Pressure-sensitive adhesive with improved chemical stability

Abstract

The present invention relates to a pressure-sensitive adhesive comprising: a) one or more poly(meth)acrylates having a weight-average molecular weight Mw of 200,000 g / mol or more in a combined mass fraction of 50% or more with respect to the mass of the pressure-sensitive adhesive; and b) one or more bonding resins having a weight-average molecular weight Mw of 20,000 g / mol or less in a combined mass fraction ranging from 1 to 25% with respect to the mass of the pressure-sensitive adhesive, wherein the one or more bonding resins can be produced by polymerization of a first monomer composition, and the first monomer composition comprises, with respect to the mass of the first monomer composition: i) one or more first monomers selected from the group consisting of aromatic (meth)acrylates and styrene in a combined mass fraction ranging from 5% to 40%; ii) one or more second monomers selected from the group consisting of methyl methacrylate and ethyl methacrylate in a combined mass fraction ranging from 35% to 68%; and iii) a combined mass ranging from 5% to 40% The present invention relates to a pressure-sensitive adhesive comprising one or more third monomers selected from the group consisting of (meth)acrylates having a fraction of cycloaliphatic groups.

Description

Technology Field

[0001] explanation

[0002] The present invention relates to pressure-sensitive adhesives and corresponding pressure-sensitive adhesive tapes, and also to the use of specific tackifying resins for increasing peel adhesion and chemical resistance in poly(meth)acrylate-based adhesives. The use of corresponding pressure-sensitive adhesive tapes for creating weather-resistant bonds is also disclosed. Background Technology

[0003] The joining of individual elements is one of the core processes in manufacturing. For example, in addition to other methods such as welding and soldering, adhesive bonding—that is, joining using adhesives—is particularly important today. For instance, one alternative to the use of non-adhesives applied from tubes is so-called adhesive tape, the adhesive effect of which depends on the adhesive used.

[0004] For many technical applications, pressure-sensitive adhesive tapes are particularly relevant, in which the pressure-sensitive adhesive ensures a continuously tacky and adhesive bonding effect under normal ambient conditions. The corresponding pressure-sensitive adhesive tape can be applied to a substrate by pressure and remain adhered thereto, but can subsequently be removed in a relatively residue-free manner.

[0005] In the field of pressure-sensitive adhesives, poly(meth)acrylates have proven to be particularly useful base materials. These polymer compounds generally possess physicochemical properties that make them ideal for use in pressure-sensitive adhesives, such as high light resistance, weather resistance, and resistance to various chemicals, as well as high intrinsic peel adhesion and favorable aging resistance. Furthermore, poly(meth)acrylate-based adhesives can generally be used on a wide range of substrates, particularly polar and less polar substrates, such as glass and steel, as well as plastics, such as polystyrene or polycarbonate. Therefore, in the field of adhesive technology, there is ongoing interest in improving the physicochemical properties of poly(meth)acrylate-based pressure-sensitive adhesives, particularly their technical adhesive properties.

[0006] One known approach to increase adhesion and improve substrate wetting is to add tackifying resins (so-called "tackifiers"), such as terpene-phenol resins or rosin resins, to poly(meth)acrylate-based pressure-sensitive adhesives. While the established use of tackifying resins in poly(meth)acrylate-based pressure-sensitive adhesives is advantageous in many respects for obtaining particularly strong pressure-sensitive adhesives, it is also associated with certain disadvantages, particularly regarding chemical resistance. Starting from the generally excellent inherent chemical resistance of typical poly(meth)acrylate-based pressure-sensitive adhesives, chemical resistance is actually generally compromised by the use of conventional tackifying resins. However, high chemical resistance is highly desirable for most applications where the corresponding pressure-sensitive adhesives and the pressure-sensitive adhesive tapes produced therefrom are exposed to relatively demanding environments and weathering conditions. In practice, chemical resistance is important for the ability of pressure-sensitive adhesives and pressure-sensitive adhesive tapes to perform their intended function when bonding elements over a long period, even when in contact with chemicals such as acids or oils, for example, in vehicles.

[0007] The relevance of chemical resistance to the use of pressure-sensitive adhesive tapes is significant, as many requirement profiles for corresponding tapes from, for example, the automotive or electronics industries, stipulate that the corresponding pressure-sensitive adhesive must meet specific minimum regulatory conditions regarding chemical resistance to obtain approval for use. However, compliance with these regulatory conditions by poly(meth)acrylate-based pressure-sensitive adhesives is often made more difficult by the mandatory use of conventional tackifying resins.

[0008] Therefore, in the latest technology, there generally conflicting objectives exist between, on the one hand, highly significant pressure-sensitive adhesive properties, particularly high peel adhesion, and on the other hand, favorable chemical resistance, that is, minimal degradation of peel adhesion under the influence of chemicals.

[0009] The main objective of the present invention was to eliminate or at least reduce the disadvantages described above regarding the prior art.

[0010] In particular, the objective of the present invention was to specify a pressure-sensitive adhesive having excellent pressure-sensitive adhesion, particularly to ethanol / water mixtures and oleic acid, while simultaneously possessing sufficient chemical resistance.

[0011] Therefore, the objective of the present invention was to specify a pressure-sensitive adhesive that best resolves the conflict of objectives between, on the one hand, the highest possible peel adhesion strength, particularly for steel and plastics, and on the other hand, excellent chemical resistance.

[0012] In this context, it was an additional objective of the present invention that the pressure-sensitive adhesive to be specified to enable time and cost-effective production should be ideally producible using starting materials and processes already used in the field of adhesive technology.

[0013] An additional objective of the present invention was to specify an advantageous pressure-sensitive adhesive tape.

[0014] In addition, a secondary objective of the present invention was to specify the use of a specific tackifying resin to enhance peel adhesion and chemical resistance in poly(meth)acrylate-based pressure-sensitive adhesives.

[0015] The inventors have now discovered that the purpose described above can be surprisingly achieved when a specific (meth)acrylate-based tackifying resin is used in a poly(meth)acrylate-based pressure-sensitive adhesive as defined in the claims.

