JP2008219739A - Biaxial orientation polyester film for planar speaker substrate and laminating member for planar speaker constituted thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a biaxial orientation polyester film for a planar speaker substrate in which the distortion of a substrate film caused by the heating of a coil is reduced and sound quality reproducibility is improved by improving both characteristics of thermo-resistant dimensional stability and rigidity. <P>SOLUTION: The present invention relates to a biaxial orientation polyester film for a planar speaker substrate of which a thermal shrinkage percentage in treatment for 10 minutes at 200°C is ≥0% and ≤0.5%, respectively, in a length direction and a width direction, a Young's modulus is ≥6 GPa and ≤8 GPa, respectively, in the length direction and the width direction, and a variation in film thickness represented as a formula (1): film thickness variation (%)=ä(maximum value of film thickness-minimum value of film thickness)/average value of film thickness}×100 is ≥0% and ≤10%. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a thin biaxially oriented polyester film for a flat speaker substrate. More specifically, the present invention relates to a flat speaker substrate having a structure in which a coil is laminated on a vibrating membrane circuit substrate of a flat speaker. The present invention relates to a biaxially oriented polyester film for a flat speaker substrate that has low distortion and excellent sound quality reproducibility.

Conventionally, biaxially oriented films such as polyethylene terephthalate and polyethylene naphthalate have been studied as diaphragms for plastic speakers (Patent Documents 1, 2, 3, etc.).
In recent years, there has been a demand for space-saving speakers, and the development of flat speakers with thinner thickness than before has been underway. Since such a flat speaker can be thinned, it is suitable for a speaker mounted on a wall-mounted television or a notebook computer. It can also be incorporated into automobile pillars and sun visors.

  Various configurations have been proposed as a flat speaker, and as an example, a flat speaker is proposed in which tensile tension is applied to the four sides of a rectangular diaphragm, and driven by a vibrator from the back side of the diaphragm. Since the all-round pull type flat speaker is configured to drive point vibration at the center of the back of the diaphragm, the stroke of the diaphragm is regulated by the length of the short side, and the length of the long side is reproduced in the low frequency range. The bass reproduction ability is difficult because it is not utilized in Therefore, Patent Document 4 proposes that an instruction frame is provided around the vibration film and a tensile tension is applied in a part of the direction, and polyethylene naphthalate is disclosed as a material of the vibration film.

  In the case of a flat speaker, since the main part of the diaphragm has a flat shape, the strength near the center of the diaphragm may be structurally weak. In this regard, for example, Patent Document 5 proposes to form a main part thicker than the edge part in order to improve strength and improve sound quality, and polyethylene terephthalate, polycarbonate, Polyethylene naphthalate, polyetherimide, polyimide and the like have been proposed.

  On the other hand, the flat speaker proposed in Patent Document 6 is composed of a flat yoke made of an iron plate (magnetic metal plate), and a plurality of permanent magnets attached to one side of the yoke with the magnetic axis perpendicular to each other. The yokes are attached so that the polarities are opposite to each other at a predetermined interval in the plane direction of the yoke. A diaphragm in which spiral coils (hereinafter sometimes referred to as conductive circuits) are stacked is arranged in parallel near the poles of the planar magnets arranged on a plane.

  However, in the flat speaker of the type shown in Patent Document 6, a spiral film occupies most of the region of the vibration film, and each coil generates heat due to Joule heat. The influence of heat on the water cannot be ignored. In addition, such a type of flat speaker may come into contact with the permanent magnet and generate noise when the vibration membrane vibrates greatly. This problem becomes more prominent when the vibration film is distorted by the heat generation described above.

JP 7-284193 A JP-A-1-256298 JP-A-2-152400 JP 2001-275187 A JP 2004-328531 A International Publication WO99 / 03304

  The object of the present invention is to eliminate the problems of the prior art and to use a film excellent in both heat-resistant dimensional stability and rigidity as a substrate film of a vibration film of a flat speaker, so that the distortion of the substrate film due to heat generation of the coil can be reduced. An object of the present invention is to provide a small biaxially oriented polyester film for a flat speaker substrate having excellent sound quality reproducibility.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have obtained a flat speaker using a biaxially oriented polyester film having a small dimensional change at 200 ° C., a certain rigidity, and a small variation in film thickness. In the flat speaker having a structure in which the coil is laminated on the substrate film, the distortion of the substrate film due to the heat generated by the coil is small, so that the generation of noise is reduced. It has been found that the sound quality reproducibility itself is improved when it is included, and the present invention has been completed.

That is, according to the present invention, the object of the present invention is to have a thermal shrinkage rate of 0% or more and 0.5% or less in the longitudinal direction and the width direction when treated at 200 ° C. for 10 minutes, and a Young's modulus in the longitudinal direction and the width direction, respectively. 6 GPa or more and 8 GPa or less and the following formula (1)
Variation in film thickness (%) = {(maximum value of film thickness−minimum value of film thickness) / average value of film thickness} × 100 (1)
Is achieved by a biaxially oriented polyester film for a flat speaker substrate in which the variation in film thickness represented by is from 0% to 10%.

