JP2000141381A - Disc-shaped plastic molded product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow the outer peripheral surface of various kinds of disc-shaped plastic molded product to have a highly accurate transferred surface by fixing the position of an untransfer part by prescribing the shape and size of the untransferred part and controlling the quantity of generation of a sink. SOLUTION: At least one of the outer and inner peripheral parts of a disc- shaped plastic injection-molded product 1 has a transfer part 3 and the other part thereof has at least one untransferred part 2a. By this constitution, a sink is preferentially generated in the untransferred part 2a to prevent the generation of the sink in the outer peripheral surface 3 requiring a highly accurate transfer surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to precision transmission parts such as gears (spur gears, bevel gears, straight bevel gears, etc.) and pulleys, and in particular, paper for precision equipment such as digital copying machines, printers and facsimile machines. This relates to a high-precision disc-shaped plastic molded product used for transmission elements such as a feed drive mechanism and a photoreceptor drive mechanism, and by controlling the amount of sink marks by fixing the position of the untransferred part, The outer peripheral surface of the disk-shaped plastic molded product (transparent amorphous resin such as polycarbonate, acrylic and amorphous polyolefin, opaque crystalline resin such as polyacetal and polyamide, and resin molded product such as inorganic-filled reinforced polycarbonate) This is effective for making an accurate disk shape.

[0002]

2. Description of the Related Art In a normal injection molding method, a resin is injected and filled into a cavity having a fixed volume where the mold temperature is about the thermal deformation temperature of the resin, and after cooling while controlling the holding pressure, the mold is opened. And take out the molded product. In this way, even if the high-precision machined surface of the mold cavity corresponding to the outer peripheral surface of the disk is transferred to produce a high-precision disk-shaped plastic molded product, the temperature distribution during cooling becomes the pressure distribution as it is. As a result, the density distribution and the shrinkage are non-uniform, so that a plastic molded article having a highly accurate transfer surface cannot be obtained. In particular, uneven thickness, a thick shape, and a shape having ribs, uneven distribution of pressure occurs, and when using a crystalline resin, a shrinkage distribution due to a crystallinity distribution is also added, and high accuracy. No molded product is obtained. On the other hand, there is known a molding method in which a mold temperature is kept constant around its thermal deformation temperature, and after injection filling at a low pressure, a compression mechanism is provided in the mold to compensate for shrinkage due to cooling and solidification of the resin. Since this method involves compression from a certain direction, it is affected by temperature distribution and pressure distribution due to quenching and solidification of the resin. During compression, pressure is unevenly distributed in the compression direction and the direction perpendicular to the compression direction. Since it is difficult to apply the resin in the same direction, a molded product with high accuracy cannot be obtained (see Japanese Patent Application Laid-Open No. 63-114614). On the other hand, for resin molded products such as gears having an annular portion, it is known that the annular portion has a thin hollow structure over substantially the entire circumference in order to prevent sinks from occurring in the thick annular outer peripheral portion. In this case, since the hollow portion is formed over substantially the entire circumference of the annular portion, the portion has to be enlarged in order to secure the strength and rigidity of the annular portion. As a result, the molded product itself becomes large. (See Japanese Patent Application Laid-Open No. H8-156053).

[0003]

In the case of the former one of the above-mentioned conventional molding methods, sink is generated not only on the outer peripheral surface but also on other surfaces, and the position and amount of the sink are controlled. Therefore, it is not possible to manufacture a disc-shaped plastic molded product having a highly accurate outer peripheral surface. In the latter method for avoiding this problem, it is inevitable that the molded product becomes large due to the hollow structure. The present invention fixes the position of the untransferred portion by defining the shape and size of the untransferred portion, and controls the amount of generation of sink marks so that the outer peripheral surface of various disc-shaped plastic molded products can be reduced. An object of the present invention is to devise the shape of a disc-shaped plastic molded product and a method of manufacturing the same so as to obtain a highly accurate transfer surface.

