JPH0219285A - Retort packaging container - Google Patents

Abstract

PURPOSE:To provide a container having a retort sterilizing and sealing performance and excellent in the easily separable characteristics by forming at least the inner surface of the container with a flange of polyolefin resin and the inner surface of a lid of the metal foil provided with an acid modified polyolefin on a heat seal surface as an inner surface protection coating. CONSTITUTION:A container 1 is made of a sheet 5 by sheet forming method. This sheet 5 consists of a metal foil 6, an inner film layer 7 and an outer film protection layer 8. The inner film layer 7 consists of polyolefin film which is adhesively bonded to the metal foil 6 with a polyurethane adhesive agent. On the other hand, a lid 2 is composed of a laminate 10 and has almost the same size and shape as the outer periphery of the container flange. A heat seal part 9 is formed between the lid and the flange 4. This laminate 10 consists of a base layer 11, an inner film layer 12 and an outer protection layer 13. The inner layer 12 of the lid is formed of a coating material containing an acid modified polyolefin in such small amounts as to impart an easily separable characteristics to a heat seal surface.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a packaging container for retort (sterilization), and more specifically, it has sealing performance, easy-opening performance, and durability that can withstand retort sterilization and subsequent storage. The present invention relates to a heat sheet container having a combination of phasing properties.

(Prior Art) Conventionally, containers made by heat-sealing a flange-equipped container whose inner surface is made of resin and a lid whose inner surface is made of a resin metal foil sheet have been used in many fields such as food packaging. widely used in

Resin films such as polyolefin are used as the inner material of the lid in most cases due to their heat-sealing properties, but they are widely used as can inner surface coatings due to their barrier properties against corrosive components, that is, their corrosion resistance. The paint used is excellent. However, most of these paints have adhesive properties to the polyolefin that makes up the inner surface of the container, and acid-modified olefin resins are generally used in the coating film to increase the adhesion between the coating film and the olefin resin. It is already known from Japanese Patent Publication No. 58-2825 that the thermal adhesion between the two can be improved by adding a resin and preferentially distributing the acid-modified olefin resin on the surface of the coating film.

(Problems to be Solved by the Invention) According to the above prior art, it is possible to obtain the advantage of introducing a strong adhesive bond between the coating film and the olefin resin layer, or to heat seal the lid body and the flange. There is a problem in that the seal strength is too strong for use as a so-called peelable sealed container, in which the seal is opened by manually peeling at the interface.

In order to solve this problem, Japanese Patent Publication No. 58-385 proposes a multi-coat structure with 1 f
It is known in Japanese Patent Publication No. 5B-22699 that the distribution of acid-modified olefin resin in the coating film is controlled by an underlying distribution control agent layer to impart easy peelability. . However, it is troublesome that these steps must be carried out in two stages.

Therefore, it is an object of the present invention that at least the inner surface of the container body is made of polyolefin, the lid is made of a metal foil sheet with a coating film provided on the inner surface, and the heat-sealed portion formed between the two is suitable for retort sterilization. It is an object of the present invention to provide a packaging container for a retort, which has a sealing performance that can withstand subsequent storage, and which can be easily peeled off at the heat-sealed interface between the two when unsealed, without causing any phasing.

(Means for Solving the Problems) According to the present invention, there is provided a container in which a flanged container body and a lid are heat-sealed at the flange portion, wherein at least the inner surface of the flanged container body is made of polyolefin. The container body is made of resin, and the lid has an inner surface protective coating formed of a paint containing a small amount of acid-modified polyolefin to impart easy peelability to the heat-sealed surface. A retort packaging container is provided, which is characterized in that it is made of metal foil.

The paint containing the acid-modified polyolefin is preferably composed of a thermosetting resin paint, especially a paint containing an epoxy resin and a curing agent resin for it, and the inner surface protective coating formed is as follows: Formula, where L represents the thickness (μm) of the inner surface protective coating, X is the number of parts by weight of the acid-modified polyolefin per 100 parts by weight of the thermosetting resin, and d is the density of the thermosetting resin. (g/cm3), and d2 is the density (g/cm3) of the acid-modified polyolefin.
It is preferable that the value be within the range of 5 to 5.

