DE10208039A1 - Pressure sensitive adhesives containing polyethylene - Google Patents

Abstract

Aqueous dispersion of a polymer containing at least 40% by weight of so-called main monomers selected from C1 to C20 alkyl (meth) acrylates, vinyl esters of carboxylic acids containing up to 20 C atoms, vinyl aromatics with up to 20 C atoms, ethylenically unsaturated Nitriles, vinyl halides, vinyl ethers of alcohols containing 1 to 10 carbon atoms, aliphatic hydrocarbons with 4 to 8 carbon atoms and two double bonds or mixtures of these monomers, characterized in that the aqueous dispersion further comprises a polyethylene dissolved or dispersed in the dispersion , which is composed of at least 40% by weight of ethylene.

Description

The invention relates to an aqueous dispersion of a polymer, which consists of at least 40% by weight of so-called main monomers, selected from C1 to C20 alkyl (meth) acrylates, vinyl esters of up to 20 carbon atoms containing carboxylic acids, vinyl aromatics up to 20 carbon atoms, ethylenically unsaturated nitriles, Vinyl halides, vinyl ethers containing 1 to 10 C atoms Alcohols, aliphatic hydrocarbons with 4 to 8 C atoms and built up two double bonds or mixtures of these monomers is characterized in that the aqueous dispersion furthermore a solution dissolved or dispersed in the dispersion Polyethylene, which is made up of at least 40% by weight of ethylene is contains.

The invention further relates to the use of the dispersion as a pressure sensitive adhesive.

With pressure sensitive adhesives, there is a high level of stickiness (tack, Adhesion) as well as high cohesion, i.e. H. a high inner Cohesion in the adhesive layer, desired.

It is known to improve polymer adhesion To use binders, which contain monomers with long Have side chains. So-called tackifiers are also used Adhesion improvement added.

However, such measures generally worsen the Cohesion.

From WO 93/10177 the addition of small amounts of a wax Emulsion to improve the cutability of with Pressure sensitive adhesive coated papers and also the releasability known.

In contrast, the object of the present invention was that Improve the adhesion of the pressure sensitive adhesives without sacrificing it Cohesion. Another task was to improve water resistance of the bonds obtained. In particular, they should advantageous properties even when bonding on non-polar Surfaces can be achieved. In particular, these properties are said to can also be achieved if the pressure sensitive adhesives are wetting agents contain the adhesion and water resistance in general severely affect.

Accordingly, the dispersion defined at the outset and its Found use as a pressure sensitive adhesive.

The polymer dispersed in the aqueous dispersion is through radical polymerization of ethylenically unsaturated Compounds (monomers) available.

The polymer consists of at least 40% by weight, preferably of at least 60% by weight, particularly preferably at least 80% by weight so-called main monomers.

The main monomers are selected from C ₁ -C ₂₀ alkyl (meth) acrylates, vinyl esters of carboxylic acids containing up to 20 C atoms, vinyl aromatics with up to 20 C atoms, ethylenically unsaturated nitriles, vinyl halides, vinyl ethers from 1 to 10 C Alcohol-containing atoms, aliphatic hydrocarbons with 4 to 8 carbon atoms and 2 double bonds or mixtures of these monomers.

To mention are z. B. (meth) acrylic acid alkyl ester with a C ₁ -C ₁₀ alkyl radical, such as methyl methacrylate, methyl acrylate, n-butyl acrylate, ethyl acrylate and 2-ethylhexyl acrylate.

In particular, mixtures of the (meth) acrylic acid alkyl esters suitable.

Vinyl esters of carboxylic acids with 1 to 20 carbon atoms are e.g. B. Vinyl laurate, stearate, vinyl propionate, vinyl versatic acid and vinyl acetate.

Suitable vinyl aromatic compounds are vinyl toluene, a- and p- Methylstyrene, a-butylstyrene, 4-n-butylstyrene, 4-n-decylstyrene and preferably styrene. Examples of nitriles are Acrylonitrile and methacrylonitrile.

