DE102020204065A1 - Process for the production of a multilayer adhesive tape with a foam backing - Google Patents

Abstract

The aim is to provide an efficient process for the production of adhesive tapes with high interlaminate adhesion, which are suitable for bonding to low-energy surfaces. This is achieved with a method for producing a multilayer adhesive tape, which comprises the following process steps: the shaping of a pressure-sensitive adhesive layer on a separating, web-like material; a treatment of the free side of this pressure-sensitive adhesive layer with a plasma or by means of corona; and the molding of a syntactically foamed, pressure-sensitive adhesive backing layer on the treated side of this pressure-sensitive adhesive layer, these process steps being carried out on a moving web of this pressure-sensitive adhesive layer. The subject matter of the invention is also an adhesive tape obtainable by a process according to the invention and the use of such a tape Adhesive tape for the production of bonds on low-energy substrates.

Description

The invention lies in the field of adhesive tapes, as they are often used in technology for joining a wide variety of substrates. In particular, the invention relates to a method for producing a multilayer adhesive tape, specifically a method for producing an adhesive tape, the pressure-sensitive adhesive layer thereof being applied to a carrier layer directly after physical pretreatment.

In many areas of technology, components have to be bonded with adhesive tapes on so-called low-energy surfaces (LSE surfaces = Low Surface Energy surfaces). For example, in automobile construction, external add-on parts such as bumper strips, emblems, decorative strips, etc. are often attached to the vehicles with adhesive tapes. Due to the increasing proportion of SUV vehicles, the need for adhesive tapes for such applications in automobile construction is steadily increasing. The add-on parts are usually made of plastics, plastics with LSE surfaces such as PP or PP / EPDM making up a large proportion of the materials used due to their positive processing properties and the low material costs. In order to achieve adequate adhesion of the adhesive tapes to these substrates, it is customary in the prior art to pretreat the plastic surfaces chemically - with adhesion promoters - or the plastic or adhesive surfaces physically - for example with flame, corona or plasma - before bonding.

WO 2008/068150 A1 For example, describes a self-adhesive tape which comprises at least two pressure-sensitive adhesive layers laminated directly to one another, one or both of which have been chemically and / or physically pretreated prior to being laminated to one another.

WO 2013/178462 A1 discloses a double-sided adhesive tape with a pressure-sensitive adhesive and a heat-activatable side, the heat-activatable side being based on a thermoplastic material and being corona or plasma pretreated in an atmosphere of nitrogen, carbon dioxide, a noble gas or a mixture of these gases before being brought into contact with the pressure-sensitive adhesive layer .

Since this pretreatment is associated with an additional process step and thus with additional costs, there is great interest in not doing this step.

This is made possible, among other things, by using pressure-sensitive adhesives based on synthetic rubbers and / or poly (meth) acrylates, whether pure or as part of blends. With such compounds, good to very good adhesive properties can be achieved on non-pretreated, low-energy plastics. However, it is disadvantageous that these adhesives are limited in terms of their durability at elevated temperatures, probably because of their frequently high adhesive resin contents. For this reason, they are often used as a pressure-sensitive adhesive layer in multilayer adhesive tapes, the carrier layer of which consists of foamed, filled or even pure poly (meth) acrylates, which, because of the unnecessary use of adhesive resins and their chemical crosslinking, generally have good durability even at higher temperatures demonstrate.

Three-layer, double-sided adhesive tapes are generally the subject of the DE 10 2009 048 036 A1 , wherein a viscoelastic polymer layer made of (meth) acrylate monomers is provided in the center and the main polymer component of a pressure-sensitive adhesive layer is also built up from such monomers.

Special synthetic rubber PSAs with a linear and a multi-armed block copolymer, each with an elastomeric and a glass-like block, are disclosed in WO 2008/073669 A1 described.

WO 2008/070386 A1 describes pressure-sensitive adhesives which contain more than 90% by weight of a block copolymer composition and also an acrylate composition, and their use in adhesive tapes.

Adhesive tapes with a poly (meth) acrylate-based carrier layer and at least one pressure-sensitive adhesive based on (synthetic) rubber are for example in EP 2 767 567 A2 and WO 2010/101738 A1 described.

An adhesive tape with a carrier material composed of an acrylate-based foam layer, to which at least one pressure-sensitive adhesive layer based on a mixture of at least two different synthetic rubbers is applied, is the subject matter of EP 2 690 147 A2 .

In the case of multilayer adhesive tapes with a carrier layer and pressure-sensitive adhesive layer (s), the problem arises that the strength of the bond is often limited by the interlaminate adhesion, that is to say the adhesion of the individual layers of the adhesive tape to one another. This means that in the case of many bonds, the adhesive bond between the outer PSA layer of the adhesive tape and the substrate to be bonded is stronger than the bond between this PSA layer and the carrier layer of the adhesive tape. In such a case, the result is a break in the laminate, i.e. a break within the adhesive tape.

With the aim, inter alia, of avoiding such a result, in particular two production processes for the multilayer adhesive tapes described with synthetic rubber-based PSA layer or layers have established themselves in the prior art.

• - Beschichtung und Ausformung einer oder mehrerer Haftklebmasseschichten auf einem mit Trennmittel ausgerüsteten, bahnförmigen Material, z.B. einem Trennpapier oder einer Trennfolie;
• - Beschichtung und Ausformung einer Trägerschicht auf einem mit Trennmittel ausgerüsteten, bahnförmigen Material, z.B. einem Trennpapier oder einer Trennfolie;
• - Laminierung der Haftklebmasseschicht(en) auf die Trägerschicht, nachdem nur die Haftklebmasseschicht(en), diese und die Trägerschicht oder nur die Trägerschicht mit einer physikalischen Behandlungsmethode wie Plasma oder Corona vorbehandelt wurden, um die Interlaminathaftung zu erhöhen.

The first of these processes can be summarized as lamination in the offline process and comprises the steps

• Coating and shaping of one or more pressure-sensitive adhesive layers on a web-shaped material equipped with a release agent, for example a release paper or a release film;
• Coating and shaping of a carrier layer on a web-shaped material equipped with a release agent, for example a release paper or a release film;
• Lamination of the pressure-sensitive adhesive layer (s) onto the carrier layer after only the pressure-sensitive adhesive layer (s), this and the carrier layer or only the carrier layer have been pretreated with a physical treatment method such as plasma or corona in order to increase the interlaminate adhesion.

• - Beschichtung und Ausformung einer Trägerschicht auf einem mit Trennmittel ausgerüsteten, bahnförmigen Material, z.B. einem Trennpapier oder einer Trennfolie;
• - Beschichtung und Ausformung einer oder mehrerer Haftklebmasseschichten direkt auf die Trägerschicht; hierbei wird üblicherweise die zu beschichtende Trägerschichtseite mit einer physikalischen Behandlungsmethode wie Plasma oder Corona vorbehandelt.

The second process can be referred to as the direct coating process of the previously formed core or carrier layer and comprises the following steps:

• Coating and shaping of a carrier layer on a web-shaped material equipped with a release agent, for example a release paper or a release film;
• - Coating and shaping of one or more pressure-sensitive adhesive layers directly onto the carrier layer; here the side of the carrier layer to be coated is usually pretreated with a physical treatment method such as plasma or corona.

Due to the simpler handling in terms of process technology, the first variant is predominantly used, which, however, is often associated with increased costs due to the additional process step of lamination.

There is a continuing need for methods of producing multilayer adhesive tapes which have a good profile of properties within the meaning of the above statements. The object of the invention is therefore to provide an efficient method for producing adhesive tapes with high interlaminate adhesion, which are suitable for bonding to low-energy surfaces. In particular, it is of interest to provide multi-layer adhesive tapes with a foamed carrier layer which adhere so strongly to a large number of surfaces that, given a corresponding load, the adhesive bond predictably fails due to a break within the foamed carrier layer.

• - das Ausformen einer Haftklebmasseschicht auf einem trennend ausgerüsteten, bahnförmigen Material;
• - eine Behandlung der freien Seite dieser Haftklebmasseschicht mit einem Plasma oder mittels Corona; und
• - das Ausformen einer syntaktisch geschäumten, haftklebrigen Trägerschicht auf die behandelte Seite dieser Haftklebmasseschicht,

wobei diese Verfahrensschritte auf einer laufenden Bahn dieser Haftklebmasseschicht durchgeführt werden.A first and general object of the invention, with which the above object is achieved, is a method for producing a multilayer adhesive tape, which comprises the following method steps:

• the shaping of a pressure-sensitive adhesive layer on a separating, web-like material;
• a treatment of the free side of this pressure-sensitive adhesive layer with a plasma or by means of corona; and
• the shaping of a syntactically foamed, pressure-sensitive adhesive backing layer on the treated side of this pressure-sensitive adhesive layer,

these process steps being carried out on a moving web of this pressure-sensitive adhesive layer.

The method according to the invention enables the production of adhesive tapes with improved interlaminate adhesion compared with the adhesive tapes resulting from the previously known methods, with which high-performance bonds are achieved on non-polar, low-energy surfaces.

