Abstract:
A foil-decorating injection molding method and a foil-decorating injection molding apparatus adjust the tautness of a decorative sheet fed onto a parting surface of a female mold so that tensions T 1 , T 2  and T 3  of the decorative sheet during a sheet feed operation of the sheet feed means, at the start of the sheet clamping operation of the clamper for pressing and fixing the decorative sheet and at a moment immediately before the completion of the sheet clamping operation, respectively, meet an inequality: T 1 ≧T 2 &gt;T 3  to prevent the decorative sheet from breaking or slipping off the clamper when clamping the decorative sheet on the parting surface of the female mold.

Description:
This is a Division of application Ser. No. 08/904,308 filed Jul. 31, 1997. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a foil-decorating injection molding method that molds decorative sheet carrying patterns and characters into a molding in a mold by injection molding to produce a molding decorated with the patterns and the characters, and a foil-decorating injection molding apparatus for carrying out the foil-decorating injection molding method. 
     2. Description of the Related Art 
     There have been proposed many foil-decorating injection molding methods that mold a decorative sheet carrying patterns and characters into a molding in a mold by injection molding to produce a molding decorated with the patterns and the characters. Most of those previously proposed foil-decorating injection molding methods carry out all or some of the following processes (a) to (i) in that order or in order of a sequence different from that of the processes (a) to (i) sequentially or some of those processes are carried out simultaneously or parallelly. 
     Process (a): A decorative sheet feed process for feeding a decorative sheet onto a parting surface of a female mold of an injection mold employed in injection molding 
     Process (b): A sheet clamping process for clamping the decorative sheet to hold the decorative sheet fixedly on the parting surface of the female mold 
     Process (c): A softening process for heating and softening the decorative sheet by a hot plate or the like 
     Process (d): A drawing process for drawing the softened decorative sheet by vacuum forming and/or pressure forming so that the decorative sheet may conform to the inner surface of the female mold (Preparatory molding process) 
     Process (e): A mold closing process for closing the injection mold by moving the female mold to a male mold or by moving the male mold to the female mold 
     Process (f): An injection molding process for injecting a fluid resin (molten resin) through the male mold into a cavity defined by the male mold and the female mold 
     Process (g): A mold opening process for separating the male mold and the female mold 
     Process (h): A trimming process for removing marginal portions of the decorative sheet 
     Process (i): An ejecting process for ejecting the molding decorated with the decorative sheet from the female mold 
     In a simultaneous process implementation mode, the plurality of processes are carried out simultaneously. For example, the process (b) for clamping the decorative sheet and the process (e) for closing the mold are accomplished simultaneously if the decorative sheet is held between the male mold and the female mold in the mold closing process. The process (d) for drawing the decorative sheet and the process (f) for injecting the molten resin into the injection mold can simultaneously be accomplished if the decorative sheet is drawn by the heat and the pressure of the molten resin injected into the injection mold. 
     A laminated decorative sheet or a transfer decorative sheet is used selectively depending on the type of product to be produced. If a laminated decorative sheet is used, the laminated decorative sheet is attached integrally to the surface of an injection-molded molding to form a decorative layer. If a transfer decorative sheet having a substrate and a decorative transfer layer formed on the substrate is used, the transfer decorative sheet is attached to the surface of a molding, and then the substrate is removed from the molding, so that only the decorative transfer layer remains on the surface of the molding. 
     In the conventional foil-decorating injection molding method comprising the foregoing processes, the tension of the decorative sheet is kept constant during the sheet feed process, at the start of the sheet clamping process and at a moment immediately before the completion of the sheet clamping process, or the tension of the decorative sheet is increased in the sheet clamping process subsequent to the feed of the decorative sheet onto the parting surface of the female mold, which is described in, for example, JP-B No. 1-59095 and JP-U No. 4-34004. The decorative sheet is broken sometimes when the same is clamped if the decorative sheet is tautened excessively or the decorative sheet sometimes is slackened to crease or the decorative sheet is dislocated from a correct position if the decorative sheet is excessively slack. 
