WO2024017946A1

WO2024017946A1 - Shock-resistant pressure-sensitive adhesive compound

Info

Publication number: WO2024017946A1
Application number: PCT/EP2023/070015
Authority: WO
Inventors: Julia Befuss; Claudia Moehrke; Lena Claussen
Original assignee: Tesa Se
Priority date: 2022-07-21
Filing date: 2023-07-19
Publication date: 2024-01-25
Also published as: DE102022118334A1

Abstract

The invention relates to providing a pressure-sensitive adhesive compound which has good shock resistance, even with small layer thicknesses, without foaming having to be performed during production of the pressure-sensitive adhesive compound. In addition, the pressure-sensitive adhesive compound is intended to exhibit good adhesive properties in a wide temperature range and in particular also under heat and moisture conditions. This is achieved by means of a pressure-sensitive adhesive compound which contains: - at least one poly(meth)acrylate and - at least one filler containing in total at least 70 wt.%, based on the total weight of the filler, of one or more polyolefins, and/or one or more olefin copolymers; and is characterised in that the pressure-sensitive adhesive compound contains in total 1-13 wt.% of one or more of these fillers , based on the total weight of the pressure-sensitive adhesive compound. The invention also relates to an adhesive tape which comprises a pressure-sensitive adhesive compound according to the invention, and to uses of adhesive tapes according to the invention.

Description

Shock-resistant pressure sensitive adhesive

The present invention relates to the technical field of pressure-sensitive adhesives, as they are often used for the temporary and permanent bonding of a wide variety of substrates and components. More specifically, the invention proposes a specially filled pressure-sensitive adhesive based on poly(meth)acrylate, which, in addition to good adhesive properties, also achieves high shock resistance.

Joining separate elements is one of the central processes in manufacturing technology. In addition to other methods, such as welding and soldering, bonding, i.e. joining using an adhesive, is particularly important today. An alternative to using shapeless adhesives, which are applied from a tube, for example, are so-called adhesive tapes. The advantage of adhesive tapes is that they can be applied much more easily and with more precise positioning than liquid adhesives. They are therefore particularly suitable for miniaturized applications, such as those required in the electronics industry. It is becoming more and more important to realize the connections between the components very precisely and in a space-saving manner. In addition, due to the still considerable demand for communication and entertainment electronics worldwide, the requirements for the performance of the devices are constantly increasing, so that the adhesive tapes used are constantly subject to new, or at least growing, performance requirements.

In this context, the electronics market requires adhesive tapes with increasingly narrow geometries, especially for transportable devices such as smartphones or pads - web widths of less than 0.5 mm are now sometimes required. Nevertheless, these adhesive tapes must meet the highest performance requirements. It is therefore necessary that the bonds can withstand even the strongest shocks, such as those that occur when the device is dropped.

A common approach to meeting this requirement is to use foamed adhesive tapes. EP 2 862 901 A1 describes a viscoelastic layer which comprises microparticles with a D90 particle diameter of 30 pm or less, the proportion of the microparticles being 15 - 40% by volume, based on the volume of the viscoelastic layer, and the viscoelastic Layer can function both as a pressure-sensitive adhesive layer and as a substrate in an adhesive tape. The viscoelastic layer contains an acrylate polymer as the base polymer. The microparticles are preferably inorganic hollow bodies, in particular hollow glass spheres.

WO 2009/090119 A1 is concerned with a pressure-sensitive adhesive which contains expanded microballoons, the adhesive strength of the adhesive containing the expanded microballoons being compared to the adhesive strength of an adhesive of identical basis weight and recipe, which is achieved by destroying the cavities created by the expanded microballoons is defoamed is reduced by a maximum of 30%.

WO 2016/156305 A1 describes a pressure-sensitive adhesive strip that can be removed essentially in the bonding plane without residue or destruction by stretching and consists of one or more layers of adhesive, all of which consist of a pressure-sensitive adhesive that is foamed with microballoons, and optionally one or several intermediate carrier layers, wherein the pressure-sensitive adhesive strip consists exclusively of the said adhesive layers and optionally intermediate carrier layers and the outer upper and an outer lower surface of the pressure-sensitive adhesive strip are formed by the said adhesive layer or layers.

The subject of WO 2019/106194 A1 is a polyacrylate which is due to the following monomer composition: a) 30 to 75% by weight of at least one acrylic acid ester according to the formula (I)

CH ₂ =CH-C(O)OR ¹ (I), in which R ¹ represents a linear or branched alkyl group with 1 to 10 carbon atoms; b) 20 to 65% by weight of at least one acrylic acid ester according to the formula (II)

CH ₂ =CH-C(O)OR ² (II), in which R ² represents a phenoxyalkyl radical; c) 0 to 40% by weight of at least one acrylic acid ester of the formula (III)

CH ₂ =C(O)OR ³ (III), in which R ³ represents an alkyldiglycol radical or an alkoxyalkyl radical; d) 0.5 to 10% by weight of at least one acrylate monomer according to the formula (IV) CH ₂ =CH-C(G)OOR ⁴ (IV), in which R ⁴ represents an H atom or a hydroxyalkyl radical with 1 to 4 C atoms.

This polyacrylate serves as the basis of a pressure-sensitive adhesive, which in one embodiment is foamed. The pressure-sensitive adhesive has particularly good chemical resistance.

The foaming of pressure-sensitive adhesives using expanding foaming agents is particularly challenging in terms of processing technology, as it usually involves the introduction of heat or the application of pressure differences. Such process steps can lead to undesirable side effects, for example to premature initiation of crosslinking and thus to undesirable gelling of the mass while still in the mixing apparatus. In addition, they always require additional energy expenditure or even an additional work step and are therefore also to be viewed as critical from a sustainability perspective.