In accordance with the general understanding, the term “pressure-sensitive adhesive” here describes materials that are either inherently tacky or are formulated to be tacky through the addition of tackifying resins (“tackifiers”). According to the present invention, pressure-sensitive adhesives and / or pressure-sensitive adhesive products include materials and / or finished products that are to be classified as such according to one of the known methods for determining pressure-sensitive adhesives and in particular include those materials and / or finished products that are classified as pressure-sensitive adhesives according to one or more of the following methods are to be classified.

According to the "Glossary of Terms Used in the Pressure Sensitive Tape Industry", published in August 1985 by the Pressure Sensitive Tape Council, a pressure sensitive adhesive is characterized and can accordingly be determined as such that it has an aggressive and permanent tack at room temperature and firmly glued to a variety of different surfaces after mere contact without further application of greater pressure than when attaching with the finger or hand.

In particular, pressure-sensitive adhesives according to the present invention are defined by the fact that they are to be classified as such according to at least one of the two processes listed below.

According to a first method, pressure-sensitive adhesives are defined by the Dahlquist criteria, which are described, inter alia, in D. Satas, Handbook of Pressure Sensitive Adhesives, 2nd Edition, page 172, 1989. According to one of these criteria, a material is defined as a good pressure-sensitive adhesive if it has a modulus of elasticity of less than 1 · 10 ⁶ Pa at the application temperature.

According to a second method, a further criterion for determining pressure-sensitive adhesives is that their storage modulus at room temperature (25 ° C.) is within the following ranges measured by means of a frequency sweep: within a range from 2 · 10 ⁵ to 4 · 10 ⁵ Pa for a Frequency of 0.1 rad / sec (0.017 Hz) and within a module range of 2 · 10 ⁶ to 8 · 10 ⁶ Pa at a frequency of 100 rad / sec (17 Hz) (shown e.g. in Table 8-16 in D. Satas, Handbook of Pressure Sensitive Adhesive Technology, 2nd Edition, page 173, 1989 ).

In one embodiment of the invention, the pressure-sensitive adhesive layer of the adhesive tape which can be produced by the process according to the invention contains a synthetic rubber.

Synthetic rubber is preferably contained in the pressure-sensitive adhesive layer to the extent of at least 30% by weight, more preferably at least 40% by weight, based in each case on the total weight of the pressure-sensitive adhesive layer. One (single) synthetic rubber or several synthetic rubbers can be contained in the pressure-sensitive adhesive layer. In particular, the pressure-sensitive adhesive layer contains synthetic rubber (s) in a total of 30 to 70% by weight, for example a total of 40 to 60% by weight.

• - die Blöcke A unabhängig voneinander für ein Polymer, gebildet durch Polymerisation mindestens eines Vinylaromaten;
• - die Blöcke B unabhängig voneinander für ein Polymer, gebildet durch Polymerisation von konjugierten Dienen mit 4 bis 18 C-Atomen und/oder Isobutylen, oder für ein teil- oder vollhydriertes Derivat eines solchen Polymers;
• - X für den Rest eines Kopplungsreagenzes oder Initiators und
• - n für eine ganze Zahl ≥ 2 stehen.

The at least one synthetic rubber of the pressure-sensitive adhesive layer is preferably a block copolymer with a structure AB, ABA, (AB) _n , (AB) _n X or (ABA) _n X,
wherein

• - The blocks A independently of one another for a polymer formed by the polymerization of at least one vinyl aromatic;
• the blocks B independently of one another for a polymer formed by polymerizing conjugated dienes with 4 to 18 carbon atoms and / or isobutylene, or for a partially or fully hydrogenated derivative of such a polymer;
• - X for the remainder of a coupling reagent or initiator and
• - n stand for an integer ≥ 2.

In particular, if several synthetic rubbers are present, all synthetic rubbers of the pressure-sensitive adhesive layer are block copolymers with a structure as set out above. The pressure-sensitive adhesive layer can thus also contain mixtures of different block copolymers with a structure as above.

Suitable block copolymers (vinyl aromatic block copolymers) thus comprise one or more rubber-like blocks B (soft blocks) and one or more glass-like blocks A (hard blocks). The synthetic rubber of the pressure-sensitive adhesive layer is particularly preferably a block copolymer with a structure AB, ABA, (AB) ₃ X or (AB) ₄ X, where A, B and X are as defined above. If several synthetic rubbers are present, all synthetic rubbers of the PSA layer are very particularly preferred block copolymers with a structure AB, ABA, (AB) ₃ X or (AB) ₄ X, where A, B and X are as defined above. In particular, the synthetic rubber of the pressure-sensitive adhesive layer is a mixture of block copolymers with a structure AB, ABA, (AB) ₃ X or (AB) ₄ X, which preferably contains at least diblock copolymers AB and / or triblock copolymers ABA.

The block A is generally a vitreous block with a preferred glass transition temperature (Tg, DSC) which is above room temperature. The Tg of the vitreous block is particularly preferably at least 40.degree. C., in particular at least 60.degree. C., very particularly preferably at least 80.degree. C. and extremely preferably 85 to 100.degree. The proportion of vinyl aromatic blocks A in the total block copolymers of the pressure-sensitive adhesive layer is preferably 10 to 40% by weight, particularly preferably 20 to 33% by weight. Vinyl aromatics for building up block A are preferably selected from the group comprising styrene, vinyl toluene, α-methylstyrene, chlorostyrene, o- and p-methylstyrene, 2,5-dimethylstyrene, p-methoxystyrene and p-tert-butylstyrene. The block A can thus be present as a homo- or copolymer. Block A is particularly preferably a polystyrene; the at least one synthetic rubber of the pressure-sensitive adhesive layer is thus preferably a styrene block copolymer.

The block copolymer also generally has a rubber-like block B or soft block with a preferred Tg of less than room temperature. The Tg of the soft block is particularly preferably less than 0 ° C, in particular less than -10 ° C, for example less than -40 ° C and very particularly preferably less than -60 ° C.

Preferred conjugated dienes as monomers for the soft block B are in particular selected from the group consisting of butadiene, isoprene, ethylbutadiene, phenylbutadiene, piperylene, pentadiene, hexadiene, ethylhexadiene, dimethylbutadiene and the Farnese isomers and any mixtures of these monomers. Block B can also be present as a homopolymer or as a copolymer.

The conjugated dienes are particularly preferred as monomers for the soft block B selected from butadiene and isoprene. For example, the soft block B is a polyisoprene, a polybutadiene or a partially or fully hydrogenated derivative of one of these two polymers, such as, in particular, polybutylene butadiene; or a polymer made from a mixture of butadiene and isoprene. Block B is very particularly preferably a polybutadiene.

In the embodiment of the invention described here, the pressure-sensitive adhesive layer preferably contains at least one adhesive resin in addition to the synthetic rubber. The adhesive resin is preferably a non-polar adhesive resin. The adhesive resin is preferably selected from the group consisting of non-hydrogenated, partially or fully hydrogenated resins based on rosin or rosin derivatives; hydrogenated polymers of dicyclopentadiene; non-hydrogenated, partially, selectively or fully hydrogenated hydrocarbon resins based on C5, C5 / C9 and C9 monomer streams; and polyterpene resins based on α-pinene and / or β-pinene and / or δ-limonene. The pressure-sensitive adhesive layer can contain one or more adhesive resins; in the latter case it preferably contains a mixture of two or more of the abovementioned adhesive resins.

In one embodiment, the pressure-sensitive adhesive layer contains a fully hydrogenated hydrocarbon resin and / or a polyterpene resin based on α-pinene. These resins show an extremely low tendency to migrate into the carrier layer.

The pressure-sensitive adhesive layer preferably contains adhesive resins in a total of 30 to 70% by weight, particularly preferably in a total of 40 to 60% by weight.

The pressure-sensitive adhesive layer preferably contains two resins with a glass transition temperature of at least 60 ° C., more preferably of at least 65 ° C., in particular of at least 70 ° C. and a softening point (ring and ball) of at least 115 ° C., in particular of at least 120 ° C; one of the resins being compatible with the elastomer block and the other being primarily compatible with the glassy block of the block copolymer. Mainly compatible here means that the resin is in any case compatible with the glass-like block and possibly with the elastomer block. The weight ratio of the elastomer block-compatible resin to the resin mainly compatible with the vitreous block is preferably from 1: 1 to 19: 1.

The pressure-sensitive adhesive layer can contain other polymers or, in addition to the at least one synthetic rubber, further polymers. For example, the pressure-sensitive adhesive layer can also be based on one or more poly (meth) acrylates or, in the borderline case, also consist of one or more poly (meth) acrylates.

The pressure-sensitive adhesive layer can each contain, independently of one another, as further additives: primary antioxidants, for example sterically hindered phenols; secondary antioxidants, for example phosphites or thioethers; Process stabilizers, for example carbon radical scavengers; Light stabilizers, for example UV absorbers or sterically hindered amines; Processing aids; Anti-aging agents and other polymers of an elastomeric nature, for example those based on pure hydrocarbons such as unsaturated polydienes, natural or synthetic polyisoprene or polybutadiene, chemically essentially saturated elastomers such as saturated ethylene-propylene copolymers, α-olefin copolymers, polyisobutylene, butyl rubber, ethylene Propylene rubber and chemically functionalized hydrocarbons such as halogen-containing, acrylate-containing or vinyl ether-containing polyolefins.

