JPS6047796B2 - Structure for audio equipment and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a structure having improved acoustic performance, and more particularly to a structure for audio equipment that is less likely to cause resonance and has excellent vibration-proofing function.

In general, housing members in audio equipment must be designed so that they do not resonate due to their structure or materials, which requires special attention to vibrations from mechanical, acoustic vibration sources, or others. Conventionally used materials for acoustic casings include metal, wood, and plastic, but each has advantages and disadvantages in terms of performance as an acoustic casing, and depending on the purpose, take into account acoustic performance and mechanical strength. It is necessary to select materials accordingly, and various structural measures have been taken to compensate for the deficiencies of these materials, such as increasing the thickness or inserting auxiliary dynamic materials.

For example, Japanese Patent Publication No. 52-28657 proposes a sandwich-shaped speaker cabinet to prevent resonance.

That is, the outer and inner layers of the cabinet body are molded from a mixture of fine particles such as limestone and hard synthetic resin such as hard unsaturated polyester resin to obtain the necessary mechanical strength and mass, and the middle layer is and soft synthetic resin with lower hardness than the inner layer,
For example, it is molded from soft synthetic resin, and measures are taken to suppress resonance between the outer and inner layers and reduce unnecessary vibrations. This type of method is convenient for manufacturing relatively simple structures, but it is useful for manufacturing complex structures, such as structures where thick and thin parts vary, or thick parts When molding a structure with a complex series of thick and thin sections, so-called whiskers may occur where the thick and thin sections differ, which may reduce mechanical strength or cause defects in appearance. There is. In the case of audio equipment, for example, in the case of a sealed speaker box, if the joint surfaces of the box components are not airtight, the equivalent stiffness of the cabinet will change, especially the lowest resonant frequency when installed in the cabinet, and the low frequency Peaks and troughs occur in the sound pressure level.Also, when the four or five sides are integrally molded, there are no joint surfaces and they are continuous, so the above disadvantages can be prevented, but the thick parts may have whiskers. If this occurs, it will affect plate vibration and sound insulation, degrading the sound quality of the system.

Further, when the player cabinet is integrally molded and the motor is attached to the cabinet, the motor cannot be fixed horizontally if there are hairs. Since modern players are direct drive, precision is required for motor installation. If the motor is not installed horizontally, the turntable itself will roll, causing surface runout, core runout, wow, and flutter (uneven rotation), which will further impair the effective vibration-proofing properties. The present invention has been made to correct these drawbacks.

That is, the present invention provides the following features: 3. consisting of a surface layer and a core layer; A structure in which the layers are integrally injection molded is made of a foamable synthetic resin containing at least one type of filler with a specific gravity of 2 or more, which substantially inhibits foaming, and contains a small amount of air bubbles, but its surface is smooth and has no whiskers. It consists of a surface layer without foam and a core layer made of foamed or non-foamed synthetic resin. In the method for injection molding the structure for an audio device and the above three-layer structure, the surface layer is composed of a mixture of a foamable synthetic resin and at least one filler having a specific gravity of 2 or more, and the core layer is The above-mentioned surface layer material and core layer material are injected and filled into a mold made of a foamable or non-foamable synthetic resin and filled in advance with gas at a pressure capable of suppressing the foaming and foaming of the foamable synthetic resin. The present invention provides a method for manufacturing a structure for an audio device having a smooth surface and no whiskers, in which the gas in the mold is released after injection is completed. According to the present invention, a structure with a high Young's modulus and a large internal loss, that is, a low resonance sharpness Q can be obtained due to the presence of the filler, and the surface is smooth by molding while suppressing foaming. It is possible to obtain a structure, that is, a structure that has a surface without a foam pattern and does not have defects such as whiskers in the thick portion.

Further, even if the structure has a complicated shape, it is possible to easily obtain a structure of uniform quality at low cost. l Next, the structure for audio equipment and the manufacturing method thereof according to the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a sectional view of a portion of a structure of an audio device such as a speaker cabinet, a player cabinet, a frame chassis, a turntable, etc. In Figure 1,
The structure is composed of a surface layer 1 and a core layer 2, which are molded into a saw body by injection molding, as will be described later. As described below, the surface layer 1 is composed of a mixture of a foamable synthetic resin that substantially inhibits foaming and contains fine air bubbles, and at least one type of filler having a specific gravity of 2 or more. is smooth and has no whiskers. As the synthetic resin constituting the surface layer, all resins that can be normally injection molded are used.

