JP2012136611A - Flame-retardant polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a film having good flame retardancy, thin film thickness and printability without deteriorating outer appearance, transparency, mechanical properties and chemical properties which polyester films originally have.SOLUTION: The flame-retardant polyester film has a coating layer applied in the production process of the film to one surface of a polyester film satisfying D×P≥26.0 wherein D (μm) is the thickness of the polyester film and P (wt.%) is phosphorus content measured by XRF, and containing a compound represented by chemical formula. (In the chemical formula, A is a bivalent or trivalent organic residue; Q is a 1-18C hydrocarbon group; and Z is an ester-forming functional group).

Description

  The present invention relates to a flame retardant polyester film. More specifically, the present invention provides flame retardancy, thinning, and without losing characteristics such as appearance, transparency, mechanical strength, thermal properties, electrical properties, and higher workability of the oriented polyester film, and The present invention relates to a film that achieves printability.

  Biaxially stretched polyester film excels in transparency, dimensional stability, mechanical properties, heat resistance, electrical properties, gas barrier properties, chemical resistance, etc., packaging materials, electrical insulation materials, metal deposition materials, plate making materials, It is used in many applications such as magnetic recording materials, display materials, transfer materials, and window paste materials.

  With the recent increase in heat generation due to downsizing and higher efficiency of personal computers and mobile phones, the polyester film for labels used in the batteries of these devices requires a thin film on the label from the viewpoint of miniaturization, and heat generation. From the viewpoint of fire prevention from the origin, there is an increasing demand for flame-retardant labels. In general, as an indicator of flame retardancy, certification under the standard UL94 of UNDERWRITERS LABORATORIES is often used.

  As a flame-retarding technique for polyester films, for example, as disclosed in Patent Documents 1 to 4, various phosphorus-containing compounds, halogen-containing compounds, metal compounds, etc. are added or mixed or copolymerized melt extrusion molding is proposed. Has been.

  However, in order to impart sufficient flame retardancy to the film, it is necessary to add a large amount of flame retardant compound, so that the thermal stability and mechanical strength are lowered. In particular, when an organic halogen compound and antimony dioxide are used in combination, good flame retardancy is obtained, but the above-mentioned drawbacks are remarkable, and a gel compound is generated when these compounds are melted and kneaded.

  Patent Document 5 describes an invention relating to a flame-retardant polyester film using a specific phosphorus compound. When the film is used as a battery label, it is necessary to apply a primer offline after forming a polyester film in order to improve printability. Since the primer itself is not a polymer material such as a polyester film, it is difficult to self-extinguish once burned, and the flame retardancy is lowered. Therefore, it cannot be said that the invention itself has a printing function, and even after the primer layer is provided, it has flame retardancy.

  Patent Document 6 proposes that a primer layer is applied at the time of forming a polyester film. The polyester film described in Patent Document 6 has good printability and is also considered to have flame retardancy without applying a primer offline. Generally, from the viewpoint of specific surface area, ordinary plastic films become more flammable as the film becomes thinner. However, the present invention is intended for thick polyester films, and thin films are not considered. That is, the film disclosed in Patent Document 6 satisfies flame retardancy and printability, but cannot satisfy thin film properties.

Japanese Patent Publication No.51-19858 Japanese Patent Publication No. 55-41610 Japanese Examined Patent Publication No. 62-61235 Japanese Patent Laid-Open No. 62-132955 Japanese Patent Laid-Open No. 63-19254 JP 2001-158070 A

  The present invention has been made in view of the above circumstances, and its solution is to achieve flame retardancy and thin film properties without impairing the appearance, transparency, mechanical properties, and chemical properties inherent to the polyester film. And providing a film that achieves printability.

  As a result of intensive studies in view of the above problems, the present inventors have found that a flame-retardant polyester film having excellent characteristics can be obtained by using a specific film configuration, and the present invention has been completed. .

  That is, the gist of the present invention is that the product (D × P) of the thickness D (μm) of the polyester film and the phosphorus content P (wt%) obtained by XRF is 26.0 or more, and is represented by the following chemical formula. A flame-retardant polyester film comprising a coating layer provided in a production process of the film on one side of a polyester film containing the compound to be produced.

