Improvements in or relating to structural adhesives

Abstract

The present invention relates to improvements in or relating to structural adhesives that can be used to bond components, in particular metal components used in the vehicle industry.

Description

[0001] This application is a divisional application of a Chinese patent application with an application date of October 7, 2015, application number 201580066881.X, and invention name “Improvements in structural adhesives or improvements related to structural adhesives”.

[0002] This application claims priority to GB1417985.7 filed on October 10, 2014. Technical Field

[0003] The present invention relates to structural adhesives and in particular to heat activated structural adhesives useful for bonding parts, particularly metal parts used in the automotive industry. Background Art

[0004] Activatable structural adhesives are known from, for example, WO 2009 / 124709. The adhesive is typically a paste or liquid, which then enables implementation between two objects to be bonded, such as metal panels to be joined together. Usually the adhesive comprises two components which react when mixed and are therefore supplied as two separate materials, which are mixed at the location where a bond is to be formed. Structural adhesives can be used in vehicle reinforcements, such as cavity reinforcements, etc. Or in a variety of industries, they can be used to bond surfaces such as metal and plastic surfaces together.

[0005] Paste or liquid structural adhesives require special handling and storage to prevent or inhibit pre-reaction of the adhesive. In addition, they may suffer from the disadvantage that they will flow after application, making it difficult to position the bond and requiring the use of materials other than those required to produce the bond. In addition, it has not been possible to provide an adhesive formation that can be formed in an uncured state and can be cured to provide the high-strength bond required for structural adhesives.

[0006] However, there are applications where it is beneficial to have a dry and sufficiently flexible structural adhesive that can be formed at a temperature lower than the temperature at which it cures so that it has a definable shape prior to curing. In particular, it is useful to have a structural adhesive that can be provided in the form of a tape or strip and that can be configured into the desired shape between the surfaces to be bonded and then cured to bond the surfaces. It is also useful if the tape can be stored and provided in a reel.

[0007] Foamable structural adhesives which can be formed in their unformed state by extrusion or injection molding are known, for example materials used for bonding structural reinforcements in mold cavities of vehicle structures such as pillars and rails. However, there is a need to improve the processability of such materials in the uncured state, and in addition, it is desirable to increase the strength of the bonds formed, in particular from foamed materials, especially at low expansions, for example below 100%, to protect the fine tolerances required to ensure uniform strength of the bonds between the components.

[0008] Structural adhesives are typically curable materials that can be converted to a hardened adhesive material by heating within a certain temperature range for a certain period of time.

[0009] For curing structural adhesives, the temperature to be used and the time that can be specified can depend on the application in which the adhesive will be used. For example, when using adhesives for bonding in vehicle applications and aviation applications, the temperature and time can be different. The curing conditions to be used will affect the composition and reactivity of the adhesive. In order to make the adhesive have the required flexibility during blending and before curing, and have the required reactivity during bond formation, it is important that the pre-reaction of the adhesive is minimized during blending and processing and application and curing.

[0010] Known structural adhesives can be applied to substrates and subsequently cured by heating. It is also known that adhesives can be applied to substrates, then passed through an anti-corrosion bath, where an anti-corrosion coating is deposited on the substrate, and then baked to dry and hardened coatings. Structural adhesives can be formulated so that they are cured at the temperature experienced in the baking operation. Adhesives can typically be applied in the form of pastes by pumping the adhesive to the desired position on the substrate. However, the disadvantage that this can suffer is that when the substrate carrying the adhesive paste passes through the anti-corrosion coating bath, some adhesives may be washed off. The disadvantage that the use of pastes also suffers is that the uncured adhesive on the substrate is liquid and viscous to some extent, and dust or dirt can be accumulated. In addition, when two substrates to be joined are pressed together, it can be squeezed out from the position. This can also lead to fractures in the cured adhesive, providing sites for the potential corrosion of the metal bonded using it.

[0011] US2008 / 0305362 discloses two different material plates that can be bonded with a structural adhesive composition, the structural adhesive composition comprising microcapsules containing an anti-corrosion material for protecting the plates from corrosion. For example, an epoxy adhesive can be used to bond a steel door outer panel to an aluminum alloy or magnesium alloy inner panel. Dispersed in the uncured adhesive are a large number of microcapsules filled with a liquid or flowing material for reacting with iron and / or aluminum or magnesium to inhibit corrosion generated by the contact surface of the mixed metal plates. The protective material is released from the microcapsules and diffused through a cured or uncured interfacial adhesive to react with the surface of one or both plates and form a protective coating on the surface.

[0012] US2015 / 0050075 discloses a method for providing a corrosion-resistant barrier between dissimilar metals that are bolted together, comprising the following steps: placing an epoxy adhesive tape on at least one of a first metal member and a second metal member, curing the epoxy adhesive tape, applying a corrosion-resistant layer to the first metal member and the second metal member, and bolting the first metal member and the second metal member together so that the cured epoxy adhesive tape is located between the first metal member and the second metal member.

[0013] It has also been proposed that the adhesive can be a solid that is dry to the touch at ambient temperature. Such adhesives are described in PCT Publication WO 2013 / 068819. These adhesives can be applied to a substrate in a molten state so that they will adhere to the substrate but not solidify into their final solidified state to provide a structural adhesive. The adhesive can then be reheated to its solidification temperature when bonding is required. Unlike pumpable adhesives, these adhesives have a viscosity / temperature profile in which their structure is reversible until a certain temperature when solidification of the adhesive occurs, and is irreversible above a certain temperature.

[0014] We have now found that the use of adhesives of this type for bonding substrate structures together, particularly when at least one of the substrates is metal, enables the application of a continuous bead of adhesive which, when cured, has greatly reduced (if any) break points within the adhesive bead and, therefore, has a greatly reduced likelihood of corrosion forming over time along areas of the substrate surface to which the adhesive has been applied. Summary of the invention

[0015] Thus, the present invention provides a use of an adhesive for providing corrosion resistance to a substrate to which the adhesive is adhered, wherein the adhesive is reformable at a temperature in the range of about 60°C to about 120°C, and wherein the adhesive is curable at a temperature in the range of about 130°C to about 230°C; and wherein

[0016] - Storage modulus G of the adhesive I Greater than the loss modulus G of the adhesiveII That is G I >G II The temperature range in which the G I >G II The temperature range is no narrower than about 10°C to about 30°C; and

[0017] - Loss modulus G of the adhesive II Greater than the storage modulus G of the adhesive I That is G II >G I The temperature range of G II >G I The temperature range is not narrower than about 110°C to about 120°C.

[0018] It has surprisingly been found that the adhesive according to the invention, which is characterized by specific rheological properties at specific temperatures, can be advantageously used to prevent corrosion of substrates which are otherwise susceptible to corrosion.

[0019] Without wishing to be bound by any scientific theory, it appears that the use of a specific adhesive according to the invention provides a continuous protective layer of the substrate, preferably on a metal surface, thereby avoiding direct contact of the substrate with other metal surfaces applied to the other side of the adhesive along the bond line. Thus, when two substrates are bonded to each other, the adhesive is able to form a continuous insulating layer in the middle. The adhesive according to the invention, due to its specific properties, is able to creep into cavities of various shapes and cover surfaces under the conditions of application, so that after activation, i.e. heat treatment, the adhesive cures and develops its full adhesive properties, thereby providing corrosion resistance to the substrate to which it is applied and to the substrates to which it is bonded to each other, respectively.

[0020] Preferably, the adhesive is used to form a bond on a substrate that is not susceptible to causing corrosion on the substrate along the length of the bond. Preferably, the substrate comprises a metal or alloy that is susceptible to corrosion. Preferably, the adhesive is used in a manner such that a continuous tape or strip of adhesive is applied to the substrate.

[0021] Preferably, the adhesive according to the invention contains no corrosion inhibitors.

