Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1999-08-04
2002-08-27
Gallagher, John J. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S333000, C524S238000, C524S417000
Reexamination Certificate
active
06440259
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to adhesive compositions, especially aqueous-based contact adhesive compositions. The adhesive finds particularly preferred use for bonding substrates such as high-pressure laminate (HPL), to particleboard for kitchen counter tops in the decorative laminate industry.
BACKGROUND OF THE INVENTION
In the past decade, environmental considerations have forced reevaluation of many established products. Contact adhesives based on elastomeric polymers, which have been available commercially for several decades, fall into this category.
The term contact adhesive refers to an adhesive which is typically applied to two surfaces to be adhered together, dried to form film adhesive layers, and brought into contact with pressure so as to form an immediate, durable bond. Once the contact adhesive is pressed together, the adhered pieces are ready for further processing such as cutting.
Many contact adhesive applications require that soon after applying the adhesive to the substrates to be contacted that the adhesive film dries and forms a film within five minutes and thereafter pressing the coated substrates together, the adhesive rapidly bonds to itself. That is, the adhesive undergoes auto adhesion and forms a semi-solid film with sufficient strength to hold the substrates together and resist subsequent forces on the fresh bond line that might cause failure. Adhesives that provide a dried adhesive film within five minutes and develops handling strength properties immediately after bonding without adhesive squeeze out can be referred to as “fast set” contact adhesives. Quick-drying flammable and chlorinated organic solvents have been conventionally utilized as carriers for fast-set contact adhesives since their quick drying film forming properties facilitate quick holding together of the bonded parts after their coated surfaces are mated and pressed together within five minutes after applying to the substrate.
Flammable and chlorinated solvent-based contact adhesives have traditionally dominated the high-pressure laminate industry. The low boiling point organic solvents used as carriers for contact adhesives provide the advantage of rapid dry times, whereupon the workpieces may be contact adhered within five minutes after application of the adhesive compositions. While such products have been used both in consumer and industrial applications, generally the use of solvent-based systems has declined as a result of concerns related to the presence of volatile and organic solvents. It is, therefore, a goal of the adhesive industry to develop alternative contact adhesives, which exhibit fast set and physical properties equivalent to those of solvent-based adhesives, but wherein the amount of organic solvent is substantially reduced or completely eliminated.
Most of the commercially available water-based contact adhesives are based on polychloroprene and/or acrylic/vinyl acrylic type latices, typically in combination with materials such as resins, plasticizers, antioxidants, and other ingredients commonly used in adhesive compositions (see U.S. Pat. No. 5,543,455). The current one-part water-based adhesives have experienced only gradual industry acceptance due to longer dry times and relatively slow rate of strength build. (See U.S. Pat. No. 5,264,467, showing a one hour dry time). To overcome such limitations, two-part, co-sprayed, water-dispersed, high solid content adhesive systems have been developed that demonstrate similar dry times to solvent-based adhesives and provide strength build within seconds. (See DuPont Dow Elastomer, Technical Information, AquaStik™, “
Water Based Adhesive for Furniture Foam: Quick Break Adhesives
.”) Current two-part adhesives typically consist of a bulk adhesive and an external coagulant. Typically an external coagulant based on an acid such as citric, lactic or acetic acid, or salts such as zinc sulfate are used as a co-spray in predetermined ratio. Such two-part adhesive systems are not entirely satisfactory because the equipment is expensive and requires regular maintenance as well as the need to monitor the ratio of coagulant to base adhesive.
Fast-set adhesives have not been obtained without decreasing storage stability at room and elevated temperatures. To date, fast set times and storage stability has not been satisfactorily obtained within the same adhesive composition in a one-part system. The problem has been that in order to achieve a fast-setting adhesive composition, it is necessary to find some additive or additives to make the resulting adhesive composition sensitized and unstable enough that the colloid polymer system immediately “breaks” on application and forms a high strength film, but yet does not make the composition unstable to the point that it will coagulate during storage and before application. Such additives are sometimes referred to as internal coagulants or gelling agents.
Additives used to sensitize anionic-stabilized latex compounds and improve their ability to break upon application are often acidic. The reaction of the acid is immediate depending upon the type of acid. Therefore, the acid must be added at the point of application. For example, Carl, J. C., “Fluid Properties,”
Neoprene Latex: Principles of Compounding and Processing
, E.I. DuPont de Nemours & Co., p. 18-19 (1962) discusses the use of sodium and potassium silicofluorides.
Amino acids, such as glycine, do not coagulate neoprene latex but do destabilize by reducing pH. For example, in the production of neoprene foam and dipped goods, pH reduction with glycine is advantageous. Glycine shortens the interval between the addition of gelling agent and the start of coagulation. Anionic neoprene latex compounds are unstable at a pH of less than 10.5.
To comply with consumer demand, it would be desirable to find a storage-stable one-part aqueous-based adhesive that facilitates fast set similar to solvent-based adhesives. Initially it was found that by lowering the pH of anionically stabilized, high crystallinity, low gel content polychloroprene latices, faster set would result. Adjusting the latex pH to 9.5-10.5 maintains an adequate shelf and pumping stability but sufficiently destabilizes the latex to create fast breaking properties on spraying. However, the resulting fast breaking adhesive demonstrates an inadequate immediate bonding capability with fairly low strength characteristics. Further, lowering the pH results in poor colloidal stability at room and elevated temperature and thus loss of formulating latitude with typical materials used in polychloroprene adhesive compositions. (See PCT WO 98/53019).
Another approach to fast break technology is to formulate a polymeric latex blend with relatively low shear stability, which can be spray-applied but coagulates very quickly through moisture loss. In this particular approach, fast crystallizing and/or low molecular weight polychloroprene lattices whose pH ranges are between 10 and 13, are blended with an acrylate dispersion whose pH range is between 3 and 5. The acrylate dispersion provides “some initial tack and also has a destabilizing effect, which accelerates coagulation”. (See Gerlach, Dieter, “Polychloroprene-An Evergreen Product for the Formulation of Water Based Contact Adhesives,”
Advances in Adhesives & Sealants Technology
, paper 14). Adhesives formulated with this technology typically show very poor storage stability and mechanical instability.
Thus, there is a need for an aqueous-based polychloroprene contact adhesive that is available in one part. The contact adhesive must be storage stable, yet capable of fast setting. It is also desirable that the contact adhesive be capable of developing enough strength for demanding applications within a short period of time.
SUMMARY OF THE INVENTION
In one aspect, the invention provides a stabilized, one-part, water-based contact adhesive composition that comprises an adhesive component comprising polychloroprene rubber, a resinous component, and an internal coagulant. The resinous component is selected from ethylene-vin
Bardell Scott A.
Gallagher John J.
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