Foamable pressure-sensitive adhesive formulation containing hydrated vinyl aromatic block copolymers

Abstract

The present invention relates to foamable pressure-sensitive adhesive formulations for self-adhesive tapes, a foamed pressure-sensitive adhesive layer comprising the pressure-sensitive adhesive formulation, a self-adhesive product comprising at least one layer of the pressure-sensitive adhesive formulation in the form of a foam, respective methods for producing the foamable pressure-sensitive adhesive formulation, the foamed pressure-sensitive adhesive layer and the self-adhesive product, and to the use thereof.

Description

[0001] Foamable pressure-sensitive adhesive formulation containing hydrogenated vinyl aromatic block copolymers

[0002] The present invention relates to foamable pressure-sensitive adhesive formulations for self-adhesive tapes, a foamed pressure-sensitive adhesive layer comprising the pressure-sensitive adhesive formulation, a self-adhesive product comprising at least one layer of the pressure-sensitive adhesive formulation in foamed form, and to processes for producing the foamable pressure-sensitive adhesive formulation, the foamed pressure-sensitive adhesive layer, and the self-adhesive product, and to the use thereof.

[0003] Adhesives and adhesive tapes are generally used to join two substrates together, creating a temporary or permanent bond. Self-adhesive tapes containing at least one layer of a pressure-sensitive adhesive formulation are widely used. Tack is the property of a material or formulation to form a strong bond with a bonded surface at room temperature under light pressure, without undergoing any chemical or physical change. They are characterized by their permanent tack and thus differ from other adhesive systems, particularly liquid adhesives. This property leads to advantages in handling and use during the bonding process. Self-adhesive tapes have therefore found their way into a wide variety of industrial applications and in the consumer sector.

[0004] Particularly, but not exclusively, in the automotive and transport sectors, lightweight construction is becoming an increasingly important design requirement, as a vehicle's weight directly impacts energy consumption. This applies not only to vehicles with fuel-burning engines, but also to electric vehicles. For the latter, the range increases with decreasing vehicle weight while maintaining the same battery capacity. Therefore, the demand for weight savings is not only present in the automotive sector, but also in all components, including self-adhesive tapes. This leads to adhesive tapes being used for applications for which previous adhesive tape products were not foreseen or developed. In addition to the mechanical stress and the critical substrates for adhesive applications, there are also constantly increasing requirements for UV and weathering stability, especially for permanent bonds.A requirement for self-adhesive tapes often concerns not only the bonding performance on the components to be joined, but also a specific adhesive tape thickness in order to bridge or close design-specific gaps. Adhesive tape thicknesses can therefore be in the range of several hundred micrometers or even more than 1 mm. To achieve these dimensions without excessively increasing the overall weight of the finished product, self-adhesive tapes with reduced density are suitable, which can be achieved by foaming individual or multiple layers. The self-adhesive tape should also meet other key requirements regarding bond strength and durability. Pressure-sensitive adhesives based on rubber are particularly suitable when components made of materials with low surface energy, such as polyolefins, are to be bonded.

[0005] Foamed pressure-sensitive adhesive layers can also provide mechanical and / or acoustic damping or contribute to resistance to shock. This is a common requirement in mobile (portable) electronic devices, for example, and tends to involve thinner layers, which can be less than 100 μm thick.

[0006] Formulations based on polyvinylaromatic block copolymers represent one of the classic pressure-sensitive adhesive families. In combination with adhesive resins and, if necessary, other admixtures, adhesives for self-adhesive tapes can be created that exhibit excellent adhesive properties, even on nonpolar substrates, with good cohesion. Due to their characteristic physical crosslinking principle of reversible formation of a two-phase morphology with domains formed from polyvinylaromatic segments that soften at temperatures above room temperature, such formulations can be processed practically solvent-based or solvent-free in the melt (FC Jagisch, JM Tancrede in Handbook of Pressure Sensitive Adhesive Technology, D. Satas (ed.), 3rd ed., 1999, Satas & Associates, Warwick).A disadvantage of the typically used polystyrene-polyisoprene-polystyrene block copolymer (SIS) and polystyrene-polybutadiene-polystyrene (SBS)-based pressure-sensitive adhesive formulations is their aging stability. Hydrogenated block copolymers have been proposed that exhibit increased aging stability.

[0007] Foamed pressure-sensitive adhesive systems have been known for some time and are described in the prior art. For example, they have lower densities than comparable non-foamed systems and are often characterized by non-destructive removability and repositionability. Polymer foams can generally be produced in two ways. Firstly, through the action of a propellant gas, either added as such or resulting from a chemical reaction, and secondly, by incorporating hollow spheres into the material matrix. Foams produced by the latter method are referred to as syntactic foams. In a syntactic foam, hollow spheres such as glass spheres or ceramic hollow spheres (microspheres) or microballoons are embedded in a polymer matrix.As a result, in a syntactic foam, the cavities are separated from one another, and the substances contained within the cavities (gas, air) are separated from the surrounding matrix by a membrane. Foams foamed with hollow microspheres are characterized by a defined cell structure with a uniform size distribution of the foam cells. Hollow microspheres produce closed-cell foams without cavities, which, compared to open-cell variants, offer, among other things, better sealing against dust and liquid media. Furthermore, chemically or physically foamed materials are more susceptible to irreversible collapse under pressure and temperature and often exhibit lower cohesive strength. Particularly advantageous properties can be achieved when expandable microspheres (also known as "microballoons") are used as microspheres for foaming.Due to their flexible, thermoplastic polymer shell, such foams possess greater conformability than those filled with non-expandable, non-polymeric hollow microspheres (e.g., hollow glass spheres). They are better suited to compensating for manufacturing tolerances, such as those commonly found in injection-molded parts, and, due to their foam nature, can also better compensate for thermal stresses.

[0008] Foamed self-adhesive layers based on styrene block copolymers are known.

[0009] DE 10 2008 004 388 A1 relates to a pressure-sensitive adhesive containing expanded microballoons, wherein the adhesive strength of the adhesive containing the expanded microballoons is reduced by a maximum of 30%, preferably a maximum of 20%, particularly preferably 10%, compared to the adhesive strength of an adhesive of identical basis weight and formulation, which is defoamed by the destruction of the cavities created by the expanded microballoons. Suitable elastomers include SBS and SIS; (partially) hydrogenated block copolymers are not mentioned.

[0010] DE 10 2008 004 388 A1 demonstrates, based on the degree of achievable density reduction at a given microballoon content, that the foaming of SIS-based formulations is not as effective as that of those based on natural rubber. This suggests that the foamability of pressure-sensitive adhesives depends on the composition of the base formulation. It is reasonable to assume that the cohesion of the base formulation at the temperature at which foaming is carried out has a key influence on foaming efficiency. DE 10 2008 004 388 reveals differences in the foaming efficiency of pressure-sensitive adhesive formulations based on polydiene rubbers containing polystyrene segments (polystyrene-polydiene block copolymers using SIS as an example) compared to those based on pure polydiene rubbers (using natural rubber as an example) (see Figure 1).Pressure-sensitive adhesives containing polystyrene-polydiene block copolymers exhibit lower foaming efficiency than those without. The specific nature of the two-phase structure in polystyrene block copolymers appears to impede foaming behavior. Table 3 compares formulations based on SIS with those based on hydrogenated polystyrene-polydiene block copolymers. With the same amount of microballoons and a comparable foaming process, a significantly lower density is achieved for SIS than for those based on hydrogenated polystyrene-polydiene block copolymers. These explicitly stated formulations do not contain any plasticizers.

[0011] DE 10 2017 218 519 A1 teaches pressure-sensitive adhesive strips with an adhesive based on polydiene block copolymers, which can be provided with microballoons and irradiated with electrons. Hydrogenated block copolymers are not mentioned.

[0012] EP 2 832 779 A1 describes a rubber-based pressure-sensitive foam with special adhesive resins and plasticizers. A number of different elastomers are listed that can serve as the basis for these foams. Natural rubbers, synthetic rubbers, thermoplastic elastomers, non-thermoplastic elastomers, thermoplastic hydrocarbon elastomers, and non-thermoplastic hydrocarbon elastomers are mentioned very generally. Among the block copolymers, only SIS is explicitly listed in the examples.

[0013] To ensure the longevity of bonded joints, pressure-sensitive adhesive formulations based on saturated elastomers such as polyacrylates are often preferred. However, these do not always offer the required bond strengths on the nonpolar materials mentioned above, for example, and some other materials. For applications requiring optimized longevity, hydrogenated vinyl aromatic block copolymers are offered in the rubber sector. Although it is generally known that hydrogenated styrene block copolymers are very difficult to tackify (Jagisch and Tancrede in D. Satas, Handbook of Pressure Sensitive Adhesive Technology, 3rd ed., 1999, D. Satas & Associates, Warwick, p. 367, Table 16-5), there have been various approaches to formulating pressure-sensitive adhesives using such block copolymers.

