One-component foamable thermosetting epoxy compositions with reduced VOC emissions

Abstract

The present invention relates to a one-component heat-curable epoxy resin composition comprising an epoxy resin A having an average of more than one epoxide group per molecule, a latent curing agent for the epoxy resin, a physical or chemical blowing agent BA, and at least one copolymer CP containing ethylene monomer residues and residues of a first comonomer having one or more functional groups selected from the group consisting of carboxylic acids and their salts, carboxylic acid anhydrides, and epoxides. The epoxy resin adhesive is characterized by a low VOC content, especially after full curing at about 200°C for 30 minutes.

Description

[Technical Field]

[0001] The present invention relates to the field of heat-foamable, one-component, thermosetting epoxy resin compositions, in particular for producing structural foams and reinforcing elements for hollow structures comprising such heat-foamable compositions, to a method for producing such reinforcing elements, to their use for reinforcing hollow structures, and to a method for reinforcing hollow structures. [Background technology]

[0002] Heat-foaming, thermosetting epoxy resin adhesives have found an important application area in vehicle manufacturing, particularly when foam cavities are formed in the body-in-white.

[0003] Manufactured products often contain openings and cavities or other hollow parts that are formed as a result of the manufacturing process and / or are designed for other reasons, such as weight reduction. For example, an automobile may contain several such openings and cavities throughout the vehicle, such as in the vehicle pillars.

[0004] In many cases, it is desirable to reinforce the hollow structures of manufactured products, such as vehicle pillars, with reinforcing elements incorporated into the openings or cavities to increase their resistance to mechanical stresses while retaining the advantage of the low weight of the hollow structures.

[0005] Such elements used for reinforcement, which often consist of a carrier made of plastic, metal, or other rigid material and one or more layers of epoxy resin additive bonded thereto, particularly by injection molding, can expand their volume when heat or other physical or chemical forms of energy are introduced. Such components may even consist entirely of foamable materials. Using appropriate structures, it is possible to insert the reinforcing elements into the cavities of the structure to be reinforced during the manufacturing process while simultaneously making the internal walls and / or cavities of the structure to be reinforced liquid-compatible. For example, during the vehicle manufacturing process, hollow parts of a metal frame can be mostly coated with an electrocoat coating solution after the reinforcing elements are installed. During a subsequent heat treatment step, the epoxy resin composition expands and the reinforcing elements fill, i.e., reinforce, the cavities.

[0006] Currently used heat-foamable epoxy resin compositions are often composed of a solid epoxy resin. These compositions also contain a blowing agent. The epoxy resin is activated under activation conditions, such as high temperature, during which the blowing agent decomposes to release gases such as nitrogen or carbon monoxide, or physically expands. This results in the aforementioned volume expansion and the formation of a stable foam, which ideally fills the cavity as intended and adheres to its walls.

[0007] Such heat-foamable epoxy resin compositions currently contain dispersing aids or homogenizers (sometimes also called wetting agents or surfactants) to facilitate obtaining a uniformly mixed composition.

[0008] For example, the document US Patent No. 11,447,599 describes a material suitable for reinforcing vehicles in the transportation industry, which discloses a material comprising an epoxy resin, a hardener, a foaming agent, and also an ethylene homopolymer wax as a processing aid.

[0009] Heat-foamable epoxy resin compositions are cured at high temperatures, typically around 175°C, but the drawback of such curing temperatures is that the cured material may release significant amounts of components, which can be tracked by solids content measurements, VOC measurements, or fogging experiments.

[0010] It would therefore be desirable to have heat-foamable compositions that do not suffer from such limitations and that, after curing, exhibit particularly good material properties, in particular good adhesion onto metal substrates. Summary of the Invention [Problem to be solved by the invention]

[0011] It is therefore an object of the present invention to provide a heat-foamable epoxy resin composition that provides a low VOC content, and exhibits good material properties and good adhesion to substrates, especially metal substrates, especially after full curing at about 200°C for 30 minutes. [Means for solving the problem]

[0012] Surprisingly, it has been found that this object can be achieved by means of one-component heat-curing epoxy compositions as defined in claim 1. In addition, those one-component heat-curing epoxy compositions exhibit good mechanical properties and good adhesion onto metal-based substrates.

[0013] It has been surprisingly found that the addition of ethylene homopolymer wax as a processing aid contributes to a significant reduction in the VOC content emitted from the cured material, while still providing improved processability. Even more surprisingly, it has been found that the substitution of at least one copolymer CP, as described below, strongly reduces the increase in VOC and FOG emissions, in some cases even below the values ​​for compositions that do not contain any processing aid.

[0014] Further aspects of the invention are the subject of further independent claims. Particularly preferred embodiments of the invention are the subject of the dependent claims. DETAILED DESCRIPTION OF THE INVENTION

[0015] Thus, the present invention provides: a) at least one epoxy resin A having an average of more than one epoxide group per molecule; b) at least one latent hardener for the epoxy resin; and c) at least one physical or chemical blowing agent BA; and d) at least one copolymer CP comprising residues of an ethylene monomer and a first comonomer having one or more functional groups selected from the group consisting of carboxylic acids and their salts, carboxylic acid anhydrides, and epoxides, wherein the at least one copolymer CP is present in an amount of 1 to 10 wt %, preferably 2 to 5 wt %, and more preferably 2.5 to 4 wt %, based on the total weight of the one-component heat-curable epoxy resin composition. The present invention relates to a one-component heat-curable epoxy resin composition comprising:

[0016] The epoxy resin composition is a one-component system, meaning that the components of the epoxy resin composition, more specifically the epoxy resin and its curing agent, are present in one component and curing does not occur at normal ambient or room temperature, and therefore can be handled in this form, as opposed to a two-component system, where the components cannot be mixed until just before use.

