JPH0453690B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of the Invention] The present invention relates to a mold used for injection molding, and more particularly to a mold heated by a high-frequency induction heating method. [Prior Art to the Invention] Conventionally, injection molding by heating a mold using high-frequency heating has been described in Japanese Patent Application Laid-Open No. 50-45039, etc. The mold is equipped with an external oscillator and a cooling water pump, and when filling with resin, the mold is instantaneously heated by an oscillating electrode installed inside the mold, and after filling is completed, the oscillation is stopped and the cooling water pump is used to heat the mold. A method has been proposed in which cooling water is poured into a mold to cool it and solidify the resin. Furthermore, JP-A-58-40504 discloses that when injection molding a thermoplastic resin, the surface of the mold on which the surface of the injection molded product is to be formed is preheated by high-frequency induction to a temperature higher than the heating deformation temperature of the thermoplastic resin. An injection molding method for injection molding has been proposed. Mold materials include rolled steel (SS), mechanical structural carbon steel (SS, SCK), tool steel (SK, SKS), high-speed steel (SNC), chrome-molybdenum steel, and other steel materials that are cast and rolled. Or, heat treatment. Then, a mold is formed by cutting and finishing assembly. The above-mentioned iron-based mold material is suitable for heating the mold by the above-mentioned high frequency induction heating method. In addition to the iron-based materials mentioned above, there are materials such as copper-based, aluminum-based, and phosphor bronze as mold materials. [Problems to be Solved by the Invention] Molded products such as optical parts that require high molding precision, such as lenses and Fresnel lenses, require surface finishing precision and lens curvature forming precision.
In the case of a lens, the molten resin injected into the cavity of a mold is cooled and solidified by cooling of the mold after the injection is completed, and the lens shape is formed.
At this time, if the cooling temperature of the mold is improperly controlled, sink marks will occur on the lens surface and become the main part of the lens, making it impossible to obtain the desired shape of lens curvature. In the case of the Fresnel lens shown in FIG. 9, if the mold temperature is not properly controlled, the apex 10
The sharp corner of the tip of 0A is not formed. If the mold is heated by high-frequency induction heating, the mold can be heated to a high temperature within a short time. When the above-mentioned iron-based material is used as the mold material, heating by the high-frequency induction heating can be efficiently performed. However, the above-mentioned iron-based materials, especially the steel-based materials that are frequently used these days, have difficulties in machinability. That is,
Because it is a super hard material, it is difficult to create a curved surface by cutting the cavity surface while maintaining a high precision surface roughness, or to process a Fresnel shape on the cavity surface.In particular, in the case of a Fresnel lens, it is difficult to form micrometer-sized irregularities. Have difficulty. In order to form fine irregularities on the cavity surface, mold materials with good workability are preferred, and the aforementioned copper-based or aluminum-based materials are suitable; cannot use any means. The present invention makes it possible to cut a fine shape on the cavity surface, and also enables heating using a high-frequency induction heating method in order to make it easier for the molten resin injected into the cavity to be injected into the fine irregularities in the cavity. The purpose is to propose a new mold. Another object of the present invention is to improve the productivity of molded products, such as optical parts such as lenses and Fresnel lenses, which require high accuracy in molding surface roughness. Mirror cutting was not possible with the previously used molds mainly made of steel. The present invention improves the transfer rate of fine shapes of molded products by providing a composition that can mirror-finish the surface layer of the cavity of the mold, and also heats the surface layer of the cavity at a high temperature in a short time using high-frequency induction heating means at the base of the mold. We propose a mold that can shorten the molding cycle and improve productivity per hour. Table 1 shows the specularity (surface roughness accuracy) and mold heating rate by high-frequency heating means when carbon steel (S45C) is used as conventional example (1) and phosphor bronze is used as conventional example (2). , as shown in the table, the heating rate of carbon steel is
It is fast at 22℃/sec, but mirror finishing is impossible. or,
Phosphor bronze can be mirror-finished, but the heating rate is 3
C/sec, which makes them both unsuitable as mold materials. The present invention proposes a mold that can be mirror-finished and can be heated at high speed by high-frequency induction heating means for molding optical components. [Means for Solving the Problems] In the mold according to the present invention, the base of the mold is made of an iron-based metal, and an electroless nickel-phosphorus plating layer is formed on the surface of the iron-based metal base. The present invention uses nickel Ni and phosphorus P, or nickel
Focusing on the characteristics of the composition that combines Ni, phosphorus P, and cobalt Co, we focused on the properties of the composition that combines Ni, phosphorus P, and cobalt Co.