(In the above chemical formula, A is a divalent or trivalent organic residue, Q is a hydrocarbon having 1 to 18 carbon atoms, and Z is an ester-forming functional group)
A functional group)

  ADVANTAGE OF THE INVENTION According to this invention, the film which achieved the flame retardance, thin film property, and printability can be provided, without impairing the external appearance, transparency, mechanical property, and chemical property which a polyester film has originally. . The film of the present invention can be suitably used as a label used for a battery of a personal computer or a mobile phone, and the industrial value of the present invention is high.

  The polyester as referred to in the present invention refers to a polyester that is extruded by a coextrusion method in which all layers are co-melt extruded from a die and then heat-set as necessary. Hereinafter, although a film having a three-layer structure will be described as a polyester film, the polyester film in the present invention is not limited to a three-layer polyester film as long as the purpose is satisfied, and a multilayer of three or more layers may be two layers. May be.

  In the present invention, the polymer constituting each layer of the film is mainly polyester obtained by using aromatic dicarboxylic acid or its ester and glycol as main starting materials, and 60% or more of the repeating structural units are ethylene terephthalate. Refers to a polyester having units or ethylene-2,6-naphthalate units. And if it is the conditions which do not deviate from said range, the other 3rd component may be contained.

  As the aromatic dicarboxylic acid component, in addition to terephthalic acid and 2,6-naphthalenedicarboxylic acid, for example, isophthalic acid, phthalic acid, adipic acid, sebacic acid, oxycarboxylic acid (for example, p-oxyethoxybenzoic acid, etc.), etc. Can be used. As the glycol component, in addition to ethylene glycol, for example, one or more of diethylene glycol, propylene glycol, butanediol, 1,4-cyclohexanedimethanol, neopentyl glycol and the like can be used.

  The viscosity IV of the polyester composition constituting each layer of the film of the present invention is usually 0.52 to 0.75 dl / g, preferably 0.55 to 0.70 dl / g, and more preferably 0.58 to 0.00. The range is 67 dl / g. When the IV value is less than 0.52 dl / g, the heat resistance, mechanical strength, and the like, which are excellent characteristics of the polyester film when used as a film, tend to be inferior. Moreover, when IV value exceeds 0.75 dl / g, there exists a tendency for the negative in the extrusion process at the time of polyester film manufacture to become large too much, and there exists a possibility that productivity may fall.

  The total thickness D [μm] of the laminated film of the present invention is usually 20.0 to 100.0 μm, preferably 40.0 to 80.0 μm. When the total thickness of the laminated film is less than 20.0 μm, the specific surface area is large, and thus flame retardancy may not be exhibited. On the other hand, if the thickness exceeds 100.0 μm, it may be difficult to satisfy the demand for downsizing of the battery.

  The phosphorus element amount P in the polyester film of the present invention is determined by XRF described later. The range of the amount of phosphorus element is usually 0.30 to 2.00% by weight, preferably 0.50 to 1.40% by weight or less, and more preferably 0.60 to 1.00% by weight. If the amount of phosphorus element is less than 0.30% by weight, flame retardancy may not be exhibited. On the other hand, if the amount of phosphorus element exceeds 2.00% by weight, the film tends to break with a tenter, and the flame retardancy of the obtained film is good, but the mechanical strength tends to decrease.

  In the present invention, a flame retardant compound represented by the following chemical formula is used.

  In the above chemical formula, A is a divalent or trivalent organic residue, and preferred examples include a methylene group, a lower alkylene group such as ethylene, 1,2-propylene, and 1,3-propylene, 1,3-phenylene, Examples thereof include an arylene group such as 1,4-phenylene, and a divalent group such as 1,3-xylylene, 1,4-xylylene. The above hydrocarbon group may be substituted with a halogen atom such as a chlorine atom or a bromine atom.

