JPS6119496B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an easy-to-open heat-sealed package, and more specifically, the present invention relates to an easy-to-open heat-sealed package, and more particularly, it has an excellent combination of sealing reliability and easy-to-open properties, and also reduces feathering that occurs when the lid is peeled and opened. The present invention relates to an easy-to-open heat-sealed package that improves the appearance of the unsealed part due to (stringing) etc.

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, in such a blend, different resin components that are difficult to mix with each other are blended with polypropylene, resulting in a non-uniformly dispersed structure.When the lid is peeled off, feathering occurs at the peeled part. There is a problem in that it causes fluffing or stringiness, which is commonly called ``fuzziness'', and causes a poor appearance at the peeled-open portion. This feathering is also thought to be caused by the resin having the above-mentioned dispersed structure becoming fibrillated due to the tension applied during peeling.

The inventors of the present invention have conducted extensive studies on the problem of feathering that occurs when the heat-sealed part is peeled off, and have found that the higher the strength of the entire heat-sealable resin layer, the more likely it is that feathering will occur. First, we learned that the higher the adhesive strength of the polypropylene resin layer to the base material, the less likely it is that phasing will occur, and based on this knowledge, we developed crystalline propylene with a relatively high melt index. A heat-sealable lid is produced by blending a polyethylene resin and polyethylene in a fixed ratio, and extrusion coating this blend onto a base material through an acid or acid anhydride modified propylene resin layer in the form of a thin layer. It has been found that when manufacturing a heat-sealed package, it is easy to obtain a heat-sealed package that has a combination of sealing reliability and ease of opening, and also effectively eliminates feathering.

That is, according to the present invention, the container body is made of polypropylene, and the lid body is provided with a heat-sealable resin layer on the base material, and the polypropylene surface of the container body and the heat-sealable resin layer of the lid body are made of polypropylene. In a package in which heat-sealing is performed between the heat-sealable resin layer and the heat-sealable resin layer,
Crystalline propylene resin with a melt index of 100 and polyethylene with a melt index of 2 to 50 in a ratio of 50:50 to 50:50.
It consists of a layer with a thickness of 5 to 25 microns of a resin blend containing a resin blend in a weight ratio of 95:5, and this resin blend layer is coated with the aforementioned group through a modified propylene resin layer modified with an acid or an acid anhydride. Provided is an easily openable heat-sealed package characterized in that the package is bonded to a material.

The invention will be described in detail below with reference to the accompanying drawings.

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.
It consists of a base material 3 and a heat-sealing resin layer 5 applied to the base material via an adhesive layer 4. The container main body 1 has a heat-sealable part 6 such as a flange, and is arranged so that the polypropylene surface of the heat-sealable part 6 and the heat-sealable resin layer 5 of the lid are in contact with each other.
Heat sealing is performed between the two by pressure heating.

An important feature of the present invention is that this heat sealable resin layer 5
As a melt index (ASTM D-
1238, g/10 min) of 5 to 100, particularly 15 to 50, and polyethylene having a melt index of 2 to 50, particularly 3 to 15,
A resin blend containing a weight ratio of 50:50 to 95:5, particularly 55:45 to 80:20 is used, and this blend is added to the modified propylene resin layer 4 modified with an acid or an acid anhydride. Through the thickness of 5 to
It is provided in the form of a thin layer of 25 microns, especially 7 to 20 microns.

In the present invention, the use of a blend of propylene resin and polyethylene each having a melt index within the above-mentioned high range has a double effect in preventing feathering when opening the package. . In other words, the melt index of these resins is related to the molecular weight of the resin, and by selecting a resin with a high melt index, it is possible to suppress the strength of the entire heat sealable resin layer to a relatively low range. becomes. In addition, by selecting a combination of resins with a high melt index, melt moldability is improved and extrusion coating becomes possible, allowing the thickness of the heat-sealable resin layer to be reduced to 5 to 25 microns, especially a thin layer of 7 to 20 microns. This makes it possible to suppress the strength of the entire heat-sealable resin layer to a lower range.

In the present invention, the fact that the heat-sealing resin layer is within the above-mentioned thin range is also important in terms of preventing feathering, and the layer of propylene resin/polyethylene blend is, for example, 30 mm thick.
If the layer is formed as a thick layer of microns or more, not only will feathering occur when the package is opened, but also cleavage within the layer will occur due to the non-uniform dispersion structure mentioned above, resulting in the thin film after rupture. This may cause inconveniences such as sticking and remaining on the mouth of the container.

