DE102020215673A1 - Adhesive tape with a foamed pressure-sensitive adhesive layer and structuring on the surface - Google Patents

Abstract

The invention relates to an adhesive tape comprising at least one adhesive layer, at least one of the adhesive layers being foamed and at least one outwardly facing surface of an adhesive of the adhesive tape being structured in order to achieve easy redetachability with solvents.

Description

The invention relates to adhesive tapes which have at least one foamed adhesive layer and are structured on the surface, and the use of double-sided adhesive variants of the adhesive tapes in a composite with two substrates.

Nowadays, many small components, especially in the consumer electronics sector, are bonded with adhesive tapes. It is advantageous if these adhesive tapes can be removed again easily and with as little residue as possible. The reason for this requirement is, on the one hand, the desire to replace defective components as easily as possible. This replacement can be necessary immediately after or during production if there were problems during production, but also after prolonged use if the consumer discovers an error. In addition, there are more and more efforts and legal regulations that request or require the recycling of different components.

The term “mobile devices” includes, for example, devices from the consumer electronics industry, which include electronic, optical and precision mechanical devices, in particular mobile phones, smart phones and tablets for the purposes of this application.

Different ways of releasing pressure-sensitive adhesive tapes are described in the literature. A simple option is to heat the adhesive tape and thereby reduce the bond strength. The disadvantage here is that the electronic components often cannot withstand the high temperatures required and are also damaged. In addition, the adhesive is softened during this process, which means that it loses cohesion. When the bond breaks, part of the adhesive then remains on both surfaces, resulting in a cohesive break. The result is an often time-consuming cleaning process that is necessary in order to be able to use at least one of the two bonding partners again.

Different methods have been described for this process to bring the heat into the bond plane, e.g. by heating the entire device in an oven, or using a laser to bring the heat into the bonded joint.

Another way of removing an adhesive tape is to use so-called stretch-release adhesive tapes. These reduce their bond strength when stretched into the bond plane. The disadvantage of this method is that you need a handle to pull the adhesive tape out of the bonded joint. This handle sometimes obstructs other components and disrupts the look. In addition, there are problems if the adhesive tape should tear during the detachment process, since detachment is then no longer possible.

When gluing at least one transparent joining partner, an adhesive tape can also be used that cures by means of UV light and thus loses its adhesive strength, as is used with adhesive tapes for the production of silicone wafers. The disadvantage is that this only works with transparent joining partners.

The task was to develop a pressure-sensitive adhesive product that has a high adhesive performance and can nevertheless be removed again with as little residue as possible.

Here an attempt was made to release the adhesive bond again using a solvent by applying the solvent around the adhesive surface and then slowly moving it between the adhesive tape and the substrate in order to significantly reduce the holding power. With most adhesive tapes, this process is very slow, especially with larger areas to be bonded, and is hardly suitable for an industrial process. To accelerate this process, adhesive tapes with a rough surface were used, which means that the solvent can migrate into the bond area much more quickly through the channels created.

The structuring of the adhesive can be implemented using different methods. The focus here is on the use of a structured liner onto which the adhesive is coated.

A liner (release paper, release film) is not part of an adhesive tape, but only an aid for its production, storage or for further processing by punching. In addition, unlike an adhesive tape backing, a liner is not firmly connected to an adhesive layer.

Since the electronic devices should always be carried, they are getting smaller and lighter. Carrying these mobile devices with them means they are exposed to increased - in particular mechanical - loads, for example from bumping into edges, from dropping them, from contact with other hard objects in the pocket, but also from the permanent movement of being carried around. However, mobile devices are also more exposed to the effects of moisture, temperature and the like than such "immobile" devices, which are usually installed indoors and are hardly or not at all moved.

For these mobile devices, adhesive tapes in particular are required that have a high holding capacity. In some cases there is also a desire for later removability. In many applications, high strength is also required at elevated temperatures.

Furthermore, it is particularly important that the adhesive tapes do not fail in their holding capacity if the mobile device, for example a cell phone, is dropped and hits the ground. The adhesive strip or the adhesive bond must therefore have a very high shock resistance.

Foamed adhesives have been shown to be suitable for increasing the shock resistance. Here, the entire adhesive can be foamed, or if there are several layers, only one of the layers.

In principle, polymer foams can be produced in two ways. On the one hand through the action of a propellant gas, be it added as such or resulting from a chemical reaction, on the other hand through the incorporation of hollow spheres into the material matrix. Foams made in the latter way are known as syntactic foams.

In a syntactic foam, hollow spheres such as glass spheres or ceramic hollow spheres (microspheres) or microballoons are incorporated in a polymer matrix. As a result, in a syntactic foam, the cavities are separated from one another and the substances (gas, air) in the cavities are separated from the surrounding matrix by a membrane.

Masses foamed with hollow microspheres are characterized by a defined cell structure with a uniform size distribution of the foam cells. With hollow microspheres, closed-cell foams without cavities are obtained, which, compared to open-cell variants, are characterized, among other things, by a better sealing effect against dust and liquid media. In addition, chemically or physically foamed materials are more prone to irreversible collapse under pressure and temperature and often show a lower cohesive strength.

Particularly advantageous properties can be achieved if expandable microspheres (also referred to as “microballoons”) are used as microspheres for foaming. Due to their flexible, thermoplastic polymer shell, such foams are more adaptable than those filled with non-expandable, non-polymeric hollow microspheres (for example hollow glass spheres). They are better suited to compensate for manufacturing tolerances, as they are the rule for injection molded parts, for example, and, due to their foam character, can also better compensate for thermal stresses.

In addition, the selection of the thermoplastic resin for the polymer shell can further influence the mechanical properties of the foam. For example, even if the foam has a lower density than the matrix, it is possible to produce foams with higher cohesive strength than with the polymer matrix alone. Typical foam properties such as adaptability to rough surfaces can be combined with high cohesive strength for self-adhesive foams.

When using expandable microballoons, there is often the problem that the microballoons protrude from the adhesive after foaming and thereby significantly reduce the bond strength of the adhesive tape.

The WO 2009/090119 A1 describes a pressure-sensitive adhesive which contains expanded microballoons, the adhesive strength of the adhesive containing the expanded microballoons being reduced by a maximum of 30% compared to the adhesive strength of an adhesive which is identical in areal weight and formulation and which is defoamed by destroying the cavities created by the expanded microballoons is. Here, an at least partially foamed PSA is applied between two liners by means of at least two rollers shaped. The high pressure in the nip pushes the microballoons breaking through the surface back into the polymer matrix in order to create a smooth surface without disturbing broken microballoons.

Many of the structured liners available on the market are made up of at least one polyethylene terephthalate layer and at least one polyethylene layer, the polyethylene layer having the structure and also being the side that is siliconized. PET films with two PE layers are also often used. The problem with such liners is that the PE begins to melt at relatively low temperatures. These melting temperatures are below the temperatures required for foaming. In these cases, foaming leads to changes in the liner, and this increases the risk that silicone or polyethylene will migrate into the adhesive and change it, which can result in poor adhesive strength or impaired removability of the liner.

Another way to solve this problem is to use a multilayer structure. The layer of adhesive that is directly adjacent to the structured liner does not contain any microballoons and is not foamed. A second layer that does not come into contact with the structured liner can then be foamed by adding microballoons. The shock effect is better, the thicker the foamed layer is compared to the non-foamed layer. With this structure, both the same (with the exception of the microballoons) and different adhesive compositions can be used in terms of composition. When using the same adhesive, once without and once with microballoons, there are no problems with diffusion of individual components from one layer into the other. Such a diffusion of individual constituents, in particular resins or plasticizers, can change the properties of both layers, which is usually not desirable.

It has also been shown that it is advantageous to select an adhesive, in particular in the layer which directly adjoins the structured liner, in such a way that it exhibits the lowest possible flow behavior so that the structure is retained for as long as possible. If the structure disappears quickly through the use of very soft adhesives, it is no longer possible to remove it. It is therefore preferred to use adhesives with a high degree of cohesion. Suitable adhesives can be, for example, adhesives based on vinyl aromatic block copolymers, such as styrene block copolymers, crosslinked adhesives based on nitrile rubbers, natural rubbers, polyurethanes or highly crosslinked acrylates. Preference is given to using styrene block copolymers or nitrile rubber as the basis for the adhesives. An adhesive based on a certain polymer (or a certain polymer mixture) typically means that the elastomer part of the adhesive consists of at least 50% by weight of this polymer or this polymer mixture, and preferably at least 90% by weight. In a further preferred embodiment, in addition to the base polymer, the adhesive does not contain any further elastomers in amounts which significantly influence the essential properties of the base polymer.

