Impact resistant pressure sensitive adhesive

Abstract

The purpose of the present invention is to provide a pressure-sensitive adhesive which exhibits good impact resistance even at a low layer thickness without foaming during the production of the pressure-sensitive adhesive. In addition, the pressure-sensitive adhesive has good technical adhesive properties over a wide temperature range and in particular even under humid and hot conditions. This is achieved by a pressure-sensitive adhesive comprising at least one poly (meth) acrylate, and at least one filler comprising at least 70% by weight in total of one or more polyolefins and / or one or more olefin copolymers, based on the total weight of the filler, and characterized in that the total weight of the filler is at least 70% by weight. The pressure-sensitive adhesive comprises a total of 1-13% by weight of one or more of these fillers, based on the total weight of the pressure-sensitive adhesive. The invention also relates to an adhesive tape comprising a pressure-sensitive adhesive according to the invention, and to the use of an adhesive tape according to the invention.

Description

Technical Field

[0001] The present invention relates to the technical field of pressure-sensitive adhesives, such as those widely used for temporary and permanent (durable) connection of various substrates and components. The present invention more particularly proposes specially filled pressure-sensitive adhesives based on poly(meth)acrylates, which have high impact resistance and good technical bonding properties. Background Art

[0002] The joining of individual components is one of the core methods of manufacturing technology. In addition to other methods such as welding and soldering, bonding, i.e. joining with adhesives, is now particularly important. In this case, an alternative to the use of shapeless adhesives (which are applied, for example, from tubes) is the so-called adhesive tape. The advantage of adhesive tapes is that they can be applied more easily and with greater positional accuracy than liquid adhesives. Therefore, they are particularly suitable for miniaturized applications of the kind required in the electronics industry, for example. Here, it is becoming increasingly important to achieve connections between components in a very precise and space-saving manner. In addition, since there is still a considerable demand for communication and entertainment electronics worldwide, the requirements for device performance are also increasing, and thus new, or at least growing, requirements are constantly being placed on the adhesive tapes used in terms of their performance.

[0003] In this context, especially for portable devices such as smartphones or tablets, the electronics market requires adhesive tapes with increasingly narrow geometries, in some cases now requiring edge widths (or widths) of less than 0.5 mm. However, these adhesive tapes must meet very demanding performance requirements. For example, the adhesive bond itself must withstand the strongest shocks, such as occur, for example, when the device is dropped.

[0004] A common method of meeting this requirement is to use foam tape.

[0005] Thus, EP2862901 A1 describes a viscoelastic layer comprising microparticles having a D90 particle size of 30 μm or less, wherein the fraction (or proportion) of the microparticles is 15-40% by volume, based on the volume of the viscoelastic layer, and the viscoelastic layer can be used as a pressure-sensitive adhesive layer and substrate in an adhesive tape. The viscoelastic layer comprises an acrylate polymer as a base polymer. The microparticles are preferably inorganic hollow bodies, more particularly hollow glass spheres.

[0006] WO2009 / 090119 A1 relates to a pressure-sensitive adhesive comprising expanded microspheres, wherein the adhesion of the adhesive comprising expanded microspheres is reduced by up to 30% compared to the adhesion (or peel adhesion) of an adhesive of the same area weight and formulation due to defoaming by destroying the cavities caused by the expanded microspheres.

[0007] WO2016 / 156305 A1 describes a pressure-sensitive adhesive strip which can be separated without residue and without destruction by stretching essentially in the bonding plane and consists of one or more adhesive layers, all of which consist of a pressure-sensitive adhesive foamed with microspheres, and optionally of one or more intermediate carrier layers, wherein the pressure-sensitive adhesive strip consists only of the mentioned adhesive layers and optionally of the intermediate carrier layers, and the outer upper surface and the outer lower surface of the pressure-sensitive adhesive strip are formed by the mentioned adhesive layers.

[0008] WO2019 / 106194 A1 relates to polyacrylates traceable from the following monomer composition:

[0009] a) 30 to 75% by weight of at least one acrylate according to formula (I)

[0010] ,

[0011] Where R 1 is a straight or branched chain alkyl group having 1 to 10 carbon atoms;

[0012] b) 20 to 65% by weight of at least one acrylic ester of the formula (II)

[0013] ,

[0014] Where R 2 is a phenoxyalkyl group;

[0015] c) 0 to 40% by weight of at least one acrylic ester of the formula (III)

[0016] ,

[0017] Where R 3 is an alkyl diglycol group or an alkoxyalkyl group;

[0018] d) 0.5 to 10% by weight of at least one acrylate monomer of formula (IV)

[0019] ,

[0020] Where R 4 is a hydrogen atom or a hydroxyalkyl group having 1 to 4 carbon atoms.

[0021] Such polyacrylates are used as the basis for pressure-sensitive adhesives which, in one embodiment, are foamed. The pressure-sensitive adhesives exhibit particularly good chemical resistance.

[0022] In particular, foaming pressure-sensitive adhesives by expanding blowing agents is technically challenging, since it generally requires the introduction of heat or the application of a pressure difference. These types of processing steps can lead to undesirable side effects: for example, premature initiation of crosslinking and thus undesirable gelation of the substance (or composition) still in the mixing device. In addition, they always require additional energy consumption or even additional operating steps, and are therefore also considered critical in terms of sustainability.

[0023] Of course, it is also possible to consider incorporating hollow bodies which have undergone expansion into pressure-sensitive adhesive formulations, such bodies being, for example, hollow glass spheres or expanded polymer spheres. However, due to their low density and relatively high volume, these types of hollow bodies are usually difficult or even no longer processable.

[0024] 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 above requirements.

[0025] In this regard, EP1832638 A1 describes a pressure-sensitive adhesive which comprises an organic filler and can be obtained by the following process:

[0026] The crosslinking agent is added to the polyacrylate copolymer based on acrylate and / or methacrylate ("polyacrylate") in the melt,

[0027] At least one filler is added to the polyacrylate,

[0028] The polyacrylate provided with the crosslinking agent and the filler is conveyed to a coating unit, where it is applied to the web-like layer of the further material and crosslinked after the application.

