Patent Application
20110177310
1. Field
The present invention relates generally to transparent laminate structures for use in safety and security applications. Particularly, this invention relates to transparent laminate structures and a method of making same using an ultra-high modulus thermo-plastic elastomer as a stabilizer of rigid substrates, and a energy absorbing layer, and further, to transparent laminate structures formed from combinations of one of two modules, where one module includes a rigid laminate structure stabilized by an ultra-high modulus thermo-plastic elastomer, and a second module includes a energy absorbing layer.
2. Description of the Problem and Related Art
Impact resistant glass laminates were first introduced in the early 1900s and are well known in the art today for use in safety and security glass applications, and have been traditionally constructed using alternating layers of glass and plastic sheeting in the form of thermosets, or thermoplastics with adhesive and or heat bonding interlays. For example, bullet resistant glass is sometimes constructed with several glass sheets connected together with thin sheets of polyvinyl butyral, or polyester interposed there between with a polycarbonate layer bonded on the inside face of the final glass sheet using a thermoplastic polyurethane layer. The polycarbonate layer provides additional strength, and to a small degree, elasticity, to the glass upon impact but is used primarily to provide good resistance to spalling.
However, excessive layering of glass and polycarbonate sheets creates problems. First, using such materials, the weight and thickness of the transparent laminar assembly requires a heavily engineered and reinforced support structure. Next, such laminar assemblies suffer delamination in the presence of heat, either localized heat from high-velocity projectile, heat from the bonding process, or ambient heat from, for example, desert environments. Additionally, current transparent laminar structures also suffer from other safety concerns such as leaching of biphenyl “A′s”. Such characteristics decrease life cycle of the systems and structural stability, ultimately reducing or negating their effectiveness.
Other materials such as aromatics and ether-based have exhibited a great resistance to heat, and can provide desirable mechanical properties of greater elasticity and lighter weight. However, heretofore, such compositions have not been suitable for use in transparent armor because over time light transmissiveness degrades.
The present disclosure is directed to a transparent projectile-resistant laminate assembly.
For purposes of summarizing the invention, certain aspects, advantages, and novel features of the invention have been described herein. It is to be understood that not necessarily all such advantages may be achieved in accordance with any one particular embodiment of the invention. Thus, the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other advantages as may be taught or suggested herein.
It should also be noted that the term “projectile” may refer to any object that may strike the surface of a transparent assembly and cause degradation or failure. These may include projectiles such as bullets, shrapnel, thrown objects such as bricks, stones and other similar objects and self-propelled items such as RPG's, IED's, missiles, and other rocket like projectiles. Projectiles may also include objects that become self-propelled by an Act of God or nature as a result of severe weather conditions such as tornadoes, hurricanes, sand storms, typhoons and high winds. Projectiles may also include objects used to directly strike the surface of the assembly such as bats, bricks, metal objects, wooden clubs, etc. Projectiles may also include objects that come into contact with the transparent assembly if used in a vehicle and that vehicle was to become part of an accident or intentional hazard.
A projectile-resistant transparent laminate includes a rigid laminate assembly with first and second rigid transparent lamina bonded together with a transparent, ether-based thermoplastic elastomer layer interposed therebetween. The thermoplastic elastomer layer includes a transparent polyurethane having an ultra-high modulus of elasticity. The laminate also includes an energy absorbing assembly that includes a transparent, quasi-thermoset layer from a cast aliphatic urethane.
These and other embodiments of the present invention will also become readily apparent to those skilled in the art from the following detailed description of the embodiments having reference to the attached figures, the invention not being limited to any particular embodiment(s) disclosed.
The present invention is described with reference to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements. Additionally, the left-most digit(s) of a reference number identifies the drawing in which the reference number first appears.
The various embodiments of the present invention and their advantages are best understood by referring to
This invention may be provided in other specific forms and embodiments without departing from the essential characteristics as described herein. The embodiments described above are to be considered in all aspects as illustrative only and not restrictive in any manner.
The following claims rather than the foregoing description indicate the scope of the invention.
Referring to the drawings,
The thermoplastic elastomer layer 104 is an ultra-high modulus thermoplastic elastomer (“UHMTPE”) having super elastic shape memory. These characteristics are achieved with an aromatic polyether-based, rather than ester-based, thermoplastic, long-molecular chain, polyurethane, at about 96% by weight, and about 4% by weight of a stabilizer composition that includes an anti-oxidant and a light stabilizer. Those skilled in the relevant arts with the benefit of this disclosure will recognize that heretofore, ether-based polymers have not been used in glass and polycarbonate laminations. This is because they breakdown in the presence of heat from the lamination process and from the environment. However, the inventors hereof have discovered the use of certain stabilizers counters these deleterious effects. Specifically, the anti-oxidant prevents thermally induced oxidation of polymers during coating and heat lamination, traps free radicals formed during heating in the presence of oxygen and prevents discoloration and change of mechanical properties incumbent to the polymer. In other words, mechanical properties such as elasticity, and light transmissiveness are maintained even in the presence of heat. An example of such anti-oxidant is a phenolic stabilizer offered by Ciba Specialty Chemical Corporation, Tarrytown, N.Y., under the trademark Irganox®.
