JPS62271717A - Mold for plastic molding - Google Patents

Abstract

PURPOSE:To mold a molded product which is superior in dimensional accuracy at a shortened molding cycle by preventing thermal effect on an insertion piece from a rest, by a method wherein the insertion piece and rest are separated from each other from a view point of temperature control, only the temperature of the insertion piece is controlled positively and the rest is made of ceramics which is a material whose heat conductivity is low. CONSTITUTION:An insertion piece K is made of steel, which can control the temperature of the insertion piece K and is provided with a heat medium passage 8 within which the heat medium flows. A rest G is made of zirconia which has low heat conductivity and superior heat resistance, wear resistance and compression resistance as compared with the steel which is a material of the insertion piece K. The inside of a cavity 5 of a mold for plastic molding, which has been clamped through a movable retainer plate 4, is filled with molten plastics through a sprue 9 and gate 10. the plastics is cooled and solidified by cooling water passing through the heat medium passage 8 and having controlled temperature and a desired molded product is obtained. As the lapse of time after completion of filling of the molten plastics into the cavity 5 is extremely little, the molded product is improved in its dimensional accuracy and capable of shortening of a molding cycle.

Description

[Detailed description of the invention] 3. Detailed description of the invention [Industrial application field] The present invention relates to a mold for plastic molding, and particularly to a mold for molding plastics.

The present invention relates to a plastic molding die suitable for molding a molded product with excellent dimensional accuracy in a shortened molding cycle.

[Conventional technology]

In plastic molding, if each part of the plastic is not cooled uniformly within the mold cavity, the entire molded product may warp or local "sink" may occur, resulting in poor performance in one dimension. It is a well-known fact that molding defects occur. The above-mentioned warping and "sinking" are caused by non-uniformity in temperature distribution on the cavity surface that is in contact with the plastic filled into the mold. In particular, when the speed of the molding cycle is increased with the aim of reducing the cost of molded products, the non-uniformity of the temperature distribution increases. The non-uniformity of the temperature distribution is due to the fact that since the frame directly holds the insert pieces that form the cavity, the insert pieces are sensitive to the influence of the frame temperature. That is, since the frame is constantly exposed to air, its temperature itself is unstable, and because it has a large heat capacity, it is not possible to quickly control the temperature.

Therefore, the entering piece is constantly affected by the unstable frame temperature, due to the temperature gradient that occurs between the entering piece and the frame.

Cavity surface temperature cannot be uniform. and,
When the speed of the molding cycle is increased, the temperature in the cavity increases, and the frame with a large heat capacity cannot follow this increase, and the temperature gradient between the input piece and the frame increases further. As described above, the idea of the prior art of controlling the temperature of the entire frame including the insert pieces was the main cause of the above-mentioned non-uniformity of temperature distribution.

[Problem that the invention seeks to solve]

As described above, in the conventional technology, the temperature distribution on the cavity surface is non-uniform, and therefore the dimensional accuracy of the molded product is not sufficient, and the molding cycle cannot be increased in speed.

As a way to solve this problem, for example,
As shown in Japanese Unexamined Patent Publication No. 58-12715, a method has been proposed in which a plate material with low thermal conductivity is interposed on the outside of the fixed frame and the movable frame to reduce the volume of the mold whose temperature must be controlled. . However, even with this method, there were obstacles such as the volume of the frame being large and a part of the frame being exposed to the outside air, and it was not a fundamental solution. One object of the present invention is to provide a mold for plastic molding that can improve the problems of the prior art described above and mold a molded product with excellent one-dimensional performance in a shortened molding cycle. It is something.

[Means for solving problems]

In order to solve the above problems, the configuration of the plastic molding die according to the present invention includes a fixed insert piece and a movable insert piece that form a cavity having almost the same shape as the molded product when the mold is closed; It has a fixed frame that holds the fixed inserted piece, and a frame that is a movable JJ frame that holds the movable inserted piece,
This frame is equipped with a guide pin that guides mold closing and opening, a sprue that introduces molten plastic into the cavity, and an extrusion pin that projects the molded product into the cavity. In the mold, the inserting piece is made of steel and is equipped with heating and cooling means that can control the temperature of the inserting piece, and the frame is made of ceramic.

[Effect]

By separating the inserting piece and the frame for temperature control and actively controlling the temperature of only the inserting piece, it is possible to speed up the molding cycle, and the frame is made of a material with low thermal conductivity. By making it made of ceramic, it is possible to prevent the influence of heat from the frame to the pieces.

