JPH051133A - Polyester - Google Patents

Abstract

PURPOSE:To provide polyesters composed of a specified ratio of an aromatic dicarboxylic acid, butanediol, respectively specified dimerized fatty acid and glycol, having a prescribed melting viscosity, excellent in flexibility, transparency and thermal resistance, and useful as a fiber, etc. CONSTITUTION:The objective polyesters composed of (A) 50-95mol% aromatic dicarboxylic acid residue and 5-50mol% residue consisting of dimerized fatty acid (Ratios of monomer, dimer and trimer are respectively <=3mol%, >=95mol% and <=3mol%) synthesized, e.g. by dimerization of a 18C unsaturated fatty acid such as linoleic acid and (B) 40-90mol% 1,4-butanediol residue and 10-60mol% residue of a <=10C glycol except 1,4-butanediol in the repeating units constituting the polyesters, and showing <2500 poise melting viscosity at 250 deg.C.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a polyester capable of forming a flexible molded article. More specifically, the present invention relates to a polyester capable of easily forming a flexible molded article having excellent moldability such as transparency, elastic recovery, heat resistance, and extrusion molding such as film formation.

[0002]

Polyester, especially polyethylene terephthalate, polybutylene terephthalate or poly-
1,4-cyclohexane dimethylene terephthalate and polyesters based on these have excellent physical properties,
It has chemical properties and is widely used as fibers, films and molded products.

However, all of them are limited in flexibility and elasticity recovery at room temperature, so that there is a limit to expansion of applications. In order to improve such a defect, a method of copolymerizing a polyester with a soft segment has been considered. For example, JP-B-57-48577 discloses a copolymer of polybutylene terephthalate with a long-chain polyether such as polytetramethylene glycol, and JP-B-42-8709 discloses polyethylene terephthalate with a dimerized fatty acid. Copolymerized long-chain aliphatic dicarboxylic acid, and Japanese Patent Publication No. 5
JP-A-4-15913 discloses polybutylene terephthalate copolymerized with a dimerized fatty acid.

[0004]

However, those obtained by copolymerizing polybutylene terephthalate with a long-chain polyether are inferior in weather resistance, heat resistance, and transparency, and polyethylene terephthalate is copolymerized with a long-chain aliphatic dicarboxylic acid. The polymerized product has a slow crystallization rate and is difficult to be molded into a fiber, a film, a sheet, and other molded articles. Further, a copolymer of polybutylene terephthalate and a dimerized fatty acid has a high crystallinity and a high melt viscosity, and when formed into a film or the like, a film having a uniform thickness cannot be obtained and is partially whitened. There was a defect that transparency was lost.

An object of the present invention is to eliminate the above-mentioned conventional drawbacks, and to provide a polyester capable of easily forming a flexible molded article excellent in transparency, elastic recovery, heat resistance and moldability. To do.

[0006]

The above-mentioned object of the present invention is to provide, in a repeating unit constituting a polyester, a residue 5 consisting of 50 to 95 mol% of an aromatic dicarboxylic acid residue as an acid component and a dimerized fatty acid. ˜50 mol% and 1,4-butanediol residue 4 as glycol component
A polyester composed of 0 to 90 mol% and 10 to 60 mol% of a glycol residue having a carbon number of 10 or less other than 1,4-butanediol and contained in the dimerized fatty acid (i) The ratio of the monomer, (ii) dimer and (iii) trimer is (i): 3% or less (ii): 95% or more (iii): 3% or less, and the polyester melts. 2 at a viscosity of 250 ° C
Achievable with polyesters characterized by less than 500 poise.

In the present invention, the polyester is a hard segment having an aromatic dicarboxylic acid residue as a main constituent as an acid component, a soft segment having a residue composed of a dimerized fatty acid as a main constituent, and a glycol component as a glycol component. It is composed of a 1,4-butanediol residue and a glycol residue having 10 or less carbon atoms other than 1,4-butanediol.

In the present invention, the aromatic dicarboxylic acid residue constituting the hard segment is formed from an aromatic dicarboxylic acid and its ester-forming derivative. Specifically, the following may be mentioned.

[0009]

[Chemical 1]

(X in the formula is -O-, -SO-, -SO _2- , -C
(CH ₃ ) _2- , -CO-, n is 0 or 1. Further, the hydrogen atom bonded to the aromatic ring may be substituted with a halogen group. ).

