Method for producing adhesive structure, adhesive structure and use of said adhesive structure for producing motor vehicle component

Abstract

A method of making a bonded structure, the method comprising flame treating a surface of a first component comprising a polyolefin to provide an activated polyolefin surface; applying an acrylic structural adhesive directly to the activated polyolefin surface and the surface of the second component; and curing the adhesive to form an adhesion between the first component and the second component.

Description

Background Technology

[0001] Polymer materials can be bonded by applying an adhesive to the bonding surfaces of the materials to be bonded. This requires depositing the adhesive onto the bonding surfaces of the polymer materials. Due to the inherent incompatible chemistry of the two materials (adhesive and polymer), adhesion between the adhesive and the bonding surfaces can be difficult to achieve.

[0002] For example, due to the low surface energy and low polarity of polyolefins, it may be difficult to adhere a polyolefin (e.g., polypropylene) surface to another surface (e.g., another polyolefin surface). For example, acrylic adhesives may not be recommended for adhering a polyolefin surface to another surface.

[0003] Therefore, there is a need for improved methods to prepare adhesive structures with desired adhesive strength.

[0004] Purpose of the invention

[0005] The purpose of this invention is to provide a method for improving adhesion.

[0006] Another object of the present invention is to provide an adhesive structure suitable for the manufacture of automotive parts. Summary of the Invention

[0007] A method for preparing an adhesive structure is provided, the method comprising: flame treating a surface of a first component comprising a polyolefin to provide an activated polyolefin surface; applying an acrylic structural adhesive directly to the activated polyolefin surface and a surface of a second component; and curing the adhesive to form an adhesive between the first component and the second component.

[0008] Acrylic structural adhesives may contain methacrylates. Polyolefins may contain polypropylene. Polyolefins may contain polyethylene. The first component may also contain glass fiber. The first component may also contain flame retardant additives.

[0009] The first component may also include a combination of glass fiber and flame-retardant additives.

[0010] The second component may contain polyolefin. After conditioning at 23±2°C and 50±6% relative humidity for 168 hours, the bond exhibits an lap shear strength greater than or equal to 1.5 MPa or 1.75 MPa according to DIN EN 1465:2009. After conditioning at 23±2°C and 50±6% relative humidity for 168 hours and undergoing heating and cooling cycles at various relative humidities, the bond exhibits an lap shear strength greater than or equal to 2.0 MPa or 2.25 MPa according to DIN EN 1465:2009.

[0011] The second component may contain polypropylene. The second component may contain polyethylene.

[0012] The second component may contain metal. The second component may not be exposed to laser radiation. After conditioning at 23±2°C and 50±6% relative humidity for 168 hours, the bond exhibits an lap shear strength greater than or equal to 2.0 MPa, 2.25 MPa, or 2.5 MPa according to DIN EN 1465:2009. After conditioning at 23±2°C and 50±6% relative humidity for 168 hours and undergoing heating and cooling cycles at various relative humidities, the bond exhibits an lap shear strength greater than or equal to 6.0 MPa, 6.25 MPa, or 6.5 MPa according to DIN EN 1465:2009. After conditioning at 23±2°C and 50±6% relative humidity for 168 hours and complete immersion in ethylene glycol / water at 65°C for 45 days, the bond exhibits an lap shear strength greater than or equal to 6.0 MPa, 6.25 MPa, or 6.5 MPa according to DIN EN 1465:2009.

[0013] The propane-containing gas may contain at least 80% by weight (wt%) of propane based on the weight of the propane-containing gas, wherein the flame is generated by burning a mixture of air and propane-containing gas during treatment with the propane-containing gas flame.

[0014] During treatment with a flame containing propane gas, the volume ratio of propane to oxygen is equal to or less than 1:5.01.

[0015] Activated polyolefin surfaces can have surface energies of less than 34 millinewtons per meter, as determined according to ISO 8296:2003.

[0016] Acrylic structural adhesives can contain two components.

[0017] The method also provides adhesive structures prepared by the method, for example configured for use in batteries, such as batteries for electric vehicles.

[0018] Electric vehicles incorporating this adhesive structure are also provided.

[0019] A method for preparing an adhesive structure, the adhesive structure comprising a first polyolefin component having at least a first adhesive surface, the method comprising the following steps:

[0020] a) Flame treatment of at least a portion of the first adhesive surface of the first polyolefin component with a flame containing propane gas, the propane gas being propane or a mixture comprising: at least 50% by weight of propane based on the weight of the propane gas, and one or more gases selected from methane, ethane, butane, pentane, and hexane, wherein during the flame treatment with the propane gas flame, the flame is generated by burning the mixture of air and propane gas, wherein the gas-to-air ratio is selected such that the volume ratio of propane to oxygen is equal to or less than 1:5.01, for example less than 1:5.00, and preferably at least 1:3.50, to obtain a first polyolefin component having a flame-treated first polyolefin adhesive surface.

[0021] The first polyolefin component can be prepared from a composition comprising polypropylene and long glass fibers, for example from STAMAX, a product commercially available from SABIC. TM Preparation of polypropylene compositions.

[0022] The first polyolefin component can be prepared from a composition comprising polypropylene and mineral fillers.

[0023] In another embodiment, the method further includes the following steps in sequence:

[0024] b1) Provide a second component, wherein the second component has a second adhesive surface, and

[0025] c1) The first and second adhesive surfaces are brought into contact with the acrylic structural adhesive by bringing at least a portion of the flame-treated first polyolefin adhesive surface and at least a portion of the second adhesive surface into contact with the acrylic structural adhesive (3).

