Patent Publication Number: US-6702469-B1

Title: Resin molded article

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a resin molded article consisting of a plurality of members incorporated therein, more preferably, to a resin molded article eliminating the necessity of assembling steps and making it possible to easily obtain an appropriate clearance between the members. 
     2. Description of Prior Art 
     Equipment such as copying machines, printers, scanners or the like is structured by assembling many parts such as roller members for conveying sheets, gear members for transmitting driving force to the roller members, bearing members, and the like, and the parts to be used for the equipment are often constituted of resins. 
     In order to manufacture such a resin molded part, it is generally assumed that each of parts is first molded by injection molding or the like, and then two or more of the parts are assembled to constitute a unit. In the case of a gear unit, for example, a gear member and a bearing member are separately molded to be assembled together, and further a slip stopper is attached thereto for preventing those parts from slipping. In the case of a bearing unit, an outer ring, an inner ring, roller members to be arranged between the both rings, or the like are first molded, and then those are assembled to constitute a unit. 
     Such a conventional manner, however, requires a step of manufacturing independently a plurality of parts and then engagingly assembling those parts, which has become a factor in increasing costs. 
     In addition, when a plurality of parts were assembled, especially in the case of rotary members such as rollers, gears or the like, a clearance between the members was required to be controlled with accuracy, but measurement errors easily occured at the time of manufacturing independently a plurality of the parts. Therefore, maintaining control with accuracy was not easy. 
     SUMMARY OF THE INVENTION 
     The present invention was accomplished in view of the aforementioned conventional problems, and an object of the present invention is to provide a resin molded article that eliminates a step of independently manufacturing a plurality of parts and assembling them and that facilitates the control of a clearance between the members at a low cost. 
     In order to accomplish the aforementioned object, a representative structure according to the present invention is so constituted that at least a first resin material and a second resin material, which are substantially insoluble (having substantially no compatibility) in one another are used and molded by insert molding or two-color molding, in a state where the first resin material and the second resin material are incorporated, and a clearance is produced between the first member and the second member. 
     In the structure as mentioned above, since there is substantially insolubility between the first member and the second member, each of the plural members, molded by insert molding or two-color molding, is to be separated in a state of being assembled. This, therefore, eliminates the necessity of steps for assembling a plural number of parts. In addition, by making a mold shrinkage factor differ between the first resin material and the second resin material, a clearance between the members can be controlled easily and with good accuracy. 
     Thus, a bearing part, roller part or drive unit, which is constituted of incorporated plural members, can be easily manufactured. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects and features of the invention are apparent to those skilled in the art from the following preferred embodiments thereof when considered in conjunction with the accompanied drawings, in which: 
     FIG. 1 is a view of a bearing; (a) is a front elevation of the bearing; and (b) is a perspective explanation view of the bearing; 
     FIG. 2 is a perspective explanation view of a retainer retaining cylindrical rollers: 
     FIG. 3 is a perspective explanation view showing another example of a bearing of a first embodiment; 
     FIG. 4 is a partial cross-sectional explanation view showing yet another example of the bearing of the first embodiment; 
     FIG. 5 is a partial cross-sectional explanation view showing still yet another example of the bearing of the first embodiment; 
     FIG. 6 is a perspective explanation view of a conventional roller unit; 
     FIG. 7 is a view showing a roller unit according to a second embodiment; (a) is a perspective view; and (b) is a cross-sectional explanation view; 
     FIG. 8 is a cross-sectional explanation view showing another example of the roller unit of the second embodiment; 
     FIG. 9 is a front elevation explanation view of a one-way clutch according to a third embodiment; 
     FIG. 10 is a perspective explanation view of the one-way clutch; 
     FIG. 11 is an enlarged explanation view showing one roller member  22  at the time of forming the roller members  22  and a housing member  21  by insert molding or two-color molding; 
     FIG. 12 is a cross-sectional explanation view showing another example of the one-way clutch of the third embodiment; 
     FIG. 13 is a perspective explanation view showing further another example of the one-way clutch of the third embodiment; 
     FIG. 14 is a perspective explanation view of a drive unit according to a fourth embodiment; 
     FIG. 15 is a perspective explanation view showing another example of the drive unit of the fourth embodiment; 
     FIG. 16 is a perspective explanation view showing yet another example of the drive unit of the fourth embodiment; 
     FIG. 17 is a perspective explanation view showing still yet another example of the drive unit; 
     FIG. 18 is a perspective explanation view of a pendulum gear unit as another example of the drive unit; 
     FIG. 19 is a perspective explanation view of a pendulum gear unit as another example of the drive unit; 
     FIG. 20 is views showing a screw unit according to a fifth embodiment; (a) is a perspective view; and (b) is a cross-sectional explanation view; 
     FIG. 21 is a perspective explanation view showing another example of the screw unit; 
     FIG. 22 is views showing yet another example of the screw unit; (a) is a cross-sectional view; and (b) is a perspective explanation view; 
     FIG. 23 is a perspective explanation view of a conventional slide unit; 
     FIG. 24 is a perspective explanation view of a slide unit according to a sixth embodiment; 
     FIG. 25 is a perspective explanation view showing another example of the slide unit; 
     FIG. 26 is a perspective explanation view showing yet another example of the slide unit; 
     FIG. 27 is a perspective explanation view showing yet another example of the slide unit; 
     FIG. 28 is a cross-sectional explanation view of a conventional syringe; 
     FIG. 29 is a cross-sectional explanation view of a syringe unit according to a seventh embodment; 
     FIG. 30 is a cross-sectional explanation view showing another example of the syringe unit; and 
     FIG. 31 is a cross-sectional explanation view showing yet another example of the syringe unit. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Next, referring to the drawings, resin molded articles according to respective embodiment of the present invention will be specifically described. 