In addition, the preferred embodiment of the flat speaker substrate film of the present invention is that the polyester is polyethylene naphthalene dicarboxylate, the total light transmittance is 50% or more, and the film surface roughness WRa is 1 nm or more and 100 nm or less. It is also preferable that the film has at least one of density of 1.3 g / cm ^{3 to} 1.4 g / cm ³ and film thickness of 5 μm to 125 μm. Include.

The biaxially oriented polyester film for a flat speaker substrate of the present invention is suitably used as a vibration membrane or a vibration membrane circuit substrate for a flat speaker.
Furthermore, this invention relates to the laminated member for planar speakers by which metal foil or a coil is arrange | positioned at least on one side of the biaxially oriented polyester film for planar speaker substrates of this invention.

  The biaxially oriented polyester film of the present invention is excellent in heat-resistant dimensional stability at 200 ° C., has a certain rigidity, and has little variation in film thickness, and therefore has a structure in which a coil is laminated on a substrate film. When used as a substrate film for a speaker, the distortion of the substrate film due to the heat generated by the coil is small, so that the generation of noise is reduced. In addition, the sound quality reproducibility itself is improved when these film characteristics are provided.

The present invention will be described in detail below.
<Polyester>
The polyester film of the present invention is formed by a polyester obtained by condensation polymerization of dicarboxylic acid and glycol. Examples of the dicarboxylic acid component include terephthalic acid, isophthalic acid, and naphthalenedicarboxylic acid, and examples of the glycol component include ethylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol, and 1,6-hexanediol.

  Among the polyesters obtained from these components, the main components are preferably polyethylene terephthalate and polyethylene naphthalene dicarboxylate, and polyethylene naphthalene dicarboxylate is most preferable in terms of the balance between dimensional stability at high temperature and rigidity. Such polyethylene naphthalene dicarboxylate comprises naphthalenedicarboxylic acid as a dicarboxylic acid component and ethylene glycol as a glycol component. Here, “main” means 80 mol% or more of all repeating structural units in the polymer component. In the polyethylene naphthalene dicarboxylate of the present invention, 80% by mole or more of all repeating units are ethylene-2,6-naphthalene dicarboxylate, ethylene-2,7-naphthalene dicarboxylate, ethylene-1,5-naphthalene dicarboxylate. It is preferably at least one selected from the group consisting of rates, particularly ethylene-2,6-naphthalenedicarboxylate. More preferably, 90 mol% or more, particularly preferably 95 mol% or more of all repeating units is ethylene-2,6-naphthalene dicarboxylate, and particularly a substantially single weight of polyethylene-2,6-naphthalene dicarboxylate. It is preferably a coalescence.

  The polyethylene naphthalene dicarboxylate of the present invention may be a polyethylene naphthalene dicarboxylate copolymer having a copolymerization component of 20 mol% or less. When polyethylene naphthalene dicarboxylate is a copolymer, a compound having two ester-forming functional groups in the molecule can be used as a copolymerization component. Examples of such compounds include oxalic acid, adipic acid, phthalic acid, sebacic acid, dodecanedicarboxylic acid, isophthalic acid, terephthalic acid, 2,7-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid. Dicarboxylic acids such as acid, 4,4′-diphenyldicarboxylic acid, phenylindanedicarboxylic acid, tetralindicarboxylic acid, decalindicarboxylic acid, diphenyletherdicarboxylic acid; oxycarboxylic such as p-oxybenzoic acid and p-oxyethoxybenzoic acid Acid; or diethylene glycol, propylene glycol, trimethylene glycol, tetramethylene glycol, hexamethylene glycol, cyclohexane methylene glycol, neopentyl glycol, bisphenol sulfone ethylene Emissions oxide adducts, ethylene oxide adducts of bisphenol A, can be used diethylene glycol, dihydric alcohols such as such as polyethylene oxide glycol. These copolymerization components may be used alone or in combination of two or more. Among the copolymer components, isophthalic acid, terephthalic acid, 4,4′-diphenyldicarboxylic acid, 2,7-naphthalenedicarboxylic acid, and p-oxybenzoic acid are used as the acid component, and diethylene glycol and trimethylene are used as the glycol components. Preferred examples include ethylene oxide adducts of glycol, hexamethylene glycol, neopentyl glycol, and bisphenol sulfone.

  The polyethylene naphthalene dicarboxylate may be one in which a terminal hydroxyl group and / or a carboxyl group is partially or entirely blocked with a monofunctional compound such as benzoic acid or methoxypolyalkylene glycol, or for example, It may be a copolymer obtained by using a trifunctional or higher functional ester-forming compound such as glycerin and pentaerythritol within a range in which a substantially linear polymer is obtained.

