A polyester and its preparation method, a hydrolysis-resistant polyester film and its preparation method and application

Abstract

The present invention discloses a hydrolysis-resistant polyester and its preparation method, a hydrolysis-resistant film thereof and its preparation method and application. The polyester is obtained by reacting components including diol, dicarboxylic acid and maleic anhydride-grafted polyolefin. The polyester film is obtained by an extrusion film-forming process from the polyester. The polyester film can be applied in a solar cell backplane and has excellent hydrolysis resistance.

Description

Technical Field

[0001] The present invention relates to the field of polyester films, and specifically, to a polyester and its preparation method, a hydrolysis-resistant polyester film and its preparation method and application. Background Art

[0002] As a crystalline polymer, thermoplastic polyester has advantages such as good mechanical properties, dimensional stability, dielectric properties, and chemical corrosion resistance, and has been widely used in fields such as fibers and films. However, due to the large number of ester bonds in polyester, its hydrolysis resistance is poor, and it is very easy to degrade especially in humid and hot conditions. For example, when applied in the field of photovoltaic backsheets, ordinary polyester cannot meet the requirements of the service life of photovoltaic modules, and its hydrolysis resistance needs to be improved and optimized.

[0003] In order to improve the hydrolysis resistance of polyester, the prior art adds a phosphorus-containing compound during the polyester synthesis stage (for example, Patent CN103261265A provides a polyester composition suitable as a film for solar cells due to excellent hydrolysis resistance, heat resistance, and cost. The polyester is formed from a dicarboxylic acid component mainly composed of terephthalic acid and a diol component mainly composed of ethylene glycol, and this polyester composition satisfies the following formulas (1) to (5): 0.65 ≤ intrinsic viscosity ≤ 0.90... (1); 0.7 ≤ M / P ≤ 1.3... (2); 200 ppm ≤ P ≤ 600 ppm... (3); carboxyl end groups ≤ 15 equivalents / t... (4); methoxy end groups ≤ 10 equivalents / t... (5). Among them, in formula (2), M represents the number of moles of alkali metal elements and alkaline earth metal elements per 106 g of polyester, and P represents the number of moles of phosphorus elements per 106 g of polyester.), reduces the content of terminal carboxyl groups, or introduces a third monomer, such as cyclohexanedimethanol, naphthalenedicarboxylic acid, etc. These technologies have improved the hydrolysis resistance of polyester films to a certain extent, but cannot reduce the water absorption rate of the films, and still cannot meet the requirements for use as photovoltaic modules.

[0004] There are patents that introduce micron-sized aluminosilicate particles during the processing of polyester films (for example, Patent CN103946285A provides a polyester film. Even if this polyester film is embedded in a solar cell backsheet or a solar cell, its resistance to damp heat does not decrease. A polyester film, the peak count SPc (400 nm) on at least one surface of this polyester film is 100 or more, and SPc (4000 nm) is 10 or less, and the carboxyl end group amount is 0 to 25 equivalents / t. This invention can provide a polyester film with excellent resistance to damp heat, effectively utilize its characteristics, and is suitable for use as a film for solar cell backsheets.) or blend with modified polyolefins, or add carbodiimides (for example, Patent Publication No. CN102812072A discloses a film that contains a composition obtained by mixing the following compound with a polymer compound having an acidic group. The compound contains at least a cyclic structure in which a first nitrogen and a second nitrogen of a carbodiimide group are bonded through a bonding group. This invention can provide a film with improved hydrolysis resistance and without generating free isocyanate compounds), glycidyl ester end-capping agents, which improve the water resistance and hydrolysis resistance of the polyester film, but reduce the mechanical properties of the polyester film. During long-term service, there are problems such as precipitation of additives, affecting the long-term hydrolysis resistance of the polyester film.

