Surface treatment method, film, and packaging bag using the same

Abstract

The present invention makes it possible to obtain a flatter roll film when performing a surface treatment that imparts heat sealability to a stretched polyester film. A surface treatment method according to the present invention irradiates a stretched polyester film entirely or partly with an infrared-wavelength laser beam, forming a heat seal precursor. The surface treatment method is characterized in that the variation in scanning energy density distribution in the irradiation range of the laser beam is from 0 J / cm3 to less than 100 J / cm3.

Description

[Technical Field]

[0001] The present invention relates to a method for treating the surface of a film and a film surface-treated by the method. [Background technology]

[0002] Thermoplastic polyesters such as polyethylene terephthalate (PET) have excellent physical properties such as mechanical strength, creep resistance, impact resistance, and transparency, making them excellent materials for food containers. Bottles made from stretch-blow molded polyesters and containers made from laminates using these materials are widely used as sealed containers for filling food.

[0003] Furthermore, by biaxially stretching and crystallizing polyester film after film formation, it is possible to improve surface properties such as strength, heat resistance, various barrier properties, transparency, and slipperiness, and this stretched polyester film is used as a variety of industrial films. Stretched polyester film is also attracting attention for its low adsorption properties, and since it has little adsorption or permeation of medicinal ingredients and aromatic components of the contents, it is particularly effective as an inner lining for soft packaging containing anti-inflammatory and analgesic drugs and the like.

[0004] However, stretched polyester films have a problem in that their heat-sealing properties are reduced due to their high melting point in the crystalline state. To solve this problem, the surface of the inner layer to be heat-sealed is irradiated with a laser beam having an infrared wavelength to modify the surface, thereby imparting heat-sealing properties (see Patent Document 1 below). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 7-80502 Summary of the Invention [Problem to be solved by the invention]

[0006] It has been confirmed that when a stretched polyester film is subjected to the above-described surface modification treatment to impart heat-sealability to the treated areas, if the treated areas are overlapped to form a roll film after the treatment, the overlapping areas of the treated areas may bulge, preventing the roll film from having a flat surface. When the treated areas extend along the longitudinal direction of the roll film, the above-described bulge may become a band-like bulge. Furthermore, when the entire surface of the film is irradiated with laser light, partial irregularities occur within the treated areas, which also reduces the flatness of the roll film.

[0007] The present invention has been proposed to address these problems, and aims to provide a flatter roll film when a surface treatment is performed on a stretched polyester film to impart heat sealability. [Means for solving the problem]

[0008] In order to solve such problems, the present invention has the following configuration. Surface treatment in which stretched polyester film is entirely or partially irradiated with infrared laser light to form a heat seal precursor. Method for manufacturing the film The difference in scanning energy density distribution within the irradiation range of the laser light is 0 J / cm 3 End 10.8 J / cm 3 below A surface treatment characterized by: Method for manufacturing the film . The scanning energy density defined in the present invention is the amount of energy per unit volume at any point of the laser spot during scanning. Also, the scanning energy density at the center of the spot diameter of the laser light L and the scanning energy density at the point where the scanning energy density is 1 / e of the peak value are 2 The difference between the scanning energy density at the point where

