JP5063932B2 - Laminated film and method for producing laminated film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laminated film having high adhesive strength even if the laminated film is manufactured by thermal pressure bonding without using an adhesive layer or an anchor coating layer and capable of holding the high adhesive strength even if the adhesive layer is brought into contact with moisture. <P>SOLUTION: The laminated film has a laminated structure wherein the treatment surface of a second resin film subjected to surface treatment by an oxygen atom and/or a nitrogen atom is bonded to the treatment surface of a first resin film subjected to surface treatment by the nitrogen atom under pressure without interposing the adhesive layer between both treatment surfaces. The adhesive strength of the laminated structure measured according to "adhesive peel adhesive strength testing method the first section 90&deg; peeling" of JIS K 6854-1 after water is brought into contact with the lamination interface of the laminated structure is 2.0 N/15 mm or above. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to a laminated film having a laminated structure in which resin films are laminated, for example, a laminated film used for packaging materials and the like, and a method for producing the same. More specifically, the present invention relates to a laminated film having a laminated structure in which one resin film and another resin film are pressure-bonded without using an adhesive layer or an anchor coat layer, and a manufacturing method thereof.

  In the field of packaging containers and bags (hereinafter collectively referred to as “packaging containers”) used for packaging foods, beverages, pharmaceuticals, etc., the contents of the contents to be laminated and packaged by combining two or more types of resin films A laminated film having a necessary function is used depending on the property, the method of using the packaged package, and the like. As such a laminated film, for example, a polyolefin such as polyethylene having excellent sealing properties on the inner surface of the packaging container serving as a sealing surface in order to heat-seal and seal the filling port of the packaging container after filling the contents A resin layer is used as a sealant layer. The laminated film is laminated with a resin film such as polyester, nylon, or polypropylene in order to reinforce the strength or impart other functions. For this reason, a laminated film in which a polyethylene resin and, for example, a polyester film are laminated in advance is prepared and molded into a final packaging container.

  By the way, when a polyethylene resin and another resin film are laminated by pressure bonding, the adhesive strength may be insufficient unless an adhesive layer or an anchor coat layer is used. However, when an anchor coat layer or an adhesive layer is used, VOC (volatile organic compound) generated by evaporating and drying the solvent in forming them is a problem that is dissipated into the atmosphere. In addition, when an adhesive layer is used, an aging period of about several days is required after dry lamination, and there is a problem of production efficiency. Furthermore, in the contents, for example, medical fluids such as infusion solutions, a solvent remaining in the anchor coat layer or the adhesive layer, or a low molecular component resulting from the anchor coat agent or the adhesive may cause an interaction. Also, odor may be a problem in foods and the like. For this reason, it is required to produce a laminated film having high adhesive strength without using an anchor coat layer or an adhesive layer.

In response to such a demand, various proposals have been made regarding manufacturing a laminated film without using an anchor coat layer or an adhesive layer by performing a treatment for increasing the adhesive strength (for example, Patent Document 1). ~ 4).
In Patent Document 1, at least one surface of a plastic substrate is oxidized by corona treatment, plasma treatment, flame plasma treatment, electron beam irradiation, ultraviolet irradiation, etc., and at least one surface of a melt-extruded film is subjected to ozone treatment. An extrusion laminating method in which both are brought into contact with each other and pressure-bonded is described.
In Patent Document 2, at least one surface of a plastic substrate is subjected to electron beam irradiation treatment, low-pressure plasma treatment, atmospheric pressure plasma treatment, or corona discharge treatment in an atmosphere of an inert gas such as argon, helium, krypton, neon, xenon, or nitrogen. And an extrusion laminating method in which at least one surface of a melt-extruded film is subjected to ozone treatment and then brought into contact with each other and pressure-bonded.

In Patent Document 3, in order to activate the surface of the synthetic resin and improve the adhesion to the printing ink and the metal vapor deposition film, a mixed gas atmosphere substantially composed of nitrogen and carbon dioxide (preferably the oxygen concentration is 0.1 vol. % Or less), a surface treatment method for a synthetic resin is described.
Patent Document 4 discloses the number of nitrogen and carbon atoms on the surface of a substrate film by ESCA method by corona discharge treatment in nitrogen gas (oxygen concentration of 3 vol% or less), carbon dioxide gas or a mixed gas atmosphere of nitrogen / carbon dioxide gas. A surface to be processed having a ratio (N / C) in the range of 0.001 to 0.1 is generated, and a water / lower alcohol mixed solution or water is used as a solvent on the surface to be processed. A method for producing a gas barrier film is described in which a coating agent containing a layered compound as a main constituent is applied and dried to form a coating film.
JP 7-314629 A JP-A-9-234845 Japanese Patent Publication No.57-30854 Japanese Patent Laid-Open No. 9-1111017

