A method for joining components with minimal lead-through deformation

Abstract

Disclosed is a method for joining two substrates, comprising the sequential steps of: i) applying a pumpable heat-foamable filler composition onto a first substrate S1; and ii) positioning a second substrate S2 such that the distance between the first substrate S1 and the second substrate S2 at the application position of the pumpable heat-foamable filler composition is between 2 and 10 mm; and iii) after step ii), heating the first substrate S1 and the second substrate S2 to a temperature above the activation temperature of the blowing agent to foam the pumpable heat-foamable filler composition, wherein between steps ii) and iii), the applied pumpable heat-foamable filler composition is not in contact with the second substrate S2. The pumpable heat-foamable filler composition includes at least one rubber, polyvinyl chloride resin and / or acrylic resin powder, and a foaming agent. The method of bonding substrates using a thermally expandable composition results in a reduction of the bond line read-through (BLRT) phenomenon.

Description

[Technical Field]

[0001] The present invention relates to a method for bonding substrates, particularly substrates in the automotive industry or white goods articles, using a pumpable heat-expandable filler composition. [Background technology]

[0002] Manufactured articles often include hollow members that result from the manufacturing process and / or are designed into the product for various purposes, such as weight reduction. For example, an automotive vehicle may include several such hollow members throughout the vehicle, such as in the vehicle roof, hood, trunk lid, and vehicle doors. In many cases, it is also desirable, at least at certain locations, to bond / join multiple members / substrates to form hollow members to minimize vibrations caused by the movement of the vehicle and noise resulting from such vibrations.

[0003] Compositions suitable for bonding these components / substrates to reduce vibration can expand in volume upon application of heat, increasing their flexibility and, for aesthetic reasons, reducing surface changes (so-called "read-through") in the bonded components. For example, in the vehicle manufacturing process, hollow vehicle roof components can include beads of uncured composition applied between the roof beams and roof layers. These beads are applied so that the applied uncured composition is thick enough to ensure firm and direct contact with the roof beams and roof layers. This application in specific locations allows for the electrodeposition coating solution to cover a large area while pre-inserting the bead of uncured composition applied between the upper and lower roof layers. The expandable composition then expands during a heat treatment step, firmly bonding the two layers and minimizing vibrations caused by vehicle movement and noise resulting from such vibrations.

[0004] With regard to the previously mentioned bond line read-through (BLRT) phenomenon, the specific physical properties of the cured bonding composition are of essential importance. Bond BLRT is the visible distortion of the substrate above the bond line of the cured bond. These deformations are primarily a result of the difference in the thermal expansion coefficients between the substrate and the bond. The trend toward lightweighting in the automotive industry (for example) has led to the use of thinner and thinner metal sheets in automobile construction. As the thickness and bending stiffness of steel sheets decrease, the composition-induced BLRT phenomenon becomes more and more frequent. Therefore, there is an increasing need for bonding compositions with optimized BLRT.

[0005] WO2020048905A1 describes a rubber composition having improved BLRT performance, the rubber composition comprising at least one solid rubber, a processing oil, a vulcanization system, a filler, and a foaming agent. However, the BLRT performance still needs further improvement.

[0006] It would therefore be desirable to provide a method for bonding substrates using thermally expandable compositions that would be advantageous in terms of improved BLRT performance. Summary of the Invention [Problem to be solved by the invention]

[0007] It is an object of the present invention to provide a method for bonding substrates using a thermally expandable composition that reduces the BLRT phenomenon. [Means for solving the problem]

[0008] Surprisingly, the present invention provides a solution to that problem by providing a method for bonding two substrates, comprising the following sequential steps: i) applying a pumpable heat-expandable filler composition onto a first substrate S1; and - ii) placing a second substrate S2 such that at the application position of the pumpable heat-expandable filler composition, the distance between the first substrate S1 and the second substrate S2 is between 2 and 10 mm; and - iii) heating the first substrate S1 and the second substrate S2 to a temperature above the activation temperature of the blowing agent to foam the pumpable heat-foamable filler composition, wherein between steps ii) and iii) the applied pumpable heat-foamable filler composition is not in contact with the second substrate S2, and the pumpable heat-foamable filler composition comprises: - at least one rubber, preferably a synthetic rubber, more preferably a partially crosslinked synthetic rubber, more preferably a diene rubber, preferably present in an amount of 1 to 20%, preferably 3 to 15% by weight, more preferably 5 to 10% by weight, based on the total weight of the composition; - preferably 5 to 40 wt. %, 8 to 30 wt. %, preferably 10 to 20 wt. %, based on the total weight of the pumpable heat-expandable filler composition, of polyvinyl chloride resin and / or acrylic resin powder, preferably polyvinyl chloride resin; - Preferably 1 to 10 wt. %, 2 to 8 wt. %, preferably 3 to 6 wt. % of a blowing agent, based on the total weight of the pumpable heat-expandable filler composition.

[0009] The method according to the invention is particularly suitable for use in sound damping / vibration reduction, for example in automotive applications. Further aspects of the invention are the subject of other independent claims. Preferred embodiments of the invention are the subject of the dependent claims. DETAILED DESCRIPTION OF THE INVENTION

[0010] Unless otherwise specified, the unit term "wt. %" refers to a weight percentage based on the total weight of the respective composition. The terms "weight" and "mass" are used interchangeably throughout this specification.

