EP4196509A1

EP4196509A1 - Pressure-sensitive adhesive composition

Info

Publication number: EP4196509A1
Application number: EP21765858.2A
Authority: EP
Inventors: Jos Tasche; André RELLMANN-SPRINK
Original assignee: Tesa SE
Current assignee: Tesa SE
Priority date: 2020-08-14
Filing date: 2021-08-16
Publication date: 2023-06-21
Also published as: CN116075571A; US20230295473A1; WO2022034247A1; JP2023538015A; KR20230048632A

Abstract

The invention relates to a pressure-sensitive adhesive composition which exhibits good adhesive forces, in particular on polar adhesive substrates, as well as good shear strength, and a significant proportion of which can be produced from bio-based raw materials. This is achieved using a pressure-sensitive adhesive composition comprising: at least one copolymer which can be reduced to a monomer composition comprising d) 45 - 75 wt.% of at least one monomer selected from the group consisting of i-amyl acrylate, n-heptyl acrylate, and 2-octyl acrylate, e) 24 - 50 wt.% of at least one alkyl (meth)acrylate, the alcohol component of which has 1 to 4 carbon atoms, and f) 0.5 to 10 wt.% of acrylic acid; and at least one adhesive force-enhancing resin. The invention also relates to: an adhesive tape comprising a carrier material and, on at least one of its two outer sides, a pressure-sensitive adhesive composition according to the invention; and the use of a pressure-sensitive adhesive composition according to the invention or of an adhesive tape according to the invention for producing adhesive bonds in electronic, optical and/or precision mechanical devices.

Description

pressure sensitive adhesive

The invention relates to the technical field of pressure-sensitive adhesives, such as are often used for the temporary or permanent joining of parts to be joined. More specifically, the invention proposes a pressure-sensitive adhesive based on a specially composed polyacrylate copolymer, which has good bond strengths and shear strengths, in particular on polar adhesive substrates, and at the same time makes it possible for a significant proportion of the components to be based on renewable raw materials.

The demands on the quality of PSAs have increased dramatically in recent years. An example of this is the use of pressure-sensitive adhesives in electronic products such as smartphones and tablet computers. The adhesive masses should have distinctive technical adhesive properties, e.g. high shock resistance, but they must also be compatible with the often highly sensitive electronic components. Increasingly, ecological and social criteria are also coming into focus, e.g. regarding the origin of the raw materials.

In this context, there is a particular demand for raw materials that come partly or even entirely from biological sources (so-called bio-based raw materials). This is part of the currently generally observed trend towards sustainable products and addresses in particular the finite oil reserves and the resulting need to use them sparingly; Corresponding products are increasingly being actively requested by the customers of the adhesive mass manufacturers. In addition to the aspect of scarcity of resources, the "ecological footprint" resulting from the extraction and manufacture of the components is also taken into account. The main issue here is the amount of CO2 that occurs during the corresponding processes. This is generally lower for products from renewable sources, and some of the substances produced even have a negative CO2 balance. There is therefore a particularly ecologically motivated interest in pressure-sensitive adhesives which combine good technical adhesive performance with the raw materials originating as far as possible from renewable sources. In view of the aspects mentioned, poly(meth)acrylates have repeatedly proven to be useful starting materials. Accordingly, work is continuing on suitable formulations for poly(meth)acrylate-based PSAs.

An aqueous pressure-sensitive adhesive composition which is essentially based on an acrylate polymer dispersed in water is described, for example, in EP 2 062 955 A1.

Typical of acrylate-based pressure-sensitive adhesives based on vegetable raw materials are adhesive compositions based on a copolymer, which is the reaction product of

90 to 99.5% by weight of 2-octyl (meth)acrylate,

0.5 to 10% by weight of (meth)acrylic acid and less than 10% by weight of further monomers, as described in WO 2008/046000 A1.

EP 3 013 767 A1 discloses the use of a polymer resulting from the polymerisation of 2-octyl acrylate of renewable origin and optionally at least one other monomer as a binder for the preparation of a coating composition, the polymer having a glass transition temperature of from -30°C to 30 °C.

EP 2 626 397 A1 relates to a PSA comprising a polymer component based on acrylate, where at least 50% by weight of the monomers used to produce the polymer component can be traced back entirely to renewable raw materials.

However, it is still problematic that bio-based raw materials for the production of polyacrylate-based PSAs are only available to a very limited extent. It is therefore still a challenge to formulate high-performance pressure-sensitive adhesives based on the comparatively narrow spectrum of available bio-based starting materials. The object of the invention was to provide a pressure-sensitive adhesive which has good bond strengths, in particular on polar substrates, and good shear strength, and can be produced to a high proportion from bio-based raw materials.

