Pressure-sensitive adhesive compound

Abstract

The aim of the invention is to provide a pressure-sensitive adhesive compound or foam which exhibits good adhesive forces, in particular on polar adhesion substrates, as well as good shear strength, and a significant proportion of which can be produced from bio-based raw materials. This is achieved with a pressure-sensitive adhesive compound comprising - at least one copolymer A which is based on a monomer composition comprising or consisting of a) 75 to 98 wt.% of at least one alkyl acrylate, the alcohol component of which has 5 to 8 C atoms; b) 1 to 24 wt.% of at least one alkyl(meth)acrylate, the alcohol component of which has 1 to 4 C atoms; and c) 1 to 15 wt.% acrylic acid; and - one or more cross-linking agents. The invention is characterized in that the monomer composition contains 2-octyl acrylate with a maximum content of 87 wt.%. The invention also relates to an adhesive tape at least comprising a pressure-sensitive adhesive compound according to the invention; and the use of a pressure-sensitive adhesive compound 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

[0001] Pressure-sensitive adhesive

[0002] The invention relates to the technical field of pressure-sensitive adhesives, which are frequently used for the temporary or permanent bonding of components. More specifically, the invention proposes a pressure-sensitive adhesive and a foam based on a specially formulated polyacrylate copolymer that enables good bond strengths with good shear life and peel adhesion, particularly on polar adhesive substrates. A high proportion of the polyacrylate copolymer is based on renewable raw materials.

[0003] The demands on the quality of pressure-sensitive adhesives have increased dramatically in recent years. One example of this is the use of pressure-sensitive adhesives in electronic products such as smartphones and tablet computers. The adhesives are required to exhibit outstanding adhesive properties, such as high shock resistance, but must also be compatible with the often highly sensitive electronic components. Ecological and social criteria are also increasingly coming into focus, for example with regard to the origin of raw materials. In this context, raw materials that come partly or even entirely from biological sources are in particular demand. This is part of the currently general trend towards sustainable products and addresses in particular the finite nature of crude oil reserves and the resulting need to use them economically; customers of adhesive manufacturers are increasingly actively demanding corresponding products.

[0004] Poly(meth)acrylates have repeatedly proven to be highly usable starting materials under these aspects. Accordingly, work is ongoing on suitable formulations for poly(meth)acrylate-based pressure-sensitive adhesives.

[0005] An aqueous pressure-sensitive adhesive composition based essentially on an acrylate polymer dispersed in water is described, for example, in EP 2 062 955 A1.

[0006] Typical for acrylate-based pressure-sensitive adhesives based on plant raw materials are adhesive compositions based on a copolymer which comprises the reaction product of 90 to 99.5 wt.% 2-octyl (meth)acrylate, 0.5 to 10 wt.% (meth)acrylic acid and less than 10 wt.% of further monomers, as described in WO 2008 / 046000 A1.

[0007] EP 3 013 767 A1 discloses the use of a polymer resulting from the polymerization of 2-octyl acrylate of renewable origin and optionally at least one other monomer as a binder for the preparation of a coating composition, wherein the polymer has a glass transition temperature of -30 °C to 30 °C.

[0008] EP 2 626 397 A1 discloses a pressure-sensitive adhesive comprising an acrylate-based polymer component, wherein at least 50% by weight of the monomers used to produce the polymer component are derived entirely from renewable raw materials.

[0009] EP 4 196 509 A1 discloses a pressure-sensitive adhesive comprising at least one copolymer which can be traced back to a monomer composition comprising 45-75 wt.% of at least one monomer selected from the group consisting of i-amyl acrylate, n-heptyl acrylate, and 2-octyl acrylate, 24-50 wt.% of at least one alkyl (meth)acrylate whose alcohol component has 1 to 4 C atoms, and 0.5 to 10 wt.% of acrylic acid; and at least one adhesion-promoting resin.

[0010] The object of the invention was to provide a pressure-sensitive adhesive and a foamed pressure-sensitive adhesive which has good adhesive strengths, particularly on polar substrates, as well as good shear life and peel adhesion, and which can be produced to a high extent from bio-based raw materials.

[0011] A first and general subject matter of the invention with which the object is achieved is a pressure-sensitive adhesive comprising

[0012] - at least one copolymer A which can be traced back to a monomer composition comprising or consisting of a) 75 to 98% by weight of at least one alkyl acrylate whose alcohol component has 5 to 8 C atoms; b) 1 to 24% by weight of at least one alkyl (meth)acrylate whose alcohol component has 1 to 4 C atoms; and c) 1 to 15% by weight of acrylic acid; and one or more crosslinkers, characterized in that the monomer composition comprises not more than 87% by weight, preferably not more than 85% by weight, of 2-octyl acrylate.

[0013] Optionally, the pressure-sensitive adhesive contains an adhesive strength-enhancing resin.

[0014] Such a pressure-sensitive adhesive exhibits the good adhesive properties required for the task, whereby both the (co)polymer component and the optional resin component can be formulated largely on the basis of renewable raw materials.

[0015] For the purposes of the invention, a pressure-sensitive adhesive is understood, as is common parlance, to be a substance that 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 adhered there, whereby the pressure to be applied and the duration of this pressure are not defined in more detail. In general, however, depending on the exact type of pressure-sensitive adhesive and the substrate, the temperature, and the humidity, the application of short-term, minimal pressure, which does not go beyond a light touch for a brief moment, is sufficient to achieve the adhesion effect; in other cases, a longer exposure period of higher pressure may be necessary.

[0016] Pressure-sensitive adhesives have special, characteristic viscoelastic properties that lead to their permanent tack and adhesive strength. They are characterized by the fact that, when mechanically deformed, both viscous flow processes and the development of elastic restoring forces occur. The respective proportions of both processes are in a specific relationship to each other, depending on the precise composition, structure, and degree of crosslinking of the pressure-sensitive adhesive, as well as the speed and duration of the deformation and the temperature.

[0017] The viscous flow component is necessary to achieve adhesion. Only the viscous components, often caused by macromolecules with relatively high mobility, enable good wetting and flow onto the substrate to be bonded. A high proportion of viscous flow leads to high pressure-sensitive adhesion (also referred to as tack or surface stickiness) and thus often to high adhesion. Highly cross-linked systems, crystalline, or glass-like polymers, are generally not or at least only slightly pressure-sensitive due to the lack of flowable components.

[0018] The proportional elastic restoring forces are necessary to achieve cohesion. They are caused, for example, by very long-chain and highly entangled macromolecules, as well as by physically or chemically cross-linked macromolecules, and enable the transfer of forces acting on an adhesive bond. They ensure that an adhesive bond can sufficiently withstand continuous loading, for example, in the form of permanent shear stress, over an extended period of time.

[0019] For a more precise description and quantification of the degree of elastic and viscous components, as well as the relationship between the components, the storage modulus (G') and loss modulus (G"), which can be determined using Dynamic Mechanical Analysis (DMA), are used. G' is a measure of the elastic component, G" a measure of the viscous component of a material. Both parameters depend on the deformation frequency and the temperature.

[0020] These parameters can be determined using a rheometer. The material under test is subjected to sinusoidal oscillating shear stress, for example, in a plate-on-plate arrangement. Shear stress-controlled devices measure the deformation as a function of time and the temporal offset of this deformation relative to the application of the shear stress. This temporal offset is referred to as the phase angle δ.

[0021] 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(ö) (T = shear stress, y = deformation, ö = phase angle = phase shift between shear stress and deformation vector).

[0022] A mass is considered to be a pressure-sensitive adhesive and is defined as such in the sense 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. “Partially” means that at least a section of the G' curve lies within the window defined by the deformation frequency range from 10° to 10 1 rad / sec (abscissa) and the range of G' values ​​from 10 3 up to and including 10 7 Pa (ordinate) and if at least one section of the G curve also lies within the corresponding window.

[0023] The pressure-sensitive adhesive according to the invention comprises at least one copolymer A which can be traced back to a monomer composition which comprises or consists of a) 75 to 98% by weight of at least one alkyl acrylate whose alcohol component has 5 to 8 C atoms; b) 1 to 24% by weight of at least one alkyl (meth)acrylate whose alcohol component has 1 to 4 C atoms; and c) 1 to 15% by weight of acrylic acid.

