As electronic displays are becoming more commonplace in new automobiles, and as these displays are becoming ever larger, the problem of glare on the displays is an increasingly important issue.
Sunlight reflecting off the display can make it difficult or even impossible to read the information. The solution is to make the clear plastic part on the front of the display (usually polycarbonate or acrylic) have anti-glare properties. Up until recently a clear plastic part was coated with an coating containing small particles giving anti-glare properties. Indeed, this was the solution offered by HighLine Polycarbonate to a number of our customers.
Even though the anti-glare coating did achieve the aim of reducing glare from the surface of the display and had a number of other advantages, it is important to note that it was not a solution without problems. The aim of this post is to identify some of the advantages and disadvantages of anti-glare coatings for this application and discuss an alternative approach.
Advantages
The main advantage of an anti-glare coating is that by varying the amount of anti-glare additive in the coating, you can vary the level of anti-glare properties or “gloss” of the finished sheet. We offered anti-glare coated sheet with gloss levels of between 20% and 90%. By taking this approach you are able to produce a custom gloss level, which is optimized for the customer. Perversely, most manufacturers of anti-glare sheet choose to standardize gloss levels and only offer two or three gloss levels in their range – this standardization has the result of almost eliminating the main advantage of anti-glare coatings.
The next advantage is that the coating provides a barrier on the surface of the sheet that offers some protection against scratches and solvents damaging the sheet. Even though it is undeniable that there is some increased protection, it is minimal when the claim is examined in detail. The scratch protection offered by the coating offers little extra protection to real world damage when compared to uncoated product. This can be easily seen when car keys are thrown lightly at the coated surface (a not uncommon occurrence when car keys are no longer inserted into an ignition but rather stored near the center display). The coating, like the base polymer is easily scratched.
Also when the claim of protection against solvents is examined, the protection is not as great as implied. The coating looses protection in the area of any scratches and only the face of the sheet is protected. The edges of the sheet are not coated and so any solvents getting to the edge of the sheet would do damage.
Disadvantages
The main disadvantage of coatings is that it is very difficult to control the level of anti-glare or “gloss” properties from batch to batch, within a batch and over the surface of an individual sheet. To explain the above statement, we need to examine how the coating is applied.
The coating is usually applied in a flow coating process (other processes such as spray and dip coating can cause even greater variation). Flow coating involves hanging the sheet vertically and then flowing a coating solution down the sheet over the surface. Excess coating flows off the bottom edge of the sheet and is recycled for use on the next sheet. The sheet is then cured in an oven.
The problem is that the coating contains heavy anti-glare additives and these additives tend to flow towards the bottom of the sheet. This process makes the bottom of the sheet have much less gloss than the top of the sheet. This variation in gloss can be minimized by coating a smaller sheet; giving less distance between the top and bottom of the sheet. When we produced by this method we were able to reduce the difference in gloss between the top and bottom of the sheet to less than 7% by reducing the sheet size to 24” wide. Most coaters prefer to coat sheets of 48” and 72” wide to improve the economics; this size of sheet has even more significant variation in gloss. When automobile manufacturers are increasingly trying to reduce variations in gloss to 1-2%, coating becomes very problematic.
Also as the coating process moves from sheet to sheet, the solvent level in the coating can vary. This makes variation between sheets and between batches notoriously difficult to control
Another problem with anti-glare coatings is the cost. Coating is naturally an expensive process; when coupled with a low yield for trying to get a tight tolerance on the gloss levels, it can become very expensive. Coupled with other problems associated with coating such as delamination and dust particles in the coating (which become critical in this application), it is unsurprising that automobile manufactures are moving away from coatings for anti-glare displays.
Alternative approach
HighLine Polycarbonate has moved away from offering anti-glare coated product for automobile displays. We now offer an anti-glare texture on the surface of the sheet that is applied during the extrusion of the sheet. This texture has been specifically developed for display applications. It maintains clarity of the information displayed while significantly reducing glare.
The main advantage is that it eliminates variation in glare between the top and bottom of the sheets, between individual sheets in a batch and from batch to batch. The gloss level specification can be held to within 1%.
The greater control of the gloss level makes for a much more consistent product at a much lower cost than coating can achieve.
The sheet does loose some of the resistance to scratches and solvents, but as discussed earlier, these claims are really little more than marketing ploys and offer little real world protection.
The other issue is that at this time we are only able to offer one level of anti-glare that has been selected for this application. Coatings can offer a wide range of anti-glare levels in theory, but in practice, manufactures have avoided offering their customers this option.
HighLine Polycarbonate is able to offer samples of their anti-glare polycarbonate upon request.