JPH0122128B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is capable of imparting a thermoplastic resin injection-molded product with a surface that has excellent transferability on the mold surface, and in particular, an excellent surface gloss that substantially corresponds to the mold surface gloss. Related to injection molding equipment. Conventionally, in injection molding of thermoplastic resin molded products, the plasticity of the thermoplastic resin is utilized, in other words, the thermoplastic resin is heated and flow-molded using a screw etc., and then cooled in a mold. The basic principle is to obtain molded products through solidification.
That is, in order to solidify and release the molded product from the mold, it is cooled below the heating deformation temperature of the thermoplastic resin and taken out of the mold. Therefore, the mold is generally maintained at a temperature lower than the heating deformation temperature. Furthermore, in order to increase productivity, the mold is cooled to a temperature on the verge of condensation using a refrigerant. Even when the mold is cooled and heated and stored at the temperature of the molten resin, in principle the mold temperature is controlled so as not to exceed the heating deformation temperature of the thermoplastic resin. In other words, when the mold surface and thermoplastic resin come into contact, the thermoplastic resin is rapidly cooled at the contact surface and the fluidity of the thermoplastic resin becomes extremely poor, resulting in poor adhesion of the thermoplastic resin to the mold surface and the molded product. The surface is extremely uneven. In addition, when reinforcing materials and/or fillers are included, the reinforcing materials and/or fillers and the thermoplastic resin generally have poor compatibility, resulting in the formation of minute voids at the interface between the reinforcing materials and/or fillers and the thermoplastic resin. It is thought that if this is injection molded, it will become a silver streak. That is, the reinforcing material and/or filler material appears on the surface of the molded product, resulting in severe unevenness and silver streaks, resulting in a molded product with an unsatisfactory appearance. In this way, when producing molded articles of thermoplastic resin, especially thermoplastic resin compositions containing reinforcing materials and/or fillers, by injection molding, the molten raw material is cooled while flowing in the mold. It is important to prevent it from solidifying. As a method of preventing such cooling solidification, it has generally been proposed to increase the mold temperature. However, when the mold temperature is raised, the cooling time naturally becomes longer, and furthermore, the molded product removed from the mold is still soft and lacks dimensional stability. Therefore, in reality, the temperature of the mold is adjusted to a temperature that appropriately balances these contradictory conditions. To talk about typical examples of the prior art, for example, Japanese Patent Publication No. 45-22020 discloses a method in which a high-temperature heating fluid is flowed into the mold to preheat the surface layer of the mold, and then molten raw material is injected into the mold. Proposed. However, since this method heats the mold by flowing fluid into the mold, the residual fluid may cause various marks on the surface of the molded product, and depending on the shape of the molded product, the use of heating fluid may cause the mold to be heated. Convex portions (for example, rib-shaped or pin portions) of the mold are heated more than the flat portions, and the heat uniformity of the mold surface is impaired, causing sink marks and uneven gloss of the molded product. Or, in severe cases, the resin sticks to the mold, resulting in poor mold release, resulting in inconveniences such as the molded product cracking during release, making it impossible to obtain a molded product with a satisfactory appearance. On the other hand, the surface gloss of injection molded products is an extremely important characteristic that influences the commercial value of various products. This characteristic of surface gloss can also be called a transfer characteristic of the smooth mold surface.
