Polyester resin comprising recycled monomer and powder coating composition comprising same

Abstract

The present invention relates to a polyester resin obtained by copolymerizing recycled bis (2-hydroxyethyl) terephthalate, an acid comprising a dicarboxylic acid or a derivative thereof, and a polyol different from the recycled bis (2-hydroxyethyl) terephthalate, the polyester resin has a structure in which a moiety derived from bis-2-hydroxyethyl terephthalate, an acid moiety derived from a dicarboxylic acid or a derivative thereof, and an alcohol moiety derived from a polyol are repeated, the moiety derived from the recycled bis-2-hydroxyethyl terephthalate is contained in a content of 1 part by weight to 50 parts by weight.

Description

Technical Field

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of priority from Korean Patent Application No. 10-2022-0132210 filed on October 14, 2022, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety.

[0003] The present invention relates to a polyester resin comprising recycled monomers and a powder coating composition comprising the polyester resin. Background Art

[0004] Powder coating is suitable for coating the surface to be coated by electrostatic method, and melting and homogenizing the powder particles by heating drying such as thermal curing, thereby improving the coating method of the coating film. Compared with liquid paint, this coating has low poisoning risk caused by solvent volatilization and low fire risk, is easy to handle and easy to recycle, and is therefore in demand in various fields.

[0005] Representative raw materials of powder coatings include polyester. Because polyester has excellent mechanical strength, heat resistance, transparency and gas barrier properties, polyester is suitable for use as powder coating. In addition to powder coatings, polyester is produced worldwide as a material for beverage filling containers, packaging films, audio and video films and the like, industrial materials such as medical fibers or tire cords and the like. Because polyester sheets have good transparency and excellent mechanical strength, polyester sheets are being widely used as materials for boxes, boxes, partitions, store shelves, protective panels, blister packaging, building materials, interior materials and exterior materials and the like.

[0006] Meanwhile, waste plastics, which account for about 70% of marine pollution, have recently become a serious social problem, and therefore, each country is regulating the use of disposable plastics and is simultaneously planning the recycling of waste plastics. The method of recycling waste plastics can be roughly divided into two methods, one of which is to recover, grind and clean the waste plastics, and then melt-extrude the waste plastics to re-granulate and use them as raw materials, and the other method is to use the material obtained by depolymerization of waste plastics as a monomer for synthetic plastics. In the latter case, by depolymerization of PET or PETG in waste plastics, bis-2-hydroxyethyl terephthalate can be obtained, and research has been conducted on the use of bis-2-hydroxyethyl terephthalate as a monomer for polyester copolymers.

[0007] Therefore, the inventors of the present disclosure have confirmed that by using recycled bis-2-hydroxyethyl terephthalate as a comonomer of a polyester resin and controlling the amount used, uniform quality of a polyester resin prepared from a material obtained by depolymerization of waste plastics and a powder coating composition including the same can be achieved, and have completed the present invention. Summary of the invention

[0008] Technical issues

[0009] An object of the present invention is to provide a polyester resin and a powder coating composition comprising the same, the polyester resin comprising recycled monomers but achieving uniform quality.

[0010] Technical Solutions

[0011] To achieve the object, a polyester resin is provided, which is polymerized from:

[0012] 1) recycled bis-2-hydroxyethyl terephthalate,

[0013] 2) Acids including dicarboxylic acids or their derivatives, and

[0014] 3) a polyol other than recycled bis-2-hydroxyethyl terephthalate, and

[0015] The polyester resin has a structure in which a portion derived from bis-2-hydroxyethyl terephthalate, a portion derived from a dicarboxylic acid or a derivative thereof, and a portion derived from a polyol are repeated,

[0016] Herein, the portion derived from recycled bis-2-hydroxyethyl terephthalate is included in an amount of 1 to 50 parts by weight based on 100 parts by weight of the polyester resin.

[0017] Definition of terms

[0018] The polyester resin according to the present invention relates to a copolymer prepared by copolymerizing a dicarboxylic acid or a derivative thereof with a polyol, wherein during the copolymerization process, recycled bis-2-hydroxyethyl terephthalate participates in the reaction.

[0019] The term "derived" means a certain part or a certain unit derived from a specific compound contained in a product of a chemical reaction when the specific compound participates in a chemical reaction. Specifically, the acid part derived from a dicarboxylic acid or a derivative thereof and the alcohol part derived from a polyol respectively mean a repeating unit in a polyester copolymer formed by an esterification reaction or a polycondensation reaction. In addition, the part derived from bis-2-hydroxyethyl terephthalate means a repeating unit in a polyester copolymer formed by an esterification reaction in a copolymerization reaction.

[0020] Recycled bis-2-hydroxyethyl terephthalate

[0021] As used herein, the term 'recycled bis-2-hydroxyethyl terephthalate' means a material obtained from waste plastics collected after use. As waste plastics from which bis-2-hydroxyethyl terephthalate can be obtained, PET and PETG and the like can be mentioned. For example, bis-2-hydroxyethyl terephthalate can be obtained from PET collected after use by glycolysis, hydrolysis, methanolysis and the like, and such methods are well known in the art.