  In the above chemical formula, Q is a hydrocarbon group having 1 to 18 carbon atoms, and in addition to an alkyl group, a cycloalkyl group, an aryl group, an alkoxy group, an allyloxy group, the hydrocarbon group is a chlorine atom, a bromine atom, or the like. And a group substituted by a halogen atom.

  Z is an ester-forming functional group, and specifically, an alkyl ester, a cycloalkyl ester, an aryl ester, a hydroxy group, or a carbon group having 2 to 7 carbon atoms having 1 to 6 carbon atoms in the carboxy group or carboxyl group. And the like.

  When the flame retardant polyester used in the present invention is produced, the method for adding the flame retardant compound to the polyester production system is not particularly limited. That is, for example, when a polyester is produced by a so-called transesterification method of a dicarboxylic acid diester and a diol, a flame retardant compound may be added during the transesterification reaction, or before the polycondensation reaction after the transesterification reaction. Alternatively, it can be added at a relatively early stage of polycondensation. Further, when a polyester is produced by a so-called esterification method of a dicarboxylic acid and a diol, it can be added at any esterification stage.

  The product M (P × D) of the phosphorus element amount P and the thickness D in the polyester film is 26.0 or more, preferably 33.0 or more, more preferably 40.0 or more. When M is less than 26.0, flame retardancy is not exhibited. Although the upper limit of M is not particularly provided, the upper limit of P and D is preferably 200.0.

  The fine inert particles used in the present invention are preferably those having an average particle size of 0.5 to 3.0 μm, and more preferably an average particle size of 0.8 to 2.0 μm. When the average particle size is less than 0.5 μm, workability tends to be inferior. On the other hand, if the average particle size exceeds 3.0 μm, the flatness of the film surface may be impaired or the transparency may be impaired. Further, the addition amount of the particles is preferably in the range of 0.005 to 0.5% by weight, more preferably 0.01 to 0.1% by weight. When the added amount of the particles is less than 0.005% by weight, the winding properties of the film tend to be inferior. Moreover, when the addition amount of particle | grains exceeds 0.5 weight%, the degree of the roughening of the film surface will become large too much, and there exists a possibility that the transparency of a film may be impaired.

  Examples of inert particles used in the present invention include silicon oxide, titanium oxide, zeolite, silicon nitride, boron nitride, celite, alumina, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, barium sulfate, calcium phosphate, phosphoric acid. Lithium, magnesium phosphate, lithium fluoride, aluminum oxide, silicon oxide, titanium oxide, kaolin, talc, carbon black, silicon nitride, boron nitride and crosslinked polymer fine powder as described in JP-B-59-5216 Of course, it is not limited to these. At this time, the inert particles to be blended may be a single component, or two or more components may be used simultaneously.

  Further, in the present invention, the method of adding inert particles or the like to the polyester is not particularly limited, but a method of adding to the polymerization step, a method of kneading the particles in advance using an extruder, etc. are adopted, A preferred method is a method in which particles are directly added and mixed in the extrusion step during the film production step. As the extruder at that time, a twin screw extruder with a vent is preferable. In order to improve the dispersion of the particles, a different-direction twin screw extruder is preferable to the same-direction twin screw extruder.

  The film of the present invention is preferably a film in which all the layers are stretched and heat-set in a biaxial direction by a co-extrusion method in which all layers are co-melt extruded from a die. As a coextrusion method, any of a feed block type or a multi-manifold type may be used. Although the manufacturing method of the laminated | multilayer film of this invention is demonstrated more concretely, as long as the structural requirements of this invention are satisfied, it is not specifically limited to the following illustrations.

  Supply the polyester (inner layer) containing the flame retardant compound and a predetermined amount of inert particles and, if necessary, the polyester (both outer layers) containing the flame retardant compound to separate melt-extrusion apparatuses, and the melting point of the polymer or higher It is heated to the temperature of and melted. Next, the molten polymer is bonded and laminated in a laminar flow in an extrusion die, extruded from a slit die, rapidly cooled and solidified on a rotating cooling drum to a temperature below the glass transition temperature, and substantially amorphous. An unoriented sheet in a state is obtained. In this case, in order to improve the flatness of the sheet, it is preferable to improve the adhesion between the sheet and the rotary cooling drum. In the present invention, an electrostatic application adhesion method and / or a liquid application adhesion method is preferably employed.

