Abstract:
An injection molding system ( 10 ) generally includes a molding device ( 100 ), a mold controller ( 200 ), and a negative pressure apparatus ( 300 ). The molding device defines a molding cavity ( 160 ) and a plurality of cooling channels ( 110 ) therein and has a plurality of heating elements ( 120 ). The heating elements are used for heating the molding cavity to a determined temperature. A cooling medium is supplied in the cooling channels to cool the molding cavity. The negative pressure apparatus is used for keeping the cooling channels in a negative pressure state, thereby improving the fluidity of the cooling medium during heat removal and avoiding leaving a portion of the cooling medium in the cooling channels during heating. Accordingly, the negative pressure apparatus can effectively decrease the heating and cooling terms/lengths. A method for using this system to manufacture a product made from a thermoplastic material is also provided.

Description:
BACKGROUND  
       [0001]     1. Technical Field  
         [0002]     The invention relates generally to injection molding systems and, particularly, to an injection molding system with a rapid heating and cooling capability for manufacturing high quality components such as light guide plates. The invention also relates to a method for using such an injection molding system.  
         [0003]     2. Discussion of Related Art  
         [0004]     In an injection molding processes, particularly for a process suited for the molding of thermoplastic material, a mold temperature controller is an absolute necessity. Conventionally, the mold temperature controller relies upon water circulation. The mold temperature controller generally has a heating apparatus and a cooling apparatus. Before the molten thermoplastic material fills into a molding cavity of a molding device, the heating apparatus heats the water to a determined temperature. The hot water cycles in the molding cavity to heat the molding cavity, thereby keeping the molten thermoplastic material flowing. After the molten thermoplastic material fills into the molding cavity, the cooling apparatus cools the water. The cold water cycles in the molding device to cool the molding cavity, thereby forming the desired molded products.  
         [0005]     The higher the temperature of the molding cavity is able to be during the filling of the molten thermoplastic material into the molding cavity, the better the fluidity of the thermoplastic material and, ultimately, the surface characteristics (e.g., smoothness) of the products are.  
         [0006]     For high quality components used in the photoelectric field such as light guide plates, it is important that the components have good transparency and convertibility. Accordingly, it is important for the degree of surface smoothness thereof to be maximized, especially for non-diffuse surfaces. Thus, the temperature of the molding cavity of the molding device in the injection molding processes should be in the range from about 90° C. to about 200° C., to achieve sufficient flow. However, the highest temperature of the molding cavity of the molding device that the controller using water circulation can perform is less than 90° C., which cannot meet the temperature requirements for manufacturing the high quality components.  
         [0007]     To settle this problem, another kind of mold temperature controller using oil circulation is utilized. In this kind controller, the oil is used to replace the water as a heating and cooling medium and a high temperature (i.e., more than 90° C.) of the molding cavity can be achieved. However, the thermal conduction coefficient of the oil is lower than that of water and the oil is a smeary material (i.e., does not flow as well as water, instead tending to leave a residue), thereby increasing the heating and cooling terms and decreasing productivity of the injection molding processes.  
         [0008]     Recently, a mold temperature controller for heating and cooling a molding cavity of a molding device, combining steam and water, has been developed. In the heating process, the hot steam is filled into the molding device to heat the molding cavity to a temperature of more than 90° C. In the cooling process, the liquid medium is filled into the molding device to cool the molding cavity. In the next heating process, the liquid medium is firstly withdrawn and the hot steam is then filled. In the utilization of this controller, the heating process and the cooling process are provided to heat and cool the molding cavity, in turn, and an amount of leftover liquid medium is likely to remain in the molding device after cooling, so that the heating and cooling terms are increased. Furthermore, this controller is expensive and dangerous to operate in the heating process, thereby increasing the manufacturing cost.  
         [0009]     What is needed, therefore, is an injection molding system with a rapid heating and cooling capability for manufacturing high quality components such as light guide plates.  
         [0010]     What is also needed is a method for using such an injection molding system,  
       SUMMARY  
       [0011]     In one embodiment, an injection molding system is provided for manufacturing a product made from a thermoplastic material. The injection molding system generally includes a mold controller, a molding device, and a negative pressure apparatus. The molding device defines a molding cavity and a plurality of cooling channels therein and has a plurality of heating elements. Before the molten thermoplastic material fills into the molding cavity of the molding device, the heating elements are used for heating the molding cavity to a determined temperature to keep the thermoplastic material flowing. After the melt thermoplastic material fills into the molding cavity of the molding device, a cooling medium is cycled in the cooling channels to cool the molding cavity. The negative pressure is used for keeping the cooling channels in a negative pressure state, thereby improving the fluidity of the cooling medium. The improved flow helps improve the thermal conduction efficiency during cooling, reducing cooling times. Likewise, such flow helps to avoid having an amount of the cooling medium remain in the cooling channels during heating. Such a reduction in remnant cooling fluid, otherwise present during the heating cycle, helps decrease the heating terms (e.g., duration; energy input; etc.), as well.  
