KR102516587B1 - Method for gas barrier membrane with reduced oxygen permeability comprising a step of biaxial stretching - Google Patents

Abstract

The present invention relates to a method for manufacturing a gas barrier membrane with reduced oxygen permeability, including a step of biaxially stretching a nanocomposite sheet including a thermoplastic resin and nanoclay. The present invention contains only inorganic materials, so that heat resistance can also be improved, thereby being widely used as an oxygen barrier membrane or a packaging material.

Description

Method for manufacturing a gas barrier membrane with reduced oxygen permeability comprising a step of biaxial stretching

The present invention relates to a method for manufacturing a gas barrier film having reduced oxygen permeability, comprising biaxially stretching a nanocomposite sheet comprising a thermoplastic resin and nanoclay.

Plastics have been widely used as packaging materials from the past due to their low unit cost, excellent mechanical strength, and easy processability. However, in recent years, the plastic waste problem has been attracting attention. First of all, plastic packaging waste is rapidly increasing as the consumption of packaged food, fresh food, and delivered food surges during the lockdown period caused by the COVID-19 pandemic. Additionally, the continued growth of the e-commerce market and e-commerce services tends to consume more packaging than traditional retailers. Although it takes less than a week to produce most of the plastics used in the packaging industry, plastics' greatest asset—durability—leads to the accumulation of waste. In order to solve this problem, it is necessary to develop a single material that is rapidly degradable or recyclable and has performance as a packaging material in which two or more types of polymers do not coexist.

Polypropylene (PP), a type of thermoplastic material, may be an excellent candidate for a packaging material due to its low unit cost, high mechanical strength, excellent water barrier properties, easy processability, and high recyclability. However, PP is still limited in its use in packaging fields requiring oxygen barrier performance due to its poor oxygen barrier properties. Accordingly, various attempts have been made to improve the oxygen barrier properties of PP. For example, among these methods, a method of manufacturing a composite material using additives (protein, polyelectrolyte, silicate, and graphene oxide) and additionally performing processes such as coating or stretching may be effective.

As a result of intensive research efforts to provide a material with improved oxygen barrier properties by including nanoclay as an additive to a thermoplastic resin, the present inventors have prepared a composite sheet containing a thermoplastic resin and nanoclay, and then sequentially in the longitudinal and transverse directions. It was confirmed that a material having more improved oxygen barrier properties could be provided by biaxial stretching and/or stretching at different ratios in the machine and transverse directions, and the present invention was completed.

Each description and embodiment disclosed in the present invention can also be applied to each other description and embodiment. That is, all combinations of the various elements disclosed herein fall within the scope of the present invention. In addition, it cannot be said that the scope of the present invention is limited by the specific description described below.

In addition, those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. Also, such equivalents are intended to be included in this invention.

In addition, in the entire specification of the present invention, when a part "includes" a certain component, this means that it may further include other components, not excluding other components unless otherwise stated. it means.

Hereinafter, the present invention will be described in more detail.

A first aspect of the present invention is a first step of preparing a nanocomposite sheet in which a thermoplastic resin and 0.5wt% to 10wt% nanoclay are melt-mixed; and a second step of biaxially stretching the nanocomposite sheet.

For example, the biaxial stretching may be performed at different magnifications in the machine direction (MD) and the transverse direction (TD) of the sheet, but is not limited thereto.

In addition, the biaxial stretching may be performed by first stretching in one of the longitudinal and transverse directions and then sequentially stretching in the other direction, but is not limited thereto.

In a specific embodiment of the present invention, in performing biaxial stretching, even if the final magnification is the same, compared to the case of stretching at the same magnification in the machine direction and the transverse direction or simultaneously stretching in the machine direction and the transverse direction, i) in both directions It was confirmed that a sheet having superior oxygen barrier ability can be provided when the sheet is stretched at a different ratio or ii) when first stretched on one side and then on the other side, that is, when the sheet is stretched sequentially. Furthermore, iii) it was confirmed that a sheet having synergistically improved oxygen barrier properties can be provided when the sheets are stretched at different magnifications in both directions but sequentially stretched.

For example, the thermoplastic resin may be polypropylene (PP), polyethylene terephthalate (PET), or polyethylene (PE). Specifically, polypropylene may be used, but is not limited thereto.

In this case, the thermoplastic resin may be used in the form of microparticles surface-modified by plasma treatment prior to melting and mixing with the nanoclay, but is not limited thereto.

