Primer composition for thermally removable multilayer structures bonded with thermosetting adhesives - Patent Application 20070122999

Abstract

The thermoplastic primer composition can include a high surface energy thermoplastic resin having a weight percent (wt%) of 55% to 90% with a surface energy of 37 dynes / cm or greater and a low surface energy thermoplastic resin having a surface energy of less than 37 dynes / cm at 10% to 45% by weight, the thermoplastic primer composition having a glass transition temperature in the range of 60° C. to 120° C. The multi-layer composition can include a substrate having a surface energy of 37 dynes / cm or greater, a primer layer containing the thermoplastic primer composition, and one or more thermosetting adhesive layers.

Description

[Technical Field]

[0001] Embodiments relate to methods and systems including thermoplastic polymer blends for use in removable battery assemblies and other applications.

[0002] (Introduction) Thermoplastic and thermosetting adhesives are utilized in many industrial applications, including flexible packaging and electric vehicle (EV) battery attachment. In most applications, thermosetting adhesives are selected based on bond strength, substrate compatibility, and long-term durability under operating conditions. However, in many applications, bonded components must be separated for part maintenance or replacement. Physical removal methods, such as prying, cutting, or laser ablation, are typically used to remove EV batteries bonded to a thermosetting adhesive layer. Other approaches involve the use of solvents or acids to remove the thermosetting adhesive, which can create chemical hazards and provide limited penetration into the adhesive layer. Another concern with common removal methods is their effectiveness in high-surface area attachments, including those present in EV battery packs, which can lead to damage to the bonded components. Summary of the Invention

[0003] The thermoplastic primer composition can include a high surface energy thermoplastic resin having a weight percent (wt%) of 55% to 90% with a surface energy of 37 dynes / cm or greater and a low surface energy thermoplastic resin having a surface energy of less than 37 dynes / cm at 10% to 45% by weight, the thermoplastic primer composition having a glass transition temperature in the range of 60°C to 120°C. DETAILED DESCRIPTION OF THE INVENTION

[0004] Embodiments relate to thermoplastic primer compositions containing a blend of two or more resins with different surface energies. In particular, the thermoplastic primer composition may include a high-surface energy thermoplastic resin having a surface energy of 37 dynes / cm or greater and a low-surface energy thermoplastic resin having a surface energy of less than 37 dynes / cm. In some cases, the thermoplastic primer composition may be incorporated into a multilayer structure as a thermoplastic primer layer that enables temperature-dependent removal of a thermosetting adhesive layer from one or more high-surface energy (>37 dynes / cm) substrates.

[0005] Surface energy measurements provide a quantitative estimate of the polarity of a polymer and its suitability for adhesion to high energy substrates. Surface energy can be calculated based on the surface free energy (SFE) of a solid using contact angle measurements. Surface free energy is closely related to the cohesive energy (E) and the atomic dispersion (E d ), molecular dipole interaction (E p ), and hydrogen bonding interactions (E h ) can be divided into three parts corresponding to the SFE. The SFE is based on three factors: 1) variance (δ d ), 2) polarity (δ p ), and 3) hydrogen bonding strength (δ h The surface energy can be calculated using the Owens-Wendt method from the contact angle of water (18 ohm deionized water) measured with a contact angle goniometer by the Cecil drop method.

[0006] Generally, polymers with high surface energies of 34 dynes / cm or greater adhere better to a wide variety of solid and foamed polar polymer products, such as polyurethanes, than polymers with low surface energies (often 32 dynes / cm or less), such as polyolefins. The thermoplastic primer compositions disclosed herein may allow for tunable adhesive strength to high surface energy substrates by blending two or more thermoplastic polymers such that the primer composition exhibits good adhesive properties at temperatures below 60°C and is releasable at elevated temperatures.

