WO2005068531A1

WO2005068531A1 - Polyester resin with improved infrared absorbing properties

Info

Publication number: WO2005068531A1
Application number: PCT/KR2004/003379
Authority: WO
Inventors: Jin-Gi Lee; Yeon-Suk Kim; Byeong-Ok Choi; Kyeong-Jin Park
Original assignee: Taekwang Ind Co., Ltd; Daehan Synthetic Fiber Co., Ltd
Priority date: 2004-01-16
Filing date: 2004-12-21
Publication date: 2005-07-28
Also published as: KR100455456B1

Abstract

The present invention is related to polyester resins for the manufacture of containers and the methods of their manufacture, in which productivity may be improved by increasing the efficiency of absorbance of infrared light during molding of polyester containers. The present invention is characterized by that the colors of polyester resins are not changed during polyester polymerization and the red irion oxide compound coated with well-dispersible and heat-resistant manganese oxide is input prior to or in the middle of the polymerization reaction in an amount of 100 ppm. The efficiency of absorbance of infrared light of preforms manufactured with the polyester resins according to the present invention after they pass through the IR heater zone is improved by greater than 7% compared to that of those having no additives added. And the preforms manufactured according to the present invention have superior colors, transparency, and molding capacity.

Description

POLYESTER RESIN WITH IMPROVED INFRARED ABSORBING PROPERTIES

[Technical Field]

The present invention is related to thermoplastic polyester (hereinafter referred to as 'PET') resins having superior colors and infrared-absorbing efficiency and the methods of manufacture of these resins. PET resins are materials of which amounts of use for containers for various kinds of carbonated drinks, natural water, and fruit juices, and for sheet, etc. are on the increasing trend day by day since they have superior physical properties in stability, strength, etc. Therefore, there has been an increasing demand for resins that have been transparent and have had superior colors while increasing productivity during molding. There are a few methods of manufacture of PET containers for drinks including a method of manufacture of high-pressure blowing before resins are solidified completely after they are ejected from a machine, and a method of ejection of preforms in the first step and re-heating of these preforms and high-pressure blowing in molding frames in the second step. Among them, the 2-step method is utilized mostly owing to the productivity and variety of the kinds of containers. In the manufacture of molding containers in the 2- step method, the core requisite for increasing productivity is shortening of the re-heating time. Important factors in re-heating of preforms are how efficiently infrared light is absorbed, the temperature of PET resins is increased evenly and promptly higher than the glass transition temperature (Tg), and the resins are softened since infrared heaters are used usually. Also, the colors, transparency, black spots, evenness in thickness, etc. of molding containers are elements for the evaluation of the quality of molded products. Many methods have been devised in order to shorten the time of heating with infrared light of preforms of PET containers. For example, disclosed in the U.S. Patents No. 4,408,004, No. 4,476,272, and No. 4,535,118 are methods of improving absorbancy of infrared light by adding carbon black during re-heating of preforms; and disclosed in the U.S. Patents No. 5,925,710 and No. 6,034,167 and Laid-Open No. 2001-0,043,209 are methods of improving absorbancy of infrared light by adding graphite. However, the use of carbon black or graphite is problematic in that it is extremely difficult to disperse them since they are non-polar, and therefore, they may appear in the form of black spots, and the color tends to be darker even if a small amount is added. A method of combining antimony particles, phosphorus compounds, etc. is disclosed in the U.S. Patent No. 5,419,936. However, this method is not effective for shortening the time of re-heating although transparency may be maintained. Disclosed in the U.S. Patents No. 4,250,078 and No. 4,420,581 are methods of shortening the time of re-heating by adding red iron oxide. In this case, the red color appears although absorbancy of infrared light is improved, and therefore, the green color is maintained by using anthraquinone dyes. That is, it is difficult to employ these methods to have the original colors of PET resins, and it is problematic in that the application of these methods is very limited. The elements to be equipped by the resins in the manufacture of molded containers in the 2-step method are not only that the time of re-heating should be shortened by improving absorbancy of infrared light in order to improve productivity, but also that the colors, transparency, and homogeneous molding capacity should be satisfied. [Disclosure of the Invention]