[0005] There are patents that laminate a polyester film with a polyolefin film. For example, Patent CN108520905A discloses a novel composite structure fluorine-free photovoltaic backsheet. The novel composite structure fluorine-free photovoltaic backsheet includes an outer layer, an intermediate layer, and an inner layer. The outer layer is a PET polyester film, and the PET polyester film is a biaxially stretched PET polyester film used as a barrier filler. The intermediate layer is a polyurethane resin adhesive, and the inner layer is a PE film. The film is a white polyethylene film added with TiO 2 as a barrier filler. Coating acrylic coatings, metal and metal oxide coatings, and inorganic non-metal coatings can reduce the water vapor permeability, but the process is complex and the preparation cost is increased. 2 Summary of the Invention

[0006] To solve the problems existing in the above prior art, the present invention provides a hydrolysis-resistant polyester film, its manufacturing method, and application. The film has excellent hydrolysis resistance.

[0007] One object of the present invention is to provide a polyester containing a structural unit represented by formula (I), a structural unit represented by formula (II), and a structural unit represented by formula (III):

[0008]

[0009] -O-R 2 -O- (II),

[0010]

[0011] Among them, R 1 is R 2 is -CH 2 CH 2 -, -CH 2 CH 2 CH 2 -, -CH 2 CH 2 CH 2 CH 2 -; -CH 2 CH 2 -O-CH 2 CH 2 -;

[0012] R 3 is an olefin polymer, preferably polyethylene, polypropylene, or a styrene-ethylene-butene-styrene copolymer.

[0013] For the polyester according to the present invention, the structural unit shown in formula (III) is 0.1 to 10 wt%, preferably 0.5 to 6 wt%, of all the structural units (i.e., the structural units shown in formula (I), formula (II), and formula (III));

[0014] The molar ratio of the structural unit shown in formula (I) to the structural unit shown in formula (II) is 0.95 to 1.05, preferably 0.98 to 1.02.

[0015] The intrinsic viscosity of the polyester according to the present invention is 0.65 to 0.85 dL / g.

[0016] A second object of the present invention is to provide a method for preparing the polyester, which is obtained by reacting components including a diol, a dicarboxylic acid, and a maleic anhydride-grafted polyolefin.

[0017] Preferably, the method for preparing the polyester includes the following steps:

[0018] Mix the dicarboxylic acid, the diol, and the catalyst uniformly, carry out an esterification reaction, then add the maleic anhydride-grafted polyolefin, and carry out a polycondensation reaction to obtain the polyester.

[0019] Among them, the diol is preferably at least one selected from ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,4-cyclohexanedimethanol, and diethylene glycol.

[0020] The dibasic acid is preferably at least one selected from terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 4,4'-biphenyldicarboxylic acid, 4,4'-diphenylether dicarboxylic acid.

[0021] The maleic anhydride grafted polyolefin is preferably at least one selected from maleic anhydride grafted polyethylene, maleic anhydride grafted polypropylene, maleic anhydride grafted styrene-ethylene-butene-styrene copolymer.

[0022] Among them, the proportion of maleic anhydride in the maleic anhydride grafted polyolefin is 0.1 - 3 wt%, preferably 0.2 - 1 wt%.

[0023] The catalyst can be a catalyst commonly used in the art, preferably at least one selected from antimony glycolate, antimony acetate, antimony trioxide, tetrabutyl titanate, titanium glycolate, tetraisopropyl titanate, aluminum acetate, aluminum isopropoxide, sodium aluminate, zinc acetate, cobalt acetate, manganese acetate, manganese glycolate.

[0024] According to the preparation method of the polyester of the present invention, the molar ratio of the diol to the dibasic acid is 1.0 - 1.5, preferably 1.05 - 1.35.

[0025] According to the preparation method of the polyester of the present invention, the dosage of the maleic anhydride grafted polyolefin is 0.1 - 10 wt% of the total mass of the diol, the dibasic acid and the maleic anhydride grafted polyolefin, preferably 0.5 - 6 wt%.

[0026] According to the preparation method of the hydrolysis-resistant polyester of the present invention, the dosage of the catalyst is 5 - 500 ppm of the total mass of the diol, the dibasic acid and the maleic anhydride grafted polyolefin, preferably 20 - 300 ppm.

[0027] According to the preparation method of the polyester of the present invention, the conditions of the esterification reaction are a temperature of 230 - 260 °C, a pressure of 220 - 300 kPa, and a time of 1.5 - 2.5 h.

