Method for modifying surface of food packaging material by using femtosecond laser

Abstract

A method for modifying a film for food packaging, according to an embodiment of the present invention, comprises the steps of: applying a femtosecond laser of a predetermined condition onto the film; performing patterning of a predetermined shape by the applied femtosecond laser; and changing surface properties of the film by the patterning, wherein the film for food packaging is a polymer film.

Description

Method for surface modification of food packaging materials using femtosecond laser

[0001] The present invention relates to a modification method for changing the surface properties of a food packaging material made of a polymer material using a femtosecond laser.

[0002] Depending on the type of food, various food packaging films and containers are developed and used.

[0003] A variety of functional packaging materials and systems are being developed to maintain high-quality food products and ensure safe storage during distribution and consumption, depending on their characteristics. Among these, food packaging films can be given the ability to control storage and shelf life based on their surface properties.

[0004] Furthermore, food contents stick to the surfaces of food packaging films and containers, rendering them unusable and resulting in significant waste, resulting in economic losses and environmental pollution. For example, 3-15% of sauces, 17-25% of cosmetics, 7-16% of detergents, and 1-13% of toothpaste contents stick to the surfaces of containers, rendering them unusable and ending up as waste. Furthermore, many viscous food contents are often lost due to this type of waste. Furthermore, the cost of removing substances stuck to the surfaces of systems, including food packaging and food processing equipment, accounts for over 75% of total maintenance and management costs, resulting in significant economic losses. In particular, removing foulants stuck to the surfaces of processing equipment in dairy processing systems is a costly and time-consuming process. Microorganisms, including proteins, adhere to these surfaces, forming biofilms and causing secondary contamination.

[0005] Research is ongoing to address these issues. For example, solutions can be found by introducing various patterning surfaces or chemical groups, such as polymer brushes. Furthermore, various superhydrophilic and superhydrophobic surfaces and surface coating methods are being studied. However, the introduction of chemical groups primarily involves fluorine-based chemicals, which are not biodegradable and pose a risk of adverse effects on the ecosystem. The fabrication of various patterning surfaces requires lithography processes, which are often used in semiconductor manufacturing. Consequently, hazardous chemicals are used at each process step, posing both economic and environmental challenges.

[0006] The present invention aims to solve the above-mentioned problems and other problems related thereto, and provides a surface modification method that can implement a desired pattern on the surface of a food packaging film in a single process using femtosecond laser technology, and can impart predetermined characteristics to the film in an economical and environmentally friendly manner without using any chemicals through such patterning.

[0007] The technical problems according to the technical idea disclosed in this specification are not limited to the problems mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the description below.

[0008] In order to achieve the technical task described above, a method for modifying a food packaging film according to an embodiment of the present invention includes the steps of applying a femtosecond laser under predetermined conditions to the film; performing patterning of a predetermined shape by the applied femtosecond laser; and changing the surface properties of the film by the performed patterning, wherein the food packaging film is any polymer film.

[0009] The patterning step comprises one of: large-area circular patterning, large-area roughness patterning with superimposed single pulses, and large-area roughness patterning with superimposed linear patterning, wherein the surface properties of the film are changed to hydrophilic by one of the patterning, and the film comprises one of HDPE, PP, and PET.

[0010] The above patterning step includes large-area grid patterning, and is characterized in that the surface property of the film is changed to hydrophobic by the large-area grid patterning, and the film is characterized in that it is an HDPE film.

[0011] The application conditions of the femtosecond laser are: pulse energy of 2.55 μJ or more, spot diameter size of 5 to 10 μm, and scanning speed of 1 to 10 mm / s.

[0012] According to the present invention, the problems described above and other problems related thereto can be solved, and in particular, a desired pattern can be implemented on the surface of a food packaging film in a single process using femtosecond laser technology, and only through such patterning, the surface of a food packaging film can be economically and environmentally modified without using any chemicals.

[0013] Meanwhile, these effects are merely exemplary, and effects predicted or expected from the detailed configuration of the present invention from the perspective of those skilled in the art may also be added to the inherent effects of the present invention.

