JPH03254939A - Heat resistant container - Google Patents

Abstract

PURPOSE:To obtain a vessel for food which has excellent heat resistance and heat insulating properties and does not deteriorate taste and flavor of food after cooking and has a deep bottom by thermally forming the laminated com posite sheet comprising a film made of polypropylene resin and a film made of polybutylene terephthalate resin so that the polybutylene terephthalate resin layer is provided to the inside of the vessel. CONSTITUTION:A film made of polyethylene terephthalate resin and a film made of polypropyrene resin are laminated by a dry lamination method. The obtained laminated composite sheet is vacuum-formed by utilizing a vacuum forming machine so that the film layer made of polybutylene terephthalate resin becomes the inside face. Thereby a vessel is obtained which has draw ratio of at least 0.25 especially at least 0.5. This heat resistant vessel holds food and is directly heated by a radar range and cooking is enabled. Further the whole thickness of the composite sheet is regulated to at least 40mum espe cially preferably to 0.5-3mm. The thickness of the film made of polybutylene terephthalate resin is regulated to at least 20mum especially preferably to 20-100mum.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a heat-resistant container using a heat-resistant composite sheet.

[Conventional technology and its issues]

BACKGROUND ART Conventionally, sheets made of polyolefin such as polypropylene are well known as materials for plastic food containers, especially containers that require heat resistance.

However, polypropylene has poor heat resistance and chemical resistance, and also has a strong odor called olefin odor, which can impair the taste and odor of foods.

Therefore, in order to compensate for these drawbacks of polypropylene, inorganic fillers such as talc are added to polypropylene to improve its heat resistance, and even polycarbonate 1 is added to polypropylene.
・Laminated sheets laminated with stretched or unstretched polyethylene terephthalate, etc., are used.

Although heat resistance is somewhat improved by such a method, it is still insufficient and is particularly unsuitable for containers for cooking oily foods in a microwave oven. That is, when cooking oily foods in a microwave oven, the temperature of the food often rises to 100° C. or more, and the above-mentioned sheet has poor heat resistance.

Furthermore, containers made of composite sheets laminated with unstretched polyethylene terephthalate films so that the polyethylene terephthalate layer side is on the inside do not impair the taste or odor of the food, but are inferior in heat resistance. On the other hand, a composite sheet made by laminating biaxially oriented or -axially oriented polyethylene terephthalate films has excellent heat resistance, tasteless, and odorless properties, but when the composite sheet is thermoformed, the polyethylene terephthalate film layer peels off or breaks, making the container unsatisfactory. However, it is still unsatisfactory as a composite sheet for heat-resistant containers.

Furthermore, resin sheets are formed into containers by thermoforming, especially vacuum forming or pressure forming, or a combination of these, but conventional laminated sheets with heat resistance have low elongation and cannot be deep drawn. However, there was also the problem that only shallow-bottomed products could be produced, which limited the applications.

[Means to solve the problem]

As a result of intensive studies to solve the above problems, the present inventors found that a polybutylene terephthalate resin film has high heat resistance, high rigidity, excellent moldability, low oxygen permeability, and It has excellent aroma retention and is tasteless and odorless, so it does not impair the taste or odor of food even when it comes into contact with food.In addition, the composite sheet of this film and polypropylene film is heat resistant and can be formed into a container shape. They found that the material has very good properties and can be deep-drawn by thermoforming, and has low oxygen permeability, so when made into a container, it has excellent preservation of food products, leading to the completion of the present invention.

That is, the present invention provides a heat-resistant container having a drawing ratio of 0.25 or more, which is obtained by thermoforming a laminated composite sheet of a polypropylene resin film and a polybutylene terephthalate resin film so that the polybutylene terephthalate resin layer is on the inside of the container. This is what we provide.

Polybutylene terephthalate in the present invention means a polyester whose main repeating unit is butylene terephthalate, and specifically, a polyester obtained by condensing 1,4-butanediol and terephthalic acid or its lower alcohol ester. , or a copolymer mainly composed of polybutylene terephthalate. A homopolymer or a branched polymer is preferred from the viewpoint of heat resistance, gas barrier properties, and fragrance retention. Here, the copolymer is mainly composed of terephthalic acid or its lower alcohol ester as a dibasic acid component, and contains 40% of other dibasic acid components.
It refers to a polyester composed of mo 1% or less, or a polyester composed mainly of 1,4-butanediol as a glycol component and other glycol components of 4.0 mo 1% or less. Furthermore, the main components are terephthalic acid or its lower alcohol ester and 1,4-butanediol, and also includes polyesters in which the total amount of other dibasic acid components and other glycol components is 40 mo1% or less.

