Patent Publication Number: US-2019193384-A1

Title: Thermosettable adhesive taped articles

Description:
TECHNICAL FIELD 
     The present invention relates to thermosettable adhesive tape, in particular such tape having a black surface, and articles comprising such tape, as well as methods of making same. 
     BACKGROUND 
     Many different types of adhesive tape have been used in a variety of ways to adhere many different types of substrates together. For example, in U.S. Pat. No. 5,086,088, a pressure-sensitive thermosetting adhesive is disclosed that comprises a photo-polymerizable prepolymeric or monomeric syrup containing an acrylic ester and a polar copolymerizable monomer, an epoxy resin or a mixture of epoxy resins containing no photo-polymerizable groups, a heat-activatable hardener for the epoxy resin, a photoinitiator, and a photocrosslinking agent. In addition, U.S. Pat. No. 6,348,118 also discloses a method of bonding a component to glass, where the method comprises disposing a pressure-sensitive adhesive sheet material between the component and the glass so that the adhesive sheet material is adhered to the component and the glass. A disclosed adhesive sheet material comprises the photo-polymerization reaction product of starting materials comprising: (a) a monomeric mixture or partially prepolymerized syrup comprising at least one acrylic acid ester of an alkyl alcohol and at least one copolymerizable monomer; (b) an epoxy resin or a mixture of epoxy resins, (c) a heat-activatable hardener for the epoxy resin or mixture of epoxy resins, (d) a photoinitiator, and (e) a pigment. 
     The present invention provides an improvement in such adhesive technology. 
     DISCLOSURE OF INVENTION 
     In accordance with one aspect of the present invention, a thermosettable adhesive tape is provided. The tape comprises two adhesive layers bonded together, each of which has a thickness and comprises a thermosettable adhesive, which is the photo-polymerization reaction product of starting materials. The starting materials for each adhesive layer comprises at least a photo-polymerizable acrylic component (e.g., with ultraviolet light) and a thermosettable (e.g., heat curable) epoxy component. The acrylic component can include, for example, a partially polymerized composition (e.g., a prepolymerized syrup) and/or a monomeric mixture comprising at least one acrylic acid ester or methacrylic acid ester of an alkyl alcohol (e.g., a non-tertiary alcohol). The acrylic component can also include a copolymerizable monomer (e.g., a moderately polar copolymerizable monomer) and a photoinitiator. The epoxy component can include, for example, a curable epoxy resin or a mixture of epoxy resins. The curable epoxy resin can be, or the mixture of epoxy resins can include, a heat curable epoxy resin. The starting materials for either or both of the adhesive layers can include a heat curable epoxy resin. When a heat curable epoxy resin is used, a heat-activatable hardener can be included in the applicable starting materials. The epoxy component can contain some or no photo-polymerizable groups. The starting materials for the two adhesive layers can have the same or different acrylic component and/or epoxy component. 
     The thermosettable adhesive, used for either of the two adhesive layers, is not black when fully cured without the presence of a black coloring pigment. The thermosettable adhesive (i.e., a first adhesive) used for one of the adhesive layers (i.e., a first adhesive layer) includes a black coloring pigment (e.g., carbon black), and the starting materials for this first adhesive includes a sufficient amount of the black coloring pigment to cause the first adhesive to have a black color after the first adhesive is substantially cured. The starting materials for the thermosettable adhesive (i.e., a second adhesive) used for the other adhesive layer (i.e., a second adhesive layer) either do not include any black coloring pigment (e.g., carbon black) or at least do not contain an amount of a black coloring pigment that would cause the second adhesive to have a black color after the second adhesive is substantially cured. As used here, substantially cured refers to the adhesive being completely cured or at least cured enough so the resulting adhesive layer is suitable for use in structurally bonding together two desired substrates. 
     The present tape has the first adhesive layer bonded to one major surface of the second adhesive layer. Optionally, another or third adhesive layer can be bonded to the opposite major surface of the second adhesive layer, where this other adhesive layer is the same as, or similar to, the first adhesive layer in that the other adhesive layer is substantially photo-polymerized and has enough black coloring pigment to have a black color. 
     The first adhesive layer is made from a layer of starting materials that is thin enough to allow substantial photo-polymerization (e.g., with ultraviolet (UV) light) of the starting materials, at least the acrylic component, even with the starting materials containing a sufficient amount of the black coloring pigment to cause the first adhesive to have a black color after the first adhesive is substantially cured. As used here, substantial photo-polymerization refers to complete polymerization, as a practical matter, or at least the degree of polymerization needed to allow the resulting photo-polymerized layer to be used in the desired thermosettable adhesive tape. In accordance with the present invention, the term black can refer to a range of colors from dark grey to black. The color black, as used herein, can also be seen as having an L* specular excluded number of 32 or less, or preferably of 30 or less. The second adhesive layer is made from a layer of starting materials which has a thickness that would be sufficiently thick to prevent substantial photo-polymerization (e.g., with UV light) of the starting materials, at least the acrylic component (i.e., completely prevented or at least prevented enough to stop the resulting photo-polymerized layer from being effectively used in the desired thermosettable adhesive tape), if the starting materials contained enough of a black coloring pigment to cause the second adhesive to have a black color after the second adhesive is cured. 
     In accordance with another aspect of the present invention, an article is provided that includes the above describe adhesive tape adhered to at least one substrate. The tape can have one side defined by the first adhesive layer and another side defined by the second adhesive layer, with a release liner being disposed so as to protect at least one side or the other, or both sides, of the tape. An opaque or translucent substrate (e.g., a mirror button or hinge plate) can be adhered to the second adhesive layer of the tape. The tape can have a periphery in the shape of the opaque or translucent substrate (e.g., a mirror button or a hinge plate) or a number of the substrates can be adhered at separate locations on the second adhesive layer of the tape. The first adhesive layer of the tape can be adhered to a transparent substrate such as, for example a window (e.g., a windshield of a vehicle such as, for example, an automobile, watercraft, aircraft, spacecraft). As used here, a transparent substrate refers to a substrate that is optically clear or at least partially transparent to visible light, that is, the substrate is sufficiently transparent that an observer can see whether the first adhesive layer is black through the substrate (e.g., transparent enough to allow at least about 15%, or at least about 30%, of visible light to be transmitted therethrough). 