The constituent component of the polymer in the polyester film of the present invention is mainly composed of a homopolymer or copolymer of polyethylene naphthalene dicarboxylate, but may be a mixture with other polyesters or organic polymers other than polyester. Good.
Polyesters that can be mixed with polyethylene naphthalene dicarboxylate or organic polymers other than polyester include polyethylene terephthalate, polyethylene isophthalate, polytrimethylene terephthalate, polyethylene 4,4'-tetramethylene diphenyl dicarboxylate, polyethylene-2,7- Naphthalene dicarboxylate, polytrimethylene-2,6-naphthalene dicarboxylate, polyneopentylene-2,6-naphthalene dicarboxylate, poly (bis (4-ethyleneoxyphenyl) sulfone) -2,6-naphthalene Polyesters such as dicarboxylate can be mentioned, and among these, polyethylene isophthalate, polytrimethylene terephthalate, polytrimethylene-2,6-naphthalene dicarboxylate Xylates and poly (bis (4-ethyleneoxyphenyl) sulfone) -2,6-naphthalenedicarboxylate are preferred. These polyesters or organic polymers other than polyester may be used alone or in combination of two or more.

The polyester of the present invention can be obtained by directly reacting a dicarboxylic acid with a glycol to obtain a low polymerization degree polyester, or by transesterifying a lower alkyl ester of a dicarboxylic acid with a glycol to obtain a low polymerization degree polyester. It can be produced by a method of further polymerizing in the presence of a polymerization catalyst to obtain a polyester.
The intrinsic viscosity of the polyester film after being formed into a biaxially oriented film is preferably 0.4 dl / g or more at 35 ° C. in o-chlorophenol.

<Additives>
In order to improve the handleability of the biaxially oriented polyester film of the present invention, inert particles or the like may be added within a range not impairing the effects of the invention. Examples of the inert particles include inorganic particles (for example, kaolin, alumina, titanium oxide, calcium carbonate, silicon dioxide, etc.) containing the elements of Periodic Tables IIA, IIB, IVA, and IVB, crosslinked silicone resins, Fine particles made of a polymer having high heat resistance such as crosslinked polystyrene and crosslinked acrylic resin particles can be contained. When the inert particles are contained, the average particle diameter of the inert particles is preferably in the range of 0.001 to 5 μm, 0.01 to 10% by weight, more preferably 0.05 to 5% by weight with respect to the total weight of the film. It is preferable to contain in the range of%. In addition, the biaxially oriented polyester film of the present invention may contain a small amount of an ultraviolet absorber, an antioxidant, an antistatic agent, a light stabilizer, and a heat stabilizer as necessary.

<Heat shrinkage>
The biaxially oriented polyester film of the present invention is referred to as a longitudinal direction (hereinafter, referred to as a longitudinal direction, a continuous film-forming direction, or an MD direction) after being heat-treated at 200 ° C. for 10 minutes for the purpose of enhancing heat-resistant dimensional stability against heat generation of the coil. The thermal shrinkage in the width direction (hereinafter sometimes referred to as the transverse direction and the TD direction) must be 0% or more and 0.5% or less, preferably 0.1% or more. 0.4% or less. If the heat shrinkage rate exceeds the upper limit, when the coil is used as a substrate film for a flat speaker having a structure in which the coil is laminated on the substrate film, the film is deformed by the heat generated by the coil, causing distortion and noise. The sound quality reproducibility of the speaker decreases. It is preferable that the thermal shrinkage rate at 200 ° C. is smaller if it is in the range of 0.5% or less. On the other hand, when the thermal shrinkage rate is less than 0%, on the contrary, deformation accompanying film expansion occurs.
Specific means for bringing the thermal shrinkage rate into such a range is that the film is stretched in the longitudinal direction and the width direction in a magnification range of 2.8 to 3.8 times, respectively, and further in the temperature range of 200 to 250 ° C. It can be achieved by performing a fixing treatment and then performing a thermal relaxation treatment at a relaxation rate of 0.5 to 5% in the longitudinal direction and / or the width direction in a temperature range of 150 ° C. to 230 ° C.