     First Embodiment 
     First, shown is a case where the present invention is applied to a bearing as a first embodiment. FIG. 1 is a view showing a bearing; (a) is a front elevation view of the bearing; and (b) is a perspective explanation view of the bearing. FIG. 2 is a perspective explanation view of a retainer in which cylindrical rollers are retained. 
     As shown in FIG. 1, the bearing is provided with an inner ring member  1  having an inner ring track on an outer peripheral surface of the inner ring member  1 ; an outer ring member  2  having an outer ring track on an inner peripheral surface of the outer ring member  2 ; cylindrical rollers  3 , as a plural number of roller members, provided between the inner ring track and the outer ring track in a freely rollable manner; and a retainer  4 , as a housing member, provided between the inner ring track and the outer ring track in a freely rotatable manner in a state of retaining the plural number of the cylindrical rollers  3 . 
     Molding can be made for forming the cylindrical rollers  3 , the retainer  4 , the outer ring member  2  and the inner ring member  1  by insert molding or two-color molding in a state as shown in FIG. 2, by using resin materials for the cylindrical rollers  3  and those for the retainer  4 , the outer ring member  2 , or the inner ring member  3  that are substantially insoluble in one another. Also, making a mold shrinkage factor of the material for the cylindrical rollers  3  larger than that of the material for the retainer  4  can secure a minute clearance of approximately 0.01 mm to 0.05 mm between the cylindrical roller  3  and the retainer  4 , where the cylindrical rollers  3  are freely rotatable in a state of being retained by the retainer  4 . Thus, the inner ring member  1  and the outer ring member  2  rotate smoothly through a plurality of the cylindrical rollers  3 . 
     It is to be noted that, as a first resin material constituting the cylindrical rollers  3  being insoluble and having a different mold shrinkage factor, it is preferable to use polypropylene, POM or the like, having a larger mold shrinkage factor than that of a second resin material. As the second resin material constituting the retainer  4 , it is preferable to use ABS, PS, polycarbonate or the like. 
     FIG. 3 is a perspective explanation view showing another example of the bearing of the first embodiment. 
     A bearing as shown in FIG. 3 is provided with cylindrical rollers  5  as a plural number of roller members, as well as with a retainer  6  as a housing member, retaining the cylindrical rollers  5  in a freely rotatable manner and having a cylindrical hollow portion, at the center, into which a shaft is designed to be fitted. Although each of the cylindrical rollers  5  is kept by the retainer  6  in a freely rotatable manner, a partial portion of the cylindrical roller  5  is designed to stick out to the cylindrical hollow portion of the retainer  6 . Then, when the shaft (not shown) is fitted to the cylindrical hollow portion of the retainer  6 , the partial portion of the cylindrical roller  5  is to protrude from an inner peripheral surface of the retainer  6 . Thus, the inner peripheral surface of the retainer  6  is not directly contacted with the outer peripheral surface of the shaft. Instead, the cylindrical rollers  5  are contacted with the shaft (not shown). 
     The cylindrical rollers  5  and the retainer  6  can be produced by insert molding or two-color molding in a state as shown in FIG. 4 with the resin materials being substantially insoluble in one another. In addition, making a mold shrinkage factor of the material for the cylindrical rollers  5  larger than that of the material for the retainer  6  can rotate freely the cylindrical rollers  5  in a state of being retained by the retainer  6 . 
     Thus, the retainer  6  concurrently serving as an outer ring member of the bearing and a shaft (not shown) fitting in the cylindrical hollow portion of the retainer  6  are to rotate smoothly through a plural number of the cylindrical rollers  5 . 
     FIG. 4 is a partial cross-sectional explanation view showing yet another example of the bearing of the first embodiment of the present invention. 
     As shown in FIG.  4 ( a ), this embodiment is provided with a plural number of the cylindrical rollers  5  and the retainer  6 , retaining the cylindrical rollers  5  in a freely rotatable manner, as well as having the cylindrical hollow portion, at the center, into which a shaft is fitted. The cylindrical roller  5  has stepped portions, consisting of roller shaft portions  5   a , with a small diameter, that is axially supported with the retainer  6  and a roller portion  5   b , with a large diameter, that is contacted with a shaft (not shown) fitted into the cylindrical hollow portion of the retainer  6 . 
     Also in this embodiment, the cylindrical roller  5  and the retainer  6  are formed by insert molding or two-color molding, by using the resin materials that are substantially insoluble in one another. In addition, by making the mold shrinkage factor of the cylindrical roller  5  greater than that of the material for the retainer  6 , the cylindrical roller  5  shrinks in both the shaft and radial directions to produce a minute clearance between the cylindrical roller  5  and the retainer  6 , with the result that the cylindrical roller  5  can freely rotate in a state of being retained by the retainer  6 . 
     Thus, by providing the cylindrical roller  5  with the stepped portions so that portions to be axially supported with the retainer are only limited to the roller shaft portions  5   a  having a smaller diameter than that of the roller portion  5   b , a resistance against sliding between the cylindrical roller  5  and the retainer  6  can be further reduced. 
     Furthermore, in order to make the resistance against sliding between the cylindrical roller  5  and the retainer  6  even smaller, the roller shaft portions  5   a  may have a conical shape as shown in FIG.  4 ( b ). 
     FIG. 5 is a partial cross-sectional explanation view showing yet another example of the bearing of the first embodiment. The bearing of the embodiment, as shown in FIG. 5, is constituted by assembling spherical balls  7  as a plural number of the roller members and a retainer  8 , as a housing, retaining the balls  7  in a freely rotatable manner, as well as having a cylindrical hollow portion into which a shaft (not shown) is to be fit in the center. 
     Although the retainer  8  retains the balls  7  in a manner incapable of dropping as well as in a freely rotatable manner, a partial portion of the ball  7  is designed to stick out to the side of the cylindrical hollow portion of the retainer  8 . When a shaft (not shown) is fitted into the cylindrical hollow portion of the retainer  8 , a partial portion of the ball  7  is to protrude from an inner peripheral surface of the retainer  8 , with the result that the inner peripheral surface of the retainer  8  is not directly contacted with an outer peripheral surface of the shaft. Instead, the balls  7  are contacted with the shaft (not shown). 