[0011] The volume change of a thermally expansive substance is determined using the density determination method of DIN EN ISO 1183 (Archimedes' principle) by combining the mass of the sample measured by a precision balance in deionized water.

[0012] The pumpable heat-expandable filler composition preferably comprises a liquid epoxy resin. The liquid epoxy resin is a material that is liquid or at least flowable at ambient temperature (23°C). Polyepoxides, known to those skilled in the art as "reactive diluents," are also referred to herein as liquid epoxy resins.

[0013] Liquid epoxy resins suitable for use in the compositions of the present invention include those of formula (I): [ka] (wherein R' and R" are each independently a hydrogen atom or a methyl group, and s has an average value of 0 to 1). Liquid resins of formula (I) in which the index s has an average value of less than 0.2 are preferred.

[0014] The liquid epoxy resins of formula (I) are diglycidyl ethers of bisphenol A, bisphenol F, and bisphenol A / F, where A represents acetone and F represents formaldehyde, which serve as reactants for preparing these bisphenols. Thus, as R' and R" in formula (I), bisphenol A liquid resins have methyl groups, bisphenol F liquid resins have hydrogen atoms, and bisphenol A / F liquid resins have both methyl groups and hydrogen atoms. In the case of bisphenol F, it can exist as positional isomers, particularly derived from 2,4'- and 2,2'-hydroxyphenylmethane.

[0015] Such liquid epoxy resins are commercially available, for example, as Araldite® GY204, Araldite® GY250, Araldite® GY260, Araldite® GY281, Araldite® GY282, Araldite® GY285, Araldite® PY304, Araldite® PY720 (manufactured by Huntsman); DER® 330, DER® 331, DER® 332, DER® 336, DER® 354, DER® 351, DER® 352, DER® 356 (manufactured by Dow); Epikote® 162, Epikote® 827, Epikote® 828, Epikote® 158, Epikote® 862, Epikote® 169, Epikote® 144, Epikote® 238, Epikote® 232, Epikote® 235 (manufactured by Hexion), Epalloy® 7190, Epalloy® 8220, Epalloy® 8230, Epalloy® 7138, Epalloy® 7170, Epalloy® 9237-70 (manufactured by CVC), Chem Res® E20, Chem Res® E30 (manufactured by Cognis), Beckopox® EP 1 16, Beckopox® EP140 (manufactured by Cytec), Epiclon EXA-4850 (manufactured by Sun Chemical).

[0016] Further suitable liquid epoxy resins are the glycidyl reaction products of: dihydroxybenzene derivatives such as resorcinol, hydroquinone, and catechol; further bisphenols or polyphenols such as bis(4-hydroxy-3-methylphenyl)methane, 2,2-bis(4-hydroxy-3-methylphenyl)propane (bisphenol C), bis(3,5-dimethyl-4-hydroxyphenyl)methane, 2,2-bis(3,5-dimethyl-4-hydroxyphenyl)propane, 2,2 -bis(3,5-dibromo-4-hydroxyphenyl)propane, 2,2-bis(4-hydroxy-3-tert-butyl-phenyl)propane, 2,2-bis(4-hydroxyphenyl)butane (bisphenol B), 3,3-bis(4-hydroxyphenyl)pentane, 3,4-bis(4-hydroxyphenyl)hexane, 4,4-bis(4-hydroxyphenyl)heptane, 2,4-bis(4-hydroxyphenyl)-2-methylbutane, 2,4-bis(3,5-dimethyl-4-hydroxyphenyl)-2-methylbutane Tylbutane, 1,1-bis(4-hydroxyphenyl)cyclohexane (bisphenol Z), 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane (bisphenol TMC), 1,1-bis(4-hydroxyphenyl)-1-phenyl-ethane, 1,4-bis[2-(4-hydroxyphenyl)-2-propyl]benzene) (bisphenol P), 1,3-bis[2-(4-hydroxyphenyl)-2-propyl]benzene) (bisphenol M), 4,4'-dihydroxydiphenyl ( DOD), 4,4'-dihydroxybenzophenone, bis(2-hydroxynaphth-1-yl)methane, bis(4-hydroxynaphth-1-yl)methane, 1,5-dihydroxynaphthalene, tris(4-hydroxyphenyl)methane, 1,1,2,2-tetrakis(4-hydroxyphenyl)ethane, bis(4-hydroxyphenyl)ether, bis(4-hydroxyphenyl)sulfone; condensation products of phenol and formaldehyde obtained under acidic conditions, such as phenol novolac or cresol novolac;Aromatic amines, such as aniline, toluidine, 4-aminophenol, 4,4'-methylenediphenyldiamine (MDA), 4,4'-methylenediphenyldi(N-methyl)amine, 4,4'-[1,4-phenylenebis(1-methylethylidene)]bisaniline (bisaniline P), 4,4'-[1,3-phenylenebis(1-methylethylidene)]bisaniline (bisaniline M);

[0017] In a further embodiment, the liquid epoxy resin is an aliphatic or alicyclic polyepoxide, such as: diglycidyl ethers; glycidyl ethers of saturated or unsaturated, branched or unbranched, cyclic or open-chain C2-C3 diols, such as ethylene glycol, propylene glycol, butylene glycol, hexanediol, octanediol, polypropylene glycol, dimethylolcyclohexane, neopentyl glycol; trifunctional or tetrafunctional, saturated or unsaturated, branched or unbranched, cyclic or open-chain polyols; For example, glycidyl ethers of castor oil, trimethylolpropane, trimethylolethane, pentaerythritol, sorbitol, or glycerol, and alkoxylated glycerol or alkoxylated trimethylolpropane; hydrogenated bisphenol A, F, or A / F liquid resins, or glycidyl reaction products of hydrogenated bisphenol A, F, or A / F; N-glycidyl derivatives of amide or heterocyclic nitrogen bases, such as triglycidyl cyanurate and triglycidyl isocyanurate, and reaction products of epichlorohydrin with hydantoin.