A first and general subject matter of the invention, with which the object is achieved, is a pressure-sensitive adhesive which has at least one copolymer which is based on a monomer composition which a) 45-75% by weight of at least one monomer selected from the group consisting of i- amyl acrylate, n-heptyl acrylate, and 2-octyl acrylate, b) 24-50% by weight of at least one alkyl (meth)acrylate whose alcohol component has 1 to 4 carbon atoms, and c) 0.5 to 10% by weight acrylic acid can be recycled; and at least one tackifying resin.

A PSA of this type has the good adhesive properties required for its task, with both the polymer component and the resin content being able to be formulated largely on the basis of renewable raw materials. In particular, the monomers a) are now readily available as bio-based substances. As has been established, a composition according to the invention, even if only the alcohol components of the monomers a) are actually produced from bio-based raw materials, also has a lower ecological footprint (carbon footprint) than comparable pressure-sensitive adhesives produced entirely on a petroleum basis, which as monomers correspond to a ) often use 2-ethylhexyl acrylate. This can essentially be attributed to the extraction and production of the relevant monomers a).

According to the invention, a pressure-sensitive adhesive or a pressure-sensitive adhesive is understood, as is customary in general usage, to mean a substance which is permanently tacky and adhesive at least at room temperature. A characteristic of a pressure-sensitive adhesive is that it can be applied to a substrate by pressure and remains stuck there, with the pressure to be applied and the duration of action of this pressure not being defined in more detail. In general, but depending on the exact nature of the pressure-sensitive adhesive and the substrate, the temperature and humidity, exposure to a short-term, minimum pressure, not exceeding a light touch for a short moment, in order to achieve the adhesion effect, in other cases a longer period of exposure to higher pressure may be necessary.

Pressure-sensitive adhesives have special, characteristic viscoelastic properties that lead to permanent tack and adhesiveness. They are characterized by the fact that when they are mechanically deformed, both viscous flow processes and the build-up of elastic restoring forces occur. In terms of their respective proportion, both processes are in a specific relationship to one another, depending both on the exact composition, the structure and the degree of crosslinking of the PSA and on the speed and duration of the deformation and on the temperature.

The proportionate viscous flow is necessary to achieve adhesion. Only the viscous portions, often caused by macromolecules with relatively high mobility, enable good wetting and good flow onto the substrate to be bonded. A high proportion of viscous flow leads to high pressure-sensitive tack (also known as tack or surface tack) and therefore often to high adhesion. Highly crosslinked systems, crystalline or glass-like solidified polymers are generally not, or at least only slightly, tacky due to the lack of free-flowing components.

The proportional elastic restoring forces are necessary to achieve cohesion. They are caused, for example, by very long-chained and heavily entangled macromolecules as well as by physically or chemically crosslinked macromolecules and enable the forces acting on an adhesive bond to be transmitted. They mean that an adhesive bond can withstand a permanent load acting on it, for example in the form of a permanent shearing load, to a sufficient extent over a longer period of time.

The storage modulus (G') and loss modulus (G"), which can be determined using dynamic mechanical analysis (DMA), are used for a more precise description and quantification of the extent of the elastic and viscous parts and the ratio of the parts to one another. G' is a measure of the elastic part, G" a measure of the viscous part of a substance. Both quantities depend on the deformation frequency and the temperature.

The sizes can be determined using a rheometer. The material to be examined is placed, for example, in a plate-plate arrangement in a sinusoidally oscillating exposed to variable shear stress. In the case of shear stress-controlled devices, the deformation is measured as a function of time and the time offset of this deformation in relation to the introduction of the shear stress. This time offset is referred to as the phase angle δ.

The storage modulus G' is defined as follows: G' = (T/y) »cos(ö) (T = shear stress, Y = deformation, ö = phase angle = phase shift between shear stress and deformation vector). The definition of the loss modulus G" is: G"=(T/Y)·sin(δ) (T=shear stress, y=deformation, δ=phase angle=phase shift between shear stress and deformation vector).

A mass is considered to be a pressure-sensitive adhesive and is defined as such in the context of the invention in particular if, at 23° C. in the deformation frequency range from 10° to 10 ¹ rad/sec, both G' and G" are at least partly in the range of 10 ³ up to 10 ⁷ Pa. "Partly" means that at least a portion of the G' curve lies within the window defined by the strain frequency range from 10° to 10 ¹ rad/sec inclusive (abscissa) and the range of G' values from 10 ³ inclusive up to and including 10 ⁷ Pa (ordinate) and if at least part of the G” curve also lies within the corresponding window.

The PSA of the invention comprises at least one copolymer which can be traced back to a monomer composition which a) 45-75% by weight of at least one monomer selected from the group consisting of i-amyl acrylate, n-heptyl acrylate and 2-octyl acrylate, b) 24-50% by weight of at least one alkyl (meth)acrylate whose alcohol component has 1 to 4 carbon atoms, and c) 0.5 to 10% by weight of acrylic acid.

