Co-extruded eco-friendly foam multilayer film and ice pack using the same

Abstract

To provide a co-extruded eco-friendly foamed multilayer film and an ice pack using the same.SOLUTION: A non-oriented polyethylene foamed multilayer film comprising a surface layer 110, a foamed layer 120 and an inner face layer 130 is provided, in which the surface layer is made of a high-density polyethylene resin having a density in the range of 0.948 to 0.968 g / cm3, either alone or in a mixture with other polyethylene resin having a density different from the above density, the foamed layer uses a low-density polyethylene resin added with a foaming agent alone or is used while the low-density polyethylene resin is mixed with the linear low-density polyethylene resin or vinyl acetate, the inner surface layer uses low- density or linear low-density polyethylene having a density of 0.915 to 0.925 g / cm3 in a polyolefin elastomer having a density of 0.860 to 0.900 g / cm3 while being mixed therewith, and the foam multilayer film is produced through one blow co-extrusion process.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an eco-friendly co-extruded foamed multilayer film and an ice pack using the same. More specifically, the present invention relates to an ice pack using a non-oriented polyethylene foamed multilayer film composed of a surface layer 110, a foamed layer 120, and an inner layer 130, which is manufactured in a single co-extrusion process using foaming technology. [Background technology]

[0002] Recently, as the impact of the coronavirus (COVID-19) has increased the transportation industry, demand for food that requires rapid delivery has increased. Furthermore, as sales in online food markets have increased, competition has intensified among distribution companies that deliver fresh food at dawn. In particular, a major challenge is finding a solution to the problem of food spoilage during the delivery process.

[0003] Food can spoil quickly, so it must be kept fresh by being stored at low temperatures. Dry ice or ice packs are commonly used to keep food frozen or refrigerated during transportation.

[0004] Ice packs are made by mixing a refrigerant with water, which has a high specific heat capacity, and then freezing it. The ice pack's heat absorption effect helps maintain a low temperature in the surrounding area. Unlike dry ice, ice packs are easy to handle and store, and are therefore widely used.

[0005] Most existing ice packs are made from petrochemical products, and materials such as nylon / polyethylene or nonwoven fabric (PP, PE) / polyethylene are commonly used.

[0006] The nylon / polyethylene material is made of a multi-material consisting of two or more types of materials, namely, stretched nylon film, which has excellent impact resistance and toughness, and polyethylene film, which has excellent bag formability, bonded together. Therefore, it is impossible to recycle it, and the only option is to incinerate the entire product or to landfill it, which causes serious environmental pollution.

[0007] In addition, in the case of polyethylene / polyethylene materials, both the outer and inner layers are made of a single polyethylene material, which is advantageous from the viewpoint of recycling. However, in order to maintain impact resistance, toughness, etc., the outer layer of the film must be laminated using a uniaxially or biaxially stretched polyethylene film rather than a non-stretched film (see Patent Documents 1 and 2). Since processing of polyethylene stretched film is only possible using specific machines, excessive capital investment costs are required, resulting in very high production costs. Furthermore, since physical properties vary significantly depending on the characteristics of the equipment or the stretch ratio, it is difficult to produce a uniform stretched film.

[0008] In addition, in the case of a non-oriented polyethylene foam multilayer sheet, two laminated sheets can be laminated by separate dry lamination or laminated and bonded together using polyethylene melt discharged through a T-die (see Patent Document 3), but there are some problems with adding a foam layer to the inside in just one process.

[0009] Although a blown coextrusion method has been proposed as a technique for processing multilayer films, this is a case where chemically different materials are combined (see Patent Document 4).

[0010] Although ice packs made of paper have been developed, they have not yet been widely adopted, taking into consideration the function and effectiveness of the ice packs and their future reusability. That is, ice packs made of such materials have the problem of being poor in cushioning effect against external shocks and being very weak in durability against moisture (see Patent Document 5).

[0011] In addition, ice packs are sometimes filled with a mixture of water and a highly absorbent polymer with a gel-like cross-linked structure, which is then frozen and used as a refrigerant.When these packs are disposed of, the melted gel-like refrigerant is simply discarded, which clogs sewers and is another cause of serious water pollution.

[0012] As an alternative to this, ice pack products, which are made by filling a plastic packaging material with water and freezing it, have recently become popular, using ice as a refrigerant. However, when the packaging material is damaged by impact, the ice serving as the refrigerant breaks into sharp, pointed pieces, which can cause various problems, such as perforations caused by ice fragments when dropped. Therefore, packaging materials for ice packs using ice as a refrigerant are required to have excellent impact resistance or drop resistance.