         [0012]     A method, for using the above-mentioned injection molding system to make a product made from thermoplastic, includes a series of steps: 
    (a) assembling the cavity side mold and the core side mold by a closing process, thereby defining the molding cavity therebetween, the molding cavity being shaped according to the desired product features;     (b) heating the molding cavity by the heating elements to a determined temperature, the temperature being higher than a melting point of the thermoplastic material;     (c) filling the molten thermoplastic material into the molding cavity and heating the molten thermoplastic material by way of the heating elements;     (d) applying a cooling medium to cycle in the cooling channels of the molding device to cool the molding cavity to obtain the product, and starting the negative pressure apparatus to keep the cooling channels in the negative pressure state, and     (e) disassembling the cavity side mold and the core side mold by an opening process, and removing the product from the molding device.    
 
         [0018]     Other advantages and novel features of the present injection molding system and method for using such will become more apparent from the following detailed description of preferred embodiments when taken in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]     Many aspects of the present injection molding system and method for using such can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, the emphasis instead being placed upon clearly illustrating the principles of the present injection molding system and method for using such.  
         [0020]      FIG. 1  is a schematic view of an injection molding system, in accordance with an exemplary embodiment of the present system;  
         [0021]      FIG. 2  is a cross-section view of a molding device of the injection molding system of  FIG. 1 , showing the molding device as assembled;  
         [0022]      FIG. 3  is a cross-section view of the molding device, showing molten thermoplastic material filled into a molding cavity of the molding device;  
         [0023]      FIG. 4  is a cross-section view of the molding device, showing a formed product;  
         [0024]      FIG. 5  is a cross-section view of the molding device, showing the molding device in a disassembled state;  
         [0025]      FIG. 6  is a cross-section view of the molding device, showing the product ejected from the molding device; and  
         [0026]      FIG. 7  is a coordinate graph, showing the temperature of molding cavity of the molding device in the utilization of the injection molding system. 
     
    
       [0027]     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate at least one preferred embodiment of the present injection molding system and method for using such, in one form, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.  
       DETAILED DESCRIPTION  
       [0028]     Reference will now be made to the drawings to describe embodiments of the present injection molding system and method for using such, in detail.  
         [0029]     Referring to  FIG. 1 , an injection molding system  10 , in accordance with an exemplary embodiment of the present system, is schematically shown. Generally, the injection molding system  10  includes a molding device  100 , a mold controller  200 , and a negative pressure apparatus  300  connected with the controller  200 . The molding device  100  has a molding cavity  160  ( FIG. 2 ) and a plurality of cooling channels  110  defined therein and has a plurality of heating elements  120 . The molding cavity  160  is formed with a space shaped corresponding to a desired product and in which the molten thermoplastic material is cast.  
         [0030]     The cooling channels  110  are utilized/configured for accommodating a cooling medium such as water or oil therein to cool the molding cavity  160  and for thus achieving a sufficient setting/hardening rate for the product formed using the molding device  100 . Generally, the cooling channels  110  are defined in portions of the molding device  100  with a linear, parallel arrangement. Alternatively, a series of, e.g., zigzag or wave-shaped cooling channels (not shown) may be used instead of the illustrated arrangement of cooling channels  110 .  
         [0031]     The heating elements  120  are connected with and controlled by the controller  200 . The heating elements  120  are embedded in portions of the molding device  100  near the molding cavity  160  to heating the molding cavity  160  and are configured for heating the thermoplastic material received in the molding cavity  160 . The heating elements  120  are advantageously selected from an electrical resistance heating component and a high frequency induction heating component. The electrical resistance heating component preferably has a form selected from an electrical heating rod and an electrical heating plate. The high frequency induction heating component is beneficially a high frequency shock inductor.  
         [0032]     The negative pressure apparatus  300  is connected with and controlled by the controller  200  and is in communication with the cooling channels  110 . The negative pressure apparatus  300  is preferably selected from a negative pressure pump and a vacuum pump. During the cooling process, the negative pressure apparatus  300  is used for keeping the cooling channels  110  of the molding device  100  in a negative pressure state. Thus, the speed/flow of the cooling medium is improved, thereby aiding the cooling rate. Likewise, the opportunity for leftover/remnant cooling medium existing in the cooling channels  110  during heating is avoided/reduced, thereby ensuring an improved heating efficiency, relative to prior art systems, and thus a relatively short heating cycle.  
