WO2024080819A1 - Polyethylene multilayer film - Google Patents

Abstract

The present invention pertains to a polyethylene multilayer film. More specifically, the present invention pertains to: a polyethylene multilayer film having excellent strength against internal and external impacts; and a packaging material using same. An aspect of the present invention pertains to a polyethylene multilayer film containing polyethylene as the main component, wherein at least one layer contains polyethylene A satisfying the following properties (1) and (2), and the difference in melting temperature between a first surface layer (outer layer) and a second surface layer (inner layer) is at least 20°C. (1) There is at least one cross fractionation chromatography (CFC) peak between 88°C and 100°C and at least one CFC peak between 40°C and 75°C, and the weight average molecular weight in the range of 40-75°C is at least 90,000 g/mol. (2) The melt index measured at 190°C and 2.16 kg according to ASTM D1238 is 0.2-10 g/10 min.

Description

Polyethylene multilayer film

The present invention relates to a polyethylene multilayer film, and more specifically, to a polyethylene multilayer film with excellent strength against internal and external impacts and packaging materials using the same.

Packaging materials are mainly manufactured through resin films composed of resin materials. Among them, resin films made of polyolefin are widely used in packaging materials because they have moderate flexibility and excellent transparency.

Resin films made of polyolefin are used by bonding them with resin films made of polyester, polyamide, etc., which have superior mechanical and thermal properties, with polyurethane-based adhesives or acrylic-based adhesives. Therefore, typical packaging materials are heat-sealed with the substrate. It consists of a laminated film whose layers are made of different materials. Accordingly, recycling of conventional packaging materials is practically impossible because it is difficult to separate different types of resin materials, so it is emerging as a major social problem from an environmental perspective.

In order to solve these problems, the development of technology to implement recyclable packaging materials, especially technology to implement packaging materials through resin films made only of polyolefin-based materials, is continuously being developed. However, as mentioned above, polyolefin resin has lower mechanical properties compared to the resin used as a conventional substrate, so the durability of the packaging material is reduced, which increases the possibility of defects occurring in the printing process of the packaging material and during use processes such as transportation and storage. There is a problem that the packaging material is easily damaged. In addition, polyolefin resin has lower heat resistance compared to resins used as conventional substrates, so there is a high possibility of defects occurring during the heat sealing process to form packaging materials, leading to a problem of reduced heat sealability.

Accordingly, while using only a single polyolefin material, films with a multi-layer structure in which polyolefin resins with different mechanical and thermal properties based on differences in density, additives, composition ratio, etc. are laminated are continuously being developed, but still have excellent mechanical and thermal properties. It is difficult to obtain, and commercialization is not easy in terms of cost. In particular, there are limitations in implementing packaging materials that can be used even at low temperatures, so improvements are required.

For example, Japanese Patent Publication No. 2020-037189 discloses a laminated film for packaging materials in which the polyolefin content of the entire film is 80 parts by weight or more, but there is still a problem of reduced durability at low temperatures, and the Japanese registered patent No. 6814287 discloses a recyclable polyethylene single material laminated film, but it is still difficult to obtain excellent heat resistance and there is a problem of poor heat sealability.

Therefore, as a resin film made of only a single material, it is easy to recycle and solves environmental problems. At the same time, the mechanical and thermal properties are not significantly reduced compared to the conventional composite film of different materials, and the excellent properties are maintained in a wide temperature range, making it commercializable. There is a need for the development of new films and packaging materials that are possible and have excellent processability.

In particular, when packaging materials made of multi-layered polyethylene films are used in low temperature conditions and are subject to shock due to vibration or dropping, ruptures, tears, holes, or scratches occur on the film surface, causing frequent leakage of the contents to the outside. It is becoming. In addition, when thermally bonding a film, damage to the film due to the high-temperature bonding process and rupture due to impact at the thermal bonding boundary under low-temperature conditions also frequently occur. To prevent such problems, the durability of the multi-layered polyethylene film is improved. Impact strength is essential.

