Stretch hood film containing recycled polyethylene and having surface protrusion structure, and manufacturing method therefor

Abstract

The present invention relates to a stretch hood film having surface protrusions and, more particularly, to a stretch hood film, which has protrusions formed on the surface thereof so that defects caused by surface abrasion can be reduced and durability can be improved, has excellent processability since a predetermined level of post-consumer recycled (PCR) resin is applied to a polyethylene film, and has physical properties equivalent to those of a virgin resin film.

Description

Stretch hood film containing recycled polyethylene and having a surface protrusion structure and method for manufacturing the same

[0001] The present invention relates to the field of packaging film technology, and in particular to a stretch hood packaging film for protecting and securing articles loaded on a pallet.

[0002] More specifically, the invention relates to a recycled polyethylene-containing stretch hood film and a method for manufacturing the same, which includes a post-consumer recycled resin (PCR), prevents deterioration of physical properties due to its incorporation, and improves wear resistance, anti-slip properties, and durability by functionally utilizing a micro-protrusion structure formed on the film surface.

[0003]

[0004] Typically, goods loaded on pallets pose a risk of worker injury or product damage due to shaking or falling during transportation. To prevent these risks and ensure safety during transport, palletized loads are generally wrapped in plastic wrap or tubular stretch hood film. Since stretch hood film must possess sufficient mechanical strength and elongation properties to withstand a certain load while maintaining the shape of the package, multilayer films based primarily on low-density polyethylene (LDPE) have traditionally been used. However, due to recent stricter environmental regulations, there is a growing demand for packaging materials to contain a certain percentage of recycled materials, particularly post-consumer recycled resin (PCR). This regulation is clearly reflected in the EU's Packaging Recycling Regulation (PPWR), which mandates the inclusion of recycled materials in packaging films. However, applying high proportions of recycled LDPE or LLDPE frequently results in problems such as reduced optical transparency, increased gel formation, and decreased tensile strength and elongation. Furthermore, recycled materials are prone to retaining trace amounts of volatile low-molecular-weight components. During the extrusion and cooling processes, these components migrate to the surface, forming non-uniform structures such as micro-protrusions or pinholes. Conventional technologies have regarded this phenomenon as a mere defect, approaching it solely by adjusting processing conditions or using additives to eliminate it. However, through various experiments, the inventors confirmed that the regular and uniform micro-protrusion structures formed under specific compositions and cooling conditions actually contribute to the improvement of film functionality. Specifically, they discovered that these protrusion structures provide a friction-reducing effect during packaging and handling, and enhance packaging stability by mitigating film adhesion to improve anti-slip and abrasion resistance.Therefore, the technical objective of the present invention is to improve the practical performance of a stretch hood film for packaging by maintaining the physical performance and appearance quality of the film while containing recycled LDPE or LLDPE in a certain proportion or more, and at the same time functionally utilizing the surface protrusion structure that is naturally formed when recycled materials are applied.

[0005]

[0006] The present invention aims to provide a stretch hood film that solves the problem of physical property degradation caused by the application of recycled polyethylene resin and ensures mechanical and optical properties equivalent to those of virgin resin films while complying with environmental regulations (such as EU PPWR). Due to the presence of impurities and low-molecular-weight components, recycled resin exhibits unstable thermal behavior and is prone to problems such as gel formation, surface non-uniformity, and reduced interlayer adhesion during the extrusion process.

[0007] The present invention aims to implement a thermally balanced structure that can improve processing stability and interlayer adhesion by controlling the resin composition and thermal properties of each layer, thereby maintaining the difference between the melting point (Tm) and crystallization temperature (Tc) between the outer layer and the inner layer within a specific range, and thereby suppressing non-uniformity of crystallinity of the film even when recycled resin is incorporated.

[0008] According to the present invention, even when recycled low-density polyethylene (PCR-LDPE) and recycled linear low-density polyethylene (PCR-LLDPE) are applied in high proportions, mechanical properties such as tensile strength and elongation of the film can be maintained at a level substantially equivalent to that of a film using virgin resin.

