Abstract:
A secondary molding apparatus includes a transfer path for a primary molded product, and an internal heating unit disposed vertically at a predetermined interval across the transfer path, the internal heating unit disposed to come into contact with a rear surface of a flat base material and to melt top portions of protrusions located on a front surface of the flat base material. The secondary molding apparatus also includes a pressing member disposed vertically at a predetermined interval across the transfer path, the pressing member configured to press and deform the top portions of the protrusion to a desired shape, the pressing member being a non-heating member.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a secondary molding apparatus for forming a final product by melting and deforming a top portion of each of protrusions of a primary molded product having a plurality of the protrusions erected on a surface of a flat base material made of thermoplastic synthetic resin. 
     2. Description of the Related Art 
     According to Published Japanese Translations of PCT International Publication No. 8-508910, Japanese Patent Application Laid-Open No. 9-322811 and No. 9-322812, a primary product having a plurality of protrusions erected integrally on the surface of a flat base material is continuously molded of thermoplastic synthetic resin and then the base material is transferred through a transfer path. Meanwhile, the base material is supported from below in a secondary molding area provided halfway of the transfer path, and a top portion of each of the protrusions is heated and pressed by a heating/pressing unit such as a heating roller, a heating plate or the like so that it is deformed. As a result, for example,. male members of a surface fastener are molded. 
     According to the aforementioned Publication No. 8-508910, molten resin is supplied from an extruder or the like to the surface of a rotating cylinder having a plurality of blind holes formed in a circumferential face along an axis and in the circumferential direction such that they are directed linearly toward the axis. Part of the molten resin is pressed into the blind holes so as to mold each protrusion. At the same time, flat base material is molded with the molten resin continuously on the surface of the cylinder integrally with proximal ends of the protrusions. This continuously molded product is supported by a surface of the rotating cylinder and cooled while it is rotated. Then, after being separated from the cylinder, the male surface fastener primary product is obtained. This male surface fastener primary product is transferred to the secondary molding area, in which a circular engaging head portion whose top surface is dented is molded on a tip end of each protrusion erected on the surface of the base material so that the male surface fastener as a final. product is produced. 
     On the other hand, as disclosed in the aforementioned Japanese Patent Application Laid-Open No. 9-322811 and No. 9-322812, a plurality of V-shaped or Y-shaped blind holes are formed in the circumferential surface of the rotating cylinder like the above described example. The primary molded product of the male surface fastener is molded by a rotation of the cylinder as described above, and after that, the tip end of the V-shaped or Y-shaped protrusion erected on the surface of the base material is heated and pressed in the secondary molding area so that it is deformed. As a result, the engaging head portion having a peculiar shape in which the tip portion of each of the protrusions erected from the surface of the base material is deformed to substantially inverse L shape or substantially T shape, and expanding portions expanding horizontally to the right and left on the tip portion is molded so as to produce the male surface fastenet as the final product. 
     According to production methods for the male surface fasteners disclosed in the patent publications, because an engaging element each having a peculiar engaging head portion is molded, although an engaging force thereof is lower than that of a conventional mushroom-shaped engaging element, minute engaging elements can be molded in a high density since the protrusion of the primary molded product has a simple configuration. For example, this is effective for an engaging/disengaging device of a disposable diaper. Particularly, in the engaging element formed in a substantially inverse L shape or substantially T shape, having an engaging head portion with horizontally expanding portions molded at a tip thereof, the engaging head portion itself has a higher stiffness than the other portions of the engaging element. Therefore, a necessary engaging force and some extent of separation resistance are secured with the existence of the expanding portions. 
     On the other hand, deformation of the aforementioned protrusion of the primary molded product which comes into contact with a heating member such as a heating roller and a heating plate disposed on the pressing side of the heating/pressing unit installed in the secondary molding area is determined depending on the heating temperature and contact time of the heating member. When it is intended to press and deform the engaging element to desired shape, the pressing force needs to be controlled to be optimum as well as the heating time and contact time. Further, in order to make the secondary molding speed adapt to the primary molding speed, the secondary molding speed has to be high. For this purpose, a desired thermal capacity and heating source have to be secured. As a result, multi-purpose control system is needed so that inevitably the apparatus is enlarged thereby a large installation space being required. 