     The balls  7  and the retainer  8  are formed by insert molding or two-color molding by using the aforementioned materials that are substantially insoluble in one another. In addition, making a shrinkage factor of the material for the balls  7  greater than that of the material for the retainer  8  can make the balls  7  freely rotate while being retained by the retainer  8 . 
     With this arrangement, the retainer  8  concurrently serving as an outer ring member of the bearing and the shaft (not shown) fitted into the cylindrical hollow portion of the retainer  8  can rotate smoothly through a plural number of the balls  7 . 
     It is to be noted that radial bearings are exemplified in the aforementioned embodiments, but embodiments of thrust bearings can be structured in the same manner. 
     Second Embodiment 
     Next, an embodiment where the present invention is applied to a roller unit will be described as a second embodiment. 
     FIG. 6 is a perspective explanation view of a conventional roller unit. As shown in FIG. 6, the roller unit for pressing a sheet on a conveying roller or the like is conventionally structured by manufacturing two parts, independently as a roller member  100  and a shaft member  101 , which are later assembled. Then, a stop ring  102  is attached thereto in order for the roller member  100  not to slip in a shaft direction. This, however, results in an increase in cost, because such a method requires the assembling step. 
     Here, as shown in FIG. 7, the present embodiment is formed by molding the roller member and the shaft member in an already assembled state. Incidentally, FIG. 7 is a view showing a roller unit according to the second embodiment; (a) is a perspective view; and (b) is a cross-sectional explanation view. 
     As shown in FIG. 7, a roller member  10  is rotatable around a shaft member.  11 , where the shaft member  11  forms slip stopping portions  11   a  for preventing the roller member  10  from slipping in a shaft direction and the roller member  10  forms a fitted portions  10   a  for being fitted with the slip stopping portions  11   a . As in a state shown in FIG. 7, the insert molding or two-color molding is carried out with a combination of resin materials that are substantially insoluble in one another. For example, a combination of a resin material for the roller member  10  having a smaller mold shrinkage factor, such as ABS, PS, polycarbonate or the like, can be used with a resin material for the shaft member  11  having a larger mold shrinkage factor, such as polypropylene, POM or the like, to produce a roller unit. Since the mold shrinkage factor of the resin material selected for the shaft member  11  is greater than that of the resin material used for the roller member, after molding is completed, there is formed, between the roller member  10  and the shaft member  11 , a minute clearance of approximately 0.01 mm to 0.05 mm, which is in a range capable of assuring the rotation of the roller member  10 . Therefore, the roller member  10  is supported around the shaft member  11  in a freely rotatable manner. 
     In addition, a similar clearance is produced between the slip stopping portions  11   a  and the fitted portions  10   a , so prevention of the roller member  10  from slipping in the shaft direction is achieved without disturbing the rotation of the roller member  10 . 
     FIG. 8 is a cross-sectional explanation view showing another example of the roller unit of the second embodiment. In this example, a cylindrical elastic member  12  is provided on an outer peripheral cylindrical surface of the roller member  10 . 
     As for a rotation stopping of the roller member  10  and the elastic member  12 , resin materials having compatibility with one another may be utilized for fixing; or even with the resin materials that are substantially insoluble in one another, protrusions  11   b  for the rotation stopping may be formed on the outer periphery of the roller member  10  as shown in FIG.  8 ( a ). The material for forming the elastic member  12  is, for example, an elastomer or the like, which has a mold shrinkage factor greater than that of the material for forming the roller member  10 . Therefore, after molding is completed, the elastic member  12  is to tighten the roller member  10 . Thus, the rotation stopping becomes further strengthened. 
     As for a stoppage in a thrust direction of the roller member  10  and the elastic member  12 , resin materials that are soluble in one another may be utilized for fixing; or even with the resin materials that are substantially incompatible with one another, protrusions  10   c  for the thrust stopping may be formed in the roller member  10  as shown in FIG.  8 ( b ). 
     Thus, as mentioned above, a roller unit is formed with a combination of resin materials that are substantially insoluble in one another at least for the roller member  10 , the shaft member  11 , the elastic member  12 , which are provided by insert molding or three-color molding. 
     Since the mold shrinkage factor of the elastic member  12  is greater than that of the material for forming the roller member  10 , a minute difference in level, indicated by L as shown in FIG. 8, is produced. Thus, when the roller member  10  is incorporated into a product, only the roller member  10  is in a frictional sliding movement with respect to the shaft member  11  and the elastic member  12  is not in a frictional sliding movement with respect to the shaft member  11 . Especially in the case where the elastic member  12  is a friction member, an increase in a sliding load can be prevented. 
     It is to be noted that, as the elastic member  12 , various types of materials such as those having an elasticity, high friction coefficient, low friction coefficient, water repelling ability, or the like are usable. 
     Third Embodiment 
     Next, an embodiment where the present invention is applied to a one-way clutch will be described as a third embodiment. 
     Generally, clutches used in power transmission systems include a one-way clutch for transmitting a rotary torque in one direction only, when a drive shaft is reversely rotated. This construct is used in various types of apparatuses, such as image forming apparatuses. 
     The aforementioned one way clutch employs various types of structures. In a wrap spring type one-way clutch, for example, one end of a coiled spring is secured to a drive shaft, while the other end portion of the coiled spring is wrapped around a driven shaft, and a torque is transmitted by winding the coiled spring in a forward rotation. The coiled spring is relaxed to be freely rotatable in a reverse rotation. In a roller type one-way clutch, a portion of an outer peripheral surface of an inner ring member and a portion of an inner peripheral surface of an outer ring member are designed to approach each other in a peripheral direction. A roller forced by the spring is interposed therebetween, where, in a forward rotation, the roller is moved, resisting the spring is force, to be fitted between both rings, thus to transmit a torque. In a reverse rotation, the roller becomes free. 