Of course, the incorporation of already expanded hollow bodies into PSA formulations, e.g. hollow glass spheres or expanded polymer spheres, is also an option. However, such hollow bodies are often very difficult or impossible to process because of their low density and comparatively large volumes.

In the prior art, attempts have also been made to equip pressure-sensitive adhesives with fillers that do not cause foaming in order to meet the requirements outlined above.

In this context, EP 1 832 638 A1 describes a pressure-sensitive adhesive containing organic fillers, which is obtainable by a process in which a crosslinker is added to the polyacrylate in the melt to form a polyacrylate copolymer ("polyacrylate") based on acrylic acid esters and/or methacrylic acid esters at least one filler is or will be added, the polyacrylate provided with the crosslinker and the filler is conveyed to a coating unit, there is applied to a web-shaped layer of another material and is crosslinked after application. The crosslinker is a thermal crosslinker, some of the acrylic acid esters and/or methacrylic acid esters contain primary hydroxy groups, and the at least one filler is an organic filler. A high proportion of fillers should be possible, while still achieving a uniform and homogeneous layer pattern when coating onto a substrate.

There is a continuing need for pressure-sensitive adhesives that have a property profile similar to that of foamed pressure-sensitive adhesives, but are nevertheless not foamed. Against this background, it was an object of the invention to provide a pressure-sensitive adhesive which has good shock resistance even at low layer thicknesses. It was a further object of the invention to provide such a pressure-sensitive adhesive without foaming having to be carried out in the production of the pressure-sensitive adhesive. In addition, the pressure-sensitive adhesive should have good adhesive properties in a wide temperature range and in particular under humid-heat conditions. A further additional object of the invention was to design the pressure-sensitive adhesive in such a way that it can be produced cost-effectively overall and efficiently in terms of the use of materials and energy.

The solution to the problem is based on the idea of equipping a poly(meth)acrylate-based pressure-sensitive adhesive with specially selected fillers.

A first and general subject of the invention is a pressure-sensitive adhesive which contains at least one poly(meth)acrylate and at least one filler, containing a total of at least 70% by weight, based on the total weight of the filler, of one or more polyolefins and/or one or more olefin copolymers; contains and is characterized in that the pressure-sensitive adhesive contains one or more of these fillers to a total of 1-13% by weight, based on the total weight of the pressure-sensitive adhesive.

According to the professional understanding, a pressure-sensitive adhesive is an adhesive that has pressure-sensitive adhesive properties, ie can form a permanent bond to a substrate even under relatively weak pressure. Corresponding pressure-sensitive adhesive tapes are often essentially free of residue from the adhesive base after use removable again. However, the connection between a pressure-sensitive adhesive and the substrate can also be so strong that a permanent bond is created that cannot be easily removed again. In general, pressure sensitive adhesives are usually permanently self-adhesive even at room temperature, which means that they have a certain viscosity and tackiness, so that they wet the surface of a substrate even with low pressure.

The adhesiveness of a pressure-sensitive adhesive tape results from the fact that a pressure-sensitive adhesive is used as the adhesive. Without wishing to be bound to this theory, it is often assumed that a pressure-sensitive adhesive can be viewed as an extremely high-viscosity liquid with an elastic component, which therefore has characteristic viscoelastic properties that lead to the permanent inherent tack and pressure-sensitive adhesive ability described above. It is assumed that mechanical deformation of PSA leads to both viscous flow processes and the build-up of elastic restoring forces. The proportionate viscous flow serves to achieve adhesion, while the proportionate elastic restoring forces are necessary in particular to achieve cohesion. The connections between rheology and pressure sensitive tack are known in the art and are described, for example, in “Satas, Handbook of Pressure Sensitive Adhesives Technology”, Third Edition, (1999), pages 153 to 203. To characterize the degree of elastic and viscous proportion, the storage modulus (G') and the loss modulus (G") are usually used, which can be determined using dynamic mechanical analysis (DMA), for example using a rheometer, as described, for example, in WO 2015/189323 A1 is disclosed. In the context of the present invention, an adhesive is preferably understood to be pressure-sensitive and therefore a pressure-sensitive adhesive if at a temperature of 23 ° C in the deformation frequency range of 10 ° to 10 ¹ rad / sec G 'and G "are each at least partially in the range of 10 ³ to 10 ⁷ Pa.

As has been shown, pressure-sensitive adhesives according to the invention have properties which make them appear particularly suitable for use in the production of electronic products. Adhesive tapes equipped with the pressure-sensitive adhesives showed good adhesive properties in conjunction with shock resistance that corresponded to or even exceeded those of foamed adhesive tapes commonly used in the electronics industry. In particular, pressure sensitive adhesives according to the invention have proven to be extremely advantageous after storage at elevated temperatures or under moist heat conditions. Within the scope of the present invention, the term “poly(meth)acrylates” includes both polyacrylates and polymethacrylates as well as copolymers of acrylates and methacrylates in accordance with those skilled in the art. Poly(meth)acrylates can contain small amounts of monomer units that are not derived from (meth)acrylates. In the context of the present invention, a “poly(meth)acrylate” is understood to mean a (co)polymer whose monomer base consists of monomers in a mass proportion of 70% or more, preferably 90% or more, particularly preferably 98% or more which are selected from the group consisting of acrylic acid, methacrylic acid, acrylic acid esters and methacrylic acid esters, the proportions being based on the mass of the monomer base. The mass fraction of acrylic acid ester and/or methacrylic acid ester is preferably 50% or more, particularly preferably 70% or more. Poly(meth)acrylates are generally accessible through radical polymerization of acrylic and/or methacrylic-based monomers and, if appropriate, other copolymerizable monomers.

