JP7573816B2 - Polyester containers and polyester preforms - Google Patents

Description

The present invention relates to polyester containers and polyester preforms.

In recent years, attempts have been made to recycle plastic products in order to reduce the burden on the environment. For example, polyester containers such as used PET bottles are recycled. Recycled polyester obtained by recycling polyester containers is used in a variety of products. Known examples of such recycled polyester include chemically recycled polyester and mechanically recycled polyester.

Chemically recycled polyester is polyester obtained by chemically breaking down used polyester containers into monomer units, which are then purified and repolymerized. Therefore, chemically recycled polyester has physical properties and characteristics comparable to those of virgin polyester. However, chemically recycled polyester has the problem of high recycling costs. Here, virgin polyester is polyester produced by conventional methods from dicarboxylic acids and diols made from petroleum and other raw materials.

Mechanically recycled polyester is polyester obtained by crushing and washing used polyester containers to remove contaminants and foreign matter, obtaining flakes, and further treating the flakes at high temperature and reduced pressure for a certain period of time to remove contaminants inside the resin, or by pelletizing the washed flakes and further treating the pellets at high temperature and reduced pressure for a certain period of time to remove contaminants inside the resin. Mechanical recycling can obtain recycled polyester without chemical decomposition, so the recycling cost is cheaper than chemical recycling. Therefore, from the viewpoint of cost, it is desirable to use mechanically recycled polyester as the recycled polyester.

When flakes and pellets made of mechanically recycled polyester are used to manufacture polyester containers, slight amounts of impurities remaining in the flakes and pellets may cause yellowing of the polyester containers after molding.
In order to reduce the yellowish tinge of the resin caused by yellowing and make it transparent, Patent Document 1 proposes using pigments such as optical brighteners and blue pigments in molded articles obtained from resin compositions containing recycled polyester. Such additives such as fluorescent brighteners and blue pigments that reduce the yellowish tinge of the resin and make it transparent are generally called bluing agents (see, for example, Patent Document 2).

JP 2004-359914 A JP 2001-166101 A

Since flakes and pellets made from mechanically recycled polyester are used for various containers, it is desirable that the additives used in the polyester container before mechanical recycling do not remain in the flakes and pellets. From this perspective, when a polyester container containing a bluing agent is mechanically recycled, it is desirable that the bluing agent is removed from the resulting flakes and pellets made from mechanically recycled polyester.

The inventors have now discovered that when polyester containers containing a pigment as a bluing agent are mechanically recycled, the bluing agent cannot be removed.

Accordingly, an object of the present invention is to provide a polyester container which has a reduced yellowing and from which a bluing agent can be easily removed when the polyester container is mechanically recycled.
Another object of the present invention is to provide a polyester preform for use in the manufacture of the polyester container.

The inventors have discovered that the above problems can be solved by using a specific dye as a bluing agent.

Accordingly, the present invention provides a polyester container comprising mechanically recycled polyester and a bluing agent,
The content of the bluing agent relative to the content of the mechanically recycled polyester is 0.0001% by mass or more and 0.00125% by mass or less,
The bluing agent is a dye having a vaporization temperature of less than 230° C. at 15 mbar, in a polyester container.

In the polyester container according to the present invention, the bluing agent may be an anthraquinone-based bluing agent.

In the polyester container according to the present invention, the content of the mechanically recycled polyester relative to the total polyester constituting the polyester container may be 95% by mass or more.

The polyester container according to the present invention has a mouth, a neck, a shoulder, a body, and a bottom,
The thickness of the body may be 0.05 mm or more and 0.54 mm or less.

In the polyester container according to the present invention, the contents may be a colorless, transparent liquid.

In the polyester container according to the present invention, the mechanically recycled polyester may have a b ^* value in the L ^* a ^* b ^* color system of +3.0 or more.

The present invention is a polyester preform used in the manufacture of the polyester container.

According to the present invention, it is possible to provide a polyester container which has a reduced yellowish color and from which a bluing agent can be easily removed during mechanical recycling.
According to the present invention, a polyester preform for use in producing the polyester container can be provided.

