JPS62275134A - Bonding - Google Patents

Abstract

PURPOSE:To bond a polar group-containing thermoplastic resin film to an ethylene/unsaturated ester copolymer film without using any adhesive, by subjecting the bonding surface of each film to corona discharge treatment and heating each surface to a specified temperature. CONSTITUTION:The bonding surface of each of a polar group-containing thermoplastic resin film (A) (e.g., polyester film) and an ethylene/unsaturated ester copolymer film (e.g., ethylene/vinyl acetate copolymer film) which is a copolymer (B) of ethylene with a vinyl ester or an unsaturated carboxylic acid produced by a high-pressure radical polymerization process is subjected to corona discharge treatment, and components A and B are bonded together by heating at a temperature of from the m.p. of component B to the m.p. of component A.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for adhering a thermoplastic resin film having a polar group and an ethylene-unsaturated ester copolymer film.

[Prior art and problems to be solved by the invention] Thermoplastic resins have various characteristics such as mechanical properties, heat resistance, and gas barrier properties, and can be processed into films or sheets and used as packaging materials. It's being used. For example, polyester film has excellent heat resistance, mechanical properties, dimensional stability, electrical insulation, etc., and is widely used as an industrial material. Furthermore, it has excellent transparency, aroma retention, gas barrier properties, etc., and is widely used as a packaging material for foods and the like.

When used as packaging materials, polyester films, nylon films, and other films with poor self-thermal adhesive properties are generally used by laminating them with polyolefin resins that have excellent self-thermal adhesive properties.

As for lamination methods, for example, polyester, nylon, etc. and polyolefin generally do not adhere to each other with sufficient strength even if they are heat-fused, so conventional methods require the use of solvent-based adhesives. Met. For example, conventional methods include applying a solvent-based adhesive to the corona-discharge treated side of a polyester film and extrusion coating the polyolefin at temperatures above 300'C; Examples include a method of coating the polyolefin film and heat-pressing it to the corona discharge treated surface of the polyolefin film at a temperature of 40 to 100°C.

However, the use of an adhesive may cause the solvent constituting the adhesive to remain in the film, which may be undesirable depending on the intended use of the resulting laminated film. Furthermore, these methods have the disadvantage that the steps are complicated.

[Means for solving the problem] As a result of intensive research by the present inventors to solve the problem,
Among thermoplastic resins, thermoplastic resin films with polar groups and polyolefin films can be used for bonding, which was previously considered impossible without the use of solvent-based adhesives.
In particular, we have found a method for bonding ethylene-unsaturated ester copolymer films in combination and have arrived at the present invention.

That is, the gist of the present invention is to apply a corona discharge treatment to the adhesive surfaces of a thermoplastic resin film having a polar group and an ethylene-unsaturated ester copolymer film, and to The present invention relates to a method of bonding these by heat bonding at a temperature range equal to or higher than the melting point of the saturated ester copolymer.

In the heat bonding method of the present invention, it is necessary to subject both the adhesive surfaces of the thermoplastic resin film having polar groups and the ethylene-unsaturated ester copolymer film to corona discharge treatment, and only one of them must be subjected to corona discharge treatment. In this case, the adhesive strength becomes extremely small and it is impossible to use it practically.

In general, corona discharge treatment is a well-known technique for treating the surface of non-polar resins such as polyolefins in order to improve their affinity for coating materials such as adhesives, inks, and paints, and is generally commonly performed. It is.

Furthermore, a technique for obtaining a laminate by pressing corona discharge treated surfaces together is also known (Japanese Patent Publication No. 39-27657).
This technique achieves adhesion to the extent that the laminate can be peeled off by bending. This was an unimaginable technique for adhering polyolefins so strongly that they could not be peeled off.

The thermoplastic resin having a polar group used in the present invention is
polyester, nylon, cellophane, polyvinyl chloride,
It is a polymer such as polystyrene or fluororesin, and the film can be used either unstretched or stretched. Furthermore, thermoplastic resins having polar groups other than those mentioned above can also be used.

