GLASS FLAKES

Glass flakes are extremely thin glass plates with an average thickness of 5 ± 2 micrometers.

Manufacture
There are two main methods to manufacture glass flakes. 
The first is the "bubble method", where a glass marble is turned into liquid and then blown into a bubble. 
Glass Flakes is then smashed into glass flakes and sieved by particle-size distribution. 
The second method is the "centrifuge method", in which high-temperature liquid glass in a rotating tub creates glass flakes due to the centrifugal force.

Application
Glass flakes can be applied in anti-corrosive coatings, paints and pigments to prevent corrosion.
Glass flakes can also be used as a reinforcement material in the manufacture of composite materials.

Glassflakes or Glass Flakes particles form dense, inert barriers within the paint film. Overlapping layers of glass resist water and chemicals permeating the paint film. 
The addition of glass also increases the flexibility, hardness and abrasion resistance of coatings.

Classification
The Glass Flakes could be classified by the particle-size distribution of diameter

Surface treatment
Glass flakes may be surface treated by silane coupline agents for better coupling with resin which is a main material of anti-corrosion coating. 
Silane coupline agents include KH-570, KH-560, KH-550, A-174, Z-603, KBM-503, GF-31. Glass flakes with surface treated include C-90E, C-150V and RCF-160T.

Glassflake is utilised in a diverse range of applications, giving improvements in areas such as barrier, reinforcement and thermal properties.

Glassflake Applications

Coatings
Glassflake offers a range of performance enhancements to the coating formulator, through the high aspect ratio of the individual platelets of glass. 
Glass Flakes has an extensive history of use in the coatings industry, this has expanded from traditional applications in heavy duty protective coatings to almost any commercial coating material, where there is a requirement for service longevity.

Thin platelets of Glass Flakes overlap within coating films, creating a lengthened 'tortuous' path for any permeation of moisture or destructive ions. 
This effect is used to provide a barrier to moisture in anti-corrosion coatings such as those used on offshore installations, through to providing an oxygen barrier in fire retardant systems.

The chemical resistance of ECR Glassflake offers excellent substrate protection in the harshest of conditions. 
This protection extends to physical attack, the hardness of the flake increases the resistance of the overall coating system to abrasion and wear.

PERFORMANCE ENHANCEMENTS IN COATINGS
Barrier protection from moisture permeation
Improved thermal stability
Abrasion and scratch resistance
Long term chemical resistance
Isotropic mechanical reinforcement
Improved fracture toughness
Enhanced undercutting resistance
Reduced cathodic disbondment

Glassflake is a platelet material, of high aspect ratio, controlled by manipulation of the thickness and diameter of individual flakes.
The Glassflake Group uses an innovative manufacturing process which has enabled accurate control of glass composition and the production of thinner flake (as low as 100nm) with uniform thickness and exceptional consistency. 
Flake is typically produced from 4 core glass formulations, though specific glass types can be formulated to accommodate customer requirements. 
The broad range of standard grades coupled with the capacity to manufacture tailored products allows our customers to improve both their products and processes.

Polymers
Glassflake provides reinforcement to a wide range of plastics, from commodity products such as food packaging, through to high performance plastics for the medical, electronics and automotive sectors. 
The morphology of the flake offers excellent isotropic reinforcement to a range of systems, due to its high surface area. 
The neutral mass colour tone, allows the flake to be used in a range of systems where aesthetics are key.

Glassflakes are high aspect ratio platelets that impart isotropic reinforcement in contrast to fibres which typically give anisotropic reinforcement. 
This isotropic reinforcement is evidenced under a number of test regimes, from warpage evaluations to heat deflection temperature values. 
This change to the composite behaviour under strain is due to the high surface area of the glassflake used, restricting the free movement of polymer chains over the surface of the flakes. 
As glass flakes are synthetic with a controlled composition they have very low impurities - as such they are suitable for inclusion in materials for food contact and medical and dental applications.

