Adhesive film strip

Stock material or miscellaneous articles – Composite – Of fluorinated addition polymer from unsaturated monomers

Reexamination Certificate

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Details

C428S040100, C428S041700, C428S041800, C428S041900, C428S194000, C428S192000

Reexamination Certificate

active

06284378

ABSTRACT:

DESCRIPTION
The invention relates to an adhesive film strip for a temporary bond, which strip can be detached without residue and without damage by pulling in the direction of the bond plane, and to its use for such bonds.
BACKGROUND OF THE INVENTION
Highly elastic adhesive films for temporary bonds which can be re-released by pulling in the direction of the bond plane are known and are obtainable commercially under the designation “tesa Power-Strips”. Bonds produced therewith offer a powerful hold and yet can be released again without trace and without damage to the substrate or to the adherends, as is described in DE 33 31 016 C2.
DE 37 14 453, DE 42 22 849, DE 42 33 872, DE 43 39 604, DE 44 28 587, DE 44 31 914 and DE 195 11 288 describe specific embodiments and applications of prior adhesive films.
The adhesive films described in these documents are subject to stringent requirements, for instance:
For flawless functioning they must offer a degree of finger tack (for light bonding=low applied pressure and for immediate loading) and bond strength (throughout the application) which are sufficient for the application in question.
Prerequisites for the detachment process are high extensibility coupled with low offset yield stress and a tear strength which is high in comparison with the detachment force (stripping force).
A marked reduction in finger tack on stretching is advantageous for the detachment process.
For longer-term bonds, an appropriate ageing resistance in the bond joint is essential.
Under high mechanical stresses (high shear loads and tip-shear loads) there may, if unsaturated styrene block copolymers (styrene-isoprene, styrene-butadiene block copolymers) are used, be development of ozone cracks in the adhesive and thus inward tearing of the adhesive films during the detachment process or detachment of the bonded article during the application period.
Especially in the case of bonds which are subject to high shear loads and tip-shear loads, at application temperatures>about 35° C. a very high thermal shear strength is essential for sufficient bond strength.
Many applications desire that the adhesive film be pigmented. The use of pigments, for example TiO
2
, may, however, have adverse effects on the bond strength, especially when used at high concentrations.
The abovementioned adhesive films consist of only a single layer of adhesive which is required to meet, sufficiently, all of the abovementioned properties for a large number of applications. In this case, varying the formulation of the adhesive layer influences totally a number of these properties. Many product properties, moreover, are in mutual contradiction, and some are almost totally mutually exclusive. The formulation of the adhesives is accordingly complex, with many combinations of properties being impossible to establish to a sufficient degree if at all.
Against the background of this state of the art, the aim of the present invention was to provide highly elastic adhesive films which permit extensively independent control and broad formulatability of individual product properties. This is achieved through the use of adhesive film laminates which consist of a plurality of adhesive layers. It is possible optionally to integrate, between the individual adhesive layers, diffusion barrier layers, which act as diffusion barriers for migratable formulation constituents in adjacent adhesive layers. Through the multilayer structure it is possible to control in a targeted manner and separately from one another the overall properties of novel adhesive film laminates, by varying, for example, the composition (formulation), the thickness and the number of the individual layers, and thus to produce a spectrum of properties denied to the known single-layer systems. In this arrangement, the profile of properties of individual adhesive film layers can be controlled by the nature and amount of the formulation constituents used (polymers, fillers), which show little or no migration capacity, and via the thicknesses of the individual adhesive layers. In the case of adhesive films comprising diffusion barrier layers integrated between the individual adhesive film layers, the concentrations of migratable adhesive film constituents can be adjusted within very wide ranges.
However, the prior art also includes multilayer adhesive films which can be released without residue from the adherends by pulling in the lengthwise direction of the film. However, these films too have grave disadvantages:
Thus WO 92/11333 describes an adhesive tape which is redetachable by pulling in the bond plane and which as backing uses a highly stretchable, substantially nonresilient (nonelastomeric) film having less than 50% resilience after stretching.
WO 92/11332 describes an adhesive tape which is redetachable by pulling in the bond plane and for which it is possible, as backing, to use either a stretchable, highly elastic (elastomeric) film or a highly stretchable, substantially nonresilient film. Adhesive compositions employed are exclusively UV-crosslinked acrylate copolymers.
WO 95/06691 describes adhesive tapes which are redetachable by pulling in the bond plane and which use as their backing a foamed film backing which does not have contact adhesion.
Highly elastic backing materials comprising tackifier resins or plasticizer oils as blend components are not described in WO 11332 or in WO 11333 or in WO 94/21157. Consequently, there is a gap here, which is significant for practical use and limits the application possibilities, for the use of pressure-sensitive adhesive compositions comprising low molecular mass migratable constituents which can migrate into the highly elastic backing materials.
Finally, U.S. Pat. No. 4,024,312 describes highly stretchable adhesive films which possess a backing of highly elastic, thermoplastically processable styrene block copolymers. The backing is coated on at least one side with a pressure-sensitive adhesive composition. The pressure-sensitive adhesives used employ either polyisoprene (e.g. natural rubber) or the styrene block copolymer-based synthetic rubbers which are also employed for the backing material, in a blend with tackifier resins and, if desired, with further blend components. The adhesive tapes can be removed readily from the substrate by stretching parallel to the bond surface. The backing of these adhesive films is described as “basically non-tacky” (col. 1, line 10), although it may include admixed resins. Accordingly, these resins are also described as being those resins which associate with the A blocks of the ABA block copolymers (col. 2, lines 11-16) and are compatible with them (col. 3, lines 10-22). The pressure-sensitive adhesive used can also include resins, i.e. tackifier resins, which associate with the B blocks of the ABA block copolymers (col. 3, lines 58-63).
Although products according to U.S. Pat. No. 4,024,312 may be adequate for some applications, they still have the grave disadvantage for normal practical use that the two types of resin, on account of their relatively low molar masses, migrate, especially at relatively high temperatures, and partition themselves between backing and adhesive composition with the result that it is impossible to obtain constant adhesion properties.
Self-adhesive tapes of this kind do not have constant product properties: mechanical strengths of the backing and properties of the pressure-sensitive adhesive compositions used are irreversibly altered by the diffusion of the resins. Specific formulation and control of the product properties, which is essential for industrial bonds, is therefore impossible.
In the light of this it was an object of the invention to provide adhesive films which are devoid of such disadvantages, or at least do not have them to the same extent, and which nevertheless do not abandon the undisputed advantages of this prior art.
SUMMARY OF THE INVENTION
The invention relates accordingly to adhesive film strips as characterized in more detail in the claims, in particular to an adhesive film strip for a tempor

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