  However, in the methods proposed in Patent Documents 1 and 2, the adhesive strength may be insufficient only by performing a combination of a corona treatment in a known air atmosphere and a UV / ozone treatment. Furthermore, the laminated sheets obtained by the methods proposed in these methods have a problem that the adhesive strength is greatly reduced when the adhesive interface comes into contact with moisture. In the field of packaging materials, this problem is serious, meaning that it is not suitable for packaging of contents containing moisture or packaging of contents subjected to sterilization treatment such as boil sterilization and retort sterilization. When packaging the contents containing moisture, the moisture reaches the adhesion interface through the sealant layer, so the adhesion strength at the adhesion interface decreases. In addition, in the case of contents to be sterilized, moisture enters into the adhesive interface through the resin film on the surface layer or from the end face through the process of boil sterilization with hot water or steam and retort sterilization. This is because the adhesive strength of the resin decreases.

Patent Documents 3 and 4 describe methods for improving the adhesion by modifying the surface of a synthetic resin by corona discharge treatment in a nitrogen atmosphere. However, these patent documents do not describe the lamination of resin films. The object to be bonded is a nitrocellulose-based printing ink, a metal vapor-deposited film, a water-soluble polymer, and a layered clay compound that are unrelated to the resin film.
Therefore, no solution is shown for improving the adhesive strength at the lamination interface in the lamination of the resin films.

  The present invention has been made in view of the above problems, and even if it is laminated by thermocompression bonding without using an adhesive layer or an anchor coat layer (hereinafter collectively referred to as “adhesive layer”), high adhesion is achieved. Providing a laminated film or sheet having a strength and having a laminated structure that retains high adhesive strength even when the adhesive interface comes into contact with moisture (hereinafter collectively referred to as “film”) and a method for producing the same. Let it be an issue.

To solve the above problems, the present invention is, in a nitrogen gas atmosphere, the nitrogen gas oxygen gas concentration in the atmosphere is below 2% volume ratio, the more corona discharge treatment, was subjected to a surface treatment with a nitrogen atom on the treated surface of the first resin film, the in an atmosphere containing oxygen gas and / or nitrogen gas, corona discharge treatment, or more UV / ozone treatment was subjected to a surface treatment with oxygen and / or nitrogen atom 2 is a laminated film having a laminated structure in which the treated surface of the resin film is thermocompression bonded by thermal lamination without using an adhesive layer, and the resin constituting the first resin film is the second film. It has a glass transition temperature higher than that of the resin constituting the resin film, and the laminated structure is formed by bringing water into contact with the laminated interface, and JIS K 6854-1 “Adhesive Peeling Adhesive Strength Test Method” Provided is a laminated film having an adhesive strength measured in accordance with “Part 1: 90 degree peeling” of 2.0 N / 15 mm or more.
In the surface treatment of the first resin film, the oxygen gas concentration in the nitrogen gas atmosphere is preferably 50 ppm or less.
The laminated structure preferably has an adhesive strength of 3.0 N / 15 mm or more measured according to JIS K 6854-1 “Adhesive Peeling Adhesive Strength Test Method Part 1: 90 ° Peeling”.
It is preferable that the first resin film is made of polyester or polyamide, and the second resin film is made of polyolefin.

Further, the present invention provides a method for producing a laminated film described above, the surface of the first resin film, a first processing step of performing more surface treatment corona discharge treatment under the nitrogen gas atmosphere, the on the surface of the second resin film, in an atmosphere containing oxygen gas and / or nitrogen gas, corona discharge treatment, or a second processing step of performing more surface treatment UV / ozone treatment, said first resin film A method for producing a laminated film, comprising: a laminating step of superposing the surface of the second resin film on which the surface treatment has been performed and performing thermocompression bonding by thermal lamination. provide.
Note that 1 gf / inch = 9.8 mN / 25.4 mm = 5.79 mN / 15 mm.

  According to the present invention, a laminated film that has high adhesive strength when laminated by thermocompression bonding without using an adhesive layer or an anchor coat layer and that can maintain high adhesive strength even when the adhesive interface comes into contact with moisture is produced. can do. Such adhesive performance cannot be obtained with a laminate using a conventional adhesive or anchor coat layer, and it is difficult to explain only with an adhesive mechanism based on hydrogen bonding or intermolecular force at the adhesive interface. By using a nitrogen functional group on the other side, not only van der Waals force and hydrogen bond, but also coulomb force can be used, which is considered to further increase the adhesive strength.