For example, low-density and high-density polyethylene, polypropylene, polystyrene, rubber-reinforced polystyrene, styrene-acrylonitrile copolymer, styrene-acrylonitrile-butadiene copolymer, methacrylic resin, polyamide resin, thermoplastic polyester resin, polybutylene terephthalate resin, polycarbonate resin , modified polyphenylene oxide resin, polyacetal, and blade resin of polyvinyl chloride and styrene-acrylonitrile-butadiene copolymer are preferably used. In particular, in the case of a structure that requires high resistance to resistance, a resin containing a known resistance agent to the above-mentioned resin or a resin with excellent resistance to resistance is used. A foaming agent is added to the resin constituting the surface layer.

Foaming agents are known hydrocarbons such as pentane and freon,
Volatile liquids such as halogenated hydrocarbons, organic and inorganic thermal decomposition types such as sodium bicarbonate and azodicarbonamide, and blowing agents such as gases such as nitrogen and carbon dioxide are used alone or in combination. Further, hygroscopic water or volatile content of synthetic resins can also be used as the foaming agent of the present invention. In the case of molded products that particularly require high retardancy, use blowing agents such as halogenated hydrocarbons, thermal decomposition types, nitrogen, and carbon dioxide from among the above-mentioned blowing agents to combine with the above-mentioned resins with excellent retardancy. Used in combination. Note that the amount of the foaming agent may be at most an amount that substantially inhibits foaming under the pressure of the pressurized gas that fills the mold cavity in advance.

However, a sufficient amount is necessary to prevent hairs from forming in the thick portions of the structure. In this thick part of the surface layer, there is a trace amount of microscopic air bubbles due to foaming in an amount corresponding to the whiskers. For example, the ratio of asodicarbonamide is 0.05 to 0. In the case of pentane, a trace amount of about 0.1 to 1% by weight is used. Furthermore, a filler is mixed with the foamable resin constituting the surface layer 1. This filler uses a material with a specific gravity of 2 or more. Fillers with a specific gravity of 2 or more include metal powders such as iron, copper, and lead, metal salts such as barium sulfate and calcium carbonate, metal oxides such as iron oxide and zinc oxide, and inorganic powders such as glass, graphite, and silica. Selected from fibrous materials such as body, glass, carbon, and asbestos. One or more of these filled materials are mixed and the amount is preferably 1% or more based on the foamable synthetic resin, preferably 35% or more.
It is mixed by weight% or more. Note that the mechanical strength of a mixture of a filler and a foamable synthetic resin tends to decrease as the mixing ratio of the filler increases. Therefore, by selecting a filler with a high specific gravity, it is possible to form a surface layer with a high specific gravity without significantly reducing the mechanical properties of the structure. Experimentally, it has been found that when the amount of filler added is less than 1% by volume compared to the foamable synthetic resin, there is little internal loss and almost no acoustic effect.
Moreover, if the amount is more than 8%, the structure becomes brittle and is not suitable for practical use. Next, as the resin forming the core layer 2, a synthetic resin that can be usually injection molded is used, but preferably a synthetic resin of the same type or different type from the synthetic resin used for the surface layer is used.

For example, in addition to the synthetic resins used for the surface layer, so-called elastomers such as flexible polyvinyl chloride resins, thermoplastic polyurethanes, styrene-butadiene block copolymers, and ethylene-vinyl acetate copolymers are also preferably used. Furthermore, if a resin that can be thermally bonded to the synthetic resin used for the surface layer is used for the core layer 2, the bond between both layers will be stronger, and the acoustic and mechanical effects will be greater.