     As mentioned in JP-A No. 7-227877, when a molding to be produced is, for example, a control panel P as shown in FIG.  8 (A) for a rice boiler, having the shape of a curved surface having a relatively great height and resembling a portion of a circular cylinder, an injection molding apparatus sometimes employs a special damper  25  as shown in FIG.  8 (B). The special damper  25  has a frame-shaped clamping part  25   a  having the shape of a frame to press and hold a decorative sheet on the parting surface of the female mold, and a sheet pressing part  25   b  having the shape of a two-dimensional curved surface to press part of the decorative sheet into a recess formed in the female mold. When the special damper  25  is employed, it is possible that a further problem arises in addition to the foregoing problems; that is, the tension of a decorative sheet S increases sharply as the special damper  25  presses the decorative sheet S to clamp and hold the decorative sheet S and, as shown in FIG.  8 (C), portions of the opposite sides of the decorative sheet S slip off the opposite side members of the frame-shaped clamping part  25   a  into the recess as shown in FIG.  8 (C) and, consequently, the decorative sheet cannot properly be clamped. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in view of the foregoing problems in the prior art and it is therefore an object of the present invention to provide a foil-decorating injection molding method that adjusts the tension of a decorative sheet so that the decorative sheet may not break, may not slip off a clamper, may not crease and may not be dislocated when the clamper clamps the decorative sheet. 
     Another object of the present invention is to provide a foil-decorating injection molding apparatus capable of adjusting the tension of a decorative sheet so that the decorative sheet may not break, may not slip off a clamper, may not crease and may not be dislocated when the clamper clamps the decorative sheet. 
     According to one aspect of the present invention, a foil-decorating injection molding method comprises, as basic steps, a sheet feed process for feeding a web-fed decorative sheet unwound from a roll of web onto a parting surface of a female mold of an injection mold, a sheet clamping process for pressing and fixing the decorative sheet on the parting surface of the female mold, a drawing process for drawing the decorative sheet so as to conform to the inner surface of the female mold defining a cavity, moving the female mold toward a male mold of the same injection mold or moving the male mold toward the female mold to close the injection mold so that the cavity is formed, an injection molding process for injecting a fluid resin through the male mold into the female mold to fill up the cavity, a mold opening process for separating the male mold and the female mold from each other to open the injection mold, and a mold ejecting process for ejecting an injection-molded molding from the female mold. Those processes are carried out in the foregoing order or in order of a sequence different from the foregoing order sequentially or some of those processes are carried out simultaneously or parallelly. 
     The tensions T 1 , T 2  and T 3  of the decorative sheet during the sheet feed process, at a moment when the sheet clamping process is started and at a moment immediately before the completion of the sheet clamping process, respectively, are adjusted so as to meet an inequality: T 1 ≧T 2 &gt;T 3 . 
     Desirably, the decorative sheet is heated by a hot plate or the like for softening by a softening process before the drawing process. However, the softening process is not essential. 
     According to another aspect of the present invention, a foil-decorating injection molding apparatus comprises an injection mold having a male mold and a female mold, one of the male mold and the female mold is movable relative to the other, sheet feed mechanism for feeding a decorative sheet from a roll of web having decorative sheet onto a parting surface of the female mold, a damper capable of moving in directions perpendicular to the parting surface of the female mold and of pressing the decorative sheet against the parting surface of the female mold to hold the decorative sheet on the parting surface of the female mold for a sheet clamping operation, and a resin injecting mechanism for injecting a fluid resin through the male mold into a cavity formed between the male mold and the female mold to fill up the cavity with the fluid resin. The foil-decorating injection molding apparatus is characterized by a tension adjusting means for adjusting the tautness of the decorative sheet so that tensions T 1 , T 2  and T 3  of the decorative sheet during a sheet feed operation of the sheet feed mechanism, at the start of the sheet clamping operation of the damper for pressing and fixing the decorative sheet and at a moment immediately before the completion of the sheet clamping operation, respectively, meet an inequality: T 1 ≧T 2 &gt;T 3 . 