[0017] Curing of one-component epoxy resin compositions is typically achieved by heating at temperatures above 70°C, for example in the range of 100 to 220°C.

[0018] The prefix "poly" in expressions such as polyol or polyisocyanate indicates that the compound has two or more of the listed groups. For example, a polyisocyanate is a compound with two or more isocyanate groups.

[0019] The expression "independently of each other" as used below means that in the same molecule, two or more similarly expressed substituents may have the same or different meanings, depending on their definition.

[0020] The dotted lines in the formulae herein represent in each case the bond between the substituent in question and the associated remainder of the molecule.

[0021] In this case, room temperature refers to a temperature of 23°C unless otherwise specified.

[0022] The thermosetting one-component epoxy resin composition comprises at least one epoxy resin A containing, on average, more than one epoxide group per molecule, the epoxide groups preferably being in the form of glycidyl ether groups.

[0023] The proportion of the epoxy resin A having an average of more than one epoxide group per molecule is preferably 30 to 90% by weight, 35 to 85% by weight, 40 to 75% by weight, more preferably 45 to 60% by weight, based on the total weight of the one-component thermosetting epoxy resin composition.

[0024] Epoxy resin A, which has an average of more than one epoxide group per molecule, is preferably a liquid or solid epoxy resin, more preferably a solid epoxy resin. The term "solid epoxy resin" is very familiar to those skilled in the epoxide field and is used in contrast to "liquid epoxy resin." Solid resins have glass transition temperatures above room temperature, meaning that at room temperature they can be pulverized into a pourable powder. Preferably, more than 70% by weight of epoxy resin A is a solid epoxy resin, more preferably more than 80%, 90%, 95%, or 98% by weight.

[0025] A preferred epoxy resin has the formula (I): [ka]

[0026] In this formula, the substituents R' and R" are, independently of each other, either H or CH3.

[0027] In solid epoxy resins, the subscript s has a value greater than 1.5, more particularly between 2 and 12.

[0028] Solid epoxy resins of this type are commercially available from, for example, Dow or Huntsman or Hexion.

[0029] Compounds of formula (I) having a subscript s of 1 to 1.5 are known in the art as semi-solid epoxy resins. For purposes of the present invention, they are considered equivalent to solid resins. However, preferred solid epoxy resins are those in the narrower sense, i.e., epoxy resins whose subscript s is greater than 1.5.

[0030] In the case of liquid epoxy resins, the subscript s has a value lower than 1. Preferably, s has a value lower than 0.2.

[0031] The resins in question are therefore preferably diglycidyl ethers of bisphenol A (DGEBA), bisphenol F or even bisphenol A / F. Liquid resins of these types are commercially available, for example, as Araldite® GY250, Araldite® PY304, Araldite® GY282 (Huntsman), or DER® 331 or DER® 330 (Dow), or Epikote 828 (Hexion).

[0032] Further preferred epoxy resins A are those known as epoxy novolacs. These compounds specifically have the formula: [ka] or CH2, R1 is H or methyl, and z is 0-7.

[0033] More particularly, they are phenol-epoxy or cresol-epoxy novolacs (R2 = CH2).

[0034] These types of epoxy resins are commercially available from Huntsman under the tradenames EPN or ECN, also Tactix®, or from DOW Chemical as part of the DEN™ product line.

[0035] The epoxy resin A is preferably a solid epoxy resin of formula (I).

[0036] The thermosetting one-component epoxy resin composition further includes at least one latent curing agent for the epoxy resin. The latent curing agent is substantially inactive at room temperature, but is activated by elevated temperature, typically at temperatures above 70°C, thereby initiating the curing reaction. Conventional latent curing agents for epoxy resins can be used. Nitrogen-containing latent curing agents for epoxy resins are preferred.

[0037] The latent hardener is preferably selected from the following: dicyandiamide, guanamine, guanidine, aminoguanidine and their derivatives, substituted ureas, imidazoles, and amine complexes, preferably dicyandiamide.

[0038] The latent curing agent is preferably used in a stoichiometric amount based on the epoxy groups in the composition, and the molar ratio of epoxy groups to active hydrogens in the latent curing agent is preferably 0.8 to 1.2, particularly 0.9 to 1.1, and preferably 0.95 to 1.05.

[0039] The proportion of the latent curing agent is preferably 0.1 to 15% by weight, more preferably 0.2 to 5% by weight, and more particularly 0.5 to 3% by weight, based on the total weight of the epoxy resin composition.

[0040] The one-component heat-curable epoxy resin composition includes d) at least one copolymer CP comprising residues of an ethylene monomer and a first comonomer having one or more functional groups selected from the group consisting of carboxylic acids and their salts, carboxylic acid anhydrides, and epoxides.

[0041] It has been surprisingly found that polymers typically used as processing waxes for thermosetting epoxy resin compositions, particularly polymers based on ethylene monomer residues without the comonomer, cause a significant increase in VOC and FOG emissions. This is shown, for example, in Table 2, by comparing Ref. 1 with Ref. 2 and Ref. 3. Even more surprisingly, it has been found that replacing these polymers with copolymers CP from a first comonomer having one or more functional groups selected from the group consisting of carboxylic acids and their salts, carboxylic acid anhydrides, and epoxides significantly reduces the increase in VOC and FOG emissions, in some cases even lower than the values ​​for compositions without any processing wax. This is shown, for example, in Table 2, by comparing Ex. 1 to Ex. 5 with Ref. 1, Ref. 2, and Ref. 3.

