JP3644665B2 - Plastic mold and plastic molding method - Google Patents

Description

[0001]
[Industrial application fields]
TECHNICAL FIELD The present invention relates to a plastic injection molded product whose shape, size, and surface are molded with high accuracy and a molding die thereof, and a high-precision plastic optical molding such as a precision plastic transmission part such as a copying machine and a facsimile and a plastic lens. It is effective when used for manufacturing technology.
[0002]
[Prior art]
One of the conventional technologies related to the molding technology of high-precision plastic molded products is that plastic gears are provided with a groove whose width and depth are not constant in the radially inner part of the rim, so that the pressure difference in the cavity is uniform. To prevent the deformation of the outer shape of the gear (Japanese Patent Laid-Open No. 8-132542), and the thick rim and rib of the gear are hollow-molded to cause the rim and rib to sink and deform. (For example, Japanese Patent Laid-Open No. 8-156053).
Conventionally, in order to obtain a highly accurate molded product, the shape of the molded product and the molding method have been devised. For example, in the case of gears, gears are generally molded by multi-point gate injection molding. However, as shown in FIG. When deformed, a highly accurate shape cannot be obtained, and represented by the gear JISB 1702, there is a problem that the tooth sway increases and the grade decreases. FIG. 1B shows a cross-sectional shape when there is no deformation, but the cross-sectional shape when the pressure is too high swells outward in the radial direction as shown in FIG. After that, the cross-sectional shape is recessed inward in the radial direction as shown in FIG. As shown in FIG. 2, the main cause of the deformation is that the resistance to the flow of the molten resin injected from the multi-point gate differs depending on the portion, so that the resin pressure in the cavity during molding is different. The distribution becomes non-uniform, and this non-uniform pressure distribution makes the density distribution of the resin non-uniform, resulting in non-uniform shrinkage, resulting in non-uniform finished dimensions at each part. It means that. In order to eliminate this non-uniform pressure distribution as much as possible, the cross-sectional shape is changed as described in JP-A-8-132542, or ribs such as those described in JP-A-2-66363 are used. Various contrivances have been made such as changing the shape or changing the thickness of the disk portion as described in JP-A-9-166199. If by these methods, since it is not easy to ensure forming accuracy of a molded article shape for obtaining, by a molded article dimension based, repeated attempts while applying a prediction, by repeating the correction, resulting predetermined molded article What with the modification to the mold at present until et be. For this reason, the correction amount may be incorrect, and a part of the cavity surface may be shaved too much.In the worst case, the nesting that constitutes a part of the cavity surface may be recreated. There is a problem that costs are too high. In addition, it is extremely difficult to completely compensate for the non-uniformity of molding due to the pressure distribution difference in the cavity. Therefore, it is very difficult to achieve high molding accuracy with the conventional injection molding method described above. .
On the other hand, there is a compression molding method as a molding method for improving molding accuracy. However, in this compression molding method, the mold becomes complicated, and for this reason, the compression mechanism depends on the shape of the molded product. For this reason, there is a case where the compression molding method cannot be adopted. Therefore, there is a problem that molding by this is limited to a molded product having a relatively simple shape.
Further, in recent years, gas assist molding and low pressure molding methods that intentionally generate sink marks in a predetermined part (Japanese Patent Laid-Open No. 2-175115, Japanese Patent Laid-Open No. 7-100877, Japanese Patent Laid-Open No. 6-304973, Japanese Patent Laid-Open No. 8-156053) has been developed, and when this molding method is used, since the resin can move within the cavity, it is relatively easy to equalize the pressure distribution. A precision molded product is obtained. This molding method (that can not be successfully induced the sink at this stage, such as the apparatus of shrinkage induction is complex) to the mean are technically always sufficiently complete so, not be necessarily fully realized its benefits is the current situation.