<Young's modulus>
In the biaxially oriented polyester film of the present invention, the Young's modulus in the longitudinal direction and the width direction of the film is preferably 6 GPa or more and 8 GPa or less, more preferably 6.1 GPa or more and 7.0 GPa or less, and particularly preferably 6.1 GPa. The above is 6.8 GPa or less. If the Young's modulus is less than the lower limit, the film does not have a low stiffness, so the performance as a vibrating membrane is low, and the acoustic characteristics are adversely affected. On the other hand, when the Young's modulus exceeds the upper limit, the thermal shrinkage at 200 ° C. exceeds 0.5%, and film deformation occurs when the coil generates heat.
The Young's modulus in the longitudinal direction and the width direction of the film can be adjusted by the magnification at the time of stretching, and is achieved by performing stretching in the film longitudinal direction and the width direction in a magnification range of 2.8 to 3.8 times, respectively. The

<Dispersion of film thickness>
In the biaxially oriented polyester film of the present invention, the film thickness variation represented by the following formula (1) needs to be 0% or more and 10% or less. The variation in film thickness is more preferably 0% or more and 5% or less.
Variation in film thickness (%) = {(maximum value of film thickness−minimum value of film thickness) / average value of film thickness} × 100 (1)
Here, each item of the above formula (1) is obtained by the following measuring method using a dot-type film thickness meter. That is, at any 50 locations in the film width direction and at a position near the center of the film width, the thickness is measured at any 50 locations along the longitudinal direction, and the number average value of all 100 locations is taken as the average value of the film thickness. To do. Moreover, the average value of 5 points from the larger measured value among the measured values at all 100 locations is the maximum value of the film thickness, and the average value of 5 points from the smaller measured value among the measured values at all 100 locations is the film. The minimum thickness.
When the variation in the film thickness exceeds the upper limit, the variation occurs in the vibration, the performance as the vibration film is lowered, and the acoustic characteristics are lowered. The smaller the variation in the film thickness, the better if it is within the above-mentioned range.

  Variations in the thickness of the film of the present invention can be achieved by adjusting the draw ratio and the heat setting temperature. Like the heat shrinkage, the film lengthwise and widthwise stretches are 2.8 to 3.8 times, respectively. This is achieved by performing heat setting in a temperature range of 200 to 250 ° C. Also, within this range, the variation becomes smaller as the draw ratio increases. Furthermore, the variation in film thickness can be reduced more in the range where the temperature during the heat setting treatment is lower.

<Total light transmittance>
The biaxially oriented polyester film of the present invention preferably has a total light transmittance of 50% or more, more preferably 60% or more, and particularly preferably 70% or more. When the total light transmittance is less than the lower limit, when used as a substrate film for a flat speaker, the transparency is lowered, so that the alignment accuracy in processing the coil may be lowered. Here, the total light transmittance of the film is determined in accordance with JIS standard K7105. In order to achieve the total light transmittance, the additive content to be blended in the film is preferably in the range of 0.05 to 5% by weight.

<Film surface roughness WRa>
The biaxially oriented polyester film of the present invention preferably has a film surface roughness WRa (central surface average roughness) of 1 nm to 100 nm. The film surface roughness WRa is more preferably 5 nm or more and 80 nm or less. When the film surface roughness WRa is less than the lower limit, the slipping property during film processing may be reduced, and productivity may be reduced. On the other hand, when the film surface roughness WRa exceeds the upper limit, the adhesiveness with the coil arranged on the film for a substrate is lowered, or the processing accuracy of the coil is lowered when the metal foil is processed to create the coil. Sometimes.

<Density>
The biaxially oriented polyester film of the present invention preferably has a density of 1.3 g / cm ³ or more and 1.4 g / cm ³ or less. The lower limit of the density of the film is preferably 1.33 g / cm ³ or more, more preferably 1.35 g / cm ³ or more. The upper limit of the film density is preferably 1.38 g / cm ³ or less, more preferably 1.36 g / cm ³ or less. When the density is less than the lower limit, the sound quality change is large and the acoustic characteristics may be deteriorated. On the other hand, when the density exceeds the upper limit, the film may become brittle due to high crystallinity of the film. In order to bring the density of the film into such a range, the film is stretched in the longitudinal direction and the width direction in a magnification range of 2.8 to 3.8 times, respectively, and further subjected to heat setting treatment in a temperature range of 200 to 250 ° C. Can be achieved.

<Thickness>
The thickness of the biaxially oriented polyester film of the present invention is not particularly limited, but is preferably 5 μm or more and 125 μm or less, more preferably 7 μm or more and 100 μm or less, further preferably 10 μm or more and 50 μm or less, and particularly preferably 10 μm or more and 30 μm or less. It is. When the film thickness is less than the lower limit, the sound quality reproducibility may be insufficient as a substrate film for a flat speaker. On the other hand, when film thickness exceeds an upper limit, handling property may fall.

