Polyester-based resin, polyester-based container, polyester-based film, polyester-based fiber, and method for producing polyester-based resin

Abstract

Provided is a polyester-based resin, which has excellent mechanical recyclability and optical characteristics, and which is configured such that the mechanical characteristics thereof will not deteriorate even in a case where an adhesive is involved in mechanical recycling process.　The polyester-based resin is a reaction product of a polyester (A) having a glass transition temperature of at least 30°C but less than 140°C and a polyester (B1) having a glass transition temperature of at least -80°C but less than 30°C.

Description

Polyester resin, polyester container, polyester film, polyester fiber, and method for producing polyester resin

[0001] The present invention relates to a polyester resin, a polyester container, a polyester film, a polyester fiber, and a method for producing a polyester resin, and more specifically to a polyester resin, a polyester container, a polyester film, a polyester fiber, and a method for producing a polyester resin that does not deteriorate the mechanical properties of the resin and has excellent mechanical recyclability and optical properties.

[0002] In recent years, due to problems such as environmental pollution and the depletion of petroleum resources, there has been a strong demand for recycling polyester resin molded products such as polyester containers, polyester films, and polyester fibers. Mechanical recycling and chemical recycling are known methods for recycling polyester resin molded products, with mechanical recycling being the mainstream from a cost perspective. Mechanical recycling typically involves crushing used polyester resin molded products into pellets or flakes, then heating and melting the resulting material to homogenize it, and using the resulting recycled resin again as a material for polyester resin molded products.

[0003] Typically, polyester containers such as polyethylene terephthalate (PET) bottles have adhesive labels affixed to their surfaces, carrying various pieces of information. Furthermore, adhesive tapes using PET film as a substrate typically have an adhesive layer formed on the PET film. When such adhesive-coated polyester resin molded products are mechanically recycled, the adhesive acts as a foreign substance, degrading the mechanical properties of the resin, resulting in problems such as reduced recyclability and optical properties. Therefore, mechanical recycling of adhesive-coated polyester resin molded products requires extremely cumbersome procedures, such as peeling and removing the adhesive.

[0004] For example, Patent Document 1 discloses an adhesive label comprising a polyester resin substrate that is compatible with a polyester container as an adherend, and a coating layer that can be peeled from the substrate by washing and immersing in an alkaline aqueous solution and has printability and is provided on one side of the substrate, and a polyester adhesive layer is provided on the other side.

[0005] Furthermore, Patent Document 2 discloses an adhesive label that enables polyester containers to be recycled without being peeled off from the polyester container, and the printed portion of which can be removed (peeled off) in a short time in an alkaline aqueous solution at a low temperature (about 70°C).

[0006] JP 2000-10489 A JP 2023-69194 A

[0007] Although the aforementioned Patent Documents 1 and 2 have excellent print layer detachability, there remain issues with the recyclability and optical properties of polyester-based resin molded products. Therefore, in order to improve the mechanical recyclability of polyester-based resin molded products, there is a need for a monomaterial that includes the pressure-sensitive adhesive and for improving the recyclability of the pressure-sensitive adhesive. Generally, acrylic pressure-sensitive adhesives are widely used in polyester molded products. However, acrylic pressure-sensitive adhesives become foreign matter during mechanical recycling of polyester, resulting in reduced mechanical properties, mechanical recyclability, and optical properties.

[0008] Therefore, against this background, the present invention provides a polyester-based resin that has excellent mechanical recyclability and optical properties, even when the adhesive is included in a mechanical recycling process, without reducing the mechanical properties, and a method for producing the polyester-based resin.

[0009] However, the present inventors have found that a polyester resin, which is a reaction product of a polyester (A) having a glass transition temperature of 30°C or higher and lower than 140°C and a polyester (B1) having a glass transition temperature of -80°C or higher and lower than 30°C, does not deteriorate in mechanical properties and has excellent mechanical recyclability and optical properties.

[0010] That is, the gist of the present invention is the following [1] to

[23] . [1] A polyester-based resin that is a reaction product of a polyester (A) having a glass transition temperature of 30°C or higher but lower than 140°C and a polyester (B1) having a glass transition temperature of -80°C or higher but lower than 30°C. [2] The polyester-based resin according to [1], wherein the nitrogen atom content in the polyester-based resin is 0.1 to 1,000 ppm. [3] The polyester-based resin according to [1] or [2], wherein the content of structural units derived from the polyester (B1) in the polyester-based resin is 10% by mass or less. [4] The polyester-based resin according to any one of [1] to [3], wherein the glass transition temperature of the polyester-based resin is 30°C or higher. [5] The polyester-based resin according to any one of [1] to [4], wherein the weight-average molecular weight of the polyester-based resin is 5,000 to 300,000. [6] The polyester-based resin according to any one of [1] to [5], wherein the acid value of the polyester-based resin is 5 mgKOH / g or less. [7] The polyester-based resin according to any one of [1] to [6], wherein the polyester-based resin has structural units derived from polycarboxylic acids and structural units derived from polyhydric alcohols, and the content of structural units derived from aromatic dicarboxylic acids in the polyester-based resin is 10 to 90% by mass. [8] The polyester-based resin according to any one of [1] to [7], wherein the polyester-based resin has a haze of 5% or less when formed into a sheet having a thickness of 50 μm. [9] The polyester-based resin according to any one of [1] to [8], wherein the polyester (A) has structural units derived from terephthalic acids and structural units derived from ethylene glycol.

[10] The polyester-based resin according to any one of [1] to [9], wherein the polyester (A) has structural units derived from recycled thermoplastic polyester (A1).

[11] The polyester-based resin according to any one of [1] to

[10] , wherein the polyester (B1) has structural units derived from aromatic dicarboxylic acids.

[12] The polyester-based resin according to any one of [1] to

[11] , wherein the content of aromatic dicarboxylic acids in the structural units derived from the polyvalent carboxylic acids (Ba) of the polyester (B1) is 10 to 100 mol%.

[13] The polyester-based resin according to any one of [1] to

[12] , wherein the content of aliphatic diols having 1 to 5 carbon atoms in the structural units derived from the polyhydric alcohols (Bb) of the polyester (B1) is 10 to 100 mol %.

[14] The polyester-based resin according to any one of [1] to

[13] , wherein the crystalline heat of fusion of the polyester (B1) is 10 J / g or less.

[15] The polyester-based resin according to any one of [1] to

[14] , wherein the polyester (B1) is a crosslinked product.

[16] The polyester-based resin according to any one of [1] to

[15] , wherein the crosslinked product of the polyester-based resin (B1) has a gel fraction of 10 to 100%.

[17] A polyester-based container comprising the polyester-based resin according to any one of [1] to

[16] .

[18] A polyester-based film comprising the polyester-based resin according to any one of [1] to

[16] .

[19] A polyester-based fiber comprising the polyester-based resin according to any one of [1] to

[16] .

[20] A method for producing a polyester-based resin, comprising a step of reacting a polyester (A) having a glass transition temperature of 30°C or higher but lower than 140°C with a polyester (B1) having a glass transition temperature of -80°C or higher but lower than 30°C.

[21] A method for producing a polyester-based resin according to

[20] , wherein the step is carried out under a nitrogen atmosphere.

[22] A method for producing a polyester-based resin according to

[20] or

[21] , wherein the step is carried out under vacuum conditions of 0.1 to 50 torr.

[23] A method for producing a polyester-based resin according to any one of

[20] to

[22] , wherein the step comprises heating to 160 to 280°C and melting.

[0011] The present invention involves reacting a polyester having a glass transition temperature of 30°C or higher and lower than 140°C with a polyester contained in a polyester-based pressure-sensitive adhesive and having a glass transition temperature of -80°C or higher and lower than 30°C. This eliminates the need to remove the pressure-sensitive adhesive, prevents deterioration of the mechanical properties of the resin, and provides excellent mechanical recyclability and optical properties.

[0012] The present invention will be described below based on examples of modes for carrying out the present invention, but the present invention is not limited to the embodiments described below.

[0013] In this specification, "X and / or Y (X and Y are any configuration)" means at least one of X and Y, and can mean three possibilities: X only, Y only, or X and Y. In addition, in this specification, when "X to Y" (X and Y are any numbers) is expressed, unless otherwise specified, it also means "X or more and Y or less", as well as "preferably larger than X" or "preferably smaller than Y". Furthermore, when "X or more" (X is any number) or "Y or less" (Y is any number) is expressed, it also means "preferably larger than X" or "preferably smaller than Y".

[0014] As used herein, the term "film" encompasses "tape" and "sheet." Furthermore, in this specification, the term "type" suffixed to a compound name encompasses not only the compound but also its derivatives. For example, the term "carboxylic acids" encompasses not only carboxylic acids but also carboxylic acid derivatives such as carboxylic acid salts, carboxylic acid anhydrides, carboxylic acid halides, and carboxylic acid esters. As used herein, the term "major component" refers to a component that significantly affects the properties of the target object. The content of the component is typically 50% by mass or more, preferably 55% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more, or even 100% by mass. Regarding the numerical ranges described in stages in this specification, the upper or lower limit of one stage can be arbitrarily combined with the upper or lower limit of another stage. Furthermore, in the numerical ranges described herein, the upper or lower limit of the numerical range can also be replaced with the values ​​shown in the examples.