[0026] The method described in this implementation is particularly suitable for manufacturing tailgates or roof spoilers.

[0027] Prior to step c1), at least a portion of the second polyolefin adhesive surface may be flame-treated with a propane-containing gas flame, wherein the propane-containing gas is propane or a mixture comprising at least 50% by weight of propane and one or more gases selected from ethane, butane, and hexane, wherein preferably, during the flame-treatment with the propane-containing gas flame, the flame is generated by burning the mixture of air and propane-containing gas, wherein the gas-to-air ratio is selected such that the volume ratio of propane to oxygen is equal to or less than 1:5.01, for example less than 1:5.00 and preferably at least 1:3.50, to obtain a second polyolefin component having a flame-treated second polyolefin adhesive surface.

[0028] The propane-containing gas may contain at least 80% by weight of propane, preferably at least 95% by weight of propane, more preferably at least 99% by weight of propane, or even 100% by weight of propane-containing gas.

[0029] A burner may be used to generate a flame, the burner comprising at least one nozzle for providing a mixture of air to be burned and propane-containing gas, wherein the gap between at least one nozzle and the first adhesive surface and / or the second adhesive surface is 5 cm to 15 cm, preferably 8 cm.

[0030] During flame treatment with a flame containing propane gas, the temperature reached on the flame-treated first polyolefin bonding surface and / or the flame-treated second bonding surface may be, for example, 30°C to 90°C, preferably 50°C to 80°C, more preferably 60°C to 65°C.

[0031] The surface energy of the flame-treated first polyolefin bonding surface and / or the flame-treated second polyolefin bonding surface is preferably higher than 30 millinewtons per meter (mN / m), as determined according to ISO 8296:2003, and the polar portion of the surface energy is preferably higher than 1.5 mN / m, more preferably higher than 2 mN / m.

[0032] "The first polyolefin component may comprise a polymer" means that the first polyolefin component comprises at least 35% by weight, for example at least 50% by weight, for example at least 75% by weight, or at least 83% by weight, or even 99% by weight, or 100% by weight of one or more polymers based on the weight of the first polyolefin component.

[0033] "The second component may contain a polymer" means that the second component contains at least 35% by weight, for example at least 50% by weight, for example at least 75% by weight, or at least 83% by weight, or even 99% by weight, or 100% by weight of one or more polymers based on the weight of the second component.

[0034] The first polyolefin component and the second component may contain the same polymer.

[0035] The polyolefin may be polypropylene or a combination of polypropylene and polyethylene, wherein the preferred polyolefin comprises at least 45% by weight of polypropylene based on the total weight of the polyolefin.

[0036] In another respect, the present invention relates to adhesive structures that can be obtained or acquired by the method according to the invention.

[0037] On the other hand, the present invention relates to the use of adhesive structures as automotive components, such as tailgates, roof spoilers, or bumpers.

[0038] Unless otherwise stated, all embodiments specified according to the method of the invention also apply to the product and its use.

[0039] definition

[0040] The following definitions are used in this specification.

[0041] As used in this application, "adhesive" means a material capable of holding two surfaces together, typically producing a smooth bond. Adhesives are also known as adhesives.

[0042] As used in this application, "gap between burner nozzle and surface" means the distance between the burner nozzle and the surface to be flame-treated (e.g., the surface of a polyolefin component).

[0043] As used in this application, "gas to air ratio" means the ratio of the gas portion to the air portion used in the flame (i.e., in the total gas and air flow rate). Unless otherwise stated, this ratio is a volume ratio. For example, 1:17 means that for 1 liter (L) of gas fed into the flame, 17 L of air is used as the oxidant.

[0044] As used in this application, "flame treatment rate" means the length of surface exposed to flame per unit time; for example, the length of surface of a polyolefin component exposed to flame per unit time. In this sense, a flame treatment rate of 300 mm / s means, for example, 300 mm of surface of a polyolefin component exposed to flame per second.

[0045] As used in this application, "total flow rate of gas-air mixture" means the number of liters of gas-air mixture fed into the burner per unit time for the purpose of generating a flame. For example, a total flow rate of 300 liters / minute (L / min) of gas-air mixture means that 300 liters of gas-air mixture are fed into the burner for the purpose of generating a flame.

[0046] As used in this application, “surface activation” means the chemical modification of the surface of a solid (e.g., a polyolefin component) that results in an increase in its surface energy (also known as surface free energy (SFE)), an increase in the polar portion that contributes to the surface energy, and / or a decrease in the surface contact angle with water.

[0047] As used in this application, "surface energy" refers to the surface energy calculated according to the Owens, Wendt, Rabel, and Kaelble method, a standard method for calculating the surface energy of a solid from its contact angles with two liquids (water and diiodomethane). This allows for the determination of the surface energy, which is divided into a polar component and a dispersed (or dispersive) component. Based on the theory of Owens, Wendt, Rabel, and Kaelble, surface tension (σ) can be divided into polar and dispersed components as follows:

[0048]

[0049] Where P represents polarity, D represents dispersion, s represents solid, and l represents liquid.

