Primer for producing releasable adhesive bonds

Abstract

The invention relates to a primer for producing a detachable adhesive bond, which primer is based on a pressure-sensitive adhesive comprising a chemical or physical blowing agent.

Description

Technical Field

[0001] This invention relates to primers for producing separable adhesive bonds and to separable layered structures designed and configured to separate after long-term bonding. The invention also includes methods for separating long-term bonds produced by means of such layered structures. Background Technology

[0002] In electronic equipment recycling and repair plants, the need to repair electronic equipment or motor vehicles or to disassemble and / or recycle them as extensively as possible is becoming increasingly important for both environmental and economic reasons.

[0003] Here, there are different kinds of electronic devices that differ in their recyclability and degree of recyclability:

[0004] Large household appliances (also known as white goods): such as washing machines, refrigerators and freezers, ovens;

[0005] Small household appliances (also included in white goods): such as vacuum cleaners, coffee makers, and microwave ovens;

[0006] • Information technology and communication equipment, such as computers, monitors, printers, mobile phones, and telephones;

[0007] Consumer electronic devices (also known as brown market appliances): such as televisions, video recorders, and digital cameras.

[0008] In particular, electrical and electronic equipment contains a variety of substances and materials. If used electrical and electronic equipment is improperly disposed of, for example through municipal solid waste, it may still contain pollutants that could pose environmental risks in some cases. However, in addition to pollutants such as heavy metals and HCFCs, used electrical and electronic equipment also contains a range of valuable substances that should be recycled and thus reused. Conversely, if used electrical and electronic equipment is properly treated, it can replace primary raw materials (and therefore their expensive and laborious extraction) and make a significant contribution to the conservation of natural resources.

[0009] To achieve these objectives, Germany, in implementing the Directive 2012 / 19 / EU on Waste Electrical and Electronic Equipment (WEEE), establishes specific obligations for all relevant actors (manufacturers, traders, municipalities, owners, waste managers) under the Electrical and Electronic Equipment Law (ElektroG), which governs the sale, return, and environmentally sound disposal of electrical and electronic equipment. By avoiding waste, by conducting reasonable testing of the possibility of reusing entire devices or individual components, and by requiring the broader recovery of value from waste, the aim is to make a significant contribution to the protection of natural resources and the reduction of pollutant emissions.

[0010] A design that facilitates recycling is needed, enabling disassembly (removal on demand). Recyclable designs include separable adhesives, as the trend towards adhesively bonded components is particularly pronounced in small electronic devices, often for extended periods rather than in a way that allows for mechanical detachment.

[0011] EP 1 814 935 A1 describes a method for assembling two substrates by means of adhesive bonding using at least one sealing joint, the sealing joint being composed of a polymer material and a migration agent, the latter being able to migrate to the interface to form a layer with weak cohesion.

[0012] It also describes a method for separating previously formed adhesives by supplying energy to the sealing joint and / or a migration agent. The migration agent migrates to the interface and creates weak cohesive sites, thereby enabling the separation of the substrate.

[0013] The primer is not disclosed. The medium is an adhesive that includes migration agents that migrate to the interface. The pressure-sensitive tape is not disclosed.

[0014] WO 00 / 75254 A1 relates to a composition, its use, and a method of using it as an enamel adhesive. The composition comprises an adhesive incorporating dispersed, heat-expandable microcapsules that act as pressure triggers. The microcapsules are thermally triggered to release at least one expandable volatile active ingredient encapsulated within a microcapsule shell.

[0015] EP 2 265 681 A1 describes a composition for separating adhesive bonds between two substrates. The composition consists of an adhesive base polymer and an active ingredient designed to separate assemblies. The active ingredient is encapsulated in a wax.

[0016] Encapsulation includes microencapsulation, thermal gelation, or other methods described herein.

[0017] WO 2005 / 028583 A1 relates to destructive agents (3-40% by weight) for use in adhesive compositions. The polymer base includes epoxy, acrylic, or urethane species. The destructive agent is thermally activated and is derived from hydrazine groups (particularly pTSH) and, particularly, sulfonyl hydrazides.

[0018] Additionally, an activator (1-5% by weight) from the carbamate family (especially urea) is used. The relationship between viscosity and target layer thickness is also mentioned.

[0019] What is known from EP 1 111 020 A1 are adhesive compositions for separable adhesive bonding, which contain a heat-activated release agent that is solid at room temperature.

[0020] Adding heat-activated substances from dicarboxylic acids, azo compounds, carbonates, substances containing water of crystallization, and polyols to commercially available adhesives enables thermal debonding of the adhesive bond. In this way, the bond can be easily separated again by heat, thereby promoting the recycling of the bonded components.

[0021] EP 1 611 217 A1 describes a method for assembling two substrates by adhesive bonding. This is done by applying an adhesive primer to one substrate for controlled removal. The primer consists of a polymer base and an adhesive degradation agent. Energy is supplied to separate the adhesive, causing the degradation agent to degrade the bond between the primer and the substrate or material.

[0022] The primer can be in diluted form for applying a particularly thin layer. The primer consists of a polymer base or wax and a degradation agent. The degradation agent is pTSH. The only polymer base disclosed for the primer is epoxy resin. Toluene is the solvent.

