Polyester resin composition

Abstract

To provide a polyester resin composition suitable for use in a film for high-sensitivity thermal stencil printing base paper, which is excellent in perforation sensitivity and can improve film formability.SOLUTION: A polyester resin composition contains a polyester resin containing polyethylene terephthalate and polybutylene terephthalate as main components, and has a minimum melting point (Tm1) of 219±2°C and a maximum melting point (Tm2) of 223±2°C.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a polyester resin composition, and more particularly to a polyester resin composition suitable for use as a film for a highly sensitive heat-sensitive stencil printing base paper. [Background technology]

[0002] Conventionally, thermal stencil printing base paper has been known, in which porous tissue paper is laminated to a thermoplastic resin film (substrate film) such as polyester film. Required properties of the substrate film used in thermal stencil printing base paper include film winding properties, perforation sensitivity, curl resistance, and improved image resolution and density during printing. In recent years, in order to improve film productivity, there has also been a demand for films that are wrinkle-resistant even when the film production speed is increased and have excellent film-forming properties.

[0003] As a film for thermal stencil printing base paper that satisfies various required properties, for example, Patent Document 1 proposes a biaxially oriented film made of a specific polyester and containing two or more specific types of particles. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 9-164782 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in recent years, there has been a demand for printing higher-resolution images, and the film disclosed in Patent Document 1 did not have sufficient perforation sensitivity, resulting in unclear images in some cases. Furthermore, conventional polyester resin compositions have high volume resistivities, which limits the increase in film production speed, and there is also room for improvement in terms of film productivity.

[0006] In view of the above-mentioned prior art, the present invention aims to provide a polyester resin composition suitable for use as a film for high-sensitivity heat-sensitive stencil printing base paper, which has excellent perforation sensitivity and can improve film-forming properties. [Means for solving the problem]

[0007] As a result of intensive research conducted by the present inventors to solve the above problems, it has been discovered that by controlling the melting point of a polyester resin composition within a specific range, when a film for a highly sensitive thermal stencil printing base paper is formed from the polyester resin composition, the perforation sensitivity can be increased and the film formability can be improved.

[0008] That is, the present invention is summarized as follows.

[0009] [1] A polyester resin composition containing a polyester resin primarily composed of polyethylene terephthalate (hereinafter also referred to as PET) and polybutylene terephthalate (hereinafter also referred to as PBT), having a minimum melting point (Tm1) of 219±2°C and a maximum melting point (Tm2) of 223±2°C.

[0010] [2] The polyester resin composition according to [1], wherein the amount of magnesium derived from the catalyst in the polyester resin composition is 20 ppm or less.

[0011] [3] Volume resistivity is 2×10 7 The polyester resin composition according to [1] or [2], having a resistivity of Ω·cm or less.

[0012] [4] The polyester resin composition according to any one of [1] to [3], which is used for a film for a highly sensitive heat-sensitive stencil printing base paper. [Effects of the Invention]

[0013] According to the present invention, when a film for a highly sensitive heat-sensitive stencil printing sheet is formed from a polyester resin composition, the perforation sensitivity can be increased and the film formability can be improved. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention will be described in detail below. The following description may be based on representative embodiments or specific examples, but the present invention is not limited to such embodiments. In this specification, when "X to Y" (X and Y are arbitrary numbers) is used, it means "X or more and Y or less" unless otherwise specified, and also includes "preferably greater than X" or "preferably less than Y." Furthermore, when "X or more" (X is an arbitrary number) or "Y or less" (Y is an arbitrary number), it also includes the meaning "preferably greater than X" or "preferably less than Y." In the following description, the terms "film" and "sheet" are not clearly distinguished from each other, and the term "film" includes the term "sheet," and the term "sheet" includes the term "film."

