Special Topics Review

Application and development of adhesive in micro speaker

Cheng Zhenzhen, Wang Hairong, Tan Caihua, Zhang Zenghui, Wang Mengmei, Liu Chunli, Zhou Houqiang, Li Chun

(Goertek Inc., Weifang  261000, Shandong, China)

【Abstract】Micro speaker is widely used in electronic products, especially in daily applications such as mobile phones, watches, headphones, and VR. One of the most important assembly methods for micro speaker is bonding, and the role of adhesive is crucial. A comprehensive overview of commonly used adhesive for micro speaker was provided in this article, such as UV cured adhesive, instant adhesive, modified silicone adhesive, anaerobic adhesive, and reactive hot melt adhesive, as well as common bonding applications, including bonding between the dome and diaphragm, the dome and voice coil, the diaphragm and frame, the magnet and basin holder, the basin holder and frame, the individual unit and module, and the upper and lower shells. The development trend of adhesive for micro speaker was also discussed.

【Keywords】micro speaker; adhesive; assembly; application

Research Report

Research on the influence of shellac flake type and surface state of bonding substrate on bonding strength and its fluctuation

Xie Yujie^1,2, Pan Xiaolei¹, Wu Yeping¹, Li Gaoming¹, Gu Yunsong², Zhao Xiuli¹, Zhang Ping², Zhang Yinyu¹

（1.Institute of Chemical Materials, China Academy of Engineering Physics, Mianyang  621900, Sichuan, China; 2.School of Materials and Chemistry, Southwest University of Science and Technology, Mianyang  621010, Sichuan, China）

【Abstract】Shellac flakes, as natural adhesive, have received significant attention due to their ease of application and favorable mechanical properties. However, the performance of raw shellac is easily affected by climate and variety, and there is currently a lack of research on bonding processes for plastic and metal substrates, resulting in significant fluctuations in bonding strength and affecting the reliability of bonding connections. It was found in this article that the bonding strength of shellac flakes was closely related to their physical and chemical properties by changing variables such as the type of shellac flakes, the effective period of shellac-ethanol solution (shellac paint) preparation, the drying time, and the type of bonding substrate. Shellac flakes that met the acid value standard and had higher solution viscosity exhibited better bonding performance, while shellac flakes with higher melting points (T_m) and melting enthalpy (ΔH_m), as well as lower melting ranges (ΔT_m) typically had higher bonding strength. In terms of bonding process, the substrate surface was uniformly coated with a single layer of shellac paint, and the lamination was completed immediately after bonding to achieve the best bonding performance. In addition, the bonding material had a significant impact on the curing process and bonding performance of shellac flakes, with polymethyl methacrylate (PMMA) having the highest bonding strength (about 2.8 MPa), followed by aluminum sheet (about 1.0 MPa), and polyether ether ketone (PEEK) having the lowest (about 0.5 MPa). Although polishing the substrate could improve the bonding strength, it was necessary to extend the curing time to achieve optimal performance. This article provided theoretical basis and practical guidance for optimizing the bonding process of shellac flakes and improving their bonding performance on different substrates.

【Keywords】shellac flake; shellac flake type; bonding process; surface state of bonding substrate; bonding performance

Development of emulsion-type acrylate pressure sensitive adhesive for automotive interior trim

Li Mingjie, Li Jianxiong

（Crown New Materials Technology Co., Ltd., Zhongshan  528478, Guangdong, China）

【Abstract】Using butyl acrylate (BA), 2-ethylhexyl acrylate (2-EHA), acrylic acid (AA), dibutyl maleate (DBM), and methyl methacrylate (MMA) as monomers, allyl ether sulfonate as emulsifier, potassium persulfate (KPS)-sodium bisulfite redox system as initiator, and sodium bicarbonate as pH regulator, and adding composite wetting agent, associative thickener, neutralizer and rosin resin tackifying emulsion, a kind of emulsion-type acrylate pressure sensitive adhesive with high peel strength, anti-rebound, low odor and low volatile organic compound (VOC) for automotive interior trim was prepared. The effects of the amount of reactive emulsifier, initiator, functional monomer, DBM monomer and waterborne rosin tackifying emulsion on the 180° peel strength and application performance of emulsion-type pressure sensitive adhesive were investigated by single factor test. The research results showed that, the amount of emulsifier was 2.0% of the total mass of monomer, the amount of initiator was 0.7% of the total mass of monomer, the amount of functional monomer was 2.5% of the total mass of monomer, the amount of DBM was 2.0% of the total mass of monomer, the amount of water-borne rosin tackifying emulsion was 10% of the mass of acrylate emulsion, the performance of emulsion-type pressure sensitive adhesive was relatively optimal. The amount of reactive emulsifier affected the emulsion polymerization process as well as the molecular weight and distribution of acrylate polymer. The amount of functional monomer affected the 180° peel force of pressure sensitive adhesive and the stability of emulsion polymerization. An appropriate amount of DBM monomer could improve the initial tack and anti rebound performance of emulsion-type pressure sensitive adhesive. The waterborne rosin tackifying emulsion could significantly improve the 180° peel force of emulsion-type pressure sensitive adhesive, but affected the anti rebound performance. The smell of the prepared tape product was between 2.5 and 3.5 levels, and the anti rebound performance was A+. The emulsion-type pressure sensitive adhesive met the industry standard and application performance requirements of low odor, low VOC, and low release odor substance (FOG) required for automotive interior trim.

