WO2015076112A1

WO2015076112A1 - Biaxially oriented polyester film and method for producing same

Info

Publication number: WO2015076112A1
Application number: PCT/JP2014/079434
Authority: WO
Inventors: 町田哲也; 秋山律文; 長谷川正大
Original assignee: 東レ株式会社
Priority date: 2013-11-21
Filing date: 2014-11-06
Publication date: 2015-05-28
Also published as: JP6372355B2; JPWO2015076112A1; TW201524775A; KR20160089360A; CN105637018A; TWI635958B; CN105637018B

Abstract

The purpose of the present invention is to provide: a biaxially oriented polyester film having excellent light-shielding performance, covering performance and flame retardancy and also having excellent continuous productivity; and a method for producing the biaxially oriented polyester film. The present invention is a biaxially oriented polyester film which satisfies the following requirements (1) to (4): (1) carbon black particles are contained in a polyester resin composition that constitutes the film; (2) a flame retardant agent or a dispersant is not contained substantially in the polyester resin composition that constitutes the film; (3) the optical density of the film is 3.5 or more; and (4) the flame retardancy is VTM-0, VTM-1 or VTM-2.

Description

Biaxially oriented polyester film and method for producing the same

The present invention relates to a biaxially oriented polyester film excellent in light-shielding property, concealing property and flame retardancy and excellent in continuous productivity, and a method for producing the same.

Polyester (especially polyethylene terephthalate, polyethylene 2,6-naphthalene dicarboxylate, etc.) resins are excellent in mechanical properties, thermal properties, chemical resistance, electrical properties and moldability, and are used in various applications. Polyester films made from polyester, especially biaxially oriented polyester films, are used for electrical insulation materials, building materials, and sensations used in optical devices, solar battery backsheets, and motors because of their mechanical and electrical properties. It is used as various industrial materials such as thermal transfer applications and process paper.

Of these uses, electrical insulating materials are required to have flame retardancy. In addition, in optical devices, particularly for cellular phones, cameras, and video cameras, in addition to miniaturization and weight reduction of devices, flame retardant properties have been required for the members constituting them.

Conventionally, metals have been used for light shielding members of optical devices such as shutters and diaphragms, but synthetic resin films have been increasingly used along with miniaturization and weight reduction. As a method for imparting light-shielding properties to a synthetic resin film, it is common to add carbon black to a polyester film. For example, a polyester film composed of a polyester resin composition in which carbon black particles are added to a polyester resin having an intrinsic viscosity [η] of 0.5 to 0.85 dl / g has been devised (Patent Document 1).

In addition, among the electrically insulating materials, for solar cell backsheet applications, in recent years, it has been desired that the wiring to the power generation element and the like cannot be seen from the outside from the viewpoint of design as well as flame retardancy. . Therefore, not only flame retardancy but also high concealability is required for the solar cell backsheet. In general, it is effective to blacken a polyester film in order to improve the concealability of the film, and it has been devised to use a polyester film to which a carbon black is added as a black pigment for a solar battery backsheet. (Patent Documents 2 and 3).

JP 2008-56771 A International Publication No. 2012/121076 Pamphlet JP2011-119651A

However, although the polyester films described in Patent Documents 1 to 3 are excellent in light-shielding properties and concealing properties, the flame retardancy of the polyester films is not sufficient.

In order to increase the flame retardancy of the polyester film described in Patent Documents 1 to 3, the present inventors add a conventionally known flame retardant to the polyester resin composition constituting the film. A study was conducted. As a result, the polyester films described in Patent Documents 1 to 3 can obtain a certain effect of improving flame retardancy by adding and containing a flame retardant, but in order to obtain sufficient flame retardancy, a large amount is required. It was found that there was a problem that the addition of a large amount of flame retardant, and when such a large amount of flame retardant was added, the film formability deteriorated and the continuous productivity deteriorated. .

In addition, when a large amount of flame retardant or carbon black particles is added to the polyester resin composition constituting the film, a conventionally known dispersant may be added to prevent aggregation of the flame retardant or carbon black particles. Although necessary, it has been found that the addition of a dispersant has the problem that flame retardancy deteriorates.

Therefore, the present invention aims to solve these problems, and to provide a biaxially oriented polyester film excellent in light shielding properties, concealing properties, flame retardancy, and excellent in continuous productivity and a method for producing the same. is there.

In order to solve the above problems, the present invention has the following configuration. That is,
[I] A biaxially oriented polyester film satisfying the following (1) to (4).
(1) Carbon black particles are contained in the polyester resin composition constituting the film.
(2) The flame retardant and dispersant are not substantially contained in the polyester resin composition constituting the film.
(3) The optical density of the film is 3.5 or more.
(4) The flame retardancy required by the following method is VTM-0, VTM-1, or VTM-2.
<Flame retardancy evaluation method>
(I) Sample preparation A measurement sample (biaxially oriented polyester film) is cut into 20 cm x 5 cm.
Sample A left at 23 ° C. and 50% RH for 48 hours is sample A, temperature 70 ° C., left for 168 hours, then cooled to 23 ° C. and 20% RH or less for 4 hours as sample B, and 5 samples each. Prepare as a set.

(Ii) Measuring method A line is drawn in a direction parallel to the short side at 125 mm from the short side of each sample, and wound around a rod having a diameter of 12.7 mm so that the short side is in the vertical direction. In the 75mm part above the 125mm mark, stick with pressure sensitive tape and pull out the stick. The top of the sample is closed during the test so that there is no chimney effect. Next, each sample is set vertically, and absorbent cotton is placed 300 mm below. Using a Bunsen burner with a diameter of 9.5 mm and a flame length of 20 mm as a heating source so that the burner tube is located 10 mm from the lower end of the sample, a blue flame is indirectly flamed at the center of the lower end of the sample for 3 seconds. Measure the combustion time (t1) after the flame release. Then, as soon as the flame has disappeared, the indirect flame is again emitted for 3 seconds, and the combustion time (t2) and the fire type time (t3) after the second flame-off are measured. In addition, at the time of the first and second flame contact, observation is also made as to whether there was combustion that burned up to the 125 mm mark, and whether there was a burning fallen object that would ignite absorbent cotton. For sample A and sample B, the above measurement is performed for each set (five pieces).