<Loss modulus peak>
The biaxially oriented polyester film of the present invention preferably has a loss modulus peak (sometimes referred to as E ″) of 80 to 180 ° C., more preferably 90 to 170 ° C., still more preferably 100 to 160 ° C., It is particularly preferably 130 to 156 ° C. When the loss elastic modulus peak is less than the lower limit, the molecular orientation of the film is not sufficient, so that the performance as a vibrating membrane is lowered, and the acoustic characteristics may be adversely affected. When the loss elastic modulus peak exceeds the upper limit, the heat shrinkage rate at 200 ° C. exceeds 0.5%, and film deformation may occur when the coil generates heat. For the peak, a device for measuring dynamic viscoelasticity, for example, a Vibron device of DDV-01FP manufactured by Orientec Co., Ltd., load 10 g, frequency 10 z is obtained by a measuring method in which the temperature is increased from room temperature to 200 ° C. at a temperature increase rate of 5 ° C./min. This is achieved by performing in a magnification range of 2.8 to 3.8 times.

<Coating layer>
In the present invention, a coating layer can be provided on at least one side of the polyester film. An example of the coating layer is a coating layer formed by coating. As the binder resin for forming the coating layer, thermoplastic resins and thermosetting resins can be used. Polyester, polyimide, polyamide, polyesteramide, polyvinyl chloride, poly (meth) acrylic ester, polyurethane, Examples thereof include polyvinyl chloride, polyolefin, and copolymers and blends thereof.

<Film forming method>
The biaxially oriented polyester film of the present invention can be produced using a conventionally known film production method such as a tenter method or an inflation method.
The polyester resin dried beforehand is supplied to an extruder heated to 280 ° C., and formed into a sheet form from a T-die. The film extruded from the T-die is cooled and solidified with a cooling drum having a surface temperature of 10 to 60 ° C., the unstretched film is heated by roll heating, infrared heating, or the like, and stretched in the longitudinal direction to obtain a longitudinally stretched film. This stretching is preferably performed by utilizing the difference in peripheral speed between two or more rolls. The stretching temperature is preferably higher than the glass transition point (Tg) of the polyester, more preferably 20 to 40 ° C. higher than Tg.

  The longitudinally stretched film is successively subjected to transverse stretching, heat setting, and thermal relaxation treatment to form a biaxially oriented film. These treatments are performed while the film is running. The transverse stretching treatment starts from a temperature 20 ° C. higher than the glass transition point (Tg) of the polyester and is performed while raising the temperature to a temperature lower by 120 to 30 ° C. than the melting point (Tm) of the polyester. The starting temperature of the transverse stretching is preferably (Tg + 40) ° C. or lower. Moreover, it is preferable that the maximum temperature of transverse stretching is a temperature lower than Tm by (100 to 40) ° C.

  The temperature increase in the transverse stretching process may be continuous or stepwise (sequential). Usually, the temperature is raised sequentially. For example, the transverse stretching zone of the stenter is divided into a plurality along the film running direction, and the temperature is raised by flowing a heating medium of a predetermined temperature for each zone. If the transverse stretching start temperature is too low, film breakage may occur. On the other hand, if the maximum transverse stretching temperature is lower than (Tm−120) ° C., the thermal shrinkage rate of the film may increase. On the other hand, when the maximum transverse stretching temperature is higher than (Tm-30) ° C., the film becomes too soft and the film may be broken due to disturbance or the like.

  The draw ratio is preferably 2.8 times or more and 3.8 times or less in both the longitudinal direction and the transverse direction. The lower limit of the draw ratio is more preferably 3.0 times or more. Further, the upper limit of the draw ratio is more preferably 3.6 times or less, still more preferably 3.4 times or less, and particularly preferably 3.3 times or less. If the draw ratio is less than the lower limit, sufficient Young's modulus may not be obtained. Moreover, when a draw ratio exceeds an upper limit, a thermal contraction rate may exceed an upper limit.

The biaxially stretched film is then heat set. By performing heat setting, the thermal dimensional stability of the film is improved. Further, by performing the heat setting treatment, the crystallization of the polymer proceeds and the density of the film increases. The heat setting is preferably performed at a temperature of (Tm-100) ° C. or higher. The heat setting temperature is preferably 200 to 250 ° C, more preferably 220 to 245 ° C. In order to further improve the thermal dimensional stability, heat relaxation treatment is further carried out for 1 to 60 seconds at a relaxation rate of 0.5 to 5% in the longitudinal direction and / or width direction in the temperature range of 150 to 230 ° C. after heat setting. An annealing process may be performed in which annealing is further performed at 50 to 80 ° C.
In the biaxially oriented polyester film thus obtained, functional layers such as a coating layer, a metal thin film, and a hard coat layer can be further laminated on one side or both sides.

<Plane speaker board>
The biaxially oriented polyester film of the present invention can be used for flat speaker substrate applications, and is preferably used as a vibrating membrane or a vibrating membrane circuit substrate in which spiral coils are arranged on both sides of the substrate film. Can be preferably used. Since the biaxially oriented polyester film of the present invention is excellent in heat-resistant dimensional stability at 200 ° C., has a certain rigidity, and has little variation in film thickness, a flat speaker having a structure in which a coil is laminated on a substrate film. When used as a film for a substrate, the distortion of the substrate film due to the heat generated by the coil is small, noise is reduced, and these film characteristics are excellent in sound quality reproducibility.