The vinyl halides are substituted with chlorine, fluorine or bromine ethylenically unsaturated compounds, preferably vinyl chloride and Vinylidene chloride.

Examples of vinyl ethers include B. vinyl methyl ether or Isobutyl ether. Vinyl ether of 1 to 4 carbon atoms is preferred containing alcohols.

As hydrocarbons with 4 to 8 carbon atoms and two olefinic Double bonds are butadiene, isoprene and chloroprene.

Preferred main monomers are the C ₁ to C ₁₀ alkyl acrylates and methacrylates, in particular C ₁ to C ₈ alkyl acrylates and methacrylates and vinyl aromatics, in particular styrene and mixtures thereof.

Methyl acrylate, methyl methacrylate, Ethyl acrylate, n-butyl acrylate, n-hexyl acrylate, octyl acrylate and 2-ethylhexyl acrylate, styrene and mixtures of these monomers.

In addition to the main monomers, the polymer can contain other monomers included, e.g. B. monomers with carboxylic acid, sulfonic acid or Phosphonic. Carboxylic acid groups are preferred. Be mentioned z. As acrylic acid, methacrylic acid, itaconic acid, maleic acid or Fumaric acid.

Other monomers are e.g. B. also hydroxyl-containing monomers, especially C ₁ -C ₁₀ hydroxyalkyl (meth) acrylates, (meth) acrylamide.

Be further as further monomers Phenyloxyethyl glycol mono (meth) acrylate, glycidyl acrylate, glycidyl methacrylate, Amino (meth) acrylates such as 2-aminoethyl (meth) acrylate called.

Crosslinking monomers may also be mentioned as further monomers.

The polymers are prepared in a preferred manner Embodiment by emulsion polymerization, it is therefore an emulsion polymer.

However, the manufacture can e.g. B. also by solution polymerization followed by dispersion in water.

In emulsion polymerization, ionic and / or non- ionic emulsifiers and / or protective colloids or stabilizers used as surfactant compounds.

A detailed description of suitable protective colloids can be found in Houben-Weyl, Methods of Organic Chemistry, Volume XIV / 1, Macromolecular Substances, Georg-Thieme-Verlag, Stuttgart, 1961, pp. 411 to 420. Both anionic, cationic and nonionic emulsifiers. Preferably, only accompanying emulsifiers are used as accompanying surface-active substances, the molecular weight of which, in contrast to the protective colloids, is usually below 2000 g / mol. Of course, if mixtures of surface-active substances are used, the individual components must be compatible with one another, which can be checked in the case of doubt using a few preliminary tests. Anionic and nonionic emulsifiers are preferably used as surface-active substances. Common accompanying emulsifiers are e.g. B. ethoxylated fatty alcohols (EO grade: 3 to 50, alkyl radical: C ₈ - to C ₃₆ ), ethoxylated mono-, di- and tri-alkylphenols (EO degree: 3 to 50, alkyl radical: C ₄ - to C ₉ ), Alkali metal salts of dialkyl esters of sulfosuccinic acid and alkali and ammonium salts of alkyl sulfates (alkyl radical: C ₈ - to C ₁₂ ), of ethoxylated alkanols (EO grade: 4 to 30, alkyl radical: C ₁₂ - to C ₁₈ ), of ethoxylated alkyl phenols (EO grade: 3 to 50, alkyl radical: C ₄ - to C ₉ ), of alkyl sulfonic acids (alkyl radical: C ₁₂ - to C ₁₈ ) and of alkylarylsulfonic acids (alkyl radical: C ₉ - to C ₁₈ ).

