Preparation And Properties Of Polyimide Adhesives Modified By Inorganic Filler

In recent years, polyimide materials exhibited excellent performance in many fields, including aerospace, microelectronics, military vehicles and so on. However, for its rigid structure, polyimide has poor solubility and poor melt process ability which limited its application. To solve these problems, modified polyimide adhesive by compounding with the inorganic filler was prepared. The material that we prepared not only has excellent thermal stability, solvent resistance, adhesion properties and dielectric properties, etc. of the polyimide adhesive, but also has a higher melting point and the high temperature performance properties of the active inorganic filler. Compounding with the inorganic filler is one of the hotspots of the polyimide-based composite materials in the field.In this paper, we added the active inorganic filler B₄C and nano SiO₂ into the pre-polymer PAA by directly dispersing, a high temperature heat curing process and the thermal imidization to prepare polyimide resin-based composite adhesive.In this paper, there are three aspects results will studied:1. Studied the influence of ratio of anhydride and diamine monomer, the solid content of the PAA and the reaction time on the polyimide resin thermal stability. This paper designed an orthogonal experiment of three factors and four levels. This experiment selected 3,3’,4,4’-benzophenone tetra carboxylic anhydride and metaphenylene diamine as monomer, took the reaction in N’N-dimethylacetamide （a strong polar aprotic solvent）. We took two-step process to prepare a thermoplastic polyimide resin and a polyimide film was prepared by casting. We used TG to analyze thermal stability. The optimal solution for the orthogonal experiment was that the molar ratio of anhydride to diamine was 1.05:1, the solid content of the PAA was 25% and the reaction time was 7 hours. Meantime, the polyimide resin T5% is 514℃, T50% is 569℃, and at 800℃ the carbon residue rate of polyimide resin is 11.71%, the carbon residue rate of B₄C modified polyimide resin is 120%, the carbon residue rate of nano-SiO₂ with B₄C modified polyimide resin is 131%, increased by 108.29% and 119.29% respectively.2. Studied the influence of activity inorganic filler B₄C （1-10μm） on polyimide resin properties. This paper used B₄C with different proportions to modify polyimide adhesives. The results showed that bonding strength increased significantly through ceramics B₄C modification. The best molar ratio of B₄C and polyamide acid solution （solids content 25%） is 1:1. At 1000℃ bonding strength reached a maximum value 61MPa.3. Using the silane coupling agent （KH550） to deal with the inorganic filler （nano SiO₂ and B₄C）, then blend nano SiO₂ and B₄C powder with polyimide resin matrix. The mole ratio of polyamide acid and inorganic filler is 1:1. This paper explored the effect of nano SiO₂ on the mechanical properties of modified polyimide adhesives. We studied adhesive performance in 700-1100 ℃. The results showed that the bonding strength is close to maximum 60MPa at 900℃. When SiO₂ accounted for 4%of total B₄C, the mechanical property is optimal. At 800℃ and 1100℃, and the mechanical property are superior to B₄C modified adhesive.