[0007] Electric vehicle battery designs often include one or more battery packs containing multiple battery cells individually bonded to various types of substrates. EV batteries may also include numerous external features to protect the battery pack and battery cell array, which may include multiple housings and substrates. The large surface contact area of ​​the battery components (e.g., approximately 0.5 m² of a pack block) can be a significant challenge. 2 From the entire pack 1.5m 2 Thermosetting adhesives are often used to provide bond strength between the battery and the underlying or overlying substrates and structures over a wide operating temperature range (e.g., -20°C to 60°C). However, the bond strength of thermosetting adhesives makes it difficult to remove the battery pack or pack substrate without damaging the bonded components.

[0008] The methods and systems disclosed herein are directed to thermoplastic primer compositions that can be used as part of a multi-layer adhesive composition for removably securing battery components (e.g., battery packs, battery cells) to various types of substrates. The multi-layer composition can include one or more thermoplastic primer layers and one or more thermosetting adhesive layers interspersed between two substrates, such as one or more battery cells and a pack substrate (e.g., a battery pack cover, a battery pack bottom, or a thermal management plate). The thermoplastic primer layers disclosed herein can melt or soften at elevated temperatures (e.g., 60°C to 120°C), which reduces the bond strength of the multi-layer composition and enables automatic or mechanically assisted release of the thermoplastic primer composition from the attached surface (e.g., a high surface energy substrate, a thermosetting adhesive layer, etc.).

[0009] The thermoplastic primer compositions disclosed herein can be prepared as a thermosetting adhesive layer and a primer layer that is removably bonded to one or more of the one or more substrates. The thermoplastic primer layer remains solid and maintains adhesive performance throughout the operating temperatures of most applications (e.g., below or up to 50°C), but not below the glass transition temperature (T g ) or melting point temperature (Tm The thermoplastic primer layer disclosed herein may soften and / or melt at temperatures above a glass transition temperature (T ) in the range of 60°C to 130°C, 60°C to 120°C, 60°C to 110°C, or 60°C to 90°C. g ).

[0010] The multilayer composition can include a high surface energy substrate onto which one or more thermoplastic primer compositions are formed, applied, or deposited. Examples of high surface energy substrates include surfaces of battery components (e.g., battery packs or cell frames), substrate packs, thermal management plates, and other surfaces. Battery components disclosed herein can include EV battery packs and substrates, including prismatic or pouch cell-based batteries, cylindrical cell batteries, battery packs, etc.

[0011] As used herein, "high surface energy substrate" refers to a substrate having a surface energy of 37 dynes / cm or greater. High surface energy substrates disclosed herein include metals such as aluminum, steel or alloys, zinc, etc.; non-metals including glass; polar polymers such as epoxy, polyurethane, or polyester; and coated materials such as epoxy-coated aluminum, polyacrylate-coated aluminum, and polyester-liner-covered aluminum. Table 1 includes additional examples of suitable high energy substrates.

[0012] [Table 1]

[0013] The high surface energy substrate can be placed in contact with a multi-layer composition containing one or more thermoplastic primer compositions assembled onto a second substrate or surface. In some cases, the multi-layer composition can include a thermoplastic primer layer in contact with the high surface energy substrate and a thermosetting adhesive in contact with the thermoplastic primer layer. The thermosetting adhesive can also mediate adhesion to a second substrate, such as a heat management plate.

[0014] The multilayer composition may include one or more thermosetting adhesive layers, which may include one or more polyurethanes, epoxies, polyacrylates, polyesters, cross-linked derivatives thereof, and the like. The thermosetting adhesives may include structural adhesives and / or thermally conductive adhesives having a thermal conductivity of 0.2 W / mK or greater, such as in the range of 0.2 W / mK to 3 W / mK. The thermosetting adhesives disclosed herein may be water-based, solvent-based, or solvent-free.

[0015] The thermoplastic primer composition can include thermoplastic resins and polymers with mixed surface energies, including a first high surface energy thermoplastic resin and a second low surface energy thermoplastic resin. High surface energy thermoplastic resins include polar thermoplastic polymers and resins substituted with carboxyl, hydroxyl, and other polar groups that have a surface energy of 37 dynes / cm or greater. High surface energy thermoplastic polymer resins include thermoplastics such as polyurethane, polyacrylic, polyethylene terephthalate (PET), polyester, epoxy, polyether, polycarbonate, and the like.

