Elastic transparent compounds for sealing elements of electro radio products

Abstract

To ensure climatic stability of electro radio prod ucts (ERPs) and various instruments, transparent sealing materials able to keep high electrical insulating properties for a long time in high humidity conditions are required: the volume resistivity (ρ ν ) should be at least 5 ×10 10 Ω m at 20 ± 5°C.Currently, to seal frameless ERP elements-in particular, capacitors-VGO 1 silicone sealant is widely used, to which EP 730 and UR 231 epoxy var nishes, used later to cover the entire board, have no adhesion. Therefore, the technological process of board manufacture is complicated by the fact that we have to remove the varnish from the surface of the ele ments sealed by VGO 1. In addition, when this hap pens, the percentage of defects is increased. Other available sealing insulating materials with good adhe sion to elements and epoxy varnishes are hardly trans parent, repairable, and rather water resistant: after the effect of humidity (up to 98%) for 30 days, a significant reduction of ρ ν values to 10 5 -10 4 Ω m is observed. Therefore, to create a nonwaste high performance technology of moisture protection for ground and space based radioelectronic equipment (capacitors, microcircuitry, electronic universal modules, etc.) development of a transparent (without the use of vac uum) elastic sealing compound was required. The developed compound had to meet the following requirements:• curing for 6 h at 65 ± 5°C or 24 h at room tem perature;• transparency and freedom from air inclusions after hardening;• a density not exceeding 1.0 g/cm 3 ;• flexibility with a relative elongation in tension of at least 80%;• a good adhesion to aluminum alloys (shear strength of adhesive joints of at least 2 MPa), ceramics, fiberglass, etc.;• reparability, i.e., the possibility of cutting it with a knife;• ρ ν at least 5 × 10 10 Ω m at 20 ± 5°C, at least 1 × 10 8 Ω m after holding for 30 days at 20 ± 5°C, and rel ative humidity of 95%;• electric strength (E st. ) at least 25 kV/mm at 50 Hz and (20 ± 5)°C;• ability to withstand ab operating temperature of from -60 to +80°C (up to 120°C for a short time);• minimum values with respect to the gas release (according to GOST 50109 92) when exposed to vac uum and temperature of 125°C for 24 h;• high thixotropic properties, not flowing down from elements up to 4 mm in height, creating a protec tive layer on their surface with a thickness at least 1 mm; and• resistance to a total dose of ionizing radiation of 1 × 10 8 rad.As a polymer base for the compound, oligodie neurethanepoxide of PDI 3AK grade modified by reactive diluents such as Laproksid was chosen [1]. The choice was dictated by the fact that, in the process of curing PDI 3AK epoxidized polydiene-a product of the reaction of brand PDI 1 oligodienediols with an excess of toluylenediisocyanate with subsequent reac tion of the formed prepolymer with glycidol-elastic freeze resisting compounds with good dielectric prop erties, hydrolytic stability, and resistance to ionization Abstract-Developed elastic insulating materials, which allow one t...