     The damper employed in the foil-decorating injection molding apparatus of the present invention may be such as having only a flat frame-shaped clamping part for pressing and fixing the decorative sheet on the parting surface of the female mold or such as having a flat frame-shaped clamping part and a two-dimensionally curved or bent sheet pressing part for pressing part of the decorative sheet into the recess formed in the female mold. The effect of the present invention is conspicuous particularly when the latter clamper is employed. 
     The tension adjusting mechanism of the foil-decorating injection molding apparatus of the present invention may be a known tension adjusting mechanism such as disclosed in JP-B No. 1-59095 comprising a sheet feed mechanism including a reel on which a web of decorative sheet is wound in a roll, and a variable braking device capable of applying a desired braking force to the reel, and a pair of feed rollers disposed below the sheet feed mechanism with respect to a decorative sheet feed direction, or may be such as disclosed in JP-U No. 4-34004 comprising pull rollers disposed below the female mold with respect to a decorative sheet feed direction to pull the decorative sheet so that the decorative sheet is extended over the parting surface of the female mold, and a dancer roller capable of biasing the decorative sheet in a direction perpendicular to the decorative sheet feed direction. 
     As mentioned above, the foil-decorating injection molding apparatus is provided with the damper capable of moving in directions perpendicular to the parting surface of the female mold and of pressing the decorative sheet against the parting surface of the female mold to hold the decorative sheet on the parting surface of the female mold, and the damper is advanced toward and moved away from the parting surface (the decorative sheet) in directions perpendicular to the parting surface of the female mold by a drive means. The drive means may comprise a pneumatic cylinder actuator for driving the clamper, and a control means for controlling the pneumatic cylinder actuator or an ejector pin driving means may be used also as a drive means for driving the clamper. 
     The male mold and the female mold are made of a metal, such as an iron base alloy, or a ceramic material, and may be composite molds if the shape of a molding to be molded therein requires. When the decorative sheet is subjected to a preforming process, the foil-decorating injection molding apparatus is provided with a heating-and-softening means, such as a hot plate, and the male mold and the female mold are provided with pores to supply compressed air into the cavity for preforming or to evacuate the cavity for vacuum forming. 
     Positioning marks, such as +-shaped marks, −-shaped marks or I-shaped marks, may be formed on the decorative sheet, the positioning marks may be detected by detectors, such as photoelectric cells or image sensors, disposed around or on the female mold, and the operation of a driving means, such as a servomotor, included in the sheet feed mechanism on the basis of the output signals of the detectors to position a decorative pattern formed on the decorative sheet in a high accuracy relative to the inner surface of the female mold defining a cavity. If the decorative sheets are those not requiring accurate positioning, such as unfigured ones or those provided with repetitious patterns, the web of decorative sheet may simply be fed by a fixed length at a time by controlling a stepping motor or the like included in the sheet feed mechanism. The decorative sheet may be a laminated decorative sheet consisting of a base sheet and a decorative layer laminated to the base sheet or a transfer decorative sheet consisting of a base sheet and a decorative transfer layer. The laminated decorative sheet is incorporated into a molding to form a decorating layer. The transfer decorative sheet is attached to a molding, and then only the base sheet is removed from the molding and the decorative transfer layer is left on the molding. 
     The base sheet may be made of a thermoplastic resin, such as polyvinyl chloride, an acrylic resin, polystyrene, an ABS resin, a polycarbonate resin, a polyester resin or polypropylene. The thickness of the base sheet is in the range of about 20 to about 500 μm. The decorative layer may be an aesthetic layer, such as a film provided with printed patterns, a colored or transparent film or a metal thin film, or a functional layer, such as a hard film, an antidim film or a conductive film. 
     The fluid resin to be injected into the injection mold by the resin injecting mechanism may be any one of generally known resins suitable for foil-decorating injection molding including heated and melted thermoplastic resins, such as an ABS resin (acrylonitrile-butadiene-styrene copolymer resin), polystyrene, polycarbonate and polypropylene, two-part resins and catalytic curing resins, such as polyurethane resins and unsaturated polyesters. 
