Laminating apparatuses are widely used for laminating a sheet material such as paper between two pieces of plastic films. A conventional laminating apparatus shown in FIG. 1(a) principally comprises two pairs of rollers, i.e. front rollers 10 and rear rollers 11, and a heating unit 12. The front rollers 10 comprise an upper front roller 101 and a lower front roller 102, while the rear rollers 11 comprise an upper rear roller 111 and a lower rear roller 112. The heating unit 12 comprises an upper heating element 121 and a lower heating element 122. The heating unit produces heat from electricity. The process for laminating a sheet material by way of the laminating apparatus is illustrated as follows. The sheet material is sandwiched between a pair of plastic films. The sandwiched structure is then fed to the passage between the upper heating element 121 and the lower heating element 122 by means of the front rollers 10, and the plastic films are heated and thus softened. Then, the sandwiched structure advances and is pressed to laminate by means the rear rollers 11 so as to bond the sheet material with the plastic films.
In the above-mentioned laminating apparatus, since the heating mechanism and pressing mechanism are separately performed by two individual units, the materials of the sheet and the plastic films should be limited to some special combinations in view of the heating and laminating timings. In addition, the laminating effect of such laminating apparatus is sometimes not satisfied, for example, due to formation of some bubbles in the resulting article.
In order to overcome the drawbacks, another laminating apparatus as shown in FIG. 1(b) was developed. Such laminating apparatus, also referred as “hot shoe”, comprises only a pair of rollers 22. The heat generated by heating plates 21 is uniformly distributed over aluminum extrusion elements 20, and radiated to heat up the rollers 22. Therefore, when the sheet material sandwiched between a pair of plastic films is fed through the rollers 22, the heating and pressing mechanisms are simultaneously performed thereon so as to avoid the problem of forming bubbles. Since heat for pressing the sandwiched structure is transferred to the rollers 22 through air gaps between the aluminum extrusion elements 20 and the rollers 22, a relatively long waiting time, for example 10-15 minutes, is required to warm up the laminating apparatus.
In order to reduce the warming-up period, another laminating apparatus as shown in FIG. 1(c) was developed. The laminating apparatus comprises a pair of heaters 30 and a pair of rollers 31. Each heater 30 is located inside one roller 31 to provide heat to the exterior surface of the roller 31. The rollers 31 with heaters 30 therein simultaneously perform the heating and pressing operations, and the rotation of the rollers 31 transmits the sheet material and the plastic films to move forwards. Since the heat is transferred from the heaters 30 to the outer surfaces of the rollers 31 in a manner of conduction other than radiation, relatively short time is enough to reach the working temperature for laminating the thin films. In addition, a compact size of the laminating apparatus can be obtained. Since the heaters 30 are rotated with the rollers 31, it is critical for the rotating heaters 30 to continuously receive power.
Please refer to FIG. 2. In a conventional method, the continuous power supply to a rotating heater 40 is assured of by arranging a copper resilient strip 41 by a conductive shaft 401 of the rotating heater 40. When the conductive shaft 401 rotates, the circumferential surface of the conductive shaft 401 is kept in contact with the still copper resilient strip 41. The rotation of the rollers 31 relative to the copper resilient strip 41, however, is likely to lead to serious abrasion of the conductive shaft 401 and even spark. Due to the considerations of safety and minimal abrasion, it is required to improve the electric contact means in order to continuously supply power to the rotating heaters.