JP2011079998A - Surface-treated polyamide film and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface-treated polyamide film which has an excellent wet laminate strength, has excellent properties in low hot-water shrinkage and thickness accuracy, and can be suitably used as a base film of packaging bags, for example, for foodstuffs, chemicals, industrial products, and the like, and to provide a method for producing the same. <P>SOLUTION: The polyamide film includes an aliphatic polyamide resin as a main component. At least one of the film surfaces is subjected to surface treatment by electrodischarge treatment in an atmosphere having an inert gas concentration of 99% or more and an active gas concentration of 1% or less. The surface-treated surface has a wet laminate strength of 3.9 N/15 mm or more. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention has excellent laminate strength when wet, and also has excellent properties such as low hot water shrinkage and thickness accuracy, and is suitable as a base film for packaging bags of food, medicine, industrial products, etc. The present invention relates to a surface-treated polyamide-based film, a surface-treated polyamide-based laminate film, and a method for producing the same.

  Films mainly composed of polyamide resins such as nylon 6 and laminated films composed of polyamide resins as layers are excellent in tensile strength and impact strength, so that these polyamide-based films can be used for packaging foods, medicines, etc. It is secondarily processed into packaging bags and manufactured and sold in various forms.

  In recent years, adaptation to retort sterilization has become important from the viewpoint of consumer convenience, extension of the expiration date, and improvement of storage stability. Usually, when using a polyamide-based film for such an application (after printing in many cases), a laminate film is prepared by laminating with a sealant film or other films, and the sealant layers of the laminate film are bonded together. After heat-sealing to form a bag and filling the contents, the opening is sealed by heat-sealing and used as a container. Moreover, the method of extending the shelf life of a content or maintaining a flavor is performed by performing the retort sterilization process at high temperature after filling with the content.

However, since the internal pressure increases during the retort process, troubles such as broken bags and delamination often occur when a retort process is performed on a packaging bag using a film having poor laminate strength.

  Therefore, a packaging material that does not cause defects such as broken bags or delamination when retort sterilizing at high temperature after filling the contents with a bag made of a composite film made of a functional resin film such as nylon and a sealant. It has been demanded. Properties required for the functional resin film used for such a packaging material include basic properties such as strength and gas barrier properties, and high laminate strength to prevent delamination.

  Here, for example, in Patent Document 1, there is a method of controlling the orientation of the resin on the film surface layer as means for imparting high laminate strength to the functional resin film itself such as nylon of the polyamide film. However, in this case, the purpose is to prevent delamination due to cohesive peeling of the film surface, and it does not improve the adhesive force between the adhesive and the film, so the substantial laminate strength is not improved.

  In addition, as another method, for example, Patent Document 2 proposes a method for preventing troubles such as printing omission due to processing unevenness by uniformly processing a polyamide film by performing surface treatment twice or more. . However, the uniform treatment can prevent printing omission due to treatment unevenness and decrease in the laminate strength, but it does not improve the laminate strength itself, so it has not led to a fundamental solution.

Patent Document 3 describes a method of bonding films without using an adhesive layer by treating the film surface with nitrogen atoms. However, in this method, the laminate strength when wet is as low as 2.0 N / 15 mm or more, and it cannot be used for applications requiring high wet laminate strength such as retort treatment.

JP-A-9-239930 JP2008-297416 JP2007-307771

  Therefore, an object of the present invention is to provide a surface-treated polyamide film having excellent mechanical strength such as tensile strength and impact strength, and having high laminate strength when wet, and a method for producing the same.

  In view of the current situation, the present inventors have made extensive studies and have found a polyamide-based film that can solve the conventional problems.

That is, the present invention provides the following surface-treated polyamide film and a method for producing the same.