[0029] Here, the crosslinker is a thermal crosslinker, some of the acrylates and / or methacrylates contain primary hydroxyl groups, and at least one filler is an organic filler. The goal is to achieve a high fraction of filler while still achieving a uniform and homogeneous coating when applied to a substrate. Summary of the invention

[0030] There is a continuing demand for a pressure-sensitive adhesive having a performance profile similar to that of a foamed pressure-sensitive adhesive, but being non-foamed. Against this background, the object of the present invention is to provide a pressure-sensitive adhesive which exhibits good impact resistance even at low layer thicknesses. Another object of the present invention is to provide such a pressure-sensitive adhesive without the need for foaming in the manufacture of the pressure-sensitive adhesive. In addition, the pressure-sensitive adhesive should have good technical adhesive properties over a wide temperature range and even under wet heat conditions in particular. Another additional object of the present invention is to design a pressure-sensitive adhesive so that it can be effectively manufactured in an overall cost-effective manner and in terms of the use of materials and energy.

[0031] The object is achieved based on the idea of ​​providing a pressure-sensitive adhesive based on poly(meth)acrylates with specifically selected fillers.

[0032] A first and general subject of the present invention is a pressure-sensitive adhesive comprising

[0033] at least one poly(meth)acrylate and

[0034] at least one filler comprising a total of at least 70% by weight of one or more polyolefins and / or one or more olefin copolymers, based on the total weight of the filler;

[0035] And characterized in that the pressure-sensitive adhesive contains a total of 1-13% by weight of one or more of these fillers, based on the total weight of the pressure-sensitive adhesive.

[0036] In line with the understanding of those skilled in the art, pressure-sensitive adhesive is the following adhesive, which has pressure-sensitive adhesive properties, that is, even under relatively weak applied pressure, also can form a lasting connection with the adhesion substrate. The corresponding pressure-sensitive adhesive tape can be separated again from the adhesion substrate in a substantially residue-free mode after use usually. However, the connection of pressure-sensitive adhesive to the adhesion substrate can even be so strong that the lasting adhesion that is not easy to separate again is produced. Generally, pressure-sensitive adhesive has permanent inherent viscosity at room temperature usually, which means that they have certain viscosity and contact (touch) viscosity, so that they also can wet the surface of substrate even under low applied pressure.

[0037] The pressure-sensitive adhesiveness of pressure-sensitive tape is the result of the adhesive used as pressure-sensitive adhesive. In the case of not wishing to be bound by this theory, it is often assumed that pressure-sensitive adhesive can be regarded as a liquid with extremely high viscosity of elastic component (component), which correspondingly has the characteristic viscoelastic properties causing the above-mentioned lasting inherent viscosity and pressure-sensitive adhesive ability. Assume that, for pressure-sensitive adhesive, when mechanically deformed, there are both the formation of viscous flow process and elastic restoring force. Proportional (at a certain proportion) viscous flow is used to realize adhesion here, and proportional (at a certain proportion) elastic restoring force component is especially necessary for realizing cohesion. The correlation between rheology and pressure-sensitive adhesive is known in the prior art and is for example described in Satas, " Handbook of Pressure Sensitive Adhesives Technology ", the third edition (1999), in pages 153 to 203. To characterize the magnitude of the elastic component and the viscous component, the storage modulus (G') and the loss modulus (G'') are usually used, which can be determined by dynamic mechanical analysis (DMA), for example using a rheometer, as disclosed in WO 2015 / 189232A1. Within the scope of the present invention, when at a temperature of 23 ° C for 100 Up to 10 1 rad / s, G' and G'' are each at least partially within 10 3 Up to 10 7 Pa, the adhesive is preferably understood to have pressure-sensitive adhesiveness and is therefore understood to be a pressure-sensitive adhesive.

[0038] As has been shown, the pressure-sensitive adhesives according to the invention have properties that make them particularly suitable for use in the manufacture of electronic products. Adhesive tapes equipped with said pressure-sensitive adhesives exhibit good technical adhesive properties related to impact resistance, which are comparable to or even exceed those of the foamed adhesive tapes commonly used in the electronics industry. In particular, the pressure-sensitive adhesives according to the invention have proven to be particularly advantageous after storage at elevated temperatures or under hot and humid conditions.

[0039] In the scope of the present invention, in accordance with the understanding of those skilled in the art, the expression "poly (meth) acrylate" includes not only polyacrylates, but also polymethacrylates and copolymers of acrylates and methacrylates. Poly (meth) acrylates may contain relatively small amounts of monomer units not derived from (meth) acrylates. Therefore, in the scope of the present invention, "poly (meth) acrylate" is understood to mean a (co) polymer whose monomer base is composed of monomers selected from acrylic acid, methacrylic acid, acrylates and methacrylates to the extent of 70% or more, preferably 90% or more, more preferably 98% or more of the mass fraction, wherein the fraction is based on the mass of the monomer base. Preferably, the mass fraction of acrylates and / or methacrylates is 50% or more, more preferably 70% or more. Poly (meth) acrylates can generally be obtained by free radical polymerization of monomers based on acrylic acid and / or methacrylic acid and optionally other copolymerizable monomers.

[0040] The monomer base of the poly(meth)acrylate of the pressure-sensitive adhesive according to the invention is in principle arbitrary. The monomer composition on which the at least one poly(meth)acrylate is based preferably comprises at least two, more preferably exactly two, acrylates according to formula (I)

[0041] ,

[0042] Where R 1 is a straight or branched alkyl group having 1 to 10 carbon atoms. More preferably, R in formula (I) 1is an n-butyl group; therefore, the monomer composition more preferably comprises n-butyl acrylate. Particularly preferably, the monomer composition comprises at least 40% by weight of n-butyl acrylate. As has been shown, this allows the manufacture of particularly effective pressure-sensitive adhesives with a wide range of properties. In particular, the monomer composition comprises 42 to 92% by weight, for example 45 to 90% by weight of n-butyl acrylate.