[0022] For purposes of this description, "not narrower than" means that at least throughout the specified temperature range, the adhesive has the specified properties. Thus, this definition also includes embodiments where the adhesive may, but need not, have the specified properties at certain temperatures outside the specified temperature range.

[0023] Preferably, G I >G IIThe temperature range is not narrower than about 10°C to about 35°C, more preferably not narrower than about 10°C to about 40°C, still more preferably not narrower than about 10°C to about 45°C, and most preferably not narrower than about 10°C to about 50°C.

[0024] Preferably, in G I >G II The storage modulus G of the adhesive is I and the loss modulus G of the adhesive II The relative difference G I -G II The adhesive is preferably at least about 10,000 Pa, more preferably at least about 20,000 Pa, and still more preferably at least about 30,000 Pa. In this regard, the adhesive need not meet this criterion at any temperature within the entire specified temperature range. Rather, when within the specified temperature range, it is sufficient that there is at least one temperature that meets the criterion at that temperature, without excluding the situation where this is more than one temperature and / or additional temperatures are outside the specified temperature range.

[0025] Preferably, G II >G I The temperature range is not narrower than about 105°C to about 120°C, more preferably not narrower than about 100°C to about 120°C; more preferably not narrower than about 95°C to about 120°C; still more preferably not narrower than about 90°C to about 120°C; even more preferably not narrower than about 85°C to about 120°C; and most preferably not narrower than about 80°C to about 120°C.

[0026] Preferably, in G II >G I The loss modulus G of the adhesive is II Storage modulus G of adhesive I The relative difference G II -G I At least about 3000 Pa, more preferably at least 4000 Pa, still more preferably at least about 5000 Pa, and in particular at least about 6000 Pa. In this respect, the adhesive does not need to meet this criterion at any temperature throughout the specific temperature range. On the contrary, when within the specific temperature range, it is sufficient that there is at least one temperature within which the criterion is met, without excluding the situation where this is more than one temperature and / or additional temperatures are outside the specific temperature range.

[0027] Preferably, at a crossover temperature in the temperature range of about 30°C to about 110°C, more preferably about 35°C to about 105°C, still more preferably about 35°C to about 100°C; still more preferably about 40°C to about 95°C; even more preferably about 40°C to about 90°C; most preferably about 45°C to about 85°C; and particularly about 50°C to about 80°C, the storage modulus G of the adhesive is I Equal to the loss modulus G of the adhesive II .

[0028] Preferably, the adhesive begins to cure at about 125°C, more preferably at about 130°C, to yield a thermosetting structural adhesive.

[0029] Preferably, the present invention provides the use of an adhesive for forming a bond on a substrate that is not susceptible to causing corrosion on the substrate along the length of the bond, wherein the adhesive

[0030] i) thermal activation at a temperature in the range of about 130°C to about 230°C;

[0031] ii)) is re-formable within a temperature range of about 60°C to about 120°C and curable within a temperature range of about 130°C to about 230°C, and has

[0032] a) For temperatures up to about 50°C, the storage modulus G I Greater than its loss modulus G II ;

[0033] b) Loss modulus G in the temperature range of about 60°C to about 120°C II Greater than its storage modulus G I ;and

[0034] c) Curing begins at about 130°C to obtain a thermosetting structural adhesive.

[0035] The structural adhesives of the present invention can be applied to a variety of articles for adding structural integrity to parts or components of an article or for sealing an article. Examples of such articles include, but are not limited to, household or industrial equipment, furniture, storage containers, buildings, structures, and the like. In a preferred embodiment, the structural adhesives of the present invention are used to bond parts of a vehicle or aircraft, such as the body or frame members (e.g., frame rails) of a vehicle.

[0036] The present invention provides a structural adhesive composition and its use having the following preferred properties:

[0037] i. it is not tacky to the touch at ambient temperature; and / or

[0038] ii. it is a flexible solid at temperatures ranging from ambient temperature to about 50°C; and / or

[0039] iii. it is a high viscosity liquid within a range of about 50°C to about 120°C; and / or

[0040] iv. it crosslinks at a temperature in the temperature range of about 120°C to about 230°C and develops adhesive properties; and / or

[0041] v. It provides a shear strength in the range of greater than about 10 MPa after crosslinking and cooling to ambient temperature.

[0042] Preferably, for non-swellable materials, the shear strength of the cured adhesive is greater than about 15 MPa, more preferably greater than about 20 MPa.

[0043] The term flexible solid means that within this temperature range the composition will retain its shape but is sufficiently ductile that it can be formed in situ in the area where a bond is to be formed. That a material is a flexible solid is a reflection of its viscoelastic behavior, which is determined by observing the material's response to an oscillating torque under a strain of ωRad / s.

[0044] Preferably, the structural adhesive according to the present invention is characterized in that the specific rheological properties at a specific temperature include viscoelasticity. Viscoelasticity is the property of a material that exhibits both viscous and elastic properties when subjected to deformation. When stress is applied, viscous materials resist shear flow and strain linearly over time. Elastic materials strain when stretched and quickly return to their original state once the stress is removed. Viscoelastic materials have elements of these properties and themselves exhibit time-dependent strain. The viscosity of the viscoelastic material gives the material a strain rate that is dependent on time. When a load is applied and then removed, the viscoelastic material loses energy. Hysteresis is observed in the stress-strain curve, and the area of ​​the loop is equal to the energy loss during the loading cycle. Since viscosity is a resistance to heat-activated plastic deformation, viscous materials will lose energy through the loading cycle. Plastic deformation leads to loss of energy, which is a non-specific reaction of pure elastic materials to loading cycles.

[0045] Viscoelasticity is studied using dynamic mechanical analysis, applying small oscillatory stresses and measuring the resulting strains. The principle of viscosity measurement is to apply a shear force to a material in an oscillatory or rotational mode and record the torque resistance. This torque is converted into a viscosity value (Pa·s) at a given shear rate and a given temperature. Purely elastic materials have stress and strain in phase so that the response of one caused by the other is direct. In a purely viscous material, the strain lags the stress through a 90 degree phase lag. Viscoelastic materials behave roughly in between these two materials, showing some strain hysteresis.

[0046] The complex dynamic modulus G can be used to express the relationship between oscillatory stress and strain. It has two components: storage modulus G I(elastic component) and loss modulus G II (viscous component). The maximum loss modulus G is observed II The temperature at which this occurs is also used in polymer science to determine the softening point (softening temperature) of viscoelastic materials and their glass transition temperature.

[0047] According to the present invention, the sample is preferably analyzed using an Anton Paar rheometer in shear mode at a frequency of ωRad / s and a heating rate of about 50°C to about 160°C over a period of about 90 minutes. A person skilled in the art knows how to measure the G I and G II The viscosity of the material is measured according to ASTM D 4092 and ASTM D 4065. Anton Paar rheometer device is preferably used for the viscosity measurement. The sample is a disk with a diameter of 24 mm and a height of 1 mm. The viscosity measurement is carried out at a frequency of 1 Hz, with a reduced strain of 1% to 0.1%, a temperature ramp between 120°C and 40°C of 3°C / min. The strain range has been selected to fit within the linear viscoelastic domain.

[0048] Viscoelastic behavior can be characterized by measuring the viscosity or the dynamic modulus. The storage modulus or elastic modulus (G I ), and the loss modulus or viscous modulus (G II ). If G I Greater than G II , the material is considered a flexible solid. However, for machinability, G I It must not be too large and within the temperature range of material processing (transformation). After the material is cross-linked, G I and G II Preferably, before cross-linking, the ratio G II / G I Close to 1, less than 1 from ambient temperature to about 50°C, and greater than 1 from about 50°C to about 120°C.

[0049] These properties of structural adhesives can be adjusted or changed in specific directions. I and G II This can be adjusted or varied by adjusting the epoxy equivalent weight (EEW) of the epoxy resin, or when the epoxy resin comprises one or more epoxy components selected from a solid epoxy resin and a liquid epoxy resin, by adjusting the relative amounts of the two epoxy components. This is a routine preliminary test.