[0042] In addition, it was surprisingly found that, although these copolymers CP provide expansion suppression at high and low expansion temperatures (160°C and 200°C, respectively), their expansion behavior at the standard curing temperature in the automotive industry (about 175°C) is comparable to that of thermosetting epoxy resin compositions containing processing aids or processing aids based purely on ethylene monomer residues. Such suppression in expansion is always associated with improvements in the mechanical properties of the cured expansion composition, such as tensile strength, modulus, and elongation at break. In particular, in the context of higher or lower curing temperatures, it is sometimes difficult to obtain sufficiently good mechanical properties due to suboptimal curing conditions caused by technical problems or special requirements during the curing process. Therefore, suppression of expansion, especially at these temperatures, is particularly desirable. This is particularly important at high temperatures such as 200°C, where this problem is most pronounced.

[0043] The one-component heat-curable epoxy resin composition contains d) at least one copolymer CP in an amount of 1 to 10 wt %, preferably 2 to 5 wt %, more preferably 2.5 to 4 wt %, based on the total weight of the one-component heat-curable epoxy resin composition.

[0044] If the amount exceeds 10% by weight, it is disadvantageous in terms of adhesion of the cured thermosetting epoxy resin composition, particularly to metals, whereas if the amount is less than 1% by weight, it is disadvantageous in terms of improving the processing performance of the thermosetting epoxy resin composition.

[0045] Preferably, the at least one copolymer CP has a melt flow index ("MFI") in the range of 2 to 20 g / 10 min, preferably 4 to 10 g / 10 min, measured according to ASTM D-1238 (2020 edition, 190°C / 2.16 kg).

[0046] It is further preferred if the at least one copolymer CP has a melting point, measured according to ISO 11357-3:2018, in the range of 60° C. to 120° C., preferably 85° C. to 110° C. Temperatures below 60° C. are disadvantageous in that they increase the tack of the uncured thermosetting epoxy resin composition.

[0047] Preferably, the ethylene monomer of the copolymer comprises at least 50 weight percent ("wt %), more preferably at least 60 wt %, and most preferably at least 70 wt % of the total α-olefin content of the copolymer CP.

[0048] The at least one copolymer CP comprises residues of a first comonomer having one or more functional groups selected from the group consisting of carboxylic acids and their salts, carboxylic acid anhydrides, and epoxides.

[0049] A preferred first comonomer having a carboxylic acid functionality is selected from the group consisting of acrylic acid and methacrylic acid, preferably methacrylic acid. Examples of commercially available copolymers are Surlyn 1802 (MA) and Nucrel 3990 (AA).

[0050] The fact that the first comonomer is methacrylic acid is advantageous in terms of VOC and FOG, especially low VOC values, and also contributes to a stronger suppression of expansion at 200°C. This can be seen, for example, by comparing Ex.2 with Ex.1 and Ex.3.

[0051] A suitable first comonomer having carboxylic acid anhydride functionality has maleic anhydride functionality. An example of a commercially available copolymer is Lotader™ 3210, which is an anhydride-functionalized polyethylene (poly(ethylene-co-butyl acrylate-co-maleic anhydride random terpolymer) available from Arkema, Inc.

[0052] A suitable first comonomer having an epoxide functionality is a glycidyl ester of a carboxylic acid, preferably an ester of acrylic or methacrylic acid, more preferably selected from the group consisting of glycidyl acrylate, glycidyl methacrylate, and allyl glycidyl ether, and most preferably glycidyl methacrylate. One example of a commercially available copolymer is Lotader™ AX8840, which is an epoxy-functionalized polyethylene (random copolymer of poly(ethylene-co-glycidyl methacrylate)) available from Arkema, Inc.

[0053] Copolymers CP containing a first comonomer with an epoxide functionality are advantageous in that they have lower VOC and FOG values, which also contribute to a stronger suppression of expansion at 160°C. This can be seen, for example, by comparing Ex.1 with Ex.2 and Ex.3.

[0054] This effect is particularly pronounced when the copolymer CP does not contain any additional comonomers in addition to the first comonomer having one or more functional groups selected from the group consisting of carboxylic acids and their salts, carboxylic anhydrides, and epoxides. Such additional comonomers are, for example, those described below. Therefore, it is particularly advantageous if the copolymer CP consists of ethylene monomer residues and residues of a first comonomer having one or more functional groups selected from the group consisting of carboxylic acids and their salts, carboxylic anhydrides, and epoxides. It is most preferred if the copolymer CP consists of ethylene monomer residues and residues of a first comonomer selected from the group consisting of methacrylic acid and glycidyl methacrylate.

[0055] This can be seen, for example, in a comparison of Ex. 1 with Ex. 4 and Ex. 5, where Ex. 1 shows higher expansion inhibition at 200°C and lower VOC figures.

[0056] The copolymer CP preferably contains the first comonomer in an amount of 0.5 to 12 wt %, preferably 2 to 10 wt %, based on the total weight of the copolymer CP. The amount of the first comonomer can be confirmed by analytical methods known in the art, such as, but not limited to, Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance, and differential scanning calorimetry. Preferably, the amount of the first comonomer is determined by Fourier transform infrared spectroscopy (FTIR).

