Filled Cyanoacrylate Adhesive Compositon

ISSN 1811-2382, Polymer Science, Ser. C, 2007, Vol. 49, No. 1, pp. 50–51. © Pleiades Publishing, Ltd., 2007. Original Russian Text © O.N. Klenovich, A.M. Vetrova, 2006, published in Klei. Germetiki. Tekhnologii, 2006, No. 1, pp. 21–22. Filled Cyanoacrylate Adhesive Compositions O. N. Klenovich and A. M. Vetrova Federal State Unitary Enterprise, Kargin Polymer Chemistry and Technology Research Institute, Dzerzhinsk, Nizhni Novgorod oblast, 606000 Russia e-mail: niip@kis.ru Abstract—Filled cyanoacrylate adhesive compositions possessing electro- and heat-conducting properties have been developed. These compositions are recommended for panel wiring of electro- and radioelements and hermetic sealing of aluminum casting. DOI: 10.1134/S1811238207010110 A wide application of cyanoacrylate adhesives in industry, medicine, and private life is due to the high rate of bonding (from several seconds to minutes) of diverse materials, such as metals, glass, ceramics, plastics, wood, rubber, and living tissues, giving rise to strong adhesive joints [1]. These adhesives are solventfree, low-toxicity, and are handled rather easily. In this study, cyanoacrylate compositions were tested as binding agents for the manufacture of filled adhesives with functional properties. As is known, filled adhesives are two-phase systems in which particles of one phase (filler) are joined by a thin layer of the binding agent phase. The thickness of the binding layer in such a system should be minimum so that the whole polymer could transform into the ultimately structured state [2]. The mechanical characteristics of such systems take the highest values since the three-dimensional matrix appears in these systems in the course of hardening in which filler particles are strongly held [3]. Some metal fillers render polymers conductive and reduce their gas and vapor permeability. Formulations filled with boron nitrides and aluminum oxides offer promise as heat-conducting dielectric materials. Conducting adhesives. Conducting materials, such as metals and their alloys, are usually joined by soldering or welding methods. This process related to the heating of materials to high temperatures cannot be used in some electronic units, in assembly of microminiature radio components, and for conductive joining of ceramics [4]. In this case, it is advisable to bond items via adhesion with the use of conductive adhesives. The conducting behavior of adhesive formulations is provided by metal fillers, such as silver, copper, iron, and nickel carbonyl, which are characterized by good conductivity. In the development of conductive adhesives, we tested powders of silver as the most conducting metal and nickel carbonyl of the PNK-1L5 grade as less prone to form passivating films on the surface of particles. As binding agents, we used cyanoacrylate adhesives TK-200 and TK-300 developed at our institute. These adhesives were chosen since the TK-200 adhesive forms the strongest joints, while the TK-300 adhesive is thermally stable and can withstand short-term heating to 250–300°C. Cyanoacrylate adhesives were additionally modified so that the pot life of filled formulations was no less than 30–60 min. These times are sufficient for practical applications and maintenance of the optimal combination of properties (Table 1). Heat-conducting adhesives. Adhesive heat-conducting formulations have found wide use for mounting of semiconductors, transistors, and thermistors. Unfilled adhesives are characterized by low heat conductivity. A difference in the heat conductivities of an adhesive and a material to be bonded leads to a temperature jump at the bonding boundary and causes an additional increase in the temperature of the working area of a construction during heat flux passage. The heat conductivity of adhesives may be governed via incorporation of fillers that impart high dielectric Table 1. Mechanical and electrical characteristics of conductive adhesives Trade mark Peel strength, Shear strength, of adhesive MPa at 20°C MPa at 20°C Volume resistivity, Ohm cm TK-200 (Ni) 20/25* 15 1–3 TK-200 (Ag) 20/23* 15 1 × 10–2 TK-300 (Ni) 15/20** 10 1–3 TK-300 (Ag) 18/18** 12 1 × 10–2 Notes: * After heat cycling from –60 to +90°C for 3 h, 12 cycles. ** After heat cycling from –60 to +200°C for 3 h, 12 cycles. 