[0050] In a preferred embodiment of the present invention, the structural adhesive is a one-component adhesive formulation that is heat activated and does not require the addition of additional reactive components to the formulation for bond formation to occur.

[0051] We have found that structural adhesives having these properties can be obtained from formulations comprising:

[0052] - high molecular weight resins;

[0053] - impact modifiers, and

[0054] -Curing agent for resin.

[0055] Preferred resins are high molecular weight epoxy resins, for example bisphenol A based solid epoxy resins, EPN or ECN epoxy resins. Other resins can be used, for example thermosetting polyurethanes. The impact modifier can be a core-shell polymer or a modified rubber, for example an epoxy resin / elastomer adduct (elastomer-modified epoxy resin) (for example rubber-modified epoxy resin, or an adduct of an epoxy resin and a solid carboxyl-terminated rubber such as a solid carboxyl-terminated acrylonitrile-butadiene rubber).

[0056] Dry materials can be formed by using fillers, particularly high surface area fillers, reducing or eliminating liquid components and including elastomeric and / or thermoplastic materials. Structural adhesives are crosslinkable and typically contain a curing agent for a resin component such as an epoxy, phenoxy or polyurethane resin, particularly an epoxy or phenoxy resin. Curing agents are generally heat activated, although they may react slowly at lower temperatures, but rapidly activate at the activation temperature. Prior to the activation temperature, the structural adhesive may be softened by heating, such as by G I and G II However, when the activation temperature of the curing agent is reached, the curing (cross-linking) of the resin will begin, G I and G II Both will increase. They will continue to increase until crosslinking is complete or the temperature is lowered, and when the temperature is lowered, they will remain at a high level, thereby providing the strong bond required for structural adhesives.

[0057] In one embodiment, the material of the present invention can be an expandable material, although non-expandable materials are included. In the case of expandable materials, the material can expand (e.g., foam) to a volume larger than the volume in the unexpanded state (e.g., at least about 5%, at least about 50%, at least about 100% relative to the original unexpanded volume). Similarly, it is typically preferred that at least for enhanced applications, the volume expansion makes the expanded volume less than about 400%, more typically less than about 300%, even more typically less than about 200%, and in some cases less than about 100% relative to the original unexpanded volume. Compared with the structural adhesives that have been foamed before, the adhesive of the present invention has improved strength. The present invention can be used for low-expanding foams with a degree of expansion lower than about 100%, such as about 40% to about 100%, especially about 50% to about 100%, relative to the original unexpanded volume, wherein the strength increase is greater relative to the previous structural foaming adhesive. It is also believed that after activation, the volume of the material may be smaller due to the curing (e.g., cross-linking) of the foamed or unfoamed variants of the structural adhesive.

[0058] The required performance of structural adhesive is in the temperature and environmental condition range that adhesive can withstand, good lap shear, high T peeling and good performance in Wedge impact test.Temperature range depends on the application that adhesive is put into use.Yet, in vehicle and aircraft industry, vehicle and aircraft can suffer from wide temperature range.Other required properties are included in various types of exposure conditions, for example under high humidity, salt water and high and low temperature, good bonding durability, and keep physical properties over time.In some applications, high elastic modulus, high Tg, high failure strain and other physical properties may be needed.When using the bond line test of for example 0.3mm thickness, structural adhesive of the present invention can have the elastic modulus typically greater than about 1GPa and the lap shear strength typically greater than about 10MPa.

[0059] Materials that can be used in the structural adhesive of the present invention are described below.

[0060] Modified Rubber-Epoxy / Elastomer Adducts:

[0061] Modified rubber, preferably epoxy / elastomer adducts, can be used to impart flexibility and the ability to induce plastic deformation to the structural adhesive. Various epoxy / elastomer adducts can be used in the present invention. An epoxy / elastomer adduct (or hybrid) of up to about 50 wt% of the structural adhesive can be included. The epoxy / elastomer adduct is about at least 5 wt% of the structural adhesive, more typically at least about 7 wt%, and even more typically at least about 10 wt%, and based on the structural adhesive, more preferably about 5 wt% to about 20 wt% of the epoxy / elastomer adduct. The epoxy / elastomer adduct can be a combination of two or more specific adducts, and the adduct can be a solid adduct, a semi-solid, or a combination thereof at a temperature of 23°C. Solid epoxy / elastomer adducts are preferred. In a preferred embodiment, the epoxy / elastomer adduct is substantially completely (i.e., at least about 70 wt%, about 80 wt%, about 90 wt% or more) composed of one or more epoxy / elastomer adducts that are solid at a temperature of 23°C. We have unexpectedly discovered that when the epoxy / elastomer adduct is used with a core / shell polymer and a phenoxy resin, desirable adhesive properties can be achieved over a wide temperature range using relatively small amounts of the epoxy / elastomer adduct. The relatively low amounts of epoxy / elastomer adduct, e.g., from about 5 wt % to about 15 wt %, impart high temperature stability to the structural adhesive because there is little undesirable drop in the Tg of the formulation.

[0062] The epoxy / elastomer adduct itself typically includes about 1:5 to 5:1 parts epoxy:elastomer, and more preferably about 1:3 to 3:1 parts epoxy:elastomer. More typically, the epoxy / elastomer adduct includes at least about 10 wt%, more typically at least about 20 wt%, and even more typically at least about 40 wt% elastomer, and also typically includes no more than about 60 wt% elastomer, relative to the total weight of the epoxy / elastomer adduct, although higher or lower percentages are possible. Elastomer compounds suitable for the epoxy / elastomer adduct can be thermosetting elastomers, although this is not required. Exemplary elastomers include, without limitation, natural rubber, styrene-butadiene rubber, polyisoprene, polyisobutylene, polybutadiene, isoprene-butadiene copolymers, neoprene, nitrile rubbers (e.g., nitrile, e.g., carboxyl-terminated nitrile rubber), butyl rubber, polysulfide elastomers, acrylic elastomers, acrylonitrile elastomers, silicone rubber, polysiloxanes, polyester rubbers, diisocyanate-linked condensation elastomers, EPDM (ethylene-propylene diene rubber), chlorosulfonated polyethylene, and fluorinated hydrocarbons, etc. In one embodiment, recycled tire rubber is used. Examples of additional or alternative epoxy / elastomer adducts suitable for use in the present invention are disclosed in U.S. Patent Publication No. 2004 / 0204551. Although epoxy / elastomer adducts may contain residual reactive epoxy functional groups, for the purposes of this specification, epoxy / elastomer adducts are not considered epoxy resins - these components are separate from each other.

[0063] The epoxy / elastomer adducts are included to modify the structural properties of the structural adhesive, such as strength, toughness, stiffness, flexural modulus, etc. Additionally, the epoxy / elastomer adducts may be selected to render the structural adhesive more compatible with coatings, such as waterborne paint or primer systems or other conventional coatings.

[0064] Phenoxy resin

[0065] Phenoxy resins can be used as high molecular weight resins. Phenoxy resins are high molecular weight thermoplastic condensation products of bisphenol A and epichlorohydrin and its derivatives. Typically, the phenoxy resins that can be used have the following basic formula:

[0066]

[0067] Wherein n is typically from 30 to 100, preferably from 50 to 90. Modified phenoxy resins may also be used. Examples of usable phenoxy resins are products sold by Inchem Corp. Examples of suitable materials are PKHB, PKHC, PKHH, PKHJ, PKHP pellets and powders. Alternatively, phenoxy / polyester hybrids and epoxy / phenoxy hybrids may be used. In order to enhance the production of structural adhesives, phenoxy resins may be supplied to the other components in the form of a solution. Although any solvent may be used, it is particularly preferred to use a liquid epoxy resin as a solvent because once activated, it may also contribute to adhesive properties. Based on the weight of the structural adhesive, we prefer to use a phenoxy resin greater than about 30wt%. Phenoxy resins typically do not contain residual reactive epoxy functional groups. Therefore, for the purposes of this specification, phenoxy resins are not considered to be epoxy resins - these components are separate from each other.

