JPS636426B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an easy-to-open heat-sealable lid, and more particularly to a heat-sealable lid that has strong heat-sealing strength, can be subjected to sterilization treatment such as retort sterilization, and is easy to open. Regarding.

BACKGROUND ART Conventionally, a so-called peelable seal lid is known as a heat seal lid that has both sealing performance and ease of opening. This peelable seal lid has a layer of heat sealant on a flexible base such as metal foil, and the heat sealant is made by blending wax, tackifier, elastomer, etc. with olefin resin such as polyethylene. In some cases, sealing strength adjusted to the order of 1 kg/15 mm is used. This type of peelable seal lid lacks sealing reliability when the package filled with contents is heat sterilized, and Ministry of Health and Welfare Notification No. 17 (enforced on August 1, 1976) also states that heat sealing Food containers that are sealed and sterilized by pressure and heat are required to have a heat seal strength of 2.3 kg/15 mm or more.

However, it is extremely difficult to peel off the heat-sealed lid sealed with such high sealing strength by hand at the heat-sealed interface;
A tool such as a can cutter is used to open the package.

On the other hand, there is a so-called easy-open can lid, which can be easily opened by hand without using any special equipment. This can lid is made of a can lid made of an aluminum metal sheet, with an opening section marked with a score, a rivet formed in this opening section, and a pull ring fixed with the rivet on this opening section. It is used by double seaming with the flange part of the can body member.

Such easy-open can lids can withstand pressure and heat sterilization and have excellent opening properties, but they require the use of a large amount of expensive aluminum metal material and a complex and time-consuming processing process. Therefore, it has the disadvantage that it is considerably more expensive than the flexible heat seal lid described above.

Moreover, such an easy-open can lid has a limitation in terms of its use, in that the containers to which it can be applied are limited to those with high heat resistance, such as cans.
In other words, it is difficult to double-seal such an easy-open can lid with a plastic cup-shaped container formed by drawing to form a highly reliable seal, and it is difficult to heat it. Under intermediate filling and retort sterilization conditions, the cup flange softens at this temperature, making a reliable seal even more difficult.

Therefore, an object of the present invention is to provide a heat-sealable lid that can form a sealed portion with high heat-sealing strength, can be subjected to sterilization treatment such as retort sterilization, and is easy to open.

Another object of the present invention is to provide an easy-to-open heat-sealed lid that allows the laminated sheet to be sheared smoothly and neatly along the intended opening line when unsealing.

Still another object of the present invention is to provide an easy-to-open heat-sealable lid that can be suitably used for sealing containers that are difficult to double-seal, such as plastic containers or aluminum foil containers.

Still another object of the present invention is to provide an easy-to-open heat-sealed lid that uses a small amount of expensive metal material, is easy to process into a lid, and is therefore relatively inexpensive.

According to the present invention, in the easy-to-open heat-sealable lid for sealing the container body by forming a heat-sealed portion with the container body, the lid is mainly composed of a propylene-based resin inner material and a metal foil. The lid is made of a laminate that is heat-sealed via an acid or acid anhydride-modified olefin resin made of propylene, and a portion to be opened is defined inside the portion of the lid that is to be heat-sealed. There is provided an easily openable heat-sealable lid characterized in that the score is provided so as to reach halfway in the thickness direction of the metal foil from the outside of the lid.

The present invention will be described in detail below based on specific examples shown in the accompanying drawings.

As shown in FIGS. 1, 2 and 3, the heat seal lid 1 of the present invention is made of a laminate including at least a propylene resin inner surface material 2 and a metal foil 3. As shown in FIGS. As shown in more detail in the enlarged view of FIG. 3, inside the portion 4 of the lid 1 that is to be heat-sealed, a score 7 that demarcates the portion 5 to be opened is located midway in the thickness direction of the metal foil 3. It is set up to reach. On the outer surface of this heat-sealed lid, an opening tab 8 having a tearing tip 6 at one end and a gripping portion 6' at the other end is arranged in a positional relationship such that the tearing tip 6 and the score 7 almost match. They are bonded together via an adhesive layer 9.

