A dynamically vulcanized NBR toughener for one-component epoxy resin composition

Abstract

The present invention relates to a thermoplastic dynamic vulcanizate (TPV) toughener, in particular for epoxy-based structural adhesives, a method for producing such a toughener, and the use of such a toughener for toughening epoxy-based structural adhesives.

Description

[0001] A DYNAMICALLY VULCANIZED NBR TOUGHENER FOR ONE-COMPONENT EPOXY RESIN COMPOSITION

[0002] Technical field

[0003] The present invention relates to a thermoplastic dynamic vulcanizate (TPV) toughener, in particular for epoxy-based structural adhesives, in particular for one-component epoxy based structural adhesives, a method for producing such a toughener, and the use of such a toughener.

[0004] Background of the invention

[0005] Structural adhesives are high-performance adhesives designed to bond load-bearing structures. They provide significant strength, durability, and resistance to environmental factors, making them suitable for applications in the automotive sector. Epoxy based structural adhesives are composed of epoxy resins and curing agents that, when mixed, undergo a chemical reaction forming a highly cross-linked, rigid thermoset polymer.

[0006] An important area of application of epoxy based structural adhesives, also known as thermally expandable, thermosetting epoxy resin compositions, is found in vehicle construction, especially when foaming cavities in the body-in-white. Manufactured products often contain openings and cavities or other hollow parts that result from the manufacturing process and / or are designed for other reasons such as weight reduction. Motor vehicles, for example, comprise several such openings and cavities in the entire vehicle, for example in the vehicle pillars.

[0007] It is often desirable to reinforce such openings and cavities with reinforcement elements built into the opening or cavity to reinforce the hollow structure of the manufactured product, for example a vehicle pillar, so that it becomes more resistant to mechanical stress, but maintaining the low weight of the hollow structure.

[0008] To further improve the properties of structural adhesives tougheners are added. Tougheners are additives incorporated into polymers to enhance their toughness, which is the ability to absorb energy and plastically deform without fracturing.Therefore, tougheners aim to improve the impact resistance and durability of the base material.

[0009] Even if tougheners according to prior art can improve the properties of structural adhesives, such structural adhesives are often difficult to press into shape and are therefore difficult to form and process.

[0010] Accordingly, there is a need for a toughener that can be processed like a thermoplastic polymer and still provide an epoxy-based structural adhesive with good adhesion to oily metal, good toughness and heat aging.

[0011] Summary of the invention

[0012] Accordingly, it is an object of the present invention to provide a toughener that can be processed like a thermoplastic and still is an efficacious toughener, in particular for epoxy-based structural adhesives, providing good adhesion to oily metal components, good toughness and appropriate heat aging.

[0013] Surprisingly, it has been found that this objective can be achieved by a toughener consisting of a multiphase system in which dynamically vulcanized rubber particles as a discontinuous phase are dispersed in a continuous matrix phase of polymers.

[0014] Accordingly, the present invention is directed to a thermoplastic dynamic vulcanizate (TPV) toughener, in particular for epoxy-based structural adhesives, wherein the TPV toughener comprises a discrete crosslinked rubber phase formed by dynamic vulcanization of rubber, in particular acrylonitrile butadiene rubber (NBR), under shear stress in the presence of a peroxide crosslinking agent, and a continuous thermoplastic matrix phase comprising at least one solid epoxy resin and optionally one or more thermoplastic polymers, wherein the discrete crosslinked rubber phase is dispersed throughout the continuous thermoplastic matrix phase, in particular as a discontinuous phase. In an embodiment, the TPV toughener is specifically designed for toughening epoxy-based structural adhesives.

[0015] Surprisingly, it has been found that dynamic vulcanization of a crosslinkable rubber with at least one solid epoxy resin and optionally one or more thermoplastic polymersresults in a mixture, in which the rubber phase is dispersed in the polymer matrix, producing a thermoplastic dynamic vulcanizate (TPV) that is capable of improving adhesion to oily metal, toughness and heat ageing of structural adhesives.

[0016] As used herein, the term "under shear stress" refers to conditions in which mechanical forces are applied to a material in a manner that causes layers or portions of the material to slide relative to one another. In the context of dynamic vulcanization, shear stress may be applied through mixing, kneading, or stirring operations, such as those performed in a dispersion mixer, planetary mixer, Brabender mixer, twin screw mixer, continuous mixer, or extruder. The application of shear stress during vulcanization may cause the curing rubber to be tom apart into smaller domains as its molecular weight and viscosity increase due to crosslinking. In some aspects, the shear stress may be sufficient to refine the morphology of the rubber phase to produce discrete domains having a size of about one micron or smaller.

[0017] In one embodiment, a thermoplastic dynamic vulcanizate (TPV) toughener is provided. The TPV toughener comprises a discrete crosslinked rubber phase formed by dynamic vulcanization of rubber, in particular acrylonitrile butadiene rubber (NBR), under shear stress in the presence of a peroxide crosslinking agent (CA). The TPV toughener further comprises a continuous thermoplastic matrix phase comprising at least one solid epoxy resin (EP) and optionally one or more thermoplastic polymers. The discrete crosslinked rubber phase is dispersed throughout the continuous thermoplastic matrix phase, in particular as a discontinuous phase. In an embodiment, the thermoplastic dynamic vulcanizate (TPV) toughener is specifically designed for toughening epoxy-based structural adhesives.

[0018] The combination of a discrete crosslinked rubber phase dispersed in a continuous thermoplastic matrix phase provides a toughener that exhibits thermoplastic processing characteristics while delivering rubber toughening functionality. This morphology allows the toughener to flow and be shaped under heat and pressure like a thermoplastic, facilitating ease of incorporation into adhesive formulations, while the crosslinked rubber domains provide energy absorption and fracture resistance in the cured adhesive.

[0019] In an embodiment, the thermoplastic dynamic vulcanizate (TPV) toughener is specifically designed for toughening epoxy-based structural adhesives, wherein thecomposition and morphology provide compatibility with epoxy-based structural adhesives. The use of a solid epoxy resin as part of the continuous thermoplastic matrix phase may facilitate chemical compatibility between the TPV toughener and epoxy adhesive formulations into which it is incorporated. In some aspects, the discrete crosslinked rubber phase may be epoxy-functionalized, which may allow the rubber domains to react into the crosslinked epoxy network when the adhesive is cured, thereby improving interfacial adhesion between the toughener and the adhesive matrix. The morphology of finely dispersed crosslinked rubber domains within the epoxy-containing matrix may provide effective stress transfer and energy dissipation when the TPV toughener is blended into an epoxy-based structural adhesive composition.

[0020] In other embodiments, the TPV toughener may include one or more of the following features. The discrete crosslinked rubber phase may comprise rubber domains having a size of about 10 micrometer or smaller, in particular a domain size of 10-0.6 micrometer, in particular 5-0.6 micrometer, in particular 2-0.6 micrometer, in particular 1-0.6 micrometer, in particular 1-0.75 micrometer., formed by the shear stress tearing apart the curing rubber during dynamic vulcanization.

[0021] The formation of rubber domains having a size of about 10 micrometer or smaller, in particular a domain size of 10-0.6 micrometer, in particular 5-0.6 micrometer, in particular 2-0.6 micrometer, in particular 1-0.6 micrometer, in particular 1-0.75 micrometer, through shear-induced tearing during dynamic vulcanization provides a fine dispersion of the rubber phase throughout the matrix. This fine morphology enhances the toughening efficiency by increasing the interfacial area between the rubber and matrix phases, thereby improving stress transfer and energy dissipation during mechanical loading.

[0022] In an embodiment, the discrete crosslinked rubber phase may not re-agglomerate after removal of shear stress due to the crosslinked structure of the rubber domains. The prevention of re-agglomeration due to the crosslinked structure of the rubber domains ensures morphological stability of the TPV toughener during storage and subsequent processing. This stability maintains the fine dispersion of rubber domains achieved during dynamic vulcanization, preserving the toughening performance of the material over time.In an embodiment, the rubber, in particular acrylonitrile butadiene rubber (NBR), may be epoxy-functionalized.

[0023] Epoxy-functionalization of the rubber improves compatibility between the rubber phase and the epoxy resin matrix. This enhanced compatibility facilitates better interfacial adhesion, which improves stress transfer between phases and allows the epoxy-functionalized rubber to react into the crosslinked epoxy network when the adhesive is cured, further enhancing mechanical properties.

[0024] In an embodiment, the combination of rubber, in particular acrylonitrile butadiene rubber (NBR), solid epoxy resin matrix, and peroxide crosslinking agent (CA) may provide an epoxy toughener intermediate for use in epoxy adhesive formulations. Providing an epoxy toughener intermediate allows for a two-stage manufacturing approach where the toughener is first prepared and then incorporated into adhesive formulations. This approach simplifies adhesive manufacturing, enables quality control of the toughener prior to adhesive formulation, and provides flexibility in formulating adhesives with varying toughener concentrations.

[0025] In an embodiment, the solid epoxy resin may have an epoxy equivalent weight (EEW) of from 800 to 6000 g / eq, preferably from 1200 to 3500 g / eq, more preferably from 1600 to 2000 g / eq.

