JPH0450185B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to impact resistant laminates. More particularly, the present invention relates to a bulletproof double glazed structure that provides protection against repeated shots from high-powered handguns and rifles. The improved double glazing structure includes a back laminate located opposite the direction of impact and a front laminate located forward of the back laminate with respect to the direction of impact; comprises a plurality of laminates selected from the group consisting of polycarbonate, glass and solid resin materials, the laminates of the back laminate being joined by an intimate adhesive;
The front glass laminate comprises a plurality of glass laminates, the glass lamina having a thickness of about 30 to about 220 mils facing the direction of impact, and a front glass laminate having a thickness of about 30 to about 220 mils facing the direction of impact; a back glass laminate having a thickness of from 30 to about 220 mils, and at least one relatively thick inner glass lamina located intermediate the back and back laminates, the glass lamina of the front laminate; are joined by intimate adhesive. The use of so-called safety or anti-penetration glasses for windows, windshields, etc. using multiple layers of polycarbonate, glass and other resinous materials is well known. For example, a laminate of glass and polycarbonate resin is described in US Pat. No. 3,666,614, in which the glass and polycarbonate are bonded together using an ethylene-vinyl copolymer. U.S. Pat. No. 3,520,768 describes a relatively thick glass laminate with relatively thin polycarbonate flakes as adhesive material. It is also known to utilize certain polysiloxane polycarbonate block copolymers as adhesives when preparing polycarbonate-containing laminates, as described in U.S. Pat. No. 4,027,072.
Although generally effective, these laminates have the disadvantage of not being able to withstand multiple shots, especially when fired with high velocity bullets such as those fired from a rifle. Thus, for example, in prior art laminates using thick front (impacted) glass layers, multiple shots to the thick front layer of glass would result in many glass cracks, and removal of the glass from the laminate would be difficult. Makes it vulnerable to repeated shots. In order to withstand multiple high velocity bullet shots, and especially high velocity rifle bullets, previously known laminates had to be extremely thick and heavy. Even these thick and heavy laminates were not completely effective,
This is because crushing on the rear or downstream side of the laminates posed a risk of injury to people behind these laminates due to this crushing. Accordingly, there is a need for a laminate that is relatively thin, lightweight, and capable of withstanding repeated firing by high velocity projectiles. The present invention has a relatively light weight, is relatively thin,
Moreover, the present invention provides a laminated structure that can withstand repeated firing of high-speed bullets without penetrating the bullet or shattering the back surface or downstream layer. FIG. 1 is a side view of a double glazed structure of the invention with one intermediate air space between the back laminate and the front laminate. The present invention comprises an improved impact resistant double glazed structure including a back laminate located opposite the direction of impact, the back laminate being made of polycarbonate,
It includes a plurality of laminates selected from the group consisting of glass and solid resin materials, the laminates of the backside laminate being joined by a cohesive adhesive. The improvement includes a front laminate located forward of the back laminate with respect to the direction of impact, the front laminate having a front surface having a thickness of about 30 to about 220 mils facing the direction of impact. Glass layer body, about 30 on the opposite side of the impact direction
a back glass ply having a thickness of about 220 mils to about 220 mils, and a relatively thick glass core located intermediate the front and back glass plies;
The glass laminates of the front laminate are joined by intimate adhesive. The thickness of the front and back glass laminates in a front glass laminate is critical. The upper limit on the thickness of these front and back glass layers must be approximately 220 mils. If these front and back glass laminates are thicker than about 220 mils, the resistance of the double glazed structure to multiple shots is adversely affected. The lower limit on the thickness of these front and back glass layers is not critical, but is limited only by practical considerations. For ease of handling and optical properties, this lower limit is about 30 mils. The inner glass core located intermediate the front and back glass laminates is relatively thick, i.e.
