Method of manufacturing hollow molded articles

Abstract: A method of manufacturing hollow molded articles having a beautiful surface at a low cost and by a simple and efficient process is disclosed. The method comprises providing a hollow elastic molding die (10) made of an elastic film and having an opening port (8), feeding the a material to be molded of an amount smaller than the internal volume of said elastic molding die into said elastic molding die through said opening port, closing said opening port, for instance by cover (7), solidifying said material to be molded while said elastic molding die is rotated to all directions, and parting the solidified hollow molded article from the elastic molding die. Arrangement for preventing the elastic molding die from being deformed while it is rotated to all directions by holding it firm by a holding member conforming to the internal shape thereof or by positioning it in a fluid or powdery material are also disclosed.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a method of manufacturing hollow molded articles, such as chocolates, candies, dolls, stationary ornaments, and the like, using an elastic molding die. Description of the Prior Art Hollow molded articles, such as hollow chocolates, hollow candies, dolls, stationary ornaments, and the like, are conventionally known. Such hollow molded articles are manufactured using a plurality of separable molding dies made of a rigid material with a shape conforming to the shape of the articles to be molded. The materials to be molded of an amount smaller than the internal volume of the separable molding dies are fed into the molding dies through their opening ports, and, after closing the opening ports, the separable molding dies are installed in a spinner to be rotated to all directions. The materials to be molded are solidified along the internal surface of the separable molding dies to form hollow articles, while the molding dies are rotated to all directions. After this, the separable molding dies are divided to take out the hollow molded articles. The hollow molded articles manufactured by this type of separable molding dies, however, have partition lines of the separable molding dies on their surface, giving rise to the deterioration of their commercial value. In particular, a number of separable molding dies are required when complicated hollow molded articles are to be manufactured, making it difficult to manufacture hollow molded articles with a beautiful surface appearance. The use of many separable molding dies also renders the manufacturing process complicated. In addition, because the separable molding dies are made of rigid materials, their manufacturing cost is significant, greatly affecting the manufacturing cost of the hollow molded articles. In particular, in the case where a variety of different hollow molded articles are manufactured, each in a small number, a significant portion among the total manufacturing cost of the hollow molded articles must be shared by the cost for manufacturing the separable molding dies. It is thus extremely difficult in actual practice to manufacture such hollow molded articles at an acceptable cost. Furthermore, conventional separable molding dies made of synthetic resin such as polycarbonate exhibit poor heat conductivity, giving rise to an impaired work efficiency in the molding operation for manufacturing hollow molded articles, for which heating or cooling are essential in order to solidify the material to be molded while the separable molding dies are rotated to all directions. A method for molding hollow articles using an elastic molding die is disclosed in JP-A-01097611. This method comprises feeding a molding material to the elastic molding die from an opening, closing the opening after injecting pressurized air, rotating the molding die to solidify the molding material, and cutting out the elastic molding die to draw out the molded hollow article. The elastic molding die in this method can be used only once, because the die must be cut out to remove the molded hollow article. This considerably increases the cost for manufacturing the hollow articles. SUMMARY OF THE INVENTION An object of the present invention therefore is to solve and improve the above-mentioned drawbacks and problems in the manufacture of hollow molded articles using conventional separable molding dies, to provide an inexpensive, simple, and efficient method of manufacturing hollow molded articles using an elastic molding die, and to provide hollow molded articles with beautiful surface. The inventors of the present invention completed this invention by focussing their attention on the application of a hollow elastic molding die made of an elastic film and having an opening port, instead of the separable molding dies, for molding the hollow articles. Specifically, the above object is achieved according to the present invention by the provision of a method of manufacturing a hollow molded article, which comprises providing a hollow elastic molding die made of an elastic film and having an opening port and a supporting member expanding outwardly and conically from the opening port, feeding a material to be molded of an amount smaller than the internal volume of said elastic molding die into said elastic molding die through said opening port, closing said opening port with a closing member having a shape of a truncated cone which conforms to the internal shape of the supporting member, solidifying said material to be molded while said elastic molding die is rotated about at least two axes, and parting the solidified hollow molded article from the elastic molding die. In a preferred embodiment of the present invention, the elastic molding die is rotated about said at least two axes while positioned in a fluid or powdery material. In another preferred embodiment of the present invention the elastic molding die is expanded by the application of a pressure difference in order to remove the molded article therefrom. Preferably, said at least two axes are perpendicular to each other. The above and other objects, features