According to the invention, the pressure-sensitive adhesive layer should first be applied to a web-like material with a release finish. If the web-like material is not given a separating finish on both sides, the pressure-sensitive adhesive layer is preferably applied to its separating side.

The web-like material with a separating finish is preferably a release liner, which in principle is not subject to any further restrictions. A release liner is usually and also according to the invention a paper or film carrier which is equipped with an adhesive coating compound (also referred to as a adhesive or anti-adhesive compound) which can withstand the tendency of a pressure-sensitive adhesive to adhere and can be separated from it with little effort (release-effective Function) and is therefore also referred to as a release layer or release coating. A large number of different substances can be used as adhesive coating compounds, which are also called “release coatings”: waxes, fluorinated or partially fluorinated compounds, polycarbamates and silicones as well as various copolymers with silicone components.

The separating layer of the release liner is preferably a silicone layer or a polycarbamate layer.

The silicone layer can preferably be traced back to a crosslinkable silicone system. These crosslinkable silicone systems include mixtures of crosslinking catalysts and so-called curable polysiloxanes. Systems containing silicone for the production of release coatings can be obtained commercially. The silicone separating layer is usually applied in the uncrosslinked state and subsequently crosslinked.

The silicone layer can be traced back to solvent-containing and / or solvent-free systems; it can preferably be traced back to a solvent-containing system.

The silicone layer can preferably be traced back to a radiation (UV or electron beam), condensation or addition crosslinking system, particularly preferably to an addition crosslinking system.

• ein Alkenylgruppen enthaltendes, lineares oder verzweigtes Polydiorganosiloxan,
• ein Polyorganowasserstoffsiloxan-Vernetzungsmittel sowie
• einen Hydrosilylierungskatalysator.

Such silicone-based release agents on an addition-crosslinking basis can generally be cured by hydrosilylation. The formulations for making these release agents typically include the following ingredients:

• a linear or branched polydiorganosiloxane containing alkenyl groups,
• a polyorganohydrogensiloxane crosslinking agent and
• a hydrosilation catalyst.

As catalysts for addition-crosslinking silicone systems (hydrosilylation catalysts), platinum or platinum compounds, such as, for example, the Karstedt catalyst (a Pt (0) complex compound) have proven particularly useful.

• ein lineares oder verzweigtes Dimethylpolysiloxan, welches aus ca. 80 bis 200 Dimethylpolysiloxan-Einheiten besteht und an den Kettenenden mit Vinyldimethylsiloxy-Einheiten abgestoppt ist. Typische Vertreter sind zum Beispiel lösungsmittelfreie, additionsvernetzende Silikonöle mit endständigen Vinylgruppen;
• einen linearen oder verzweigten Vernetzer, welcher entweder nur Methylhydrogensiloxy-Einheiten in der Kette aufweist (Homopolymer-Vernetzer) oder aus Methylhydrogensiloxy- und Dimethylsiloxy-Einheiten zusammengesetzt ist (Copolymer-Vernetzer), wobei die Kettenenden entweder mit Trimethylsiloxy-Gruppen oder Dimethylhydrogensiloxy-Gruppen abgesättigt sind; typische Vertreter dieser Produktklasse sind zum Beispiel Hydrogenpolysiloxane mit hohem Gehalt an reaktivem Si-H wie die Vernetzer V24, V90 oder V06, welche bei der Wacker-Chemie GmbH kommerziell erhältlich sind;
• ein Silikon-MQ-Harz, welches als M-Einheit neben den üblicherweise verwendeten Trimethylsiloxy-Einheiten auch über Vinyldimethylsiloxy-Einheiten verfügt;
• einen silikonlöslichen Platinkatalysator wie zum Beispiel einen Platindivinyltetramethyldisiloxan-Komplex, welcher üblicherweise als Karstedt-Komplex bezeichnet wird.

More specifically, such addition-crosslinking release coatings can comprise the following components:

• a linear or branched dimethylpolysiloxane, which consists of approx. 80 to 200 dimethylpolysiloxane units and is terminated at the chain ends with vinyldimethylsiloxy units. Typical representatives are, for example, solvent-free, addition-crosslinking silicone oils with terminal vinyl groups;
• a linear or branched crosslinker, which either has only methylhydrogensiloxy units in the chain (homopolymer crosslinker) or is composed of methylhydrogensiloxy and dimethylsiloxy units (copolymer crosslinker), the chain ends either being saturated with trimethylsiloxy groups or dimethylhydrogensiloxy groups are; Typical representatives of this product class are, for example, hydrogen polysiloxanes with a high content of reactive Si — H such as the crosslinkers V24, V90 or V06, which are commercially available from Wacker-Chemie GmbH;
• a silicone MQ resin which, as an M unit, has vinyldimethylsiloxy units in addition to the trimethylsiloxy units commonly used;
• a silicone-soluble platinum catalyst such as a platinum divinyltetramethyldisiloxane complex, which is commonly referred to as the Karstedt complex.

An undesirable property of addition-crosslinking silicone systems, however, is their sensitivity to catalyst poisons, such as heavy metal, sulfur and nitrogen compounds (cf. “Chemical technology, processes and products” by R. Dittmeyer et al., Volume 5, 5th edition, Wiley-VCH, Weinheim, Germany, 2005, Chapter 6-5.3.2, page 1142 ). In general, electron donors can be viewed as platinum poisons (A. Colas, Silicone Chemistry Overview, Technical Paper, Dow Corning). Accordingly, phosphorus compounds such as phosphines and phosphites are also to be regarded as platinum poisons. The presence of catalyst poisons means that the crosslinking reaction between the different constituents of a silicone release agent no longer takes place or only takes place to a small extent. Therefore, in the production of anti-adhesive silicone coatings, the presence of catalyst poisons, in particular platinum poisons, is generally strictly avoided.

Depending on the character of the pressure-sensitive adhesive to be coated, the silicone layer can also contain further additives, for example stabilizers or flow control agents.

According to the invention, the free side of the pressure-sensitive adhesive layer — that is to say the side not provided with the separating, web-like material — is to be treated with a plasma or by means of corona. In particular, the free side of the pressure-sensitive adhesive layer is treated by means of corona.

In the present case, a “plasma” is understood to mean a gas in which electrical discharges are caused and whose properties are determined by the splitting of a large number of its molecules into ions and electrons. The treatment of the pressure-sensitive adhesive layer preferably takes place by means of a nozzle. The plasma is initially subject to the dynamic pressure generated in the nozzle, but is then released in a space that is subject to atmospheric pressure. The mean electron velocity in the plasma is usually very high, with the mean kinetic energy of the electrons being significantly higher than that of the ions. Hence an electron temperature defined by this energy is different from the temperature of the ions, and the plasma is not in thermal equilibrium; it is cold".

A known method of generating a plasma is corona treatment. The physical pretreatment technique commonly referred to as “corona” is mostly a “dielectric barrier discharge” (DBD), see also Wagner et al., Vacuum, 71: 417-436 (2003) . In this case, the substrate to be treated is passed in the form of a web between two high-voltage electrodes, at least one electrode consisting of a dielectric material or being coated with it. The treatment intensity of a corona treatment is given as a "dose" in [Wmin / m ² ], with the dose D = P / b * v, with P = electrical power [W], b = electrode width [m], and v = web speed [ m / min].

A suitably high web tension is used to press the substrate onto the counter-electrode, which is designed as a roller, in order to prevent air inclusions. The treatment distance is typically about 1 to 2 mm. A fundamental disadvantage of such a two-electrode geometry with a treatment in the space between the electrode and the counter-electrode is the possible rear side treatment. In the case of the smallest air or gas inclusions on the reverse side, for example if the web tension is too low in a roll-to-roll treatment, a mostly undesirable corona treatment of the reverse side takes place.

During treatment with the high-frequency alternating voltage in the kV range, brief discrete discharge channels are created between the electrode and the substrate, with accelerated electrons also striking the surface of the substrate. When the electrons hit, the energy can be two to three times that Binding energy of most of the molecular bonds of the substrates usually treated (plastics, pressure-sensitive adhesives, metals, glass) and thus break them. Secondary reactions create functional and polar groups on the surface. The formation of polar groups, for example, makes a major contribution to increasing the surface energy. Due to the effect of the high-energy accelerated electrons, such a treatment is very efficient in relation to the electrical energy used, and very powerful in relation to the possible reactions triggered. The generation of a high density of polar and functional groups is in competition with the degradation of material through chain breaks and oxidation.

The simple corona treatment or DBD is often used to treat non-polar surfaces and foils so that their surface energy and wettability increase. For example, plastic films are often subjected to a corona treatment prior to printing or the application of adhesives.

In one embodiment, the plasma treatment of the method according to the invention is carried out as a homogeneous and discharge-free treatment. For example, such a homogeneous plasma can be generated by using noble gases, sometimes with admixtures. The treatment takes place in a reaction chamber that is homogeneously filled with plasma.

