DE102017212854A1 - Web-shaped, with microballoons foamed pressure-sensitive adhesive - Google Patents

Abstract

It is a foamed, double-sided adhesive tape with different adhesive properties are provided on both sides, without the need for Nachstrichmassen must be used. This is achieved with a web-shaped, microballoon-foamed pressure-sensitive adhesive which contains a blend of at least one poly (meth) acrylate and at least one synthetic rubber and a multiplicity of expandable microballoons and which is characterized in that the proportion of the microballoons at any one of a Section of the web surface and a depth of 20 microns formed volume of the top of the proportion of the microballoons at any, formed from a section of the web surface and a depth of 20 microns volume of the underside of the web-shaped pressure-sensitive adhesive by at least 12%. The object of the invention also a method for producing such a pressure-sensitive adhesive and its use.

Description

The invention relates to the technical field of pressure-sensitive adhesives, as they are often used for the production of temporary or permanent bonds. More specifically, a sheet-shaped pressure-sensitive adhesive having different adhesive-relevant properties is proposed on its top and bottom surfaces. The application also relates to a process for producing such a pressure-sensitive adhesive and its use for bonding components of electronic devices.

In many cases foamed adhesive tapes are used for bonding substrates by means of adhesive tapes. These allow on the one hand by the density reduction of the adhesive a weight and cost savings, on the other hand they can give the bonding special properties, for example, improved shock resistance, an improved compression modulus and / or a higher stiffness of the bond. However, foamed adhesives or adhesive tapes generally have rougher surfaces compared to their unfoamed counterparts, and they are also stiffer and can therefore less readily wet the substrate surfaces. This leads to a slower mounting, so that the bond initially withstands high loads. To compensate for these disadvantages, but nevertheless to profit from the advantageous foam properties, foamed adhesive tapes are often provided with so-called Nachstrichmassen and thus provided as a two- or three-layered products.

It may also be desirable to provide foamed, double-sided adhesive tapes having different top and bottom adhesive properties, for example, to stably bond different substrates together. Also for this purpose, first offer to the respective substrate to be bonded coordinated aftermarket.

However, the production of foamed, provided with Nachstrichmassen tapes is significantly more complex compared to single-layer products and usually associated with higher costs, for example, to ensure sufficient interlaminate adhesion of the individual layers. For this purpose, surface treatment by means of corona or other physical or chemical processes must in many cases be carried out prior to the connection of the layers to one another.

Three-layer adhesive tapes with an optionally foamed viscoelastic carrier layer are the subject of EP 2 062 951 A1 , Both the carrier layer and the Nachstrichmassen based on poly (meth) acrylates.

Multilayer adhesive tapes of comparable construction are the subject of EP 1 995 282 A1 ,

The foaming of certain layers of adhesive tapes can in principle be achieved with blowing agents introduced as compressed gases or released in the mass by chemical reaction, such as nitrogen or CO _2, or with blowing agents, such as hollow spheres made of glass, ceramic or polymers. Often, controlled foaming is desired, leading to predictable and controllable foam properties. For this, the introduction of micro hollow bodies has proved to be advantageous, with which one achieves closed-cell, syntactic foams. Among the micro hollow bodies which can be used, microballoons have proven to be advantageous.

By "microballoons" is meant elastic, in its ground state expandable hollow microspheres having a thermoplastic polymer shell. These balls are filled with low-boiling liquids or liquefied gas. As shell material find in particular polyacrylonitrile, PVDC, PVC or polyacrylates use. Hydrocarbons of the lower alkanes, for example isobutane or isopentane, which are enclosed in the polymer shell as a liquefied gas under pressure, are particularly suitable as the low-boiling liquid.

By acting on the microballoons, in particular by a heat, softens the outer polymer shell. At the same time, the liquid propellant gas in the casing changes into its gaseous state. The microballoons expand irreversibly and expand in three dimensions. The expansion is completed when the internal and external pressures equalize. As the polymeric shell is preserved, this results in a closed-cell foam.

For example, foam-containing products made using expandable microspheres are the subject of WO 00/06637 A1 ,

Microballoon foamed PSAs based on poly (meth) acrylate and synthetic rubber are the subject of DE 10 2013 215 296 A1 and DE 10 2013 215 297 A1 , Similar adhesives for bonding components in optical, electronic or precision mechanical devices are in DE 10 2014 207 974 A1 described.

There is a continuing need for high performance foamed adhesive tapes suitable for bonding different substrates. The object of the invention is therefore to provide a foamed, double-sided adhesive tape with different adhesive properties on both sides and thereby avoid the disadvantages associated with the use of Nachstrichmassen. The object of the invention is based on the idea of modifying the properties of the two sides by means of the pore fractions produced by expanded microballoons.

• - einen Blend aus mindestens einem Poly(meth)acrylat und mindestens einem Synthesekautschuk sowie
• - eine Vielzahl expandierbarer Mikroballons enthält

und dadurch gekennzeichnet ist, dass sich der Anteil der Mikroballons an einem beliebigen, aus einem Ausschnitt der Bahnoberfläche und einer Tiefe von 20 µm gebildeten Volumen der Oberseite von dem Anteil der Mikroballons an einem beliebigen, aus einem Ausschnitt der Bahnoberfläche und einer Tiefe von 20 µm gebildeten Volumen der Unterseite der bahnförmigen Haftklebmasse um mindestens 12 % unterscheidet.A first and general object of the invention is a sheet-like microballoon foamed pressure-sensitive adhesive which

• a blend of at least one poly (meth) acrylate and at least one synthetic rubber and
• - Contains a variety of expandable microballoons

and characterized in that the proportion of the microballoons at any volume of the top surface formed from a section of the web surface and a depth of 20 microns from the proportion of microballoons at any, from a section of the web surface and a depth of 20 microns formed volume of the underside of the web-shaped pressure-sensitive adhesive differs by at least 12%.

A pressure-sensitive adhesive according to the invention represents a single-layered adhesive tape with the property profile of a two-layered adhesive tape. It has different adhesive properties on its top and bottom side and can thus meet specific requirements for the bonding of different substrates. Since this is realized within a single adhesive, the disadvantages of applied Nachstrichmassen be avoided. In addition, further advantageous properties can be realized, which will be discussed in more detail below.

By lamination of two sheet-like PSAs of the invention according to the scheme ABBA or BAAB, a two-layer product can be obtained which has the property profile of a symmetrical three-layer product, but for this only a pretreatment step to produce a good interlaminate adhesion is necessary instead of two in conventional products and processes.

Under a pressure-sensitive adhesive or a pressure-sensitive adhesive according to the invention, as is common in common usage, understood a substance which is permanently tacky and tacky at least at room temperature. It is characteristic of a pressure-sensitive adhesive that it can be applied by pressure to a substrate and adhere there, whereby the pressure to be applied and the duration of this pressure are not further defined. In general, but basically depending on the precise nature of the pressure-sensitive adhesive and the substrate, the temperature and the humidity, the application of a short-term, minimal pressure, which does not exceed a slight touch for a short moment to achieve the adhesion effect ranges in In other cases, a longer-term exposure time of higher pressure may be necessary.

Pressure-sensitive adhesives have special, characteristic viscoelastic properties which lead to permanent tackiness and adhesiveness. Characteristic of them is that when they are mechanically deformed, it comes both to viscous flow processes as well as to build elastic restoring forces. Both processes are in a certain ratio with regard to their respective proportions, depending on the exact composition, the structure and the degree of crosslinking of the PSA as well as on the speed and duration of the deformation and on the temperature.

The proportional viscous flow is necessary to achieve adhesion. Only the viscous components, often caused by macromolecules with relatively high mobility, allow good wetting and good flow onto the substrate to be bonded. A high proportion of viscous flow leads to a high pressure tack (also referred to as tack or surface tack) and thus often to a high adhesion. Strongly crosslinked systems, crystalline or glassy solidified polymers are usually not or at least only slightly tacky due to the lack of flowable components.

The proportional elastic restoring forces are necessary to achieve cohesion. They are caused for example by very long-chained and strongly entangled as well as by physically or chemically crosslinked macromolecules and allow the transmission of forces acting on an adhesive bond forces. They result in an adhesive bond being able to withstand a sustained load acting on it, for example in the form of a permanent shearing load, to a sufficient extent over a relatively long period of time.

For a more detailed description and quantification of the amount of elastic and viscous portion and the ratio of the proportions to one another, the variables storage modulus (G ') and loss modulus (G ") which can be determined by means of dynamic mechanical analysis (DMA) are used Proportion, G "is a measure of the viscous component of a substance. Both quantities depend on the deformation frequency and the temperature.

The sizes can be determined with the help of a rheometer. The material to be examined is exposed to a sinusoidal oscillating shear stress in a plate-and-plate arrangement, for example. In shear stress controlled devices, the deformation as a function of time and the time lag of this deformation are compared with the introduction of the shear stress measured. This time offset is referred to as the phase angle δ.