     In order to manufacture the one-way clutches as mentioned above, plural assembly steps are required to put tog ether respective parts after those parts are molded independently. 
     In the present invention, as shown in FIG. 9, roller members having a cylindrical shape respectively, as well as a housing member including retainer portions for retaining the roller members and, at its center, a fitted portion to which a shaft is to be fitted are formed by insert molding or two-color molding in an already assembled state, thereby eliminating the necessity of the assembling steps. FIG. 9 is a front elevation of a one-way clutch according to the third embodiment, and FIG. 10 is a perspective explanation view of the one-way clutch. 
     In the one-way clutch of the present embodiment, a drive force is inputted from an input shaft  20  to be outputted to a housing member  21  as an outer ring member of the one-way clutch. 
     The housing member  21  forms a fitted portion  21   a  to which the input shaft  20  to be fitted and retainer portions  21   b  for retaining cylindrical roller members  22 , which can freely rotate at the retainer portions  21   b . The roller members  22  are formed by insert molding or two-color molding, using a resin material that is substantially insoluble in the housing member  21 . In addition, by using the material for the roller member  22  having a greater mold shrinkage factor than that of the material for housing member  21 , the housing member  21  retains the roller members  22  with a slightly uneven surface. 
     When the input shaft  20  is fitted to the fitted portion  21   a , the retainer portion  21   b  is structured so that a distance between an inside wall surface  21   b   1  and the input shaft  20  is to be shorter than the diameter of the roller member  22  in one side (locked side) and longer in the other side (unlocked side) with respect to the rotating direction. In addition, the housing member  21  is provided with elastic members  21   c  for forcing the roller members  22  into the locked side of the inside wall surface  21   b   1  of the retainer portion  21   b , and the same material as that of the housing member  21  is used for the elastic members  21   c  and it is molded integrally and simultaneously with the housing member  21 . 
     FIG. 11 is an enlarged explanation view of one roller member  22  when the roller members  22  and the housing member  21  are formed by insert molding or two-color molding. Although the roller member  22  and the housing member  21  are in contact with each other at a contacting portion  21   d , since they are molded from resin materials that are substantially insoluble in each other, the roller member  22  is detached from the housing member  21  after molding is completed. At the time of driving, the roller member  22  is designed to exist in a position indicated by a dotted line in FIG.  11 . 
     When the driving force is inputted into the input shaft  20  and the input shaft  20  is rotated in a direction indicated by arrow A in FIG. 11, each of the roller members  22  in the retainer portion  21   b  becomes sandwiched in the narrow, locked side between the inside wall surface  21   b   1  and the input shaft  20 , and then the input shaft  20  and the housing member  21  are in a locked state. Due to this, the driving force is transmitted from the input shaft  20  through the respective roller members  22  to the housing member  21 , and the housing member  21  is to be rotated in the same direction. 
     On the other hand, when the input shaft  20  receives the driving force to move in a direction indicated by arrow B in FIG. 11, each of the roller members  22  tends to move to the wider unlocked side between the inside wall surface  21   b   1  and the input shaft  20 , and the roller member  22  comes to be in a unlocked state, capable of freely rotating in the retainer portion  21   b . Therefore, the input shaft  20  runs idle without transmitting the driving to the housing member  21 . 
     As mentioned above, by forming the roller members  22  and the housing member  21  by insert molding or two-color molding with the use of the resin materials that are substantially insoluble in one another, a predetermined space between the roller member  22  and the housing member  21 , is secured in order to achieve the molded article in an already assembled state. Therefore, the one-way clutch can be easily manufactured. 
     FIG. 12 is a cross-sectional explanation view showing another example of the one-way clutch of the third embodiment. The one-way clutch shown in FIG. 12 is formed, in the same manner as that in FIG. 9, by insert molding or two-color molding with the use of the resin materials that have substantially no compatibility with one another. 
     In the aforementioned one-way clutch, the elastic member  21   c  for forcing the roller member to the locked side is formed with the same material as that of the housing member and molded integrally therewith. In this example, on the other hand, an elastic member  23  for forcing the roller member  22  to the locked side is formed by two-color molding with a resin material, which is soluble (has compatibility) with the housing member  21 , but is of a different kind. Thus, a material having an elasticity suitable for the function of forcing the roller member  22  to the locked side of the retainer portion  21   b  can be used for the elastic member  23 . 
     In addition, FIG. 13 is a perspective explanation view showing yet another example of the one-way clutch of the third embodiment. In this one-way clutch, elastic members  24   a  are integrally molded with a frame  24 , which is separated from the housing member  21 , and the elastic members  24   a  (and the frame  24 ) and the housing member  21  are molded, by two-color molding, from the resin materials that are substantially insoluble in one another. With this configuration, the same effects can be obtained as those in the aforementioned embodiments. 
     Fourth Embodiment 
     Next, an embodiment where the present invention is applied to a drive unit will be described as a fourth embodiment. FIG. 14 is a perspective explanation view of the drive unit according to the fourth embodiment. 
     In FIG. 14, a gear member  30  has a shape in which a shaft portion  30   b  having a common center with a gear portion  30   a  is protruding. A bearing member  31  is provided with a hollow portion  31   a  placed so as to be engaged with the shaft portion  31   b . With this configuration, the gear, retained by the bearing member  31 , becomes rotatable. The drive unit constituted of the gear member  30  and the bearing member like.  31  is used in various types of apparatuses such as an image forming apparatuses or the 
     As for the two members of the drive unit, used are the resin materials being substantially insoluble due to their different melting points or the like. The materials having no compatibility include, for example, a polybutylene and polystyrene, and the like. With these materials, two-color molding by injection molding is carried out. At this time, the materials in use are so selected that a mold shrinkage factor of the gear member  30  is greater than that of the bearing member  31 . Due to this, after the molding is completed, there is obtained, between the gear member  30  and the bearing member  31 , a clearance that can assure the rotation of the gear member  30 . In FIG. 14, the clearance is shown as being larger so as to make sure that the shaft portion  30   b  of the gear member  30  is inserted into the bearing member  31 . Practically however, the clearance is desirably set from 0.01 mm or higher to 0.1 or lower. 