An important feature of the present invention is that propylene resin is selected as the inner material for heat sealing, and this inner material 2
was thermally fused to the metal foil 3 via a layer 10 of acid- or acid anhydride-modified olefin resin (hereinafter simply referred to as acid-modified propylene resin) whose main constituent olefin monomer is propylene. There is a particular thing.

That is, in order to tear a laminate consisting of a resin film and a metal foil accurately and smoothly along the scores provided on the metal foil, the resin film and the metal foil are subjected to retort sterilization. This is based on the basic knowledge that it is necessary for the resin film to be firmly bonded and to be maintained in a state with little elongation even after undergoing severe heat treatment such as.

That is, when the propylene resin film 2 is thermally fused to the metal foil 3 via the acid-modified propylene resin layer 10, the adhesive strength is higher than when the film 2 and the metal foil 3 are bonded via any other adhesive layer. Also, delamination, that is, delamination during shearing of the laminate, is suppressed. Conventionally, it has been known that isocyanate-based adhesives give the best results as adhesives between propylene-based resin films and metal foils. However, when a laminated material in which the two are bonded together via an isocyanate adhesive is subjected to retort sterilization treatment and then manually torn at the score, separation occurs between the metal foil and the propylene resin film. is recognized. However, when such delamination occurs at the tearing part of the laminate, both the metal foil and the film are torn in different directions from the score, and as a result, the lid can be accurately and smoothly moved along the score. It is difficult to tear and open the seal, and the resin film remains in the opening in the form of fragments or a film.

The ease with which a laminate is torn is also related to the elongation of the film attached to the metal foil, such as a laminate made by heat-sealing a regular polyethylene film to a metal foil, or a laminate made by bonding polypropylene to a metal foil using an isocyanate-based adhesive. In the bonded laminate, the elongation of the film is too large, making it difficult to peel off the film sharply at the score.

The propylene resin used in the present invention has a chemical structure characterized by the presence of every other tertiary carbon atom in the polymer chain, and therefore has the property of being susceptible to thermal degradation. ing. Furthermore, this propylene polymer is characterized in that crystallization tends to proceed at high temperatures.

Thus, in the present invention, when a propylene resin film is heat-sealed to a metal foil through an acid-modified propylene resin layer, the acid-modified propylene resin has a carboxyl group that has a high affinity for the metal foil. Moreover, since the main constituent olefin unit is common to propylene resin, strong interlayer adhesion that can withstand retort sterilization and tearing can be obtained, and it can also resist degradation and crystallization that occur during thermal fusion of propylene resin films. This reduces the elongation of the film itself, which makes it possible to tear accurately and smoothly along the score.

In the present invention, light metal foil such as aluminum foil is preferably used as the metal foil, but it is of course also possible to use iron foil, steel foil, tin foil, etc. From the viewpoint of heat sterilization resistance, these metal foils are preferably subjected to pretreatment such as alumite treatment, boehmite treatment, chemical treatment with phosphoric acid and/or chromic acid, or chemical conversion treatment.

The metal foil needs to have some rigidity so that it can be torn with a score, and from this point of view it is desirable to have a thickness of 50μ or more, particularly 80μ or more. The upper limit of the thickness of the metal foil is desirably 200 μm or less, particularly 150 μm or less, from the viewpoint of economy and prevention of damage to fingers etc. when opening the package.

It is important that the score given to the metal foil stays midway in the thickness direction of the metal foil, from the viewpoint of gas barrier properties, pressure resistance, drop impact resistance, etc. From the viewpoint of the above characteristics and ease of opening, the thickness of the metal foil is in the range of 3/10 to 7/10, especially 2/5 to 3/5, and the thickness of the metal foil remaining in the score part is 20μ or more, especially Preferably, the thickness is 30μ or more.

Isotactic polypropylene is most suitable as the propylene resin, but crystalline propylene/ethylene copolymers can also be used as long as the ethylene content is 15 mol% or less, especially 10 mol% or less. . It is generally desirable that these propylene resins have a melting index (ASTM D-1505) of 5 to 100 g/10 min.
If the thickness of the propylene resin film is too large, it will be difficult to tear the laminate at the score, and if the thickness is too small, the heat sealability will deteriorate.
A range of 100μ is preferable.