[0013] Therefore, it is necessary to develop an environmentally friendly foamed multilayer film and ice packs that have good low-temperature cooling properties when used as a refrigerant, excellent impact resistance, drop resistance, and bag formability for packaging, and can be recycled after use using a single material. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] Korean Patent No. 10-2261130 (Registered on May 31, 2021) [Patent Document 2] Korean Patent No. 10-2240271 (Registered on April 8, 2021) [Patent Document 3] Korean Patent No. 10-2473886 (Registered on November 30, 2022) [Patent Document 4] Korean Patent Publication No. 10-2015-0106964 (Publication date: 2015.09.22) [Patent Document 5] Korean Patent Publication No. 10-2021-0122924 (Publication date: October 13, 2021) [Non-patent literature]

[0015] [Non-Patent Document 1] Lee Jeong-il, "Manufacturing Methods and Trends of Co-extruded Multilayer Blown Films," Packaging Information, October 1994, pp. 55-61. Summary of the Invention [Problem to be solved by the invention]

[0016] The present invention provides a foamed multi-layer film for ice packs, which is made of only unstretched polyethylene film, to provide impact resistance and cold insulation for packaging materials using ice as a refrigerant.

[0017] Furthermore, since the packaging material is made of only polyethylene, it is environmentally friendly and can be recycled after use without any problems.

[0018] It also seeks to simplify the many separate process steps required to manufacture existing foam multilayer sheets for ice packs. [Means for solving the problem]

[0019] The present invention is a non-stretched polyethylene foam multilayer film comprising a surface layer 110, a foam layer 120, and an inner layer 130, wherein the surface layer has a density of 0.948 to 0.968 g / cm 3 A high density polyethylene resin having a density of 0.920 to 0.940 g / cm3 is used alone, or a high density polyethylene resin having a density of 0.920 to 0.940 g / cm3 is used in a weight ratio of 80% by weight of the high density polyethylene resin. 3 and a polyethylene resin having a density in the range of 0.860 to 0.900 g / cm. The foam layer is made of a low-density polyethylene resin containing a foaming agent, either alone or in a mixture of 90 to 50 parts by weight of the low-density polyethylene resin and 10 to 50 parts by weight of linear low-density polyethylene or vinyl acetate, and the melt index of these is in the range of 0.2 to 8 g / 10 min. The inner layer is made of a polyethylene resin having a density in the range of 0.860 to 0.900 g / cm. 3Polyolefin elastomer having a viscosity of 0.880 to 0.910 g / cm 3 The weight ratio of ultra-low density polyethylene is 70 to 100, and the density is 0.915 to 0.925 g / cm 3 and a low-density or linear low-density polyethylene in a weight ratio of 0 to 30, and the foamed multilayer film is produced through a single blow co-extrusion process.

[0020] The surface layer is characterized in that the high density polyethylene has an MFR of 25 to 60, an MI of 0.5 to 1.5 g / 10 min, and a Vicat softening point of 125 to 129°C.

[0021] The foam layer has a foaming ratio of 20% to 200%.

[0022] The inner surface layer is characterized by selecting a resin having a heat-sew temperature of less than 125°C.

[0023] An ice pack is provided that includes the unstretched polyethylene foam multilayer film. [Effects of the Invention]

[0024] The present invention has demonstrated that the use of a foamed multi-layer film including the foam layer 120 provides the ice pack packaging material with excellent drop resistance and cooling effect.

[0025] In addition, since the packaging material is made entirely of a single material consisting of polyethylene, there is no problem of the shrinkage rate changing during the process of laminating multiple layers, and it can be used effectively as an environmentally friendly ice pack with excellent recyclability after use.

[0026] In particular, since it uses unstretched polyethylene film, no special stretching equipment is required, and a three-layer foam multi-layer film is manufactured through a single blown film extrusion process, without going through three steps: manufacturing a stretched film, manufacturing a foam film that can be seamed at low temperature, and then T-die coating or dry lamination. Therefore, the carbon emissions generated during the extrusion process are reduced from the previous three steps to one process, which not only reduces emissions to about one-third, but also has the effect of reducing production costs in the entire film manufacturing process. [Brief explanation of the drawings]

[0027] [Figure 1] 1 is a diagram illustrating a coextrusion process for producing a foamed multilayer film of the present invention. [Figure 2] 1 is an enlarged view of a cross section of one side of a foamed multilayer film according to an embodiment of the present invention. [Figure 3] 1 is an enlarged view of a cross section of one side of a foamed multilayer film according to an embodiment of the prior art. BEST MODE FOR CARRYING OUT THE INVENTION

[0028] The present invention will be described in more detail below. However, the following examples are merely a reference for explaining the present invention in detail, and the present invention is not limited thereto, and may be embodied in various different forms.

[0029] Most conventional ice packs are manufactured by processing a film made of synthetic resin into a bag, injecting water or the like into the bag, and then sealing the film.

[0030] In general, polyethylene resins are widely used in various packaging materials and blow moldings because they are inexpensive, have excellent mechanical properties, hygienic compatibility, water vapor permeability resistance, and produce good appearances when molded. However, when used as products containing contents such as water or ice, they can break due to insufficient drop impact strength at low temperatures. This has led to demands for improvements, such as changing the material or designing a multilayer film structure.