(Iii) Evaluation of flame retardancy Based on the following criteria, flame retardancy is evaluated as follows.
VTM-0: Satisfy any of the criteria (A), (I), (U), (E), (O).
VTM-1: Judgment criteria (A '), (I'), (U '), (E), (O) are all satisfied.
VTM-2: Satisfy all of the criteria (A '), (I'), (U '), and (E).
No VTM: Does not correspond to any of VTM-0, VTM-1, and VTM-2.
Criteria (A): In all samples, the longer combustion time (t1) after the first flame release or the second combustion time (t2) after the second flame release is 10 seconds or less.
Judgment criteria (A '): In all samples, the longer combustion time after the first flame release (t1) or the second combustion time after the flame release (t2) is 30 seconds or less.
Judgment criteria (I): The total of the burning time after flame removal per set (the total of the burning time after flame removal of five samples (t1 + t2)) is 50 seconds or less for both sample A and sample B.
Criteria (I '): The total burning time after flame removal per set (the total burning time after flame removal (t1 + t2) of 5 samples) is less than 250 seconds for both sample A and sample B .
Judgment standard (U): In all samples, the sum of the combustion time (t2) and the ignition time (t3) after the second flame-off is 30 seconds or less.
Judgment criteria (U '): In all samples, the sum of the combustion time (t2) and the ignition time (t3) after the second flame-off is 60 seconds or less.
Judgment criteria (e): In all samples, combustion or fire type does not reach the 125 mm mark.
Judgment criteria (O): In all samples, absorbent cotton is not ignited by the fall of the burned sample.
[II] The biaxially oriented polyester film according to [I], wherein the film has a thickness of 50 μm or more and 300 μm or less.
[III] The biaxially oriented polyester film according to [I] or [II], wherein the content of carbon black particles in the polyester resin composition constituting the film is in the range of 1 to 5% by weight.
[IV] The biaxially oriented polyester film according to any one of [I] to [III], which is used for a light shielding member of an optical device or a solar battery backsheet.
[V] The method for producing a biaxially oriented polyester film according to any one of [I] to [IV], comprising the steps of satisfying the following (5) to (6):
(5) A carbon black-containing polyester resin composition master obtained by kneading a polyester resin composition (a) having an intrinsic viscosity [η] of 0.7 dl / g or more and carbon black particles into a polyester raw material for producing a film Including (b).
(6) When producing the carbon black-containing polyester resin composition master (b), the intrinsic viscosity of the polyester resin of the polyester resin composition (a) before kneading and the resulting carbon black-containing polyester resin composition master ( The intrinsic viscosity of the polyester resin of b) satisfies the following formula (6-1).
(6-1) 0.75 ≦ [η] b / [η] a ≦ 0.90
[Η] a: Intrinsic viscosity (dl / g) of the polyester resin of the polyester resin composition (a) of 0.7 dl / g or more
[Η] b: Intrinsic viscosity (dl / g) of the polyester resin of the carbon black-containing polyester resin composition master (b)
[VI] The method for producing a biaxially oriented polyester film according to [V], wherein the carbon black particle content in the carbon black-containing polyester resin composition master (b) is 5 wt% or more and 30 wt% or less.
[VII] The method for producing a biaxially oriented polyester film according to [V] or [VI], which satisfies the following (7) to (9):
(7) The polyester raw material for producing the film contains the carbon black-containing polyester resin composition master (b) and the polyester resin composition (c) not containing carbon black.
(8) The intrinsic viscosity of the polyester resin of the carbon black-containing polyester resin composition master (b) and the polyester resin composition (c) not containing carbon black satisfies the following formula (8-1).
(8-1) 0.75 ≦ [η] b / [η] c ≦ 1.10
[Η] b: Intrinsic viscosity (dl / g) of the polyester resin of the carbon black-containing polyester resin composition master (b)
[Η] c: Intrinsic viscosity (dl / g) of the polyester resin of the polyester resin composition (c) not containing carbon black
(9) The content Wb (% by weight) of the carbon black-containing polyester resin composition master with respect to the entire polyester raw material for producing the film and the content Wc (% by weight) of the polyester resin composition (c) that does not contain carbon black. And satisfying the following formula (9-1).
(9-1) 0.03 ≦ Wb / Wc ≦ 0.5
Wb: Content (% by weight) of the carbon black-containing polyester resin composition master (b) with respect to the entire polyester raw material for producing the film
Wc: content (% by weight) of the polyester resin composition (c) containing no carbon black with respect to the entire polyester raw material for producing the film

According to the present invention, it is possible to provide a biaxially oriented polyester film that satisfies high light-shielding properties, concealment properties, and flame retardancy and is excellent in continuous productivity. Furthermore, by using such a film, it is possible to provide a light shielding member of an optical device or a solar battery back sheet that has high light shielding properties, concealment properties, and flame retardancy.

The polyester resin composition constituting the biaxially oriented polyester film of the present invention comprises carbon black particles in the polyester resin composition.

The content of the polyester resin in the polyester resin composition is 85% by weight or more, more preferably 90% by weight or more, particularly preferably 95% by weight or more based on the entire resin composition constituting the film. By setting the content of the polyester resin in the above range, the mechanical properties of the film can be improved.

The polyester constituting the polyester film in the present invention is a polymer having an ester bond as a main bond chain of the main chain, obtained by reacting a dicarboxylic acid component and a diol component.

Examples of the dicarboxylic acid component constituting the polyester include malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, dodecanedioic acid, dimer acid, eicosandioic acid, pimelic acid, azelaic acid, methylmalon. Aliphatic dicarboxylic acids such as acid, ethylmalonic acid and the like, adamantane dicarboxylic acid, norbornene dicarboxylic acid, isosorbide, cyclohexanedicarboxylic acid, decalin dicarboxylic acid, terephthalic acid, isophthalic acid, phthalic acid, 1,4 -Naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 4,4'-diphenylether dicarboxylic acid, 5-sodium Sulfoy Examples include dicarboxylic acids such as phthalic acid, phenylendanedicarboxylic acid, anthracene dicarboxylic acid, phenanthrene dicarboxylic acid, 9,9′-bis (4-carboxyphenyl) fluorenic acid and other aromatic dicarboxylic acids, or ester derivatives thereof. It is not limited.

Examples of the diol component constituting the polyester include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-butanediol, and 1,3-butanediol. Aliphatic diols such as cyclohexanedimethanol, spiroglycol and isosorbide, bisphenol A, 1,3-benzenedimethanol, 1,4-benzenedimethanol, 9,9′-bis (4 Examples include, but are not limited to, diols such as -hydroxyphenyl) fluorene and aromatic diols, and a series of a plurality of the above-mentioned diols.

The polyester used in the present invention is preferably polyethylene terephthalate or polyethylene naphthalate from the viewpoints of mechanical properties, electrical properties, durability, and productivity.

The biaxially oriented polyester film of the present invention preferably contains 1% by weight or more and 5% by weight or less of carbon black particles with respect to the entire polyester resin composition constituting the film. If the content of the carbon black particles is less than 1% by weight, the light shielding property may not be sufficient. On the other hand, when the content of the carbon black particles exceeds 5% by weight, aggregates are generated due to deterioration of dispersibility of the carbon black particles, flame retardancy is deteriorated, and productivity may be deteriorated. A more preferred lower limit is 1.5% by weight or more. Moreover, as a more preferable upper limit, it is 4 weight% or less, More preferably, it is 3 weight% or less.

In addition, the biaxially oriented polyester film of the present invention needs to have any one of VTM-0, VTM-1, and VTM-2 for flame retardancy required by the method described later. The biaxially oriented polyester film of the present invention has excellent flame retardancy, and achieves such flame retardancy without substantially containing a flame retardant. In the present invention, “substantially not containing” means that the content is less than 0.05% by weight. In the present invention, the content of the carbon black particles, the flame retardant, and the dispersant in the polyester resin composition constituting the polyester film is the amount added to the polyester resin composition constituting the polyester film. Further, in the present invention, the flame retardant represents a compound or resin having a function of improving the flame retardancy of the resin (increasing the limit oxygen index value (LOI value) of the resin) by being added to the resin.

It is widely known to add a flame retardant in order to improve the flame retardancy of resins typified by polyester resins. There are various conventionally known flame retardants. For example, chlorine flame retardants, bromine flame retardants, inorganic flame retardants, nitrogen flame retardants, phosphorus flame retardants, silicone compounds, ammonium polyphosphate flame retardants, metal oxidation Things.

For example, examples of the chlorinated flame retardant include chlorinated paraffin, chlorinated polyethylene, tetrachlorophthalic anhydride, and chlorendic acid. Brominated flame retardants include bromine-containing polyol, decabromodiphenyl oxide, ethylene glycose bis (pentabromophenyl), ethylene bispentabromophenol, tribromophenol, hexabromobenzene, tetradecabromodiphenoxybenzene, tetrabromobisphenol A (TBBA), TBBA / epoxy oligomer, TBBA / carbonate oligomer, tribromophenyl allyl ether, hexabromocyclododecane, ethylenebistetrabromophthalimide, brominated polystyrene, decabromophenyl oxide. Examples of the inorganic flame retardant include magnesium hydroxide, aluminum hydroxide, and antimony oxide. Examples of the antimony oxide include antimony trioxide and antimony pentoxide. Examples of nitrogen-based flame retardants include melamine compounds, guanidine compounds, and triazine compounds. Phosphorus flame retardants include phosphate ester compounds, ammonium polyphosphate, and the like, such as triphenyl phosphate, tricresyl phosphate, resorcinol bis (diphenyl phosphate), bisphenol A bis (diphenyl phosphate), resorcinol N bis (di) -2,6-Xylyl) phosphate, phosphoric acid amide, red phosphorus, polyphosphate, phosphazene compound, ethylenediamine phosphate compound, triazine compound. Silicone compounds include high molecular weight silicone oils and silicone elastomers.