[0050]

[0051] As is well known, according to Young, the surface tension σ between a solid and a liquid is... s，l Surface energy γ between solids and liquids sl The correlation between the contact angle θ and the contact angle θ can be described as follows:

[0052]

[0053] Owens and Wendt hypothesized the following equation regarding surface energy:

[0054]

[0055] The combination of equations (2) and (3) produces the following linear equation:

[0056]

[0057] By using linear regression in the xy coordinate system, σ can be estimated from the square of the slope m. s P Furthermore, σ can be estimated by the square of the y-intercept b. s D .

[0058] To estimate the polarity and dispersion, water and diiodomethane were used, due to their different properties. Compare. Detailed Implementation

[0059] In a first aspect, this application relates to a method for preparing an adhesive structure comprising a first polyolefin component having at least a first adhesive surface, an acrylic structural adhesive, and a second component having a second adhesive surface, wherein the first and second adhesive surfaces are in contact with the acrylic structural adhesive, the method preferably comprising the following steps:

[0060] a) Flame treatment of at least a portion of the first adhesive surface of the first polyolefin component with a flame containing propane gas, wherein the propane gas is propane or a mixture comprising: at least 50% by weight of propane based on the weight of the propane gas, and one or more gases selected from methane, ethane, butane, pentane and hexane, to obtain a first polyolefin component having a flame-treated first polyolefin adhesive surface.

[0061] b) Provide a second component having a second adhesive surface;

[0062] c) The first polyolefin component and the second component are bonded together by contacting at least a portion of the flame-treated first polyolefin bonding surface and at least a portion of the second bonding surface with the acrylic structural adhesive.

[0063] An adhesive structure with high adhesive shear strength was obtained using the method according to the invention. At least the adhesive surface of the first polyolefin component was activated, and good adhesion was achieved between the acrylic structural adhesive and the adhesive surface.

[0064] Prior to step c1), at least a portion of the second polyolefin adhesive surface may be treated with a flame containing propane gas to obtain a second component having a flame-treated second polyolefin adhesive surface, wherein the propane gas is propane or a mixture comprising at least 50% by weight of propane and one or more gases selected from ethane, butane and hexane.

[0065] The first adhesive surface can be washed, followed by step a) according to the method of the present invention. Alternatively, the second adhesive surface can be washed, then bonded to the first polyolefin component, or subsequently treated with a flame containing propane gas. The second adhesive surface can also be activated using various activation methods, such as treating the surface with atmospheric plasma, low-pressure plasma, corona treatment, or fluorination.

[0066] The washing step can be performed by immersing the polyolefin component in a solution containing a detergent (such as a surfactant). The washing step may also include immersing the polyolefin component in a solvent (such as an alcohol, preferably an alcohol selected from propanol and isopropanol, more preferably isopropanol with a purity higher than 96% by weight).

[0067] The washing step can be replaced by a cleaning step, which includes applying a solution containing a detergent or solvent to the adhesive surface, and optionally rinsing the surface with water thereafter.

[0068] At least a portion of the first adhesive surface or at least a portion of the second adhesive surface is treated, respectively, means preferably at least 80%, more preferably at least 90%, even more preferably at least 95%, or even at least 99% or 100% of the first adhesive surface or the second adhesive surface is treated.

[0069] It will be understood that the larger the surface area of ​​the treated adhesive surface, the better the surface is activated, and thus the adhesion between the adhesive surface and the acrylic structural adhesive is improved, resulting in an adhesive structure with high adhesive shear strength.

[0070] Before proceeding to step c1), it is not necessary to apply primer to the flame-treated first polyolefin bonding surface and / or (flame-treated) second bonding surface to ensure proper adhesion.

[0071] Before contacting the surface with the acrylic structural adhesive, it is not necessary to apply a primer (also known as an adhesion promoter) to the bonding surface to ensure proper adhesion between the acrylic structural adhesive and the bonding surface.

[0072] Without using a primer, acrylic structural adhesives can be applied directly to the activated polyolefin surface and the surface of the second component.

[0073] The inventors have surprisingly discovered that, although acrylic adhesives may not be recommended for adhering polyolefin surfaces to another surface, as disclosed herein, flame treatment of polyolefin (e.g., polypropylene) surfaces using acrylic structural adhesives can generate surface energy between the polyolefin and a second component (e.g., containing polyolefin (e.g., polypropylene) or a metal) that provides the desired adhesion (both initially and in the long term).

[0074] In this application, the first adhesive surface may also be a first adhesive surface that has been washed or cleaned.

[0075] In this application, the second adhesive surface may also be a second adhesive surface that has been washed or cleaned. Furthermore, the second adhesive surface may also be a second polyolefin adhesive surface that has been flame-treated, i.e., a flame-treated second polyolefin adhesive surface.

[0076] Flame treatment can be performed using a burner that generates a flame. The burner is fed a defined mixture of fuel (containing propane gas) and oxidizer (air), which is thoroughly premixed before combustion. During flame treatment, as heat is applied by the flame, the bonds between atomic and / or molecular chains break at the surface, and the oxygen contents contained in the flame bind to the break points. In this way, polar molecules appear on the surface of the originally nonpolar material. The mechanical properties of the surface remain unchanged.

[0077] Variables affecting flame treatment include, for example, the gas-to-air ratio, gas composition, the gap between the burner nozzle and the bonded surface, the flame treatment rate, and the total flow rate of the gas-to-air mixture. These variables affect the temperature reached on the flame-treated bonded surface during flame treatment.

