Stock material or miscellaneous articles – Composite
Reexamination Certificate
2000-07-07
2003-11-25
Kiliman, Leszek (Department: 1773)
Stock material or miscellaneous articles
Composite
C428S501000, C428S502000, C428S521000, C428S522000, C428S524000, C156S082000, C156S283000, C156S309600, C156S309900, C156S325000, C156S326000, C156S331300, C522S033000, C522S036000, C522S039000
Reexamination Certificate
active
06652970
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to crosslinkers useful in preparing crosslinked polymer compositions and further compositions therefrom.
BACKGROUND OF THE INVENTION
Polymers are generally crosslinked to increase the cohesive strength, rigidity, heat resistance, or solvent resistance of a polymer composition. However, the use of certain crosslinkers can make it difficult to apply the compositions to a substrate in, for example, the form of a coating. Certain compositions that are hot-MELT processable materials must have a sufficiently low viscosity upon melting, such that they can be readily hot-melt processed (e.g., applied to a substrate). The presence of crosslinks in a material generally increases the melt viscosity of the material, many times making it impossible to hot-melt process the materials.
In an attempt to provide materials having sufficient cohesive strength and/or rigidity, as well as processability, thermally reversible crosslinks have been used. It is well known to incorporate thermally reversible crosslinks into polymers. Upon heating, the crosslinks dissociate or break. Upon cooling, the crosslinks reform. This sequence can be performed repeatedly. Thermally reversible crosslinks find many uses, for example, in hot-melt processable and re-moldable (or recyclable) materials. By incorporating thermally reversible crosslinks into polymers, a composition can be heated to form a coating or mold from the composition and then return to its original crosslinked state.
For examples of thermally reversibly crosslinked polymers, see U.S. Pat. No. 3,435,003 (Craven); U.S. Pat. No. 4,617,354 (Augustin et al.); and U.S. Pat. No. 5,641,856 (Meurs). Also see, PCT Publication Numbers WO 95/00,576 (Heyboer) and WO 99/42,536 (Stark et al.), as well as Canary et al., “Thermally Reversible Crosslinking of Polystyrene via the Furan-Maleimide Diels-Alder Reaction,”
Journal of Polymer Science Part A: Polymer Chemistry
, Vol. 30, pp. 1755-9 (1992) and Chujo et al., “Reversible Gelation of Polyoxazoline by Means of Diels-Alder Reaction,”
Macromolecules
, Vol. 23, pp. 2636-41 (1990).
Further examples of thermally reversibly crosslinked polymers are thermoplastic elastomers, such as those described in
Kirk
-
Othmer Encyclopedia of Chemical Technology
, 4
th
Edition, Wiley: 1994, Vol. 9, pages 15-37. Such thermoplastic elastomers have many of the physical properties of rubbers (e.g., softness, flexibility, and resilience), but, in contrast to conventional rubbers, they are hot-melt processable. With such thermoplastic elastomers, the transition from a processable hot-melt to a solid, rubberlike composition is rapid, reversible, and takes place upon cooling.
Such thermoplastic elastomers are often multiphase compositions in which the phases are intimately dispersed. In many cases, the phases are chemically bonded by block- or graft-polymerization. At least one phase consists of a material is that is relatively hard or glassy at room temperature, but becomes rubbery upon heating. Another phase consists of a softer material that is rubberlike at room temperature (i.e., an elastomer). For example, a simple structure of a multiphase thermoplastic elastomer is an A-B-A block copolymer, where A is a hard phase and B is an elastomer (e.g., poly(styrene-b-elastomer-b-styrene)). Examples of these materials are included in, for example, U.S. Pat. No. 3,639,517 (Kitchen et al.) and U.S. Pat. No. 4,221,884 (Bi et al.), and Japanese Patent Publication Number 52[11977]-129795. References describing the use of these materials in formulating adhesives include, for example, U.S. Pat. No. 4,444,953 (St. Clair); U.S. Pat. No. 4,556,464 (St. Clair); U.S. Pat. No. 3,239,478 (Harlan); and U.S. Pat. No. 3,932,328 (Korpman).