Other suitable emulsifiers are compounds of the general formula II


wherein R ⁵ and R ^{6 are} hydrogen or C ₄ - to C ₁₄ -alkyl and are not simultaneously hydrogen, and X and Y can be alkali metal ions and / or ammonium ions. R ⁵ , R ^{6 are} preferably linear or branched alkyl radicals having 6 to 18 carbon atoms or hydrogen and in particular having 6, 12 and 16 carbon atoms, where R ⁵ and R ^{6 are} not both hydrogen at the same time. X and Y are preferably sodium, potassium or ammonium ions, with sodium being particularly preferred. Compounds II in which X and Y are sodium, R ^{5 is} a branched alkyl radical having 12 C atoms and R ^{6 is} hydrogen or R ⁵ are particularly advantageous. Technical mixtures are frequently used which have a proportion of 50 to 90% by weight of the monoalkylated product, for example Dowfax® 2A1 (trademark of the Dow Chemical Company).

Suitable emulsifiers can also be found in Houben-Weyl, Methods der organic chemistry, volume 14/1, macromolecular substances, Georg Thieme Verlag, Stuttgart, 1961, pages 192 to 208.

Trade names of emulsifiers are e.g. B. Dowfax®2 A1, Emulan® NP 50, Dextrol® OC 50, emulsifier 825, emulsifier 825 S. Emulan® OG, Texapon® NSO, Nekanil® 904 S. Lumiten® I-RA, Lumiten E 3065, Disponil FES 77, Lutensol AT 18, Steinapol VSL, Emulphor NPS 25.

The surfactant is usually used in amounts of 0.1 to 10 wt .-%, based on the monomers to be polymerized used.

Water-soluble initiators for emulsion polymerization are z. B. ammonium and alkali metal salts of peroxidic sulfuric acid, z. As sodium peroxodisulfate, hydrogen peroxide or organic Peroxides, e.g. B. tert-butyl hydroperoxide.

So-called are also suitable Reduction-Oxygen (Red-Ox) initiator systems.

The Red-Ox initiator systems usually consist of at least one inorganic reducing agent and an inorganic or organic oxidizing agent.

The oxidation component is e.g. B. the already The aforementioned initiators for emulsion polymerization.

The reduction components are e.g. B. um Alkali metal salts of sulfurous acid, such as. B. sodium sulfite, Sodium hydrogen sulfite, alkali salts of disulfuric acid such as Sodium disulfite, bisulfite addition compounds more aliphatic Aldehydes and ketones such as acetone bisulfite or reducing agents such as Hydroxymethanesulfinic acid and its salts, or ascorbic acid. The Red-Ox initiator systems can be more soluble when used Metal compounds, their metallic component in several Severity levels can occur.

Common red-ox initiator systems are e.g. B. Ascorbic acid / iron (II) sulfate / sodium peroxodisulfate, tert-butyl hydroperoxide / sodium disulfite, tert-butyl hydroperoxide / Na hydroxymethanesulfinate. The individual components, e.g. B. the reduction component, can also be mixtures e.g. B. a mixture of the Sodium salt of hydroxymethanesulfinic acid and sodium disulfite.

The compounds mentioned are mostly in the form of aqueous solutions used, the lower concentration by the in the Dispersion acceptable amount of water and the upper concentration determines the solubility of the compound in question in water is. The concentration is generally 0.1 to 30% by weight, preferably 0.5 to 20% by weight, particularly preferably 1.0 to 10 wt .-%, based on the solution.

The amount of initiators is generally 0.1 to 10 wt .-%, preferably 0.5 to 5 wt .-%, based on the polymerizing monomers. There can also be several different ones Initiators are used in emulsion polymerization.

Regulators can be used in the polymerization, e.g. B. in Amounts from 0 to 0.8 parts by weight, based on 100 parts by weight of the monomers to be polymerized, by means of which the molecular weight is reduced becomes. Are suitable for. B. Compounds with a thiol group such as tert-butyl mercaptan, ethyl thioglycolate, Mercaptoethynol, mercaptopropyltrimethoxysilane or tert-dodecyl mercaptan.