  In the present invention, the sheet thus obtained is stretched biaxially to form a film. Specifically describing the stretching conditions, the unstretched sheet is preferably stretched 2 to 6 times in the longitudinal direction at 70 to 145 ° C. to form a longitudinally uniaxially stretched film, and then a coating solution is applied to at least one side of the film. It is preferable to perform moderate drying or undried, stretch 2 to 6 times at 90 to 160 ° C in the transverse direction, and heat-treat at 150 to 250 ° C for 1 to 600 seconds. Further, at this time, a method of relaxing 0.1 to 20% in the longitudinal direction and / or the transverse direction in the maximum temperature zone of the heat treatment and / or the cooling zone at the heat treatment outlet is preferable. Further, it is possible to add re-longitudinal stretching and re-lateral stretching as necessary.

  When the film of the present invention is used for a battery label, it is usually printed to indicate the name of the battery. In this case, since the polyester film is generally inactive, the printability is poor, and it is preferable to provide a coating layer in advance in order to improve the adhesion with the print layer.

  As a method for forming the coating layer, a so-called in-line coating method in which coating is performed before the tenter entrance (before completion of orientation crystallization) and drying in the tenter is preferable. Such application may be performed on one side or both sides.

  In the laminated polyester film of the present invention, the coating layer formed on the biaxially stretched polyester film consists of a combination of a crosslinking agent and various binder resins, and the binder resin is an acrylic resin or polyester based from the viewpoint of adhesiveness. Resins are preferred.

  The amount of the acrylic resin in the coating agent is usually 5 to 70% by weight, preferably 10 to 60% by weight. When the blending amount of the acrylic resin is less than 5% by weight, the adhesiveness with the active energy ray-curable resin layer may be insufficient, and when it exceeds 70% by weight, the stretchability of the coating layer itself may be It may deteriorate and the uniformity of the coating film may deteriorate.

  The compounding quantity of the polyester-type resin in a coating agent is 10 to 85 weight% normally, Preferably it is the range of 15 to 70 weight%. When the blending amount of the polyester resin is less than 10% by weight, sufficient adhesive strength may not be exhibited, and when it exceeds 85% by weight, the sticking resistance tends to be insufficient.

  As the crosslinking agent resin, melamine-based, epoxy-based, and oxazoline-based resins are used, and melamine-based resins are particularly preferable from the viewpoints of coatability and durable adhesiveness. The melamine resin is not particularly limited, but melamine, a methylolated melamine derivative obtained by condensing melamine and formaldehyde, a compound partially or completely etherified by reacting methylolated melamine with a lower alcohol, And a mixture thereof can be used.

  In addition, the melamine resin may be either a monomer or a condensate composed of a dimer or higher multimer, or a mixture thereof.

  As the lower alcohol used for the etherification, methyl alcohol, ethyl alcohol, isopropyl alcohol, n-butanol, isobutanol and the like can be preferably used. The functional group has an imino group, a methylol group, or an alkoxymethyl group such as a methoxymethyl group or a butoxymethyl group in one molecule, and an imino group type methylated melamine resin, a methylol group type melamine resin, or a methylol group type. A methylated melamine resin, a fully alkyl type methylated melamine resin, or the like can be used. Of these, methylolated melamine resins are most preferred. Further, an acidic catalyst such as p-toluenesulfonic acid can be used to accelerate the thermal curing of the melamine-based crosslinking agent.

  The compounding quantity of the melamine resin in a coating agent is 1 to 50 weight% normally, Preferably it is the range of 5 to 30 weight%. When the blending amount of the crosslinking agent resin is less than 1% by weight, the durable adhesiveness may not be sufficiently exhibited, and the effect of improving the solvent resistance may be insufficient. When the blending amount exceeds 50% by weight, sufficient adhesion is achieved. Sexuality may not be exhibited.

  In the present invention, it is preferable to contain inorganic particles or organic particles in the coating layer in order to further improve the slidability, adhesion and the like of the film.