Another possibility of obtaining a structured adhesive is the use of embossed liners. These could be PET-based liners that are embossed after siliconization. The siliconization is retained during embossing because the silicon is flexible. Such liners have the advantage that the adhesive can also be foamed on the structured liner; a multilayer structure is not necessary, although not excluded. It has been shown that embossing the adhesive at temperatures higher than the foaming temperature is advantageous, since the PET shows a so-called memory effect and, when heated, would like to return to its original shape during foaming and the structuring is thereby reduced or even disappears.

In addition to temperature-resistant liners based on embossed PET, paper liners can also be used, mostly CCK (clay coated Kraft paper), which contains mineral components that provide structuring.

There are also liners based on PET in which the structuring is not applied via a PE layer, but rather via more temperature-stable polypropylene or via a UV-crosslinkable acrylate.

The adhesives used in the adhesive tapes of the invention are typically pressure-sensitive adhesives. A pressure-sensitive adhesive is an adhesive which allows a permanent bond with almost all substrates even under relatively light pressure and, if necessary, can be removed again from the substrate after use, essentially without leaving any residue. A pressure-sensitive adhesive has a permanent pressure-sensitive adhesive effect at room temperature, that is to say has a sufficiently low viscosity and high tack, so that it wets the surface of the respective adhesive base even when there is little pressure. The bondability of the adhesive is based on its adhesive properties and the redetachability their cohesive properties. According to the invention, the terms “pressure-sensitive adhesive” and “self-adhesive” (or terms derived therefrom) are used synonymously.

Adhesives based on vinyl aromatic block copolymers

Synthetic rubber-based PSAs which contain vinyl aromatic block copolymers are well known and are used in a wide variety of applications. Advantages of this type of PSA are the high bond strength on substrates of different surface energy and, above all, on substrates with low surface energy. At the same time, they impress with their very high holding power under normal ambient conditions.

PSAs based on vinyl aromatic block copolymers which have advantageous shock resistance are also described. DE 10 2016 202 018 A1 teaches that improved shock resistance can be achieved through the selection of suitable block copolymers. Furthermore, it is possible to improve shock resistance if the pressure-sensitive adhesive is in the form of a foam and, for this purpose, contains, for example, expanded microballoons.

In order to give polydienes a pressure-sensitive adhesive character, adhesive resins have to be added to them. This also applies to vinyl aromatic block copolymers which contain polydiene blocks.

EP 3 075 775 A1 describes foamed block copolymer blends with adhesive resin (combinations). In addition to hydrocarbon and polyterpene resins, oxygen-containing adhesive resins can be used, but these are not specified further.

DE 10 2008 056 980 A1 and DE 10 2008 004 388 A1 teach formulations made tacky with tackifier resins and disclose a formulation containing, inter alia, a polystyrene-polyisoprene block copolymer and, for example, a rosin ester. The adhesives contain microballoons in a relatively high proportion, which accordingly leads to very low densities.

Elastomer component (a)

• - 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;
• - X für den Rest eines Kopplungsreagenzes oder multifunktionellen Initiators und
• - n für eine ganze Zahl ≥ 2 stehen.

The elastomer component typically contains at least one synthetic rubber in the form of a block copolymer with a structure ABA, (AB) _n , (AB) _n X or (ABA) _n X, in which

• - 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 the polymerization of conjugated dienes having 4 to 18 carbon atoms;
• - X for the remainder of a coupling reagent or multifunctional initiator and
• - n stand for an integer ≥ 2.

In one embodiment, all synthetic rubbers of the pressure-sensitive adhesive (layer) of the invention can be block copolymers with a structure as set out above. The pressure-sensitive adhesive (layer) of the invention can thus also contain mixtures of different block copolymers with a structure as above.

The at least one suitable block copolymer thus typically comprises one or more rubber-like blocks B (soft blocks) and at least two glass-like blocks A (hard blocks). The elastomer component can also contain one or more diblock copolymers AB. In particular, the synthetic rubber of the pressure-sensitive adhesive (layer) of the invention 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 PSAs or PSA layers typically found are those based on block copolymers comprising polymer blocks predominantly formed by vinyl aromatics (A blocks), preferably styrene, and those predominantly formed by the polymerization of 1,3-dienes (B blocks) such as butadiene and isoprene or a copolymer from these applications.

The block copolymers of the PSAs or PSA layers preferably have polystyrene end blocks.

Instead of the preferred polystyrene blocks, polymer blocks based on other aromatic-containing homopolymers and copolymers (preferably C ₈ to C ₁₂ aromatics) with glass transition temperatures according to test IV of greater than 75 ° C, such as α-methylstyrene-containing aromatic blocks, can also be used as vinyl aromatics. It can also contain the same or different A blocks.

Preferred conjugated dienes as monomers for the soft block B are in particular selected from the group consisting of butadiene, isoprene, and mixtures of these monomers and their hydrogenated homologues. Block B can also be present as a homopolymer or as a copolymer.

The proportion of hard block (block A) in the block copolymers is at least 12% by weight and a maximum of 40% by weight, preferably at least 15% by weight and a maximum of 35% by weight

In a preferred embodiment, the proportion of vinyl aromatic block copolymers, in particular styrene block copolymers, based on the total pressure-sensitive adhesive (layer), is at least 35% by weight and at most 65% by weight, more preferably at least 45% by weight and at most 55% by weight. %.

Adhesive resin component (b)

In addition to the at least one vinyl aromatic block copolymer, the foamable PSAs or foamed PSA layers have at least one adhesive resin in order to increase the adhesion in the desired manner. The adhesive resin should be compatible with the elastomer block of the block copolymers.

According to the general understanding of the skilled person, an “adhesive resin” is understood to mean an oligomeric or polymeric resin which increases the adhesion (the tack, the inherent tack) of the PSA in comparison to the PSA which does not contain adhesive resin but is otherwise identical.

Adhesive resins are special compounds with a lower molar mass compared to elastomers, usually with a weight-average molecular weight (test V) M _W <5,000 g / mol. The weight average molecular weight is typically from 400 to less than 5,000 g / mol, preferably from 500 to 2,000 g / mol.

Suitable tackifier resins include preferably 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 C-5, C-5 / C-9 or C-9 monomer streams, or polyterpene resins based on α-pinene and / or β-pinene and / or δ-limonene. The abovementioned tackifier resins can be used either alone or as a mixture. In addition, the adhesive formulation can also contain tackifier resins which are liquid at room temperature.

Soft resin component (c)

The optionally usable soft resin or soft resin mixture typically has a softening temperature of <30 ° C (* Ring & Ball, Test VI). The soft resin can be a rosin-based or, very preferably, a hydrocarbon or polyterpene-based soft resin. The soft resin or the soft resin mixture is used in relation to the entire adhesive (layer) in a proportion of 0% by weight to 15% by weight, and preferably of at least 2% by weight and at most 10% by weight. Too high a proportion of soft resin leads to a reduction in cohesion, which has a negative effect on the thermal shear strength.

Optional further components (d)

The foamable PSA or foamed PSA layer, but also any non-foamed adhesive layer, can be added as further additives, especially protective agents. Primary and secondary aging inhibitors, light and UV protection agents and flame retardants may be mentioned here, but also fillers, dyes and pigments. The adhesive (layer) can be colored as desired or white, gray or black.