The storage modulus G 'is defined as follows: G' = (τ / γ) * cos (δ) (τ = shear stress, γ = deformation, δ = phase angle = phase shift between shear stress vector and deformation vector). The definition of the loss modulus G "is: G" = (τ / γ) · sin (δ) (τ = shear stress, γ = deformation, δ = phase angle = phase shift between shear stress vector and deformation vector).

A composition is especially considered as a pressure-sensitive adhesive and is defined as such in the context of the invention, if at 23 ° C in the deformation frequency range of 10 ⁰ to 10 ¹ rad / sec both G 'and G "at least partially in the range of 10 ^third There are up to 10 ⁷ Pa. "part" means that at least a portion of the G 'curve is within the window formed by the deformation of the frequency range including 10 ⁰ through 10 ¹ rad / sec (abscissa) and the range of the G' Values of 10 ³ up to and including 10 ⁷ Pa (ordinate) are clamped, and if at least a portion of the G "curve is also within the corresponding window.

A "poly (meth) acrylate" is understood as meaning a polymer obtainable by free-radical polymerization of acrylic and / or methacrylic monomers and optionally further copolymerizable monomers. In particular, a "poly (meth) acrylate" is understood as meaning a polymer whose monomer base consists of at least 50% by weight of acrylic acid, methacrylic acid, acrylic acid esters and / or methacrylic acid esters, acrylic esters and / or methacrylates being at least partly, preferably at least 30% by weight .-%, based on the total monomer base of the polymer concerned, are included.

Preferably, the pressure-sensitive adhesive composition according to the invention contains poly (meth) acrylate to a total of 40 to 70 wt .-%, more preferably to a total of 45 to 60 wt .-%, each based on the total weight of the PSA. It may contain one (single) poly (meth) acrylate or more poly (meth) acrylates.

The glass transition temperature of the poly (meth) acrylate of the pressure-sensitive adhesive of the invention is preferably <0 ° C., more preferably between -20 and -50 ° C. The glass transition temperature of polymers or of polymer blocks in block copolymers is determined according to the invention by means of dynamic scanning calorimetry (DSC). For this, approx. 5 mg of an untreated polymer sample are weighed into an aluminum crucible (volume: 25 μl) and closed with a perforated lid. For measurement, a DSC 204 F1 from Netzsch is used. It is worked for the purpose of inertization under nitrogen. The sample is first cooled to-150 ° C, then heated at a heating rate of 10 K / min to +150 ° C and cooled again to -150 ° C. The subsequent second heating curve is driven again at 10 K / min and recorded the change in heat capacity. Glass transitions are recognized as steps in the thermogram.

The glass transition temperature is obtained as follows (see 1 ):

The respective linearly extending area of the measurement curve before and after the step is extended in the direction of rising (range before the stage) or falling (range after stage) temperatures (extension line ① and ②). In the area of the step, a balance line ⑤ parallel to the ordinate is placed so that it intersects the two extension lines, so that two areas ③ and ④ (between the one extension line, the equalization line and the measurement curve) of the same content arise. The intersection of the thus positioned regression line with the trace gives the glass transition temperature.

The poly (meth) acrylate of the pressure-sensitive adhesive composition according to the invention preferably contains at least one functional polymer which is copolymerized in a proportionate manner and which is particularly preferably reactive with epoxide groups to form a covalent bond. Most preferably, the proportionately copolymerized functional, more preferably reactive with epoxy groups to form a covalent bond monomer contains at least one functional group selected from the group consisting of carboxylic acid groups, sulfonic acid groups, phosphonic acid groups, hydroxy groups, acid anhydride groups, epoxy groups and amino groups; In particular, it contains at least one carboxylic acid group. Most preferably, the poly (meth) acrylate of the pressure-sensitive adhesive of the invention contains proportionately copolymerized acrylic acid and / or methacrylic acid. All of the groups mentioned have a reactivity with epoxide groups, as a result of which the poly (meth) acrylate advantageously becomes accessible to thermal crosslinking with incorporated epoxides.

1. a) mindestens ein Acrylsäureester und/oder Methacrylsäureester der folgenden Formel (1) CH₂=C(R^I)(COOR^II) (1), worin R^I = H oder CH₃ und R" ein Alkylrest mit 4 bis 18 C-Atomen ist;
2. b) mindestens ein olefinisch ungesättigtes Monomer mit mindestens einer funktionellen Gruppe ausgewählt aus der Gruppe bestehend aus Carbonsäuregruppen, Sulfonsäuregruppen, Phosphonsäuregruppen, Hydroxygruppen, Säureanhydridgruppen, Epoxidgruppen und Aminogruppen;
3. c) optional weitere Acrylsäureester und/oder Methacrylsäureester und/oder olefinisch ungesättigte Monomere, die mit der Komponente (a) copolymerisierbar sind.

The poly (meth) acrylate of the pressure-sensitive adhesive of the invention may preferably be attributed to the following monomer composition:

1. a) at least one acrylic ester and / or methacrylic acid ester of the following formula (1) CH ₂ = C (R ^I ) (COOR ^II ) (1), wherein R ^I = H or CH ₃ and R "is an alkyl group having 4 to 18 C atoms;
2. b) at least one olefinically unsaturated monomer having at least one functional group selected from the group consisting of carboxylic acid groups, sulfonic acid groups, phosphonic acid groups, hydroxyl groups, acid anhydride groups, epoxide groups and amino groups;
3. c) optionally further acrylic esters and / or methacrylic acid esters and / or olefinically unsaturated monomers which are copolymerizable with component (a).

It is particularly advantageous, the monomers of component a) in a proportion of 45 to 99 wt .-%, the monomers of component b) in a proportion of 1 to 15 wt .-% and the monomers of component c) in a proportion from 0 to 40 wt .-%, wherein the data are based on the monomer mixture for the base polymer without additives of any additives such as resins, etc.

The monomers of component a) are generally softening, rather nonpolar monomers. R ^II in the monomers a) is particularly preferably an alkyl radical having 4 to 10 C atoms or 2-propylheptyl acrylate or 2-propylheptyl methacrylate. The monomers of formula (1) are especially selected from the group consisting of n-butyl acrylate, n-butyl methacrylate, n-pentyl acrylate, n-pentyl methacrylate, n-amyl acrylate, n-hexyl acrylate, n-hexyl methacrylate, n-heptyl acrylate, n-octyl acrylate , n-octyl methacrylate, n-nonyl acrylate, isobutyl acrylate, isooctyl acrylate, isooctyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, 2-propylheptyl acrylate and 2-propylheptyl methacrylate.

The monomers of component b) are particularly preferably selected from the group consisting of acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, aconitic acid, dimethylacrylic acid, .beta.-acryloyloxypropionic acid, trichloroacrylic acid, vinylacetic acid, vinylphosphonic acid, maleic anhydride, hydroxyethyl acrylate, in particular 2-hydroxyethyl acrylate, Hydroxypropyl acrylate, in particular 3-hydroxypropyl acrylate, hydroxybutyl acrylate, in particular 4-hydroxybutyl acrylate, hydroxyhexyl acrylate, in particular 6-hydroxyhexyl acrylate, hydroxyethyl methacrylate, in particular 2-hydroxyethyl methacrylate, hydroxypropyl methacrylate, in particular 3-hydroxypropyl methacrylate, hydroxybutyl methacrylate, in particular 4-hydroxybutyl methacrylate, hydroxyhexyl methacrylate, in particular 6-hydroxyhexyl methacrylate, allyl alcohol , Glycidyl acrylate, glycidyl methacrylate.