Although the adhesion mechanism by which high adhesive strength is obtained between the resin layers of the laminated film according to the present invention is not clear, for example, the following adhesion mechanism can be considered.
First, the surface of the first resin film is subjected to a surface treatment by corona discharge treatment in a nitrogen gas atmosphere with an oxygen gas concentration in the nitrogen gas atmosphere of 2% or less in volume ratio , whereby a surface of the resin film is obtained. , Nitrogen functional groups such as amino groups (—NH ₂ ) are generated in the main chain and side chains of the polymer. In addition, the surface of the second resin film laminated with the first resin film is subjected to surface treatment by corona discharge treatment or UV / ozone treatment in an atmosphere containing oxygen gas and / or nitrogen gas. , the surface of the second resin film, the main chain or side chain of the polymer, a carbonyl group (> CO) or an acid-containing functional group or an amino group such as a carboxyl group (-COOH) (-NH ₂₎ nitrogen, such as A functional group is generated.
Then, by superposing the resin films subjected to these surface treatments and thermocompression bonding with a thermal laminate , the functional groups on both surfaces are bonded to each other, and a chemical bond such as an amide group (—NHCO—) is formed. It is presumed that the polymer chain on the first resin film side and the polymer chain on the second resin film side are firmly bonded through these chemical bonds. Alternatively, it is presumed that the low molecular weight compound is generated by the surface treatment with the breakage of the polymer chain of the resin constituting the first and / or second film, and these contribute to the adhesive action.

The present invention will be described below based on the best mode.
The resin film used by this invention is not specifically limited, According to the use of a laminated film, it can select suitably. For example, if the laminated film of the present invention is for packaging materials, such as polyesters such as polyethylene terephthalate and polyethylene naphthalate (PET), polyamides (PA) such as 6-nylon and 66-nylon, polyethylene (PE) and polypropylene, etc. A film made of a thermoplastic resin such as polyolefin, ethylene-vinyl alcohol copolymer, polyvinylidene chloride, polystyrene, or polyvinyl chloride is preferred. In addition, if the laminated film of the present invention is for electronic materials or electrical materials, a curable resin film made of polyimide, epoxy resin, or the like can also be used.

The laminated structure used for the laminated film of the present invention is the treatment of the second resin film surface-treated with oxygen atoms and / or nitrogen atoms on the treated surface of the first resin film surface-treated with nitrogen atoms. It is a laminated structure in which the surface is pressure-bonded without using an adhesive layer.
This laminated structure can be formed, for example, by performing the following steps (1) to (3).
(1) A first treatment step in which a surface treatment is performed on the surface of the first resin film by corona discharge treatment in a nitrogen gas atmosphere with an oxygen gas concentration in the nitrogen gas atmosphere of 2% or less by volume .
(2) A second treatment step in which the surface of the second resin film is subjected to surface treatment by corona discharge treatment or UV / ozone treatment in an atmosphere containing oxygen gas and / or nitrogen gas.
(3) A laminating step in which the surface of the first resin film subjected to the surface treatment is overlapped with the surface of the second resin film subjected to the surface treatment , and thermocompression bonding is performed by thermal lamination .
Hereinafter, these forming steps will be described in detail.

(First processing step)
In this step, the surface treatment of the first film is performed with nitrogen atoms by a discharge treatment.
Discharge treatment, in this process, a corona discharge treatment in a nitrogen gas atmosphere is preferred.

  Corona discharge treatment has long been used to improve the adhesiveness of various resin films including thermoplastic polyolefin resin films such as polyethylene and polypropylene. In particular, since the polyolefin film does not have a polar group in the surface layer, the printability of the ink and the adhesiveness with other resins such as an adhesive are low. For this reason, in order to improve the printability of ink and the adhesiveness with other resins such as an adhesive, the resin film surface has been modified by corona discharge treatment in air. Corona discharge treatment uses a high-frequency voltage to generate corona discharge in the atmosphere, irradiates the surface of the resin film with electrons that are generated, and adds functional groups based on oxygen atoms to the surface of the resin film. The surface of the film is modified.

    In the corona discharge surface treatment performed in a normal air atmosphere, active oxygen atoms (oxygen radicals) are generated, so the oxygen gas content in air is much smaller than that of nitrogen gas. First, the surface of the resin film subjected to corona discharge treatment is surface-treated with oxygen atoms. That is, the surface of the resin film is oxidized, and oxygen functional groups such as a carbonyl group (> CO) and a carboxyl group (—COOH) are mainly formed on the main chain and side chain of the polymer film on the surface of the resin film. And it is thought that these functional groups contribute to adhesive performance. However, since this active oxygen atom has a strong action of cutting a polymer to lower the molecular weight when generating a functional group, a low molecular compound containing an oxygen atom is generated in a very thin layer on the surface of the resin film. . This low molecular weight compound layer is considered to have a relatively small molecular weight, and is considered to have a low physical strength such as cohesive force.