In order to resolve the above-described problems, an object of the present invention is to provide with thermoplastic PET resins containing the red iron oxide compound coated with manganese oxide having improved productivity, as well as superior colors and transparency, by increasing absorbancy of infrared light so that preforms are heated higher than the glass transition temperature in a shorter time compared to using general PET resins having no additives added when manufacturing containers through reheating and blow molding of preforms after they are made, and to provide with the methods of manufacture of these resins. Another object of the present invention is to provide with preforms manufactured by using thermoplastic PET resins containing the red iron oxide compound coated with manganese oxide. Still another object of the present inention is to provide with containers manufactured with thermoplastic PET resin preforms containing the red iron oxide compound coated with the above manganese oxide. The main component of MFO, which is the additive of the present invention, is the compound of red iron oxide and manganese oxide. And a small amount of a part of the compound of silicon oxide and/or aluminum oxide is mixed and sintered at a high temperature. It is a black heat-resistant inorganic oxide containing 50 to 90 weight % of the red iron oxide compound, 8 to 43 weight % of the manganese oxide compound, and 2 to 5 weight % of the silicon oxide and/or aluminum oxide compound as another component. Also, the above MFO is dispersed and distributed evenly in the resins irrespective to when it is added, i.e., in the early stage or at any time of a reaction, during the polymerization of PET resins, since it has superior heat resistance and dispersibility. And it has superior colors since its colors are not changed. When making and re-heating preforms with an infrared heater, the efficiency of absorbance of infrared light is improved if MFO is added compared to the case that it is not added. As to the amount of input of MFO in the present invention, it is preferable to have 3 to 100 ppm of MFO contained with respect to the amount of PET resins, more preferably, 5 to 50 ppm of MFO, in order to produce resins having improved absorbancy of infrared light and colors. If its concentration is lower than 3 ppm, its efficiency of absorbance of infrared light is lowered although its colors may be improved; and if its concentration is greater than 100 ppm, it is not desirable in that white turbidity occurs during blow molding and it becomes opaque since its color becomes inferior and the speed of crystallization becomes faster. Also, as to the particle size of MFO in the present invention, it is preferable to maintain 0.1 to 20 microns (micrometers), more preferably, 0.1 to 10 microns. If the particle size is too small, the ratio of generation of sub-standard products during blow molding is increased and black spots are found in molded products since particles are aggregated, dispersion becomes uneven, and the absorbancy of infrared light of preforms is deviated; and if the particle size becomes too large, the surface of molded products is not smooth and opaque. The present invention is illustrated in detail below: The resins according to the present invention are applicable to both of thermoplastic homopolymers and copolymers that may be crystallized. However, the most desirable thermoplastic polymers in the present invention are PET resins, that are thermoplastic polymers produced by the stoichiometric reaction of dicarboxylic acid and/or its derivatives and diol components. Generally, known methods of manufature of PET resins include a method of production of bis(2-hydroxyethyl) terephthalate (hereinafter referred to as 'BHET') through transesterification of dimethyl terephthalate (hereinafter referred to as 'DMT') and ethylene glycol (hereinafter referred to as 'EG') in the presence of catalysts such as manganese, calcium, lithium, sodium compounds, etc., or a method of manufacture through the production of BHET according to the direct esterification of terephthalic acid (hereinafter referred to as 'TPA') and EG, and then, the condensation polymerization reaction of this BHET at 265 to 295°C under the vacuum below 1 torr in the presence of condensation polymerization catalysts such as antimony, titanium, germanium compounds, etc. The main components that may be used for the synthesis of the resins according to the present invention include dicarboxylic acids and their derivatives such as phthalic acid, isophthalic acid, terephthalic acid, cyclohexanedicarboxylic acid, cyclohexanediacetic acid, naphthalene-2,6-dicarboxylic acid, sebacic acid, adipic acid, succinic acid, etc.; anhydrides and esters corresponding to the above; diols such as ethylene glycol, diethylene glycol, triethylene glycol, 1,4-cyclohexanedimethanol, 1,3- propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2,2-dimethyl-l,3- propanediol, 2,2-diethyl-l,3-propanediol, 2-methyl-l,4-pentanediol, 1,3-hexanediol, etc. As to reaction catalysts, one or more kinds of catalysts selected from transesterification catalysts in the above-described DMT method such as manganese, calcium, lithium, sodium, zinc, cobalt compounds, etc. and polymerization condensation reaction catalysts such as antimony, titanium, germanium, etc. may be combined and used. It is also acceptable to add complementary coloring agents such as cobalt acetate, etc., heat resistance agents such as phosphorus compounds, etc., charging prevention agents, UN cut-off agents, fluorescence enhancing agents, coloring agents, etc. The present invention is illustrated in still more detail below: Into a reator, 40 to 45 moles of terephthalic acid, 80 to 90 moles of ethylene glycol, and 0 to 5 moles of isophthalic acid are put, mixed for about 10 minutes, heated to 230 to 240°C, and made to have the maximum pressure of the inside of the reactor of below 4.5 kg_f /cm² in order to perform esterification. When esterification is progressed 97 to 98% with respect to the throughput of water produced during the reaction, the pressure inside of the reactor is increased slowly by controlling a valve. Thereafter, 200 to 600 ppm of antimony trioxide is input as a polymerization condensation catalyst, 50 to 300 ppm of cobalt acetate as a complementary coloring agent, and 50 to 150 ppm of phosphoric acid as the thermal stabilizer of BHET, and the temperature is increased up to 270 to 280°C while reducing the pressure slowly for 60 minutes. Thermoplastic PET resins are manufactured by reacting at 285 to 290°C for the final-stage temperature of the polymerization condensation reaction for 130 minutes in a vacuum state below 1.0 torr, where the intrinsic viscosity of polymers is at a level of 0.58 to 0.65 dl/g. MFO which is an additive for the improvement of absorbancy of infrared light disclosed in the present invention is input in the early stage or during a reaction in the above process. Preferably, 3 to 100 ppm of MFO, more preferably, 5 to 50 ppm, with respect to the amount of PET resins, is added into ethylene glycol to have 0.5 weight % in advance to prepare for a mixed solution. It is observed that, if more than 200 ppm of MFO is added, the speed of the condensation polymerization reaction is increased rapidly due to the catalytic action of manganese oxide or red iron oxide; and if less than 100 ppm of MFO is added, no particular changes are observed during the reaction. In order to use PET for containers or sheet in the present invention, it is difficult to increase the degree of polymerization up to a molecular weight having a required strength only by performing the above liquid-phase polymerization process. It is because the time for polymerization should be extended, or the amounts of catalysts should be increased, in which case the color becomes inferior. Therefore, the degree of polymerization should be increased by performing a separate polymerization process in a solid state after the liquid-phase polymerization process. In order to prevent coagulation of chips, the surface of resin chips is crystallized by putting the chips manufactured according to the above-described liquid-phase polymerization into a rotary solid-phase polymerization reactor, and heating slowly up to 160°, while rotating at 20 rpm. And the solid-phase polymerization is performed at 160 to 210°C for 10 to 15 hours, where the degree of vacuum is maintained below 0.5 torrs, and the intrinsic viscosity of polymers having the solid-phase polymerization completed is made to be greater than 0.70 dl/g. Preforms are manufactured by ejecting solid-phase-polymerized chips at 280 to 290°C, and bottle molded products are manufactured through high-pressure blowing of the above preforms after measuring the temperature of the surface of the preforms by using an infrared thermometer after passing them through an infrared heater in a 2-cavity-2-stage blow molder (Frontier). The results of measurement of the characteristics of the chips that are solid-phase polymerized in the above-described method and absorbance efficiency of infrared light of preforms show that the absorbance efficiency of infrared light is improved by greater than 7.5% if 5 to 50 ppm of MFO is input compared to the case that MFO is not input; the colors and transparency are very superior in that the color-L value is greater than 73.3 and the color-b value is below -2.0; and the molding capacity is equivalent to the case that MFO is not input. General and physical properties of polymers are measured in the following methods in the present invention:

