JPH09193223A - Plastic injection mold and method for injection molding plastic using the mold - Google Patents

Abstract

PROBLEM TO BE SOLVED: To carry out the improvement in the transfer rate by suppressing the temperature distribution irregularity to a specified range and reduce or delete the molding failure. SOLUTION: This plastic injection mold comprises a plurality of channels 8 near the cavity 7 of the mold to feed a heating medium to the plurality of channels 8. In this case, pressure water or cooling water at 100 deg.C or higher at a specified flow rate is fed to the channels 8 to abruptly raise the temperature of the wall surface of the cavity 7, rapidly cooled and further the water surface distance ratio Kt obtained by the general formula (wherein the distance from the wall of the cavity 7 to the wall of the channel 8 is Y, the diameter of the channel 8 is (d) and the pitch distance is P) is set to 2.0 or less or preferably 1.5 or less. Thus, the temperature distribution irregularity of the mold wall surface is suppressed to the range which does not interfere in practical use.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a molding die and a molding method used for plastic injection molding.

[0002]

2. Description of the Related Art Injection molding of plastic is performed by injecting molten plastic into a molding die having a cavity having the same shape as a desired product shape, and cooling and solidifying the molten plastic. The appearance of the resulting product is, of course, approximately equal to the mold cavity, but strictly different.

In particular, fine irregularities on the cavity surface are often not accurately transferred. This is because a thin solidified layer is formed on the surface of the molten plastic at the moment when the molten plastic comes into contact with the surface of the cavity, which hinders accurate transfer of fine irregularities on the surface of the cavity. The ratio of the size of the fine irregularities on the surface of the cavity to the size of the fine irregularities on the surface of the obtained plastic molded product is called the transfer rate. In precise plastic injection molding, increase this transfer rate. That is one of the challenges.

There are three major defect items called "weld", "hake", and "silver" as defective products in plastic injection molding. It is the injection process to reduce or eliminate these three major defects. Is extremely important in the field.

The above-described method for improving the transfer rate, and
A molding method called high-temperature molding is known as a measure for reducing large defects. This delays the formation of the solidified layer of molten plastic by raising the temperature of the cavity surface in advance, accurately transfers the fine irregularities on the cavity surface, and then cools the mold to completely solidify the plastic molded product. It is a method of taking out. By using this high-temperature molding, the above-mentioned three major defects of molding can also be reduced or eliminated. Thus, the high-temperature molding method is an excellent method for injection molding.

However, in the high temperature molding, it generally takes time to heat up and cool down the mold, so that the molding cost cannot be kept within the normal injection molding cycle time and the molding cost becomes high.

For example, as a typical example of high temperature molding, there is a method of embedding an electric heater in a mold for heating the mold. In this method, in order to raise the mold wall temperature, the portion in which the electric heater is embedded must also be heated, so that the heat capacity of the heated portion increases, and it takes a long time to heat to a predetermined temperature, and cooling Time will be extended. The time required for heating and cooling varies greatly depending on the size of the mold, the use environment, and the like. For example, when the mold wall temperature is to be raised or lowered by 50 ° C., such a method in which the electric heater is embedded is It usually took several minutes to several tens of minutes. Naturally, this is unacceptable for molding sites seeking to reduce molding time by competing for several seconds.

A method has been proposed in which an appropriate flow path is provided in a mold in place of an electric heater, and a high-temperature heat medium is passed through this flow path. For example, Japanese Patent Application Laid-Open Nos. 62-117716 and 1
There is a publication of -115606.

One of the advantages of this method is that the heating time can be shortened by providing the flow path close to the mold wall. This is because, in addition to improving the heat conduction between the flow path and the mold wall surface, the heat capacity of the heated portion can be reduced. Further, a great advantage of this method is that a high-temperature heat medium flows through the flow path during heating and a low-temperature heat medium flows during cooling, so that not only the heating time but also the cooling time can be reduced.

In the high temperature molding, the temperature distribution on the mold wall is uniform as a practically important item along with the heating rate and the cooling rate. Even if a large heating rate is obtained, and as a result, the molding cycle can be shortened, if the temperature distribution on the mold wall is not uniform, the injection molded product's properties and finish will be uneven, which is rather than normal molding. It may even look bad.

The above-mentioned Japanese Patent Application Laid-Open No. 62-117716 proposes to form the cavity with a good heat conductive material in order to reduce the thermal resistance between the flow path and the mold wall surface.
It does not mention uneven temperature distribution.

Further, Japanese Patent Laid-Open No. 1-115606 considers the uniformity of temperature distribution, but it is not sufficient as will be described later. Furthermore, JP-A-1-11560
The temperature increase rate disclosed in Japanese Patent Laid-Open No. 6 requires about 1 minute to 1 minute and a half to increase the temperature at 50 ° C., and the temperature increase rate is insufficient.

