JPH0712649B2 - Transparent plastic film with excellent gas barrier properties - Google Patents

Description

TECHNICAL FIELD The present invention relates to a transparent plastic film having excellent gas barrier properties. More specifically, the present invention relates to a transparent plastic film having excellent gas barrier properties, which is preferably used as a packaging material or the like.

(Prior art) Transparent plastic films used for packaging materials such as foods, pharmaceuticals, and chemicals are made of materials with low gas permeability such as water vapor and oxygen to prevent deterioration of the packaged contents. Has been. In the case of a packaging material that requires a higher gas barrier property, a film in which an aluminum foil is attached or a film in which aluminum is vapor-deposited has been used. However, a packaging material using such a metal foil has excellent gas barrier properties against water vapor, oxygen, etc., but is opaque and the contents cannot be seen from the outside. There was a side that was not suitable for.

On the other hand, polyvinylidene chloride, vinylidene chloride as a main component, other compounds copolymerizable therewith, for example, vinyl chloride, methyl acrylate, methyl methacrylate, a film made of vinylidene chloride resin such as acrylonitrile copolymer, A vinylidene chloride resin-coated film obtained by coating a film made of polypropylene, polyester, polyamide or the like with these vinylidene chloride resins is also used as a packaging material having gas barrier properties. These vinylidene chloride resin films have gas barrier properties against water vapor, oxygen, etc., but these gas barrier properties are not sufficient, and are not suitable for packaging materials that require a high degree of gas barrier properties. It was suitable.

Further, polyvinyl alcohol films and polyvinyl alcohol films such as ethylene-vinyl alcohol copolymer films are widely used as packaging materials because they have excellent oxygen barrier properties. However, the polyvinyl alcohol-based film is inferior in water vapor barrier property and further has a defect that the oxygen barrier property is deteriorated under the condition of high humidity. Therefore, when a polyvinyl alcohol-based film is used as a packaging material, a film having a water vapor barrier property such as a polypropylene film, a polyethylene film, and a polyester film is usually used as a laminated film obtained by laminating the polyvinyl alcohol-based film. However, such a laminated film has not been able to sufficiently fulfill its purpose as a packaging material which requires a high gas barrier property.

Therefore, in order to impart a high degree of gas barrier property to such a laminated film, the thickness of the laminated film must be increased. When the thickness of the film is increased, the transparency and flexibility of the laminated film are impaired. However, there is a drawback that the preferable properties as a packaging material are lost.

Films prepared by vapor-depositing silicon oxide or magnesium oxide on polyethylene terephthalate film, polypropylene film, polyamide film, etc. have also been proposed (Japanese Patent Publication No. 53-12953 and Japanese Patent Laid-Open No. 60-27532), but these films are also available. It is insufficient for applications that require a high degree of gas barrier properties.

In particular, the polyamide-based film is widely used as a packaging material because of its excellent strength, but it easily absorbs moisture,
Since there is a drawback that the gas barrier property is remarkably impaired by absorbing moisture, there is a problem that it is difficult to apply it to an application requiring a high gas barrier property. Also, a film obtained by vapor-depositing silicon oxide or magnesium oxide on a polyamide-based film is inferior in gas barrier property to a film obtained by vapor-depositing silicon oxide or magnesium oxide on a polyethylene terephthalate film or a polypropylene film, and requires a high gas barrier property. It was difficult to apply to the intended use.

(Problems to be Solved by the Invention) In view of the above-mentioned circumstances, the present invention has an object of providing a plastic film having excellent transparency and a high degree of gas barrier property and having a preferable performance as a packaging material. To do. As described above, the polyamide-based film is generally easy to absorb moisture, and the gas barrier property is significantly impaired by absorbing moisture. As a result of diligent studies on the physical properties of the polyamide-based film and its application, the present inventors have used a stretched polyamide-based film having both a small dimensional change rate at elevated temperature and a small volatilization loss, and a transparent thin film layer of silicon oxide in this film. It was found that the laminated film obtained has excellent transparency and exhibits an extremely excellent gas barrier property when the above is provided, and the present invention has been completed based on this finding.

