Patent Publication Number: US-2013230699-A1

Title: Forming Method For Polymeric Laminated Wafers Comprising Different Film Materials

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. patent application Ser. No. 13/192,399 filed Jul. 27, 2011 entitled Forming Method For Polymeric Laminated Waters Comprising Different Film Materials, which is a continuation of U.S. patent application Ser. No. 11/368,929 filed Mar. 6, 2006 entitled Forming Method For Polymeric Laminated Wafers Comprising Different Film Materials (now U.S. Pat. No. 8,002,935 issued Aug. 23, 2011), which is related to and claims priority from U.S. provisional application Ser. No. 60/658,800 filed on Mar. 4, 2005 entitled Forming Method For Polymeric Laminated Wafers Comprising Different Film Materials, all of which are incorporated herein by reference in their entireties. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a method for forming polymeric laminates. 
     BACKGROUND OF THE INVENTION 
     Formed wafers are curved laminates often produced as an intermediate step to a completed lens. For example, a wafer may be produced having a delicate functional layer, such as a polarizing or photochromic layer, sandwiched by a first, protective layer and a second, base layer. The wafer is then formed to have a base curve. The formed wafer is then placed in an injection mold chamber where a molten lens material is injected behind the wafer to form a lens against the base layer of the wafer. In the alternative, the formed wafer can be used simply as a plano lens by itself, e.g., as a plano polarized or photochromic sunglass lens or sungoggle, i.e., without injecting a molten lens material behind the wafer. An example of such a wafer is disclosed in publication EP 0 299 509 A2 by Kawaki et al., incorporated by reference herein in its entirety. 
     The wafers are typically formed via a process that includes first heating the polymeric wafer to a softening temperature. This heating step may be accomplished in a variety of ways such as with hot air or heated forming molds. Next the softened wafer is placed in a forming cup and either pressed or sucked into the forming cup. The wafer is held in the cup until it sets, thus assuming the shape of the forming cup. The wafer is then removed and cooled to ambient temperature. 
     Typical heating or softening temperatures for use in forming the laminated wafer are determined by the thermal properties of the materials chosen for producing the laminated wafer. One example of materials that have been previously used in making laminated wafers is polycarbonate resin films or sheets. Polycarbonate films or sheets include general aromatic polycarbonate resin sheets prepared from bisphenols (e.g., bisphenol A) and phosgene or carbonic esters and sheets prepared from transparent copolycarbonate resins or transparent resin compositions containing other resins. If desired, these polycarbonate sheets may thereafter be coated or otherwise treated with a functional coating, such as heat-formable hard coat, an anti-fogging coat, an infrared-reflective or infrared-absorbable coat, an ultra-violet reflective or ultra-violet absorbable coat or other similar functional coatings that are known in the art. 
     Other materials contemplated for use in making laminated wafers may include adhesives or functional materials such as polarizing films or photochromic films. Examples of adhesives that are contemplated for use in laminated wafers may include PVA adhesives or urethane adhesives that are commonly known in the polycarbonate lens industry. Examples of a polarizing film suitable for use in laminated wafers include a polarizing film containing components such as polyvinyl alcohol polymer (PVA) film, which is monoaxially stretched before dyeing, or dyed before monoaxial stretching, and subjected to fixing treatment with a boron compound (in some cases, the dyeing and fixing treatment are conducted simultaneously). Other examples of functional materials may include polyester polarizers or photochromic polarizing films. 
     Once the functional layer, such as a polarizing PVA film, has been incorporated, then a protective film having optical transparency and mechanical strength is normally laminated on each surface or one surface thereof. Examples of protective layer materials would typically include materials such as cellulose tri-acetate (CTA) film, cellulose acetate butyrate (CAB) and other cellulose resins, cyclic olefin, polyesters, such as polyethylenetelephthalate (PET) and its alloy or modified resin, polycarbonate alloy and copolymer with other polymer(s), polyethylenenaphthalate (PEN), and acrylic resins, such as polymethyl methacrylate (PMMA). 