[0043] Of the at least two, preferably exactly two, acrylates according to formula (I), more preferably one is n-butyl acrylate and the second is selected from methyl acrylate, ethyl acrylate and 2-ethylhexyl acrylate.

[0044] In a specific 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 imparts to the polymer and thus the pressure-sensitive adhesive improved chemical resistance as well as improved resistance to moisture and heat.

[0045] In this embodiment, the at least one poly(meth)acrylate can preferably be traced from the following monomer composition:

[0046] a) 50 to 80% by weight of at least one acrylic ester according to formula (I)

[0047] ,

[0048] Where R 1 is a straight-chain or branched alkyl group having 1 to 10 carbon atoms;

[0049] b) 15 to 45% by weight of at least one acrylate according to formula (II)

[0050] ,

[0051] Where R 2 is a phenoxyalkyl group;

[0052] c) 0.5 to 10% by weight of at least one acrylate monomer according to formula (III)

[0053] ,

[0054] Where R 3 is a hydrogen atom or a hydroxyalkyl group having 1 to 4 carbon atoms. The data in wt. % (percent by weight) are based in each case on the total weight of the monomer composition.

[0055] Here, R in formula (I) 1 Preferred is a group selected from the group consisting of a methyl group, an n-butyl group and a 2-ethylhexyl group, and more preferred is a methyl group or an n-butyl group.

[0056] R in formula (II) 2 Phenoxyethyl groups, more particularly 2-phenoxyethyl groups, are preferred.Phenoxyethyl acrylate is preferably present in the monomer composition of the poly(meth)acrylate in an amount of 22 to 38% by weight.

[0057] R in formula (III) 3 Preferred are hydrogen atoms. The monomer composition of the poly(meth)acrylate preferably comprises 0.8 to 6% by weight of acrylic acid.

[0058] In particular, in the embodiment with phenoxyalkyl acrylates, the at least one poly(meth)acrylate of the pressure-sensitive adhesive according to the invention can be traced from the following monomer composition: 35 to 55% by weight of n-butyl acrylate, 5 to 35% by weight of methyl acrylate, 20 to 45% by weight of phenoxyethyl acrylate and 1 to 5% by weight of acrylic acid, in each case based on the total weight of the monomer composition.

[0059] Particularly preferably, in this embodiment, the poly(meth)acrylate is traceable from the following monomer composition: 40 to 55% by weight of n-butyl acrylate, 15 to 25% by weight of methyl acrylate, 25 to 35% by weight of phenoxyethyl acrylate and 1.5 to 4.5% by weight of acrylic acid, in each case based on the total weight of the monomer composition.

[0060] At least one poly(meth)acrylate of the pressure-sensitive adhesive according to the invention is preferably crosslinked. More preferably, at least one poly(meth)acrylate is thermally crosslinked. Thermal crosslinking can be carried out under substantially milder conditions than, for example, radiation-induced crosslinking, which can sometimes even be destructive. However, according to the invention, it is also possible to crosslink the poly(meth)acrylate only or additionally by actinic radiation, wherein optionally necessary or useful crosslinker substances, such as UV crosslinkers, can be added.

[0061] Preferably, the at least one poly(meth)acrylate is also thermally crosslinked, i.e. with the aid of one or more substances which, under the influence of thermal energy, allow (initiate) and / or promote a crosslinking reaction. The at least one poly(meth)acrylate of the pressure-sensitive adhesive according to the invention is more preferably crosslinked with the aid of one or more covalently reactive crosslinking agents, more particularly with the aid of one or more epoxides, and / or with the aid of one or more coordination crosslinking agents, more particularly with the aid of one or more metal chelates, very preferably with the aid of one or more aluminum, titanium, zirconium and / or iron chelates. Thus, it is also possible to use a combination of different thermal crosslinking agents, for example a combination of one or more epoxides with one or more metal chelates.

[0062] In particular, the at least one poly(meth)acrylate of the pressure-sensitive adhesive according to the invention is crosslinked at least by means of a compound containing two or more epoxy groups, particularly preferably by a compound containing two or more epoxy groups and additionally containing a tertiary amine function, for example tetraglycidyl-m-xylene diamine ( -tetra(oxiranylmethyl)-1,3-phenylenediamine) crosslinking. These compounds are used in an amount of preferably 0.03 to 0.1 part by weight, more preferably 0.04 to 0.07 part by weight, in each case based on 100 parts by weight of the total amount of poly(meth)acrylate (solvent-free).

[0063] In one embodiment, at least one poly(meth)acrylate is crosslinked at least by means of a compound containing two or more 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, more preferably 0.05 to 0.1 parts by weight, in each case based on 100 parts by weight of the total amount of poly(meth)acrylate (solvent-free).

[0064] In order to prepare poly(meth)acrylates, in principle all free radical or free radical controlled polymerizations can be carried out, including combinations of different polymerization processes. In addition to conventional free radical polymerizations, these methods also include, for example, ATRP, nitroxide (nitroxide free radical) / TEMPO-controlled polymerization or RAFT methods.

[0065] The pressure-sensitive adhesive according to the invention may contain one or more poly(meth)acrylates. If it contains two or more poly(meth)acrylates, preferably all poly(meth)acrylates are preferred poly(meth)acrylates in the sense of the above-mentioned embodiments. Accordingly, for the case where the pressure-sensitive adhesive according to the invention contains two or more poly(meth)acrylates, even when for all these poly(meth)acrylates they are described only as "at least one poly(meth)acrylate", all the above-mentioned embodiments are preferred to some extent.

[0066] Besides one or more poly(meth)acrylates, the pressure-sensitive adhesive according to the invention comprises at least one filler which comprises in total at least 70% by weight of one or more polyolefins and / or one or more olefin copolymers, based on the total weight of the filler.

