JPH0539393A - Resin composition for heat sealing - Google Patents

Abstract

PURPOSE:To provide a resin composition which facilitates heat sealing and can give a constant opening strength over a wide temperature range. CONSTITUTION:The objective sealant composition consists of 65-90wt.% crystalline polypropylene resin and 35-10wt.% ethylene/propylene random copolymer having a melt index greater than that of the propylene resin. With this composition, opening is effected not by interfacial separation generally employed in heat sealing but by the cohesive failure of a sealant layer; therefore, the opening strength can be estabilished by adjusting the breaking strength of the sealant without being affected by heat sealing conditions.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is easy to heat seal, has a proper sealing strength, and has a uniform size upon opening, not by interfacial peeling which is affected by heat sealing conditions but by cohesive failure of the sealant layer. The present invention relates to a heat-sealing resin composition having peel strength, and an easily-openable container, a lid material and a film for automatic packaging using the resin composition.

[0002]

2. Description of the Related Art Conventionally, a heat-sealable resin layer is provided on a laminated container substrate using a gas barrier film such as a saponified ethylene-vinyl acetate copolymer film, a vinylidene chloride film or an aluminum foil, or a metal foil. A container body and a lid provided with a heat-sealable resin layer on a base material such as a synthetic resin film or a metal foil, and the heat-sealable resin surface of the container and the heat-sealable resin surface of the lid. A simple packaging container that is sealed by heat sealing is widely used in the field of food packaging containers and the like because of its superiority in cost, lightness, and productivity.

Regarding the heat-sealing strength of these packaging containers, not only a heat-sealing structure excellent in gas barrier property and sealing reliability can be formed, but also the formed heat-sealing structure can be easily peeled by hand when opening. It must have a certain level of strength, and it is generally said that a peel strength of 800 to 1500 g / 15 mm is suitable.

For example, in order to obtain sealing reliability, as shown in FIG. 2, two laminates using a heat-sealable film such as polyethylene are superposed on the innermost layer 1 and a heat-sealing portion is provided and sealed. there were. However, when this is unsealed, in general heat sealing, the heat sealing strength is so strong that it is generally very difficult to open it.

Therefore, as an improvement method which has been carried out to improve the unsealing property, as disclosed in JP-B-46-35513, both sealing layers are made of a thin film containing at least one polyolefin, and the sealing is performed. There is an easy-open technology that allows the parts to be separated along the first interface without breaking the constituent materials.

However, this technique is used in the case of a combination of certain polyolefin-containing thin films (for example, a film made of a blend of polyisobutylene and an ethylene-butene copolymer and a polypropylene film, an ionomer resin film and a low-density polyethylene). It is effective only in combination with the film, etc.), and must be polyisobutylene and / or ethylene-butene copolymer or ionomer resin, which is inferior in processability and expensive as a constituent material of the one-side seal layer. However, there is a drawback that these materials are special.

In addition, as a method of making the sheet easy to open, the sealing strength (interfacial peel strength) is appropriately controlled by changing the composition of the resin constituting the sealing layer of the lid material (for example, 600 to 1000 g / mm). There is one that peels off the interface between the lid and the container to open the container.

However, the sealing strength depends on the sealing condition,
It is easily affected by environmental temperature and adhesion of contents, and variations in strength often occur. If this variation is biased toward the weak side, there is a risk of leaking the seal. Conversely, if it is biased toward the strong side, the peeling property deteriorates and it becomes difficult to open the seal. In general, seal leakage is a fatal defect, and in order to avoid this phenomenon and ensure safety, the sealing temperature and pressure are increased even if the easy-open property is sacrificed.

In order to solve such problems, a method of opening the heat seal layer by delamination between the heat seal layer and a layer adjacent to the heat seal layer (for example, Japanese Patent Publication No. 50-37598) has been tried. In the method, the sealing layer did not break well and the difficulty of opening was not so different.