     Laminated wafers having the above-described materials are thereafter formed into curved laminates. This process is commonly accomplished using a machine, such as those made by Lema of Italy. The Lema machines have a thermostatically-controlled electric heating chamber with an air blower, and forming cups mounted on a rotating turret. A vacuum hole at the bottom of each forming cup allows the wafers to be sucked into the cups and held in place with a vacuum. Vacuum control valves hold the wafers until they reach a designated position on the rotating turret at which time they are released. 
     Other machines that are suitable for use in making laminated wafers are produced by Japanese companies such as Wintec and Fuji Kasei. These are similar to the Lema machine but also include wafer pre-heating units, pick and place mechanisms, and plungers to mechanically press the wafers into the vacuum cups. Some machines also have a cooling conveyor or other apparatus used to achieve desired formation(s) of selected wafer components. 
     These machines perform adequately when forming a wafer that has a protective layer and a base layer having similar properties and/or materials. However, they are found to be deficient to form wafers where the protective layer is different than its base layer. Materials having similar properties, such as softening properties, can be heated and formed uniformly at a uniform temperature. For example, the softening temperature of a laminated wafer having a protective layer and a base layer comprised entirely of polycarbonate materials, or similar-propertied materials, is at or near approximately 285° F. Therefore, placing the laminated wafer in a heated environment possessing a uniform temperature of approximately 285° F. over a prescribed amount of time will result in a softening and formation of a uniformly curved laminated wafer, appropriate for use thereafter in a manufacturing process, such as injection molding. However, preparing a laminated wafer where one or more layers have properties and/or materials that are different from other layers, and exposing such a wafer to a uniform heat that is outside a prescribed or required softening temperature for one of the materials will result either in inadequate softening and forming (e.g. when the temperature is too low) or, alternatively, a softening of the material to a point of damaging the material (e.g. when the temperature is too high). 
     One example of a laminated wafer having different layer materials is a wafer having a CAB film as a protective layer, a PVA film as a polarizer functional layer, and a polycarbonate film as a base layer. The optimum softening and forming temperature for the polycarbonate film base layer occurs at or near 285° F. At temperatures substantially below this temperature (e.g. t 270° F. or below), polycarbonate does not undergo adequate softening due to its chemical and structural properties, namely its thermal properties. Alternatively, at temperatures above 260° F., CAB becomes too soft because the temperature is too high to maintain the chemical and structural integrity of the material due to its underlying thermal properties. Thus, the aforementioned machines are unable to form a wafer including, for example, a CAB film protective layer and a polycarbonate film base layer because there is no operational temperature window that satisfies both layers. 
     There is thus a need for a machine that is able to soften and form laminated wafers having different layers of materials with diverse thermal properties. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     In view of the foregoing, it is an object of the present invention to provide a process of making a laminated wafer that overcomes the limitations of the prior art. 
     It is another object to provide a process wherein the method of making the present invention is efficient and economical. 
     These and other objects not specifically enumerated here are addressed by the present invention wherein one object of the present invention provides a method for forming a laminated wafer having at least a first layer and a second layer comprising placing the wafer in a heated environment having a first temperature capable of softening the first layer, exposing the second layer, and not the first layer, to a second temperature higher than the first temperature, the second temperature capable of softening the second layer, and forming the laminated wafer into a desired shape. 
     Another object of the present invention relates to a laminated wafer comprising different materials that are formed at different softening temperatures. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a typical laminated wafer to which the present invention is directed; 
         FIG. 2  is a cross-sectional view of the wafer of  FIG. 1  having been formed in accordance with the methods of the present invention; 
         FIG. 3  is a plan view of an embodiment of a device useable in practicing the method of the present invention. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     The present invention provides a method for forming wafers whereby different temperatures are applied to either side of the wafer, in which each side has different materials and/or thermal properties. An example of such a wafer is shown in  FIG. 1 . The wafer  10  is laminated and includes a first layer  12  and a second layer  14 . Sandwiched between the first layer  12  and the second layer  14  is a functional layer  16 . 