In particular, the monomers listed under a) can all be produced from renewable raw materials. A process for producing bio-based acrylic acid, which can be used as monomer c) and as an acid component for monomers a) and b), starts with glycerol, which occurs in large quantities, for example, in the transesterification of vegetable oils with methanol to produce biodiesel and therefore available. The process includes dehydrating the glycerol to acrolein; the acrolein is then oxidized to acrylic acid in a one- or two-stage process. Such a method is described, for example, in US 2007/0129570 A1.

WO 2006/092272 A2 discloses a similar process in which glycerol is first converted to a dehydration product containing acrolein and then a gas-phase oxidation of this dehydration product is carried out, with a product containing acrylic acid being produced. Acrylic acid is obtained by contacting the oxidation product with a quenching agent and processing the quenched phase. This process enables the production of acrylic acid from renewable raw materials without the use of reactive compounds. The glycerol is preferably obtained from the saponification of animal or vegetable fats.

Bio-based acrylic acid can also be obtained by a method in which lactic acid (2-hydroxypropionic acid) or 3-hydroxypropionic acid is produced from biological material as a fluid - in particular in the aqueous phase - the hydroxypropionic acid is dehydrated to obtain a fluid containing acrylic acid and the acrylic acid containing fluid is purified. The required hydroxypropionic acid can be produced by fermentation. Fermentative reactions are often highly selective, with high yields and almost free of by-products due to the high selectivity of the microorganisms used. Secondary reactions are also avoided because the fermentation processes are carried out at low temperatures of 30 - 60 °C. Large-scale chemical processes in petrochemistry, on the other hand, are often carried out at much higher temperatures of mostly > 200 °C to optimize the yields. However, high reaction temperatures always lead to side reactions and the formation of cracking products.

The process just described is described, for example, in DE 102006 039203 A1, the purification of the fluid containing acrylic acid being carried out by suspension crystallization or layer crystallization. Various processes are also available for the production of alcohols from renewable raw materials.

For example, butanol can be obtained by fermenting plant biomass, which is usually processed beforehand. One starts with sucrose, starch or cellulose, for example, and genetically modified microorganisms are sometimes used (so-called “white biotechnology”). In the so-called A.B.E. process (A.B.E. for acetone, butanol, ethanol), the bacterium Clostridium acetobutylicum is used for fermentation to produce 1-butanol.

2-Octanol can be obtained and isolated as a by-product in the oxidation of ricinic acid to sebacic acid. n-Heptanol can be obtained from heptanal, which is obtained during the thermal decomposition of ricinic acid (pyrolytic decomposition to heptanal and undecenoic acid).

The monomers a) lower the glass transition temperature of the copolymer compared to the other monomers present. This is advantageous because it promotes the attachment of the PSA to the adhesive substrate. In addition, the compound can absorb more resin, which also has a positive effect on the adhesive performance.

The monomer composition of the copolymer of the pressure-sensitive adhesive of the invention comprises monomers a) according to the invention at a total of 45 to 75% by weight. The monomer composition of the copolymer of the pressure-sensitive adhesive of the invention preferably comprises monomers a) to a total of 50 to 72% by weight, in particular to a total of 60 to 70% by weight. In principle, the monomer composition can comprise one (single) or more than one monomer a).

The monomer composition of the copolymer of the PSA of the invention preferably comprises at least 2-octyl acrylate as monomer a). This is particularly advantageous because this monomer further reduces the glass transition temperature of the copolymer. In addition, it does not introduce any side-chain crystallinity and thus makes a particularly strong contribution to the development of pressure-sensitive adhesive properties. Especially comprises the monomer composition as monomer a) 2-octyl acrylate. This means that only 2-octyl acrylate is included as monomer a).

According to the invention, the monomer composition of the copolymer of the PSA of the invention also comprises 24-50% by weight of at least one alkyl (meth)acrylate whose alcohol component has 1 to 4 carbon atoms (monomers b)). The monomer composition of the copolymer of the pressure-sensitive adhesive of the invention comprises monomers b), that is to say a total of 24 to 50% by weight. The monomer composition of the copolymer of the pressure-sensitive adhesive of the invention preferably comprises monomers b) to a total of 25 to 40% by weight, in particular to a total of 27 to 35% by weight. The monomer composition can in principle comprise one (single) or more than one monomer b).

Preference is given to at least one alkyl (meth)acrylate whose alcohol component has 1 to 4 carbon atoms, selected from the group consisting of methyl acrylate, ethyl acrylate, n-butyl methacrylate and i-butyl acrylate. The monomer composition of the copolymer according to the invention particularly preferably comprises i-butyl acrylate as monomer b). i-Butyl acrylate is bio-based and has a smaller ecological footprint in terms of raw material extraction and production, especially compared to the commonly used, petroleum-based n-butyl acrylate.