[0067] In accordance with the understanding of the skilled person, polyolefins are understood to mean polymers generally produced from olefins by chain polymerization. More particularly, they are understood to mean polymers constructed exclusively from unsubstituted olefins.

[0068] In accordance with the understanding of those skilled in the art, olefin copolymers are understood to mean polymers prepared only from different unsubstituted olefins or from at least one olefin and at least one additional vinyl monomer. It should be understood that each monomer participating in the construction of the copolymer must be present in a technically reasonable fraction.

[0069] At least one filler of the pressure-sensitive adhesive according to the present invention is preferably in particle form. Therefore, in the pure state, the filler is preferably processed in the form of a powder. In the pressure-sensitive adhesive according to the present invention, the particles of the filler can in principle be present in the form of fine distribution or agglomerates.

[0070] The at least one filler preferably has a D90 value of the volume particle size distribution determined by laser diffraction as described herein of 25-110 μm, more preferably of 30 to 95 μm, more particularly of 35 to 90 μm.

[0071] It is also preferred that the particles of at least one filler are irregularly shaped; therefore, they at least mostly do not have a geometrically regular shape such as a cube, cuboid, cone, sphere, etc. In this context, it is considered to be unimportant that the particles with a geometrically regular shape occur randomly to a lesser extent. Without wishing to be bound by this theory, the inventors assume that the irregular shape of the particles or their irregularly shaped surfaces are in particular the essential reason for the excellent shock-absorbing properties of the pressure-sensitive adhesive according to the invention.

[0072] In principle, at least one filler or filler particles can be present as hollow bodies or solid bodies. The filler or filler particles are preferably in the form of solid bodies. It is also preferred that, in addition to at least one filler, the pressure-sensitive adhesive according to the invention does not contain foaming components, so it is preferably non-foaming.

[0073] At least one filler of the pressure-sensitive adhesive according to the present invention comprises one or more polyolefins and / or one or more olefin copolymers, preferably with a total of at least 90 weight %, more preferably a total of at least 95 weight %, and more particularly a total of at least 99 weight %, in each case based on the total weight of the filler. Particularly preferably, at least one filler is composed of one or more polyolefins and / or one or more olefin copolymers. Polyolefins and / or olefin copolymers described herein are preferably selected from polyethylene (PE), polypropylene (PP) and ethylene-vinyl acetate copolymer (EVA). Polyethylene is preferably selected from low-density polyethylene (LDPE) and high-density polyethylene (HDPE) in turn.

[0074] More preferably, at least one filler of the pressure-sensitive adhesive according to the present invention comprises at least 90% by weight, more preferably at least 95% by weight, and more particularly at least 99% by weight of one or more polyolefins, in each case based on the total weight of the filler. Particularly preferably, at least one filler consists of one or more polyolefins. The polyolefin described herein is preferably selected from polyethylene (PE) and polypropylene (PP). Polyethylene is preferably selected from low-density polyethylene (LDPE) and high-density polyethylene (HDPE).

[0075] In one embodiment, at least one filler of the pressure-sensitive adhesive according to the invention comprises at least 70% by weight, more preferably at least 90% by weight, more particularly at least 99% by weight of polyethylene, in each case based on the total weight of the filler. Particularly preferably, at least one filler consists of polyethylene. The polyethylene may be a specific polyethylene or a mixture of different polyethylenes.

[0076] More preferably, at least one filler of the pressure-sensitive adhesive according to the invention comprises at least 70% by weight, more preferably at least 90% by weight in total, and more particularly at least 99% by weight in total of low-density polyethylene (LDPE), in each case based on the total weight of the filler. Particularly preferably, at least one filler consists essentially of low-density polyethylene (LDPE), more particularly of low-density polyethylene (LDPE). Here, it also applies that the low-density polyethylene can be a specific LDPE or a mixture of different low-density polyethylenes.

[0077] In one embodiment, the pressure-sensitive adhesive according to the invention comprises at least one tackifier resin and / or at least one plasticizer.

[0078] Tackifier resins, also called tackifying resins, are often added to pressure-sensitive adhesives to fine-tune the pressure-sensitive adhesive properties.

[0079] According to the invention, "resin" is understood to mean in particular oligomers and (oligo)polymeric compounds whose number-average molar mass M n Not more than 5000 g / mol. Of course, short-chain polymer products which are produced during the polymerization of the polyacrylates according to the invention and thus introduced into the pressure-sensitive adhesive according to the invention are not included in the term "resin". Tackifier resins generally increase the cohesion (or peel adhesion) of the pressure-sensitive adhesive, in particular also the "contact tack", so-called tack.

[0080] Tackifier resins generally have a softening point in the range of 80 to 150° C. The softening point T of oligomeric and polymeric compounds such as resins sThe data are based on the ring and ball method according to DIN EN 1427:2007 with the regulations applied appropriately (instead of bitumen, oligomer samples or polymer samples were investigated, the method operation otherwise remained the same). The measurements were carried out in a glycerol bath.

[0081] The pressure-sensitive adhesive according to the present invention may contain at least one tackifier resin selected from the group consisting of pinene and indene resins; rosin and rosin derivatives such as rosin esters, including rosin derivatives stabilized by, for example, hydrogenation or disproportionation; polyterpene resins; terpene-phenol resins; alkylphenol resins; and aliphatic, aromatic and aliphatic-aromatic hydrocarbon resins.

[0082] In the pressure-sensitive adhesive according to the present invention, preferably include tackifier resin in the degree that is no more than 30 % by weight in total. One or more tackifier resins may be included. As already shown, the behavior of the pressure-sensitive adhesive according to the present invention under continuous pressure load can be improved by adding tackifier resin.

[0083] However, more preferably, the pressure-sensitive adhesive according to the present invention contains no tackifier resin.

[0084] In addition to this, the pressure-sensitive adhesive according to the invention may also contain reactive resins. Reactive resins are those resins which have functional groups which enable them to react chemically with the further components of the pressure-sensitive adhesive, more particularly the polyacrylates, under suitable activation.

[0085] The pressure-sensitive adhesive according to the invention preferably contains no reactive resins.