[0018] Aliphatic or cycloaliphatic liquid epoxy resins are commercially available, for example, as Araldite® DY-C, Araldite® DY-F, Araldite® DY-H, Araldite® DY-T, Araldite® DY0397, Araldite® DY3601 (manufactured by Huntsman), DER® 732, DER® 736 (manufactured by Dow); Heloxy® BD, Heloxy® HD, Heloxy® TP, Epikote® 877 (manufactured by Hexion), Beckopox® EP075 (manufactured by Cytec). Mixtures of aliphatic or cycloaliphatic polyepoxides with aromatic epoxides of formula (I) can also be used, such as, in particular, mixtures of the diglycidyl ethers of bisphenol A, bisphenol F and bisphenol A / F with the diglycidyl ethers of α,ω-alkanediols, where the α,ω-alkanediols preferably contain from 2 to 10 carbon atoms. Such mixtures are also commercially available, for example, from Dow as DER358.

[0019] In a further embodiment, the liquid epoxy resin is a polyepoxide prepared by oxidizing an olefin, for example, vinylcyclohexene, dicyclopentadiene, cyclohexadiene, cyclododecadiene, cyclododecatriene, isoprene, 1,5-hexadiene, butadiene, polybutadiene, or divinylbenzene.

[0020] The liquid epoxy resin is preferably the liquid resin of formula (I) listed above, and more preferably the liquid epoxy resins listed above as preferred.

[0021] In the context of the present application, particularly preferred liquid epoxy resins are those based on bisphenol A diglycidyl ether and having an epoxy equivalent weight of 156 to 250 g / eq, such as DER® 331 (manufactured by Dow).

[0022] The liquid epoxy resin is preferably contained in the composition in an amount of 5 to 40% by weight, based on the total weight of the composition. In a more preferred embodiment, the liquid epoxy resin is contained in the composition in an amount of 8 to 30% by weight, 10 to 25% by weight, and particularly 12.5 to 20% by weight.

[0023] The pumpable heat-expandable filler composition of the present invention contains, as an essential component, a powder of polyvinyl chloride resin and / or acrylic resin.

[0024] As can be seen from the comparison between Example 1 and Reference Example 2 in Table 2, the absence of polyvinyl chloride resin and / or acrylic resin powder results in poor expansion behavior and an unfavorable breathable pore structure.

[0025] The polyvinyl chloride (PVC) resin in the composition of the present application may be a polyvinyl chloride homopolymer or copolymer, preferably a polyvinyl chloride copolymer. When the polyvinyl chloride is a copolymer, it preferably contains a vinyl ester, such as vinyl acetate or vinyl propionate, as a comonomer for vinyl chloride. The amount of the comonomer is preferably in the range of 1 to 25%, more typically 2 to 20%, 2 to 15%, 2 to 10%, and most preferably 3 to 7%, based on the total weight of the copolymer.

[0026] A preferred PVC homopolymer in the context of the present application is Formolon KVH (manufactured by Formosa). A particularly preferred PVC copolymer in the context of the present application is Formolon F40, also manufactured by Formosa.

[0027] There are no particular limitations on the acrylic resin powder that can be used in place of or in addition to the polyvinyl chloride resin, but it is preferable that it is solid at ambient temperature (23°C). The acrylic resin powder preferably has a glass transition temperature Tg in the range of 50°C to 120°C, and even more preferably in the range of 70°C to 90°C. The glass transition temperature is measured by DSC. In addition, it is preferable that the acrylic resin powder can form a plastisol.

[0028] The acrylic resin in the acrylic resin powder may be a homopolymer or a copolymer. A preferred acrylic resin is a methyl methacrylate-based resin, such as those commercially available as Dialal LP-3106 or Dialal LP-3202 (manufactured by Dialal America Inc.). Another commercially available acrylic resin that can be advantageously used in the present application is Kane Ace U506 (manufactured by Kaneka).

[0029] The one or more polyvinyl chloride resins and / or one or more acrylic resin powders are suitably contained in the composition in an amount ranging from 5 to 40% by weight, preferably from 8 to 30% by weight, and most preferably from 10 to 20% by weight.

[0030] The pumpable heat-expandable filler composition of the present invention also includes a blowing agent as another essential component. Any substance may be used as the blowing agent for use in the present invention, as long as it decomposes upon heating to generate a gas. Preferably, the blowing agent is a chemical blowing agent. More preferably, the blowing agent is selected from the list consisting of azo compounds, nitroso compounds, and hydrazine derivatives, more preferably azodicarbonamide, N,N-dinitrosopentamethylenetetraamine, and diphenylsulfone-3,3'-disulfohydrazide. These blowing agents may be used alone or in combination. In the context of the present application, dicyandiamide is particularly preferred as at least part of the blowing agent, since its decomposition reaction product (ammonia) contributes to the curing and crosslinking of liquid epoxy resins.