[0028] According to the preparation method of the polyester of the present invention, the conditions of the polycondensation reaction are a temperature of 260 - 280 °C and a pressure of 10 - 200 Pa.

[0029] According to a preferred embodiment of the present invention, the preparation method includes mixing the dibasic acid, the diol and the catalyst evenly, adding them to a reaction kettle for esterification reaction; reducing the pressure of the reaction kettle to atmospheric pressure, adding the maleic anhydride modified polyolefin to the reaction kettle for polycondensation reaction; after the reaction is completed, introducing nitrogen, discharging, and pelletizing to obtain the polyester.

[0030] Compared with the prior art, the reaction of the present invention is more uniform and the reaction degree is higher.

[0031] A third object of the present invention is to provide a hydrolysis-resistant polyester film, which is made of the polyester obtained by the polyester or the preparation method.

[0032] The elongation at break retention rate of the polyester film after 48 hours in an environment of 121°C and 100% RH is above 25%, preferably above 30%, and more preferably above 40%.

[0033] A fourth object of the present invention is to provide a preparation method of the hydrolysis-resistant polyester film, which includes obtaining the polyester film by subjecting the polyester to an extrusion film-forming process.

[0034] According to the preparation method of the polyester film of the present invention, there is no particular limitation on the extrusion film-forming process, and the extrusion film-forming process can be one or a combination of a casting process, a calendering process, and a biaxial stretching process, and preferably a casting process is adopted.

[0035] Preferably, the preparation method of the polyester film further includes a step of heat-treating the obtained polyester film.

[0036] According to a preferred embodiment of the present invention, the preparation method of the polyester film includes obtaining a polyester film by subjecting the polyester to an extrusion film-forming process, and then performing heat treatment to obtain a hydrolysis-resistant polyester film.

[0037] Among them, the temperature of the heat treatment is 60 to 150°C, preferably 80 to 140°C;

[0038] The time of the heat treatment is 1 to 120 minutes, preferably 1 to 60 minutes.

[0039] A fifth object of the present invention is to provide an application of the polyester film or the polyester film obtained by the preparation method in a solar cell backplane.

[0040] Compared with the prior art, the present invention has the following advantages:

[0041] ① Different degrees of reaction

[0042] Compared with the polyester obtained by adding maleic anhydride-grafted polyolefin during processing and extrusion in the prior art, maleic anhydride-grafted polyolefin is added in the polyester synthesis stage in the present invention.

[0043] The polyester obtained by adding during the synthesis stage can be completely dissolved in phenol-tetrachloroethane, while the polyester obtained by adding during processing and extrusion contains insoluble substances in phenol-tetrachloroethane. These insoluble substances indicate that maleic anhydride-grafted polyolefin has not reacted completely with the polyester, and the degree of reaction is low.

[0044] ② Different mechanical properties

[0045] Compared with the polyester film obtained by adding maleic anhydride grafted polyolefin during processing and extrusion in the prior art, the modulus of the film of the present invention has no obvious difference from that of the film in the prior art, but the film of the present invention has a higher elongation at break and better toughness.

[0046] ③ Hydrophobicity

[0047] In the method of the present invention, the obtained polyester film is heat-treated, and the polyolefin chain segments migrate to the film surface, reducing the surface free energy, thereby improving the hydrophobicity of the polyester film. Specific Embodiments

[0048] The present invention will be specifically described below in conjunction with specific embodiments. It is necessary to point out here that the following embodiments are only used for further illustration of the present invention and should not be construed as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention still fall within the protection scope of the present invention.

[0049] The raw materials used in the specific embodiments of the present invention are obtained commercially.

[0050] Example 1

[0051] 600 g of terephthalic acid, 300 g of ethylene glycol and 0.27 g of antimony glycolate were mixed evenly and added to a reaction kettle for esterification reaction. The reaction conditions were a temperature of 255 °C, a pressure of 260 kPa, and a time of 2 h; the reaction kettle was depressurized to atmospheric pressure, and 4.5 g of maleic anhydride grafted polyethylene (the mass of maleic anhydride accounted for 0.5 wt% of the mass of maleic anhydride grafted polyethylene) was added to the reaction kettle for polycondensation reaction, the temperature was 270 °C, and the pressure was 100 Pa; after the reaction was completed, nitrogen was introduced, the material was discharged, and pellets were obtained to obtain a hydrolysis-resistant polyester with an intrinsic viscosity of 0.72 dL / g; the obtained polyester was made into a hydrolysis-resistant polyester film through an extrusion casting process and heat treatment at 120 °C for 5 minutes.