[0026] Selecting a solid epoxy resin with an EEW in the specified ranges provides a viscosity that better matches the viscosity of the crosslinkable rubber during processing. This viscosity matching improves blending efficiency and morphological refinement of the rubber phase both before and during dynamic vulcanization, resulting in a finer and more uniform dispersion of rubber domains.

[0027] In an embodiment, the peroxide crosslinking agent may crosslink the NBR through the unsaturation in the butadiene portion of the rubber, in particular acrylonitrile butadiene rubber (NBR), backbone via free radical polymerization.

[0028] Crosslinking through the butadiene unsaturation via free radical polymerization provides a selective crosslinking mechanism that cures the rubber without affecting the epoxy resin matrix. This selectivity ensures that the matrix remains thermoplastic and processable while the rubber phase becomes crosslinked and elastomeric.

[0029] In an embodiment, the weight ratio of rubber, in particular acrylonitrile butadiene rubber (NBR), to the total weight of solid epoxy resin and optional thermoplastic polymers may be from 0.3 to 3.0, preferably 0.5 to 2.3, more preferably 0.7 to 1.5.Maintaining the weight ratio within the specified ranges ensures an appropriate balance between the rubber and matrix phases. This balance provides sufficient rubber content for effective toughening while maintaining enough matrix material to form a continuous phase that enables thermoplastic processing behavior.

[0030] In an embodiment, the toughener comprises the (optional) one or more thermoplastic polymers, which may be selected from polyvinyl butyral (PVB), polyvinyl chloride (PVC), polystyrene (PS), acrylonitrile butadiene styrene (ABS), polymethyl methacrylate (PMMA), polycarbonate (PC), polylactic acid (PLA), polyetherimide (PEI), thermoplastic epoxy resins such as polyhydroxy amino ethers (PHAE) or a combination thereof.

[0031] The selection of thermoplastic polymers from the specified group provides flexibility in tailoring the matrix properties to match the requirements of the target adhesive formulation. These thermoplastic polymers can contribute additional toughening, modify viscosity, or improve compatibility with other adhesive components.

[0032] In an embodiment, the TPV toughener may have a melt flow index (MFI) of 0.5 to 15 g / 10 min, in particular 1 to 10 g / 10 min, preferably 1 to 7 g / 10 min, more preferably 1 to 5 g / 10 min, determined at 150 °C, 5 kg in accordance with ASTM D1238:2023. A melt flow index within the specified ranges indicates that the TPV toughener has appropriate flowability for thermoplastic processing. This flowability enables the toughener to be readily incorporated into adhesive formulations through conventional mixing equipment and allows the toughener to be formed into various shapes such as pellets, flakes, or powder for ease of handling and storage.

[0033] The rubber of the TPV toughener may be acrylonitrile butadiene rubber (NBR) having a nitrile content of from 20% to 45% by weight, or from 25% to 40% by weight, or from 30% to 36% by weight. The solid epoxy resin may be a bisphenol A glycidyl ether solid epoxy resin, such as a type-7 solid epoxy resin having an EEW of 1750 to 1950 g / eq and a softening point of 115 to 125 °C. The optional thermoplastic polymer may be polyvinyl butyral (PVB) having a vinyl alcohol content in the range of 8 to 20 wt.-%, or 10 to 18 wt.-%, and a vinylacetate content of 0.1 to 6 wt.-%, or 0.5 to 5 wt.-%. The TPV toughener may further comprise at least one liquid epoxy resin, such as a difunctional glycidyl ether liquid epoxy resin or a cardanol based difunctional glycidyl ether liquid epoxy resin, wherein the weight ratio of solid epoxy resin to liquid epoxy resin may be in the range of 20:1 to 1:1, or 12:1 to 1.5:1, or 8:1 to 2:1. The TPV toughener may further comprise at least one filler selected from calcium carbonate,calcium oxide, talc, glass fibers, fumed silicas, wollastonite, mica, clay, carbon black, hollow glass sphere or mixtures thereof.

[0034] In another embodiment, a method for producing a thermoplastic dynamic vulcanizate (TPV) toughener for epoxy-based structural adhesives is provided. The method comprises heating and mixing rubber, in particular acrylonitrile butadiene rubber (NBR), with at least one solid epoxy resin (EP) and optionally one or more thermoplastic polymers to form a melt mixture. The method further comprises adding a peroxide crosslinking agent (CA) to the melt mixture. The method further comprises dynamically vulcanizing the melt mixture under shear stress, wherein crosslinking of the rubber, in particular acrylonitrile butadiene rubber (NBR), occurs concurrently with mixing such that a discrete crosslinked rubber phase is formed and dispersed in a continuous thermoplastic matrix phase comprising the solid epoxy resin.

[0035] In other words, the method further comprises dynamically vulcanizing the melt mixture under shear stress to simultaneously crosslink the rubber, in particular acrylonitrile butadiene rubber (NBR), and form a discrete crosslinked rubber phase dispersed in a continuous thermoplastic matrix phase comprising the solid epoxy resin.

[0036] The method of dynamic vulcanization provides a process for producing a TPV toughener in which the rubber phase is crosslinked while being simultaneously dispersed in the matrix phase. This simultaneous crosslinking and dispersion under shear stress enables the formation of fine rubber domains that are locked in place by the crosslinking reaction, preventing re-agglomeration and ensuring a stable morphology.

[0037] As used herein, 'simultaneously crosslink and form' refers to the dynamic vulcanization process in which the crosslinking reaction and the morphological refinement of the rubber phase occur during the same mixing operation. The crosslinking and phase formation need not occur at precisely the same instant, but rather occur concurrently during the application of shear stress, such that the rubber is crosslinked while being dispersed and refined into discrete domains.

[0038] In other embodiments, the method may include one or more of the following features. The shear stress may tear the curing rubber apart into discrete domains having a size of about 10 micrometer or smaller, in particular a domain size of 10-0.6 micrometer,in particular 5-0.6 micrometer, in particular 2-0.6 micrometer, in particular 1-0.6 micrometer, in particular 1-0.75 micrometer.

[0039] Tearing the curing rubber into discrete domains of about 10 micrometer or smaller, in particular a domain size of 10-0.6 micrometer, in particular 5-0.6 micrometer, in particular 2-0.6 micrometer, in particular 1-0.6 micrometer, in particular 1-0.75 micrometer, through shear stress provides a mechanism for achieving fine morphology that would be difficult to obtain through simple blending. The combination of crosslinking and shear stress refines the rubber phase to a size scale that provides effective toughening.

[0040] In an embodiment, the method may further comprise adding a mono-functional epoxy compound that reacts with the rubber, in particular acrylonitrile butadiene rubber (NBR), to provide epoxy-functionalization.

[0041] Adding a mono-functional epoxy compound that reacts with the rubber provides a route to epoxy-functionalize the rubber phase during the dynamic vulcanization process. This in-situ functionalization improves compatibility between the rubber and epoxy matrix and enables the rubber to participate in the epoxy curing reaction when the toughener is incorporated into an adhesive formulation.

[0042] In an embodiment, the optional one or more thermoplastic polymers may be selected from polyvinyl butyral (PVB), polyvinyl chloride (PVC), polystyrene (PS), acrylonitrile butadiene styrene (ABS), polymethyl methacrylate (PMMA), polycarbonate (PC), polylactic acid (PLA), polyetherimide (PEI), thermoplastic epoxy resins such as polyhydroxy amino ethers (PHAE) or a combination thereof. The at least one crosslinkable rubber may be selected from acrylonitrile butadiene rubber (NBR), silicone (MQ), polychloroprene (CR), polyurethane elastomers (PU), ethylene propylene diene monomer (EPDM), fluoroelastomers (FKM), butyl rubber (HR), styrene-butadiene rubber (SBR), natural rubber (NR) and hydrogenated nitrile rubber (HNBR) or a combination thereof. The at least one crosslinkable rubber may preferably be selected from acrylonitrile butadiene rubber (NBR).

[0043] The selection of thermoplastic polymers and crosslinkable rubbers from the specified groups provides flexibility in tailoring the TPV toughener composition to meet specific performance requirements. Different combinations of rubber and thermoplastic polymer can be selected to optimize compatibility, processing characteristics, and toughening performance for particular adhesive applications.In an embodiment, the method may further comprise adding a liquid epoxy resin as a viscosity modifier.

[0044] Adding a liquid epoxy resin as a viscosity modifier provides a means to adjust the melt flow characteristics of the TPV toughener. This viscosity adjustment facilitates processing and enables the toughener to be tailored for incorporation into adhesive formulations with varying viscosity requirements.

[0045] The method may be carried out in a mixing or kneading device selected from a dispersion mixer, planetary mixer, Brabender mixer, twin screw mixer, continuous mixer, or extruder, wherein a twin-screw extruder may be preferred. The monofunctional epoxy compound may be a cardanol based mono-functional epoxy compound having an aliphatic group including one, two or more carbon carbon double bonds. The liquid epoxy resin may be a cardanol based difunctional glycidyl ether liquid epoxy resin. The temperature of the melt mixture during addition of the crosslinker may be in the range of 120°C to 170°C, or 130°C to 160°C. The vulcanization temperature of the melt mixture may be in the range of 125°C to 200°C, or 130°C to 190°C, or 135°C to 180°C.

