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
2000-02-25
2003-02-11
Gorr, Rachel (Department: 1711)
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...
C528S059000, C528S076000, C528S905000, C428S423700, C428S424800, C428S425500, C428S3550EN
Reexamination Certificate
active
06518359
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to polyurethane-based pressure-sensitive adhesives, systems (e.g., 100% solids, waterborne, and solventborne) for such adhesives, articles therefrom, and methods of their preparation.
BACKGROUND OF THE INVENTION
A wide variety of polyurethane-based adhesives are known. For example, see U.S. Pat. No. 5,910,536 (Kydonieus et al.), which describes a particular type of polyurethane-based adhesive—a pressure-sensitive poly[urethane-(meth)acrylate]-based adhesive. The adhesives therein are prepared from 100% solids (i.e., essentially solvent-free and water-free) systems.
In addition to 100% solids systems, it is known to produce polyurethane-based adhesives in both solventborne (i.e., those using mostly organic solvents as a solvating medium) and waterborne (i.e., those using mostly water as a dispersing medium) systems. These adhesive systems are applied to a substrate in the form of a solution or dispersion, respectively. Generally, whether the adhesive system is solventborne or waterborne, it must be coated onto a desired substrate and dried to remove solvating or dispersing medium (i.e., organic solvent or water, respectively) in order to form an adhesive coating.
Reactive polyurethane-based adhesive systems have been described in the literature, but coatable mixtures prepared from such systems generally have a limited useful life. Examples of reactive polyurethane-based adhesive systems include those described in U.S. Pat. No. 3,246,049 (Webber); U.S. Pat. No. 3,437,622 (Dahl); U.S. Pat. No. 3,718,712 (Tushaus); U.S. Pat. No. 3,879,248 (Kest); U.S. Pat. No. 3,925,283 (Dahl); U.S. Pat. No. 4,087,392 (Hartmann); U.S. Pat. No. 5,102,714 (Mobley et al.); U.S. Pat. No. 5,486,570 (St. Clair); U.S. Pat. No. 5,591,820 (Kydonieus); and U.S. Pat. No. 5,714,543 (Shah). Further descriptions include those in GB 1,113,925 (Weller); GB 1,216,672 (Grindley); and PCT Publication Number WO 97/22,642 (Chang).
In reactive systems, typically multiple parts must be mixed to form a coatable reacting mixture. The reacting mixture must then be coated onto a substrate within a short period of time. If the reacting mixture is not coated within a short period of time, the viscosity of the composition will become too high, rendering the composition uncoatable. Thus, storage-stable, coatable adhesive systems are not obtainable when the adhesive system is a reactive system.
In addition to not being storage-stable, there are other disadvantages associated with reactive systems. Typically the parts of a reactive polyurethane-based adhesive system include an isocyanate-containing part (i.e., an isocyanate-terminated polyurethane prepolymer) and a chain extending part. Due to the presence of isocyanate-functional groups on the polyurethane prepolymer, storage of that part must be carefully controlled so that moisture does not react with the isocyanate-functional groups, rendering the composition non-reactive and, thus, unusable. Sensitivity to moisture can also lead to variations in properties of these coated adhesives due to, for example, local variations in ambient temperature and humidity when the adhesive is coated. Furthermore, special handling procedures may be required for the multi-part system, especially by those that are sensitive to isocyanate chemicals.
Thus, essentially non-reactive systems are preferable over reactive systems from at least a storage stability standpoint and ease of use standpoint. Premixing of components and special storage considerations for the components are not required in non-reactive systems.
When using a non-reactive, solventborne or waterborne system, to form an adhesive coating on a substrate, one merely applies the composition, which contains a fully reacted polymer in the form of a solution or dispersion, to the substrate and then dries the solvating or dispersing medium to form the adhesive coating. However, such non-reactive systems may require the addition of external emulsifiers or cationic stabilization agents to maintain stability of the solution or dispersion prior to coating to form the adhesive.