[0004]

Means for solving the above problems are as follows. For a disk-shaped plastic injection molded product, at least one of an outer peripheral portion and an inner peripheral portion has a transfer portion, and at least one of the other portions has a transfer portion. By having the above-mentioned untransferred portion, the sink is preferentially generated in the untransferred portion, so that the sink is not generated on the outer peripheral surface where a highly accurate transfer surface is required.

[0005]

[Embodiment 1] Embodiment 1 is that the shape of the outer peripheral portion of the above solution 1 is a tooth shape having irregularities in the circumferential direction. In the second embodiment, a high-precision molded product cannot be obtained unless the untransferred portion is formed in a ring shape, that is, if the untransferred portion is not provided corresponding to the transfer portion. The transferred portion is an outer peripheral portion, and in a disk shape, the outer peripheral surface perpendicular to the rotation center axis is substantially circular, so that the untransferred portion is also formed in a ring shape corresponding to the transfer portion. . In addition, the above "ring shape"
A shape formed by two circular shapes (including approximate circles, arcs, repetitions of arcs, ellipses, etc.), or 2
The surface portion formed by the two circular shapes is the untransferred portion. When the diameter of the circular shape is almost equal, the shape is a cylindrical shape, and the portion of the cylinder is an untransferred portion.
It comes in various shapes. Embodiment 3 is that the above-mentioned ring-shaped untransferred portion of Embodiment 2 forms a concentric circle with the outer peripheral circle of the transfer portion. Embodiment 4 is that the above-mentioned ring-shaped untransferred portion of Embodiment 3 is composed of a plurality of small untransferred portions. In a fifth embodiment, the ratio of the untransferred portion to the transfer portion in the ring shape including the plurality of untransferred portions in the fourth embodiment is 1.0 or more. Embodiment 6 is that the above-mentioned ring-shaped untransferred portion of Solution 1 is at least 1 mm or more away from the effective area of the transfer surface.

Embodiment 7 is as follows. That is, at least one or more cavities are defined, and each of the cavities is defined by a pair of dies having at least one or more transfer surfaces. In the state of holding at a temperature of less than, the molten resin is injection-filled, a resin pressure is generated on the transfer surface, and the resin is brought into close contact with the transfer surface, and when cooled from its melting temperature to around the heat deformation temperature lower than its softening temperature, After sliding the piece of the cavity generating surface of the cavity to forcibly generate a gap between at least one portion of at least one surface other than the transfer surface and the resin, the mold is opened and the transfer surface is transferred. A method of manufacturing a disc-shaped plastic molded product to be taken out, wherein the timing of generating the voids is such that the surface layer portion of the resin in the cavity is solidified below the softening temperature,
A method for forming a transferred portion on the outer peripheral portion and an untransferred portion on the other portion when the central portion is at or above its softening temperature and the average temperature from the surface to the center is at or above the softening temperature of the resin. As a result, the disk-shaped plastic molded product of Solution 1 is manufactured.

Embodiment 8 is as follows. That is, at least one or more cavities are defined, and the cavities defined by a pair of dies each having at least one or more transfer surfaces are filled with the dies below the softening temperature of the filling resin. In the state where the temperature is maintained at the temperature, the molten resin is injected and filled, a resin pressure is generated on the transfer surface to make it adhere to the transfer surface, and when cooling from the melting temperature to about the heat deformation temperature lower than the softening temperature, the transfer is performed. A vent opening corresponding to at least one vent that is open outside the plane with a predetermined area and communicates with at least one or more communication ports that apply a predetermined gas pressure to the molding material; A pressure difference is generated between the transfer portion corresponding to the surface, a non-transfer portion is generated in the vent portion, a transfer portion on the outer peripheral portion, by a manufacturing method of forming an untransfer portion on the other portion, Solution 1 disk Is that of producing a plastic molded article.