The plasma contains radicals and free electrons as reactive species, which can react quickly with many chemical groups in the substrate surface. This leads to the formation of gaseous reaction products and highly reactive, free radicals on the surface. These free radicals can react quickly through secondary reactions with oxygen or other gases and form various chemical functional groups on the substrate surface. As with all plasma technologies, the generation of functional groups is in competition with material degradation.

Instead of being exposed to the reaction chamber of a two-electrode geometry, the substrate to be treated can also only be exposed to the discharge-free plasma ("indirect" plasma). The plasma is then mostly potential-free to a good approximation. The plasma is mostly driven away from the discharge zone by a gas stream and after a short distance is directed onto the substrate without the need for a counter electrode. The lifetime (and thus also the usable distance) of the reactive plasma, often called "afterglow", is determined by the precise details of the recombination reactions and the plasma chemistry. Usually an exponential decay of the reactivity with the distance from the discharge source is observed.

The plasma treatment of the method according to the invention is preferably based on a nozzle principle. The plasma therefore preferably emerges from a nozzle, and this nozzle is at an angle of 45 to 90 °, more preferably 60 to 90 °, in particular 75 to 90 °, very particularly preferably 90 °, in each case to the surface of the pressure-sensitive adhesive layer , directional. Here, the nozzle can be round or linear; Rotary nozzles are sometimes used. The rotating nozzle principle is advantageous because of its flexibility and its inherently one-sided treatment. Such nozzles, for example from Plasmatreat, are widely used in industry for pretreating substrates before bonding. Disadvantages are the indirect and less efficient, since discharge-free treatment, and thus the reduced web speeds. The usual design of a round nozzle is, however, particularly well suited to treating narrow webs of material, for example an adhesive tape or an adhesive layer with a width of a few cm.

There are different plasma generators on the market, which differ in the technology for plasma generation, the nozzle geometry and the gas atmosphere. Although the treatments differ in terms of efficiency, among other things, the basic effects are mostly similar and primarily determined by the gas atmosphere used. A plasma treatment can take place in different atmospheres, whereby the atmosphere can also comprise air. According to the invention, the free side of the pressure-sensitive adhesive layer is preferably treated with a plasma or by means of corona in a process gas atmosphere other than air, in particular in a process gas atmosphere selected from N ₂ , O ₂ , H ₂ , CO ₂ , Ar, He, ammonia and mixtures of two or more of these gases; it is very particularly preferably carried out in a process gas atmosphere composed of N ₂ .

In principle, the preferred treatment atmospheres described above comprise optional admixtures of water vapor and / or other constituents in minor proportions.

In principle, coating or polymerizing constituents can also be added to the treatment atmosphere, namely as a gas (for example ethylene) or liquid (atomized as an aerosol). There is almost no restriction on the aerosols that can be used. Especially those who work indirectly Plasma technologies are suitable for the use of aerosols, as there is no risk of contamination of the electrodes.

As has been shown, the described plasma or corona treatment of the free side of the pressure-sensitive adhesive layer is sufficient to ensure sufficiently strong interlaminate adhesion in the multilayer adhesive tape to be produced according to the invention. In particular, the PSA layer and the carrier layer are preferably not treated with a primer or with a flame.

According to the invention, a syntactically foamed, pressure-sensitive adhesive carrier layer is to be applied to the treated side of the pressure-sensitive adhesive layer. The syntactically foamed, pressure-sensitive adhesive carrier layer is preferably shaped onto the treated side of the pressure-sensitive adhesive layer by means of a calender with two or more rollers.

According to the invention, the carrier layer itself is pressure-sensitively adhesive. An adhesive tape according to the invention can accordingly consist only of the carrier layer and the pressure-sensitive adhesive layer and nevertheless be regarded as a double-sided adhesive tape. Depending on the extent of the pressure-sensitive adhesive properties of the backing layer, however, in such an embodiment the adhesive tape can also be viewed as being adhesive only on one side. In any case, the adhesive performance of the at least one side of the adhesive tape equipped with the pressure-sensitive adhesive layer is essential to the invention. In addition, the adhesive tape of the invention preferably has a pressure-sensitive adhesive layer on both sides of the carrier layer and is thus a double-sided adhesive tape. The adhesive tape of the invention particularly preferably has a synthetic rubber-containing PSA layer as described above on both sides of the backing layer. In particular, the two pressure-sensitive adhesive layers are identical in terms of their composition.

The carrier layer is likewise preferably thicker than the pressure-sensitive adhesive layer or - in the case of pressure-sensitive adhesive layers lying on both sides - than each of the pressure-sensitive adhesive layers.

The carrier layer preferably contains at least one poly (meth) acrylate.

A “poly (meth) acrylate” is understood to mean a polymer whose monomer base consists of at least 70% by weight of acrylic acid, methacrylic acid, acrylic acid esters and / or methacrylic acid esters, acrylic acid esters and / or methacrylic acid esters being at least 50% by weight , in each case based on the total monomer composition of the polymer in question. Poly (meth) acrylates are generally accessible by free-radical polymerization of acrylic and / or methacrylic monomers and, if appropriate, other copolymerizable monomers. According to the invention, the term “poly (meth) acrylate” encompasses both polymers based on acrylic acid and its derivatives and those based on acrylic acid and methacrylic acid and their derivatives as well as those based on methacrylic acid and their derivatives.

The carrier layer can contain one or more poly (meth) acrylates. The carrier layer preferably contains a total of at least 50% by weight of poly (meth) acrylates, based on the total weight of the carrier layer. This also includes that the carrier layer contains only a single poly (meth) acrylate, of which at least 50% by weight, based on the total weight of the carrier layer, is then present.

• 65 bis 97 Gew.-% Ethylhexylacrylat und/oder Butylacrylat,
• 0 bis 30 Gew.-% Methylacrylat,
• 3 bis 15 Gew.-% Acrylsäure.

In particular, the carrier layer contains at least 50% by weight, based on the total weight of the carrier layer, of at least one polyacrylate which can be attributed to the following monomer composition:

• 65 to 97% by weight of ethylhexyl acrylate and / or butyl acrylate,
• 0 to 30% by weight methyl acrylate,
• 3 to 15% by weight acrylic acid.

In addition to the at least one poly (meth) acrylate, the carrier layer can contain at least one further polymer selected from the group consisting of rubbers, in particular natural rubbers, polyurethanes and styrene block copolymers and blends of the polymers mentioned.

The poly (meth) acrylate (s) of the carrier layer preferably have a weight-average molecular weight M _w of at least 500,000 g / mol, particularly preferably of at least 700,000 g / mol. The poly (meth) acrylate (s) of the carrier layer likewise preferably has a weight-average molecular weight M _w of a maximum of 1,700,000 g / mol. The polydispersity PD, i.e. the breadth of the molar mass distribution, which is the quotient of the weight average molecular weight M _w and the number average Molecular weight M _{n is} determined, for the polymers contained in the foamed carrier is preferably 10 PD 100, particularly preferably 20 PD 80.

• - sowohl eine ausreichend lange Verarbeitungszeit gewährleisten, sodass es nicht zu einer Vergelung während des Verarbeitungsprozesses, insbesondere des Extrusionsprozesses, kommt,
• - als auch zu einer schnellen Nachvernetzung des Polymers auf den gewünschten Vernetzungsgrad bei niedrigeren Temperaturen als der Verarbeitungstemperatur, insbesondere bei Raumtemperatur, führen.

The poly (meth) acrylate (s) of the carrier layer are preferably crosslinked at least by means of a divalent crosslinker. “Bivalent crosslinker” means that the crosslinker has exactly two points of attachment via which the connection to the polymer molecules to be crosslinked can be established. The crosslinker can be a thermal and / or a condensing crosslinker; both a thermal and a condensing crosslinker can also be involved in the crosslinking. The crosslinker is particularly preferably a thermal crosslinker. In principle, all thermal crosslinkers can be used that

• - ensure a sufficiently long processing time so that gelation does not occur during the processing process, in particular the extrusion process,
• - As well as lead to rapid post-crosslinking of the polymer to the desired degree of crosslinking at temperatures lower than the processing temperature, in particular at room temperature.

Crosslinkers, in particular thermal crosslinkers, are preferably used in a total of 0.1 to 5% by weight, in particular 0.2 to 1% by weight, based on the total amount of the polymer to be crosslinked.

An - optionally additional - crosslinking via complexing agents, also referred to as chelates, is possible. A preferred complexing agent is, for example, aluminum acetylacetonate.

The poly (meth) acrylates of the pressure-sensitive adhesive of the invention are preferably crosslinked by means of epoxy (s) or by means of one or more substance (s) containing epoxy groups. The substances containing epoxide groups can also be hydrolyzable organosilanes containing epoxide groups.

The substances containing epoxy groups are in particular multifunctional epoxides, that is to say those with at least two epoxy groups; accordingly, overall there is an indirect linkage of the building blocks of the poly (meth) acrylates which carry the functional groups. The substances containing epoxy groups can be both aromatic and aliphatic compounds.

