JPS6032576B2 - Method of laminating synthetic resin film on metal surface - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a three-layer laminated film for food packaging, in which another layer of synthetic resin film is laminated on a metal foil laminated on a synthetic resin film.

A three-layer laminated sheet with a metal foil as an intermediate layer and synthetic resin film layers on both sides is known, and is used for packaging, interior decoration, bag fabric, etc.

In particular, one layer of the synthetic resin film contains a heat-sealable crystalline olefin resin that is allowed to come into contact with food;
On the other hand, laminated sheets using a heat-resistant resin such as polyethylene terephthalate are widely used for food packaging bags that can be filled with food, sealed, and heat-sterilized. In the production of the above-mentioned three-layer laminated sheet, bonding between metal foil and synthetic resin film, especially in the case of heat-sterilized food packaging bags, the crystalline olefin resin and metal foil currently used in the layer that comes into contact with the food contents. Adhesion is one important issue.

For adhesion between metal foil and synthetic resin film, isocyanate-based or vinylidene chloride-based adhesives are mainly used. At a temperature of 100q0 or less, the layers are laminated by bonding using the above-mentioned adhesive by a roll pressure bonding method or the like.

The above-mentioned isocyanate-based adhesive has an excellent property that the adhesive layer does not peel or deteriorate even when subjected to high-temperature retort sterilization treatment at temperatures above about 120°C. It requires a cumbersome process of being kept for about a week for curing, and there are also some concerns about hygiene.

On the other hand, vinylidene chloride-based adhesives have the problem that the adhesive layer peels off during the overflow tort sterilization process, which limits the use of laminates using this type of adhesive. . Instead of using isocyanate-based or vinylidene chloride-based adhesives, a method has been proposed in which an organic solvent dispersion of maleic anhydride-modified polypropylene is used as an adhesive (Japanese Patent Application Laid-open No. 84088/1988).

In the proposed method, a synthetic resin film (
A two-layer sheet is used as a base, and another synthetic resin film (third layer) is adhered to the metal foil (second layer) surface of the two-layer sheet via the adhesive. ,
At that time, the base two-layer sheet with adhesive applied to the metal foil surface is heated to a temperature of approximately 200°C or higher for a considerable period of time, for example, longer than the sand in No. 1, to remove the solvent and form the modified polypropylene. It is necessary to perform melting, and this heating adversely affects the adhesion between the metal foil of the base two-layer sheet and the synthetic resin film (first layer). There is also a problem with the adhesion between the metal foil and the third layer of synthetic resin film, and when used in heat-sterilized food packaging bags, after heat-sterilization treatment, dot-like peeling phenomena appear between each layer, and pinholes occur. Cause. Furthermore, the problem of environmental pollution arises due to the use of organic solvents. Accordingly, an object of the present invention is to provide a method for laminating metal foil and synthetic resin film that is hygienically harmless and provides excellent adhesion.

A further object of the present invention is to provide a method for adhering a third layer of synthetic resin film to the surface of a metal foil without impairing the adhesion of the two-layer sheet made of synthetic resin film and metal foil.

A specific object of the present invention is to provide a three-layer laminate sheet of synthetic resin film-metal foil-synthetic resin film that is hygienically harmless and suitable for manufacturing heat-sterilized food packaging bags with excellent adhesion between each layer. .

The object of the present invention is to provide a method for laminating a synthetic resin film on the surface of a base metal foil, in which an adhesive synthetic resin powder is applied to the surface of the metal foil, the powder is heated and melted, and the synthetic resin powder is bonded. This is achieved by the metal foil/synthetic resin film laminating method of the present invention, which is characterized in that a synthetic resin film is layered thereon, heat-pressed, and then cooled.

The adhesive synthetic resin powder used in the method of the present invention has a solid particle size of 0.1 μm to 200 μm at room temperature, preferably <0.
．． It is a powder of 1 French to 100 r.

