Dual-curing adhesive

Abstract

Provided is a dual-curing adhesive for manufacturing an electronic device, the dual-curing adhesive comprising: a compound comprising at least one epoxy group and at least one radically polymerizable group, a multifunctional epoxy resin, a thermal curing agent, and a photoinitiator.

Description

[0001] Dual-Curing Adhesive

[0002] The present invention relates to a dual-curing adhesive, a method of forming a joint between two or more work pieces to be joined using the dual-curing adhesive, a method of manufacturing the dual-curing adhesive, an electronic device formed using the dualcuring adhesive, and an electronic device comprising the dual-curing adhesive in cured form.

[0003] Adhesives curable by actinic radiation (e.g., “UV adhesives”) are used in methods of manufacturing electronic devices, such as digital cameras. Such adhesives may be cured relatively quickly by exposure to a radiation source, typically UV, including traditional UV (arc and microwave types) and UV-LED light sources. The fast cure allows manufacturers to increase throughput. However, because circuit boards and other electronic components have highly contoured surfaces, such UV adhesives suffer from a phenomenon whereby areas of the coating which cannot easily be exposed to UV light due to the contours (i.e. , the “shadow” areas) remain uncured.

[0004] To address this issue, so-called “dual curing adhesives” have been employed. In use of such adhesives, curing by means of actinic radiation, particularly in the UV / VIS range, is combined with a second curing mechanism, which may be curing by using heat or moisture. Examples of dual-curing adhesives are described in CN 113896694, CN113652186, WO2023092575, CN110194941 and CN102337099.

[0005] The oldest type of dual-curing adhesives is dual-curing acrylate adhesives. Light curing of the acrylate groups is induced by photoinitiators, and heat curing is performed using substances such as peroxides, which form free radicals when heated. However, with acrylates there is the problem of oxygen inhibition, whereby the surfaces remain moist as the growing chains at the surface of the adhesive are terminated by oxygen radicals present in the air. Current approaches to avoid the problem of oxygen inhibition can involve carrying out the curing in an inert atmosphere (e.g. nitrogen) or by using hard radiation in the UV-B or UV-C range. However, this may increase the cost and complexity of such a process.

[0006] Moreover, acrylate adhesives exhibit extreme shrinkage, poor temperature resistance and moderate moisture resistance. In particular, the lack of resistance to a combination of moisture and temperature, often tested in the so-called 85 / 85 test (85% humidity at 85 °C., usually for 1000 hours), is a problem. This is why acrylate adhesives have not been used so far at a large scale, for example, in the electronics industry.

[0007] The present invention seeks to tackle at least some of the problems associated with the prior art, or at least to provide a commercially acceptable alternative solution thereto.

[0008] In a first aspect, the present invention provides a dual-curing adhesive for manufacturing an electronic device, the dual-curing adhesive comprising: a compound comprising at least one epoxy group and at least one radically polymerizable group, a multifunctional epoxy resin, a thermal curing agent, and a photoinitiator.

[0009] Each aspect or embodiment as defined herein may be combined with any other aspect(s) or embodiment(s) unless clearly indicated to the contrary. In particular, any features indicated as being preferred or advantageous may be combined with any other feature indicated as being preferred or advantageous.

[0010] The inventors have surprisingly found that, in comparison to conventional dual-curing acrylate adhesives, the dual-curing adhesives of the present invention, once cured, may exhibit a greater temperature resistance and / or a greater moisture resistance. For example, in comparison to conventional dual-curing acrylate adhesives, the dual-curing adhesives of the present invention may perform better in an 85 °C 185 % RH test, such as, for example, a steady-state temperature humidity bias (THB) life test, e.g. the Joint Electron Device Engineering Council (JEDEC) test JESD22-A101, in which units are exposed to 85 °C I 85 % RH for 1000 hours

[0011] In comparison to conventional dual-curing acrylate adhesives, the dual-curing adhesives of the present invention, once cured, may exhibit less tackiness. Without being bound by theory, it is considered that this is because oxygen inhibition is less likely to occur, and typically does not occur at all. Advantageously, such a reduction in tackiness can be achieved without the use of an inert atmosphere and / or UVB / UVC radiation during curing. Accordingly, a manufacturing method using the adhesive may be lower cost and less complicated than a corresponding method using conventional dual-curing acrylate adhesive.