[0022] Since recycled bis-2-hydroxyethyl terephthalate passes through many chemical steps during the process of obtaining it from waste plastics, in the case where it is used as a monomer of a copolymer, the product quality may inevitably deteriorate. In particular, in the case where it is used as a monomer of a polyester resin, the color quality may deteriorate and a large amount of by-products may be generated, as described later.

[0023] Therefore, in the present disclosure, recycled bis-2-hydroxyethyl terephthalate is used as a main monomer constituting the polyester resin according to the present invention, but the polyester resin is controlled so that the polyester resin may contain the recycled bis-2-hydroxyethyl terephthalate in an amount of 1 to 50 parts by weight based on 100 parts by weight of the polyester resin. If the portion derived from recycled bis-2-hydroxyethyl terephthalate is greater than 50 parts by weight, the color quality and transparency of the polyester copolymer may be deteriorated, and if the portion derived from recycled bis-2-hydroxyethyl terephthalate is less than 1 part by weight, the utilization of the recycled monomer may be insufficient.

[0024] Preferably, the portion derived from recycled bis-2-hydroxyethyl terephthalate is contained in an amount of 2 parts by weight or more, 3 parts by weight or more, or 4 parts by weight or more and 45 parts by weight or less, 40 parts by weight or less, 35 parts by weight or less, or 30 parts by weight or less, based on 100 parts by weight of the polyester resin.

[0025] Acids including dicarboxylic acids or their derivatives

[0026] The dicarboxylic acid or its derivative used herein means a main monomer constituting the polyester copolymer together with the polyol component. Specifically, the acid includes an aromatic dicarboxylic acid or its derivative and an aliphatic dicarboxylic acid or its derivative.

[0027] The aromatic dicarboxylic acid or its derivative may be a C8-20 aromatic dicarboxylic acid or its derivative, preferably a C8-14 aromatic dicarboxylic acid or its derivative, or a mixture thereof. Examples of aromatic dicarboxylic acids or their derivatives may include one or more selected from the group consisting of terephthalic acid, isophthalic acid, phthalic acid, trimellitic acid, 2,6-naphthalene dicarboxylic acid, diphenyl dicarboxylic acid, 4,4'-stilbene dicarboxylic acid, 2,5-furan dicarboxylic acid, 2,5-thiophene dicarboxylic acid, dimethyl terephthalate, dimethyl isophthalate, trimellitic anhydride and phthalic anhydride, but specific examples of aromatic dicarboxylic acids are not limited thereto.

[0028] Preferably, the portion derived from the aromatic dicarboxylic acid or its derivatives may be contained in an amount of 20 to 80 parts by weight based on 100 parts by weight of the polyester resin. In the case where the portion derived from the aromatic dicarboxylic acid or its derivatives is contained in the above content range, the properties of the polyester resin according to the present invention may be improved, and the polyester resin may be suitable for use as a powder coating as described later. More preferably, the portion derived from the aromatic dicarboxylic acid or its derivatives may be contained in an amount of 25 parts by weight or more, 30 parts by weight or more, or 35 parts by weight or more and 75 parts by weight or less, 70 parts by weight or less, or 65 parts by weight or less, based on 100 parts by weight of the polyester resin.

[0029] Meanwhile, in the polyester resin according to the present invention, the acid may include an aliphatic dicarboxylic acid or a derivative thereof. Wherein, the aliphatic dicarboxylic acid may be an alicyclic dicarboxylic acid containing one or more rings, or the aliphatic dicarboxylic acid may be a straight or branched aliphatic dicarboxylic acid without a ring. The aliphatic dicarboxylic acid or a derivative thereof may be a C4-20 aliphatic dicarboxylic acid or a derivative thereof, preferably a C4-12 aliphatic dicarboxylic acid or a derivative thereof, or a mixture thereof. The aliphatic dicarboxylic acid or a derivative thereof may include one or more selected from the group consisting of the following items: a straight, branched or cyclic aliphatic dicarboxylic acid component, such as adipic acid, succinic acid, sebacic acid, isodecyl succinic acid, maleic acid, fumaric acid, glutaric acid, azelaic acid and the like; cyclohexanedicarboxylic acid, such as 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid and the like; and hexahydrophthalic anhydride, but the specific examples of the aliphatic dicarboxylic acid are not limited thereto.

