JPS6239630B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an easy-to-open heat-sealable package, and more specifically, the present invention relates to an easy-to-open heat-sealable package, and more specifically, the present invention relates to an easy-to-open heat-sealable package, and more particularly, to a defective appearance of the opened part due to feathering (stringing) that occurs when the lid is peeled and opened, and a poor appearance of the heat-sealable resin layer of the lid. The present invention relates to an easy-open heat-sealed package with improved smoothness. Conventionally, the container body consists of a thermoplastic plastic such as polypropylene, and a lid body with a heat-sealable resin layer on a base material such as metal foil. BACKGROUND ART Packaging bodies that are sealed with a sealing resin layer by heat sealing are widely used in fields such as food packaging. This heat-sealing resin layer can not only be heat-sealed to the polypropylene surface to form a heat-sealed structure with excellent sealing reliability, but also the formed heat-sealed structure can be easily opened by hand. It must have enough strength to be peelable. For this purpose, the heat sealable resin layer is
The base material used is polypropylene, which is blended with a resin or rubber that does not exhibit fusion properties to polypropylene, or if it does exhibit it, the degree of fusion is low. However, such blends contain different resin components that are difficult to mix with polypropylene, so it is necessary to form the blend into a film that has a uniform thickness and a smooth appearance. This in itself is difficult, and the heat-sealable resin layer that forms the inner surface of the lid often has a matte finish and tends to have poor appearance characteristics and smoothness. In addition, as a result of the difficulty in making the two components compatible with each other, the strength of this braided product itself is generally low, and when the lid is peeled off, the heat-sealable resin layer exhibits cohesive failure, resulting in a poor appearance of the peeled part. It also has the disadvantage of being defective. Furthermore, if the blended resin component is soft such as low-density polyethylene, it tends to cause fuzzing or stringing, commonly called feathering, at the peeled part, resulting in poor appearance at the peeled part. Is recognized. The present inventors have developed a product in which polypropylene is blended with polyethylene having a density of 0.94 g/cc or more and an ethylene-vinyl acetate copolymer with a vinyl acetate content of 3 to 15% by weight. When used as a heat-sealable resin layer, the above-mentioned drawbacks of conventional packaging are eliminated at once, and the appearance characteristics of the inner surface of the lid and the unsealed part, heat-sealability, sealing reliability, ease of opening, and resistance to sterilization are improved. It has been found that a package with an excellent combination of heat resistance and the like can be obtained. According to the present invention, the container main body is made of polypropylene, and the lid body is provided with a heat-sealing resin layer on the base material, and the polypropylene surface of the container body and the heat-sealing resin layer forming the lid are bonded to each other. In a package in which heat-sealing is performed between the layers, the heat-sealable resin layer is made of a crystalline propylene-based resin, with a density of 0.94 g/cc of 5 to 80% by weight per propylene-based resin.
Vinyl acetate content of 5 to 50% by weight per polyethylene and polypropylene resin of 3 to 15%
An easy-open, heat-sealable package is provided comprising a blend of ethylene-vinyl acetate copolymer in a weight percentage of ethylene-vinyl acetate copolymer. In FIG. 1 showing the heat-sealed package of the present invention,
This package consists of a container body 1 made of polypropylene and a lid 2.