(Means for Solving the Problem) That is, the gist of the present invention is that the sum of the absolute values of the dimensional change rates in the longitudinal direction and the lateral direction under conditions of 120 ° C. and 5 minutes is 2% or less, Further, the volatilization loss under the above conditions is 2% by weight or less, and a transparent thin film layer of silicon oxide is formed on one surface of a polyamide-based film stretched at least 3 times in a uniaxial direction. A transparent plastic film having excellent gas barrier properties, and another transparent plastic thin film laminated on the surface of the transparent thin film layer of silicon oxide formed on the transparent plastic film. Exists in excellent transparent plastic film.

The present invention will be described in detail below.

The polyamide-based film used in the transparent plastic film according to the present invention is a film made of a homopolymer of nylon 6, nylon 66, nylon 6-10, nylon 4-6 or the like, or a mixture thereof, and further a homopolymer thereof. A film made of a copolymer or the like in a range that does not change the basic properties of the polymer can be mentioned, and the homopolymer and the copolymer include those to which additives such as a lubricant and an antioxidant are added.

Polyamide film used in the present invention, 120 ℃,
The sum of absolute values of the dimensional change rates in the machine direction and the transverse direction under the condition of 5 minutes is 2% or less, and the volatilization loss under the above condition is 2% by weight or less, and the film is stretched at least uniaxially 3 times or more. It is necessary to use a polyamide based film.

When a polyamide film having a dimensional change rate exceeding 120 ° C. under the conditions of 120 ° C. and 5 minutes is used, even if a transparent thin film layer of silicon oxide is provided on one surface of the film, the gas barrier property is significantly improved. do not do. Although the detailed reason is not clear, the polyamide-based film is heated when the transparent thin film layer of silicon oxide is formed by means such as vacuum deposition, sputtering, or ion plating, and the heated polyamide is used. When the dimensional change occurs due to shrinkage or expansion of the system film and the dimensional change rate exceeds 2%, cracks, thickness irregularities, pinholes, etc. occur in the silicon oxide thin film layer, resulting in a uniform and dense film. It is presumed that this is because it is not a thin film layer.

When a polyamide film having a volatilization loss exceeding the above range is used, even if a transparent thin film layer of silicon oxide is provided on one surface of the film, the gas barrier property is not improved so much. Although the detailed reason for this is not clear, the film is heated when the transparent thin film layer of silicon oxide is formed on this film, and a volatile component such as a monomer volatilized from the heated film is formed normally. It is presumed that this is to inhibit

Furthermore, when a non-stretched film or a film having a stretch ratio less than the above range is used as the polyamide film, the gas barrier property is not improved so much even if a transparent thin film layer of silicon oxide is provided on one surface of this film. As long as the draw ratio is 3 times or more, it may be uniaxially stretched only or may be biaxially stretched. This polyamide-based film is not limited to a film stretched in one step, and may be a film stretched in multiple steps.

Dimensional change rate at elevated temperature, volatilization loss is within the above range, and the draw ratio is to obtain a polyamide-based film within the above range, after stretching the unstretched polyamide-based film to a predetermined draw ratio, The stretched film may be heated under a temperature condition of not less than the glass transition point and less than the melting point, a so-called heat setting operation may be performed, and the volatile components may be reduced within a predetermined range. In order to reduce the amount of volatile components within a predetermined range, the heat-fixed film is usually heat-treated at a temperature not higher than the heat-setting operation temperature under atmospheric pressure. The heat setting operation and the adjustment of the volatile components may be carried out simultaneously or separately under different conditions. When the volatile component is adjusted separately from the heat setting operation, the heat treatment for adjusting the volatile component can be performed under reduced pressure. The thickness of the polyamide-based film is selected from the range of 5 to 400 μm, particularly preferably 10 to 200 μm.