(Function) In the first-rut packaging container of the present invention, a coating film is present on the lid side, and a heat-sealable polyolefin is present on the container body side. The biggest problem that occurs when opening a container whose flanged container body and lid are heat-sealed at the flange by peeling them off at the heat-sealed surface is that clean peeling does not occur at the heat-sealed section, and the heat-sealable resin is damaged. This causes so-called phasing, which causes cohesive failure in the form of fragments, which impairs the appearance characteristics of the opening. In the present invention, when a coating film is provided on the inner surface of the lid and a polyolefin is provided on the container body side, polyolefin is present only in the flange part within the plane including the heat sealing surface, and moreover, there are 11 polyolefins in the flange part. The lid body, which is located in almost the same plane, has a coating film that has excellent adhesion to the metal foil and has a much greater cohesive force than polyolefin, which effectively prevents the above-mentioned phasing from occurring. It is something that will be done.

Using a coating film on the lid side and polyolefin on the container body side also brings advantages in terms of corrosion resistance. When both the lid and the container body have metal bases, the container body is formed by drawing a material into a cup shape, while the lid is formed by shearing the material into a predetermined shape. Thus, the container body is subjected to severe processing, and from the standpoint of preventing scratches during processing, it is effective to cover the container with a resin film that is much thicker than the paint film.

On the other hand, since the degree of processing on the lid body is small and there are almost no scratches caused by processing, it is possible to apply a coating film with a small thickness that has excellent barrier properties against corrosive components compared to resin films. That's a good translation.

By the way, since there is almost no adhesion between the coating film on the lid side and the polyolefin on the container body side, according to the present invention, acid-modified polyolefin is blended into the coating film on the lid side. Adding acid-modified polyolefin to the coating film to improve the adhesion with the polyolefin was disclosed in the above-mentioned Japanese Patent Publication No. 51
Although it is known from Japanese Patent No. 1-2825, the present invention is characterized in that it is contained in the coating film in such a small amount that it imparts easy peelability to the heat-sealed surface with the polyolefin. The term "easy peelability" as used herein refers to a property in which sufficient sealing performance is maintained during retort processing and subsequent storage, but the product is easily peeled off at the interface by hand when the package is opened.

More specifically, regarding the thickness L of the inner protective coating film, the number of blended parts X of acid-modified polyolefin, the coating resin density d0, and the acid-modified polyolefin density d2! Then, if the blending amount of the acid-modified polyolefin is selected so that the coverage (, Q) of the formula (1) is in the range of 0.3 to 1o, particularly 0.4 to 5,
Satisfactory static characteristics can be obtained. That is, when the coverage (U) is smaller than the above range, the beer strength and sealing reliability tend to be inferior to those within the above range, whereas when this value is larger than the above range, is inferior in terms of easy-opening performance.

(Preferred Embodiment of the Invention) Packaging Container In FIG. 1 showing an example of the packaging container of the present invention, this packaging container consists of a container body 1 and a lid 2. As shown in FIG. Container body 1
A tapered or cylindrical body wall portion 3A formed by sheet drawing as described below, and a bottom portion 3 connected to the lower end of the body wall portion.
B and a flange portion 4 that continues to the upper end of the body wall portion. In FIG. 2 showing an example of the cross-sectional structure of a container body sheet, this sheet 5 includes a metal foil 6, an inner coating layer 7 applied to the surface of the metal foil that will become the inner surface of the container, and a surface that will become the outer surface of the container. It consists of a protective outer covering layer 8.

In the present invention, as described above, the inner surface coating layer 7 is made of a polyolefin film, and the polyolefin film 7 and the metal foil 6 are bonded together using a polyurethane adhesive, an epoxy adhesive, or an acid-modified polyolefin adhesive (not shown).
Can be glued through.