         [0033]     The controller  200  is preferably selected from a programmable apparatus and a computer system. By means of determined programs, the controller  200  can control the heating of the heating elements  120 ; the supply of the cooling medium for the molding device  100 ; the molding device  100 ; and the negative pressure apparatus  300  automatically, thereby increasing the productivity of the injection molding system  10 .  
         [0034]     Preferably, a temperature sensor  130  is disposed near the molding cavity  160  of the molding device  100 . The sensor  130  is connected with the controller  200 . The function of the sensor  130  is for transmitting signals of the temperature of the molding cavity  160  to the controller  200 , thus allowing the controller  200  to control the temperature of the molding cavity  160  precisely. The sensor  130  is preferably selected from a temperature wire (e.g., a thermocouple) and a temperature probe.  
         [0035]     A valve  400  is preferably disposed in the injection molding system  10 . The valve  400  is connected with and controlled by the controller  200 . The valve  400  is disposed near the cooling channels  110  and is configured for controlling the cooling medium flow during cooling and for preventing the cooling medium from leaking into the cooling channels  110  during heating. It is to be understood that a plurality of valves  400  could be provided, especially if a larger molding device (e.g., a multi-product mold) is to be used.  
         [0036]     An example of the injection molding system  10 , according to an preferred embodiment of the present system, is provided for describing the configuration thereof and method for using it to manufacture high quality productions, such as light guide plates, in detail, considering  FIGS. 1-6  together. The injection molding system  10  has the molding device  100 , the negative pressure apparatus  300  (e.g., a vacuum pump) and the controller  200  (e.g., a programmable apparatus). The vacuum pump is advantageously selected as the negative pressure apparatus  300 . The programmable apparatus is opportunely chosen as the mold controller  200 . The vacuum pump  300  and the molding device  100  are connected with and controlled by the programmable apparatus  200 , respectively.  
         [0037]     Referring to  FIGS. 2 and 6 , the cross-section views of the molding device  100  is shown. The molding device  100  includes a cavity side mold  140  and a core side mold  150 . The molding cavity  160  is defined between the cavity side mold  140  and the core side mold  150 . The molding cavity  160  is shaped as a rectangular shape corresponding to a desired product, such as a light guide plate (i.e., the cavity shape conforming to a desired product shape). A pair of cavity surfaces  142 ,  152  is formed on the cavity side mold  140  and the core side mold  150 , respectively The cooling channels  110  are defined in each of the cavity side mold  140  and the core side mold  150 . The cooling channels  110  are arranged in a parallel manner and communicate with the vacuum pump  300 .  
         [0038]     The heating elements  120  are advantageously in the form of a plurality of electrical heating rods and are embedded in each of the cavity side mold  140  and the core side mold  150 , respectively. Preferably, a thermal conducting layer (not shown), such as a copper layer, is coated on each of the electrical heating rods  120  to increase the thermal conductivity thereof. The cooling channels  110  and the electrical heating rods  120  are arranged in lines, respectively. The individual electrical heating rods  120  are nearer to the molding cavity  160  than that the respective cooling channels  110 . Two heat insulators  148 ,  158  are disposed on the cavity side mold  140  and the core side mold  150 , respectively. The temperature sensor  130  is usefully in the form of a thermocouple, embedded in the cavity side mold  140 , near the cavity surface  142  associated with the cavity side mold  140 . A runner  180  is defined in the core side mold  150 , perpendicular to and communicating with the molding cavity  160 . The runner  180  forms a sprue gate  182  in a top portion of the core side mold  150 . An ejector  190  is disposed on the cavity side mold  140 .  
         [0039]     In the above molding device  100 , it is known that the arrangement of the cooling channels  110  and the electrical heating rods  120  may be altered. For example, the cooling channels  110  may be in a row that, instead, is nearer to the molding cavity  160  than a row formed by the electrical heating rods  120 . The cooling channels  110  and the electrical heating rods  120  could be staggered within a row or several rows. Generally, it is to be understood that various configurations, individually and collectively, of the cooling channels  110  and/or the heating elements  120  are possible and are considered to be within the scope of the present system. In addition, the thermocouple  130  may be disposed in the core side mold  150 , near the cavity surface  152  of the core side mold  150 . The hot runner  180  may be defined in the cavity side mold  140  and/or inclined to the molding cavity  160 .  