Examples of adhesive synthetic resin powders suitable for use in the present invention are maleic acid, fumaric acid, crotonic acid, itaconic acid,
Grafting with organic acids such as citraconic acid and acrylic acid or their esters or metal salts or acid anhydrides such as maleic anhydride, citraconic anhydride, and tetrahydrophthalic anhydride;
Modified polyolefin resin such as flock or random copolymerized modified polyethylene, modified polypropylene, modified ethylene-propylene copolymer, modified poly-4-methylbentene-1, or a mixture of the above-mentioned modified polyolefin resin and unmodified polyolefin resin; nylon 6,
These are powders of nylon resins such as nylon 60, nylon-11, nylon-12, or copolymerized nylon resins thereof, epoxy resins, polyester resins, polyester ether resins, fluorine resins, and the like.

The adhesive synthetic resin powder exemplified above is coated onto the surface of the metal foil base without using any liquid medium while it is in the form of a solid powder.

The most preferred coating method is an electrostatic coating method such as a static dew spraying method or an electrostatic moving bed method, but a method of simply scattering the powdered resin onto the surface of the metal foil can also be used. The amount of adhesion of the adhesive synthetic resin powder is preferably 0.1 to 1.0 evening/day, and more preferably 1.0 to 5.0 evening/day. The adhered adhesive synthetic resin powder is then heated and melted at a temperature higher than its melting temperature, preferably at a temperature 10 to 100 oo higher than its melting temperature.

As described above, a synthetic resin film having adhesive properties with the adhesive synthetic resin is placed on the coating layer of the adhesive synthetic resin formed on one surface of the base metal foil, preferably on the coating layer in a molten state. are preferably melt-extruded, stacked, and heat-pressed to obtain a desired laminate.

Examples of synthetic resin films used include polyethylene, polypropylene, ethylene-propylene random or block copolymer, poly-4-methyl-bentene-1, nylon-6, nylon-16, nylon-11, and nylon-1.
12, or a copolymer thereof nylon, polyethylene terephthalate, polybutylene terephthalate, polyethylene isophthalate or a copolymer polyester thereof,
The film is made of synthetic resin such as polyester ether or fluororesin and has a thickness of 30 to 150 mm, preferably 50 to 80 mm.

The temperature and pressure for heat-pressing these films should be selected depending on the type of synthetic resin that makes up the film, but in general, the temperature and pressure are 150 to 3
Temperature of 50oo, preferably 180-30pi0, 0.5
The pressure ranges from ~30 k9/kg, preferably from 1 to 10 kg/kg.

The metal foil used in the present invention is aluminum, copper,
Foils such as iron, zinc, tin or chromium-treated iron.

A two-layer laminate in which a synthetic resin film, such as a heat-resistant synthetic resin film such as polyethylene terephthalate, nylon 6, nylon 60, Teflon, or polyimide, is adhered to one side of the metal foil with an adhesive, or an epoxy resin, It is possible to use a coated metal foil that is coated on one side of the metal foil with a glazing paint made of a thermosetting resin such as a silicone resin, an epoxyphenol resin, an alkyd resin, or a polyimide resin. A sheet with a three-layer structure is obtained in which synthetic resin films are laminated on both sides of metal foil, and the synthetic resin films on both sides may be of the same type or of different types. The method of the present invention described above is characterized in that a crystalline polyolefin, such as polyethylene, polypropylene, It is particularly suitable for producing three-layer laminated sheets for use in heat-sterilized food packaging bags by laminating films of ethylene propylene random or block copolymers, poly-4-methylbentene-1, etc.

For this purpose, it is preferable to use a maleic acid-modified polypropylene powder having an average molecular weight of 0.5 to 2.2 in intrinsic viscosity measured at 1360 in decalin. mosquito)
The metal foil-heat-resistant synthetic resin film two-layer sheet used for manufacturing the three-layer laminated sheet is a metal foil with a thickness of 5 to 30 Å, preferably 7 to 12 Å, and is coated with isocyanate-based or epoxy-isocyanate-based adhesive. Thickness 3-30A depending on agent
, preferably one made by adhesively laminating heat-resistant synthetic resin films of 5 to 15 degrees, and a crystalline polyolefin film is laminated on the metal foil surface of this laminated sheet by the method of the present invention.