[0086] Pressure-sensitive adhesive according to the present invention may include at least one plasticizer.Plasticizer is preferably selected from (meth) acrylate oligomers, phthalates, hydrocarbon oils, cyclohexane dicarboxylates, benzoates, water-soluble plasticizers, plasticizer resins, phosphoric acid esters (or phosphates) and polyphosphates (or polyphosphates).Plasticizer is more preferably selected from phthalates, cyclohexane dicarboxylates and benzoates.More particularly, plasticizer is benzoate, particularly preferably dibenzoate, for example diethylene glycol dibenzoate.In pressure-sensitive adhesive of the present invention, preferably include plasticizer in a degree of no more than 30% by weight, more preferably no more than 20% by weight, more particularly no more than 15% by weight in total.

[0087] As has been shown, the impact resistance of the pressure-sensitive adhesive according to the invention can be improved by adding one or more plasticizers without thereby substantially adversely affecting the chemical resistance. This effect can be achieved to a particularly high degree by adding diethylene glycol dibenzoate.

[0088] However, more preferably, the pressure-sensitive adhesive according to the invention contains no plasticizer.

[0089] When present, tackifier resins and plasticizers account for a fraction of not more than 40% by weight of the pressure-sensitive adhesive according to the invention.

[0090] In order to optimize the properties of the pressure-sensitive adhesive according to the invention, it may also contain further common additives such as dyes, pigments, electrically conductive fillers, thermally conductive fillers, etc. and / or flame retardants, for example ammonium polyphosphate and its derivatives.

[0091] The pressure-sensitive adhesive according to the present invention is preferably manufactured in the following manner: first, poly(meth)acrylate is manufactured from the corresponding basic monomer mixture by free radical polymerization, and preferably further processed in solution form. In the case of two or more poly(meth)acrylates, they are then fully mixed. If an adhesive is provided, a crosslinking agent is added during polymerization or preferably after polymerization. If additional additives should be added, they are also mixed.

[0092] The pressure-sensitive adhesive according to the invention (according to the preceding paragraph) is preferably applied as a solution (optionally after setting a certain solid content) to a carrier or a release liner. The coating is preferably carried out by conventional coating techniques, such as engraved roller coating, comma rod coating, multi-roll coating or in a printing process. The solvent can then be removed in a drying tunnel (drying tunnel) or a drying oven.

[0093] When using thermal crosslinkers, crosslinking usually takes place to a lesser extent at room temperature and to a greater extent when heat is supplied, in particular during the removal of the solvent. Coordinating crosslinkers usually crosslink the polyacrylates independently of temperature; for this reason, substances are sometimes added which initially block the crosslinker. These substances are then removed together with the solvent, so that crosslinking starts immediately at this point in time.

[0094] Alternatively, coating can also be carried out in a solvent-free process. For this purpose, the polyacrylate is heated and melted in an extruder. Further process steps such as mixing with additives, filtering or degassing can be carried out in the extruder. The melt is then applied as a layer to a carrier or a release liner via a calender.

[0095] A further subject matter of the invention is an adhesive tape comprising the pressure-sensitive adhesive according to the invention.

[0096] In the simplest embodiment, the adhesive tape according to the invention consists only of a layer of the pressure-sensitive adhesive according to the invention. In order to be able to apply the adhesive tape that is rolled up to form a sheet roll or cross-wound to form a spool without it adhering to itself, the pressure-sensitive adhesive is preferably lined with (or covered with) at least one release liner. In the understanding of those skilled in the art, the release liner is only regarded as an auxiliary and not as a component of the adhesive tape. The layer thickness of the adhesive tape according to the invention, which consists only of a layer of the pressure-sensitive adhesive according to the invention, is preferably not more than 500 μm, more preferably not more than 450 μm, more particularly not more than 400 μm, and particularly preferably not more than 370 μm.

[0097] In the production of assembly bonds, more preferably in the production of assembly bonds in electronic, optical or precision mechanical devices, the above-mentioned adhesive tapes are preferably used as adhesives generally for the long-term, in particular permanent, bonding of two substrates.

[0098] In addition to the pressure-sensitive adhesive according to the present invention, the adhesive tape according to the present invention may also include at least one carrier and optionally other layers, such as other pressure-sensitive adhesive layers, barrier layers, other reinforcing carrier layers, etc. There is basically no restriction on the design of the carrier and other layers. Conventional carrier materials are, for example, woven fabrics, laying scrims and polymer films, such as PET films, polyolefin films and polyurethane films. In one embodiment, the adhesive tape according to the present invention includes a polymer film that arranges the layer of the pressure-sensitive adhesive according to the present invention on the top side and the bottom side separately. Also in the embodiment with a carrier layer and optionally other layers, at least one pressure-sensitive adhesive of the adhesive tape is preferably lined with a release liner, so as to realize trouble-free deployment and protect the pressure-sensitive adhesive from contamination. The release liner is usually composed of a single-sided or double-sided siliconized polymer film (such as PET or PP) or a siliconized paper carrier. They are not considered to be a part of the adhesive tape, but are only temporarily connected to the adhesive tape as an auxiliary.

[0099] In one embodiment, the adhesive tape according to the invention comprises a PET film or alternatively a polyurethane film or a synthetic rubber film as carrier layer.

[0100] In a first variant of the above-described embodiment, if the adhesive tape comprises a PET film as a carrier layer, the PET film preferably has a thickness of 10 to 100 μm, more preferably 12 to 80 μm, more particularly 15 to 60 μm. It is also preferred that a layer of a pressure-sensitive adhesive according to the invention is arranged on the top side and the bottom side, wherein the layers are more preferably substantially identical. The thickness of the two pressure-sensitive adhesive layers is preferably 15 to 200 μm, more particularly 30 to 150 μm, independently of each other. The adhesive tape according to this variant is preferably used as an adhesive in the manufacture of assembly bonding, more preferably in the manufacture of assembly bonding in electronic, optical or precision mechanical devices.