     When carrying out the foil-decorating injection molding method of the present invention by the foil-decorating injection molding apparatus of the present invention, a necessary length of the web of decorative sheet, i.e., a length of the web of decorative sheet for one injection molding cycle is fed at a time from the reel by a pair of feed rollers and a pair of pulling rollers included in, for example, a tension adjusting mechanism onto the parting surface of the female mold so as to cover the recess formed in the female mold. A brake device included in the tension adjusting mechanism exerts a maximum braking force during the decorative sheet feed operation to adjust the tension of the decorative sheet to a highest tension T 1  of 13 kg. Then, the clamper is advanced toward the female mold to start a decorative sheet pressing and fixing operation, i.e., a decorative sheet clamping operation and, at the same time, one of the pair of feed rollers is separated from the decorative sheet and the braking force of the brake device is reduced. Consequently, a short length of the web of decorative sheet is unwound from the reel and the tension of the decorative sheet is reduced to a tension T 2  lower than the tension T 1  at the start of the clamping operation. The tension T 2  is, for example, 10 kg. The decorative sheet thus tautened is pressed against the parting surface of the female mold by the clamper. If the damper is a special damper similar to the special damper shown in FIG.  8 (B) having the sheet pressing part having the shape of a two-dimensional curved surface, part of the decorative sheet is pressed into the recess formed in the female mold by the sheet pressing part. The braking force of the brake device included in the tension adjusting mechanism is further reduced immediately before the decorative sheet is pressed against the parting surface of the female mold by the clamping frame part of the damper to unwind another length of the web of decorative sheets from the reel, so that the tension of the decorative sheet is further reduced to a tension T 3  of, for example, 3 kg, which is lower than the tension T 2 . Since the decorative sheet is tautened at the maximum tension when the same is fed onto the parting surface of the female mold, the decorative sheet will not crease and will not be dislocated. Since the tension of the decorative sheet is reduced gradually at the start of the sheet clamping operation and at a moment immediately before the completion of the sheet clamping operation, the decorative sheet will not break and will not slip off the clamper. 
     After the completion of the sheet clamping process, the softening process for heating and softening the decorative sheet by a hot plate or the like, the drawing process for drawing the decorative sheet so as to conform to the inner surface of the female mold by vacuum forming and/or pressure forming, the mold closing process for closing the injection mold by moving the female mold toward the male mold of the same injection mold or moving the male mold toward the female mold so that the cavity is formed between the male mold and the female mold, the injection molding process for injecting a fluid resin (molten resin) through the male mold into the female mold to fill up the cavity, and the mold opening process for separating the male mold. These processes are carried out in that order or in order of a sequence different from the foregoing sequence of the processes sequentially or some of those processes are carried out simultaneously or parallelly. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantage of the present invention will become more apparent from the following description taken in connection with the accompanying drawings, in which: 
     FIG. 1 is a schematic perspective view of an essential portion of a foil-decorating injection molding apparatus in a first embodiment according to the present invention; 
     FIG. 2 is a schematic side view of the foil-decorating injection molding apparatus of FIG. 1; 
     FIG. 3 is a view similar to FIG. 2, for assistance in explaining the operation of the foil-decorating injection molding apparatus of FIG. 1; 
     FIG. 4 is a view similar to FIG. 2, for assistance in explaining an operation of the foil-decorating injection molding apparatus of FIG. 1 for an injection molding process; 
     FIGS.  5 (A) and  5 (B) are perspective views of a molding molded by a foil-decorating injection molding apparatus in a second embodiment according to the present invention and a clamper employed by the same foil-decorating injection molding apparatus, respectively; 
     FIG. 6 is a schematic side view of the foil-decorating injection molding apparatus in the second embodiment; 
     FIG. 7 is a view similar to FIG. 6, for assistance in explaining the operation of the foil-decorating injection molding apparatus of FIG. 6; and 