     The thickness of the first adhesive layer can be in the range of from about 3 mils to about 12 mils, in the range of from about 4 mils to about 8 mils, or in the range of from at least about 5 mils up to about 6 mils. The thickness of the second adhesive layer can be in the range of from about 15 mils to about 30 mils or can also be in the range of from about 20 mils to about 25 mils. The black coloring pigment content in the starting materials of the first adhesive should be at least about 0.125% and may be up to about 5% or even more, by weight of the starting materials. The black coloring pigment content in the starting materials of the first adhesive can preferably be in the range of at least about 0.25% and up to about 0.75% or more, by weight of the starting materials. The black coloring pigment content in the starting materials of the second adhesive can be in the range of from 0.0% up to about 0.1% by weight of the starting materials. In general, it is believed that the weight percent (wt. %) concentration of pigment can be increased as the pigment particle size being used is increased. 
     In accordance with an additional aspect of the present invention, a method of making a thermosettable adhesive tape is provided. The method comprises: forming a first starting materials layer of photo-polymerizable first starting materials; forming a second starting materials layer of photo-polymerizable second starting materials; photo-polymerizing (e.g., with ultraviolet (UV) light) the first starting materials layer so as to produce a first adhesive layer having a first thickness and comprising a first thermosettable adhesive; photo-polymerizing (e.g., with ultraviolet (UV) light) the second starting materials layer so as to produce a second adhesive layer having a second thickness and comprising a second thermosettable adhesive; and bonding the first adhesive layer to a major surface of the second adhesive layer. 
     The first starting materials comprise a photo-polymerizable acrylic component (e.g., like that described above), a thermosettable epoxy component (e.g., like that described above), and a black coloring pigment (e.g., carbon black). The second starting materials comprise a photo-polymerizable acrylic component (e.g., like that described above) and a thermosettable epoxy component (e.g., like that described above). The first starting materials and the second starting materials can have the same or different acrylic component and/or epoxy component. The epoxy component of either starting materials, or both starting materials, can be heat curable. The first adhesive is not black when cured (e.g., by heat curing) without the presence of the black coloring pigment. The first starting materials include a sufficient amount of the black coloring pigment to cause the first adhesive to have a black color after the first adhesive is substantially cured. The second adhesive is not black when cured (e.g., by heat curing) without the second adhesive including enough of a black coloring pigment. The second starting materials either do not include any black coloring pigment (e.g., carbon black) or at least do not contain an amount of a black coloring pigment that would cause the second adhesive to have a black color after the second adhesive is substantially cured. As used here, substantially cured refers to the adhesive being completely cured or at least cured enough so the resulting adhesive layer is suitable for use in structurally bonding together two desired substrates. 
     The first starting materials layer is thin enough to allow substantial photo-polymerization (e.g., with ultraviolet (UV) light) of the first starting materials, at least the acrylic component, even with the first starting materials containing a sufficient amount of the black coloring pigment to cause the first adhesive to have a black color after the first adhesive is substantially cured. As used here, substantial photo-polymerization refers to complete polymerization, as a practical matter, or at least the degree of polymerization needed to allow the resulting photo-polymerized layer to be used in the desired thermosettable adhesive tape. The second starting materials layer has a thickness that would be sufficiently thick to prevent substantial photo-polymerization (e.g., with UV light) of the second starting materials, at least the acrylic component (i.e., completely prevented or at least prevented enough to stop the resulting photo-polymerized layer from being effectively used in the desired thermosettable adhesive tape), if the second starting materials contained enough of a black coloring pigment to cause the second adhesive to have a black color after the second adhesive is cured. 
     The method can further comprise disposing a release liner, so as to protect, at least one or both of the first adhesive layer and the second adhesive layer. The method can also further comprise laminating the first adhesive layer and the second adhesive layer so as to be adhered together. In addition, each starting materials layer can be disposed between two transparent, and preferably optically clear, liners during its corresponding photo-polymerizing. 
     In accordance with a further aspect of the present invention, a method of making an assembly is provided, where the method comprises making a tape as described above and adhering an opaque or translucent substrate to the second adhesive layer. The substrate being adhered to the second adhesive layer can be, for example, a mirror button or a hinge plate. With such an assembly, the tape can have a periphery in the shape of the opaque or translucent substrate (e.g., a mirror button or a hinge plate) or a number of the substrates can be adhered at separate locations on the second adhesive layer of the tape. The first adhesive layer of the tape can be adhered to a transparent substrate such as, for example a window (e.g., a windshield of a vehicle such as, for example, an automobile, watercraft, aircraft, spacecraft). As used here, a transparent substrate refers to a substrate that is optically clear or at least partially transparent to visible light, that is, the substrate is sufficiently transparent that an observer can see whether the first adhesive layer is black through the substrate (e.g., transparent enough to allow at least about 15%, or at least about 30%, of visible light to be transmitted therethrough). 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is cross-sectional view of an assembly according to one embodiment of the present invention. 
     