[0023] FR 2837114 A1 describes a method (consisting of five stages) for separating a coating containing additives by supplying thermal or electromagnetic energy.

[0024] These five stages are:

[0025] • Stage 1 (Formulation) – Additives and Adhesives

[0026] Phase 2 (Adjustment)

[0027] Phase 3 (Formula Implementation) – Generate Adhesion

[0028] Phase 4 (Operation Phase)

[0029] Phase 5 (Controlled Separation Phase)

[0030] EP 2 519 596 A1 discloses a method for disintegrating an assembly consisting of two substrates bonded together by an adhesive layer. The polymeric material used for the adhesive layer is composed of polyurethane or silicone and includes a migrating agent that migrates to one of the interfaces and causes separation of the interface upon exposure to heat. Heating to the activation temperature of the migrating agent must be performed. Separation is caused by the generated gas.

[0031] WO 2021 / 028457 A1 describes a removable composition comprising a polyamide or a mixture of a polyamide soluble in an alcohol and an expandable additive having an expansion temperature higher than the melting point of the polyamide.

[0032] The alcohol is selected from light aliphatic alcohols or benzyl alcohol.

[0033] Polyamides that are insoluble in alcohol are copolyamides.

[0034] The expandable additives can be temperature-activated expandable microspheres, azodicarbonamide, expandable graphite, polycarboxylic acids, and sulfonyl hydrazides. The ratio of polymer to additive is described.

[0035] This specification describes a primer that allows for easy removal of unwanted paint through microsphere foaming. The base material consists of an acrylic resin or polyvinyl acetate. The material expands thermally with temperature. Summary of the Invention

[0036] Therefore, the object of the present invention is to provide a primer for layered structures that, on the one hand, enables long-term and reliable bonding of components with tape, and on the other hand, enables clean and reliable separation of the tape from the components when needed.

[0037] This objective is achieved according to the invention by means of a primer as described herein. Advantageous embodiments of the primer are described in the preferred sections. The invention also includes a layered structure having the primer and a method for separating the layered structure.

[0038] Therefore, the present invention relates to a primer for producing separable adhesive bonds, the primer being based on a pressure-sensitive adhesive comprising a chemical or physical foaming agent. Detailed Implementation

[0039] In the context of this invention, the term "primer" refers to a base coat applied to a substrate that interacts (on a chemical or physical basis) with two material layers, enabling their adhesion. In other words, without the use of a primer, adhesion is substantially not impaired, but not necessarily improved. "Substantially not impaired" means that, with the use of a primer, the peel adhesion between the two material layers is no less than 75% of the peel adhesion between the two material layers without the primer.

[0040] A primer is generally considered a formulated product (which typically contains more than one component) and is applied from the liquid phase by a specific method (immersion, spreading, spraying, etc.). By this definition, a primer should not only have the ability to achieve adhesion, but also the ability to form a uniform primer coating on the substrate surface by adapting its viscosity, wetting properties, drying rate, etc.

[0041] In this invention, the primer is formulated based on a pressure-sensitive adhesive and includes a chemical or physical foaming agent that, upon activation, enables the adhesive to separate.

[0042] In this context, "based on" or "on the basis of" means that the properties of the primer are determined by the pressure-sensitive adhesive. In other words, the base polymer of the primer has a certain degree of touch tack.

[0043] As is generally understood in this invention, "pressure-sensitive adhesive" (PSA) is a substance that is, in particular, permanently tacky and adhesive at room temperature. PSA is characterized by being able to adhere to a substrate by applying pressure and therein without further limiting the pressure applied or the duration of exposure to that pressure. In some cases, depending on the precise properties of the PSA, temperature and atmospheric humidity, and the substrate, the effect of minimal pressure for a short period (not exceeding brief, gentle contact) is sufficient to achieve an adhesive effect, while in other cases, prolonged exposure to high pressure may be necessary.

[0044] PSA possesses specific characteristic viscoelastic properties, resulting in permanent tack and adhesiveness. These adhesives are characterized by the presence of a viscous flow process and the formation of an elastic restoring force when they undergo mechanical deformation. These two processes are related to each other in their respective proportions, depending not only on the precise composition, structure, and degree of cross-linking of the PSA, but also on the rate and duration of deformation, as well as the temperature.

[0045] Proportional (in a certain proportion) viscous flow is necessary for adhesion. The viscous component (part) generated solely by macromolecules with relatively high mobility allows for effective wetting and adaptation to the substrate to be bonded. A high viscous flow component results in high touch tack (also known as tack or surface tack), and therefore often also high peel tack. Highly cross-linked systems, crystalline polymers, or polymers with glassy curing properties lack a flowable component and typically lack tack or have only very low tack.

[0046] Proportional (in a certain proportion) elastic restoring forces are necessary for the realization of cohesion. They are generated, for example, by very long-chain macromolecules with high entanglement and by macromolecules that are physically or chemically cross-linked, and they enable the transmission of forces acting on the adhesive bond. As a result of these restoring forces, the adhesive bond is able to withstand long-term loads acting on it, for example, in the form of sustained shear loads, to a sufficient extent for a relatively long period of time.