Outstandingly suitable multifunctional epoxides are oligomers of epichlorohydrin, epoxy ethers of polyhydric alcohols, in particular ethylene, propylene and butylene glycols, polyglycols, thiodiglycols, glycerol, pentaerythritol, sorbitol, polyvinyl alcohol, polyallyl alcohol and the like; Epoxy ethers of polyhydric phenols, in particular resorcinol, hydroquinone, bis (4-hydroxyphenyl) methane, bis (4-hydroxy-3-methylphenyl) methane, bis (4-hydroxy-3,5-dibromophenyl) methane, bis - (4-hydroxy-3,5-difluorophenyl) methane, 1,1-bis- (4-hydroxyphenyl) ethane, 2,2-bis- (4-hydroxyphenyl) propane, 2,2-bis- (4- hydroxy-3-methylphenyl) propane, 2,2-bis (4-hydroxy-3-chlorophenyl) propane, 2,2-bis (4-hydroxy-3,5-dichlorophenyl) propane, 2.2 -Bis- (4-hydroxy-3,5-dichlorophenyl) -propane, bis- (4-hydroxyphenyl) -phenylmethane, bis- (4-hydroxyphenyl) -phenylmethane, bis- (4-hydroxyphenyl) diphenylmethane, bis (4- hydroxyphenyl) -4'-methylphenylmethane, 1,1-bis- (4-hydroxyphenyl) -2,2,2-trichloroethane, bis- (4-hydroxyphenyl) - (4-chlorophenyl) methane, 1,1-bis- (4-hydroxyphenyl) -cyclohexane, bis- (4-hydroxyphenyl) -cyclohexylmethane, 4,4'-dihydroxydiphenyl, 2,2'-dihydroxydiphenyl, 4,4'-dihydroxydiphenyl sulfone and their hydroxyethyl ethers; Hydrolyzable organosilanes containing amino or epoxy groups; Phenol-formaldehyde condensation products such as phenol alcohols and phenol aldehyde resins; S- and N-containing epoxides, for example N, N-diglycidylaniline and N, N'-dimethyldiglycidyl-4,4-diaminodiphenylmethane; and epoxides which have been prepared from polyunsaturated carboxylic acids or monounsaturated carboxylic acid esters of unsaturated alcohols by conventional processes; Glycidyl ester; Polyglycidyl esters which can be obtained by polymerization or copolymerization of glycidyl esters of unsaturated acids or are obtainable from other acidic compounds, for example from cyanuric acid, diglycidyl sulfide or cyclic trimethylene trisulfone or its derivatives.

The hydrolyzable organosilanes containing epoxide groups are, in particular, organosilanes corresponding to the formula (1) R ¹ -Si (OR ² ) nR ³ _m (1), wherein R ^{1 is} a radical containing a cyclic ether function,
the radicals R ² independently of one another each represent an alkyl or acyl radical,
R ^{3 represents} a hydroxyl group or an alkyl radical, and
n stands for 2 or 3 and m for the number resulting from 3 - n

Particularly preferably, the thermal crosslinking agent is selected from the group consisting of 1,4-butanediol diglycidyl ether, polyglycerol-3-glycidyl ether, Cyclohexandimethanoldiglycidether, Glycerintriglycidether, Neopentylglykoldiglycidether, pentaerythritol tetraglycidyl ether, 1,6-hexanediol diglycidyl ether, Polypropylenglykoldiglycidether, trimethylolpropane triglycidyl ether, pentaerythritol tetraglycidyl ether, bisphenol A diglycidyl ether, Bisphenol-F-diglycidether, 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate (UVACure1500), (3-glycidyloxypropyl) trimethoxysilane, (3-glycidyloxypropyl) triethoxysilane, (3-glycidyloxysilane, (3-glycidyloxysilane), (3-glycidyloxysilane, (3-glycidyloxysilane) methyldimethyldimethyl (3-glycidyloxysilane) (3-glycidyloxysilane, 3-glycidyloxysilane, 3-glycidyloxysilane, (3-glycidyloxysilane) methyl , 6-epoxyhexyltriethoxysilane, [2- (3,4-epoxycyclohexyl) ethyl] trimethoxysilane, [2- (3,4-epoxycyclohexyl) ethyl] triethoxysilane, and triethoxy [3 - [(3-ethyl-3-oxetanyl) methoxy] propyl ] silane

The poly (meth) acrylates are particularly preferably crosslinked by means of a crosslinker-accelerator system (“crosslinking system”) in order to obtain better control over the processing time, the crosslinking kinetics and the degree of crosslinking. The crosslinker-accelerator system preferably comprises at least one substance containing epoxy groups as crosslinker and at least one substance that accelerates crosslinking reactions by means of compounds containing epoxy groups at a temperature below the melting temperature of the polymer to be crosslinked.

According to the invention, amines are particularly preferably used as accelerators. Formally, these are to be understood as substitution products for ammonia; In the following formulas, the substituents are represented by “R” and include, in particular, alkyl and / or aryl radicals. Particular preference is given to using those amines which enter into no or only slight reactions with the polymers to be crosslinked.

In principle, both primary (NRH ₂ ), secondary (NR ₂ H) and tertiary amines (NR ₃ ) can be selected as accelerators, of course also those which have several primary and / or secondary and / or tertiary amino groups. Particularly preferred accelerators are tertiary amines such as, for example, triethylamine, triethylenediamine, benzyldimethylamine, dimethylaminomethylphenol, 2,4,6-tris (N, N-dimethylaminomethyl) phenol, N, N'-bis (3- (dimethylamino) propyl) urea. Further preferred accelerators are multifunctional amines such as diamines, triamines and / or tetramines, for example diethylenetriamine, triethylenetetramine, trimethylhexamethylenediamine.

Further preferred accelerators are amino alcohols, in particular secondary and / or tertiary amino alcohols, in the case of several amino functionalities per molecule preferably at least one, particularly preferably all amino functionalities being secondary and / or tertiary. Particularly preferred accelerators of this type are triethanolamine, N, N-bis (2-hydroxypropyl) ethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, 2-aminocyclohexanol, bis (2-hydroxycyclohexyl) methylamine, 2- (diisopropylamino) ethanol, 2- ( Dibutylamino) ethanol, N-butyldiethanolamine, N-butylethanolamine, 2- [bis (2-hydroxyethyl) amino] -2- (hydroxymethyl) -1,3-propanediol, 1- [bis (2-hydroxyethyl) amino] -2- propanol, triisopropanolamine, 2- (dimethylamino) ethanol, 2- (diethylamino) ethanol, 2- (2-dimethylaminoethoxy) ethanol, N, N, N'-trimethyl-N'-hydroxyethylbisaminoethyl ether, N, N, N'-trimethylaminoethylethanolamine and N, N, N'-trimethylaminopropylethanolamine.

Further suitable accelerators are pyridine, imidazoles such as, for example, 2-methylimidazole and 1,8-diazabicyclo [5.4.0] undec-7-ene. Cycloaliphatic polyamines can also be used as accelerators. Accelerators based on phosphorus, such as phosphines and / or phosphonium compounds, for example triphenylphosphine or tetraphenylphosphonium tetraphenylborate, are also suitable.

Quaternary ammonium compounds can also be used as accelerators; Examples are tetrabutylammonium hydroxide, cetyltrimethylammonium bromide and benzalkonium chloride.

A foamed layer or a foam is understood to mean a structure of gas-filled, spherical or polyhedral cells which are delimited by liquid, semi-liquid, higher viscosity or solid cell webs and which are present in such a proportion that the density of the foam compared to the density of the Matrix material, that is to say the entirety of the non-gaseous materials from which the layer in question is constructed, is reduced. According to the invention, the carrier layer is syntactically foamed, i.e. the foam cells are not delimited by the matrix material itself. The foamed carrier layer preferably contains one or more foaming agents selected from expanded microballoons; other hollow microspheres such as hollow polymer spheres, hollow glass spheres and hollow ceramic spheres as well as solid spheres such as solid polymer spheres, solid glass spheres, solid ceramic spheres and solid carbon spheres.

In particular, the foamed carrier layer comprises a multiplicity of hollow microspheres, and this multiplicity of hollow microspheres has an average diameter of at least 50 μm, more preferably of at least 60 µm, in particular of at least 70 µm. The multiplicity of hollow microspheres likewise preferably has an average diameter of at most 150 μm, more preferably of at most 130 μm, in particular of at most 85 μm. For example, the foamed carrier layer comprises a large number of hollow microspheres, and this large number of hollow microspheres has an average diameter of 60 to 140 μm, particularly preferably 65 to 125 μm, in particular 70 to 90 μm.

The carrier layer particularly preferably contains at least partially expanded microballoons. “Microballoons” are understood to mean elastic and thus expandable microspheres in their basic state, which have a thermoplastic polymer shell. These balls are filled with low-boiling liquids or liquefied gas. In particular, polyacrylonitrile, PVDC, PVC or polyacrylates are used as the shell material. Hydrocarbons of the lower alkanes, for example isobutane or isopentane, which are enclosed as a liquefied gas under pressure in the polymer shell, are particularly common as the low-boiling liquid.

By acting on the microballoons, in particular by applying heat, the outer polymer shell softens. At the same time, the liquid propellant in the envelope changes into its gaseous state. The microballoons expand irreversibly and expand three-dimensionally. The expansion is finished when the internal and external pressures equalize. Since the polymer shell is retained, a closed-cell foam is achieved.