1. A polyamide-based film containing an aliphatic polyamide resin as a main component, and at least one film surface is subjected to surface treatment by discharge treatment in an atmosphere having an inert gas concentration of 99% or more and an active gas concentration of 1% or less. A surface-treated polyamide film having a laminate strength when the surface-treated surface is wet is 3.9 N / 15 mm or more.
The hot water shrinkage rate in the film flow direction (MD) at 2.95 ° C. × 5 minutes is 3.0% or less, and the thickness variation rate in the width direction (TD) of the film is 10% or less of the average thickness. 2. The surface-treated polyamide film according to 1 above.
3. 3. The surface-treated polyamide film according to 1 or 2 above, wherein the atmosphere during the surface treatment is an inert gas concentration of 99% or more, an active gas concentration of 1% or less, and a reactive gas concentration of 1% or less.
4). 4. The surface-treated polyamide film according to any one of 1 to 3, wherein the inert gas is at least one gas selected from nitrogen, helium, neon, argon, and krypton.
5). 5. The surface-treated polyamide film having a multilayer structure in which the surface-treated surface in the surface-treated polyamide film according to any one of 1 to 4 is disposed so as to constitute at least one surface of a resin laminate. 6). 6. A surface-treated polyamide-based laminate film obtained by laminating a sealant film on the surface-treated surface of the surface-treated polyamide-based film according to any one of 1 to 5 above.
7). A bag comprising the surface-treated polyamide-based laminate film described in 6 above.
8). After a step of stretching an unstretched film mainly composed of an aliphatic polyamide-based resin extruded from a flat die by a tenter-type sequential biaxial stretching method at a stretching ratio of 2.4 times or more for both MD and TD, 200 ° C or more In addition, an inert gas is formed on at least one surface of the film through a step of heat setting at a temperature not higher than 10 ° C. higher than the extrapolated melting start temperature (measured in accordance with JIS K 7121) of the aliphatic polyamide resin. A method for producing a surface-treated polyamide film, comprising a step of performing a surface treatment by a discharge treatment of any one of corona treatment and plasma treatment in an atmosphere having a concentration of 99% or more and an active gas concentration of 1% or less.

  ADVANTAGE OF THE INVENTION According to this invention, while being excellent in mechanical strength, such as tensile strength and impact strength, the surface treatment polyamide-type film which has the lamination strength at the time of high wetness, and its manufacturing method can be provided.

Hereinafter, the present invention will be described in detail, but the scope of the present invention is not limited to the embodiments described below.
First, the surface-treated polyamide film of the present invention contains an aliphatic polyamide resin.
Here, the aliphatic polyamide resin is not particularly limited, and examples thereof include a ring-opening polymer of cyclic lactam, a polycondensate of aminocarboxylic acid, and a polycondensate of dicarboxylic acid and diamine. Specifically, a homopolymer of ε-caprolactam called nylon 6 or polyhexamethylene adipamide called nylon 66 can be obtained at low cost, and the stretching operation can be performed smoothly. To preferred.

  The content ratio of the aliphatic polyamide resin in the surface-treated polyamide film can be 45 to 100% by mass. When the content of the aliphatic polyamide resin is lower than 45% by mass, mechanical strength such as tensile strength and impact strength becomes insufficient.

  In addition to the aliphatic polyamide resin, the above-mentioned polyamide-based film may have an impact modifier, a lubricant, an antistatic agent, an antioxidant, an antiblocking agent, a stable agent, as necessary, within the scope not exceeding the gist of the present invention. Various additives such as an agent, a dye, a pigment, and inorganic fine particles can be added. Specific examples include impact modifiers (such as elastomers), anti-blocking agents (such as inorganic fillers), water repellents (such as ethylene bisstearic acid esters), and lubricants (such as ethylene bisstearic acid amides).

  Furthermore, the surface-treated polyamide-based film of the present invention includes a non-standard film and a cut edge that are generated when the surface-treated polyamide-based film of the present invention is produced, as necessary, within the range not exceeding the gist of the present invention. Material (ear trim) can be added.