[0015] A polyester-based resin according to one embodiment of the present invention (hereinafter sometimes referred to as "the polyester-based resin") is a reaction product of a polyester (A) having a glass transition temperature of 30°C or more and less than 140°C and a polyester (B1) having a glass transition temperature of -80°C or more and less than 30°C. Hereinafter, "polyester (A) having a glass transition temperature of 30°C or more and less than 140°C" may be referred to as "polyester (A)." "Polyester (B1) having a glass transition temperature of -80°C or more and less than 30°C" may be referred to as "polyester (B1)."

[0016] As the polyester (A) and polyester (B1), there can be used used products collected as recyclable waste, scrap materials generated in the manufacturing process, unused products, and the like.

[0017] The form of the polyester (A) is not particularly limited, but is preferably a resin. Specific examples of the resin include molded products, such as containers for liquids, and base films for adhesive tapes.

[0018] In addition, because the polyester (B1) has excellent mechanical recyclability with the polyester (A), it is preferably contained in a polyester-based pressure-sensitive adhesive (B) used as an adhesive for attaching a label to a container containing the polyester (A) or as an adhesive layer of a pressure-sensitive adhesive tape using a film containing the polyester (A) as a substrate. Each component will be described below.

[0019] <Polyester (A)> The polyester (A) has a glass transition temperature of 30°C or higher and lower than 140°C. The polyester (A) preferably contains a structural unit derived from a polycarboxylic acid (Aa) and a structural unit derived from a polyhydric alcohol (Ab) in the molecule, in order to achieve excellent moldability, strength, heat resistance, and mechanical recyclability with the polyester (B1). Such a polyester (A) is usually obtained by esterifying the polycarboxylic acid (Aa) and the polyhydric alcohol (Ab).

[0020] Examples of the polyvalent carboxylic acids (Aa) include aromatic dicarboxylic acids such as terephthalic acids, isophthalic acids, 2-chloroterephthalic acids, 2,5-dichloroterephthalic acids, 2-methylterephthalic acids, 4,4-stilbene dicarboxylic acids, 4,4-biphenyl dicarboxylic acids, orthophthalic acids, 2,6-naphthalenedicarboxylic acids, 2,7-naphthalenedicarboxylic acids, anthracene dicarboxylic acids, 4,4-diphenyl ether dicarboxylic acids, 4,4-diphenoxyethane dicarboxylic acids, and 5-sodium sulfoisophthalic acids; adipic acids; sebacic acids; and Examples of suitable dicarboxylic acids include zelaic acids, dodecanedioic acids, malonic acids, succinic acids, glutaric acids, trimethyladipic acids, pimelic acids, 3-methylglutaric acids, 2,2-dimethylglutaric acids, 1,9-nonanedicarboxylic acids, dimer acids derived by dimerizing unsaturated monocarboxylic acids such as oleic acid, linoleic acid, linolenic acid, and erucic acid, and hydrogenated dimer acids obtained by hydrogenating dimer acids, aliphatic dicarboxylic acids such as fumaric acids, maleic acids, and itaconic acids, and alicyclic dicarboxylic acids such as 1,3-cyclohexanedicarboxylic acids and 1,4-cyclohexanedicarboxylic acids. These may be used alone or in combination of two or more. Among these, aromatic dicarboxylic acids are preferred from the viewpoint of excellent moldability, strength, heat resistance, and mechanical recyclability, and terephthalic acids, isophthalic acids, and orthophthalic acids are preferred from the viewpoint of even better mechanical recyclability and optical properties, with terephthalic acid being more preferred.

[0021] Examples of the polyhydric alcohols (Ab) include unsaturated monocalcium carbonates such as ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,9-nonanediol, 1,10-decanediol, 1,2-propylene glycol, 2-methyl-1,3-propanediol, neopentyl glycol, 3-methyl-1,5-pentanediol, 2-ethyl-2-butylpropanediol, oleic acid, linoleic acid, linolenic acid, and erucic acid. Examples of suitable diols include aliphatic diols such as dimer diol, which is a reduced form of dimer acids derived by dimerizing carboxylic acid; alicyclic diols such as cyclohexanediol; bifunctional alcohols such as aromatic diols such as p-xylenediol, bisphenol A, tetrabromobisphenol A, and tetrabromobisphenol A-bis(2-hydroxyethyl ether); and trifunctional or higher alcohols such as glycerin, trimethylolpropane, pentaerythritol, trimellitic acid, and pyromellitic acid. These may be used alone or in combination of two or more. Among these, aliphatic diols are preferred in terms of excellent moldability, strength, heat resistance, and mechanical recyclability. Aliphatic diols having 1 to 5 carbon atoms are more preferred in terms of excellent mechanical recyclability and optical properties, and ethylene glycol is even more preferred.

[0022] In addition, the polycarboxylic acids (Aa) and polyhydric alcohols (Ab) are preferably recycled thermoplastic polyesters (A1) such as unused molded products of polyester (A), crushed products left over from the production of molded products of polyester (A), and recycled products recovered from waste and washed. Among these, the use of recycled products is preferred from the viewpoint of the global environment. These can be obtained commercially in the form of washed, dried, pelletized, or flaked products.

[0023] The polyester (A) can be produced by polycondensation reaction of polymerization components containing polycarboxylic acids (Aa) and polyhydric alcohols (Ab) in the presence of a catalyst by a known method, and in the polycondensation reaction, an esterification reaction and / or a transesterification reaction is first carried out, followed by the polycondensation reaction. When recycled thermoplastic polyester (A1) is used as the polycarboxylic acids (Aa) and the polyhydric alcohols (Ab), the recycled thermoplastic polyester (A1) can be directly contained in the polymerization components, and the resulting polyester resin (A) will have structural units derived from the recycled thermoplastic polyester (A1).

[0024] Furthermore, the polyester (A) is preferably obtained using a polyhydric alcohol (Ab) having hydroxyl groups in a molar ratio of 1.01 or more per mole of carboxyl groups in the polycarboxylic acid (Aa), and the molar ratio is more preferably 1.05 to 2.5, more preferably 1.1 to 2.0, and even more preferably 1.2 to 1.7. That is, if the molar ratio is too small, the esterification reaction and / or transesterification reaction tends to be insufficient. On the other hand, if the molar ratio is too large, too much glycol is distilled, which tends to be less economical.

[0025] Specific examples of the polyester (A) include polyethylene terephthalate resins, polypropylene terephthalate resins, polybutylene terephthalate resins, polyethylene isophthalate resins, polyethylene naphthalate resins, polybutylene naphthalate resins, polyethylene terephthalate / isophthalate resins, polyethylene / neopentyl terephthalate resins, polybutylene succinate resins, 3-hydroxybutyrate / 3-hydroxyhexanoate polymers, etc. Among these, the polyester (A) preferably has a structural unit derived from terephthalic acids and a structural unit derived from ethylene glycol from the viewpoints of moldability, strength, heat resistance, and mechanical recyclability, and is more preferably a polyethylene terephthalate resin, and even more preferably a recycled polyethylene terephthalate resin.

[0026] The polyester (A) may have structural units derived from polyvalent carboxylic acids (Aa) other than the polyvalent carboxylic acids (Aa) constituting the basic structure, and / or structural units derived from polyhydric alcohols (Ab) other than the polyhydric alcohols (Ab) constituting the basic structure, in an amount of 50 mass% or less of the structural units.

[0027] The content of structural units derived from aromatic dicarboxylic acids in the polyester (A) is usually 10 to 90 mass%, preferably 30 to 85 mass%, more preferably 40 to 80 mass%, even more preferably 50 to 75 mass%, and most preferably 60 to 70 mass%. When the content of structural units derived from aromatic polycarboxylic acids is within the above range, the polyester (A) tends to have excellent moldability, strength, heat resistance, mechanical recyclability, and optical properties.

[0028] The content of structural units derived from aliphatic diols having 1 to 5 carbon atoms in the polyester (A) is usually 10 to 90 mass%, preferably 15 to 70 mass%, more preferably 20 to 60 mass%, even more preferably 25 to 50 mass%, and most preferably 30 to 40 mass%. When the content of structural units derived from aliphatic diols having 1 to 5 carbon atoms is within the above range, the polyester (A) tends to have excellent moldability, strength, heat resistance, mechanical recyclability, and optical properties.

[0029] When recycled thermoplastic polyester (A1) is used as a polymerization component, the content of structural units derived from recycled thermoplastic polyester (A1) in polyester (A) is usually preferably 10% by mass or more, more preferably 20 to 100% by mass, even more preferably 30 to 90% by mass, and most preferably 40 to 80% by mass. When the content of structural units derived from recycled thermoplastic polyester (A1) is within the above range, mechanical recyclability, optical properties, and environmental load reduction effects tend to be excellent.

[0030] When the polyester (A) has structural units derived from aromatic dicarboxylic acids, the content of the structural units derived from aromatic dicarboxylic acids relative to the structural units derived from polycarboxylic acids (Aa) is preferably 20 mol% or more, more preferably 40 mol% or more, even more preferably 60 mol% or more, particularly preferably 80 mol% or more, and most preferably 90 mol% or more. When the content of the structural units derived from aromatic dicarboxylic acids is within the above range, the polyester tends to have excellent moldability, strength, heat resistance, mechanical recyclability, and optical properties.

