JPS6258290B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to injection molded audio equipment parts. Thermoplastic resins have good moldability and can be easily molded into complex shapes, making it possible to mass produce parts with the same shape. Taking advantage of this characteristic,
Speaker boxes, speaker frames, record player boards, radio cabinets,
It is widely used as parts of audio equipment such as radio cassettes, teleco cabinets, tape recorder cabinets, and television cabinets. On the other hand, in addition to the above-mentioned performance required for the thermoplastic resin as a structural material, the following properties are particularly required for materials for audio equipment parts. (b) The density is large (according to the mass law for sound transmission, the higher the density, the better the sound insulation) (b) The internal loss is large (the vibration damping effect inherent to the material itself is large) (c) High rigidity (high rigidity is preferred in order to reduce deformation caused by sound waves) However, ordinary thermoplastic resins do not necessarily satisfy all of these requirements, and for this reason, for example, howling may occur, etc. This may cause problems. Filled thermoplastic resin has improved each of the points (a), (b), and (c) above and is a preferred material for audio equipment, but since the filler is not thermoplastic, the surface will be rough when injection molded. It has a poor appearance and is not put into practical use. Although there are examples of speaker frames etc. being put into practical use by painting,
The cost is high because it requires painting. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an audio equipment component which is made of a thermoplastic resin containing a filler and has a skin layer made of a thermoplastic resin that does not contain a filler, thereby eliminating the above-mentioned defects in appearance. be. DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to preferred embodiments illustrated in the accompanying drawings. An injection molding apparatus is shown in FIGS. 1 and 2. This example shows an inductor insertion method, and includes an injection molding machine and a high-frequency oscillator comprising an injection cylinder part 3 for melting and injecting synthetic resin, a stationary mold 4, and a movable mold 5. 1 and an inductor 2 connected to the inductor 2 and placed near the mold surface. Thermoplastic synthetic resins for injection molding include, for example, polystyrene (including polystyrene reinforced with HIPS rubber), acrylonitrile-styrene copolymer (AS resin), acrylonitrile-butadiene-styrene copolymer, acrylonitrile-butadiene-styrene-α-methyl Styrene, acrylonitrile-methyl methacrylate-butadiene-
Styrene (generally known as ABS resin), polypropylene,
Olefin resin such as polyethylene, polycarbonate, polyphenylene ether, etc. Preferred are ABS resin and polystyrene. The fillers mixed in this are Fe, Fe ₂ O ₂ , Al,
Powders of metals and alloys such as ZnO and their oxides, inorganic substances such as CaCO ₃ and glass beads, etc., with an average particle size of 1 to 100μ and a filling amount of
The amount is 20 to 80% by weight, preferably 30 to 80% by weight.
A metal powder with an average particle size of 1 μm or less becomes expensive, and a metal powder of 100 μm or more increases molding troubles such as wear of the molding machine. Furthermore, if the amount of filler is less than 20% by weight, the sound quality improvement effect will not be sufficient, and if it is more than 80% by weight, injection molding will be difficult. Further, if desired, glass fibers having a diameter of 5 to 20 μm may be mixed. Such materials are injection molded, and at this time, as shown in the enlarged view of Fig. 2, the fixed side mold 4 is
A high-frequency induction heating inductor 2 is installed between the movable mold 5 and the movable mold 5. When the inductor 2 is inserted between the movable mold 5 and the stationary mold 4 and a high frequency is oscillated in the sandwiched state, only the mold surface (point A and point B) is oscillated as shown in Fig. 3. The temperature rises rapidly, and the temperature inside the mold (point C and point D) hardly rises due to high-frequency induction heating. In the case of the example shown in FIG. 3, 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. Thereafter, the molds 4 and 5 are opened once, the inductor 2 is extracted from between the fixed and movable molds 4 and 5, the mold is closed again, and the above-mentioned thermoplastic resin with filler is injected in the same manner as in normal injection molding. Perform injection molding. FIG. 4 shows an optical microscope observation sketch of the cut surface in the thickness direction of the injection molded product thus obtained. The magnification is 440x. For reference, the same material was injection molded using the same mold at a mold temperature of 60° C. without using the inductor 2, and the same cross section was observed and sketched in the same manner as shown in FIG. The magnification is 440x. In both drawings, the island pattern is the filler, and the horizontal line is the surface of the molded product. As is clear from comparing Figures 4 and 5, in the case of the molded product according to the present invention, the filler A' does not appear on the surface of the molded product and is heated to a temperature of at least 1 to 30μ. It can be seen that the plastic resin B' layer is formed on the surface layer of the molded product. In addition, as shown in Figure 4, filler material