FIG. 1 is a schematic half-sectional view showing one embodiment of a polyester container according to the present invention. FIG. 1 is a schematic half-sectional view showing one embodiment of a polyester preform according to the present invention.

[Polyester container]
The polyester container according to the present invention comprises mechanically recycled polyester and a bluing agent.
In this specification, a "polyester container" is a container containing polyester as a main component. In this specification, a "main component" means a component that accounts for more than 50% by mass of the total. The content of polyester in a polyester container is preferably 70% by mass or more, more preferably 90% by mass or more, and even more preferably 99% by mass or more.

In this specification, the term "container" refers to a molded body that contains an article. Examples of containers include molded bodies such as compression molded bodies, injection molded bodies, blow molded bodies, and thermoformed bodies. Specific examples of containers include bottles, vials, cups, trays, and packs.

In this specification, the term "polyester" refers to a polymer that is polymerized through ester bonds. Such polyesters are usually obtained by polycondensation of a dicarboxylic acid compound and a diol compound.
Examples of the dicarboxylic acid compound include malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, dodecanedioic acid, eicosanedioic acid, pimelic acid, azelaic acid, methylmalonic acid, ethylmalonic acid, adamantanedicarboxylic acid, norbornenedicarboxylic acid, cyclohexanedicarboxylic acid, decalindicarboxylic acid, terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, 5-sodiumsulfoisophthalic acid, phenylendanedicarboxylic acid, anthracenedicarboxylic acid, phenanthrenedicarboxylic acid, 9,9'-bis(4-carboxyphenyl)fluorene acid, and ester derivatives thereof.
Examples of the diol compound include ethylene glycol, 1,2-propanediol, 1,3-propanediol, butanediol, 2-methyl-1,3-propanediol, hexanediol, neopentyl glycol, cyclohexanedimethanol, cyclohexanediethanol, decahydronaphthalenedimethanol, decahydronaphthalenediethanol, norbornanedimethanol, norbornanediethanol, tricyclodecanedimethanol, tricyclodecaneethanol, tetracyclododecanedimethanol, tetracyclododecanediethanol, decalindimethanol, decalindiethanol, and 5-methylol-5-ethyl 2-(1,1-dimethyl-2-hydroxyethyl)-1,3-dioxane, cyclohexanediol, bicyclohexyl-4,4'-diol, 2,2-bis(4-hydroxycyclohexylpropane), 2,2-bis(4-(2-hydroxyethoxy)cyclohexyl)propane, cyclopentanediol, 3-methyl-1,2-cyclopentadiol, 4-cyclopentene-1,3-diol, adamantanediol, paraxylene glycol, bisphenol A, bisphenol S, styrene glycol, trimethylolpropane, pentaerythritol, and bis-β-hydroxyethyl terephthalate (BHET).
In the polyester container according to the present invention, the polyester is preferably polyethylene terephthalate or a modified polyethylene terephthalate obtained by polymerizing a raw material monomer of polyethylene terephthalate with a copolymerizable monomer, and particularly preferably polyethylene terephthalate.

As long as the characteristics of the present invention are not impaired, the polyester may contain monomers other than the dicarboxylic acid compound and the diol compound, but the content of such monomers is preferably 10 mol % or less, more preferably 5 mol % or less, and even more preferably 3 mol % or less, based on the total constituent units.

The mechanically recycled polyester and blueing agent contained in the polyester container according to the present invention are described below.

<Mechanically recycled polyester>
In this specification, "mechanically recycled polyester" refers to polyester obtained by crushing and washing used polyester containers to remove contaminants and foreign matter, obtaining flakes, further treating the flakes at high temperature and reduced pressure for a certain period of time to remove contaminants inside the resin, and pelletizing the flakes, or by pelletizing the washed flakes and then further treating the pellets at high temperature and reduced pressure for a certain period of time to remove contaminants inside the resin.
The mechanically recycled polyester contained in the polyester container according to the present invention is preferably mechanically recycled polyethylene terephthalate.

