JP4242621B2 - Injection molding method for plastic optical components - Google Patents

Description

【００１９】
表１から、比較例１及び２に対し実施の形態１及び２では、成形品の品質が良好であると共に、成形のサイクルタイムが短くなっている。これは、実施の形態１及び２が、入子の転写面を転写させ、成形品に変形が発生しない表面の弾性強度を得た後、非光学面３を有する移動入子４を樹脂圧力によって移動させ、光学面を金型内に保持した状態でキャビティ内の樹脂の比容積を低下させるため、変形を伴うことなくキャビティ内の余分な樹脂圧力を効率的に降下させることが可能で、光学部品中に応力・歪みを封じ込めることがないためである。
【００２０】
なお、表１において、Ｐ×Ｖの最大値と第２のピークの比は０．８、０．６としているが、０．４５〜０．９の範囲であれば同様な効果が得られる。この比は、０．５〜０．９であればさらに良く、０．６〜０．８であればより良く、０．６〜０．７５であれば特に良い。
【００２１】
【発明の効果】
以上説明したように、本発明によれば、成形品をキャビティの内部に保持した状態で効率的に応力緩和ができ、キャビティ内の樹脂を冷却することができるため、短いサイクルで歪みが少なく高精度な光学面形状精度を有したプラスチック光学部品を得ることが可能となる。
【図面の簡単な説明】
【図１】通常の成形におけるＰ×Ｖと時間との特性図である。
【図２】本発明におけるＰ×Ｖと時間との特性図である。
【図３】本発明の実施の形態におけるキャビティを示す断面図である、
【図４】移動入子を移動させた状態を示す断面図である。
【図５】比較例１の成形におけるＰ×Ｖと時間との特性図である。
【図６】比較例２におけるＰ×Ｖと時間との特性図である。
【符号の説明】
１ キャビティ
２ 光学面
３ 非光学面
４ 移動入子
７ 固定入子[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an injection molding method for plastic optical components that require high optical performance and are used in an optical system such as a camera.
[0002]
[Prior art]
In recent years, plastic optical components have been manufactured by developing various injection molding methods and manufacturing equipment. For example, Japanese Patent Laid-Open No. 11-28745 describes a method for molding a plastic optical component with low distortion. In the case of plastic optical parts, the problem of molding is to relieve the residual stress inside the parts and to ensure the shape accuracy of the optical surface. In the fθ lens used in laser printers and the like, these problems have caused the conventional problems. Glass lenses have been used. In the method described in JP-A-11-28745, a gap is formed between the moving piece provided in the cavity and the resin to induce a sink in a part of the product, and the sink induction site is deformed as a free surface. The generation of internal distortion due to cooling shrinkage is absorbed, and the shape accuracy of the optical surface can be improved and the birefringence can be reduced, thereby enabling the fθ lens to be made plastic.
[0003]
[Problems to be solved by the invention]
However, in the method described in Japanese Patent Application Laid-Open No. 11-28745, a gap is forcibly defined between the moving piece and the resin in order to induce sink marks on the non-optical surface. An air insulation layer is formed between them. Therefore, in this method, the cooling rate of the resin from the cavity surface (in this case, the non-optical surface) facing the void portion by the heat insulating layer and the resin surface that is in contact with other non-moving pieces other than the moving piece is in contact. As a result, there is a difference in the cooling rate, resulting in non-uniform cooling and local distortion and refractive index distribution.
[0004]
In addition, since the air insulating layer has a portion where the cooling rate is remarkably reduced in the resin in the cavity, the molding cycle time is long. Such a long molding cycle is a factor that impairs mass productivity and cost merit, which are the advantages of plastic injection molding.
[0005]
In addition, a special hydraulic circuit, pneumatic circuit, electric motor, and other pressure control mechanisms are required to slide the moving piece inside or outside the mold and forcibly define the gap. The mechanism is complicated and the mold cost is high, and there is a problem that the merit of plasticization cannot be maximized.
[0006]
The present invention has been made in consideration of these problems, and is a low-cost plastic optical device that uniformly suppresses distortion inside a molded product in a short molding cycle and has excellent optical characteristics such as surface shape accuracy and refractive index distribution. It is an object of the present invention to provide a plastic optical component injection molding method capable of manufacturing a component.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the plastic optical component injection molding method according to the first aspect of the present invention is a method of injecting and filling molten resin into a cavity of a mold and generating a transfer pressure to transfer a desired shape to the plastic. In the injection molding method of cooling the plastic part after molding the optical part and taking out the plastic optical part from the mold , a cavity is formed by a member including a movable nest for molding the non-optical surface of the optical part, If the pressure inside the cavity and P, and the cavity volume is V, the resin filled into the cavity, said P × V when transferring the cavity shape by applying pressure to the cavity inside the resin, in one cycle of the molding in after the maximum value, the by retracting the transfer pressure of the movable insert resins, small P × V than the maximum value to expand the cavity volume P × V is obtained by moving the nest following the cooling shrinkage of the resin while the transfer surface of the movable nest and the resin are in close contact with each other. It is characterized by decreasing.
[0008]
FIG. 1 is a characteristic diagram in which changes in the product of cavity internal pressure P and cavity volume V during normal molding are plotted as a function of time. P × V rises due to injection filling and holding pressure, and the maximum value is generated at time A1 by generating the peak pressure. Thereafter, the shrinkage of the resin accompanying the cooling is started, whereby the pressure is lowered, and P × V is also gradually decreased.
[0009]