  The spiral coil formed on the polyester film is a method of forming a wiring pattern by pattern etching a copper-clad laminate film called a subtractive method, or an electroless plating or electroless plating and electrolysis on a substrate film called an additive method. It can be formed by any method of forming a wiring pattern by using plating together. Another example is a method of forming a circuit using a conductive paste.

  In general, the subtractive method has low dimensional stability of the wiring pattern due to the effect of side etching, and it is difficult to reduce the variation in coil impedance. However, the additive method has high dimensional stability of the wiring pattern. Thus, variation in coil impedance can be further reduced.

  As a step before being processed into a coil, a metal foil can be laminated on the substrate film. As for metal foil, copper foil and aluminum foil are illustrated. As these metal foils, those obtained by a general method such as those produced by rolling and those produced by electrolysis can be used. Examples of a method for laminating these metal foils include a method using an adhesive and a method of directly sealing a film surface layer by melting it. Although a commercially available adhesive can be used, a curable resin is preferable from the viewpoint of heat resistance. Examples of the curable resin include epoxy resins, phenol resins, acrylic resins, polyimide resins, polyamide resins, polyisocyanate resins, polyester resins, polyphenyl ether resins, and alicyclic olefin polymers. Further, as a method not using an adhesive, a method of directly forming a metal foil on a substrate film by plating, sputtering, cladding, or the like may be used.

Any of the above methods may be used as a method for forming the coil on the substrate film. However, in the case of the flat speaker of the present invention, the adhesive property may adversely affect the acoustic characteristics. The method of forming on a substrate film is more preferable.
Further, a spiral coil may be formed on the substrate film, and a coverlay may be further laminated. Examples of the type of coverlay include a film and a solder resist. When using a film type, it is preferable to use the same material as the substrate film because curling may occur after bonding. Other components can be blended in the coverlay film as desired. Compounding agents include UV absorbers, soft polymers, fillers, heat stabilizers, weathering stabilizers, anti-aging agents, leveling agents, antistatic agents, slip agents, antiblocking agents, antifogging agents, dyes, pigments, natural Oils, synthetic oils, waxes, emulsions, fillers, hardeners, flame retardants and the like.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited only to these Examples. Each characteristic value was measured by the following method. Moreover, unless otherwise indicated, the part and% in an Example mean a weight part and weight%, respectively.

(1) Intrinsic viscosity Measured at 35 ° C. using o-chlorophenol as a solvent (unit: dl / g). The intrinsic viscosity of the film was obtained by sampling a biaxially oriented film.

(2) Heat shrinkage ratio The longitudinal direction and the width direction of the biaxially oriented film are marked, and a 30 cm long film whose exact length has been measured in advance is placed in an oven set at a temperature of 200 ° C. with no load, After leaving it to stand for 10 minutes, it is taken out and returned to room temperature, and then its dimensional change is read. From the length (L ₀ ) before the heat treatment and the dimensional change (ΔL) due to the heat treatment, the thermal contraction rates in the longitudinal direction and the width direction were obtained according to the following equation (2). The thermal contraction rate in each direction was evaluated with the number of samples n = 5, and the average value was used.
Thermal contraction rate (%) = ΔL / L ₀ × 100 (2)

(3) Young's modulus Using a Tensilon UCT-100 model manufactured by Orientec Co., Ltd., a biaxially oriented film was cut to a sample width of 10 mm and a length of 15 cm in a room adjusted to a temperature of 20 ° C. and a humidity of 50%, and the chuck spacing was 100 mm. The Young's modulus is calculated from the tangent of the rising portion of the load-elongation curve obtained by pulling at a tensile speed of 10 mm / min and a chart speed of 500 mm / min. In addition, the Young's modulus in the longitudinal direction is that in which the longitudinal direction of the film is the measurement direction, and the Young's modulus in the width direction is that in which the width direction of the film is the measurement direction. Each Young's modulus was measured 10 times and the average value was used.

(4) Density Measured according to JIS standard C2151.

(5) Total light transmittance Total light transmittance Tt (%) was measured according to JIS standard K7105.

(6) Film surface roughness WRa
Built in the roughness meter using a non-contact type three-dimensional roughness meter (NT-2000) manufactured by WYKO under the conditions of a measurement magnification of 25 times and a measurement area of 246.6 μm × 187.5 μm (0.0462 mm ² ). The center surface average roughness (WRa) is obtained by the following equation (3) by the surface analysis software thus performed. The measurement was repeated 10 times, and the average value thereof was used.