[0068] Core / Shell Impact Modifiers

[0069] Core / shell polymers can be used as impact modifiers. The term core / shell polymer as used herein refers to a polymeric material wherein a major portion (e.g., greater than about 30 wt%, about 50 wt%, about 70 wt%, or greater, relative to the gross weight of the core / shell polymer) of the polymer consists of a first polymeric material (i.e., a first or core material) that is substantially entirely encapsulated by a second polymeric material (i.e., a second or shell material). The first and second polymeric materials used herein may consist of one, two, three or more polymers that are combined and / or reacted together (e.g., sequentially polymerized) or may be a separate or identical core / shell system. The core / shell polymer should be compatible with the other components in the formulation, and preferably has a ductile core and a rigid shell that is compatible with the other components in the structural adhesive formulation.

[0070] The first and second polymer materials of the core / shell polymer can include elastomers, polymers, thermoplastic materials, copolymers, other components, or combinations thereof. In preferred embodiments, the first polymer material, the second polymer material, or both include or are substantially completely (e.g., at least about 70 wt%, about 80 wt%, about 90 wt% or more, relative to the total weight of the core / shell polymer) composed of more than one thermoplastic material. Exemplary thermoplastic materials include, without limitation, styrenes, acrylonitriles, acrylates, acetates, polyamides, or polyethylenes, etc.

[0071] Preferred core / shell polymers are formed by emulsion polymerization followed by coagulation or spray drying. For core / shell polymers, it is also preferred to be formed by core-shell graft copolymers or at least include core-shell graft copolymers. The glass transition temperature of the first or core polymer material of the graft copolymer is preferably significantly lower (i.e., at least 10°C, 20°C, 40°C or more) than the glass transition temperature of the second or shell polymer material. Moreover, although not required, it is desirable that the glass transition temperature of the first or core polymer material be lower than about 23°C, while the glass transition temperature of the second or shell polymer material be higher than about 23°C.

[0072] Examples of useful core-shell graft copolymers are those in which hard segment-containing compounds, such as styrene, acrylonitrile or methyl methacrylate, are grafted onto a core made of a soft or elastic compound, such as a polymer of butadiene or butyl acrylate. U.S. Pat. No. 3,985,703 discloses useful core-shell polymers whose cores are made of butyl acrylate, but can be based on ethyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate or other alkyl esters of acrylic acid or mixtures thereof. The core polymer may also include other copolymerizable compounds, such as styrene, vinyl acetate, methyl methacrylate, butadiene, or isoprene, etc. The core polymer material may also include crosslinking monomers having two or more non-conjugated double bonds of approximately equal reactivity, such as ethylene glycol diacrylate, butanediol dimethacrylate, etc. The core polymer material may also include grafted monomers having two or more non-conjugated double bonds of unequal reactivity, such as diallyl maleate and allyl methacrylate.

[0073] The shell portion is preferably polymerized from methyl acrylate, such as methyl methacrylate and optionally other alkyl esters of acrylic and methacrylic acid, such as ethyl acrylate or methacrylate, butyl ester or mixtures thereof, because these materials are compatible with the phenoxy resin and any epoxy resin used in the formulation. Up to about 40 wt% or more of the shell monomer can be styrene, vinyl acetate, vinyl chloride, etc. Additional core-shell graft copolymers useful in embodiments of the present invention are disclosed in U.S. Pat. Nos. 3,984,497; 4,096,202; 4,034,013; 3,944,631; 4,306,040; 4,495,324; 4,304,709; and 4,536,436. Examples of core-shell graft copolymers include, but are not limited to, "MBS" (methacrylate-butadiene-styrene) polymers, which are made by polymerizing methyl methacrylate in the presence of polybutadiene or a polybutadiene copolymer rubber. MBS graft copolymer resins typically have a styrene butadiene rubber core and an acrylic polymer or copolymer shell. Other useful examples of core-shell graft copolymer resins include ABS (acrylonitrile-butadiene-styrene), MABS (methacrylate-acrylonitrile-butadiene-styrene), ASA (acrylate-styrene-acrylonitrile), all acrylics, SAEPDM (styrene-acrylonitrile grafted onto an elastomeric backbone of ethylene-propylene diene monomers), MAS (methacrylic-acrylic rubber styrene), the like and mixtures thereof.

[0074] Examples of useful core / shell polymers include, but are not limited to, those commercially available from Rohm & Haas Co. sold under the trade name PARALOID. A particularly preferred grade of PARALOID impact modifier has a polymethyl methacrylate shell and an MBS core modifier and is sold under the designation EXL-2650; the product E-950 sold by Akema with equal effectiveness may also be used. We prefer to use about 5 to 30 wt% of the core-shell polymer relative to the total weight of the structural adhesive.

[0075] Curing agent:

[0076] One or more curing agents are included in the structural adhesives of the present invention. The curing agents will cause the high molecular weight resin to crosslink / cure (solidify) at elevated temperatures, thereby increasing G I and G IIOptionally, a curing agent accelerator may also be included. The amount of curing agent and curing agent accelerator used may vary widely, depending on the type of structure desired, the desired properties of the structural adhesive, and in embodiments where the material is expandable, the desired amount of expansion of the structural adhesive and the desired rate of expansion. An exemplary range of curing agent or curing agent accelerator present in the structural adhesive is from about 0.001 wt % to about 7 wt % relative to the total weight of the structural adhesive.

[0077] The curing agent assists in curing the structural adhesive by crosslinking of polymers, phenoxy resins, epoxy resins or both. For the curing agent, it is also preferred to assist in heat curing the structural adhesive. Useful groups of curing agents are selected from aliphatic or aromatic amines or their respective adducts, amidoamines, polyamides, alicyclic amines, anhydrides, polycarboxylic acid polyesters, isocyanates, materials in phenolic resins (e.g., phenol or cresol novolac resins, copolymers such as those of phenol terpenes, polyvinylphenol, or bisphenol-A formaldehyde copolymers, bishydroxyphenylalkanes, etc.). Particularly preferred curing agents include modified and unmodified polyamines or polyamides, such as triethylenetetramine, diethylenetriamine, tetraethylenepentamine, cyanoguanidine, dicyandiamide, etc. If an accelerator for a curing agent is used, examples of the material include modified or unmodified ureas, such as methylenediphenylbisurea, imidazoles or combinations thereof.

[0078] Epoxy resin:

[0079] High molecular weight resin can also be or include epoxy resin. Epoxy resin is used herein to refer to any conventional dimerization, oligomerization or polymerization epoxy material containing at least one epoxy functional group. Important epoxy content is currently greater than about 40wt%. And the term epoxy resin can be used to represent a combination of an epoxy resin or a variety of epoxy resins. Polymer-based materials can be epoxy-containing materials with more than one oxirane ring polymerizable by ring-opening reaction. In a preferred embodiment, the structural adhesive is included in an epoxy resin between about 2wt% to about 75wt%, more preferably an epoxy resin between about 4wt% to about 60wt%, and even more preferably an epoxy resin between about 25wt% to about 50wt%. Of course, the amount of epoxy resin can be larger or lower, depending on the intended application of the structural adhesive.

[0080] Epoxy resins can be aliphatic, alicyclic, aromatic, etc. Epoxy resins can be supplied as solids (e.g., in pellets, chunks, flakes, etc.) or liquids (e.g., epoxy resins), although solid resins are preferred for preparing dry structural adhesive materials. Liquid resins can sometimes be used as solvents for additional components in the formulation, such as phenoxy resins (or to increase the crosslinking density of the formulation). Unless otherwise specified, if the resin used herein is solid at a temperature of 23°C, the resin is a solid resin, and if it is liquid at a temperature of 23°C, it is a liquid resin. Epoxy resins may include ethylene copolymers or terpolymers. As copolymers or terpolymers, the polymer is composed of two or three different monomers, i.e., small molecules with high chemical reactivity that can react with similar molecules.