[0052] The elongation at break retention rate of the prepared polyester film after 48 h in an environment of temperature 121 °C and humidity 100% RH was 50%.

[0053] The polyester film prepared in this example was put into phenol - tetrachloroethane, and the polyester could be completely dissolved in phenol - tetrachloroethane.

[0054] Example 2

[0055] Mix 700 g of 2,6-naphthalenedicarboxylic acid, 295 g of 1,3-propanediol and 0.02 g of tetrabutyl titanate evenly, add them to a reaction kettle for esterification reaction. The reaction conditions are a temperature of 240 °C, a pressure of 230 kPa, and a time of 1.6 h; when the pressure in the reaction kettle drops to atmospheric pressure, add 29.5 g of maleic anhydride grafted styrene-ethylene-butene-styrene copolymer (the mass of the maleic anhydride accounts for 1 wt% of the mass of the maleic anhydride grafted styrene-ethylene-butene-styrene copolymer) to the reaction kettle for polycondensation reaction, with a temperature of 262 °C and a pressure of 20 Pa; after the reaction is completed, introduce nitrogen, discharge the material, and obtain a hydrolysis-resistant polyester with an intrinsic viscosity of 0.66 dL / g after pelletizing; subject the obtained polyester to an extrusion and calendering process and heat treatment at 80 °C for 60 minutes to obtain a hydrolysis-resistant polyester film.

[0056] The elongation at break retention rate of the obtained polyester film is 60% after 48 h in an environment of temperature 121 °C and humidity 100% RH.

[0057] Example 3

[0058] Mix 500 g of 4,4'-biphenyldicarboxylic acid, 310 g of 1,4-cyclohexanedimethanol and 0.08 g of aluminum acetate evenly, add them to a reaction kettle for esterification reaction. The reaction conditions are a temperature of 250 °C, a pressure of 290 kPa, and a time of 2.4 h; when the pressure in the reaction kettle drops to atmospheric pressure, add 48 g of maleic anhydride grafted polypropylene (the mass of the maleic anhydride accounts for 0.2 wt% of the mass of the maleic anhydride grafted polypropylene) to the reaction kettle for polycondensation reaction, with a temperature of 275 °C and a pressure of 180 Pa; after the reaction is completed, introduce nitrogen, discharge the material, and obtain a hydrolysis-resistant polyester with an intrinsic viscosity of 0.81 dL / g after pelletizing; subject the obtained polyester to an extrusion and calendering process and heat treatment at 140 °C for 2 minutes to obtain a hydrolysis-resistant polyester film.

[0059] The elongation at break retention rate of the obtained polyester film is 40% after 48 h in an environment of temperature 121 °C and humidity 100% RH.

[0060] Example 4

[0061] Mix 600 g of terephthalic acid, 300 g of ethylene glycol and 0.27 g of antimony glycolate evenly, add them to a reaction kettle for esterification reaction. The reaction conditions are a temperature of 255 °C, a pressure of 260 kPa, and a time of 2 h; when the pressure in the reaction kettle drops to atmospheric pressure, add 100 g of maleic anhydride grafted polyethylene (the mass of the maleic anhydride accounts for 0.5 wt% of the mass of the maleic anhydride grafted polyethylene) to the reaction kettle for polycondensation reaction, with a temperature of 270 °C and a pressure of 100 Pa; after the reaction is completed, introduce nitrogen, discharge the material, and obtain a hydrolysis-resistant polyester with an intrinsic viscosity of 0.70 dL / g after pelletizing; subject the obtained polyester to an extrusion and casting process and heat treatment at 120 °C for 5 minutes to obtain a hydrolysis-resistant polyester film.