[0030] Preferably, the portion derived from the aliphatic dicarboxylic acid or its derivatives may be contained in an amount of 1 to 15 parts by weight based on 100 parts by weight of the polyester resin. In the case where the portion derived from the aliphatic dicarboxylic acid or its derivatives is contained in the above content range, the impact resistance and appearance properties of the powder coating may be improved, and at the same time, the storage stability of the coating may be maintained. More specifically, the portion derived from the aliphatic dicarboxylic acid or its derivatives may be contained in an amount of 2 parts by weight or more, 3 parts by weight or more, or 4 parts by weight or more and 14 parts by weight or less, 13 parts by weight or less, or 12 parts by weight or less, based on 100 parts by weight of the polyester resin.

[0031] Polyols

[0032] The polyol used herein means a main monomer constituting the polyester copolymer together with the above-mentioned dicarboxylic acid or its derivative.

[0033] The polyol may include one or more selected from the group consisting of ethylene glycol, diethylene glycol, neopentyl glycol, cyclohexanedimethanol, 1,2-propylene glycol, 1,3-propylene glycol, 2-methyl-1,3-propylene glycol, 2-methylene-1,3-propylene glycol, 2-ethyl-1,3-propylene glycol, 2-isopropyl-1,3-propylene glycol, 2,2-dimethyl-1,3-propylene glycol, 2-butyl-2-ethyl-1,3-propylene glycol, 1,4-butanediol, 2,3-butanediol, 3-methyl-1,5-pentanediol, 3-methyl-2,4-pentanediol, 1,6-hexanediol, 1,2-cyclohexanediol, 1,4-cyclohexanediol and pentaerythritol, but specific examples of the polyol are not limited thereto.

[0034] Preferably, based on 100 parts by weight of the polyester resin, the part derived from the polyol is included in an amount of 2 to 60 parts by weight. In the case where the polyol is included in the above content range, the polyol may be suitable for preparing the polyester resin together with the dicarboxylic acid. More preferably, based on 100 parts by weight of the polyester resin, the part derived from the polyol may be included in an amount of 3 parts by weight or more, 4 parts by weight or more, or 5 parts by weight or more and 55 parts by weight or less, 50 parts by weight or less, or 45 parts by weight or less.

[0035] Polyester copolymer

[0036] The polyester resin according to the present invention can be prepared by the following steps: copolymerizing the above-mentioned recycled bis-2-hydroxyethyl terephthalate, dicarboxylic acid or its derivative and polyol to prepare a prepolymer (step 1); and preparing the prepolymer into a polyester resin having a carboxyl terminal or a hydroxyl terminal (step 2).

[0037] Prepolymer preparation steps

[0038] The prepolymer preparation step includes an esterification reaction step (step 1-1), and if necessary, a polycondensation reaction step (step 1-2) may be sequentially performed.

[0039] The esterification reaction may be performed in the presence of an esterification catalyst, and as the esterification catalyst, a titanium-based compound, a germanium-based compound, an antimony-based compound, an aluminum-based compound, a tin-based compound, or a mixture thereof may be used.

[0040] As examples of titanium-based compounds, mention may be made of tetraethyl titanate, acetyl tripropyl titanate, tetrapropyl titanate, tetrabutyl titanate, 2-ethylhexyl titanate, octanediol titanate, lactic acid titanate ( lactatetitanate), triethanolamine titanate ( triethanolamine titanate), titanate acetylacetonate ( acetylacetonate titanate, acetylacetonate titanate As examples of germanium-based compounds, germanium dioxide, germanium tetrachloride, ethylene glycol germanium, germanium acetate, copolymers using them, or mixtures thereof, and the like can be mentioned. Preferably, germanium dioxide can be used, and as such germanium dioxide, both crystalline germanium dioxide and amorphous germanium dioxide can be used, and ethylene glycol-soluble germanium dioxide can also be used. As examples of tin-based compounds, monobutyl tin oxide, dibutyl tin oxide, tetrabutyl dibutoxy tin oxide, and the like can be mentioned. Preferably, tin-based compounds can be used.

[0041] Esterification reaction can be carried out at 0kg / cm 2 The esterification reaction conditions can be appropriately controlled according to the specific properties of the prepared polyester, the component ratio or the process conditions. Specifically, preferred examples of the esterification reaction conditions may include 0 kg / cm2, 10.0 kg / cm2, 150 ° C to 300 ° C. 2 Up to 5.0kg / cm 2 , more preferably 0.1 kg / cm 2 Up to 3.0kg / cm 2 200 ℃ to 270 ℃, more preferably 230 ℃ to 260 ℃ temperature.

[0042] In addition, the esterification reaction can be carried out batchwise or continuously, and the raw materials can be introduced separately, but preferably in the form of a slurry in which the dicarboxylic acid component and the recycled bis(2-hydroxyethyl) terephthalate are mixed with the alcohol component. In addition, an alcohol component that is solid at room temperature, such as neopentyl glycol (2,2-dimethyl-1,3-propanediol), can be dissolved in water and then mixed with a dicarboxylic acid component such as terephthalic acid to form a slurry. Alternatively, after neopentyl glycol melts at 60 °C or higher, neopentyl glycol can be mixed with a dicarboxylic acid component such as terephthalic acid and other alcohol components to form a slurry. In addition, water can be additionally introduced into the mixed slurry to help improve the fluidity of the slurry.