In order to improve the flame retardancy of the present invention, the flame retardant as described above needs to be added to the film by several weight percent. If a flame retardant is added and contained, there may be an increase in surface defects due to resin moldability, mechanical strength reduction, and additive bleed out. In particular, in a biaxially oriented polyester film including a step of biaxially orienting a film composed of a polyester resin composition containing carbon black particles at a high concentration, when a large amount of the above flame retardant is added, Film breakage during film formation is likely to occur, and mechanical strength is likely to decrease. The biaxially oriented polyester film of the present invention does not substantially contain the above flame retardant in the polyester resin composition constituting the film. Therefore, it is excellent in productivity and moldability, and particularly excellent in continuous productivity. In addition, the compound exemplified as the flame retardant is a factor that reduces the continuous productivity of the film even if it is added and contained in the polyester resin composition constituting the film for the purpose other than improving flame retardancy. Become. Therefore, it is important that the flame retardant exemplified above is not substantially contained in the polyester resin composition constituting the film, even for purposes other than improving flame retardancy.

In the biaxially oriented polyester film of the present invention, it is particularly important from the viewpoint of improving flame retardancy that the polyester resin composition constituting the film does not substantially contain a dispersant.

Dispersants added for the purpose of improving the dispersibility of carbon black particles and flame retardants include stearic acid, zinc stearate, magnesium stearate, aluminum stearate, calcium stearate metal soaps, ethylene bisamide, polyethylene Examples include waxes, hydrocarbon waxes such as polypropylene wax, and derivatives thereof, and waxes composed of acid-modified products and hydroxyl-modified products. For example, a metallocene polyolefin wax polymerized with a metallocene compound catalyst is generally used.

The metallocene compound is a generic name for compounds in which at least one or more ligands having a cyclopentadienyl skeleton are coordinated to a tetravalent transition metal such as titanium, zirconium, nickel, palladium, hafnium, niobium, and platinum. The ligand having a cyclopentadienyl skeleton includes a cyclopentadienyl group; a methylcyclopentadienyl group, an ethylcyclopentadienyl group, an n- or i-propylcyclopentadienyl group, an n-, i-, sec -, Tert-butylcyclopentadienyl group, hexylcyclopentadienyl group, alkyl monosubstituted cyclopentadienyl group such as octylcyclopentadienyl group; dimethylcyclopentadienyl group, methylethylcyclopentadienyl group, Alkyl disubstituted cyclopentadienyl groups such as methylpropylcyclopentadienyl group, methylbutylcyclopentadienyl group, methylhexylcyclopentadienyl group, ethylbutylcyclopentadienyl group, ethylhexylcyclopentadienyl group; trimethyl Cyclopentadie Alkyl group, tetramethylcyclopentadienyl group, alkyl polysubstituted cyclopentadienyl group such as pentamethylcyclopentadienyl group; cycloalkyl substituted cyclopentadienyl group such as methylcyclohexylcyclopentadienyl group; indenyl group, Examples include 4,5,6,7-tetrahydroindenyl group and fluorenyl group.

Examples of ligands other than the ligand having a cyclopentadienyl skeleton include monovalent anion ligands such as base and bromine, divalent anion chelate ligands, hydrocarbon groups, alkoxides, amides, arylamides, aryloxides, phosphides, Examples include aryl phosphide, silyl group, and substituted silyl group. Examples of the hydrocarbon group include those having about 1 to 12 carbon atoms, such as a methyl group, an ethyl group, a propyl group, a butyl group, an isobutyl group, an amyl group, an isoamyl group, a hexyl group, a hebutyl group, and an octyl group. Alkyl groups such as nonyl group, decyl group, ceyl group and 2-ethylhexyl group; cycloalkyl groups such as cyclohexyl group and cyclopentyl group; aryl groups such as phenyl group and tolyl group; aralkyl groups such as benzyl group and neophyll group; Nonylphenyl group etc. are mentioned.

Specific examples of metallocene compounds coordinated with a ligand having a cyclopentadienyl skeleton include cyclopentadienyl titanium tris (dimethylamide), methylcyclopentadienyl titanium tris (dimethylamide), and bis (cyclopentadiene). Enyl) titanium dichloride, dimethylsilyltetramethylcyclopentadienyl-tert-butylamidozirconium dichloride, dimethylsilyltetramethylcyclopentadienyl-pn-butylphenylamidozirconium dichloride, methylphenylsilyltetramethylcyclopentadienyl- tert-Butylamide Hafnium Dichloride, Dimethylsilyltetramethylcyclopentadienyl-tert-Butylamide Hafnium Dichloride, Indenyl Titanium Tri (Dimethylamide), indenyl titanium tris (diethylamide), indenyl titanium bis (di -n- butylamide), indenyl titanium bis (di -n- propyl amide) and the like.

The dispersant as described above can improve the dispersibility of the carbon black particles and the flame retardant contained in the resin composition, but greatly reduces the flame retardance of the resin. The biaxially oriented polyester film of the present invention does not substantially contain the above dispersant in the polyester resin composition constituting the film. Therefore, it is particularly excellent in flame retardancy. In addition, even if it adds and contains the compound illustrated as said dispersing agent in the polyester resin composition which comprises a film for the objectives other than improving a dispersibility, it becomes a factor which reduces the flame retardance of a film. . Therefore, it is important that the above exemplified dispersants are not substantially contained in the polyester resin composition constituting the film, even for purposes other than improving the dispersibility.

The biaxially oriented polyester film of the present invention is required to have an optical density of 3.5 or more from the viewpoint of obtaining excellent light shielding properties and hiding properties. Preferably, it is 4 or more, more preferably 5 or more. The optical density can be adjusted by the thickness of the film and the content of carbon black particles in the polyester resin composition constituting the film. When the optical density is less than 3, the light shielding property and the concealing property become insufficient and the optical function cannot be exhibited. The upper limit of the optical density is not particularly limited, but in order to obtain a film having an optical density of more than 6, it is necessary to increase the film thickness or to increase the content of carbon black particles, and the film forming property is deteriorated. There is. Therefore, the optical density is preferably 6 or less.

The thickness of the biaxially oriented polyester film of the present invention is preferably in the range of 50 μm or more and 300 μm or less. A more preferable lower limit is 50 μm or more. Moreover, as a more preferable upper limit, it is 150 micrometers or less. When the thickness of the polyester film is in the above-described range, it is preferable from the viewpoint that all of the light shielding property, concealing property, flame retardancy, and continuous productivity are improved.

The biaxially oriented polyester film of the present invention is measured by the following method (according to the flame retardancy test (UL94VTM combustion test) of the American Insurer Safety Laboratory (underwriters Laboratories Inc.)). It is necessary that the flame retardancy to be achieved is any one of VTM-0, VTM-1, and VTM-2. By having the above flame retardancy, it can be suitably used for a light shielding member of an optical device or a concealing member of a solar battery backsheet.

<Flame retardancy evaluation method>
(I) Sample preparation A measurement sample (biaxially oriented polyester film) is cut into 20 cm x 5 cm.
Sample A left at 23 ° C. and 50% RH for 48 hours is sample A, temperature 70 ° C., left for 168 hours, then cooled to 23 ° C. and 20% RH or less for 4 hours as sample B, and 5 samples each. Prepare as a set.

(Iii) Evaluation of flame retardancy Based on the following criteria, flame retardancy is evaluated as follows.
VTM-0: Satisfy any of the criteria (A), (I), (U), (E), (O).
VTM-1: Judgment criteria (A '), (I'), (U '), (E), (O) are all satisfied.
VTM-2: Satisfy all of the criteria (A '), (I'), (U '), and (E).
No VTM: Does not correspond to any of VTM-0, VTM-1, and VTM-2.
Criteria (A): In all samples, the longer combustion time (t1) after the first flame release or the second combustion time (t2) after the second flame release is 10 seconds or less.
Judgment criteria (A '): In all samples, the longer combustion time after the first flame release (t1) or the second combustion time after the flame release (t2) is 30 seconds or less.
Judgment criteria (I): The total of the burning time after flame removal per set (the total of the burning time after flame removal of five samples (t1 + t2)) is 50 seconds or less for both sample A and sample B.
Criteria (I '): The total burning time after flame removal per set (the total burning time after flame removal (t1 + t2) of 5 samples) is less than 250 seconds for both sample A and sample B .
Judgment standard (U): In all samples, the sum of the combustion time (t2) and the ignition time (t3) after the second flame-off is 30 seconds or less.
Judgment criteria (U '): In all samples, the sum of the combustion time (t2) and the ignition time (t3) after the second flame-off is 60 seconds or less.
Judgment criteria (e): In all samples, combustion or fire type does not reach the 125 mm mark.
Judgment criteria (O): In all samples, absorbent cotton is not ignited by the fall of the burned sample.