In the transparent plastic film according to the present invention, a transparent thin film layer of silicon oxide is formed on one surface of the polyamide film. In order to form a transparent thin film layer of silicon oxide on one surface of the polyamide-based film, any one of a vacuum deposition method, a sputtering method and an ion plating method may be used. For example, in the case of vacuum deposition, using a silicon monoxide or silicon dioxide as a deposition material, ^10-3
It is heated and evaporated by electron beam, high frequency induction heating resistance heating method under vacuum of ~ 10 ^-5 Torr. Further, a reactive vapor deposition method performed while supplying oxygen gas can also be adopted, and in this case, the vapor deposition material may be metallic silicon.

The transparent thin film layer of silicon oxide can also be formed by a sputtering method or an ion plating method, and these methods can form a transparent thin film layer having higher adhesion than the vacuum deposition method. The silicon oxide content is 10% by weight.
In the following cases, even if calcium, magnesium or their oxides are mixed in as impurities, the gas barrier property of the transparent plastic film is not extremely lowered. The thickness of the transparent thin film layer of silicon oxide is 5-50
It is preferable to select in the range of 0 nm. The thickness of the transparent thin film layer is 5 nm
Is less than 500n, the gas barrier property is insufficient.
If it exceeds m, curling occurs in the film, which causes a problem, or cracks or peeling easily occur in the transparent thin film layer itself.

The object of the present invention, on one side of the polyamide film,
This is more effectively achieved by newly providing another transparent plastic thin film on the surface of the transparent thin film layer of the film provided with the transparent thin film layer of silicon oxide. To provide another transparent plastic thin film, a method of laminating a transparent plastic film or forming a coating film of a transparent plastic material is adopted.

The new transparent plastic thin film (film or coating film) to be newly provided is not particularly limited, but the water vapor permeability measured at a temperature of 40 ° C. and a relative humidity of 90% is 50 g / m ² in accordance with ASTM F372. A material having a characteristic of 24 hrs. Or less is preferable, and its thickness can be selected in the range of 5 to 400 μm.

When a transparent plastic thin film is provided by laminating films, the plastic film preferably used is
Film made of olefin resin such as polyethylene and ethylene copolymer, polypropylene and propylene copolymer, film made of vinyl chloride resin such as polyvinyl chloride and its copolymer, vinylidene chloride-vinyl chloride copolymer Film made of vinylidene chloride resin such as, a film made of polyester resin such as polyethylene terephthalate, a film made of fluororesin such as polytetrafluoroethylene, and these films coated with other resin such as vinylidene chloride resin Examples include coated films. These films may be either unstretched or uniaxially or biaxially stretched. When laminating such another transparent plastic film on a transparent thin film layer of silicon oxide, a dry laminating method and an extrusion laminating method using a urethane adhesive, an acrylic adhesive, a polyester adhesive, etc. The known method of is adopted.

On the other hand, a coating agent is used when another transparent plastic thin film is formed by coating. Examples of suitable coating agents include vinylidene chloride-vinyl chloride-based resins such as vinylidene chloride-based resins, polyester resins such as polyethylene terephthalate, and solutions or emulsions of fluororesins such as polytetrafluoroethylene. A solution of a vinylidene-based resin latex and a vinylidene chloride-based resin dissolved in a solvent such as tetrahydrofuran is preferable. When the vinylidene chloride resin is applied to the transparent thin film layer of silicon oxide, an anchor coating agent is used to increase the adhesive strength of the vinylidene chloride resin. Suitable anchor coating agents include isocyanate-based, polyethyleneimine-based, organic titanium-based and other adhesion promoters, and polyurethane-based and polyester-based adhesives.

The thickness of the transparent plastic film having an excellent gas barrier property according to the present invention is 10 in terms of strength, flexibility, economy and the like.
It can be selected according to the application in the range of ~ 500 μm,
The thickness is more preferably 10 to 200 μm. In addition, the transparent plastic film of the present invention may be coated or laminated on the surface or other surface of the polyamide-based film, or on both sides with a substance that improves the heat-sealing property of the film depending on the usage form. Good. Examples of the substance that improves the heat-sealing property include low-density polyethylene, ethylene-vinyl acetate copolymer, polypropylene, and ionomer.

