Most bullet resistant laminates are constructed from three types of material. The first material is something that absorbs the energy of the projectile. For low calibre defense, this material can be cell cast acrylic (usually 1.25" or more thick), for higher calibre and military applications it is more usually glass. When the glass breaks it absorbs the energy of the projectile. Often the strike face uses hardened glass to break up the projectile before it hits secondary layers of glass. The second type of material is usually a polycarbonate or similar to act as a spall shield. The spall shield is used to prevent fragments of glass injuring personnel behind the transparent armor - it really doesn't matter if you are hit by the projectile or the glass, they can both injure or kill. Polycarbonate works because it is virtually unbreakable and flexible (unlike acrylic) and therefore retains the fragments. For VIP and diplomatic protection cars the spall shield layer is usually 3mm or 1/8" thick. For military applications we have supplied 6mm and even 9mm polycarbonate. The type of Polycarbonate is also critical, most commodity Polycarbonate performs extremely poorly. There is a viewpoint that two 3mm layers actually act as a better spall shield than one 6mm layer. The third type of material in the laminate is in effect an adhesive between the glass and polycarbonate, or the glass and glass layers. Materials such as TPU are used for this adhesive. The TPU also is used to protect the laminate from the different expansion rates of Polycarbonate and Glass. The laminates are produced in an autoclave, often at 250 F for 8 hours.
The thickness of the glass laminate and the polycarbonate in the laminate depend on the size of the projectile and the velocity of the projectile. At HighLine Polycarbonate we typically recommend 3mm Polycarbonate for low end threats. For high end military applications the structure of the laminates are often confidential or classified.
In theory a film would act as a spall shield for low calibre, low velocity projectiles. For example a glass window with a laminated PC film would prevent fragments of glass from hitting occupants if a rock was thrown at the window. For a high velocity NATO round I would not want to use a film as a spall shield layer.
We have just published a blog post on the different types of transparent armor at http://www.highlinepc.blogspot.com if you are interested.
HighLinePC, what are you adding here? if you look back through the posts you will see that the subject of how bullet resistant glass is manufactured has been well covered. Most, if not all bullet resistant laminates are manufactured using glass and not plastic. Furthermore "Spall Shield" would be the final layer in the makeup on the inside. You forgot to mention "Low Spall" and" No Spall" Also, if given a certain ballistic threat it would be a simple solution to stop a required round, there is no mystery of "confidential or classified". Your company is not an approved vendor to the US Military or Government and has no site clearance and or security clearances to manufacturer glass of a "Classified" nature. The use of "Film" for "Smash Grab applications has also been well discussed on this forum.
To address some of your comments:
Most bullet resistant laminates are a combination of glass and plastic, particularly in higher threat applications. Saying that most, if not all, do not use plastic is not correct. Even the Dupont Spall shield product is a plastic film consisting PVB, PET and a hard-coat.
Your comment that spall shield layer would be on the inside is correct. Spall shield layers need to be on the inside to retain the glass fragments.
Low spall and no spall are general terms that attempt to quantify the effectiveness of the spall shield layer. The effectiveness of the spall shied layer is better quantified by testing to an approved standard such as ATPD-2352. Under the terms that you use, most of our customers produce no spall products. Typically we would not use these terms, this is the reason why I made no mention of them.
In a general sense you are correct that to stop a given ballistic threat it is easy for a laminator to construct an effective laminate - they would just need to keep adding layers of material until there is enough material to absorb the energy of the round - no great mystery here. However, this approach ignores a number of other critical design parameters, not least of which are weight, cost and resistance to environmental conditions (temperature, sand etc.). Just adding material will increase both weight and cost. The confidential information is how to achieve the desired ballistic performance within weight and cost constraints. The classified information is the level of ballistic threat that needs to be stopped (Anyone can download the specification ATPC-2352, but you will not be able to get hold of drawing DTA 184044 which contains the threat level information).
You state that we are not an approved vendor to the US Military or Government. We certainly do not sell Polycarbonate directly to the US Military or Government for ballistics laminates and transparent armor, because neither they nor us produce the transparent armor. We sell Polycarbonate to laminators that produce transparent armor for the US military. We work with these laminators under confidentiality and other agreements to assist in the design of the laminates.
HightLinePC.............What is your point,? so you sell polycarbonate that is made in Japan and have had a website as of 7-23-08.
All of the Bullet Resistant Glass manufacturers we know would use the far superior GE product that is made in the USA. Of course DuPont Spall Shield is a laminated plastic product, it has to be, to be a spall liner.
Low Spall or No Spall is very simple " Low Spall" as you must know is simply glass as the final inside layer of glass, some customers use this as you must know for ease of cleaning and ability to not discolor or scratch, and are not concerned with the glass spalling from impact. "No-Spall" as again you must know is where polycarbonate or DuPont Spall Shield is used the final layer on the inside, where glass spalling from impact is of high concern. Again what is your point?
I am correct, as would anyone else on this forum that knows ballistics and ballistic threats. It is a very simple process to stop the threat. A customer has a given round to stop and there is a given thickness and lay-up of glass and yes polycarbonate to stop the threat and yes the higher the threat the thicker and heavier the glass has to be, that is the law of physics, It's not confidential or classified information.
Not to be rude, but all of the Bullet Resistant Glass manufacturers we have dealt with have in -house ballistic engineers and would also have their glass tested by an approved testing laboratory. You would have no exposure to classified information and talking about ATPC-2352 is meaningless to most on this forum. We are an approved vendor to the US Military and Government and have been doing so for over 12 years, providing Bullet Resistant solutions, but are not here to try and impress anyone, or to be arrogant. I can see not further need to respond to any of your comments, as again Bullet Resistant Glass has been well covered here, and your comments are nothing new.