JPH0124053B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the structure of an injection mold. In detail, it mainly prevents inappropriate temperature distribution in the cavity, prevents uneven molding shrinkage of injection molded products to the maximum extent possible, and prevents injection molded products from deforming. In addition, it relates to a mold structure for improving productivity by shortening the time required to stabilize the mold temperature at a constant temperature.

It is well known that among the many molding conditions in injection molding, the temperature of the mold has an extremely large effect on mold shrinkage rate and other quality, and this is especially noticeable for crystalline resins. .
Therefore, it is now common sense to take active measures to maintain the mold temperature at a certain constant temperature. However, there are some problems with the current temperature control methods.

The basic concept of current mold temperature control is to treat the mold as a single piece of iron, and to circulate a heating medium at a constant temperature through the piece of iron to maintain the entire mold at a constant temperature. There are two major problems that can be raised with this approach.

First, it takes a long time for the mold temperature to settle down to a steady state (a state in which a constant temperature is maintained stably) after temperature control is started. Until a steady state is reached, the quality of the molded product changes because the mold temperature changes, and therefore regular production is not possible, which impairs productivity.

Originally, the temperature of the cavity and the flow path leading to the cavity (parts called sprues and runners) directly affect the quality of the molded product, and these parts are only a part of the mold. do not have.
Therefore, basically it is only necessary to control the temperature of these parts, but since the material that makes up the mold is usually iron-based and is a relatively good heat conductor, it is necessary to control the temperature of some parts. Even if you intend to control the temperature, you end up controlling the temperature of the entire mold. Since the temperature of a portion with a larger heat capacity than necessary is controlled, the amount of heat required to stabilize the temperature inevitably increases, and it takes a long time to stabilize the temperature.

In fact, there are ways to improve this point, and they are proving effective. FIG. 1 shows an example of a mold structure incorporating this improvement method. The figure shows a longitudinal section of the mold, and shows how many cavity pieces 10 (two in the figure) form the cavity 2, and the cavity piece holding plate 11a (generally called a cavity plate). It is stored in. A backup plate 12 is arranged on the back side of the cavity piece holding plate 11a with the heat insulating plate 4a in between, and a spacer block 13 and a fixing plate 15 are each firmly fixed in this order.
5 is firmly fixed to the movable die plate 5 of the injection molding machine with the heat insulating plate 4b interposed therebetween.

In FIG. 1, 14 is an ejector pin, 16 is an ejector plate, and the ejector pin 14 is connected to the back-up plate 12 and the heat insulating plate 4.
a, a cavity piece 10a on the moving side is inserted through the mold, and after molding, the mold on the moving side is moved, the ejector plate 14 is pushed and the ejector pin 16 is pushed out into the cavity 2, and the molded product is taken out from the mold. 7 is a sprue bush, 8 is a sprue runner, 9 is an intermediate plate, 17 is a mounting plate, and 18 is a die plate. FIG. 2 is an explanatory diagram for showing the flow path shape of the temperature regulating water hole 6, and shows the state observed from the vertical direction of the cross section of FIG. 1.

A conventional general mold structure is one in which the heat insulating plates 4a and 4b are removed from such a structure, and in that case, as explained above, not only the entire mold becomes symmetrical for temperature control, but also the molding machine Because of the structure in which heat is easily transferred to the die plate on the moving side, there is a disadvantage that the temperature must be controlled using a portion with a larger heat capacity. Therefore, as shown in FIG. 1, by inserting a heat insulating plate, it is possible to reduce the substantial heat capacity of the portion where the temperature is to be controlled. Especially the cavity 2 like the heat insulating plate 4a.
By placing the insulation board as close as possible, the actual heat capacity can be minimized,
As a result, the temperature of the cavity can reach a stable state very quickly. However, this improvement method has some drawbacks. In other words, the insulation board must be able to withstand the mold clamping force sufficiently, so expensive materials must be used, and even then, it is difficult to obtain the same strength as steel, so the thickness of the insulation board increases as the mold thickness. However, this may lead to inconvenience when installing it to the molding machine.

Now, the second problem with the conventional concept of temperature control is particularly pointed out in multi-cavity molds. Figure 3 shows the problem in a safe manner. This figure shows the moving side cavity plate viewed from the parting surface side, and shows four square cavities 2 on the cavity plate 1 (the cavity plate 1 is formed from a cavity piece 10 and a cavity holding plate 11). There are several locations. Curves a, b, c, d, and e indicate isothermal lines of the planar temperature distribution of cavity plate 1, and curves a to e
The temperature is decreasing in this order. The situation shown in the figure is at a certain point in time when a substantially steady state has been reached after a certain degree of continuous molding. In the cavity arrangement as shown in the figure, the temperature in the central part of the mold tends to be high because the heat supplied from the resin flows in from four directions, resulting in a temperature distribution as shown in the figure. In such a case, if we look at the temperature distribution within one cavity, the parts near the center of the mold or the parts near other cavities tend to be hotter than the parts near the outer periphery of the mold. Since the shrinkage rate is greater in the higher temperature parts, there will be differences in the shrinkage rate within each part. Of course, the distribution of this shrinkage rate itself is a problem as a matter of practical observation, but even more so, especially when the molded product is thin, deformation is likely to occur due to the positional difference in this shrinkage rate. becomes a problem. The inventors discovered the fact that in thin-walled disk-shaped molded products, the temperature distribution inside the mold based on the cavity arrangement strongly affects the deformation of the molded product, making it difficult to mold it into a good product. I have experienced many.