In the above description of the "means for solving the problem", the term "disc shape" means that the fracture surface of the outer peripheral surface in the direction perpendicular to the center axis of the disc is simply mathematical. In addition to accurate shapes such as elliptical, arc, and repetition of circular arcs, not only simple circles but also round shapes are included. In addition, as in the case of having a tooth profile, the locus of the center position of each tooth profile (pitch circle) ) Also corresponds to the above-mentioned disk shape.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, according to the conventional manufacturing method, a disc-shaped plastic molded product 10 shown in FIG. 1 (a sink 11 is formed in a thick portion at the center and a sink 12 is formed on an outer peripheral surface) is provided. One embodiment is shown in FIG. The disk portion 2 other than the outer peripheral portion of the disc-shaped plastic molded article 1 has an untransferred portion 2a, and the untransferred portion 2a is not a transfer of the surface roughness of the mold cavity, but the shape thereof. The accuracy is much lower than that of the transfer surface 3. For example, when the mold accuracy is compared with the shape accuracy corresponding to the cavity of the plastic molded product, the shape accuracy of the outer transfer surface 3 is on the order of microns. In contrast, the untransferred portion 2a of the disk portion 2 is on the order of several hundred microns.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Prior to the description of the embodiments, a disk-shaped plastic molded product by a conventional molding method shown in FIG. This is injection molded into a fixed volume cavity having a transfer surface held at the thermal deformation temperature of the injection molding resin, and molded by injection filling. The resin at the melting temperature at that time solidifies rapidly from the end (thin wall). As a result, as shown in FIG. 1, sink marks 11 occur in the central thick portion. In addition, the resin internal pressure remains in the thin portion at the end, and expands due to the release of pressure when the mold is opened. The position where the sink occurs and the size of the sink at each position vary for each molding shot (one resin injection molding). There is a method of correcting the sink mark in advance by using the cavity surface of the mold, but this method has almost no effect. As a result, it is impossible to stably obtain a molded product having a highly accurate transfer surface by the conventional molding method. 3, 4, 5 and 6 show an embodiment of the present invention. In the example shown in FIG. 3A, ring-shaped untransferred portions 24 and 25 are formed on the side surfaces (disk surfaces) of the small-diameter portion and the large-diameter portion of the multi-stage disk 2 used for a compound gear, a compound pulley, and the like, respectively. Highly accurate transfer surfaces 26 and 27 are formed on the outer peripheral surface. FIG.
The example shown in (b) is a spur gear 3, in which a ring-shaped untransferred portion 34 is provided on the disk surface, thereby preventing sinks from occurring on the teeth on the outer periphery. There is no difference between this tooth profile and the helical tooth profile. FIG.
The example shown in (c) has a rim with a thickness of 1 mm on the outer circumference,
The rim-attached disc 4 has an inner peripheral surface of the rim 41 as a ring-shaped untransferred portion 42 to prevent sinks from occurring on the outer peripheral transfer surface 43. FIGS. 4 (a) and 4 (b) show a ring-shaped untransferred image on the disk surface of an elliptical disk 5, a circular arc or a disk with a repetition of cyclones (a disk having an arc-shaped convex portion on the outer periphery) 6, respectively. A portion 52 is provided to prevent sinks on the transfer surface 53 on the outer periphery thereof. This disk 5 is used for a transmission element such as a special gear. In a second embodiment shown in FIG. 5, a ring-shaped untransferred portion 72 is formed on the disk surface of a simple disk-shaped disk 7 concentrically with a transfer surface 71 on the outer periphery thereof.
The distance between the ring-shaped untransferred portion 72 and the outer peripheral transfer surface 71 is 1 mm or more (preferably 1 to 1.5 mm), and the ring width of the ring-shaped untransferred portion 72 is 1 to 1.5 mm.