The biaxially oriented polyester film of the present invention is characterized by achieving the above flame retardancy without substantially containing a flame retardant in the polyester resin composition constituting the film. The method for achieving the above flame retardancy without substantially containing a flame retardant in the polyester resin composition constituting the film is to substantially contain a dispersant in the polyester resin composition constituting the film. And producing a film by a production method including the following steps (5) and (6).

The biaxially oriented polyester film of the present invention can be obtained by a production method including the steps satisfying (5) and (6), so that the polyester resin composition constituting the film does not substantially contain a dispersant. This is preferable because the dispersibility of carbon black in the polyester resin composition constituting the film is good and the flame retardancy and continuous productivity are excellent.

(5) A carbon black-containing polyester resin composition master obtained by kneading a polyester resin composition (a) having an intrinsic viscosity [η] of 0.7 dl / g or more and carbon black particles into a polyester raw material for producing a film Including (b).

(6) When producing the carbon black-containing polyester resin composition master (b), the intrinsic viscosity of the polyester resin of the polyester resin composition (a) before kneading and the resulting carbon black-containing polyester resin composition master ( The intrinsic viscosity of the polyester resin of b) satisfies the following formula (6-1).

(6-1) 0.75 ≦ [η] b / [η] a ≦ 0.90
[Η] a: Intrinsic viscosity (dl / g) of the polyester resin of the polyester resin composition (a) of 0.7 dl / g or more
[Η] b: Intrinsic viscosity (dl / g) of the polyester resin of the carbon black-containing polyester resin composition master (b)
The carbon black-containing polyester resin composition master (b) of the present invention comprises a polyester resin composition (a) having an intrinsic viscosity [η] of the polyester resin of 0.7 g / dl or more, more preferably 0.72 g / dl or more. The carbon black particles are preferably obtained by kneading. Here, the intrinsic viscosity [η] a of the polyester resin of the polyester resin composition (a) and the intrinsic viscosity [η] b of the polyester resin of the carbon black-containing polyester resin composition master (b) are expressed by the following formula (5-1): Is preferably satisfied.
(6-1) 0.75 ≦ [η] b / [η] a ≦ 0.90
[Η] b / [η] a has a more preferable lower limit of 0.76 or more, and more preferably 0.78 or more. Moreover, a more preferable upper limit is 0.88 or less, More preferably, it is 0.85 or less. When [η] b / [η] a is less than 0.75, the decrease in intrinsic viscosity of the master material is great, the mechanical properties of the film are deteriorated, and film-forming breakage often occurs. If it exceeds 0.90, shearing in melt kneading becomes insufficient, dispersibility of carbon black particles deteriorates, light shielding properties and concealing properties deteriorate, and filtration pressure increases during film formation, resulting in poor continuous productivity. There is a case.

In the present invention, it is found that it is important not to use a dispersant from the viewpoint of flame retardancy, and [η] b / [η] a is in a range satisfying the formula (6-1). In addition, the polyester resin composition (a) and the carbon black particles are melt-kneaded to improve the dispersibility of the carbon black particles without containing a dispersant, and to have flame retardancy, light shielding properties, and hiding properties. It was found that a polyester film excellent in continuous productivity can be obtained.

[Η] b / [η] a satisfies formula (6-1) by appropriately adjusting the temperature of the melt-kneading part, the melt-kneading time (polymer residence time), and the shearing force applied during melt-kneading. This can be achieved. The melt kneading apparatus may be a single screw extruder or a twin screw extruder, but a method using a high shear mixer with high shear stress such as a twin screw extruder is preferably exemplified. . In addition, from the viewpoint of reducing defective dispersion, it is preferable to equip a three- and two-screw type screw. When a twin screw extruder is used, the melt kneading part preferably has a temperature range of 200 ° C to 280 ° C. A more preferred temperature range is 210 ° C. to 280 ° C., and a further preferred temperature range is 220 ° C. to 280 ° C. At this time, the residence time of the polymer is preferably in the range of 1 to 5 minutes. The biaxial screw rotation speed is preferably 100 to 500 rotations / minute, more preferably 200 to 300 rotations / minute. By setting the screw rotation speed within a preferable range, high shear stress can be easily applied, the dispersibility of carbon black particles can be improved, and the decomposition reaction of polyester caused by excessive shear stress is suppressed. can do. The ratio (L / D) of (screw shaft length / screw shaft diameter) of the twin screw extruder is preferably in the range of 20 to 60, more preferably in the range of 30 to 50.

Further, in the screw configuration of the twin-screw extruder, it is preferable to provide a kneading part by a kneading paddle (kneading disk) or the like in order to increase the kneading force, and the kneading part is preferably two or more, more preferably three. It is preferable to use the screw configuration provided above. At this time, the mixing order of the polyester resin composition (a) and the carbon black particles is not particularly limited, and the polyester resin composition (a) in pellet form and the carbon black particles are mixed and melt-kneaded by the above method. Any method may be used, such as a method of mixing the carbon black particles using a side feeder during melt extrusion of the polyester resin composition (a) with a single or biaxial extruder.

The content of carbon black particles in the carbon black-containing polyester resin composition master (b) is preferably 5% by weight or more and 30% by weight or less. A more preferred lower limit is 10% by weight or more. Moreover, a more preferable upper limit is 25 weight% or less. When the content of carbon black exceeds 30% by weight, it is difficult to control shearing heat generation and the dispersibility may be deteriorated. When the content of carbon black is less than 5% by weight, shear heat generation is not sufficient and dispersibility may deteriorate.

In the biaxially oriented polyester film of the present invention, it is preferable that at least one surface has a center plane average roughness (SRa) of 40 nm or less. More preferably, it is 35 nm or less. When the center plane average roughness exceeds 40 nm, film-forming breakage may occur frequently. In addition, it is considered that carbon black contains poorly dispersible, flame retardancy may deteriorate, and optical density variation may increase.

Here, the center surface average roughness (SRa) is a stylus type three-dimensional roughness meter with a stylus radius of curvature of 2 μm, with a cutoff value of 0.25 mm, a measurement length of 0.5 mm, and in a certain direction. The average roughness of the center line when measured 40 times at intervals of 5 μm in a direction orthogonal to the above.

In order to set the center plane average roughness (SRa) of the biaxially oriented polyester film within the above range, for example, a method of containing carbon black in the film with good dispersibility is preferably used. In order to contain carbon black in the film with good dispersibility, a twin screw extruder is used as a melt kneading apparatus, the temperature of the melt kneading part, the time of melt kneading (polymer residence time), the shear force applied during melt kneading, A method for producing a film by a production method including a step of satisfying the above-mentioned (5) and (6) by setting the ratio of (screw shaft length / screw shaft diameter) of the twin-screw extruder to the above-mentioned preferable range. Can be mentioned.

The biaxially oriented polyester film of the present invention preferably has a thermal shrinkage rate of 3.0% or less in both the longitudinal direction and the width direction when heat-treated at 190 ° C. for 30 minutes. More preferably, it is 2.5% or less. When the heat shrinkage rate after heat treatment at 190 ° C. for 30 minutes exceeds 3.0%, in the flame retardancy evaluation, the variation in the burning time becomes large, and the flame retardancy may be deteriorated. In addition, the thermal contraction rate in this invention is calculated | required by the below-mentioned measuring method. In the present invention, if the film longitudinal direction (MD direction) is a biaxially oriented polyester film on a roll, the roll winding direction is the film longitudinal direction, and the roll width direction is the film width direction (TD direction). Equivalent to. On the other hand, in the case of a cut sheet, the long side direction of the film is regarded as the film longitudinal direction for calculation. When the film has a substantially square shape, the calculation is performed by regarding any of the directions parallel to each side as the longitudinal direction and the width direction.