A method has also been proposed in which a flange is provided with a notch in order to facilitate the separation between the release layer and the adjacent layer (JP-A-62-251363 and JP-A-63).
-78, JP-A-63-25037, JP-B-63-44467 and the like) have a container of these structures, the periphery of the container at the cut portion must be sealed from the outside at the manufacturing stage. Therefore, there is a manufacturing problem that strict control is required for position stability during sealing. In addition, in the method of peeling the main container seal layer and the seal layer, it is necessary to start the peeling from the peripheral edge portion because of the sealing up to the peripheral edge portion of the flange portion. It had the drawback of being constrained.

Further, it has been proposed to use a polypropylene as a heat-sealable resin layer, which is blended with a resin which does not exhibit fusion-bonding property to polypropylene or which has a small degree to that extent. For example, in JP-A-58-1672, as a heat seal layer, a crystalline propylene resin having a melt flow rate of 5 to 100 g / 10 min and a melt flow rate of 2 to 50 are used.
g / 10 min polyethylene with 50:50 to 9
It is described to use a resin blend layer containing a weight ratio of 5: 5.

However, in such a blend, since different resin components which are hard to be compatible with each other are dispersed in polypropylene, the peel strength varies when the lid is peeled off, and the easy peelability is aimed at. There was a problem that it was difficult to achieve.

[0013]

Since the conventional heat-sealing resin composition is prepared by peeling the seal interface, its adhesive strength is affected by the heat-sealing conditions, and in general, incomplete sealing is caused. For the purpose of prevention, stronger heat sealing is performed than necessary. Therefore, such a sealed container is not only difficult to open, but may even destroy the container body.

The present invention is a resin composition for a heat sealant, which can be completely sealed by performing strong heat sealing in packaging, and is not peeled off at the seal interface at the time of opening, and can be opened by cohesive failure of the sealant layer by a stable force. Another object is to develop an easy-open container using this resin composition.

[0015]

According to the present invention, a crystalline polypropylene resin (65 to 90% by weight) and an ethylene-propylene random copolymer having a melt flow rate higher than that of the crystalline polypropylene resin (35 to 10% by weight) are used. The present invention relates to a heat-sealing resin composition comprising: Furthermore, a multilayer film containing at least a gas barrier resin layer and the heat-sealing resin composition layer on the inner surface of the container body, the heat-sealing resin composition layer is laminated so as to contact the sealing surface, A lid material for an easy-open container comprising a multilayer film containing at least the substrate film and the above-mentioned heat-sealing resin composition layer in the other outermost layer, and further the heat-sealing resin composition at least on the substrate film and the heat-sealing surface. The above objects have been achieved by developing an automatic packaging film in which layers are laminated.

The crystalline polypropylene resin used in the present invention is a polymer containing propylene as a component and has a melt flow rate of 0.1 g / 10 min to 10 g / 10.
min, preferably 4 g / 10 min to 6 g / 10
The min type is preferably used for molding.

If α-olefin such as ethylene or 1-hexene is contained in the polymerized component of the crystalline polypropylene resin, not only the cuttability at the time of peeling is deteriorated but also the tendency of stringing or the like occurs. Homopolymers are preferred. The melt flow rate of this resin is 10 g / 1
If it exceeds 0 min, stringing or the like will occur in the sealant layer when the container is opened, and the appearance of the opened container will be deteriorated. Conversely, if the melt flow rate is less than 0.1 g / 10 min, molding will be extremely difficult.

The ethylene-propylene copolymer has a propylene content of 10 to 35% by weight in the copolymer component, and the melt flow rate of the copolymer is higher than that of the crystalline polypropylene resin to be mixed. Are necessary, and those having a difference of 2 g / 10 min or more are particularly preferable.