[0057] Furthermore, it may be preferred if the at least one copolymer CP comprises additional comonomer residues, preferably selected from the group consisting of unsaturated esters and acetates, more preferably methyl acrylate, ethyl acrylate, butyl acrylate, and vinyl acetate, most preferably butyl acrylate.

[0058] The comonomer residues are preferably present in an amount of 1 to 30% by weight, preferably 5 to 25% by weight, based on the total weight of the copolymer CP.

[0059] An example of an additional commercially available copolymer CP containing vinyl acetate as a comonomer residue is LOTADER® AX8670T from Arkema Inc., which is a random ethylene-vinyl acetate-glycidyl methacrylate terpolymer (EVA-GMA). An example of a commercially available copolymer CP containing butyl acrylate as an additional comonomer residue is LOTADER® 3210 from Arkema Inc., which is a random ethylene-butyl acrylate-maleic anhydride terpolymer. An example of a commercially available copolymer CP containing methyl acrylate as an additional comonomer residue is LOTADER® AX8900 from Arkema Inc., which is a random ethylene-methyl acrylate-glycidyl methacrylate terpolymer.

[0060] If the copolymer CP contains additional comonomer residues, it is particularly preferred that the copolymer CP contains a first comonomer having an epoxide functionality as previously described, most preferably glycidyl methacrylate.

[0061] If the copolymer CP comprises additional comonomer residues, it is particularly preferred if the copolymer CP consists of ethylene monomer residues, residues of a first comonomer having one or more functional groups selected from the group consisting of carboxylic acids and their salts, carboxylic acid anhydrides, and epoxides, and the additional comonomer residues.

[0062] The one-component heat-curable epoxy resin composition may further comprise at least one toughening agent D. The toughening agents D may be solid or liquid. More specifically, the toughening agent D is selected from the group consisting of end-blocked polyurethane polymer D1, liquid rubber D2, and core-shell polymer D3. Preferably, the additional toughening agent D is selected from the group consisting of end-blocked polyurethane polymer D1 and liquid rubber D2, and most preferably liquid rubber D2.

[0063] Suitable liquid rubbers D2 are carboxyl group (eg carboxylic acid group) containing acrylonitrile / butadiene rubbers ABR and their reaction products with polyepoxides and / or polyphenols.

[0064] Such carboxyl-containing acrylonitrile / butadiene rubber ABR may contain pendant carboxyl groups or carboxyl groups.

[0065] The carboxyl group-containing acrylonitrile / butadiene rubber ABR preferably has a carboxyl content of 0.005 EPHR (equivalents per hundred parts of rubber) to 0.4 EPHR, more preferably 0.01 EPHR to 0.2 EPHR, and even more preferably 0.05 EPHR to 0.1 EPHR.

[0066] In the case of a carboxyl group-containing acrylonitrile / butadiene rubber ABR, the carboxyl group is preferably provided by a termonomer, such as methacrylic acid, and the carboxyl group-containing acrylonitrile / butadiene rubber ABR is preferably an acrylonitrile / butadiene / methacrylic acid rubber.

[0067] A particularly preferred carboxyl group-containing acrylonitrile / butadiene rubber ABR is available from Nippon Zeon under the trade name Hycar (now available under the trade name NIPOL).

[0068] The carboxyl group-containing acrylonitrile / butadiene rubber ABR preferably contains 10% by weight to 50% by weight of nitrile, more preferably 20% by weight to 40% by weight of nitrile, and even more preferably 25% by weight to 35% by weight of nitrile.

[0069] More preferably, the liquid rubber D2 is an epoxy resin-modified acrylonitrile-butadiene copolymer. For example, it can be produced by reacting a carboxy- or epoxy-terminated acrylonitrile-butadiene copolymer (also called liquid rubber) with a polyepoxide and / or a polyphenol. Preferably, the at least one epoxy resin-modified acrylonitrile-butadiene copolymer is obtained by reacting one or more carboxyl-terminated butadiene-acrylonitrile copolymers (CTBN) with one or more solid epoxy resins of formula (I) and / or one or more liquid epoxy resins of formula (I) and / or one or more novolac-type epoxy resins.

[0070] Suitable epoxy resin-modified acrylonitrile-butadiene copolymers are commercially available, for example, from Schill & Seilacher Gruppe (Germany) under the Struktol® trade name, such as Struktol® 3604, Struktol® 3606, Struktol® 3611, Struktol® 3614, Struktol® 3654, and Struktol® 3656. Suitable epoxy resin-modified acrylonitrile-butadiene copolymers also include the polymer mixtures disclosed in U.S. Pat. No. 9,796,809 B2 as "impact strength improving agents for epoxy resin compositions."

[0071] The proportion of toughness improver D is preferably 1 to 10% by weight, more preferably 2.5 to 7.5% by weight, based on the total weight of the epoxy resin composition.

[0072] In a preferred embodiment, the one-component thermosetting epoxy resin composition further comprises at least one filler F. Preferred fillers include mica, talc, kaolin, wollastonite, feldspar, syenite, chlorite, bentonite, montmorillonite, calcium carbonate (precipitated or ground), dolomite, quartz, silica (fumed or precipitated), cristobalite, calcium oxide, aluminum hydroxide, magnesium oxide, hollow ceramic beads, hollow glass beads, hollow organic beads, glass beads, glass fibers, and color pigments. Particularly preferred fillers are selected from the group consisting of calcium carbonate, calcium oxide, talc, glass fibers, hollow glass beads, and fumed silica, more preferably talc, glass fibers, hollow glass beads, calcium carbonate, and fumed silica.