The emulsion polymerization usually takes place at 30 to 130, preferably 50 to 90 ° C. The polymerization medium can both only from water, as well as from mixtures of water and thus miscible liquids such as methanol exist. Preferably only water is used. The emulsion polymerization can be both Batch process as well as in the form of a feed process, including step or gradient driving. The feed process is preferred, in which one part of the Submit polymerization approach to the polymerization temperature heated, polymerized and then the rest of the Polymerization approach, usually over several spatially separated Inlets, one or more of which are in pure monomer or contained in emulsified form, continuously, in stages or by superimposing a concentration gradient below Maintenance of the polymerization of the polymerization zone supplies. In the polymerization, z. B. for better Setting the particle size a polymer seed can be submitted.

The way in which the initiator over the course of the radical aqueous emulsion polymerization the polymerization vessel is added is known to those of ordinary skill in the art. It can both completely placed in the polymerization vessel, as also according to its consumption in the course of the radical aqueous emulsion polymerization continuously or in stages be used. In particular, this depends on the chemical Nature of the initiator system as well as of the Polymerization temperature from. A part is preferably presented and the rest after Provided the consumption of the polymerization zone.

To remove the residual monomers is usually also after End of actual emulsion polymerization, d. H. after one Conversion of the monomers of at least 95%, initiator added.

The individual components can the reactor in the feed process from above, in the side or from below through the reactor floor be added.

In the emulsion polymerization, aqueous dispersions of Polymers usually with solids contents of 15 to 75% by weight, preferably from 40 to 75% by weight.

For a high space / time yield of the reactor are dispersions preferred with the highest possible solids content. Around To be able to reach solids contents> 60% by weight, one should or adjust the polymodal particle size, otherwise the viscosity becomes too high and the dispersion is no longer manageable. The Generation of a new generation of particles can, for example by adding seeds (EP 81083), by adding excess Emulsifier amounts or by adding mini emulsions. Another advantage with the low viscosity at high Solid content is the better Coating behavior at high solids contents. The generation of a new / new generations of particles can occur at any time respectively. It depends on the for a low viscosity desired particle size distribution.

The polymer thus produced is preferably in the form of its aqueous dispersion used.

The glass transition temperature of the polymer or Emulsion polymer is preferably -60 to 0 ° C, particularly preferred -60 to -10 ° C and very particularly preferably -50 to -20 ° C.

The glass transition temperature can be as usual Differential thermal analysis or differentail scanning calorimetry (see eg ASTM 3418/82, so-called "midpoint temperature").

The dispersion of the invention contains, in addition to the above Polymers a polyethylene in dissolved or preferably dispersed Shape.

Polyethylene is understood to mean a polymer which at least 40% by weight, in particular at least 60% by weight, of ethylene is constructed.

In addition to ethylene, the polyethylene can contain other monomers Construction components included.

May be mentioned for. B. olefins such as propylene, 1-butene, 1-pentene, 1-hexene, 1-octene or 1-decene, or those already mentioned above Main monomers or other monomers.

The polyethylene is dissolved in the aqueous dispersion or dispersed.

For this purpose, the polyethylenes preferably have a polar content Groups, especially hydroxyl groups, amino groups, acid groups or salt groups.

The polyethylenes preferably contain acid groups, especially carboxylic acid groups.

Polar groups, especially acid groups, can be formed by Copolymerization with appropriate monomers in the polyethylene be introduced.

In particular, mono- or dicarboxylic acids such as Acrylic acid, methacrylic acid or maleic acid.

A content of polar groups, e.g. B. carboxylic acid groups, in However, polyethylene can also be added by subsequent polymer-analog Implementation, e.g. B. oxidation with oxygen can be achieved.

The polyethylene preferably contains polar groups (see above), particularly preferred especially by acid groups of carboxylic acid groups from 0.01 to 1 mole per 100 g of polyethylene; the content is particularly preferably at least 0.2 mol per 100 g polyethylene. The content generally does not exceed 0.8 moles, or 0.6 moles per 100 g.

