JPH0292606A - Mold for injection molding - Google Patents

Abstract

PURPOSE:To decrease the internal strain of a molded item and consequently obtain a highly accurate plastic molded item by a method wherein a resistance part, which is formed for changing the cross-section of molten material flow path, is provided on a land portion at the inlet of a cavity. CONSTITUTION:When plastic material such as polycarbonate (PC), which is melted in an injection molder, is injected in an injection mold for a plastic lens, the material flows through a sprue and a runner 6 in a land 5, by passing through recessed part 3 and projected parts 4 provided in which, the speed of flow of the material is changed. As a result, shearing action and consequent shearing heat are developed within PC and the lowering of the viscosity of plastic material and the improvement of its fluidity is generated at its passing through the gate 8 and its flowing in a cavity so as to fill the cavity 2 with the plastic material in order to mold a plastic lens. B the procedure as mentioned above, the injection speed of the plastic material can be decreased and consequently favorable surface accuracy can be obtained and, at the same time, since the moldability is improved due to the heat generated at the land, the internal strain is decreased, resulting in allowing to obtain a plastic molded item having small birefringence.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an injection molding mold for injection molding using a plastic material, etc., and is particularly characterized by the shape of the gate portion and the land portion. The present invention relates to an injection mold having a mold for injection molding.

[Conventional technology]

Traditionally, the types of gates used in plastic molding include spool gates, rectangular side gates, overlap gates, fan gates, tab gates, diaphragm gates, and ring gates.

Film gates include pin gates, submarine gates, etc. In the type with a land, the thickness of the land is constant or changes in one direction toward the cavity. Furthermore, Japanese Patent Application Laid-Open No. 54-129054 discloses a structure in which the land is curved without changing the wall thickness of the land so that a uniformly isotropic molded product can be obtained.

[Problem that the invention seeks to solve]

However, when plastic is molded using a mold having these types of gates and lands, the shearing action of the plastic material itself occurs when the plastic material injected from the injection device of the molding machine is injected into the mold and passes through the gate section. was not carried out sufficiently, and the decrease in viscosity of the plastic material due to shear heat generation was small, so the fluidity of the plastic material was poor and internal distortion was likely to occur in the molded product. In particular, in plastic lens molding, in order to ensure surface accuracy, it is necessary to reduce the speed at which the plastic material passes through the gate part, and the shearing action becomes even smaller, resulting in large internal strains and large birefringence. This resulted in a molded product, making it impossible to obtain a high-precision plastic lens. It is generally known that when the speed of passing through the gate section is increased, the flow of the plastic material within the cavity is disturbed and air is drawn in, resulting in poor surface accuracy.

Therefore, the present invention was developed in view of the above-mentioned problems with conventional injection molding molds, and even if the speed of the plastic material passing through the gate part is low, sufficient shearing action is performed inside the plastic material. , the shear heat generation reduces the viscosity of the plastic material, improves its fluidity, and reduces the internal distortion of the molded product, thereby promoting an injection molding mold that can obtain a high-precision plastic molded product. The purpose is to

Means for Solving Problem C] The injection mold of the present invention is constructed by providing a resistance portion that changes the cross-sectional area of the molten material flow path in the land portion leading to the gate portion at the entrance of the cavity. be.

[For production]

In the present invention, the cross-sectional area of the molten material flow path in the land portion is changed by the concave and convex portions continuously arranged in the land portion leading to the gate portion of the cavity entrance, thereby sufficiently shearing between the insides of the plastic material. This shearing action lowers the viscosity of the plastic material, improving its fluidity and reducing the internal strain of the molded product.

〔Example〕

Hereinafter, one embodiment of the injection molding mold of the present invention will be described with reference to the drawings.

Figure 1 is an external view of the main parts of the injection mold of the present invention, Figure 2 (
a) is an explanatory diagram of the land portion of the mold, and FIG. 3 shows changes in material temperature due to the injection mold according to the embodiment of the present invention.

In FIG. 1, a runner 6 into which plastic material flows is formed in the lower mold 1, and this runner 6
A land portion 5 is provided in connection with. The end of the land portion on the cavity 2 side is formed as a gate 8. The land portion 5 is composed of a concave portion 3 and a convex portion 4, and forms an intermittent weir. In addition, in FIG. 2, 7 indicates an upper mold.

When Pc (polycarbonate), a plastic material melted by an injection molding machine, is injected into a mold for injection molding a plastic lens, it flows into the land 5 through a sprue (not shown) and a runner 6, and forms a concave portion 3 provided in the land 5. While passing through the convex portion 4, the flow rate changes. As a result, a shearing action occurs inside the PC, creating a shearing heat. As a result, the viscosity of the plastic material decreases, and the plastic material passes through the gate 8 and further flows into the cavity 2 while improving its fluidity. As a result, the plastic material fills the cavity 2 and a plastic lens is molded.

In this example, the total length of the land portion is 12 mm,
The diameter of the land 5 on the runner 6 side is 1.5 mm, and
The protrusion of the convex portion 4 is 0.9 mm, and therefore the diameter at the convex portion is 0.6 mm. Each of the uneven portions has a width of 2 mm. The diameter of the gate portion is also 0.6 mm.

The injection molding conditions of this example are the melting temperature of the material: 295@C
, mold temperature 140'C, injection speed was Rand.

Gate part 2.5mm/sec, cavity part 5m
m/sec, and the material is PC (polycarbonate).

As a result of injection molding using the injection mold of this example and the conventional mold under the present molding conditions, material temperature changes as shown in FIGS. 3 and 4 and the table below were observed. still,
The land shape of the conventional type is similar to that shown in FIG. 2(a), except that the convex portion 4 is removed and the other parts are the same.

