JPH06179473A - Retort sterilizing packing material - Google Patents

Abstract

PURPOSE:To prevent cracking a thin film made of inorganic materials by using in a barrier film on which a thin film layer made of inorganic materials is formed and a laminated material containing a sealant layer composed of not- drawn polypropylene whose coefficient of contraction is less than the specific value, and containing no rubber component. CONSTITUTION:A barrier film 1 wherein a thin film layer 12 made of inorganic materials is formed on a plastic film 11 and a sealant layer 2 made of non- oriented polypropylene are laminated to each other by adhesives 4. The non- oriented polypropylene of the sealant layer 2 has the coefficients of contraction of 0.5% or less in both directions when it is heated by oil at 120 deg.C for twenty minutes. A printing layer 31 is formed on one side of a printing base material 3, and the printing base material 3 is laminated to the barrier film 1 so that the printing layer 31 may be faced to the food side. Thereby the gas barrier performance can be held without generating any crack on the thin film 12 made of inorganic materials. Moreover, transparency can be maintaived without causing the whitening.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a packaging material for retort sterilization, and more particularly to a packaging material for forming a pouch, and more particularly to a transparent packaging material for retort sterilization containing no metal foil.

[0002]

2. Description of the Related Art Conventionally, a packaging material which constitutes a pouch for retort sterilization mainly comprises a plastic film and contains a metal foil. For example, polyethylene terephthalate (PET) / aluminum foil (Al foil) /
Non-stretched polypropylene (CPP); Stretched polypropylene (OPP) / Al foil / CPP; Stretched nylon (ONy)
/ Al foil / CPP; PET / Al foil / Nylon (Ny)
/ CPP; OPP / Al foil / Ny / CPP; ONy / A
One having a structure such as 1 foil / Ny / CPP is in practical use, and a two-component curing type urethane adhesive is used for laminating each layer. The packaging material uses CPP as a sealant to withstand the heat and humidity of the retort.
PP is excellent in heat resistance and strength, for example, unstretched polypropylene manufactured by Toray Gosei Co., Ltd .; ZK-93,
Alternatively, 3931 (all grade names) was used. This CPP has a shrinkage factor of 1 in the longitudinal direction and / or 1 in the transverse direction when heated at 120 ° C. for 20 minutes.
Was ~ 5%.

The aluminum foil used in the above conventional packaging material is excellent as a barrier layer that does not allow the permeation of gases such as oxygen and water vapor, and the conventional packaging material has the aluminum foil for the purpose of this barrier property. Is used. However, since the aluminum foil is a metal, it is not transparent and there is a problem that the contents of the pouch cannot be seen through. Moreover, since it is a metal foil, there is a problem that the pouch cannot be heated in a microwave oven.

A material in which a thin film of an inorganic substance is formed on a plastic film has been proposed as a material that allows gas such as oxygen and water vapor to pass through while allowing the contents to be seen through or heated by a microwave oven. For example, in Japanese Examined Patent Publication No. 53-12953, a film of polyethylene terephthalate, polypropylene or the like is formed with a thickness of 1000Å of silicon oxide by vacuum deposition.
A barrier material is shown.

[0005]

Therefore, if the barrier material having a thin film of the above-mentioned inorganic substance (hereinafter referred to as a barrier film) is used in place of the conventional aluminum foil, the contents can be seen through and the microwave oven can be used. It has been considered that a packaging material for retort sterilization, which is excellent in gas barrier properties against oxygen and water vapor while enabling heating, is obtained.

However, it has been found that the following problems occur when the barrier foil is simply substituted for the aluminum foil having the above-mentioned conventional packaging material structure.

That is, since a thin film of an inorganic substance, particularly a thin film of silicon oxide, is glass-like, fine cracks are likely to occur, and when the cracks occur, the barrier properties against gases such as oxygen and water vapor are significantly lowered. Will end up. When the barrier film was adopted in the above-mentioned conventional structure, cracks were generated in the thin film of the inorganic substance after the retort sterilization.

In the case of a packaging material using a barrier film, after retort sterilization, the sealant layer of the packaging material sometimes becomes cloudy (whitened), resulting in a marked decrease in transparency. This is a matter that does not pose a problem because the aluminum foil is opaque in the configuration including the conventional aluminum foil.