[0015] (Polyester resin composition) The polyester resin composition of the present invention contains a polyester resin composed primarily of polyethylene terephthalate and polybutylene terephthalate. "Composed primarily of" means that the combined mass of polyethylene terephthalate and polybutylene terephthalate is 50% by mass or more, preferably 65% ​​by mass or more, and particularly preferably 80% by mass or more, based on the total mass of the polyester resin. By keeping the combined mass of polyethylene terephthalate and polybutylene terephthalate within the above range, the required properties of the film used in the thermal stencil printing base paper tend to be well-balanced. The upper limit of the combined mass of polyethylene terephthalate and polybutylene terephthalate is preferably 99% by mass or less, more preferably 95% by mass or less, and particularly preferably 90% by mass or less.

[0016] The polyethylene terephthalate of the present invention can be obtained by using terephthalic acid or dimethyl terephthalate as the difunctional acid component and ethylene glycol as the glycol component.

[0017] The intrinsic viscosity of the polyethylene terephthalate in the present invention is preferably 0.550 to 0.850 dL / g, and more preferably 0.600 to 0.800 dL / g.

[0018] The polybutylene terephthalate of the present invention can be obtained by using terephthalic acid or dimethyl terephthalate as the difunctional acid component and butylene glycol as the glycol component.

[0019] The intrinsic viscosity of the polyethylene terephthalate in the present invention is preferably 0.800 to 2.00 dL / g, and more preferably 0.900 to 1.90 dL / g.

[0020] The polyethylene terephthalate and polybutylene terephthalate of the present invention may be copolymerized with other components in addition to those mentioned above, and examples of acid components include 2,6-naphthalenedicarboxylic acid, dimethyl 2,6-naphthalenedicarboxylate, adipic acid, sebacic acid, phthalic acid, isophthalic acid, trimellitic acid, and pyromellitic acid, and examples of glycol components include ethylene glycol, butylene glycol, propylene glycol, polyethylene glycol, 1,4-cyclohexanedimethanol, diethylene glycol, neopentyl glycol, and polyalkylene glycol. The copolymerization amount of other components is preferably 15 mol % or less, and more preferably 10 mol % or less, based on the total repeating units of polyethylene terephthalate or polybutylene terephthalate.

[0021] The polyester resin composition of the present invention may contain a polyester other than polyethylene terephthalate and polybutylene terephthalate as the polyester resin. Examples of polyesters other than polyethylene terephthalate and polybutylene terephthalate include polyethylene naphthalate and polybutylene naphthalate.

[0022] The intrinsic viscosity of the polyester resin composition of the present invention is preferably 0.550 to 0.850 dL / g, and more preferably 0.600 to 0.800 dL / g.

[0023] The polybutylene terephthalate and polybutylene terephthalate of the present invention may contain fillers such as various organic particles and inorganic particles, and various additives such as crystal nucleating agents, antioxidants, heat stabilizers, lubricants, antistatic agents, flame retardants, flame retardant assistants, antiblocking agents, viscosity modifiers, and color inhibitors, within the scope of the present invention.

[0024] The blending ratio of polyethylene terephthalate and polybutylene terephthalate in the polyester resin composition of the present invention is preferably 30 to 70% by mass of polyethylene terephthalate and 70 to 30% by mass of polybutylene terephthalate, and more preferably 40 to 60% by mass of polyethylene terephthalate and 60 to 40% by mass of polybutylene terephthalate. When the blending amount of polyethylene terephthalate is equal to or greater than the above-mentioned lower limit or equal to or less than the above-mentioned upper limit, the thermal stability is improved, resulting in good heat-resistant dimensional stability of the final film. This can prevent curling during the base paper production process or storage, and deterioration of the gradation of printed images. Conversely, when the blending amount of polybutylene terephthalate is equal to or greater than the above-mentioned lower limit or equal to or less than the above-mentioned upper limit of polyethylene terephthalate, the thermal energy required for perforation can be reduced, resulting in improved resolution and print quality during printing of the final film.

[0025] The polyester resin composition of the present invention is obtained by melt-kneading polyethylene terephthalate and polybutylene terephthalate, and optionally other polyesters. In the melt-kneading process, a vented extruder is preferred because it has the advantage of eliminating the polyester drying step, and a twin-screw extruder is more preferred than a single-screw extruder because it can promote randomization and prepare a highly sensitive film material.

