JPH05222273A - Polyester-based resin composition and its film - Google Patents

Abstract

PURPOSE:To obtain the subject composition excellent in mechanical strength, heat resistance, slippage, transparency and impact resistance and suitable for a packaging film, etc., by blending polybutylene terephthalate, etc., with a prescribed amount of an inorganic fine powder. CONSTITUTION:The objective composition is obtained by blending (A) a modified polybutylene terephthalate composed of polybutylene terephthalate or polybutylene terephthalate and a thermoplastic elastomer or polycaprolactone with (B) 0.01 to 0.4wt.%, preferably 0.1 to 0.25wt.% inorganic fine powder such as kaolin having 1 to 10mum average particle size.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a polyester resin composition and a film suitable as various packaging films.

[0002]

BACKGROUND OF THE INVENTION As various packaging materials, low density polyethylene, linear low density polyethylene, ethylene-vinyl acetate copolymer, olefin polymers such as ionomers, polyethylene terephthalate, nylon, etc. Film is used. However, these polymer films have low mechanical strength and heat resistance.

On the other hand, polybutylene terephthalate is known as a polymer film having high mechanical strength and heat resistance. This film, unlike the above-mentioned film, has the advantage of exhibiting high mechanical strength without stretching. However, when heat is applied to the polybutylene terephthalate film by, for example, retort treatment or thermal lamination, impact resistance is significantly reduced. Therefore, although the polybutylene terephthalate film has excellent properties, its use is limited.

The polymer film is required to have a small friction coefficient in terms of workability. However, in the polybutylene terephthalate film, if the coefficient of friction is reduced by adjusting the cooling temperature or the like at the time of film production, the transparency and impact resistance decrease. for that reason,
It is generally difficult to obtain a polybutylene terephthalate film having a small coefficient of friction and excellent transparency and impact resistance.

Therefore, an object of the present invention is to provide a polyester resin composition having high heat resistance which can maintain high mechanical strength even when heat is applied.

Another object of the present invention is to provide a film which is excellent in heat resistance and whose mechanical strength is not deteriorated by heat.

Still another object of the present invention is to provide a film having excellent slipperiness, transparency and impact resistance.

[0008]

In order to achieve the above object, the present inventor has
As a result of diligent study on the polyester resin composition, it is possible to improve slipperiness, transparency and impact resistance by adding a small amount of inorganic fine powder to polybutylene terephthalate or modified polybutylene terephthalate, and further thermoplastic elastomer and / or With the addition of polycaprolactone,
The inventors have found that the impact resistance is remarkably improved and completed the present invention.

That is, the present invention provides a resin composition containing polybutylene terephthalate or modified polybutylene terephthalate, which is a polyester resin composition containing 0.01 to 0.4% by weight of inorganic fine powder.

The present invention also provides a film formed of the polyester resin composition.

In the present specification, the term "modified polybutylene terephthalate" means 1,4 which is a constituent monomer.
A polybutylene terephthalate internally modified by substituting a part of the components of either butanediol or terephthalic acid with another diol and / or dicarboxylic acid; by adding a polymer to polybutylene terephthalate, It means an externally modified polybutylene terephthalate.

The term "aromatic diol" means not only a compound in which a hydroxy group is directly bonded to an aromatic ring but also a hydroxy group indirectly bonded to the aromatic ring via an alkylene group or an alkylenedioxy group. Is also used to include a compound to which is bound.

Unless otherwise specified, the term "terephthalic acid", "dicarboxylic acid" and "dicarboxylic acid component" are used for esterification reaction such as lower alkyl ester, acid anhydride and acid halide. It is also used to include a derivative of a commonly used carboxylic acid.

The term "film" is used to include substantially all flat structures sometimes referred to as sheets by those skilled in the art.

"Melting point" means a differential scanning calorimeter (DS)
C) means the melting peak temperature (T _pm ) when measured at a temperature rising rate of 10 ± 1 ° C./min according to the measuring method defined in JIS K 7121.

The present invention applies to polybutylene terephthalate or modified polybutylene terephthalate. The internally modified polybutylene terephthalate is
(A) A dicarboxylic acid consisting of a diol component selected from aliphatic diols, alicyclic diols and aromatic diols and containing at least 1,4-butanediol, and terephthalic acid or two or more dicarboxylic acids containing at least terephthalic acid. It is a copolyester derived from an acid component. However, when the dicarboxylic acid component in the modified polybutylene terephthalate is terephthalic acid, the diol component is not 1,4-butanediol alone.

