Polyurethane glue with heat conduction and insulation characteristics for self-adhesive label and preparation method of polyurethane glue

Abstract

The invention discloses polyurethane glue with heat conduction and insulation characteristics for a self-adhesive label and a preparation method of the polyurethane glue, raw materials of the glue comprise a polyurethane prepolymer, an organic silicon modifier, nano montmorillonite and the like, and a glue layer has a structure in which a heat conduction compact phase and an insulation porous phase are combined with each other. The organic silicon modifier endows hydrophobicity, and the nano-montmorillonite hinders moisture permeation, reinforces the fiber to support a cellular structure and improves mechanical properties. The preparation method comprises the following steps: preparing a polyurethane prepolymer, modifying organic silicon, dispersing nano montmorillonite and the like, and synergistically improving various properties of the glue by controlling the conditions of each step and the ratio of raw materials. The glue disclosed by the invention is excellent in moisture-proof, heat-conducting, insulating and mechanical properties, can meet the use requirements of the self-adhesive label in a complex environment, and solves the problems that the existing glue is single in performance and cannot meet high-end application scenes.

Description

Technical Field

[0001] The invention relates to the technical field of polyurethane glue preparation, in particular to polyurethane glue for self-adhesive labels with both thermal conductivity and insulation properties and a preparation method thereof. Background Art

[0002] At present, self-adhesive labels are widely used in many fields, such as food and beverage, daily chemical products, electronic appliances and other industries, for marking product information, brand promotion, etc.

[0003] However, existing glues for self-adhesive labels suffer from numerous performance issues, making them difficult to meet practical application requirements. Common glues, in humid environments, easily allow moisture to penetrate the adhesive layer, reducing the adhesive's viscosity and causing the labels to peel or warp. Traditional glues often focus solely on adhesion, neglecting the synergistic improvement of other properties. Applications with specialized labeling requirements, such as electronic equipment, require both excellent thermal conductivity to dissipate heat generated by the equipment and insulation to prevent the risk of electrical leakage. However, existing glues struggle to simultaneously meet these performance requirements, limiting the application of self-adhesive labels in high-end applications. Some glues also face limitations in their raw material selection, resulting in high costs, poor environmental performance, and simple, crude manufacturing processes. For example, the fillers used in some glues have poor dispersibility, preventing them from being evenly distributed throughout the adhesive layer, impacting the glue's performance stability. Furthermore, inaccurate control of temperature, pressure, and other conditions during the manufacturing process leads to inconsistent product quality and hinders large-scale industrial production.

[0004] Therefore, it is necessary to provide a polyurethane glue for self-adhesive labels having both thermal conductivity and insulation properties and a preparation method thereof, so that the moisture-proof polyurethane glue not only has excellent moisture-proof performance, but also can take into account multiple properties such as thermal conductivity and insulation to solve the above technical problems. Summary of the Invention

[0005] The purpose of the present invention is to provide a polyurethane glue for self-adhesive labels with both thermal conductivity and insulation properties and a preparation method thereof, aiming to solve the performance defects of existing glue for self-adhesive labels and prepare a polyurethane glue with moisture-proof, thermal conductivity, insulation and good mechanical properties.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] In a first aspect, the present invention provides a polyurethane glue for self-adhesive labels having both thermal conductivity and insulation properties. The raw materials include, by weight: 50-70 parts of a polyurethane prepolymer, 5-15 parts of a thermally conductive filler, 5-10.5 parts of an insulating filler, 5-15 parts of an organosilicon modifier, 3-8 parts of nano-montmorillonite, 0.5-2 parts of an antioxidant, 0.1-0.5 parts of a catalyst, 20-30 parts of a solvent, 1-5 parts of a reinforcing fiber, 0.25-2.1 parts of a foaming agent, and 0.05-0.7 parts of a foam stabilizer.

[0008] The adhesive layer formed by the glue includes:

[0009] a) Thermally conductive dense phase: It is composed of a polyurethane matrix continuous phase coated with a thermally conductive filler, with a thermal conductivity coefficient of ≥1.5W / m·K;

[0010] b) Insulating porous phase: composed of foamed polyurethane containing insulating fillers, with a dielectric strength of ≥30kV / mm; the two phases form an interpenetrating network structure through chemical cross-linking.

[0011] The present invention addresses the thermal conductivity-insulation conflict encountered in polyurethane adhesives for self-adhesive labels that combine both thermal conductivity and insulation properties. The adhesive layer comprises a structure combining a dense thermally conductive phase and an insulating porous phase. The dense thermally conductive phase contains 5-15 parts of a thermally conductive filler, while the insulating porous phase is 25-35 parts of polyurethane containing the insulating filler. Thermally conductive fillers (such as boron nitride and aluminum oxide) are intimately contacted within the polyurethane matrix, forming a continuous thermally conductive network. Insulating fillers (such as silica) and polyurethane, under the action of a foaming agent, form a connected porous structure. The two phases interpenetrate and bond through chemical crosslinking, maintaining their respective properties while synergistically functioning. The dense thermally conductive phase forms a continuous thermal pathway, rapidly conducting heat. The insulating porous phase isolates current through its porous structure, meeting the dual heat dissipation and insulation requirements of electronic devices.

[0012] To address the problem of the porous phase's pore structure collapsing or deforming during use, affecting insulation performance and overall structural stability, the present invention adds reinforcing fibers, evenly distributed throughout the insulating porous phase. These fibers serve as a "three-dimensional physical skeleton" supporting the cellular structure, ensuring the long-term stability of the porous phase's insulation performance. Furthermore, the fibers are treated with a silane coupling agent to form a chemical bond with the polyurethane matrix, enhancing the adhesive layer's tensile strength and impact resistance, ensuring reliable label adhesion in complex environments.

