JP2013147547A - Copolyester resin, and polyester film for metal plate coating formed by film-forming the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester resin in which: a film-forming property is excellent; when being applied to a polyester film for metal plate coating, the break (hair) and the cut (galling) to the film are hardly caused at squeezing and ironing processes, a film surface is not damaged even if a content is enclosed in a can to be commercialized as a film for an inner surface of a metal can and then fall and external impact (dent) are given; and the corrosion of the metal can is hardly caused.SOLUTION: A copolyester resin includes, as structural units: 50 to 93 mass% of an ester oligomer (A) that contains a dicarboxylic acid unit (a1) containing at least 70 mol% of a terephthalic acid component and a diol unit (a2) containing at least 70 mol% of an ethylene glycol component, and in which the number average molecular weight is at most 700; and 7 to 50 mass% of a polyester polyol (B) that contains a hydrogenation dimer acid unit (b1) and a 1,4-butanediol unit (b2), and in which the number average molecular weight is 1,500 to 3,000.

Description

  The present invention relates to a copolymerized polyester resin and a polyester film for coating a metal plate obtained by forming the same, and in particular, a flexibility and an impact resistance suitable for a polyester film for coating a metal plate used for the purpose of preventing corrosion of a metal can. The present invention relates to an excellent copolyester resin.

  Conventionally, paints have been applied to the inner and outer surfaces of metal cans to prevent corrosion, but steel, tinplate, etc. are used for reasons such as harm to the human body, adverse effects on the environment, and deterioration in productivity due to prolonged drying. It has been studied to laminate a polyester film on a metal plate such as aluminum by heating and pressurization, and then to make a can. On the other hand, for beverage cans, a metal plate is rolled into a cylindrical shape and formed into a cylinder by welding, and then a so-called three-piece can in which a lid is attached to the upper and lower openings, and a metal plate is drawn and ironed to form a container. There is what is called a two-piece can that is molded and the lid is wound around the upper surface opening.

  Here, when trying to manufacture a two-piece can using a metal plate laminated with a polyester film, film peeling (delaminate) occurs due to insufficient adhesion to the metal plate, or a film for the outer surface of the metal can In the case of squeezing and ironing process, when the film breaks (hair), scrapes (galling), or the film is used for the inner surface of a metal can, it falls after the contents are enclosed in the can and commercialized. There was a problem that the film surface was damaged by external impact (dent) and the metal can was corroded. Furthermore, during the two-piece can molding process, the crystallization of the laminated polyester film is promoted and becomes brittle during several heating steps such as volatilization of the lubricant and drying of the printing ink. There is a problem that it is complicated and inefficient in terms of process, for example, it is necessary to rapidly cool and maintain an amorphous state.

  In order to solve these problems, for example, it has been proposed to blend polytetramethylene terephthalate-polytetramethylene oxide block copolymerized polyester (PBT-PTMG) and polyethylene wax as a flexible component to a polyester resin. (See Patent Document 1). However, in the film using this resin composition, the problems of delaminating, hair, and galling are improved, but the film is cracked by dent after enclosing the contents. The problem remains that corrosion is likely to occur. Furthermore, since PBT-PTMG resin has a high crystallization rate and crystallization is accelerated by heating during the molding process, a rapid cooling treatment after heating and drying is essential to maintain an amorphous state, and a dedicated cooling facility is required. Since it is necessary, there is a problem that the process is complicated and inefficient.

  In addition, a copolyester resin containing a specific amount of a dimer acid having 36 carbon atoms as a soft component has also been proposed (see Patent Documents 2 to 4). However, even in the case of a film using this resin composition, although hair and galling are improved, the dent resistance due to external impact is still insufficient, and it is satisfactory as a resin film for protecting the inner and outer surfaces of metal cans. It was not a thing.

  On the other hand, as a polyester elastomer, a block copolymer obtained by copolymerizing an aromatic polyester and an aliphatic polyester composed of dimer acid and butanediol has been proposed (see Patent Document 5). However, when this resin composition is used, since the high molecular weight aromatic polyester having a number average molecular weight of 5000 to 3000 is used as the hard segment, the resulting copolymer is divided into a hard segment and a soft segment. It becomes a block-like structure and becomes a cloudy appearance. In addition, when this copolymer is mixed with other polyester resins to form a sheet or film, the compatibility is poor, and thus a surging phenomenon (discharge unstable phenomenon) occurs during melt extrusion. Another problem is that the film cannot be formed.