[0081] Epoxy resins can be added to structural adhesives to increase the adhesion, flow properties, strength or rigidity of the material. An exemplary epoxy resin can be a phenolic resin, which can be a novolac type or other types of resins. Other preferred epoxy-containing materials can include bisphenol-A epichlorohydrin ether polymers, or bisphenol-A epoxy resins modified with butadiene or other polymer additives, or bisphenol-F type epoxy resins. Moreover, various mixtures of a variety of different epoxy resins can be used equally. Examples of suitable epoxy resins are sold under the trade names Araldite GY282, GY281 and GY285 supplied by Huntsman.

[0082] Other Ingredients:

[0083] The composition of the present invention may contain other ingredients, such as one or more of the following

[0084] i) polymers or copolymers;

[0085] ii) a blowing agent;

[0086] iii) fillers;

[0087] iv) flow control materials;

[0088] v) nanoparticles;

[0089] vi) pigments;

[0090] vii) flame retardants;

[0091] viii) fibers; and / or

[0092] ix) Moisture scavengers.

[0093] Polymer or copolymer:

[0094] Depending on the application for which the structural adhesive is to be used, it may include one or more additional polymers or copolymers, which may or may not contain functional groups, which may include a variety of different polymers, such as thermoplastics, elastomers, plastomers, combinations thereof, etc. For example, and without limitation, polymers that may be suitably incorporated into structural adhesives include halogenated polymers, polycarbonates, polyketones, polyurethanes, polyesters, silanes, sulfones, allyls, olefins, styrenes, acrylates, methacrylates, epoxies, silicones, phenols, rubbers, polyphenylene oxides, terephthalates, acetates (e.g., EVA), acrylates, methacrylates (e.g., ethylene methyl acrylate polymers), or mixtures thereof. Other potential polymeric materials may be or may include without limitation polyolefins (e.g., polyethylene, polypropylene), polystyrene, polyacrylates, poly(ethylene oxide), poly(ethyleneimine), polyesters, polyurethanes, polysiloxanes, polyethers, polyphosphazenes, polyamides, polyimides, polyisobutylene, polyacrylonitrile, poly(vinyl chloride), poly(methyl methacrylate), polyvinyl acetate, poly(vinylidene chloride), polytetrafluoroethylene, polyisoprene, polyacrylamide, polyacrylic acid, and polymethacrylate.

[0095] When used, these polymers may include a small portion or a more significant portion of the material. When used, one or more additional polymers preferably include from about 0.1 wt % to about 50 wt %, more preferably from about 1 wt % to about 20 wt % and even more preferably from about 2 wt % to about 10 wt % of the structural adhesive.

[0096] In certain embodiments, it may be desirable to include more than one thermoplastic polyether and / or thermoplastic epoxy resin in the structural adhesive. When included, the more than one thermoplastic polyether is preferably included in between about 1 wt % to about 90 wt % of the structural adhesive, more preferably between about 3 wt % to about 60 wt % of the structural adhesive, and even more preferably between about 4 wt % to about 25 wt % of the structural adhesive. However, with respect to other materials, more or less thermoplastic polyethers may be used, depending on the intended use of the structural adhesive.

[0097] Thermoplastic polyethers typically include pendant hydroxyl moieties. Thermoplastic polyethers may also include aromatic ether / amine repeating units within their backbones. Thermoplastic polyethers preferably have a melt index between about 5 and about 100 g / 10 min, and more preferably between about 25 and about 75 g / 10 min, and even more preferably between about 40 and about 60 g / 10 min, for a 2.16 kg sample weighed at a temperature of about 190° C. Of course, thermoplastic polyethers may have a higher or lower melt index, depending on their intended use. Preferred thermoplastic polyethers include, without limitation, polyetheramines, poly(amino ethers), copolymers of monoethanolamine and diglycidyl ether, combinations thereof, and the like.

[0098] Preferably, the thermoplastic polyether is formed by reacting an amine having an average functionality of 2 or less (e.g., a difunctional amine) with a glycidyl ether (e.g., a diglycidyl ether). As used herein, the term difunctional amine refers to an amine having an average of 2 reactive groups (e.g., reactive hydrogens).

[0099] According to one embodiment, the thermoplastic polyether is formed by reacting a primary amine, a bis(secondary)diamine, a cyclic diamine, or a combination thereof, or the like (e.g., monoethanolamine) with a diglycidyl ether or by reacting an amine with an epoxy-functionalized poly(alkylene oxide) to form a poly(amino ether). According to another embodiment, the thermoplastic polyether is prepared by reacting a difunctional amine with a diglycidyl ether or a diepoxy-functionalized poly(alkylene oxide) under conditions sufficient to cause the amine moieties to react with the epoxy moieties to form a polymer backbone having amine linkages, ether linkages, and pendant hydroxyl moieties. Optionally, the polymer may be treated with a monofunctional nucleophile, which may or may not be an amine, primary or secondary amine.

[0100] Additionally, it is believed that amines (e.g., cyclic amines) having one reactive group (e.g., one reactive hydrogen) may be used to form thermoplastic polyethers. Advantageously, such amines may assist in controlling the molecular weight of the thermoplastic ether formed.

[0101] Examples of preferred thermoplastic polyethers and methods of forming them are disclosed in US Pat. Nos. 5,275,853; 5,464924; and 5,962,093. Advantageously, thermoplastic polyethers can provide structural adhesives having various desirable characteristics, such as desirable physical and chemical properties, for use in a wide variety of applications as further described herein.

[0102] Although not required, the formulation may include more than one ethylene polymer or copolymer, such as ethylene acrylate copolymer, ethylene vinyl acetate copolymer. Ethylene methacrylate and ethylene vinyl acetate are two preferred ethylene copolymers.

[0103] It may also be desirable to include reactive polyethylene resins modified with more than one reactive group, such as glycidyl methacrylate or maleic anhydride. Examples of such polyethylene resins are marketed under the trade names (e.g., LOTADERAX 8900) is sold and commercially available from Arkema Group.

[0104] Foaming agent:

[0105] The present invention contemplates both non-expandable and expandable structural adhesives, although non-expandable materials are more typical. If the structural adhesive is expandable, one or more blowing agents may be added to generate an inert gas that forms an open-cell and closed-cell structure within the structural adhesive as desired. In this manner, the density of the article manufactured by using the structural adhesive may be reduced. In addition, expansion of the material may help improve sealing capabilities, sound damping, and particularly adhesion to the bonding substrate.

[0106] The blowing agent may include more than one nitrogen-containing group, such as amides and amines. Examples of suitable blowing agents include azodicarbonamide, dinitropentamethylenetetramine, azodicarbonamide, dinitropentamethylenetetramine, 4,4'-oxy-bis-(benzenesulfonylhydrazide), trihydrazide triazine and N,N'-dimethyl-N,N'-dinitroterephthalamide. A promoter for the blowing agent may also be provided. Various promoters may be used to increase the rate at which the blowing agent forms an inert gas. A preferred blowing agent promoter is a metal salt, or an oxide, such as a metal oxide, such as zinc oxide. Other preferred promoters include modified and unmodified thiazoles or imidazoles (ureas).

[0107] Another group of blowing agents are physical blowing agents, such as the Expancel products sold by Akzo-Nobel. These blowing agents consist of polymer particles with a volatile liquid in the center. When the temperature rises, the polymer shell softens and the gas inside the particles causes the polymer particles to expand. In this way, a foamed product is produced.

[0108] The amount of blowing agent and blowing agent promoter used can vary widely, depending on the type of cell structure desired, the desired amount of expansion of the structural adhesive, and the desired rate of expansion, etc. Exemplary amounts of blowing agents and blowing agent promoters in the structural adhesive range from about 0.001 wt % to about 5 wt %, relative to the total weight of the structural adhesive, and are preferably present in the structural adhesive as a weight percent.

