EP1576064A1

EP1576064A1 - Self-adhesive article with at least one layer of a thermally-conducting adhesive mass and method for production thereof

Info

Publication number: EP1576064A1
Application number: EP03767624A
Authority: EP
Inventors: Marc Husemann; Stephan ZÖLLNER
Original assignee: Tesa SE
Current assignee: Tesa SE
Priority date: 2002-12-19
Filing date: 2003-11-24
Publication date: 2005-09-21
Also published as: DE10259549A1; KR20050084414A; WO2004056933A1; JP2006510762A; AU2003292089A1

Abstract

In a method for production of a self-adhesive article a thermally-conducting adhesive mass containing acrylate is coated on a support in a hot-melt coating method with stretching or orientation such that an anisotropic thermally-conducting layer with a back-shrinkage of at least 3 % measured on the free adhesive mass film is generated. Stampings for use in the electrical and electronic industries can be produced from said material.

Description

description

PSA article with at least one layer of an electrically conductive PSA and process for its production

The invention relates to a method for producing a pressure-sensitive adhesive article which has at least one layer of a thermally conductive pressure-sensitive adhesive, and to a pressure-sensitive adhesive article obtainable in this way, in particular for bonds in the field of electrical and electronic components.

In the age of computerization, electrically conductive PSAs are increasingly being used to bond electrodes or electromagnetic components. The goal is to maintain electrical conductivity and avoid electrical flashovers.

As a rule, electrically conductive acrylic PSA tapes are used for these applications. The electrical conductivity can be achieved by two different methods. On the one hand, conductive foils or fabrics are used, on the other hand, the PSA is modified by electrically conductive components and thus itself electrically conductive.

Examples of electrically conductive carrier materials are e.g. in US 5,939,190 and 6,235,385 and the patents cited therein.

Electrically conductive acrylic PSAs have also been known for a long time. US 4,113,981 describes that electrical conductivity can be achieved by adding metal powder or SiC powder. The conductivity can be varied by the degree of filling. Furthermore, if the mass is enclosed between two electrodes, an electrical conductivity is only achieved in the z direction by limiting it to 30%. In US 5,300,340 silver-plated glass beads and metal beads are mixed with a PSA. The diameter of these beads is at least as large as the layer thickness of the PSA. The electrical conductivity is thus achieved through the direct contact of the conductive beads with the conductive substances to be glued (eg electrodes).

US Pat. No. 5,620,795 and US Pat. No. 6,126,865 use polyacrylates of a certain comonomer composition as electrically conductive acrylic PSAs. The comonomer composition of the polyacrylates is chosen such that very non-polar resins are compatible with the polyacrylate and thus high adhesive strengths can be achieved on non-polar surfaces with the electrically conductive PSA.

Miniaturization in the electronics / computer industry places ever increasing demands on electrically conductive PSAs. The electrical components to be bonded are getting smaller and smaller, so that often only diecuts can be used for bonding. Furthermore, the distance between the circuits decreases continuously, so that electrically conductive PSAs are required which have only a very low flow behavior in a certain direction (to the next electrically conductive component).

The object of the invention is therefore to provide electrically conductive PSAs, in particular for the electrical and electronics industry, in which the disadvantages in the prior art are avoided and, in particular, the PSA is reliably prevented from swelling or flowing out at the edge of the adhesive bond ,

The problem is solved surprisingly and for the person skilled in the art in an unforeseeable manner by means of a method by means of which anisotropic, oriented PSAs with a shrinkback of at least 3% are coated on a carrier (optionally also a temporary carrier from which the PSAs are removed again) can) be obtained, as well as by the associated pressure-sensitive adhesive articles obtainable in this way. Further developments of the invention are characterized in the subclaims. The solution to the problem of the invention comprises a method for producing a pressure-sensitive adhesive article for the bonding of electrical or electronic parts, which has at least one layer of an electrically conductive pressure-sensitive adhesive, ie a pressure-sensitive adhesive based on polyacrylates and / or polymethacrylates with optionally further comonomers, wherein in a coating process by stretching, stretching or compressing an at least one property anisotropic layer is produced from the electrically conductive PSA, which in at least one direction along the layer plane has a shrinkback of at least 3% with respect to the linear expansion of the layer, measured with a shrinkback measurement according to test B. on free film.

Anisotropy means that at least one property of the PSA in one spatial direction within the layer of PSA differs from the same property in at least one other direction; i.e. Anisotropic properties are vectorial and not uniform within the material.

Preferably the PSA has an orientation as known as such, i.e. a preferred direction within the polymer structure.

The coating process can be, for example, a "hot melt" or hot melt roll coating process, a melt nozzle coating process or an extrusion coating process.

In an alternative embodiment of the invention, the coating method is a conventional coating method, for example from solution, in which stretching or stretching is carried out after the coating, preferably on a stretchable carrier.

The electrically conductive PSA can be coated on one or both sides with the coating method onto a sheet-like or tape-like carrier, which can also be a transfer tape or a release liner. PSAs which can be used according to the invention

According to the invention, PSAs with a resilience or also anisotropically oriented or simply "oriented" PSAs are used. Anisotropically oriented PSAs tend to move back to their original state after being stretched in a given direction by the "entropy-elastic behavior".

(Meth) acrylate PSAs are preferably used as the electrically conductive PSAs with a resilience.

For the purposes of the invention, preference is given to a PSA which can be obtained by radical polymerization, where

At least 50% by weight of the PSA is based on at least one acrylic monomer from the group of the compounds of the following general formula:

where R ₁ = H or CH ₃ and the radical R ₂ = H or CH ₃ or is selected from the group of branched or unbranched, saturated alkyl groups with 2-30

Carbon atoms.

The average molecular weight M _{w of} the PSA is at least 200,000 g / mol,

• The pressure-sensitive adhesive applied to a carrier has a preferred direction which, according to test B, can be determined via the shrinkback in the free film and is at least greater than 3%.

• which contains an effective portion of at least one electrically conductive component

The monomers are preferably chosen such that the resulting polymers can be used as pressure-sensitive adhesives at room temperature or higher temperatures, in particular in such a way that the resulting polymers have pressure-sensitive adhesive properties. create according to the "Handbook of Pressure Sensitive Adhesive Technology" by Donatas Satas (van Nostrand, New York 1989).

In a further inventive design, the comonomer composition is selected such that the PSAs can be used as heat-activatable PSAs.

The polymers, which are preferably used as electrically conductive PSAs with a resilience, can preferably be obtained by polymerizing a monomer mixture which consists of acrylic acid esters and / or methacrylic acid esters and / or their free acids with the formula CH ₂ = C (R ) (COOR ₂ ), where Ri = H or CH ₃ and R _{2 is} an alkyl chain with 1 - 20 C atoms or H.

The molecular weights M _{w of} the polyacrylates used are preferably M _w > 200,000 g / mol.

