Abstract:
An injection molding comprises: a fixed mold; a movable mold which is capable of contacting to and separating from the fixed mold; and an injection unit which supplies molten resin to a space formed between the fixed mold and the movable mold when being pressed to a non-molding face of the fixed mold. The injection unit comprises: a nozzle portion which injects molten resin to the space formed between the molds; an injecting portion which applies molten resin pressure toward the space formed between the fixed mold and the movable mold though the nozzle portion; a heater and a temperature sensor provided on the nozzle portion; and a heater and a temperature sensor provided on the injecting portion, and detection accuracy of the sensor of the nozzle portion is higher than that of the injecting potion. There is thus provided an injection molding machine capable of manufacturing optics with high accuracy without considerable cost-up by realizing stable and highly accurate injection.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2005-283045 filed on Sep. 28, 2005, the entire contents of which are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to an injection molding machine for molding an optical element with a mold. More particularly, it relates to an injection molding machine which controls temperature with high accuracy to improve molding accuracy.  
         [0004]     2. Description of the Related Art  
         [0005]     There have conventionally been manufactured various molded items by injection molding. For example, JP Unexamined Patent Publication No. 10-323872 discloses an injection molding machine for molding disks utilized as information recording media.  FIG. 4  shows schematic structure of the molding injection machine directed to the Publication No. 10-323872. The molding injection machine includes a fixed platen  101  and a cylinder  103 . Four tie-bars  104  are laid between the fixed platen  101  and the cylinder  103  to link them. The tie-bars  104  are supporting a movable platen  105  which is slidable. The movable platen  105  is driven by the cylinder  103 . A fixed mold  107  and a movable mold  108  are attached to the fixed platen  101  and the movable platen  105 , respectively. The movable mold  108  is clamped to the fixed mold  107  by the cylinder  103 . With this state, resin material is supplied from an injection unit  111  to mold a disk.  
         [0006]     Such an injection unit of an injection molding machine is required to control temperature with high accuracy so as to carry out stable mold injection with high accuracy. If temperature is too low, molding accuracy deteriorates. If temperature is too high, resin deteriorates or gets stringiness. Therefore, there has conventionally been provided heat adjusting means for a nozzle portion and a cylinder portion. For example, JP Unexamined Patent Publication No. 2005-7629 discloses an injection unit equipped with a heater and a temperature sensor at each zone. In the Publication No. 2005-7629, a thermo couple is disclosed as an example of temperature sensor. Since a thermo couple was cheap and satisfied sufficient accuracy in comparison with conventional accuracy demand, it was used widely.  
         [0007]     However, with the advance of accuracy of optical elements, temperature control accuracy managed by the conventional injection molding machine has become insufficient. Especially, as to micro molding machine, its one-shot volume is small and its nozzle portion sometimes has volume of several shots. As one-shot volume is smaller, higher accuracy in proportion to the smallness is required for injection performance and temperature control accuracy. In the case the conventional injection molding machine intends to control temperature with high accuracy, it is required to use a temperature sensor of higher accuracy. As an example of a temperature sensor of which accuracy is higher than a thermo couple, a platinum temperature-sensing element, a quartz temperature sensor, and the like can be utilized. However, they are expensive items. As described, the conventional injection molding machine has plural temperature control means at respective zones and if all of them are replaced with highly accurate temperature sensors, the replacement accompanies considerable cost-up.  
       SUMMARY OF THE INVENTION  
       [0008]     The present invention has been attempted to solve the above-noted problems involved in the conventional injection molding machine. Thus, an object of the invention is to provide an injection molding machine capable of manufacturing an optical element with high accuracy without considerable cost-up by realizing stable and highly accurate injection.  
         [0009]     According to a first aspect of the present invention, there is provided an injection molding machine comprising: a fixed mold; a movable mold which is capable of contacting to and separating from the fixed mold; and an injection unit which supplies molten resin to a space formed between the fixed mold and the movable mold when being pressed to a non-molding face of the fixed mold, wherein the injection unit comprises: a nozzle portion which injects molten resin to the space formed between the fixed mold and the movable mold; an injecting portion which applies molten resin pressure toward the space formed between the fixed mold and the movable mold through the nozzle portion; a first heater and a first temperature sensor which are provided at a tip side within the nozzle portion; a second heater and a second temperature sensor which are provided at a side near to the injecting portion within the nozzle portion; and a third heater and a third temperature sensor which are provided within the injecting portion, and wherein a target temperature of the first heater is lower than a target temperature of the second heater, and the target temperature of the second heater is higher than a target temperature of the third heater.  
         [0010]     According to the injection molding machine directed to the first aspect of the present invention, the movable mold is made to get contact with the fixed mold and an optical element is mold by injecting resin to a space formed between the molds in contact with each other. Different target temperatures are set for respective portions appropriately, whereby stringing of resin is avoided. Furthermore, stable molding is carried out with high accuracy.  