To make the heat shrinkage rate of the biaxially oriented polyester film in the above range, for example, a method of performing a heat treatment after biaxial stretching, a method of performing a relaxation treatment in the longitudinal and / or width direction simultaneously with the heat treatment in the heat treatment step, Although it can obtain by the method of performing an annealing process after heat-processing, it is not limited to these.

The biaxially oriented polyester film of the present invention is preferably used as a raw material by mixing the carbon black-containing polyester resin composition master (b) and the polyester resin composition (c) containing no carbon black particles. In particular, it is preferable that it is obtained by a production method including steps satisfying the following (7) to (9) from the viewpoint of manifesting effects of light shielding properties, hiding properties, flame retardancy, and continuous productivity.

(7) The polyester raw material for producing the film contains the carbon black-containing polyester resin composition master (b) and the polyester resin composition (c) not containing carbon black.

(8) The intrinsic viscosity of the polyester resin of the carbon black-containing polyester resin composition master (b) and the polyester resin composition (c) not containing carbon black satisfies the following formula (8-1).
(8-1) 0.75 ≦ [η] b / [η] c ≦ 1.10
[Η] b: Intrinsic viscosity (dl / g) of the polyester resin of the carbon black-containing polyester resin composition master (b)
[Η] c: Intrinsic viscosity (dl / g) of the polyester resin of the polyester resin composition (c) not containing carbon black
(9) The content Wb (% by weight) of the carbon black-containing polyester resin composition master with respect to the entire polyester raw material for producing the film and the content Wc (% by weight) of the polyester resin composition (c) that does not contain carbon black. And satisfying the following formula (9-1).
(9-1) 0.03 ≦ Wb / Wc ≦ 0.5
Wb: Content (% by weight) of the carbon black-containing polyester resin composition master (b) with respect to the entire polyester raw material for producing the film
Wc: content (% by weight) of the polyester resin composition (c) containing no carbon black with respect to the entire polyester raw material for producing the film
If [η] b / [η] c and Wb / Wc are out of the above preferred ranges, the light shielding property and flame retardancy are deteriorated and the continuous productivity is deteriorated (an increase in the filtration pressure during film formation occurs). There is a case. The cause of this is not clarified in detail at the present time. However, if [η] b / [η] c and Wb / Wc deviate from the above preferable ranges, the carbon black-containing polyester resin composition master (b ), Even if the carbon black particles are uniformly dispersed, the particles are aggregated during melt film formation, and the aggregates are estimated to cause deterioration of flame retardancy and continuous productivity. is doing. [Η] b / [η] c is more preferably a lower limit of 0.85 or more, more preferably 0.90 or more, from the viewpoints of flame retardancy and continuous productivity. Moreover, a more preferable upper limit is 1.05 or less, More preferably, it is 0.95 or less. Moreover, a more preferable lower limit of Wb / Wc is 0.03 or more. A more preferred upper limit is 0.3 or less, and even more preferred is 0.15 or less.

The biaxially oriented polyester film of the present invention is melt-extruded into a sheet form from a film forming die and is formed, for example, under the following conditions. After being melt-extruded into a sheet form from a die of a film forming machine, it is closely cooled and solidified by static electricity on a drum cooled to a surface temperature of 10 ° C. or more and 60 ° C. or less to produce an unstretched sheet. The unstretched sheet thus obtained is biaxially stretched in the longitudinal and lateral directions to be formed into a sheet having a necessary and optimum thickness. For the stretching, a sequential biaxial stretching method or a simultaneous biaxial stretching method can be used. For example, in the case of sequential biaxial stretching, the unstretched sheet is guided to a roll group heated to 70 to 120 ° C., stretched 2 to 5 times in the longitudinal direction (longitudinal direction, that is, the traveling direction of the film), and 20 to 30 ° C. Cool with rolls. Subsequently, the both ends of the stretched film are guided to the tenter while holding both ends of the stretched film in the longitudinal direction, and stretched 2 to 5 times in the direction perpendicular to the longitudinal direction (lateral direction) in an atmosphere heated to 90 to 150 ° C. The biaxially stretched film thus obtained is subjected to a heat treatment step at 150 to 240 ° C. for 1 to 30 seconds in order to complete crystal orientation and impart flatness and thermal dimensional stability. Then, after cooling uniformly, it cools to room temperature and winds up. During the heat treatment step, a relaxation treatment of 3 to 12% may be performed in the longitudinal direction and / or the width direction as necessary.

The biaxially oriented polyester film of the present invention has high light-shielding properties, concealability and flame retardancy, and excellent continuous productivity. Taking advantage of these features, optical devices such as mobile phones, cameras and video cameras, solar It can be used as an electrical insulating material used for battery backsheets or motors, various industrial materials such as building materials, thermal transfer applications, process paper, etc. Among them, optical devices that require flame retardancy, light shielding properties, and concealability It is suitably used for a solar cell backsheet.

[Characteristic evaluation method]
(1) Melting point Using a differential scanning calorimeter DSC (RDC220) manufactured by Seiko Instruments Inc. according to JIS K7121-1987 and a disk station (SSC / 5200) manufactured by the same company as a data analyzer, 5 mg of a sample is room temperature on an aluminum tray. The mixture was heated from 300 to 300 ° C. at a temperature rising rate of 20 ° C./min, melted and held at 300 ° C. for 5 minutes, rapidly solidified and held for 5 minutes, and then heated from room temperature at a temperature rising rate of 20 ° C./min. At that time, the peak temperature of the endothermic peak of melting observed was defined as the melting point.

(2) Intrinsic viscosity A measurement sample is dissolved in 100 ml of orthochlorophenol (solution concentration C = 1.2 g / dl), and the viscosity of the solution at 25 ° C. is measured using an Ostwald viscometer. Similarly, the viscosity of the solvent is measured. [Η] (dl / g) is calculated by the following formula (a) using the obtained solution viscosity and solvent viscosity, and the obtained value is used as the intrinsic viscosity.
(A) ηsp / C = [η] + K [η] ² · C
(Where ηsp = (solution viscosity (dl / g) / solvent viscosity (dl / g)) − 1, K is a Huggins constant (assuming 0.343)).

In addition, when there existed insoluble matters, such as inorganic particles, in the solution in which the measurement sample was dissolved, the measurement was performed using the following method.
i) A measurement sample is dissolved in 100 mL of orthochlorophenol to prepare a solution having a solution concentration higher than 1.2 mg / mL. Here, let the weight of the measurement sample used for orthochlorophenol be a measurement sample weight.
ii) Next, the solution containing the insoluble matter is filtered, and the weight of the insoluble matter and the volume of the filtrate after filtration are measured.
iii) Orthochlorophenol was added to the filtrate after filtration, and (measured sample weight (g) −insoluble matter weight (g)) / (volume of filtrate after filtration (mL) + volume of orthochlorophenol added) (ML)) is adjusted to 1.2 g / 100 mL.
(For example, when a concentrated solution having a measurement sample weight of 2.0 g / solution volume of 100 mL was prepared, the weight of insoluble matter when the solution was filtered was 0.2 g, and the filtrate volume after filtration was 99 mL Adjust to add 51 mL of orthochlorophenol ((2.0 g-0.2 g) / (99 mL + 51 mL) = 1.2 g / mL))
iv) Using the solution obtained in iii), the viscosity at 25 ° C. is measured using an Ostwald viscometer, and the obtained solution viscosity and solvent viscosity are used to calculate [η] according to the above formula (C). And the obtained value is taken as the intrinsic viscosity.

(3) Light-shielding property and concealing property Optical density was evaluated based on the former JIS K7605, and light-shielding property and concealing property were evaluated according to the following criteria.