• • Plastifizierungsmittel wie zum Beispiel niedermolekulare flüssige Polymere, wie zum Beispiel niedermolekulare Polybutene, vorzugsweise mit einem Anteil von 0,2 bis unter 5 Gew.-% bezogen auf das Gesamtgewicht der Haftklebemasse(schicht)
• • primäre Antioxidantien wie zum Beispiel sterisch gehinderte Phenole, vorzugsweise mit einem Anteil von 0,2 bis 1 Gew.-% bezogen auf das Gesamtgewicht der Haftklebemasse(schicht),
• • sekundäre Antioxidantien, wie zum Beispiel Phosphite oder Thioether, vorzugsweise mit einem Anteil von 0,2 bis 1 Gew.-% bezogen auf das Gesamtgewicht der Haftklebemasse(schicht),
• • Prozessstabilisatoren wie zum Beispiel C-Radikalfänger, vorzugsweise mit einem Anteil von 0,2 bis 1 Gew.-% bezogen auf das Gesamtgewicht der Haftklebemasse(schicht),
• • Lichtschutzmittel wie zum Beispiel UV-Absorber oder sterisch gehinderte Amine, vorzugsweise mit einem Anteil von 0,2 bis 1 Gew.-% bezogen auf das Gesamtgewicht der Haftklebemasse(schicht),
• • Verarbeitungshilfsmittel, vorzugsweise mit einem Anteil von 0,2 bis 1 Gew.-% bezogen auf das Gesamtgewicht der Haftklebemasse(schicht),
• • Endblockverstärkerharze, falls gewünscht vorzugsweise mit einem Anteil von 0,2 bis 10 Gew.-% bezogen auf das Gesamtgewicht der Haftklebemasse(schicht) sowie
• • gegebenenfalls weitere Polymere von bevorzugt elastomerer Natur; entsprechend nutzbare Elastomere beinhalten unter anderem solche auf Basis reiner Kohlenwasserstoffe, zum Beispiel ungesättigte Polydiene wie natürliches oder synthetisch erzeugtes Polyisopren oder Polybutadien, chemisch im wesentlichen gesättigte Elastomere wie zum Beispiel gesättigte Ethylen-Propylen-Copolymere, α-Olefincopolymere, Polyisobutylen, Butylkautschuk, Ethylen-Propylenkautschuk, sowie chemisch funktionalisierte Kohlenwasserstoffe wie zum Beispiel halogenhaltige, acrylathaltige, allyl- oder vinyletherhaltige Polyolefine, vorzugsweise mit einem Anteil von 0,2 bis 10 Gew.-% bezogen auf das Gesamtgewicht der Haftklebemasse(schicht).

As such or other additional additives can typically be used:

• • Plasticizers such as, for example, low molecular weight liquid polymers, such as, for example, low molecular weight polybutenes, preferably with a proportion of 0.2 to less than 5% by weight based on the total weight of the pressure-sensitive adhesive (layer)
• Primary antioxidants such as sterically hindered phenols, preferably in a proportion of 0.2 to 1% by weight based on the total weight of the pressure-sensitive adhesive (layer),
• Secondary antioxidants, such as phosphites or thioethers, preferably in a proportion of 0.2 to 1% by weight based on the total weight of the pressure-sensitive adhesive (layer),
• • Process stabilizers such as C radical scavengers, preferably with a proportion of 0.2 to 1% by weight based on the total weight of the pressure-sensitive adhesive (layer),
• • light stabilizers such as UV absorbers or sterically hindered amines, preferably in a proportion of 0.2 to 1% by weight based on the total weight of the pressure-sensitive adhesive (layer),
• • Processing aids, preferably in a proportion of 0.2 to 1% by weight based on the total weight of the pressure-sensitive adhesive (layer),
• • End block reinforcement resins, if desired, preferably in a proportion of 0.2 to 10% by weight based on the total weight of the pressure-sensitive adhesive (layer) and
• • if appropriate, further polymers, preferably of an elastomeric nature; appropriately usable elastomers include those based on pure hydrocarbons, for example unsaturated polydienes such as 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, allyl or vinyl ether-containing polyolefins, preferably in a proportion of 0.2 to 10% by weight based on the total weight of the pressure-sensitive adhesive (layer).

The type and amount of the mixing components can be selected as required. and the latter are also higher than the preferred upper limits. It is also according to the invention if the adhesive layer does not have some or even all of the additives mentioned in each case.

Nitrile rubber adhesives

In addition to vinyl aromatic block copolymers, other elastomers can also serve as the basis for the pressure-sensitive adhesive. Another well-suited group of elastomers are nitrile rubbers.

Adhesives based on nitrile rubbers contain as base polymer at least one or more solid acrylonitrile-butadiene rubbers and adhesive resins, the proportion of adhesive resins being 20-55% by weight, and the acrylonitrile content in the solid acrylonitrile-butadiene or Rubber (s) is between 10 and 30% by weight.

The acrylonitrile content in the solid acrylonitrile-butadiene rubber (s) is preferably between 10 and 25% by weight.

Inert separating aids such as talc, silicates (talc, clay, mica), zinc stearate and PVC powder can be added to the acrylonitrile-butadiene rubbers, in particular in the order of 3% by weight. The separating aids are preferably selected from the group consisting of talc, silicates (talc, clay, mica), zinc stearate and PVC powder.

With further preference thermoplastic elastomers such as synthetic rubbers can be added to the acrylonitrile-butadiene rubber in a proportion of up to 5% by weight in order to improve the processability. The particularly compatible styrene-isoprene-styrene (SIS) and styrene-butadiene-styrene (SBS) types should be mentioned here as representatives.

In addition to one or more solid acrylonitrile-butadiene rubber (s), pressure-sensitive adhesives according to the invention can contain at least one liquid acrylonitrile-butadiene rubber, the acrylonitrile content in the liquid acrylonitrile-butadiene rubber (s) likewise being between 10 and 30% by weight .-% lies.

The proportion of liquid acrylonitrile-butadiene rubbers is preferably up to 20% by weight.

Liquid rubbers are distinguished from solid rubbers in that they have a softening point of <40 ° C.

The information on the softening point TE of oligomeric and polymeric compounds, such as resins, relate to the ring-ball method in accordance with DIN EN 1427: 2007 with appropriate application of the provisions (examination of the oligomer or polymer sample instead of bitumen with otherwise retained Procedure); the measurements are carried out in a glycerol bath.

In addition to the acrylonitrile-butadiene rubbers, there is preferably no further polymer present in the pressure-sensitive adhesive. In this case, the pressure-sensitive adhesive is a composition of solid and liquid acrylonitrile-butadiene rubbers, one or more adhesive resin (s), preferably anti-aging agent (s) and, if appropriate, release aids, which is a preferred embodiment. In addition, the plasticizers, fillers and / or dyes explained later can optionally be contained in small amounts.

Alternatively, the base polymer contains more than 90% by weight, preferably more than 95% by weight, of solid and liquid acrylonitrile-butadiene rubber.

The adhesive resins used in the self-adhesive, for example, as the main component are, in particular, hydrogenated and non-hydrogenated hydrocarbon resins and polyterpene resins. Hydrogenated polymers of dicyclopentadiene, hydrogenated polymers of preferably C8 and C9 aromatics, among others, are particularly suitable. These can flow through the hydrogenation of polymers from pure aromatic streams or else they can be based on mixtures of different aromatics through the hydrogenation of polymers. Partially hydrogenated polymers of C8 and C9 aromatics, hydrogenated polyterpene resins, hydrogenated C5 / C9 polymers, aromatic-modified, selectively hydrogenated dicyclopentadiene derivatives are also suitable. The aforementioned adhesive resins can be used either alone or in a mixture.

Hydrogenated hydrocarbon resins are used as a blending component, for example in EP 0 447 855 A1 , U.S. 4,133,731 A and U.S. 4,820,746 A described, particularly suitable because the absence of double bonds means that the crosslinking cannot be disturbed. In addition, however, non-hydrogenated resins can also be used if crosslinking promoters such as, for example, multifunctional acrylates are used. Other non-hydrogenated hydrocarbon resins, non-hydrogenated analogs of the hydrogenated resins described above, can also be used.

Furthermore, rosin-based resins can be used.

The use of polyterpene resins based on α-pinene and / or ß-pinene and / or δ-limonene or terpene phenol resins is particularly preferred.

To stabilize the PSA, primary antioxidants such as sterically hindered phenols, secondary antioxidants such as phosphites or thioethers and / or carbon radical scavengers are usually added.

Any combinations of these can be used in order to adjust the properties of the resulting PSA as desired. The presentation of the state of knowledge in the “Handbook of Pressure Sensitive Adhesive Technology” by Donatas Satas (van Nostrand, 1989) is expressly referred to.

The amount by weight of the resins is 20 to 55% by weight, preferably 30 to 55% by weight, more preferably 35 to 50% by weight.

The acrylonitrile-butadiene rubber-based pressure-sensitive adhesive may contain additives such as fillers, dyes or anti-aging agents (antiozonants, antioxidants (primary and secondary), light stabilizers, etc.) in order to establish optical and technical adhesive properties.