Therefore, the present invention provides a packaging material for retort sterilization which employs a barrier film, in which a thin film of an inorganic substance is not cracked and which is excellent in transparency without whitening. It is provided.

[0010]

That is, the present invention is a laminated material including a barrier film having a thin film layer of an inorganic substance formed thereon and a sealant layer, wherein the sealant layer is 1
A packaging material for retort sterilization, which is a non-stretched polypropylene having a shrinkage rate of 0.5% or less in each of a longitudinal direction and a transverse direction when heated at 20 ° C. for 20 minutes and containing no rubber component. .

In a preferred embodiment of the present invention, the inorganic material thin film layer of the barrier film and the sealant layer are laminated with an adhesive. Further, as the inorganic substance of the present invention, silicon oxide is a preferable material.

[0012]

In the present invention, the contraction rate when heated at 120 ° C. for 20 minutes is 0.5% or less in each of the longitudinal direction and the lateral direction, and CPP containing no rubber component is used, so that after retort sterilization No cracks were formed in the thin film layer of the inorganic substance, and no whitening occurred.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 is a sectional explanatory view showing an embodiment of the present invention.

As shown in FIG. 1, the packaging material of the present invention comprises:
A packaging material having a barrier film 1 in which a thin film layer 12 of an inorganic substance is formed on a plastic film 11 and a sealant layer 2 made of unstretched polypropylene.

First, the thin film layer 12 of an inorganic substance is a transparent thin film of silicon oxide, magnesium oxide, magnesium fluoride, aluminum oxide, etc.
Gives the packaging material barrier properties against gases such as oxygen and water vapor. The thin film layer 12 is formed on the plastic film by a known method such as vacuum deposition, ion plating, sputtering, or plasma CVD method. The thickness of the thin film layer 12 varies depending on the material and the intended performance, but it is preferably 200 to 2000 Å. If it is thinner than this, sufficient gas barrier properties cannot be obtained. On the other hand, if it is thicker than this, improvement in gas barrier properties cannot be expected, and the thin film layer 12 tends to crack.

The plastic film 11 as the base material of the thin film layer 12 is not particularly limited as long as it is a material capable of forming the thin film layer 12 by the above-mentioned method, but a film such as polyethylene terephthalate, oriented polypropylene or nylon is preferably used. it can.

The sealant layer 2 is made of unstretched polypropylene. This is because unstretched polypropylene can withstand wet heat during retort sterilization (for example, 120 ° C., 30 minutes) and is excellent in heat-sealing property required when making a pouch.

The present invention further specifies this unstretched polypropylene, and has a shrinkage rate of 0.5% or less in each of the longitudinal direction and the transverse direction when heated with oil at 120 ° C. for 20 minutes. The unstretched polypropylene that can be used in the present invention does not contain a rubber component.

As will be apparent from the experiments described below, if the shrinkage ratio exceeds 0.5%, cracks occur in the thin film layer 12 of inorganic material. Further, unstretched polypropylene containing a rubber component causes whitening after retort sterilization, resulting in a marked decrease in transparency. Specific examples of the unstretched polypropylene that can be used in the present invention include Allomer U (trade name) manufactured by Showa Denko KK.

The barrier film 1 and the sealant layer 2 are
It is laminated with the adhesive 4. At this time, it is preferable that the thin film layer 12 of the inorganic material faces the sealant layer 2 side. As shown in the figure, a surface layer such as a printing substrate 3 is usually laminated on the side opposite to the sealant layer 2 side of the barrier film 1. However, when the thin film layer 12 of the inorganic substance is directed toward the printing substrate 3 side, Although the reason is not clear, the plastic film 11 and the thin film layer 12 may be separated after the retort sterilization treatment.

The adhesive 4 must be one that can withstand wet heat during retort sterilization, such as a two-component curing adhesive.

The packaging material of the present invention is mainly used by being formed into a pouch. Examples of the shape of the pouch include known three-way or four-way seal bags and standing pouches. It can also be used as a lid material for cup-shaped containers and tray-shaped containers.