JP 2006-199915 A Japanese Patent No. 3303999 Japanese Patent No. 3304000 Japanese Patent No. 3304003 JP 2005-60645 A

  The present invention has been made for the purpose of solving the problems of the prior art. That is, the problems to be solved by the present invention are that the film-forming property is good, and when applied to a polyester film for coating a metal plate, the film is broken (haired) and scraped (caged) in the drawing and ironing process. ) And the inner surface of the metal can, and after the contents are enclosed in the can, the product surface is not damaged even if it is dropped or subjected to external impact (dent). An object of the present invention is to provide a polyester resin excellent in various properties such that corrosion hardly occurs (dent resistance).

  As a result of intensive investigations to solve the above problems, the present inventors have found that a low molecular weight ester oligomer (A) mainly composed of ethylene terephthalate and a dimer acid-derived polyester polyol (B) having a specific molecular weight. Polyester resin obtained by random copolymerization has good film-forming properties, and when applied to a polyester film for metal plate coating, there is no rupture or scraping when forming a metal can, and it further improves dent resistance. Was found to be excellent, and the present invention was reached.

That is, the copolymer polyester resin according to the present invention comprises a dicarboxylic acid unit (a1) containing 70 mol% or more of a terephthalic acid component and a diol unit (a2) containing 70 mol% or more of an ethylene glycol component, and has a number average. A polyester polyol having a number average molecular weight of 1500 to 3000, comprising 50 to 93% by mass of an ester oligomer (A) having a molecular weight of 700 or less, a hydrogenated dimer acid unit (b1), and a 1,4-butanediol unit (b2). B) 7-50 mass% is included as a structural unit, It is characterized by the above-mentioned.
Moreover, in the said copolyester resin, it is suitable that intrinsic viscosity is 0.7-0.9.

The polyester film for covering a metal plate according to the present invention is characterized in that the copolymerized polyester resin is formed alone or mixed with another resin to form a film.
The polyester film-coated metal can according to the present invention is characterized in that the metal film-covering polyester film is coated on the inner surface and / or the outer surface of the metal can.

In addition, the method for producing a copolyester resin according to the present invention includes a dicarboxylic acid unit (a1) containing 70 mol% or more of a terephthalic acid component and a diol unit (a2) containing 70 mol% or more of an ethylene glycol component. After the condensation reaction, a depolymerization reaction is performed to obtain an ester oligomer (A) having a number average molecular weight of 700 or less, the ester oligomer (A) obtained by the above step, and a hydrogenated dimer acid unit (b1 ) And 1,4-butanediol unit (b2), and a polycondensation reaction is performed with a polyester polyol (B) having a number average molecular weight of 1500 to 3000, and the ester oligomer (A) is 50 to 93% by mass, the polyester And a step of obtaining a copolymerized polyester resin containing 7 to 50% by mass of polyol (B). A.

  The copolymerized polyester resin according to the present invention has good film-forming properties, and when used as a polyester film for coating a metal plate, the film is broken (hair) and scraped (galling) in the drawing and ironing process. As a film for the inner surface of a metal can, it is difficult to occur, and after the contents are enclosed in the can and commercialized, the film surface is not damaged even if it is dropped or subjected to an external impact (dent), and the metal can is corroded. Excellent properties such as resistance to dents (dent resistance).

Hereinafter, the present invention will be described in more detail.
The copolymer polyester resin according to the present invention comprises a dicarboxylic acid unit (a1) containing 70 mol% or more of a terephthalic acid component and a diol unit (a2) containing 70 mol% or more of an ethylene glycol component, and has a number average molecular weight of 700. A polyester polyol (B) having a number average molecular weight of 1500 to 3000, comprising 50 to 93% by mass of the following ester oligomer (A), a hydrogenated dimer acid unit (b1), and a 1,4-butanediol unit (b2). 7 to 50% by mass is included as a structural unit.

