Polyester composition and preparation method thereof

Abstract

The invention discloses a polyester composition, which mainly contains a terephthalic acid structural unit and an alkylene glycol structural unit, and the polyester composition contains an isophthalic acid structural unit accounting for 1.0-10.0 wt% of the polyester composition and an aromatic sulfonate structural unit accounting for 2000-4500 ppm of the polyester composition in terms of sulfur element. The melting enthalpy of the polyester composition is 10-40 J / g. The polyester composition is dyeable at low temperature, has high shrinkage performance, and does not have the problem of adhesion when being dried.

Description

Technical Field

[0001] The present invention relates to a polyester composition and a preparation method thereof, and in particular to a polyester composition with excellent low-temperature dyeability, shrinkage and spinnability. Background Art

[0002] Due to its excellent mechanical properties and chemical characteristics, polyester resin is widely used in various fields, especially in daily textiles such as clothing and bedding.

[0003] Generally, clothing fibers are required to have certain dyeability and shrinkage properties. Because polyester molecular structures are highly regular and symmetrical, they have high crystallinity and poor shrinkage. Furthermore, polyester molecules do not contain dye-affinity groups, making dyeing difficult. Disperse dyes are generally required for dyeing under high temperature and high pressure or with a carrier, but the color spectrum is limited and the color is not bright enough. To improve the dyeability of polyester, lower the dyeing temperature, and obtain high-shrinkage polyester fibers, modified comonomers such as isophthalic acid components containing sulfonate groups and polyethylene glycol are generally added to the polyester. Chinese Patent CN101857671A discloses a high-shrinkage cationic normal-pressure easy-dyeing polyester chip and its preparation method. The polyester is modified using an isophthalic acid component containing a sulfonate group, polyethylene glycol, adipic acid, and an isophthalic acid component. The resulting modified polyester exhibits low-temperature dyeability and high shrinkage. However, polyethylene glycol can cause the polyester product to have poor light resistance, and the addition of a large amount of copolymer components can also cause the polyester's crystallinity to deteriorate, resulting in sticking during drying and low physical properties of the resulting yarn. Summary of the Invention

[0004] The present invention aims to provide a polyester composition having good light fastness, low temperature dyeability, and suitable crystallinity, and a method for preparing the same. Fibers made from the polyester have the characteristics of high boiling yield, high strength, and excellent color tone after low temperature dyeing.

[0005] The technical solution of the present invention:

[0006] A polyester composition mainly comprises terephthalic acid structural units and alkylene glycol structural units. The polyester composition contains 1.0 to 10.0 wt% of isophthalic acid structural units and 2000 to 4500 ppm of aromatic sulfonate structural units in terms of sulfur. The polyester composition has a melting enthalpy of 10 to 40 J / g.

[0007] The polyester composition preferably contains 5 to 10 wt% of an aliphatic dibasic acid structural unit as shown in Formula 1.

[0008]

[0009] In Formula 1, n is an integer of 6 to 12.

[0010] The aromatic sulfonate structural unit is preferably an isophthalic acid-5-sulfonate structural unit and / or a monocarboxybenzenesulfonate structural unit.

[0011] The glass transition temperature of the polyester composition is preferably 50 to 65° C., and the melt viscosity is preferably 2000 to 4000 poise.

[0012] The present invention also discloses a method for preparing the polyester composition. The method comprises adding terephthalic acid or its esterified derivative and alkylene glycol to an esterification kettle for esterification or transesterification, and then transferring the mixture to a polycondensation kettle for polycondensation to produce the polyester composition. At any stage before the end of the polycondensation reaction, an amount of isophthalic acid or its esterified derivative equivalent to 1.0 to 10.0 wt% of the polyester composition and an amount of aromatic sulfonate equivalent to 2000 to 4500 ppm of sulfur, calculated as elemental sulfur, are added to the polyester composition.

[0013] It is preferred to add an aliphatic dibasic acid represented by Formula 2 equivalent to 5 to 10 wt% of the polyester composition at any stage before the end of the polycondensation reaction.

[0014]

[0015] In Formula 2, n is an integer of 6 to 12.