It depends on the polishing accuracy of the mold surface under the same molding conditions. That is, the surface gloss is best when a mold with a completely mirror surface is used. However,
The best result, gloss, depends on the resin composition and generally decreases with increasing additives such as reinforcing materials and/or fillers. In particular, injection molded products made of resin compositions that contain additives in amounts that provide a sufficient reinforcing or filling effect lack gloss under normal injection conditions, and have significantly lower gloss than molded products made from resin alone. do not. An object of the present invention is to provide an injection molded thermoplastic resin product that is free from surface defects such as silver streaks and has excellent surface gloss. Another object of the present invention is to provide an injection molding method capable of producing a thermoplastic resin composition having the above-mentioned excellent surface properties in a short molding cycle. A further object of the present invention is to provide an injection molding apparatus suitable for carrying out the above injection molding method. The above objects of the present invention are achieved in an injection molding apparatus having the following configuration: (a) a resin injection apparatus equipped with means for melting, measuring and injecting resin; and (b) means for cooling and solidifying the molded resin. (c) a high-frequency induction heating device comprising a high-frequency oscillation device and an inductor connected to the high-frequency induction heating device, and the inductor is located near the mold; placed in
The injection molding device is characterized in that the output of the high frequency oscillator is 0.01 to 10 KW/cm ² per unit surface area of the molded product, and the device is installed to be able to selectively heat the inner surface of the mold. . In the present invention, "surface selective heating" means instantaneously heating only the surface layer of the mold using high frequency induction heating. Such instantaneous heating is made possible by using a special heating method called high-frequency induction heating, and in order to achieve the purpose of the present invention, it is necessary to raise the temperature near the surface of the mold in a short period of time. (preferably above the heat deformation temperature of the resin). The specific heating rate is determined by taking into consideration the thermal deformation temperature of the resin material used, the mold temperature at the time of mold release, etc., which is appropriately determined correspondingly, for each resin, but it is usually 80°C/min or more. It is preferable to heat to a predetermined temperature at a heating rate of preferably 480° C./min or more, more preferably 1200° C./min or more.
According to this instantaneous heating method, heat is conducted inside the mold so that the entire mold does not reach a high temperature, and only the area near the surface is heated above the resin deformation temperature, so heat removal is extremely quick. This can be done in a matter of hours, making the injection molding cycle short. Furthermore, in high-frequency induction heating, heating is performed in a completely dry state without using substances that cause mold contamination, such as heating fluids, so there is no possibility of contamination of molded products and molds by such substances. It is advantageous because there is no Other advantages of high frequency induction heating include: (a) Temperature control is easy. (b) Selective heating (in addition to surface selection, this also includes heating specific points on the surface) is possible, and it is possible to heat only the necessary parts of the mold. (c) Do not cause thermal distress to workers. (d) Automatic operation is possible with a single button. In the following, the principles of the present invention will be explained with reference to the drawings in order to make it easier to understand the principles of the present invention. Fig. 2 shows a schematic diagram of an example of another device; Fig. 3 shows a vertical sectional view of the mold part of the inductor inserting method; Fig. 4 shows the mold part of the inductor built-in method. Figure 3 shows a vertical cross-sectional view of the mold part. FIG. 5 shows an example of the temperature distribution of the mold in the apparatus shown in FIG. 3. As shown in FIGS. 1 and 2, the apparatus of the present invention includes an injection cylinder portion 3 for melting and injecting resin, and mold portions 4 (stationary mold) and 5 (movable mold). and a high-frequency induction heating machine including a high-frequency oscillation device 1 and a coil (inductor) 2 connected to the high-frequency oscillation device 1 and arranged near the surface of the mold. 1st
In the example shown in the figure, the inductor 2 is of a type in which heating is performed by being squeezed between the stationary mold and the movable mold when the mold is opened, while the inductor 2 In the example shown in the figure, the inductor 2 is built inside the mold. FIG. 3 is an enlarged view of the mold part and inductor in FIG. 1. In injection molding of thermoplastic resin,