The ethylene-unsaturated ester copolymer (hereinafter referred to as ethylene copolymer) used in the present invention is a copolymer of ethylene and vinyl ester produced by high-pressure radical polymerization method, or an unsaturated carboxylic acid copolymer. It is an ester copolymer. Specifically, ethylene and vinyl ester copolymers such as vinyl acetate, vinyl butyrate, vinyl propionate, and vinyl benzoate, or ethylene and unsaturated carboxylic acids such as methyl, ethyl, n-butyl, and isobutyl of acrylic acid or methacrylic acid. Examples include acid ester copolymers. The content of the comonomer in these copolymers is not particularly limited, but is preferably 3% by weight or more. Further, the ethylene copolymer used in the present invention may be a graft copolymer of an unsaturated carboxylic acid or an unsaturated carboxylic acid anhydride, if necessary.

Furthermore, the ethylene copolymer used in the present invention may be blended with a tackifying resin, if necessary. Examples of the tackifying resin used here include aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, terpene resins, rosins, and styrene resins. These are used in an amount of 1 to 20 vt% of the blend. In addition, the ethylene copolymer used in the present invention may contain processability improvers, antioxidants, weather resistance improvers, and inorganic materials that are usually added to polyolefins, as long as they do not impair the effects of the present invention during film forming. Fillers can also be blended.

The corona discharge treatment in the present invention is carried out by a conventional method, that is, a high voltage (several thousand volts) is applied between a grounded metal roll and a knife-shaped electrode placed at a certain distance (several lIII) to generate a corona discharge. This can be carried out by a method in which the object to be processed (film, etc.) is passed between an electrode and a roll at high speed.

Although the degree of corona discharge treatment in the present invention is not particularly strictly limited, this treatment improves the wetting properties of the film surface to be adhered, that is, the wetting tension (J Is
-8788) is 40 dyn/cm or more (by the way, the surface of untreated polyester film is 30 to 34 dyn/cm)
yn/cm) is sufficient.

Films whose surfaces have been treated in this way are heat-bonded by bringing the treated surfaces together, but heat bonding is difficult at temperatures below the melting point of the thermoplastic resin with polar groups and above the melting point of the ethylene-unsaturated ester copolymer. Heat bonding within a temperature range. The two films will not adhere unless the temperature is above the melting point of the ethylene-unsaturated ester copolymer. Preferably 100
~200°C. As the heat bonding method, a conventionally used method can be used as is. Specifically, hot press, thermal laminator, vacuum forming, etc. can be mentioned.

[Effects of the Invention] According to the present invention, thermoplastic resin films with polar groups and polyolefins, which could not be bonded conventionally without the use of an adhesive, can now be easily bonded without using a specific polyolefin. However, it is possible to bond not only two layers of a thermoplastic resin with a polar group and polyolefin, but also three layers, for example, polyester/polyolefin/polyester and polyvinyl chloride/polyolefin/nylon, by corona treatment on both sides of the polyolefin film. can be obtained without using an adhesive. Conversely, by subjecting both sides of the polyester film to a corona discharge treatment, a three-layer structure of polyolefin/polyester/polyolefin can also be obtained.

Furthermore, for example, by using a polyolefin grafted with an unsaturated carboxylic acid, polyester/
It is also possible to obtain a three-layer composition: polyolefin/metal.

As described above, it is a feature of the present invention that a wide variety of (1) products can be obtained by using the adhesive method of the present invention.

[Example] Next, the present invention will be further explained with reference to Examples.

(Example 1) Using a high-frequency oscillator, a biaxially stretched polyester (polyethylene terephthalate) film (thickness 12 μm) and an ethylene-vinyl acetate copolymer film (thickness 40 μm
A corona discharge treatment (processing capacity 50 watts/rrl') was performed on one side of each ethylene-vinyl acetate copolymer (abbreviated as EVA) having a vinyl acetate content of 15 weight x 1 or less. Wetting tension of corona discharge treated surface (J Is-8788
According to ), the polyester film is 48 dyn/amS
The EVA was 45 dyn/cm, and it was confirmed that the discharge treatment was sufficiently performed in all cases.

The corona discharge-treated surfaces of these films were placed together and heat-pressed using a thermal laminator (roll temperature: 135° C., line speed: 411/m1n).

The peel strength of this two-layer polyester/EVA film was measured. The results are shown in Table-1.