[0013] After the fiber is surface-grafted with a silane coupling agent, the active groups on its surface (such as amino groups) react with the isocyanate groups of the polyurethane prepolymer to form covalent bonds, which firmly bond the fiber to the matrix. During the formation of the porous phase, the fibers penetrate between the pore walls, limiting excessive expansion or collapse of the pores while bearing part of the external load and reducing matrix deformation.

[0014] Preferably, the thermally conductive filler is one or more of boron nitride, aluminum oxide, and silicon carbide;

[0015] The insulating filler is one or more of silicon dioxide and boron nitride;

[0016] The reinforcing fibers are one or more of glass fibers, carbon fibers, and aramid fibers.

[0017] Boron nitride (high thermal conductivity) and aluminum oxide (high cost-effectiveness) are combined to balance performance and cost. Silicon dioxide (low dielectric constant) and boron nitride (high insulation) complement each other's particle size, shape, and surface properties. For example, the flaky structure of boron nitride interweaves with the granular structure of aluminum oxide, creating a denser thermal conductivity path. Silicon dioxide's porous surface absorbs bubbles, assisting the foam stabilizer in stabilizing the cells, improving insulation resistance while reducing the agglomeration problem of a single filler.

[0018] The compounding of glass fiber (low cost) and carbon fiber (high strength) makes the difference in modulus of different fibers (such as carbon fiber modulus > glass fiber) make the load more evenly distributed in the matrix, avoiding the stress concentration problem of a single fiber, improving the overall mechanical properties, and improving the tensile strength compared to a single fiber, and fatigue resistance (number of cyclic loads).

[0019] Preferably, the polyurethane prepolymer is prepared by reacting diisocyanate and polyether polyol, and the molar ratio of diisocyanate to polyol is (2-3):1.

[0020] Preferably, the organosilicon modifier is γ-aminopropyltriethoxysilane. The amino groups (-NH2) of the silane react with the -NCO groups of the prepolymer at 60-70°C to form urea bonds (-NH-CO-). Simultaneously, the ethoxy groups hydrolyze to form silanols, which react with the hydroxyl groups on the montmorillonite surface to form a "polyurethane-silane-montmorillonite" interfacial chemical bond, enhancing the three-phase compatibility. The silane molecules act as a "bridge" connecting the polyurethane matrix and the nano-montmorillonite, improving the dispersibility of the montmorillonite and reducing agglomeration. The ethoxy groups (-OEt) in the γ-aminopropyltriethoxysilane hydrolyze to form silanols (-Si-OH), which react with the -NCO groups of the prepolymer to introduce silane groups (-SiR3) into the polyurethane segments, increasing the water contact angle from 70° to 110° and reducing water adsorption.

[0021] Preferably, the nano-montmorillonite is subjected to an organic treatment, specifically using hexadecyltrimethylammonium bromide to perform intercalation modification on the montmorillonite. The montmorillonite flakes are evenly dispersed in the matrix, hindering the movement of the molecular chain, and improving the tensile strength and tear strength. The quaternary ammonium salt cations enter the interlayer of the montmorillonite and replace the original sodium ions through ion exchange, destroying the interlayer hydrogen bonds, causing the montmorillonite to change from an aggregated state to a peeled state, forming nano-scale flakes in the matrix, which have both barrier properties and reinforcement effects. After the hexadecyltrimethylammonium bromide intercalation modification, the montmorillonite interlayer spacing is expanded from 1.2nm to 2.5-3.0nm, forming a "nano-sheet maze", extending the water penetration path by more than 3 times, and improving moisture resistance.

[0022] Preferably, the antioxidant is hindered phenol antioxidant 1010, the catalyst is dibutyltin dilaurate, and the solvent is ethyl acetate.

[0023] In a second aspect, the present invention provides a method for preparing polyurethane glue for self-adhesive labels having both thermal conductivity and insulation properties, comprising the following steps:

[0024] Step 1: Preparation of polyurethane prepolymer

[0025] Add diisocyanate and polyether polyol into a reaction kettle at a ratio of (2-3):1, and stir and react at 80-90°C for 2-3 hours. The different hydroxyl groups of the polyether polyol react with multiple diisocyanate molecules to gradually generate a polyurethane prepolymer containing repeating urethane units.

[0026] During the reaction, the hydroxyl groups (-OH) in the polyether polyol attack the isocyanate groups (-NCO) in the diisocyanate to form a urethane bond (-NH-CO-O-). The diisocyanate and polyether polyol are added in a ratio of (2-3):1, so that the NCO:OH molar ratio is greater than 1 (e.g., 2:1 to 3:1). This ensures that the -NCO groups remain at the ends of the prepolymer, facilitating subsequent crosslinking.

[0027] Step 2: Silicone modification

[0028] Add γ-aminopropyltriethoxysilane to the polyurethane prepolymer and react at 60-70°C for 1-2 hours;

[0029] The amino group of the aminosilane reacts with the isocyanate group of the polyurethane prepolymer to form a urea bond structure, thereby grafting the silicone portion onto the polyurethane chain. This modification can enhance the material's compatibility and thermal stability, as well as subsequent interaction with fillers, and is conducive to the formation of a thermally conductive dense phase structure.

[0030] The introduced silane chain segments can regulate the polarity and molecular chain flexibility of the polyurethane molecules, promote the directional arrangement of thermal conductive fillers in the matrix in the subsequent system (by reducing the interfacial thermal resistance), and thus build a dense thermal conductive path.