    
    
     MODES FOR CARRYING OUT THE INVENTION 
     Thermosettable pressure sensitive adhesive tapes, like those disclosed in U.S. Pat. Nos. 5,086,088 and 6,348,118, have been used to bond substrates together, like rear view mirror brackets or buttons to the inside surface of automotive windshields. These tapes are typically 20 to 25 mils thick and have an ultraviolet (UV) photo-polymerized pressure sensitive acrylic component and a heat curable epoxy component. Automotive windshields are usually a laminate of two sheets of glass bonded together by an intermediate thermoplastic adhesive layer of polyvinyl butyral (PVB) at elevated temperature and pressure using, for example, conventional autoclave equipment and processing. The mirror button is typically initially adhered with the PSA characteristics of this tape to the windshield before the windshield is autoclaved. The epoxy component of the tape is then heat cured during the autoclave process to provide a structural bond between the mirror button and the windshield. Prior to the final heat cure the tape is typically black. After final heat curing, the tape changes to a medium grey or lighter color, because of a phase separation that is believed to occur between epoxy and acrylate phases during the heat curing process. A black color has been considered more aesthetically desirable then the lighter colors. One way to make the use of such a tape more acceptable would be to apply a black frit to the surface of the windshield so as to cover the adhesive surface. However, the use of such frit has been known to weaken the windshield glass and is, therefore, not desirable. 
     Prior to this invention, the technical assessment of making a black thermosettable tape was pessimistic due to the inability to adequately UV photo-polymerize the entire thickness (e.g., about 20 mils or more) of such a tape that has been loaded with enough pigment to achieve a black color. Surprisingly, it has been found that such thermosettable adhesive tapes can be made to exhibit a black color, on one or both of its major surfaces, even after final heat curing. To accomplish this, a relatively thin veneer of adhesive (e.g., 5 mil), made from highly pigmented starting materials, is laminated to one or both sides of a relatively thick layer of adhesive (e.g., 20 mil), made from starting materials that had a conventionally low level of pigment (i.e., an amount that was low enough not to significantly inhibit UV photo-polymerization of the entire thickness). Because the highly pigmented veneer is much thinner, UV radiation is able to reach the center of the adhesive layer and substantially UV cure or photo-polymerize the starting materials. If the highly pigmented starting material is coated at the standard thicknesses for one-layer tapes, the center of the adhesive layer is not adequately UV photo-polymerized, because the higher amounts of pigment absorb too much of the UV radiation, thus preventing enough UV energy from reaching, and curing, the center of the adhesive layer. 
     Referring to  FIG. 1 , a thermosettable pressure sensitive adhesive (PSA) tape  10 , according to one embodiment of the present invention, is shown adhering a substrate  12  (e.g., a mirror button) to the surface of a window  14  (e.g., a windshield for a vehicle). The tape  10  comprises a first adhesive layer  16  bonded to a major surface of a second adhesive layer  18 , each of which has a thickness and comprises a thermosettable pressure sensitive adhesive, which is the photo-polymerization reaction product of starting materials. Examples of such adhesives can be found in U.S. Pat. Nos. 5,086,088 and 6,348,118, which are incorporated herein by reference in their entirety. The starting materials for each adhesive layer  16  and  18  comprise an acrylic component that is photo-polymerizable with ultraviolet light and a heat curable epoxy component. The acrylic component includes a partially polymerized composition (e.g., a prepolymerized syrup) and/or a monomeric mixture comprising at least one acrylic acid ester or methacrylic acid ester of an alkyl alcohol (e.g., a non-tertiary alcohol). The acrylic component also includes a copolymerizable monomer (e.g., a moderately polar copolymerizable monomer) and a photoinitiator. The epoxy component includes a heat curable epoxy resin or a mixture of epoxy resins that include a heat curable epoxy resin and a heat-activatable hardener or curing agent for at least the epoxy resin. The starting materials for the two adhesive layers  16  and  18  have the same or different acrylic components and epoxy components. 
     The first adhesive layer  16  is made from a layer of the first starting materials that is thin enough to allow substantial UV photo-polymerization of the acrylic component, even though the first starting materials contain a sufficient amount of black coloring pigment to cause the first adhesive to have a black color after the first adhesive is substantially heat cured. The second adhesive layer  18  is made from a layer of the second starting materials which has a thickness that would be sufficiently thick to prevent substantial UV photo-polymerization of the starting materials, if the starting materials contained enough of a black coloring pigment to cause the second adhesive to have a black color after the second adhesive is cured. 
     In accordance with the present invention, the term black refers to a range of colors from dark grey to black. The color black, as used herein, can also be seen as having a pigment concentration and/or an L* specular number as indicated below: 
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                 Pigment limits: 
                 L* specular excluded limits 
               