[0043] The polycondensation reaction can be carried out by subjecting the esterification reaction product to a reaction at a temperature of 150 °C to 300 °C and a reduced pressure of 600 mmHg to 0.01 mmHg for 1 hour to 24 hours.

[0044] Such a polycondensation reaction can be carried out at a reaction temperature of 150 °C to 300 °C, preferably 200 °C to 290 °C, more preferably 230 °C to 260 °C; and a reduced pressure of 600 mmHg to 0.01 mmHg, preferably 200 mmHg to 0.05 mmHg, more preferably 100 mmHg to 0.1 mmHg. By applying reduced pressure conditions to the polycondensation reaction, the by-product ethylene glycol of the polycondensation can be removed outside the system, and thus, if the reduced pressure conditions of the polycondensation reaction do not fall within the range of 400 mmHg to 0.01 mmHg, the removal of the by-product may be insufficient. In addition, in the case where the polycondensation reaction is carried out outside the temperature range of 150 °C to 300 °C, if the polycondensation reaction is carried out at 150 °C or lower, the by-product ethylene glycol of the polycondensation reaction may not be effectively removed to the outside, and thus, the intrinsic viscosity of the final reaction product may be low, and the properties of the prepared resin may deteriorate, and if the reaction is carried out at 300 °C or higher, the prepared polyester resin may turn yellow. In addition, the polycondensation reaction can be carried out for a certain period of time until the intrinsic viscosity of the final reaction product reaches an appropriate level, for example, with an average residence time of 1 hour to 24 hours.

[0045] The polycondensation reaction can be carried out in the presence of a polycondensation catalyst comprising a titanium-based compound, a germanium-based compound, an antimony-based compound, an aluminum-based compound, a tin-based compound, or a mixture thereof.

[0046] As examples of titanium-based compounds, tetraethyl titanate, acetyl tripropyl titanate, tetrapropyl titanate, tetrabutyl titanate, 2-ethylhexyl titanate, octanediol titanate, lactic acid titanate, triethanolamine titanate, acetylacetonate titanate, ethyl acetoacetate titanate, isostearyl titanate, titanium dioxide and the like can be mentioned. As examples of germanium-based compounds, germanium dioxide, germanium tetrachloride, ethylene glycol germanium, germanium acetate, copolymers using them or mixtures thereof, and the like can be mentioned. As examples of tin-based compounds, monobutyl tin oxide, dibutyl tin oxide, tetrabutyl dibutoxy tin oxide and the like can be mentioned. Preferably, tin-based compounds can be used.

[0047] Preparation steps of carboxyl-terminated polyester resin or hydroxyl-terminated polyester resin

[0048] After the prepolymer is prepared, in order to prepare the polyester resin for powder coatings, a carboxyl-terminated polyester or a hydroxyl-terminated polyester is prepared.

[0049] In order to use the prepolymer prepared in step 1 as a powder coating, the terminal should consist of a functional group that reacts with a curing agent. The functional group at the terminal varies depending on the type of curing agent and can be roughly divided into a carboxylic acid terminal and a hydroxyl terminal.

[0050] For the carboxyl end-capping reaction, a polyvalent carboxylic acid or its anhydride can be used, and the example of the carboxylic acid can mention the above-mentioned dicarboxylic acid. Preferably, isophthalic acid, adipic acid or trimellitic anhydride can be used. Meanwhile, in order to promote the introduction of the carboxylic acid, the carboxyl end-capping can be carried out after the hydroxyl end-capping of the prepolymer. The hydroxyl end-capping reaction can be carried out by controlling the reaction conditions without the need for additional materials.

[0051] The carboxyl end-capping reaction can be carried out at a reaction temperature of 150°C to 300°C, preferably 180°C to 250°C; and a reduced pressure of 600mmHg to 0.01mmHg, preferably 200mmHg to 1mmHg. By applying reduced pressure conditions to the carboxyl end-capping reaction, the molecular weight of the polyester resin can be appropriately controlled. In addition, if the carboxyl end-capping reaction is carried out at a temperature lower than 150°C, the condensed water may not be effectively removed to the outside of the system, thereby deteriorating the properties of the polyester resin, and if the carboxyl end-capping reaction is carried out at a temperature higher than 300°C, the prepared polyester resin is likely to turn yellow. In addition, the reaction can be carried out until the target acid value and viscosity of the final reaction product are reached, and the average residence time of 1 hour to 24 hours can be carried out.

[0052] The polyester resin of the present invention prepared through the series of preparation steps as described above is terminated with an acid moiety derived from a dicarboxylic acid or a derivative thereof and thus has carboxyl groups at both ends. Therefore, when used in a powder coating composition, it can react smoothly with a curing agent.