An amorphous structure having a composition of Ni and phosphorus P is formed on the mold surface. [Function] The composition of Nickel Ni containing phosphorus P becomes amorphous, and a mirror finish on the mold surface can be achieved by mirror cutting using a diamond cutting tool.
Due to the magnetism of Ni or cobalt Co, the temperature of the surface layer of the mold cavity can be raised in a short time by high-frequency induction heating. [Explanation of Examples] Fig. 1 is a block diagram of an injection molding apparatus using a mold described later in the present invention, Fig. 2 is a temperature curve diagram of the mold, and Fig. 3 is a diagram of each unit constituting the apparatus. It is a timing chart diagram. In the figure, reference numeral 1 indicates the main body of the injection molding machine, which includes a stationary mold 2A having a cavity (not shown) for forming a molded product, a movable mold 2B, and a template 4A supporting the mold. 4B, a moving guide member 6, a hopper 8, an injection cylinder 10, a driving means 12 for opening and closing the mold, and the like. 14 is a temperature regulator that adjusts the temperature of the mold, and the regulator 14 is connected to the molds 2A and 2 via a pipe 14A.
It is connected to a cooling medium flow path (not shown) in B, and the cooling medium can be circulated by a pump (not shown). Reference numeral 18 indicates a high-frequency induction heating means, which includes a high-frequency induction control section 18A, a coil section 18B, and a support member 18 that supports the coil section 18B.
C, and a moving means 18D that drives the support member forward and backward in the direction of arrow A in the figure. 20A and 20B are temperature detection sensors, which are embedded in appropriate positions of the mold to detect the temperature of the cavity surface of the mold and output a detection signal, and the detection signal is sent to the lead wire 22A.
The temperature is inputted to the temperature detection means 22 via the temperature detection means 22. Reference numeral 24 indicates a molded product take-out means, and the means 24 takes out the molded product molded by the automatic hand 24A. 26 is a controller that controls the entire molding apparatus. [First Example of Mold] FIG. 3 shows a mold composed of an iron-based metal layer 100 and a plating layer 110. S55C as ferrous metal
was used. FIG. 4 shows the manufacturing process of the mold of the first embodiment. First, the cavity shape of the molded product is processed on the surface of ferrous metal S55C (a). Surface roughness accuracy
Rmax is processed to 1μm or less. Thereafter, 110 electroless nickel-phosphorous plating layers are plated on the S55C cavity surface to a thickness of 100 μm in a plating solution with a phosphorus content of 11% (b). After forming the plating layer, heat treatment was performed at 250℃ for 2 hours in an atmospheric temperature chamber.
(c). After heat treatment, a cavity surface was formed by cutting a 50 μm deep chevron groove into a mirror surface using precision lathe using a diamond tool. The surface roughness accuracy of the cavity surface was maintained at Rmax0.01μm or less (d). The mold according to the first embodiment is mounted on the molding apparatus shown in FIG. 1, and a temperature sensor is installed in the mold. The space interval between the heating coil 16B of the high-frequency induction heating means 16 and the mold cavity surface is set to 2 mm, and the high-frequency output is 8.2 Kwatt and the frequency is 132 KHz. When measured, the surface temperature of the cavity surface was instantaneously heated from 55°C to 244°C in 9.5 seconds. The heating rate of the mold in this example is per second
It was 20℃. In Table 1, when comparing the specularity and heating rate between this example and conventional examples 1 and 2, the mold of this example is superior in all respects. Table 2 shows a comparison between the mold of the first example having a phosphorus content of 11% and other comparative examples. Comparative Example 1 shows the accuracy of the surface roughness when diamond cutting a molded material that had been heat treated at 250°C for 2 hours with a phosphorus content of 4%.
The limit was 0.15 μm. The heating rate by high-frequency heating was 21° C./sec, but this is not suitable for mold materials that require a high degree of surface roughness precision for optical parts and the like. Comparative example 2 is the data of the mold material heat-treated at 400℃ for 2 hours with a content of 11%, and comparative example 3 is the data of a mold with a content of 14%.