consists of a base material 3 and a heat-sealable resin layer 4 applied to the base material 3. The container main body 1 has a heat-sealable part 5 such as a flange, and the polypropylene surface of the heat-sealable part 5 is arranged so as to be in contact with the heat-sealing resin layer 4 of the lid, and there is no air between the two. Heat sealing is performed by pressurizing and heating. An important feature of the present invention is that this heat sealable resin layer 4
As, crystalline propylene resin and density 0.94
The purpose is to use a blend of polyethylene with a polyethylene content of at least g/cc and an ethylene-vinyl acetate copolymer with a vinyl acetate content of 3 to 15% by weight. Conventionally, it has already been known to use polypropylene blended with medium-low pressure polyethylene as a heat-sealable resin layer (Japanese Patent Application Laid-open No. 59596/1983). However, with this blend, it is difficult to make polyethylene compatible with polypropylene, and therefore, as mentioned above, there are problems such as poor film forming properties, poor surface appearance and smoothness, and cohesive failure of the layer itself upon peeling. Disadvantages are often observed, such as the tendency to cause oxidation, and the tendency to cause phasing at the interface after peeling. In contrast, when polypropylene is blended with polyethylene having a density of 0.94 g/cc or more and an ethylene-vinyl acetate copolymer having a vinyl acetate content of 3 to 15% by weight in accordance with the present invention, such drawbacks can be effectively overcome. It was discovered that this can be done. Moreover, this improvement according to the invention is only achieved when both resin components are blended together. In other words, in a blend of polypropylene and ethylene-vinyl acetate copolymer alone, compared to a blend of polyethylene alone, significant feathering occurs at the interface after peeling, resulting in an extremely poor appearance. It becomes. On the other hand, when both resins are blended together in polypropylene according to the present invention, the occurrence of feathering at the interface after peeling is effectively suppressed, and the film-forming properties of the heat-sealable resin layer and the surface It has been found that the appearance, smoothness, etc. of the resin layer are significantly improved, and the tendency for the mechanical strength of the resin layer itself to decrease significantly is suppressed. Although the exact reason for this is unknown, the ethylene-vinyl acetate copolymer used in the present invention exhibits excellent compatibility with both polyethylene and polypropylene, and the ethylene-vinyl acetate copolymer is used as a mediator. This is presumed to be due to the improved compatibility between polypropylene and polyethylene. In the present invention, the propylene resin includes:
In addition to crystalline (isotactic) polypropylene, crystalline propylene-ethylene copolymers can also be used. The molecular weight thereof is preferably in the range of 0.2 to 80 g/10 min as expressed by melt index. As the polyethylene, polyethylene having a density of 0.94 g/cc or more, particularly 0.945 g/cc or more is used. Such polyethylene is readily available as medium to high density polyethylene. Ordinary low-density polyethylene has a problem with the heat resistance of the heat-sealed part, and also tends to cause the aforementioned feathering in the peeled and unsealed part, making it unsuitable for the purpose of the present invention.
The polyethylene preferably has a melt index in the range of 0.2 to 20 g/10 min. As the ethylene-vinyl acetate copolymer, one having a vinyl acetate content of 3 to 15% by weight, particularly 5 to 10% by weight is used. That is, if the vinyl acetate content is outside the above range, it cannot be expected to have the effect of increasing the compatibility between polyethylene and polypropylene, and if this content is high, the heat resistance of the heat-sealed part will decrease. There are also problems in terms of flavor retention and extraction resistance for food contents. The melt index of the ethylene-vinyl acetate copolymer is preferably in the range of 0.2 to 30 g/10 minutes. In the present invention, 5 to 80% by weight, more preferably 10 to 60% by weight of polyethylene and 5 to 50% by weight, more preferably 8 to 30% by weight of ethylene-acetic acid, based on the crystalline propylene resin. It is also important to blend it with a vinyl copolymer. That is, if the blending amounts of both resins are outside the above range, it becomes difficult to maintain heat sealability and easy peelability while completely preventing feathering from occurring at the peeling interface. The three-component resin blends described above have excellent compatibility, so they are usually mixed by dry blending and simply feeding this mixture to a film-forming extruder can improve film-forming properties, smoothness, and homogeneity. It can be made into an excellent blend. Of course, it is also possible to knead this three-component composition in advance with a pelletizer or the like and feed the pellets to the extruder, but it should be understood that such considerations are generally not necessary. Of course, these resins may contain one or more compounding agents known per se, such as lubricants, antioxidants, antiblocking agents, colorants, fillers, tackifiers, impact modifiers, etc. More than one species can be blended according to known formulations. To form the blend into a heat sealable resin layer,
Known film forming methods such as an inflation film forming method and a T-die (cast) film forming method are used. Moreover, instead of forming the film into a film shape in advance, the heat-sealable resin layer can also be formed by extrusion coating onto the base material. The thickness of the heat sealable resin layer is generally 10 to 80 μm.
It is desirable that it be within the range of . As a base material, metal foil such as aluminum foil, tin foil, steel foil, tin foil, biaxially stretched polyethylene terephthalate film, biaxially stretched nylon film, etc.