Exemplary monomers of component c) are:

Methylacrylate, ethylacrylate, propylacrylate, methylmethacrylate, ethylmethacrylate, benzylacrylate, benzylmethacrylate, sec-butylacrylate, tert-butylacrylate, phenylacrylate, phenylmethacrylate, isobornylacrylate, isobornylmethacrylate, tert-butylphenylacrylate, tert-butylaphenylmethacrylate, dodecylmethacrylate, isodecylacrylate, laurylacrylate, n-undecylacrylate, stearylacrylate, Tridecyl acrylate, behenyl acrylate, cyclohexyl methacrylate, cyclopentyl methacrylate, phenoxyethyl acrylate, phenoxyethyl methacrylate, 2-butoxyethyl methacrylate, 2-butoxyethyl acrylate, 3,3,5-trimethylcyclohexyl acrylate, 3,5-dimethyladamantyl acrylate, 4-cumylphenyl methacrylate, cyanoethyl acrylate, cyanoethyl methacrylate, 4-biphenyl acrylate, 4-biphenyl methacrylate, 2-naphthyl acrylate, 2-naphthyl methacrylate, tetrahydrofufuryl acrylate, diethylaminoethyl acrylate, diethylaminoethyl methacrylate, dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, 3-methoxyacrylic acid methyl ester, 3-methoxybutyl acrylate, 2-phenoxyethyl methacrylate, butyl diglycol methac rylate, ethylene glycol acrylate, Ethylene glycol monomethyl acrylate, methoxypolyethylene glycol methacrylate 350, methoxypolyethylene glycol methacrylate 500, propylene glycol monomethacrylate, butoxy diethylene glycol methacrylate, ethoxy triethylene glycol methacrylate, octafluoropentyl acrylate, octafluoropentyl methacrylate, 2,2,2-trifluoroethyl methacrylate, 1,1,1,3,3,3-hexafluoroisopropyl acrylate, 1,1,1,3,3, 3-hexafluoroisopropyl methacrylate, 2,2,3,3,3-pentafluoropropyl methacrylate, 2,2,3,4,4,4-hexafluorobutyl methacrylate, 2,2,3,3,4,4,4-heptafluorobutyl acrylate, 2,2, 3,3,4,4,4-heptafluorobutyl methacrylate, 2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentadecafluorooctyl methacrylate, dimethylaminopropylacrylamide, dimethylaminopropylmethacrylamide, N- (1-methylundecyl) acrylamide, N- (n-butoxymethyl) acrylamide, N- (butoxymethyl) methacrylamide, N- (ethoxymethyl) acrylamide, N- (n-octadecyl) acrylamide; N, N-dialkyl substituted amides such as N, N-dimethylacrylamide and N, N-dimethylmethacrylamide; N-benzylacrylamide, N-isopropylacrylamide, N-tert-butylacrylamide, N-tert-octylacrylamide, N-methylolacrylamide, N-methylolmethacrylamide, acrylonitrile, methacrylonitrile; Vinyl ethers such as vinyl methyl ether, ethyl vinyl ether, vinyl isobutyl ether; Vinyl esters such as vinyl acetate; Vinyl halides, vinylidene halides, vinylpyridine, 4-vinylpyridine, N-vinylphthalimide, N-vinyllactam, N-vinylpyrrolidone, styrene, α- and p-methylstyrene, α-butylstyrene, 4-n-butylstyrene, 4-n-decylstyrene, 3,4 -Dimethoxystyrol; Macromonomers such as 2-polystyrene ethyl methacrylate (weight-average molecular weight Mw, as determined by GPC, from 4000 to 13000 g / mol), poly (methyl methacrylate) ethyl methacrylate (Mw from 2000 to 8000 g / mol).

Monomers of component c) may advantageously also be chosen such that they contain functional groups which promote a subsequent radiation-chemical crosslinking (for example by electron beams, UV). Suitable copolymerizable photoinitiators are, for example, benzoin acrylate and acrylate-functionalized benzophenone derivatives. Monomers which promote electron beam crosslinking are, for example, tetrahydrofurfuryl acrylate, N-tert-butylacrylamide and allyl acrylate.

The preparation of the poly (meth) acrylates is preferably carried out by conventional free-radical polymerizations or controlled free-radical polymerizations. The poly (meth) acrylates can be prepared by copolymerization of the monomers using conventional polymerization initiators and optionally regulators, being polymerized at the usual temperatures in bulk, in emulsion, for example in water or liquid hydrocarbons, or in solution.

The poly (meth) acrylates are preferably prepared by copolymerization of the monomers in solvents, particularly preferably in solvents having a boiling range from 50 to 150 ° C., in particular from 60 to 120 ° C., using from 0.01 to 5% by weight, in particular from 0.1 to 2% by weight, in each case based on the total weight of the monomers, of polymerization initiators.

In principle, all conventional initiators are suitable. Examples of radical sources are peroxides, hydroperoxides and azo compounds, for example dibenzoyl peroxide, cumene hydroperoxide, cyclohexanone peroxide, di-t-butyl peroxide, cyclohexylsulfonyl acetyl peroxide, diisopropyl percarbonate, t-butyl peroctoate and benzpinacol. Preferred free-radical initiators are 2,2'-azobis (2-methylbutyronitrile) (Vazo® 67 ™ from DuPont) or 2,2'-azobis (2-methylpropionitrile) (2,2'-azobisisobutyronitrile; AIBN; Vazo® 64 ™ the company DuPont).

Preferred solvents for the preparation of the poly (meth) acrylates are alcohols such as methanol, ethanol, n- and iso-propanol, n- and iso-butanol, in particular isopropanol and / or isobutanol; Hydrocarbons such as toluene and in particular gasoline having a boiling range of 60 to 120 ° C; Ketones, in particular acetone, methyl ethyl ketone, methyl isobutyl ketone; Esters such as ethyl acetate and mixtures of the abovementioned solvents. Particularly preferred solvents are mixtures containing isopropanol in amounts of from 2 to 15% by weight, in particular from 3 to 10% by weight, based in each case on the solvent mixture used.

Preferably, after the preparation (polymerization) of the poly (meth) acrylates, a concentration takes place, and further processing of the poly (meth) acrylates takes place essentially solvent-free. The concentration of the polymer can be done in the absence of crosslinker and accelerator substances. However, it is also possible to add one of these classes of compounds to the polymer even before the concentration, so that the concentration then takes place in the presence of this substance (s).

The polymers can be converted into a compounder after the concentration step. Optionally, the concentration and the compounding can also take place in the same reactor.

The weight-average molecular weights M _{w of} the polyacrylates are preferably in a range from 20,000 to 2,000,000 g / mol; more preferably in a range of 100,000 to 1,500,000 g / mol, most preferably in a range of 150,000 to 1,000,000 g / mol. For this it may be advantageous to polymerize in the presence of suitable polymerization regulators such as thiols, halogen compounds and / or alcohols to adjust the desired average molecular weight.

The details of the number-average molar mass M _n and the weight-average molar mass M _w in this document refer to the per se known determination by gel permeation chromatography (GPC). The determination is made on 100 μl of clear filtered sample (sample concentration 4 g / l). The eluent used is tetrahydrofuran with 0.1% by volume of trifluoroacetic acid. The measurement takes place at 25 ° C.

The precolumn is a PSS-SDV column, 5 μm, 10 ³ Å, 8.0 mm * 50 mm (here and below in the order: type, particle size, porosity, inner diameter * length, 1Å = 10 ^-10 m ) used. For separation, a combination of PSS-SDV, 5 μm, 10 ³ Å and 10 ⁵ Å and 10 ⁶ Å columns of 8.0 mm * 300 mm each is used (Polymer Standards Service columns, Shodex RI71 differential refractometer detection ). The flow rate is 1.0 ml per minute. Calibration is performed with poly (meth) acrylates against PMMA standards (polymethyl methacrylate calibration) and otherwise (resins, elastomers) against PS standards (polystyrene calibration).

The poly (meth) acrylates preferably have a K value of from 30 to 90, more preferably from 40 to 70, measured in toluene (1% solution, 21 ° C). The Fikentscher K value is a measure of the molecular weight and viscosity of polymers.

The principle of the method is based on the capillary-viscometric determination of the relative solution viscosity. For this purpose, the test substance is dissolved in toluene by shaking for 30 minutes, so that a 1% solution is obtained. In a Vogel-Ossag viscometer, the flow time is measured at 25 ° C and determined therefrom in relation to the viscosity of the pure solvent, the relative viscosity of the sample solution. According to Fikentscher [P. E. Hinkamp, Polymer, 1967, 8, 381] read off the K value (K = 1000 k).

The poly (meth) acrylate of the pressure-sensitive adhesive of the invention preferably has a polydispersity PD <4 and thus a relatively narrow molecular weight distribution. Masses based thereon, despite a relatively low molecular weight after crosslinking, have a particularly good shear strength. In addition, the lower polydispersity allows for easier melt-processing, since the flow viscosity is lower compared to a more widely distributed poly (meth) acrylate with substantially the same application properties. Narrowly distributed poly (meth) acrylates can advantageously be prepared by anionic polymerization or by controlled radical polymerization methods, the latter being particularly well suited. Also via N-Oxyle can be prepared corresponding poly (meth) acrylates. Furthermore, atom transfer radical polymerization (ATRP) can advantageously be used for the synthesis of narrowly dispersed poly (meth) acrylates, preferably monofunctional or difunctional secondary or tertiary halides being used as the initiator, and for the abstraction of the halides Cu, Ni, Fe, Pd, Pt, Ru, Os, Rh, Co, Ir, Ag or Au complexes are used. RAFT polymerization is also suitable.

• - 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) acrylates of the PSA of the invention are preferably crosslinked by linking reactions - especially in the sense of addition or substitution reactions - of functional groups contained in them with thermal crosslinkers. All thermal crosslinkers can be used

• both ensure a sufficiently long processing time, so that there is no gelling during the processing process, in particular the extrusion process,
• - As well as a rapid post-crosslinking of the polymer to the desired degree of crosslinking at lower temperatures than the processing temperature, especially at room temperature, lead.