Crystalline propylene resin and polyethylene,
Using the blend ratio described above has an important meaning in terms of the combination of sealing reliability and ease of opening. That is, if the blending ratio of polyethylene is less than the above range, the heat seal strength at the heat sealed part tends to be too high, making it difficult to open. If the amount is too high, the heat sealing strength becomes too low, and the sealing reliability is lowered, such as breakage of the sealed portion due to an accidental external force, and furthermore, the film-forming properties of the blend are also deteriorated. According to the present invention, by setting the blending ratio of both resins within the above range, it is possible to adjust the heat seal strength to a range called easy-open heat sealing, that is, a range of 0.5 to 3.0 kg/1.5 cm. .

Furthermore, in order to prevent feathering due to peeling at the heat-sealed part, it is extremely important to thermally bond the above-mentioned resin blend to the gas barrier base material via an acid or acid anhydride-modified propylene resin. It is. That is, crystalline propylene resin/
When a polyethylene blend is extrusion coated onto a substrate using an ordinary isocyanate-based or organic titanate-based anchoring agent, even when the above-mentioned conditions are met, feathering still occurs when the package is opened. cannot be avoided. According to the present invention, the resin blend to be extruded is extrusion coated onto the substrate via the acid or acid anhydride modified propylene resin layer, so that the resin blend adheres to the substrate and prevents feathering. outbreak is prevented.

In the easy-open heat-sealable package of the present invention, as described above, the heat-sealable resin layer has a structure weakened by the blend of polyethylene by selecting the melt index; The heat-sealable resin layer is provided with a considerably thinner thickness than conventional ones. Furthermore, this weakened heat-sealable resin layer is extremely firmly bonded to the base material via the modified propylene resin layer. When peeling is performed by tension between the heat-sealed lid and the container body flange, peeling will inevitably occur in the vicinity of the container body flange.
Furthermore, the heat-sealing resin layer is easily broken at the edge portion of the flange, thereby preventing fage ring and film tearing.

In the present invention, the propylene resin includes:
In addition to crystalline (isotactic) polypropylene, crystalline propylene-ethylene copolymers can also be used. As the polyethylene, any of low density, medium density, and high density polyethylene can be used. From the viewpoint of extrusion coatability, particularly melt tension, it is particularly desirable to use low density polyethylene with a density of 0.935 g/cc or less.

The heat-sealing blend of the present invention may contain a third resin component to improve its compatibility. As such a third resin component,
Ethylene-vinyl acetate copolymer, ethylene-acrylate copolymer, crystalline ethylene-propylene copolymer, crystalline ethylene-propylene-butene-1 copolymer, ethylene-propylene rubber, ethylene-propylene-nonconjugated diene - Rubber and ionically crosslinked olefin copolymers (ionomers) may be used alone or in combination of two or more. These third resin components are polypropylene
It is preferable to use it in an amount of 5 to 30 parts by weight per 100 parts by weight.

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 modified propylene resin, those obtained by graft-modifying a backbone polymer such as crystalline polypropylene or crystalline propylene-ethylene copolymer with an ethylenically unsaturated carboxylic acid or its acid anhydride are used. Suitable examples of acids and acid anhydrides to be used are as follows.

A Ethylenically unsaturated carboxylic acid: 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, itaconic anhydride, 5-norbornene-2,3-dicarboxylic anhydride, tetrahydrophthalic anhydride.

These ethylenically unsaturated carboxylic acids or their anhydrides have a carboxyl group of 5 to 600 milliequivalents (meq)/100g of the polymer, especially
It is preferably bound into the backbone polymer at a concentration of 10 to 300 (meq)/100 g of polymer.

The modified propylene resin can be applied to the substrate by various methods, such as applying it in the form of a solution or dispersion, applying it in the form of a powder or film, or extrusion coating in the form of a melt. will be adopted. Generally speaking, the thickness of the modified propylene resin layer is preferably in the range of 1 to 50 microns, particularly 3 to 20 microns.

The aforementioned blend is extrusion coated onto the base material coated with this modified propylene resin. The above-mentioned resins may be mixed by dry blending and this mixture may be directly supplied to a film-forming extruder, or after being kneaded in advance with a pelletizer, mixer, etc.
It may also be supplied during extrusion. Of course, these resin compositions contain additives that are well known per se, such as lubricants,
One or more of antioxidants, antiblocking agents, fillers, tackifiers, impact modifiers, etc. can be blended according to known formulations.

Extrusion coating can be carried out by means known per se, except that the thickness of the final heat-sealable resin layer is within the range specified in the present invention. In order to make the thickness of the coating layer as thin as possible, the feeding speed of the base material is increased compared to the extrusion speed of the resin blend from the die lip so that the extruded resin film is sufficiently stretched. It is better. A blend of polyethylene, especially low-density polyethylene within the above range, is particularly excellent in such drawdown properties. Thermal bonding of the blend layer to the base material may be performed at the same time as extrusion coating, but generally the laminate after extrusion coating is heated to melt the modified propylene resin layer and blend layer to complete thermal bonding. It is better to let

It should be understood that instead of separately coating the modified propylene resin layer and the blend layer, both layers can be coextruded through multiple dies and the coextrudate coated onto the substrate.