Here, dibasic acid components other than terephthalic acid or its lower alcohol ester include isophthalic acid, phthalic acid,
Adipic acid, sebacic acid, succinic acid, oxalic acid, etc. and lower alcohol esters thereof can be used. Also, 1,
As the glycol component other than 4-butanediol, common alkylene glycols such as ethylene glycol, diethylene glycol, propylene glycol, trimethylene glycol, hexamethylene glycol, neopentyl glycol, cyclohexane dimetatool, etc. can be used.

Also, branched polymers belonging to copolymers can be used. The PBT branched polymer referred to herein is a polyester mainly composed of so-called polybutylene terephthalate or butylene terephthalate units, which is branched by adding a polyfunctional compound. Polyfunctional compounds that can be used here include trimesic acid, trimellitic acid, pyromellitic acid and alcohol esters thereof, glycerin, trimethylolethane, trimethylolpropane, pentaerythritol, and the like.

The amount of these polyfunctional compounds added is 1 mo 1% or less as an acid component or a glycol component.

The film made of polybutylene terephthalate resin of the present invention is formed into a film using a polybutylene terephthalate resin by a normal molding method, such as an inflation method or a T-die method. In particular, films prepared by the inflation molding method have many advantages over films obtained by other manufacturing methods, such as the T-die method, such as higher tensile strength and better gas barrier properties, and can be manufactured at a lower cost. Therefore, it is preferable. In addition, from the viewpoint of film production, it is preferable to use a polybutylene terephthalate resin having an intrinsic viscosity of 1.0 or more.

Further, the polybutylene terephthalate resin film used in the present invention may be a stretched film or an unstretched film, but
Considering that a so-called deep drawing process is performed to make containers, an elongation of approximately 200% or more is required at the temperature during deep drawing (140 to 170°C), and from this point of view, unstretched films are particularly important. preferable. Further, a stretched film can also be used as long as the stretching ratio is 1.5 times or less.

On the other hand, in the present invention, polypropylene refers to a polymer mainly obtained by polymerizing propylene, and copolymers with other monomers, such as ethylene or ethylene hydrocarbon compounds having up to 10 carbon atoms, such as butene, pentene, etc. or copolymers with acrylic acid, methacrylic acid, fumaric acid, maleic acid, and esters of these carboxylic acids.

When laminating a polybutylene terephthalate resin film and a polypropylene resin film, ordinary synthetic resin sheets or general adhesives used for adhering films can be used, but urethane adhesives may be used. etc. are suitable. As a lamination method, a method called a dry lamination method (7) is preferably used.

The composite sheet used in the present invention includes not only one laminated one layer each of a polybutylene terephthalate resin (PBT) film and a polypropylene resin (PP) film, but also a three-layered one such as PBT/PP/PBT. In short, it is sufficient that at least one surface is made of PBT, and depending on the case, other resin films may be included in the inner layer.

In the present invention, the thickness of the composite sheet is not particularly limited, but the total thickness of the composite sheet is preferably 40μ or more in view of its use as a microwave cooking container, processability into a container, strength of the container, heat resistance, etc. is 0.3 to 711111 mm, particularly preferably 0.5 to 3 mm, and the thickness of the polybutylene terephthalate resin film is 20 IEn or more, especially 2
It is preferably 0 to 100-.

When molding this composite sheet into a container, it is necessary to mold it so that the polybutylene terephthalate resin film layer becomes the inner surface of the container.

A heat-resistant container configured in this manner is particularly suitable as a container for a microwave oven because it can store food and cook the food directly in a microwave oven.

The composite sheet of the present invention having the above structure can be formed by vacuum forming, and has excellent elongation, so unlike containers made of conventional composite sheets, it can be deep drawn to a drawing ratio of 0.25 or more, especially 0.5 or more. Yes, we are now able to offer containers with deep bottoms.

Here, the drawing ratio refers to the ratio of the drawing depth of the drawn product to the width (diameter) of the opening, and is the value of H/W in FIG. 1.

Further, the thermoforming method may be any conventional method, such as vacuum forming such as a straight method, prolag assist method, drape method, or pressure forming, but it is most desirable to use both in combination.

In addition, polybutylene terephthalate resin can be used for the purpose of use of the present invention, that is, if it is a substance that does not cause food hygiene problems when it comes into contact with food and is cooked in a microwave oven, or is a substance that is not extracted by food and does not contaminate food, it can be used in general. Known substances added to thermoplastic resins and thermosetting resins, such as plasticizers, stabilizers such as antioxidants and ultraviolet absorbers, antistatic agents, surfactants, colorants such as dyes and pigments, and A lubricant, a crystallization promoter (nucleating agent), etc. for improving fluidity can also be used as appropriate depending on the required performance. Further, depending on the purpose, a small amount of other thermoplastic resin or inorganic filler may be added as an auxiliary to the extent that the effects of the present invention are not impaired.

