Anti-scratch coating is a type of protective coating or film applied to an object's surface for mitigation against scratches. Scratches are small surface-level cuts left on a surface following interaction with a sharper object. Anti-scratch coatings provide scratch resistances by containing tiny microscopic materials with scratch-resistant properties. Scratch resistance materials come in the form of additives,

filters Filter, filtering or filters may refer to: Science and technology Computing * Filter (higher-order function), in functional programming * Filter (software), a computer program to process a data stream * Filter (video), a software component tha ...

, and

binders Ring binders (loose leaf binders, looseleaf binders, or sometimes called files in Britain) are large folders that contain file folders or hole punched papers. These binders come in various sizes and can accommodate an array of paper sizes. The ...

. Besides materials, scratch resistances is impacted by coating formation techniques. Scratch resistance is measured using the Scratch-hardness test. Commercially, anti-scratch coatings are used in the automotive, optical, photographic, and electronics industries, where resale and/or functionality is impaired by scratches. Anti-scratch coatings are of growing importance as traditional scratch resistance materials like metals and glass are replaced with low-scratch resistant plastics.

Applications

Automotive, Optical, and Electronics are major sectors of anti-scratch coatings.

Automotive

Anti-scratch coatings in the automotive industry maintain a car's appearance and prevent damage of a car's anti-corrosion layer. The anti-corrosion layer protects car metals from environmental harm. Automotive anti-scratch coatings are becoming stronger (from 10

newtons The newton (symbol: N) is the unit of force in the International System of Units (SI). It is defined as 1 kg⋅m/s, the force which gives a mass of 1 kilogram an acceleration of 1 metre per second per second. It is named after Isaac Newton in r ...

to 15 newtons of protection) to counter scratch resistance lost due to the industry shift from

steel Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistant ty ...

to lightweight, but low-scratch resistant plastics and aluminium. Currently, scratch-formation is decreased with a primer and clear coat. The primer is made of

polyolefin A polyolefin is a type of polymer with the general formula (CH2CHR)n where R is an alkyl group. They are usually derived from a small set of simple olefins (alkenes). Dominant in a commercial sense are polyethylene and polypropylene. More speciali ...

-resin, while the clear coat contains the additives siloxane and erucamide.

Optical

Scratch-resistant coatings are added to glasses due to scratches' extreme ability to impact a wearer's vision. Even when optical glasses are made of high scratch-resistances glass,

polycarbonate Polycarbonates (PC) are a group of thermoplastic polymers containing carbonate groups in their chemical structures. Polycarbonates used in engineering are strong, tough materials, and some grades are optically transparent. They are easily work ...

, or

CR-39 Poly(allyl diglycol carbonate) (PADC) is a plastic commonly used in the manufacture of eyeglass lenses alongside the material PMMA (polymethyl methacrylate). The monomer is allyl diglycol carbonate (ADC). The term CR-39 technically refers to the ...

, coatings are still used. Optical coatings include

diamond-like carbon Diamond-like carbon (DLC) is a class of amorphous carbon material that displays some of the typical properties of diamond. DLC is usually applied as coatings to other materials that could benefit from such properties. DLC exists in seven diffe ...

(DLC) and anti-reflective-scratch hybrid coatings. Diamond-like Carbon is a coating that shares diamonds' extreme scratch resistance. Anti-reflective Scratch hybrid coatings contain scratch-resistant additives with

anti-reflective coating An antireflective, antiglare or anti-reflection (AR) coating is a type of optical coating applied to the surface of lenses, other optical elements, and photovoltaic cells to reduce reflection. In typical imaging systems, this improves the effic ...

materials.

Electronics

In the electronics industry, scratches-resistances coatings are applied to electronic screens to prevent primary fingernails scratches. Screens are made of either

(the highest Scratch-resistant plastic) or higher-end glass. Electronics Industry Anti-Scratch coatings often contain the anti-scratch additives siloxane, and the anti-Scratch filters TiO₂ (titanium dioxide) and SiO2 (silicon dioxide). The additives and Filters are combined with a Fluorocarbons resin. Fluorocarbon resin is an oleophobic material. Oleophobic materials are materials that repeal oils caused by fingerprints.

Other uses

Anti-scratch coatings are often used on plastic products wherever optical clarity, weathering, and chemical resistance are required. Examples include optical discs, displays, injection-molded parts, gauges and other instruments, mirrors, signs, eye safety/protective goggles, and cosmetic packaging. These coatings are usually water-based or solvent-based.

Anti-scratch coating compositions

Scratch-resistant materials are present in anti-Starch coating either as binders, additives, and/or

. Binder, additives, filters make up Anti-Scratch coating's Thin-film, a thin nano-meter to micro-meter layer applied to a substrate (an object's surface).