[0016] The aromatic sulfonate is preferably 5-sulfonate of isophthalic acid or an esterified derivative thereof, and / or monocarboxybenzenesulfonate or an esterified derivative thereof.

[0017] The present invention controls the contents of isophthalic acid structural units and aromatic sulfonate structural units in the polyester composition, and adjusts the contents of the isophthalic acid structural units and aromatic sulfonate structural units within a limited range according to their contributions to the melting enthalpy of the polyester composition, so that the melting enthalpy of the polyester composition is within the range of 10 to 40 J / g. In this way, the polyester composition can be dyed at low temperatures and has high shrinkage properties, and will not cause the problem of sticking during drying. DETAILED DESCRIPTION

[0018] The polyester composition of the present invention primarily comprises terephthalic acid structural units and alkylene glycol structural units. Specifically, the alkylene glycol structural units may be ethylene glycol structural units, propylene glycol structural units, butylene glycol structural units, etc. Depending on the alkylene glycol structural units, the polyester composition may be specifically polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, etc.

[0019] At the same time, the polyester composition also contains isophthalic acid structural units and aromatic sulfonate structural units.

[0020] The isophthalic acid structural unit can effectively increase the amorphous region in the polyester composition, thereby reducing the crystallinity of the polyester composition and improving the shrinkage of the polyester composition. In addition, the increase in the amorphous region also helps to increase the contact space between the dye and the polyester composition molecules, reduce the dyeing temperature, and improve the dyeing performance of the polyester composition.

[0021] The isophthalic acid structural units are derived from isophthalic acid or its esterified derivatives added during the preparation of the polyester composition, and their content accounts for 1.0 to 10.0 wt% of the polyester composition. When the content of the isophthalic acid structural units in the polyester composition is less than 1.0 wt%, the amorphous region in the polyester composition cannot be effectively increased, the shrinkage of the polyester composition cannot be improved, and the purpose of low-temperature dyeing cannot be achieved. When the content of the isophthalic acid structural units in the polyester composition is higher than 10.0 wt%, a large amount of isophthalic acid structural units will lead to a significant increase in the amorphous region in the polyester composition and a rapid decrease in crystallinity, causing the polyester composition slices to easily stick together during the subsequent drying process, which is not conducive to spinning. At the same time, a large amount of isophthalic acid structural units will also lead to poor strength and hydrolysis resistance of the polyester composition. After the polyester composition is made into fibers and undergoes the dyeing process, the strength of the fibers is further reduced. Taking into account the dyeability, shrinkage, strength and hydrolysis resistance of the polyester composition, the content of the isophthalic acid structural unit in the polyester composition of the present invention is preferably 4.0 to 10.0 wt%, more preferably 6.0 to 9.0 wt%.

[0022] The aromatic sulfonate structural unit contains sulfonate groups, which bind well to cationic dyes and thus impart cationic dyeability to the polyester composition. The aromatic sulfonate structural unit is present in an amount of 2000 to 4500 ppm, calculated as elemental sulfur, of the polyester composition. If the aromatic sulfonate structural unit is present in an amount less than 2000 ppm, the resulting polyester composition product may struggle to achieve satisfactory color depth after dyeing. If the aromatic sulfonate structural unit is present in an amount greater than 4500 ppm, the viscosity-increasing effect of the sulfonate groups inhibits the growth of the polyester molecular chain during synthesis, resulting in poor physical properties such as strength. Considering the dyeability and physical properties of the polyester composition, the aromatic sulfonate structural unit of the present invention is preferably present in an amount of 3000 to 4000 ppm, calculated as elemental sulfur, of the polyester composition.

[0023] The present invention does not particularly limit the specific material of the aromatic sulfonate structural unit; any material conventionally used to impart cationic dyeability to polymers may be used. Considering the dyeability and spinnability of the polyester composition, the aromatic sulfonate structural unit is preferably an isophthalic acid 5-sulfonate structural unit and / or a monocarboxybenzenesulfonate structural unit. The sulfonate may be sodium sulfonate, lithium sulfonate, potassium sulfonate, or the like.