[0062] The elongation at break retention rate of the obtained polyester film after 48 h in an environment of temperature 121 °C and humidity 100% RH is 30%.

[0063] Example 5

[0064] 600 g of terephthalic acid, 300 g of ethylene glycol and 0.27 g of antimony glycolate were mixed evenly and added to a reaction kettle for esterification reaction. The reaction conditions were temperature 255 °C, pressure 260 kPa and time 2 h; after the reaction kettle was reduced to normal pressure, 4.5 g of maleic anhydride grafted polyethylene (the mass of maleic anhydride accounted for 0.5 wt% of the mass of maleic anhydride grafted polyethylene) was added to the reaction kettle for polycondensation reaction, the temperature was 270 °C and the pressure was 100 Pa; after the reaction was completed, nitrogen was passed through, the material was discharged, and after pelletizing, a hydrolysis-resistant polyester with an intrinsic viscosity of 0.72 dL / g was obtained; the obtained polyester was made into a polyester film by an extrusion casting process.

[0065] The elongation at break retention rate of the obtained polyester film after 48 h in an environment of temperature 121 °C and humidity 100% RH is 25%.

[0066] Comparative Example 1

[0067] 600 g of terephthalic acid, 300 g of ethylene glycol and 0.27 g of antimony glycolate were mixed evenly and added to a reaction kettle for esterification reaction. The reaction conditions were temperature 255 °C, pressure 260 kPa and time 2 h; then polycondensation reaction was carried out, the temperature was 270 °C and the pressure was 100 Pa; after the reaction was completed, nitrogen was passed through, the material was discharged, and after pelletizing, a polyester with an intrinsic viscosity of 0.72 dL / g was obtained; the obtained polyester was melt-blended and extruded with 4.5 g of maleic anhydride grafted polyethylene (the mass of maleic anhydride accounted for 0.5 wt% of the mass of maleic anhydride grafted polyethylene) into a film and heat-treated at 120 °C for 5 minutes to obtain a polyester film.

[0068] The elongation at break retention rate of the obtained polyester film after 48 h in an environment of temperature 121 °C and humidity 100% RH is 20%.

[0069] The polyester film prepared in this comparative example was put into phenol-tetrachloroethane, and it was found that there were insoluble substances in phenol-tetrachloroethane. These insoluble substances indicated that maleic anhydride grafted polyethylene did not react completely with the polyester and the reaction degree was low. After filtration and drying of these insoluble substances, the proportion in the polyester was measured to be 2.3 ± 0.2 wt%.

[0070] Comparison of mechanical properties

[0071] The moduli and elongations at break of the two polyester films obtained in Example 1 and Comparative Example 1 were compared. The specific results are shown in Table 1 below.

[0072] Table 1

[0073] Addition method of maleic anhydride grafted polyolefin Modulus / MPa Elongation at break / % Example 1 - Synthesis stage 1320±55 310±20 Comparative Example 1 - Extrusion processing stage 1280±92 78±12

[0074] As can be seen from Table 1, although there is no obvious difference in the modulus of the two films, the film with maleic anhydride grafted polyolefin added in the synthesis stage has a higher elongation at break and better toughness.

[0075] Hydrophobic property comparison

[0076] The water contact angles of the films obtained in Example 1 and Example 5 were tested.

[0077] The water contact angle of the film in Example 5 is 53°; the film in Example 1 was heat-treated, and its water contact angle is 89°. This shows that the hydrophobicity of the film is enhanced after heat treatment, which may improve the hydrolysis resistance of the film.

[0078] In the above hydrophobicity test, taking PET as an example, in the PET synthesis stage, maleic anhydride grafted polyolefin was added, and an ester exchange reaction occurred with ethylene glycol to obtain polyester. The polyester was formed into a film by a casting process and then heat-treated. The polyolefin chain segments migrated to the film surface, improving the hydrophobicity of the PET film.

[0079] Hydrolysis resistance comparison

[0080] The obtained films were aged in a PCT aging oven for 48 hours, and the viscosity drop before and after aging was measured. The specific results are shown in Table 2 below.