In addition to using the same type of resin, for example, the surface layer 1 is made of styrene-acrylonitrile-butadiene copolymer, and the layer 2
A styrene-butadiene block copolymer may be used. It is preferable to use a relatively soft synthetic resin for the core layer. Furthermore, if the resin constituting the core layer is made of a resin mixed with a foaming agent and the core layer is made of a foam, the resonance sharpness is lowered, so that the vibration damping performance of the structure is improved and a structure with excellent acoustic effects can be obtained. The method for molding the structure of the present invention is to inject the surface layer material and the core layer material into a mold filled with gas at a pressure that can suppress foaming of the foamable resin, and after the injection is completed, the gas in the mold is The following method is used as the basis for the injection order of the surface layer material and the core layer material. In addition to the method of injecting the first synthetic resin (surface layer material) to a volume smaller than the volume of the mold cavity and injecting the second synthetic resin (core layer material) from the same sprue, there is a method in which a part of the first synthetic resin is injected. injection, and then simultaneously injecting the first and second synthetic resins, or separating and metering the first synthetic resin into the front chamber and the second resin into the rear chamber via a movable mandrel;
A method of injecting with an original injection cylinder can be used. Normally, when forming an axially symmetric rotating body with a uniform thickness into a sandwich structure as shown in FIG. 2, all parts are composed of a surface layer 1 and a core layer 2, as shown in a cross-sectional view of FIG. 3. be done.

However, when forming a molded body as shown in FIG. 4 into a sandwich structure in which the surface layer 11 includes the core layer 12, the convex portion that becomes the thick portion 3 is not only formed by the surface layer 11, but also has a so-called beard. yields 4. When the resin is cooled and solidified in the mold, thermal contraction occurs concentrated in the thick portion 3 of the cypress 4. However, according to the method of the present invention as described above, the pressure of the pressurized gas that fills the mold cavity in advance may be lower than the level at which foaming is substantially inhibited. As shown in FIG. 5, the thick part 3 has a sandwich structure of a smooth skin 21 and a core layer 22, which has no whiskers and no foam pattern. You get a body.

9 In addition, the pressure of the pressurized gas prevents roughening of the surface layer surface due to the filler, making it possible to obtain a structure with a smooth surface, and facilitating post-processing such as painting.

Furthermore, when a foamable resin is used for the core layer, foaming during injection is suppressed, and defects such as the core layer resin being exposed due to the surface layer breaking at the flow end are less likely to occur, and the surface layer encompasses the core layer. Sandwich structures can be easily obtained. If a non-magnetic material is used as the filler that constitutes the surface layer, the molded body itself can have characteristics such as providing a shielding effect.

Acoustic housing, microphones, headphones, speaker boxes, player boards, and various acoustic cabinets (
Ideal for radios, tape recorders, cassettes, etc. In addition, if a mixture of powder and fibrous material, such as glass fiber, is used as the filler, the mutual bond between these fillers and the foamed resin becomes stronger, making it possible to obtain a highly rigid structure. . Next, examples of the present invention and comparative examples will be shown.

Example 1 ABS resin (manufactured by Asahi Tau Co., Ltd. - Styrac Kl9l)
) 5 parts of commercially available ferrous oxide powder (specific gravity: 5), 0.1 parts of azodicarbonamide with a decomposition temperature of 200°C.
A mixture of parts by weight is used as a surface resin, and ABS resin (
(manufactured by Asahi Tau Co., Ltd. - Styrac K3Ol) 100 parts by weight of azizocarbonamide with a decomposition temperature of 2000C.
A mixture of 5 parts by weight was used as the core layer resin.

Next, the surface resin and the core layer resin were plasticized and weighed in separate injection moldings at a temperature of 220'C, and then 200×100×
After filling the cavity of a speaker box mold with an outer diameter of 100mm and an average wall thickness of 8WL with 8k9/c compressed air to suppress the foaming of the foaming agent, the surface resin was poured from the same sprue, and then The core layer resin was injected at 500k9/d, and after the injection was completed, the compressed air was released, and the resin was cooled and solidified to take out the molded product to obtain the structure of the present invention.

The structure consists of a core layer surrounded by a smooth skin surface layer with no foam pattern. It had an inch-shaped structure and was in good condition with no whiskers. Comparative Example 1 ABS resin ((manufactured by Asahi Tau Co., Ltd. - Styrac)
191) Mixing 65 parts by weight of commercially available ferrous oxide (specific gravity 5) powder, 35 parts by weight, at a cylinder temperature of 220'C;
Injection molding was performed at an injection pressure of 500k9/c into a speaker box mold having the same outer diameter and average wall thickness as in Example 1.
After cooling and solidifying, the structure was taken out.