         [0011]     According to a second aspect of the present invention, there is provided an injection molding machine comprising: a fixed mold; a movable mold which is capable of contacting to and separating from the fixed mold; and an injection unit which supplies molten resin to a space formed between the fixed mold and the movable mold when being pressed to a non-molding face of the fixed mold, wherein the injection unit comprises: a nozzle portion which injects molten resin to the space formed between the fixed mold and the movable mold; an injecting portion which applies molten resin pressure toward the space formed between the fixed mold and the movable mold though the nozzle portion; a nozzle heater and a nozzle temperature sensor provided within the nozzle portion; and an injecting portion heater and an injecting portion temperature sensor provided within the injecting portion, and wherein detection accuracy of the nozzle temperature sensor is higher than detection accuracy of the injecting potion temperature sensor.  
         [0012]     According to the injection molding machine directed to the second aspect of the present invention, since a highly accurate temperature sensor is employed for the nozzle portion only, it does not accompany considerable cost-up. Furthermore, since temperature at the nozzle portion in which about-to-be-injected resin is collected is controlled with high accuracy, stable injection molding can be carried out with high accuracy. Therefore, an optical element is manufactured with high accuracy.  
         [0013]     According to a third aspect of the present invention, there is provided an injection molding machine comprising: a fixed mold; a movable mold which is capable of contacting to and separating from the fixed mold; and an injection unit which supplies molten resin to a space formed between the fixed mold and the movable mold when being pressed to a non-molding face of the fixed mold, wherein the injection unit comprises: a nozzle portion which injects molten resin to the space formed between the fixed mold and the movable mold; an injecting portion which applies molten resin pressure toward the space formed between the fixed mold and the movable mold through the nozzle portion; a first heater and a first temperature sensor which are provided at a tip side within the nozzle portion; a second heater and a second temperature sensor which are provided at a side near to the injecting portion within the nozzle portion; and a third heater and a third temperature sensor which are provided within the injecting portion, and wherein a target temperature of the second heater is higher than a target temperature of the third heater.  
         [0014]     According to a fourth aspect of the present invention, there is provided an injection molding machine comprising: a fixed mold; a movable mold which is capable of contacting to and separating from the fixed mold; and an injection unit which supplies molten resin to a space formed between the fixed mold and the movable mold when being pressed to a non-molding face of the fixed mold, wherein the injection unit comprises: a nozzle portion which injects molten resin to the space formed between the fixed mold and the movable mold; an injecting portion which applies molten resin pressure toward the space formed between the fixed mold and the movable mold through the nozzle portion; a first heater and a first temperature sensor which are provided at a tip side within the nozzle portion; a second heater and a second temperature sensor which are provided at a side near to the injecting portion within the nozzle portion; and a third heater and a third temperature sensor which are provided within the injection molding portion, and wherein a target temperature of the first heater is lower than a target temperature of the second heater.  
         [0015]     According to the inventive injection molding machine, an optical element is manufactured with high accuracy without considerable cost-up by realizing stable and highly accurate injection. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]     These and other objects and advantages of this invention will become more fully apparent from the following detailed description taken with the accompanying drawings in which:  
         [0017]      FIG. 1  is a front view showing schematic structure of a lens molding device directed to an embodiment;  
         [0018]      FIG. 2  is a cross sectional view showing schematic structure of an injection unit of the embodiment; and  
         [0019]      FIG. 3  is a cross sectional view showing schematic structure of a nozzle portion of the injection unit. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0020]     Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. In this embodiment, the present invention is applied to a lens molding device for manufacturing a plurality of lenses of a camera to be installed in a portable terminal at once. The lens molding device of the present embodiment is to mold a small optical element of which outside diameter is 12 nm or smaller, and an optical element to be mold is required to keep accuracy such as Ra 20 nm or smaller surface roughness of its optical surface. The present embodiment is applied to micro injection molding devices of which clamping force is 150 kN or lower.  
         [0021]     The lens molding device of the present embodiment is such structured as shown in  FIG. 1 . That is, a fixed platen  1  and a rear platen  3  are fixedly provided on a frame  2 . Those platens  1  and  3  are substantially square shaped when looked from the left or right side with reference to  FIG. 1 . Four tie-bars  4  are laid between the fixed platen  1  and the rear platen  3  to link them. The tie-bars  4  are arranged at respective four corners of the fixed platen  1  and the rear platen  3  fixedly. They are arranged in parallel to one another.  