[0013]

In injection molding, high temperature molding in which the temperature of the mold wall surface is preliminarily raised before injection of resin is effective as a measure for improving the transfer rate and as a countermeasure against the three major so-called molding defects. It has already been mentioned that it is a means.

In order to bring out the effect of high temperature molding, it is necessary to keep the temperature of the mold wall surface before resin injection near the glass transition point of the resin, preferably above the glass transition point. The glass transition point of resin varies depending on the type of resin, but is generally 1
The temperature is 00 ° C to 120 ° C or higher. Moreover, since the mold wall surface temperature during cooling is usually 40 ° C. to 80 ° C., the temperature rise temperature range and the cooling temperature range are 40 ° C. to 80 ° C. On the other hand, in order to prevent the extension of the molding cycle, the time devoted to heating and cooling must be suppressed to 40 seconds at maximum, preferably to several seconds.

Therefore, the temperature rising rate and the cooling rate need to be 1 ° C./sec or more. Therefore, as a concrete means for obtaining such a large temperature rising rate and cooling rate, as described in the conventional example. There has been proposed a method in which a flow path is provided in the vicinity of the mold wall surface and a high-temperature or low-temperature heat medium is caused to flow through the flow path.

By the way, in general, the state of temperature rise when an object is heated can often be approximated by the step response in the first-order lag element as shown by the curve A in FIG. As will be described later, our experimental results also show that the temperature rise of the mold wall surface is almost the same as the curve A in FIG. The value of the time constant T1 is defined in the step response in which the temperature rise is the first-order lag element, and it is known that the temperature at the time constant T1 is about 63% of the final reached temperature θ _H. Further, assuming that the elapsed time that is twice the time constant T1 is T2, the temperature θ2 at T2 is about 86 times the final reached temperature θ _H.
%. Furthermore, the elapsed time that is three times the time constant T1 is set to T3.
Then, the temperature θ3 at T3 is about 95% of the final reached temperature θ _H , and when the elapsed time that is four times the time constant T1 is T4, the temperature θ4 at T4 is about 98% of the final reached temperature θ _H. . Therefore, we use the above T2, T3 ... And θ2, θ3 ... As an index for comparing the heating rates. 12 shows the average heating rate until the gradient of the broken line B in FIG. 12 reaches the temperature θ2. Rate of temperature rise of mold wall above 1 ℃
The value of not less than / sec may be interpreted as a value of not less than 1 ° C./sec as the average rate of temperature rise, which is the slope of the broken line B in FIG. On the other hand, the slope of the tangent line C of the curve A in FIG. 12 indicates the heating rate at the start of heating, and the value is about twice the heating rate indicated by the broken line B. That is, in order to increase the temperature rising rate of the mold wall surface to a value of 1 ° C./second or more, the heating rate at the start of heating needs to be about 2 ° C./second or more.

That is, in order to suppress the extension of the molding cycle and put the high temperature molding into practical use, the temperature rising rate at the start of heating must be about 2 ° C./sec or more. There was a problem in that it was necessary to properly select the arrangement relationship and various quantities related to heat transfer such as the type of heat medium used and the flow rate.

First, regarding the heat medium for heating the mold, an example using a fluid containing oil as a main component has been reported. This is probably because the oil-based heat medium has a high saturation temperature at normal pressure and is unlikely to boil and is therefore easy to handle. For example, a paper published in the academic journal "Molding processing VOL.6, NO.2" published by the Japan Society for Molding Processing:
"Mold rapid heating / cooling system and its application examples" (below,
Reference 1) uses oil as a heat medium. However, in our study results, the heat transfer rate between the oil-based heat transfer medium and the wall surface of the flow channel becomes small due to the high viscosity,
There was a problem that it was difficult to obtain sufficient heating rate and cooling rate. In addition, as in Japanese Patent Laid-Open No. 1-115606, for example, a proposal of using saturated steam instead of oil has been proposed. However, in this case as well, there is a problem that the value of the heat transfer rate between the steam and the wall surface of the flow path is small, and a sufficient temperature rising rate and cooling rate cannot be obtained.

Further, even if the flow path is provided in the vicinity of the mold wall surface, it does not mean that the flow path is unnecessarily brought close to the mold wall surface, and it must be arranged in consideration of the uniformity of the temperature distribution on the mold wall surface. I won't. As a general tendency, in order to increase the temperature rising rate and the cooling rate, it is better to bring the flow path closer to the mold wall surface, but if the flow path is closer to the mold wall surface, the uniformity of the temperature distribution tends to deteriorate. Although it has already been stated that the transfer rate of molded products by high temperature molding improves, unevenness in the temperature distribution on the mold wall will cause uneven gloss in the appearance of the molded product. The appearance may be inferior to the molded product. For that reason, increasing the heating rate and cooling rate and ensuring the uniformity of the temperature distribution was a difficult problem in practice.

