JPH07329235A - Metal oxide laminated polypropylene composite film - Google Patents

Abstract

PURPOSE:To provide a metal oxide laminated polypropylene composite film excellent in oxygen barrier properties and steam barrier properties. CONSTITUTION:A metal oxide laminated polypropylene composite film is obtained by providing a resin layer of syndiotactic polypropylene or a mixed resin layer of syndiotactic polypropylene and isotactic polypropylene on at least the single surface of a base layer based on polypropylene and laminating a metal oxide layer to the surface of the resin layer.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a metal oxide laminated polypropylene film. More specifically, it relates to a metal oxide-laminated polypropylene composite film having excellent gas barrier properties against oxygen and water vapor, which is used for food packaging.

[0002]

2. Description of the Related Art Conventionally, polypropylene films have been widely used for food packaging applications because of their excellent transparency, mechanical properties, moisture resistance and the like. Furthermore, for the purpose of improving the gas barrier property against oxygen and water vapor of the film, a vinylidene chloride-coated polypropylene film obtained by applying a copolymer of vinylidene chloride and acrylonitrile or acrylic acid in the form of an emulsion and drying it has excellent gas barrier properties. It is widely used as a transparent film.

However, it has been pointed out that vinylidene chloride has an adverse effect on the environment because it generates chlorine gas when it is incinerated for disposal, and that the load on an incinerator for purifying exhaust gas is also large.

As a packaging film that solves this environmental problem, a gas barrier film having a metal oxide deposited thereon has been developed. Among them, those obtained by vapor-depositing silicon oxide and aluminum oxide on a plastic film are transparent and have attracted attention because they have a considerably high gas barrier performance.
The one in which silicon oxide is formed on a plastic film is known from Japanese Patent Publication No. 53-12953. Further, a material in which aluminum oxide is formed on a polymer resin film substrate is known from Japanese Patent Application Laid-Open No. 62-179935. As an improved version of this, Japanese Patent Laid-Open No. 5-338
Japanese Unexamined Patent Publication No. 072 discloses a structure in which a layer containing incomplete aluminum oxide and containing a metal is provided inside. Further, a method of forming incomplete aluminum oxide described in EP0437946A2 on a polymer film is also known.

However, these techniques are mainly intended for polyethylene terephthalate films, and are not intended to exhibit high gas barrier performance for polypropylene films.

[0006]

DISCLOSURE OF THE INVENTION The present invention provides a transparent polypropylene composite film having a high gas barrier performance, which has not been achieved by such a conventional technique and which does not coat a vinylidene chloride resin.

[0007]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the present invention shows that a syndiotactic polypropylene polymer is formed on at least one surface of a base layer (A layer) containing a polypropylene polymer as a main component. Alternatively, a metal oxide-laminated polypropylene composite film in which a mixed resin layer (B layer) of a syndiotactic polypropylene polymer and an isotactic polypropylene polymer is present, and a metal oxide layer is laminated on the surface of the resin layer, It is provided.

The polypropylene polymer (hereinafter abbreviated as iPP-1) used in the base layer (A layer) containing the polypropylene polymer as a main component of the present invention is crystalline polypropylene, and is a homopolymer of propylene, or ethylene, Copolymers obtained by copolymerizing α-olefins such as butene-1 in an amount of 10% by weight or less, preferably 6% by weight, and more preferably 4% by weight or less are also included. It is preferably a propylene homopolymer. The melt flow index (MFI) of the polypropylene polymer is preferably in the range of 1.0 to 10 g / 10 minutes, more preferably 2.5 to 6 g / 10 minutes. The isotactic index (II) is 95-9.
9.5% is preferable, and the range of 97 to 99.0% is more preferable because the crystallinity of the film can be increased and the film is moisture-proof. In addition, in manufacturing the film, the edges of the film are cut off, and when these are reused as the recovered raw material for the A layer constituting the present invention, the production cost of the film can be reduced, which is preferable. The layer A of the present invention includes a mixture of the layer B resin to be laminated in an amount of 15% by weight or less.

The syndiotactic polypropylene polymer (hereinafter abbreviated as sPP) constituting the layer B of the present invention is
A homopolymer having a substantially syndiotactic structure or 10% by weight or less, preferably 5% by weight or less α-
It is a copolymer obtained by copolymerizing olefins. Preferably s
It is a PP homopolymer. Such sPP is polymerized using, for example, a metallocene catalyst, and known methods thereof include JP-A-2-41303, JP-A-2-41305, and JP-A-4-25514. S of the present invention
The PP homopolymer has a syndiotactic fraction measured by ¹³ C-NMR of 0.7 or more, preferably 0.8 or more. The syndiotactic fraction of the sPP copolymer is preferably 0.5 or more. Examples of the α-olefin monomer copolymerized with sPP include ethylene, butene-1, pentene-1, 4-methylpentene-1, hexene-1, octene-1 and the like, with ethylene and butene-1 being particularly preferable. The preferred molecular weight of sPP is 135 ° C.
The intrinsic viscosity measured with a tetralin solution is 0.5 to 3.
A range of 0 is preferred. The melting point of sPP is 125 to 16
The range of 0 ° C is preferable, and the range of 135 to 155 ° C is more preferable. The MFI of sPP is 1.0 to 10 g.
/ 10 minutes is preferable, and further 2.5 to 6.0 g /
The range of 10 minutes is more preferable.

