polyethylene sheet and deterioration of the hot-melt adhesive. The hot-melt adhesives are generally desired to have a melt viscosity of not larger than 5,000 cps at a temperature of 150° C. However, a hot-melt adhesive composed of a styrene-isoprene block copolymer, which has such a low melt-viscosity upon fusion and exhibits satisfactory peel adhesion and shear adhesion failure temperature (SAFT), has not been proposed yet.
In U.S. Pat. No. 5,399,627, a styrene-isoprene block copolymer composition is disclosed, which is produced by a process wherein a polystyrene-polyisoprene diblock copolymer having a minor proportion of a poybutadiene block bound to a terminal thereof is coupled with a coupling agent having four functionalities, and which is composed of a predominant proportion of the thus-produced copolymer with four branches and a minor proportion of an unreacted diblock copolymer. This block copolymer composition contains only not larger than 29% by weight of the unreacted diblock copolymer, and exhibits a poor peel adhesion when it is applied to a hot-melt adhesive.
In Japanese Unexamined Patent Publication No. H1-266156, a styrene-isoprene block copolymer composition is disclosed, which is produced by a process wherein a polystyrene-polyisoprene diblock copolymer is reacted with a tetrafunctional coupling agent in an amount of at least equivalent to an initiator, and which is composed of a branched copolymer with three branches and an unreacted diblock copolymer. An adhesive made of this block copolymer composition has a poor peel adhesion and a low shear adhesion failure temperature.
Further, in the above-mentioned Japanese patent publication, another styrene-isoprene block copolymer composition is disclosed which is composed of a large amount of a polystyrene-polyisoprene diblock copolymer and a minor amount of a branched copolymer with three branches. An adhesive of this block copolymer composition has a low shear adhesion failure temperature.
DISCLOSURE OF INVENTION
An object of the present invention is to provide a block copolymer composition which is useful as a hot-melt adhesive or other adhesives, which has satisfactory properties required for a hot-melt adhesive, especially has a low melt-viscosity and a low application temperature, and exhibits well balanced and high peel adhesion and shear adhesion failure temperature; and a process for producing the block copolymer composition.
Another object of the present invention is to provide an adhesive or pressure sensitive adhesive composition useful as a hot-melt adhesive or other adhesives, which has a low melt-viscosity and a low application temperature, and exhibits well balanced and high peel adhesion and shear adhesion failure temperature.
The inventors conducted extensive research for achieving the above-mentioned objects, and, found that an adhesive or pressure sensitive adhesive composition comprising a specific styrene-isoprene block copolymer composition and a tackifier is highly effective as an adhesive attaining the objects, which is easily produced by a process wherein styrene is polymerized by using an organic lithium initiator to give a polymer block A of styrene; isoprene is polymerized in the presence of the polymer block A to prepare a polymer block B of isoprene and further bind the two polymer blocks A and B together to give an A-B block copolymer; and then the A-B block copolymer is allowed to react with a predetermined amount of a coupling agent having at least four functionalities, and which comprises 5 to 43.9% by weight of a branched copolymer having at least four branches and 56.1 to 95% by weight of an unreacted diblock copolymer. Based on this finding, the present invention has been completed.
Thus, in accordance with the present invention, there is provided an aromatic vinyl compound-isoprene block copolymer composition comprising:
(i) 5 to 43.9% by weight of a branched copolymer having at least four branches, represented by the following general formula (I):
(A-B)
n
X (I)
wherein A is a polymer block of an aromatic vinyl monomer, B is a polymer block of isoprene, X is a residue of a polyfunctional coupling agent having at least four functionalities, and n is an integer of at least 4, and
(ii) 56.1 to 95% by weight of a diblock copolymer represented by the following general formula (II):
A′-B (II)
wherein A′ is a polymer block of an aromatic vinyl monomer, which may be the same as or different from the polymer block A, and B is a polymer block of isoprene; said block copolymer composition having a weight average molecular weight of 10,000 to 500,000.
In accordance with the present invention, there is further provided a process for producing the above-mentioned aromatic vinyl compound-isoprene block copolymer which comprises the steps of:
allowing an aromatic vinyl monomer to contact with an organic lithium initiator to prepare a polymer block A composed of aromatic vinyl monomer units and having an active terminal exhibiting a polymerization activity;
incorporating isoprene to the polymer block A-containing polymerization system whereby an A-B block copolymer is prepared, which has a structure such that the polymer block A of aromatic vinyl monomer is directly bonded to a polymer block B composed of isoprene units and having an active terminal exhibiting a polymerization activity; and then,
adding a coupling agent having at least four functionalities to the A-B block copolymer-containing polymerization system to convert 5 to 43.9% by weight of the A-B block copolymer to a branched copolymer having at least four branches represented by formula (I).
In accordance with the present invention, there is further provided an adhesive or pressure sensitive adhesive composition comprising the above-mentioned aromatic vinyl compound-isoprene block copolymer composition and a tackifier.
Best Mode for Carrying Out the Invention
Aromatic vinyl compound-isoprene block copolymer composition
The aromatic vinyl compound-isoprene block copolymer composition of the present invention is characterized as comprising the branched copolymer of formula (I) and the diblock copolymer of formula (II).
(1) Branched copolymer
The first ingredient, i.e., the branched copolymer of formula (I) contained in the block copolymer composition of the present invention is a block copolymer having at least four branches which is prepared by coupling an A-B block copolymer composed of a polymer block A of aromatic vinyl monomer and a polymer block B of isoprene having an active terminal exhibiting a polymerization activity, with a polyfunctional coupling agent having at least four functionalities.
The aromatic vinyl monomer used for the preparation of the branched copolymer is not particularly limited, and includes, for example, styrene, &agr;-methylstyrene, vinyltoluene and vinylnaphthalene. Of these, s
Komatsuzaki Shigeru
Matsubara Tetsuaki
Tsubaki Hidemi
Birch & Stewart Kolasch & Birch, LLP
Nippon Zeon Co. Ltd.
Yoon Tae H.
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