Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Adhesive outermost layer
Reexamination Certificate
2001-04-04
2003-09-09
Seidleck, James J. (Department: 1711)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Adhesive outermost layer
C428S343000, C428S356000, C428S3550RA, C428S3550EN, C428S3550BL, C428S3550CN, C428S3550EN
Reexamination Certificate
active
06617020
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a hot melt processable pressure sensitive adhesive comprising organophilic clay plate-like particles, articles prepared therefrom, and a method of making the pressure sensitive adhesive.
BACKGROUND OF THE INVENTION
Pressure sensitive adhesives (PSAs) have found use in a variety of applications. PSAs are 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 strength. Obtaining the proper balance of properties is not a simple process.
PSAs with performance features are needed that can withstand demanding environments, such as elevated temperatures. The desired performance features can include good peel adhesion, good shear strength, and clean removability.
Additionally, environmental concerns about the use of solvents in the processing of PSAs has led to increased emphasis on solventless processing methods such as hot melt processing. Hot melt processability, however, restricts the polymers that can be used in PSA formulations. For example, crosslinked polymers that have high shear strength are generally not hot melt processable. Accordingly, to otherwise enhance shear strength of a hot-melt processable PSA, some have explored the use of thermoplastic elastomers in such PSA formulations and/or crosslinking the compositions after coating. Nevertheless, these approaches are sometimes limited in the performance characteristics that they are able to achieve.
SUMMARY OF THE INVENTION
A need therefore exists for alternative hot melt processable pressure sensitive adhesive (PSA) compositions. A need also exists for hot melt processable PSA compositions that preferably exhibit good high temperature shear strength and good high temperature peel strength, as well as clean removability from an adherend.
In one embodiment, the composition of the invention comprises: (a) at least one elastomer; (b) organophilic clay plate-like particles; and (c) at least one non-volatile organophilic exfoliating agent. The composition is a hot melt processable PSA. In a further embodiment, the organophilic clay plate-like particles are oriented.
The PSA composition of the invention demonstrates good high temperature shear strength in one embodiment. The PSA composition of the invention demonstrates good high temperature peel strength in a further embodiment. The PSA composition of the invention also demonstrates clean removal from an adherend in a further embodiment. Ideally, the PSA composition of the invention also demonstrates good cohesive strength. Good cohesive strength provides a combination of good shear resistance, good peel strength, and clean removability.
The term “non-volatile,” as used herein, refers to those exfoliating agents that generate less than about three weight percent VOC (volatile organic content) when the exfoliating agent is exposed to a temperature of about 110° C. ±5° C. in a forced draft oven for one hour according to ASTM Test Method DS403-93.
The term “organophilic clay,” as used herein, refers to a clay that has been surface-modified to convert at least a portion of its surface nature from an organophobic state to an organophilic state (preferably to a hydrophobic state). For example, in one embodiment, a clay may initially have both organophobic and organophilic sites. However, upon modification according to the present invention, at least a portion of the organophobic sites are converted to organophilic sites. In other embodiments, a clay initially contains essentially only organophobic sites and, upon modification according to the present invention, at least a portion of the organophobic sites are converted to organophilic sites. Preferably, at least about 50% of exchangeable cations on the unmodified organophilic clay are exchanged with organophilic modifying cations.
The term “organophilic exfoliating agent,” as used herein, refers to an organophilic material capable of separating an organophilic clay sheet into plate-like particles and maintaining the clay in plate-like particles at the use temperature (typically room temperature, i.e., about 21° C.).
The term “solventless,” as used herein, refers to compositions that are essentially 100 percent solid systems (i.e., systems essentially free of VOC and water). Typically, such compositions have no more than about five weight percent VOC and water, more typically no more than about three weight percent VOC and water. Most typically, such compositions are free of VOC and water.
The term “hot melt processable,” as used herein, refers to a composition that can transform, for example, by heat and pressure from a solid to a viscous fluid. The composition should be capable of being hot melt processed without being such that the composition chemically transforms, rendering it unusable for the intended application. Typically, hot melt processable compositions are solventless.
The term “oriented,” as used herein, refers to plate-like particles being positioned in a non-random manner. One skilled in the art would typically be able to observe a composition and determine if the plate-like particles were oriented and, if so, whether or not the plate-like particles were uniaxially or biaxially oriented. In a biaxially oriented system, typically the major surfaces of a majority of the plate-like particles are roughly parallel. This may be the case, for example, for a film that has been stretched in both the x-direction and y-direction. In an uniaxially oriented system, typically a majority of the plate-like particles are aligned via their largest dimension (i.e., their length) roughly in parallel. For example, this would be the y-direction (or “down-web” direction) in the case of a film extruded onto a web and stretched in the y-direction.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
The hot melt processable pressure sensitive adhesive (PSA) composition of the present invention comprises at least one elastomer, organophilic clay plate-like particles, at least one non-volatile organophilic exfoliating agent, and optional additives.
Elastomers
An elastomer should be selected that is hot melt processable in order that the composition of the invention be hot melt processable. Hot melt processable elastomers include certain conventional elastomers as well as certain thermoplastic elastomers. These hot melt processable elastomers are typically linear or branched polymers with little or no crosslinking. The composition of the invention typically comprises about 25 to about 98 percent by weight of elastomer based on the total weight of the composition.
Conventional Elastomers
Useful conventional elastomers typically form one phase at about 21° C. and have a glass transition temperature of less than about 20° C. (more typically less than about 0° C.) in addition to exhibiting elastomeric properties. Examples of conventional elastomers that are useful in the present invention include, but are not limited to, natural and synthetic rubbers, polyvinyl ethers, poly(meth)acrylates, polyurethanes, poly-&agr;-olefins, silicones, and combinations thereof.
Natural rubber elastomers useful for formulation as PSAs generally contain masticated natural rubber. Natural rubber may range in grade from a light pale crepe grade to a darker ribbed smoked sheet grade. Representative examples include CV-60 from Goodyear Tire and Rubber Co.; Akron, Ohio, which is a controlled viscosity rubber grade, and SMR-5 from Cargill Inc.; Ontario, N.Y., which is a ribbed smoked sheet rubber grade. Natural rubbers are generally non-tacky and are, therefore, typically formulated with tackifying resins to form PSAs. Other additives, such as antioxidants,
Ma JingJing
Peterson James R.
Zhou Zhiming
3M Innovative Properties Company
Pribnow Scott R.
Ribar Travis B
Seidleck James J.
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