JP2989252B2 - Polyester resin multilayer sheet and container - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a polyester resin multilayer sheet which is excellent in impact resistance, heat deformation resistance, and adhesion to a lid film, and which can be subjected to a microwave oven and a retort sterilization treatment. For containers.

(Related Art) In general, retort sterilization treatment, that is, high-temperature and high-pressure sterilization treatment food has been spread mainly in aluminum pouch bags as food that can be distributed at room temperature. The development of containers for containers is desired.

The performance required for a container capable of being subjected to a microwave oven and a retort treatment includes a low dielectric constant, good heat resistance, high oxygen barrier properties, fragrance retention and low elution at high temperatures.

The most suitable container material that satisfies these container performances is a partially crystallized polyester resin (hereinafter abbreviated as C-PET), but C-PET is characterized by its high heat resistance and good chemical resistance. And the heat-sealing property with the lid film is inferior, and there is a fatal problem that the container and the lid are peeled off on the adhesive surface during the retort treatment.

(Problems to be Solved by the Invention) As a method of improving the heat sealing property between a container and a lid material using C-PET, a heat seal portion of the container is formed when the container is thermoformed from a C-PET sheet. There is a method of suppressing crystallization by bringing a portion into contact with a cooling member. However, in the container thus obtained, crystallization progresses again during retort due to high temperature heating in the retort treatment, and the portion where crystallization is suppressed during thermoforming for producing the container shows a relatively large increase in crystallinity. .

Due to the uneven shrinkage caused by the non-uniform increase in crystallization, the obtained container after retort treatment is deformed and twisted and cannot be put to practical use.

The present invention relates to a microwave oven and a retort container as C
-It is necessary to provide a polyester resin multilayer sheet and a container which have improved heat sealability with a lid material without deteriorating the characteristics of PET and without causing heat deformation due to retort treatment which is a disadvantage of the conventional technology. Is what you do.

(Means for Solving the Problems) That is, in the present invention, the core layer is made of a polyethylene terephthalate resin and an olefin resin, and the skin layer is made of a 1.5 to 5 times by weight of the olefin resin in a weight ratio of the olefin resin of the core layer. A polyester resin, which is a multilayer sheet of polyethylene terephthalate resin, wherein the weight ratio of the skin layer to the entire multilayer sheet is 10 to 40% by weight, and the polyethylene terephthalate resin of the skin layer has the following composition: Multi-layer sheet.

(A) 10 to 40% by weight of a copolymer of an ethylene glycol monomer and a terephthalic acid monomer (B) 90 to 90% of a copolymer of an ethylene glycol monomer and a terephthalic acid monomer and a 1,4-cyclohexanedimethanol monomer or an isophthalic acid monomer 60% by weight and the container comprising the multilayer sheet.

Here, as the PET resin used for the core layer of the present invention,
Refers to a resin obtained by polycondensation of a terephthalic acid monomer and an ethylene glycol monomer, but to the extent that heat resistance is not impaired, a terephthalic acid monomer and an ethylene glycol monomer, and one or more monomers copolymerizable therewith, That is, copolymerized PET with isophthalic acid, 4,4'-diphenylenedicarboxylic acid, adipic acid, azelaic acid, sebacic acid, pentamethylene glycol, heptamethylene glycol, diethylene glycol, 1,4-cyclohexanedimethanol, tetraethylene glycol, and the like. Resins and mixtures thereof can be used, and can further contain other resins such as polybutylene terephthalate resin and polycarbonate resin and additives such as antioxidants, coloring agents, and fillers.

Further, the olefin resin constituting the core layer contains at least one kind of low-density polyethylene, high-density polyethylene, linear low-density polyethylene, polypropylene, and polybutene, which function as a crystal nucleating agent and a reinforcing agent, in the core layer resin.
It is used in an amount of 0.2 to 3% by weight, preferably 0.5 to 2% by weight.

If the content of the olefin resin is less than 0.2% by weight,
The progress of crystallization of the core layer during the thermoforming for producing the container from the sheet is slowed down, and the heat resistance of the container cannot be obtained.
If it exceeds 300, the moldability and heat resistance of the container are reduced, and a satisfactory product cannot be obtained.

