Adhesive tape

Details Adhesive tape Adhesive tape

1997-11-24

2002-04-16

Zirker, Daniel (Department: 1771)

Stock material or miscellaneous articles

Web or sheet containing structurally defined element or...

Composite having voids in a component

C428S343000, C428S354000, C428S3550BL

Reexamination Certificate

active

06372335

ABSTRACT:

The invention relates to an adhesive tape for a bond which can be redetached by pulling, without residue or damage, and to its use.
Highly extensible elastic adhesive films for redetachable bonds, which are redetachable by pulling essentially 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 4.222.849, DE 4.233.872, DE 4.428.587, DE 4.431.914 and DE 195 11 288 describe, inter alia, specific embodiments and applications of prior adhesive films.
Multilayer adhesive films which comprise highly extensible film backings of low elasticity, or highly extensible, elastic film backings, and uses of the same adhesive films, are likewise known, for instance from 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 photo-polymerized acrylic PSA), WO 92/11333 (PSA tape using highly extensible essentially inelastic backing), WO 93/01979 “Securing stacks with stretch adhesive tape”, and WO 94/21157 “Article support using stretch releasing adhesive”.
WO 92/11333, for instance, describes an adhesive tape which can be released again by pulling in the bond plane and which uses as its backing a highly stretchable, essentially nonresilient (nonelastomeric) film having a resilience after stretching of < about 50%. U.S. Pat. No. 4,024,312 describes, correspondingly, deadhering self-adhesive tapes which are essentially elastomeric in nature.
In practice it is found that it is possible in general to achieve high bond strengths with the abovementioned self-adhesive tapes on smooth and firm substrates. On rough substrates the bond strength, especially for thin products but also for self-adhesive tapes of relatively high layer thickness, is inadequate for many applications. The apparent reason for the inadequate bond strength is primarily an insufficient bond area, caused by insufficient conformability of the adhesive tapes to rough and irregular surfaces, especially when two rough substrates are to be bonded to one another. For example, when planar materials are bonded by means of tesa Power-Strips to coated woodchip wallpaper at the pressures customarily employed for press-on applications (100 N/7.4 cm
2
), bond areas of only about 10% to 40% of the adhesive area are often achieved. However, even when bonding onto smooth planar surfaces, an inadequate bond area may be the reason for deficient bond strength. The cause is probably the inclusion of air bubbles in the bond areas. Such air bubbles can often not be removed completely even by means of high application pressures. In adverse cases, bonds having such air inclusions may be the cause of drastically reduced bond strengths relative to samples bonded over the whole area and without air bubbles.
U.S. Pat. No. 5,516,581 and WO 95/06691 describe self-adhesive tapes which are redetachable by extension substantially in the bond plane and whose backings comprise polymeric foams. In particular, WO 95/06691 describes how, by using backing materials comprising polymer foams, it is possible to obtain self-adhesive tapes which can be redetached by stretching and which have a markedly improved conformity to rough and irregular surfaces. As a consequence of the resulting increase in bond area, these products can be used to achieve high bond strengths even on rough and irregularly shaped substrates.
The foam backings described in U.S. Pat. No. 5,516,581 and WO 95/06691, however, have a number of serious disadvantages:
The foam backings employed are exclusively those which do not tear when the adhesive tapes are being detached again. Such tear proof backings, however, require a multicoat structure which is in some cases very complex; cf. claims 13, 14, 17 in U.S. Pat. No. 5,516,581 and claims 4, 15 in WO 95/06691.
Single-layer foam backings are of only limited use:
Single-layer foam backings according to claim 1 of WO 95/06691 have a minimum thickness of at least 30 mils=760 &mgr;m.
Single-layer foam backings according to claim 1 in WO 95/06691 are limited, furthermore, in that only those having a modulus of elasticity (Young's modulus)<about 2400 psi=16.9 MPa are suitable.
The resilience of the adhesive tapes described in U.S. Pat. No. 5,516,581 is in all cases<about 50% after the redetachment process. Adhesive tapes having a markedly elastic resilience, therefore, cannot be employed in accordance with the invention.
A substantial proportion of the thin-layer polymer foams which are obtainable on the market are therefore unsuitable as a material for use in the abovementioned application.
The object of the present invention was to overcome the abovementioned disadvantages.
This is achieved by means of adhesive tapes as characterized in more detail in the claims, especially
the use as backing materials of polymeric foams which are characterized by a modulus of elasticity of less than 16 MPa and a layer thickness of from about 200 to about 600 &mgr;m, preferably between 300 and 550 &mgr;m,
in combination with pressure-sensitive adhesive compositions which couple high stretchability with a high tear strength, as a result of which
resulting self-adhesive tapes can be redetached without residue by stretching, especially in the bond plane, and neither the pressure-sensitive adhesive composition nor the foam backing used tears during the detachment process.
It is only the combination of highly stretchable pressure-sensitive adhesive compositions of high tear strength with the abovementioned polymeric foams which do not tear during the detachment process in combination with pressure-sensitive adhesive compositions employed in accordance with the invention that makes it possible to realize very thin-layer and yet highly conformative self-adhesive tapes which can be redetached without residue and without destruction by stretching, especially in the bond plane. By virtue of the high conformability even to rough substrates, such as coated woodchip wallpaper, very high bond areas are achieved in comparison with adhesive films which do not employ an intermediate foam backing.
The use of appropriate thin-layer foams makes it possible at the same time to realize low detachment forces (stripping forces), a significant advantage for practical use. In relation to the greater ease of handling of the adhesive films in the course of the detachment process, low stripping forces also make it possible to effect detachment without destruction even from highly sensitive substrates, as constituted, for example, by many wallpapers.
Another advantage of the self-adhesive tapes according to the invention is that when bonding thin flexible materials to very rough substrates, for example when bonding posters made from thin paper to woodchip wallpaper, the structure of the rough substrate is reproduced to a far lesser extent in the bonded area.
Further advantages include the small amount of material required to produce adhesive films which contain an intermediate foam backing and which can be redetached without residue or without destruction by stretching, especially in the bond plane.
Exemplary applications:
Self-adhesive tapes which can be redetached without residue and without destruction for:
Original closure applications, single- and double-sided adhesive.
The fixing of posters, pictures, calendars, postcards, signs, self-adhesive hooks, including those which are ready-made,
labels, for example price labels,
generally, for joining materials which are to be parted again at a later point in time.
Materials employed
Pressure-sensitive adhesive compositions
The pressure-sensitive adhesive compositions used are preferably those based on block copolymers comprising polymer blocks formed from vinylaromatic compounds (A blocks), preferably styrene, and those fo

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