JP2023088586A - Multilayer polyester sheet and packaging container using the same - Google Patents

Abstract

To provide a multilayer polyester sheet which maintains transparency, heat resistance and impact resistance and is excellent in heat sealability, and a packaging container using the same.SOLUTION: A heat-sealable multilayer polyester sheet has a surface layer (A layer) mainly containing a copolymerization polyester resin stacked on at least one surface of a base material layer (B layer) mainly containing a polyester-based resin, and satisfies the following requirements (1) to (3). (1) A glass transition temperature measured by a differential scan calorimeter (DSC) of the skin surface layer (A layer) of 76°C or lower. (2) A temperature rising crystallization temperature measured by the differential scan calorimeter (DSC) of the surface layer (A layer) of 110°C or higher and 140°C or lower. (3) A melting point measured by the differential scan calorimeter (DSC) of the surface layer (A layer) of 200°C or higher and 245°C or lower.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to a multi-layer polyester sheet which maintains transparency, heat resistance and impact resistance and has excellent heat sealability, and a packaging container using the same.

2. Description of the Related Art Conventionally, packaging bodies have been used for many distributed goods represented by foods, medicines and industrial products. Packages include containers formed from plastic films or sheets. Sealant films made of plastic are often used as lids for such plastic containers. In this case, after the container is filled with the contents, the lid member is heat-sealed to the flange of the container to complete the package, which has the functions of protecting the contents and preventing leakage. Containers made of polyester-based materials such as polyethylene terephthalate (PET) are widely used, considering not only their beautiful appearance such as transparency and luster, but also that they are recyclable materials. . When the container is made of a polyester-based material, the lid is often made of the same polyester-based material. This is due to the technical problem that heat sealing between different materials is difficult to achieve.
As a conventional sealant, from the viewpoint of sealing performance and cost, sealants made of polyolefin materials such as polypropylene and polyethylene have been widely used as lid materials. However, it has the disadvantage that it easily adsorbs and permeates organic compounds such as On the other hand, polyester-based sealants are not only easy to adhere to polyester-based containers by the following method, but also have the characteristic of being difficult to absorb and permeate the contents of the contents. there is In general, polyester sheets are poor in heat-sealing properties, and there are problems such as the inability to heat-seal containers thermoformed from them. In order to improve the heat sealability, there is a method of coextrusion or lamination of a polyester sheet with a copolyester.

For example, Patent Document 1 discloses a multilayer polyester sheet obtained by co-extrusion of an aromatic polyester and a copolyester.
According to such a technique, as the copolyester to be coextruded, isophthalic acid or 2,6-naphthalenedicarboxylic acid is used as part of the terephthalic acid component, and 1,4-cyclohexanedimethanol is used as part of the glycol component. By copolymerizing and controlling the heat of crystal fusion and the intrinsic viscosity of the copolyester within a certain range, a polyester sheet having heat-sealing properties, impact resistance and transparency can be obtained.

However, amorphous polyester resins such as copolyesters are amorphous, have no melting point, and have the property of being welded at low temperatures. In the case of an amorphous polyester resin, it can be dried only at a temperature below the glass transition temperature (Tg) because blocking occurs between the pellets above the glass transition temperature (Tg). Therefore, the drying process before molding requires a long time, and it is common to dry at 70° C. for 12 hours or more before molding, which is troublesome. Further, when a laminated sheet is obtained using a vented kneading extruder, if the raw material is insufficiently dried and water is contained in the raw material, the contained water may hydrolyze the raw material, resulting in a decrease in viscosity. When the intrinsic viscosity of the resulting laminated sheet is low, the mechanical strength of the final product after thermoforming is insufficient, and impact resistance and heat resistance are particularly affected. In addition, the amorphous polyester resin has high self-adhesiveness and tends to deposit and adhere to the surface of the screw groove of the extruder, which may cause problems in handling.

Japanese Patent No. 3229463

An object of the present invention is to solve the problems of the prior art and to provide a multi-layered polyester sheet which maintains transparency, heat resistance and impact resistance and has excellent heat-sealing properties, and a packaging container using the same. be.

The present invention, which solves the above problems, has the following configuration.
1. A multi-layered polyester sheet having heat-sealing properties, in which a surface layer (A layer) mainly composed of a copolymer polyester resin is laminated on at least one side of a substrate layer (B layer) mainly composed of a polyester resin, A multilayer polyester sheet characterized by satisfying the following requirements (1) to (3).
(1) The surface layer (layer A) has a glass transition temperature of 76° C. or less as measured by a differential scanning calorimeter (DSC).
(2) The temperature-rising crystallization temperature of the surface layer (A layer) measured by a differential scanning calorimeter (DSC) is 110° C. or higher and 140° C. or lower.
(3) The melting point of the surface layer (A layer) measured by a differential scanning calorimeter (DSC) is 200° C. or higher and 245° C. or lower.

2. The surface layer (A layer) of the multilayer polyester sheet contains 5 mol % or more and 40 mol % or less of structural units derived from diethylene glycol in 100 mol % of the total amount of glycol components in all polyester resin components.

3. The surface layer (A layer) of the multilayer polyester sheet contains 0 mol % or more and 5 mol % or less of structural units derived from a monomer component that can be an amorphous component in all the polyester resin components.

4. The haze of the multilayer polyester sheet is 5% or less.

5. The intrinsic viscosity of the multilayer polyester sheet is 0.50 dl/g or more and 0.85 dl/g or less.

6. 1 above. ~ 5. A packaging container obtained by shaping the multi-layered polyester sheet according to any one of 1 above by thermoforming selected from hot plate forming, vacuum forming, pressure forming or vacuum pressure forming.