     One embodiment of the wafer having a first layer  12  and a second layer  14 , includes a first layer comprising CAB film and a second layer  14  comprising a polycarbonate film. CAB film is commercially available by companies such as Kodak (sold under the name KODACEL®) and comes in various grades. In another embodiment, any material possessing low to no birefringence at Tg between 100° C. and 150° C., such as CAB film, is a good candidate for a first layer  12  (also referred to as a protective layer) of the wafer  10 . As for the polycarbonate second layer  12 , commercial sources of polycarbonate film include GE (LEXAN® T2FOQ), Teijin (PANLITE® 1151, 2151), and Bayer (Makrofoil DE). Modified polycarbonates and polycarbonate alloy film would also be well-suited for use as layers in the present invention. 
     The functional layer  16  typically gives the lens to which the wafer  10  will be applied a desired property. For example, the functional layer  16  may include a photochromic or polarizing layer, such as a polyester polarizer, a multi-layer film for reflecting and transmitting a specific wave length, or a combination of these properties, as found in a photochromic polarizing layer. The first layer  12  is often a protective layer that protects the functional layer  16  from the elements. The second layer  14  is often referred to as a base layer and, in one embodiment, is eventually fused to a lens. However, the present invention contemplates interchangeable use of materials for a first layer and a second layer of a laminated wafer, as herein described. 
       FIG. 2  shows the wafer  10  after it has been formed. The wafer  10  has been curved to match the curve either of a plano lens or a curve of a lens blank to which the wafer may be adhered. Formed wafers  10  are often used in manufacturing processes such as injection molding operations, such as those employed in production of ophthalmic lenses. The curve of the wafer  10  thus substantially matches the curve of the inside mold cavity wall. In this case, the first layer  12  would be placed against the anterior wall of the mold and the lens material is injected into the posterior side of the mold against the second layer  14 . 
     Referring now to  FIG. 3 , the machine of the present invention includes a heating chamber  17  containing a turret unit  18  having a plurality of vacuum suction forming cups or molds  20  for receiving the wafers  10 . The wafer  10  is placed in a forming cup  20  and the vacuum level is set in the heating chamber  17  at 10-760 mmHg, and most preferably, 100-650 mmHg. 
     The heating chamber  17  also contains electric heaters and a convection blower (not shown). This heating chamber  17  provides a first heating temperature that is distributed uniformly throughout the heating environment. Most preferably, the first heating temperature will be set to a temperature sufficient to soften a first layer of wafer material, based on its thermal properties (typically, a lower temperature than a second temperature that is required to soften a second layer of wafer material). The heating chamber  17  may further provide one temperature controller that maintains the air temperature throughout the heating chamber at a desired setting (e.g., a first temperature) as well as the temperature of the forming cups  20 . In a preferred embodiment, the heating chamber  17  will provide an air temperature that is set near the first layer material&#39;s glass transition temperature (Tg) or slightly lower (5-15° C.) than Tg. 
     The heating chamber  17  further contains a second source for introducing heat into the chamber  17 . This second heat source enables the chamber  17  to direct heat specifically to one layer of each wafer and thereby heat that layer with heat at a temperature different from the air temperature otherwise being generated by the chamber  17 . This second heat source therefore allows two different temperatures to be imparted onto the wafers. In one embodiment, the chamber  17  heats (through its first heat source (e.g. electrical heater and convection blower) the protective and functional layers  12 ,  16  to a first air temperature in the chamber  17  while the base layer  14  is heated to a higher temperature from the second heat source. 
     The second heating source may be provided by heating devices such as infrared heaters, directed hot air jet(s), or hot metal plunger(s) that are placed in contact with a second (or, higher softening temperature) material, holding a wafer between the lower temperature moving, forming cups  20  and hot metal plungers (not shown). 
