JP4817729B2 - Flame retardant stretched polyester film - Google Patents

Description

  The present invention relates to a stretched polyester film having flame retardancy, and more specifically, polyethylene-2,6-, which is excellent in flame retardancy, dimensional stability at high temperatures, mechanical properties and hydrolysis resistance. The present invention relates to a stretched polyester film made of naphthalene dicarboxylate resin.

Polyester films, especially biaxially stretched films of polyethylene terephthalate and polyethylene naphthalate, have excellent mechanical properties, heat resistance, and chemical resistance. Therefore, magnetic tape, ferromagnetic thin film tape, photographic film, packaging film, electronic parts It is widely used as a material such as a film for electric use, an electrical insulating film, a metal laminating film and a protective film.
In recent years, with the enforcement of the Product Liability Act, there has been a strong demand for flame retarding of resins in order to ensure safety against fire.

  Halogen-based flame retardants such as organic halogen compounds and halogen-containing organophosphorus compounds that have been used in the past have a high flame-retardant effect, but halogen is liberated during molding and processing, generating corrosive hydrogen halide gas, It has been pointed out that it may corrode molding and processing equipment and worsen the working environment. There is also a report that the flame retardant generates a gas such as hydrogen halide upon combustion such as a fire. Therefore, in recent years, there has been a strong demand for using a flame retardant containing no halogen in place of the halogen flame retardant.

Examples of flame retardant methods using flame retardants that do not contain halogen include inorganic compounds typified by magnesium hydroxide, inorganic phosphorus compounds typified by red phosphorus, phosphorus compounds such as phosphate esters, phosphonic acid compounds, and phosphinic acid compounds. Are known.
Among these, inorganic flame retardants such as inorganic phosphorus compounds and inorganic compounds are not as toxic as halogen flame retardants, but have poor compatibility with the resin and may significantly impair the transparency of the resin. The flame retardant method using a phosphoric ester compound is a technique related to a so-called blending method in which a flame retardant is added to a polyester after polymerization and kneaded. When added in a large amount, the bleed-out resistance may be lowered. there were.

  On the other hand, a method of copolymerizing a phosphorus compound with polyester has also been studied. For example, JP-A-59-91122 discloses a method of copolymerizing phosphonic acid as a phosphorus compound, and JP-A-1-40521 discloses a phosphine. A method of copolymerizing an oxide derivative and a method of copolymerizing carboxyphosphinic acid with polyethylene terephthalate are disclosed in JP-A No. 53-13479. However, since these phosphorus compounds are used alone and a large amount of addition is required to obtain higher flame retardancy, the amount of phosphorus compounds scattered in the production process may increase when phosphonic acid is included. When copolymerizing a large amount of phosphine oxide derivatives, the mechanical properties of the polyester may decrease. When copolymerizing a large amount of carboxyphosphinic acid, the hydrolysis resistance may decrease. It was difficult to achieve compatibility with other characteristics.

  As described above, since the polyester resin, due to its flammability, when a large amount of the above phosphorus compound is blended as a flame retardant in order to obtain higher flame retardancy, properties other than flame retardancy are reduced. By combining the phosphorus compound, the present situation is that deterioration of properties other than the flame retardancy is suppressed while ensuring the flame retardancy. For example, Japanese Patent Application Laid-Open No. 7-268088 discloses a polyester resin composition in which two types of phosphorus compounds of a phosphine oxide derivative and a carboxyphosphinic acid derivative are used in combination with polyester, and Japanese Patent Application Laid-Open No. 9-272734 discloses a dicarboxylic acid type phosphine. A laminated polyester film in which an oxide-containing layer and a phosphate-containing layer are laminated is disclosed.

  By the way, in particular, when attention is paid to a flexible printed circuit board (hereinafter sometimes abbreviated as FPC) whose demand is increasing with technological progress of electronic devices such as mobile phones or electronic devices mounted on automobiles, Polyimide is mainly used as the film. However, due to the nature of the material of polyimide, it is difficult to reduce the thickness of the film, and it is easy to absorb water, so that dimensional change and shape change may occur. Accordingly, polyethylene naphthalate having excellent heat resistance, mechanical properties, hygroscopicity and the like has been studied as a resin to replace polyimide. However, since polyethylene naphthalate has low flame retardancy compared to polyimide, improvement in flame retardancy is required. However, as described above, polyester is made flame retardant while suppressing deterioration of properties other than flame retardancy. It is difficult to achieve this, and the present situation is that it is required to have further heat-resistant dimensional stability, mechanical properties, and hydrolyzability that can withstand the use environment and manufacturing conditions of FPC.

JP 59-91122 A JP-A 64-40521 Japanese Patent Laid-Open No. 53-13479 Japanese Patent Laid-Open No. 7-268088 JP-A-9-272734

  The object of the present invention is to provide a flame-retardant stretched polyester film that eliminates the problems of the prior art and has high flame resistance and also has heat-resistant dimensional stability at high temperatures, mechanical properties, and hydrolysis resistance. There is to do. Another object of the present invention is to provide a flame-retardant stretched polyester film suitable for a flexible printed circuit board having high flame retardancy, heat-resistant dimensional stability, mechanical properties and hydrolyzability, and having high adhesion to a metal foil. And providing a flexible printed circuit board.

As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that among carboxyphosphinic acid compounds, R ¹ represented by the following general formula (I) is an aryl group having 6 to 18 carbon atoms. By using a carboxyphosphinic acid compound, high flame retardancy can be imparted to polyethylene-2,6-naphthalenedicarboxylate in a small amount without using another phosphorus compound, and polyethylene-2,6-naphthalenedicarboxyl can be imparted. It is found that the heat resistance dimensional stability, mechanical properties and hydrolysis resistance inherent in the rate can be suppressed, and a flexible printed circuit board in which these properties are required, that is, a thin base film itself during processing is sufficient. Have mechanical properties, excellent dimensional stability at high temperatures in the manufacturing process and usage environment, pattern formation and It is particularly suitable as a base film for flexible printed circuit boards that are required to have sufficient hydrolyzability because it has many manufacturing processes that use water, such as a etching process, and is also placed in a hot and humid environment. As a result, the present invention has been completed.