[0047] To more accurately describe and quantify the degree of elastic and viscous components, and the relationships between them, the variables of storage modulus (G') and loss modulus (G”) can be used, and determined by dynamic mechanical analysis (DMA). G' is a measure of the elastic component of a substance, and G” is a measure of the viscous component. Both variables depend on the deformation frequency and temperature.

[0048] The variable can be determined using a rheometer. In this case, for example, the material under study is exposed to sinusoidal oscillating shear stress in a plate / plate apparatus. When using an instrument with shear stress-controlled operation, the deformation is measured as a function of time, and the time shift of this deformation relative to the introduction of shear stress is measured. This time shift is called the phase angle δ.

[0049] The storage modulus G' is defined as follows: G' = (τ / γ)·cos(δ) (τ = shear stress, γ = deformation, δ = phase angle = phase shift between the shear stress vector and the deformation vector). The loss modulus G” is defined as follows: G” = (τ / γ)·sin(δ) (τ = shear stress, γ = deformation, δ = phase angle = phase shift between the shear stress vector and the deformation vector).

[0050] If at room temperature (23°C by definition here), at 10 0 -10 1 Within the deformation frequency range of rad / s (radians / second), G' is at least partially located at 10 3 -10 7The composition is generally considered to have tactile tackiness if the G' curve is also at least partially within the range of Pa, and is defined as having tactile tackiness for the purposes of this invention. "Partially" means that at least a portion (partially) of the G' curve lies within the range of 10. 0 (including endpoints) up to 10 1 (Including endpoints) rad / s deformation frequency range (horizontal axis) and 10 3 (including endpoints) to 10 7 The range of G' values ​​(vertical axis) across Pa (including endpoints) is within the window spanned. This applies accordingly to G'.

[0051] Therefore, PSA is permanently tacky at room temperature, thus possessing sufficiently low viscosity and high contact adhesion, allowing it to wet the surface of the corresponding adhesive substrate even with low applied pressure. The adhesiveness of PSA derives from its adhesive properties, while its reseparability (depending on the inherent peel adhesion of PSA) derives from its cohesive properties.

[0052] If the primer of the present invention produces at least 50%, preferably at least 75%, a reduction in peel adhesion at 23°C after activation, then in the context of the present invention, adhesive bonding is, for example and particularly, “separable”.

[0053] As pressure-sensitive adhesives for primers, all PSAs known to those skilled in the art can be used, examples of which include those based on: acrylates and / or methacrylates, polyurethanes, natural rubbers, synthetic rubbers, styrene block copolymers having elastomeric blocks composed of unsaturated or hydrogenated polydiene blocks (polybutadiene, polyisoprene, copolymers of both, and other elastomeric blocks familiar to those skilled in the art), polyurethanes, fluoropolymers, and / or silicones (organosilicones). The term also includes other components having tactile adhesive properties according to Donatas Satas's "Handbook of Pressure Sensitive Adhesive Technology" (Satas & Associates, Warwick 1999).

[0054] The pressure-sensitive adhesive of the primer is preferably based on acrylate.

[0055] When referring to acrylate-based pressure-sensitive adhesives in the context of this specification, the term includes (even without implied representation) methacrylate-based and acrylate- and methacrylate-based pressure-sensitive adhesives, unless otherwise explicitly stated. Also in the sense of this invention are combinations and blends of two or more base polymers, as well as adhesives with added tackifying resins, fillers, aging inhibitors, and crosslinking agents; the list of additives is illustrative only and not limiting.

[0056] Particularly preferred, the pressure-sensitive adhesive comprises an acrylate-based copolymer.

[0057] Very particularly preferred, the pressure-sensitive adhesive is a copolymer of at least one acrylate and vinylcaprolactam.

[0058] More preferably, the pressure-sensitive adhesive is free of acrylic acid.

[0059] The primer can be expanded using chemical or physical foaming agents. Expandability here means that the volume of the primer after expansion is greater than the volume of the primer before expansion, measured at the same temperature (typically room temperature) in their respective cases. The volume increase is preferably greater than 5%, more preferably greater than 20%. Expansion can be carried out chemically or physically. The adhesive preferably comprises a heat-activated foaming agent.

[0060] Based on the presence of 100% by weight of the base polymer, the foaming agent is preferably present in the primer composition at a concentration of 10% by weight to 120% by weight.

[0061] The foaming agent is preferably a particulate foaming agent. The median particle size (d50) before activation is preferably less than 25 μm, particularly preferably less than 17 μm. Very particularly preferably, the median particle size is less than 3 μm, because this allows for a thin primer layer.

[0062] More preferably, the particle size is higher than 500 nm, which allows for a foaming effect that is technically usable for separation.

[0063] In the sense defined in DIN 53206-1:1972-08, "particles" of a foaming agent are understood to refer to primary particles, aggregates, and agglomerates of the foaming agent. "Particle size" refers to the maximum range of particles. Particle size is preferably determined by means of laser scattering according to ISO 13320 (where agglomerates are dispersed in the dispersion step, rather than aggregates), although other methods known to those skilled in the art are also suitable.