[0014] Figure 1 is a process diagram of a method for modifying a food packaging film according to one embodiment of the present invention.

[0015] Figure 2 is an SEM image of the surface of HDPE and PP packaging films under single pulse conditions of a femtosecond laser.

[0016] Figure 3 is an SEM image showing the results of large-area patterning using a femtosecond laser on the surface of HDPE and PP films.

[0017] Figure 4 is an SEM image (Scanning speed: 1 mm / s, Line spacing: 7 μm) showing the results of straight-line patterning using a femtosecond laser on the surfaces of HDPE, PP, and PET films.

[0018] Figure 5 is an SEM image (Scanning speed: 4 mm / s) showing the results of lattice patterning using a femtosecond laser on the surface of an HDPE film.

[0019] Figure 6 is an AFM image of the surface of a large-area circular and full-roughness large-area patterned HDPE film.

[0020] Figure 7 is an AFM image of the large-area circular and full-roughness large-area patterned PP film surface.

[0021] Figure 8 shows the surface contact angles of HDPE (control) and large-area circular patterned HDPE films, respectively.

[0022] Figure 9 shows the surface contact angles of PP (control) and large-area circular patterned PP films, respectively.

[0023] Figure 10 shows the surface contact angles of PET (control) and full roughness patterned PET films, respectively.

[0024] Figure 11 shows the large-area grid patterned HDPE film and surface contact angle, respectively.

[0025] Hereinafter, embodiments disclosed in this specification will be described in detail with reference to the attached drawings. Regardless of the drawing numbers, identical or similar components will be given the same reference numerals and redundant descriptions thereof will be omitted. In describing embodiments disclosed in this specification, if a detailed description of related known technologies is determined to obscure the gist of the embodiments disclosed in this specification, the detailed description thereof will be omitted. In addition, the attached drawings are only intended to facilitate easy understanding of the embodiments disclosed in this specification, and the technical ideas disclosed in this specification are not limited by the attached drawings, and should be understood to include all modifications, equivalents, or substitutes included in the spirit and technical scope of the present invention. In addition, in this application, terms such as “comprises” or “has” are intended to specify the presence of features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, but should be understood to not preclude the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0026]

[0027] The method for modifying a food packaging film according to the present invention includes, as illustrated in FIG. 1a, a step (s10) of applying a femtosecond laser under predetermined conditions to a film, a step (s20) of performing patterning of a predetermined shape by the applied femtosecond laser, and a step (s30) of changing the surface properties of the film by the performed patterning, and the food packaging film is characterized in that it is a polymer film.

[0028] The femtosecond laser used in the present invention is 10 -15 It refers to a laser with a very short pulse width of 10 seconds. -15Due to the extremely short pulse width of a few seconds and high peak power, the duration of the irradiated laser pulse is shorter than the thermal diffusion time of the processing surface, enabling processing without thermal deformation of the material and surface. In addition, since it produces high peak power with relatively less energy than conventional continuous wave or nanosecond lasers, it reduces the shock to the processing material and surface, enabling high-quality, ultra-precision micromachining. In other words, compared to continuous wave or nanosecond lasers, femtosecond lasers can minimize heat-affected zone, thermal damage, cracks, debris generation, and surface distortion caused by shock waves.

[0029] Research on transforming and controlling the properties of various surfaces, including packaging films, in the food industry using laser technology, including femtosecond lasers, has not yet been attempted. As part of this effort, the present invention aims to provide a technology for surface patterning of food packaging films using femtosecond lasers. After confirming the feasibility of patterning the surface of a polymer film for food packaging using a femtosecond laser, the optimal process conditions for femtosecond lasers for nano- and micro-surface patterning were established. Furthermore, based on this, nano- and micro-patterning was implemented on the surfaces of HDPE, PP, and PET films, and the surface characteristics according to the surface patterning structure and size were analyzed. The specific experimental conditions and results supporting this are described in detail below.

[0030]

[0031] Conditions and Methods

[0032]

[0033] 1. Film material for food packaging

[0034] The femtosecond laser-based patterning technology of the present invention is applicable to packaging films used in the food industry. These packaging films may include low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP), or polyethylene terephthalate (PET). These are merely examples and can be applied to all currently used food packaging films made of various polymer materials.

