IMPROVED IMPACT RESISTANT LAMINATE

Abstract: Improved impact or shock resistant laminates are provided comprising a plurality of laminae including a back polycarbonate lamina of controlled thickness opposite the direction of impact of shock and at least one acrylic resin lamina facing the direction of impact or shock, said polycarbonate lamina having a relatively brittle overlayer or coating on the outer surface thereof opposite said acrylic resin lamina.

Description: - l - Description Improved Impact Resistant Laminate This invention relates to improved impact resistant laminates. More particularly, it relates to such laminates having a plurality of ' layer ' s ** of' * laminae'-including a- back polycarbonate- lamina of . controlled thickness opposite the direction of impact or shock and at least one acrylic resin based lamina facing the direction of impact or shock, said polycarbonate lamina having on the side thereof opposite the acrylic based lamina a relatively brittle coating. The laminates are particularly characterized by control of the thickness of the back polycarbonate laminae which reduces spalling or other failure of the polycarbonate surface when the laminates are subject to impact or shock, thereby improving the. erformance of the laminates. BACKGROUND OF THE INVENTION The use of so-called safety glazing or- enetration resistant glazing for windows, windshields and the like utilizing polycar¬ bonate resin layers as a structural component is well known. For example, glass. olycarbonate resin laminates are described in U.S. Patent 3,666,614, the glass and polycarbonate being cohered together using an ethylene-vinyl acetate copolymer. In U.S. Patent 3,520,768, there are described laminates of relatively thick glass having a comparatively thin polycarbonate foil as the cohering material. It is also known to utilize certain poly- siloxane-polycarbonate block copolymers described more particu¬ larly hereinafter as the adhesive layers. It is normal practice in constructing certain such laminates to utilize glass or re¬ latively hard solid resinous materials as the impact or shock receiving layers' while utilizing polycarbonate as the back or inner or downstream layer or that presented to the person or ob¬ ject being protected. In those cases where polycarbonate is used as a layer of a laminate, it is often, because of the relative softness of the polycarbonate, protected, especially on its exposed surface, with a mar- or scratch-resistant and transparency preserving layer usually less than 2 mils thick and, preferably, from about 0.05 to 2 mils thick. The minimum thickness is re¬ stricted only by current application technology and the desired durability of the mar-resistant coating. Maximum acceptable coating thickness is a function of the relative brittleness of the mar-resistant finish. In general, such' mar-resistant layers, which are well known, can be metal oxides; modified melamines; ultraviolet hardenable organics such as acr lated monomers or mixtures of these monomers wich acrylate-modified polymeric resins; inorganic, glasses such as silica or alumina; polyurethanes; sili- cone resins derived from epoxy terminated silanes; silicone resins with recurring organic groups such as polymethyl methacrylate; silicone resins; silica, such as colloidal silica, filled silicone resins; polyamide ester resins; and, ion-beam deposited carbon, among others, are harder and relatively more brittle than the under- lying polycarbonate layer which they protect. It has been found that in impact shock-resistant laminates utilizing such relatively brittle layers along with polycarbonate, the relatively brittle material cracks under impact causing the rear-most polycarbonate layer to spall, causing damage to exposed objects behind the laminate. Such spalling occurs -because of the so-called "notch sensitive" character of polycarbonates.. Thus, if an overlying brittle layer is broken, the fracture lines propagate to the poly¬ carbonate and act as "critical" notches causing the polycarbonate to fail in a brittle manner with little of the energy absorption typical of this normally impact-resistant material. It will thus be seen that there is a need for providing impact shock resistant laminates using polycarbonate and overlying rela¬ tively more brittle material which are reduced in this so-called notch sensitivity, thus making them more useful from a practical point of view. DESCRIPTION OF THE INVENTION According to the present invention, there are provided improved shock and impact resistant laminates comprised of a plurality of laminae including at least one acrylic resin based lamina facing the direction of impact or shock and a back poly- - • - -^._-carbonate ^ lamina-.o * &-conferolled--thickness--opposite...the...direction of impact or shock having a relatively brittle overlayer or 5 coating on the outside surface, i.e., the surface opposite the