In a very preferred manner, acrylic or methacrylic monomers are used which consist of acrylic and methacrylic acid esters with alkyl groups of 4 to 14 carbon atoms, preferably comprising 4 to 9 carbon atoms. Specific examples, without wishing to be limited by this list, are methacrylate, methyl methacrylate, ethyl acrylate, n-butyl acrylate, n-butyl methacrylate, n-pentia acrylate, n-hexyl acrylate, n-heptyl acrylate, n-octyl acrylate, n-octyl methacrylate , n-nonyl acrylate, lauryl acrylate, stearyl acrylate, behenyl acrylate, and their branched isomers, such as Isobutyl acrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, isooctyl acrylate, isooctyl methacrylate. Further classes of compound to be used are monofunctional acrylates or methacrylates of bridged cycloalkyl alcohols, consisting of at least 6 carbon atoms. The cycloalkyl alcohols can also be substituted, e.g. by C-1-6 alkyl groups, halogen atoms or cyano groups. Specific examples are cyclohexyl methacrylate, isobornyl acrylate, isobomyl methacrylate and 3,5-dimethyladamantylacrylate.

In one procedure, monomers are used which contain polar groups such as carboxyl radicals, sulfonic and phosphonic acid, hydroxyl radicals, lactam and lactone, N-substituted amide, N-substituted amine, carbamate, epoxy, thiol, alkoxy. Wear cyan residue, ether or similar. Moderate basic monomers are, for example, N, N-dialkyl-substituted amides, such as, for example, N, N-dimethylacrylamide, N, N-dimethylmethylmethacrylamide, N-tert.-butylacrylamide, N-vinylpyrrolidone, N-vinyllactam, dimethylaminoethyl methacrylate, dimethylaminoethylacrylate, diethylamethylamate, diethylamate , N-methylol methacrylamide, N- (buthoxymethyl) methacrylamide, N-methylolacrylamide, N- (ethoxymethyl) acrylamide, N-isopropylacrylamide, although this list is not exhaustive.

Further preferred examples are hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, allyl alcohol, maleic anhydride, itaconic anhydride, itaconic acid, glyceridyl methacrylate, phenoxyethylacrylate, phenoxyethyl methacrylate, 2-butoxyethyl methacrylate methacrylate, 2-butoxyethyl methacrylate methacrylate, 2-butoxyethyl methacrylate methacrylate, Vinylacetic acid, tetrahydrofufurylacrlyat, ß-acryloyloxypropionic acid, trichloracrylic acid, fumaric acid, crotonic acid, aconitic acid, dimethylacrylic acid, although this list is not exhaustive.

In a further very preferred procedure, vinyl esters, vinyl ethers, vinyl halides, vinylidene halides, vinyl compounds with aromatic cycles and heterocycles in the α-position are used as monomers. Here too, a few examples are not exclusively mentioned: vinyl acetate, vinylformamide, vinylpyridine, ethylvinyiether, vinyl chloride, vinylidene chloride and acrylonitrile.

In a further procedure, photoinitiators with a copolymerizable double bond are also used. Norrish-I and -Il photoinitiators are suitable as photoinitiators. Examples are, for example, benzoin acrylate and an acrylated benzophenone from UCB (Ebecryl P 36 ^® ). In principle, all photoinitiators known to the person skilled in the art can be copolymerized, which can crosslink the polymer via a radical mechanism under UV radiation. An overview of possible usable photoinitiators that can be functionalized with a double bond is given in Fouassier: "Photoinititation, Photopolymerization and Photocuring: Fundamentals and Applications", Hanser-Verlag, Munich 1995. In addition, Carroy et al. In "Chemistry and Technology of UV and EB Formulation for Coatings, Inks and Paints ", Oldring (ed.), 1994, SITA, London.

In a further preferred procedure, monomers are added to the described comonomers which have a high static glass transition temperature. Zen. Aromatic vinyl compounds, such as, for example, styrene, are suitable as components, the aromatic nuclei preferably consisting of C ₄ to C _{18 building} blocks and also being able to contain heteroatoms. Particularly preferred examples are 4-vinylpyridine, N-vinylphthalimide, methylstyrene, 3,4-dimethoxystyrene, 4-vinylbenzoic acid, benzyl acrylate, benzyl methacrylate, phenyl acrylate, phenyl methacrylate, t-butylphenyl acrylate, t-butylphenyl methacrylate, 4-biphenyl acrylate and 2-methacrylate Naphylacrylate and methacrylate as well as mixtures of those monomers, although this list is not exhaustive.

It is also a component of the inventive PSA that the PSA has a shrinkback, the shrinkback being at least 3% by a determination according to test B (shrinkback measurement in the free film). In preferred developments, PSAs are used in which the shrinkback is at least 30%, very preferably at least 50%.

Furthermore, part of the inventive PSA is an addition of an electrically conductive connection. In a preferred embodiment, electrically conductive filling materials are therefore used. Such materials include, without being restricted by this list, metal particles, metal powder, metal balls, metal fibers, where as metals e.g. Nickel, gold, silver, iron, lead, tin, zinc, stainless steel, bronze and copper or nickel coatings on copper particles, on nickel particles, on polymer balls or particles or glass microspheres can be used. Also useful are e.g. also lead / tin alloys with different compositions, e.g. by Sherrit Gordon, Ltd. Tobe offered.

In a further embodiment of the invention, electrically conductive polymers are added, such as, for example, polythiophene, substituted polythiophenes, polyethylene dioxythiophenes, polyaniline, substituted polyanilines, polyparaphenyls, substituted polyparaphenylenes, polypyrrole, substituted polypyrroles, polyacetylenes, substituted polyacetylenes, poly, phenylphenyl, poly, phenylphenyl substituted polyfurans polyalkylfluorene, substituted polyalkylfluorenes and mixtures of the above-mentioned polymers. So-called dopants can be added to improve conductivity. Various metal salts or Lewis acid or electrophiles can be used here. Examples that do not claim to be complete are p-toluenesulfonic acid or camphorsulfonic acid. sen polyvinylbenzyltrimethylammonium chloride and similar compounds cited in US 5,061,294.

In a further preferred embodiment of the invention, the diameter of the electrically conductive fillers is less than the layer thickness of the PSA. In a preferred embodiment, dispersions from ORMECON are used. Depending on the dopant and chemical composition, the added electrically conductive polymers have a conductivity between 1 and 500 S / cm.

In a further configuration, carbon compounds, such as e.g. C-60 can be added. With these compounds as well, an improved electrical conductivity can be achieved by targeted doping. Furthermore, hygroscopic salts, which are described in US Pat. No. 4,973,338, can also be used as electrically conductive substances.

Electrically conductive substances up to 50% by weight based on the poly (meth) acrylate are added. In a preferred embodiment, the proportion is 30% by weight, based on the poly (meth) acrylate. The proportion is selected in accordance with the desired electrical conductivity to be achieved. However, the proportion should not exceed an amount, so that the pressure sensitive adhesive loses the adhesive properties.