ここで、Ｚ_ｊｋは測定方向（２４６．６μｍ）、それと直行する方向（１８７．５μｍ）をそれぞれＭ分割、Ｎ分割したときの各方向のｊ番目、ｋ番目の位置における３次元粗さチャート上の高さである。

Here, Z _jk is a three-dimensional roughness chart at the j-th and k-th positions in each direction when the measurement direction (246.6 μm) and the direction orthogonal thereto (187.5 μm) are divided into M and N, respectively. Of height.

(7) Variation in film thickness and film thickness Using a dot-type film thickness gauge, the thickness is measured at any 50 locations in the film width direction and at any location near the center of the film width along the longitudinal direction. Measurement was made and the number average value at all 100 locations was taken as the film thickness.
Moreover, the variation (%) in film thickness was determined according to the following formula (1).
Variation in film thickness (%) = {(maximum value of film thickness−minimum value of film thickness) / average value of film thickness} × 100 (1)
Here, each item of the above formula (1) is obtained by the following measuring method using a dot-type film thickness meter. That is, according to the method for measuring film thickness, the total thickness of 100 locations is measured, and the number average value of all 100 locations is taken as the average value of the film thickness. Moreover, the average value of 5 points from the larger measured value among the measured values at all 100 locations is the maximum value of the film thickness, and the average value of 5 points from the smaller measured value among the measured values at all 100 locations is the film. The minimum thickness.

(8) Dynamic Loss Modulus Peak Temperature A biaxially oriented film was cut into a width of 4 mm and a length of 50 mm, and 5 V from room temperature to 200 ° C. at a load of 10 g and a frequency of 10 Hz using a DDV-01FP Vibron apparatus manufactured by Orientec. The temperature is measured at a temperature increase rate of ° C / min. The peak temperature of the dynamic loss modulus is obtained from the obtained chart.

(9) Acoustic characteristics
Spiral coils are formed on both sides using a biaxially oriented film as a vibrating membrane circuit board, arranged parallel to the surface on which the planar magnets are arranged, and incorporated into a flat speaker. The flat speaker complies with JIS standard C5532. Measure the frequency characteristics and compare the frequency characteristics of the film not subjected to the following acceleration test with the film subjected to the acceleration test. Therefore, it was evaluated. The film subjected to the acceleration test was evaluated for the presence or absence of noise called chatter according to the following criteria.
As an accelerated test for measuring the effect of film deformation caused by coil heat generation on the acoustic characteristics, the film after coil formation was placed in an oven set at a temperature of 200 ° C. with no load, left for 10 minutes, and then taken out. It was assembled in a flat speaker after returning to.
◎: There is no change in frequency characteristics before and after the acceleration test, and there is no noise such as chatter in the film evaluation after the acceleration test. ○: There is a slight change in frequency characteristics before and after the acceleration test, but the film evaluation after the acceleration test. There is no noise such as chatter. ×: There is a large change in frequency characteristics before and after the acceleration test, and there is noise such as chatter during film evaluation after the acceleration test.

[Example 1]
0.1% of spherical silica particles having an average particle diameter of 0.3 μm are added to polyethylene-2,6-naphthalene dicarboxylate resin, and the resulting mixture is supplied to an extruder heated to 290 ° C. to form a sheet from a 290 ° C. die. Molded. Furthermore, the unstretched film obtained by cooling and solidifying this sheet with a cooling drum having a surface temperature of 60 ° C. is led to a roll group heated to 140 ° C., and stretched 3.1 times in the longitudinal direction (longitudinal direction). Cooled down. Subsequently, both ends of the longitudinally stretched film were guided to a tenter while being held with clips, and stretched 3.3 times in a direction (width direction) perpendicular to the longitudinal direction in an atmosphere heated to 150 ° C. Thereafter, heat setting was performed in a tenter under a temperature condition of 235 ° C., heat relaxation was performed in a 2% width direction at 200 ° C., and then uniformly cooled and cooled to room temperature to obtain a 25 μm thick biaxially oriented film. The properties of the obtained film are shown in Table 1. The film of this example was excellent in heat-resistant dimensional stability at 200 ° C., and no noise was generated in the acoustic characteristic evaluation, and the sound quality reproducibility was excellent.

[Example 2]
The same operation as in Example 1 was repeated except that the draw ratio in the longitudinal direction was 3.0 times, the draw ratio in the width direction was 3.2 times, and the thermal relaxation temperature condition was 230 ° C. The properties of the obtained film are shown in Table 1. The film of this example was excellent in heat-resistant dimensional stability at 200 ° C., and no noise was generated in the acoustic characteristic evaluation, and the sound quality reproducibility was excellent.

[Example 3]
The same operation as in Example 1 was repeated except that the heat setting treatment temperature was 250 ° C., the temperature condition of heat relaxation was 230 ° C., and heat relaxation was performed by 2% in both the longitudinal direction and the width direction. The properties of the obtained film are shown in Table 1. The film of this example was excellent in heat-resistant dimensional stability at 200 ° C., and no noise was generated in the evaluation of acoustic characteristics.