FIG. 13 is an example showing a temperature distribution on the mold wall surface when a flow path is provided in the vicinity of the mold wall surface and a high temperature heat medium is caused to flow through the flow path. FIG. 13B shows a cross-sectional view cut perpendicularly to the flow path provided near the mold wall surface, and FIG. 13A shows the temperature at the corresponding position in FIG. 13B. In FIG. 13B, 14 is a mold wall surface, and 8 is a flow path for the heat medium. The position where the flow path exists is indicated by the alternate long and short dash line F1-
F1, F2-F2, F3-F3 are shown, and the middle positions of the flow paths are shown by alternate long and short dash lines G1-G1, G2-G2. As shown in the figure, the mold wall temperature at the position where the flow path is present is higher than the mold wall temperature at other positions. That is, there is uneven temperature distribution. The temperature distribution indicated by the curve S1 at a certain time moves upward with the passage of time, and becomes the temperature distribution indicated by the curve S2. That is, the temperature distribution tends to become uniform over time. However, conversely, it takes time to obtain a uniform temperature distribution, which contradicts the desire to avoid extending the molding cycle.

Here, in the temperature distributions shown by the curves S1 and S2, the temperatures at positions where the flow path exists (positions indicated by alternate long and short dash lines F1-F1) are θf1 and θf2, respectively, and intermediate positions (positions indicated by alternate long and short dashed lines G1 to G1). The temperature at
1, θg2, the ratio between θf and θg, that is, Rθ1
The value of θg1 / θf1 and Rθ2 = θg2 / θf2 is used as a measure of the temperature distribution unevenness. Of course, the closer the value of Rθ is to 1, the more uniform the temperature distribution.

In order to bring the temperature distribution unevenness Rθ close to 1 while suppressing the extension of the molding cycle to a minimum, the diameter d of the channel 8 shown in FIG. 13, the distance Y between the channel 8 and the wall surface 14 and the flow rate are shown. The value of the pitch distance p of the path 8 must be set to an appropriate value.

FIG. 14 is No. 5 "Injection Mold" supervised by Kiyoshi Okada.
Edition: Published by Plastic Age (hereinafter referred to as Literature 2)
FIG. 49 is an example of a conventional example showing the cooling hole diameter and its positional relationship. When the hole diameter is 1, the pitch distance between the holes is 5, and the distance between the center of the holes and the mold wall surface is 3.
It says that. That is, the pitch distance between the holes is larger than the distance between the holes and the mold wall surface. Since this figure shows a general arrangement of cooling holes under normal molding conditions, it is a matter of course that the arrangement is different from the passage arrangement in the case of rapid heating and rapid cooling, which is the object of the present invention. When the flow path arrangement in such a normal mold is used for high temperature molding, the temperature distribution unevenness shown in FIG. 13 becomes large.

Further, Japanese Unexamined Patent Application Publication No. 1-115606 discloses in this regard that "the flow channel pitch is preferably set to the flow channel width +4 mm or the flow channel width +10 mm, particularly the flow channel width +10 mm.
If the temperature exceeds this value, the temperature rise rate will become slower and the temperature spots will tend to become larger. ”While taking into consideration the uniformity of the temperature distribution, it is only the flow that affects the temperature distribution unevenness. Not only the path pitch distance but the flow path 8 shown in FIG.
Diameter (or flow channel width) d, the distance Y between the flow channel 8 and the mold wall surface 14 and the pitch distance p of the flow channel 8 are all related, and the relationship between the distance Y and the pitch distance p is particularly important. However, there is no description on this point.

In the above-mentioned document 1, Y = 1
Since p = 28.5 mm with respect to 0 mm, as will be described later, in the result of our study, the uniformity of the temperature distribution is insufficient.

As described above, there has been a problem in the prior art that means for realizing a practical temperature rising rate and cooling rate to keep the temperature distribution unevenness within a predetermined range has not been solved.

[0027]

In order to solve this problem, the present invention provides a flow path for flowing a heat medium in the vicinity of a mold wall surface,
By providing selection means for selecting three factors of the diameter or width d of the flow path, the distance Y between the flow path and the mold wall surface, and the pitch distance p of the flow path to appropriate values, and by appropriately using the above selection means The mold for injection molding is for high temperature molding in which the temperature distribution unevenness is minimal and the mold wall surface heating rate and cooling rate are high. Further, an injection molding method is provided in which a means for selecting the type, flow rate and flow path diameter of the heat medium is provided, and the temperature rising rate and cooling rate of the mold wall surface are further increased by appropriately using the above selecting means.