【Keywords】emulsion-type pressure sensitive adhesive; acrylate; anti rebound; low odor; low VOC

Preparation and mechanical properties of epoxy adhesive modified by CTBN/PPE

Hou Yan¹, Wang Jinzhao¹, Yang Yang², Chen Tao¹, Lin Xinzhi¹, Zhang Hongyuan¹, Zeng Fei¹

（1.Luoyang Sunrui Rubber & Plastic Science and Technology Co., Ltd., Luoyang  471003, Henan, China; 2.China Railway 17th Bureau Group Shenzhen Construction Co., Ltd., Shenzhen  518000, Guangdong, China)

【Abstract】The epoxy adhesive was modified to meet the requirements of ethylene-vinyl acetate copolymer (EVA) foam board for large thickness and marine environment resistance. In this paper, carboxyl terminated nitrile rubber (CTBN) and hydroxyl terminated polyphenylene ether (PPE) were used to toughen epoxy resin (EP). Polyamide and polyether amine were used as curing agents. The effects of different addition amounts of CTBN/PPE on the mechanical properties and bonding properties of modified epoxy adhesive were studied, and its mechanical properties and gel time were measured. The research results showed that CTBN/PPE modified epoxy adhesive could significantly promote the curing of EP. When the mass addition of CTBN/PPE was 15%, the flexural strength of modified EP system reached its maximum value of 62.5 MPa, and the impact strength reached its maximum value of 19.1 kJ/m², which was 66.4% and 65.3% higher than the unmodified EP system, respectively. When modified epoxy adhesive was used to bond EVA-EVA boards, it exhibited good peel strength and tensile shear strength, and maintained good peel strength even after immersion in artificial seawater at 70 ℃. When bonding the fiberglass-fiberglass composite panels, the tensile shear strength reached its maximum value of 17.2 MPa when the CTBN/PPE addition amount was 15%, which was 81.2% higher than the tensile shear strength of unmodified EP.

【Keywords】epoxy adhesive; artificial seawater; bonding property; mechanical property

Study on influencing factors of low temperature curing of fuel tank protective adhesive

Qin Li, Ren Fei, Li Shoufeng, Luo Zhichao

(Shenyang Parkerizing Co., Ltd., Shenyang  110122, Liaoning, China)

【Abstract】Fuel tank protective adhesive is used to protect the surface of car fuel tanks, playing a role in corrosion prevention, shock absorption, and noise reduction. In order to meet the requirements of automobile manufacturers to reduce baking temperature and shorten baking time, the factors affecting the low temperature curing of fuel tank protective adhesive and effective adjustment methods were investigated in this study. A fuel tank protective adhesive was prepared by compounding plasticizers (DINP, Mesamoll) and synergistically mixing PVC blended resin with vinyl chloride-acetate copolymer. The adhesion, mechanical properties, and operability of the coating film were studied to meet the requirements of low temperature curing. The research results showed that, ⑴ In the low temperature plasticization screening of PVC resin, vinyl chloride-acetate copolymer performed the best, followed by PVC paste resin, and finally PVC blended resin. When w(vinyl chloride-acetate copolymer)=15%, the final choice of w(PVC blended resin)=3% resulted in relatively optimal spraying application and coating performance. ⑵ After studying the types and ratios of plasticizers, DINP was ultimately selected as the plasticizer and Mesamoll was used in combination as the auxiliary plasticizer. It has been preliminarily determined that the proportion of plasticizer compound used was 30%, with Mesamoll ratio ranging from 3% to 7%. ⑶ The contribution of polyamide tackifier in low temperature curing was not significant, but good adhesion could be achieved when the proportion of tackifier was 1.3%. ⑷ Considering both economic benefits and product performance, the optimal ratio for plasticizer w(Mesamoll) was 3% and w(DINP) was 27%.