  When using the surface-treated polyamide film of the present invention as a packaging bag, from the viewpoint of maintaining the quality of the contents and preventing spoilage, a gas barrier resin layer is further laminated, a metal such as aluminum, silicon dioxide, and alumina. Gas barrier properties and moisture resistance can be further improved by subjecting metal oxides such as vapor deposition and coating with a gas barrier coating agent.

  Next, it is important that the surface-treated polyamide film of the present invention has the following feature (1), and preferably has the features (2) and (3). These can be controlled by manufacturing conditions (stretch ratio, heat setting temperature, etc.) in addition to the surface treatment of the film.

  (1) The laminate strength when wet must be 3.9 N / 15 mm or more. Here, if the laminate strength when wet is 3.9 N / 15 mm or more, troubles such as delamination and broken bags are unlikely to occur even in a state where stress is applied by lamination, retort processing after bag making, or the like. In the present invention, “lamination strength when wet” refers to the peel strength between the laminated surface-treated polyamide film and the sealant, and is specifically a value obtained by the measurement method described below.

  (2) It is preferable that the hot water shrinkage in the flow direction (MD) of the film at 95 ° C. for 5 minutes is 3.0% or less. Here, if the hot water shrinkage rate of MD is 3.0% or less, it is possible to suppress the occurrence of troubles such as pitch deviation due to heat shrinkage in processes such as printing and laminating.

  (3) It is preferable that the thickness variation rate in the width direction (TD) of the film is 10% or less of the average thickness. Here, if the thickness variation rate is 10% or less of the average thickness, wrinkles due to thickness unevenness and / or tarmi are generated and printing registration is shifted, or the film path is meandering and the printing pitch is shifted. The occurrence of such troubles can be suppressed.

Thus, by having the characteristics of (2) and (3), it is possible to obtain a surface-treated polyamide film having characteristics excellent in low hot water shrinkage and thickness accuracy.

  Hereinafter, a production method suitable for obtaining the surface-treated polyamide film of the present invention will be described.

That is, using a polyamide-based resin as a raw material, a film that is substantially amorphous and not oriented (hereinafter referred to as “unstretched film”) is usually produced by an extrusion method. The unstretched film can be produced by, for example, an extrusion method in which the raw material is melted by an extruder, extruded from a flat die, and then rapidly cooled to form a flat unstretched film.

  Next, the unstretched film is stretched in the biaxial direction in terms of stretching effect, film strength, and the like in the film flow direction (MD) and the width direction (TD) which is the orthogonal direction. As the biaxial stretching method, any conventionally known stretching method such as tenter-type sequential biaxial stretching, tenter-type simultaneous biaxial stretching, tubular simultaneous biaxial stretching, and the like can be adopted. For example, in the case of the tenter-type sequential biaxial stretching method, it is important that the unstretched film is heated to a temperature range of 50 to 110 ° C. and stretched 2.4 times or more in the longitudinal direction by a roll-type longitudinal stretching machine. . Here, when the longitudinal stretching ratio is less than 2.4 times, stretching unevenness occurs, the thickness becomes non-uniform, or the strength of the film decreases due to insufficient orientation.

  The longitudinally stretched film stretched by the above method can be subsequently stretched at a TD of 2.4 times or more within a temperature range of 60 to 140 ° C. by a tenter-type lateral stretcher while holding the end with a tenter clip. is important. Here, when the transverse draw ratio is less than 2.4 times, the transverse draw ratio is too low, and non-stretched portions such as unstretched portions are generated, resulting in uneven thickness and insufficient film orientation due to insufficient orientation. There is a problem that it falls.

  The biaxially stretched film stretched by the above method continues to hold the end portion with a tenter clip, at a temperature of 200 ° C. or higher in a tenter oven, and 10 ° C. or lower than the extrapolated melting start temperature of the above aliphatic polyamide resin. The heat setting is performed for about 1 second to 2 minutes, preferably 1 second to 30 seconds, more preferably 3 to 15 seconds.