     In a preferred embodiment of the present invention, the second source of heat is provided by infrared heaters  22  as shown in  FIG. 3 . The infrared heaters  22  are positioned inside the heating chamber  17  above the moving, forming cups  20 . Infrared heaters  22  are selected such that they will emit infrared rays having a wavelength that is efficiently absorbed by the base layer  14  material and not passed through to the functional layers  16  and/or the protective layer  12  of each wafer. For example, a polycarbonate film has been shown to pass infrared rays that are between 800 to 2300 nm (near infrared) but absorb infrared having a wavelength longer than 2300 nm (far infrared). Thus, the infrared heaters  22  are selected to emit infrared rays in the far infrared range rather than in the near infrared range, as corresponding with the thermal properties of the selected wafer materials. One example of an infrared heater  22  contemplated for use in the present invention is a Watlow Quartz Heater, having a ⅜″ diameter×19 inches long and further having a 204 volt×15 amp maximum power capacity. A quartz infrared heater  22  of these specifications emits a peak wavelength of 2500 nm, which can be adjusted to a desired percent output based on the selected wafer material for heating. For example, a quartz infrared heater set to 90% output would emit a peak wavelength of about 2300 nm. 
     Further, if necessary, filters may be used between the infrared heaters and the wafers to ensure the functional and protective layers  16 ,  12  do not encounter the infrared rays. Infrared rays will be absorbed or passed at different wavelengths, based on the properties of the selected wafer materials. Any directed energy sources, as described herein, that produce the same practical effect of softening and/or forming a wafer with different materials, are therefore contemplated for use in the present invention. 
     In a preferred embodiment as shown in  FIG. 3 , the heating chamber  17  has a rotating turret  18  which further includes support arms extending to the forming, molding cups  20  that support each wafer  10 . The vacuum suction of the forming cup  20  holds the wafer  10  to the forming cup  20  while the turret  18  rotates the wafers through the heating chamber in a predetermined heating cycle. In this embodiment, wafers  10  are rotated through the heating chamber  17  at a cycle rate correlating to the number of wafers  10  to be heated. For example, when one wafer  10  is placed into the heating chamber  17  and run through a cycle, the cycle duration is 25 seconds times 1 wafer  10 , resulting in a 25-second cycle. However, when ten wafers  10  are placed in 10 forming cups  20  (as shown in  FIG. 10 ) in the heating chamber  17  and run through a cycle, the total cycle time or cycle duration is 25 seconds times 10 wafers, resulting in a 250-second cycle time. 
     This process may further be accomplished by manual or other automated mechanisms that promote forming or curving of wafers in any environment that permits different softening conditions or temperatures for different material properties of the layers, and are thus not limited to the illustrative examples of heating chambers as described and disclosed herein. 
     EXAMPLES 
     The device and method of forming polymeric laminated wafers comprising different film materials of the present invention will now be described in more detail in reference to examples, which are for illustrative purposes only and should not in any way be construed as a limitation upon the scope of the invention. The following are examples of wafers made using the present invention and comparative examples using various prior art methods. The first two comparative examples use a wafer having base layers and protective layers that are comprised of the same material in order to demonstrate the required settings to achieve the desired base form. The second two comparative examples attempt to form a wafer using the materials used in the Example. 
     Example 1 
     A wafer produced by Polaroid Corporation having a polarizer laminate comprising 1.35 mil CAB protective layer (KODACEL® brand CAB film, product code K7755), 1.2 mil PVA polarizer layer (custom formulated from raw material PVA: Vinylon made by Kuraray of Japan) and 10 mil polycarbonate base layer was punched into an 80 mm diameter disc and placed in a Lema P-10 forming machine with a quartz infrared heater 3 inches above the forming cups with a power controller. Air temperature was set to 225° F., bringing the cup temperature to approximately 220° F. The infrared heater power, having a power capacity of 204 volt×15 amp maximum (thereby a 2500 nm maximum wavelength output), was set to 90%. Cycle time for one wafer was set at 25 seconds and the forming cup was a 6 base. 
     Result: The wafer was formed to 6 base without any damage to the CAB protective layer of the wafer or to the adhesive that joins the layers of the wafer together. 
     Comparative Example 1A 
     A wafer made by Fuji Kasei of Japan having polycarbonate as a base layer, a PVA polarizing element as a functional layer, and polycarbonate as a protective layer was formed using a Lema P-10 forming machine without using infrared heating. The temperature was set to 235° F. Cycle time for one wafer was set at 25 seconds. 
     Result: The wafer stayed almost flat and was not formed to a 6 base due to insufficient heat for forming the polycarbonate. 
