Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2002-04-16
2004-04-20
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S563000, C524S570000, C526S318400, C526S320000, C526S326000, C525S094000, C156S275500
Reexamination Certificate
active
06723786
ABSTRACT:
The invention relates to pressure sensitive adhesives based on block copolymers, said block copolymers comprising at least the unit P(A)-P(B)-P(A), composed of a middle polymer block P(B) and of two polymer blocks P(A) surrounding the middle polymer block P(B), or the unit P(B)-P(A)-P(B), composed of a middle polymer block P(A) and of two polymer blocks P(B) surrounding the middle polymer block P(A), to the use of such adhesives, and to a process for preparing them.
BACKGROUND OF THE INVENTION
In industry, hotmelt processes operating with solventless coating technology are of growing importance in the preparation of pressure sensitive adhesives. In general, environmental regulations and increasing costs are forcing forward the development process of such adhesives. Besides SIS (styrene-isoprene-styrene copolymers) systems, acrylic polymers are increasingly being applied from the melt as a polymer film to backing materials. Moreover, for specialty applications, pressure sensitive adhesive tapes which feature very low outgassing are needed. This is something which can be ensured only by means of hotmelt processes, since conventional coatings applied from solution always still contain small fractions of residual solvent.
As a result of the changeover to hotmelt processes, some of the crosslinking mechanisms employed to date are becoming redundant. For example, thermal crosslinking processes using metal chelates or polyfunctional isocyanates, which are very popular with the solvent-based systems, can no longer be employed. As a result, the crosslinking of polyacrylate pressure sensitive adhesives by irradiation with ultraviolet light (UV) or with electron beams (EB), the latter being known as electron beam curing (EBC), is being strongly promoted at the present time.
Furthermore, there is an increasing demand for repositionable pressure sensitive adhesive tapes. These tapes show no peel increase on a variety of substrates; that is, even after being bonded for several days or weeks, there is no change in the bond strength and the tapes can be removed from the substrate without residue.
In order, then, to lower the bond strengths to polar substrates, such as steel, for example, and to ensure repositionability, it is very common to add apolar resins. An unwanted side effect of this method is often the migration of the resins within the pressure sensitive adhesive.
More recent methods use microparticles in the pressure sensitive adhesives. In this case, heat-expandable microparticles [U.S. Pat. No. 5,441,810 A] are used which following temperature exposure expand and permit easier removal from the substrate. The temperature increase required before the adhesive is removed is a disadvantage.
Further examples of the use of microspherical particles are given in U.S. Pat. No. 5,746,625 A. Here again, repositionable pressure sensitive adhesives and corresponding tapes with the addition of these additives are produced.
U.S. Pat. Nos. 4,166,152 A, 4,495,318 A, and 4,598,112 A likewise describe tacky particles which can be “reused” as adhesives.
A disadvantage common to all adhesives containing microspherical particles is that they cannot be used as hotmelt pressure sensitive adhesives. Since in the hotmelt process high shear forces are exerted by the extrusion procedure on the adhesive and on the particles, with the consequence that the particles are destroyed in the course of processing.
EP 0 707 604 A1 uses polyethylene/butylene macromonomers for copolymerization with acrylates. As a result, phases are formed which have a low glass transition temperature, which in turn allow the adhesives to flow on apolar surfaces, and which therefore ensure high bond strengths to PE and PP.
Additionally, these adhesives, owing to their low polarity, are said to possess a low peel increase at least on polar substrates. A disadvantage is the poor conversion of the polymerization process described. Moreover, these pressure sensitive adhesives require crosslinking, since otherwise the cohesion of the pressure sensitive adhesive tapes becomes too low. Moreover, it is very difficult to process these polyacrylates as hotmelts, since the high residual monomer fractions impact negatively on the concentration process, and migration in the adhesive tape can adversely affect the long-term technological properties.
U.S. Pat. Nos. 5,614,586 A and 5,674,275 A describe tacky hydrogels which can be prepared from ethoxylated comonomers. The materials produced are repositionable, but are not pressure sensitive adhesives.
U.S. Pat. No. 5,314,962 A describes A-B-A block copolymers as elastomers for adhesives, which possess A domain formation as their cohesion-forming feature. As a result of the selection of the comonomers used, however, desired repositionable pressure sensitive adhesives cannot be produced.
EP 0 921 170 A1 describes A-B-A block copolymers which have been modified with additions of resin. Here again, owing to the selection of the comonomers and added resins, pressure sensitive adhesives with good repositionability cannot be achieved.
EP 0 408 429 A1 and EP 0 408 420 A1 describe A-B-A block copolymers which, however, were synthesized by living anionic polymerization. Because of the absence of an acrylic acid fraction, however, these polymers are unsuited to use as pressure sensitive adhesives, since the internal cohesion of the middle block is too low. Additionally, because of the anionic polymerization, it is not possible to use readily deprotonated comonomers such as hydroxyl-functionalized or ethoxy-functionalized acrylates or methacrylates, for example.
In U.S. Pat. No. 6,069,205 A, diblock and triblock copolymers are prepared by an atom transfer polymerization and utilized for adhesives. This method is also unsuitable for preparing pressure sensitive adhesives, since it uses relatively high catalytic amounts of heavy metal compounds which would have to be removed, in a cumbersome operation, by extraction processes.
EP 1 008 640 A1 describes styrene block copolymers comprising an acrylate middle block composed, however, of the common C
2
to C
14
alkylacrylates. Because of the restriction of the comonomers this method can also not be used to produce repositionable pressure sensitive adhesives. Moreover, metal salts are used to prepare these polymers too (in analogy to U.S. Pat. No. 6,069,205 A), which would have to be removed, again a cumbersome operation, for pressure sensitive adhesive tape applications.
It is an object of the invention to provide improved pressure sensitive adhesives which do not have the disadvantages of the prior art, or only to a reduced extent, and which, therefore, can be coated even in the uncrosslinked state, possess consistent bond strength to a variety of substrates, can be processed as hotmelt adhesives, and exhibit good cohesion.
SUMMARY OF THE INVENTION
The invention accordingly provides a pressure sensitive adhesive based on block copolymers, said block copolymers having at least one unit composed of three successive polymer blocks, said three successive polymer blocks being chosen in alternation from the group of the polymer blocks P(A) and P(B), wherein
P(A) represents a homopolymer or copolymer block obtainable from a component A which is composed of at least two monomers A1, A2, the polymer block P(A) having a softening temperature of from −80° C. to 0° C.,
at least one (A1) of the monomers of component A is an acrylic or methacrylic acid derivative of the general formula
CH
2
═CH(R
I
)(COOR
II
) (I)
in which R
I
=H or CH
3
and R
II
is an aliphatic linear, branched or cyclic, substituted or unsubstituted, saturated or unsaturated alkyl radical having from 1 to 20 carbon atoms,
at least one further (A2) of the monomers of component A is an acrylated monomer of the general formula
CH
2
═CH(R
III
)(COOR
IV
) (II)
in which R
III
=H or CH
3
and R
IV
is an oligomeric or polymeric glycol with at least two glycol units,
P(B) represents a homopolymer or copolymer block obtainable from a component B which is co
Husemann Marc
Zöllner Stephan
Norris & McLaughlin & Marcus
Sastri Satya
tesa AG
Wu David W.
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