[0101] In a second variation of the above embodiment, the adhesive tape according to the present invention comprises a polyurethane film or a synthetic rubber film and a layer of a pressure-sensitive adhesive according to the present invention on the top side and the bottom side, respectively; preferably, the adhesive tape consists of a polyurethane film or a synthetic rubber film and a layer of a pressure-sensitive adhesive according to the present invention on the top side and the bottom side, respectively. The thickness of the film is preferably 10 to 250 μm, more preferably 20 to 220 μm. In a specific embodiment, the thickness of the film is up to 250 μm, preferably 70 μm to 230 μm. In another specific manner, the thickness of the polyurethane film is 5 to 70 μm, more particularly 10 to 30 μm. In the film, a polyurethane film is particularly preferred.

[0102] The thickness of the pressure-sensitive adhesive layers is preferably independently of one another in each case from 10 to 120 μm, more preferably independently of one another in each case from 15 to 110 μm. Particularly preferably, the two pressure-sensitive adhesive layers are substantially identical.

[0103] The adhesive tape according to this variant is preferably used as an adhesive tape which can be separated again by stretching, more preferably for producing bonds in electronic, optical or precision mechanical devices.

[0104] A further subject of the invention is the use of the pressure-sensitive adhesive according to the invention and / or the adhesive tape according to the invention as adhesive in assembly bonds and / or in the production of assembly bonds in electronic, optical or precision mechanical devices.

[0105] In the sense of the present application, electronic, optical and precision mechanical apparatus are in particular those apparatus as classified in class 9 of the International Classification of Goods and Services for the Purposes of the Registration of Trademarks (Nice Classification); 10th edition (NCL (10-2013)), provided that these are electronic, optical or precision mechanical apparatus, and clocks and timepieces according to class 14 (NCL (10-2013)), such as, in particular,

[0106] Scientific, nautical, surveying, photographic, cinematographic, optical, weighing, measuring, signalling, monitoring, life-saving and teaching apparatus and instruments;

[0107] Apparatus and instruments for conducting, switching, converting, storing, regulating and monitoring electricity;

[0108] Image recording, processing, transmission, and reproduction equipment, such as televisions;

[0109] Acoustic recording, processing, transmission, and reproduction equipment, such as broadcasting equipment;

[0110] Computers, calculators and data processing equipment, mathematical equipment and instruments, computer accessories, office equipment such as printers, fax machines, copiers, typewriters, data storage devices;

[0111] Telecommunications equipment and multi-function equipment with telecommunications capabilities, such as telephones and answering machines;

[0112] Chemical and physical measuring devices, control equipment, and instruments, such as battery chargers, multimeters, lamps, and tachometers;

[0113] Navigational equipment and instruments;

[0114] optical equipment and instruments;

[0115] medical equipment and instruments and those used by athletes;

[0116] Clocks and chronometers;

[0117] Solar cell modules, such as electrochemical dye-sensitized solar cells, organic solar cells, and thin-film batteries; and

[0118] Fire-fighting equipment.

[0119] Meanwhile, technological developments tend to focus on the following equipment: it is smaller and lighter in design, so that they can be carried by their owners at any time. This is usually achieved by realizing the low weight or suitable size of such equipment. Such equipment is also referred to as mobile equipment or portable equipment. Under this development trend, precision machinery and optical equipment are (also) increasingly provided with electronic components, which improves the possibility of miniaturization. Because mobile equipment is carried, they are exposed to increased (especially mechanical and chemical) loads, such as by edge collisions, by falling, by contacting with other hard articles in a bag, and by the long-term movement caused by carrying itself. However, compared with those "non-mobile (fixed)" equipment that are usually installed inside and rarely move or do not move at all, mobile equipment is also exposed to stronger loads due to moisture exposure, temperature effects, etc. Pressure-sensitive adhesive materials according to the present invention have been proven to be particularly preferably able to resist such interference and can also be weakened or compensated in an ideal situation.

[0120] Therefore, the pressure-sensitive adhesive according to the invention and / or the adhesive tape according to the invention are preferably used for bonding in the production of portable electronic, optical or precision mechanical devices. Such portable electronic devices are in particular:

[0121] Cameras, digital cameras, camera accessories (such as exposure meters, flashes, apertures, camera housings, lenses, etc.), film cameras, video cameras

[0122] Small computers (mobile computers, handheld computers, handheld calculators), laptops, notebooks, netbooks, ultrabooks, tablet computers, handheld devices, electronic organizers and organizers (so-called "electronic organizers" or "personal digital assistants", PDAs, handheld computers), modems;

[0123] Computer accessories and operating units for electronic devices, such as mice, drawing pads, drawing tablets, microphones, speakers, game consoles, joysticks, remote controllers, remote controls, touch pads ("touch pads");

[0124] Monitors, displays, screens, touch-sensitive screens (sensor screens, “touch screen devices”), projectors;

[0125] Electronic book reading devices (“e-books”);

[0126] Mini TVs, pocket TVs, movie playing devices, video players;

[0127] Radios (including mini radios and pocket radios), Walkmans, CD players, music players for example CD, DVD, Blu-ray, cassette, USB, MP3, headphones

[0128] Cordless telephone, mobile phone (or cell phone), smart phone, walkie-talkie (two-way radio), speakerphone, pager (pager, beeper);

[0129] Mobile defibrillator, blood glucose meter, blood pressure monitor, pedometer, pulse meter;

[0130] Flashlight, laser pointer;

[0131] Motion detectors, optical amplifiers, binoculars, night vision equipment, GPS equipment, navigation equipment, portable interface equipment for satellite communications;

[0132] Data storage devices (USB sticks, external hard drives, memory cards); and

[0133] Wristwatches, digital watches, pocket watches, chain watches and stopwatches.