[0035] 2. Femtosecond laser device

[0036] The femtosecond laser device for surface patterning according to the present invention comprises a femtosecond laser generating portion, a shutter and beam expander portion, a laser head portion including a lens, an NIR reflector, and an objective lens, and a scanner and a sample-mounting 3D stage portion. The femtosecond laser device used in the present invention is a conventional device, and a detailed description thereof will be omitted.

[0037] 3. Nano and micro pattern process conditions applicable to the surface of food packaging films

[0038] To find the critical energy at which the single pulse energy of a femtosecond laser affects HDPE and PP films used as food packaging films, a single pulse experiment was conducted based on the following process conditions.

[0039] Wavelength (515 nm), Pulse width (400 fs), Pulse rate (1 kHz), Pulse energy (2.55, 0.85, 0.425, 0.216, 0.144, 0.072 μJ), Scanning speed (10 ㎜ / s), Beam spot size (~10 ㎛)

[0040] Based on the results of the single pulse experiment, experiments were conducted under the following process conditions to implement a large-area surface with overall roughness at the nano- and micrometer-level.

[0041] Wavelength (515 nm), Pulse width (400 fs), Pulse rate (10 kHz), Pulse energy (2.55, 0.85, 0.425, 0.216, 0.144, 0.072 μJ), Scanning speed (100 ㎜ / s), Beam spot size (~10 ㎛)

[0042] To implement straight-line patterns on the surfaces of HDPE, PP, and PET films, experiments were conducted based on the following process conditions.

[0043] Wavelength (515 nm), Pulse width (400 fs), Pulse rate (1 kHz), Pulse energy (150 nJ), Scanning speed (1, 3 ㎜ / s), Beam spot size (~10 ㎛), Line spacing (3, 5, 7 ㎛).

[0044] To produce a grid patterned surface, experiments were conducted based on the following process conditions.

[0045] Wavelength (343 nm), Pulse width (400 fs), Pulse rate (1 kHz), Pulse energy (17 μJ), Beam spot size (125 ㎛), Line spacing (50 ㎛), Scanning speed (10 ㎜ / s).

[0046] 4. Creating nano and micro patterns on the surface of food packaging films

[0047] Using the optimized process conditions of the femtosecond laser, nano- and micro-patterns ranging from hundreds of nanometers to tens of micrometers in size were produced on the surfaces of HDPE, PP, and PET films used as food packaging films, including large-area circular patterns by single pulses, large-area surfaces with full roughness by overlapping single pulses by 30%, linear patterns, and grid patterns.

[0048] 5. Analysis of surface properties of the fabricated patterned film

[0049] The surface morphology of the patterned samples was observed using a scanning electron microscope. Completely dried samples were mounted on stubs and coated with platinum for 60 seconds using a sputter coater. The roughness of the patterned surfaces was measured using an atomic force microscope. Non-contact mode was used to examine the surface using a non-contact cantilever. The surface contact angle was measured using a contact angle analyzer.

[0050]

[0051] Process optimization and film modification results

[0052]

[0053] 1. Optimization of nano- and micro-patterning process conditions on the surface of food packaging films.

[0054] Single pulse experiments were performed to optimize the parameters of a femtosecond laser for surface patterning of HDPE and PP films for food packaging.

[0055] First, while fixing other laser process conditions, the surface images of the films tested by varying the pulse energy from 0.072 to 2.55 μJ were confirmed by SEM image analysis (see Fig. 2). The blue dotted rectangle area shows the area where the laser dwells before the stage moves, indicating a significant overlap of pulses. At the single-pulse level, both HDPE and PP films were confirmed to have no effect when the pulse energy was less than 0.85 μJ. The most obvious modification of the film surface was confirmed when the pulse energy was 2.55 μJ. In this way, each process condition for femtosecond laser patterning was optimized.

