Adhesives Desmodur

The saturated analogue of MDI, 4,4 -dicy-clohexyl methane diisocyanate, has found limited use as an aiphatic isocyanate in adhesives. This material is known by a variety of names including Desmodur W (Bayer), hydrogenated MDI (or HMDI or Hl2MDI), reduced MDI (RMDI), and saturated MDI (SMDI), It is a low-viscosity liquid with a fairly high vapor pressure, so it too must be handled with care. In adhesive compositions, the diisocyanate usually is used to make an isocyanate functional prepolymer by reacting excess diisocyanate with a hydroxyl or amine functional polymer such as a polyester diol. 

Desmodur [Bayer AG]. TM for a group of isocyanates and isocyanate prepolymers for urethane coatings, foams, adhesives, etc. 

A comparison of the durability of the adhesive bonds formed by the two binders is provided by the wet internal bond and by the thickness swell values shown graphically in Figures 5 and 6, respectively. The former, measured after a 2 hour water boil, are strikingly superior for the Desmodur PU-1520A 20 vs. the phenolic binder at all press times. The same can be said for thickness swell after 2 and 2k hour water soaks. 

Desmodur . [Bayer Miles] Polyurethane and isocyanates a esive for bonding textiles, leather, wood, metal, plastics crosslinking agent for adhesives. 

Polyurethane bulk and thin-film samples are prepared from a two-part PU adhesive formed by polyaddition of Bayer Desmodur CD (89% diphenylmethane-4,4 -diisocyanate 1 with 11% uretoneimine triisocyanate 2 as additive) with a polyol mixture of Bayer Desmophen 2060BD (linear poly(propylene ether) diol... 

The most important polyurethane adhesive components are toluene diisocyanate (TDI), 4,4 -diphenylmethane diisocyanate (MDI), p-anisidine diisocyanate (DADI), hexamethylene diisocyanate (HDI) and triphenyl-methane triisocyanate (Desmodur R) (see Fig. 8.1), together with various polyester and polyether glycols. (See Fig. 1.9 of Chapter 1 for the formulae of TDI, MDI and HDI, and Fig. 8.5 for the formula of DADI.) Toluidine diisocyanate (TODI) (Fig. 8.1) is also used. 

In this, one part consists of a polyester or polyether dissolved in an inert solvent and this is mixed with its molar equivalent of a diisocyanate dissolved in solvent. Usually ethyl acetate is the solvent and typical solution concentrations are 70% total solids. A suitable diisocyanate would be Desmodur HH (see Fig. 8.6) in ethyl acetate at 75% solids content. At room temperature such a cement has a pot life of 1-2 days and with accelerator, only 3 h. The setting time of this cement, containing accelerators, in wood adhesion, is 4-5 h at 10°C, 7h at O C, overnight at less than 0°C. 

Fig. 8.6. Isocyanate for a two-part adhesive system (Desmodur HH, an adduct from 1,6-hexamethylene diisocyanate (3mol) and 3-methylolpentylene...

Fig. 8.7. Isocyanate adhesive promoter for use with thermoplastic polyurethanes (Desmodur RF, a 20% solution of thiophosphoric acid tris (p-isocyanatophenyl ester) in methylene chloride).

In bonding strong substrates, and if solvent and greater heat resistance are required in the adhesive bond, then the Desmocolls may be mixed with appropriate amounts of isocyanates such as TDI,4,4, 4"-triphenylmethane triisocyanate (Desmodur R) or Desmodur RF (Fig. 8.7), which is thiophosphoric acid (p-isocyanatophenyl ester) used as a 20% solution in methylene chloride. 

The aromatic triisocyanate (13) is obtained in the reaction of 4-nitrophenol and thiophosphoryl chloride, followed by reduction and phosgenation. (19). This triisocyanate is sold under the trade name Desmodur RF (Bayer) as a glue for rubber adhesive solutions. 

One can easily observe the similarity between coatings and adhesives. Poly isocyanates used for adhesives should have high molecular weight and thus, low vapor pressure at the reaction temperature. Adducts such as Desmodur L, or crude MDI are often used, as are triisocyanates such as triphenyl methane-4,4, 4"-triisocyanate (a) or tris(p-isocyanatophenyl) ester of thiophosphoric acid (b) dissolved in methylene chloride or ethyl acetate ... 

Terpene phenolic resins, such as Schenectady s SP-560 or Occidental s Durez 12603, are also often used in Neoprene adhesives. They are nonreactive and thermoplastic in nature and so provide longer open tack time and a softer glue line than the f-butyl phenolics, but offer less hot cohesive strength. Terpene phenolic resins are often used in combination with a polyisocyanate curing agent, such as Bayer s Desmodur RF, in a two-part adhesive system to obtain better hot bond strength. 

In somewhat greater detail the varieties sold in small amounts as Polystal were tough, resistant combinations of a flexible alkyd such as Desmophen 1200 (IV) with an isocyanate such as Desmodur TH (V) and an auxiliary such as an amine or anything which would change the pH. Cures were immensely speeded by acid, alkali, or a little triethylam-ine. For a tough, cold-curing wood adhesive, to be used where vibration was bad, they proposed 40 parts of a 70% ethyl acetate solution of Desmophen 900 (VI) and 1(X) parts of a 75 % ethyl acetate solution of Desmodur TH ... 

Ex. 3. System (b), a two-part adhesive system, is exemplified in the following. One part of Polystal U-I [a 70% solution of Desmophen 900 (VI) in ethyl acetate] is mixed with 2—2.5 parts of Polystal UII [Desmodur HH (XI) in 75% ethyl acetate solution]. At room temper-... 

Dollhausen M (1988) Polyurethane adhesives based on Baycoll, DesmocoU and Desmodur. Technical report. Bayer AG, Leverkusen... 

Disperse items 1 2 by a Cowles mixer or bead mill. Uralac SN808 S2G3-50 (Ex DSM) is a saturated polyester resin specially designed for metal decorating and for cure by a benzoguanamine in the ratio 90/10 - 80/20 (solid/solid). In this example a ratio of 87/13 is used. To optimise flexibility, crosslinking with benzoguanamine, and also blocked isocyanate Desmodur BL 3175, are used to increase adhesion. Adhesion is fiuther enhanced by the use of an epoxy resin (Epikote 836 (Ex Shell)). 

Urethanes Urethane adhesion promoters are used widely to bond PVC to polyester, nylon, and other fabrics, including sized glass fiber. In multicoat operations, the additive is used only in the first coat. With, polyester fabric, the isocyanate component in urethane formation can be used alone. Solvent or plasticizer solutions of oligomerized toluene diisocyanate (TDl) are available under the trade names Vulcabond (Akzo Nobel), Vanchem HM-50 (Vanderbilt), Thanecure T9 (TSE Industries), and Desmodur (Bayer). For improved resistance of the bond to heat and moisture, products based on bisphenyl diisocyanate (MDl) are also used. These include Vanchem HM-4346 and Rubinate 9480 (Huntsman). These are typically used at 3-7 phr levels in plastisols for coating polyester fabric. The second or subsequent coats should contain titanium dioxide and UV light stabilizer for outdoor service. With translucent products, an aliphatic isocyanate such as Desmodur N-lOO or TMl META (Cytec) should be used. 

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