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[0009] According to the surface treatment method having such characteristics and the film treated thereby, a flatter roll film can be obtained when a stretched polyester film is subjected to a surface treatment to impart heat sealability. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 2 is an explanatory diagram illustrating a surface treatment for imparting heat sealability to a stretched polyester film. [Figure 2] An explanatory diagram showing the state of the modified area formed after surface treatment ((a) is a scanning electron microscope photograph showing the surface state, (b) is a scanning electron microscope photograph of the cross section of the modified area, and (c) is a schematic diagram of the cross section of the modified area). [Figure 3] An explanatory diagram of optical radiation pressure. [Figure 4] FIG. 1 is an explanatory diagram illustrating the relationship between the scanning energy density distribution of laser light and the spot diameter at the point where it becomes 1 / e2 (13.5%). [Figure 5] An explanatory diagram showing the mechanism of the resin swelling that occurs around the periphery of the laser light irradiation area ((a) shows the plasticized state of the resin in the irradiation area, (b) shows the flow state of the resin, and (c) shows the state of swelling). [Figure 6-1] FIG. 10 is an explanatory diagram showing the measurement results of the difference in the scanning energy density distribution of the laser light and the height of the rise at the end of the modified portion. [Figure 6-2] FIG. 10 is an explanatory diagram showing the measurement results of the scanning energy density distribution gradient of the laser light and the height of the rise at the end of the modified portion. [Figure 7]Photographs showing the difference in the scanning energy density distribution of the laser light and the state of the raised area at the end of the modified area ((a) is when the energy density difference is 26.4 J / cm3, (b) is when the scanning energy density distribution difference is 10.7 J / cm3). [Figure 8] (a) is a schematic diagram showing the crystallinity distribution in the thickness direction at the end of the modified region, and (b) is an explanatory diagram showing the relationship between the difference in the scanning energy density distribution of the laser light and the difference in crystallinity between the surface and bottom at the end of the modified region. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. As shown in Fig. 1, surface treatment of a stretched polyester film (hereinafter referred to as film) F is performed by irradiating the film surface Fa with laser light L. The laser light L is a spot light with an infrared wavelength (for example, a wavelength of 10.6 µm (far infrared)), and a CO2 laser light source or the like can be used as the light source S.

[0012] Laser light L is irradiated onto the film surface Fa within an irradiation range La of a set spot diameter, and when processing a specified range, the irradiation range La is moved (scanned) to irradiate the entire or part of the film surface Fa with laser light L. When laser light L is irradiated, the temperature of the film surface Fa rises instantaneously due to localized heating caused by light absorption, and the temperature drops immediately after the irradiation range La of laser light L has passed.

[0013] When the film surface Fa is subjected to surface treatment in this way by irradiating it with laser light L, the crystallized stretched polyester film has a reduced degree of crystallization. For example, if the crystallization degree before treatment is 51%, the crystallization degree after treatment will be 10% or less. Modified regions Re with reduced crystallization degree are formed in the areas irradiated with laser light L, and these modified regions Re impart heat sealability. The modified regions Re are formed as heat seal precursor regions within an appropriate range of the areas H to be heat sealed of the film F.

[0014] It was confirmed that the modified region Re, whose crystallinity was reduced by irradiation with laser light L, had a partial protuberance, as shown in Figure 2. As shown schematically in Figure 2(c), this protuberance has a height h (e.g., about 8 μm) that is most noticeable at the edge of the modified region Re, but this height h itself is not noticeable by visual observation. However, if several thousand sheets of film F on which such modified regions Re have been formed are stacked so that the modified regions Re overlap to form a roll film, visible protuberances will form on the surface where the modified regions Re overlap, compromising the flatness of the roll film.

[0015] After careful investigation into the cause of this bulge in the modified area Re, we discovered that the optical radiation pressure applied to the film surface Fa by irradiation with laser light L causes the heated and plasticized resin to flow.

[0016] As shown in Figure 3, optical radiation pressure increases according to the scanning energy density and acts in a direction perpendicular to the light incident interface. On the other hand, it is generally known that the scanning energy density distribution of laser light L is close to a Gaussian distribution, with the highest energy density at the center of the irradiation area La, as shown in Figure 4. Therefore, optical radiation pressure is high at the center of the irradiation area La and low at the periphery of the irradiation area La, in accordance with the energy density distribution of laser light L.

[0017] As shown in Fig. 5, when laser light L is irradiated onto the film surface Fa, the resin plasticizes within the irradiation area La as shown in Fig. 5(a), but as mentioned above, the light radiation pressure in the irradiation area La is high in the center of the irradiation area La and low at the periphery of the irradiation area La, so it is expected that the resin will flow from the center to the periphery of the irradiation area La as shown in Fig. 5(b). This resin flow can explain the rise of the resin at the periphery of the irradiation area La of the laser light L as shown in Fig. 5(c).

