KR100230673B1 - Acoustic diaphragm and method for producing same - Google Patents

Abstract

The present invention relates to an acoustic diaphragm obtained by forming fine fibrillated cellulose into a web by a process similar to the papermaking process. Finely fibrillated cellulose is cellulose or bacterial cellulose obtained by beating until Canadian standard degrees of freedom are below 300 ml. Since the wet strength of the finely fibrillated cellulose is very poor, it is reinforced with a reinforcement and formed into a web on a wire screen under reinforcement. The reinforcing material can be used as an acoustic diaphragm, which is produced after the web is formed, or can be peeled off or laminated to the cellulose web.

Description

Acoustic diaphragm

1 is a schematic cross-sectional view showing a web forming process using a cone shaped wire screen,

2a to 2c show a method of manufacturing a hemispherical diaphragm using a drawing press, specifically,

2a is a schematic cross sectional view showing a cellulose-fabric composite in the form of a plate,

FIG. 2B is a schematic cross sectional view showing a drawing press working process, and FIG. 2C is a schematic cross sectional view showing a cellulose-fabric composite molded in a hemispherical shape.

The present invention relates to an acoustic diaphragm used in a loudspeaker or the like and a method of manufacturing such a diaphragm. In particular, the present invention relates to acoustic diaphragms using micro-fibrillated cellulose and methods of making such diaphragms.

Until now, cone paper made from pulp has been widely used as an acoustic diaphragm for loudspeakers and the like.

Conical paper is a process step of beating the pulp (biting), dispersing and swelling the beating pulp in water, and forming the pulp dispersed in water into the desired web form using a process similar to the papermaking process Manufacture through them. However, a web obtained by simply dispersing pulp obtained from wood in water in a similar process to the papermaking process can hardly be used as a diaphragm because of poor crisp feel and inferior mechanical strength. The reason is that the individual fibers making up the pulp are not strongly fixed to each other.

Fixing force can be increased by softening and degrading (fibrillating) the fibers with component fibrils in order to increase the number of points of contact between the fibers to increase the number of hydrogen bonds.

This mechanical fibrillation of the individual fibers is called beating and is usually performed using a device known as a beater.

On the other hand, an acoustic diaphragm is required for a faster longitudinal wave propagating velocity or a faster acoustic wave propagation velocity (C). It may be advantageous to use a light and large Young's modulus material as the acoustic diaphragm material. .

The physical properties of the conical paper (eg Young's modulus or tensile strength) are determined by the degree of beating as described above, in order to produce conical paper with a higher Young's modulus, the increased degree of beating and thus the increased It is necessary to use cellulose showing the degree of fibrillation. That is, in the conical paper used as the diaphragm material, the larger the degree of beating of the cellulose used to manufacture the web, the larger the Young's modulus of the conical paper.

However, highly bituring the cellulose used to make the web of conical paper results in difficulty in handling and shape maintenance because the strength of the cellulose in the wet state during the web manufacturing process is extremely degraded. For example, if the web formed in the wet state is to be moved to another metallic mold, the shape of the web may collapse.

On the other hand, since cellulose is easily introduced into the mesh of the wire screen of the web manufacturing apparatus, when the web (conical paper) formed from the wire screen is removed after drying, the stiffness of the wire screen of the web forming apparatus becomes larger. Due to this, an excessive force that breaks the web is likely to be instantaneously applied to the web.

On the other hand, when a flat web is formed and molded into a desired shape by a press acting under the aid of a metallic mold, excessive force tends to break the web.

Therefore, although it is expected that a high degree of fibrillation in terms of characteristics is desirable due to manufacturing difficulties, it is considered difficult to produce a web for acoustic diaphragm from excessively highly fibrillated cellulose. Above all, it is extremely difficult to manufacture a thin diaphragm.

Therefore, the main object of the present invention is to provide an acoustic diaphragm having excellent physical properties such as Young's modulus and tensile strength.