[0014] DE 10 2007 021 504 A1 discloses, among other things, formulations containing polystyrene-poly(ethylene / butylene)-polystyrene (SEBS) block copolymer and a high proportion of liquid resin. Foaming of such formulations is not intended. Even though the description does not provide specific information on the polyvinylaromatic content, DE 10 2007 021 504 suggests through the examples that pressure-sensitive adhesives based on hydrogenated polystyrene-polydiene block copolymers are typically advantageously produced when block copolymers with a low polyvinylaromatic content are selected.

[0015] DE 102006037627 A1 describes pressure-sensitive adhesives containing hydrogenated block copolymers, tackifier resin, and polyisobutylene. The description does not make a specific selection of the hydrogenated block copolymers; the examples only mention those with a polyvinylaromatic content of 13 wt. Foaming of the pressure-sensitive adhesive is not intended.

[0016] Among hydrogenated polystyrene block copolymers, those with a low polystyrene content (< 15 wt.%) are frequently cited as base elastomers. Such block copolymers typically exhibit a higher melt flow index (MFI) compared to other hydrogenated polystyrene block copolymers with a polystyrene content of > 25 wt.%, which leads to improved processability in solvent-free processes. However, as a result of the low polystyrene content, the thermal shear strength of formulations based on these types of hydrogenated polystyrene block copolymers is not at the level required in many contemporary applications, particularly in the automotive sector.

[0017] The foaming of pressure-sensitive adhesives based on such hydrogenated block copolymers is described in WO 00 / 06637 A1, which discloses, among other things, a foamed layer composed of SEBS Kraton G1657 and adhesive resin Arkon P90 in equal proportions. According to the manufacturer, the polystyrene content of Kraton G1657 is 13 wt.%.

[0018] Therefore, pressure-sensitive adhesives for self-adhesive tapes with reduced dead weight are still sought, which have sufficient adhesion to materials with different surface energies, have sufficient cohesion even at high temperatures and, above all, offer improved durability.

[0019] The object is achieved according to the invention by a foamable pressure-sensitive adhesive formulation as defined in claim 1. Preferred further developments of this pressure-sensitive adhesive formulation are set out in the subclaims.

[0020] Accordingly, a first subject matter of the present invention is a foamable pressure-sensitive adhesive formulation comprising: a) at least one elastomer component; b) at least one adhesive resin component; c) at least 2.5% by weight of a plasticizer component, based on the total weight of the pressure-sensitive adhesive formulation; d) a foaming agent, and e) optionally a reinforcing component, characterized in that the elastomer component comprises at least 90% by weight, based on the total weight of the elastomer component, of one or more polyvinylaromatic-polydiene block copolymers, of which at least one is present with at least two polyvinylaromatic blocks (A), wherein

[0021] • the polydiene blocks (B) are hydrogenated to at least 90% by weight, based on the block copolymer; and

[0022] • the proportion of polyvinyl aromatic blocks (A) is at least 18 wt.%, based on the block copolymer.

[0023] DE 10 2008 004 388 reveals differences in the foaming efficiency of pressure-sensitive adhesive formulations based on polydiene rubbers containing polystyrene segments (polystyrene-polydiene block copolymers, exemplified by SIS) compared to those based on pure polydiene rubbers (example: natural rubber). Pressure-sensitive adhesives containing polystyrene-polydiene block copolymers exhibit lower foaming efficiency than those without polystyrene. The specific nature of the two-phase structure in polystyrene block copolymers appears to complicate foaming behavior.

[0024] Surprisingly, it was discovered within the scope of the present invention that even with pressure-sensitive adhesive formulations based on hydrogenated block copolymers with a high proportion of polyvinyl aromatics, a foaming efficiency comparable to that of non-hydrogenated block copolymers, such as SIS, can be achieved if the formulation additionally contains a plasticizer component. This offers the advantage that efficient weight reduction can be achieved even with a low foaming agent content. Thus, a suitable pressure-sensitive adhesive formulation can provide a satisfactory balance between good processability, high thermal shear strength, and low weight. a) Elastomer component

[0025] Pressure-sensitive adhesive formulations according to the invention contain at least 90% by weight, based on the total weight of the elastomer component, of at least one type of a polyvinylaromatic-polydiene block copolymer in which the polydiene blocks are hydrogenated to at least 90% by weight, based on the block copolymer, which has at least two polyvinylaromatic blocks (A) and in which the proportion of polyvinylaromatic blocks, based on the total weight of all polyvinylaromatic-polydiene block copolymers in the elastomer component, is at least 18% by weight.

[0026] It is preferred if the block copolymer or block copolymers are hydrogenated to at least 95% by weight, preferably at least 99% by weight, based on the block copolymer, of the polydiene blocks (B blocks). The ethylene content in the B blocks is preferably at least 50% by weight. In a preferred embodiment, the elastomer component is in the form of hydrogenated polyvinylaromatic-polydiene block copolymers having a structure of the form ABA, (AB) n , (AWAY) n X or (ABA) n X, in which

[0027] • the blocks A independently represent a polymer formed by polymerization of at least one vinyl aromatic compound;

[0028] • the blocks B independently represent a polymer formed by polymerization of one or more conjugated dienes having 4 to 18 carbon atoms, which were subsequently hydrogenated;

[0029] • X represents the residue of a coupling reagent or multifunctional initiator and

[0030] • n stands for an integer > 2.

[0031] The hydrogenated polyvinylaromatic-polydiene block copolymers preferably each comprise one or more rubbery blocks B (elastomer blocks, soft blocks) and at least two glassy blocks A (hard blocks). Particular preference in the embodiment described here is given to at least one hydrogenated polyvinylaromatic-polydiene block copolymer having a structure ABA, (AB)2X, (AB)aX, or (AB)4X, where A, B, and X are as defined above. The elastomer component preferably contains at least one triblock copolymer or higher multiblock copolymer, which may be linear or multi-armed, such as radial or star-shaped.

[0032] Pressure-sensitive adhesive formulations with a high proportion of polyvinylaromatic blocks are generally characterized by good thermal shear strength. In the context of the present invention, it has surprisingly been found that this advantageous property can be combined with the advantage of low weight, as achieved through foaming. In order to achieve a property profile that meets the requirements, a minimum of 18 wt. % polyvinylaromatic content is selected in the at least one block copolymer of this type. However, this should not be too high, since too high a proportion reduces the adhesive strength. It is advantageous if the polyvinylaromatic content is not higher than 35 wt. A polyvinylaromatic content in a range between 22 wt. % and 33 wt. % is favorable. The proportion of polyvinylaromatics in the hydrogenated polyvinylaromatic-polydiene block copolymers can be adjusted, for example, by means of 1 H- or 13C-NMR (Test VI). The polyvinylaromatic content of commercially available hydrogenated polyvinylaromatic-polydiene block copolymers can also be determined from the manufacturer's information.

[0033] Against this background, an embodiment of the pressure-sensitive adhesive formulation according to the invention is preferred in which the proportion of polyvinylaromatic blocks (A blocks) is at least 22 wt. %, based on the total amount of all hydrogenated polyvinylaromatic-polydiene block copolymers in the elastomer component. Furthermore, it has proven advantageous to limit the proportion of polyvinylaromatic blocks, based on the total amount of all hydrogenated polyvinylaromatic-polydiene block copolymers in the elastomer component, to a maximum of 35 wt. %. In this respect, an embodiment of the pressure-sensitive adhesive formulation according to the invention is particularly preferred in which the proportion of polyvinylaromatic blocks (A blocks) is at least 22 wt. % and a maximum of 33 wt. %, based on the total amount of all hydrogenated polyvinylaromatic-polydiene block copolymers in the elastomer component.

[0034] Vinylaromatics for constructing block A of the hydrogenated polyvinylaromatic-polydiene block copolymer used according to the invention preferably comprise styrene, α-methylstyrene, and / or other styrene derivatives. Block A can thus be present as a homopolymer or copolymer. Block A is particularly preferably a polystyrene.

[0035] The hydrogenated polyvinylaromatic-polydiene block copolymers used in the pressure-sensitive adhesive formulation according to the invention are preferably those obtained by anionic polymerization and sequential addition of the monomers for the respective polymer blocks, vinylaromatics for the A blocks and dienes for the B blocks. In many manufacturing processes, diblock intermediates AB" are converted into triblock copolymers (2 AB" + Z') using a coupling agent Z'. AB-Z-BA) or radial copolymers. The B blocks are then selectively hydrogenated, resulting in preferentially ethylene and butylene from a polybutadiene block or ethylene and propylene from a polyisoprene block as B blocks.

[0036] Block copolymers of this type form the backbone of the formulation. However, an excessive proportion or an unfavorable choice of molecular weight of this type can reduce the adhesive strength. To optimally balance these properties, it has been shown that block copolymers of this type should have a peak molecular weight of at least 70,000 g / mol and at most 400,000 g / mol. The higher the molecular weight, the more challenging the processability of the material becomes. Therefore, a peak molecular weight of at most 250,000 g / mol is preferred. Linear triblock copolymers or radial block copolymers with a peak molecular weight between 90,000 g / mol and 200,000 g / mol, especially between 100,000 g / mol and 180,000 g / mol, are very advantageous. The peak molecular weight can be determined, for example, using GPC, as described under Test Methods (Test 1a).

[0037] According to preferred embodiments of the invention, the elastomer component contained in the pressure-sensitive adhesive is not sulfonated in the vinyl aromatic blocks.

