Adhesive tape

Details Adhesive tape Adhesive tape

1999-04-20

2001-08-28

Zirker, Daniel (Department: 1771)

Stock material or miscellaneous articles

Web or sheet containing structurally defined element or...

Adhesive outermost layer

C428S317300, C428S317700, C428S3550BL, C428S3550RA, C427S208000, C248S205300

Reexamination Certificate

active

06280840

ABSTRACT:

The invention relates to an adhesive tape for a bond which is redetachable without residue or damage by pulling, and to its use.
Highly extensible elastic adhesive films for bonds which are redetachable by pulling essentially in the direction of the bond plane are known and are commercially available under the name “tesa Power-Strips”. Bonds produced with such films offer a powerful hold and yet can be redetached without leaving any trace and without damage to the substrate or adherends, as described in DE 33 31 016 C2. DE 42 22 849, DE 42 33 872, DE 44 28 587, DE 44 31 914, DE 195 11 288 and DE 197 08 366 describe, inter alia, specific embodiments and applications of aforesaid adhesive films.
Multilayer adhesive films comprising highly extensible film backings, either 15 elastic or of low elasticity, and applications of these adhesive films are likewise known from, for instance, U.S. Pat No. 4,024,312 “Pressure-sensitive adhesive tape for medical use—having an extensible, elastic block copolymer backing”, WO 92/11332 “Removable adhesive tape” (PSA tape using highly extensible backing with photopolymerized acrylic PSA), WO 92/11333 (PSA tape using highly extensible essentially inelastic backing), WO 93/01979 “Securement of stacks using stretch adhesive tape” and WO 94/21157 “Article support using stretch releasing adhesive”.
WO 92/11333, for instance, describes an adhesive tape which is redetachable by pulling in the bond plane and which as its backing makes use of a highly stretchable, essentially non-resilient (nonelastomeric) film having a resiliency of <about 50% after stretching. The combination of high extension and tear strength required for the detachment process is produced by the backing that is used. U.S. Pat. No. 4,024,312 describes correspondingly debonding self-adhesive tapes of an essentially elastomeric nature.
When selecting the backing films it is found in practice that they must meet very specific requirements. Films having a high Young's modulus and/or low maximum extensions, for instance, are unsuitable because adhesive films produced from them cannot be stretched with sufficient ease and/or force to enable them to be redetached from the substrates without residue or destruction by stretching essentially in the bond plane. In addition, very thick film backings cannot generally be used owing to the above restrictions.
In practice it is also found that high bond strengths can generally be achieved with the abovementioned self-adhesive tapes on smooth and firm substrates. On rough substrates the bond strength is inadequate for many applications, especially for thin self-adhesive tapes but even for those which are relatively thick. The probable cause of the inadequate bond strength is primarily an inadequate bonding area, caused in turn by deficient conformability of the adhesive tapes to rough and irregular surfaces, especially if two rough substrates are to be bonded to one another. For example, when bonding planar materials to coated woodchip wallpaper using tesa Power-Strips at service pressures (100 N/7.4 cm
2
) the bonding areas achieved are often only about 10 to 40% of the area covered by the pressure-sensitive adhesive. Even when bonding to smooth planar surfaces, however, an inadequate bonding area may be the reason for inadequate bond strength. The cause is probably the inclusion of air bubbles in the bond areas. Such air bubbles are often impossible to eliminate completely, even by applying high pressures. In many cases bonds featuring such air inclusions will result in bond strengths markedly reduced in comparison to samples bonded over the whole area without air bubbles.
U.S. Pat. No. 5,516,581 and WO 95/06691 claim self-adhesive tapes which are redetachable by extension essentially in the bond plane and whose backings comprise polymeric foams. WO 95/06691 in particular describes how by using backing materials comprising polymer foams it is possible to obtain self-adhesive tapes redetachable by stretching which have markedly improved conformability to rough and irregular surfaces. As a consequence of the higher bonding area achieved by this means, high bond strengths can be realized with these products even on rough and irregularly formed substrates. The extension and tear strength necessary for the detachment process are brought about in all cases by way of the backing materials employed.
The primary determinants of the conformability of the desired self-adhesive tapes to rough and irregular surfaces and hence the achievable bond strength on corresponding substrates are the mechanical properties of the self-adhesive tape perpendicular to the bond plane (compressive strength, tensile stress/elongation behaviour, splitting resistance, surface finish, compression set, etc.) and the thickness of the self-adhesive tape, properties which are defined essentially by the profile of properties of the particular foam-based backing in precisely this preferential direction and by its thickness. The mechanical properties in the stretching direction, which critically influence the detachment process, and those perpendicular to the bond plane, which critically determine the conformability to rough and irregular substrates, however, cannot be controlled at will independently of one another with the prior art adhesive films. The detachment process requires, in particular, low stripping forces in order firstly to enable easy and pleasant detachment and secondly to ensure that detachment is free from destruction, even from highly sensitive substrates such as wallpapers, for example. Easy detachment is generally observed when the self-adhesive tapes combine high extension with very low yield stress.
The object of the present invention was to overcome the abovementioned drawbacks and, in particular, to obtain self-adhesive tapes
which are redetachable without residue or destruction by stretching, especially in the bond plane,
which permit graduated control of the detachment forces (stripping forces) by appropriate modification of the backings used, as a result of which
a large number of commercially available film backings can be utilized in accordance with the invention and
a large number of commercially available foams can be used, including a large number of foam-film laminates,
which through the optional use of foam-based backings possess high conformability to rough and irregularly formed surfaces and so permit high bond strengths on such substrates, and
where the foamless backings, foam-based backings and foam-film laminates used do not need to contribute to the tear strength that is required for detachment without residue or destruction by stretching essentially in the bond plane.
This object is achieved by adhesive tapes as are characterized in more detail in the claims, especially
adhesive films which are redetachable without residue or destruction by stretching, especially in the bond plane, and which comprise foamless backings, foam-based backings or backings based on foam-film laminates, where
such backings have been modified in a graduated manner by damage/pretreatment, such as cutting, perforation or punching, for example, as a result of which
the forces required to stretch the aforesaid backings are controllable and lower than the stretching forces of backings which have not been so pretreated, with the consequence that
resulting adhesive films which utilize the aforesaid backings possess reduced detachment forces and thus improved detachment characteristics;
the optional use of foam-based backings or foam-film laminates provides high conformability and hence bond strength on rough bond substrates.
The residueless and nondestructive redetachment of self-adhesive tapes of the invention is achieved by sufficiently high tear strength and elongation at break of the pressure-sensitive adhesive compositions utilized in combination with the aforesaid backings.
As a consequence of the possibility, described herein, of the graduated pretreatment of the backings (damaging) a very large selection is available of polymer films, foams and foam-film laminat

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