The monomer base of the poly(meth)acrylate of the PSA according to the invention is basically arbitrary. The monomer composition on which the at least one poly(meth)acrylate is based preferably comprises at least two, more preferably exactly two, acrylic acid esters according to the formula (I)

CH ₂ =CH-C(O)OR ¹ (I), in which R ¹ represents a linear or branched alkyl group with 1 to 10 carbon atoms. R ¹ in the formula (I) particularly preferably represents an n-butyl group; The monomer composition therefore particularly preferably comprises n-butyl acrylate. Very particularly preferably, the monomer composition comprises at least 40% by weight of n-butyl acrylate. As has been shown, this can be used to produce particularly high-performance pressure-sensitive adhesives with a wide range of properties. In particular, the monomer composition comprises n-butyl acrylate at 42 to 92% by weight, for example at 45 to 90% by weight.

Of the at least two, preferably exactly two, acrylic acid esters according to the formula (I), one is particularly preferably n-butyl acrylate and the second is selected from the group consisting of methyl acrylate, ethyl acrylate and 2-ethylhexyl acrylate. In a particular embodiment, the monomer composition on which the at least one poly(meth)acrylate is based comprises at least one phenoxyalkyl (meth)acrylate. It has been found that such a component gives the polymer and thus the pressure sensitive adhesive improved chemical resistance and also improved moisture-heat resistance.

In this embodiment, the at least one poly(meth)acrylate is preferably due to the following monomer composition: a) 50 to 80% by weight of at least one acrylic acid ester according to the formula (I)

CH ₂ =CH-C(O)OR ¹ (I), in which R ¹ represents a linear or branched alkyl group with 1 to 10 carbon atoms; b) 15 to 45% by weight of at least one acrylic acid ester according to the formula (II)

CH ₂ =CH-C(O)OR ² (II), in which R ² represents a phenoxyalkyl radical; c) 0.5 to 10% by weight of at least one acrylate monomer according to the formula (III)

CH ₂ =CH-C(O)OR ³ (III), in which R ³ represents an H atom or a hydroxyalkyl radical with 1 to 4 carbon atoms. The percentage by weight is based on the total weight of the monomer composition.

R ¹ in the formula (I) preferably represents a radical selected from the group consisting of methyl, n-butyl and 2-ethylhexyl radicals, particularly preferably a methyl or n-butyl radical.

R ² in the formula (II) preferably represents a phenoxyethyl radical, in particular a 2-phenoxyethyl radical. Phenoxyethyl acrylate is preferably contained in the monomer composition of the poly(meth)acrylate at 22 to 38% by weight.

R ³ in the formula (III) preferably represents a hydrogen atom. The monomer composition of the poly(meth)acrylate preferably contains 0.8 to 6% by weight of acrylic acid. In particular, in the embodiment with phenoxyalkyl acrylate, the at least one poly(meth)acrylate of the PSA according to the invention is due to the following monomer composition: n-butyl acrylate at 35 to 55% by weight, methyl acrylate at 5 to 35% by weight, phenoxyethyl acrylate at 20 to 45 % by weight and acrylic acid at 1 to 5% by weight, each based on the total weight of the

Monomer composition.

In this embodiment, the poly(meth)acrylate is particularly preferably due to the following monomer composition: n-butyl acrylate at 40 to 55% by weight, methyl acrylate at 15 to 25% by weight, phenoxyethyl acrylate at 25 to 35% by weight and Acrylic acid at 1.5 to 4.5% by weight, based in each case on the total weight of the monomer composition.

The at least one poly(meth)acrylate of the PSA according to the invention is preferably crosslinked. Particularly preferably, the at least one poly(meth)acrylate is thermally crosslinked. Thermal crosslinking can be carried out under significantly milder conditions than, for example, radiation-induced crosslinking, which can occasionally have a destructive effect. According to the invention, however, it is also possible to effect crosslinking of the poly(meth)acrylate exclusively or additionally by actinic radiation, whereby any necessary or promoting crosslinking substances can be added, for example UV crosslinkers.

Preferably, the at least one poly(meth)acrylate is thermally crosslinked, i.e. by means of one or more substances that enable (initiate) and/or promote a crosslinking reaction under the influence of thermal energy. Particularly preferably, the at least one poly(meth)acrylate of the PSA according to the invention is crosslinked by means of one or more covalently reacting crosslinkers, in particular by means of one or more epoxides, and/or by means of one or more coordinative crosslinkers, in particular by means of one or more metal chelates, very particularly preferred using one or more aluminum, titanium, zirconium and/or iron chelates. Combinations of different thermal crosslinkers, for example a combination of one or more epoxides with one or more metal chelates, can therefore also be used.

In particular, the at least one poly(meth)acrylate of the PSA according to the invention is crosslinked at least by means of a compound containing several epoxy groups, very particularly preferably by means of a compound containing several epoxy groups Compound which additionally contains tertiary amine functions such as tetraglycidyl meta-xylenediamine (N,N,N',N'-tetrakis(oxiranylmethyl)-1,3-benzenedimethanamine). These compounds are preferably used in an amount of 0.03 to 0.1 part by weight, particularly preferably 0.04 to 0.07 part by weight, based in each case on 100 parts by weight of the total amount of poly( meth)acrylate (solvent-free), used.

In one embodiment, the at least one poly(meth)acrylate is crosslinked at least by means of a compound containing several epoxy groups and additionally by means of at least one aluminum chelate, for example by means of aluminum (III) acetylacetonate. Metal chelate crosslinkers are preferably used in an amount of 0.01 to 0.2 parts by weight, particularly preferably 0.05 to 0.1 parts by weight, based in each case on 100 parts by weight of the total amount of poly(meth )acrylate (solvent-free), used.