acrylic based lamina. The back polycarbonate lamina has a thickness restricted to less than about 220 mils and preferably from about 30 to about 150 mils. It has been found that in this thickness range, i.e., below about 220 mils, the notch sensitivity 10 of the polycarbonate lamina coated with a relatively brittle mar-resistant coating is substantially reduced, thereby greatly improving the performance and practical utility of the laminates. The minimum thickness of the polycarbonate lamina is restricted only by current coating application technology and maintenance of 15 good optics of the coated product. Thicknesses less than about 30 mils tend to be somewhat impractical. The acrylic resin based lamina is of a thickness greater than the thickness of the polycarbonate lamina. The thickness of the acrylic resin lamina depends upon the degree of shock or 20 impact that it is desired for the laminates to withstand. The greater the shock or impact that the laminates are desired to * successfully withstand, the greater the thickness of the acrylic resin lamina. Thus, for example, in the case of laminates used as bullet resistant laminates if the laminate is required to 25 withstand "Medium Power" bullets, e.g., 9 mm Lager, .38 and .38 super, the thickness of the acrylic resin lamina is about 375 mils. If the laminates are to successfully withstand the impact of high caliber bullets, the thickness of the acrylic resin lamina should be greater than 375 mils. Generally, the thickness 30 of the acrylic resin lamina ranges from about 250 mils to an upper thickness limit which is dependent on the degree of shock and impact resistance being desired. The upper thickness limit 4 will generally be limited by practical consideration such as weight and bulkinesε and, therefore, generally is about 4,000 mils, with 3,000 mils being preferred, and 1,000 mils being more pre¬ ferred. Instead of using a single acrylic ply, two or more plies of the acrylic resin may be used for the construction. If two or ' more acrylic laminae are used, they may be bonded together by the hereinbelow described adhesive. It has been found that a laminate of the present invention constructed of multi-plies of acrylic has better impact resistance, for the same thickness of acrylic, than a laminate containing a single ply of acrylic. Thus, for example, a laminate containing two 250 mil plies of acrylic bonded together by means of the herein described adhesive possesses generally im¬ proved impact and penetration-resistance than a laminate containing a single $00 mil ply of acrylic. In addition,to the polycarbαnate ply having a mar- or scratch- resistant transparency preserving layer on its exposed surface, the exposed surface of the acrylic lamina may also contain a mar- or scratch-resistant transparency preserving layer. The nature and thickness of this layer is generally similar to that deposited on the polycarbonate lamina and has been described hereinabove. Any polycarbonate resin can be used as lamina including but not limited to those described in U.S. Patents 3,161,615; 3,220,973; 3,312,659; 3,312,660; 3,313,777; 3,666,614, among others, all of which are included herein by reference. Preferred polycarbonate resins are the aromatic polycarbonate resins. The term "acrylic resin" as it appears herein is meant to em¬ brace within its scope those polymers or resins resulting from the polymerization of one or more acrylates such as, for example, methyl acrylate, ethyl aer late, butyl aerylate, 2-ethylhexyl acrylate, etc., as well as the methacrylates such as, for instance, methyl methacr late, ethyl methacrylate, butyl methacrylate, hexyl methacrylate, etc. Copolymers of the above acrylate and methacry- lie monomers are also included within the term acrylic resin as it - appears^herein. The- pelymerization-of -the--monomeric-aerylates and methacrylates to provide the polyacr late resins useful in the practice of the invention may be accomplished by any of the well - - nown-polymerization-technigues-r- .-A-preferred acrylic resin is~poly 5 (meth lmethacrylate) . Where desirable, adhesion promoting primers can be used to promote adhesion, such materials being well known and including, among others, vinyl alkoxy silanes, aminoalkylalkoxy silanes-, alkoxy silanes, silyl peroxides and amino-alkoxy silanes, such 10 materials being described in the above U.S. Patent 3,666,614 and elsewhere. A present advantage is that primers are usually not necessary in connection with any polycarbonate or acrylic resin used although they can be used where indicated. Any conventional adhesives may be used between the laminae 15 including polyvinylbutyrals, ethylene terpolymers, epoxies, poly- urethanes, silicones, acrylics, and ethylene acrylic acids, among others. The adhesive interlayer in contact with the polycarbonate lamina must provide not only good adhesion but also must be chem¬ ically compatible with the