[0016] Surprisingly, in poly(meth)acrylate-based pressure-sensitive adhesives, excellent peel adhesion stability against the influence of various chemicals could be achieved through the use of a specific (meth)acrylate-based tackifying resin produced from a defined monomer composition containing a significant fraction of aromatic (meth)acrylate and / or styrene.

[0017] The inventors have succeeded in identifying in this invention a composition particularly suitable for a (meth)acrylate-based tackifying resin, the poly(meth)acrylate used, and a corresponding pressure-sensitive adhesive, wherein the corresponding pressure-sensitive adhesive and individual components can advantageously be produced by using conventional starting materials and processes in the field of adhesive technology, thereby enabling time and cost-effective production without the need for specific devices or specific chemicals.

[0018] Accordingly, the above-mentioned objective is achieved by the subject matter of the present invention as defined in the claims. A preferred embodiment according to the present invention is derived from the dependent claims and the following observations.

[0019] An embodiment designated as preferred below is combined with features of another embodiment designated as preferred in a particularly preferred embodiment. Accordingly, a combination of two or more of the embodiments designated as particularly preferred below is highly particularly preferred. An embodiment in which features of one embodiment designated as preferred to any degree are combined with one or more additional features of another embodiment designated as preferred to any degree is also preferred. The features of the preferred pressure-sensitive adhesive tape and its application are derived from the features of the preferred adhesive.

[0020] Insofar as both a specific amount or fraction of an element, e.g., a tackifying resin or a specific monomer, and a preferred embodiment of the element are subsequently disclosed with respect to such element, this is a case where a specific amount or fraction of the particularly preferredly embodied element is also disclosed. Additionally, it is disclosed that at least a portion of the element may be preferably configured in a corresponding specific total amount or total fraction of the element, and in particular, the element preferably configured within the specific total amount or total fraction may also be present in turn in a specific amount or fraction.

[0021] The present invention

[0022] a) Weight-average molecular weight M of 200,000 g / mol or more in a combined mass fraction of 50% or more based on the mass of the pressure-sensitive adhesive w One or more poly(meth)acrylates having, and

[0023] b) Weight-average molecular weight M of 20,000 g / mol or less in a combined mass fraction ranging from 1 to 25% based on the mass of the pressure-sensitive adhesive w One or more tackifying resins having

[0024] The invention relates to a pressure-sensitive adhesive comprising,

[0025] One or more tackifying resins, based on the mass of the first monomer composition,

[0026] i) one or more first monomers selected from the group consisting of aromatic (meth)acrylates and styrene, in a combined mass fraction ranging from 5 to 40%,

[0027] ii) one or more second monomers selected from the group consisting of methyl methacrylate and ethyl methacrylate, in a combined mass fraction ranging from 35 to 68%, and

[0028] iii) One or more third monomers selected from the group consisting of (meth)acrylates having alicyclic radicals, in a combined mass fraction ranging from 5 to 40%

[0029] It can be produced by polymerizing a first monomer composition containing

[0030] According to expert understanding, pressure-sensitive adhesives are adhesives that possess pressure-sensitive adhesive properties, namely, the ability to bond durably to an adhesive base even under relatively low applied pressure. Corresponding pressure-sensitive adhesive tapes are generally separable from the adhesive base after use without leaving any residue and are typically permanently self-adhesive even at room temperature; this implies that they possess specific viscosity and contact-tackiness, allowing them to wet the surface of the substrate even under low pressure. The pressure-sensitive adhesiveness of pressure-sensitive adhesive tapes stems from the fact that the adhesive used is a pressure-sensitive adhesive. While not intended to be limited to this theory, pressure-sensitive adhesives can generally be regarded as very high-viscosity fluids with elastic components, and it is commonly assumed that this consequently possesses inherent viscoelastic properties, leading to the aforementioned durable self-adhesion and pressure-sensitive adhesive capabilities. In the case of corresponding pressure-sensitive adhesives, mechanical deformation is presumed to result in both viscous flow processes and the accumulation of elastic resilience. Proportional viscous flow is used to achieve adhesion, whereas proportional elastic resilience is particularly required to achieve cohesion. The relationship between rheology and pressure-sensitive adhesiveness is known in the prior art and is described, for example, in the literature [Satas, "Handbook of Pressure Sensitive Adhesive Technology", third edition (1999), pp. 153 to 203]. For example, as disclosed in WO 2015 / 189323, the storage modulus (G') and loss modulus (G''), which can be determined by dynamic mechanical analysis (DMA) using a rheometer, for example, are generally used to characterize the degree of elastic and viscous components. In the context of the present invention, the adhesive is preferably a pressure-sensitive adhesive, and accordingly 10 0 to 101 At a temperature of 23°C in a deformation frequency range of rad / sec, G' and G'' are each at least partially 10 3 to 10 7 It is understood to be a pressure-sensitive adhesive when in the range of Pa.

[0031] The pressure-sensitive adhesive of the present invention comprises poly(meth)acrylate and a tackifying resin, which may subsequently be various monomers or prepared therefrom. Each of these components is used as "one or more" as understood by the expert. The term "one or more" refers to the chemical properties of the compounds, rather than the quantity of the material, in the manner customary in the relevant field herein. For example, the first monomer composition may comprise only styrene as the first monomer, which would mean that the monomer composition comprises a plurality of styrene molecules.

[0032] In the context of the present invention, as understood by the expert, the expression “poly(meth)acrylate” comprises polyacrylates and polymethacrylates, and also copolymers of these polymers. Poly(meth)acrylates may contain a smaller amount of monomer units not derived from (meth)acrylates. In the context of the present invention, “poly(meth)acrylate” therefore means a (co)polymer composed of monomers selected from the group consisting of acrylic acid, methacrylic acid, acrylic acid esters, and methacrylic acid esters, wherein the monomer base comprises at least 70%, preferably at least 90%, and particularly preferably at least 98% by mass fraction of the monomer base. Preferably, the mass fraction of acrylic acid esters and / or methacrylic acid esters is at least 50%, and particularly preferably at least 70%. Poly(meth)acrylates can generally be accessed through radical polymerization of acrylic- and / or methacrylic-based monomers and optionally other copolymerizable monomers.