The monomer composition of the copolymer according to the invention particularly preferably comprises i-butyl acrylate and methyl acrylate as monomers b).

The monomers b) bring about an increase in the glass transition temperature of the copolymer, particularly in comparison with the monomers a). This is advantageous because it allows the properties of the pressure-sensitive adhesive to be tailored to the particular requirements by shifting the proportions by weight of the monomers a) and b). In addition, it is assumed that they introduce entanglements into the copolymer. This is advantageous because it gives the PSA greater toughness and cohesion.

The monomer composition of the copolymer of the pressure-sensitive adhesive of the invention preferably comprises from 1 to 7% by weight, in particular from 2 to 4% by weight, of acrylic acid. The monomer composition of the copolymer of the PSA according to the invention preferably consists of a) 45-75% by weight of at least one monomer selected from the group consisting of i-amyl acrylate, n-heptyl acrylate and 2-octyl acrylate, b) 24-50% by weight at least one alkyl (meth)acrylate whose alcohol component has 1 to 4 carbon atoms, and c) 0.5 to 10% by weight of acrylic acid or of the monomers described above as being preferred in the proportions specified there.

The copolymers are preferably prepared by conventional free-radical polymerizations or controlled free-radical polymerizations. The copolymers can be prepared by copolymerizing the monomers using customary polymerization initiators and, if appropriate, regulators, polymerization being carried out at the customary temperatures in bulk, in emulsion, for example in water or liquid hydrocarbons, or in solution.

The copolymers are preferably prepared by copolymerizing the monomers in solvents, particularly preferably in solvents with a boiling point range from 50 to 150° C., in particular from 60 to 120° C., using from 0.01 to 5% by weight, in particular from 0. 1 to 2% by weight, based in each case on the total weight of the monomers, of polymerization initiators.

In principle, all customary initiators are suitable. Examples of radical sources are peroxides, hydroperoxides and azo compounds, for example dibenzoyl peroxide, cumene hydroperoxide, cyclohexanone peroxide, di-t-butyl peroxide, cyclohexylsulfonyl acetyl peroxide,

diisopropyl percarbonate, t-butyl peroctoate and benzpinacol. Preferred radical initiators are 2,2'-azobis(2-methylbutyronitrile) (Vazo® 67™ from DuPont) or 2,2'-azobis(2-methylpropionitrile) (2,2'-azobisisobutyronitrile; AIBN; Vazo® 64™ from the DuPont company).

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

The copolymer of the pressure-sensitive adhesive of the invention preferably has a weight-average molecular weight M _w of from 750,000 to 2,000,000 g/mol. The polydispersity (M _w /M _n ) of the copolymer is preferably 50 to 170.

The copolymer of the PSA of the invention preferably has a K value of from 50 to 100, more preferably from 60 to 90, in particular from 65 to 85. The Fikentscher K value is a measure of the molecular weight and viscosity of polymers.

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

The pressure-sensitive adhesive of the invention can in principle comprise one (single) or more than one copolymer of the type described above; it preferably comprises exactly one such copolymer.

The pressure-sensitive adhesive of the invention preferably comprises copolymers as described above at a total of 40 to 80% by weight, more preferably at a total of 45-75% by weight, in particular at a total of 50 to 70% by weight, very particularly preferably at a total of 55 to 65% % by weight, based in each case on the total weight of the pressure-sensitive adhesive. The pressure-sensitive adhesive of the invention particularly preferably comprises (precisely) a copolymer as described above at 40 to 80% by weight, more preferably at 45-75% by weight, in particular at 50 to 70% by weight, very particularly preferably at 55 to 65% by weight, based in each case on the total weight of the PSA.

The copolymer or copolymers of the pressure-sensitive adhesive of the invention are preferably chemically crosslinked, in particular thermally crosslinked. "Thermally crosslinked" refers to crosslinking by means of substances that form under the influence of thermal energy Enable (initiate) and/or promote crosslinking reaction. Preferred thermal crosslinkers are covalently reacting crosslinkers, in particular epoxides, isocyanates and/or aziridines, and coordinative crosslinkers, particularly preferably metal chelates, in particular aluminum, titanium, zirconium and/or iron chelates. Combinations of different crosslinkers, e.g. B. a combination of one or more epoxides with one or more metal chelates can be used.

The copolymer is particularly preferably crosslinked with an epoxide, in particular with a quadruple functionalized epoxide with tertiary amine functions. An example of such a thermal crosslinker is tetraglycidyl-metaxylenediamine (N,N,N',N'-tetrakis(oxiranylmethyl)-1,3-benzenedimethanamine). Such crosslinkers are preferably used in an amount of from 0.03 to 0.1 part by weight, particularly preferably from 0.04 to 0.07 part by weight, based in each case on 100 parts by weight of the copolymer (solvent-free). .