[0009] This is the result of effectively suppressing the reduction in crystallinity, uneven interlayer shrinkage, and gel formation caused by the incorporation of recycled resin by optimizing the composition ratio and thermal properties (melting point Tm, crystallization temperature Tc) of each layer.

[0010] In addition, the present invention improves interlayer adhesion and the thermal stability of the film by controlling the thermal behavior of the outer layer to maintain the melting point at approximately 120 to 121°C and the crystallization temperature at approximately 106 to 107°C, and the melting point of the inner layer at approximately 100°C and the crystallization temperature at approximately 83°C. Through such control of thermal characteristics, crystallinity is maintained uniformly even when recycled LDPE / LLDPE is incorporated, and non-uniformity of the film surface, gel formation, or delamination is minimized during processing.

[0011] Furthermore, the present invention functionally utilizes a fine protrusion structure naturally formed on the surface of the outer layer to reduce friction between films during packaging and handling processes, and has the effect of improving anti-slip and wear resistance.

[0012] As a result, defects such as scratches or surface wear that may occur during packaging are significantly reduced, and the appearance quality and durability of the film are simultaneously improved.

[0013] As a result, the stretch hood film according to the present invention can secure excellent processability, stable mechanical properties, and uniform optical properties even when containing a certain proportion (about 30 to 50 weight%) of post-consumer recycled resin (PCR).

[0014] Therefore, the present invention provides the effect of offering a high-quality, high-durability, eco-friendly stretch hood film while satisfying international environmental regulatory requirements such as the EU Packaging Recycling Regulation (PPWR).

[0015]

[0016] FIG. 1 is a graph comparing strength according to the content of recycled raw materials (LDPE / LLDPE mixing ratios of 30 / 70 and 10 / 90) according to the present invention.

[0017] FIG. 2 is a cross-sectional view of a three-layer stretch hood film according to the present invention.

[0018] FIG. 3 is a cross-sectional view of a 5-layer stretch hood film according to the present invention.

[0019] Figure 4 is the temperature profile of the new LLDPE.

[0020] Figure 5 is the temperature profile of recycled LDPE / LLDPE.

[0021] FIG. 6 is an SEM magnified image of a protrusion formed on the outer layer of a stretch hood film according to the present invention.

[0022] Figure 7 shows the pyrolysis profiles of a new LDPE film and a recycled (PCR) LPDE film.

[0023] Figure 8 is a graph of the component analysis of protrusions formed on a new LDPE film and a recycled (PCR) LPDE film.

[0024] Figure 9 is a graph comparing the melting points (Tm) of a total of four types, including a new LLDPE film, a recycled (PCR) LLPDE film, and films having protrusions formed thereon.

[0025] Figure 10 is a graph comparing the crystallization temperature (Tc) for a total of four types, including a new LLDPE film, a recycled (PCR) LLPDE film, and films having protrusions formed thereon.

[0026] FIG. 11 is a surface protrusion shape image measured with a laser confocal microscope of an embodiment according to the present invention and a microscope image of a comparative example.

[0027]

[0028] In the present invention, the thermal behavior of the applied raw materials and mixed resins was precisely controlled to prevent the deterioration of physical properties of a film containing recycled resin and to secure mechanical and optical properties comparable to those of a virgin film. That is, by controlling the melting point (Tm) and crystallization temperature (Tc) of the resin used for each layer to be within a specific temperature range, crystallinity non-uniformity or gel formation caused by the incorporation of recycled resin was suppressed.

[0029] In particular, the resin used in the outer layer was set to have a melting point of about 120 to 121°C and a crystallization temperature of about 106 to 107°C, and the resin used in the inner layer was set to have a melting point of about 100°C and a crystallization temperature of about 83°C.

[0030] Through this combination of thermal properties, excellent adhesion and a uniform film structure can be secured while minimizing the difference in thermal shrinkage between each layer, and as a result, strength, elongation, and transparency comparable to those of a new film can be maintained even in multilayer films containing recycled LDPE and recycled LLDPE.