The flakes and pellets made of the mechanically recycled polyester contain a small amount of impurities. These impurities are inevitable impurities that cannot be completely removed even when treated at high temperature and reduced pressure for a certain period of time. In the production of polyester containers, the flakes and pellets are melted, and if there are trace impurities in the flakes and pellets, the polyester will turn yellow due to the heat generated during melting. Therefore, the mechanically recycled polyester contained in the polyester container according to the present invention has a yellowish color.
The polyester container according to the present invention can reduce the yellowish color of the polyester container by containing a bluing agent in a specific range described below. Such a polyester container with reduced yellowish color is particularly suitable when the content is a colorless and transparent liquid. The colorless and transparent liquid is not particularly limited, and examples thereof include drinking water.

In the polyester container according to the present invention, the b ^* value in the L ^* a ^* b ^* color system of the mechanically recycled polyester may be +3.0 or more, +4.0 or more, or +4.5 or more, while the b ^* value in the L ^* a ^* b ^* color system of the mechanically recycled polyester may be +20.0 or less, +10.0 or less, or +7.0 or less.
In this specification, the b ^* value in the L ^* a ^* b ^* color system of the mechanically recycled polyester is measured in accordance with JIS Z8722:2009.
Specifically, mechanically recycled polyester having an arbitrary shape is freeze-pulverized to prepare a powder, and this powder is measured by reflected light using a spectrophotometer. The measurement conditions are SCE (specular reflection excluded), 10° field of view, and D65 light source. As the spectrophotometer, for example, CMS-35SP manufactured by Murakami Color Research Laboratory Co., Ltd. can be used.

In the polyester container according to the present invention, the content of the mechanically recycled polyester relative to the total polyester constituting the polyester container is preferably 95% by mass or more, more preferably 97% by mass or more, even more preferably 99% by mass or more, and particularly preferably 99.9% by mass or more. This makes it possible to provide a polyester container with a reduced environmental load.
The polyester container according to the present invention may contain polyesters such as virgin polyester and chemically recycled polyester in addition to mechanically recycled polyester.

<Bluing agent>
In this specification, the term "bluing agent" refers to an additive that absorbs light in the wavelength range of, for example, orange to yellow within the visible light range, and adjusts the hue.
In this specification, the "visible light region" refers to the region from 380 nm to 780 nm.

The bluing agent contained in the polyester container according to the present invention is a dye having a vaporization temperature of 230° C. or less at 15 mbar. By using such a dye as the bluing agent, the bluing agent can be easily removed when the polyester container is mechanically recycled, because the bluing agent can be easily removed together with contaminants inside the resin when the flakes or pellets are treated at high temperature and reduced pressure for a certain period of time in the mechanical recycling.
From the viewpoint of easier removal of the bluing agent from the flakes or pellets, the vaporization temperature of the dye used as the bluing agent is preferably 225° C. or less, more preferably 220° C. or less, at 15 mbar.
On the other hand, the vaporization temperature of the dye used as the bluing agent at 1013.25 mbar (atmospheric pressure) is preferably 300° C. or higher, and more preferably 350° C. or higher. By using a dye with such a vaporization temperature or higher, the amount of dye released into the atmosphere during the production of a polyester container can be reduced, and the content of the bluing agent in the polyester container after molding can be easily adjusted.

In the polyester container according to the present invention, the content of the bluing agent relative to the mechanically recycled polyester is 0.0001% by mass or more and 0.00125% by mass or less. If the content of the bluing agent is in this range, the yellowness of the polyester container can be reduced and the polyester container can be made transparent. Furthermore, by setting the content of the bluing agent in this range, the bluing agent can be easily removed when the polyester container according to the present invention is mechanically recycled.
The content of the bluing agent is preferably 0.00025% by mass or more, more preferably 0.0004% by mass or more, while the content of the bluing agent is preferably 0.001% by mass or less, more preferably 0.0008% by mass or less.