[0031] Step 3: Disperse nano-montmorillonite

[0032] Adding the organically treated nano-montmorillonite to the product obtained in step 2, stirring to uniformly disperse the nano-montmorillonite in the polyurethane prepolymer, further improving the matrix composition of the thermally conductive dense phase;

[0033] Step 4: Pre-treating the reinforcing fibers

[0034] After the reinforcing fiber is treated with a silane coupling agent, the active groups on its surface react with the isocyanate groups of the polyurethane prepolymer to form a covalent bond. The reinforcing fiber is combined with the polyurethane prepolymer to become part of the heat-conducting dense phase matrix.

[0035] Step 5: Add fillers, fibers and additives

[0036] Add thermal conductive filler, pretreated reinforcing fiber, foaming agent and foam stabilizer to the mixture obtained in step 3 and stir evenly;

[0037] Among them, the thermal conductive filler is further integrated with the previously formed system consisting of polyurethane prepolymer, silicone modifier, nano-montmorillonite, and reinforcing fiber to initially form a thermally conductive dense phase;

[0038] Step 6: Foaming

[0039] Add insulating filler to the mixture obtained in step 5, stir evenly, and then inject into the mold cavity, control the foaming temperature at 50-90°C, the foaming pressure at 0.3-0.8MPa, and the foaming time at 10-30min;

[0040] During the foaming process, the gas generated by the foaming agent forms bubbles of varying sizes in the polyurethane matrix. Simultaneously, the polyurethane prepolymer further crosslinks and solidifies, fixing these bubbles in the system and forming a porous structure. The insulating filler is evenly dispersed around the bubbles and in the pore walls. Simultaneously, the thermally conductive dense phase system initially formed in step five further reacts and fuses during this process, making the thermally conductive dense phase structure more stable. Ultimately, a structure comprising a thermally conductive dense phase and an insulating porous phase bonded together is formed in the adhesive layer.

[0041] Step 7: Add additives and dilute

[0042] An antioxidant and a catalyst are sequentially added to the foamed product, and the mixture is stirred evenly. Then, a solvent is added and the mixture is stirred evenly to obtain a polyurethane glue for self-adhesive labels having both thermal conductivity and insulation properties.

[0043] Thermally conductive fillers and insulating fillers are dispersed before the foaming agent to ensure the continuous path of the thermally conductive phase and the initial structure of the insulating phase; the foaming agent decomposes (such as pentane vaporization and exothermic decomposition of azodicarbonamide) to produce gas, which forms uniform bubbles under the action of the foam stabilizer, and the reinforcing fibers are synchronously embedded in the porous phase to form an interlocking structure of "fiber-bubble-matrix".

[0044] Preferably, the foaming agent is a combination of one or more of azodicarbonamide, sodium bicarbonate, and pentane;

[0045] The foam stabilizer is either a silicone or polyether foam stabilizer. The decomposition temperatures and gas generation types of the different foaming agents complement each other. Pentane (a physical foaming agent) provides the initial bubble nuclei, while azodicarbonamide (a chemical foaming agent) continuously replenishes gas, avoiding the discontinuous gas generation problem associated with a single foaming agent. The foam stabilizer molecules align at the gas-liquid interface, reducing surface tension and forming a mechanically strong liquid film that inhibits cell rupture or collapse. The combined foaming agent (such as azodicarbonamide + pentane) generates gas in stages at temperatures between 50 and 90°C. During the low-temperature range (50-60°C), pentane vaporizes to form the initial bubble nuclei, while during the high-temperature range (70-90°C), azodicarbonamide decomposes to maintain cell growth, resulting in a narrow cell size distribution. The silicone foam stabilizer forms an elastic film on the cell surface, reducing cell merging and increasing the closed-cell ratio from 60% to 80%, resulting in more stable insulation performance.

[0046] Preferably, before step five, the step of pre-treating the thermal conductive filler and the insulating filler is as follows: surface treating the thermal conductive filler and the insulating filler respectively, and modifying their surfaces with a silane coupling agent.

[0047] Preferably, in step six, micro-nano protrusions are provided on the surface of the mold, wherein the height of the micro-nano protrusions is in the range of 5-20 μm and the width is in the range of 3-15 μm, and the growth and distribution of the pores are regulated by the micro-nano protrusions;

[0048] And / or, nanoparticles can be added to the mixture. The nanoparticles can be one or more of nanosilica and nanocalcium carbonate, with an addition amount of 1%-3% by weight of the polyurethane prepolymer. The nanosilica particle size ranges from 20-100 nm, and the nanocalcium carbonate particle size ranges from 30-120 nm. The geometric constraints created by the micro-nano protrusions exert lateral pressure on the cells during growth, inhibiting disordered expansion and forming oriented, ellipsoidal cells. The nanoparticles adsorb at the air-liquid interface, reducing nucleation energy, promoting the formation of more small cells, and refining the cell structure. The mold's micro-nano protrusions guide cell growth along the protrusion gaps, reducing the average pore size from 150 μm in the uncontrolled state to 80 μm. Nanoparticles (such as 20-100 nm silica) act as heterogeneous nucleation sites, increasing cell density by 50% and achieving size uniformity of over 90%. Regular cells reduce the disruption of thermal paths, narrowing the fluctuation range of thermal conductivity and improving insulation resistance consistency.