For example, the first step may be achieved by compressing a nanocomposite in which a thermoplastic resin and 0.5wt% to 10wt% of nanoclay are melt-mixed at 170 to 210 ° C., but is not limited thereto, and the temperature is the thermoplastic used It can be determined by comprehensively considering the physical properties of the resin and/or the content of the nanoclay.

For example, the nanoclay may be plate-shaped nanoclay having an average diameter of tens to hundreds of nanometers, but is not limited thereto.

As used herein, the term "clay" refers to fine-grained soil containing at least one mineral containing a trace amount of metal oxide, classified by size and/or mineralogy. It can be. In general, clay may be present in a plate shape having a large surface area compared to thickness, and may be composed of a facet of silica and aluminum. As the clay of the present invention, natural clay, synthetic clay, or a mixture thereof may be used. Non-limiting examples of such clays include laponite (LN), montmorillonite (MMT), hectorite, saponite, beidellite and nontronite and cationic clays such as clay and anionic clays such as layered double hydroxide (LDH). The membrane of the present invention can be produced by using any one of these clays alone or by mixing two or more of them.

A second aspect of the present invention is obtained by biaxially stretching a nanocomposite sheet in which a thermoplastic resin and nanoclay are melt-mixed at 0.5 wt% to 10 wt%, with reduced oxygen compared to an unstretched sheet containing the same amount of nanoclay. A gas barrier membrane having permeability is provided.

For example, the gas barrier membrane of the present invention may exhibit increased tensile strength, Young's modulus, or both, compared to an unstretched sheet containing the same amount of nanoclay.

In a specific embodiment of the present invention, in the case of an unstretched sheet, even if the content of nanoclay increases, the tensile strength and/or Young's modulus do not increase and maintain a level similar to that of a pure thermoplastic resin sheet without nanoclay, but the sheet of the present invention showed increased tensile strength and/or Young's modulus, that is, improved mechanical properties, depending on elongation and/or the inclusion of nanoclay.

A third aspect of the present invention provides an electronic device having a gas barrier film obtained by biaxially stretching a nanocomposite sheet in which a thermoplastic resin and 0.5 wt % to 10 wt % nanoclay are melt-mixed as an oxygen barrier film.

Most electronic devices contain metals with high electron conductivity. However, these materials are sensitive to oxidation, ie reaction with oxygen. Therefore, it is preferable to coat with a film or the like capable of blocking oxygen. Non-limiting examples of electronic devices requiring such an oxygen barrier may include batteries, organic light emitting devices, display devices, photovoltaic devices, integrated circuits, pressure sensors, chemical sensors, biosensors, solar devices, and lighting devices. there is.

A fourth aspect of the present invention provides a packaging material including a gas barrier film obtained by biaxially stretching a nanocomposite sheet in which a thermoplastic resin and 0.5 wt % to 10 wt % nanoclay are melt-mixed as an oxygen barrier film.

Metallic substances, foods, nutrients, etc. can react with oxygen in the air and oxidize. Therefore, currently, in order to increase shelf life, a film on which aluminum or inorganic materials are deposited or a composite film on which a gas barrier resin is laminated is used, but the packaging material including these may become opaque, and the production cost increases. Thickness can be increased.

However, the sheet of the present invention not only exhibits significantly improved oxygen blocking ability, but also has excellent transparency and flexibility, and exhibits excellent blocking ability even with a thin thickness, so that the thickness can be reduced and easily applied using existing coating equipment. Since it can be produced, it is easy to manufacture and has the effect of reducing costs, so it can be usefully used as a packaging material. In addition, since only inorganic substances are included without organic substances such as binders, heat resistance is improved and oxygen blocking ability can be expected to be maintained even at high temperatures. At this time, the packaging material may be formed by additionally including a base layer, a printing layer, a sealing layer for water vapor barrier and / or heat sealing to maintain strength in the sheet of the present invention, or may be coated on an existing packaging material.

The manufacturing method of the present invention can provide a thermoplastic resin-based sheet having improved oxygen barrier properties by a simple method of adjusting the stretching order and/or magnification. Compared to the case of using materials, since it contains only inorganic materials, heat resistance can also be improved, so it can be widely used as an oxygen barrier film for electronic devices, etc., or packaging materials.