Next, the skin layer of the multilayer sheet of the present invention comprises a PET resin and an olefin resin similarly to the core layer, and the content ratio of the olefin resin is 1.5 to 5 times by weight of the olefin resin of the core layer. It is. And P that constitutes the skin layer
The ET resin is a PET resin (A) obtained by polymerization of an ethylene glycol monomer and a terephthalic acid monomer (A) in an amount of 10 to 40% by weight, an ethylene glycol monomer, a terephthalic acid monomer, a 1,4-cyclohexanedimethanol monomer, or an isophthalic acid monomer. Obtained by polymerization with
It is a mixture of PET resin (B) 90 to 60 wt%.

The skin layer made of the resin composition is usually provided on one side, since it is provided on the side to be the adhesive surface when the container is formed from the multilayer sheet, but may be provided on both sides of the core layer.

Here, when the weight ratio of the olefin-based resin contained in the skin layer is less than 1.5 times the amount of the olefin-based resin occupied in the core layer, the heat-sealing property with the lid film is excellent, but the container is deformed by the retort treatment. If the amount exceeds twice, improvement in heat sealability cannot be expected.

Also, regarding the ratio of PET resin (A) and (B),
If the amount of (A) is less than 10% by weight, the skin layer is softened by retort and microwave treatment, so that traces of the contents are deformed by heat load remaining on the container surface. Does not improve.

The weight composition ratio of the skin layer to the entire multilayer sheet of the present invention is 10 to 40% by weight, and if it is less than 10% by weight, it is difficult to control the thickness of the skin layer at the time of sheet production, and the reliability of heat sealability in a container is low. poor. On the other hand, if it exceeds 40% by weight,
It is not preferable because the heat resistance of the container is reduced.

Here, similarly to the core layer, the PET resin constituting the skin layer may further contain additives such as an antioxidant, a coloring agent, and a filler.

The multilayer sheet of the present invention includes a method of directly extruding a multilayer sheet using a multilayer extruder, a method of extruding a sheet of each layer, and a method of forming a multilayer sheet by a dry lamination method.

Next, as a method of manufacturing a container, the container is manufactured by shaping and crystallizing the multilayer sheet by a vacuum forming method using a heating mold as shown in, for example, Japanese Patent Publication No. 62-026297. However, the present invention is not limited to this.

The lid material film used for the container of the present invention is not particularly limited, but a polyester resin is preferable as the sealant, and is produced by extrusion lamination or dry lamination with aluminum foil, a barrier film, an easily printable film, or the like. Can be used.

(Examples) Hereinafter, the present invention will be described in more detail with reference to Examples.
The physical properties of the container were measured as follows.

(1) Thermal deformation resistance The container is empty and the standard retort temperature is 12
Oven treatment was performed at 0 ° C. for 2 hours, and the degree of external deformation such as warpage and distortion was evaluated according to the following criteria.

 ：: No deformation is observed as in the untreated container.

 Δ: Some deformation such as a part of the flange is observed.

 X: Clear deformation is seen in the container.

(2) Deformation under heat load A coin (10 yen) is raised at the bottom of the container, oven-treated at 120 ° C, which is the standard retort temperature condition, for 2 hours, and cooled to room temperature. Compared.

 ：: No trace of coin.

 Δ: Slight traces of coins are observed.

 ×: Marks of coins clearly remain.

(3) Thermoformability Using a Sanwa vacuum forming machine equipped with a mold adjusted to a temperature of 180 ° C., a container was formed with a sheet preheating time of 9 seconds.

 The shapeability of the obtained containers was compared.

：: Good shapeability ×: Poor shapeability, sweet corners (4) Heat seal strength The seal between the container flange and the lid film is 15 mm wide
, And measured with a tensile tester under the conditions of 90 ° direction and a tensile speed of 200 mm / min.

Examples 1 to 3, Comparative Examples 1 and 2 98% by weight of a PET resin (trade name: PET9902, manufactured by Eastman Kodak Co.) composed of a terephthalic acid monomer and an ethylene glycol monomer and 2% by weight of a polypropylene resin
The resin composition constituting the core layer was obtained by melt-mixing using a 5 mm extruder.