Isotactic polypropylene (hereinafter abbreviated as iPP-2) mixed with the sPP of the B layer of the present invention.
Is 10% by weight or less, preferably 6% by weight or less, and more preferably 4% by weight of a polypropylene homopolymer having a substantially isotactic structure or an α-olefin monomer such as ethylene or butene-1. % Or less copolymerized copolymer is also included. Preferred is an isotactic polypropylene homopolymer. The melt flow index (MFI) of polypropylene polymer is 1.0
The range is preferably 10 to 10 g / 10 minutes, more preferably 2.5 to 6 g / 10 minutes. Further, the isotactic index (II) is preferably in the range of 95-99.5%.

The mixing ratio of sPP to the entire B layer is 10%
The above range is preferable. If it is less than 10%, the gas barrier property after the metal oxide film is laminated tends to be insufficient. More preferably 10% or more and 90% or less, still more preferably 50% or more 8
It is 0% or less. If it is 90% or more, the film after film formation may have white turbidity due to surface roughness, which may limit the appearance in terms of application.

The composite film of the present invention is a non-oriented film,
Either a uniaxially stretched uniaxially oriented film or a biaxially oriented biaxially oriented polypropylene composite film may be used, but a biaxially oriented film is preferably used from the viewpoint of gas barrier properties.

The structure of the composite film of the present invention is A layer / B layer, or B layer / A layer / B layer, preferably A layer / B layer, in which case B layer / A layer / history. The heat seal layer may be laminated so as to form a to seal layer. Although the total thickness of the composite film is not limited,
Preferably 10 to 40 μm, more preferably 15 to 25
It is in the range of μm. The thickness of the B layer is preferably 0.02 μm or more, more preferably 0.05 μm or more. When the thickness of the B layer is less than 0.02 μm, surface unevenness occurs due to uneven stacking on the surface of the B layer, which causes variations in properties such as gas barrier properties, which is not preferable.

The film of the present invention preferably contains a small amount of a heat stabilizer, an antioxidant, an inorganic lubricant, etc., if necessary. For example, as the heat stabilizer, 2,6-di-tert-butyl-4-methylphenol (BHT) or the like is 0.5 wt% or less, and as the antioxidant, tetrakis-
(Methylene- (3,5-di-tert-butyl-4-hydroxy-4-hydroxycinnamate)) butane and the like.
It is preferably added in an amount of 1% by weight or less. Further, it is preferable to use no lubricant such as stearic acid amide, but use lubricant for inorganic particles such as silica and zeolite, or organic crosslinked particles such as crosslinked styrene.

Next, as an example of the present invention, a method for producing a polypropylene composite film comprising biaxially oriented A layer / B layer will be described.

First, the layer A resin containing the polypropylene polymer of the present invention as a main component, and sPP or sPP and iPP.
The resin for layer B consisting of the mixed resin of (1) is prepared, the raw materials are supplied to different extruders, melt-extruded at a temperature of 230 to 280 ° C., and after passing through a filtration filter, in a short tube or in a die, Layers / B layers or A layers / B layers / A layers are merged, extruded from a slit-shaped die, wound on a metal drum, and cooled and solidified in a sheet form to obtain an unstretched film. In this case, the temperature of the cooling metal drum is 30 to 7
It is preferable to crystallize the film at 0 ° C. This unstretched film is biaxially stretched and biaxially oriented. As the stretching method, a sequential biaxial stretching method or a simultaneous biaxial stretching method can be used, and the sequential biaxial stretching method is particularly preferable from the viewpoint of moisture resistance of the film. As a sequential stretching method, first, the unstretched film is heated to a temperature of 120 to 150 ° C., stretched 4 to 7 times in the longitudinal direction, cooled, and then introduced into a tenter-type stretching machine, and 140 to 165 ° C. After heating to the temperature of 6 to 10 times in the width direction, relaxation heat treatment is performed at a temperature of 155 to 170 ° C., and cooling is performed. In the cooling process from the heat treatment temperature, it is preferable to maintain the temperature at 70 to 120 ° C. for 1 to 20 seconds and then cool to room temperature because the lubricity of the B layer surface of the film is improved.