[0026] The polyester resin composition of the present invention may contain, as necessary, fillers such as various organic particles and inorganic particles, and various additives such as a crystal nucleating agent, an antioxidant, a heat stabilizer, a lubricant, an antistatic agent, a flame retardant, a flame retardant aid, an antiblocking agent, a viscosity modifier, and a coloring inhibitor.

[0027] The polyester resin composition of the present invention preferably contains organic particles from the viewpoint of film winding properties. The organic particles may be made of acrylic resin, styrene resin, acrylic-styrene copolymer resin, etc., but from the viewpoint of heat resistance, organic particles made of styrene resin are preferred.

[0028] The average particle size of the organic particles is preferably 0.1 μm to 3.0 μm, more preferably 0.3 μm to 2.0 μm. When the average particle size is in this range, the winding properties of the film become good.

[0029] The amount of organic particles added is preferably 0.1 to 3.0% by mass, more preferably 0.3 to 2.0% by mass, relative to the total mass of the polyester resin composition. When the amount added is within this range, the winding properties of the film become good.

[0030] Examples of commercially available organic particles that can be used include Techpolymer (manufactured by Sekisui Chemical Industry Co., Ltd.) and Chemisnow (manufactured by Soken Chemical & Engineering Co., Ltd.).

[0031] The method for blending the above-mentioned additives and the like is not particularly limited, and examples thereof include a method in which the additives are directly blended with polyester chips, and a so-called masterbatch method in which masterbatch chips in which the additives are blended in advance in a high concentration in polyester are obtained and then blended again with polyester.

[0032] The polyester resin composition of the present invention has a minimum melting point (Tm1) that satisfies the range of 219±2°C and a maximum melting point (Tm2) that satisfies the range of 223±2°C. When the melting points are within such a narrow range and the difference between the minimum melting point (Tm1) and the maximum melting point (Tm2) is within the above range, good perforation properties can be obtained. By keeping the melting points within the above range, a decrease in perforation sensitivity can be suppressed, allowing perforation to be performed uniformly. As a result, resolution during printing is improved, and print quality is enhanced.

[0033] The melting point of the polyester resin composition can be measured using, for example, a DSC822 (manufactured by Mettler Toledo). Approximately 5 mg of the polyester resin composition is placed in the DSC device, and the temperature is raised at a rate of 20°C / min. Measurement is performed in the range of 20°C to 280°C. The apexes of the melting endothermic peaks are defined as the minimum melting point (Tm1) and the maximum melting point (Tm2), respectively.

[0034] Metal catalysts are generally used in the polycondensation of polyesters. However, in the present study, it was found that the catalyst in the polyester lowers the melting point and affects perforation sensitivity. Specifically, the amount of magnesium derived from the catalyst in the polyester resin contained in the polyester resin composition of the present invention is preferably 20 ppm or less, more preferably 15 ppm or less, and particularly preferably 10 ppm or less. By adjusting the amount of magnesium derived from the catalyst in the polyester resin to the above range, the decrease in the melting point of the polyester resin composition can be suppressed. The amount of magnesium derived from the catalyst in the polyester resin is preferably 3 ppm or more, more preferably 5 ppm or more. Note that the amount of magnesium derived from the catalyst in this specification refers to the amount of catalyst used in producing the polyester. By controlling the amount of magnesium derived from the catalyst in the polyester resin within the above range, the minimum melting point (Tm1) and maximum melting point (Tm2) of the polyester resin composition can be adjusted to the desired range, resulting in the production of a film with excellent perforation sensitivity and suitable for use in high-sensitivity thermal stencil printing base paper.

[0035] The total amount of magnesium contained in the polyester resin composition of the present invention is preferably 80 to 250 ppm, more preferably 90 to 240 ppm, and particularly preferably 100 to 230 ppm, in order to reduce the volume resistivity of the polyester resin composition and to provide excellent thermal stability.