A large number of types of microballoons are commercially available, which differ essentially in terms of their size (6 to 45 μm diameter in the unexpanded state) and the starting temperatures (75 to 220 ° C.) required for expansion. Unexpanded types of microballoons are also available as aqueous dispersions with a solids or microballoon content of approx. 40 to 45% by weight, and also as polymer-bound microballoons (masterbatches), for example in ethylene vinyl acetate with a microballoon concentration of approx. 65% by weight. Both the microballoon dispersions and the masterbatches, like the unexpanded microballoons, are suitable as such for foaming the carrier layer.

The foamed carrier layer can also be produced with so-called pre-expanded microballoons. In this group, expansion takes place before it is mixed into the polymer matrix. The carrier layer preferably contains at least partially expanded microballoons, regardless of the manufacturing route and the initial shape used for the microballoons.

The term “at least partially expanded microballoons” is understood to mean that the microballoons are expanded at least to the extent that a reduction in density of the carrier layer is effected to a technically meaningful extent compared to the same layer with the unexpanded microballoons. This means that the microballoons do not necessarily have to be completely expanded. The “at least partially expanded microballoons” are preferably each expanded to at least twice their maximum extent in the unexpanded state.

The expression “at least partially expanded” relates to the state of expansion of the individual microballoons and is not intended to express that only a part of the microballoons in question need to be (on) expanded. If “at least partially expanded microballoons” are contained in the carrier layer, then this means that all of these “at least partially expanded microballoons” are at least partially expanded in the above sense and unexpanded microballoons do not belong to the “at least partially expanded microballoons”.

In particular, the foamed carrier layer comprises a multiplicity of at least partially expanded microballoons, and this multiplicity of at least partially expanded microballoons has an average diameter of at least 50 μm, more preferably of at least 60 μm, in particular of at least 70 μm. The plurality of at least partially expanded microballoons likewise preferably has a mean diameter of at most 150 μm, more preferably of at most 130 μm, in particular of at most 85 μm. For example, the foamed carrier layer comprises a plurality of at least partially expanded microballoons, and this plurality of at least partially expanded microballoons has an average diameter of 60 to 140 μm, particularly preferably 65 to 125 μm, in particular 70 to 90 μm.

The foamed carrier layer preferably contains silica, particularly preferably precipitated silica that has been surface-modified with dimethyldichlorosilane. This is advantageous because it allows the thermal shear strength of the carrier layer to be set, in particular to be increased. Silicas can also be used excellent for use on transparent substrates. Silica is preferably present in up to 15% by weight, based on the entirety of all polymers contained in the foamed carrier layer, in the foamed carrier layer.

Further constituents of the foamed backing layer, as well as the backing layer in general, can be, for example, plasticizers, anti-aging agents, fillers and / or flame retardants.

The thickness of the carrier layer, in particular the foamed carrier layer, is preferably from 300 to 2,500 μm, more preferably from 400 to 2,400 μm.

The invention also provides a multilayer adhesive tape which can be obtained by a process according to the invention.

The invention also relates to the use of an adhesive tape according to the invention for producing bonds on low-energy substrates. “Low-energy substrates” are understood to mean substrates with a surface energy of <100 mJ / m ² , in particular of <50 mJ / m ^2. The substrates are preferably selected from the group consisting of paints; substrates pretreated with a primer; Plastic substrates, in particular polyolefin surfaces, for example PE, PP or PE / PP copolymer surfaces; Polypropylene / EPDM surfaces, ethylene propylene diene terpolymer (EPDM), ABS (acrylonitrile butadiene styrene) and polycarbonate surfaces. The substrates are particularly preferably selected from the group consisting of paints, substrates pretreated with a primer, ethylene-propylene-diene terpolymer (EPDM) surfaces, polyolefin surfaces and polypropylene / EPDM surfaces. In particular, the substrates are selected from the group consisting of paints, ethylene-propylene-diene terpolymer (EPDM) surfaces, polyolefin surfaces and polypropylene / EPDM surfaces; they are very particularly preferably selected from lacquers and polypropylene / EPDM surfaces. The paints are particularly preferably paints such as those used in automobile construction, in particular for painting body parts. The lacquers clearcoats (clearcoats, topcoats) such as, for example, TMAC 8000 from PPG or Uregloss FF 79 (BASF) are very particularly preferred.

Sample part

Measurement and test methods

Solid content (measurement method A1):

The solids content is a measure of the proportion of non-evaporable components in a polymer solution. It is determined gravimetrically by weighing the solution, then evaporating the vaporizable components in a drying cabinet for 2 hours at 120 ° C. and reweighing the residue.

K-value (according to FIKENTSCHER) (measuring method A2):

The K value is a measure of the average molecular size of high polymer substances. For the measurement, one percent (1 g / 100 ml) toluene polymer solutions were prepared and their kinematic viscosities were determined with the aid of a VOGEL-OSSAG viscometer. After normalization to the viscosity of the toluene, the relative viscosity is obtained, from which the K value can be calculated according to FIKENTSCHER (Polymer 8/1967, 381 ff.)

Gel permeation chromatography GPC (measurement method A3):

The details of the molecular weight M _w and the polydispersity PD in this document relate to the determination by gel permeation chromatography. The determination is carried out on 100 µl clear-filtered sample (sample concentration 4 g / l). Tetrahydrofuran with 0.1% by volume of trifluoroacetic acid is used as the eluent. The measurement takes place at 25 ° C. A column type PSS-SDV, 5 μ, 10 ³ Å, ID 8.0 mm is used as the guard column. 50 mm used. The columns of the type PSS-SDV, 5 µ, 10 ³ Å as well as 10 ⁵ Å and 10 ⁶ Å, each with ID 8.0 mm x 300 mm, are used for separation (columns from Polymer Standards Service; detection using a Shodex RI71 differential refractometer) . The flow rate is 1.0 ml per minute. The calibration is carried out against PMMA standards (polymethyl methacrylate calibration)].

Density determination via the mass application and the layer thickness (measuring method A4):

MA

= Masseauftrag/Flächengewicht (ohne Linergewicht) in [kg/m²]

d

= Schichtdicke (ohne Linerdicke) in [m]

The volume weight or the density ρ of a coated self-adhesive is determined by the ratio of the weight per unit area to the respective layer thickness: $$\rho =\frac{m}{V}=\frac{\mathrm{M.}\mathrm{A.}}{d}\left[\rho \right]=\frac{\left[kG\right]}{\left[m^2\right]\cdot \left[m\right]}=\left[\frac{kG}{m^3}\right]$$

MA

= Application of mass / weight per unit area (without liner weight) in [kg / m ² ]

d

= Layer thickness (without liner thickness) in [m]

The bulk density is retained in this process.

This density determination is particularly suitable for determining the total density of finished products, including multi-layer products.

Static shear test (measurement method A5):

The shear strength was determined in a test climate of 23 ° C +/- 1 ° C temperature and 50% +/- 5% rel. Humidity.

The test samples were cut to a width of 13 ± 0.2 mm and stored in the air for at least 16 h. For the test, 50 × 25 mm ASTM steel plates with a thickness of 2 mm and a 20 mm marking line were used, which were intensively cleaned several times with acetone before bonding and then allowed to dry for 1-10 minutes. The bond area was 13 × 20 ± 0.2 mm. The test strip was applied in the longitudinal direction in the center of the primer, avoiding air inclusions, by wiping over it with the finger or a suitable wiper, so that the upper edge of the test sample was exactly on the 20 mm marking line.

Another ASTM plate was applied to the remaining side of the sample so that the edges of both plates were flush with the tape (pressing time 60 s, 100 N / cm ² ). The ASTM plates had a hole; A 1 kg weight was hung into one of the plates without jolts.

The pull-up time between pressing and loading was 3 days. The time in minutes until the bond failed, the measurement results are averaged from three measurements.

Adhesive strength (measurement method A6):

The bond strength was determined in a test climate of 23 ° C. +/- 1 ° C. temperature and 50% +/- 5% rel. Humidity. The samples were cut to a width of 20 mm and glued to a substrate plate (material is indicated in the examples). Before the measurement, the substrate plate was cleaned and conditioned using customary methods.

The side of the adhesive tape facing away from the test substrate was then covered with a 75 μm aluminum foil, which prevented the sample from stretching during the measurement. The test sample was then rolled onto the substrate plate. For this purpose, the tape was rolled back and forth five times with a 2 kg roller at a winding speed of 10 m / min. Immediately or after waiting for a peeling time after rolling, the glued substrate plate was pushed into a special holder, which enables the pattern to be peeled off upwards at an angle of 90 °. The bond strength was measured using a Zwick tensile testing machine. The measurement results are given in N / cm and are averaged from three measurements.