（式中、Ｒ^１は炭素数６〜１８のアリール基、Ｒ^２及びＲ^３は炭素数１〜１８のアルキル基、アリール基、モノヒドロキシアルキル基または水素原子、Ｘは炭素数１〜１８の２価の炭化水素基をそれぞれ表わし、Ｒ^１〜Ｒ^３はそれぞれ同一でも異なっていてもよい。）

(In the formula, R ¹ is an aryl group having 6 to 18 carbon atoms, R ² and R ³ are an alkyl group having 1 to 18 carbon atoms, an aryl group, a monohydroxyalkyl group or a hydrogen atom, and X is an alkyl group having 1 to 18 carbon atoms. Each represents a divalent hydrocarbon group, and R ^{1 to} R ³ may be the same or different.)

That is, according to the present invention, an object of the present invention consists of a polyester containing a carboxyphosphinic acid compound represented by the following formula (I) as a phosphorus compound, the main constituent being ethylene-2,6-naphthalenedicarboxylate. Carboxyphosphinic acid comprising at least one layer, wherein the amount of phosphorus in the layer is 0.01% by weight or more and 3% by weight or less as phosphorus atoms with respect to the weight of the layer, and the total phosphorus amount is represented by the formula (I) It is achieved by a flame-retardant stretched polyester film for a flexible printed circuit board derived from a compound and laminated with a metal foil .

（式中、Ｒ^１は炭素数６〜１８のアリール基、Ｒ^２及びＲ^３は炭素数１〜１８のアルキル基、アリール基、モノヒドロキシアルキル基または水素原子、Ｘは炭素数１〜１８の２価の炭化水素基をそれぞれ表わし、Ｒ^１〜Ｒ^３はそれぞれ同一でも異なっていてもよい。）

(In the formula, R ¹ is an aryl group having 6 to 18 carbon atoms, R ² and R ³ are an alkyl group having 1 to 18 carbon atoms, an aryl group, a monohydroxyalkyl group or a hydrogen atom, and X is an alkyl group having 1 to 18 carbon atoms. Each represents a divalent hydrocarbon group, and R ^{1 to} R ³ may be the same or different.)

ポリエチレン−２，６−ナフタレンジカルボキシレート樹脂を主たる成分としてなる層をさらに有すること、２００℃×１０分における熱収縮率がフィルムの長手方向および幅方向のいずれも−３〜３％であること、カルボキシホスフィン酸化合物の３０〜１００モル％が共重合化していること、の少なくともいずれかを具備するものを好ましい態様として包含する。 In the flame-retardant stretched polyester film of the present invention, as a preferred embodiment, the carboxyphosphinic acid compound is at least one selected from the group consisting of compounds represented by the following formula (II) and the following formula (III). thing,

It further has a layer mainly composed of polyethylene-2,6-naphthalene dicarboxylate resin, and the thermal shrinkage at 200 ° C. for 10 minutes is −3 to 3% in both the longitudinal direction and the width direction of the film. A preferable embodiment includes those having at least one of 30 to 100 mol% of a carboxyphosphinic acid compound.

  Furthermore, according to this invention, the flame-retardant stretched polyester film of this invention is used for the base film of a flexible printed circuit board, One side of the layer containing the carboxyphosphinic acid compound of the flame-retardant stretched polyester film of this invention Also included is a flexible printed circuit board including a structure in which metal foils are laminated on each other.

  According to the present invention, a flame-retardant stretched polyester film in which polyethylene-2,6-naphthalene dicarboxylate contains a small amount of a specific carboxyphosphinic acid compound as a phosphorus compound is highly difficult without using another phosphorus compound in combination. Since it has flammability and is excellent in heat-resistant dimensional stability, mechanical properties and hydrolysis resistance, it is possible to provide a flame-retardant stretched polyester film suitable for a base film of a flexible printed circuit board. Value is extremely high.

  Furthermore, according to the present invention, a flexible printed circuit board including a structure in which a metal foil is laminated on one surface of a layer containing a carboxyphosphinic acid compound of the flame retardant stretched polyester film of the present invention has a flame retardant, heat resistant dimension. Two-layer type flexible printed circuit board that is excellent in stability, mechanical properties and hydrolysis resistance, and has high adhesiveness between the base film and metal foil. It is also suitable.

（式中、Ｒ^１は炭素数６〜１８のアリール基、Ｒ^２及びＲ^３は炭素数１〜１８のアルキル基、アリール基、モノヒドロキシアルキル基または水素原子、Ｘは炭素数１〜１８の２価の炭化水素基をそれぞれ表わし、Ｒ^１〜Ｒ^３はそれぞれ同一でも異なっていてもよい。） The present invention will be described in detail below.
<Carboxyphosphinic acid compound>
The flame-retardant stretched polyester film of the present invention contains a carboxyphosphinic acid compound represented by the following formula (I) as a component imparting flame retardancy.

(In the formula, R ¹ is an aryl group having 6 to 18 carbon atoms, R ² and R ³ are an alkyl group having 1 to 18 carbon atoms, an aryl group, a monohydroxyalkyl group or a hydrogen atom, and X is an alkyl group having 1 to 18 carbon atoms. Each represents a divalent hydrocarbon group, and R ^{1 to} R ³ may be the same or different.)

  By using the carboxyphosphinic acid compound represented by the above formula (I) as the phosphorus compound, high flame retardancy is exhibited without using another phosphorus compound, and polyethylene-2,6-naphthalenedicarboxylate is obtained. Is inherently less resistant to dimensional stability, mechanical properties and hydrolysis resistance. On the other hand, when a carboxyphosphinic acid compound other than formula (I) is used, it is difficult to maintain the excellent hydrolysis resistance inherent in polyethylene-2,6-naphthalenedicarboxylate, and the same difficulty. In order to obtain flammability, since it is necessary to add a larger amount, the heat-resistant dimensional stability, mechanical properties and hydrolysis resistance are impaired.

  Examples of the carboxyphosphinic acid compound represented by the formula (I) include carboxymethylphenylphosphinic acid, (2-carboxyethyl) phenylphosphinic acid, (2-carboxyethyl) toluylphosphinic acid, (2-carboxyethyl) 2,5- Dimethylphenylphosphinic acid, (2-carboxyethyl) cyclohexylphosphinic acid, (carboxypropyl) phenylphosphinic acid, (4-carboxyphenyl) phenylphosphinic acid, (3-carboxyphenyl) phenylphosphinic acid and their lower alcohol esters, lower Examples include alcohol diesters. Among these, particularly preferred compounds include (2-carboxyethyl) phenylphosphinic acid and (carboxypropyl) phenylphosphinic acid, and two or more of the above carboxyphosphinic acid compounds may be used in combination.