[0036] The volume resistivity of the polyester resin composition of the present invention is 10×10 7 Ω·cm or less is preferable, and 8×10 7 Ω·cm or less, more preferably 5×10 7 Ω·cm or less, particularly preferably 2×10 7 The volume resistivity is Ω·cm or less. When the volume resistivity is in this range, adhesion to the cooling drum using the electrostatic application adhesion method during film production is improved, which increases the film production speed and improves productivity. The lower limit of the volume resistivity of the polyester resin composition is not particularly limited, but it is preferably 0.01 Ω·cm or more.

[0037] The volume resistivity of a polyester resin composition is measured by the following method. First, the polyester resin composition (resin sample) is placed in a test tube with a side branch, and after thoroughly replacing the inside of the tube with nitrogen, it is immersed in an oil bath at 160°C, and the inside of the tube is reduced to 1 Torr or less using a vacuum pump and vacuum dried for 4 hours. Next, the oil bath temperature is raised to 285°C to melt the resin sample, and then the nitrogen pressure is repeatedly increased and reduced to remove any air bubbles present. Then, a 1cm2 particle diameter sample is poured into the melt. 2 Two stainless steel electrode plates are inserted parallel to each other with a gap of 5 mm (the opposing back surfaces are covered with an insulator). After the temperature has stabilized, a DC voltage of 100 V is applied between the electrodes with a resistance meter, and the volume resistivity (Ω·cm) is calculated from the resistance value at that time.

[0038] In the present invention, adding magnesium stearate to the polyester resin composition is preferred in terms of reducing volume resistivity. The amount of magnesium stearate added is preferably 0.1 to 1.0 mass %, more preferably 0.2 to 0.9 mass %, based on the total mass of the polyester resin composition. When the magnesium stearate is within this range, the volume resistivity of the resulting polyester resin composition is sufficiently reduced to a specific range or less, and the thermal stability is also improved. Note that the amount of magnesium stearate added above is the amount of magnesium stearate added separately from the magnesium derived from the polyester resin catalyst.

[0039] (Method of producing polyester resin composition) The method for producing a polyester resin composition preferably includes a step of melt-kneading polyethylene terephthalate and polybutylene terephthalate. Here, the total amount of catalyst-derived magnesium contained in the polyethylene terephthalate and polybutylene terephthalate is preferably 20 ppm or less, more preferably 15 ppm or less, and particularly preferably 10 ppm or less. Furthermore, the total amount of catalyst-derived magnesium contained in the polyethylene terephthalate and polybutylene terephthalate is preferably 5 ppm or more, more preferably 3 ppm or more.

[0040] In this specification, the amount of magnesium derived from the catalyst refers to the amount of catalyst charged when producing the polyester. That is, the method for producing a polyester resin composition preferably includes, before the step of melt-kneading polyethylene terephthalate and polybutylene terephthalate, a step of producing polyethylene terephthalate by adding a magnesium catalyst in an amount of 20 ppm or less, preferably 15 ppm or less, and more preferably 10 ppm or less, and a step of producing polybutylene terephthalate by adding a magnesium catalyst in an amount of 20 ppm or less, preferably 15 ppm or less, and more preferably 10 ppm or less.

[0041] In the melt-kneading step of polyethylene terephthalate and polybutylene terephthalate, the blending ratio of polyethylene terephthalate and polybutylene terephthalate is preferably 30 to 70% by mass of polyethylene terephthalate and 70 to 30% by mass of polybutylene terephthalate, and more preferably 40 to 60% by mass of polyethylene terephthalate and 60 to 40% by mass of polybutylene terephthalate. Furthermore, in the melt-kneading step, polyesters other than polyethylene terephthalate and polybutylene terephthalate can also be added as needed. Examples of polyesters other than polyethylene terephthalate and polybutylene terephthalate include polyethylene naphthalate and polybutylene naphthalate.

[0042] The step of melt-kneading polyethylene terephthalate and polybutylene terephthalate preferably further includes a step of adding magnesium stearate. In this case, the amount of magnesium stearate added is preferably 0.1 to 1.0 mass% and more preferably 0.2 to 0.9 mass% based on the total mass of the polyester resin composition. When the magnesium stearate is in this range, the volume resistivity of the resulting polyester resin composition is sufficiently reduced to a specific range or less, and the thermal stability is also improved.

