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
2001-02-06
2003-07-15
Szekely, Peter (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...
C524S271000, C526S149000
Reexamination Certificate
active
06593407
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a low application temperature hot melt adhesive composition possessing high heat resistance, fast set speed and good cold adhesion.
BACKGROUND OF THE INVENTION
Hot melt adhesives are widely used for various commercial applications such as product assembly and packaging, including cardboard case sealing and carton closing operations. Such hot melt adhesives are applied to a substrate while in its molten state and cooled to harden the adhesive layer.
Most commercially available hot melt adhesives require temperatures of 350° F. (177° C.) or greater to ensure complete melting of all the components and also to achieve a satisfactory application viscosity. While adhesive formulations that can be applied at temperatures below 300° F. (121° C.) can be prepared using low molecular weight components or a high wax content, application viscosity and adhesive properties suffer. While softer or more amorphous components may be added in order to improve adhesion, these components reduce the effective heat resistance.
The use of a hot melt adhesive with exceptionally high heat resistance and, in addition, good cold resistance is important in hot filled packaging applications, e.g., sealing and closing operations for cartons, cases or trays used for packaging molten cheese, yogurt or freshly baked goods, which are subsequently subjected to refrigeration or freezing.
There continues to be a need in the art for improved hot melt adhesives that can be applied at low temperatures, possess high heat resistance and good cold adhesion.
SUMMARY OF THE INVENTION
The invention provides a hot melt adhesive comprising an adhesive polymer and a tackifer. Tackifiers required for use in the practice of the invention are modified rosins and/or modified terpenes, specifically modified rosins and/or terpenes having a molecular weight to softening point ratio of less than about 10, preferably less than about 8.5, typically between about 2.0 and 8.5. The adhesives of the invention exhibit high heat resistance and good cold resistance.
One aspect of the invention is directed to a hot melt adhesive comprising an adhesive copolymer, and a modified rosin and/or modified terpene having a molecular weight to softening point ratio of from about 2 to about 10, preferably less than about 8.5. The adhesive compositions of the invention will also preferably comprise a wax. Preferred modified rosins for use in the practice of the invention are phenolic-modified rosin. Preferred modified terpenes for use in the practice of the invention are terpene phenolics.
In a preferred embodiment, the adhesive copolymer comprises at least one ethylene copolymer. A particularly preferred embodiment comprises an ethylene n-butyl acrylate copolymer and/or an ethylene vinyl acetate copolymer.
Another aspect of the invention is directed to a method of sealing and/or making or forming a case, a carton, a tray, a box or a bag. These methods comprise using a hot melt adhesive comprising an adhesive polymer and a modified rosin and/or a modified terpene having a molecular weight to softening point ratio of less than about 10.
Still another aspect of the invention is directed to an article of manufacture comprising an adhesive polymer and a modified rosin and/or a modified terpene having a molecular weight to softening point ratio of less than about 10. In one embodiment, the article of manufacture is a carton, case, tray or bag used for packaging products, said carton, case, tray or bag formed using a hot melt adhesive comprising an adhesive polymer and a modified rosin and/or a modified terpene having a molecular weight to softening point ratio of less than about 10. The packaged article may comprise cardboard or paperboard which has been adhered by such hot melt adhesives. In another embodiment, the adhesive is pre-applied to the article, e.g., carton, case, tray or bag during the manufacture thereof, and prior to packaging of a product.
Yet another aspect of the invention is directed to packaged articles contained within a carton, case, tray or bag, in particular packaged food, wherein the carton, case, tray or bag comprises an adhesive containing an adhesive polymer and a modified rosin and/or a modified terpene having a molecular weight to softening point ratio of less than about 10.
Another aspect of the invention is directed to a process for bonding a substrate to a similar or dissimilar substrate comprising applying to at least one substrate a molten hot melt adhesive composition and bonding said substrates together, said hot melt adhesive comprising an adhesive copolymer and a modified rosin and/or modified terpene having a molecular weight to softening point ratio of less than about 10.
Still another aspect of the invention is directed to a method of increasing resistance of a hot melt adhesive to heat and cold comprising using a tackifer comprising at least one modified rosin and/or modified terpene which has a molecular weight to softening point ratio of less than about 10.
DETAILED DESCRIPTION OF THE INVENTION
All documents cited herein are incorporated in their entireties by reference.
The invention is directed to a low application temperature, high heat resistant hot melt adhesive comprising an adhesive polymer, a modified rosin and/or modified terpene, wherein the tackifier has a molecular weight to softening point ratio of from about 2 to less than about 10, preferable less than about 8.5 down to about 4, and optionally a wax. The adhesive of the invention is particularly well-suited for hot filled packaging applications.
It has now been discovered that modified rosins and modified terpenes, having a molecular weight to softening point ratio of less than about 10, when used as tackifer, alone or in combination, in a hot melt adhesive provides hot melt adhesives which can be applied at low temperature and exhibit high heat resistance and good cold resistance. A preferred modified rosin for use in the practice of the invention is a phenolic-modified rosin. A preferred modified terpene for use in the practice of the invention is a terpene phenolic. The phenol moiety may be substituted or unsubstituted.
Rosins useful in the preparation of modified rosin may be any standard material of commerce known as “rosin”, or a feedstock containing rosin. Rosin is mainly a mixture of C
20
, tricyclic fused-ring, monocarboxylic acids, typified by pimaric and abietic acids, which are commonly referred to as “resin acids.” Any one or more of the C
20
cyclic carboxylic acid-containing isomers present in rosin may be used.
Rosin which is suitable for use can be obtained from many sources, and can have a wide range of purities. For example, wood rosin may be used, where wood rosin is obtained from Pinus stumps after harvesting the stumps, chipping the stumps into small chips, extracting the chips with hexane or higher-boiling paraffin, and distilling the hexane or paraffin to yield wood rosin. Gum rosin, which is the name given to rosin that is obtained after scoring a pine tree, collecting the exudate sap, and then distilling away the volatile components, may also be used. The rosin may be tall oil rosin, which is a by-product of the Kraft (i.e., sulfate) pulping process for making paper. According to the Kraft process, pinewood is digested with alkali and sulfide, producing tall oil soap and crude sulfate turpentine as by-products. Acidification of this soap followed by fractionation of the crude tall oil yields tall oil rosin and fatty acids. Depending on the fractionation conditions, the rosin may contain variable amounts of fatty acids. Preferably, the rosin used in the present invention contains at least 90 wt % resin acids, and less than 10 wt % fatty acids. Some rosin dimerization product, which may form during the fractionation process, may also be present in the tall oil rosin. A standard grade of rosin is available commercially from Union Camp Corporation (Wayne, N.J.) under the UNITOL® trademark. Gum rosin, including Chinese gum rosin, is another rosin which can be used to prepare modified
Carillo Brian
Haner Dale L.
Mehaffy Justin
Foulke Cynthia L.
National Starch and Chemical Investment Holding Corporation
Szekely Peter
LandOfFree
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