               
                   
                   
               
             
            
               
                   
                 First adhesive layer: 
                 Black Colors: 
               
               
                   
                 Minimum: 0.125% 
                 32 
               
               
                   
                 Maximum: 5% 
                  1 
               
               
                   
                 Preferred 
               
               
                   
                 Minimum: 0.25% 
                 30 
               
               
                   
                 Maximum: 0.75% 
                  8 
               
               
                   
                 Second adhesive layer 
                 Colors not Black 
               
               
                   
                 Minimum: 0.0% 
                 90 
               
               
                   
                 Maximum: 0.1% 
                 33 
               
               
                   
                   
               
            
           
         
       
     
     In addition to being provided alone, the tape  10  can be provided in the form of an article or assembly that includes the tape  10  adhered to one or both of the substrates  12  and  14 . The tape  10  can also be provided with an additional or third adhesive layer (not shown), which is the same as, or similar to, the first adhesive layer  16 , bonded to the opposite major surface of the second adhesive layer  18 . Such a three layer construction may be desirable when both of the substrates, being adhered together with the tape, are transparent substrates. The tape  10  has one side or major surface  20  defined by the first adhesive layer  16  and an opposite side or major surface  22  defined by the second adhesive layer  18 . When the tape  10  is sold alone or with only one of the substrates  12  or  14 , a conventional release liner (not shown) is disposed so as to protect any of the sides  20  and  22  that are left exposed (i.e., not adhered to the substrate  12  or  14 ). As shown in  FIG. 1 , the tape  10  has a periphery in the shape of the mirror button substrate  12 . 
     The thermosettable pressure sensitive adhesive tape  10  is made by forming a first starting materials layer of the first starting materials; forming a second starting materials layer of the second starting materials; UV photo-polymerizing the first starting materials layer so as to produce the first adhesive layer  16 ; UV photo-polymerizing the second starting materials layer so as to produce the second adhesive layer  18 ; and bonding the two layers  16  and  18  together at major surfaces. Each starting materials layer can be formed using conventional methods and techniques, such as that disclosed in the above incorporated patents. 
     Such a conventional process can use an upper and lower optically clear process liner (e.g., 2 mil thick silicone coated polyester liners), unwind stands with tension control springs to provide frictional tension to the process liners, a notch bar coater with a gap that is adjustable to achieve a desire thickness, and two banks of adjustable low intensity UV lights. In the process, the lower process liner is suspended so as to pass through the gap in the bar coater and through the banks of UV lights. An adhesive starting material is applied on top of the lower process liner and forms a rolling bank at the notch bar coater. The upper process liner wraps around the notch bar coater above the lower liner, passes through the bar coater gap and sandwiches the starting materials therebetween. The two process liners carry the starting materials through the bank of UV lights where UV polymerization of the starting materials, especially the acrylic component, occurs. One bank of the UV lights is positioned above and below the sandwiched starting materials. The UV lights have 90% of emissions between 300 and 400 NM and a peak at 351 nm. Intensity of approximately 2 millwatts per square centimeter, with total energy of about 650 milijoules per square centimeter above and 650 milijoules per square centimeter below. Rubber coated driven nip rollers are used to pull the process liners through notchbar coater gap and banks of UV light. 
     EXAMPLES 
     Base Solution for Examples 1 and 6 