As the diol component constituting the copolyester (a), conventional aliphatic, alicyclic and aromatic diols are used. The diol component contains at least 1,4-butanediol.

Examples of the aliphatic diol include ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, polypropylene glycol, 1,3-butanediol, neopentyl glycol, 1,5. -Pentanediol, 1,6-hexanediol, polymethylene glycol and the like.

Examples of the alicyclic diol include 1,4
-Cyclohexanediol, 1,4-cyclohexanedimethanol, 2,2-bis (4-hydroxyethoxycyclohexyl) propane, hydrogenated bisphenol A
And an addition product of alkylene oxide such as ethylene oxide or propylene oxide.

As the aromatic diol, for example, resorcinol, naphthalene diol, 2,2-bis (4-hydroxyphenyl) propane, bisphenol A and an adduct of alkylene oxide such as ethylene oxide or propylene oxide, for example, 2 , 2-bis (4
-Hydroxyethoxyphenyl) propane, 2,2-bis (4-hydroxydiethoxyphenyl) propane,
2,2-bis (4-hydroxytriethoxyphenyl)
Propane, 2,2-bis (4-hydroxypolyethoxyphenyl) propane, 2,2-bis (4-hydroxypropoxyphenyl) propane, 2,2-bis (4-hydroxydipropoxyphenyl) propane, 2,2- Bis (4-hydroxytripropoxyphenyl) propane,
2,2-bis (4-hydroxypolypropoxyphenyl) propane and the like are exemplified.

These diols can be used as a mixture of two or more kinds with 1,4-butanediol.

The dicarboxylic acid component is composed of terephthalic acid; and two or more dicarboxylic acids containing at least terephthalic acid. Preferred derivatives of terephthalic acid include terephthalic acid methyl ester.

Examples of the dicarboxylic acid which can be used in combination with the terephthalic acid include aliphatic dicarboxylic acids such as maleic acid, succinic acid, adipic acid, suberic acid, azelaic acid, sebacic acid and dodecanoic acid; 1,4-cyclohexanedicarboxylic acid. Alicyclic dicarboxylic acids such as acids; phthalic acid, isophthalic acid, naphthalene-2,6-dicarboxylic acid, diphenyl-4,4'-dicarboxylic acid, aromatic dicarboxylic acids such as 3-sulfoisophthalic acid, and the like. .. These other dicarboxylic acids can be used alone or in combination of two or more.

At least one of the diol component and the dicarboxylic acid component constitutes a modified polyester together with 1,4-butanediol and / or terephthalic acid. That is, when the (1) diol component is 1,4-butanediol, two or more dicarboxylic acids containing at least terephthalic acid are used as the dicarboxylic acid component. On the other hand, (2) when the diol component is two or more diols containing 1,4-butanediol, terephthalic acid alone or two or more dicarboxylic acids containing at least terephthalic acid are used as the dicarboxylic acid component. To be done.

In the above embodiments (1) and (2), when at least 1,4-butanediol is used as the diol component,
The crystallinity during film formation is large, and the heat resistance required in the sterilization process such as retort can be increased. In the aspect of (2), examples of the diol that can be substituted with a part of 1,4-butanediol include (a) an aliphatic diol containing at least diethylene glycol,
In particular, (a1) diethylene glycol, (a2) ethylene glycol and diethylene glycol, (b) the following general formula [I]
Aromatic diols represented by are preferred.

[0026]

[Chemical 1] (In the formula, R ₁ , R ₂ , R ₃ and R ₄ are the same or different and each represents a hydrogen atom or a methyl group, and l and m represent a positive integer.) The fragrance represented by the general formula [I] In the group diol,
l and m are integers of 1 to 10, preferably 1 to 5.
Among the aromatic diols represented by the general formula [I], 2,2-bis (4-hydroxyethoxyphenyl) propane and 2,2-bis (4-hydroxydiethoxyphenyl) propane are particularly preferable.

In the embodiments (1) and (2), the dicarboxylic acid that can be substituted for a part of terephthalic acid is preferably, for example, isophthalic acid.