In principle, all radical or radical-controlled polymerizations can be used to produce the poly(meth)acrylate, as can combinations of different polymerization processes. In addition to conventional, free radical polymerization, these include, for example: E.g. ATRP, nitroxide/TEMPO-controlled polymerization or the RAFT process.

The pressure sensitive adhesive according to the invention can contain one or more poly(meth)acrylates. If it contains several poly(meth)acrylates, all poly(meth)acrylates are preferred poly(meth)acrylates in the sense of the above statements. Accordingly, all of the embodiments described above in some way as preferred, even if they are only described for “the at least one poly(meth)acrylate”, apply to all of these poly(meth)acrylates in the event that the PSA according to the invention contains several poly(meth)acrylates )acrylates.

In addition to the poly(meth)acrylate(s), the pressure-sensitive adhesive according to the invention contains at least one filler, which totals at least 70% by weight, based on the total weight of the filler, of one or more polyolefins and/or one or more olefin copolymers contains. According to the expert understanding, polyolefins are polymers that are produced from alkenes, usually by chain polymerization. In particular, this refers to polymers that are made up exclusively of unsubstituted alkenes.

Olefin copolymers are understood, in accordance with those skilled in the art, to mean polymers which are produced either exclusively from various unsubstituted olefins or from at least one olefin and at least one other vinyl monomer. It goes without saying that each of the monomers involved in the construction of the copolymer must be contained in a technically sensible proportion.

The at least one filler of the PSA according to the invention is preferably in the form of particles, also referred to as particles. In its pure state, the filler is therefore preferably processed in the form of a powder. The particles of the filler can in principle be present in the pressure-sensitive adhesive according to the invention both finely divided and in the form of agglomerates.

Preferably, the at least one filler has a D90 value of the volumetric particle size distribution, determined by laser diffraction as described herein, of 25 to 110 pm, more preferably of 30 to 95 pm, in particular of 35 to 90 pm.

The particles of the at least one filler are also preferably irregularly shaped; At least the majority of them do not have a geometrically regular shape such as cubes, cuboids, cones, spheres and the like. A random occurrence of particles with a geometrically regular shape to a minor extent is considered irrelevant. Without wishing to be bound to this theory, the inventors assume that the irregular shape of the particles or their irregularly shaped surface is a key reason for the excellent shock-damping properties of the pressure-sensitive adhesive according to the invention.

In principle, the at least one filler or the filler particles can be present as hollow or solid bodies. The filler or filler particles are preferably in the form of solid bodies. The PSA according to the invention also preferably contains no foaming components beyond the at least one filler, so it is preferably unfoamed. The at least one filler of the pressure-sensitive adhesive according to the invention contains one or more polyolefins and/or one or more olefin copolymers, preferably in a total amount of at least 90% by weight, more preferably in a total amount of at least 95% by weight and in particular in a total amount of at least 99% by weight. %, based on the total weight of the filler. Very particularly preferably, the at least one filler consists of one or more polyolefins and/or one or more olefin copolymers. The polyolefins and/or olefin copolymers referred to here are preferably selected from the group consisting of polyethylene (PE), polypropylene (PP) and ethylene-vinyl acetate copolymers (EVA). Polyethylene, for its part, is preferably selected from low density polyethylene (LDPE) and high density polyethylene (HDPE).

Particularly preferably, the at least one filler of the PSA according to the invention contains one or more polyolefins to a total of at least 90% by weight, more preferably to a total of at least 95% by weight and in particular to a total of at least 99% by weight, in each case based on the total weight of the filler. Very particularly preferably, the at least one filler consists of one or more polyolefins. The polyolefins referred to here are preferably selected from the group consisting of polyethylene (PE) and polypropylene (PP). Polyethylene, for its part, is preferably selected from low density polyethylene (LDPE) and high density polyethylene (HDPE).

In one embodiment, the at least one filler of the PSA according to the invention contains a total of at least 70% by weight, more preferably a total of at least 90% by weight and in particular a total of at least 99% by weight, in each case based on the total weight of the filler, of polyethylene . Very particularly preferably, the at least one filler consists of polyethylene. The polyethylene can be a specific polyethylene or a mixture of different polyethylenes.

Particularly preferably, the at least one filler of the PSA according to the invention contains a total of at least 70% by weight, more preferably a total of at least 90% by weight and in particular a total of at least 99% by weight, in each case based on the total weight of the filler, of low density Polyethylene (LDPE). Very particularly preferably, the at least one filler essentially consists of low density polyethylene (LDPE), in particular it consists of low density polyethylene (LDPE). Here too applies that the low density polyethylene can be a specific LDPE or a mixture of different low density polyethylenes.

In one embodiment, the PSA according to the invention contains at least one adhesive resin and/or at least one plasticizer.

Adhesive resins, also known as tackifying resins, are often added to pressure-sensitive adhesives to fine-tune the pressure-sensitive adhesive properties.

According to the invention, “resins” are understood to mean, in particular, those oligo- and (low-)polymer compounds whose number-average molar mass M _n is not more than 5,000 g/mol. Of course, short-chain polymerization products that arise during the polymerization of the polyacrylate according to the invention and are thereby introduced into the pressure-sensitive adhesive according to the invention are not subsumed under the term “resins”. Adhesive resins generally increase the adhesive strength, especially the “tack”, the so-called tack of a pressure sensitive adhesive.

Adhesive resins often have softening points in the range of 80 to 150 °C. The information on the softening point TE of oligomeric and polymeric compounds, such as resins, refers to the ring-ball method in accordance with DIN EN 1427:2007 with appropriate application of the provisions (examination of the oligomer or polymer sample instead of bitumen with otherwise retained procedure). The measurements are carried out in a glycerol bath.