FIG. 6 shows a disk 8 similar to the disk shown in FIG.
This is a third embodiment in which an untransferred portion 82 having a concentric circle and a broken ring shape is formed. 5 in which a continuous ring-shaped untransferred portion 72 is formed, a broken ring-shaped untransferred portion 8 is formed.
The advantage of using No. 2 is that the influence of thermal distortion on the transfer surface due to the presence of the untransferred portion can be reduced as compared with a ring-shaped one in which the untransferred portion is continuous. Regarding the shape of the broken line, it is necessary that the interval c between adjacent fragments is equal to or less than the length d of the fragment (c ≦ d), and the disk 8 has a diameter of 50 mm, a thickness of 6 mm, and a ring-like shape. When the ring width of the transfer portion 82 is 2 to 8 mm, the line interval c is 0.5
〜3 mm is desirable. If this interval c is 0.5mm or less, the advantage of a broken line a ring untransferred portion is almost lost and is opposite to 3 m m or more, the effect of the provision of the ring-shaped non-transferred portion Is lost. In consideration of this, the number of dashed lines and the size of the interval c between dashed lines may be optimally selected according to the size of the molded product, the material, and the like.
The shape of the untransferred portion in the above embodiment is various, and is a simple concave shape on the disk surface as shown in FIG. 9A, and a simple concave shape on the disk surface as shown in FIG. 9B. There is a convex shape, a concave and convex shape on the disk surface as shown in FIG. 9C, and a concave and convex shape on the back surface of the rim as shown in FIG. 9D.

[0012]

[Others] As described above, the manufacturing apparatus and the manufacturing method for actually implementing the present invention can be based on various conventional ones. The outline of typical ones will be described with reference to FIGS. I do. The molding die shown in FIG. 7 locally induces sink marks by a moving piece. The movable pieces 103 and 104 are provided on the fixed mold and the movable mold 102, respectively, and the inner ends of the movable pieces 103 and 104 are removed at appropriate times during the process of cooling the molten resin filled in the cavity 105. The inner resin is receded from the surface and separated therefrom, and a gap is formed in the separated portion to induce sink marks on the resin surface in contact with the gap. Cavity 105
Is an accurate transfer surface by the movable mold 102, and both upper and lower surfaces are non-transfer surfaces. Therefore, an untransfer surface due to the gap is formed in a part of the non-transfer surface. The timing of retreating the moving piece depends on the temperature state of the portion where the moving piece faces, but the temperature distribution of the molded article depends on the shape of the molded article. Therefore, it is appropriately selected by performing simulation for each individual molded article. . Since fluctuations in the resin internal pressure induce irregular sink marks, appropriate pressure-holding control is also performed to prevent this. FIG. 8 shows an air flow path 206 which is opened on the non-transfer surface of the cavity 205 and faces the non-transfer surface of the cavity 205. The cavity 205 is filled with resin while injecting air from the air flow path 206. A gap is formed between a part of the non-transfer surface of the resin surface 205 and the cavity surface of the mold, and sink is induced on the resin surface in contact with the gap. The temperature of the surface layer of the resin in the cavity, the softening temperature at the center, and the average temperature from the surface to the center drop over time during the cooling process after filling the molten resin, and this situation was confirmed by computer simulation. Therefore, the setting of the “timing for generating the gap” in the seventh embodiment can be easily performed. Since the temperature drop rate of each part differs depending on the shape, size and temperature control of the mold, the above timing is determined by the shape, size and temperature control of the mold. become. For details of the molding method and molding apparatus described above, refer to Japanese Patent Application No. 9-164316 and Japanese Patent Application No.
See No. 58921.

[0013]

According to the first aspect of the present invention, a disc-shaped plastic molded product having a high-precision outer peripheral surface can be obtained because a sink is not generated on the outer peripheral surface where a high-precision transfer surface is required. it can. According to the second aspect of the present invention, since the outer peripheral portion has a tooth shape having irregularities in the circumferential direction, a highly accurate plastic gear can be molded. Claim 3
In the invention according to the seventh to seventh aspects, since the untransferred portion has a ring shape, the transfer surface on the outer periphery can be formed with higher precision.

[Brief description of the drawings]

FIG. 1A is a perspective view of a disc-shaped plastic molded product obtained by a conventional manufacturing method, and FIG. 1B is a perspective view of X in FIG. 1A.
FIG.

FIG. 2A is a perspective view of a disc-shaped plastic molded product conceptually showing an embodiment of the present invention, and FIG. 2B is a sectional view taken along line XX in FIG. 2A.

3A is a perspective view of one disk shape of the first embodiment, FIG. 3B is a perspective view of another disk shape of the first embodiment, and FIG. It is sectional drawing of other disk shape.