Furthermore, when a polybutylene terephthalate resin film is used as a lid material by adhering to the container of the present invention, the oxygen permeability can be kept even lower, resulting in a container with excellent long-term storage stability.

〔Example〕

The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited thereto.

Examples 1 to 10, Comparative Example 1 - Various polybutylene terephthalate resin films (thicknesses are shown in Table-1) and polypropylene resin films (thicknesses are shown in Table-1) extruded by the fin fusion method or T-die method. ) were laminated by dry lamination. The obtained laminate was vacuum formed into containers with various drawing ratios shown in Figure 1 at 1.50"C using a vacuum forming machine so that the polybutylene terephthalate resin film layer was on the inside surface.
Its moldability was investigated.

A heat resistance test was conducted on the resulting container by putting various fillings into the container and heating it using the microwave oven described below.

In addition, a test was conducted regarding the change in odor of the heated filling. Furthermore, chemical resistance was also tested. Table 1 shows these results.
Shown below.

Microwave oven manufactured by Toshiba ER620S Oscillation frequency: 2,450 M1lz Maximum output: 500 mm Also, as a comparative example, containers were tried to be molded from polypropylene single-layer sheets and laminated sheets of polypropylene, polycarbonate, polyethylene terephthalate, etc., and tested in the same manner as in the examples.

For the heat resistance test, fill a container with olive oil and heat it for 10 minutes. The degree of deformation of the container was evaluated using the following criteria.

○: No deformation △: Slightly deformed ×: Significantly deformed Regarding the change in odor of heated fillings, we compared the change in the odor of the heated filling with milk, water, orange juice, etc. to a Pyrex glass container. We investigated the degree of The evaluation was carried out by 10 panelists and evaluated based on the following criteria.

O: No polymer odor △: Slight polymer odor ×: Polymer odor Regarding chemical resistance, 5% of the container volume was added to various containers.
% aqueous sodium hydroxide, 98% ethyl acetate or 9%
After adding 9.5% ethanol and leaving the container at room temperature for 7 days, deformation and discoloration of the container were evaluated using the following criteria.

○: No deformation or discoloration Δ: Slightly deformed or slightly discolored 2 ×: Largely deformed or significantly discolored 15 (Notes to Table 1) *15% sodium hydroxide aqueous solution *298% ethyl acetate *3 99.5% ethanol * 4 Modified PET-A; Copolymerized PET containing isophthalic acid as an acid component *5 Modified PET-B; Copolymerized PET containing cyclohexane dimekul as an alcohol component *6 Modified PBT-A; Copolymerized PET containing isophthalic acid as an acid component PBT *7 i-type PBT-B; co-electropolymerized PBT containing an ethylene oxide adduct to bisphenol as an alcohol component *8 branched PBT; branched copolymerized PBT containing trimellitic acid as an acid component [Effects of the invention] The present invention The heat-resistant composite sheet produced by the company has good thermoformability, high heat resistance, excellent chemical resistance, and is tasteless and odorless, so containers obtained by molding this composite sheet have excellent heat resistance. It has heat insulating properties and does not impair the taste or odor of the food after cooking, making it extremely suitable for cooking in a microwave oven. In addition, it has a low oxygen permeability and can be heat-sealed, which is advantageous for storing foods and the like as a container. Furthermore, since the container can be made with a deep bottom, it can be used in a variety of fields as a resin container, such as food containers for microwave cooking, retort food, etc., and storage containers for medicines, ink, etc. It can be suitably used as

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view showing the shape of a heat-resistant container. H: Container drawing depth W: width of container opening

Claims (1)

[Claims] 1. A laminated composite sheet of a polypropylene resin film and a polybutylene terephthalate resin film is thermoformed so that the polybutylene terephthalate resin layer is on the inside of the container, and the drawing ratio is 0.25 or more. Heat-resistant container. 2. The heat-resistant container according to claim 1, which has an aperture ratio of 0.5 or more. 3. The thickness of the polybutylene terephthalate resin layer is 20μ
The heat-resistant container according to claim 1 or 2, wherein the heat-resistant container is greater than or equal to m. 4. The heat-resistant container according to claim 1, 2 or 3, wherein the total thickness of the laminated composite sheet is 40 μm or more. 5. The heat-resistant container according to claim 1, wherein the thermoforming is vacuum forming or pressure forming. 6. A heat-resistant container made by adhering a lid material whose main component is a polybutylene terephthalate resin film to the heat-resistant container according to any one of claims 1 to 5.