[0024] In particular, the monomers listed under a) can all be produced from renewable raw materials.

[0025] According to the present disclosure, bio-based materials are materials produced from renewable raw materials.

[0026] A process for producing bio-based acrylic acid, which can be used as monomer c) and as the acid component for monomers a) and b), starts from glycerol, which is obtained in large quantities, for example, during the transesterification of vegetable oils with methanol to produce biodiesel and is therefore readily available. The process involves dehydrating the glycerol to acrolein; then, in a one- or two-step process, the acrolein is oxidized to acrylic acid. Such a process is described, for example, in US 2007 / 0129570 A1.

[0027] Another way to produce acrylic acid with a certain bio-based content is via the (bio)mass balance approach.

[0028] 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, producing an acrylic acid-containing product. Acrylic acid is obtained by contacting the oxidation product with a quenching agent and processing the quenching 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.

[0029] Bio-based acrylic acid can also be obtained by a process in which lactic acid (2-hydroxypropionic acid) or 3-hydroxypropionic acid is produced from biological material as a fluid—particularly in the aqueous phase—the hydroxypropionic acid is dehydrated to obtain a fluid containing acrylic acid, and the fluid containing the acrylic acid is purified. The required hydroxypropionic acid can be produced by fermentation. Fermentation reactions are often highly selective, with high yields and virtually free of by-products due to the high selectivity of the microorganisms used. Side reactions are also avoided by conducting the fermentation processes at low temperatures of 30–60 °C. Large-scale chemical processes in the petrochemical industry, on the other hand, are often carried out at much higher temperatures, usually > 200 °C, to optimize yields.However, high reaction temperatures always lead to side reactions and the formation of cracking products.

[0030] The process just described is described, for example, in DE 10 2006039 203 A1, wherein the purification of the fluid containing acrylic acid is carried out by suspension crystallization or layer crystallization.

[0031] Different processes are also available for producing alcohols from renewable raw materials.

[0032] Butanol is obtained through the fermentation of plant-based, usually previously processed biomass. This process starts with sucrose, starch, or cellulose, for example; genetically modified microorganisms are sometimes used (so-called "white biotechnology"). In the so-called ABE process (ABE for acetone, butanol, ethanol), the bacterium Clostridium acetobutylicum is used for fermentation to produce 1-butanol.

[0033] 2-Octanol can be obtained and isolated as a byproduct of the oxidation of castor acid to sebacic acid. n-Heptanol can be obtained from heptanal, which is produced during the thermal decomposition of castor acid (pyrolytic decomposition to heptanal and undecenoic acid).

[0034] Monomers a) lower the glass transition temperature of the copolymer compared to the other monomers contained in the copolymer. This is advantageous because it promotes the adhesion of the pressure-sensitive adhesive to the substrate. Furthermore, the adhesive can absorb more resin, which also has a positive effect on the adhesive performance.

[0035] The monomer composition of copolymer A of the pressure-sensitive adhesive of the invention comprises monomers a) in a total amount of 75 to 98 wt. Preferably, the monomer composition of copolymer A of the pressure-sensitive adhesive of the invention comprises monomers a) in a total amount of 76 to 86 wt. %, in particular in a total amount of 77 to 81 wt. %, particularly preferably in a total amount of 77 to 79 wt. The monomer composition can in principle comprise one (single) or more monomers a).

[0036] In one embodiment, the monomer composition comprises a (single) monomer a).

[0037] In a further embodiment, the monomer composition comprises two monomers a). In a further embodiment, the monomer composition comprises three monomers a).

[0038] In a preferred embodiment, the monomer composition of the copolymer A comprises as monomer a) at least one monomer selected from the group consisting of i-amyl acrylate, n-hexyl acrylate, n-heptyl acrylate, and 2-octyl acrylate.

[0039] In one embodiment, the pressure-sensitive adhesive comprises at least one copolymer A which can be traced back to a monomer composition comprising or consisting of a) 75 to 98% by weight of at least one monomer selected from the group consisting of i-amyl acrylate, n-hexyl acrylate, n-heptyl acrylate, and 2-octyl acrylate; b) 1 to 24% by weight of at least one alkyl (meth)acrylate whose alcohol component has 1 to 4 C atoms; and c) 1 to 15% by weight of acrylic acid; and

[0040] - one or more crosslinkers, characterized in that the monomer composition comprises 2-octyl acrylate in an amount of not more than 87% by weight, preferably not more than 85% by weight.

[0041] The monomer composition of copolymer A of the pressure-sensitive adhesive 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 copolymer A. Furthermore, it does not introduce side-chain crystallinity and thus contributes particularly strongly to the development of pressure-sensitive adhesive properties. In particular, the monomer composition of copolymer A comprises 2-octyl acrylate as monomer a). This means that 2-octyl acrylate is exclusively included as monomer a).

[0042] According to the invention, the monomer composition of copolymer A of the pressure-sensitive adhesive of the invention further comprises one or more alkyl (meth)acrylates whose alcohol component has 1 to 4 carbon atoms, [monomers b)]. The monomer composition of copolymer A of the pressure-sensitive adhesive of the invention thus comprises monomers b) in a total of 1 to 24 wt. Preferably, the monomer composition of copolymer A of the pressure-sensitive adhesive of the invention comprises monomers b) in a total of 9 to 16 wt. %, in particular in a total of 10 to 15 wt. The monomer composition can in principle comprise one (single) or more monomers b).

[0043] Preferably, the one or more alkyl (meth)acrylates whose alcohol component has 1 to 4 carbon atoms are selected from the group consisting of methyl acrylate, ethyl acrylate, n-butyl methacrylate, and i-butyl acrylate. Particularly preferably, the monomer composition of the copolymer A according to the invention comprises i-butyl acrylate and methyl acrylate as monomers b).

[0044] Monomers b) increase the glass transition temperature of copolymer A, particularly compared to monomers a). This is advantageous because the properties of the pressure-sensitive adhesive can be tailored to specific requirements by shifting the weight proportions of monomers a) and b). Furthermore, it is suspected that they introduce entanglements into the copolymer. This is advantageous because it imparts greater toughness and cohesion to the pressure-sensitive adhesive.

[0045] The monomer composition of the copolymer A of the pressure-sensitive adhesive according to the invention comprises acrylic acid at 1 to 15 wt.%, preferably at 2 to 8 wt.%, in particular at 3 to 7 wt.%.

[0046] The monomer composition of copolymer A of the pressure-sensitive adhesive according to the invention preferably consists of a) one or more monomers selected from the group consisting of i-amyl acrylate, n-hexyl acrylate, n-heptyl acrylate, and 2-octyl acrylate in a total of 76 to 89 wt. %, b) one or more alkyl (meth)acrylates whose alcohol component has 1 to 4 C atoms in a total of 9 to 16 wt. %, and c) 2 to 8 wt. % acrylic acid; or of the monomers described above as preferred in the proportions stated therein.

[0047] The copolymers A are preferably prepared by conventional free-radical polymerizations or controlled free-radical polymerizations. The copolymers A can be prepared by copolymerizing the monomers using customary polymerization initiators and, if appropriate, regulators, polymerization being carried out at customary temperatures in bulk, in emulsion, for example in water or liquid hydrocarbons, or in solution. The copolymers A are preferably prepared by copolymerizing the monomers in solvents, particularly preferably in solvents having a boiling range of 50 to 150°C, in particular of 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.

[0048] In principle, all common 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, cyclohexylsulfonylacetyl peroxide,

[0049] 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 DuPont).

[0050] Preferred solvents for the preparation of copolymers A are alcohols such as methanol, ethanol, n- and isopropanol, n- and isobutanol, especially isopropanol and / or isobutanol; hydrocarbons such as toluene and especially gasolines with a boiling range of 60 to 120 °C; ketones, especially acetone, methyl ethyl ketone, and methyl isobutyl ketone; esters such as ethyl acetate, and mixtures of the aforementioned solvents. Particularly preferred solvents are mixtures containing isopropanol in amounts of 2 to 15 wt. %, especially 3 to 10 wt. %, based in each case on the solvent mixture used.