As the acid-modified propylene resin, an olefin resin whose main constituent olefin monomer unit is propylene is graft-modified with an ethylenically unsaturated carboxylic acid or its anhydride.

Suitable acid-modified propylene-based resins contain carboxyl groups or their anhydrides in a concentration of 1 to 600, particularly 10 to 300 meq/100g polymer. Furthermore, this modified propylene-based resin has a weight of 5 g /
It is preferable to have a melting tangent of 10 min or more.

As the acid or its anhydride used for modification, the following can be used alone or in combination of two or more.

A. Ethylenically unsaturated carboxylic acids: acrylic acid, methacrylic acid, maleic acid, fumaric acid, crotonic acid, itaconic acid, citraconic acid, 5-norbornene-2,3-dicarboxylic acid.

B Ethylenically unsaturated carboxylic anhydride: maleic anhydride, citraconic anhydride, 5-norbornene-2,3-dicarboxylic anhydride, tetrahydrophthalic anhydride.

Among these, maleic anhydride-modified polypropylene is most advantageous for the purpose of the present invention.

The modification treatment is carried out by introducing the monomer into the main chain or side chain of the propylene resin by known means such as graft copolymerization and terminal treatment. For example, a modified propylene resin can be easily obtained by bringing a backbone polymer consisting of a propylene resin into contact with an ethylenically unsaturated monomer containing an acid group in the presence of a radical initiator or radical initiation means. . The above-mentioned modified propylene resin is generally interposed between the metal foil and the propylene resin layer to a thickness of 0.5 to 20 μm, particularly 1 to 10 μm.

To manufacture the easy-open heat seal lid of the present invention,
Propylene resin film is used as opposed to metal foil.
Heat fusion is performed via a modified propylene resin layer.
This heat fusion can be performed by various means. For example, a modified propylene resin is applied to a metal foil in the form of a film, powder, dispersion, or solution, and then heated to melt the modified propylene resin, and at the same time, the propylene resin previously formed on the metal foil is coated with a modified propylene resin. Layer resin films and fuse them to metal foil. Coating of the modified propylene resin can be carried out by electrostatic coating, electrophoretic coating, roll coating, dip coating, bar coating, thermal spraying, fluidized dipping, etc., or by extrusion coating. The coated metal foil can be heated by high-frequency induction heating, infrared heating, a hot air oven, or the like.

Furthermore, instead of applying the modified propylene resin and the propylene resin separately to the metal foil, both resins are coextruded through a multilayer die, and this coextruded two-layer film is thermally fused to the metal foil. Good too.

In the present invention, it is particularly desirable to crystallize the propylene-based resin or increase the size of the crystals during this heat-sealing from the viewpoint of the above-mentioned ease of opening. The crystallinity of a propylene resin is closely related to the density of the resin. Conventionally, in laminates for retort pouches with propylene resin as the inner material, the laminate was rapidly cooled after heat fusion to suppress crystallization from the viewpoint of pouch strength and heat sealability. ing. On the other hand, in the present invention, the density of the propylene resin is reduced by adopting a slow cooling method as described in detail later.
0.885g/cc or more, especially 0.890g/cc or more.
In addition, by this slow cooling method, the size of the spherulites can be
The thickness should be 12μ or more, especially 15μ or more. still,
The size of spherulites can be determined by a light scattering method.

Fusion of propylene resin is carried out at a temperature above its melting point and below its decomposition temperature, particularly at a temperature of 160 to 260°C. This fusion is easily performed by passing the laminate maintained at the above temperature through a pressure roll, and then quenching the laminate by passing it through a cooling roll (chill roll). In the present invention, at this time, the cooling from fusion to a temperature lower than the crystallization temperature is performed gradually for 2 seconds or more, particularly 3 seconds or more.

The thus formed laminate is press-formed (draw-formed), and formed into a lid by punching, forming a peripheral curl part, and drawing a panel part,
Next, a score is engraved on the metal foil.