  Here, when the heat setting temperature is lower than 200 ° C. or when the processing time is 1 second or less, the hot water shrinkage of MD cannot be suppressed to 3.0% or less, and printing, laminating, and the like. This causes problems such as shrinkage and shift in pitch. On the other hand, if the heat setting temperature exceeds 10 ° C. higher than the extrapolated melting start temperature of the aliphatic polyamide resin described above, or if the treatment time exceeds 2 minutes, the stress of melting or crystallization of the film during heat setting Breakage occurs due to the shortage of mechanical properties of the film.

  The extrapolated melting start temperature described above is a straight line obtained by extending the low-temperature base line of the melting peak in the differential scanning calorimetry (DSC) described in JIS K 7121: 1987 to the high-temperature side. This is the temperature obtained from the intersection of the tangent lines drawn at the point where the gradient is maximum on the low temperature side curve.

  The biaxially stretched film stretched by the above method is subsequently subjected to corona treatment and plasma treatment in an atmosphere having an inert gas concentration of 99% or more, an active gas concentration of 1% or less, and a reactive gas concentration of 1% or less on at least one surface. It is necessary to carry out surface treatment by electric discharge treatment such as. At this time, if the inert gas concentration is 99% or more and the active gas concentration is 1% or less, the laminate strength when the laminate film is wet is drastically improved, and 3.9 N / 15 mm or more can be achieved. I can do it.

  The higher the concentration of the inert gas, the better the laminate strength when wet, and it is necessary to be 99% or more, preferably 99.9% or more, more preferably 99.98% or more. However, when productivity and cost in the case of normal production are considered, oxygen, which is an active gas contained in the atmosphere to some extent, flows in as a carrier flow during processing. If the amount of inert gas blown is increased, the concentration of the active gas can be lowered, but the amount of inert gas used per product increases and the cost increases. For this reason, it is desirable to reduce the amount of the inert gas used within a range that is sufficiently effective in order to reduce costs. Further, if the amount of the inert gas blown is increased, exhaust may not be in time, in which case the oxygen concentration in the indoor atmosphere is lowered, and the operator may be deficient in oxygen. In order to maintain the oxygen concentration in the indoor atmosphere from the viewpoint of safety, it is realistic that the concentration of the inert gas is up to 99.999%. On the other hand, the concentration of the active gas needs to be 1% or less, preferably 0.1% or less, more preferably 0.02% or less.

  In the present invention, the inert gas refers to nitrogen, helium, neon, argon, krypton, etc., and is preferable from the viewpoint that nitrogen, argon, etc. can be obtained at low cost, and the surface treatment operation can be performed safely and smoothly. . Further, in the present invention, the active gas refers to oxygen, carbon dioxide, carbon monoxide, ozone, etc., from the point that oxygen and carbon dioxide can be obtained at low cost, and the surface treatment operation can be performed safely and smoothly. preferable. The inert gas and the active gas may be a mixture of a plurality of substances.

  In order to further improve the laminate strength when wet, a reactive gas can be added in addition to the inert gas and the active gas. The addition amount of the reactive gas is preferably 1% or less from the viewpoint that the surface treatment operation can be performed safely and smoothly.

  In the present invention, the reactive gas refers to hydrogen, ammonia, acetylene, methane, etc., and is preferable from the viewpoint that hydrogen and ammonia can be obtained at low cost and the surface treatment operation can be performed smoothly. The reactive gas may be a mixture of a plurality of substances.

  The discharge treatment method is not particularly limited, and examples thereof include corona treatment, atmospheric pressure plasma treatment, and remote plasma treatment. Specifically, corona treatment and atmospheric pressure plasma treatment are preferable because they are simple and can perform the surface treatment operation safely and smoothly.

  As an embodiment of the present invention, there is a surface-treated polyamide-based laminate film obtained by laminating a sealant film on the surface-treated surface of the surface-treated polyamide-based film.

Examples of the laminate film include those in which a sealant film (layer) is disposed on at least one side surface on which the surface-treated polyamide-based laminate film has been subjected to surface treatment.