On the other hand, the lid body 2 is composed of a laminate as described below, has approximately the same dimensions and shape as the outer circumference of the flange portion of the container body, and has a heat-sealed portion between it and the flange portion 4. 9 is formed. In FIG. 3 showing the cross-sectional structure of the laminate that constitutes the lid 2, the laminate 1
0 consists of a base layer 11 made of metal foil or the like, an inner surface coating layer 12 provided on the innermost side of the container of the base 11, and an outer surface protective layer 13 provided on the outer surface of the base layer 11. Become.

As already mentioned, the inner surface coating 12 of the lid body is formed from a paint containing acid-modified polyolefin in a small amount so as to impart easy peelability to the heat-sealed surface. The film-forming resin in the paint preferably comprises a thermosetting resin, most preferably a combination of an epoxy resin and a hardener resin therefor. The acid-modified polyolefin contained in the paint is used for coating the inner surface of the container.
It is preferable to have a polyolefin main chain skeleton that shares the main olefin unit with the polyolefin constituting No. 2.

In addition, the base layer 11 and the acid-modified polyolefin-containing type 1] 11
2a, there may be an intermediate layer 12b such as a coating film that does not contain acid-modified polyolefin.

As the acid-modified olefin resin used for the inner surface coating of the V-embryonic tectum, a resin obtained by graft-modifying an olefin resin with an ethylenically unsaturated carboxylic acid or its anhydride is used. As the olefin resin backbone polymer, low-medium or high-
Density polyethylene, linear low density polyethylene, homopolypropylene, crystalline propylene-ethylene copolymer,
Examples include polybutene-1, polypentene-1, butene-1/propylene copolymer, butene-1/propylene/engineered tyrene terpolymer, and the like. From the point of view of retort resistance, homopolypropylene is suitable. Examples of ethylenically unsaturated carboxylic acids and their anhydrides include acrylic acid,
Methacrylic acid, maleic acid, fumaric acid, crotonic acid, itaconic acid, citraconic acid, 5-norbornene-2,3-
Dicarboxylic acid, 71twin acid anhydride, citraconic anhydride,
Examples include 5-norbornene-2,3-dicarboxylic anhydride and tetrahydrophthalic anhydride, but maleic anhydride is most suitable from the viewpoint of heat sealability. The acid-modified olefin resin used changes the acid group to a carbonyl group (
= CO) per 0.01 to 600 mm @7100
g resin, particularly at a concentration of 1.0 to 200 meq/100 g resin.

As the paint for dispersing the acid-modified polyolefin, any metal paint with excellent adhesion to metal foil can be used, but generally thermosetting paints, especially glass coated by thermomechanical analysis (TMA), are used. Preference is given to thermosetting coatings whose turn point (Tg) is in the range from 90 to 130°C, in particular from 95 to 120°C. Among these, from the standpoint of adhesion to metal foil and barrier properties against corrosive components,
It is best to use an epoxy resin and a hardener resin therefor. As an epoxy resin, bisphenol A
Bisphenol type epoxy resins obtained by m-condensation of bisphenols such as and epihalodrin are suitable, and the epoxy equivalent thereof is generally 400 to 20,000,
In particular, it is preferably in the range of 1,000 to 5,000. Examples of resin curing agents that are reactive with epoxy resins include resins that have functional groups that are reactive with hydroxyl groups and oxirane rings of epoxy resins, such as hydroxyl groups, amino groups, and carboxyl groups; for example, resol type and/or Or one or a combination of two or more of novolac type phenol formaldehyde resin, urea formaldehyde resin, melamine formaldehyde resin, alkyd resin, polyester resin, acrylic resin, polyurethane resin, xylene resin, epoxy ester resin, butyral resin, etc. is used. Among these, methylol group-containing thermosetting resins, particularly resol type phenol resins and amino resins, are preferred.

The ratio of epoxy resin to hardener resin is from 95:5 to 40:60 by weight, especially from 90:10 to 50:
Preferably, the weight ratio is within the range of 50.