[Physical Property Measurement Method 1. Intrinsic viscosity (IN)] Into 50 ml of the 6:4 mixed solvent by weight % of phenol to tetrachloroethane, 0.2 g of a freeze-pulverized resin sample is weighed precisely, input, and dissolved, after which its viscosity is measured at 30°C by using a Ubbelode capillary viscosimeter.

[Physical Property Measurement Method 2. Acetaldehyde amount (AA)] Into a container having an inner volume of 50 ml, 5.0 g of a resin sample is weighed precisely and input. And thermal extraction is performed at 16°C for 2 hours after adding 10 ml of distilled water and closing tightly with nitrogen. The amount of acetaldehyde in the solution thus extracted is analyzed quantitatively through gas chromatography (HP 5890-11) by using isobutyl alcohol as the standard material.

[Physical Property Measurement Method 3. color-L and color-b] The tone of color of resin chips that are solution polymerized or solid-phase polymerized is measured by using a tintometer. It is shown to be white as the color-L value is higher, while it is black as the value is lower. As to the color-b value, it is shown to be yellow as the value is higher, while it is blue as the value is lower. [Physical Property Measurement Method 4. IR absorbance efficiency (%)] Preforms are manufactured through fusion ejection of resin chips that are solid- phase polymerized, and the infrared absorbance efficiency is computed according to the following equation by measuring the temperature of the surface of preforms with an infrared thermometer after passing them through an infrared heater zone in a 2-cavity-2- stage blow molder (Frontier) in the state that the speed of passing is adjusted to be consistent: IR absorbance efficiency (%) = 100 x (a - b) / b where a is the temperature measured of the surface of preforms manufactured by inputting additives; and b is the temperature measured of the surface of preforms manufactured without inputting additives.