and advantages of the invention will become more apparent from the following description when taken in conjunction with the accompanying drawings, in which: BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a perspective view of one embodiment of a spinner used in the method of the present invention. Figure 2 is a perspective view of one embodiment of a container to be mounted on the spinner of Figure 1 used in the method of the present invention. Figure 3 is a perspective view of one embodiment of an elastic molding die used in the method of the present invention. DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS The elastic mold used in the method of the present invention is a hollow elastic molding die made of an elastic film and having an opening port. The elastic molding die is made of an elastic film of an elastomer such as natural rubber, chloroprene rubber, or the like. The elastic molding dies are well known per se in the art. The method of molding articles using the elastic molding dies are also conventionally known. In the present invention, the material to be molded is fed into this elastic molding die, and, after closing or clogging the opening port of the elastic molding die, the elastic molding die is rotated to all directions, while the material to be molded in the elastic molding die is solidified. In this instance, use of the material to be molded of an amount smaller than the internal volume of the elastic molding die ensures solidification of that material along the internal surface of the elastic molding die providing a hollow space therein, thus affording a hollow molded article. The solidification of the molding material can be effected by heating or cooling while rotating to all directions. The use of a spinner as shown in Figure 1 is preferred for rotating the elastic molding die to all directions. In Figure 1, spinner 1 has a shape of an octagonal prism, which is rotatable around axis 2. Provided on each surface of spinner 1 are a plurality of axes of rotation 3. Container 4 has a hole (not shown in the Figure) in the center of the bottom for engaging said axis of rotation 3 on the surface of spinner 1 for mounting the container 4 thereon. Elastic molding dies in which a prescribed amount of the material to be molded is filled are housed in container 4, which is then mounted on spinner 1 by engagement with the axis of rotation 3 provided on the surface of spinner 1. Spinner 1 is then rotated, while the container 4 mounted on the surface of the spinner also rotates by the rotation of the axis of rotation 3, thus enabling the elastic molding die housed in the container 4 to rotate in all directions. The rotation rate of the spinner is desirably 4-5 perminute for both the axes of rotation 2 and 3. It is necessary in the method of the present invention to tightly seal the opening port of the elastic molding die so as to prevent the materials to be molded from escaping from this opening port, since the elastic molding die is rotated to all directions after the materials have been filled in the molding die. This tight seal of the elastic molding die can be achieved by the following method. Figure 2 shows an example of the method of achieving such tight seal, in which 4 designates the whole container to be engaged with the axis of rotation 3 provided on the surface of spinner 1. The container has a main body 5 and a medium cover 6, in which holes 8 are provided for holding the edge of supporting member b of the elastic molding die 10 shown in Figure 3. Main cover 7 for container 4 is provided on its back with protrusions 9 made of an elastic material and having a shape conforming to the supporting member b of elastic molding die 10. Each elastic molding die 10, as shown in Figure 3, consists of an elastic molding portion a, a supporting member b, and an opening port c. The supporting member b has a conical shape, for example, expanding outwardly from the opening port c. First, the elastic molding die is inserted into hole 8 provided on medium cover 6 of container 4. The edge of supporting member b is held by hole 8, thus bringing elastic molding die 10 to the state where it is suspended from medium cover 6. Next, a prescribed amount of the material to be molded is fed into elastic molding portion a of elastic molding die 10 from opening port c, following which main cover 7 is put on main body 5 of container 4. Because main cover 7 is provided with projections 9 having a shape of a truncated cone made of an elastic material which conform to conically shaped supporting member b of the elastic molding die, covering the container with the main cover 7 enables opening port c of the elastic molding die to be closed by the projections 9 having a shape of a truncated cone provided on the back of the main cover 7, thus ensuring tight sealing of opening port c of the elastic molding die. This prevents the material to be molded from escaping from the elastic molding die, even if it is rotated to all directions. Differently from separable molding dies which are made of rigid synthetic resins, the elastic molding dies are susceptible to deformation due to external forces. Hollow molded articles having a normal shape cannot be manufactured if the dies are deformed. Because of this reason, any actions of the elastic molding dies which may cause their deformation while the dies are rotated to all direction, such as contact between the elastic molding dies and vibration, must be avoided. In order to prevent such deformation of elastic molding dies, the dies should be rotated to all directions while their original shape is kept as is. For preventing deformation of the elastic molding die when it is rotated to all directions is an arrangement wherein the container is filled with a fluid or powdery material so as to keep the elastic molding die still in such a fluid or powdery material. For example, in the case of the embodiment illustrated in conjunction with Figures 2 and 3, the container may be filled with a prescribed amount of a fluid or powdery material after feeding the material to be molded into the elastic molding