For example, a combination of carboxy-, amino- and / or hydroxyl-containing polymers and isocyanates, in particular aliphatic or blocked isocyanates, for example trimerized isocyanates deactivated with amines, as crosslinkers is possible. Suitable isocyanates are in particular trimerized derivatives of MDI [4,4-methylenedi (phenyl isocyanate)], HDI [hexamethylene diisocyanate, 1,6-hexylene diisocyanate] and IPDI [isophorone diisocyanate, 5-isocyanato-1-isocyanatomethyl-1,3,3-trimethylcyclohexane] , for example, the types Desmodur® N3600 and XP2410 (each BAYER AG: aliphatic polyisocyanates, low-viscosity HDI trimers). Also suitable is the surface-deactivated dispersion of micronized, trimerized IPDI BUEJ 339®, now HF9® (BAYER AG).

Preference is given to using thermal crosslinkers at 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 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 epoxide (s) or by means of one or more epoxide group-containing substance (s). The epoxide group-containing substances are in particular multifunctional epoxides, ie those having at least two epoxide groups; Accordingly, there is an overall indirect linkage of the functional groups bearing blocks of poly (meth) acrylates. The epoxide group-containing substances can be both aromatic and aliphatic compounds.

Excellent multifunctional epoxides are oligomers of epichlorohydrin, polyether polyhydric alcohols, especially ethylene, propylene and butylene glycols, polyglycols, thiodiglycols, glycerine, pentaerythritol, sorbitol, polyvinyl alcohol, polyallylalcohol 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-bis (4-hydroxyphenyl) propane). 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'-dihydroxydiphenylsulfone and their hydroxyethyl ethers; Phenol-formaldehyde condensation products such as phenolic alcohols and phenolaldehyde resins; S- and N-containing epoxides, for example N, N-diglycidylaniline and N, N'-dimethyldiglycidyl-4,4-diaminodiphenylmethane; and epoxides which have been prepared by conventional methods from polyunsaturated carboxylic acids or monounsaturated carboxylic acid esters of unsaturated alcohols; glycidyl; Polyglycidylester, which can be obtained by polymerization or copolymerization of glycidyl esters of unsaturated acids or from other acidic compounds, for example from cyanuric acid, diglycidyl sulfide or cyclic trimethylene trisulfone or its derivatives are available.

Very suitable ethers are for example 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 and bisphenol F diglycidyl ether.

Further preferred epoxides are cycloaliphatic epoxides such as 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate (UVACure1500).

Most preferably, the poly (meth) acrylates are crosslinked by a crosslinker-accelerator system ("crosslinking system") to provide better control over both processing time, crosslinking kinetics and degree of crosslinking. The crosslinker-accelerator system preferably comprises at least one substance containing epoxide groups as crosslinking agent and at least one substance accelerating at a temperature below the melting temperature of the polymer to be crosslinked for crosslinking reactions by means of epoxide group-containing compounds as accelerator.

As accelerators, particular preference is given to using amines according to the invention. These are formally to be regarded as substitution products of 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 undergo little or no reaction with the polymers to be crosslinked.

In principle, it is possible to choose both primary (NRH ₂ ), secondary (NR ₂ H) and tertiary amines (NR ₃ ) as accelerators, of course also those which have a plurality of primary and / or secondary and / or tertiary amino groups. Particularly preferred accelerators are tertiary amines such as 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, especially secondary and / or tertiary amino alcohols, wherein in the case of several amino functionalities per molecule preferably at least one, particularly preferably all amino functionalities are secondary and / or tertiary. Particularly preferred such promoters 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'-hydroxyethyl bisaminoethyl ether, N, N, N'-trimethylaminoethylethanolamine and N, N, N'-Trimethylaminopropylethanolamin.

Other suitable accelerators are pyridine, imidazoles such as 2-methylimidazole and 1,8-diazabicyclo [5.4.0] undec-7-ene. Cycloaliphatic polyamines can also be used as accelerators. Phosphorus-based promoters 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.

The PSA of the invention further contains at least one synthetic rubber.

Preferably, the PSA contains synthetic rubber to a total of 15 to 50 wt .-%, more preferably to a total of 20 to 40 wt .-%, each based on the total weight of the PSA. It may be a synthetic rubber or more synthetic rubbers contained in the pressure-sensitive adhesive of the invention.

• - 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 synthetic rubber of the pressure-sensitive adhesive of the invention is preferably a block copolymer having 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 polymerization of at least one vinyl aromatic;
• - the blocks B independently of one another for a polymer formed by polymerization of conjugated dienes having 4 to 18 C 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 stands for an integer ≥ 2.

In particular, all synthetic rubbers of the pressure-sensitive adhesive composition of the invention are block copolymers having a structure as stated above. The pressure-sensitive adhesive of the invention can thus also contain mixtures of various block copolymers having a structure as above.

Thus, the preferred synthetic rubbers, also referred to as vinyl aromatic block copolymers, comprise one or more rubbery blocks B (soft blocks) and one or more glassy blocks A (hard blocks). The synthetic rubber of the pressure-sensitive adhesive of the invention is particularly preferably a block copolymer having a structure AB, ABA, (AB) ₃ X or (AB) ₄ X, where A, B and X are as defined above. Very particular preference is given to all synthetic rubbers of the PSA block copolymers according to the invention having 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 of the invention is a mixture of block copolymers having a structure AB, ABA, (AB) ₃ X or (AB) ₄ X, which preferably contains at least diblock copolymers AB and / or triblock copolymers ABA.

In particular, block A is a vitreous block having a preferred glass transition temperature (Tg, DSC) above room temperature. More preferably, the Tg of the glassy block is at least 40 ° C, especially at least 60 ° C, most preferably at least 80 ° C and most preferably at least 100 ° C. The proportion of vinylaromatic blocks A in the entirety of the block copolymers is preferably 10 to 40% by weight, particularly preferably 20 to 33% by weight. Vinyl aromatics for the construction of block A preferably comprise styrene and α-methylstyrene. The block A can thus be present as a homo- or copolymer. More preferably, block A is a polystyrene.

The block B is in particular a rubber-like block 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 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 desired 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, in particular polybutylene-butadiene; or a polymer of a mixture of butadiene and isoprene. Most preferably, the block B is a polybutadiene.

The synthetic rubber is preferably dispersed in the PSA according to the invention in the poly (meth) acrylate. Accordingly, poly (meth) acrylate and synthetic rubber are preferably in each case homogeneous phases. The poly (meth) acrylates and synthetic rubbers contained in the pressure-sensitive adhesive are preferably chosen so that they are not miscible to homogeneity at 23 ° C. The PSA of the invention is thus at least microscopically and preferably at least at room temperature in at least two-phase morphology. With particular preference, poly (meth) acrylate (e) and synthetic rubber (e) are not homogeneously miscible with one another in a temperature range from 0 ° C. to 50 ° C., in particular from -30 ° C. to 80 ° C., so that the pressure-sensitive adhesive in these temperature ranges at least microscopically present at least two phases.

For the purposes of this specification, components are defined as "not homogeneously miscible with one another", even if the formation of at least two stable phases can be detected physically and / or chemically, at least microscopically, with one phase rich in one component and the second Phase is rich in the other component. The presence of negligible amounts of one component in the other, which does not preclude the formation of multiphase, is considered to be irrelevant. Thus, in the poly (meth) acrylate phase, small amounts of synthetic rubber and / or small amounts of poly (meth) acrylate component may be present in the synthetic rubber phase, provided that these are not essential amounts which influence the phase separation.

The phase separation may in particular be realized in such a way that discrete regions ("domains") which are rich in synthetic rubber - ie essentially formed of synthetic rubber - in a continuous matrix which is rich in poly (meth) acrylate - thus substantially is formed from poly (meth) acrylate - present. A suitable analysis system for a phase separation is, for example, scanning electron microscopy. However, phase separation can also be recognized, for example, by the fact that the different phases have two independent glass transition temperatures in differential scanning calorimetry (DDK, DSC) or dynamic mechanical analysis (DMA). Phase separation according to the invention is present if it can be clearly demonstrated by at least one of the analytical methods.

Within the synthetic rubber-rich domains, the fine structure may also have additional multiphase, with the A blocks forming one phase and the B blocks forming a second phase.

A pressure-sensitive adhesive of the invention preferably contains 40-70% by weight of at least one poly (meth) acrylate and 15-50% by weight, in each case based on the total weight of the pressure-sensitive adhesive, of at least one synthetic rubber.

"Expandable" microballoons include not yet expanded microballoons as well as partially expanded but still further expandable microballoons.