The copolyester can be obtained by using the diol component and the dicarboxylic acid component in substantially equimolar amounts and subjecting them to an esterification reaction. In the embodiments of (1) and (2), the molar ratio of a plurality of diols constituting the diol component,
The molar ratio of the plurality of dicarboxylic acids constituting the dicarboxylic acid component can be selected according to the types of diol and dicarboxylic acid, the desired heat sealing temperature, and the like.

In the embodiment (1), the preferred copolyester is 50 mol% of 1,4-butanediol and terephthalic acid / other dicarboxylic acid = 5-95 / 95-5.
(Molar ratio), preferably 10 to 75/90 to 25 (molar ratio), and more preferably 20 to 50/80 to 50 (molar ratio), and a copolymerized polyester with 50 mol% of dicarboxylic acid component. .. More specifically, when the copolyester is a copolymerized polyester of 1,4-butanediol and terephthalic acid / isophthalic acid, terephthalic acid / isophthalic acid = 15 to 90/85 to 10 (molar ratio), particularly It is preferably about 20 to 50/80 to 50 (molar ratio).

In the above embodiment (2), the preferred copolyester is 1,4-butanediol / other diol =
25-95 / 75-5 (molar ratio), preferably 50-9
0/50 to 10 (molar ratio), more preferably 70 to 9
It is a copolyester of 50 mol% of a diol component consisting of 0/30 to 10 (molar ratio) and 50 mol% of terephthalic acid. More specifically, when the copolyester is a copolyester of terephthalic acid, 1,4-butanediol and 2,2-bis (4-hydroxyethoxyphenyl) propane, 1,4-butanediol /
2,2-bis (4-hydroxyethoxyphenyl) propane = 60-95 / 40-5 (molar ratio), especially 70-9
It is preferably about 0/30 to 10 (molar ratio).

The melting point of the copolyester is, for example, 150
It is in the range of to 210 ° C. The melting point of copolyester is 15
When the temperature is lower than 0 ° C., the films are likely to be blocked in the process of heat sterilization such as retort, and when the temperature is higher than 210 ° C., heat sealing under normal conditions becomes difficult and the bag-making speed decreases. The film formed of the polyester resin composition containing the copolyester having the above melting point can be heat-sealed by a general bag-making device.

The polybutylene terephthalate and the copolyester may have an appropriate molecular weight within a range that does not impair the moldability and mechanical strength. The weight average molecular weight of the polybutylene terephthalate and the copolyester is usually 5,000 to 1,000,000, preferably 1.
It is about 0000 to 500000.

The intrinsic viscosity of polybutylene terephthalate and copolyesters is at least about 0.5 dl / when using solvent o-chlorophenol at a temperature of 25 ± 1 ° C.
g or more, preferably about 0.5 to 2.5 dl / g.

The method for producing the polybutylene terephthalate and the copolyester is not particularly limited, and a conventional method such as a transesterification method or a direct esterification method can be used.

In any of these methods, the molecular weight may be increased by using a solid phase polymerization method after the polymerization reaction, if necessary. In particular, it is preferable to use the solid phase polymerization method in order to ensure the necessary viscosity during film formation.

The externally modified polybutylene terephthalate can be composed of polybutylene terephthalate and various thermoplastic polymers. Preferred thermoplastic polymers for externally modifying polybutylene terephthalate include, for example:
Includes thermoplastic elastomers and / or polycaprolactone.

Examples of the thermoplastic elastomer include various block copolymers such as terephthalic acid and 1,4
-A block copolymerized polyester elastomer containing butanediol and polytetramethylene glycol and / or polycaprolactone as constituent monomers. At least one kind of these thermoplastic elastomers may be used.

The molecular weight of polytetramethylene glycol and polycaprolactone in the block copolymerized polyester elastomer is, for example, 300 to 5,000,
It is preferably about 500 to 3000. The molar ratio of polytetramethylene glycol and polycaprolactone in the block copolymerized polyester elastomer is 10 to 80 mol%, preferably 20 to 75 mol% of the total diol components. The block copolymerized polyester-based elastomer is obtained by a conventional method, for example, an esterification method of directly esterifying the components, or a transesterification reaction of polybutylene terephthalate with polytetramethylene glycol and / or polycaprolactone. You can

The ratio of polybutylene terephthalate to thermoplastic elastomer and / or polycaprolactone is
For example, polybutylene terephthalate 70 to 99 / thermoplastic elastomer 1 to 30 (% by weight), preferably 75
It is about 98/2 to 25 (% by weight).

