Patent Publication Number: US-2012043696-A1

Title: Method of injection molding

Description:
FIELD OF THE INVENTION 
     The present invention relates to an apparatus and method of injection molding for molding an article of synthetic resin simultaneously with integrating a sheet-like material, such as a decorative sheet, onto a surface of the molded article in a cavity of an injection mold, and more particularly, to an apparatus and method of injection molding for molding an article of synthetic resign and simultaneously unifying a sheet-like material on a surface of the molded article in a cavity of an injection mold without causing damage to the sheet-like material during a molding process. 
     BACKGROUND OF THE INVENTION 
     As disclosed in Japanese Patent Public Disclosure No. 2004-017508, Japanese Patent Publication No. S50-19132 and Japanese Patent Publication No. S43-27488, it has been proposed to perform a method of injection molding in order to unify a sheet-like material, such as a decorative or ornamental sheet, on a surface of a molded article during a molding process and add new value or optional function to the molded article due to the properties of the sheet-like material, such as color, pattern, quality of material and the like. A conventional method of injection molding of this kind exemplifies the following steps of: installing a decorative sheet in an injection mold; injecting a molten resin to fill the mold cavity with the molten resin; and solidifying the resin in the cavity to form an injection molded body simultaneously with integrating the decorative sheet onto a surface of the injection molded body. 
     In this method, the sheet-like material such as a decorative sheet is pre-shaped, as required, by an appropriate forming process such as vacuum forming to be adapted to the shape of the mold cavity while installed in the mold or before installed in the mold. When installed in the mold, the sheet-like material such as a decorative sheet covers the whole or part of the mold cavity, and the area of the mold cavity that is covered with the sheet-like material corresponds to the surface of the injection molded body onto which the sheet-like material should be integrated. At this time, the remaining portion of the sheet-like material which protrudes outside the mold cavity is clamped between the parting surfaces or dividing surfaces or abutting surfaces of the first and second mold sections, for example, a cavity mold and a core mold forming opposite sides of the mold cavity, so that the sheet-like material should not be displaced by injection pressure. 
     To take a pair of a cavity mold and a core mold as an example, the sheet-like material installed on the cavity mold extends continuously from a mold cavity on to a parting surface of the cavity mold, via the peripheral edge of the mold cavity of the cavity mold. Then the core mold is closed against the cavity mold and the sheet-like material is clamped between the parting surfaces of the core mold and the cavity mold while the sheet-like material extends in the mold cavity. The sheet-like material extending in the mold cavity is defined by the peripheral edge of the mold cavity. When molten resign is injected into the mold cavity from an injection gate of the core mold, the molten resin flows along a surface of the sheet-like material to the peripheral edge of the mold cavity. Thereby, the mold cavity is filled with the molten resign and the sheet-like material defined by the peripheral edge of the mold cavity. 
     The sheet-like material installed in the mold cavity is affected by the temperature of the molten resin injected into the mold cavity and also affected by the injection pressure of the molten resin produced to fill the mold cavity up with the molten resin. The injected molted resin tends to apply a large pressure to the sheet-like material, in particular, in the vicinity of the peripheral edge of the mold cavity. Depending on conditions of injection molding, the sheet-like material may deform around the peripheral edge of the mold cavity. Especially when the sheet-like material extends along an elongated peripheral edge of the mold cavity, there is an increased risk of serious damage to the sheet-like material because of uneven dispersion of the molten resin. In the event that the sheet-like material is damaged, the molten resin leaks out of the mold cavity from the peripheral edge thereof and produce a flash between the parting surfaces of the mold sections. In addition, the molten resin may penetrate through the sheet-like material and damage the outer surface of an injection molded article to be produced. When the sheet-like material is made of an olefin-based thermoplastic elastomer (TPO) with soft texture or the like, the above-mentioned disadvantages may cause serious damage to an injection molded article. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an apparatus of injection molding for molding an injection molded body and integrating a sheet-like material onto a surface of the injection molded body without causing damage to the sheet-like material. 
     Another object of the present invention is to provide an apparatus of injection molding for integrating a sheet-like material onto a surface of an injection molded body without causing damage to the sheet-like material. 