Many polyurethane-based and polyurethane-urea-based dispersions are known in the literature. For example, see U.S. Pat. No. 5,037,864 (Anand et al.); U.S. Pat. No. 5,354,807 (Dochniak); U.S. Pat. No. 5,354,808 (Onwumere et al.); U.S. Pat. No. 5,554,686 (Frisch, Jr. et al.); U.S. Pat. No. 5,608,000 (Duan); U.S. Pat. No. 5,807,919 (Duan); and U.S. Pat. No. 5,863,980 (Choi et al.) as well as JP-07-102,233 (Sekisui Chemical). Most of the literature references, however, do not describe how to prepare pressure-sensitive adhesive (PSA)s from the dispersions.
PSA compositions are a unique subset of adhesives well known to those of ordinary skill in the art to possess properties including the following: (1) aggressive and permanent tack, (2) adherence with no more than finger pressure, (3) sufficient ability to hold onto an adherend, and (4) sufficient cohesive strength to be removed cleanly from the adherend. Materials that have been found to function well as PSAs are polymers designed and formulated to exhibit the requisite viscoelastic properties resulting in a desired balance of tack, peel adhesion, and shear holding power.
U.S. Pat. No. 5,910,536 (Kydonieus et al.), described supra, describes how a “suitable balance of elastic and viscous properties which is required in pressure-sensitive adhesives has not been readily attainable in conventional polyurethane materials.” Although Kydonieus et al. did not teach polyurethane-based PSA dispersions, they were able to obtain polyurethane-based PSAs from a 100% solids system. Yet, in order to obtain the balance of properties requisite to PSAS, the polyurethane-based PSAs described therein were poly[urethane-(meth)acrylate]-based, containing both urethane and acrylate linkages in their polymeric backbone. However, as recognized by Kydonieus et al., disadvantages with these types of polymers include the fact that acrylic-based adhesives are not as strong as polyurethane-based adhesives. Furthermore, acrylic-based adhesives, such as those described by Kydonieus et al., are generally more irritating to human skin than polyurethane-based adhesives.
Certain few references do describe preparation of PSAs from polyurethane-based dispersions. For example, PCT Publication Number WO 98/31,760 (Dow Chemical Company) describes a polyurethane PSA-forming latex composition comprising a polyurethane PSA-forming material, wherein a polyurethane PSA is obtained by dehydrating the PSA-forming latex composition. The process for preparing the polyurethane PSA includes emulsifying a polyurethane prepolymer in water, chemically reacting the prepolymer to react substantially all unreacted functional groups, and dehydrating the aqueous dispersion. The polyurethane prepolymer is formed from reactants including polyisocyanates and active hydrogen compounds, such as polyols. It is stated that polyols can be employed individually or in mixtures as di-, or a combination thereof, polyoxyalkylene polyols. Suitable active hydrogen compounds are polyols having a molecular weight less than 6,000.
Also see U.S. Pat. No. 3,796,678 (Bartizal), where highly branched, capped polyurethane dispersions for preparing PSAs are described. It is stated that at least about 20 weight percent pendant chains extend from the polyurethane and polyurethane-urea polymers therein. The polymers are formed in and dispersed in an aqueous medium.
Still further polyurethane-based chemistries for preparing PSAs are desirable. It would be particularly desirable to provide polyurethane-based PSAs that can be tailored to have a wide range of peel adhesion and shear strength properties.
SUMMARY OF THE INVENTION
Polyurethane-based pressure-sensitive adhesives (PSAs) of the invention comprise the reaction product of: a polyol component comprising at least one diol having a weight average molecular weight of at least about 2,000, wherein the at least one diol comprises less than about 8 weight % monols; an isocyanate
Clemens Lawrence M.
Hansen Richard G.
3M Innovative Properties Co.
Gorr Rachel
Pribnow Scott R.
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