[0031] Hereinafter, the present invention will be described in detail with reference to the drawings.

[0032] As shown in Fig. 1, it can be seen that the strength and elongation of the film were best when the mixed recycled resin was 40 to 50 wt% and the mixing ratio of recycled LDPE and recycled LLDPE was 10 / 90 or 30 / 70.

[0033] In this specification, the term “mixed recycled resin” means a resin composed of recycled low-density polyethylene (PCR-LDPE) recovered after consumer use and recycled linear low-density polyethylene (PCR-LLDPE) blended in a certain ratio.

[0034] In other words, it can be seen that in the present invention, even when a recycled mixed resin comprising recycled LDPE and recycled LLDPE is applied as a raw material for a film, excellent mechanical properties can be maintained compared to new LLDPE.

[0035] Figure 2 illustrates the cross-sectional structure of a stretch hood film according to one embodiment of the present invention.

[0036] As illustrated in FIG. 2, the stretch hood film according to the present invention has a multilayer structure consisting of an inner layer (10) and outer layers (20) respectively placed above and below it.

[0037] If necessary, an adhesive layer or an intermediate layer may be further included between each layer, and the total thickness is preferably around 80 μm.

[0038] The inner layer (10) is a layer that primarily provides the mechanical strength and resilience of the film and is composed of linear low-density polyethylene (LLDPE) or polyolefin elastomer (POE).

[0039] The above polyolefin elastomer (POE) is an elastomer obtained by copolymerizing ethylene with α-olefins such as octene and butene, and exhibits superior elastic recovery and shock absorption compared to LLDPE.

[0040] Accordingly, the inner layer (10) prevents the film from bursting in response to deformation, impact, tensile load, etc. that may occur during packaging, and provides stretch performance that is stably restored even after stretching.

[0041] The outer layer (20) is a layer that is laminated above and below the inner layer (10) to control the surface properties, wear resistance, and optical quality of the film, and may include low-density polyethylene (LDPE) or linear low-density polyethylene (LLDPE), and may further include a mixed recycled resin in which recycled LDPE and recycled LLDPE are mixed.

[0042] As used in this specification, “LDPE (low-density polyethylene)” is used as a concept including linear low-density polyethylene (LLDPE) as understood by a person skilled in the art, and this should be interpreted to encompass all low-density polyethylene resins with similar material properties.

[0043] The polyethylene resin used in the present invention is composed of polyethylene (PE) series olefinic polymers (linear or branched copolymers) that do not contain heterogeneous elastomers such as PP (polypropylene) and EVA (ethylene-vinyl acetate copolymer) in order to maximize recycling efficiency within a closed-loop recycling system.

[0044] This is intended to prevent problems caused by crystalline particles (gels) of PP or incompatible components of EVA, which can act as foreign substances in the recycling process and lead to thickness non-uniformity and surface defects within the film.

[0045] In addition, it is desirable that the polyethylene resin satisfies a tensile strength of about 30 to 50 MPa and an elongation of about 700 to 900% in terms of tensile strength and elongation.

[0046] This range of physical properties ensures the film's elongation and recovery characteristics, while simultaneously enabling the maintenance of mechanical stability at the level of conventional new films, even when containing recycled materials.

[0047] Accordingly, the composition according to the present invention provides an optimal combination capable of simultaneously achieving mechanical performance, surface uniformity, and recyclability of the film.

[0048] The outer layer (20) according to the present invention may include a mixed recycled resin in which recycled LDPE and recycled LLDPE are mixed, and the mixing ratio of the recycled LDPE and recycled LLDPE is preferably in the range of 10:90 to 30:70.

[0049] Within the above mixing ratio range, even if the recycled resin content increases, key physical properties such as tensile strength, elongation, and transparency of the film can be maintained at a level similar to that of a virgin film.