[0038] It is known that an increasing proportion of diblock copolymer in the elastomer component can result in a certain increase in peel strength. For example, as can be seen from Figures 16-18 in D. Satas, Handbook of Pressure Sensitive Adhesive Technology, 3rd ed., 1999, D. Satas & Associates, Warwick, p. 370, a formulation containing 20% ​​diblock copolymer (SIS) achieved an approximately 12% increase in bond strength compared to a diblock-free formulation (bond strength for the diblock-free reference formulation corresponds to 0%). Surprisingly, it has been shown that the proportion of diblock copolymer in the elastomer component in formulations based on hydrogenated polyvinylaromatic-polydiene block copolymers can result in a significantly greater increase in bond strength when foamed.Therefore, an embodiment is preferred in which the hydrogenated polyvinylaromatic-polydiene block copolymer used according to the invention has a diblock content AB of at least 10 wt.% and at most 50 wt.%, in each case based on the elastomer component, based on the total amount of all hydrogenated polyvinylaromatic-polydiene block copolymers in the elastomer component.

[0039] According to the invention, pressure-sensitive adhesive formulations are preferred in which the elastomer component accounts for a proportion of at least 35 wt. %, based on the total weight of the pressure-sensitive adhesive formulation. Preferably, the proportion of the elastomer component should not exceed 60 wt. %, so that an embodiment is preferred in which the proportion of elastomer component in the pressure-sensitive adhesive formulation is 35 to 60 wt. %, preferably 40 to 55 wt. %, based in each case on the total weight of the pressure-sensitive adhesive formulation. b) Adhesive resin component

[0040] The pressure-sensitive adhesive formulation according to the invention further contains at least one adhesive resin component.

[0041] The adhesive resin component is in particular one or more adhesive resins.

[0042] The adhesive resin component used in the pressure-sensitive adhesive formulation according to the invention is preferably substantially incompatible with the polyvinylaromatic blocks of the hydrogenated polyvinylaromatic-polydiene block copolymer and thus differs from the optionally present reinforcing component. The at least one adhesive resin component is therefore preferably selected such that it is miscible (compatible) primarily with the regions of the pressure-sensitive adhesive dominated by the hydrogenated polydiene blocks.

[0043] The adhesive resin component is used in particular to adjust the adhesion as desired. According to the general understanding of the skilled person, an "adhesive resin" is understood to be an oligomeric or polymeric resin that increases the adhesion, i.e., the inherent tackiness of the pressure-sensitive adhesive compared to an otherwise identical pressure-sensitive adhesive containing no adhesive resin. Adhesive resins are special compounds with a low molecular weight compared to elastomers, usually with a weight-average molecular weight M w of less than 5,000 g / mol. Typically, the weight-average molecular weight of an adhesive resin component used in the present invention is from 400 to 5,000 g / mol, preferably from 500 to 2,000 g / mol, as determined by GPC (Test Ib). This preferably applies to each adhesive resin used in the adhesive resin component.

[0044] The proportion of adhesive resin in the pressure-sensitive adhesive formulation has a positive effect on the bond strength. Therefore, the proportion of adhesive resin should not be too low. However, it has been shown that too high a proportion of adhesive resin(s) can have a negative impact on the thermal shear strength.

[0045] The proportion of the adhesive resin component, based on the total weight of the pressure-sensitive adhesive formulation, is preferably at least 25 wt.% to a maximum of 62.5 wt.%, preferably at least 35 wt.% to a maximum of 52 wt.%.

[0046] At least one adhesive resin is further characterized by having a softening temperature according to the ring-and-ball method of greater than 95 °C, but not more than 135 °C. The softening temperature can be determined according to ASTM E28 (Test III) as described below. Preferably, all adhesive resins in the adhesive resin component have a softening temperature in this range.

[0047] Preferably, adhesive resins selected from the group consisting of partially or fully hydrogenated resin based on dicyclopentadiene, partially or fully hydrogenated hydrocarbon resins based on C5, C5 / C9 or C9 monomer streams, partially or fully hydrogenated polyterpene resins based on α-pinene and / or β-pinene and δ-limonene and a hydrogenated polymer of pure C8 or C9 aromatics are used in the adhesive resin component, wherein the resin is partially or in particular fully hydrogenated.

[0048] For the purposes of the present invention, "partially hydrogenated" means a degree of hydrogenation of at least 80%, preferably at least 85%.

[0049] The pressure-sensitive adhesive formulation according to the invention preferably comprises at least one tackifier resin in the tackifier resin component that has a DACP (diacetone alcohol cloud point) of at least 30°C, preferably of at least 40°C and at most 80°C. The DACP is determined according to Test IV, as described below. Preferably, all tackifier resins in the tackifier resin component have a DACP in this range.

[0050] In a further preferred embodiment, the pressure-sensitive adhesive formulation according to the invention comprises, in the adhesive resin component, at least one adhesive resin having an MMAP (mixed methylcyclohexane aniline point) of greater than 60°C, preferably greater than 70°C and at most 105°C. The MMAP is determined according to Test V as described below. Preferably, all adhesive resins in the adhesive resin component have an MMAP in this range.

[0051] In addition to the at least one adhesive resin described above, the adhesive resin component may also contain one or more additional adhesive resins that do not correspond to the specified definitions with regard to softening temperature and / or DACP and / or MMAP cloud point. Adhesive resins with a softening temperature below 95°C, such as 90°C or 85°C, can also be used in a proportion of up to 10 wt.% or even up to 20 wt.%, based on the composition of the adhesive resin component. Adhesive resins with a softening temperature above 135°C, such as 140°C, can also be used in a proportion of up to 10 wt.% or even up to 20 wt.%, based on the composition of the adhesive resin component.

[0052] Adhesive resins with an MMAP cloud point below 60°C or even below 45°C and / or a DACP cloud point below 30°C or even below 15°C can also be used, with a proportion of up to 20% by weight or even up to 40% by weight of the adhesive resin component. Examples of such adhesive resins are terpene-phenolic resins, particularly with an OH number of no more than 100 mg KOH / g, and rosin esters, which may be partially hydrogenated, fully hydrogenated, or disproportionated. c) Plasticizer component

[0053] In addition to the elastomer component and the adhesive resin component, it is essential that the pressure-sensitive adhesive formulation according to the invention further contains at least 2.5 wt.% of a plasticizer component, based on the total weight of the pressure-sensitive adhesive formulation.

[0054] The plasticizer component is in particular one or more plasticizers.

[0055] The proportion of plasticizer component, based on the total weight of the pressure-sensitive adhesive, can be up to 20 wt.% and is preferably between 4 and 15 wt.%. Surprisingly, it has been found that even a small proportion of plasticizer component in the amounts mentioned is sufficient to obtain a pressure-sensitive adhesive formulation with sufficiently high bond strength and, above all, leads to increased foaming efficiency. This contrasts with what the prior art teaches, which sometimes assumes a plasticizer content of 60 to 95 wt.%.

[0056] The plasticizer component is preferably selected from the group consisting of ethylene / propylene copolymer, ethylene / butylene copolymer, butylene / iso-butylene (co)polymer, butylene homopolymer and / iso-butylene homopolymer, with the amorphous representatives being preferred in each case.

[0057] In a further preferred embodiment, the plasticizer has a weight-average molecular mass, determined by GPC (Test Ib), of at least 100,000 g / mol and at most 1,000,000 g / mol. In these cases, the plasticizer is preferably an ethylene / propylene copolymer or ethylene / butylene copolymer with a linear or radial structure. These copolymers containing as plasticizer component are not block copolymers containing rigid blocks within the scope of the present invention.

[0058] In a more preferred embodiment, the plasticizer component has a weight-average molecular weight, determined by GPC (Test Ib), of at least 3,000 g / mol and at most 20,000 g / mol. In this case, the plasticizer is preferably a butylene / isobutylene (co)polymer.

[0059] Soft resins based on rosin are also suitable, especially methyl esters of rosin or partially or fully hydrogenated rosin.

[0060] It is also possible to use mineral oil as a plasticizer, especially naphthenic oil. d) Foaming agent

[0061] An adhesive tape obtained from the pressure-sensitive adhesive formulation of the invention is characterized, among other things, by a low density, which is achieved by foaming the pressure-sensitive adhesive formulation. For this purpose, the pressure-sensitive adhesive formulation of the invention further comprises a foaming agent. The proportion of foaming agent in the pressure-sensitive adhesive formulation is preferably at least 0.5 wt.% and at most 10 wt.%, preferably at most 7.5 wt.%, and more preferably at most 5 wt.%, particularly preferably at most 2.5 wt.%, in each case based on the total weight of the pressure-sensitive adhesive formulation.

[0062] A physical blowing agent, for example, can be used as a foaming agent. Such blowing agents can be used individually or as a mixture of different blowing agents. Blowing agents can be selected from a wide variety of materials, including hydrocarbons, ethers, esters, and the like. Typical physical blowing agents have a boiling point in the range from -50°C to +100°C, and preferably from -50°C to +50°C. Preferred physical blowing agents include hydrocarbons such as n-pentane, isopentane, and cyclopentane, methylene chloride, or any combination of the aforementioned compounds. Such blowing agents can preferably be used in amounts of from 5% to 50% by weight of the reaction mixture, in particular from 10% to 30% by weight of the reaction mixture.