[0031] Even if the outer and inner layers of the packaging material are made of a single polyethylene material, if the outer layer is made of uniaxially or biaxially stretched polyethylene film for ultra-impact resistance, the shrinkage rate of the film will change significantly during the dry lamination process with the inner layer of unstretched polyethylene film, which can cause the film to twist or curl.

[0032] Therefore, the inventors selected unstretched polyethylene for all the resins used in the multilayer film, and produced a three-layer laminated film in a single process using a blow co-extruder (see Figure 1). However, the inventors completed the present invention by making the surface layer 110 a layer with excellent heat resistance, the foam layer 120 an intermediate layer for low-temperature impact resistance and cold insulation effect, and the inner layer 130 a layer that allows low-temperature heat stitching.

[0033] As can be seen in Figure 1, three extruders are used to extrude the surface layer, foam layer, and inner layer into a ring shape, and air is transported inside to expand the film. The expanded cylindrical multilayer film is then taken up through nip rollers.

[0034] The eco-friendly ice pack 10 of the present invention is characterized by being made of a non-stretched polyethylene foam multilayer film. Figure 2 is an enlarged cross-sectional view of one side of a foam multilayer film according to one embodiment of the present invention.

[0035] The surface layer 110 is made of high-density unstretched polyethylene with high thermal stability, the inner layer 130 is made of low-density unstretched polyolefin elastomer that can be heat-sewn at low temperature, and the foam layer 120 is made of low-density unstretched polyethylene with a foaming agent added, which is introduced as the middle layer, forming a three-layer structure.

[0036] In this case, the multilayer film is characterized by being produced as a non-stretched film, so there is no need for an additional film stretching process. Therefore, the present invention produces a multilayer film in a single process using a blown film multilayer extruder.

[0037] Generally, methods for manufacturing multilayer films include coating, lamination, and co-extrusion. In particular, co-extrusion is a method for manufacturing multilayer films by melting multiple raw materials in an extruder, combining the molten raw materials in a die, and simultaneously extruding multiple layers of film. Since co-extruded multilayer films are made using multiple different raw materials, they require advanced technology as well as many years of experience and know-how.

[0038] Depending on the manufacturing method, blown film can be classified into blown method and casting method. Although blown film has disadvantages compared to cast film such as thickness deviation and transparency, it has the advantage of being strong and easy to change elongation and thickness as molecular orientation is possible in both machine direction (MD) and cross direction (TD). Also, since no solvent is used during processing, there is no odor problem, making it very useful especially in the field of functional packaging materials.

[0039] PE co-extrusion film is rarely produced using casting equipment, but is mostly produced using blown equipment, which is manufactured domestically in Korea and is of excellent quality.Recently, new automatic thickness control devices and cooling methods have been developed to solve the drawbacks of the blown method.

[0040] In particular, with blown film manufacturing technology, no problems are found when the film is made from a single material. However, when multiple resin materials are extruded into layers to produce a multilayer film, the melting points, softening points, and crystallization temperatures of the resins vary depending on the type of resin. Therefore, conventional cooling techniques can cause stress due to deformation between the resin materials in the film, resulting in curling (bending) of the resin film. In other words, if the cooling rate is inappropriate, crystallization of the resin material progresses, resulting in haze, which can cause quality problems for the product. Therefore, the co-extrusion process must be carried out with careful consideration of these conditions. Furthermore, since a foam layer is formed in the middle layer of a multilayer film, the resin material of the foam layer is important, but the resin properties of the outer and inner layers must also be unique.

[0041] Therefore, the technical significance of this invention lies in the development of a process that can manufacture a three-layer structure with a foamed layer in the middle layer in a single blowing process and the development of an optimal material suitable for this. In particular, manufacturing using a non-stretched film is important for packaging materials such as ice packs.

[0042] The foamed multilayer film of the present invention has a three-layer structure consisting of a surface layer, a foamed layer, and an inner layer. When comparing the thickness before and after foaming, the following differences occur.

[0043] The thickness ratio of the film before foaming is typically 1:2:1, and if the total film thickness is 140 μm, the thicknesses of each layer are calculated to be 35 μm, 70 μm, and 35 μm, respectively. However, since foaming occurs only in the middle layer, the film thickness of the foam layer increases. Therefore, if the film thickness after foaming is to be 200 μm, the foaming ratio of the foam layer will be about 1.9 to 2.0 times. In total, the thickness ratio of each layer of the three-layer film after foaming is about 1:3.7:1, and the film thickness of the foam layer will increase significantly to about 130 μm.