According to this embodiment, the temperature of the plastic material starts to rise from the initial temperature while passing through the land 5, and the temperature difference between the entrance of the land 5 and the position of the gate 8 is about 13.2@c.
The maximum temperature is 308.2@C. As is clear from FIG. 5, which shows the relationship between polycarbonate material temperature and its viscosity, a considerable reduction in the viscosity of the plastic material can be obtained.

The figure is based on tests conducted using a Koka-type flow tester, with a nozzle of 1 mmφ x 10 mmL, and conducted under a pressure of 40 kg/cj.

In contrast, with conventional molds, this temperature difference is approximately 2
．． It can be seen that the effect is low at 7°C and the maximum temperature is 297.7'''C. PC is known to have a large viscosity gradient with respect to temperature, and to improve moldability it is necessary to lower the temperature. It is effective to increase

Judging the effect by the birefringence of the molded product, when the mold of this embodiment is used, the birefringence is (1 to 10)xlo-' (anonymous number), but with the mold of the conventional technology, it is (10 to 20)xlO -', and it is clear that the effect of this example is large.

When such an injection molding mold is used for injection molding of plastic lenses, molding conditions that improve the surface area of the lens,
- It is possible to obtain a plastic lens molded product with reduced birefringence, which is internal strain, while keeping the material temperature, mold temperature, and especially low injection speed.

Note that it is natural to lower the viscosity by increasing the melting temperature of the plastic material in the plasticizer of the injection molding machine, but in the case of PC, the upper limit is about 295"C as shown in this example. Yes, because if the temperature is set even higher, the plastic material will remain at a higher temperature for a longer time than the injection time inside the visualization device, causing problems such as thermal decomposition, yellowing, and gasification. This is because the quality of a plastic lens cannot be obtained basically.

What is shown in FIGS. 2(b) to 2(e) represents the land portion of an injection molding die according to another embodiment of the present invention. In addition, the width of the land is changed instead of the land thickness in the figure (d), and the shape of the convex portion is not limited to a rectangle, but also a semi-cylindrical shape as shown in the figure (e). In this way, the shape of the weir at the land part is not limited to these,
Various shapes that change the cross-sectional area of the land can be applied.

The dimensions of the gate and land are not limited to this example.

In the above embodiments, the case where the mold is applied to a mold for injection molding of plastic lenses is described, and PC (polycarbonate) is also described as the plastic material, but the mold of the present invention is limited to the mold for injection molding of plastic lenses. Rather, it can be applied to any mold for molding that has an injection process. Regarding the type of plastic material, it goes without saying that any thermoplastic can be used.

Even in injection molding processes that use materials other than plastic materials, if the characteristics of those materials are such that their viscosity decreases with temperature rise, the mold of the present invention can be applied to improve moldability. Obtainable. In this respect, the invention is not limited to injection molding processing of plastics.

〔effect〕

According to the present invention, it is possible to obtain good surface accuracy by slowing down the injection injection speed of the plastic material, and improve moldability due to heat generation at the land, thereby reducing internal strain and birefringence compared to conventional injection molding. This technology has the effect of making it possible to obtain plastic molded products that simultaneously satisfy two contradictory qualities: area density and birefringence.

4,

[Brief explanation of the drawing]

FIG. 1 is an external view of the main parts showing one embodiment of the injection mold of the present invention, FIG. 2(a) is an explanatory view of the land portion, and FIG.
b) to (e) are explanatory diagrams of land portions in other embodiments; FIG. 3 shows material temperature changes due to injection molding molds in embodiments of the present invention; FIG. 4 is illustrations of conventional injection molding molds. FIG. 5 is a diagram showing the material temperature change due to the mold, and FIG. 5 is a diagram showing the relationship between the polycarbonate material f4 temperature and viscosity. 1... Lower mold 2... Cavity 3... Concave portion 4... Convex portion 5... Land portion 6... Runner 7... Upper mold 8... Gate area σ] Regret procedure Written amendment (voluntary) February 13, 1989 1. Indication of the case 1988 Patent Application No. 246389 2. Name of the invention Injection mold 3. Person making the amendment Relationship to the case Patent applicant address 2-43-2 Hatagaya, Shibuya-ku, Tokyo Name
(037) Representative of Olympus Optical Industry Co., Ltd.
Satoshi Yama, Department 4, Agent 105 Address: 2-2-15-7, Hamamatsucho, Minato-ku, Tokyo Contents of amendment (1) Detailed Description Damage, page 4, line 9, ``Due to this shearing action,
The statement "by the heat generated by this shearing action" is corrected. (2) In the first line of page 6 of the same book, the statement ``The diameter of the six runners of the land 5 is'' is corrected to ``The maximum thickness of the land 5 is.'' (3) In the third line of page 6 of the same book, the statement ``The diameter at the convex portion is'' is corrected to ``The thickness at the convex portion.'' (4) The diameter is ro, 6aun on page 6, line 5 of the same book. ” indicates a thickness of 6M. ” he corrected. (5) Circular, page 7, line 16.17 r (10-20)
×10-'J [(20-30)XIO-'J
and correct it. (6) The statement ``approximately 5.200 J'' on page 8, line 3 of the same book is corrected to ``approximately 4.500 J.'' (7) The statement ``(1-10) (1-10) XIO-'J.
Corrected to ``about 200''. (9) “(20-30)XIOJ” on page 8, line 4 of the same book
The description is corrected to [(20-30)XIO-'J. 00) Figure 5 of the drawings attached to this application is amended as shown in the attached amended drawing. 8゜Inventory of attached documents

Claims (1)

[Claims] 1. An injection molding mold, characterized in that a resistor portion for changing the cross-sectional area of a molten material flow path is provided in a land portion leading to a gate portion at a cavity entrance.