All glassflake is available with silane surface treatments or 'sizings' - these are especially important for use in plastics where this aids in both the manufacturing process and end application. 
Similarly to other glass and mineral fillers, organo-functional silanes are used, providing a silicon end to bind to the glass surface and organic functional group to interact with the surrounding polymer chains. 
The silane is readily bonded to the Glass Flakes surface aiding wet out, and facilitates dispersion in the polymer. 
The effect on physical properties will be determined by the degree of interaction between the silane, Glass Flakes and polymer. 
E glassflake is also available in an agglomerated form, using an epoxy resinous binder to facilitate easier processing and handling.

Pigments
Glassflake, commonly known as borosilicate, is used extensively as substrate in the production of effect pigments. 
The glassflake offers uniform thickness and are highly planar and smooth, as well as being completely transparent. 
When coated with metal oxides, they display colour purity, and high chroma.

Glassflake is produced to a range of nominal thicknesses and particle size diameters. 
Both the absolute thickness and deviation of thickness play an important role, as large variance can result in an inconsistent visual effect - by producing glassflake with a very narrow distribution of thicknesses, the overall thickness of the metal oxide coated flakes remains consistent, enhancing the pearlescent effect. 
Given the importance of consistency in glassflake thickness, this is measured by two methods, both SEM and spectroscopic analysis. 
Glasslake is offered in 3 nominal particle size distributions (nmilled, milled and micronised), each of which is measured by laser diffraction. In addition to these standard particle diameter distributions, we can work with customers to provide specified particle diameter distributions, to produce a 'Reactor Ready' grade, removing any requirements for excess customer processing.

Glassflake composition has a vital role to play in core areas such as: the harsh processing of coating with metal oxides, meeting strict regulatory requirements for the food and cosmetic markets; and maintaining surface chemistry suitable to accept metal or metal oxide coatings. 
Glassflake test the heavy metal content of glassflake both externally and internally by ICP-OES and ICP-MS, using complete dissolution by hydrofluoric acid with microwave assistance.

Using thinner glassflake platelets as substrate for metal oxide coatings offers particles of higher aspect ratio. 
Where thinner glassflake substrate is used, diameters can be reduced to produce pigments suitable for use in high gloss systems, with pearlescent effects at lower loading levels.

Specialist
Beyond core markets of coatings, plastics and effect pigments, the performance enhancing properties of glassflake are used by materials engineers in an ever widening range of applications. 
This expansion of glassflake applications can take one of two shapes, firstly in the use of existing glassflake technology in novel applications and secondly in the development of novel glassflake materials to solve challenging problems.

A key example of this is the reinforcing properties of glassflake used in the tyre manufacturing industry to prolong the lifespan and control rolling resistance of vehicle tyres. 
Glassflake is also used extensively across a number of flooring applications, from the more traditional liquid applied coatings, through to tiles of both laminate and carpet.

By example, the morphology of the flake can be tailored to meet specific requirements both in the thickness and particle size distribution. 
Where the flake is being used in a novel resin system, a tailored surface treatment can be applied to the glassflake surface to ensure improved glass-resin interaction. 
For specialist applications, the glass composition used to produce the flake can be altered, one example being a low melt temperature glass containing further fire retardant materials to improve fire scenario performance.

These thin glass flakes have a very high aspect ratio of flake width to thickness. 
They have a low deviation in thickness and particle size distribution.

Used for:
Glass flakes are used as an additive in anti-corrosion coatings in which they overlap each other within the coating matrix and form an effective diffusion barrier. 
The addition of glass flakes in coatings also improves abrasion resistance and dimensional stability. 
Glass Flakes filled coatings are used to protect industrial processing equipment, offshore structures, and steel buildings and bridges. 
The flakes are also used as a filler in plastics to increase stiffness and reduce shrinkage and warpage. 
Silver-coated flakes are used in pearlescent-effect pigments and in the cosmetics industries.

Details:
The flakes are available in different types of glass in thicknesses from 100 nanometers to 7 microns. 
There are different particle sizes to suit different application requirements.