Binders

In anti-scratch coatings, binders (coatings' glue-like cohesive structure) provide scratch resistance or/and provide structure for scratch resistant additives and filters. Binders that offer scratch resistances and structure include: * Ceramic-(Inorganic-non metal-based) binders *

Polysilazane Polysilazanes are polymers in which silicon and nitrogen atoms alternate to form the basic backbone. Since each silicon atom is bound to two separate nitrogen atoms and each nitrogen atom to two silicon atoms, both chains and rings of the formula ...

s *

Diamond-like Carbon Diamond-like carbon (DLC) is a class of amorphous carbon material that displays some of the typical properties of diamond. DLC is usually applied as coatings to other materials that could benefit from such properties. DLC exists in seven diffe ...

* Resin (organic polymer-based) binders *

epoxy Epoxy is the family of basic components or cured end products of epoxy resins. Epoxy resins, also known as polyepoxides, are a class of reactive prepolymers and polymers which contain epoxide groups. The epoxide functional group is also coll ...

* polyethylene https://pdhonline.com/courses/m223/EM%201110-2-3400_Chapter4.pdf

Fillers

Scratch-resistant coatings use special Scratch-resistant fillers.

Fillers In processed animal foods, a filler is an ingredient added to provide dietary fiber, bulk or some other non-nutritive purpose. Products like corncobs, feathers, soy, cottonseed hulls, peanut hulls, citrus pulp, screening, weeds, straw, and cere ...

are particles that enhance specific functional properties of coatings with/or with binders. Common Scratch-resistant fillers include: - titanium dioxide(TiO₂) - zirconium dioxide( ZrO₂) - Aluminum oxide hydroxide(AlOOH) - Silicon monoxide(SiO)

Additives

Anti-scratch coatings use additives with specific Scratch-resistant properties. Additives are particles dispersed in a thin film in quantities of less than one percent. Additives that decrease scratch visibility include: * Siloxane * Eruamides (A type of fatty acid used in coatings due to fatty acid amide's scratch-resistant properties) Additives that lower friction, an important part of Scratch resistance, include: * MoS₂, * graphite. *

oleic acid amide Oleamide is an organic compound with the formula CH3(CH2)7CH=CH(CH2)7CONH2(. It is the amide derived from the fatty acid oleic acid. It is a colorless waxy solid and occurs in nature. Sometimes labeled as a fatty acid primary amide (FAPA), it is ...

Additives that control for micro-cracking, a micro-sized step in Scratch formation, include: * ZnO (Zinc oxide) * BaO (Barium oxide) *

PbO Lead(II) oxide, also called lead monoxide, is the inorganic compound with the molecular formula Pb O. PbO occurs in two polymorphs: litharge having a tetragonal crystal structure, and massicot having an orthorhombic crystal structure. Modern ap ...

( lead dioxide)

Theory

Anti-scratch coatings change the substrate's Tribological (Properties resulting from surface-environment interaction) and

Mechanical Mechanical may refer to: Machine * Machine (mechanical), a system of mechanisms that shape the actuator input to achieve a specific application of output forces and movement * Mechanical calculator, a device used to perform the basic operations of ...

(a material's physical properties) properties. Changed Tribological and Mechanical properties impact Scratch's

deformation Mechanisms A deformation mechanism, in geology, is a process occurring at a microscopic scale that is responsible for changes in a material's internal structure, shape and volume. The process involves planar discontinuity and/or displacement of atoms from th ...

(microscopic effects of deforming a material), Scratch visibility, friction, and other additional considerations.

Impact on deformation Mechanisms

Scratch-resistant coatings lessen the impacts of scratches three primary

deformation mechanism A deformation mechanism, in geology, is a process occurring at a microscopic scale that is responsible for changes in a material's internal structure, shape and volume. The process involves planar discontinuity and/or displacement of atoms from th ...

s: Ironing, micro-cracking, and plowing.

Plowing

The dislocation of atoms into weaker Atomic planes due to Plowing's plastic deformations. Plowing is when an indenture breaks a material's surface and leaves scratch marks. Anti-Scratch coatings contain filter-based materials with high ductility (ability to withstand plastic deformations) to limit plowing. Plastic deformations occur when the

atomic bonds A chemical bond is a lasting attraction between atoms or ions that enables the formation of Molecule, molecules and crystals. The bond may result from the Coulomb's law, electrostatic force between oppositely charged ions as in Ionic bonding, ...

holding atomic planes break, causing the planes to dislocate into weaker positions. Control for plowing is important as every additional plowing event leaves a scratch and greater risk for internal damage, which will decrease products lifespan.