[0012] The term “dual-curing adhesive” as used herein may encompass an adhesive that undergoes both curing caused by actinic radiation and curing caused by heat.

[0013] The dual-curing adhesive comprises the recited components. The term “comprising” as used herein encompasses the situation in which components other than those recited may also be present. Alternatively, the dual-curing adhesive may “consist of” or “consist essentially of’ the recited elements. The term “consist of” or “consisting of’ as used herein encompasses the situation in which only the recited components may be present. The term “consist essentially of” or “consisting essentially of” as used herein encompasses the situation in which components other than those recited may also be present, but only if they do not materially affect the essential characteristics of the adhesive.

[0014] The dual-curing adhesive may contain unavoidable impurities, for example impurities resulting from its method of manufacture. Such unavoidable impurities, if present, are typically present in an amount of less than 1 wt.%, more typically less than 0.1 wt.%.

[0015] The dual-curing adhesive comprises a compound comprising at least one epoxy group and at least one radically polymerizable group (sometimes referred to herein as a “hybrid compound”). The term “epoxy group” as used herein encompasses a cyclic ether functional group, where the ether forms a three-atom ring: two atoms of carbon and one atom of oxygen. Epoxy groups are also known as epoxide groups, oxirane groups, and ethoxyline groups. The term “radically polymerizable group” may encompass a functional group that is capable of undergoing a method of polymerization by which a polymer forms by the successive addition of free-radical building blocks. The radically polymerizable group is not an epoxy group, i.e. the at least one epoxy group and the at least one radically polymerizable group are different groups. The compound is typically a resin.

[0016] The dual-curing adhesive comprises a multifunctional epoxy resin. The term “multifunctional epoxy resin” as used herein may encompass a resin that contains at least two epoxy groups. The dual-curing adhesive comprises a thermal curing agent. The term “thermal curing agent” as used herein may encompass a species that, when exposed to heat, initiates a polymerisation reaction.

[0017] Preferably the thermal curing agent does not generate radicals when exposed to heat. Preferably the thermal curing agent is capable of undergoing an addition reaction with an epoxy group. Preferably the thermal curing agent is capable of undergoing an SN2 reaction with an epoxy group. Without being bound by theory, it is considered that oxygen inhibition may be avoided because the curing agent (e.g. amine curing agent) reacts with the epoxide ring with an SN2 reaction, i.e. in the absence of radicals. In contrast, with acrylate adhesives, the curing agent generates radicals to react with the acrylate group. Since no radicals are generated, no reaction with atmospheric oxygen occurs.

[0018] The dual-curing adhesive comprises a photoinitiator. The term “a photoinitiator” as used herein may encompass a species that, when exposed to actinic radiation, generates reactive species, typically radicals. Such reactive species may result in polymerisation.

[0019] Without being bound by theory, it is considered that on exposure to actinic radiation (typically UV), the photoinitiator may cause reaction between the radically polymerizable group of one molecule of the hybrid compound with the radically polymerizable group of another molecule of the hybrid compound. On the application of heat, molecules of multifunctional epoxy resin polymerise with each other via the thermal curing agent. In addition, on the application of heat, the epoxy group of a molecule of the hybrid compound polymerises with a molecule of bifunctional epoxy resin via the thermal curing agent. As a result, any molecules of the hybrid compound not polymerized during UV curing (due to oxygen inhibition) will be polymerised during the subsequent thermal curing due to the presence of the epoxy group on the hybrid compound. In other words, the presence of the epoxy group in the hybrid compound allows for thermal curing as a secondary curing mechanism. This may result in the reduced tackiness in comparison to conventional dual-curing acrylate adhesives.

[0020] The adhesive is preferably a “single component” adhesive. In other words, it does not need to be combined with another species immediately prior to application. The at least one radically polymerizable group preferably comprises acrylate and / or methacrylate. Such functional groups are particularly suitable for undergoing radical polymerisation, and are therefore particularly suitable during UV curing.

[0021] The compound comprising at least one epoxy group and at least one radically polymerizable group preferably comprises a bisphenol group, more preferably a bisphenol A group, i.e. a bisphenol E group, i.e. and / or a bisphenol F group, i.e.