[0043] The total amount of magnesium contained in the polyester resin composition obtained through the melt-kneading step is preferably 80 to 250 ppm, more preferably 90 to 240 ppm, and particularly preferably 100 to 230 ppm.

[0044] In the step of melt-kneading polyethylene terephthalate and polybutylene terephthalate, various fillers such as organic particles and inorganic particles, and various additives such as crystal nucleating agents, antioxidants, heat stabilizers, lubricants, antistatic agents, flame retardants, flame retardant assistants, antiblocking agents, viscosity modifiers, and color inhibitors may be added within the scope of the present invention.

[0045] In the melt-kneading step, the melt-kneading temperature is preferably 200 to 280° C., more preferably 210 to 270° C. The screw rotation speed is preferably 100 to 250 rpm, more preferably 110 to 240 rpm. The raw material resin supply rate during kneading is preferably 90 to 160 kg / h, more preferably 100 to 150 kg / h.

[0046] The polyester resin composition obtained through the above steps has a minimum melting point (Tm1) of 219±2° C. and a maximum melting point (Tm2) of 223±2° C. The volume resistivity of the polyester resin composition is 10×10 7 Ω·cm or less is preferable, and 8×10 7 Ω·cm or less, more preferably 5×10 7 Ω·cm or less, particularly preferably 2×10 7 When the volume resistivity is in this range, adhesion to the cooling drum using the electrostatic application adhesion method during film production improves, which increases the film production speed and improves productivity.

[0047] (Production method of polyester film) The method for producing a polyester film preferably includes a step of extruding dried pellets of a polyester resin composition from a die using an extruder to form a molten sheet, and then cooling and solidifying the molten sheet with a cooling roll to obtain an unstretched sheet. In this case, it is preferable to increase the adhesion between the sheet and a rotating cooling drum to improve the flatness of the sheet, and an electrostatic application adhesion method and / or a liquid application adhesion method are preferably used.

[0048] Next, the resulting unstretched sheet is stretched in one direction using a roll or tenter-type stretching machine. The stretching temperature is usually 70 to 120°C, preferably 80 to 110°C, and the stretching ratio is usually 2.5 to 7 times, preferably 3 to 6 times. Next, the sheet is stretched in a direction perpendicular to the first-stage stretching direction, usually at 70 to 170°C, and at a stretching ratio of usually 2.5 to 7 times, preferably 3 to 6 times. Subsequently, the sheet is heat-treated at a temperature of 180 to 270°C under tension or relaxation of 30% or less to obtain a biaxially oriented film. The above stretching can also be performed in one direction in two or more stages. In this case, it is preferable to perform the stretching so that the final stretching ratios in both directions are each within the above range.

[0049] A simultaneous biaxial stretching method can also be used to produce polyester films. In this method, an unstretched sheet is simultaneously stretched and oriented in both the machine direction and the width direction under temperature control, typically at 70 to 120°C, and preferably at 80 to 110°C. The area stretch ratio is typically 4 to 50 times, preferably 7 to 35 times, and more preferably 10 to 25 times. Subsequently, the sheet is heat-treated at a temperature of 170 to 270°C under tension or relaxation of 30% or less to obtain a stretched and oriented film. Regarding the simultaneous biaxial stretching apparatus used in the above-described stretching method, any conventionally known stretching method, such as a screw method, a pantograph method, or a linear drive method, can be used. [Example]

[0050] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples as long as it does not depart from the gist of the invention.

[0051] [Measurement and evaluation method] In the following examples and comparative examples, the methods for measuring physical properties and evaluating effects were as follows.