The pressure-sensitive adhesive of the invention also comprises at least one bond-boosting resin. According to the general understanding of the art, this means an oligomeric or polymeric resin which increases the autohesion (the tack, the intrinsic tack) of the pressure-sensitive adhesive compared to the pressure-sensitive adhesive which contains no bond-strengthening resin but is otherwise identical. In addition, bond strength-boosting resins can advantageously also improve the wetting properties of the PSA in relation to the substrate to be bonded, its release behavior and/or its adhesion.

The at least one bond-boosting resin of the pressure-sensitive adhesive of the invention can in principle be any adhesive resin that is compatible with the pressure-sensitive adhesive and in particular with the copolymer or copolymers of the pressure-sensitive adhesive. In one embodiment, the tackifying resin is selected from the group consisting of aliphatic, aromatic, and alkyl aromatic hydrocarbon resins; hydrocarbon resins based on pure monomers; hydrogenated hydrocarbon resins; functional hydrocarbon resins and optionally derivatized natural resins; preferably the tackifying resin is selected from the group consisting of pinene, indene and rosins, their disproportionated, hydrogenated, polymerized, esterified derivatives and salts; aliphatic and aromatic hydrocarbon resins; Terpene resins and terpene phenolic resins as well as Cs, Cg and other hydrocarbon resins. the PSA of the invention can in principle comprise one (single) or more bond strength-boosting resins.

The at least one adhesion-promoting resin is particularly preferably selected from rosin resins and polyterpene-based resins. These resins can be used advantageously because they can be produced or obtained to a large extent, in particular entirely, from renewable raw materials.

In particular, the tackifying resin is selected from rosins and polyterpene phenolic resins. These tackifying resins can be prepared from renewable raw materials and have proven to be particularly suitable for improving the technical adhesive properties of the pressure-sensitive adhesive of the invention to a particular degree.

Most preferably, the tackifying resin is a fully hydrogenated rosin. This is particularly advantageous because these resins have a comparatively low softening point and thus make an advantageous contribution to developing pressure-sensitive adhesive properties. In addition, they have particularly good aging stability.

The pressure-sensitive adhesive of the invention preferably comprises a total of 15 to 60% by weight, more preferably a total of 25 to 55% by weight, in particular a total of 30 to 50% by weight, very particularly preferably a total of 35 to 45% by weight of adhesion-boosting resins. -%, based in each case on the total weight of the PSA.

The pressure-sensitive adhesive of the invention can also comprise further components, for example softeners (plasticizers); Fillers, in particular fibres, carbon black, zinc oxide, titanium dioxide, spinels, dyes, pigments, chalk, solid or hollow glass spheres, microspheres made from other materials, e.g. polymeric hollow microspheres, silicic acid and/or silicates; nucleating agents; blowing agents; compounding agents; Stabilizers and/or anti-aging agents, e.g. primary and/or secondary antioxidants and/or light stabilizers.

In one embodiment, at least 50% by weight, preferably at least 60% by weight, in particular at least 65% by weight, of the PSA of the invention is biobased. Another advantage of the PSA of the invention is that the proportion bio-based components can be detected using the established radiocarbon method ( ¹⁴ C method).

The PSA of the invention is preferably prepared from solution, i.e. the components are dispersed or dissolved in a suitable solvent and mixed; the solvent is removed after the end of the mixing process using conventional methods.

The pressure-sensitive adhesive of the invention can be used as such, e.g. in the form of a laminate or an unsupported layer of the pressure-sensitive adhesive of the invention, which is also referred to as “adhesive transfer tape”. Such a transfer adhesive tape is preferably only applied to a material that serves temporarily to protect the adhesive surface, to make it easier to handle and to make it easier to apply the pressure-sensitive adhesive. Materials of this type are also referred to as release liners or simply as “liners” and are generally easily removable again, in particular by means of suitable surface coatings. The second side of the adhesive transfer tape can also be provided with a liner.

The release liners are, in particular, carrier materials which have been (coated or treated) antiadhesively on one side or, preferably, on both sides. Various papers, for example, can be used as carrier material for release liners, optionally also in combination with a stabilizing extrusion coating. Other suitable liner carrier materials are foils, in particular polyolefin foils, for example based on ethylene, propylene, butylene and/or hexylene. Preferred carrier materials are papers, e.g. glassine papers. Last but not least, papers are preferred because the concept of the origin of the components from renewable raw materials can also be extended to auxiliary materials of the adhesive tape.

Silicone systems are often used as an anti-adhesive release coating. The liners commonly used include, for example, siliconized papers and siliconized foils.

To use the adhesive transfer tape for bonding to a substrate surface, the liner or liners are then removed, so that the two adhesive sides each come into direct contact with the substrate surfaces to be bonded to one another. The liner is therefore not a productive component and is therefore not counted as part of the adhesive tape, but rather merely represents an aid for handling the same.