[0053] Meanwhile, the polyester resin of the present invention has an acid value of 20 mgKOH / g to 100 mgKOH / g. The specific acid value measurement method is embodied in the embodiments described later. If the acid value is less than 20 mgKOH / g, due to high viscosity, grindability, dispersibility and similar properties may deteriorate, and therefore the polyester resin may not be suitable for powder coatings, and if the acid value is greater than 100 mgKOH / g, due to low molecular weight, the polyester resin may not be suitable for use as a resin for powder coatings. More preferably, the acid value of the polyester resin may be 25 mgKOH / g or greater, or 27 mgKOH / g or greater and 90 mgKOH / g or less, 80 mgKOH / g or less, or 75 mgKOH / g or less.

[0054] In addition, as described above, the hydroxyl-terminated reaction can be carried out by controlling the reaction conditions after preparing the prepolymer. Specifically, after preparing the prepolymer, by polymerizing under a vacuum condition of 10 mmHg to 100 mmHg, and breaking the vacuum to terminate the reaction when the target hydroxyl value and viscosity are reached, a hydroxyl-terminated polyester resin can be prepared.

[0055] After the hydroxyl-terminated reaction, the polyester resin of the present invention has a hydroxyl value of 20 mgKOH / g to 100 mgKOH / g. The hydroxyl value can be measured by a method commonly used in the art, and for example, the hydroxyl value can be measured based on the titration of 0.5 N KOH after the polyester resin dissolved in a neutral solvent is subjected to an acetylation reaction. If the hydroxyl value is less than 20 mgKOH / g, due to high viscosity, abrasiveness, dispersibility and similar properties may deteriorate, and therefore the polyester resin may not be suitable for powder coatings, and if the hydroxyl value is greater than 100 mgKOH / g, due to low molecular weight, the polyester resin may not be suitable for use as a resin for powder coatings. More preferably, the hydroxyl value of the polyester resin may be 25 mgKOH / g or greater, or 27 mgKOH / g or greater and 90 mgKOH / g or less, 80 mgKOH / g or less, or 75 mgKOH / g or less.

[0056] In addition, according to the present invention, a powder coating composition comprising a polyester resin is provided. Preferably, the polyester resin is contained in an amount of 20 to 80 parts by weight, more preferably 25 parts by weight or more, 30 parts by weight or more, 40 parts by weight or more, or 45 parts by weight or more and 75 parts by weight or less, 70 parts by weight or less, 65 parts by weight or less, or 60 parts by weight or less, based on 100 parts by weight of the powder coating composition.

[0057] In addition, the powder coating composition of the present invention may further contain a curing agent, a filler, a catalyst, a flow improver, an anti-pinhole agent, a leveling agent, an antioxidant and the like.

[0058] Effect

[0059] The above polyester resin according to the present invention contains recycled monomers and is thus environmentally friendly, and when a powder coating composition is prepared, the quality is not deteriorated and the properties are uniform, and thus the polyester resin can replace general polyester resins.

[0060] Best Mode for Carrying Out the Invention

[0061] Hereinafter, preferred embodiments will be provided to help understand the present invention. However, the following embodiments are provided only for better understanding of the present invention, and the scope of the present invention is not limited thereto.

[0062] Example 1-1

[0063] Step 1: Preparation of prepolymer

[0064] Terephthalic acid (309 g), adipic acid (41 g), neopentyl glycol (88 g), bis-2-hydroxyethyl terephthalate (476 g) and monobutyltin oxide (0.5 g) as a catalyst were added to a four-necked flask. While the contents of the flask were stirred, they were heated to a temperature of about 230° C. under nitrogen. The reaction was carried out until the contents became transparent and no condensed water appeared.

[0065] Step 2: Preparation of carboxyl terminated polyester resin

[0066] After adding isophthalic acid (85 g) at 230° C., the reaction was carried out while removing condensed water. After confirming transparency, a vacuum reaction (10 mmHg to 100 mmHg) was carried out to achieve the target molecular weight. When the target acid value (30 mg KOH / g to 33 mg KOH / g) was reached, the vacuum was broken and the temperature was lowered to 200° C., and then discharged.

[0067] Example 1-2

[0068] Step 1: Preparation of prepolymer

[0069] Terephthalic acid (394 g), adipic acid (24 g), neopentyl glycol (160 g), bis-2-hydroxyethyl terephthalate (365 g) and monobutyltin oxide (0.5 g) as a catalyst were added to a four-necked flask. While the contents of the flask were stirred, they were heated to a temperature of about 230° C. under nitrogen. The reaction was carried out until the contents became transparent and no condensed water appeared.

[0070] Step 2: Preparation of carboxyl terminated polyester resin

[0071] After adding isophthalic acid (57 g) at 230° C., the reaction was carried out while removing condensed water. After confirming transparency, a vacuum reaction (10 mmHg to 100 mmHg) was carried out to achieve the target molecular weight. When the target acid value (30 mg KOH / g to 33 mg KOH / g) was reached, the vacuum was broken and the temperature was lowered to 200° C., and then discharged.