[0052] <Intrinsic viscosity (IV)> The intrinsic viscosity of polyethylene terephthalate, polybutylene terephthalate, and polyester resin compositions was measured by the following method. Approximately 0.25 g of a sample was dissolved in approximately 25 mL of a mixed solvent of phenol and 1,1,2,2-tetrachloroethane (1 / 1 by mass) to a concentration of 1.00 g / dL, and then cooled to 30°C. At 30°C, the number of seconds it took for the sample solution and the solvent alone to fall was measured using a fully automatic solution viscometer (DT553, manufactured by Sentec Co., Ltd.), and the intrinsic viscosity (IV) was calculated using the following formula. IV=((1+4K H η sp ) 0.5 -1) / (2K H C) where η sp =η / η0-1, where η is the time it takes for the sample solution to fall, η0 is the time it takes for the solvent alone to fall, C is the concentration of the sample solution (g / dL), and K H is Huggins' constant. K H The melting temperature was 110°C for 30 minutes.

[0053] <Melting point> The melting point of the polyester resin composition was measured using a DSC822 (Mettler Toledo). Approximately 5 mg of the sample was placed in the DSC device, and the temperature was raised at a rate of 20°C / min. Measurements were performed in the range of 20°C to 280°C. The apexes of the melting endothermic peaks were taken as the minimum melting point (Tm1) and the maximum melting point (Tm2), respectively.

[0054] <Volume resistivity> 23 g of polyester resin composition (resin sample) was placed in a branched test tube with an inner diameter of 20 mm and a length of 180 mm. After thoroughly replacing the inside of the tube with nitrogen, the tube was immersed in an oil bath at 160°C and vacuum-dried for 4 hours by reducing the inside of the tube to 1 Torr or less using a vacuum pump. The oil bath temperature was then raised to 285°C to melt the resin sample, and the nitrogen pressure was repeatedly restored and reduced to remove any air bubbles present. A sample with an area of ​​1 cm was placed in the melt. 2Two stainless steel electrode plates were inserted parallel to each other with a gap of 5 mm (the opposing back surfaces were covered with an insulator), and after the temperature had stabilized, a DC voltage of 100 V was applied between the electrodes using a resistance meter (Hewlett-Packard "MODEL HP4339B"), and the volume resistivity (Ω·cm) was calculated from the resistance value at that time.

[0055] <Average particle size> Measurement was performed using a laser diffraction particle size distribution analyzer (MT-3000II) manufactured by Nikkiso Co., Ltd.

[0056] <Film-forming property evaluation> The resulting polyester resin composition was extruded into a sheet at 265°C from an extruder and rapidly solidified using an electrostatically applied cooling method on a rotating cooling drum with a surface temperature set to 30°C, resulting in a substantially amorphous sheet with a thickness of 13.5 μm. The resulting sheet was stretched 2.5 times in the machine direction at 65°C, further stretched 1.2 times at 75°C, and then stretched 3.0 times in the transverse direction at 80°C, after which it was heat-treated at 90°C for 6 seconds to produce a biaxially oriented film with a thickness of 1.2 μm. Film formability was evaluated using the following four-point scale. ◎:High speed film production (300mm / min or more) is possible, and there are no wrinkles in the film Good: Slight film wrinkles occur when high-speed film production (300 mm / min or more) is performed. △: Many wrinkles occur in the film when high-speed film production (300 mm / min or more) is performed. ×: It is difficult to perform high-speed film production (300 mm / min or more).