[0056] 2. Creating nano and micro patterns on the surface of food packaging films

[0057] In the case of continuous lasers and nanosecond lasers, specific patterning was not implemented on the surface of the polymer film because the conditions did not match with the polymer. Using a femtosecond laser, large-area circular patterns were created on the surfaces of HDPE and PP films with a single pulse, and a large-area surface with full roughness was created by overlapping the single pulses by 30% (see Fig. 3). In the single pulse experiment, when the pulse energy was 2.55 μJ, the spot diameter sizes on the surfaces of HDPE and PP films were approximately 10 and 7 μm, respectively, but in the large-area patterning experiment with full roughness, they were confirmed to be 7 and 5 μm on the HDPE and PP films, respectively.

[0058] Figure 4 shows the results of linear patterning on the surfaces of HDPE, PP, and PET films at a scanning speed of 1 mm / s and a line spacing of 7 μm. Under all conditions of the femtosecond laser process, linear patterns were successfully created, and a rough surface with nano- and micrometer-scale roughness was formed in the patterned area. In particular, the clearest linear pattern was achieved on the PET film.

[0059] The surface of a lotus leaf, which has superhydrophobicity, has numerous protrusion structures measuring 3 to 10 μm in size, and each micro-sized protrusion has nano-sized protrusions on its surface. This nano-micro-sized protrusion structure plays a role in making the surface superhydrophobic. In particular, because these nano-sized protrusions have high surface tension, they cause water droplets to form in a round shape rather than spreading out. In the present invention, in order to implement a hydrophobic surface with a shape similar to the surface structure of a lotus leaf, a grid pattern capable of having a nano-micro structure was designed and patterned on an HDPE film using a femtosecond laser. At a scanning speed of 10 mm / s, a grid pattern created by intersecting straight patterns was not clearly implemented. By lowering the scanning speed to 4 mm / s, a grid pattern similar to an egg carton shape was implemented (see Figure 5). Although the structure is different from the distinct nano-micro-sized protrusion structure on the surface of the lotus leaf, the regular protrusion structure of 50 μm in size and the protrusion surface formed various nano-sized rough structures, thereby changing the surface structure so that the film surface could be hydrophobic after patterning. However, a similar lattice pattern was not realized in a PP film with different physical properties from HDPE under the same conditions.

[0060] 3. Analysis of surface properties of the fabricated patterned film

[0061] Patterned films were fabricated using a femtosecond laser on the surface of HDPE, PP, and PET films to form large-area circular patterns, large-area surfaces with a 30% overlap of single pulses to form overall roughness, linear patterns, and grid patterns. The surface images and characteristics of the patterns were confirmed by SEM analysis (see Figs. 2 to 5).

[0062] The surface roughness of circular large-area patterning and overall roughness large-area surface patterning HDPE and PP films was analyzed by AFM.

[0063] The surface of the HDPE film, which is the control group without patterning, showed a surface roughness of approximately 2 to 300 nm, whereas the 10 ㎛ circular large-area patterning and 7 ㎛ overall roughness large-area patterning surfaces were confirmed to have roughnesses of approximately 1.5 and 2 ㎛, respectively (see Fig. 6). In the case of the PP film, the surface of the control group PP film showed a surface roughness of approximately 20 nm, whereas the 7 ㎛ circular large-area patterning and 5 ㎛ overall roughness large-area patterning surfaces showed roughnesses of approximately 500 nm and 1.5 ㎛, respectively (see Fig. 7).

[0064] Changes in surface properties were confirmed through contact angle analysis of large-area PET films and large-area grid-patterned HDPE films. The HDPE film surface without femtosecond laser patterning had a contact angle of 76.6°. After large-area circular patterning, the surface contact angle decreased to 35.6°. This indicates that the HDPE film surface became hydrophilic after circular patterning (Fig. 8).

[0065] Similar to the results for the HDPE film, the surface of the PP control film without femtosecond laser patterning had a contact angle of 77.7°. After large-area circular patterning, the surface contact angle dropped to 37.5°, indicating that the PP film became a hydrophilic surface after patterning (Fig. 9). The PET film surface without femtosecond laser patterning showed a contact angle of 84.5°. The contact angle of the overall roughness large-area patterned surface realized by overlapping linear patterning dropped to 27.1°, indicating that the PET film became a hydrophilic surface after patterning (Fig. 10). The overall roughness large-area patterned film surface realized by overlapping linear patterning became more hydrophilic than the circular large-area patterned film surface.