On the other hand, corona discharge treatment in a nitrogen gas atmosphere that is preferably used in the first treatment step and contains substantially no oxygen gas has an amino group of nitrogen atoms in the polymer main chain or side chain on the surface of the resin film. It is thought that nitrogen functional groups such as (—NH ₂ ) are mainly produced. Further, the corona discharge treatment in the nitrogen gas atmosphere is different from the corona discharge treatment in the normal air atmosphere, and the discharge occurs in the nitrogen gas, so that the generation amount of active oxygen atoms is small, and the active nitrogen atoms are reduced. Since the function of cutting the polymer to lower the molecular weight when generating the functional group is weak, the generation of low molecular weight compounds generated when corona discharge treatment is performed in an air atmosphere can be suppressed.
That is, the low molecular weight compound has a higher molecular weight than that produced during corona discharge treatment in an air atmosphere, and the physical strength such as the cohesive force of the low molecular weight layer is also increased. For this reason, the effect of improving the adhesiveness can be obtained by using the polyolefin film.
In the present invention, when two different types of resin films are thermocompression bonded, the corona discharge treatment in the nitrogen gas atmosphere is performed on the resin film having the higher Tg (glass transition temperature) to be used. Nitrogen functional groups such as amino groups (—NH ₂ ) that are advantageous for adhesion can be efficiently introduced with almost no weakening of the molecular compound layer.

In order to efficiently introduce the nitrogen functional group, it is necessary to lower the oxygen gas concentration in the treatment atmosphere in which the corona discharge treatment is performed as described in Patent Documents 3 and 4. In Patent Documents 3 and 4, it is presumed that CO ₂ is intentionally introduced into the atmospheric gas for corona discharge treatment to form an amide group (—NHCO—) instead of an amino group. . Since CO ₂ becomes radicals in the plasma atmosphere and CO radicals and oxygen radicals are generated, an amide group is preferentially generated over an amino group in the same manner as corona treatment in a normal air atmosphere. Can not be introduced.

Therefore, in the first treatment step, it is preferable to intentionally introduce more amino groups than amide groups, so that oxygen gas is not substantially contained in the atmosphere gas of the corona discharge treatment. The oxygen gas concentration is controlled to 2% or less, preferably 50 ppm or less, more preferably 20 ppm or less, although it depends on the resin film to be treated, processing conditions, and the like. At the same time, it is preferable not to introduce a material for supplying oxygen atoms (for example, CO ₂ or N ₂ O) into the discharge atmosphere other than the resin film. In order to introduce amino groups more actively, a material that absorbs oxygen atoms (for example, H ₂ , NH ₃ , CH _4, etc.) may be added to the discharge atmosphere.

Conventionally, low-pressure plasma treatment for discharging in a vacuum state has been used for surface modification. However, since vacuum equipment is required, there is a drawback that the apparatus becomes large and the operation is complicated. For this reason, an atmospheric pressure plasma treatment apparatus that generates a glow discharge state that can only be generated in a vacuum state at atmospheric pressure and performs surface modification using the reaction radicals, electrons, etc. generated by the glow discharge state is usually It has come to be used simply for improvement and adhesion improvement.
Ordinary atmospheric pressure plasma treatment has the feature that the glow discharge is stably maintained by using a rare gas such as helium or argon as the atmospheric gas. Strictly speaking, it is called atmospheric pressure glow discharge. There is also.
In the first treatment step, atmospheric pressure plasma treatment in a nitrogen gas atmosphere can also be used. In this case, a rare gas may be mixed for stable glow discharge. And the ratio of a noble gas can also exceed half.

(Second processing step)
In this step, the surface treatment of the second film is performed with oxygen atoms and / or nitrogen atoms. Specifically, surface treatment is performed by corona discharge treatment or UV / ozone treatment in an atmosphere containing oxygen gas and / or nitrogen gas.
These surface treatments may be performed in an atmosphere containing oxygen gas, or, similarly to the first treatment step , the corona discharge treatment may be performed in a nitrogen gas atmosphere substantially not containing oxygen gas .

In the corona charging Densho management in an atmosphere containing oxygen gas, the surface of the resin film, the main chain or side chain of the polymer, a carbonyl group (> CO) or an acid-containing functional groups such as carboxyl group (-COOH) Is considered to be mainly generated. As long as they are generated, the atmosphere is not good in the air. In addition to rare gases, nitrogen-based gases such as N ₂ and N ₂ O are mixed, and hydrogen gas, oxygen gas, carbon dioxide gas, etc. are mixed to intentionally introduce amino groups and amide groups. can do.