[0049] Compared with the prior art, the present invention has the following beneficial effects:

[0050] 1. The present invention significantly improves the moisture resistance of the glue through the synergistic effect of the organosilicon modifier and nano-montmorillonite. The organosilicon modifier γ-aminopropyltriethoxysilane and nano-montmorillonite work together to improve moisture resistance. The amino group of the silane reacts with the -NCO group of the polyurethane prepolymer, and the silanol generated by hydrolysis reacts with the hydroxyl group on the surface of the montmorillonite to form a "polyurethane-silane-montmorillonite" interface chemical bond, which enhances the three-phase compatibility. This allows the montmorillonite to be better dispersed in the polyurethane matrix and reduce agglomeration. At the same time, the silane introduces silane groups into the polyurethane chain segment, increasing the water contact angle from 70° to 110° and reducing moisture adsorption; after the montmorillonite is intercalated and modified, the interlayer spacing increases, forming a "nanosheet maze" that extends the moisture penetration path by more than 3 times. The two work together to significantly improve the moisture resistance of the glue.

[0051] 2. The structure of the thermally conductive dense phase and the insulating porous phase combined with each other in the adhesive layer of the present invention brings thermal conductivity and insulation properties to the glue. The thermally conductive filler is in close contact with the polyurethane matrix to form a continuous thermal conductive network, and the insulating filler and polyurethane form a connected porous structure under the action of the foaming agent. They penetrate each other in space and do not interfere with each other. The thermally conductive dense phase is responsible for the rapid conduction of heat, and the insulating porous phase isolates the current, meeting the dual requirements of electronic equipment for heat dissipation and insulation. For example, boron nitride is compounded with aluminum oxide to form a denser thermal conductive path, and silicon dioxide is compounded with boron nitride to improve insulation resistance. Different fillers complement each other in particle size, shape and surface properties and work synergistically.

[0052] 3. The addition of the reinforcing fibers of the present invention plays a key role in improving the mechanical properties of the glue. The reinforcing fibers are evenly distributed in the insulating porous phase, serving as a "three-dimensional physical skeleton" to support the pore structure. After the fibers are treated with a silane coupling agent, the surface active groups react with the polyurethane prepolymer to form chemical bonds, which firmly bond the fibers to the matrix. During the formation of the porous phase, the fibers are interspersed between the pore walls, limiting excessive expansion or collapse of the pores, while bearing part of the external load and reducing deformation of the matrix. As the amount of reinforcing fibers added increases, mechanical properties such as tensile strength and impact resistance are significantly improved, ensuring the reliability of the self-adhesive labels in complex environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 A line analysis chart comparing the thermal conductivity of the glues prepared in the embodiments and comparative examples provided by the present invention;

[0054] Figure 2 A broken line analysis chart comparing the insulation resistance of the glues prepared in the embodiments and comparative examples provided by the present invention;

[0055] Figure 3 The figure is a line analysis chart comparing the cell collapse rates of the glues prepared in the examples and comparative examples provided by the present invention. DETAILED DESCRIPTION

[0056] The technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0057] Example 1:

[0058] 1. Raw material preparation (by weight): 70 parts of polyurethane prepolymer, 15 parts of thermal conductive filler (such as a compound of boron nitride and alumina), 10.5 parts of insulating filler (such as a compound of silicon dioxide and boron nitride), 15 parts of organosilicon modifier (γ-aminopropyltriethoxysilane), 8 parts of nano-montmorillonite (modified by intercalation of hexadecyltrimethylammonium bromide), 2 parts of antioxidant (hindered phenol antioxidant 1010), 0.5 parts of catalyst (dibutyltin dilaurate), 30 parts of solvent (ethyl acetate), 5 parts of reinforcing fiber (such as a compound of glass fiber and carbon fiber), 2.1 parts of foaming agent (such as a compound of azodicarbonamide and pentane), and 0.7 parts of foam stabilizer (organosilicon foam stabilizer).

[0059] 2. Preparation of polyurethane prepolymer: Add diisocyanate and polyether polyol into the reactor in a ratio of 3:1, stir and react at 90°C for 3 hours. The hydroxyl group of the polyether polyol reacts with the isocyanate group of the diisocyanate to generate a polyurethane prepolymer containing repeating carbamate units and retaining the -NCO group at the end.

[0060] 3. Silicone Modification: Add γ-aminopropyltriethoxysilane to the polyurethane prepolymer and react at 70°C for 2 hours. The amino groups of the aminosilane react with the isocyanate groups of the polyurethane prepolymer to form urea bonds. The ethoxy groups hydrolyze to form silanols, which react with the polyurethane and montmorillonite, respectively, forming a "polyurethane-silane-montmorillonite" interfacial chemical bond. The introduction of silane groups improves hydrophobicity.

[0061] 4. Disperse nano-montmorillonite: Add the organically treated nano-montmorillonite to the product of the previous step, stir it to make it evenly dispersed in the polyurethane prepolymer, and improve the matrix composition of the thermally conductive dense phase.

[0062] 5. Pretreatment of reinforcing fibers: After the reinforcing fibers are treated with a silane coupling agent, the surface active groups react with the isocyanate groups of the polyurethane prepolymer to form covalent bonds, so that the reinforcing fibers are combined with the polyurethane prepolymer and become part of the heat-conducting dense phase matrix.

[0063] 6. Add fillers, fibers and additives: Add thermally conductive fillers, pretreated reinforcing fibers, foaming agents and foam stabilizers to the mixture obtained in step 3, stir evenly, and initially form a thermally conductive dense phase.

[0064] 7. Foaming: Add insulating filler to the mixture obtained in step 6, stir thoroughly, and then inject into a mold cavity with micro-nano projections (20μm height, 15μm width). (The mold surface is provided with micro-nano projections.) Add nanoparticles (nano-silica, nano-calcium carbonate) at a concentration of 3% by weight of the polyurethane prepolymer. Maintain the foaming temperature at 90°C, the foaming pressure at 0.8MPa, and the foaming time at 30 minutes. The blowing agent generates gas to form bubbles, which then crosslink and solidify the polyurethane prepolymer, forming a porous structure. The insulating filler is dispersed around the bubbles and in the pore walls, further stabilizing the thermally conductive dense phase structure, resulting in a structure consisting of a thermally conductive dense phase and an insulating porous phase.