[0134] In particular, the pressure-sensitive adhesive according to the invention and / or the adhesive tape according to the invention are used for producing bonds in smartphones (mobile phones), tablets, notebooks, cameras, camcorders, keyboards or touchpads. DETAILED DESCRIPTION

[0135] Example

[0136] Preparation of poly(meth)acrylate

[0137] A total of 100 kg of the monomers indicated in Table 2 (corresponding to the compositions also indicated therein) and 72.4 kg of volatile oil / acetone (70:30) were added to a conventional 300 L reactor for free radical polymerization. After nitrogen was passed through for 45 minutes under stirring, the reactor was heated to 58° C. and 50 g of 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, a further 50 g of After 3 hours, the mixture was diluted with 20 kg of volatile oil / acetone (70:30) and after 6 hours, 10.0 kg of volatile oil / acetone (70:30). To reduce the residual initiator, 0.15 kg of The reaction was stopped after a reaction time of 24 hours and cooled to room temperature. The solution was adjusted to a solid content of 38% by weight.

[0138] Table 1: Composition of polyacrylates

[0139]

[0140] Meaning of the abbreviation

[0141] AS Acrylic

[0142] n-BA n-Butyl acrylate

[0143] MA Methyl acrylate

[0144] PEA Phenoxyethyl acrylate

[0145] 2-EHA 2-Ethylhexyl acrylate

[0146] EA Ethyl Acrylate

[0147] Preparation of pressure-sensitive adhesive

[0148] The polyacrylate is introduced into the solution together with the crosslinking agent (see the preparation of polyacrylate) and the filler in powder form is added. Optionally, the solvent is metered to set the required solid content. If provided, the dye is slurried with a small amount of acetone and added to the polymer solution. Subsequently, the components are uniformly mixed with a stirrer. In the short time before coating, the crosslinking agent system (see Table 3) is added as a 5% strength acetone solution and stirred.

[0149] The composition thus obtained was coated as solution onto a release liner (siliconized PET film) using a comma rod (layer thickness see Table 3). The solvent was removed in a drying tunnel (10 minutes, 105° C.).

[0150] Table 2: Other raw materials used

[0151]

[0152]

[0153] Preparation of tape

[0154] For transfer tapes (single-layer adhesive tapes), the pressure-sensitive adhesive is applied to a release liner in the relevant layer thickness (see "Manufacture of pressure-sensitive adhesives"). In the case of multilayer products, the pressure-sensitive adhesive is applied to a release liner in the relevant layer thickness (see "Manufacture of pressure-sensitive adhesives") and subsequently laminated onto the corresponding carrier. The adhesive tape is lined with a release liner on both sides.

[0155] Carrier

[0156] PUF-polyurethane film, thickness 30μm

[0157] PET-F-polyethylene terephthalate film, thickness 50 μm

[0158] Table 4: Tapes

[0159]

[0160] (V) Comparative experiment, not according to the present invention

[0161] Test Method

[0162] Method 1:

[0163] Instant adhesion on plastic and steel

[0164] The determination is carried out under test conditions of 23°C + / - 1°C and 50% + / - 5% relative air humidity.

[0165] Test substrate:

[0166] Steel Test Plates-ASTM

[0167] Plastic test plate - PBT plate reinforced with 30% glass fiber, surface roughness 1μm

[0168] Before measuring, the test plate was cleaned and conditioned by first wiping with ethanol (PBT test plate) or acetone (steel plate) and then standing in 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 a 36 μm etched PET film to prevent the sample from stretching during the measurement. The tape was then applied to the test substrate by rolling back and forth twice with a 2 kg rubber roller at a rolling speed of 10 m / min. Immediately thereafter, the tape was pulled away from the test substrate at an angle of 180 °, wherein the force required for this was measured with a Zwick tensile tester. The measurement results were reported as the average value of three separate measurements in N / cm.

[0169] An adhesion of at least 3.0 N / cm is considered a good result.

[0170] Method 2:

[0171] DuPont test in z direction (puncture resistance (Durchschlagzähigkeit))

[0172] A square frame sample (external dimensions 33 mm x 33 mm; edge width 2.0 mm; internal dimensions (window cutout) 29 mm x 29 mm) was cut from the tape (pressure-sensitive adhesive strip) to be inspected. The sample was pasted to a polycarbonate (PC) frame (external dimensions 45 mm x 45 mm; edge width 10 mm; internal dimensions (window cutout) 25 mm x 25 mm; thickness 3 mm). A 35 mm x 35 mm PC window was pasted to the other side of the tape. The PC frame, tape frame and PC window were bonded so that the geometric center and diagonal lines were each superimposed on each other (corner to corner). The bonding area was 248 mm². The adhesive was pressed with 248 N for 5 seconds and stored for 24 hours at 23°C / 50% relative humidity.

[0173] Immediately after storage, the bonded assembly consisting of the PC frame, adhesive tape and PC window was clamped in the sample holder with the protruding edge of the PC frame so that the assembly was oriented horizontally and the PC window was below the frame. The sample holder was then inserted centrally into the holder of the set "DuPont Impact Tester". A 190 g punch was used so that a circular impact geometry with a diameter of 20 mm was centered and flush against the window side of the PC window.

[0174] 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 consisting of the sample holder, sample and punch arranged in this way (measurement conditions: 23°C, 50% relative humidity). The height of the falling weight was increased in steps of 5 cm until the introduced impact energy destroyed the sample as a result of the impact stress and the PC window was separated from the PC frame.

[0175] In order to be able to compare experiments with different samples, the energy was calculated as follows:

[0176]

[0177] Five samples of each product were tested and the average energy value was reported as an indicator of puncture resistance.

[0178] Method 3:

[0179] Drop tower test (puncture resistance)

[0180] The drop tower test method, which is an instrumented drop device test, is also used to measure puncture resistance.

[0181] Cut a square frame sample (area 180mm) from the tape to be inspected. 2; Edge width 2 mm). The sample was pasted to the steel frame cleaned with acetone. The steel window cleaned with acetone was pasted on the other side of the tape. The steel frame, tape frame and steel window were bonded so that the geometric center and diagonal were superimposed on each other (corner to corner). The adhesive was pressed with 62N for 10 seconds and stored at 23°C / 50% relative humidity for 24 hours.

