JP3036163B2 - Manufacturing method of diaphragm - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a diaphragm for a loudspeaker, and more particularly to a method for manufacturing a diaphragm in which an ultrahigh molecular weight polyolefin is highly oriented and exhibits an excellent elastic modulus. .

[0002]

2. Description of the Related Art Various characteristics are required for a diaphragm of a speaker in order to pursue higher quality reproduced sound. As one of them, first, in order to expand the reproduction frequency band, longitudinal wave propagation velocity [= (specific elastic modulus) ^1/2 = (elastic modulus / density) ^1/2 ]
Is large. For this purpose, a material having a higher elastic modulus and a lower density is more advantageous. At the same time, it is necessary to have an appropriate internal loss in order to absorb an abnormal sound and a distortion component generated due to the divided vibration particularly in a high frequency range.

However, a material having a large elastic modulus and a large longitudinal wave propagation velocity usually has a small internal loss, and it is difficult to satisfy these contradictory characteristics simultaneously with a single material. Therefore, conventionally, in order to obtain a large specific elastic modulus, for example, a material having a large internal loss such as paper pulp or polypropylene is mixed with a reinforcing material such as carbon fiber or mica having a high elastic modulus, or a super-drawn polyethylene woven fabric or the like is used. It has been practiced to use a fiber-reinforced plastic obtained by compounding the above. On the other hand, the internal loss is improved by applying or impregnating the surface of the diaphragm with an organic paint having a large internal loss, a so-called dumping agent.

However, the method of mixing the reinforcing material has a problem that the mixing amount is naturally limited, and particularly when mixed with a polymer material, the melt viscosity increases and molding becomes difficult. Much cannot be desired for the increase in modulus. In the case of fiber reinforced plastics, so-called strength anisotropy, which indicates high strength along the weave direction of the woven fabric, appears, and mass production by injection molding is impossible, so that the number of manufacturing steps is large and the cost is high. There is a problem.

On the other hand, in the latter case, the application and impregnation of a dumping agent for improving the internal loss has a problem that the specific elastic modulus is lowered while the internal loss is increased.

As a material which can be injection-molded and has a high modulus of elasticity and a high internal loss, liquid crystal polymers have attracted attention in recent years. However, in the case of a liquid crystal polymer, since rigid molecules are highly oriented by injection pressure during molding, there is a problem that strength anisotropy of a molded product is too large and cracks easily along the orientation direction. In order to alleviate the strength anisotropy, it is necessary to mix short carbon fibers or the like, but this causes deterioration in sound quality and moldability.

[0007] As a material of interest other than the liquid crystal polymer, there is an ultrahigh molecular weight polyolefin. In order to realize a high specific elastic modulus and a high internal loss in this ultrahigh molecular weight polyolefin, it is necessary that the molecular chains of the polyolefin are aligned in one direction. Then, when using as a diaphragm material, it is common to use fibers etc. previously drawn by a technique such as a gel drawing method.

For example, Japanese Patent Application Laid-Open No. 58-182994 discloses a technique in which an ultra-high molecular weight polyethylene fiber having a longitudinal wave propagation speed of 4000 m / sec or more is wet-formed, dried and pressed with a pressure to form a diaphragm for a speaker. It has been disclosed.

However, in the diaphragm made by the papermaking technique as described above, since the fibers are randomly oriented, there is a problem that the specific elastic modulus is significantly lower than the specific elastic modulus of the fiber itself. I haven't been able to take full advantage of the special features. Further, polyolefin fibers have an inactive surface and are difficult to mold, and the use of a binder or the like has little effect.

In order to solve this problem, the present applicant has previously disclosed in Japanese Patent Application Laid-Open No. Hei 3-136598 a multistage polyolefin having an ultrahigh molecular weight polyolefin having a high melt viscosity and a low molecular weight or high molecular weight polyolefin having a low melt viscosity. It discloses a technique of using a polyolefin composition polymerized by a legal method, orienting the molecular chains of ultrahigh molecular weight polyolefin radially by injection molding using the difference in fluidity of these two components, and improving the elastic modulus. . In this technique, it is an important factor that two components having significantly different melt viscosities are finely mixed in the polyolefin composition. When the polyolefin composition polymerized by the multi-stage polymerization method is melted and fluidized, the low viscosity component acts as an internal lubricant, and the ultra-high molecular weight polyolefin, which is the high viscosity component, is stretched in the flow direction, achieving high orientation. It is done. In a composition in which an ultrahigh molecular weight polyolefin and a low molecular weight or high molecular weight polyolefin are simply mixed, such a high orientation cannot be realized because the high viscosity component is not finely dispersed.