The sealant film may be any resin that can be heat-sealed, and generally includes a polyolefin-based resin, a polyester-based resin, and the like. Specifically, polypropylene, low density polyethylene, linear low density polyethylene, ethylene-vinyl acetate copolymer, ethylene- (meth) acrylic acid copolymer, ethylene- (meth) acrylic acid ester copolymer, ionomer Resins, ethylene / α-olefin copolymers, amorphous polyesters and the like may be mentioned, but are not limited thereto. The thickness of the sealant film is generally preferably about 15 to 100 μm. When the sealant film is thin, the sealing strength at the time of heat sealing tends to be inferior, whereas when it is too thick, it tends to be unsuitable for packaging applications.

Further, the method for laminating the surface-treated polyamide-based laminated film and the sealant film is not particularly limited, and examples thereof include a dry laminating method, a wet laminating method, and an extrusion laminating method. Specifically, a dry laminating method and an extrusion laminating method are usually used.

  Furthermore, as another embodiment of the present invention, there is a bag made of the surface-treated polyamide-based laminate film. This is a secondary process of the above laminate film, and is obtained by heat-sealing sealant layers to form a bag. Examples of the contents of the bag include foods, pharmaceuticals, chemicals, and fragrances that do not want to be altered by oxygen. For applications that require higher wet laminate strength, such as when the weight of the contents is large, or for applications that require higher pressure than the inside, such as packaging for foods that undergo retort processing, airbag cushioning materials, etc. Are preferably used.

  Hereinafter, the contents and effects of the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples unless it exceeds the gist thereof. The evaluation and measurement methods for the film were performed by the following methods.

(1) Laminate strength when wet
Dry laminate On the treated surface of the surface-treated polyamide film formed, Toyo Morton AD-900 as the main agent, Toyo Morton CAT-RT85 as the curing agent, and acetic acid as the diluting solvent Ethyl was mixed at 37.7%, 5.7%, and 56.6%, respectively, and after gravure coating, it was dried at 80 ° C. to remove ethyl acetate to make the adhesive coating amount 3 g / m ² . LLDPE film manufactured by Tosero Corporation as a sealant U. After adhering 50 μm of X FCS at 90 ° C. by dry lamination, aging was performed at 40 ° C. for 3 days.

Lamination strength when wet after lamination The layer between the polyamide resin laminated film dry-laminated by the above method and the sealant is peeled off with tweezers using water or ethanol. When the peeled part becomes about 1 cm, a rappy tape (cemedine 18 mm width) is adhered in the longitudinal direction of the film so as to cover the peeled part. The film with the rappy tape is cut into strips with a width of 15 mm and a length of 100 mm in a direction perpendicular to the flow direction, and the peeled portion is expanded to about 50 mm while applying water. Both sides of the peeled film were gripped by an autograph (manufactured by Toyo Seiki) and pulled at a speed of 50 mm / min while water was applied to the peeled portion of the film. The initial peak value was measured at n = 5, and the average value was defined as the laminate strength when wet (N / 15 mm).

Measurement results When the laminate strength when wet is 3.9 N / 15 mm or more (◯),
If the laminate strength when wet is less than 3.9 N / 15 mm (×)
(2) Hot-water shrinkage From the two ends of the obtained film and the central three points, 120 mm × TD is cut into 120 mm on the MD, and three reference lines of about 100 mm are drawn on the MD of this sample. This sample is left in an atmosphere of 23 ° C. and 50% RH for 24 hours, and the reference line is measured. The measured length before heat treatment is F. This sample is immersed in hot water maintained at 95 ° C., heated for 5 minutes, and then taken out. Further, after being left in an atmosphere of 23 ° C. and 50% RH for 30 minutes, the reference line is measured, and the length after the heat treatment is defined as G.

The hot water shrinkage rate is calculated by the following formula, and the average value of the three (rounded off the second decimal place of the average value) is the hot water shrinkage rate of MD, and the maximum of the three points at both ends and the center. The following evaluation was performed on the product.