Micro cracking

Micro-cracking is micro-sized cracks that form on brittle surfaces due to the jerking indentor movement known as

stick-slip The stick–slip phenomenon, also known as the slip–stick phenomenon or simply stick–slip, is the spontaneous jerking motion that can occur while two objects are sliding over each other. Cause Below is a simple, heuristic description of stick ...

. Anti-scratch coatings control for Micro-cracking by containing either filters, binders, or additives with high tensile strength. Recently, anti-scratch research is focusing on nano-cracking, the nanotribical version of microcracking by creating nano-specific additives.

Ironing

Anti-scratch coatings control scratch ironing by either prolonging or preventing elastic deformations. Elastic deformations are non-permanent stretching of

occurring before plastic deformation. Anti-scratch coatings control elastic deformations, which causes a short-term grooving effect, by decreasing

elasticity Elasticity often refers to: *Elasticity (physics), continuum mechanics of bodies that deform reversibly under stress Elasticity may also refer to: Information technology * Elasticity (data store), the flexibility of the data model and the cl ...

and increasing ductility. Decreasing elasticity, however, must be balanced since low elasticity causes micro-cracking. Scratch resistance can also be increased by prolonging the ironing period with yield point materials. Yield point is the point a materials change from elastic to plastic deformations. Higher yield point materials decrease permeant plowing, by increasing non-permeant ironing.

Friction

Scratch resistance coatings contain low friction, the sliding resistance force, surfaces. Low friction surfaces are smooth. Smooth surfaces are important since rougher surfaces are scratches prone: as shown by the Archard Wear Equation. Archard equation: W: volume of Wear created during a scratch event. S: The distance during which both objects were in contact with each other. N: normal force or amount of pressure applied by the indenting object. H: Hardness of the material, measured by a given

coefficient In mathematics, a coefficient is a multiplicative factor in some term of a polynomial, a series, or an expression; it is usually a number, but may be any expression (including variables such as , and ). When the coefficients are themselves var ...

. K: The Archard Wear dimensionless constant value of 1x10⁸.

Considerations for plastics

Scratch-resistant coatings applied to substrates control for Plastic low-Scratch-Hardness by being coated with non-plastic materials. Plastics contain low- Scratch-Hardness due to plastic's high viscoelasticity (highly viscous and elastic deformations) and low

crystallinity Crystallinity refers to the degree of structural order in a solid. In a crystal, the atoms or molecules are arranged in a regular, periodic manner. The degree of crystallinity has a big influence on hardness, density, Transparency and translucen ...

(High ordered Structure).

Decreasing scratch visibility

Surface topology map showing waviness and lay

Scratch visibility is impacted by surface grooving. Grooving surrounding a scratch site changes the

angle of reflection Reflection is the change in direction of a wavefront at an interface between two different media so that the wavefront returns into the medium from which it originated. Common examples include the reflection of light, sound and water waves. The ' ...

(direction of light causing waves). When the angle of reflection is greater than 3 percent, scratch's become visible. Anti-scratch coatings control scratch visibility by having a low grooving surface. Besides friction, low grooving surfaces depend on the topology (surface) factors of surface texture (

lay Lay may refer to: Places *Lay Range, a subrange of mountains in British Columbia, Canada *Lay, Loire, a French commune *Lay (river), France *Lay, Iran, a village *Lay, Kansas, United States, an unincorporated community People * Lay (surname) * ...

) and spacing of irregularities (

waviness Waviness is the measurement of the more widely spaced component of surface texture. It is a broader view of roughness because it is more strictly defined as "the irregularities whose spacing is greater than the roughness sampling length". It can ...

). Topology is controlled by extreme precision during the coating formation process.

Coating formation

Main section coating formation Coating formation is the process of coating-substrate adhesion(attachment). Anti-scratch coatings are generally applied via spray (hand or automated), dip, spin, roll or flow coating. Coating Formation uses "Precision factor" to affect topology-dependent Scratch properties. "Precision factors" include additive concentration, coating thickness, and Viscosity. Most coating types can be cleaned with a non-ammonia based glass cleaner and a soft cloth.

Testing of Scratch Resistance

ASTM International, American Society for Testing and Materials, set material testing standards for materials, including Anti-scratch coatings. Most scratch-resistant coatings fall under ASTM standard D7027 - 20 (See External Links). Standard scratch resistance tests involve scratching coatings with a diamond indentor.

References

External links

* {{cite web, url=https://www.astm.org/Standards/D7027.htm , title=Standards for Anti-Scratch Coating , publisher=American Society for Testing and Materials Thin-film optics