[0073] The proportion of all fillers F taken together is advantageously between 5 and 50% by weight, preferably between 15 and 45% by weight, more preferably between 20 and 40% by weight, based on the total weight of the epoxy resin composition.

[0074] The one-component heat-curable epoxy resin composition may contain further components, such as catalysts, thixotropic agents, plasticizers, solvents, dyes and pigments, corrosion inhibitors, defoamers, and adhesion promoters, among others.

[0075] The one-component heat-curable epoxy resin composition includes at least one physical or chemical blowing agent BA.

[0076] Chemical blowing agents are organic or inorganic substances that form or separate gaseous substances under the influence of temperature, humidity, electromagnetic radiation, or chemicals. Such substances are specifically azodicarbonamides, sulfohydrazides, bicarbonates, or carbonates. Compounds that change into a gaseous state upon a change in temperature, pressure, or volume, especially upon an increase in temperature, thereby forming a foam structure through volume expansion, can be used as physical blowing agents. Such physical blowing agents are, in particular, liquids that evaporate at elevated temperatures. Furthermore, gases and low-boiling liquids can also be used as physical blowing agents, but they are introduced into the composition in microencapsulated form. Both chemical and physical blowing agents can form a foam structure in a polymer composition.

[0077] Suitable physical blowing agents are expandable microspheres consisting of a thermoplastic shell filled with a heat-expandable liquid or gas, such as those commercially available from Akzo Nobel (Netherlands) under the trade name Expancel®.

[0078] Preferably, the at least one physical or chemical blowing agent BA has an activation temperature of 120°C to 220°C, preferably 140°C to 200°C.

[0079] The proportion of the blowing agent BA is advantageously between 0.1 and 5% by weight, preferably between 0.1 and 3% by weight, in particular between 1 and 2% by weight, based on the total weight of the epoxy resin composition.

[0080] The one-component heat-curable epoxy resin composition may further contain one or more additives. Preferred additives that can be used are antioxidants, UV stabilizers, dyes, insecticides, or flame retardants.

[0081] The proportion of processing aids is advantageously between 1 and 8% by weight, preferably between 2 and 5% by weight, based on the total weight of the composition.

[0082] The one-component thermosetting epoxy resin composition preferably has a melt flow index (MFI) of 0.5 to 15 g / 10 min, particularly 1 to 10 g / 10 min, preferably 1 to 5 g / 10 min, and most preferably 1 to 3 g / 10 min, measured according to ASTM D1238 (2020 edition) at 110°C and 2.16 kg.

[0083] Preferably, the one-component thermosetting epoxy resin composition is an injection-moldable mixture, i.e., the mixture has a viscosity suitable for injection molding at the processing temperature, and in particular can be injection-molded without foaming.

[0084] Particularly preferred thermosetting one-component epoxy resin compositions include: - 30 to 90 wt. %, 35 to 85 wt. %, 40 to 75 wt. %, more preferably 45 to 60 wt. %, based on the total weight of the one-component heat-curable epoxy resin composition, of at least one epoxy resin A having an average of more than one epoxide group per molecule; - 1 to 10 wt. %, preferably 2 to 5 wt. %, more preferably 2.5 to 4 wt. %, based on the total weight of the one-component heat-curable epoxy resin composition, of at least one copolymer CP comprising residues of ethylene monomers and of a first comonomer having one or more functional groups selected from the group consisting of carboxylic acids and their salts, carboxylic acid anhydrides, and epoxides; - 0.1 to 15% by weight, more preferably 0.2 to 5% by weight, more particularly 0.5 to 3% by weight, of at least one latent curing agent for epoxy resins, more particularly dicyandiamide, based on the total weight of the one-component heat-curable epoxy resin composition; - preferably 1 to 10 wt. %, more preferably 2.5 to 7.5 wt. %, based on the total weight of the one-component heat-curable epoxy resin composition, of at least one toughening agent D selected from the group consisting of end-blocked polyurethane polymers D1, liquid rubbers D2, and core-shell polymers D3, preferably liquid rubbers D2, more preferably carboxyl-group (e.g., carboxylic acid)-containing acrylonitrile / butadiene rubbers ABR and their reaction products with polyepoxides and / or polyphenols; - 0.1 to 5% by weight, preferably 0.1 to 3% by weight, in particular 1 to 2% by weight, of a blowing agent BA, based on the total weight of the epoxy resin composition; - preferably 5 to 50 wt. %, more preferably 15 to 45 wt. %, and most preferably 20 to 40 wt. % of a filler F selected from the group consisting of talc, glass fiber, hollow glass beads, calcium carbonate, and fumed silica, based on the total weight of the epoxy resin composition.

[0085] It can be further advantageous if the preferred one-component heat-curable epoxy resin composition comprises the above-mentioned components in an amount of more than 80% by weight, preferably more than 90% by weight, more particularly more than 95% by weight, particularly preferably more than 98% by weight, and most preferably more than 99% by weight, based on the total weight of the epoxy resin composition.

[0086] Preferably, the one-component heat-curable epoxy resin composition is tack-free at 23° C. The term “tack-free” is understood herein to mean immediate tack, i.e., a “tack” that has such low adhesive strength at 23° C. that even if you press your thumb onto the one-component heat-curable epoxy resin composition with a pressure of about 5 kg for 1 second, your thumb will not adhere to the surface layer of the composition layer, i.e., you will not be able to lift off the one-component heat-curable epoxy resin composition.