As the optical densitometer, XRite 361T (manufactured by Nippon Flat Plate Machinery Co., Ltd.) was used, and the sample was irradiated with a vertically transmitted light beam, and the ratio of the state with no sample expressed in log (logarithm) was defined as the optical density. The light flux width was circular with a diameter of 1 mm or wider.
S: Optical density is 5 or more A: Optical density is 4 or more and less than 5 B: Optical density is 3.5 or more and less than 4 C: Optical density is less than 3.5 S to B are good, and S is the best among them ing.

(4) 190 ° C heat shrinkage rate Two lines were drawn on the surface of the measurement sample so that the width was 10 mm and the measurement length was about 100 mm, and the distance between the two lines was measured at 23 ° C. To do. This measurement sample was left in a hot air oven “HIGH-TEMP-OVEN PHH-200” manufactured by Espec Co., Ltd. set at 190 ° C. (air flow gauge “7”) for 30 minutes under a load of 3 g, and then two again. The distance between these lines was measured at 23 ° C., and this was taken as L1, and the heat shrinkage rate was determined by the following equation. The measurement was carried out for 5 samples each in the longitudinal direction and the width direction, and the average value was evaluated.
Thermal shrinkage (%) = (L0−L1) / L0 × 100
(5) Surface roughness (SRa)
The average center line roughness (SRa) on both surfaces of the film was measured under the following conditions using Surfcorder ET30HK manufactured by Kosaka Laboratory, and the average value was obtained.

Stylus radius of curvature: 2 μm
Cut-off: 0.25mm
Measurement length: 0.5mm
Measurement interval: 5 μm
Number of measurements: 40 times.

(6) Flame resistance
Based on the UL-94 VTM method, the following method was used for evaluation.

(I) Sample preparation A measurement sample (biaxially oriented polyester film) is cut into 20 cm x 5 cm.
Sample A left at 23 ° C. and 50% RH for 48 hours is sample A, temperature 70 ° C., left for 168 hours, then cooled to 23 ° C. and 20% RH or less for 4 hours as sample B, and 5 samples each. Prepare as a set.

(Ii) Measuring method A line is drawn at 125 mm from the bottom of the long side of each sample and wound around a rod having a diameter of 12.7 mm. In the 75mm part above the 125mm mark, stick with pressure sensitive tape and pull out the stick. The top of the sample is closed during the test so that there is no chimney effect. Next, each sample is set vertically, and absorbent cotton is placed 300 mm below. Using a Bunsen burner with a diameter of 9.5 mm and a flame length of 20 mm as a heating source so that the burner tube is located 10 mm from the lower end of the sample, a blue flame is indirectly flamed at the center of the lower end of the sample for 3 seconds. Measure the combustion time (t1) after the flame release. Then, as soon as the flame has disappeared, the indirect flame is again emitted for 3 seconds, and the combustion time (t2) and the fire type time (t3) after the second flame-off are measured. In addition, at the time of the first and second flame contact, observation is also made as to whether there was combustion that burned up to the 125 mm mark, and whether there was a burning fallen object that would ignite absorbent cotton. For sample A and sample B, the above measurement is performed for each set (five pieces).

(Iii) Evaluation of flame retardance Based on the following criteria, flame retardancy was evaluated as follows.
VTM-0: Satisfy any of the criteria (A), (I), (U), (E), (O).
VTM-1: Judgment criteria (A '), (I'), (U '), (E), (O) are all satisfied.
VTM-2: Satisfy all of the criteria (A '), (I'), (U '), and (E).
No VTM: Does not correspond to any of VTM-0, VTM-1, and VTM-2.
Judgment criteria (A): The longer combustion time (t1) after the first flame-off of each sample or the combustion time (t2) after the second flame-off is 10 seconds or less in all samples.
Judgment criteria (A '): The longer the combustion time after the first flame release (t1) or the second combustion time after the flame release (t2) of each sample is 30 seconds or less.
Judgment criteria (I): The total of the burning time after flame removal per set (the total of the burning time after flame removal of five samples (t1 + t2)) is 50 seconds or less for both sample A and sample B.
Criteria (I '): The total burning time after flame removal per set (the total burning time after flame removal (t1 + t2) of 5 samples) is less than 250 seconds for both sample A and sample B .
Judgment standard (U): The total of the combustion time (t2) and the fire type time (t3) after the second flame-off is 30 seconds or less in all the samples.
Judgment standard (U '): The total of the combustion time (t2) and the fire type time (t3) after the second flame-off is 60 seconds or less in all the samples.
Criterion (E): Combustion or fire type is not reached in all samples up to the 125 mm mark.
Judgment criteria (O): Absorbent cotton is not ignited by the fall of the burned sample in all samples.

(7) Continuous productivity Continuous productivity is calculated by converting the number of film breaks per 24 hours when the film was formed for 48 hours under the conditions of the examples and comparative examples, and the examples and comparative examples. The film raw materials used in the above were judged on the basis of the following criteria using the increased filtration pressure when the filterability test was conducted under the following conditions.
S: Less than one break per 24 hours and an increase in filtration pressure of less than 80 kg / cm ² A: Less than one break per 24 hours and an increase in filtration pressure of 80 kg / cm ² or more and less than 100 kg / cm ² B : Less than one break per 24 hours and a filtration pressure increase value of 100 kg / cm ² or more and less than 120 kg / cm ² C: One or more breaks per 24 hours or a filtration pressure increase value of 120 kg / cm ² or more B is good, and S is the best among them.
<Conditions for filterability test>
The raw materials used in Examples and Comparative Examples are dried at 140 ° C. for 8 hours under reduced pressure of 133 Pa or less. Using a single screw extruder, the pellets were dried using a X4 type 20 μm Dynaloy filter (filtering area 4.5 cm ² ) manufactured by Watanabe Seisakusho, polymer temperature 280 ° C., passing amount 10 g / Filter in minutes. From the start of filtration, the filtration pressure (R0) at the time when the polymer passage amount is 1200 g and the filtration pressure (R1) at the time of 8400 g are measured, and R1-R0 (kg / cm ² ) is defined as the filtration pressure increase value.

(8) Film thickness The film thickness was measured according to JIS C 2151 (2006) “micrometer method”. The measuring instrument used a micrometer, measured so that it may become substantially equal intervals along the product width direction, and made it the average value of 30 points | pieces of the width direction.

Hereinafter, the present invention will be described with reference to examples, but the present invention is not necessarily limited thereto.

(Reference Example 1) Production of polyethylene terephthalate resin A To a mixture of dimethyl terephthalate and ethylene glycol, 0.09% by weight of calcium acetate and 0.03% by weight of antimony trioxide with respect to dimethyl terephthalate were added. The temperature was raised by heating to conduct transesterification. Next, after adding 0.15% by weight of lithium acetate and 0.21% by weight of trimethyl phosphate to the raw material dimethyl terephthalate, the resulting transesterification product was transferred to a polymerization reaction tank, Subsequently, the reaction system was gradually depressurized while being heated and heated, and polymerization was performed at 290 ° C. under a reduced pressure of 1 mmHg by a conventional method to obtain polyethylene terephthalate (PET) having an intrinsic viscosity of 0.54 dl / g. The obtained PET polymer was heat-treated at a temperature of 225 ° C. for 35 hours under a reduced pressure of 1 mmHg or less using a rotary vacuum polymerization apparatus, and a polyethylene terephthalate resin A (PET) having a melting point of 255 ° C. and an intrinsic viscosity of 0.73 dl / g. Chip A) was obtained.

(Reference Example 2) Production of polyethylene terephthalate resin B In the same manner as in Reference Example 1 except that polyethylene terephthalate (PET) having an intrinsic viscosity of 0.54 dl / g in Reference Example 1 was heat-treated for 20 hours, the melting point was 255 ° C. Polyethylene terephthalate resin B (PET chip B) having a viscosity of 0.63 dl / g was obtained.

(Reference Example 3) Production of polyethylene terephthalate resin C In the same manner as in Reference Example 1 except that polyethylene terephthalate (PET) having an intrinsic viscosity of 0.54 dl / g in Reference Example 1 was heat-treated for 50 hours, the melting point was 255 ° C. A polyethylene terephthalate resin C (PET chip C) having a viscosity of 0.80 dl / g was obtained.