[0078] The applicant has observed that the adhesive surface of polyolefin components is activated by using a propane-containing gas (which is propane or a mixture containing at least 50% by weight of propane). Preferably, the propane-containing gas contains at least 80% by weight of propane, more preferably at least 95% by weight of propane, such as at least 99% by weight of propane or even 100% by weight of propane.

[0079] During treatment with a propane-containing flame, the flame is generated by burning a mixture of air and propane-containing gas, wherein the gas-to-air ratio is selected such that the volume ratio of propane to oxygen is equal to or less than 1:5.01. This also helps to further activate the adhesive surface of the polyolefin component.

[0080] The propane to oxygen volume ratio within the disclosed range can provide, for example, a surface energy of more than 30 and less than 34 mN / m to the surface of an activated polyolefin (e.g., polypropylene) to be bonded to a second component using an acrylic structural adhesive, as determined according to ISO 8296:2003, the benefits of which are disclosed herein.

[0081] The polyolefin component, namely the first polyolefin component and / or the second polyolefin component, may comprise a polyolefin selected from: propylene-based polymers (polypropylene), ethylene, and elastomers of α-olefin comonomers having 4 to 8 carbon atoms, and any mixtures thereof. Preferably, the polyolefin comprises a propylene-based polymer. Preferably, the thermoplastic polymer composition comprises at least 80% by weight of a propylene-based polymer, for example, at least 90%, at least 93%, at least 95%, at least 97%, at least 98%, or at least 99% by weight of a propylene-based polymer, based on the thermoplastic polymer composition. In a particular embodiment, the thermoplastic polymer composition consists of a propylene-based polymer.

[0082] The propylene-based polymer may be at least one selected from propylene homopolymers, propylene random copolymers, and multiphase propylene copolymers and mixtures thereof, preferably wherein the polyolefin comprises propylene random copolymers; propylene homopolymers and multiphase propylene copolymers; or propylene homopolymers and propylene random copolymers.

[0083] Propylene homopolymers can be obtained by polymerizing propylene under suitable polymerization conditions. Propylene copolymers can be obtained by copolymerizing propylene with one or more other α-olefins (preferably ethylene) under suitable polymerization conditions. The preparation of propylene homopolymers and copolymers is described, for example, in Moore, EP (1996) Polypropylene Handbook. Polymerization, Characterization, Properties, Processing, Applications, Hanser Publishers: New York.

[0084] The random propylene copolymer may contain ethylene as a comonomer and / or an α-olefin selected from α-olefins having 4 to 10 carbon atoms, preferably ethylene, 1-butene, 1-hexene, or any mixture thereof. The amount of comonomer is preferably up to 10% by weight based on the random propylene copolymer, for example, in the range of 2 to 7% by weight based on the random propylene copolymer.

[0085] Polypropylene can be manufactured using any known polymerization technique and any known polymerization catalyst system. Regarding the technique, slurry, solution, or gas-phase polymerization may be mentioned; regarding the catalyst system, Ziegler-Natta, metallocene, or single-point catalyst systems may be mentioned. These are all known in the art.

[0086] Multiphase propylene copolymers are typically prepared in one or more reactors by polymerizing propylene in the presence of a catalyst and subsequently polymerizing an ethylene-α-olefin mixture. The resulting polymer material is multiphase, but its specific morphology usually depends on the preparation method and the ratio of monomers used.

[0087] Multiphase propylene copolymers can be produced using any conventional techniques known to those skilled in the art (e.g., multi-stage process polymerization, such as bulk polymerization, gas-phase polymerization, slurry polymerization, solution polymerization, or any combination thereof). Any conventional catalyst system can be used, such as Ziegler-Natta or metallocene. Such techniques and catalysts are described, for example, in WO06 / 010414; Polypropylene and other Polyolefins, Ser van der en, Studies in Polymer Science 7, Elsevier 1990; WO06 / 010414, US4399054, and US4472524.

[0088] The polymer or thermoplastic material may be a linear polymer or a branched polymer or a combination thereof. The plastic may optionally be reinforced, for example with fibers, granules, sheets, and combinations comprising at least one of the foregoing, such as, in particular, long glass fibers, short glass fibers, glass beads, talc, mica, inorganic fillers, natural fibers, conductive fillers, and / or carbon fibers. For example, the thermoplastic second component may be formed from STAMAX® material, which is commercially available from SABIC long glass fiber reinforced polypropylene.

[0089] The polymer may contain additives such as stabilizers, antioxidants, and pigments; preferably, the polymer contains up to 5% additives. The composition may be a blend or copolymer. The polymer may be filled with mineral fillers (e.g., talc) or glass fibers; for example, the polymer may contain up to 45% by weight of filler, such as up to 40% by weight of filler, based on the total weight of the polymer. In embodiments, the polymer may contain flame-retardant additives, such as nitrogen-phosphorus based flame retardants.

[0090] In an embodiment, the polymer may comprise 20 to 40 wt% or 25 to 30 wt% of long glass fibers; 20 to 40 wt% or 25 to 30 wt% of short glass fibers; or 30 to 50 wt% or 35 to 45 wt% of long glass fibers.

[0091] The polymer may contain a combination of glass fibers and flame-retardant additives.