In the present invention, examples of the acid component constituting the aromatic dicarboxylic acid residue include the following.

[0012]

[Chemical 2]

(Wherein R _{1 to} R ₆ are hydrogen atoms or alkyl groups, X is —O—, —SO—, —SO ₂ —, —C (CH ₃ ) ₂ —, —
CO-, n is 0 or 1. Further, the hydrogen atom bonded to the aromatic ring may be substituted with a halogen group. ).

Specific examples thereof include terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, diphenyldicarboxylic acid, diphenylsulfonedicarboxylic acid, diphenyletherdicarboxylic acid, benzophenonedicarboxylic acid, and ester-forming derivatives thereof. Of these, terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, and ester-forming derivatives thereof are preferable. These aromatic dicarboxylic acid components may be used alone or in combination of two or more.

In the present invention, the amount of the aromatic dicarboxylic acid residue is required to be 50 to 95 mol% of the acid component, more preferably 55 to 93 mol%, and further preferably 60 to 90 mol%. %. When the amount of the aromatic dicarboxylic acid residue is less than 50 mol%, the heat resistance of the polyester is lowered, and the mechanical properties of a molded product obtained from the polyester are lowered, which is not preferable. On the other hand, when it exceeds 95 mol%, the flexibility of the molded product is lowered, which is not preferable.

In the present invention, the dimerized fatty acid residue constituting the soft segment has 10 carbon atoms represented by the following formula.
It is formed from a dimerized fatty acid obtained by dimerizing 30 to 30 unsaturated fatty acids or an ester-forming derivative thereof.

CH ₃ (CH ₂ ) _k (CH = CH-CH ₂ ) _l (CH ₂ ) _m COOR (wherein R is a hydrogen atom or an alkyl group, and k is 1 to 2).
An integer of 5, l is an integer of 1 to 5, m is an integer of 0 to 25,
k, l and m satisfy the relational expression 8 ≦ k + 3l + m ≦ 28. ).

In the dimerization reaction of this unsaturated fatty acid,
Monomers, trimers, etc. are produced together with dimers, but the respective ratios must be 3% or less for the monomer, 95% or more for the dimer, and 3% or less for the trimer. More preferably, the monomer is 2% or less, the dimer is 96% or more, the trimer is 2% or less, and further preferably the monomer is 1.5% or less.
%, Dimers are 97% or more, and trimers are 1.5% or less. When the amount of the monomer is more than 3%, the reactivity of the polyester is lowered and the degree of polymerization cannot be increased, which is not preferable. Also,
If the dimer content is less than 95%, the flexibility of the molded product is reduced, which is not preferable. Further, if the trimer content exceeds 3%, the degree of crosslinking of the polyester increases, which lowers the degree of polymerization and mechanical properties, which is not preferable.

The dimerized fatty acid used in the polyester of the present invention has an unsaturated bond formed by the dimerization reaction, but even if it is used as it is, it is reduced by the hydrogenation reaction and used. It doesn't matter. However, hydrogenated dimerized fatty acid is preferable especially when heat resistance and weather resistance are required.

As the dimerized fatty acid that can be used in the polyester of the present invention, dimer acid which is a dimerized fatty acid having 36 carbon atoms is preferable. Dimer acid is obtained by dimerizing unsaturated fatty acid having 18 carbon atoms such as linoleic acid and linolenic acid, and is produced by many companies. Among them, the above conditions are met. As a high-quality dimer acid, Unichema International
"Pripol", or various ester-forming derivatives thereof, are commercially available from the National Corporation.
As these compounds, those which meet the conditions of the polyester polymerization reaction can be used. Further, one kind or two or more kinds of the above compounds may be used in combination.

In the present invention, the amount of the dimerized fatty acid residue is required to be 5 to 50 mol% of the acid component, more preferably 7 to 45 mol%, and further preferably 10 to 4 mol%.
It is 0 mol%. 50 mol% of dimerized fatty acid residue
If it exceeds, the heat resistance of the polyester is lowered, and the mechanical properties of a molded product obtained from the polyester are lowered, which is not preferable. On the other hand, if the amount of the dimerized fatty acid residue is less than 5 mol%, the flexibility of the molded product obtained from the polyester is lowered, which is not preferable.