[0109] filler:

[0110] Structural adhesives may also include more than one filler, including but not limited to granular materials (e.g., powders), beads, microspheres such as Zeospheres from Zeelan Industries, etc. Preferably, fillers include materials that are usually non-reactive with other components present in the structural adhesive. However, the surface may be treated to improve adhesion or compatibility with the adhesive matrix. Although fillers may be present in structural adhesives generally, occupying space at relatively low weight and cost, it is believed that fillers may also impart properties such as strength and impact resistance to structural adhesives.

[0111] Examples of fillers that can be used include silica, diatomaceous earth, glass, clay (e.g., including nanoclay), talc, pigments, colorants, glass beads or bubbles, glass, carbon or ceramic fibers, nylon or polyamide fibers (e.g., Kevlar), antioxidants, and the like. Such fillers, particularly clays, can assist the structural adhesive in leveling itself during the flow of the material. Clays that can be used as fillers can include calcined clays from the kaolinite, illite, chlorite, montmorillonite or sepiolite groups. Examples of suitable fillers include, without limitation, talc, vermiculite, pyrophyllite, sauconite, saponite, nontronite, montmorillonite or mixtures thereof. Clays can also include trace amounts of other ingredients, such as carbonates, feldspars, mica and quartz. Fillers can also include ammonium chlorides, such as dimethylammonium chloride and dimethylbenzylammonium chloride. Titanium dioxide can also be used.

[0112] In a preferred embodiment, one or more inorganic or stone type fillers, such as calcium carbonate, sodium carbonate, etc., can be used as fillers. In another preferred embodiment, silicate minerals, such as mica, can be used as fillers.

[0113] When used, the filler in the structural adhesive can be about 10wt% or less to about 70wt% or more of the structural adhesive. According to some embodiments, the structural adhesive may include about 0wt% to about 3wt% relative to the gross weight of the structural adhesive, and more preferably a little less than about 1wt% clay or similar filler. The filler of the mineral type of pulverization (e.g., average diameter of about 0.01 to about 50 microns, and more preferably about 1 to 25 microns) may include about 5wt% to 70wt% relative to the gross weight of the structural adhesive, more preferably about 10wt% to about 50wt%.

[0114] Other components and additives:

[0115] It is contemplated that most any additional chemical, material, or other substance may be added to the structural adhesive, provided they are suitable for the selected application of the structural adhesive.

[0116] Other additives, agents or performance modifiers may also be included as desired, including, but not limited to, antioxidants, UV inhibitors, flame retardants, heat stabilizers, colorants, processing aids, lubricants, reinforcing agents (e.g., chopped or continuous glass, ceramic, aramid, or carbon fibers, or particulates). Particularly epoxidized liquid polysulfides can be used to improve environmental exposure of the adhesive, such as exposure to moisture and salt water.

[0117] When determining suitable components for structural adhesives, it is important to form materials that will activate (e.g., flow, foam, or otherwise change state) only at the appropriate time or temperature. For example, it is not desirable for the material to be reactive at ambient temperature within the assembly environment. More typically, structural adhesives become activated at higher processing temperatures. As an example, temperatures such as those encountered in a vehicle assembly shop may be suitable, particularly when the structural adhesive is processed together with other components at elevated temperatures or at higher applied energy levels, such as during a paint preparation step. Temperatures encountered in many coating operations (e.g., in paint and / or e-coat curing ovens), for example, range up to about 250°C or more.

[0118] The relative proportions of the materials that should be used will depend on the intended use of the structural adhesive. However, we prefer to use from about 40 wt% to about 75 wt% of a high molecular weight resin, from about 10 wt% to about 25 wt% of an impact modifier, and from about 0.5 wt% to about 10 wt% of a curing agent. Preferred amounts of other optional ingredients are as follows: from about 5 wt% to about 75 wt% of one or more epoxy resins, preferably liquid epoxy resins, from about 0.2 wt% to about 3 wt% of a curing accelerator, from about 0.1 wt% to about 50 wt% of a mineral filler, and from about 0.1 wt% to about 3.0 wt% of clay and / or silica.

[0119] Formation, processing, storage and application of structural adhesives:

[0120] The formation of structural adhesive can be realized according to various new or known technologies. According to one embodiment, it is possible to melt blend with curing agent to form structural adhesive by supplying resin, such as high molecular weight resin and solid form such as pellet, bulk, etc., and at a temperature lower than the temperature when curing agent is activated. Alternatively, if phenoxy resin is used, a phenoxy resin solution in liquid epoxy resin can be used, and blended with core / shell polymer, then filler can be added, and finally, preferably under vacuum to remove any entrained air, curing agent and optionally any curing agent accelerator are added and mixed. Typically, each component is combined in more than one blender, such as large bins or other containers. Preferably, a container can be used, by rotating or otherwise moving the container, to mix each component. Afterwards, heat, pressure or its combination can be applied to soften or liquefy solid components so that each component can be mixed into a single uniform composition by stirring or other means. Then heat and pressure can be relaxed to obtain the dry structural adhesive of the present invention, as the flexible solid described herein. The pellets may then be pelletized, and the pellets may be further processed, such as by injection molding or blow molding, to form structural adhesive shaped materials, or the pellets may be extruded to form flexible strips or tapes of structural adhesive.

[0121] It is important to ensure that once the curing agent has been added, the temperature of the components is kept below the curing temperature of the adhesive during blending and processing so that G I and G II Keep it low and avoid significant pre-reaction. Additionally, when the structural adhesive contains a blowing agent, it is desirable to maintain the temperature of the structural adhesive below a temperature that would activate the blowing agent during formation and processing of the structural adhesive.

[0122] In use, the structural adhesive of the present invention is typically formed at a temperature below the curing (crosslinking) temperature to produce a flexible shaped body of the desired shape, which may be a preformed component or tape or strip. The adhesive can then be placed together with the components to be bonded together and activated to cure / crosslink the structural adhesive. Activation can be achieved in a paint oven. In this case, the formulated adhesive is activated at a desired temperature, which ranges from about 120°C to about 230°C. In vehicle manufacturing, where activation typically occurs at an elevated temperature in the range of about 140°C to about 200°C, the time required for curing / crosslinking of the adhesive depends on the requirements of the assembly line and the temperature used therein, with about 30 minutes being typical. In the case where the structural adhesive includes a blowing agent, the activation of the material may also include at least a certain degree of foaming or bubbling. Such foaming or bubbling can assist the structural adhesive in wetting the substrate and forming a tight bond with the substrate. In a further embodiment, the structural adhesive can be extruded in situ at the location where it is to be activated to form a bond, although the adhesive is particularly suitable for being formed into any desired shape and preassembled with the materials to be bonded together, and the adhesive is activated by heating to a curing temperature and for a desired time so that it bonds the materials together. During activation, the adhesive crosslinks to increase G I and G II , where subsequently when the temperature drops, the G I and G II will remain at a high level.

[0123] The adhesive of the present invention is applied in any suitable form. For example, it can be extruded into a tape, strip or film, it can be extruded and granulated, it can be blown, injection molded, thermoformed or hot pressed into the final shape of the desired adhesive. It is particularly useful that the adhesive can be formed at a temperature lower than the temperature at which significant thermal curing occurs and at a temperature at which it is flexible (up to about 120° C.), and then can be cooled to form an integral structure, such as a formed part, tape or strip, which can be wound into a coil for storage and supply. Alternatively, the adhesive can be applied to the surface of one of the carrier or components to be bonded together and transported to a place where it can be assembled with other components and heated to produce bonding between the carrier or component and the other components.

[0124] The carrier or assembly provided with the adhesive can be produced at one location and transported to another location where the bond is generated. The adhesive can be supplied to one or more surfaces to be bonded in a ductile form that allows it to be attached to one or more surfaces. The surfaces to be bonded can then be bonded together by bringing the adhesive therebetween and by heating the adhesive to a temperature range (about 120°C to about 230°C) where it will crosslink. The structure can then be allowed to cool to provide a strong bond between the two surfaces.