  These carboxyphosphinic acid compounds are contained in the range of 0.01 wt% or more and 3 wt% or less as phosphorus atoms with respect to the weight of the layer containing the carboxyphosphinic acid compound (hereinafter sometimes abbreviated as layer A). The Further, the lower limit of the content of the carboxyphosphinic acid compound is preferably 0.05% by weight or more, more preferably 0.1% by weight or more, and particularly preferably 0.5% by weight or more. The upper limit of the content of the carboxyphosphinic acid compound is preferably 2% by weight or less, more preferably 1.5% by weight or less, and particularly preferably 1.0% by weight or less. When the content of the carboxyphosphinic acid compound is less than the lower limit, sufficient flame retardancy performance as a film does not appear, and when it exceeds the upper limit, the excellent heat-resistant dimensional stability inherent to polyethylene-2,6-naphthalenecarboxylate Polyester film that maintains the properties, mechanical properties and hydrolysis resistance may not be obtained.

<Polyester>
The flame-retardant stretched polyester film of the present invention includes a polyester (hereinafter referred to as PEN (hereinafter referred to as PEN)) which contains a carboxyphosphinic acid compound represented by the following formula (I) as a phosphorus compound and whose main constituent is ethylene-2,6-naphthalenedicarboxylate. A) may be abbreviated as A). Here, “main” means 65% by weight or more, preferably 70% by weight or more based on the weight of the layer containing carboxyphosphinic acid compound and ethylene-2,6-naphthalenedicarboxylate as the main structural unit (layer A). More preferably, it means 80% by weight or more, particularly preferably 85% by weight or more.

  The polyester of the present invention may further have a copolymer component other than the carboxyphosphinic acid compound within a range of 10% by weight or less based on the weight of the layer A. As a copolymer component constituting the copolymer, a compound having two ester-forming functional groups in the molecule can be used. For example, oxalic acid, adipic acid, phthalic acid, sebacic acid, dodecanedicarboxylic acid, isophthalic acid, terephthalic acid Dicarboxylic acids such as acids, 1,4-cyclohexanedicarboxylic acid, 4,4′-diphenyldicarboxylic acid, phenylindanedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, tetralindicarboxylic acid, decalindicarboxylic acid, diphenyletherdicarboxylic acid; An oxycarboxylic acid such as oxybenzoic acid, p-oxyethoxybenzoic acid; or an ester of trimethylene glycol, tetramethylene glycol, hexamethylene glycol, cyclohexanemethylene glycol, neopentyl glycol, bisphenolsulfone Alkylene oxide adducts, ethylene oxide adducts of bisphenol A, diethylene glycol, can be preferably used such diol polyethylene oxide glycol. These copolymer components may be used alone or in combination of two or more. Among these copolymer components, preferred acid components are isophthalic acid, terephthalic acid, 4,4′-diphenyldicarboxylic acid, 2,7-naphthalenedicarboxylic acid, p-oxybenzoic acid, and preferred diol components. Is an ethylene oxide adduct of trimethylene glycol, hexamethylene glycol, neopentyl glycol, bisphenol sulfone.

  Further, the polyester of the present invention may be one in which part or all of the terminal hydroxyl group and / or carboxyl group is blocked with a monofunctional compound such as benzoic acid or methoxypolyalkylene glycol, and a very small amount thereof. For example, it may be a copolymer obtained from a trifunctional or higher functional ester-forming compound such as glycerin or pentaerythritol within a range in which a substantially linear polymer is obtained.

  The polyester of the present invention is a conventionally known method, for example, a method of directly obtaining a low polymerization degree polyester by reaction of dicarboxylic acid and glycol, or a lower alkyl ester of dicarboxylic acid and glycol are conventionally known transesterification catalysts, such as sodium It can be obtained by performing a polymerization reaction in the presence of a polymerization catalyst after reacting with one or more of compounds containing potassium, magnesium, calcium, zinc, strontium, titanium, zirconium, manganese, and cobalt. it can. Polymerization catalysts include antimony compounds such as antimony trioxide and antimony pentoxide, germanium compounds represented by germanium dioxide, tetraethyl titanate, tetrapropyl titanate, tetraphenyl titanate or partial hydrolysates thereof, and titanyl ammonium oxalate. , Titanium compounds such as potassium titanyl oxalate and titanium trisacetylacetonate can be used.

  The carboxyphosphinic acid compound is added at any time during the production of the polyester, but a more preferable addition time is after the completion of the first stage reaction for producing a low polymer by esterification or transesterification, This is until the start of the second stage in which the obtained low polymer is subjected to a polycondensation reaction.

  In particular, when polymerization is performed via a transesterification reaction, phosphorous such as trimethyl phosphate, triethyl phosphate, tri-n-butyl phosphate, or normal phosphoric acid is usually used to deactivate the transesterification catalyst before the polycondensation reaction. Although the compound is usually added, the same effect can be obtained without adding the transesterification inhibitor by adding the carboxyphosphinic acid compound of the present invention after the transesterification reaction and before the start of the polycondensation reaction. Is obtained. For the purpose of further deactivating the transesterification catalyst, the phosphorus compound usually used as a deactivator of the transesterification catalyst in the polycondensation step may be used as a phosphorus element in a very small range of 100 ppm or less, The amount thereof is extremely small and is not added for the purpose of imparting flame retardancy.

  The intrinsic viscosity of the polyester in the present invention is preferably 0.40 dl / g or more, more preferably 0.40 to 0.90 dl / g at 35 ° C. in o-chlorophenol. If the intrinsic viscosity is less than 0.40 dl / g, process cutting may occur frequently. On the other hand, if the intrinsic viscosity is higher than 0.9 dl / g, melt extrusion is difficult because of high melt viscosity, and the polymerization time is long and uneconomical.

  In the flame-retardant stretched polyester film of the present invention, 30 to 100 mol% of all the carboxyphosphinic acid compounds contained are preferably copolymerized as a copolymerization component of the polyester, more preferably 60 to 100 mol%, particularly Preferably it is 80-100 mol%. By copolymerizing the carboxyphosphinic acid compound with the polyester within the above range, it becomes possible to achieve both flame retardancy, heat-resistant dimensional stability, mechanical properties, and hydrolysis resistance.

