Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Patent
1998-01-08
2000-08-22
Szekely, Peter A.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
526348, 5263482, 5263483, 5263484, 5263485, 5263486, 5263487, 525210, 525211, 525216, 525240, 524274, 524275, 524277, 524478, 524479, 524487, 524488, 524489, 524499, C08F21008, C08F21014, C08K 501, C08L 9304
Patent
active
061074306
DESCRIPTION:
BRIEF SUMMARY
The subject invention pertains to hot melt adhesives. In particular, the subject invention pertains to hot melt adhesives comprising at least one first ethylene polymer, and optionally at least one wax and/or tackifier. In particular, this invention relates to low viscosity hot melt adhesives comprising at least one homogeneous linear or substantially linear interpolymer of ethylene with at least one C.sub.3 -C.sub.20 .alpha.-olefin, further characterized by each said interpolymer having a polydispersity less than 2.5. In preferred embodiments, the inventive hot melt adhesives may be applied at application temperatures of less than 150.degree. C. These hot melt adhesives are particularly useful for case and carton sealing, and for tray forming applications in the packaging industry. Also disclosed is a dual reactor process for the preparation of such hot melt adhesives. Also disclosed are preferred hot melt adhesives for the bonding of cardboard or paperboard, as well as the resultant packaging articles comprising cardboard or paperboard which have been adhered by such hot melt adhesives.
Hot melt adhesives are used widely in the packaging industry for such applications as case and carton sealing, tray forming and box forming. The substrates to be bonded include virgin and recycled kraft, high and low density kraft, chipboard and various types of treated and coated kraft and chipboard. Composite materials are also used for packaging applications such as for the packaging of alcoholic beverages. These composite materials may include chipboard laminated to an aluminum foil which is further laminated to film materials such as polyethylene, mylar, polypropylene, polyvinylidene chloride, ethylene vinyl acetate and various other types of films. Additionally, these film materials also may be bonded directly to chipboard or kraft. The aforementioned substrates by no means represent an exhaustive list, as a tremendous variety of substrates, especially composite materials, find utility in the packaging industry.
Hot melt adhesives for packaging are generally extruded in bead form onto a substrate using piston pump or gear pump extrusion equipment. Hot melt application equipment is available from several suppliers including Nordson, ITW and Slautterback. Wheel applicators are also commonly used for applying hot melt adhesives, but are used less frequently than extrusion equipment.
Hot melts are required to have sufficient adhesion to substrates to firmly hold the package together, and in many cases, end users of hot melt adhesives require full fiber tearing bonds, meaning substantially all the fiber is removed from the substrate along the entire length of the adhesive application when the bond is separated by hand. Generally, in order to get full fiber tearing bonds, hot melts need to be applied at temperatures of 175.degree. C. or greater. This increases the open time of the adhesive and lowers the viscosity for better penetration into the substrate. Open time refers to the amount of time that the adhesive can form a bond to the substrate.
In addition to bonding requirements, customers are demanding higher performance in other areas, such as thermal stability. Good thermal stability means that the product will not darken in the glue pot with prolonged exposure to high temperatures, will not produce char, skin or gel, and will not exhibit a substantial viscosity change over time. High application temperatures, along with exposure to oxygen, can increase the degradation of the hot melt adhesives. This problem is most commonly alleviated with the use of antioxidants such as Irganox.RTM. 565, 1010 and 1076, which are hindered phenolic antioxidants produced by Ciba-Geigy, located in Hawthorne, N.Y.
Another way to reduce char, skin, gel formation, discoloration and viscosity changes, is to lower the application temperature of the hot melt adhesive. In addition to improving thermal stability, lowering the application temperature also reduces the risk of severe burns to hot melt equipment operators, decreases the amount of
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Albrecht Steven W.
Dubois Robert A.
Eichler Beth M.
Kauffman Thomas F.
Lawrence Maynard
H.B. Fuller Licensing & Financing Inc.
Szekely Peter A.
The Dow Chemical Company
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