1 is a diagram schematically illustrating a method for manufacturing a biaxially stretched PP/nanoclay nanocomposite film according to an embodiment of the present invention.
Figure 2 is a diagram showing SEM images according to the stretching ratio of the 2.0 wt% nanoclay-containing PP / nanoclay nanocomposite according to an embodiment of the present invention. (a) to (d) show images at ×1.0, ×9.0, ×13.5, and ×18.0 magnification, respectively, and (e) is a schematic diagram of the overall shape evolution of the biaxially stretched PP/nanoclay nanocomposite.
Figure 3 is a diagram showing TEM images according to the stretching ratio of 2.0 wt% nanoclay-containing PP / nanoclay nanocomposite according to an embodiment of the present invention: (a), (a') × 1.0, (b), ( b') x 9.0, (c), (c') x 13.5, and (d), (d') x 18.0.
4 is a diagram showing the results of characterization between layers of nanoclay by (a) TEM and (b) XRD measurements in a PP/nanoclay nanocomposite according to an embodiment of the present invention. The number next to the plot in the graph indicates the amount of nanoclay contained in the PP/nanoclay nanocomposite.
5 is (a) thermogravimetric (TG) of an unstretched film (×1.0) and a stretched film (×18.0) of neat PP and PP/nanoclay nanocomposites according to an embodiment of the present invention. ) curve and (b) ( T _-10% and T _onset ) It is a diagram showing the difference in value.
6 is a diagram showing a stress-strain (ss) curve as a function of a stretching ratio of a PP/nanoclay nanocomposite according to an embodiment of the present invention. (a) and (b) show the results in MD and TD, respectively, and (c) and (d) show the results for pure PP and PP/nanoclay nanocomposites containing 3.4 wt% nanoclay, respectively.
7 is a diagram showing tensile strength and Young's modulus according to MD and TD of pure PP and PP/nanoclay nanocomposites according to an embodiment of the present invention. (a) and (c) are tensile strengths in MD and TD, respectively, and (b) and (d) are Young's moduli in MD and TD, respectively.
8 is a diagram showing oxygen permeability of pure PP and PP/nanoclay nanocomposites according to an embodiment of the present invention. (a) shows the oxygen permeability change according to the increase in the stretching ratio at 0% RH, and (b) shows the oxygen permeability change according to the increase in RH%.

Hereinafter, the configuration and effects of the present invention will be described in more detail through examples. These examples are only for illustrating the present invention, and the scope of the present invention is not limited by these examples.

<substance>

PP resin T3410 (melt index 7 g/10 min at 230° C., melting point 134.4±0.7° C., LG Chemical, South Korea) was used as a matrix material. The PP was produced into micro-sized particles by cryo-grinding. Nanoclay (Cloisite 20A) was purchased from BYK Additives and Instruments (USA) and used. For the nanoclay, the quaternary ammonium used as the organic modifier was dimethyl, dihydrogenated resin (tallow), with most of the doublets hydrogenated. The concentration of the modifier was 95 meq/100 g clay for clay.

Example 1: Preparation of Biaxially Stretched PP/Nanoclay Nanocomposite Film

The micro-sized PP was surface-modified by plasma treatment. Modification of micro-sized PP was performed using a radio frequency plasma generator (FEMTO Version E of 13.56 MHz, Diener electronic, Germany) with a 10-minute exposure time, N ₂ gas, and 50 W of It was performed under controlled conditions of plasma power. All PP/nanoclay nanocomposites were prepared using an internal mixer (W50 Plastograph, Brabender GmbH & Co KG, Germany) with a twin-screw at 80 rpm rotation speed at 190 °C. was made with The surface-modified micro-sized PP and nanoclay were first pre-mixed for 1 minute and then melt-mixed for 5 minutes in an airtight mixer.

The bulk-shaped nanocomposite sample was pulverized and dried at 105 ° C for 12 hours, and then the nanocomposite granules were compression molded at 190 ° C using a hot press system (QM900A, QMESYS, South Korea) compression-molded). After compression molding, the amount of nanoclay in the nanocomposite sheet was analyzed by a thermogravimetric analyzer (TGA, Q500, TA Instruments, USA). The PP / nanoclay nanocomposite sheet was biaxially oriented at a strain rate of 100 mm/s at 130 ° C using a biaxial stretcher (Biaxial Drawing Machine, Plus Ko-lab, South Korea), and the stretch ratio were 3.0×3.0 (×9.0), 3.0×4.5 (×13.5), and 3.0×6.0 (×18.0). Biaxial stretching was performed as sequential stretching, and the sheet was stretched to a target stretch ratio of ×3.0 in the transverse direction (TD) while constrained in the machine direction (MD). After a 1 second pause imposed by the machine, the sheet was stretched in MD to the target draw ratio while being restrained in TD. A method for preparing a stretched PP/nanoclay nanocomposite film is schematically shown in FIG. 1 .