The bluing agent contained in the polyester container according to the present invention preferably has a maximum absorption peak in the wavelength region of 500 nm or more and 650 nm or less in the visible light region. By using a bluing agent having a maximum absorption peak in such a wavelength region, the yellowish color of the polyester container can be efficiently reduced. More preferably, the bluing agent has a maximum absorption peak in the wavelength region of 550 nm or more and 600 nm or less in the visible light region.
In this specification, the maximum absorption peak can be measured, for example, by using a photodiode array detector SPD-M20A manufactured by Shimadzu Corporation. As a solvent for dissolving the bluing agent, for example, acetonitrile can be used.

Examples of the bluing agents mentioned above include dyes such as anthraquinone-based bluing agents and indigo-based bluing agents.

で表されるアントラキノン環を含有するブルーイング剤である。アントラキノン系ブルー
イング剤として、好ましくは、式（２）：

［式（２）中、Ｘ^１はＯＨ、ＮＨＲ^１又はＮＲ^１Ｒ^２を表し、Ｘ^２はＮＨＲ^３又はＮＲ^３Ｒ^４を表し、Ｒ^１、Ｒ^２、Ｒ^３及びＲ^４は、互いに独立して、炭素数１以上６以下の直鎖状又は分枝状アルキル基、又は、炭素数１以上６以下の直鎖状又は分枝状アルキル基で置換されたフェニル基を表す。］
で表される一般式を有する化合物が挙げられる。式（２）中のＸ^１及びＸ^２は、互いに同
一でも、異なってもよい。式（２）で表される化合物は、好ましくは、式中のＸ^１及びＸ^２のうち少なくとも１つが、炭素数１以上６以下の直鎖状又は分枝状アルキル基で置換されたフェニル基を有し、より好ましくは、式中のＸ^１又はＸ^２が炭素数１以上６以下の直鎖状又は分枝状アルキル基で置換されたフェニル基を有する。 The anthraquinone-based bluing agent has the formula (1):

As the anthraquinone-based bluing agent, a bluing agent containing an anthraquinone ring represented by the formula (2):

[In formula (2), ^X1 represents OH, ^{NHR1 or NR1R2} , ^X2 represents ^NHR3 or ^NR3R4 , and ^R1 , ^R2 , ^R3 and ^R4 each independently represent a linear or branched alkyl group having 1 to 6 carbon atoms, or a phenyl group substituted ^with a linear or branched alkyl group having 1 to 6 carbon atoms.]
Examples of the compound represented by the general formula are: X ¹ and X ² in formula (2) may be the same or different from each other. In the compound represented by formula (2), preferably, at least one of X ¹ and X ² in the formula has a phenyl group substituted with a linear or branched alkyl group having 1 to 6 carbon atoms, and more preferably, X ¹ or X ² in the formula has a phenyl group substituted with a linear or branched alkyl group having 1 to 6 carbon atoms.

More preferred examples of the anthraquinone-based bluing agent include the compounds represented by formulae (3) to (5).

Indigo-based bluing agents are bluing agents that contain indoxyl or thioindoxyl.

From the viewpoint of heat resistance and solubility (dispersibility), the bluing agent contained in the polyester container according to the present invention is preferably an anthraquinone-based bluing agent, more preferably at least one type of bluing agent having a structure represented by formula (1), even more preferably at least one type of bluing agent having a structure represented by formula (2), even more preferably at least one type of bluing agent selected from the group consisting of compounds represented by formulas (3) to (5), and particularly preferably a bluing agent represented by formula (3).

The bluing agent may be used alone or in combination of two or more. In addition, in the production of the polyester container according to the present invention, the bluing agent may be used together with an oil component in order to disperse well in the polyester container. Examples of the oil component include ester compounds such as glycerol diacetyl monooleate.
In one embodiment, the bluing agent can be added to the polyester container by using a masterbatch that includes the bluing agent and a polyester, which may include the oil component described above.
In one embodiment, the bluing agent may be added during the pelletizing process of the flakes in mechanical recycling.

Below, one embodiment of the structure of a polyester container according to the present invention will be explained using FIG. 1 as an example.