[0064] In the dry, unactivated primer layer, the foaming agent, more particularly the particulate foaming agent, is preferably present substantially in multiple (at least two) filler layers. The filler improves the expansion of the bonded assembly and thus its separability.

[0065] More preferably, the foaming agent, more particularly particulate foaming agent, exists essentially as a single layer in the dried, unactivated primer layer. This limitation to a single layer allows the primer layer to be applied thinner, thus providing advantages in application (e.g., shorter flash times, fewer runs) and in primer effectiveness.

[0066] "Basically" here means that the particles are arranged on more than 60% of the area (area) of the primer-coated area.

[0067] The primer preferably includes rheology modifiers that reduce the settling of particulate foaming agents.

[0068] Preferred rheology modifiers are thixotropic agents, such as those derived from... The company sells it under the trade name Disparlon, and BYK sells it under the trade names Tixogel, Rheobyk, and BYK-GO.

[0069] Chemical foaming agents can be broadly classified into organic and inorganic compounds based on their properties. They are further distinguished as exothermic (1-5) and endothermic (6) foaming agents based on their decomposition behavior. Specifically, the compounds discussed are, for example, compounds from the following product categories:

[0070] 1. Azo compounds:

[0071] Preferred azodicarbonamide (ADC)

[0072] 2. Hydrazine derivatives:

[0073] p-Toluenesulfonylhydrazide (TSH) is preferred.

[0074] and p,p'-oxobis(benzenesulfonylhydrazine) (OBSH)

[0075] 3. Sulfonamide:

[0076] p-Toluenesulfonamide (TSSC) is preferred.

[0077] 4. Tetrazol:

[0078] 5-Phenylenetetrazole (5-PT) is preferred.

[0079] 5. N-nitroso compounds:

[0080] N,N'-Dinitrospentamethylenetetramine (DNPT) is preferred.

[0081] 6. Carbonates:

[0082] Sodium bicarbonate (NaHCO3) and zinc carbonate (ZnCO3) are preferred.

[0083] As a physical foaming agent, all physical foaming agents known to those skilled in the art can be used.

[0084] The preferred foaming agent is a physical foaming agent;

[0085] Expandable thermoplastic microspheres (microspheres) are preferred.

[0086] More preferably, thermoplastic microspheres that can expand thermally.

[0087] Expandable thermoplastic microspheres, comprising a thermoplastic polymer shell and a foaming agent encapsulated therein, can be marketed, for example, under the trade name... Commercially available. In these microspheres, the foaming agent is typically a liquid with a boiling point not exceeding the softening temperature of the thermoplastic polymer shell.

[0088] The softening temperature of the polymer shell according to the preferred embodiment is in the range of 0 to 140°C, most preferably 30 to 100°C. Upon heating, the foaming agent evaporates, increasing the internal pressure in the process, while the shell softens, leading to significant expansion of the microspheres. The temperature at which expansion begins is referred to as T. 开始 The temperature at which the maximum expansion is achieved is called T. 最大 T of expandable microspheres 开始 The preferred temperature is 40 to 140°C, and the most preferred temperature is 50 to 100°C. The T-type of expandable microspheres... 最大 Higher than T 开始 The preferred temperature is 80 to 200°C, and the most preferred temperature is 100 to 170°C.

[0089] According to a preferred embodiment, the foaming agent has an expansion temperature of 100 to 150°C.

[0090] According to a particularly preferred embodiment, the foaming agent has an expansion initiation temperature greater than 130°C, because better durability of the dried primer has been determined at a higher softening temperature of the polymer shell.

[0091] According to another particularly preferred embodiment, the foaming agent has an expansion initiation temperature of less than 130°C because the activation temperature is low in this case.

[0092] Expansion temperature can usually be found in the supplier's datasheet. For expandable microspheres, it is determined by thermomechanical analysis (TMA) at a heating rate of 20 K / min and 50% relative humidity. For chemical blowing agents, DSC is started at a heating rate of 20 K / min.

[0093] According to a particularly preferred embodiment, the primer comprises microspheres having an average diameter of 3 μm-30 μm, more particularly 5 μm-20 μm, in an unexpanded state at 25°C, and / or having an average diameter of 10 μm-200 μm, more particularly 15 μm-90 μm, after expansion. The average diameter of the unexpanded microspheres is preferably less than the thickness of the primer layer.

[0094] Preferably, the foaming agent is a mixture of physical and chemical foaming agents.

[0095] Another part of the invention is a layered structure, comprising:

[0096] ·First component,

[0097] • A primer layer on the component, the primer being based on a pressure-sensitive adhesive including a chemical or physical foaming agent, and applied from the liquid phase in a layer thickness not exceeding 30 μm (after drying).

[0098] • Adhesive tape, more specifically pressure-sensitive adhesive tape, which is attached to the first component via a primer layer.

[0099] The primer layer can have a thickness within the usual range, that is, a thickness of about 0.1 μm to 100 μm.

[0100] The primer preferably has a thickness of less than 25 μm, more preferably less than 15 μm.

[0101] Very preferably, the primer has a thickness of no more than 1 μm in the dry state, and more particularly, a thickness of more than 5 μm.