Experimental Example 1: Morphological analysis

The low-magnification morphology of the PP/nanoclay nanocomposite was observed by field emission scanning microscopy (FE-SEM, SU8020, Hitachi, Japan). The film samples were cryo-microtomed through the thickness at -100 °C. Microtomed surfaces were obtained using a cryo-microtome (LEICA ULTRACUT UC7, Leica, Germany) equipped with a diamond knife. All samples were coated with Pt/Pd alloy using ion sputter (E-1045, Hitachi, Japan).

Furthermore, a transmission emission microscope (TEM, HT7700, Hitachi, Japan) was used to observe the PP/nanoclay nanocomposite at high magnification. A TEM sample of about 80 nm was prepared from the PP/nanoclay nanocomposite extracted from the film using a cryogenic microtome.

2 shows a SEM image of a cross section of a 2.0 wt% nanoclay-containing PP/nanoclay nanocomposite. As shown in FIG. 2, as the stretching ratio increased from ×1.0 to ×18.0, a change in the shape of the nanoclay was observed in the PP matrix.

As shown in FIG. 2a , although the nanoclay was dispersed in the PP matrix, nanoclay aggregation with a size of about 5 μm was partially observed. However, as the stretching ratio increased, the observed aggregation of the nanoclay gradually decreased. In Figs. 2c and 2d with a draw ratio of ×13.5 and ×18.0, this phenomenon appeared more clearly, and no aggregation of nanoclay was observed. This phenomenon can be attributed to the chain behavior of PP that occurs when the PP/nanoclay nanocomposite is stretched. As the randomly distributed PP chains were stretched, these chains were aligned along the direction of stretching. At this time, the nanoclay aggregate is subjected to shear stress by the PP chain, and the nanoclay aggregate is crushed or compressed. Another possibility is that a rupture mechanism may act on the aggregation of the nanoclay. Since the PP/nanoclay nanocomposite experiences a biaxial stretching process in a semi-molten state, it is assumed that the high-viscosity polymer applies shear stress to particle aggregation, causing rupture.

In order to observe the behavior of the nanoclay according to the increase in the stretching ratio, the TEM image of the PP/nanoclay nanocomposite containing 2.0 wt% nanoclay is shown in FIG. 3 . Comparing Figs. 3a and 3b, it was observed that when the draw ratio increased from ×1.0 to ×9.0, the agglomerated nanoclay was separated and better distributed within the PP matrix. It was confirmed that the plate-shaped nanoclay was exfoliated as the stretching ratio sequentially increased to ×13.5 and ×18.0. As previously confirmed from the SEM analysis, it was confirmed through TEM analysis that the nanoclay was uniformly distributed or dispersed in the PP matrix due to the shear stress caused by the PP matrix when the PP/nanoclay nanocomposite was stretched. In addition, since nanoclays completely exfoliated in the PP matrix were not observed in low-magnification SEM analysis, the amount of nanoclay shown in FIG. 2d was smaller than that in FIG. 2c.

Experimental Example 2: X-ray diffraction analysis

Nanoclay dispersion and structural analysis of the PP/nanoclay nanocomposites were performed by X-ray diffraction (XRD, D8 ADVANCE, BRUKER, USA) with CuK _α radiation (λ=0.154 nm). Diffraction spectra were acquired in the 2θ range of 1 to 10, and the interlayer distance ( d ₀₀₁ ) was calculated using Bragg's equation:

(1)

(One)

Here, λ is the wavelength, θ is the diffraction angle, and d is the interlayer distance between the nanoclays.