Glass flake, first produced commercially around 60 years ago, has been used for a number of years to reduce gas and moisture vapor diffusion through coating films. 
However, advances in Glass Flakes production have allowed thinner and more consistent flakes to be produced, and this has led to investigative work into the properties that can be attained using Glass Flakes reinforcement.

Glass Flakes looks like microscopic pieces of broken window pane. 
The high aspect ratio of flakes, compared to fibers or granular fillers, imparts unique properties to materials to which they are added. 
Care has to be taken in choosing the addition level and size distribution to obtain the required result and for the optimization of a particular characteristic.

Originally glass flakes were produced with a mean thickness of around 8 microns, but Glassflake Ltd. pioneered a new production process in the early 80s allowing flakes to be produced at much lower thicknesses. 
These are now being produced from 7 microns down to an incredible 100 nanometers, with the bulk of flake used in the paint industry being from 7 to 3 microns.

Areas of interest where the addition of Glass Flakes can make significant improvements include: fire retardancy, moisture vapor or gas permeation reduction, mechanical reinforcement, viscosity and thixotropic changes, abrasion resistance, dimensional stability and UV light resistance. 
Improved properties can be achieved in most coating resins but Glass Flakes has been used predominantly in thermoset materials such as unsaturated polyesters and epoxies. 
Interestingly, the benefits also extend into materials such as polypropylene, PTFE, paper and cement. 
As always there are benefits and pitfalls in using glass flakes, and some of these, along with some areas of potential use, are presented here.

Properties Affected by Glass Flake
A variety of coating properties are affected by the addition of Glass Flakes to a formulation. These include:

 Vapor and gas permeation/diffusion;
 Chemical resistance;
 UV light resistance;
 Mechanical properties – tensile, compressive strength, flexural modulus, etc.;
 Abrasion resistance;
 Shrinkage – in mold (thermoplastics) on polymerization (thermosets);
 Dimensional stability e.g., creep resistance, warp and sag;
 Impact resistance;
 Dielectric strength and electrical resistivity;
 Fire resistance and smoke emissions, sag resistance in combustion;
 Heat distortion temperature;
 Chemical reaction.

Except for coatings for component parts, most coatings are based on organic resins. 
However, all organic coatings will, to some extent or another, convey or absorb moisture vapor and gases.
Preventing or resisting this is desirable to extend corrosion protection, and it is in this area that glass flakes initially found their niche.
They were later used to improve other areas of interest.

The benefits of using plate-like barrier pigments, such as mica and micaceous iron oxide, in anti-corrosive coatings to reduce moisture vapor transmission have been known for a substantial number of years. 
Other barrier pigments such as aluminum and zinc flakes have also been used as combination anodic and barrier fillers with varying degrees of success. 
Glass flakes have gained popularity for several reasons. 
They have a large aspect ratio and, unlike mica, are totally impervious to moisture vapor and are consistent in composition. 
Other barrier pigments commonly used are opaque and often strongly colored, micaceous iron oxide in particular makes coatings difficult to tint in light shades, while Glass Flakes is clear. 
In addition, Glass Flakes manufactured from ‘C’ or ECR glass is highly chemical resistant and inert in most environments, has good mechanical properties and is generally considered a simple dust hazard or non-hazardous, particularly when compared with small fibers and some other pigments.

Unfortunately the effects of using different concentrations of flake, flake aspect ratios, particle size distribution, and the unusual effects on viscosity and critical pigment volume concentration are rarely understood. 
There is also relatively poor understanding of how the glass bonds within the various resin matrices, and although Glass Flakes is impervious to moisture vapor and gas diffusion it does not present a continuous barrier in a resin matrix. 
The resin carrier, therefore, plays a very important role, i.e., Glass Flakes cannot make a poor resin film into an excellent coating, although it may substantially improve it. 
On the other hand, even excellent resins can benefit from the addition of flake. 
Flake also offers differing aspects to mechanical reinforcement and fire resistance than those attained by adding fiber or other fillers.