• • primäre Antioxidantien wie zum Beispiel sterisch gehinderte Phenole
• • sekundäre Antioxidantien wie zum Beispiel Phosphite oder Thioether
• • Lichtschutzmittel wie zum Beispiel UV-Absorber oder sterisch gehinderte Amine

The following are typically used as additives to the adhesive:

• • primary antioxidants such as sterically hindered phenols
• • secondary antioxidants such as phosphites or thioethers
• • Light stabilizers such as UV absorbers or sterically hindered amines

The fillers can be reinforcing or non-reinforcing. Above all, silicon dioxides (spherical, needle-shaped or irregular like pyrogenic silicas), sheet silicates, calcium carbonates, zinc oxides, titanium dioxides, aluminum oxides or aluminum oxide hydroxides should be mentioned here.

The concentration of the additives influencing the optical and technical adhesive properties is preferably up to 20% by weight, more preferably up to 15% by weight, more preferably up to 5% by weight.

According to the invention, the proportions of all added substances (in addition to acrylonitrile butadiene rubber and adhesive resin) such as synthetic rubbers and / or thermoplastic elastomers and / or fillers and / or dyes and / or anti-aging agents should total 5% by weight, preferably 2% by weight. % do not exceed.

In order to obtain sufficient cohesion and to suppress the cold flow of the adhesives, it is advantageous for the nitrile rubber compositions to be crosslinked so that the structures still remain in place even after the liner has been removed.

There are basically two ways of networking. Chemical crosslinking can take place via the double bonds that are still present, e.g. by addition reaction or radical crosslinking. Crosslinking by means of radiation such as UV or, preferably, electron beams is also possible.

Polyacrylates

In addition to the adhesives described, it is also possible to use those based on polyacrylates.

“Polyacrylates” are understood to mean polymers whose monomer base, based on the amount of substance, consists of at least 30% acrylic acid, methacrylic acid, acrylic acid esters and / or methacrylic acid esters, acrylic acid esters and / or methacrylic acid esters being at least proportionally generally and preferably at least 30%. In particular, a “polyacrylate” is understood to mean a polymer which can be obtained by free-radical polymerization of acrylic and / or methacrylic monomers and, if appropriate, further, copolymerizable monomers.

1. a) Acrylsäureester und/oder Methacrylsäureester der folgenden Formel CH₂ = C(R^I)(COO^II) wobei R^I = H oder CH₃ und R^II ein Alkylrest mit 4 bis 14 C-Atomen ist,
2. b) olefinisch ungesättigte Monomere mit funktionellen Gruppen, die beispielsweise gegenüber Epoxidgruppen reaktiv sind,
3. c) optional weitere Acrylate und/oder Methacrylate und/oder olefinisch ungesättigte Monomere, die mit der Komponente (a) copolymerisierbar sind.

A polyacrylate is preferably used that can be attributed to the following monomer composition:

1. a) Acrylic acid esters and / or methacrylic acid esters of the following formula CH ₂ = C (R ^I ) (COO ^II ) where R ^I = H or CH ₃ and R ^{II is} an alkyl radical with 4 to 14 carbon atoms,
2. b) olefinically unsaturated monomers with functional groups that are reactive towards epoxy groups, for example,
3. c) optionally further acrylates and / or methacrylates and / or olefinically unsaturated monomers which are copolymerizable with component (a).

To use the polyacrylate as a pressure-sensitive adhesive, the proportions of the corresponding components (a), (b), and (c) are selected such that the polymerization product has, in particular, a glass transition temperature of 15 ° C. (DMA at low frequencies).

In particular for the production of PSAs it is very advantageous to use the monomers of component (a) in a proportion of 45 to 99% by weight, the monomers of component (b) in a proportion of 1 to 15% by weight and the monomers to choose component (c) with a proportion of 0 to 40% by weight (The information is based on the monomer mixture for the “base polymer”, ie without the addition of any additives to the finished polymer, such as resins, etc.).

The monomers of component (a) are in particular plasticizing and / or non-polar monomers. Acrylic and methacrylic esters with alkyl groups consisting of 4 to 14 carbon atoms, particularly preferably 4 to 9 carbon atoms, are preferably used as monomers (a). Examples of such monomers are n-butyl acrylate, n-butyl methacrylate, n-pentyl acrylate, n-pentyl methacrylate, n-amyl acrylate, n-hexyl acrylate, hexyl methacrylate, n-heptyl acrylate, n-octyl acrylate, n-octyl methacrylate, n-nonylacrylate, isobutyl acrylate, isobutyl acrylate, isobutyl acrylate , Isooctyl methacrylate, and their branched isomers, such as 2-ethylhexyl acrylate or 2-ethylhexyl methacrylate.

The monomers of component (b) are in particular olefinically unsaturated monomers with functional groups, in particular with functional groups which can react with epoxy groups.

For component (b) it is preferred to use monomers with functional groups which are selected from the group comprising: hydroxy, carboxy, sulfonic acid or phosphonic acid groups, acid anhydrides, epoxides, amines. Particularly preferred examples of monomers of component (b) are acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, aconitic acid, dimethylacrylic acid, β-acryloyloxypropionic acid, trichloroacrylic acid, vinylacetic acid, vinylphosphonic acid, itasconic acid, maleic acid anhydride, hydroxypropyl acrylate, maleic anhydride, hydroxyethyl acrylate, maleic anhydride, hydroxyethyl acrylate, maleic anhydride, hydroxypropyl methacrylate, maleic anhydride, hydroxypropyl acrylate, maleic anhydride, hydroxyethyl acrylate -Hydroxyhexyl methacrylate, allyl alcohol, glycidyl acrylate, glycidyl methacrylate.

In principle, all vinylically functionalized compounds which are copolymerizable with component (a) and / or component (b) can be used as component (c). The monomers of component (c) can serve to adjust the properties of the resulting PSA.

The polyacrylates can be prepared by processes familiar to the person skilled in the art, particularly advantageously by conventional free-radical polymerizations or controlled free-radical polymerizations. The polyacrylates can be prepared by copolymerizing the monomeric components using the customary polymerization initiators and, if appropriate, regulators, polymerizing at the customary temperatures in bulk, in emulsion, for example in water or liquid hydrocarbons, or in solution.

The weight-average molecular weights M _{W of} the polyacrylates are preferably in a range from 20,000 to 2,000,000 g / mol; very preferably in a range from 100,000 to 1,000,000 g / mol, extremely preferably in a range from 150,000 to 500,000 g / mol [the information on the average molecular weight M _W and the polydispersity PD in this document relate to the determination by gel permeation chromatography ( see test V; experimental part)]. For this purpose it can be advantageous to carry out the polymerization in the presence of suitable polymerization regulators such as thiols, halogen compounds and / or alcohols in order to set the desired average molecular weight.

The poly (meth) acrylates are preferably crosslinked by linking reactions - in particular in the sense of addition or substitution reactions - of functional groups contained in them with crosslinkers.

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

Crosslinking via complexing agents, also known as chelates, is also possible. A preferred complexing agent is, for example, aluminum acetylacetonate.

The acrylates can also be crosslinked by means of radiation such as UV or electron beams.

The decisive factor here is that the adhesives are so strongly crosslinked that they show no or only very little cold flow and the structure in the adhesive is retained when the liner is removed.

To increase the adhesion, adhesive resins can also be added to the polyacrylates.

These are preferably rosins as described above or terpene phenol resins. The proportion of adhesive resins is between 5 and 30% by weight, preferably between 10 and 25% by weight

Microballoons

The present invention relates to a foamable pressure-sensitive adhesive which contains expandable, i.e. unexpanded, microballoons. It also relates to a foamed pressure-sensitive adhesive layer which contains microballoons which are at least partially expanded.

According to the invention, the term “at least partially expanded microballoons” is typically understood to mean that the microballoons in their entirety are expanded at least to the extent that this brings about a reduction in density of the adhesive to a technically meaningful extent compared to the same adhesive with the unexpanded microballoons. This means that the microballoons do not necessarily have to be completely expanded. The individual microballoons, viewed individually, are preferably expanded to at least twice their maximum extent in the unexpanded state. In addition, the term “at least partially expanded microballoons” can also mean that only some of the microballoons under consideration are (on) expanded. In a preferred embodiment of the foamed pressure-sensitive adhesive layer, the microballoons are fully expanded, i.e. the layer has been foamed in such a way that a minimum density of the layer is achieved for a given proportion of microballoons.