(Effect of the invention) The transparent plastic film according to the present invention is excellent in transparency and exhibits an extremely excellent gas barrier property, is flexible, and is also excellent in strength and economical efficiency. In addition, the gas barrier property is not impaired even when used for a long period under high humidity conditions. Therefore, food, medicine,
It can be used as a packaging material for a wide range of applications where a high gas barrier property is required, including packaging materials such as chemicals, and its industrial utility value is great.

(Examples) Hereinafter, the present invention will be described in detail based on Examples and in comparison with Comparative Examples, but the present invention is not limited to the following Examples unless the gist thereof is exceeded.

In the following examples, the dimensional change rate and volatilization loss of the polyamide-based film during heating, and the moisture permeability, oxygen permeability and transparency of the obtained transparent plastic film were measured or determined by the following methods. Further, the thickness of the transparent thin film layer of silicon oxide was measured by a crystal type film thickness meter.

Dimensional change rate and volatilization loss of polyamide film during heating: (1) Heat treatment film: Two films cut into 300 x 300 mm, each at a temperature of 25 ° C,
Conditioned at 50% relative humidity, 80 ℃
Heat treatment for 60 minutes at 100 ° C or 60 minutes at 100 ° C. After the heat-treated film was left in an atmosphere of temperature 25 ° C and relative humidity 0% for 48 hours, one film was weighed and the other film had a side length of 200 m.
A square mark of m was drawn so that each side of the square was parallel to the machine and transverse directions of the film. Then, the two films were heated in an oven at 120 ° C. for 5 minutes and then taken out, and left again in an atmosphere of a temperature of 25 ° C. and a relative humidity of 0% for 48 hours. The weight change and the square size change before and after heating in an oven at 120 ° C were measured, and the dimensional change rate and volatilization loss were calculated by the following formulas.

(2) Film not subjected to heat treatment In the above method for measuring the dimensional change rate and volatilization loss of the heat treated film, after conditioning in an atmosphere at a temperature of 25 ° C and a relative humidity of 50%, the temperature is kept at 80 ° C for 60 minutes or 100%.
The dimensional change rate and the volatilization loss were obtained by performing the same treatment as that of the heat-treated film except that the heat treatment was not performed at 60 ° C. for 60 minutes.

Vertical dimensional change (%) = I-I '/ I x 100 I: 120 ° C, vertical dimension before heat treatment for 5 minutes I': 120 ° C, vertical dimension after heat treatment for 5 minutes Horizontal Dimensional change rate (%) = II-II '/ II x 100 II: 120 ° C, lateral dimension before heat treatment for 5 minutes II': 120 ° C, lateral dimension after heat treatment for 5 minutes Volatile loss (%) = W−W ′ / W × 100 W: 120 ° C., film weight before heat treatment for 5 minutes W ′: 120 ° C., film weight after heat treatment for 5 minutes Moisture vapor transmission rate: According to ASTM F372, temperature 40 (B) In the case of a transparent plastic film in which only a silicon oxide thin film layer is formed on one side of a polyamide-based film at 90 ° C and a relative humidity of 90%, the silicon oxide thin film layer is highly humidified (90RH).
Side, the polyamide-based film was positioned on the absolutely dry side, and the measurement was performed. Further, on the surface of the thin film layer of (b) silicon oxide,
In the case of a transparent plastic film on which another plastic thin film other than polyamide-based film is further formed, the surface of this plastic thin film is placed on the high humidity (90% RH) side and the other surface is placed on the absolute dry state side for measurement. did.

Oxygen permeability: Measured under the conditions of a temperature of 30 ° C. and a relative humidity of 80% using an OX-TRAN100 type oxygen permeability measuring device manufactured by Modern Control Co.

Transparency: Evaluation was made with the naked eye, and those showing good transparency are indicated by ⊚.