Further, since the plastic injection mold of the present invention has the above-mentioned structure, the temperature distribution unevenness of the mold wall surface can be practically hindered while realizing the rapid temperature rising rate and cooling rate of the mold wall temperature. It became possible to hold down to. Therefore, by using the plastic injection mold of the present invention, it is possible to exhibit the characteristics of high temperature molding while minimizing the extension of the molding cycle, so that it is possible to remarkably improve the transfer rate. "Hike",
It has become possible to reduce or eliminate the three major defects of so-called plastic molding such as "silver".

Further, by using the plastic injection mold of the present invention and adopting the injection molding method of the present invention, the heat transfer rate in the flow path of the heat medium can be remarkably improved. The speed was enabled and the extension of the molding cycle could be minimized.

[0030]

BEST MODE FOR CARRYING OUT THE INVENTION According to the present invention, a plurality of flow passages are provided in the vicinity of a cavity of a mold, the diameter or width of the flow passages is set to d, the pitch distance between the flow passages is set to p, and the flow path is set to p. Let Y be the distance from the mold wall of the cavity to the wall of the flow path at the road position, and tc be the distance from the mold wall of the cavity to the wall of the flow path at the center between the flow paths. When expressed as Kt, which is the wall surface distance ratio, the numerical value determined by the allowable temperature distribution unevenness of the mold wall surface is substituted into the wall surface distance ratio Kt to find d / Y and p / Y that satisfy Equation 1, and the calculated p / Y The present invention provides a plastic injection mold having a mold dimension of p / Y smaller than the value of.

Further, in the present invention, when a plurality of flow paths are provided in the vicinity of the cavity of the mold and the distance from the mold wall surface of the cavity at the flow path position to the wall of the flow path is Y, the above Y
Provided is a plastic injection molding die which realizes a rapid temperature rising rate and a cooling rate of a mold wall surface temperature by setting the dimension to a value of 6 mm or less.

Further, according to the present invention, when the distance between the mold wall surface of the cavity and the wall of the flow path is selected so as to satisfy Y, the flow path diameter d, and the pitch distance p, it is substituted into Kt of Expression 1. By providing a value of 2.0 or less, preferably by assigning a value of 1.5 or less to Kt, a plastic injection molding die is provided in which the temperature distribution unevenness on the mold wall is suppressed within a practically acceptable range. Is.

Further, in the present invention, the distance Y from the mold wall surface of the cavity to the wall of the flow path is set to a value of 6 mm or less, and the ratio relating to the Y dimension, the flow path diameter d, and the pitch distance p is selected so as to satisfy the expression 1. At times, by selecting the value to be substituted for Kt in Equation 1 to be 2.0 or less, preferably the value to be substituted for Kt to be 1.5 or less, the rapid heating rate and cooling rate of the mold wall surface temperature can be increased. The present invention provides a plastic injection molding die in which the temperature distribution unevenness on the die wall surface is suppressed within a practically acceptable range while being realized.

Furthermore, in the present invention, a plurality of flow paths are provided in the vicinity of the cavity of the mold, the diameter or width of the flow paths is set to d, the pitch distance between the flow paths is set to p, and the flow path position The distance from the mold wall surface of the cavity to the flow channel is Y, the distance from the mold wall surface of the cavity to the flow channel wall at the central position between the flow channels is tc, and tc / Y is called the wall surface distance ratio. When expressed by Kt, the numerical value determined by the allowable temperature distribution unevenness of the mold wall surface is substituted into the wall surface distance ratio Kt, and the following formula is used.
D / Y and p / Y satisfying the above conditions are obtained, and a plastic injection mold having a p / Y value smaller than the obtained p / Y is used as a mold dimension, and pressure water of fresh water is used as a heat medium flowing in the flow path. Is a plastic injection molding method in which the flow rate and the flow path diameter are selected so as to satisfy Equation 2.

[0035]