The copolyester resin used in the present invention is a raw material having crystallinity, so it can be dried at 100 ° C. to 120 ° C. for 4 hours, it is difficult to cause viscosity reduction due to hydrolysis, and it has excellent handling properties. By using the copolymerized polyester resin, it is possible to provide a multi-layered polyester sheet that maintains transparency, heat resistance and impact resistance and has excellent heat-sealing properties, and a packaging container using the same.

BRIEF DESCRIPTION OF THE DRAWINGS Examples of preparation of a multilayer polyester sheet of the present invention are shown, (a) is a cross-sectional view of a three-layer structure multilayer sheet, and (b) is a cross-sectional view of a two-layer structure multilayer sheet.

The present invention will be described in detail below.
The present invention is a heat-sealable multi-layer polyester sheet in which a surface layer (A layer) mainly composed of a copolymer polyester resin is laminated on at least one side of a substrate layer (B layer) mainly composed of a polyester resin. A multilayer polyester sheet characterized by satisfying the following requirements (1) to (3).
(1) The glass transition temperature of the skin surface layer (A layer) measured by a differential scanning calorimeter (DSC) is 76° C. or less.
(2) The temperature-rising crystallization temperature of the surface layer (layer A) measured by a differential scanning calorimeter (DSC) is 110° C. or higher and 140° C. or lower.
(3) The melting point of the surface layer (A layer) measured by a differential scanning calorimeter (DSC) is 200° C. or higher and 245° C. or lower.

[Copolyester resin]
The multilayer polyester sheet in the present invention preferably uses the following copolymerized polyester resin (hereinafter sometimes referred to as polyester raw material). By using a copolymerized polyester resin for the surface layer (layer A), it is possible to obtain a multilayer polyester sheet having excellent heat sealability, transparency, heat resistance and impact resistance.

The copolymer polyester resin in the present invention preferably contains 5 mol % or more and 40 mol % or less of structural units derived from diethylene glycol in 100 mol % of the total amount of glycol components. As will be described later, structural units derived from diethylene glycol cause the generation of foreign substances during film production. Therefore, it was common to avoid using them as much as possible when considering the quality of the film. Since the polymerized polyester resin has a low melt viscosity even at a resin temperature of 250° C., it can be extruded at a temperature lower than that of ordinary polyester resins. Therefore, despite containing a large amount of diethylene glycol-derived structural units of 5 mol% or more and 40 mol% or less in the total amount of 100 mol% of the glycol component, foreign matter and defects are generated when formed into a sheet with a thickness of 350 μm. can be reduced.

One of the techniques for improving the heat-sealing property of a polyester sheet is, for example, a monomer component that constitutes a unit that can be an amorphous component in a sheet containing ethylene terephthalate as a main component (hereinafter simply referred to as an amorphous component There is a means to increase the amount. However, 1,4-cyclohexanedimethanol and openthyl glycol, which are used as amorphous components as described in Patent Document 1, have the problem of being expensive. Therefore, the present inventors focused on diethylene glycol (hereinafter also simply referred to as "DEG"), which is less expensive.

When the content of diethylene glycol in the polyester sheet increases, the heat resistance of the polyester sheet deteriorates and the ejection of foreign matter increases during melt extrusion. However, the present inventors found that when a predetermined amount of diethylene glycol is used in the surface layer (A layer) as a constituent unit of the copolymerized polyester resin, the Tg of the sheet surface is lowered, the heat sealability of the polyester sheet is improved, and the transparency, It was found that heat resistance and impact resistance can be maintained.

The copolymer polyester resin used for producing the multilayer polyester sheet in the present invention preferably contains an ethylene terephthalate unit as a main component. Here, to be the main constituent means to account for 50 mol % or more of the total constituents. The ethylene terephthalate unit accounts for preferably 50 mol% or more, more preferably 60 mol% or more, and even more preferably 70 mol% or more in 100 mol% of the constituent units of the polyester.

Examples of dicarboxylic acid components other than terephthalic acid constituting the copolymerized polyester resin of the present invention include isophthalic acid, orthophthalic acid, aromatic dicarboxylic acids such as 2,6-naphthalenedicarboxylic acid, adipic acid, azelaic acid, and sebacic acid. , aliphatic dicarboxylic acids such as decanedicarboxylic acid, and alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid. In the present invention, it is preferable not to contain dicarboxylic acid components other than terephthalic acid.

Here, the interpretation of the term "can be an amorphous component" is explained in detail.

In the present invention, the term "amorphous polymer" specifically refers to a polymer that does not have an endothermic peak due to melting as measured by a DSC (differential scanning calorimeter). Amorphous polymers have not substantially progressed in crystallization and cannot take a crystalline state, or even if they are crystallized, the degree of crystallinity is extremely low.

In the present invention, the term "crystalline polymer" refers to a polymer that is not the above-mentioned "amorphous polymer", that is, has an endothermic peak due to melting as measured by a DSC differential scanning calorimeter. A crystalline polymer is one that has crystallizable properties or is already crystallized, such that the polymer can be crystallized upon elevated temperature.

In general, for polymers in which a large number of monomer units are bonded, the stereoregularity of the polymer is low, the symmetry of the polymer is poor, the side chain of the polymer is large, the branching of the polymer is large, and the intermolecular If it has various conditions such as low cohesive force, it becomes an amorphous polymer. However, depending on the state of existence, crystallization may proceed sufficiently to form a crystalline polymer. For example, even a polymer with large side chains can be sufficiently crystallized and become crystalline when the polymer is composed of a single monomer unit. Therefore, even if the same monomer unit is used, the polymer may become crystalline or amorphous in some cases. Therefore, in the present invention, the expression "a unit derived from a monomer that can be an amorphous component" is used. Using.