[0044] In the prior art patent (Korean Patent Registration No. 10-2473886), the surface layer sheet, which acts as a heat-resistant layer, is manufactured to a thickness of 40 μm, and the inner layer sheet, which includes the foam layer and inner layer, is manufactured to a thickness of 140 μm. The two sheets are then T-die coated and laminated together to a thickness of 20 μm, resulting in a total thickness of 200 μm. In this case, the inner layer sheet, including the foam layer, is 100 μm before foaming and 140 μm after foaming. Since foaming only occurs in the middle layer, the foam layer is ultimately about 90 μm thick. Therefore, the thickness of the foam layer in the present invention is about 1.4 times thicker than that of the prior art patent.

[0045] Therefore, because the foam layer is thicker, when the film is finally heat-sewn to produce an ice pack, the thicker foam layer makes heat-sew even more difficult than in the existing patent, and a higher temperature is required for smooth heat-sewn seaming. This is because when heat is applied to the outer surface of the foam layer, the heat must be transferred through the foam layer to the inner layer in order for the inner layer to be heat-sewn. Ultimately, if the heat resistance of the surface layer is not strengthened, the surface layer may melt or become distorted during the heat-sewn process.

[0046] That is, in order to solve the above problems, it is necessary to differentiate the heat resistance of the resins used as follows.

[0047] Outer layer of film: Surface layer 110 The resin used for the surface layer of the ice pack is high-density polyethylene, which has high heat resistance and stability, so that the film does not twist or melt during hot stitching, allowing for high-speed stitching (adhesion). The surface layer is also called the heat-resistant layer.

[0048] Therefore, in the present invention, the above problems can be solved by selecting and using high density polyethylene having a specific molecular structure.

[0049] The resin used for the surface layer has a density of 0.948 to 0.968 g / cm3 A high density polyethylene resin having a density of 0.920 to 0.940 g / cm is used alone, or a high density polyethylene resin having a density of 0.920 to 0.940 g / cm is used in a weight ratio of 80% by weight of the high density polyethylene resin. 3 The polyethylene resin is characterized by being mixed with another polyethylene resin in a range of 20 weight ratio.

[0050] Density 0.920~0.940g / cm 3 Generally, when high density polyethylene is used alone, wrinkles may occur on the surface of the film. However, mixing a small amount of the low density polyethylene resin solves this problem.

[0051] Therefore, it is best to use high density polyethylene alone, but if wrinkles occur on the surface of the film due to the characteristics of the extruder, it is better to mix in a low density polyethylene resin at a weight ratio of 5 to 20.

[0052] Furthermore, the high-density polyethylene preferably has a narrow molecular weight distribution. This can usually be expressed by MFR (Melt flow ratio, ratio of MI21.6 kg / MI2.16 kg). The MFR of high-density polyethylene for film is generally in the range of about 30 to 160, with the MFR most commonly used for ordinary film being in the range of 130 to 160. However, in the present invention, one with an MFR of 25 to 60 is preferred, and one with an MFR of 25 to 35 is more preferred.

[0053] In other words, high density polyethylene with a wide MFR means that the amount of low molecular weight components increases accordingly, and the smaller the MFR, the less low molecular weight components there are. Therefore, even if the polyethylene has a high density, it has poor heat resistance, so the less low molecular weight components there are, the higher the heat resistance.

[0054] Furthermore, for application to blown films, the MI (melt index) of high-density polyethylene is also important. The lower the MI, the better the film, but the MI suitable for the present invention is at the level of 0.5 to 1.5 g / 10 min. If high-density polyethylene with an MI of 0.5 or less is used, gel will form on the surface of the film, making it impossible to produce a good film, and if a product with an MI of 1.5 or more is used, it will be unsuitable due to its poor heat resistance.

[0055] Another important factor is the Vicat softening point (ASTM D1525), which indicates the heat resistance of high-density polyethylene. The Vicat softening point of ordinary high-density polyethylene for film is about 123 to 129°C, but resins suitable for the present invention have a Vicat softening point of 125 to 129°C. Additionally, resins with a crystallization temperature in the range of 117 to 122°C are also preferred.

[0056] Therefore, if the product has a wide molecular weight distribution or a relatively low crystallization temperature, when the film is heat-sewn after being made into a three-layer multi-layer film, the heat resistance may decrease, causing poor heat-sewn joints such as the outer layer of the film melting and sticking.

[0057] Middle layer of film: Foam layer 120 The middle layer of the ice pack film is a foam layer 120, the main purpose of which is to improve the cooling effect and low temperature impact resistance.

[0058] The foam layer 120 is produced using a blown film extruder using a low-density polyethylene resin containing a foaming agent. Since film formation is difficult in this case, the melt index (MI) of the resin must be carefully considered. Generally, during the foaming process, void spaces are generated by foam cells, and their distribution significantly affects the mechanical strength. Therefore, among the physical properties of the resin, flowability must be considered as a key factor. Therefore, the melt index (MI) of the resin used is preferably in the range of 0.2 to 8 g / 10 min.