sensitive polycarbonate. The preferred 20 interlayer for contact with the polycarbonate lamina is a poly- siloxane-polycarbonate block copolymer. The polysiloxane-polycarbonate block copolymers can be ex¬ where n is at least 1, and preferably n is -an integer equal to from 1 to about 1000, inclusive, a is equal to from 1 to about 200, inclusive, b is equal to from about 5 to about 200, inclusive, 30 and preferably b has an average value from about 15 to about 90, inclusive, while the ratio of a to b can vary from about .05 to about 3, inclusive, and when b has an average value of from about 15 to about 90, inclusive, the ratio of a to b is preferably from about 0.67 to about 0.45, inclusive, and d is 1 or more, Y is OMPI . WIPO .v Φ?NATlθ A is a member selected from the class of hydrogen and p -C-OR" R is a member selected from the class of hydrogen, monovalent hydrocarbon radicals and halogenated monovalent hydrocarbon radicals, r" is a member selected from the class of monovalent hydrocarbon radicals, halogenated * monovalent hydrocarbon radicals and cyanoalkyl radicals, r" is a member selected from the class consisting of monovalent hydrocarbon radicals and halogenated hydrocarbon radicals, and Z is a member selected from the class of hydrogen, lower alkyl radicals and halogen radicals and mix- tures thereof. Included within the radicals represented by R of Formula 1 are aryl radicals and halogenated aryl radicals such as phenyl, chlorophenyl, xylyl, tolyl, etc.; aralkyl radicals such as phenylethyl, benzyl, etc.; aliphatic, haloaliphatic and cyclo- aliphatic radicals such as alkyl, alkenyl, cycloalkyl, haloalkyl, including methyl, ethyl, propyl / chlorobutyl, cyclohexyl, etc.; R can be all the same radical or any two or more of the afore¬ mentioned radicals, while R is preferably methyl, R* includes all radicals included by R above except hydrogen, where R * can also be all the same radical or any two or more of the aforementioned R radicals except hydrogen, and R* is preferably methyl. R' also includes, in addition to all the radicals included by R, except hydrogen, cyanoalkyl radicals such as cyanoethyl, cyanobutyl, etc. radicals. Radicals that are included within the definition of Z of Formula 1 are hydrogen, methyl, ethyl, propyl, chloro, bromo, iodo, etc. and combinations thereof, and Z is preferably hydrogen. The hydrolytically stable copoly ers of the present invention can be further described as comprising recurring copolymeric units of a polydiorganosiloxane joined by substituted aryloxy-silicon linkages to a polyester of dihydric phenol and a precursor of car- bonate acid, where each of said recurring copolymeric units com¬ prises by average weight from about 10% to about 75% of said poly¬ diorganosiloxane, and preferably from about 40 to 70% by weight. The copolymers of Formula 1 can be produced by reacting at temperatures in the range of 0°C to 100°C, preferably, 20°C to 50°C f and in the presence of an acid acceptor, a mixture of a halogen chain-stopped polydiorganosiloxane having the formula and a dihydric phenol having the formula and thereafter phosgenating said reaction product until the re¬ sulting copolymer achieves a maximum intrinsic viscosity, where R, R' , Z and b are as defined above, and X is a halogen radical, pre¬ ferably chloro. The halogen chain-stopped polydiorganosiloxanes of Formula 2 can be made by conventional procedures such as by the controlled hydrolysis of a diorganodihalosidane, for example, dimethyldi- chlorosilane as taught in Patnode Patent 2,381,366 and Hyde Patents 2,629,726 and 2,902,507. Another procedure that can be employed involves equilibrating a mixture of a diorganodichlorosilane and a cyclic polydiorgano¬ siloxane in the presence of a metal catalyst such as ferric chlo¬ ride as shown in Sauer Patent 2,421,653. Although the various pro¬ cedures utilized in forming the halogen chain-stopped polysiloxane are not critical, generally it has been found desirable to main¬ tain the halogen content of the resulting halogen chain-stopped polysiloxane in the range of about 0.4 to about 35% by weight, and preferably from about 1 to about 10% by weight of said halogen chain-stopped polysiloxane. The halogen chain-stopped polysiloxane is preferably in the form of a chlorinated polydimeth lsiloxane. Dihydric phenols that are included in Formula 3 are, for example, 2,2-bis(4-hydroxyphenyl)-propane (bisphenol-A); 2,4'- dihydroxydiphenylmethane; bis-(2-hydroxyphenyl)-methane; bis-(4- hydroxyphenyl)-methane; 1,1-bis-( -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; ,3-bis- (3-methyl-4-hydroxyphenyl)-propane; 2,2'bis-(3-isopropyl-4- hydroxyphenyl)-propane, etc. Mixtures can also be used. Others will occur to those skilled in the art. " The copolymers of the present invention essentially comprise recurring units consisting of a polydiorganosiloxane interconnected by substituted aryloxy-silicon linkages