[0072] Examples 1-3

[0073] Step 1: Preparation of prepolymer

[0074] Terephthalic acid (432 g), adipic acid (18 g), neopentyl glycol (222 g), bis-2-hydroxyethyl terephthalate (258 g) and monobutyltin oxide (0.5 g) as a catalyst were added to a four-necked flask. While the contents of the flask were stirred, they were heated to a temperature of about 230° C. under nitrogen. The reaction was carried out until the contents became transparent and no condensed water appeared.

[0075] Step 2: Preparation of carboxyl terminated polyester resin

[0076] After adding isophthalic acid (70 g) at 230° C., the reaction was carried out while removing condensed water. After confirming transparency, a vacuum reaction (10 mmHg to 100 mmHg) was carried out to achieve the target molecular weight. When the target acid value (30 mg KOH / g to 33 mg KOH / g) was reached, the vacuum was broken and the temperature was lowered to 200° C., and then discharged.

[0077] Examples 1-4

[0078] Step 1: Preparation of prepolymer

[0079] Terephthalic acid (457 g), adipic acid (18 g), neopentyl glycol (263 g), bis-2-hydroxyethyl terephthalate (187 g) and monobutyltin oxide (0.5 g) as a catalyst were added to a four-necked flask. While the contents of the flask were stirred, they were heated to a temperature of about 230° C. under nitrogen. The reaction was carried out until the contents became transparent and no condensed water appeared.

[0080] Step 2: Preparation of carboxyl terminated polyester resin

[0081] After adding isophthalic acid (74 g) at 230° C., the reaction was carried out while removing condensed water. After confirming transparency, a vacuum reaction (10 mmHg to 100 mmHg) was carried out to achieve the target molecular weight. When the target acid value (30 mg KOH / g to 33 mg KOH / g) was reached, the vacuum was broken and the temperature was lowered to 200° C., and then discharged.

[0082] Examples 1 - 5

[0083] Step 1: Preparation of prepolymer

[0084] Add terephthalic acid (534 g), adipic acid (25 g), neopentyl glycol (304 g), bis(2 - hydroxyethyl) terephthalate (69 g), and monobutyltin oxide (0.5 g) as a catalyst into a four - necked flask. While stirring the contents of the flask, heat them to a temperature of about 230 °C under nitrogen. Carry out the reaction until the contents become transparent and no condensed water appears.

[0085] Step 2: Preparation of carboxyl - terminated polyester resin

[0086] After adding isophthalic acid (67 g) at 230 °C, carry out the reaction while removing condensed water. After confirming transparency, carry out a vacuum reaction (10 mmHg - 100 mmHg) to achieve the target molecular weight. When the target acid value (30 mg KOH / g - 33 mg KOH / g) is reached, break the vacuum, lower the temperature to 200 °C, and then carry out discharging.

[0087] Examples 1 - 6

[0088] Step 1: Preparation of prepolymer

[0089] Add terephthalic acid (413 g), adipic acid (22 g), neopentyl glycol (242 g), diethylene glycol (43 g), bis(2 - hydroxyethyl) terephthalate (167 g), and monobutyltin oxide (0.5 g) as a catalyst into a four - necked flask. While stirring the contents of the flask, heat them to a temperature of about 230 °C under nitrogen. Carry out the reaction until the contents become transparent and no condensed water appears.

[0090] Step 2 - 1: Preparation of hydroxyl - terminated polyester resin

[0091] To achieve the target molecular weight, carry out a vacuum reaction (10 mmHg - 100 mmHg). When the acid value drops below 5, break the vacuum and lower the temperature to 185 °C.

[0092] Step 2 - 2: Preparation of carboxyl - terminated polyester resin

[0093] After adding trimellitic anhydride (112 g) at 185 °C, carry out an atmospheric - pressure reaction until the target acid value is reached. When the target acid value (70 mg KOH / g - 75 mg KOH / g) is reached, carry out discharging.

[0094] Examples 1 - 7

[0095] Step 1: Preparation of prepolymer

[0096] Terephthalic acid (438 g), adipic acid (22 g), neopentyl glycol (241 g), diethylene glycol (46 g), bis-2-hydroxyethyl terephthalate (174 g) and monobutyltin oxide (0.5 g) as a catalyst were added to a four-necked flask. While the contents of the flask were stirred, they were heated to a temperature of about 230° C. under nitrogen. The reaction was carried out until the contents became transparent and no condensed water appeared.

[0097] Step 2-1: Preparation of hydroxyl-terminated polyester resin

[0098] To achieve the target molecular weight, the reaction was carried out under vacuum (10 mmHg to 100 mmHg). When the acid value dropped below 5, the vacuum was broken and the temperature was lowered to 185°C.