[Problem to be solved]
An object of the present invention is to provide a molding method so that a highly accurate molded product can be obtained while taking advantage of the low-pressure molding method in which sink marks occur in part and without spending time and cost for mold correction and the like. It is to devise a molding die so that a highly accurate molded product can be obtained.
[0003]
[Measures taken to solve the problem]
The main points of the measures taken to solve the above problems are that fine grooves are provided at a high density in any part of the surface of the nest constituting the non-transfer surface of the cavity, and the length of the fine grooves and the number of grooves The density (the number of grooves per unit width) is appropriately adjusted to reliably induce a sink of a predetermined depth at a predetermined position.
The above-mentioned “fine grooves” means grooves having such a small width that the filled molten resin cannot enter the grooves, and “high density” means that a group of many fine grooves are integrated. It means that the minute grooves are dense enough to function and generate one sink.
[0004]
[Action]
Since the molten resin in the cavity cannot enter the fine groove, the gas layer (confined in the fine groove) is formed between the cavity surface and the resin. A layer formed by the gas) is interposed, and sinking is surely induced in this portion by the interposition of the gas layer. And the range of this gas layer (region where a group of fine grooves is provided) and the sinking function of this gas layer are the length of the groove, the number of grooves (or the region where a group of grooves are formed). Width), adjusted by adjusting the density of the groove. That is, the longer the groove length, the greater the number of grooves, and the higher the density of the grooves, the wider and deeper the sink marks that are induced. The adjustment of the length of the groove is simple, and since the groove is fine, the processing for increasing and decreasing the groove is simple and easy. The length of the groove, the number of grooves, the number of grooves In spite of the modification of the density, there is no risk of significant damage to the nested cavity surface. Therefore, the depth of the sink induced by adjusting the length of the fine groove and increasing / decreasing the number can be adjusted easily and reliably. In addition, since these fine grooves are easily formed on the cavity surface having a complicated shape, the position where the sink mark is induced can be selected as the optimum position regardless of the shape of the molded product. In addition, the spread of the sink marks is selected easily and easily.
[0005]
Embodiment
In order to clarify the technical significance of the solution and the meaning of the action, the embodiment will be described.
[About the shape of the molded product]
FIG. 3 shows the shape of a molded product in which sink marks are generated in portions where transferability is necessary, that is, most of the portions other than the tooth profile and the hub, and the amount of sink marks is changed at an arbitrary position.
In the disk portion of this, when viewed in a plane (FIG. 3A), the amount of sink in the portion along the radial line La passing through the intermediate point between the adjacent gate traces g, g is maximized and passes through the gate trace g. The amount of sink marks in the portion along the ray Lb is minimized. Further, actinomycetes cross section (FIG. 3 (b), (c) ) when viewed in the radial inward most shrinkage amount is small the gate is provided, shrinkage amount is large enough radially outward. In the rim portion, the rim portion provided with teeth on the outer periphery causes sink marks in portions other than the tooth profile portion such as the inner peripheral surface of the rim portion, and the sink marks in the part on the line passing through the gate mark g on the inner peripheral surface of the rim portion. The amount of sink marks in the part on the line passing through the middle of the gate marks g and g is maximized by reducing the amount.
The pressure distribution in the cavity immediately after injection filling when molding the molded article shown in FIG. 3 is as shown in FIG. If there is a pressure difference, a density difference will occur, which will cause a shrinkage rate difference, resulting in a large dimensional variation in the molded product. As described above, the pressure in the direction of the line La between the gate marks g and g and the pressure in the outer circumferential direction. By positively increasing the amount of sink at the portion where becomes small, the density difference can be reduced, and as a result, the dimensional variation can be reduced. That is, in the case of the conventional injection molding, it is very difficult to relax the pressure distribution because the cavity volume is constant. However, by actively controlling the amount of the sink part as in the present invention, the sink is Even in the case of low pressure molding that occurs, the pressure distribution can be relaxed, the density difference can be reduced, and as a result, the dimensional variation can be reduced.