to a polyester of carbonic ■ acid precursor and a dihydric phenol. Materials of the above nature are also described in U.S. Patent 3,189,662 included herein by reference and can be used either alone as such or in conjunction with well known modifiers to provide particular desired characteristics. Illustrative of the above block copolymers is General Electric 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, a tear strength (Die C) of 400 lbs./in., and a brittleness temperature below -76°F and a heat deflection temperature (10 mils under 66 psi Load) of 160°F. Another such block copolymer, specifically General Electric LR-5530, has a specific gravity of 1.07, a tensile strength of 2200 to 2500 psi, an elongation of 500-700T, a tear (Die C) of 200 lbs./in. , and a brittleness temperature below -76 F and a heat deflection temperature (66 psi) of 130°F. Where a polycarbonate layer without further description or designation is mentioned herein, it is the polycarbonate of bisphenol-A or 2,2-bis(4-hydroxyphenol) propane. DESCRIPTION OF THE PREFERRED EMBODIMENT In order to more fully and clearly illustrate the present invention, the following specific examples are presented. It id intended that the examples be considered as illustrative rather than limiting the invention disclosed and claimed herein. In the examples, all parts and percentages are on a weight basis un¬ less otherwise specified. EXAMPLE 1 This example illustrates a prior art laminate over which the present invention represents an improvement. There were laminated in an autoclave using a vacuum bag with a temperature of 290°F, a pressure of 240 to 250 psi and a hold time of 45 ' minutes a laminate consisting of strengthened primed glass 125 mils thick bonded by 60 mils of LR-5530 polysiloxane-polycarbonate block copolymer to a 250 mil sheet of polycarbonate bonded in turn through 30 mils of LR-3320 polysiloxane-polycarbonate block copoly¬ mer to a 375 mil thick layer of polycarbonate, the latter having a relatively more brittle mar-resistant coating on its back, exposed or inboard laminate surface. When a "Medium Power" bullet was fired at the glass surface in accordance with Underwriters Laboratory Standard for Bullet-Resisting Equipment, specifically UL 752, dated February 23, 1973, at a temperature of 55°F, the exposed surface of the 375 mil polycarbonate ply or layer spalled in a brittle manner, although there was no bullet penetration, damaging cardboard indicators placed approximately about 18 inches behind the test laminate. This example illustrates the so-called notch sensitivity of the relatively thick polycarbonate layer when it is subjected to impact shock. Reference to various powered ammunition and other test materials are as specified in the above Standard. EXAMPLE 2 This example illustrates another typical prior art impact shock-resistant laminate utilizing polycarbonate layers. There was prepared in an air autoclave using a vacuum bag at ' a tempera¬ ture of 290°F, a pressure of 240 to 250 psi and a hold time of 30 minutes, a laminate having a front or impact shock receiving ply of 250 mils of polycarbonate with a relatively more brittle mar-resistant outer surface. This polycarbonate layer was bonded using a 20-25 mil thick layer of LR-3320 block copolymer to a 500 mil thick layer of polycarbonate bonded in turn by a similar thick¬ ness of LR-3320 block copolymer to a back ply of polycarbonate 250 mils thick,, the latter ply having a relatively more brittle mar-resistant coating on its outer or downstream surface. The total thickness of this laminate was approximately 1 3/64" with a total polycarbonate thickness of 1". This laminate was tested in accordance with the above UL 752 Standard after the front outer surface aws exposed to a temperature of -25 F for a minimum of three hours, the inboard surface or back ply being exposed to ambient room temperature. When a "Medium Power" bullet was fired at the front ply, while there was no bullet penetration, a brittle punch-out type spall from the back or inboard polycarbon¬ ate surface caused damage to a cardboard indicator placed about 18 inches behind the laminate. EXAMPLE 3 A laminate was prepared using two polymethyl methacrylate plies each 250 mils thick bonded to each other by 34 mils of LR- 3320 copolymer. This two-ply polymethyl methacrylate construction was bonded in turn by 34 mils of LR-3320 copolymer to a back ply 125 mils thick of polycarbonate with a mar-resistant coating on its outer surface. The laminate was prepared in an air autoclave using a vacuum bag at a temperature of 290 F, a pressure of 100 to 110 psi and a hold time of 30 minutes. The resulting laminate was resistant, at room temperature, to multiple .38 automatic slugs fired from a distance of 15 feet into the front polymethyl methacrylate face of the laminate. There was no spall from the 'BUR OM mar-resistant coated 125 mil thick polycarbonate back