JPH04180958A - Multilayered polyester resin sheet and container - Google Patents

Abstract

PURPOSE:To prepare the title sheet excellent in impact strength, resistance to heat distortion, and bonding to a lid film by laminating a core layer comprising a PET resin and an olefin resin with skin layers comprising an olefin resin and a specific PET resin. CONSTITUTION:The title sheet comprises a core layer consisting of a PET resin and an olefin resin and skin layers consisting of an olefin resin in a wt. of 1.5-5 times that of the olefin resin in the core layer and a PET resin that is made up of 10-40wt.% copolymer of ethylene glycol and terephthalic acid and 90-60wt.% copolymer of ethylene glycol, terephthalic acid, and 1,4- cyclohexanedimethanol or isophthalic acid. The wt. of the skin layer accounts for 10-40% of the total wt. of the sheet.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention provides a polyester resin multilayer sheet that has excellent impact resistance, heat deformation resistance, and adhesion to lidding films, and is capable of being sterilized in a microwave oven and retort. Regarding containers.

(Prior art) In general, retort sterilization, that is, high-temperature and high-pressure sterilized food, has been widely used mainly in aluminum pouch bags as food that can be distributed at room temperature. Development of a container for use is desired.

The properties required for a container that can be processed in a microwave oven and in a retort include a low dielectric constant, good heat resistance, high oxygen barrier properties, aroma retention, and low dissolution under high temperatures.

Partially crystallized polyester resin (hereinafter abbreviated as C-PUT) is the most suitable container material that satisfies these container properties, but C-PET has its own characteristics of high heat resistance and good chemical resistance. There is a fatal problem in that the heat sealability with the lidding film is poor due to the opposite effect, and the container and lid peel off at the adhesive surface during retort processing.

(Problems to be Solved by the Invention) As a method for improving the heat-sealability between a container and a lid material using C-PET, there is a method to improve the heat-sealability of a container using C-PET and a lid material, which becomes the heat-sealing part of the container when the container is thermoformed from a C-PET sheet. There is a method of suppressing crystallization by bringing the portion into contact with a cooling member. However, in the container thus obtained, crystallization proceeds again during retort due to high temperature heating during retort treatment, and the portion where crystallization was suppressed shows a relatively large increase in crystallinity during the ripening process for manufacturing the container. .

Due to uneven shrinkage due to non-uniform increase in crystallization,
The resulting container after retort treatment is deformed and twisted and cannot be put to practical use.

The present invention provides C-
To provide a polyester resin multilayer sheet and a container that have improved heat-sealability with a lid material without deteriorating the characteristics of PET or causing heat deformation due to retort treatment, which is a drawback of conventional technology. It is something.

(Means for Solving the Problem) 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 an olefin resin in an amount of 1.5 to 5 times the weight ratio of the olefin resin in the core layer. A multilayer sheet made of resin and polyethylene terephthalate resin, characterized in that the weight composition 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: Polyester resin multilayer sheet.

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

Here, as the PUT resin used for the core layer of the present invention,
Refers to a resin obtained by polycondensing a terephthalic acid monomer and an ethylene glycol monomer, but monomers copolymerizable with the terephthalic acid monomer and ethylene glycol monomer and -m or more to the extent that heat resistance is not impaired. , namely isophthalic acid, 4,4'-diphenylene dicarboxylic acid, adipic acid, azelaic acid, sebacic acid, pentamethylene glycol, heptamethylene glycol,
Copolymerized PE with diethylene glycol, 1,4-cyclohexane dimetatool, tetraethylene glycol, etc.
T resin and mixtures thereof can be used, and it is also possible to include other resins such as polybutylene terephthalate resin and polycarbonate resin, and additives such as antioxidants, colorants, and fillers.

In addition, the olefin resin constituting the core layer contains at least one of low density polyethylene, high density polyethylene, linear low density polyethylene, polypropylene, polybutene, etc., which functions as a crystal nucleation side and a reinforcing agent. 0
．． It is used in an amount of 2 to 3% by weight, preferably 0.5 to 2% by weight.

When the content ratio of olefin resin is less than 0.2% by weight,
During thermoforming to make a container from a sheet, the progress of crystallization in the core layer becomes slow, making it impossible to obtain the heat resistance of the container.
If it exceeds this value, the moldability and heat resistance of the container will deteriorate, making it impossible to obtain a satisfactory product.

Next, the skin layer of the multilayer sheet of the present invention is made of PET resin and olefin resin like the core layer, but the content ratio of the olefin resin is 1.5 to 5 by weight ratio of the olefin resin in the core layer. It's double the amount. The PET resin that makes up the skin layer is a PET resin obtained by polymerizing ethylene glycol monomer and terephthalic acid monomer (^)
It is a mixture of PET resin (B) 90-60-tχ obtained by polymerizing 10-40% by weight of ethylene glycol monomer, terephthalic acid monomer, and 1,4-cyclohexanedimethanol monomer or isophthalic acid monomer.