[0102] Very preferably, the primer layer thickness is 1 to 10 μm to maintain a low layer thickness, and additionally 10 to 25 μm to obtain the maximum expansion volume.

[0103] The primer is preferably applied to a continuous area on the component (over the entire area).

[0104] The primer is preferably applied using a sponge or pencil. More preferably, the primer is applied using a guided metering nozzle, an example being the "EV Series Automatic Dispensing System" from Nordson EFD.

[0105] The tape can have a layer thickness within the usual range, that is, a layer thickness of about 2 μm to 2000 μm.

[0106] The tape preferably has a layer thickness of less than 300 μm, more preferably less than 100 μm.

[0107] The tape preferably has a layer thickness of more than 30 μm, more preferably more than 100 μm.

[0108] The ratio of primer thickness to tape thickness is preferably no greater than 1:10, and more particularly no greater than 1:20.

[0109] In the context of this invention, the term "tape" generally refers to all sheet-like structures whose extent in two spatial directions (x-direction and y-direction; length and width) is significantly greater than that in a third spatial direction (z-direction; thickness), such as films or film portions (segments), strips with extended length and finite width, strip portions (segments), die-cut pieces, labels, etc.

[0110] The tape can be supplied in fixed lengths, such as products by the meter, or as a continuous product on a roll (Archimedes spiral), i.e., a disc roll of tape, referred to in the art as a "pancake".

[0111] Alternatively, the tape can be wound around the core like woven yarn, with its length significantly greater than its width. Through the superposition of the core's rotational movement and the axial movement of the core or tape guiding mechanism, the tape initially forms a first radially innermost spiral turn. To complete the first layer and move to the second layer, the direction of the axial movement is reversed, while the rotational movement remains unchanged. To complete the second layer and move to the third layer, the direction of the axial movement is reversed again, returning to its original direction, while the rotational movement remains constant. The pitch angle remains constant between each point of directional reversal. In this way, many layers of turns can be formed, their turns intersecting each other (cross-wound loops).

[0112] "Tape" includes a carrier material having a (pressure-sensitive) adhesive on one or both sides and optionally having an additional layer therebetween.

[0113] More specifically, in the context of this invention, the term "tape" includes so-called "transfer tapes," which are carrier-free tapes. In the case of transfer tapes, the adhesive is instead applied between flexible pads provided with a release layer and / or having anti-adhesive properties before application. For application, generally, the pads are first removed, the adhesive is applied, and then the second pad is removed. Thus, the two surfaces can be directly bonded using the adhesive. These types of carrier-free transfer tapes are particularly preferred in this invention. Such tacky carrier-free transfer tapes enable very precise adhesion in terms of positioning and dosage.

[0114] Adhesive tape can be manufactured in roll form, in other words, in the form of an Archimedean spiral wound on itself, or with a release material, such as silicone paper or silicone film, lining the adhesive side.

[0115] Suitable release materials are preferably non-linting materials such as polymeric films or appropriately sized (well-glued) long-fiber paper.

[0116] According to another preferred embodiment, the tape is implemented as a tape having an activatable adhesive.

[0117] The activatable adhesives used can, in principle, include all conventional adhesive systems that exhibit activated adhesion. Activation is typically accomplished by inputting energy, such as through photochemical radiation, heat, or mechanical energy, such as ultrasound or friction.

[0118] Heat-activated adhesives can be fundamentally divided into two categories: thermoplastic heat-activated adhesives (hot melt adhesives) and reactive heat-activated adhesives (reactive adhesives). This classification also includes adhesives that fall into both categories, namely reactive thermoplastic heat-activated adhesives (reactive hot melt adhesives). Even at room temperature, heat-activated adhesives can be pressure-sensitive. Heat activation increases bond strength.

[0119] Thermoplastic adhesives are based on polymers that undergo reversible softening upon heating and re-curing upon cooling. Advantageous thermoplastic adhesives have particularly been those based on polyolefins and polyolefin copolymers and their acid-modified derivatives, ionomers, thermoplastic polyurethanes, polyamides, polyesters and their copolymers, and those based on block copolymers such as styrene block copolymers.

[0120] Conversely, reactive heat-activated adhesives include reactive components. These latter components, also known as "reactive resins," initiate a cross-linking process through heating, ensuring a durable and stable bond after the cross-linking reaction is complete. Such adhesives preferably also include elastic components, such as synthetic nitrile rubber or styrene block copolymers. These elastic components, due to their high flow viscosity, give heat-activated adhesives particularly high dimensional stability, even under pressure.

[0121] Radiation-activated adhesives are also based on reactive components. These components may include, for example, polymers or reactive resins, in which irradiation initiates a cross-linking process, ensuring a durable and stable bond after the cross-linking reaction is complete. Such adhesives preferably also include elastic components of the types described above.

[0122] Radiation-activated PSAs should differ from radiation-crosslinked PSAs in which the pressure-sensitive adhesive properties are established through radiation crosslinking during tape manufacturing. For radiation-activated PSAs, radiation activation occurs during application. After radiation activation, the adhesive is generally no longer tacky.

[0123] As disclosed in DE 10 2013 222739 A1, activatable pressure-sensitive tapes also include pressure-sensitive tapes assembled from two or more adhesive films. They are activated by contacting two or more adhesive films.