It is generally preferable to use the acid-modified poly-1-nofin in an amount of 0.2 to 15% by weight, particularly 05 to 10% by weight, and within a range that satisfies formula (1). To form a coating film, acid-modified olefin resin is dispersed in the coating solution mentioned above, and this coating is applied onto metal foil. Formed by baking. The thickness of the coating film is generally 2 to 30μ
m, preferably in the range of 5 to 20 μm.

Baking of the coating film can be carried out at 180 to 250°C for 30 seconds to 10 minutes.

The protective coating provided on the outer surface of the metal foil is made of, for example, phenol.
Formaldehyde resin, urea/formaldehyde resin,
Thermosetting resin consisting of melamine/formaldehyde resin, xylene/formaldehyde resin, epoxy resin, alkyd resin, polyester resin, thermosetting acrylic resin, urethane resin alone or in combination of two or more: or acrylic resin, vinyl chloride-acetic acid It may be a coating film of a thermoplastic resin such as a vinyl copolymer, a vinyl chloride-vinyl acetate maleic acid copolymer, a vinyl resin such as a vinyl butyral resin, a styrene-butadiene-acrylic acid ester copolymer, or a polyamide resin. Further, the outer surface protective layer may be composed of a thermoplastic resin film such as a biaxially oriented polyethylene terephthalate film, an axially oriented nylon film, or a polycarbonate film; various papers; or a laminate of two or more of these.

Container body The container body of the present invention can be a container made of only polyolefin, as long as at least the inner surface is made of polyolefin.
It may consist of a laminated container of polyolefin and other resin, or a laminated container of polyolefin and metal foil.

The polyolefin constituting the inner surface of the container body includes those exemplified as the backbone polymer of acid-modified polyolefin, namely, low-1 medium- or high-density polyethylene, linear low-density polyethylene, homopolypropylene, crystalline propylene-ethylene copolymer, Polybutene-1, polypentene-
1, butene-1/propylene copolymer, butene-1/propylene/engineered tyrene terpolymer, and the like. In terms of retort resistance, homopolypropylene or propylene copolymers are preferred. Of course, instead of using the exemplified polyolefin inner material in East Germany, a blend or copolymer containing two or more thereof can also be used.

The inner surface material used in the present invention preferably contains the same olefin units as the olefin units of the acid-modified olefin resin, and preferably contains the olefin units in an amount of 50 to 95% by weight, particularly 65 to 85% by weight. That is, the inner surface material used in this aspect of the present invention contains 5 to 50% by weight of olefin units other than the olefin units contained in the acid-modified reflex polymer in the form of a copolymer or polymer blend.

For example, when the acid-modified olefin resin is maleic anhydride-modified polypropylene, the inner material has 5 propylene units.
It contains 0 to 95% by weight and 5 to 50% by weight of olefin units other than propylene, such as ethylene or butene-1, in the form of copolymers or blends. This similarly applies when the acid-modified olefin resin is acid-modified polyethylene.

-IQ has previously pointed out that from the standpoint of rut resistance, it is preferable for the inner surface material to contain homopolypropylene or a propylene-ethylene copolymer mainly composed of propylene units; The olefin unit different from the olefin resin is preferably contained in the inner surface material in the form of a polymer blend. Thus, for acid-modified propylene resin, homopolypropylene or propylene-ethylene copolymer and polyethylene are mixed in a ratio of 50:50 to 95:5, particularly 60:40 to 80%, as the inner material.
: It is recommended to use a blend with a weight ratio of 20.

The container body may be made of a sheet made of the aforementioned polyolefin alone, or a sheet made of the polyolefin as an inner and outer layer and an oxygen barrier resin such as an ethylene vinyl alcohol copolymer.
A plastic cup container made by vacuum forming, pressure forming, or plug assist forming a laminated sheet made of aliphatic or aromatic polyamide or vinylidene chloride copolymer with an intermediate layer at the melting temperature of the resin, and the above. It may be a single or biaxially stretched plastic cup container made by molding various sheets in the same way at stretching temperatures (same temperature).