[0051] The copolymer A of the pressure-sensitive adhesive according to the invention preferably has a weight-average molecular weight M w from 500,000 to 3,000,000 g / mol, particularly preferably a weight-average molecular weight M w from 700,000 to 1,500,000 g / mol.

[0052] The copolymer A of the pressure-sensitive adhesive according to the invention preferably has a Fikentscher K value of 30 to 100, preferably 40 to 90 and most preferably 50 to 80.

[0053] The pressure-sensitive adhesive according to the invention can in principle comprise one (single) or more copolymers A of the type described above; preferably, it comprises precisely one such copolymer A.

[0054] The pressure-sensitive adhesive of the invention preferably comprises copolymers A as described above in a total of 35 to 90 wt. %, more preferably in a total of 40 to 75 wt. %, in particular in a total of 45 to 70 wt. %, based in each case on the total weight of the pressure-sensitive adhesive. Particularly preferably, the pressure-sensitive adhesive of the invention comprises (exactly) one copolymer A as described above in a total of 35 to 90 wt. %, more preferably in a total of 40 to 75 wt. %, in particular in a total of 45 to 70 wt. %, based in each case on the total weight of the pressure-sensitive adhesive.

[0055] The pressure-sensitive adhesive according to the invention comprises one or more crosslinkers.

[0056] The copolymer A or the copolymers A 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 enable (initiate) and / or promote a crosslinking reaction under the influence of thermal energy. 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, zinc and / or iron chelates. Combinations of different crosslinkers, e.g., a combination of one or more epoxides with one or more metal chelates, can also be used.

[0057] The pressure-sensitive adhesive according to the invention comprises at least one coordinative and / or at least one covalent crosslinker.

[0058] The pressure-sensitive adhesive according to the invention preferably comprises a covalent crosslinker.

[0059] In a preferred embodiment of the invention, glycidylamines are used as covalent crosslinkers for the present invention. Examples of particularly preferred crosslinkers according to the invention are N,N,N',N'-tetrakis(2,3-epoxypropyl)cyclohexane-1,3-dimethylamine and N,N,N',N'-tetrakis(2,3-epoxypropyl)-m-xylene-a,a'-diamine.

[0060] Polyfunctional epoxides, especially epoxycyclohexylcarboxylates, can also be advantageously used as covalent crosslinkers. Examples include 2,2-bis(hydroxymethyl)-1,3-propanediol and (3,4-epoxycyclohexane)methyl-3,4-epoxycyclohexylcarboxylate.

[0061] Furthermore, multifunctional azeridines can be used according to the invention. Examples include trimethylolpropane tris(2-methyl-1-aziridinepropionate).

[0062] In a further preferred embodiment of the invention, isocyanates are used as covalent crosslinkers, particularly multifunctional isocyanate compounds. Examples of multifunctional isocyanate compounds that can be used are tolylene diisocyanate (TDI), 2,4-tolylene diisocyanate dimer, naphthylene 1,5-diisocyanate (NDI), o-tolylene diisocyanate (TODI), diphenylmethane diisocyanate (MDI), triphenylmethane triisocyanate, tris(p-isocyanatophenyl)thiophosphite, and polymethylene polyphenyl isocyanate. They can be used alone or in a combination of two or more types. Preferably, at least one covalent crosslinker is used, but two or more covalent crosslinkers can also be used, for example, the two aforementioned diamine compounds in combination with one another.

[0063] Suitable coordinative crosslinkers for the present invention are, in particular, chelate compounds, in particular polyvalent metal chelate compounds. The term “polyvalent metal chelate compound” refers to compounds in which a polyvalent metal is coordinately bonded to one or more organic compounds. The polyvalent metal atom used may be Al(III), Zr(IV), Co(II), Cu(I), Cu(II), Fe(II), Fe(III), Ni(II), V(II), V(III), V(IV), V(V), Zn(II), In(III), Ca(II), Mg(II), Mn(II), Y(III), Ce(II), Ce(IV), St(II), Ba(II), Mo(II), Mo(IV), Mo(VI), La(III), Sn(II), Sn(IV), Ti(IV), and the like. Of these, Al(III), Fe(III), Zn(II), Zr(IV) and Ti(IV) are preferred, particularly preferred are Fe(III) and Al(III).

[0064] In principle, any known ligand can be used as ligands for the coordinative crosslinking agents. However, the atoms used for the coordinative bonding of the organic compound can, in particular, be atoms that have free electron pairs, such as oxygen atoms, sulfur atoms, nitrogen atoms, and the like. Examples of organic compounds that can be used include alkyl esters, alcohol compounds, carboxylic acid compounds, ether compounds, ketone compounds, and the like.In particular, iron(III) acetylacetonate (Fe chelate), titanium chelate compounds such as titanium dipropoxide bis(acetylacetonate), titanium dibutoxide bis(octylene glycolate), titanium dipropoxide bis(ethyl acetoacetate), titanium dipropoxide bis(lactate), titanium dipropoxide bis(triethanolaminate), titanium di-n-butoxide bis(triethanolaminate), titanium tri-n-butoxide monostearate, butyl titanate dimer, poly(titanium acetylacetonate) and the like; aluminum chelate compounds such as aluminum diisopropoxide monoethyl acetate, aluminum di-n-butoxide monomethyl acetoacetate, aluminum di-i-butoxide monomethyl acetoacetate, aluminum di-n-butoxide monoethyl acetoacetate, aluminum disec-butoxide monoethyl acetoacetate, aluminum triacetylacetonate.

[0065] Aluminum triethylacetoacetonate, aluminum monoacetylacetonate bis(ethylacetoacetonate), and the like, and zirconium chelate compounds such as zirconium tetraacetylacetonate and the like are illustratively listed. Of these, aluminum triacetylacetonate (Al chelate) and aluminum dipropoxide are preferred. They can be used alone or in a combination of two or more types.

[0066] Covalent crosslinkers are preferably used in a total amount of 0.02 to 0.5 part by weight, preferably 0.04 to 0.3 part by weight, based on 100 parts by weight of the total copolymers A. Coordinative crosslinkers are preferably used in an amount of 0.05 to 0.50 part by weight, preferably 0.1 to 0.3 part by weight, based on 100 parts by weight of the total copolymers A.

[0067] In one embodiment, covalent and coordinative crosslinkers are used, preferably in the above-mentioned quantity ranges.

[0068] Adhesive strength-enhancing resin, synonymous with "adhesive resin" in the present disclosure, is understood, according to the general understanding of those skilled in the art, to be an oligomeric or polymeric resin that increases the autohesion (tack, inherent adhesiveness) of the pressure-sensitive adhesive compared to an otherwise identical pressure-sensitive adhesive that does not contain an adhesive strength-enhancing resin. Adhesive strength-enhancing resins can also advantageously improve the wetting properties of the pressure-sensitive adhesive with respect to the substrate to be bonded, its flow behavior, and / or its adhesion.

[0069] The pressure-sensitive adhesive of the invention may further comprise at least one bond-strengthening resin. According to the general understanding of those skilled in the art, this is understood to mean an oligomeric or polymeric resin that increases the autohesion (tack, inherent adhesiveness) of the pressure-sensitive adhesive compared to an otherwise identical pressure-sensitive adhesive containing no bond-strengthening resin. Furthermore, bond-strengthening resins can advantageously also improve the wetting properties of the pressure-sensitive adhesive with respect to the substrate to be bonded, its flow behavior, and / or its adhesion.

[0070] The one or more adhesive strength-enhancing resins can in principle be any adhesive resin compatible with the pressure-sensitive adhesive and in particular with the copolymer A or the copolymers A of the pressure-sensitive adhesive.