  The amount of the particles in the coating agent is usually 0.5 to 10% by weight, preferably 1 to 5% by weight. When the blending amount is less than 0.5% by weight, the blocking resistance may be insufficient. When the blending amount exceeds 10% by weight, the transparency of the film is hindered and the sharpness of the image tends to be lowered.

  Examples of the inorganic particles include silicon dioxide, alumina, zirconium oxide, kaolin, talc, calcium carbonate, titanium oxide, barium oxide, carbon black, molybdenum sulfide, and antimony oxide. Among these, silicon dioxide is easy to use because it is inexpensive and has various particle sizes.

  Examples of the organic particles include polystyrene or polyacrylate polymethacrylate in which a crosslinked structure is achieved by a compound (for example, divinylbenzene) containing two or more carbon-carbon double bonds in one molecule.

  The above inorganic particles and organic particles may be surface-treated. Examples of the surface treatment agent include a surfactant, a polymer as a dispersant, a silane coupling agent, a titanium coupling agent, and the like.

Further, the coating layer may contain an antistatic agent, an antifoaming agent, a coating property improving agent, a thickener, an antioxidant, an ultraviolet absorber, a foaming agent, a dye, a pigment, and the like.
As long as water is the main medium, the coating agent may contain a small amount of an organic solvent for the purpose of improving dispersion in water or improving the film-forming performance. The organic solvent is preferably used as long as it is soluble in water. Examples of the organic solvent include aliphatic or alicyclic alcohols such as n-butyl alcohol, n-propyl alcohol, isopropyl alcohol, ethyl alcohol, and methyl alcohol, glycols such as propylene glycol, ethylene glycol, and diethylene glycol, n-butyl cellosolve, Examples include glycol derivatives such as ethyl cellosolve, methyl cellosolve, propylene glycol monomethyl ether, ethers such as dioxane and tetrahydrofuran, esters such as ethyl acetate and amyl acetate, ketones such as methyl ethyl ketone and acetone, and amides such as N-methylpyrrolidone. Can be mentioned. These organic solvents may be used in combination of two or more as required.

  As a coating method of the coating agent, for example, reverse roll coater, gravure coater, rod coater, air doctor coater or the like other than those shown by Yuji Harasaki, Tsuji Shoten, published in 1979, “Coating Method” A coating device can be used.

  The coating layer may be formed only on one side of the polyester film or on both sides. When formed only on one side, other characteristics can be imparted by forming a coating layer different from the above-mentioned coating layer on the opposite surface as necessary. In addition, in order to improve the applicability | paintability and adhesiveness to the film of a coating agent, you may give a chemical process and an electrical discharge process to a film before application | coating. Further, in order to further improve the surface characteristics, a discharge treatment may be performed after the coating layer is formed.

  The thickness of the coating layer is usually in the range of 0.02 to 0.5 μm, preferably 0.03 to 0.3 μm, as the final dry thickness. When the thickness of the coating layer is less than 0.02 μm, the effect of the present invention is not sufficiently exhibited. When the thickness of the coating layer exceeds 0.5 μm, the films are easily fixed to each other. In particular, when the coating film is re-stretched to increase the strength of the film, it tends to adhere to the roll in the process. The above problem of sticking appears particularly when the same coating layer is formed on both sides of the film.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to a following example, unless the summary is exceeded. The physical property measurement method used in the present invention is shown below.

(1) Film thickness D [μm]
Measured with a micrometer.

(2) Evaluation of film-forming property When the amorphous sheet was stretched in the horizontal direction after being stretched, the situation in which the film was broken at the time of stretching in a lateral stretching machine (tenter) was evaluated based on the following three rank criteria.
Rank ○: Almost no film breakage and good productivity Rank △: Occasionally film breakage and poor productivity Rank ×: Always breakage, no productivity at all

(3) Phosphorus element amount P [wt%]
XRF: The amount of elements in the film was determined by single-sheet measurement under the conditions shown in Table 1 below using a fluorescent X-ray analyzer (model “XRF-1800” manufactured by Shimadzu Corporation).