     Further object of the present invention is to provide an apparatus of injection molding for manufacturing an injection molded article integral with a sheet-like material. 
     Another object of the present invention is to provide a method of injection molding for integrating a sheet-like material onto a surface of an injection molded article during fabrication of the injection molded article. 
     Further object of the present invention is to provide a method of injection molding for manufacturing an injection molded article onto which a sheet-like material is integrated during fabrication of the injection molded article. 
     Another object of the present invention is to provide a method of injection molding for molding an injection molded article and integrating a sheet-like material with the injection molded article during fabrication of the injection molded article, without causing damage to the sheet-like material. 
     According to the first aspect of the present invention, there is provided an apparatus of injection molding comprising: at least a pair of mold sections that can be closed and opened, wherein a sheet-like material can be disposed between said mold sections; a fixing device for fixing said sheet-like material at a set place interposed between said mold sections; at least one mold cavity defined in said mold sections when said mold sections are closed; and 
     an injection gate for injecting a molten resin into said mold cavity; characterized in that a groove or recess portion is formed outside the peripheral edge of said mold cavity, and said groove or recess portion is adapted to receive a molten resin that is injected into said mold cavity and flows into said groove or a recess portion through the peripheral edge of said mold cavity. 
     According the second aspect of the present invention, there is provided a method of injection molding wherein a molten resin injected into a mold cavity and a sheet-like material supplied in mold sections are integrated in said mold sections, and said molten resin integrated with said sheet-like material is molded by said mold sections, characterized by the steps of: disposing said sheet-like material in said mold sections to expand from the interior of said mold cavity to the exterior of said mold cavity continuously; fixing said sheet-like material to said mold sections; injecting said molten resin into said mold cavity to mold an injection molded body made from the molten resin filled in said mold cavity and mold a protrusion made from the molten resin flowing out of the peripheral edge of said mold cavity, wherein said injection molded body is in close contact with said sheet-like material in the interior of said mold cavity, said protrusion is in close contact with said sheet-like material in the exterior of said mold cavity, and said protrusion has a predetermined thickness; cooling said mold sections and increasing a resin viscosity of said protrusion more rapidly than a resin viscosity of said injection molded body in said mold sections due to the difference of the volume capacities between said protrusion and said injection molded body; and applying a predetermined pressure to said molted resin injected into said mold cavity when the resin viscosity of said protrusion has increased to a predetermined value, and integrate said injection molded body and said protrusion with said sheet-like material in said mold sections. 
     According to the third aspect of the present invention, there is provided a method of injection molding for manufacturing an injection molded article with which a surface material is integrated, characterized by the steps of: disposing said sheet-like material in said mold sections to expand from the interior of said mold cavity to the exterior of said mold cavity continuously; fixing said sheet-like material to said mold sections; injecting said molten resin into said mold cavity to mold an injection molded body made from the molten resin filled in said mold cavity and mold a protrusion made from the molten resin flowing out of the peripheral edge of said mold cavity, wherein said injection molded body is in close contact with said sheet-like material in the interior of said mold cavity, said protrusion is in close contact with said sheet-like material in the exterior of said mold cavity, and said protrusion has a predetermined thickness; cooling said mold sections and increasing a resin viscosity of said protrusion more rapidly than a resin viscosity of said injection molded body in said mold sections due to the difference of the volume capacities between said protrusion and said injection molded body; applying a predetermined pressure to said molted resin injected into said mold cavity when the resin viscosity of said protrusion has increased to a predetermined value, and integrate said injection molded body and said protrusion with said sheet-like material in said mold sections; and taking said injection molded body out of said mold sections, wherein said injection molded body has been integrated with said sheet-like material and molded into a predetermined shape, and cutting out said protrusion together with the sheet-like material extending outside said mold cavity from said injection molded body. 