     FIGS.  8 (A),  8 (B) and  8 (C) are a perspective view of a molding produced by a foil-decorating injection molding apparatus, a perspective view of a clamper employed in producing the molding, and a plan view of assistance in explaining problems in producing the molding, respectively. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIGS. 1 and 2, a foil-decorating injection molding apparatus  10  in a first embodiment according to the present invention is provided with an injection mold having a female mold  12  and a male mold  40 . A cavity corresponding to a molding P, FIG.  8 (A), to be molded is defined by the female mold  12  and the male mold  40 . The female mold  12  is fixedly held on a movable mold platen  11 . The movable mold platen  11  is moved transversely (horizontally) as viewed in FIG. 1 by a ram  15  included in a hydraulic actuator; that is, the female mold  12  is moved toward and away from the male mold  40 . The female mold  12  need not necessarily be moved horizontally relative to the male mold  40 ; the female mold  12  and the male mold  40  may be disposed in a vertical arrangement, and the female mold  12  may be moved relative to the male mold  40  or the male mold  40  may be moved relative to the female mold  12 . A recess  13  for forming a cavity and corresponding to the shape of a molding P, such as the curved molding shown in FIG.  8 (A), to be produced is formed in the female mold  12 . Suction passages  17  are formed in the female mold  12  so as to open in the inner surface forming the recess  13  of the female mold  12 . The suction passages  17  are connected by a pipe  19  to an external vacuum pump. The female mold  12  has a parting surface  12   a  and an O ring, not shown, is fitted in a groove formed in the parting surface  12   a  so as to surround the open end of the recess  13 . 
     The male mold  40  is fixedly held on a stationary mold platen  44  fixedly mounted on a nozzle  50 . The male mold  40  is provided in its central portion with a core  41  (FIG. 2) which forms a cavity in combination with the recess  13  of the female mold  12 . A runner  42  is formed through the male mold  40  to inject a molten resin therethrough into the cavity defined by the recess  13  of the female mold  12  and the core  41  of the male mold  40 . Four tie bars, not shown, are extended through the four corners of each of the movable mold platen  11  and the stationary mold platen  44  in a direction parallel to the X-axis (FIG.  1 ). The female mold  12  is restrained from movement in directions perpendicular to the X-axis by the tie bars and moves toward and away from the male mold  40  along the tie bars. 
     A clamper  25  is supported on an actuating rod  26   a  included in a cylinder actuator  26 , and a hot plate  30  for heating and softening a decorative sheet S is supported on an actuating rod  27   a  included in a cylinder actuator  27 . The cylinder actuator  26  moves the damper  25  and the cylinder actuator  27  moves the hot plate  30  in directions parallel to the parting surface  12   a  of the female mold  12 , i.e., parallel to the Y-axis (FIG.  1 ), into and away from the path of the female mold  12  and in directions perpendicular to the parting surface  12   a  of the female mold  12 , i.e., parallel to the X-axis. The damper  25 , similarly to that shown in FIG.  8 (B), has a frame-shaped clamping part  25   a  for fixedly pressing the decorative sheet S on the parting surface  12   a  of the female mold  12 , and a two-dimensionally curved pressing part  25   b  for pressing part of the decorative sheet S into the recess  13  of the female mold  12 . The hot plate  30  has a curved heating surface  30   a  corresponding to the molding P. 
     A decorative sheet feed unit  60  (FIG. 2) feeds a decorative sheet S. The decorative sheet feed unit  60  comprises a reel  62  supporting a roll of a web of decorative sheets S, a tension adjusting mechanism  61  including a belt-and-pulley transmission mechanism  66 , a variable electromagnetic brake device  65  for properly braking the reel  62  and a motor  67 , a pair of feed rollers  72  disposed above the path of the female mold  12 , and a pair of pull rollers  74  disposed below the path of the female mold  12 . The rotative driving force of the motor  67  is transmitted through the belt-and-pulley transmission mechanism  66  to the brake device  65 . The rotative driving force of the brake device  65  is transmitted through a belt-and-pulley transmission mechanism  63  to the reel  62 . The torque of the reel  62  can be changed by the braking force of the brake device  65 . A roller  57   a  of a roll diameter measuring device  57  is pressed against the surface of the roll of a web of decorative sheet S supported on the reel  62 . The braking force of the brake device  65 , i.e., power supplied to the brake device  65 , must be regulated according to the diameter of the roll of a web of decorative sheets S to regulate the decorative sheet S unwound from the roll of a web at a desired tension. Therefore, the diameter of the roll is measured continuously by the roll diameter measuring device  57 . 