[0071] The at least one bond-strengthening resin of the pressure-sensitive adhesive of the invention can in principle be any adhesive resin compatible with the pressure-sensitive adhesive and in particular with the copolymer(s) of the pressure-sensitive adhesive. In one embodiment, the bond-strengthening resin is selected from the group consisting of aliphatic, aromatic, and alkylaromatic hydrocarbon resins; hydrocarbon resins based on pure monomers; hydrogenated hydrocarbon resins; functional hydrocarbon resins, and optionally derivatized natural resins; preferably, the adhesive resin is selected from the group consisting of pinene, indene, and rosin resins, their disproportionated, hydrogenated, polymerized, and esterified derivatives and salts; aliphatic and aromatic hydrocarbon resins; terpene resins and terpene-phenolic resins, and C5, C8, and other hydrocarbon resins.The pressure-sensitive adhesive according to the invention can in principle comprise one (single) or several adhesive strength-enhancing resins.

[0072] Preferably, the at least one adhesive strength-enhancing resin is selected from acrylate resins, rosin resins, and polyterpene-based resins. These resins are based on at least 30% by weight of renewable raw materials.

[0073] Particularly preferably, the at least one adhesive strength-enhancing resin is selected from rosin resins and polyterpene-based resins. These resins are advantageous because they can be produced or obtained largely, especially entirely, from renewable raw materials.

[0074] In particular, the adhesive strength-enhancing resin is selected from rosin resins and polyterpene-phenolic resins. These adhesive resins can be produced from renewable raw materials and have proven particularly suitable for significantly improving the adhesive properties of the pressure-sensitive adhesive of the invention.

[0075] Rosin resins are a group of resins which include their disproportionated, hydrogenated, polymerized, modified derivatives and salts.

[0076] Modified derivatives of rosin include esterified derivatives and / or further substituted derivatives such as maleate resin (GAS: 68038-41-5).

[0077] Rosin resins are advantageous because they can be produced or obtained largely, especially entirely, from renewable raw materials. These adhesive resins can be produced from renewable raw materials and have proven particularly suitable for significantly improving the adhesive properties of the pressure-sensitive adhesive of the invention.

[0078] The adhesive strength-enhancing resin is most preferably a fully hydrogenated rosin resin. This is particularly advantageous because these resins have a comparatively low softening temperature and thus contribute advantageously to the development of pressure-sensitive adhesive properties. Furthermore, they exhibit particularly good aging stability.

[0079] The pressure-sensitive adhesive according to the invention preferably comprises one or more adhesive strength-enhancing resins in a total of 5 to 50 wt. %, more preferably in a total of 7 to 45 wt. %, in particular in a total of 9 to 35 wt. %, very particularly preferably in a total of 10 to 32 wt. %, in each case based on the total weight of the pressure-sensitive adhesive.

[0080] In one embodiment, the pressure-sensitive adhesive of the invention is non-foamed and comprises one or more adhesion-enhancing resins in a total amount of 20 to 40 wt. %, preferably in a total amount of 25 to 35 wt. In a preferred embodiment, the pressure-sensitive adhesive of the invention is a foam (equivalent to a foamed pressure-sensitive adhesive according to the present disclosure) and comprises one or more adhesion-enhancing resins in a total amount of 10 to 22 wt. %, preferably in a total amount of 12 to 20 wt. %.

[0081] The pressure-sensitive adhesive according to the invention preferably comprises one or more adhesive strength-enhancing resins which have a softening temperature of 60 to 150 °C, preferably 70 to 130 °C, wherein the softening temperature is determined by the ring-ball method (“ring & ball”) according to ASTM E28-18 (standard published on July 1, 2018).

[0082] The pressure-sensitive adhesive according to the invention may further comprise further components, e.g. plasticizers; fillers, in particular fibers, carbon black, zinc oxide, titanium dioxide, spinels, dyes, pigments, chalk, solid or hollow glass spheres, microspheres made of other materials, e.g. polymeric hollow microspheres, silicic acid and / or silicates; nucleating agents; blowing agents; compounding agents; stabilizers and / or age inhibitors, e.g. primary and / or secondary antioxidants and / or light stabilizers.

[0083] The adhesive layer can optionally be foamed, resulting in advantageous further developments of the invention. In other advantageous embodiments of the invention, however, the adhesive is unfoamed. Whether foaming should occur depends, for example, on the intended application of the adhesive. For example, foamed adhesives can increase the shock absorption effect, allowing the adhesive to absorb or dissipate impact energy in the adhesive film.

[0084] Foaming can be achieved using any desired chemical and / or physical methods. However, a foamed pressure-sensitive adhesive according to the invention is preferably obtained by introducing and subsequently expanding microballoons. "Microballoons" are understood to be elastic and thus expandable hollow microspheres that have a thermoplastic polymer shell. These spheres are filled with low-boiling liquids or liquefied gas. Polyacrylonitrile, PVDC, PVC, or polyacrylates are particularly used as shell materials. Particularly suitable low-boiling liquids are hydrocarbons of the lower alkanes, for example isobutane or isopentane, which are enclosed in the polymer shell as liquefied gas under pressure.

[0085] When exposed to external influences, particularly heat, the outer polymer shell softens. At the same time, the liquid propellant gas contained within the shell transforms into a gaseous state. The microballoons expand irreversibly and expand three-dimensionally. The expansion is complete when the internal and external pressures equalize. Since the polymer shell remains intact, a closed-cell foam is created.

[0086] A wide variety of microballoon types are commercially available, differing essentially in their size (6 to 45 μm diameter in the unexpanded state) and the starting temperatures required for expansion (75 to 220 °C). One example of commercially available microballoons is the Expancel® DU types (DU = dry unexpanded) from Akzo Nobel. Unexpanded microballoon types are also available as an aqueous dispersion with a solids or microballoon content of approximately 40 to 45 wt. %, and also as polymer-bound microballoons (masterbatch), for example in ethyl vinyl acetate with a microballoon concentration of approximately 65 wt. %. Both the microballoon dispersions and the masterbatch, like the DU types, are suitable for producing a foamed pressure-sensitive adhesive according to the invention.

[0087] A foamed pressure-sensitive adhesive according to the invention can also be produced using so-called pre-expanded microballoons. In this group, expansion occurs before mixing into the polymer matrix. Pre-expanded microballoons are commercially available, for example, under the name Dualite® or with the type designation DE (Dry Expanded).

[0088] In the case of foamed adhesive layers, the density of the adhesive films is preferably between 200 kg / m 3 and 1000 kg / m 3 , more preferably between 500 kg / m 3 and 980 kg / m 3 , very preferably between 700 kg / m 3 and 950 kg / m 3 .

[0089] The poly(meth)acrylates are preferably crosslinked with a crosslinker-accelerator system.

[0090] A particularly preferred crosslinker-accelerator system comprises at least one substance containing epoxy groups as a crosslinker and at least one substance that accelerates the crosslinking reaction at a temperature below the melting temperature of the poly(meth)acrylate as an accelerator. The system requires the polymers to contain functional groups that can enter into crosslinking reactions with epoxy groups. Suitable substances containing epoxy groups include multifunctional epoxides, in particular bifunctional or trifunctional (i.e., epoxides with two or three epoxy groups), but also higher-functional epoxides or mixtures of differently functional epoxides. Amines (formally understood as substitution products of ammonia), for example, primary and / or secondary amines, and in particular tertiary and / or multifunctional amines, can be used as accelerators.Substances containing multiple amine groups can also be used, whereby these amine groups can be primary and / or secondary and / or tertiary amine groups, especially diamines, triamines, and / or tetramines. Amines that react little or not at all with the polymer building blocks are particularly preferred. Phosphorus-based accelerators, such as phosphines and / or phosphonium compounds, can also be used.

[0091] Particularly suitable functional groups for the poly(meth)acrylate to be crosslinked are acid groups (e.g., carboxylic acid, sulfonic acid, and / or phosphonic acid groups), and / or hydroxyl groups, and / or acid anhydride groups, and / or epoxy groups, and / or amine groups. The polymer particularly preferably contains polymerized acrylic acid and / or methacrylic acid.

