The binder resin for magnetic recording media and its performance evaluation are shown in the table. The use of these resins alone is not common, and they are generally used in combination with good overall performance. Usually the resin composition consists of three parts: (1) Hydroxyl-containing components such as epoxy resins, acrylic resins, Polyester resins, chloroacetic resins, nitrocellulose, etc.; (2) Aminoesterification with the above resins The polyisocyanate component, such as biuret type, trimer type polyisocyanate, polyol isocyanate adduct; (3) modified elastomer components, such as thermoplastic polyurethane, nitrile rubber.
Tape adhesives require the following features:
(1) The magnetic coating can be well bonded to the base film; (2) The magnetic powder is well dispersed in the adhesive; (3) The coating has good wear resistance; (4) Has moderate softness; (5 ) Low coefficient of friction; (6) Low electrical resistance; (7) Good chemical resistance; (8) No stickiness after curing of the coating; (9) Wide temperature range of coating application; (10) Long-term preservation without aging .
Polyurethane resin has good adhesiveness to many substrates, and is excellent in abrasion resistance and durability. It is the main resin in magnetic coatings. Most magnetic coatings contain PU resins. Nowadays, the development trend of magnetic coatings is the formulation simplification. In some cases, the binder resin only includes vinyl resin and thermoplastic polyurethane “TPU”. It was reported recently in a video tape magnetic coating formulation. Use TPU only.
The PU resin used for the magnetic recording medium is generally polybutylene adipate, polyhexylene adipate, polycaprolactone or phthalate polyester polyol, and polyisocyanates such as MDI, TDI, HDI, and IPDI. The synthesized TPU resin has a molecular weight of 1 to 10 thousand. The adhesives are of single-component and two-component type. TPUs for tape adhesives generally have the following properties:
(1) Very good solubility in solvents;
(2) Good dispersion of magnetic powder, good adhesion to magnetic powder and base film;
(3) No tackiness in the contact layer (surface layer);
(4) has particular physicochemical properties such as relatively high hardness, abrasion resistance, elasticity and gloss, very good molecular weight A/-/d4. distributed.
Formula example
The use of PU in magnetic coatings for adhesives can be said to have two aspects.
One is a polyurethane resin (usually a TPU, or a mixture of an oligomer polyol such as polyester and a diisocyanate) used alone or in combination with other resins, and dissolved in a solvent as a main component of a tape adhesive. Due to the good blending property of PU adhesive and various resins, the magnetic powder can be well dispersed in the resin solution, has excellent adhesion to various substrates, and the obtained magnetic coating has excellent wear resistance and durability. Excellent flexibility, so most magnetic coating formulations contain PU.
Second, most magnetic coating formulations use polyisocyanate as the cross-linking component of the adhesive, which constitutes a two-component magnetic coating. The use of a two-component magnetic coating has a limited pot life, but the resulting magnetic recording material is superior in heat resistance and durability to a single component without a cross-linking agent.
Here are some magnetic coating formulations.
1. Main component of resin composed of TPU elastomer as binder Most PU adhesives used for magnetic coatings are thermoplastic polyurethanes, which gives TPU excellent mechanical strength and elastic modulus. TPU resins for magnetic coating adhesives are not completely versatile with TyU resins used as shoe covers and the like and generally require special preparation. TyU made from polyester containing pendant methyl groups has better performance.
One of TDK's patented formulas is as follows:
Quality Score Quality Score
Co-r-Fe2O3 400 Lubricant 5
Polyurethane Resin 55 Carbon Black 5
Epoxy Resin 30 Methyl Ethyl Ketone 500
Nitrocellulose 15 Methyl Isobutyl Ketone 250
Dispersant 6 Cyclohexanone 25
The insufficiency of the dispersibility of the ordinary crystalline polyester hepatic U powder can be improved by introducing an SQ3M, a CO2M plasma group into the molecular chain. One such magnetic coating formulation is as follows:
r-Fe2O3 100 Polyisocyanate Coronanate L 3
Polyurethane Resin 25 Solvents
* PU resin formula: the use of HOCH2CH2C (SO3Na) (CH3) CH2CH2OH as a starter poly-caprolactone (Mw200) 100 parts by mass; poly (ethylene adipate diol) (Mw200) 100 parts; MDl 24.8 parts; 0.02 parts of Dabco catalyst. The resin contains an ionic group, which improves the dispersibility of the magnetic powder.
In the two-component magnetic coating, no catalyst is generally added, but in order to shorten the curing time and guarantee a certain applicator, the formulation with a small amount of catalyst has been studied:
Co-r-Fe2O3 400 stearic acid 4
PU resin (N-2304) 50 stearate 4
Vinyl Chloride - Vinyl Acetate - Vinyl Alcohol 50 Methyl Ethyl Ketone 400
Copolymer Toluene 500
Tertiary Amine Formate Catalyst 0.2 Polyisocyanate (Takede E-31) 25