     A premix composition was prepared by mixing 75 parts of n-butyl acrylate, 25 parts of N vinyl caprolactam, and 0.04 parts of photoinitiator (alpha, alpha-dimethoxy-alpha-phenylacetophenone available under the tradename Irgacure 651 from Ciba Specialty Chemicals Corporation, Tarrytown N.Y.) and exposing to ultraviolet black lamps to form a syrup having a viscosity of about 1500 cps. 
     An adhesive composition was prepared by mixing 42.6 parts of the premix composition, 3.2 parts of 2-hydroxy-3-phenoxy propyl acrylate, 29.8 parts of liquid epoxy resin (bisphenol-A epichlorhydrin available under the tradename Epon 828 from Resolution Performance Products LLC, Houston, Tex.) and 16.0 parts of solid epoxy (Epon 1101F) resin (phenol, 4,4′-(1-methylethylidene) bis-, polymer with 2,2′((1-methylethylidene) bis(4,1-phenylene oxymethylene)) bis(oxirane) with a propellor mixer set at high speed for 30 minutes while heating to about 49° C. to form a uniform mixture. The mixture was then cooled to about 32° C. with continuous mixing and the following were added and mixed for about 30 minutes: 0.02 part of 1,6-hexanedioldiacrylate, 1.1 parts of micronized epoxy accelerator (2,4-diamino-(2′-methylimidazoleyl-(1′))ethyl-S-triazine available under the tradename, Curezol 2MZ-Azine, from Air Products and Chemicals Inc., Allentown, Pa.), 0.05 part of antioxidant (benzene propanoic acid available under the tradename, Irganox 1010, from Ciba Specialty Chemicals Corp.), 3.6 parts of dicyandiamide, 0.6 part of silane (trimethoxy (3-(oxiranylmethoxy)propyl)-silane available under the product number G6720 from Degussa Corp.), and 0.35 part of black pigment dispersion (the dispersion having approximately 15% carbon black pigment in an acrylic carrier available under the tradename Penncolor 9B117 from Penn Color, Inc., Doylestown, Pa.), 2.7 parts fumed silica (fumed silica available under the tradename, Cabosil M-5, available from Cabot Corporation, Billerica, Mass.), and 0.07 part Irgacure 651 photoinitiator were added and mixed at 32° C. for 30 minutes. The uniform mixture was cooled to about 27° C. with continued mixing, and then filtered. 
     Base Solution for Examples 2, 3, 4, 5 
     An adhesive composition was prepared by mixing 30.7 parts of a 50/50 mixture of n-butyl acrylate and N-vinylcaprolactam, 22.35 parts of butyl acrylate, 23.84 parts of liquid epoxy resin (bisphenol-A epichlorhydrin available under the tradename Epon 828 from Resolution Performance Products LLC, Houston, Tex.) and 13.2 parts of solid epoxy (Epon 1101F) resin (phenol, 4,4′-(1-methylethylidene) bis-, polymer with 2,2′((1-methylethylidene) bis(4,1-phenylene oxymethylene)) bis(oxirane) with a propellor mixer set at high speed for 30 minutes while heating to about 49° C. to form a uniform mixture. The mixture was then cooled to about 32° C. with continuous mixing and the following were added and mixed for about 30 minutes: 0.025 parts of 1,6-hexanedioldiacrylate, 1.4 parts of non-micronized epoxy accelerator (2,4-diamino-(2′-methylimidazoleyl-(1′))ethyl-S-triazine available under the tradename, Curezol 2MZ-Azine, from Air Products and Chemicals Inc., Allentown, Pa.), 0.05 part of antioxidant (benzene propanoic acid available under the tradename, Irganox 1010, from Ciba Specialty Chemicals Corp.), 3.7 parts of dicyandiamide, and 0.30 part of black pigment dispersion (the dispersion having approximately 15% carbon black pigment in an acrylic carrier available under the tradename Penncolor 9B117 from Penn Color, Inc., Doylestown, Pa.), 4.2 parts fumed silica (fumed silica available under the tradename, Cabosil M-5, available from Cabot Corporation, Billerica, Mass.), and 0.15 part Irgacure 651 photoinitiator were added and mixed at 32° C. for 30 minutes. The uniform mixture was cooled to about 27° C. with continued mixing, and then filtered. 
     The solution for example one was competed by adding 1 gram of Penncolor 9B117 and 2.5 grams of powdered carbon black To 100 grams of the base solution for example 1 then mixing until evenly dispersed. 
     The solution for example two was completed by adding 1 gram of Penncolor 9B117 to 100 grams of the base solution for examples 2, 3, 4, 5 then mixing until evenly dispersed. 
     The solution for example three was completed by adding 2 grams of Penncolor 9B117 to 100 grams of the base solution for examples 2, 3, 4, 5 then mixing until evenly dispersed. 