It is another object of the present invention to provide a method for producing an acoustic diaphragm which can handle the web even if the wet strength of the web of conical paper is low, and can form an acoustic diaphragm having a high Young's modulus from the micro-fibrillated cellulose. To provide.

According to the present invention, an acoustic diaphragm obtained by forming a web with micro-fibrillated cellulose by a process similar to the papermaking process is provided.

According to the invention, there is also provided an acoustic diaphragm in which the micro-fibrillated cellulose web and the reinforcement are present stacked on one another.

According to the invention, there is also provided a method for producing an acoustic diaphragm, characterized in that a composite web is formed by placing a reinforcement on a wire screen and forming a cellulose having a Canadian standard freeness of 300 ml or less on the reinforcement. Also provided.

According to the present invention, by producing a web for acoustic diaphragm from micro-fibrillated cellulose, an acoustic diaphragm having excellent physical properties such as Young's modulus and tensile strength is provided.

According to the present invention, by a process similar to the papermaking process, the web for acoustic diaphragm is formed from the micro-fibrillated cellulose by reinforcing cellulose with a reinforcing material located on the wire screen of the web forming apparatus. Therefore, even if the wet strength of the web is low, the web can be handled, so that an acoustic diaphragm having excellent physical properties and a high profitability can be manufactured.

Since the conical paper of the acoustic diaphragm of the present invention consists of micro-fibrillated cellulose, the number of points of contact between the fibers and accordingly to improve the physical properties of the acoustic diaphragm (eg, zero modulus or tensile strength) The number of hydrogen bonds can be increased. In addition, cellulose is laminated on and integrated with the reinforcement to further enhance the mechanical strength of the conical paper.

On the other hand, according to the method of manufacturing the acoustic diaphragm of the present invention, micro-fibrillated cellulose is formed into a web on a reinforcing material placed on a wire screen forming a web. Webs formed from micro-fibrillated cellulose can be handled easily even under wet conditions, while retaining the shape of the webs, even though the wet strength is low, reinforced by the reinforcement described above.

When the reinforcement is removed from the web after drying, the reinforcement can be gradually removed from the web due to the flexibility of the reinforcement without inadvertently applying a large force to the web.

The cellulose used to make the webs according to the invention is highly micro-fibrillated cellulose with a Canadian standard degree of freedom of 300 ml or less. If the Canadian standard freedom value exceeds 300 ml, cellulose having a Canadian standard freedom value of 300 ml or less should be used because the Young's modulus of the web of the acoustic diaphragm produced is insufficient.

Cellulose (hereinafter referred to as micro-fibrillated cellulose) having a Canadian standard degree of freedom of 300 ml or less is a pulped pulp, ie, a mechanically pulped pulp using a beater. Canadian standard degrees of freedom of 300 ml or less can be easily obtained by suitably adjusting the beating conditions of the beater, such as the beating time or the strength of force applied during the beating.

Bacterial cellulose produced microbially by culturing certain types of bacteria under certain conditions can also be advantageously used as micro-fibrillated cellulose.

The above-mentioned bacterial cellulose is composed of α-cellulose having high crystallinity, and due to its very strong surface orientation characteristic, the strength is very high. Moreover, the thickness is very thin as 200-500 GPa.

Common bacteria that provide bacterial cellulose include acetic acid bacteria such as Acetobacter aceti, Acetobacter xylinum, Acetobacter rancens, Sarcina bentrikul Ventriculi, Bacterium xyloides, Acetobacter pasteurianus and Agrobacterium tumefaciens. Further examples of such bacteria include the genus Pseudomonas and the genus Rhizobium.

The above bacterial cellulose can be prepared as a gelled material having a certain thickness at the interface between the culture surface and the air or by aeration and agitation culturing. The prepared bacterial cellulose can be broken down in water to form a web.