[0059] The resin used is preferably low density polyethylene alone, but if necessary, 90 to 50 parts by weight of low density polyethylene resin can be mixed with 10 to 50 parts by weight of linear low density polyethylene or ethylene vinyl acetate.

[0060] In order to improve the blow moldability, various additives generally used in polyethylene resins, such as heat stabilizers, weather stabilizers, ultraviolet absorbers, radiation-resistant agents, crystal nucleating agents, inorganic fillers, lubricants, plasticizers, organic peroxides, neutralizing agents, crosslinking agents, pigments, and dyes, as well as auxiliary materials such as elastomers for improving mechanical properties, may be added as necessary.

[0061] The foam layer 120 has an expansion rate of 20% to 200%, and the expansion rate can be adjusted using an inorganic or organic foaming agent or a gas foaming agent. If the expansion rate is 200% or more, the cold insulation effect and low-temperature impact resistance are improved, but the foam layer becomes thick, and heat transfer from the foam layer to the inner heat-sewn layer during heat-sewn sealing of the film is insufficient, which may result in poor heat-sewn sealing. If the expansion rate is less than 20%, the cold insulation effect and low-temperature impact resistance are insufficient. The expansion rate is most preferably 100% to 200%.

[0062] Specific examples of the blowing agent that can be used include organic or inorganic thermal decomposition type blowing agents, and gases such as nitrogen, carbon dioxide, propane, butane, etc. The blowing agent may be added directly to the resin used, but it can also be added as a masterbatch in advance to the resin component to enhance dispersibility.

[0063] Foaming aids that can be blended include talc, silica, titanium oxide, stearic acid, phthalic acid, zinc stearate, lead stearate, magnesium stearate, calcium stearate, ethylene glycol, glycerin, ethanolamine, urea, urea derivatives, melamine, dibasic lead phosphite, tribasic lead sulfate, and zinc oxide.

[0064] In particular, in order to produce a multilayer film including the foam layer 120, not only the component ratios but also the production conditions are very important, but are not particularly limited here.

[0065] Inner layer of film: Inner layer 130 It is important that the inner film layer 130 allows for fast, relatively low-temperature heat stitching so that the film can be easily heat-sealed when a refrigerant such as ice is filled inside the film of the ice pack and the film can be sealed. This is also called the heat stitching layer.

[0066] The heat stitching temperature of the resin used for the inner surface layer is preferably less than 125° C. It is most preferable to select a resin with a heat stitching temperature of 90 to 110° C.

[0067] The polyethylene resin for these properties has a density of 0.860 to 0.900 g / cm 3 Polyolefin elastomer, 0.880~0.910g / cm 3 Ultra-low density polyethylene, 0.915~0.925g / cm 3 Low density polyethylene, and 0.915 to 0.925 g / cm 3 The polyethylene may be one or a mixture of two or more selected from the group consisting of linear low density polyethylenes in the form of

[0068] Comparing the present invention with the prior art patents, the foam layer is thicker, and therefore the low-temperature heat-sewability is better than before. In other words, to produce a foamed multi-layer film using only one blow co-extrusion process, the properties of the unstretched polyethylene resin used in each layer must be differentiated.

[0069] To be suitable for the present invention, the density must be 0.860 to 0.900 g / cm 3 Polyolefin elastomer having a viscosity of 0.880 to 0.910 g / cm 3 The weight ratio of ultra-low density polyethylene is 70 to 100, and the density is 0.915 to 0.925 g / cm 3It is preferable to mix low density or linear low density polyethylene at a weight ratio of 0 to 30. If the mixing ratio is other than this, sufficient low temperature heat stitching properties are not exhibited, resulting in problems such as poor or slow heat stitching speed.

[0070] The present invention will be described below mainly with reference to the following examples and comparative examples.

[0071] [Example 1] The ice pack film was made using a three-layer blow co-extruder. The resin for the surface layer 110 of the ice pack film was 3390 (MI: 1.0, density: 0.952 g / cm) manufactured by Hanwha Solutions. 3 ) and Lotte's UL912A (MI: 1.2, density: 0.920 g / cm 3 ) were mixed and used in a content ratio of 90:10.

[0072] The resin used for the foam layer, which is the middle layer of the ice pack, is LDPE 5302 (MI: 0.3, density 0.922 g / cm) manufactured by Hanwha Solutions. 3 ) and the foaming agent was a 1:1 mixture of sodium bicarbonate and azodicarbonamide, which was then mixed with LDPE 5321 manufactured by Hanwha Solutions to prepare a 30% concentrated masterbatch, which was then mixed into the foam layer 120 at 3%.

[0073] The resin used for the inner layer 130 of the ice pack must be able to exhibit heat stitching properties at low temperatures, so Supreme 891 (MI: 1.0, density 0.885 g / cm) manufactured by SK Corporation was used. 3 ) and Hanwha Solutions' 4200D (MI: 1.6, density 0.920g / cm 3 ) were mixed in a weight ratio of 80:20.