According to the invention, the proportion of the microballoons at any volume of the upper surface formed from a section of the web surface and a depth of 20 μm differs from the proportion of the microballoons at any volume of the underside formed from a section of the web surface and a depth of 20 μm the web-shaped PSA by at least 12%. As has been shown in the investigations within the scope of the invention, in the presence of such a difference in the volume fraction of the microballoons between the top and bottom of the sheet-like pressure-sensitive adhesive of the invention, different adhesive properties are obtained on both sides of the pressure-sensitive adhesive. In particular, different bond strengths are obtained at low Aufziehzeiten. Although the bond strength difference between the two sides decreases as time progresses, it remains significant even after complete application of the adhesive. This allows on the side with the lower instant adhesive force in many applications an initial repositionability, as is often desired, to correct the position of the possibly already connected to an object to be bonded adhesive tape after the initial bonding once or more times. After the correct position is found, the bond strengths of the two sides can then approach each other, so that ultimately a generally stable and strong bond is achieved.

The proportion of the microballoons at any volume of the upper side formed from a section of the web surface and a depth of 20 μm preferably differs from the proportion of the microballoons at any volume of the underside formed from a section of the web surface and a depth of 20 μm the web-shaped pressure-sensitive adhesive by at least 15%. Also preferably, the proportion of the microballoons at any volume of the top surface formed from a section of the web surface and a depth of 20 microns differs from the proportion of microballoons at any, from a section of the web surface and a depth of 20 microns formed volume of Bottom of the web-shaped pressure-sensitive adhesive by a maximum of 30, in particular by a maximum of 24%. As has been shown, particularly stable adhesions can be achieved with corresponding pressure-sensitive adhesives according to the invention.

The proportion of the microballoons in a given volume of the pressure-sensitive adhesive of the invention is determined according to the invention by means of computed tomography (CT). In particular, a high-resolution X-ray microtomograph was used. The computed tomography allows a clear differentiation of gas (pores generated by the microballoons) and solid (adhesive mass matrix), which can also be graphically presented excellent. By evaluating with a suitable analysis and visualization software, the volume fraction of the microballoons in the considered volume can be determined exactly. The concrete device parameters are described in the experimental part.

A pressure-sensitive adhesive of the invention preferably contains at least one tackifier compatible with the poly (meth) acrylate, which may also be referred to as an adhesion promoter or tackifier resin. A "tackifier" is understood, according to the general expert understanding, to be an oligomeric or polymeric resin which increases the auto-adhesion (tack, inherent tack) of the PSA in comparison to the PSA-containing but otherwise identical PSA.

By a "poly (meth) acrylate compatible tackifier" is meant a tackifier which alters the glass transition temperature of the system obtained after thorough mixing of poly (meth) acrylate and tackifier compared to the pure poly (meth) acrylate, including the mixture from poly (meth) acrylate and tackifier only one Tg can be assigned. A tackifier incompatible with the poly (meth) acrylate would result in two Tg in the system obtained after thorough mixing of poly (meth) acrylate and tackifier, one of which would be associated with the poly (meth) acrylate and the other with the resin domains , The determination of the Tg is carried out in this context calorimetrically by means of DSC (differential scanning calorimetry).

The tackifier compatible with the poly (meth) acrylate preferably has a DACP value of less than 0 ° C., very preferably of at most -20 ° C., and / or preferably a MMAP value of less than 40 ° C., very preferably of maximum 20 ° C, on. For determination of DACP and MMAP values, see C. Donker, PSTC Annual Technical Seminar, Proceedings, pp. 149-164, May 2001.

The tackifier compatible with the poly (meth) acrylate is particularly preferably a terpene-phenolic resin or a rosin derivative, in particular a terpene-phenolic resin. A pressure-sensitive adhesive according to the invention may also contain mixtures of several tackifiers. Among the rosin derivatives, rosin esters are preferred.

A pressure-sensitive adhesive composition according to the invention preferably contains tackifiers compatible with the poly (meth) acrylate to a total of 7 to 25 wt .-%, particularly preferably to a total of 12 to 20 wt .-%, each based on the total weight of the PSA. Preferably, the tackifier compatible with the poly (meth) acrylate is also compatible with the synthetic rubber, in particular with its soft block B, or at least partially compatible, the above definition of the term "compatible" correspondingly applying. Polymer-resin compatibility depends inter alia on the molecular weight of the polymers or resins. The compatibility is better when the molecular weights are lower. For a given polymer, it may be possible for the low molecular weight Components of the resin molecular weight distribution are compatible with the polymer, the higher molecular weight but not. This is an example of partial compatibility.

The weight ratio of poly (meth) acrylate to synthetic rubber in the pressure-sensitive adhesive of the invention is preferably from 1: 1 to 3: 1, in particular from 1.8: 1 to 2.2: 1.

The weight ratio of tackifier compatible with the poly (meth) acrylate to synthetic rubber in the pressure-sensitive adhesive of the invention is preferably not more than 2: 1, in particular not more than 1: 1. At least this weight ratio is preferably 1: 4.

1. a) 50 - 60 Gew.-% mindestens eines Poly(meth)acrylats;
2. b) 20 - 40 Gew.-% mindestens eines Synthesekautschuks; und
3. c) 7 - 25 Gew.-% mindestens eines mit dem Poly(meth)acrylat verträglichen Tackifiers, jeweils bezogen auf das Gesamtgewicht der Haftklebmasse.

The pressure-sensitive adhesive composition according to the invention particularly preferably contains

1. a) 50-60% by weight of at least one poly (meth) acrylate;
2. b) 20-40% by weight of at least one synthetic rubber; and
3. c) 7 to 25% by weight of at least one tackifier compatible with the poly (meth) acrylate, in each case based on the total weight of the PSA.

Depending on the field of application and desired properties of the pressure-sensitive adhesive of the invention, it may comprise further components and / or additives, in each case alone or in combination with one or more other additives or components.

Thus, the pressure-sensitive adhesive of the invention, for example, powder and granular, especially abrasive and reinforcing, fillers, dyes and pigments such. As chalk (CaCO3), titanium dioxide, zinc oxides and / or carbon blacks.

Preferably, the PSA of the invention contains one or more chalk (s) as a filler. The pressure-sensitive adhesive of the invention contains chalk, preferably up to a total of up to 20% by weight. With such proportions, essential adhesive properties such as the shear strength at room temperature and the instantaneous bond strength to steel and PE by the addition of filler practically do not change. In addition, various organic fillers may be included.

Suitable additives for the PSA according to the invention are also - independently selected from other additives - non-expandable polymer hollow spheres, polymer solid spheres, glass hollow spheres, glass solid spheres, ceramic hollow spheres, ceramic solid spheres and / or full carbon carbon spheres ("Carbon Micro Balloons").

Furthermore, the pressure-sensitive adhesive composition of the invention can be flame-resistant fillers, for example ammonium polyphosphate; electrically conductive fillers, such as Leitruß, carbon fibers and / or silver-coated balls; thermally conductive materials, such as boron nitride, alumina, silicon carbide; ferromagnetic additives, for example, iron (III) oxides; organic, renewable raw materials, for example wood flour; organic and / or inorganic nanoparticles; Contain fibers, compounding agents, anti-aging agents, light stabilizers and / or antiozonants.

Optionally, the PSA of the invention contains one or more plasticizers. As plasticizers, e.g. (Meth) acrylate oligomers, phthalates, hydrocarbon oils, Cyclohexandicarbonsäureester, water-soluble plasticizers, soft resins, phosphates or polyphosphates are added.

Preferably, the pressure-sensitive adhesive of the invention comprises silicic acids, particularly preferably precipitated silica, in particular precipitated silica surface-modified with dimethyldichlorosilane. Advantageously, the heat resistance of the pressure-sensitive adhesive can be adjusted with this additive.

A pressure-sensitive adhesive according to the invention may comprise, in addition to the constituents listed above, one or more hydrocarbon resins which are not compatible with the poly (meth) acrylate. Such hydrocarbon resins, which are also tackifiers, preferably comprise hydrogenated polymers of dicyclopentadiene; non, partially, selectively or completely hydrogenated hydrocarbon resins based on C5, C5 / C9 or C9 monomer streams and polyterpene resins based on α-pinene and / or of β-pinene and / or of δ-limonene. The hydrocarbon resins preferably have a DACP value of at least 0 ° C, more preferably at least 20 ° C, and / or preferably a MMAP value of at least 40 ° C, more preferably at least 60 ° C. For determination of DACP and MMAP values, see C. Donker, PSTC Annual Technical Seminar, Proceedings, pp. 149-164, May 2001. The aforementioned Hydrocarbon resins can be contained both individually and in admixture in the pressure-sensitive adhesive. Particularly preferred hydrocarbon resins are polyterpene resins based on α-pinene and / or β-pinene and / or δ-limonene.

The density of a PSA according to the invention is preferably 500 to 1000 kg / m ³ , more preferably 600 to 990 kg / m ³ , in particular 700 to 980 kg / m ³ .

