Resistance scratch

In spite of the fact that scratch resistance is very important requirement only a limited number of credible studies have been done. This research is very difficult to conduct.Recently, image analysis was employed to overcome some of the technical difficulties associated with the interpretation of observations. In addition to the damage of the scratch itself, the surrounding areas show stress whitening which adds to the perceived damage. The use of plastics in the automotive industry, especially the wide use of polypropylene makes these studies very important in the development of high quality finished products. 

When inks are used which contain pigments as coloring materials, superior images are formed in comparison to dye-based inks (65). However, the images formed with pigment inks have the problem that they are inferior as the coloring materials may be scraped off when images are rubbed, i.e., they have an inferior scratch resistance. 

To eliminate such problems, it has been proposed to use a protective-layer transfer sheet. Also, ink types with film forming properties have been suggested to protect the images. 

However, the scratch resistance required for images displayed outdoors, such as posters or panels, is so much higher as to not be sufficient. Moreover, printed posters and advertisements are fairly large and it is common for them to be roUed up into a cylindrical shape when transported. 

A composition that contains a modified siloxane compoimd together with a polymer has been proposed as a better alternative to improve the scratch resistance. The siloxane is a poly(dimethyl siloxane) with poly(ethylene oxide) and poly(propylene oxide) end groups (65). 

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The constmction of the E-111 windshield shown in Eigure 8 replaced a glass—silicone laminate previously used. The all-plastic windshield has improved impact resistance so that it is birdproof to 250 m/s (33). In this instance, the scratch resistance of glass was waived to obtain the impact performance at the allowed weight. 

Vinyl-coated fabrics exhibit high density, extremely low water vapor and air permeabiUty, cold touch, poor flex endurance, and plasticizer migration. However, they have good scratch resistance and colorabiUty and are inexpensive. 

Floor poHshes typically are evaluated for gloss, appHcation and leveling properties, discoloration, sHp resistance, scratch resistance, heel-mark resistance, scuff resistance, damp-mopping and detergent resistance, repairabiHty, lack of sediment, and removabiHty (3). RecoatabiHty and formula stabiHty are also important. A review of test methods is available (35). More than 20 ASTM test methods for floor poHshes exist. From the standpoint of product safety, sHp resistance is a particularly important variable and many test methods are available (39). 

Scratch resistance of polymer from DADC is improved by novel mixtures of peroxide initiators such as 5% isopropyl percarbonate with 3.5% benzoyl peroxide (16). In order to force completion of polymerization and attain the best scratch resistance in lenses, uv radiation is appHed (17). Eyeglass lenses can be made by prepolymerization in molds followed by removal for final thermal cross-linking (18). 

DiaHyl esters find Htde appHcation in lenses. However, DAP and DAIP can be polymerized by high energy radiation in lens molds (74). Coatings of sihca and alumina by vaporization give antiglare, scratch-resistant lenses. 

Decorative. Titanium nitride has a golden color and is used extensively to coat steel and cemented carbide substrates for watch cases, watch bands, eyeglass frames, etc. It provides exceUent scratch resistance as weU as the desired aesthetic appearance, and it replaces gold coatings used previously. 

The resulting films are usually hard and scratch-resistant but often show considerable stress (152). Such films can be used as corrosion-resistant coatings on metals or as membranes in gas sensor devices (153,154)... 

Hard lenses can be defined as plastic lenses that contain no water, have moduli in excess of 5 MPa (500 g/mm ), and have T well above the temperature of the ocular environment. Poly(methyl methacrylate) (PMMA) has excellent optical and mechanical properties and scratch resistance and was the first and only plastic used as a hard lens material before higher oxygen-permeable materials were developed. PMMA lenses also show excellent wetting in the ocular environment even though they are hydrophobic, eg, the contact angle is 66°. 

Surface modification of a contact lens can be grouped into physical and chemical types of treatment. Physical treatments include plasma treatments with water vapor (siUcone lens) and oxygen (176) and plasma polymerization for which the material surface is exposed to the plasma in the presence of a reactive monomer (177). Surfaces are also altered with exposure to uv radiation (178) or bombardment with oxides of nitrogen (179). Ion implantation (qv) of RGP plastics (180) can greatiy increase the surface hardness and hence the scratch resistance without seriously affecting the transmission of light. 

Abrasion Resistance. Porcelain enamel is the most scratch resistant and hardest of commercial coatings (see Hardness). This property is used to distinguish between porcelain enamel and organic enamel or painted coatings. The rate of abrasive wear in surface abrasion increases with time, and the subsurface abrasion which follows exhibits a higher, but constant rate of wear. Abrasion resistance can be evaluated by loss of gloss or weight (35). 

A more recent development of interest with this material is that scratch-resistant coatings may be stoved on at temperatures not feasible with conventional bisphenol A polycarbonates to give products with a scratch resistance comparable to glass. 

Compared with the phenolic resins they have a better colour range, track resistance and scratch resistance. They have a similar order of heat resistance, although their dimensional stability when exposed to hot dry conditions is not so... 

Decorative laminates have achieved remarkable success because of their heat resistance, scratch resistance and solvent resistance. Their availability in a wide range of colours has led to their well-known applications in table tops and as a wall-cladding in public buildings and public transport vehicles. 

The heat resistance and water resistance of the resins are attractive properties for surface coatings but the poor scratch resistance of the materials has limited applications of straight silicone resins. 

Surface hardness Low - scratches easily Much higher. Scratch resistant. 

Aminoplastics In this group, melamine-formaldehyde resins with their good heat resistance, scratch resistance and stain resistance, are usually preferred to urea-formaldehyde resins where chemical resistance is important. Unlike the phenolics these materials are not restricted to dark colours. 

Polyimides having the structure shown are used as coatings on glass and plastics to improve scratch resistance. How would you synthesize n poJvimide (See Problem 21.53.)... 

Plastic s main disadvantages are its lower scratch resistance and, in some systems, comparative intolerance to severe temperature fluctuations. Even if plastic does have less temperature tolerance than glass, most optical systems do not operate in ambient temperatures beyond the thermal limits of plastics or the human body. 

Allyl diglycol carbonate (CR-39) is the most highly scratch resistant of the transparent plastics. Unlike most of the other transparent plastics that are TP, CR-39 is a TS plastic that has been in use for over a half century in applications such as bullet-proof shields, high temperature steel blast furnace eye and face guards, aircraft window side panels, etc. Processing methods include injection molding and casting. 

Hardness is closely related to strength, stiffness, scratch resistance, wear resistance, and brittleness. The opposite characteristic, softness, is associated with ductility. There are different kinds of hardness that measure a number of different properties (Fig. 5-5). The usual hardness tests are listed in three categories (a) to measure the resistance of a material to indentation by an indentor some measure indentation with the load applied, some the residual indentation after it is removed, such as tests using Brinell hardness,... 

Vickers and Knoop indentors, Barcol hardness, and Shore durometers (2) (b) to measure the resistance of a material to scratching by another material or by a sharp point, such as the Bierbaum hardness or scratch-resistance test and the Moh one for hardness and (c) to measure rebound efficiency or resilience, such as the various Rockwell hardness tests. The various tests provide different behavior characteristics for plastics, as described by different ASTM standards such as D 785. The ASTM and other sources provide different degrees of comparison for some of these tests. 

Mohs hardness It is a measure of the scratch resistance of a material. The higher the number, the greater scratch resistance with number 10 being termed diamond. 

Scratch Resistance Acrylic Allyl diglycol carbonate (C-39)... 

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. 

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