[0050] The outer layer (20) has excellent processability even when containing mixed recycled resin, and has excellent adhesion and interfacial stability with the inner layer (10), making it suitable for a multilayer co-extrusion process.

[0051] Since the above mixed recycled resin contains a relatively large amount of low-molecular-weight hydrocarbon components compared to the new material, some volatile components may be finely vaporized during the cooling process during the extrusion process, and fine protrusions (30) may be naturally formed on the surface of the outer layer (20).

[0052] The above protrusions (30) reduce friction between films and provide anti-slip, improved wear resistance, and reduced surface damage during the packaging process.

[0053] FIG. 3 shows a cross-sectional view of a five-layer stretch hood film according to another embodiment of the present invention.

[0054] As illustrated in FIG. 3, the stretch hood film according to the present invention is composed of an inner layer (10), an outer layer (20) positioned above and below the inner layer, and a protective layer (40) additionally formed on the outer side of each outer layer.

[0055] The above protective layer (40) is located on the outermost surface of the film and performs the function of protecting the inner and outer layers from friction with the load, external impact, contamination, and exposure to ultraviolet rays.

[0056] With the addition of the protective layer (40), the degree to which the protrusion structure (30) formed on the outer layer (20) comes into direct contact with the outside is reduced, so scratches, wear, and contamination on the film surface can be suppressed more effectively.

[0057] The 5-layer stretch hood film configured in this way exhibits improved performance in terms of surface durability, printability, and barrier properties compared to a 3-layer structure, while simultaneously maintaining the tensile and recovery characteristics of the inner layer (10) and the effect of applying recycled resin to the outer layer (20).

[0058] Figures 4 and 5 are graphs showing the raw material temperature profile and thermal behavior characteristics of the stretch hood film according to the present invention.

[0059] To solve problems such as reduced crystallinity, gel formation, and optical non-uniformity that may occur when applying mixed recycled resin, the thermal behavior of the resin in each layer (melting point Tm and crystallization temperature Tc) was precisely controlled.

[0060] The resin applied to the outer layer (20) is designed to have a melting point in the range of 118 to 123°C and a crystallization temperature in the range of about 104 to 108°C, and the resin used in the inner layer (10) is designed to maintain a melting point in the range of about 100°C and a crystallization temperature in the range of about 83°C.

[0061] This temperature combination ensures that each layer melts stably individually during the multilayer extrusion process, while preventing shrinkage, delamination, or crystal non-uniformity caused by temperature differences between layers.

[0062] The above thermal control is implemented through fine temperature control for each cylinder and die section of the co-extrusion device, and is set to maintain a balance in the melt viscosity and crystallization rate of each resin.

[0063] By adjusting the difference between Tm and Tc according to the material of each layer and stabilizing the thermal behavior in the extrusion process, the crystallinity, tensile strength, elongation, and transparency of the entire film are maintained at a level similar to that of a new film, even when mixed recycled resin is included in a high proportion (30 to 50 wt%).

[0064] In addition, the optimization of the thermal profile maintains a uniform adhesive interface between the inner layer (10) and the outer layer (20), thereby enabling the realization of a stable multilayer structure without interlayer delamination or deformation.

[0065] In this way, by precisely adjusting the difference between the melting point (Tm) and the crystallization temperature (Tc) according to the material of each layer and stabilizing the thermal behavior during the extrusion process, the crystallinity of the entire film can be maintained uniformly even when the mixed recycled resin is included in a high proportion (about 30 to 50 weight%).

[0066] Therefore, the stretch hood film according to the present invention can simultaneously ensure processing stability and product quality while applying a high proportion of mixed recycled resin, and is realized as a high-performance packaging material that satisfies both mechanical performance and appearance quality.

[0067] The combination of such thermal behavior control and extrusion temperature profiles provides a key technical basis that enables the film of the present invention to maintain novel material-level physical properties while meeting environmental regulatory requirements (such as EU PPWR).