The ozone treatment is a surface treatment with active oxygen atoms generated by spraying ozone onto the resin film surface and decomposing ozone. Although there is no restriction | limiting in the generation | occurrence | production method of ozone, UV / ozone treatment is preferable. The UV / ozone treatment uses a light source that generates ultraviolet rays, such as a low-pressure mercury lamp and an Xe excimer lamp, and a synergistic effect of the energy of the light source irradiated on the resin surface and the ozone generated by the irradiation of the light source can be obtained. is there. Ultraviolet light having a wavelength of 240 nm or less decomposes oxygen to generate ozone, and when a low-pressure mercury lamp is used, a 185 nm line is used to generate ozone. UV / ozone treatment is said to be effective in modifying and cleaning the resin surface, but if the energy of the illuminating light source is higher than the molecular bond energy of the resin compound, the molecular bond is broken and the decomposition reaction product Therefore, it is preferable to adjust by the resin film to be treated.
Moreover, although the effect of UV / ozone treatment varies depending on the chemical composition of the resin, active oxygen generated by decomposition of ozone contributes to surface modification, and on the surface of the resin film, the main chain and side chain of the polymer In addition, oxygen functional groups such as carbonyl groups (> CO) and carboxyl groups (—COOH) are mainly formed, and active oxygen atoms mainly act, so nitrogen functional groups such as amino groups (—NH ₂ ) Do not generate.

(Lamination process)
This process, to the surface treatment has been performed the surface of the first resin film, superposed surface on which the surface treatment is performed in the second resin film is thermocompression bonding is the so-called thermal lamination process .
Thermal lamination is performed by heating and thermocompression bonding in a state where two resin films are superposed. The conditions for thermocompression bonding may be appropriately selected as long as the target adhesive strength can be obtained. The adhesive strength is improved by increasing the thermocompression bonding temperature, time, and pressure. For example, even in a combination of a polyester film and a polyethylene film, it can be set to about 6 N / 15 mm. This is considered to be due to the moderate diffusion of the low molecular weight compound produced by the discharge treatment. However, if the temperature, pressure and time are increased too much, the thickness of the polyethylene will change, the thermal shrinkage of the polyester film, the processing speed will be slow, and the equipment will become large. It is preferable to select.

In the present invention, when two different types of resin films are thermocompression bonded, a corona discharge treatment in which the oxygen gas concentration in the nitrogen gas atmosphere is 2% or less of the capacity ratio is applied to a resin film made of a resin having a higher Tg. By performing the first treatment step, it is possible to efficiently introduce a nitrogen functional group such as an amino group (—NH ₂ ) that is advantageous for adhesion without inducing weakening of the low molecular compound layer. .
On the other hand, by performing a corona discharge treatment in an atmosphere containing oxygen gas on a resin film made of a resin having a lower Tg, that is, by performing the second treatment step, a carbonyl group (> CO that is advantageous for adhesion). ) And carboxyl functional groups (—COOH) can be efficiently introduced.
By thermocompression bonding these two types of resin films, an amide bond is generated, and a laminated structure having a strong adhesive strength against moisture as well as during drying is realized.

  Here, in the second treatment step, the active oxygen atom has a strong action of cutting the polymer to lower the molecular weight when generating the oxygen functional group, so that the low molecular compound containing the oxygen atom on the surface of the resin film Is produced in a very thin layer. This low molecular weight compound layer is considered to have a relatively small molecular weight, and is considered to have a low physical strength such as cohesive force. Therefore, even if two types of resin films are thermocompression bonded and an amide bond is generated to achieve strong adhesion, cohesive failure occurs in the surface layer of the second resin film. It is considered that the adhesive strength at the laminated interface does not increase.

However, when thermocompression bonding was actually performed, a laminated structure having strong adhesive strength against moisture as well as during drying was realized.
The reason for this is not clear, but is estimated as follows.
That is, it is considered that softening or melting occurs from the surface of the layer of the low-molecular compound containing oxygen atoms generated in the second treatment step to the very shallow interior due to heat during thermocompression bonding. The molecular weight of low molecular weight compounds is widely distributed from small to large, and it is estimated that the smaller the molecular weight, the closer to the surface. Due to this softening and melting, flow starts from a low molecular weight compound having a low molecular weight, and moves into the surface layer. As a result, a relatively large molecular weight is exposed on the surface. On the other hand, since the resin of the first resin film has the same or higher Tg than that of the resin of the second resin film, the degree of softening of the surface layer of the first film that is rough due to surface treatment and has fine irregularities is the second resin film. Equal or smaller. When both resin films are pressure-bonded in this state, the low molecular weight layer of the second resin film follows the fine irregularities of the surface layer of the first resin film, and an anchoring effect is produced. And the oxygen functional group which the low molecular compound with a comparatively large molecular weight of the 2nd resin film has and the nitrogen functional group which the 1st resin film has couple | bonds together, an amide bond produces | generates, and high adhesive strength expresses.

