Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2001-04-17
2002-12-10
Crispino, Richard (Department: 1734)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C427S207100, C427S428010
Reexamination Certificate
active
06491783
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a process for coating and laminating film using 100% solids adhesive at room temperature.
Traditionally, when preparing some packaging intended to be used to package food products, film is printed on one side, adhesive is applied on top of the printing as well as on the clear areas surrounding the printing, and then the film is laminated to a second film at a laminating nip. In in-line printing, the adhesive is coated on top of the freshly printed ink or the opposite web and immediately thereafter is laminated.
On web machines having a width of 30 inches to 60 inches or more, coating is typically accomplished by employing rotogravure and flexo coating, although other techniques may be used. In many cases, lamination is accomplished “out of line”, meaning that a printed roll is taken to another location for lamination.
In the early years of lamination of such packaging materials, solvent borne polyurethane adhesives were employed that gave good “green” tack and cured further to create good laminations. Over the last 20 years, water borne adhesives have replaced many of the solvent-based adhesives due to the reduction of emissions of noxious vapors (VOCs). Of course, solvent-based adhesives are still employed. Water borne adhesives include urethanes, acrylics and other hybrids.
As the industry has evolved, the desire to reduce solvent emissions created a demand for water-based adhesives. However, a 100% solids polyurethane chemistry using a very expensive four or five roll coating head evolved and is currently making big inroads into the market for laminating adhesives. Such systems are prevalent in Europe and are gaining more acceptance in the United States. When the four or five roll coating head systems are used, no oven is employed for drying but most of the adhesives, if not all of them, must be kept hot or heated during application because the adhesives have high viscosities. As should be understood, heating the adhesives reduces the viscosity. However, at the same time, application of heat severely reduces pot life. In other words, application of heat initially reduces viscosity but speeds the initiation of the exothermic reaction that results in adhesive curing and rapid viscosity increase. The pot life of an adhesive is the time period from the moment it is mixed until the moment the exothermic curing reaction begins to make it unusable. When reaction begins, viscosity rapidly increases.
The adhesives employed with the four or five roll coating system are typically two component systems that must be mixed. Such adhesives are adversely affected by moisture in the air and their higher viscosity, in the range of 1000 cps or more, requires use of the four or five roll coating system.
In the normal use of 100% solids urethane adhesives, there is a major health issue that has surfaced in which the urethanes can pose a health hazard when used in laminating film for flexible packaging used for foodstuffs. In essence, the isocyanate in the adhesive reacts and can form aromatic diamine which is a suspected health hazard and which can also migrate through the film.
For some convertors using the four or five roll system, they heat the polyurethane adhesives as high as 150° to 160° F. in order to obtain a runnable viscosity. When such heating is done and the film is run at a speed of over 500 feet per minute, misting can occur which fouls many of the parts of the machinery, and contaminates the atmosphere around the machine thereby creating a potential health hazard for the operator of the machine. To prevent this problem, often, the machinery must be slowed down to prevent misting. Although, four and five roll coating systems can run adhesives having a viscosity of 1,000 cps or higher, the misting issue must be addressed in order to effectively coat film while avoiding expensive machinery upkeep and danger to the health of the machine operator.
Often, products are sold using a “just in time” inventory storage procedure and, due to this procedure, demand is increasing for packaging that may be printed and laminated on narrow web presses such as those having a width of 26 inches or less. One example of such an application is the creation of bottle labels of film-film laminations. Flexographic presses are often used to print images on the film. In such systems, in order to make the presses capable of laminating, a system was devised to use an ultraviolet cured adhesive having a low enough viscosity to allow coating by flexographic presses with curing being accomplished immediately thereafter using an ultraviolet light source. Ultraviolet curing has a severe limitation—it cannot be used to cure adhesive on a metallized web combined with a reverse printed web because the ultraviolet light will not penetrate the ink or metal. The same is true where the film is white or opaque.
As is well known in the art, water or solvent-based adhesives are not preferred to be used on flexographic presses because it is quite difficult to apply a sufficient amount of adhesive in a flexographic press and such adhesives are difficult to dry. With typical printing, it has been found that the only way to use water or solvent-based adhesives in a flexographic press is to slow the speed of production or equip with a much larger drying oven. Limitations on production speed are problematic. Thus, the ultraviolet curing system is a preferred system for use with narrow width presses with the UV cured adhesive having a viscosity of about 300 cps.
Such a system works adequately for ultraviolet bottle label applications but has been found to be unacceptable for applications where one of the films comes into contact with a food product. It has been found that the ultraviolet photo-initiators do not fully respond to the ultraviolet light and, as such, the U.S. Food and Drug Administration has not accepted such adhesives for use in indirect food packaging.
Manufacturers of solvent borne adhesives have attempted to make very high solids (65%) adhesives that can be coated on a gravure press. Such an application reduces the emissions but has not been commercially successful. Water-based adhesives comprising up to 60% solids have been developed with such configuration helping in drying and coating weight but only limited applications have been found for such adhesives.
The adhesive disclosed in Parent application Ser. No. 09/699,437 includes, in some formulations, a flexible epoxy known as DOW 736. Applicant has found that this flexible epoxy causes emission of odors that preclude use of the inventive adhesive in applications where the foodstuff has the ability to absorb odors. One example of such a foodstuff is coffee. As such, a need has developed for an adhesive that will effectively adhere films together without odor emission.
Applicants are aware of U.S. Pat. No. 4,216,252 to Moeller which discloses a solventless release coating. While the solventless nature of the release coating is analogous to the adhesive employed in the inventive process of the present invention, the particular coating employed is significantly different from the adhesive employed herein, and is used for a different purpose.
Each of the techniques and adhesives described above presents significant limitations of one kind or another, whether it be noxious emissions, including misting, requirement for quick production, difficulties in uniform curing, heating requirements coupled with short pot lives, etc. Additionally, some adhesives can cause smudging or bleeding of some inks used to print on the films to be laminated which can cause poor print quality on the finished packaging. As such, a need has developed for a coating technique that employs an adhesive having a sufficiently low enough viscosity at room temperature to permit even and predictable flow, wherein the adhesive does not emit noxious fumes, is not affected by moisture, where pot life is extended to a sufficient degree to increase efficiency of production, and wherein the adhesive employed in the process is deemed acceptable
Adlamco, Inc.
Chan Sing P
Crispino Richard
Spiegel H. Jay
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