Example 1 Nylon 6 (Novamid 1020CA manufactured by Mitsubishi Kasei) is used as 280
Extruded into a sheet form from the extruder at ℃, cooled rapidly with a cooling drum,
It was fixed to obtain an amorphous film. This film is 3 times in the machine direction at 50 ° C and 3 times in the transverse direction at 80 ° C (stretching ratio 3 × 3
Stretched and heat set at 130 ℃ for 2 seconds, thickness 15μ
A biaxially stretched film of m was obtained.

About the obtained biaxially stretched nylon 6 film, 100 ° C
After heat-treating for 60 minutes in the oven, heat-treat at 120 ° C for 5 minutes according to the method for measuring the dimensional change rate and volatilization loss, and measure the dimensional change rate and volatility loss in the vertical and horizontal directions. The results obtained are shown in Table 1.

This nylon 6 film is supplied to a vacuum evaporation device,
Under vacuum of 10 ^-5 Torr, by electron beam heating method of 10 kw,
99.9% pure silicon monoxide was evaporated by heating to obtain a transparent plastic film having a transparent thin film layer of silicon oxide having a thickness of 50 nm formed on one side of nylon 6 film.
With respect to the obtained transparent plastic film, the water vapor transmission rate and the oxygen transmission rate were measured by the methods described above, and the transparency was evaluated. The results are shown first.

Example 2 100 of biaxially stretched nylon 6 film in Example 1
The dimensional change rate and the volatilization loss in the longitudinal direction and the lateral direction were measured by the same method as in Example 1 except that the heat treatment conditions of 60 ° C. and 60 minutes were 80 ° C. and 60 minutes. The moisture vapor transmission rate and the oxygen transmission rate of the transparent plastic film obtained by vacuum-depositing silicon monoxide by the completely same method were measured, and the transparency was evaluated. The results are shown in Table 1.

Example 3 The same processes and evaluations as in Example 1 were performed, except that the thickness of the transparent silicon oxide thin film layer vacuum-deposited on one surface of the nylon 6 film was 20 nm.
The results are shown in Table 1.

Example 4 The same treatment and evaluation as in Example 1 were carried out except that the thickness of the transparent silicon oxide thin film layer vacuum-deposited on one surface of the nylon 6 film was 100 nm. The results are shown in Table 1.

Example 5 Instead of the biaxially stretched nylon 6 film stretched at a draw ratio of 3 × 3 used in Example 1, a biaxially stretched nylon 6 film stretched at a draw ratio of 3 × 5 was used. Otherwise, the same processing and evaluation as in Example 1 were performed. The results are shown in Table 1.

Example 6 The same treatment and evaluation as in Example 1 were carried out except that silicon dioxide (SiO ₂ ) was used instead of silicon monoxide (SiO) used as the vapor deposition material in Example 1. The results are shown in Table 1.

Comparative Example 1 100 of biaxially stretched nylon 6 film in Example 1
Example 1 except that no heat treatment was performed at 60 ° C. for 60 minutes.
The same treatment and evaluation as in the above were performed. The results are shown in Table 1.

Comparative Example 2 Instead of the biaxially stretched nylon 6 film stretched at a draw ratio of 3 × 3 used in Example 1, a biaxially stretched nylon 6 film stretched at a draw ratio of 2 × 2 was used. Was subjected to the same treatment and evaluation as in Example 1. The results are shown in Table 1.

Example 7 In a transparent plastic film obtained in Example 1 in which a transparent thin film layer of silicon oxide is formed on one surface of a nylon 6 film, the surface on which the silicon oxide is deposited is coated with vinylidene chloride resin. A 23 μm-thick polypropylene film (stretching ratio 5 × 5 times, moisture permeability 2.0 g / m ² · 24 hrs.) With a coat layer (thickness 3 μm) laminated (hereinafter referred to as “K-OPP”) , So that the vinylidene chloride resin coating layer and the silicon oxide vapor deposition surface are in contact with each other, a urethane adhesive (Takelac A-60, manufactured by Takeda Pharmaceutical Co., Ltd.
Two-component adhesive with a ratio of 6 to Takenate A-10 9: 1)
(Thickness 2 μm) was laminated to obtain a transparent plastic film. With respect to this transparent plastic film, the water vapor transmission rate and the oxygen transmission rate were measured by the above-mentioned methods, and the transparency was visually evaluated. The measurement results are shown in Table 2.