The pressure sensitive adhesive according to the invention can contain at least one adhesive resin selected from the group consisting of pinene and indene resins; Rosin and rosin derivatives such as rosin esters, also through e.g. B. Disproportionation or hydrogenation-stabilized rosin derivatives; polyterpene resins; terpene phenolic resins; alkylphenol resins; and aliphatic, aromatic and aliphatic-aromatic hydrocarbon resins.

Adhesive resins are preferably contained in a maximum total of 30% by weight in the PSA according to the invention. One or more adhesive resins may be included. As has been shown, the behavior of a pressure-sensitive adhesive according to the invention under permanent pressure can be improved by adding adhesive resins. However, the pressure-sensitive adhesive according to the invention is particularly preferably free of adhesive resins.

In addition, a pressure sensitive adhesive according to the invention can also contain reactive resins. Reactive resins are understood to mean resins that have such functional groups that they can react chemically with other components of the pressure-sensitive adhesive, in particular the polyacrylate or polyacrylates, with suitable activation.

The pressure-sensitive adhesive according to the invention is preferably free of reactive resins.

The pressure sensitive adhesive according to the invention can contain at least one plasticizer. The plasticizer is preferably selected from the group consisting of (meth)acrylate oligomers, phthalates, hydrocarbon oils, cyclohexanedicarboxylic acid esters, benzoic acid esters, water-soluble plasticizers, soft resins, phosphates and polyphosphates. The plasticizer is particularly preferably selected from the group consisting of phthalates, cyclohexanedicarboxylic acid esters and benzoic acid esters. In particular, the plasticizer is a benzoic acid ester, very particularly preferably a dibenzoic acid ester, for example diethylene glycol dibenzoate. Plasticizers are preferably contained in the pressure-sensitive adhesive according to the invention to a total of a maximum of 30% by weight, particularly preferably a maximum of 20% by weight, in particular a maximum of 15% by weight.

As has been shown, the addition of one or more plasticizers can improve the shock resistance of a pressure sensitive adhesive according to the invention without significantly impairing the chemical resistance. This effect can be achieved to a particularly high degree by adding diethylene glycol dibenzoate.

However, the pressure-sensitive adhesive according to the invention is particularly preferably free of plasticizers.

If present, the proportion of adhesive resins and plasticizers together in the PSA according to the invention is a maximum of 40% by weight.

To optimize the properties of the PSA according to the invention, it can also contain other common additives such as dyes, pigments, electrically conductive fillers, thermally conductive fillers and the like and/or flame retardants, for example ammonium polyphosphate and its derivatives. The production of a pressure-sensitive adhesive according to the invention is preferably carried out in such a way that the poly(meth)acrylate or poly(meth)acrylates are first produced from the corresponding underlying monomer mixtures by radical polymerization and are preferably further processed as a solution. In the case of several poly(meth)acrylates, these are then thoroughly mixed. If provided, crosslinkers are added during or preferably after polymerization. If further additives are to be added, these are also added.

A pressure-sensitive adhesive according to the invention is - in accordance with the previous paragraph - preferably coated as a solution - if necessary after setting a certain solids content - onto a carrier or a release liner. The coating is preferably carried out using conventional coating processes such as anilox roller application, comma knife coating, multi-roll coating or in a printing process. The solvent can then be removed in a drying tunnel or oven.

When using thermal crosslinkers, crosslinking usually occurs in smaller proportions at room temperature and in larger proportions when heat is applied, especially during the removal of the solvent. Coordinative crosslinkers generally crosslink the polyacrylate regardless of temperature; For this reason, substances are occasionally added that initially block the crosslinker. These are then removed with the solvent so that crosslinking begins immediately at this point.

Alternatively, the coating can also be carried out using a solvent-free process. For this purpose, the polyacrylate is heated and melted in an extruder. Further process steps such as mixing with additives, filtration or degassing can take place in the extruder. The melt is then applied as a layer onto a carrier or a release liner using a calender.

Another subject of the invention is an adhesive tape which comprises a pressure-sensitive adhesive according to the invention.

In the simplest embodiment, an adhesive tape according to the invention consists of only one layer of a pressure-sensitive adhesive according to the invention. In order to be able to apply the adhesive tape rolled up into a plate roll or cross-wound into a coil without it sticking to itself, the pressure-sensitive adhesive is preferably covered with at least one release liner. In the professional understanding, release liners are only seen as an aid and not as part of the adhesive tape. The layer thickness of an adhesive tape according to the invention, which consists of only one layer of a pressure-sensitive adhesive according to the invention, is preferably a maximum of 500 pm, more preferably a maximum of 450 pm, in particular a maximum of 400 pm, very particularly preferably a maximum of 370 pm.

An adhesive tape described above is preferably used as an adhesive in the production of assembly bonds, more preferably in the production of assembly bonds in electronic, optical or precision mechanical devices. Assembly bonds are generally used for long-term, in particular permanent, bonding of two substrates.

In addition to a pressure-sensitive adhesive according to the invention, an adhesive tape according to the invention can also comprise at least one carrier and optionally also further layers, for example further pressure-sensitive adhesive layers, barrier layers, further reinforcing carrier layers, etc. In principle, there are no restrictions with regard to the design of the carrier and the other layers. Common carrier materials include fabrics, scrims and plastic films, for example PET films, polyolefin films and polyurethane films. In one embodiment, the adhesive tape according to the invention comprises a plastic film on which a layer of a pressure-sensitive adhesive according to the invention is arranged on the top and bottom. Even in the embodiments with a backing layer and possibly further layers, at least one PSA of the adhesive tape is preferably covered with a release liner in order to enable problem-free unwinding and to protect the PSA(s) from contamination. Release liners usually consist of a plastic film siliconized on one or both sides (e.g. PET or PP) or a siliconized paper carrier. They are not included in the adhesive tape, but are only temporarily connected to it as an aid.