It is also important that it be thicker than either the front or back glass layer. This internal glass core should generally be thicker than about 250 mils and may consist of a single layer of glass, or it may consist of several layers of glass joined by intimate adhesive. You can leave it there. Any of the common types of glass used in so-called safety applications can be used as the glass laminate of the front glass laminate of the present invention, coated or uncoated and chemically and thermally Includes toughened or hardened glass as well as ordinary unhardened glass. The improved double glazing structure of the present invention is illustrated in FIG. FIG. 1 shows one embodiment of the double glazed structure of the present invention. In this embodiment, the double glazing structure A consists of a back laminate 6 and a front glazing laminate 1 located in front of the back laminate with respect to the direction of impact, the front laminate 1 being separated by one air space 5. It is spaced apart from the back layer 6. The back laminate 6 is composed of a plurality of laminates 8, 9, 10 selected from the group consisting of polycarbonate, glass and solid resin materials. the front glass laminate 1 has a relatively thin back glass laminate 2 having a thickness of from about 30 to about 220 mils;
It consists of a relatively thin back glass layer 4 having a thickness of from about 30 to about 220 mils, and a relatively thick inner glass core 3 disposed intermediate the front glass layer 2 and the back glass layer 4. ing. The inner glass core 3 is thicker than either the front glass layer 2 or the back glass layer 4 and generally has a thickness greater than 250 mils, preferably greater than about 350 mils. The upper limit of the thickness of the inner glass core 3 is limited only by practical considerations of the thickness and weight of the glass laminate 1 and thus the structure A.
When the inner core 3 is a single layer of glass, the thickness of the inner core 3 preferably ranges from about 220 mils to about 1000 mils. The inner core 3 may consist of a single layer of glass or may consist of multiple glass layers joined together with an intimate adhesive. The front glass lamina 2 and the back glass lamina 4 are joined to the inner glass core by means of an intimate adhesive. In FIG. 1, the back glass laminate 6 is shown to be composed of three layers, but
It need not contain three layers. It may contain only two layers, or it may contain three or more layers. The back laminate 6 is composed of a plurality of laminates selected from glass, polycarbonate, and solid resin materials. Preferably, the back laminate 6 contains at least one polycarbonate laminate and at least one laminate selected from the group consisting of glass and resin materials. Thus, for example, the back laminate may include one polycarbonate laminate bonded to an acrylic laminate, two polycarbonate laminates bonded to each other, or one polycarbonate laminate bonded to an acrylic laminate. A polycarbonate layer in which the acrylic layer is bonded to another polycarbonate layer, a glass layer bonded to a polycarbonate layer, or a glass layer bonded to an acrylic layer. In one polycarbonate layer, the acrylic layer can further include a glass layer bonded to one layer. One useful type of backside laminate 6 is one in which all of the laminates are polycarbonate. Backside laminate 6 can include any ballistic laminate known in the art. Some suitable types of backside laminates 6 that can be used in the present invention include U.S. Pat. No. 4,027,072;
Same No. 4123588, Same No. 4126730, Same No. 3624238,
and No. 3657057. All of these are incorporated herein by reference for reference. In the embodiment shown in FIG. 1, the front laminate 1 is separated from the back laminate 6 by an air space 5. In the embodiment shown in FIG. The distance by which the back laminate 6 is separated from the front laminate 1 can vary over a wide range, one of the purposes being to improve the optical properties of the double glazed laminate A. . Generally, air space 5 has a width of about 1/10 to about 3/4 inch, preferably about 1/8 to about 1/2 inch. Frame member 7 is not critical to the effective use of structure A, but is used to aid in its easy handling and manipulation and to generally strengthen and protect the structure. In a further preferred embodiment of the invention illustrated in FIG. 1, the back laminate 6 of the laminate structure A is comprised of a plurality of impact-receiving layers selected from the group consisting of polycarbonate, glass, and solid resin materials. and includes one back polycarbonate layer opposite the direction of impact, the back polycarbonate layer having a thickness of 2 mils or less on its exposed surface opposite the direction of impact and having a harder and relatively brittle layer than the polycarbonate layer. The back polycarbonate layer has a thickness of from about 30 mils to about 220 mils. This type of laminate is used as the back laminate 6 in the double glazing structure A.