[0031] The amount of blowing agent in the pumpable heat-expandable filler composition of the present invention is typically in the range of 1 to 10 wt %, 2 to 8 wt %, preferably 3 to 6 wt %.

[0032] The "pumpable" characteristic of the heat-expandable filler composition of the present application is understood to mean that the filler has a viscosity suitable for pumping at ambient temperature (20°C), preferably a paste-like viscosity. The viscosity of the pumpable heat-expandable filler composition is preferably in the range of 50 to 500 Pa.s, more preferably 150 to 400 Pa.s, as measured by a rheometer (MCR301, manufactured by Anton Paar) equipped with a heatable plate (gap: 1000 μm, measuring plate diameter: 25 mm (plate / plate), deformation: 0.01 to 10%, 10 Hz, temperature: 45°C). If the viscosity is lower than 50 Pa.s, dripping may easily occur, and the material may not be able to maintain its shape adequately during processing. On the other hand, if the viscosity exceeds 500 Pa.s, the processability of the material becomes extremely poor.

[0033] As a further essential component, the pumpable heat-expandable filler composition of the present invention includes rubber, particularly synthetic rubber, preferably partially crosslinked synthetic rubber. Examples of partially crosslinked rubbers for use in the filler composition of the present invention include partially crosslinked diene rubbers, more preferably rubbers selected from the group consisting of acrylonitrile-isoprene copolymer rubber (NIR), acrylonitrile-butadiene copolymer rubber (NBR), styrene-butadiene copolymer rubber (SBR), butadiene rubber (BR), and isoprene rubber (IR). The crosslinking may be the result of adding a crosslinking agent, such as divinylbenzene or sulfur. The addition of rubber provides the resulting filler composition with the advantages of improved rheological properties, sag resistance, wash-off resistance, and higher volume expansion.

[0034] The rubber is typically incorporated into the filler composition of the present invention in an amount of 1 to 20%, preferably 3 to 15%, more preferably 5 to 10% by weight, based on the total weight of the composition.

[0035] Following the ingredients listed above, the pumpable heat-expandable filler composition may include additional ingredients.

[0036] Another component that can be advantageously used in the pumpable heat-expandable filler composition of the present application is a plasticizer. Therefore, the pumpable heat-expandable filler composition of the present application preferably contains at least one plasticizer. The combination of a low-viscosity plasticizer with PVC and / or acrylic resin powder is favorable for a stable paste-like state and for obtaining a cured material with good physical strength and good expansion rate, especially after storage in a humid environment.

[0037] Any plasticizer may be used, provided that it is one in which polyvinyl chloride swells and dissolves. Examples of plasticizers include phthalate esters such as di(2-ethylhexyl) phthalate, butyl benzyl phthalate, dinonyl phthalate, diisononyl phthalate (DIDP), diisodecyl phthalate (DIDP), diundecyl phthalate, ditridecyl phthalate (DTDP), diheptyl phthalate, and butylphthalyl butyl glycolate; aliphatic dibasic acid esters such as dioctyl adipate, didecyl adipate, and dioctyl sebacate; polyglycol benzoate esters such as polyoxyethylene glycol dibenzoate and polyoxypropylene glycol dibenzoate; phosphate esters such as tributyl phosphate and tricresyl phosphate; hydrocarbons such as alkyl-substituted diphenyls, alkyl-substituted terphenyls, partially hydrogenated terphenyls, aromatic process oils, and pile oils. These plasticizers may be used alone or as a mixture of two or more thereof. In the context of the present application, preferred among the above-mentioned plasticizers are phthalate esters, in particular diisononyl phthalate (DINP), ditridecyl phthalate (DTDP), and diisodecyl phthalate (DIDP).

[0038] In the context of the present application, suitable amounts of plasticizer are 5 to 40% by weight, preferably 10 to 30% by weight, 15 to 25% by weight, especially 10 to 20% by weight, based on the total weight of the composition.

[0039] The pumpable heat-expandable filler composition of the present application preferably also contains a curing agent for the liquid epoxy resin. The curing agent preferably includes a latent curing agent, which provides cure by heating and can usually be activated at temperatures between 80 and 250°C. Specific examples of latent curing agents include dicyandiamide, 4,4'-diaminodiphenyl sulfone, imidazole derivatives such as 2-N-heptadecylimidazole, isophthaldihydrazide, N,N-dialkylurea derivatives, N,N-dialkylthiourea derivatives, and melamine derivatives. These curing agents may be used independently or as a mixture of two or more thereof, depending on the curing conditions and their properties. A particularly preferred curing agent for use in the context of the present application is dicyandiamide. In one preferred embodiment, dicyandiamide is used as the sole epoxy curing agent in the composition, since it has been observed that combining a liquid epoxy resin with dicyandiamide results in a mixture with extremely high storage stability.

[0040] The amount of curing agent is preferably within the range of 0.05 to 2.0 wt%, 0.1 to 1.5 wt%, 0.2 to 1.2 wt%, 0.4 to 1.0 wt%, and more preferably 0.5 to 0.8 wt%, based on the total weight of the composition. It has been observed that combining a large amount of liquid epoxy resin with a small amount of curing agent results in a material that, upon curing, undergoes a moderate level of crosslinking and provides good adhesion, even on oily metal substrates. In addition, this system also provides good physical strength.