The pressure-sensitive adhesive of the invention is preferably used in the construction or for the production of multilayer adhesive tapes. Corresponding multilayer adhesive tapes usually comprise at least one backing layer and can have an outer layer of a pressure-sensitive adhesive of the invention on one or both sides. In the case of adhesive tapes with an adhesive finish on both sides, either one of the outer layers or else both outer layers can be pressure-sensitive adhesives of the invention. In the latter case, the pressure-sensitive adhesive layers can differ in terms of their chemical composition and/or their chemical and/or physical properties and/or their geometry (eg the layer thickness), but they are particularly preferred with regard to their chemical composition and/or their chemical and/or physical properties identical. In the case of multilayer adhesive tapes too, one or else both outer PSA layers can be covered with liners.

The adhesive tapes can have additional layers, e.g. additional carrier layers, functional layers or the like.

Bio-based materials are preferably selected as carrier materials for the multi-layer adhesive tape, for example those selected from the list consisting of papers; bio-based fabrics or fleeces, for example made of cotton or viscose; Cellophane; cellulose acetate; bio-based polyethylene films (PE) and polypropylene films (PP); films of thermoplastic starch; bio-based polyester films, e.g. films made from polylactide (PLA; polylactic acid), polyethylene terephthalate (PET), polyethylene tetrahydrofuranoate (PEF) or polyhydroxyalkanoate (PHA). The carrier material is particularly preferably a PET film. PET films are preferred, for example, because they can be used as recycled material and thus take the idea of sustainability into account in this way.

A further subject of the invention is thus an adhesive tape which comprises a backing material and at least one of its two outer sides, preferably both outer sides, a pressure-sensitive adhesive of the invention. The carrier material is preferably a PET film. The PET film preferably has a thickness of 1 to 5 μm; the layer or layers of the pressure-sensitive adhesive of the invention preferably each have a layer thickness of from 20 to 30 μm. The preferred overall thickness of the adhesive tape of the invention is therefore 41 to 65 μm.

For anchoring the PSA on the backing or on another substrate, it may be advantageous if the composition and/or the substrate is treated with corona or plasma before coating. Furthermore, for the anchoring of the pressure-sensitive adhesive layer on other layers, in particular on a backing layer, it can be advantageous if chemical anchoring, e.g. B. via a primer takes place.

A further subject matter of the invention is the use of a pressure-sensitive adhesive of the invention or of an adhesive tape of the invention for producing bonds in electronic, optical and/or precision engineering devices.

Electronic, optical and precision mechanical devices within the meaning of this application are, in particular, such devices as are included in class 9 of the International Classification of Goods and Services for the registration of trade marks (Nice Classification); 10th Edition (NCL(10-2013)); insofar as electronic, optical or precision mechanical devices are involved, as well as clocks and timepieces in accordance with class 14 (NCL(10-2013)), such as in particular scientific, nautical, surveying, photographic, film, optical, weighing, measuring -, signalling, checking (supervision), life-saving and teaching apparatus and instruments;

Apparatus and instruments for conducting, switching, transforming, accumulating, regulating or controlling electricity;

image recording, processing, transmission and reproducing apparatus such as televisions and the like; acoustic recording, processing, transmission and reproduction devices such as radios and the like;

computers, calculating and data processing equipment, mathematical equipment and instruments, computer accessories; office equipment such as printers, facsimile machines, copiers, typewriters; and data storage devices; long-distance communication and multifunctional devices with long-distance communication function such as telephones and answering machines; chemical and physical measuring devices, control devices and instruments such as battery chargers, multimeters, lamps, tachometers; nautical apparatus 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 extinguishers.

The focus of technical developments in the electronics sector is now often on devices that are becoming smaller and lighter so that their owners can carry them with them at all times. This is usually done by making such devices lighter and/or of a suitable size. Such devices are also referred to as mobile devices or portable devices. In this context, precision mechanical and optical devices are increasingly being provided with electronic components, which increases the possibilities for minimization. Because mobile devices are carried along, they are increasingly exposed to mechanical stress, such as bumping against edges, being dropped, contact with other hard objects in the bag, but also due to the permanent movement caused by carrying 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 ever moved. The pressure-sensitive adhesive of the invention has proven to be particularly preferred for surviving such disruptive influences and weakening or compensating for them. The pressure-sensitive adhesive of the invention or the adhesive tape of the invention are therefore preferably used to produce bonds in portable electronic devices.