ply. EXAMPLE 4 A ' laminate was prepared-using a single polymethyl:-methacry¬ late ply 500 mils thick and a back ply 125 mils thick of poly- carbonate with a mar-resistant coating on its outer surface bonded by 34 mils of LR-3320 copolymer to the polymethyl methacrylate. The laminate was prepared in an air autoclave using a vacuum bag at a temperature of 290°F, a pressure of 100 to 110 psi and a hold time of 30 minutes. The resulting laminate was not resistant, at room temperature, to multiple .38 automatic slugs fired from a distance of 15 feet into the front polymethyl methac¬ rylate face of the laminate. EXAMPLE 5 A laminate was prepared using a single polymethyl methacry- late ply 750 mils thick and a back ply 125 mils thick of polycar¬ bonate with a mar-resistant coating on its outer surface bonded by 34 mils of LR-3320 copolymer to the polymethyl methacrylate. The laminate was prepared in an air autoclave using a vacuum bag at a temperature of 290°F, a pressure of 100 to 110 psi and a hold time of 30 minutes. The resulting laminate was resistant, at room temperature, to multiple .38 automatic slugs fired from a distance of 15 feet into the front polymethyl methacrylate face of the laminate. There was no spall from the mar-resistant coated 125 mil thick polycarbonate back ply. Comparison of Examples 3-5 shows that while a laminate of the present invention containing two 250 mil polymethyl methacrylate plies bonded together by the LR-3320 copolymer successfully with¬ stands multiple shots from a .38 automatic, it takes a laminate containing a single ply of polymethyl methacrylate 750 mils thick to provide the same impact and penetration resistance. There are provided, then,, by the present invention improved impact shock-resistant laminates which overcome any notch sensi¬ tivity tendency of polycarbonate layers when overlaid with rela¬ tively more -brittle material on the side opposite the impact receiving direction. The invention further makes possible and practical laminates of the type described which are not only improved in impact resistance but are resistant to marring and scratching and similar abuse which detracts from clarity or transparency when such laminates are used as windshields, windows, view ports, glazing and the like. Heating elements or detection means such as wires, films and the like well known to those skilled in the art can also be incorporated in the present struc¬ tures.

Claims: Claims 1. Impact or shock resistant laminate comprising a plurality ----- • of * 'laminae-including--a * -back~ρo ycarbon * ate- * -la_rai * πa:'-opposi-te- the - direction of impact or shock, said back polycarbonate lamina having a mar-resistant coating on the exposed surface thereof opposite the direction of impact, and at least one acrylic resin lamina facing the direction of impact or shock bonded to said polycarbonate lamina by a compatible adhesive. .2. The laminate according to claim 1 wherein said back polycarbonate lamina has a thickness from about 30 mils to about 220 mils. 3. The laminate according to claim 2 wherein said mar resistant coating is from about 0.05 mils to about 2 mils thick. 4. The laminate according to claim 3 wherein said mar resistant coating is harder and more brittle than the underlying polycarbonate. 5. The laminate according to claim 3 wherein said adhesive is comprised of a block polysiloxane-polycarbonate copolymer prepared by reacting (A) a halogen chain-stopped polydiorgano¬ siloxane composed of from about 5 to 200 chemically combined 5 diorganosiloxy units consisting essentially of dialkylsiloxy units which are connected to each other by silicon-oxygen-silicon linkages wherein each of the silicon atoms has two organo radi¬ cals attached through a carbon-silicon bond, and (B) a dihydric phenol having the formula where Z is a member selected from the class consisting of hydrogen, lower alkyl radicals and halogen radicals and combinations thereof, 15 and R is a member selected from the class consisting of hydrogen, hydrocarbon and halogenated hydrocarbon radicals, and phosgenating the purified reaction product. ' 6. The laminate according to claim 5 wherein said laminate contains one acrylic resin lamina honded by said adhesive to said back polycarbonate lamina. 7. The laminate according to claim 5 wherein said laminate contains at least two acrylic resin laminae bonded to each other by said adhesive, said laminae in turn being bonded to said back polycarbonate lamina by said adhesive. 8. The laminate according to claim 6 wherein said acrylic resin lamina has a mar-resistant coating on the exposed surface thereof. 9. The laminate according to claim 7 wherein the acrylic lamina facing the direction of shock or impact has a mar- resistant coating on the exposed surface thereof.

Inventors: MOLARI R
Applicants: GEN ELECTRIC, GENERAL ELECTRIC CO
Application year: 1979
Main classification: B32B27
IPC codes: B32B27