When A' is located relatively close to the surface of the molded product, the thermoplastic resin layer forms the surface layer and the filler material
Even if the surface layer is slightly uneven due to the influence of A', the fifth
Compared to the case shown in the figure, a molded product with a glossy appearance due to gentle unevenness is obtained. On the other hand, in the case of a normal molded product, as shown in Figure 5, if the filler A' protrudes from the surface of the molded product, or if the filler A' is near the surface layer, the flow of resin on the mold surface will be hindered. Perhaps because of this, silver streak-like irregularities occur on the surface, and only molded products with so-called dull and rough surfaces can be obtained. To quantify the good appearance and gloss of the molded product of the present invention
The glossiness Gs (60°) of the molded product was measured according to ASTM D523 and was 98%. On the other hand, the molded product with a mold temperature of 60°C had a gloss level of 45%, demonstrating the smoothness and good gloss of the molded product appearance of the present invention. Also, perhaps because the molded product of the present invention has low flow resistance during injection molding and is less likely to cause orientation distortion, when the heat distortion temperature specified in JIS K6871 was measured, the heat distortion temperature was 3 to 3. The so-called practical heat resistance temperature is improved by 5°C, and as a result of comparing the drop strength of molded products, the practical toughness is also improved. Example 1 A treble tweeter/speaker frame as shown in FIG. 6 was injection molded using ABS resin to which 50% by weight of Fe ₂ O ₃ powder with an average particle size of 40 μm was added. The mold was made from NAK material (carbide mold steel) and was able to form a speaker frame with outer dimensions of approximately 9cm x 9cm, depth of 1.5cm, and average wall thickness of 3.5mm. The molded product forming surface of the mold has a mirror finish. The gate is a mold with four side gates. The inductor was made by arranging copper tubes with a diameter of 5 mm in a spiral disk shape at 10 mm intervals, and in order to fix the shape, it was cast with a non-magnetic resin (epoxy resin) and solidified into a flat plate shape. The injection molding conditions are such that the temperature of the Fe ₂ O ₃ -added ABS resin is
The cylinder temperature was set to 240℃. Applicable
Before injecting the Fe ₂ O ₃ -added ABS resin into the mold, the above-mentioned inductor was inserted between the molds and the 7KHz,
A 20KW high frequency oscillator oscillated for 15 seconds, then the mold was opened, the inductor was pulled out from between the molds, and the mold was closed again. In this process, the temperature of the surface of the mold on which the molded product is to be formed is 120 to 130°C because only the vicinity of the surface of the mold is selectively heated by high-frequency induction heating immediately before injection molding of the resin. However, from the surface of the mold
The temperature inside the 5 cm mold was 50 to 60°C. Then, as in normal injection molding, 60 kg/cm ² of the resin was placed in a mold that was selectively heated only near the surface of the mold.
The molded product was injected for 10 seconds at an injection pressure of 100 mL, and then cooled for 20 seconds by passing cooling water through the mold, and then the molded product was taken out. The entire molding cycle was 60 seconds. Gloss Gs (60
) was 98%, resulting in a speaker frame with extremely high gloss and no flow marks, silver streaks, jetting, etc. We also assembled and created a treble tweeter using this speaker frame and conducted a sound quality test.We found that the tweeter produced a sound with a flatter frequency response and no distortion than a tweeter using an ABS speaker frame of the same shape. Ta. Comparative Example 1 Glass fiber 20 was used as the resin used in Example 1.
When we tested a high-pitched tweeter made in exactly the same way except for using ABS resin with weight percent addition, we found that the sound quality was improved compared to ABS resin that does not contain fillers, but the sound quality was not as good as that of the resin of Example 1. It had not been improved. Example 2 Using ABS resin containing 50% by weight of Fe ₂ O ₃ powder, injection molding was carried out using the method described in Example 1, in which the mold surface was heated by high-frequency induction heating, to produce the mold shown in Figure 7.
I made a record player board measuring 40cm x 50cm. This characteristic was obtained using the conventional injection molding method.
Table 1 shows a comparison with ABS resin molded products.