Further, the container body may be a cup-shaped container made by drawing and forming a laminated sheet with a metal foil as an intermediate layer and polyolefin film layers on both sides between a die and a punch. In this case, the metal foil may be the same as described above for the lid, and the thickness of the inner surface material is generally in the range of 10 to 200 μm, and preferably in the range of 30 to 100 μm.

Applications The packaging container of the present invention includes
It is widely applied to containers that require sterilization operations such as sterilization. That is, after filling the container body with the contents and performing operations such as nitrogen replacement and steam replacement as necessary, a lid is applied to the container flange, and heat treatment such as a heat seal bar, high frequency induction heating, ultrasonic irradiation, etc. Using sealing means, 170
Heat seal and seal at a temperature of 250°C to 250°C. The sealed packaging container is sterilized at a temperature of 100 to 135° C. for 10 to 60 minutes to form a package that can withstand storage. Furthermore, by opening the package and placing it in a microwave oven or toaster oven, the contents can be heated and eaten.

(Effects of the Invention) According to the present invention, the flanged container body is made of a polyolefin resin at least on the inner surface,
On the other hand, by making the lid body a metal foil sheet with an inner surface protective coating formed of a paint containing a small amount of acid-modified polyolefin on the inner side to impart easy peelability to the heat-sealed surface, both The heat-sealed part formed between the seals has a sealing performance that can withstand retort sterilization and subsequent storage, and when the package is opened, the ♀IJ separation can be easily performed without the occurrence of phasing at the interface between the two heat-seals. It is played. This container also has the advantage of being excellent in corrosion resistance.

(Example) Example 1 A coating amount of 65 mg of yellow epoxy phenol paint was applied to one side of a 70 μm thick soft aluminum.
/dm2.

Next, the other side is first subjected to an acrylic-Zr surface treatment, and then a bisphenol A type epoxy resin and a resol type phenol/formaldehyde resin consisting of a dinuclear component are contained in a weight ratio of 80:20. Epoxyphenol paint (specific gravity d, = 1.20g/cm3) 10
Powder (specific gravity d 2
= 0.90g/cm3) 3 parts by weight (2.9wt%
) was applied and baked at 230°C for 40 seconds. The coating amount was 95 mg/dm2.

The coverage l of the obtained modified PP-containing coating film is expressed by the formula 1=I=/
It was calculated as (1+100-d2/X-di) and found to be 3.4. (However, L = 88.3 μm, d,
=1.20g/cm3. d2=0.90g/cm'
) A lid material having a size of 85 mm x 85+ nm and having an opening knob at a part of the corner was punched out from the thus obtained coated material.

On the other hand, a blank with a blank diameter of 135 mm was punched out from a laminate of 70 μm titanium white-containing PP/75 μm steel foil/40 μm titanium white-containing PP using a urethane adhesive, and a blank with a blank diameter of 135 mm was punched using a drawing method using an elastic punch. A square container with a length of 25 mm, an outer diameter of 83 mm, an inner diameter of 70 mm, a corner radius of 25 mm, and a flange portion curled outward was molded.

Next, flavored tuna flakes were filled into the rectangular molded container, and the lid material was heat-sealed. This sealed container is 120
Retort sterilization was performed at ℃ for 30 minutes. The heat seal strength between the container body and the lid after retort sterilization was measured and found to be 2.8 kg and 715 mm. Furthermore, when the lid material was opened from the opening knob, the beer could be easily peeled off.

On the other hand, 50 containers were similarly filled with flavored tuna flakes and sterilized by retort, and each 25 containers were heated at 50°C for 1 hour.
Storage tests were conducted for 1 month and 3 months. The contents of flavored tuna flakes are highly corrosive, and
Although storage at 0°C for 3 months was a severe storage condition, the results after opening were very good, and no corrosion or peeling was observed on the inner surface of the M material. The same was true for the inner surface of the container body.