In this case, what is important is that after coating the adhesive synthetic resin powder in solid form on the surface of the metal foil of the two-layer laminate sheet, the heat applied when melting it should be 0.1 to 1 sand, preferably 0. .1
This is done for a very short time of ~3 seconds so that the adhesion between the metal foil of the two-layer laminate sheet and the heat-resistant synthetic resin film is not impaired. For this purpose, the surface of the metal book is heated to 150 to 350 o0, preferably 180 to 350 o0, by high-frequency induction heating.
The best method is to heat to 250 oo for the short time described above. A method and apparatus for performing high-frequency induction heating on the surface of a metal foil and subsequent thermocompression bonding of a third layer of synthetic resin film are disclosed in the patent application filed in 1986 by the inventors of the present invention.
The high frequency induction heating and thermocompression bonding method and apparatus described in the specification of No. 044 can be suitably used.

It is described in the specification of Tokujo No. 53-186044. In a high-frequency induction heating device in which the ferrite core of a high-frequency coil is slidable toward the heated object, a steel plate is further slidably attached to the coil, making it easier to adjust the heating temperature. It is better. In other words, in this device, the temperature rise in the part of the sheet that faces the part where the ferrite core is attached increases, and the temperature rise in the part of the sheet that faces the part where the steel plate is attached decreases, so that the temperature distribution can be arbitrarily controlled. Can be adjusted. The method of the present invention improves the adhesive strength between each layer, especially compared to the method using an organic solvent dispersion of maleic anhydride-modified polypropylene.
The heat resistance Ck of adhesive strength is remarkably excellent, and after heat sterilization, there is little decrease in adhesive strength between each layer during long-term storage of food contents, and the peeling phenomenon that appears in dots that causes pinholes is also reduced.

Moreover, the flavor of the food contents is well maintained even after sterilization. Another advantage is that there is little variation in the printing pitch of printed products. Examples and comparative examples are given below,
The present invention and its advantages will be specifically explained. The tests shown in Examples were conducted as follows.

Laminate strength The laminate was cut into 15 strips and tested using an Instron tensile tester at a tensile speed of 30 m/min.
Perform 800 peel test.

Flair/I-Test A bag to be tested is filled with pure water, heat sterilized at 135°C for 10 minutes, and a panel of 25 people are asked to drink the treated pure water and evaluate its taste and odor.

Example 1 A printed polyethylene terephthalate film of 12 mm and 9 mm aluminum foil were mirror-layered with a urethane adhesive.

The aluminum foil surface of this laminate, which moves at a continuous speed of 10 times, has an average grain size of 50 peaks and a melt index (MI
) is 30 evening/1 hour, and the average carbonyl group concentration is 7
Powder of maleic acid-modified polypropylene resin (density of resin 0.90) having a milliequivalent weight/100 mm polymer and a melting point of 16 mm was applied with an electrostatic coating gas at a coating amount of 2.0 mm/cm. .

The discharge pressure was 1.1k9/ground, and the applied voltage was 90KVolt. Thereafter, the high frequency voltage of the high frequency conductive heating coil installed at a distance of 1.5 ground from the polyethylene terephthalate film side of the moving film is increased by 2.5 ground. Make the skin V and apply aluminum foil of powder coated laminate to approx.
The powder was heated for seconds to melt and adhere to the aluminum foil.

After that, the powder-coated surface of this laminate was coated with a powder having a melting point of 158°C.
A film of 70 molar thickness of an ethylene-propylene block copolymer having a density of 0.90 m/s, a melt index of 8.0 m/1 ratio, and an ethylene content of 5 mol% was brought into contact with 230 qo. 6k between the heat roll on the 9th side and the silicone rubber roll on the 9th side heated to
The laminated film and the polypropylene film were formed into a mirror layer by thermocompression bonding at a pressure of 9/mass.