[0022] Even more preferably, the compound comprising at least one epoxy group and at least one radically polymerizable group comprises a bisphenol A group. Such functional groups may provide the cured adhesive with particularly favourable physical properties.

[0023] The compound comprising at least one epoxy group and at least one radically polymerizable group preferably comprises:

[0024] Such a compound is particularly suitable for undergoing both UV and thermal curing.

[0025] The dual-curing adhesive preferably comprises from 5 to 50 wt.% of the compound comprising at least one epoxy group and at least one radically polymerizable group, based on the total weight of the dual-curing adhesive, preferably from 5 to 20 wt.%, more preferably from 9 to 16 wt.%. Lower amounts may result in insufficient UV curing. Accordingly, during a typical electronic device manufacturing process, following UV curing the adhesive may not remain in a desired location, or components bonded by the adhesive may not be adequately fixed, before undergoing the subsequent thermal curing. Accordingly, faults in the electronic device may occur.

[0026] The multifunctional epoxy resin preferably comprises bifunctional epoxy resin, i.e. comprises two epoxy groups. Bifunctional epoxy resins are low cost and widely available.

[0027] The multifunctional epoxy resin preferably comprises a bisphenol-based epoxy resin, more preferably a bisphenol A-based epoxy resin and / or a bisphenol E-based epoxy resin and / or a bisphenol F-based epoxy resin, preferably a bisphenol A-based epoxy resin and a bisphenol E-based epoxy resin. Such epoxy resins may provide the cured adhesive with particularly favourable physical properties. In addition, such epoxy resins are low cost and widely available. Furthermore, such epoxy resins are particularly capable of undergoing thermal curing.

[0028] The dual-curing adhesive preferably comprises from 5 to 50 wt.% of the multifunctional epoxy resin, based on the total weight of the dual-curing adhesive, more preferably from 10 to 35 wt.%, even more preferably from 13 to 30 wt.%. Lower levels may result in insufficient curing during the thermal curing step. Higher levels may mean that insufficient amounts of the hybrid compound are present, thereby resulting in inadequate curing during the UV curing step.

[0029] The multifunctional epoxy resin preferably comprises at least two types of multifunctional epoxy resin. This may enable one to tune one or more properties of the cured adhesive such as, for example, flexibility, hardness, chemical resistance, and adhesion characteristics. For example, bisphenol A-based resins may confer high mechanical strength, whereas bisphenol F-based resins may provide the adhesive with lower viscosity and superior electrical insulation properties. Novolac resins may offer enhanced chemical resistance and thermal stability, while aliphatic resins may provide increased flexibility and UV stability.

[0030] For instance, bisphenol A-based resins typically confer high mechanical strength, whereas bisphenol F-based resins are characterized by lower viscosity and superior electrical insulation properties. Novolac resins offer enhanced chemical resistance and thermal stability, while aliphatic resins provide increased flexibility and UV stability. In addition, different epoxy resins can have different curing kinetics. By using multiple types of multifunctional epoxy resin, the curing characteristics of the adhesive may be improved.

[0031] The multifunctional epoxy resin preferably comprises one or more of bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, bisphenol E diglycidyl ether, and 1 ,4- cyclohexanedimethanol diglycidyl ether, preferably one or more of bisphenol A diglycidyl ether, bisphenol E diglycidyl ether, and 1,4-cyclohexanedimethanol diglycidyl ether, even more preferably two or more. The term “bisphenol A diglycidyl ether” may encompass:

[0032] The term “bisphenol F diglycidyl ether” may encompass:

[0033] The term ““bisphenol E diglycidyl ether” may encompass:

[0034] The term “1,4-cyclohexanedimethanol diglycidyl ether” may encompass:

[0035] Such epoxy resins may provide the adhesive with particularly favourable thermal curing characteristics and / or may provide the cured adhesive with particularly favourable mechanical properties.

[0036] The dual-curing adhesive preferably comprises, based on the total weight of the dualcuring adhesive: from 1 to 15 wt.% of the bisphenol A diglycidyl ether, preferably from 7 to 13 wt.%, more preferably from 9 to 12 wt.%; and / or from 1 to 15 wt.% of the bisphenol E diglycidyl ether, preferably from 7 to 13 wt.%, more preferably from 9 to 12 wt.%; and / or from 1 to 10 wt.% of the 1,4-cyclohexanedimethanol diglycidyl ether, preferably from 3 to 7 wt.%, more preferably from 4 to 6 wt.%.