【Keywords】fuel tank protective adhesive; low temperature curing; PVC resin; plasticizer

Process and Application

Preparation and performance study of one-component epoxy conductive silver adhesive with high chip shear strength

Yang Xiaoyang^1,2, Lin Zefeng^1,2, Lun Yinghui³, Wang Dongxue^1,2, Wang Tong¹, Zhou Yingchun^1,2

(1. Technology Research and Development Centre, Shenzhen Academy of Metrology & Quality Inspection, Shenzhen  518055, Guangdong, China; 2. Technology Innovation Center of Intelligent Opto-Electronic Sensing, State Administration for Market Regulation, Shenzhen  518000, Guangdong, China; 3. School of Materials Science and Engineering, Hunan Institute of Technology, Hengyang  421002, Hunan, China)

【Abstract】The influence of important factors such as silver powder type, curing agent type and dosage, and accelerator type on the electrical and mechanical properties of conductive silver adhesive was studied and analyzed in this article, and the mechanical properties of conductive silver adhesive bonding at different interfaces were evaluated and analyzed. Finally, the one-component conductive silver adhesive with the long room temperature applicability period was prepared with the silver powder loading of 80%, the melamine curing agent added to the resin of 8.3%, and the composite promoter selected. The research results showed that, the conductive silver adhesive had excellent electrical and mechanical properties, with the volume resistivity as low as 1.11×10^-4 Ω•cm. The chip shear strength for bonding Si-Ag, Ni-Ni, Au-Au, Cu-Cu, and Ag-Ag interfaces was 36.17, 33.38, 30.22, 18.01, and 11.07 kgf, respectively, which was comparable to the performance of commercially available imported conductive silver adhesive. In addition, it has found that the mechanical properties of interface bonding between different materials could be improved by fine-tuning the conductive silver adhesive formula.

【Keywords】epoxy resin; conductive silver adhesive; chip shear strength; volume resistivity; isotropic

Adhesive selection for windscreen of railway vehicle

Zhao Hui¹, Hou Minqiao¹, Sun Yuying¹, Xie Jingsi¹, Li Wei¹, Geng Shujiang²

（1.CRRC Tangshan Co., Ltd., Tangshan  063035, Hebei, China; 2.Northeastern University, Shenyang  110819, Liaoning, China）

【Abstract】To solve the problem of selecting adhesive for the windscreen of railway vehicle, finite element analysis method was adopted in this study to analyze the force on the adhesive joint of the windscreen of rail vehicle. The mechanical performance parameters of the adhesive were measured through experiments, and some of the parameters were used for finite element calculations, which were subjected to joint analysis. The research results showed that, ⑴ Under different temperature and humidity conditions, the mechanical properties of adhesive showed a decreasing trend with the increase of temperature and humidity. ⑵ After 43 days of hydrothermal aging, both the shear strength and tensile strength of the adhesive were lost, but the remaining strength after hydrothermal aging and fatigue aging was greater than 80%. In complex environments, adhesive had good resistance to moisture and fatigue. However, after 10⁷ cycles of fatigue aging, the shear strength of the adhesive decreased to 6.4% of its original strength, indicating a significant decrease in strength. ⑶ With the increase of UV aging time, the overall trend of changes in tensile strength, tensile strength at break, and elongation at break was not significant, indicating that the adhesive had excellent UV resistance. ⑷ Based on comprehensive finite element calculations, the adhesive met the application requirements under 12 static strength working conditions and 2 fatigue strength working conditions.

【Keywords】windscreen; adhesive; finite element; test

Study on material selection and key properties of hot melt adhesive for smooth aluminum bonding protective layer of high-voltage cable

Zhou Hong¹, Chen Jiawei¹, Li Yinyue², Wang Yong², Liu Ying²

(1. State Grid Shanghai Electric Power Company Cable Branch, Shanghai  200072, China; 2. School of Electrical Engineering, Xi’an Jiaotong University, Xi’an  710049, Shaanxi, China))