[0031] When the polyester (A) has structural units derived from aliphatic dicarboxylic acids, the content of the structural units derived from aliphatic dicarboxylic acids relative to the structural units derived from polycarboxylic acids (Aa) is preferably 80 mol % or less, more preferably 60 mol % or less, even more preferably 40 mol % or less, particularly preferably 20 mol % or less, and most preferably 10 mol % or less. When the content of the structural units derived from aliphatic dicarboxylic acids is within the above range, the polyester tends to have excellent moldability, strength, heat resistance, mechanical recyclability, and optical properties.

[0032] When the polyester (A) has structural units derived from aliphatic diols having 1 to 5 carbon atoms, the content of the structural units derived from aliphatic diols having 1 to 5 carbon atoms relative to the structural units derived from the polyhydric alcohols (Ab) is preferably 20 mol% or more, more preferably 40 mol% or more, even more preferably 60 mol% or more, particularly preferably 80 mol% or more, and most preferably 90 mol% or more. When the content of the structural units derived from aliphatic diols having 1 to 5 carbon atoms is within the above range, the polyester tends to have excellent moldability, strength, heat resistance, mechanical recyclability, and optical properties.

[0033] The glass transition temperature (Tg) of the polyester (A) is 30° C. or higher and lower than 140° C., preferably 40 to 130° C., more preferably 50 to 120° C., and even more preferably 60 to 100° C. When the glass transition temperature (Tg) is within the above range, the polyester (A) tends to have excellent moldability, strength, heat resistance, mechanical recyclability, and optical properties.

[0034] The polyester (A) may have a melting point in order to provide excellent moldability, strength, and heat resistance. The melting point (Tm) of the polyester (A) is usually 60°C or higher, preferably 100 to 300°C, more preferably 150 to 280°C, and even more preferably 200 to 260°C. When the melting point (Tm) is within the above range, the polyester (A) tends to provide excellent moldability, strength, and heat resistance.

[0035] The polyester (A) may have a heat of crystalline fusion in order to provide excellent moldability, strength, and heat resistance. The heat of crystalline fusion of the polyester (A) is usually 100 J / g or less, preferably 0.1 to 80 J / g, more preferably 1 to 60 J / g, 3 to 40 J / g, and even more preferably 5 to 35 J / g. When the heat of crystalline fusion is within the above range, the polyester (A) tends to provide excellent moldability, strength, and heat resistance.

[0036] The glass transition temperature (Tg), melting point (Tm), and heat of crystalline fusion are measured using a differential scanning calorimeter (DSC) (for example, a differential scanning calorimeter "Q20" manufactured by TA Instruments). The measurement temperature range is -90 to 200°C, and the temperature rise rate is 10°C / min.

[0037] The weight average molecular weight of the polyester (A) is usually 5,000 to 300,000, preferably 10,000 to 150,000, more preferably 20,000 to 100,000, and even more preferably 30,000 to 75,000. When the weight average molecular weight is within the above range, the polyester tends to have excellent moldability, strength, heat resistance, and mechanical recyclability.

[0038] The weight-average molecular weight is a weight-average molecular weight converted into a standard polystyrene molecular weight. The weight-average molecular weight was measured using a high-performance liquid chromatograph (manufactured by Tosoh Corporation, "HLC-8320GPC") equipped with a column: TSKgel SuperMultipore HZ-M (exclusion limit molecular weight: 2 × 10 6 The measurement is carried out by using two columns in series (theoretical plate number: 16,000 / column, filler material: styrene-divinylbenzene copolymer, filler particle size: 4 μm).

[0039] The ester bond concentration of the polyester (A) is usually 1 to 14 mmol / g, preferably 4 to 13 mmol / g, more preferably 8 to 12 mmol / g, and even more preferably 9 to 11 mmol / g. When the ester bond concentration is within the above range, the polyester (A) tends to have excellent moldability, strength, heat resistance, and mechanical recyclability.

[0040] The ester bond concentration (mmol / g) refers to the number of moles of ester bonds in 1 g of polyester (A), and can be calculated, for example, from the amounts charged. The calculation method is to divide the number of moles of the polycarboxylic acids (Aa) or the polyhydric alcohols (Ab), whichever is charged in smaller amounts, by the total weight, and an example of the calculation formula is shown below. Note that, when a monomer having both a carboxyl group and a hydroxyl group is used or when the polyester is produced from caprolactone or the like, the calculation method will be changed appropriately.

[0041] <When the amount of polycarboxylic acids (Aa) is less than the amount of polyhydric alcohols (Ab)> Ester bond concentration (mmol / g) = [(D1 / d1 x m1 + D2 / d2 x m2 + D3 / d3 x m3 ...) / Z] x 1000 D: amount of polycarboxylic acids (Aa) charged (g) d: molecular weight of polycarboxylic acids (Aa) m: number of carboxylic acid groups per molecule of polycarboxylic acids (Aa) Z: finished weight (g) <When the amount of polyhydric alcohols (Ab) is less than the amount of polycarboxylic acids (Aa)> Ester group concentration (mmol / g) = [(E1 / e1 x n1 + E2 / e2 x n2 + E3 / e3 x n3 ...) / Z] x 1000 E: amount of polyhydric alcohols (Ab) charged (g) e: molecular weight of polyhydric alcohols (Ab) n: number of hydroxyl groups per molecule of polyhydric alcohol (Ab) Z: finished weight (g)

[0042] The ester bond concentration can also be measured by a known method using NMR or the like.

[0043] Examples of a method for adjusting the ester bond concentration include a method of selecting a polyhydric alcohol having 4 or less carbon atoms as the polyhydric alcohol (Ab), a method of increasing the content of linear alkyl aliphatic dicarboxylic acids as the polycarboxylic acids (Aa), and a method of combining both of these.

[0044] The acid value of the polyester (A) is usually 5 mgKOH / g or less, preferably 4.5 mgKOH / g or less, more preferably 4 mgKOH / g or less, even more preferably 3.5 mgKOH / g or less, particularly preferably 3 mgKOH / g or less, and most preferably 1 mgKOH / g or less. If the acid value is within the above range, the polyester tends to have excellent hydrolysis resistance, heat resistance, mechanical recyclability, and optical properties. The acid value is determined by neutralization titration according to JIS K0070.

[0045] <Polyester-Based Pressure-Sensitive Adhesive (B)> The polyester-based pressure-sensitive adhesive (B) contains a polyester (B1) as a main component, has adhesive properties at 25°C, and can be used as an adhesive for bonding materials. Having adhesive properties refers to a ball number of 1 or greater obtained when an inclined ball tack test is performed at 25°C using an inclined plate at an angle of 30° in accordance with JIS Z 0237:2009. From the viewpoints of mechanical recyclability and optical properties, the polyester-based pressure-sensitive adhesive (B) preferably contains a polyester (B1) having structural units derived from polycarboxylic acids (Ba) and structural units derived from polyhydric alcohols (Bb). It is more preferable that the structural units derived from the polycarboxylic acids (Ba) are aromatic dicarboxylic acids, and the structural units derived from the polyhydric alcohols (Bb) are aliphatic diols having 1 to 5 carbon atoms.

[0046] [Polyester (B1)] The polyester (B1) has a glass transition temperature of −80° C. or higher and lower than 30° C. The polyester (B1) is obtained by copolymerizing (condensation polymerizing) polymerization components containing polycarboxylic acids (Ba) and polyhydric alcohols (Bb) as constituent raw materials, and has a resin composition including structural units derived from the polycarboxylic acids (Ba) and structural units derived from the polyhydric alcohols (Bb).

[0047] [Polycarboxylic Acids (Ba)] Examples of the polycarboxylic acids (Ba) include dicarboxylic acids and trivalent or higher polycarboxylic acids, and dicarboxylic acids are preferred because they can stably produce the polyester (B1). These polycarboxylic acids (Ba) can be used alone or in combination of two or more.

[0048] Examples of the dicarboxylic acids include aromatic dicarboxylic acids such as terephthalic acids, isophthalic acids, 2-chloroterephthalic acids, 2,5-dichloroterephthalic acids, 2-methylterephthalic acids, 4,4-stilbene dicarboxylic acids, 4,4-biphenyl dicarboxylic acids, orthophthalic acids, 2,6-naphthalenedicarboxylic acids, 2,7-naphthalenedicarboxylic acids, anthracene dicarboxylic acids, 4,4-diphenyl ether dicarboxylic acids, 4,4-diphenoxyethane dicarboxylic acids, and 5-sodium sulfoisophthalic acids; adipic acids, sebacic acids, azelaic acids, and the like. Examples of the trivalent or higher polyvalent carboxylic acids include dimer acids derived by dimerization of unsaturated monocarboxylic acids such as carboxylic acids, dodecanedioic acids, malonic acids, succinic acids, glutaric acids, trimethyladipic acids, pimelic acids, 3-methylglutaric acids, 2,2-dimethylglutaric acids, 1,9-nonanedicarboxylic acids, oleic acid, linoleic acid, linolenic acid, and erucic acid, and hydrogenated dimer acids obtained by hydrogenating dimer acids, aliphatic dicarboxylic acids such as fumaric acids, maleic acids, and itaconic acids, and alicyclic dicarboxylic acids such as 1,3-cyclohexanedicarboxylic acids and 1,4-cyclohexanedicarboxylic acids. Examples of the trivalent or higher polyvalent carboxylic acids include trimellitic acids, pyromellitic acids, adamantanetricarboxylic acids, and trimesic acids.