The foaming takes place in particular by the introduction and subsequent expansion of 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 suitable 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. An example of commercially available microballoons are the Expancel DU ^® types (DU = dry unexpanded) by the company Nouryon, another ^® Matsumoto Microsphere F / FN by Matsumoto Yushi Seiyaku.

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 DU types, are conceivable for producing a foamed PSA of the invention.

A foamed pressure-sensitive adhesive layer according to the invention can also be produced with so-called pre-expanded microballoons. In this group, expansion takes place before it is mixed into the polymer matrix. Pre-expanded microballoons, for example, under the name Dualite® ^® from Chase Corp. or with the type designation Expancel DE (Dry Expanded) commercially available from Nouryon.

According to the invention, at least 90% of all voids formed by microballoons in the foamed pressure-sensitive adhesive layer preferably have a maximum diameter of from 20 to 75 μm, more preferably from 25 to 65 μm. The “maximum diameter” is understood to mean the maximum expansion of a microballoon in any spatial direction of the cryogenic fracture edge in the SEM.

The diameter is determined using a cryogenic edge in the scanning electron microscope (SEM) at 500-fold magnification. The diameter of each individual microballoon is determined graphically.

If foaming is carried out using microballoons, the microballoons can be added to the formulation as a batch, paste or as an uncut or blended powder. Furthermore, they can be suspended in a solvent.

According to the invention, the proportion of microballoons in the adhesive (layer) is typically from 0.3% by weight to 2.5% by weight, preferably between 0.5% by weight and 2.0% by weight and very particularly between 0.7% by weight and 1.7% by weight, based in each case on the overall composition of the adhesive (layer). With regard to the foamable adhesive, the information relates typically to unexpanded microballoons, and with regard to the foamed adhesive layer, typically to the unexpanded or pre-expanded microballoons used.

A pressure-sensitive adhesive comprising expandable hollow microspheres used according to the invention may additionally also contain non-expandable hollow microspheres. The only decisive factor is that almost all caverns containing gas are closed by a permanently tight membrane, regardless of whether this membrane consists of an elastic and thermoplastic stretchable polymer mixture or, for example, of elastic and - within the range of temperatures possible in plastics processing - non-thermoplastic glass.

More important than the amount of microballoons used with regard to the performance of the pressure-sensitive adhesive layer is its density. The density of the foamed PSA layer of the invention, as determined in accordance with Test VII, is at least 600 kg / m ³ and at most 920 kg / m ³ , preferably at least 650 kg / m ³ and at most 870 kg / m ³ , very preferably at least 700 kg / m ³ and a maximum of 820 kg / m ³ . With the same amount used, lower densities can be achieved with larger microballoons. In order to achieve the performance required in the context of the present task, larger microballoons are used correspondingly less than smaller ones. The typical application quantity range is particularly advantageous for microballoons with a maximum diameter of less than 40 μm. In the case of microballoons with an expanded diameter of 40 µm, less than 2.0% is used.

The invention also relates to self-adhesive products, especially double-sided self-adhesive products, i.e. in particular double-sided adhesive tapes which contain at least one pressure-sensitive adhesive layer according to the invention. Transfer adhesive tapes are particularly advantageous. Alternatively, the self-adhesive product can also contain a (permanent) intermediate carrier.

• • einschichtige, beidseitig selbstklebende Klebebänder, sogenannte „Transfertapes“ aus einer einzigen erfindungsgemäßen Haftklebemasseschicht;
• • mehrschichtige beidseitig selbstklebende Klebebänder, bei denen die Schichten jeweils aus den erfindungsgemäßen Haftklebemasseschichten bestehen oder einer erfindungsgemäßen Haftklebemasseschicht und einer nicht erfindungsgemäßen Haftklebemasseschicht;
• • beidseitig selbstklebend ausgerüstete Klebebänder mit einem Zwischenträger (ein sogenannter Permanentträger), der entweder in einer Klebemassenschicht oder zwischen zwei Klebemassenschichten angeordnet ist.

Self-adhesive tapes produced using at least one pressure-sensitive adhesive layer of the invention can accordingly in particular be designed as

• Single-layer adhesive tapes, self-adhesive on both sides, so-called “transfer tapes” made from a single pressure-sensitive adhesive layer according to the invention;
• Multilayer, double-sided self-adhesive tapes in which the layers each consist of the pressure-sensitive adhesive layers of the invention or a pressure-sensitive adhesive layer of the invention and a pressure-sensitive adhesive layer not according to the invention;
• • Adhesive tapes which are self-adhesive on both sides and have an intermediate carrier (a so-called permanent carrier) which is arranged either in a layer of adhesive or between two layers of adhesive.

In addition, an embodiment of the self-adhesive product is preferred in which the intermediate carrier consists of only a single layer, in particular a polymer film. It is also preferred if the intermediate carrier contains at least one layer of a formulation which contains at least one type of vinyl aromatic block copolymer and at least one type of adhesive resin. The double-sided products, regardless of the type of intermediate carrier, can have a symmetrical or an asymmetrical product structure with regard to the type of pressure-sensitive adhesive layers, such as, for example, the composition and / or thickness of the pressure-sensitive adhesive layers.

Typical forms of manufacture of the PSA layer of the invention are rolls of adhesive tape and adhesive strips, such as are obtained, for example, in the form of diecuts. All layers are preferably connected to one another over the entire surface.

In the context of this invention, the general expression “adhesive tape” encompasses all flat structures such as films or film sections extended in two dimensions, tapes with extended length and limited width, tape sections and the like, ultimately also diecuts or labels.

In particular, the adhesive tape is in web form. A path is understood to mean an object whose length is many times greater than the width and the width is preferably designed to be exactly the same along the entire length.

The adhesive tape can be produced in the form of a roll, that is to say rolled up on itself in the form of an Archimedean spiral.

Foamed PSA layers according to the invention are used as described above in self-adhesive products. These self-adhesive products can be designed as an adhesive film, adhesive tape or adhesive die cut. The self-adhesive products contain at least one foamed pressure-sensitive adhesive layer according to the invention. This layer can have a layer thickness of 10 to 2000 μm. The thickness is preferably between 15 μm and 250 μm, more preferably between 25 μm and 150 μm, in particular it is at most 100 μm. The self-adhesive products are typically designed to be adhesive on both sides. The advantages of the formulations according to the invention can be used particularly well in double-sided adhesive self-adhesive products when two components, and in particular in a mobile device, are to be glued to one another.

Polyester films and particularly preferably films based on polyethylene terephthalate (PET) or polybutylene terephthalate (PBT) are particularly suitable as film material for the at least one layer of a possible carrier for this embodiment. Polyester films are preferably biaxially stretched. Films made from polyolefins, in particular made from polybutene, cyclo-olefin copolymer, polymethylpentene, polypropylene or polyethylene, for example made from monoaxially stretched polypropylene, biaxially stretched polypropylene or biaxially stretched polyethylene, are also conceivable. This list is intended to show examples; the person skilled in the art is familiar with further systems which correspond to the concept of the present invention.

It is also possible to use stretchable supports, such as supports based on polyurethane, polyamide or different rubbers.

However, metal foils, fabrics, fleeces or other knitted or woven supports or paper supports are also conceivable.

Foams in web form (for example made of polyethylene and polyurethane) are also suitable.

The intermediate carriers can be designed in multiple layers.

Furthermore, the intermediate carriers can have cover layers, for example barrier layers, which prevent the penetration of components from the adhesive into the intermediate carrier or vice versa. These cover layers can also have barrier properties in order to prevent water vapor and / or oxygen from diffusing through.

For better anchoring of the PSAs on the intermediate carrier, the intermediate carriers can be pretreated using known measures such as corona, plasma or flames. The use of a primer is also possible. Ideally, however, pre-treatment can be dispensed with.

The thickness of the intermediate carrier layer is typically in the range from 2 μm to 200 μm, preferably between 5 and 100 μm and in particular between 10 and 80 μm.

The adhesive tape preferably does not contain a film carrier and consists only of one or more layers of the adhesive.

The adhesive tape is covered on one or both sides with a liner, that is to say a temporary carrier that has an anti-adhesive coating on one or both sides.

One of these liners has a structure that is transferred to the surface of the same during the production of the adhesive tape, so that the adhesive tape is also structured. Different liners with different structuring options can be used.

One way of structuring is to use PET films with a polyethylene layer that is siliconized, the polyethylene layer being embossed and thus containing a structure. Instead of Polyethylene layers of polypropylene or crosslinkable polyolefins can also be used to increase the temperature stability. PET liners with an acrylate layer that is structured and cross-linked and then siliconized can also be used. This has the advantage of an even higher temperature stability.

