Multilayer composite body

Details Multilayer composite body Multilayer composite body

1999-07-16

2002-01-08

Ahmad, Nasser (Department: 1772)

Stock material or miscellaneous articles

Layer or component removable to expose adhesive

C428S040200, C428S041400, C428S323000, C428S324000, C428S447000

Reexamination Certificate

active

06337116

ABSTRACT:

The present invention concerns a multi-layer composite body, having a flexible auxiliary carrier and a separation layer arranged on at least one side of the auxiliary carrier, which modifies the full separation or the local limited detachment of a functional layer positioned in flat contact with same.
A multi-layer composite body of the addressed type is, for example, the protective foil for self-adhesive decorative surface foils, self-adhesive labels, one- or dual-sided adhesive tapes, etc. The multi-layer composite body can constitute, as well, only a small part of a commercial product, for example the protective foil of a self-adhesive flap of an envelope. The multi-layer composite body can also be the protective foil of a self-adhesive wound-dressing bandage. All these applications have in common that the functional layer is a pressure-sensitive cement- or adhesive substance layer and the composite body constitutes a carrier or a protective foil, which prevents soiling of the adhesive layer or unwelcome adhesion to surfaces. Before utilization, this carrier or protective foil is pulled off.
Another use are applications where a functional layer is produced from a melt, a solution and/or a dispersion, and the carrier is immediately removed or removed subsequently with later application. In this connection, mention should be made of multi-layer correction ribbons, for example, for which a pigmented cover layer is formed on a carrier and, in most cases, an adhesive layer on same. This laminate serves to cover up errors in printed characters. In addition, mention can be made of color-transfer ribbons where a color-transfer layer is arranged on a carrier. During the printing process, the color-transfer layer is, for example, detached from the carrier and, by means of a heated print-head, transferred pictorially to a receiving substrate.
The flexible auxiliary carrier of the composite body is most frequently paper, however, a there is a strong trend towards foil substrates, because, based on the increased stability of foils in comparison with paper, it is possible to reduce, for economic reasons, the thickness of the flexible auxiliary carrier, and, with respect to winding, for reasons of capacity. To facilitate the separation between auxiliary carrier and functional layer, a separation is formed between auxiliary layer and functional layer which usually contains polyorganosiloxanes. Foil substrates have the advantage here that their surface, compared with paper, is non-porous and lesser amounts of polyorganosiloxanes for coating can be employed in economically beneficial manner. The lower surface roughness, however, constitutes, at the same time, one of the major draw-backs of the employed foil substrates, inasmuch as a smooth carrier layer requires a smooth coating. This smooth surface leads, in turn, to problems in handling.
With respect to applications where the adhesive layer is temporarily covered with a carrier, the smooth surface leads to full surface contact between adhesive layer and carrier, which, in turn, results in that the carrier can only be detached with great effort from the adhesive layer, which, under certain circumstances, may lead, for example, to tearing of labels.
In applications where a layer is precipitated from a liquid phase onto a carrier, one observes that the surface of the layer has an unwelcome shiny appearance after the carrier is removed, which can be attributed to its smooth surface. The smooth surface of the transferred layers also leads to more difficult lettering, for example, with respect to correction material.
Disclosure of U.S. Pat. No. 5,165,976 is helpful for better comprehension of the hereinafter described invention. This patent specification describes a substrate with a release layer. This release layer is obtained in that an emulsion is applied of a curable silicone system and a particle-shaped component, preferably a resin. The silicone-system is hardened under the influence of heat. Simultaneously, water is removed. As a result, a release layer with adjustable separation effect is created for the substrate, specifically in connection with applied adhesives. The substrate is preferably made of paper, preferably inexpensive, porous paper. With a content of approximately 35% by weight of silicone in the release layer, same is present in continuous phase, which envelopes the discrete particles. A lower percentage of silicone is not sufficient for envelopment of the particles, so that the properties of the resulting mixture are determined by both the silicone as well as by the particles. The release effect can therefore also be regulated by the quantity ratio of silicone to particles, by the type of particles, by degree of reciprocal action between silicone and particles, by cross-linkage degree of hardened silicone and by the coating weight. Based on the indication that an “emulsion” must be employed for coating of the substrates, one can conclude that overall a liquid system is involved, i.e. the emulsive dispersed particles, which finally are more or less embedded or bonded in the hardened silicone, do not constitute solid particles.
The silicone contents in the release layer ranges between 5 and 80% by weight, preferably between approximately 20 and 40% by weight in proportion to the total amount of the above two components. It appears from all this that with presence of a larger percentage in the total mass, the emulsive particles act counter to the release effect, i.e. the emulsive particles, if they are present, for example in the permissible amount of 95% by weight, largely exclude the release effect or even produce an adhesive effect. This is documented by the type of employed particles, for example, in form of an acrylic resin or a styrene/butadiene resin (SBR). In contrast thereto, the hereinafter described invention requires the bonding of a solid filler in the separation layer, which does not influence the properties of the silicone, but which produces a surface roughening of the release- or separation layer. The contents of DE 299 522 A5 largely agrees with the discussed U.S. Pat. No. 5,165,976. By way of technological background for the present invention, mention is made of the following reference material: DE 27 53 675 A1, DE 41 14 964 A1, DE 38 34 007 A1, DE 26 22 126 C3 and “Adhesion”, 1984, volume 9, page 18/19.
The above indicated problems with respect to the state of the art are remedied according to the invention in that the separation layer contains a continuous phase and a particle-shaped filler in a concentration of approximately 0.01 to 50% by weight, relative to the separation layer, whereby the surface of the filler particles are totally covered by the continuous phase,—the continuous phase contains inter-linked polyorganosiloxanes and the surface roughness of the separation layer, facing away from the auxiliary layer, has a roughness depth Rt of approximately 400 to 50000 nm and a median roughness value of approximately 40 to 5000 nm.
By incorporating the filler, the surface of the separation layer facing away from the auxiliary layer is made rough, so that a cross section of the profile shows elevations and depressions (“peaks” or “valleys”).
In one specific embodiment, the functional layer can be a layer with a smooth surface. In this case, the functional layer comes into contact only with the “peaks” of the rough separation layer, whereby the smaller contact area permits easier detachment of the functional layer from the composite body. This specific embodiment is of particular interest with respect to applications where the functional layer is an adhesive layer. Specifically, the functional layer can be a cement layer, an adhesive layer, a transparent or tinted plastic layer, specifically a pigmented layer, a laminated cement layer and a transparent or tinted, specifically a pigmented layer. In another specific embodiment, the functional layer is in full contact with the separation layer. A functional layer, for example, the cover layer of a correction ribbon according to the invention can, correspond

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