Here, after completion of the holding pressure, the shrinkage due to cooling further proceeds, and the cavity internal pressure P further decreases. On the other hand, since the resin temperature is filled in the cavity of the mold while forming the skin layer, there is a temperature distribution in the cross-sectional direction from the temperature difference between the cavity surface and the cavity center from the beginning of filling. . The resin in the cavity can be removed from the viewpoint of temperature by being cooled to such an extent that it has an elastic strength that does not cause deformation due to the removal of the product from the mold, but in reality the internal pressure of the cavity has a distribution. As a result, the molded product expands rapidly upon removal, and the surface around the portion where the internal pressure is particularly high greatly expands and deforms. Therefore, if the take-out time is early, a large amount of internal pressure remains in the cavity, so that the expansion of the molded product due to the take-out increases further, and the movement displacement with respect to the original target shape including the subsequent shrinkage due to cooling becomes large. It becomes difficult to obtain an optical surface shape.
[0010]
FIG. 2 is a characteristic diagram in which P × V of the present invention described above is plotted according to time. The point at which the maximum value of P × V is generated at time A1 is the same as in normal molding. Thereafter, the nest having one or more movable non-optical surfaces is moved by the transfer pressure of the resin to expand the volume of the resin cavity. As a result, a second peak of P × V smaller than the maximum value is generated at time A2. After that, the resin is cooled, and at this time, the nest is transferred following the cooling shrinkage of the resin while the transfer surface of the nest having a non-optical surface and the resin are in close contact with each other. To decrease P × V.
[0011]
In such molding, the pressure in the part where the residual stress is particularly high is achieved by lowering the cavity internal pressure, that is, the transfer pressure, with the corresponding resin part that forms the originally required optical surface in close contact with the mold. Therefore, it is possible to reduce the movement displacement of the resin surface after removal without lengthening the molding cycle, and it is possible to obtain a plastic optical component with good surface shape accuracy.
[0012]
In addition, during molding, it is sufficient that the pressure enough to allow the corresponding resin portion that forms the optical surface to be in close contact with the mold, and excess cavity pressure can be released. It is possible to obtain a plastic optical component having good optical characteristics with less distortion.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
3 and 4 show a molding state in the embodiment of the present invention, in which the cavity 1 has a fixed insert 7 having an optical surface 2, a moving insert 4 having a non-optical surface 3, and an ejecting pin 5 ( Hereinafter, it is referred to as an E pin 5) and a gate portion 6. The cavity 1 flows through a sprue portion and a runner portion (not shown) and is filled with a molten resin injected from the gate portion 6 to form a plastic optical component that is a molded product. Further, the moving nest 4 is provided with a position sensor (not shown), and the change in the volume of the cavity 1 accompanying the movement of the moving nest 4 is measured. Furthermore, a pressure sensor (not shown) is attached to the rear end of the E pin 5 to measure the internal pressure in the cavity 1. Here, the movable nest 4 having the non-optical surface 3 can be moved by the transfer pressure of the resin filled in the cavity 1.
[0014]
The optical resin melted and measured by the heating cylinder of the injection molding machine is injected and filled into the cavity 1 in the mold at a predetermined injection rate. After injection filling, the shape of the cavity 1 is reversed by applying a holding pressure to generate a necessary transfer pressure. At this time, the internal pressure of the cavity 1 is measured by the pressure sensor via the E pin 5, while the volume of the cavity 1 is measured via the moving nest 4.
[0015]
After the filling of the resin is completed and the elastic strength of the surface that does not cause deformation of the molded product is obtained, the movable insert 4 is moved in the direction in which the cavity volume is expanded by the pressing force of the resin, that is, the transfer pressure (see FIG. 4). ). At this time, a second peak in a range where the product P × V of the internal pressure P of the cavity 1 and the volume V of the cavity 1 does not exceed the maximum value immediately after filling occurs (see FIG. 2). Thereafter, the resin in the cavity 1 shrinks as it cools, but the movable nest 4 is moved in the shrinking direction of the resin following the shrinkage.
[0016]
In such injection molding, the transfer surface of each of the fixed insert 7 and the movable insert 4 is transferred to obtain the elastic strength of the surface on which the molded product is not deformed, and then the moving having the non-optical surface 3. By moving (retracting) the insert 4 by the resin pressure, the specific volume of the resin in the cavity 1 is reduced while the optical surface is held in the mold, so that the excess resin in the cavity 1 is not deformed. The pressure can be lowered efficiently, and stress and strain are not contained in the optical component. Further, since the moving nest 4 having the non-optical surface 3 moves following the contraction of the resin, the nests 4 and 7 are always in contact with the resin, and there is a difference in the resin cooling rate from each surface. It becomes possible to cool without generating. Accordingly, the release of unnecessary pressure and cooling can be efficiently promoted by these, and it becomes possible to mold a plastic optical component having a low distortion and a uniform and high optical surface accuracy in a short cycle.
[0017]
Table 1 shows the molding in Embodiments 1 and 2 and Comparative Examples 1 and 2 and the evaluation thereof. In Embodiments 1 and 2, the second peak of P × V is set to a ratio of 0.8 and 0.6 with respect to the maximum value of P × V, and in Comparative Example 1, the second peak is P × V. The ratio is 1.2, which is larger than the maximum value, and in Comparative Example 2, the ratio is 0.3. FIG. 5 is a characteristic diagram of Comparative Example 1 and FIG. 6 is a characteristic diagram of Comparative Example 2.
[0018]
[Table 1]