[0037] The presence of these species in the recited amounts may provide the adhesive with particularly favourable thermal curing characteristics and / or may provide the cured adhesive with particularly favourable mechanical properties. The thermal curing agent preferably comprises nitrogen, more preferably wherein the thermal curing agent comprises amine or imidazole, even more preferably amine, still even more preferably primary amine. The amine preferably has an amine value of from 100 to 170, more preferably from 110 to 160, even more preferably from 110 to 120 or from 140 to 160. The amine is preferably multifunctional amine, i.e. it comprises more than one amine functional group. Such curing agents may result in curing at favourably low temperatures. Suitable commercial examples of the thermal curing agent include FXR-1061 and FXR-1081 from T&K Toka. Nitrogen-containing compounds, such as amines, may be capable of undergoing an addition reaction with an epoxy group. For example, an addition reaction of a primary amine may form a hydroxyl group and a secondary amine. The secondary amine may further react with an epoxide to form a tertiary amine and an additional hydroxyl group. As a result, thermal curing agents comprising nitrogen, in particular amines and imidazole, may provide particularly favourable thermal curing characteristics. Amines and imidazole, in particular amines, may exhibit superior curing characteristics (in particular with the combination of the compound and multifunctional epoxy resin described herein) to other thermal curing agents, such as amides, hydrazides, hexafluorantimonates, and boron trifluoride-amine complexes. Preferably, the curing agent does not comprise amides, hydrazides, hexafluorantimonates, and / or boron trifluoride-amine complexes. Amides may exhibit lower heat and chemical resistance in comparison to amines, and may exhibit slower curing times. They can also exhibit lower moisture resistance, resulting in poor curing performance. Hydrazides can be sensitive to temperature or pH changes, leading to premature degradation or undesired reactions, leading to unwanted byproducts, which may degrade the performance of the cured adhesive. Hexafluorantimonates are toxic, exhibit low shelf lives and are prone to under-curing. In comparison to amine curing agents, boron trifluoride -amine complex curing agents can have poor moisture resistance, leading to degradation of the cured resin, particularly in humid environments. Boron trifluoride can be corrosive, especially to metals like aluminium, which may be problematic when using the dual-cure adhesive to manufacture electronics. Preferably the curing agent is substantially devoid of, more preferably devoid of, boron trifluoride. Preferably, the amine is not in the form of a complex.

[0038] The dual-curing adhesive preferably comprises from 1 to 20 wt.% of the thermal curing agent, based on the total weight of the dual-curing adhesive, more preferably from 2 to 10 wt.%, even more preferably from 3 to 7 wt.%. Lower levels may result in insufficient thermal curing. Higher levels may not result in higher levels of thermal curing. In addition, higher levels may result in the presence of unreacted thermal curing agent after curing is completed, which may be undesirable.

[0039] Preferably, the photoinitiator is a UV photoinitiator, preferably wherein the photoinitiator absorbs light having a wavelength of from 325 to 425 nm, more preferably from 345 to 410 nm, even more preferably from 365 to 400 nm. Such wavelengths may result in particularly favourable UV curing. Furthermore, advantageously such wavelengths may be generated using a conventional UV lamp or UV LED.

[0040] Preferably, the photoinitator comprises at least two different photoinitator species. In other words, preferably the dual-curing adhesive comprises at least two different photoinitiators. This may increase the speed of the UV curing.

[0041] Preferably, the photoinitiator comprises one or both of: phenyl bis (2,4,6-trimethyl benzoyl) phosphine oxide and benzil dimethyl ketal, preferably both. The term “phenyl bis (2,4,6-trimethyl benzoyl) phosphine oxide” may encompass:

[0042] The term “benzil dimethyl ketal” may encompass:

[0043] Such photoinitiators may be particularly suitable for generating free-radicals, and thereby initiating radical polymerisation, on exposure to UV radiation of around 365 nm. The inclusion of both phenyl bis (2,4,6-trimethyl benzoyl) phosphine oxide and benzil dimethyl ketal may result in particularly fast UV curing. This may allow increased throughput of a manufacturing method using the dual-cure adhesive. The dual-curing adhesive preferably comprises from 0.5 to 5 wt.% of the photoinitiator, based on the total weight of the dual-curing adhesive, more preferably from 1 to 4 wt.%. Lower levels may result in insufficient UV curing. Higher levels may not result in higher levels of UV curing. In addition, higher levels may result in the presence of unreacted photoinitiator after curing is completed, which may be undesirable.