【Example】

(Embodiment 1) FIG. 1 is a sectional view of a plastic injection mold showing an embodiment of the present invention, and FIG. 2 is an arrow M- of FIG.
FIG. 3 is a sectional view taken along line M in FIG. 1, and FIG. 3 is an enlarged sectional view taken along line N in FIG. 1 is a fixed type, 2 is a movable type, 3 is a mold mounting plate, 4 is a locate ring,
Reference numeral 5 is a sprue hole, and 6 is an ejector pin. The space formed by closing the fixed mold 1 and the movable mold 2 is a cavity 7
It is. The fixed mold 1 is positioned at a predetermined position of the injection molding machine by the locate ring 4. The molten resin is injected from the injection nozzle (not shown) into the cavity 7 through the sprue hole 5. A large number of flow paths 8 are provided along the cavity 7 of the fixed mold 1 as shown in FIG. As shown in FIG. 2, tanks 9A and 9B are provided before and after the fixed mold 1, and the flow path 8 is connected to the tanks 9A and 9B by connecting pipes 10A and 10B. Tanks 9A and 9B are supply pipes 11A and 1
It is connected to the water source by 1B. Plugs 12A, 12
B is for fixing the supply pipes 11A and 11B to the fixed mold 1. The plugs 12A and 12B are provided with thermocouples so that the supply water temperature can be detected. Although the construction of the plastic injection molding die in which the flow path 8 is arranged as described above is known, the problem is that the diameter d of the flow path 8 and the dimension Y of the flow path 8 and the wall surface of the cavity 7 as shown in FIG. It is how to select the pitch distance p between the flow paths 8 and how to determine the parameters such as the type and flow rate of the heat medium flowing in the flow paths 8.

First, in this embodiment, heated fresh water is used as the heat medium. Since the mold wall surface temperature during heating is 100 ° C. to 120 ° C. or higher as described above, the heating temperature of fresh water is 130 ° C. or higher. Naturally, a pressure higher than the saturation pressure is applied to fresh water to prevent evaporation.

Usually, oil having a high saturation temperature is often used as the heat medium, but since oil generally has a high viscosity, the heat transfer coefficient (also referred to as a film coefficient) between the oil and the flow path wall becomes small, As a result, it was difficult to obtain a large heating rate according to our study results.

There is also a plan to use saturated steam, but the above heat transfer rate is still small when steam is used as it is. When steam condenses and forms a water film on the channel wall, the heat transfer rate increases, but it is necessary to increase the water flow rate to obtain a sufficient heat transfer rate. Is most suitable.

Even if compressed water is used, the flow velocity of water changes depending on the flow rate and the diameter of the flow path, so that the flow rate and the diameter of the flow path must be selected as appropriate values in order to obtain a large heat transfer rate. According to the experimental results, when the diameter d of the flow path 8 is expressed in millimeters and the flow rate Q is expressed in liters / minute, by selecting the flow path diameter and the flow rate so as to satisfy the empirical formula shown in Equation 2, a sufficiently large heat can be obtained. I found that a passover rate was obtained.

From the practical pump capacity and the like, the value of the flow rate is
It is appropriate that the standard is 15 liters / minute or less for one flow path. In addition, it is necessary to select the diameter of the flow path to be 3 mm or more due to the limitation of the strength of the mold and the limitation of the work.

The flow rate and the flow path diameter are determined based on the restrictions on the flow rate and the flow path diameter, and the need to satisfy the equation (2). As will be described later, the shape of the flow path of the heat medium does not necessarily have to be circular.
In that case, instead of the channel diameter, the channel width or a representative dimension corresponding to the channel diameter is used as the value of d.

Next, the value of the distance Y (see FIG. 3 or FIG. 13) between the wall surface of the flow path 8 and the mold wall surface of the cavity 7,
If the selection is made from the viewpoint of simply increasing the temperature rising rate and the cooling rate, the value of Y may be selected as small as possible within the range allowed by the die strength. However, considering the uniformity of the temperature distribution, the value of Y is limited by the value of the diameter d of the flow path 8, which will be described below.

First, it has been described that the temperature distribution unevenness in the present invention is represented by Rθ = θg / θf in FIG.

Then, as conditions for ensuring the uniformity of the temperature distribution, the above-mentioned flow path diameter d, Y dimension and pitch distance p are set.
As a result of examining the relationship with, it was found that there is a relationship shown in Formula 1.

In this equation, Kt is a numerical value called the wall surface distance ratio. Then, the value of Kt to be substituted into Equation 1 is
It is determined from the value of Rθ, which is a measure of the uniformity of temperature distribution. For example, in order to keep Rθ at 60% or more at the time of T2, the value of Kt may be 2.0 or less, but Rθ at the time of T2 is 80 or less.
The value of Kt needs to be 1.5 or less in order to maintain at least%.

As described later, the relationship between Rθ and Kt is first found by simulation calculation and then experimentally confirmed.

The value of Rθ varies depending on the degree of surface properties of the molded product required. The value of Rθ may be 60% or more for a normal molded product, but if the uniformity of the surface properties of the molded product is extremely strict, the value of Rθ should be 80% or more. There is a need.

That is, the value of Rθ to be achieved is determined according to the desired surface properties of the molded product. When the value of Rθ is determined, the value of Kt necessary for that is determined, and when the value of Kt is determined, the formula 1 is satisfied. P / Y and d / Y can be obtained. The values of p / Y and d / Y that satisfy the equation 1 are (p
/ Y) c and (d / Y) c, the value of p / Y actually adopted in the die design is more than the value of (p / Y) c in order to ensure the uniformity of temperature distribution. Must be small. That is, it is necessary to satisfy the relationship of Expression 3.