In the present invention, the glycol component is 1,4
-Butanediol residue and 10 carbon atoms represented by the following formula
It consists of glycol residues other than 1,4-butanediol below. —O—Y—O— (Y in the formula is an alkylene group having 2 to 10 carbon atoms other than a tetramethylene group, or a alkylene group having a side chain of 1 to 4 alkyl groups or cycloalkyl groups. , Or a cycloalkylene group and an alkylene group, and the total number of carbon atoms thereof does not exceed 10.).

Specific compounds constituting the glycol residue here include ethylene glycol, 1,3-propanediol, 1,2-propanediol, 2-methyl-1,3-propanediol, 1,3- Butanediol, 1,2-butanediol, 1,5-pentyl glycol, 2,2-dimethyl-1,3-propanediol,
2-ethyl-1,3-propanediol, 1,6-hexanediol, 2-methyl-2-ethyl-1,3-propanediol, 1,8-octanediol, 1,10-
Decanediol, 1,3-cyclobutane dimethanol,
1,3-cyclopentane dimethanol, 1,4-cyclohexane dimethanol and the like can be mentioned.

In the present invention, the amount of the 1,4-butanediol residue is required to be 40 to 90 mol%, more preferably 42 to 88 mol%, and still more preferably 45 to 90 mol%.
It is 85 mol%. On the other hand, the amount of glycol residue residues having 10 or less carbon atoms other than 1,4-butanediol is 10 to 6
0 mol% is preferable, and 12 to 58 mol% is more preferable.
And more preferably 15 to 55 mol%.
When the amount of the 1,4-butanediol residue exceeds 90 mol%, or the number of carbon atoms other than 1,4-butanediol is 10
When the amount of the following glycol residue residue is less than 10 mol%,
The flexibility of the molded product obtained from polyester is lowered, which is not preferable. On the other hand, when the amount of 1,4-butanediol residue is less than 40 mol%, or the amount of glycol residue residue having 10 or less carbon atoms other than 1,4-butanediol is 60% or less.
If it exceeds mol%, the crystallization rate of the polyester will decrease, and during molding, adhesion will occur and molding will be difficult, and the transparency of the resulting molded article will also decrease, such being undesirable.

As described above, the objects of the present invention are 1,4-
It can be achieved only by copolymerizing both butanediol and glycol having 10 or less carbon atoms other than 1,4-butanediol within a specific range. 1,
When 4-butanediol is used alone or in an amount of 90 mol% or more, the flexibility of the molded product obtained from polyester decreases and the crystallization rate is too high. It is not preferable because it becomes transparent and loses transparency. On the other hand, when only glycols having 10 or less carbon atoms other than 1,4-butanediol are used, the polyester crystallization rate becomes low and molding becomes difficult, which is not preferable.

As the structure of the polyester of the present invention, for example, each segment represented by the following formula is preferably a linear polymer in which block or random arrangement is made. p [-OC-Ar-COO- Y-0-] q [-OC-Ar-COOCH 2 CH 2 CH 2 CH 2 0-] r [-OC-D-COO-Y-0-] s [-OC -D-COO-CH ₂ CH ₂ CH ₂ CH ₂ 0-] (However, Ar in the formula is

[0027]

[Chemical 3]

X is --O-- which is an aromatic functional group represented by
_{, -SO-, -SO 2 -, -C} (CH 3) 2 -, - CO-, n is 0 or 1, a hydrogen atom bonded to the aromatic ring may be substituted with a halogen group. D is a portion of the dimerized fatty acid excluding the carboxyl group, and Y is an alkylene group having 2 to 10 carbon atoms other than the tetramethylene group, or a side chain composed of 1 to 4 alkyl groups in the alkylene group. And the total number of carbon atoms in the main chain and side chains is 1
It does not exceed 0. Furthermore, p, q, r, and s are coefficients representing the number of each segment in one polyester molecule, and are integers of 1 to 50. ). The total value (p + q + r + s) of the coefficients of the above formula is not particularly limited, but is preferably 5 or more and 200 or less in order to obtain good moldability and mechanical properties.