[0024] Melting enthalpy (ΔHm) is an indicator used to characterize the crystallinity of a polyester composition. A higher ΔHm indicates a greater number of crystalline regions within the polyester composition. This indicates excellent crystallinity, effectively preventing chip sticking during the subsequent drying process, and resulting in fibers with excellent strength and elongation. As the ΔHm value decreases, the amorphous regions in the polyester composition increase, improving shrinkage and lowering dyeing temperatures. However, when ΔHm decreases to a certain level, chips tend to stick during drying, negatively impacting spinning. Therefore, only by controlling ΔHm within an appropriate range can a polyester composition with high shrinkage, good strength, easy dyeing, and no sticking during drying be achieved.

[0025] The present invention mainly controls the ΔHm of the polyester composition by limiting the content of the isophthalic acid structural unit and the aromatic sulfonate structural unit in the polyester composition. However, it does not mean that as long as the content of the isophthalic acid structural unit and the aromatic sulfonate structural unit is within the limited range, a polyester composition with a ΔHm of 10 to 40 J / g can be obtained. This is because the isophthalic acid structural unit and the aromatic sulfonate structural unit have different contributions to the ΔHm of the polyester composition. Therefore, a polyester composition with a ΔHm of 10 to 40 J / g needs to be obtained through a reasonable combination within the limited range of the content of the isophthalic acid structural unit and the aromatic sulfonate structural unit. Specifically, the relationship between the ΔHm of the polyester composition and the isophthalic acid structural unit and the aromatic sulfonate structural unit can be expressed by the following formula,

[0026] ΔHm=67 J / g-(content of isophthalic acid structural units×355 J / g+content of sulfur element×0.006 J / g).

[0027] When calculating the isophthalic acid content, divide the percentage by 100. Substitute the sulfur content in ppm for the percentage. For example, if the isophthalic acid content is 7.5 wt% and the sulfur content is 3600 ppm, ΔHm = 67 J / g - (0.075 × 355 J / g + 3600 × 0.006 J / g) = 18.775 J / g, approximately 19 J / g.

[0028] Therefore, the ΔHm described in the present invention can be regarded as a further limitation on the composition of the polyester composition.

[0029] The polyester composition of the present invention preferably contains 5 to 10 wt% of the aliphatic dibasic acid structural unit as shown in Formula 1.

[0030]

[0031] In Formula 1, n is an integer of 6 to 12.

[0032] The aliphatic dibasic acid structural unit represented by Formula 1 further improves the shrinkage of the polyester composition. If the molecular chain of the aliphatic dibasic acid structural unit represented by Formula 1 is too short or the content is too low, the shrinkage of the polyester composition will not be effectively improved. If the molecular chain of the aliphatic dibasic acid structural unit represented by Formula 1 is too long or the content is too high, the crystallinity of the polyester composition will be further reduced, resulting in sticking during subsequent drying and low strength of the resulting fiber. Considering the shrinkage and drying properties of the polyester composition, the content of the aliphatic dibasic acid structural unit represented by Formula 1 is more preferably 7-10 wt%, and most preferably 8-10 wt%.

[0033] While the aliphatic dibasic acid structural unit shown in Formula 1 can improve the shrinkage of the polyester composition, it also reduces the melting enthalpy of the polyester composition. If the aliphatic dibasic acid structural unit is not present properly, the melting enthalpy of the polyester composition may be reduced, making it more susceptible to sticking during drying. The effect of the aliphatic dibasic acid structural unit shown in Formula 1 on the melting enthalpy of the polyester composition can be expressed by the following formula:

[0034] ΔHm=67 J / g-(content of isophthalic acid structural units×355 J / g+content of sulfur element×0.006 J / g)-content of aliphatic dibasic acid structural units×aJ / g.

[0035] Similar to the content of isophthalic acid structural units, the content of aliphatic dibasic acid structural units is calculated by dividing the percentage by 100. The value of a in this formula varies depending on the number of n in the aliphatic dibasic acid structural unit, as shown in Formula 1. Specifically, when n = 6, a is 14; when n = 7, a is 20; when n = 8, a is 25; when n = 9, a is 27; when n = 10, a is 28; when n = 11, a is 30; and when n = 12, a is 35.