If the mixing ratio of the ethylene-propylene copolymer in the resin composition is less than 10%, the seal temperature dependency of the sealing strength becomes extremely large, and if it exceeds 35%, the sealing strength becomes too low. The same applies to the propylene content of the ethylene-propylene copolymer. If the propylene content of the ethylene-propylene copolymer is less than 20% by weight, the seal strength is generally reduced and the seal strength varies. Conversely, 30% by weight
If it exceeds the above range, the seal strength is lowered in a low temperature range, particularly in the range of 150 ° C. to 170 ° C., and the stability of the seal strength in a wide range is insufficient.

When the melt flow rate of the ethylene-propylene copolymer is smaller than that of the crystalline polypropylene resin, the ethylene-propylene copolymer is not localized in a layered state in the mixed resin layer and is easy to open. The stability of the seal strength cannot be obtained.

The melt flow rate in the present invention means a temperature of 230 ° C. according to JIS K 7210,
It is a value measured using a load of 2.16 Kg. Since the heat-sealing resin composition of the present invention is a mixture of a crystalline polypropylene resin and an ethylene-propylene random copolymer, it is extremely easy to blend and can be easily blended using an extruder or the like. Also, the T-die molding method,
The film is manufactured by the inflation molding method,
A method of adhering to a base film, a base molded body by a dry laminating method, a polypropylene resin or a gas barrier resin (aluminum foil may be used) and maleic anhydride,
There is also a method in which an adhesive resin such as modified polypropylene is used as a multilayer film, or this is used as a sealant for heat sealing of other base resin moldings.

There is also a method of use such as ordinary hot melt in which the present resin composition is melt coated.

The thickness of the resin composition layer for heat sealant in the present invention is not particularly limited, but is 15 μm.
m to 40 μm is preferable. When the thickness is less than 15 μm, the easy-open property deteriorates with respect to the rise in heat-sealing temperature and pressure, and when the thickness is more than 40 μm, a stable opening force cannot be obtained.

It is particularly preferable when the resin composition of the present invention is used in an easily openable simple packaging container body or a lid pair.
One side of these packaging containers and the like to be adhered is a thermoplastic resin containing ethylene, propylene, styrene or the like as a polymer component, and the other side is a thermoplastic resin such as polypropylene or polystyrene, or a gas barrier resin film or aluminum foil thereof. A container body formed by forming the resin composition layer on a surface including a heat-sealing surface in a container body made of a laminate with, a biaxially stretched polypropylene film, an aluminum foil, a base film such as a biaxially stretched polypropylene film, and the like. A container lid in which the present resin composition layer is formed on the sealing surface, or a biaxially stretched polypropylene film or the like and the present resin composition layer are laminated, and the present resin composition layer is used as a sealant to produce a bag-like package, etc. Can be applied to. The base film means a film including a printed layer.

In this case, the present resin composition layer is prepared by laminating the above-mentioned film and then laminating it, or by making a multilayer laminate having the present resin composition layer as one outermost layer in advance, or the present resin. Various methods can be adopted as the layer forming method such as melt coating of the composition.

Further, such a sheet-like laminated body can be formed into a molded body by a method such as pressure molding or vacuum molding.

[0027]

[Function] In the conventional easy-open heat seal, the interface peeling method is generally adopted. The case where the sealant is adhered to the lid will be described. Normally, as shown in FIG. 2, when the sealant 2 is adhered to the lid 3, the container body 1
And peeling of the sealant interface (interface peeling method).

[0028] However, a phenomenon such as peeling during movement adhesion of the sealant 2 and the container body 1 and the weak will happen is a fatal, there is a tendency to strengthen the absolutely safe side that is adhesive strength in order to avoid this.

Even if this is a multi-layered sealant layer shown in FIG. 3, the film is broken by the first layer 21 of the sealant layer and the peeling of the sealant layer between the first layer 21 and the second layer 22 is performed. Even in the method), variations in seal strength cannot be avoided.