To form the web, highly polymeric fibers such as carbon fibers, glass fibers, arimid fibers, polyolefin fibers, super-stretched polyolefin resins or polyester resins can be incorporated into the micro-fibrillated cellulose as reinforcement. . In addition, papermaking additives (eg, so-called sizing agents or fillers) may optionally be added to the micro-fibrillated cellulose.

On the other hand, a reinforcement located on the wire screen is used to enhance the wet strength of the web formed from the micro-fibrillated cellulose. For example, woven or nonwoven fabrics exhibiting specific flexibility or flexibility can typically be used as reinforcement.

The material type or thickness of the woven or nonwoven can be chosen arbitrarily when the above reinforcement is simply used as a web reinforcement. However, when integrating a woven or nonwoven directly with a web of micro-fibrillated cellulose, the material type or thickness of the reinforcement may be selected as a function of the desired properties of the acoustic diaphragm, as described below. On the other hand, when the reinforcement is simply used as a reinforcement for the web, it is preferable that the reinforcement such as a woven or nonwoven fabric is easily removed from the micro-fibrillated cellulose. On the other hand, when the reinforcement is directly integrated with the web of micro-fibrillated cellulose, the reinforcement is preferably in strong contact with the micro-fibrillated cellulose while maintaining high strength and elastic modulus.

In particular, a woven or nonwoven fabric of carbon fiber, glass fiber, polyester fiber, aramid fiber or silk can be selectively used by considering the above requirements.

According to the invention, as shown in FIG. 1, the wire screen 2 is first placed on the bottom of the paper machine 1, and the reinforcement 3 described above is placed on the wire screen 2, Here, the micro-fibrillated fibers can be formed by supplying a suspension 4 containing micro-fibrillated cellulose in a dispersed state to prepare a web 5.

The web 5 thus produced is introduced into a drying step for drying. At this time, the web 5 formed from the micro-fibrillated cellulose may be moved to a drying process while being placed on the wire screen 2. The web can also be separated from the wire screen 2 along the reinforcement 3 and repositioned on another metallic mold before moving the web to the drying process. In the latter case, since the web 5 formed by the micro-fibrillated cellulose is treated simultaneously with the reinforcing material 3, even if the wet strength of the web is poor, there is no risk of breaking the web 5 or the wheels. .

After drying, by removing the reinforcing material from the web (conical paper) of the micro-fibrillated cellulose, the web formed solely by the micro-fibrillated cellulose can be used as the acoustic diaphragm. It is also possible to use the resulting web-woven or web-nonwoven composite as a composite acoustic diaphragm by integrating the reinforcement directly into the web.

Using the method described above, the shape of the resulting conical paper is determined according to the shape of the wire screen 2. However, according to the invention, the web of micro-fibrillated cellulose, which is present in the form of a plate, can be obtained, for example, by drawing using a metal mold.

In all of the above methods, conventional wire screens 2 can be used, such as wire mesh or punched or perforated metal plates.

From the above, it can be seen that by using a web of micro-fibrillated cellulose and laminatinagly unifying the reinforcement into the web, it is possible to provide an acoustic diaphragm with significantly improved physical properties such as Young's modulus or tensile strength. Can be.

In addition, according to the method of the present invention, since the reinforcement is placed on the wire screen and the cellulose is placed on the reinforcement for web manufacturing, it is possible to easily handle cellulose having low wet strength, such as micro-fibrillated cellulose. Therefore, the acoustic diaphragm with a large Young's modulus can be manufactured efficiently.

In addition, according to the method of the present invention, the diaphragm formed of the composite formed by the micro-fibrillated cellulose and various additives can be easily manufactured to have various desired properties depending on the intended use and the product, if desired. have.

The invention will be described in more detail with reference to a number of the following examples.