[0065] 8. Adding additives and diluting: Add antioxidants and catalysts to the foamed product in sequence, stir evenly, then add solvent, continue stirring evenly, and obtain polyurethane glue for self-adhesive labels with both thermal conductivity and insulation properties.

[0066] Example 2:

[0067] 1. Raw material preparation (by weight): 60 parts of polyurethane prepolymer, 10 parts of thermal conductive filler (such as a compound of boron nitride and alumina), 8 parts of insulating filler (such as a compound of silicon dioxide and boron nitride), 10 parts of organosilicon modifier (γ-aminopropyltriethoxysilane), 6 parts of nano-montmorillonite (modified by intercalation of hexadecyltrimethylammonium bromide), 1.5 parts of antioxidant (hindered phenol antioxidant 1010), 0.3 parts of catalyst (dibutyltin dilaurate), 25 parts of solvent (ethyl acetate), 3 parts of reinforcing fiber (such as a compound of glass fiber and carbon fiber), 1.5 parts of foaming agent (such as a compound of azodicarbonamide and pentane), and 0.5 parts of foam stabilizer (organosilicon foam stabilizer).

[0068] 2. Preparation of polyurethane prepolymer: Add diisocyanate and polyether polyol into the reactor at a ratio of 2.5:1, stir and react at 85°C for 2.5 hours to generate polyurethane prepolymer.

[0069] 3. Silicone modification: Add γ-aminopropyltriethoxysilane to the polyurethane prepolymer and react at 65°C for 1.5 hours to achieve silicone modification.

[0070] 4. Dispersing nano-montmorillonite: Add the organically treated nano-montmorillonite to the product of step 2 and stir evenly.

[0071] 5. Pretreatment of reinforcing fibers: The reinforcing fibers are treated with a silane coupling agent and then combined with the polyurethane prepolymer.

[0072] 6. Add fillers, fibers and additives: Add thermally conductive fillers, pretreated reinforcing fibers, foaming agents and foam stabilizers, and stir to form a preliminary thermally conductive dense phase.

[0073] 7. Foaming: Add insulating filler, stir evenly, and inject into a mold cavity with micro-nano protrusions (15μm height, 10μm width). (Micro-nano protrusions are designed on the mold surface.) Add nanoparticles (nano-silica, nano-calcium carbonate) at 2% by weight of the polyurethane prepolymer. Maintain the foaming temperature at 70°C, the pressure at 0.6MPa, and the time for 20 minutes to form a dual-phase structure.

[0074] 8. Add additives and dilute: Add antioxidant and catalyst in sequence, stir evenly, then add solvent and stir again to obtain glue.

[0075] Example 3:

[0076] 1. Raw material preparation (by weight): 50 parts of polyurethane prepolymer, 5 parts of thermal conductive filler (such as a compound of boron nitride and alumina), 5 parts of insulating filler (such as a compound of silicon dioxide and boron nitride), 5 parts of organosilicon modifier (γ-aminopropyltriethoxysilane), 3 parts of nano-montmorillonite (modified by intercalation of hexadecyltrimethylammonium bromide), 0.5 parts of antioxidant (hindered phenol antioxidant 1010), 0.1 parts of catalyst (dibutyltin dilaurate), 20 parts of solvent (ethyl acetate), 1 part of reinforcing fiber (such as a compound of glass fiber and carbon fiber), 0.25 parts of foaming agent (such as a compound of azodicarbonamide and pentane), and 0.05 parts of foam stabilizer (organosilicon foam stabilizer).

[0077] 2. Preparation of polyurethane prepolymer: Add diisocyanate and polyether polyol into a reactor at a ratio of 2:1, stir and react at 80°C for 2 hours to obtain a polyurethane prepolymer.

[0078] 3. Silicone modification: Add γ-aminopropyltriethoxysilane to the polyurethane prepolymer and react at 60°C for 1 hour to complete the silicone modification.

[0079] 4. Dispersing nano-montmorillonite: Add the organically treated nano-montmorillonite to the product of step 2 and stir evenly.

[0080] 5. Pre-treatment of reinforcing fibers: After treatment of the reinforcing fibers, they are combined with the polyurethane prepolymer.

[0081] 6. Add fillers, fibers and additives: Add thermally conductive fillers, pretreated reinforcing fibers, foaming agents and foam stabilizers, and stir to initially form a thermally conductive dense phase.

[0082] 7. Foaming: Add insulating filler, stir evenly, and inject into a mold cavity with micro-nano protrusions (5μm height, 3μm width). (Micro-nano protrusions are provided on the mold surface.) Add nanoparticles (nano-silica, nano-calcium carbonate) at 1% of the polyurethane prepolymer weight. Maintain the foaming temperature at 50°C, the pressure at 0.3MPa, and the time for 10 minutes to form a glue layer.

[0083] 8. Add additives and dilute: Add antioxidant and catalyst in sequence, stir evenly, then add solvent and stir to obtain the final polyurethane glue.

[0084] Comparative Example 1: Compared with the embodiment, the thermally conductive dense phase is removed (only the insulating porous phase is retained)

[0085] No thermally conductive filler is added to the raw materials, the proportion of the insulating porous phase is increased to 50 parts (35 parts in the original Example 1), and the other ingredients and preparation process remain unchanged.

[0086] Expected effect difference:

[0087] The thermal conductivity is greatly reduced: there is no thermally conductive filler to form a continuous path, heat cannot be effectively conducted, and the thermal conductivity of the adhesive layer is significantly reduced.