In the present invention, in addition to the above components, other components may be copolymerized within the range not impairing the object of the present invention. For example, as the acid component, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid,
1,2-cyclohexanedicarboxylic acid, 5-sodium sulfoisophthalic acid, trimellitic acid, trimesic acid, etc., or their ester derivatives, p-oxybenzoic acid, p-hydroxymethylbenzoic acid, etc. as a hydroxycarboxylic acid component, or them 1, 12-dodecanediol, diethylene glycol, polyoxyalkylene glycol, 1,2-cyclohexanediol, 1,3-cyclohexanediol, 1,4-cyclohexanediol, spiroglycol or bisphenol as an alcohol component A, bisphenol S and ethylene oxide adducts thereof,
Trimethylolpropane and the like can be mentioned.

The polyester of the present invention comprises a crystal nucleating agent, an antioxidant, an anti-coloring agent, a pigment, a dye, an ultraviolet absorber, a releasing agent, a lubricant, a flame retardant, an antistatic agent, an inorganic and It is possible to mix organic particles and / or the like.

In the present invention, the melt viscosity of the polyester at 250 ° C. is required to be less than 2500 poise, more preferably less than 2400 poise, and further preferably less than 2300 poise.
When the melt viscosity of the polyester is 2500 poise or more, when the polyester is extrusion-molded into a film or the like, the extrusion state is not stable and a film having an uneven film thickness is provided. Furthermore, it is not preferable because the part where the wall thickness is partially becomes white and becomes spotted.

In the present invention, the intrinsic viscosity of the polyester is 0.2 in order to obtain good moldability and mechanical properties.
Is preferably 3.0 to 3.0, more preferably 0.3.
To 2.0, and more preferably 0.4 to 1.5.

In the present invention, the glass transition point (Tg) of the polyester is preferably 20 ° C. or lower, more preferably 15 ° C. or lower, and further preferably 10 ° C. or lower in order to obtain good flexibility. .

In the present invention, the melting point (T
m) is 1 in order to obtain good heat resistance and mechanical properties.
The temperature is preferably 20 ° C. or higher, more preferably 150 ° C. or higher, still more preferably 170 ° C. or higher.

In the present invention, the crystallization rate (ΔTc) of the polyester is preferably 40 ° C. or higher, more preferably 50 ° C. or higher, and further preferably 60 ° C. or higher in order to obtain good moldability. ..

The method for producing the polyester in the present invention is not particularly limited. For example, aromatic dicarboxylic acid and dimerized fatty acid or lower alkyl ester thereof, and 1,4-butanediol and 1,4 -From glycols having 10 or less carbon atoms other than butanediol,
The most general method is to produce by a first-step reaction for producing a low polymer by an esterification reaction or a transesterification reaction and a second-step reaction for polycondensing this low polymer. More specifically explaining the above method, dimethyl terephthalate, dimethyl dimer acid, ethylene glycol, 1,4-butanediol, charged into a polymerization reactor equipped with a stirrer, a nitrogen gas introduction tube, a vacuum distillation apparatus, The transesterification reaction is carried out by heating with stirring at a temperature of 150 to 250 ° C. while flowing nitrogen.
After that, the pressure is gradually reduced, and the pressure is reduced to 0.001 to 3 Torr.
Polycondensation reaction is performed at a temperature of 200 to 300 ° C. to obtain polyester. During this reaction, transesterification catalysts such as titanium, lead, zinc, calcium, magnesium and manganese compounds, polycondensation catalysts such as antimony, germanium and titanium compounds, antioxidants and stabilizers such as phosphorus compounds are used. be able to. Further, it is possible to increase the molecular weight by solid phase polymerization within the scope of the present invention.

The polyester of the present invention can be molded into fibers, films and other molded products for use. The molding method will be described below by taking a film as an example. The obtained polyester is sufficiently dried, melt-extruded by an extruder, discharged from a sheet-shaped or cylindrical die, and introduced into a cooling roll or a refrigerant such as water to be cooled and solidified. Here, when it is extruded into a sheet, a calender casting method in which it is cooled and solidified while being pressurized between at least a pair of rolls is preferable because the transparency and mechanical properties of the obtained film are good.

In the present invention, the film haze of the film obtained from polyester is 10% or less, or 5% or less, and further 3% or less in the case of a film having a thickness of 400 μm or less, and transparency is good.

In the present invention, the Young's modulus of the film obtained from polyester is 1 to 30 kg / mm ² , or ² to 28 kg / mm ² , and further 3 to 25 kg / m 2.
It has m ² and is excellent in shape retention and flexibility.

