Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
2000-03-02
2002-11-26
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Compositions to be polymerized by wave energy wherein said...
C522S149000, C525S090000, C525S314000
Reexamination Certificate
active
06486229
ABSTRACT:
BACKGROUND OF THE INVENTION
Hot melt pressure sensitive adhesives are very popular for use in tapes and labels primarily because the inherent tackiness at room temperature allows them to adhere to substrates even after they have cooled from their molten state. Labels and tapes may be coated with hot melt pressure sensitive adhesives and laminated with release liner allowing end users to adhere or seal them at a later time.
Multi-block copolymers known for use in hot melt pressure-sensitive adhesive formulations include, for example, poly(styrene-isoprene-styrene) and poly(styrene-butadiene-styrene). These multi-block copolymers are usually formulated with tackifiers and oils to form hot melt pressure-sensitive adhesives.
The use of block copolymers in adhesive applications has grown in recent years. Their advantage over homopolymers or random copolymers such as natural rubber and styrene-butadiene rubber relates to their shear and high temperature performance. This derives from the persistence of polystyrene phase structure in the tackified adhesive formulations. These high glass transition temperature (Tg) domains function as physical cross-links, or fillers, which enhance modulus at high temperature and/or creep resistance over long periods of time.
The use of high vinyl styrene-butadiene-styrene polymers in radiation curable adhesives is known and described in U.S. Pat. No. 5,777,039 (De Crane et al) and U.S. Pat. No. 5,300,582 (Debier et al).
U.S. Pat. No. 5,777,039 describes block copolymers for use in hot melt adhesive compositions. These block copolymers comprise poly(vinylaromatic) and poly(butadiene) blocks and have a vinyl content in the range of 25 to 75% by weight.
U.S. Pat. No. 5,300,582 describes block copolymers for user in radiation curable adhesive compositions. These comprise a block of polymerized styrene and a block of polybutadiene having a vinyl content in the range 35 to 70% by weight.
Despite the prior art relating to adhesive compositions containing radiation curable block copolymers, it would be an advantage to provide block copolymers which demonstrate improved UV or EB radiation sensitivity in hot melt compositions whilst showing a superior balance of peel and tack over the known compositions.
This invention relates to superior adhesive compositions comprising styrenic multi-block copolymers having good heat resistance properties. These compositions may be used in pressure sensitive tape and label applications.
SUMMARY OF THE INVENTION
Accordingly, one object of the present invention is to provide an adhesive composition suitable as a radiation-curable hot melt adhesive or radiation-curable hot melt pressure-sensitive adhesive, which composition has excellent flexibility at low temperature, good compatibility with a variety of the additives used in various hot melt adhesive compositions, a comparatively low melt viscosity to permit easy coating work at low temperature, small change of the melt viscosity at different temperatures, excellent process stability, and excellent adhesion, peel, tack and cohesion.
Briefly, this object and other objects of the present invention as hereinafter will become more readily apparent can be attained by the use of at least one block copolymer comprising a high vinyl radial multi-block styrene-butadiene-styrene copolymer.
The present invention provides high vinyl, radial multi-block styrene-butadiene-styrene-containing hot melt adhesive compositions that are radiation-curable to yield pressure-sensitive adhesive films with improved peel adhesion and cohesive strength, especially at elevated temperatures. The pressure-sensitive adhesive tapes of the invention are ideally suited for tape and label applications requiring good cohesive strength at elevated temperatures and yet are readily removed from painted or other surfaces leaving no adhesive residue.
The present invention provides a radiation-curable hot-melt adhesive composition which comprises:
(a) from about 5% to about 40% by weight of at least one high vinyl, radial multi-block styrene-butadiene copolymer;
(b) from about 30% to about 80% by weight of at least one solid tackifier;
(c) from about 0.05% to about 5% by weight of at least one photoinitiator;
(d) from about 0% to about 15% by weight of at least one high vinyl, linear styrene-butadiene-styrene or multi-block styrene-butadiene copolymer;
(e) from about 0% to about 15% by weight of at least one high diblock conventional low vinyl styrene-butadiene-styrene or styrene-isoprene-styrene block copolymer;
(f) from about 0% to about 40% by weight of at least one oil or liquid tackifier; and
(g) from about 0% to about 3% by weight of at least one antioxidant.
DETAILED DESCRIPTION OF THE INVENTION
The term “adhesive” or “adhesive composition”, as used hereinafter means an adhesive or adhesive composition including a pressure-sensitive adhesive or a pressure-sensitive adhesive composition, respectively.
The term “hot melt adhesive” or “hot melt adhesive composition”, as used hereinafter, means an adhesive or adhesive composition which is used for adhesion which is effected by melting an adhesive or adhesive composition by heating, applying it to an adherend in a molten state and then solidifying it at low temperature. The term “pressure-sensitive adhesive” or “pressure-sensitive adhesive composition”, as used hereinafter, means an adhesive or adhesive composition which carries out pressure sensitive adhesion with tack. The term “hot melt pressure-sensitive adhesive” or “hot melt pressure-sensitive adhesive composition” as used hereinafter means an adhesive or adhesive composition which, upon production of adhesive goods such as adhesive tapes and adhesive sheets by applying an adhesive or adhesive composition to a base material such as paper, cloth or plastic film, is capable of forming a layer of the pressure-sensitive adhesive or pressure-sensitive adhesive composition on the base material by applying it to the base material as a hot-melt.
The term “high vinyl” as used herein is intended to mean having a vinyl content of 20% or higher, preferably 40% to 70%.
The term “high diblock” as used herein is intended to mean having a diblock content of 30% or higher, preferably greater than 50%.
The term “tackifier” as used herein means any composition which is useful to impart tack to the hot melt adhesive composition. ASTM D-1878-1T defines tack as “the property of a material which enables it to form a bond of measurable strength immediately on contact with another surface”.
The term “radiation-curable adhesive” as used herein means an adhesive composition which is curable upon exposure to actinic and/or ionizing radiation. The term “curable” is used herein in its conventional sense as meaning capable of forming covalent cross-links.
The term “radiation” is used herein to include actinic radiation such as ultraviolet radiation and ionizing radiation created by the emission of electrons or highly accelerated nuclear particles such as neutrons, alpha-particles etc.
The radiation curable adhesive compositions of the present invention are particularly useful for hot melt pressure sensitive adhesive applications such as tapes, labels, and a wide variety of self-adhesive products. The inventive compositions are particularly useful for more demanding pressure sensitive adhesive applications requiring high heat resistance and/or plasticizer resistance and/or chemical resistance such as printer labels, tapes and labels for under the hood of automobiles and medical tapes, devices and bandages which are adhered to skin. The uncured composition is applied to a substrate such as films including polyvinyl chloride, polyester, polyolefins, polymeric foams, foil or paper and then cured by exposure to a radiant energy source.
Multi-block copolymers have greater structural heterogeneity and a broader molecular weight distribution compared to the materials as described in U.S. Pat. No. 5,300,582 (Debier et al) such as KX-222C as used in the comparative examples herein. It is believed this heterogeneity provides the improved properties o
Hu Ziyi
Paul Charles W.
Foulke Cynthia L.
Harlan R.
National Starch and Chemical Investment Holding Corporation
Wu David W.
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