Ester oligomer (A)
In the ester oligomer (A) used in the present invention, the dicarboxylic acid unit (a1) contains 70 mol% or more of terephthalic acid units. The total amount of dicarboxylic acid units may be terephthalic acid units. When the terephthalic acid unit is less than 70 mol%, hair tends to be easily generated in the molding stage of the metal can. The dicarboxylic acid component other than terephthalic acid may be contained in a range of less than 30 mol% within a range that does not impair the laminating property to the metal plate and the characteristics during metal can molding. For example, isophthalic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, 1,4-naphthalenedicarboxylic acid, 4,4'-biphenyldicarboxylic acid, 1,12-dodecanoic acid, 1,2-cyclohexanedicarboxylic acid, 1 , 3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid and the like, and these may be used alone or in admixture of two or more. Of these, from the viewpoint of improving the dent resistance by controlling the crystallinity of the copolyester resin, for example, isophthalic acid can be suitably used in the range of about 1 to 30 mol%.

  The diol unit (a2) contains 70 mol% or more of an ethylene glycol unit. The total amount of diol units may be ethylene glycol units. When the ethylene glycol unit is less than 70 mol%, for example, when blended with a polyethylene terephthalate resin and used for a film, the compatibility is poor and the dent resistance may be poor. Diol components other than ethylene glycol may be contained in a range of less than 30 mol%, for example, propylene glycol, butanediol, neopentyl glycol, diethylene glycol, cyclohexane dimethanol and the like are used alone. Or you may use it, mixing 2 or more types.

  The number average molecular weight of the ester oligomer (A) used in the present invention is 700 or less, preferably 300 to 700. By performing the copolymer using the ester oligomer (A) having a number average molecular weight of 700 or less, a polyester polyol (B) is randomly bonded in the polymer chain, and a copolymer polyester resin having a transparent appearance is obtained. . In addition, since the obtained copolyester resin has good compatibility with other resins, problems such as surging phenomenon (unstable discharge phenomenon) occur when blended with other resins and melt-extruded. Without forming a stable film.

  On the other hand, for example, when an ester oligomer having a number average molecular weight exceeding 700 and using around 1000 is used, the polymerization reaction reaches a peak in the copolymerization reaction with the polyester polyol (B). A high viscosity copolyester resin of about 7 to 0.9 cannot be obtained. Further, when a polyester having a number average molecular weight exceeding 5,000 is used, a polymer copolyester resin can be obtained without causing a peaking phenomenon of the polymerization reaction, but the copolyester resin obtained is an ester (A). Since the molecular weight of the unit is large, it becomes a-(A)-(B) -type block copolymer, and the appearance of the resin becomes cloudy due to phase separation. Furthermore, since such a block copolymer is poorly compatible with other resins, a surging phenomenon (discharge unstable phenomenon) occurs during melt extrusion, and a sheet or film can be formed. There is also a problem that it cannot be done.

  The ester oligomer (A) is obtained by esterifying the dicarboxylic acid component (a1) mainly containing terephthalic acid and the diol component (a2) mainly containing ethylene glycol by a known method. For example, a method of obtaining an oligomer by performing a transesterification reaction with the diol component (a2) by adding a catalyst using a starting material in which a methyl group is added to the end of the dicarboxylic acid component (a1), or an unmodified dicarboxylic acid component ( A method of obtaining an oligomer by a direct esterification reaction with the diol component (a2) using a1) as a starting material.

  In the production of the ester oligomer (A), for example, after reaching a predetermined esterification rate at a reaction temperature of 230 to 250 ° C., 3 to 10% by weight of diol (ethylene glycol) is added to the total oligomer obtained. It is desirable to carry out the depolymerization reaction for about 30 minutes to 1 hour in a state where it is put into the system and the internal temperature is maintained at 230 to 250 ° C. After the esterification reaction, the number average molecular weight of the ester oligomer (A) can be adjusted to 700 or less by performing a depolymerization reaction using a diol (ethylene glycol). On the other hand, when the depolymerization reaction is not performed, the number average molecular weight of the ester oligomer becomes high exceeding 700 under normal conditions. Alternatively, when the depolymerization reaction is not performed, the number average molecular weight can be controlled to 700 or less by setting the molar ratio of the diol component to the dicarboxylic acid component in a high range of 1.25 to 1.60. If the molar ratio is less than 1.25, the number average molecular weight exceeds 700.