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

Here, if the weight ratio of the olefin resin contained in the skin layer is less than 1.5 times the weight of the olefin resin contained in the core layer, the heat sealability with the lid film is excellent, but the container may be deformed during retort processing. If the amount exceeds 5 times, no improvement in heat sealability can be expected.

In addition, regarding the ratio of PET resins (A) and (B), (
If the amount of ^) is less than 10% by weight, the skin layer will be softened by retorting or microwave processing, resulting in heat load deformation that leaves traces of the contents on the container surface, and if it exceeds 40% by weight, heat sealing properties will improve. do not.

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 during sheet production, and the reliability of the heat sealability in the container is reduced. is scarce. - On the other hand, if it exceeds 40% by weight, the heat deformation resistance of the container decreases, which is not preferable.

Here, similarly to the core layer, the PET resin constituting the skin layer can also contain additives such as an antioxidant, a colorant, and a filler.

The multilayer sheet of the present invention can be produced by directly extruding the multilayer sheet using a multilayer extruder, or by extruding each layer of the sheet,
There is a method of creating a multilayer sheet using a dry lamination method.

Next, as a method for manufacturing a container, the multilayer sheet described above is shaped and crystallized by a vacuum forming method using a heating mold as shown in Japanese Patent Publication No. 62-026297, for example. , but is not limited to this.

The lidding film used in the container of the present invention is not particularly limited, but polyester resin is preferable as a sealant, and it can be made by extrusion lamination or dry lamination with aluminum foil, barrier film, easily printable film, etc. You can use whatever you want.

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

(1) With the heat deformable container empty, the standard retort temperature condition is 12
An oven treatment was performed at 0° C. for 2 hours, and the degree of appearance deformation such as warpage and distortion was evaluated based on the following criteria.

○: Same as untreated container, no deformation observed.

△: Slight deformation is observed in some parts of the flange, etc.

×: Clear deformation is observed in the container.

(2) Place a coin (10 yen) on the bottom of a heat load deformation container, heat it in an oven for 2 hours at 120℃, which is the standard retort temperature condition, and then cool it to room temperature. Remove the coin and check for any traces of the coin. compared.

○: No trace of coin.

△: Slight traces of coins are observed.

×: Traces of coins clearly remain.

(3) Aging formability A container was formed using a three-phase vacuum forming machine equipped with a mold whose temperature was adjusted to 180° C., with a sheet preheating time of 9 seconds.

The shapeability of the obtained containers was compared.

○: Good formability ×: Poor formability (corners are sweet (4) Heat seal strength The sealed portion between the container flange and the lidding film was cut into a strip shape with a width of 15 days, and the width was 90" using a tensile tester. direction,
The measurement was performed under the condition of a pulling speed of 200 m/win.

Examples 1 to 3, Comparative Example 1.2 98% by weight of PET resin (manufactured by Eastman Kodak Company, trade name: PET9902) consisting of terephthalic acid monomer and ethylene glycol monomer and 2% by weight of polypropylene resin were mixed using a 65cm extruder. A resin composition constituting the core layer was obtained by melt-mixing.

The PET resin constituting the skin layer is a PET resin consisting of the same terephthalic acid monomer and ethylene glycol monomer as the core layer (manufactured by Eastman Kodak Company, trade name PE79902) (A) 20% by weight, terephthalic acid monomer and glycol. It consists of a mixture of 80% by weight of PET resin (B) obtained by polymerization with 70% ethylene glycol and 1,4-cyclohexanedimethanol in a molar ratio of 2:1 as components.
The same polypropylene resin (PP) as the core layer is added to the resin mixture.
A resin composition constituting the skin layer was obtained by melt-mixing the following resins in the proportions shown in Table 1 using a 65cm extruder.

Next, using a resin composition constituting the core layer and each resin composition constituting the skin layer, a 655 m extruder and a 40 m extruder were used.
A 0.6-thick multilayer sheet with a skin layer weight composition ratio of 20% (
(hereinafter abbreviated as sheet) was obtained by rapidly cooling it on a chill roll immediately after dicing.

Using a three-phase vacuum forming machine equipped with a mold whose temperature was adjusted to 180°C, the skin layer resin layer side of the sheet was set as the adhesion flange side with the lidding film, and the sheet was preheated for 9 seconds to form a 170 x 120 sheet. A flanged container with a height of 28 m was molded, and the thermoformability was compared and the molded container was obtained.