Important Considerations When Using Glass Flake
Many different types of coating resin are used with glass flakes, including polyesters, epoxies, chlor-rubbers, alkyds, coal tars, vinyls and water-based acrylics. 
Although the addition of flake will generally improve the moisture vapor transmission resistance of almost any coating film or membrane, there may be other benefits with new properties being imparted or old ones improved. 
The level at which the Glass Flakes should be added, the particle size distribution and adhesion to the carrier is of paramount importance.

Although glass flakes with aspect ratios as low as 10:1 will provide benefits, generally the higher the aspect ratio the better the barrier presented. 
This premise has to be tempered to some extent, however, as out-of-alignment, large-aspect-ratio flakes can afford a direct path through the film where the film is less thick than the nominal diameter of the flake, or cause stress raisers for crack propagation. 
In addition, there are some properties that may be adversely affected when using large flakes, such as flexibility and elongation-to-break. 
Glass Flakes is also important to consider the practicality of using large flakes; i.e., when a coating is sprayed, the gun tip size is limited by several factors and the flake will have to be small enough to pass through the spray tip. 
Glass Flakes is, therefore, common that flakes of around 250 µm and below are used for spray application, and flakes above this size (as large as 1,000 µm) are used for hand-applied materials. 
Large flakes also tend to produce rough surface finishes.

Flake size and thickness are only one of the issues involved in obtaining performance. 
The quantity of Glass Flakes added and particle distribution is also critical. 
Glass Flakes is obvious that if thin flakes of glass are used there are many more flakes for the same weight than if thick ones are used. 
Therefore, the surface area to be wetted with the thin flakes is vastly greater. 
This means that it is impossible to just simply state the requirement for an amount of flake. 
Glass Flakes may be possible to add 20% by weight of flake at a thickness of 5 µm and not exceed the critical pigment volume concentration to resin ratio (CPVC). 
But if the same quantity of flake at 2 µm thickness were added, the surface area of this flake would be at least two and a half times that of the thicker flake, and there may be insufficient resin for wet-out, thus exceeding the CPVC level. 
In any case, the viscosity increase may be so high when changing from thick flake to thin flake that addition at the same level becomes impossible. As with any formulation, minor modifications can render significant changes. 
This is especially so with glass flake, and it is necessary to carry out a full evaluation.

Glass Flakes is obvious from the preceding statements that once a thickness of flake has been chosen it is important to optimize particle size and addition level. 
That level will depend upon the type of resin being used and what other pigments or fillers are being used in conjunction with it.

Adhesion to the substrate plays a substantial role in the performance of organic materials in corrosion protection.
Equally important is the bonding of fillers into the resin to obtain performance both from a corrosion resistance point of view and in mechanical performance. 
Silanes have been used for many years in the glass fiber industry to improve bonding and performance. 
This improvement in performance is often seen both as an increase in some of the mechanical properties and a decrease in moisture vapor transmission. 
In thermoset resins it is possible to get substantial performance improvements simply by adding the silane chosen to the resin component either just before or just after the Glass Flakes is added. 
With thermoplastic materials, however, this is generally not possible, and the Glass Flakes has to be pre-treated with silane. 
Glass Flakes is noticeable that pre-treated flake will often improve the bonding performance not only in thermoplastics but also in thermosets and to a higher level than that achievable by adding the silane indirectly via the resin.

Where the silane is added to the resin, it is normal to observe that there is a critical level, and the optimization peak is often very steep. 
This is true for each particular resin, glass thickness, particle distribution and addition level. 
Glass Flakes should also be noted that other fillers or additives, such as thixotropic agents, will affect the optimization level. 
When the silane is added by pre-treating the glass, the level of silane used is not so critical, provided that saturation of the flake causing agglomeration is not achieved. 
Glass Flakes is also observed that with pre-treated glass a much higher level of Glass Flakes can be added to the resin (in particular to the thermosets) without exceeding the CPVC level. 
One disadvantage of using pre-treated flake however, is the cost and change in safety hazard classification of the flake.

