JPS5932960B2 - Manufacturing method of polyimide diaphragm for audio equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a polyimide diaphragm for audio equipment such as speakers, microphones, and headsets.

Traditionally, diaphragms for audio equipment have been made by bonding a pyromellitic acid-based polyimide film (manufactured by DuPont, trade name: Kapton) to metal foil with an epoxy or urethane adhesive, and then etching the metal foil. manufactured by the method.

However, in the above conventional method, an adhesive is used to bond the polyimide film and metal foil.
Because the heat resistance of this adhesive is inferior to that of polyimide film, the power of the audio equipment cannot be increased to the allowable limit of the polyimide film, and the audio equipment can only be used in a low power state below the allowable limit of the adhesive. The problem is that it is not possible.

In recent years, the development of audio equipment has been remarkable, and as a result, the demands on diaphragms to increase their power have become even more severe (this demand is particularly pronounced for diaphragms for ribbon-type tweeters). The reality is that the use of such adhesives cannot meet such demands.

Furthermore, with respect to diaphragms for audio equipment, in addition to the above-mentioned demands for increased power, there are also demands for improvements in acoustic properties such as frequency characteristics, impedance characteristics, and frequency division characteristics.

It is known that the acoustic properties of a diaphragm can be improved by reducing the thickness of the film or by using a film bonded to the metal foil that has elastic properties that comply with Hooke's law as much as possible. With the conventional method, it is difficult to obtain a film with a thickness of 7.5 μm or less considering the level of film forming technology, and if the conventional method is used, it is not possible to expect much improvement in acoustic characteristics. The present invention solves the above-mentioned problems of the conventional method, and provides a method for manufacturing a polyimide diaphragm for audio equipment that not only increases power but also allows thinner products.

That is, the method for manufacturing a polyimide diaphragm for audio equipment according to the present invention is based on biphenyltetracarboxylic acid 2 represented by the general formula
A polyamic acid solution with an intrinsic viscosity of 0.5 or more obtained by reacting an anhydride (hereinafter referred to as BPDA) and an aromatic diamine in an organic polar solvent is applied onto one side of the metal foil and then heated. It is dried to remove the solvent by evaporation and convert the polyamic acid into polyimide to obtain a diaphragm material consisting of a metal foil and a polyimide layer.Then, the metal foil of the diaphragm material is etched to form a conductive circuit in a predetermined shape. It is characterized by 2.

In the present invention, first, BPD represented by the above general formula
React approximately equimolar amounts of A and aromatic diamine in an organic polar solvent to obtain a polyamic acid solution with an intrinsic viscosity of 0.5 or more, and then apply the two polyamic acid solutions on at least one side of metal foil. After that, it is calorically dried to evaporate the solvent and convert the polyamic acid into polyimide, thereby obtaining a diaphragm material in which the metal foil and the polyimide layer are directly bonded.

Specific examples of BPDA used in this step include 3,4,3',4'-BPDA, 2,3,3',4'-
Examples include BPDA, 2,3,2',3'-BPDA, etc. Among these, 3,4,3',4'-BPDA
Trigrams and 2, 3, 3', 4-nickel BPDA are preferred.

On the other hand, specific examples of aromatic diamines to be reacted with the BPDA include m-phenylene diamine, p-phenylene diamine, 4,4'-diaminodiphenylmethane, 4,
4'-diaminodiphenyl ester, 4,4'-diaminodiphenylpropane, 4,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfone, 3,3-diaminodiphenyl Sulfone, 1,5-diaminonaphthalene, 2,6-diaminonaphthalene, 3,4
'-diaminobenzanilide and the like.

According to the present invention, the above BPDA and aromatic diamine are N,
N,N-dialkylcarboxylamides such as N-dimethylformamide, N,N-diethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, N,N-dimethylmethoxyacetamide, dimethylsulfoxide, N-methyl- The reaction is carried out in an organic polar solvent such as 2-pyrrolidone, dimethylsulfone, or hexamethylphosphoramide.

The concentrations of BPDA and aromatic diamine in the organic polar solvent during this reaction can be set depending on various conditions, but
It is usually 5 to 30% by weight, preferably 10 to 25% by weight.

In addition, the reaction temperature is usually 80°C or less, preferably 5 to 50°C.
The reaction time is usually about 1 to 10 hours. In the present invention, BPDA, aromatic diamine, and organic polar solvent may be used alone or in combination of two or more.

Furthermore, organic polar solvents include aromatic hydrocarbons such as benzene, toluene, and xylene, ethers such as dioxane, ketones such as methyl ethyl ketone, alcohols such as methanol and ethanol, and phenols such as phenol and cresol. 〇 When BPDA and aromatic diamine are reacted in an organic polar solvent in this way, polyamic acid is produced and the solution viscosity increases as the reaction progresses, but this method is suitable for the present invention. A polyamic acid solution having an intrinsic viscosity of 0.5 or more is obtained.