[0063] Physical foaming is also possible by incorporating gases such as carbon dioxide or nitrogen.

[0064] It is also possible to use a chemical blowing agent in addition or as an alternative. Chemical blowing agents are substances that release gas only during the processing process due to a chemical reaction – usually initiated by the application of heat – and thus enable the creation of a foam structure in the polymer. The cause of the gas release can be either the thermal decomposition of the blowing agent or a chemical reaction of various substances contained in the blowing agent. The resulting gas is usually N2, CO2, or CO.

[0065] The foaming agent particularly preferably comprises microballoons (also referred to as "p-balloons" in the context of the present disclosure). Particularly when using such a foaming agent, it has surprisingly been found that, despite the comparatively high proportion of polyvinyl aromatic blocks in the pressure-sensitive adhesive formulation according to the invention, a foaming efficiency comparable to that of pressure-sensitive adhesive formulations that do not contain hydrogenated block copolymers is achieved by combining it with a plasticizer component. In this way, it is possible to advantageously reduce the weight of a corresponding adhesive tape even with only a small proportion of foaming agent, as required, for example, for applications in the automotive industry.

[0066] "Microballoons" are elastic, and thus expandable in their ground state, hollow microspheres with a thermoplastic polymer shell. These spheres are filled with low-boiling liquids or liquefied gas. Polyacrylonitrile, polyvinylidene chloride (PVDC), polyvinyl chloride (PVC), or polyacrylate are particularly used as shell materials. Low-boiling liquids, such as isobutane or isopentane, are particularly suitable, enclosed as liquefied gases under pressure in the polymer shell.

[0067] When the microballoons are exposed to external influences, particularly heat, the outer polymer shell softens. At the same time, the liquid propellant gas contained in 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. Because the polymer shell is retained, a closed-cell foam is produced. A variety of microballoon types are commercially available, which differ primarily in their size, preferably 5 to 45 pm in diameter in the unexpanded state, and the initial temperatures required for expansion, preferably 75 to 220 °C. One example of commercially available microballoons is the Expancel® DU types (DU = dry unexpanded) from Nouryon, and another is Matsumoto Microsphere® F / FN from Matsumoto Yushi Seiyaku.

[0068] Unexpanded microballoon types are also available as aqueous dispersions with a solids or microballoon content of approximately 40 to 45 wt.%, and also as polymer-bound microballoons (masterbatches), for example in ethyl vinyl acetate with a microballoon concentration of approximately 50 wt.%.

[0069] According to the invention, the average diameter of the cavities formed by the microballoons in the foamed pressure-sensitive adhesive layer is preferably 10 to 200 μm, more preferably 15 to 200 μm. Since the diameters of the cavities formed by the microballoons in the foamed pressure-sensitive adhesive layer are measured here, the diameters are the diameters of the cavities formed by the expanded microballoons. The average diameter refers to the arithmetic mean of the diameters of the cavities formed by the microballoons in the foamed pressure-sensitive adhesive layer. The average diameter of the cavities formed by the microballoons can be determined using a scanning electron microscope (SEM).The diameters of the microballoons visible in the images are determined graphically in such a way that the maximum extension in any (two-dimensional) direction of each individual microballoon is taken from the SEM images and is considered as its diameter.

[0070] In addition to expandable hollow microspheres, non-expandable hollow microspheres may also be present. Hollow microspheres may also be partially expanded, i.e., not fully expanded.

[0071] Also suitable - independently of other additives - are solid polymer spheres, hollow glass spheres, solid glass spheres, hollow ceramic spheres, solid ceramic spheres, and / or solid carbon spheres ("Carbon Micro Balloons"). e) Reinforcing component

[0072] The pressure-sensitive adhesive formulation according to the invention may further contain a reinforcing component. The reinforcing component differs from the adhesive resin component primarily in that it is essentially incompatible with the hydrogenated polydiene blocks of the elastomer component.

[0073] According to the invention, so-called end block amplifiers are used as amplification components.

[0074] Endblock reinforcing agents are understood to be materials that are essentially compatible with the polyvinyl aromatic blocks of the hydrogenated polyvinyl aromatic-polydiene block copolymers of the elastomer component.

[0075] The reinforcing component preferably comprises at least one resin based on at least one, in particular aromatic, hydrocarbon compound, which is preferably selected from the group consisting of styrene, alpha-methylstyrene, para-methylstyrene and copolymers thereof.

[0076] The at least one resin of the reinforcing component preferably has a weight-average molecular weight M w from 1,000 g / mol to 15,000 g / mol, preferably 2,000 g / mol to 10,000 g / mol, determined by GPC (Test Ib).

[0077] The at least one resin of the reinforcing component preferably has an MMAP cloud point (Mixed Methylcyclohexane Aniline Cloud Point, Test V) of -10 °C to +30 °C, preferably of 0 °C to +20 °C.

[0078] The softening point of the at least one resin of the reinforcing component is preferably at least 140 °C, preferably at least 150 °C, determined according to Test III.

[0079] The proportion of the reinforcing component, based on the total weight of the pressure-sensitive adhesive formulation, is preferably at least 2.5 wt.% and at most 22 wt.%, preferably at least 4 wt.% and at most 18 wt.%.

[0080] The expression “essentially incompatible” or “essentially not compatible” is understood in the context of the present invention to mean in particular that the constituents or components in question are miscible with one another to a maximum of 10% by weight, preferably to a maximum of 5% by weight.

[0081] In the context of the present invention, the term "substantially compatible" is understood in particular to mean that the constituents or components mentioned are miscible with one another to an extent of at least 90% by weight, preferably at least 95% by weight. f) Further additives: To further adapt the property profile of the pressure-sensitive adhesive formulation according to the invention, further additives can be added to the pressure-sensitive adhesive formulation.These are preferably those selected from the group consisting of primary antioxidants such as sterically hindered phenols, secondary antioxidants such as phosphites or thioethers, process stabilizers such as C radical scavengers, light stabilizers such as UV absorbers or sterically hindered amines, processing aids, and other elastomers such as those based on pure hydrocarbons such as unsaturated polydienes, natural or synthetically produced polyisoprenes or polybutadienes, chemically substantially saturated elastomers such as saturated ethylene-propylene copolymers, α-olefin copolymers, polyisobutylene, butyl rubber, ethylene-propylene rubber, and functionalized hydrocarbons such as halogen-containing, acrylate-containing, or vinyl ether-containing polyolefins. Furthermore, organic or inorganic fillers, dyes, and color pigments may be used. The pressure-sensitive adhesive formulation can be black, grey, white or coloured.

[0082] The amount of further additives in the pressure-sensitive adhesive formulation is preferably not more than 18% by weight, more preferably not more than 10% by weight, based on the total weight of the pressure-sensitive adhesive formulation.

[0083] Pressure-sensitive adhesive formulations according to the invention are used in particular as pressure-sensitive adhesive layers in self-adhesive products. Therefore, the present invention further provides a foamed pressure-sensitive adhesive layer comprising a foamable pressure-sensitive adhesive formulation for self-adhesive tapes, the pressure-sensitive adhesive formulation comprising: a) at least one elastomer component; b) at least one adhesive resin component; c) at least 2.5% by weight of a plasticizer component, based on the total weight of the pressure-sensitive adhesive formulation; d) a foaming agent, and e) optionally a reinforcing component, characterized in that the elastomer component comprises at least 90% by weight, based on the total weight of the elastomer component, of one or more polyvinylaromatic-polydiene block copolymers, at least one of which is present with at least two polyvinylaromatic blocks (A), where • the polydiene blocks (B) are hydrogenated to at least 90% by weight, based on the block copolymer;

[0084] • the proportion of polyvinylaromatic blocks (A) is at least 18 wt.%, based on the total amount of all polyvinylaromatic-polydiene block copolymers in the elastomer component.

[0085] The pressure-sensitive adhesive formulation contained is preferably a formulation according to the present invention.

[0086] The contained pressure-sensitive adhesive formulation can be applied in foamed or unfoamed form as a pressure-sensitive adhesive layer. Regardless of the application method, the foamed pressure-sensitive adhesive layer advantageously meets one or more criteria of the following performance profile:

[0087] Table 1

[0088] Accordingly, an embodiment is preferred in which the foamed pressure-sensitive adhesive layer (in 50 g / m 2) has an adhesive strength, determined as peel strength, on steel of at least 2.0 N / cm, preferably at least 4 N / cm. The adhesive strength on steel can be determined according to Test II as described below.

[0089] The foamed pressure-sensitive adhesive layer according to the invention is particularly characterized by its thermal shear strength (SAFT). This is for a foamed sample with a 50 g / m 2 Coating at 200 g load preferably at least 100 °C, preferably at least 140 °C, and most preferably at least 170 °C. Thermal shear strength can be determined according to Test VII.

