JPH09300417A - Injection molding, injection molding die and injection molding device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an injection molding method by which it is possible to control a weld line without particularly increasing a resin molding temperature and an injection pressure, and an injection molding die and an injection molding device used in this method. SOLUTION: This injection molding method is to flow a molten resin consisting of a thermoplastic resin from a gate part 25 leading to a cavity 15 into the cavity 15 formed along the split faces 11a, 21a of a molding die, and solidify the molten resin by cooling. In this case, an electric heater 32 is provided near a confluence position 16, in the cavity 15, where the molten resin which is flowed from the gate part 25 and diverted into two streams, has these streams again united. In the cooling period of a molding cycle, the molding die temperature near the confluence position 16 is maintained at a deflection temperature under load of thermoplastic resin +(5-30) deg.C by the electric heater 32.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermoplastic resin injection molding method, and an injection molding die and an injection molding apparatus used therein.

[0002]

2. Description of the Related Art Generally, in injection molding of a thermoplastic resin, a weld line occurs depending on the shape of the molded product. This weld line is generated when the molten resin flowing in the cavity for forming the molded product merges and is not completely fused due to the decrease in resin temperature. If the weld line is strong, the molded product on the cavity surface Not only the transferability is inferior and the appearance is deteriorated, but also the adhesiveness of the merging surface portion is inferior and the strength is lowered, which causes various molding defects.

Conventionally, in order to suppress the weld line, the resin molding temperature is raised in order to improve the fluidity of the resin, or the injection pressure (and hence the injection speed) is increased in order to prevent the resin temperature from decreasing at the time of merging. However, in the former case, there is a problem that burr or resin material is decomposed or gas burns occur, and in the latter case, there is a problem that burr or product deformation occurs. No successful control results have been obtained.

[0004]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems, and an injection molding method, an injection molding die, and an injection molding mold capable of suppressing the weld line without increasing the resin molding temperature and the injection pressure. It is intended to provide an injection molding device.

[0005]

A method for molding a thermoplastic resin according to the present invention comprises a molten resin made of a thermoplastic resin from a gate portion following the cavity in a cavity formed along a dividing surface of a mold. In the injection molding method of injecting and cooling and solidifying the molten resin, a heater is provided in the mold in the vicinity of the confluence position in the cavity where the molten resin that flows in from the gate portion and is split in the cavity is merged again, In the cooling period of the cycle, the mold temperature near the confluence position is maintained at the deflection temperature of the thermoplastic resin under load plus (5 to 30) ° C. by the heater.

The mold for injection molding according to the present invention is a mold for thermoplastic resin injection molding in which a cavity and a gate portion following the cavity are formed along the dividing surface of the mold, and the mold flows from the gate portion. An electric heater and a temperature detector are provided in the mold in the vicinity of the confluence position in the cavity where the molten resins split in the cavity merge again.

Further, the injection molding apparatus of the present invention is a mold for thermoplastic resin injection molding in which a cavity and a gate portion following this cavity are formed along a dividing surface of the mold, and the thermoplastic resin is injected from the gate portion. An electric heater and a temperature detector are provided in the mold near the confluence position in the cavity where the molten resins split in the cavity merge again, and the electric heater and the temperature detector are used to detect the temperature. The amount of power supplied to the electric heater is adjusted in accordance with the output of the heater to adjust the mold temperature of the temperature detector installation portion to the deflection temperature under load of the thermoplastic resin + (5 to 30) ° C. in the cooling period of the molding cycle. It is characterized in that it is connected to a temperature control device maintained at.

The thermoplastic resin in the present invention includes AB
Various thermoplastic resins such as S resin, polystyrene, polyethylene, polypropylene, polyacetal, polycarbonate, nylon and the like are included.