A metal oxide layer is laminated on the surface of the B layer of the polypropylene composite film consisting of the A layer / B layer. Prior to the lamination, a known surface treatment, that is, a low temperature plasma treatment or a corona discharge treatment is performed on the surface of the B layer. It may be done.

The method for forming the metal oxide layer in the present invention includes, for example, vacuum vapor deposition and baking after coating with a metal alkoxide. However, reactive vapor deposition in an oxidizing atmosphere is preferable in terms of productivity. More preferable. The oxidizing atmosphere means an oxygen gas alone or an oxygen gas diluted with an inert gas, which is introduced into a vacuum vapor deposition machine in a required amount. The inert gas refers to a rare gas such as argon or helium, a nitrogen gas, or a mixed gas thereof. Reactive vapor deposition is a method of evaporating a metal or a metal oxide from an evaporation source in such an oxidizing atmosphere to cause an oxidation reaction in the vicinity of the base film to form it on the base film.
The evaporation source for this purpose includes, but is not particularly limited to, a resistance heating type boat type, a crucible type using radiation or high frequency heating, and an electron beam heating type.

The metal or metal oxide to be evaporated can be selected from Al, Si, Mg, Ti, Zn, Sn, In and these oxides, but from the viewpoint of productivity and gas barrier performance, Al, Si and Si oxides can be selected. More preferable is Al, and most preferable is Al from the viewpoint of production cost.

It is most preferable that the metal oxide layer is a completely oxide film and is completely transparent. However, in general, when an attempt is made to form a completely oxide film, an excessively oxidized portion is likely to be formed, and this portion is highly likely to be formed. It is known that the gas barrier performance of No. 1 is inferior and a high gas barrier performance cannot be obtained as a whole. Therefore, even an incomplete oxide film with some metal components remaining can be preferably formed if there is no practical problem regarding transparency. With respect to transparency, the light transmittance of the original film after vapor deposition is more preferably 80% or more, further preferably 90% or more.

The thickness of the metal oxide layer is preferably in the range of 5 to 100 nm in terms of gas barrier properties and flexibility. If it is less than 5 nm, the gas barrier property is not sufficient,
If the film thickness is thick, if it exceeds 100 nm, heat loss occurs during vapor deposition, the flexibility of the vapor deposited film deteriorates, and further, cracking or peeling easily occurs due to bending or the like. More preferably, it is 10 to 50 nm.

The metal oxide-laminated polypropylene composite film according to the present invention can be preferably used for packaging snack foods, processed meats, dairy products such as cheese, pickles and the like because of its excellent gas barrier performance and transparency.

[0023]

[Measurement Method of Physical Properties and Evaluation Method of Effect] The characteristic values of the present invention are based on the following measurement methods.

(1) Oxygen transmission rate According to ASTM D-3985, it was measured under the conditions of 20 ° C. and 0% RH using an oxygen transmission rate measuring device OX-TRAN100 manufactured by Modern Control.

(2) Water vapor transmission rate Modern control's water vapor transmission rate meter PERMATR
It measured using AN-W1A on 40 degreeC and 90% RH conditions.

(3) Syndiotactic Fraction The composite layer polymer was assigned to the syndiotactic structure appearing at about 20.2 ppm based on tetramethylsilane when measured by ¹³ C-NMR in trichlorobenzene at 135 ° C. The peak of the formed methyl group is divided by the sum of the peaks of all the methyl groups.

(4) Isotactic index (I
I) Vacuum dry the sample at 130 ° C. for 2 hours. Weight W from now on
A sample (mg) is taken, put in a Soxhlet extractor, and extracted with boiling n-heptane for 12 hours. Next, this sample is taken out, thoroughly washed with acetone, dried at 130 ° C. for 6 hours, and then the weight W ′ (mg) is measured and calculated by the following formula.

II = W '/ W × 100 (%) (5) Melt flow index (MFI) JIS K-6758 Polypropylene test method (230
The value was measured at 2.degree. C. and 2.16 kgf).

(6) Lamination Thickness of Each Layer The cross section of the film was photographed with a transmission electron microscope (TEM) under the following conditions to measure the lamination thickness.

Apparatus: JEM-1200EX manufactured by JEOL Magnification: 10000 times Acceleration voltage: 100 kV Section thickness: 1000 angstrom (7) Metal oxide layer thickness: Same as (6) except that the magnification was 400000 times. It was measured.

[0031]

EXAMPLES The present invention will be described with reference to examples.