[0033] The tackifying resin used according to the present invention is produced or can be produced by the polymerization of a first monomer composition composed mostly of (meth)acrylate, so the tackifying resin may be described as a (meth)acrylate-based tackifying resin.

[0034] In accordance with the understanding of experts and the usual procedures of the field, it is convenient to define polymeric and oligomeric compounds, such as tackifying resins and poly(meth)acrylates, through the production process or the starting materials used in production, because otherwise it would be impossible to define the corresponding materials in a meaningful way.

[0035] The production of poly(meth)acrylates and also (meth)acrylate-based tackifying resins from each monomer can be carried out by conventional processes, particularly by conventional radical polymerization or controlled radical polymerization. Polymers or oligomers can be prepared by copolymerization of monomer components using a conventional polymerization initiator and optionally a chain transfer agent, wherein polymerization can be carried out at conventional temperatures, for example, in bulk, emulsion, for example, in water or liquid hydrocarbons, or in solution. Preferably, poly(meth)acrylates and / or tackifying resins are produced by polymerization in a solvent using a conventional amount of polymerization initiator, more preferably in a solvent having a boiling temperature in the range of 50 to 150°C, more preferably in the range of 60 to 120°C, and the polymerization initiator is generally added to the monomer composition in a ratio of about 0.01% to 5%, particularly 0.1% to 2%, based on the mass of the monomer composition.

[0036] Suitable polymerization initiators are, for example, radical sources, such as peroxides, hydroperoxides, and azo compounds, such as dibenzoyl peroxide, cumene hydroperoxide, cyclohexanone peroxide, di-t-butyl peroxide, cyclohexylsulfonyl acetyl peroxide, diisopropyl percarbonate, t-butyl peroctoate, or benzopinacol. Particularly preferably, 2,2'-azobis(2-methylbutyronitrile) or 2,2'-azobis(2-methylpropionitrile) is used as a radical initiator. In particular, alcohols, e.g., methanol, ethanol, n- and iso-propanol, n- and iso-butanol, preferably isopropanol and / or isobutanol, and also hydrocarbons, e.g., toluene and particularly benzine having a boiling temperature in the range of 60°C to 120°C are candidate substances as solvents. In particular, ketones, e.g., acetone, methyl ethyl ketone and methyl isobutyl ketone, and esters, e.g., ethyl acetate, and also mixtures of these solvents may be used.

[0037] In contrast to tackifying resins, for the purpose of establishing adhesive properties, particularly high cohesiveness, of the pressure-sensitive adhesive tape of the present invention, it is preferable that the poly(meth)acrylates be partially cross-linked to one another by crosslinking so that the pressure-sensitive adhesive comprises cross-linked poly(meth)acrylates. Accordingly, a pressure-sensitive adhesive of the present invention is preferred in which one or more poly(meth)acrylates can be produced by the polymerization of a second monomer composition and subsequent crosslinking of the polymer, wherein the crosslinking preferably occurs by a chemical crosslinking agent and / or a physical crosslinking agent. Preferably, the poly(meth)acrylates of the pressure-sensitive adhesive of the present invention are thermally crosslinked using at least one covalent crosslinking agent or a combination of at least one covalent crosslinking agent and at least one coordination crosslinking agent.

[0038] Preferred covalent crosslinking agents are epoxycyclohexyl derivatives and N,N-diglycidylamines. Preferred coordination crosslinking agents are chelate compounds, more particularly polyvalent metal chelate compounds. While thermal crosslinking generally results in particularly homogeneous crosslinking, crosslinking profiles with varying crosslinking densities can be observed, for example, for radiation-crosslinked compositions.

[0039] Preferred thermal crosslinking agents 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 and epoxycyclohexyl carboxylates, in particular (3,4-epoxycyclohexane)methyl 3,4-epoxycyclohexylcarboxylate and bis(3,4-epoxycyclohexylmethyl) adipate.

[0040] A preferred coordination crosslinker is a polyvalent metal chelate compound in which a polyvalent metal is coordinately bonded to one or more organic compounds. The polyvalent metal atoms are preferably Al(lll), Zr(IV), Co(l), Cu(l), Cu(l), Fe(lll), Fe(lll), Ni(l), V(lll), V(lll), V(IV), V(V), Zn(l), In(lll), Ca(l), Mg(l), Mn(l), Y(lll), Ce(l), Ce(IV), St(l), Ba(l), Mo(l), Mo(IV), Mo(VI), La(lll), Sn(l), Sn(IV), and Ti(IV), in particular Al(lll), Zr(IV), and Ti(IV). The ligands used are preferably alkyl esters, alcohol compounds, carboxylic acid compounds, ether compounds, and ketone compounds. Particularly preferred coordination crosslinking agents are 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, and poly(titanium acetylacetonate); Aluminum diisopropoxide monoethyl acetate, aluminum di-n-butoxide monomethyl acetoacetate, aluminum di-i-butoxide monomethyl acetoacetate, aluminum di-n-butoxide monoethyl acetoacetate, aluminum di-secondary-butoxide monoethyl acetoacetate, aluminum triacetylacetonate, aluminum monoacetylacetonate bis(ethyl acetoacetonate), and zirconium tetraacetylacetonate; more particularly aluminum triacetylacetonate and aluminum diisopropoxide monoethyl acetate.

[0041] Those skilled in the art understand that in the pressure-sensitive adhesive of the present invention, both the poly(meth)acrylate and the tackifying resin may be produced at least partially from the (meth)acrylate. In the aforementioned definition of the pressure-sensitive adhesive of the present invention, the weight-average molecular weight is defined to ensure a clear distinction between the high molecular weight poly(meth)acrylate and the short-chain tackifying resin, so that a clear distinction can be made between these components. In this way, the information also indicates the difference between the two components by parameters that allow those skilled in the art to actually distinguish between the poly(meth)acrylate and the tackifying resin.