In the present invention, the deflection temperature under load of the thermoplastic resin means the temperature measured by Method A of the test method specified in JIS K7207. Further, in the present invention, at the time of injection molding, the mold temperature in the vicinity of the confluence position where the molten resin merges in the cavity, or the mold temperature of the installation part of the temperature sensor provided in the vicinity of the confluence position is set to the deflection temperature under load. Maintaining in the range of + (5-30) ° C.
If the mold temperature is less than the deflection temperature under load + 5 ° C, the control of the weld line will be insufficient, and the deflection temperature under load +3
This is because if the temperature exceeds 0 ° C, surface defects such as melting of the resin surface occur.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. In the figure, 1 is an injection molding die, which is a fixed-side die 3 attached to a fixed-side platen 2 of an injection molding machine.
And a movable mold 5 attached to the movable platen 4. 6 is a nozzle of the injection molding machine, and 7 is an ejector rod, which is reciprocally driven by a cylinder (not shown). The fixed-side mold 3 includes a fixed-side mold plate 11, a fixed-side mounting plate 12, and a sprue bush 13, and a runner 14 is formed in the sprue bush 13. A concave surface portion for forming the cavity 15 for molding the product 40 is provided on the dividing surface (mold opening surface) 11a of the fixed-side template 11. This product 40
As shown in FIGS. 2 and 3, each has a rectangular small container shape that opens downward and has a square hole 42 at the center of the top plate 41.

The movable side mold 5 has a movable side mold plate 21, a spacer block 22, and a movable side mounting plate 23 as main constituent members, and a split surface (mold opening surface) 21a of the movable side mold plate 21 has a cavity. Protrusion 2 with convex surface for forming tee 15
4, a gate 25 and a runner 26 communicating with the cavity 15 are provided, and an end of the runner 26 communicates with the runner 14 when the mold is closed. The protrusion 24 is
A prismatic large diameter portion 2 for forming the inner surface of the container body of the product 40.
4a and a small diameter portion projecting on the top of the product 40
And a small diameter portion 24b for forming the square hole 42. Reference numeral 27 denotes an ejector pin for projecting a product, the base of which is fixedly attached to a projecting plate 28 housed in the space behind the movable side mold plate 21.

On the other hand, 31 is a temperature detector comprising a thermocouple, 3
2 is a resistance heating type electrothermal heater, both of which are fixed-side template 1
It is buried in 1. And these temperature detectors 31
Also, the electric heater 32 is located in the vicinity of the confluence position 16 (see FIGS. 2 and 3) in the cavity 15 where the molten resin flowing into the cavity 15 from the gate 25 merges again, that is, on the opposite side of the gate 25 attachment part. Is arranged so that each tip is located in the vicinity of the cavity.

Reference numeral 33 is a temperature control device to which a temperature detector 31 and an electric heater 32 are connected. The temperature control device 33 compares the temperature set value of the setter 33a with the output signal of the temperature detector 31 and, depending on the deviation, It is composed of a PID control type temperature controller for turning on / off the voltage applied to the electric heater 32. The set temperature of the setter 33a is set in consideration of the temperature control accuracy of the temperature control device 33 so that the mold temperature of the fixed-side mold plate 11 near the tip of the temperature detector 31 is the same as that of the resin during injection molding. The control target temperature selected from the above range is set so as to be maintained within the range of the deflection temperature under load + (5 to 30 ° C.).

Next, an injection molding method using the injection molding die 1 having the above structure will be described with reference to FIG. 4 as well. First, in the filling period of the molding cycle, the molten resin made of the thermoplastic resin is sprue bushed. 13 runways 14
Then, it flows into the cavity 15 from the gate 25 through the inside of the runner 26. Since this molten resin has the protrusion 24 of the movable side mold plate 21, the molten resin is shunted to the left and right and the large diameter portion 24a
The molten resin flowing along the side of the upper part of the gate and the gate 25 part flows upward in the cavity 15 above the large diameter part 24 a corresponding to the top plate 41, and the small diameter part 24 b of the protrusion 24. Therefore, as shown by the arrow in FIG. 3, the flow splits to the right and left, and the split molten resin streams merge at the merge position 16 shown in FIGS. 2 and 3. Next, in the compression period, the supply pressure of the molten resin is increased, and when it reaches a predetermined injection pressure, it is switched to the cooling period and cooling of the mold is started.

