Method for producing cross-linked adhesive

Abstract

The invention relates to a method for preparing a cross-linked adhesive, in particular in the scope of a 3D printing process, comprising the method steps: a) preparing a prepolymer composition comprising one or more polyurethane prepolymers wherein the one or more polyurethane prepolymers can be prepared by the reaction of a starting composition, the starting composition includes i) one or more diisocyanate compounds, ii) one or more first diol compounds, where the first diol compounds are selected from the group consisting of diols having a terminal C-C double bond, and iii) one or more second diol compounds different from the first diol compounds, where the second diol compounds are selected from the group consisting of diols having a terminal C-C double bond. And b) cross-linking the polyurethane prepolymer in the prepolymer composition by a free radical reaction of a terminal C-C double bond of the first diol compound to obtain a cross-linked polyurethane polymer.

Description

Field of the Invention

[0001] The present invention relates to a method for preparing a crosslinked adhesive (especially within the scope of 3D printing processes), a method for preparing a tape based on this method and / or a method for preparing a crosslinked three-dimensional adhesive structure in 3D printing processes, and also includes the crosslinked adhesive prepared by this method. In addition, the corresponding tape and / or the corresponding crosslinked three-dimensional adhesive structure are disclosed, as well as the use of a prepolymer composition as a printing material for manufacturing a three-dimensional adhesive structure in 3D printing processes. Background Art

[0002] The joining of individual elements is a core method in manufacturing technology. In addition to other methods such as welding and soldering, adhesive bonding technology, i.e., the joining method using adhesives, is of great significance currently. As an alternative to amorphous adhesives applied, for example, from a tube, so-called tapes are provided here, and the adhesive effect of the tape is based on the adhesive used.

[0003] In a large number of technical applications, polyurethane systems have proven to be excellent base materials for manufacturing high-performance adhesives, as disclosed in the document EP3155034A1. These polymer compounds are usually obtained by polyaddition of polyols and polyisocyanates, and generally have physicochemical properties that can be used in adhesive compounds for various high-performance applications, especially in the field of electronics. In addition to generally very favorable adhesive properties, these properties also include light resistance, resistance to harsh climate conditions, and resistance to various chemicals, etc. Therefore, the physicochemical properties of polyurethanes can be specifically adapted to the corresponding application requirements by selecting raw materials in many cases, which is considered particularly advantageous.

[0004] When preparing polyurethane-based adhesives, a so-called polyurethane prepolymer is usually first prepared, that is, a polyurethane with a relatively low average molecular weight set by the mixing ratio of raw materials and reaction conditions. Thus, the polyurethane prepolymer, which is usually hydroxyl-terminated and still substantially meltable, can still be processed well, for example, by mixing the polyurethane prepolymer with other components such as an adhesive resin, where the resulting still-meltable composition can be efficiently formed, for example, into a subsequent adhesive layer of a tape. The adhesive is obtained by crosslinking the polyurethane prepolymer or prepolymer composition. In the prior art, it is usually achieved by crosslinking the hydroxyl-terminated polyurethane prepolymer using a polyfunctional isocyanate.

[0005] Although the polyurethane-based adhesives known in the prior art have various advantages, this system is still considered disadvantageous in some aspects.

[0006] In many cases, limited by the reactivity of the polyfunctional isocyanates used, the crosslinking of polyurethane prepolymers known in the prior art exhibits a strong correlation with the ambient air humidity, which may be disadvantageous for the reproducibility of crosslinking. In addition, other processing steps are usually required for crosslinking, in which polyfunctional isocyanates are added, and solvents are usually used in this process. However, the addition of polyfunctional isocyanates initiates the crosslinking reaction, thereby starting to reduce the processability and the so-called pot life. It is also often found that the crosslinking in the classical manner may take a relatively long time to reach the desired final degree of crosslinking, which largely determines the final mechanical properties of the crosslinked adhesive, and in the methods known in the prior art, this often lasts for more than two weeks.

[0007] In addition, in many cases, adhesives based on polyurethanes prepared by the crosslinking processes known in the prior art are disadvantageously restricted in terms of other additives that can be added to the polyurethane prepolymer composition before crosslinking, because hydroxyl groups, such as those in resins or plasticizers, particularly have a negative impact on crosslinking.

[0008] The above aspects particularly mean that adhesives based on polyurethanes known in the prior art are generally not suitable for additive manufacturing processes, commonly referred to as 3D printing processes. This is generally considered a disadvantage because these modern manufacturing processes - like in many other industries - also open up many interesting applications in the field of adhesive technology, especially in the targeted formation of three-dimensional adhesive structures, whose shape and size can be precisely matched to the intended application, which is considered particularly advantageous in the field of electronics production.

[0009] It is generally not feasible to process crosslinked adhesives based on polyurethanes suitable for the required application purposes in 3D printing processes. This means that only meltable polyurethane prepolymers or corresponding polyurethane prepolymer compositions can be shaped using a 3D printer. However, for technical reasons of operation, the addition of the polyfunctional isocyanates required for crosslinking cannot be carried out after shaping. At the same time, the addition time of the polyfunctional isocyanates cannot be too early to avoid crosslinking and affecting the processing performance in the case of a short pot life. Since there is a risk of blockage in the fluid supply line, it is also not realistic to supply the already crosslinked adhesive through the fluid supply line. Therefore, the equipment requirements for 3D printing equipment will increase significantly because it must mix the polyurethane prepolymer composition and the polyfunctional isocyanates as evenly as possible immediately before shaping, and in many cases, the required solvents will also make the use of 3D printers more difficult. This will also greatly increase the cleaning and maintenance workload because there is still a possibility of being contaminated by the over-crosslinked adhesive even in the case of late mixing.

[0010] Furthermore, considering production costs, most additive manufacturing processes available for printing polyurethane prepolymer compositions are not carried out in an inert gas environment, especially in large-scale production, and the 3D printing equipment used usually does not have such conditions. However, since the crosslinking chemistry known in the prior art is susceptible to influence, this will also have a particularly adverse effect on the reproducibility of printing quality, especially for many high-performance applications, which will be unacceptable. In addition, the curing time required to achieve the desired final degree of crosslinking is relatively long, and according to the inventors' assessment, this will hinder reasonable use in additive manufacturing. Summary of the Invention

[0011] The main technical problem of the present invention is to eliminate or at least reduce the above-mentioned disadvantages of the prior art.

[0012] In particular, the technical problem to be solved by the present invention is to provide a method for producing a crosslinked adhesive based on polyurethane, which produces a crosslinked adhesive having the advantages of a polyurethane-based adhesive without showing the disadvantages of the crosslinking processes known in the prior art during the production process.

[0013] Another technical problem to be solved by the present invention is that the disclosed method should also exhibit good reproducibility under changing environmental conditions and a higher tolerance to the use of different additives.

[0014] In addition, another technical problem to be solved by the present invention is that the disclosed method should be able to produce a crosslinked adhesive having excellent adhesive properties.

[0015] In addition, the technical problem to be solved by the present invention is that the disclosed method should be able to produce a crosslinked adhesive in a particularly time-saving and cost-effective manner, especially should be able to improve the curing time until the final degree of crosslinking is obtained. What is desired here is that such a method should still provide particularly high process reliability.

[0016] Another technical problem to be solved by the present invention is that in the provided method, the production of the crosslinked adhesive should be advantageous from the perspectives of environmental and occupational safety, especially should reduce the risk of contact with or release of isocyanate compounds and the need for solvents.

[0017] In addition, another technical problem to be solved by the present invention is that the provided method should be able to prepare a crosslinked adhesive having favorable biodegradability.

[0018] In addition, another technical problem to be solved by the present invention is that the provided method should be able to prepare a crosslinked adhesive having improved damping properties.

[0019] In particular, the technical problem to be solved by the present invention is that the provided method should also be able to effectively prepare a crosslinked adhesive within the scope of the 3D printing process, so as to enable 3D printing of an adhesive structure with a polyurethane-based adhesive. In this case, it is desirable that the provided method places as few equipment requirements as possible on the 3D printing equipment used.

[0020] The technical problem to be solved by the present invention is to provide a crosslinked adhesive that can be prepared by the proposed method, which has a polyurethane-based adhesive, but can be produced in a particularly time-saving and cost-effective manner and has a high degree of reproducibility.

[0021] The supplementary technical problem to be solved by the present invention is to provide two methods for preparing a tape or a three-dimensional adhesive structure based on the provided method. Here, the second technical problem to be solved by the present invention is to further provide the corresponding tape and three-dimensional adhesive structure generated by the method.

[0022] In addition, the second technical problem to be solved by the present invention is to provide the use of a polyurethane prepolymer composition as a printing material in a 3D printing process for generating a three-dimensional adhesive structure.

[0023] The inventors of the present invention have now found that, surprisingly, the aforementioned technical problems can be solved by using such a polyurethane prepolymer in a prepolymer composition when preparing an adhesive, which prepolymer is not only composed of a diisocyanate compound and a conventionally used diol compound, but also contains terminal C-C double bonds in its polymer chain, which are purposefully introduced by polymerizing at least one unsaturated diol with terminal C-C double bonds, and the crosslinking of the polyurethane prepolymer is subsequently carried out by free radical crosslinking, as defined in the claims.