[0011]

According to the technique disclosed by the present applicant in Japanese Patent Application Laid-Open No. 3-136598, when the polyethylene is used as the polyolefin, the elastic modulus is maintained while maintaining a suitable internal loss. Increases,
A diaphragm having significantly improved properties as compared with the conventional polypropylene molded body could be produced.

[0012] However, the elastic modulus achieved is still far from the theoretical value, and efforts to bring the elastic modulus of the polyolefin composition closer to the theoretical value at all are still necessary. Therefore, the present invention aims to propose a new technology for more highly oriented ultra-high molecular weight polyolefin molecular chains,
It is an object of the present invention to provide a method capable of manufacturing a diaphragm excellent in both specific elastic modulus and internal loss by a general-purpose molding technique.

[0013]

The present inventors have made intensive studies to achieve the above-mentioned object, and as a result, have found that the above-mentioned polyolefin composition has a temperature close to its melting point, that is, a temperature considerably lower than the usual common-sense injection temperature. It has been found that an extremely high molecular orientation is achieved when injection is performed while applying a large acceleration in a region, and the present invention has been proposed.

That is, the method for producing a diaphragm according to the present invention has a limiting viscosity of 1 in a decalin solution at 135 ° C.
0-40 dl / g of ultra-high molecular weight polyolefin and 1
The intrinsic viscosity measured in a 35 ° C decalin solution is 0.1 to 5
dl / g of low molecular weight or high molecular weight polyolefin, and a molding material mainly composed of a polyolefin composition produced by a multi-stage polymerization method is injection-molded at an injection temperature range of 150 to 200 ° C. The molecular chain is oriented radially from the center of symmetry of the diaphragm.

In the present invention, the polyolefin composition used as a molding material includes, for example, ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-decene, 1-dosene, and 4-methyl. It is composed of α-olefin homopolymer or copolymer (copolymer) such as -1-pentene, 3-methyl-1-pentene, etc., and two components having remarkably different melt viscosities are finely mixed. An important factor is the formation of the polymer alloy.

That is, the composition has an intrinsic viscosity of 10 to 10.
An ultrahigh molecular weight polyolefin of 40 dl / g and a low molecular weight to high molecular weight polyolefin of an intrinsic viscosity of 0.1 to 5 dl / g are finely mixed.

Such a polyolefin composition is known per se, and its production method is exemplified in, for example, JP-A-1-144533. Specifically, a specific highly active solid titanium catalyst component and an organoaluminum compound It can be prepared by a multistage polymerization method in which an olefin is polymerized in multiple stages in the presence of a catalyst mainly composed of a catalyst component.

In the multi-stage polymerization method, the olefin polymerization process is divided into multi-stages in the presence of a Ziegler-type catalyst comprising a highly active titanium catalyst component containing magnesium, titanium and halogen as essential components and an organoaluminum compound catalyst component. In at least one polymerization step, the intrinsic viscosity is 10 to 40 dl /
g of an ultrahigh molecular weight polyolefin, and in another polymerization step, the olefin is polymerized in the presence of hydrogen to produce a low molecular weight or high molecular weight polyolefin having an intrinsic viscosity of 0.1 to 5 dl / g.

Therefore, at the time of polymerization, a multi-stage polymerization apparatus in which at least two or more polymerization tanks are usually connected in series is employed. For example, a two-stage polymerization method, a three-stage polymerization method,
... The n-stage polymerization method is performed. Alternatively, it is also possible to carry out a multi-stage polymerization method by a batch polymerization method in one polymerization tank. In the multi-stage polymerization method, the polymerization reaction for producing an ultrahigh molecular weight polyolefin or the polymerization reaction for producing a low molecular weight to high molecular weight polyolefin can be carried out by any of a gas phase polymerization method and a liquid phase polymerization method.
In any case, in the polymerization step for producing a polyolefin, the polymerization reaction is carried out in the presence of an inert medium such as an aliphatic hydrocarbon, an alicyclic hydrocarbon, an aromatic hydrocarbon, or a halogen hydrocarbon, if necessary. Is done. However, in order to produce an ultrahigh molecular weight polyolefin in the polymerization step, it is preferable to carry out the polymerization reaction in the absence of hydrogen. On the other hand, in other polymerization steps other than the polymerization step for producing the ultrahigh molecular weight polyolefin, a polymerization reaction of the remaining olefin is carried out in the presence of hydrogen.