Polyester polyol (B)
The polyester polyol (B) used in the present invention has a dicarboxylic acid unit consisting of a hydrogenated dimer acid unit (b1). Dimer acid is a C36 dicarboxylic acid compound obtained by dimerizing an unsaturated fatty acid having 18 carbon atoms such as oleic acid or linoleic acid. The dimer acid in which the unsaturated double bond remaining after dimerization is saturated by hydrogenation is a hydrogenated dimer acid, and the dicarboxylic acid unit of the polyester polyol (B) is composed of this hydrogenated dimer acid unit (b1). . Normally, hydrogenated dimer acid is obtained as a mixture of a compound having a linear branched structure compound, an alicyclic structure, etc., and these contents differ depending on the production process. It is not limited. The diol unit of the polyester polyol (B) is composed of a 1,4-butanediol unit (b2). The terminal of the polyester polyol (B) is a hydroxyl group derived from the 1,4-butanediol unit (b2).

  The number average molecular weight of the polyester polyol (B) is 1500 to 3000, preferably 1800 to 2500. When the average molecular weight is within this range, the reactivity during copolymerization is excellent, and the performance of the obtained copolymer polyester resin as a metal plate coating film is also excellent. In contrast, when the average molecular weight is less than 1500, the reactivity at the time of copolymerization is good, but when the obtained copolymer polyester resin is used for a film for protecting the inner and outer surfaces of a metal can, the dent resistance is improved. There is a tendency to be inferior. On the other hand, when the average molecular weight exceeds 3000, the reactivity at the time of copolymerization is poor, and a copolymer polyester resin having a desired molecular weight may not be obtained.

  The polyester polyol (B) can be obtained by esterifying the hydrogenated dimer acid unit (b1) and the 1,4-butanediol unit (b2) by a known method. Thus, it is necessary to adjust the molar ratio during the reaction. Alternatively, a commercially available product may be used as the polyester polyol (B). For example, Priplast 3199 (manufactured by Croda) is commercially available as a polyester polyol having a number average molecular weight of 2200 consisting of hydrogenated dimer acid and 1,4-butanediol. In addition, Priplast 3162, 3192, 3196, 2101, 2104 (both manufactured by CRODA Co., Ltd.) and the like are available as other commercially available polyester polyol products.

Copolymerized polyester resin The copolymerized polyester resin of the present invention is obtained by copolymerizing 50 to 93% by mass of an ester oligomer (A) and 7 to 50% by mass of a polyester polyol (B). Here, content which occupies in all the polymers of polyester polyol (B) is 7-50 mass%, Preferably it is 15-35 mass%. When the content of the polyester polyol (B) is in the above range, the copolymerization reactivity is excellent, and when the obtained copolymer polyester resin is used for a film for protecting the inner and outer surfaces of a metal can, particularly dent resistance. Is excellent. Furthermore, since a copolyester resin in which the polyester polyol (B) is randomly bonded in the polymer chain is obtained, the appearance becomes colorless and transparent or light yellow and transparent. On the other hand, when the content of the polyester polyol (B) is less than 7% by mass, the dent resistance is inferior when used for a film for protecting the inner and outer surfaces of a metal can. In addition to being inferior, in the obtained copolyester resin, phase separation of the polyester polyol (B) occurs, and the appearance may become cloudy.

  The copolymerization reaction of the ester oligomer (A) and the polyester polyol (B) can be performed by a conventionally known method. For example, the reaction system to which each component is added is gradually depressurized from atmospheric pressure to 133.3 Pa. A series of reactions can be performed under the following high vacuum. It is desirable to control the temperature during the reaction between 250 and 270 ° C. If the temperature exceeds 270 ° C., a viscosity decrease due to deterioration occurs in the latter half of the copolymerization reaction, and the copolymerization reaction does not proceed below 250 ° C. There is. As the polymerization catalyst used for the copolymerization reaction, antimony trioxide, germanium dioxide, titanium compound, etc. can be used. Of these, tetrabutyl titanate and tetraisosodium are used in terms of reactivity, safety and price. It is preferable to use a titanium compound such as propoxy titanate.