A preferred resin composition comprises an externally modified polybutylene terephthalate.

The resin composition of the present invention contains an inorganic fine powder. As the inorganic fine powder, for example, kaolin, talc, mica, diatomaceous earth, calcium carbonate, magnesium carbonate, barium sulfate, silica, zinc oxide, magnesium oxide, zirconium oxide, titanium oxide, alumina, aluminum hydroxide, potassium titanate, Examples thereof include carbon black. Among these inorganic fine powders, powders that do not impair transparency and have a small particle size, such as silica, are preferable.

The average particle size of the inorganic fine powder can be selected within a range that does not impair the transparency, and is, for example, 0.1 to 50 μm, preferably 0.5 to 25 μm, more preferably 1 to 10 μm.
It is about m. Particularly preferable average particle size of the inorganic fine powder is
The thickness is 2.5 to 7.5 μm, and particularly about 4 to 6 μm.

The content of these inorganic fine powders in the composition is 0.01 to 0.4% by weight, preferably 0.05 to 0.4%.
It is 0.3% by weight, and more preferably about 0.1 to 0.25% by weight. When the content of the inorganic fine powder is less than 0.01% by weight, when the film is formed under the condition that the transparency of the film can be secured, for example, under the cooling condition, the slipperiness is deteriorated, and it becomes difficult to wind the film, and the film is resistant to winding. Impact resistance is not so much improved,
If it exceeds 0.4% by weight, the impact resistance tends to decrease, and the mechanical properties tend to be impaired.

The reason why the impact resistance of the polybutylene terephthalate film is lowered by the heat treatment is that a part of the crystal nuclei abnormally grown due to the crystallization of the polybutylene terephthalate is destroyed when it is impacted. It is speculated that it acts as a starting point. By adding inorganic fine powder,
The detailed reason why the decrease in heat resistance due to heat treatment is alleviated is
Although it is unknown, it is presumed that the addition of the inorganic fine powder produces a large number of fine crystal nuclei in the resin and the crystal growth is suppressed even when subjected to heat treatment.

The addition of the above-mentioned inorganic fine powder can not only secure the slipperiness of the film, but also significantly suppress the deterioration of the transparency and the impact resistance.

The resin composition of the present invention optionally contains various polymers such as olefin polymers, polyvinyl chloride, styrene polymers, polyethylene terephthalate, nylon or polyamide, polyacrylonitrile and polycarbonate. May be.

Further, the resin composition of the present invention contains various additives such as an antioxidant, an ultraviolet absorber, a heat stabilizer,
It may contain a plasticizer, an antistatic agent, a tackifier, a filler, a wax, a lubricant, a dye or pigment, and the like.

The resin composition of the present invention is a usual molding material,
Although it can be used as a fiber reinforced composite material, it is suitable as a film forming material.

The film of the present invention comprises (i) a single layer film formed of the polyester resin composition, and (ii) one surface of a layer formed of the polyester resin composition,
It is roughly classified into a composite film in which at least one base material layer is laminated.

In the latter composite film, the base material layer includes paper; a metal thin film such as an aluminum thin film; and a polymer layer. The metal thin film can be formed by a film forming means such as vapor deposition or a laminate.

As the polymer constituting the polymer layer,
For example, olefin polymers such as polyethylene, ethylene-ethyl acrylate copolymer, ionomer, polypropylene, ethylene-propylene copolymer, poly-4-methylpentene-1; ethylene-vinyl alcohol copolymer; polyvinyl chloride; Vinylidene chloride-acrylic acid ester copolymers, vinylidene chloride-vinyl chloride copolymers, vinylidene chloride-acrylonitrile copolymers and other vinylidene chloride polymers; polystyrene, styrene-acrylonitrile copolymers, styrene-acrylonitrile-butadiene copolymers. Polystyrene such as polyethylene terephthalate and polybutylene terephthalate;
Nylon such as nylon-6 and nylon-66, polyamide such as aromatic polyamide; polyacetal; polyacrylonitrile; polycarbonate; polyphenylene oxide; polyphenylene sulfide; polysulfone; polyarylate; polyethersulfone; polyetheretherketone; polyamideimide; Polyetherimide;
Polyimide; cellophane and the like can be mentioned. Of these polymers, olefin polymers (particularly polypropylene), polyester and nylon are preferred. Further, among these polymers, polycarbonate, polyester (particularly polybutylene terephthalate), polyarylate and the like can be laminated by the co-extrusion method and the heat resistance is not impaired.