[0041] In addition to the above components, the pumpable heat-expandable filler composition of the present application preferably further comprises a filler, particularly an inorganic filler. Suitable inorganic fillers include, for example, calcium carbonate, silica, clay, and fly ash. These inorganic fillers may be used alone or as a mixture of two or more thereof. It is also possible to use two or more modified fillers, such as calcium carbonates with different modifications.

[0042] The amount of filler, especially inorganic filler, in the context of the present application is not particularly limited, but depends on the viscosity of the composition without the filler (i.e., a lower viscosity allows for the incorporation of a larger amount of filler, while a higher viscosity without the filler allows for the incorporation of only a smaller amount of filler), while still maintaining the composition pumpable. Thus, the amount of filler is typically in the range of 10 to 55% by weight, preferably 15 to 45% by weight, more preferably 20 to 35% by weight, based on the total weight of the composition.

[0043] The pumpable heat-expandable filler composition of the present application may further contain other additives in appropriate amounts, if desired, such as, for example: thixotropic agents such as organic bentonite, fumed silica, castor oil derivatives, pigments such as carbon black, titanium dioxide, zinc dioxide or other inorganic pigments, dehydrating agents such as calcium oxide and powdered silica gel, and / or PVC-stabilizers.

[0044] There is no particular limit to the amount of these additional additives, however, it is preferred that the content does not exceed 15% by weight, more preferably not more than 10% by weight, and even more preferably not more than 8% by weight.

[0045] In a particularly preferred embodiment of the present application, the pumpable heat-expandable filler composition of the present application comprises: - 8 to 30% by weight, 10 to 25% by weight, preferably 12.5 to 20% by weight of a liquid epoxy resin, preferably a liquid resin of formula (I); - 5 to 40% by weight, 8 to 30% by weight, preferably 10 to 20% by weight of polyvinyl chloride resin and / or acrylic resin powder, preferably polyvinyl chloride resin; - 1 to 20%, 3 to 15% by weight, preferably 5 to 10% by weight of rubber, preferably synthetic rubber, more preferably diene rubber; - 1 to 10% by weight, 2 to 8% by weight, preferably 3 to 6% by weight of a blowing agent; - 5-40% by weight, 10-30% by weight, 15-25% by weight, preferably 10-20% by weight of a plasticizer, preferably a phthalate; - 0.05 to 2.0 wt. %, 0.1 to 1.5 wt. %, 0.2 to 1.2 wt. %, 0.4 to 1.0 wt. %, preferably 0.5 to 0.8 wt. % of a hardener, preferably a latent hardener; 10 to 55% by weight, 15 to 45% by weight, preferably 20 to 35% by weight of fillers, preferably inorganic fillers. The weight percentages stated above are based on the total weight of the composition.

[0046] The pumpable heat-expandable filler composition of the present invention can be produced by mixing the above-mentioned components in a mixer. There are no particular restrictions on the mixer used, and various mixers such as planetary mixers and kneaders can be used.

[0047] The method for joining two substrates includes the following sequential steps: i) applying a pumpable heat-expandable filler composition onto a first substrate S1; and - ii) placing a second substrate S2 such that at the application position of the pumpable heat-expandable filler composition, the distance between the first substrate S1 and the second substrate S2 is between 2 and 10 mm; and - iii) heating the first substrate S1 and the second substrate S2 to a temperature above the activation temperature of the blowing agent to foam the pumpable heat-foamable filler composition. Between the time step ii) is performed and the time step iii) is started, the applied pumpable heat-foamable filler composition is prevented from coming into contact with the second substrate S2. During this time, the applied pumpable heat-foamable filler composition is preferably in an unfoamed state.

[0048] As can be seen in Table 1 by comparing Example 1 with Reference Example 1, the pumpable heat-expandable filler composition of Example 1 applied without contact with the second substrate S2 after S2 placement provides improved bondline lead-through compared to the prior art composition similar to Example 1 but placed in contact with the second substrate S2 after S2 placement. Even more surprisingly, it was found that the two application methods of the composition of Example 1 provided equivalent lap shear strengths.

[0049] In step i), the pumpable heat-expandable filler composition is advantageously applied in the form of a bead having a width of 3 to 18 mm, preferably 6 to 12 mm, more preferably 10 to 12 mm.

[0050] It is further advantageous if in step i) the pumpable heat-expandable filler composition is applied in the form of a bead having a height of 1 to 8 mm, preferably 1 to 4 mm, more preferably 1.5 to 3 mm, most preferably 1.5 to 2.5 mm.

[0051] It is further preferred if in step i) the pumpable heat-expandable filler composition is applied in the form of a bead having a length of 10 mm to 2 m, preferably a length of 2 cm to 10 cm or a length of 0.5 m to 3 m. The former is advantageous when the composition is applied as a spotted bead, for example, for bonding a vehicle hood. The latter is beneficial when the composition is applied continuously, for example, for bonding a vehicle roof.

[0052] In step i), the pumpable heat-expandable filler composition is preferably applied as a rectangular bead, the width-to-height ratio of which is preferably 2-10, preferably 3-8, more preferably 5-8.