As shown in FIG. 3, an inductor 2 for high-frequency induction heating is installed between the stationary mold 4 and the movable mold 5. When an inductor is sandwiched between the movable mold and the stationary mold, and high-frequency waves are oscillated in the sandwiched state, only the mold surface (points A and B) suddenly oscillates, as shown in Figure 5. It can be confirmed that the temperature increases, and the temperature inside the mold (point C and point D) hardly increases due to high-frequency induction heating. In the example shown in FIG. 5, the mold is not cooled with cooling water, but simply shows an example of the change over time in the temperature distribution of the mold due to high-frequency induction heating. When the mold temperature reaches a predetermined temperature, open the mold once, pull out the inductor 2 from between the stationary mold 4 and the movable mold 5, close the mold again, and inject the thermoplastic resin in the same manner as normal injection molding. Performs injection molding. FIG. 4 shows an example of an embodiment of the device of the present invention in which an inductor is built into a mold. FIG. 4 is a cross-sectional view of a dish-shaped mold for a molded product with a diameter of about 10 cm. In this case, it is a center direct gate and two split metal types. A and A' are the parts where the shape and appearance of the injection molded product are to be formed, and are ordinary mold materials, S-
Use SC materials such as 45C and S-55C, plated versions thereof, carbide mold materials (alloy tool steel), such as NAK materials, mold steel materials such as SKD11, etc. B and B' are inductors for high-frequency induction heating, which are made by spirally forming a copper tube and casting and solidifying it with epoxy resin or the like to fix the shape. C and C' are high frequency shielding layers which will be described in detail later and are made of non-magnetic metal material. D and D' are master molds into which other functional parts necessary for injection molding are installed. The mother die may be equipped with guide pins, collars and holes for attaching the mold, ejector pins, etc. The base material may be any mold material, and general steel materials such as SC materials such as S-45C and S-55C can usually be used in terms of mold durability. Mold cooling water holes may be drilled in the mother mold,
In order to further increase the cooling effect, water may be passed through holes in the A and A' sections. Further, depending on the shape of the molded product, C, C' and D, D' may be combined and the same material as the C and C' materials, such as Be--Cu, may be used. If an inductor is simply built into a mold (buried), all the molds near the inductor are heated, and the inside of the mold is heated. Or, depending on the output capacity of the high-frequency oscillator, the oscillator may become overloaded due to heating unnecessary parts (inside the mold) compared to the size of the mold, resulting in overload cutoff. The machine starts operating and the high-frequency oscillation stops, making it impossible to heat the necessary parts of the mold. Therefore, the present inventors focused on the fact that materials heated by high-frequency induction heating have selectivity, and after various studies, they focused on applying non-magnetic metal materials to mold materials. In other words, steel materials (S-45C, S-55C, S-55C,
We discovered that the parts that do not require heating can be manufactured using non-magnetic metal materials by using mold materials whose main component is NAK material. Furthermore, non-magnetic metal materials other than beryllium steel, such as Be-Cu materials, are soft and cannot necessarily be considered suitable mold materials from the viewpoint of durability as a matrix material.As a result of various studies regarding this point, we found that materials other than beryllium steel such as Be-Cu materials It was also discovered that high frequencies can be shielded by installing a thin layer of the above-mentioned non-magnetic metal material between the unused mold material. In the present invention, a thin layer is defined as a thickness of 0.5 mm or more, which has a sufficient shielding effect for this purpose, and a thin layer of 0.5 mm or less, for example, 0.1 mm of Al foil, the Al foil is heated and melted and high frequency Does not form a shielding layer. In other words, in a mold for high-frequency induction heating, an inductor is built into the mold, and in order to selectively heat only the vicinity of the mold surface where the surface of the injection molded product is to be formed, the inductor is placed in contact with the inductor. Effective injection molding method and device that uses a mold with a high-frequency shielding layer between the mold material and the inductor in the direction where heating is not required, and enables the mold to be rapidly heated and rapidly cooled using high-frequency induction heating. It is. Non-magnetic metal materials refer to Cu, Al, Be, or alloys containing these metals as main components, and also include alloys such as brass and beryllium copper. Although there are ceramics, glass, wood, etc. as non-magnetic materials, they are not necessarily advantageous as mold materials of the present invention because they have good durability and thermal conductivity. The oscillation method of the high frequency oscillator that can be used in the present invention is a motor generator type, an electron tube type,
It is a thyristor inverter type oscillator. Frequencies of 50Hz to 10MHz can be used, but frequencies of 1 to 1000KHz are convenient for practical use. The output of the high frequency oscillator can be approximately 1 to 5,000 kW, and is appropriately determined depending on the size of the mold to be heated, the temperature to be heated, and the heating speed. Note that the amount of heat generated by high-frequency induction heating P is calculated by the following equation. P=8π ⁵ a ⁴ f ² μ _S ² n ² I ₂ /ρ×10 ^-4 (P: calorific value; a: coil radius; f: frequency; μ _s : relative magnetic permeability; n: number of coil turns/m; I: Current flowing in the coil; ρ: Specific resistance) For example, using an S-45C mold and an inductor made of a 5 mm diameter copper pipe spirally wound at 5 mm intervals, the distance between the mold and the inductor is set to 1 cm. keep,
When using a 400KHz oscillator, raising the heating temperature to 40℃ to 50℃ higher than the mold temperature during normal molding (approximately 40 to 90℃), and setting the heating time to 10 to 15 seconds. The output is per unit surface of the molded product.