Structure A has not only been found to be resistant to penetration by multiple shots of high-velocity projectiles, but also has greatly improved shatter resistance when used in the art. Such a laminate was created in 1977
The applicant's application number, which was filed in the United States on December 21st, is
No. 862775, which is incorporated herein by reference. Briefly, in these laminates, i.e., back laminates 6 having a coated back polycarbonate layer having a thickness of from about 30 mils to about 220 mils, the back polycarbonate laminate 6 has a relatively brittle coating. Notch brittleness is substantially reduced if the thickness of such layers is limited to less than about 220 mils, preferably from about 30 mils to about 150 mils. The minimum thickness of the polycarbonate back layer is limited only by current coating techniques and maintaining good optical properties of the coated product. Thicknesses below about 30 mils tend to be somewhat impractical. The upper limit of the coated back polycarbonate layer thickness, ie 220 mils, is critical in providing improved crush resistance. If the coated back polycarbonate layer is approximately 220
There is no significant improvement in the crush resistance of Structure A if it is thicker than the mill. In the preferred embodiment described above, the back layer of laminate 6 has a thickness of from about 30 mils to about 220 mils and has a scratch-resistant coating on the exposed surface of the polycarbonate layer opposite the direction of impact. In the embodiment described above, the scratch-resistant, hard, brittle coating has an effective brittleness and hardness to protect the underlying polycarbonate from abrasion, marring, and scratching. Such scratch-resistant coatings are known in the art and include metal oxides, modified melamines; UV-curable organic materials, such as acrylated monomers or polymeric resins modified with these monomers and acrylics. mixtures with for example acrylic modified polyurethanes; inorganic glasses such as silica or alumina; polyurethanes; silicone resins; silicone resins with organic repeating groups such as polymethyl acrylate or methacrylate; filled with silica such as colloidal silica. Silicone resins; include silicone resins derived from epoxy-terminated silanes; polyamide ester resins and melamine-based coatings. Preferred scratch-resistant coatings are silicone resins, especially silicone resins filled with colloidal silica, and melamine-based coatings.
Scratch-resistant coatings in the form of silicone resins filled with colloidal silica are described in US Pat. No. 4,027,073 and US Pat. No. 4,159,206. All of these patents are incorporated herein by reference. These scratch-resistant coatings may be applied directly to the surface of the polycarbonate layer of controlled thickness, or the surface of the polycarbonate layer may first be primed with an adhesion-promoting primer and then the primed surface may be scratch-treated. A resistive coating may also be applied. Solid resin materials which can constitute the layers of the laminate 6 are inter alia epoxies, polyurethanes, chlorinated aromatic ethers, polyethersulfones, acrylics (polymethyl methacrylate) and rubber-modified acrylics, polyarylsulfones, polystyrenes, cellulose acetate butyrate,
Polyesters, bisphenolfluorenone polycarbonates, and phenolphthalein-based polycarbonates can be included. As laminates for back laminates, in particular U.S. Pat.
Same No. 3312660, Same No. 3313777, and Same No.
Any polycarbonate resin described in, but not limited to, No. 3,666,614 can be used. All such patents are incorporated herein by reference. Any conventional adhesive can be used between the laminates of the back and front laminates, including polyvinyl butyral, ethylene terpolymer, epoxy, polyurethane, silicone, acrylic, and ethylene acrylic acid, among others. The tie layer in contact with any polycarbonate layer (and especially the polycarbonate back layer) must not only provide good attachment, but also be chemically compatible with the sensitive polycarbonate. A preferred tie layer for contacting the polycarbonate layer is a polysiloxane polycarbonate block copolymer. Polysiloxane polycarbonate block copolymer has the general formula It can be expressed by In this formula,
n is at least 1, and preferably n is an integer equal to 1 to about 1000, a is equal to 1 to about 200, b is equal to about 5 to about 200, and b is preferably about 15 to about 90, while the ratio of a to b is about
can vary from 0.05 to about 3, and b
has an average value of from about 15 to 90, the ratio of a to b is preferably from about 0.067 to about 0.45, and d is 1 or more, and Y
teeth

[Formula], and A is hydrogen and

is a member selected from the group consisting of [Formula], R is a member selected from the group consisting of hydrogen, a monovalent hydrocarbon group, and a halogenated monovalent hydrocarbon group, and R' is 1 a member selected from the group consisting of a valent hydrocarbon group, a halogenated monovalent hydrocarbon group, and a cyanoalkyl group,
R″ is a member selected from the group consisting of monovalent hydrocarbon groups and halogenated hydrocarbon groups, and Z is selected from the group consisting of hydrogen, lower alkyl groups, halogen groups, and mixtures thereof. Among the groups represented by R in formula 1 are aryl and halogenated aryl groups such as phenyl, chlorophenyl, xylyl, tolyl, etc.; aralkyl groups such as phenylethyl, benzyl, etc.; methyl; aliphatic, haloaliphatic and cycloaliphatic groups such as alkyl, alkenyl, cycloalkyl, haloalkyl, etc., including ethyl, propyl, chlorobutyl, cyclohexyl, etc. R are all the same group or Any two or more of the groups can be present, but R is preferably methyl. R' includes all the groups included in R above except hydrogen. Also, R' can all be the same group or any two or more of the above R groups excluding hydrogen, but preferably R' is methyl. R' also excludes hydrogen, R In addition to all groups encompassed by
Includes cyanoalkyl groups such as cyanoethyl, cyanobutyl groups, and the like. Groups included within the definition of Z in Formula 1 are hydrogen, methyl, ethyl, propyl, chloro, bromo, iodo, etc. and combinations thereof, with Z being preferably hydrogen. The hydrolytically stable copolymers of the present invention are described as containing copolymerized repeating units of polydiorganosiloxane linked to a polyester of divalent phenol and carbonic acid precursors by substituted aryl-oxy-silicon linkages. can do. However, the copolymerized repeating unit contains from about 10% to about 75% by weight, preferably from about 40% to 70% by weight, of the polydiorganosiloxane. The copolymer of formula 1 is heated between 0°C and 100°C, preferably at 20°C.
