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  Adhesives having a microreplicated topography and methods of making and using sameUSPTO Application #: 20060225838Title: Adhesives having a microreplicated topography and methods of making and using same Abstract: Adhesives having a microreplicated topography are prepared from contacting a microembossed pattern to a layer of adhesive. When an adhesion interface is established between the layer of adhesive and a supporting substrate, the topography of the adhesive surface controls the performance of the adhesion interface. Articles having microreplicated adhesive surfaces are also disclosed that have an advantage of providing microchannels for fluid egress for an effective period of time. Multiple microembossed patterns produce microreplicated adhesive surfaces having both microchannels for fluid egress and pegs for improved adhesive properties. (end of abstract) Agent: 3m Innovative Properties Company - St. Paul, MN, US Inventors: Frank T. Sher, Larry A. Meixner, Francis V. Loncar, Clyde D. Calhoun USPTO Applicaton #: 20060225838 - Class: 156290000 (USPTO) The Patent Description & Claims data below is from USPTO Patent Application 20060225838. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS REFERENCE TO RELATED APPLICATIONS [0001] This application is a continuation of U.S. Ser. No. 10/217,056, filed on Aug. 12, 2002, now pending; which is a continuation of U.S. Ser. No. 09/685,164, filed Oct. 10, 2000, now abandoned; which is a continuation of U.S. Ser. No. 08/775,844, filed Dec. 31, 1996, now issued as U.S. Pat. No. 6,197,397, issued on Mar. 6, 2001; and related patent family member filed as a continuation, U.S. Ser. No. 10/427,010, filed Apr. 30, 2003, now issued as U.S. Pat. No. 6,911,243, issued on Jun. 28, 2005; FIELD OF INVENTION [0002] This invention relates to adhesives having a controlled topographical surface of microchannels and the methods of making and using them. BACKGROUND OF INVENTION [0003] Pressure sensitive adhesives are useful for the joining of two materials. The interfaces between the adhesive and the materials are vital to the performance of the joined materials. The loss of adhesion at either interface can doom the usage of the materials. [0004] One example of an adhesion interface requiring peak performance is a durable film displaying image graphics adhered to substrates, where the film is a backing material upon which an adhesive layer is added for adhesion to the substrate. Adhesion of a large image graphic film to substrates encounters the problem of entrapped air between the film and the substrate. Anyone who has ever attempted to hang wallpaper can appreciate the frustration that can arise when entrapped air beneath an adhesive-backed film can not be removed easily. The most common solutions to this problem are to remove and reapply the film or to perforate the film to release the entrapped air. Multiple attempts to adhere the same film to a substrate can compromise the pressure sensitive adhesive or increase the probability of uneven or misaligned film on the substrate. Perforating a film mars its appearance. The removal of air bubbles is also labor intensive. [0005] Prior approaches have addressed facile adhesion of image graphics film to substrate by concentrating on specialized topographical constructions of the pressure sensitive adhesive. Commercially superior pressure sensitive adhesives for image graphics are available on image graphic films by 3M of St. Paul, Minn., USA. Pressure sensitive adhesives having this utility are disclosed in a variety of patents. Representative examples of patents describing such materials include U.S. Pat. Nos. 5,296,277 and 5,362,516 (both Wilson et al.) and U.S. Pat. No. 5,141,790 (Calhoun et al.). These patents disclose how the adhesive's topography is built from the interface between the adhesive and the release liner. The principal topographical features in the adhesive surface are isolated protrusions from the adhesive surface with identified contact areas. [0006] Another approach to topographical adhesives is the formation of ridges or recesses in a release or transfer liner to generate a temporary topography on the adhesive. For example, British Patent Specification 1,511,060 discloses a heat- and pressure sensitive adhesive on an impermeable backing that is formed by application of heat and pressure and a release liner having a specific topography or by coating the adhesive onto the release liner, whereupon the release liner is removed. Then, bonding of the adhesive to the desired substrate also requires a step of heat and pressure that adheres the adhesive layer to the substrate. This step is also required to improve the appearance of the final product. This complicated procedure of generating the adhesion of the layer to the backing and then generating the adhesion to the final substrate minimizes utility of the construction for use in large format graphics and other industrial requirements. Furthermore, the depth of the recesses used to create an effective temporary topography on the nontacky adhesive surface is at least 45 .mu.m, and then only if the width of the recesses is at least 130 .mu.m. [0007] Another example of a temporary topography formed on an adhesive surface is disclosed in U.S. Pat. Nos. 5,344,681 and 5,449,540 (both Calhoun et al.). A segmented pressure-sensitive adhesive transfer tape is designed to prevent lateral flow of the adhesive prior to transfer but allows flow after transfer to form a continuous adhesive bond. The small adhesive segments have controllable thickness. An adhesive transfer tape comprises: a carrier with two opposed surfaces with one containing a series of recesses and the other being relatively smooth; a pressure sensitive adhesive being present in the recesses which are surrounded by an adhesive free area such that when the tape is wound about itself with the surfaces contacting and then unwound, adhesive transfers from the one surface to the other. Preferably, the recesses are formed by embossing and are in spaced-apart relationship. Preferably, they are oval, circular, polygonal or rectangular in cross section. Preferably, the adhesive is acrylic or rubber resin, pressure sensitive. [0008] Another example of a temporary topography formed on an adhesive surface is disclosed