[0049]

(Equation 3)

On the other hand, if the value of p / Y is too small,
Since the flow paths 8 and 8 interfere with each other, the value of p / Y must be larger than the value of (d / Y) c in order to avoid the interference. That is, it is necessary to satisfy the equation 4.

[0051]

(Equation 4)

This relationship will be described with reference to FIGS. 11 (a) and 11 (b). The curve Py of FIG.
The relationship between d / Y and p / Y when t = 2.0 is shown. Therefore, the region that satisfies the equation 3 is the region below the curve Py in the figure. Further, the straight line Pd in FIG.
Since / Y = d / Y is shown, the area above the straight line Pd must be satisfied in order to satisfy Expression 4. Therefore, after all, the shaded area S is the area that can be actually adopted for the die design. That is, the value of d / Y is required to be about 6.0 or less.

The curve Py in FIG. 11 (b) shows the relationship between d / Y and p / Y when Kt = 1.5 in equation (1). Therefore, the region that satisfies the equation 3 is the region below the curve Py in the figure. Further, since the straight line Pd in FIG. 11B shows p / Y = d / Y, the region must be above the straight line Pd in order to satisfy Expression 4.
Therefore, after all, the shaded area S is the area that can be actually adopted for the die design. That is, the value of d / Y is about 3.45.
The following is required:

From the viewpoint of simply increasing the temperature rising rate and the cooling rate, it is better to make the value of Y as small as possible within the range allowed by the die strength, but if the value of Y is made small, the above d / Y The value becomes large. Therefore, the value of Y is selected in consideration of satisfying the equations 1, 3 and 4.

On the other hand, as described above, it is necessary to secure the rate of temperature rise of the mold wall surface at 2 ° C./sec or more immediately after the start of heating. Therefore, the relationship between the temperature rising rate and the Y dimension was obtained by simulation calculation, and the result was verified by making an experimental type.

FIG. 6 shows the result of obtaining the relationship between the temperature rising rate and the Y dimension by simulation calculation. The horizontal axis represents the Y dimension, and the vertical axis represents the heating rate up to time T2.

In FIG. 7, an experimental mold similar to that of FIG. 1 described above was manufactured by using a steel material, and the response of the mold wall temperature when hot water of 110 ° C. as a heat medium was passed through the flow channel was tested. The result. In FIG. 7, the vertical axis represents temperature and the horizontal axis represents time. However, since the data obtained by automatically recording the experimental results is used as is, note that the time elapses toward the left. As described above, the response characteristic of the mold wall temperature shown in FIG. 7 is very similar to the step response of the first-order lag element. Although there are some points that do not agree with rigorous verification, we decided to handle the response of the mold wall temperature in Fig. 7 as the step response of the first-order lag element, considering the ease of handling. Then, the time T2 for reaching the temperature of 86% of the rise width of the mold wall surface was read from FIG. 7 and the temperature rising rate was obtained. The same experiment was performed by changing the Y dimension to 6 mm and 11 mm, and the experimental data of the obtained temperature rising rate are shown in FIG. The arrow indicates the range of variation of the experimental data.

As can be seen from FIG. 6, the temperature increase rate is slower in the experimental result than in the simulation result. There are various factors that can be considered as the reason, but the largest factor is that the heat medium in the flow channel is immediately changed from low temperature to high temperature in the calculation. It can be mentioned that low temperature water adheres to and is not immediately replaced by high temperature water. As described above, the agreement between the calculation and the experimental result is not always accurate, but the tendency that the temperature rising rate decreases as the Y dimension increases is in agreement. Therefore, the Y dimension needs to be at least 10 mm or less in order to increase the temperature rising rate immediately after the start of heating to 2 ° C./sec or more, and it is necessary to set it to 6 mm or less in consideration of the variation factor in the practical type. It can be read from 6.

In this way, R of the desired temperature distribution unevenness is obtained.
The value of Kt is selected based on the value of θ, the ratio of the Y dimension to the flow path diameter d and the pitch distance p is calculated by Equation 1, and the Y dimension is suppressed to 6 mm or less, so that the mold wall surface is rapidly heated, While cooling, it is possible to suppress uneven temperature distribution on the mold wall surface to a desired value or less.