[0018] According to the above-mentioned findings, if the difference in optical radiation pressure in the irradiation range La of the laser light L is reduced, it is possible to suppress the flow of the resin described above and to prevent the resin from swelling around the periphery of the irradiation range La. In order to reduce the difference in optical radiation pressure, it is effective to reduce the difference in the scanning energy density distribution within the irradiation range La of the laser light L.

[0019] Furthermore, as a result of various investigations by the inventors, it was found that three factors, namely, laser output, laser scanning speed, and spot diameter of the laser light L, are related to reducing the difference in energy density distribution. As an example, Figure 4 shows the relationship between the difference in scanning energy density distribution of laser light L and the spot diameter of laser light L. If the irradiation energy within the spot of laser light L is constant, the smaller the spot diameter, the higher the energy density at the center of the spot diameter, and the larger the difference in energy density distribution. In this case, it was found that the difference in energy density distribution becomes smaller as the spot diameter becomes larger.

[0020] When the difference in the scanning energy density distribution in the irradiation range La of the laser light L was changed by optically changing the spot diameter of one laser light L, the height of the protrusion at the end of the modified area Re caused by surface treatment with the laser light L was measured, and the measurement results shown in Figure 6-1 were obtained.

[0021] As is clear from Figure 6-1, the difference in scanning energy density distribution is 100 J / cm 3 When the difference in scanning energy density is less than 100 J / cm, the height h of the protrusion at the end of the modified region Re can be suppressed as the difference in scanning energy density is reduced. 3 Above this, the rise height h at the end of the modified area Re reaches a plateau. Therefore, the difference in the scanning energy density distribution within the irradiation range La of the laser light L irradiated in the surface treatment is set to 0 J / cm 3 More than 100J / cm 3By setting the height h of the protrusion at the end of the modified region Re to less than 13.5 μm, it is possible to effectively keep the height h of the protrusion at the end of the modified region Re within the range of 0 μm or more and less than 13.5 μm. Note that the height h of the protrusion at the end of the modified region Re refers to the height of the apex of the protrusion at the end of the modified region Re when the film surface Fa other than the modified region is used as the reference plane, as shown in Figures 1 and 2(c).

[0022] When the laser beam L is irradiated perpendicularly to the film surface Fa, the difference in the scanning energy density distribution of the laser beam L is 0 to 180 nN s / cm, based on the definition of the optical radiation pressure shown in Figure 3. 3 This allows the difference in the optical radiation pressure of the laser light L to be 0 nN s / cm 3 More than 180nN·s / cm 3 By setting the height h of the protrusion at the end of the modified region Re to be less than 100 mm, the protrusion height h at the end of the modified region Re can be effectively suppressed.

[0023] Figure 7 shows micrographs showing the difference in the scanning energy density distribution of the laser light L and the state of the raised area at the end of the modified area Re. (a) shows the difference in the scanning energy density distribution of 26.4 J / cm 3 In this case, the height of the protrusion at the end of the modified area Re is about 8 μm. In contrast, in (b), the difference in the scanning energy density distribution is 10.7 J / cm 3 In this case, the height of the rise at the end of the modified region Re could be suppressed to about 1.1 μm.