50 FILLED CYANOACRYLATE ADHESIVE COMPOSITIONS 51 Table 2. Mechanical characteristics of heat-conductive adhesives Trade mark of adhesive Peel strength, MPa at 20°C Shear strength, MPa at 20°C Heat conductivity coefficient, V/(m K) Volume resistivity, Ohm cm TK-200 (NB) 25/28* 15 1.4 1 × 1013 TK-300 (NB) 20/25** 12 1.5 1 × 1013 Notes: * After heat cycling from –60 to +90°C for 3 h, 12 cycles. ** After heat cycling from –60 to +200°C for 3 h, 12 cycles. characteristics to the adhesives. Boron nitride was employed as such filler. The distinctive feature of hexagonal boron nitride is a flaky structure of its dispersed particles. This fact explains high heat conductivity of the boron nitridefilled systems. It was shown that, at a filling degree of 25–30 wt %, boron nitride particles form a continuous three-dimensional framework in the polymer matrix that also serves as a heat bridge [5]. On the basis of modified cyanoacrylate adhesives TK-200 and TK-300, we developed two-component heat-conducting adhesives TK-200 (NB) and TK-300 (NB) with high dielectric parameters (Table 2). Sealing of aluminum casting. Articles manufactured by various casting methods contain inevitable defects as pores or blisters that sometimes occupy up to 40% of the surface. The development of a method for improvement of casting defects with the use of highly filled polymer materials is an urgent problem. A filled cyanoacrylate formulation based on the TK201 adhesive with a viscosity of 1000–2000 cSt and an aluminum powder was prepared. The TK-201 adhesive shows sufficient elasticity and heat resistance to 160°C in combination with high strength (Table 3). The TK-201-based formulation filled with the aluminum powder is characterized by a set of excellent Table 3. Mechanical characteristics of the TK-201 adhesive filled with the aluminum powder Trade mark Shear strength, of adhesive MPa at 20°C TK-201 TK-201 + aluminum powder Compressive Compressive yield stress, yield strain, % MPa at 20°C 10 38 60 10/12* 30/45* 50/70* * After heat cycling from –50 to +90°C for 3 h, 12 cycles. POLYMER SCIENCE Series C Vol. 49 No. 1 2007 mechanical properties, including heat cycling stability, indicating its elasticity. All the above-described cyanoacrylate formulations exhibit good moisture resistance, which was estimated from the peel strength after 1-month storage of bonded specimens at 40°C at a humidity of 98%. This parameter was found to be 70–80% of the initial value. A reduction in the peel strength of unfilled adhesives TK-200, TK-201, and TK-300 under these conditions was as high as 50%. Techniques of adhesive preparation and bonding. Filled adhesive formulations were prepared directly before use via mixing of a binding agent (modified TK-200, TK-201, and TK-300) and fillers. The mixture was stirred for 5–10 min in a clean dry container until a homogeneous paste was obtained. Before use, fillers were dried to the content of the moisture weight fraction not higher than 0.01%. The treatment and bonding of the surface of articles are similar to those of traditional employment of unfilled cyanoacrylate adhesives. Thus, on the basis of modified cyanoacrylate adhesives, formulations with electro- and heat-conductive properties have been developed. These formulations show promise for wide use in the instrument-making industry, electronics, radio engineering, engineering industry, and other branches of industry. REFERENCES 1. L. M. Pritykin, D. A. Kardashov, and V. L. Vakula, Monomer Adhesives (Khimiya, Moscow, 1988) [in Russian]. 2. Metallopolymer Materials and Products: A Handbook, Ed. by V. A. Belyi (Khimiya, Moscow, 1979). 3. Yu. S. Lipatov, Plast. Massy, No. 11, 6 (1976). 4. F. F. Bazarova and L. S. Kolesova, Adhesives in Electronics Production (Energiya, Moscow, 1975) [in Russian]. 5. Ya. A. Abeliov, Klei Germet. Tekhnol., No. 8, 26 (2005).