Reference Example 4 Production of Carbon Black-Containing Polyester Resin Composition Master A Kneading paddle kneading 80% by weight of PET chip A prepared in Reference Example 1 and 20% by weight of furnace black (# 3030B) manufactured by Mitsubishi Chemical Corporation as carbon black particles. Into a co-rotating twin-screw kneading extruder equipped with a vacuum vent (L / D = 40), melt-extruded at a residence time of 90 seconds, a screw speed of 300 rpm, and 290 ° C., and discharged into a strand After cooling with water at a temperature of 25 ° C., it was immediately cut to prepare a carbon black-containing polyester resin composition master A (master chip A) having an intrinsic viscosity of 0.58 dl / g.

(Reference Example 5) Production of Carbon Black-Containing Polyester Resin Composition Master B Reference Example 4 was the same as Reference Example 4 except that the screw rotation speed of the vented co-rotating biaxial kneading extruder was 100 revolutions / minute. Similarly, a carbon black-containing polyester resin composition master B (master chip B) having an intrinsic viscosity of 0.64 dl / g was produced.

(Reference Example 6) Production of Carbon Black-Containing Polyester Resin Composition Master C Reference Example 4 was the same as Reference Example 4 except that the screw rotation speed of the vented co-rotating twin-screw kneading extruder was 400 rpm. Similarly, a carbon black-containing polyester resin composition master C (master chip C) having an intrinsic viscosity of 0.55 dl / g was produced.

Reference Example 7 Production of Carbon Black-Containing Polyester Resin Composition Master D In Reference Example 4, the same procedure as in Reference Example 4 was conducted except that the PET chip A obtained in Reference Example 1 was 90% by weight and the carbon black was 10% by weight. Thus, a carbon black-containing polyester resin composition master D (master chip D) having an intrinsic viscosity of 0.63 dl / g was produced.

Reference Example 8 Production of Carbon Black-Containing Polyester Resin Composition Master E The same as Reference Example 4 except that in Reference Example 4, the PET chip A obtained in Reference Example 1 was 94% by weight and the carbon black was 6% by weight. Thus, a carbon black-containing polyester resin composition master E (master chip E) having an intrinsic viscosity of 0.65 dl / g was produced.

Reference Example 9 Production of Carbon Black-Containing Polyester Resin Composition Master F In Reference Example 4, 78% by weight of PET chip A obtained in Reference Example 1, 20% by weight of carbon black, and olefin wax “Licowax PP230” as a dispersant. A carbon black-containing polyester resin composition master F (master chip F) having an intrinsic viscosity of 0.55 dl / g was produced in the same manner as in Reference Example 4 except that 2% by weight (manufactured by Clariant) was added.

Reference Example 10 Production of Carbon Black-Containing Polyester Resin Composition Master G In Reference Example 4, the intrinsic viscosity was 0.46 dl / g in the same manner as Reference Example 4 except that PET chip B prepared in Reference Example 2 was used. Of carbon black-containing polyester resin composition master G (master chip G).

Reference Example 11 Production of Carbon Black-Containing Polyester Resin Composition Master H In Reference Example 4, 78 wt% PET chip A obtained in Reference Example 1, 20 wt% carbon black, a condensed phosphate ester (large) as a flame retardant A carbon black-containing polyester resin composition master H (master chip H) having an intrinsic viscosity of 0.55 dl / g was produced in the same manner as in Reference Example 4 except that PX200 (manufactured by Yachi Chemical Co., Ltd.) was added in an amount of 2% by weight.

Reference Example 12 Production of Carbon Black-Containing Polyester Resin Composition Master I In Reference Example 4, the same procedure as in Reference Example 4 was conducted except that the PET chip A obtained in Reference Example 1 was 65% by weight and the carbon black was 35% by weight. A carbon black-containing polyester resin composition master I (master chip I) having an intrinsic viscosity of 0.49 dl / g was produced.

Example 1
10% by weight of the master chip A obtained in Reference Example 4 and 90% by weight of the polyethylene terephthalate resin B obtained in Reference Example 2 were each vacuum dried at a temperature of 180 ° C. for 2 hours. Subsequently, it supplied to the extruder under nitrogen atmosphere. After the polymer melted by the extruder is filtered through a filter set at a temperature of 290 ° C., it is melt-extruded from a die of a T die set at a temperature of 280 ° C. and solidified by cooling while applying an electrostatic charge to a cast drum having a surface temperature of 25 ° C. And the unstretched film was produced.

This unstretched film was stretched at a magnification of 3.3 times in the longitudinal direction of the film at a temperature of 90 ° C. using a difference in peripheral speed of the roll using a longitudinal stretching machine composed of a plurality of heated roll groups. . Thereafter, both ends of the film are gripped with a clip, guided to a tenter, stretched in the width direction of the film at a stretching temperature of 95 ° C. and a stretching ratio of 3.5 times, heat-treated at 225 ° C. for 8 seconds, and a thickness of 50 μm. A biaxially oriented polyester film was obtained.

The properties of the obtained biaxially stretched polyester film are shown in the table.

(Example 2)
A biaxially stretched polyester film was obtained in the same manner as in Example 1 except that the thickness of the film in Example 1 was changed to 100 μm. The properties of the obtained biaxially stretched polyester film are shown in the table.

Example 3
A biaxially stretched polyester film was obtained in the same manner as in Example 1 except that the contents of the master chip A and the polyethylene terephthalate resin B were changed as shown in the table and the thickness of the film was 200 μm. The properties of the obtained biaxially stretched polyester film are shown in the table.

Example 4
A biaxially stretched polyester film was obtained in the same manner as in Example 1 except that the contents of the master chip A and the polyethylene terephthalate resin B were changed as shown in the table. The properties of the obtained biaxially stretched polyester film are shown in the table.

(Example 5)
A biaxially stretched polyester film was obtained in the same manner as in Example 1 except that 10% by weight of the master chip B obtained in Reference Example 5 was used instead of the master chip A. The properties of the obtained biaxially stretched polyester film are shown in the table.

(Example 6)
A biaxially stretched polyester film was obtained in the same manner as in Example 1 except that 10% by weight of the master chip C obtained in Reference Example 6 was used instead of the master chip A. The properties of the obtained biaxially stretched polyester film are shown in the table.

(Example 7)
As a polyester raw material for producing a film, the same procedure as in Example 1 was used except that 20% by weight of the master chip D obtained in Reference Example 7 was used and 80% by weight of the polyethylene terephthalate resin B obtained in Reference Example 2 was used. An axially stretched polyester film was obtained. The properties of the obtained biaxially stretched polyester film are shown in the table.

(Example 8)
Biaxial biaxially in the same manner as in Example 1 except that 33% by weight of the master chip E obtained in Reference Example 8 and 67% by weight of the polyethylene terephthalate resin B obtained in Reference Example 2 were used as the polyester raw material for producing the film. A stretched polyester film was obtained. The properties of the obtained biaxially stretched polyester film are shown in the table.

Example 9
In Example 1, a biaxially stretched polyester film was prepared in the same manner as in Example 1 except that 10% by weight of the master chip A obtained in Reference Example 4 and 90% by weight of the polyethylene terephthalate resin C obtained in Reference Example 3 were used. Got. The properties of the obtained biaxially stretched polyester film are shown in the table.

(Example 10)
A biaxially stretched polyester film was obtained in the same manner as in Example 1 except that the heat treatment in Example 1 was changed to 235 ° C. The properties of the obtained biaxially stretched polyester film are shown in the table.

(Comparative Example 1)
A biaxially stretched polyester film was obtained in the same manner as in Example 1 except that the master chip F obtained in Reference Example 9 was used instead of the master chip A. The properties of the obtained biaxially stretched polyester film are shown in the table.

(Comparative Example 2)
Biaxial stretching in the same manner as in Example 1 except that the polyester raw material for producing the film is 35% by weight of the master chip A obtained in Reference Example 4 and 65% by weight of the polyester resin obtained in Reference Example 2. A polyester film was obtained. The properties of the obtained biaxially stretched polyester film are shown in the table.