As the PET resin constituting the skin layer, a PET resin (trade name PET9902 manufactured by Eastman Kodak Co.) composed of the same terephthalic acid monomer and ethylene glycol monomer as the core layer (A) 20% by weight, a terephthalic acid monomer and glycol Ethylene glycol and 1,4-
PET resin (B) obtained by polymerization with a monomer having a molar ratio of cyclohexane dimethanol of 2: 1 was obtained by mixing 80% by weight of the PET resin (B), and the same polypropylene resin (PP) as the core layer was added to the PET resin mixture. (Abbreviated as resin) at a ratio shown in Table 1 using a 65 mm extruder to obtain a resin composition constituting a skin layer.

Next, using the resin composition part constituting the core layer and each resin composition constituting the skin layer, the weight composition ratio of the skin layer was determined by a two-type two-layer sheet molding machine composed of a 65 mm extruder and a 40 mm extruder. Was obtained by quenching a multilayer sheet having a thickness of 0.6 mm (hereinafter abbreviated as a sheet) having a thickness of 20% with a chill roll immediately after the die.

Using a Sanwa vacuum forming machine equipped with a mold adjusted to a temperature of 180 ° C. using the skin layer resin layer side of the sheet as the adhesive flange side with the lid material film, the preheating time of the sheet was 170 × Molding a container with a flange of 120 x 28 mm height,
The thermoformed properties were compared and a molded container was obtained.

Using a one-shot heat sealer as a lid film, a laminated film of PET resin / aluminum / PET resin film (trade name: Denka Seal Film T02, manufactured by Denki Kagaku Kogyo Co., Ltd.) was used for the formed container, and the sealing temperature was 210 ° C. The lid was sealed with a wire seal at a sealing time of 2 sec.

Physical properties were measured using each molded container and a container with a lid seal.

 Table 1 shows the measurement results.

By making the weight ratio of the PP content of the skin layer resin composition to the PP content of the core layer resin composition 1.5 to 5 times, excellent in heat deformation resistance, heat load deformability and thermoformability,
Also, high heat seal strength was obtained.

On the other hand, when the weight ratio is set to 1 time, heat deformation resistance is inferior, and when the weight ratio is set to 7 time, thermoformability is inferior and heat seal strength is low.

Examples 4 to 6, Comparative Examples 3 and 4 The same resin composition as in Example 1 was used as the core layer resin composition. On the other hand, as the PET resin constituting the skin layer, a PET resin (trade name PET9902 manufactured by Eastman Kodak Co., Ltd.) (A) composed of the same terephthalic acid monomer and ethylene glycol monomer as the core layer, and a terephthalic acid monomer and a glycol component Ethylene glycol and 1,
PET resin (B) obtained by polymerization with a monomer having a molar ratio of 4-cyclohexanedimethanol of 2: 1 was mixed with the PET resin (B) at a ratio shown in Table-2.
95% by weight of resin mixture and 5% by weight of PP resin similar to skin layer
Was melt-mixed using a 65 mm extruder to obtain a resin composition constituting a skin layer.

Next, a two-layer two-layer sheet was extruded using the resin composition constituting the core layer and the respective resin compositions constituting the skin layer by the same operation as in Example 1, and then a container was prepared using the sheet. Then, the lid was sealed to the container.

Physical properties were measured using each of the molded container and the lid-sealed container.

 Table 2 shows the measurement results.

By making the weight ratio of (A) and (B) 10:90 to 40:60 as the PET resin constituting the skin layer, it is excellent in heat deformation resistance, heat load deformation property and thermoformability, and high heat sealing. Strength was obtained.

On the other hand, when the weight ratio was 5:95, the heat load deformability was poor, and when the weight ratio was 50:50, the obtained heat seal strength was low.