(Examples 2 to B, Comparative Examples 1 to 6) Instead of the polyester film used in Example 1, nylon film (thickness 15 μm) (Example 2), hard polyvinyl chloride (thickness 65 μff1) (Example 3) , cellophane (thickness 23 μm) (Example 4), high impact polystyrene (thickness 350 μm) (Example 5), surface fluorinated low density polyethylene (thickness 100 μm) (
The procedure was the same as in Example 1 except that Example 6) was used. The results are shown in Table-1.

(Example 7) Using a high frequency oscillator, a biaxially stretched polyester (polyethylene terephthalate) film (thickness 50 μm) and E
One side of each VA (thickness: 50 μm, vinyl acetate content: 7% by weight) was subjected to corona discharge treatment.

The corona discharge treated surfaces of these films were placed together and heat-pressed using a thermal laminator (roll temperature: 160° C., line speed: 2 I/win).

This two-layer film of polyester/EVA was heat-sealed so that the EVA was placed on the inner surface (heat-sealing temperature: 140°C, heat-sealing time: 1 second).
. The adhesive strength of the corona discharge treated surface was measured by measuring the heat seal strength of this heat sealed laminate. The results are shown in Table 2 (the heat seal strength in Table 2 indicates the adhesive strength).

(Examples 8 to 10) Using the ethylene copolymers shown in Table 2,
Adhesion was carried out in the same manner as in Example 1, and the heat seal strength was measured. The results are shown in Table-2.

(Example 11) Both sides of the EVA film used in Example 7 were corona treated, and a three-layer laminate polyester/EVA was formed around it.
/ Adhesion was carried out in the same manner as in Example 8 except that polyester was used. Table 2 shows the peel strength of this three-layer laminate.

(Example 12) A three-layer laminate polyester was prepared using a corona-treated film of a composition consisting of 90% EVA with a vinyl acetate content of 10% by weight and 10% alicyclic hydrocarbon as a tackifying resin. Adhesion was carried out in the same manner as in Example 8 except that /EVA/high impact polystyrene was used. This 3
Table 3 shows the peel strength of the layer laminate.

(Example 13) Adhesion was carried out in the same manner as in Example 12, except that kraft paper was used instead of high impact polystyrene. This 3
Table 2 shows the peel strength of the layer laminate.

(Comparative Examples 1 to 6) Examples 1 to B were carried out except that the adhesive surface of the ethylene-vinyl acetate copolymer film was not corona-treated and the adhesive surface of the adhered substrate (polyester film, etc.) was corona-treated. It was the same as Examples 1 to 6.

(Comparative Example 7) In place of the polyester film in Example 1, biaxially oriented polypropylene (OPP thickness 25
μl! The procedure was the same as in Example 1 except that 1) was used.

(Comparative Example 8) In Comparative Example 1, instead of the polyester film, a non-polar resin film of biaxially oriented polypropylene (thickness: 25 μl) was used.
The procedure was the same as in Example 1 except that 1) was used.

(Comparative Example 9) Adhesion was carried out in the same manner as in Example 7, except that a polyester film that had not been subjected to corona treatment was used, and the heat seal strength was measured. The results are shown in Table-2.

(Comparative Example 10) Adhesion was carried out in the same manner as in Example 6, except that a polyester film that had not been subjected to corona treatment was used, and the peel strength of this laminate was measured. The results are shown in Table-2.

From Table 8, it can be seen that the adhesive bonded according to the present invention exhibits excellent adhesive properties.

In addition, P-E in Table-1 on the next page: Polyester film N-Y
: Nylon film II-PVC: Rigid polyvinyl chloride film III-P
S: High impact polystyrene F-LDPE
: Fluorinated low density polyethylene PP: Biaxially oriented polypropylene.

Moreover, the bonding conditions are as follows.

Adhesion method: Carmal laminator Heating temperature: 135°C

Claims (1)

[Claims] 1) The adhesive surfaces of the thermoplastic resin film having polar groups and the ethylene-unsaturated ester copolymer film are each subjected to a corona discharge treatment, and the adhesive surfaces of the thermoplastic resin film having polar groups and the ethylene-unsaturated ester copolymer film are 1. A method for adhering a film, characterized by heat adhesion at a temperature range equal to or higher than the melting point of the unsaturated ester copolymer. 2) The method according to claim 1, wherein the thermoplastic resin having a polar group is a resin selected from the group of polyester, nylon, polyvinyl chloride, cellophane, polystyrene, and fluororesin.