The polymer layer may be laminated directly on the layer formed of the resin composition by coating or laminating, or may be laminated via an adhesive or an adhesive resin layer. The polymer layer may be further coated with the vinylidene chloride polymer, and a metal thin film may be formed by means such as vapor deposition. The polymer layer may be unstretched or may be uniaxially or biaxially stretched. Furthermore, the polymer layer may be composed of a plurality of layers of the same or different polymers. The base material layer may contain a polymer and the additives exemplified above.

The layer thickness of the polymer layer can be appropriately set,
Usually 10 to 1000 μm, preferably 15 to 500 μm
It is a degree.

The monolayer film of the present invention can be produced by a conventional method, for example, a usual T-die method using an extruder, an extrusion method such as an inflation method. In addition, the composite film is a conventional method, for example, a co-extrusion molding method in which a co-extrusion molding machine is used for laminating; a extrusion process in which a molten resin composition is extruded to form a laminated layer on a substrate film that constitutes a substrate layer. Laminating method: It can be manufactured by a dry laminating method or the like in which a base film and a heat-sealing layer are laminated via an adhesive layer.
According to the coextrusion molding method, the productivity of the composite film is high.

In the co-extrusion molding method for producing a composite film by using a plurality of polymers, for example, a feed block system in which each resin layer is joined upstream of a die having a single channel; Multi-manifold die method in which a plurality of flow paths are provided and merged and discharged in the die before discharging; in the multi-manifold die method, a vane die method in which the shape of the flow paths can be changed; There is a multi-slot system provided with.

Since the film of the present invention exhibits a large mechanical strength even in the non-stretched state, the stretching treatment is not always necessary, but the film may be uniaxially or biaxially stretched if necessary.

The surface of the film of the present invention may be subjected to surface treatment such as corona discharge treatment, high frequency treatment, flame treatment, chromic acid treatment and solvent treatment. In particular, the corona discharge treatment is preferable because it improves the dry lamination strength between the film of the present invention and the base film.

Further, on the surface of the film, a coating layer may be formed according to the intended use such as a gas barrier layer, an antistatic layer, a slipping layer and the like.

The films of the present invention have a wide range of applications, such as:
It can be used as various films such as individual packaging for retort foods, packaging films for interiors and exteriors, and the like.

[0060]

The polyester resin composition and film of the present invention have high heat resistance and can maintain high mechanical strength even when heat is applied.

[0061]

EXAMPLES The present invention will be described in more detail based on the following examples.

Comparative Example 1, Comparative Example 2 and Example 1 Polybutylene terephthalate [Polyplastic Co., Ltd.
Manufactured by DURANEX 600FP: weight average molecular weight 645
00] to 0% by weight of fine silica powder having an average particle size of 5 μm
(Comparative Example 1), 0.18 wt% (Example 1), 0.5 wt% (Comparative Example 2) were added to prepare a resin composition. Each of the obtained resin compositions was extruded using a T-die forming machine equipped with a melt extruder to obtain a film having a thickness of about 50 μm.

Example 2 The polybutylene terephthalate used in Example 1 was
0.18% by weight of fine silica powder having an average particle size of 5 μm, block copolymer ester elastomer [Toray DuPont Co., Ltd.]
Manufactured, Hytrel 4057] was added in the same manner as in Example 1 except that 5% by weight was added to obtain a film having a thickness of about 50 μm.

The block copolymer ester type elastomer is a polybutylene terephthalate structural unit 7
6 mol% and polytetramethylene glycol (molecular weight 10
00) 24 mol% with a melting point of 157 ° C. and a melt index of 12.5 at 235 ° C.
g / 10 minutes.

Example 3 In the same manner as in Example 1 except that polybutylene terephthalate of Example 1 was replaced by polybutylene terephthalate having a large molecular weight [Duranex 700FP manufactured by Polyplastics Co., Ltd .: weight average molecular weight 98000]. To obtain a film having a thickness of 50 μm.

