F256 (RF/JQ-4)

Trade NameRF / JQ-4

Similar Name

Molecular Formula

Tris(4-isocyanatophenyl) thiophosphate; Thiophosphoric acid tris(4-isocyanatophenyl ester);  Tris(p-isocyanatophenyl) thiophosphate; Desmodur RFE; tris(p-isocyanatophenyl) thiophosphate


CAS Number:4151-51-3

The light-color Hartdur F256, known as RF or JQ-4, is a clear yellow color universal curing agent for adhesive based on hydroxyl polyurethane (PU), natural and synthetic rubbers. Hartdur F256 can be used whenever sensitive materials need to bond, in particular to rubber materials, mostly for graft-adhesive. Adding Hartdur F256 into adhesive can trigger a crosslinking reaction to harden the adhesive. Thus, it can bond the material firmly, in particularly to rubber materials. Furthermore, Hartdur F256 is good to applied on pale-color demanding products.

Compatibility with solvents

Hartdur F256 can be diluted with anhydrous and alcohol-free methylene Chloride dichloropropane, trichloroethylene, acetone, ethyl ketone, methyl ethyl ketone, toluene and other similar solvents. The addition of relatively large proportions of aliphatic hydrocarbons can cause turbidity; but the solutions of natural rubber in aliphatic hydrocarbons show good compatibility with Hartdur F256 without adding other solvents.


  1. 1 KG / Aluminum bottle ; 20 Bottles / Carton.
  2. 250 KG / Iron Drum

It can be packaged on demand. Please inquire.     

Hartdur F256 is a two-component adhesive. After a certain proportion of Hardtur F256 is added to the adhesive, this mixed adhesive must be used within the operational period (pot life) which is influenced not only by its content of rubber, but also by other ingredients of the formulation (e.g. resins, antioxidants, solvents, and etc.). When the operating period is not used in time (usually delayed by a few hours or even one working day), the adhesive will become very thick and too viscous to use.


For curing adhesive of 100 parts by weight (p.b.w.) based on:

Graft-Chloroprene rubber

(rubber content approx. 16%)

3-5% p.b.w. Hartdur C528

Chloroprene rubber

(rubber content approx. 20%)

5-7% p.b.w. Hartdur C528

Hydroxyl polyurethane

(polyurethane content approx. 15%)

3-5% p.b.w. Hartdur C528

Generally, the usage amount of curing agent is about 3%~5% of the adhesive, but when the humidity in the air increases, the amount of curing agent should be slightly increased. However, please don’t add over 10%. Meanwhile, when the room temperature increases, the reaction speed of the curing agent and the adhesive increases, too. Therefore, the amount of curing agent should be decreased.

Chemical compositionContains 20% thiophosphoric-tris-( p-isocyanato-phenyl ester) and 80% methylene chloride (MC)
Intrinsic colorClear yellow to brownish liquid
NCO%5.4 ± 0.2
SolubilitySoluble in acetone, ethyl acetate, toluene and methyl ethyl ketone.
Storage stabilityReacts readily with moisture; for best performance it should be kept dry and stored at temperatures between 5℃~32℃
PackageA: 1 KG / Aluminum bottle ; 20 Bottles / Carton
 B: 250 KG / Iron Drum

High purity of Hartdur F256 is reflected in its good crystallization property and with better photo-resistance.

Hartdur F256 can be used as an adhesive for rubber and metal, and as a crosslinking curing agent for rubber solution adhesives and solvent-based polyurethane adhesives.

The amount is generally 4% to 7% of the above-mentioned solvent-based adhesives. It is especially used for bonding colorless or light-colored products.

Application including:

  • Bonding for vulcanized (or unvulcanized) rubber and PVC, PU, SBS and other polymers bonding of materials and metals (iron/aluminum).
  • As a curing agent for neoprene adhesives to improve the bonding strength; curing agent for rubber and fabric bonding.
  • As a cross-linking agent for the hydroxyl components of polyurethane products (elastomers, coatings, etc.).
  • As a cross-linking agent for hydroxyl-terminated polyurethane adhesives used in the shoe industry, which can improve the initial adhesion strength, heat resistance and other indicators.
  • Mostly applied on footwear, suitcase, bags industries to bond the fabric with PVC and/or PU.