<Other additives>
The layer A constituting the flame-retardant stretched polyester film of the present invention may further contain a resin component other than the above polyester, such as polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polybutylene naphthalate, Examples include polycarbonate, polyarylate, polyetherimide, polyphenylene ether, and phenoxy resin. Such a resin can be used in an amount of preferably 30% by weight or less, more preferably 20% by weight or less based on the weight of the layer A. When such a resin is used in excess of the upper limit, the physical properties inherent to polyethylene-2,6-naphthalenedicarboxylate may be impaired.

In order to improve the handleability of the film, an inert particle or the like may be added to the flame retardant stretched polyester film of the present invention as long as the effects of the invention are not impaired. Examples of the inert particles include inorganic particles (for example, kaolin, alumina, titanium oxide, calcium carbonate, silicon dioxide) containing the elements of Periodic Tables IIA, IIB, IVA, and IVB, and crosslinked silicone resins. Further, 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, and preferably in the range of 0.01 to 10% by weight with respect to the total weight of the film.

If necessary, the flame retardant stretched polyester film of the present invention may further contain additives such as a heat stabilizer, an antioxidant, an ultraviolet absorber, a release agent, a colorant, an antistatic agent and a lubricant. It can mix | blend in the range which does not impair the objective.
The inert particles and these additives may be blended in any layer when the flame-retardant stretched polyester film has a laminated structure of two or more layers.

<Flame retardant stretched polyester film>
The flame-retardant stretched polyester film of the present invention includes at least one layer containing the carboxyphosphinic acid compound of the present invention and a layer (layer A) made of polyester whose main constituent is ethylene-2,6-naphthalenedicarboxylate. It consists of

  The flame-retardant stretched polyester film of the present invention is a layer mainly composed of polyethylene-2,6-naphthalenedicarboxylate resin (hereinafter sometimes abbreviated as PEN (B)) on at least one surface of the layer A. (Hereinafter may be abbreviated as layer B). Here, “main” means that the content of the polyethylene-2,6-naphthalenedicarboxylate resin is 80% by weight or more, more preferably 90% by weight or more, particularly preferably 95% by weight or more based on the weight of the layer B. Means. Layer B is 20% by weight or less, more preferably 10% by weight or less, and particularly preferably 5% by weight or less based on the weight of Layer B, except for the carboxyphosphinic acid compound of the present invention, inert particles, and PEN. A thermoplastic resin and other additives may be contained, but the content of the carboxyphosphinic acid compound is 1.0% by weight or less as a phosphorus atom with respect to the weight of the layer B, and the carboxyphosphinic acid in the layer A The content is preferably less than the compound content. When the flame-retardant stretched polyester film has a laminated structure of two or more layers, the layer A mainly has a function of expressing flame retardancy, and the layer B mainly has a function of maintaining heat-resistant dimensional stability and mechanical properties. Have.

The layer structure of the flame-retarded stretched polyester film of the present invention may be three or more layers in addition to the two-layer structure described above. For example, layer A / layer B / layer A, layer B / layer A / layer B is exemplified. The upper limit of the number of layers is not particularly limited, but is preferably 201 layers.
The flame-retardant stretched polyester film preferably has a film thickness of 3 to 125 μm, more preferably 5 to 100 μm, and still more preferably 7 to 75 μm. Also when the stretched polyester film in this invention has a laminated structure, it is preferable that it is the range of the said film thickness.

<Coating layer>
In the present invention, a coating layer may be formed on at least one surface in order to impart various functions to the surface of the flame-retardant stretched polyester film. As binder resin which comprises a coating-film layer, various resin of a thermoplastic resin or a thermosetting resin can be used. Examples thereof include polyester, polyimide, polyamide, polyesteramide, polyvinyl chloride, poly (meth) acrylic ester, polyurethane, polyvinyl chloride, polystyrene, and polyolefin, and copolymers and blends thereof. Of these, polyester, polyimide, poly (meth) acrylic acid ester, and polyurethane are preferred. Such a binder resin may be further crosslinked by adding a crosslinking agent. The coating layer is preferably formed by coating, and organic solvents and mixtures such as toluene, ethyl acetate and methyl ethyl ketone are used as a solvent for the coating agent, and water may be used as a solvent. The coating layer of the present invention may further contain a surfactant such as polyalkylene oxide and inert particles as constituent components. Moreover, as a component which forms a coating-film layer, in the range which does not impair the objective of this invention, in addition to the said component, resin other than the above, such as a melamine resin, a soft polymer, a filler, a heat stabilizer, a weather stabilizer, anti-aging Agents, leveling agents, antistatic agents, slip agents, antiblocking agents, antifogging agents, dyes, pigments, natural oils, synthetic oils, waxes, emulsions, fillers, curing agents, flame retardants, and the like may be added.

As a method of forming a coating film comprising the above components on at least one surface of a polyester film, for example, after applying an aqueous solution containing a coating film forming component to a stretchable polyester film, drying, stretching, and laminating by heat treatment as necessary I can do it.
The stretchable polyester film is an unstretched polyester film, a uniaxially stretched polyester film or a biaxially stretched polyester film, and among these, a longitudinally stretched polyester film uniaxially stretched in the film extrusion direction (longitudinal direction or longitudinal direction). Is particularly preferred.

When applying a coating agent to a biaxially stretched polyester film, dust, dust, etc. are involved in the normal coating process, that is, after biaxial stretching, in a heat-set polyester film separated from the film production process. easy. From such a viewpoint, application in a clean atmosphere, that is, application in a film stretching process is preferred. And according to this application | coating, the adhesiveness to the polyester film of a coating film further improves.
Any known coating method can be applied as the coating method. For example, a roll coating method, a gravure coating method, a roll brush method, a spray coating method, an air knife coating method, an impregnation method, and a curtain coating method can be used alone or in combination.

<Heat shrinkage>
The heat shrinkage ratio of the flame-retardant stretched polyester film of the present invention is preferably −3 to 3% in both the longitudinal direction and the width direction of the film under the condition of 200 ° C. × 10 minutes. Further, the heat shrinkage rate in the present invention is preferably -2 to 2%, particularly preferably -1.5 to 1.5%. When the thermal contraction rate of the film is less than the lower limit or exceeds the upper limit, for example, in the process of forming the circuit board, the film has a large thermal contraction, and thus a good circuit pattern may not be formed.