It may be desired, however, to provide a composition that is chemically and/or physically different (e.g., having different adhesive properties) after application to a substrate as compared to the composition prior to its application. For example, U.S. Pat. No. 5,322,731 (Callahan, Jr. et al.) describes adhesive beads comprising a pressure-sensitive adhesive (PSA) core and a discontinuous organic polymer shell that makes the bead essentially non-tacky at room temperature. Upon application of heat and/or pressure to the bead, the core and shell materials can be blended to form a resultant PSA. By providing compositions that are essentially non-tacky before application, easier handling of the compositions is facilitated. That is, conventional handling and coating equipment, such as hopper feeders, powder conveyers, and hot-melt stick applicators can be used, without requiring specialized handling and coating equipment.
However, when using the adhesive beads described by Callahan, Jr. et al., the core and shell materials must be selected both such that they are respectively tacky and non-tacky to the touch at room temperature and such that, upon application, they combine to result in a composition having PSA properties. Furthermore, when the tacky core materials are uncrosslinked, the beads tend to be deformable, especially under pressure or at high temperatures. The shell could potentially rupture due to this deformation, causing the beads to prematurely agglomerate. As another example, see U.S. Pat. No. 5,804,610 (Hamer et
As an alternative to the multi-layer constructions of, for example, Callahan, Jr. et al. and Hamer et al., U.S. Pat. No. 3,909,497 (Hendry et al.) describes solid polymers that are thermally degradable to flowable (or at least softened) compositions. The polymers contain heat-sensitive groups that cleave at a temperature substantially lower than that at which the thermal degradation would occur in their absence. Cleavage is effected essentially in the absence of materials reactive with the resulting molecular fragments. The degradation products are useful as adhesives, plasticizers, fillers, etc.
Heat-sensitive groups of Hendry et al. are taught to be azo groups, carbonate groups, ester groups, and amine-oxide groups conforming to specific formulas recited therein. However, azo groups and amine-oxide groups typically fragment into fragments containing free radicals or fragments (containing ethylenic unsaturation) susceptible to free radical polymerization, which are disadvantageously susceptible to recombination and degradation (e.g., affecting weatherability and durability of the resulting composition). The same applies to ester groups and carbonate groups, depending on their particular chemistry. Those of ordinary skill in the art will recognize that fragmentation of ester groups and carbonate groups of hydroxy compounds having active &bgr;-hydrogens, as taught by Hendry et al., results in fragments containing ethylenic unsaturation.
PCT Application Number US99/06,007 (Everaerts et al.) describes a base copolymer that exhibits little or no tack prior to its combination with a plasticizing agent. Thus, the base copolymer can be transported and processed without special handling and processing equipment. However, formulation latitude is also compromised with those compositions because the base copolymer is typically a high glass transition temperature, Tg (i.e., a Tg of at least about 0° C.), high shear storage modulus (i.e., a shear storage modulus of at least about 5×10
5
Pascals when measured at 23° C. and 1 Hertz) base copolymer in order for useful pressure-sensitive adhesive materials to be formed when the base copolymer is combined with the plasticizing agent.
Further compositions that are chemically different (e.g., leading to compositions having different adhesive properties) after application to a substrate as compared to the composition prior to its application are desired. It is also desired to provide formulations that are relatively stable after transformation to their altered chemical state, as compared to, for example, the compositions of Hendry et al. that contain free radicals or fragments containing ethylenic unsaturation that are susceptible to recombination or degradation.
SUMMARY OF THE INVENTION
The
Everaerts Albert I.
Leir Charles M.
Mader Roger A.
Stark Peter A.
3M Innovative Properties Company
Kiliman Leszek
Lambert Nancy M.
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