JP2901274B2 - Laminate - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a laminate having excellent barrier properties against gas and water vapor. More specifically, the present invention relates to a laminate having not only good gas barrier properties used for packaging materials for foodstuffs, but also excellent transparency and good retort barrier properties.

[Conventional technology]

2. Description of the Related Art Conventionally, flexible packaging materials for foods have various difficult requirements, that is, sanitary properties, gas barrier properties, moisture proof properties, ultraviolet barrier properties, water resistance, heat resistance, and the like. To meet these requirements, plastic films such as polyester resin (especially polyethylene terephthalate), polyamide resin (nylon), and polyolefin resin, aluminum foil, saponified ethylene-vinyl acetate copolymer (ethylene-vinyl alcohol copolymer) ) Or a composite film in which a polyvinylidene chloride resin is laminated or coated. In the case of composite films with laminated aluminum foil, there is almost no problem with gas barrier properties, moisture barrier properties, ultraviolet barrier properties, etc., but when used as a food packaging material, consumers will see the contents when opaque. Can reduce the attractiveness of the product. In addition, there is a disadvantage that it cannot be used for a microwave oven. Further, a composite film provided with a saponified layer of an ethylene-vinyl acetate copolymer has an excellent oxygen gas barrier property, but has a drawback of poor moisture permeability. For this reason, there is a problem in that the flavor is impaired due to, for example, water emanating from the food. In addition, there is a disadvantage that the oxygen gas barrier property is significantly reduced after the retort sterilization treatment.
Furthermore, although providing a polyvinylidene chloride resin layer improves moisture permeability and oxygen gas barrier properties, it can only be applied by a coating method (coating method) to provide a polyvinylidene chloride resin. Has poor adhesion and boiling resistance. As a result, there is a problem of minute defects, that is, alteration of the contents because oxidation occurs due to generation of pinholes.

In order to solve these problems, there is a method of improving the moisture permeability (water vapor barrier property) and gas barrier property (gas barrier property) by laminating thin layers of various inorganic substances on the surface of a plastic film by vapor deposition or the like. It has been implemented.

First, there has been proposed a method in which silicon oxide is used in place of aluminum which has been conventionally used as a barrier layer, the transparency is excellent, and the microwave oven is improved (Japanese Patent Laid-Open No. 49-41469). Such).

Secondly, the barrier property is improved by improving the adhesiveness of the metal deposition film from the film by bombarding the surface of the polypropylene resin film with inert gas ions having a kinetic energy of 100 eV to 10 KeV before and after vapor deposition. (Japanese Patent Laid-Open No. 60-159567).

[Problems to be solved by the invention]

In the first case, since the base material is deposited on an unstretched or biaxially stretched film of a polypropylene resin which is not particularly treated or a biaxially stretched film of a polyester resin, for example, a film of unstretched polypropylene resin (thickness: When silicon oxide is deposited to a thickness of 120 nm to a thickness of 50 μm), it exhibits an oxygen permeation rate of 400 cc / m ² · atm / day and does not have sufficient barrier properties. When a polyester resin film is used as a base material, the oxygen permeation amount is 1 to 3 cc when 120 nm is deposited on a film having a thickness of 12 μm.
/ m ² · atmosphere · day, exhibiting relatively good barrier properties, but poor heat sealability.

In the second case, the main purpose is to improve the adhesion between the deposited film and the substrate, and the barrier property has not been improved.

From these facts, the present invention not only has excellent adhesion between the deposited film and the substrate, but also has good gas barrier properties, and has excellent water vapor, and further has good transparency. Therefore, an object of the present invention is to obtain an optimum base material for food packaging.

[Means and actions for solving the problem]

According to the present invention, these problems are solved by the general formula SiO _x (where 0 <x ≦ 2) on the surface of a thin polypropylene resin having a crystallinity of 60% or more by a vacuum evaporation method. A laminate characterized by providing a silicon oxide thin film layer having the following composition: Hereinafter, the present invention will be described specifically.

(A) Polypropylene resin As the polypropylene resin used in the present invention, propylene homopolymer, propylene and at most 20% by weight (preferably 18% by weight or less, preferably 15% by weight)
And a copolymer obtained by random or block copolymerization of ethylene and / or another α-olefin having at most 12 (preferably 8) carbon atoms.