Therefore, in the present invention, the reason why the corona discharge treatment is preferable to the plasma treatment for the surface treatment of the first resin film is presumed to be due to such an adhesion mechanism.
In the present invention, in the second treatment step, as in the first treatment step, high adhesion strength can be obtained even when surface treatment is performed by discharge in a nitrogen gas atmosphere that does not substantially contain oxygen gas. However, in this case, it is estimated as follows.
In addition to the anchoring effect described above, a low molecular compound layer having a nitrogen functional group is formed on both the surface of the first resin film and the surface of the second resin film, and these have good compatibility. Therefore, diffusive mixing occurs easily. By this diffusive mixing, a high adhesive strength can be obtained by mutual intertwining of molecular chains.
On the contrary, it is presumed that the improvement of the adhesive strength due to such entanglement of molecular chains occurs even when the surface treatment of the first and second resin films is both due to oxygen atoms. However, in this case, even if there is an entanglement of molecular chains generated by diffusion mixing, it is considered that the entanglement is easy to unwind because the molecular weight of the low molecular weight compound generated by the surface treatment with oxygen atoms is low. Moreover, even if the adhesive strength can be increased to some extent, it is presumed that the adhesive interface tends to be hydrophilic and the resistance to moisture is reduced.

  In the present invention having the above-described adhesion mechanism, the two resin films to be thermocompression bonded are not particularly limited, but considering the use of packaging materials, etc., one of the resin films is made of polyolefin, and the other resin film is It is preferably made of polyester or polyamide. The surface treatment for the two resin films to be laminated may be performed first before thermocompression bonding, or may be performed simultaneously or in parallel. When three or more resin films are subjected to thermocompression bonding, the surface treatment on the surface to be laminated and the process of thermocompression bonding can be repeated as many times as necessary to produce a laminated film of three or more layers. In addition, after surface treatment of both surfaces of the resin film, two other surface-treated resin films are superposed on both surfaces of the resin film and thermocompression bonded, whereby another resin film is thermocompression bonded to each surface of the resin film. It is also possible to produce a three-layer laminated film.

Although the laminated film of the present invention can be applied to various uses, it can be preferably used as a packaging material for the production of various packaging bags. The form of the packaging bag is a self-supporting bag (standing pouch), a relatively small flexible packaging bag (pouch) such as a three-sided bag, a four-sided bag, a jointed bag, a gusset bag, or an inner bag or drum for a bag-in-box Large bags such as interior bags can be used without particular limitation.
In the method for producing a laminated film of the present invention, a predetermined surface treatment is applied to the surface on which two resin films are laminated, and then thermocompression bonding is performed to laminate using an adhesive layer or an anchor coat layer. It has the same or higher adhesive strength as Moreover, the adhesive layer can maintain high adhesive strength even when it comes into contact with moisture.
For this reason, when packaging the content containing moisture, high adhesive strength can be maintained even when moisture reaches the adhesion interface through the heat seal layer. In addition, in the case of contents to be sterilized, moisture is passed over time from the surface resin film or from the end face of the laminated film by passing through a boil sterilization process using hot water or steam and a retort sterilization process. Even if it penetrates, high adhesive strength can be maintained. Therefore, it is suitable for packaging of contents containing moisture and packaging of contents subjected to sterilization treatment such as boil sterilization and retort sterilization. Examples of this type of content include foods, beverages, and pharmaceuticals.