The polyethylene is preferably a Polyethylene wax.

The polyethylene preferably has a weight average Molecular weight Mw from 1000 to 20,000 g / mol, particularly preferably from 3000 to 18,000 g / mol and very particularly preferably from 5,000 to 15,000 g / mol (determined by gel permeation chromatography).

The polyethylenes preferably have a density of 0.8 to 1.0 g / cm ³ , preferably 0.90 to 0.96 g / cm ³ and particularly preferably 0.93 to 0.95 g / cm ³ , measured at 23 ° C. The melt viscosities are preferably in the range from 20 to 20,000 centri Stokes (cSt), preferably in the range from 800 to 2,000 cSt, measured at 120 ° C., which corresponds to a molecular weight M _w of at most 40,000 g, preferably at most 10,000 g and particularly preferably at most 7500 g. The molecular weight distribution is preferably in the range from 2 to 10. The melting points are preferably in the range from 60 to 125 ° C., preferably 80 to 120 ° C.

Polyethylenes are made by polymerization or copolymerization made by ethylene.

The manufacturing process can be roughly described in Low pressure processes, carried out at 20 to 100 bar, and high pressure processes, performed at 500 to 4000 bar, divide. The High pressure process is a radical polymerization process, which in the Generally works without a catalyst. To start the radical chain reaction is usually used one or more organic peroxides, for example the Trigonox® or Perkadox® brands from Akzo Nobel, or air or atmospheric oxygen. The cheapest and therefore most widely used radical starter is air or atmospheric oxygen.

To adjust the appropriate molecular weight you can use suitable molecular weight regulators.

A commonly used regulator is hydrogen, but it is used in the Use of air or atmospheric oxygen as a radical starter Formation of oxyhydrogen gas can result and therefore causes safety concerns.

Other commonly used regulators are carbon monoxide CO and alkanes such as ethane or propane. Carbon monoxide is strong toxic, so consuming when used Security measures are required. Gaseous regulators such as ethane and propane also require strict security rules.

The polyethylenes can first be dissolved in water or be dispersed and this solution or dispersion can then Polymer dispersion can be added.

The polyethylenes can also be incorporated directly into the polymer dispersion are given.

As far as the content of polar groups is not sufficient, the To disperse polyethylene, emulsifiers and Protective colloids are used. Consider z. B. the above mentioned emulsifiers and protective colloids.

The weight fraction of the polyethylene is preferably 2 to 20 parts by weight per 100 g parts by weight of the sum of polymer and Polyethylene (solid, i.e. without water, solvent).

In particular, the proportion by weight of the polyethylene is at least 4 parts by weight per 100 parts by weight of polymer + polyethylene.

The content of the polyethylene is preferably less than 15% by weight. Parts, particularly preferably less than 10 parts by weight, based on 100 parts by weight of polymer + polyethylene.

The aqueous dispersion according to the invention is particularly suitable as an adhesive, particularly preferably as a pressure sensitive adhesive.

The aqueous polymer dispersion can do this without further additives Find use.

When used as a pressure sensitive adhesive, the aqueous dispersion a tackifier, d. H. a tackifying resin can be added. Tackifiers are e.g. B. from Adhesive Age, July 1987, pages 19-23 or Polym. Mater. Sci. Closely. 61 (1989), pages 588-592.

Tackifiers are e.g. B. natural resins such as rosins and their by disproportionation or isomerization, polymerization, Dimerization, hydrogenation resulting derivatives. These can be in their salt form (e.g. with mono- or polyvalent counterions (Cations) or preferably in their esterified form. Alcohols used for the esterification can be one or be multivalued. Examples are methanol, ethanediol, Diethylene glycol, triethylene glycol, 1,2,3-propanethiol, pentaerythritol.

