Patent Application
20080020210
A multi-layered metal/organic polymer composite exhibiting desirable decorative and forming characteristics is disclosed. The composite includes as essential components a polymeric layer, a metal layer, and a protective layer. The inventive composite is formable, a feature that in the present context means that it is capable of being formed without delamination or separation of the metal layer from the polymeric substrate. By “forming” we mean that at least a portion of the inventive composite is stretched to undergo a significant dimensional change. Quantitatively, at least a portion of the area of the composite may be extended by at least 5 percent without exhibiting objectionable micro cracks that adversely affect the mirror-like appearance of the formed composite. The inventive composite may be thermoformed to produce a formed insert for making a part by FIM. The protective layer of the inventive composite was found to adhesively bond to the solidified injected resin. In the instances where ink is applied to the protective layer, both the ink and the layer adhere to the molded article.
The clear polymeric layers of the inventive composite may be prepared by conventional means of polycarbonate, Polycyclohexylenedimethylene terephthalate glycol (PCTG), PETG, PMMA, polystyrene, polyurethane and clear blends of these resins. In the context of the invention the terms clear refers to total light transmission greater than 90% and haze value of not greater than 1.5% as determined in accordance with ASTM 1003 method B. These materials and films thereof are known and are available in commerce. In the preferred embodiment the polymeric layer is polycarbonate or a composition that contains polycarbonate. Suitable such polycarbonate films are available commercially under the trademarks Makrofol and Bayfol from Bayer MaterialScience LLC, of Pittsburgh, Pa. Polycarbonate film is preferred because of its high light transmittance, low haze, impact resistance and high heat deflection temperature. Furthermore, polycarbonate film is particularly suitable in applications where printing by conventional techniques such as screen and offset printing is desired. Moreover, polycarbonate film may be easily formed, stamped, die-cut, and embossed.
The polymeric layer needs to be sufficiently thick to enable forming the composite and is generally in the range of 100 to 1,000 microns, preferably 125 to 750 microns, most preferably 175 to 625 microns in thickness. At least one of the surfaces of the polymeric layer, the surface to be metallized needs to be glossy. The other surface may be glossy, matte, velvet or suede. Having glossy finish for both surfaces of the polymeric layer is preferred because this highly transparent layer with the underlying metallic layer provides a bright mirror-like appearance.
The metal layer comprise an alloy of Indium, Tin and Copper, preferably Indium-Tin, most preferably an Indium-Tin-Copper alloy. Preferably, the Indium-Tin-Copper contains Indium in an amount of 5 to 100, more preferably 85 to 95 percent, Tin in an amount of 1 to 95, more preferably 5 to 15 percent and Copper in an amount of 1 to 15, more preferably 5 to 10 percent, the percents being relative to the weight of the alloy. These known alloys are suitably ductile and does not form an oxide film in moist environment and are thus suitable for metallizing the polymeric layer in the context of the invention. The proximity of their melt temperatures to the temperatures at which conventional forming takes place make these alloys particularly suitable for the preparation of the formed composites of the invention.
The protective layer of the inventive composite is formed of an anionic and/or nonionic aliphatic dispersion of polycarbonate urethane resin. This layer provides improved abrasion-resistance and promotes the adhesion of inks and/or injection molding resins to the metallic layer. This suitable dispersion (herein PUD) is characterized in solids contents of about 20 to 60%, preferably 30 to 50% more preferably 33 to 37%; viscosity, at 25° C. of 10 to 3000 cps, preferably 10 to 1000, more preferably 20 to 400; pH of 6 to 12 , preferably 7 to 9; glass transition temperature of −65 to −25° C., preferably −27 to −37° C. N-Methyl-2-Pyrrolidone (NMP) in an amount of 0 to 15, preferably 6 to 10, most preferably 8% percent by weight may be included in the course of synthesis, or in the alternative may be blended with the suitable PUD. NMP is preferably included in the course of synthesis. Methods for preparing PUD are well known and suitable ones are available commercially from Bayer MaterialScience LLC.
The PUD may optionally contain efficacious amounts of conventional functional additives known for their utility in enhancing adhesion and clarity. Suitable additives include wetting agents, e.g. polyether modified polydimethylsiloxane, flow agents, e.g., polyether-modified methyl polysiloxane.
The multi-layered composites of the present invention may be prepared by any conventional method for making multi-layered metal/organic polymer composites. For example, the metal may be applied as a coating by a conventional metallization technique such as an electroless process described by F. A. Lowenheim in “Metal Coatings of Plastics,” Noyes Date Corporation, (1970), by Pinter, S. H. et al., Plastics: Surface and Finish, Daniel Davey & Company, Inc., 172-186 (1971) or in U.S. Pat. No. 2,464,143. An especially preferred metallization technique in the practice of this invention is a vacuum deposition technique wherein the metal is vacuum evaporated and then deposited onto the polymer layer as described by William Goldie in Metallic Coating of Plastics, Vol. 1, Electrochemical Publications Limited, Chap. 12 (1968). Another preferred metallization technique includes sputter coating as described in Chapter 13 of Goldie, supra. Also suitable is electroplating and ion plating. In addition, the multi-layered composite may be formed by lamination of metal foil to the polymer layer including extrusion coating of the polymer layer onto a metal foil.