Here, the monomer unit in the present invention means a repeating unit constituting a polymer derived from one polyhydric alcohol molecule and one polyhydric carboxylic acid molecule.

When a monomer unit composed of terephthalic acid and ethylene glycol (ethylene terephthalate unit) is the main monomer unit that constitutes the polymer, other monomer units include a monomer unit composed of isophthalic acid and ethylene glycol, and a monomer unit composed of terephthalic acid and neopentyl glycol. a monomer unit consisting of terephthalic acid and 1,4-cyclohexanedimethanol; and a monomer unit consisting of isophthalic acid and butanediol. In the present invention, it is preferable not to contain the other monomer unit.

Diol components other than the ethylene terephthalate unit constituting the polyester resin include 1,3-propanediol, 2,2-diethyl-1,3-propanediol, and 2-n-butyl-2-ethyl-1,3-propane. Diol, 2,2-isopropyl-1,3-propanediol, 2,2-di-n-butyl-1,3-propanediol, 1,4-butanediol, hexanediol, neopentyl glycol, hexanediol, etc. Aliphatic diols, alicyclic diols such as 1,4-cyclohexanedimethanol, and aromatic diols such as bisphenol A can be used. Diethylene glycol is used as a diol component other than the ethylene terephthalate unit constituting the copolymer polyester of the present invention.

The copolyester resin used for producing the multilayer polyester sheet in the present invention must contain a structural unit derived from diethylene glycol. The constituent unit derived from diethylene glycol is preferably 5 mol% or more, more preferably 7 mol% or more, and still more preferably 9 mol% or more, in 100 mol% of the constituent units of the polyester. The upper limit of the constituent units derived from diethylene glycol is preferably 40 mol% or less, more preferably 38 mol% or less, and even more preferably 36 mol% or less. When the constituent unit derived from diethylene glycol is contained in an amount of 5 mol% or more, the glass transition temperature of the polyester is lowered, the heat sealability of the polyester sheet is improved, and the transparency, heat resistance, and impact resistance can be maintained, which is preferable.
On the other hand, when the content of the diethylene glycol component exceeds 40 mol%, the resin softens and tends to stick to the cooling roll in the cooling and solidification step after melt extrusion, which is not preferable because the productivity deteriorates.

Among the monomer components described above, examples of monomers that can be amorphous components include neopentyl glycol, 1,4-cyclohexanedimethanol, isophthalic acid, 1,4-cyclohexanedicarboxylic acid, and 2,6-naphthalene dicarboxylic acid. acid, 2,2-diethyl-1,3-propanediol, 2-n-butyl-2-ethyl-1,3-propanediol, 2,2-isopropyl-1,3-propanediol, 2,2-di Mention may also be made of -n-butyl-1,3-propanediol, hexanediol. The content of the monomer that can be the amorphous component in the copolyester is preferably 0 mol % or more and 5 mol % or less, and more preferably not contained (that is, 0 mol %).

Further, by adjusting the amount of constituent units derived from diethylene glycol to the above range, the copolymerized polyester resin can be obtained with the glass transition temperature (Tg) adjusted within the predetermined range.

Diethylene glycol in the polyester is preferably copolymerized. Copolymerization eliminates the concern about segregation of raw materials, and it is possible to prevent changes in sheet physical properties due to fluctuations in the composition of sheet raw materials. Furthermore, copolymerization is preferable in terms of heat sealability and impact resistance.

The intrinsic viscosity of the copolyester resin in the present invention is preferably 0.56 dl/g or more and 0.87 dl/g or less. The intrinsic viscosity of the multilayer polyester sheet can be adjusted to 0.50 dl/g or more and 0.85 dl/g or less by combining the intrinsic viscosity within this range with the melt extrusion conditions described below. If the intrinsic viscosity of the copolyester resin exceeds 0.87 dl/g, the resin may be difficult to be extruded from the extruder, resulting in a decrease in productivity, which is not very preferable. If the intrinsic viscosity of the copolyester resin is less than 0.50 dl/g, the impact resistance is lowered, which is not preferable. Moreover, it is preferably 0.50 dl/g or more from the viewpoint of mechanical strength as a product after thermoforming and thermoforming.

Further, the copolyester resin having a glass transition temperature (Tg) adjusted to 55 to 76° C. can be obtained by adjusting the amount of diethylene glycol-derived constituent units within the above range. If the Tg is lower than 55°C, the physical properties change due to the movement of the molecules of the raw material resin during storage at room temperature in a warehouse, etc. in the summer.

Various additives, such as waxes, antioxidants, antistatic agents, crystal nucleating agents, viscosity reducing agents, heat stabilizers, coloring agents, may optionally be added to the resin forming the multilayer polyester sheet of the present invention. A pigment for coloring, an anti-coloring agent, an ultraviolet absorber, etc. can be added.

The resin forming the multilayer polyester sheet of the present invention preferably contains at least one particle selected from the group consisting of inorganic particles, organic particles, and particles consisting of mixtures thereof.

Examples of inorganic particles to be used include silica (silicon oxide), alumina (aluminum oxide), titanium dioxide, calcium carbonate, kaolin, crystalline glass filler, kaolin, talc, alumina, silica-alumina composite oxide particles, and sulfuric acid. Particles made of barium may be mentioned. Examples of organic particles include acrylic resin particles, melamine resin particles, silicone resin particles, and particles made of crosslinked polystyrene. Among them, particles composed of silica (silicon oxide), calcium carbonate, or alumina (aluminum oxide), or particles composed of polymethacrylate, polymethyl acrylate, or derivatives thereof are preferable, and particles composed of silica (silicon oxide) or calcium carbonate are preferable. It is more preferable, and silica (silicon oxide) is particularly preferable from the viewpoint of reducing haze.

