Stabilized monomer adhesive compositions

Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...

Reexamination Certificate

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C424S078350, C514S527000, C523S118000, C523S122000, C523S176000, C523S177000, C558S305000, C558S306000, C558S307000, C602S048000, C602S052000, C602S058000

Reexamination Certificate

active

06512023

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to monomer and polymer adhesive and sealant compositions, and to their production for industrial and medical uses.
2. State of the Art
Monomer and polymer adhesives are used in both industrial (including household) and medical applications. Included among these adhesives are the 1,1-disubstituted ethylene monomers and polymers, such as the &agr;-cyanoacrylates. Since the discovery of the adhesive properties of such monomers and polymers, they have found wide use due to the speed with which they cure, the strength of the resulting bond formed, and their relative ease of use. These characteristics have made the &agr;-cyanoacrylate adhesives the primary choice for numerous applications such as bonding plastics, rubbers, glass, metals, wood, and, more recently, biological tissues.
Industrial production of 1,1-disubstituted ethylene adhesive compositions has been optimized to provide adhesives with rapid cure rates and high bond strengths. However, the desire to provide an adhesive with a rapid cure rate has led to problems with shelf-life. The shelf-life of these adhesives is primarily related to stability (i.e., constancy of compositional nature), uncured physical properties, rate of cure of the adhesive, as well as final cured properties of the composition. For example, the shelf-life of a monomeric a-cyanoacrylate composition is related to the amount of time the composition can be stored before unacceptable levels of polymerization occur. Unacceptable levels are indicated by a level of polymerization product that reduces the usefulness of the composition in the application for which it is produced.
It is known that monomeric forms of &agr;-cyanoacrylates are extremely reactive, polymerizing rapidly in the presence of even minute amounts of an initiator, including moisture present in the air or on moist surfaces such as animal tissue. Monomers of &agr;-cyanoacrylates are anionically polymerizable or free radical polymerizable, or polymerizable by zwitterions or ion pairs to form polymers. Once polymerization has been initiated, the cure rate can be very rapid. Therefore, in order to obtain a monomeric &agr;-cyanoacrylate composition with an extended shelf-life, polymerization inhibitors such as anionic and free radical stabilizers are often added to the compositions. However, addition of such stabilizers can result in substantial retardation of the cure rate of the composition. Therefore, in the production of industrial acyanoacrylate adhesives, the amount of stabilizers added is minimized so that the cure rate is not adversely affected.
One anionic stabilizer that has been used is sulfur dioxide. Unfortunately, the use of this stabilizer, while providing stabilization, results in a loss in cure rate as the composition ages. This is because the sulfur dioxide is continuously being oxidized to sulfuric acid, which is also an anionic stabilizer. As the sulfuric acid concentration increases in the composition, the cure rate of the composition decreases. This effect is often referred to as “speed loss” and is a significant problem encountered with the production and storage of industrial &agr;-cyanoacrylate adhesives. In extreme cases, the levels of sulfuric acid become so high that the monomer composition cannot polymerize. Additionally, the conversion of sulfur dioxide to sulfuric acid reduces the amount of sulfur dioxide in the vapor phase, which results, eventually, in the formation of polymers in the head space (vapor phase) of the container. This polymerization within the container further contributes to the loss in shelf-life of the composition.
In addition to their uses in industrial settings, 1,1-disubstituted ethylene adhesives have been used in medical applications. These applications include use as an alternate and an adjunct to surgical sutures and staples in wound closure as well as for covering and protecting surface wounds such as lacerations, abrasions, burns, stomatitis, sores, and other open surface wounds. Cyanoacrylate adhesives for use in medical applications preferably have a shelf-life of at least twelve months. In order to achieve a useful shelf-life, anionic and free-radical stabilizers are added to the monomer compositions.
As disclosed in U.S. Pat. No. 3,559,652 to Banitt et al. and U.S. Pat. No. 5,582,834 to Leung et al., for example, suitable stabilizers for medically useful &agr;-cyanoacrylate compositions include Lewis acids such as sulfur dioxide, nitric oxide, and boron trifluoride, as well as free-radical stabilizers including hydroquinone, monomethyl ether hydroquinone, nitrohydroquinone, catechol, and monoethyl ether hydroquinone. The combination of the two anionic stabilizers sulfur dioxide and sulfonic acid is also known and is disclosed in, for example, British Patent Application GB 2 107 328 A. However, the use of these two anionic stabilizers in combination does not overcome the “speed loss” seen in other 1,1-disubstituted ethylene adhesive compositions.
In addition to having an extended shelf-life, cyanoacrylate compositions for use in medical applications should be sterile. Due to the importance of achieving and maintaining sterility of these compositions, when an additive, such as an anionic or free-radical stabilizer, is added to an &agr;-cyanoacrylate composition, it should be added prior to sterilization. However, regardless of the type and number of additives, sterilization of &agr;-cyanoacrylate adhesive compositions is often difficult to achieve. For example, widely practiced methods of sterilization, such as heat sterilization and ionizing radiation are often not suitable for use with monomeric cyanoacrylate compositions. Problems arise due to polymerization of the monomer during the sterilization process, even in the presence of stabilizers. In many cases, sterilization-induced polymerization is so severe that the resulting product is unusable. Furthermore, even when the sterilized product is still useable, the shelf-life at room temperature can be shortened to such a degree that the product is not suitable for commercialization.
Methods currently used to package and sterilize &agr;-cyanoacrylate monomer compositions have been developed with the recognition that, to improve efficiency and productivity, the packaging and sterilizing steps should be performed in rapid succession. However, these methods do not provide the desired shelf-life of the adhesive compositions in all packaging materials.
Furthermore, during sterilization, much or all of the stabilizer can be consumed or converted to another compound. For example, U.S. Pat. No. 5,530,037 to McDonnell et al. discloses that when a low level of sulfur dioxide is used to stabilize a cyanoacrylate composition, all of the sulfur dioxide is converted to sulfuric acid during the sterilization process. Thus, although polymerization during sterilization can be minimized by use of low levels of sulfur dioxide, and shelf-life of the sterilized &agr;-cyanoacrylate adhesive composition can be increased, shelf-life might be improved by the presence of increased amounts of sulfur dioxide in the initial composition. Unfortunately, at initial high levels of a stabilizer, the general performance of the adhesive can be impaired and the shelf life provided still is less than desired.
Interestingly, McDonnell et al. also teach that the use of the free radical stabilizers butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT), in combination with 100 parts per million (final concentration) sulfur dioxide, are not effective at stabilizing acyanoacrylate compositions during gamma irradiation sterilization until they are present in concentrations substantially above 1000 parts per million or higher (see Example 4 of McDonnell et al.).
Thus, a need exists for improved monomer cyanoacrylate adhesive compositions, for both industrial and medical uses, having a longer shelf-life without sacrificing the performance of the adhesive.
SUMMARY OF THE INVENTION
The present invention provides an improved adhesive composition,

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