[0024] The inventors have found that, surprisingly, a crosslinked adhesive can be obtained by using the method according to the invention, which has the advantages of adhesives based on polyurethanes, in particular with regard to adhesive technical properties, without showing the disadvantages of the crosslinking chemistry known from the prior art during preparation. In particular, the sensitivity to air humidity is reduced, and the use of additives with hydroxyl groups is also made easier. In addition, the free-radical crosslinking can be initiated, for example, based on radiation, which also solves the problem of too short a pot life and allows time-efficient and cost-effective crosslinking in the case of a very short curing time. It is also possible to advantageously dispense with isocyanates during crosslinking and, if necessary, to carry out the crosslinking step solvent-free. In particular, the method according to the invention can be used to efficiently produce three-dimensional adhesive structures from crosslinked polyurethan-based adhesives by means of three-dimensional printing technology, where the equipment requirements for the three-dimensional printing device are low, since, for example, only a radiation source needs to be provided for radiation-activated crosslinking and the crosslinking can also be carried out downstream. In particular, the method according to the invention can also be used to obtain crosslinked adhesives with good biodegradability.

[0025] In addition, the inventors have also found that, surprisingly, a crosslinked adhesive is formed during the specific implementation of the method, which surprisingly has improved damping properties compared to conventionally prepared crosslinked polyurethan-based adhesives. Without wishing to be bound by this theory, the inventors believe that this is because the crosslinking in the method according to the invention does not take place via terminal hydroxyl groups. According to the hypothesis, since the unsaturated diols with terminal C-C double bonds are present essentially randomly in the chains of the polyurethane prepolymer, the crosslinking mainly takes place along the polymer chains, thereby obtaining a network with a large number of freely movable side chains, which the inventors consider to have better damping properties, where, according to the inventors' knowledge, this effect can be further enhanced if raw materials with side chains, such as diols based on polyfarnesene or fatty acid esters, are also used in the polyurethane prepolymer.

[0026] Thus, the above technical problem is solved by the subject matter defined in the claims of the present invention. Preferred embodiments according to the invention are given in the dependent claims and the following description.

[0027] This hereinafter referred to as the preferred embodiment is combined in a particularly preferred embodiment with the features of other hereinafter referred to as particularly preferred embodiments. Thus, a combination of two or more of the hereinafter referred to as particularly preferred embodiments is further particularly preferred. Some embodiments are equally preferred, where a feature referred to as preferred to any extent in one embodiment is combined with one or more further features referred to as preferred to any extent in other embodiments. The features of the preferred adhesives, tapes, three-dimensional adhesive structures and applications are given by the features of the preferred method.

[0028] The following discloses the specific amounts or proportions of certain elements, such as diisocyanate compounds or first diol compounds, and preferred embodiments of such elements, and thus also specifically discloses the specific amounts or proportions of the preferred design elements. It is also disclosed that, in the corresponding total amounts or total proportions of the elements, at least some of the elements can be of a preferred design, and in particular, it is disclosed that the elements of a preferred design in the specific total amounts or total proportions can be present in specific amounts or proportions.

[0029] The present invention relates to a method for preparing a crosslinked binder, in particular within the scope of a 3D printing process, the method comprising the method steps:

[0030] a) preparing a prepolymer composition comprising one or more polyurethane prepolymers, wherein the one or more polyurethane prepolymers can be prepared by the reaction of a starting composition comprising:

[0031] i) one or more diisocyanate compounds,

[0032] ii) one or more first diol compounds, wherein the first diol compounds are selected from the group consisting of diols having terminal C-C double bonds / molecule, and

[0033] iii) one or more second diol compounds different from the first diol compounds, and

[0034] b) crosslinking the polyurethane prepolymers in the prepolymer composition by a free radical reaction of the terminal C-C double bonds of the first diol compounds to obtain a crosslinked polyurethane polymer.

[0035] In the method according to the invention, first a prepolymer composition is prepared or provided, which is subsequently crosslinked to obtain a crosslinked binder. The prepolymer composition further comprises other components in addition to the polyurethane prepolymers, and these other components should be included in the crosslinked binder during the crosslinking process later, such as a binder resin, pigments or other additives that a person skilled in the art should add according to the desired application purpose. The important component of the prepolymer composition for the present invention is the special polyurethane prepolymer.

[0036] Based on professional common sense, those skilled in the art are very familiar with polyurethane itself, the polyurethane group from which the name polyurethane is derived, and its basic chemical composition. In particular, they are also very familiar with the concept of polyurethane prepolymers. The polyurethane prepolymer used in accordance with the present invention is a copolymer prepared or preparable from a specific starting composition through a polymerization reaction, more precisely through an addition reaction. Herein, this expression should also include compounds that are also referred to as polyurethane pre-oligomers due to their chain length, because the distinction between oligomers and polymers is not fixed in any case and ultimately varies according to the will, so there is no need to make a distinction here. According to professional understanding and the usual procedures in the technical field, it is more appropriate to define such copolymers by the preparation process or the raw materials used for preparation, because it is basically impossible to comprehensively define the corresponding materials in any other conclusive way.

[0037] According to this common practice in the art, the preparability herein is with respect to the starting composition. According to the understanding of those skilled in the art, the starting composition includes all individual compounds that are converted into the constituent units of the polyurethane prepolymer during the polymerization process. Sometimes, the corresponding starting composition used for preparing the copolymer is also referred to as a monomer composition, but this term is not used in the present invention because, in particular, many commonly used diols, such as the compound used as the second diol compound, are, strictly speaking, already oligomers or polymeric compounds in themselves. According to the understanding of those skilled in the art, the starting composition does not include any other components that may be present in the reaction mixture during the polymerization process but are not added to the polyurethane prepolymer during the polymerization process, such as solvents or other non-reactive compounds.

[0038] According to the understanding of those skilled in the art, these components in the starting composition defined above are all "one or more". The term "one or more" refers to the chemical nature of the corresponding compound, rather than its amount of substance, which is customary in the industry. For example, the starting composition may only contain hexamethylene diisocyanate as the diisocyanate compound, which means that the starting composition contains a large number of corresponding molecules.

[0039] As understood by those skilled in the art, the prepolymer composition, or more precisely the polyurethane prepolymer, remains uncrosslinked in the prepolymer composition but can be crosslinked to produce a crosslinked adhesive. Those skilled in the art understand that the term "non-crosslinked" refers to chemical crosslinking, i.e., individual copolymer chains are covalently linked to each other to form a network, rather than any physical crosslinking of the copolymer chains, such as by entanglement, phase separation, or crystallization, so that the polyurethane prepolymer has regular fusibility. Those skilled in the art understand that the uncrosslinked polyurethane prepolymer is not necessarily linear and can also be a branched copolymer chain, especially if the starting composition contains high-value polyisocyanates and / or polyols in addition to diisocyanates and diols. Even though the transition from a branched copolymer chain to a crosslinked network in the crosslinked adhesive may seem ambiguous in theory, for those skilled in the art, the non-crosslinked state or crosslinked state is relatively easy to determine in practice, and those skilled in the art can determine it by methods such as temperature-related rheological properties or simple solubility tests. In the crosslinked adhesive, the molecular weight of the resulting crosslinked polyurethane increases significantly, so it is usually no longer soluble in organic solvents or no longer able to be melted, and thus only irreversible liquefaction can be achieved through decomposition.

[0040] The inventors hereby propose a range for the average molar mass of the polyurethane prepolymer, and by this method, the inventors can achieve a particularly advantageous method implementation empirically. Therefore, a preferred method according to the present invention is one in which the one or more polyurethane prepolymers have an average molar mass M 4 determined by GPC in the range of 1.0×10 4 to 8.0×10 4 g / mol, preferably in the range of 1.5×10 4 to 6.0×10 4 g / mol, and particularly preferably in the range of 2.0×10 4 to 4.0×10 W .

[0041] Within the scope of the present invention, all specifications for the weight-average molar mass M W are based on the determination by gel permeation chromatography (GPC). The determination is carried out with degassed tetrahydrofuran (THF) as the mobile medium, an injection volume of 50 µL, a sample concentration of 3 g / L, a flow rate of 1 mL / min, a temperature of 25 °C, and the system consists of a PSS-SECcurity 1260 HPLC pump, a PSS SDV 10 µm ID 8 mm×50 mm pre-column, a PSS SDV 5 µm 10 3 Å ID 8 mm×300 mm, a PSS SDV 5 µm 10 5 Å ID 8 mm×300 mm, a PSS SDV5 µm 106 An ID 8 mm × 300 mm and a SECcurity differential refractive index detector (RI). Data was recorded and analyzed using PSS - WinGPCUniChrome version 8.4 software. Calibration was performed using polystyrene standards and converted to polystyrene calibration uniformly using the Mark Houwink coefficients K and α.

[0042] In the process according to the present invention, a crosslinked binder is prepared from a prepolymer composition by crosslinking a polyurethane prepolymer. The crosslinked binder includes, in addition to any other components of the prepolymer composition and its reaction products, a crosslinked polyurethane polymer. Those skilled in the art will understand that the crosslinked binder can also be a polyurethane copolymer, depending on the form of crosslinking or other components of the crosslinked binder. In the simplest case, the obtained crosslinked polyurethane polymer constitutes the crosslinked binder. However, preferably, in the method according to the present invention, the total mass fraction (or combined mass fraction) of the crosslinked polyurethane polymer contained in the crosslinked binder, relative to the mass of the crosslinked binder, is in the range of 30% to 100%, preferably in the range of 40% to 100%, and particularly preferably in the range of 50% to 100%.