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 Maleic anhydride was grafted onto isotactic polypropylene on the aluminum side surface of a laminate in which a 12μ thick biaxially stretched polyethylene terephthalate film and a 50μ thick aluminum foil were bonded together using a urethane adhesive. Average carboxyl group concentration is 20meq/100g polymer, melting point is
Using a first extruder having a screw with a diameter of 50 mmφ, modified polypropylene with an MI of 40 g/10 min at 163°C, and with a melting point of 154°C and a density of 0.90 g/cm ³ ,
MI is 25g/10min, ethylene-propylene with 5 mol% ethylene content, 60% by weight random copolymer, melting point 109℃, density 0.915g/cm ³ , MI 12
A dry blend of 40% by weight of low-density polyethylene at a rate of g/10min is processed by a second extruder with a screw of 65mmφ in diameter at a resin temperature of 230°C at the die part, and then extruded into a coat hanger type 2 with a width of 650mm. The modified polypropylene is co-extruded from a layer T-type die in a positional relationship in contact with the aluminum foil, and a chill roll with a diameter of 400 mmφ and a chill roll with a diameter of 200 mm are coated.
Temporary adhesion was performed by pressing with a mmφ silicone roll. Next, this temporarily bonded laminate is thermocompressed using a heat treatment roll with a diameter of 400 mmφ maintained at a temperature of 200°C and a silicone roll with a diameter of 200 mmφ.
By cooling with a silicone roll of 200 mmφ, a laminate having a structure of 12μ biaxially oriented polyethylene terephthalate layer/50μ aluminum foil/5μ modified polypropylene layer/10μ ethylene-propylene copolymer blend layer was obtained.

Next, a circular lid member with a diameter of 75 mm and a tab was punched out from this laminate.

Next, the 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 cup had a flange at the opening and had a diameter of 75 mmφ. 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 tab was opened, it was easy to open, and no feathering was observed on the peeled surface of the flange. The seal strength of the seal lid was separately measured and found to be 1210 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 for 2 seconds to determine the seal strength (T-peel).
Figure 2 shows the measurement results. 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 Maleic anhydride was grafted onto isotactic polypropylene on the aluminum side surface of a laminate in which a 12μ thick biaxially stretched polyethylene terephthalate film and a 30μ thick aluminum foil were bonded together using a urethane adhesive. Average carboxyl group concentration is 25meq/100g polymer, melting point is
Modified polypropylene powder with an MI of 90 g/10 min at 162°C was applied by electrostatic coating and fixed on the aluminum surface by high-frequency induction heating. Next, the melting point is 154℃, the density is 0.90g/cm ³ , and the MI is 25.
g/10min, 65% by weight ethylene-propylene random copolymer with 5 mol% ethylene content, melting point 109℃, density 0.915g/cm ² , MI 12g/cm 2
10min low density polyethylene 20% by weight and melting point
104℃, density 0.927g/10min, MI 9g/
For 10 min, a dry blend of 15% by weight of ethylene-vinyl acetate copolymer with a vinyl acetate content of 10% by weight was passed through a T-die with a width of 650mm using an extruder having a screw with a diameter of 65mmφ to form the modified polypropylene of the laminate. Melt extrusion coating is applied to the powder coated surface, and a chill roll with a diameter of 400mmφ and a diameter of 200mm are applied.
Temporary adhesion was performed by pressing with a φ silicone roll. Next, this temporarily bonded laminate is thermocompressed using a heat treatment roll with a diameter of 400 mmφ maintained at a temperature of 200°C and a silicone roll with a diameter of 200 mmφ.
By cooling with mmφ silicone roll,
A laminate having a structure of 12μ biaxially oriented polyethylene terephthalate layer/30μ aluminum foil/2μ modified polypropylene layer/15μ ethylene-propylene copolymer ternary 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 orange 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. Separately, the seal strength of the seal lid was measured and found to be 1350 g/1.5 cm.

Comparative Example 1 Instead of coating the aluminum foil surface with modified polypropylene powder in Example 2, a urethane-based anchoring agent was applied, and after drying, the same ethylene-propylene copolymer ternary as used in Example 2 was applied thereon. By extrusion coating the blend, the composition is 12μ biaxially oriented polyethylene terephthalate layer/30μ aluminum foil/15μ ethylene layer.
A laminate of propylene copolymer ternary blend layers was obtained.

Using this laminate, a sealing lid similar to that in Example 2 was prepared, and a similar aluminum molded cup was filled and sealed. When this seal lid was peeled off and opened, peeling occurred between the aluminum foil of the seal lid and the ethylene-propylene copolymer ternary blend layer, and a film of ethylene-propylene copolymer remained on the flange of the aluminum molded cup. .