[Table] Example 3 Using ABS resin containing 50% by weight of Fe ₂ O ₃ powder, the audio cassette shown in FIG. I made a half. Its properties are shown in Table 2 in comparison with MIPS (medium impact polystyrene) molded products obtained by conventional injection molding.

[Table] I was able to obtain an audio cassette half with good sound reproducibility, perhaps because it looks beautiful, has a heavy feel, is rigid, and has good dimensional stability, but the reason is not clear. In general, Table 3 shows the performance of the audio equipment component according to the present invention and the conventional audio equipment component in comparison.

[Table] In Table 3, the internal loss Q was calculated as follows.
The test piece is vibrated and the relationship between vibration frequency and vibration speed is measured. An example measured in this manner is shown in FIG. The frequency at which the vibration velocity (or change) decreases by 3 dB at the resonant frequency ( _O ), _H
Measure and _L , and find Q using the following formula. Q= _O / _H - _L Judgment Criteria A was graded into excellent ◎, good ○, average △, and poor ×, paying attention mainly to the presence or absence of howling through trial listening. Judgment Criteria B was classified as 0 if there were no external defects such as silver streaks, flow marks, jetting, etc., almost no uneven gloss, and virtually no weld lines, and other grades were classified as fair △ and poor. .

[Brief explanation of the drawing]

Fig. 1 is a conceptual side view of an injection molding machine using an inductor sandwiching method used to manufacture parts of the present invention, Fig. 2 is a vertical sectional view of the mold and inductor, and Fig. 3 is a cross-sectional view of the injection molding machine of the inductor sandwiching method used for manufacturing parts of the present invention. Figure 2 is a graph showing the temperature distribution of the mold in the injection molding machine, Figure 4 is an enlarged sketch of the cut surface of the part of the present invention, Figure 5 is a similar drawing of the conventional part, Figures 6 to 6. FIG. 8 is a perspective view of the audio equipment component of the present invention, and FIG. 9 shows an example of vibration of a test piece. 1... High frequency oscillator, 2... Inductor,
3...Injection cylinder part, 4, 5...Mold, a
=3dB, b...when Q is small, c...when Q is large.

Claims (1)

[Scope of Claims] 1. In a thermoplastic resin injection molded audio equipment part containing a filler that requires good appearance, the skin layer of the thermoplastic resin that does not substantially contain a filler has no bonding interface. It is integrally formed during injection molding, and has a gloss level Gs (60°) specified by ASTM D523.
% or more, an internal loss Q of 50 or more, a specific gravity of 1.1, and a flexural modulus of 29000 Kg/cm ² or more. 2. The audio equipment component according to claim 1, wherein the filler is an inorganic filler with an average particle size of 1 to 100 μm, and the content thereof is 30 to 80% by weight. 3. The audio equipment component according to claim 2, wherein the inorganic filler is a metal or alloy with a specific gravity of 3 or more, such as Fe, Fe ₂ O ₃ , or ZnO, or an oxide thereof. 4. The audio equipment component according to claim 1, wherein at least a portion of the filler is glass fiber. 5. The audio equipment component according to claim 1, wherein the thermoplastic resin is an acrylonitrile-butadiene-styrene resin or polystyrene.