The structure was a structure with whiskers on the thick wall portion. Comparative Example 2 ABS resin ((Stylac [F] 1 manufactured by Asahi Tau Co., Ltd.)
A structure was obtained in the same manner as in Comparative Example 1 using Comparative Example 1.

This was a structure with whiskers in its thick parts. Comparative Example 3 Polystyrene resin ((Styron (S) 683 manufactured by Asahi Tau Co., Ltd.) was used as the surface resin, and rubber reinforced polystyrene resin ((Styron [F] 470 manufactured by Asahi Tau Co., Ltd.) 45
A mixture of 55 parts by weight of commercially available ferrous oxide (specific gravity 5) and 0.5 parts by weight of azodicarbonamide having a decomposition temperature of 170°C was used as the core layer resin, and the same molding machine as in Example 1 was used. Both the surface layer resin and the core layer resin were plasticized and weighed at 200° C., and sandwich injection molded using the same mold as in Comparative Example 1 at an injection pressure of 500 k9/CTI. After cooling and solidifying, the structure was taken out.

The structure not only has a foam patterned surface with the core layer resin exposed at the flow end, but also has a foamed surface formed only from the surface layer resin.
Whiskers were found near the weld line and in the thick part of the protrusion. Table 1 shows the strength and acoustic properties of the acoustic members used in the structures of the above examples and comparative examples for comparison.

As is clear from Table 1, the member of Example 1 obtained by the method of the present invention is integrally molded into three layers, the surface layer is made of high specific gravity resin and the core layer is made of foam. It is possible to obtain well-balanced results in terms of acoustic physical characteristics.

That is, it has low resonance characteristics and vibration-proofing performance, and can provide a high-strength material, resulting in excellent mechanical and acoustic performance. As described above, the structure according to the present invention has a high Young's modulus, a large internal loss (low resonance sharpness Q), and is a good structure with no defects such as whiskers even in thick parts. Both optical strength and acoustic properties are required.

Acoustic components can be easily provided at low cost and with uniform quality. In addition, since there are no hairline defects in the thick-walled parts, the connection between the assembly part and the mating part is good, and there is not only no acoustic defect such as sound leakage, but also the self-tapping part can be tightened stably and firmly. To enable easy assembly without causing defects such as loosening of fastening parts.

Furthermore, since the type and amount of filler added to the surface layer can be changed arbitrarily by selecting the type and amount, it is possible to design according to the characteristics required for each individual part.

Therefore, the structure of the present invention is suitable for player boards, speaker boxes, microphones, headphone housings, and general audio equipment housings.

[Brief explanation of the drawing]

Fig. 1 is a partially cross-sectional explanatory diagram of a molded structure according to the present invention, Fig. 2 is a perspective view of an example of a general sandwich molded product, Fig. 3 is a sectional view taken along the line A-A in Fig. 2, and Fig. 4 is a conventional Fig. 5 is a partial cross-sectional explanatory view of an example of a three-layer integrally molded structure manufactured by the method of the present invention.

Claims (1)

[Scope of Claims] 1. A structure in which three layers consisting of a surface layer and a core layer are integrally injection molded in one step, and is made of a foamable synthetic resin containing at least one type of filler having a specific gravity of 2 or more; 1. A structure for an audio device, comprising a surface layer having a smooth surface and no sink marks, and a core layer made of foamable or non-foamable synthetic resin. 2. The structure for an audio device according to claim 1, wherein the filler is a mixture of powder and fibrous material. 3. The structure for an audio device according to claim 1 or 2, wherein the core layer is made of a soft synthetic resin. 4 In a method of injection molding a three-layer structure consisting of a surface layer and a core layer, the surface layer is made of a mixture of a foamable synthetic resin and at least one type of filler having a specific gravity of 2 or more, and the core layer is made of a foamed material. The above-mentioned surface layer material and core layer material are injected and filled into a mold made of a foamable or non-foamable synthetic resin and filled in advance with gas at a pressure that can suppress the foaming of the foamable synthetic resin, and after the injection is completed. A method for manufacturing a structure for an acoustic device with a smooth surface and no sink mark, characterized by releasing the gas in the mold.