Abrasion and Mar Resistance

In this test for transparent plastics, the loss of optical effects is measured when a specimen is exposed to the action of a special abrading wheel. In one type of test the amount of material lost by a specimen is determined when the specimen is exposed to falling abrasive particles or to the action of an abrasive belt. In another test, the loss of gloss due to the dropping of loose abrasive on the specimen is measured. The results produced by the different tests may be of value for research and development work when it is desired to improve a material with respect to one of the test methods. The variables that enter into tests of this type are 

Styrene acrylonitrile Styrene butadiene Styrene maleic anhydride Styrene methyl methacrylate Thermoplastic urethane, rigid 

Excellent thermal stability, resists creep, inherent high color Excellent processibility, poor UV resistance, brittle Excellent thermal/hydrolytic stability, poor weatherability/ impact strength 

Excellent chemical resistance/electrical properties, weatherable, decomposition evolves HC1 gas 

Good stress-crack and craze resistance, brittle Good processibility, no stress whitening Higher-heat styrenic, brittle 

---

Thermoplastic polyurethanes exhibit good abrasion and mar resistance. They are stable to attack by oxygen and hydrocarbons, but are sensitive to moisture and acidic and basic solutions, which can result in hydrolytic chain scission. They are used as coatings and adhesives and in footwear and automotive parts. 

Features Lighttast extreme toughness, abrasion and mar resist. exc. water/chem. resist. unusually high m.p. can be crosslinked to enhance performance... 

Non-scratch inks Inks, which have high abrasion and mar-resistance when dry. 

Abrasion and Mar Resistance. Abrasion is the wearing away of a surface marring is a disturbance of a surface that alters its appearance (see Weak). A study of the mechanical properties of a series of floor coatings with known wear life concluded that work-to-break values best represented the relative wear lives... 

Currently, these tests are of no practical value to the designer and the only approach to the problem of scratch, mar, and abrasion resistance is to simulate actual performance needs. For optical purposes, a cast sheet in the allyl family of plastics known as CR39 has been used as a standard of comparison in evaluating scratch and mar resistance of a material. The CR39 is used for eye lenses and other optical products where the advantages of plastics are a consideration. Coatings have been developed for polycarbonate, acrylics, and other plastics that dramatically improve the scratch and mar resistance of these materials. 

Although hardness is a somewhat nebulous term, it can be defined in terms of the tensile modulus of elasticity. From a more practical side, it is usually characterized by a combination of three measurable parameters (1) scratch resistance (2) abrasion or mar resistance and (3) indentation under load. To measure scratch resistance or hardness, an approach is where a specimen is moved laterally under a loaded diamond point. The hardness value is expressed as the load divided by the width of the scratch. In other tests, especially in the paint industry, the surface is scratched with lead pencils of different hardnesses. The hardness of the surface is defined by the pencil hardness that first causes a visible scratch. Other tests include a sand-blast spray evaluation. 

For example, the abrasion-resistant coatings based on a silicone-silica hybrid (33) have provided a scratch- and mar-resistant finish for polycarbonate as well as metals. The chemistry involved is discussed by Vincent, Kimball and Boundy (3iL). The coating consists of polysiloxane and silane-modified submicron silica particles, microscopically dispersed in the solution. The coating is then cured at elevated temperatures. Currently, this type of abrasion resistant coating is marketed in the U.S. by Dow Corning and General Electric Company. 

Good impact resistance, abrasion resistance, mar resistance and chemical resistance are other key benefits. 

Scratch tests can also be viewed as a form of abrasion test, although they are often seen as a measure of hardness. They are not favored for hardness, probably because of poor reproducibility, and in the abrasion sense they are probably best considered as a measure of mar resistance, but even here they find little application. 

Mention has already been made in Section 1 to the use of Moh s scale and peneil hardness, which are somewhat more concerned with mar resistance than they are with hardness as such, although harder materials tend to give better abrasion resistance, generally speaking. 

Scratch hardness is particularly important in plastics used for their optical properties and is usually determined by some of mar-resistance test. In one type of test a specimen is subjected to an abrasive treatment by allowing exposure to a controlled stream of abrasive, and its gloss (specular reflection) is measured before and after the treatment. In some tests the light transmission property of the plastic is measured before and after marring. 

Chem. Descrip. Silicone glycol copolymer in toluene Uses Mar resist, aid, slip agent, rub resist, aid, abrasion resist, aid in org. resin inks, paints/coatings, water-based, solv.-based, and high-solids formulations... 

Uses Texturizer, mar resist, aid, abrasion resist, aid, matting agent tor decorative and protective coatings tor automotive and marine trim, office furniture, household appliances, electronic housings, powd. coat-... 

Chem. Descrip. PTFE disp. in wafer/glycol efher Uses Abrasion resisf. aid, mar resist aid for waferborne wood, UV, fwo-part urefhane, archifecfural, and air dried/baked coatings, and wafer-borne inks mold release agenf for plastics and rubber molds Properties Wh. vise, liq. Hegman +7 particle size 2-3 avg. particle size dens. 11.4 Ib/gal pH 6.5-7.5 VOC 0.75 Ib/gal 50% act solids Use Level 1-6%... 

Chem. Descrip. PTFE-modified polyethylene wax Uses Surf, modifier, slip agent, abrasion resist, aid, mar resist, aid for wood finishes, UV-cured coatings, can and coil coatings, powd. and industrial coatings based on acrylics, alkyds, PU, NC and blends, epoxies, polyesters, hybrid systems... 

Uses Surf, modifier, surf, protectant, scratch/abrasion/mar resist, aid, slip agent, matting agent for solvent-borne wood coatings and general industrial coatings... 

Chem. Descrip. 141° Paraffin emulsion CAS m2-lA-2 EINECS/ELINCS 232-315-6 Uses Lubricant, antiblocking agent, water resist, aid in nat. and syn. mbber, paints, coatings, and varnishes improves banier props., water repellency, MVTR props., rub/scuff/abrasion/mar resist, in latex coatings, printing inks, medical devices Features Usable pH 7+ low VOC Regular FDA compliance... 

---