     According to the present invention, one or more groove portions or recess portions are formed on the whole or part of the peripheral edges of the mold cavity in such a manner as to protrude from the mold cavity along the surface of the sheet-like material in the direction in which the sheet-like material extends. Therefore, the molten material which flows into the groove or recess portions from the mold cavity flows smoothly along the sheet-like material at the peripheral edge of the mold cavity. Thereby, it is possible to eliminate a risk where an excessive pressure is applied to the sheet-like material lying at the peripheral edge of the mold cavity. Consequently, the temperature and/or pressure of the molten resin does not cause damage to the sheet-like material lying in the vicinity of the peripheral edge of the mold cavity during molding process. 
     Due to the difference of the volume capacities between the protrusion and the injection molded body according to the present invention, a resin viscosity of said protrusion increases more rapidly than a resin viscosity of said injection molded body when cooling the mold sections. In other wards, the fluidity of the resinous material in the vicinity of the peripheral edge of the mold cavity is diminished more quickly than the fluidity of the resinous material in the mold cavity by cooling the mold sections. Therefore, the sheet-like material lying in the vicinity of the peripheral edge of the cavity mold comes to be covered by the resinous material of diminished fluidity or increased viscosity so that the sheet-like material is protected against exposure to heat and/or pressure in the vicinity of the peripheral edge of said cavity mold. 
     In addition, the molten material flows smoothly in the vicinity of the edge portion of the mold cavity when the molten material is being injected, because the molten resin is received by the groove or recess portion at the peripheral edge of the mold cavity. Therefore, the sheet-like material can be prevented from being damaged by the heat and/or pressure of the molten resin accumulated in the vicinity of the peripheral edge of the mold cavity. 
     These and other objects and advantages of the present invention will be more fully and readily understood by referring to the following detailed description of the present invention and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows exemplarily an apparatus of injection molding according to the present invention, wherein  FIG. 1A  shows a state in which a mold is opened, and  FIG. 1B  shows a state in which the mold is closed. 
         FIG. 2A  shows an enlarged sectional view of the area indicated by an arrow IIA in  FIG. 1A , and  FIG. 2B  shows an enlarged sectional view of the area indicated by an arrow IIB in  FIG. 1B . 
         FIG. 3  shows a perspective view of a meter cluster housing for vehicles with which a TPO sheet is integrated. 
         FIG. 4  shows a vertical sectional view of an apparatus of injection molding for manufacturing the interior component for vehicles shown in  FIG. 3 , with a cavity mold and a core mold separated from each other to open the cavity mold. 
         FIG. 5  shows a sectional view of a main part of the cavity mold and the core mold in  FIG. 4 , which are brought into mating engagement to close the mold cavity. 
         FIG. 6  shows as shown in  FIG. 5 . 
         FIG. 7  shows the vicinity of the peripheral edge of the mold cavity wherein a molten resin is injected into the mold cavity shown in  FIG. 6 . 
         FIG. 8  shows an enlarged sectional view of an edge portion of an injection molded article which is taken out of the mold sections shown in  FIG. 6 . 
         FIG. 9  shows an enlarged sectional view of an edge portion of an injection molded article after an unnecessary portion is trimmed off from the injection molded article shown in  FIG. 8 . 
         FIG. 10  shows an enlarged sectional view of the vicinity of a peripheral edge in a conventional mold cavity. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The First Embodiment 
     For a preferred embodiment of the present invention, one or more shallow grooves are formed on a parting surface of a core mold. The grooves extend from an edge portion of a cavity in the core mold outwards of a mold cavity so that an injected molten material flows into the grooves smoothly and is cooled quickly in the vicinity of an edge portion of the mold cavity. When the injected molten material reached the edge portion of the cavity in the core mold, the molted material flows smoothly without staying on the edge portion of the cavity. 
       FIGS. 1 and 2  are drawings which show exemplarily an apparatus of injection molding according to the present invention, wherein the mold sections are open in  FIG. 1A , while the mold sections are closed in  FIG. 1B . An apparatus of injection molding  1  has a cavity mold  2  and a core mold  3  in those figures, and when the core mold  3  are closed against the cavity mold  2  as shown in  FIG. 1B , a mold cavity  4  is formed between the cavity mold  2  and the core mold  3 . 