die, following which the cover is applied to the container. Then, the opening port of the elastic molding die is closed, the container itself is tightly sealed, and the spinner is rotated. Because the elastic molding die is positioned in the fluid or powdery material, it does not deform while rotated to all directions. In the case of this latter embodiment of Figures 2 and 3, it is also possible to use the container body in which holes conforming to the external shape of the elastic molding die are provided for preventing its deformation while rotated to all directions. The use of a viscous liquid, e.g., that having a viscosity of 1,000 to 100,000 cP, is preferred for use as the fluid material for preventing the deformation of the elastic molding die. If the viscosity is extremely small, the fluid material cannot prevent deformation of the elastic molding die due to vibration when the material to be molded is solidified while the die is rotated to all directions. If the viscosity is too high, it is difficult to position the elastic molding die in the high viscosity fluid material. In the case where a powdery material is used, its particle size, specific gravity, and the like should be taken into account. As the materials to be molded by the method of the present invention, those capable of being solidified by cooling, such as chocolates, candies, and the like can be preferably used. There are no restrictions, however, to the types of such materials so long as the same can be solidified along passage of time after filling. There are also no specific limitations to the amount of the material to be molded to be charged into the elastic molding die, inasmuch as such an amount is smaller, preferably 50% or less, than the internal volume of the elastic molding die, and greater than the amount to form a hollow molded article by solidifying along the whole internal surface of the elastic molding die. Any conventional methods can be applied to parting the solidified hollow molded articles from the elastic molding die. The partition can be done, for example, (i) by covering the whole elastic molding die with a cup which is provided with a breather and discharging the air from the cup via the breather by suction to reduce the pressure therein, thus expanding the elastic molding die; (ii) by covering the supporting member side of the elastic molding die with a cup which is provided with a breather and introducing the air into the cup via the breather to increase the pressure in the cup, thus expanding the elastic molding die; or (iii) expanding the whole elastic molding die by the combination of the methods (i) and (ii). The molded articles are then parted from the expanded elastic molding die and discharged from the expanded opening port. As illustrated above, according to the method of the present invention, in which a hollow elastic molding die made of an elastic film and having an opening port is provided for feeding the material to be molded of an amount smaller than the internal volume of said elastic molding die thereinto through said opening port, closing said opening port, and solidifying said material to be molded while said elastic molding die is rotated to all directions, can ensure solidification of the material along the internal surface of the elastic molding die with a hollow space therein, thus producing beautiful hollow molded articles with no partition lines on the surface as in the case of the conventional separable molding die. In addition, the elastic molding die can be manufactured not only at a low production cost, but also by a simple process, even if such a die has a complicated shape. These advantages make it possible to easily manufacture a wide variety of complicated hollow molded articles. Furthermore, the application of the arrangement by which the elastic molding die is held firm by a holding member conforming to the internal shape of the elastic molding die or the arrangement wherein the elastic molding die is positioned in a fluid or powdery material, effectively prevents the die from being deformed while it is rotated to all directions, ensuring the manufacture of hollow molded articles having an intended shape. Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.

Claims: A method of manufacturing a hollow molded article, which comprises providing a hollow elastic molding die (10) made of an elastic film and having an opening port (c) and a supporting member (b) expanding outwardly and conically from the opening port (c), feeding a material to be molded of an amount smaller than the internal volume of said elastic molding die (10) into said elastic molding die (10) through said opening port (c), closing said opening port (c) with a closing member (9) having a shape of a truncated cone which conforms to the internal shape of the supporting member (b), solidifying said material to be molded while said elastic molding die (10) is rotated about at least two axes (2, 3), and parting the solidified hollow molded article from the elastic molding die (10). The method of manufacturing a hollow molded article according to claim 1, characterized in that the elastic molding die (10) is rotated about said at least two axes (2, 3) while positioned in a fluid or powdery material. The method of manufacturing a hollow molded article according to claim 1, characterized in that the elastic molding die (10) is expanded by the application of a pressure difference in order to remove the molded article therefrom. The method of manufacturing a hollow molded article according to claim 1, 2 or 3, characterized in that said at least two axes (2, 3) are perpendicular to each other.

Inventors: HAYASHI TOSHIHIRO, HORIGUCHI ITARU, KOHNO HIROSHIGE, WATANABE AKINORI, HAYASHI, TOSHIHIRO, HORIGUCHI, ITARU, KOHNO, HIROSHIGE, WATANABE, AKINORI, Hayashi, Toshihiro, c/o Asahi Denka Kogyo K.K., KOHNO, HIROSHIGE, C/O ASAHI DENKA KOGYO K.K.
Applicants: ASAHI DENKA KOGYO KK, OKAMOTO IND INC, ASAHI DENKA KOGYO KABUSHIKI KAISHA, OKAMOTO INDUSTRIES, INC.
Application year: 1993
Main classification: A23G1
IPC codes: B29C41, B29L31, A23G3, A23G1, A23P1