[0068] FIG. 6 is an SEM magnified image of a protrusion (30) formed on an outer layer (20) of a stretch hood film according to the present invention, wherein the protrusion (30) may be 3 to 50 μm in diameter and 100 to 600 μm in diameter. The protrusion (30) is formed because the hydrocarbon vaporized during the extrusion process (100 to 350°C) of film manufacturing is not ejected by the outer layer (20), thus having the advantage that there is no need to add a separate process for forming the protrusion.

[0069] The inside of the protrusion (30) is air, moisture, C 6-10 It is composed of hydrocarbon molecules and may additionally contain less than 1% inorganic matter (Si, Al, metals on the surface, etc.). This can be seen from the fact that trace amounts of inorganic matter may be generated in the PCR film compared to the novel film as shown in Fig. 7, and that the carbon content increased in the PCR film compared to the novel film as shown in Fig. 8.

[0070] The protrusion (30) according to the present invention does not contain any additives such as a separate foaming agent or blocking agent. The protrusion has the advantage of protecting the fabric from friction and wear that occur during the film fabric handling and packaging process.

[0071] Figure 9 is a graph comparing the melting points (Tm) of a total of four types, including virgin LPDE films, recycled (PCR) LPDE films, and films with protrusions formed on each of them. As shown in Table 1 below, the melting points of the virgin film and the film with protrusion defects (impurities) on the virgin film are similar at approximately 118°C, and the melting points of the PCR film and the PCR film with protrusion defects formed on the surface of the PCR film are also similar at approximately 120°C, indicating that the physical properties of the PCR film are not significantly inferior to those of the virgin film.

[0072] Inner layer (POE) melting point, Tm(°C) Outer layer_LLDPE (Virgin&PCR) melting point, Tm(°C)#1_Virgin_OK101.15118.48#2_Virgin_OK_Impurity100.97118.08#3_PCR_NG100.56120.42#4_PCR_NG_Impurity100.54120.23

[0073] Figure 10 is a graph comparing the crystallization temperatures (Tc) of a total of four types, including virgin LPDE films, recycled (PCR) LPDE films, and films with protrusions formed thereon. As shown in Table 2 below, the crystallization temperatures (Tc) of the virgin film and the film with protrusion defects (Impurity) on the virgin film were analyzed to be at the level of 105–106°C, while the crystallization temperatures of the PCR film and the PCR film with surface protrusion defects formed were analyzed to be at the level of 109°C. In particular, for the PCR film, another crystallization temperature peak was observed around 101°C.

[0074] Inner layer (POE) crystallization temperature, Tc(°C) LLDPE (Virgin & PCR) crystallization temperature, Tc(°C) LDPE PCR only crystallization temperature, Tc(°C) #1_Virgin_OK89.49105.01-#2_Virgin_OK_Impurity89.86106.13-#3_PCR_NG89.19109.16100.96#4_PCR_NG_Impurity89.49109.30100.87

[0075] Ultimately, as shown in FIGS. 9 and 10, the melting point (Tm) of the PCR film has a 1 peak, and the extrusion temperature can be introduced under conditions equivalent to those of the new material. The crystallization temperature (Tc) of the PCR film has a 2 peak, and LLDPE, which has better crystallinity than LDPE, showed a sharper peak at a higher temperature (~110℃). In the PCR 35% sample, the Tc range and shape are equivalent regardless of the presence of protruding foreign matter, which is a characteristic attributed to the LGC recycled pellet characteristics, and it is determined that this is not affected by recycling or extrusion degradation. The thickness of the inner layer (10) is preferably 40 to 60% of the total thickness, and the upper and lower outer layers (20) are each preferably 20 to 30% of the total thickness. This allows for the maintenance of tensile strength and elongation properties by maintaining the thickness of the inner layer (10) relatively thick. If necessary, the thickness of the inner layer (10) can be designed to be 60 to 80% of the total thickness, thereby compensating for the decrease in tensile strength caused by the application of PCR to the outer layer (20).