In addition, paper liners can also be used that have a clay coat that is structured and then siliconized on the coated side. These liners are also relatively temperature-stable.

Another possibility of structuring is embossing a structure in a film liner, e.g. on the basis of PET. Care must be taken that the siliconization of the liner is not damaged by the structure.

If expandable microballoons are used in the adhesive layers, it is advantageous if the liner can withstand a foaming process at high temperatures, e.g. 150 - 200 ° C, depending on the microballoons used, without damage. Liner with a PE coating often already melt and lose their structure. There may even be transfers of the silicone or polyethylene into the adhesive.

When using expandable microballoons, there is often the problem that the microballoons protrude from the adhesive after foaming and thereby significantly reduce the bond strength of the adhesive tape.

One way to get around this is e.g. shaping the at least partially foamed adhesive between two liners by means of at least two rollers. As a result of the high roller pressure, the microballoons are pressed back into the adhesive, as a result of which a smooth surface can be produced without troublesome broken microballoons.

In order to solve the problem of the low resistance of the PE-containing liners, a multi-layer structure can be used. A first layer of adhesive that lies directly on the structured liner does not contain any microballoons or pre-expanded balloons, preferably no microballoons. In a second layer, which can be directly adjacent to the first layer or, for example, is separated by a carrier as described above or by a barrier layer, there are microballoons that can also be foamed. The second layer is first coated and foamed between two smooth liners and is then subsequently laminated to the first layer on the structured liner.

In the case of this 2-layer laminate, the properties can be controlled via the layer thickness distribution. The thicker the second foamed layer, the better the shock resistance. The thicker the first layer, the better the structure and removability.

The type of structure is also decisive for the redetachability. Continuous structures which lead to connected channels in the adhesive and, after gluing, in the glued joint have been shown to be particularly advantageous. In this case, the solvent can migrate more easily and quickly into the bonded joint. Lattice patterns such as honeycombs or squares or rhombuses are preferred here, but irregular structures such as irregular polygons are also conceivable.

The formulations, i.e. pressure-sensitive adhesives, and the coatings or self-adhesive products produced therefrom can be produced using organic solvents or without solvents.

In the method according to the invention, the substrate is preferably a planar element, in particular a carrier material, a film, a (release) liner, a transfer material and / or a cover material. Substrates can also be the surfaces of the production line in the manufacturing process. A pressure-sensitive adhesive is processed into at least one pressure-sensitive adhesive layer with a thickness of greater than or equal to 15 μm or even greater than or equal to 10 μm, and the flatly applied pressure-sensitive adhesive layer is optionally dried or the solvents are removed.

To apply the pressure-sensitive adhesive, the coating processes used for the planar elements used according to the invention include knife-edge processes, knife-edge knife processes, roller-bar nozzle processes, extrusion nozzle processes, pouring nozzles and pouring processes. Likewise according to the invention are application methods such as roller application methods, printing methods, screen printing methods, anilox roller methods, inkjet methods and spraying methods. Hotmelt processes (extrusion, nozzle) are preferred.

If necessary, further layers or material layers are then laminated or coated inline or offline, so that multi-layer / multi-layer product structures can also be produced.

In a further embodiment of the method according to the invention, the resulting combination of planar element and pressure-sensitive adhesive is cut to length goods comprising tapes and / or diecuts are punched out, and the tapes are optionally rolled up to form a band.

Finally, the invention also extends to adhesive composites obtained by using self-adhesive products which contain at least one pressure-sensitive adhesive layer according to the invention. That is to say, the invention relates to a composite of an adhesive tape according to the invention and two substrates, such as in particular components of a mobile device, which are connected with the adhesive tape. The adhesive tape is therefore preferably used for gluing and possible re-detachment of electronic components.

The adhesive tapes structured on the surface should be easily removable without leaving any residue after bonding by applying a solvent around the adhesive partners. This solvent then flows into the channels obtained by the structuring between adhesive and substrate and thereby leads to a reduction in the bond strength.

In principle, almost all solvents can serve as solvents, although it is preferred that the solvents are not absorbed very well by the adhesives so that they are not absorbed before they can penetrate the channels. Particularly preferred are solvents that do not react with the other components in the electronic device and those that are neither dangerous to employees nor to the environment. Ethanol and water are therefore particularly preferred, but also water that contains different detergents, e.g. soapy water, in order to reduce the surface tension of the water and enable it to flow more easily into the channels.

Test methods

Unless otherwise stated, all measurements for determining adhesive properties were carried out at 23 ° C. and 50% rel. Humidity carried out.

Test I - Adhesion

The determination of the bond strength (according to AFERA 5001) is carried out as follows. A polished steel plate with a thickness of 2 mm is used as a defined primer. The bondable surface element to be examined (which is equipped on the back with a 36 µm etched PET film as a support film) is cut to a width of 20 mm and a length of about 25 cm, provided with a handling section and immediately afterwards with a steel roller of 4 kg at a feed rate of 10 m / min onto the chosen primer. Immediately thereafter, the bondable surface element is peeled off the primer at an angle of 180 ° with a tensile tester (from Zwick) at a speed of v = 300 mm / min and the force required for this at room temperature is measured. The measured value (in N / cm) is the mean value from three individual measurements.

To measure the bond strength after exposure to ethanol, the test is modified as follows. After gluing the primer and rolling it over with the steel roller, the glued steel plate is briefly immersed in ethanol for 2 s. Then the glued steel plate is removed from the ethanol and stored on the horizontal table for 1 min. Then measure as described above.

Test II - dielectric strength; z-plane (DuPont test)

A square, frame-shaped sample is cut out of the adhesive tape to be examined (external dimensions 33 mm × 33 mm; web width 2.0 mm; internal dimensions (window cutout) 29 mm × 29 mm). This sample is glued to a polycarbonate (PC) frame (external dimensions 45 mm × 45 mm; web width 10 mm; internal dimensions (window cutout) 25 mm × 25 mm; thickness 3 mm). A PC window of 35 mm × 35 mm is stuck on the other side of the double-sided adhesive tape. The PC frame, adhesive tape frame and PC window are glued in such a way that the geometric centers and the diagonals are each superimposed (Corner on corner). The bond area is 248 mm ² . The bond is pressed with 248 N for 5 s and conditioned for 24 hours at 23 ° C / 50% relative humidity.

Immediately after storage, the adhesive composite of PC frame, adhesive tape and PC window is clamped with the protruding edges of the PC frame in a sample holder in such a way that the composite is aligned horizontally. The PC frame lies flat on the protruding edges of the sample holder, so that the PC window is freely floating (held by the adhesive tape pattern) below the PC frame. The specimen holder is then placed centrically in the intended receptacle of the "DuPont Impact Tester". The 150 g impact head is used in such a way that the circular impact geometry with a diameter of 24 mm rests centrally and flush on the surface of the PC window that is freely accessible from above.

A weight of 150 g, guided on two guide rods, is dropped vertically from a height of 5 cm onto the assembly of sample holder, sample and impact head arranged in this way (measuring conditions 23 ° C., 50% relative humidity). The height of the falling weight is increased in 5 cm steps until the impact energy introduced destroys the sample due to the impact load and the PC window detaches from the PC frame.

In order to be able to compare experiments with different samples, the energy is calculated as follows: $$\text{E.}\left[\text{J}\right]=\text{height}\left[\text{m}\right]*\text{mass weight}\left[\text{kg}\right]*9.81\text{kg / m}*{\text{s}}^2$$

Five samples per product are tested and the average energy value is given as a key figure for the dielectric strength.

Test III - Push Out

A rectangular sample measuring 10 cm × 6 cm is cut out of the adhesive tape to be examined. This sample is glued to a rectangle of the same size made of 2 mm thick polyvinyl chloride. The other joining partner is an aluminum body that has a recess that is 0.5 cm larger in both directions than the PVC plate. The aluminum body has a 3 × 3 cm hole in the middle of the recess. The PVC plate is then glued in the middle of the recess.

The two bonding partners are pressed together with 100 kg for 5s and the test setup is stored for 24h or 336h (or 14d) at room temperature (23 ° C) and 50% RH. Then the PVC plate is pressed out of the metal body through the hole with a stamp and the force is measured.