If the intrinsic viscosity of the polyamic acid solution is 0.5 or less, the polyimide layer formed on the metal foil by the conversion of the polyamic acid will be brittle and prone to cracking, tearing, etc., making it difficult to use as a diaphragm. This is not preferable because it reduces the The intrinsic viscosity of the polyamic acid solution in the present invention can be determined by the following formula (1) after taking out the polyamic acid from the polyamic acid solution, dissolving this polyamic acid in a predetermined solvent, and measuring the solution viscosity. This is the value calculated by.

It is.

The polyamic acid solution obtained in this way is viscous, and the solution viscosity is usually about 10 to 10 when the concentration of polyamic acid is 5 to 30% by weight, measured with a B-type viscometer at a temperature of 30°C. It shows 108 poise.

In the present invention, the polyamic acid solution obtained by reacting BPDA and aromatic diamine in an organic polar solvent as described above is then processed into a metal foil having a thickness of usually 50 μm or less,
For example, it is applied on at least one side of aluminum foil, copper foil, etc.

Various methods can be applied to apply the polyamic acid solution to the surface of these metal foils, such as 5 methods of immersing the metal foil in the polyamic acid solution, pulling it up, and squeezing out excess polyamic acid with a doctor knife, 5 reverse roll method, etc. Specific examples thereof include a method in which a polyamic acid solution is transfer-coated onto the surface of a metal foil using a coater, and a method in which a polyamic acid solution is extruded and applied onto the surface of a metal foil using a T-die.

In this coating process, the polyamic acid solution may be applied as is to the surface of the metal foil, but the solution may be diluted with an appropriate solvent or heated to adjust its viscosity before application. You can also. The thickness of the polyamic acid solution applied to the metal foil is such that the thickness of the polyimide layer formed by conversion of the polyamic acid is usually 50 microns or less, preferably 2 to 25 microns.

The metal foil whose surface is coated with the polyamic acid solution as described above is then heated and dried.

This heating drying is carried out to convert the polyamic acid in the polyamic acid solution applied to the surface of the metal foil into polyimide and to evaporate and remove volatile components such as the solvent.
The force and heat temperature in this case may vary depending on various conditions, but is usually 50 to 500°C, preferably 50 to 200°C.
After pre-drying at ℃, the temperature is further increased to 200-500℃.
It is preferable to raise the temperature to a certain temperature and then perform post-drying.

According to this two-stage drying method, first, most of the solvent is removed by evaporation in the pre-drying step 1fC, and then in the post-drying step, volatile components such as remaining solvent are removed by evaporation, and the polyamic acid is converted into polyimide. Since the conversion takes place, even when a polyamic acid solution containing a large amount of solvent is used or the coating thickness is increased, foaming due to evaporation of volatile components can be prevented, and a uniform polyimide layer without a board can be formed. It has the advantage of being able to form By this heat drying, a diaphragm material is obtained in which a polyimide layer having a volatile content of 5% by weight or less, preferably 1% by weight or less is formed on the surface of the metal foil. The volatile content (% by weight) of the polyimide layer of the diaphragm material is a value calculated by the following equation (). W in the above formula () is the weight of the diaphragm material before drying,
Wd indicates the weight after heat drying the material at 350° C. for 2 hours DI, and Wb indicates the weight of the metal foil.

In the present invention, the metal foil of the diaphragm material obtained as described above is etched to form a conductive circuit in a predetermined shape, and the conductive circuit of the metal foil is directly bonded onto the polyimide layer. A polyimide diaphragm is obtained. This etching process can be performed by a photo etching method or a sputter etching method. In the case of the photo etching method, for example, the diaphragm material is cut to a predetermined size, and after degreasing, washing, and drying, a photoresist ( A photosensitive resin) layer is formed, a predetermined part of the layer is masked, and exposed to light.
A conductive circuit of metal foil was formed on the polyimide layer by developing, removing the unexposed (uncured) photoresist layer, etching, and removing the exposed (hardened) photoresist layer. A polyimide diaphragm is obtained.

According to the present invention, in order to perform etching on a metal foil used as a diaphragm material in which polyimide layers are formed on both sides of the metal foil, one polyimide layer must be etched with an aqueous solution of hydrazine or sodium hydroxide. The exposed metal foil is then etched.

The present invention is structured as described above, and since the polyimide layer and metal foil are directly bonded, a polyimide diaphragm that can be used with high power can be obtained, and by applying a polyamic acid solution, a polyimide layer is formed on the surface of the metal foil. As a result, a thin polyimide layer can be formed, and a polyimide diaphragm with excellent acoustic properties can be obtained.

Hereinafter, the present invention will be explained in more detail with reference to Examples.

All "%" in the examples indicate "% by weight". Example 1 3,4,3',4'-BPD All 769 (4 mol) and 4,4'-diaminodiphenyl ether 8009 (4 mol) were mixed in 14.5 kg of N-methyl-2-pyrrolidone at a temperature of 5 to 30 mol. The reaction was carried out at ℃ for 5 hours to obtain a polyamic acid solution having an intrinsic viscosity of 2.5.

