JPH07101954B2 - Film for speaker diaphragm - Google Patents

Description

TECHNICAL FIELD The present invention relates to a film for a speaker diaphragm, and more particularly to a biaxially oriented polyethylene-2,6-
The present invention relates to a film for a speaker diaphragm, which is made of a naphthalate film and has excellent high-frequency reproduction characteristics and has a small change in sound quality under high temperature and high humidity conditions.

Problems of Prior Art Conventionally, biaxially oriented polyethylene terephthalate film has been used as a diaphragm for a speaker made of plastic. However, this polyethylene terephthalate film has a problem that the elastic modulus is small, the high resonance frequency fH is low in the case of a full-range speaker, and high-pitched sound reproduction is not always good.

Further, recently, the use for in-vehicle applications and outdoor applications has been increasing, and the temperature characteristics have become particularly important. For this reason, there has been a demand for a diaphragm material that has a small dimensional change under high temperature and high quality conditions and has no deterioration in sound quality characteristics.
As a solution to such a problem, Japanese Unexamined Patent Publication No. 62-263797 discloses a film carrier containing polyethylene naphthalate as a main component or a film in which a reinforcing agent such as potassium titanate fiber or alumina powder is mixed in a polyethylene naphthalate resin. The speaker diaphragm used has been proposed. By using the film, the diaphragm with a thickness of 50 μm or more is 10
It is described that thermal deformation does not occur even in a temperature atmosphere of 0 ° C. However, it is necessary to make the film diaphragm thin in order to exert an excellent effect as a diaphragm for a small speaker or a headphone. It is described in the above publication that when the thickness is about 10 μm, thermal deformation occurs in an atmosphere of 90 ° C. Also,
In the in-vehicle use and outdoor use, heat resistance that does not deform even under high temperature and humidity is required, and it is required to endure a temperature of about 100 ° C. or higher.

DISCLOSURE OF THE INVENTION An object of the present invention is to provide a biaxially oriented polyethylene having elastic modulus, dimensional change rate, and isotropy index thereof in a specific range as a result of earnest research for developing a material for a diaphragm in which these points are improved. The inventors have found that -2,6-naphthalate film exhibits extremely excellent properties as the above-mentioned material, and have reached the present invention.

Therefore, an object of the present invention is to provide a film for a speaker diaphragm, which has excellent reproduction characteristics, particularly high-pitched sound reproduction characteristics, excellent dimensional stability under a high temperature and high humidity atmosphere, and small change in sound quality.

According to the present invention, a biaxially oriented polyethylene-2,6-naphthalate film has a modulus of elasticity of 10 × 10 ^{10 to} 17 in both biaxial directions. Within the range of × 10 ¹⁰ dyn / cm ² , the dimensional change rate when held at 150 ° C free length for 0.5 hours is 2% or less in both biaxial directions, and the isotropic index of elastic modulus and dimensional change rate. Are in the range of 0.6 to 1.5, respectively.

Polyethylene-2,6-naphthalate in the present invention,
Not only polyethylene-2,6-naphthalate homopolymer, but also polyethylene-2,6-naphthalate copolymer modified with a small proportion (for example, 10 mol% or less, further 5 mol% or less) of the third component and a small proportion It also includes a blend polymer in which a third component (for example, 20% by weight or less, further 10% by weight or less) is mixed.

Such polyethylene-2,6-naphthalate is basically known and can be produced by a known method.
Polyethylene-2,6-naphthalate, for example, is generally
It is produced by subjecting naphthalene-2,6-dicarboxylic acid or its ester-forming derivative and ethylene glycol or its ester-forming derivative to polycondensation reaction in the presence of a catalyst. In the case of producing a copolymer, the third component may be added and reacted at a stage until the polycondensation reaction is completed, and in the case of producing a blend polymer, the polymer of the third component may be added before the film formation. Should be mixed.

Suitable third component is a compound having a divalent ester-forming functional group such as oxalic acid, adipic acid, phthalic acid, isophthalic acid, terephthalic acid, naphthalene-2,7-
Dicarboxylic acids such as dicarboxylic acids and diphenyl ether dicarboxylic acids or lower alkyl esters thereof; oxycarboxylic acids such as p-oxybenzoic acid and p-oxyethoxybenzoic acid or lower alkyl esters thereof; or propylene glycol, trimethylene glycol, tetra Examples thereof include dihydric alcohols such as metrene glycol, hexamethylene glycol, neopentyl glycol and the like.