[0044] The dual-curing adhesive preferably further comprises one or more additives selected from: a hardener, preferably a thiol-based hardener, more preferably comprising one or both of 2,2-bis{[(3-sulfanylpropanoyl)oxy]methyl}butyl 3-sulfanylpropanoate and pentaerythritol tetrakis (3-mercaptobutylate); a reactive diluent, preferably comprising a trifunctional acrylic monomer or a diacrylate monomer, more preferably comprising one or both of trimethylolpropane triacrylate (TMPTA) monomer and tricyclodecane dimethanol diacrylate (TCDDMDA) monomer; an inorganic filler, preferably comprising one or both of silica and fumed silica; a toughening agent, preferably comprising core-shell rubber; a stabilizer, preferably comprising organic acid; and carbon black.

[0045] The hardener may improve the thermal curing properties of the adhesive, i.e. it may promote thermal curing and / or enable thermal curing to be accelerated or carried out at a lower temperature. The reactive diluent may also improve the thermal curing properties. The toughening agent may improve the toughness of the cured adhesive. The stabilizer may improve the stability of the adhesive. The inorganic filler may improve the physical properties of the adhesive, for example it may increase the hardness and strength of the cured adhesive. The inorganic filler may also provide the adhesive with favourable viscosity for easier application and may improve the chemical and / or thermal resistance. The carbon black may provide the adhesive with a black colour, which may prevent light penetration into a device containing the cured adhesive.

[0046] The dual-curing adhesive preferably comprises from 30 to 80 wt.% in total of the one or more additives, based on the total weight of the dual-curing adhesive, more preferably grom 50 to 75 wt.%, even more preferably from 55 to 70 wt.%. The dual-curing adhesive preferably comprises, based on the total weight of the dualcuring adhesive: from 10 to 35 wt.% of the hardener, preferably from 20 to 30 wt.%, more preferably from 22 to 28 wt.%; and / or from 1 to 15 wt.% of the reactive diluent, preferably from 4 to 12 wt.%; and / or from 15 to 30 wt.% of the inorganic filler, preferably from 17 to 28 wt.%; and / or from 1 to 6 wt.% of the toughening agent, preferably from 3 to 5 wt.%; and / or from 0.1 to 1 wt.% of the stabilizer, preferably from 0.4 to 0.7 wt.%; and / or from 0.001 to 0.1 wt.% of carbon black, preferably from 0.005 to 0.05, more preferably from 0.01 to 0.03 wt.%.

[0047] The dual-curing adhesive is preferably solvent-free. For adhesive used in camera modules, the use of solvents poses a challenge due to their potential to evaporate and cause contamination of sensitive components such as lenses. Accordingly, when the dual-curing adhesive is solvent-free, the adhesive is particularly suitable for use in manufacturing a digital camera.

[0048] The electronic device preferably comprises a digital camera.

[0049] The dual-curing adhesive preferably exhibits: a viscosity of from 30,000 cP to 55,000 cP; and / or a thixotropic index of from 4 to 8.

[0050] Such properties may enable the adhesive to be applied more easily. Such properties may also ensure that the adhesive remains in a desired location prior to curing.

[0051] In a further aspect, the present invention provides a method of forming a joint between two or more work pieces to be joined, the method comprising: disposing the dual-curing adhesive described herein in the vicinity of two or more work pieces to be joined; exposing at least some of the dual-curing adhesive to actinic radiation in air; and heating the dual-curing adhesive to a temperature of from 40 to 90 °C for a period of time of from 10 to 150 minutes.

[0052] The advantages and preferable features of the first aspect apply equally to this aspect. The two or more workpieces may comprise, for example, electronic components, or an electronic component and a substrate or printed circuit board.