Examples of portable electronic devices are:

cameras, digital cameras; photography accessories such as exposure meters, flash units, shutters, photo housings, lenses; film cameras, video cameras; Small computers (mobile computers, handheld computers, pocket calculators), laptops, notebooks, netbooks, ultrabooks, tablet computers, handhelds, electronic diaries and organizers (so-called "electronic organizers" or "personal digital assistants", PDAs, 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, touch pads ("touchpads");

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

electronic book readers (“e-books”);

small televisions, pocket televisions, film players, video players;

Radios (including small and pocket radios), Walkmen, Disemen, music players for e.g. CD, DVD, Blueray, cassettes, USB, MP3; Headphones; cordless telephones, mobile telephones, smart phones, walkie-talkies, hands-free devices, pagers (beepers); mobile defibrillators, blood sugar measuring devices, blood pressure measuring devices, pedometers, heart rate monitors;

torches, laser pointers; mobile detectors, optical magnifiers, long-distance vision devices, night vision devices;

GPS devices, navigation devices, portable satellite communications interface devices;

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

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

examples

Measurement and test methods:

Method 1—Determination of the Glass Transition Temperature _Tg of the Pressure-Sensitive Adhesives The static glass transition temperature of the PSAs was determined by means of differential scanning calorimetry (DDK) or—synonymously—dynamic scanning calorimetry (DSC). To do this, about 5 mg of an untreated sample of the PSA were weighed into a small aluminum crucible (volume 25 μl) and sealed with a perforated lid. A DSC 204 F1 from Netzsch was used for the measurement. It was worked under nitrogen for the purpose of inerting. The sample was first cooled to -150 °C, then heated up to +150 °C at a heating rate of 10 K/min and cooled again to -150 °C. The subsequent second heating curve was run again at 10 K/min and the change in heat capacity was recorded. Glass transitions are recognized as steps in the thermogram (heat flow-temperature diagram, see FIG. 1).

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

The respective linear area of the measurement curve before and after the step is extended in the direction of rising (area before the step) or falling (area after the step) temperatures (extension lines © and @). In the area of the step, a regression line © is laid parallel to the ordinate in such a way that it intersects the two extension lines in such a way that two areas ® and @ (between the extension line, the regression line and the measurement curve) of the same content are created. The point of intersection of the regression line positioned in this way with the measurement curve gives the glass transition temperature.

Method 2 - Determination of Molecular Weight

The details of the number-average molar mass M _n and the weight-average molar mass M _w in this document relate to the determination by gel permeation chromatography (GPC), which is known per se. The determination is carried out on a 100 μl sample that has been filtered until clear (sample concentration 4 g/l). Tetrahydrofuran with 0.1% by volume of trifluoroacetic acid is used as the eluent. The measurement takes place at 25 °C.

A column type PSS-SDV, 5 pm, 10 ³ Å, 8.0 mm * 50 mm (details here and below in the following order: type, particle size, porosity, inner diameter * length; 1 Å = 10 ^-10 m) used. A combination of columns of the type PSS-SDV, 5 μm, 10 ³ Å and 10 ⁵ Å and 10 ⁶ Å, each with 8.0 mm * 300 mm, is used for the separation (columns from Polymer Standards Service; detection using a Shodex RI71 differential refractometer ). The flow rate is 1.0 ml per minute. The calibration is carried out using the commercially available ReadyCal kit poly(styrene) high from PSS Polymer Standard Service GmbH, Mainz. This is based on the Mark-Houwink parameters K and alpha universally converted to polymethyl methacrylate (PMMA), so that the data is given in PMMA mass equivalents.

Method 3 - Determination of the tack

In this test, a steel ball weighing 5.6 g rolled down a ramp 65 mm high (angle of inclination 21°) onto a horizontal strip of the adhesive to be tested. The distance until the ball came to a standstill was measured (test climate 23° C., 50% relative humidity). A maximum distance of 300 mm is considered a good result.

Before the measurement, the balls were cleaned with cellulose and acetone and conditioned openly in the test atmosphere for 30 minutes.

Before the measurement, the adhesive was conditioned in the test climate for 1 day.

Method 4 - Determination of Shear Life

The shear strength was determined in a test climate of 23 +/-1 °C temperature and 50% +/-5% rel. humidity.

The test samples were cut to a width of 13 ± 0.2 mm and stored in a climatic environment for at least 16 hours. For the test, 50 x 25 mm ASTM steel plates with a thickness of 2 mm and a 20 mm marking line were used, which were intensively cleaned several times with acetone before bonding and then left to dry for 10 minutes. The bond area was 13 x 20 ± 0.2 mm. The test strip was applied to the middle of the substrate by rubbing it with a wiper in the longitudinal direction, avoiding air pockets, so that the upper edge of the test sample lay exactly on the 20 mm marking line.

The back of the test sample was masked with aluminum foil. The free protruding end was taped off 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.

An adapter plate was then attached to the front of the shear test panel with a screw and nut. To ensure that the adapter plate was firmly seated on the plate, the screw was tightened firmly by hand.