[0053] It has also been found to be advantageous to apply the pumpable heat-expandable filler composition in the form of a bead in step i), and to set the ratio of the distance DI between the first substrate S1 and the second substrate S2 to the height HT of the bead at the location where the pumpable heat-expandable filler composition is applied (DI / HT) in step ii) to be greater than 1 and 6.5, preferably 1.2-4.5, and most preferably 1.5-2.75. As can be seen from the comparison of the various height / distance ratios in Table 4, this is advantageous in terms of the quality of contact with the upper substrate, which results in better corrosion resistance, adhesion to the substrate, and reduced vibration.

[0054] In one preferred method, in step i), the pumpable heat-expandable filler composition is applied in the form of a rectangular bead, the bead height HT is 1.0-3.5 mm, preferably 1.5-2.5 mm, and the distance DI between the first substrate S1 and the second substrate S2 at the location where the pumpable heat-expandable filler composition is applied is 3-6 mm, preferably 4-5 mm.

[0055] The first substrate S1 and / or the second substrate S2 are preferably metal substrates, more preferably oil-treated metal substrates. However, if appropriate, heat-resistant plastics can also be used. The first substrate S1 and the second substrate S2 can be made of the same material or different materials.

[0056] Preferred metal substrates are those which have been used, for example, in the manufacture of vehicles, for example in the automotive industry, or in the manufacture of white goods. The method of the present invention is therefore particularly suitable for joining metal substrates for the manufacture of vehicles, in particular cars, buses, trucks, rail vehicles, ships or aircraft, or white goods, in particular washing machines, drum dryers or dishwashers, or components thereof, preferably automotive vehicles or assemblies thereof.

[0057] It is most preferred if the first substrate S1 is a support frame for a vehicle hood, trunk or door, or a cross beam for a vehicle roof, and the second substrate S2 is a vehicle hood, trunk or door panel, or a vehicle roof panel.

[0058] Preferably, the metal substrates are oiled substrates, meaning that they are coated with a corrosion inhibitor oil known to those skilled in the art, one example of such a corrosion inhibitor oil is Anticorit PL 3802-39S.

[0059] Preferred examples of the metal substrate are metal substrates selected from the list consisting of steel sheet, aluminum, and magnesium, in particular, metal substrates selected from the list consisting of galvanized steel sheet, hot-dip galvanized steel sheet, bonazinc-coated steel sheet, post-phosphate-coated steel sheet, aluminum, magnesium, and magnesium alloys. Preferably, the substrate is an oil-treated substrate.

[0060] In step (a) of the method of the present invention, a pumpable heat-expandable filler composition is applied to the first substrate S1. This is done, for example, at an application temperature of the pumpable heat-expandable filler composition between 10°C and 80°C, preferably between 25°C and 50°C, more preferably between 30°C and 40°C. The application is preferably done in the form of a bead. Automatic application is preferred.

[0061] The pumpable heat-foamable filler composition can be applied to the entire surface or a portion of the surface of the first substrate S1 facing the second substrate S2. In a preferred application, particularly when the first substrate S1 is a vehicle support frame, hood, trunk, or door, the pumpable heat-foamable filler composition is applied to only a small portion, preferably less than 20%, less than 10%, less than 5%, preferably less than 2%, of the surface of the first substrate S1 facing the second substrate S2.

[0062] In a subsequent step ii), a second substrate S2 is placed at the application position of the pumpable heat-expandable filler composition such that the distance between the first substrate S1 and the second substrate S2 is between 2 and 10 mm. After the positioning, the first substrate S1 and the second substrate S2 are preferably fixed in position, preferably by mechanical fixing means, preferably mechanical clamping, more preferably mechanical clamping followed by spot welding or laser welding, so that the distance between the first substrate S1 and the second substrate S2, preferably the position where the pumpable heat-expandable filler composition was applied onto the first substrate S1, does not change until step iii) is completed.

[0063] After step ii), the first substrate S1 and the second substrate S2 are heated to a temperature above the activation temperature of the blowing agent to expand the pumpable heat-foamable filler composition (wherein between steps ii) and iii), the applied pumpable heat-foamable filler composition is not in contact with the second substrate S2).

[0064] In step iii), the pumpable heat-expandable filler composition is heated, preferably cured, by heating the pumpable heat-expandable filler composition to a temperature in the range of 150 to 220°C, preferably 160 to 200°C, preferably 170 to 190°C, and most preferably 180°C. The heating can be carried out, for example, by means of infrared or induction heating or in an oven, such as a cathodic electrodeposition coating oven. In this way, an adhesive bond with the pumpable heat-expandable filler composition is achieved.

[0065] Preferably, the duration of the heating step is from 10 to 60 minutes, preferably from 10 to 40 minutes, from 10 to 30 minutes, most preferably from 10 to 20 minutes.

[0066] Preferably, after step iii), the pumpable heat-foamable filler composition foams, cures, and forms an adhesive bond between the first substrate S1 and the second substrate S2, with the two substrates being in direct contact.

[0067] In the adhesive bond, the pumpable heat-expandable filler composition may be cured in one step, but it can also be cured in two or more steps, with intermediate steps between or during the curing steps, such as cleaning and / or a substrate immersion coating operation, e.g., a cathodic electrodeposition coating operation followed by a cleaning operation.

[0068] Another aspect of the present invention is an article obtainable by said method, in particular a component of a means of transport in the automotive industry, or a white goods article, most preferably an article selected from the list consisting of a vehicle roof, a bonnet, a trunk lid, and a vehicle door.