Thermoplastic resin films such as polycarbonate films, various papers, and laminates thereof are used. In the case of a transparent lid, a film base material such as nylon or polyester is used,
On the other hand, in the case of a lid that strictly requires gas barrier properties, aluminum foil or a laminate of aluminum foil and film or paper is used as the base material. As the container body, various molded containers are used in which the constituent material is polypropylene and the heat-sealed portion is made of polypropylene. Of course, this container is a blow-molded container made solely of polypropylene,
It may be an injection-molded container, or a draw-molded container by pressure forming, plug-assist molding, vacuum forming, etc. from a film, sheet, etc., or a container formed from a laminate of polypropylene and other plastics, paper, metal foil, etc. It may be a similar container. The heat sealing operation can be performed using a heat sealing means known per se such as a heat seal bar, high frequency induction heating, etc. The package according to the present invention can be easily heat-sealed,
Not only is it possible to form a heat-sealed part that has excellent sealing reliability and can withstand heat sterilization, but it also has the excellent advantage of being easy to open by peeling, and opening can be done without leaving any feathering on the peeled part. has. The invention is illustrated by the following example. Example 1 Melting point is 150°C, density is 0.90g/cm ³ , MI is 7g/cm 3
10min ethylene-propylene copolymer 60% by weight, melting point 135℃, density 0.955g/cm ³ , MI 0.5
g/10min high density polyethylene 30% by weight, melting point 106℃, density 0.92g/cm ³ , MI 2g/cm 3
For 10 min, a dry blend of 10% by weight of ethylene-vinyl acetate copolymer with a vinyl acetate content of 5% by weight was melt-extruded from a single-layer die using an extruder with a screw diameter of 65mmφ, and the inflation A film having a thickness of 30 μm and having one side subjected to corona discharge treatment was obtained by this method. The blended film thus obtained and an 80 μm thick aluminum foil with printing on one side were laminated using an isocyanate adhesive.
Next, a circular lid member with a diameter of 75 mm and a tab was punched out from this laminated sheet. Next, coffee jelly was molded from a laminated sheet having a layered structure of polypropylene/maleic anhydride-modified polypropylene/ethylene-vinyl alcohol copolymer/maleic anhydride polypropylene/polypropylene, and the coffee jelly was placed in a cup with a diameter of 75 mmφ and a flange at the opening. The sealing lid was then heat-sealed to the opening flange. This filled and sealed cup was retort sterilized at 105°C for 30 minutes. As a result of this retort sterilization, no damage to the seal portion was observed, and the sealing performance was perfect. Furthermore, when the seal lid was opened from the tab portion, it was easy to open and no feathering was observed on the peeled surface of the flange portion. The seal strength of the seal lid was separately measured and found to be 1430 g/1.5 cm. Furthermore, a test piece with a width of 1.5 cm was cut out from the seal lid material and heat-sealed to a polypropylene laminated sheet under various temperature conditions at a constant pressure of 2 Kg/cm ² and a constant time of 2 seconds to determine the seal strength (T-peel).
The results of the measurements are shown in Figure 2. As is clear from the figure, it was possible to peel from the seal interface over a wide temperature range, and the seal strength was maintained at a low value. Furthermore, when retort sterilization was performed at 120°C for 30 minutes, there was almost no difference in the seal strength before and after the retort. Example 2 A biaxially oriented polyethylene terephthalate film with a thickness of 12μ and an aluminum foil with a thickness of 30μ were laminated using a urethane adhesive. An isocyanate-based anchoring agent is applied to the aluminum foil surface of this laminated sheet, dried, and the anchoring agent-coated surface is coated with
Melting point is 149℃, density is 0.90g/cm ³ , MI is 22g/cm 3
10min ethylene-propylene copolymer 60% by weight, melting point 131℃, density 0.950g/cm ³ , MI 10
g/10min high density polyethylene 25% by weight, melting point 104℃, density 0.927g/10min, MI 9g/10min
For 10 min, melt-extrusion coat a dry blend of 15% by weight of ethylene-vinyl acetate copolymer with a vinyl acetate content of 10% by weight through a T-die with a width of 650mm using an extruder with a screw having a diameter of 65mmφ. As a result, a laminated sheet having a configuration of 12μ biaxially oriented polyethylene terephthalate layer/30μ aluminum foil/30μ blend layer was obtained. A circular seal lid with a diameter of 70 mmφ and a tab was punched out from the laminated sheet thus obtained, and the configuration was
A cup having a diameter of 70 mm and having a flange at the opening formed from a laminated sheet of 70 μ polypropylene/100 μ aluminum foil was filled with fruit jelly, and the sealing lid was heat-sealed to the opening flange. This filled and sealed cup was retort sterilized at 120°C for 30 minutes. As a result of this retort sterilization, no damage to the seal portion was observed, and the sealing performance was perfect. Furthermore, when the seal lid was opened from the tab portion, it was easy to open, and no feathering was observed on the peeled surface of the flange portion. The seal strength of the seal lid was separately measured and found to be 1280 g/1.5 cm. Comparative Example 1 As a blend in Example 1, Example 1
60% by weight of the same ethylene-propylene copolymer used in and 40% by weight of high-density polyethylene.