Manufacture of adhesive tapes

Table 1: Commercially available chemicals used Chemical compound Trade name Manufacturer CAS no. SBS (76% by weight diblock, block polystyrene content: 31% by weight) Kraton® D 1118 Kraton Polymers 9003-55-8 SBS (16% by weight diblock, block polystyrene content: 31% by weight) Kraton® D 1101 Kraton Polymers 9003-55-8 α-pinene resin (softening temperature: 115 ° C) Dercolyte A 115 DRT 25766-18-1 2,2'-azobis (isobutyronitrile) (AIBN) Vazo® 64 DuPont 78-67-1 Bis (4-tert-butylcyclohexyl) peroxydicarbonate Perkadox® 16 Akzo Nobel 15520-11-3 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate Uvacure ^® 1500 Cytec Industries Inc. 2386-87-0 3-glycidyloxypropyltriethoxysilane Dynasylan® GLYEO Evonik 2602-34-8 3-aminopropyltrimethoxysilane Dynasylan® AMEO Evonik Pentaerythritol tetraglycidether Polypox® R16 UPPC AG 3126-63-4 Triethylenetetramine Epicurus 925 Hexion Specialty Chemicals 112-24-3 Aqueous black pigment Levanyl® Black N-LF 02 Lanxess Microballoons (MB) (dry, unexpanded microspheres, diameter 9 to 15 µm, expansion start temperature 106 to 111 ° C, TMA density ≤ 25 kg / m ³ ) Expancel® 051 DU 40 Nouryon Microballoons (MB) (dry, unexpanded microspheres, diameter 18 - 24 µm, expansion start temperature 123 - 133 ° C, TMA density ≤ 14 kg / m ³ ) Expancel® 920 DU 80 Nouryon Microballoons (MB) (dry, unexpanded microspheres, diameter 10 - 16 µm, expansion start temperature 123 - 133 ° C, TMA density ≤ 17 kg / m ³ ) Expancel® 920 DU 40 Nouryon Microballoons (MB) (dry, unexpanded microspheres, diameter 28-38 µm, expansion start temperature 122 - 132 ° C, TMA density ≤ 14 kg / m ³ ) Expancel® 920 DU 120 Nouryon

B1) Production of the Polymers

Production of base polymer P1 for foamed carrier layer:

A 100 l glass reactor conventional for free radical polymerizations was charged with 1.5 kg of acrylic acid, 25.5 kg of butyl acrylate, 13.0 kg of 2-ethylhexyl acrylate and 26.7 kg of acetone / isopropanol (94: 6). After 45 The reactor was heated to 58 ° C. and 30 g of AIBN were added while nitrogen gas was passed through it for a minute. The external heating bath was then heated to 75 ° C. and the reaction was carried out constantly at this external temperature. After a reaction time of 1 hour, another 30 g of AIBN were added. After 4 and 8 hours, the mixture was diluted with 10.0 kg of acetone / isopropanol (94: 6) mixture each time. To reduce the residual initiators, 90 g of bis (4-tert-butylcyclohexyl) peroxydicarbonate were added after 8 and after 10 h. The reaction was terminated after a reaction time of 24 hours and the mixture was cooled to room temperature. The polyacrylate has a K value of 77.8, a solids content of 55.9%, an average molecular weight of M _w = 1,040,000 g / mol, polydispersity D (M _w / M _n ) = 13.3 and a static Glass transition temperature of Tg = - 45.1 ° C.

Production of base polymer P2 for foamed carrier layer:

A reactor conventional for radical polymerizations was charged with 72.0 kg of 2-ethylhexyl acrylate, 20.0 kg of methyl acrylate, 8.0 kg of acrylic acid and 66.6 kg of acetone / isopropanol (94: 6). After nitrogen gas had been passed through for 45 minutes with stirring, the reactor was heated to 58 ° C. and 50 g of AIBN, dissolved in 500 g of acetone, were added. The external heating bath was then heated to 75 ° C. and the reaction was carried out constantly at this external temperature. After 1 hour, another 50 g of AIBN, dissolved in 500 g of acetone, were added and after 4 hours the mixture was diluted with 10 kg of acetone / isopropanol mixture (94: 6).

After 5 h and after 7 h, 150 g of bis (4-tert-butylcyclohexyl) peroxydicarbonate, each dissolved in 500 g of acetone, were reinitiated. After a reaction time of 22 h, the polymerization was terminated and the mixture was cooled to room temperature. The product had a solids content of 55.8%. The resulting polyacrylate had a K value of 58.9, an average molecular weight of M _w = 748,000 g / mol, a polydispersity of D (M _w / M _n ) = 8.9 and a static glass transition temperature of Tg = -35, 2 ° C.

B2) Production of foamed carrier layers

Method 1: Concentration / production of the hotmelt pressure-sensitive adhesives:

The base polymer P was largely freed from the solvent by means of a single-screw extruder (concentration extruder, Berstorff GmbH, Germany) (residual solvent content 0.3% by weight). The parameters for the concentration of the base polymer were as follows: The speed of the screw was 150 rpm, the motor current was 15 A and a throughput of 58.0 kg / h in liquid form was achieved. A vacuum was applied to three different domes for concentration. The negative pressures were in each case between 20 mbar and 300 mbar. The outlet temperature of the concentrated hotmelt P was approx. 115 ° C. The solids content after this concentration step was 99.8%.

Process 2: Production of the adhesive tapes of the invention, blending with the crosslinker-accelerator system for thermal crosslinking and coating

The foaming took place in a test facility, which is the representation in 1 is equivalent to.

The concentrated base polymer P was made according to Procedure 1 in a feed extruder 1 melted and with this as a polymer melt via a heatable hose 11 in a planetary roller extruder 2 (PWE) of the company ENTEX (Bochum) (in particular a PWE with four independently heatable modules T1, T2, T3, T4 was used). Via the dosing opening 22nd there was the possibility of adding additional additives or fillers, such as color pastes and / or microballoons. At point 23 the crosslinker was added. All components were mixed to form a homogeneous polymer melt.

Using a melt pump 24a the polymer melt was in a twin screw extruder 30th (BERSTORFF company) transferred (input position 33 ). At position 34 the accelerator component was added. The entire mixture was then freed from all gas inclusions in a vacuum dome V at a pressure of 175 mbar (see above for the criterion for freedom from gas). Following the vacuum zone, there was a blister B on the screw, which enabled pressure to be built up in the segment S that followed. By suitable control of the extruder speed and the melt pump 37a was in segment S between blister B and melt pump 37a a pressure of more than 8 bar built up at the metering point 35 the microballoons (possibly embedded in a dispersing aid according to the information in Table 3) are added and incorporated homogeneously into the premix by means of a mixing element. The resulting melt mixture was fed into a nozzle 5 convicted.

After leaving the nozzle 5 , that is to say after the pressure drop, the incorporated microballoons expanded, with low-shear, in particular shear-free, cooling of the polymer mass taking place as a result of the pressure drop. A foamed pressure-sensitive adhesive was produced, which is then coated either between two release materials, which can be reused after removal (process liner), and by means of a roller calender 4th was formed in the form of a web (offline) or directly by means of a roller calender 4th was formed in the form of a web (inline) between the pressure-sensitive adhesive layers to be applied thereon.

B3) Production of the pressure-sensitive adhesive layers

The pressure-sensitive adhesive layers 1 , 2 and 4th were prepared by mixing the components indicated in Table 2 in solution, then applying them to a 79 μm thick, siliconized PET film and then drying. The application of mass was 50 g / m ^{2 in} each case. Table 2: Composition of PSA layers 1, 2 and 4 (% by weight) Hkm no. → 1 2 4th Components ↓ Kraton D1101 25th 23 Kraton D 1118 25th 23 17th Dercolyte A 115 48 47 Wingtack 10 2 2 P2 5 Vector 4113 33 Escorez 2203 48 Shellflex 371 2

Pressure sensitive adhesive 3 was produced as a pure acrylic mass as follows:

A 200 l glass reactor conventional for free radical polymerizations was charged with 9.6 kg of acrylic acid, 20.0 kg of butyl acrylate, 50.4 kg of 2-ethylhexyl acrylate and 53.4 kg of acetone / petrol 60/95 (1: 1). After nitrogen gas had been passed through for 45 minutes with stirring, the reactor was heated to 58 ° C. and 60 g of AIBN were added. The external heating bath was then heated to 75 ° C. and the reaction was carried out constantly at this external temperature. After a reaction time of 1 h, another 60 g of AIBN were added. After 4 hours and 8 hours, the mixture was diluted with 20.0 kg of acetone / petrol 60/95 (1: 1) mixture each time. To reduce the residual initiators, 180 g of bis (4-tert-butylcyclohexyl) peroxydicarbonate were added after 8 hours and after 10 hours. The reaction was terminated after a reaction time of 24 hours and the mixture was cooled to room temperature. The polyacrylate was then mixed with 0.2% by weight Uvacure® 1500, diluted to a solids content of 30% with acetone and then coated from solution onto a siliconized release film (50 μm polyester) (coating speed 2.5 m / min, drying tunnel 15 m, temperatures: Zone 1: 40 ° C, Zone 2: 70 ° C, Zone 3: 95 ° C, Zone 4: 105 ° C). The application of mass was 50 g / m ² .

B4) Manufacture of the adhesive tapes

The corona treatments of the layers provided according to the invention and possibly further corona treatments were carried out as indicated in Table 4 with a corona system from VITAPHONE, Denmark, at 70 W · min / m ² . The PSA layers were each treated on the side which was then brought into contact with the foamed backing layer.