     SUMMARY OF THE INVENTION 
     The present invention has been accomplished to solve the above problems, and therefore, an object of the present invention is to provide a secondary molding apparatus for molding protrusions of synthetic resin erected on the surface of a flat base material, which can be installed in a small installation space and in which the secondary molding speed can be changed arbitrarily and no useless heat history is given to other portions than a portion to be deformed upon deformation. 
     The above object of the invention can be achieved as described below. 
     There is provided in this invention a secondary molding apparatus for molding a top portion of each of a plurality of protrusions of a primary molded product having the protrusions integrally erected on the surface of a flat base material to a desired shape by melting and deforming the top portion thereof, the secondary molding apparatus for molding the protrusions of synthetic resin erected on the surface of the flat base material, comprising: a transfer path for the primary molded product; and a pressing member and an internal heating unit disposed vertically at a predetermined interval across the transfer path, wherein the pressing member is disposed at a position in which it presses and deforms the top portion of the protrusion and the internal heating unit is disposed at a position in which it comes into contact with a rear surface of the flat base material. 
     The primary molded product having a plurality of the protrusions erected on the surface of the flat base material molded by the primary molding apparatus is supplied continuously through the transfer path to the secondary molding apparatus. In the primary molded product supplied to the secondary molding apparatus, the rear surface of the flat base material is supported by the internal heating unit and the top end of the protrusion erected on the surface of the flat base material is pressed by the pressing member. The internal heating unit mentioned here means a unit for heating the synthetic resin molded product by itself as a heat generating body. This internal heating unit intensively heats the top end of the protrusion pressed by the pressing member. Therefore, thermal capacity is concentrated on only the molten and deformed portion, so that molding is enabled without giving unnecessary heat history to other portions. Further, because the internal heating unit is capable of controlling a local heating speed easily and allows quick heating/cooling, molding temperature and molding speed can be controlled arbitrarily. Therefore, the secondary molding suitable for a molding speed of the primary molded product can be achieved. 
     Preferably, use of the ultrasonic oscillator or high frequency oscillator is provided as the internal heating unit. Because these internal heating units are capable of securing a desired heating speed and temperature without enlarging the size of the internal heating unit, the installation space can be reduced, a desired molding speed can be obtained and the above described function effect can be exhibited sufficiently. 
     Further preferably, the pressing member is provided, and still preferably, a rotating roller supported by a shaft disposed perpendicular to a direction of crossing the transfer path is employed as the pressing member. Further preferably, a sheet material including an area in which a gap relative to the transfer path decreases gradually is employed. Because the heating area for-the secondary molded product heated by the internal heating unit is concentrated on the pressing area pressed by the pressing member, the heating speed may be increased quickly, thereby the molding speed is increased. As a result, regardless of whether the rotating roller or the sheet material is used, the size of the secondary molding apparatus is reduced effectively as compared to the conventional one. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an explanatory diagram when a secondary molding apparatus having an internal heating unit according to a typical embodiment of the present invention is applied to a molded surface fastener manufacturing machine. 
     FIG. 2 is a side view showing a configuration of a primary molded product molded with the primary molding apparatus applied to the manufacturing machine. 
     FIG. 3 is a side view showing another example of pressing member of the secondary molding apparatus. 
     FIG. 4 is a partial side view showing a configuration of a male molded surface fastener which is a final product after the secondary molding with the secondary molding apparatus. 
     FIG. 5 is a partial plan view of the male molded surface fastener. 
     FIG. 6 is a side view showing another example of the secondary molding process. 
     FIG. 7 is a side view showing still another example of the secondary molding process. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, the preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 shows schematically a manufacturing machine for a molded surface fastener, having a secondary molding apparatus according to a typical embodiment of the present invention. This molded surface fastener has a plurality of male engaging elements formed in, for example, a hook shape, erected on a surface of a flat base material as described in detail later, and this molded surface fastener engages with/disengages from a female surface fastener having a plurality of loop like engaging elements erected on a surface of a mating flat base material. 
     According to this embodiment, the manufacturing machine for the molded surface fastener comprises a primary molding apparatus  10  for molding a primary molded product SF′ of the molded surface fastener SF and a secondary molding apparatus  20  for producing a molded surface fastener SF which is a final product by secondary-molding the primary molded product SF′ molded by the primary molding apparatus  10 . Here, the primary molding apparatus  10  for the molded surface fastener SF is substantially similar to the primary molding apparatus disclosed in Japanese Patent Application Laid-Open No. 9-322811 and No. 9-322812 previously developed by the same inventor of this invention. Therefore, the primary molding apparatus will only be described schematically. 