[0024] Furthermore, as a result of intensive research by the inventors, it was found that even when the central scanning energy density (peak value of scanning energy density) is the same, the rise at the edge of the irradiation area is smaller when the spot diameter of the laser light L is larger. This can be explained by the distribution of scanning energy density; when the central scanning energy density is the same, the smaller the spot diameter, the larger (steeper) the scanning energy density distribution gradient, which is thought to be why the plasticized resin tends to flow toward the irradiation edge where the scanning energy density is smaller. In order to suppress this flow, it is more effective to reduce the scanning energy density distribution gradient. The scanning energy density distribution gradient defined in the present invention is calculated from the scanning energy density distribution gradient = difference in scanning energy density distribution / spot radius. Here, the spot radius is the distance from the center of the spot diameter where the scanning energy density is 1 / e of the peak value. 2 The distance to the point where

[0025] When the spot diameter of one laser beam L was optically changed to change the scanning energy density distribution gradient in the irradiation range La of the laser beam L, the height of the protrusion at the end of the modified area Re caused by surface treatment with the laser beam L was measured, and the measurement results shown in Figure 6-2 were obtained.

[0026] As is clear from Figure 6-2, the scanning energy density distribution gradient is 4000J / cm 4 When the scanning energy density distribution gradient is less than 4000 J / cm, the height h of the protrusion at the end of the modified region Re can be suppressed as the scanning energy density distribution gradient is reduced. 4 Above this, the height h of the rise at the end of the modified area Re reaches a plateau. Therefore, the scanning energy density distribution gradient within the irradiation range La of the laser light L irradiated in the surface treatment is set to 0 J / cm 4 More than 4000J / cm 4 By setting the height h of the protrusion at the end of the modified region Re to be less than 13.5 μm, the height h of the protrusion at the end of the modified region Re can be effectively kept within the range of 0 μm or more and less than 13.5 μm.

[0027] When the laser beam L is irradiated perpendicularly to the film surface Fa, the gradient of the scanning energy density distribution of the laser beam L is 0 to 360 nN s / cm, based on the definition of the optical radiation pressure shown in Figure 3. 4 This allows the optical radiation pressure distribution gradient of the laser light L to be 0 nN s / cm 4 More than 360nN·s / cm 4 By setting the height h of the protrusion at the end of the modified region Re to be less than 100 mm, the protrusion height h at the end of the modified region Re can be effectively suppressed.

[0028] Next, we focus on the crystallinity of the modified Re region. The scanning energy distribution density is small at the edge of the modified Re region, making it difficult for the crystallinity to decrease. It is believed that the plasticized resin is pushed there, creating a difference (distribution) in the crystallinity between the surface and bottom at the edge of the modified Re region. Figure 8(a) shows a schematic diagram. When a bulge forms at the edge of the modified Re region, the crystallinity is sufficiently reduced in the upper layer of the bulge, but the crystallinity remains high in the layer below. In this case, the crystallinity distribution in the thickness direction at the edge of the modified Re region shows a large difference in crystallinity between the surface and bottom of the edge of the modified Re region.

[0029] According to this finding, when the difference in crystallinity between the surface and bottom of the modified section Re end is large, it can be said that a relatively large protrusion occurs at the modified section Re end, and when the difference in crystallinity between the surface and bottom of the modified section Re end is small, it can be said that the protrusion at the modified section Re end is small. Therefore, when the modified sections Re are stacked to form a roll film, the protrusions in the roll film can be suppressed by reducing the difference in crystallinity between the surface and bottom of each modified section Re end.

[0030] Figure 8(b) shows the results of measuring the difference in crystallinity between the surface and bottom at the end of the modified region Re by changing the difference in the scanning energy density distribution of the laser light L. As is clear from the figure, when the difference in the scanning energy density distribution of the laser light L is 100 J / cm 3 When the difference in the scanning energy density distribution is smaller than this, the difference in the crystallinity at the end of the modified region Re can be made smaller as the difference in the scanning energy density distribution is made smaller.

[0031] In this case, the difference in scanning energy density distribution is 100 J / cm 3 The difference in crystallinity at the modified Re end is 32.55%, and when the difference in scanning energy density distribution is increased, the difference in crystallinity plateaus at approximately 35%. Therefore, by setting the difference in crystallinity between the surface and bottom of the modified Re end to between 0% and 35%, it is possible to suppress the protrusion of the modified Re end.