[0092] Glass fibers used as fillers in polymers can be long glass fibers and / or short glass fibers. Short glass fibers in polymers can have an average length of up to 1.0 mm. Long glass fibers in polymers can have an average length of 1.0 to 4.5 mm, for example, 2.0 to 4.0 mm. The diameter of the glass fibers can be 5.0 to 50.0 micrometers, specifically 8.0 to 30.0 micrometers, more specifically 10.0 to 20.0 micrometers. The length and diameter of the glass fibers can be determined based on photographic images using image analysis software. The term "average" refers to the arithmetic mean.

[0093] For example, a polyolefin is polypropylene or a combination of polypropylene and polyethylene, wherein the preferred polyolefin contains at least 45% by weight of polypropylene based on the total weight of the polyolefin.

[0094] For example, a polyolefin component, namely a first polyolefin component and / or a second component, comprises a polyolefin filled with up to 40% by weight of filler based on the total weight of the polyolefin, wherein the polyolefin comprises polypropylene or a combination of polypropylene and polyethylene, wherein preferably the polyolefin comprises at least 45% by weight of polypropylene based on the total weight of the polyolefin.

[0095] "Combination of polypropylene and polyethylene" refers to multiphase propylene copolymers or polypropylene impact copolymers, which are polypropylene blended with elastomer impact modifiers (such as polyethylene particles, C2-C8 (ethylene-octene copolymer) elastomer impact modifiers, or C2-C4 (ethylene-butene copolymer) impact modifiers).

[0096] For example, the adhesive structure may include a first polyolefin component and a second component, each independently comprising a polymer selected from polypropylene, combinations of polypropylene and polyethylene, and combinations thereof. The polymer may be filled with mineral fillers (e.g., talc) or glass fibers, wherein the polymer contains up to 45% by weight of filler, such as up to 40% by weight of filler, based on the total weight of the polymer.

[0097] The first polyolefin component and the second component may contain the same polymer, for example, be composed of the same polymer.

[0098] A burner can be used to generate a flame, the burner comprising at least one nozzle for providing a mixture of air to be burned and a propane-containing gas, wherein a person skilled in the art can readily determine the gap between the at least one nozzle and the bonding surface. For example, the gap between the first or second bonding surface is, for example, 5 cm to 15 cm, such as 8 cm. This gap affects the degree of activation achieved by flame treatment. A distance that is too large between the flame cone and the bonding surface results in reduced surface activation. A distance that is too small between the flame cone and the bonding surface can damage the surface.

[0099] For example, a gap of less than 5 cm between the burner nozzle and the surface can result in a surface energy of, for example, 34 to 60 mN / m, 38 to 58 mN / m, or 40 to 50 mN / m for the activated polyolefin surface, as determined according to ISO 8296:2003. Conversely, a gap within the disclosed range between the burner nozzle and the surface can result in a surface energy of more than 30 and less than 34 mN / m for the activated polyolefin (e.g., polypropylene) surface to be bonded to the second component using an acrylic structural adhesive, as determined according to ISO 8296:2003, the benefits of which are disclosed herein.

[0100] During treatment with a flame containing propane gas, the temperature reached on the flame-treated first polyolefin bonding surface and / or the flame-treated second bonding surface can be from 30°C to 90°C, preferably from 50°C to 80°C, more preferably from 60°C to 65°C; for example, 60°C. At temperatures below 30°C and above 90°C (or when the surface is overtreated), the desired increase in surface energy, the increase in the polar portion of the surface energy, and the increase in the wettability of the bonding surface are not achieved. Preferably, the surface energy of the flame-treated first polyolefin bonding surface and / or the flame-treated second polyolefin bonding surface is greater than 30 mN / m, as determined according to ISO 8296:2003, and the polar portion of the surface energy is greater than 1.5 mN / m, preferably greater than 2 mN / m.

[0101] Activation of polymer surfaces can be characterized by quantifying changes in surface energy and wettability. Surface energy quantifies the breaking of intermolecular bonds that occurs when a surface is formed. Surface energy is the energy required to increase the surface size of a phase. It can be considered to have both polar and dispersed (or dispersive) components. Wettability is the ability of a liquid (e.g., water) to maintain contact with a solid surface. Wettability is typically determined by measuring the contact angle between water and a surface.

[0102] Then, activation of the polymer surface can lead to an increase in its surface energy, an increase in the polar portion of the surface energy, and / or a decrease in the surface contact angle with water.

[0103] The current understanding in the industry is that surface energy of 38 to 42 mN / m promotes good adhesion conditions for plastics, and surface energy of up to 72 mN / m is possible for many plastics.

[0104] The inventors were surprised to discover that acrylic structural adhesives provided the desired adhesion to a second component by using surface energies of activated polyolefins (e.g., polypropylene) with a surface energy of less than 34 mN / m, preferably less than or equal to 33 mN / m, as determined according to ISO 8296:2003. The surface energy value determined according to ISO 8296:2003 can be measured using a test ink series of C-ethanol (dyne test, available from Rycobel).

[0105] The surface energy of the activated polyolefin (e.g., polypropylene) surface may be, for example, greater than 30 to less than 34 mN / m, preferably 31 to 33 mN / m or 31 to 32 mN / m, as determined according to ISO 8296:2003. More preferably, the surface energy of the activated polyolefin (e.g., polypropylene) surface is greater than 31 mN / m, as determined according to ISO 8296:2003.