[0074] During film processing, the total thickness of the three-layer film was 140 μm before foaming, but was adjusted to 200 μm after foaming. After foaming, the thickness of the foam layer 120 located in the middle of the three-layer film increased significantly to a level of approximately 130 μm.

[0075] The drop resistance and cooling effect of the ice pack bag film made from the foamed three-layer film were measured, and the results are shown in Table 3.

[0076] [Example 2] When manufacturing the three-layer film of the ice pack, the processing conditions, including the resins used in each layer and their content ratios, were the same as in Example 1, except that nitrogen was used as a gas blowing agent for the middle foam layer.

[0077] [Example 3] The resin of the surface layer 110 of the ice pack is SK 8300 (MI: 0.7, density: 0.963 g / cm 3 ) and Lotte's UL912A (MI: 1.2, density: 0.920 g / cm 3 ) were mixed at a content ratio of 80:20, and Supreme 891 (MI: 1.0, density 0.885 g / cm) manufactured by SK Corporation was used as the resin for the inner layer 130 of the ice pack. 3 ) and Hanwha Solutions' 4200D (MI: 1.6, density 0.920g / cm 3 The same procedure as in Example 1 was carried out except that the two compounds were mixed and used in a weight ratio of 70:30.

[0078] [Example 4] The resin for the surface layer of the three-layer film of the ice pack was the same as in Example 3, and the blowing agent for the middle layer was a nitrogen blowing agent, the same as in Example 2. The rest was the same as in Example 1.

[0079] [Comparative Example 1] The ice pack film was produced using a three-layer blow co-extruder, as in Example 1. The resin for the surface layer 110 of the ice pack was C440A (MI: 2.1, density: 0.968 g / cm) manufactured by Hanwha Total Corporation. 3 ) and Lotte's UL912A (MI: 1.2, density: 0.920 g / cm 3 ) were mixed and used in a content ratio of 80:20.

[0080] The resin used for the foam layer 120, which is the middle layer of the ice pack, is LDPE 5302 (MI: 0.3, density 0.922 g / cm) manufactured by Hanwha Solutions. 3 ) and the foaming agent was a 1:1 mixture of sodium bicarbonate and azodicarbonamide, which was then mixed with LDPE 5321 manufactured by Hanwha Solutions to prepare a 30% concentrated masterbatch, which was then mixed into the foam layer 120 at 3%.

[0081] The resin used for the inner layer 130 of the ice pack is SK Corporation's 891 (MI: 1.0, density 0.885 g / cm 3 ) and Hanwha Solutions' 4200D (MI: 1.6, density 0.920g / cm 3 ) were mixed in a weight ratio of 70:30.

[0082] Comparative Example 2 The ice pack film was produced using a three-layer blow co-extruder, as in Example 1. The resin for the surface layer 110 of the ice pack was F920A (MI: 1.0, density: 0.956 g / cm) manufactured by Hanwha Total Corporation. 3 ) and Lotte's UL912A (MI: 1.2, density: 0.920 g / cm 3 ) were mixed and used in a content ratio of 90:10.

[0083] The resin used for the foam layer 120, which is the middle layer of the ice pack, is LDPE 5302 (MI: 0.3, density 0.922 g / cm) manufactured by Hanwha Solutions. 3 ) and the foaming agent was a 1:1 mixture of sodium bicarbonate and azodicarbonamide, which was then mixed with LDPE 5321 manufactured by Hanwha Solutions to prepare a 30% concentrated masterbatch, which was then mixed into the foam layer 120 at 3%.

[0084] The resin used for the inner layer 130 of the ice pack is LF100A (MI: 1.2, density 0.903 g / cm) manufactured by LG. 3 ) and Hanwha Solutions' 4200D (MI: 1.6, density 0.920g / cm 3 ) were mixed in a weight ratio of 60:40.

[0085] Comparative Example 3 The layer structure of the ice pack was prepared by manufacturing two films and then laminating them together to produce an ice pack bag film. The two films refer to a multilayer film manufactured by laminating two films, a surface layer sheet 210 and an inner layer sheet 220, as shown in Figure 3 (see Example 1 of Korean Patent Registration No. 10-2473886).

[0086] The surface layer sheet 210 is a polyethylene unstretched film, and a two-layer blow extruder is used. In the surface layer sheet, the resin of the outer layer A (211) in FIG. 3 is C440A (MI: 2.1, density: 0.968 g / cm) manufactured by Hanwha Total Corporation. 3 ) and Lotte's UL912A (MI: 1.2, density: 0.920 g / cm 3 ) were mixed and used in a content ratio of 50:50, and the resin for the inner layer A (212) in Figure 3 was a mixture of C440A manufactured by Hanwha Total and UL912A manufactured by Lotte in a content (weight) ratio of 20:80. In this case, the thickness of the surface layer sheet was 30 μm in total.