Figure 1 is a schematic half-sectional view showing one embodiment of a polyester container 10 according to the present invention. As shown in Figure 1, the polyester container 10 has a mouth portion 11, a neck portion 12, a shoulder portion 13, a body portion 14, and a bottom portion 15.

In one embodiment, the mouth portion 11 includes a threaded portion 16 onto which the cap is screwed, a cap 17 below the threaded portion 16, and a support ring 18 below the cap 17, as shown in FIG. 1.

In one embodiment, as shown in FIG. 1, the neck portion 12 is located between the support ring 18 and the shoulder portion 13, and has a generally cylindrical shape with a generally uniform diameter. In another embodiment, the shoulder portion 13 has a cylindrical shape whose diameter gradually increases from the neck portion 12 side toward the body portion 14 side.

In one embodiment, the body 14 is located between the shoulder 13 and the bottom 15 as shown in FIG. 1. Also, in one embodiment, the body 14 has a panel portion 21 that is recessed inward as shown in FIG. 1. This configuration can prevent deformation of the polyester container due to an increase or decrease in internal pressure when filling the polyester container with heated contents or when the polyester container is heated after filling with contents.

1, the bottom 15 has a centrally located recessed portion 19 and a grounding portion 20 provided around the recessed portion 19, and is connected to the body 14 at the grounding portion 20. With this configuration, it is possible to prevent deformation of the polyester container due to an increase or decrease in internal pressure when the polyester container is filled with heated contents or when the polyester is heated after being filled with contents.
In one embodiment, the "bottom" refers to the part inside from the part that touches the ground when the polyester container is placed on its own.

The polyester container according to the present invention has a reduced yellowish color, so that the thickness of the polyester container can be increased. This is because, even if the thickness of the polyester container is increased, the color of the contents is unlikely to change when the contents are visually observed from the outside of the polyester container. Therefore, the polyester container according to the present invention can improve the strength of the polyester container while suppressing the influence of the color on the contents. The cross-sectional thickness of the body of the polyester container is preferably 0.05 mm or more, more preferably 0.1 mm or more.
On the other hand, from the viewpoint of reducing the amount of polyester containers used, the cross-sectional thickness of the body of the polyester container is preferably 0.54 mm or less, and more preferably 0.5 mm or less.
The cross-sectional thickness of the body of the polyester container refers to the location where the thickness is the thinnest.

In the polyester container according to the present invention, the ratio of volume to mass (volume/mass) is preferably 5 mL/g or more, more preferably 8 mL/g or more, from the viewpoint of moldability of the polyester container.
On the other hand, from the viewpoint of the strength of the polyester container, the volume/mass is preferably 50 mL/g or less, and more preferably 45 mL/g or less.

The polyester container according to the present invention may have a single-layer structure or a multi-layer structure of two or more layers. In addition, when the polyester container has a multi-layer structure, each layer may have the same composition or different compositions.

In one embodiment, the polyester container may have a vapor-deposited film on its surface. This can improve the gas barrier properties of the polyester container. The vapor-deposited film may be located on either the inner or outer surface of the polyester container, but is preferably located on the inner surface.

Examples of the vapor-deposited film include vapor-deposited films composed of metals such as aluminum, inorganic oxides such as aluminum oxide, silicon oxide, magnesium oxide, calcium oxide, zirconium oxide, titanium oxide, boron oxide, hafnium oxide, and barium oxide, organosilicon compounds such as hexamethyldisiloxane, and hard carbon films such as DLC (Diamond Like Carbon) films.
The hard carbon film made of DLC is a hard carbon film also called an i-carbon film or a hydrogenated amorphous carbon film (aC:H), which is an amorphous carbon film mainly composed of ^SP3 bonds.

The thickness of the deposited film is not particularly limited and can be, for example, 1 nm or more and 150 nm or less.

The deposition film can be formed by a conventional method, for example, physical vapor deposition methods (PVD methods) such as vacuum deposition, sputtering, and ion plating, and chemical vapor deposition methods (CVD methods) such as plasma chemical vapor deposition, thermal chemical vapor deposition, and photochemical vapor deposition.
The thickness of the vapor-deposited layer can be measured, for example, at the body of a polyester container, and refers to the location where the thickness is the thinnest.

