ARMORFILM Adhesives

ARMORFILM adhesives are GTS proprietary adhesives designed to bond armor plates while protecting heat-sensitive components.  Our adhesives are non-flammable, low VOC, odorless and are California Proposition 65 compliant.

One of the most important parts of building armor plates is bonding all of the materials together into an effective system. For an armor plate to work properly (and safely) the materials have to be kept in close proximity to one another. Any separation in the materials layup results in decreased performance.  The materials only work when they work together, as an armor system.  If you shot the type of ballistic tile used in an RF3 armor on its own, the projectile would likely penetrate the ceramic and continue along, striking the next thing in its path.  If you separated the ceramic strike face and the polyethylene (PE) backer by 1"-2", you would see marked reduced effectiveness and possibly a complete penetration (depending on the design) of both materials.  Keeping the armor plate bonded encourages all sections of the the plate edges to remain together. This reduces projectile, jacket and ceramic fragmentation parallel to the strike face which could emanate from points between the ceramic and PE backing.

We noticed some vulnerabilities in the adhesives being used in hard armor and set out to improve the bond between dissimilar ballistic layering.  

The types of adhesives used worldwide is tied to geography.  Armor built in China normally incorporates super glue or neoprene liquid type adhesives.  Professional armor construction in the USA normally utilizes a thermally activated sheet. There are problems with both.

The issues with super glue (cyanoacrylate) and neoprene type adhesives are their ability to bond effectively with low-energy polyethylene.  These adhesives are manually applied to the backing out of large tubs of pre-mixed adhesive (via squeegee). The ceramic tile is then applied and the armor is allowed to sit until cured.  This process is seen below and accounts for the vast majority of low-priced armor imported into the USA (text continues below video).

 

Using a liquid adhesive can have some disadvantages.  The main one is related to the uniformity of the adhesive layer between the ceramic and the low-energy PE backing material.  The more variation in the thickness of this layer, the more difficult it is to predict ballistic energy routing (performance). This variation can also create weaknesses in materials bonding.

For maximum strength, a thermally-activated adhesive sheet may be used.  This produces consistency in the adhesive layer.  Under pressure, this layer will not only be more uniform in thickness, it will also be free of air bubbles. The below image shows an adhesive sheet (pre-processing state) resting between the ceramic and the PE layer.

Thermally-activated adhesive sheets are superior to adhesives applied in the liquid state. But, there are problems related to the temperatures required for bonding with respect to influences on the PE material.  Understanding these drawbacks was the catalyst for developing ARMORFILM.

There are two main problems with the thermally-activated adhesive sheets normally used by armor builders in the USA. Both of these problems are solved by ARMORFILM.

1. Problems of debonding (delamination) involving pressed PE backing plates.
2. Temperature damage and molecular realignment of PE chemical chains.

"Most" serious armor in the USA is built by assembling ceramic strike faces to polyethylene backing materials.  The first step is to build the PE backing plate. This is accomplished by pressing polyethylene sheets (called plies) together under heat (usually about 130°C) into a shape that matches the curvature of the ballistic tile to be used.  This pressing procedure involves high tonnage (about 1000 ton) press machines and 3500 PSI+.  The pressed backers are allowed to cool under pressure so that an excellent bond between the PE plies is maintained during a return to room temperature.

The next general step is to bond the PE backing plate and the ceramic strike face.  This is done through the use of a thermally-activated adhesive sheet (as described above).  The adhesive sheet is placed between the materials, the armor is placed in vacuum film (or vacuum bags) and vacuum is applied to hold the materials together.  The armor is then placed in a commercial oven.  While the vacuum is maintained, the temperature is increased until the adhesive sheet can be melted (activated).  While vacuum is maintained, the armor temperature returns to room temperature.

The problem with the above step is that the pressure provided by the vacuum is not even close to the original press machine pressure of 3500 PSI+.  This lower "pressure" acting on the backing plate when combined with heat (which softens the resins within the PE material) serves to loosen the strength and bonding of the pressed backer itself.  The degree of this delaminating tendency varies with the quality of the original press and the amount of temperature involved (and several other factors).  To offset this issue (and since the oven activation vacuum cannot provide 3500 PSI+) the only viable strategy is to activate the adhesive sheet at the lowest temperature possible.

The other issue is that many of the adhesive sheets used by US armor manufacturers originate from a single source in Europe.  The melting point for the adhesive sheet products is almost always around 110°C (230°F). Even with transitory temperatures in this range, it can cause molecular realignment in the PE and noticeable weakening in the backing material.  PE melting point is around 295°F. However, we have seen (and documented) PE weakening significantly below that temperature.  The solution here is to also activate the adhesive sheet at the lowest temperature possible so that the chemical integrity of the PE can be maintained.

Even autoclave-based armor manufacturing introduces elevated temperatures to the PE backing. Most autoclaves cannot match the press machine pressures at 3500 PSI+ and bond armor in the 150 PSI - 300 PSI range (for most armor plates).

There are other, ongoing issues with ballistics adhesives.  A full chapter (or more) could be written about acoustics, shockwaves, shear effects, and a balanced approach.  Epoxy-type adhesives can effectively bond ceramic to UHMWPE, but can shear quickly, creating air gaps that decrease multiple-hit effectiveness.  Polyurethane adhesives can provide more flexibility but the range of motion permitted may result in increased damage between parts of the ceramic plate separated by either fracture (from previous hits) or via design (mosaic tile array).  Polyolefin adhesives are very effective, but have high temperature activation ranges that threaten the UHMWPE integrity. 

Now, we have set the stage for the problems above - we introduce our ARMORFILM.

ARMORFILM can be thermally activated at around 200°F (depends on the exact materials layup).  This is more than 30°F less than most adhesive sheets on the market today.  Some might question the low activation temperature and wonder if this could lead to adhesion problems in very hot environments.  The answer lies in the required dwell time at the activation temperature.  National Institute of Justice (NIJ) 0101.07 temperature conditioning requires temperature conditioning periods of up to 194°F for two hours. We designed the dwell time of the activation process to outlast transitory, super hot environmental temperatures.   

ARMORFILM creates strong bonds while maintaining the lamination and chemical integrity of the PE pressed backing material.  We suspect that elevated temperatures cause some industry armor failures.  Our adhesives will help eliminate those issues.

ARMORFILM creates a balance between shear strength and flexibility.  It's not so rigid (like an epoxy) where it would create problems with multiple-hits, and remains loose enough to allow undisturbed ceramic to still move autonomously - all while being activated at temperatures that protect the UHMWPE's chemistry.