Next, the derivation process of the above equation 1 will be described. FIG. 8 illustrates the calculation results by the computer and the simulation. When the diameter d of the flow path and the distance between the wall surface of the flow path and the mold wall surface of the cavity are Y, the temperature of the mold wall surface directly above the flow path and the temperature of the mold wall surface at an angle of θ from directly above the elapsed time It shows how it changes with T2, T3, and T4. The vertical axis represents temperature, and the horizontal axis represents the mold wall surface position at an angle of θ from directly above. The temperature of the mold wall directly above the flow path is highest, and the temperature of the mold wall decreases as it moves away from directly above. Further, in FIG. 9, the horizontal axis represents the mold wall surface position at an angle of θ from just above the flow path, and the vertical axis represents FIG.
The value of Rθ described in 3 is shown in percent. Although the elapsed times T2, T3, T4 shown in the figure have already been described, assuming that the time constant is T1, T2 = T1 × 2, T3 = T
The time is in the relation of 1 × 3, T4 = T1 × 4.

On the other hand, as shown in FIG. 13, the diameter d of the flow path, the distance Y between the wall surface of the flow path and the mold wall surface of the cavity,
Letting the pitch distance p of the flow path be tc, the distance between the wall surface of the flow path and the mold wall surface of the cavity at the center point of the pitch is tc
tc is expressed by the equation 5. Equation 6 can be easily obtained from Equation 5, but in Equation 6, the left side is represented by tc / Y.

[0062]

(Equation 5)

[0063]

(Equation 6)

The horizontal axis of FIG. 9 is the mold wall surface position at an angle of θ from directly above the flow path. When the distance between the wall surface of the flow path and the mold wall surface of the cavity is t, the horizontal axis of FIG. Can be replaced by t / Y. FIG. 10 is a diagram in which t / Y is plotted on the horizontal axis and values on the vertical axis are rewritten using FIG. 9 as they are.

If the distance between the wall surface of the flow path and the cavity wall surface at the center point of the pitch is represented by tc, the value of Rθ at the center point of the pitch can be obtained by changing the value on the horizontal axis of FIG. 10 to tc / Y. Should be read as

For example, in FIG. 10, the distance Y between the wall surface of the flow path and the mold wall surface of the cavity at the flow path position, and the distance tc between the wall surface of the flow path and the mold wall surface of the cavity at the pitch center point.
For example, the reached temperature at the mold wall surface position of tc / Y = 2 is about 62% (Rθ = 62%) compared with the reached temperature at the passage center at the elapsed time T2, and at the elapsed time T3. Approximately 73% (Rθ = 7
3%), which means that it is necessary to wait until the elapsed time T4 until the ultimate temperature of Rθ = 80% or more is reached.

Usually, the mold wall temperature at the center point of the pitch is the lowest with respect to the mold wall temperature at the center of the flow path. Therefore, in order to set Rθ, which is a measure of the temperature unevenness of the mold wall surface, to a desired value, it is sufficient to set Rθ at the pitch center point to a desired value. Therefore, the elapsed time T2, T3
Can be read from FIG. In other words, tc / Y required to fit within the desired Rθ within the desired elapsed time
The value of can be read from FIG. In this way, the value of tc / Y thus obtained is set as Kt and is substituted into the equation 1.
It can be seen from FIG. 10 that Kt = 2.0 is sufficient because Rθ = 60% or more can be secured in a normal molded product. Further, when strict surface properties are required, it is necessary to secure Rθ = 80% or more, so Kt = 1.
It can be read from FIG. 10 that it is necessary to set the number to 5 or less.
By selecting the value of Kt in this way, it is possible to ensure the uniformity of the mold wall surface temperature required for each case, that is, Rθ.

Given the value of Kt, d /
Since the values of Y and p / Y can be calculated, it is possible to determine the mold structure that secures the required temperature uniformity.

(Embodiment 2) FIGS. 4 and 5 show another embodiment of the present invention. In FIG. 4, the fixed die is divided into a fixed die 1a and a fixed die 1b. And the some flow path 8 is carved in the upper surface of the fixed die 1b. The heat medium is supplied from the supply pipe 11 shown in FIG. 4, enters the tank 9 shown in FIG. 5, and is further supplied to the flow path 8 through the connecting pipe 10. Although not shown, an appropriate O-ring is sealed between the fixed mold 1a and the fixed mold 1b so that the heat medium does not leak from the gap between the fixed mold 1a and the fixed mold 1b.

In FIG. 1 and FIG. 2, the heat medium passage 8 was drilled in the fixed mold, whereas in FIG. 4 and FIG. 5, it was formed by carving a groove on the upper surface of the fixed mold 1b with a milling machine. ing.

In the structure shown in FIGS. 1 and 2, the flow path 8 is limited to a circular shape and a linear shape, and when the mold size is large, deep hole drilling is required, which makes mold processing difficult, and thus there are restrictions on the arrangement of the flow path. receive. On the other hand, the structures of FIGS. 4 and 5 are less restricted in the arrangement of the flow paths, but there is a drawback that it is necessary to prevent water leakage from the gap because the fixed mold is divided.