     The solution for example four was complete by adding 1 gram of Penncolor 9B117 and 2.5 grams of powdered carbon black to 100 grams of the base solution for examples 2, 3, 4, 5 then mixing until evenly dispersed. 
     The solution for example five was the base solution for examples 2, 3, 4, 5 with no additional pigment. 
     The solution for example six was the base solution for examples 1 and 6 with no additional pigment. 
     The compositions were degassed and coated between two silicone release coated polyester films and irradiated with ultraviolet light from the above and below the web as described in the examples of U.S. Pat. No. 6,348,118 for about 3 minutes to form a black tape. The total energy used to cure the adhesive is about 1300 milliJoules/square centimeter (mJ/sq cm). Examples 1, 2, 3, and 4 were coated at 5 mils thick. Examples 5 and 6 were coated at 25 mils thick. 
     Sample Preparation: 
     Each of the tapes from Examples 1-4 were laminated to a layer of 20 mil thick 9214 Structural Bonding Tape, sold by 3M Company, St. Paul, Minn. These two layer tapes were subsequently laminated to clean smallfoot mirror buttons with the second layer (thicker/less pigment) attached to the mirror button. The taped mirror buttons were then adhered with the first layer (thinner/more pigment) to the tin side of clean 2 inch by 5 inch tempered glass plates. The glass plates were pre-warmed to 90 C prior to the application of the button. A pneumatic press with a 2-inch cylinder set at 70 psig was used to adhere the taped buttons to the warm glass plates. The mirror button/glass plate assemblies were then autoclaved at about 141° C. and 170 psig with 30 minutes at peak temperature to cure the epoxy phase of the adhesive. The samples were conditioned at ambient temperature overnight before testing. 
     The sample preparation for examples 5 and 6 was the same as examples 1-4 except the tapes for examples 5 and 6 were not laminated to the 20 mil layer of 9214 Structural Bonding Tape. 
     Testing: 
     Torque Testing: 
     Torque measurements were obtained using a 12-inch lever arm affixed on one end to the mirror button on a firmly mounted mirror button/glass assembly and on the other end to an Instron force measurement machine. The crosshead speed was 6 inches per minutes. The peak force in foot-pounds was recorded. The force exerted on the attached button was in plane with the button as it was attached to the glass. The Failure Mode is also noted as Cohesive (C) in which the adhesive breaks within the adhesive layer leaving material on both the mirror button and the glass; and adhesive from glass (A-G) where most of the adhesive remains on the button and just a thin residual film remains on the glass. Test results are shown in Table 1. 
     Cleavage Testing: 
     The cleavage test is a measure of how well a mirror button adheres to a glass plate. Test samples are prepared as described above, and conditioned for at least 24 hours at room temperature and 40-60% relative humidity. The glass plate with the mirror button attached is mounted in a test fixture that is clamped into an Instron Tensile Tester. A 70 mm long lever arm with an attachment end designed to slide over the mirror button in a manner upside-down from how a rearview mirror would attach to it on a windshield. The lever arm is clamped into the jaw of the tensile tester and moved upwardly at a rate of 2.5 millimeters per minute. The maximum value at break, i.e., when the mirror button breaks loose from the glass plate, the force is recorded in pounds. The mode of failure is also observed using the same criteria as for the Torque test. 
     Color Testing: 
     Visual subjective color testing was conducted on a three level scale. The levels were Grey, Dark Grey and Black. 
     Color measurements were also measured using a calibrated X-Rite SP-60 Sphere spectrophotometer using a D-65 light source and a 10 degree angle. L* values were recorded with specular effects include and specular effects excluded. When specular effects are excluded the effect of gloss is reduced and is the preferred method. 
     The samples for X-rite color measurement were laminated to silicone coater paper then cured in an atmospheric oven at 285 C for 35 minutes. After cooling to room temperature the L* measurements were taken. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Carbon black 
                   