Resins may be added to the inventive PSAs for further development. All of the previously known adhesive resins described in the literature can be used as tackifying resins to be added. Representative are the pinene, indene and rosin resins, their disproportionated, hydrogenated, polymerized, esterified derivatives and salts, the aliphatic and aromatic hydrocarbon resins, terpene resins and terpene-phenolic resins as well as C5, C9 and other hydrocarbon resins. Any combination of these and other resins can be used to adjust the properties of the resulting adhesive as desired. In general, all (soluble) resins compatible with the corresponding polyacrylate can be used, in particular reference is made to all aliphatic, aromatic, alkylaromatic hydrocarbon resins, hydrocarbon resins based on pure monomers, hydrogenated hydrocarbon resins, functional hydrocarbon resins and natural resins. On the presentation of the state of knowledge in the "Handbook of Pressure Sensitive Adhesive Technology "by Donatas Satas (van Nostrand, 1989) is expressly pointed out.

Furthermore, plasticizers (plasticizers), other fillers (such as fibers, carbon black, zinc oxide, chalk, solid or hollow glass spheres, microspheres made of other materials, silicic acid, silicates), nucleating agents, blowing agents, compounding agents and / or anti-aging agents can optionally be used, eg in the form of primary and secondary antioxidants or in the form of light stabilizers.

Crosslinkers and promoters can also be added for crosslinking. Suitable crosslinkers for electron beam crosslinking and UV crosslinking are, for example, bi- or multifunctional acrylates, bi- or multifunctional isocyanates (also in blocked form) or bi- or multifunctional epoxies.

For an optional crosslinking with UV light, UV-absorbing photoinitiators can be added to the polyacrylate PSAs. Useful photoinitiators that are very easy to use are benzoin ethers, such as. As benzoin methyl ether and benzoin isopropyl ether, substituted acetophenones, such as. B. 2,2-diethoxyacetophenone (available as Irgacure 651 ^® from Ciba Geigy ^® ), 2,2-dimethoxy-2-phenyl-1-phenylethanone, dimethoxyhydroxyacetophenone, substituted α-ketols, such as. B. 2-methoxy-2-hydroxypropiophenone, aromatic sulfonyl chlorides, such as. B. 2-naphthyl sulfonyl chloride, and photoactive oximes such. B. 1-phenyl-1,2-propanedione-2- (O-ethoxycarbonyl) oxime.

The above-mentioned and other usable photoinitiators and others of the Norrish I or Norrish II type can contain the following radicals: benzophenone, acetophenone, benzil, benzoin, hydroxyalkylphenone, phenylcyclohexyl ketone, anthraquinone,

Trimethyibenzoylphosphine oxide, methylthiophenylmorpholine ketone, aminoketone, azobenzoin, thioxanthone, hexarylbisimidazole, triazine, or fluorenone, each of which

Residues can additionally be substituted with one or more halogen atoms and / or one or more alkyloxy groups and / or one or more amino groups or hydroxy groups. A representative overview is provided by Fouassier: "Photoinititation,

Photopolymerization and Photocuring: Fundamentals and Applications ", Hanser-Verlag,

Munich 1995. In addition, Carroy et al. in "Chemistry and Technology of

UV and EB Formulation for Coatings, Inks and Paints ", Oldring (ed.), 1994, SITA, London. Manufacturing process for the inventive PSAs

For the polymerization, the monomers are chosen such that the resulting polymers can be used as pressure-sensitive adhesives at room temperature or higher temperatures, in particular in such a way that the resulting polymers have pressure-sensitive adhesive properties in accordance with the "Handbook of Pressure Sensitive Adhesive Technology" by Donatas Satas (van Nostrand , New York 1989) To achieve a preferred glass transition temperature T _{G of} the polymers of T _G <25 ° C. for PSAs, the monomers are very preferably selected in accordance with what has been said above, and the quantitative composition of the monomer mixture is advantageously chosen such that after the Fox equation (G1) (cf. TG Fox, Bull. Am. Phys. Soc. 1 (1956) 123) gives the desired T _G value for the polymer.

(G1)

J - T «,

Herein n represents the running number of the monomers used, w _n the mass fraction of the respective monomer n (% by weight) and T _G , _n the respective glass transition temperature of the homopolymer from the respective monomers n in K.

Conventional radical polymerizations are advantageously carried out to prepare the poly (meth) acrylate PSAs. Initiator systems which additionally contain further radical initiators for the polymerization, in particular thermally decomposing radical-forming azo or peroxo initiators, are preferably used for the radical polymerizations. In principle, however, all of the usual initiators known to those skilled in the art for acrylates are suitable. The production of C-centered radicals is described in Houben Weyl, Methods of Organic Chemistry, Vol. E 19a, pp. 60 - 147. These methods are preferably used in analogy. Examples of radical sources are peroxides, hydroperoxides and azo compounds, and some non-exclusive examples of typical free radical initiators are potassium peroxodisulfate, dibenzoyl peroxide, cumene hydroperoxide, cyclohexanone peroxide, di-t-butyl peroxide, azodiisoic acid butyronitrile, cyclohexyl peroxyl peroxetyl peroxetyl peroxetyl peroxetyl peroxetyl peroxetyl peroxetyl peroxetyl peroxetyl peroxetyl peroxetyl peroxyl peroxyl peroxyl peroxyl peroxyl peroxyl peroxyl peroxyl peroxyl peroxyl peroxyl peroxide tetraperyl tetra peroxo In a very preferred interpretation, as radical initiator 1, 1 '-azo-bis- (cyclohexanecarbonsäuritriI) (Vazo 88 ™ from DuPont) or azodisobutyronitrile (AIBN) used.

The electrically conductive materials can be added to the monomers before the polymerization and / or after the end of the polymerization.

The average molecular weights M of the PSAs formed in the radical polymerization are very preferably selected such that they are in a range from 200,000 to 4,000,000 g / mol; PSAs with average molecular weights M _w of 400,000 to 1,400,000 g / mol are produced especially for further use as electrically conductive hotmelt PSAs with resilience. The average molecular weight is determined using size exclusion chromatography (GPC) or matrix-assisted laser desorption / ionization mass spectrometry (MALDI-MS).