[0087] The inner layer sheet 220 is also a polyethylene non-stretched foamed film, and a two-layer blow extruder was used. The resin used for the foamed layer 221 of the inner layer sheet in FIG. 3 is LDPE 5302 (MI: 0.3, density 0.922 g / cm) manufactured by Hanwha Solutions. 3 ) and the foaming agent was a 1:1 mixture of sodium bicarbonate and azodicarbonamide, which was then mixed with LDPE5321 manufactured by Hanwha Solutions to prepare a masterbatch that was concentrated to 30% in advance, and then mixed at 3% into the foam layer 221. At this time, the thickness of the unstretched foam layer 221 was 100 μm before foaming, and was adjusted to 140 μm after foaming.

[0088] In particular, the inner layer B (222) of the inner layer sheet must be able to exhibit heat stitching properties at a relatively low temperature, so Supreme 891 (MI: 1.0, density 0.885 g / cm) manufactured by SK Corporation was used. 3) and Hanwha Solutions' 4200D (MI: 1.6, density 0.920g / cm 3 ) were mixed and used in a 50:50 content ratio.

[0089] The thickness ratio of the inner layer sheet before foaming was foam layer 221 / inner layer B (222) = 2 / 1 (calculated as 67 μm / 33 μm in thickness). After foaming occurred only in the foam layer, the ratio became foam layer / inner layer B = 3.2 / 1 (calculated as 107 μm / 33 μm in thickness). The thickness was 67 μm before foaming, but became 107 μm after foaming.

[0090] The two sheets thus produced, i.e., the unstretched film of the surface layer sheet and the inner layer sheet (including the foam layer) of the ice pack, were bonded together by T-die coating to produce a multilayer sheet. The resin used for T-die coating was LDPE 950 (MI: 7.5, density 0.919 g / cm) manufactured by Hanwha Solutions. 3 ) were used and laminated while extruding at a temperature of 160 to 180°C. The final ice pack film thickness after three processes was 200µm in total (surface layer sheet 40µm, inner layer sheet 140µm, laminated 20µm).

[0091] Comparative Example 4 A commercially available ice pack packaging film was selected as Comparative Example 4. It was not clear how it was manufactured, but it was visually confirmed that it was not a packaging material containing a foam layer 221. Ice packs made of a single PE material used by Coupang, a delivery company, were obtained and left at room temperature for a long period of time until the water had completely dissolved. Then, the breakage resistance and cooling effect were measured in the same manner as in Example 1, and the results are shown in Table 4.

[0092] The types, mixing ratios and physical properties of the resins used in the examples and comparative examples are summarized in Table 3.

[0093] Evaluation 1. Results of thermal suture The results of the heat stitching were compared by measuring the heat stitching start temperature and heat stitching strength. The measurement method was based on the ASTM F88 method, and the pressure during heat stitching was 2 kgf / cm. 2 The heat-sewn temperature at which the sealing strength reached 2 kgf or more after 1.5 seconds of heat-sewn sealing was recorded as the heat-sewn initiation temperature. The heat-sewn strength was measured at the point at which the sealing strength finally stabilized after heat-sewn sealing. After heat-sewn sealing, the appearance of the heat-sewn surface was compared and evaluated to see if it was clean or if the film surface had melted due to the heat.

[0094] Table 3 shows the heat-sew starting temperature, heat-sew strength, and appearance properties after heat-sew of the ice pack bag films manufactured using the multi-layer films of the Examples and Comparative Examples.

[0095] In the examples, the temperature at which hot stitching began was 105 to 110°C, whereas in the comparative examples it was relatively high at 120°C or higher. With the exception of comparative example 3, the appearance after hot stitching in the other comparative examples showed poor adhesion due to surface melting.

[0096] Evaluation 2. Drop resistance Drop resistance can simultaneously demonstrate low-temperature impact resistance and puncture resistance. The surface and inner layer films of the ice pack were dry-laminated and then bonded together to form a bag measuring 150 mm wide and 200 mm long. 300 g of water was filled into the bag, hot-sewn, and thoroughly frozen to produce an ice pack sample. The ice pack was then dropped from a height of 2 m, and the breakage rate was measured and compared on a scale of four. Ten samples were prepared and dropped, and the average breakage rate was measured. Table 1 below shows the four-grade classification based on the breakage rate.

[0097] [Table 1]

[0098] The drop resistance of the ice packs manufactured by sealing with the multilayer films of the Examples and Comparative Examples was measured, and the results are shown in Table 4.

[0099] Rating 3. Cooling effect To evaluate the cooling effect, ice packs were made in the same way as for the drop resistance evaluation, filled with 300g of water, and hot-sewn. Once the water had sufficiently frozen, the ice packs were left in a room at room temperature of 25°C for 2 hours and 4 hours, and then opened and the weight of the water that had been released was measured and compared. Table 2 below shows the four classifications based on the amount of water that had melted.