FIG. 4A is a perspective view of an elliptical disk according to the first embodiment,
(B) is a perspective view of a disk having an arc-shaped convex portion on the outer periphery.

FIG. 5 is a perspective view of a second embodiment.

FIG. 6 is a perspective view of a third embodiment.

FIG. 7 is a cross-sectional view of a conventional plastic molded product manufacturing apparatus.

FIG. 8 is a cross-sectional view of another apparatus for manufacturing a conventional plastic molded product.

FIGS. 9A to 9D are cross-sectional views each showing the shape of a sink mark.

[Explanation of symbols]

1,2,3,4,5,6,7,8; disk-shaped plastic molded articles 2a, 24,25,34,42,52,62,72,8
2: Untransferred part 3: 26, 27, 33, 43, 63, 71, 81: Transferred part

Continued on the front page F term (reference) 4F202 AG05 AG19 AH12 AH33 AM34 AM35 CA11 CB29 CK06 CK15 CK17 CK42 CK52 CL42 CN05 CP04

Claims (9)

[Claims] 1. A disk-shaped plastic molded article having a transfer portion on at least one of an outer peripheral portion and an inner peripheral portion and at least one or more untransferred portions on other portions. 2. The disk-shaped plastic molded product according to claim 1, wherein the outer peripheral portion has a tooth shape having irregularities in a circumferential direction. 3. The disk-shaped plastic molded product according to claim 1, wherein the untransferred portion has a ring shape. 4. The disk-shaped plastic molded product according to claim 3, wherein the ring-shaped untransferred portion is concentric with the outer peripheral circle of the transfer portion. 5. The disk-shaped plastic molded product according to claim 4, wherein the ring-shaped untransferred portion comprises a plurality of small untransferred portions. 6. The disk-shaped plastic molded product according to claim 5, wherein in a ring shape comprising a plurality of small untransferred portions, the ratio of the untransferred portion to the transfer portion is 1.0 or more. 7. The disc-shaped plastic molded product according to claim 1, wherein the untransferred portion of the dulling shape is shifted by at least 1 mm from the effective area of the transfer surface. 8. A cavity defined by a pair of dies defining at least one or more cavities, each cavity having at least one or more transfer surfaces.
In a state where the mold is maintained at a temperature lower than the softening temperature of the filling resin, the molten resin is injection-filled, a resin pressure is generated on the transfer surface and the transfer surface is brought into close contact with the transfer surface, and the melting temperature is lower than the softening temperature. When cooling to about the thermal deformation temperature of the cavity, by sliding the piece of the void generating surface of the cavity, forcibly generating a void between at least one appropriate portion of the non-transfer surface and the resin, A method for manufacturing a disc-shaped plastic molded product, which is opened, transferred and transferred to a transfer surface, wherein the timing of generating the voids is determined in a state where a surface layer portion of a resin in a cavity is solidified below a softening temperature. Is higher than the softening temperature, and when the average temperature from the surface to the center is higher than the softening temperature of the resin, a transfer portion is formed on the outer peripheral portion and an untransferred portion is formed on other portions. The, disk-shaped plastic article according to claim 1. 9. A cavity defined by a pair of dies defining at least one or more cavities, each cavity having at least one or more transfer surfaces.
In a state where the mold is maintained at a temperature lower than the softening temperature of the filling resin, the molten resin is injection-filled, a resin pressure is generated on the transfer surface and the transfer surface is brought into close contact with the transfer surface, and the melting temperature is lower than the softening temperature. When cooled to around the heat deformation temperature, it corresponds to at least one or more vents that are open at a predetermined area outside the transfer surface and communicate with at least one or more communication ports that apply a predetermined gas pressure to the molding material. To generate a pressure difference between the vent portion and the transfer portion corresponding to the transfer surface of the molding material,
2. The disk-shaped plastic molded product according to claim 1, wherein a non-transferred portion is generated in the vent portion, and a transfer portion is formed in an outer peripheral portion and a non-transferred portion is formed in other portions.