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
2001-05-04
2003-07-08
Yoon, Tae H. (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...
C524S047000, C524S270000, C528S489000, C106S145100, C427S208000
Reexamination Certificate
active
06590019
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to aqueous adhesive formulations. More particularly, the invention relates to an aqueous bottle labeling adhesive that is formulated to provide an optimum balance of cold water resistance and label removability.
BACKGROUND OF THE INVENTION
Ice-proof or cold water resistant labeling adhesives have been used for many years for conditions where extreme humidity resistance and label removal are required, as for example in labeling beer and soda bottles, and some pharmaceuticals. Heretofore, most of these adhesives were based on casein in combination with metallic salts; however, the problems associated with caseins, e.g. cost, availability, variations in quality, etc., instigated searches for casein substitutes, especially those based on low cost, readily available starches.
While starch based adhesives are acceptable for some applications, these adhesives do pose a significant problem when used on returnable/reusable beverage bottles which must be cleaned prior to refilling. Typically bottlers use dilute hot caustic solutions to remove the labels, disinfect and clean the bottles; however, the labels bonded with the starch based adhesives which are formulated to give water resistance often resist removal under these conditions and separate steps must be taken to completely scrub off the labels and any residual adhesive.
The requirement for removability is countered by a requirement that the adhesive remain on the bottle during storage and use, a particularly difficult requirement when the bottles are cooled by immersion in ice water coolers. Thus, while adhesives based on starch and ammonium salts of styrene-maleic anhydride resins exhibit superior ice-proof properties, the bond formed by most of these adhesives is so strong that removal of the label, even upon soaking in hot alkaline water, is difficult or impossible under such conditions and equipment as are used in commercial operations.
Due to the recent ecological pressure which has reversed the trend toward “non-returnable” bottles and reemphasized the need for “returnables” which require removal of the labels prior to reutilization, the inability to remove the labels has made these recently developed adhesives unacceptable for commercial operations.
There is thus a need in the art for an ice-proof adhesive for labels which possesses the optimum balance in properties of being sufficiently cold water resistant to remain on the bottles during use yet may be easily removed or stripped from the bottles to facilitate reutilization.
SUMMARY OF THE INVENTION
It has now been found that ice-proof adhesives which possess an optimum balance of water resistance and label removability comprises:
a) water;
b) an effective amount of a water soluble adhesive polymer;
c) at least one styrene maleic anhydride copolymer having a styrene to maleic anhydride ratio of 1:1 to 3:1, said styrene maleic anhydride copolymer being present in an amount sufficient to provide 4.8 to 20 parts styrene maleic anhydride per 100 parts adhesive polymer;
d) 0.5 to 25% by weight of a rosin;
e) sufficient alkali to give a pH within the range of 7 to 11.
The resulting adhesive can form adhesive bonds between a large variety of bonded surfaces in many end uses. Further, the use of such formulations not only possess superior ice water resistance; they can significantly improve the aqueous cleanability of the adhesive materials from manufacturing equipment, application equipment, and end uses.
DETAILED DESCRIPTION OF THE INVENTION
As an adhesive base for the improved adhesives of the present invention can be either natural or synthetic and may include raw starches or converted or modified starches, or casein as well as conventionally employed synthetic polymers or mixtures thereof. When starches are used, they may be derived from any plant source including corn, potato, sweet potato, wheat, rice, sago, tapioca, waxy maize, sorghum, high amylose corn, etc. may be employed as may the corresponding conversion products as those dextrins prepared by the hydrolytic motion of acid and/or heat, the oxidized starches prepared by treatment with oxidants such as sodium hypochlorite, fluidity or thin boiling starches prepared by enzyme conversion or by mild acid hydrolysis or the corresponding ester or ether starch derivatives. The starches may be used singly or in combination to achieve various final properties in the adhesive composition. The preferred starches are amioca based since these starches, when cooked, have a higher resistance toward pasting up on aging. Raw cornstarch or other starch derivatives may additionally be blended into the mixture for the desired rheological or machining properties.
Suitable synthetic polymers include polyvinyl pyrrolidone, polyacrylic acid derivatives, polyvinyl alcohol, ethylene vinyl acetate polymers and derivatives thereof such as carboxylated or surfactant stabilized ethylene vinyl acetate, vinyl acetate polymers and copolymers such as copolymers of vinyl acetate and butyl acrylate, ethyl hexyl acrylate or dioctyl maleate, polyvinyl acrylate homopolymers, acrylic polymers, styrene butadiene polymers, polyurethanes, neoprene and styrene acrylic polymers.
The adhesive composition generally comprises 20 to 80% by weight of the base polymer, preferably about 25 to 40% by weight.
The term “styrene-maleic anhydride resin” as used herein is also meant to include the corresponding acid functionalities as well as the preformed salts of the resins. In general, the styrene-maleic anhydride copolymers will vary in molar ratio of styrene to maleic anhydride from 1:1 to 3:1. They may vary in molecular weight from 1,600 to 50,000 and may include the respective half ester modifications with alcohols.
The styrene and maleic anhydride can be polymerized to form resins for use in this invention by any conventional polymerization methods. Solution polymerization methods can be employed where the monomers are polymerized in a suitable solvent using as a polymerization catalyst a free-radical catalyst, such as benzoyl peroxide or dicumyl peroxide, at a temperature of about 750 to 300° C. or more. Suitable solvents include the aromatic hydrocarbons such as cumene, p-cymene, xylene, toluene and the like.
The partial esters of these styrene-maleic anhydride resins can be prepared for use in this invention in conventional manners from alkanols of about 3 to 20 carbon atoms, preferably from hexanol or octanol. The extent of the half-esterification of the styrene-maleic anhydride copolymer will generally be about 10 to 100%, preferably 20 to 80%. That is, about 5 to 50%, preferably 20 to 40% of the total number of carboxyl groups of the copolymer are esterified with alcohol. The esterification can be effected by simply heating a mixture of the appropriate quantities of sytrene-maleic anhydride copolymer with the alcohol at elevated temperatures, usually about 100° to 200° C. Preparations of these esters are described in U.S. Pat. Nos. 3,342,787 and 3,392,155.
Among the preferred resins employed in this invention are the styrene-maleic anhydride (SMA) copolymers having a styrene to maleic anhydride ratio of 3:1 and a molecular weight of 1900 and sold under the name SMA 3000A by Arco. A half ester, sold by Arco as SMA 2625A, having a styrene to maleic anhydride ratio of about 2:1, a molecular weight of 1900 and comprising a 50% hexyl half ester modification is also preferred. Another preferred resin has a styrene to maleic anhydride ratio of 1:1, a molecular weight of 50,000 and is available from Monsanto under the tradename Lytron 810.
Also useful herein is the half ester, Scripset 550 from Monsanto, which is available in a powdery form, has a softening temperature of 175-180° C. and an acid number of approximately 175. Also useful are Scripset 700 (acid number 95) and Scripset 720 (acid number 270) from Monsanto as well as SMA 2000 (acid number 350) and SMA 3000 (acid number 280) from Elf Ato Chem.
The ratio of the styrene maleic anhydride to starch will generally vary between about 4 and 40 parts styrene maleic anhyd
Bladon Sarah L.
Dheret Cecile
Harrington John
Hayes Patrick J.
Sardina Melissa
Foulke Cynthia L.
National Starch and Chemical Investment Holding Corporation
Yoon Tae H.
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