[Polyester preform]
In this specification, the term "polyester preform" refers to a preform prior to blow molding into a polyester container.
The polyester preform according to the present invention is used for producing the polyester container according to the present invention. Therefore, the polyester preform according to the present invention contains a mechanically recycled polyester and a bluing agent. By configuring the polyester preform in this way, the polyester container according to the present invention can be produced.
The mechanically recycled polyester and the bluing agent contained in the polyester preform according to the present invention may be the same as those used in the polyester container according to the present invention.

Below, one embodiment of the structure of a polyester preform according to the present invention will be described with reference to Figure 2.

Figure 2 is a schematic half-sectional view showing one embodiment of a polyester preform 30 according to the present invention. As shown in Figure 2, the polyester preform 30 comprises a mouth portion 31, a body portion 32 connected to the mouth portion 31, and a bottom portion 33 connected to the body portion 32. Of these, the mouth portion 31 corresponds to the mouth portion 11 of the polyester container 10 and has approximately the same shape as the mouth portion 11. The body portion 32 corresponds to the neck portion 12, shoulder portion 13, and body portion 14 of the polyester container 10 and has an approximately cylindrical shape. The bottom portion 33 corresponds to the bottom portion 15 of the polyester container 10 and has an approximately hemispherical shape.

The mouth portion 31 has a threaded portion 34 that corresponds to the threaded portion 16 of the polyester container 10 to which a cap (not shown) is screwed, a cap 35 that is provided below the threaded portion 34 and corresponds to the cap 17 of the polyester container 10, and a support ring 36 that is provided below the cap 35 and corresponds to the support ring 18 of the polyester container 10. The shape of the mouth portion 31 may be a conventionally known shape.

The cross-sectional thickness of the body of the polyester preform according to the present invention is preferably 1.3 mm or more, more preferably 1.7 mm or more. On the other hand, the cross-sectional thickness of the body of the polyester preform is preferably 4.7 mm or less, more preferably 4.0 mm or less.
The polyester container according to the present invention can be produced by controlling the cross-sectional thickness of the body of the polyester preform to fall within the above range.
The cross-sectional thickness of the body of the polyester preform refers to the location where the thickness is the thinnest.

The present invention will now be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

[Example 1]
Pellets A made of mechanically recycled polyester and pellets B made of a polyethylene terephthalate master batch containing an anthraquinone-based bluing agent having the structure of formula (3) were prepared. The vaporization temperature of the bluing agent was 215° C. at 15 mbar.
First, a mixture was obtained by dry blending 97 parts by mass of pellets A and 3 parts by mass of pellets B. The content of the bluing agent in the obtained mixture relative to the mechanically recycled polyester was 0.0005% by mass.
Next, the obtained mixture was melted and the molten material was injected using an injection molding machine to produce a polyester preform shown in Fig. 2. The body of the polyester preform had a thickness of 3.5 mm and a basis weight of 22 g.

The polyester preform was then heated to 110°C and biaxially stretched and blow molded in a blow molding die to produce a polyester container with a capacity of 500 mL as shown in Figure 1. The cross-sectional thickness of the body of the polyester container was 0.32 mm.

[Example 2]
A polyester preform shown in Fig. 2 was produced in the same manner as in Example 1, except that pellets A and B were dry blended so that the content of the bluing agent relative to the mechanically recycled polyester was 0.00035% by mass. The body of the polyester preform had a thickness of 3.5 mm and a basis weight of 22 g.

Next, a polyester container was produced from the polyester preform in the same manner as in Example 1. The cross-sectional thickness of the body of the polyester container was 0.32 mm.

[Example 3]
A polyester preform shown in Fig. 2 was produced in the same manner as in Example 1, except that pellets A and B were dry blended so that the content of the bluing agent in the mechanically recycled polyester was 0.0002% by mass. The body of the polyester preform had a thickness of 3.5 mm and a basis weight of 22 g.