[0053] Disposing the dual-curing adhesive described herein in the vicinity of two or more work pieces to be joined may comprise contacting the adhesive with the two or more workpieces, for example sandwiching the adhesive between the two or more workpieces. Disposing the dual-curing adhesive described herein in the vicinity of two or more work pieces to be joined may be carried out, for example, using one or more of brushing, spraying, dispensing and dip coating.

[0054] Preferably, disposing the dual-curing adhesive described herein in the vicinity of two or more work pieces to be joined comprises applying the dual-curing adhesive to one or more of the workpieces and contacting the workpieces with each other via the dualcuring adhesive.

[0055] By exposing at least some of the dual-curing adhesive to actinic radiation in air, rather than in an inert atmosphere, the cost and complexity of the method may be reduced.

[0056] The actinic radiation is preferably UV radiation, more preferably UV radiation having the wavelengths discussed above. Exposing at least some of the dual-curing adhesive to actinic radiation may be carried out with, for example, a UV LED.

[0057] Exposing at least some of the dual-curing adhesive to actinic radiation is preferably carried out for from 0.1 to 5 seconds, more preferably from 0.5 to 2 seconds even more preferably about 1 second. Shorter times may result in inadequate levels of UV curing. Longer times may be unnecessary to achieve adequate levels of UV curing, and thereby unnecessarily slow down a production line carrying out the method.

[0058] Exposing at least some of the dual-curing adhesive to actinic radiation is preferably carried out using an intensity of from 500 to 1500 mW / cm2, more preferably from 800 to 1200 mW / cm2, even more preferably about 1000 mW / cm2. Lower intensities may result in inadequate UV curing. Higher intensities may increase the cost and / or complexity of the method without any (or any beneficial) corresponding increase in the level of curing achieved. In a preferred embodiment: exposing at least some of the dual-curing adhesive to actinic radiation comprises exposing the adhesive to UV radiation from a UV LED for one second at having a wavelength of 365 nm to 400 nm and an intensity of 1000 mW / cm2for one second; and heating the dual-curing adhesive is carried out at 60 °C for 90 minutes.

[0059] In another preferred embodiment: exposing at least some of the dual-curing adhesive to actinic radiation comprises exposing the adhesive to UV radiation from a UV LED for one second at having a wavelength of 365 nm to 400 nm and an intensity of 1000 mW / cm2for one second; and heating the dual-curing adhesive is carried out at 80 °C for 30 minutes.

[0060] In a further aspect, the present invention provides a method of manufacturing the dualcuring adhesive described herein, the method comprising: providing a first mixture of photoinitiator and a compound comprising at least one epoxy group and at least one radically polymerizable group; providing a second mixture of a multifunctional epoxy resin and a thermal curing agent; and combining the first mixture and the second mixture.

[0061] The advantages and preferable features of the first aspect apply equally to this aspect.

[0062] Providing a first mixture of photoinitiator and a compound comprising at least one epoxy group and at least one radically polymerizable group is preferably carried out in the absence of UV radiation, more preferably providing a first mixture of photoinitiator and a compound comprising at least one epoxy group and at least one radically polymerizable group is preferably carried out under yellow light. This may avoid premature polymerisation of the compound.

[0063] The method may further comprise combining the combined first and second mixture with one or more of: a hardener, a reactive diluent, a toughening agent, a stabilizer, and carbon black. Thereafter, the method may further comprise combining the combined first and second mixture with an inorganic filler. In a further aspect, the present invention provides an electronic device manufactured using the adhesive described herein.

[0064] The advantages and preferable features of the first aspect apply equally to this aspect.

[0065] The electronic device may comprise a digital camera.

[0066] In a further aspect, the present invention provides an electronic device comprising the adhesive described herein in cured form.

[0067] The advantages and preferable features of the first aspect apply equally to this aspect.

[0068] The electronic device may comprise a digital camera.

[0069] The invention will now be further described with reference to the following non-limiting drawings in which:

[0070] Figure 1 shows a plan view of a camera module of a digital camera according to the present invention.

[0071] Figure 2 shows an exploded view of the camera module of Figure 1.

[0072] Referring to Figures 1 and 2, there is shown a camera module (shown generally at 1) of a digital camera according to the present invention. Dual-curing adhesive 2 according to the present invention is used to actively align the lens 4 and barrel 5 to the mount 6. Image sensor 7 is mounted on PCB 8 which is mounted on flexible PCB 9. Mount 6 and PCB 8 are connected via dual-curing adhesive 3 according to the present invention.