In the present invention, the elastic recovery rate of the film obtained from polyester is 50% or more, or 60%.
% Or more, and further 70% or more, the mechanical properties are good.

[0041]

EXAMPLES The present invention will now be described in more detail with reference to examples. The characteristics in the examples were measured as follows.

(1) Composition ratio of dimer acid The composition ratio was determined from the peak area of each component by analysis by high performance liquid chromatography.

(2) Intrinsic viscosity of polyester Measured at 25 ° C. using o-chlorophenol as a solvent.

(3) Thermal Characteristics of Polyester 10 mg of polyester was placed in a sample pan and scanned with a differential scanning calorimeter at a speed of 10 to 20 ° C./min to obtain Tg and T.
m, Tc, and Tc 'were measured. In addition, ΔTc was calculated by the following equation.

ΔTc = Tc'-Tc Tc: Crystallization temperature when increasing temperature Tc ': Crystallization temperature when decreasing temperature (4) Polyester composition analysis Polyester is hydrolyzed with an alkali to obtain an acid component and a glycol component, respectively. Separated, each component was analyzed by gas chromatography or high performance liquid chromatography, and the composition ratio was determined from the peak area of each component.

(5) Melt viscosity of polyester It was measured at 250 ° C. using a melt index.

(6) Film haze Regarding the film obtained from polyester, JIS
The film haze was measured according to K-6714, and converted into 100 μm by the following formula to obtain.

H ₁₀₀ (%) = H × 100 / d H: Measured value of haze (%) d: Film thickness of the haze measurement part (μm) (7) Young's modulus ASTM of a film obtained from polyester
Young's modulus was measured according to D-882-81 (method A).

(8) Elastic Recovery Rate A film obtained from polyester was sampled in a width of 10 mm, mounted on a tensile tester so that the test length was 50 mm, and the tensile speed was 10 mm / min.
A tensile deformation of 0% was applied, and the sample was immediately contracted at the same speed, and the sample length (L) when the tensile stress became 0 was measured and calculated by the following formula.

Elastic recovery rate = (75−L) / 25 × 100 (%) Example 1 61 parts by weight of dimethyl terephthalate, 0.1% of monomer,
36 carbons consisting of 98.5% dimer and 1.4% trimer
33 parts by weight of dimethyl dimer acid, 20 parts by weight of ethylene glycol, 40 parts by weight of 1,4-butanediol and 0.1 part by weight of tetrabutyl titanate as a transcondensation reaction catalyst are added according to a conventional method. Then, polycondensation reaction was carried out at a high temperature under reduced pressure to obtain a copolyester having a melt viscosity of 1300 poise and an intrinsic viscosity of 0.85. The composition of the obtained polyester was 85 mol% of terephthalic acid residues and 1 of dimer acid residues.
5 mol%, ethylene glycol residue 20 mol%, 1,4
-Butanediol residue was 80 mol%. The infrared absorption spectrum of polyester measured by the thin film method is shown in FIG.
It was as shown in. As is clear from FIG. 1, the absorption due to the C═O stretching vibration based on the ester bond was 1730
The absorption due to the CO stretching vibration is 1270 and 12 cm- ^1.
It was observed at 50, 1170, 1150 cm ⁻¹ and the formation of polyester was confirmed. Further, absorption by the aliphatic C—H stretching vibration was observed at 2940 and 2860 cm ^−1, and the presence of dimer acid was confirmed. The obtained polyester had a Tg of -4 ° C, a Tm of 180 ° C and a ΔTc of 150 ° C, and had a high melting point and high crystallinity. The obtained polyester was formed into a film by a conventional method. The film-forming property was good, and a film having a thickness of 100 μm was obtained. The resulting film had a haze of 1.0%, a Young's modulus of 15 kg / mm ² , and an elastic recovery rate of 82%, and was excellent in transparency, flexibility and elastic recovery.