The tear tab is then adhered to the top surface of the lid to form the easy-open seal lid of the present invention.

The easy-open seal lid of the present invention can be made of a multilayer laminate of three or more layers. In FIG. 4 showing this example, the outer surface of the metal foil 3 can have a resin protective layer 11. As the resin protective layer 11, high strength plastic films such as biaxially oriented polyester film, biaxially oriented polypropylene film, biaxially oriented nylon film, etc., epoxy-phenol paint, epoxy-urea paint, epoxy-melamine paint, etc. vinyl paint,
Coatings such as acrylic paints and epoxy-acrylic paints are used. When the resin protective layer 11 used is a plastic film, it is necessary that the resin protective layer 11 is completely cut at the position of score 7, as shown in FIG.
If 1 is a paint film, there is no particular problem even if the top of the score 7 is covered with a paint film.

The lid of the present invention can be used for any container, such as a metal can, wide mouth bottle, plastic cup container, metal foil container, etc.
It is advantageously used as a heat seal lid for sealing metal foil/plastic composite containers etc. by heat sealing. In particular, the present invention is advantageous for sealing easily buckling containers that can be double-sealed and packaging containers that require treatments such as hot filling and heat sterilization. Katsupu,
It is suitably used as a heat seal lid for uniaxially or biaxially stretched plastic cups made by plug assist molding, pressure forming, etc., metal foil containers made by drawing molding, and the like. In addition, the shape of the score is not limited to circular, square, rectangular, etc. shapes that open the entire inside of the seal part, but also small circular or raindrop-shaped scores are carved only on a part of the inside of the seal part, and from this part. It is also possible to open it.

In FIG. 5, which shows an example of such a use,
After hot or cold filling the contents into the container body 12 and replacing the atmosphere with water vapor, nitrogen, etc. as necessary, the lid 1 is attached to the container body 12, the flange 13 and the propylene resin film layer 2 on the lid side. Heat sealing is performed by stacking them so that they face each other and heating the flange portions under pressure. This heating temperature is higher than the melting point of the film layer 2, and the pressurization is generally carried out under a pressure of 1 to 10 kg/cm ² gauge. This heat-sealing operation can be performed using, for example, a heat-sealing bar,
This can be easily carried out using a heat sealing means known per se, such as high frequency induction heating.

The heat-sealed portion formed using the lid of the present invention can withstand sterilization operations such as hot filling, boiling water sterilization, and retort sterilization, and has a high degree of sealing reliability. It has the advantage that food products can be stored stably for a long period of time, and that it can be opened easily and reliably.

The excellent effects of the present invention will be explained with the following examples.

Example 1 Thickness of epoxy phenol paint applied to the outside surface
A laminate was produced by thermally bonding a 100μ soft aluminum foil and a 50μ thick polypropylene film with a 10μ thick maleic anhydride modified polypropylene melted at 200°C and cooling it for 3 seconds with a cooling roll. This laminated material was punched, molded, scored, and tabbed to create a lid having the shape shown in FIG. 1. Next, 80 ml of water was poured into a cup made of multilayer plastic material formed by solid-state pressure forming into a truncated cone shape with an inner diameter of 65 mm, a depth of 30 mm, and a flange width and thickness of 3 mm and 0.8 mm. After filling the container, the container was covered with the lid described above and sealed by high-frequency induction heating. The material composition of the multilayer plastic material is, from the outside, B/B'/C/A/C/B'/B.
It is. Here, A is a saponified ethylene-vinyl acetate copolymer with an ethylene content of 30% mol% and a saponification degree of 99.2%, and B is a saponified ethylene-vinyl acetate copolymer with a melt index (ASTM-1238) of 1.4 g/10 minutes and a density (ASTM
D-1505) is 0.91 g/cc of isotactic polypropylene, C is maleic anhydride-modified polypropylene,
B' has a mixing ratio of A:B:C of substantially 5:
It means a mixture of 93:2 (weight ratio).