In the molded container, PET resin/aluminum/P
A laminated film of ET resin film (manufactured by Denki Kagaku Kogyo Co., Ltd., trade name Denka Seal Film T02) was used as a lidding film using a single-shot heat sealer, and the sealing temperature was 21.
Lid sealing was performed using a wire seal at 0° C. for a sealing time of 2 sec.

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

The measurement results are shown in Table-1.

By setting the weight ratio of the pp content of the skin layer resin composition to the PP content of the core layer resin composition to be 1.5 to 5 times the amount, the resulting product has excellent heat deformation resistance, heat load deformability, and thermoformability. Also, high heat seal strength was obtained.

On the other hand, when the weight ratio is 1 times the amount, the heat deformation resistance is poor, and when the weight ratio is 7 times the amount, the thermoformability is poor and the heat sealing strength is also low.

Examples 4 to 6, Comparative Example 3.4 The same core layer resin composition as in Example 1 was used. On the other hand, the PET resin constituting the skin layer includes a PUT resin (manufactured by Eastman Kodak Company, trade name PE79902) (A) consisting of the same terephthalic acid monomer and ethylene glycol monomer as the core layer, and a terephthalic acid monomer and glycol component. PET resin (B) obtained by polymerization with a monomer of ethylene glycol and 1,4-cyclohexane dimetatool in a molar ratio of 2:1 is mixed in the ratio shown in Table 2,
A resin composition constituting the skin layer was obtained by melt-mixing 95% by weight of each PET resin mixture and 5% by weight of the same PP resin as the skin layer using a 65 Kasumi extruder.

Next, using the resin composition constituting the core layer and each resin composition constituting the skin layer, two
A two-layer seed sheet was extruded, then a container was made using the sheet, and a lid was sealed on the container.

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

The measurement results are shown in Table-2.

By setting the weight ratio of (A) and (B) as PET resins constituting the skin layer to 10:90 to 40:60, it has excellent heat deformation resistance, heat load deformability, and thermoformability, and also has high heat sealability. Strength was obtained.

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

Example 7 The same core layer resin composition as in Example 1 was used. On the other hand, the PET resin constituting the skin layer is PET resin (manufactured by Eastman Kodak Company, trade name PET9902) (^) 301 EI%, which is made of the same terephthalic acid monomer and ethylene glycol monomer as the core layer, and ethylene glycol monomer. PET resin (B) obtained by polymerization with a monomer containing terephthalic acid and isophthalic acid in a molar ratio of 2:1 as dicarboxylic acid components
70% by weight of the PET resin mixture, 95% by weight of the PET resin mixture and 5% by weight of the same PP resin as the core layer.
A resin composition constituting the skin layer was obtained by melt-mixing using a W extruder.

Next, using the resin composition constituting the core layer and each resin composition constituting the skin layer, two
A two-layer seed sheet was extruded, then a container was made using the sheet, and a lid was sealed on the container.

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

The measurement results are shown in Table 3.

The molded container and lid-sealed container had excellent heat deformation resistance, heat load deformability, and thermoformability, and high heat seal strength was obtained.

Comparative Example 5 The same core layer resin composition as in Example 1 was used. On the other hand, the PET resin constituting the skin layer was a PET resin (manufactured by Eastman Kodak Company, trade name PE79902) consisting of the same terephthalic acid monomer and ethylene glycol monomer as the core layer.

A resin composition constituting the skin layer was obtained by melt-mixing 95% by weight of the PET resin and 5% by weight of the same PP resin as the core layer using a 65m extruder.

Next, using the resin composition constituting the core layer and each resin composition constituting the skin layer, two
A two-layer seed sheet was extruded, then a container was made using the sheet, and a lid was sealed on the container.

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

The measurement results are shown in Table 3.

It has poor thermoformability and heat sealability, making it impractical.

Example 8.9, Comparative Example 6.7 Using the resin compositions of the skin layer and core layer obtained in the same manner as in Example 1, two types and two layers were prepared using a 65 Tsuru extruder and a 40m extruder. Each sheet with a thickness of 0.6 m was obtained using a sheet molding machine having the weight composition ratio of the skin layer shown in Table 4.

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

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

The measurement results are shown in Table-4.

If the weight composition ratio of the skin layer is less than 10% by weight, the heat sealing strength will vary and the reliability will be poor, and if it exceeds 40% by weight, the heat deformation resistance of the container will decrease, so a range of 10 to 40% by weight is preferable.

(Effects of the Invention) As described above, the present invention has a multilayer structure in which a specific PET resin is provided in the skin layer that is the adhesive part with the lid sealing film when producing a retort processed food container made of PET resin. By making the container li, good heat resistance,
It has the effect of obtaining adhesiveness and thermoformability.

Patent applicant Denki Kagaku Kogyo Co., Ltd.

Claims (1)

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