When a film was formed using the inflation method, the bubbles were extremely unstable, resulting in a film with many wrinkles and thickness fluctuations. Moreover, the smoothness of the obtained film was also poor. A seal lid similar to that in Example 1 was prepared using this film, and the same filling test was conducted. The seal strength of the seal lid was measured, and the opening performance was poor at 1710 g/1.5 cm. Furthermore, the peeled surface was not smooth. Comparative Example 2 In Example 1, Example 1 was used as a blend.
A film was formed using 60% by weight of the same ethylene-propylene copolymer and 40% by weight of the same ethylene-vinyl acetate copolymer used in Example 1, and the same sealing lid as in Example 1 was prepared and the same filling test was conducted. As a result, the seal strength of the seal lid was found to be 700 g/1.5 cm, which was insufficient. Additionally, feathering was observed on the peeled surface of the flange. Examples 3 and 4 Seal layer films were formed using the materials shown in Table 1 by the same inflation method as in Example 1 to obtain laminated sheets having the configurations shown in Table 1. Seal lids were punched out from the laminated sheet thus obtained, and after filling the containers shown in Table 2 with the contents of Table 2, the seal lids were thermally fused to the container flange portions using a heat sealer. The filled and sealed cups were subjected to retort sterilization at 105°C for 30 minutes in Example 3 and at 115°C for 30 minutes in Example 4. As a result of this retort sterilization, no damage to the seal portion was observed, and the sealing performance was perfect. Furthermore, when the seal lid was opened from the tab portion, it was easy to open and no feathering was observed on the peeled surface of the flange portion. The seal strength of the seal lid was measured separately and was as shown in Table 2. Examples 5 and 6 Laminated sheets having the configurations shown in Table 1 were obtained by the same extrusion coating method as in Example 2 using the materials shown in Table 1, respectively. Seal lids were punched out from the laminated sheets thus obtained, and the containers shown in Table 2 were filled with the contents of Table 2, and then the seal lids were heat-sealed to the container flange portions by high-frequency conduction heating. When this heat-sealed seal lid was opened from the tab portion, it was easy to unseal, and no feathering was observed on the peeled surface of the flange portion. Further, the seal strength of the seal lid was measured, and the results were as shown in Table 2.

【table】

【table】

【table】 [Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the structure of a sealed container sealed with an easy-to-open seal lid, which is an embodiment of the present invention, and FIG. In this diagram, reference numeral 1 indicates a container body made of polypropylene, 2 indicates a lid, 3 indicates a base material, 4 indicates a heat-sealable resin layer, and 5 indicates a portion to be heat-sealed.

Claims (1)

[Claims] 1 Consists of a container body made of polypropylene and a lid with a heat-sealing resin layer on the base material, and a heat-sealing layer is formed between the polypropylene surface of the container body and the heat-sealing resin layer of the lid. In the sealed package, the heat-sealing resin layer is
Crystalline propylene resin, polyethylene with a density of 0.94 g/cc or more and 5 to 80% by weight per said propylene resin, and 5 to 50% by weight per said polypropylene resin.
1. An easily openable heat-sealed package comprising a blend of ethylene-vinyl acetate copolymer having a vinyl acetate content of 3 to 15% by weight.