In such cases, it is of course possible in principle to reduce the temperature distribution inside the mold by devising temperature control channels, but there is not much freedom in arranging the temperature control channels, and the temperature distribution Since it is determined by the balance between heat supply and heat radiation, it is necessary to change the design of the water channel every time the molding conditions change, and above all, calculating (or experimentally measuring) the heat balance itself is extremely difficult. difficult. Therefore, although the method of making the temperature distribution uniform through waterway design is effective in principle, it must be said that it is extremely difficult in practice.

The present invention provides means for effectively improving the above two problems.

That is, the present invention provides a multi-cavity mold in which a plurality of cavity pieces each having a temperature adjustment means are held on a cavity piece holding plate, and a heat insulating layer is provided between each cavity piece and the cavity piece holding plate. This is the structure of an injection mold.

The heat insulating layer in the present invention has the function of suppressing the influence of heat between the cavities and dividing the area to be temperature controlled into smaller areas, thereby reducing the substantial heat capacity of the area to be temperature controlled by each temperature adjusting means. It is what you do.

In order to effectively and specifically fulfill this function, the present invention forms a heat insulating piece around each part forming the cavity.

The present invention will be further explained with reference to Examples. Fourth
5 and 5 are structural diagrams showing one embodiment of the present invention, FIG. 4 is a plan view of the moving side of the mold viewed from the parting surface side, and FIG. FIG. 4 is a vertical sectional view taken along a plane passing through X and Y shown in FIG. 4; 4 and 5, a cavity piece 10 forming a cavity 2 is housed in a cavity holding plate 11 (generally called a cavity plate), and a back-up plate 12 is provided on the back side of this cavity piece holding plate 11. The spacer block 13 and the fixing plate 15 are each firmly fixed in this order. A heat insulating air layer 3 is formed around each of the cavity pieces 10, and therefore, the cavity pieces 10 and the cavity piece holding plate 11 have a structure in which heat is not directly transmitted to them except for a part. Although not shown in the figure, the main path of the temperature control waterway is arranged in the backup plate 12, and the branch paths are led to each cavity piece 10, and each cavity piece 10 is connected to the temperature control heat medium. Temperature controlled.

In such a structure, as described above, heat transfer between the cavities 2 is not carried out in the shortest distance through the cavity piece holding plate 11, but from the cavity 2 through the cavity piece 10.
A route is taken in which it passes through the backup plate 12 and further passes through another cavity piece 10 to reach the portion of the cavity 2 provided in that cavity piece 10. Therefore, the heat transfer path between the cavities becomes longer than in the past, and the mutual influence of heat between the cavities becomes extremely small. This effect is achieved by the cavity piece 10 and the cavity piece holding plate 11.
It is clear that the deeper the depth (the length in the direction perpendicular to the parting surface) of the insulating air layer 3 provided between the parts, the larger it becomes, but according to the inventors' experiments,
For example, the depth may be about 20 mm in absolute value, or if expressed in another way, even if it is about one-fifth of the planar dimension of the molded product (the diameter of the circular cavity 2 in Fig. 4). A sufficient improvement effect was observed. Moreover, considering this point in principle, it is clear that the effect can be obtained regardless of the depth. In addition, it is easy and effective to make this heat insulating layer an air layer like the above-mentioned heat insulating air layer 3, but if strength or rigidity is required in the same part, a heat insulating layer such as ceramic or the like can be used instead of air. Of course, it is also possible to use a synthetic material.

Next, FIG. 6 shows an example in which a heat insulating plate 4 is interposed between the cavity piece 11a and the backup plate 12. This heat insulating plate 4 allows the cavity piece 11a to
The insulation will be more complete. In addition, cavity piece 1
The temperature control water channels 6 provided at 0a and 10b have a circular tubular flow path shape when viewed in a plan view.

As described above, the present invention minimizes the influence of heat between cavities, especially in multi-cavity molds, thereby minimizing uneven shrinkage and deformation, and enables high-quality molding. In addition, since the actual heat capacity of the area to be temperature controlled can be reduced, the time required to start temperature control and reach a constant stable temperature state is shortened, thus increasing productivity and molding. It is very effective in reducing costs.

[Brief explanation of drawings]

Fig. 1 is a vertical cross-sectional view showing the structure of a conventional mold, Fig. 2 is an explanatory diagram showing the temperature control water hole in Fig. 1,
FIG. 3 is a diagram showing an example of temperature distribution in a conventional mold, and FIGS. 4 and 5 are examples of a mold structure according to the present invention.
The figure is a longitudinal sectional view, and FIG. 6 is a longitudinal sectional view showing another embodiment of the present invention. 1...Cavity plate, 2...Cavity, 3
...Insulating air layer, 4, 4a, 4b...Insulating board, 5a...
Moving side die plate, 5b...fixed side die plate, 6...temperature control water hole, 7...sprue bush, 8
... Sprull runner, 9... Intermediate plate, 10a... Cavity piece on moving side, 10b... Cavity piece on fixed side, 11a... Cavity piece holding plate on moving side, 11b... Cavity piece holding plate on fixed side, 12... Backup plate, 13...Spacer block, 14...Ejector plate, 15 Fixing plate, 16...Ejector pin, 17...Mounting plate.

Claims (1)

[Claims] 1. A multi-cavity mold in which a plurality of cavity pieces each having a temperature adjustment means are held on a cavity piece holding plate is characterized in that a heat insulating layer is provided between each cavity piece and the cavity piece holding plate. Structure of injection mold.