[0042] Here, the weight-average molecular weight is determined by gel permeation chromatography (GPC) on 100 mL of clear-filtered sample (sample concentration 0.5 g / L). Tetrahydrofuran containing 0.1 vol% trifluoroacetic acid is used as the eluent. Measurements are performed at 25°C. The protective column used is a PSS-SDV type column, 10 μm, ID 8.0 mm x 50 mm. For separation, Type PSS-SDV columns with IDs of 8.0 mm x 300 mm, 5 μm, and 10 3 Å(SN9090201) and 5 μm, 10 2 An Å (SN9090200) column is used (detection by differential refractometer PSS-SECurity 1260 RID). The flow rate is 0.5 mL / min. Calibration is performed against a PMMA standard (polymethyl methacrylate calibration).

[0043] However, the inventors have succeeded in identifying a desirable weight-average molecular weight for both components of the pressure-sensitive adhesive that, when established, results in the particularly advantageous pressure-sensitive adhesive of the present invention. In particular, regarding the tackifying resin, it has been found that a relatively short-chain tackifying resin can be used to achieve particularly excellent chemical resistance along with excellent pressure-sensitive adhesion. Indeed, one or more poly(meth)acrylates have a weight-average molecular weight M of 400,000 g / mol or more, preferably 500,000 g / mol or more, more preferably 600,000 g / mol or more, and very preferably 750,000 g / mol or more. w A pressure-sensitive adhesive of the present invention having is preferred. Additionally or alternatively, one or more tackifying resins have a weight-average molecular weight M in the range of 1,000 to 15,000 g / mol, preferably in the range of 1,500 to 10,000 g / mol, and more preferably in the range of 2,000 to 5,000 g / mol. w A pressure-sensitive adhesive of the present invention having [this] is preferred.

[0044] In addition to the components provided according to the present invention, it may be considered an advantage of the pressure-sensitive adhesive of the present invention that additional components, such as typical additives, may also be used. However, it has been proven that when the pressure-sensitive adhesive is composed mainly of the components specified above, it is particularly advantageous, especially in terms of optimal chemical resistance. Accordingly, a pressure-sensitive adhesive of the present invention is preferred in which the combined mass fraction of one or more poly(meth)acrylates and one or more tackifying resins is 95% or more, preferably 98% or more, and more preferably 99% or more based on the mass of the pressure-sensitive adhesive.

[0045] In this context, it has been proven as a specific advantage of the pressure-sensitive adhesive of the present invention that the fraction of the tackifying resin can be selected to be relatively high, because the chemical-resistant tackifying resin of the present invention has little or no adverse effect on the chemical resistance of the pressure-sensitive adhesive even at a relatively large mass fraction. In this regard, the inventors were able to identify an optimal mass range to resolve the trade-off between excellent adhesive properties and high chemical resistance, including particularly for materials such as oleic acid. In practice, the pressure-sensitive adhesive of the present invention is preferred in which the combined mass fraction of one or more tackifying resins is in the range of 5 to 25%, preferably in the range of 7.5 to 22.5%, and more preferably in the range of 10 to 20% based on the mass of the pressure-sensitive adhesive. Alternatively, the pressure-sensitive adhesive of the present invention is preferred in which the combined mass fraction of one or more poly(meth)acrylates is 75% or more, preferably 77.5% or more, and more preferably 80% or more based on the mass of the pressure-sensitive adhesive.

[0046] It can be seen as a major advantage of the pressure-sensitive adhesive of the present invention that the poly(meth)acrylate used can be selected very flexibly with respect to the chemical properties of the monomer, and that the pressure-sensitive adhesive can be particularly suited to the requirements of each specific application, particularly because many poly(meth)acrylates inherently possess advantageous chemical resistance. However, based on the inventors' own research, as disclosed, for example, in WO 2019 / 106194 and WO 2019 / 106195, the inventors have succeeded in providing a particularly advantageous composition for poly(meth)acrylates for the pressure-sensitive adhesive tape of the present invention, which inherently possesses particularly high chemical resistance, thereby allowing the particularly strong pressure-sensitive adhesive of the present invention to be obtained in combination with an advantageous tackifying resin. A pressure-sensitive adhesive tape of the present invention that can be produced by the polymerization of a second monomer composition comprising one or more poly(meth)acrylates based on the mass of the second monomer composition is particularly preferred:

[0047] iv) One or more fourth monomers selected from the group consisting of acrylic esters of formula (I):

[0048] CH2=CH-C(O)OR 1 (I)

[0049] [In the above formula, R 1 [is a linear or branched alkyl group having 1 to 10 C atoms in a combined mass fraction of 30 to 80%, preferably 40 to 70%, preferably methyl acrylate, ethyl acrylate, n-butyl acrylate, and ethylhexyl acrylate],

[0050] v) One or more fifth monomers selected from the group consisting of acrylic esters of formula (II):

[0051] CH2=CH-C(O)OR 2 (II)

[0052] [In the above formula, R 2[is a phenoxyalkyl radical or alkoxyalkyl radical having 2 to 5 C atoms, preferably phenoxyethyl acrylate and methoxyethyl acrylate, in a combined mass fraction in the range of 20 to 70%, preferably in the range of 30 to 50%, and

[0053] vi) One or more sixth monomers selected from the group consisting of acrylate monomers of chemical formula (III):

[0054] CH2=CH-C(O)OR 3 (III)

[0055] [In the above formula, R 3 [is a hydroxyalkyl radical having an H atom or 1 to 4 C atoms, preferably acrylic acid, in a combined mass fraction in the range of 0.5 to 10%, preferably in the range of 1 to 5%],

[0056] and preferably additionally

[0057] vii) One or more seventh monomers selected from the group consisting of acrylic acid esters of chemical formula (IV):

[0058] CH2=CH-C(O)OR 4 (IV)

[0059] [In the above formula, R 4 [is an alkyl diglycol radical, preferably ethyl diglycol acrylate, in a combined mass fraction of 0.5 to 40%, preferably 5 to 20%.]