  In addition, in the copolymerized polyester resin of the present invention, a metal salt such as magnesium acetate, calcium acetate or magnesium chloride may be added to stabilize the electrostatic adhesion to the cooling roll when forming a melt-extruded film. Is possible. Furthermore, as an anti-blocking agent for film rolls, an appropriate amount of inert particles such as silica, alumina, calcium carbonate, and titanium dioxide can be blended, and the average particle size of the inert particles is 1.0 to 4.0 μm. preferable. If it is less than 1.0 μm, the anti-blocking property is inferior, and if it exceeds 4.0 μm, particles may fall off due to wear or breakage may occur during film stretching.

  Moreover, the copolyester resin of this invention may contain additives, such as a heat stabilizer, antioxidant, and an ultraviolet absorber, as needed. Antioxidants include hindered phenol-based antioxidants, phosphorus-based antioxidants, sulfur-based antioxidants, and the like, and hindered phenol-based antioxidants are particularly preferable. These antioxidants may be added in combination or added, and the content is preferably 100 to 5000 ppm.

  The copolymerized polyester resin of the present invention can be used by forming a film alone, but it is desirable to use it by blending with another polyester resin. In particular, when used as a film for protecting the inner and outer surfaces of metal cans, the copolymer polyester resin of the present invention is modified using, for example, polyethylene terephthalate resin, polyethylene terephthalate-isophthalate copolymer resin, and other third and fourth components. It is desirable to form a film by blending with another polyester resin such as a modified polyethylene terephthalate resin. When blended with other polyester resins, it is desirable to blend the copolymerized polyester resin of the present invention in the range of 2 to 90% by mass, more preferably 7 to 50% by mass.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further more concretely, this invention is not limited to these Examples. In addition, the various characteristic values in an Example are evaluated by the method shown below.

(1) Intrinsic viscosity (dl / g)
Various copolyester resins obtained in Examples and Comparative Examples were dissolved in a mixed solvent of phenol / tetrachloroethane = 60/40 (weight ratio), and an automatic viscosity measuring apparatus equipped with an Ubbelohde viscometer (Sun Electronics Industry) The solution viscosity was measured at 20 ° C. using ALC-6C).
(2) Resin appearance About the various copolyester resin obtained in the Example and the test example, the state of the external appearance was determined visually.
(3) Glass transition temperature (Tg), crystallization temperature (Tc) and melting point (Tm)
10 mg of a polyester resin composition was added to a scanning differential calorimeter DSC (Perkin
Measurement was performed at a heating rate of 10 ° C./min using DSC7) manufactured by Elmer.
(4) Film moldability 10% by mass of various copolyester resins obtained in Examples and Comparative Examples, 90% by mass of solid-phase polymerized isophthalic acid 10 mol% copolymerized polyethylene terephthalate resin (intrinsic viscosity 0.75) Were kneaded at 250 ° C. with a twin-screw kneading extruder (TEX30α manufactured by Nippon Steel). Thereafter, after drying the obtained kneaded resin, a single-layer sheet having a width of 350 mm and a thickness of 80 μm was formed at 250 ° C. using a sheet-forming machine equipped with a φ35 mm short-axis extruder and a T-die. A uniaxial stretching roll film (single layer) having a width of 190 mm and a thickness of 20 μm was collected after the end surface was cut by stretching four times at a stretched part roll surface temperature of 85 to 100 ° C. with a uniaxial stretching machine. The moldability in the above series of film forming steps was evaluated for each copolymer polyester resin.
(5) Occurrence of hair and galling in a can-making process of a film-coated metal can After various types of film-coated aluminum plates obtained as described above are cup-shaped with a φ66 mm punch so that the polyester film-coated surface becomes the inner surface, A trimmer process was performed by squeezing with a three-stage die, and then an amorphous process was performed at 240 ° C., followed by natural cooling without applying a rapid cooling process, and then a flange process for the neck part was performed to obtain a two-piece can. In the above series of metal can making processes, when the film surface is damaged by squeaking with a die, scratches generated in the molding direction are galling, and the beard-like film fragments generated on the end surface of the can due to the scratches are removed. A hair having a frequency of less than 5% with respect to the total number of cans was evaluated as ◎, a product having a frequency of less than 5 to 10% was evaluated as ◯, and 10% or more was evaluated as ×.
(6) Dent resistance in film-coated metal cans After filling sports drinks (Pocari Sweat: Coca-Cola) into the various two-piece cans obtained as described above, the cans are covered and metal cans at 5 ° C. A slit-like dent was given to the outside, stored at 55 ° C., and after 1 month, the corrosion state of the dent was examined and evaluated according to the following criteria.
No corrosion: ◎
Less than half of the corroded part (more than half of the dent part is not corroded): ○
Slight corrosion (corrosion partially over the entire area of the dent): △
Total corrosion (all areas of the dent are completely corroded): ×