         [0040]     A method uses the injection molding system  10  to manufacture a light guide plate  600 . The light guide plate  600  is made from a thermoplastic material  500 . The method generally includes a series of steps: 
    (a) assembling the cavity side mold  140  and the core side mold  150  by a closing process and using the heating elements  120  to heat the cavity surfaces  142 ,  152  to a determined temperature that is higher than the melting point of the thermoplastic material  500 ;     (b) filling the molten thermoplastic material  500  into the molding cavity  160  and keeping the cavity surfaces  142 ,  152  at the determined temperature;     (c) starting/activating the negative pressure apparatus  300  and applying the cooling medium, the cooling medium thereby filling into the cooling channels  110 , the cooling channels  110  being kept in a negative pressure state, the cooled temperature of the cavity surfaces  142 ,  152  being lower than the melting point (advantageously lower than a setting/softening point) of the thermoplastic material  500  to obtain the light guide plate  600 ; and     (d) disassembling the cavity side mold  140  and the core side mold  150  by an opening process, removing the light guide plate  600  from the molding device  100  by, e.g., an ejecting process or a manual step, and excluding/evacuating any leftover amount of the cooling medium by the negative pressure apparatus  300 .    
 
         [0045]     In the step (a), the original temperature of the core side molds  140  and the cavity side mold  150  is about 30° C. Under the controlling of the programmable apparatus as the controller, the electric heating rods  120  are electrified in order to heat the cavity surfaces  142 ,  152  to the determined temperature. The temperature is determined by the melting point of the thermoplastic material  500 . Generally, the thermoplastic material  500  is preferably selected from a polycarbonate (PC) material, such as mokrolon PC, LC1500, and polymethyl methacrylate (PMMA) material, such as MG5, MGSS. If the thermoplastic material  500  is MG5 that has a melting point of about 107° C., the determined temperature heated by the electrical heating rods  120  is preferably about 130° C. That is, the determined heating temperature is chosen so as to result in a viscosity of the thermoplastic material  500  that will facilitate fluid flow thereof.  
         [0046]     In the step (b), when the temperature of the cavity surfaces  142 ,  152  is about 130° C., the temperature wire  130  transmits the signals to the programmable apparatus  200 . Under the control of the programmable apparatus  200 , the molten thermoplastic material  500  is filled into the molding cavity  160  via the sprue gate  182 . The temperature of the cavity surfaces  142 ,  152  is kept at the temperature of about 130° C. by means of the electrical heating rods  120  being electrified intermittently, as needed to maintain the desired mold temperature.  
         [0047]     In the step (c), after the molten thermoplastic material  500  is filled into the molding cavity  160 , the valve  400  is opened and the vacuum pump  300  is started, both under the control of the programmable apparatus  200 . Cooling water, being advantageously selected as the cooling medium, is applied to cycle in the cooling channels  110  of the molding device  100  to cool the cavity surfaces  142 ,  152 , thereby forming the light guide plate  600 . The vacuum pump  300  keeps the cooling channels  110  in the negative pressure state to improve the fluidity/flow rate of the water and to maximize the cooling rate.  
         [0048]     In the step (d), when the temperature sensor  130  registers that the temperature of the cavity surfaces  142 ,  152  is about 30° C., the programmable apparatus  200  recognizes that the molding apparatus  100  has sufficiently cooled. Under the operation of the programmable apparatus  200 , the valve  400  is closed to temporarily prevent further cooling water from entering the molding device  100 . The core side mold  150  and the cavity side mold  140  are disassembled. The ejector  190  ejects the light guide plate  600  from the molding device  100 . The vacuum pump  300  is used to help evacuate/remove the leftover water from/out of the cooling channels  110 . It is to be understood that the ejector  190  may be eliminated in some designs (e.g., relying on manual removal of the finished product). Likewise, the cavity surfaces  142 ,  152  may be coated with a mold-release material, which would facilitate removal of the molded product upon its completion.  
         [0049]     In the above-mentioned steps, the programmable apparatus  200  works automatically via one or more determined programs. The temperature of the cavity surfaces  142 ,  152  in the utilization of the injection molding system  10  in steps (a)-(d) is shown in  FIG. 7 . The variable associated with such steps, while not graphed per se, is time.  
         [0050]     Finally, it is to be understood that the above-described embodiments are intended to illustrate rather than limit the invention. Variations may be made to the embodiments without departing from the spirit of the invention as claimed. The above-described embodiments illustrate the scope of the invention but do not restrict the scope of the invention.