[0043] Different from the prior art, the crosslinking in the method of the present invention is not or at least not completely, preferably not at all, carried out by reacting with a polyfunctional isocyanate, but is based on free radical polymerization. However, typical polyurethane prepolymers cannot actually be crosslinked by free radical polymerization. This can only be achieved by constructing terminal C-C double bonds in a specific polyurethane prepolymer using a first diol compound. Here, the inventors recognized that not only the presence of terminal C-C double bonds is required, but also the first diol compound used must be a diol with only one (i.e., exactly one) terminal C-C double bond in order to achieve ideal crosslinking while endowing the crosslinked binder with advantageous properties, particularly good damping and adhesion properties, and the possibility of achieving favorable biodegradability.

[0044] The inventors have recognized that, considering the crosslinking step and the adjustable physicochemical properties in the crosslinked binder, not only the first diol compound but also at least a second diol compound should be used. By the second diol compound, the concentration of the units derived from the first diol compound in the polyurethane prepolymer can be controlled, thereby regulating the concentration of terminal C-C double bonds. Those skilled in the art will understand that the expression "different from the first diol compound" means that the second diol compound does not fall within the definition scope of the first diol compound. Two different diol compounds, each having one, i.e., exactly one, terminal C-C double bond per molecule, are not the first and second diol compounds in the sense of the present invention, but two different first diol compounds.

[0045] The polyurethane obtained in method step b) is crosslinked, and the crosslinked adhesives containing these polyurethanes produced according to the process of the present invention are also crosslinked. It is understood by those skilled in the art that this means that the polyurethane prepolymer has at least been partially crosslinked, which is the result of method step b), and method step b) is inevitably specified according to the present invention. According to the understanding of those skilled in the art, this does not require achieving the theoretically maximum possible crosslinking, that is, complete crosslinking of the adhesive. Therefore, any crosslinking carried out during method step b) according to the requirements defined above is sufficient, and thus the system in which the crosslinking reaction occurs is also regarded as crosslinked in the sense of the present invention.

[0046] The components used in the starting composition will be described in detail first below. In this regard, the inventors have successfully determined in each case particularly preferred embodiments and the mass fractions of the respective components, and favorable polyurethane prepolymers or high-performance crosslinked adhesives can be obtained with these components during the process according to the present invention. According to industry practice, the mass fraction is specified in each case as the total mass fraction of one or more components, thus indicating that the mass fractions of the respective components formed together meet the corresponding criteria. In the absence of other information, the mass of the starting composition is used as the reference system in each case.

[0047] To obtain a crosslinked adhesive with favorable biodegradability, the inventors considered it appropriate, based on prior judgment, to use aliphatic compounds instead of isocyanates. Therefore, according to a preferred method of the present invention, the diisocyanate compound is selected from the group of aliphatic diisocyanates.

[0048] Especially when biodegradability is not emphasized, in addition to aliphatic diisocyanates, aromatic diisocyanates can also be used, which allows for more flexible adjustment of the physicochemical properties. However, according to the inventors' evaluation, in these cases, it is also preferably not to choose too high a proportion. Therefore, a preferred method according to the present invention is as follows, wherein the starting composition contains one or more aromatic polyisocyanate compounds having a total mass fraction of 30% or less, particularly preferably 20% or less, and very particularly preferably 15% or less relative to the mass of the starting composition, and / or wherein the total mass fraction of the aromatic polyisocyanate compounds in the starting composition relative to the mass of the starting composition is 10% or less, particularly preferably 5% or less, and very particularly preferably 1% or less.

[0049] Taking into account that the average molar mass of the polyurethane prepolymer will be affected, the process according to the present invention is preferred, wherein the starting composition contains one or more diisocyanate compounds, preferably aliphatic diisocyanates, having a total mass fraction between 1% and 30%, preferably between 4% and 20%, and particularly preferably between 5% and 15% based on the mass of the starting composition.

[0050] Furthermore, polyisocyanates of higher value can also be used in the starting composition to adjust the physicochemical properties. However, according to the assessment of the inventors, the branching of the resulting polyurethane prepolymer should be minimized. For this purpose, a method according to the invention is preferably used, in which the starting composition comprises one or more polyisocyanate compounds having three or more isocyanate groups, which have a total mass fraction of 10% or less, particularly preferably 5% or less, very particularly preferably 3% or less, and especially preferably 0.5% or less, relative to the mass of the starting composition, and / or in which the total mass fraction of the polyisocyanate compounds having three or more isocyanate groups in the starting composition is 10% or less, particularly preferably 5% or less, very particularly preferably 1% or less, relative to the mass of the starting composition.

[0051] In principle, a large number of suitable diisocyanate compounds are known to the person skilled in the art. However, according to the assessment of the inventors, a method according to the invention is preferably used, in which one or more diisocyanate compounds are selected from hexamethylene diisocyanate, 1,6 - diisocyanato - 2,2,4 - trimethylhexane, pentamethylene diisocyanate, (S) - ethyl 2,6 - diisocyanatohexanoate, (R) - ethyl 2,6 - diisocyanatohexanoate, isophorone diisocyanate, 1,1'-methylenebis(4 - isocyanatocyclohexane), 4,4′-methylenebis(phenyl isocyanate), toluene - 2,4 - diisocyanate, naphthalene - 1,5 - diisocyanate and m - tetramethylxylene diisocyanate, preferably selected from the following group: hexamethylene diisocyanate, 1,6 - diisocyanato - 2,2,4 - trimethylhexane, pentamethylene diisocyanate, (S) - ethyl 2,6 - diisocyanatohexanoate, (R) - ethyl 2,6 - diisocyanatohexanoate, isophorone diisocyanate, 1,1'-methylenebis(4 - isocyanatocyclohexane) and 4,4′-methylenebis(phenyl isocyanate). In order to obtain a crosslinkable binder with good biodegradability, a method according to the invention is particularly preferred according to the assessment of the inventors, in which one or more diisocyanate compounds are selected from the group consisting of hexamethylene diisocyanate, 1,6 - diisocyanato - 2,2,4 - trimethylhexane, pentamethylene diisocyanate, (S) - ethyl 2,6 - diisocyanatohexanoate and (R) - ethyl 2,6 - diisocyanatohexanoate. As a supplement or alternative, a method according to the invention is preferably used, in which the diisocyanate compound is selected from diisocyanates having two or more, preferably three or more, alkyl groups, preferably methyl groups, along the main chain.

[0052] According to the inventor's assessment, it is preferred to use shorter diisocyanate compounds, and thus preferably the method according to the invention, in which one or more diisocyanate compounds are selected from the group consisting of aliphatic diisocyanates having 3 to 20 carbon atoms, preferably 4 to 18 carbon atoms, especially 5 to 15 carbon atoms.

[0053] In order to obtain a crosslinking adhesive with advantages in terms of sustainable development, the inventor proposes to use bio-based diisocyanate compounds, which are very suitable for the method according to the invention. Therefore, preferably the method according to the invention, in which one or more diisocyanate compounds are produced from renewable raw materials, and the preparation process preferably includes the conversion of plant biomass.

[0054] According to the inventor's assessment, in order to obtain a particularly advantageous polyurethane prepolymer or a favorable crosslinking adhesive, the first diol compound is preferably designed to be quite short. In this way, the first diol compound can not only introduce the terminal double bonds required for crosslinking in the polyurethane prepolymer, but also maintain a relatively high polyurethane group density in the polyurethane (pre) polymer. Due to the relatively rigid functional groups and the formation of hydrogen bonds in the high-density structure, the so-called hard segments are generated, which is beneficial to improving the adhesion performance of the crosslinking adhesive. In this context, preferably first of all the method according to the invention, in which the first diol compound is selected from diols having 4 to 60 carbon atoms, preferably 5 to 30 carbon atoms, particularly preferably 6 to 10 carbon atoms. In addition, in the method according to the invention, the first diol compound is selected from diols having a molar mass in the range of 70 to 750 g / mol, preferably 100 to 500 g / mol, particularly preferably 140 to 250 g / mol.

[0055] According to the inventor's judgment, especially mono(meth)acrylate is particularly suitable as the first diol compound. Particularly preferred is the method according to the invention, in which one or more first diol compounds are selected from the group consisting of acrylate and methacrylate, preferably methacrylate.

[0056] Basically independent of the specific selection of the first diol compound, the method according to the invention is preferred, in which the starting composition comprises one or more first diol compounds having a total mass fraction in the range of 0.05% to 20%, preferably in the range of 0.5% to 6%, more preferably in the range of 1% to 3.5% based on the mass of the starting composition.

[0057] It can be seen that the advantage of the present invention lies in its great flexibility with respect to other diols, i.e., the second diol compounds, and thereby enables flexible adjustment of the physicochemical properties according to the corresponding required requirements. However, considering the crosslinking kinetics, the resulting adhesion properties, and the possibility of regulating favorable biodegradability, according to the inventors' assessment, it is preferably not to use monomeric diols having multiple groups that can be polymerized during the free radical polymerization process. Particularly advantageously, the content of monomeric second diols having two or more C-C double bonds in each molecule is kept at a rather low level. Correspondingly, a preferred method according to the present invention is one in which the starting composition comprises one or more diols, preferably monomeric diols, having two or more C-C double bonds in each molecule, and the diols have a total mass fraction of 30% or less, particularly preferably 20% or less, and very particularly preferably 10% or less relative to the mass of the starting composition, and / or in which the total mass fraction of the diols having two or more C-C double bonds in each molecule in the starting composition is 10% or less, particularly preferably 5% or less, and very particularly preferably 1% or less relative to the mass of the starting composition.