[0049] Among the polycarboxylic acids (Ba), aromatic dicarboxylic acids are preferred from the viewpoint of providing the polyester (B1) with excellent hydrolysis resistance, heat resistance, mechanical recyclability, and optical properties. Furthermore, among the aromatic dicarboxylic acids, terephthalic acids, isophthalic acids, orthophthalic acids, naphthalenedicarboxylic acids, and furandicarboxylic acids are more preferred from the viewpoint of providing excellent mechanical recyclability, and isophthalic acids, orthophthalic acids, and furandicarboxylic acids are even more preferred from the viewpoint of adjusting the crystallinity of the polyester resin and providing excellent tackiness and adhesive strength.

[0050] Furthermore, the polyvalent carboxylic acids (Ba) preferably contain aliphatic dicarboxylic acids having 4 or more carbon atoms (including the carbon atoms of the carboxy group), and among these, it is more preferable to contain aliphatic dicarboxylic acids having 6 to 12 carbon atoms (including the carbon atoms of the carboxy group), such as adipic acids, pimelic acids, azelaic acids, and sebacic acids, in view of their excellent adhesive strength, mechanical recyclability, and optical properties.

[0051] [Polyhydric Alcohols (Bb)] Examples of the polyhydric alcohols (Bb) include diols and trihydric or higher polyhydric alcohols. The polyols (Bb) can be used alone or in combination of two or more.

[0052] Examples of the diols include ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,9-nonanediol, 1,10-decanediol, 1,2-propylene glycol, 2-methyl-1,3-propanediol, neopentyl glycol, 3-methyl-1,5-pentanediol, 2-ethyl-2-butylpropanediol, dimer diol, which is a reduced product of dimer acids derived by dimerizing unsaturated monocarboxylic acids such as oleic acid, linoleic acid, linolenic acid, and erucic acid, 2,4-diethyl-1,5-pentanediol, and 2,2,4-trimethyl-1, aliphatic diols such as 3-pentanediol; alicyclic diols such as 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, spiroglycol, tricyclodecane dimethanol, adamantanediol, and 2,2,4,4-tetramethyl-1,3-cyclobutanediol; and aromatic diols such as 4,4'-thiodiphenol, 4,4'-methylenediphenol, 4,4'-dihydroxybiphenyl, o-, m-, and p-dihydroxybenzene, 2,5-naphthalenediol, p-xylenediol, and ethylene oxide adducts and propylene oxide adducts thereof. Among these, aliphatic diols are preferred from the viewpoint of excellent mechanical recyclability with the polyester (A), aliphatic diols having 1 to 5 carbon atoms are more preferred, and ethylene glycol, 1,3-propanediol, 1,4-butanediol, and 2,2-dimethyl-1,3-propanediol (neopentyl glycol) are even more preferred.

[0053] Examples of the trihydric or higher polyhydric alcohols include pentaerythritol, dipentaerythritol, tripentaerythritol, glycerin, trimethylolpropane, trimethylolethane, 1,2,4-butanetriol, 1,2,5-pentanetriol, 1,2,6-hexanetriol, 1,3,6-hexanetriol, and adamantanetriol.

[0054] Among the polyhydric alcohols (Bb), diols having a hydrocarbon group on the side chain are preferred because they can increase the number of branching points and disrupt crystallinity. Examples of such diols having a hydrocarbon group on the side chain include 1,2-propylene glycol, 2,4-dimethyl-2-ethylhexane-1,3-diol, 2-methyl-1,3-propanediol, neopentyl glycol, 2-methyl-2-ethyl-1,3-propanediol, 2-ethyl-2-butyl-1,3-propanediol, 2-ethyl-2-isobutyl-1,3-propanediol, 1,3-butanediol, 3-methyl-1,5-pentanediol, and 2,2,4-trimethyl-1,6-hexanediol. Examples of suitable diols include aliphatic diols having a branched structure, such as dimer diols, which are reduced forms of dimer acids derived by dimerizing unsaturated monocarboxylic acids such as ethanol, oleic acid, linoleic acid, linolenic acid, and erucic acid, and alicyclic diols having a branched structure, such as 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, spiroglycol, tricyclodecane dimethanol, adamantanediol, and 2,2,4,4-tetramethyl-1,3-cyclobutanediol.

[0055] Among these, as diols having a hydrocarbon group in a side chain, aliphatic diols having 1 to 5 carbon atoms and a branched structure are preferred from the viewpoint of making them less susceptible to crystallization while maintaining mechanical strength and heat resistance, and 2-methyl-1,3-propanediol and neopentyl glycol are more preferred from the viewpoint of excellent mechanical recyclability.

[0056] From the viewpoint of adjusting the glass transition temperature (Tg) of the polyester (B1), it is preferable to use a linear aliphatic diol as the polyhydric alcohol (Bb), more preferably a linear aliphatic diol having 1 to 10 carbon atoms, and even more preferably ethylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,5-pentanediol, or 1,6-hexanediol. Of these, 1,4-butanediol is most preferable from the viewpoint of being able to lower the glass transition temperature (Tg) of the polyester (B1).

[0057] Furthermore, trivalent or higher polyhydric alcohols may be used as the polyhydric alcohol (Bb) in order to form reactive sites with the crosslinking agent described below in the polyester (B1) and increase the cohesive strength. Among these, trimethylolpropane, trimethylolethane, glycerin, pentaerythritol, 1,2,4-butanetriol, 1,2,5-pentanetriol, and 1,2,6-hexanetriol are preferred. Of these, trimethylolpropane is preferred because it is relatively less likely to form a gel.

[0058] The polyester (B1) can be produced by subjecting any of the polyvalent carboxylic acids (Ba) and polyhydric alcohols (Bb) to a polycondensation reaction in the presence of a catalyst by a known method. In the polycondensation reaction, an esterification reaction and / or a transesterification reaction is first carried out, and then the polycondensation reaction is carried out.

[0059] The blending ratio of the polyvalent carboxylic acids (Ba) and the polyhydric alcohols (Bb) is not particularly limited, but from the viewpoint of the ability to arbitrarily adjust the weight average molecular weight and the yield, the ratio of the polyhydric alcohols (Bb) per equivalent of the polyvalent carboxylic acids (Ba) is preferably 1.01 or more, more preferably 1.05 to 2.5 equivalents, even more preferably 1.1 to 2.0 equivalents, and most preferably 1.2 to 1.7 equivalents.

[0060] The polyester (B1) thus obtained preferably has a structural unit derived from an aromatic dicarboxylic acid as a structural unit derived from a polyvalent carboxylic acid (Ba) from the viewpoints of mechanical recyclability, mechanical properties, and transparency.

[0061] When the polyester (B1) has structural units derived from aromatic dicarboxylic acids, the content of the structural units derived from the polycarboxylic acids (Ba) is preferably 10 to 100 mol %, more preferably 15 to 95 mol %, even more preferably 25 to 90 mol %, particularly preferably 35 to 85 mol %, especially preferably 45 to 80 mol %, and most preferably 55 to 75 mol %. When the content of the structural units derived from aromatic dicarboxylic acids is within the above range, the polyester tends to have excellent hydrolysis resistance, heat resistance, mechanical recyclability, and optical properties.

[0062] When the polyester (B1) has a structural unit derived from an aromatic dicarboxylic acid, the content thereof is usually 1 to 70 mass%, preferably 5 to 60 mass%, more preferably 10 to 55 mass%, even more preferably 15 to 50 mass%, particularly preferably 20 to 45 mass%, and most preferably 25 to 40 mass%, of the polyester (B1). When the content of the structural unit derived from an aromatic dicarboxylic acid is within the above range, the polyester (B1) tends to have excellent mechanical recyclability and optical properties.

[0063] When the polyester (B1) has structural units derived from aliphatic dicarboxylic acids, the content of the structural units derived from the polycarboxylic acids (Ba) is preferably 95 mol % or less, more preferably 5 to 85 mol %, even more preferably 10 to 75 mol %, particularly preferably 15 to 65 mol %, especially preferably 20 to 55 mol %, and most preferably 25 to 45 mol %. When the content of the structural units derived from aliphatic dicarboxylic acids is within the above range, the polyester tends to have excellent adhesive strength, tackiness, mechanical recyclability, and optical properties.

[0064] When the polyester (B1) has a structural unit derived from an aliphatic dicarboxylic acid, the content thereof is usually 1 to 70 mass%, preferably 3 to 55 mass%, more preferably 5 to 45 mass%, even more preferably 10 to 35 mass%, and most preferably 15 to 30 mass%, of the polyester (B1). When the content of the structural unit derived from an aliphatic dicarboxylic acid is within the above range, the polyester (B1) tends to have excellent adhesive strength, tackiness, mechanical recyclability, and optical properties.