As described above, the gear (gear) by the multipoint gate has been described as an example. However, it can be applied to a molded product whose pressure balance is broken as shown in FIG. 4 or a molded product requiring high precision molding such as a lens. From the shape of the product, it is possible to obtain a high-precision molded product by more actively increasing the depth of the sink in the portion where the dimensional accuracy is small.
[0006]
[Regarding the control method of molded product shape]
The shape control method will be described with reference to FIGS.
The molding apparatus shown in FIG. 5 inserts inserts A and B into a lower mold 1 and an upper mold 2, respectively, and forms a gear by forming the lower and upper surfaces of the cavity by the inserts A and B.
In this product, a cavity D is formed by inserts A and B forming the lower surface and the upper surface of the web of the molded product, and inserts C forming the tooth profile portions. The groove 4 having a width of 5 to 50 μm is provided on the molding surface of the insert B. The large number of groups of grooves 4 are independent without intersecting each other , and communicate with each other by connecting grooves 6 (see FIGS. 6 and 7 ). The depth of the groove may be equal to or greater than the width.
In addition, the interval between the grooves may be appropriately selected within a range in which a large number of fine grooves are excellent as a group, and according to the intended function, the smaller the interval, the better. Taking into consideration that there is no hindrance to the modification of the length, number, and width of the groove, it may be appropriately selected in the range of approximately 10 to 70 μm according to the above-mentioned circumstances.
Further, as is clear from FIG. 6A, the distance from the gate position in the group of grooves is longer, so that the depth of sink becomes deeper as the distance from the gate position increases. .
Although than is press-fitted compressed gas from the communicating hole 5 in the groove 4, or increase the length of the groove A larger shrinkage amount of planned size range of density of the groove, a group of grooves provided Kusuru.
The width of each groove 4 is appropriately selected within a range of 5 to 50 μm in order to prevent the resin from entering the groove, but the maximum value of the groove width that can prevent the resin from entering varies depending on the viscosity of the resin. It has been experimentally confirmed that when the molding resin is PC (polycarbonate), POM (polyacetal), or amorphous polyolefin, these resins do not enter the groove if the groove width is 30 μm or less. As long as the resin does not enter, a larger groove width is advantageous in practice.
[0007]
Due to the presence of the groove 4, the contact area is reduced, the adhesion with the resin is reduced, and a high-pressure gas is pressed into the groove during resin filling, and the mold is warmed with the resin, so that the gas pressure in the groove is further increased. Therefore, it becomes easy to release the resin and the mold. Induction of shrinkage by these, the magnitude of the generated sink mark, suitably by changing the groove width, length, depth, they are easily adjusted.
In addition, it is possible to easily add or fill a groove to the planned depth of the sink mark depending on the size. Further, the adjustment of the groove for adjusting the depth of sink marks is a slight amount, and the influence on the quality is extremely small.
In this embodiment, as shown in FIG. 7, a communication hole 5 is provided between the groove and the outside of the mold, and the compressed gas is fed into the groove through this communication hole. There is no need to use.
[0008]
【The invention's effect】
As described above, fine grooves are densely provided on the surface other than the high-precision transfer surface of the cavity, that is, the non-high-precision transfer surface, and the length, depth, and number of the grooves are adjusted. Sink marks can be guided to any position on the non- high-accuracy transfer surface, and the depth and size of the induced sink marks are appropriately controlled by adjusting the length, depth, and number of grooves, and the high-accuracy transfer surface The occurrence of sink marks can be avoided, and the influence of sink marks and distortion on other parts can be easily avoided. Therefore, a molded product having a high precision transfer surface and molded with high precision can be obtained.
In addition, since it is easy to adjust the shape of the group of grooves on the cavity surface so that the depth of sinking increases as the distance from the gate position increases, the grooves are arranged in this way, more adjusting the shape can be reduced as much as possible by a relatively simple, easy means the influence of the high-precision transfer surface transfer precision of the gate position.