[0058] Conversely, according to the inventors' assessment, it is particularly advantageous that the second diol compounds do not have terminal C-C double bonds, and particularly preferably do not have C-C double bonds at all, so that they are saturated diol compounds. Thus, a preferred method according to the present invention is one in which the second diol compounds are selected from the group of diols without terminal C-C double bonds. Accordingly, a particularly preferred method according to the present invention is one in which the second diol compounds are selected from the group consisting of saturated diols.

[0059] In principle, the second diol compounds can be relatively short molecules, so-called chain extenders, or oligomeric or polymeric diols, and these can also be mixed with each other. According to the inventors' assessment, the use of oligomeric and polymeric diols is particularly advantageous here. For a specific application, a preferred method according to the present invention is one in which the one or more second diol compounds are selected from the group consisting of saturated diols having 5 to 600 carbon atoms, preferably 8 to 350 carbon atoms, and particularly preferably 10 to 250 carbon atoms. However, a particularly preferred method according to the present invention is one in which one or more second diol compounds are selected from the group consisting of diols having a weight average molar mass M W in the range of 200 to 6000 g / mol, preferably 300 to 4500 g / mol, and particularly preferably 400 to 3000 g / mol as determined by GPC.

[0060] Most particularly preferably, such a compound present in amorphous or semi-crystalline form is used for the oligomeric or polymeric diol compound. Preferred is a process according to the invention, in which the second diol compound is selected from the group consisting of amorphous or semi-crystalline, preferably amorphous diols.

[0061] Essentially independent of the specific choice of the second diol compound, preferred is a process according to the invention, in which the starting composition comprises one or more second diol compounds having a total mass fraction in the range of 50% to 99%, preferably in the range of 60% to 97%, more preferably in the range of 70% to 95% relative to the mass of the starting composition. However, it is particularly preferred to use saturated diols and in this regard preferred is a process according to the invention, in which the total mass fraction of the saturated diol is in the range of 50 to 99%, preferably in the range of 60 to 97%, particularly preferably in the range of 70 to 95% relative to the mass of the starting composition.

[0062] Similar to the description of the polyisocyanate above, higher-valued polyols can also be used in the starting composition to adjust the physicochemical properties. However, according to the assessment of the inventors, the branching of the resulting polyurethane prepolymer should be minimized in this case. For this purpose, preferred is a process according to the invention, in which the starting composition comprises one or more polyol compounds having three or more hydroxyl groups, having a total mass fraction of 30% or less, particularly preferably 15% or less, very particularly preferably 3% or less, especially preferably 0.5% or less relative to the mass of the starting composition, and / or in which the total mass fraction of the polyol compounds having three or more hydroxyl groups in the starting composition is 10% or less, particularly preferably 5% or less, very particularly preferably 1% or less relative to the mass of the starting composition.

[0063] According to the assessment of the inventors, polyester diols or polyether diols are particularly suitable for the second diol compound and sometimes also for the first diol compound, since these diols can produce crosslinked adhesives with good adhesion properties. Therefore, preferred is a process according to the invention, in which the first diol compound and / or the second diol compound, preferably the second diol compound, is selected from the group consisting of diols having one or more, preferably two or more, especially preferably a plurality of functional groups selected from ether groups and ester groups, preferably ester groups, and / or in which the first diol compound and / or the second diol compound, preferably the second diol compound, is selected from polyester diols and polyether diols, preferably polyester diols.

[0064] According to the inventors' assessment, it is particularly advantageous to also use hydroxy-modified polyterpenes, polybutadiene diols, fatty acid-based polyesters or castor oil-based polyesters, preferably hydroxy-modified polyterpenes, in the starting composition. According to the inventors' assessment, these compounds, in particular the so-called polyfarnesenes in hydroxy-modified polyterpenes, have particularly good damping properties. The corresponding compounds are known to the person skilled in the art from the prior art. The following formula (I) shows exemplary diols having a backbone formed from polyfarnesene.

[0065]

[0066] Thus, a preferred method according to the invention is one in which the starting composition comprises one or more polyol compounds having a backbone made of polyisoprene units and / or a backbone made of polyterpenes, preferably a backbone made of polyfarnesene, which preferably has a total mass fraction in the range from 5 to 95%, particularly preferably in the range from 10 to 90%, and even more particularly preferably in the range from 15 to 80% relative to the mass of the starting composition.

[0067] In order to obtain a crosslinkable adhesive that has advantages in terms of sustainable development, the inventors propose, with regard to the diols used, to use bio-based compounds, which are very suitable for the method according to the invention and are particularly preferably capable of being combined with bio-based diisocyanates. A preferred method according to the invention is one in which the first diol compound and / or the second diol compound, preferably the first diol compound and the second diol compound, are prepared from renewable raw materials, where the preparation preferably includes the conversion of plant biomass.

[0068] According to the assessment of the present inventors, another particular advantage of the present invention is that subsequent crosslinking does not require terminal hydroxyl groups. Thus, in addition to diols and diisocyanates, monofunctional alcohols or isocyanates can also be used in the starting composition. These monofunctional building blocks can terminate the polymer chains obtained by the polymerization reaction, thereby effectively adjusting the desired average molar mass. In addition, by using these monofunctional compounds, polyurethane prepolymers can be obtained whose ends carry neither hydroxyl nor isocyanate groups, which is particularly advantageous for the storage stability of the polyurethane prepolymers. Thus, the following method according to the present invention is preferred, wherein the starting composition comprises one or more monofunctional compounds selected from the group consisting of monofunctional alcohols and monofunctional isocyanates, which preferably have a total mass fraction of 0.1% or more, preferably 1% or more, particularly preferably 3% or more relative to the mass of the starting composition, and / or a total amount of substance in the range from 0.5*[A] to 1.5*[A], preferably from 0.8*[A] to 1.2*[A], particularly preferably from 0.95*[A] to 1.05*[A], where [A] is the total amount of substance of the terminal OH groups or isocyanate groups of the polyurethane prepolymer, and [A] can be determined by measurement or estimated using typical simulation methods to set, for example, the characteristics of the reference sample.

[0069] The inventors have found an advantageous process for preparing polyurethane prepolymers, which can be carried out either in a solvent or without a solvent, with the former being preferred. When using a solvent, the following method according to the present invention is preferred, wherein one or more polyurethane prepolymers can be prepared by reacting the starting composition in a solvent, where the solvent is selected from the group consisting of ketones (such as acetone or butan-2-one), esters (such as ethyl acetate), ethers, amides, hydrocarbons (such as gasoline 60 / 90), toluene, halogenated hydrocarbons, and mixtures of these solvents.

[0070] Regardless of whether a solvent is used or not, the following method according to the present invention is preferred, wherein one or more polyurethane prepolymers are prepared by reacting the starting composition in a temperature range from 0 to 120 °C, preferably from 10 to 100 °C, particularly preferably from 20 to 80 °C.

[0071] According to the assessment of the inventors, in many cases, it is expedient to provide a catalyst for the preparation of the polyurethane prepolymer. The method according to the present invention in this regard consists, for example, in that one or more polyurethane prepolymers can be prepared by reacting the starting composition in the presence of a catalyst, where the catalyst is selected from the group consisting of organic bismuth compounds, organic tin compounds, organic zirconium compounds, organic zinc compounds, tertiary amine compounds, morphine-containing compounds, iron salts, and potassium salts.

[0072] For the crosslinking of the polyurethane prepolymer in method step b), a typical initiator system can be advantageously used, which is known to the person skilled in the art for free radical crosslinking, for example for (meth)acrylate-based systems, where according to the inventors' assessment, radiation-based curing is particularly advantageous, especially for applications in 3D printing. In this regard, the following method according to the invention is preferred, wherein the crosslinking of the polyurethane prepolymer in the prepolymer composition is initiated by a free radical reaction of the terminal C-C double bonds of the first diol compound by means of one or more initiator compounds, wherein the one or more initiator compounds are selected from the group consisting of radiation-activated initiators, thermally-activated initiators and redox initiators, preferably from the group consisting of thermally-activated initiators and radiation-activated initiators, and particularly preferably radiation-activated initiators. In this regard, the following method according to the invention is preferred, wherein the one or more initiator compounds are selected from the group consisting of α-hydroxy ketones, α-alkoxy ketones, α-amino aryl ketones, diaryl ketones, azo compounds, acyl phosphine oxides, organic or inorganic peroxides, camphorquinone and camphorquinone derivatives. As a supplement or alternative, the method according to the invention is preferred, wherein one or more initiator compounds are used, which have a total mass fraction in the range from 0.001% to 5%, preferably in the range from 0.05% to 1%, relative to the mass of the polyurethane prepolymer in the prepolymer composition. The person skilled in the art will understand that in this context, the following method according to the invention is concerned, wherein the prepolymer composition comprises the corresponding initiator compounds.