[0073] The invention will now be further described with reference to the following examples.

[0074] Six adhesives according to the invention were produced having the compositions set out in Table 1 below: Table 1 (compositions quoted in parts by weight)

[0075]

[0076] Various properties of the adhesives were measured, and the results are set out in Table 2 below:

[0077] Table 2

[0078] The properties of all the examples rendered them suitable for use in the manufacture of an electronic device. Example 6 was particularly suitable in view of its high pre-fix adhesion strength (strength after UV curing but not thermal curing) and its long pot life.

[0079] The foregoing detailed description has been provided by way of explanation and illustration and is not intended to limit the scope of the appended claims. Many variations in the presently preferred embodiments illustrated herein will be apparent to one of ordinary skill in the art, and remain within the scope of the appended claims and their equivalents.

Claims

Claims1. A dual-curing adhesive for manufacturing an electronic device, the dual-curing adhesive comprising: a compound comprising at least one epoxy group and at least one radically polymerizable group, a multifunctional epoxy resin, a thermal curing agent, and a photoinitiator.

2. The dual-curing adhesive according to claim 1, wherein the at least one radically polymerizable group comprises acrylate and / or methacrylate.

3. The dual-curing adhesive according to claim 1 or claim 2, wherein the compound comprising at least one epoxy group and at least one radically polymerizable group comprises a bisphenol group, preferably a bisphenol A group a bisphenol E group and / or a bisphenol F group, more preferably a bisphenol A group.

4. The dual-curing adhesive according to any preceding claim, wherein the compound comprising at least one epoxy group and at least one radically polymerizable group comprises:

5. The dual-curing adhesive according to any preceding claim, comprising from 5 to 50 wt.% of the compound comprising at least one epoxy group and at least one radically polymerizable group, based on the total weight of the dual-curing adhesive, preferably from 5 to 20 wt.%, more preferably from 9 to 16 wt.%.

6. The dual-curing adhesive according to any preceding claim, wherein the multifunctional epoxy resin comprises bifunctional epoxy resin.

7. The dual-curing adhesive according to any preceding claim, wherein the multifunctional epoxy resin comprises a bisphenol-based epoxy resin, preferably a bisphenol A-based epoxy resin and / or bisphenol E-based epoxy resin and / or a bisphenol F-based epoxy resin, more preferably a bisphenol A-based epoxy resin and bisphenol E- based epoxy resin.

8. The dual-curing adhesive according to any preceding claim, comprising from 5 to 50 wt.% of the multifunctional epoxy resin, based on the total weight of the dual-curing adhesive, preferably from 10 to 35 wt.%, more preferably from 13 to 30 wt.%.

9. The dual-curing adhesive according to any preceding claim, wherein the multifunctional epoxy resin comprises one or more of bisphenol A diglycidyl ether, bisphenol E diglycidyl ether, and 1,4-cyclohexanedimethanol diglycidyl ether, preferably two or more.

10. The dual-curing adhesive according to claim 9, comprising, based on the total weight of the dual-curing adhesive: from 1 to 15 wt.% of the bisphenol A diglycidyl ether, preferably from 7 to 13 wt.%, more preferably from 9 to 12 wt.%; and / or from 1 to 15 wt.% of the bisphenol E diglycidyl ether, preferably from 7 to 13 wt.%, more preferably from 9 to 12 wt.%; and / or from 1 to 10 wt.% of the 1,4-cyclohexanedimethanol diglycidyl ether, preferably from 3 to 7 wt.%, more preferably from 4 to 6 wt.%.

11. The dual-curing adhesive according to any preceding claim, wherein the thermal curing agent comprises nitrogen, preferably wherein the thermal curing agent comprises amine or imidazole, more preferably amine, even more preferably primary amine.

12. The dual-curing adhesive according to claim 11, wherein the amine has an amine value of from 100 to 170, preferably from 110 to 160, more preferably from 110 to 120 or from 140 to 160.

13. The dual-curing adhesive according to any preceding claim, comprising from 1 to20 wt.% of the thermal curing agent, based on the total weight of the dual-curing adhesive, preferably from 2 to 10 wt.%, more preferably from 3 to 7 wt.%.