The plate prepared in this way was attached to a counter clock via the adapter plate by means of a hook; A 1 kg weight was then hung smoothly into the belt loop. The pull-up time between rolling and loading was 12 minutes. The time in minutes before the bond failed was measured; the measurement results are the average of three measurements. A shearing life of at least 3,000 minutes is considered a good result.

Method 5 - Adhesion steel

The adhesive strength was determined in a test atmosphere of 23 °C +/- 1 °C temperature and 50% +/- 5% rel. humidity. The samples were cut to 20mm width and glued to a steel plate (ASTM). The steel plate was cleaned and conditioned before the measurement. For this purpose, the plate was first wiped with solvent and then left in the air for 5 minutes so that the solvent could evaporate. The side of the adhesive tape facing away from the test substrate was then covered with 25 μm thick, etched PET film, which prevented the sample from stretching during the measurement. The test sample was then rolled onto the substrate. For this purpose, the tape was rolled back and forth five times with a 4 kg roller at a winding speed of 10 m/min. 1 min after rolling, the plate was pushed into a special holder. The bond strength was measured using a Zwick tensile testing machine; the samples were peeled off at an angle of 180° at a speed of 300 mm/min. The measurement results are given in N/cm and are averaged from five individual measurements.

Table 1: Commercially available chemicals used

Production of the polyacrylates and the PSAs:

A 3 L vessel conventional for free-radical polymerizations was filled with the amounts of acrylic acid (AA) and 2-octyl acrylate (2-OA) and optionally i-butyl acrylate (iBA) and/or methyl acrylate (MA) and 724 g of petrol given in the examples /acetone (70:30). After bubbling nitrogen gas through it for 45 minutes with stirring, the reactor was heated to 58°C and 0.5 g of Vazo® 67 was added. The jacket temperature was then set to 75° C. and the reaction was carried out constantly at this outside temperature. After a reaction time of 1 hour, another 0.5 g of Vazo® 67 was added. After 3 h it was diluted with 200 g of petrol/acetone (70:30) and after 6 h with 100 g of petrol/acetone (70:30). To reduce the residual initiators, 1.5 g each were added after 5.5 and after 7 h Added Perkadox® 16. The reaction was terminated after a reaction time of 24 h and cooled to room temperature.

The polyacrylate was then mixed with the adhesive resin and the crosslinker. The composition obtained in this way was coated from solution onto a siliconized release film (50 μm polyester) using a doctor blade and then dried (coating speed 2.5 m/min, drying tunnel 15 m, temperatures zone 1: 40° C., zone 2: 70° C , zone 3: 95° C., zone 4: 105° C.) The applied mass after drying was 50 g/m ² .

Table 2: Composition of the polymers and PSAs

See - Comparative Experiment Table 3: Results

See - Comparative experiment n.e. - not determined

Claims

24

Claims Pressure-sensitive adhesive comprising at least one copolymer which is based on a monomer composition comprising a) 45-75% by weight of at least one monomer selected from the group consisting of i-amyl acrylate, n-heptyl acrylate and 2-octyl acrylate, b) 24-50% by weight % of at least one alkyl (meth)acrylate, the alcohol component of which has 1 to 4 carbon atoms, and c) 0.5 to 10% by weight of acrylic acid can be recycled; at least one tackifying resin. Pressure-sensitive adhesive according to Claim 1, characterized in that the monomer composition comprises monomers a) to a total of 60 to 70% by weight. Pressure-sensitive adhesive according to either of Claims 1 and 2, characterized in that the monomer composition comprises 2-octyl acrylate as monomer a). Pressure-sensitive adhesive according to any one of the preceding claims, characterized in that the monomer composition comprises monomers b) to a total of 27 to 35% by weight. Pressure-sensitive adhesive according to one of the preceding claims, characterized in that the pressure-sensitive adhesive is a copolymer based on a monomer composition comprising a) 45-75% by weight of at least one monomer selected from the group consisting of i-amyl acrylate, n-heptyl acrylate, and 2- octyl acrylate, b) 24-50% by weight of at least one alkyl (meth)acrylate whose alcohol component has 1 to 4 carbon atoms, and c) 0.5 to 10% by weight of acrylic acid can be attributed to 40 to 80% by weight, based on the total weight of the PSA. Pressure-sensitive adhesive according to any one of the preceding claims, characterized in that the adhesion-boosting resin is selected from colophony resins and polyterpene-based resins. Pressure-sensitive adhesive according to one of the preceding claims, characterized in that the pressure-sensitive adhesive comprises a total of 25 to 50% by weight, based on the total weight of the pressure-sensitive adhesive. Adhesive tape comprising a backing material and at least on one of its two outer sides a pressure-sensitive adhesive according to any one of claims 1 to 7. Use of a pressure-sensitive adhesive according to any one of claims 1 to 7 or an adhesive tape according to claim 8 for the production of bonds in electronic, optical and / or precision mechanics Devices.