Further, polyethylene-2,6-naphthalate may be, for example, one obtained by blocking a part or all of the terminal hydroxyl group and / or carboxyl group with a monofunctional compound such as benzoic acid or methoxypolyalkylene glycol, or For example, it may be a compound modified with a trifunctional or higher functional ester-forming compound such as glycerin or pentaerythritol in a very small amount within a range where a substantially linear polymer is obtained.

Polyethylene-2,6 constituting the film in the present invention
-Naphthalate is in an orthochlorophenol solution
Intrinsic viscosity number at 35 ℃ is 0.40 or more, further 0.50 or more,
Particularly preferred is 0.5 to 0.70.

Such polyethylene-2,6-naphthalate may contain a lubricant such as finely divided silica, talc, clay, etc. for imparting a slip property to the film, and other additives such as a stabilizer, an ultraviolet absorber, A flame retardant or the like may be added.

In the present invention, the biaxially oriented film made of polyethylene-2,6-naphthalate should have an elastic modulus in the range of 10 × 10 ^{10 to} 17 × 10 ¹⁰ dyn / cm ² in both biaxial directions. It is preferably in the range of 10 × 10 ¹⁰ to 15 × 10 ¹⁰ dyn / cm ² . If the elastic modulus is less than 10 × 10 ¹⁰ dyn / cm ² , the high resonance frequency fH cannot be increased, and 17 × 10 ¹⁰ dyn / cm ²
If it is larger than the above range, it becomes difficult to form a speaker diaphragm, and in particular, it is difficult to form a diaphragm having a delicate sectional shape, which is not preferable.

The above-mentioned biaxially oriented film is further heated at a temperature of 150 ° C.
The rate of dimensional change is 2% or less after the holding treatment for 0.5 hours. It is preferably 1% or less. This dimensional change rate is 2%
If it is larger, the amount of shrinkage during molding of the diaphragm becomes large, it becomes difficult to accurately reproduce the shape of the mold, the sound is not faithfully reproduced, and the sound quality deteriorates, which is not preferable.

The biaxially oriented film further has an isotropic index of elasticity and dimensional change in the range of 0.6 to 1.5, preferably 0.8.
It is in the range of ~ 1.2. If this isotropic index does not fall within the above range, the in-plane anisotropy of the speaker diaphragm becomes large and split vibration is likely to occur, which is not preferable.

Here, the isotropic index of the elastic modulus is the ratio of the elastic modulus in the longitudinal direction of the film to the elastic modulus in the lateral direction, and the isotropic index of the dimensional change rate is the dimensional change rate in the longitudinal direction of the film and the lateral direction. Is the ratio of the dimensional change rate.

If the isotropic index is not within the above range, anisotropy becomes large in the plane of the speaker diaphragm, which causes a problem that split vibration easily occurs, which is not preferable.

The biaxially oriented polyethylene-2,6-naphthalate film of the present invention needs to satisfy the above-mentioned elastic modulus, dimensional change rate and isotropic index, but these characteristics are such that the stretching ratio and heat It can be obtained by properly selecting conditions such as fixed temperature.

For example, polyethylene-2,6-naphthalate is sufficiently dried and then made into an unstretched film by a melt extrusion method, and this unstretched film is stretched at a stretching temperature of 130 to 150 ° C in the longitudinal direction by 3.5 to 4.5 times, and then transversely. Stretching is carried out at a temperature of 120 to 150 ° C in the range of 3.6 to 4.8 times in the direction and larger than [longitudinal stretching ratio +0.1] times and smaller than [longitudinal stretching ratio +0.3] times. Furthermore, it is advisable to heat-set at 220 to 255 ° C for 5 seconds to 1 minute. The heat setting may be performed under the limited shrinkage. Further, it is preferable to employ an electrostatic contact method at the time of melt extrusion.

As described above, the film can have improved isotropy by controlling the stretching ratio and the heat setting temperature. In addition, when reducing the dimensional change rate, it can be lowered by raising the heat setting (crystallization) temperature after biaxial stretching to about 255 ° C, but the dimensional change rate around 110 ° C is further improved. In order to do so, it is preferable to heat-treat the film which has been heat-set after biaxial stretching at a temperature of 120 to 150 ° C. in a relaxed state.

Biaxially oriented film has a thickness of 1 to 50 μm, and further 5 to 20
μm is preferred.

The biaxially oriented polyethylene-2,6-naphthalate film of the present invention has the following advantages.

Compared with the conventional polyethylene terephthalate film, the density is lower and the elastic modulus is higher, so the inelastic modulus is higher, the reproduction frequency band can be expanded, and the high frequency distortion is reduced and the transient characteristics are improved.