     The primary molding apparatus  10  has a continuous injection nozzle  11  and a die wheel  12 . An end of the injection nozzle  11  is a circular face having substantially the same curvature as that of the die wheel  12 . The injection nozzle  11  is disposed to oppose a curved surface of the die wheel  12  with a gap corresponding to the thickness of the flat base material  1  of the primary molded product SF′ to be molded. Molten resin  3  is injected in form of a sheet continuously under a predetermined resin pressure and at a constant flow rate through a resin injection port  11   a  formed in the center of the curved surface at the end of the injection nozzle  11 . 
     The die wheel  12  is formed in a hollow drum shape having a water-cooling jacket  12   a  which is internal cooling means. A plurality of donut-shaped plate materials are overlaid and fixed along an axis thereof so as to form the die wheel  12 . A circumferential face thereof has a function for molding part of a surface of the primary molded product SF′. Then, the aforementioned gap is secured between the circular face at the end of the injection nozzle  11  and the die Wheel  12 , and an axis of the die wheel  12  is set up in parallel to the injection port  11   a . A plurality of rows of the engaging element molding cavities  13  disposed in the circumferential direction are formed along a rotating axis at a predetermined interval on the circumferential surface of the die wheel  12 . Each of the engaging element molding cavities  13  has a configuration curved in substantially Y shape inside the die wheel  12 . The die wheel  12  having such a structure is driven and rotated in a direction indicated by an arrow in FIG. 1 by a known driving unit (not shown). 
     A water-cooling bath  14  is provided below the die wheel  12  so that a lower portion of the die wheel  12  is immersed inside the water-cooling bath  14 . A take-up roll  15  is disposed obliquely in upper front of this cooling water bath  14  and a pair of first feed rolls  16 ,  17  having upper and lower rolls are provided in front of the take-up roll  15 . Further, a trimming unit (not shown) having cutting means for cutting off ear portions of the primary molded product SF′ which is a base material of the molded surface fastener SF which is to be secondary molded and which is a final product of the present invention is provided. A plurality of concave grooves (not shown) are formed in parallel rows in the circumferential direction on a circumferential surface of the upper roll  17  of the pair of the first feed rolls  16  and  17 . As a result, when the primary molded product SF′ is transferred, it is transferred with the engaging element  2  which is a protrusion erected on the surface of the flat base material  1  fit into the concave groove. 
     In order to mold the primary molded product SF′ with the primary molding apparatus having such a structure, molten resin injected continuously from the injection nozzle  11  at a predetermined resin pressure is introduced continuously into the gap formed between the injection nozzle  11  and the rotating die wheel  12 . At this time, part of the molten resin is filled in the gap so as to mold the base material  1  and at the same time, it is filled successively in the engaging element molding cavities  13  formed in the circumferential surface of the die wheel  12 . As a result, with a rotation of the die wheel  12 , the primary molded surface fastener SF′ having a plurality of the engaging elements  2  molded integrally on the surface of the base material  1  thereof is continuously molded. 
     On the circumferential surface of the die wheel  12 , the primary molded product SF′ having the primary configuration which is a base material of the molded surface fastener as a final product is guided along a substantially half circumferential surface of the die wheel  12  by the take-up roll  15  so that it is rotated. Meanwhile, the primary surface fastener SF′ is cooled positively by the water-cooling jacket  12   a  from inside of the die wheel  12  and passed through the inside of the water-cooling bath  14  in which cooling water at a low temperature (substantially 15° C.) circulates so that it is cooled rapidly and hardening thereof is accelerated. By rapid cooling, the primary molded product SF′ is hardened before crystallization proceeds, and the base material  1  and engaging element  2  become entirely flexible. 
     When the base material  1  hardened in this way is pulled out by the first feed rolls  16  and  17 , each of the substantially Y-shaped engaging elements molded and hardened by cooling in the engaging element molding cavity  13  is extracted from the cavity  13  smoothly in a condition in which it is deformed linearly. At this time, although the engaging element  2  intends to return to its original shape, the shape is not restored completely, so that the configuration of the engaging head portion  2   b  is slightly more erected in terms of its bending angle from an erected portion  2   a  than the substantial Y-shape of the engaging element molding cavity  13 . 
