BACKGROUND

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 may result in failure of the materials.

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 cannot be removed easily. The most common solutions to this problem are to remove and re-apply 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.

Prior approaches have addressed facile adhesion of image graphics film to substrate by concentrating on specialized topographical constructions of the pressure sensitive adhesive, often by coating the adhesive onto a structured release liner and thereby allowing the structure of the release liner to imprint into the adhesive layer. To this end, various technologies have been developed to manufacture such release liners. See, for e.g., U.S. Pat. No. 5,897,930 “Multiple Embossed Webs” (Calhoun, et. al), and US Pat. No. “Adhesive Having a Microreplicated Topography and Methods of Making and Using the Same” (Sher et. al.).

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 μm, and then only if the width of the recesses is at least 130 μm.

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.

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 μm deep in the underlying adhesive surface.).

Good 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.

SUMMARY

The art needs films having air egress, tack control, or both, with less complicated manufacturing techniques. In some of the embodiments described herein, tack control and air egress are provided by a single mechanical feature: filaments, which are partially disposed in the adhesive layer of an adhesive-backed film in such a way that portions of them sit proud from the major adhesive surface, holding the adhesive layer out, away from an installation surface somewhat, thus providing tackiness (until the presence of intentional application pressure, as from a squeegee or other application device). The filaments also introduce channels for air or fluid egress into the adhesive layer.

An installer of graphic film as described herein upon a wall may take advantage of the tack control by positioning and repositioning the graphic film until it is just right, then may use a squeegee, hand, or other pressure device to push the film further onto the application surface, working air or fluid bubbles out to the edges of the film via egress pathways provided by the filaments. In some embodiments, the filaments are hot melt adhesive, such that an installation technique that involves heat may improve the bonding of the graphic film to the substrate.

In some embodiments, such films have simplified manufacturing, because they may eliminate the need for distinct manufacturing techniques related to air egress and tack control features. In some embodiments, as for example where the filaments comprise hot melt adhesive, the resultant bond between the graphic film and the installation surface, after installation in the presence of heat, is improved.

Air egress and repositionability are desirable features for some adhesive backed graphic films, allowing an installer to reposition the graphic on a surface multiple times until the positioning is acceptable, and then allowing the installer to remove air or fluid pockets with the use of a or other application device.

In one embodiment, filaments are pressed into a release liner, such that some of the filaments extend past the major surface of the release liner. The adhesive side of an adhesive backed film contacted to the filament-containing release liner, such that the adhesive layer bonds to and encompassing portions of the filaments extending past the major surface of the release liner. When the release liner is removed, the resultant structure is an adhesive-backed film wherein the adhesive layer includes portions of filaments embedded therein. These filaments, in various embodiments, serve to hold portions of the adhesive layer up, away from an installation surface (facilitating tack control, which assists may translate to repositionability), and also create channels on either side of the filament (facilitating air or fluid egress). Particular embodiments may be generated that are tuned to one of these features or the other.

In another embodiment, filaments are blown onto the adhesive side of an adhesive backed film. A first blowing station blows oriented filament pieces according to a first direction relative to the down-web, and a second blowing station blows oriented filament pieces according to a second direction relative to the down web. The first and second direction may be orthogonal relative to one another, or at another suitable angle, such that both down-web and cross-web egress is effected. A heated release liner is then nipped onto the adhesive and filament surface, with appropriate pressure such that the filaments remain only partially embedded in the adhesive layer.