Also find hydrocarbon resins, e.g. B. coumarone Inden resins, polyterpene resins, hydrocarbon resins based unsaturated CH compounds, such as butadiene, pentene, methylbutene, Isoprene, piperylene, divinyl methane, pentadiene, cyclopentene, Cyclopentadiene, cyclohexadiene, styrene, α-methylstyrene, vinyl toluene Use.

Polyacrylates which have a low molecular weight are also increasingly being used as tackifiers. These polyacrylates preferably have a weight-average molecular weight M _{w of} less than 30,000. The polyacrylates preferably consist of at least 60, in particular at least 80% by weight of C ₁ -C ₈ alkyl (meth) acrylates.

Preferred tackifiers are natural or chemically modified Rosins. Rosin resins mainly exist Part from abietic acid or abietic acid derivatives.

The tackifiers can easily be the inventive Polymers, preferably the aqueous dispersions of the Polymers are added. The tackifiers are preferably present itself in the form of an aqueous dispersion.

The amount by weight of the tackifier is preferably 5 to 100 parts by weight. particularly preferably 10 to 50 parts by weight. based per 100 parts by weight of polymer. (Solid / solid).

In addition to tackifiers, e.g. B. other additives such. B. Thickeners, preferably associative thickeners, defoamers, Plasticizers, pigments, wetting agents or fillers at Find use as a pressure sensitive adhesive. The PSAs according to the invention therefore contain, in addition to the aqueous Polymer dispersion, if necessary, also tackifier and / or the above additives.

For better wetting of surfaces, the Pressure sensitive adhesives, in particular wetting aids, e.g. B. Fatty alcohol ethoxylates, alkylphenol ethoxylates, sulfosuccinic acid esters, Nonylphenol ethoxylates, polyoxyethylenes / propylenes or Contain sodium dodecyl sulfonates. The amount is generally 0.05 to 5 parts by weight, in particular 0.1 to 3 parts by weight per 100 parts by weight Parts polymer (solid).

The pressure sensitive adhesives are suitable for the production of self-adhesive Articles such as labels, foils or adhesive tapes. The pressure sensitive adhesive can by conventional methods, for. B. by rolling, knife coating, brushing etc. on carrier, e.g. B. paper or polymer films, preferred Consisting of polyethylene, polypropylene, the biaxial or monoaxial can be stretched, polyethylene terephthalate, polyvinyl chloride, Polystyrene, polyamide or metal can be applied. In particular are also suitable carriers with non-polar surfaces, for. B. from Polyolefins, especially polyethylene or polypropylene, because the Dispersions according to the invention adhere well to them. The water can preferably removed by drying at 50 to 150 ° C. The Carriers may too before or after applying the adhesive Adhesive tapes, labels or foils can be cut. For later The side of the surface coated with pressure sensitive adhesive can be used Substrates, with a release paper, e.g. B. with a siliconized paper.

The self-adhesive articles according to the invention have very good Adhesive properties, in particular good adhesion to the Substrates and high cohesion (internal strength in the Adhesive layer). These good properties are also achieved if the dispersions or pressure sensitive adhesives wetting aids contain. They also have good adhesion to non-polar ones Surfaces and are therefore particularly suitable for substrates non-polar surfaces, e.g. B. polyolefin surfaces, e.g. B. Polyethylene (HDPE or LDPE) or polypropylene.

The pressure sensitive adhesive also does not tend to rewind, i. H. he remains on the carrier after peeling z. B. the label.

The self-adhesive articles also have high water resistance. Example Acronal® A 220: aqueous dispersion of a polyacrylate, which is offered as a pressure sensitive adhesive (BASF)
Epotal® DS 2343: aqueous dispersion of a polyethylene with and an acrylic acid content of 20% by weight (commercial product from BASF)
Poligen® WE 6: aqueous dispersion of an oxidized polyethylene, dispersed in water with the help of an emulsifier (commercial product from BASF)
Lumiten® I-SC: wetting aids (sulfosuccinic acid esters)

From these starting materials the ones given in the table were given Mixed pressure sensitive adhesives and the application tests performed with the pressure sensitive adhesives.