(Comparative Example 3)
A biaxially stretched polyester film was obtained in the same manner as in Example 1 except that the master chip G obtained in Reference Example 10 was used instead of the master chip A. The properties of the obtained biaxially stretched polyester film are shown in the table.

(Comparative Example 4)
Example 1 except that 2.5% by weight of the master chip A obtained in Reference Example 4 and 97.5% by weight of the polyethylene terephthalate resin B obtained in Reference Example 2 were used as the polyester raw material for producing the film. A biaxially stretched polyester film was obtained in the same manner. The properties of the obtained biaxially stretched polyester film are shown in the table.

(Comparative Example 5)
A biaxially stretched polyester film was obtained in the same manner as in Example 1 except that the master chip H obtained in Reference Example 11 was used instead of the master chip A. The properties of the obtained biaxially stretched polyester film are shown in the table.

(Comparative Example 6)
A biaxially stretched polyester film was obtained in the same manner as in Example 1 except that the heat treatment in Example 1 was changed to 200 ° C. The properties of the obtained biaxially stretched polyester film are shown in the table.

(Comparative Example 7)
A biaxially stretched polyester film was obtained in the same manner as in Example 1 except that 6% by weight of the master chip I obtained in Reference Example 12 and 94% by weight of the polyethylene terephthalate resin B obtained in Reference Example 2 were used. . The properties of the obtained biaxially stretched polyester film are shown in the table.

According to the present invention, it is possible to provide a biaxially oriented polyester film that satisfies high light-shielding properties, concealability, and flame retardancy, and is excellent in continuous productivity. Furthermore, by using such a film, it is possible to provide a light shielding member for an optical device or a solar battery back sheet having both high light shielding properties and flame retardancy.

Claims

A biaxially oriented polyester film satisfying the following (1) to (4).
(1) Carbon black particles are contained in the polyester resin composition constituting the film.
(2) The flame retardant and dispersant are not substantially contained in the polyester resin composition constituting the film.
(3) The optical density of the film is 3.5 or more.
(4) The flame retardancy required by the following method is VTM-0, VTM-1, or VTM-2.
<Flame retardancy evaluation method>
(I) Sample preparation A measurement sample (biaxially oriented polyester film) is cut into 20 cm x 5 cm.
Sample A left at 23 ° C. and 50% RH for 48 hours is sample A, temperature 70 ° C., left for 168 hours, then cooled to 23 ° C. and 20% RH or less for 4 hours as sample B, and 5 samples each. Prepare as a set.
(Ii) Measuring method A line is drawn in a direction parallel to the short side at 125 mm from the short side of each sample, and wound around a rod having a diameter of 12.7 mm so that the short side is in the vertical direction. In the 75mm part above the 125mm mark, stick with pressure sensitive tape and pull out the stick. The top of the sample is closed during the test so that there is no chimney effect. Next, each sample is set vertically, and absorbent cotton is placed 300 mm below. Using a Bunsen burner with a diameter of 9.5 mm and a flame length of 20 mm as a heating source so that the burner tube is located 10 mm from the lower end of the sample, a blue flame is indirectly flamed at the center of the lower end of the sample for 3 seconds. Measure the combustion time (t1) after the flame release. Then, as soon as the flame has disappeared, the indirect flame is again emitted for 3 seconds, and the combustion time (t2) and the fire type time (t3) after the second flame-off are measured. In addition, at the time of the first and second flame contact, observation is also made as to whether there was combustion that burned up to the 125 mm mark, and whether there was a burning fallen object that would ignite absorbent cotton. For sample A and sample B, the above measurement is performed for each set (five pieces).
(Iii) Evaluation of flame retardancy Based on the following criteria, flame retardancy is evaluated as follows.
VTM-0: Satisfy any of the criteria (A), (I), (U), (E), (O).
VTM-1: Judgment criteria (A '), (I'), (U '), (E), (O) are all satisfied.
VTM-2: Satisfy all of the criteria (A '), (I'), (U '), and (E).
No VTM: Does not correspond to any of VTM-0, VTM-1, and VTM-2.
Criteria (A): In all samples, the longer combustion time (t1) after the first flame release or the second combustion time (t2) after the second flame release is 10 seconds or less.
Judgment criteria (A '): In all samples, the longer combustion time after the first flame release (t1) or the second combustion time after the flame release (t2) is 30 seconds or less.
Judgment criteria (I): The total of the burning time after flame removal per set (the total of the burning time after flame removal of five samples (t1 + t2)) is 50 seconds or less for both sample A and sample B.
Criteria (I '): The total burning time after flame removal per set (the total burning time after flame removal (t1 + t2) of 5 samples) is less than 250 seconds for both sample A and sample B .
Judgment standard (U): In all samples, the sum of the combustion time (t2) and the ignition time (t3) after the second flame-off is 30 seconds or less.
Judgment criteria (U '): In all samples, the sum of the combustion time (t2) and the ignition time (t3) after the second flame-off is 60 seconds or less.
Judgment criteria (e): In all samples, combustion or fire type does not reach the 125 mm mark.
Judgment criteria (O): In all samples, absorbent cotton is not ignited by the fall of the burned sample.
The biaxially oriented polyester film according to claim 1, wherein the film has a thickness of 50 μm or more and 300 μm or less.
The biaxially oriented polyester film according to claim 1 or 2, wherein the content of carbon black particles in the polyester resin composition constituting the film is in the range of 1 to 5% by weight.
The biaxially oriented polyester film according to any one of claims 1 to 3, which is used for either a light shielding member of an optical device or a solar battery backsheet.
The method for producing a biaxially oriented polyester film according to any one of claims 1 to 4, comprising a step of satisfying the following (5) to (6).
(5) A carbon black-containing polyester resin composition master obtained by kneading a polyester resin composition (a) having an intrinsic viscosity [η] of 0.7 dl / g or more and carbon black particles into a polyester raw material for producing a film Including (b).
(6) When producing the carbon black-containing polyester resin composition master (b), the intrinsic viscosity of the polyester resin of the polyester resin composition (a) before kneading and the resulting carbon black-containing polyester resin composition master ( The intrinsic viscosity of the polyester resin of b) satisfies the following formula (6-1).
(6-1) 0.75 ≦ [η] b / [η] a ≦ 0.90
[Η] a: Intrinsic viscosity (dl / g) of the polyester resin of the polyester resin composition (a) of 0.7 dl / g or more
[Η] b: Intrinsic viscosity (dl / g) of the polyester resin of the carbon black-containing polyester resin composition master (b)
The method for producing a biaxially oriented polyester film according to claim 5, wherein the carbon black particle content in the carbon black-containing polyester resin composition master (b) is 5 wt% or more and 30 wt% or less.
The method for producing a biaxially oriented polyester film according to claim 5 or 6, wherein the following (7) to (9) are satisfied.
(7) The polyester raw material for producing the film contains the carbon black-containing polyester resin composition master (b) and the polyester resin composition (c) not containing carbon black.
(8) The intrinsic viscosity of the polyester resin of the carbon black-containing polyester resin composition master (b) and the polyester resin composition (c) not containing carbon black satisfies the following formula (8-1).
(8-1) 0.75 ≦ [η] b / [η] c ≦ 1.10
[Η] b: Intrinsic viscosity (dl / g) of the polyester resin of the carbon black-containing polyester resin composition master (b)
[Η] c: Intrinsic viscosity (dl / g) of the polyester resin of the polyester resin composition (c) not containing carbon black
(9) The content Wb (% by weight) of the carbon black-containing polyester resin composition master with respect to the entire polyester raw material for producing the film and the content Wc (% by weight) of the polyester resin composition (c) that does not contain carbon black. And satisfying the following formula (9-1).
(9-1) 0.03 ≦ Wb / Wc ≦ 0.5
Wb: Content (% by weight) of the carbon black-containing polyester resin composition master (b) with respect to the entire polyester raw material for producing the film
Wc: content (% by weight) of the polyester resin composition (c) containing no carbon black with respect to the entire polyester raw material for producing the film