The polymerization can be carried out in bulk, in the presence of one or more organic solvents, in the presence of water or in mixtures of organic solvents and water. The aim is to keep the amount of solvent used as low as possible. Suitable organic solvents are pure alkanes (eg hexane, heptane, octane, isooctane), aromatic hydrocarbons (eg benzene, toluene, xylene), esters (eg ethyl acetate, propyl, butyl or hexyl acetate), halogenated hydrocarbons (e.g. chlorobenzene), alkanols (e.g. methanol, ethanol, ethylene glycol, ethylene glycol monomethyl ether) and ethers (e.g. diethyl ether, dibutyl ether) or mixtures thereof. A water-miscible or hydrophilic cosolvent can be added to the aqueous polymerization reactions in order to ensure that the reaction mixture is in the form of a homogeneous phase during the monomer conversion. Cosolvents which can be used advantageously for the present invention are selected from the following group consisting of aliphatic alcohols, glycols, ethers, glycol ethers, pyrrolidines, N-alkylpyrrolidinones, N-alkylpyrrolidones, polyethylene glycols, polypropylene glycols, amides, carboxylic acids and salts thereof, esters, organosulfides, Sulfoxides, sulfones, alcohol derivatives, hydroxy ether derivatives, amino alcohols, ketones and the like, as well as derivatives and mixtures thereof. The polymerization time is - depending on the conversion and temperature - between 2 and 72 hours. The higher the reaction temperature that can be selected, that is, the higher the thermal stability of the reaction mixture, the shorter the reaction time that can be selected.

In order to initiate the polymerization, the entry of heat is essential for the thermally decomposing initiators. The polymerization can be initiated for the thermally decomposing initiators by heating to 50 to 160 ° C., depending on the type of initiator.

For the production, it may also be advantageous to polymerize the acrylic PSAs in bulk. The prepolymerization technique is particularly suitable here. The polymerization is initiated with UV light, but only leads to a low conversion of approximately 10 to 30%. This polymer syrup can then be e.g. are welded into foils (in the simplest case ice cubes) and then polymerized through in water to a high conversion. These pellets can then be used as acrylic hot-melt adhesives, with film materials which are compatible with the polyacrylate being particularly preferably used for the melting process. For this preparation method too, the thermally conductive material additives can be added before or after the polymerization.

Another advantageous production process for the poly (meth) acrylate PSAs is anionic polymerization. Inert solvents are preferably used as the reaction medium, e.g. aliphatic and cycloaliphatic hydrocarbons, or also aromatic hydrocarbons.

The living polymer in this case is generally represented by the structure P _L (A) -Me, where Me is a Group I metal such as lithium, sodium or potassium, and P _L (A) is a growing polymer of the acrylate monomers , The molar mass of the polymer to be produced is controlled by the ratio of the initiator concentration to the monomer concentration. Suitable polymerization initiators are, for. B. n-propyllithium, n-butyllithium, sec-butyllithium, 2-naphthyllithium, cyclohexyllithium or octyllithium, this list does not claim to be complete. Initiators based on samarium complexes for the polymerization of acrylates are also known (Macromolecules, 1995, 28, 7886) and can be used here. Difunctional initiators can also be used, such as 1, 1, 4,4-tetraphenyl-1,4-diithiobutane or 1,1,4,4-tetraphenyl-1,4-diithioisobutane. Coinitiators can also be used. Suitable coinitiators include lithium halides, alkali metal alkoxides or alkyl aluminum compounds. In a very preferred version, the ligands and coinitiators are selected so that acrylate monomers, such as, for example, n-butyl acrylate and 2-ethylhexyl acrylate, can be polymerized directly and do not have to be generated in the polymer by transesterification with the corresponding alcohol.

Controlled radical polymerization methods are also suitable for the production of polyacrylate PSAs with a narrow molecular weight distribution. A contra-reagent of the general formula is then preferably used for the polymerization:

R. -, / .R ¹ R. "S""S""-S""R ¹

0) (II)

wherein R and R ^{1 are} independently selected or the same - branched and unbranched C to C ₁₈ alkyl radicals; C ₃ to C ₁₈ alkenyl radicals; C ₃ - to C-is-alkynyl radicals;

- C to C ₁₈ alkoxy residues

- C to C ₁₈ alkyl radicals substituted by at least one OH group or a halogen atom or a silyl ether; C ₃ to C ₁₈ alkenyl radicals; C ₃ to C ₁₈ alkynyl radicals;

C ₂ -C ₁₈ heteroalkyl radicals having at least one O atom and / or one NR ^* group in the carbon chain, where R * can be any (in particular organic) radical,

- With at least one ester group, amine group, carbonate group, cyano group, isocyano group and / or epoxy group and / or C substituted with sulfur

C ₁₈ alkyl residues, C ₃ -C ₁₈ alkenyl residues, C ₃ -C ₁₈ alkynyl residues;

- C ₃ -C ₁₂ cycloalkyl radicals

- C ₆ -C ₁₈ aryl or benzyl radicals

- represent hydrogen. Control reagents of type (I) preferably consist of the following further restricted compounds:

Halogen atoms are preferably F, Cl, Br or I, more preferably Cl and Br. Both linear and branched chains are outstandingly suitable as alkyl, alkenyl and alkynyl radicals in the various substituents.

Examples of alkyl radicals which contain 1 to 18 carbon atoms are methyl, ethyl, propyl, isopropyl, butyl, isobutyl, t-butyl, pentyl, 2-pentyl, hexyl, heptyl, octyl, 2-ethylhexyl, t-octyl, Nonyl, decyl, undecyl, tridecyl, tetradecyl, hexadecyl and octadecyl. Examples of alkenyl radicals having 3 to 18 carbon atoms are propenyl, 2-butenyl, 3-butenyl, isobutenyl, n-2,4-pentadienyl, 3-methyl-2-butenyl, n-2-octenyl, n-2-dodecenyl and isododecenyl and oleyl.

Examples of alkynyl having 3 to 18 carbon atoms are propynyl, 2-butynyl, 3-butynyl, n-2-octynyl and n-2-octadecynyl. Examples of hydroxy-substituted alkyl radicals are hydroxypropyl, hydroxybutyl or hydroxy hexyl.

Examples of halogen-substituted alkyl radicals are dichlorobutyl, monobromobutyl or trichlorohexyl.

A suitable C ₂ -C ₁₈ heteroalkyl radical with at least one O atom in the carbon chain is, for example, -CH ₂ -CH ₂ -O-CH ₂ -CH ₃ . Cyclopropyl, cyclopentyl, cyclohexyl or trimethylcyclohexyl are used, for example, as C ₃ -C ₁₂ cycloalkyl radicals.

Examples of C ₆ -C ₁₈ aryl radicals are phenyl, naphthyl, benzyl, 4-tert-butylbenzyl- or other substituted phenyl, such as, for example, ethyl, toluene, xylene, mesitylene, isopropylbenzene, dichlorobenzene or bromotoluene. The above lists serve only as examples for the respective connection groups and are not exhaustive.

Also suitable are compounds de r follow ligand types as Kontrollt eagenzien ^'insertion bar

where R ^{2 can} also be selected independently of R and R ¹ from the group listed above for these radicals.