In one embodiment, the adhesive tape according to the invention comprises a PET film or alternatively a polyurethane or synthetic rubber film as a carrier layer.

If the adhesive tape in a first variant of the above embodiment comprises a PET film as a carrier layer, this preferably has a thickness of 10 to 100 μm, thicker preferably from 12 to 80 pm, in particular from 15 to 60 pm. Also preferably, a layer of a pressure-sensitive adhesive according to the invention is arranged on the top and bottom, the layers particularly preferably being essentially identical. The thickness of the two PSA layers, independently of each other, is preferably 15 to 200 μm, in particular 30 to 150 μm. Adhesive tapes according to this variant are preferably used as adhesives in the production of assembly bonds, more preferably in the production of assembly bonds in electronic, optical or precision mechanical devices

In the second variant of the above-mentioned embodiment, the adhesive tape according to the invention comprises a polyurethane film or a synthetic rubber film and a layer of a pressure-sensitive adhesive according to the invention on the top and bottom sides; The adhesive tape preferably consists of a polyurethane film or a synthetic rubber film and a layer of a pressure-sensitive adhesive according to the invention on the top and bottom. The thickness of the film is preferably 10 to 250 pm, more preferably 20 to 220 pm. In a special embodiment, the thickness of the film is up to 250 pm, preferably 70 to 230 pm. In a further special embodiment, the thickness of the polyurethane film is 5 to 70 pm, in particular 10 to 30 pm. Polyurethane films are particularly preferred among the films.

The thickness of the PSA layers is preferably 10 to 120 pm, independently of each other, more preferably 15 to 110 pm, independently of each other. Particularly preferably, both PSA layers are essentially identical.

An adhesive tape according to this variant is preferably used as an adhesive tape that can be removed by stretching, particularly preferably for producing bonds in electronic, optical or precision mechanical devices.

A further subject of the invention is the use of a pressure-sensitive adhesive according to the invention and/or an adhesive tape according to the invention as an adhesive in the production of assembly bonds and/or bonds in electronic, optical or precision mechanical devices.

Electronic, optical and precision mechanical devices within the meaning of the invention are in particular devices such as those in Class 9 of the International Classification of Goods and Services for the Registration of Trademarks (Nice Classification); 10th edition (NCL(10-2013)); are to be classified if they are electronic, optical or precision mechanical devices, as well as clocks and timepieces in accordance with Class 14 (NCL(10-2013)), such as scientific, nautical, surveying, photographic, film, optical, weighing, measuring, signaling, control and rescue devices - and teaching apparatus and instruments;

Apparatus and instruments for conducting, switching, converting, storing, regulating and controlling electricity;

image recording, processing, transmission and reproduction devices, such as televisions and the like;

Acoustic recording, processing, transmission and reproduction apparatus, such as radios and the like;

Computers, computing devices and data processing devices, mathematical devices and instruments, computer accessories, office equipment - such as printers, fax machines, copiers, typewriters -, data storage devices;

Remote communication and multifunctional devices with remote communication functions, such as telephones, answering machines;

Chemical and physical measuring devices, control devices and instruments, such as battery chargers, multimeters, lamps, tachometers;

nautical equipment and instruments;

Optical devices and instruments;

Medical devices and instruments and those for athletes;

clocks and chronometers;

solar cell modules such as electrochemical dye solar cells, organic solar cells, thin film cells; and

Fire extinguishing equipment.

Technical development is increasingly aimed at devices that are becoming smaller and lighter so that their owner can carry them with them at all times. This is usually done by implementing low weights and suitable sizes for such devices. Such devices are called mobile devices or portable devices. At According to this development trend, precision mechanical and optical devices are increasingly (also) equipped with electronic components, which increases the possibilities for minimization. Because mobile devices are carried with them, they are exposed to increased stress - especially mechanical and chemical ones - such as bumping into edges, dropping them, coming into contact with other hard objects in the bag, but also the constant movement caused by carrying them with them. However, mobile devices are also exposed to greater stress due to the effects of moisture, temperature influences and the like than "immobile" devices, which are usually installed indoors and are not or hardly moved. Pressure-sensitive adhesives according to the invention have proven to be particularly preferred for withstanding such disruptive influences and, ideally, also to mitigate or compensate.

A pressure-sensitive adhesive according to the invention and/or an adhesive tape according to the invention is therefore preferably used for producing bonds in portable electronic, optical or precision mechanical devices. Such portable devices are in particular:

Photographic cameras, digital cameras, photography accessories (such as light meters, flash units, apertures, camera housings, lenses, etc.), film cameras, video cameras, small computers (mobile computers, pocket computers, calculators), laptops, notebooks, netbooks, ultrabooks, tablet computers, handhelds, electronic diaries and organizers (so-called “electronic organizers” or “personal digital assistants”, PDA, palmtops), modems;

Computer accessories and control units for electronic devices, such as mice, drawing pads, graphics tablets, microphones, speakers, game consoles, gamepads, remote controls, remote controls, touchpads ("touchpads");

Monitors, displays, screens, touch-sensitive screens (touchscreen devices), projectors;

Readers for electronic books (“e-books”);

Small televisions, pocket televisions, film players, video players, radios (including small and pocket radios), Walkmen, Disemen, music players for example CD, DVD, Bluray, cassettes, USB, MP3, headphones, cordless telephones, mobile phones, smartphones, walkie-talkies, hands-free devices, pagers ( pager, beeper); Mobile defibrillators, blood glucose meters, blood pressure monitors, pedometers, heart rate monitors;

flashlights, laser pointers;

Mobile detectors, optical magnifiers, long-distance vision devices, night vision devices, GPS devices, navigation devices, portable satellite communication interface devices;

data storage devices (USB sticks, external hard drives, memory cards); and

Wristwatches, digital watches, pocket watches, chain watches, stopwatches.