     A sheet-like material  5  such as a decorative sheet for a molded article is formed of an olefin-based thermoplastic elastomer (TPO) or the like so as to provide a surface of the molded article with soft texture. The sheet-like material  5  may be pre-shaped by an apparatus of injection molding  1  using a suitable forming technique such as vacuum forming or the like so as to match a cavity configuration of the cavity mold or may be pre-shaped using any other vacuum forming system than the apparatus  1 . As shown in  FIG. 1A , the sheet-like material  5 , which has been pre-shaped, is placed in the cavity mold  2 . The pre-shaped sheet-like material  5  has a formed portion  5   a  which is closely secured to a cavity surface  2   a  of the cavity mold  2  and a holding portion  5   b  which extends along a parting surface  2   b  of the cavity mold  2 . 
     As shown in  FIG. 2A , a groove portion  3   c  is formed on an edge portion  3   b  of a cavity surface  3   a  of the core mold  3 . The groove portion  3   c  is made of a single annular groove which is open in a parting surface  3   d  of the core mold  3 . The groove portion  3   c  extends from the edge portion  3   b  of the cavity surface  3   a  outwards of the core mold  3  and exists along the edge portion  3   b  of the cavity surface  3   a  in the core mold  3 . 
     As shown in  FIG. 1B , the core mold  3  is closed against the cavity mold  2  and then a molten resin  7  is injected into the mold cavity  4  from an injection gate  6  in the core mold  3 . The molten resin  7  injected into the mold cavity  4  flows along an upper surface of the sheet-like material  5  mounted in the cavity mold  2  and reaches the edge portion  3   b  of the cavity surface  3   a . As shown in  FIG. 2B , the groove portion  3   c  is made to open in the edge portion  3   b . Thereby, the molten resin  7  flows along the upper surface of the sheet-like material  5  and smoothly into the groove portion  3   c  without staying on the edge portion  3   b . When the mold cavity  4  and the groove portion  3   c  are filled with the molten resin  7 , the molten resin  7  is held under pressure in the mold sections  2  and  3  for a certain period of time. Simultaneously, the mold sections  2  and  3  are cooled by a cooling apparatus (not shown). Due to the cooling process, the molten resin  7  is solidified to form a molded body (not shown) in the mold cavity  4 , and the molded body is integrated onto the upper surface of the sheet-like material  5 . During the cooling process, the molten resin  7  in the groove portion  3   c  is hardened sooner than the molten resin  7  in the mold cavity  4  becomes hardened, because the volume capacity of the groove portion  3   c  is far smaller than the volume capacity of the mold cavity  4 . As the viscosity of the molten resin  7  is increased in the groove portion  3   c , the fluidity of the molten resin  7  becomes diminished not only in the groove portion  3   c  but also in the vicinity of the edge portion  3   c  of the cavity surface  3   a  or a peripheral edge A of the mold cavity  4 . 
     The diminished fluidity of the molten resin  7  prevents a further volume of the molten resin  7  from flowing into the groove portion  3   c  from the mold cavity  4  and also prevents the migration of the molten resin  7  in the vicinity of the peripheral edge A of the mold cavity  4 . In the vicinity of the peripheral edge A of the mold cavity  4 , the sheet-like material  5  comes to be covered by the molten resin  7  of increased viscosity and protected against exposure to heat and/or pressure. Thereby, the molten resin  7  does not leak out between the parting surface  3   d  and the upper surface of the sheet-like material  5  to form a flash, even in the process that the molten resin  7  is pressurized at a hold pressure in the mold sections  2  and  3 . In addition, the sheet-like material lying in the vicinity of the peripheral edge A of the mold cavity  4  is prevented from being deformed or damaged by the pressure and/or heat of the molten resin  7 , because of the protective resin coating over the peripheral edge A of the mold cavity  4 . 
     When the cooling process is completed, the mold sections  2  and  3  are separated to open the mold cavity  4  and detach a semi-fabricated article consisting of the sheet-like material  5  and an injection molded body of the resin  7 . The injection molded boy of the resin  7  is integrated onto the upper surface of the sheet-like material  5 . The semi-fabricated article includes an extra part of the sheet-like material  5  which extended between the parting surfaces  2   b  and  3   d  of the mold sections  2  and  3  when molded. The semi-finished article also includes an extra part of the molded body in the form of an annular flange or the like, which was formed by the groove portion  3   c  when molded. Therefore, the extra parts of the sheet-like material  5  and the molded body are cut to be removed from the semi-fabricated article to obtain a finished product of the injection molded article. 