[0036] The present invention controls the contents of isophthalic acid structural units and aromatic sulfonate structural units to conform to certain rules. When aliphatic dibasic acid structural units are further contained, their contents are also adjusted so that the melting enthalpy of the final polyester composition is within the range of 10 to 40 J / g, thereby achieving the effects of high shrinkage, high strength, easy dyeing and non-stickiness.

[0037] The glass transition temperature of the polyester composition of the present invention is preferably 50-65° C., so that the polyester composition can be dyed at low temperatures while avoiding adhesion during storage or drying.

[0038] The melt viscosity of the polyester composition is preferably 2000 to 4000 poise, so as to maintain the strength of the polyester composition.

[0039] The present invention does not impose any particular limitation on the synthesis method of the polyester composition. Depending on the raw materials, it can be a direct polymerization method or an ester exchange method. Depending on the polymerization process, it can be a batch polymerization method or a continuous polymerization method.

[0040] Specifically, the present invention provides a synthesis method, comprising adding terephthalic acid or an esterified derivative thereof and an alkylene glycol to an esterification reactor for esterification or transesterification, and then transferring the mixture to a polycondensation reactor for polycondensation to produce a polyester composition. At any stage before the end of the polycondensation reaction, an amount of isophthalic acid or an esterified derivative thereof equivalent to 1.0 to 10.0 wt% of the polyester composition and an amount of an aromatic sulfonate equivalent to 2000 to 4500 ppm of elemental sulfur to the polyester composition are added.

[0041] The arbitrary stage before the end of the polycondensation reaction may be the start of the esterification or transesterification reaction, the stage after the end of the esterification or transesterification reaction and before the polycondensation reaction, or the stage during the polycondensation reaction.

[0042] When the amount of isophthalic acid or its esterified derivative added is less than 1.0 wt% relative to the polyester composition, the amorphous region in the polyester composition cannot be effectively increased, the shrinkage of the polyester composition cannot be improved, and the purpose of low-temperature dyeing cannot be achieved. When the amount of isophthalic acid or its esterified derivative added is greater than 10.0 wt% relative to the polyester composition, a large amount of isophthalic acid or its esterified derivative will lead to a significant increase in the amorphous region in the polyester composition and a rapid decrease in crystallinity, causing the polyester composition slices to easily stick together during the subsequent drying process, which is not conducive to spinning. Furthermore, a large amount of isophthalic acid or its esterified derivative will also reduce the strength and hydrolysis resistance of the polyester composition. After the polyester composition is formed into fibers and subjected to the dyeing process, the strength of the fibers is further reduced. Considering the dyeability, shrinkage, strength, and hydrolysis resistance of the polyester composition, the amount of isophthalic acid or its esterified derivative added in the present invention is preferably 4.0 to 10.0 wt% relative to the polyester composition, and more preferably 6.0 to 9.0 wt%.

[0043] When the amount of the aromatic sulfonate added is less than 2000 ppm, calculated as elemental sulfur, in the polyester composition, the resulting polyester composition product fails to achieve satisfactory color depth after dyeing. When the amount of the aromatic sulfonate added is greater than 4500 ppm, the viscosity-increasing effect of the sulfonate groups inhibits the growth of the polyester molecular chain during the synthesis process, resulting in poor physical properties such as strength. Considering the dyeability and physical properties of the polyester composition, the amount of the aromatic sulfonate added in the present invention is preferably 3000 to 4000 ppm, calculated as elemental sulfur, in the polyester composition.