[0125] We have found that the structural adhesive, whether pellets, preformed components, tapes or strips or deposited on a carrier or component surface, can be stored and transported at a temperature ranging from about 10°C to about 80°C (e.g., about 50°C) without any undesirable pre-reaction and without the onset of significant crosslinking. Storage for 21 days without significant crosslinking is considered to exhibit storage stability.

[0126] In another embodiment, the adhesive can be extruded onto one surface of an article at a temperature in a range where the adhesive remains flexible and then allowed to cool to provide a desired pattern of heat-activatable adhesive on the surface that is dry to the touch. The article can then be contacted with the surface of another article so that the adhesive contacts the other surface and is heated to a temperature for a cross-linking reaction to create a bond between the surfaces. This method is disclosed in European Patent Publication 1331080.

[0127] In a preferred embodiment, the adhesive is in the form of a tape, strip or film produced by extrusion. The preferred dimensions of the tape, strip or film will depend on the application for which it is put to use, however, tapes used for structural bonding in the automotive and aircraft industries typically have a thickness of about 0.3 to about 15 mm and a width of about 10 to about 100 mm.

[0128] In further embodiments, the adhesive may be supplied with a backing material that may be removed once the adhesive is positioned to form a bond.

[0129] Depending on the intended application, the structural adhesive can be applied and activated in different ways and at different times. The material can be formed into strips and applied to any place where it is to be used by hand or machinery. The material can be extruded to the position where it is to be used. Therefore, the exemplary use of structural adhesives is discussed below to set forth the preferred method for the application and activation of structural adhesives. In particular, structural adhesives can be particularly used for strengthening, sealing or bonding, etc.

[0130] Enhancements:

[0131] Structural adhesives can be used to reinforce structural elements of manufactured articles. When used for reinforcement, the structural adhesive can be used by itself, it can be used in conjunction with other materials (such as linings), or it can be applied to a carrier element or the like. Structural adhesives are particularly useful for providing strength to metal welds, such as weld flanges, and can be applied between metal sheets that are subsequently welded together. In a further preferred use, the material is used to bond metal components together, thereby eliminating the need for welding.

[0132] According to one embodiment, the structural adhesive of the present invention is applied to a carrier element, a reinforcement element is formed and the reinforcement element is inserted into a cavity formed by a structural element of a vehicle. The structural element of the vehicle can be any element of the vehicle, including but not limited to, a frame element, a track, a body element, a pillar structure, a cover, a roof assembly, a bumper, or a combination thereof.

[0133] The carrier element can be selected from a variety of conventional and novel structures. The structural adhesive of the present invention can thus be applied to a carrier element, such as a formed, extruded or stamped element (e.g., metal or plastic, foamed or unfoamed; exemplary materials thereof include aluminum, magnesium, titanium, steel, molding compounds (e.g., sheet molding compounds or integral molding compounds), polyamides (e.g., nylon 6 or nylon 6,6), polysulfones, thermoplastic imides, polyetherimides, polyethersulfones or mixtures thereof. The adhesive can be applied at a temperature lower than the temperature at which crosslinking begins, so that it adheres to the carrier, and cooled to provide a material that is not tacky to the touch, ready for subsequent activation and crosslinking.

[0134] It has been found that the material of the present invention is an effective structural adhesive which has the desired performance in the extended temperature range, particularly in the Wedge impact test. It has been found that the material maintains their adhesive properties in the extended time period and is effective in humidity or salt spray environments. They can be used for structural bonding in various applications, such as in automobiles, aircraft, aerospace, railroad vehicles, trucks, public vehicles, sporting goods, structures and furniture industries. It has been found that they can be used particularly in the enhanced welded areas, and in some cases, in the areas welded so far, avoid the need for welding.

[0135] Another aspect of the invention relates to a method for providing corrosion resistance to a substrate, comprising applying an adhesive according to the invention as defined above for use as a continuous tape or strip to a substrate, positioning the adhesive adjacent the adhesive-laden substrate to a second substrate and activating the adhesive to bond the two substrates together.

[0136] All preferred embodiments according to the invention which have been described above in connection with the use also apply analogously to the method according to the invention.

[0137] Preferably, the method according to the present invention is used to form a bond on a substrate that is not susceptible to causing corrosion on the substrate along the length of the bond.

[0138] In a preferred embodiment of the method according to the invention, a continuous tape or strip of adhesive is applied to the substrate.

[0139] Preferably, the substrate comprises a metal or alloy that is susceptible to corrosion.

[0140] Preferably, the present invention provides a method for forming a non-corrosion resistant bond comprising applying a structural adhesive as a continuous tape or strip to a substrate, positioning the adhesive on the adhesive-laden substrate adjacent a second substrate, and activating the adhesive to bond the two substrates together, wherein the adhesive

[0141] i) thermal activation at a temperature in the range of about 130°C to about 230°C;

[0142] ii) re-formable within a temperature range of about 60°C to about 120°C, and curable within a temperature range of about 130°C to about 230°C, and having

[0143] a) For temperatures up to about 50°C, the storage modulus G I Greater than its loss modulus G II ;

[0144] b) Loss modulus G in the temperature range of about 60°C to about 120°C II Greater than its storage modulus G I ;and

[0145] c) Curing begins at about 130°C to obtain a thermosetting structural adhesive. BRIEF DESCRIPTION OF THE DRAWINGS

[0146] Figures 1 to 4 is the storage modulus G of the structural adhesive of the present invention I and loss modulus G II . DETAILED DESCRIPTION

[0147] The following examples further illustrate the present invention but should not be construed as limiting its scope.

[0148] Embodiment 1:

[0149] Structural adhesive formulations containing a curable polymer and a curing agent that begins to cure at about 125°C were prepared and their storage modulus G was measured over a temperature range of about 30°C to about 110°C. I and loss modulus G II ,like Figure 1 shown.

[0150] The storage modulus G was also measured during heating of the adhesive at about 30°C to about 110°C over a period of 3500 seconds. 1 and loss modulus G II , and then dropped to about 40°C. Storage modulus G I and loss modulus G II The changes are shown in Figure 2, it is shown that at about 70°C the product changes from a solid state to a viscous liquid and that this is reversible up to a temperature of about 11°C.

[0151] It has been found that the adhesive can be applied to a metal surface at a temperature of about 10°C to provide a continuous strip of adhesive which cures to obtain a well-defined structural bond which appears to provide long-term corrosion resistance to controlled areas of the metal surface.

[0152] Embodiment 2:

[0153] According to Example 1, a structural adhesive formulation containing a curable polymer and a curing agent that begins to cure at about 125°C was prepared from the following ingredients in the following amounts:

[0154]

[0155] like Figure 3 As shown, the storage modulus G is measured in the temperature range of about 30°C to about 110°C. I and loss modulus G II The absolute value of the difference between G' and G' is also shown (y-axis to the right). The crossover temperature is observed at about 66.5°C.

[0156] Embodiment 3:

[0157] According to Examples 1 and 2, a structural adhesive formulation containing a curable polymer and a curing agent that begins to cure at about 125°C was prepared from the following ingredients in the following amounts:

[0158] Element wt% Solid epoxy resin type I (EEW ​​450-530g / eq) 4.00 Liquid epoxy resin (EEW ​​200g / eq) 22.00 MBS-based core-shell impact modifier 13.40 Polyvinyl butyral 4.85 Phenolic resin derived from bisphenol A 16.95 Epoxy terminated CTBN adduct 20.00 Micronized polyamide 6 / 12 (particle size 20 μm) 8.00 talc 1.01 Calcium Oxide 5.00 Thixotropic agent (organoclay) 0.76 pigment 0.05 Disubstituted urea 0.35 Dicyandiamide 3.00 Chemical foaming agent ADCA 0.63 Total 100.00

[0159] like Figure 4 As shown, the storage modulus G is measured in the temperature range of about 30°C to about 120°C. I and loss modulus G II The absolute value of the difference between G' and G' is also shown (y-axis to the right). A crossover temperature is observed at about 94°C.