As a method of blending the particles in the resin forming the multilayer polyester sheet, for example, the particles can be added at any stage in the production of the polyester resin. It is preferable to add a slurry dispersed in ethylene glycol or the like before starting the polycondensation reaction to proceed with the polycondensation reaction. In addition, a method of blending a slurry of particles dispersed in ethylene glycol or water or the like with a polyester resin raw material using a kneading extruder with a vent, or using a kneading extruder, dried particles and the polyester resin raw material It is also preferable to carry out by a method of blending and the like.

[Manufacturing method of multilayer polyester sheet]
The multilayer polyester sheet of the present invention is generally obtained by molding a resin such as a polyester resin into a sheet. Normally, the raw material resin is in the form of granules called chips or pellets, and when such resin is molded into a sheet, a process for drying the raw material resin is provided to remove excess moisture. The raw material is dried or dried with hot air so that the moisture content is less than 100 ppm.

The moisture content after drying of the raw material resin used in the multilayer polyester sheet of the present invention is preferably 100 ppm or less. The fact that the moisture content of the resin after drying is 100 ppm or less means that the resin has been dried to a level sufficient for producing a resin molding. If the moisture content of the resin after drying exceeds 100 ppm, the moisture content of the resin is high, and when the resin is formed into a molded article, the hydrolysis of the resin may proceed and the mechanical strength may decrease, and the film formability may deteriorate. Sometimes. Although there is no particular lower limit for the moisture content of the resin after drying, the lower limit is 30 ppm from the viewpoint of feasibility in consideration of drying time efficiency. Note that the moisture content of the raw material resin is calculated on a mass basis.

The multilayer polyester sheet of the present invention can be manufactured using a multilayer sheet manufacturing apparatus using a general coextrusion method. For example, the base layer (B layer) and the above-mentioned copolymerized polyester resin constituting the base layer (B layer) are supplied and mixed to an extruder equipped with a hopper, and the resin melted and extruded by each extruder is subjected to a multilayer die. By forming an integral sheet with , it is possible to obtain a multilayer sheet having a two-layer structure of A layer/B layer structure or a three-layer structure of A layer/B layer/A layer structure (see FIG. 1).

The multilayer polyester sheet of the present invention comprises a substrate layer (B layer) having both front and back surfaces, and a surface layer (A layer) provided on at least one side of the substrate layer (B layer). be.

The base material layer (B layer) of the multilayer polyester sheet of the present invention is mainly composed of polyethylene terephthalate (PET) resin. The polyester-based resin used in the base material layer (B layer) is preferably amorphous polyethylene terephthalate (APET, where A means amorphous). The melting point of general APET is around 260°C. Other dicarboxylic acid components other than terephthalic acid constituting the polyester resin of the present invention include isophthalic acid, orthophthalic acid, aromatic dicarboxylic acids such as 2,6-naphthalenedicarboxylic acid, adipic acid, azelaic acid, sebacic acid, Examples include aliphatic dicarboxylic acids such as decanedicarboxylic acid, and alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid. In the present invention, it is preferable not to contain dicarboxylic acid components other than terephthalic acid.

The thickness of the substrate layer (layer B) of the multilayer polyester sheet of the present invention is preferably 100 μm to 1 mm. It is more preferably 200 μm to 800 μm. If the thickness of the base material layer (layer B) is less than 100 μm, the thickness of the container obtained by thermoforming the multilayer polyester sheet will be too thin, making it difficult to ensure the necessary performance in terms of rigidity and strength of the container. . If the thickness of the base material layer (B layer) exceeds 1 mm, the formability in thermoforming may be deteriorated.

The surface layer (layer A) of the multilayer polyester sheet of the present invention is composed mainly of the copolyester resin described above. The copolymerized polyester resin used in the surface layer (layer A) preferably uses diethylene glycol as a constituent unit of the polyester resin, and the amount of constituent units derived from diethylene glycol is within the above range.

The thickness of the surface layer (layer A) of the multilayer polyester sheet of the present invention is preferably 10 to 100 μm. It is more preferably 15 μm to 60 μm. If the thickness of the surface layer (layer A) is less than 10 µm, it becomes difficult to ensure the necessary performance in terms of heat sealability and impact resistance. If the thickness of the surface layer (layer A) exceeds 100 µm, heat-sealing property is improved, but heat resistance and mechanical strength are lowered, which is not preferable.

The multilayer polyester sheet of the present invention can be subjected to corona treatment, coating treatment, flame treatment, etc. in order to improve the adhesiveness of the sheet surface.

The multilayer polyester sheet of the present invention can be formed into a packaging container by using a known thermoforming technique (for example, hot platen molding, vacuum molding, air pressure molding, vacuum pressure molding, reverse draw molding, or a molding method combining these). can be shaped into

[Characteristics of multilayer polyester sheet and container of the present invention]
A multi-layered polyester sheet having heat-sealing properties, in which a surface layer (A layer) mainly composed of a copolymer polyester resin is laminated on at least one side of a substrate layer (B layer) mainly composed of a polyester resin, The surface layer (A layer) preferably satisfies all of the following requirements (1) to (3). Each will be explained in detail.
(1) The surface layer (layer A) has a glass transition temperature of 76° C. or less as measured by a differential scanning calorimeter (DSC).
(2) The temperature-rising crystallization temperature of the surface layer (A layer) measured by a differential scanning calorimeter (DSC) is 110° C. or more and 140° C. or less (3) The surface layer (A layer) of the differential scanning calorimeter ( The melting point measured by DSC) is 200° C. or higher and 245° C. or lower.