[0046] In yet another embodiment, an epoxy-based structural adhesive composition is provided. The epoxy-based structural adhesive composition comprises 15 to 50 wt% of the thermoplastic dynamic vulcanizate (TPV) toughener as described above. The TPV toughener provides impact resistance and toughness to the cured adhesive. Incorporating the TPV toughener at 15 to 50 wt% provides sufficient rubber content to impart impact resistance and toughness to the cured adhesive while maintaining the structural and adhesive properties of the epoxy matrix. The TPV toughener disperses readily in the adhesive formulation due to its thermoplastic processing characteristics, ensuring uniform distribution of the toughening phase.

[0047] The epoxy-based structural adhesive composition may be a one-component thermosetting epoxy resin composition. The epoxy-based structural adhesive composition may be a foaming, one-component thermosetting epoxy resin composition. The epoxy-based structural adhesive composition may include amine-based curing agents. The epoxy-based structural adhesive composition may have a melt flow index (MFI) of 0.5 to 15 g / 10 min, or 1 to 10 g / 10 min, or 1 to 7 g / 10 min, or 3 to 6 g / 10 min, determined at 100 °C, 5 kg in accordance with ASTM D1238:2023. In a further embodiment, a use of the thermoplastic dynamic vulcanizate (TPV) toughener as described above as a toughening agent in one-component epoxy-basedstructural adhesives is provided. The discrete crosslinked rubber phase provides fracture toughness while the continuous thermoplastic matrix phase ensures processability.

[0048] The use of the TPV toughener in one-component epoxy-based structural adhesives provides a toughening solution that combines the benefits of rubber toughening with thermoplastic processability. The discrete crosslinked rubber phase absorbs energy and resists crack propagation, while the continuous thermoplastic matrix phase enables the toughener to be readily incorporated and processed with the adhesive components.

[0049] Further aspects of the invention are illustrated in the appended drawings, wherein

[0050] Fig. 1 shows processing details of an example for manufacturing of an inventive TPV toughener as a graphical representation.

[0051] Fig. 2 shows processing details of a further example for manufacturing of an inventive TPV toughener as a graphical representation

[0052] Fig. 3 is a diagram of stress-stain data for inventive structural adhesives prepared in the examples: Formulation 1 (CC01-122), Formulation 2 (CC01-123) and Formulation 3 (CC01-125).

[0053] Fig. 4 is a diagram of peak stress data as a function of cylinder density of the cylinder compression for inventive structural adhesives prepared in the examples: Formulation 1 (CC01-122), Formulation 2 (CC01-123) and Formulation 3 (CC01-125).

[0054] Fig. 5 is a diagram of modulus data as a function of cylinder density of the cylinder compression for inventive structural adhesives prepared in the examples: Formulation 1 (CC01-122), Formulation 2 (CC01-123) and Formulation 3 (CC01-125).

[0055] Further aspects of the invention are subject of further independent claims. Particularly preferred embodiments of the invention are described in the dependent claims.

[0056] Detailed description of the invention

[0057] The present invention relates to a thermoplastic dynamic vulcanizate (TPV) toughener, in particular for epoxy-based structural adhesive, wherein the TPVtoughener comprises or is made of dynamically vulcanized rubber particles made of at least one rubber dispersed in a matrix comprising at least one solid epoxy resin and optionally one or more thermoplastic polymers.

[0058] The terms "rubber particles" and "discrete crosslinked rubber phase" refer to the same structures within the TPV toughener and may be used interchangeably throughout this disclosure. Both terms describe the crosslinked rubber domains that are formed during the dynamic vulcanization process and dispersed throughout the continuous thermoplastic matrix phase. The use of "phase" terminology provides a more general description of the morphology, encompassing various possible shapes and sizes of the rubber domains, while "particles" more specifically suggests discrete, separated entities. Regardless of the terminology used, these structures represent the discontinuous rubber component of the TPV toughener that provides the toughening functionality when incorporated into epoxy-based structural adhesives.

[0059] The terms "rubber particles" and "discrete crosslinked rubber phase" refer to the same structures within the TPV toughener and may be used interchangeably throughout this disclosure. Both terms describe the crosslinked rubber domains that are formed during the dynamic vulcanization process and dispersed throughout the continuous thermoplastic matrix phase. The use of "phase" terminology provides a more general description of the morphology, encompassing various possible shapes and sizes of the rubber domains, while "particles" more specifically suggests discrete, separated entities. Regardless of the terminology used, these structures represent the discontinuous rubber component of the TPV toughener that provides the toughening functionality when incorporated into epoxy-based structural adhesives.

[0060] In general, vulcanization is a chemical process for crosslinking rubber compounds containing crosslinkable rubber, typically based on natural rubbers and / or synthetic rubbers. This process results in a vulcanized rubber material also termed elastomers.

[0061] Dynamic vulcanization is a process, in which vulcanization occurs simultaneously with the mixing of the crosslinkable rubber and another polymer that does not crosslink, usually under high shear conditions and in the presence of a curing agent. This process is typically carried out at high temperatures and under shear conditions, allowing the rubber to vulcanize in the presence of another polymer that does not cure.The resulting material has a dispersed rubber phase in form of domains within a continuous polymer matrix.

[0062] When the rubber and epoxy are blended together prior to adding the curative, the rubber and epoxy each exist as separate phases. Depending on their concentrations and mutual compatibility, these phases may be co-continuous, or one material may form the continuous phase while the other becomes a discrete (discontinuous) phase. This discrete phase can take the form of large spherical domains (typically greater than 50 microns) or elongated domains. However, such a blend is not optimal because its ultimate properties are poor. Ideally, the rubber phase should be discrete, with domains about a micron (micrometer) in size or smaller, in particular a size of 600nm to the most.

[0063] In various aspects, the discrete crosslinked rubber phase may comprise rubber domains having a size of about 10 micrometer or smaller. In some aspects, the rubber domains may have a size in the range of 10 to 0.6 micrometer. In some aspects, the rubber domains may have a size in the range of 5 to 0.6 micrometer. In some aspects, the rubber domains may have a size in the range of 2 to 0.6 micrometer. In some aspects, the rubber domains may have a size in the range of 1 to 0.6 micrometer. In some aspects, the rubber domains may have a size in the range of 1 to 0.75 micrometer. The lower limit of about 0.6 micrometer (600 nm) distinguishes the rubber domains of the present invention from conventional core-shell rubber particles, which are typically produced by emulsion processes to form spheres on the order of 500 nm or less in diameter. The rubber domains formed by dynamic vulcanization under shear stress have a different morphology and size distribution compared to such pre-formed core-shell particles.

[0064] Dynamic vulcanization achieves this desired morphology. By adding a curative to crosslink the rubber, its molecular weight and viscosity increase. If this occurs under high shear stress, the stress tears the curing rubber apart into small domains. This forces the rubber to become the discrete phase, while the uncured epoxy / thermoplastic remains the continuous phase — even when the rubber concentration is very high compared to the epoxy / thermoplastic. Once the shear stress is removed, the rubber does not re-agglomerate because the domains are crosslinked.Thermoplastic dynamic vulcanizate (TPV) is a material that is produced by dynamic vulcanization and combines the elastic properties of rubber with the processability of thermoplastics. Accordingly, TPV behaves like vulcanized rubber at room temperature but can be processed like a thermoplastic when heated.

[0065] The TPV toughener of the present invention is fundamentally distinct from conventional epoxy toughening technologies. Conventional tougheners include urethane tougheners, rubber-modified epoxy resins using carboxyl-term inated butadiene rubber (CTBN), and core-shell rubber particles. These technologies involve different chemistries, manufacturing processes, and morphologies compared to the present invention.

[0066] In particular, CTBN-based tougheners are liquid rubber components that react with epoxy to compatibilize with the epoxy resin matrix. Core-shell rubber particles are typically produced by emulsion processes to form spheres with a rubber core and plastic shell, typically on the order of 500 nm or less in diameter.

[0067] In contrast, the present invention uses dynamic vulcanization to produce crosslinked rubber domains, potentially about 1 micron in diameter, dispersed in an epoxy / thermoplastic matrix. The toughener of the present invention has different chemistry (e.g., no carboxylated rubber or blocked urethane) and different morphology (e.g., crosslinked rubber domains formed under shear stress, not pre-formed core / shell spheres or liquid rubber additives).

[0068] Furthermore, the present invention contemplates a novel use for dynamic vulcanization: to produce an epoxy toughener intermediate that can then be used to toughen epoxy adhesive formulations. This application of dynamic vulcanization technology has not been previously suggested in the art of epoxy toughening.

[0069] The rubber particles present in the TPV toughener according to the invention are made of one or more rubbers or crosslinkable rubbers, respectively, wherein the type of rubber is generally not limited.

[0070] Examples of suitable rubbers or crosslinkable rubbers, respectively, are acrylonitrile butadiene rubber (NBR), silicone (MQ), polychloroprene (CR), polyurethane elastomers (PU), ethylene propylene diene monomer (EPDM), fluoroelastomers (FKM), butyl rubber (HR), styrene-butadiene rubber (SBR), natural rubber (NR) and hydrogenated nitrile rubber (HNBR) or a combination thereof. These rubber types aresuitable in that they have compatibility with the polymer phase matrix (i.e. the solid epoxy and optional one or more thermoplastic polymers) and are crosslinkable with a curing agent that does not cure the polymers of the matrix phase.