[0092] However, it can also be advantageous to omit accelerators, as they can, for example, tend to yellow (particularly nitrogen-containing substances). Suitable crosslinkers that do not require the addition of accelerators include epoxycyclohexyl derivatives, particularly when carboxylic acid groups are present in the poly(meth)acrylate to be crosslinked. This can be achieved, for example, by incorporating at least 5% by weight of acrylic acid into the polymer. It is advantageous, in particular, for the polymer to be crosslinked to contain no proton acceptors, no electron pair donors (Lewis bases), and / or no electron pair acceptors (Lewis acids). The absence of these substances refers in particular to accelerators added externally, i.e., not polymerized or incorporated into the polymer backbone; however, it is particularly preferred to have neither externally added nor polymerized accelerators present, and in particular, no accelerators at all.The crosslinker is particularly preferably an epoxycyclohexylcarboxylate, in particular (3,4-epoxycyclohexane)methyl-3,4-epoxycyclohexylcarboxylate (Uvacure® 1500).

[0093] In one embodiment, the pressure-sensitive adhesive of the invention comprises a further polymer, preferably a rubber, particularly preferably a natural rubber or synthetic rubber.

[0094] Natural rubber is an elastic polymer derived from plant products, primarily latex. Natural rubber is processed as an essential raw material into natural rubber adhesives. Natural rubber is an elastomer that, due to its natural origin, contains other impurities such as proteins. Natural rubber per se does not exhibit pressure-sensitive adhesive properties. To impart pressure-sensitive adhesive properties to natural rubber, the addition of adhesive resins is required, which are usually rosin- or hydrocarbon-resin-based. In addition, natural rubber-based adhesives typically contain anti-aging agents to protect the double bonds present in the natural rubber from oxidative degradation. In addition to the aforementioned formulation ingredients, fillers are often added to natural rubber formulations.

[0095] The synthetic rubber is preferably an acrylonitrile-butadiene rubber or a block copolymer with a structure AB, ABA, (AB) n , (AWAY) n X or (ABA) n X, where

[0096] - the blocks A independently represent a polymer formed by polymerization of at least one vinyl aromatic compound;

[0097] - the blocks B independently represent a polymer formed by polymerisation of conjugated dienes having 4 to 18 carbon atoms and / or isobutylene, or a partially or fully hydrogenated derivative of such a polymer;

[0098] - X represents the residue of a coupling reagent or initiator and

[0099] - n stands for an integer > 2.

[0100] In particular, if the pressure-sensitive adhesive of the invention contains a plurality of synthetic rubbers, all synthetic rubbers are, independently of one another, an acrylonitrile-butadiene rubber or a block copolymer with a structure as set out above. The pressure-sensitive adhesive of the invention can thus also contain mixtures of different synthetic rubbers with a structure as set out above.

[0101] Suitable block copolymers (vinyl aromatic block copolymers) therefore preferably comprise one or more rubber-like blocks B (soft blocks) and one or more glassy blocks A (hard blocks). Particularly preferably, at least one synthetic rubber is a block copolymer having a structure AB, ABA, (AB)2X, (AB)3X, or (AB)4X, where A, B, and X have the above meanings. In particular, the pressure-sensitive adhesive contains a mixture of several block copolymers having a structure AB, ABA, (AB)2X, (AB)3X, or (AB)4X, which preferably contains at least diblock copolymers AB, triblock copolymers ABA, and / or triblock copolymers (AB)2X.

[0102] Block A is generally a glassy block with a preferred glass transition temperature (Tg, DSC) above room temperature. The Tg of the glassy block is particularly preferably at least 40°C, in particular at least 60°C, very particularly preferably at least 80°C, and extremely preferably at least 100°C. The proportion of vinylaromatic blocks A in the total block copolymers is preferably 10 to 40% by weight, particularly preferably 20 to 33% by weight. Vinylaromatics for constructing block A preferably include styrene and its derivatives, in particular styrene and α-methylstyrene. Block A can thus be present as a homopolymer or copolymer. Block A is particularly preferably a polystyrene.

[0103] The vinylaromatic block copolymer generally further comprises a rubbery block B or soft block with a preferred Tg of less than room temperature. The Tg of the soft block is particularly preferably less than 0°C, in particular less than -10°C, for example less than -40°C, and most preferably less than -60°C.

[0104] Preferred conjugated dienes as monomers for soft block B are selected in particular from the group consisting of butadiene, isoprene, ethylbutadiene, phenylbutadiene, piperylene, pentadiene, hexadiene, ethylhexadiene, dimethylbutadiene, and the farnesene isomers, as well as any desired mixtures of these monomers. Block B can also be present as a homopolymer or as a copolymer.

[0105] Particularly preferably, the conjugated dienes used as monomers for soft block B are selected from butadiene and isoprene. For example, soft block B is a polyisoprene, a polybutadiene, or a partially or fully hydrogenated derivative of one of these two polymers, such as, in particular, polybutylenebutadiene; or a polymer made from a mixture of butadiene and isoprene. Block B is most preferably a polybutadiene.

[0106] In one embodiment, the pressure-sensitive adhesive of the invention comprises a blend of at least one copolymer A and at least one rubber, preferably a synthetic rubber, in particular according to the above description of these polymers.

[0107] In one embodiment, the pressure-sensitive adhesive of the invention comprises a blend of at least one copolymer A and at least one rubber, preferably a synthetic rubber, in a total of 10 to 40 wt.%.

[0108] The pressure-sensitive adhesive composition of the invention is preferably prepared from solution, ie the components are dispersed or dissolved in a suitable solvent and mixed; the solvent is removed by conventional methods after the mixing process has been completed.

[0109] The pressure-sensitive adhesive of the invention can be used as such, e.g., in the form of a laminate or a carrier-free layer of the pressure-sensitive adhesive of the invention, which is also referred to as a "transfer adhesive tape." Such a transfer adhesive tape is preferably applied only to a material that temporarily serves to protect the adhesive surface, facilitate handling, and facilitate the application of the pressure-sensitive adhesive. Such materials are also referred to as release liners or simply "liners" and are generally easily removable, particularly by means of suitable surface coatings. The second side of the transfer adhesive tape can also be provided with a liner.

[0110] The release liners are, in particular, carrier materials that are anti-adhesive (coated or treated) on one or, preferably, both sides. Various papers, optionally in combination with a stabilizing extrusion coating, can be used as carrier materials for release liners. Other suitable liner carrier materials are films, particularly polyolefin films, for example, based on ethylene, propylene, butylene, and / or hexylene. Preferred carrier materials are papers, such as glassine papers. Papers are also preferred because the concept of the origin of the components from renewable raw materials can thus be extended to the auxiliary materials of the adhesive tape.

[0111] Silicone systems are often used as anti-adhesive release coatings. Commonly used liners include siliconized papers and siliconized films.

[0112] To use the transfer tape for bonding to a substrate surface, the liner(s) are removed so that the two adhesive sides make direct contact with the substrate surfaces to be bonded. The liner therefore does not represent a productive component and is therefore not considered part of the adhesive tape, but rather merely serves as an aid for handling it.

[0113] 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 typically comprise at least one carrier layer and can have an outer layer of a pressure-sensitive adhesive of the invention on one or both sides. In the case of double-sided adhesive tapes, either one of the outer layers or both outer layers can be pressure-sensitive adhesives of the invention. In the latter case, the pressure-sensitive adhesive layers can differ with regard to their chemical composition and / or their chemical and / or physical properties and / or their geometry (e.g., layer thickness), but they are particularly preferably identical with regard to their chemical composition and / or their chemical and / or physical properties.Even with multi-layer adhesive tapes, one or both outer layers of pressure-sensitive adhesive can be covered with liners.

[0114] 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 multilayer adhesive tape, for example, those selected from the list consisting of paper; bio-based fabrics or nonwovens, e.g., made of cotton or viscose; cellophane; cellulose acetate; bio-based polyethylene (PE) and polypropylene (PP) films; films made of thermoplastic starch; bio-based polyester films, e.g., films made of polylactide (PLA; polylactic acid), polyethylene terephthalate (PET), polyethylene tetrahydrofuranoate (PEF), or polyhydroxyalkanoate (PHA). The carrier material is particularly preferably a PET film. PET films, for example, are preferred because they can be used as recycled material and thus take sustainability into account.