(1) Glass transition temperature (Tg)
The glass transition temperature of the surface layer (layer A) of the multilayer polyester sheet of the present invention is preferably 76°C or lower, more preferably 74°C or lower. If the glass transition temperature of the surface layer (layer A) is high, the heat-sealing property of the multilayer polyester sheet is deteriorated, which is not preferable.

(2) Temperature-rising crystallization temperature (Tc1)
The temperature-rising crystallization temperature obtained when the surface layer (layer A) of the multilayer polyester sheet of the present invention is measured by a differential scanning calorimeter (DSC) is preferably 110°C or higher and 140°C or lower, more preferably 115°C. °C or higher and 135 °C or lower.
If the crystallization temperature of the surface layer (layer A) is lower than 110°C, crystallization is likely to occur at a lower temperature, and the heat during molding promotes crystallization, resulting in poor transparency. I don't like it. If the crystallization temperature of the surface layer (layer A) is higher than 140° C., the content of diethylene glycol as a constituent unit of the polyester resin is reduced, which is undesirable because the heat-sealing property is deteriorated.

(3) Melting point (Tm)
The melting point obtained when the surface layer (layer A) of the multilayer polyester sheet of the present invention is measured by a differential scanning calorimeter (DSC) is preferably 200°C or higher and 245°C or lower, more preferably 202°C or higher and 242°C. It is below. A detailed method for measuring the melting point will be described later in Examples, but when two or more melting peaks are observed, the peak appearing on the lowest temperature side is taken as the melting point. If the melting point of the surface layer (layer A) is lower than 200° C., the heat sealability is improved, but the heat resistance and mechanical strength are lowered, which is not preferable. If the melting point of the surface layer (layer A) exceeds 245° C., the melting of the surface layer (layer A) is difficult to occur, and the heat-sealing property is lowered, which is not preferable.

The haze of the multilayer polyester sheet of the present invention is preferably 5% or less, more preferably 3% or less, from the viewpoint of the transparency (haze) of the sheet and the final product.

The peel strength (heat-sealing property) when the multilayer polyester sheet of the present invention and the easy-open film are heat-sealed is preferably 10 N/15 mm or more. If the peel strength is less than 10 N/15 mm, the sealed portion is easily peeled off and cannot be used as a package.

Next, the present invention will be specifically described using examples and comparative examples, but the present invention is not limited to the aspects of these examples, and can be used as appropriate without departing from the scope of the present invention. It is possible to change. Methods for evaluating polyester raw materials and multilayer polyester sheets are shown below.

A. Evaluation methods for polyester raw materials are as follows.
[Glass transition temperature (Tg)]
Using a differential scanning calorimeter (DSC6220, manufactured by SII Nanotechnology Co., Ltd.), 5 mg of a resin sample was melted to 280°C under a nitrogen atmosphere, held for 5 minutes, then quenched with liquid nitrogen and cooled to room temperature. It was determined from the endothermic curve obtained by increasing the temperature at a temperature increase rate of 20° C./min. The temperature at the intersection of the extended line of the baseline below the glass transition temperature and the tangent line showing the maximum slope at the transition portion was defined as the glass transition temperature (Tg).

[Diethylene glycol content]
5 mg of the resin sample was dissolved in 0.7 ml of a mixed solution of deuterated chloroform and trifluoroacetic acid (volume ratio 9/1), and 1H-NMR (manufactured by Varian, UNITY50) was used to calculate the amount of diethylene glycol units present. Mole % was determined.

[Intrinsic viscosity (IV)]
0.2 g of a resin sample was dissolved in 50 ml of a mixed solvent of phenol/1,1,2,2-tetrachloroethane (60/40 (weight ratio)) and measured at 30° C. using an Ostwald viscometer. The unit is dl/g.

[Moisture percentage]
The water content (ppm) of the resin was measured by the Karl Fischer method using a Karl Fischer moisture analyzer (CA-200 manufactured by Mitsubishi Chemical Corporation). "Aquamicron" (registered trademark) AX/CXU was used as a reagent, and the moisture content of the resin was calculated on a mass basis.

B. The evaluation method of the multilayer polyester sheet is as follows. In addition, when obtaining the heating crystallization temperature (Tc1), melting point, glass transition temperature (Tg), and intrinsic viscosity (IV) of the surface layer shown below, only the surface layer is scraped off from the surface layer of the sheet with a feather blade. sampled. The cross section of the sheet sample after scraping was observed with an electron scanning microscope (SEM) to confirm whether layers other than the surface layer were scraped.

[Sheet thickness]
It was measured using a dial gauge in accordance with JIS K7130-1999 A method.

[Sheet film formability]
Appearance evaluation of the obtained multilayer polyester sheet was evaluated by ◯ and x. If there was no dirt or foreign matter and the film formability was good, it was rated as ◯. If there was dirt or foreign matter, or if the film forming property was not good, it was evaluated as x.

[Glass transition temperature (Tg) (surface layer)]
Using a differential scanning calorimeter (DSC6220 manufactured by SII Nanotechnology Co., Ltd.), 5 mg of a resin sample sampled from the surface layer of the sheet was heated from 25°C to 320°C at a heating rate of 10°C/min under a nitrogen atmosphere. It was melted, rapidly cooled with liquid nitrogen at 300°C/min, held at room temperature for 3 minutes, then heated from 25°C to 320°C at a rate of temperature increase of 10°C/min, and obtained from the endothermic curve. The temperature at the intersection of the extended line of the baseline below the glass transition temperature and the tangent line showing the maximum slope at the transition portion was defined as the glass transition temperature (Tg).