[0087] The compositions according to the invention can be obtained by mixing the components in any suitable mixing device, such as, for example: a dispersing mixer, a planetary mixer, a twin-screw mixer, a continuous mixer, an extruder, or a twin-screw extruder.

[0088] After mixing, the resulting composition can be formed into the desired shape, for example, by extrusion, blow molding, pelletizing, injection molding, compression molding, stamping or punching, or any other suitable method.

[0089] Mixing the ingredients preferably includes an extrusion step, and the mixed and extruded composition is then granulated. The granulated composition is then preferably injection molded into the desired shape.

[0090] The foaming of the one-component thermosetting epoxy resin composition is preferably carried out independently of, and particularly before, the curing of the epoxy resin composition. As a result, the epoxy resin composition only cures after most of the foaming of the epoxy resin composition has occurred. Alternatively, the epoxy resin composition is allowed to reach the target location via foaming after curing. Therefore, the curing temperature of the epoxy resin composition is preferably set higher than the foaming temperature of the epoxy resin composition.

[0091] Preferably, the foamable epoxy resin composition exhibits the following properties (measurements are described in the experimental section): - Swelling at 175°C for 30 minutes: 100% to 300%, preferably 120% to 170%. - Swelling at 160°C for 30 minutes: 100% to 300%, preferably 100% to 200%. - Expansion at 200°C for 30 minutes: 100% to 300%, preferably 100% to 170%.

[0092] It is further preferred if the foamable epoxy resin composition exhibits the following adhesive and mechanical properties: - tensile strength: 3 MPa or more, preferably 4 MPa or more, more preferably 5 MPa or more; and / or preferably modulus: 400 MPa or more, preferably 500 MPa or more, more preferably 600 MPa or more; and / or preferably - Elongation at break: 0.5 to 2%, preferably 0.75 to 1.5%, more preferably 1 to 1.25%.

[0093] Another aspect of the present invention is a reinforcing element comprising the one-component thermosetting epoxy resin composition, in particular intended for reinforcement in cavities of structural members.

[0094] The one-component heat-curable epoxy resin composition is preferably coated or adhered to a carrier member.

[0095] The carrier member may be constructed from a variety of materials, with preferred materials being: plastics, especially polyurethanes, polyamides, polyesters, and polyolefins, preferably heat-resistant polymers such as poly(phenylene ether), polysulfone, or polyethersulfone (especially foamed versions); metals, especially aluminum and steel; or various combinations of these materials.

[0096] Furthermore, the carrier member may have any structure. For example, it may be solid, hollow, or have a lattice-like structure. The surface of the carrier member may typically be smooth, rough, or structured. In addition to its function as a carrier for the foam material, the carrier member may also contribute to its structural reinforcement.

[0097] It is also possible for the reinforcing element to have no carrier member and to consist entirely of the one-component thermosetting epoxy resin composition.

[0098] The carrier member and the reinforcing element comprising the one-component thermosetting epoxy resin composition are preferably manufactured by injection molding.

[0099] If the carrier member is made of a material that can be processed by injection molding, a two-component injection molding process is typically used. First, the first component (in this case, the carrier member) is injection molded. After the first component solidifies, the cavity in the mold is expanded or adapted, or the molded part is transferred to a new mold, and the second component (in this case, an epoxy resin composition) is molded onto the first component using a second injection unit. If the carrier member is made of a material, such as metal, that cannot be manufactured by the injection molding process, the carrier member is placed in a suitable molding tool, and the epoxy resin composition is injection molded onto the carrier member.

[0100] Of course, the possibility exists for securing the epoxy resin composition to the carrier member by a variety of other securing means or methods.

[0101] In the case of the above-mentioned reinforcing elements, it is further advantageous if the epoxy resin composition can be foamed and cured by heating at a temperature between 120°C and 220°C, preferably between 140°C and 200°C, preferably at said temperature for a time period between 10 and 60 minutes.

[0102] Furthermore, the present invention also includes the use of a reinforcing element as described above to reinforce cavities in structural members. Structural members of this type are preferably used in the bodies and / or frames of transport means and vehicles, especially water, land or air vehicles. The present invention also includes the use of a reinforcing element according to the invention in the body or frame, preferably in automobiles (especially A-, B-, C- or D-pillars), trucks, rail vehicles, boats, ships, helicopters and aircraft, most preferably in automobiles.

[0103] Thus, a further aspect of the present invention is a method for producing a medicament for use in a method comprising the steps of: i) placing a reinforcing element in the cavity according to the previous description; ii) heating the reinforcing element at a temperature between 120°C and 220°C, preferably between 140°C and 200°C, preferably for 10 to 60 minutes. The present invention relates to a method for reinforcing a structural member, comprising:

[0104] Preferably, step i) is followed by step ii).

[0105] Therefore, yet another aspect of the present invention is the use of a copolymer CP, as previously described, comprising residues of an ethylene monomer and a first comonomer having one or more functional groups selected from the group consisting of carboxylic acids and their salts, carboxylic acid anhydrides, and epoxides, for reducing the VOC emissions of a one-component heat-curable epoxy resin composition after curing the composition at a temperature in the range of 160-200°C, preferably 180-200°C, most preferably at 200°C, for 30 minutes.

[0106] Preferably, the copolymer CP has the preferred characteristics and / or ratios as previously described and is included in the preferred amounts in the one-component heat-curable epoxy resin composition.

