PVB Bulletproof Glass

1. Overview

The principle behind bulletproof glass is its ability to convert the kinetic energy of bullets into the elastic potential energy of the glass and the surface energy of the fragments. Generally, glass has strong abilities to absorb and disperse vibrations, while plastic is lightweight and tough, making it difficult to shatter. To increase strength and durability, a layer of film can be sandwiched between two layers of glass. However, when these materials are used alone, they are not sufficient to stop bullets fired from firearms with higher lethality. Bulletproof glass is made by bonding 2 to 3 layers of bullet-resistant materials with an interlayer of film, which prevents incoming bullets. Once the outer layer is shattered, the inner film can also hold the fragments in place, preventing them from detaching. Generally, the more layers it has, the better the bulletproof effect. Some bulletproof glasses even have air layers to reduce vibrations. The total thickness of bulletproof glass is usually above 20mm, and for higher-level protection, it can reach over 50mm. However, it is important to note that with continuous close-range shooting, bullets can still penetrate or shatter the bulletproof glass.

2. Safety of Glass

2.1 Ordinary glass

Ordinary glass (annealed, tempered, semi-tempered) when subjected to the impact of a bomb explosion, the glass shards scatter, and the glass experiences penetrative damage, causing severe injuries to people and indoor facilities. RET≈0~0.2.

2.2 Ordinary laminated glass

Ordinary laminated glass, when subjected to the impact of a bomb explosion, shatters, and the shock wave enters indoors. In severe cases, the entire broken glass flies up and causes serious injuries when hitting the human body. However, the overall damage range is smaller than that of ordinary glass. RET≈0.3~0.5.

2.3 Bulletproof laminated glass

Bulletproof laminated glass, when subjected to the impact of a bomb explosion, bends backward, and the frame system compresses and cushions backward. The glass remains intact or may have cracks but no fragments are splashed out, ensuring that indoor personnel and facilities are not harmed. For example, the combination of bulletproof laminated glass: DFB10 + polymer material (usually PVB) + DFB10 (10mm high-strength single-piece cesium-potassium fire-resistant laminated glass + polymer material + 10mm high-strength single-piece cesium-potassium fire-resistant laminated glass), RET≈1.0.

RET stands for Retention, representing the overall retention of the glass within the frame.

When RET=1.0, the glass remains intact within the frame, and no fragments are scattered, and there is no penetration; when RET=0, the entire glass piece detaches from the frame, fragments scatter, and penetration failure occurs.

3. Bulletproof Glass Structure

Bulletproof laminated glass is actually made by bonding multiple pieces of glass or high-strength organic sheets together with transparent adhesive materials. It generally consists of three layers: load-bearing layer, transition layer, and safety protection layer.

The load-bearing layer is the first to withstand the impact and shatter, and it is typically made of thick and high-strength glass. It can destroy the bullet or alter its shape, causing it to lose the ability to continue forward.

The transition layer is usually made of organic adhesive materials with strong bonding capabilities and good light resistance. It can absorb some of the impact energy and alter the direction of the bullet.

A very strong and transparent chemical film is sandwiched in the laminated glass. This not only effectively prevents bullet shots but also provides properties such as resistance to shock waves, explosions, seismic events, and the prevention of cracks after impact.

The safety protection layer is made of high-strength glass or high-strength transparent organic materials. It possesses good elasticity and toughness, absorbing the majority of the impact energy and ensuring that the bullet cannot penetrate this layer. Mature organic transparent materials used for this purpose include Methyl Methacrylate (commonly known as organic glass or PMMA) and Polycarbonate (PC), with the latter having better toughness.

3.1 All-Inorganic Bulletproof Glass

The structure of all-inorganic bulletproof glass is formed by bonding multiple layers of glass with a polyvinyl butyral (PVB) interlayer film. It is processed through high-temperature and high-pressure treatment to form a laminated structure, also known as PVB laminated bulletproof glass. This type of bulletproof glass exhibits good optical properties, impact resistance, and environmental stability, with a long service life and resistance to aging. It is cost-effective and easy to maintain; however, it is relatively heavy and more suitable for installation in fixed locations. For example, the most widely used bulletproof glass in bank counters consists of 3 to 4 layers of float glass laminated with PVB, with a total thickness of over 24mm.

4. Factors Affecting the Performance of Bulletproof Laminated Glass

There are several factors that influence the performance of bulletproof laminated glass, including the type, thickness, number of layers, processing methods, size, installation method, and the type of bullets (lead-core or steel-core).

4.1 Material Properties

According to bulletproof theory, the performance of bulletproof glass is mainly related to the material’s hardness and toughness, rather than its strength. Therefore, when the backing material is made of organic materials, bulletproof glass made with polycarbonate is superior to organic glass (PMMA) under the same conditions. If inorganic glass is used as the panel material, chemically toughened or physically tempered glass provides better bulletproof effects compared to annealed glass.

4.2 Thickness

4.3 Combination

For PVB laminated bulletproof glass, the arrangement of individual inorganic glass sheets from the impact surface to the back surface with decreasing thickness (also known as degressive arrangement) enhances bulletproof ability. Particularly, the thinner the last layer of glass, the fewer splinters produced, resulting in better bulletproof effects. When combining organic and inorganic materials, to some extent, the greater proportion of organic materials leads to stronger bulletproof capabilities.

4.4 Size

Larger glass size allows for more significant elastic deformation when the glass is impacted. More impact energy is converted into elastic potential energy, resulting in less glass damage and stronger bulletproof ability.

4.5 Installation Method

If the bulletproof glass is firmly fixed around its perimeter or is non-elastically connected to the frame, the elastic deformation of the glass is restricted upon impact, reducing its bulletproof capability.

5. Production Process

The manufacturing process of bulletproof laminated glass is similar to the preparation process of regular laminated glass. The steps include:

5.1 Cutting and Cleaning

The raw materials, typically glass sheets, are cut into the desired sizes and thoroughly cleaned to ensure a clean and dust-free surface.

5.2 Tempering

The glass sheets may undergo a tempering process to increase their strength and toughness. Tempering involves heating the glass to a high temperature and then rapidly cooling it, which results in compressive stresses on the glass surface and tensile stresses in the center. This process makes the glass more resistant to impact and less prone to shattering into large, dangerous shards.

5.3 Bonding and Rolling

The individual layers of glass sheets are bonded together with the interlayer material, which is often a polyvinyl butyral (PVB) film. The layers are then subjected to pressure and rolling to ensure proper adhesion and eliminate air bubbles.

5.4 Lamination

The bonded layers are assembled together to form the final laminated glass structure. The number of layers and the composition of the materials can be adjusted to meet specific bulletproof requirements.

5.5 Installation Method

The edges of the laminated glass are polished to ensure smooth and safe edges.

5.6 Inspection

After the production process is complete, the bulletproof laminated glass undergoes thorough inspection to check for any defects, air bubbles, or other issues that could affect its performance.