[0065] The polyester (B1) preferably has a structural unit derived from an aliphatic diol having 1 to 5 carbon atoms as a structural unit derived from a polyhydric alcohol (Bb), from the viewpoints of adhesive strength, tackiness, mechanical recyclability, and optical properties.

[0066] When the polyester (B1) has a structural unit derived from an aliphatic diol having 1 to 5 carbon atoms as a structural unit derived from a polyhydric alcohol (Bb), the content of the structural unit derived from an aliphatic diol having 1 to 5 carbon atoms is preferably 10 to 100 mol %, more preferably 30 to 95 mol %, and even more preferably 50 to 90 mol % of the structural unit derived from the polyhydric alcohol (Bb). When the content of the structural unit derived from an aliphatic diol having 1 to 5 carbon atoms is within the above range, the polyester tends to have excellent mechanical recyclability and optical properties.

[0067] When the polyester (B1) has a structural unit derived from an aliphatic diol having 1 to 5 carbon atoms, the content thereof is usually 10 to 70 mass%, preferably 15 to 60 mass%, and more preferably 25 to 45 mass%, of the polyester (B1). When the content of the structural unit derived from an aliphatic diol having 1 to 5 carbon atoms is within the above range, the polyester (B1) tends to have excellent mechanical recyclability and optical properties.

[0068] When the polyester (B1) has a structural unit derived from a trihydric or higher polyhydric alcohol, the content thereof is not particularly limited. However, from the viewpoints of crosslinking efficiency, mechanical recyclability, optical properties, production efficiency, etc., the content thereof is preferably 10 mol % or less, more preferably 0.1 to 5 mol %, of the structural unit derived from the polyhydric alcohol (Bb).

[0069] When the polyester (B1) has a structural unit derived from a trihydric or higher polyhydric alcohol, the content thereof is usually 0.1 to 10 mass %, preferably 0.3 to 5 mass %, and more preferably 0.5 to 3 mass %, of the polyester (B1). When the content of the structural unit derived from a trihydric or higher polyhydric alcohol is within the above range, the crosslinking efficiency, mechanical recyclability, and optical properties tend to be excellent.

[0070] Here, the proportion (compositional proportion) of structural units derived from each component of the polyester (B1) can be determined, for example, by nuclear magnetic resonance (NMR).

[0071] The weight average molecular weight of the polyester (B1) is preferably 2,000 to 500,000, more preferably 10,000 to 300,000, even more preferably 20,000 to 200,000, particularly preferably 30,000 to 150,000, especially preferably 50,000 to 130,000, and most preferably 70,000 to 110,000. When the weight average molecular weight is within the above range, the polyester tends to have excellent adhesive strength, holding power, heat resistance, and mechanical recyclability. The weight average molecular weight of the polyester (B1) can be measured by the same method as for the polyester (A).

[0072] The glass transition temperature (Tg) of the polyester (B1) is -80°C or higher and lower than 30°C, more preferably -70 to 20°C, even more preferably -60 to 15°C, particularly preferably -50 to 10°C, especially preferably -40 to 5°C, and most preferably -25 to 3°C. When the glass transition temperature is within the above range, the polyester (B1) tends to have excellent adhesive strength, mechanical recyclability, and optical properties. The glass transition temperature of the polyester (B1) can be measured by the same method as for the polyester (A).

[0073] The heat of crystalline fusion of polyester (B1) measured by a differential scanning calorimeter is preferably 10 J / g or less, more preferably 5 J / g or less, even more preferably 3 J / g or less, particularly preferably 1 J / g or less, and most preferably no crystallization peak (0 J / g). When the heat of crystalline fusion is within the above range, the tackiness and adhesive strength tend to be excellent. The heat of crystalline fusion refers to the energy consumed when heating and melting a crystallized substance, and can be measured by a differential scanning calorimeter (DSC).

[0074] Examples of methods for adjusting the heat of crystalline fusion include a method of appropriately using polycarboxylic acids having an alkyl group in the side chain or diols having a hydrocarbon group in the side chain, and a method of using three or more, preferably four or more, copolymerizable monomer components.

[0075] The acid value of the polyester (B1) is usually 30 mgKOH / g or less, preferably 20 mgKOH / g or less, more preferably 10 mgKOH / g or less, even more preferably 5 mgKOH / g or less, and most preferably 1 mgKOH / g or less. If the acid value is too high, the moist heat resistance, mechanical recyclability, and optical properties tend to decrease. The acid value of the polyester (B1) can be determined by neutralization titration according to JIS K0070. Examples of ways to adjust the acid value include increasing the proportion of polyhydric alcohols during the esterification reaction or transesterification reaction, or adjusting the reaction conditions. The lower limit of the acid value is usually 0 mgKOH / g.

[0076] The content of the polyester (B1) in the polyester-based pressure-sensitive adhesive (B) is usually 80% by mass or more, preferably 85% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, from the viewpoint of excellent mechanical recyclability and optical properties.

[0077] The polyester-based pressure-sensitive adhesive (B) is preferably a crosslinked product crosslinked with a crosslinking agent, and more preferably a crosslinked product of the polyester (B1) crosslinked with a crosslinking agent, in view of excellent adhesive strength, tackiness, holding power, and heat resistance.

[0078] [Crosslinking Agent] Examples of the crosslinking agent include compounds having a functional group that reacts with at least one of the hydroxyl group and the carboxyl group contained in the polyester (B1), such as polyisocyanate compounds, polyepoxy compounds, polyoxazoline compounds, and polycarbodiimide compounds. Furthermore, polyfunctional acrylic monomers and urethane acrylate oligomers that increase cohesive strength without reacting with the polyester (B1) can also be used. Among these, polyisocyanate compounds and polycarbodiimide compounds are preferred, and polyisocyanate compounds are particularly preferred, because they can achieve a good balance between initial adhesive strength, mechanical strength, and heat resistance, and also have excellent thermal decomposition properties and mechanical recyclability. These crosslinking agents may be used alone or in combination of two or more.

[0079] Examples of such polyisocyanate compounds include aromatic isocyanate compounds such as tolylene diisocyanate compounds such as 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate, xylylene diisocyanate compounds such as 1,3-xylylene diisocyanate, diphenylmethane compounds such as diphenylmethane-4,4-diisocyanate, and naphthalene diisocyanate compounds such as 1,5-naphthalene diisocyanate; Examples of suitable polyisocyanate compounds include alicyclic isocyanate compounds such as cyclohexanediisocyanate, 4,4'-dicyclohexylmethane diisocyanate, methylcyclohexane diisocyanate, isopropylidenedicyclohexyl-4,4'-diisocyanate, 1,3-diisocyanatomethylcyclohexane, and norbornane diisocyanate; aliphatic isocyanate compounds such as hexamethylene diisocyanate and trimethylhexamethylene diisocyanate; and adducts, biurets, and isocyanurates of the above-mentioned isocyanate compounds. Note that the polyisocyanate compounds may also be those in which the isocyanate moiety is blocked with phenol, lactam, or the like.

[0080] Examples of the polycarbodiimide-based compound include those obtained by decarboxylation condensation of diisocyanates. Examples of such diisocyanates include 4,4'-diphenylmethane diisocyanate, 3,3'-dimethoxy-4,4'-diphenylmethane diisocyanate, 3,3'-dimethyl-4,4'-diphenylmethane diisocyanate, 4,4'-diphenylether diisocyanate, 3,3'-dimethyl-4,4'-diphenylether diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 1-methoxyphenyl-2,4-diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, and tetramethylxylylene diisocyanate. These compounds can be used alone or in combination of two or more. It should be noted that the polycarbodiimide-based compound can also be used in which the terminal isocyanate moieties are blocked with an alcohol or the like.

[0081] The content of the crosslinking agent can be appropriately selected depending on the molecular weight of the polyester (B1) and the intended use, but typically the crosslinking agent is contained in a proportion such that the reactive groups contained in the crosslinking agent are 0.1 to 10 equivalents, more preferably 0.2 to 5 equivalents, even more preferably 0.3 to 3 equivalents, and particularly preferably 0.5 to 1.5 equivalents, per equivalent of the hydroxyl groups and / or carboxyl groups contained in the polyester (B1). The above equivalent ranges are preferred from the viewpoints of cohesive strength, mechanical recyclability, and optical properties.

[0082] The content of the crosslinking agent is preferably 0.01 to 15 parts by mass, more preferably 0.1 to 10 parts by mass, even more preferably 0.3 to 6 parts by mass, particularly preferably 0.5 to 4 parts by mass, especially preferably 0.75 to 3 parts by mass, and most preferably 1 to 2 parts by mass, relative to 100 parts by mass of the polyester (B1). The above-mentioned range of parts by mass is preferable from the viewpoints of adhesive strength, cohesive strength, mechanical recyclability, and optical properties.

[0083] In addition to the polyester (B1) and crosslinking agent, the polyester-based pressure-sensitive adhesive (B) may contain additives such as hydrolysis inhibitors, urethane catalysts, antioxidants, tackifier resins, softeners, UV absorbers, stabilizers, antistatic agents, etc., as well as inorganic or organic fillers, powders such as metal powders and pigments, or particulate compounding agents, within a range that does not impair the effects of the present invention (for example, usually 20% by mass or less, preferably 10% by mass or less of the polyester-based pressure-sensitive adhesive (B)). These may be used alone or in combination of two or more. In addition, the polyester-based pressure-sensitive adhesive (B) may contain small amounts of impurities contained in the manufacturing raw materials of the constituent components.