(4) Flame retardance A UL94VTM test is conducted in accordance with the vertical combustion test method of UL94, a flammability test standard for plastic materials issued by Underwriters Laboratories. As for the evaluation criteria, this test method varies the results of the combustion test evaluation, and the UL follow-up service gives you up to 3 occasions, so for one polyester film sample, a series of VTM tests The evaluation work was performed three times. Below, a flame-retardant evaluation procedure is demonstrated.
(I) Prepare 30 test pieces according to UL94 VTM test.
(Ii) Select 10 at random from i.
(Iii) The UL94VTM test is performed on five test pieces, and the test ends when the test piece passes VTM-0. If it is unacceptable, the UL94VTM test is performed on the remaining five test pieces to determine whether the VTM-0 is acceptable or not.
(Iv) Repeat steps ii and iii three times.
(V) Evaluate the 3 results obtained in iv. The evaluation criteria are as follows.
Rank ◎ Passed VTM-0 three times Rank ○ Passed VTM-0 twice Rank △ Passed VTM-0 once Rank x Passed VTM-0 0 times.
If the evaluation was ◎ / ○ / △ in the accepting state (23 ° C./50% RH / 48 h), the VTM test was performed in the same procedure after aging (after 70 ° C./168 h). A pass / fail judgment of 0 is performed.

(5) Printability On the polyester film, draw a 50 mm long line with Teranishi Chemical Industries oil-based marker magic ink extra fine black M700-T1. After 30 seconds, apply cellophane tape from above. After 15 seconds, the cellophane tape is peeled off at high speed. The printability was evaluated based on the following criteria by visual observation.
○: Magic mark remains ×: Magic mark is faint and hardly remains

(6) Viscosity (IV)
The polyester film was dissolved in a mixed solvent of phenol / tetrachloroethane = 50/50 (weight ratio), and the flow time of the solution having a concentration of 1.0 (g / dl) using a capillary viscometer, and the solvent alone Viscosity: IV was calculated from these time ratios using the Huggins formula. At that time, the Huggins constant was assumed to be 0.33.

The manufacturing method of the polyester raw material used in the following Examples and Comparative Examples is as follows.
≪Manufacture of polyester A≫
100 parts by weight of dimethyl terephthalate and 60 parts of ethylene glycol are used as starting materials, 0.09 parts by weight of magnesium acetate tetrahydrate as a catalyst is placed in the reactor, the reaction start temperature is set to 150 ° C., and the methanol is gradually distilled off. The reaction temperature was raised to 230 ° C. after 3 hours. After 4 hours, the transesterification reaction was substantially completed. To this reaction mixture, 0.04 part of ethyl acid phosphate and 0.04 part of antimony trioxide were added, and a polycondensation reaction was carried out for 4 hours. That is, the temperature was gradually raised from 230 ° C. to 280 ° C. On the other hand, the pressure was gradually reduced from normal pressure, and finally 0.3 mmHg. After 4 hours from the start of the reaction, the reaction was stopped and the polymer was discharged under nitrogen pressure. The viscosity of the obtained polyester was 0.66.

≪Manufacture of polyester B≫
In the production of polyester A, after completion of transesterification, a flame retardant compound represented by the following chemical formula (a), 10- [2,3-di (2-hydroxyethoxy) carbonylpropyl] -9,10-dihydro-9-oxa A polyester B was obtained in the same manner as the polyester A except that -10-phosphenanthrene-10-oxide was added to the polymer so that the amount of phosphorus element was 1.5% by weight. The viscosity of the obtained polyester was 0.65.

≪Manufacture of polyester C≫
In the production of polyester B, polyester C was obtained in the same manner as polyester-B, except that the amount of the flame retardant compound added was 3.0% by weight of the phosphorus element with respect to the polymer. The viscosity of the obtained polyester was 0.60.
≪Production of polyester D≫
In the production of polyester A, after completion of the transesterification, polyester-D was obtained in the same manner as for polyester A, except that 0.1 part by weight of silica particles having an average particle size of 2.3 μm was used. The viscosity of the obtained polyester was 0.65.
Moreover, the solid content ratio and the content of the water-based paint applied before completion of orientation crystallization used in the following Examples and Comparative Examples are as follows.