[0100] [Table 2]

[0101] The cooling effect of the ice packs prepared by sealing with the multilayer films of the Examples and Comparative Examples was measured, and the results are shown in Table 4.

[0102] [Table 3]

[0103] As a result of comprehensively examining the above evaluations 2 and 3, it can be seen that the examples of the present invention generally have some differences in drop resistance and cooling effect compared to the comparative examples.

[0104] In particular, in Comparative Examples 1 and 2, three-layer films were produced using a single blow co-extrusion process, as in the Examples, but the resin properties and blending ratios of the outer layer (heat-resistant layer) and the inner layer (thermal stitching layer) were different, resulting in poor thermal stitching properties and making them unsuitable for use as ice packs. In other words, the drop resistance and cooling effect were too poor to be evaluated.

[0105] However, in Comparative Example 3, unlike Examples 1 to 4, a surface layer sheet and an inner layer foam sheet were separately manufactured and then the two sheets were bonded together to manufacture the ice pack, so the surface after heat seaming was good and there were no problems in applying it to products. However, because three processes were required, the cost of the film was inevitably more than three times higher than when manufacturing it at the same thickness.

[0106] In general, the drop resistance and cold insulation effect of the Examples, except for Comparative Examples 1 and 2, are excellent or good, but have drawbacks such as high manufacturing costs and large carbon emissions, as can be seen from Table 4. In particular, in the case of Comparative Example 3, when comparing the amount of dissolved water after 2 hours and 4 hours, even though it was rated as 'excellent', the amount of water was somewhat higher than in the Examples, so the cold insulation effect appears to be somewhat insufficient. This is thought to be because, as mentioned above, when the final ice pack thickness is the same, the thickness of the foam layer is relatively thin, resulting in a somewhat inferior cold insulation effect.

[0107] [Table 4]

[0108] The foamed multi-layer film of the present invention is manufactured by simultaneously performing a three-layer structure of a surface layer, a foamed layer, and an inner layer through a single co-extrusion process, and a thicker foamed layer 220 can be introduced as an intermediate layer. This allows for lower manufacturing costs and relatively less carbon emissions than conventional processes, and also provides excellent drop resistance and cooling effect, making it highly suitable for use as packaging materials such as eco-friendly ice packs. [Explanation of symbols]

[0109] 10 Ice Packs 110 Surface layer 120 foam layer 130 inner layer 20 Ice Packs 210 Surface layer sheet 220 Inner layer sheet 221 Foam layer

Claims

1. A method for producing a non-oriented polyethylene foam multilayer film comprising a surface layer (110), a foam layer (120), and an inner layer (130), The surface layer has a density of 0.948 to 0.968 g / cm ３ The density is 0.920 to 0.940 g / cm3 for a high density polyethylene resin 90 weight ratio. ３ or a high density polyethylene resin having a density of 0.920 to 0.940 g / cm3 with respect to a high density polyethylene resin having a density of 80 to 100 g / cm3. ３ and other polyethylene resins in the range of 20% by weight. The foam layer is made of a low-density polyethylene resin containing a foaming agent, either alone or in a mixture of 90 to 50 parts by weight of the low-density polyethylene resin and 10 to 50 parts by weight of linear low-density polyethylene or vinyl acetate, with the melt index of each being in the range of 0.2 to 8 g / 10 min; The inner surface layer has a density of 0.860 to 0.900 g / cm ３ or a polyolefin elastomer having a viscosity of 0.880 to 0.910 g / cm ３ The density is 0.915 to 0.925 g / cm3 for a weight ratio of 70 to 100 ultra-low density polyethylene. ３ low density or linear low density polyethylene is mixed in a weight ratio of 0 to 30, The surface layer is made of high-density polyethylene having an MFR of 25 to 60, an MI of 0.5 to 1.5 g / 10 min, and a Vicat softening point of 125 to 129°C, The foam layer has an expansion ratio of 20% to 200%; The foaming agent is a masterbatch foaming agent made by mixing sodium bicarbonate and azodicarbonamide in a 1:1 ratio and pre-concentrating it to 30% with LDPE 5321 manufactured by Hanwha Solutions Co., Ltd., or a nitrogen gas foaming agent. The inner surface layer is made of a resin having a heat-sew temperature of 100 to 110°C. Produced through a single blow co-extrusion process A method for producing a non-stretched polyethylene foam multilayer film, characterized in that the blow co-extrusion process includes extruding the surface layer, the foam layer, and the inner layer using a multilayer extruder, and then winding them up through nip rollers without stretching them.

2. A method for producing an ice pack, comprising the method for producing the non-oriented polyethylene foam multi-layer film according to claim 1.

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