  The heat shrinkage rate of the present invention is achieved by the fact that the type of polyester is polyethylene-2,6-naphthalenedicarboxylate resin and the carboxyphosphinic acid compound is the specific phosphorus compound described above. More preferably (Tm-100 ° C.) or more, particularly preferably by subjecting to a heat setting treatment at 220 ° C. to 250 ° C. Moreover, you may perform the annealing process which heat-processes at 150-220 degreeC after this heat setting at 150-220 degreeC for 1 to 60 seconds, and removes cooling at 50-80 degreeC.

<Film formation>
Although the flame-retardant stretched polyester film of the present invention needs to be at least uniaxially stretched, a biaxially stretched polyester film is preferable from the viewpoint of reducing the thickness unevenness of the film. As the stretching method, a conventionally known film forming method such as a tenter method or an inflation method can be used.

  For example, pre-dried polyester is supplied to an extruder heated to 300 ° C. and formed into a sheet form from a T-die. The sheet-like molded product extruded from the T-die is cooled and solidified with a cooling drum having a surface temperature of 60 ° C., and this unstretched film is heated by roll heating, infrared heating, etc., and stretched in the longitudinal direction to obtain a longitudinally stretched film. . Such stretching is preferably performed by utilizing a difference in peripheral speed between two or more rolls. The longitudinal stretching temperature is preferably higher than the glass transition point (Tg) of the polyester, more preferably 20 to 40 ° C. higher than Tg. The longitudinal draw ratio may be appropriately adjusted according to the requirements of the intended use, but is preferably 2.5 times or more and 4.0 times or less, more preferably 2.8 times or more and 3.9 times or less. When the longitudinal draw ratio is 2.5 or less, the thickness unevenness of the film is deteriorated and a good film may not be obtained. Further, when the longitudinal draw ratio is 4.0 times or more, breakage tends to occur during film formation.

  The obtained longitudinally stretched film is subsequently subjected to lateral stretching, heat setting, and thermal relaxation 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 20 ° C. than the melting point (Tm) of the polyester. The transverse stretching start temperature is preferably (Tg + 40) ° C. or lower. The maximum transverse stretching temperature is preferably (100 to 40) ° C. lower than Tm. When the transverse stretching start temperature is too low, the film is easily broken. When the maximum transverse stretching temperature is lower than (Tm−120) ° C., the thermal shrinkage rate of the obtained film increases, and the uniformity of physical properties in the width direction tends to be lowered. On the other hand, if the maximum transverse stretching temperature is higher than (Tm−20) ° C., the film becomes too soft and the film is easily broken during film formation.

The temperature increase in the transverse stretching process may be continuous or stepwise (sequential), but usually the temperature is increased 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.
The transverse draw ratio is preferably 2.5 times or more and 4.0 times or less, although it depends on the required characteristics of this application. More preferably, they are 2.8 times or more and 3.9 times or less. If the transverse draw ratio is less than 2.5 times, the thickness unevenness of the film may be deteriorated and a good film may not be obtained. On the other hand, if it exceeds 4.0 times, breakage may easily occur during film formation. is there.

  The biaxially stretched film is then heat set. By performing the heat setting, the thermal dimensional stability of the film is improved, and for example, it can be achieved by performing a heat setting process at a temperature of (Tm-100 ° C.) or higher. Further, in order to further suppress the thermal shrinkage, the film may be subjected to an annealing process in which, for example, heat treatment is performed at 150 to 220 ° C. for 1 to 60 seconds in an offline process, and the film is cooled at 50 to 80 ° C.

  When the polyester film of this invention has a laminated structure, an unstretched film is created with the following method and the subsequent extending process is performed according to the above-mentioned method. In the case of a two-layer structure, the polyester (PEN (A)) prepared for the layer A is first dried and then melted in an extruder within a temperature range of (Tm) to (Tm + 70) ° C. At the same time, polyethylene-2,6-naphthalenedicarboxylate (PEN (B)) prepared for layer B is dried and then supplied to another extruder and melted within a temperature range of (Tm) to (Tm + 70) ° C. To do. Subsequently, a laminated unstretched film is manufactured by a method of laminating both molten resins inside the die, for example, a simultaneous lamination extrusion method using a multi-manifold die. According to the simultaneous lamination extrusion method, the melt of the resin forming the layer A and the melt of the resin forming the layer B are laminated inside the die and formed into a sheet form from the die while maintaining the laminated form.

<Flexible printed circuit board>
The flame-retardant stretched polyester film of the present invention may be a laminate in which another layer is further laminated on one side or both sides for the purpose of imparting other functions. Examples of other layers herein include transparent polyester films, metal foils, and hard coat layers.

  When laminating the metal foil, it is preferable that the metal foil is laminated on one surface of the layer (layer A) containing the carboxyphosphinic acid compound of the flame retardant stretched polyester film and used as a flexible printed circuit board. Since the layer (layer A) containing the carboxyphosphinic acid compound of the present invention also has a function as an adhesive layer, the adhesion between the metal foil and the layer A is increased by bonding the layer A and the metal foil. A flexible printed circuit board with less peeling can be obtained without using an adhesive layer containing components. Moreover, in order for the layer A to also have a function as an adhesive layer, the content of the carboxyphosphinic acid compound is preferably more than 5% by weight.

  The flexible printed circuit board of the present invention may further have an adhesive layer between the layer A and the metal foil depending on the case. An example of the metal foil used in the present invention is a copper foil. There are no particular limitations on the means for joining and shape of the metal foil. For example, a so-called subtractive method in which the metal foil is bonded to the flame retardant stretched polyester film and then the metal foil is subjected to pattern etching, on the flame retardant stretched polyester film. An additive method of plating copper or the like in a pattern, a stamping foil for bonding a metal foil punched in a pattern to a flame retardant stretched polyester film, or the like can be used.

  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,% in an Example means weight%.

1. Method for measuring phosphorus content The phosphorus atom content of the obtained polyester was measured by fluorescent X-rays.

（式中、ＴｍはＰＥＮ共重合体の融点、ＴｍＡはＰＥＮ単独重合体の融点、△ＨｕはＰＥＮ単独重合体の融解熱、ｐはエステル交換率、Ｒは気体定数をそれぞれ示す。） 2. Copolymerization rate measurement method The copolymerization rate is determined according to the Flory equation represented by the following equation (1).