The thickness of the metal layer in the multi-layered composite is that which would form a reflective, essentially continuous film over the surface of the polymer layer the metal layer enabling light transmittance through the metallized polycarbonate film. When light transmittance, determined in accordance with ASTM D1003 method B, is higher than 60%, the metal layer loses its shininess and appears brownish in color. Preferably, light transmittance is in the range of 0.1% to 60.0%, most preferably 0.2% to 40%. When the metallized composite is used in a backlit application, preferred light transmittance ranges from 0.3% to 30%, most preferably 1.4% to 25%.
Following its preparation the multi-layered composite may be formed by a conventional forming process, e.g., thermoforming or solid phase forming, to the desired shape. Preferably, the forming process is a conventional thermoforming process for shaping sheet or film stock, which process is normally carried out at an elevated film surface-temperature. In forming composites wherein the polymeric layer is of polycarbonate the surface-temperature of the film is about 190° C. Exemplary thermoforming processes include differential air pressure thermoforming, match thermoforming, vacuum forming, plug assist-vacuum forming, draw forming, impact forming, rubber pad forming, hydroforming, drape molding and the like. Exemplary solid phase forming methods include cold rolling, impact extrusion, forging, forward extrusion, cold heading, and rubber-pad forming, e.g., as such methods are further described by P. M. Coffman in Soc. Plas. Eng. Journal, Vol. 25, January, 1969 (50-54) and Soc. Auto. Eng. Journal, Vol. 76, No. 6, 36-41 (1968), all incorporated herein by reference.
In the forming operation, the entire composite or a portion thereof, is formed or shaped in a manner such that at least a portion of the composite undergoes a cumulative surface dimensional change of at least 5 percent. The term “cumulative surface dimensional change” refers to the combined change of length and width wherein a decrease as well as an increase in a particular dimension is treated as a positive change. Either one or both surface dimensions may be changed in the forming operation. Techniques for observing surface dimensional changes are described by A. Nadai in Plasticity, McGraw-Hill (1931). The formed composite may be die-cut and then molded using Film Inset Molding technology. U.S. Pat. Nos. 3,654,062 and 6,117,384 that relate to Film Insert Molding, or as it is sometimes referred to In Mold Decoration, are incorporated herein by reference.
The method of using the inventive multi-layered composite entails the technology known as FIM or in-mold-decoration. Essentially the method entails forming the composite to produce a formed composite, placing the formed composite in a mold, and introducing molten resin into the mold to form an article that includes the formed composite.
The following examples illustrate the invention and should not be construed as limiting the scope thereof.
To a polycarbonate film (0.010″ thick) metallized with an alloy of In/Sb (90/10) there was applied, on the metallized side, a protective coating of the composition described below. The thus protected metallized composite was formed and its adhesive integrity evaluated. Each of the polyurethane dispersions that are described in Table 1 was applied in its “as supplied” or blended with one or more additives or with another polyurethane dispersion. These were hand mixed at room temperature and applied to the metal layer using a draw down method. A #34 Mayer rod was used in sequence 1 and a #30 rod was used in sequences 2 and 3.
The examples referred to as Sequence 1 were air-dried at room temperature for 24 hours.
The examples referred to as sequences 2 and 3 were dried at 90° C. for 5 minutes in a continuous air-impinged, high velocity tunnel jet dryer.
Adhesion testing identified failures in the interfaces between the polymeric layer and metal layer or between it and the protective layer. Multi-layered structures measuring 2×3″ were cut and used for making molded specimens by FIM, polycarbonate (Makrolon® 2458 resin, a product of Bayer MaterialScience LLC) being injection molded behind the multilayered composite. The resin temperature was 290° C., mold temperature was 50° C. , and the injection speed was 50 mm/s. The molded samples were then post cured for 24 hours at room temperature.
The specimens referred to as sequence 1 were tested for adhesion by hand pulling a corner of the film to determine where the failure occurred. The integrity of the adhesion in the examples of sequences 2 and 3 was determined in accordance with ASTM D429, method B, 90° peel test at 305 in/min., and the results were reported in lb/in.
In this sequence the polyurethane dispersions were used as protective layer and evaluated, the description and results are shown in Table 1.
In a still additional series of tests the effects of alternative co-solvent on the adhesion were determined. Alternative solvents such as IPA and Ethanol, were post added. The examples and the resulting adhesions are shown in Table 2.
An additional set of experiments showed the dependence of the adhesion on the amount of incorporated NMP in PUD 3 Example 18 entails the addition of PUD6 as adhesion promoter.
Although the invention has been described in detail in the foregoing for the purpose of illustration, it is to be understood that such detail is solely for that purpose and that variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention except as it may be limited by the claims.