[0106] For example, a surface energy of less than 34 mN / m, as determined according to ISO 8296:2003, allows for the desired adhesion of polypropylene (a material with inherently low surface energy) to a second component using acrylic structural adhesives. For instance, a surface energy of 31 to 32 mN / m, as determined according to ISO 8296:2003, results in good initial adhesion and adhesion after extended conditioning, an indicator of long-term adhesion, as disclosed herein. While surface energies of 35 mN / m and higher, as determined according to ISO 8296:2003, provide good initial adhesion, surface energies of 35 mN / m and higher, as determined according to ISO 8296:2003, can exhibit adhesion failure after extended conditioning, an indicator of long-term adhesion.

[0107] The flame treatment speed can be, for example, from 200 mm / s to 1,200 mm / s, preferably from 250 mm / s to 1,000 mm / s, more preferably from 250 mm / s to 700 mm / s, such as 300 mm / s. Furthermore, the total flow rate of the gas-air mixture can be from 200 L / min to 750 L / min, preferably 450 L / min.

[0108] Following surface activation, polyolefins can achieve surface chemistry that facilitates further secondary processing without adversely affecting long-term adhesion or the original properties of the substrate. Developing specific surface chemistry on polyolefins can contribute to strong initial and long-term adhesion of the adhesive system, thereby achieving the expected long lifespan and safety of automotive components under real-world environmental conditions.

[0109] Acrylic structural adhesives can be one-component adhesives. These one-component adhesives can be moisture-curing adhesives, containing isocyanate-terminated prepolymers that cure by reacting with moisture in the air.

[0110] Acrylic structural adhesives can be two-component adhesives. The first component may contain an adhesive resin component comprising methacrylate monomers, amines, toughening agents, and rubber, and the second component may contain a peroxide-based activator paste. When the first and second components are combined, a chemical reaction occurs to form the acrylic structural adhesive.

[0111] Different types of acrylic structural adhesives include methyl methacrylate (MMA) acrylic, low-odor acrylic, and low-surface-energy (LSE) acrylic.

[0112] An acrylic structural adhesive can be applied to a first flame-treated bonding surface and / or a second bonding surface.

[0113] In the embodiments, the second component may comprise a polyolefin and, after being bonded at 23±2°C and 50±6% relative humidity for 168 hours, have an lap shear strength greater than or equal to 1.5 MPa or 1.75 MPa according to DIN EN 1465:2009; after being bonded at 23±2°C and 50±6% relative humidity for 168 hours and subjected to heating and cooling cycles at various relative humidities, have an lap shear strength greater than or equal to 2.0 MPa or 2.25 MPa according to DIN EN 1465:2009; or a combination thereof.

[0114] The second component may comprise metal, may not be subjected to laser radiation, and, after bonding and conditioning at 23±2°C and 50±6% relative humidity for 168 hours, shall have an lap shear strength greater than or equal to 2.0 MPa, 2.25 MPa, or 2.5 MPa according to DIN EN 1465:2009; after bonding and conditioning at 23±2°C and 50±6% relative humidity for 168 hours and subjecting to heating and cooling cycles at various relative humidities, shall have an lap shear strength greater than or equal to 6.0 MPa, 6.25 MPa, or 6.5 MPa according to DIN EN 1465:2009; after bonding and conditioning at 23±2°C and 50±6% relative humidity for 168 hours and complete immersion in ethylene glycol / water at 65°C for 45 days, shall have an lap shear strength greater than or equal to 6.0 MPa, 6.25 MPa, or 6.5 MPa according to DIN EN 1465:2009; or a combination thereof.

[0115] In this embodiment, the second component may be a metal component, which may be an automotive component, such as a component of a vehicle's (e.g., an electric vehicle's) battery. In this embodiment, the metal component is aluminum.

[0116] The inventors have surprisingly discovered that by using acrylic structural adhesives, polyolefins and metals can be bonded without roughening the metal surface (e.g., by laser irradiation). The metal surface can be cleaned with isopropanol prior to bonding.

[0117] An adhesive structure can be obtained using the method according to the invention. Such an adhesive structure can be used, for example, as automotive parts, such as tailgates, roof spoilers, or bumpers. When the second part is metal, the adhesive structure can be used, for example, in batteries, such as batteries for electric vehicles.

[0118] In the implementation scheme, the electric vehicle includes an adhesive structure that includes a second component that is metal.

[0119] It should be noted that the present invention relates to all possible combinations of features described herein, with particular preference given to those combinations of features present in the claims.

[0120] It should also be noted that the term "comprising" does not exclude the presence of other elements. However, it should also be understood that a description of a product / composition comprising certain components also discloses a product / composition composed of those components. A product / composition composed of these components can be advantageous because it provides a simpler and more economical method for preparing the product / composition. Similarly, it should be understood that a description of a method comprising certain steps also discloses a method composed of those steps. A method composed of these steps can be advantageous because it provides a simpler and more economical method. When lower and upper limits are mentioned, it is also understood that the range formed by combinations of lower and upper limits is also disclosed.

[0121] As used herein, the terms “vehicle” or “automobile” or “transportation” or other similar terms include conventional motor vehicles such as passenger cars (including SUVs), buses, trucks, various commercial vehicles, watercraft (including various boats and ships), aircraft, etc., and include hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles, and other alternative fuel vehicles (e.g., fuels derived from resources other than petroleum). As referred to herein, a hybrid vehicle is a vehicle having two or more power sources, such as both gasoline-powered and electric-powered vehicles.

[0122] The present invention will now be illustrated by the following embodiments, but the present invention is not limited thereto.

[0123] Example

[0124] The following examples are intended to explain the invention, but not to limit it.