(In the formula, Tm represents the melting point of the PEN copolymer, TmA represents the melting point of the PEN homopolymer, ΔHu represents the heat of fusion of the PEN homopolymer, p represents the transesterification rate, and R represents the gas constant.)

3. Heat shrinkage rate Marks are attached to film samples at intervals of 30 cm, heat treatment is carried out in an oven at 200 ° C. for 10 minutes without applying a load, the distance between the marks after heat treatment is measured, and the film is continuously formed (MD direction) ) And the direction perpendicular to the film forming direction (TD direction), the thermal contraction rate was calculated by the following formula.
Thermal contraction rate (%) = (distance between the pre-heat treatment gauge points−distance between the heat treatment gauge points) / distance between the pre-heat treatment gauge points × 100

4). Melting point Approximately 10 mg of a film sample was sealed in an aluminum pan for measurement and mounted on a differential calorimeter (trade name “DSC2920” manufactured by TA instruments), and the temperature was raised from 25 ° C. to 300 ° C. at a rate of 20 ° C./min. The melting point (° C.) was measured.

5). Flammability Film samples were evaluated according to the UL-94 VTM method. The sample was cut into 20 cm × 5 cm and left in 23 ± 2 ° C. and 50 ± 5% RH for 48 hours, and then the lower end of the sample was held 10 mm above the burner and held vertically. The bottom end of the sample was indirectly heated for 3 seconds using a Bunsen burner having an inner diameter of 9.5 mm and a flame length of 19 mm as a heating source. Flame retardancy was evaluated according to the evaluation criteria of VTM-0, VTM-1, and VTM-2.

6). Mechanical properties A 200 mm × 10 mm strip film was measured using a Tensilon UTM-4-100 model manufactured by ORIENTEC, with a chuck distance of 10 cm and a tensile speed of 10 mm / sec. Tensile stress was determined.

7). Hydrolysis resistance A 200 mm × 10 mm strip-shaped film is suspended with a stainless steel clip in an environmental tester set to 121 ° C., 2 atm, wet saturation mode, and 100% RH. After 150 hours, the film was taken out from the environmental tester, and the tensile stress was measured at 10 cm / sec between the chucks using a Tensilon UTM-4-100 model manufactured by ORIENTEC. The strength retention was calculated. The measurement was performed 5 times, and the hydrolysis resistance was determined from the average value according to the following criteria.
Strength retention (%) = (tensile stress after 150 hours / initial tensile stress) × 100
○: Strength retention 80% to 100% Δ: Strength retention 60% to less than 80% ×: Strength retention 0% to less than 60%

8). Adhesion A copper foil layer having a thickness of 35 μm is formed on one side of a layer (layer A) formed by blending a carboxyphosphinic acid compound of a film sample by hot pressing, and the obtained laminate is sampled 10 mm × 200 mm, and then JIS The peel strength was measured according to method B (180 ° peel) of C 06471 8.1. Based on the measured value, the following criteria were used.
○: Peel strength 0.5 N / mm or more Δ: Peel strength 0.2 N / mm or more and less than 0.5 N / mm ×: Peel strength 0.2 N / mm or less

[Example 1]
First, 100 parts by weight of naphthalene-2,6-dicarboxylic acid dimethyl ester and 60 parts by weight of ethylene glycol were transesterified according to a conventional method using 0.03 parts by weight of manganese acetate tetrahydrate as a transesterification catalyst. Thereafter, spherical silica having an average particle size of 0.3 μm dispersed in ethylene glycol was added at a ratio shown in Table 1. Then, 2-carboxyethylphenylphosphinic acid represented by the following formula (II) was added at a ratio shown in Table 1, 0.024 part by weight of antimony trioxide was added, and subsequently, in a conventional manner under high temperature and high vacuum. A polycondensation reaction was performed to obtain a polyester having an intrinsic viscosity of 0.61 dl / g.

The obtained polyester was dried with a 180 ° C. dryer for 6 hours, put into an extruder, melt-kneaded at 295 ° C., and formed into a sheet form from a 290 ° C. die. 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 by 3.1 times in the longitudinal direction (longitudinal direction). Cooled down. Subsequently, the film was stretched by 3.3 times in a direction perpendicular to the longitudinal direction (lateral direction) in an atmosphere heated to 150 ° C. while being guided to a tenter while holding both ends of the longitudinally stretched film with clips. Thereafter, heat setting was performed at 200 ° C. in a tenter, and after 3% relaxation at 180 ° C., the film was uniformly removed and cooled to room temperature to obtain a biaxially stretched film having a thickness of 50 μm. The properties of the obtained film are as shown in Table 1. The film of this example was excellent in high temperature dimensional stability, flame retardancy, mechanical properties, and hydrolysis resistance. Moreover, in the obtained biaxially oriented polyester film, the copolymerization rate of carboxyphosphinic acid was 100%. Furthermore, comparatively good adhesiveness was obtained in the evaluation of adhesiveness bonded to the copper foil.

[Example 2]
Polycondensation was performed in the same manner as in Example 1 except that the contents of 2-carboxyethylphenylphosphinic acid and ethylene-2,6-naphthalenedicarboxylate units were changed to the ratios shown in Table 1.
The obtained polyester was dried with a 180 ° C. dryer for 6 hours, put into an extruder, melt-kneaded at 295 ° C., and formed into a sheet form from a 290 ° C. die. 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 by 3.1 times in the longitudinal direction (longitudinal direction). Cooled down. Subsequently, the film was stretched by 3.3 times in a direction perpendicular to the longitudinal direction (lateral direction) in an atmosphere heated to 150 ° C. while being guided to a tenter while holding both ends of the longitudinally stretched film with clips. Thereafter, heat setting was performed at 200 ° C. in a tenter, and after 3% relaxation at 180 ° C., the film was uniformly removed and cooled to room temperature to obtain a biaxially stretched film having a thickness of 50 μm. The properties of the obtained film are as shown in Table 1. The film of this example was excellent in high temperature dimensional stability, flame retardancy, mechanical properties, and hydrolysis resistance. Furthermore, high adhesiveness was obtained in the adhesiveness evaluation bonded to the copper foil.