     By carrying out the insert molding or two-color molding in a state shown in FIG. 14, the drive unit with two assembled members can be manufactured at one time. Also, the step of assembling the members after molding can be eliminated. The drive unit thus formed can be used widely as a part of a torque transmission drive of a respective mechanical apparatus. 
     FIG. 15 is a perspective explanation view showing another example of the drive unit of the fourth embodiment. The drive unit shown in FIG. 15 is constituted of the gear member  30  and the bearing member  31 . This embodiment has a different point from the embodiment shown in FIG. 14 in that a diameter of the tip of the shaft portion of the gear member  30  is made larger to form a slip stopping portion  30   b   1 . 
     The slip stopping portion  30   b   1  has a function of preventing the gear member  30  from slipping down after the gear member  30  hits the wall of the bearing member  31  when moving from side to side. Generally, it is difficult for the drive unit having this type of shape to be provided with a slip stopping shape of sufficient strength. This is because the slip stopping structure, if it is formed, becomes a hindrance when the gear member is incorporated, causing that the gear member not to be incorporated or leading to the gear member not being provided with sufficient strength. In order to deal with this problem, a slip stopping member is added, and the bearing member is incorporated into the gear member, and thereafter the slip stopping member is assembled, thereby increasing the number of the assembly steps. 
     In the present invention, on the other hand, molding can be carried out by insert molding or two-color molding in a state of being incorporated, and therefore the drive unit with the number of parts and the number of assembly steps greatly reduced can be provided. 
     FIG. 16 is a perspective explanation view showing yet another example of the drive unit of the fourth embodiment. The drive unit shown in FIG. 16 has a different point from the embodiment shown in FIG. 14 in that the gear member forms a hollow portion and the bearing member forms a shaft portion. 
     In other words, in this embodiment, the gear member  32  includes a gear portion  32   a  and a hollow portion  32   b  having a common center with the gear portion  32   a . The bearing member  33  is, on the other hand, provided with a shaft portion  33   a  which is designed to engage the hollow portion  32   b . As for materials used for the respective members, in the same manner as in the aforementioned drive unit in FIG. 14, usable are such materials that are substantially insoluble (for example, a polybutylene and polystyrene, or the like) due to their different melting, points, or the like. Then, with these materials, insert molding or two-color molding by injection molding is carried out. 
     Contrary to the case of the drive unit in FIG. 14, the materials for use in this embodiment are so selected that a mold shrinkage factor of the bearing member  33  is larger than that of the gear member  32 . Due to this, after the molding is completed, there is obtained, between the gear member  32  and the bearing member  33 , a clearance, which can assure the rotation of the gear member  32 . Thus, by carrying out insert molding or two-color molding, manufacturing can be achieved without the need for assembly, with the plural members being incorporated. 
     FIG. 17 is a perspective explanation view showing yet another example of the drive unit. The drive unit shown in FIG. 17 is a drive unit using plural numbers of gears. 
     In other words, a first gear member  34  is constituted of a gear portion  34   a  and a hollow portion  34   b  having a common center with the gear portion  34   a . A second gear member  35  is constituted of a gear portion  35   a  and a shaft portion  35   b  having a common center with the gear portion  35   a . Further, a base member  36  is structured so as to support both gear members in a position where the first gear member  34  and the second gear member  35  are engaged. 
     The base member  36  is provided with a shaft portion  36   a  in a protruding manner in a position opposite to the first gear member  34 , so the shaft portion  36   a  is engaged with the hollow portion  34   b  of the first gear member  34 . The base member  36  is further provided with a hollow portion  36   b  in a position opposite to the second gear member  35 , so the shaft portion  35   b  of the second gear member  35  is structured to engage the hollow portion  36   b . Thus, the first gear member  34  and the second gear member  35  are rotatably retained by the shaft portion  36   a  and the hollow portion  36   b  of the base member  36 , respectively. 
     The base member has a function of controlling a distance between the shafts of the first gear member  34  and the second gear member  35 , as well as of retaining both gear members  34  and  35 . Thus, there can be formed a drive unit usable in the various types of apparatuses and constituted of gear series and a base member for retaining the gear series. 
     Here, the materials used for the three members of the drive unit are those that are substantially insoluble due to their different melting points. The materials having substantially no compatibility are, for example, polybutylene and polystyrene, as mentioned above. Then, with the use of these resin materials, a three-color molding by injection molding is carried out. 
     At this time, the three kinds of the materials are selected to have mold shrinkage factors such that the first gear member has a mold shrinkage factor smaller than the base member and the mold shrinkage factor of the base member is smaller than that of the second gear member (the first gear member &lt;the base member &lt;the second gear member). Thus, after molding is completed, there are obtainable a clearance between the hollow portion  34   b  of the first gear member  34  and the shaft portion  36   a  of the base member  36 , as well as a clearance between the hollow portion  36   b  of the base member  36  and the shaft portion  35   b  of the second gear member  35 . These clearances can assure the rotation of the respective gears. It is to be noted that a value of the clearance may be the same as that in the aforementioned drive unit in FIG.  14 . 
     With this arrangement, a gear series unit engaging the plural gear members can be molded by three-color molding or the concurrent use of insert molding and two-color molding in an already assembled form thereby capable of greatly decreasing the number of parts and the number of assembly steps. 