Comparative Example 1 66 parts by weight of dimethyl terephthalate, 0.1% of monomer,
36 carbons consisting of 98.5% dimer and 1.4% trimer
A copolymerized polyester having a melt viscosity of 2000 poise and an intrinsic viscosity of 0.65 was obtained in the same manner as in Example 1 except that 35 parts by weight of dimethyl dimer acid and 50 parts by weight of ethylene glycol were used. The composition of the obtained polyester was 85 mol% of terephthalic acid residues, 15 mol% of dimer acid residues, and 100 mol% of ethylene glycol residues. Tg of the obtained polyester is 20 ° C., Tm is 220 ° C.,
ΔTc was 35 ° C., which was low crystallinity. The obtained polyester was formed into a film by the same method as in Example 1, but it was difficult to form a film due to strong adhesion to the drum during film formation. The haze of the obtained film is 40.0% and the Young's modulus is 45 kg.
/ Mm ² , elastic recovery rate is 40%, transparency, flexibility,
The elastic recovery was poor.

Examples 2 to 10 and Comparative Examples 2 to 6 As shown in Tables 1 and 2, polyesters of each composition and films thereof were produced by the same method as in Example 1. However, in Example 6 and Comparative Example 6, solid phase polymerization was performed to prepare a predetermined degree of polymerization (intrinsic viscosity, melt viscosity).

[0053]

[Table 1]

[0054]

[Table 2]

The abbreviations in the table indicate the following compounds.

DMT: dimethyl terephthalate DMN: dimethyl 2,6-naphthalenedicarboxylate C36: dimethyl dimer (main chain carbon number 36) C44: dimerized fatty acid dimethyl (main chain carbon number 44) BG: ethylene glycol EG : 1,4-butanediol CHDM: 1,4-cyclohexanedimethanol NPG: 2,2-dimethyl-1,3-propanediol Further, each melt viscosity, intrinsic viscosity, glass transition point, melting point, crystallization rate, The film haze, Young's modulus, and elastic recovery rate were as shown in Table 3.

[0057]

[Table 3]

All of Examples 2 to 10 are within the scope of the present invention, and the obtained polyesters have heat resistance,
The crystallinity was excellent, the moldability was good, and the obtained film had good transparency, flexibility, and elastic recovery.

On the other hand, in Comparative Example 2, the glycol component consisted of only 1,4-butanediol and was outside the scope of the present invention, and the obtained polyester film had poor flexibility. Comparative Example 3 has a small dimer content of dimer acid, which is a dimerized fatty acid, and a large trimer content, which is outside the scope of the present invention, and the obtained polyester is gelled into a film or the like. Could not be molded. Comparative Example 4 had a large content of dimer acid, which is a dimerized fatty acid, and was outside the scope of the present invention. The obtained polyester had a low melting point and a low crystallization rate, and film formation was difficult. In Comparative Example 5, the content of dimer acid, which is a dimerized fatty acid, was small and was outside the range of the present invention, and the film made of the obtained polyester had a large Young's modulus and poor flexibility. Comparative Example 6 had a large melt viscosity, which was outside the range of the present invention, and the casting property at the time of molding was poor, and it was not possible to obtain a uniform film such as partial whitening and whitening.

[0060]

As described above, the polyester of the present invention has an aromatic dicarboxylic acid residue and a dimerized fatty acid residue as the acid component, and a 1,4-butanediol residue and a 1,4-butanediol residue as the glycol component. A glycol residue having 10 or less carbon atoms other than butanediol is constituted in a specific component ratio, and further adjusted to have a predetermined melt viscosity, so that unprecedented flexibility, transparency, heat resistance, film formation, etc. It has excellent moldability.

From the polyester of the present invention, fibers, films, sheets and other molded articles which have good flexibility, transparency and heat resistance and whose characteristic changes little with time can be obtained. In particular, since the polyester of the present invention has a high crystallization rate, it is easy to form films, sheets and other molded articles.

[Brief description of drawings]

FIG. 1 is an infrared absorption spectrum diagram of the polyester of Example 1 of the present invention.

Claims (1)

Claim: What is claimed is: 1. A repeating unit constituting a polyester, wherein an aromatic dicarboxylic acid residue of 50 to 95 is used as an acid component.
Mol% and residues of dimerized fatty acid of 5 to 50 mol%, glycol component of 1,4-butanediol residue of 40 to 90 mol% and glycol residue having 10 or less carbon atoms other than 1,4-butanediol (I) a monomer, (ii) a dimer and (i) a polyester composed of 10 to 60 mol% of groups and contained in a dimerized fatty acid.
ii) The proportion of trimers is (i): 3% or less (ii): 95% or more (iii): 3% or less, and the melt viscosity of the polyester is 2 at 250 ° C.
Polyester characterized by being less than 500 poise.