[0016] Non-limiting examples of high surface energy thermoplastics are listed in Table 2.

[0017] [Table 2]

[0018] The first high surface energy thermoplastic resin may have a glass transition temperature in the range of 50° C. to 120° C. or 60° C. to 110° C. The resin formulation of the high surface energy thermoplastic may have a solids content by weight percent in a suitable solvent of 55% to 95% or 65% to 95% by weight.

[0019] The thermoplastic primer composition can include a second low surface energy thermoplastic resin having a surface energy of less than 37 dynes / cm. The low surface energy thermoplastic resin can include maleic anhydride grafted polymers and prepolymers such as maleic anhydride grafted polyolefin (MAH-g-POE), maleic anhydride grafted ethylene-vinyl acetate (MAH-g-EVA), and maleic anhydride grafted styrene-ethylene-butylene-styrene (MAH-g-SEBS). In some cases, the grafted polyolefin is not a halogenated polyolefin.

[0020] Non-limiting examples of low surface energy thermoplastics are listed in Table 3.

[0021] [Table 3]

[0022] In addition to maleic acid, examples of reactive compounds that can be grafted onto the polymer hydrocarbon backbone include ethylenically unsaturated carboxylic acids such as fumaric acid, itaconic acid, acrylic acid, methacrylic acid, crotonic acid, glycidyl acrylate, glycidyl methacrylate, and the like; acid anhydrides such as maleic anhydride and itaconic anhydride; etc. The degree of incorporation or grafting of the reactive compound can depend on the application and can in some cases be up to 10 wt%, 5 wt%, 2 wt%, or 1 wt%, and in some cases can be 0.01 wt%, 0.1 wt%, or 0.2 wt% or more by weight (wt%).

[0023] The second low surface energy thermoplastic resin may have a glass transition temperature in the range of 50° C. to 120° C. or 60° C. to 110° C. The resin formulation of the low surface energy thermoplastic may have a solids content by weight percent in a suitable solvent of 5% to 45% or 5% to 35% by weight.

[0024] In some cases, the polarity of the thermoplastic primer composition layer can be adjusted to minimize changes in lap shear strength and cross tensile strength due to incompatibility with the thermosetting adhesive layer. For example, the thermoplastic primer composition can be modified to contain more or less high surface energy resin to increase adhesion to polar thermosetting resins such as polyurethanes and epoxies, or to lower the melt temperature of the layer for removal purposes. The thermoplastic primer composition can have a ratio of high surface energy resin to low surface energy resin of 55:45 or greater, 70:30 or greater, or within the range of 55:45 to 90:10, or 70:30 to 90:10.

[0025] Thermoplastic primer compositions also include tackifying resins such as rosin, terpene and modified terpene, aliphatic, cycloaliphatic, and aromatic resins (e.g., C5 aliphatic resins, C9 aromatic resins, and C5 / C9 aliphatic / aromatic resins), hydrogenated hydrocarbon resins, terpene-phenolic resins, novolacs, and hydrocarbons, paraffins (e.g., C n H 2n+2 The liquid crystal material may contain additives, including organic phase change materials (PCMs) such as cellulose, cellulose acetate, and lipids, as well as liquid crystal materials that have phase change properties within a temperature range of 60°C to 120°C.

[0026] The thermoplastic resin primer composition layer can be applied to the adhesive layer and / or substrate layer as a solid, thin film, hot melt, or powder (e.g., 100% solids by weight). The thermoplastic primer layer can be produced by solvating a first and / or second thermoplastic resin, optionally with one or more additional thermoplastic polymers, in a suitable solvent and depositing the resulting solvated resin composition onto a substrate or surface. The solvent is then evaporated as the thermoplastic primer layer is formed. Suitable solvents can vary depending on the solubility of the selected primer resin or resin mixture and can include aqueous or organic solvents. Mixtures of non-polar and polar organic solvents can be used. Non-polar solvents can include cycloalkyl or aromatic species such as toluene, methylcyclohexane, etc. Polar organic solvents can include methyl ethyl ketone, ethyl acetate, butyl acetate, etc.