[0071] The at least one rubber such as the examples mentioned above can be functionalized, e.g. epoxy-functionalized, in the toughener to adjust the properties of the rubbers and improve compatibility with the matrix components of the inventive TPV toughener.

[0072] According to a preferred embodiment, the at least one rubber is acrylonitrile butadiene rubber (NBR). NBR is also designated as nitrile butadiene rubber. NBR is commonly a random copolymer derived from acrylonitrile (ACN) and butadiene which can be readily crosslinked, by a peroxide for example, through the unsaturation in the butadiene portion of the backbone.

[0073] The acrylonitrile butadiene rubber may have a nitrile content of from 20% to 45% by weight, preferably 25 to 40% by weight, more preferably 30 to 36% by weight.

[0074] The acrylonitrile butadiene rubber (NBR) can be functionalized, e.g. epoxyfunctionalized, to adjust the properties of the rubbers and improve compatibility with the matrix components of the inventive TPV toughener.

[0075] It may be advantageous to select the rubber and polymer to ensure compatibility of these two groups of the components. In the course of research carried out for this application, it was found that the compatibility of the acrylonitrile butadiene rubber with the solid epoxy resin could be improved by functionalizing acrylonitrile butadiene rubber with epoxy groups.

[0076] Accordingly, the dynamically vulcanized rubber particles of the inventive TPV toughener are preferably made of epoxy-functionalized acrylonitrile butadiene rubber.

[0077] Preferably, the at least one rubber is an acrylonitrile butadiene rubber (NBR) which is epoxy functionalized by a mono-functional epoxy compound containing a reactive group, which is reactive with the crosslinkable rubber. A preferred example of such reactive group is an aliphatic group including one, two or more carbon carbon doublebonds (unsaturation). A further example of such a reactive group are runs or series of secondary hydrogens of -CH2- groups linked with each other. These hydrogens are easily abstracted by free radicals generated by peroxide initiated reactions and will propagate, building a crosslinked structure. The crosslinking of polyethylene is one example of this chemistry.

[0078] Although NBR has good compatibility with the epoxy resin, which varies with acrylonitrile content, epoxidizing the NBR greatly improves the compatibility. Particularly since the epoxy functionalized NBR can now react into the crosslinked epoxy network at the time of epoxy crosslinking.

[0079] In the context of the present invention, a mono-functional epoxy compound means organic compounds having only one epoxy group, such as a glycidylether group. The mono-functional epoxy compound is preferably a liquid epoxy compound. The monofunctional epoxy compound contains an additional reactive group, which is reactive with crosslinkable rubber. Preferably, the mono-functional epoxy compound has as the reactive group an aliphatic group including one, two or more double bonds, which is reactive with the unvulcanized rubber, e.g. through a peroxide initialized free radical polymerization. As a result, the rubber is functionalized with epoxy groups.

[0080] In a preferred embodiment, the mono-functional epoxy compound containing an additional reactive group, which is reactive with crosslinkable rubber, is a cardanol based mono-functional epoxy compound having a reactive group, which is reactive with unvulcanized rubber, such as an aliphatic group including unsaturation, in particular an aliphatic group including one, two or more carbon carbon double bonds. The cardanol based mono-functional epoxy compound is preferably a liquid epoxy compound.

[0081] Cardanol is a phenolic lipid obtained from anacardic acid, the main component of cashew nutshell liquid (CNSL), a byproduct of cashew nut processing. CNSL is a natural, non-food chain, and annually renewable biomaterial. Cardanol based monofunctional epoxy compound having a functional group reactive with crosslinkable rubber are available from Cardolite.The weight ratio of at least one rubber to the total weight of the at least one solid epoxy resin and the optional one or more thermoplastic polymers in the inventive TPV toughener is not limited and can be adjusted as required. In particular, it is possible to select the ratio of at least one rubber to the total weight of the at least one solid epoxy resin and the optional one or more thermoplastic polymers independently of the composition of the optional one or more thermoplastic polymers.

[0082] According to a preferred embodiment, the weight ratio of the at least one rubber to the total weight of the at least one solid epoxy resin and the optional one or more thermoplastic polymers is from 0.3 to 3.0, preferably 0.5 to 2.3, more preferably 0.7 to 1.5.

[0083] The matrix comprises at least one solid epoxy resin. As solid epoxy resin one or more solid epoxy resins may be used.

[0084] The matrix may optionally comprise in addition to the at least one solid epoxy resin one or more thermoplastic polymers. The one or more thermoplastic polymers optionally used are different from the solid epoxy resin. It is preferred that the matrix comprises the at least one solid epoxy resin and the one or more thermoplastic polymers. The selection is preferably made in view of the polymers contained in the adhesive composition, in particular the epoxy-based structural adhesive, to which the TPV toughening agent according to the invention is added in order to improve compatibility of the toughener and the adhesive polymers.

[0085] Suitable examples of the one or more thermoplastic polymers, if used, are selected from polyvinyl butyral (PVB), polyvinyl chloride (PVC), polystyrene (PS), acrylonitrile butadiene styrene (ABS), polymethyl methacrylate (PMMA), polycarbonate (PC), polylactic acid (PLA), polyetherimide (PEI), thermoplastic epoxy resins such as polyhydroxy amino ethers (PHAE) or a combination thereof. These polymers are common polymers. PHAE is e.g. discussed in US 5275853A. In a preferred embodiment, the optional one or more thermoplastic polymers is polyvinyl butyral (PVB).If the one or more thermoplastic polymers such as those mentioned above are contained in the matrix, the weight ratio of solid epoxy resin to the one or more thermoplastic polymers is preferably in the range of 3:1 to 1 :2, preferably 2:1 to 1:1.5, more preferably 2:1 to 1 : 1 or 1.5: 1 to 1 : 1.

[0086] In a preferred embodiment, the at least one polymer is selected from solid epoxy resin or a combination of solid epoxy resin and polyvinyl butyral (PVB). More preferably the matrix comprises solid epoxy resin and polyvinyl butyral (PVB), wherein the weight ratio of solid epoxy resin to PVB is preferably in the range of 3:1 to 1 :2, preferably 2:1 to 1:1.5, more preferably 2:1 to 1:1 or 1.5:1 to 1:1.

[0087] The at least one solid epoxy resin and the optional one or more thermoplastic polymers, preferably polyvinyl butyral (PVB), forms the matrix. That is, the matrix is a polymer matrix. The matrix is generally a thermoplastic matrix. The polymer matrix may include components other than these matrix forming polymers such as liquid epoxy resins which can be used as flexibilizer or viscosity modifiers. The amount of the at least one solid epoxy resin and the optional one or more thermoplastic polymers such as those mentioned above, preferably polyvinyl butyral (PVB), may be e.g. from 30 to 100% by weight, preferably 40 to 90% by weight, more preferably 50 to 80% by weight, based on the total weight of the matrix including components incorporated in the matrix but excluding the dynamically vulcanized rubber particles.

[0088] PVB is a thermoplastic resin used in applications requiring strong binding, optical clarity, adhesion to many surfaces, toughness and flexibility. PVB is generally produced by acetalization of polyvinyl alcohol with butanal. Hence, the basic chemical structure is generally a terpolymer of vinyl butyral, vinyl alcohol, and vinyl acetate. Preferably, PVB is a PVB having a vinyl alcohol content in the range of 8 to 20 wt.-%, preferably 10 to 18 wt.-%, and a vinylacetate content of 0.1 to 6 wt.-%, preferably 0.5 to 5 wt.-%, the remainder being vinyl butyral.

[0089] In a particular preferred embodiment, the inventive TPV toughener is made of dynamically vulcanized epoxy-functionalized acrylonitrile butadiene rubber particles dispersed in a matrix comprising solid epoxy resin and polyvinyl butyral (PVB).Preferably, the solid epoxy resin has on average more than one epoxy group per molecule. The epoxide group is preferably in the form of a glycidyl ether group. Preferably, the at least one solid epoxy resin is a bisphenol A glycidyl ether solid epoxy resin.

[0090] The fraction of the solid epoxy resin, preferably solid epoxy resin having on average more than one epoxide group per molecule, is preferably from 10 to 40 wt%, 12 to 30 wt%, more preferably 16 to 25 wt%, based on the total weight of the inventive TPV toughener.

[0091] The term “solid epoxy resin” is very familiar to the person skilled in the epoxide art and is used in contrast to “liquid epoxy resins”. The glass transition temperature of solid resins is above room temperature such as 23°C, meaning that at room temperature they can be comminuted into pourable powders. Likewise, the glass transition temperature of liquid epoxy resins is below room temperature.

[0092] Preferred epoxy resins have the formula (I)

[0093]

[0094] In this formula, the substituents R’ and R” independently of one another are either H or CH3. In solid epoxy resins, the index s has a value of > 1.5, more particularly from 2 to 12.

[0095] Solid epoxy resins of this kind are available commercially, for example, from Olin Corp, (formerly from Dow), Huntsman, Westlake Chemical (formerly Hexion) or Kukdo. The resins in question are therefore preferably diglycidyl ethers of bisphenol A (DGEBA).