The number average molecular weight of the ester oligomer (A) was evaluated as follows.
(I) After adding 25 mL of benzyl alcohol to 0.5 g of ester oligomer and heating, further adding 25 mL of diethylene glycol, further heating, cooling, adding 25 mL of methyl alcohol and phenolphthalein as an indicator, and adding 0.1 normal hydroxylation The solution was titrated with a sodium solution, and the acid value was determined from the following formula.
Acid value (mgKOH / g) = (A−B) × factor × 5.61 / sample weight A: titration in blank test B: titration in main test (ii) ester using deuterated chloroform / trifluoroacetic acid as solvent H-NMR was measured about the oligomer and the molar ratio C of the ester oligomer was calculated | required from the integral ratio of the peak based on ethylene glycol and the peak based on an acid component.
(Iii) From the esterification rate Es and the molar ratio C of the ester oligomer, the number average molecular weight was calculated from the following formula. The esterification rate Es can be calculated by a conventional method based on the acid value.
Number average molecular weight = 192.2 / (1 + C-2 × Es)

  The inventors of the present invention produced copolymer polyester resins of the following examples and comparative examples, and evaluated various physical properties using the methods described above. The raw material preparation amount of the copolymer polyester resin of each Example and a comparative example and the evaluation result of each resin are put together in Tables 1-3, and are shown.

<Example 1>
The theoretical scale of the final copolymer polyester resin is 11 kg, and 5.38 kg of bishydroxyethylene terephthalate (BHET), 3.52 kg of terephthalic acid (TPA), and 0.5 kg of ethylene glycol are charged into a 30-liter autoclave equipped with a rectifying column. The esterification reaction is carried out while raising the internal temperature to 250 ° C. under atmospheric pressure with nitrogen flow, the water distilled by the reaction is distilled off, and a predetermined amount is removed from the system to an esterification rate of 95% or more. An esterification reaction was performed. Thereafter, ethylene glycol was introduced into the 0.66 kg system to raise the decreasing internal temperature, and a depolymerization reaction was performed at 250 ° C. for 30 minutes or more. The number average molecular weight of the obtained ester oligomer was 340. Thereafter, 2.75 kg of a polyester polyol (Priplast 3199: manufactured by Croda; acid value: 1 mgKOH / g) having a number average molecular weight of 2200 consisting of hydrogenated dimer acid and 1,4 butanediol was added to the system and stirred for 30 minutes or more. An additional esterification reaction was performed. Subsequently, after adding 60 ppm of tetrabutoxy titanate as a titanium element as a polycondensation catalyst and stirring, the pressure was reduced to 13.3 kPa or less in 1 hour. During this time, the internal temperature was increased from 250 ° C. to 265 ° C., and a high vacuum of 13.3 kPa or less. A copolymerization reaction was carried out by stirring to a predetermined viscosity below, extruded into water from the die in a cord shape, and cut with a pelletizer to obtain copolymer resin pellets. In addition, the external appearance of the obtained pellet was light yellow transparent. The obtained copolymer polyester resin was vacuum-dried at 70 ° C. for 12 hours or more and kneaded with 10 mol% copolymer polyethylene terephthalate resin having an intrinsic viscosity of 0.75. Made cans.

<Example 2>
Esterification reaction as in Example 1 except that the amount of TPA was changed to 2.25 kg, isophthalic acid (IPA) was changed to 1.27 kg, and the content of isophthalic acid in the dicarboxylic acid component was 18 mol%. And copolymerization reaction was performed and the copolymerization polyester resin was obtained. In addition, the obtained copolymer polyester resin was produced in the same manner as in Example 1 to produce a single-layer film and a film-coated metal can.
<Examples 3 to 6>
The esterification reaction and copolymerization reaction were carried out in the same manner as in Example 1 except that the amount of the polyester polyol composed of hydrogenated dimer acid and 1,4 butanediol was changed in the range of 7 to 50% by mass. A polyester resin was obtained. The obtained copolymer polyester resin was produced in the same manner as in Example 1 to produce a single-layer film and a film-coated metal can.