[0073] In this regard, the inventors have identified a temperature range within which particularly advantageous results in crosslinking are allowed. The method according to the invention is preferred when using a thermally-active initiator, wherein the crosslinking of the polyurethane prepolymer in the prepolymer composition is carried out in the temperature range from 40 to 300 °C, preferably from 50 to 280 °C, particularly preferably from 60 to 150 °C. As an alternative, the method according to the invention is preferred when using a radiation-activated initiator, wherein the crosslinking of the polyurethane prepolymer in the prepolymer composition is carried out in the temperature range from -10 to 40 °C, preferably from 10 to 30 °C, particularly preferably from 20 to 25 °C.

[0074] According to the inventor's assessment, for a specific application, it is particularly advantageous that the crosslinking of the polyurethane prepolymer is at least partially achieved by reaction with other unsaturated compounds, so that at least a part of the polymer units derived from the first diol compound do not directly combine with each other, but are combined through components derived from the other unsaturated compounds. Here, in addition to monofunctional unsaturated compounds, also known as reactive diluents, polyfunctional unsaturated compounds can also be considered. According to the inventor's assessment, if good biodegradability is to be pursued, the concentration of such polyfunctional unsaturated compounds should be kept very low. Thus, the following method according to the invention is preferred, wherein, during the crosslinking process of the polyurethane prepolymer in the prepolymer composition, at least partially, a radical reaction of the terminal C-C double bonds of the first diol compound with one or more chain extender molecules is carried out, and the chain extender molecules are preferably selected from the group consisting of compounds each having one C-C double bond per molecule. Here, the following method according to the invention is particularly preferred, wherein one or more chain extender molecules are selected from the group consisting of monofunctional (meth)acrylates. As a supplement or alternative, the method according to the invention is particularly preferred, wherein one or more chain extender molecules are used, which have a total mass fraction in the range of 0.5% to 49%, preferably in the range of 1% to 10%, relative to the mass of the polyurethane prepolymer in the prepolymer composition.

[0075] As an alternative or supplement, the following method according to the invention is preferred, wherein the crosslinking of the polyurethane prepolymer is at least partially, preferably substantially, carried out by a radical reaction of the terminal C-C double bonds of the first diol compound with one or more crosslinking molecules, and the crosslinking molecules are preferably selected from the group consisting of compounds each having two or more, preferably exactly two, C-C double bonds, preferably terminal C-C double bonds, per molecule. Here, the following method according to the invention is particularly preferred, wherein one or more crosslinking molecules are selected from the group consisting of monofunctional, preferably bifunctional, (meth)acrylates. As a supplement or alternative, the following method according to the invention is particularly preferred, wherein one or more crosslinking molecules are used, which have a total mass fraction in the range of 0.5% to 49%, preferably in the range of 1% to 20%, relative to the mass of the polyurethane prepolymer in the prepolymer composition.

[0076] Advantageously according to the inventor, the crosslinked binder produced also comprises a resin, in particular a tackifying resin. In this regard, the following method according to the invention is preferred, in which the crosslinked binder comprises one or more resins having a total mass fraction, relative to the mass of the crosslinked binder, of preferably 70% or less, particularly preferably 60% or less, and most particularly preferably 50% or less. Examples of such tackifying resins include hydrocarbon resins (such as polymers based on unsaturated C5 or C9 monomers), terpene phenolic resins, polyterpene resins based on α-pinene and / or β-pinene and / or δ-limonene, aromatic resins such as coumarone-indene resins or resins based on styrene or α-methylstyrene, and rosin and its derivatives, such as disproportionated, dimerized or esterified resins, for example reaction products with ethylene glycol, glycerol or pentaerythritol.

[0077] However, according to the inventor, certain polyurethane-based resins are particularly suitable for polyurethane-based crosslinked binders. The inventor has specifically adapted certain polyurethane-based resins to the requirements of the method according to the invention and considers them to be particularly advantageous, especially in relation to the use of 3D printing processes. Accordingly, the following method according to the invention is particularly preferred, in which the resin is selected from the group consisting of polyurethane resins. Of course, the polyurethane resins mentioned here are not the polyurethane prepolymers or crosslinked polyurethane polymers in the method of the present invention. On the contrary, the polyurethane resins are different from them. Apparently, the polyurethane resins are incorporated or added to the crosslinked binder prepared by the method according to the invention.

[0078] The method according to the invention is particularly preferred, in which the polyurethane resin can be prepared by the reaction of a resin starting composition comprising:

[0079] i) one or more diisocyanate components, and

[0080] ii) one or more polyol components, preferably diol components.

[0081] In this regard, advantageously according to the inventor, monomeric polyols rather than oligomers are used in the corresponding resin starting composition, so that a high density of polyurethane groups can be obtained. Accordingly, the method according to the invention is preferred, in which the polyol component has a weight-average molar mass M WAt 400 g / mol or less, preferably at 250 g / mol or less. As an alternative or addition, the method according to the invention is also preferred, wherein the oligomer and the polyol component have a total mass fraction of 10% or less, preferably 5% or less, particularly preferably 1% or less, and most particularly preferably 0.1% or less relative to the mass of the resin starting composition. As an alternative or addition, the following method according to the invention is correspondingly preferred, wherein the polyol component is a monomeric polyol component.

[0082] Furthermore, the method according to the invention is preferred, wherein the polyol component is not a first diol compound. In this regard, the method according to the invention is particularly preferred, wherein the polyol component does not include terminal C-C double bonds, preferably substantially does not include C-C double bonds.

[0083] The method according to the invention is preferred, wherein the resin, preferably a polyurethane resin, has a weight-average molar mass M measured by GPC W in the range between 300 and 4000 g / mol, preferably between 500 and 1500 g / mol. As an alternative or addition, the following method according to the invention is also preferred, wherein the resin, preferably a polyurethane resin, has a glass transition temperature measured by DSC of -20 °C or higher, preferably 0 °C or higher. As an alternative or addition, the following method according to the invention is still preferred, wherein the resin, preferably a polyurethane resin, is semi-crystalline or amorphous.

[0084] In terms of the selection of the diisocyanate component, the following method according to the invention is preferred, wherein one or more diisocyanate components are selected from hexamethylene diisocyanate, 1,6 - diisocyanate - 2,2,4 - trimethylhexane, pentamethylene diisocyanate, (S)-ethyl 2,6 - diisocyanatohexanoate, (R)-ethyl 2,6 - diisocyanatohexanoate, isophorone diisocyanate, 1,1'-methylenebis(4 - isocyanatocyclohexane), 4,4'-methylenebis(phenyl isocyanate), toluene - 2,4 - diisocyanate, naphthalene - 1,5 - diisocyanate and m - tetramethylxylylene diisocyanate, preferably selected from the following group: hexamethylene diisocyanate, 1,6 - diisocyanate - 2,2,4 - trimethylhexane, pentamethylene diisocyanate, (S)-ethyl 2,6 - diisocyanatohexanoate, (R)-ethyl 2,6 - diisocyanatohexanoate, isophorone diisocyanate, 1,1'-methylenebis(4 - isocyanatocyclohexane) and 4,4'-methylenebis(phenyl isocyanate). In order to obtain a polyurethane resin with good biodegradability, which is excellently suitable for combination with crosslinked polyurethanes of corresponding designs, the following method according to the invention is particularly preferred according to the inventor's evaluation, wherein one or more diisocyanate components are selected from the group consisting of hexamethylene diisocyanate, 1,6 - diisocyanate - 2,2,4 - trimethylhexane and pentamethylene diisocyanate. In terms of the polyol component, the following method according to the invention is preferred, wherein one or more polyol components are selected from the group consisting of 2 - ethyl - 1,3 - hexanediol, 2 - methyl - 2,4 - pentanediol, 2,2,4 - trimethyl - 1,3 - pentanediol, 2 - methyl - 1,3 - propanediol, 2 - butyl - 2 - ethyl - 1,3 - propanediol, 1,3 - butanediol, 1,4 - butanediol, 3 - methyl - 1,5 - pentanediol, 2,2 - dimethyl - 1,3 - propanediol, 1,2 - propanediol, 2,4 - pentanediol, tripropylene glycol, polyethylene glycol Mn200 and polyethylene glycol Mn300, preferably selected from the group consisting of 2 - ethyl - 1,3 - hexanediol and 2 - methyl - 2,4 - pentanediol.

[0085] In terms of the specific composition of the resin starting composition, the method according to the invention is preferred, wherein the resin starting composition comprises one or more diisocyanate components which have a total mass fraction in the range of 30% to 70%, preferably in the range of 40% to 60%, particularly preferably in the range of 45% to 55% relative to the mass of the resin starting composition. As an alternative or supplement, the method according to the invention is preferred in this regard, wherein the resin starting composition comprises one or more polyol compounds which have a total mass fraction in the range of 30% to 70%, preferably in the range of 40% to 60%, particularly preferably in the range of 45% to 55% relative to the mass of the resin starting composition.

[0086] According to the inventor's assessment, similar to the previous description, the advantage for the preferably used polyurethane resin is that in the resin starting composition, in addition to diols and diisocyanates, monofunctional alcohols or isocyanates are also used. Correspondingly, the method according to the invention is preferred, wherein the resin starting composition comprises one or more monofunctional compounds selected from the group consisting of monofunctional alcohols and monofunctional isocyanates, which preferably have a total mass fraction of 10% or more, preferably 15% or more, particularly preferably 20% or more relative to the mass of the resin starting composition, and / or a total amount of substances in the range of 0.5*[B] to 1.5*[B], preferably 0.8*[B] to 1.2*[B], particularly preferably 0.95*[B] to 1.05*[B], where [B] is the total amount of terminal OH groups or isocyanate groups of the polyurethane resin, and [B] can be measured or estimated using typical simulation methods to set this characteristic for, for example, a reference sample.