[0099] Step 2-2: Preparation of carboxyl-terminated polyester resin

[0100] After trimellitic anhydride (79 g) was added at 185°C, the reaction was carried out under atmospheric pressure until the target acid value was reached. When the target acid value (50 mg KOH / g to 55 mg KOH / g) was reached, the mixture was discharged.

[0101] Comparative Example 1-1

[0102] Step 1: Preparation of prepolymer

[0103] Terephthalic acid (554 g), adipic acid (19 g), neopentyl glycol (291 g), ethylene glycol (57 g) and monobutyltin oxide (0.5 g) as a catalyst were added to a four-necked flask. While the contents of the flask were stirred, they were heated to a temperature of about 230° C. under nitrogen. The reaction was carried out until the contents became transparent and no condensed water appeared.

[0104] Step 2: Preparation of carboxyl terminated polyester resin

[0105] After adding isophthalic acid (77 g) at 230° C., the reaction was carried out while removing condensed water. After confirming transparency, a vacuum reaction (10 mmHg to 100 mmHg) was carried out to achieve the target molecular weight. When the target acid value (30 mg KOH / g to 33 mg KOH / g) was reached, the vacuum was broken and the temperature was lowered to 200° C., and then discharged.

[0106] Comparative Example 1-2

[0107] Step 1: Preparation of prepolymer

[0108] Terephthalic acid (534 g), adipic acid (23 g), neopentyl glycol (278 g), ethylene glycol (28 g), diethylene glycol (58 g) and monobutyltin oxide (0.5 g) as a catalyst were added to a four-necked flask. While the contents of the flask were stirred, they were heated to a temperature of about 230° C. under nitrogen. The reaction was carried out until the contents became transparent and no condensed water appeared.

[0109] Step 2-1: Preparation of hydroxyl-terminated polyester resin

[0110] To achieve the target molecular weight, the reaction was carried out under vacuum (10 mmHg to 100 mmHg). When the acid value dropped below 5, the vacuum was broken and the temperature was lowered to 185°C.

[0111] Step 2-2: Preparation of carboxyl-terminated polyester resin

[0112] After trimellitic anhydride (79 g) was added at 185°C, the reaction was carried out under atmospheric pressure until the target acid value was reached. When the target acid value (50 mg KOH / g to 55 mg KOH / g) was reached, the mixture was discharged.

[0113] For the polyester resins of Example 1-1 to Example 1-7 and Comparative Example 1-1 and Comparative Example 1-2, properties were measured as follows, and the results are shown in Table 1 below.

[0114] (1) Acid value (mg KOH / g)

[0115] The acid value was measured based on titration with 0.5 N KOH.

[0116] (2) Viscosity (cps)

[0117] The melt viscosity was measured at 200°C using a Brookfield viscometer equipped with a viscometer (CAP 2000).

[0118] Table 1

[0119]

[0120] As demonstrated in Table 1, the polyester resin using the recycled monomer according to the present invention has an acid value and a viscosity equal to or higher than those of the polyester resin not including the recycled monomer.

[0121] To the polyester resins prepared in Examples 1 to 7 and Comparative Example 1, a curing agent, a pigment, a pinhole improver, a flow improver, and the like were added in the amounts described in Table 2 below to prepare powder coatings.

[0122] Curing agent: Epikote 193 (epoxy resin from Hexion), HAA (hydroxyalkylamide)

[0123] Pigment: TiO 2 (Titanium dioxide, white pigment)

[0124] Pinhole improver: Benzoin

[0125] Flow improver: Modaflow 6000 (from Allnex)

[0126] Curing catalyst: AD P964 (product from ENTIS)

[0127] Table 2

[0128]

[0129] For the powder coating compositions prepared in Example 2-1 to Example 2-7 and Comparative Example 2-1, properties were evaluated as follows.

[0130] (1) Curing speed (gel time)

[0131] 0.2 g of the coating was placed on a flat heater to 180° C., and then the time required for curing from a liquid state was measured.

[0132] (2) Glossiness

[0133] According to ASTM D523, using a gloss meter (BYK, AG 4446), light was emitted to the coating film at angles of 20° and 60°, and the amount of reflected light was measured.

[0134] (3) Impact

[0135] According to ASTM D2794, a weight of 2 kg is dropped from a height of 60 cm, and it is confirmed whether cracks are generated or noticed.

[0136] -DI: Direct impact strength

[0137] -RI: Reverse impact strength

[0138] (4) Appearance (PCI smoothness standard)

[0139] The appearance of the coating film was compared with a standard plate (manufacturing company: ACT manufacture, PIC powder smoothness standard) by naked eye and marked with a numerical value from 1 to 10.

[0140] 1: Severe orange peel

[0141] 10: Excellent appearance

[0142] (5) Chemical resistance

[0143] The upper portion of the coating film was rubbed back and forth 50 times with a cotton pad impregnated with MEK (methyl ethyl ketone), and then the state of the coating film was confirmed.