[0107] The reduction in VOC emissions is compared to a one-component heat-curable epoxy resin composition that does not have the above-mentioned feature of d) at least one copolymer CP, but instead contains a dispersing aid preferably selected from a hydrocarbon resin and an ethylene homopolymer, preferably from an ethylene homopolymer. The reduction in VOC emissions is preferably determined according to the VDA 278 standard, more preferably as described in the experimental section.

[0108] In the following text, the invention will be further explained by means of examples, which are not intended to limit the invention in any way. [Example]

[0109] The raw materials in this example and the test methods used to test their respective properties are as follows:

[0110] [Table 1]

[0111] [Table 2]

[0112] Preparation of the Composition Reference compositions Ref.1 to Ref.3 and compositions Ex.1 to Ex.5 according to the present invention were prepared according to the information in Tables 1 and 2. The amounts of the base formulation shown in Table 1 are expressed in parts by weight. For compositions Ref.1 to Ref.3 and compositions Ex.1 to Ex.5 shown in Table 2, the base formulation in Table 1 was used as a base, and the indicated amounts of EH1 to EH2 or IP1 to IP5, respectively, were added, with the same amount of filler mixture removed from the base formulation in Table 1. For example, in the final formulation of Ex.1, 3 wt. % IP1 was used, based on the total weight of formulation Ex.1, and 21.1 wt. % filler mixture was used, based on the total weight of formulation Ex.1. For Ref.1, the base formulation in Table 1 was used without any changes.

[0113] The raw materials were mixed for 10 minutes using a tumble mixer. The mixture was then introduced into a twin-screw extruder (Dr. Collin ZK25 T SCD15) and compounded at a throughput of 2.5 kg / h. It was discharged onto a conveyor belt through a single-hole nozzle (3 mm). The strands thus obtained were cooled using forced air and then granulated using a Dr. Collin granulator integrated into the system. The granules thus obtained were then processed into 3 mm thick sheets using a Krauss-Maffei 110t injection molding machine.

[0114] The test methods used to test each property in this example are as follows:

[0115] Measurement of foam density / volume expansion ("expansion ratio") All samples were tested for expansion stability by heat treating each sample in an oven for 30 minutes at the temperature indicated in Table 2 (target temperature: 160°C, 175°C, or 200°C).

[0116] The volume expansion rate was quantified by measuring each sample before and after expansion. The density was determined using the water immersion method in deionized water (Archimedes' principle) according to DIN EN ISO 1183, and the mass was measured using a precision balance. The results are shown in Table 2.

[0117] Adhesion Test ("Adhesion") Cleaned and oiled steel (0.8 mm thick) specimens were bonded to a 50 x 50 x 3 mm strip of material using a 5 mm Teflon spacer and cured in a jig, maintaining a cured material thickness of 5 mm. The curing conditions were 175°C for 30 minutes. The specimens were peeled apart by hand.

[0118] The following visual evaluation was used for the appearance of the fractures thus obtained: the results were classified as CF (cohesive failure) and AF (adhesive failure), and the magnitude of the above-mentioned fractures was calculated as a % of the total fracture patterns and is shown in Table 2.

[0119] VOC / FOG measurement (“VOC”, “FOG”) VDA278 The VDA278 standard describes an analytical method for measuring emissions from components or adhesives used in automobiles. The method includes a thermal desorption step (heating a small amount of test material according to a specified process to release volatile substances), a cryofocus step (immobilizing the volatile substances in a cold trap), and a step of rapidly heating to 280°C to evaporate the volatile substances. The volatile substances are then resolved by gas chromatographic separation, and the isolated substances are detected by mass spectrometry.

[0120] This method determines two semi-quantitative cumulative values: VOC value (the sum of readily volatile to moderately volatile substances calculated as toluene equivalent to n-pentacosane (C25)) and FOG value (low-volatile substances calculated as hexadecane equivalent, with boiling points ranging from C14 to C32 n-alkanes that readily condense at room temperature). To determine the VOC value, the sample is heated to 90°C for 30 minutes. The FOG value is determined by reheating the sample used to determine the VOC value at 120°C for 60 minutes. The VDA278 standard does not specify any acceptable limits for VOC or FOG values.

[0121] Preferred values ​​are less than 0.5 mg / g, more preferably less than 0.1 mg / g, even more preferably less than 0.05 mg / g for VOCs, and less than 2 mg / g, more preferably less than 0.1 mg / g, even more preferably less than 0.05 mg / g for FOGs.

[0122] [Table 3]

[0123] [Table 4]

Claims

1. A one-component thermosetting epoxy resin composition, a) at least one epoxy resin A having an average of more than one epoxide group per molecule; b) at least one latent hardener for the epoxy resin; and c) at least one physical or chemical blowing agent BA; and d) at least one copolymer CP, the at least one copolymer CP comprising residues of an ethylene monomer and a first comonomer having one or more functional groups selected from the group consisting of carboxylic acids and their salts, carboxylic acid anhydrides, and epoxides, wherein the at least one copolymer CP is present in an amount of 1 to 10 wt %, preferably 2 to 5 wt %, and more preferably 2.5 to 4 wt %, based on the total weight of the one-component heat-curable epoxy resin composition. A one-component heat-curable epoxy resin composition comprising:

2. 2. The one-component heat-curable epoxy resin composition according to claim 1, wherein the proportion of the epoxy resin A having an average of more than one epoxide group per molecule is 30 to 90 wt %, 35 to 85 wt %, 40 to 75 wt %, more preferably 45 to 60 wt %, based on the total weight of the one-component heat-curable epoxy resin composition.