[0087] The advantage of the method according to the invention can be that, in addition to the resin and especially the polyurethane resin, other components can be added, which can be added to the prepolymer composition and are accordingly included in the crosslinked binder. The benefit of this is that the physico-chemical properties of the crosslinked binder can be made particularly suitable for the corresponding application requirements. The following method according to the invention is exemplary, wherein the crosslinked binder comprises one or more other components, wherein the other components are selected from the group consisting of rheological additives, stabilizers, antioxidants and colorants, and wherein the combined mass fraction of the other components is preferably in the range of 0.1 to 30%, more preferably in the range of 0.5 to 20%, particularly preferably in the range of 1 to 20% based on the mass of the crosslinked binder.

[0088] Taking into account the subsequent processing of the crosslinked binder, the crosslinked binder is preferably implemented as a pressure-sensitive adhesive, which can be achieved in particular by adding a resin, and it is completely particularly preferred to add the above-mentioned polyurethane resin. Correspondingly, the method according to the invention is preferred, wherein the crosslinked binder is preferably a pressure-sensitive adhesive.

[0089] According to professional understanding, a pressure-sensitive adhesive is an adhesive with adhesive properties, that is, it can form a strong bond with an adherent substrate even under relatively low contact pressure. Such pressure-sensitive tapes can generally be re-peeled from the adherent substrate with substantially no residue after use and generally have permanent tack even at room temperature, which means they have a certain viscosity and contact tack, so they can wet the surface of the substrate even under low contact pressure. The pressure-sensitive tack of pressure-sensitive tapes comes from the use of pressure-sensitive adhesives as adhesives. Without wishing to be bound by this theory, it is generally assumed that pressure-sensitive adhesives can be regarded as liquids with extremely high viscosities having an elastic component, and thus have unique viscoelastic properties, resulting in the above-mentioned permanent inherent tack and pressure-sensitive tack. It is assumed that during the mechanical deformation process, a viscous flow process and the establishment of elastic restoring forces will occur in the corresponding pressure-sensitive adhesive. A certain proportion of viscous flow enables adhesion, while a certain proportion of elastic restoring force is necessary to achieve cohesion. The relationship between rheology and pressure-sensitive tack is known in the prior art, for example, it is described in "Satas, Handbook of Pressure Sensitive Adhesives Technology", Third Edition (1999), pages 153 to 203. The storage modulus (G') and loss modulus (G'') can be determined by dynamic mechanical analysis (DMA), for example, using a rheometer, as described in WO2015 / 189323, and are generally used to characterize the degree of elastic and viscous content. In the present invention, the following adhesives are preferably considered to have pressure-sensitive tack and are considered pressure-sensitive adhesives, that is, at a temperature of 23 °C and a deformation frequency range of 10 0 to 10 1 radians per second, G' and G'' are each at least partially in the range of 10 3 to 10 7 Pa.

[0090] A special case of other components for adjusting the properties of crosslinked adhesives is insoluble fillers, which can be added to the prepolymer composition to obtain a filled crosslinked adhesive after crosslinking. These insoluble fillers are, for example, particulate fillers with an average particle diameter (D50) of 5 µm or more, preferably 10 µm or more, and particularly preferably 20 µm or more, which are insoluble in the prepolymer composition and thus exist in the prepolymer composition in the form of a dispersion, or are macroscopic fillers such as fibers. Preferably, the insoluble fillers are selected from the group consisting of particulate fillers. Particularly preferably, the insoluble fillers are selected from expandable hollow polymer spheres, non-expandable hollow polymer spheres, solid polymer spheres, hollow glass spheres, solid glass spheres, hollow ceramic spheres, solid ceramic spheres, solid carbon spheres, and powdered inorganic compounds. However, fibers, fabrics, sheets, and rods made of materials insoluble in the prepolymer composition can also be used as insoluble fillers. Since they sometimes have macroscopic dimensions and are insoluble, they generally do not have a significant impact on the relationship between the above prepolymer composition and the crosslinking chemical reaction. Therefore, in the present invention, these insoluble fillers are not included in the prepolymer composition, and these insoluble fillers are not considered when calculating the mass fraction relative to the mass of the prepolymer composition. It is stipulated within the scope of the present invention that adding insoluble fillers to the prepolymer composition results in a filled prepolymer composition. Therefore, in this case, a method according to the present invention is involved, wherein the prepolymer composition is a filled prepolymer composition, including:

[0091] aa.1) a prepolymer composition, and

[0092] aa.2) one or more insoluble fillers,

[0093] wherein, based on the mass of the prepolymer composition, the total mass fraction of the insoluble fillers is preferably in the range of 0.1 to 20%, particularly preferably in the range of 0.5 to 15%, and most particularly preferably in the range of 1 to 10%.

[0094] The method according to the present invention can be used not only for the production of tapes but also for 3D printing processes to produce more complex three-dimensional adhesive structures. Nevertheless, the production of tapes is still of great industrial significance.

[0095] Therefore, the present invention mainly also relates to a method for producing a tape, including the method steps of preparing a crosslinked adhesive according to the present invention, and, before or during method step b), preferably before method step b):

[0096] b1a) forming a prepolymer layer composed of the prepolymer composition on a carrier layer or a release layer.

[0097] Here, the term "tape" is clear to a person skilled in the art of adhesive technology. In the present invention, the term "tape" refers to all thin and flat structures, i.e., structures that mainly extend in a two-dimensional range, in particular films, film parts, and labels, preferably tapes with an extended length and a limited width, as well as corresponding tape parts.

[0098] The material usage (coating thickness) of the prepolymer composition is preferably between 10 and 1000 g / m 2 and preferably between 15 and 500 g / m 2 and particularly preferably between 20 and 100 g / m 2 between.

[0099] Generally, in order to obtain the best operating performance as much as possible, it is particularly advantageous that the crosslinked adhesive according to the present invention is used as the adhesive layer of a single-sided or double-sided tape, and the tape further includes a carrier layer; or the adhesive layer is arranged on a release layer, such as a backing, and the adhesive layer can be easily peeled off from the release layer.

[0100] In this regard, the following method for preparing a tape is preferred, in which a prepolymer layer is formed on a release layer. In this regard, the following method for preparing a tape is preferred, in which the release layer is composed of one or more materials selected from polyethylene, polypropylene, polyethylene terephthalate, paper, and combinations of these materials, and the release material is preferably coated with a release layer on one or both sides, particularly preferably on both sides, preferably a urethane or silicone release layer, particularly preferably a silicone release layer, and the silicone release layer is particularly preferably prepared by crosslinking a crosslinkable silicone system including one or more polysiloxanes.

[0101] Different from the release layer, the term "carrier layer" generally refers to the layer in a multi-layer tape that plays an important role in determining the mechanical and physical properties of the tape, such as tear resistance, elasticity, insulation, or resilience. Common materials for the carrier layer include fabrics, gauzes, papers, and plastic films, such as PET films and polyolefin films.

[0102] When adding a carrier layer, it is advantageous to use an adhesion promoter (i.e., a so-called primer layer) between the carrier material and the prepolymer composition or to physically pretreat the carrier surface to improve the adhesion of the crosslinked adhesive to the carrier material. In the tape with a carrier layer according to the present invention, the adhesive layer can be sequentially covered by a release cover layer, a so-called release liner, to achieve smooth unwinding and protect the adhesive from contamination. Here, in the case of a single-sided tape, the carrier can be provided with a release layer on one side, and the release layer can be silicone-based, urethane-based, acrylate-based, etc.

[0103] However, since the method according to the invention is particularly suitable for 3D printing processes, the invention also particularly relates to a method for producing a crosslinked three-dimensional adhesive structure by means of a 3D printing process, comprising the method steps of the method according to the invention for producing a crosslinked adhesive, and the following method steps before or during method step b), preferably before method step b):

[0104] b1b) Shaping the prepolymer composition using the application unit of a 3D printing device to form a three-dimensional adhesive structure.

[0105] Those skilled in the art are familiar with numerous methods in the prior art for producing three-dimensional target structures using 3D printing devices, especially the so-called material extrusion methods. Those skilled in the art understand that the method according to the invention is basically compatible with various 3D printing devices and 3D printing processes. In this regard, a method for producing a 3D adhesive structure is preferred, wherein the production of the 3D adhesive structure is carried out in a melt coating method.

[0106] This 3D printing process mainly involves producing a 3D adhesive structure from a prepolymer composition, which is crosslinked in method step b) to obtain a crosslinked 3D adhesive structure.