The molding material used in the present invention is mainly composed of the above-mentioned polyolefin composition.
Further, a filler such as mica or glass fiber may be included. In this case, from the viewpoint of fluidity, the content of the filler is
It is recommended that the maximum be about 40% by weight.

The diaphragm is prepared by injection molding the above-mentioned polyolefin composition. In the present invention, the range of the injection temperature is limited to 150 to 200 ° C. This temperature range is considerably lower than the temperature range in which injection molding of the conventional polyolefin composition is performed, and is set near the melting point. This is because the external force applied to the composition acts as a shear force while securing the minimum fluidity required for injection molding. If the temperature is lower than 150 ° C., the composition does not melt and injection molding becomes impossible. If the temperature exceeds 200 ° C., the degree of orientation cannot be sufficiently improved.

The structure of the mold and the like are not particularly limited. However, since it is necessary to orient molecular chains radially with respect to the center of symmetry of the diaphragm, the composition injected from the gate located at the center of the diaphragm is required. It is preferable that the structure is such that the object can flow in the peripheral direction.

[0023]

It is known that when the molecular chains of an organic polymer material are oriented in one direction, physical properties such as elastic modulus and tensile strength are greatly improved. For example, when the molecular chain of polyethylene, which is a general-purpose polymer, is highly oriented, its elastic modulus is theoretically calculated to be 250 GPa. Therefore, the molecular chain orientation of the organic polymer material is an effective means for improving the elastic modulus required for the speaker diaphragm.

However, unlike rigid molecules, such as liquid crystal polymers, which can be relatively easily oriented by molding pressure, long molecular chains that are entangled in a filiform shape while being bent like polyethylene are completely elongated into a rod shape. The technology is not yet known. In recent years, polyethylene fibers having an elastic modulus of 200 GPa have been obtained at the research level by a gel drawing method, and fibers having an elastic modulus of about 90 to 100 GPa are commercially available. However, this is a value achievable in spinning technology, and not a value achievable in injection molding.

In the present invention, the injection temperature range is set to 150 to 200 ° C. in order to enhance the orientation of the molecular chain of the ultrahigh molecular weight polyolefin in the injection molding. The above temperature range is near the melting point of the composition, which is a considerably low temperature range in consideration of the fact that this type of polyolefin composition is conventionally injection-molded at around 250 ° C. Therefore, the viscosity of the polyolefin composition at the time of injection is high, and a considerably higher injection pressure than usual is required. However, when a sufficiently high injection pressure (substantially, acceleration at the time of injection is an important factor) is applied in such a state, a large shearing force is applied to the composition, and the composition is forced to flow along the flow direction of the resin. The molecular chains can be highly oriented. Therefore, if a gate is provided at the center of symmetry of the diaphragm and injection molding is performed, molecular chains are oriented radially from the center of the diaphragm toward the peripheral edge, and a diaphragm having high rigidity can be manufactured.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on specific experimental results.

Examples 1 to 3 In this example, first, a polyethylene composition was prepared as a polyolefin composition. Preparation of polyethylene composition The polyethylene composition was prepared by a two-stage polymerization method in the presence of a catalyst mainly composed of a highly active solid titanium catalyst component and an organoaluminum compound catalyst component.

Content of each component Ultra high molecular weight polyethylene (intrinsic viscosity 30 dl / g): 25% by weight Low molecular weight or high molecular weight polyethylene (intrinsic viscosity 0.7 dl / g): 75% by weight Limit of prepared polyethylene composition Viscosity: 8.1 dl / g

Preparation of Diaphragm by Injection Molding The polyethylene composition was injection molded by using an injection molding machine (manufactured by Sumitomo Heavy Industries, model name: SG-150U).
A molded product of a cone-type full-range speaker diaphragm as shown in (1) was prepared. This molded body includes a diaphragm 2 having a diameter of 16 cm and a thickness of 400 μm, and a sprue 1 connected to the center of the diaphragm 2. The sprue 1 corresponds to a portion solidified inside the gate of the mold, and is an unnecessary portion cut off in a later process. The arrows in the figure indicate the flow direction of the polyethylene composition.

The injection molding conditions are as follows. Specifications of injection molding machine Mold clamping pressure: 180 t Model name of injection device: C560M Screw diameter: 40 mm Maximum injection pressure: 2780 kgf / cm ² Maximum injection speed: 300 mm / sec Injection conditions Injection temperature (cylinder temperature): 150 ° C. (Example) 1) 160 ° C. (Example 2) 200 ° C. (Example 3) Injection speed: 40 to 50 of the maximum injection speed
% Mold temperature: 32 ° C (water cooling)

Comparative Example 1 and Comparative Example 2 In this comparative example, the injection temperature was set to 220 ° C. (Comparative Example 1).
Except that the temperature was set to 0 ° C. (Comparative Example 2), a molded body was prepared in the same manner as in the above-described example, and the characteristics were similarly evaluated.