     FIG. 18 is a perspective explanation view of a pendulum gear unit shown as still further example of the drive unit. This unit is constituted of a gear member  37  having a gear portion  37   a  and a hollow portion  37   b , which has the same center with the gear portion  37   a , and a base member  38  having a shaft portion  38   a  designed to be fitted into hollow portion  37   b . By making the shaft portion  38   a  fit into the hollow portion  37   b , the gear member  37  can be rotated. In addition, the base member  38  forms the hollow portion  38   b , and, when a shaft (not shown) or the like is fitted into this hollow portion  38   b , thus to retain the base member  38 , the base member  38  becomes rotatable on the hollow portion  38   b  as a center in the directions indicated by arrows in FIG.  18 . Consequently, the gear member  37  functions as a pendulum gear. 
     Here, the materials used for the gear member  37  and the base member  38  are such that they are substantially insoluble due having different melting points, or the like. Then, the materials are selected so that a mold shrinkage factor of the base member  38  is greater than that of the gear member  37 . With this arrangement, in the same manner as in the embodiments mentioned above, molding can be carried out by insert molding or two-color molding so that the gear member  37  and the base member  38  are already incorporated and a predetermined clearance is obtained at the rotating portion. 
     FIG. 19 is a perspective explanation view of a pendulum gear unit shown as a still further example of the drive unit. This unit is provided by extending the shaft portion  35   b  of the second gear member  35  of the gear series unit shown in FIG. 17 to make the base member  36  swingable on the shaft portion  35   b  as a center in a direction indicated by an arrow in FIG. 19, thereby serving as a pendulum gear unit. Thus, the pendulum gear unit with the plural gear members engaged can be easily manufactured. 
     Fifth Embodiment 
     Next, an embodiment where the present invention is applied to a screw unit will be described as a fifth embodiment. FIG. 20 shows a screw unit according to the fifth embodiment; (a) is a perspective view and (b) is a cross-sectional explanation view. 
     Referring to FIG. 20, a male screw member  40  is a first member constituted of a male screw portion  40   a  and a head portion  40   b  having a knurled portion  40   b   1  around it. A female screw member  41  is a second member and includes a female screw portion  41   a , which is spirally engaged with the male screw portion  40   a.    
     The male screw member  40  and the female screw member  41  are molded from resin materials that are substantially insoluble in one another due to their different melting points, or the like. As a result, two-color molding in an assembled state as shown in FIG.  20 ( b ) can be achieved. 
     In addition, in this embodiment, the resin materials constituting the male screw member  40  and the female screw member  41  have approximately the same mold shrinkage factors. For example, a combination of polypropylene with nylon or the like is used as the resin materials for the male screw member  40  and the female screw member  41 . Due to this, defects after molding, such as galling caused by inconformity of a screw thread, are preventable. 
     Then, since the both materials are substantially insoluble in one another, they are separated and are capable of being released from the screw fastening as needed. In this embodiment, it is to be noted that the male screw portion  40   a  can be removed from the female screw member  41  by manually turning the knurled portion  40   b   1  formed in the male screw portion  40   a . It may also be possible to remove the male screw portion by providing a bit hole for a driver on the head portion of the screw, instead of using the knurled portion. 
     Thus, by carrying out the insert molding or two-color molding with the materials that are substantially insoluble in one another, the male screw member and the female screw member are molded in an already assembled state, thereby decreasing the number of assembly steps. 
     FIG. 21 is a perspective explanation view showing another example of the screw unit. The screw unit shown in FIG. 21 is a unit molded by three-color molding with the materials insoluble in each other, so that an intermediate member  42  is sandwiched between the male screw portion  40  and the female screw portion  41  shown in FIG.  20 . 
     As a material for constituting the intermediate member  42 , a material having a smaller mold shrinkage factor than those of the male screw member  40  and the female screw member  41  is used. Examples of such a material include ABS, PS, polycarbonate, or the like. Due to this, after molding is completed, the intermediate member  42  is fastened by the male screw member  40  and the female screw member  41 . Therefore, the mold, with, no assembly unevenness, can be provided for use as it is. Then, the intermediate member  42  can be removed by manually turning the knurled portion  40   b   1  of the male screw member  40  in the same way as that of the aforementioned embodiment. 
     FIG. 22 shows yet another example of the screw unit; (a) is a cross-sectional view and (b) is a perspective explanation view. The screw unit shown in FIG. 22 includes a male screw member  43  as a first member constituted of a male screw portion  43   a  and a head portion  43   b  having, around it, a bit hole  43   b   1  for a driver; and a washer member  44  as a second member, which is fitted in a freely rotatable manner around a straight portion  43   c  at the root of the screw portion of the male screw member  43 , but which is so structured not to be re moved due to the male screw portion  43   a  of the male screw member  43  serving as a slip stopper. 
     Then, the male screw member  43  and the washer member  44  can be manufactured by two-color molding with resin materials being substantially insoluble in each other in the same way as the aforementioned screw unit. At this time, the resin materials are selected so that a mold shrinkage factor of the resin material for the male screw member  43  is greater than that for the washer member  44 . Due to this, the washer member  43  is freely rotatable with respect to the male screw member  43  without falling off. 
     It is to be noted that the washer member is not limited to the flat washer, but various types of washers, for example, a spring washer, a washer with dents, or the like are applicable as the washer member. 
     Sixth Embodiment 
     Next, an embodiment where the present invention is applied to a slide unit will be described as a sixth embodiment. 
     FIG. 23 is a perspective explanation view of a conventional slide unit. Conventionally, as shown in FIG. 23, a rail member  200  having a rail portion  200   a  and a slide member  201  moving along the rail portion  200   a  have been independently manufactured as a first member, and further a slip stopping member  202  has been added, with the result that the slide unit has been manufactured by engagingly assembling those three members. 