[0027] The organic solvent-salted resin composition may contain one or more primer resins (e.g., solids) at a weight percent (wt%) within the range of 1 wt% to 35 wt%, 1 wt% to 20 wt%, or 3 wt% to 20 wt%. The organic solvent-salted resin composition may contain a non-polar organic solvent at a weight percent (wt%) within the range of 60 wt% to 99 wt%, 65 wt% to 99 wt%, or 70 wt% to 99 wt%. The organic solvent-salted resin composition may contain a polar organic solvent at a weight percent (wt%) within the range of 1 wt% to 40 wt%, 1 wt% to 45 wt%, or 1 wt% to 30 wt%.

[0028] The hydrated resin composition may comprise one or more primer resins in a weight percent (wt%) range of 15% to 65%, 20% to 60%, or 30% to 55%. The aqueous solvated resin composition may comprise an aqueous fluid in a weight percent (wt%) range of 35% to 85%, 40% to 80%, or 45% to 70%.

[0029] The thermoplastic primer layer disclosed herein can maintain good bond strength between the adhesive layer and the substrate. The multilayer composition disclosed herein can have a lap shear strength at room temperature that is reduced by less than 30% compared to a comparative multilayer composition that does not include a thermoplastic primer composition layer. The multilayer composition disclosed herein can have a cross tensile strength at room temperature that is reduced by less than 30% compared to a comparative multilayer composition that does not include a thermoplastic primer layer.

[0030] A method for preparing the removable multilayer compositions disclosed herein can include providing a substrate surface, one or more thermoplastic primer composition layers, and one or more thermosetting adhesive layers. The thermoplastic primer composition layers and thermosetting adhesive layers can be produced by solid deposition or by coating from a solvent composition using known methods such as roller coating, flow coating, dip coating, spin coating, spray coating, knife coating, and die coating. The multilayer compositions disclosed herein can include a thermoplastic primer layer having a thickness within a range of 5 μm to 150 μm, 10 μm to 100 μm, or 10 μm to 60 μm.

[0031] The system may include a removable electric vehicle battery system including an electric vehicle battery; a multi-layer composition that adheres the battery to a pack substrate, the multi-layer composition including one or more thermoplastic primer layers having a transition temperature in the range of 60°C to 120°C and one or more thermosetting adhesive layers; and a heat source in contact with or functioning as a layer of the multi-layer composition (e.g., the thermoplastic primer layer or the thermosetting adhesive layer is directly bonded to a thermal management plate or other heat source), wherein the pack substrate is one or more of a pack bottom, a pack cover, or a heat source, and the heat source is configured to heat the multi-layer composition to a removal temperature in the range of 60°C to 120°C to enable removal of the electric vehicle battery.

[0032] A method for removing a battery pack adhered to a substrate by a multi-layer composition may include heating the multi-layer composition to a "removal temperature" above 60°C to induce softening or melting of the thermoplastic primer layer, followed by separating one or more layers of the multi-layer composition to remove the battery pack from the substrate. The removal method may include mechanically separating the primer and / or adhesive layer from the substrate layer by suitable techniques such as prying, wedging, and / or impact. In some cases, gravity or other "passive" techniques may be used to separate one or more layers of the multi-layer composition.

[0033] The application of heat to the multi-layer composition may involve the use of an external heat source, such as an electric heating platform, an electric heating pad, an electric heating sheet, an electric heating blanket, or an internal heat source, such as a heat management plate, a heat management pad, or an embedded heating element.