[Example 4]
The same operation as in Example 1 was repeated except that the heat setting treatment temperature was changed to 210 ° C. The properties of the obtained film are shown in Table 1. The film of this example was excellent in heat-resistant dimensional stability at 200 ° C., and no noise was generated in the evaluation of acoustic characteristics.

[Comparative Example 1]
0.1% of spherical silica particles having an average particle diameter of 0.3 μm were added to polyethylene terephthalate resin, and the resulting mixture was supplied to an extruder heated to 280 ° C. and molded into a sheet form from a die at 280 ° C. Furthermore, the unstretched film obtained by cooling and solidifying this sheet with a cooling drum having a surface temperature of 20 ° C. is led to a roll group heated to 110 ° C., and stretched 3.1 times in the longitudinal direction (longitudinal direction). Cooled down. Subsequently, the both ends of the longitudinally stretched film were guided to a tenter while being held by clips, and stretched 3.3 times in a direction (width direction) perpendicular to the longitudinal direction in an atmosphere heated to 120 ° C. Thereafter, heat setting was performed in a tenter under a temperature condition of 230 ° C., heat relaxation was performed in a width direction of 2% at 200 ° C., and then uniformly cooled and cooled to room temperature to obtain a 25 μm thick biaxially oriented film. The properties of the obtained film are shown in Table 1. The film of this comparative example was poor in heat-resistant dimensional stability at 200 ° C., noise was generated even in the evaluation of acoustic characteristics, and sound quality reproducibility was poor.

[Comparative Example 2]
Example 1 except that the draw ratio in the longitudinal direction is 2.5 times, the draw ratio in the width direction is 2.6 times, the heat setting temperature is 180 ° C., and the thermal relaxation conditions are changed to 240 ° C. and 3%. The same operation was repeated. The properties of the obtained film are shown in Table 1. The film of this comparative example was poor in heat-resistant dimensional stability at 200 ° C., generated noise in the evaluation of acoustic characteristics, and also had poor sound quality reproducibility due to its low Young's modulus.

[Comparative Example 3]
The same operation as in Example 1 was repeated except that the draw ratio in the longitudinal direction was 3.5 times, the draw ratio in the width direction was 3.6 times, the heat setting temperature was 245 ° C., and heat relaxation was not performed. The properties of the obtained film are shown in Table 1. The film of this comparative example was poor in heat-resistant dimensional stability at 200 ° C., noise was generated even in the evaluation of acoustic characteristics, and sound quality reproducibility was poor.

  The biaxially oriented polyester film in the present invention has a small dimensional change under heat resistance when used as a substrate film for a flat speaker having a structure in which a coil is laminated on a substrate film. Is small, noise is reduced, heat resistance dimensional stability and rigidity are combined, and the variation in film thickness is small, resulting in excellent sound quality reproducibility.

Claims (10)

The thermal contraction rate when treated at 200 ° C. for 10 minutes is 0% or more and 0.5% or less in the longitudinal direction and the width direction, Young's modulus is 6 GPa or more and 8 GPa or less in the longitudinal direction and the width direction, respectively, and the following formula (1) The biaxially oriented polyester film for a flat speaker substrate is characterized in that the variation in film thickness represented by the formula is 0% or more and 10% or less.
Variation in film thickness (%) = {(maximum value of film thickness−minimum value of film thickness) / average value of film thickness} × 100 (1)   The biaxially oriented polyester film for a flat speaker substrate according to claim 1, wherein the polyester is polyethylene naphthalene dicarboxylate.   The biaxially oriented polyester film for a flat speaker substrate according to claim 1 or 2, wherein the total light transmittance is 50% or more.   The biaxially oriented polyester film for a flat speaker substrate according to any one of claims 1 to 3, wherein the film surface roughness WRa is from 1 nm to 100 nm. The biaxially oriented polyester film for a flat speaker substrate according to any one of claims 1 to 4, wherein the density of the film is 1.3 g / cm ³ or more and 1.4 g / cm ³ or less.   The biaxially oriented polyester film for a flat speaker substrate according to any one of claims 1 to 5, wherein the film thickness is 5 µm or more and 125 µm or less.   The biaxially oriented polyester film for a flat speaker substrate according to any one of claims 1 to 6, which is used for a vibration membrane of a flat speaker.   The biaxially oriented polyester film for a flat speaker substrate according to any one of claims 1 to 6, which is used for a vibrating membrane circuit substrate of a flat speaker.   A laminated member for a flat speaker in which a metal foil is disposed on at least one side of the biaxially oriented polyester film for a flat speaker substrate according to any one of claims 1 to 8.   A laminated member for a flat speaker in which a coil is disposed on at least one side of the biaxially oriented polyester film for a flat speaker substrate according to any one of claims 1 to 8.