In particular, a pressure-sensitive adhesive according to the invention and/or an adhesive tape according to the invention is used to produce bonds in smartphones (mobile phones), tablets, notebooks, cameras, video cameras, keyboards or touchpads.

Examples

Production of poly(meth)acrylates

A 300 L reactor conventional for radical polymerizations was filled with a total of 100 kg of the monomers listed in Table 2 corresponding to the composition also given there, as well as 72.4 kg of gasoline/acetone (70:30). After passing through nitrogen gas for 45 minutes while stirring, the reactor was heated to 58 ° C and 50 g of Vazo® 67 were added. The jacket temperature was then heated to 75 °C and the reaction was carried out constantly at this external temperature. After a reaction time of 1 hour, 50 g of Vazo® 67 were added again. After 3 hours it was diluted with 20 kg of petrol/acetone (70:30) and after 6 hours with 10.0 kg of petrol/acetone (70:30). To reduce the residual initiators, 0.15 kg of Perkadox® 16 were added after 5.5 and 7 hours. The reaction was stopped after a reaction time of 24 hours and cooled to room temperature. The solution was adjusted to a solids content of 38% by weight.

Table 1: Composition of the polyacrylates

Meaning of the abbreviations

AS acrylic acid n-BA n-butyl acrylate

MA methyl acrylate

PEA phenoxyethyl acrylate

2-EHA 2-Ethylhexyl acrylate

EA Ethyl Acrylate Production of the pressure-sensitive adhesives

The polyacrylate including the crosslinker was placed in solution (see Production of Polyacrylates) and the filler was added as a powder. If necessary, solvent was added to adjust the desired solids content. If intended, the dye was slurried with some acetone and added to the polymer solution. The components were then mixed homogeneously with a stirrer. Shortly before coating, the crosslinking system (see Table 3) was added as a 5% solution in acetone and stirred in homogeneously.

The composition thus obtained was coated in solution onto a release liner (siliconized PET film) using a comma knife (see Table 3 for layer thickness). The solvent was removed in a drying tunnel (10 min, 105 °C).

Table 2: Other raw materials used

Table 3: PSAs

Production of adhesive tapes

For transfer adhesive tapes (single-layer adhesive tapes), the pressure-sensitive adhesive was applied to the release liner in the relevant layer thickness (see “Production of pressure-sensitive adhesives”). For multi-layer products, the pressure-sensitive adhesives were applied to the release liner in the relevant layer thickness (see “Production of pressure-sensitive adhesives”) and then laminated to the respective carrier. The adhesive tapes were covered on both sides with release liners.

Carrier PU-F - polyurethane film, thickness 30 pm

PET-F - polyethylene terephthalate film, thickness 50 pm

Table 4: Adhesive tapes

(V) - Comparative experiment, not according to the invention

Test methods

Method 1:

Instant adhesion to plastic and steel

The determination was carried out in a test climate of 23 °C +/- 1 °C and 50% +/- 5% relative humidity.

Test substrates:

Test plate steel - ASTM

Plastic test plate - plate made of PBT, reinforced with 30% glass fiber, surface roughness of 1 pm

Before the measurement, the test plates were first wiped with ethanol (PBT test plate) or acetone (steel plate) for cleaning and conditioning and then left in the air for 5 minutes to allow the solvent to evaporate. The side of the tape facing away from the test substrate was then covered with 36 pm etched PET film, preventing the sample from stretching during measurement. The adhesive tape was then rolled back and forth twice with a 2 kg rubber roller Rolling speed of 10 m/min was applied to the test substrate. Immediately afterwards, the adhesive tape was peeled off the test substrate at an angle of 180 ° C, with the force required to do this being measured using a Zwick tensile testing machine. The measurement results are given in N/cm and are averaged from three individual measurements.

An adhesive strength of at least 3.0 N/cm is considered a good result.

Method 2:

DuPont test in z-direction (puncture strength)

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

Immediately after storage, the adhesive composite consisting of the PC frame, adhesive tape and PC window was stretched into a sample holder with the protruding edges of the PC frame in such a way that the composite was aligned horizontally and the PC window was below the frame. The sample holder was then inserted centrally into the intended holder of the “DuPont Impact Tester”. The 190 g impact head was inserted so that the circular impact geometry with a diameter of 20 mm rested centrally and flush on the window side of the PC window.

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

In order to be able to compare tests with different samples, the energy was calculated as follows:

E [J] = height [m]* weight [kg]* 9.81 m/s ² .

Five samples per product were tested and the average energy value was given as an indicator of the puncture strength.

Method 3:

Droptower test (puncture strength)

The drop tower test method as an instrumented drop mechanism test is also used to measure the puncture strength.

A square, frame-shaped sample was cut out of the adhesive tape to be examined (area 180 mm ² , web width 2.0 mm). This sample was glued to a steel frame that had been cleaned with acetone. A steel window cleaned with acetone was glued to the other side of the adhesive tape. The steel frames, adhesive tape frames and steel windows were bonded in such a way that the geometric centers and diagonals were on top of each other (corner-to-corner). The bond was pressed with 62 N for 10 s and stored conditioned at 23 °C / 50% relative humidity for 24 hours.