“Offline” means that the layers were initially produced completely, subsequently treated with corona if necessary and then laminated on top of one another, with these steps being carried out on separate devices / stations.

• 0 - keine Vorbehandlung
• A - beidseitig Corona (Haftklebmasseschichten, Trägerschicht beidseitig, Prozessgas Luft)
• B - einseitig Corona (nur Haftklebmasseschichten; Prozessgas N₂)
• C - einseitig Corona (nur Haftklebmasseschichten; Prozessgas Luft)

“Inline” means that the pressure-sensitive adhesive layers are produced separately from the foamed backing layer, but the multilayer product is built up directly together with the shaping of the foamed backing layer in such a way that the backing layer is shaped into the web between the pressure-sensitive adhesive layers to be applied to it. The PSA layers are - provided that the Corona treatment is provided - corona treated immediately before application to the foamed carrier layer.

• 0 - no pretreatment
• A - Corona on both sides (pressure-sensitive adhesive layers, carrier layer on both sides, process gas air)
• B - Corona on one side (only pressure-sensitive adhesive layers; process gas N ₂ )
• C - Corona on one side (only pressure-sensitive adhesive layers; process gas air)

The web speed when passing through the coating system was 30 m / min.

After leaving the nip, an anti-adhesive carrier was covered, if necessary, and the finished three-layer product was wound up with the remaining second anti-adhesive carrier. Table 3: Structure of the adhesive tapes 1-8 No. Base polymer foamed layer Microballoons (type + proportion in% by weight) Networking system of the foamed layer Pressure-sensitive adhesive layers on both sides No. 1 P1 Expancel® 920 DU 80; 3.4 wt% Polypox® R16 + Epikure 925 (0.15 + 0.25% by weight) 1 2 P1 Expancel® 920 DU 80; 3.4 wt% Polypox® R16 + Epikure 925 (0.15 + 0.25% by weight) 2 3 P1 Expancel® 920 DU 80; 3.4 wt% Dynasylan® GLYEO + Dynasylan AMEO (0.2 + 0.2% by weight) 1 4th P1 Expancel® 920 DU 80; 3.4 wt% Uvacure ^® 1500 (0.2% by weight) 1 5 P2 Expancel® 051 DU 40, 2% by weight, dosed as a paste (40% by weight in Levanyl) Uvacure ^® 1500 (0.2% by weight) 2 6th P1 Expancel® 051 DU 40, 2% by weight, dosed as a paste (40% by weight in Levanyl) Polypox® R16 + Epikure 925 (0.15 + 0.25% by weight) 1 7th P1 Expancel® 920 DU 80; 3.4 wt% Polypox® R16 + Epikure 925 (0.15 + 0.25% by weight) 3 8th P1 Expancel® 920 DU 80; 3.4 wt% Polypox® R16 + Epikure 925 (0.15 + 0.25% by weight) 4th

The proportions by weight of the microballoons are based on the total weight of the foamed layer; the weight fractions of the crosslinking system are based on the weight of the polymer to be crosslinked.

There were more adhesive tapes 9-22 with a foamed carrier based on the base polymer P1 (crosslinking system Polypox® R16 + Epikure 925; 0.15 + 0.25% by weight) with different types and proportions of microballoons (Table 5), and coated on both sides with the pressure-sensitive adhesive 1 manufactured according to the "Inline C" process.

These were examined with regard to their bond strength and the fracture pattern produced; the results are contained in Tables 5 and 6.

For the measurement of “adhesive strength with foam split”, the steel ^{substrate was pretreated with the primer tesa ®} 60153 Adhesion Promoter Fast Cure before the adhesive tape to be tested was bonded in order to force a cohesive failure of the bond and thus a foam split. The bond strength achieved up to the point where the foam split was consequently measured. In principle, the aim is to tear the foam core in a defined bond strength range, for example 35-45 N / cm.

Results

Table 4: Results after different procedures (static shear test, values in min) Tape no. Offline A (ne) Offline B (ne) Offline C (ne) Inline B Inline C Offline 0 (ne) Inline 0 (ne) 1 10,000 10,000 456 10,000 10,000 31 55 2 10,000 10,000 552 10,000 10,000 12th 17th 3 32 37 28 10,000 10,000 18th 15th 4th 28 44 37 10,000 10,000 12th 15th 5 24 51 18th 10,000 10,000 23 17th 6th 10,000 10,000 772 10,000 10,000 12th 32 7th 10,000 10,000 488 10,000 10,000 52 47 8th 10,000 10,000 605 10,000 10,000 69 47 1 (2 kg weight) 10,000 4362 ne = not according to the invention Table 5: Microballoons of adhesive tapes 9-22 and results Microballoons No. Microballoons - Type mean size after expansion (µm) Weight fraction (%) Volume fraction (%) Density foamed carrier (kg / m ³ ) Adhesive strength with foam split, (ASTM; N / cm) 9 920DU120 120 1 26th 787 34 10 920DU120 120 1.5 37 673 32 11 920DU120 120 2 40 636 31 12th 920DU120 120 3 53 513 30th 13th 920DU80 80 1.9 35 690 41 14th 920DU80 80 2.0 37 671 44 15th 920DU80 80 3.0 46 582 40 16 920DU80 80 3.0 46 582 40 17th 920DU80 80 3.4 46 589 40 18th 920DU80 80 3.4 46 587 37 19th 920DU40 40 2 30th 748 49 20th 920DU40 40 2 35 700 46 21 920DU40 40 3 40 652 51 22nd 920DU40 40 3 40 652 52 Table 6: Further results No. Breakage pattern / adhesive strength TMAC 8000 (20 min, N / cm) Adhesive strength PP / EPDM (20 min, N / cm) 2 (inline C) 33, fs 43, fs 6 (inline A) 23, ad 54, fs 7 (inline 0), no 2, ad 3, ad 9 fs 10 fs 11 fs 12th fs 13th fs 14th fs 15th fs 16 fs 17th fs 42, fs 18th fs 19th ad / mixed 20th ad / mixed 21 ad / mixed 22nd ad / mixed The times given are the pull-up times after the adhesive tape has been rolled onto the test surface.
fs = foam split
ad = adhesive break

TMAC 8000 is a paint (clearcoat) from the manufacturer PPG used in the automotive industry. For the measurement, the paint was applied to an aluminum plate provided with a primer (30 μm) and a base coating (15 μm) in a thickness of 40 μm (after drying in the oven).

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• WO 2008/068150 A1 [0003]
• WO 2013/178462 A1 [0004]
• DE 102009048036 A1 [0007]
• WO 2008/073669 A1 [0008]
• WO 2008/070386 A1 [0009]
• EP 2767567 A2 [0010]
• WO 2010/101738 A1 [0010]
• EP 2690147 A2 [0011]

Non-patent literature cited

• Table 8-16 in D. Satas, Handbook of Pressure Sensitive Adhesive Technology, 2nd Edition, page 173, 1989 [0024]
• "Chemical technology, processes and products" by R. Dittmeyer et al., Volume 5, 5th edition, Wiley-VCH, Weinheim, Germany, 2005, Chapter 6-5.3.2, page 1142 [0049]
• Wagner et al., Vacuum, 71 (2003), 417-436 [0053]

Claims (12)

Process for the production of a multilayer adhesive tape, comprising the following process steps: the shaping of a pressure-sensitive adhesive layer on a separating, web-like material; a treatment of the free side of this pressure-sensitive adhesive layer with a plasma or by means of corona; and the molding of a syntactically foamed, pressure-sensitive adhesive backing layer onto the treated side of this pressure-sensitive adhesive layer, these process steps being carried out on a moving web of this pressure-sensitive adhesive layer. Procedure according to Claim 1 , characterized in that the pressure-sensitive adhesive layer contains at least one synthetic rubber. Method according to one of the Claims 1 and 2 , characterized in that the pressure-sensitive adhesive layer contains at least one styrene block copolymer. Method according to one of the preceding claims, characterized in that the treatment of the free side of the pressure-sensitive adhesive layer takes place with a plasma or by means of corona in a process gas atmosphere different from air. Method according to one of the preceding claims, characterized in that the pressure-sensitive adhesive layer and the carrier layer are not treated with a primer or with a flame. Method according to one of the preceding claims, characterized in that the carrier layer contains a poly (meth) acrylate. Method according to one of the preceding claims, characterized in that the poly (meth) acrylate (s) of the carrier layer are crosslinked at least by means of a divalent crosslinker. Method according to one of the preceding claims, characterized in that the syntactically foamed, pressure-sensitive adhesive carrier layer is shaped onto the treated side of the pressure-sensitive adhesive layer by means of a calender with two or more rollers. Multilayer adhesive tape obtainable by a process according to one of the preceding claims. Multi-layer tape according to Claim 9 , characterized in that - the foamed carrier layer comprises a multiplicity of hollow microspheres and this multiplicity of hollow microspheres has an average diameter of at least 50 µm. Use of a multilayer adhesive tape according to one of the Claims 9 and 10 for the production of bonds on low-energy substrates. Use according to Claim 11 The substrates are selected from the group consisting of paints, substrates pretreated with a primer, ethylene-propylene-diene terpolymers (EPDM), polyolefins and polypropylene / EPDM substrates.

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