14. The dual-curing adhesive according to any preceding claim, wherein: the photoinitiator is a UV photoinitiator, preferably wherein the photoinitiator absorbs light having a wavelength of from 325 to 425 nm, more preferably from 345 to 410 nm, even more preferably from 365 to 400 nm; and / or the photoinitiator comprises one or both of: phenyl bis (2,4,6-trimethyl benzoyl) phosphine oxide and benzil dimethyl ketal, preferably both.

15. The dual-curing adhesive according to any preceding claim, comprising from 0.5 to 5 wt.% of the photoinitiator, based on the total weight of the dual-curing adhesive, preferably from 1 to 4 wt.%.

16. The dual-curing adhesive according to any preceding claim, wherein the dualcuring adhesive further comprises one or more additives selected from: a hardener, preferably a thiol-based hardener, more preferably comprising one or both of 2,2-bis{[(3-sulfanylpropanoyl)oxy]methyl}butyl 3-sulfanylpropanoate and pentaerythritol tetrakis (3-mercaptobutylate); a reactive diluent, preferably comprising a trifunctional acrylic monomer or a diacrylate monomer, more preferably comprising one or both of trimethylolpropane triacrylate (TMPTA) monomer and tricyclodecane dimethanol diacrylate (TCDDMDA) monomer; an inorganic filler, preferably comprising one or both of silica and fumed silica; a toughening agent, preferably comprising core-shell rubber; a stabilizer, preferably comprising organic acid; and carbon black.

17. The dual-curing adhesive according to claim 16, wherein the dual-curing adhesive comprises from 30 to 80 wt.% in total of the one or more additives, based on the total weight of the dual-curing adhesive, preferably grom 50 to 75 wt.%, more preferably from 55 to 70 wt.%.

18. The dual-curing adhesive according to claim 16 or claim 17, wherein the dualcuring adhesive comprises, based on the total weight of the dual-curing adhesive: from 10 to 35 wt.% of the hardener, preferably from 20 to 30 wt.%, more preferably from 22 to 28 wt.%; and / or from 1 to 15 wt.% of the reactive diluent, preferably from 4 to 12 wt.%; and / or from 15 to 30 wt.% of the inorganic filler, preferably from 17 to 28 wt.%; and / or from 1 to 6 wt.% of the toughening agent, preferably from 3 to 5 wt.%; and / or from 0.1 to 1 wt.% of the stabilizer, preferably from 0.4 to 0.7 wt.%; and / or from 0.001 to 0.1 wt.% of carbon black, preferably from 0.005 to 0.05, more preferably from 0.01 to 0.03 wt.%.

19. The dual-curing adhesive according to any preceding claim, wherein: the dual-curing adhesive is solvent-free; and / or the electronic device comprises a digital camera.

20. The dual-curing adhesive according to any preceding claim, wherein the dualcuring adhesive exhibits: a viscosity of from 30,000 cP to 55,000 cP; and / or a thixotropic index of from 4 to 8.

21. A method of forming a joint between two or more work pieces to be joined, the method comprising: disposing the dual-curing adhesive of any preceding claim in the vicinity of two or more work pieces to be joined; exposing at least some of the dual-curing adhesive to actinic radiation in air; heating the dual-curing adhesive to a temperature of from 40 to 90 °C for a period of time of from 10 to 150 minutes.

22. The method of claim 22, wherein disposing the dual-curing adhesive of any preceding claim in the vicinity of two or more work pieces to be joined comprises applying the dual-curing adhesive to one or more of the workpieces and contacting the workpieces with each other via the dual-curing adhesive.

23. A method of manufacturing the dual-curing adhesive of any of claims 1 to 20, the method comprising:providing a first mixture of photoinitiator and a compound comprising at least one epoxy group and at least one radically polymerizable group; providing a second mixture of a multifunctional epoxy resin and a thermal curing agent; and combining the first mixture and the second mixture.

24. An electronic device manufactured using the adhesive of any of claims 1 to 20.

25. An electronic device comprising the adhesive of any of claims 1 to 20 in cured form.

26. The electronic device of claim 24 or claim 25, wherein the electronic device comprises a digital camera.

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