In the presence of acid acceptors at temperatures ranging from °C to 50 °C, the formula A halogen chain-terminated polydiorganosiloxane with the formula reacting a mixture with a dihydric phenol having
The reaction product is then phosgenated and phosgenation is continued until the resulting copolymer reaches its maximum intrinsic viscosity. However, in the above formula, R, R', Z and b are the same as defined above, and X is a halogen group, preferably a chloro group. The halogen chain-terminated polydiorganosiloxane of Formula 2 is described in Patnode, US Pat. No. 2,381,336.
No. 2,629,726 and Hyde U.S. Pat.
No. 2,902,507, it can be made by conventional methods, such as by controlled hydrolysis of diorganodihalosilanes, such as dimethyldichlorosilane. Another method that can be used is to prepare a mixture of diorganodichlorosilane and cyclic polydiorganosiloxane in the presence of a metal catalyst such as ferric chloride, as shown in U.S. Pat. It is about balancing. Although the various methods used to form the halogen chain-terminated polysiloxane are not critical, the halogen content of the resulting halogen chain-terminated polysiloxane can range from about 0.4% to about 35% by weight, preferably It has been found that it is desirable to maintain the halogen-terminated polysiloxane in the range of about 1% to about 10% by weight of the halogen chain terminated polysiloxane. Preferably, the halogen chain-terminated polysiloxane is in the form of a chlorinated polydimethylsiloxane. The divalent phenol included in formula 3 is, for example, 2,2-bis(4-hydroxyphenyl)-
Propane (bisphenol-A); 2,4'-dihydroxydiphenylmethane;bis-(2-hydroxyphenyl)-methane;bis-(4-hydroxyphenyl)-methane; 1,1-bis-(4 -hydroxyphenyl)-ethane; 1,2-bis-(4-hydroxyphenyl)-ethane; 1,1-bis-(4
-hydroxy-2-chlorophenyl)-ethane;
1,1-bis-(2,5-dimethyl-4-hydroxyphenyl)-ethane; 1,3-bis-(3-methyl-4-hydroxyphenyl)-propane; 2,
2-bis-(3-isopropyl-4-hydroxyphenyl)-propane, and the like. Mixtures can also be used. Others may seem overwhelming to experts in this technical field. The copolymers of the present invention essentially include repeating units consisting of a carbonic acid precursor and a polyester of dihydric phenol, interconnected by substituted aryloxy silicon bonds, and polydiorganosiloxane. The materials described above are also described in U.S. Pat. can. An example of the above copolymer is General Electric's LR-3320. This material has a specific gravity of 1.12, a tensile strength of 2500 to 3900 psi, an elongation of 230 to 430%, and a 400
It has a tear strength (Die C) of lb/in, and a embrittlement temperature of less than -76〓 and a heat distortion temperature of 160〓 (10 mils at 66psi load). Another such block copolymer, specifically General Electric's LR-5530, has a specific gravity of 1.07, a tensile strength of 2200 to 2500 psi, and a tensile strength of 500 to
Elongation up to 700%, tear (Die C) of 200 lb/in and embrittlement temperature below -76〓 and 130〓
It has a heat distortion temperature of (66psi). When reference is made herein to a polycarbonate layer without further description or indication, it is a polycarbonate of bisphenol A or 2,2-bis(4-hydroxyphenol)propane. In order to more fully and clearly explain the invention,
We present the following special example. It is intended that these examples be considered as illustrative of, rather than limiting, the invention disclosed and claimed herein. All parts and percentages in the examples are by weight unless otherwise specified. Example 1 (Reference Example) This example describes the preparation of a backside laminate of a double glazed structure. Standard edge bagging technique in an autoclave
One laminate was laminated using a laminate at a temperature of 142° C., a pressure of 100 psi, and a hold time of 20 minutes. This laminate has a 125 mil thick polycarbonate layer with a scratch resistant coating on its exposed impact surface facing the direction of impact. This layer is LR−
With a 34 mil thick tie layer of 3320 polysiloxane polycarbonate block copolymer
A 500 mil thick acrylic layer is bonded to a 188 mil thick polycarbonate layer, which is further bonded to a 188 mil thick polycarbonate layer by a 34 mil thick LR-3320 tie layer. A tie layer of mil-thick LR-3320 is bonded to a 125-mil thick back polycarbonate layer on the side opposite the direction of impact, which Has a scratch-resistant coating. Example 2 (Reference Example) This example describes the preparation of a front glass laminate that is outside the scope of the present invention. The intermediate glass layer with a thickness of 250 mils was heated to 100 psi at a temperature of 135°C using standard edge bagging methods in an autoclave.