[0084] The gel fraction of the crosslinked product of the polyester (B1) [polyester-based pressure-sensitive adhesive (B)] is preferably 10 to 100%, more preferably 15 to 80%, even more preferably 20 to 70%, particularly preferably 25 to 60%, and most preferably 30 to 50%. When the gel fraction is within the above range, the adhesive strength, holding power, heat resistance, mechanical recyclability, and optical properties tend to be excellent.

[0085] The gel fraction is an index of the degree of crosslinking and is calculated, for example, by the following method: Polyester (B1) [polyester-based pressure-sensitive adhesive (B)] is wrapped in a 200-mesh SUS wire netting and immersed in toluene at 23°C for 24 hours, and the gel fraction is determined as the mass percentage of the insoluble polyester (B1) [polyester-based pressure-sensitive adhesive (B)] component remaining in the wire netting after immersion relative to the mass of polyester (B1) [polyester-based pressure-sensitive adhesive (B)] before immersion.

[0086] <Method of producing polyester-based resin> Next, a method of producing the polyester-based resin will be described. The method of producing the polyester-based resin includes a step of reacting a polyester (A) having a glass transition temperature of 30° C. or higher but lower than 140° C. with a polyester (B1) having a glass transition temperature of −80° C. or higher but lower than 30° C. Furthermore, a polyester-based resin composition containing the polyester-based resin can be obtained by this production method.

[0087] As described above, the polyester (A) and the polyester-based pressure-sensitive adhesive (B) containing the polyester (B1) can be made from used products collected separately as recyclable waste, scrap materials generated during the manufacturing process, unused products, etc.

[0088] The polyester (A) and the polyester-based pressure-sensitive adhesive (B) containing the polyester (B1) may be crushed into pellets or flakes as needed, and washed by a known washing means such as alkali washing or hot water washing to remove dirt remaining on the surface of the crushed pellets or flakes and foreign matter mixed in. The washed pellets or flakes may also be dried as needed.

[0089] In the method for producing the polyester resin of the present invention, the polyester (A) and the polyester (B1) contained in the polyester pressure-sensitive adhesive (B) are heated and melted to react with each other.

[0090] The mass ratio of polyester (A) to polyester (B1) during the reaction is usually 0.1 to 10 parts by mass, preferably 0.2 to 8 parts by mass, more preferably 0.3 to 8 parts by mass, and most preferably 0.5 to 5 parts by mass of polyester (B1) relative to 100 parts by mass of polyester (A). When the mass ratio of polyester (A) to polyester (B1) is within the above range, the resulting product tends to be excellent in moldability, strength, heat resistance, mechanical recyclability, and optical properties.

[0091] Furthermore, when the polyester (A) and the polyester (B1) are reacted, a known antioxidant is typically contained in an amount of 0.01 to 10 parts by mass, preferably 0.05 to 5 parts by mass, more preferably 0.1 to 3 parts by mass, and even more preferably 0.3 to 1.5 parts by mass, per 100 parts by mass of the total of the polyester (A) and the polyester (B1). When the content of the antioxidant is within the above range, the resulting composition tends to be excellent in moldability, strength, heat resistance, mechanical recyclability, and optical properties.

[0092] Examples of the antioxidant include phenol-based antioxidants, hindered phenol-based antioxidants, amine-based antioxidants, hindered amine-based antioxidants, sulfur-based antioxidants, and phosphoric acid-based antioxidants. Among these, at least one selected from hindered phenol-based antioxidants, hindered amine-based antioxidants, and phosphoric acid-based antioxidants is preferred, and hindered phenol-based antioxidants are more preferred. Examples of the hindered phenol-based antioxidant include antioxidants having a hindered phenol structure in which a group with large steric hindrance, such as a tertiary butyl group, is bonded to at least one of the carbon atoms adjacent to the carbon atom on the aromatic ring to which the phenolic hydroxyl group is bonded.

[0093] When the polyester (A) and the polyester (B1) are reacted, the reaction is preferably carried out under an inert gas atmosphere, more preferably under a nitrogen atmosphere, from the viewpoints of moldability, strength, heat resistance, mechanical recyclability, and optical properties.

[0094] When the polyester (A) and the polyester (B1) are reacted, from the viewpoints of moldability, strength, heat resistance, mechanical recyclability, and optical properties, the reaction is preferably carried out under vacuum conditions of 0.1 to 50 torr, more preferably 0.3 to 40 torr, still more preferably 0.5 to 30 torr, particularly preferably 1 to 20 torr, and especially preferably 3 to 10 torr. When the vacuum conditions are within the above ranges, oxidative degradation of the polyester (A) and the polyester (B1) is suppressed, and the resulting mixture tends to have excellent moldability, strength, heat resistance, mechanical recyclability, and optical properties.

[0095] From the viewpoint of mechanical recyclability, the heat-melting temperature is preferably 160 to 280°C, more preferably 180 to 275°C, even more preferably 200 to 270°C, and most preferably 220 to 265°C. When the heat-melting temperature is within the above range, the transesterification reaction between the polyester (A) and the polyester (B1) proceeds efficiently, and the resulting product tends to have excellent mechanical recyclability and optical properties. Furthermore, from the viewpoint of mechanical recyclability and transparency, the heating time is preferably 1 to 24 hours, more preferably 2 to 10 hours.

[0096] By carrying out the reaction under such reaction conditions, a transesterification reaction occurs between the polyester (A) and the polyester (B1), and the present polyester resin, which is the reaction product thereof, is obtained.

[0097] The content of the structural units derived from polyester (B1) in the polyester-based resin is preferably 10% by mass or less, more preferably 8% by mass or less, even more preferably 6% by mass or less, particularly preferably 4% by mass or less, and most preferably 2% by mass or less. When the content of the structural units derived from polyester (B1) is within the above range, the resin tends to have excellent moldability, strength, heat resistance, mechanical recyclability, and optical properties.

[0098] The polyester resin has structural units derived from polycarboxylic acids and structural units derived from polyhydric alcohols, and the content of structural units derived from aromatic dicarboxylic acids in the polyester resin is preferably 10 to 90% by mass, more preferably 30 to 85% by mass, even more preferably 40 to 80% by mass, particularly preferably 50 to 75% by mass, and most preferably 60 to 70% by mass. When the content of structural units derived from aromatic dicarboxylic acids is within the above range, the polyester resin tends to have excellent moldability, strength, heat resistance, mechanical recyclability, and optical properties.

[0099] The content of structural units derived from aliphatic diols having 1 to 5 carbon atoms in the polyester resin is usually 10 to 90 mass%, preferably 15 to 70 mass%, more preferably 20 to 60 mass%, particularly preferably 25 to 50 mass%, and most preferably 30 to 40 mass%. When the content of structural units derived from aliphatic diols having 1 to 5 carbon atoms is within the above range, the polyester resin tends to have excellent moldability, strength, heat resistance, mechanical recyclability, and optical properties.

[0100] The content of the polyester resin in the polyester resin composition is usually 80% by mass or more, preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 98% by mass or more, from the viewpoint of excellent mechanical recyclability and optical properties.

[0101] The polyester resin composition may contain, depending on its intended use, a crystal nucleating agent, an antioxidant, a chain extender, a hydrolysis inhibitor, a color inhibitor, a pigment, a dye, an ultraviolet absorber, a release agent, a lubricant, a flame retardant, an antistatic agent, inorganic and / or organic particles, etc., within a range that does not impair the effects of the present invention (for example, 10% by mass or less, preferably 5% by mass or less of the polyester resin composition). The polyester resin composition may also contain additives derived from a molded article containing polyester (A), additives derived from polyester (B1), or compounding agents within a range that does not impair the effects of the present invention. The polyester resin composition may also contain a resin other than the polyester resin. The amount of the other resin is preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 3% by mass or less, even more preferably 1% by mass or less, particularly preferably 0.1% by mass or less, and most preferably 0% by mass, based on the total amount of the polyester resin composition.

[0102] The water content of the polyester resin composition is preferably 0.5% or less, more preferably 0.3% or less, even more preferably 0.1% or less, particularly preferably 0.05% or less, especially preferably 0.03% or less, and most preferably 0.01% or less. When the water content is within the above range, the resin composition tends to have excellent moldability, strength, heat resistance, and mechanical recyclability. The water content of the resin composition is measured using a Karl Fischer moisture analyzer.

[0103] <Polyester-Based Resin> The nitrogen atom content of the polyester-based resin is preferably 0.1 to 1000 ppm, more preferably 1 to 750 ppm, even more preferably 3 to 500 ppm, particularly preferably 5 to 300 ppm, especially preferably 10 to 200 ppm, and most preferably 20 to 100 ppm. A nitrogen atom content within the above range tends to result in excellent mechanical recyclability, mechanical properties, and optical properties. The nitrogen atom content can be measured using a total nitrogen trace analyzer. The nitrogen atoms contained in the polyester-based resin are those contained when an isocyanate-based compound is used as a crosslinking agent for polyester (B1) or when a carbodiimide-based compound is used as a hydrolysis inhibitor, and in particular, those derived from isocyanate groups are preferred.