Example 7 The same resin composition as in Example 1 was used as the core layer resin composition. On the other hand, as the PET resin constituting the skin layer, 30% by weight of a PET resin (trade name PET9902 manufactured by Eastman Kodak Co., Ltd.) (A) composed of the same terephthalic acid monomer and ethylene glycol monomer as the core layer, and ethylene glycol monomer And 70% by weight of a PET resin (B) obtained by polymerization of a monomer having a molar ratio of terephthalic acid and isophthalic acid of 2: 1 as a dicarboxylic acid component, and 95% by weight of the PET resin mixture. Then, 5% by weight of the same PP resin as the core layer was melt-mixed using a 65 mm extruder to obtain a resin composition constituting the skin layer.

Next, a two-layer two-layer sheet was extruded using the resin composition constituting the core layer and the respective resin compositions constituting the skin layer by the same operation as in Example 1, and then a container was prepared using the sheet. Then, the lid was sealed to the container.

Physical properties were measured using the molded container and the lid-sealed container.

 Table 3 shows the measurement results.

The molded container and the lid-sealed container were excellent in heat deformation resistance, heat load deformation resistance and thermoforming property, and high heat sealing strength was obtained.

Comparative Example 5 The same resin composition as in Example 1 was used as the core layer resin composition. On the other hand, the PET resin constituting the skin layer is a PET resin comprising the same terephthalic acid monomer and ethylene glycol monomer as the core layer (manufactured by Eastman Kodak Company,
Product name PET9902).

95% by weight of the PET resin and 5% by weight of the same PP resin as the core layer
Was melt-mixed using a 65 mm extruder to obtain a resin composition constituting a skin layer.

Next, a two-layer two-layer sheet was extruded using the resin composition constituting the core layer and the respective resin compositions constituting the skin layer by the same operation as in Example 1, and then a container was prepared using the sheet. , A lid seal to the container was implemented.

Physical properties were measured using the molded container and the lid-sealed container.

 Table 3 shows the measurement results.

It is inferior in thermoformability and heat sealability and is not practical.

Examples 8 and 9, Comparative Examples 6 and 7 Two kinds of two layers composed of a 65 mm extruder and a 40 mm extruder were used by using the resin composition of the skin layer and the core layer obtained in the same manner as in Example 1. Each sheet having a thickness of 0.6 mm was obtained using a sheet forming machine at the weight composition ratio of the skin layer shown in Table-4.

Next, in the same manner as in Example 1, a container was prepared, and a lid was sealed to the container.

Physical properties were measured using each of the molded container and the lid-sealed container.

 Table 4 shows the measurement results.

If the weight composition ratio of the skin layer is less than 10% by weight, the heat sealing strength varies and the reliability is poor. If it exceeds 40% by weight, the heat deformation resistance of the container decreases, and the range of 10 to 40% by weight is preferable.

(Effects of the Invention) As described above, the present invention provides a multi-layer structure in which a specific PET resin is provided on a skin layer that is an adhesive portion with a lid seal film when a container for retorted food is made from a PET resin. By using such a container, there is an effect of obtaining good heat resistance, adhesiveness and thermoformability.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI // B29C 51/14 B29C 51/14 B29K 67:00 B29L 9:00 22:00 (58) Field surveyed (Int.Cl. ⁶ , DB name) C08L 67/00-67/08 C08L 23/00-57/12 B32B 27/32 B32B 27/36 B65D 65/40

Claims (2)

(57) [Claims] 1. A core sheet comprising a polyethylene terephthalate resin and an olefin resin, and a skin layer comprising a multilayer sheet comprising 1.5 to 5 times by weight of the olefin resin of the core layer and a polyethylene terephthalate resin. Weight composition ratio of skin layer to the entire multilayer sheet
A polyester resin multilayer sheet comprising 10 to 40% by weight, and wherein the polyethylene terephthalate resin of the skin layer has the following composition. (A) 10 to 40% by weight of a copolymer of an ethylene glycol monomer and a terephthalic acid monomer (B) 90 to 90% of a copolymer of an ethylene glycol monomer and a terephthalic acid monomer and a 1,4-cyclohexanedimethanol monomer or an isophthalic acid monomer 60% by weight 2. A polyester resin container comprising the multilayer sheet according to claim 1.