Hot water shrinkage = [(F−G) / F] × 100 (%)
MDs with hot water shrinkage of 3.0% or less (○), those with more than 3.0% (×)
(3) Thickness fluctuation rate (%)
Using a striking-point thickness meter, the thickness is measured at intervals of 20 mm in the width direction of the obtained film, the maximum value at that time is Tmax, the minimum value is Tmin, the average value obtained by summing all the measurement points and dividing by the number of measurement points Tave.

The thickness fluctuation rate was calculated by the following formula (rounded to the first decimal place), and the following evaluation was performed.

Thickness variation rate = [(Tmax−Tmin) / Tave] × 100 (%)
Thickness fluctuation rate of 10% or less (○), 10% or more (×)
Example 1
As an aliphatic polyamide resin, nylon 6 “Mitsubishi Engineering Plastics Co., Ltd., trade name Novamid 1022C6, extrapolation melting start temperature: 215 ° C.” was used, and this was put into a 65 mmφ single screw extruder (L / D = 28). Then, it was melted and kneaded at a set temperature of 260 ° C., extruded with a T-die, and closely cooled to a cast roll at 30 ° C. to obtain an unstretched film of about 140 μm.

  The obtained unstretched film was stretched 2.7 times in the machine direction by using a roll-type stretcher under the condition of 60 ° C., and then the end of the longitudinally stretched film was held with a tenter clip, and 100% in a tenter oven. The film was stretched 3.4 times in the transverse direction under the condition of ° C., and then heat-fixed at 215 ° C. for 6 seconds. The heat-fixed film was trimmed at both end portions corresponding to the clip holding portion.

One side of the trimmed film was subjected to corona treatment in an atmosphere using nitrogen gas as the inert gas, nitrogen concentration of 99.9%, oxygen gas as the active gas, and oxygen concentration of 0.1%. .

After the surface treatment, the film was wound into a roll to obtain a surface-treated polyamide film having a thickness of about 15 μm.

The results of evaluation using the obtained surface-treated polyamide film are shown in Table 1.

(Example 2)
A film was obtained in the same manner as in Example 1 except that the nitrogen concentration during the surface treatment was 99% and the oxygen concentration was 1%, and the same evaluation was performed. The results are shown in Table 1.

(Example 3)
A film was obtained in the same manner as in Example 1 except that the nitrogen concentration during the surface treatment was 99.995% and the oxygen concentration was 0.005%, and the same evaluation was performed. The results are shown in Table 1.

Example 4
A film was obtained in the same manner as in Example 1 except that the stretching ratio in the longitudinal direction was 2.4 times, and the same evaluation was performed. The results are shown in Table 1.

(Example 5)
A film was obtained in the same manner as in Example 1 except that the heat setting temperature after stretching was 200 ° C., and the same evaluation was performed. The results are shown in Table 1.

(Example 6)
A film was obtained in the same manner as in Example 1 except that the heat setting temperature after stretching was 225 ° C., and the same evaluation was performed. The results are shown in Table 1.

(Example 7)
A film was obtained in the same manner as in Example 1, except that the nitrogen concentration during the surface treatment was 99.8%, the oxygen concentration was 0.1%, and 0.1% of hydrogen was added as a reactive gas. Was evaluated. The results are shown in Table 1.

(Comparative Example 1)
A film was obtained in the same manner as in Example 1 except that the nitrogen concentration during the surface treatment was 90% and the oxygen concentration was 10%, and the same evaluation was performed. The results are shown in Table 1.

(Comparative Example 2)
A film was obtained in the same manner as in Example 1 except that the stretching ratio in the longitudinal direction was 2.3 times, and the same evaluation was performed. The results are shown in Table 1.

(Comparative Example 3)
A film was obtained in the same manner as Example 1 except that the heat setting temperature after stretching was 190 ° C., and the same evaluation was performed. The results are shown in Table 1.