[Physical Property Measurement Method 5. Molding capacity] The shapes, surface states, transparency, etc. of containers manufactured after blow molding are observed with the naked eyes and determined, where: very superior refers to cases that 1 or no abnormal containers are generated among 100 containers; superior refers to cases that 2 to 3 abnormal containers are generated among 100 containers; and inferior refers to cases that 4 or more abnormal containers are generated among 100 containers.

[Description of the Preferred Embodiments of the Invention] Hereinafter, preferred embodiments of the pressent invention are illustrated along with general physical properties of PET resins measured in preferred embodiments and comparative preferred embodiments as shown in Tables 1 and 2:

[Preferred Embodiment 1] Esterification is performed by inputting 6,688 g of terephthalic acid (TPA), 5,120 g of EG, 160 g of isophthalic acid (IPA), and 104 g of diethylene glycol (DEG) into a stainless steel reactor having an inner volume of 20 liters, stirring for 10 minutes, and inputting 20 ppm of the red iron oxide compound (Bayferrox '303T' of Bayer AG Company) coated with manganese oxide which is dispersed into EG in advance to have a concentration of 0.5 weight %. Esterification is performed at 235°C while maintaining 4.5 kg_f/cm² for the maximum pressure inside of the reactor, and terminated by controlling slowly the pressure valve and opening it completely after it is confirmed from the amount of water generated that the esterification reaction is progressed to the degree of 97%. Thereafter, 114 ppm of cobalt acetate, 540 ppm of antimony trioxide, and 70 ppm of phosphoric acid are input, and the temperature is increased to 270°C throughout 60 minutes while reducing the pressure slowly. The final-stage temperature of the polymeerization condensation reaction is 285°C, and the reaction is continued for 130 minutes under a vacuum of 0.8 torrs. Thereafter, chips having a diameter of 2.5 mm and a length of 3 mm are manufactured by ejecting polymers through a 5-hole nozzle to a 20- °C cooling water bath, cooling, and cutting with a cutter. The intrinsic viscosity (IN) of these polymers is 0.61 dl/g. The chips manufactured in the above method are made through solid-phase polymerization in order to increase the degree of polymerization. The chips manufactured in the above are put into a 20-liter rotary solid-phase polymerization reactor, rotated at 20 rpm, heated slowly up to 160°C in order to prevent coagulation among chips, and solid-phase polymerized at 160 to 210°C for 12 hours, where the final degree of vacuum is 0.2 torrs, and the intrinsic viscosity of polymers is 0.79 dl/g. Preforms are manufactured by ejecting solid-phase-polymerized chips at 285°C, and bottle molded products are manufactured through high-pressure blowing of the above preforms after measuring the temperature of the surface of the preforms by using an infrared thermometer after passing them through an infrared heater in a 2-cavity-2-stage blow molder (Frontier).

[Preferred Embodiments 2 through 4] Liquid-phase polymerization condensation reaction, solid-phase polymerization, and manufacture of preforms and bottle molded products are performed in the same method as that of Preferred Embodiment 1 except that the amounts of input of the red iron oxide compound coated with manganese oxide are changed as shown in Tables 1 and 2.

The results are also shown in Tables 1 and 2.

[Preferred Embodiment 5] Liquid-phase polymerization condensation reaction, solid-phase polymerization, and manufacture of preforms and bottle molded products are performed in the same method as that of Preferred Embodiment 1 except that the red iron oxide compound coated with manganese oxide is input after the esterification reaction is terminated, not in the early stage of the esterification reaction, in an amount of 30 ppm. The results are shown in Tables 1 and 2.

[Preferred Embodiment 6] Liquid-phase polymerization condensation reaction, solid-phase polymerization, and manufacture of preforms and bottle molded products are performed in the same method as that of Preferred Embodiment 1 except that the red iron oxide compound coated with manganese oxide is input after the esterification reaction is terminated, not in the early stage of the esterification reaction, in an amount of 5 ppm. The results are shown in Tables 1 and 2.

[Comparative Preferred Embodiment 1] Polymerization condensation reaction is performed in the same method as that of Preferred Embodiment 1 except that 200 ppm of the red iron oxide compound coated with manganese oxide is input. The time for the polymerization condensation reaction is for 110 minutes, and there occurs a phenomenon that the degree of polymerization is increased rapidly after 105 minutes. The intrinsic viscosity of the polymers thus obtained is 0.64 dl/g. Solid-phase polymerization, and manufacture of preforms and bottle molded products are performed in the same method as that of Preferred Embodiment 1, of which results are shown in Tables 1 and 2.