[0069] The present invention is further illustrated in the following examples section, but these descriptions should not be construed as limiting the scope of the present invention. [Example]

[0070] A reference heat-expandable rubber composition (Reference Example 1) identical to composition E15 described in WO2020048905A1 was prepared and compared with the composition of Example 1 of the pumpable heat-expandable filler of the present invention described below.

[0071] To prepare pumpable heat-expandable filler compositions Examples 1 to 3 and reference compositions Reference Examples 2 and 3, the components were blended according to the blending amounts shown in Table 1. The premix for Example 1 contained 12.9 wt.% styrene-butadiene rubber, 26.8 wt.% DIDP plasticizer, 39.9 wt.% calcium carbonate filler, and 20.4 wt.% liquid epoxy resin (based on bisphenol A / epichlorohydrin with an epoxy equivalent weight of 180-190 g / eq). The amounts of each component in the premixes for compositions Examples 2 to 3 and Reference Examples 2 and 3 were adjusted to match the premix for Example 1, maintaining the same weight ratios among the components of the premixes.

[0072] [Table 1]

[0073] Measurement of expansion The volume gains in Table 3 are determined using the density determination method according to DIN EN ISO 1183 (Archimedes' principle) in combination with the mass of the sample measured on a precision balance in deionized water.

[0074] Lead-through measurement The compositions of Reference Example 1 and Example 1 were applied as a single bead (length: 50 mm, rectangular shape, width: 6 mm, height; as shown in Table 2) to the center of a test specimen (steel plate EG (DC06+ZE, 75 / 75), thickness: 0.25 mm, 150-105 mm). The test specimen was then fixed in a frame, and a thin, one-sidedly painted steel sheet (DC01 C590, 0.25 mm) was placed on top of the other specimen at a distance of 4.5 mm (using a Teflon® spacer), so that the unpainted side was wetted with the bead-applied composition. Both metal sheets were fixed by overlapping and screwing the frame segments at their outer edges. The test specimen was then placed in an oven at 200°C for 20 minutes. After cooling to 23°C, the upper side of the test specimen (white painted sheet metal surface) was analyzed with a deflectometer. The completed specimen is placed in the deflectometer's measurement chamber, and its white-painted steel surface is illuminated with a periodic pattern of parallel white and black lines. A camera records the pattern reflected from the white sheet metal surface. Computer post-processing of the data (filtering and profile extraction) allows the underlying strain to be visualized.

[0075] The curvature profiles thus obtained were then compared with the results obtained by using beads made of a commercially available prior art product (SikaSeal-710 LS, manufactured by Sika Germany) as a reference. Compositions with a curvature profile equivalent to, respectively slightly better than, that obtained with the reference composition in terms of BLRT performance were given a rating of "4" (equivalent, visible curvature) or "3" (slightly reduced curvature), respectively. Compositions with a significantly improved curvature profile compared to that obtained with the reference (very barely detectable bond line-read-through or no detectable significant bond line-read-through) were given a rating of "2" or "1", respectively. The results are shown in Table 2.

[0076] Measuring the contact quality of the substrate In Table 4, the contact quality between the expanded composition and an upper one ("upper substrate") placed on top of the first test piece ("base substrate") containing the applied composition was measured using a procedure similar to that described above for measuring read-through.

[0077] In all measurements, the composition of Example 1 was applied as a single bead (length: 50 mm, rectangular shape, width: 12 mm, height; as shown in Table 4) to the center of a first test specimen ("base substrate", steel sheet EG (DC06+ZE 75 / 75), thickness: 0.25 mm, 150 × 105 mm). The test specimen was then fixed in a predetermined frame, and a second test specimen ("upper substrate", steel sheet EG (DC06+ZE 75 / 75), thickness: 0.25 mm, 150 × 105 mm) was placed on top of the first test specimen at the distance shown in Table 4 (using Teflon® spacers, "Thickness spacer (mm)"). Both metal sheets were fixed by overlapping and screwing the frame segments at their outer edges. The test specimen was then placed in an oven at 200 ° C. for 20 minutes. After cooling to 23°C, the contact area between the expanded composition and the upper substrate was compared to the contact area with the base. The following rating system was applied: ++ = The contact area with the upper substrate is 100% or more of the contact area with the base substrate + = The contact area with the upper substrate is less than 100% to 85% of the contact area with the base substrate + / - = The contact area with the upper substrate is less than 85% to 70% of the contact area with the base substrate.

[0078] Tensile strength (TS) (DIN ISO 527) Curing conditions: 15 minutes at a target temperature of 180°C The tensile strength was measured in accordance with DIN ISO 527 using a tensile tester at a pulling rate of 10 mm / min, repeated three times.

[0079] Lap shear strength (LSS) (DIN EN 1465) For Reference Example 1 and Example 1, cleaned and oiled (Anticorit PL3802-39S) steel specimens (thickness: 0.8 mm) were bonded to a 25 x 20 mm bonding surface with the composition in a layer thickness of 2.0 mm using a Teflon spacer and cured. For Example 1, an additional sample (rightmost column in Table 2) was prepared with a thickness of 2.0 mm using a Teflon spacer as described above, except that the applied bead was only 1.0 mm thick, so that the applied Example 1 composition was not in contact with the upper steel specimen before curing.

[0080] Curing conditions: 15 minutes at a target temperature of 180°C The lap shear strength was determined in accordance with DIN EN 1465 using a tensile tester at a pulling rate of 10 mm / min in triplicate.