Next, a polyester container was produced from the polyester preform in the same manner as in Example 1. The cross-sectional thickness of the body of the polyester container was 0.32 mm.

[Comparative Example 1]
A polyester preform shown in Fig. 2 was produced in the same manner as in Example 1, except that only pellet A was used. The body of the polyester preform had a thickness of 3.5 mm and a basis weight of 22 g.

Next, a polyester container was produced from the polyester preform in the same manner as in Example 1. The cross-sectional thickness of the body of the polyester container was 0.32 mm.

[Comparative Example 2]
Pellet C was prepared, which was made of a polyethylene terephthalate master batch containing a cobalt-based pigment (cobalt blue) as a bluing agent.
A polyester preform shown in Fig. 2 was produced in the same manner as in Example 1, except that pellets A and C were dry blended so that the content of the bluing agent in the mechanically recycled polyester was 0.0005% by mass. The body of the polyester preform had a thickness of 3.5 mm and a basis weight of 22 g.

Next, a polyester container was produced from the polyester preform in the same manner as in Example 1. The cross-sectional thickness of the body of the polyester container was 0.32 mm.

<<Color measurement>>
The samples obtained by cutting only the mouths of the polyester containers prepared in the examples and comparative examples into small pieces were pre-cooled for 10 minutes under liquid nitrogen using a freeze grinder (SPEX, 6870 type Freezer/Mill), and then freeze-ground for 10 minutes under liquid nitrogen to obtain powder. The powder was then measured for L ^* , a ^* , and b ^* values in the L ^* a ^* b ^* color system using a spectrophotometer (Murakami Color Research Laboratory, CMS-35SP) in reflected light. The measurement conditions were SCE (specular reflection removed), 10° field of view, and D65 light source. The measurements were performed in accordance with JIS Z8722:2009. The measurement results are shown in Table 1.

<<Measurement of bluing agent content>>
The polyester containers produced in the Examples and Comparative Examples were crushed to obtain flakes. The flakes were then treated at 230° C. and 15 mbar for 2 hours. The content of the bluing agent in the treated flakes was measured by LC-MS (Maxis Impact, manufactured by Bruker Japan, Ltd.) in the Examples, and by ICP-AES (ICPE-9820, manufactured by Shimadzu Corporation) in Comparative Example 2. The measurement results are shown in Table 1.

It can be seen that the polyester container according to the present invention has a reduced yellow color. It can also be seen that the bluing agent can be easily removed from the polyester container according to the present invention by the high temperature and reduced pressure treatment carried out in mechanical recycling.

10: Polyester container 11: Mouth 12: Neck 13: Shoulder 14: Body 15: Bottom 16: Threaded 17: Turnip 18: Support ring 19: Depression 20: Grounding 21: Panel 30: Polyester preform 31: Mouth 32: Body 33: Bottom 34: Threaded 35: Turnip 36: Support ring

Claims (7)

A polyester container comprising mechanically recycled polyester and a bluing agent,
The content of the bluing agent relative to the content of the mechanically recycled polyester is 0.0001% by mass or more and 0.00125% by mass or less,
A polyester container, wherein the bluing agent is a dye having a vaporization temperature of less than or equal to 230° C. at 15 mbar. The polyester container according to claim 1, wherein the bluing agent is an anthraquinone-based bluing agent. The polyester container according to claim 1 or 2, wherein the content of the mechanically recycled polyester relative to the total polyester constituting the polyester container is 95% by mass or more. The container has a mouth, a neck, a shoulder, a body, and a bottom,
The polyester container according to any one of claims 1 to 3, wherein the thickness of the body portion is 0.05 mm or more and 0.54 mm or less. The polyester container according to any one of claims 1 to 4, wherein the content is a colorless, transparent liquid. The polyester container according to any one of claims 1 to 5, wherein the mechanically recycled polyester has a b ^* value in the L ^* a ^* b ^* color system of +3.0 or more. A polyester preform used in the manufacture of a polyester container according to any one of claims 1 to 6.