The portion of the vibrating plate 2 of the molded product prepared in Examples 1 to 3 and Comparative Example 2 was cut in the direction of the arrow in the figure, that is, in the flow direction of the polyethylene composition, The dynamic elastic modulus was measured using a viscoelasticity measuring device (manufactured by Orientec; trade name: Vibron). FIG. 2 shows the measurement results. In the figure, the vertical axis represents the dynamic elastic modulus (GPa),
The horizontal axis represents the measured temperature (° C), and the broken line represents the injection temperature of 150 ° C.
(Example 1), the two-dot chain line indicates the data of the molded body obtained at 160 ° C. (Example 2), the one-dot chain line indicates the data of the molded body obtained at 200 ° C. (Example 3), and the solid line indicates the data of the molded body obtained at 260 ° C. (Comparative Example 2). From this result, it is clear that the dynamic elastic modulus of the molded body tends to show a higher value as the injection temperature is lower over almost the entire measurement temperature range.

Incidentally, the dynamic elastic modulus was also measured for a molded article having an injection temperature of 260 ° C. or higher, and the result was not much different from that of Comparative Example 2 described above.

Next, the longitudinal wave propagation velocity was calculated based on the measured value and the density at 20 ° C. of the results of the measurement of the dynamic elastic modulus. Table 1 shows the results. Here, the density is 95
It was 0 kg / m ³ . The table also shows the measurement results of the anisotropic texture ratio by an optical anisotropy analyzer (manufactured by Nippon Steel Corporation; model name: MT-2000). In addition, the anisotropic texture ratio is an area ratio of a molecular chain oriented portion to a cross-sectional area of a molded article.

[0035]

[Table 1]

From Table 1, it is apparent that the dynamic elastic modulus increases and the longitudinal wave propagation velocity increases as the injection temperature becomes lower. The longitudinal wave propagation velocity of the molded body at an injection temperature of 150 ° C. is increased by about 27% as compared with that of the molded body at 260 ° C. In the compact in the low temperature range, the anisotropic structure ratio was also remarkably improved, and the compact at 150 ° C. was actually 5.3 times higher than the compact at 220 ° C. This result also supports that the improvement of the dynamic elastic modulus depends on the orientation of the molecular chain of the ultrahigh molecular weight polyethylene.

[0037]

As is clear from the above description, in the present invention, a polyolefin composition obtained by polymerizing an ultrahigh molecular weight polyolefin having a high melt viscosity and a low molecular weight or high molecular weight polyolefin having a low melt viscosity by a multi-stage polymerization method. Injection molding is performed while applying a large shearing force in an injection temperature range near the melting point. Therefore, it is possible to manufacture a diaphragm having a higher elastic modulus than before, while further improving the orientation of the molecular chains and maintaining an appropriate internal loss.

The vibration plate can be easily formed by a general-purpose molding technique called injection molding, which is extremely advantageous from the viewpoint of productivity and economy.

[Brief description of the drawings]

FIG. 1A is a side view of a molded body serving as a prototype of a speaker diaphragm, and FIG. 1B is a front view thereof.

FIG. 2 is a characteristic diagram showing the measured temperature dependence of the dynamic elastic modulus of a molded article produced at various injection temperatures.

[Explanation of symbols]

 1 ... sprue 2 ... diaphragm

Continuation of the front page (51) Int.Cl. ⁷ identification code FI B29L 31:34 (58) Fields investigated (Int.Cl. ⁷ , DB name) H04R 7/02 B29C 45/00 H04R 31/00 C08L 23 / 02 B29K 23:00 B29L 31:34

Claims (1)

(57) [Claims] 1. An ultrahigh molecular weight polyolefin having an intrinsic viscosity of 10 to 40 dl / g measured in a 135 ° C decalin solution and a low molecular weight having an intrinsic viscosity of 0.1 to 5 dl / g measured in a 135 ° C decalin solution. Or a molding material mainly composed of a polyolefin composition made of a high molecular weight polyolefin and produced by a multi-stage polymerization method.
A method for producing a diaphragm, comprising: injection molding in an injection temperature range of 0 ° C., and orienting a molecular chain of the ultrahigh molecular weight polyolefin radially from a center of symmetry of the diaphragm.