[0144] -None: No abnormality in appearance

[0145] -S: Some scratches

[0146] -SS: Partial loss of gloss

[0147] -SSS: significant loss of gloss

[0148] (6) Boiling water resistance

[0149] After the coated specimen was placed in boiling water for 2 hours, the initial gloss before placement and the gloss (60°) after placement were measured, and boiling water resistance was measured as follows.

[0150] Boiling water resistance (%) = gloss after standing / initial gloss

[0151] The results are shown in Table 3 below.

[0152] Table 3

[0153]

[0154] As confirmed in Table 3, although the powder coating composition comprising a polyester resin containing recycled bis-2-hydroxyethyl terephthalate of the present invention comprises a polyester resin using a recycled monomer, the powder coating composition has gloss, impact, appearance properties, and chemical resistance comparable to or higher than those of the powder coating composition of the comparative example, and achieves properties suitable for powder coatings.

Claims

1. Polyester resins, polymerized from: 1) recycled bis-2-hydroxyethyl terephthalate, 2) Acids including dicarboxylic acids or their derivatives, and 3) a polyol different from the recycled bis-2-hydroxyethyl terephthalate, and The polyester resin has a structure in which a portion derived from the bis-2-hydroxyethyl terephthalate, a portion derived from the dicarboxylic acid or a derivative thereof, and a portion derived from the polyol are repeated, in, The portion derived from the recycled bis-2-hydroxyethyl terephthalate is included in the content of 1 part by weight to 50 parts by weight based on 100 parts by weight of the polyester resin.

2. The polyester resin according to claim 1, in, The portion derived from the recycled bis-2-hydroxyethyl terephthalate is included in the content of 4 to 30 parts by weight based on 100 parts by weight of the polyester resin. 3 . The polyester resin according to claim 1 , wherein the acid comprises an aromatic dicarboxylic acid or a derivative thereof and an aliphatic dicarboxylic acid or a derivative thereof.

4. The polyester resin according to claim 3, wherein the aromatic dicarboxylic acid or its derivative comprises one or more selected from the group consisting of terephthalic acid, isophthalic acid, phthalic acid, trimellitic acid, 2,6-naphthalene dicarboxylate, diphenyl dicarboxylic acid, 4,4'-stilbene dicarboxylic acid, 2,5-furan dicarboxylic acid, 2,5-thiophene dicarboxylic acid, dimethyl terephthalate, dimethyl isophthalate, trimellitic anhydride and phthalic anhydride.

5. The polyester resin according to claim 3, in, The portion derived from the aromatic dicarboxylic acid or the derivative thereof is included in the content of 20 parts by weight to 80 parts by weight based on 100 parts by weight of the polyester resin.

6. The polyester resin according to claim 3, wherein the aliphatic dicarboxylic acid or a derivative thereof comprises one or more selected from the group consisting of adipic acid, succinic acid, sebacic acid, isodecylsuccinic acid, maleic acid, fumaric acid, glutaric acid, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid and hexahydrophthalic anhydride.

7. The polyester resin according to claim 3, in, The portion derived from the aliphatic dicarboxylic acid or the derivative thereof is included in the content of 1 part by weight to 15 parts by weight based on 100 parts by weight of the polyester resin.

8. The polyester resin according to claim 1, wherein the polyol comprises one or more selected from the group consisting of ethylene glycol, diethylene glycol, neopentyl glycol, cyclohexanedimethanol, 1,2-propylene glycol, 1,3-propylene glycol, 2-methyl-1,3-propylene glycol, 2-methylene-1,3-propylene glycol, 2-ethyl-1,3-propylene glycol, 2-isopropyl-1,3-propylene glycol, 2,2-dimethyl-1,3-propylene glycol, 2-butyl-2-ethyl-1,3-propylene glycol, 1,4-butanediol, 2,3-butanediol, 3-methyl-1,5-pentanediol, 3-methyl-2,4-pentanediol, 1,6-hexanediol, 1,2-cyclohexanediol, 1,4-cyclohexanediol and pentaerythritol.

9. The polyester resin according to claim 1, in, The portion derived from the polyol is included in the content of 2 parts by weight to 60 parts by weight based on 100 parts by weight of the polyester resin. 10 . The polyester resin according to claim 1 , wherein the polyester resin is blocked with an acid moiety derived from a dicarboxylic acid or a derivative thereof, and has carboxyl groups at both ends. 11 . The polyester resin according to claim 1 , wherein the polyester resin has an acid value of 20 to 100 mgKOH / g. 12 . The polyester resin according to claim 1 , wherein the polyester resin has a hydroxyl value of 20 to 100 mgKOH / g.

13. A powder coating composition comprising the polyester resin according to any one of claims 1 to 12.

14. The powder coating composition according to claim 13, in, The polyester resin may be included in an amount of about 20 parts by weight to about 80 parts by weight, based on about 100 parts by weight of the powder coating composition.

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