The light stabilizer includes an ultra violet (UV) absorber and a hindered amine light stabilizer (HALS). The UV absorber filters harmful UV light and prevents discoloration that degrades light transmission and prevents delamination when heating. HALS also trap free radicals formed under heat and are primarily useful in maintaining surface properties such as gloss. HALS also prevents cracking and chalking of the polymer. When used together, they have a complimentary synergistic effect. One such light stabilizer is offered under the mark Tinuvin®, also by Ciba.
A suitable polyether-based thermoplastic polyurethane with such heat resistance, and light preservation as described above can be obtained as “VT-0124,” offered by MBM Technologies, of Houston, Tex. The thermoplastic elastomer is applied as a film and can be between about 3 mils to about 10 mils in thickness. This layer increases the elasticity of the glass layers and substantially reduces the area of local gross deformation of the laminate assembly 100 at the point of impact. The laminate assembly is assembled by a conventional autoclave process using iterative application of heat (e.g., up to about 360° F.) and pressure (e.g., up to about 60 psi).
Preferably, all bonded surfaces of the rigid layers 102a, b to which the thermoplastic elastomer layer is to be bonded are cleaned before the bonding process with a bonding and cleaning agent. A preferred bonding and cleaning agent is a silane-based solution comprising an organofunctional silane to facilitate the bonding of the inorganic glass to the organic thermoplastic layer, an alcohol to act as a solvent, and a silicone glycol copolymer that acts as a wetting and leveling compound. Further, the solution may be diluted with water, preferably de-ionized water. An example of a suitable bonding and cleaning agent is known as XO Bond™, offered by XO Armor, LLP of Houston, Tex.
Transparent armor of this disclosure includes in a variety of combinations using the above described rigid laminate assembly 100, and a backing energy distribution layer consisting of a cast quasi-thermoset. For example, a first embodiment of a transparent armor 200 is disclosed with reference to
The above-described laminate demonstrates extraordinary strength when loaded by energies associated with rigid body impactors, while resulting in a structure that is thinner and lighter than current transparent armors. At the same time, optical quality of the laminate is only minimally degraded, if at all.
During an impact event, a projectile strikes the strike face of the structure, impacting first the rigid laminate assembly 100. In essence, the rigid laminate assembly 100 acts to strip a projectile jacket, and dissipate kinetic energy. It also begins erosion and/or ablation of the projectile tip that further slows the projectile's velocity. The described ultra high modulus properties of the polyether-based thermoplastic elastomer provide stability to the rigid layers, and increases to some degree their elasticity, allowing the rigid layers 102 to bend significantly under impact loads without breaking. The polyether-based thermoplastic elastomer layer 104 also increases material interface between the rigid layers and allows for local impact energies to be dispersed and dissipated over a greater surface area thereby improving management of the impact event. This is a result of super elastic shape memory provided by the extremely long molecular chain associated with the polymer and is measured at a 27 in accordance with measurements contained in the ASTM D790. Therefore, substrate stability, superior optical qualities, and ability to withstand temperatures in excess of 200 degrees C. make the material unique and optimum for superior performance of this application.
Once the projectile travels through the rigid laminate assembly 100 it encounters the energy absorbing layer 202. Since the energy absorbing layer comprises a quasi-thermoset, it softens in response to the addition of heat, and exhibits elasticity and shape memory of a thermoplastic. As the projectile penetrates the energy absorbing layer 202, its energy is further dissipated, especially since the projectile tip has been blunted by its encounter with the rigid laminate assembly.
A further embodiment is illustrated in
A second optical film layer 304b is bonded to the non-strike side surface of the second rigid laminate assembly 100b. Each optical film layer 304 may be comprised of two or more layers of a film, each of which may be a transparent polyethylene terephthalate (PET) and may be between about 0.11 mils and about 0.21 mils in thickness. Interlayer bonding material 302 may be between about 0.015 and about 0.050 inches and comprise another, secondary thermoplastic elastomer layer, to bond the rigid laminate assemblies 100 to either surface of the energy absorbing layer 202. In the alternative, interlayer material 302 may also be an aliphatic thermoplastic polyurethane film. Suitable materials include the above-described VT-0124, or the A4700 produced by Deerfield Urethane, of South Deerfield, Mass., or the Texstars 851, 1451 from Texstars, Inc., of Houston, Tex. Each of the layers may be bonded in a manner similar to that used for the rigid laminate assembly.
With reference now to
energy absorbing layerenergy absorbing layerenergy absorbing layerA further embodiment using components and principals described above is shown in
It may be advantageous to interpose a second polycarbonate layer 602b between the flex module and the 601b without bonding. The inventors herein have discovered in prototype testing that the layering of different materials presents a projectile penetrating the laminate with layers varying in density, rigidity, and elasticity. Each time the projectile encounters a different material, its path alters somewhat, slowing its velocity. The lack of bonding between the intermediate polycarbonate layer 602b and the flex module 603 and the second rigid module 601b results in an air gap on the order of microns in thickness which serves as yet a different medium through which the projectile passes and turns yet again.
As described above and shown in the associated drawings, the present invention comprises a projectile resistant transparent laminate. While particular embodiments of the invention have been described, it will be understood, however, that the invention is not limited thereto, since modifications may be made by those skilled in the art, particularly in light of the foregoing teachings. It is, therefore, contemplated by the appended claims to cover any such modifications that incorporate those features or those improvements that embody the spirit and scope of the present invention.