[0124] According to a preferred embodiment of the invention, a second component is adhered to the free side of the tape.

[0125] More preferably, an additional primer layer of the present invention may be applied between the tape and the second component.

[0126] Another part of the invention is a method for separating a layered structure, the layered structure comprising, and preferably consisting of, the following:

[0127] ·First component,

[0128] A primer layer is applied to the component, the primer being based on a pressure-sensitive adhesive including a chemical or physical foaming agent, and applied from the liquid phase in a layer thickness not exceeding 30 μm (after drying).

[0129] • The first tape, more specifically the pressure-sensitive tape, is attached to the first component via a primer layer.

[0130] The layered structure is heated until the foaming agent present in the primer expands, reducing the peel adhesion of the primer layer to a level that allows the tape to be removed from the component.

[0131] "Removable" here means that the peel adhesion of the assembly after heating the layered structure is less than 40%, preferably less than 20%, and more preferably less than 10% of the peel adhesion before heating.

[0132] Layered structures can be heated by any form of heat supply, such as by convection (e.g., in an oven, using a hot air blower), by radiant heat (e.g., by infrared lamps or laser radiation), by thermal conduction (e.g., on a heating plate), or by generating heat within the layered structure (e.g., by induction, electric current, chemical reaction, or microwaves).

[0133] Thermal activation of foaming agents can be accomplished through a variety of techniques, particularly through non-contact heating (e.g., induction or microwave), electrical heating (Joule effect), or thermal heating (oven, heating plate, infrared lamp, tunnel, hot air, thermal decomposition).

[0134] The fillers used for induction heating or microwave heating may specifically be the following: PEG, ferrite, carbonyl iron (high-purity iron powder).

[0135] For heating by electrical conduction, the following fillers may be used in particular: silver-coated copper particles, silver-coated silica particles, graphite, carbon black, carbon nanotubes, and silver particles. These fillers can be used to impart sufficient conductivity to the compositions of the present invention, thereby enabling heating via the Joule effect under the influence of an electric current. These charges can also be used to allow the conductivity of the compositions of the present invention to be maintained within the assembly, which may be necessary for certain applications, particularly for the dissipation of static charges.

[0136] To improve the thermal conductivity of the composition, the following fillers may be used in particular: graphite, metallic fillers, boron nitride, alumina, and aluminum hydroxide. This thermal conductivity may be necessary in certain assemblies, such as in the case of adhesive bonding of heating elements.

[0137] After thermal activation, separation is preferably carried out at room temperature, which is advantageous because it allows for easier handling of the material (especially the carrier) and eliminates the need for special equipment for handling hot surfaces. Separation can be performed manually or automatically.

[0138] Exposure to heat causes the liquid contained within the microspheres to evaporate, while simultaneously softening the outer polymer shell. The capsule thus undergoes irreversible stretching and expansion in three dimensions. The expansion ends when the internal and external pressures are matched.

[0139] The tape and components are forcibly separated through the expansion of microspheres or, typically, through the expansion of a foaming agent. Simultaneously, the primer reduces the peel adhesion of the tape and / or components.

[0140] There are many possible applications for the layered structure of the present invention. One example is the removal of touch panels. This is a particularly important area of ​​use given the high importance of mobile phones. On the other hand, very strong adhesive bonding and particularly sealing adhesive bonding are required for mobile phone displays. Furthermore, it is often necessary to remove the display. The layered structure of the present invention is particularly suitable for this intended use.

[0141] Finally, a topic of increasing importance is "reprocessability." In the automotive industry, for example, there is a growing demand for the disposal of products at the end of their life cycle using materials that are separated from the material. Therefore, it is important that components composed of different materials be separated back into individual components before disposal, even if these components were previously "inseparable" connected to each other. This invention enables very strong and durable adhesion between different components, while still allowing these components to be separated as needed.

[0142] Measurement methods

[0143] Measurements were taken under test conditions of 23±1℃ and 50±5% relative humidity, unless otherwise explicitly stated.

[0144] Peel adhesion

[0145] Peel adhesion was determined similarly to ISO 29862 (Method 3) at 23°C and 50% relative humidity at a removal speed of 300 mm / min and a removal angle of 180°. The thickness of the primer layer was 15 or 25 μm. An etched PET film with a thickness of 36 μm was used as the reinforcing film, and it was of a type available from Coveme (Italy).

[0146] The substrate used includes standard steel plates (50mm × 125mm × 1.1mm). A measuring strip (13mm) is bonded using a roller press at 23°C and 4kg. The time between the final roll and removal of the tape is 60 minutes.

[0147] The measurements (in N / cm) were obtained as the average of three separate measurements. In addition to peel adhesion, the failure modes of the adhesive bond were also determined.

[0148] K value

[0149] The K-value is a measure of the average size of polymer molecules. To perform the measurement, solutions of toluene polymers with a strength of 1% (1 g / 100 ml) were prepared, and their kinetic viscosities were determined using a Vogel-Ossag viscometer. After normalization to the viscosity of toluene, the relative viscosity was obtained, and the K-value could then be calculated using Fickentscher's method (Polymer 8 / 1967, 381 ff.).