[0019]
From Table 1, in comparison with Comparative Examples 1 and 2, in Embodiments 1 and 2, the quality of the molded product is good, and the cycle time of molding is short. This is because the first and second embodiments transfer the transfer surface of the insert and obtain the elastic strength of the surface that does not cause deformation of the molded product, and then move the moving insert 4 having the non-optical surface 3 by resin pressure. Since the specific volume of the resin in the cavity is lowered with the optical surface held in the mold, it is possible to efficiently drop the excess resin pressure in the cavity without deformation. This is because stress and strain are not contained in the part.
[0020]
In Table 1, the ratio between the maximum value of P × V and the second peak is 0.8 and 0.6, but the same effect can be obtained if it is in the range of 0.45 to 0.9. This ratio is better if it is 0.5 to 0.9, better if it is 0.6 to 0.8, and particularly good if it is 0.6 to 0.75.
[0021]
【The invention's effect】
As described above, according to the present invention, stress can be relaxed efficiently while the molded product is held inside the cavity, and the resin in the cavity can be cooled. It is possible to obtain a plastic optical component having an accurate optical surface shape accuracy.
[Brief description of the drawings]
FIG. 1 is a characteristic diagram of P × V and time in normal molding.
FIG. 2 is a characteristic diagram of P × V and time in the present invention.
FIG. 3 is a cross-sectional view showing a cavity in an embodiment of the present invention.
FIG. 4 is a cross-sectional view showing a state in which a moving nest is moved.
5 is a characteristic diagram of P × V and time in molding of Comparative Example 1. FIG.
6 is a characteristic diagram of P × V and time in Comparative Example 2. FIG.
[Explanation of symbols]
1 Cavity 2 Optical surface 3 Non-optical surface 4 Moving insert 7 Fixed insert

Claims (1)

Injection molding is performed by injecting and filling molten resin into the mold cavity, generating a transfer pressure to transfer the desired shape to the resin, forming a plastic optical component, and then cooling it to take out the plastic optical component from the mold. In the method
Forming a cavity with a member including a movable nest that molds the non-optical surface of the optical component;
If the pressure inside the cavity and P, and the cavity volume is V, the cavity of the resin filled in, the P × V when transferring the cavity shape by applying pressure to the cavity inside the resin, one cycle of molding After setting the maximum value in
The movable insert by retracting the transfer pressure of the resin, to form a second peak of less P × V than the maximum value to expand the cavity volume,
Thereafter, P × V is decreased by moving the nest following the cooling shrinkage of the resin while the transfer surface of the movable nest and the resin are in close contact with each other. Injection molding method for parts.

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