     The Second Embodiment 
       FIG. 3  illustrates a perspective view an automotive interior part, that is, a meter cluster housing  8 . As a decorative sheet, a TPO sheet  9  having a soft texture is integrated onto a surface of the housing  8 . Hereinafter, the present invention will be described further by taking as an example a manufacture of the meter cluster housing  8  with which the TPO sheet  9  is integrated. The flange-like protrusion that is made from the molten resin  7  filled in the groove portion  3   c  in  FIG. 2B  is formed along a front edge portion  8 A of the meter cluster housing  8  and is positioned on a back side of the TPO sheet  9  extending toward the outside of the front edge portion  8 A. 
     In  FIG. 4 , the TPO sheet  9  is heated by a heating device (not shown) so as to be softened and fixed to a parting surface of a cavity mold  11  of an apparatus of injection molding  10  by means of clampers  12 ,  12 . In this example, the cavity mold  11  is a stationary mold held by a base member  13  and a plurality of suction ports  14 ,  15 ,  16  are formed in the cavity mold  11  and the base member  13 . The TPO sheet  9  supplied on the cavity mold  11  is sucked by virtue of vacuum created in air suction ports  14 ,  15 ,  16  so as to be closely secured to a mold surface of the cavity mold  11  by means of vacuum forming. Thereby, the TPO sheet  9  is pre-shaped to conform with the mold surface of the cavity mold  11 , which corresponds to a surface configuration of a meter cluster housing  8  to be molded. 
     A core mold  17  disposed above the cavity mold  11  is held by an upper flame  18  as a movable mold of the apparatus of injection molding  10 . In the core mold  17 , a pair of injection gates  20   a ,  20   b  and a pair of ejector rods or ejector pins  21 ,  22  are installed in order to remove a molded article from the mold sections  11 ,  17 . When the pre-shaping of the TPO sheet  9  is completed, the core mold  17  is lowered together with the upper frame  18  and the core mold  17  is closed against the cavity mold  11  to define a mold cavities  19   a ,  19   b  between the core mold  17  and the cavity mold  11  as illustrated in  FIG. 5 . Then, a molten resin is injected into the mold cavity  19   a  from a injection gate  20   a  to form a visor portion  8   a  of the meter cluster housing  8  and simultaneously, a molten resin is injected into the mold cavity  19   b  from an injection gate  20   b  to form a shelf portions  8   b ,  8   b  of the meter cluster housing  8 . Since the mold cavities  19   a ,  19   b  communicate with each other via one or more communicating paths (not shown) formed between the mold cavities  19   a ,  19   b , the molted resin flowed into the communicating paths forms a mounting portion  8   c  on which various instruments such as meters are mounted. In those figures, reference numeral  23  denotes a seal member for sealing a gap between the TPO sheet  9  and the parting surface of the cavity mold  11  in cooperation with the dampers  12 . Reference numeral  24  denotes a detachable piece which makes up part of the cavity mold  11  to be replaced when it gets worn. 
     As illustrated in  FIG. 6 , a groove portion  17   b  is formed on the parting surface of the core mold  17 . The groove portion  17   b  is in the form of an elongated step extending along the end portion  17   a  of the cavity surface in the core mold  17 . The end portion  17   a  corresponds to a peripheral edge A of the mold cavity  19   a  as shown in  FIG. 6 . The groove portion  17   b  is made up of a single groove that extends to curve along an outer side of the peripheral edge A of the mold cavity  19   a  as to form a thin protrusion  25   a  of a molded body  25  as illustrated in  FIG. 8 . The thin protrusion  25   a  is in the form of a flap that is made from a molten resin injected into the mold cavity  19   a  and integrated onto an upper surface of the TPO sheet  9  as shown in  FIGS. 7 and 8 . The thin protrusion  25   a  is made of resin flowing into the groove portion  17   b  from the mold cavity  19   a  as illustrated in  FIG. 7 . 