[Example 3]
Polycondensation was performed in the same manner as in Example 1 except that the contents of 2-carboxyethylphenylphosphinic acid and ethylene-2,6-naphthalenedicarboxylate units were changed to the ratios shown in Table 1.
The obtained polyester was dried with a 180 ° C. dryer for 6 hours, put into an extruder, melt-kneaded at 295 ° C., and formed into a sheet form from a 290 ° C. die. 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 by 3.1 times in the longitudinal direction (longitudinal direction). Cooled down. Subsequently, the film was stretched by 3.3 times in a direction perpendicular to the longitudinal direction (lateral direction) in an atmosphere heated to 150 ° C. while being guided to a tenter while holding both ends of the longitudinally stretched film with clips. Thereafter, heat setting was performed at 180 ° C. in a tenter, and after 3% relaxation at 170 ° C., the film was uniformly removed and cooled to room temperature to obtain a biaxially stretched film having a thickness of 50 μm. The properties of the obtained film are as shown in Table 1. The film of this example was excellent in flame retardancy. Further, the mechanical properties, hydrolysis resistance and high temperature dimensional stability were within the practical range although they were slightly lower than the original properties of PEN. Furthermore, high adhesiveness was obtained in the adhesiveness evaluation bonded to the copper foil.

[Example 4]
Polycondensation was performed in the same manner as in Example 1 except that 3 -carboxypropylphenylphosphinic acid represented by the following formula (III) was used instead of 2-carboxyethylphenylphosphinic acid and the blending amount was changed to the ratio shown in Table 1. Went.
The obtained polyester was dried with a 180 ° C. dryer for 6 hours, put into an extruder, melt-kneaded at 295 ° C., and formed into a sheet form from a 290 ° C. die. 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 by 3.1 times in the longitudinal direction (longitudinal direction). Cooled down. Subsequently, the film was stretched by 3.3 times in a direction perpendicular to the longitudinal direction (lateral direction) in an atmosphere heated to 150 ° C. while being guided to a tenter while holding both ends of the longitudinally stretched film with clips. Thereafter, heat setting was performed at 200 ° C. in a tenter, and after 3% relaxation at 180 ° C., the film was uniformly removed and cooled to room temperature to obtain a biaxially stretched film having a thickness of 50 μm. The properties of the obtained film are as shown in Table 1. The film of this example was excellent in high temperature dimensional stability, flame retardancy, mechanical properties, and hydrolysis resistance. Furthermore, comparatively good adhesiveness was obtained in the evaluation of adhesiveness bonded to the copper foil.

[Example 5]
The polyester obtained by the same method as in Example 1 was dried with a 180 ° C. dryer for 6 hours, then charged into an extruder, and melt-kneaded at 295 ° C. (Layer A). On the other hand, 100 parts by weight of naphthalene-2,6-dicarboxylic acid dimethyl ester and 60 parts by weight of ethylene glycol were transesterified according to a conventional method using 0.03 parts by weight of manganese acetate tetrahydrate as a transesterification catalyst. Thereafter, 0.023 part by weight of trimethyl phosphate was added to substantially stop the transesterification reaction. Subsequently, 0.024 parts by weight of antimony trioxide was added, and then a polycondensation reaction was carried out in a conventional manner under high temperature and high vacuum to obtain a polyethylene having an intrinsic viscosity of 0.61 dl / g and a DEG copolymerization amount of 1.3 mol%. 2,6-Naphthalenedicarboxylate (PEN) was obtained. The obtained polyethylene-2,6-naphthalenedicarboxylate was dried with a 180 ° C. dryer for 6 hours and then charged into the other extruder (layer B), and laminated in two layers in a melted state (thickness ratio layer A). : Layer B = 1: 4), a stretched film was obtained in the same manner as in Example 1 except that the laminated structure was maintained and a sheet was formed from a die. The film thickness of the obtained film is 50 μm (layer A: 10 μm, layer B: 40 μm), and the characteristics are shown in Table 1. The film of this example was excellent in high temperature dimensional stability, flame retardancy, mechanical properties, and hydrolysis resistance. Furthermore, comparatively good adhesiveness was obtained in the evaluation of adhesiveness bonded to the copper foil.

[Example 6]
The polyester forming layer A was obtained by polycondensation as in Example 2, while the PEN forming layer B was obtained by polycondensation as in Example 5.
The obtained polyester for layer A was dried with a 180 ° C. dryer for 6 hours and then charged into an extruder, melted and kneaded at 295 ° C. (layer A), while the PEN for layer B was dried with a 180 ° C. dryer for 6 hours. The other extruder (layer B) is laminated in two layers in a melted state (thickness ratio layer A: layer B = 1: 4), and the sheet is formed into a sheet from the die while maintaining such a laminated structure. A stretched film was obtained in the same manner as in Example 1 except that the film was molded. The film thickness of the obtained film is 50 μm (layer A: 10 μm, layer B: 40 μm), and the characteristics are shown in Table 1. The film of this example was excellent in high temperature dimensional stability, flame retardancy, mechanical properties, and hydrolysis resistance. Furthermore, high adhesiveness was obtained in the adhesiveness evaluation bonded to the copper foil.

[Example 7]
The polyester forming layer A was obtained by polycondensation as in Example 3, while the PEN forming layer B was obtained by polycondensation as in Example 5.
The obtained polyester for layer A was dried with a 180 ° C. dryer for 6 hours and then charged into an extruder, melted and kneaded at 295 ° C. (layer A), while the PEN for layer B was dried with a 180 ° C. dryer for 6 hours. The other extruder (layer B) is laminated in two layers in a melted state (thickness ratio layer A: layer B = 1: 4), and the sheet is formed into a sheet from the die while maintaining such a laminated structure. A stretched film was obtained in the same manner as in Example 1 except that the film was molded. The film thickness of the obtained film is 50 μm (layer A: 10 μm, layer B: 40 μm), and the characteristics are shown in Table 1. The film of this example was excellent in high temperature dimensional stability, flame retardancy, mechanical properties, and hydrolysis resistance. Furthermore, high adhesiveness was obtained in the adhesiveness evaluation bonded to the copper foil.