[0034] During heating and removal of the multilayer composition, the method and system can utilize direct heating of the multilayer composition to minimize the measured temperature of the battery pack. If the battery cells are directly bonded to a substrate (e.g., a thermal management plate in an EV battery pack), the substrate can function as an internal heat source. If the battery cells are directly bonded to a pack substrate (e.g., the bottom or cover of an EV battery pack), the heat source can also be external, such as a thermal management platform / pad / blanket that contacts the multilayer composition. In either case, the use of an external or internal heat source results in an initial temperature rise at the contact points (e.g., the thermoplastic primer layer and / or the thermosetting adhesive layer), while limited heat transfer results in delayed heating of the separated components (e.g., the battery cells). [Example]

[0035] The following examples are provided to illustrate embodiments of the present invention, but are not intended to limit its scope. All parts and percentages are by weight unless otherwise indicated. Table 4 lists the materials used in the following examples.

[0036] [Table 4]

[0037] Lap shear strength tests were performed in accordance with GB / T 7124. The tested substrates included epoxy-coated Type 3 aluminum (3003), Type 3 aluminum (3003), and Type 5 aluminum (5754) with a thickness of 2.5 mm and a surface area of ​​25 mm x 12.5 mm. The substrate surfaces were cleaned with ethanol, brush-coated with a thermoplastic primer composition, and allowed to dry. A thermosetting adhesive was applied by mixing the isocyanate component and the isocyanate-reactive component under vacuum conditions, and 0.5 g to 1.5 g of adhesive was applied to the substrate. A second substrate with the same bonding area was applied along the length of the adhesive layer. Pressure was applied, and the multilayer composition was cured at 23°C for 7 days. Lap shear strength was tested using an Instron testing system. A lap shear strength of ≥ 8 MPa is desired.

[0038] Cross-tensile strength tests were performed in accordance with GB / T 6329. The tested substrates included epoxy-coated Type 3 aluminum (3003) with a 60 mm high, 15 mm diameter cylinder. Prior to treatment, the cylinder head surface was cleaned, a thermoplastic primer composition was applied, and the surface was allowed to dry. A control sample without primer treatment was also prepared. An adhesive composition was then prepared, and 0.5 g to 1.0 g was applied to the substrate. A second substrate was applied, and the flat surfaces of the substrates were bonded together by curing at 23°C for 7 days. Cross-tensile strength was measured using an Instron tensile tester. A cross-tensile strength of ≥ 8 MPa was desired.

[0039] The removal test was carried out using a qualitative method established in the laboratory, with the following process. 1) The substrate surface (100 mm x 150 mm x 2 mm) is cleaned by wiping with ethanol. 2) The substrate is then coated with primer using a brush and allowed to dry. A comparative sample without primer treatment was also prepared. 3) A thermoset adhesive layer was prepared by combining Part A and Part B of the 2K PU adhesive in a speed mixer at 1,000 rpm for 1 minute. 4) Apply approximately 10 g to 15 g of adhesive to the substrate using two copper wires with a diameter of 1 mm to control the layer thickness. 5) A second substrate was then laminated lengthwise. The bonding surfaces of the substrates were then brought into contact and held in place with clips. The bonded substrates were then cured at 23°C for 7 days. 6) Before the removal test, the samples were heated in an oven at 80°C for 10 minutes. 7) The sample was then removed and, while held in place by the bending clamp, the substrate was manually pried apart using a screwdriver. Removal in less than one minute was considered "successful." "Failure" was demonstrated by two modes: cohesive failure (adhesive on both sides after removal) and adhesive failure (adhesive on one side after removal).

[0040] Example 1: Application of a thermoplastic primer composition to Type 3 aluminum In this example, thermoplastic resin samples with different surface energies were prepared and investigated for adhesion performance and removability against a comparative primer composition. Primer composition samples were prepared by solubilizing 5 wt. % resin in toluene with heating and stirring at 80°C for 1 hour. The resulting solution was then cooled and transferred to a sealed container. Toluene was used as the solvent for thermoplastic polyurethane (TPU), polyethylene terephthalate (PET), and maleic acid-grafted ethylene vinyl acetate (MAH-g-EVA), while toluene was used for the acrylate resin, either alone or as a blend with Cellosolve.