[Temperature-rising crystallization temperature (Tc1) (surface layer)]
Using a differential scanning calorimeter (DSC6220 manufactured by SII Nanotechnology Co., Ltd.), 5 mg of a resin sample sampled from the surface layer of the sheet was heated from 25°C to 320°C at a heating rate of 10°C/min under a nitrogen atmosphere. Melt, quench at 300°C/min with liquid nitrogen, hold at room temperature for 3 minutes, then heat from 25°C to 320°C at a rate of temperature increase of 10°C/min. The peak top temperature of the curve was taken as the heating crystallization temperature (Tc1).

[Melting point (Tm) (surface layer)]
Using a differential scanning calorimeter (DSC6220 manufactured by SII Nanotechnology Co., Ltd.), 5 mg of a resin sample sampled from the surface layer of the sheet was heated from 25°C to 320°C at a heating rate of 10°C/min under a nitrogen atmosphere. Melt, quench at 300°C/min with liquid nitrogen, hold at room temperature for 3 minutes, then raise temperature from 25°C to 320°C at a rate of temperature increase of 10°C/min. was taken as the melting point. The term "endothermic peak" as used herein refers to one appearing in the temperature range of 160 to 280°C. Also, when two or more melting points appear in the temperature range of 160 to 280° C., the one on the lowest temperature side was taken as the melting point.

[Haze]
According to JIS-K7136, a 5 cm long×5 cm wide area was cut from the obtained sheet, and the haze was measured using a haze meter (NDH5000) manufactured by Nippon Denshoku Industries Co., Ltd. The measurement was performed 3 times and the average value was obtained.
[Intrinsic viscosity (IV) (sheet)]
0.2 g of the multilayer polyester sheet was dissolved in 50 ml of a mixed solvent of phenol/1,1,2,2-tetrachloroethane (60/40 (weight ratio)) and measured at 30° C. using an Ostwald viscometer. The unit is dl/g.

[Heat sealability]
Using a multilayer polyester sheet and an easy-open film (manufactured by Mitsui Chemicals Tohcello (trade name) ABF65C), the peel strength was measured by heat-sealing at a heater temperature of 120 ° C to 160 ° C for 1.0 seconds and a pressure of 0.5 MPa. . The adhesive sample was cut so that the seal width was 15 mm. The peel strength was measured using a universal tensile tester "DSS-100" (manufactured by Shimadzu Corporation) at a tensile speed of 200 mm/min. The peel strength is expressed as strength per 15 mm (N/15 mm). The evaluation of the heat-sealing property was performed with a target value of 10 N/15 mm or more, with ◯ when the value was equal to or more than the target value, and x when the value was less than the target value.

[Impact strength]
A 181 film impact tester manufactured by Yasuda Seiki Seisakusho Co., Ltd. was used as a measurement device to measure the impact strength of the multilayer polyester sheet. Specifically, a test sample having an area of 5 cm in the longitudinal direction and 5 cm in the width direction was cut out from the obtained sheet, and the sample was left at the environmental temperature for measurement for 24 hours before measurement.

C. The evaluation method of the container is as follows. A standard size transparent container (length 125 mm×width 125 mm×height 35 mm, flange width 5 mm) was prepared by thermoforming the multilayer polyester sheet.

[Heat resistance (container)]
As a measuring device, PHH-202M manufactured by Espec Co., Ltd. was used to measure the heat resistance of the container. The obtained container is left for 1 hour in a perfect oven (constant temperature vessel) set at a test temperature of 50°C to 70°C. The presence or absence of dimensional change and deformation of the container before and after heating was evaluated by ◯ and ×. A case where there was no dimensional change or deformation of the container was rated as ◯, and a case where there was a dimensional change or deformation of the container was rated as x.
[Heat sealability (container)]
An easy-open film (manufactured by Mitsui Chemicals Tohcello Co., Ltd. (trade name) ABF65C) is cut into a size of 13.5 cm in the longitudinal direction × 13.5 cm in the width direction, and heat-sealed to the container using a hand sealer manufactured by Acing Pack Industry Co., Ltd. Then, a packaging container was produced. The heat sealing conditions were a heater temperature of 140° C. to 160° C., a time of 1.0 second, and a pressure of 0.5 MPa, and the peel strength was measured. The peel strength was measured using a universal tensile tester "DSS-100" (manufactured by Shimadzu Corporation) at a tensile speed of 200 mm/min. The peel strength is expressed as strength per 15 mm (N/15 mm). The evaluation of the heat-sealing property was performed with a target value of 10 N/15 mm or more, with ◯ when the value was equal to or more than the target value, and x when the value was less than the target value.