It is 0.01~10KW/ ^cm2 . If it is less than 0.01 KW/cm ² , the temperature rise speed of the mold is slow and impractical, and in some cases overload may occur, so heating may not be possible due to activation of the overload prevention device. If it exceeds 10 KW/cm ² , the temperature increase speed is too rapid, making it difficult to control the mold temperature, and if the mold has a large area, uniform heating will not be possible. If there is temperature unevenness of 50℃ or more on the mold surface, the surface of the molded product will have uneven gloss,
There is a risk of sink marks etc. The reason why an injection molded product with excellent gloss can be obtained using the injection molding apparatus of the present invention is that the thermoplastic resin is sufficiently fluidized on the mold surface by the preheating treatment operation, and thus It is thought that a smooth skin layer consisting essentially only of the resin component, containing no filler or the like, is formed to completely cover the uneven portions caused by the filler or the like. Furthermore, because the preheating treatment of the present invention allows the entire surface of the mold to be uniformly heated above the heat distortion temperature, the resin does not cool and solidify when it flows into the mold, and fluidization occurs uniformly over the entire surface. Therefore, substantially the same level of gloss can be obtained regardless of where the resin is present, that is, at the gate portion and the dead end portion of the mold. The difference in gloss per unit length from the gate part to the dead end part is called the gloss gradient, and in the case of the injection molded product of the present invention, this gradient is 0 to 0.5%/cm.
Preferably 0-0.2%/cm, more preferably 0-0.2%/cm
It is extremely small at 0.1%/cm. In particular, this glossiness gradient is the ratio L/t of the resin flow distance L and the molded product wall thickness t=
For molded products of 20 to 30 or more, it is often 1 to 5%/cm. On the other hand, it can be seen that the injection molded product of the present invention is an injection molded product that has a uniform and high gloss level with no gloss unevenness, which is unimaginable for conventional injection molded products. The thermoplastic resin referred to in the present invention is polystyrene,
Rubber reinforced polystyrene (hereinafter collectively abbreviated as PS)
AS resin, acrylonitrile-butadiene-styrene polymer, acrylonitrile-butadiene-styrene-α-methylstyrene, acrylonitrile-methyl methacrylate-butadiene-styrene (hereinafter collectively referred to as ABS resin), polyethylene,
It includes all so-called thermoplastic resins such as polypropylene, polycarbonate, polyphenylene ether, polyoxymethylene, and nylon. The filler used in the present invention refers to powders and hollow bodies of inorganic materials such as glass fiber, glass bulb calcium carbonate, mica, and asbestos, and metals such as iron, copper, zinc, aluminum, and their oxides. It refers to particles with a small particle size of 5 mesh or less. The reinforcing material used in the present invention refers to toughness reinforcing materials mainly made of rubber, such as polybutadiene rubber, SB block polymer, nitrile rubber, etc., which are graft polymerized with various monomers found in HIPS and ABS resins.
Also includes rubber such as EPDM. The injection molding apparatus of the present invention can be particularly effectively applied to molding thermoplastic resin compositions containing reinforcing materials and/or fillers, which cannot be obtained with good appearance using ordinary injection molding apparatuses. For example 5
In the case of so-called high-impact polystyrene (HIPS) reinforced with ~20% by weight of rubber (e.g. polybutadiene), it is possible to achieve a gloss of about 90-105%, and the gate in the molded product To obtain a uniform, high-gloss injection molded product with almost the same gloss at the dead end portion and the dead end portion and without a so-called gloss gradient. EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to examples, but the present invention is not limited to these examples. Example 1 In Figure 4, A and A' are NAK with a thickness of 10 to 25 mm.