[0115] In the present disclosure, the term "bio-content" describes the proportion of a monomer, a composition (e.g., copolymer component A), or a composition (e.g., the pressure-sensitive adhesive) in wt. % that is based entirely on renewable raw materials. The minimum bio-content thus describes the lower limit of the bio-content of a monomer, a composition, or a composition.

[0116] Similarly, a monomer has a certain minimum bio-content if, for example, the alcohol groups were produced using bio-based methods, but the acid group is based on a petrochemical process or a partially bio-based process, e.g., a (bio) mass balance approach. In the above example, the bio-based content of the alcohol group is used as the lower limit of the bio-content, i.e., the minimum bio-content (excluding the proportion of the acid group, which would or could result from the (bio) mass balance approach).

[0117] In one embodiment, the pressure-sensitive adhesive is characterized in that at least 50% by weight, preferably at least 60% by weight, particularly preferably more than 70% by weight of the monomers used to produce copolymer component A are based entirely on renewable raw materials. As described above, the definition of "based entirely on renewable raw materials" also encompasses that a certain proportion in wt. % of a monomer is based entirely on renewable raw materials and not necessarily the entirety of a monomer (for example, 2-octyl acrylate, which, for example, is based entirely on renewable raw materials to an extent of 40% by weight).

[0118] In one embodiment, the pressure-sensitive adhesive is characterized in that it is based on at least 50 wt. %, preferably at least 60 wt. %, particularly preferably more than 70 wt. % on renewable raw materials. In contrast to petrochemical-based products, those (bio-based products) which are derived to a significant extent, preferably entirely, from renewable raw materials have a natural proportion of radioactive carbon atoms ( 14 C isotopes). The proportion of these isotopes can be determined and provides information about the amount of natural raw material used. The proportion of renewable raw materials is determined using the 14 C radiocarbon method according to ASTM D6866-04. The method is based on the measurement of the isotope 14 C, which occurs in nature (i.e. in biomass) with a frequency of 10' 10% in carbon. The half-life of 5730 years is long enough that no significant change in the carbon content occurs during the usage periods of common adhesive products, such as pressure-sensitive adhesive tapes. 14 C content through decay (but short enough that historical objects made from biological matter can be dated). The measurement of the isotope 14 C is determined using liquid scintillation spectrometry or mass spectrometry. Due to the above-mentioned half-life, no carbon samples older than 60,000 years are detectable within the detection limit. 14 C isotopes are no longer detectable. The carbon in petroleum-based petrochemical raw materials, which are several million years old, therefore no longer contains C isotopes. The same applies to natural gas and coal-based raw materials.

[0119] The invention thus further provides an adhesive tape comprising a carrier material and, on at least one of its two outer sides, a pressure-sensitive adhesive according to 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 according to the invention preferably each have a layer thickness of 20 to 30 μm. The preferred total thickness of the adhesive tape according to the invention is thus 41 to 65 μm. In a preferred embodiment, a PET film made from recycled material is used as the carrier material.

[0120] To anchor the pressure-sensitive adhesive to the carrier or another substrate, it can be advantageous if the adhesive and / or the substrate are treated with corona or plasma prior to coating. Furthermore, chemical anchoring, e.g., via a primer, can be advantageous for anchoring the pressure-sensitive adhesive layer to other layers, especially to a carrier layer.

[0121] The invention further relates to the use of a pressure-sensitive adhesive according to the invention or an adhesive tape according to the invention for producing bonds in electronic, optical and / or precision mechanical devices.

[0122] Electronic, optical and precision mechanical devices within the meaning of this application are, in particular, devices as classified in Class 9 of the International Classification of Goods and Services for the Purposes of the Registration of Marks (Nice Classification), 10th Edition (NCL(10-2013)); insofar as these are electronic, optical or precision mechanical devices, also clocks and chronometric instruments according to Class 14 (NCL(10-2013)), such as, in particular, scientific, nautical, surveying, photographic, cinematographic, optical, weighing, measuring, signalling, checking (supervision), life-saving and teaching apparatus and instruments;

[0123] Apparatus and instruments for conducting, switching, transforming, accumulating, regulating or controlling electricity;

[0124] Image recording, processing, transmission, and reproduction devices, such as televisions and the like; acoustic recording, processing, transmission, and reproduction devices, such as radios and the like;

[0125] Computers, calculating and data processing equipment, mathematical devices and instruments, computer accessories; office equipment such as printers, fax machines, copiers, typewriters; and data storage devices;

[0126] Telecommunication and multifunctional devices with a telecommunication function, such as telephones and answering machines; chemical and physical measuring devices, control devices and instruments, such as battery chargers, multimeters, lamps, speedometers; nautical devices and instruments; optical devices and instruments; medical devices and instruments and those for sports;

[0127] Clocks and chronometers;

[0128] Solar cell modules such as electrochemical dye solar cells, organic solar cells, thin-film cells; and

[0129] Fire extinguishers.

[0130] Technical developments in the electronics sector are now often focused on devices that are becoming increasingly smaller and lighter so that their owners can carry them with them at all times. This is usually achieved by realizing low weight and / or a suitable size for such devices. Such devices are also referred to as mobile devices or portable devices. In this context, precision mechanical and optical devices are also increasingly being equipped with electronic components, which increases the possibilities for minimization. Because mobile devices are carried around, they are increasingly exposed to mechanical stress, for example from bumping into edges, being dropped, coming into contact with other hard objects in their pockets, but also simply from the constant movement caused by being carried.However, mobile devices are also exposed to greater stress due to exposure to moisture, temperature influences, and the like than "immobile" devices, which are typically installed indoors and are rarely or not at all moved. The pressure-sensitive adhesive of the invention has proven particularly well-suited for withstanding such disruptive influences and for mitigating or compensating for them. The pressure-sensitive adhesive of the invention or the adhesive tape of the invention are therefore preferably used for producing bonds in portable electronic devices.

[0131] Portable electronic devices include:

[0132] Cameras, digital cameras; photographic accessories such as light meters, flash units, apertures, camera housings, lenses; film cameras, video cameras;

[0133] Small computers (mobile computers, pocket computers, calculators), laptops, notebooks, netbooks, ultrabooks, tablet computers, handhelds, electronic diaries and organizers (so-called “electronic organizers” or “personal digital assistants”, PDAs, palmtops), modems;

[0134] Computer accessories and control units for electronic devices, such as mice, drawing pads, graphics tablets, microphones, speakers, game consoles, gamepads, remote controls, remote controls, touchpads;

[0135] Monitors, displays, screens, touch-sensitive screens (sensor screens, “touchscreen devices”), projectors;

[0136] Readers for electronic books (“e-books”);

[0137] Small televisions, pocket televisions, film players, video players;

[0138] Radios (including small and pocket radios), walkmans, disc recorders, music players for CDs, DVDs, Blu-rays, cassettes, USB, MP3s; headphones; cordless telephones, mobile phones, smartphones, walkie-talkies, hands-free devices, personal call devices (pagers, beepers); mobile defibrillators, blood glucose meters, blood pressure monitors, pedometers, heart rate monitors;

[0139] Flashlights, laser pointers; mobile detectors, optical magnifiers, long-range vision devices, night vision devices;

[0140] GPS devices, navigation devices, portable satellite communication interface devices;

[0141] Data storage devices (USB sticks, external hard drives, memory cards); and

[0142] Wristwatches, digital watches, pocket watches, chain watches and stopwatches.

[0143] The invention further relates to a process for producing a pressure-sensitive adhesive according to the invention or an adhesive tape according to the invention.

[0144] The production of a pressure-sensitive adhesive composition or an adhesive tape according to the invention is carried out by means of polymerization, which can be carried out in an organic solvent; as emulsion polymerization; in a closed shell or as a syrup.

[0145] In one embodiment, the polymerization of the pressure-sensitive adhesive takes place in an organic solvent or an organic solvent mixture.