     This method, however, requires the step of independently manufacturing these three parts and thereafter engagingly assembling these parts, which has become a factor in increasing cost. In addition, since each part has been independently manufactured, errors in size and shape easily occur. Further, the slip stopping member  202  is required to prevent the sliding member from slipping off from the rail member  200 , thereby increasing the number of the parts. 
     Hence, the present embodiment, solving these problems, is to provide a slide unit, which is easily manufactured without causing the errors in size and shape. 
     FIG. 24 is a perspective explanation view of a slide unit according to the sixth embodiment. A rail member  50  as a first member is engaged with a slide member  51  is a second member, which is slidable along the rail member  50 . The slide member  51  is guided by a rail portion  50   a  of the rail member  50 . 
     The slide member  51  is provided with screw holes  51   a . With the use of the screw holes  51   a , an apparatus (not shown) is to be attached. Thus, the present slide unit is usable as a slide unit mechanism in various kinds of mechanical apparatuses. 
     It is to be noted that, as materials for the rail member  50  and the slide member  51  constituting the slide unit, materials that are substantially insoluble in each other due to their different melting points or the like are used. Here, it is preferable to use, for example, a polybutylene and polystyrene, or the like as the materials having substantially no compatibility. Then, for example, two-color molding is carried out by injection molding with the use of the resin materials. 
     The materials are selected so that a mold shrinkage factor of the material for the rail member is greater than that for the slide member, when the injection molding is carried out. Due to this, after molding is completed, there is obtained between the rail member  50  and the slide member  51  a clearance, which can assure the movement of the slide member. With this arrangement, as shown in FIG. 24, manufacturing can be carried out at one time by insert molding or two-color molding so that rail member  50  and the slide member  51  are formed in an assembled state. 
     It is to be noted that the present embodiment has a structure where the screw holes  51   a  are provided so as to attach another mechanical apparatus, but when the other apparatus is not required to be attached to the slide member, for example, the slide member is used as a density control knob or the like in an image forming apparatus, the screw holes  51  are not required to be provided. 
     FIG. 25 is a perspective explanation view showing another example of the slide unit. In the slide unit shown in FIG. 25, the slip stopping portion  50   b  for preventing the side member  51  of the aforementioned slide unit in FIG. 24 from slipping down is integrally formed with both end portions in a sliding direction of the shown rail member  50 . Thus, when sliding to the end portion of the rail portion  50   a , the old slide member  51  does not hit the slip stopping portion  50   b  and then fall off from the rail member  50 . 
     FIG.  25 ( b ) is a bottom plane view of the slide unit shown in FIG.  25 ( a ), and at the bottom surface of the rail member  50 , there is an angular hollow portion  50   c  as an extracting hollow in consideration of injection molding. 
     Generally, it is difficult for the slide unit having this type of shape to be provided with a slip stopping shape of sufficient strength. This is because the slip stopping structure, if it is formed, becomes a hindrance when the slide member is incorporated, resulting in the slide member not being incorporated or not having sufficient strength. In order to deal with this problem, conventionally, a slip stopping member is added, and the slide member  51  is incorporated into the rail member  50 . Thereafter, the slip stopping member is assembled. However, the present embodiment can provide the slide unit with the number of parts and the number of the assembly steps greatly decreased. 
     FIG. 26 is a perspective explanation view showing yet another example of the slide unit. The slide unit shown in FIG. 26 is constituted of three parts in a rod antenna shape, the three parts including a front end member  52  as a first member, an intermediate member  53  as a second member, and a rear end member  54  as a third member. In addition, this embodiment is provided with slip stopping portions  53   a  and  54   a  respectively for the intermediate member  53  and the rear end member  54 . 
     Each of the three members  52 ,  53 , and  54  is retractably movable along its adjacent members. At this time, the materials for the three parts are substantially insoluble in the same manner as those in the aforementioned embodiment, but the same materials may be used for the front end member  52  and the rear end member  54  as long as the intermediate member  53  has substantially no compatibility with the front end member  52  and the rear end member  54  respectively. This means that, when a structure includes three or more members, the members can slidingly move as long as each of the parts has substantially no compatibility only with its adjacent members. In addition, the materials are selected so that mold shrinkage factors of the parts decrease in the order starting from the front end member  53 , which has the greatest mold shrinkage factor, to the intermediate member  53  and to the rear end member  54 , which has the smallest mold shrinkage factor. Due to this, clearances between the respective adjacent members can be obtained. 
     With the structure as mentioned above, a slide unit including two or more parts in a retractable rod antenna shape with a slip stopping mechanism can be manufactured. Thus is also usable as a retractable shaft, an antenna by providing its material an electroconductive property, and further a tray having a flat shape. 
     FIG. 27 is a perspective explanation view showing further another example of the slide unit. The slide unit shown in FIG. 27 is constituted of a shaft member  55  and a bearing member  56 . In this case, manufacturing is performed by two-color molding where the shaft member  55  is first molded and thereafter the bearing member  56  is molded. When molding is being conducted, the bearing member  56  is molded in a shape following the outside shape of the shaft member  55 . Thus, a relation between the size of the outside shape of the shaft member  55  and the size of the hollow of the being member  56  is maintained, thereby securing an appropriate clearance therebetween. 
     Although the materials for the two members are substantially insoluble in one another in the same manner as in the aforementioned embodiment, only the mold shrinkage factors of the two, materials can control the size of the outside shape of the shaft member and the size of the hollow of the bearing member. That is, the materials are selected so that a mold shrinkage factor of the shaft member  55  is greater than that of the bearing member  56 . Thus, a stable slide bearing unit with a controlled clearance between the shaft member and the bearing member controlled can be manufactured. This unit can be used as a carrier unit of a typewriter or the like. It is to be noted that the shaft member  55  has an ecliptic cross-sectional shape, but it may be a square bar shape, and a freely shaped shaft member and a bearing member with a shape following that of the shaft member can be manufactured. 
     Seventh Embodiment 
     Next, an embodiment where the present invention is applied to a syringe unit will be described as a seventh embodiment. 