[0150] The present invention will be illustrated in more detail below by way of examples, but it is not intended to limit the invention thereto.

[0151] Example

[0152] Base polymers used in primers:

[0153] • Pressure-sensitive adhesive (PSA1) for use as a primer

[0154] The PSA copolymer contained in the primer according to the present invention is manufactured using the following raw materials:

[0155] • 70% by weight n-butyl acrylate (CAS: 141-32-2), and

[0156] • 30% by weight vinylcaprolactam (CAS: 2235-00-9)

[0157] The copolymer was prepared by free radical polymerization in a solvent mixture of ethyl acetate / isopropanol (168 / 1) in a manner known to those skilled in the art. The copolymer had a K value of about 84 and was adjusted to a solid content (SC) of 30 wt%.

[0158] In the peel adhesion test, when coated on an etched PET film (36 μm) with a thickness of 25 μm, the copolymer exhibited a peel adhesion of 2.5 N / cm. Therefore, it is a pressure-sensitive adhesive.

[0159] Primer polymer 2 used for comparison

[0160] To prepare a comparative primer base, thermoplastic copolyamide Platamid M 1276 (from Arkema) was dissolved in the following solvent mixture:

[0161] 60% wt% ethanol,

[0162] 18% by weight isopropanol,

[0163] 18% by weight of methylcyclohexane, and

[0164] 4% by weight water

[0165] And adjust to a solid content of 15% by weight (SC).

[0166] Primer formulation

[0167] In order to manufacture the primer of the present invention, the basic polymer described above regarding its preparation and composition is used, as well as the following raw materials, solvents and foaming agents:

[0168] Tetraisopropoxide titanium ( TPT, Lehmann & Voβ, CAS 546-68-9)

[0169] Isopropanol (CAS 67-63-0)

[0170] Microspheres from Matsumoto, FN 100SSD type

[0171] (Size: 6-11μm, T) 开始 120-130℃, T 最大 (145-155℃)

[0172] Microspheres from Matsumoto, FN 100SD type

[0173] (Size: 10-20μm, T) 开始 125-135℃, T 最大 (150-160℃)

[0174] In order to manufacture the primer according to the invention, in addition to the solvent contained in the primer PSA, the primer PSA1 is further diluted with isopropanol to a solid content (SC) of 10% by weight.

[0175] In all embodiments, the solid content is selected, in its respective case, to enable sufficient layer formation to allow for corresponding comparative experiments.

[0176] The raw materials / components specified in the examples are used from Mix with a magnetic stirrer and magnetic stirring bath for about 20 minutes.

[0177] Example 1

[0178] Primer composition:

[0179]

[0180]

[0181] Example 2

[0182] Primer composition:

[0183] Solution of primer 1 (SC 10.0 wt%) 89.60 Tyzor TPT 0.40 Matsumoto FN 100 SD 10.00

[0184] Example 3

[0185] Primer composition:

[0186] Solution of primer 1 (SC 10.0 wt%) 97.10 Tyzor TPT 0.40 Matsumoto FN 100 SD 2.5

[0187] Example 4 (Comparative Example)

[0188] Comparison of primer compositions:

[0189] Solution of primer polymer 2 (SC 15.0 wt%) 90 Matsumoto FN 100 SSD 10

[0190] In their respective cases, the specified solids content of the corresponding polymer in the solution can be used to definitively determine the weight fraction of microspheres relative to the base polymer in the primer composition.

[0191] Manufacturing test specimens

[0192] A layer of primer having the present invention is manufactured in a manner known to those skilled in the art as follows: First, the primer is applied (using a knife coating technique) to a substrate (steel plate) to a defined layer thickness. Then, the solvent can be evaporated, after which test tape can be applied to the substrate, which now carries a dried primer layer of 15 or 25 μm thickness, respectively. The time elapsed between the application and evaporation of the solvent and the application of the test tape can be only a few minutes, or several days or weeks.

[0193] The test tape used to test the primer is based on polyacrylate (PSA). The tape discussed is an acrylic foam tape. 75120.

[0194] 75120 is a black double-sided tape composed of black acrylic foam that provides a high level of impact damping.

[0195] The thickness is 200μm.

[0196] Peel adhesion to steel (initial) is 13 N / cm; peel adhesion to polycarbonate (initial) is 10.9 N / cm.

[0197] Activated foaming agent

[0198] For the activation of the foaming agent, the test sample was stored in an air-circulating oven at 150°C for 5 minutes. Activation of the foaming agent reduced the measured peel adhesion. After thermal activation, peel adhesion was measured at room temperature, preferably after a 5-minute cooling time.

[0199] Alternatively, if the substrate is a thermally conductive substrate, the foaming agent can be activated by placing the test sample on a precision heating plate (at 155°C for 1 minute).

[0200] To characterize the sample manufactured according to the present invention, peel adhesion was measured before and after activation in an air-circulating heated oven. The results obtained from this measurement are as follows:

[0201]

[0202] A = Adhesive separation of tape

[0203] Examples 1, 2 and 3 clearly and explicitly demonstrate the effect of the primer of the present invention in causing a significantly greater reduction in peel adhesion than the comparative primer, and more particularly, a reduction in peel adhesion of more than 75%.