[0146] In one embodiment, the polymerization of the pressure-sensitive adhesive takes place in a closed shell. This is understood to mean any system, in principle, whose design does not impede the polymerization process and which spatially delimits and completely surrounds the composition to be polymerized or in the process of polymerization, at least limiting, and preferably preventing, the passage of at least air, water, and the enclosed monomers.

[0147] The material of the closed sleeve is preferably selected from the group consisting of ethylene-vinyl acetate copolymers, ethylene-acrylic acid copolymers, polyethylene, polypropylene, polybutadiene, ionomer films, and mixtures thereof; more preferably, it is selected from polyethylene, ethylene-vinyl acetate copolymers, and mixtures thereof. The thickness of the material of the closed sleeve is preferably 30 to 100 μm, more preferably 35 to 70 μm, in particular 40 to 60 μm. The thickness of a closed sleeve filled with the materials to be polymerized is preferably 2 to 22 mm, more preferably 5 to 21 mm, in particular 7 to 20 mm. The closed sleeve is produced, for example, by placing two film webs on top of each other and heat-sealing them along the long sides and the lowermost side edge. The monomer mixture is then filled using a liquid form, fill, and seal machine.The seal is then applied section by section through the liquid level, resulting in several filled, closed shells, which are then separated from each other. In one embodiment, the pressure-sensitive adhesive is polymerized using emulsion polymerization.

[0148] Descriptions of this process can be found, for example, in “Emulsion Polymerization and Emulsion Polymers” by Peter A. Lovell and Mohamed S. El- Aasser - Wiley-VCH 1997 - ISBN 0-471-96746-7 or in EP 1 378 527 B1 .

[0149] In emulsion polymerization, it cannot be ruled out that not all monomers will be converted into polymers. It is obvious that the residual monomer content should be as low as possible.

[0150] Preferably, acrylate pressure-sensitive adhesives comprising the polymer dispersion with a residual monomer content of less than or equal to 1 wt.%, in particular less than or equal to 0.5 wt.% (based on the mass of the base polymers) are provided.

[0151] In one embodiment, the polymerization of the pressure-sensitive adhesive takes place as a syrup.

[0152] The monomer mixtures usually have a viscosity that is too low to be easily handled. To increase the viscosity, the monomer mixture is prepolymerized to a syrupy consistency; this can advantageously be done up to a conversion of 2-20%. This forms a syrup that is easily coated onto a carrier material. UV light with a wavelength of 280-450 nm is preferably used to initiate prepolymerization.

[0153] Furthermore, the monomers are optionally blended with resins after or preferably before prepolymerization. Before complete polymerization, additional monomers can be added or blended into the syrup.

[0154] The process according to the invention is particularly advantageous for the production of, for example, adhesive tapes, since the prepolymer can be coated onto a carrier as a syrup.

[0155] Measurement and testing methods:

[0156] Determination of the glass transition temperature Tg of the pressure-sensitive adhesives

[0157] The static glass transition temperature of the pressure-sensitive adhesives was determined using differential scanning calorimetry (DSC) or, synonymously, dynamic scanning calorimetry (DSC). For this purpose, approximately 5 mg of an untreated sample of the pressure-sensitive adhesive was weighed into an aluminum crucible (volume 25 μl) and sealed with a perforated lid. A Netzsch DSC 204 F1 was used for the measurement. The test was carried out under nitrogen for inerting purposes. The sample was first cooled to -150 °C, then heated at a heating rate of 10 K / min to +150 °C and cooled again to -150 °C. The subsequent second heating curve was again run at 10 K / min, and the change in heat capacity was recorded. Glass transitions are identified as steps in the thermogram (heat flow-temperature diagram).The glass transition temperature Tg is obtained as follows: The linear sections of the measurement curve before and after the step are extended in the direction of increasing (section before the step) or decreasing (section after the step) temperatures. In the step region, a best-fit line is placed parallel to the ordinate so that it intersects the two extension lines, creating two areas of equal area (between the extension line, the best-fit line, and the measurement curve). The intersection point of the best-fit line positioned in this way with the measurement curve yields the glass transition temperature.

[0158] Determination of molecular weight

[0159] The number average molecular weight M n and the weight-average molecular weight M wThe measurements in this document refer to the conventional determination by gel permeation chromatography (GPC). The determination is carried out on 100 μl of a clear-filtered sample (sample concentration 4 g / l). Tetrahydrofuran with 0.1 vol% trifluoroacetic acid is used as the eluent. The measurement is carried out at 25 °C.

[0160] The guard column is a column type PSS-SDV, 5 pm, 10 3 Ä, 8.0 mm x 50 mm (information here and below in the order: type, particle size, porosity, inner diameter x length; 1 Ä = 10' 1 ° m). For separation, a combination of columns of the type PSS-SDV, 5 pm, 10 3 Ä and 10 5 Ä and 10 6Ä, each measuring 8.0 mm x 300 mm, were used (columns from Polymer Standards Service; detection using a Shodex RI71 differential refractometer). The flow rate was 1.0 ml per minute. Calibration was performed using the commercially available ReadyCal kit Poly(styrene) high from PSS Polymer Standard Service GmbH, Mainz. This was universally converted to polymethyl methacrylate (PMMA) using the Mark-Houwink parameters K and alpha, so that the data were expressed in PMMA mass equivalents.

[0161] Determination of shear stability time (“SSZ 23°C; 1 kg” and “SSZ 70°C; 0.5 kg”)

[0162] Shear strength was determined using the shear strength test at a temperature of 23 + / - 1 °C and 50% + / - 5% relative humidity (“SSZ 23°C; 1 kg”). The test specimens were cut to a width of 13 ± 0.2 mm and stored in the test atmosphere for at least 16 hours. 50 x 25 mm ASTM steel plates, 2 mm thick and with a 20 mm marking line, were used for the test. These plates were thoroughly cleaned several times with acetone before bonding and then allowed to dry for 10 minutes. The bonded area was 13 x 20 ± 0.2 mm. The test strip was applied lengthwise to the center of the substrate using a wiper, avoiding any air pockets, so that the upper edge of the test specimen was exactly aligned with the 20 mm marking line.

[0163] The back of the test sample was taped with aluminum foil. The free, protruding end was taped with paper. The adhesive strip was then rolled back and forth twice using a 2 kg roller. After rolling, a belt loop (weight 5-7 g) was attached to the protruding end of the adhesive tape.

[0164] An adapter plate was then attached to the front of the shear test plate using a screw and nut. To ensure the adapter plate was firmly seated on the plate, the screw was firmly tightened by hand.

[0165] The prepared plate was attached to a counter clock using a hook on the adapter plate; a 1 kg weight was then smoothly hooked into the belt loop.

[0166] The application time between rolling and loading was 12 minutes. The time until bond failure was measured in minutes; the results are averaged from three measurements. A shear strength of over 10,000 minutes is considered a good result.

[0167] The shear strength determination at a test environment of 70 ±1 °C and 10% ±10% relative humidity ("SSZ 70°C; 0.5 kg") is carried out analogously to the above procedure, whereby the prepared panel was equilibrated for 30 minutes under the test conditions at 70 °C before suspending a 0.5 kg weight. A shear strength of over 10,000 minutes at 70 °C is considered a good result.

[0168] Adhesive strength steel

[0169] The adhesive strength was determined under a test environment of 23 °C + / - 1 °C and 50% + / - 5% relative humidity. The samples were cut to a width of 20 mm and adhered to a steel plate (ASTM). The steel plate was cleaned and conditioned prior to measurement. To do this, the plate was first wiped with solvent and then left to air for 5 minutes to allow the solvent to 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 using a 4 kg roller at a winding speed of 10 m / min. One minute after rolling, the plate was pushed into a special holder.The adhesive 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.

[0170] K-value (according to Fikentscher)

[0171] The K value is a measure of the average molecular size of high-polymer materials. For the measurement, one percent (1 g / 100 mL) toluene polymer solutions were prepared, and their kinematic viscosities were determined using a Vogel-Ossag viscometer. After normalization to the viscosity of toluene, the relative viscosity is obtained, from which the K value can be calculated according to Fikentscher (Polymer 1967, 8, 381 ff).