                 Torque 
                   
               
               
                 Ex 
                 (wt %) 
                 Color 
                 (foot-pounds) 
                 Failure Mode 
               
               
                   
               
             
            
               
                 1 
                 2.60 
                 Black 
                 25.3 
                 Cohesive 
               
               
                 2 
                 0.19 
                 Dark gray 
                 45.3 
                 A-G 
               
               
                 3 
                 0.34 
                 Black 
                 42.5 
                 A-G 
               
               
                 4 
                 2.60 
                 Black 
                 31.5 
                 A-G 
               
               
                 5 
                 0.05 
                 Gray 
                 50.4 
                 A-G 
               
               
                 6 
                 0.05 
                 Gray 
                 35.2 
                 Cohesive 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
             
               
                 TABLE 1-A 
               
               
                   
               
               
                 EX 
                 L* speular excluded 
                 L* Specular included 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 1 
                 21.58 
                 30.17 
               
               
                 2 
                 26.17 
                 31.68 
               
               
                 3 
                 23 
                 29.4 
               
               
                 4 
                 22 
                 28.5 
               
               
                 5 
                 39.23 
                 42.2 
               
               
                 6 
                 Na 
                 Na 
               
               
                   
               
            
           
         
       
     
     Examples 7-13 
     Tapes for Examples 7-13 were prepared according to the procedure for the base solution for examples 2,3,4,5 except that the accelerator used was micronized 2MZ-Azine, and the amounts of the carbon black dispersion (Pennco 9B117) were 0.23%, 1.5%, 2.5%, and 3.5% based on the total weight of the composition, and coated in thicknesses of 5 mils and 25 mils. The pigment content, i.e., only the carbon black, is shown in Table 2 also included is the first layer thickness, acrylic cure success, color evaluation, and torque testing. Tapes having a thickness of 25 mils were tested without laminating to another layer of adhesive. The 5 mil tapes were laminated to a 20 mil thick 9214 Structural Bonding Tape. When bonding these two layer samples to glass the first layer (thinner/more pigment) is attached to the glass, the second layer (thicker/less pigment) is attached to the mirror button. 
     25 mil tapes in Examples 11 and 13 exhibited incomplete acrylic cure and were not be tested for color or torque. All other examples were tested for torque after autoclaving following the procedure in examples 1-6. Samples tested for 100F/100RH were first conditioned 24 hours at room temperature prior to exposure. These samples were then conditioned at 100° F. and 100% relative humidity for 24 hour prior to torque testing. 
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                   
                 % Carbon 
                 First layer 
                 Acrylic 
                   
                 RT 
                 100 F./100RH 
               
               
                 Ex 
                 black 
                 thickness 
                 cure 
                 Color 
                 torque 
                 torque 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 7 
                 0.045% 
                 25 
                 mil 
                 Yes 
                 Grey 
                 47.6 
                 30.0 
               
               
                 8 
                 0.22% 
                 5 
                 mil 
                 Yes 
                 Dark 
                 41.1 
                 26.5 
               
               
                   
                   
                   
                   
                   
                 grey 
               
               
                 9 
                 0.22% 
                 25 
                 mil 
                 Yes 
                 Dark 
                 24.8 
                 Na 
               
               
                   
                   
                   
                   
                   
                 grey 
               
               
                 10 
                 0.37% 
                 5 
                 mil 
                 Yes 
                 Black 
                 37.4 
                 26.9 
               
               
                 11 
                 0.37% 
                 25 
                 mil 
                 No 
                 na 
                 na 
                 na 
               
               
                 12 
                 0.51% 
                 5 
                 mil 
                 Yes 
                 Black 
                 34.4 
                 25   
               
               
                 13 
                 0.51% 
                 25 
                 mil 
                 No 
                 na 
                 na 
                 na 
               
               
                   
               
            
           
         
       
     
     Examples 14-19 
     Solutions and tapes were prepared for Examples 14-19 according to the procedure for the base solution of 2,3,4,5 except that the pigment dispersions amounts were either 2.8% (0.42% carbon black) or 3.8% (0.57% carbon black). The target thicknesses were 5, 8, and 10 mils for each pigment amount although the actual thicknesses were higher as shown in Table 3. Tapes were prepared by laminating to 9214 Structural Bonding Tape and tested for torque and cleavage with results shown in Table 3. All of the tapes were essentially black in color. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                   
                   