[0096] Compounds of the formula (I) having an index s of 1 to 1.5 are referred to by the person skilled in the art as semi-solid epoxy resins. For the purposes of the present invention, they are considered likewise to be solid resins. Preferred solid epoxy resins,however, are epoxy resins in the narrower sense, in other words where the index s has a value of > 1.5.

[0097] In the case of liquid epoxy resins, the index s has a value of less than 1. Preferably s has a value of less than 0.2.

[0098] The solid epoxy resins in question are therefore preferably diglycidyl ethers of bisphenol A (DGEBA), of bisphenol F and also of bisphenol A / F. Liquid resins of these kinds are available for example as Araldite® GY 250, Araldite® PY 304, Araldite® GY 282 (Huntsman) or D.E.R.™ 331 or D.E.R.™ 330 (Olin formerly Dow) or Epikote 828 (Westlake Chemical formerly Hexion).

[0099] Of further suitability as epoxy resin are what are called epoxy novolacs. These compounds have, in particular, the following formula:

[0100]

[0101] More particularly these are phenol-epoxy or cresol-epoxy novolacs (R2 = CH2).

[0102] Epoxy resins of these kinds are available commercially under the tradename EPN or ECN and also Tactix®from Huntsman, or within the product series D.E.N.™ from Olin Corp, (formerly from Dow).

[0103] The solid epoxy resin is preferably an epoxy resin of the formula (I).Epoxy compounds can be characterized by the epoxy equivalent weight (EEW). The EEW is defined as the fraction of average molecular weight divided by the number of epoxy functionalities. For example, a solid epoxy resin with an average molecular weight of 1000 g / mol and 2 epoxy functionalities has an EEW of 500. The unit of EEW is g / eq. The unit may be omitted.

[0104] Surprisingly, a solid epoxy resin with a higher EEW than the commonly used solid epoxy resins was found to result in a viscosity that better matches the viscosity of the crosslinkable rubber in the TPV toughener. Reducing the viscosity difference between the crosslinkable rubber and the solid epoxy resin results in more efficient mixing and improves the morphological refinement of the rubber even before it is dynamically vulcanized. In addition, the morphology of the vulcanized rubber particles can be adjusted to a finer particle size during the dynamic vulcanization process.

[0105] According to a preferred embodiment, the solid epoxy resin has an epoxy equivalent weight (EEW) of from 800 to 6000 g / eq, preferably from 1200 to 3500 g / eq, more preferably from 1600 to 2000 g / eq.

[0106] The viscosity of the TPV toughener plays an important role in achieving uniform distribution of the dynamically vulcanized rubber particles in the matrix and also in improving the processability of the TPV toughener. The melt flow index (MFI) is a measure of the viscosity of a melt and serves as an indicator for the flowability of the melt.

[0107] According to preferred embodiments, the inventive TPV toughener 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 7 g 1 10 min, most preferably 1 to 5 g / 10 min, determined at 150 °C, 5 kg in accordance with ASTM D1238:2023.

[0108] In order to adjust the melt flow index of the TPV toughener according to the invention, it may be advantageous to add a liquid epoxy resin. Such a liquid epoxy resin can act as a viscosity modifier or diluent by lowering the viscosity of the TPV toughener. The liquid epoxy resin generally has no reactive group, which is reactive with crosslinkable rubber.According to a preferred embodiment, the TPV toughener further comprises at least one liquid epoxy resin, preferably a difunctional glycidyl ether liquid epoxy resin such as a cardanol based difunctional glycidyl ether liquid epoxy resin. Further examples of useful liquid epoxy resins are bisphenol A liquid epoxy resins, e.g. DER 331 from Olin Corp. (EEW = 182-192), YD-128 from Kukdo Chemical Co. (EEW = 184-190) and Epon Resin 828 from Westlake Corporation. The liquid epoxy resin is usually incorporated in the matrix or polymer matrix, respectively, of the TPV toughener.

[0109] Examples of suitable liquid epoxy resin may have the structures discussed above. In a preferred embodiment, the liquid epoxy resin is a cardanol based liquid epoxy resin, in particularly a cardanol based difunctional glycidyl ether liquid epoxy resin. Cardanol has been discussed above. Cardanol based liquid epoxy resins are available from Cardolite.

[0110] In a particular preferred embodiment, the inventive TPV toughener comprises or is made of dynamically vulcanized epoxy-functionalized acrylonitrile butadiene rubber particles dispersed in a matrix comprising solid epoxy resin, polyvinyl butyral (PVB) and at least one liquid epoxy resin.

[0111] A relevant factor in adjusting the viscosity of the TPV toughener has been found to be the ratio of the solid epoxy resin to the liquid epoxy resin, if added.

[0112] According to a preferred embodiment, the weight ratio of the least one solid epoxy resin to the at least one liquid epoxy resin is in the range of 20: 1 to 1 : 1 , preferably 12:1 to 1.5:1, more preferably 8:1 to 2: 1.

[0113] If present, the content of liquid epoxy resin in the TPV toughener may be e.g. from 1 % by weight to 25% by weight, preferably 3% by weight to 20% by weight, based on the total weight of the TPV toughener.

[0114] The inventive TPV toughener may further comprise additives such as fillers. Examples of suitable fillers are chemically non-functional fillers commonly used in rubber and plastic compounds. Preferably, the inventive TPV toughener further comprises at least one filler. The filler may be selected e.g. from calcium carbonate, calcium oxide, talc,glass fibers, fumed silicas, wollastonite, mica, clay, carbon black, hollow glass sphere or mixtures of two or more thereof, preferably calcium carbonate. The filler may also serve as a carrier or activator for the crosslinker.

[0115] The inventive TPV toughener is solid. The solid can take many forms to facilitate further processing. Examples include ground particles, pellets, flakes or powder.

[0116] The inventive TPV toughener is preferably obtained or obtainable by the inventive process described below.

[0117] All aspects, proportions and embodiments described above for the inventive TPV toughener, in particular with respect to the at least one rubber, the at least one solid epoxy resin, the optional one or more thermoplastic polymers, the at least one liquid epoxy resin and the at least on mono-functional epoxy compound also apply to the inventive method discussed below so that reference is made thereto.

[0118] As described above, dynamic vulcanization generally involves the simultaneous mixing and cross-linking of rubber within a polymer matrix. This process typically occurs in a mixing or kneading device, where the rubber and the polymer are subjected to high temperatures and shear forces. Crosslinking agents are added during mixing to vulcanize the rubber, which becomes finely dispersed within the matrix phase.

[0119] Accordingly, the present invention is also directed to a method for producing a thermoplastic dynamic vulcanizate (TPV) toughener, in particular an inventive TPV toughener as described above, wherein dynamically vulcanized rubber particles are dispersed in a matrix, wherein the method comprising the following steps:

[0120] a) heating and mixing a mixture comprising at least one crosslinkable rubber and at least one solid epoxy resin and optionally one or more thermoplastic polymers, preferably polyvinyl butyral (PVB), to form a melt mixture,

[0121] b) adding at least one crosslinking agent for the crosslinkable rubber to the melt mixture, wherein the at least one crosslinking agent is preferably at least one peroxide,c) dynamically vulcanizing the melt mixture including the added at least one crosslinking agent under shear stress to form dynamically vulcanized rubber particles (aka discrete crosslinked rubber phase) dispersed in a polymer matrix.

[0122] The shear stress in step c) can be applied by various technical means, e.g. by stirring, kneading, mixing or similar, and primarily depends on the device used to carry out the process. In a mixer, for example, the shear stress is applied by stirring. Preferably, the step of dynamic vulcanization of the inventive method is carried out in a mixing or kneading device selected from a dispersion mixer, planetary mixer, Brabender mixer, twin screw mixer, continuous mixer, extruder, such as a twin-screw extruder, wherein a twin-screw extruder is preferred.

[0123] The same mixing or kneading devices can be also used for heating and mixing in step a). Process steps a), b) and c) are usually carried out in the same mixing or kneading device.

[0124] The at least one crosslinkable rubber is preferably selected from acrylonitrile butadiene rubber (NBR), silicone (MQ), polychloroprene (CR), polyurethane elastomers (PU), ethylene propylene diene monomer (EPDM), fluoroelastomers (FKM), butyl rubber (HR), styrene-butadiene rubber (SBR), natural rubber (NR) and hydrogenated nitrile rubber (HNBR) or a combination thereof. According to a preferred embodiment, the at least one crosslinkable rubber is acrylonitrile butadiene rubber (NBR).

[0125] According to a preferred embodiment, the optional one or more thermoplastic polymers is selected from PVB.

[0126] In step a) the mixture comprising at least one crosslinkable rubber and at least one solid epoxy resin and optionally one or more thermoplastic polymers, preferably polyvinyl butyral (PVB), is heated and mixed to form a melt mixture. The heating a mixing operation allows to provide a homogeneous melt mixture. As known by the skilled person, a melt mixture here refers to a mixture which is processable like a melt and does not necessarily refer to melting in a classical sense. Technically, polymerslike the solid epoxy resins and PVB are amorphous materials. They are not crystalline or semi-crystalline and thus do not “melt” in a classical sense. In the mixer they are softened with temperature above their glass transition temperatures (Tg) to a point that they are not only soft but have low enough viscosity that they are easily “melt” processable to achieve the melt mixture. That is their viscosities become low enough that they easily flow, can be reshaped, blended together, etc.