[0081] [Table 2]

[0082] [Table 3]

[0083] [Table 4]

Claims

1. A method for joining two substrates, - i) The step of applying a pumpable, heat-expandable filler composition onto a first substrate S1, and - ii) The step of arranging the second substrate S2 at the application site of the pumpable heat-expandable filler composition such that the distance between the first substrate S1 and the second substrate S2 is between 2 and 10 mm, and - iii) Heating the first substrate S1 and the second substrate S2 to a temperature higher than the activation temperature of the foaming agent, thereby foaming the pumpable heat-foaming filler composition. This includes the following sequential steps: Between step ii) and step iii), the applied pumpable heat-foaming filler composition is not in contact with the second substrate S2. The pumpable, heat-expandable filler composition is: - Preferably, at least one type of rubber, preferably synthetic rubber, more preferably partially crosslinked synthetic rubber, more preferably diene rubber, present in an amount of 1 to 20%, preferably 3 to 15% by weight, and more preferably 5 to 10% by weight, based on the total weight of the composition; - Based on the total weight of the pumpable, heat-expandable filler composition, preferably 5 to 40% by weight, 8 to 30% by weight, and preferably 10 to 20% by weight of polyvinyl chloride resin and / or acrylic resin powder, preferably polyvinyl chloride resin; - A blowing agent in an amount of preferably 1 to 10% by weight, 2 to 8% by weight, and preferably 3 to 6% by weight, based on the total weight of the pumpable heat-expandable filler composition; Methods that include...

2. The method according to claim 1, characterized in that, in step i), the pumpable, heat-expandable filler composition is applied in the form of a bead having a width of 3 to 18 mm, preferably 6 to 12 mm, and more preferably 10 to 12 mm.

3. The method according to any one of claims 1 to 2, characterized in that, in step i), the pumpable, heat-expandable filler composition is applied in the form of a bead having a height of 1 to 8 mm, preferably 1 to 4 mm, more preferably 1.5 to 3 mm, and most preferably 1.5 to 2.5 mm.

4. The method according to any one of claims 1 to 2, characterized in that, in step i), the pumpable, heat-expandable filler composition is applied in the form of a bead having a length of 10 mm to 2 m, preferably 2 cm to 10 cm or 0.5 m to 3 m.

5. The method according to any one of claims 1 to 2, characterized in that, in step i), the pumpable, heat-expandable filler composition is applied in the form of a rectangular bead, preferably the width-to-height ratio of the rectangular bead is 2 to 10, preferably 3 to 8, more preferably 5 to 8.

6. The method according to any one of claims 1 to 2, characterized in that, in step i), the pumpable heat-expandable filler composition is applied in the form of a bead, and in step ii), the ratio (DI / HT) of the distance DI between the first substrate S1 and the second substrate S2 at the location where the pumpable heat-expandable filler composition is applied to the height HT of the bead is greater than 1 to 6.5, preferably 1.2 to 4.5, and most preferably 1.5 to 2.

75.

7. The method according to any one of claims 1 to 2, characterized in that, in step i), the pumpable heat-expandable filler composition is applied in the form of a rectangular bead, the height HT of the bead at the location where the pumpable heat-expandable filler composition is applied is 1.0 to 3.5 mm, preferably 1.5 to 2.5 mm, and the distance DI between the first substrate S1 and the second substrate S2 is 3 to 6 mm, preferably 4 to 5 mm.

8. The method according to any one of claims 1 to 2, characterized in that the amount of polyvinyl chloride resin and / or acrylic resin powder, preferably polyvinyl chloride resin, is 5 to 40% by weight, preferably 8 to 30% by weight, and more preferably 10 to 20% by weight, based on the total weight of the pumpable heat-foamable filler composition.

9. The method according to any one of claims 1 to 2, characterized in that the first base material S1 is a support frame for a vehicle hood or a crossbeam for a vehicle roof, and the second base material S2 is a vehicle hood panel or a vehicle roof panel.

10. The method according to any one of claims 1 to 2, characterized in that the pumpable, heat-expandable filler composition further contains a liquid epoxy resin in an amount preferably 8 to 30% by weight, 10 to 25% by weight, and preferably 12.5 to 20% by weight, based on the total weight of the pumpable, heat-expandable filler composition.

11. The method according to claim 10, characterized in that the pumpable heat-foaming filler composition further contains a curing agent, preferably a latent curing agent, more preferably a dicyandiamide, for the liquid epoxy resin, preferably in an amount within the range of 0.05 to 2.0% by weight, 0.1 to 1.5% by weight, 0.2 to 1.2% by weight, 0.4 to 1.0% by weight, more preferably 0.5 to 0.8% by weight, based on the total weight of the pumpable heat-foaming filler composition.

12. The method according to any one of claims 1 to 2, wherein the blowing agent is a chemical blowing agent, and more preferably the blowing agent is selected from a list consisting of azo compounds, nitroso compounds, and hydrazine derivatives, and more preferably selected from a list consisting of azodicarbonamide, N,N-dinitrosopentamethylenetetraamine, and diphenylsulfone-3,3'-disulfohydrazide.

13. Articles obtained by the method of any one of claims 1 to 2, which are particularly components of means of transport, particularly components of means of transport in the automotive industry, or white goods articles, most preferably selected from the list consisting of roofs, hoods, trunk lids and doors of vehicles.

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