Since the density is low, the weight of the diaphragm is light and the output level for the same input can be increased. Therefore, there is an advantage that the drive unit can be made lighter and smaller when the same output is obtained.

Further, since it has excellent environment resistance against temperature and humidity, it can withstand use in in-vehicle applications and outdoor applications. Polyethylene terephthalate film has a larger amount of deformation than polyethylene-2,6-naphthalate film at 70 ° C for a long time (treatment), and its heat resistance is insufficient for in-vehicle use or outdoor use. On the other hand, polyethylene-2,6-naphthalate polymer has a glass transition temperature of 113 ° C, which is significantly higher than that of polyethylene terephthalate (Tg = 70 ° C), so it can be used as a speaker diaphragm with improved heat resistance. It can also be used in hot and humid environments for outdoor use.

Internal loss of polyethylene-2,6-naphthalate (tan δ)
Is larger than polyethylene terephthalate, the divided vibration of the diaphragm is limited and the frequency characteristics become flat,
There is an advantage that distortion is reduced.

EXAMPLES Hereinafter, the present invention will be further described with reference to examples. The film characteristics are measured as follows.

(1) Modulus of elasticity Dynamic modular tester PP manufactured by Toyo Seisakusho Co., Ltd.
Measured with M-5R.

(2) Dimensional change rate A film sample is used as the measuring method, with a length of 350 mm or more and a width of 10 mm.
Cut into strips with. A 300 mm long mark was attached to this sample, and it was placed in a thermostatic chamber at a temperature of 23 ° C x 60% RH for 24 hours with a free length.
After holding for at least the time, read the dimension between gauge marks with a reading microscope. Then, this strip-shaped sample is heated to a predetermined temperature (150 ° C)
After keeping it in the air oven set for a predetermined length of time (0.5 hr), it was placed in a constant temperature and humidity chamber at 23 ° C x 60% RH again.
Keep the length at least 24 hours and then read the dimension between gauges. The difference in size between the gauge marks before and after the treatment is calculated as a 100-percentage ratio to the dimension between the original gauge marks, and is shown as the dimensional change rate.

(3) Isotropic Index The isotropic index of the elastic modulus is obtained by calculating the elastic modulus in the longitudinal direction and the elastic modulus in the lateral direction and showing the ratio thereof. Further, the isotropic index of the dimensional change rate is shown by the ratio of the dimensional change rate in the vertical direction and the dimensional change rate in the horizontal direction.

(4) High range resonance frequency fH Obtain the output sound pressure frequency characteristics according to JIS C 5531, and obtain it based on the definition on page 274 of the Audio Handbook (Ohm Co.). However, the sound pressure at the point where the output voltage is equivalent to 0.1 W and 0.5 m is measured.

Examples 1 to 6 and Comparative Examples 1 to 3 Polyethylene-2,6-naphthalate having an intrinsic viscosity of 0.60 was melt extruded and cooled and solidified on a casting drum to prepare an unstretched film. Then, this was biaxially stretched under the conditions as shown in Table 1 and heat-set. The properties of the biaxially stretched polyethylene-2,6-naphthalate film thus obtained are shown in Table 1.

A diaphragm was formed from these films by a pressure forming method to obtain a cone-shaped diaphragm having a diameter of 40 mm. The acoustic characteristics of the speaker using this diaphragm were investigated. The result is first
Shown in the table.

From Table 1, the speaker using the film diaphragm of the present invention has a high elastic modulus and thus a high resonance frequency fH.
It can be seen that the regeneration at high temperature is good.

Claims (4)

[Claims] 1. A biaxially oriented polyethylene-2,6-naphthalate film having a modulus of elasticity of 10 × 10 6 in both biaxial directions.
It is in the range of ^{10 to} 17 × 10 ¹⁰ dyn / cm ² , and is 0 at 150 ° C free length.
For a speaker diaphragm, characterized in that the dimensional change rate after holding for 5 hours is 2% or less in both biaxial directions, and the elastic modulus and dimensional change rate isocratic index are in the range of 0.6 to 1.5, respectively. Film. 2. The film according to claim 1, which has a modulus of elasticity of 10 × 10 ¹⁰ to 15 × 10 ¹⁰ dyn / cm ² . 3. The film according to claim 1, wherein the isotropic indices of elastic modulus and dimensional change rate are in the range of 0.8 to 1.2, respectively. 4. The film according to claim 1, 2 or 3, wherein the film thickness is 1 μm or more and 50 μm or less.