Examples 2-4. Comparative Examples 1 to 3 In Example 1, only the amount of maleic anhydride-modified PP added to the modified polypropylene-added epoxyphenol paint used for the inner surface coating of the lid material was changed as shown in Table 1, and the coating property (l) was changed. Each sample was prepared and
The heat seal strength after the retort treatment was measured and was as shown in Table 1.

When modified PP was not added as in Comparative Example 1, heat sealing with the container body could not be performed and it could not be used as a lid material. In addition, when the coverage (<=) was very small as in Comparative Example 2, the heat sealing strength with the container body was a low value, making it insufficient as a sealing container lid. Furthermore, if the covering property 1 is too large as in Comparative Example 3, the heat sealing strength with the container body becomes too high, making it impossible to obtain easy opening properties.

Examples 5 to 10 Lid materials were prepared using thermosetting resins as shown in Table 2 in the modified polypropylene-added thermosetting paint used for coating the inner surface of the lid material in Example 1. These lid materials were heat-sealed after filling the contents shown in Table 2 into the respective container bodies shown in Table 2. Next, Examples 5 to 8 were subjected to tort sterilization at 115°C for 40 minutes, and Example 910 was tort sterilized at 105°C for 30 minutes, and the heat seal strength of the resulting containers was measured. As shown in Table 2, all of them had beer opening properties.

A storage test was also carried out at 50°C for 3 months, but no problems were found, and no corrosion or peeling of the inner surface was observed.

Example 11 In Example 1, the average carbonyl group concentration was 160+req/100g instead of maleic anhydride-modified polypropylene.
A lid material was prepared using a paint in which 3 parts by weight (2.9 wt%) of a maleic anhydride-modified high-density polyethylene powder (specific gravity d 2 =0.95 g/cm') of a polymer was dispersed.

The coatability of the obtained modified HD PE-containing coating film was 3.
It was 2.

Next, the height is 40 ml! , outer diameter 75mm, inner diameter 65mm
After heat-sealing the lid material (outer diameter 80 mm with tab) to a round injection molded container having a flange filled with jelly, retort sterilization was performed at 95° C. for 30 minutes. The heat seal strength between the container body and the lid after retort sterilization was measured and found to be 2.1 kg and 715 mm. Furthermore, when the lid material was opened from the opening tab, the beer could be easily peeled off. In addition, the results of a storage test at 50°C for 3 months were also good.

Table 1

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an example of the packaging container of the present invention, FIG. 2 is a cross-sectional view showing an example of the container main body sheet of the present invention, and FIG. 3 is a structure of an example of the lid body of the present invention. 1 is a cross-sectional view of a laminate, in which reference numeral 1 indicates the container body, 2 indicates the lid, 3A indicates the body wall, and 3B
4 is a bottom part, 4 is a flange part, 5 is a container body sheet, 6 is a metal foil, 7 is an inner polyolefin film, 8 is an outer coating protective layer, 9 is a heat seal part, 10 is a laminate constituting a lid, 11 is a The base body, 12 is an inner coating layer, and 13 is an outer protective layer.

Claims (3)

[Claims] (1) A container formed by heat-sealing a flanged container body and a lid body at the flange portion, wherein the flanged container body is a container body whose at least the inner surface side is formed of polyolefin resin, and the lid body for retorts, characterized in that it is made of a metal foil with an inner surface protective coating formed of a paint containing a small amount of acid-modified polyolefin to impart easy peelability to the heat-sealed surface. packaging container. (2) The container according to claim 1, wherein the acid-modified polyolefin-containing paint is a paint in which acid-modified polyolefin is dispersed in a thermosetting resin paint. (3) The inner surface protective coating is formed by the following formula: l=L/[1+(100/x)・(d_2/d_1)] In the formula, L represents the thickness (μm) of the inner surface protective coating, and x is the number of parts by weight of the acid-modified polyolefin per 100 parts by weight of the thermosetting resin, d_1 is the density of the thermosetting resin (g/cm^3), and d_2 is the density of the acid-modified polyolefin (g/cm^3) 3)
The container according to claim 2, wherein the coverability (l) defined by: is in the range of 0.3 to 10.