The thickness of a sheet-like pressure-sensitive adhesive of the invention is preferably 50 to 1500 .mu.m, more preferably 70 to 1200 .mu.m, in particular 100 to 800 .mu.m, for example 150 .mu.m to 500 .mu.m or 200 .mu.m to 400 .mu.m.

1. a) die Herstellung einer Haftklebmasse, die einen Blend aus mindestens einem Poly(meth)acrylat und mindestens einem Synthesekautschuk sowie eine Vielzahl expandierbarer Mikroballons enthält; und
2. b) das Ausformen der Haftklebmasse zur Bahn in einem Kalanderspalt umfasst, wobei die Haftklebmasse so durch den Kalanderspalt geführt wird, dass sich vor dem Kalanderspalt ein Knet bildet und die Temperatur der Haftklebmasse im Knet über der Expansionstemperatur der Mikroballons liegt und die Temperatur der Haftklebmasse im Knet
   • - über der Expansionstemperatur der Mikroballons liegt und
   • - mindestens 5 K mehr als die Temperatur der Haftklebmasse unmittelbar nach ihrer Herstellung beträgt.

Another object of the invention is a process for producing a web-shaped microballoon foamed pressure-sensitive adhesive which

1. a) the preparation of a PSA comprising a blend of at least one poly (meth) acrylate and at least one synthetic rubber and a plurality of expandable microballoons; and
2. b) the molding of the PSA to the web in a calender nip comprises, wherein the PSA is passed through the calender nip, that forms a kneading in front of the calender nip and the temperature of the PSA in the kneading is above the expansion temperature of the microballoons and the temperature of the PSA in the kneading
   • - is above the expansion temperature of the microballoons and
   • - Is at least 5 K more than the temperature of the pressure-sensitive adhesive immediately after their preparation.

The method according to the invention makes it possible to produce sheet-like PSAs which have the difference already described with regard to the volume fraction of the microballoons between their upper and lower sides and the associated advantages. In addition, the extent of this difference and thus also of the properties can be controlled by the targeted setting of certain process parameters, which will be discussed in more detail below. Thus, it is possible to produce single-layer adhesive tapes with the properties of multilayer adhesive tapes, whereby the specific problems of multi-layer adhesive tapes, as resulting, for example, from the required interlaminate adhesion, can be circumvented. In addition, from the products of the method according to the invention in only one lamination an adhesive tape with the properties of a three-layer adhesive tape with top and bottom identical Nachstrichmassen produced by the sides are laminated with identical micro balloon content of two resulting adhesive tapes on each other.

As regards the poly (meth) acrylate and the synthetic rubber of the process according to the invention, what has already been said in the description of the pressure-sensitive adhesive of the invention applies.

The process according to the invention for producing a sheet-shaped pressure-sensitive adhesive is preferably a continuous process.

The preparation of the PSA until its formation to the web in the calender nip is basically not critical. All that needs to be done is a mass which can be formed in the calendering gap, with expandable - that is, not yet expanded or already (expanded), but still further expandable - microballoons. Preferably, the preparation of the pressure-sensitive adhesive takes place from the meltdown. In particular, the pressure-sensitive adhesive composition is present in the kneading before the calendering nip as well as in the calendering nip itself as a melt during shaping to form the web. If the composition used for the preparation of the pressure-sensitive adhesive composition comprises solvent components, these are removed from the composition at the latest in the kneading before the calendering nip.

The process for the preparation of the pressure-sensitive adhesive may initially comprise a concentration of the resulting from the polymer preparation poly (meth) acrylate solution or dispersion. The concentration of the polymer can be done in the absence of crosslinker and accelerator substances. However, it is also possible to add a maximum of one of these substances to the polymer before the concentration, so that the concentration then takes place in the presence of this substance.

The preparation of the pressure-sensitive adhesive preferably comprises passing through a compounding and extrusion device. The aggregate optionally used to concentrate the mass may or may not be part of this compounding and extrusion apparatus. After passing through the compounding and extrusion device, the PSA is preferably present as a melt. In particular, the pressure-sensitive adhesive composition is present as a melt in a calendering gap at the beginning of molding to form the web.

The synthetic rubber, optionally together with a poly (meth) acrylate-compatible resin, can be introduced into a compounder via a solids meter. Via a sidefeeder, the concentrated and possibly already melted poly (meth) acrylate can be introduced into the compounder. In special embodiments of the process, it is also possible that concentration and compounding take place in the same reactor. Optionally, poly (meth) acrylate-compatible or other resins may also be reacted via a resin melt and another sidefeeder at a different process position, eg. B. after the input of synthetic rubber and poly (meth) acrylate, are supplied.

Other additives and / or plasticizers may also be supplied as solids or melt or as a batch in combination with another formulation component.

As a compounder or as part of the compounding and extrusion device, in particular an extruder is used. The polymers are preferably present in the melt in the compounder, either because they are already introduced in the melt state or by being heated to melt in the compounder. Advantageously, the polymers are held in the compounder by heating in the melt.

If accelerator substances are used for crosslinking the poly (meth) acrylate, they are preferably added to the polymers only shortly before further processing, in particular shortly before coating or other shaping. The time window of the addition before the coating depends in particular on the available pot life, ie the processing time in the melt, without the properties of the resulting product being adversely affected.

The crosslinkers, for example epoxides, and if appropriate the accelerators can also both be added shortly before the further processing of the composition, that is to say advantageously in the phase as described above for the accelerators. For this purpose, it is advantageous if crosslinkers and accelerators are simultaneously introduced into the process at one and the same point, optionally as an epoxide-accelerator mixture. In principle, it is also possible to exchange the addition times or addition points for crosslinker and accelerator in the above-described embodiments, so that the accelerator can be added before the crosslinker substances.

After compounding and applying the finished pressure-sensitive adhesive, according to the invention, the pressure-sensitive adhesive composition is shaped to form the web in a calendering nip. The coating calenders can consist of two, three, four or more rolls.

Preferably, at least one of the rolls is provided with an anti-adhesive roll surface. Particularly preferably, all rolls of the calender, which come into contact with the pressure-sensitive adhesive, are anti-adhesive. As an anti-adhesive roll surface, a steel-ceramic-silicone composite is preferably used. Such roll surfaces are resistant to thermal and mechanical stress.

It has been found to be particularly advantageous when roll surfaces are used which have a surface structure, in particular in such a way that the surface does not make complete contact with the mass layer to be processed, so that the contact surface - compared to a smooth roller - is lower. Structured rolls such as metal anilox rolls, for example steel lathing rolls, are particularly favorable.

The coating can be done on a temporary support. A temporary carrier is removed in the further processing process, for example during the preparation of the adhesive tape, or in the application of the adhesive layer. The temporary carrier is preferably a release liner. The pressure-sensitive adhesive can also be covered on both sides with a temporary carrier or in each case a release liner.

In the process of the invention, a plurality of microballoons before the mass is formed in a calendering gap to the web, expandable. Preferably, the average degree of expansion of the microballoon immediately after leaving the extrusion device is at most 80%, particularly preferably at most 70%, in particular at most 60%, for example at most 50%, in each case based on the theoretical maximum extent. It is also possible that a multiplicity of microballoons at this time is only minimal or not yet expanded.

According to the invention, the pressure-sensitive adhesive is passed through the calendering gap so that a kneading forms in front of it. The kneading preferably has an extent orthogonal to the plane defined by the machine direction and calendering gap of 1.0-10 cm.

In the context of the invention, there is a temperature difference of at least 5 K between the pressure-sensitive adhesive immediately after its production, for example after passing through a nozzle, and the pressure-sensitive adhesive prior to the calendering gap, wherein the higher temperature prevails in the kneading. It is assumed that the kneading produces the higher temperature in the kneading due to the flow conditions, for example swirling, which according to the invention is above the expansion temperature of the microballoons. In this way it would come in the kneading to a continuation or even to start the expansion of certain microballoons. Probably due to the flow conditions in the kneading, this expansion is likely to take place at different levels in different zones, so that the gradient according to the invention sets in the volume fraction of the microballoons.

Preferably, the preparation of the pressure-sensitive adhesive comprises passing through a compounding and extrusion device, the temperature of the pressure-sensitive adhesive immediately after leaving the extrusion device, for example after passing through a nozzle, is above the expansion temperature of the microballoons, and the temperature of the pressure-sensitive adhesive in the kneading is at least 10 K, more preferably at least 15 K, in particular at least 20 K higher than the temperature of the pressure-sensitive adhesive immediately after leaving the extrusion device. In principle, however, not only does the melt temperature in the kneading have an influence on the formation of the gradient according to the invention in the volume fraction of the microballoons, but also the residence time of the mass in the kneading. Thus, it has been found that in a procedure with a large kneading diameter, which causes a longer residence time of the mass in the kneading, even a small temperature difference may be sufficient to produce a pressure-sensitive adhesive according to the invention.