Hereinafter, the present invention will be specifically described with reference to examples.
Example 1
A laminated film was prepared using a 12 μm polyester film as the first film and a 40 μm polyolefin film as the second film.
As the polyester film, trade name: Diafoil T100, which is a biaxially stretched polyethylene terephthalate film manufactured by Mitsubishi Chemical Polyester Film, was used. The Tg of the resin constituting this film was approximately 70 ° C.
A polyethylene film was used as the polyolefin film. As the polyethylene film, trade name: SK615P, which is an unstretched linear low-density polyethylene film made of Tamapoly, was used. The Tg of the resin constituting this film was approximately −125 ° C.
As the first treatment step, the polyester film was subjected to corona discharge treatment using a batch corona discharge treatment apparatus manufactured in-house under a nitrogen gas atmosphere filled with nitrogen gas and maintained at an oxygen concentration of 20 ppm.
As a 2nd process process, the corona discharge process in the air atmosphere was implemented by the desktop corona treatment by Type | Sophthala, and Type3003 with respect to a polyethylene film.
They were thermocompression bonded at 180 ° C. for 20 seconds and 0.4 MPa with a heat sealer to prepare a laminated film.
In order to measure the adhesive strength of the laminated film, as a result of measurement by the measurement method defined in JIS K 6854-1, “Adhesive Peeling Adhesive Strength Test Method Part 1: 90 degree Peeling”, the speed at 90 degree peeling The adhesive strength when peeled at 5 mm / min (may be referred to as “adhesive strength during drying”) was 3.76 N / 15 mm (650 g / inch).
Further, in order to measure the adhesive strength when contacted with water, a dropper is placed on the forefront where the laminated interface of the laminated film peels off during the measurement of the adhesive strength defined in JISK 6854-1 using a roller type peeling device. Water was deposited over the entire width. By making the water follow the progress of the forefront of peeling by surface tension and gravity, the water was always peeled while being in contact with water. The measurement result of the adhesive strength when peeled while bringing water into contact with the peeled surface of the laminated film (sometimes referred to as “adhesive strength at the time of water contact”) was 2.72 N / 15 mm (470 g / inch). It was.
When the peeled surface of the laminated film is measured by Fourier transform infrared spectroscopy (FT-IR), the peak of the compound considered to be derived from the polyethylene film is strong on the polyester film side. Presumed to be destruction.

(Example 2)
Except that the second treatment step is the corona discharge treatment under the nitrogen gas atmosphere of Example 1, the surface modification treatment is performed in the same manner as in Example 1, and the laminated film is thermocompression-bonded in the same manner as in Example 1. The adhesive strength at the time of drying and the adhesive strength at the time of water contact was measured.
The adhesive strength during drying was 3.88 N / 15 mm (670 g / inch). Moreover, the adhesive strength at the time of water contact was 2.55 N / 15 mm (440 g / inch).
When the peeled surface of the laminated film was measured by FT-IR, the peak of the compound considered to be derived from the polyethylene film was strong on the polyester film side, and from this, it was estimated that the peeled surface was cohesive failure of the polyethylene film.

(Example 3)
The surface modification treatment was performed in the same manner as in Example 1 except that the oxygen concentration in the first treatment step was set to 50 ppm, and the second treatment step was changed to UV / ozone treatment. A laminated film was prepared by thermocompression bonding, and the adhesive strength during drying and the adhesive strength during water contact were measured.
The UV / ozone treatment was performed for 5 minutes using a UV / ozone treatment apparatus manufactured by Sen Special Light Source Co., Ltd. having a model number PL-2002N-18.
The adhesive strength at the time of drying was 3.18 N / 15 mm (550 g / inch). Moreover, the adhesive strength at the time of water contact was 2.60 N / 15 mm (450 g / inch).
When the peeling interface of the laminated film was measured by FT-IR, the peak of the compound considered to be derived from the polyethylene film was strong on the polyester film side. From this, the peeling surface was estimated to be cohesive failure of the polyethylene film.

Example 4
Except that a 15 μm biaxially stretched nylon (PA) film was used as the first film, surface modification treatment was performed in the same manner as in Example 1, and thermocompression bonding was performed in the same manner as in Example 1 to create a laminated film. Then, the adhesive strength of the laminated film and the adhesive strength when brought into contact with water were measured.
As the nylon film, trade name: Bonile RX, manufactured by Kojin Co., Ltd. was used. The Tg of the resin constituting this film was approximately 50 ° C.
The adhesive strength at the time of drying was 15.63 N / 15 mm (2700 gf / inch). Moreover, the adhesive strength at the time of water contact was 4.86 N / 15 mm (840 gf / inch).
When the peeling interface of the laminated film was measured by FT-IR, the peak of the compound considered to be derived from the polyethylene film was strong on the polyamide film side. From this, it was estimated that the peeled surface was a cohesive failure of the polyethylene film.

(Example 5)
Thermocompression bonding and measurement were performed in the same manner as in Example 1 except that the oxygen concentration in the first treatment step was 2%.
The adhesive strength at the time of drying was 3.59 N / 15 mm (620 g / inch). Moreover, the adhesive strength of water contact was 2.20 N / 15 mm (380 g / inch).
When the peeling interface was measured by FT-IR, the peak of the compound considered to be derived from the polyethylene film was strong on the polyamide film side, and from this, the peeling surface was estimated to be cohesive failure of the polyethylene film.