[0127] It is generally appropriate to effect the heating and mixing such that the mixture is homogenized as best as possible. Preferably this can be done at the activation temperature of the crosslinking agent.

[0128] In step b) at least one crosslinking agent for the crosslinkable rubber is added to the melt mixture. It is preferred to add the at least one crosslinking agent, in particular the peroxide, to the melt mixture at the temperature required to activate the crosslinking agent (crosslinking temperature or activation temperature). It is not necessary, but desirable to reduce mixing time, so that the peroxide activate (chemically decompose to produce radicals) as it enters the mixer.

[0129] In step c), the melt mixture including the added at least one crosslinking agent is dynamically vulcanized under shear stress to form dynamically vulcanized rubber particles dispersed in a polymer matrix. Usually, the temperature of the melt mixture increases in step c) due to shearing action and crosslinking reaction.

[0130] Step c) can start immediately upon addition of the at least one crosslinking agent. In a preferred embodiment, simultaneously with addition of the at least one crosslinking agent the rotor speed of the mixer is raised to a high level needed to properly facilitate the dynamic vulcanization process so the morphology of the rubber particles are refiner to a small as possible through mechanical stress while crosslinking. The crosslinking agent is generally dispersed quickly because of the high mixing speeds.

[0131] A suitable crosslinking temperature, also designated activation temperature, i.e. the temperature at which dynamically vulcanizing is effected, strongly depends e.g. on the type of the polymer materials used, the type of crosslinking agent used and the desired duration for completion of the crosslinking. For instance, when the method is carriedout batchwise, the crosslinking duration can be adjusted as desired, e.g. a crosslinking duration of 3 to 20 min or 5 to 15 min may be selected. If the method is carried out as a continuous process, e.g. in a continuous mixer such as a twin screw extruder, the temperature has to be set such that the dynamic vulcanization takes place prior to the material exiting the mixer. This may be on the order of 30 to 120 seconds, e.g. in the order of 60 seconds. Hence, the crosslinking temperature may vary in wide ranges.

[0132] Having said this, the temperature of the melt mixture during addition of the crosslinker may be, for instance, in the range of 120°C to 170°C, preferably 130 to 160°C. The vulcanization temperature of the melt mixture in step c) may be, for instance, in the range of 125°C to 200°C, preferably 130 to 190°C, more preferably 135 to 180°C.

[0133] The at least one crosslinkable rubber is dynamically vulcanized in the presence of at least one crosslinking agent. The at least crosslinking agent can be one or more crosslinking agents. The crosslinking agents common in this technical field can be used. Preferably, the at least one crosslinking agent is a peroxide, more preferably an organic peroxide such as organic peroxide selected from dialkylperoxides, alkylaralkyl peroxides, diaralkyl peroxides, diacylperoxides, peroxyketals, or peroxyesters. Examples of other suitable crosslinking agents are sulfur or resole type phenolic resins such as the non-brominated SP-1045 which requires a halogen donating activator or the brominated SP-1056 which does not require the halogenated activator. Both resins are supplied by the SI Group. Sulfur and the resole type phenolic resins usually requires that the rubber contains carbon-carbon double bonds.

[0134] A suitable crosslinking temperature of the crosslinking agent depends from the rubber and polymer material used and in particular from the crosslinking agent, in particular peroxide, used and may be e.g. in the range of from 125 to 165°C, preferably 135 to 155°C.

[0135] According to a preferred embodiment, the method further comprises a step of adding to the melt mixture a mono-functional epoxy compound containing a reactive group, which is reactive with crosslinkable rubber. Preferably, the mono-functional epoxy compound contains as a reactive group an aliphatic group having one, two or more carbon carbon double bonds. The mono-functional epoxy compound has beendiscussed above with respect to the TPV toughener so that reference is made thereto. As described, the mono-functional epoxy compound serves to functionalize the rubber to obtain epoxy-functionalized vulcanized rubber particles.

[0136] According to a preferred embodiment, the method further comprises a step of adding to the melt mixture a liquid epoxy resin, preferably a liquid di-functional epoxy resin. The liquid epoxy resin has been discussed above with respect to the TPV toughener so that reference is made thereto, also e.g. with respect to suitable amounts and weight ratios for solid and liquid epoxy resins. As described, the liquid epoxy resin serves as a flexibilizer and viscosity modifier or diluent.

[0137] In a particularly preferred embodiment, the method comprises a step of adding to the melt mixture both a mono-functional epoxy compound containing a reactive group, which is reactive with the crosslinkable rubber and liquid epoxy resin.

[0138] Preferably, the addition of the mono-functional epoxy compound and / or the liquid epoxy resin, or a mixture of both components to the mixture is carried out before the crosslinking agent is added. To adjust the viscosity of the mixture, it is also possible to add further quantities of the at least one liquid epoxy resin after the addition of the crosslinking agent.

[0139] Further additives may be added to the melt mixture such as fillers. Fillers have been described above so that reference is made thereto.

[0140] In a preferred embodiment, the described inventive method for producing a thermoplastic dynamic vulcanizate (TPV) toughener, in particular the inventive TPV toughener, wherein dynamically vulcanized rubber particles are dispersed in a matrix, comprises the following steps:

[0141] a) heating and mixing a mixture comprising at least one crosslinkable rubber and at least one solid epoxy resin and optionally one or more thermoplastic polymers, preferably polyvinyl butyral (PVB), to form a melt mixture,

[0142] b) adding a mono-functional epoxy compound containing a reactive group, which is reactive with the crosslinkable rubber, preferably an aliphaticgroup having one, two or more carbon carbon double bonds, and a liquid epoxy resin, preferably a liquid di-functional epoxy resin, c) adding at least one crosslinking agent for the crosslinkable rubber to the melt mixture, wherein the at least one crosslinking agent is preferably at least one peroxide,

[0143] d) dynamically vulcanizing the melt mixture including the added at least one crosslinking agent under shear stress to form dynamically vulcanized rubber particles (aka discrete crosslinked rubber phase) dispersed in the polymer matrix.

[0144] In a particular preferred embodiment, the described inventive method for producing a thermoplastic dynamic vulcanizate (TPV) toughener, in particular the inventive TPV toughener, wherein dynamically vulcanized epoxy-functionalized acrylonitrile butadiene rubber (NBR) particles are dispersed in a matrix, comprises the following steps:

[0145] a) heating and mixing a mixture comprising NBR, at least one solid epoxy resin and polyvinyl butyral (PVB) to form a melt mixture, b) adding a mono-functional epoxy compound containing an aliphatic group containing one, two or more double bonds, and a liquid difunctional epoxy resin,

[0146] c) adding at least one crosslinking agent for the NBR to the melt mixture and mixing to obtain a melt mixture, wherein the at least one crosslinking agent is preferably at least one peroxide,

[0147] d) dynamically vulcanizing the melt mixture including the added at least one crosslinking agent under shear stress to form dynamically vulcanized epoxy-functionalized rubber particles (aka discrete crosslinked rubber phase) dispersed in the polymer matrix.

[0148] The invention is also directed to a TPV toughener according to the invention obtainable by the method according to the invention as described above.

[0149] All aspects, proportions and embodiments described above for the inventive TPV toughener, in particular with respect to the at least one rubber, the at least one solid epoxy resin, the optional one or more thermoplastic polymers, the at least one liquidepoxy resin and the at least on mono-functional epoxy compound also apply to the inventive epoxy-based structural adhesive comprising the inventive TPV toughener so that reference is made thereto.

[0150] The present invention is further directed to a structural adhesive, preferably an epoxybased structural adhesive, comprising the inventive TPV toughener. Preferably, the inventive epoxy-based structural adhesive is a one-component thermosetting epoxy resin composition. More preferably, the inventive epoxy-based structural adhesive is a foaming, one-component thermosetting epoxy resin composition.

[0151] According to a preferred embodiment, the inventive structural adhesive, in particular the epoxy-based structural adhesive, contains the inventive TPV toughener in an amount of 15 to 50 wt.-%, more preferably in an amount of 30 to 40 wt.-%, based on the total weight of the structural adhesive.

[0152] According to a preferred embodiment, the inventive structural adhesive, in particular epoxy-based structural adhesive, includes amine-based curing agents.

[0153] Preferably, the inventive structural adhesive, in particular the epoxy-based structural adhesive, 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 7 g / 10 min, most preferably 3 to 6 g / 10 min, determined at 100 °C, 5 kg in accordance with ASTM D1238 :2023.

[0154] Moreover, the present invention is directed to the use of the inventive dynamically vulcanized toughener as a toughener for structural adhesive, preferably epoxy-based structural adhesive, more preferably one-component epoxy-based structural adhesive.

[0155] The invention is elucidated further in the text below by means of examples, which, however, are not intended to restrict the invention in any way.

[0156] Examples

[0157] The raw materials used are indicated in Table 1 :Table 1: Raw materials used.

[0158]

[0159] The NBR rubber grade used was chosen for its high ACN content (31-34%), low Mooney viscosity (20-30 MML 1+4 @ 100 °C) and ease of handling since it is granulated.