[0088] The insulation performance is slightly improved but the mechanical properties are unbalanced: the increase in the density of the porous phase leads to a slight increase in the insulation resistance, but due to the lack of support from the thermal conductive phase, the stability of the pore structure decreases, and the mechanical properties (tensile strength, impact resistance) decrease significantly.

[0089] Moisture-proof performance is partially weakened: the moisture-proof effect of nano-montmorillonite and silicone modifier still exists, but the imbalance of the two-phase structure leads to a decrease in overall barrier performance and an increase in water absorption.

[0090] Comparative Example 2: Compared to the example, no reinforcing fiber is used

[0091] The reinforcing fibers are removed from the raw materials, and the other components remain unchanged; the fiber pretreatment step is omitted in step 4, and the other preparation processes remain unchanged.

[0092] Expected effect difference:

[0093] The stability of the porous phase is severely reduced: the insulating porous phase lacks fiber support, the cell collapse rate is increased compared with the embodiment, the adhesive layer structure is loose, and the insulation performance fluctuates greatly.

[0094] Mechanical properties are greatly reduced: the "skeleton support" and interface reinforcement effects of the fiber disappear, the tensile strength, peel strength, and impact resistance are significantly reduced, and the label is easily fallen off or damaged due to external force.

[0095] Comparative Example 3: Compared with the embodiment, the reinforcing fiber was not pretreated with a silane coupling agent.

[0096] The reinforcing fibers were not treated with a silane coupling agent, i.e., step 4 was omitted and the reinforcing fibers were directly added to the system, with other components and processes remaining unchanged.

[0097] Expected effect difference:

[0098] Insufficient interfacial bonding strength: The fiber and the polyurethane matrix are only bonded by physical adsorption, and no chemical bond is formed. The interfacial bonding strength decreases, causing the fiber to be easily pulled out of the matrix.

[0099] The improvement of mechanical properties is limited: the fiber dispersion is poor, the agglomeration phenomenon is obvious, the supporting effect on the porous phase is weakened, and the tensile strength and fatigue resistance are lower than those of the embodiment.

[0100] Comparative Example 4: Compared with the embodiment, a single foaming agent

[0101] The foaming agent used is only azodicarbonamide (added in an amount of 3%), without sodium bicarbonate and pentane. Other ingredients and processes remain unchanged.

[0102] Expected effect difference:

[0103] The foaming process is out of control: the decomposition temperature of azodicarbonamide is relatively high (about 200°C), which does not match the foaming temperature of 50-90°C in the embodiment. The actual gas production efficiency is low and the amount of foam cells generated is insufficient.

[0104] Uneven cell structure: A single foaming agent cannot produce gas in stages, resulting in large differences in cell size, a decreased closed cell ratio, and unstable insulation and mechanical properties.

[0105] Comparative Example 5: Compared to the example, no mold micro-nano protrusions are set and no nanoparticles are added

[0106] In step six, no micro-nano protrusions are set on the mold, and no nanoparticles are added, and other process parameters remain unchanged.

[0107] Expected effect difference:

[0108] The cell growth is disordered: lacking mold surface constraints and nanoparticle nucleation points, the cell size distribution is wide (20-200 μm), and the uniformity is lower than that of the embodiment.

[0109] Dual-phase structure destruction: irregular bubbles cut the heat conduction path, the thermal conductivity coefficient fluctuates greatly, the insulation resistance consistency decreases, and the overall performance of the adhesive layer is unstable.

[0110] Comparative Example 6: Compared with the example, the amount of nanoparticles added exceeded the limit (5%)

[0111] The addition amount of nanoparticles (nano-silica + nano-calcium carbonate) is increased to 5%, exceeding the range of 1%-3%. Other ingredients and processes remain unchanged.

[0112] Expected effect difference:

[0113] Severe agglomeration of nanoparticles: Excessive particles cannot be evenly dispersed, and there is a lot of agglomeration, which blocks the pore growth path, increases the density of the porous phase, and reduces the insulation resistance.

[0114] System performance deteriorates: Viscosity increases significantly, and uneven filler dispersion leads to decreased tensile strength and thermal conductivity, resulting in poor construction performance.

[0115] The following tests were conducted on adhesive samples from the Examples and Comparative Examples using standard thermal conductivity and insulation resistance testing methods to accurately determine the thermal conductivity and insulation performance of each sample. By comparing the data from different Examples and Comparative Examples, we demonstrate the effectiveness of the adhesive layer's unique structure (combining a thermally conductive dense phase with an insulating porous phase), raw material formulation, and preparation process in enhancing the adhesive's thermal conductivity and insulation performance.

[0116] Thermal conductivity test method

[0117] 1. Test Principle: The laser flash method is used for testing. This method is based on the principle of thermal diffusion. When a short laser pulse is irradiated on the front surface of a sample, the sample absorbs the laser energy, causing its temperature to rise instantaneously. Heat then propagates from the heated surface to the back of the sample in the form of a heat wave. By measuring the temperature change curve of the back of the sample over time and combining it with parameters such as sample thickness, the thermal diffusion coefficient is calculated using relevant formulas. The thermal conductivity is then calculated based on data such as the sample's specific heat capacity and density.

[0118] 2. Sample Preparation: Select smooth, bubble-free, and uniformly thick adhesive layer samples from the glue prepared in the Examples and Comparative Examples and process them into discs with a diameter of 12.7 mm and a thickness of 2-3 mm. If the sample thickness does not meet the requirements, polish it to ensure a smooth surface to reduce test errors.