Claims

1. Use of an adhesive for providing corrosion resistance to a substrate to which the adhesive is adhered, wherein the adhesive is reformable at a temperature in the range of 60°C to 120°C, and wherein the adhesive is curable at a temperature in the range of 130°C to 230°C; and wherein - Storage modulus G of the adhesive I Greater than the loss modulus G of the adhesive II G I >G II The temperature range of G I >G II The temperature range is not narrower than 10°C to 30°C; and - Loss modulus G of the adhesive II Greater than the storage modulus G of the adhesive I That is G II >G I The temperature range of G II >G I The temperature range is not narrower than 110°C to 120°C.

2. The use according to claim 1, wherein the G I >G II The temperature range is not narrower than 10°C to 35°C.

3. The use according to claim 2, wherein the G I >G II The temperature range is not narrower than 10°C to 40°C.

4. The use according to claim 3, wherein the G I >G II The temperature range is not narrower than 10°C to 45°C.

5. The use according to claim 4, wherein the G I >G II The temperature range is not narrower than 10°C to 50°C.

6. The use according to any one of claims 1 to 5, wherein in the G I >G II The storage modulus G of the adhesive is I and the loss modulus G of the adhesive II The relative difference G I -G II At least 10,000Pa.

7. The use according to claim 6, wherein in the G I >G II The storage modulus G of the adhesive is I and the loss modulus G of the adhesive II The relative difference G I -G II At least 30,000Pa.

8. The use according to any one of claims 1 to 5, wherein the G II >G I The temperature range is not narrower than 105°C to 120°C.

9. The use according to claim 8, wherein the G II >G I The temperature range is not narrower than 100°C to 120°C.

10. The use according to claim 9, wherein the G II >G I The temperature range is not narrower than 95°C to 120°C.

11. The use according to claim 10, wherein the G II >G I The temperature range is not narrower than 90°C to 120°C.

12. The use according to claim 11, wherein the G II >G I The temperature range is not narrower than 85°C to 120°C.

13. The use according to claim 12, wherein the G II >G I The temperature range is not narrower than 80°C to 120°C.

14. The use according to any one of claims 1 to 5, wherein in the G II >G I The loss modulus G of the adhesive is II The storage modulus G of the adhesive I The relative difference G II -G I At least 3000Pa.

15. The use according to any one of claims 1 to 5, wherein in the G II >G I The loss modulus G of the adhesive is II The storage modulus G of the adhesive I The relative difference G II -G I At least 6000Pa.

16. The use according to any one of claims 1 to 5, wherein at a crossover temperature in the temperature range of 30°C to 110°C, the storage modulus G of the adhesive is I Equal to the loss modulus G of the adhesive II .

17. Use according to claim 16, wherein the crossover temperature is in the temperature range of 35°C to 105°C.

18. Use according to claim 17, wherein the crossover temperature is in the temperature range of 35°C to 100°C.

19. The use according to claim 16, wherein the crossover temperature is in the temperature range of 40°C to 95°C.

20. The use according to claim 17, wherein the crossover temperature is in the temperature range of 40°C to 90°C.

21. The use according to claim 18, wherein the crossover temperature is in the temperature range of 45°C to 85°C.

22. The use according to claim 19, wherein the crossover temperature is in the temperature range of 50°C to 80°C.

23. The use according to any one of claims 1 to 5, wherein the adhesive starts to cure at 125°C to obtain a thermosetting structural adhesive.

24. Use according to any one of claims 1 to 5, wherein the adhesive starts to cure at 130°C to obtain a thermosetting structural adhesive.

25. The use according to any one of claims 1 to 5, wherein the adhesive is used to form a bond on the substrate and is not susceptible to causing corrosion on the substrate along the length of the bond, wherein the adhesive - thermal activation at a temperature in the range of 130°C to 230°C; - Reformable within the temperature range of 60°C to 120°C; - curable at a temperature in the range of 130°C to 230°C; and The adhesive has -For temperatures below 50°C, the storage modulus G I Greater than its loss modulus G II ; -In the temperature range of 60℃ to 120℃, the loss modulus G II Greater than its storage modulus G I ; and - Curing starts at 130°C to obtain a thermosetting structural adhesive.

26. The use according to any one of claims 1 to 5, wherein the adhesive is non-tacky to the touch at ambient temperature.

27. Use according to any one of claims 1 to 5, wherein the adhesive is a flexible solid at a temperature in the range of ambient temperature to 50°C.

28. Use according to any one of claims 1 to 5, wherein the adhesive is a high viscosity liquid at a temperature in the temperature range of 50°C to 120°C.

29. The use according to any one of claims 1 to 5, wherein the adhesive crosslinks and develops adhesive properties at a temperature in the temperature range of 120°C to 230°C.

30. The use according to any one of claims 1 to 5, wherein the adhesive provides a shear strength of greater than 10 MPa after crosslinking and cooling to ambient temperature.

31. The use according to claim 30, wherein the shear strength of the adhesive is greater than 15 MPa.

32. The use according to claim 31, wherein the shear strength of the adhesive is greater than 20 MPa.

33. The use according to any one of claims 1 to 5, wherein the adhesive comprises an epoxy resin.

34. The use according to claim 33, wherein the epoxy resin comprises one or more epoxy components selected from solid epoxy resins and liquid epoxy resins.

35. The use according to claim 33, wherein the content of the epoxy resin is in the range of 2 wt% to 75 wt% relative to the total weight of the adhesive.

36. Use according to any one of claims 1 to 5, wherein the adhesive comprises a curing agent.

37. The use according to claim 36, wherein the curing agent comprises dicyandiamide.

38. The use according to claim 36, wherein the content of the curing agent is in the range of 1.0 wt% to 10 wt% relative to the total weight of the adhesive.

39. Use according to any one of claims 1 to 5, wherein the adhesive comprises an impact modifier.

40. The use according to claim 39, wherein the impact modifier comprises a core-shell polymer and / or a modified rubber.

41. The use according to claim 39, wherein the content of the impact modifier is in the range of 10 wt% to 20 wt% relative to the total weight of the adhesive.

42. The use according to any one of claims 1 to 5, wherein the adhesive comprises a phenoxy resin.

43. The use according to claim 42, wherein the content of the phenoxy resin is in the range of 10 wt% to 20 wt% relative to the total weight of the adhesive.

44. Use according to any one of claims 1 to 5, wherein the adhesive comprises a blowing agent.

45. The use according to claim 44, wherein the blowing agent is a chemical blowing agent or a physical blowing agent.

46. ​​The use according to claim 44, wherein the content of the foaming agent is in the range of 0.001 wt% to 5.0 wt% relative to the total weight of the adhesive.

47. Use according to any one of claims 1 to 5 for forming a bond on a substrate which is not susceptible to causing corrosion on the substrate along the length of the bond.

48. Use according to any one of claims 1 to 5, wherein a continuous tape or strip of the adhesive is applied to a substrate.

49. Use according to any one of claims 1 to 5, wherein the substrate comprises a metal or alloy susceptible to corrosion.

50. A method of providing corrosion resistance to a substrate comprising applying an adhesive according to any one of claims 1 to 46 as a continuous tape or strip to a substrate, positioning the adhesive on an adhesive-laden substrate adjacent a second substrate, and activating the adhesive to bond the two substrates together.

51. The method of claim 50 for forming a bond on a substrate that is not susceptible to causing corrosion on the substrate along the length of the bond.

52. A method according to claim 50 or 51 wherein a continuous tape or strip of the adhesive is applied to the substrate.

53. The method of claim 50 or 51, wherein the substrate comprises a metal or alloy susceptible to corrosion.

Images