[0107] The inventors propose that when implementing the corresponding 3D printing process, the viscosity or its temperature dependence of the prepolymer composition should be specifically optimized to obtain particularly advantageous application properties, i.e., the prepolymer composition can be easily and precisely applied, while at the same time exhibiting sufficient structural integrity to form a 3D adhesive structure and maintaining this shape before crosslinking. In this regard, the inventors have successfully determined particularly preferred viscosity ranges, and by adjusting these viscosity ranges, prepolymer compositions that are very suitable for various 3D printing processes (especially melt coating methods) can be obtained. Preferably, the method according to the invention is such that the dynamic viscosity of the prepolymer composition at 25 °C ranges from 500 to 500,000 Pa s, preferably from 1000 to 200,000 Pa s, and particularly preferably from 2000 to 100,000 Pa s. As an alternative or supplement, preferably, the method according to the invention is such that the dynamic viscosity of the prepolymer composition at 100 °C ranges from 2 to 2500 Pa s, preferably from 5 to 2000 Pa s, particularly preferably from 10 to 1000 Pa s, and most particularly preferably from 15 to 300 Pa s. In the present invention, the dynamic viscosity is determined according to the DIN 53019-1 standard of 2008; at the corresponding temperature, the shear rate is 1 s -1 .

[0108] Those skilled in the art can understand that the present invention also relates to a crosslinked adhesive, which is prepared by using the method for preparing a crosslinked adhesive according to the present invention, or can be prepared by using the method for preparing a crosslinked adhesive according to the present invention.

[0109] Based on the method for preparing a tape or a 3D bonding structure according to the present invention, products obtained thereby are also disclosed within the scope of the present invention.

[0110] Therefore, first, a tape is disclosed, which is prepared by or capable of being prepared by the method for preparing a tape according to the present invention, and includes an adhesive layer composed of the crosslinked adhesive according to the present invention, wherein the adhesive layer is disposed on a carrier layer or a release layer.

[0111] A crosslinked 3D bonding structure is also disclosed, the 3D bonding structure is prepared by or can be prepared by the method according to the present invention, and the 3D bonding structure includes a three-dimensionally shaped crosslinked adhesive according to the present invention.

[0112] Finally, the use of the above-mentioned prepolymer composition is also disclosed, that is, a prepolymer composition containing one or more polyurethane prepolymers, wherein one or more polyurethane prepolymers can be prepared by the reaction of a starting composition, and the starting composition includes:

[0113] i.v) one or more diisocyanate compounds,

[0114] ii.v) one or more first diol compounds, wherein the first diol compounds are selected from the group consisting of diols having at least one C-C double bond / molecule, and

[0115] iii.v) one or more second diol compounds different from the first diol compounds,

[0116] As a printing material in a 3D printing process, especially a hot melt coating process, for generating a 3D bonding structure, preferably in the method for preparing a crosslinked three-dimensional bonding structure according to the present invention.

[0117] The present invention and preferred embodiments thereof will be further explained and illustrated below in conjunction with experiments.

[0118] The substances used herein are described in Table 1 below.

[0119]

[0120]

[0121] Samples prepared within the scope of the present invention were analyzed using the following methods. Unless otherwise specified, the measurements were carried out in a test environment of 23 ± 1°C and 50 ± 5% relative humidity.

[0122] Finger stickiness test:

[0123] As a method for qualitatively evaluating tack, the "finger tack test" established in the technical field is carried out by an experienced person skilled in the art of adhesive preparation. This involves touching the tape with a finger and making a qualitative assessment of the degree to which the tape "sticks to the finger". The end-users of such tapes generally expect the tape to have good finger tack.

[0124] Glass transition temperature (DSC):

[0125] The glass transition temperature (Tg) is determined by differential scanning calorimetry (DSC). For this purpose, approximately 5 mg of the sample is weighed into an aluminum crucible (volume 25 µL), and the crucible is sealed with a perforated lid. The measurement is carried out using a Netzsch DSC Sirius 3500 device under a nitrogen atmosphere. After cooling the sample to -140 °C, it is heated to 150 °C at a heating rate of 10 K / min, and then cooled again to -140 °C. For the second heating curve, it is heated to 150 °C again at a rate of 10 K / min. The change in heat capacity is recorded in order to identify the glass transition process as a step in the graph. The glass transition temperature is analyzed by the conventional method: a tangent is applied to the baseline of the thermogram before and after the step. In the region of the step, a leveling line is drawn parallel to the ordinate so that it intersects the two tangents, thus forming two regions and (between each tangent, the leveling line and the measurement curve) the same area. The intersection of the leveling line positioned in this way with the measurement curve represents the glass transition temperature.

[0126] Adhesive force

[0127] The adhesive force (peel strength) is tested in accordance with PSTC-1. A 2-cm-wide pressure-sensitive tape (consisting of a 23-µm-thick PET film etched with trichloroacetic acid and a pressure-sensitive adhesive film attached thereto) is adhered to a test plate, and a 4-kg roller is rolled over the test plate 5 times. The test plate is clamped, and the self-adhesive tape is pulled out from its free end at a speed of 300 mm / min using a tensile testing machine, with a peel angle of 180°. The required tensile force is measured by a tensile force tester. The measurement results are the average of three measurements and are standardized by the tape width, with the unit of N / cm. The test plate is a polished steel plate with a thickness of 2 mm.

[0128] Shear strength:

[0129] The shear strength is tested in accordance with PSTC-7. A self-adhesive tape with a width of 1.3 cm is adhered to a polished steel disc with a length of 2 cm, and a 2-kg roller is rolled twice on the steel disc. The plate is balanced without load for 30 minutes under the test conditions. Then, the test weight is connected, a shear load parallel to the bonding surface is applied, and the time before bond failure is measured in minutes. If a holding time of 10,000 minutes is reached, the test is terminated before bond failure.

[0130] Biodegradability and decomposition characteristics:

[0131] DIN EN 13432:2000-12 provides the basis for verifying the compostability of plastics, especially packaging. As part of the test, the aerobic biodegradability of the sample must be verified on the one hand, and the decomposition characteristics must be verified on the other hand.

[0132] The aerobic biodegradability of plastics based on organic compounds can be determined according to EN ISO 14855:2013-04. Industrial compostability is simulated under static, controlled composting conditions. This involves chemical tests in which a degradation rate of at least 90% compared to a reference substance must be achieved within a six-month test period. The CO2 release is measured. Degradation necessarily produces water, carbon dioxide, and biomass. Cellulose is used as the reference substance.

[0133] The decomposition characteristics of the polymer were tested under laboratory-simulated composting conditions according to DIN EN ISO 20200:2016-05. Decomposition means the physical breakdown of the material into very small fragments. To pass the test, at least 90% of the material must be broken down into particles smaller than 2 mm within 6 months. The decomposition test uses commercially available compost soil, in this case, the tangocomp brand compost soil from VKN-Vertriebsgesellschaft Kompostprodukte Nord mbH. The water content of the compost soil is set at 55% to 60%. To determine the water content, three 10-g samples of the compost soil are first dried at 120 °C for 2 hours, and then the water loss is measured, and thus the water content of the soil is determined. The missing water is replenished in the form of chlorine-free tap water.

[0134] When conducting the decomposition test, first, 150 g of compost soil with a water content of 60% is placed in a 1000-ml polyethylene beaker. Then, a piece of about 25 cm 2The sample to be analyzed is placed on the first layer of soil. The sample is an adhesive (layer thickness: 200 µm), which is applied on a cellophane film (a carrier material with known degradation properties) with a thickness of 25 µm during testing. A second layer of compost soil weighing 150 g is placed on the sample. The PE cup is covered with a lid. In order to ventilate the compost, two holes with a diameter of 2.0 mm each are pre-drilled in the lid. The sample prepared in this way can be stored at 60 ± 2 °C for up to 180 days, and water is added every 3 - 4 days to compensate for water loss. After 12 weeks, the decomposition progress of the sample is evaluated by visual inspection.

[0135] Due to the large workload and high cost, the above-mentioned aerobic biodegradability test was only carried out on some samples. The decomposition characteristics of all samples were evaluated. Based on the comparison of the samples on which these two tests were carried out, the degradation characteristics of the remaining samples were qualitatively evaluated. Then the results were classified as follows according to the degree of decomposition after 12 weeks:

[0136] (+) More than 90% of the samples decomposed into particles < 2 mm;

[0137] (o) 50% to 90% of the samples decomposed into particles < 2 mm; and

[0138] (-) Less than 50% of the samples decomposed into particles < 2 mm.

[0139] Impact resistance (DuPont test)

[0140] To conduct the impact resistance test, transfer tapes were made, and the thickness of the adhesive film of each tape was 50 µm. The sample was cut into a square frame shape (outer width: 33 mm x 33 mm; tab width: 2 mm; inner size (window opening): 29 mm x 29 mm) using a laser cutting machine. Then the sample was adhered to a polycarbonate (PC) window (35 mm x 35 mm, thickness: 3 mm). On the other side of the transfer tape, a polycarbonate frame (outer width: 45 mm x 45 mm; tab width: 10 mm; inner size (window cutout): 25 mm x 25 mm; thickness: 3 mm) was adhered. The bonding area was 248 mm 2 . The bonding part was completed such that the geometric centers and diagonals were respectively overlapped with each other (corner to corner). Then the bonding part was pressed with a pressure of 248 Newtons for 5 seconds and stored for 24 hours.

[0141] Tighten the assembly of the PC frame, tape, and PC window in the sample holder, keeping the protruding edge of the frame flat. Orient the assembly horizontally. The window is adhered below the PC frame and fixed only by an adhesive connection ("free-floating"). Then insert the specimen holder into the predefined frame of the "DuPont impact tester". Insert the impact head (weight: 150 g) so that the circular impact geometry with a diameter of 24 mm is centered and flush with the freely accessible surface of the PC window from above. A weight guided by two guide rods drops vertically from a height of 5 cm. The height from which the weight drops is incremented in units of 5 cm until the applied impact energy breaks the adhesive connection and the PC window detaches from the PC frame. Perform five measurements on each sample and then determine the average value.

