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
1999-03-12
2001-04-03
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...
C524S505000, C525S098000, C525S314000
Reexamination Certificate
active
06211272
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to poly-1-butene based blends useful as hot melt adhesives. Particularly, this invention relates to the use of polymeric blends containing poly-1-butene and liquid/semi-liquid hydrogenated polydiene polymers as hot melt adhesives capable of adhering to smooth substrates such as plastic-based or plastic-finished constructions, particularly high density polyethylene films.
BACKGROUND OF THE INVENTION
Hot melt adhesives have found extensive use in industry in bonding, joining or fabrication of various structures, including construction of structures from synthetic polymeric films, such as polyethylene, polypropylene, etc.; foil, including metal foil such as aluminum foil, wax-coated or wax-impregnated cellulosic structures; and various non-woven materials whose constituents are based on polyolefins, polyesters, polyamides and acrylic-type polymers.
The modern trend in the packaging and disposable article industry, for example, is to use more of the plastic-based or plastic-finished constructions, such as polyethylene or polypropylene based extrusion coated, spray coated, or laminated composite constructions. The change in various packaging and disposable laminate from fibrous substrates, such as fabrics and paper or paperboard, to plastics based on synthetic polymers also necessitates that the various adhesives chosen to hold the structures together be compatible with the materials of construction, since the altered surface chemistry of such materials may not be adhesion compatible with traditionally-available hot melt adhesives.
Hot melt adhesives based on homopolymers or copolymers of 1-butene (hereinafter “poly-1-butenes”) are commonly used to bond fabrics or non-woven sheets to other porous or semi-porous substrates. Poly-1-butenes' polymorphic nature and unique crystallization half-life allow adhesives based on this polymer to flow and remain tacky long after they have cooled to room temperature and thus have relatively long open time. As used herein, adhesion open time is the maximum time at which adhesion (adhesion to itself or to a substrate) can take place for material after it is cooled from the melt to room temperature. Consequently, poly-1-butene based hot melt adhesives can be easily applied to cold substrates and will cold flow into porous substrates before the material undergoes further transition and densification.
On smooth substrates such as olefinic films and metals especially painted metals and coated metals, the surface is much different from those with porous substrates. As a result, poly-1-butene based hot melt adhesives do not adequately wet the smooth surfaces and tend to pop off or delaminate after the phase transition.
Disposable articles such as baby diapers, adult incontinence briefs, sanitary napkins, etc. typically use adhesives between the outer spun-bonded non-woven fabric, often made of polyolefins such as polypropylene, and the adsorbent core. Adhesives are also used between the absorbent core and the polyolefin liquid barrier, typically a polyolefin film such as a polyethylene film. These adhesives typically have hot melt (350° F.) viscosities of less than 10,000 cP and therefore can be applied by spray coating techniques.
Poly-1-butene adhesives have offered formulators unique opportunities in the market as the adhesive between the polypropylene fabric and the absorbent core.
However, poly-1-butene inherently does not adhere very well to smooth surfaces, which have less surface areas than fabrics, such as painted/coated metals and polyolefin films, especially those outer liquid barrier films made of polyolefins such as polyethylenes. Because of this, formulators and diaper manufacturers were not able to utilize poly-1-butene based adhesives to adhere outer liquid barrier films until Lakshmanan et al. (U.S. Pat. No. 4,833,192) added liquid polybutenes, copolymers of isobutylene and butenes, to poly-1-butene adhesives to enhance their adhesion to polyethylene film. The present invention provides poly-1-butene based hot melt adhesives with good adhesion to both polyolefin fabrics and smooth polyolefin films which are superior to those containing liquid polybutenes.
SUMMARY OF THE INVENTION
It has been surprisingly found that certain properties including adhesion strength to smooth surfaces may be improved by making hot melt adhesives from blends comprising a poly-1-butene polymer, a tackifier resin, and from 3 wt. % to 25 wt. % of a liquid or semi-liquid, hydrogenated or partially hydrogenated, low molecular weight conjugated diene polymer prepared by anionic polymerization. Any one of the following three polymers can be used in the adhesive formulation of this invention:
1) A hydrogenated styrene isoprene diblock copolymer having a molecular weight from 4000 to 30,000, preferably 6000 to 15,000, a polystyrene content of 5 to 15 percent by weight, preferably 8 to 12 percent by weight, which is at least 75 percent hydrogenated, preferably at least 85 percent hydrogenated.
2) A hydrogenated polydiene polymer which may have one diene block of either isoprene or butadiene or may be a diblock polymer wherein one block is of isoprene and the other block is of butadiene, and wherein the polymer may have a terminal hydroxy group. The polymer has a molecular weight of 500 to 20,000, preferably 1000 to 10,000, and is at least 75 percent hydrogenated, preferably at least 85 percent hydrogenated.
3) A polyisoprene homopolymer having a molecular weight of 15,000 to 40,000, preferably 20,000 to 30,000 which is at least 75 percent hydrogenated, preferably at least 85 percent hydrogenated.
DESCRIPTION OF THE EMBODIMENTS
While the present invention is described in connection with the preferred embodiments, it will be understood that it is not intended to limit the invention to those embodiments. On the contrary, it is intended to cover all alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.
The present invention is directed to a composition suitable for making a hot melt comprising (i) from about 20 wt. %. to about 60 wt. %, specifically from about 30 wt. %. to about 55 wt. %, more specifically from about 34 wt. % to about 43 wt. % of poly-1-butene polymer; (ii) from about 3 wt. % to about 25 wt. %, specifically from about 5 wt. % to about 20 wt. %, more specifically from about 7 wt. % to about 16 wt. % of the liquid or semi-liquid, low molecular weight and/or low viscosity hydrogenated polydiene polymer; (iii) from about 30 wt. % to about 75 wt. %, specifically from about 35 wt. % to about 65 wt. %, more specifically from about 45 wt. % to about 55 wt. % of tackifier resin; and (iv) from about 0 to about 5 wt. %, specifically from about 0 wt. % to about 2 wt. %, more specifically from about 0 wt. % to about 1 wt. % of a stabilizer such as an antioxidant. As used herein, all the wt. % referred to for ingredients contained in blends are based on total weights of the blends and wt % is percent by weight.
The present adhesive blend has improved adhesion to smooth substrates such as polyolefin films, specifically polyethylene films, and metal surfaces especially painted or coated metal substrates. The specific liquid/semi-liquid polymers described herein exhibit good compatibility with poly-1-butene.
The term poly-1-butene polymer (polybutylene) used herein refers a homopolymer or copolymer containing more than 50 mole % butene-1 having a melt index of from about 0.05 to about 5,000, specifically from about 1 to about 4,000, and more specifically from about 20 to about 2,000 dg/min., as determined by ASTM D-1238 condition E, at 190° C. Butene-1 homopolymers and copolymers useful with the present invention are primarily linear chain molecules with regular and spatially ordered arrangements of ethyl side groups; the groups that result when butene-1 is polymerized across the 1,2 carbon double bond along an ethylene chain backbone (see for example U.S. Pat. No. 3,362,940 which is herein incorporated by reference). When cooled fro
Erickson James Robert
Hansen David Romme
Kegley Larry McArthur
Shafer David Lee
Haas Donald F.
Niland Patrick D.
Shell Oil Company
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