As a representative dimension of the flow path 8 in the case of adopting the structure of FIGS. 4 and 5, the width d of the flow path is used as shown in FIG. However, when the flow rate is determined using Equation 2, if the depth h of the flow channel is twice or more as large as the width d of the flow channel, the cross-sectional area of the flow channel is calculated and the circle corresponding to the cross-sectional area is calculated. Number 2
Substitute as d.

In the description of the above embodiments, the case where pressure water of fresh water is used as the heat medium has been described. However, the matters relating to the equation 1 regarding the temperature distribution unevenness are heat medium other than water,
For example, it has been confirmed that this also applies to the case where oil or the like is used, so the heat medium of the present invention is not limited to the pressure water of fresh water.

[0074]

As described above, the present invention provides a plastic injection molding die having a structure in which a plurality of flow paths are provided in the vicinity of a cavity of a mold and a heat medium is flown through the plurality of flow paths. It is possible to rapidly raise the temperature of the cavity surface and cool it by flowing pressure water or cooling water of 100 ° C or more at a flow rate specified in Equation 2 to Y. When selecting the ratio of the flow path diameter d and the pitch distance p so as to satisfy the equation 1,
The value to be substituted for Kt in Equation 1 is 2.0 or less, preferably 1.
By selecting 5 or less, the temperature distribution unevenness on the mold wall surface can be suppressed to a range that does not hinder practical use.

As a result, the extension of the molding cycle can be suppressed to a minimum, and it is possible to realize the improvement of the transfer rate and the reduction or elimination of molding defects, which are the features of high temperature molding.

[Brief description of the drawings]

FIG. 1 is a sectional view of a molding die according to an embodiment of the present invention.

FIG. 2 is a sectional view taken along the line MM in FIG.

FIG. 3 is an enlarged cross-sectional view of a portion N in FIG.

FIG. 4 is a sectional view of a molding die of another embodiment using the present invention.

5 is a cross-sectional perspective view taken along the line NN of FIG.

FIG. 6 is a diagram showing the Y dimension of FIG. 3 on the horizontal axis and the temperature rising rate on the vertical axis.

FIG. 7: Experimental data of temperature rising rate in an experimental mold having the same structure as the forming mold of the present invention

FIG. 8 is an explanatory diagram showing calculation results showing a time course of temperature distribution of a mold wall surface centering on a flow path.

FIG. 9 is an explanatory view showing a calculation result showing a time course of Rθ of a mold wall surface centering on a flow path.

FIG. 10 is an explanatory diagram showing a calculation result showing a time course of Rθ using t / Y on the horizontal axis.

FIG. 11 is an explanatory diagram showing the relationship between Equations 1, 2 and 3.

FIG. 12 is an explanatory diagram of a temperature response having a first-order lag element.

FIG. 13 is an explanatory view of uneven temperature distribution on the mold wall surface.

FIG. 14 is an explanatory diagram of a flow path arrangement of a conventional example.

[Explanation of symbols]

 7 cavity 8 flow path

Claims (6)

[Claims] 1. An injection molding die in which a plurality of flow passages are provided in the vicinity of a cavity of a mold, wherein the diameter or width of the flow passages is d, the pitch distance between the flow passages is p, and the flow passages are Let Y be the distance from the mold wall surface of the cavity to the wall of the flow path at the position, and tc be the distance from the mold wall surface of the cavity to the wall of the flow path at the central position between the flow paths.
Y is the wall surface distance ratio Kt, and the wall surface distance ratio Kt in Equation 1
P obtained by substituting a value determined by the allowable temperature distribution unevenness into
A plastic injection molding die in which the temperature distribution unevenness on the die wall surface is set within an allowable range with the pitch distance p and the distance Y that are equal to or less than the value of / Y as die dimensions. [Equation 1] 2. The plastic injection molding die according to claim 1, wherein a rapid temperature rising rate and a rapid cooling rate are obtained by setting the distance Y to 6 mm or less. 3. The plastic injection mold according to claim 1, wherein the wall surface distance ratio Kt is 2.0 or less to ensure the uniformity of temperature distribution. 4. The plastic injection mold according to claim 3, wherein the wall distance ratio Kt is set to 1.5 or less to ensure the uniformity of temperature distribution. 5. The uniformity of the temperature distribution is ensured while the distance Y is set to a value of 6 mm or less and the wall surface distance ratio Kt is set to a value of 1.5 or less to obtain a rapid heating rate and a cooling rate. The described plastic injection mold. 6. The plastic injection molding die according to claim 1, wherein fresh water pressure water is used as a heat medium flowing in the flow path,
A plastic injection molding method in which the flow rate and the diameter of the flow path satisfy the expression 2. [Equation 2]