[0044] The aromatic sulfonate is preferably 5-isophthalic acid sulfonate or its esterified derivatives, and / or monocarboxybenzenesulfonate or its esterified derivatives. Specifically, the 5-isophthalic acid sulfonate or its esterified derivatives may be a small molecular weight sulfonate such as 5-isophthalic acid sulfonate, dimethyl isophthalate-5-sulfonate, monomethyl isophthalate-5-sulfonate, monoethyl isophthalate-5-sulfonate, diethylene glycol isophthalate-5-sulfonate, or dibutylene glycol isophthalate-5-sulfonate; the monocarboxybenzenesulfonate or its esterified derivatives may be 3-carboxybenzenesulfonate, 3-ethylene glycol formate benzenesulfonate, 3-methyl formate benzenesulfonate, methyl p-formate benzenesulfonate, p-carboxybenzenesulfonate, or ethylene glycol p-formate benzenesulfonate. The sulfonate may be sodium sulfonate, lithium sulfonate, potassium sulfonate, or the like.

[0045] At any stage before the end of the polycondensation reaction, it is also preferred to add 5 to 10 wt% of the polyester composition.

[0046] The aliphatic dibasic acid shown in formula 2,

[0047]

[0048] n is an integer from 6 to 12.

[0049] If the molecular chain of the aliphatic dibasic acid represented by Formula 2 is too short or the amount added is too small, the shrinkage of the polyester composition will not be effectively improved. If the molecular chain of the aliphatic dibasic acid represented by Formula 2 is too long or the amount added is too large, the crystallinity of the polyester composition will be further reduced, resulting in sticking during subsequent drying and low strength of the resulting fiber. Considering the shrinkage and drying properties of the polyester composition, the addition amount of the aliphatic dibasic acid represented by Formula 2 is more preferably 7-10 wt%, and most preferably 8-10 wt%.

[0050] According to conventional polyester preparation methods, appropriate reaction temperatures, pressures, and catalysts can be selected during the esterification or transesterification reaction and the polycondensation reaction. For example, the catalyst can include antimony catalysts such as antimony glycolate and antimony trioxide; titanium catalysts such as tetrabutyl titanate, tetraethyl titanate, tetraisopropyl titanate, and tert-butyl titanate; acetate catalysts such as lithium acetate, sodium acetate, zinc acetate, manganese acetate, calcium acetate, cobalt acetate, and magnesium acetate; and other metal oxide catalysts such as zinc oxide, tin oxide, and stannous oxide. Depending on the desired functionality, one or more of the following may be added during the polyester synthesis process: compatibilizers, plasticizers, fluorescent brighteners, mold release agents, antimicrobial agents, nucleating agents, antioxidants, antistatic agents, conditioning agents, matting agents, defoaming agents, preservatives, gelling agents, emulsifiers, fillers, inks, colorants, dyes, pigments, and fragrances. Anti-adhesion agents, pigments, and colorants may also be added during the drying process of the polyester chips.

[0051] The physical properties mentioned in the examples were measured by the following methods.

[0052] (1) Dyeing performance (L value)

[0053] Cationic dyeable polyester fiber (yarn varieties 36T-33f) was knitted into a tube. The fabric was then dyed with a commercially available cationic black dye (5% owf) at 105°C. The fabric was then soaped, washed, and air-dried. The fabric's lightness (L) value was measured. A lower L value indicates better dyeing. The final data was the average of 10 tests.

[0054] (2) Boiling water shrinkage

[0055] Polyester chips were melt-spun at 285°C and a spinning speed of 2500 m / s to produce polyester fiber yarn. The resulting yarn was then stretched to an elongation of 35% to 40%, resulting in a yarn variety of 36T-33f. Ten turns of yarn were then wound using a 1-meter / turn yarn winder. A weight equal to the yarn weight was applied, and the yarn length, L1, was measured. The yarn was then placed in boiling water at 95°C for 30 minutes, air-dried for 24 hours, and measured using the same method as above for length, L2. Boiling water shrinkage = (L1-L2) / L1 × 100%.

[0056] (3) Sulfur content

[0057] After 5 g of the polyester composition was pressed into a pellet, the intensity of the elements was measured using a fluorescent X-ray analyzer and converted using a test line prepared in advance for a sample with a known sulfur content.

[0058] (4) Glass transition temperature, melting enthalpy ΔHm

[0059] Using a differential scanning calorimeter, the polyester composition chips were heated from room temperature to 300° C. at a rate of 5° C. / min, and the glass transition temperature and the enthalpy during melting endotherm were measured, which was the melting enthalpy.