[0076]

[0077] [Preparation Example I] Outer layer: LDPE, Inner layer: LLDPE

[0078] Extrusion conditions: 90~150℃ (100~130), 1~30kg / cm² 2 A three-layer stretch hood film according to Table 3 below was manufactured by blown extrusion under conditions (1–10). (Outer layer thickness: 28% of total thickness, inner layer thickness: 44% of total thickness)

[0079] Stretch Hood Film Interlayer Composition (Weight%) Upper / Lower Outer Layer Inner Layer Comparative Example 1: LDPE 44.0% LLDPE 56.0% Preparation Example 1: LDPE 17.6% PCR-LDPE 26.4% LLDPE 56.0% Preparation Example 2: LDPE 11.2% PCR-LDPE 44.8% LLDPE 44.0%

[0080] [Experimental Evaluation]

[0081] 1. Measurement of surface roughness of stretch hood film

[0082] The surface roughness of the stretch hood films according to Manufacturing Examples 1 and 2 and Comparative Example 1 prepared above was measured, and the results shown in Table 4 below were obtained.

[0083] Stretch hood film surface roughness average protrusion height protrusion peak height abrasion evaluation * Protrusion Inclination Comparison Example 13.2 16.6 0.5 1.8 Manufacturing Example 19.6 37.2 0.9 1.7 Manufacturing Example 211.9 41.4 0.9 1.6

[0084] * Wear measurement: 1 mm using a laser confocal microscope 2 As can be seen in Table 4 and Figure 9, the surface of the sample in the region was measured five or more times, and it was confirmed that the protrusions of Preparation Examples 1 and 2 according to the present invention were larger and occurred more frequently than those of Comparative Example 1. In addition, the wear evaluation was also relatively superior in Preparation Examples 1 and 2 compared to Comparative Example 1.

[0085] Figures 4 and 5 are graphs showing the thermal characteristics (melting point Tm and crystallization temperature Tc) of each raw material used in the present invention. As shown in Table 5 below, the Tm and Tc of the virgin material and recycled resin used in the outer layer and inner layer are as follows.

[0086] Classification Melting Point Crystallization Temperature Tm (°C Tc (°C) 1-1. LGC_Outer Layer_New LLDPE121.13107.311-2. DOW_AT1601_Inner Layer_POE100.6783.191-3. LGC_LC180_Inner Layer_POE72.13702-1. Greenpol_PCR LLDPE_Yellow119.37106.32-2. Greenpol_PCR LLDPE_White121.36108.173. Dicarbon_PCR LLDPE120.62108.31

[0087] As confirmed in Table 5 above, the thermal behavior of the new LLDPE (Tm: 121.13℃, Tc: 107.31℃) and recycled LLDPE (Tm: 119 to 121℃, Tc: 106 to 108℃) used in the outer layer is close to each other, so even if the outer layer contains 40 to 50 weight% of recycled resin, there is almost no difference in melt viscosity or variation in crystallization. Accordingly, gel formation or non-uniform interlayer shrinkage caused by the incorporation of recycled resin is suppressed, ensuring interfacial stability between the outer layer and the protective layer, and maintaining the mechanical strength and elongation of the entire film.

[0088] On the other hand, the polyolefin elastomer (POE) used in the inner layer has a low Tm of about 100°C (DOW AT1601) to 72°C (LGC LC180), which prevents interfacial interference during extrusion and improves the film's stretch recovery and shock absorption by ensuring a temperature difference of about 20°C or more compared to the outer layer.

[0089] Therefore, in the present invention, the thermal behavior of the resin applied to each layer acts complementarily through the difference between Tm and Tc, thereby enabling the securing of physical properties equivalent to those of a new film even when including recycled LDPE / LLDPE resin.

[0090] To verify the effects of the present invention, stretch hood films were manufactured by varying the composition ratio of the outer layer and the content of the mixed recycled resin while maintaining a constant thickness of the inner layer as shown in Table 6 below.