[0125] As described above, the present invention relates to a method for preparing an adhesive structure. This adhesive structure is formed by bonding a first polyolefin component and a second component.

[0126] Different polypropylene (PP) samples were tested. A summary is provided in Table 1.

[0127] Table 1

[0128]

[0129] Adhesion overlap tests are conducted to examine the adhesive behavior of the bonded structure. Figure 1 The setup for the lap shear test according to an embodiment is shown. The lap shear test was performed using an lap shear specimen with dimensions of 100 × 25 × 4 mm.

[0130] The bonded structures were subjected to different forms of conditioning. “Initial” conditioning involved 168 hours at 23±2°C and 50±6% relative humidity. Samples undergoing “Extended” conditioning first underwent initial conditioning, followed by heating and cooling cycles at various relative humidities. Samples undergoing “ethylene glycol” or “EG” conditioning first underwent initial conditioning, followed by complete immersion in ethylene glycol / water (50 / 50) at 65°C for 45 days.

[0131] Subsequently, each sample was subjected to an lap shear test in accordance with DIN EN 1465:2009 (determination of tensile lap shear strength of bonded components).

[0132] Failure analysis was performed according to DIN EN ISO 10365. Figure 2 The failure types of adhesive bonding are shown (DIN ENISO 10365). For example... Figure 2 As shown, substrate failure can include normal substrate failure (SF), cohesive substrate failure (CSF), or delamination failure (DF). As used herein, "substrate failure" or "SF" means a breakage of the adhesive material on one of the adhesive components in a region adjacent to the acrylic structural adhesive and generally along the center of an acrylic structural adhesive plane perpendicular to the adhesive surfaces, without internal damage to the acrylic structural adhesive. As used herein, "cohesive substrate failure" or "CSF" means a breakage of the adhesive material. Internal damage exists on one of the adhesive components in a region adjacent to the adhesive and generally along the center of an acrylic structural adhesive plane parallel to both adhesive surfaces, without internal damage to the acrylic structural adhesive.

[0133] Cohesive failure can be categorized into normal cohesive failure (CF) and special cohesive failure (SCF). As used herein, "cohesive failure" or "CF" refers to the breakage of the adhesive material within an acrylic structural adhesive. This involves internal damage to the acrylic structural adhesive, occurring generally along the center of a plane of the acrylic structural adhesive parallel to the two adhesive surfaces. This is also known as normal cohesive failure. As used herein, "special cohesive failure" or "SCF" refers to the breakage of the adhesive material within the bonded component. This involves internal damage to the bonded component, characterized by the fact that the damage does not occur generally along the center of a plane of the acrylic structural adhesive parallel to the two adhesive surfaces; for example, it may occur perpendicular to or not generally along the center of a plane of the acrylic structural adhesive parallel to the two adhesive surfaces.

[0134] As used in this article, "SCF / CF" refers to adhesive failure between acrylic structural adhesives and bonded surfaces, exhibiting a combination of special cohesive failure and normal cohesive failure. More than 50% of the bonded area shows special cohesive failure after debonding.

[0135] Adhesion failure can be further divided into normal adhesion failure (AF) and adhesive cohesive failure with peeling (ACFP). As used herein, "adhesion failure" or "AF" refers to the breakdown of the bond between the adhesive and the bonded surfaces. The adhesive remains on only one surface of the bonded surfaces.

[0136] As used herein, "CF / AF" refers to adhesive failure between acrylic structural adhesives and bonded surfaces, exhibiting a combination of cohesive and adhesive failure. After debonding, areas of the bonded surface show no adhesive residue, while areas on the same bonded surface show adhesive residue. More than 50% of the bonded area exhibits cohesive failure after debonding.

[0137] As used herein, "AF / CF" refers to adhesive failure between acrylic structural adhesives and bonded surfaces, exhibiting a combination of adhesive and cohesive failure. After unbonding, areas of the bonded surface show no adhesive residue, while areas on the same bonded surface show adhesive residue. More than 50% of the bonded area shows adhesive failure after unbonding.

[0138] Table 2 presents the results of using 3M™ Scotch-Weld™ Flexible Acrylic Adhesive DP8610NS (a two-component acrylic structural adhesive) for two polypropylene components (including identical polypropylene components bonded to each other). Figure 3 The figure shows the results of Table 2.

[0139] The first polypropylene (PP) component was flame-treated to provide an activated PP surface, which was then bonded to the second PP component using an acrylic structural adhesive. The flame treatment involved a total gas-air mixture flow rate of 450 liters per minute (L / min), a burner nozzle-to-surface gap of 8 centimeters (cm), a flame treatment velocity of 300 millimeters per second (mm / s), two flame passes, and a gas-to-air volume ratio of 1:21.5 to 1:25. The surface energy of the activated PP surface was less than 34 millinewtons per meter (mN / m).

[0140] Table 2

[0141]

[0142] In Table 2, "AF 100%" means that 100% of the test joints showed adhesion failure. An average lap shear strength of 2.86–4.26 MPa was achieved using the initial conditioning, and an average lap shear strength of 2.68–4.54 MPa was achieved using the extended conditioning.

[0143] Table 3 presents the results of using 3M™ Scotch-Weld™ Nylon Adhesive Structural Adhesive DP8910NS (a two-component acrylic adhesive) for two polypropylene components (including identical polypropylene components bonded to each other). Figure 4 The figure shows the results of Table 3.