[0142] To make different samples comparable, the energy (E) is calculated as follows: E [J] = height [m] * object weight [kg] * 9.81 kg / m*s 2 .

[0143] A. Preparation of polyurethane prepolymer:

[0144] The polyurethane prepolymer is prepared using the solvents of the components listed in Table 2. Additionally, the polyurethane prepolymer can also be prepared solvent-free.

[0145] In each case, the method for preparing the polyurethane prepolymer is to place the solvent, all first and second diol compounds, and (if necessary) other polyols and catalysts into a reaction vessel. Homogenize the mixture using a laboratory mechanical stirrer in an inert gas environment. Add the diisocyanate and stir for 1.5 hours in an inert gas environment at room temperature. Then store the mixture in a heating cabinet at 40°C for 48 hours to complete the reaction.

[0146]

[0147]

[0148] B. Preparation of polyurethane prepolymer:

[0149] Add the photoinitiator listed in Table 2 to the polyurethane prepolymer prepared at point A, and add resin if necessary. Then homogenize the mixture for at least 5 minutes. To produce the tape, coat the mixture on a carrier made of etched PET film or a PET liner coated with a silicone release agent using a laboratory coating table. Evaporate the solvent in a convection oven at 80°C (for etched PET film) or 60°C (for PET liner coated with silicone release agent) for 15 minutes. Cover the dried film with a siliconized PET film. Irradiate the uncrosslinked film with an ultraviolet light source compatible with the initiator (dose: 1800 - 2400 mJ / cm 2)。A crosslinked film with pressure-sensitive adhesiveness having a layer thickness of 25 - 30 microns (unless otherwise specified) can be obtained.

[0150] The crosslinking of reference V2 was carried out using polyisocyanate.

[0151] C. Inspect the prepared tape

[0152] Test the performance of the tape produced according to points A and B by the above method. The results obtained are summarized in Table 3.

[0153] Table 3 - Test results

[0154]

[0155] The test results listed in Table 3 show that excellent pressure-sensitive adhesives can be obtained using another crosslinking chemistry method according to the method of the present invention, and this method can meet the various application requirements of those skilled in the art. In particular, favorable adhesive force, shear time, and impact resistance can be obtained through this method. In addition, pressure-sensitive adhesives with favorable aerobic biodegradability and good decomposition characteristics can also be obtained using the method of the present invention.

[0156] Here, pressure-sensitive adhesives with advantageous properties can be obtained in a favorable manner without showing the disadvantages of the crosslinking processes known in the prior art during the manufacturing process, thus particularly minimizing the risk of contact with or release of isocyanate compounds. The corresponding preparation method has strong tolerance to changing environmental conditions and good tolerance to the presence of additives that may react with hydroxyl or isocyanate groups. Since radiation activation can be carried out, the preparation process is very safe to use and can be carried out with time and cost savings.

[0157] D. Preparation of polyurethane resin

[0158] Prepare a favorable polyurethane resin for the crosslinked adhesive of the present invention using the components listed in Table 4. In each case, the method for preparing the polyurethane resin is to put the solvent, all polyol components, and the catalyst into a reaction vessel (of course, a solvent-free preparation method can also be adopted). Homogenize the mixture using a laboratory mechanical stirrer in an inert gas environment. Add the diisocyanate component and stir for 1.5 hours in a room-temperature inert gas environment. Then store the mixture in a heating cabinet at 40°C for 48 hours to complete the reaction. The obtained polyurethane resin can be used in solvent form or solvent-free form.

[0159] Table 4 - Preparation of polyurethane resin

[0160]

[0161] A resin-containing crosslinked adhesive has been prepared, in the process of which different resins are added to the polyurethane prepolymer according to E1 before crosslinking. Table 5 lists the obtained pressure-sensitive adhesives and the properties measured for these pressure-sensitive adhesives.

[0162] Table 5 - Resin-containing crosslinked adhesives

[0163]

[0164] The results summarized in Table 5 show that excellent adhesive properties can be obtained by using specific polyurethane resins in combination with the crosslinked adhesives produced according to the present invention, without affecting the degradation characteristics.

[0165] E. 3D printing of adhesives:

[0166] The crosslinked adhesive according to the present invention is produced by a 3D printing process and formed into a circular geometry. For this purpose, the E6 formulation prepared without solvent is used for the adhesive.

[0167] The polyurethane prepolymer used for this purpose is prepared by weighing all the first and second diol compounds and the catalyst into a reaction vessel. The mixture is homogenized using a laboratory mechanical stirrer in an inert gas environment. Diisocyanate is added, and the mixture is stirred for 0.5 hours in an inert gas environment at 40°C. Then the mixture is heated to 80°C and stirred for another 2 hours until the reaction is complete. Then an ultraviolet light initiator is added and stirred evenly for 10 minutes. Finally, it is stirred and degassed under vacuum at 80°C for 0.5 hours, and the polymer is transferred to the printing cartridge without bubbles.

[0168] The 3D printing test was successfully carried out using an X400 printer from InnovatiQ. The feeding temperature during printing was 90°C, so it was possible to ensure that the extrusion temperature was at least 70°C. At an extrusion pressure of 2.5 bar, the required circular geometry can be printed onto a plastic sheet using a 0.4 mm wide nozzle operating according to the endless piston principle. The previously uncrosslinked adhesive was irradiated with an ultraviolet light source (dose: 1800 - 2400 mJ / cm2) matching the initiator to crosslink the adhesive in the previously produced geometry.

Claims

1. A method for preparing a crosslinked adhesive, especially within the scope of a 3D printing process, the method comprising the method steps: a) Preparing a prepolymer composition comprising one or more polyurethane prepolymers, wherein, The one or more polyurethane prepolymers can be prepared by the reaction of a starting composition, the starting composition comprising: i) one or more diisocyanate compounds, ii) one or more first diol compounds, wherein the first diol compounds are selected from the group consisting of diols having terminal C-C double bonds / molecule, and iii) one or more second diol compounds different from the first diol compounds, and b) Crosslinking the polyurethane prepolymer in the prepolymer composition by a free radical reaction of the terminal C-C double bonds of the first diol compound to obtain a crosslinked polyurethane polymer.

2. The method according to claim 1, wherein, The total mass fraction of the one or more diisocyanate compounds comprised in the starting composition relative to the mass of the starting composition is from 1% to 30%.

3. The method according to claim 1 or 2, wherein, The one or more first diol compounds are selected from the group consisting of acrylates and methacrylates, preferably methacrylates.

4. The method according to any one of claims 1 to 3, wherein The total mass fraction of the one or more first diol compounds comprised in the starting composition relative to the mass of the starting composition is from 0.05% to 20%.

5. The method according to any one of claims 1 to 4, wherein The second diol compounds are selected from the group consisting of diols, the weight average molar mass Mw of which, determined by GPC, is in the range from 200 to 6000 g / mol.

6. The method according to any one of claims 1 to 5, wherein, The second diol compounds are selected from the group consisting of diols having a polyisoprene unit backbone and / or diols having a polyterpene backbone.

7. The method according to any one of claims 1 to 6, wherein, The total mass fraction of the one or more second diol compounds comprised in the starting composition relative to the mass of the starting composition is from 50% to 95%.

8. The method according to any one of claims 1 to 7, wherein, The crosslinking of the polyurethane prepolymer is effected at least in part by a free radical reaction of the terminal C-C double bonds of the first diol compound with one or more crosslinking molecules, wherein the crosslinking molecules are preferably selected from the group consisting of compounds having two or more C-C double bonds per molecule.

9. The method according to any one of claims 1 to 8, wherein During the crosslinking of the polyurethane prepolymer in the prepolymer composition, a free radical reaction of the terminal C-C double bonds of the first diol compound with one or more chain extending molecules is effected at least in part, wherein the chain extending molecules are selected from the group consisting of compounds having one C-C double bond per molecule.

10. The method according to any one of claims 1 to 9, wherein The crosslinked adhesive comprises one or more resins, wherein the resins are selected from the group consisting of polyurethane resins.

11. The method according to any one of claims 1 to 10, wherein The prepolymer composition has a dynamic viscosity in the range from 500 to 500000 Pa·s at 25°C, and / or wherein the prepolymer composition has a dynamic viscosity in the range from 2 to 2500 Pa·s at 100°C.

12. The method according to any one of claims 1 to 11, wherein, The crosslinked adhesive is a pressure-sensitive adhesive.

13. A method for preparing a tape, comprising the method steps of the method according to any one of claims 1 to 12, and further comprising, before or during method step b), the method step: b1a) Forming a prepolymer layer consisting of the prepolymer composition on a carrier layer or a release layer.

14. A method for forming a crosslinked three-dimensional adhesive structure by a 3D printing process, comprising the method steps of the method according to any one of claims 1 to 12, and further comprising the method step before or during method step b): b1b) Molding a prepolymer composition using an application unit of a 3D printing device to form a three-dimensional adhesive structure.

15. A crosslinked adhesive which is manufactured or can be manufactured by the method according to any one of claims 1 to 14.

Images