Application test

The pressure-sensitive adhesives were coated with an application amount of 20 g / m ² on polyethylene film and dried at 90 ° C. for 3 minutes.

The peel strength (adhesion) and Shear strength (cohesion) determined.

The backing coated with pressure sensitive adhesive was cut into 25 mm wide test strips. To determine the shear strength, the test strips with a bonded area of 25 mm ^{2 were} glued to a V2A test plate, rolled up once with a 1 kg roll, stored for 10 minutes (in a standard atmosphere, 50% relative atmospheric humidity 1 bar, 23 ° C) ) and then suspended with a 1 kg weight (in a normal climate). The measure of the shear strength was the time until the weight dropped; the average of 5 measurements was calculated.

The peel strength (adhesion) was determined in each case a 2.5 cm wide test strip on a test specimen Polyethylene (HDPE) glued and with a 1 kg roll once rolled. He was then end up in the upper cheeks clamped in a tensile strain test apparatus. The tape was at 300 mm / min at a 180 ° angle from the test surface deducted d. H. the adhesive strip was bent over and parallel to the Pulled off the test sheet and measured the required force. The measure for the peel strength was the force in N / 2.5 cm, the was the average of five measurements.

The peel strength was determined 1 minute and 24 hours after the Adhesion determined. After this time, the adhesive strength is full educated.

water resistance

To determine the water resistance, the above test strips were stuck onto commercially available polyethylene shampoo bottles. The bottles were placed in a 5% aqueous shampoo solution for 24 hours. After that, the labels had not peeled off, and no peeling was discernible at the edges either. The labels were peeled off, the adhesive layer remained on the label, there were no adhesive residues on the bottle (no rewinding).

Claims (11)

1. Aqueous dispersion of a polymer which comprises at least 40% by weight of so-called main monomers selected from C1 to C20 alkyl (meth) acrylates, vinyl esters of carboxylic acids containing up to 20 C atoms, vinyl aromatics with up to 20 C atoms, is composed of ethylenically unsaturated nitriles, vinyl halides, vinyl ethers of alcohols containing 1 to 10 C atoms, aliphatic hydrocarbons with 4 to 8 C atoms and two double bonds or mixtures of these monomers, characterized in that the aqueous dispersion also contains a solution which is dissolved or dispersed in the dispersion Polyethylene, which is composed of at least 40 wt .-% of ethylene. 2. Aqueous dispersion according to claim 1, characterized in that the polymer is at least 40% by weight from C1 to C20 Alkyl (meth) acrylates. 3. Aqueous dispersion according to claim 1 or 2, characterized characterized in that the polymer is a Emulsion polymer is. 4. Aqueous dispersion according to one of claims 1 to 3, characterized in that the glass transition temperature of the Polymers is -60 to 0 ° C. 5. Aqueous dispersion according to one of claims 1 to 4, characterized in that the polyethylene in the water is dispersed. 6. Aqueous dispersion according to one of claims 1 to 5, characterized in that the polyethylene has a content of 0.01 to 1 mole of carboxylic acid groups (calculated as COOH) per 100 g of polyethylene. 7. Aqueous dispersion according to one of claims 1 to 6, characterized in that the polyethylene a weight average molecular weight of 5000 to 15000 g / mol. 8. Aqueous dispersion according to one of claims 1 to 7, characterized in that the amount of polyethylene is 2 to 20 parts by weight, based on 100 parts by weight of the total weight of the polymer and the polyethylene. 9. Use of the aqueous dispersion according to one of the claims 1 to 8 as a pressure sensitive adhesive. 10. Self-adhesive articles, in particular labels, adhesive tapes or films, available using an aqueous Dispersion according to one of claims 1 to 9 as a pressure sensitive adhesive. 11. Use of the self-adhesive article according to claim 10 non-polar surfaces.