Stock material or miscellaneous articles – Layer or component removable to expose adhesive
Reexamination Certificate
2001-01-25
2003-09-02
Ahmad, Nasser (Department: 1772)
Stock material or miscellaneous articles
Layer or component removable to expose adhesive
C428S041300, C428S041500, C428S041700, C428S041800, C428S042100, C428S343000, C428S354000, C428S480000
Reexamination Certificate
active
06613411
ABSTRACT:
TECHNICAL FIELD
This invention relates to conformable multi-layer sheet materials, their method of production and their use as graphic films. The invention is also related to a method of providing a graphic film with a design as well as a method of providing a surface of a substrate with a graphic design.
BACKGROUND OF THE INVENTION
Graphic films are used for example to apply designs, e.g. images, graphics, text and/or information, on windows, buildings, pavements or vehicles such as autos, vans, buses, trucks, streetcars and the like for e.g. advertising or decorative purposes. Many of the surfaces of the mentioned substrates, e.g. vehicles, are irregular and/or uneven, such as rivets overlaying flat surfaces, corrugated panels, curvatures or various surface molding, e.g. body-side, structural or decorative molding.
For graphic films, it is desirable to have a film that accommodates curves, depressions or projections on a substrate surface so that the film may be stretched around curves or projections, or may be pressed down into depressions without breaking or delaminating the film (conformability). It is also desirable to have a film that can be applied over irregular and/or uneven surfaces without subsequent delaminating or releasing from the substrate surface (popping-up). In addition, it is desirable that graphic films are imageable (i.e. have a receptive surface for printing and/or graphics) and exhibit good weathering for outdoor applications.
Polyvinyl chloride (PVC) films are conventionally used for a wide of variety of applications including graphic films. PVC has many properties that are advantageous for such applications. For example, PVC graphic films are conformable to the varying topographies present on the exterior of a substrate, e.g. a vehicle. But PVC films and their use as graphic films suffer from a number of disadvantages. In general, the application of halogen-containing plastics is undesirable for environmental reasons. Another disadvantage of PVC films is the accompanying use of plasticizers in such films. Plasticizers are typically needed in PVC graphic films in order to make the films more flexible and more conformable. However, plasticizers can migrate within the film and such migration can change the performance of the film. Furthermore, such plasticizers may degrade adjacent adhesive layers, reducing the adherence of the film to the surface of the substrate. Another disadvantage of PVC graphic films is that they tend to pop up after application.
Although polyolefin films and their corresponding use as graphic films are advantageous in that they typically do not contain halogen or plasticizers, polyolefin films are difficult to image and thus require the application of an additional image receptive layer, such as an ink receptive layer, toner receptive layer, primer layer or the like. Furthermore, polyolefin graphic films like PVC graphic films show a tendency to pop up.
Popping-up typically results from the presence of residual stress in the graphic film at irregular surface locations during application, which exceeds the holding power of the adhesive. In previous attempts to minimize the problem of popping up, graphic films have been provided with highly tacking adhesives to provide high holding power and/or applied to the substrate surface at relatively high temperatures well above 100° C. in order to try to fully relax the film.
SUMMARY OF THE INVENTION
There is an ongoing need for sheet materials and/or films for use in inter alia graphic applications which may be bonded to uneven and/or irregular surfaces and have a variety of properties not possessed by known products or film materials. There is further a desire to produce such sheet materials in a cost effective and convenient way. It is also preferred that the sheet materials display good printability, are suitable for outdoors usage and conform well to uneven substrate surfaces.
In particular, it is desirable to provide sheet materials, which can be easy to apply under the application of relatively mild heat, i.e. between about 40 and about 80° C., exhibit a low residual stress at such application temperatures and at the same time show good handleability at room temperature.
It has been found that good handleability as well as ease in mild heat-mediated application onto irregular substrate surfaces can be realized by providing a base film for sheet materials comprising a blend comprising at least two substantially amorphous polyesters. In addition, it has been found that films comprising a blend comprising at least two substantially amorphous polyesters have good stress relaxation properties at 60° C., and sheet materials comprising such films show a low tendency towards popping up after application to a substrate surface. Also, such films can be readily printed and applied with a design.
Accordingly, the present invention provides a multi-layer sheet material comprising:
(i) a film of a polyester blend comprising a first and a second polyester, said polyesters being substantially amorphous, such that the film is capable of being softened at temperature in the range of about 40 to about 80° C. and exhibits a E-modulus in the range of 70 to 1000 N/mm
2
at room temperature, an elongation at break greater than 50% at room temperature and percent residual stress at 60° C. less than 40%, said film having a first major surface and a second major surface;
(ii) an adhesive layer on the first major surface of said film; and
(iii) optionally, a release liner.
The multi-layer sheet materials according to the invention exhibit advantageously excellent handleability similar to vinyl-based films or sheet materials at room temperature (i.e. 23° C., preferably at 50% relative humidity). Further, the multi-layer sheet materials according to the invention can be readily softened under the application of relatively mild heat, for example using a heat gun, and thus can be easily applied to uneven and/or irregular substrate surfaces, for example, by hand or using a standard squeegee. In particular, the film of the multi-layer sheet materials according to the invention does not require the presence of an added plasticizer in order to yield a conformable sheet material. The film is preferably essentially free of any plasticizer. By “essentially free of any plasticizer” is meant that the film contains no more than 0.25% by weight of plasticizer based on the total weight of the film. More preferably the film contains no plasticizer.
The film of the multi-layer sheet materials according to the invention also exhibits good stress relaxation properties at 60° C., and thus, the multi-layer sheet materials according to the invention exhibit an advantageously low tendency to pop up after application to an uneven and/or irregular surface. In particular, the application of highly tacking adhesives is not necessary to minimize popping up, and therefore, weakly adhering, removable and/or repositionable adhesives can be effectively applied. Sheet materials with such adhesives are very desirable for short term or non-permanent applications.
The film of the multi-layer sheet materials according to the invention is generally directly imageable without the additional layers, although image receptivity may be further enhanced through the application of an image receptive layer. In particular, the film of the multi-layer sheet materials according to the invention is advantageously directly imageable by conventional screen printing and electrostatic printing techniques with standard inks and/or toners without applying an additional image receptive layer onto the film surface.
Accordingly, other aspects of the present invention are the use of a multi-layer sheet material according to the invention as a graphic film as well as the provision of an imaged graphic film comprising a multi-layer sheet material according to the invention, wherein the film is imaged.
A further aspect of the invention is a method of providing a graphic film with a design comprising the following steps: (a) providing a multi-layer sheet material according
Johannsen Heiner
Kollaja Richard A.
Konrad Sabine
Ree Buren R.
3M Innovative Properties Company
Ahmad Nasser
Peters Carolyn V.
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