The films obtained in Comparative Example 1, Comparative Example 2 and Examples 1 to 3 were heat-treated at the temperature shown in Table 1 for a predetermined time, and the temperature was 5 ° C. and the relative humidity was 50%.
The impact strength [measuring instrument: Toyo Seiki Co., Ltd., Dart Impact Tester] was measured according to the A method of 1709. The results are shown in Table 1.

[0067]

[Table 1] From Table 1, the films obtained in Examples 1 to 3 show little decrease in impact strength even after heat treatment.

Examples 4 to 6 0.2% by weight of silica fine powder having an average particle size of 5 μm was added to the polybutylene terephthalate used in Example 1, and polycaprolactone [manufactured by Daicel Chemical Industries, Ltd.,
Praxel H7: number average molecular weight 70000] 5% by weight
(Example 4) In the same manner as in Example 1 except that 10% by weight (Example 5) and 15% by weight (Example 6) were added,
A film having a thickness of 50 μm was obtained.

Examples 7 and 8 To the polybutylene terephthalate used in Example 1, 0.05% by weight of silica fine powder having an average particle size of 5 to 10 μm (Example 7) and 0.3% by weight (Example 8) ) With addition,
A film having a thickness of 50 μm was obtained in the same manner as in Example 1 except that 5% by weight of polycaprolactone used in Example 4 was added.

Then, the impact strength of the films obtained in Examples 4 to 8 was measured in the same manner as in Example 1. The results are shown in Table 2.

[0071]

[Table 2] Examples 9 to 11 and Comparative Examples 3 and 4 Polybutylene terephthalate used in Example 1 was prepared by adding silica fine powder having an average particle size of 5 to 10 μm and modified polybutylene terephthalate [Toyobo Co., Ltd., Helplen S]. ,
A film having a thickness of 50 μm was obtained in the same manner as in Example 1 except that the polycaprolactone used in Example 4 was added as follows. The modified polybutylene terephthalate is an internally modified polybutylene terephthalate obtained by transesterification reaction between polybutylene terephthalate and polycaprolactone.

Example 9: Silica fine powder 0.2% by weight Modified polybutylene terephthalate 2.5% by weight Polycaprolactone 2.5% by weight Comparative Example 3: Silica fine powder 0.5% by weight Modified polybutylene terephthalate 2.5 % By weight Polycaprolactone 2.5% by weight Example 10: Silica fine powder 0.2% by weight Modified polybutylene terephthalate 5% by weight Polycaprolactone 5% by weight Comparative Example 4: Silica fine powder 0.5% by weight Modified polybutylene terephthalate 5 % By weight Polycaprolactone 5% by weight Example 11: Silica fine powder 0.2% by weight Modified polybutylene terephthalate 10% by weight Polycaprolactone 10% by weight Then, of the films obtained in Examples 9 to 11 and Comparative Examples 3 and 4. The impact strength was measured in the same manner as in Example 1.
The results are shown in Table 3.

[0073]

[Table 3] From Table 3, the films obtained in Examples 9 to 11 show little reduction in impact strength even after heat treatment.

Further, a film was prepared in the same manner as in Example 1, Comparative Example 1 and Comparative Example 2 except that the cooling conditions were changed. The slipperiness of the obtained film was measured by ASTM D
Measure according to 1894-63 and test speed 1
The static friction coefficient and the dynamic friction coefficient at 5.2 ± 3 cm / min were measured, and the haze of the film was measured according to JIS K 71.
In addition to the measurement according to 05, the impact strength was also measured. The results are shown in Table 4.

[0075]

[Table 4] From Table 4, the films of Comparative Example 1 in which silica fine powder was not added and Comparative Example 2 in which silica fine powder was excessively added could not satisfy slipperiness, transparency and impact resistance,
The film of Example 1 is excellent in all of the above properties.

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Claims (3)

[Claims] 1. A resin composition containing polybutylene terephthalate or modified polybutylene terephthalate, comprising:
A polyester resin composition containing 0.01 to 0.4% by weight of inorganic fine powder. 2. The polyester resin composition according to claim 1, wherein the modified polybutylene terephthalate is composed of polybutylene terephthalate and a thermoplastic elastomer or polycaprolactone. 3. A film formed from the polyester resin composition according to claim 1.