The data for the mold material heat treated at 250°C for 2 hours is shown. As understood from the comparative data in Table 2, increasing the phosphorus content can improve the specularity. In addition, although nickel itself has magnetism, it has low specularity, and the plating layer of nickel containing phosphorus has an amorphous composition, so it has good specular machinability, and
Since the material becomes magnetized by heat treatment depending on the heat treatment conditions, high frequency heating can be performed efficiently. As a result of repeated work of various experimental studies, the phosphorus content was reduced from 8% to 13% and the heat treatment temperature was increased to 200%.
For molds formed by heat treatment between ℃ and 350℃ and heat treatment time between 1 hour and 3 hours, the surface roughness of the plating layer can be cut with an accuracy of 0.01 μm or less, and high frequency induction The heating rate by heating means is
It was found that a speed of 20°C/sec or higher was obtained. Table 3 shows data when a Fresnel lens was molded using the mold shown in the first embodiment. Next, the operation of the apparatus shown in FIG. 1 will be explained with reference to FIG. The movable mold 2 in the initial mold opening position is moved by the molding starting operation (not shown) of the controller 26.
B starts moving in the direction of closing the mold, and when the movable mold 2B comes to the first position where it is kept at a predetermined distance from the stationary mold 2A, the movable mold 2B stops moving. When the movable mold 2B reaches the first position and stops, a signal _P1 for controlling the high frequency induction heating means 16 is output from the controller 26. In response to the control signal _P1 , the moving means 16D moves the heating coil 18B, which had been evacuated outside the opening/closing movement area of the molds 2A and 2B, to the movable mold 2B and the fixed mold 2A.
Start the approach between The heating coil 18BV is located at a position facing a cavity surface (not shown) of the mold, and stops when it reaches a position suitable for heating the cavity surface. As the heating coil 18B is stopped, the high frequency induction control section 16A outputs
8.2Kwatt, high frequency oscillation of 132KHz,
As a result, high-frequency oscillation is transmitted to the heating coil 18B, and the molds 2A and 2B are heated by a known high-frequency induction heating operation, so that the temperature reaches the temperature t A at the oscillation start time t ₁ as shown in _FIG. from peak temperature t _B
It rises along curve a toward . A signal _P2 for activating the temperature regulator 14 is activated from the control unit 26, and the temperature regulator 14 is activated at the initial operation of the molding start-up operation of the controller. The temperature regulator 14 adjusts the temperature of the cooling medium in a storage tank (not shown) to a predetermined temperature of 80° C., and at the same time operates a pump (not shown) to supply the cooling medium into the stationary mold and the movable mold through the flow path 14A. circulate. While the cooling medium circulates within the mold, the cavity of the mold rapidly reaches the peak temperature _tB of 244 shown in FIG.
The temperature rises to ℃. The temperature of the mold is detected by sensors 20A and 20B installed in each mold, and the detection signal is input to the temperature detection means 22. The temperature detection means 22 has a sensor that detects the peak temperature.
_tB When 244°C is detected, an oscillation stop signal is sent to the high frequency oscillation control unit 16A, and at the same time, the moving means 16
D, the heating coil 16B is retracted. Simultaneously with the completion of retraction of the heating coil 16B, the movable mold 2B is closed by the mold driving means 12, and a mold clamping operation is performed. When the mold clamping operation is completed, the mold is ready for injection of the resin material (polycarbonate), but from the heating stop due to the heating coil's oscillation stop described above to the completion of the mold clamping operation, the mold is ready for injection.