[0104] The glass transition temperature (Tg) of the polyester resin is preferably 30°C or higher, more preferably 40 to 140°C, even more preferably 50 to 120°C, and most preferably 60 to 100°C. When the glass transition temperature (Tg) is within the above range, the polyester resin tends to have excellent moldability, strength, and heat resistance. The glass transition temperature of the polyester resin can be measured by the same method as for polyester (A).

[0105] The weight-average molecular weight of the polyester resin is preferably 5,000 to 300,000, more preferably 10,000 to 150,000, even more preferably 20,000 to 100,000, and particularly preferably 30,000 to 75,000. When the weight-average molecular weight is within the above range, the polyester resin tends to have excellent moldability, strength, heat resistance, and mechanical recyclability. The weight-average molecular weight of the polyester resin can be measured by the same method as for polyester (A).

[0106] The intrinsic viscosity of the polyester resin is preferably 0.3 to 1.5 dL / g, more preferably 0.4 to 1.3 dL / g, even more preferably 0.5 to 1.1 dL / g, particularly preferably 0.6 to 1.0 dL / g, especially preferably 0.65 to 0.9 dL / g, and most preferably 0.7 to 0.8 dL / g. When the intrinsic viscosity is within the above range, the resin tends to exhibit excellent moldability, strength, heat resistance, and mechanical recyclability. The intrinsic viscosity of the polyester resin is measured in accordance with JIS K7367.

[0107] The acid value of the polyester resin is preferably 5 mgKOH / g or less, more preferably 4.5 mgKOH / g or less, even more preferably 4 mgKOH / g or less, particularly preferably 3.5 mgKOH / g or less, especially preferably 3 mgKOH / g or less, and most preferably 1 mgKOH / g or less. When the acid value is within the above range, the resin tends to have excellent hydrolysis resistance, heat resistance, mechanical recyclability, and optical properties. The acid value of the polyester resin can be determined by neutralization titration according to JIS K0070.

[0108] The polyester resin preferably has a haze of 5% or less, more preferably 4% or less, and even more preferably 3% or less, when formed into a sheet having a thickness of 50 μm. When the haze is less than the above value, the optical properties tend to be excellent. The haze is measured in accordance with JIS K7136.

[0109] The present polyester resin and a polyester resin composition containing the present polyester resin can be suitably used as molded articles such as polyester containers, polyester films, and polyester fibers. The molding method for the molded articles is not particularly limited, and examples include injection molding, extrusion molding, blow molding, and in-mold molding. For example, the present polyester resin or polyester resin composition can be extrusion molded into a sheet, and the sheet can be formed into a desired shape by vacuum forming or the like to form a container. These are useful as beverage bottles and their lids, trays and containers for foods such as fried foods and prepared foods, and the like. The sheet can also be stretched into a film or the like and used as a food packaging material or a protective film for the inner and outer surfaces of trays and containers. The polyester containers, polyester films, and polyester fibers may contain the present polyester resin. For example, they may consist solely of the present polyester resin or polyester resin composition, or they may be laminates of the present polyester resin or polyester resin composition with other resins.

[0110] 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. In the examples, "parts" and "%" are based on mass.

[0111] First, a polyester (A) and a polyester-based pressure-sensitive adhesive (B) were prepared as follows.

[0112] [Polyester (A)] [Preparation of Polyester (A-1)] A reactor equipped with a heating device, thermometer, stirrer, rectification column, nitrogen inlet tube, and vacuum device was charged with 323 parts of isophthalic acid as polycarboxylic acids (Aa), 60.3 parts of ethylene glycol as polyhydric alcohols (Ab), 243 parts of neopentyl glycol, and 373.7 parts of recycled polyethylene terephthalate (256.9 parts of recycled terephthalic acid, 116.8 parts of recycled ethylene glycol), and 0.1 parts of zinc acetate as a catalyst. The temperature was gradually increased to an internal temperature of 260 ° C., and the esterification reaction was carried out over 4 hours. Thereafter, 0.05 parts of tetrabutyl titanate was charged as a catalyst, and the internal temperature was reduced to 260 ° C. and 1.33 hPa. A polycondensation reaction was carried out over 3 hours to obtain polyester (A-1). The glass transition temperature (Tg) of the resulting polyester (A-1) was 68 ° C., and the weight average molecular weight (Mw) was 38,000. Other physical properties were as shown in Table 1. The final component ratios were: polycarboxylic acids (Aa) was isophthalic acid / recycled terephthalic acid = 50 mol% / 50 mol%, polyhydric alcohols (Ab) was recycled ethylene glycol / ethylene glycol / neopentyl glycol = 39 mol% / 18 mol% / 45 mol%, and the content of structural units derived from recycled polyethylene terephthalate in polyester (A-1) was 42 mass%.

[0113] [Polyester-based Pressure-Sensitive Adhesive (B)] [Preparation of Polyester (B1-1)] A reactor equipped with a heater, thermometer, stirrer, rectification column, nitrogen inlet tube, and vacuum device was charged with 96.1 parts of isophthalic acid as polycarboxylic acids (Ba), 467.8 parts of sebacic acid, 271 parts of neopentyl glycol as polyhydric alcohols (Bb), 130.3 parts of 1,4-butanediol, 29.7 parts of 1,6-hexanediol, 5 parts of trimethylolpropane, and 0.1 parts of zinc acetate as a catalyst, and the temperature was gradually increased to an internal temperature of 260 ° C., and an esterification reaction was carried out over 4 hours. Thereafter, 0.05 parts of tetrabutyl titanate was charged as a catalyst, and the internal temperature was reduced to 260 ° C. and 1.33 hPa, and a polycondensation reaction was carried out over 3 hours to obtain polyester (B1-1). The resulting polyester (B1-1) had a glass transition temperature (Tg) of -48°C and a weight average molecular weight (Mw) of 84,000. Other physical properties were as shown in Table 2 below. The final component ratios were: isophthalic acid / sebacic acid = 20 mol% / 80 mol% as polyvalent carboxylic acids (Ba), and neopentyl glycol / 1,4-butanediol / 1,6-hexanediol / trimethylolpropane = 59 mol% / 34 mol% / 6 mol% / 1 mol% as polyhydric alcohols (Bb).

[0114] [Preparation of Polyesters (B1-2) and (B1-3)] Polyesters (B1-2) and (B1-3) were obtained in the same manner as in the preparation of polyester (B1-1), except that the final component ratios of polycarboxylic acids (Ba) and polyhydric alcohols (Bb) were adjusted to the ratios shown in Table 2 below. The obtained polyester (B1-2) had a glass transition temperature (Tg) of -32°C and a weight average molecular weight (Mw) of 88,000. Other physical properties were as shown in Table 2 below. The obtained polyester (B1-3) had a glass transition temperature (Tg) of 1°C and a weight average molecular weight (Mw) of 94,000. Other physical properties were as shown in Table 2 below.

[0115] [Preparation of Acrylic Resin (B1'-1)] A four-necked round-bottom flask equipped with a reflux condenser, a stirrer, a nitrogen gas inlet, and a thermometer was charged with 919 parts of butyl acrylate, 80 parts of acrylic acid, 1 part of 2-hydroxyethyl methacrylate, and 800 parts of ethyl acetate. After heating to reflux, 5 parts of azobisisobutyronitrile (AIBN) was added as a polymerization initiator. The mixture was reacted for 7 hours at the ethyl acetate reflux temperature, and then diluted with ethyl acetate to obtain an acrylic resin (B1'-1) solution. The resulting acrylic resin (B1'-1) had a glass transition temperature of -48°C and a weight-average molecular weight of 280,000. The glass transition temperature was calculated using the Fox equation, and the weight-average molecular weight was measured in the same manner as for polyester (B1).

[0116] [Polyester-based Pressure-Sensitive Adhesive (B)] [Preparation of Polyester-based Pressure-Sensitive Adhesive (B-1)] The polyester (B1-1) obtained above was diluted with ethyl acetate to a solids concentration of 50%, and 2 parts (solids) of a polyisocyanate compound [Takenate D101E (trimethylolpropane adduct of toluene diisocyanate: nitrogen atom content 12.8%), manufactured by Mitsui Chemicals, Inc.] as a crosslinking agent and 0.1 parts of an antioxidant (IRGANOX1010, manufactured by BASF) were blended with this polyester (B1-1) (100 parts as solids), and the mixture was stirred and mixed to obtain a polyester-based pressure-sensitive adhesive composition. The obtained polyester-based pressure-sensitive adhesive composition was applied using an applicator to a 38 μm thick PET release film (manufactured by Mitsui Chemicals Tocello, Inc., SP-PET-03-BU) and dried at 120°C for 4 minutes to obtain a single-sided release film-attached pressure-sensitive adhesive sheet with a pressure-sensitive adhesive composition layer thickness of 50 μm. Next, the pressure-sensitive adhesive composition layer surface of the obtained single-sided release film-attached pressure-sensitive adhesive sheet was covered with a 38 μm thick PET release film (manufactured by Mitsui Chemicals Tocello, Inc., SP-PET-01-BU) and subjected to aging treatment at 40°C for 4 days, after which the double-sided release films were peeled off to obtain polyester-based pressure-sensitive adhesive (B-1). The composition and gel fraction of polyester-based pressure-sensitive adhesive (B-1) are shown in Table 3 below.