[0041] Type 3 Al substrates (either epoxy-coated or uncoated) were first coated with a 5 wt% thermoplastic primer composition solution and bonded with a 2K PU thermosetting adhesive (Voratron™ MA8202S). After a one-week aging period at room temperature, cross-tensile strength and removal properties were measured. For comparison, blank samples without primer treatment were also prepared and applied in the test.

[0042] The results are summarized in Table 5. Suitable adhesive performance is indicated as having a lap shear strength of 8 MPa or greater at room temperature and a cross tensile strength of 8 MPa or greater at room temperature. Of particular note, the thermoplastic primer compositions in IE4 and IE5 containing TPU+MAH-g-EVA and acrylate+MAH-g-EVA (weight ratio of about 8 / 2) provided high shear strength at lower temperatures, allowing for removal at elevated temperatures.

[0043] [Table 5]

[0044] Example 2: Application of a thermoplastic primer composition to epoxy-coated Type 3 Al In this example, the thermoplastic primer composition and samples were prepared as described in Example 1. After a one-week aging period at room temperature, the cross-tensile strength and removal properties were measured. For comparison, a blank sample without primer treatment was also prepared and applied in the test.

[0045] The results are summarized in Table 6. Of particular note, the thermoplastic primer compositions in IE2, IE7, and IE8 (with a weight ratio of about 8 / 2) provided high shear strength at lower temperatures, allowing removal of the 2K PU adhesive at elevated temperatures.

[0046] [Table 6]

[0047] While the foregoing is directed to exemplary embodiments, other and further embodiments may be devised without departing from the basic scope thereof, which scope is determined by the claims that follow.

Claims

1. 1. A thermoplastic primer composition comprising: a high surface energy thermoplastic resin having a surface energy of 37 dynes / cm or greater at a weight percent (wt%) of 55% to 90%; 10% to 45% by weight of a low surface energy thermoplastic resin having a surface energy of less than 37 dynes / cm; The thermoplastic primer composition has a glass transition temperature in the range of 60°C to 120°C.

2. 10. The composition of claim 1, wherein the weight ratio of the high surface energy thermoplastic resin to the low surface energy thermoplastic resin is 55 / 45 or greater.

3. The composition of claim 1 , wherein the high surface energy thermoplastic resin is one or more selected from the group consisting of polyurethanes, polyesters, epoxies, polyacrylates, and polycarbonates.

4. 10. The composition of claim 1, wherein the second thermoplastic polymer is a maleic anhydride grafted chlorinated polyolefin having a degree of maleic anhydride grafting greater than 1%.

5. 10. The composition of claim 1, wherein the second thermoplastic polymer is one or more of the group consisting of maleic anhydride grafted polyolefin (MAH-g-POE), maleic anhydride grafted ethylene-vinyl acetate (MAH-g-EVA), maleic anhydride grafted styrene-ethylene-butylene-styrene (MAH-g-SEBS).

6. A thermoplastic primer prepared by solubilizing the high surface energy thermoplastic resin and the low surface energy thermoplastic resin in an organic solvent and applying the solubilized resins to a substrate.

7. 1. A multi-layer composition comprising: a substrate having a surface energy of 37 dynes / cm or greater; A primer layer comprising the primer composition according to claim 1; and one or more thermosetting adhesive layers.

8. 10. The multilayer composition of claim 1, wherein the cross tensile strength of the multilayer composition has a decrease of less than 30% at 23°C compared to a comparative multilayer composition that does not include the one or more thermoplastic primer layers.

9. The multi-layer composition of claim 5, wherein the primer layer has a thickness in the range of 10 μm to 100 μm.

10. An electric vehicle battery assembly comprising the multilayer composition of claim 1.

Images