In the conventional “RAFT process”, polymerization is usually carried out only to a small extent (WO 98/01478 A1) in order to achieve the narrowest possible molecular weight distributions. However, due to the low sales, these polymers cannot be used as PSAs and especially not as hotmelt PSAs, since the high proportion of residual monomers negatively influences the adhesive properties, the residual monomers contaminate the recycled solvent in the concentration process and the corresponding self-adhesive tapes have a very high outgassing behavior would show. To avoid this disadvantage of low sales, the polymerization is initiated several times in a particularly preferred procedure.

As a further controlled radical polymerization method, nitroxide-controlled polymerizations can be carried out. For radical stabilization, nitroxides of type (Va) or (Vb) are used in a favorable procedure:

(Va) (Vb)

where R ³ , R ⁴ , R ⁵ , R ⁶ , R ⁷ , R ⁸ , R ⁹ , R ¹⁰ independently of one another denote the following compounds or atoms: i) halides, such as chlorine, bromine or iodine ii) linear, branched, cyclic and heterocyclic hydrocarbons with 1 to 20 carbon atoms, which can be saturated, unsaturated or aromatic, iii) esters -COOR ¹ , alkoxides -OR ¹² and / or phosphonates -PO (OR ¹³ ) ₂ , where R ¹¹ , R ² or R ¹³ represent residues from group ii). Compounds of (Va) or (Vb) can also be bound to polymer chains of any kind (primarily in the sense that at least one of the abovementioned radicals is one of the represents polymer chain) and thus used to build up polyacrylate PSAs.

Controlled regulators for the polymerization of compounds of the type: 2,2,5,5-tetramethyl-1-pyrrolidinyloxyl (PROXYL), 3-carbamoyl-PROXYL,

2,2-dimethyl-4,5-cyclohexyl-PROXYL, 3-oxo-PROXYL, 3-hydroxylimine-PROXYL, 3-aminomethyl-PROXYL, 3-methoxy-PROXYL, 3-t-butyl-PROXYL, 3,4- Di-t-butyl-PROXYL • 2,2,6,6-tetramethyl-1-piperidinyloxy pyrrolidinyloxyl (TEMPO), 4-benzoyloxy-TEMPO, 4-methoxy-TEMPO, 4-chloro-TEMPO, 4-hydroxy-TEMPO, 4-oxo-TEMPO,

4-amino-TEMPO, 2,2,6,6, -Tetraethyl-1-piperidinyloxyl, 2,2,6-trimethyl-6-ethyl-1-pipidinyloxyl

N-tert-butyl-1-phenyl-2-methyl propyl nitroxide N-tert-butyl-1- (2-naphthyl) -2-methyl propyl nitroxide • N-tert-butyl-1-diethylphosphono-2, 2-dimethyl propyl nitroxide N-tert-butyi-1-dibenzylphosphono-2,2-dimethyl propyl nitroxide N- (1-phenyl-2-methyl propyl) -1-diethylphosphono-1-methyl ethyl nitroxide di-t-butyl nitroxide Diphenyl nitroxide • t-Butyl-t-amyl nitroxide

A number of other polymerization methods by which the PSAs can be prepared in an alternative procedure can be selected from the prior art: US 4,581,429 A discloses a controlled radical polymerization process which uses a compound of the formula R'R "NOY as an initiator, where Y is a free radical species which can polymerize unsaturated monomers, but the reactions generally have low conversions. Polymerization of acrylates, which proceeds only in very low yields and molar masses, is particularly problematic. WO 98/13392 A1 describes open-chain alkoxyamine compounds "EP 735 052 A1 discloses a process for the production of thermoplastic elastomers with narrow molar mass distributions. WO 96/24620 A1 describes a polymerization process in which very special radical compounds, such as phosphorus-containing nitroxides, which are based on imidazolidine. ***" ren, are used. WHERE 98/44008 A1 discloses special nitroxyls which are based on morpholines, piperazinones and piperazinediones. DE 199 49 352 A1 describes heterocyclic alkoxyamines as regulators in controlled radical polymerizations. Corresponding further developments of the alkoxyamines and the corresponding free nitroxides improve the efficiency for the production of polyacrylates (Hawker, contribution to the General Meeting of the American Chemical Society, spring 1997; Husemann, contribution to the IUPAC World Polymer Meeting 1998, Gold Coast).

Atom Transfer Radical Polymerization (ATRP) can advantageously be used as a further controlled polymerization method for the synthesis of the polyacrylate PSAs, preferably monofunctional or difunctional secondary or tertiary halides as initiators and for the abstraction of the (r) halide (s) Cu, Ni, , Fe, Pd, Pt, Ru, Os, Rh, Co, Ir, Ag or Au complexes (EP 0 824 111 A1; EP 826 698 A1; EP 824 110 A1; EP 841 346 A1; EP 850 957 A1) can be used. The different possibilities of the ATRP are further described in the documents US 5,945,491 A, US 5,854,364 A and US 5,789,487 A.

Orientation, coating process, finishing of the carrier material with the electrically conductive PSA

To produce oriented PSAs, the polymers described above are preferably coated as hotmelt systems (ie from the melt). It may therefore be necessary for the manufacturing process to remove the solvent from the PSA. In principle, all methods known to the person skilled in the art can be used here. A very preferred method is the concentration via a single or twin screw extruder. The twin screw extruder can be operated in the same or opposite directions. The solvent or water is preferably distilled off over several vacuum stages. In addition, depending on the distillation temperature of the solvent, counter-heating is carried out. The residual solvent proportions are preferably <1%, more preferably <0.5% and very preferably <0.2%. The hot melt is processed from the melt.

The orientation within the PSA is generated during the coating by the coating process. For coating as a hot melt and thus also for Different coating processes can be used for orientation. In one embodiment, the electrically conductive PSAs are coated using a roll coating process and the orientation is generated by stretching. Different roller coating processes are described in the "Handbook of Pressure Sensitive Adhesive Technology" by Donatas Satas (van Nostrand, New York 1989). In a further embodiment, orientation is achieved by coating via a melting nozzle. Here, a distinction can be made between the contact and the contactless process The orientation of the electrically conductive PSA can be generated by the nozzle design inside the coating nozzle or by a stretching process after the nozzle emerges. The orientation can be freely adjusted. The stretching ratio can be controlled, for example, by the width of the nozzle gap always when the layer thickness of the PSA film on the substrate to be coated is less than the width of the nozzle gap.

In a further preferred method, the orientation is achieved by the extrusion coating. The extrusion coating is preferably carried out with an extrusion die. The extrusion dies used can advantageously come from one of the following three categories: T-die, fish-tail die and bow-die. The individual types differ in the shape of their flow channel. The shape of the extrusion nozzle can also generate an orientation within the hotmelt PSA. Furthermore, analogous to the melt nozzle coating, orientation can also be achieved after stretching out the nozzle by stretching the PSA film.

To produce oriented (meth) acrylate PSAs, it is particularly preferred to coat an ironing nozzle on a carrier, in such a way that a polymer layer is formed on the carrier by a relative movement from nozzle to carrier. The time between the coating and the crosslinking is advantageously short. In a preferred procedure, crosslinking takes place after less than 60 minutes, in a more preferred procedure after less than 3 minutes, in an extremely preferred procedure in the in-line process after less than 5 seconds.