The melt index of these polypropylene resins (measured under conditions of 14 according to JIS K-7210, hereinafter referred to as “M
I)) is usually 0.005-80 g / 10 min, especially 0.
A polypropylene resin of 01 to 40 g / 10 minutes is desirable. MI
When a polypropylene resin of less than 0.005 g / 10 minutes is used,
Poor moldability makes it difficult to produce thin objects. on the other hand,
When using a polypropylene resin exceeding 80 g / 10 minutes,
It is not possible to produce a thin product having sufficient adhesion strength.

(B) Thin material To manufacture a thin material of the polypropylene resin,
A method generally used in the field of producing a polypropylene resin film or sheet may be applied, and typical molding methods include a T-die molding method and an inflation molding method. The molding temperature is a temperature at which the used polypropylene resin melts. But,
If carried out at a high temperature, the polypropylene resin used may be decomposed. For these reasons, molding is generally performed at a resin temperature of 190 to 270 ° C (preferably 200 to 260 ° C).

The thickness of the thin material is 10 μm to 5 μm (preferably 10 μm to 1 m) from the viewpoint of practicality such as moldability and strength.
m).

The crystallinity of the thin material (based on the following method) is 60% or more, preferably 70% or more, and particularly preferably 75% or more. If the crystallinity of the thin material is less than 60%, the adhesiveness between the thin film layer and the thin material is insufficient, which is not practical.

The degree of crystallinity is based on the density measured by the density gradient tube method by the D method according to JIS K-7112, and based on the density measured by the density gradient tube method, Kenji Takagi, Heizo Sasaki, "Plastic Materials Course [7] Polypropylene Resin" (Showa 57 The Nikkan Kogyo Shimbun, page 45 (3,2
Equation) That is, it was calculated by the following equation.

In this equation, X (%) is the required crystallinity,
d is the actually measured density, dc is the density in the case of perfect crystals (0.936 g / cm ³ ), and da is the density in the case of perfect amorphous (0.850 g / cm ³ ).

(C) Silicon oxide thin film layer The silicon oxide thin film layer used as the barrier layer in the present invention is obtained by vacuum-depositing silicon, silicon monoxide, silicon dioxide or a mixture thereof as described below. Among them, silicon monoxide or a mixture of silicon monoxide and silicon dioxide is preferable, and high-purity silicon monoxide is particularly preferable. The thin film layer of silicon oxide in the present invention has the general formula SiO
_x (where 0 <x ≦ 2). The ratio of silicon and oxygen in the thin film layer, ie, x, is an X-ray photoelectron spectrometer [manufactured by Silicon Systems (USA), Model SSX-1
It can be calculated from the area ratio of the peak of the binding energy of the 2p orbital of silicon and the binding energy of the 1s orbital of oxygen by using (type 00). Regardless, even if metal silicon is formed on a thin material of the polypropylene-based resin by a vacuum evaporation method in the absence of oxygen at all, for example, in the presence of an inert gas such as nitrogen gas, carbon dioxide gas, or argon, it is actually used. At last, oxygen in the air oxidizes metallic silicon deposited in vacuum. For these reasons, the ratio of the oxygen element to silicon (that is, the above-mentioned x) is preferably 0.5 or more, and particularly preferably 1.0 or more. On the other hand, if x exceeds 2.0, the particles on the surface of the base material will grow large in vacuum deposition, and the defects at the interface of the grown grains will also increase, so that it cannot be put to practical use as a deposited thin object.

(D) Vacuum deposition The laminated thin material of the present invention can be manufactured by vacuum-depositing the silicon oxide on at least one surface of the thin polypropylene resin material obtained as described above.

For vacuum deposition of silicon oxide, a general vacuum deposition method may be applied. That is, using a vacuum deposition apparatus,
By heating the deposition material (silicon oxide) with an electron beam under a reduced pressure of × 10 ⁻⁴ Torr or less, a target thin film can be obtained. If the deposition exceeds 1 × 10 ⁻⁴ Torr, the deposition cannot be stably performed. In addition, the temperature of the thin material (film or sheet) of the polypropylene-based resin as the base material at the time of vapor deposition is preferably 80 to 105 ° C, particularly 85 to 100 ° C.
C is preferred. If the temperature of the thin polypropylene resin is less than 80 ° C., water molecules and the like existing near the thin material cannot be sufficiently removed. The adhesion of the deposited film becomes weak. On the other hand, if the temperature exceeds 105 ° C., adverse effects such as denaturation of the thin material itself will occur. Further, the electron beam power is a factor related to the deposition rate, but is preferably 40 to 200 mA,
Especially, 60 to 160 mA is preferable. Electron beam power is 4
At less than 0 mA, no evaporation occurs. On the other hand, if it exceeds 200 mA, decomposition of the silicon oxide itself occurs.