[0117] [Preparation of Polyester-Based Pressure-Sensitive Adhesives (B-2) and (B-3)] Polyester-based pressure-sensitive adhesives (B-2) and (B-3) were obtained in the same manner as in the polyester-based pressure-sensitive adhesive (B-1), except that the polyester (B1-1) used was changed to polyester (B1-2) and (B1-3), respectively. The compositions and gel fractions of the polyester-based pressure-sensitive adhesives (B-2) and (B-3) are shown in Table 3 below.

[0118] [Preparation of Acrylic Pressure-Sensitive Adhesive (B'-1)] The acrylic resin (B1'-1) obtained above was diluted with ethyl acetate to a solids concentration of 50%, and this acrylic resin (B1'-1) (100 parts as solids) was blended with 0.5 parts (solids) of a polyisocyanate crosslinking agent (Takenate D101E, manufactured by Mitsui Chemicals, Inc.) and 0.1 parts of an antioxidant (IRGANOX 1010, manufactured by BASF), followed by stirring and mixing to obtain an acrylic pressure-sensitive adhesive composition. The obtained acrylic pressure-sensitive adhesive composition was applied using an applicator to a 38 μm-thick PET release film (SP-PET-03-BU, manufactured by Mitsui Chemicals Tocello, Inc.) and dried at 120°C for 4 minutes to obtain a pressure-sensitive adhesive sheet with a single-sided release film having a pressure-sensitive adhesive composition layer thickness of 50 μm. The surface of the pressure-sensitive adhesive composition layer of the obtained pressure-sensitive adhesive sheet with one-sided release film was then covered with a 38 μm-thick PET release film (SP-PET-01-BU, manufactured by Mitsui Chemicals Tocello Inc.), and aging treatment was carried out at 40° C. for 4 days. The double-sided release films were then peeled off to obtain acrylic pressure-sensitive adhesive (B'-1). The composition and gel fraction of acrylic pressure-sensitive adhesive (B'-1) are shown in Table 3 below.

[0119] Example 1 A reactor equipped with a heater, a thermometer, a stirrer, a rectification column, a nitrogen inlet tube, and a vacuum device was charged with 500 parts of the polyester resin (A-1) obtained above, 5 parts of a polyester pressure-sensitive adhesive (B-1), and 0.5 parts of an antioxidant (IRGANOX 1010, manufactured by BASF), and the atmosphere inside the reactor was replaced with nitrogen. Thereafter, the internal temperature was raised to 260°C, the pressure was reduced to 7.5 torr, and the contents were heated and stirred over 5 hours to obtain a mechanically recycled polyester resin composition of Example 1.

[0120] <Examples 2 to 6, Comparative Example 1> Polyester-based resin compositions of Examples 2 to 6 and Comparative Example 1 were obtained in the same manner as in Example 1, except that the types and blending amounts of the polyester (A) and polyester-based pressure-sensitive adhesive (B) used were changed to the ratios shown in Table 4 below.

[0121] The optical properties (haze) and mechanical recyclability were evaluated using the obtained polyester resin compositions of Examples 1 to 6 and Comparative Example 1. The evaluation results are shown in Table 4 below.

[0122] [Optical Properties (Haze)] The polyester resin compositions of Examples 1 to 6 and Comparative Example 1 were each diluted with toluene / methyl ethyl ketone = 70 / 30 (mass ratio) to a solids concentration of 40% to obtain a polyester resin composition solution. The obtained polyester resin composition solution was applied to a PET release film (Mitsui Chemicals Tocello, Inc., SP-PET-03-BU) using an applicator, dried at 120 °C for 5 minutes, and the release film was peeled off to obtain a film with a thickness of 50 μm. The obtained film was cut into a size of 30 mm x 50 mm in an environment of 23 °C and 50% RH to prepare a test specimen. The haze of the test specimen was measured using a HAZE MATER NDH2000 (Nippon Denshoku Industries Co., Ltd.) and evaluated according to the following evaluation criteria. (Evaluation criteria) ◎ (excellent) ... 2.5 or less ○ (very good) ... more than 2.5 and less than 3.5 △ (good) ... more than 3.5 and less than 5 × (poor) ... more than 5

[0123] [Mechanical recyclability] The polyester resin compositions obtained in Examples 1 to 6 and Comparative Example 1 were each diluted with toluene / methyl ethyl ketone = 70 / 30 (mass ratio) to a solids concentration of 40% to obtain a polyester resin composition solution. 500 g of the obtained polyester resin composition solution was filtered using a nylon mesh filter (nylon 250T: average mesh size 59 μm, opening rate 33%, wire diameter 43 μm, thickness 78 μm), and evaluated according to the following evaluation criteria. (Evaluation criteria) ⊚ (excellent): Filterable × (poor): Filter clogged with foreign matter, making filtration impossible

[0124]

[0125]

[0126]

[0127]

[0128] The results in Table 4 show that the polyester resin compositions of Examples 1 to 6, which contained a polyester resin that was a reaction product of polyester (A) and polyester (B1), did not exhibit a decrease in the mechanical properties of the resin, were excellent in mechanical recyclability, and also had excellent optical properties. On the other hand, the polyester resin composition of Comparative Example 1, which used an acrylic pressure-sensitive adhesive, was inferior in mechanical recyclability and optical properties.

[0129] Although the above examples show specific embodiments of the present invention, the examples are merely illustrative and should not be construed as limiting. Various modifications that are obvious to those skilled in the art are intended to fall within the scope of the present invention.

[0130] The polyester resin of the present invention does not lose its mechanical properties and has excellent mechanical recyclability and optical properties, and therefore can be suitably used as a raw material for molding containers, films, and fibers.

Claims

1. A polyester resin which is a reaction product of a polyester (A) having a glass transition temperature of 30°C or higher and lower than 140°C and a polyester (B1) having a glass transition temperature of -80°C or higher and lower than 30°C.

2. The polyester resin according to claim 1, wherein the nitrogen atom content in said polyester resin is 0.1 to 1000 ppm.

3. A polyester-based resin according to claim 1 or 2, wherein the content of structural units derived from polyester (B1) in the polyester-based resin is 10 mass% or less.

4. The polyester resin according to any one of claims 1 to 3, wherein the glass transition temperature of the polyester resin is 30°C or higher.

5. The polyester resin according to any one of claims 1 to 4, wherein the weight average molecular weight of the polyester resin is 5,000 to 300,000.

6. A polyester-based resin according to any one of claims 1 to 5, wherein the acid value of the polyester-based resin is 5 mgKOH / g or less.

7. A polyester-based resin according to any one of claims 1 to 6, which has structural units derived from polyvalent carboxylic acids and structural units derived from polyhydric alcohols, and the content of structural units derived from aromatic dicarboxylic acids in the polyester-based resin is 10 to 90 mass%.

8. The polyester-based resin according to any one of claims 1 to 7, which has a haze of 5% or less when made into a sheet having a thickness of 50 μm.

9. A polyester resin according to any one of claims 1 to 8, wherein the polyester (A) has a structural unit derived from a terephthalic acid and a structural unit derived from ethylene glycol.

10. A polyester-based resin according to any one of claims 1 to 9, wherein the polyester (A) has a structural unit derived from a recycled thermoplastic polyester (A1).

11. A polyester resin according to any one of claims 1 to 10, wherein the polyester (B1) has a structural unit derived from an aromatic dicarboxylic acid.

12. A polyester resin according to any one of claims 1 to 11, wherein the content of aromatic dicarboxylic acids in the structural units derived from the polyvalent carboxylic acids (Ba) of the polyester (B1) is 10 to 100 mol %.

13. A polyester-based resin according to any one of claims 1 to 12, wherein the content of aliphatic diols having 1 to 5 carbon atoms in the structural units derived from the polyhydric alcohols (Bb) of the polyester (B1) is 10 to 100 mol %.

14. A polyester-based resin according to any one of claims 1 to 13, wherein the heat of crystalline fusion of the polyester (B1) is 10 J / g or less.

15. The polyester resin according to any one of claims 1 to 14, wherein the polyester (B1) is a crosslinked product.

16. A polyester-based resin according to any one of claims 1 to 15, wherein the crosslinked product of the polyester-based resin (B1) has a gel fraction of 10 to 100%.

17. A polyester-based container comprising the polyester-based resin according to any one of claims 1 to 16.

18. A polyester film comprising the polyester resin according to any one of claims 1 to 16.

19. A polyester fiber comprising the polyester resin according to any one of claims 1 to 16.

20. A method for producing a polyester resin, comprising a step of reacting a polyester (A) having a glass transition temperature of 30°C or higher and lower than 140°C with a polyester (B1) having a glass transition temperature of -80°C or higher and lower than 30°C.

21. The method for producing a polyester resin according to claim 20, wherein the process is carried out in a nitrogen atmosphere.

22. The method for producing a polyester resin according to claim 20 or 21, wherein the above step is carried out under a vacuum condition of 0.1 to 50 torr.

23. The method for producing a polyester resin according to any one of claims 20 to 22, wherein the step of heating and melting the resin is performed at 160 to 280°C.

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