[0090] Furthermore, the pressure-sensitive adhesive according to the invention is characterized by its adhesive strength to polyethylene (PE), which for a foamed sample with 50 g / m 2Coating is preferably at least 1.0 N / cm, particularly preferably at least 3 N / cm. The adhesive strength to PE can be determined analogously to the adhesive strength to steel, as described under Test II. The adhesive strength to both materials, steel and PE, opens up a broad range of applications for the pressure-sensitive adhesive formulation according to the invention.

[0091] The present invention further provides a self-adhesive product, in particular an adhesive tape, comprising at least one layer of a pressure-sensitive adhesive formulation according to the invention in foamed form. The self-adhesive product according to the invention can be designed to be adhesive on one or both sides, i.e., double-sided, with the adhesive layer preferably being formed from the pressure-sensitive adhesive formulation according to the invention.

[0092] Furthermore, the self-adhesive product according to the invention may further comprise at least one layer of a temporary carrier material (“release liner”).

[0093] This temporary carrier material is in particular a film-like material from which a layer of pressure-sensitive adhesive can be detached so that the remaining part of the self-adhesive tape can then be brought into contact with a substrate to be bonded or another material which is to form a composite with the remaining part of the self-adhesive tape.

[0094] The temporary carrier material is, in particular, a release paper or film, also called a release liner. It is a material that is not firmly bonded to the pressure-sensitive adhesive layer and, in particular, has an abhesive finish, allowing the pressure-sensitive adhesive layer to be removed from it. It therefore represents an aid for its production, storage, or further processing, for example, by die-cutting.

[0095] Using the at least one aforementioned pressure-sensitive adhesive formulation, the self-adhesive product according to the invention is, according to preferred embodiments of the invention, a single-layer, double-sided self-adhesive adhesive tape consisting of a single layer of the foamed pressure-sensitive adhesive formulation according to the invention and thus a so-called “transfer tape”, or a multi-layer, double-sided self-adhesive adhesive tape, in which the layers each consist of the foamed pressure-sensitive adhesive formulation according to the invention, or a multi-layer, double-sided self-adhesive adhesive tape with a permanent carrier arranged either in a layer of the foamed pressure-sensitive adhesive formulation according to the invention or between two layers of the foamed pressure-sensitive adhesive formulation according to the invention, or a multi-layer, single-sided self-adhesive adhesive tape with a layer of the foamed pressure-sensitive adhesive formulation according to the invention and a permanent carrier,or a multilayer, double-sided self-adhesive tape comprising a layer of the foamed pressure-sensitive adhesive formulation according to the invention and a layer which need not be foamed and which is of the same or different composition with respect to the layer of the foamed pressure-sensitive adhesive formulation according to the invention.

[0096] - each in combination with a temporary carrier material.

[0097] Permanent carriers are, in particular, intermediate carriers within the self-adhesive product. In particular, the intermediate carrier is stretchable, whereby the stretchability of the intermediate carrier must be sufficient for some applications to ensure detachment of the adhesive strip by stretching. Highly stretchable films, for example, can serve as intermediate carriers. A maximum stretchability of the film in at least one direction, preferably in both directions, of at least 200%, preferably of at least 400% (ISO 527-3) is advantageous. Examples of advantageously usable stretchable intermediate carriers are versions from WO 2011 / 124782 A1, DE 10 2012 223670 A1, WO 2009 / 114683 A1, WO 2010 / 077541 A1, WO 2010 / 078396 A1.

[0098] Film-forming or extrudable polymers can be used to produce the stretchable intermediate carrier film, which can additionally be mono- or biaxially oriented.

[0099] In one embodiment, polyolefins are used. Preferred polyolefins are produced from ethylene, propylene, butylene, and / or hexylene, whereby the pure monomers can be polymerized or mixtures of the aforementioned monomers can be copolymerized. The polymerization process and the selection of the monomers allow the physical and mechanical properties of the polymer film to be controlled, such as the softening temperature and / or the tear strength.

[0100] Polyurethanes are preferably used as starting materials for stretchable intermediate carrier layers. Polyurethanes are chemically and / or physically crosslinked polycondensates, typically composed of polyols and isocyanates. Depending on the type and ratio of the individual components, stretchable materials are available that can be used advantageously in the context of this invention. Raw materials available to the person skilled in the art for this purpose are mentioned, for example, in EP 0 894 841 B1 and EP 1 308 492 B1. Other raw materials from which intermediate carrier layers according to the invention can be constructed are known to the person skilled in the art.

[0101] Furthermore, rubber-based materials can be used in intermediate carrier layers to achieve extensibility. As a starting material for extensible intermediate carrier layers, natural rubber or synthetic rubber, or blends thereof, can be selected from all available grades, such as crepe, RSS, ADS, TSR, or CV grades, depending on the required purity and viscosity level. Synthetic rubber or synthetic rubbers can be selected from the group of randomly copolymerized styrene-butadiene rubbers (SBR), butadiene rubbers (BR), synthetic polyisoprenes (IR), butyl rubbers (HR), halogenated butyl rubbers (XIIR), acrylate rubbers (ACM), ethylene-vinyl acetate copolymers (EVA), and polyurethanes and / or blends thereof.

[0102] Block copolymers are particularly advantageous for use as materials for stretchable intermediate carrier layers. Individual polymer blocks are covalently linked to one another. The block linkage can be linear, but also star-shaped or graft copolymer. An example of an advantageously usable block copolymer is a linear triblock copolymer, whose two terminal blocks have a softening temperature of at least 40 °C, preferably at least 70 °C, and whose central block has a softening temperature of at most 0 °C, preferably at most -30 °C. Higher block copolymers, such as tetrablock copolymers, can also be used.It is important that at least two polymer blocks of the same or different type are present in the block copolymer, each having a softening temperature of at least 40 °C, preferably at least 70 °C, and which are separated from one another in the polymer chain by at least one polymer block with a softening temperature of at most 0 °C, preferably at most -30 °C. Examples of polymer blocks are polyethers such as polyethylene glycol, polypropylene glycol or polytetrahydrofuran, polydienes such as polybutadiene or polyisoprene, hydrogenated polydienes such as polyethylene butylene or polyethylene propylene, polyesters such as polyethylene terephthalate, polybutanediol adipate or polyhexanediol adipate, polycarbonate, polycaprolactone, polymer blocks of vinylaromatic monomers such as polystyrene or poly-[α]-methylstyrene, polyalkyl vinyl ethers, polyvinyl acetate, polymer blocks of [α],[β]-unsaturated esters such as in particular acrylates or methacrylates.The skilled person will be familiar with the corresponding softening temperatures. Alternatively, they can look them up, for example, in the Polymer Handbook [J. Brandrup, EH Immergut, EA Grulke (eds.), Polymer Handbook, 4th ed. 1999, Wiley, New York]. Polymer blocks can be composed of copolymers.

[0103] To produce an intermediate carrier material, it may also be appropriate to add additives and other components that improve the film-forming properties, reduce the tendency to form crystalline segments and / or specifically improve or, if necessary, worsen the mechanical properties.

[0104] Furthermore, sheet-like foams (e.g. made of polyethylene, polyethylene vinyl acetate (EVA), polyacrylate copolymer and polyurethane) are suitable.

[0105] The intermediate carriers can be multilayered. Furthermore, the intermediate carriers can have cover layers, for example, barrier layers that prevent components from the adhesive from penetrating the intermediate carrier or vice versa. These cover layers can also have barrier properties to prevent the diffusion of water vapor and / or oxygen.

[0106] To better anchor the pressure-sensitive adhesives to the intermediate carrier, the intermediate carriers can be pretreated using conventional methods such as corona, plasma, or flame treatment. The use of a primer is also possible. Ideally, however, pretreatment can be omitted.

[0107] The inventive concept also encompasses structures with an intermediate carrier with a high modulus of elasticity and low extensibility within the self-adhesive product, particularly in the center of the single pressure-sensitive adhesive layer, wherein the modulus of elasticity of the intermediate carrier is advantageously at least 750 MPa, preferably at least 1 GPa (ISO 527-3), and the maximum extensibility (according to ISO 527-3) is in particular at most 200%. Such structures are particularly well suited for die-cutting processes and facilitate handling during the application process. Permanent carriers designed in this way are also advantageous if the self-adhesive product is to be removable by peeling.

[0108] For the production of such intermediate carrier films, film-forming or extrudable polymers are used, which can in particular also be mono- or biaxially oriented.

[0109] Polyester films, and particularly preferably films based on polyethylene terephthalate (PET), are particularly suitable as film materials for the at least one layer of a film for this design. Polyester films are preferably biaxially stretched. Films made of polyolefins, in particular polybutene, cycloolefin copolymer, polymethylpentene, polypropylene, or polyethylene, for example, monoaxially stretched polypropylene, biaxially stretched polypropylene, or biaxially stretched polyethylene, are also conceivable. This list is intended to illustrate examples; other systems corresponding to the concept of the present invention are known to those skilled in the art.

[0110] To produce an intermediate carrier material, it may also be appropriate to add additives and other components that improve the film-forming properties, reduce the tendency to form crystalline segments and / or specifically improve or, if necessary, worsen the mechanical properties.

[0111] The intermediate supports can be designed in multiple layers.

[0112] Furthermore, the intermediate carriers can have cover layers, for example, barrier layers that prevent components from the adhesive from penetrating the intermediate carrier or vice versa. These cover layers can also have barrier properties to prevent the diffusion of water vapor and / or oxygen.