The thickness of the deposited layer of silicon oxide is 10 nm to 5 μm, preferably 15 nm to 3 μm, more preferably 20 nm to 2 μm.
m is preferred. If the thickness of the deposited layer is less than 10 nm,
It is not possible to obtain sufficient retention of perfume components and the like. On the other hand, if it exceeds 5 μm, film formation is technically difficult.

(E) Laminated Thin Material As described above, a laminated thin material of the present invention in which silicon oxide is vacuum-deposited on one surface of a thin material of a polypropylene resin can be obtained.

FIG. 1 shows a partially enlarged cross-sectional view of the thin laminate. First
In the drawing, reference numeral 1 denotes a silicon oxide thin film layer which is vacuum-deposited, and reference numeral 2 denotes a thin film of the polypropylene resin.
In the laminate, it may be composed of the above two layers,
Further, as shown in FIG. 2, a heat-resistant layer 4 may be bonded to another surface of the silicon oxide thin film layer with or without the adhesive layer 3 interposed therebetween.

As an adhesive used for bonding the polypropylene-based resin layer 3 and the heat-resistant layer 4, those used for ordinary dry lamination can be preferably used. Typical examples are polyether urethane,
Examples include a polyester resin and an isocyanate-based curing agent.

As the adhesive used to improve the adhesion between the polypropylene resin layer 3 and the silicon oxide thin film layer 1, the above-mentioned adhesives can be used. A modified olefin resin obtained by graft-polymerizing an unsaturated carboxylic acid or a derivative thereof (for example, maleic acid or maleic anhydride) to the resin can also be preferably used.
The thickness of these adhesives may be such that the adherends are firmly adhered to each other, and is usually 0.5 to 30 μm.

[Examples and Comparative Examples]

Hereinafter, the present invention will be described in more detail with reference to examples.

In Examples and Comparative Examples, the oxygen transmission rate was measured by an oxygen transmission rate measuring device [Modern Control (USA),
[OX-TRAN 10/50], the measurement was performed under the conditions of a measurement temperature of 23 ° C., a relative humidity inside the container of 90%, and a relative humidity outside the container of 60%.

Examples 1-4, Comparative Examples 1-2 A propylene homopolymer having an MI of 0.5 g / 10 minutes was biaxially stretched at a molding temperature of 230 ° C., and the films having the thickness and crystallinity shown in Table 1 were obtained. Was manufactured.

Each of the resulting films from the longitudinal and transverse were the cut sample is 10cm, respectively, a vacuum vapor deposition apparatus to the surface of each sample (vacuum equipment Co., model BMC-500C type) used, to the degree of vacuum is 3 × 10 ^-5 no 5 × 10 ^-5 Torr, film temperature 85
The particles of the silicon oxide were vacuum-deposited from tablets of silicon oxide having an element ratio of oxygen to silicon 1 of 1.0 under the conditions of 80 ° C. and electron beam power of 80 mA to produce a laminate. Table 1 shows the thickness of the deposited silicon oxide layer in each of the obtained laminates. The oxygen permeability of the obtained laminate was measured.
Table 1 shows the results.

[Effects of the Invention] The laminate of the present invention exhibits the following effects.

(1) The oxygen barrier property is extremely superior to that of a laminate obtained by vacuum-depositing a film of a polypropylene resin having a low crystallinity.

(2) Since the film is a polypropylene resin, the film has good heat sealability.

(3) Excellent transparency and suitability for microwave oven.

(4) Various conditions are difficult to adsorb.

The laminate of the present invention can be used in various fields to exhibit the above effects. Representative applications are shown below.

(1) Retort pouch.

(2) Packaging materials for liquids (for example, various juices) containing a trace amount of a fragrance component.

[Brief description of the drawings]

1 and 2 are partially enlarged sectional views of the laminate of the present invention. DESCRIPTION OF SYMBOLS 1 ... Silicon oxide thin film layer 2 ... Polypropylene resin layer 3 ... Adhesive layer 4 ... Heat resistant layer

Continuation of the front page (56) References JP-A-63-86860 (JP, A) JP-A-63-293047 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C23C 14 / 00-14/58 B32B 1/00-35/00

Claims (1)

(57) [Claims] A thin film of a polypropylene resin having a degree of crystallinity of 60% or more has a general formula of Si on a surface thereof by a vacuum evaporation method.
A laminate comprising a silicon oxide thin film layer having a composition of O _x (where 0 <x ≦ 2).