[0060] (5) Content of isophthalic acid structural unit and aliphatic dibasic acid structural unit

[0061] A certain amount of polyester chips was dissolved in trifluoroacetic acid and subjected to H 1 -NMR test. The ratio is calculated based on the peak area of ​​the characteristic groups of the copolymer units.

[0062] (6) Fiber strength-elongation product

[0063] The polyester chips were melt-spun at 285°C and a spinning speed of 2500 m / s to obtain polyester fiber yarns. The resulting yarns were then stretched to an elongation of 35% to 40%. The resulting yarns were of the 36T-33f variety. Strength and elongation were determined in accordance with JIS L1013:2010 (Test methods for chemical fibers, medium and long fibers) 8.8.1. Strength and elongation were measured using an ORIENTEC Co., RTC-1225A strength-elongation testing machine. Strength-elongation product = strength × (elongation). 0.5 .

[0064] (7) Melt viscosity

[0065] The dried polyester was kept at 285℃ for 5min using a capillary rheometer under a nitrogen atmosphere. -1 The melt viscosity was obtained by testing at a shear rate of .

[0066] (8) Slice adhesion rate during drying

[0067] A cylindrical container with a diameter of 5 cm and a height of 20 cm is filled with polyester composition chips weighing 2-3 g per 100 particles (i.e., 100 chips weigh 2-3 g). The total height of the polyester composition chips in the container is 15 cm. The weight of the chips added is measured as m1. The cylindrical container containing the chips is then exposed to hot air at 130°C and shaken every 5 minutes. After 25 minutes, the container is removed and filtered through a 5 mm sieve. The weight of the chips remaining on the sieve is recorded as m2. The adhesion ratio = m2 / m1 × 100%.

[0068] The technical solution of the present invention is described in more detail below through specific implementation methods, but the present invention is not limited to these implementation methods.

[0069] Example 1

[0070] Add dihydroxyethyl terephthalate to the esterification tank 1, maintain the temperature at 250°C and normal pressure, mix terephthalic acid and ethylene glycol at a molar ratio of 1:1.15, and then put it into the reactor for esterification reaction. When the theoretical water output is reached, move it to the esterification tank 2, add isophthalic acid accounting for 7.5wt% of the polyester composition at a temperature of 225°C, stir for 20 minutes, and then add ethylene glycol to make the molar ratio of terephthalic acid to total ethylene glycol 1:1.4. After stirring for 10 minutes, add dihydroxyethyl terephthalate equivalent to 3600ppm of the polyester composition in terms of sulfur. After adding the ethylene glycol solution of sodium 5-ethyl sulfonate and stirring for 20 minutes, 80 ppm of phosphoric acid (calculated as P element) and 250 ppm of ethylene glycol antimony catalyst (calculated as Sb element) were added to the polyester composition. After stirring for 10 minutes, the mixture was transferred to a polymerization kettle for polycondensation. The polymerization temperature was 285°C. During the polymerization, the melt viscosity of the polymer was adjusted by adjusting the power or current of the stirring rod motor of the polymerization kettle. When the viscosity reached 3200 poise, the polymer was discharged and pelletized to obtain the desired polyester composition. The polyester composition chips were melt-spun at 285°C to produce polyester fibers. Specific physical properties are shown in Table 1.

[0071] Examples 2 to 15

[0072] A polyester composition was prepared in the same manner as in Example 1, except that the addition amount of isophthalic acid, the type and amount of aromatic sulfonate, the type and amount of aliphatic dibasic acid, and the melt viscosity during dispensing were changed. Specific data are shown in Tables 1 and 2.

[0073] Comparative Example 1

[0074] The addition amounts of isophthalic acid and sodium diethyl 5-sulfoisophthalate were changed, and the other conditions were the same as in Example 1 to prepare a polyester composition with a melting enthalpy of 5 J / g. Specific data are shown in Table 2.

[0075] Since the melting enthalpy is too low, the strength-elongation product of the polyester composition is small and the adhesion rate of the chips is high.