                   
                 Torque 
                   
               
               
                   
                 Pigment 
                 Thickness (mils) 
                 (foot-pounds)/ 
                 Cleavage 
               
               
                 Ex 
                 content (%) 
                 target/actual 
                 Failure Mode 
                 (pounds) 
               
               
                   
               
             
            
               
                 14 
                 0.42 
                 5/7 
                  36.7/TFG* 
                  185/C** 
               
               
                 15 
                 0.42 
                 8/9 
                     33/TFG 
                 161/C 
               
               
                 16 
                 0.42 
                 10/12 
                 36.4/TFG 
                 156/C 
               
               
                 17 
                 0.57 
                 5/7 
                 36.7/TFG 
                 137/C 
               
               
                 18 
                 0.57 
                 8/9 
                 38.5/TFG 
                 133/C 
               
               
                 19 
                 0.57 
                 10/12 
                     25/TFG 
                 101/C 
               
               
                   
               
               
                 *“TFG” = thin film remaining on glass. Majority of adhesive remaining on mirror button. 
               
               
                 **“C” = Cohesive failure mode (e.g., 185/C = 185 pounds of force with Cohesive failure. 
               
            
           
         
       
     
     
       
         
           
               
               
               
             
               
                 TABLE 3-A 
               
               
                   
               
               
                 Ex 
                 L* speular excluded 
                 L* Specular included 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 14 
                 22.58 
                 28.7 
               
               
                 15 
                 21.75 
                 28.55 
               
               
                 16 
                 22.2 
                 28.8 
               
               
                 17 
                 21.3 
                 27.5 
               
               
                 18 
                 21.1 
                 27.9 
               
               
                 19 
                 21 
                 28 
               
               
                   
               
            
           
         
       
     
     Examples 20-25 
     Solution and tapes were prepared for Examples 20-25 according to the procedure for the base solution for examples 2,3,4,5 and the details of Example 3 except that the total amount of carbon black dispersion is varied as shown in Table 4. 
     The total acrylic cure energy was also varied and the finished tapes were tested for Torque, Cleavage, Stress, Strain, Modulus, and Color. 
     The Stress, Strain, and Modulus were determined using a an Instron/tensile Tester according to ASTM D-412-98a approved 2002. The Color was measured using a X-Rite SP-60 and the units are reported in L* both with the specular effects excluded and included 
     
       
         
           
               
               
               
               
               
               
               
               
               
             
               
                 TABLE 4 
               
               
                   
               
               
                   
                 Pigment 
                 Pigment 
                 Total 
                   
                 RT 
                   
                   
                   
               
               
                   
                 Dispersion 
                 Content 
                 Energy 
                 Torque 
                 Cleavage 
                 Stress 
                 Strain 
                 Modulus 
               
               
                 Ex 
                 (%) 
                 (%) 
                 mJ/sq cm 
                 ft-lbs 
                 (lbs) 
                 (psi) 
                 % 
                 (ksi) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 20 
                 4.5 
                 0.65 
                 1300 
                 36 
                 107 
                 1219 
                 69 
                 10.9 
               
               
                 21 
                 3.5 
                 0.51 
                 1550 
                 39 
                 127 
                 1302 
                 73 
                 10.9 
               
               
                 22 
                 4.5 
                 0.65 
                 1800 
                 38 
                 111 
                 1251 
                 63 
                 10.9 
               
               
                 23 
                 2.5 
                 0.37 
                 1800 
                 43 
                 169 
                 1346 
                 75 
                 12.8 
               
               
                 24 
                 3.5 
                 0.51 
                 1550 
                 40 
                 148 
                 1336 
                 84 
                 10.5 
               
               
                 25 
                 2.5 
                 0.37 
                 1300 
                 44 
                 169 
                 1348 
                 84 
                 11.4 
               
               
                   
               
               
                 L* data measured with X-Rite SP-60 sphere spectrophotometer. 
               
            
           
         
       
     
     
       
         
           
               
               
               
             
               
                 TABLE 4-A 
               
               
                   
               
               
                 Ex 
                 L* specular excluded 
                 L* Specular included 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 20 
                 20.8 
                 27.7 
               
               
                 21 
                 20.5 
                 28.3 
               
               
                 22 
                 20.2 
                 27.9 
               
               
                 23 
                 22.3 
                 28.9 
               
               
                 24 
                 21 
                 28.1 
               
               
                 25 
                 21.3 
                 28.6