【Abstract】High-voltage cross-linked polyethylene (XLPE) cable with smooth aluminum sheath is a recent development hotspot in China, and its mechanical properties largely depend on whether the aluminum sheath and the outer sheath are firmly bonded. Therefore, conducting research on the key properties and selection strategies of hot melt adhesive for practical application needs in adhesive protective layer is an important task at present. Firstly, by testing and comparing the strength of various hot melt adhesive with different chemical systems when bonding aluminum sheets and polyethylene test pieces, a hot melt adhesive system suitable for smooth aluminum bonding sheath, namely polyethylene (PE) based hot melt adhesive, was selected. Afterwards, the basic components of two kinds of PE based hot melt adhesive with high bonding strength were analyzed, and crystallinity, melting temperature, and aging properties were tested. The performance differences and main reasons of two kinds of hot melt adhesive were discussed. On this basis, a four point bending simulation model was established to study the damage characteristics of hot melt adhesive layer under cable bending conditions. The influence of elastic modulus and the requirements for bonding strength were analyzed, and a basic selection strategy for hot melt adhesive for smooth aluminum bonding sheath was proposed. The research results showed that PE based hot melt adhesive exhibited good basic performance in bonding smooth aluminum and polyethylene outer sheath. After aging at 90 ℃, the bonding strength of PE hot melt adhesive increased, but the performance deteriorated significantly after aging at 130 ℃. Under the same conditions, for hot melt adhesive with higher elastic modulus, higher shear strength was required. With an elastic modulus of 200 MPa as the boundary, the shear strength should not be lower than 2.0 MPa and 4.0 MPa, respectively. The peel strength had a relatively small impact on the cumulative damage of hot melt adhesive layer, and it was recommended to take a value of not less than 0.5 N/mm.

【Keywords】smooth aluminum sheath; hot melt adhesive; bonding strength; aging property

Material Science

Experimental study on the modification of cement-based materials by cellulose ether and latex powder and their effects on properties

Liu Haoyan¹, Liu Cong²

（1.College of Architecture and Design, Jiuzhou Polytechnic, Xuzhou  221116, Jiangsu, China; 2. Xuzhou Intangible Cultural Heritage Museum, Hubushan Ming and Qing Architecture Protection Center, Xuzhou  221018, Jiangsu, China)

【Abstract】In order to improve the durability of cement-based repair materials, it was proposed to modify cement-based materials with cellulose ether and latex powder. Adding fly ash, slag, nitrate-based early strength admixture, and optimizing the ratio, in order to obtain a more durable cement-based building repair and reinforcement material. Its fluidity, setting time, mechanical properties, etc. were characterized. The research results showed that, when the dosage of hydroxypropyl methyl cellulose ether was 0.3%, the dosage of redispersible latex powder was 5%, the dosage of fly ash was 10%, the dosage of slag was 3%, and the dosage of nitrate-based early strength admixture was 1.5%, the performance of the prepared cement-based material was optimal. At this time, the fluidity of cement mortar was 165 mm, the slump was 170 mm, the setting time was 30 minutes, the bonding strength was 4.7 MPa, and the 28-days dry shrinkage rate was 3.71×10^-2%, which met the requirements of building material repair and could be used as building reinforcement and repair materials.

【Keywords】cement-based material; repair material; mechanical property; bonding strength; durability

Synthesis of vanillin-derived silicone-containing allyl monomer and its modification on epoxy resin

Wei Li, Suo Junying, Chen Xinyi, Zhou Xun

[Chengdu Aircraft Industrial (Group) Co., Ltd., Chengdu  610091, Sichuan, China]

【Abstract】In order to overcome the brittleness problem caused by excessive cross-linking density after curing of epoxy resin, a silicone-containing allyl biobased modifier derived from vanillin was designed and synthesized in this paper, to enhance the toughness of epoxy resin. Silicone-containing allyl compounds (AMTPM) were synthesized by using KH-550 and vanillin-derived alkene compounds (AM) as reaction materials. The chemical structure of AMTPM was characterized by using Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance hydrogen spectroscopy (¹H-NMR), and the effects of different amounts of AMTPM on the properties of epoxy resin were studied. The research results showed that modified E-AMTPM resins with different AMTPM contents were prepared by melt blending AMTPM with epoxy resin. AMTPM resins could lower the curing temperature of epoxy resin. The addition of AMTPM increased the residual carbon rate of E-AMTPM resin, reduced the crosslinking density of the cured resin, and thus improved the toughness of the resin. E-AMTPM resin had greater ductility, resulting in a significant improvement in tensile shear strength.

【Keywords】epoxy resin copolymerization modification; solidification behavior; thermal mechanical property; shear strength