[0057] (Production of polyethylene terephthalate A) 100 parts by mass of terephthalic acid, 30 parts by mass of isophthalic acid, and 58 parts by mass of ethylene glycol were charged into an esterification reactor equipped with a stirrer, a temperature raising device, and a distillate separation column, and heated to 250°C to melt the terephthalic acid. Next, an ethylene glycol solution of antimony trioxide was added so that 0.020 parts by mass of antimony trioxide was added per 100 parts by mass of polyethylene terephthalate to be obtained. The amount of ethylene glycol in this ethylene glycol solution was so small that it was negligible as raw material ethylene glycol. The mixture was then stirred and maintained at atmospheric pressure for 4 hours while distilling off water to carry out the esterification reaction, essentially completing the esterification reaction and obtaining an oligomer. Next, an ethylene glycol solution of magnesium acetate tetrahydrate was added to the oligomer transferred to the polycondensation reactor so that the amount of magnesium acetate added was 0.009 parts by mass per 100 parts by mass of polyethylene terephthalate to be obtained (the amount of magnesium derived from the catalyst relative to polyethylene terephthalate was 10 ppm). Furthermore, an ethylene glycol solution of ethyl acid phosphate was added as a thermal stabilizer so that the amount added was 0.020 parts by mass per 100 parts by mass of the resulting polyethylene terephthalate, and an ethylene glycol solution of antimony trioxide was added as a polycondensation catalyst so that the amount added was 0.013 parts by mass. Next, the pressure was reduced from atmospheric pressure to 0.05 kPa, the temperature was raised from 225°C to 280°C, and the mixture was held at 280°C for 2 hours to carry out a melt polycondensation reaction, yielding polyethylene terephthalate with an intrinsic viscosity of 0.715 dL / g. The resulting polyethylene terephthalate was then crystallized using a funnel-through crystallizer at a feed rate of 100 kg / h and a temperature of 100 to 110°C to yield polyethylene terephthalate A.

[0058] <Production of polyethylene terephthalate B> The production of polyethylene terephthalate A was carried out in the same manner as that of polyethylene terephthalate A, except that the amount of magnesium acetate added of the ethylene glycol solution was changed so that the amount of magnesium acetate added was 0.441 parts by mass per 100 parts by mass of the polyethylene terephthalate to be obtained (the amount of Mg derived from the catalyst relative to the polyethylene terephthalate was 50 ppm), and polyethylene terephthalate B having an intrinsic viscosity of 0.715 dL / g was obtained.

[0059] <Production of Polyethylene Terephthalate C> 100 parts by weight of dimethyl terephthalate, 22 parts by weight of dimethyl isophthalate, and 71 parts by weight of ethylene glycol were charged into a transesterification reactor equipped with a stirrer, a heating device, and a distillate separation column, and heated to 150 ° C to melt the dimethyl terephthalate. Next, an ethylene glycol solution of calcium acetate monohydrate was added so that 0.030 parts by weight of calcium acetate was added to the resulting polyester resin. The temperature was then raised to 225 ° C over 3 hours under normal pressure, and the mixture was further stirred at 225 ° C for 1 hour and 15 minutes while distilling off methanol to carry out the transesterification reaction, essentially completing the transesterification reaction and obtaining an oligomer. Next, the resulting oligomer was fed into a polycondensation reactor equipped with a stirrer, a heating device, and a pressure reducing device, and at the same time, an ethylene glycol slurry of silica particles was added to the polyester resin so that the content of silica particles having an average primary particle size of 1.2 μm was 2% by weight. Next, an ethylene glycol solution of phosphoric acid was added as a thermal stabilizer so that the phosphoric acid content was 0.063 parts by mass relative to the resulting polyester resin content, and an ethylene glycol solution of antimony trioxide was added as a polycondensation catalyst to the oligomer so that the antimony trioxide content was 0.045 parts by mass relative to the resulting polyester resin content. The pressure was then reduced from atmospheric pressure to 0.05 kPa, and the temperature was raised from 225°C to 280°C over 4 hours and maintained at 280°C for 2 hours to carry out a melt polycondensation reaction, yielding polyethylene terephthalate with an intrinsic viscosity of 0.640 dL / g. The resulting polyethylene terephthalate was then crystallized using a funnel-through crystallizer at a feed rate of 170 kg / h and a temperature of 130-140°C to yield polyethylene terephthalate C.