[0081] Table 2

[0082] Addition method of maleic anhydride grafted polyolefin Viscosity drop / % Example 1 - Synthesis stage 35 Example 5 - Synthesis stage 38 Comparative Example 1 - Extrusion processing stage 44

[0083] As can be seen from Table 2, the film with maleic anhydride grafted polyolefin added in the synthesis stage has a lower viscosity drop and better hydrolysis resistance.

[0084] The viscosity drop of the heat-treated film is smaller, indicating that heat treatment improves the hydrolysis resistance of the PET film.

Claims

1. A method for preparing a polyester film, comprising uniformly mixing a dibasic acid, a diol, and a catalyst, performing an esterification reaction, then adding a maleic anhydride-grafted polyolefin, performing a polycondensation reaction to obtain a polyester, subjecting the polyester to an extrusion film-forming process to obtain a polyester film, and performing a heat treatment on the obtained polyester film; wherein the elongation at break retention rate of the polyester film after 48 h in an environment of a temperature of 121 °C and a humidity of 100% RH is above 30%; the maleic anhydride-grafted polyolefin is selected from at least one of maleic anhydride-grafted polyethylene, maleic anhydride-grafted polypropylene, and maleic anhydride-grafted styrene-ethylene-butene-styrene copolymer; the maleic anhydride-grafted polyolefin is 0.1 to 10 wt% of the total mass of the diol, the dibasic acid, and the maleic anhydride-grafted polyolefin, and the molar ratio of the diol to the dibasic acid is 1.0 to 1.

5.

2. The method for preparing a polyester film according to claim 1, characterized in that: the temperature of the heat treatment is 60 to 150 °C; the time of the heat treatment is 1 to 120 min.

3. The method for preparing a polyester film according to claim 2, characterized in that: the temperature of the heat treatment is 80 to 140 °C; the time of the heat treatment is 1 to 60 min.

4. The method for preparing a polyester film according to claim 1, characterized in that: the diol is selected from at least one of ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,4-cyclohexanedimethanol, and diethylene glycol; and / or, the dibasic acid is selected from at least one of terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 4,4'-biphenyldicarboxylic acid, and 4,4'-diphenyletherdicarboxylic acid; and / or, the catalyst is selected from at least one of antimony glycolate, antimony acetate, antimony trioxide, tetrabutyl titanate, titanium glycolate, tetraisopropyl titanate, aluminum acetate, aluminum isopropoxide, sodium aluminate, zinc acetate, cobalt acetate, manganese acetate, and manganese glycolate.

5. The method for preparing a polyester film according to claim 1, characterized in that: the proportion of maleic anhydride in the maleic anhydride-grafted polyolefin is 0.1 to 3 wt%.

6. The method for preparing a polyester film according to claim 5, characterized in that: the proportion of maleic anhydride in the maleic anhydride-grafted polyolefin is 0.2 to 1 wt%.

7. The method for preparing a polyester film according to claim 1, characterized in that: the molar ratio of the diol to the dibasic acid is 1.05 to 1.35; and / or, the maleic anhydride-grafted polyolefin is 0.5 to 6 wt% of the total mass of the diol, the dibasic acid, and the maleic anhydride-grafted polyolefin; and / or, the catalyst is 5 to 500 ppm of the total mass of the diol, the dibasic acid, and the maleic anhydride-grafted polyolefin.

8. The method for preparing a polyester film according to claim 7, characterized in that: the catalyst is 20 to 300 ppm of the total mass of the diol, the dibasic acid, and the maleic anhydride-grafted polyolefin.

9. The method for preparing a polyester film according to claim 1, characterized in that: The conditions for the esterification reaction are a temperature of 230 - 260 °C, a pressure of 220 - 300 kPa, and a time of 1.5 - 2.5 h; and / or, The conditions for the polycondensation reaction are a temperature of 260 - 280 °C and a pressure of 10 - 200 Pa.

10. The method for preparing a polyester film according to claim 1, characterized in that: The intrinsic viscosity of the polyester is 0.65 - 0.85 dL / g.

11. The application of the polyester film obtained by the preparation method according to any one of claims 1 - 10 in a solar cell backsheet.

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