[0160] Solid epoxy resin 1 employed is a type-7 solid epoxy resin which is a high molecular weight solid epoxy resin based on a diglycidyl ether of bisphenol-A (DGEBA) with an EEW of 1750-1950 g / eq and a softening point of 115-125 °C. The type-7 resin was chosen because of its high molecular weight, leading to high melt viscosity. More consistent and efficient melt blends are achieved when viscosities of blended components are similar. Thus, higher viscosity epoxies will produce NBR blends having more distinct and better refined morphologies both before and after dynamic vulcanization.The mono-functional epoxy compound employed is a low viscosity monofunctional epoxy reactive compound that contains unsaturation. The unsaturation is used to crosslink the epoxy compound in with the NBR through a peroxide initialized free radical polymerization to epoxidize the NBR. In this way the NBR is epoxy functionalized, compatibilizing it — beyond its compatibility because of high ACN content - with blended epoxy and allowing it to react with an amine cured epoxy system. Specifically, the mono-functional epoxy compound employed is a cardanol based epoxy compound (Cardolite NC-513) and has the following structure

[0161]

[0162] The liquid epoxy resin 1 employed is a difunctional liquid epoxy resin that acts as a flexibilizer and viscosity modifier. Specifically, the liquid epoxy resin 1 employed is a cardanol based liquid epoxy resin (Cardiolite NC-514) and has the following structure

[0163]

[0164] The crosslinking agent is 1,1-di(tert-butylperoxy)-3,3,5-trimethylcyclohexane (Trigonox® 29-40B-PD-E (Nouryon, The Netherlands). It has a typical crosslinking temperature of 145 °C (t90 = 12 min), and was chosen to align with typical processing temperatures of the solid epoxy resin 1 (115 — 125 °C softening point) and PVB (typical processing temperatures of 135 to 145 °C). A crosslinking temperature of 145 °C (t90 = 12 min) means that this crosslinking temperature is the temperature at which 90% of the crosslinks in a compound are formed within about 12 minutes (crosslinking temperature t90 =12 min).Preparation of TPV tougheners

[0165] Two TPV tougheners 1 and 2 according to the invention (Examples 1 and 2) were produced with the formulations given in Table 2 (for the components see Table 1 ). Table 2:

[0166]

[0167] ‘included in the NBR rubber as partitioning agent

[0168] The formulations of Example 1 and Example 2 are similar with the primary difference being the amount of liquid epoxy resin added to improve flow. The liquid epoxy resin content was increased from about 4% (Example 1) to over 16% in formulation of Example 2 to reduce melt viscosity. In Example 2, one portion of the liquid epoxy resin (7.1 wt %) was added before the addition of crosslinker and a second portion (9.3 wt %) was added afterwards.

[0169] General description of the processingThe process of dynamic vulcanization was used to produce a discrete, particulate NBR toughener in a melt processable matrix. The basic idea behind dynamic vulcanization is to blend an elastomer (NBR in this case, #1) with a material or materials that are melt processable and will not participate in the elastomer crosslinking reaction. Typically, this melt processable material is a thermoplastic; in this instance it is a blend of a solid epoxy resin (#2) and PVB thermoplastic (#3). The solid epoxy resin is a high molecular weight resin (EEW = 1750 - 1950 g / eq) to better match the viscosity of the green state NBR. Reducing the viscosity difference between the elastomer (NBR) and thermoplastics leads to more efficient blending and begins the morphology refinement of the NBR, even before the introduction of the curative (peroxide), to a co-continuous or particulate phase. It also provides the ability to drive the morphology of the elastomer to a finer particulate size during the dynamic vulcanization process. Likewise, PVB thermoplastic (#3) plays a similar role as the solid epoxy resin (#2). Both the solid epoxy resin and PVB are not required; only one would suffice to produce the toughener. But since both epoxy and PVB are in the targeted adhesive, it makes sense to blend them in this step.

[0170] Upon charging the mixer and mixing a consistent melt mix between the elastomer and matrix materials is attained, the elastomer curing agent (peroxide, #7) is added while mixing at high blade speeds (high mixing stress). The peroxide will initiate a free radical polymerization through the unsaturation in the backbone (butadiene) of the NBR rubber, rapidly raising its molecular weight and modulus. The NBR particles whose equilibrium size has been established by the intensity of mixing (level of shear stress) with the epoxy-PVB blend is locked in place by the crosslinking reaction and possibly refined further via high shear stresses tearing apart the NBR as it crosslinks. The product of this process is a toughener having a two-phase morphology; discrete, crosslinked rubber particulates in a continuous thermoplastic matrix. This type of product is generally referred to as a thermoplastic vulcanizate (TPV); a material containing relatively high content of crosslinked rubber that processes like a thermoplastic because of its morphology.

[0171] Mixing detailsA RS7400 Brabender style lab mixer (Rheometric Services Inc., Wall, NJ) with cam blades was used to mix the raw materials for the TPV toughener. Initially, the bowl temperature was pre-set to 140°C and the blade speed to 20 rpm. The high temperature was required to achieve a good melt blend between the NBR, solid epoxy and PVB and to accommodate the peroxide activation of the crosslinking agent added (t90 of 12 minutes at 145°C).

[0172] The solid ingredients #1-4 (Table 1) were added and allowed to melt the blend until a consistent appearance and torque was achieved. Next, the liquid epoxy resin and the mono-functional epoxy compound were added (#5 & #6) and the melt blend was again allowed to equilibrate in torque and consistency. The mixer speed was raised to 90 rpm and the crosslinking agent (#7) and further filler (#8) were added. Details of the mixing procedure are given in Tables 3 and 4 and graphical representation is given in Figure 1 (Example 1 ) and Figure 2 (Example 2).

[0173] Table 3: Detailed overview of preparation of Example 1.

[0174] &

[0175] &

[0176]

[0177] The mixing steps of Example 1 are graphically presented in Fig. 1 (mixing toughener: CC01-121) showing the steady state torque value of at the time of peroxide additionto be 7.6% and for the torque to immediately increase to 9.0% with the addition. Over the period of about 10 minutes, as the morphology is refined to its final small particle state, the torque exponentially decays to a steady state value of 6.0%.

[0178] Table 4: Detailed overview of preparation of Example 2.

[0179] &

[0180]

[0181] The mixing steps of Example 2 are graphically presented in Fig. 2 (Mixing Toughener: CC01-124) showing the steady state torque value of at the time of peroxide addition to be 5.1 % and for the torque to immediately increase to 7.6% with the addition. Over the period of about 10 minutes, as the morphology is refined to its final state, the torque exponentially decays to a steady state value of 6.1% and then falls further when the final liquid addition is made.

[0182] An easy method for verifying the continuous plastic / discrete (or mostly discrete) cured rubber phase morphology is by the quality of compression molded plaques. Pressing material hot from the mixer gives smooth uniform plaques, indicating material flow and no significant elastic memory affects - all indicative of a thermoplastic. If the material is removed from the mixer and allows to cool too long, a temperature of at least 105°C should be used to meet the softening point of the plasticized solid epoxy resin and reduce the viscosity of the PVB to a point where it can flow well.

[0183] Preparation of reinforcing formulations (structural adhesives)

[0184] Three epoxy-based reinforcer formulations (each referenced as Formulation 1, Formulation 2 and Formulation 3) have been prepared. Each of the Formulations 1 to 3 contained 35 wt. % of the inventive TPV toughener 1 (Example 1) or the inventive TPV toughener 2 (Example 2) as prepared above. Formulation 1 and 2 both contain TPV toughener 1 and are identical except for blowing agent levels. Formulation 2 has less blowing agent to bring the volume expansion down below 300%. Formulation 3 contains TPV toughener 2. The formulations are given in Table 5. The components are mixed to form adhesive compositions (reinforcing formulations).

[0185] Table 5: Composition of Formulations 1 to 3.

[0186]

[0187] Determination of melt flow index (MFI)The melt flow index (MFI) also termed melt flow rate of TPV toughener 1 (Example 1 ) and TPV toughener 2 (Example 2) was determined. Three samples for each TPV toughener were measured.

[0188] The measurement of the MFI was carried out in accordance with ASTM D1238:2023 with the following conditions: temperature: 150 °C, load: 5 kg, pre-heat: 240 seconds, cut time 60 seconds. The results are given in Table 6.

[0189] Table 6: Melt flow rates of Example 1 and 2.

[0190]

[0191] The melt flow rate of TPV toughener at 150 °C / 5 kg was under 1 dg / min because of the NBR, high molecular weight epoxy and PVB thermoplastic content. With the additional liquid epoxy resin in TPV toughener 2, the melt index rises to 3.4 dg / min.

[0192] Moreover, the melt flow index (MFI) of Formulation 1 and 2 both containing TPV toughener 1 and of Formulation 3 containing TPV toughener 2 was measured. Three samples for each Formulation were measured.

[0193] The measurement of the MFI was carried out in accordance with ASTM D1238:2023 with the following conditions: temperature: 100 °C, load: 5 kg, pre-heat: 240 seconds, cut time 60 seconds. The results are given in Table 7.Table 7: Melt flow rates of Formulations 1 to 3.

[0194]

[0195] The results show increase of the MFI, i.e. reduced viscosity, for Formulation 3 with TPV toughener 2 including a higher proportion of liquid epoxy resin.