[0113] To better anchor the pressure-sensitive adhesives to the intermediate carrier, the intermediate carriers can be pretreated using conventional methods such as corona, plasma, or flame treatment. The use of a primer is also possible. Ideally, however, pretreatment can be omitted.

[0114] The general terms “self-adhesive product” and “self-adhesive tape” encompass, within the meaning of this invention, all flat structures such as films or film sections extended in two dimensions, tapes with an extended length and a limited width, tape sections and the like, and ultimately also die-cuts or labels.

[0115] The self-adhesive product thus has a longitudinal dimension and a lateral dimension. The adhesive tape also has a thickness perpendicular to both dimensions, whereby the lateral dimension and longitudinal dimension can be many times greater than the thickness. The thickness is as uniform as possible, preferably essentially the same, across the entire surface area of ​​the self-adhesive product, determined by its length and width.

[0116] Typical packaging forms of the self-adhesive products according to the invention are adhesive tape rolls and self-adhesive strips, such as those obtained in the form of die-cuts.

[0117] Preferably, all layers are essentially cuboid-shaped. Further preferably, all layers are fully bonded to one another.

[0118] The self-adhesive product preferably has a thickness of 20 pm to 3000 pm, more preferably of 30 to 2000 pm, particularly preferably 50 to 1500 pm or 100 pm, 150 pm, 200 pm, 250 pm or 500 pm, not including the temporary carrier material.

[0119] A preferred embodiment of the self-adhesive product is one in which the permanent carrier has a thickness between 2 and 200 μm, preferably 5 μm to 100 μm, very preferably 10 μm to 80 μm. If the permanent carrier is a foam layer, the thickness can also be higher, for example, above 250 μm, above 500 μm, or even above 1000 μm.

[0120] Also preferred is an embodiment of the self-adhesive tape in which no permanent carrier is included and the pressure-sensitive adhesive is present as a single layer on a temporary carrier material. The pressure-sensitive adhesive layer has a thickness between 100 μm and 2000 μm, in particular between 200 μm and 1500 μm or between 400 μm and 1200 μm. However, thinner layers between approximately 25 μm and 100 μm are also possible.

[0121] The foamed pressure-sensitive adhesive formulation as used in the self-adhesive product according to the invention preferably has a density of at most 850 kg / m 3 , preferably not more than 750 kg / m 3 and particularly preferably not more than 650 kg / m 3 . The density can be determined according to known methods.

[0122] The self-adhesive products according to the invention are ideally suited for long-term, stable permanent bonding, where high thermal shear strength and, depending on the design of the self-adhesive tape, separability of the bonded joint are required. This separability is particularly advantageous when the self-adhesive tape is a transfer tape or a double-sided self-adhesive tape with a stretchable permanent carrier (maximum stretchability of at least 200%). In many cases, removal is then possible by stretching from the bonded joint.

[0123] The need for separability of a permanent bond may exist for reworking purposes (if a bond is to be corrected during the manufacturing process of an object), for repair purposes (if a defective component of the bonded joint is to be replaced) or for recycling purposes (if the bonded joint is to be disposed of separately after its useful life).

[0124] Self-adhesive products with the pressure-sensitive adhesive formulations described here have also proven particularly advantageous in conjunction with polar surfaces, such as steel, and also low-energy surfaces such as PP / EPDM, PP / EPM, and PP / EPR. Therefore, the present invention further relates to the use of the pressure-sensitive adhesive composition of the invention or the self-adhesive product of the invention for bonding plastics, glass, and / or metals.

[0125] The substrates to be bonded can contain a variety of materials. Thus, substrates containing ethylene (co)polymer, propylene (co)polymer, EPR, EPM, and / or EPDM, or another plastic, are preferred. In particular, the pressure-sensitive adhesive formulations or the adhesive tape according to the invention are used for bonding an attachment containing ethylene (co)polymer, propylene (co)polymer, EPR, EPM, and / or EPDM, or another plastic such as ABS or polycarbonate, in or on an automobile / vehicle. The durability of the pressure-sensitive adhesive formulations according to the invention also allows the bonding of other materials such as glass, ceramic, and metal.

[0126] The present invention further provides a process for producing the pressure-sensitive adhesive formulation and pressure-sensitive adhesive layer according to the invention. It has surprisingly been found that the use of solvents can be dispensed with in the production process, which not only reduces costs but also minimizes environmental impact. Therefore, the process according to the invention is distinguished by the fact that the pressure-sensitive adhesive formulation is produced by solvent-free mixing. The coating is then also applied solvent-free. In this way, layer thicknesses above and including 100 μm, in particular above 200 μm, can be produced particularly well. Processes that are particularly suitable for use in this context include those taught by DE 10 2008 004 388 A1.

[0127] Solvent-based mixing and coating processes are also ideally suited, particularly when coatings in the range below 100 pm are desired.

[0128] The foaming of the pressure-sensitive adhesive formulation can be carried out using conventional methods. Preferably, the foaming occurs by expanding the expandable microballoons through the application of heat, either inline after coating or offline in a separate process step. This can again be carried out according to the teachings of DE 10 2008 004 388 A1.

[0129] The pressure-sensitive adhesive for the self-adhesive product according to the invention is applied either to one side of a temporary carrier material or to one side of a permanent carrier. The pressure-sensitive adhesive can be applied to the carrier by methods known to those skilled in the art, for example by doctor blade methods, nozzle doctor blade methods, roller bar die methods, extrusion die methods, pouring die methods, and casting methods. Also within the scope of the invention are application methods such as roller application methods, printing methods, screen printing methods, anilox roll methods, inkjet methods, and spraying methods. A preferred coating variant is solvent-based. For this purpose, the components of the pressure-sensitive adhesive(s) are dissolved in a suitable solvent or solvent mixture and then coated from solution, and the coated material is dried.Suitable solvents, which can also be used in combination, are aliphatic (e.g., pentane, hexane, heptane, getane, and their structural isomers), cycloaliphatic (e.g., cyclohexane and methylcyclohexane), and aromatic hydrocarbons (e.g., toluene, xylene), particularly in combination with ketones (e.g., acetone, 2-butanone, isobutyl ketone) or esters (e.g., ethyl acetate, butyl acetate, propyl acetate, isopropyl acetate). A preferred procedure involves using a mixture of toluene and ethyl acetate. A mixture of methylcyclohexane and an ester such as ethyl acetate or, in particular, butyl acetate is very advantageous. A mixture of cyclohexane and an ester, in particular, butyl acetate, is also advantageous.Another preferred manufacturing variant is hotmelt processes, in which the pressure-sensitive adhesive is mixed using a compounding unit and then applied directly (“inline”) to the carrier material by extrusion and / or nozzle and / or calender. However, the application process does not have to be direct coating. The pressure-sensitive adhesive can also be coated with another material first and then laminated to the carrier in a second step. If necessary, additional layers or plies of material can then be laminated or coated inline or offline, so that multi-layer / multi-ply product structures can also be created. Such additional layers can introduce special additional properties into the adhesive tape, such as mechanical properties.They can also promote the anchoring between the adhesive and the carrier or suppress the migration of individual components from one layer to the other.

[0130] For product structures with an intermediate carrier layer, a pressure-sensitive adhesive layer can be applied by direct coating onto the permanent carrier material or by lamination, in particular hot lamination.

[0131] The present invention is explained in more detail with reference to the following examples and figures, which are in no way to be understood as limiting the scope of the invention. i) Test methods

[0132] Unless expressly stated otherwise, the measurements are carried out in a test climate of 23 ± 1 °C and 50 ± 5 % relative humidity.

[0133] Test I - Molar mass (GPC)

[0134] (a) Peak molecular weight of individual block copolymer modes

[0135] Polymers are polymodal systems with regard to their molecular weight distribution. Mixtures of different polymers can be considered multimodal systems, with each polymer contributing its own molecular weight distribution. Mixtures of block copolymers with structures of different molecular weight distributions can also be considered multimodal systems. Each block copolymer then contributes its own molecular weight distribution. For simplicity, these are referred to here as block copolymer modes.

[0136] GPC is a suitable measurement technique for determining the molar mass of individual polymer modes in mixtures of different polymers. For the block copolymers produced by living, anionic polymerization that can be used in this invention, the molar mass distributions are typically sufficiently narrow so that polymer modes that can be assigned to triblock copolymers, diblock copolymers, or multiblock copolymers appear sufficiently resolved from one another in the elugram. The peak molar mass for the individual polymer modes can then be read from the elugrams.

[0137] Peak molecular masses (MM) are determined by gel permeation chromatography (GPC). THF is used as the eluent. The measurement is carried out at 23 °C. PSS-SDV, 5 p, 10 3 Ä, ID 8.0 mm x 50 mm. For separation, columns PSS-SDV, 5 p, 10 3 Ä and 10 4 Ä and 10 6Ä with ID 8.0 mm x 300 mm each. The sample concentration is 4 g / l, the flow rate 1.0 ml per minute. Calibration is carried out using the commercially available ReadyCal kit Poly(styrene) high from PSS Polymer Standard Service GmbH, Mainz, (p = pm; 1 Ä = 10' 10 m).