3. The epoxy resin A is a solid epoxy resin, and preferably the epoxy resin A is represented by the formula (I) 【Chemistry 1】 wherein R′ and R″ of the substituents are independently H or CH ３ and the subscript s has a value greater than 1.5, more particularly from 2 to 12.

4. 4. The one-component heat-curable epoxy resin composition according to any one of claims 1 to 3, wherein the at least one copolymer CP has a melt flow index ("MFI") in the range of 2 to 20 g / 10 min, preferably 4 to 10 g / 10 min, measured according to ASTM D-1238 (2020 edition, 190°C / 2.16 kg).

5. 5. The one-component heat-curable epoxy resin composition according to claim 1, wherein the at least one copolymer CP has a melting point, measured according to ISO 11357-3:2018, in the range of 60°C to 120°C, preferably 85°C to 110°C, temperatures below 60°C being disadvantageous in that the tack of the uncured heat-curable epoxy resin composition increases.

6. 6. The one-component heat-curable epoxy resin composition according to claim 1, wherein in the at least one copolymer CP, the first comonomer has a carboxylic acid functionality, the first comonomer being preferably selected from the group consisting of acrylic acid and methacrylic acid, preferably methacrylic acid.

7. 7. The one-component heat-curable epoxy resin composition according to any one of claims 1 to 6, wherein in the at least one copolymer CP, the first comonomer has an epoxide functional group, the first comonomer being preferably a glycidyl ester of a carboxylic acid, more preferably an ester of acrylic acid or methacrylic acid, even more preferably selected from the list consisting of glycidyl acrylate, glycidyl methacrylate, and allyl glycidyl ether, and most preferably glycidyl methacrylate.

8. 8. The one-component heat-curable epoxy resin composition according to claim 1, wherein the copolymer CP is composed of ethylene monomer residues and residues of a first comonomer having one or more functional groups selected from the group consisting of carboxylic acids and their salts, carboxylic acid anhydrides, and epoxides, and most preferably the copolymer CP is composed of ethylene monomer residues and residues of a first comonomer selected from the group consisting of methacrylic acid and glycidyl methacrylate.

9. 8. The one-component heat-curable epoxy resin composition according to any one of claims 1 to 7, wherein the at least one copolymer CP comprises an additional comonomer residue selected from the group consisting of unsaturated esters and acetates, more preferably selected from methyl acrylate, ethyl acrylate, butyl acrylate, and vinyl acetate, and most preferably butyl acrylate.

10. 10. The one-component heat-curable epoxy resin composition according to any one of claims 1 to 9, wherein the one-component heat-curable epoxy resin composition further comprises at least one toughness improver D selected from the group consisting of end-blocked polyurethane polymer D1, liquid rubber D2, and core-shell polymer D3, preferably liquid rubber D2, more preferably carboxyl group-containing acrylonitrile / butadiene rubber ABR and reaction products thereof with polyepoxides and / or polyphenols, and wherein the proportion of the toughness improver D is preferably 1 to 10 wt%, more preferably 2.5 to 7.5 wt%, based on the total weight of the one-component heat-curable epoxy resin composition.

11. The one-component heat-curable epoxy resin composition according to any one of claims 1 to 10, wherein the latent curing agent is selected from dicyandiamide, guanamine, guanidine, aminoguanidine and their derivatives, substituted ureas, imidazoles, and amine complexes, preferably dicyandiamide.

12. 12. The one-component heat-curable epoxy resin composition according to any one of claims 1 to 11, wherein the one-component heat-curable epoxy resin composition further comprises at least one filler F, wherein the at least one filler F is selected from the group consisting of calcium carbonate, calcium oxide, talc, glass fiber and fumed silica, more preferably from the group consisting of talc, glass fiber and fumed silica.

13. 13. The one-component heat-curable epoxy resin composition according to claim 1, wherein the proportion of the blowing agent BA is 0.1 to 5 wt. %, preferably 0.1 to 3 wt. %, in particular 1 to 2 wt. %, based on the total weight of the epoxy resin composition.

14. 14. The one-component heat-curable epoxy resin composition according to any one of claims 1 to 13, wherein the one-component heat-curable epoxy resin composition has a melt flow index (MFI) of 0.5 to 15 g / 10 min, in particular 1 to 10 g / 10 min, preferably 1 to 5 g / 10 min, and most preferably 1 to 3 g / 10 min, measured according to ASTM D1238 (2020 edition) at 110°C and 2.16 kg.

15. 15. A reinforcing element comprising the one-component thermosetting epoxy resin composition according to claims 1 to 14, in particular for reinforcing cavities in structural members, preferably in bodies and / or frames of means of transport and vehicles.

16. 1. A method for reinforcing a structural member, comprising: i) placing a reinforcing element according to claim 15 in a cavity of a structural member, preferably in a cavity of a structural member in the body and / or frame of a transport means and vehicle; ii) heating said reinforcing element at a temperature of 120°C to 220°C, preferably 140°C to 200°C, preferably for a period of 10 to 60 minutes; A method comprising:

17. 10. Use of a copolymer CP comprising residues of an ethylene monomer and a first comonomer having one or more functional groups selected from the group consisting of carboxylic acids and their salts, carboxylic acid anhydrides, and epoxides, preferably the copolymer CP according to any one of claims 4 to 9, for reducing VOC emissions of said one-component heat-curable epoxy resin composition after said composition has been cured at a temperature in the range of 160-200°C, preferably 180-200°C, most preferably at 200°C for 30 minutes, said reduction in VOC emissions being preferably measured according to VDA 278 standard, more preferably as described in the experimental section.

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