Time elapsed from time t ₂ to time t ₃ shown in the figure Δt ₁
There is. During this elapsed time Δt ₁ , the temperature of the mold decreases by (t _B − t _C ) = 244 − 160 = 84°C, but one of the features of this device is instantaneous heating by high-frequency dielectric heating. During the first heating period, due to the cooling operation using the cooling medium, the temperature drop curve b from the peak temperature t _B = 244°C to the injection temperature t _C = 160°C always forms a constant curve, and the injection temperature t _C =160
The temperature in °C remains constant no matter how many injection molding cycles are repeated. The control unit 26 operates the injection cylinder 10, and the molten resin material in the hopper 8 is injected into the mold cavity through a gate (not shown). After a predetermined amount of resin material is injected, the mold is cooled along a temperature curve C, and the molten resin in the cavity solidifies along the shape of the cavity to form a molded product. After that, the mold temperature becomes the temperature suitable for mold release t _D = 110
℃, a mold opening signal is sent from the control section 26 to the mold driving means 12, and the movable mold 2B is moved. When the mold opening is completed, the molding removal means 24 is activated and the molded product is taken out by the automatic hand 24A, and the molding is completed, thus completing one cycle of molding. When the above-mentioned molded product is a Fresnel lens as shown in Fig. 9, the molten resin material injected into the cavity is distributed to every corner of the cavity that forms the acute angle part of the lens, so that no voids occur. To achieve this, it is necessary to set the mold temperature to a high temperature to promote the fluidity of the resin, and at the same time, no matter how many molding cycles are repeated, the temperature shown in Figure 2 must be maintained at every cycle. Although it is necessary to maintain the curve, the present invention had a sufficiently satisfactory effect using the above-mentioned molding method. The mold material of the mold of the comparative example shown in Table 3 is SKD61, and as can be understood from Table 3, the molding cycle of the mold of the mold material shown in the first embodiment is significantly longer than that of the comparative example. I was able to shorten it. FIGS. 8A and 8B are schematic diagrams showing the molding results of molded products according to the molding method according to the present invention and the comparative example described above based on the data in Table 1. The molded products shown in FIGS. 8A and 8B above are enlarged views of the cross-section of Fresnel lenses, and FIG. 8B shows the molding method of the prior art. It is worshiped. On the other hand, FIG. 8A shows the molding method of the present invention, in which the apex angle is accurately acute and the tip is not rounded. In the case of a Fresnel lens, the incident lights X ₁ , X ₂ . . . need to be refracted at the lens surface and focused at one point on the optical axis. In the embodiment of the present invention, as shown in FIG. 4A, the light incident on the vertex is refracted accurately, so each incident light can be focused on one point, and the image called a ghost of the image is eliminated. No blurring occurs. On the other hand, in the case of the prior art, as shown in FIG. 8B, the angle of refraction of the light incident on the apex portion becomes small due to the sagging of the apex angle, and the incident light is focused at one point on the optical axis. This results in ghosting and blurring of the image. There is a method shown in FIG. 10 as a guideline for measuring the molding accuracy of Fresnel lenses. It can be said that the larger the ratio h/H of the height h actually obtained by molding to the designed height H from the bottom to the apex of the Fresnel lens, the higher the molding accuracy. According to this method, it was about 70% in the case of the conventional technology, but in the case of the above-mentioned embodiments 1 and 2 of the present invention, it was 98 to 98%.
We were able to obtain a very high value of 99%. [Second Example of Mold] This example provides a mold material in which a cobalt layer is formed on an electroless plating layer. FIG. 5 is a diagram showing the structure of the mold material of this example. In the figure, 100 is an iron-based metal, 120 is an electroless nickel-phosphorus plating layer, and 130 is a cobalt vapor deposition layer deposited on the above-mentioned plating layer. Using S55C as the iron-based metal, shape processing and phosphorus content were performed in the same manner as in the first example.
11% electroless nickel-phosphorus plating layer 120
It is formed to a thickness of 100 μm and heat treated at 250°C for 2 hours. Thereafter, a chevron-shaped groove with a depth of 50 μm was mirror-finished, and cobalt was deposited to a thickness of 2 μm on the mirror-finished surface by an ion plating method. The mold made as described above was installed in the apparatus shown in Fig. 1 above, and the high frequency induction heating means was operated at an output of 8.2 Kwatt and a frequency of 132 KHz to heat the mold, and the mold surface temperature increased in 8 seconds. The temperature rose from 55℃ to 245℃. The heating rate of the mold in this example is 24℃/sec
It was hot. Incidentally, the accuracy of the surface roughness of the cobalt vapor deposited layer was Rmax 0.01 μm. The mold of Example 2 was molded to form a Fresnel lens under the conditions of Example 2 in Table 3 to obtain the data shown in the table. As a result, the molding cycle is 58±
The cycle time was 2 seconds. As a result of the confirmation experiment of this example, the cobalt content was 2.