[0119] 3. Test Instrument: A laser thermal conductivity meter is used, which must be calibrated with standard samples to ensure measurement accuracy. The instrument mainly consists of a laser light source, a sample stage, a temperature sensor, and a data acquisition system.

[0120] 4. Test steps: Place the prepared sample on the sample stage, ensuring close contact between the sample and the sample stage to ensure good heat conduction. Start the laser thermal conductivity meter and set appropriate laser energy, pulse width and other parameters. Emit laser pulses and record the temperature change data of the back of the sample over time. Repeat the measurement 5 times for each sample and take the average value as the measurement result. According to the measured thermal diffusion coefficient, specific heat capacity and density of the sample, according to the formula γ=a*ρ*C p (where γ is thermal conductivity, a is thermal diffusivity, ρ is sample density, C p The thermal conductivity is calculated from the specific heat capacity of the sample.

[0121] Insulation resistance test method

[0122] 1. Test Principle: Insulation resistance is measured using a high resistance meter. A DC voltage is applied across the sample. The leakage current flowing through the sample is measured and the insulation resistance value is calculated according to Ohm's law: R = U / I (where R is the insulation resistance, U is the applied voltage, and I is the leakage current).

[0123] 2. Sample Preparation: Select a 100mm x 100mm adhesive layer sample and ensure that the sample surface is clean, dry, and free of impurities and moisture. For samples with uneven surfaces, use sandpaper to gently polish them to make them smooth.

[0124] 3. Test instrument: Select a high resistance meter with accuracy that meets the requirements. The measurement range of the instrument should cover the expected insulation resistance value and it must be calibrated before use.

[0125] 4. Test steps: Place the sample on the insulation test bench, place two electrodes on the upper and lower surfaces of the sample respectively, and ensure good contact between the electrodes and the sample. For samples with larger areas, multiple electrodes can be evenly distributed to reduce measurement errors. Set the measuring voltage of the high resistance meter to 500V (other suitable voltage values ​​can also be selected according to actual conditions), start the high resistance meter, measure and record the leakage current value. Calculate the insulation resistance value according to Ohm's law, repeat the measurement 5 times for each sample, and take the average value as the final insulation resistance measurement result. The following table compares the experimental data of the above embodiment and comparative example:

[0126]

[0127] Through the analysis of the above examples and comparative example experimental data, it can be seen that:

[0128] 1. As the proportion of thermally conductive filler increases from Example 3 to Example 1 (5-15 parts), the thermal conductivity increases from 0.6W / (m·K) to 0.8W / (m·K), indicating that the thermally conductive filler significantly improves thermal conductivity. At the same time, the change in the proportion of the insulating porous phase affects the insulation resistance. For example, in Example 1, when the insulating porous phase is 35 parts, the insulation resistance reaches 1.2×10¹ 4 Ω, 25 parts in Example 3, insulation resistance is 1.0×10¹ 4 Ω, reflecting the positive correlation trend between the proportion of insulating porous phase and insulation performance.

[0129] At the same time, the amount of reinforcing fiber added gradually increased from 1% in Example 3 to 5% in Example 1, the tensile strength increased from 12 MPa to 15 MPa, and the impact resistance increased from 160 J / m² to 200 J / m², indicating that the reinforcing fiber has a significant effect in improving the mechanical properties of the glue.

[0130] 2. After removing the dense thermally conductive phase from Comparative Example 1, the thermal conductivity dropped to 0.5 W / (m·K), demonstrating that the dense thermally conductive phase is key to achieving good thermal conductivity. In Comparative Example 2, without reinforcing fibers, the cell collapse rate increased to 35%, and the tensile strength dropped to 8 MPa, highlighting the importance of reinforcing fibers in maintaining a stable porous phase structure and improving mechanical properties.

[0131] Meanwhile, in Comparative Example 4, which uses a single blowing agent (no compounding), the cell size uniformity drops to 65%, a significant decrease from 90% in Example 1, demonstrating that compounding the blowing agent helps control cell uniformity. In Comparative Example 6, the nanoparticle addition level exceeds the limit (5%), and the insulation resistance drops to 8.0×10¹³Ω, indicating that the nanoparticle addition level must be strictly controlled within a reasonable range.

[0132] 3. Examples 1-3 achieve a good balance across various performance indicators, meeting diverse performance requirements. Compared to the comparative examples, the technical solution of this invention (bicontinuous structure, reinforced fiber, rational raw material ratio, and preparation process) offers significant advantages in improving the adhesive's moisture resistance, thermal conductivity, insulation, and mechanical properties. This addresses the existing problem of adhesives with limited performance and inability to meet the demands of complex applications.

[0133] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations that come within the meaning and range of equivalents of the claims be embraced therein.

Claims

1. A polyurethane glue for self-adhesive labels having both thermal conductivity and insulation properties, characterized in that: The raw materials include, by weight: 50-70 parts of polyurethane prepolymer, 5-15 parts of thermal conductive filler, 5-10.5 parts of insulating filler, 5-15 parts of organosilicon modifier, 3-8 parts of nano-montmorillonite, 0.5-2 parts of antioxidant, 0.1-0.5 parts of catalyst, 20-30 parts of solvent, 1-5 parts of reinforcing fiber, 0.25-2.1 parts of foaming agent, and 0.05-0.7 parts of foam stabilizer; The adhesive layer formed by the glue includes: a) Thermally conductive dense phase: It is composed of a polyurethane matrix continuous phase coated with a thermally conductive filler, with a thermal conductivity coefficient of ≥1.5W / m·K; b) Insulating porous phase: composed of foamed polyurethane containing insulating fillers, with a dielectric strength of ≥30kV / mm; the two phases form an interpenetrating network structure through chemical cross-linking.