Example 8 Using the transparent plastic film obtained in Example 7,
A 40 μm-thick low density polyethylene film (LDPE) was laminated on the nylon 6 film surface via the urethane adhesive used in Example 7 to obtain a transparent plastic film. About this transparent plastic film,
The moisture permeability, oxygen permeability and transparency were evaluated in the same manner as in Example 7. The results are shown in Table 2.

Example 9 In the transparent plastic film described in Example 7, a 25 μm thick biaxially oriented polyethylene terephthalate film (PET) (stretching ratio 3 ×) was used instead of K-OPP laminated on the surface on which silicon oxide was deposited. Triple, moisture permeability 20g / m ²・ 2
A transparent plastic film was obtained in the same manner as in Example 7, except that 4 hrs.) Was used. The moisture permeability, oxygen permeability and transparency of this transparent plastic film were evaluated in the same manner as in Example 7. The results are shown in Table 2.

Comparative Example 3 The transparent plastic film obtained in Comparative Example 1 was laminated with K-OPP used in Example 7 on the silicon oxide vapor-deposited side, and the nylon 6 film surface on the opposite side was laminated with the example. A low density polyethylene film (LDPE) of the same type used in 8 was laminated to obtain a transparent plastic film. The moisture permeability, oxygen permeability and transparency of this transparent plastic film were evaluated in the same manner as in Example 7. The results are shown in Table 2.

The following is clear from Tables 1 and 2.

(1) In a transparent plastic film (hereinafter referred to as “film A”) in which a transparent thin film layer of silicon oxide is formed on one surface of a polyamide-based film, the polyamide-based film at 120 ° C. for 5 minutes When the sum of the absolute values of the dimensional change rates in the machine direction and the transverse direction, the volatilization loss under the above conditions, and the draw ratio within the range specified in the present invention is used, the water vapor transmission rate of "Film A" and Both oxygen permeability is small, and this film exhibits excellent gas barrier properties (Examples 1 to 6).

(2) In "Film A", as the polyamide-based film, other than the polyamide-based film specified in the present invention, that is, the sum of the absolute values of the dimensional change rates in the longitudinal and transverse directions at 120 ° C for 5 minutes. And a polyamide-based film (comparative example 1) having a volatilization loss larger than the range specified by the present invention under the above conditions, or a polyamide-based film having a draw ratio smaller than the draw ratio specified by the present invention (comparative example 2). The gas barrier properties of the obtained films are inferior to those of Examples 1 to 6.

(3) A film in which another transparent plastic thin film is formed on the surface of the transparent thin film layer of silicon oxide of "Film A" (hereinafter referred to as "Film B") has more moisture permeability and oxygen than "Film A". The permeability is lowered, and a more excellent gas barrier property is exhibited (Examples 7 to 9).

(4) The excellent gas barrier property of "Film B" does not change even if a substance improving the heat sealing property is laminated on "Film B".

(5) The film according to the present invention not only exhibits excellent gas barrier properties, but also has good transparency.

Claims (2)

[Claims] 1. The sum of the absolute values of the dimensional change rates in the vertical and horizontal directions at 120 ° C. for 5 minutes is 2% or less,
And the volatilization loss under the above conditions is 2% by weight or less,
A transparent plastic film having an excellent gas barrier property, characterized in that a transparent thin film layer of silicon oxide is formed on one surface of a polyamide-based film stretched at least three times in a uniaxial direction. 2. A transparent plastic thin film is laminated on the surface of a transparent silicon oxide thin film layer formed on one surface of a polyamide-based film. A transparent plastic film having excellent gas barrier properties as described above.