[0138] (b) weight-average molecular weight, in particular of adhesive resins, reinforcing resins and plasticizers

[0139] The weight-average molecular weight (MW) is determined by gel permeation chromatography (GPC). THF is used as the eluent. The measurement is carried out at 23 °C. PSS-SDV, 5 p, 10 3 Ä, ID 8.0 mm x 50 mm. For separation, columns PSS-SDV, 5 p, 10 3 Ä and 10 4 Ä and 10 6Ä, each with an ID of 8.0 mm x 300 mm, are used. The sample concentration is 4 g / l, and the flow rate is 1.0 ml per minute. Calibration is performed using the commercially available ReadyCal Kit Poly(styrene) high from PSS Polymer Standard Service GmbH, Mainz.

[0140] Test II - Adhesive strength to steel (peel strength)

[0141] The bond strength determination (according to AFERA ​​5001) is carried out as follows. A polished steel plate with a thickness of 2 mm is used as the defined bonding substrate. The bondable surface element to be tested (50 g / m 2on 36 pm etched PET film or 500 pm pressure-sensitive adhesive layer as transfer adhesive layer reinforced on the back with a 75 pm polyester film) is, unless otherwise stated, cut to a width of 20 mm and a length of approximately 25 cm, provided with a handling section and immediately afterwards pressed five times onto the selected substrate using a 4 kg steel roller at a feed rate of 10 m / min. Immediately afterwards, the bondable surface element is peeled off the substrate at an angle of 180° using a tensile testing device (Zwick) at a speed of v = 300 mm / min and the force required for this is measured at room temperature. The measured value (in N / cm) is the average of three individual measurements.

[0142] The adhesive strength on PE (polyethylene) was determined analogously to the described method.

[0143] Test III - Resin Softening Temperature For individual substances: The resin softening temperature (softening point; expiration point) is determined according to the relevant methodology known as Ring & Ball, standardized according to ASTM E28.

[0144] Test IV-DACP

[0145] 5.0 g of test substance (the adhesive resin sample to be tested) are weighed into a dry sample tube and mixed with 5.0 g of xylene (mixture of isomers, CAS [1330-20-7], > 98.5%, Sigma-Aldrich #320579 or comparable). The test substance is dissolved at 130 °C and then cooled to 80 °C. Any escaped xylene is replaced with additional xylene until the total amount of xylene is 5.0 g. Subsequently, 5.0 g of diacetone alcohol (4-hydroxy-4-methyl-2-pentanone, CAS [123-42-2], 99%, Aldrich #H41544 or comparable) are added. The sample tube is shaken until the test substance has completely dissolved. For this purpose, the solution is heated to 100 °C. The sample tube containing the resin solution is then placed in a Chemotronic Cool cloud point measuring device from Novomatics and heated to 110 °C. Cooling occurs at a rate of 1.0 K / min. The cloud point is detected optically.For this purpose, the temperature at which the turbidity of the solution reaches 70% is recorded. The result is expressed in °C. The lower the DACP value, the higher the polarity of the test substance.

[0146] Test V - MMAP

[0147] 5.0 g of test substance (the adhesive resin sample to be tested) are weighed into a dry sample tube and mixed with 10 mL of dry aniline (CAS [62-53-3], > 99.5%, Sigma-Aldrich #51788 or comparable) and 5 mL of dry methylcyclohexane (CAS [108-87-2], > 99%, Sigma-Aldrich #300306 or comparable). The sample tube is shaken until the test substance has completely dissolved. To do this, the solution is heated to 100 °C. The sample tube containing the resin solution is then placed in a Chemotronic Cool cloud point meter from Novomatics and heated to 110 °C. Cooling is carried out at a cooling rate of 1.0 K / min. The cloud point is detected optically. For this purpose, the temperature at which the turbidity of the solution is 70% is recorded. The result is given in °C. The lower the MMAP value, the higher the aromaticity of the test substance.

[0148] Test VI - Polyvinyl aromatics content

[0149] The proportion of polyvinylaromatic blocks in hydrogenated polyvinylaromatic-polydiene block copolymers is determined, unless otherwise known, by means of 13 C-NMR. Using the example of determining the polystyrene content in hydrogenated polystyrene-polydiene block copolymers (SEBS), the 13 C-NMR is explained below. From the 13 For the C spectrum, the average is calculated from two integrals, namely the styrene C signal at approximately 144 to 146 ppm and the styrene CH at approximately 125 to 127 ppm. This average is set for SEBS in relation to the butylene integral (hydrogenated 1,2-polybutadiene repeat units), namely the CH3 signal at approximately 10 ppm, and the ethylene integral (hydrogenated 1,4-polybutadiene repeat units), which can be calculated from the total olefinic integral at approximately 20 to 50 ppm. The resulting mol% fractions are then converted to wt%.

[0150] Test VII - JUICE

[0151] This test is used to quickly determine the shear strength of adhesive formulations under thermal stress. A test specimen is bonded to a temperature-controlled steel plate, loaded with a weight (200 g), and the shear distance is recorded.

[0152] Sample preparation:

[0153] The test sample to be examined (50 g / m 2 on 36 pm etched PET carrier or 500 pm backed with 75 pm PET film) is cut to a size of 10 mm * 50 mm.

[0154] The cut adhesive tape sample is placed with the other adhesive side on a polished, acetone-cleaned test plate (material 1.4301, DIN EN 10088-2, surface 2R, surface roughness R a= 30 to 60 nm, dimensions 50 mm * 13 mm * 1.5 mm) in such a way that the bonding area of ​​the sample is height * width = 13 mm * 10 mm and protrudes 2 mm from the top edge of the test plate. The sample is then rolled over six times using a 2 kg steel roller at a speed of 10 m / min to secure it. The top of the sample is reinforced flush with a sturdy adhesive strip, which serves as a support for the displacement sensor. The sample is then suspended using the plate in such a way that the longer, projecting end of the test specimen points vertically downwards.

[0155] Measurement:

[0156] The sample to be measured is loaded with a weight of 200 g at its lower end. The test plate with the bonded sample is heated from 25 °C at a rate of 9 K / min to a final temperature of 200 °C.

[0157] The slip distance of the sample is monitored using a displacement sensor as a function of temperature and time. The maximum slip distance is set at 1000 pm (1 mm); if this value is exceeded, the test is terminated and the failure temperature is noted. Test conditions: room temperature 23 + / - 3 °C, relative humidity 50 + / - 5%. The result is the mean of two individual measurements and is given in °C. ii) Figures As can be seen from Jagisch and Tancrede in D. Satas, Handbook of Pressure Sensitive Adhesive Technology, 3rd edition, 1999, D. Satas Associates, Warwick, p. 367, Figs. 16-18, an increasing proportion of diblock copolymer in the elastomer component can result in a certain increase in peel strength. For example, an increase in adhesive strength of approximately 12% was achieved when 20% diblock copolymer, in this case SIS, was added to a formulation.In the context of the present invention, it has surprisingly been shown that by adjusting the proportion of diblock copolymer in an elastomer component in formulations based on hydrogenated polyvinylaromatic-polydiene block copolymers, a significantly greater increase in adhesive strength could be achieved when these were foamed. Thus, a proportion of just 14 wt.% diblock in the elastomer component led to an increase in adhesive strength of 67% (cf. Example E2, Table 5).

[0158] DE 10 2008 004 388 reveals differences in the foaming efficiency of pressure-sensitive adhesive formulations based on polydiene rubbers containing polystyrene segments (polystyrene-polydiene block copolymers, exemplified by SIS) compared to those based on pure polydiene rubbers (exemplified by natural rubber). Pressure-sensitive adhesives containing polystyrene-polydiene block copolymers exhibit lower foaming efficiency than those without polystyrene. The specific nature of the two-phase structure in polystyrene block copolymers appears to impede foaming behavior. The different foaming behavior is shown in Figure 1, where the density of the foamed formulation is given as a measure in relation to the microballoon content in the formulation.

[0159] Figure 2 shows the foaming efficiency achieved with the inventive pressure-sensitive adhesive formulations based on hydrogenated polyvinylaromatic-polydiene block copolymers (SEBS). A SIS-based formulation, as described in DE 10 2008 004 388, was chosen for comparison. As can be seen from Figure 2, the foaming efficiency of the inventive pressure-sensitive adhesive formulations is comparable to the SIS-based formulations. This is particularly interesting at low microballoon contents, since even with a low microballoon content, a noticeable weight reduction can be achieved without compromising the adhesive properties. The compositions of the tested formulations are given in Table 9.

[0160] Figure 3 shows the influence of the diblock proportion relative to the elastomer component on the density of the pressure-sensitive adhesive formulations according to the invention. Contrary to expectations, the influence of the diblock copolymer content in the elastomer component on the foaming efficiency of the pressure-sensitive adhesive formulation is small. The compositions of the tested formulations are given in Table 10. iii) Examples

[0161] Method V1 (solvent method for samples with 50 g / m 2 Coating):

[0162] The components of the pressure-sensitive adhesive formulations were dissolved in a 30% solution in special-boiling point spirit / toluene / acetone, mixed with the microballoons suspended in spirit and spread with a spreader bar onto an etched PET film with the desired basis weight. The solvent was then evaporated at 100°C for 15 minutes, thus drying the mass layer. This is possible in the examples presented because microballoons with an expansion temperature above 100°C were used. After drying, the pressure-sensitive adhesive layer was covered with a layer of a siliconized PET liner, free of any air pockets, and foamed for 30 seconds at 170°C between the etched PET film and the siliconized PET liner in a circulating air drying cabinet.