bonded to a 375 mil thick front impact glass layer by a 34 mil thick tie layer of LR-3320 on its surface facing the direction of impact and a hold time of 20 minutes. It was then bonded to a 125 mil thick back glass layer by a 34 mil thick tie layer of LR-3320 on its surface opposite the direction of impact. Example 3 (Reference Example) This example describes the preparation of a front glass laminate that is outside the scope of the present invention. The intermediate glass layer, having a thickness of 250 mils, was heated at a temperature of 135°C using standard edge bagging methods in an autoclave.
At a pressure of 100 psi and a hold time of 20 minutes, a 250 mil thick front impact glass layer with a 34 mil thick tie layer of LR-3320 on its surface facing the direction of impact. and was bonded to a 250 mil thick back glass layer by a 34 mil thick tie layer of LR-3320 on its surface opposite the direction of impact. Example 4 (Comparative Example) This example describes a double glazed structure that is outside the scope of the present invention. The double glazing structure is constructed with the back laminate of Example 1 placed 1/4 inch behind or downstream from the front glass laminate of Example 2, with the laminate of Example 2 closest to the direction of impact. Configured. Thus, the front glass laminate of Example 2 is separated from the back glass laminate of Example 1 by a 1/4 inch air space. Example 5 (Comparative) This example describes another double glazed structure that is outside the scope of the present invention. The double glazing structure is constructed with the back laminate of Example 1 placed 1/4 inch behind or downstream from the front glass laminate of Example 3, with the laminate of Example 3 closest to the direction of impact. Configured. Thus, the front glass laminate of Example 3 is separated from the back glass laminate of Example 1 by a 1/4 inch air space. Example 6 (Reference Example) This example illustrates a front glass laminate of the present invention. Front glass laminates were prepared by laminating one glass laminate in an autoclave using a standard edge bagging method at a temperature of 135°C, a pressure of 100 psi, and a holding time of 20 minutes. .
This glass laminate contains a 375 mil thick intermediate glass layer which is 125 mil thick with a 34 mil thick tie layer of LR-3320 on its surface facing the direction of impact. bonded to the front impact glass layer and to the 125 mil thick back glass layer by a 34 mil thick tie layer of LR-3320 on its surface opposite the direction of impact. has been done. Example 7 This example illustrates a double glazed structure of the present invention. A double glass structure was constructed with the back glass laminate of Example 1 placed 1/4 inch behind or downstream of the front glass laminate of Example 6 with the Example 6 laminate closest to the direction of impact. Thus, the front glass laminate of Example 6 is separated from the back glass laminate of Example 1 by a 1/4 inch air space. Example 8 (Reference Example) This example describes the preparation of a front glass laminate of the present invention. Front glass laminates were prepared by laminating the glass laminates in an autoclave using standard edge blowing methods at a temperature of 135° C., a pressure of 100 psi, and a hold time of 20 minutes. This glass laminate contains a 500 mil thick intermediate glass layer which has a 125 mil thick front surface with a 30 mil thick tie layer of polyvinyl butyral on its surface facing the direction of impact. and to a 125 mil thick back glass layer by a 30 mil thick tie layer of polyvinyl butyral on its surface opposite the direction of impact. Example 9 This example illustrates another double glazed structure of the present invention. A double glazing structure was constructed with the back laminate of Example 1 placed 1/4 inch behind or downstream of the front glass laminate of Example 8, with the laminate of Example 8 closest to the direction of impact. . Thus, the front glass laminate of Example 8 is separated from the back glass laminate of Example 1 by a 1/4 inch air space. All double glazed structures of Examples 4, 5, 7 and 9 were repeatedly fired from a distance of 10 meters with a 144 grain 7.62 mm NATO bullet reaching over 2700 fps. The results of repeated firing on these double glazed structures are listed in the table.