The temperature of the pressure-sensitive adhesive mass is therefore particularly preferably kneaded by 10 to 20 K in the case of an extension of the kneading orthogonal to the plane defined by the machine direction and calendering nip, and by an extent of kneading orthogonal to the plane defined by machine direction and calendering nip of FIGS 10 cm higher by 6 to 10 K than the temperature of the pressure-sensitive adhesive immediately after leaving the extrusion device.

It has been found that a higher difference between the temperature of the pressure-sensitive adhesive after leaving the extrusion device and the temperature of the kneading is accompanied by a more pronounced volume gradient of the microballoons, so that a possibility of controlling the gradient is given. As a further control variable, the diameter of the kneading can be used in accordance with the above, since the residence time of the mass in the kneading increases with increasing diameter.

Of course, the method according to the invention is preferably performed so that there is no shrinkage or even destruction of the expanded microballoons. Each Mikroballontype can be a temperature T _max assign up to the maximum may be heated so that it does not come to shrink or destroy the microballoons. In this sense, the temperature of the pressure-sensitive adhesive immediately after leaving the extrusion device is preferably at least 10%, more preferably at least 15%, in particular at least 20% lower than T _{max of} the relevant type of microballoon.

Another object of the invention is the use of a sheet-like, microballoon foamed PSA or a sheet-like, microballoon foamed PSA for bonding components of electronic devices, in particular of displays, or of components in or on automobiles, in particular for Bonding of electronic components in automobiles and for gluing trim or emblems on clearcoats of automobiles. Especially in the bonding of high quality items of electronic devices, such. Displays, the above-described possibility for repositioning the components is particularly advantageous. Adhesions using pressure-sensitive adhesives according to the invention can be carried out both manually and automatically.

Examples

Test Methods

Test 1: Adhesive strength of steel

The determination of the bond strength was carried out at a test climate of 23 ° C +/- 1 ° C temperature and 50% +/- 5% rel. Humidity. The samples were cut to 20 mm width and glued to a steel plate (SUS). The steel plate was cleaned and conditioned before measurement. For this purpose, the plate was first wiped with solvent and then left for 5 minutes in the air, so that the solvent could evaporate. The side of the adhesive tape facing away from the test substrate was then covered with 75 μm thick, etched PET film, which prevented the sample from stretching during the measurement. After that, the test pattern was rolled up on the ground. For this purpose, the tape was rolled over with a 4 kg roller five times back and forth at a winding speed of 10 m / min. One minute or 14 days after rolling up, the plate was pushed into a special holder, which allows the sample to be peeled off at a certain angle (indicated in the test results). The bond strength was measured with a Zwick tensile testing machine. The measurement results are given in N / cm and are averaged out of five individual measurements.

Preparation of polyacrylate base polymer:

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 passing nitrogen gas for 45 minutes with stirring, the reactor was heated to 58 ° C and 50 g of AIBN dissolved in 500 g of acetone was added. Subsequently, the outer heating bath was heated to 75 ° C and the reaction was carried out constantly at this external temperature. After 1 h, 50 g of AIBN dissolved in 500 g of acetone were again added and after 4 h, diluted with 10 kg of acetone / isopropanol mixture (94: 6).

After 5 h and after 7 h, in each case with 150 g of bis (4-tert-butylcyclohexyl) peroxydicarbonate, each dissolved in 500 g of acetone, re-initiated. After a reaction time of 22 hours, the polymerization was stopped and cooled to room temperature. The product had a solids content of 55.8% and was dried. The resulting polyacrylate had a K value of 58.9, an average molecular weight of Mw = 748,000 g / mol, a polydispersity of D (Mw / Mn) = 8.9, and a static glass transition temperature of Tg = -35.2 ° C ,

Example 1:

The synthetic rubber Kraton D1118 as well as micro balloons of the type Expancel 920DU40 were metered into a planetary roller extruder by means of solids feeders. In addition, the anti-aging agent Irganox 1726 in molten form and the anti-aging agent Irganox 1076 as a solid were metered into the planetary roller extruder. After digestion of the synthetic rubber, the terpene phenolic resin Dertophene T105 and the polyacrylate base polymer were added, each premelted in a single screw extruder. After sufficient mixing of the individual components, the crosslinker UVACure 1500 was metered into the last roll cylinder of the planetary roller extruder. Subsequently, the melt was transferred to a twin-screw extruder, degassed by applying a negative pressure and fed via a slot die a two-roll calender. The formation of the composition into a flat adhesive tape took place between two siliconized PET films. The process parameters with respect to jacket temperature and speed were selected in the twin-screw extruder so that the temperature of the melt at nozzle exit - measured by means of IR thermometer from the company Fluke, type Ti20 - at 149 ° C. The two-roll calender coating was carried out at a roll temperature of 110 ° C, with the calender being fed so as to form a kneading having a diameter of 2 cm in front of the calender rolls. The surface temperature of the kneading measured by IR thermometer (Fluke, type Ti20) was 155 ° C. The coated product had a layer thickness of 325 microns and an average density of 830 kg / m ³ , wherein the determined by μCT pore fraction at a depth of 20 microns on the covered (the side of the adhesive tape, which rests in the unrolled state of the liner ) Page 24% and on the open page was 28%.

The PSA composition was 58.7% polyacrylate, 25.4% Kraton D1118, 14.2% Dertophene T105, 1.1% Expancel 920DU40, 0.3% Irganox 1726, 0.2% Irganox 1076 and 0.1%. UVACure 1500 (in% by weight).

Example 2:

Process and dosage analogous to example 1. However, the parameters of the twin-screw extruder with regard to jacket temperature and rotational speed were chosen so that the temperature of the melt at nozzle outlet was 139 ° C. The two-roll calender coating was carried out at a roll temperature of 110 ° C, whereby the calender was charged so that a kneading having a diameter of 5 cm was formed in front of the calender rolls. The surface temperature of the kneading was 152 ° C. The coated product had a layer thickness of 280 μm and an average density of 878 kg / m ³ , the μCT-determined pore fraction at a depth of 20 μm being 18% on the covered side and 30% on the open side.

The composition of the PSA was 58.8% polyacrylate, 25.4% Kraton D1118, 14.2% Dertophene T105, 1.0% Expancel 920DU40, 0.3% Irganox 1726, 0.2% Irganox 1076 and 0.1%. UVACure 1500 (in% by weight).

Example 3:

Process and dosage analogous to Example 1. However, the parameters of the twin-screw extruder with regard to jacket temperature and rotational speed were chosen so that the temperature of the melt at nozzle outlet was 134 ° C. The two-roll calender coating was carried out at a roll temperature of 110 ° C, with the calender being fed so as to form a kneading having a diameter of 8 cm in front of the calender rolls. The surface temperature of the kneading was 153 ° C. The coated product had a layer thickness of 280 microns and a mean density of 908 kg / m ³ , wherein the determined by μCT pore fraction at a depth of 20 microns on the covered side 12% and on the open side was 30%.

The composition of the PSA was 58.8% polyacrylate, 25.4% Kraton D1118, 14.2% Dertophene T105, 1.0% Expancel 920DU40, 0.3% Irganox 1726, 0.2% Irganox 1076 and 0.1%. UVACure 1500 (in% by weight).

Example 4:

Process and dosage as in Example 1. However, the parameters of the twin-screw extruder with regard to jacket temperature and rotational speed were chosen so that the temperature of the melt at the nozzle exit was 131 ° C. The two-roll calender coating was carried out at a roll temperature of 110 ° C, with the calender being fed so as to form a kneading having a diameter of 8 cm in front of the calender rolls. The surface temperature of the kneading was 151 ° C. The coated product had a layer thickness of 280 microns and a mean density of 922 kg / m ³ , wherein the determined by μCT pore fraction at a depth of 20 microns on the covered side was 7% and 30% on the open side.

The composition of the PSA was 58.8% polyacrylate, 25.4% Kraton D1118, 14.2% Dertophene T105, 1.0% Expancel 920DU40, 0.3% Irganox 1726, 0.2% Irganox 1076 and 0.1%. UVACure 1500 (in% by weight).

Example 5:

Process and dosage analogous to Example 1. However, the parameters of the twin-screw extruder with regard to jacket temperature and rotational speed were chosen so that the temperature of the melt at nozzle outlet was 127 ° C. The two-roll calender coating was carried out at a roll temperature of 110 ° C, with the calender being fed so as to form a kneading having a diameter of 8 cm in front of the calender rolls. The surface temperature of the kneading was 153 ° C. The coated product had a layer thickness of 305 microns and an average density of 947 kg / m ^3, wherein the particular means of μCT proportion of pores at a depth of 20 microns on the hidden side of 4% and was on the open side 32%.