Example 1

Bacterial cellulose prepared by acetic acid bacteria is digested using a mixer. The degraded cellulose is formed into a web on the web forming wire screen 11 to which the polyester fiber fabric 12 is attached, as shown in FIG. 2A. The web thus formed is composed of cellulose 13 and fiber fabric 12. In the web forming process, the micro-fibrillated cellulose is degraded bacterial cellulose produced by acetic acid bacteria, but the polyester fiber fabric 12 used as reinforcing material is NBC Co., Ltd. (NBC co., Ltd.). No. 120S of the 100 mesh size (pore diameter, 200 mu m) manufactured by the present invention. The density of the web is 1 g / l. The drying condition is to dry for 5 minutes at a molding temperature of 140 ℃.

Subsequently, as shown in FIG. 2B, the composite of cellulose 13 and fiber fabric 12 is a bonded metal mold having a half 14A of a metal mold having a hemispherical portion and a protrusion matching the portion of the metal. The hemispherical composite diaphragm as shown in FIG. 2C is manufactured by drawing using the half 14B of.

Example 2

Web forming and drawing process steps are performed in the same manner as in Example 1. The polyester fiber fabric 12 is then separated from cellulose to obtain a hemispherical diaphragm formed solely by cellulose 13.

Example 3

Bleached kraft pulp (NB KP) obtained from conifers was beaten using a Hollander type beater to achieve a Canadian standard degree of freedom of 300 ml, and the web was prepared in the same manner as in Example 1. Processing into the forming and drawing process steps yields a composite diaphragm formed by cellulose and polyester fibers.

Binders commercially available from Nippon Zeon Co. Ltd. under the trade name Nipol Latex to enhance the adhesion between cellulose and polyester fiber fabrics in Examples 1 and 3 above. And the yield enhancer (wet strength enhancer of the web), sold under the trade name Kaimen 557-N (Dick Hercules Co. Ltd.), before forming into a web, Note that the amount of loss is added to the cellulose suspension in amounts of 10% and 5% by weight, respectively.

According to the vibration reed method, the internal loss rate (tan δ), Young's modulus (E), and sound velocity (C) are measured for the diaphragm obtained by the above technique. The results are shown in Table 1 below. In addition, the results obtained using a conventional paper diaphragm, prepared by forming cellulose having a Canadian standard degree of freedom of 500 ml, are also shown in Table 1 as a control example.

TABLE 1

Comparing the properties of the diaphragm obtained in the above-described examples with those of the conventional paper diaphragm, the Young's modulus of the diaphragms obtained in Examples 1 to 3 was determined by the Young's modulus obtained using the conventional paper diaphragm according to the comparative example. You can see that it is two or three times.

In addition, since the diaphragm of Examples 1 to 3 is in the form of a film without pin holes, unlike the conventional paper diaphragm, the paper diaphragm does not require a coating process or an impregnation step of the absolutely necessary bonding part filling material. The film diaphragm was as thin as about 10 micrometers.

Claims (7)

(Twice Correction) Micro-fibrillated cellulose having a convex outer surface and a recess formed therein and formed by applying a micro-fibrillated cellulose having a Canadian standard freeness value of 300 ml or less to the papermaking process. A member comprising a member and a fabric made from the group consisting of carbon fiber, glass fiber, polyester fiber, aramid fiber and silk, and comprising a reinforcement laminated on the convex outer surface of the micro-fibrillated cellulose member opposite the recess Acoustic diaphragm. (Correction) The acoustic diaphragm according to claim 1, wherein the fabric is a woven fabric. (Twice correction) The acoustic diaphragm of Claim 1 whose woven fabric is a nonwoven fabric. (Twice correction) The acoustic diaphragm of Claim 1 whose Young's modulus of elasticity of a cellulose member is the range of 6.7-8.5 GPa. (Twice correction) The acoustic diaphragm of Claim 1 whose thickness of a cellulose member is 10 mu m. (Twice correction) The acoustic diaphragm according to claim 1, wherein the recesses formed in the cellulose member are hemispherical. (Twice correction) The acoustic diaphragm according to claim 1, wherein the concave portion formed in the cellulose member is conical.