<Comparative Examples 1 and 2>
An esterification reaction and a copolymerization reaction were performed in the same manner as in Example 1 except that the amount of the polyester polyol composed of hydrogenated dimer acid and 1,4 butanediol was changed to 5 mass% and 55 mass%. A copolyester resin was obtained. The copolymerized polyester resin obtained in Comparative Example 1 was used in the same manner as in Example 1 to produce a sheet, a film film, and a film-coated metal can. In addition, the copolymerized polyester resin obtained in Comparative Example 2 was stuck to a roller during film formation, and a film could not be obtained.
<Comparative Examples 3 and 4>
The raw materials were charged in the same manner as in Examples 4 and 5, and the copolymerization reaction with the subsequent polyester polyol was performed without performing the depolymerization reaction after the esterification reaction, to obtain a copolymerized polyester resin. The number average molecular weights of the ester oligomers were 710 and 740, respectively. The obtained copolymer polyester resin was produced in the same manner as in Example 1 to produce a single-layer film and a film-coated metal can.

<Comparative Example 5>
7.24 kg of dimethyl terephthalic acid and 6.94 kg of 1,4-butanediol were added as a 34 ppm catalyst using tetrabutyl titanate as a titanium element, and after performing a transesterification reaction, hydrogenated dimer acid (Pripol 1009: manufactured by Croda) After adding 1.54 kg (6.5 mol% with respect to the acid component), an additional esterification reaction was carried out, followed by a polycondensation reaction at 245 ° C. to obtain a copolymerized polyester (PBT) resin. The obtained copolymer polyester resin was produced in the same manner as in Example 1 to produce a single-layer film and a film-coated metal can.
<Comparative Example 6>
Instead of using a polyester polyol, instead of a hydrogenated dimer acid (Pripol 1009: manufactured by Croda) having a 10 mol% copolymerization reaction with respect to the acid component, an esterification reaction and a copolymerization reaction were carried out in the same manner as in Example 1. And a copolyester resin was obtained. The obtained copolymer polyester resin was produced in the same manner as in Example 1 to produce a single-layer film and a film-coated metal can.

<Comparative Example 7>
7.74 kg of dimethyl terephthalic acid and 4.86 kg of 1,4 butanediol were added as a 34 ppm catalyst using tetrabutyl titanate as a titanium element. After transesterification at 230 ° C., tetrabutyl titanate was used as a polycondensation catalyst. After adding 95 ppm as an element, the pressure in the system was gradually reduced to 13.3 kPa in 1.5 hours, and at the same time, the internal temperature was raised to 245 ° C. to perform a polycondensation reaction. Sixty minutes after the stirring power started to increase due to the polycondensation reaction, the inside of the system was once returned to atmospheric pressure, and after adding 1.5 kg of polyester polyol having an average molecular weight of 2200 (Priplast 3199: manufactured by Claude), the inside of the system was again The polycondensation reaction was continued under reduced pressure, and the reaction was terminated with a predetermined stirring power to obtain a copolyester (PBT) resin. The obtained copolymer polyester resin was produced in the same manner as in Example 1 to produce a single-layer film and a film-coated metal can.
<Comparative Examples 8 and 9>
In the same manner as in Examples 1 and 4, the raw materials were charged, the catalyst was added without performing the depolymerization reaction after the esterification reaction, the polycondensation reaction was further advanced, and when the melt viscosity reached 80 Pa · s, the polyester polyol was added. The copolymerization reaction was advanced by adding. The number average molecular weights of the ester oligomers were 7600 and 5700, respectively. Although the obtained copolyester resin tried to form a sheet or film in the same manner as in Example 1, a film could not be obtained due to a surging phenomenon (discharge unstable phenomenon) during film formation. .

The raw material compositions and various evaluation results of the copolymerized polyester resins of the above Examples and Comparative Examples are summarized in Tables 1 to 3.