[Example 8]
Example 1 except that 1-2.5% by weight of 2-carboxyethylphenylphosphinic acid, 87.375% by weight of ethylene-2,6-naphthalenedicarboxylate unit, and 0.125% by weight of spherical silica particles were blended. In the same manner as above, polycondensation was repeated to obtain a polyester. 80% by weight of the polyester obtained and 20% by weight of polyetherimide (“Ultem” manufactured by GE Plastics) were blended, dried with a 180 ° C. dryer for 6 hours, put into an extruder, and melt-kneaded at 295 ° C. ( Layer A). The PEN forming the layer B was subjected to polycondensation in the same manner as in Example 5. The obtained polyethylene-2,6-naphthalenedicarboxylate was dried with a 180 ° C. dryer for 6 hours and then charged into the other extruder (layer). B), laminated in two layers in a melted state (thickness ratio layer A: layer B = 1: 4), and similar to Example 1 except that the laminated structure was maintained and formed into a sheet from a die. Thus, a stretched film was obtained. The film thickness of the obtained film is 50 μm (layer A: 10 μm, layer B: 40 μm), and the characteristics are shown in Table 1. The film of this example was excellent in high temperature dimensional stability, flame retardancy, mechanical properties, and hydrolysis resistance. Furthermore, high adhesiveness was obtained in the adhesiveness evaluation bonded to the copper foil.

[Comparative Example 1]
A stretched film was obtained in the same manner as in Example 1 except that polyethylene-2,6-naphthalenedicarboxylate homopolymer (intrinsic viscosity 0.61 dl / g) was used as the polyester without adding a carboxyphosphinic acid compound. The properties of the obtained film are as shown in Table 1. Although the film of this comparative example was excellent in dimensional stability, mechanical properties, and hydrolysis resistance, the flame retardancy was not sufficient. Furthermore, sufficient adhesiveness was not obtained in the evaluation of adhesiveness bonded to the copper foil.

[Comparative Example 2, Comparative Example 3]
The amount of carboxyphosphinic acid shown in Table 1 was used instead of 2-carboxyethylphenylphosphinic acid in the amount shown in Table 1, and the content of ethylene-2,6-naphthalenedicarboxylate unit was used in the amount shown in Table 1. Repeated the same operation as Example 1, and obtained the stretched film. The properties of the obtained film are as shown in Table 1. The film of this comparative example was insufficient in flame retardancy and hydrolysis resistance. High adhesiveness was obtained in the evaluation of adhesiveness bonded to the copper foil.

[Comparative Example 4]
The average particles dispersed in ethylene glycol after 100 parts by weight of dimethyl terephthalate and 60 parts by weight of ethylene glycol were transesterified according to a conventional method using 0.03 parts by weight of manganese acetate tetrahydrate as a transesterification catalyst. Spherical silica having a diameter of 0.3 μm was added at a ratio shown in Table 1. Next, 5% by weight of 2-carboxyethylphenylphosphinic acid represented by the above formula (II) is added, 0.024 part by weight of antimony trioxide is added, and then polycondensation reaction is performed in a conventional manner under high temperature and high vacuum. As a result, copolymerized PET having an intrinsic viscosity of 0.62 dl / g was obtained.

  The obtained copolymerized PET was dried with a 160 ° C. dryer for 6 hours, then charged into an extruder, melt-kneaded at 290 ° C., and formed into a sheet form from a 280 ° C. die. Further, the unstretched film obtained by cooling and solidifying the sheet with a cooling drum having a surface temperature of 20 ° C. is led to a roll group heated to 110 ° C., and stretched by 3.1 times in the longitudinal direction (longitudinal direction). Cooled down. Subsequently, the film was stretched by 3.3 times in a direction perpendicular to the longitudinal direction (lateral direction) in an atmosphere heated to 120 ° C. while being guided to a tenter while holding both ends of the longitudinally stretched film with clips. Thereafter, the film was heat-set at 180 ° C. in a tenter, relaxed by 3% at 170 ° C., then uniformly cooled and cooled to room temperature to obtain a 50 μm-thick biaxially stretched film. The properties of the obtained film are as shown in Table 1. Although the film of this comparative example had good mechanical properties and hydrolysis resistance, it was inferior in dimensional stability and flame retardancy was not sufficient at the VTM-2 level.

  The flame-retardant stretched polyester film obtained by the present invention is excellent in flame retardancy, dimensional stability at high temperatures, mechanical properties and hydrolysis resistance, so that it can be used for electrical and electronic parts that require flame retardancy or It can be used for automotive parts, and is particularly suitable for a base film of a flexible printed circuit board.

Claims (6)

The phosphorous compound includes a carboxyphosphinic acid compound represented by the following formula (I), and the main constituent component is at least one layer composed of polyester of ethylene-2,6-naphthalenedicarboxylate, and the amount of phosphorus in the layer is A metal foil, characterized in that it is 0.01 wt% or more and 3 wt% or less as phosphorus atoms with respect to the weight of the layer, and the total phosphorus amount is derived from a carboxyphosphinic acid compound represented by the formula (I). Flame-retardant stretched polyester film for flexible printed circuit boards to be laminated .

(In the formula, R ¹ is an aryl group having 6 to 18 carbon atoms, R ² and R ³ are an alkyl group having 1 to 18 carbon atoms, an aryl group, a monohydroxyalkyl group or a hydrogen atom, and X is an alkyl group having 1 to 18 carbon atoms. Each represents a divalent hydrocarbon group, and R ^{1 to} R ³ may be the same or different.) The carboxyphosphinic acid compound is at least one selected from the group consisting of compounds represented by the following formula (II) and the following formula (III): for a flexible printed circuit board on which the metal foil according to claim 1 is laminated Flame retardant stretched polyester film.

The flame-retardant stretched polyester film for flexible printed circuit boards on which the metal foil according to claim 1 or 2 is further laminated, wherein a layer mainly composed of polyethylene-2,6-naphthalenedicarboxylate resin is further laminated. The heat shrinkage rate at 200 ° C for 10 minutes is -3 to 3% in both the longitudinal direction and the width direction of the film. Difficulties for flexible printed circuit boards on which the metal foil according to any one of claims 1 to 3 is laminated Flame-stretched polyester film. The flame retardant stretched polyester film for flexible printed circuit boards on which the metal foil according to any one of claims 1 to 4 is copolymerized, wherein 30 to 100 mol% of the carboxyphosphinic acid compound is copolymerized. The structure which the metal foil was laminated | stacked on one surface of the layer containing the carboxyphosphinic acid compound of the flame-retardant stretched polyester film for flexible printed circuit boards with which the metal foil in any one of Claims 1-5 is laminated | stacked is included. Flexible printed circuit board.