(Comparative Example 4)
In Example 1, the same method was used except that the heat setting temperature after stretching was 230 ° C., but the film was frequently broken in the tenter and could not be continuously formed. The results are shown in Table 1.

  From Table 1, it can be seen that Examples 1 to 5 which are the films of the present invention show good results for all the evaluation items. In particular, compared with Example 2 in which the nitrogen concentration during the surface treatment is 99% and the oxygen concentration is 1%, the other examples in which the nitrogen concentration during the surface treatment is 99.9% and the oxygen concentration is 0.1% are laminated. It has been clarified that the strength is more excellent, and the laminate strength is superior in other examples in which the longitudinal draw ratio is 2.7 times compared to Example 4 in which the longitudinal draw ratio is 2.4 times. . Furthermore, in Example 7 in which the atmosphere during the surface treatment was such that the nitrogen concentration was 99.8%, the oxygen concentration was 0.01%, and the hydrogen gas was 0.01%, the surface treatment was performed without using hydrogen gas. It became clear that the laminate strength was superior to other examples.

  On the other hand, Comparative Example 1 in which the nitrogen gas ratio during the surface treatment was as high as 90% was less effective for the surface treatment, and the laminate strength when wet was low. Comparative Example 2 having a low longitudinal stretching ratio was a film in which stretching unevenness occurred and the thickness variation rate was large. In addition, the laminate strength when wet was also low due to the effect of stretching unevenness. In Comparative Example 3 where the heat setting temperature is low, the hot water shrinkage rate of MD is large, so that there is a problem that troubles such as shrinkage due to shrinkage in printing, laminating, and the like are likely to occur. Furthermore, the laminate strength when wet was also low due to the effect of stretch orientation. In Comparative Example 4 having a high heat setting temperature, breakage occurred frequently in the tenter, and the film could not be continuously formed.

Claims (8)

A polyamide-based film containing an aliphatic polyamide resin as a main component, and at least one film surface is subjected to surface treatment by discharge treatment in an atmosphere having an inert gas concentration of 99% or more and an active gas concentration of 1% or less. A surface-treated polyamide film having a laminate strength when the surface-treated surface is wet is 3.9 N / 15 mm or more. The hot water shrinkage rate in the film flow direction (MD) at 95 ° C. × 5 minutes is 3.0% or less, and the thickness variation rate in the width direction (TD) of the film is 10% or less of the average thickness. Item 2. The surface-treated polyamide film according to Item 1. The surface-treated polyamide film according to claim 1 or 2, wherein an atmosphere during the surface treatment has an inert gas concentration of 99% or more, an active gas concentration of 1% or less, and a reactive gas concentration of 1% or less. The surface-treated polyamide film according to any one of claims 1 to 3, wherein the inert gas is at least one gas selected from nitrogen, helium, neon, argon, and krypton. A surface-treated polyamide system comprising a multilayer structure in which the surface-treated surface of the surface-treated polyamide film according to any one of claims 1 to 4 is disposed so as to constitute at least one surface of a resin laminate. the film A surface-treated polyamide-based laminate film obtained by laminating a sealant film on the surface-treated surface of the surface-treated polyamide-based film according to any one of claims 1 to 5. A bag comprising the surface-treated polyamide-based laminate film according to claim 6. After a step of stretching an unstretched film mainly composed of an aliphatic polyamide-based resin extruded from a flat die by a tenter-type sequential biaxial stretching method at a stretching ratio of 2.4 times or more for both MD and TD, 200 ° C or more In addition, an inert gas is formed on at least one surface of the film through a step of heat setting at a temperature not higher than 10 ° C. higher than the extrapolated melting start temperature (measured in accordance with JIS K 7121) of the aliphatic polyamide resin. A method for producing a surface-treated polyamide film, comprising a step of performing a surface treatment by a discharge treatment of any one of corona treatment and plasma treatment in an atmosphere having a concentration of 99% or more and an active gas concentration of 1% or less.