         [0022]     A movable platen  5  is provided between the fixed platen  1  and the rear platen  3 . The movable platen  5  is substantially square shaped when looked from the left or right side with reference to  FIG. 1 . Each tie-bar  4  penetrates through around each of four corners of the movable platen  5 . Guide bushes  51  are provided at respective penetrating portions for the tie-bars  4 . The movable platen  5  is slidable to the four tie-bars  4 . The movable platen  5  is supported by the tie-bars  4  without getting contact with the frame  2 . A hydraulic press  6  is attached to the rear platen  3 . The hydraulic press  6  and the movable platen  5  are connected with a tie-rod  61 . That is, the movable platen  5  can be moved in left-and-right direction by driving by the hydraulic press  6 .  
         [0023]     A fixed mold  7  is attached on a face of the fixed platen  1  facing the movable platen  5 . A movable mold  8  is attached to a face of the movable platen  5  facing the fixed platen  1 . Temperatures of the movable mold  8  and the fixed mold  7  are controlled respectively.  
         [0024]     On the frame  2 , an injection unit  11  is provided at a rear side of the fixed platen  1  (right side of the fixed platen  1  in  FIG. 1 ). The injection unit  11  has such structure as shown in  FIG. 2 . The injection unit  11  has a nozzle portion  12 , an injection cylinder  13 , an injection plunger  14 , an injection hydraulic cylinder  16 , and a pressure sensor  17 , and these elements compose an injection mechanism portion. At the upper part of the injection mechanism portion, there is provided plasticizing mechanism  21  which plasticizes resin and supplies plasticized resin to the injection cylinder  13 .  
         [0025]     At some parts of the injection unit  11 , there are some heaters for plasticizing resin and keeping resin in preferable plasticized condition. Furthermore, a temperature sensor is attached near each heater to detect a temperature around there. There is also provided a temperature control portion  50  which controls respective heaters upon receipt of detection results from respective temperature sensors. Thereby, temperatures at respective portions are controlled to keep at their respective optimum ones. For example, different target temperatures as respective optimum temperatures are set for the plasticizing cylinder  21 , the injection cylinder  13 , and the nozzle portion  12  and they are controlled to approximate to their respective target temperatures.  
         [0026]     In this embodiment, as shown in  FIG. 3 , heaters  31  and  32  are arranged on the nozzle portions  12 , and so are heaters  33  and  34  on the injection cylinder  13 . The temperature sensors  41 ,  42 ,  43  and  44  are attached near the heaters  31 ,  32 ,  33  and  34 , respectively. For these temperature sensors  41 ,  42 ,  43  and  44 , target temperatures are predetermined respectively. The temperature control portion  50  controls the heaters  31 ,  32 ,  33  and  34  to make the temperature of the sensors  41 ,  42 ,  43  and  44  approximate to their respective target temperatures. In this embodiment, both the number of heaters and that of temperature sensors to be provided on the injection cylinder  13  are “2”, however, they may be more than “2” depending on size and volume of the injection cylinder  13 .  
         [0027]     Due to demand on quality stability of recent years, mold temperature stability has been required to be one degree or smaller as process variable. On the other hand, measurement accuracy of a conventional temperature measuring device including a thermo couple is ±1.5° C. +0.4%, which is not accurate enough. On that account, as further accurate temperature sensor, use of a platinum temperature sensing element or a quartz temperature sensor, for example, is required. Measurement accuracy of those sensors including its measuring device are: ±0.05° C. (quartz temperature sensor); and ±0.15° C. (platinum temperature sensing element). On the other hand, in the present invention, it is preferable that detection accuracy of a temperature sensor arranged within a range of one-shot injection volume from a tip portion of the nozzle is higher than that of the temperature sensors arranged off the range.  
         [0028]     In this embodiment, with consideration of relation between total volume of the nozzle portion  12  and the injection cylinder  13  and one-shot injection volume, detection accuracy of a temperature sensor is selected based on the following criteria. In case one-shot injection volume can be managed within internal volume of the nozzle portion  12 , only the temperature sensors  41  and  42  arranged on the nozzle portion  12  shall be highly accurate temperature sensors, and the temperature sensors  43  and  44  arranged on the injection cylinder  14  are thermo couples which are similar to the conventional ones. In the case one-shot injection volume can be managed with total volume of the nozzle portion  12  and a tip portion of the injection cylinder  13 , the temperature sensors  41  and  42  on the nozzle portion  12  and the temperature sensor  43  on the tip portion of the injection cylinder  13  shall be highly accurate temperature sensors.  
         [0029]     In the case one-shot injection volume is further larger, the temperature sensors  41  and  42  on the nozzle portion  12  and the temperature sensors  43  and  44  on the injection cylinder  13  shall be highly accurate temperature sensors. With such arrangement, temperature of at least one-shot of resin portion is adjusted within temperature monitoring accuracy of ±0.2° C. or smaller, preferably, within a range of ∓0.05° C., and a target temperature is adjusted within accuracy of ±0.3° C. or smaller, as more preferable temperature accuracy, within a range of ±0.1° C. In the case highly accurate molding is required, it is preferable that temperatures of mold base members and cavity members are controlled by highly accurate temperature sensors. Temperatures of portions other than these, e.g., plasticizing mechanism portions, can be controlled with conventional thermo couples satisfactorily.  