In the test after exposure to ethanol, 1 ml of ethanol is dripped around the PVC plate into the recess of the aluminum body immediately before the measurement. Then wait 1 min and then carry out the test as described above.

Test IV - Glass Transition Temperature (DSC)

The glass transition temperature of polymer blocks in block copolymers is determined by means of dynamic scanning calorimetry (DSC). For this purpose, approx. 5 mg of the untreated block copolymer samples are weighed into a small aluminum crucible (volume 25 µL) and closed with a perforated lid. A DSC 204 F1 from Netzsch is used for the measurement and inertization is carried out under nitrogen. The sample is first cooled to -150 ° C, heated to +150 ° C at a heating rate of 10 K / min and then cooled again to -150 ° C. The subsequent second heating curve is run again at 10 K / min and the change in heat capacity is recorded. Glass transitions are recognized as steps in the thermogram. The glass transition temperature is evaluated as follows (see 1 ). A tangent is applied to the baseline of the thermogram before 1 and after 2 of the level. In the area of the step, a regression line 3 is laid parallel to the ordinate so that it intersects the two tangents in such a way that two surfaces 4 and 5 (between the one tangent, the regression line and the measurement curve) with the same content are created. The intersection of the regression line positioned in this way with the measurement curve gives the glass transition temperature.

Test V - Molecular Weight (GPC)

Peak molar mass of individual block copolymer modes

GPC can be used as a metrological method to determine the molar mass of individual polymer modes in mixtures of different polymers. For the block copolymers produced by living anionic polymerization which can be used for the purposes of this invention, the molar mass distributions are typically sufficiently narrow so that polymer modes which can be assigned to triblock copolymers, diblock copolymers or multiblock copolymers occur sufficiently resolved from one another in the elugram. The peak molar mass for the individual polymer modes can then be read off from the elograms.

Peak molar masses M _P are determined by means of gel permeation chromatography (GPC). THF is used as the eluent. The measurement takes place at 23 ° C. PSS-SDV, 5μ, 10 ³ Å, ID 8.0 mm × 50 mm is used as the guard column. The columns PSS-SDV, 5 μ, 10 ³ Å as well as 10 ⁴ Å and 10 ⁶ Å, each with an ID of 8.0 mm × 300 mm, are used for separation. The sample concentration is 4 g / l, the flow rate 1.0 ml per minute. It is measured against PS standards (µ = µm; 1 Å = 10 ^-10 m).

weight-average molar mass, especially of tackifier resins

The weight average molecular weight M _W (MW) is determined by means of gel permeation chromatography (GPC). THF is used as the eluent. The measurement takes place at 23 ° C. PSS-SDV, 5μ, 103 Å, ID 8.0 mm × 50 mm is used as the guard column. The columns PSS-SDV, 5 μ, 10 ³ Å as well as 10 ⁴ Å and 10 ⁶ Å, each with an ID of 8.0 mm × 300 mm, are used for separation. The sample concentration is 4 g / l, the flow rate 1.0 ml per minute. It is measured against PS standards (µ = µm; 1 Å = 10 ^-10 m).

Test VI (adhesive) resin softening temperature

The (adhesive) resin softening temperature, also known as the (adhesive) resin softening point, is carried out according to the relevant methodology known as Ring & Ball and standardized according to ASTM E28.

Test VII - density

The density, i.e. absolute density, of an adhesive or adhesive layer is determined by forming the quotient of the amount applied and the thickness of the adhesive layer applied to a carrier or liner.

The application of mass can be determined by determining the mass of a section defined in terms of its length and width of such an adhesive mass (layer) applied to a carrier or liner, minus the (known or separately ascertainable) mass of a section of the same dimensions of the carrier or liner used .

The thickness of an adhesive (layer) can be determined by determining the thickness of a section defined in terms of its length and width of such an adhesive layer applied to a carrier or liner, minus the (known or separately ascertainable) thickness of a section of the same dimensions of the carrier or liner used Liners. The thickness of the adhesive (layer) can be determined using commercially available thickness measuring devices (probe test devices) with an accuracy of less than 1 µm. In the present application, the precision thickness measuring device model 2000 F from Wolf Messtechnik GmbH is used, which has a circular probe with a diameter of 10 mm (flat). The measuring force is 4 N. The value is read 1 s after the load. If fluctuations in thickness are found, the mean value of measurements is given at at least three representative points, that is to say in particular not measured at kinks, folds, specks and the like.

Examples

The pressure-sensitive adhesive tapes of the invention are described below in a preferred embodiment on the basis of several examples, without thereby wishing to restrict the invention in any way.

Furthermore, comparative examples are listed in which unsuitable adhesive tapes are shown.

In the case of the vinylaromatic block copolymer compositions, the constituents of the PSAs were dissolved in 40% strength in special boiling point gasoline / toluene / acetone, and 30% in nitrile rubber compositions in butanone and both, if necessary, with the mixed with microballoons suspended in gasoline or butanone, then spread with a spreader bar onto a PET film equipped with a separating silicone with or without structuring in the desired layer thickness. The solvent was then evaporated off at 100 ° C. for 15 minutes and the mass layer was dried in this way. This is possible in the examples listed, since microballoons are used here, the expansion temperature of which is above 100 ° C. When using other microballoons, the person skilled in the art selects appropriate manufacturing temperatures without departing from the scope of the present invention.

After drying, if the adhesive contained microballoons, the adhesive layer was covered with a second layer of PET liner as defined above, free of any air inclusions, and foamed for 30 s at 170 ° C. between the two liners in a circulating drying cabinet.

If necessary, several layers were also laminated together.

Table 1 shows the raw materials used. Table 1: Raw materials used. Elastomer component (a) Kraton D1102 (Kraton) Polystyrene-polybutadiene block copolymer Linear SBS * PS content 31% * Kraton D1118 (Kraton) Polystyrene-polybutadiene block copolymer Linear SBS * PS content 32% * Nipol DN 2850 (Nippon Zeon) Nitrile rubber ACN content 28%, Mooney viscosity 45-55 Adhesive resin component (b) Foral 105-E (Eastman Chemical) hydrogenated rosin pentaerythritol ester Softening point 101 ° C Foral 85-E (Eastman Chemical) hydrogenated rosin glycerol ester Softening point 85 ° C Dertophene T105 (DRT) Terpene phenol resin Softening point 105 ° C Dercolyte A115 (DRT) alpha pinene resin Softening point 115 ° C DACP = +35 ° C Soft resin component (c) Wingtack 10 (Cray Valley) Aliphatic C5 liquid resin Softening point 10 ° C; Melt viscosity 22 Pa s Additives (d) Irganox 1010 (BASF) Primary anti-aging agent (sterically hindered phenol derivative) Irgafos 168 (BASF) Secondary anti-aging agent (phosphoric acid ester) Microballoons Expancel 920 DU20 (Nouryon)

Tables 2 and 3 show the recipes used and their characteristics. Table 2: Recipes and their characteristics. raw materials Adhesive 1 Adhesive 2 Adhesive 3 Adhesive 4 (a) elastomer [%] Kraton D1102 29.0 29.0 29.0 29.0 Kraton D1118 20.0 20.0 20.0 20.0 (b) adhesive resin K1 [%] Dercolyte A115 45.0 45.0 30.0 30.0 (b) adhesive resin K2 [%] Foral 85 20.0 20.0 (c) soft resin [%] Wingtack 10 5.0 5.0 - - (d) additives [%] Irganox 1010 0.5 0.5 0.5 0.5 Irgafos 168 0.5 0.5 0.5 0.5 (e) microballoons Expancel 920 DU20 - X - X Table 3: other recipes and their characteristics. raw materials Adhesive 5 Adhesive 6 (a) elastomer [%] Nipol DN 2850 55.0 55.0 (b) adhesive resin K1 [%] Foral 85 44.0 44.0 (d) additives [%] Irganox 1010 0.5 0.5 Irgafos 168 0.5 0.5 (e) microballoons Expancel 920 DU20 - X

The following adhesive tapes were produced from these adhesive compositions by coating on a liner, optionally foaming and optionally lamination.

If two adhesives are laminated, any foaming always takes place before lamination.

In the following examples, a PET liner with a structured layer of PE with subsequent siliconization is used as the structured liner.

The unstructured liners are 50 µm PET liners with different levels of separation forces to enable the liners to be detached.