2. The polyurethane glue for self-adhesive labels having both thermal conductivity and insulation properties according to claim 1, characterized in that: The thermally conductive filler is one or more of boron nitride, aluminum oxide, and silicon carbide; The insulating filler is one or more of silicon dioxide and boron nitride; The reinforcing fibers are one or more of glass fibers, carbon fibers, and aramid fibers.

3. The polyurethane glue for self-adhesive labels having both thermal conductivity and insulation properties according to claim 1, characterized in that: The polyurethane prepolymer is prepared by reacting diisocyanate and polyether polyol, and the molar ratio of diisocyanate to polyol is (2-3):

1.

4. The polyurethane glue for self-adhesive labels having both thermal conductivity and insulation properties according to claim 1, characterized in that: The organosilicon modifier is γ-aminopropyltriethoxysilane.

5. The polyurethane glue for self-adhesive labels having both thermal conductivity and insulation properties according to claim 1, characterized in that: The nano-montmorillonite is subjected to organic treatment, specifically, hexadecyltrimethylammonium bromide is used to perform intercalation modification on the montmorillonite.

6. The polyurethane glue for self-adhesive labels having both thermal conductivity and insulation properties according to claim 1, characterized in that: The antioxidant is a hindered phenol antioxidant, the catalyst is dibutyltin dilaurate, and the solvent is ethyl acetate.

7. A method for preparing the polyurethane glue for self-adhesive labels having both thermal conductivity and insulation properties according to any one of claims 1 to 6, characterized in that: The following steps are involved: Step 1: Preparation of polyurethane prepolymer Add diisocyanate and polyether polyol into a reaction kettle at a ratio of (2-3):1, and stir and react at 80-90°C for 2-3 hours. The different hydroxyl groups of the polyether polyol react with multiple diisocyanate molecules to gradually generate a polyurethane prepolymer containing repeating urethane units. Step 2: Silicone modification Add γ-aminopropyltriethoxysilane to the polyurethane prepolymer and react at 60-70°C for 1-2 hours. γ-aminopropyltriethoxysilane is covalently bonded to the polyurethane chain end through a urea bond. After the silicone segment is introduced, a polyurethane-silane hybrid structure is formed. Step 3: Disperse nano-montmorillonite Adding the organically treated nano-montmorillonite to the product obtained in step 2, stirring to uniformly disperse the nano-montmorillonite in the polyurethane prepolymer, further improving the matrix composition of the thermally conductive dense phase; Step 4: Pre-treating the reinforcing fibers After the reinforcing fiber is treated with a silane coupling agent, the active groups on its surface react with the isocyanate groups of the polyurethane prepolymer to form a covalent bond. The reinforcing fiber is combined with the polyurethane prepolymer to become part of the heat-conducting dense phase matrix. Step 5: Add fillers, fibers and additives Add thermal conductive filler, pretreated reinforcing fiber, foaming agent and foam stabilizer to the mixture obtained in step 3 and stir evenly; Among them, the thermal conductive filler is further integrated with the previously formed system consisting of polyurethane prepolymer, silicone modifier, nano-montmorillonite, and reinforcing fiber to initially form a thermally conductive dense phase; Step 6: Foaming Add insulating filler to the mixture obtained in step 5, stir evenly, and then inject into the mold cavity, control the foaming temperature at 50-90°C, the foaming pressure at 0.3-0.8MPa, and the foaming time at 10-30min; During the foaming process, the gas generated by the foaming agent forms bubbles of varying sizes in the polyurethane matrix. Simultaneously, the polyurethane prepolymer further crosslinks and solidifies, fixing these bubbles in the system and forming a porous structure. The insulating filler is evenly dispersed around the bubbles and in the pore walls. Simultaneously, the thermally conductive dense phase system initially formed in step five further reacts and fuses during this process, making the thermally conductive dense phase structure more stable. Ultimately, a structure comprising a thermally conductive dense phase and an insulating porous phase bonded together is formed in the adhesive layer. Step 7: Add additives and dilute An antioxidant and a catalyst are sequentially added to the foamed product, and the mixture is stirred evenly. Then, a solvent is added and the mixture is stirred evenly to obtain a polyurethane glue for self-adhesive labels having both thermal conductivity and insulation properties.

8. The method for preparing polyurethane glue for self-adhesive labels having both thermal conductivity and insulation properties according to claim 7, characterized in that: In step (5), a foaming agent and a foam stabilizer are added, wherein the foaming agent is at least one of azodicarbonamide, sodium bicarbonate, and pentane; The foam stabilizer is an organosilicon foam stabilizer or a polyether foam stabilizer.

9. The method for preparing polyurethane glue for self-adhesive labels having both thermal conductivity and insulation properties according to claim 7, characterized in that: Before step five, the thermal conductive filler and the insulating filler are pretreated, and the surfaces of the thermal conductive filler and the insulating filler are modified respectively using a silane coupling agent.

10. The method for preparing polyurethane glue for self-adhesive labels having both thermal conductivity and insulation properties according to claim 7, characterized in that: In step six, micro-nano protrusions are provided on the mold surface, wherein the height of the micro-nano protrusions ranges from 5 to 20 μm and the width ranges from 3 to 15 μm, and the growth and distribution of the pores are regulated by the micro-nano protrusions; And / or, nanoparticles are added to the mixture, wherein the nanoparticles are one or more of nano-silicon dioxide and nano-calcium carbonate, and the added amount is 1%-3% of the weight of the polyurethane prepolymer; the particle size of the nano-silicon dioxide is in the range of 20-100 nm; the particle size of the nano-calcium carbonate is in the range of 30-120 nm.

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