The composition of the PSA was 58.8% polyacrylate, 25.4% Kraton D1118, 14.2% Dertophene T105, 1.0% Expancel 920DU40, 0.3% Irganox 1726, 0.2% Irganox 1076 and 0.1%. UVACure 1500 (in% by weight).

Example 6:

Process and dosage as in Example 1. However, the parameters of the twin-screw extruder with regard to jacket temperature and rotational speed were chosen so that the temperature of the melt at the nozzle exit was 131 ° C. The two-roll calender coating was carried out at a roll temperature of 110 ° C, with the calender being fed so as to form a kneading having a diameter of 8 cm in front of the calender rolls. The surface temperature of the kneading was 157 ° C. The coated product had a layer thickness of 450 microns and a mean density of 910 kg / m ³ , wherein the determined by μCT pore fraction at a depth of 20 microns on the covered side was 7% and on the open side 32%.

The composition of the PSA was 58.8% polyacrylate, 25.4% Kraton D1118, 14.2% Dertophene T105, 1.0% Expancel 920DU40, 0.3% Irganox 1726, 0.2% Irganox 1076 and 0.1%. UVACure 1500 (in% by weight).

Example 7:

Process and dosage analogous to Example 1. However, the parameters of the twin-screw extruder with regard to jacket temperature and rotational speed were chosen so that the temperature of the melt at the nozzle exit was 147 ° C. The two-roll calender coating was carried out at a roll temperature of 100 ° C, with the calender being fed so as to form a kneading having a diameter of 6 cm in front of the calender rolls. The surface temperature of the kneading was 161 ° C. The coated product had a layer thickness of 1150 μm and an average density of 793 kg / m ³ , the μCT-determined pore fraction at a depth of 20 μm being 21% on the covered side and 36% on the open side.

The composition of the pressure-sensitive adhesive was 58.6% polyacrylate, 25.4% Kraton D1118, 14.2% Dertophene T105, 1.2% Expancel 920DU40, 0.3% Irganox 1726, 0.2% Irganox 1076 and 0.1%. UVACure 1500 (in% by weight).

Comparative Example 1

The synthetic rubber Kraton D1118 as well as the microballoons of the type Expancel 920DU40 were metered into a planetary roller extruder by means of solids feeders. In addition, the anti-aging agent Irganox 1726 in molten form and the anti-aging agent Irganox 1076 as a solid were metered into the planetary roller extruder. After digestion of the synthetic rubber, the terpene phenolic resin Dertophene T105 and the polyacrylate base polymer were added, each premelted in a single screw extruder. After sufficient mixing of the individual components, the crosslinker UVACure 1500 was metered into the last roll cylinder of the planetary roller extruder. Subsequently, the melt was transferred to a twin-screw extruder, degassed by applying a negative pressure and fed via a slot die a two-roll calender. The formation of the composition into a flat adhesive tape took place between two siliconized PET films. The process parameters in terms of jacket temperature and speed were selected in the twin-screw extruder so that the temperature of the melt at nozzle exit - measured by means of IR thermometer from the company Fluke, type Ti20 - at 158 ° C. The two-roll calender coating was carried out at a roll temperature of 100 ° C, with the calender being fed so as to form a kneading having a diameter of 1 cm in front of the calender rolls. The surface temperature of the kneading measured by IR thermometer (Fluke, type Ti20) was 162 ° C. The coated product had a layer thickness of 420 microns and an average density of 780 kg / m ³ , wherein the determined by μCT pore fraction at a depth of 20 microns on the covered side 29% and on the open side was 30%.

The PSA composition was 58.7% polyacrylate, 25.4% Kraton D1118, 14.2% Dertophene T105, 1.1% Expancel 920DU40, 0.3% Irganox 1726, 0.2% Irganox 1076 and 0.1%. UVACure 1500 (in% by weight).

Comparative Example 2:

Process and dosage as in Comparative Example 1. However, the parameters of the twin-screw extruder with regard to jacket temperature and rotational speed were chosen so that the temperature of the melt at the die exit was 164 ° C. The coating by Zweiwalzenkalander was at a Rolling temperature of 100 ° C carried out, wherein the feed of the calender was carried out so that no kneading was formed. The coated product had a layer thickness of 330 μm and an average density of 770 kg / m ³ , the μCT-determined pore fraction at a depth of 20 μm being 31% on the covered side and 32% on the open side.

The composition of the pressure-sensitive adhesive was 58.6% polyacrylate, 25.4% Kraton D1118, 14.2% Dertophene T105, 1.2% Expancel 920DU40, 0.3% Irganox 1726, 0.2% Irganox 1076 and 0.1%. UVACure 1500 (in% by weight).

Results

Table 1: Test results Adhesive force initial aS (SUS, 300 mm / min, 180 ° / * 90 °) Adhesive force initial oS (SUS, 300 mm / min, 180 ° / * 90 °) Adhesive force 14 daS (SUS, 300 mm / min, 180 ° / * 90 °) Adhesive force 14 doS (SUS, 300 mm / min, 180 ° / * 90 °) example 1 12.2 11.3 23.4 24.1 Example 2 12.0 10.6 22.5 21.7 Example 3 12.9 10.9 23.3 22.1 Example 4 13.2 10.8 22.8 23.0 Example 5 13.3 10.7 23.3 22.7 Example 6 15.5 13.2 24.6 25.2 Example 7 * 19.7 17.7 35.6 33.8 Comparative Example 1 13.6 13.3 24.1 24.9 Comparative Example 2 11.5 11.2 23.8 23.3 aS = covered page oS = open side

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been 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.

Cited patent literature

• EP 2062951 A1 [0005]
• EP 1995282 A1 [0006]
• WO 0006637 A1 [0010]
• DE 102013215296 A1 [0011]
• DE 102013215297 A1 [0011]
• DE 102014207974 A1 [0011]

Claims (9)

A web-shaped microballoon foamed PSA comprising - a blend of at least one poly (meth) acrylate and at least one synthetic rubber, and - a plurality of expandable microballoons, characterized in that the portion of the microballoons at any of a section of the web surface and a Depth of 20 microns formed volume of the top of the proportion of the microballoons at any, formed from a section of the web surface and a depth of 20 microns volume of the underside of the web-shaped pressure-sensitive adhesive differs by at least 12%. Web-shaped pressure-sensitive adhesive according to Claim 1 , characterized in that the thickness of the web-shaped pressure-sensitive adhesive is 50 - 1500 microns. Web-shaped pressure-sensitive adhesive composition according to one of the preceding claims, characterized in that the pressure-sensitive adhesive composition comprises 40-70% by weight, of at least one poly (meth) acrylate and 15-50% by weight, of at least one synthetic rubber, in each case based on the total weight of the pressure-sensitive adhesive composition, contains. Web-shaped pressure-sensitive adhesive composition according to one of the preceding claims, characterized in that the pressure-sensitive adhesive composition comprises at least one tackifier compatible with the poly (meth) acrylate. Web-shaped pressure-sensitive adhesive composition according to one of the preceding claims, characterized in that the synthetic rubber is a block copolymer having a structure AB, ABA, (AB) _n , (AB) _n X or (ABA) _n X, where - the blocks A independently of one another Polymer formed by polymerization of at least one vinyl aromatic; - the blocks B independently of one another for a polymer formed by polymerization of conjugated dienes having 4 to 18 C atoms and / or isobutylene, or for a partially or fully hydrogenated derivative of such a polymer; - X stands for the remainder of a coupling reagent or initiator and - n stands for an integer ≥ 2. A process for producing a web-shaped, microballoon-foamed pressure-sensitive adhesive composition, comprising a) the preparation of a pressure-sensitive adhesive comprising a blend of at least one poly (meth) acrylate and at least one synthetic rubber and a variety of expandable microballoons; b) forming the pressure-sensitive adhesive mass to the web in a calendering nip, wherein the pressure-sensitive adhesive is passed through the calendering gap so that a kneading forms in front of the calendering gap and the temperature of the pressure-sensitive adhesive in the kneading - is above the expansion temperature of the microballoons and - Is at least 5 K more than the temperature of the pressure-sensitive adhesive immediately after their preparation. Method according to Claim 6 , characterized in that the method is a continuous process. Method according to one of Claims 6 and 7 characterized in that the preparation of the pressure-sensitive adhesive comprises passing through a compounding and extrusion device; the temperature of the pressure-sensitive adhesive immediately after leaving the extrusion device is above the expansion temperature of the microballoons and the temperature of the pressure-sensitive adhesive in the kneading is at least 5 K more than the temperature of the pressure-sensitive adhesive immediately after leaving the extrusion device. Use of a web-shaped, with microballoons foamed pressure-sensitive adhesive according to one of Claims 1 to 5 or a web-shaped, microballoon-foamed PSA prepared by a method according to any one of Claims 6 to 8th for the bonding of components of electronic devices or of components in automobiles.

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