     FIG. 2 shows an example of an embodiment of the primary molded product of the molded surface fastener SF molded with the primary molding apparatus. As shown in the Figure, the entire engaging elements  2  are substantially Y shaped, consisting the erected portion  2   a  which is erected on the surface of the base material  1 , and the engaging head portion  2   b  which are branched back and forth in the molding direction from the erected portion  2   a  such that they stand up linearly while inclined with respect to each other. 
     In the same Figure, an arrow indicates a molding direction. The engaging head portion  2   b  extending forward in the molding direction is raised more than the engaging head portion extending backward as shown in the Figure, because of a difference of the deformation amount of the engaging element being extracted from the Y-shaped cavity  13  when the primary molded product SF′ is peeled off from the die wheel  12 . The primary molded product SF′ molded in this way is transferred to the secondary molding apparatus  20  of the present invention. 
     Therefore, according to the present embodiment, as shown in FIG. 1, the secondary molding apparatus  20  having an internal heating unit  21  of the present invention is provided in front of the pair of the feed rolls  16  and  17 . Further, a pair of the second feed rolls  23  and  24  having upper and lower rolls, are disposed in front thereof. The secondary molding apparatus  20  consists the internal heating unit  21  and pressing roll  22 . The pressing roll  22  is disposed above and the internal heating unit  21  is disposed beneath across the primary molded product SF′ being transferred by the first and second pairs of the feed rolls  16  and  17 ;  23  and  24 . 
     According to this embodiment, a ultrasonic tool horn is employed as the internal heating unit  21 . A high frequency electrode die may be used instead of this ultrasonic horn. In the internal heating unit  21 , only an internal part of a pressed portion of the resin molded portion pressed by the pressing roll  22  is heated quickly and deformed. Thus, portions other than the deformed portion is not affected by heating. Therefore, the physical property of the resin molded portion other than the deformed portion is not changed from its initial state. Thus, according to this invention, it is not necessary to consider an influence by heating in portions other than the deformed portion which is generated by regular external heating. 
     In the internal heating unit  21 , an acting surface thereof is disposed on a transfer path for the primary molded product SF′ such that the primary molded product SF′ being transferred is supported from below. A bottom end of the circumferential face of the pressing roll  22  is disposed so as to be located slightly below a plane in which an end of the engaging head portion  2   b  of the primary molded product SF′ passes. Setting of the position at this time is determined by a scheduled dimension of expanding portion  2   c  expanding to the right and the left from a top portion  2   b ′ of the engaging head portion  2   b  of a final product which will be described later. On the other hand, a top face of the internal heating unit (ultrasonic tool horn)  21  disposed to face the bottom of the pressing roll  22  is provided so as to be located on a plane in which a bottom face of the base material  1  of the primary molded product SF′ is transferred. 
     A supporting position of the pressing roll  22  can be adjusted with height adjusting means (not shown). A heating temperature and heating speed of the internal heating unit  21  can be controlled easily by an applied electrical power. Further, on contrary to external heating with a conventional heating roll or heating plate, because a quick heating is possible, secondary molding is enabled synchronously with a molding speed of the primary molded product. Further, because heating can be concentrated locally, the pressing member such as the pressing roll  22  can be reduced in size so that an internal heating unit installation space can be reduced largely as well as the internal heating unit. The pressing roll  22  is driven and positively rotated synchronously with the transfer speed of the molded product. Further, instead of the pressing roll  22 , a flat plate material  22 ′ in which an introducing portion of the primary molded product SF′ is a downward inclined surface as shown in FIG. 3 may be employed. 
     The ear portions existing on the right and left in a width direction of the primary molded product SF′ molded in the above manner are cut off with a trimming unit (not shown) and transferred to the secondary molding apparatus  20  of the present invention. According to this embodiment, when the primary molded product SF′ is passed between the internal heating unit  21  and the pressing roller  22 , the top portion  2   b ′ of the engaging head portion  2   b  of the engaging element  2  is pressed by the pressing roller  22  and at the same time, an ultrasonic (high frequency) vibration is applied to the internal heating unit  21  from the rear surface of the base material  1 . As a result a portion in contact with the pressing roll  22  is heated quickly so that the engaging head portion  2   b  falls down from its proximal end up to its distal end and simultaneously, a top portion thereof is softened and deformed so that a top surface becomes substantially flat surface P and the expanding portion  2   c  expanding to the right and left sides is formed. As a result, a final configuration of the engaging element  2  can be obtained. Depending on molding condition, the top flat surface P may be formed such that a center portion thereof is slightly dented by subsequent cooling. 