<Solid content ratio of water-based paint>
Water-based paint a / water-based paint b / water-based paint c / water-based paint d = 55/30/10/5
<Contents of water-based paint>
Aqueous paint a: terephthalic acid / isophthalic acid / 5-sodiumsulfoisophthalic acid / ethylene glycol / neopentyl glycol / = polyester dispersion in a molar ratio of 24/25/1/25/25 Aqueous paint b: methyl methacrylate / ethyl acrylate / Methylolacrylamide = Emulsion polymer of 50/40/10 molar ratio Water-based paint c: Hexamethoxymethylmelamine Water-based paint d: Aqueous dispersion of silicon oxide (particle diameter = 0.06 μm)

Example 1:
The blend raw material of polyester A / polyester C = 54/46 was fed into the main extruder set at 285 ° C., and the blend raw material of polyester A / polyester C / polyester D = 49/46/5 was set at 285 ° C. It was sent to the extruder. Here, both the main and sub extruders used twin-screw extruders in the same direction. The discharge amount ratio per unit time was set to main: sub = 80: 20. After branching the polymer of the sub-extruder into two layers (outermost layer) of the film, the polymer from the main sub-extruder is merged with the feed block through a gear pump and a filter and extruded into a sheet, and the surface temperature is 30 ° C. The rotary cooling drum was set to 1 and rapidly cooled and solidified using an electrostatic application cooling method to obtain a substantially amorphous sheet having a thickness of 1950 μm. The obtained amorphous sheet was stretched 3.3 times in the longitudinal direction at 83 ° C., and then the aqueous paint described above was applied, and then stretched 3.2 times in the transverse direction at 120 ° C. and heat-treated at 230 ° C. And a biaxially stretched polyester film having a thickness of 2.5 μm / 20 μm / 2.5 μm and a total layer thickness of 25 μm was obtained. The evaluation results are shown in Table 2 below.

Examples 2-10:
A biaxially stretched polyester film was obtained in the same manner as in Example 1 with the raw material blending ratio and thickness shown in Table 2. The evaluation results are also shown in Table 2.

Comparative Examples 1-3:
A biaxially stretched polyester film was obtained in the same manner as in Example 1 with the raw material blending ratio and thickness shown in Table 3 below. The evaluation results are also shown in Table 3.

Comparative Example 4:
A study was conducted to obtain a biaxially stretched polyester film by the same method as in Example 1 so that the film thickness was 75 μm at the raw material compounding ratio shown in Table 3, but breakage occurred frequently in the tenter, and the film formation was abandoned. did. The amount of phosphorus was obtained by measuring film fragments after rupture with XRF. However, since the film was severely deformed, flame retardancy could not be evaluated.

Comparative Example 5:
A biaxially stretched polyester film was obtained in the same manner as in Example 1 except that the aqueous paint was not applied. The evaluation results are shown in Table 3.

Example 11:
A study was conducted to obtain a biaxially stretched polyester film in the same manner as in Example 1 with the raw material blend ratio and thickness shown in Table 2 below. Although it was confirmed from the evaluation results that the film has good flame retardancy even if the amount of phosphorus is small, it is a practical problem because the film is thick.

  The film of the present invention can be suitably used, for example, for a label used for a battery of a personal computer or a mobile phone.

Claims (2)

The product (D × P) of the thickness D (μm) of the polyester film and the phosphorus content P (wt%) obtained by XRF is 26.0 or more, and a polyester film containing a compound represented by the following chemical formula A flame-retardant polyester film having a coating layer provided in one side of the film in the production process of the film.

(In the above chemical formula, A is a divalent or trivalent organic residue, Q is a hydrocarbon having 1 to 18 carbon atoms, and Z is an ester-forming functional group) The flame-retardant polyester film according to claim 1, wherein the polyester film has a thickness D of 20.0 to 100.0 µm and a phosphorus content P obtained by XRF of 0.30 to 2.00% by weight.