With modern production methods, Glass Flakes can be produced at a consistent thickness, which may be varied for different purposes from around 10 µm thickness to as low as 100 nanometres, and almost limitless particle size distributions are possible.
 The effects of thickness, particle size, volume concentration etc., were not well understood until a substantial amount of work was carried out by Glassflake’s sister company Corrocoat, which initially evaluated Glass Flakes coating formulations using flakes of differing thickness and diameters and with differing particle distributions. 
Some of the results were surprising and others were expected, and because testing was carried out over a wide range of properties and not just diffusion and corrosion resistance, some interesting parameters were discovered. 
Of particular interest was the amount of fire resistance provided in some materials when using glass flake, including the reduction in smoke emission, shrinkage rate, heat distortion and creep. 
These results led to work on non-coating applications and engineering thermoplastics. An example of some of the coating work is shown in the following section.

Varying Flake Concentration
Tests were carried out to evaluate the change in moisture vapor transmission afforded by varying the flake concentration. 
A vinyl ester resin was used as the carrier resin, with the only difference in the materials tested being the addition level of glass flake.
Tests were conducted initially to zero in on the area of criticality, then levels of 14%, 15% and 16% were used to carry out the main evaluation.

The quantity versus permeation curve is very steep, with a 1% change in the addition level changing the permeation rate from 10.61 to 3.46. 
A further addition of glass changes the permeation rate for the worse but only marginally with further additions, showing a progressive worsening as the CPVC level is approached and exceeded.

Cathodic disbondment testing is a short, (28 days), but very effective test that evaluates electrical resistivity, moisture content, adhesion to the substrate and alkali resistance. 
Each of the four aspects, if adverse, will affect the end result. Variations in glass loadings were evaluated in the same resin matrix as those above, and the results shown in.

The results, as expected, show a similar pattern to that of the moisture vapor transmission tests, except that in this instance the 16% result is nearly as bad as the one at the 14% level.

Recent tests show the Glass Flakes has given excellent permeation resistance against H2S and methane to a vinyl ester-based pipeline coating being a magnitude better than HDPE.

Flake Aspect Ratio on Performance
Tests were carried out to evaluate the mechanical performance of a glass flake-filled polyester system with flake thickness nominally 3 µm and two different aspect ratios. 
The loading was 15% by weight in each case. 
Although expected, it is interesting to note the substantial reduction in shrinkage found when using the larger flake, the significant difference in compressive strength and elongation-to-break.
These effects were caused simply by changing the aspect ratio of the flake.

Bonding Agent Level
In order to evaluate bonding agent addition levels and the criticality, a standard vinyl ester Glass Flakes formulation was used with the level of silane bonding agent varied.
Tests were then carried out to evaluate the performance of each cured sample.

Tthe addition level of 0.6% silane improves the performance of the coating considerably. 
However, some of the test work shows initially worse results with silane addition over no addition until the level was further increased.

Effects of Mixing Time
One of the areas that greatly affects the performance of the Glass Flakes within the carrier is the mixing time. 
Mixing time affects both wet-out and distribution of the flake, having significant impact upon not only MVT rate but also the mechanical properties of the resultant coating. Tests were carried out to evaluate the parameters using different grades of flake. 
Compounding of the Glass Flakes into the resin was done using a Z-blade mixer. The mixture was then molded into a plaque using a steel compression mold with 33% by weight of glass incorporated into the resin.

The smaller-diameter flake B/1 required a longer mixing time than the other flakes with larger aspect ratios. 
Microscopy shows that samples contained poorly dispersed flakes after 45 min mixing but even distribution of the flakes after 60 min, and subsequent micrographs taken of specimens that had been mixed for 75 and 90 min show breakdown of the flakes occurring. 
Optimum mechanical results are seen from specimens that have been mixed for 60 min with Glass Flakes A/1 and A/2 and 75 minutes for the B/1. 
Overall, the higher the flakes’ apparent volume content in the specimen, the better the mechanical properties that specimen provides, given that satisfactory mixing is achieved.

