Can EVA films with below 28% adhesive still be used to make laminated glass? Yes, but you're betting on your own safety.

Let's cut to the chase: It's possible, but the finished product will be separated from "qualified laminated glass" by a crack you may not be able to withstand.
EVA film with below 28% adhesive content are not inapplicable to laminated glass, but the bonding strength, tear resistance, and weatherresistance of laminated glass are significantly reduced. It looks fine in the short term, but after six months, it will peel, blister and fatten. When a customer knocks on the door, you have no room to shirk your responsibilities.
First of all, understand: what is the limit to the amount of adhesive?
EVA stands for ethylene-vinyl acetate copolymer. The so-called "adhesive content" refers to the amount of vinyl acetate (VA). This number directly determines whether an EVA is hard or soft, brittle or hard, and binds properly.
The general consensus in the industry is that EVA levels below 25% are a thermoplastic resin-high in hardness, brittleness and weak adhesion. EVA an elastomer with flexibility and adhesion between 25% and 40%, and more than above 40% goes directly into the field of hot melt.
For EVA films used in laminated glass, the VA content is usually locked in between 26% and 35%. Why 28%? Because 28% is the entry threshold for elastomers. Below this number, there are not enough vinyl acetate units in the molecular chain, resulting in a sharp drop in chemical affinity between EVA and glass, and physical adsorption cannot support long-term loading.
Photovoltaic-grade EVA films typically require a VA content of 26% to 35% and a a light transmittance of 91% to 93%. EVA film for architectural laminates, the national standard GB9962-99 requires a 0.38mm thick transparent film with the following specifications: tensile strength ≥17MPa, fracture elongation ≥ 650%, adhesion ≥ 2kg/cm, water absorption ≤0.15%. The underlying support for these specifications is that VA levels shouldnot be too low.
What happens if it's below 28%? Three fatal flaws:
First drawback: poor adhesion. For every 5% reduction in VA content, the adhesion between vinyl and glass decreases by approximately 15 to 20 percent. The adhesion of films with 25% VA in laminated glass may be only around 1.4kg/cm, significantly lower than the national standard of 2kg/cm. With each temperature change, the glass expands and contracts, causing the film to slide between the glass and the film, making it more probable that the edges will separate after three months.
Second drawback: Can't handle tearing. EVA has lower tear resistance than PVB and SGP. When the VA content is below 28%, the elasticity is insufficient and the membrane hardens and becomes brittle. Once the glass is hit and shattered, the shards will tear straight through the film, rendering it safe to do so. PVB has a tear strength five times greater than EVA and SGP five times greater than PVB. Low-VA-content EVA don't even protect you, let alone people.
Third drawback: It ages quickly. Low-VA-content EVA has a higher proportion of ethylene units in the molecular chain, leading to an increase in crystallinity. Ultraviolet light are more likely to attack molecular chains, causing yellowing one to two times faster than standard formulas. National standards require UV aging a yellowing index ≤ YI ≤ 4.0. Low-VA films may barely meet this requirement at the plant, exceeding the standard after only six months of use.
When is' expedient '? To be fair, not all scenarios call for strict compliance with the 28% VA limit.
If you're making upholstery glass with 6mm thick non-tempered glass of a 0.38mm EVA film in an environment that doesn't require direct sunlight or drastic temperature changes, a film with 25% to 27% adhesive content may barely qualify. The products already have a low safety rating, and national standards allow them to be used for "engineering applications with low safety requirements."
However, if you are making tempered laminated glass, large size glass or curtain wall glass, it is dangerous to have below 28% adhesive. Tempered glass itself exhibits wave-like deformation and requires a highly elastic film layer to compensate. Low VA content of the film simply cannot withstand this deformation, resulting in layered edges, foam in the middle, the a drastically reduced finished product pass rate.
In short, 28% is not the legal red line, but the engineering red line. EVA films with below 28% adhesive content are suitable for small indoor non-tempered glass panels, but not at all for tempered glass, large glass and outdoor applications. The money saved by the film will eventually become stratified and recycled. In the laminated glass industry, recipes can be adjusted, but the bottom line isnot to be broken.