[0144] Table 3

[0145]

[0146] An average lap shear strength of 1.78–4.89 MPa was achieved using initial adjustment, and an average lap shear strength of 2.36–5.56 MPa was achieved using extension adjustment.

[0147] Table 4 presents the results of samples bonded using SAF Ultimate 15 (two-component) methacrylate adhesive from BOSTIK. Different polypropylene samples were bonded to aluminum parts. Before applying the adhesive, the aluminum surfaces to be bonded were either rubbed with isopropyl alcohol (IPA) or roughened by laser irradiation. During the test, the polypropylene was on top and the aluminum part was on the bottom. Figure 5 and Figure 6 The figure shows the results of Table 4.

[0148] The PP samples were flame-treated to provide an activated polypropylene surface, which was then bonded to the aluminum component using an acrylic structural adhesive. The flame treatment involved a total gas-air mixture flow rate of 450 L / min, a burner nozzle-to-surface gap of 8 cm, a flame treatment velocity of 300 mm / s, two flame passes, and a gas-to-air volume ratio of 1:21.5 to 1:25. The surface energy of the activated polypropylene surface was less than 34 mN / m.

[0149] Table 4

[0150]

[0151] Average lap shear strengths of 2.62–4.38 MPa were achieved using initial conditioning and IPA Al treatment, average lap shear strengths of 6.63–10.87 MPa were achieved using extended conditioning and IPA Al treatment, and average lap shear strengths of 6.72–10.49 MPa were achieved using ethylene glycol conditioning and IPA Al treatment.

[0152] Compared to the complex and expensive process of roughening by laser radiation, cleaning with IPA achieves comparable lap shear strength for lap shear strip joints. In some cases, cleaning with isopropyl alcohol achieves even better results compared to the complex and expensive process of roughening by laser radiation. Achieving such results without laser radiation involves using acrylic structural adhesives to bond activated polyolefin surfaces without a primer.

[0153] All embodiments clearly demonstrate that the method for preparing adhesive structures according to the invention includes at least one flame-treated adhesive surface that is an activated surface with increased surface energy, increased polarity, and reduced water contact angle. The combination of all these properties produces an adhesive surface with improved adhesion to acrylic structural adhesives, resulting in an adhesive structure with higher adhesive shear strength.

[0154] One or more objects of the invention are achieved through the embodiments cited above and in the appended claims.

Claims

1. A method for preparing an adhesive structure, comprising: The surface of the first component containing polyolefin is flame-treated to provide an activated polyolefin surface; An acrylic structural adhesive is applied directly to the surface of the activated polyolefin and the surface of the second component; and The adhesive is cured to form a bond between the first component and the second component.

2. The method of claim 1, wherein the acrylic structural adhesive comprises methacrylate.

3. The method according to claim 1 or 2, wherein the polyolefin comprises polypropylene.

4. The method according to claim 1 or 2, wherein the polyolefin comprises polyethylene.

5. The method according to any one of the preceding claims, wherein the first component further comprises glass fiber, flame retardant additives, or a combination thereof.

6. The method according to any one of the preceding claims, wherein the second component comprises a polyolefin and wherein the adhesive has the following lap shear strength according to DIN EN 1465:2009: After conditioning at 23±2℃ and 50±6% relative humidity for 168 hours, the energy content is greater than or equal to 1.5 MPa or 1.75 MPa. After conditioning at 23±2℃ and 50±6% relative humidity for 168 hours and undergoing heating and cooling cycles at various relative humidities, the result is greater than or equal to 2.0 MPa or 2.25 MPa, or Their combination.

7. The method according to any one of the preceding claims, wherein the second component comprises polypropylene.

8. The method according to any one of the preceding claims, wherein the second component comprises polyethylene.

9. The method according to any one of the preceding claims, wherein the second component comprises metal.

10. The method of claim 9, wherein the second component is not subjected to laser radiation and wherein the adhesive has the following lap shear strength according to DIN EN 1465:2009: After conditioning at 23±2℃ and 50±6% relative humidity for 168 hours, the energy content is greater than or equal to 2.0 MPa, 2.25 MPa, or 2.5 MPa. After conditioning at 23±2℃ and 50±6% relative humidity for 168 hours and undergoing heating and cooling cycles at various relative humidities, the energy output is greater than or equal to 6.0 MPa, 6.25 MPa, or 6.5 MPa. After conditioning at 23±2℃ and 50±6% relative humidity for 168 hours and complete immersion in ethylene glycol / water at 65℃ for 45 days, the result is greater than or equal to 6.0 MPa, 6.25 MPa, or 6.5 MPa. Their combination.

11. The method according to any one of the preceding claims, wherein the propane-containing gas comprises at least 80% by weight of propane based on the weight of the propane-containing gas, wherein, During treatment with the propane-containing gas flame, the flame is generated by burning a mixture of air and the propane-containing gas.

12. The method according to any one of the preceding claims, wherein, During flame treatment with the propane-containing gas flame, the volume ratio of propane to oxygen is equal to or less than 1:5.

01.

13. The method according to any one of the preceding claims, wherein the activated polyolefin surface has a surface energy of less than 34 millinewtons / meter, as determined according to ISO 8296:2003.

14. The method according to any one of the preceding claims, wherein the acrylic structural adhesive comprises two components.

15. An adhesive structure prepared by the method of claim 1, for example configured for use in a battery, for example configured for use in a battery of an electric vehicle.

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