On the other hand, the method targeted by the present invention is shown in FIG.
In the system shown in Fig. 4, no problem is to be solved in increasing the adhesive strength so as not to cause the interfacial peeling between the sealant layer 2 and the container body 1 during the movement, and the cohesive failure strength of the sealant layer 2 should be appropriately adjusted. It is possible to produce a package having stable peel strength.

[0031]

EXAMPLES Next, examples and comparative examples of the present invention will be described in detail.

[Melt flow rate] JIS K 72
The temperature was 230 ° C. and the load was 2.16 Kg.

[Heat Sealing Conditions] Molded lid and multilayer container Multilayer sheet before vacuum forming is 170 ° C. to 23 ° C. on the lid side.
A single-sided seal was performed so that the temperature was 0 ° C. (steps of 20 ° C.) and 50 ° C. on the multilayer sheet side.

[Seal Strength] The mixed resin layer of the molded lid and the multilayer sheet before vacuum molding of the multilayer container is 170 ° C. to 230 ° C.
Heat seal in a temperature range of 20 ° C (steps of 20 ° C) and peeling angle 18 using a tensile tester Toyo Seiki Tensilon UTM III
The peel strength in a 15 mm width was measured at 0 ° and a tensile speed of 300 mm / min. As for the dispersion of the measured values at that time, the difference between the maximum value and the minimum value of the seal strength at each seal temperature is indicated by R.

[Opening Appearance] The degree of the opening surface at the time of opening the heat-sealed multi-layer container and the lid is evaluated in three levels,
The non-stringed ones are indicated by ◯, the stringed ones are indicated by x, and the middle thereof is indicated by Δ.

[Gas Barrier Property] ASTM D3985-
81-Moden-Control OX-T
Using RAN 10 / 50A, the oxygen permeation amount after sealing the multilayer container and the lid was measured under the conditions of 21 ° C. and 65% RH.

(Example 1) The melt flow rate was 9.0.
An ethylene-propylene copolymer having a propylene content of 23% by weight at g / 10 min and a melt flow rate of 6.
Homopolypropylene of 0g / 10min in weight ratio of 3
Dry blending was performed at a ratio of 0:70 (this resin is abbreviated as B) to obtain a heat-sealing resin composition.

Maleic anhydride-modified polypropylene resin (abbreviated as T) is used as an adhesive resin, and ethylene content is 40 mol% and saponification degree is 99% as a gas barrier resin.
The ethylene-vinyl acetate copolymer saponified resin (abbreviated as E) of No. 3 was applied to a three-kind five-layer multi-layer T-die molding machine (manufactured by Toshiba Machine Co., Ltd.) so as to have a layer structure of B / T / E / T / B. Then, the resin composition layer was molded to have a thickness of 25 μm, the adhesive resin had a thickness of 5 μm, and the gas barrier resin layer had a thickness of 5 μm (die temperature 220 ° C.). Next, this multilayer film was laminated on a polystyrene sheet (500 μm) by a dry lamination method to form a container by vacuum molding. Furthermore, a polyvinylidene chloride coated polyester film was used as a lid base material, and a lid body was obtained by dry lamination with propylene-ethylene random copolymer (MFR 7 g / 10 min).

The obtained multi-layer container and lid were heat-sealed so that the heat-sealing resin composition layer and the propylene-ethylene random copolymer layer could be the adhesive surface. Table 1 shows the results of the unsealing strength, the dispersion of the measured values, and the unsealing appearance.

Example 2 A multilayer container was prepared in the same manner as in Example 1 except that an ethylene-propylene copolymer having a melt flow rate of 7.0 g / 10 min and a propylene content of 25% was used in the heat-sealing resin composition. And a lid were obtained. The results are shown in Table 1.

Example 3 A propylene homopolymer having a MFR of 4 g / 10 min and a MFR of 6 g / 10 min and a propylene content of 2 as a heat-sealing resin composition.
A multilayer container and a lid were obtained in the same manner as in Example 1 except that 4% by weight of ethylene-propylene copolymer was used. The results are shown in Table 1.