[Table] In the table, the code NP indicates no penetration;
P indicates penetration, NS indicates no crushing, and S indicates crushing. As clearly seen from the table, the double glazed structures of the present invention, i.e. those prepared according to Examples 7 and 9, resist penetration by six shots with a 7.62 mm caliber rifle bullet. resistant;
Furthermore, there was no shattering of the back surface of the double-glazed structure.
Double glazed structures falling outside the scope of the invention, i.e.
7.62 prepared according to Examples 4 and 5
It had no resistance to penetration when fired repeatedly by mm rifle bullets. In addition, fragmentation of the back surface of the back laminate occurred even when no penetration of the structure by the bullet occurred. Even though the dual structure of Example 7 was thinner than the structures of Examples 4 and 5, the combined thickness of the glass layers of the front glass laminate of the Example 7 structure was 625 mils. Although the combined thickness of the glass layers of the front glass laminate of the structures of Examples 4 and 5 was 750 mils, the dual structure of Example 7 was similar to that of Examples 4 and 5. It is interesting that it was better than a structure. This demonstrates the criticality of using a front glass laminate with a thin outer glass layer and a thick glass core to provide an improved double glazed structure to withstand high velocity repetitive fire. ing. It will be understood that the above embodiments are merely representative of the implementation of the invention.
It is therefore possible to make the various layers thicker or thinner if required. Additionally, although specific methods have been described for the Examples, other lamination methods can generally be applied to fabricate the structures of the Examples.

[Brief explanation of the drawing]

FIG. 1 is a side view of a double glazed structure of the present invention with one intermediate air space between the back laminate and the front laminate.

Claims (1)

[Claims] 1. A back laminate located on the side opposite to the direction of impact;
and a front glass laminate comprising a plurality of glass laminates joined by an intimate adhesive, the back glass laminate comprising a plurality of glass laminates joined by an intimate adhesive; Select the body layer from polycarbonate, glass and solid resin materials,
and wherein at least one laminate in the back laminate is a polycarbonate laminate, the front glass laminate and the back laminate being spaced apart; the body includes an intermediate glass core, a front glass layer and a back glass layer, each of the front glass layer and the back glass layer being thinner than the glass core;
and having a thickness of 30 to 220 mils. 2 The intimate adhesive consists essentially of dialkylsiloxy units bonded to each other by silicon-oxygen-silicon bonds (each silicon atom has two organo groups bonded via a carbon-silicon bond). a halogen-chain-terminated polydiorganosiloxane (A) composed of about 5 to 200 chemically bonded diorganosiloxy units having the formula (In the above formula, Z is a member selected from the group consisting of hydrogen, a lower alkyl group, a halogen group, and a combination thereof, and R is a member selected from the group consisting of hydrogen, a hydrocarbon group, and a halogenated hydrocarbon group. dihydric phenol (B)
A structure as claimed in claim 1, comprising a polysiloxane-polycarbonate block copolymer prepared by reacting a polysiloxane-polycarbonate block copolymer with a polysiloxane-polycarbonate block copolymer and phosgenating the purified reaction product. 3. A structure as claimed in claim 1, wherein the intermediate glass core disposed between the front and back glass laminates in the front area laminate contains a glass laminate. 4. Said one glass layer in said intermediate glass core has a thickness greater than the thickness of either said front layer or said back layer.
Structures listed in section. 5. The structure of claim 4, wherein said one glass layer in said intermediate glass core has a thickness greater than about 250 mils. 6. The intermediate glass core between the front and back glass laminates in the front laminate is comprised of a plurality of glass laminates, and the plurality of glass laminates in the core are bonded together by an intimate adhesive. 2. A structure as claimed in claim 1, wherein the structure is joined to one another. 7. The structure of claim 6, wherein the intermediate glass core has a thickness greater than about 250 mils.