Example 1 Isotactic polypropylene homopolymer (II = 97.0%, MFI = 2.5 g / 10 minutes, iP) was used as the layer A resin containing the polypropylene polymer of the present invention as a main component.
P-1) and a syndiotactic homopolypropylene resin having a syndiotactic fraction of 0.92 (MFI = 3.5 g / 10 min, sPP-1) are prepared as resins constituting the B layer. And B layer resin are supplied to separate extruders, melt extruded at a temperature of 260 ° C., passed through a filtration filter, and then merged to form A layer / B layer in a short pipe,
The sheet was extruded from a slit-shaped die, wound around a metal drum heated to a temperature of 40 ° C., and molded into a sheet. This sheet was heated to a temperature of 135 ° C., stretched 5 times in the longitudinal direction and cooled, then introduced into a tenter type stretching machine, heated to a temperature of 165 ° C., stretched 9 times in the width direction, and then stretched to 165 ° C. Heat treatment for 12 seconds while giving 8% relaxation in the width direction at 100
It was kept cooled at 6 ° C. (6 seconds), then cooled to room temperature and wound. The total thickness of the film is 18 μm, and the thickness of layer B is 1 μm
It was adjusted to be m.

Carbon dioxide gas was introduced into the obtained film at a pressure of 1 × 10 ^-3 Torr in an electron beam heating type vacuum vapor deposition machine, and a E type value of 20 was obtained using a planar type magnetron electrode.
Low-temperature plasma treatment was performed at an intensity of W · min / m ² , and subsequently, oxygen was introduced into the aluminum evaporation portion to perform reactive vapor deposition of aluminum oxide. This aluminum oxide vapor deposition film has a thickness of 15 nm and a light transmittance of the original film 9
It was 82% against 1%. This aluminum oxide vapor-deposited polypropylene film was used as Example 1.

Example 2, Example 3, Example 4, Example 5 In Example 1, as a resin constituting the B layer, a syndiotactic polypropylene resin having a syndiotactic fraction of 0.92 (MFI = 3. 5g / 10 minutes, sPP-
1) and sPP-1 and isotactic polypropylene homopolymer (II = 96.5%, MFI = 3.5 g / 1
Resins obtained by mixing iPP-2) for 0 minutes with the composition shown in Table 1 were designated as Example 2, Example 3, Example 4 and Example 5, respectively. Example 6 In Example 1, an unstretched film obtained by directly sampling a sheet-shaped product without introducing it into a tenter type stretching machine was used as an Example 6 to form an aluminum oxide-deposited polypropylene film vapor-deposited with aluminum oxide. At this time, the total thickness of the film was 18 μm as in Example 1, and the thickness of the layer B was 1 μm.

Example 7 In Example 1, as the resin constituting the B layer, a resin having a mixing ratio of the syndiotactic polypropylene resin shown in Table 1 of 5% was designated as Example 7.

Example 8 In Example 2, the thickness of the aluminum oxide vapor deposition film was changed to 4
The value of nm was set as Example 8.

Example 9 In Example 2, the thickness of the aluminum oxide vapor deposition film was set to 1
It was set as Example 9 what set it as 50 nm.

Comparative Example 1 Comparative Example 1 was prepared by changing the B layer resin (sPP-1) of Example 1 to only iPP-2 resin.

Comparative Example 2 In Example 1, the B layer resin was not extruded, and the A layer resin alone was used.
Comparative Example 2 had a thickness of 8 μm.

Comparative Example 3 Comparative Example 3 was prepared by using an unstretched film having a thickness of 18 μm with only the A layer resin without extruding the B layer resin in Example 6.

In this sample, the film was shrunk due to heat loss during vapor deposition, and the gas barrier property was insufficient.

The characteristics of the water vapor transmission rate and the oxygen transmission rate of the obtained film are summarized in Table 1.

[0043]

[Table 1]

[0044]

The metal oxide-laminated polypropylene composite film of the present invention is a film having an excellent gas barrier property against water vapor and oxygen, and by utilizing its excellent gas barrier property, it can be widely used as a food packaging for snacks and the like. it can.

Claims (4)

[Claims] 1. A syndiotactic polypropylene polymer or a mixed resin layer of a syndiotactic polypropylene polymer and an isotactic polypropylene polymer (B) on at least one surface of a base layer (A layer) containing a polypropylene polymer as a main component. Layer) and a metal oxide laminated polypropylene composite film in which a metal oxide layer is laminated on the surface of the resin layer (B layer). 2. The metal oxide-laminated polypropylene composite film according to claim 1, wherein the mixing ratio of the syndiotactic polypropylene polymer to the entire B layer is 10% to 90%. 3. The metal oxide laminated polypropylene composite film according to claim 1, wherein the metal oxide layer has a thickness of 5 to 100 nm. 4. A biaxially oriented structure as claimed in claim 1.
~ 3 metal oxide laminated polypropylene composite film