[0172] Gel permeation chromatography GPC

[0173] The weight-average molecular weight (Mw) and polydispersity (PD) values ​​given in this document refer to determinations by gel permeation chromatography. The determination is carried out on 100 μl of a clear-filtered sample (sample concentration 4 g / l). Tetrahydrofuran with 0.1 vol% trifluoroacetic acid is used as the eluent. The measurement is carried out at 25 °C. A PSS-SDV, 5 μg, 10 μl column is used as the precolumn. 3 Ä, ID 8.0 mm ■ 50 mm. For separation, columns of type PSS-SDV, 5 p, 10 3 Ä as well as 105 Ä and 106 Ä, each with an ID of 8.0 mm x 300 mm, were used (columns from Polymer Standards Service; detection using a Shodex RI71 differential refractometer). The flow rate is 1.0 ml per minute. Calibration is performed against PMMA standards (polymethyl methacrylate calibration).

[0174] Glass transition temperature - Dynamic Scanning Calorimetry (DSC)

[0175] For this purpose, approximately 5 mg of an untreated polymer sample is weighed into an aluminum crucible (volume 25 pL) and sealed with a perforated lid. A Netzsch DSC 204 F1 is used for the measurement. The measurement is carried out under nitrogen for inerting. The sample is first cooled to -150 °C, then heated at a heating rate of 10 K / min to +150 °C and cooled again to -150 °C. The subsequent second heating curve is again run at 10 K / min and the change in heat capacity is recorded. Glass transitions are identified as steps in the thermogram as follows: The linear section of the measurement curve before and after the step is extended in the direction of increasing (section before the step) or decreasing (section after the step) temperatures.In the step region, a best-fit line is placed parallel to the ordinate so that it intersects the two extension lines, creating two areas of equal area (between each extension line, the best-fit line, and the measurement curve). The intersection of the best-fit line positioned in this way with the measurement curve yields the glass transition temperature.

[0176] Table 1 : Commercially available chemicals used

[0177] Production of polyacrylates:

[0178] Polyacrylate Pl

[0179] A 3 L vessel conventional for radical polymerizations was charged with 50 g of acrylic acid (AA), 425 g of 2-octyl acrylate (2-OA), 425 g of n-heptyl acrylate (n-HA), 100 g of methyl acrylate (MA), and 724 g of benzine / acetone (70:30). After 45 minutes of nitrogen gas flow with stirring, the reactor was heated to 58 °C and 0.5 g of Vazo® 67 was added. The jacket temperature was then adjusted to 75 °C and the reaction was carried out at this constant external temperature. After a reaction time of 1 h, another 0.5 g of Vazo® 67 was added. After 3 h, the mixture was diluted with 200 g of benzine / acetone (70:30) and after 6 h with 100 g of benzine / acetone (70:30). To reduce the residual initiators, 1.5 g of Perkadox® 16 were added after 5.5 and 7 h, respectively. The reaction was stopped after 24 h and cooled to room temperature. Polyacrylate P-II to P-VI

[0180] Polyacrylates II to VI (P-II to P-VI) were prepared in the same way as polyacrylate I (Pl) except for the monomer composition. The monomer composition is listed in Table 2.

[0181] Table 2: Monomer composition of copolymer A

[0182] 1 based on the monomer composition of the polyacrylate [monomers a) + monomers b) + monomers c) make up 100 parts by weight of polyacrylate].

[0183] Manufacturing process of pressure-sensitive adhesives:

[0184] Process - Production of pressure-sensitive adhesives from solvent

[0185] The resulting polyacrylate was then blended with the crosslinkers and, optionally, with the adhesive resin. The resulting composition 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 coating weight after drying was 50 g / m². 2 . Table 3: Composition of the pressure-sensitive adhesives; film thickness and measurement results

[0186] 2 the stated wt.% refers to the mass composition of the pressure-sensitive adhesive [polyacrylate + optional adhesive resin equal 100 parts by weight];

[0187] 3 Crosslinker (data based on 100 parts by weight of polyacrylate) additive to 100 parts by weight of pressure-sensitive adhesive (polyacrylate + optional adhesive resin).

[0188] Foamed pressure-sensitive adhesive

[0189] Adhesive tapes produced within the scope of the investigations for the present invention further comprise a foamed pressure-sensitive adhesive comprising polyacrylate P-IV, an adhesive strength-enhancing resin (adhesive resin), microballoons, thermal crosslinkers, and rubber. In a particularly preferred further development of the invention, the aforementioned foamed pressure-sensitive adhesive comprises natural rubber as the rubber, thereby increasing the bio-content in wt. %.

[0190] Foamed pressure-sensitive adhesives were produced which exhibit layer thicknesses between 205 and 220 μm, layer densities between 775 and 920 g / L, shear times (SSZ 23°C; 1 kg and SSZ 70°C; 0.5 kg) of over 10,000 min, ASTM bond strengths of 7.1 to 9.8 N / cm and a bio content of 30 to 61%.

Claims

Patent claims 1. Pressure-sensitive adhesive comprising at least one copolymer A which can be traced back to a monomer composition comprising a) 75 to 98% by weight of at least one alkyl acrylate whose alcohol component has 5 to 8 carbon atoms; b) 1 to 24% by weight of at least one alkyl (meth)acrylate whose alcohol component has 1 to 4 carbon atoms; and c) 1 to 15% by weight of acrylic acid; and - one or more crosslinkers; characterized in that the monomer composition comprises not more than 87% by weight of 2-octyl acrylate, preferably not more than 85% by weight.

2. Pressure-sensitive adhesive according to claim 1, characterized in that the pressure-sensitive adhesive comprises one or more adhesive strength-enhancing resins.

3. Pressure-sensitive adhesive according to claim 2, characterized in that the adhesive strength-enhancing resin is based to at least 30 wt.% on renewable raw materials.

4. Pressure-sensitive adhesive according to one of the preceding claims, characterized in that the crosslinker is a covalent crosslinker.

5. Pressure-sensitive adhesive according to one of the preceding claims, characterized in that the monomer composition comprises monomers a) in a total of 76 to 89 wt. %, preferably in a total of 77 to 85 wt. %, particularly preferably in a total of 78 to 79 wt. %.

6. Pressure-sensitive adhesive according to one of the preceding claims, characterized in that the one or more monomers a) are selected from the group consisting of i-amyl acrylate, n-hexyl acrylate, n-heptyl acrylate, and 2-octyl acrylate.

7. Pressure-sensitive adhesive according to one of the preceding claims, characterized in that the monomer composition comprises 2-octyl acrylate as monomer a).

8. Pressure-sensitive adhesive according to one of the preceding claims, characterized in that the monomer composition comprises monomers b) in a total of 9 to 16 wt.%, preferably 10 to 15 wt.%.

9. Pressure-sensitive adhesive according to one of the preceding claims, characterized in that the monomer composition comprises monomers c) in a total amount of 2 to 8 wt.%, preferably 3 to 7 wt.%.

10. Pressure-sensitive adhesive according to one of the preceding claims, characterized in that at least 50% by weight, preferably at least 60% by weight, particularly preferably more than 70% by weight of the monomers used to produce the copolymer component A are based entirely on renewable raw materials.

11. Pressure-sensitive adhesive according to one of the preceding claims comprising copolymer A in a total of 35 to 90 wt. %, preferably 40 to 75 wt. %, particularly preferably 45 to 70 wt. %, based on the total weight of the pressure-sensitive adhesive.

12. Pressure-sensitive adhesive according to one of the preceding claims, characterized in that the pressure-sensitive adhesive is a foam.

13. Pressure-sensitive adhesive according to one of the preceding claims, characterized in that the pressure-sensitive adhesive comprises a rubber, preferably a natural rubber.

14. Adhesive tape comprising a pressure-sensitive adhesive according to any one of claims 1 to 13.

15. Use of a pressure-sensitive adhesive according to any one of claims 1 to 13 or of an adhesive tape according to claim 14 for producing bonds in electronic, optical and / or precision mechanical devices.

Images