<Preparation of polyester raw material>
Using terephthalic acid (TPA) and each glycol component described below, raw materials A to H were obtained by a known method of polycondensation via transesterification. Then, each raw material was dried under the drying conditions described below so that the moisture content was less than 100 ppm.
Raw Material A: Polyester composed of 22 mol % diethylene glycol, 78 mol % ethylene glycol and terephthalic acid. Dry under reduced pressure (1 Torr) at 110° C. for 4 hours. Intrinsic viscosity 0.68dl/g Glass transition temperature 67°C Moisture content 82ppm
Raw Material B: Polyester composed of 40 mol % diethylene glycol, 60 mol % ethylene glycol and terephthalic acid. Dry under reduced pressure (1 Torr) at 110° C. for 4 hours. Intrinsic viscosity 0.661 dl/g Glass transition temperature 62°C Moisture content 88 ppm
Raw Material C: Polyester composed of 60 mol % diethylene glycol, 40 mol % ethylene glycol and terephthalic acid. Dry under reduced pressure (1 Torr) at 110° C. for 4 hours. Intrinsic viscosity 0.651 dl/g Glass transition temperature 58°C Moisture content 90 ppm

Raw Material D: Polyester composed of 14 mol % diethylene glycol, 86 mol % ethylene glycol and terephthalic acid. Dry under reduced pressure (1 Torr) at 110° C. for 4 hours. Intrinsic viscosity 0.71 dl/g Glass transition temperature 69°C Moisture content 78 ppm
Raw Material E: Polyester composed of 3 mol % diethylene glycol, 97 mol % ethylene glycol and terephthalic acid. Dry under reduced pressure (1 Torr) at 110° C. for 4 hours. Intrinsic viscosity 0.731 dl/g Glass transition temperature 73°C Moisture content 75 ppm
Raw Material F: Polyester composed of 1 mol % of diethylene glycol, 69 mol % of ethylene glycol, 30 mol % of 1,4-cyclohexanedimethanol and terephthalic acid. Dry under reduced pressure (1 Torr) at 70° C. for 48 hours. Intrinsic viscosity 0.73 dl/g Glass transition temperature 80°C Moisture content 92 ppm
Raw Material G: Polyester composed of 100 mol % of ethylene glycol and terephthalic acid. Intrinsic viscosity 0.75 dl/g Glass transition temperature 83°C Moisture content 72 ppm
Raw Material H: Polyester composed of 100 mol % of ethylene glycol and terephthalic acid. Dry under reduced pressure (1 Torr) at 110° C. for 4 hours. Intrinsic viscosity 0.75 dl/g Glass transition temperature 83°C Moisture content 74 ppm

In the production of the polyester raw material H, SiO2 (Sylysia 310 manufactured by Fuji Silysia Co., Ltd.) was added as a lubricant at a rate of 7000 ppm relative to the polyester. In the table, EG is ethylene glycol, DEG is diethylene glycol, and CHDM is 1,4-cyclohexanedimethanol. In addition, each polyester was appropriately chipped.

Tables 1 and 2 show the compositions of the polyester raw materials used in Examples and Comparative Examples, the drying conditions for the raw materials, the resin compositions of the sheets in Examples and Comparative Examples, and the manufacturing conditions, respectively.

[Example 1]
A multilayer polyester sheet having a three-layer structure was formed using three extruders. The base material layer (B layer) contained polyester raw material G at 100.0% by mass, and the surface layer (A layer) contained polyester raw material A at 94.0% by mass and polyester raw material H at 6.0% by mass. After drying each raw material resin, the surface layer (A layer) forming mixed resin is melt extruded from the first and third extruders at a resin temperature of 260 ° C., and the second extruder is used to form the base layer (B layer). The formed mixed resin is melted at a resin temperature of 280 ° C., and from the side that contacts the casting drum, the surface layer (A layer) / base layer (B layer) / surface layer (A layer) in this order, in the T die The layers are combined and laminated so that the layer thickness ratio is 5/90/5, discharged from a T-shaped die, cooled and solidified in a casting drum with a surface temperature of 25 ° C., and an unstretched polyethylene terephthalate sheet is rolled. A multilayer polyester sheet with a thickness of 350 μm was continuously produced over a predetermined length by winding up.
Table 2 shows the raw material composition and film-forming conditions of the multilayer polyester sheet, the physical properties of the obtained sheet, and the evaluation results. The sheet was evaluated for the surface layer (A layer) on the side in contact with the chill roll.

Example 2
A multilayer polyester sheet having a thickness of 350 μm was produced in the same manner as in Example 1, except that the raw material A was changed to the raw material B. Table 2 shows the raw material composition and film-forming conditions of the multilayer polyester sheet, the physical properties of the obtained sheet, and the evaluation results. The sheet was evaluated for the surface layer (A layer) on the side in contact with the chill roll.

Example 3
A multilayer polyester sheet having a thickness of 350 μm was produced in the same manner as in Example 1, except that raw material A was changed to raw material D. Table 2 shows the raw material composition and film-forming conditions of the multilayer polyester sheet, the physical properties of the obtained sheet, and the evaluation results. The sheet was evaluated for the surface layer (A layer) on the side in contact with the chill roll.

Example 4
A multilayer polyester having a thickness of 350 μm was prepared in the same manner as in Example 1 except that the layer thickness ratio of surface layer (A layer) / base layer (B layer) / surface layer (A layer) was changed to 10/80/10. manufactured the sheet. Table 2 shows the raw material composition and film-forming conditions of the multilayer polyester sheet, the physical properties of the obtained sheet, and the evaluation results. The sheet was evaluated for the surface layer (A layer) on the side in contact with the chill roll.

Example 5
A multilayer polyester sheet having a thickness of 350 μm was produced in the same manner as in Example 1, except that the thickness of the multilayer polyester sheet was changed to 400 μm. Table 2 shows the raw material composition and film-forming conditions of the multilayer polyester sheet, the physical properties of the obtained sheet, and the evaluation results. The sheet was evaluated for the surface layer (A layer) on the side in contact with the chill roll.

Comparative example 1
A multilayer polyester sheet having a thickness of 350 μm was produced in the same manner as in Example 1, except that the raw material A was changed to the raw material C. Table 2 shows the raw material composition and film-forming conditions of the multilayer polyester sheet, the physical properties of the obtained sheet, and the evaluation results. The sheet was evaluated for the surface layer (A layer) on the side in contact with the chill roll.