Comparative Example 1 The same procedure as in Example 1 was carried out except that an ethylene-propylene copolymer having a melt flow rate of 0.8 g / 10 min and a propylene content of 25% by weight was used in the heat-sealing resin composition. A multilayer container and lid were obtained. The results are shown in Table 1.

Comparative Example 2 A polyethylene resin having a melt flow rate (190 ° C.) of 9.0 g / 10 min and a density of 0.93 g / cm ³ was used in place of the ethylene-propylene copolymer in the heat-sealing resin composition. A multilayer container and a lid were obtained in the same manner as in Example 1 except for the above. The results are shown in Table 1.

(Comparative Example 3) A resin composition for heat sealing had an MFR of 4 g / 10 min and a propylene content of 35.
A container and a lid were obtained by the same method as in Example 1 except that an ethylene-propylene copolymer of wt% and a propylene homopolymer having an MFR of 6 g / 10 min were used. The results are shown in Table 1.
It was shown to.

Comparative Example 4 A propylene homopolymer having an MFR of 6 g / 10 min was used in place of the heat-sealing resin composition for the inner layer of the container, and the propylene homopolymer was attached to a polystyrene sheet by a dry lamination method, and then vacuumed. It shape | molded and obtained the container. The same lid as in Example 1 was used. The results are shown in Table 1.

(Comparative Example 5) A method similar to that of Example 1 except that a crystalline polypropylene having a melt flow rate of 6.0 g / 10 min and a copolymer containing 7% by weight of ethylene was used in the heat-sealing resin composition. A container and a lid were obtained. The results are shown in Table 1.

[0047]

[0048]

When the resin composition for heat sealing of the present invention is used, the strength of opening is determined by the resin composition.
Since the heat seal strength is too weak to prevent peeling, there is no need to fear that the seal strength will increase, and a seal that does not cause interfacial peeling can be obtained over a sufficient temperature, pressure, and time.

Therefore, the heat-sealing does not fail, the heat-sealing control by the automatic packaging line is easy, and the hermetically-sealed package can be produced with high productivity.

[Brief description of drawings]

FIG. 1 is an explanatory view of opening a package according to the present invention.

FIG. 2 is an explanatory view of opening a package by a conventional interfacial peeling method.

FIG. 3 is an explanatory view of opening a package by a conventional delamination method.

[Explanation of symbols]

 1 Container Main Body 2 Sealant Layer 21 Sealant Layer First Layer 22 Sealant Layer Second Layer 3 Lid

Claims (6)

[Claims] 1. A heat comprising 65 to 90% by weight of a crystalline polypropylene resin and 35 to 10% by weight of an ethylene-propylene random copolymer having a melt flow rate higher than that of the crystalline polypropylene resin. Sealing resin composition. 2. The crystalline polypropylene resin is basically a propylene homopolymer and has a melt flow rate of 23.
0.1-10g / 10 at 0 ° C and 2.16Kg load
The heat-sealing resin composition according to claim 1, which is a minute. 3. The heat-sealing resin composition according to claim 1, wherein the ethylene-propylene random copolymer has a propylene content of 20 to 30% by weight and a melt flow rate higher than that of crystalline polypropylene by 2 g / 10 minutes or more. .. 4. A container body composed of a multilayer film in which at least a gas barrier resin layer and the heat-sealing resin composition layer according to claim 1 are laminated, wherein the heat-sealing resin is in contact with the sealing surface of the lid. An easy-open container, in which composition layers are laminated. 5. An easy-opening characterized by comprising a multilayer film in which the heat-sealing resin composition layer according to claim 1 is laminated on the outermost layer so as to come into contact with the sealing surface of a container body made of at least a thermoplastic resin. Lid material for containers. 6. An automatic packaging film, characterized in that the heat-sealing resin composition layer according to claim 1 is laminated on at least the heat-sealing surface of a substrate.