Further, a pattern or the like is usually printed on such a packaging material. The position of forming the print layer is arbitrary, but when applied to food packaging, it is desirable that the print layer is protected by a plastic film or the like so as not to come into contact with food or other pouches, as shown in FIG. It is desirable that the printing layer 31 is formed on one surface of the printing substrate 3 so that the printing layer 31 faces the food and the printing substrate 3 is laminated on the barrier film 1. The printing substrate 3 and the barrier film 1 are preferably laminated with the heat-resistant adhesive 4 as described above.

<Experiment 1> A thin film layer of silicon oxide (thickness 1500Å) was formed on a polyethylene terephthalate film (thickness 12 μm) by a vacuum deposition method to prepare a barrier film. An unstretched polypropylene film having a thickness of 60 μm (Aromar AT, Showa Denko KK, shrinkage ratio: M is formed on the thin film layer surface of this barrier film by a dry lamination method using a two-component curing type urethane adhesive.
(D = 0.3%, TD = 0.1%). On the polyethylene terephthalate film side of the barrier film, a polyethylene terephthalate film on which a pattern is printed is arranged by the dry lamination method using a two-component curing type urethane adhesive so that the printed side is the barrier film side. By laminating, a packaging material of the present invention (Example 1) was prepared.

Separately from this, a thin film layer of silicon oxide (thickness 1500 Å) was formed on a polyethylene terephthalate film (thickness 12 μm) by a vacuum deposition method to prepare a barrier film. Two sheets of this barrier film,
Laminated by a dry lamination method using a two-component curing type urethane adhesive, and further an unstretched polypropylene film having a thickness of 80 μm (Aromar AT, Showa Denko KK) was used using the two-component curing type urethane adhesive. laminated by dry lamination to give PET / silicon oxide (Si _x O _y) / adhesive / PET / Si _x O _y / adhesive / CPP configuration, the packaging material of the present invention (example 2) It was

A standing pouch (size 190 mm × 14 mm, inner volume 450 ml), which is a well-known pouch shown in FIG. 2, was prepared by using the above-mentioned Examples 1 and 2. In addition, Example 1 was used as the main body side wall A, and Example 2 was used as the bottom member B.

The standing pouch was filled with 250 ml of 4% acetic acid as a content, sealed, and retort sterilized under various conditions. After that, turbidity (Haze
Was measured.

For comparison, instead of the unstretched polypropylenes of Examples 1 and 2, unstretched polypropylene containing an elastomer as a rubber component (Aroma U, manufactured by Showa Denko KK, shrinkage ratio: MD = 0.4%, T
D = 0.3%) and a standing pouch similar to the above, and HA
The ZE degree was measured. The results are shown in Table 1.

[0029]

[Table 1]

As is clear from the above results, all of the products according to the present invention had a HAZE degree of less than 70 after retort and had transparency, but all of the comparative ones had a HAZE degree. Was over 70, and white turbidity (whitening) was remarkable.

The oxygen barrier properties of the examples and the comparative examples before and after retort sterilization were measured, and both were 0.5 ml / m ² · day · atm before retort and 1.0 ml / m ² · m after retort. day · atm,
It had a sufficient oxygen barrier property even after the retort.

[0032]

As described above, according to the present invention, after retort sterilization, the thin film of the inorganic substance does not have a crack, maintains a sufficient gas barrier property, and does not cause whitening, resulting in transparency. It is now possible to obtain a retained packaging material. Since the packaging material of the present invention has an extremely simple structure, it is easy to manufacture and the cost is low.

[Brief description of drawings]

FIG. 1 is a sectional explanatory view showing an embodiment of the present invention.

FIG. 2 is an explanatory view showing an example of a pouch created by using the packaging material of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Barrier film 11 ... Plastic film 12 ... Inorganic substance thin film layer 2 ... Sealant layer 3 ... Printing base material 31 ... Printing layer 4 ... Adhesive

Claims (3)

[Claims] 1. A laminate material comprising a barrier film having a thin film layer of an inorganic substance formed thereon and a sealant layer, wherein the sealant layer has a shrinkage factor when heated at 120 ° C. for 20 minutes.
A packaging material for retort sterilization, which is 0.5% or less in each of the lengthwise direction and the widthwise direction and is an unstretched polypropylene containing no rubber component. 2. An inorganic material thin film layer of a barrier film and a sealant layer are laminated with an adhesive.
The packaging material described in. 3. The packaging material according to claim 1, wherein the inorganic substance is silicon oxide.