This cooling is performed by a known method of circulating cooling water supplied from a mold temperature adjusting device (not shown) in water holes (not shown) provided in the fixed mold 3 and the movable mold 5. As a result, the mold temperature T in the vicinity of the cavity 15 drops sharply as shown in FIG. 4, and the resin is cooled and solidified.

At this time, the merging position 1 of the fixed-side template 11
6 The temperature in the vicinity is after the maximum temperature at the start of cooling,
The deflection temperature of the resin under load T ₀ + (5 to 30) ° C. is maintained by the electric heater 32 whose power supply amount is controlled by the temperature control device 33 as shown by the chain line T ₁ in FIG. The temperature of the resin at the subsequent merging position 16 is prevented from lowering and the temperature of the resin is maintained above the deflection temperature of load of the resin T ₀ during the cooling period. The generation of lines is suppressed. After cooling, the mold is opened and the molded product is projected by a conventional method, and a weld line is suppressed, and a product 40 having excellent transferability is obtained.

When the above-mentioned electric heater 32 is not used for heating, the temperature in the vicinity of the confluence position 16 of the stationary mold plate 11 also drops as shown by the broken line T ₂ in FIG. The time that the temperature is above the deflection temperature T ₀ is extremely short, and the occurrence of weld lines cannot be suppressed.

In the above specific example, since the resistance heating type electric heater 32 is used as the heater, the heater can be small and inexpensive, so that the mold has a simple structure and is inexpensive, and the temperature control is easy. P as the temperature control device 33
Since the temperature controller of the ID control system is used, the temperature control accuracy is high and there is an advantage that a particularly stable weld line suppressing action can be obtained. However, the present invention is not limited to the above specific examples. Instead, for example, as the temperature control device 33, a device other than the above PID control type temperature controller may be used, and as the heater,
A heater other than the resistance heating type electric heater, such as a high frequency induction heating type electric heater or a heat exchange type heater using a heating fluid such as oil or water as a heat medium, may be used.
Further, the heater and the temperature detector may be provided in the movable side mold part, or may be provided in both the fixed side mold and the movable side mold, depending on the shape of the product, that is, the shape and size of the cavity.

[0019]

Next, the present invention will be described in more detail by way of examples.

Example 1 As a thermoplastic resin, AB having a deflection temperature under load of 110.degree.
Resin molding temperature = 250 ° C., injection pressure 10 using S resin
00 kgf / cm ² , the set temperature (control target temperature) of the setter 33a of the temperature control device 33 = 120 ° C., the product 40 (however, the product size is L = 40 mm, B = 20 mm in FIG. 2,
Injection molding was carried out with H = 12 mm, wall thickness t of each part = 1.5 mm, and opening size of the square hole 42 = 6 × 6 mm.

In the product 40 obtained, almost no weld line was found at the joining position 16, the transferability of the cavity surface shape was good, and no other defects in appearance and strength were found. In addition, the temperature sensor for inspection not shown in FIG.
When the mold temperatures Tp and Tq at points P and Q at were measured, they were Tp = 120 ° C. and Tq = 120 ° C.

Example 2 Polystyrene having a deflection temperature under load of 85 ° C. was used as a thermoplastic resin, the resin molding temperature was 220 ° C., and the injection pressure was 10
00 kgf / cm ² , set temperature of setter 33a = 95 ° C.
Then, the product 40 having the same size as that of the example 1 was injection-molded.

As in the case of Example 1, the obtained product 40 had almost no weld line at the confluent position 16, good transferability of the cavity surface shape, and other defects in appearance and strength. It wasn't served. Also, the mold temperature Tp
= 95 ° C and Tq = 95 ° C.

Comparative Example 1 When injection molding was performed under the same conditions as in Example 1 except that heating by the electric heater 32 was not performed in Example 1 above, the obtained product 40 had a merging position 16
A deep weld line is generated in the part, the surface of the weld line part is recessed in a thin streak shape and the transferability of the surface is poor, and cracks are easily generated in the weld line part when external force is applied,
The strength was also inferior. Further, the mold temperature Tp = 55
C. and Tq = 55.degree. C., both of which were low temperatures below the deflection temperature under load of the resin used.