The interlayer distance of nanoclay calculated through the above equation is shown in FIG. 4 . Figure 4a shows the result of measuring the interlayer distance of intercalated (not exfoliated) nanoclay of the 2.0 wt% nanoclay-containing PP/nanoclay nanocomposite using TEM analysis. As shown in FIG. 4a, the interlayer distance value of the intercalated nanoclay decreased from 20.3 to 13.0 nm as the stretching ratio increased. As the stretching ratio increases, stronger shear stress is applied to the nanoclay in the PP matrix, so the decrease in this value is a result of the biaxial stretching process. At this time, the non-exfoliated nanoclay was compressed by an external force, and the interlayer distance rather decreased. 4b shows the interlayer distance value of nanoclay according to the nanoclay content of the PP/nanoclay nanocomposite. As shown in FIG. 4B, at a stretching ratio of × 1.0 without stretching, the spacing between nanoclay layers decreased as the nanoclay content in the PP matrix increased. As the nanoclay content increased, the nanoclay aggregation increased, and the interlayer distance value decreased because the PP chain was insufficient to effectively penetrate between the nanoclays. Comparing the interlayer distance of the 2.0 wt% nanoclay-containing PP/nanoclay nanocomposite in FIGS. 4a and 4b, there may be a slight difference in the value over the entire stretch ratio range. This difference is due to the fact that the nanoclay interlayer distance values obtained using XRD analysis include both intercalation and exfoliation cases. Fig. 4b is Fig. It showed a different trend from the result of Fig. 4a, and the d -spacing value of the nanoclay did not decrease continuously, but rather increased or maintained as the draw ratio increased from × 9.0 to × 18.0. From these results, it was confirmed that the amount of exfoliated nanoclay increased as the stretching ratio of the PP/nanoclay nanocomposite increased, and that the biaxial stretching process was effective in dispersing the nanoclay in the PP matrix.

Experimental Example 3: Thermal analysis

Thermal stability and nanoclay nanocomposites were evaluated by thermogravimetric analysis (Q500, TA Instruments, USA) at a heating rate of 10 °C/min from room temperature to 600 °C in N ₂ atmosphere. The residual amounts of clay were studied.

It is known that the addition of nanoclays to PP improves thermal stability due to a barrier effect that reduces volatiles or gases diffusion. TGA analysis was performed to compare the improvement in thermal stability according to the dispersion of nanoclay in the PP/nanoclay nanocomposite. Referring to FIG. 5a, it was confirmed that PP started pyrolysis at 388°C, whereas PP/nanoclay nanocomposites containing 3.4 wt% and 5.0 wt% nanoclay started pyrolysis at about 420°C.

In the case of the unstretched film, the TG curves were almost similar even though the amount of nanoclay was 1.6 wt% higher, indicating that the increase in nanoclay content did not contribute to the improvement in thermal stability. However, when stretching at a stretching ratio of ×18, different trends were observed, and when the content of nanoclay in the PP matrix was increased from 3.4 wt% to 5.0 wt%, these TG curves showed significant differences. Based on the TG curves, FIG. 5B shows the difference in decomposition temperatures ( T _-10% and T _{onse t} , respectively) of the stretched and unstretched films of the PP/nanoclay nanocomposites. The difference in decomposition temperature increased linearly as the nanoclay content increased, and the improvement in thermal stability was attributed to the nanoclay content. These results are another evidence for the improvement of nanoclay dispersion in PP matrix through biaxial stretching process.

Experimental Example 4: Mechanical analysis

Tensile testing was determined using a film sample using a universal testing machine (UTM, INSTRON 3367, INSTRON, USA). It was performed with a 30 kN cell force and a test speed of 10 mm/min. During the tensile test, the gauge length was fixed at 20 mm.

6 shows s-s curves of the PP/nanoclay composite containing PP and 3.4 wt% nanoclay according to the stretching ratio. As shown in FIGS. 6a and 6b, it was confirmed that the tensile strength and Young's modulus of both the PP and 3.4 wt% PP/nanoclay nanocomposites increased as the draw ratio increased. The tensile strength and Young's modulus of the PP/nanoclay nanocomposite containing 3.4 wt% nanoclay were improved compared to PP in MD and TD. At a stretching ratio of × 1.0 without stretching, the 3.4 wt% PP/nanoclay nanocomposite showed a slight increase in tensile strength compared to PP. However, as the stretching ratio increased, the difference in tensile strength and Young's modulus between PP and PP/nanoclay nanocomposites increased. At MD and stretch ratio × 18.0, the tensile strength and Young's modulus of PP were 184.3 MPa and 1.63 GPa, respectively, and the 3.4 wt% PP/nanoclay nanocomposite showed values of 210.1 MPa and 2.26 GPa, respectively. In the case of Young's modulus, as the draw ratio increased from ×1.0 to ×18.0, PP increased by about 116%, and the 3.4 wt% PP/nanoclay composite increased by about 190%.