[0066] The left photo in Fig. 11 shows a large-area HDPE grid-patterned film and the appearance when a water droplet is dropped on it. The grid-patterned HDPE film exhibits a contact angle of 120.4°, indicating that it has become a hydrophobic surface compared to the unpatterned control (76.6°).

[0067]

[0068] Ultimately, based on the experimental results examined above, the following can be confirmed:

[0069] In the case of continuous lasers and nanosecond lasers, which are widely used in the food packaging field, specific patterning could not be implemented on the surface of polymer films due to the mismatch of polymer and material property conditions. However, it was confirmed that patterning was implemented on the surface of food packaging films such as HDPE, PP, and PET using a femtosecond laser. Therefore, in the present invention, the process conditions for femtosecond laser patterning in food packaging films were established, and surface patterned films were produced, such as a large-area circular pattern by a single pulse, a large-area roughness pattern with 30% overlap of single pulses, a linear pattern, a large-area roughness pattern with overlapping linear patterning, and a grid pattern with intersecting linear patterning. In addition, the characteristics of patterned HDPE, PP, and PET films according to the surface pattern structure and size were confirmed through SEM, AFM, and contact angle analysis.

[0070] The surfaces of large-area circular-patterned HDPE and PP films, large-area roughness-patterned PET films with 30% overlapping single pulses, and large-area roughness-patterned PET films with overlapping linear patterns showed contact angles of 27.1-37.5° compared to the surfaces of each control film without femtosecond laser patterning, indicating that the HDPE, PP, and PET films became hydrophilic surfaces after patterning. In contrast, the large-area lattice-patterned HDPE film with nano- to micro-sized protrusions showed a contact angle of 120.4°, indicating that the surface became hydrophobic after patterning.

[0071] Therefore, films with hydrophilic surfaces transformed through patterning can be utilized in antifouling applications where proteins, cells, viruses, and other food substances cannot adhere or easily fall off. Furthermore, if lattice patterning with more precise nano- and micro-protrusion structures is used in the future to create superhydrophobic surfaces with an angle of 150° or higher, they can be utilized in superhydrophobic surface applications such as self-cleaning.

[0072]

[0073] Although the embodiments described above have been described by way of limited examples and drawings, those skilled in the art will appreciate that various modifications and variations can be made based on the above teachings. For example, appropriate results can still be achieved even if the described techniques are performed in a different order than described, and / or components of the described systems, structures, devices, circuits, etc. are combined or combined in a different manner than described, or are replaced or substituted with other components or equivalents.

[0074] Therefore, other implementations, other embodiments, and equivalents to the claims also fall within the scope of the claims described below.

Claims

1. A method for modifying a film for food packaging, A step of applying a femtosecond laser under predetermined conditions onto the above film; A step of performing patterning of a predetermined shape by the above-mentioned authorized femtosecond laser; and A step of changing the surface properties of the film by the above-described patterning. Including, and characterized in that the food packaging film is a polymer film, Method for modifying food packaging materials.

2. In paragraph 1, The above patterning steps are: Large area circular patterning, Large-area roughness patterning by overlapping single pulses, and Large-area roughness patterning with overlapping linear patterning characterized in that the surface property of the film is changed to hydrophilic by any one of the above patterning, Method for modifying food packaging materials.

3. In paragraph 2, The above film comprises one of HDPE, PP, and PET. Method for modifying food packaging materials.

4. In paragraph 1, The above patterning step includes large-area grid patterning, and is characterized in that the surface property of the film is changed to hydrophobic by the large-area grid patterning. Method for modifying food packaging materials.

5. In paragraph 4, The above film is characterized in that it is an HDPE film. Method for modifying food packaging materials.

6. In any one of paragraphs 1 to 5, The above femtosecond laser application conditions are: Pulse energy greater than 2.55 μJ, The spot diameter size is 5 to 10 ㎛, and Scanning speed is 1 to 10 mm / s characterized by, Method for modifying food packaging materials.

Images