     According to this embodiment, because the engaging head portion  2   b  is extended back and forth, a portion on which the pressing toll  22  acts is different between the engaging head portions  2   b  located back and forth. That is, the engaging head portion  2   b  extending forth is pressed gradually along the surface from its distal end to its proximal end, while the engaging head portion  2   b  extending back is pressed gradually along the surface from its proximal end up to its distal end. As a result, as shown in FIGS. 4 and 5, the engaging head portions  2   b  are molded differently, and the engaging head portion  2   b  extending forth is crushed largely than the engaging head portion  2   b  extending back so that the plane expansion of the flat surface P and expanding portion  2   c  is larger than the engaging head portion  2   b  extending back. The difference of the configuration between the engaging head portions  2   b  can be effective depending on the configuration of the engaging element of a mating female surface fastener. 
     That is, although not provided in the present invention, the male surface fastener which is the secondary molded product is used as, for example, an engaging/disengaging device for a disposable diaper or the like. In this case, the size of the aforementioned engaging element  2  is very small and as a mating female surface fastener, an ordinary unwoven fabric with loops not so long is used. As known well, in this ordinary unwoven fabric, the sizes of the loops exposed on the surface thereof are not equal but diversified. Considering an ease of engaging with loop different in size and its engaging strength, a single engaging element having two engaging head portions each having a different size means that a probability of engaging with various sizes of the loops increases, so that an entire engaging force is improved. 
     No special cooling means is employed for the male surface fastener SF which is a secondary molded product obtained by passing between the internal heating unit  21  and the pressing roll  22 , but it is gradually cooled under a normal temperature and then wound up to complete the production. At this time, softening the top portion of the engaging element  2  by heating it intensively and at the same time pressing, and then not quickly but gradually cooling the engaging element  2  having a substantially flat top surface and expanding portions  2   c  on the right and left sides as described above, have an important meaning. That is, when the top portion  2   b ′ of the engaging head portion  2   b  softened by heating and deformed by pressing is cooled and hardened gradually so that crystallization of the heated portion is accelerated, stiffness of the top portion  2   b ′ including the expanding portions  2   c  of the engaging head portion  2   b  becomes higher than other portions in the erected portion  2   a  and engaging head portion  2   b.    
     Because, in the base material  1  and engaging element  2  of the primary molded product SF′ having an excellent flexibility by quick hardening, only part of the engaging head portion  2   b  has more stiffness than the other portions, even when the engaging element  2  of a molded surface fastener SF is very small and has a very high flexibility, the stiffness of the engaging head portion  2   b  is secured. That means that a holding force with respect to the mating loop piece in a direction of separating is secured. 
     An existence of the expanding portions  2   c  produces various useful functions not expected in the configuration of a conventional simple engaging element. As those specific functions based on the configuration of the engaging element according to the above embodiment have been disclosed in detail in the above described patent publication, a description thereof is omitted here. 
     The secondary molding apparatus  20  of the present invention may be applied to a case for erecting a simple, linear column-like protrusion  102  on the surface of the flat base material  1  as shown in FIG.  6 . In this case, an engaging head portion  102   b  extending in the rotating direction of the pressing roll  22  is molded. This engaging head portion  102   b  is formed in a hook shape, a flat surface is formed on top thereof like the above described embodiment and the expanding portions are formed on the right and left sides. 
     In the embodiment shown in FIG. 1, the pressing roll  22  may be rotated in an opposite direction, or positively in a clockwise direction which is an opposite direction to the molding direction as shown in FIG. 7 with an arrow. In this case, the length of the engaging head portion  2   b  extending back is longer than that of the engaging head portion  2   b  extending forward. 
     According to the secondary molding apparatus for molding protrusions erected on the surface of a flat base material of the present invention, the size thereof can be reduced, molding speed may be changed arbitrarily, molding efficiency is high, and no useless heat history is given to other portions than a molded portion. As a result, a very excellent secondary molded product is obtained.