[0060] According to the present invention, a tackifying resin is obtained by polymerizing a first monomer composition comprising various monomers, namely, a first monomer selected from the group consisting of aromatic (meth)acrylates and styrene, a second monomer selected from the group consisting of methyl methacrylate and ethyl methacrylate, and a third monomer selected from the group consisting of (meth)acrylates, with a cycloaliphatic radical. According to conventional nomenclature, a (meth)acrylate having a cycloaliphatic radical is an ester of (meth)acrylic acid having a cycloaliphatic ring, i.e., a non-aromatic ring, attached to the radical through an ester functional group. Thus, the third monomer itself is a cycloaliphatic compound, which is sometimes referred to as a cycloaliphatic compound.

[0061] According to the knowledge of the inventors, the above-mentioned mass fractions for the first, second, and third monomers in the first monomer composition define each minimum corresponding monomer as a lower limit thereof, and a tackifying resin that causes excellent chemical resistance can be obtained, as it has little or no adverse effect on the inherent chemical resistance of the poly(meth)acrylate-based pressure-sensitive adhesive when used in the poly(meth)acrylate-based pressure-sensitive adhesive.

[0062] While it may be seen as an advantage of the pressure-sensitive adhesive of the present invention that the tackifying resin can be produced at least partially from additional monomers; however, in the inventor's estimation, the proportion of additional monomers should be kept significantly low to maximize chemical resistance. Nevertheless, the use of additional monomers, particularly thiols, enables targeted tuning of the physicochemical properties of the tackifying resin, thereby making it easier to optimally achieve other requirement profiles apart from chemical resistance. Accordingly, the pressure-sensitive adhesive of the present invention is preferred in which one or more additional monomers are included in a combined mass fraction of the first monomer composition in the range of 0 to 50%, preferably 0.1 to 30%, more preferably 0.5 to 15% based on the mass of the first monomer composition, and the additional monomers are preferably selected from the group consisting of other (meth)acrylates and thiols, preferably thiols, more preferably dodecanethiol and 2-ethylhexyl 3-mercaptopropionate. Alternatively, a pressure-sensitive adhesive of the present invention is preferred in which, based on the mass of the first monomer composition, the combined mass fraction of the first monomer, the second monomer, and the third monomer in the first monomer composition is 80% or more, preferably 90% or more, and very preferably 98% or more.

[0063] Based on the inventors' own experiments, the inventors reached the surprising discovery that the advantageous properties observed with respect to the composition of the tackifying resin appear only within a relatively narrow compositional range of the three monomer classes defined above. Based on this compositional range, the inventors also succeeded in identifying a particularly advantageous composition from which a particularly strong tackifying resin can be obtained. Indeed, based on the mass of the first monomer composition, the first monomer composition

[0064] i1) comprising one or more first monomers in a combined mass fraction in the range of 7.5 to 35%, preferably in the range of 10 to 30%, and / or,

[0065] ii1) comprising one or more second monomers in a combined mass fraction in the range of 40 to 65%, preferably in the range of 45 to 60%, and / or,

[0066] iii1) A pressure-sensitive adhesive of the present invention is preferred, comprising one or more third monomers in a combined mass fraction of a range of 7.5 to 35%, preferably 10 to 30%. It is particularly preferred that the corresponding or preferred ranges are established accordingly for two or more monomers, preferably all of them.

[0067] Furthermore, the inventors have succeeded in identifying compounds particularly suitable for the first, second, and third monomers, which produce a particularly strong tackifying resin that can be used in the pressure-sensitive adhesive of the present invention having particularly high chemical resistance. Accordingly, preferably in the first monomer composition

[0068] i2) One or more first monomers are selected from the group consisting of aromatic (meth)acrylates, preferably aromatic methacrylates, more preferably benzyl methacrylates and phenoxyethyl methacrylates, very preferably benzyl methacrylates, and / or,

[0069] ii2) One or more second monomers are selected from the group consisting of methyl methacrylate and ethyl methacrylate, preferably methyl methacrylate, and / or,

[0070] iii2) A pressure-sensitive adhesive of the present invention is used, wherein one or more third monomers are selected from the group consisting of methacrylates having alicyclic radicals, preferably cyclohexyl methacrylate, isobornyl methacrylate, dicyclofentanyl methacrylate and norbornyl methacrylate, preferably cyclohexyl methacrylate. It is also particularly preferred that a corresponding compound or a preferred or more preferred compound is selected accordingly for two or more, preferably all, of the monomers, and these preferred monomers are used particularly preferably in a preferred mass fraction in each case.

[0071] It has become apparent that the addition of one or more plasticizers can improve the impact resistance of the pressure-sensitive adhesive of the present invention without significantly affecting chemical resistance. Preferably, the pressure-sensitive adhesive of the present invention thus comprises at least one plasticizer, wherein the plasticizer is more preferably selected from the group consisting of (meth)acrylate oligomers, phthalates, hydrocarbon oils, cyclohexanedicarboxylic acid esters, benzoic acid esters, water-soluble plasticizers, plasticizing resins, phosphates and polyphosphates, more preferably phthalates, cyclohexanedicarboxylic acid esters and benzoic acid esters, and very preferably benzoic acid esters. Preferably, the pressure-sensitive adhesive of the present invention comprises a mass fraction of 30% or less, preferably 20% or less, and more preferably 15% or less of a plasticizer. To further optimize the physicochemical properties of the pressure-sensitive adhesive of the present invention, it may also contain other conventional additives, such as fillers, e.g., electrically conductive fillers, thermally conductive fillers, or flame retardants, e.g., ammonium polyphosphate and derivatives thereof.