in U.S. Pat. No. 5,268,228 (Orr). A double-sided adhesive-coated tape has fine grooves on one or both sides of the tape to facilitate air venting to minimize non-contact areas. The grooves in the tape are fine enough that, once the two surfaces to be bonded are in position, the grooves largely or completely disappear. Example 1 describes scribing lines through a protective sheet that placed grooves 70-150 microns deep in the underlying adhesive surface. SUMMARY OF THE INVENTION [0009] Desirable topographical adhesives face three limiting conditions to solve problems in the art of adhering one material to another, especially large format graphics on supporting substrates having large flat surfaces interrupted by rivets, seams, and the like: [0010] (1) An adhesive without channels provides no effective route for egress of fluids in the X-Y dimensions of the interface between the adhesive and the substrate, especially if the backing material, adhesive, and/or the substrate are fluid-impermeable. But if the channels are too large, a path of fluid egress could also be a path of passive ingress of the same or other fluids. [0011] (2) The backing material, and especially its outer imagable surface, can not be adversely affected by the adhesive topography chosen, thereby limiting the size of the channels in the adhesive and also limiting the method of construction. The backing material needs a flat, uniform surface for imaging and other aesthetic reasons. The formation of large channels into the laminate of backing and adhesive will adversely disrupt the flat, uniform surface of the backing material. Also, adhesive topographies that are too large will create undesired undulations or other imperfections in the appearance of the backing material on the final substrate. Such undulations or other imperfections make the image graphic unacceptable for most commercial markets. [0012] (3) The area of adhesive actually contacting the substrate and the holding power (i.e., shear and peel adhesion) of the adhesive affect bonding performance of the backing material to the substrate. If either the holding power is too weak or the area of the adhesive contact is too small, or both, the performance of the adhesive is entirely inadequate. Microspheres or other large abrupt surface patterns have been used to reduce the area of adhesive surface on the substrate, either temporarily or permanently, which can affect holding power of the adhesive or area of adhesive contact. If the size of the surface features is increased, air channels in the topography are formed but there is insufficient adhesive interface remaining to provide effective permanent adhesion. [0013] While the air bubble and fluid egress problems associated with large format graphics are easy to understand, these problems also exist for small graphics and decals where speed of application or applications without pre-masking are significant for economic or manufacturing considerations. [0014] The problem of fluid egress is even more acute whenever the two materials contacting the adhesive effectively inhibit any egress in the Z axis through either or both materials. Further if the materials are inflexible as well as fluid impermeable, such as metallic plates, there is no avenue that can be created, during application, for fluid egress. [0015] The art needs a different approach to control adhesion at the interfaces between a pressure sensitive adhesive and two materials within the three enumerated limiting conditions. Indeed, the art needs to engineer the geometry of the adhesive surface to provide a controlled topography of the adhesive surface at any adhesion interface where particular performance is required. [0016] For this invention, that particular performance should include the provision for fluid egress in the X-Y dimensions of the adhesive interface but without adversely affecting the desired appearance of the backing material which should remain flat and uniform for imaging, but preferably conformable during use. Further, fluid egress should be reconciled with adhesive bond strength for maintaining an adhesive interface. [0017] One aspect of the present invention provides a means of controlling the topography of an adhesive surface, comprising contacting a microembossed pattern to a layer of adhesive and forming a microreplicated surface, such that when an adhesion interface is established between the layer of adhesive and a supporting substrate, the topography of the adhesive surface controls the performance of the adhesion interface between that adhesive and the supporting substrate. [0018] "Adhesive" means any form of adhesive that has pressure sensitive adhesive properties at the time of application to a supporting substrate. As identified by the Pressure Sensitive Tape Council, a pressure sensitive adhesive requires firm adhesion to a variety of dissimilar surfaces upon mere contact without need of more than finger or hand pressure. [0019] Another aspect of the present invention provides a microreplicated adhesive surface formed by microreplication from any contacting technique such as casting, coating, or compressing techniques. Microreplication can be achieved by at least any of (1) casting using a tool having a microembossed pattern, (2) coating of an adhesive onto a release liner having that microembossed pattern, or (3) passing through a nip roll to compress pressure sensitive adhesive against a release liner having that microembossed pattern. Desired embossing topography can be formed in tools via any of a number of well-known techniques, selected depending in part upon the tool material and features of the desired topography. Illustrative techniques include etching (e.g., via chemical etching, mechanical etching, or other ablative means such as laser ablation or reactive ion etching, etc.), photolithography, stereolithography, micromachining, knurling (e.g., cutting knurling or acid enhanced knurling), scoring or cutting, etc. [0020] The microreplicated topography resides on at least one major surface of the pressure sensitive adhesive and can optionally reside on both major, opposing surfaces of the adhesive affecting the properties of the interface(s) in the same or different manners, as desired by those skilled in the art. Continue reading... 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