Example 1:

Adhesive 1 was coated onto a structured liner so that the adhesive layer had an application weight of 10 g / m ² after drying. Adhesive 2 was then spread on a smooth liner with an application weight of 30 g / m ² . The adhesive was covered with a second liner and foamed at 170 ° C., the web still running through a roller mill while it was still hot, thereby pushing the microballoons back into the adhesive. After foaming, the adhesive had a thickness of 40 μm. Then a liner of the foamed adhesive layer was uncovered and the first non-foamed but structured adhesive was laminated on, so that a product about 50 μm thick was created that was both structured and foamed.

Example 2:

As in Example 1, except that adhesive 1 was spread out in 25 g / m ² and adhesive 2 in 18 g / m ² , so that after foaming and lamination a product of about 50 μm was obtained again, albeit with a thinner foamed layer of compound.

• Diesmal wurde die Klebemasse 2 direkt auf den geschäumten Liner beschichtet mit einem Auftragsgewicht nach Trocknung von 38g/m². Die Klebeschicht wurde mit einem glatten Liner abgedeckt und wie oben beschrieben geschäumt, so dass erneut eine Klebemasseschicht von ca. 50µm entstand.

Counterexample 1:

• This time the adhesive 2 was coated directly onto the foamed liner with an application weight after drying of 38 g / m ² . The adhesive layer was covered with a smooth liner and foamed as described above, so that another adhesive layer of approx. 50 μm was produced.

• Wie Gegenbeispiel 1, nur dass die Klebemasse 2 diesmal auf einen unstrukturierten Liner beschichtet wurde. Nach Schäumung entstand ein Klebeband mit ca. 50µm dicker Klebemasseschicht.

Counterexample 2:

• As counterexample 1, except that this time the adhesive 2 was coated onto an unstructured liner. After foaming, an adhesive tape with an approximately 50 μm thick layer of adhesive was produced.

• Die Klebemasse 1 wurde auf den strukturierten Liner mit 50 g/m² nach der Trocknung ausgestrichen, so dass eine Klebemasseschicht von ca. 50 µm entstand. Danach wurde die Klebemasse mit einem glatten Liner eingedeckt.

Counterexample 3

• The adhesive 1 was spread onto the structured liner at 50 g / m ² after drying, so that an adhesive layer of approx. 50 μm was formed. The adhesive was then covered with a smooth liner.

Example 3

As in Example 1, except that instead of adhesives 1 and 2, adhesives 3 and 4 were used

Example 4

As in Example 2, except that instead of adhesives 1 and 2, adhesives 3 and 4 were used

Example 5

As in Example 1, except that instead of adhesives 1 and 2, adhesives 5 and 6 were used. After lamination, the adhesive tape was crosslinked with electron beams at an acceleration voltage of 250 kV and a dose of 30 kGy.

Example 6

As in Example 2, except that instead of adhesives 1 and 2, adhesives 5 and 6 were used. After lamination, the adhesive tape was crosslinked with electron beams at an acceleration voltage of 250 kV and a dose of 30 kGy.

Counterexample 4

Same as counterexample 1, but instead of adhesive 2, adhesive 6 was used. The mass was again crosslinked with electron beams as described in Example 5

Counterexample 5

Same as counterexample 2, but instead of adhesive 2, adhesive 6 was used.

The mass was again crosslinked with electron beams as described in Example 5

Counterexample 6

Like example 5, only that electron beams were no longer crosslinked.

Tables 4 and 5 show the test results of the inventive examples and the counter-examples (comparative examples). Table 4: Test results of the examples according to the invention. Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Dielectric strength [mJ] 278 253 325 303 450 431 Adhesive strength without EtOH [N / cm] 10.5 10.2 9.4 9.7 7.5 7.3 Adhesion with EtOH [N / cm] 0.9 1.1 1.1 0.8 0.8 0.7 Decrease in bond strength [%] 92 89 88 92 89 90 Push-out without EtOH [mJ] 408 390 380 411 441 421 Push-out with EtOH 24 h [mJ] 25th 40 62 34 28 41 Drop push out 24 h [%] 94 90 84 92 94 90 Push-out with EtOH 14 d [mJ] 31 52 98 77 110 95 Drop push out 14 d [%] 92 87 74 83 75 77 Table 5: Test results of the counterexamples (ie, comparative examples). Counter example 1 Counter example 2 Counter example 3 Counter example 4th Counter example 5 Counter example 6th Dielectric strength [mJ] 112 395 132 165 489 426 Adhesive strength without EtOH [N / cm] 3.2 11.3 10.2 2.6 7.0 6.8 Adhesion with EtOH [N / cm] 0.3 8.4 2.1 0.4 5.3 2.1 Decrease in bond strength [%] 91 26th 79 85 24 69 Push-out without EtOH [J] 159 537 327 118 402 378 Push-out with EtOH 24 h [Y] 7th 396 56 27 295 109 Drop push out 24 h [%] 96 26th 83 77 27 71 Push-out with EtOH 14 d [J] 15th 382 91 48 280 225 Drop push out 14d [%] 91 29 72 59 30th 40

Example 7:

Instead of the structured liner based on PET / PE, this time a liner made of PET is used, which was embossed before the coating
Otherwise everything is as in counterexample 1

Example 8:

Instead of the structured liner based on PET / PE, this time a structured liner made from clay coated paper (CCK Clay Coated Kraft Paper) is used.

Otherwise everything is as in counterexample 1.

Table 6 shows the test results of further examples according to the invention. Table 6: Test results of the examples according to the invention. Example 7 Example 8 Dielectric strength [mJ] 367 352 Adhesive strength without EtOH [N / cm] 10.6 9.8 Adhesion with EtOH [N / cm] 1.3 0.8 Decrease in bond strength [%] 88 92 Push-out without EtOH [J] 384 335 Push-out with EtOH 24 h [Y] 25th 16 Drop push out 24 h [%] 93 95 Push-out with EtOH 14 d [J] 31 36 Drop push out 14 d [%] 92 89

It has been shown that the shock performance can be significantly improved by foaming the adhesives. In addition, the shock performance is only slightly lower if only part of the adhesive tape is foamed.

Structuring the surface of the adhesive tape helps with the redetachability; without structuring, no drops in adhesive strength or push-out values of more than 40% can be achieved.

If the removability is still given even after prolonged storage, it is preferred that very soft adhesives such as counterexample 4 lose their structure and thus their easy removability over time.

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 2009/090119 A1 [0022]
• DE 102016202018 A1 [0031]
• EP 3075775 A1 [0033]
• DE 102008056980 A1 [0034]
• DE 102008004388 A1 [0034]
• EP 0447855 A1 [0064]
• US 4133731 A [0064]
• US 4820746 A [0064]

Claims (15)

Adhesive tape comprising at least one adhesive layer, at least one of the adhesive layers being foamed and at least one outwardly facing surface of an adhesive of the adhesive tape being structured in order to achieve easy redetachability with solvents. Tape after Claim 1 , characterized in that the structuring was created by a structured liner. Tape after Claim 1 or 2 , characterized in that the adhesive tape consists of the at least one layer of adhesive. Adhesive tape according to one of the preceding claims, characterized in that the adhesives are pressure-sensitive adhesives. Adhesive tape according to one of the preceding claims, characterized in that the adhesive tape consists of several layers of adhesive, of which the structured layer is not foamed. Adhesive tape according to one of the preceding claims, characterized in that the layers of adhesive are those which are based on vinyl aromatic block copolymers. Adhesive tape according to one of the preceding claims, characterized in that the layers of adhesive are those which are based on nitrile rubber. Adhesive tape according to one of the preceding claims, characterized in that the structure can still be recognized at least 2 weeks after application and storage at room temperature (23 ° C). Adhesive tape according to one of the preceding claims, characterized in that the at least one layer of adhesive is foamed with the aid of microballoons. Adhesive tape according to one of the preceding claims, characterized in that the structures in the adhesive form coherent channels through which the solvent can easily migrate. Adhesive tape according to one of the preceding claims, characterized in that the adhesive tape contains a film or fabric carrier. Duct tape after one of the Claims 1 to 10 , characterized in that the adhesive tape does not contain a film or fabric carrier. Adhesive tape according to one of the preceding claims, characterized in that the adhesive tape is double-sided. Use of an adhesive tape according to one of the Claims 1 to 13th for bonding and optionally removing electronic components. Composite of two substrates and an adhesive tape according to one of the Claims 1 to 13th , via which the substrates are connected to one another, the substrates preferably being electronic components, for example a mobile device.

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