Claims

1. A primer for producing separable adhesive bonds, the primer being based on a pressure-sensitive adhesive comprising a physical foaming agent, wherein the pressure-sensitive adhesive of the primer comprises at least one copolymer of an acrylate and vinylcaprolactam, the foaming agent being a thermally expandable thermoplastic microsphere, and the foaming agent having an expansion initiation temperature greater than 130°C.

2. The primer according to claim 1, characterized in that... The pressure-sensitive adhesive of the primer is based on acrylate.

3. The primer according to claim 1 or 2, characterized in that... The pressure-sensitive adhesive of the primer does not contain acrylic.

4. The primer according to claim 1 or 2, characterized in that... Based on a base polymer present in 100% by weight, a foaming agent is present in the primer composition at a concentration of 10% by weight to 120% by weight.

5. The primer according to claim 1 or 2, characterized in that... The foaming agent is a granular foaming agent with a median particle size d50 of less than 25 µm before activation.

6. The primer according to claim 5, characterized in that... The median particle size of the granular foaming agent before activation is less than 17µm.

7. The primer according to claim 5, characterized in that... The median particle size of the granular foaming agent before activation is less than 3 µm.

8. The primer according to claim 5, characterized in that... The particle size of the granular foaming agent is higher than 500 nm.

9. The primer according to claim 1 or 2, characterized in that... In a dry, unactivated primer layer, the foaming agent exists as at least two filler layers.

10. The primer according to claim 1 or 2, characterized in that... The foaming agent exists as a layer in the dry, unactivated primer layer.

11. The primer according to claim 1, characterized in that... The thermally expandable thermoplastic microspheres comprise a thermoplastic polymer shell and a foaming agent encapsulated therein, wherein the softening temperature of the polymer shell is in the range of 0 to 140°C.

12. The primer according to claim 11, characterized in that... The softening temperature of the polymer shell is in the range of 30 to 100°C.

13. The primer according to claim 11, characterized in that... The temperature at which thermally expandable thermoplastic microspheres begin to expand, T 开始 The temperature ranges from 40 to 140°C.

14. The primer according to claim 13, characterized in that... The temperature T at which thermally expandable thermoplastic microspheres achieve maximum expansion. 最大 Higher than T 开始 And the temperature is between 80 and 200°C.

15. The primer according to claim 14, characterized in that... T 最大 The temperature ranges from 100 to 170°C.

16. The primer according to claim 1, characterized in that... The foaming agent has an expansion temperature of 100 to 150°C.

17. The primer according to claim 1, characterized in that... The primer comprises microspheres having an average diameter of 3 µm-30 µm in the unexpanded state at 25°C and / or an average diameter of 10 µm-200 µm after expansion.

18. The primer according to claim 17, characterized in that... The microspheres have an average diameter of 5 µm-20 µm in their unexpanded state at 25°C.

19. The primer according to claim 17, characterized in that... The microspheres have an average diameter of 15 µm-90 µm after expansion.

20. A layered structure, comprising: First component, A primer layer on the component, the primer being based on a pressure-sensitive adhesive including a physical foaming agent, and applied from the liquid phase with a thickness not exceeding 30 µm after drying, and The tape, which is attached to the first component via a primer layer, The pressure-sensitive adhesive of the primer includes at least one copolymer of acrylate and vinyl caprolactam, the foaming agent is a thermally expandable thermoplastic microsphere, and the foaming agent has an expansion initiation temperature greater than 130°C.

21. The layered structure according to claim 20, characterized in that... The tape is a pressure-sensitive tape.

22. The layered structure according to claim 20 or 21, characterized in that... The second component is adhered to the free side of the tape.

23. A method for separating a layered structure, the layered structure comprising: First component, A primer layer, based on a pressure-sensitive adhesive including a physical foaming agent, is applied to the component from the liquid phase with a thickness not exceeding 30 µm after drying. The first tape is attached to the first component via a primer layer. The layered structure is heated until the foaming agent present in the primer expands, reducing the peel adhesion of the primer layer to a level that allows the tape to be removed from the component. The pressure-sensitive adhesive of the primer includes at least one copolymer of acrylate and vinyl caprolactam, the foaming agent is a thermally expandable thermoplastic microsphere, and the foaming agent has an expansion initiation temperature greater than 130°C.

24. The method according to claim 23, characterized in that... The layered structure consists of the following: First component, A primer layer, based on a pressure-sensitive adhesive including a physical foaming agent, is applied to the component from the liquid phase with a thickness not exceeding 30 µm after drying. The first tape is attached to the first component via a primer layer. The layered structure is heated until the foaming agent present in the primer expands, reducing the peel adhesion of the primer layer to a level that allows the tape to be removed from the component.

25. The method according to claim 23 or 24, characterized in that... The first tape is a pressure-sensitive tape.

26. Use of the layered structure according to any one of claims 20 to 22 in the automotive industry.

27. The use according to claim 26, characterized in that... The layered structure is used in motor vehicles.

28. Use of the layered structure according to any one of claims 20 to 22 in the electronics industry.

29. The use according to claim 28, characterized in that The layered structure is used in electronic devices.

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