The s-s curves in MD and TD showed different patterns, and the tensile strength and Young's modulus were relatively low in TD. As previously reported, in the case of sequential stretching, even if the stretching ratio is the same (3.0 × 3.0), the strength and stiffness are reported to be higher in the secondary stretching direction. It became. More interestingly, the behavior of the s-s curve changed when the stretch ratio increased from ×9.0 to ×18.0 in TD. Both PP and PP/nanoclay nanocomposites showed s-s curve behavior of elastomers or rubbery polymers at a stretch ratio of ×18.0. This phenomenon is a result of the influence of molecular orientation. This is because when the stretching ratio was further stretched in MD from ×9.0 (3.0 × 3.0) to ×18.0 (3.0 × 6.0), the stacked lamellar crystal structure was deformed in a more ductile manner. am.

7 shows the tensile strength and Young's modulus values of the PP/nanoclay nanocomposite with increasing nanoclay content. As shown in FIG. 7, in MD, when the content of nanoclay in the PP matrix increased, the tensile strength and Young's modulus showed a tendency to increase as the draw ratio increased. In the present invention, the highest mechanical property performance was shown when the nanoclay content in PP was 3.4 wt%. Up to 3.4 wt% of nanoclay, it acted as a reinforcing agent to improve mechanical properties, but when the content of nanoclay exceeded 5.0 wt%, aggregation of nanoclay inhibited tensile strength and Young's modulus.

As shown in FIG. 7c, for all PP/nanoclay nanocomposites including nanoclays except for PP, the tensile strength in TD tended to decrease when the stretch ratio increased from ×9.0 to ×18.0. This tendency was also observed in Young's modulus, and it did not significantly increase as in MD, but rather decreased or showed similar values in some cases. First, as mentioned above, these results indicate that ductility properties are realized due to a change in the crystal structure as the draw ratio increases from ×9.0 to ×18.0. The second possibility is due to the morphology of the nanoclay. In the SEM and TEM images of FIGS. 3 and 4 , it was observed that the nanoclays were arranged in the MD, which is believed to act as a defect upon stretching with TD.

Experimental Example 5: Oxygen permeability analysis

Oxygen transmission rate measurements of all sample films were recorded according to ASTM 3985 using an oxygen transmission rate analyzer (702, MOCON, USA). Permeation tests were performed under a 100% O ₂ atmosphere at 23° C. and 0% relative humidity.

8a shows the oxygen permeability results for the stretch ratio and nanoclay content of PP and PP/nanoclay nanocomposites. PP (×1.0) without biaxial stretching exhibited an oxygen permeability of 120.0 cc·mm/m ² ·day·atm. At this time, as the draw ratio increased, the oxygen permeability of PP decreased and the oxygen barrier property improved. At a draw ratio of ×18.0, PP exhibited a value of 75.4 cc·mm/m ² ·day·atm, which was reduced by about 37%. At ×1.0, the oxygen permeability decreased with increasing nanoclay content in PP, but this decreasing trend and regularity disappeared when reaching 3.4 wt%. This is the result of the nanoclay not being able to sufficiently form tortuous pathways due to aggregation in the PP matrix.

However, after the biaxial stretching process of the PP/nanoclay nanocomposite, the oxygen permeability tended to decrease as the nanoclay content increased. As a result of the stretching of the 6.4 wt% PP/nanoclay nanocomposite at a stretching ratio of ×18.0, the oxygen permeability value was 43.5 cc·mm/m ² ·day·atm, which was reduced by about 64% compared to that of PP. There are several factors that affect oxygen barrier properties such as molecular weight, crystallinity, molecular entanglement and internal structure of the polymer matrix. In this study, the oxygen barrier property was improved by reducing the free volume and chain entanglement in the polymer through biaxial stretching of the PP/nanoclay nanocomposite. Furthermore, as the biaxial stretching process affects the dispersion of the nanoclay, the formation of a tortuous path in the PP matrix acts as an effective factor for improving oxygen barrier properties. A synergistic effect was achieved by the combination of these complex factors, resulting in improved oxygen barrier properties.

Another important factor in oxygen barrier properties is the change in oxygen permeability with increasing relative humidity. This is because when the film is used as a packaging material, the oxygen barrier performance is deteriorated by the weather outside the packaging material or the humidity inside the packaging material, which may adversely affect the product. Therefore, the oxygen permeability of the sample was analyzed according to the increase in relative humidity (RH), and the results are shown in FIG. 8B. The 6.4 wt% PP/nanoclay nanocomposite with a stretch ratio of ×18.0, which showed the best oxygen barrier performance in the present invention, maintained its performance without significantly increasing oxygen permeability even under the extreme condition of 90% RH. PP is a hydrophobic polymer, and since the nanoclay is located inside rather than the surface of PP, it can be inferred as a result of PP's excellent water vapor barrier performance.