[0182] Immediately after storage, the test specimen is placed on the sample holder of the instrumented drop device in such a way that the assembly is horizontal with the steel window facing downwards. The measurement is carried out instrumentally and automatically using a 5 kg load weight and a drop height of 20 cm. The kinetic energy introduced by the load weight destroys the bond by rupture of the adhesive tape between the window and the frame, wherein the force is recorded in µs periods by a piezoelectric sensor. The accompanying software thus gives a diagram of the force-time variation after the measurement, from which the maximum force can be determined. The velocity of the falling weight is determined by two gratings shortly before the rectangular impact geometry hits the window. Assuming that the energy introduced is greater than the impact strength of the bond, the work done by the bond before complete separation, i.e. the separation work, is determined from the change in force, the time required for separation and the velocity of the falling weight. Five test specimens are checked for each sample and the final result is the separation work or the maximum force (in N) of these five specimens. ) is composed of the average value of .

[0183] Method 4:

[0184] Static shear test / holding force (shear life, Scherstandzeit)

[0185] The shear strength is determined under test conditions of 70°C + / - 1°C and 50% + / - 5% relative air humidity.

[0186] The specimen is trimmed to a width of 25+ / -0.2mm. A 50 x 25 mm ASTM steel plate with a thickness of 2mm and a 25mm marking line is used for testing, which has been cleaned three times with acetone before bonding and then left to dry for 10 minutes. The bonding area is 25 x 25 mm. In the case of avoiding air inclusions by running on it with a wiping device, the test strip is applied to the adhesive substrate centered in the longitudinal direction so that the upper edge of the test sample is accurately aligned with the 25mm marking line. The back of the test sample is pasted with a 36μm etched PET film. The free protruding end is pasted with paper. Then the adhesive strip is rolled back and forth twice with a 2kg roller.

[0187] After rolling, a belt loop (weight 5-7 g) was mounted on the protruding end of the adhesive tape. The plate thus prepared was fixed to a clock counter by means of a hook via an adapter plate, a 1 kg weight was suspended in the belt loop without pulling (ruckfrei). The pull-off time (Aufziehzeit) between rolling and load was 12 minutes. The time in minutes until the adhesive bond failed was measured and the result was the average of three measurements.

[0188] Method 5:

[0189] Tear test

[0190] Strips of 10 mm wide and 40 mm long were punched out from the tape under investigation. These strips were pasted onto battery membrane plates conditioned with ethanol over a length of 30 mm, leaving a 10 mm long protruding grip tab. An ASTM plate was pasted onto the second side of the bonded strip, specifically, so that the two plates were flush with each other. The assembly was rolled 10 times (five times back and forth) with a 4 kg roller. After a pull-off time of 4 hours and 24 hours, the strips were manually peeled off from the adhesive joint at an angle of a) 90 ° and b) 180 ° at the grip tab. The number of specimens that could be separated again without residue was evaluated.

[0191] Method 6:

[0192] Particle size distribution and particle shape

[0193] The particle size distribution was performed by laser diffraction using a "Bettersizer S3 Plus" instrument. The dispersion medium used was isopropanol. The samples were placed directly in the dispersion unit filled with isopropanol. Prior to the measurement, the samples were exposed to the internal ultrasound of the instrument (35 W) for 1 minute, without ultrasound during the measurement. The stirring speed was 1200 rpm. The evaluation was performed according to Mie, with the refractive index optimized by the instrument.

[0194] Particle shape was determined by dynamic image analysis immediately after laser diffraction. A 10x camera was used. Approximately 5000 particles were analyzed. Evaluation was performed by area equivalent diameter.

[0195] Table 5: Results

[0196]

Claims

1. Pressure-sensitive adhesives, including - at least one poly(meth)acrylate and - at least one filler comprising a total of at least 70% by weight of one or more polyolefins and / or one or more olefin copolymers, based on the total weight of said filler; It is characterized in that The pressure-sensitive adhesive contains a total of 1 to 13 wt % of one or more of these fillers, based on the total weight of the pressure-sensitive adhesive.

2. The pressure-sensitive adhesive according to any 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 volume particle size distribution determined by laser diffraction as described herein of 25-110 μm.

3. The pressure-sensitive adhesive according to any 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.

4. The pressure-sensitive adhesive according to any one of the preceding claims, characterized in that The at least one filler is in the form of a solid body.

5. The pressure-sensitive adhesive according to any one of the preceding claims, characterized in that The at least one filler comprises a total of at least 70 weight percent of one or more polyolefins, based on the total weight of the filler.

6. The pressure-sensitive adhesive according to any one of the preceding claims, characterized in that The at least one filler comprises a total of at least 70 wt % polyethylene, based on the total weight of the filler.

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

8. The 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. The pressure-sensitive adhesive according to any one of the preceding claims, characterized in that The at least one poly(meth)acrylate is obtained from the following monomer composition: a) 50 to 80% by weight of at least one acrylic ester according to formula (I) ， Where R 1 is a straight-chain or branched alkyl group having 1 to 10 carbon atoms; b) 15 to 45% by weight of at least one acrylate according to formula (II) ， Where R 2 is a phenoxyalkyl group; c) 0.5 to 10% by weight of at least one acrylate monomer according to formula (III) ， Where R 3 is a hydrogen atom or a hydroxyalkyl group having 1 to 4 carbon atoms.

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

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

12. The adhesive tape according to claim 10, characterized in that The adhesive tape comprises a PET film as a carrier layer.

13. The adhesive tape according to claim 10, characterized in that The adhesive tape comprises a polyurethane film or a synthetic rubber film as a carrier layer.

14. Use of the adhesive tape according to any one of claims 11 and 12 as an adhesive in the manufacture of assembly bonds in electronic, optical or precision mechanical devices.

15. Use of the adhesive tape according to claim 13 as an adhesive which can be separated again by stretching for producing adhesive bonds in electronic, optical or precision mechanical devices.

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