[0091]

[0092] [Preparation Example II] Outer layer: LLDPE + recycled LDPE / LLDPE, Inner layer composition: POEE

[0093] Extrusion conditions: 90~150℃ (100~130), 1~30kg / cm² 2 A three-layer stretch hood film according to Table 6 below was manufactured by blown extrusion under conditions (1–10). (Outer layer thickness: 28% of total thickness, inner layer thickness: 44% of total thickness)

[0094] Stretch Hood Film Interlayer Composition Recycled Resin Mixture Quality Comparison Outer Layer Inner Layer LDPE / LLDPE Productivity Strength Optics (Gel) Comparison Example 2 LLDPE 60.0% Recycled LDPE / LLDPE 0% Elastomer POE 40.0% -◎◎◎ Comparison Example 3 LLDPE 40.0% Recycled LDPE / LLDPE 0% Elastomer POE 60.0% -◎◎◎ Manufacturing Example 3 LLDPE 20% Recycled LDPE / LLDPE 20% Elastomer POE 60.0% 10 / 90○◎○ Manufacturing Example 4 LLDPE 20% Recycled LDPE / LLDPE 20% Elastomer POE 60.0% 30 / 70○◎○ Manufacturing Example 5 LLDPE 30% Recycled LDPE / LLDPE 30% Elastomer POE 40.0% 10 / 90 ○◎○ Manufacturing Example 6 LLDPE 30% Recycled LDPE / LLDPE 30% Elastomer POE 40.0% 30 / 70 ○◎○ Manufacturing Example 7 LLDPE 20% Recycled LDPE / LLDPE 40% Elastomer POE 40.0% 10 / 90 ○◎△ Manufacturing Example 8 LLDPE 20% Recycled LDPE / LLDPE 40% Elastomer POE 40.0% 30 / 70 ○◎△ Manufacturing Example 9 LLDPE 10% Recycled LDPE / LLDPE 50% Elastomer POE 40.0% 30 / 70 ○○△

[0095] Comparative Examples 2 and 3 are films that do not contain recycled resin, and were each manufactured with an outer layer composed of 60 wt% LLDPE / 40 wt% and an inner layer composed of 40 wt% POE / 60 wt% POE. Although they exhibited excellent transparency and appearance quality, they had limitations in terms of compliance with environmental regulations due to the 0% ratio of recycled materials. On the other hand, Preparation Examples 3 to 9 introduced a mixed recycled resin in the outer layer in the range of 20 to 50 wt%, and evaluated the changes in physical properties according to each composition by varying the mixing ratio of recycled LDPE to LLDPE to 10:90 or 30:70. The inner layer was configured to include the elastomer POE in the same way, either 40 or 60 wt%, to maintain the film's elongation and resilience.

[0096] As a result of the thermal property analysis, the melting point (Tm) of the mixed recycled resin used in the outer layer was approximately 120°C and the crystallization temperature (Tc) was approximately 106°C, while the POE in the inner layer was measured to have a Tm of approximately 100°C and a Tc of approximately 83°C. As a result, the difference in thermal behavior between each layer was maintained at approximately 20°C or more, minimizing interlayer crystallization interference during the extrusion and cooling processes and suppressing gel formation.

[0097] As a result, in Examples 3 to 6 (recycled resin content 20 to 30 wt%), the tensile strength (about 30 to 50 MPa) and elongation (about 700 to 900%) were maintained at a level equivalent to that of virgin film, and the surface uniformity and abrasion resistance were also excellent. In addition, due to the thermal stabilization of the outer layer, a fine surface protrusion structure was naturally formed during the cooling process, thereby improving anti-slip performance during packaging and handling processes.

[0098] On the other hand, when the mixed recycled resin content exceeded 40% by weight as in Manufacturing Examples 7 to 9, a tendency for the film's elongation to decrease slightly was observed, but mechanical strength and durability at a level applicable as a practical packaging film were maintained.