  As shown in Table 1 above, a polyester polyol having a number average molecular weight of 2200 comprising 50 to 93% by mass of a PET ester oligomer (A) having a number average molecular weight of 340 to 590, a hydrogenated dimer acid and 1,4-butanediol. (B) The copolymerized polyester resins of Examples 1 to 6 (intrinsic viscosity 0.705 to 0.785) obtained by copolymerizing 7 to 50% by mass have a transparent resin appearance. In addition to being excellent in film moldability and film adhesion, there was little generation of hair and galling in the can-making process of the film-coated metal can, and the dent resistance of the film-coated metal can was very good.

  On the other hand, as shown in Table 2 above, the dent resistance of the film-coated metal can is sufficiently improved in the copolymer polyester resin of Comparative Example 1 in which the content of the polyester polyol (B) is 5% by mass. It was not good. In addition, in the copolymerized polyester resin of Comparative Example 2 in which the content of the polyester polyol (B) is 55% by mass, the phase separation of the polyester polyol (B) occurs, resulting in a cloudy appearance. The film stuck to the roller and could not be obtained.

  Further, in Comparative Examples 3 and 4 where the depolymerization reaction was not performed when the ester oligomer (A) was produced, the number average molecular weights of the ester oligomers were 710 and 740, respectively, and during the subsequent copolymerization reaction with the polyester polyol (B). The reaction peaked out, and the intrinsic viscosity of the obtained copolyester resin was as low as 0.609 to 0.643. And the film covering metal can manufactured using this copolymerization polyester resin was not fully improved in dent resistance.

  Further, as shown in Table 3 above, Comparative Example 5 obtained by copolymerizing PBT ester oligomer and hydrogenated dimer acid, copolymerized PET ester oligomer similar to the present invention and hydrogenated dimer acid In the copolymerized polyester resin of Comparative Example 6 obtained as described above, both hair and galling and product dent resistance were inferior in the can-making process of the film-coated metal can. Further, in the copolymerized polyester resin of Comparative Example 7 obtained by copolymerizing the PBT ester oligomer and the same polyester polyol (B) as in the present invention, although hair generation is slightly improved, generation of galling is generated. In addition, sufficient results were not obtained for both dent resistance. In Comparative Examples 5 and 7 using a PBT ester oligomer, no transparent copolyester resin was obtained.

Further, in Comparative Examples 8 and 9 in which the polycondensation reaction was advanced until the melt viscosity became 80 Pa · s without performing the depolymerization reaction when the ester oligomer (A) was produced, the number average molecular weight of the ester oligomer was 7600, respectively. , 5700. The subsequent copolymerization reaction with the polyester polyol (B) proceeded without any problem, but the appearance of the obtained copolymerized polyester resin was clouded. Further, a surging phenomenon (discharge unstable phenomenon) occurred during melt extrusion in the film forming process, and a sheet or film could not be formed.

Claims (5)

Ester oligomer (A) 50 to 93 consisting of a dicarboxylic acid unit (a1) containing 70 mol% or more of a terephthalic acid component and a diol unit (a2) containing 70 mol% or more of an ethylene glycol component, having a number average molecular weight of 700 or less. Mass%,
It consists of a hydrogenated dimer acid unit (b1) and a 1,4-butanediol unit (b2), and contains 7 to 50% by mass of a polyester polyol (B) having a number average molecular weight of 1500 to 3000 as a constituent unit. Copolyester resin.   2. The copolyester resin according to claim 1, wherein the intrinsic viscosity is 0.7 to 0.9.   A polyester film for coating a metal plate, wherein the copolymerized polyester resin according to claim 1 or 2 is formed alone or mixed with another resin to form a film.   A polyester film-covered metal can characterized in that the metal film-covering polyester film according to claim 3 is coated on an inner surface and / or an outer surface of a metal can. By subjecting a dicarboxylic acid unit (a1) containing 70 mol% or more of a terephthalic acid component to a polycondensation reaction of a diol unit (a2) containing 70 mol% or more of an ethylene glycol component, a depolymerization reaction is performed. Obtaining an ester oligomer (A) having an average molecular weight of 700 or less;
An ester oligomer (A) obtained by the above process, a hydrogenated dimer acid unit (b1) and a 1,4-butanediol unit (b2), and a polyester polyol (B) having a number average molecular weight of 1500 to 3000. A step of polycondensation reaction to obtain a copolyester resin containing 50 to 93% by mass of the ester oligomer (A) and 7 to 50% by mass of the polyester polyol (B). Manufacturing method.