〔Example〕

The basic matters related to the present invention are (a) the temperature of only the entering piece;
It is controlled by a heating and cooling means provided in this input piece. (b) As the material for the frame, use a material that has a lower thermal conductivity (for example, about 1/3 or less lower) than the material for the insert pieces. For example, the input pieces are made of steel (thermal conductivity is approximately 0,2
cLl/ an -s, 'c).

The frame is made of ceramic whose main component is zirconia (thermal conductivity is approximately 0, OO7ca1/an-s-"c)
Make it.

This is how it was done.

The present invention will be explained below by way of examples.

Figure 1 is a schematic cross-sectional view of a plastic molding die according to an embodiment of the present invention, and Figures 2 to 5 are for explaining an example of the results of a simulation analysis of the cooling process of a plastic molding die. Fig. 2 is an isothermal diagram of the plastic molding die according to Fig. 1 at the time when the plastic in the cavity reaches the heat deformation temperature range, and Fig. 3 is an isothermal diagram of the conventional plastic molding mold. FIG. 4 is an isothermal diagram of the mold at the above-mentioned point, FIG. 4 is a cooling characteristic diagram of the plastic molding mold according to FIG. 1, and FIG. 5 is a cooling characteristic diagram of the conventional plastic molding mold according to FIG. 3. It is a diagram.

In FIG. 1, K indicates a fixed insert piece 6. which forms a cavity 5 having almost the same shape as the molded product when the mold is closed. It is an entering piece consisting of movable human pieces 7, and this entering piece has a heating medium passage 8 through which a heat medium (for example, water) flows, which is related to a heating and cooling means that can control the temperature of the entering piece. It is made of steel. In addition, this entering piece K has a cavity 5.
A gate 10 is provided for introducing molten plastic therein. Reference numeral 2 denotes a fixed frame that can hold the fixed piece 6, 3 a movable frame that can hold the movable piece 7, and the frame G includes the fixed frame 2 and the movable frame. It consists of 3. This frame G is made of steel (thermal conductivity is approximately 0, 2 cat/cs-s-
'c) has lower thermal conductivity than
It is made of zirconia (ZrO2, thermal conductivity: O, OO7cal/am-s, 'c), which has excellent compression resistance. Reference numeral 1 denotes a fixed mounting plate to which the fixed frame 2 is mounted, and 4 is a movable mounting plate to which the movable frame 3 can be mounted and which can perform mold closing and mold opening operations. 9 is a sprue that introduces molten plastic into the cavity 5 through the gate 1o.

Note that a guide pin attached to the frame G to guide closing and opening of the mold, and an extrusion pin for protruding the molded product molded into the cavity 5 are not shown.

The operation of the plastic molding die constructed in this way will be explained.

Molten plastic injected from a molding machine (not shown) is filled through a sprue 9 and a gate 10 into a cavity 5 of a plastic mold which is closed via a movable mounting plate 4 . The filled plastic is cooled and solidified by the temperature-controlled cooling water flowing through the heat medium passage 8. The mold is opened via the movable mounting plate 4, and the molded product in the cavity 5 is ejected by the extrusion pin, completing one molding cycle and obtaining the desired molded product.

An example of the results of a simulation analysis of the cooling process of this plastic mold by the cooling water is compared with that of a conventional plastic mold (a mold in which both the insert piece and the frame are made of steel). I will explain. In the plastic molding die of this embodiment, the distribution of the isomixer 11 at the time when the plastic in the cavity reaches the heat deformation temperature range is as shown in FIG. 2. That is, on the 5 sides of the cavity,
The isothermal line 111 is almost parallel to the cavity 5 and has a small temperature gradient.On the other hand, the number of isothermic lines 11' that occur on the cavity 5 surface of the conventional plastic molding die crosses the cavity 5.

This shows that the temperature gradient is large. This is due to the fact that in conventional plastic molds, heat easily escapes from the insert piece to the frame, resulting in a large temperature gradient occurring at the boundary between the insert piece and the frame.

Moreover, the temperature of the surface of the cavity 5 with respect to the elapsed time after the completion of filling the molten plastic into the cavity 5 of the plastic mold of this example, that is, the cooling time, is as shown in FIG. Temperature distribution width ΔT
is extremely small.

In contrast, the cavity surface temperature distribution width ΔT' of a conventional plastic mold is considerably large.

From the results of these simulation analyses, the molded product molded using the plastic molding mold of this example has the following properties:
It is clear that the dimensional accuracy can be improved and the molding cycle can be shortened.

A specific example will be shown.

Using the plastic molding mold of this example.

A convex lens molded from acrylic resin.