The carrier material equipped with an electrically conductive PSA can be a single-sided or double-sided adhesive tape. Transfer tapes are produced in a very preferred embodiment. All siliconized or fluorinated films with a release effect are suitable as the carrier material. BOPP, MOPP, PET, PVC, PUR, PE, PE / EVA, EPDM, PP and PE are mentioned as examples of film materials. Release papers (glassine papers, kraft papers, polyolefinically coated papers) can also be used for transfer tapes.

In the event that the carrier material remains in the PSA (e.g. in the form of a carrier film), a carrier material is preferably used which also has a high electrical conductivity. In this case e.g. Metal or metallized foils or metal-doped foils can be used.

Particularly preferred foils are made of aluminum, copper, stainless steel or metal alloys, without this list claiming to be complete. In another design, a polymeric carrier material, e.g. PE. PP, polyimide, PET, PVC, PUR or nylon selected and provided with a metal layer on one or two sides. As metals e.g. Use aluminum, chrome, nickel, copper, nickel alloys, copper alloys, silver, gold or mixtures of these. In a preferred technique, these metals are applied to the foils by the sputtering technique with very thin layers.

Furthermore, metallized fabrics can also be used as carrier materials. Examples of this are e.g. in US 5,939,190.

The best orientation effects are achieved by placing them on a cold surface. Therefore, the carrier material should be cooled directly by a roller during the coating. The roller can be cooled by a liquid film / contact film from the outside or from the inside or by a cooling gas. The cooling gas can also be used to cool the PSA emerging from the coating nozzle. In a preferred procedure, the roller is wetted with a contact medium, which is then located between the roller and the carrier material. Preferred embodiments for implementing such a technique are described below.

Both a melting die and an extrusion die can be used for this process. In a very preferred procedure, the roller is temperature, cooled to temperatures below 10 ° C in a very preferred procedure. The roller should also rotate.

In a further procedure of this manufacturing process, the roller is also used to crosslink the oriented PSA.

For UV crosslinking, irradiation is carried out using short-wave ultraviolet radiation in a wavelength range from 200 to 400 nm, depending on the UV photoinitiator used, in particular using high-pressure or medium-pressure mercury lamps at an output of 80 to 240 W / cm , The radiation intensity is adapted to the respective quantum yield of the UV photoinitiator, the degree of crosslinking to be set and the degree of orientation.

It is also possible to crosslink the electrically conductive and oriented PSAs with electron beams. Typical radiation devices that can be used are linear cathode systems, scanner systems or segment cathode systems if they are electron beam accelerators. A detailed description of the prior art and the most important process parameters can be found at Skelhome, Electron Beam Processing, in Chemistry and Technology of UV and EB formulation for Coatings, Inks and Paints, Vol. 1, 1991, SITA, London. The typical acceleration voltages are in the range between 50 kV and 500 kV, preferably 80 kV and 300 kV. The spreading doses used range between 5 and 150 kGy, in particular between 20 and 100 kGy.

Both crosslinking methods can also be used or other methods which enable high-energy radiation.

In a further preferred production method, the electrically conductive and oriented PSAs are coated on a roller provided with a contact medium. The contact medium can in turn cool the PSA very quickly. It is then advantageous to laminate onto the carrier material later.

Furthermore, a material can be used as the contact medium that is able to make contact between the PSA and the roller surface, in particular a material that fills the voids between the carrier material and the roller surface (for example, unevenness in the roller surface, bubbles). To implement this technology, a rotating cooling roller with a contact medium coated. In a preferred procedure, a liquid, such as water, is chosen as the contact medium.

For water as the contact medium, for example, alkyl alcohols such as ethanol, propanol, butanol, hexanol are suitable as additives, without wishing to restrict the choice of alcohols by these examples. Long-chain alcohols, polyglycols, ketones, amines, carboxylates, sulfonates and the like are also very advantageous. Many of these compounds lower the surface tension or increase the conductivity.

A reduction in the surface tension can also be achieved by adding small amounts of nonionic and / or anionic and / or cationic surfactants to the contact medium. In the simplest case, commercial detergents or soap solutions can be used for this, preferably in a concentration of a few g / l in water as the contact medium. Special surfactants, which can also be used at low concentrations, are particularly suitable. Examples include sulfonium surfactants (e.g. β-di (hydroxyalkyl) sulfonium salt), furthermore, for example, ethoxylated nonylphenylsulfonic acid ammonium salts or block copolymers, in particular diblocks. In particular, reference is made to the state of the art under "surfactants" in Ullmann's Encyclopedia of Industrial Chemistry, Sixth Edition, 2000 Electronic Release, Wiiey-VCH, Weinheim 2000.

The aforementioned liquids can also be used as contact media without the addition of water, either individually or in combination with one another. In order to improve the properties of the contact medium (for example to increase the shear resistance, reduce the transfer of surfactants or the like to the liner surface and thus improve cleaning options for the end product), salts, gels and similar viscosity-increasing additives can also advantageously be added to the contact medium and / or the additives used , Furthermore, the roller can be macroscopically smooth or have a slightly structured surface. It has proven useful if it has a surface structure, in particular a roughening of the surface. The wetting by the contact medium can thereby be improved. The coating process runs particularly well if the roller can be tempered, preferably in a range from -30 ° C. to 200 ° C., very particularly preferably from 5 ° C. to 25 ° C.

The contact medium will preferably be applied to the roller. A second roller, which receives the contact medium, can be used for the continuous wetting of the coating roller. But it is also possible that it is applied without contact, for example by spraying.

For the variant of the manufacturing process, in which the roller is used simultaneously e.g. is used with electron beams, a grounded metal roller is usually used, which absorbs the incident electrons and the resulting X-rays.

The roller is usually covered with a protective layer to prevent corrosion. This is preferably selected so that it is well wetted by the contact medium. Generally the surface is conductive. However, it can also be cheaper to coat them with one or more layers of insulating or semiconducting material.

In the case of a liquid as the contact medium, one can proceed in an outstanding manner if a second roller, advantageously with a wettable or absorbent surface, runs through a bath with the contact medium, is wetted or soaked with the contact medium, and is in contact with the roller Apply or spread film of this contact medium.

In a preferred procedure, the PSA is coated and crosslinked directly on the roller provided with the contact medium. The methods and systems described for UV crosslinking and ES crosslinking can in turn be used for this. After crosslinking, the electrically conductive and oriented PSA is then transferred to a carrier material. The carrier materials already cited can be used.

The degree of orientation within the electrically conductive PSAs depends on the coating process. The orientation can, for example, by the nozzle and Coating temperature and controlled by the molecular weight of the polymer.