[0076] Comparative Example 2

[0077] The amount of isophthalic acid added was changed, and the other conditions were the same as in Example 1 to prepare a polyester composition. Specific data are shown in Table 2.

[0078] Due to the excessive amount of isophthalic acid, the melting enthalpy of the polyester composition is too low to be detected, the strength-elongation product of the polyester composition is small, and the adhesion rate of the chips is high.

[0079] Comparative Example 3

[0080] The addition amounts of isophthalic acid and sodium diethyl 5-sulfoisophthalate were changed, and the other conditions were the same as in Example 1 to prepare a polyester composition with a melting enthalpy of 51 J / g. Specific data are shown in Table 2.

[0081] Since the melting enthalpy is too high, the boiling water shrinkage of the polyester composition is low and the L value after dyeing is high, which means that the dyeability is poor.

[0082] Comparative Example 4

[0083] The addition amount of sodium diethyl 5-sulfoisophthalate was changed, and the other steps were the same as in Example 1 to prepare a polyester composition. Specific data are shown in Table 2.

[0084] Since the amount of sodium diethyl 5-sulfoisophthalate is too low, the resulting polyester composition may have a problem of poor dyeability even if the melting enthalpy of the polyester composition is within a specified range.

[0085] Comparative Example 5

[0086] The addition amount of sodium diethyl 5-sulfoisophthalate was changed, and the other conditions were the same as in Example 1, to prepare a polyester composition having a melting enthalpy of 4 J / g. Specific data are shown in Table 2.

[0087] Since the melting enthalpy is too low, the strength-elongation product of the polyester composition is small and the adhesion rate of the chips is high.

[0088] Comparative Example 6

[0089] Without adding isophthalic acid, the other conditions were the same as in Example 1, and a polyester composition with a melting enthalpy of 45 J / g was prepared. Specific data are shown in Table 2.

[0090] Since no isophthalic acid is added, the polyester composition has a higher melting enthalpy, a lower boiling water shrinkage and poor dyeability.

[0091]

[0092]

Claims

1. A polyester composition comprising mainly terephthalic acid structural units and alkylene glycol structural units, characterized in that: The polyester composition contains 1.0-10.0 wt% of isophthalic acid structural units and 2000-4500 ppm of aromatic sulfonate structural units in terms of sulfur. The melting enthalpy of the polyester composition is 10-40 J / g.

2. The polyester composition according to claim 1, wherein: The polyester composition contains 5 to 10 wt% of an aliphatic dibasic acid structural unit as shown in Formula 1. In Formula 1, n is an integer of 6 to 12.

3. The polyester composition according to claim 1 or 2, characterized in that: The aromatic sulfonate structural unit is an isophthalic acid-5-sulfonate structural unit and / or a monocarboxybenzenesulfonate structural unit.

4. The polyester composition according to claim 1 or 2, characterized in that: The glass transition temperature of the polyester composition is 50-65°C.

5. The polyester composition according to claim 1 or 2, characterized in that: The polyester composition has a melt viscosity of 2000 to 4000 poise.

6. The method for preparing the polyester composition according to claim 1, wherein terephthalic acid or its esterified derivative and alkylene glycol are added to an esterification kettle for esterification or transesterification reaction, and after the reaction is completed, the mixture is transferred to a polycondensation kettle for polycondensation reaction to obtain the polyester composition, wherein: At any stage before the end of the polycondensation reaction, 1.0 to 10.0 wt% of isophthalic acid or its esterified derivative and 2000 to 4500 ppm of aromatic sulfonate are added to the polyester composition in terms of sulfur.

7. The method for preparing the polyester composition according to claim 6, wherein: At any stage before the end of the polycondensation reaction, an aliphatic dibasic acid represented by formula 2 is added, which is equivalent to 5 to 10 wt% of the polyester composition. In Formula 2, n is an integer of 6 to 12.

8. The method for preparing the polyester composition according to claim 6 or 7, characterized in that: The aromatic sulfonate is 5-isophthalic acid sulfonate or its esterified derivative, and / or monocarboxybenzene sulfonate or its esterified derivative.

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