         [0030]     Furthermore, as for the nozzle portion  12 , a target temperature near the heater  31  arranged at the tip side of the nozzle portion  12  and a target temperature near the heater  32  at the side of the injection cylinder  13  are different. That is, a target temperature of the temperature sensor  42  at the side of the injection cylinder  13  is slightly higher than that of the temperature sensor  41  at the tip side. On the other hand, same target temperatures are set for the temperature sensors  43  and  44  on the injection cylinder  13 . The target temperature of the injection cylinder  13  is set slightly lower than target temperature near the heater  32  arranged at the side of the injection cylinder  13 .  
         [0031]     Thus, the temperature control portion  50  controls the temperatures at the tip side and at the injection cylinder  13 &#39;s side of the nozzle portion  12  to different target temperatures. In the case of molding small optical elements, so is one-shot volume. Accordingly, only resin collected in the nozzle portion  12  can possibly exceed one-shot volume. By varying target temperature part by part in the nozzle portion  12 , temperature of an essential amount of resin is controlled appropriately.  
         [0032]     In such structured lens molding device of the present embodiment, resin supplied from the external is heated in the plasticizing cylinder  21  and agitated by a plasticizing screw  22 . The plasticizing screw  22  is driven by the hydraulic motor  24 . Of the plasticized resin, predetermined amount of it is supplied to the internal of the nozzle portion  12  from the injection cylinder  13 . In the injection cylinder  13 , temperature is adjusted by the heaters  33  and  34 . In the nozzle portion  12 , temperature is adjusted by the heaters  31  and  32  with high accuracy. After that, the fixed mold  7  and the movable mold  8  are clamped and the injection unit  11  is pressed to the fixed mold  7  with predetermined pressing force. In such a clamped state, the injection plunger  14  is driven by the injection hydraulic cylinder  16  and molten resin is supplied to a cavity formed between the clamped molds from the nozzle portion  12 , whereby lenses formed.  
         [0033]     Types of resin to be used may be what are disclosed in JP Unexamined Patent Publications No. 2004-144951, No. 2004-144953, and No. 2004-144954, for example. Resins disclosed in the publications generally exhibit high fluidity and therefore, injection molding condition is preferable. On the other hand, provided that the resins are left unused for long time under high temperature, they can possibly get burnt, deteriorate, or turn yellow, which is not preferable. In the present embodiment, of the nozzle portion  12 , temperature is kept comparatively high only at the portion at the side of injection cylinder  13  so as to enhance molding condition. Since temperature inside of the injection cylinder  13  is controlled by the heaters  33  and  34 , deterioration of resin is avoided.  
         [0034]     As described, the nozzle portion  12  of the present embodiment has the heaters  31  and  32  at its tip side and injection cylinder  13 &#39;s side, respectively, and different target temperatures are set for the respective portions. Furthermore, since the heaters  31  and  32  are controlled by using the highly accurate temperature sensors  41  and  42 , difference from their respective target temperatures is significantly small. Thereby, even if only small amount of resin is injected, accuracy to transfer a fine shape with resin is enhanced and highly accurate molding is realized. Furthermore, resin sufficiently which has been heated at the injection cylinder  13  side of the nozzle portion  12  and enhanced its fluidity is slightly cooled down at the tip portion of the nozzle portion  12 , thereby stringing of resin is avoided.  
         [0035]     As described, according to the lens molding device of the present embodiment, highly accurate temperature control is applied to the nozzle portion  12  only. Since an expensive and highly accurate temperature sensor is just employed at a portion within a range of one-shot injection volume, this does not accompany considerable cost-up. Furthermore, temperature of about-to-be injected resin is controlled with high accuracy. Therefore, optical elements are manufactured with high accuracy by realizing stable and highly accurate injection.  
         [0036]     The embodiments were described above merely as illustrative examples, but it is nothing to limit the invention in any way. Therefore, the invention can obviously be improved or modified in various ways without deviating from its essentials. For instance, a pre-plasticizing type is described as an example of the injection unit  11 . However, an in-line type injection unit is also applicable. Furthermore, driving means of the movable platen  5  is not restricted to the hydraulic press  6 . Hydraulic cylinder system, hydraulic toggle system, electric motor type cylinder system, electric-motor-drive toggle system, whatever, may be applicable. The present invention is also applicable to a frame-support type lens molding device in which load of the movable platen  5  is supported by the frame  2 .