[0072] In a preferred embodiment, the pressure-sensitive adhesive of the present invention is foamed. The "foamed pressure-sensitive adhesive" is a pressure-sensitive adhesive comprising a pressure-sensitive adhesive matrix material and multiple gas-filled cavities, so that the density of such pressure-sensitive adhesive is reduced compared to a simple matrix material without cavities. The foaming of the matrix material of the foamed pressure-sensitive adhesive can, in principle, be carried out in any desired manner. For example, the pressure-sensitive adhesive can be foamed by a propellant gas introduced or released into it. Preferably, the foamed pressure-sensitive adhesive contains at least partially expanded hollow microspheres. These encompass at least partially expanded microspheres that are elastic and expandable in their base state and have a thermoplastic polymer shell. These spheres are filled with a low-boiling liquid or liquefied gas in their base state. The shell material used is, in particular, polyacrylonitrile, PVDC, PVC, or polyacrylate. In particular, a hydrocarbon of a lower alkane, e.g., isobutane or isopentane, enclosed as a liquefied gas under pressure in a polymer shell is conventional as a low-boiling liquid. The term "microballoon" is also commonly used for these microspheres. The outer polymer shell of these microballoons softens as a result of exposure to heat. At the same time, the liquid propellant gas present within the shell is converted into a gaseous state. This causes the microballoon to undergo irreversible expansion and three-dimensional expansion. The expansion ends when the internal and external pressures are balanced. Because the polymer shell is preserved, a closed-cell foam is consequently created; in this regard, syntactic foaming is also referred to.

[0073] The pressure-sensitive adhesive of the present invention can be used directly, for example, as an adhesive, and depending on the method of application, it can also be provided in the form of, for example, a tape. In terms of highly advantageous handling properties, particularly advantageous results are generally achieved when the pressure-sensitive adhesive of the present invention is also used as an adhesive layer of a single-sided or double-sided pressure-sensitive adhesive tape comprising a carrier layer. Accordingly, the present invention also relates to a pressure-sensitive adhesive tape comprising a carrier layer and the pressure-sensitive adhesive of the present invention as a pressure-sensitive adhesive.

[0074] The term adhesive tape is obvious to those skilled in the art of adhesive technology. In the context of the present invention, the expression “tape” refers to any thin, flat structure, that is, a structure having a predominant degree in two dimensions, more particularly films, film portions and labels, preferably tapes having an extended length and a limited width, and corresponding tape portions.

[0075] A carrier layer generally refers to a layer of such a multilayer adhesive tape that significantly determines the mechanical and physical properties of the adhesive tape, such as tear resistance, elongation, insulation, or resilience. Common materials for the carrier layer are, for example, woven fabrics, laminated scrims, and polymer films, for example, PET films and polyolefin films. However, the carrier layer may also be a pressure-sensitive adhesive itself. In a preferred embodiment, the pressure-sensitive adhesive tape of the present invention may be a double-sided pressure-sensitive adhesive tape in which the carrier layer is provided on both sides as the pressure-sensitive adhesive of the present invention. In the pressure-sensitive adhesive tape of the present invention, the adhesive layer may be lined with a so-called release liner to enable trouble-free unwinding and to protect the pressure-sensitive adhesive from contamination. Such a release liner generally consists of a single-sided or double-sided siliconized polymer film (e.g., PET or PP) or a siliconized paper carrier.

[0076] Starting from the pressure-sensitive adhesive tape of the present invention, a use of the pressure-sensitive adhesive tape of the present invention for combining two or more components to produce a chemically resistant bond is also disclosed.

[0077] In light of the above observations, those skilled in the art understand that the use of specifically synthesized tackifying resins themselves and for the simultaneous improvement of pressure-sensitive adhesive properties and the preservation of chemical resistance is also intrinsically advantageous to poly(meth)acrylate-based pressure-sensitive adhesives. Accordingly, the present invention also relates to the use of one or more tackifying resins to enhance peel adhesive strength and chemical resistance in (meth)acrylate-based adhesives, wherein one or more tackifying resins can be produced by the polymerization of a first monomer composition comprising, based on the mass of the first monomer composition:

[0078] i) one or more first monomers selected from the group consisting of aromatic (meth)acrylates and styrene, in a combined mass fraction ranging from 5 to 40%,

[0079] ii) one or more second monomers selected from the group consisting of methyl methacrylate and ethyl methacrylate, in a combined mass fraction ranging from 35 to 68%, and

[0080] iii) One or more third monomers selected from the group consisting of (meth)acrylates having alicyclic radicals, in a combined mass fraction ranging from 5 to 40%. Specific details for implementing the invention

[0081] Preferred embodiments of the present invention are further described and explained below with reference to experiments.

[0082] 1. Production of Poly(Met)Acrylate:

[0083] Table 1 - Composition of poly(meth)acrylate,

[0084] data on mass fraction (%)

[0085]

[0086] For the production of poly(meth)acrylates P1 to P5 listed in Table 1, 100 kg of a specific monomer in a specific mass fraction and 72.4 kg of an ethyl acetate / isopropanol mixture (95:5) were loaded into a conventional reactor for radical polymerization.

[0087] After 45 minutes of passing nitrogen gas through the reactor while stirring, the reactor was heated to 58°C and 50 g of 2,2'-azobis(2-methylbutyronitrile) was added. Subsequently, the external heating bath was heated to 70°C, and the reaction was carried out at this external temperature. After 1 hour, an additional 50 g of 2,2'-azobis(2-methylbutyronitrile) was added. After 2, 3, and 4 hours, the batch was diluted each time with 15 kg of ethyl acetate / isopropanol mixture (95:5).

[0088] After 5.5 h and 7 h, the batch was restarted with 150 g of bis(4-3-butylcyclohexyl) peroxydicarbonate each time. After a reaction time of 22 h, polymerization was stopped and the mixture was cooled to room temperature. In each case, nearly quantitative conversion was achieved.