[0196] Free Volume Expansion

[0197] Free volume expansion and vertical rise were measured for Formulations 1, 2 and 3 after exposure to 3 different bake conditions: 140 °C, 171 °C and 205 °C (see Table 8). The volume expansion was calculated in the usual way:

[0198] > massbakedspecific gravitygreen

[0199] Volume expansion = - * - - - 1

[0200] massgreen specific gravitybaked

[0201] Vertical rise was measured and calculated by:

[0202] sample thicknessbaked

[0203] Vertical rise = - - — ■ — - sample thicknessgreen

[0204] where the “green” index refers to the unbaked sample and the “baked” index refers to the baked sample. The results of the free volume expansion of Formulation 1 to 3 are shown in Table 8.Table 8: Free volume expansion of Formulation 1 to 3.

[0205]

[0206] Heat aging

[0207] Heat aging of the Formulations 1 , 2 and 3 was undertaken for 5 and 10 days at 35 °C (95°F). After aging, volume expansion and vertical rise were measured at 171 °C bake temperature. Results are given in Tables 9 and 10. Less than 8% reduction in volume expansion is seen following 10 days and less than 6% in vertical rise.

[0208] Table 9: Free volume expansions of materials heat aged at 35 °C for 5 and 10 days.

[0209]

[0210] Table 10: Vertical rise of materials heat aged at 35 °C for 5 and 10 days.

[0211]

[0212] Lap Shear Strength

[0213] Lap shear strength was measured on 0.060 inch hot-dip galvanizing (HDG) steel coupons oiled with Ferrocote 61 A US using 4 mm spacer (1 mm gap) between coupons.

[0214] Two bake schedules were employed: 30 min total time at 140 °C and 20 min total time at 171 °C. All lap shear coupons showed cohesive failure (as opposed to adhesive failure) at both bake conditions. The adhesive coating at 140 °C bake temperature was thinner than 171 °C. The results are summarized in Table 11.

[0215] Table 11 : Lap shear strength of Formulations 1 to 3.

[0216]

[0217] Compression cylinders / peak stress and modulus measurements

[0218] Compression cylinders were made from Formulations 1, 2 and 3 by briefly heating at 82 °C a 76mm x 152mm x 3.2mm plaque cut from a compression molded plate and rolling it into a cylinder. The cylinder is then baked in a copper tube at 171 °C, cooled and cut to a length of about 60 mm. Final diameter is about 30 mm. These test specimens are then compressed at room temperature in am MTS test frame at 6 mm / min to 30% strain and the stress-strain data recorded.

[0219] The results are shown in Figure 3 (Formulation 1: CC01-122, Formulation 2: CC01-123 and Formulation 3: CC01-125). Formulations 1 and 2 both show good retention of stress out to 30% strain. Formulation 3 has the stress fading with strain, particularly after 23% strain. Figures 4 and 5 show the peak stress and modulus plotted against cylinder density, respectively.

[0220] The following Table 12 shows the results of peak stress and modulus measurements. Both properties are a strong function of baked cylinder density. The measurements are carried out in accordance with ASTM D1621 (2023) Standard Test Method for Compressive Properties of Rigid Cellar Plastics.

[0221] Table 12: Peak stress and modulus of Formulations 1 to 3.

[0222]

Claims

Claims1. A thermoplastic dynamic vulcanizate (TPV) toughener comprising:- a discrete crosslinked rubber phase formed by dynamic vulcanization of rubber, in particular acrylonitrile butadiene rubber (NBR), under shear stress in the presence of a peroxide crosslinking agent (CA), and- a continuous thermoplastic matrix phase comprising at least one solid epoxy resin (EP) and optionally one or more thermoplastic polymers,wherein the discrete crosslinked rubber phase is dispersed throughout the continuous thermoplastic matrix phase, and in particular wherein the thermoplastic dynamic vulcanizate (TPV) toughener is specifically designed for toughening epoxy-based structural adhesives.

2. The TPV toughener according to claim 1, wherein the discrete crosslinked rubber phase comprises rubber domains having a size of about 10 micrometer or smaller, in particular a domain size of 10-0.6 micrometer, in particular 5-0.6 micrometer, in particular 2-0.6 micrometer, in particular 1-0.6 micrometer, in particular 1-0.75 micrometer.

3. The TPV toughener according to claim 1 or 2, wherein the discrete crosslinked rubber phase does not re-agglomerate after removal of shear stress due to the crosslinked structure of the rubber domains.

4. The TPV toughener according to any of claims 1-3, wherein the rubber, in particular acrylonitrile butadiene rubber (NBR), is epoxy-functionalized.

5. The TPV toughener according to any of claims 1 -4, wherein the combination of rubber, in particular acrylonitrile butadiene rubber (NBR), solid epoxy resin matrix, and peroxide crosslinking agent (CA) provides an epoxy toughener intermediate for use in epoxy adhesive formulations.

6. The TPV toughener according to any of claims 1-5, wherein the peroxide crosslinking agent crosslinks the NBR through the unsaturation in the butadiene portion of the rubber, in particular acrylonitrile butadiene rubber (NBR), backbone via free radical polymerization.

7. The TPV toughener according to any of claims 1 -6, wherein the weight ratio of rubber, in particular acrylonitrile butadiene rubber (NBR) the total weight of solid epoxy resin and optional thermoplastic polymers is from 0.3 to 3.0, preferably 0.5 to 2.3, more preferably 0.7 to 1.5.

8. The TPV toughener according to any of the preceding claims 1 -7, wherein the toughener comprises the one or more thermoplastic polymers which is are selected from polyvinyl butyral (PVB), polyvinyl chloride (PVC), polystyrene (PS), acrylonitrile butadiene styrene (ABS), polymethyl methacrylate (PMMA), polycarbonate (PC), polylactic acid (PLA), polyetherimide (PEI), thermoplastic epoxy resins such as polyhydroxy amino ethers (PHAE) or a combination thereof, and / orwherein the TPV toughener is having a melt flow index (MFI) of 0.5 to 15 g / 10 min, in particular 1 to 10 g / 10 min, preferably 1 to 7 g / 10 min, more preferably 1 to 5 g / 10 min, determined at 150 °C, 5 kg in accordance with ASTM D1238:2023, and / orwherein the solid epoxy resin has an epoxy equivalent weight (EEW) of from 800 to 6000 g / eq, preferably from 1200 to 3500 g / eq, more preferably from 1600 to 2000 g / eq.

9. A method for producing a thermoplastic dynamic vulcanizate (TPV) toughener, in particular a TPV toughener according to any of claims 1 to 8, for epoxy-based structural adhesives, comprising:a) heating and mixing rubber, in particular acrylonitrile butadiene rubber (NBR), with at least one solid epoxy resin (EP) and optionally one or more thermoplastic polymers to form a melt mixture,b) adding a peroxide crosslinking agent (CA) to the melt mixture,c) dynamically vulcanizing the melt mixture under shear stress, wherein crosslinking of the rubber, in particular acrylonitrile butadiene rubber (NBR),occurs concurrently with mixing such that a discrete crosslinked rubber phase is formed and dispersed in a continuous thermoplastic matrix phase comprising the solid epoxy resin.

10. The method according to claim 9, wherein the shear stress tears the curing rubber apart into discrete domains having a size of about 10 micrometer or smaller, in particular a domain size of 10-0.6 micrometer, in particular 5-0.6 micrometer, in particular 2-0.6 micrometer, in particular 1-0.6 micrometer, in particular 1-0.75 micrometer.

11. The method according to claim 9 or 10, further comprising adding a monofunctional epoxy compound that reacts with the rubber, in particular acrylonitrile butadiene rubber (NBR), to provide epoxy-functionalization.

12. The method according to any of claims 9-11 , wherein the optional one or more thermoplastic polymers are selected from polyvinyl butyral (PVB), polyvinyl chloride (PVC), polystyrene (PS), acrylonitrile butadiene styrene (ABS), polymethyl methacrylate (PMMA), polycarbonate (PC), polylactic acid (PLA), polyetherimide (PEI), thermoplastic epoxy resins such as polyhydroxy amino ethers (PHAE) or a combination thereof, and / orwherein the at least one crosslinkable rubber is selected from acrylonitrile butadiene rubber (NBR), silicone (MQ), polychloroprene (CR), polyurethane elastomers (Pll), ethylene propylene diene monomer (EPDM), fluoroelastomers (FKM), butyl rubber (HR), styrene-butadiene rubber (SBR), natural rubber (NR) and hydrogenated nitrile rubber (HNBR) or a combination thereof, wherein the at least one crosslinkable rubber is preferably selected from acrylonitrile butadiene rubber (NBR).

13. The method according to any of claims 9-12, further comprising adding a liquid epoxy resin as a viscosity modifier.

14. An epoxy-based structural adhesive composition comprising 15 to 50 wt% of the thermoplastic dynamic vulcanizate (TPV) toughener according to any of claims 1-8, wherein the TPV toughener provides impact resistance and toughness to the cured adhesive.

15. Use of the thermoplastic dynamic vulcanizate (TPV) toughener according to any of claims 1-8 as a toughening agent in one-component epoxy-based structural adhesives, wherein the discrete crosslinked rubber phase provides fracture toughness while the continuous thermoplastic matrix phase ensures processability.

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