[Comparative Preferred Embodiment 2] Liquid-phase polymerization condensation reaction, solid-phase polymerization, and manufacture of preforms and bottle molded products are performed in the same method as that of Preferred Embodiment 1 except that the red iron oxide compound coated with manganese oxide is input after the esterification reaction is terminated, not in the early stage of the esterification reaction, in an amount of 3 ppm. The results are shown in Tables 1 and 2.

[Comparative Preferred Embodiment 3] Liquid-phase polymerization condensation reaction, solid-phase polymerization, and manufacture of preforms and bottle molded products are performed in the same method as that of Preferred Embodiment 1 except that the red iron oxide compound coated with manganese oxide is not input. The results are shown in Tables 1 and 2 as follows:

[Table 1]

(* 1 : Intrinsic viscosity after a liquid-phase polymerization condensation reaction)

[Table 2]

(*2: Intrinsic viscosity after a solid-phase polymerization reaction)

As shown in the above Tables 1 and 2, the absorbancy of infrared light of preforms of PET resins of the present invention is increased by greater than 7% in all cases that red iron oxide coated with manganese oxide is added, and their colors and transparency remain to be the same at the same time. Accordingly, it is seen that it is possible to provide with IR-absorbing PET resins, performs, and containers having superior physical properties according to the present invention. [Industrial Applicability]

As described in the above, the present invention is applicable extensively to the manufacture of various kinds of PET containers in that not only the productivity in molding of containers may be improved but also their colors, transparency, and molding capacity are superior by improving the absorbancy of infrared light by adding the red iron oxide compound coated with manganese oxide in the early stage or in the middle of a reaction during polyester polymerization. It will be apparent to those skilled in the art that various modifications and variations can be made in the disclosed processes and products without departing from the scope or spirit of the invention. Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.

Claims

What is claimed is:

1. A method of manufacture of infrared-absorbing polyester resins through a polymerization condensation reaction after esterification or transesterification, in which the main components are dicarboxylic acid components containing terephthalic acid or its ester-forming derivatives and diols containing ethylene glycol, characterized by that a red iron oxide compound coated with 0.1 to 20 microns of manganese oxide is input prior to or in the middle of the esterification or transesterification in an amount of 3 to 100 ppm with respect to the amount of polyester resins, and the degree of polymerization is greater than 0.58 to 0.65 dl/g of the intrinsic viscosity through the polymerization condensation reaction.

2. Infrared-absorbing polyester resins manufactured through a polymerization condensation reaction after esterification or transesterification, in which the main components are dicarboxylic acid components containing terephthalic acid or its ester- forming derivatives and diols containing ethylene glycol, characterized by that a red iron oxide compound coated with 0.1 to 20 microns of manganese oxide is input in an amount of 3 to 100 ppm with respect to the amount of polyester resins prior to or in the middle of the esterification or transesterification for the polymerization of polyester resins, after which solid-phase polymerization is performed in order to improve the efficiency of absorbance of infrared light by greater than 7.5%, and to have a color-L value of greater than 70.0 and a color-b value of less than -1.0 compared to those of the polyester resins having no red iron oxide coated with manganese oxide input.

3. The infrared-absorbing polyester resins of Claim 2, characterized by that 5 to 50 ppm of said red iron oxide compound coated with 0.1 to 20 microns of manganese oxide with respect to the amount of said polyester resins is used.

4. The infrared-absorbing polyester resins of Claim 2, characterized by that said red iron oxide compound coated with manganese oxide is a compound sintered at a high temperature, and is a heat-resistant inorganic oxide containing 55 to 90 weight % of red iron oxide, 8 to 43 weight % of manganese oxide, and 2 to 5 weight % of silicon oxide and/or aluminum oxide.

5. The infrared-absorbing polyester resins of Claim 4, characterized by that the particle size of said red iron oxide compound coated with manganese oxide is in the range of 0.1 to 10 microns.

6. The infrared-absorbing polyester resins of any of Claims 2 through 5, characterized by that the intrinsic viscosity is made to be greater than 0.70 dl/g through solid-phase polymerization.

7. Preforms manufactured through fusion ejection of said infrared-absorbing polyester resins of Claim 6 at 275 to 295°C.

8. Polyester containers manufactured through re-heating and blow molding of said preforms of Claim 7.