[0060] <Production of Polybutylene Terephthalate A> A slurry containing 1.8 moles of 1,4-butanediol per mole of 1.0 mole of terephthalic acid was continuously fed to an esterification reactor equipped with a screw agitator and filled with polybutylene terephthalate oligomer with an esterification rate of 99%, where the esterification reaction was carried out. A 1,4-butanediol solution containing a tetrabutyl titanate catalyst in an amount to provide 40 ppm of titanium relative to the polybutylene terephthalate was fed to the esterification reactor. Additional 1,4-butanediol was fed to the esterification reactor so that the molar ratio of 1,4-butanediol to terephthalic acid was 3.2. The reactor temperature was 226°C, the pressure was 60 kPa, and the average residence time was 180 minutes. The polybutylene terephthalate oligomer with an esterification rate of 96.5% was then continuously transferred to the first polycondensation reactor. In the first polycondensation reactor, a continuous polycondensation reaction was carried out in the presence of magnesium acetate tetrahydrate catalyst in an amount that resulted in 10 ppm of magnesium relative to the polybutylene terephthalate. The reaction temperature was 230°C, the pressure was 3.9 kPa, and the average residence time was 120 minutes. The product was then transferred to the second polycondensation reactor, where a continuous polycondensation reaction was carried out. The reaction temperature was 240°C, the pressure was 130 Pa, and the average residence time was 100 minutes. The resulting polymer was continuously withdrawn in the form of strands from the die head via a withdrawal line using a withdrawal gear pump and a filter, and then cut with a rotary cutter to obtain polybutylene terephthalate A with an intrinsic viscosity of 1.20 dL / g.

[0061] <Production of Polybutylene Terephthalate B> The same procedure as in the production of polybutylene terephthalate A was carried out except that magnesium acetate was not added and the polymer was withdrawn after being transferred to the second polycondensation reaction vessel, thereby obtaining polybutylene terephthalate B having an intrinsic viscosity of 1.0 dL / g.

[0062] Example 1 Polyethylene terephthalate and polybutylene terephthalate were blended in the proportions shown in Table 1, and 1% by mass of organic particles (average particle size 1 μm) of styrene-acrylic copolymer resin and 0.54% by mass of magnesium stearate were added. The mixture was kneaded in a vented twin-screw extruder at a temperature of 215°C and a resin feed rate of 110 kg / h to obtain a polyester resin composition with an intrinsic viscosity of 0.730 dL / g.

[0063] <Comparative Example 1> Polyethylene terephthalate and polybutylene terephthalate were blended in the proportions shown in Table 1, and 1% by mass of organic particles (average particle size 1 μm) of styrene-acrylic copolymer resin and 0.54% by mass of magnesium stearate were added. The mixture was kneaded in a vented twin-screw extruder at a temperature of 255°C and a resin feed rate of 120 kg / h to obtain a polyester resin composition with an intrinsic viscosity of 0.630 dL / g.

[0064] <Comparative Example 2> A polyester resin composition having an intrinsic viscosity of 0.630 dL / g was obtained in the same manner as in Comparative Example 1, except that the amount of magnesium stearate added was 0.36% by mass.

[0065] <Comparative Example 3> A polyester resin composition having an intrinsic viscosity of 0.630 dL / g was obtained in the same manner as in Comparative Example 1, except that the amount of magnesium stearate added was 0.18% by mass.

[0066] <Comparative Example 4> A polyester resin composition having an intrinsic viscosity of 0.630 dL / g was obtained in the same manner as in Comparative Example 1, except that no magnesium stearate was added.

[0067] [Table 1]

[0068] From Table 1, it can be seen that the polyester resin composition of Example 1, which satisfies the specific melting point range, is a polyester resin composition that has excellent perforation sensitivity and film-forming properties, and is suitable for use as a film for high-sensitivity thermal stencil printing base paper.

Claims

1. A polyester resin composition comprising a polyester resin primarily composed of polyethylene terephthalate and polybutylene terephthalate, the polyester resin composition having a minimum melting point (Tm1) of 219±2°C and a maximum melting point (Tm2) of 223±2°C.

2. 2. The polyester resin composition according to claim 1, wherein the amount of magnesium derived from the catalyst in the polyester resin is 20 ppm or less.

3. Volume resistivity is 2 x 10 ７ The polyester resin composition according to claim 1, having a modulus of elasticity of Ω·cm or less.

4. 2. The polyester resin composition according to claim 1, which is used for a film for high-sensitivity heat-sensitive stencil printing base paper.

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