Comparative Example 2 Injection molding was performed under the same conditions as in Example 1 except that the resin molding temperature was 270 ° C. and the injection pressure was 1300 kgf / cm ² in the above Example 1, no heating was performed by the electric heater 32. As a result, in the obtained product 40, a weld line was clearly visible at the 16-merging position, and a deep groove was confirmed when observed with a 20 × microscope.
Further, burrs were generated on the product 40, the four circumferential wall surfaces of the box were deformed inward, and gas burning was generated at the confluence position 16 part. Further, the mold temperature Tp = 60 ° C., Tq = 60
° C.

[0026]

As described above, according to the present invention,
A heater is provided in the mold in the vicinity of the confluence position where the molten resins flowing into the cavity from the gate of the injection molding mold are merged after being branched, and the temperature of the mold at the confluence position is changed by the heater to heat the resin load. Since the temperature is maintained above the deflection temperature by a predetermined temperature, the occurrence of weld lines due to the decrease in the resin temperature at the merging position can be suppressed without increasing the resin molding temperature and injection pressure, and the transferability is excellent. It is possible to obtain an excellent injection-molded product without local deterioration of

According to the second aspect of the invention, an electric heater is used as the heater, and the electric heater and the temperature detector are provided in the mold near the confluence position. The mold is easy to process, and the heater is much smaller and easier to handle than the one that uses heated fluid. This small heater efficiently heats the mold locally to ensure that the desired part is at the desired temperature. It can be heated, and heat loss due to heating of unnecessary parts is small.

According to the third aspect of the invention, since the electric heater is used as the heater and the electric heater and the temperature detector are connected to the temperature control device, the temperature of the desired portion of the mold can be accurately adjusted to the desired temperature range. Therefore, the weld line can be surely suppressed.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of an injection molding die showing an embodiment of the present invention.

2 is a perspective view of a product molded by the apparatus of FIG. 1. FIG.

FIG. 3 is a plan view of the product of FIG.

FIG. 4 is a diagram showing changes in mold temperature and cavity internal pressure during injection molding using the apparatus of FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Injection molding die, 3 ... Fixed side die, 5 ... Movable side die, 11 ... Fixed side die plate, 11a ... Dividing surface, 15 ... Cavity, 16 ... Merging position, 21 ... Movable side die plate , 21a ...
Dividing surface, 25 ... Gate, 31 ... Temperature detector, 32 ... Electric heater, 33 ... Temperature control device, 33a ... Setting device, 40 ...
Product.

Claims (3)

[Claims] 1. An injection molding method in which a molten resin made of a thermoplastic resin is allowed to flow into a cavity formed along a dividing surface of a mold from a gate portion following the cavity so as to be solidified by cooling. A heater is provided in the mold in the vicinity of the confluence position in the cavity where the molten resins that have flowed in and split in the cavity merge again, and the mold temperature in the vicinity of the confluence position in the cooling period of the molding cycle is An injection molding method characterized in that the temperature of deflection of the thermoplastic resin under load is maintained at + (5 to 30) ° C by the heater. 2. In a mold for thermoplastic resin injection molding, wherein a cavity and a gate portion following this cavity are formed along a dividing surface of the mold, the mold is flowed in from the gate portion and split in the cavity. An injection-molding die, characterized in that an electrothermal heater and a temperature detector are provided in the die near the confluence position in the cavity where the molten resins merge again. 3. In a mold for thermoplastic resin injection molding, wherein a cavity and a gate part following this cavity are formed along a dividing surface of the mold, the mold flows in from the gate part, and is split in the cavity. An electric heater and a temperature detector are provided in the mold near the confluence position in the cavity where the molten resins merge again, and the electric heater and the temperature detector are provided in accordance with the output of the temperature detector. A temperature controller for adjusting the amount of electric power supplied to the electric heater to maintain the mold temperature of the temperature detector installation portion at the deflection temperature of the thermoplastic resin under load + (5 to 30) ° C. in the cooling period of the molding cycle. , An injection molding device characterized by being connected.