The degree of orientation is freely adjustable through the width of the nozzle gap. The thicker the PSA film that is pressed out of the coating nozzle, the more the adhesive can be stretched onto a thinner PSA film on the carrier material. In addition to the freely adjustable nozzle width, this stretching process can also be freely adjusted by the web speed of the decreasing carrier material.

The orientation of the adhesive can also be measured with a polarimeter, with infrared dichroism or with X-ray scattering. It is known that the orientation in acrylic PSAs in the uncrosslinked state is in many cases only retained for a few days. The system relaxes during rest or storage and loses its preferred direction. This effect can be significantly enhanced by crosslinking after coating. The relaxation of the oriented polymer chains converges to zero, and the oriented PSAs can be stored for a very long time without losing their preferred direction.

In a preferred method, the degree of orientation is determined by measuring the shrinkback in the free film (see Test B).

In addition to the described methods, the orientation can also be generated after the coating. A stretchable carrier material is then preferably used here, in which case the PSA is also stretched when expanded. In this case, PSAs conventionally coated from solution or water can also be used. In a preferred procedure, this stretched PSA is in turn crosslinked with actinic radiation. use

Furthermore, the invention relates to the use of the electrically conductive and oriented PSAs for bonding components in the electrical and electronics industry. In a preferred embodiment, the inventive PSAs are as Transfer tapes used. In this case, the release paper is removed to bond electrically conductive substances. If very narrow conductor tracks are glued in parallel, the direction of gluing is chosen such that the inventive electrically conductive PSA has a resilience in the direction of the next parallel conductor track. In this way, short circuits can be avoided, since the PSA does not flow out in this direction compared to conventional electrically conductive PSAs.

Another advantage is the electrically conductive, pressure-sensitive die-cut parts which are particularly easy to produce and are dimensionally stable even during bonding and are therefore very effective for bonding very small electrical parts. Another advantage of the electrically conductive and oriented PSAs is their reversibility. As a result of the orientation, the inventive PSAs can be stretched in the oriented direction, which in turn leads to a decrease in the adhesive strength and the bag. In this way, electrically conductive substances bonded to the inventive PSA can be separated again. In a further embodiment, the inventive PSA has anisotropic electrically conductive properties. Due to the orientation of the polymer chains, the electrically conductive filling materials are pulled apart in a preferred direction and lose contact with one another. As a result of this process, the electrical conductivity is reduced in the orientation direction, so that the PSAs and therefore also the corresponding PSA tapes likewise have anisotropic electrical conductivities.

Examples

The invention is explained in more detail below by examples and experiments without restricting the generality.

The following test methods were used to examine the samples: G§! Permeationsch o ^

The average molecular weight M and the polydispersity PD were determined by gel permeation chromatography. THF with 0.1% by volume of trifluoroacetic acid was used as the eluent. The measurement was carried out at 25 ° C. PSS-SDV, 5 μ, 10 ³ A, ID 8.0 mm × 50 mm was used as the guard column. The columns were used for separation PSS-SDV, 5 μ, 10 ³ as well as 10 ⁵ and 10 ⁶ with ID 8.0 mm x 300 mm each. The sample concentration was 4 g / l, the flow rate 1.0 ml per minute. It was measured against PMMA standards.

Measurement of the back shrink. (Test.B) _

Strips of at least 30 mm wide and 20 cm long were cut parallel to the coating direction of the hot melt. In the case of bulk applications at 100 g / m ² , 4 strips were laminated one above the other, at 50 g / m ² 8 strips were laminated one above the other in order to obtain comparable layer thicknesses. The body obtained in this way was then cut to a width of exactly 20 mm and pasted with paper strips at the respective ends at a distance of 15 cm. The test specimen prepared in this way was then suspended vertically at RT and the change in length was followed over time until no further shrinkage of the sample could be determined. The initial length reduced by the final value was then given as a shrinkback in percent based on the initial length.

To measure the orientation after a long time, the coated and oriented PSAs were stored over a longer period of time as a rag sample and then analyzed.

Contact resistance measurement (Test C)

The electrical conductivity is measured via the electrical contact resistance using the 4-wire method. For the investigation, measurements were made against aluminum and against copper. A 50 μm thick PSA film was bonded to a solid copper plate. Before the measurement, the plates were roughened with sandpaper and cleaned with ethanol. A copper foil was glued as a foil. The measuring area was 2.54 x 2.54 cm.

A 20 mm wide strip of an acrylic PSA coated on a polyester or siliconized release paper was applied to steel plates. Depending on the direction and stretching, longitudinal or transverse patterns were glued to the steel plate. The PSA strip was pressed onto the substrate twice with a 2 kg weight. The adhesive tape was then immediately removed from the substrate at 30 mm / min and at a 180 ° angle. The steel plates were washed twice with acetone and once with isopropanol washed. The measurement results are given in N / cm and are averaged from three measurements. All measurements were carried out at room temperature under air-conditioned conditions.

Electrically conductive materials used:

Silver-coated nickel particles: 20 - 40 μm diameter available from Potter Industries. Nickel particles: diameter greater than 10 μm available from Novamet, Inc.

Preparation of the samples

Polymer.1

A conventional 200 L reactor for radical polymerizations was charged with 2400 g of acrylamide, 64 kg of 2-ethylhexyl acrylate, 6.4 kg of N-isopropylacrylamide and 53.3 kg of acetone / isopropanol (95: 5). After passing through with nitrogen gas for 45 minutes while stirring, the reactor was heated to 58 ° C. and 40 g of 2,2'-azoisobutyronitrile (AIBN) were added. The outer heating bath was then heated to 75 ° C. and the reaction was carried out constantly at this outside temperature. After a reaction time of 1 h, 40 g of AIBN were again added. After 5 h and 10 h, each was diluted with 15 kg of acetone / isopropanol (95: 5). After 6 and 8 h 100 g each were dicyclohexyl peroxydicarbonate (Perkadox ^® 16, Fa. Akzo Nobel), where each dissolved in 800 g of acetone hinzu-. The reaction was stopped after a reaction time of 24 h and cooled to room temperature. The determination of the molecular weight according to test A gave an M = 754,000 g / mol with a polydispersity M / M _n = 5.3.

Polymer.2 A 200 L reactor conventional for radical polymerizations was filled with 1200 g acrylamide, 74 kg 2-ethylhexyl acrylate, 4.8 kg N-isopropylacrylamide and 53.3 kg acetone / isopropanol (95: 5). After passing through with nitrogen gas for 45 minutes while stirring, the reactor was heated to 58 ° C. and 40 g of 2,2'-azoisobutyronitrile (AIBN) were added. The outer heating bath was then heated to 75 ° C. and the reaction was carried out constantly at this outside temperature. After a reaction time of 1 h 40 g of AIBN was again added. After 5 h and 10 h, each was diluted with 15 kg of acetone / isopropanol (95: 5). After 6 and 8 h 100 g dicyclohexyl peroxydicarbonate were each (Perkadox ^® 16, Fa. Akzo Nobel) was added dissolved in each 800 g of acetone. The reaction was terminated after a reaction time of 24 h and cooled to room temperature.