Immediately after storage, the test specimen was placed in the sample holder of the instrumented drop mechanism in such a way that the composite was horizontal with the steel window facing downwards. The measurement was carried out instrumentally and automatically using a load weight of 5 kg and a fall height of 20 cm. The kinetic energy introduced by the load weight destroyed the bond by breaking the adhesive tape between the window and the frame, with the force being recorded by a piezoelectric sensor in a ps cycle. After the measurement, the associated software displayed the graph of the force-time curve, from which the maximum force F _ma x could be determined. Shortly before the impact of the rectangular impact geometry on the window, the speed of the falling weight was two Light barriers determined. Assuming that the energy introduced is greater than the impact strength of the bond, the work done by the bond until complete detachment was determined from the force curve, the time required until detachment and the speed of the falling weight, ie the detachment work. Five test specimens from each sample were examined; the final result of the impact strength consists of the average of the release work or the maximum force (F _ma x in N) of these five samples.

Method 4:

Static shear test/shear life

The shear strength was determined in a test climate of 70 °C +/- 1 °C and 50% +/- 5% relative humidity.

The test samples were cut to a width of 25 +/- 0.2 mm. For the test, 50 x 25 mm ASTM steel plates with 2 mm thickness and a 25 mm marking line were used, which were cleaned three times with acetone before bonding and then allowed to dry for 10 min. The bonding area was 25 x 25 mm. The test strip was applied to the center of the adhesive substrate in the longitudinal direction while avoiding air pockets by brushing over it with a wiper so that the upper edge of the test sample rested exactly on the 25 mm marking line. The back of the test sample was masked with 36 pm etched PET film. The free protruding end was covered with paper. The adhesive strip was then rolled back and forth twice with a 2 kg roller.

After rolling, a strap loop (weight 5-7 g) was attached to the protruding end of the adhesive tape. The plate prepared in this way was attached to a counter clock using a hook using the adapter plate, and a 1 kg weight was hooked smoothly into the belt loop. The installation time between rolling and loading was 12 minutes. The time was measured in minutes until the bond failed; the results are averaged from three measurements.

Method 5:

Tear test

Strips 10 mm wide and 40 mm long were punched out of the adhesive tape to be examined. These strips were glued to a length of 30 mm on an ethanol-conditioned battery foil plate so that a 10 mm long handle protruded. An ASTM plate was glued to the second side of the glued strip so that the two panels lay flush on top of each other. The composite was rolled over 10 times with a 4 kg roller (5 times back and forth). After 4 hours and 24 hours of application, the strips at the handle were manually stripped from the adhesive joint at a) 90" angle and b) 180" angle. It was assessed how many samples could be removed without leaving any residue.

Method 6:

Particle size distribution and particle shape

The particle size distribution was carried out using laser diffraction with the “Bettersizer S3 Plus” device. Isopropanol was used as the dispersing medium. The sample was added directly to the dispersion unit filled with isopropanol. Before the measurement, the sample was exposed to device-internal ultrasound (35 W) for 1 min, which was no longer present during the measurement. The stirring speed was 1200 rpm. The evaluation was carried out according to Mie with the refractive index optimized by the device. The particle shape was determined using dynamic image analysis directly after laser diffraction. A 10X camera was used. Approximately 5000 particles were analyzed. The evaluation was carried out using the area equivalent diameter.

Table 5: Results

Claims

Claims Pressure-sensitive adhesive containing at least one poly(meth)acrylate and at least one filler containing a total of at least 70% by weight, based on the total weight of the filler, of one or more polyolefins and/or one or more olefin copolymers; characterized in that the pressure-sensitive adhesive contains one or more of these fillers in a total amount of 1 - 13% by weight, based on the total weight of the pressure-sensitive adhesive. Pressure sensitive adhesive according to one of the preceding claims, characterized in that the at least one filler is in the form of particles and has a D90 value of the volumetric particle size distribution, determined by laser diffraction as described herein, of 25 - 110 pm. Pressure sensitive adhesive according to one of the preceding claims, characterized in that the at least one filler is in the form of particles and the particles are irregularly shaped. Pressure-sensitive adhesive according to one of the preceding claims, characterized in that the at least one filler is in the form of solid bodies. Pressure-sensitive adhesive according to one of the preceding claims, characterized in that the at least one filler contains a total of at least 70% by weight, based on the total weight of the filler, of one or more polyolefins. Pressure-sensitive adhesive according to one of the preceding claims, characterized in that the at least one filler contains a total of at least 70% by weight, based on the total weight of the filler, of polyethylene.

7. Pressure-sensitive adhesive according to one of the preceding claims, characterized in that the at least one filler consists essentially of low density polyethylene (LDPE).

8. Pressure-sensitive adhesive according to claim 1, characterized in that the monomer composition on which the at least one poly (meth) acrylate is based comprises at least one phenoxyalkyl (meth) acrylate.

9. Pressure-sensitive adhesive according to one of the preceding claims, characterized in that the at least one poly(meth)acrylate is due to the following monomer composition: a) 50 to 80% by weight of at least one acrylic acid ester according to the formula (I)

CH ₂ =CH-C(O)OR ³ (III), in which R ³ represents an H atom or a hydroxyalkyl radical with 1 to 4 carbon atoms.

10. Adhesive tape comprising a pressure-sensitive adhesive according to one of the preceding claims.

11. Adhesive tape according to claim 10, characterized in that the adhesive tape consists of a layer of a pressure-sensitive adhesive according to one of claims 1 to 9.

12. Adhesive tape according to claim 10, characterized in that the adhesive tape comprises a PET film as a carrier layer. Adhesive tape according to claim 10, characterized in that the adhesive tape comprises a polyurethane or synthetic rubber film as a carrier layer. Use of an adhesive tape according to one of claims 11 and 12 as an adhesive in the production of assembly bonds in electronic, optical or precision mechanical devices. Use of an adhesive tape according to claim 13 as an adhesive that can be removed by stretching for producing bonds in electronic, optical or precision mechanical devices.