Comparative example 2
A multilayer polyester sheet having a thickness of 350 μm was produced in the same manner as in Example 1, except that the raw material A was changed to the raw material G. Table 2 shows the raw material composition and film-forming conditions of the multilayer polyester sheet, the physical properties of the obtained sheet, and the evaluation results. The sheet was evaluated for the surface layer (A layer) on the side in contact with the chill roll.

Comparative example 3
A multilayer polyester sheet having a thickness of 350 μm was produced in the same manner as in Example 1, except that raw material A was changed to raw material E. Table 2 shows the raw material composition and film-forming conditions of the multilayer polyester sheet, the physical properties of the obtained sheet, and the evaluation results. The sheet was evaluated for the surface layer (A layer) on the side in contact with the chill roll.

Reference example 1
A multilayer polyester sheet having a thickness of 350 μm was produced in the same manner as in Example 1, except that the raw material A was changed to the raw material F. Table 2 shows the raw material composition and film-forming conditions of the multilayer polyester sheet, the physical properties of the obtained sheet, and the evaluation results. The sheet was evaluated for the surface layer (A layer) on the side in contact with the chill roll.

Reference example 2
A multilayer polyester having a thickness of 350 μm was prepared in the same manner as in Example 1 except that the raw material G of the base layer (B layer) was changed to 94.0% by mass of the polyester raw material A and 6.0% by mass of the polyester resin raw material H. manufactured the sheet. Table 2 shows the raw material composition and film-forming conditions of the multilayer polyester sheet, the physical properties of the obtained sheet, and the evaluation results. The sheet was evaluated for the surface layer (A layer) on the side in contact with the chill roll.

As shown in Table 2, the sheets of Examples 1 to 5 have the glass transition temperature, temperature-rising crystallization temperature, and melting point of the surface layer (layer A) within the specified ranges. A multi-layered polyester sheet that maintains impact resistance and has excellent heat-sealing properties, and a packaging container using the same.

In Comparative Example 1, although the surface layer (A layer) of the obtained sheet had a glass transition temperature and a temperature-increased crystallization temperature within the specified ranges, the melting point was low, so the heat resistance was poor. In addition, the diethylene glycol content in the polyester sheet is high, and stains and foreign matter are likely to occur, so the sheet film-forming properties are reduced and the sheet cannot be stably collected, making it difficult for industrially continuously produced sheets. was inferior.

In Comparative Example 2, the glass transition temperature of the surface layer (A layer) of the obtained sheet was within the specified range, but the heating crystallization temperature and melting point of the surface layer were outside the specified range, and heat sealing was not possible. The sex evaluation was poor.

In Comparative Example 3, the glass transition temperature of the surface layer (A layer) of the obtained sheet was within the specified range, but the heating crystallization temperature and melting point of the surface layer were outside the specified range, and heat sealing was not possible. The sex evaluation was poor.

In Reference Example 1, since an amorphous polyester resin is used, the glass transition temperature of the surface layer (A layer) of the obtained sheet is within the specified range, and the temperature-rising crystallization of the surface layer (A layer) Although the temperature and melting point peaks did not appear, good sheets having physical properties equivalent to those of Examples 1 to 5 could be obtained, but the drying process before molding required a long time, and packaging containers were not produced. It was inferior as a multilayer polyester sheet for the purpose.

In Reference Example 2, the glass transition temperature of the surface layer (A layer) of the obtained sheet, the heating crystallization temperature of the surface layer (A layer), and the peak of the melting point are within the specified ranges. Although a good sheet having physical properties equivalent to those of the above can be obtained, it is inferior in heat resistance as a packaging container.

The copolyester resin used in the present invention is a raw material having crystallinity, so it can be dried at 100 ° C. to 120 ° C. for 4 hours, it is difficult to cause viscosity reduction due to hydrolysis, and it has excellent handling properties. By using the copolymerized polyester resin, it has become possible to provide a multilayer polyester sheet that maintains transparency, heat resistance, and impact resistance and has excellent heat-sealing properties, and a packaging container using the same. .
Since it can be widely applied in the field of food packaging containers, it is expected to greatly contribute to the industrial world.

Claims (6)

A multi-layered polyester sheet having heat-sealing properties, in which a surface layer (A layer) mainly composed of a copolymer polyester resin is laminated on at least one side of a substrate layer (B layer) mainly composed of a polyester resin, A multilayer polyester sheet characterized by satisfying the following requirements (1) to (3).
(1) The surface layer (layer A) has a glass transition temperature of 76° C. or less as measured by a differential scanning calorimeter (DSC).
(2) The temperature-rising crystallization temperature of the surface layer (A layer) measured by a differential scanning calorimeter (DSC) is 110° C. or higher and 140° C. or lower.
(3) The melting point of the surface layer (A layer) measured by a differential scanning calorimeter (DSC) is 200° C. or higher and 245° C. or lower. The surface layer (A layer) of the multilayer polyester sheet contains 5 mol % or more and 40 mol % or less of structural units derived from diethylene glycol in 100 mol % of the total amount of glycol components in all polyester resin components. The surface layer (A layer) of the multilayer polyester sheet contains 0 mol % or more and 5 mol % or less of structural units derived from a monomer component that can be an amorphous component in all the polyester resin components. The haze of the multilayer polyester sheet is 5% or less. The intrinsic viscosity of the multilayer polyester sheet is 0.50 dl/g or more and 0.85 dl/g or less. A packaging container obtained by using the multilayer polyester sheet according to any one of claims 1 to 5 and shaping it by thermoforming selected from hot plate forming, vacuum forming, pressure forming or vacuum pressure forming.

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