After that, this laminate was heated 19 times with a cooling roll for 20 minutes.
After cooling to 0.00, a laminate free of print pitch variations, wrinkles, and curling was obtained.

Between the aluminum foil and polypropylene film of this laminate,
The lamination strengths between the aluminum foil and the polyethylene terephthalate film were 700 mm/15 mm and 520 mm/15 mm, respectively.

When this laminate was treated with heated steam at 135o0 for 10 minutes, there was no peeling between the layers, and the laminate strengths between aluminum foil and polypropylene film and between aluminum foil and polyethylene terephthalate film were 650, respectively.
It was in the evening/15 side and 50M/15 in the skin.

A bag with a size of 13 mosquito/17 mosquito was made from this laminate, filled with water, and subjected to retort sterilization for 135 q01 min.

A flavor test was conducted on this water, and the results shown in Table 1 were obtained. In addition, this bag is filled with instant curry and heat sterilized for 13yo for 10 minutes to produce 25q.
As a result of a storage test for 3 months at 0.0, the bags with dots of peeling between the aluminum foil and polypropylene film had a 0.00
It was 1%.

Comparative Example 1 The same modified polypropylene resin powder used in Example 1 was dispersed in kerosene (boiling point 175-325°C) and
A dispersion was made that was a partial solution of % solids concentration.

This was applied using a 120-mesh gravure cylinder to the aluminum foil of a laminate of 12-mesh polyethylene terephthalate and 9-m aluminum foil printed using the same method used in Example 1, so that the coating amount was 2.0 m/m. The kerosene was evaporated and the modified polypropylene resin was melted at the same time by passing it through an oven at 240°C for 20 seconds. It was pressed and cooled to obtain a laminate. In this laminate, the polyethylene terephthalate film stretched, causing the printing pitch to become incorrect and making the bagging process difficult. In addition, the appearance of vertical wrinkles was also observed. The lamination strength between aluminum foil and polypropylene film and between aluminum foil and polyethylene terephthalate film is 6.
70 evenings/15 sides and 350 evenings/15 pieces.

When this laminate was exposed to high-temperature steam at 135° C. for 10 minutes, peeling occurred between the aluminum foil and the polypropylene film at the wrinkled portions. In addition, the lamination strength between the polyethylene terephthalate film and the aluminum foil decreased by 105/15 times. From this laminate 13 yards x 17
Make a bag the size of the ship's side, fill it with 180' of water, and
High temperature heat sterilization was performed at 5 qo for 10 minutes, and the water was subjected to a flavor test. The results are shown in Table 1. In addition, when instant curry was filled and heat sterilized at 135℃ for 10 minutes, and a long-term storage test was conducted at 25℃ for 3 months, only 1% of the bags had dots of peeling between the aluminum foil and polypropylene film. It's been found.

Table 1 Flavor test Number of panels: 25 people

Claims (1)

[Claims] 1. A method of manufacturing a three-layer laminate sheet of a synthetic resin layer-metal foil-synthetic resin layer by laminating a synthetic resin film on the metal foil surface of a two-layer laminate sheet consisting of a synthetic resin layer-metal foil. , applying an adhesive synthetic resin powder comprising a modified polyolefin resin copolymerized with an α,β-ethylenically unsaturated organic carboxylic acid or its ester, metal salt, or acid anhydride on the surface of the metal foil; The powder is heated and melted by high frequency induction heating to adhere the synthetic resin powder,
A method for producing a three-layer laminated sheet for food packaging, which comprises stacking a synthetic resin film thereon, heat-pressing it, and then cooling it. 2. The manufacturing method according to claim 1, wherein the heating time by high frequency induction heating is 0.1 seconds to 10 seconds.