The part that forms the surface of the molded product has a so-called mirror finish. This injection molded product has a diameter of 10
The mold is capable of molding plate-shaped products with a depth of 2 cm and an average wall thickness of 3.5 mm, and the gate is a center direct gate. For B and B', 5 mm diameter copper tubes were spirally arranged at 15 mm intervals and cast with epoxy resin to a thickness of 15 mm. Brass with a thickness of 3 mm was used for C and C'. D and D' used S-45C mold steel. The mold was attached to a normal in-line injection molding machine, and an AS resin containing 20% by weight of glass fiber, which is commonly commercially available as a thermoplastic resin, was molded. As for the injection molding conditions, the cylinder temperature was set so that the temperature of the glass fiber-added AS resin was 240°C.
Before injecting the glass fiber reinforced AS resin into the mold, use a high frequency oscillator with a capacity of 4KHz and 8KW in the above-mentioned inductor to oscillate for 10 seconds, and then
Subsequently, in the same manner as normal injection molding, the filled resin was injected into the mold at an injection pressure of 60 kg/cm ² for 10 seconds, and after cooling for 20 seconds, the molded product was taken out. The total cycle time was 45 seconds. The surface of this molded product had an appearance similar to that of an AS resin molded product, with no silver streaks or protrusion of glass fibers on the surface of the molded product, and a molded product with a very good appearance. Glossiness of the molded product G _s (60°)
was 102%. Comparative Example 1 For comparison, when there is no heating of the mold surface due to high frequency oscillation in Example 1, in other words, there is no high frequency oscillation of 4 KHz, 8 KW, and 10 seconds in this example, and other molds, resin to be injected, When other molding conditions are the same, the molded product has a white, dull, and silver streaky appearance that is typical of filled resin, and the gloss level G _s (60°)% is
It was 45%. Example 2 Using the same mold, high-frequency oscillator, and injection molding machine as in Example 1, only the resin to be injection molded was HIPS, ABS,
PPE and other resins were molded at the appropriate resin temperature. In the case of any resin, the appearance of the injection molded products was beautiful, overturning the concept of conventional injection molded products. In other words, all molded products have molded product glossiness.
G _s (60°)% exceeds 100%, the gloss is uniformly 100% or more everywhere without uneven gloss, and there are no visible defects such as flow marks or jetting. The following table picks up and displays the molding conditions for each resin that differ from Example 1. In addition, as in the case of Example 1, Comparative Example 2 in which there is no high-frequency oscillation is also displayed. 【table】

[Brief explanation of drawings]

FIG. 1 shows a schematic diagram of an example of an injection molding apparatus (inductor sandwiching method) according to the present invention. FIG. 2 shows a schematic diagram of another example of an injection molding apparatus (inductor built-in type) according to the present invention. FIG. 3 shows a vertical sectional view of the mold part of the inductor inserting method. FIG. 4 shows a vertical sectional view of the mold part of the built-in inductor type. FIG. 5 shows an example of the temperature distribution of the mold in the apparatus shown in FIG. 3. 1: High frequency oscillator; 2: Inductor; 3:
Injection device; 4: Fixed side mold; 5: Moving side mold.

Claims (1)

[Scope of Claims] 1. (a) A resin injection device equipped with means for melting, metering and injecting resin; and (b) A thermoplastic resin mold including a resin molding die equipped with means for cooling and solidifying the molded resin. (c) a high-frequency induction heating device comprising a high-frequency oscillation device and an inductor connected to the high-frequency induction heating device, and the inductor is disposed near the mold;
An injection molding apparatus, which is capable of selectively heating the inner surface of the mold, and (d) a high-frequency induction heating shielding layer is provided inside the mold component. 2. The device according to claim 1, in which the inductor is sandwiched between mold constituent members when the mold is opened. 3. The device according to claim 1, wherein the inductor is embedded within a mold component, and the high frequency induction heating shielding layer is provided on the opposite side of the mold surface of the embedded inductor.