     FIG. 28 is a perspective explanation view of a conventional syringe. As shown in FIG.  28 ( a ), the syringe is conventionally constituted of three parts including a cylinder member  300 , a piston member  301 , and an elastic member  302 , where the elastic member  302  is fitted to the piston member  301  beforehand, as shown in FIG.  28 ( b ), and the members thus fitted together are then inserted into the cylinder member  300 , thereby manufacturing a finished article. 
     This method, however, requires assembling three parts into an integral form, thereby increasing not only time but also cost. Furthermore, sanitary management is required until the assembly process is completed. In addition, a clearance is always produced as shown in FIG.  28 ( b ), because the piston member  301  and the elastic member  302  are to be assembled, and this allows chemicals or foreign materials to be mixed easily, and therefore it is unfavorable in terms of management. 
     Hence, the present embodiment, solving these problems, is to provide a syringe unit that eliminates assembly operations and facilitates clearance management. 
     FIG. 29 is a cross-sectional explanation view of a syringe unit according to the seventh embodiment, and the syringe unit is constituted of a cylinder member  60  and a piston member  61 . The cylinder member  60  and the piston member  61  are molded by insert molding or two-color molding in a state of being incorporated as shown in FIG.  29 ( a ) with the use of a combination of resin materials that are substantially insoluble in one another. 
     At a first stage of the molding operation, as shown in FIG.  29 ( b ), a transparent resin material is first molded into the cylinder member  60 . Next, a resin material having substantially no compatibility with the cylinder member  60  is molded into the piston member  61 , thereby manufacturing the syringe unit with the cylinder member  60  and the piston member  61  incorporated as shown in FIG.  29 ( a ). 
     Here, the material used for molding the piston member  61  is selected so as to have a smaller mold shrinkage factor than that of the cylinder member  60 . With this selection, after molding is completed, a moderate binding force is applied to the piston member  61  by means of the cylinder member  60 , so sealing property as a pump can be obtained. 
     In addition, because the materials used for molding the cylinder member  60  and the piston member  61  are substantially insoluble in one another, they are not united. As a result, the piston member  61  can be freely moved in a shaft direction indicated by an arrow shown in FIG.  29 ( c ). 
     FIG. 30 is a cross-sectional explanation view showing another example of the syringe unit. The syringe unit shown in FIG.  30 ( a ) is a unit that is the same as the syringe unit in FIG. 29, except that an elastic member  62  for a sealing purpose is also provided. Similar to the aforementioned syringe unit, the materials for cylinder member  60  and the piston member  61  are resin materials having substantially no compatibility with one another. The materials for the elastic member  62  and the cylinder member  60  are also in a combination of the resin materials that are substantially insoluble in one another, but the materials for the elastic member  62  and the piston member  61  are soluble in one another. It is to be noted that rubbers, elastic materials such as elastomer or the like, are preferably used as the elastic member  62 . 
     In order to mold this unit, as shown in FIG.  30 ( b ), a transparent resin material is first molded into the cylinder member  60 . Next, as shown in FIG.  30 ( c ), a resin material that is substantially insoluble in the cylinder member  60  is molded into the elastic member  62 . Finally, a resin material that is soluble in the elastic member  62  is molded into the piston, thereby forming the syringe unit as shown in FIG.  30 ( d ). 
     Only the elastic member  62  and the piston member  61  are united from the standpoint of the presence or absence of the compatibility with one another. As a result, in the syringe unit after it is completed, the piston member  61 , can be freely moved in a shaft direction shown by an arrow in FIG.  30 ( d ). In addition, since the mold shrinkage factor of the material for molding the elastic member  62  is smaller than that for the cylinder member  60 , after molding is completed, a moderate binding force is applied to the elastic member  62  by a means of the cylinder member  60 , and the elastic member  62  is fitted to the inside surface of the cylinder with a predetermined interference, thereby providing a sealing property as a pump. 
     FIG. 31 is a cross-sectional view showing yet another example of the syringe unit. In the syringe unit shown in FIG. 31, the elastic member  62  and the piston member  61  of the syringe unit shown in FIG. 30 are now structured with the use of a combination of resin materials that are substantially insoluble in one another. 
     In this case, where the combination of the resin materials that substantially insoluble in one another is used for the elastic member  62  and the piston member  61 , after molding is completed, the elastic member  62  and the piston member  61  are not united. Therefore, when the piston member  61  is moved, the elastic member  62  is detached therefrom. In order to prevent this problem, there may be provided with a slip stopping structure, which can prevent the elastic member  62  from being separated from the piston member  61 . 
     In order to form the structure as shown in FIG.  31 ( a ), an anchor portion  63  is provided to the piston member  61 . With this arrangement, the elastic member  62  and the piston are united, so that such a situation, after molding is completed, is preventable because the elastic member  62  is to be detached when the piston member  61  is moved. It is to be rioted that FIG.  31 ( b ) shows a situation in the middle of the molding stage, where the elastic member  62  is molded after the cylinder member  60  has been molded, and at this time, it is required for the convenience of the mold that a diameter D 1  of a portion corresponding to the anchor portion  63  be smaller than a diameter D 2  of the discharging portion of the cylinder member  60 . 
     By providing the anchor portion  63  as mentioned above, the elastic member  62  and the piston member  61  can be structured with the use of a combination of the resin materials that are substantially insoluble in one another. 
     In the present invention structured as mentioned above, since there is substantial insolubility between the first member and the second member, each of the plural members, molded by insert molding or two-color molding, is to be separated in an assembled state. This, therefore, eliminates the necessity of assembly steps for the plural parts. In addition, by making a mold shrinkage factor vary between the first resin material and the second resin material, a clearance between the members can be controlled easily and with good accuracy. 
     Thus, a bearing part, roller part or drive unit, which is constituted of incorporated plural members, can be easily manufactured.