Comparative Example 2 A film with a thickness of 70μ was formed using the same ethylene-propylene copolymer blend as that used in Example 2 by the T-die method, and the film was coated with the base material used in Example 2 and the urethane adhesive. A laminate having a structure of 12μ biaxially stretched polyethylene terephthalate layer/30μ aluminum foil/70μ ethylene-propylene ternary blend layer was obtained.

A sealing lid similar to that in Example 2 was made using this laminate, and a similar aluminum molded cup was filled and sealed, and the sealing lid was peeled off and opened.
Fasering occurred on the flange of the aluminum molded cup.

Example 3 On the surface of a base material with a composition of 70 μ paper / 15 μ maleic anhydride modified polypropylene layer / 9 μ aluminum foil,
The average carboxyl group concentration of isotactic polypropylene grafted with maleic anhydride is
50meq/100g polymer, melting point 164℃, MI 35
g/10min modified polypropylene 50% by weight, melting point 156℃, density 0.90g/cm ³ , MI 25g/10min,
A blend of 50% by weight of an ethylene-propylene random copolymer with an ethylene content of 4 mol% is extrusion coated from a first T-die with a width of 650 mm using an extruder having a screw with a diameter of 65 mmφ. Next, melting point is 154℃, density is 0.90g/cm ³ , MI
25g/10min, 65% by weight ethylene-propylene random copolymer with 5 mol% ethylene content
The melting point is 132℃, the density is 0.950g/ ^cm3 , and the MI is 3g/cm3.
10min medium density polyethylene 20% by weight and melting point
At 109℃, a dry blend of 15% by weight of low density polyethylene with a density of 0.915g/cm ³ and an MI of 12g/10min was extruded from a second T-die with a width of 65mm using an extruder with a screw having a diameter of 65mmφ. I went to court. Next, this temporarily bonded laminate is heated to a temperature of 200℃.
Heat treated in an oven kept at ℃, and the diameter
By cooling with a 400mmφ chill roll and a 200mmφ diameter silicone roll, the composition is 70μ paper/
15μ modified polypropylene layer / 9μ aluminum foil / 10μ modified polypropylene layer / 10μ ethylene
A laminate of propylene copolymer ternary blend layers was obtained.

A seal lid was punched out from the laminate thus obtained, and after filling the cup made of the paper/aluminum foil/polypropylene layer laminate with sake, the seal lid was heat-sealed to the flange of the container by high-frequency induction heating. When this heat-sealed seal lid was opened from the tab part, it was easy to open and no feathering was observed on the peeled surface of the flange part. We also measured the seal strength of the seal lid and found that it was 1540.
g/15mm.

[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. It is a diagram showing the reference numeral 1, the container body made of polypropylene, 2 the lid, 3 the base material, 4 the adhesive layer,
Reference numeral 5 indicates a heat-sealable resin layer, and 6 indicates a portion to be heat-sealed.

Claims (1)

[Claims] 1. Consisting of a container body made of polypropylene and a lid having a heat-sealing resin layer on a base material, the polypropylene surface of the container body and the heat-sealing resin layer of the lid. In a package that is sealed by heat sealing between the two, the heat sealable resin layer has a melt index of
It consists of a 5 to 25 micron thick layer of a resin blend containing a crystalline propylene resin having a melt index of 2 to 100 and a polyethylene having a melt index of 2 to 50 in a weight ratio of 50:50 to 95:5; An easily openable heat-sealed package, characterized in that the blend layer is bonded to the base material via a modified propylene resin layer modified with an acid or an acid anhydride. 2. The package according to claim 1, wherein the polyethylene is low-density polypropylene with a density of 0.935 g/cc or less. 3 Crystalline propylene resin and polyethylene
The package according to claim 1, which is a resin blend containing the resin at a weight ratio of 50:50 to 95:5. 4. The package according to claim 1, wherein the resin blend layer is applied by extrusion coating. 5 The resin blend layer contains 5 to 30 parts by weight of ethylene-vinyl acetate copolymer, ethylene-acrylate copolymer, crystalline ethylene-propylene copolymer, crystalline ethylene per 100 parts by weight of crystalline propylene resin. - The package according to claim 1, which contains a propylene-butene-1 copolymer, ethylene-propylene rubber, ethylene-propylene-nonconjugated diene rubber, or an ionically crosslinked olefin copolymer (ionomer). . 6. The modified propylene resin is a propylene resin modified with an ethylenically unsaturated carboxylic acid or its anhydride containing carboxyl groups at a concentration of 5 to 600 mm equivalent/100 g of polymer. The package according to scope 1. 7. The package according to claim 1, wherein the modified propylene resin layer has a thickness of 1 to 50 microns. 8. The package according to claim 1, wherein the resin blend layer and the modified propylene resin layer are coated on a base material by multilayer coextrusion.