Magnetic recording medium contg. new polyurethane binder - derived from poly:methyl:valerolactone diol with excellent dispersibility

摘要

Magnetic recording medium consists of a nonmagnetic substrate and a magnetic coating contg. a ferromagnetic powder (I) and a polyurethane resin (II) as binder. (II) is prepd. by reacting a polyisocyanate (III) with polymethylvalerolactone diol (IV), obtd. by polymerisation of beta-methyl-epsilon-valerolactone (sic; beta-methyl-delta-valerolactone) (V) in the presence of a di-OH cpd. (VI) contg. a metal sulphonate gp. as polymerisation initiator. USE/ADVANTAGE - (II) has excellent dispersibility. It gives a homogeneous (I) dispersion with low thixotropic property and the coatings have a smooth surface and excellent stability, even under tropical conditions. The material is useful e.g. for video tape. In an example, under N2, 1000 pts. of (A) (V), (B) epsilon-caprolactone (control) were dripped into a stirred mixt. of (A) 9.18, (B) 11.5 pts. Na di-2-hydroxyethyl-5-sulphoisophthalate and (A) 0.65, (B) 0 pt. Na in (A) 55.7, (B) 66.2 pts. ethylene glycol and the mixt. was kept 1 hr. at 40 deg.C, giving a polyester with Mn = 1000 and OH no. (A) 113, (B) 114, contg. (A) 260, (B) 30 micro-equiv./g of NaSO3 gps. 89.3 pts. 4,4'diphenylmethane diisocyanate were stirred into a homogeneous soln. of 100 pts. polyester in 323 pts. MEK at 80 deg.C and reacted 2-3 hr., giving an NCO-prepolymer. Then 11.9 pts. butan-1,4-diol and 13.9 pts. neopentyl glycol were added as chain extenders and reacted 10-15 h. at 70-85 deg.c with addn. of (A) 0.11, (B) 0.011 pt. dibutyl Sn dilaurate as urethanisation catalyst. Reaction was complete when the concn. of residual NCO gps. was max. 0.01%. The polyurethane contained (A) 120, (B) 9 micro-equiv./g of NaSO3 gps.