     The decorative sheet S used when producing a molding P by the foil-decorating injection molding apparatus  10  is a transfer decorative sheet having a 50 μm thick PET base sheet, and a decorative transfer layer formed by printing on the PET base sheet. Positioning marks are formed on an outer surface of the decorative transfer layer. 
     When the foil-decorating injection molding apparatus  10  operates for injection molding, the motor  67  of the tension adjusting mechanism  61  of the decorative sheet feed unit  60  is driven for operation, a necessary length of the web, i.e., a length of the web for one injection molding cycle corresponding to the length of one decorative sheet S, is fed at a time by the pair of feed rollers  72  and the pair of pull rollers  74  so as to extend over the parting surface  12   a  of the female mold  12  as shown in FIG.  2 . While the web is being unwound from the roll, the braking force of the brake device  65  of the decorative sheet feed unit  60  is increased to a maximum to tauten the decorative sheet S at a maximum tension T 1  of, for example, 13 kg. 
     The damper  25  which has been moved to a position opposite the parting surface  12   a  of the female mold  12  is moved toward the parting surface  12   a  of the female mold  12 , i.e., toward the decorative sheet S to start a decorative sheet pressing and fixing operation. Then, as shown in FIG. 3, one of the pair of feed rollers  72  is separated from the web of decorative sheets S, and the braking force of the brake device  65  is reduced. Consequently, some length of the web of decorative sheets S is unwound from the roll supported on the reel  62  so that the tension of the decorative sheet S is reduced from the tension T 1  to a tension T 2  of, for example, 10 kg at a moment when a sheet clamping operation is started. 
     The decorative sheet S thus tautened at the tension T 2  is pressed toward the parting surface  12   a  by the clamper  25 . Part of the decorative sheet S is pressed into the recess  13  of the female mold  12  by the sheet pressing part  25   b  of the damper  25 . 
     The braking force of the brake device  65  of the decorative sheet feed unit  60  is reduced further at a moment immediately before the completion of the sheet clamping operation, for example, 0.5 sec before the completion of the sheet clamping operation, i.e., a moment immediately before the decorative sheet S is held firmly between the frame-shaped clamping part  25   a  and the parting surface  12   a  of the female mold  12 , and, consequently, the web is further unwound from the roll supported on the reel  62  to tauten the decorative sheet S at a tension T 3  of, for example, 3 kg. Since the decorative sheet S is tautened at the maximum tension T 1  when the same is being fed, the decorative sheet S may not crease and may not be dislocated. Since the tension of the decorative sheet S is reduced stepwise at a moment immediately before the start of the sheet clamping operation and at a moment immediately before the completion of the sheet clamping operation, the decorative sheet S may not break and may not slip off the damper  25 . 
     After thus completing a sheet clamping process for clamping the decorative sheet S on the parting surface  12   a  of the female die  12 , a softening process for softening the decorative sheet S by heating the same by the hot plate  30 , a drawing process for drawing the decorative sheet S so as to conform to the inner surface  12   a  of the female mold  12  by vacuum forming (preforming process), a mold closing process for closing the injection mold by moving the female mold  12  toward the male mold  40  and joining the female mold  12  to the male mold  40  to form a cavity between the female mold  12  and the male mold  40 , an injection molding process for injecting a fluid resin (molten resin) through the male mold  40  into the cavity (FIG.  4 ), and a mold opening process for opening the injection mold by separating the female mold  12  from the male mold  40 , are carried out sequentially. 