Experimental Example 6: Water contact angle analysis

The water contact angle was measured at 23°C and 30% relative humidity using a contact angle analyzer (SmartDrop, TEMTOFAB, South Korea). Measurements were performed by dropping 3 μL water droplets on the film surface at least 5 times.

The measured image is shown together in FIG. 8B. As shown in FIG. 8B, the water contact angles of PP and 6.4 wt% PP/nanoclay nanocomposites with a stretch ratio of × 18.0 were similarly measured to be 121° and 119°, respectively. This high water contact angle means that it has a hydrophobic surface, and this hydrophobic surface can suppress moisture adsorption to the film surface or diffusion into the inside of the film. Therefore, the sheet of the present invention did not significantly increase the oxygen permeability even under the extreme condition of 90% RH and maintained its performance, which supports the above opinion.

Experimental Example 7: Effect of stretching sequence and/or (a)symmetric stretching on oxygen permeability

In order to check the effect of the stretching sequence and/or (a)symmetric stretching during the biaxial stretching process, stretching is performed at the same magnification but simultaneously (simultaneous stretching) or in either MD or TD direction, followed by stretching in the other direction. The oxygen permeability of the stretched PP/nanoclay nanocomposite was measured and shown in Table 1 below. At this time, the content of nanoclay contained in the nanocomposite was 3.4 wt%.

stretch ratio Oxygen permeability (cc mm/m ² day atm) sequential stretching simultaneous stretching ×9.0 62.40±0.53 73.95±0.49 ×13.5 57.37±1.32 67.42±1.21 ×18.0 50.98±1.32 59.98±1.31

As shown in Table 1, when stretched at the same final magnification, compared to simultaneous stretching on both sides, the oxygen permeability was about 10% lower than when first stretched to one side at a certain magnification and then stretched to the other side. That is, it was confirmed that the nanocomposite prepared by sequential stretching exhibited better oxygen barrier properties than simultaneous stretching.

In addition, in order to confirm the effect of the stretching ratio in both directions, the final magnification is the same, but a series of specimens are prepared by stretching at different ratios or at the same ratio in both directions, and the oxygen permeability of them is measured to Table 2 shows. In order to achieve the indicated final stretching ratio, only symmetric stretching was performed at a ratio of 300 × 300 in each direction for × 9.0, and asymmetric and symmetric stretching ratios for × 13.5 were 300 × 450 and 367 × 367, respectively. , Asymmetric and symmetric stretching ratios of × 18.0 were achieved under conditions of 300 × 600 and 425 × 425, respectively. At this time, stretching in each direction was performed sequentially.

stretch ratio Oxygen permeability (cc mm/m ² day atm) asymmetric stretching symmetrical stretching ×9.0 NA 62.40±0.53 ×13.5 57.37±1.32 61.88±1.17 ×18.0 50.98±1.32 54.47±1.19

As shown in Table 2, it was confirmed that even if the final stretching ratio was the same, the asymmetrically stretched specimens stretched at different ratios in both directions exhibited lower oxygen permeability, that is, better oxygen barrier properties.

Furthermore, in order to more directly compare the effects of the combination of sequential asymmetric stretching and symmetric simultaneous stretching, a series of specimens were prepared by asymmetric sequential or symmetric simultaneous stretching at the magnifications shown in Table 3 below, and the oxygen permeability of each was measured. showed up

stretch ratio Oxygen permeability (cc mm/m ² day atm) asymmetric sequential stretching symmetrical simultaneous stretching ×9.0 62.40±0.53 73.95±0.49 ×13.5 57.37±1.32 71.36±1.31 ×18.0 50.98±1.32 67.55±1.30

As shown in Table 3, the asymmetric sequentially stretched specimens exhibited lower oxygen permeability, that is, better oxygen barrier properties, than the specimens symmetrically and simultaneously stretched at the same magnification, and the difference was 12 to 17% based on oxygen permeability. reached

By controlling the stretching order and/or magnification in both directions during biaxial stretching, even a nanocomposite containing the same amount of nanoclay and biaxially stretching at the same magnification can achieve better oxygen barrier properties than when produced by sequential asymmetric stretching. confirmed that there is