[0099] From the above results, it was confirmed that the composition and temperature profile design of the present invention can secure physical properties equivalent to those of a virgin resin-based film even when the content of the mixed recycled resin in the outer layer is in the range of 30 to 50 weight%, and in particular, thermal stability and processability are maximized when the mixing ratio of recycled LDPE to recycled LLDPE of the mixed recycled resin is maintained at 10:90 or 30:70. Accordingly, it was proven that the stretch hood film of the present invention can be applied as a high-quality packaging material while meeting recycling content regulations such as EU PPWR.

Claims

1. A multilayer stretch hood film comprising an inner layer and upper and lower outer layers, The above inner layer comprises linear low-density polyethylene (LLDPE) or polyolefin elastomer (POE), and The above outer layer comprises low-density polyethylene (LDPE) or linear low-density polyethylene (LLDPE), and additionally further comprises recycled LDPE or recycled LLDPE, A stretch hood film characterized by having a micro-protrusion structure formed by volatile hydrocarbons during the extrusion process on the surface of the outer layer.

2. In Paragraph 1, The above outer layer is composed of new LLDPE and mixed recycled resin, and The above mixed recycled resin consists of recycled LDPE and recycled LLDPE, and A stretch hood film characterized by the weight ratio of the recycled LDPE and recycled LLDPE being 10:90 to 30:

70.

3. In Paragraph 2, The melting point (Tm) of the above mixed recycled resin is 118 to 123°C, and the crystallization temperature (Tc) is 104 to 108°C, and The melting point (Tm) of the above novel LLDPE is 116 to 122°C, and the crystallization temperature (Tc) is 105 to 109°C, and A stretch hood film characterized in that the polyolefin elastomer (POE) of the inner layer has a melting point (Tm) of 98 to 102°C and a crystallization temperature (Tc) of 82 to 85°C.

4. In Paragraph 2, A stretch hood film characterized in that the above-mentioned mixed recycled resin is 20 to 50 weight percent based on the total film weight.

5. In Paragraph 1, A stretch hood film characterized in that the thickness ratio of the inner layer and the outer layer is such that the outer layer accounts for 40 to 80% and the inner layer accounts for 60 to 20% based on the total film thickness.

6. In Paragraph 4, The above stretch hood film is characterized by having mechanical properties of a tensile strength of 30 to 50 MPa and an elongation of 700 to 900%.

7. In Paragraph 1, A stretch hood film characterized by the above-mentioned protrusions having a height of 3 to 50 μm and a diameter of 100 to 600 μm.

8. A method for manufacturing a stretch hood film according to any one of claims 1 to 7, The inner layer and the outer layer are each formed by a blown extrusion method, wherein the extrusion temperature is in the range of 100 to 350℃, and The above mixed recycled resin has a melting point (Tm) of 118 to 123°C and a crystallization temperature (Tc) of 104 to 108°C, and The above-mentioned novel LLDPE has a melting point (Tm) of 116 to 122°C and a crystallization temperature (Tc) of 105 to 109°C, and A method for manufacturing a stretch hood film, characterized in that the polyolefin elastomer (POE) of the inner layer has a melting point (Tm) of 98 to 102°C and a crystallization temperature (Tc) of 82 to 85°C.

9. A stretch hood film comprising an inner layer, outer layers above and below the inner layer, and a protective layer formed on the outer side of the outer layer, respectively. The above inner layer comprises a polyolefin elastomer (POE), and The above outer layer comprises a mixed recycled resin comprising a new LLPDE, recycled LDPE, and recycled LLDPE, wherein the mixed recycled resin comprises 40 to 50 weight percent based on the total weight. A stretch hood film characterized in that the protective layer comprises a mixed recycled resin comprising a new LLPDE, recycled LDPE, and recycled LLDPE, wherein the mixed recycled resin comprises 0 to 10 weight percent based on the total weight.

10. In the method for manufacturing a stretch hood film according to claim 9, The above inner layer, outer layer, and protective layer are simultaneously formed using a multilayer blown co-extrusion method, A method for manufacturing a stretch hood film, characterized in that the extrusion temperature is controlled within the range of 100 to 350℃.

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