[0089] 2. Production of Tackifying Resins:

[0090] Table 2 - Composition of tackifying resin,

[0091] data on mass fraction (%)

[0092]

[0093] 100 kg of a specific monomer in a specific mass fraction and 72.4 kg of an ethyl acetate / isopropanol mixture (96:4) were loaded into a conventional reactor for radical polymerization to produce the tackifying resins H1 to H7 listed in Table 2.

[0094] After 45 minutes of passing nitrogen gas through the reactor while stirring, the reactor was heated to 58°C and 444 g of 2,2'-azobis(2-methylbutrironitrile) (5 wt% in acetone) was added. Subsequently, the external heating bath was heated to 75°C, and the reaction was carried out at this external temperature. After 7 h of reaction time, an additional 444 g of 2,2'-azobis(2-methylbutrironitrile) (5 wt% in acetone) was added. After 22 h of reaction time, the reaction was terminated and cooled to room temperature. In each case, nearly quantitative conversion was achieved.

[0095] 3. Production of Pressure-Sensitive Adhesives

[0096] Table 3 - Composition of pressure-sensitive adhesives

[0097]

[0098] Pressure-sensitive adhesives E1 to E12 of the present invention and pressure-sensitive adhesives V1 to V11 of the non-present invention were produced according to Table 3 by mixing poly(meth)acrylates P1 to P5 corresponding to each case with tackifying resins H1 to H7 in specified mass fractions.

[0099] Each pressure-sensitive adhesive was further blended with 0.05 wt% of the crosslinking agent N,N,N',N'-tetrakis(2,3-epoxypropyl)-m-xylene-a,a'-diamine based on the poly(meth)acrylate to crosslink the poly(meth)acrylate; the tackifying resin was likewise not crosslinked because it lacked suitable functional groups. The mixture was subsequently diluted with ethyl acetate to a solid content of 30 wt% and then coated onto a siliconeized release film (50 μm polyester PET) from the solution (coating speed 2.5 m / min, drying tunnel 15 m, temperature zone 1: 40°C, zone 2: 70°C, zone 3: 95°C, zone 4: 105°C). The coating weight was 50 g / m² 2 was.

[0100] 4. Peel Adhesion and Chemical Resistance Tests

[0101] After removing the siliconeized PET film, the adhesive tape obtained as described in Section 2 above was applied to pre-washed ASTM steel plates with a width of 10 mm each and rolled down 5 times in each direction back and forth using a 4 kg roller. Subsequently, the resulting bond was stored for 24 hours under standard conditions (air, 23°C, 50% relative humidity).

[0102] Next, the sample specimens were stored in a sealed box in a water bath conditioned at 60°C for 72 hours, one sample was immersed in one of the test chemicals and completely surrounded by it, while each control sample was stored in the air.

[0103] The test chemicals used were oleic acid and an ethanol / water mixture (85 / 15, mass fraction) with a purity of > 85%. After removing the box from the water bath and the sample specimen from the box, the sample specimen was carefully washed with a cloth and conditioned for 2 hours under standard conditions, after which the peel adhesion strength was determined.

[0104] The peel adhesion strength was determined under test conditions of a temperature of 23°C + / - 1°C and a relative humidity of 50% + / - 5%. The adhesive tape was removed from the steel substrate at a speed of 300 mm / min and an angle of 180°. The measurement results in Table 4 are expressed in N / cm and correspond to the average of three measurements.

[0105] The adhesive tape is considered resistant to each test chemical if it still exhibits a peel adhesion of at least 1.0 N / cm after storage in each test chemical. It is advantageous for the difference in peel adhesion between the reference sample and the sample stored in the test chemical to be as small as possible. In summary, the entire sample is considered sufficiently chemically resistant only if a peel adhesion of at least 1.0 N / cm is still present after storage compared to both test chemicals.

[0106] Table 4 - Peel Adhesion of Pressure-Sensitive Adhesives

[0107] Data (N / cm)

[0108]

[0109] The measurements summarized in Table 4 clearly show that all poly(meth)acrylates used have some degree of chemical resistance without the addition of tackifying resins, and thus are a suitable reference system for evaluating the effect of tackifying resins.

[0110] In the pressure-sensitive adhesive of the present invention, all tackifying resins reliably induce improved peel adhesion in control samples compared to tackifying resin-free comparison samples, thereby demonstrating the high suitability of the corresponding system as a tackifying resin. However, since resistance to oleic acid decreases too much when the mass fraction is too large (see: Pressure-sensitive adhesive V6), it can also be seen from experiments that the mass fraction should not be increased too much, even in the case of certain tackifying resins of the present invention.

[0111] In terms of the composition of the tackifying resin, a comparison with pressure-sensitive adhesives V7 and V8 shows that, particularly, the content of the second monomer is too high at 70%, and while excellent resistance to ethanol / water can be achieved with these tackifying resins and corresponding pressure-sensitive adhesives, the resistance to oleic acid in these pressure-sensitive adhesives has too negative an impact on the overall positive evaluation.

[0112] It should be noted that all pressure-sensitive adhesives of the present invention for both test chemicals still show a peel adhesion strength of at least 1.0 N / cm after storage, so they are sufficiently resistant in the overall evaluation.

[0113] 5. Push-out Test:

[0114] A frame-shaped square sample was cut from the adhesive tape to be examined (external dimensions 33 mm x 33 mm; border width 2.0 mm; internal dimensions (window cut-out) 29 mm x 29 mm). This sample was attached to a polycarbonate (PC) frame (external dimensions 45 mm x 45 mm; border width 10 mm; internal dimensions (window cut-out) 25 mm x 25 mm; thickness 3 mm). A 35 mm x 35 mm PC window was attached to the other side of the double-sided adhesive tape. The PC frame, adhesive tape frame, and PC window were joined in a corner-to-corner manner, with the geometric centers and diagonals positioned above each other. The joint area is 248 mm² 2 The bond was pressed at 248 N for 5 seconds and stored at a temperature of 23°C and 50% relative humidity for 24 hours.