[0032] The stretched polyester film F according to an embodiment of the present invention is particularly useful as a stretched PET (polyethylene terephthalate) film. Stretched PET film has excellent low sorption properties. For example, when used as a soft packaging material for anti-inflammatory and analgesic drugs, the film exhibits low adsorption and permeation of the medicinal and aromatic components of the contents, allowing the efficacy and flavor to be maintained for a long period of time, eliminating the need to increase the amount of ingredients. Furthermore, delamination can be suppressed.

[0033] When forming the modified regions Re in a stretched PET film using the processing method described above, a CO2 laser with a wavelength of 10.6 μm is used with a laser beam spot diameter of 7 mm, which makes it possible to suppress the protrusion height h at the edge of the modified regions Re to 8 μm or less. When this film is wound into a roll film with the modified regions Re stacked 1,000 times or more, a relatively flat roll film with suppressed protrusions can be obtained.

[0034] Furthermore, a packaging bag can be produced using the above-described stretched polyester film. The packaging bag can be produced by heat-sealing the above-described modified portions of one or more films. In this case, the film may be a single layer, or a multilayer film that includes a film having the above-described modified portion formed on its surface and is laminated with a film having oxygen barrier properties, water vapor barrier properties, or a metal foil layer. The packaging bag obtained in this manner has excellent resistance to the contents because the innermost layer that comes into contact with the contents can be made of a stretched polyester film, which is generally stable against heat and light and is thought to have little adsorption of or interaction with medicinal ingredients.

[0035] In the above description, an example of increasing the spot diameter of the laser light L has been described as a method for reducing the difference in the scanning energy density distribution within the irradiation range La of the laser light L, but the present invention is not limited to this, and an optical element such as a beam homogenizer can be used to homogenize the scanning energy density distribution within the irradiation range La. In this case, the spot radius is defined as the distance from the center of the spot diameter of the laser light L to the edge of the irradiation range having the same energy density as the center. [Explanation of symbols]

[0036] L: laser light, S: light source, La: irradiation area F: film, Fa: film surface, Re: modified part

Claims

1. A method for producing a surface-treated film, in which a stretched polyester film is entirely or partially irradiated with a laser beam having an infrared wavelength to form a heat seal precursor portion, comprising: The difference in scanning energy density distribution within the irradiation range of the laser light is 0 J / cm ３ More than 10.7J / cm ３ A method for producing a surface-treated film, characterized in that:

2. The difference in optical radiation pressure between the center and the edge of the irradiation range is 0 nN·s / cm ３ More than 180nN・s / cm ３ 2. The method for producing a film according to claim 1, wherein the thickness is less than 1 / 2 mm.

3. The scanning energy density distribution gradient within the irradiation range is 0 J / cm ４ More than 4000J / cm ４ 3. The method for producing a film according to claim 1, wherein the thickness is less than 1 / 2 mm.

4. The optical radiation pressure distribution gradient within the irradiation area is 0 N·s / cm ４ More than 360N・s / cm ４ The method for producing a film according to any one of claims 1 to 3, wherein the thickness is less than 1 / 2 mm.

5. The method for producing a film according to any one of claims 1 to 4, wherein the object to be irradiated with the laser light is a stretched polyester film alone.

6. 5. The method for producing a film according to claim 1, wherein the object to be irradiated with the laser beam is a laminate of a stretched polyester film and an aluminum layer.

7. The method for producing a film according to any one of claims 1 to 6, wherein the stretched polyester film is a stretched polyethylene terephthalate film.

8. The laser light is CO ２ The method for producing the film according to any one of claims 1 to 7, wherein the light is laser light.

9. A stretched polyester film, The modified portion has a wholly or partially formed amorphous or low-crystallized portion, The difference in crystallinity between the surface and the bottom of the modified portion is 0% or more and less than 35%, The film has a protruding height at the end of the modified portion of 0 μm or more and 1.1 μm or less.

10. A packaging bag comprising the film according to claim 9, wherein the modified portions are heat-sealed together.

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