In the present invention, a PP/nanoclay nanocomposite was prepared while increasing the nanoclay content to 6.4 wt%, and the change in behavior of the nanoclay through biaxial stretching was evaluated. Through morphological analysis, it was confirmed that the dispersibility of the nanoclay aggregated inside the PP matrix was improved after the biaxial stretching process. In addition, partial exfoliation of the nanoclay could be observed through XRD and TEM analysis. Since the biaxial stretching process has a positive effect on the dispersion of the nanoclay within the PP matrix, the biaxially stretched PP/nanoclay nanocomposite has thermal and mechanical properties compared to conventional un-stretched PP/nanoclay nanocomposites. And it was confirmed that it exhibited excellent properties in oxygen barrier properties. Since the present invention has the advantage of being able to exhibit these effects only through a change in the process method without chemical treatment requiring toxic reagents or excessive solvents, the biaxially stretched PP / nanoclay nanocomposite is an eco-friendly packaging material. It has excellent potential for use as a material). Furthermore, the present invention provides one approach for dispersing additives, including platelets, into polymers.

From the above description, those skilled in the art to which the present invention pertains will be able to understand that the present invention may be embodied in other specific forms without changing its technical spirit or essential features. In this regard, the embodiments described above should be understood as illustrative in all respects and not limiting. The scope of the present invention should be construed as including all changes or modifications derived from the meaning and scope of the claims to be described later and equivalent concepts rather than the detailed description above are included in the scope of the present invention.

Claims (10)

A first step of preparing a nanocomposite sheet in which a thermoplastic resin and 0.5wt% to 10wt% nanoclay are melt-mixed; and
A second step of biaxially stretching the nanocomposite sheet,
The thermoplastic resin is made of at least one of polypropylene (PP), polyethylene terephthalate (PET), or polyethylene (PE),
The biaxial stretching is performed at different magnifications in the machine direction (MD) and the transverse direction (TD) of the sheet,
The method of manufacturing a gas barrier film having reduced oxygen permeability compared to a non-stretched sheet, wherein the biaxial stretching is first stretched in one direction of the machine direction and the transverse direction and then sequentially stretched in the other direction.
delete delete According to claim 1,
The thermoplastic resin is used in the form of surface-modified microparticles by plasma treatment, manufacturing method.
According to claim 1,
The first step is achieved by compression molding a nanocomposite in which a thermoplastic resin and 0.5wt% to 10wt% of nanoclay are melt-mixed at 170 to 210 ° C., a manufacturing method.
According to claim 1,
The nanoclay is a plate-shaped nanoclay, manufacturing method.
It is obtained by biaxially stretching a nanocomposite sheet in which a thermoplastic resin and 0.5 wt% to 10 wt% nanoclay are melt-mixed,
The thermoplastic resin is made of at least one of polypropylene (PP), polyethylene terephthalate (PET), or polyethylene (PE),
The biaxial stretching is performed at different magnifications in the machine direction (MD) and the transverse direction (TD) of the sheet,
The gas barrier film having reduced oxygen permeability compared to an unstretched sheet, in which the biaxial stretching is first stretched in one direction of the machine direction and the transverse direction and then sequentially stretched in the other direction.
According to claim 7,
A gas barrier film that exhibits increased tensile strength, Young's modulus, and both, compared to an unstretched sheet containing the same amount of nanoclay.
It is obtained by biaxially stretching a nanocomposite sheet in which a thermoplastic resin and 0.5 wt% to 10 wt% nanoclay are melt-mixed as an oxygen barrier film,
The thermoplastic resin is made of at least one of polypropylene (PP), polyethylene terephthalate (PET), or polyethylene (PE),
The biaxial stretching is performed at different magnifications in the machine direction (MD) and the transverse direction (TD) of the sheet,
The biaxial stretching is an electronic device having a gas barrier film in which stretching is performed first in one direction of the machine direction and the transverse direction and then sequentially stretched in the other direction.
It is obtained by biaxially stretching a nanocomposite sheet in which a thermoplastic resin and 0.5 wt% to 10 wt% nanoclay are melt-mixed as an oxygen barrier film,
The thermoplastic resin is made of at least one of polypropylene (PP), polyethylene terephthalate (PET), or polyethylene (PE),
The biaxial stretching is performed at different magnifications in the machine direction (MD) and the transverse direction (TD) of the sheet,
The biaxial stretching is a packaging material including a gas barrier film in which stretching is performed first in one direction of the machine direction and the transverse direction and then sequentially stretched in the other direction.

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