% to 10% and phosphorus content 4% to 10%
The molds subjected to heat treatment for 1 to 3 hours at a temperature of 200 DEG C. to 350 DEG C. had the data shown in Table 1, Example 2. [Third Embodiment of Mold] FIG. 6 shows the structure of a mold material according to a third embodiment. In the figure, 100 is iron-based metal S55C, 120 is an electroless nickel-phosphorus plating layer, 1
40 is a hard chrome plating layer. ferrous metals
Using S55C, the shape was processed in the same manner as in the first embodiment, an electroless nickel-phosphorus plating layer with a phosphorus content of 10% was formed to a thickness of 100 μm, and heat treatment was performed at a temperature of 200° C. for 2 hours. A hard chrome plating layer 140 having a thickness of 3 μm was formed on the nickel-phosphorus plating layer to form a mold. When the mold of the third embodiment was installed in the molding machine shown in Fig. 1 and a temperature test of the mold was performed, the output was
The temperature was measured by operating the high frequency induction heating means under the conditions of 10 Kwatt and 132 KHz frequency. As a result, it was confirmed that the temperature rose from 55°C to 198°C in 8 seconds. The specularity of this mold has a surface roughness of Rmax0.01μ
It was m. [Fourth embodiment of mold] FIG. 7 shows a fourth embodiment. 20 in the figure
0 is the base of the mold made of copper alloy, and 210 is an electroless nickel-phosphorus plating layer. The surface roughness accuracy of the copper alloy is finished to Rmax2μm. on the surface of copper alloy
An electroless nickel-phosphorus plating layer with a phosphorus content of 11% is formed to a thickness of 1 mm, and a 50 μm deep chevron groove is machined by mirror cutting. At this time, the roughness is Rmax0.01μm
It was hot. When this mold was installed in the molding machine shown in the first figure and the high frequency induction heating means was operated at an output of 30 Kwatt and a frequency of 420 KHz, the surface of the mold was heated from 55° C. to 200° C. in 10 seconds. The base of the mold in the fourth embodiment is made of a non-magnetic copper alloy that is not an iron-based metal, and by forming an electroless nickel-phosphorus plating layer on the surface of the copper alloy, the plating layer is made amorphous and the mold surface is 30Kwatt for heating to ensure mirror finish of shape processing,
It was possible to raise the temperature of the mold by oscillating at a high output of 420KHz. [Effects of the Invention] According to the present invention, by obtaining a mold material that combines the magnetism of iron-based metals and the specularity of the mold surface by heat-treating the electroless nickel-phosphorus plating layer, high-frequency induction can be achieved. It was possible to obtain a mold that has a high heating rate and can reach a high temperature in a short period of time. The mold of the present invention enables the formation of a cavity with excellent surface roughness accuracy and fine irregularities, thereby improving the molding accuracy of optical components and the like. In addition, due to the magnetism of the ferrous metal and the resistance value of the ferrous metal during high-frequency induction heating, it can be heated to a high temperature in a short time, thereby shortening the molding cycle as shown in the second figure above, and improving production. I was able to improve my sexuality.

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【table】

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【table】 [Brief explanation of the drawing]

FIG. 1 is an apparatus configuration diagram of a molding machine using a mold according to the present invention. Figure 2 is a temperature curve diagram. Figures 3 to 4
Figures a, b, c, and d show the first embodiment, Figure 3 is an explanatory diagram of the structure of the mold, and Figure 4 a, b, c, and d are mold manufacturing process diagrams. FIG. 5 is an explanatory diagram of the structure of the mold of the second embodiment. FIG. 6 is an explanatory diagram of the structure of the mold of the third embodiment. FIG. 7 is an explanatory diagram of the structure of the mold of the fourth embodiment. FIGS. 8A and 8B are explanatory diagrams of Fresnel lenses. FIG. 9 is a configuration diagram of a Fresnel lens. FIG. 10 is an explanatory diagram of a Fresnel lens. 2A, 2B... Mold, 16, 16A, 16B,
16C, 16D...High frequency induction heating means, 100
...Iron-based metal, 110,120...Electroless nickel-phosphorus plating layer.

Claims (1)

[Claims] 1. Consisting of an iron-based metal and an electroless nickel-phosphorus plating layer, the phosphorus content of the electroless nickel-phosphorus plating is 8% to 13%, and the heat treatment conditions are 200°C to 350°C.
A mold for injection molding, characterized in that the mold is kept at a temperature of 1 to 3 hours at a temperature of °C. 2 Consisting of an iron-based metal, an electroless nickel-phosphorus plating layer, and a cobalt layer, the phosphorus content of the electroless nickel-phosphorus plating layer is 4% to 10%.
The range is 2% to 10%, and the cobalt content is 2% to 10%.
An injection mold, characterized in that it is heat treated at a temperature of 200°C to 350°C for 1 to 3 hours.