[0115] Next, the combined test frame was stored in a sealed box in a water bath conditioned at 60°C for 24 hours, one sample was stored and immersed in one of the test chemicals and then completely surrounded by it, while each control sample was stored in the air.

[0116] Immediately after the storage described above, the adhesive assembly consisting of a PC frame, adhesive tape, and PC window was dried and clamped to a sample holder by the protruding edge of the PC frame in such a way that the assembly was horizontally aligned and the PC window was positioned below the frame. Subsequently, the sample holder was inserted into the center of a receiver provided by a Zwick test machine. The sample head was lowered vertically onto the plate at a speed of 10 mm / s (measurement conditions 23°C, 50% relative humidity). Table 5 reports the force (N) required to push out the PC window. The reported values ​​correspond to the average of five measurements.

[0117] Table 5 - Push-out Test

[0118] Data (N)

[0119]

[0120] The measurements summarized in Table 5 confirm that all pressure-sensitive adhesives of the present invention exhibit excellent resistance to both test chemicals and also significantly improve adhesive properties compared to control samples. In this context, it is noted that the residual peel adhesion of the samples of the present invention after chemical exposure is, in many cases, actually superior to that of systems without tackifying resins. In particular, the tackifying resins H4, H5, and H6 of pressure-sensitive adhesives E6 to E9 possess particularly advantageous properties.

Claims

Claim 1 As a pressure-sensitive adhesive, a) a weight-average molecular weight M of 200,000 g / mol or more, with a combined mass fraction of 50% or more based on the mass of the pressure-sensitive adhesive. w One or more poly(meth)acrylates having, and b) a weight-average molecular weight M of 20,000 g / mol or less in a combined mass fraction ranging from 1 to 25% based on the mass of the pressure-sensitive adhesive. w A pressure-sensitive adhesive comprising one or more tackifying resins having, wherein the one or more tackifying resins can be produced by polymerization of a first monomer composition, and the first monomer composition comprises, based on the mass of the first monomer composition, i) one or more first monomers selected from the group consisting of aromatic (meth)acrylates and styrenes, in a combined mass fraction ranging from 5 to 40%, ii) one or more second monomers selected from the group consisting of methyl methacrylates and ethyl methacrylates, in a combined mass fraction ranging from 35 to 68%, and iii) one or more third monomers selected from the group consisting of (meth)acrylates having alicyclic radicals, in a combined mass fraction ranging from 5 to 40%. Claim 2 A pressure-sensitive adhesive according to claim 1, wherein the combined mass fraction of one or more poly(meth)acrylates is 75% or more based on the mass of the pressure-sensitive adhesive. Claim 3 A pressure-sensitive adhesive according to claim 1 or 2, wherein the combined mass fraction of one or more tackifying resins is in the range of 5 to 25% based on the mass of the pressure-sensitive adhesive. Claim 4 A pressure-sensitive adhesive according to claim 1 or 2, wherein the combined mass fraction of one or more poly(meth)acrylates and one or more tackifying resins is 95% or more based on the mass of the pressure-sensitive adhesive. Claim 5 In claim 1 or 2, one or more poly(meth)acrylates can be produced by polymerization of the second monomer composition, and the second monomer composition comprises, based on the mass of the second monomer composition, iv) one or more fourth monomers selected from the group consisting of acrylic esters of formula (I): CH2=CH-C(O)OR 1 (I) [In the above equation, R 1 [is a linear or branched alkyl group having 1 to 10 C atoms in a combined mass fraction ranging from 30 to 80%],v) one or more fifth monomers selected from the group consisting of acrylic esters of formula (II): CH2=CH-C(O)OR2(II) [wherein R 2 [is a phenoxyalkyl radical or alkoxyalkyl radical having 2 to 5 C atoms in a combined mass fraction ranging from 20 to 70%], and vi) one or more sixth monomers selected from the group consisting of acrylate monomers of formula (III): CH2=CH-C(O)OR 3 (III) [In the above formula, R 3 Pressure-sensitive adhesive comprising [a hydroxyalkyl radical having an H atom or 1 to 4 C atoms in a combined mass fraction in the range of 0.5 to 10%]. Claim 6 A pressure-sensitive adhesive according to claim 1 or 2, wherein, based on the mass of the first monomer composition, the combined mass fraction of the first monomer, the second monomer, and the third monomer in the first monomer composition is 80% or more. Claim 7 A pressure-sensitive adhesive according to claim 1 or 2, wherein the first monomer composition comprises, based on the mass of the first monomer composition, i1) one or more first monomers in a combined mass fraction in the range of 7.5 to 35% and / or ii1) one or more second monomers in a combined mass fraction in the range of 40 to 65% and / or iii1) one or more third monomers in a combined mass fraction in the range of 7.5 to 35%. Claim 8 A pressure-sensitive adhesive according to claim 1 or 2, wherein in the first monomer composition, i2) one or more first monomers are selected from the group consisting of aromatic (meth)acrylates and / or ii2) one or more second monomers are selected from the group consisting of methyl methacrylate and ethyl methacrylate and / or iii2) one or more third monomers are selected from the group consisting of methacrylates having alicyclic radicals. Claim 9 A pressure-sensitive adhesive tape comprising a carrier layer and a pressure-sensitive adhesive according to claim 1 or 2 as a pressure-sensitive adhesive. Claim 10 A poly(meth)acrylate-based adhesive comprising one or more tackifying resins for enhancing peel adhesive strength and chemical resistance, wherein the one or more tackifying resins can be produced by polymerization of a first monomer composition, and the first monomer composition comprises, based on the mass of the first monomer composition, i) one or more first monomers selected from the group consisting of aromatic (meth)acrylates and styrenes in a combined mass fraction ranging from 5 to 40%, ii) one or more second monomers selected from the group consisting of methyl methacrylates and ethyl methacrylates in a combined mass fraction ranging from 35 to 68%, and iii) one or more third monomers selected from the group consisting of (meth)acrylates having alicyclic radicals in a combined mass fraction ranging from 5 to 40%.

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