       FIG. 10  shows, on the contrary, a vertical section of the mold sections  17 ,  18  that has no groove  17   b  in the peripheral edge A of the mold cavity  19   a . Comparing  FIG. 10  to  FIG. 7 , it is apparent where the thin protrusion  25   a  is formed. 
     Now, the molted resin  25  is injected from the injection gates  20   a ,  20   b  into the mold cavities  19   a ,  19   b  after the core mold  17  is closed against the cavity mold  18 . The molted resin injected into the mold cavity  19   a  flows along the upper surface of the TPO sheet  9  towards the peripheral edge A of the mold cavity  19   a  while filling the mold cavity  19   a . As the molten resin reached the peripheral edge A of the mold cavity  19   a , the molten resin passes smoothly the peripheral edge A of the mold cavity  19   a  and flows into the groove portion  17   b  without staying in the vicinity of the peripheral edge A of the mold cavity  19   a  or the end portion  17   a  of the cavity surface of the core mold  17 . When the mold cavities  19   a ,  19   b  and the groove portion  17   b  as well as the communicating paths between the mold cavities  19   a ,  19   b  are filled with the molten resin, the injected molten resin is held under pressure in the mold sections  17 ,  18  for a certain period of time and is cooled down by a cooling device (not shown). 
     When cooling down the molten metal in the mold sections  17 ,  18 , the temperature of the molten resin filled in the groove portion  17   b  decreases more quickly than the temperature of the molten resin within the mold cavities  19   a ,  19   b  because the volume capacity of the groove portion  17   c  is smaller than the volume capacity of the mold cavities  19   a ,  19   b  in the mold sections  17 ,  18 . As a result that the viscosity of the molten resin is increased in the groove portion  17   c , the fluidity of the molten resin becomes diminished not only in the groove portion  17   c  but also in the vicinity of the peripheral edge A of the mold cavity  19   a . The diminished fluidity of the molten resin prevents a further volume of the molten resin from flowing into the groove portion  17   b  from the mold cavity  19   a  and also prevents the migration of the molten resin in the vicinity of the peripheral edge A of the mold cavity  19   a . In the vicinity of the peripheral edge A of the mold cavity  19   a , thereby, the TPO sheet  9  comes to be covered by the molten resin of increased viscosity and protected against exposure to heat and/or pressure of the molten resin in the mold cavity  19   a . As a result, the TPO sheet  9  lying in the vicinity of the peripheral edge A of the mold cavity  19   a  is prevented from being deformed or damaged by the pressure and/or heat of the molten resin. Therefore, the molten resin injected into the mold cavities  19   a ,  19   b  does not leak out between the parting surface of the core mold  17  and the upper surface of the TOP sheet  9  to form a flash, even in the event that a molding pressure is applied further to the molten resin within the mold cavities  19   a ,  19   b  in the subsequent pressure holding step. 
     When the cooling down of the molten resin in the mold sections  17 ,  18  is completed, a molded body  25  is molded in the mold cavities  19   a ,  19   b  and the communicating paths (not shown) and integrated onto the upper surface of the TPO sheet  9  as illustrated in  FIGS. 7 and 8 . Simultaneously, the thin protrusion  25   a  of resin is molded in the groove portion  17   b  and integrated onto the upper surface of the TPO sheet  9 . The thin protrusion  25   a  extends from the edge of the molded body  25  as shown in  FIG. 8 . Then, the core mold  17  is lifted from the cavity mold  18  to open the mold cavities  19   a ,  19   b  and the molded body  25  is removed from the mold sections  17 ,  18  together with the TPO sheet  9  by means of the ejector rods  21 ,  22 . The molded article took out of the mold sections  17 ,  18  is a semi-fabricated article of a meter cluster housing  8 , because it includes an extra part of the TPO sheet  9  extending from the molded body  25  and the thin protrusion  25   a  integrated onto the extra part of the TPO sheet  9  as shown in  FIG. 8 . Therefore, the semi-fabricated article is processed for a trimming operation by which the extra part of the TPO sheet  9  and the thin protrusion  25   a  is trimmed off, as shown in  FIG. 9 , to obtain a finished product of the meter cluster housing  8 .