The sealed container created in this way was heated to 120℃ for 10
When heat sterilization was carried out under sterilization conditions for 30 minutes, there was no abnormality in the container. When this container was opened using a tab at the opening of the lid, it was possible to smoothly open the container along a predetermined score line with an initial opening force of 1.2 kg and a maximum opening force of 2.1 kg. The condition of the opening after opening was good, with no defects such as demamination and feathering.

Example 2 A lid of the desired shape was created by laminating a 100μ thick soft aluminum foil and a 50μ thick polypropylene film adhered using an isocyanate adhesive, and filled with water in the same manner as in Example 1. It was placed in a multilayer plastic cup and sealed, and heat sterilized at 120°C for 10 minutes. After sterilization, when this container was opened from the opening of the lid, delamination, or delamination, occurred at the adhesive interface between the aluminum foil and polypropylene while cutting along the score, making it impossible to continue cutting smoothly along the score. First, the appearance of the container after opening was extremely poor, and it was obviously difficult to take out the contents.

Example 3 A lid in the desired shape was created using a laminated material obtained by heat-sealing a 100μ thick soft aluminum foil and a 50μ thick high-density polyethylene film using molten maleic anhydride modified polyethylene. Then, it was placed on a multilayer plastic cup filled with water (same as in Examples 1 and 2) and sealed. When this container was heat sterilized at 120°C for 10 minutes, delamination occurred at the adhesive interface between the aluminum foil and high-density polyethylene of the lid.

Example 4 A lid of a desired shape was made from a laminated material made by adhering 100μ soft aluminum foil and 50μ high density polyethylene using an isocyanate adhesive. As in Examples 1, 2, and 3, this lid was placed on a multilayer plastic cup filled with water and sealed, and then heated at 120°C.
Heat sterilization was performed for 10 minutes. After sterilization, when this container was opened from the opening of the lid, delamination occurred in the adhesive layer of the aluminum foil and high-density polyethylene, and the high-density polyethylene remained at the opening on the cup side, making it impossible to open.

[Brief explanation of the drawing]

Fig. 1 is a perspective view showing the heat-sealing lid of the present invention, Fig. 2 is a sectional view of the heat-sealing lid of Fig. 1, and Fig. 3 is a partially enlarged sectional view of the heat-sealing lid of Fig. 2. , FIG. 4 is an enlarged sectional view showing another embodiment of the heat-sealing lid of the present invention, and FIG. 5 is a sectional view showing an embodiment of using the heat-sealing lid of the present invention in a container, with reference numeral 1. is a heat seal lid, 2 is a resin inner material, 3 is a metal foil, 6 is a tip for tearing, 6' is a gripping part,
7 is the score, 8 is the opening tab, 9 is the adhesive layer, 1
0 indicates an acid-modified propylene resin layer, 12 indicates a container body, and 13 indicates a flange.

Claims (1)

[Scope of Claims] 1. An easily openable heat-sealable lid for sealing the container body by forming a heat-sealed portion with the container body, the lid comprising an olefin monomer mainly composed of a propylene-based resin inner material and metal foil. The lid is made of a laminate that is heat-sealed via an acid or acid anhydride-modified olefin resin in which the polymer is propylene, and a portion to be opened is defined inside the portion of the lid that is to be heat-sealed. An easy-to-open heat-sealed lid, characterized in that the score is provided so as to reach halfway in the thickness direction of the metal foil from the outside of the lid. 2. The lid according to claim 1, wherein the propylene resin inner material is made of crystalline polypropylene having a density of 0.885 g/cc or more. 3. The lid according to claim 1, wherein the modified olefin resin has carboxyl groups or anhydrides thereof at a concentration of 1 to 600 mEquivalents/100 g of resin. 4. The container lid according to claim 1, wherein the modified olefin resin has a melting index of 5 g/10 minutes or more. 5 The metal foil has a thickness of 50 to 200μ, the modified olefin resin has a thickness of 0.5 to 20μ, and the propylene resin has a thickness of 10 to 150μ, and the score of the metal foil is 3/3 of the thickness of the metal foil. The container lid according to claim 1, which is provided at a depth of 10 to 7/10 and a residual thickness of 20 microns or more.