The determination of the molecular weight according to test A gave an M = 812,000 g / mol with a polydispersity M _w / M _n = 5.8.

Example 1: Polymer 1 was mixed with 20% by weight of silver-coated nickel particles, based on the polymer content.

Example 2:

Polymer 1 was mixed with 30% by weight of silver-coated nickel particles based on the polymer content.

Example 3:

Polymer 2 was mixed with 20 wt .-% nickel particles based on the polymer content.

Example 4:

Polymer 2 was mixed with 30 wt .-% nickel particles based on the polymer content.

i) Pattern production for determining the shrinkback

The PSAs in solution were concentrated on a Bersdorff concentration extruder with a throughput of approx. 40 kg / h at a temperature of approx. 115 ° C. The residual solvent content after the concentration was less than 0.5% by weight. Then, through a bracket extrusion die with a die gap of 300 μm and a coating width of 33 cm at a specific coating temperature (melt temperature) at a web speed of 10 m / min, onto a layer coated with 1.5 g / m ² silicone (polydimethylsiloxane) 12 μm PET film coated. With a mass application of 100 g / m ² (approx. 100 μm thick PSA layer), a stretching ratio of 3: 1 was set, with a mass application of 50 g / m ² (approx. 50 μm thick PSA layer) a stretching ratio of 6: 1 was set , The siliconized PET film is passed over a co-rotating steel roller cooled to 5 ° C. At the point of contact of the PSA film on the PET film, the PSA film is thus cooled down immediately. The mass application was 50 or 100 g / m ² . In the in-line process, the pressure-sensitive adhesive tape is then crosslinked with electron beams after a path of approximately 5 m.

For electron irradiation, networking was carried out using a device from Electron Crosslinking AB, Halmstad, Sweden. The coated PSA tape was passed over a standard cooling roller under the Lenard window of the accelerator. At the same time, atmospheric oxygen was displaced in the radiation zone by flushing with pure nitrogen. The web speed was 10 m / min in each case. It was irradiated with an acceleration voltage of 200 kV.

Test B was carried out to determine the shrinkback.

Test C was carried out to determine the electrical conductivity. The adhesive strength was determined according to test D.

results

In a first step, two polymers with an average molecular weight M of approximately 800,000 g / mol were produced. Examples 1-4 according to the invention were produced with these PSAs. Nickel particles and silver-coated nickel particles were selected as the electrically conductive materials.

The degree of orientation of the individual PSAs was determined in a first investigation. Therefore, the shrinkback in the free film was determined in the following according to test method B. The measured values are summarized in Table 1.

All of the examples in Table 1 have a pronounced resilience. Another prerequisite for the inventive PSAs is electrical conductivity. Therefore, the electrical conductivity of the individual examples was determined in the following according to test method C. The values determined are summarized in Table 2.

Table 2: Overview of the electrical resistance determined according to test C.

All electrical resistances were determined with a layer thickness of 50 μm. The materials all had low electrical resistances and thus high electrical conductivity. By increasing the electrically conductive additives to 30 w%, the electrical resistance was again significantly reduced to <0.5 Ω.

To check the technical adhesive properties, the adhesive strength on steel was also determined. For these measurements too, the layer thickness of the PSA was 50 μm. The measured values are listed in Table 3:

The values shown in Table 3 make it clear that Examples 1-4 have pressure-sensitive properties. The adhesive strength can also be controlled by the amounts of the additive. The adhesive strength drops due to high proportions of the filling material.

Claims

claims:

1. A method for producing a pressure-sensitive adhesive article which has at least one layer of an electrically conductive pressure-sensitive adhesive, characterized in that in a coating method by stretching, stretching or compressing, an at least one property anisotropic with respect to one property is produced from the electrically conductive pressure-sensitive adhesive, which in at least in one direction along the layer plane has a shrinkback of at least 3% with respect to the linear expansion of the layer, measured on the free PSA film.

2. The method according to claim 1, characterized in that the coating process is a hot melt roll coating process, a melt nozzle coating process or an extrusion coating process.

3. The method according to claim 1, characterized in that the coating method is a conventional coating method with subsequent stretching or stretching on a stretchable carrier.

4. The method according to any one of claims 1 to 3, characterized in that the electrically conductive PSA is coated on one or both sides on a sheet or tape-shaped carrier.

5. The method according to claim 4, characterized in that the carrier is a transfer belt, a release liner or an electrically conductive carrier material.

6. The method according to any one of claims 1 to 5, characterized in that the PSA used is based on polyacrylate and / or polymethacrylate.

7. The method according to claim 6, characterized in that at least 50% by weight of the PSA is based on at least one acrylic monomer from the group of the compounds of the following general formula:

where Ri = H or CH ₃ and the radical R ₂ = H or CH ₃ or is selected from the group of branched or unbranched, saturated alkyl groups having 2 to 30 carbon atoms and the average molecular weight M _{w of} the PSA at least 200,000 g / mol.

8. The method according to any one of claims 1 to 6, characterized in that crosslinking agents are added to the PSA, in particular bi- or multifunctional acrylates and / or methacrylates, bi- or multifunctional isocyanates or bi- or multifunctional epoxies.

9. The method according to claim 8, characterized in that the PSA is crosslinked immediately after or during the hot-melt coating, preferably photochemically.

10. The method according to any one of claims 1 to 9, characterized in that the pressure sensitive adhesive is mixed with electrically conductive materials, in particular metal particles, metal powder, metal balls, metal fibers, the metals being in particular nickel, gold, silver and copper or the following nickel-coated particles, namely Copper particles, nickel particles, polymer spheres, polymer particles or glass microspheres or glass microspheres.

11. The method according to claim 10, characterized in that the electrically conductive materials in a proportion up to 200 wt .-%, preferably between 5 and 50 wt .-%, further preferably between 10 and 40 wt .-%, based on the Weight of the PSA to be added.

12. The method according to any one of claims 1 to 11, characterized in that the electrical conductivity of the PSA is between 1 and 500 S / cm.

13. The method according to any one of claims 1 to 12, characterized in that the electrical conductivity is anisotropic and is lower along a plane lying in the pressure-sensitive adhesive layer than transverse to the layer plane, wherein it is at least 2 S / cm in the direction transverse to the layer plane.

14. The method according to any one of claims 1 to 13, characterized in that the PSA contains further substances or additives, such as anti-aging agents, light stabilizers, antiozonants, fatty acids, plasticizers, nucleating agents, blowing agents, accelerators and / or fillers.

15. pressure sensitive adhesive articles, in particular for the bonding of two electrical parts, obtainable by a method according to one of claims 1 to 14.

16. pressure sensitive adhesive article according to claim 15 in the form of a die cut.