     FIG.  5 (A) shows a molding Q, such as a decorative panel for an automobile AT gear, molded by a foil-decorating injection molding apparatus  20  (FIGS. 6 and 7) in a second embodiment according to the present invention. FIG.  5 (B) shows a special damper  35  employed in injection-molding the molding Q. The special damper  35  has a frame-shaped part  35   a  and a sheet pressing part  35   b  having an undulating wall. FIGS. 6 and 7 show the foil-decorating injection molding apparatus  20  in the second embodiment which uses the damper  35 , in which parts like or corresponding to those of the foregoing foil-decorating injection molding apparatus  10  in the first embodiment are designated by the same reference characters and the description thereof will be omitted. 
     Referring to FIGS. 6 and 7, the foil-decorating injection molding apparatus  10  is provided with a decorative sheet feed unit  70  provided with a tension adjusting mechanism different from the tension adjusting mechanism  61  of the first embodiment. The decorative sheet feed unit  70  comprises a pair of feed rollers  72  disposed above a female mold  12  with respect to a direction in which a web of decorative sheet S is fed, to feed the web of decorative sheets S, a pair of pull rollers  74  disposed below the female mold  12  with respect to the direction in which the web of decorative sheet S is fed to pull the web of decorative sheets S, a pair of pinch rollers  76  disposed between the female mold  12  and the pair of pull rollers  74 , and a dancer roller device including a dancer roller  75  and a swing arm  77  supporting the dancer roller  75  on its free end and pressing the dancer roller  75  against a portion of a decorative sheet S extending between the pair of pinch rollers  76  and the pair of pull rollers  74  in a direction perpendicular to the decorative sheet S. When feeding the decorative sheet S on the foil-decorating injection molding apparatus  20 , a necessary length of the web of decorative sheets S, i.e., a length of the web necessary for one injection molding cycle, is fed at a time by the pair of feed rollers  72  and the pair of pull rollers  74 , and the swing arm  77  is turned so that the dancer roller  75  pushes the decorative sheet S to an extreme position, i.e., a leftmost position as viewed in FIG.  6 . Consequently, the decorative sheet S is extended so as to cover the parting surface  12   a  of a female mold  12 . When thus feeding the decorative sheet S, the pull rollers  74  are driven for rotation at a surface velocity slightly higher than that of the feed rollers  72  to tauten the decorative sheet S at a maximum tension T 1  of, for example, 13 kg. 
     The damper  35 , which has been disposed opposite to the parting surface  12   a  of the female mold  12 , is advanced toward the parting surface  12   a  to start the sheet clamping operation. Then, as shown in FIG. 7, one of the pinch rollers  76  is separated from the decorative sheet S and the swing arm  77  is turned in the reverse direction to retract the dancer roller  75  from the decorative sheet S. Consequently, the decorative sheet S is tautened at a tension T 2  lower than the maximum tension T 1  at the start of the sheet clamping operation. The tension T 2  is, for example, 8 kg. With the decorative sheet S thus tautened, the damper  35  presses the decorative sheet S toward the parting surface  12   a  of the female mold  12 , and part of the decorative sheet S is pushed by the sheet pressing part  35   b  into a recess  13  formed in the female mold  12 . The dancer roller  75  is retracted and separated from the decorative sheet S as shown in FIG. 7 at a moment immediately before decorative sheet S is clamped between the frame-shaped part  35   a  and the parting surface  12   a  of the female mold  12  and, consequently, the decorative sheet S is tautened at a moment immediately before the completion of the sheet clamping operation at a tension T 3  lower than the tension T 2  at the start of the sheet clamping operation. The tension T 3  is, for example, 3 kg. Since the decorative sheet S is tautened at the maximum tension T 1 , when the same is being fed, the decorative sheet S may not crease and may not be dislocated. Since the tension of the decorative sheet S is reduced stepwise at a moment immediately before the start of the sheet clamping operation and at a moment immediately before the completion of the sheet clamping operation, the decorative sheet S may not break and may not slip off the damper  35 . 
     Although the invention has been described in its preferred forms with a certain degree of particularity, obviously many changes and variations are possible therein. It is therefore to be understood that the present invention may be practiced otherwise than as specifically described herein without departing from the scope and spirit thereof.