[0163] Process V2 (hot melt process for samples with 500 pm coating):

[0164] The solvent-free production of pressure-sensitive adhesive formulations was carried out using a planetary roller extruder (PWE), which comprised an infeed section and two process sections. The thrust rings had an increasing diameter in the process direction. Although various spindle configurations were suitable, configurations that amounted to at least 10% of the maximum number of spindles in the first process section were preferred. The elastomer components were metered in the infeed section of the PWE. The resin components were melted and added in the first process section of the PWE. A resin split, in which part of the resin was added in zone 1 and the remainder downstream in the second process section, was particularly suitable for producing homogeneous mixtures. The addition of both portions in solid form via side feed or thrust rings was particularly suitable, with the first portion accounting for approximately 30% by weight of the total resin quantity. Addition in liquid form would also be suitable.Plasticizer was added in zone 3, as was the stabilizer in molten form. Microballoons were also added in zone 3.

[0165] The coating was achieved by introducing the hot pressure-sensitive adhesive compound into a two-roll calender between two siliconized PET liners. After calendering, the compound was in foamed form. The following raw materials were used to produce the pressure-sensitive adhesive formulations according to the invention and the formulations used for comparison purposes. The raw materials are all commercially available under the corresponding trade names.

[0166] Table 2: Raw materials used

[0167] The following tables summarize the composition of the prepared and tested formulations, with comparative examples marked with C.

[0168] In Tables 1-7 and 9, the amounts of components (a), (b), (c) and (f) (and, if applicable, (e) of the base formulation add up to 100%. From this base formulation, the stated proportions are then used, if applicable, in combination with the proportion of foaming agent (d), whereby the sum of the amounts of base formulation and foaming agent (d) then adds up to 100%.

[0169] Tables 8 and 10 directly show the proportions in % based on the total composition.

[0170] Table 3: Comparative examples C1-C4 Table 4- Comparative examples C5-C10 (50 g / m 2 pressure-sensitive adhesive layer), nb: not determined. Table 5- Examples E1-E4 (50 g / m 2 pressure-sensitive adhesive layer)

[0171] Table 6: Examples E5-E9 (50 g / m 2 pressure-sensitive adhesive layer)

[0172] Table 7: Adhesive strength increase (50 g / m 2pressure-sensitive adhesive layer)

[0173] nb: not determined; *) unfoamed reference sample, assumed to be representative

[0174] Table 8: Examples E12-E15 (500 pm pressure-sensitive adhesive layer) Table 9: Compositions of the inventive examples of Figure 2

[0175] Table 10 - Compositions of the examples according to the invention in Figure 3

[0176] As can be seen from the examples summarized in the tables, a significant improvement in adhesive strength could be achieved by the pressure-sensitive adhesive formulations according to the invention, even in the foamed state, so that the requirements of low weight, high adhesive strength and satisfactory ageing resistance are advantageously combined in the pressure-sensitive adhesive formulations according to the invention.

Claims

Patent claims:

1. A foamable pressure-sensitive adhesive formulation for self-adhesive tapes, wherein the pressure-sensitive adhesive formulation comprises: a) at least one elastomer component; b) at least one adhesive resin component; c) at least 2.5% by weight of a plasticizer component, based on the total weight of the pressure-sensitive adhesive formulation; d) a foaming agent, and e) optionally a reinforcing component, characterized in that the elastomer component comprises at least 90% by weight, based on the total weight of the elastomer component, of one or more polyvinylaromatic-polydiene block copolymers, at least one of which is present with at least two polyvinylaromatic blocks (A), wherein • the polydiene blocks (B) are hydrogenated to at least 90% by weight, based on the block copolymer; • the proportion of polyvinylaromatic blocks (A) is at least 18 wt.%, based on the total amount of all polyvinylaromatic-polydiene block copolymers in the elastomer component.

2. Foamable pressure-sensitive adhesive formulation according to claim 1, characterized in that the polyvinylaromatic-polydiene block copolymer has a di-block content AB of at least 10 wt.% and at most 50 wt.%, based on the total amount of all polyvinylaromatic-polydiene block copolymers in the elastomer component.

3. Foamable pressure-sensitive adhesive formulation according to at least one of the preceding claims, characterized in that the proportion of elastomer component in the pressure-sensitive adhesive formulation is at least 35% by weight to a maximum of 60% by weight, preferably at least 40% by weight and a maximum of 55% by weight, based on the total weight of the pressure-sensitive adhesive formulation.

4. Foamable pressure-sensitive adhesive formulation according to at least one of the preceding claims, characterized in that the proportion of adhesive resin components in the Pressure-sensitive adhesive formulation is at least 25 wt.% to a maximum of 62.5 wt.%, preferably at least 35 wt.% and a maximum of 52 wt.%, based on the total weight of the pressure-sensitive adhesive formulation.

5. Foamable pressure-sensitive adhesive formulation according to at least one of the preceding claims, characterized in that the proportion of foaming agent in the pressure-sensitive adhesive formulation is at least 0.5% by weight and at most 10% by weight, preferably at most 7.5% by weight and more preferably at most 5% by weight, particularly preferably at most 2.5% by weight, in each case based on the total weight of the pressure-sensitive adhesive formulation, and wherein the foaming agent is preferably microballoons.

6. Foamable pressure-sensitive adhesive formulation according to at least one of the preceding claims, characterized in that the adhesive resin component is selected from the group consisting of partially or fully hydrogenated resin based on dicyclopentadiene, partially or fully hydrogenated hydrocarbon resins based on O5, C5 / C9 or C9 monomer streams, partially or fully hydrogenated polyterpene resins based on α-pinene and / or β-pinene and δ-limonene and a hydrogenated polymer of pure O8 or C9 aromatics, wherein the resin is partially or in particular fully hydrogenated.

7. Foamable pressure-sensitive adhesive formulation according to at least one of the preceding claims, characterized in that the plasticizer component is selected from the group consisting of ethylene / propylene copolymer, ethylene / butylene copolymer, butylene / iso-butylene (co)polymer, butylene homopolymer and / iso-butylene homopolymer, wherein the amorphous representatives are preferred in each case, wherein the proportion of plasticizer component in the pressure-sensitive adhesive formulation is preferably at most 20% by weight, based on the total weight of the pressure-sensitive adhesive formulation.

8. Foamable pressure-sensitive adhesive formulation according to at least one of the preceding claims, characterized in that the pressure-sensitive adhesive formulation contains further additives, preferably in an amount of not more than 18% by weight, particularly preferably not more than 10% by weight, based on the total weight of the pressure-sensitive adhesive.

9. A foamed pressure-sensitive adhesive layer comprising a foamable pressure-sensitive adhesive formulation for self-adhesive tapes, wherein the pressure-sensitive adhesive formulation comprises: a) at least one elastomer component; b) at least one adhesive resin component; c) at least 2.5% by weight of a plasticizer component, based on the total weight of the pressure-sensitive adhesive formulation; d) a foaming agent, and e) optionally a reinforcing component, characterized in that the elastomer component comprises at least 90% by weight, based on the total weight of the elastomer component, of one or more polyvinylaromatic-polydiene block copolymers, at least one of which is present with at least two polyvinylaromatic blocks (A), wherein • the polydiene blocks (B) are hydrogenated to at least 90% by weight, based on the block copolymer; • the proportion of polyvinylaromatic blocks (A) is at least 18 wt.%, based on the total amount of all polyvinylaromatic-polydiene block copolymers in the elastomer component.

10. Foamed pressure-sensitive adhesive layer according to claim 9, characterized in that the pressure-sensitive adhesive formulation has an adhesive strength expressed as peel strength (peel on steel) at a coating of 50 g / m 2 of at least 2.0 N / cm.

11. Foamed pressure-sensitive adhesive layer according to at least one of claims 9 and 10, characterized in that the pressure-sensitive adhesive formulation has a thermal shear strength (SAFT) at a coating of 50 g / m 2 and a load of 200 g of at least 100 °C, preferably at least 140 °C and particularly preferably at least 170 °C.

12. A self-adhesive product comprising at least one layer of a foamable pressure-sensitive adhesive formulation according to at least one of claims 1 to 8 or at least one foamed pressure-sensitive adhesive layer according to at least one of claims 9 to 11.

13. Self-adhesive product according to claim 12, characterized in that the foamed pressure-sensitive adhesive layer has a density of at most 850 kg / m 3 has.

14. A process for producing a pressure-sensitive adhesive formulation according to at least one of claims 1 to 10, characterized in that the pressure-sensitive adhesive formulation is produced by solvent-free mixing.

15. Use of a pressure-sensitive adhesive formulation according to at least one of claims 1 to 10 or of a self-adhesive product according to claim 11 for bonding plastics, glass and / or metals.

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