Next, this polyamic acid solution was applied to a thickness of 20μ and a width of 400m.
It was continuously coated on one side of a long piece of hard aluminum foil using a knife coater and pre-dried for 10 minutes by passing it through a dryer at 150°C to remove most of the N-methyl-2-pyrrolidone. The aluminum foil is removed by evaporation and then passed through a dryer at 250 to 300°C for 20 minutes and then dried to evaporate and remove remaining volatile components such as pyrrolidone and convert the polyamic acid into polyimide. 12 on one side
．． A long diaphragm material on which a 5 μm polyimide layer is formed is obtained.

Note that the volatile content in the polyimide layer was 0.2%. After that, this diaphragm material is 150 x 15077
! W! A polyimide diaphragm having a conductive circuit of a predetermined shape was obtained by cutting the aluminum foil into a size of 1 and photoetching the aluminum foil.

When this diaphragm was subjected to a power test (5K [sin wave input test at 1z)], no deterioration occurred even at 40W for 20 minutes.

For comparison, a diaphragm was prepared by bonding a polyimide film with a thickness of 12.5 μm (manufactured by Dupont, trade name: Kapton) and the same aluminum foil as above with an epoxy adhesive (the shape of the conductive circuit was the same as that of the diaphragm of the present invention). When a power test was conducted under the same conditions for the same product, the adhesive was carbonized after 20.20 minutes.

Further, in order to know the acoustic characteristics of the polyimide diaphragm obtained by the present invention, the polyamic acid was cast on a glass plate, and after pre-drying and post-drying under the same conditions as when obtaining the diaphragm. , 12.5μ thick after peeling off from the glass plate
A BPDA-based polyimide film with a volatile content of 0.2% was obtained, and a tensile test was conducted to create a stress-strain curve. Compared to B), it was found that the sound more closely followed Hook's law, and the acoustic characteristics were also improved compared to the conventional product. Nafu...The sample width for the tensile test is 20m7! The test was carried out under the following conditions: L, tensile speed: 50 m11/MuLS chuck interval: 100 mm, load: 100 k9, and temperature: 25°C.

Further, using the polyamic acid described above, the polyamic acid was cast onto a glass plate, followed by pre-drying, post-drying, and peeling from the glass plate in order to obtain polyimide films of various thicknesses. Figure 2 shows the relationship between film thickness and breaking load obtained by conducting a tensile test on the film under the same conditions as above. From Figure 2, it can be seen that the polyimide layer used in the present invention (straight line C) has a change in breaking load depending on the thickness compared to the Kapton film used in conventional products (straight line D).
It turns out that it is smaller than .

Diaphragms are usually assembled into speakers, etc. by being stretched on a tension frame with a predetermined tension, and this tensioning work can be done without changing the tension even if the thickness of the polyimide layer varies slightly. The work efficiency is better. Therefore, the BPDA-based polyimide layer used in the present invention has a smaller change in breaking load depending on its thickness than the conventional pyromellitic acid-based Kapton film, and is suitable for use on diaphragms during tensioning work on a tension frame. Workability is excellent because there is no need to change the tension even if the thickness of the polyimide layer changes somewhat.

Example 2 The polyamic acid solution used in Example 1 was extruded through a T-die, coated on one side of a long piece of hard aluminum foil with a thickness of 10μ and a width of 400m1L, and heated and dried under the same conditions as Example 1.
On one side of aluminum foil with a thickness of 4 μ and a volatile content of 0.05 (
:F) Obtain a long diaphragm material on which a polyimide layer is formed.

Next, this diaphragm material was cut into a size of 150 x 150 mm, and aluminum foil was photoetched to obtain a polyimide diaphragm on which a conductive circuit of a predetermined shape was formed.

When this diaphragm was subjected to a power test in the same manner as in Example 1, no deterioration occurred even at 40 W for 20 minutes.

For comparison, a diaphragm was prepared by bonding a polyimide film with a thickness of 7.5 μm (manufactured by Dupont, trade name: Kapton) and the same aluminum foil as above with a urethane adhesive (the shape of the conductive circuit was the same as that of the diaphragm of the present invention). When a power test was conducted under the same conditions for the same product, the adhesive was carbonized at 15 W for 20 minutes.

Claims (1)

[Claims] 1 A biphenyltetracarboxylic dianhydride represented by the general formula ▲ Numerical formulas, chemical formulas, tables, etc. are available▼ and an aromatic diamine obtained by reacting the biphenyltetracarboxylic dianhydride and aromatic diamine in an organic polar solvent, and the intrinsic viscosity is 0. After applying a polyamic acid solution of 5 or more on at least one side of the metal foil, it is heated and dried to evaporate the solvent and convert the polyamic acid into polyimide to obtain a diaphragm material consisting of a metal foil and a polyimide layer. A method for producing a polyimide diaphragm for audio equipment, which comprises etching a metal foil of the diaphragm material to form a conductive circuit in a predetermined shape.