Coatings craze resistant

Isophthalic acid (m.p. 347°C), made by oxidation of /w-xylene, has also been introduced for resins. The resins have higher heat distortion temperatures and flexural moduli and better craze resistance. They are also useful in the preparation of resilient gel coats. 

EP 323142 (European) 1989 Ternary polyether ketone blend wire insulations Pirelli General PLC, UK CK Alesbury, RJ Murphy Formulation shows excellent stress craze resistance, flexibility and flame resistance Blends of polyarylene ether ketones, polyether imides and polyfimide siloxanes) were coated onto wire for solvent resistance, O index and abrasion resistance. Blends without siloxane-imide copolymer did not meet these properties... 

Surface modification Adhesive improvement, protective coating, abrasion-resistant coating anti-crazing scratching... 

Formations with enhanced resistance to craze formation have been described. Increasing the molecular weight has little influence on suppressing varnish-induced crazing in PAI Aims. However, craze resistance is associated with curing and crosslinking. The ratio of imide to amide and the surface tension of the film coatings influence the tendency to craze formation. 

In general, polycarbonate resins have fair chemical resistance to aqueous solutions of acids or bases, as well as to fats and oils. Chemical attack by amines or ammonium hydroxide occurs, however, and aUphatic and aromatic hydrocarbons promote crazing of stressed molded samples. Eor these reasons, care must be exercised in the choice of solvents for painting and coating operations. Eor sheet appHcations, polycarbonate is commonly coated with a sihcone—sihcate hardcoat which provides abrasion resistance as well as increased solvent resistance. Coated films are also available. 

Provided due care is taken with respect to predrying and to crazing tendencies, polycarbonates may also be thermoformed, used for fluidised bed coating and machined and cemented. Like metals, but unlike most thermoplastics, polycarbonates may be cold formed by punching and cold rolling. Cold rolling can in fact improve the impact resistance of the resin. 

Bituminous This term is used for products obtained from both petroleum and coal tar sources but the petroleum products are the more widely used. These materials are very resistant to moisture and tolerant to poor surface preparation. They are only available as black, dark brown or aluminum pigmented. The last has reasonable outdoor durability but, without the aluminum, the film will crack and craze under the influence of sunlight. Normally they cannot be over-coated with any other type of paint, because not only will harder materials used for over-coating tend to crack or craze but there is also a possibility that the bitumen will bleed through subsequent coats. The best use is as a cheap waterproofing for items buried or out of direct sunlight. 

When the dUuent has precipitated out into PB-2.76K pools for diluent concentrations v > Vg then much more concentrated plasticization is possible in the craze borders in the manner illustrated in Fig. 31. Now the free PB, coating the surfaces of the craze subject to deformation induced negative pressures can be sorbed into a fringing craze surface layer to a depth of od, where d is the craze tuft diameter. However, the tuft diameter is itself dependent on the local plastic resistance by a product expression that is a principal finding of the meniscus interface convolution model, and is usually given in terms of the craze flow stress in the form... 

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