In addition, for plastic molded products injection-molded by a multi-point gate mold, the size of the groove on the cavity surface is such that the depth of sink marks in the part between the gates in the direction of radiation is greater than the depth of sink marks in the part between them. Since it is easy to adjust the depth, depth, and number, the influence of the presence of these multiple gates on the transfer accuracy of the high-precision transfer surface should be reduced as much as possible by relatively simple and easy means. Can do.
Further, when the molded product is a gear, it is easy to adjust the length, depth, and number of the grooves on the web and the cavity surface that forms the surface opposite to the tooth surface of the rim. By adjusting the gear, it is possible to surely induce a sink mark as planned on the surface of the web and the side opposite to the tooth surface of the rim. Can be easily formed by relatively simple means. Therefore, the gear formed in this way is highly accurate.
In addition, a gear can be obtained with higher accuracy by inducing a greater sink than the other portions of the web in the radial direction between the gates and the rim.
Further, regarding the molding method in which sink marks are generated in a part of the molded product, the above-described method is provided on the cavity surface of the plastic injection mold that causes sink marks in any part of the molded product that does not affect the appearance and dimensional accuracy. By setting the width of the groove to 5 to 50 μm, it is possible to effectively realize sink induction by the groove while reliably avoiding the penetration of the molten resin into the groove.
[Brief description of the drawings]
FIG. 1A is a plan view showing a relationship between a multi-point gate in a gear according to a conventional molding method and deformation of a molded product, FIG. 1B is a cross-sectional view of a predetermined shape, and FIG. FIG. 4 is a cross-sectional view of the product molded with the cavity internal pressure being too high, and FIG. 4D is a cross-sectional view of the product molded with the cavity internal pressure being too low.
FIG. 2 is a plan view showing the relationship between the internal pressure distribution of the cavity and the dimensional accuracy of each part when the pressure is balanced.
FIG. 3A is a perspective view showing the relationship between the position of a multipoint gate and the occurrence of sink marks in a gear molded product, and FIG. 3B is a cross-sectional view taken along the direction of the gate. (C) is sectional drawing along the direction which goes through the middle of a gate.
FIG. 4 is a plan view showing the relationship between the internal pressure distribution of the cavity and the dimensional accuracy of each part when the pressure is not balanced.
FIG. 5 is a sectional view of a mold showing an embodiment of the present invention.
6 (a) is a perspective view of putting the child A in Fig. 5 is an enlarged perspective view of (b) is 6 (a).
7A is a perspective view of the insert A in FIG. 5, and FIG. 7B is an enlarged perspective view of a main part of FIG. 7A.
[Explanation of symbols]
1: Lower mold 2: Upper mold 4: Groove 5: Communication hole 6: Communication groove A, B, C: Nesting D: Cavity g: Gate trace La: Radiation through the gate trace Lb: Radiation through the gate trace H : Hub of molded product R: Rim of molded product U: Web of molded product

Claims (4)

In plastic molding mold having a shrinkage inducing means for producing a shrinkage in any part of the molded article which does not affect the appearance and dimensional accuracy,
The sink induction means comprises by only setting the number of independent grooves surface on the width 5~50μm of a mold to form a cavity (nesting), thereby characterized in that so as to control the shrinkage depth Plastic mold. 2. The plastic mold according to claim 1, wherein a plurality of independent grooves provided on the surface of the mold (nesting) are communicated with each other through communication grooves . The length of the groove in the surface of the mold (nest), to moderate the depth of shrinkage by appropriately adjusting the gap between the number of the grooves and the grooves, plastic configuration of claim 1 or claim 2 Katachikin How to adjust the depth of sink marks in the mold. The length of the groove on the surface of the mold (nesting), the number of the grooves, and the interval between the grooves are appropriately selected, and thereby the depth of sink is adjusted . Plastic molding method using plastic mold.

Images