(Comparative Example 1)
Thermocompression bonding and measurement were performed in the same manner as in Example 1 except that the first treatment step was corona discharge treatment in an air atmosphere.
The adhesive strength at the time of drying was 3.76 N / 15 mm (650 gf / inch). Moreover, the adhesive strength at the time of water contact was 0.58 N / 15 mm (100 gf / inch).
When the peeling interface of the laminated film was measured by FT-IR, the peak of the compound considered to be derived from the polyester film was strong on the polyethylene film side. From this, it was speculated that the peeled surface was cohesive failure of the polyester film, and was peeled off at the fragile layer caused by corona treatment in an air atmosphere.

(Comparative Example 2)
Thermocompression bonding and measurement were performed in the same manner as in Example 3 except that the first treatment step was corona treatment under an air atmosphere.
The adhesive strength during drying was 0.58 N / 15 mm (100 gf / inch). Moreover, the adhesive strength at the time of water contact was 0.58 N / 15 mm (100 gf / inch).
When the peeling interface of the laminated film was measured by FT-IR, the peak of the compound considered to be derived from the polyester film was strong on the polyethylene film side. From this, it was estimated that the peeled surface was cohesive failure of the polyester film, and was peeled off at the fragile layer caused by corona treatment in an air atmosphere.

(Comparative Example 3)
Thermocompression bonding and measurement were performed in the same manner as in Example 1 except that the first treatment step was atmospheric pressure plasma treatment using only helium gas.
The atmospheric pressure plasma processing apparatus uses a “parallel plate type atmospheric pressure plasma processing apparatus”, uses helium gas, sets a film between electrodes at a flow rate of 10 L / min and an output of 100 W, and performs a discharge treatment for 5 seconds. It was.
The adhesive strength at the time of drying was 2.61 N / 15 mm (450 gf / inch). Moreover, the adhesive strength at the time of water contact was 1.62 N / 15 mm (280 gf / inch).
When the peeling interface of the laminated film was measured by FT-IR, the peak of the compound considered to be derived from the polyester film was strong on the polyethylene film side. From this, it was guessed that it was cohesive failure of the polyester film.

  Although the present invention has been described based on the best modes, the present invention is not limited to these modes, and various modifications can be made without changing the gist of the present invention. For example, the surface to which the film is bonded may be printed. Further, other resin layers such as polyvinylidene chloride may be coated. And the laminated film of this invention may be laminated | stacked by the conventionally well-known lamination | stacking method in addition to the resin structure mentioned above other than the laminated structure mentioned above.

  INDUSTRIAL APPLICATION This invention can be utilized for manufacture of the laminated | multilayer film suitable for the packaging container used for packaging of foodstuffs, a drink, a pharmaceutical, etc.

Claims (5)

In a nitrogen gas atmosphere, the nitrogen gas oxygen gas concentration in the atmosphere in a volume ratio of 2% or less, more corona discharge treatment, onto the treated surface of the first resin film subjected to surface treatment with a nitrogen atom,
In an atmosphere containing oxygen gas and / or nitrogen gas, corona discharge treatment, or more UV / ozone treatment, the treated surface of the second resin film was subjected to a surface treatment with oxygen and / or nitrogen atoms, bonded A laminated film having a laminated structure that is thermocompression bonded by thermal lamination without an agent layer,
The resin constituting the first resin film has a higher glass transition temperature than the resin constituting the second resin film;
In the laminated structure, water is brought into contact with the laminated interface, and the adhesive strength measured in accordance with JIS K 6854-1 “Test method for adhesive peel adhesion strength Part 1: 90 degree peel” is 2.0 N / 15 mm or more. A laminated film characterized by being.   2. The laminated film according to claim 1, wherein an oxygen gas concentration in the nitrogen gas atmosphere in the surface treatment of the first resin film is a volume ratio of 50 ppm or less.   The laminate structure is characterized in that an adhesive strength measured in accordance with JIS K 6854-1 "Test method for adhesive peel-off adhesion strength Part 1: 90 degree peel" is 3.0 N / 15 mm or more. Or the laminated film of 2.   The laminated film according to any one of claims 1 to 3, wherein the first resin film is made of polyester or polyamide, and the second resin film is made of polyolefin. A method for producing a laminated film according to any one of claims 1 to 4,
The surface of the first resin film, a first processing step of performing more surface treatment corona discharge treatment under the nitrogen gas atmosphere,
On the surface of the second resin film, in an atmosphere containing oxygen gas and / or nitrogen gas, and a second processing step of performing more surface treatment corona discharge treatment, or UV / ozone treatment,
A lamination step of superposing the surface of the second resin film on which the surface treatment has been performed on the surface of the first resin film and performing thermocompression bonding by heat lamination. A method for producing a laminated film.