     Comparative Example 1B 
     A wafer made by Fuji Kasei of Japan having polycarbonate as a base layer, a PVA polarizing element as a functional layer, and polycarbonate as a protective layer was formed using a Lema P-10 forming machine without using infrared heating. The temperature was set to 285° F. Cycle time for one wafer was set at 25 seconds. 
     Result: The wafer was successfully formed to a 6 base. 
     Comparative Example 1C 
     A wafer produced by Polaroid Corporation having a polarizer laminate comprising 1.35 mil CAB protective layer, 1.2 mil PVA polarizer layer and 10 mil polycarbonate base layer was punched into an 80 mm diameter disc and placed in a Lema P-10 forming machine without the presence of infrared heaters. Air temperature was set to 235° F. and the cycle time for one wafer was set at 25 seconds and the forming cup was a 6 base. 
     Result: The wafer stayed almost flat and was not formed to a 6 base due to insufficient heat to the polycarbonate layer. 
     Comparative Example 1D 
     A wafer produced by Polaroid Corporation having a polarizer laminate comprising 1.35 mil CAB protective layer, 1.2 mil PVA polarizer layer and 10 mil polycarbonate base layer was punched into an 80 mm diameter disc and placed in a Lema P-10 forming machine without the presence of infrared heaters. Air temperature was set to 285° F. and the cycle time for one wafer was set at 25 seconds and the forming cup was a 6 base. 
     Result: The wafer was badly curled and delaminated due to excessive heat to the CAB layer. 
     Example 2 
     A polarizing wafer produced by Shin-wha comprising a 1.35 mil CAB protective layer, a 1.2 mil PVA polarizer layer, and a 12 mil polycarbonate layer was punched into an 86 mm disc and formed using a Lema P-10 fitted with two quartz infrared heaters 3 inches above the forming cups with independent power controllers. The air temperature was set to 245° F. resulting in an approximate cup temperature of 240° F. The cycle time for one wafer was set to 15 seconds and the infrared heater, having a power capacity of 204 volt×15 amp maximum (thereby a 2500 nm maximum wavelength output) was set to 90% for the first heater and 70% for the second heater. The forming cup had a 4.25 base curve. 
     Result: The wafer was formed to a 4.25 base curve without any damage to the CAB protective layer or the PVA polarizer adhesive layer. 
     Example 3 
     An experiment was conducted to see if a wafer could be re-formed using the present invention. A polarizing wafer produced by Shin-wha comprising a 1.35 mil CAB protective layer, a 1.2 mil PVA polarizer layer, and a 12 mil polycarbonate layer was punched into an 86 mm disc and formed using a Lema P-10 fitted with two quartz infrared heaters 3 inches above the forming cups with independent power controllers. The air temperature was set to 245° F. resulting in an approximate cup temperature of 240° F. The cycle time for one wafer was set to 15 seconds and the infrared heater, having a power capacity of 204 volt×15 amp maximum (thereby a 2500 nm maximum wavelength output), was set to 90% for the first heater and 70% for the second heater. The forming cup had a 4.25 base curve. This wafer that was formed to a 4.25 base curve was placed back into the Lema machine and exposed to another cycle as previously described, with the exception that this time, the formed wafer was placed in a cup having an 8.00 base curve. The temperature settings remained the same with the cycle time adjusted to 13 seconds. 
     Result: The wafer was re-formed to 8.00 base without any damage to the CAB protective layer or the PVA polarizer layer. 
     Based on these illustrative examples, one skilled in the art would conclude that this method enables forming of laminates having different materials with varying softening temperatures on either side of the wafer. This invention may be applied for thermal forming of various polymeric film laminates consisting of different films having varying optimum forming temperatures, which would otherwise be very difficult, if not impossible to form using conventional forming methods. 
     Although the invention has been described in terms of particular embodiments and applications, one of ordinary skill in the art, in light of this teaching, can generate additional embodiments and modifications without departing from the spirit of or exceeding the scope of the claimed invention. Accordingly, it is to be understood that the drawings and descriptions herein are proffered by way of example to facilitate comprehension of the invention and should not be construed to limit the scope thereof.