A/2 has the best mechanical properties, probably due to the formulation having the greatest surface area for weight of Glass Flakes added, there being more reinforcement of the resin, resulting in a higher flexural modulus etc. 
The tensile strength for all three flakes is lower than the flexural strength. 
Impact flexural strength for A/2 is almost double the value for A/1 and B/1 values. 
This would correlate with A/2 glass being half the thickness of A/1 and B/1, i.e., there are twice as many flakes in this specimen than in the others.

Conclusion
There are many aspects to formulating coatings, but as can be seen, glass flakes can offer significant performance improvements in a number of ways and in a wide variety of materials, including elastomeric compounds. 
Glass flakes can be used in conjunction with other fillers and additives, and are compatible with a number of adhesion promoters or coupling agents, such as amino, vinyl and epoxy functional silanes, to enhance bonding.

Despite these advantages, careful consideration needs to be given to how much and which type of Glass Flakes and coupling agent should be used. 

What Does Glass Flakes Coating Mean?
A Glass Flakes coating is any coating material that is applied to a base material in order to prevent corrosion that has the addition of very small, thin pieces of glass. 
A Glass Flakes coating can be very thin with thicknesses ranging from 8 microns to less than 1 micron. This type of coating can have superior resistance to gas and liquid permeation.

Corrosionpedia Explains Glass Flakes Coating
Glass Flakes coatings are any type of coating that has glass flakes mixed into it. 
The glass flakes are very fine shards of glass. They have a high aspect ratio, meaning that they are much longer and wider than they are thick. 
This allows for the stacking of several layers of glass flakes while still maintaining a thin overall coating measuring less than 10 micrometers.

The glass flakes are inert and transparent, allowing them to have little interference with the rest of the coating material.
The actual type of glass that is used depends on the application, as each types of glass has its own set of benefits.

A Glass Flakes coating can have many advantages over other types of coatings. 
Because there are so many tightly overlapping glass flakes in the coating, its ability to resist the permeation of gases and liquids is quite high relative to other types of coatings such as organic resin coatings. 
Another advantage of Glass Flakes coatings are their ability to resist chemical attack because glass is not reactive to many types of aggressive chemicals. 
Glass flakes can also be used to improve the mechanical properties of a coating, such as increasing the hardness and imparting some fire resistance.

Glass Flakes is a discreet, thin plate- like particle. The production process start with a molten glass batch. After mechanical attenuation, the sheet form is further modified by milling to provide a wide range of particle sizes.
Glass flakes are normally 2 micron thick and plane length can be from a few microns up to the size of milling screen.
Glass flakes filled coatings have the following benefits when used in corrosion protection:
1) Low permeability for improved corrosion resistance
2) Ease of application even on complex surface - coatings may be sprayed or hand applied
3) Impact resistance
4) Ease of repair if damaged
5) High colour strength throughout the coating
6) Proven durability
7) High dielectric strength
8) Dimension stability over a broad range of temperature
9) Wide choice of resin matrices to select from to meet the temperature, chemical or mechanical requirements of application.
Application of Glass Flakes filled coatings

Chemicals Processing/Industries Markets

Storage tanks containing chlorine dioxide ( CIO2)
The internal of the tank was coated with a 760µ thick glass flakes compound, and has been in service for several years with no sign of deterioration.

Salt solution ( Nacl) storage tanks coated with Glass Flakes compound operating at more than 80ºC has be operating for many years with no problem

Gypsum Thickener tank with an 18m diameter was coated with Glass Flakes compound and the installation is still servicing well at room temperature.

Glass flaked filled Bisphenol- A resin exposed to process sugar. The installation has been in service for at least 5 years.

Marine Services

Glass Flakes filled coatings are used in bottom coating for ship and barges.
A 37,000 ton dead weight tanker was sand blasted and coated with Glass Flakes filled coatings.
After the coating the roughness was of the bottom was reduce from 736 micron to 254 micron.
This smoother surface account for the reduction in shaft horsepower required to maintain a speed of 15 knots.