The surface accuracy was improved to 3 μm or less, and the molding cycle was shortened to 10 minutes. When the same convex lens is molded using a conventional plastic mold, the one-plane accuracy is approximately 10μ.
m, the molding cycle was approximately 20 minutes.

According to the embodiment described above, a material with low thermal conductivity is used as the material of the frame G that holds the surroundings of the input pieces, and the temperature is controlled only for the input pieces, so that the outside air temperature is applied to the input pieces. It is hardly affected by external disturbances, such as heat dissipation from the input piece K to the frame G (or the opposite direction), and the temperature distribution on the surface of the cavity 5 can be easily controlled to be uniform. Therefore, the dimensional accuracy of the molded product is improved, the heat of the molten plastic is efficiently removed, and the molding cycle is shortened.

Another embodiment will be described.

FIG. 6 is a sectional view of a plastic molding die according to another embodiment of the present invention. In this Figure 6, the first
Parts with the same numbers as those in the figures are the same.

In this embodiment, a guide bushing 13 made of W4 is attached to the part of the movable frame 3A related to the frame, on which the guide pin 12 slides.
Further, guide bushes 15 made of steel are attached to the sliding portions of the push-out pins 14, and the sprues 9A attached to the fixed frame 2A related to the frame are made of steel.

With this configuration, in addition to the effects of the embodiment described above, the sliding surfaces of the guide bushes 13.15 on which the guide pins 12 and push-out pins 14 slide are finished with high precision, so that the guide pins 12 and This has the advantage that the ejector pin 15 slides smoothly. Similarly, since the sprue 9A is finished with high precision, it has the advantage that the molten plastic flows smoothly.

In each of the above embodiments, zirconia was used as the material for the frame G, but as shown in the table below, other ceramics such as silicon, alumina, etc., which are recommended for nitrided frames, may be used. Other materials such as stainless steel, titanium, and zinc nitride may also be used. In particular, zirconia has low thermal conductivity, as well as heat resistance, wear resistance, and compression resistance.

The best.

Furthermore, in each of the embodiments described above, the heating medium passage 8 through which temperature-controlled cooling water flows is used as heating and cooling means for the input piece.
However, a refrigerant may be used instead of the cooling water, and a heater may be embedded within the input piece.

〔Effect of the invention〕

As described in detail above, according to the present invention, it is possible to provide a plastic molding die that can mold a molded product with excellent dimensional accuracy in a shortened molding cycle.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of the shaft bearing of a plastic molding die according to an embodiment of the present invention, and Figures 2 to 5 are diagrams for explaining an example of the results of a simulation analysis of the cooling process of a plastic molding die. Fig. 2 is an isothermal diagram of the plastic molding die according to Fig. 1 at the time when the plastic in the cavity reaches the heat deformation temperature range, and Fig. 3 shows the isotherm diagram of the conventional plastic molding die. FIG. 4 is a cooling characteristic diagram of the plastic molding die according to FIG. 1, and FIG. 5 is a cooling characteristic diagram of the conventional plastic molding mold according to FIG. 3. , FIG. 6 is a sectional view of a plastic molding die according to another embodiment of the present invention. 2.2A...Fixed frame, 3,3A...Movable frame, 5
...Cavity, 6...Fixed insert piece, 7...Movable insert piece, 8...Heat medium passage, 9,9A...Sprue, 12...
...Guide pin, 13...Guide bushing, 14...
Push-out pin, 15... Guide bushing, G... Frame,
K...Irikoma.

Claims (1)

[Scope of Claims] 1. An inserting piece consisting of a fixed inserting piece and a movable inserting piece that forms a cavity having almost the same shape as the molded product when the mold is closed, a fixed frame holding the fixed inserting piece, and the movable inserting piece. The frame includes a movable frame for holding the pieces, and the frame includes a guide pin for guiding mold closing and opening, a sprue for introducing molten plastic into the cavity, and a movable frame for molding in the cavity. In a plastic molding mold equipped with an extrusion pin for ejecting a molded product, the input piece is made of steel and is equipped with heating and cooling means that can control the temperature of the input piece. A mold for plastic molding characterized by having a frame made of ceramic. 2. The mold for plastic molding according to claim 1, wherein the frame is a ceramic frame whose main component is zirconia. 3. The mold for plastic molding according to claim 1, wherein the frame is made of ceramic whose main component is silicon nitride. 4. The mold for plastic molding according to claim 1, wherein the frame is made of ceramic whose main component is alumina. 5. Claim 1, in which the portion of the frame on which the guide pin and push-out pin slide and the sprue are made of steel.
Mold for plastic molding as described in section.