In order to solve the problems of the prior art as described above, the inventors of the present invention proposed a solution that is made of a single material that can be recycled and is durable, and even better, can exhibit durability even at low temperatures, and is resistant to bursting or opening from internal materials or external impacts. The aim is to provide a polyethylene multilayer film with excellent sealing properties and strength to the extent that this does not occur, and packaging materials using the same.

In addition, one embodiment of the present invention has excellent falling ball impact strength and puncture strength in a balanced manner, so that both mechanical properties simultaneously satisfy a specific numerical range, and has excellent durability and sealing properties at low temperatures, so that it can be used in ice packs, frozen food packaging bags, etc. The aim is to provide a polyethylene film with a multilayer structure suitable for use in molded products used at low temperatures, such as frozen food containers, refrigerated food packaging bags, and refrigerated food containers, and packaging materials manufactured therefrom.

In addition, one embodiment of the present invention seeks to provide a multi-layered polyethylene film that does not damage the film or deteriorate its physical properties even within a low temperature range and has excellent heat sealability and high-speed bundling processability, and a packaging material manufactured therefrom. .

The inventors of the present invention studied to solve the above problem and found that by including a polyethylene resin that satisfies specific physical properties in one or more layers of the multilayer film, the desired durability and impact resistance can be satisfied at the same time, and in particular, the impact resistance is greatly improved. The present invention was completed by discovering improved effects.

One aspect of the present invention is a multilayer film containing polyethylene as a main component,

Provided is a polyethylene multilayer film comprising polyethylene A that satisfies the following physical properties (1) to (2) in at least one layer, and having a melt temperature difference of 20°C or more between the first surface layer (outer layer) and the second surface layer (inner layer). .

(1) On cross fractionation chromatography (CFC), at least one peak exists between 88 and 100 °C, at least one peak exists between 40 and 75 °C, and the weight ranges from 40 to 75 °C. Average molecular weight is over 90,000 g/mol

(2) The melt index measured at 190°C and 2.16kg according to ASTM D1238 is 0.2 to 10 g/10min.

In one embodiment of the present invention, the polyethylene A may satisfy the physical properties of (3) a density of 0.890 to 0.925 g/cm3 according to ASTM D1505.

In one embodiment of the present invention, the at least one layer may include polyethylene A alone or a resin mixture of polyethylene A and metallocene-polyethylene.

In one embodiment of the present invention, the at least one layer may contain 70% by weight or more of polyethylene A alone or the resin mixture, but is not limited thereto.

In one embodiment of the present invention, the resin mixture may have a content of polyethylene A of 10% by weight or more to less than 100% by weight, more specifically 10 to 99% by weight, but is not limited thereto.

In one embodiment of the present invention, the polyethylene multilayer film may have a falling ball impact strength per unit thickness of 15 gf/㎛ according to ASTM D1709, but is not limited thereto.

In one embodiment of the present invention, the polyethylene multilayer film may have a total thickness of 30 to 300 ㎛, but is not limited thereto.

In one embodiment of the present invention, the polyethylene A and metallocene-polyethylene may be an ethylene copolymer obtained by polymerizing ethylene and a C3-C18 α-olefin comonomer, but are not limited thereto.

In one embodiment of the present invention, the α-olefin comonomer may be any one or a mixture of two or more selected from 1-propylene, 1-butene, 1-hexene, 1-heptene, and 1-octene, etc. It is not limited.

In one embodiment of the present invention, the polyethylene multilayer film may be a stack of at least two layers including a layer containing the polyethylene A, but is not limited thereto.

In one embodiment of the present invention, the polyethylene multilayer film may be a stack of at least three layers including a layer containing the polyethylene A, but is not limited thereto.

In one embodiment of the present invention, it may be a functional polyethylene multilayer film including a functional layer on the surface layer of the polyethylene multilayer film, and specifically, the functional layer is any selected from a barrier coating layer, a top coating layer, and a printing layer. It may include one or two or more layers.

Another aspect of the present invention provides a packaging material including the polyethylene multilayer film according to the above aspect.

Another aspect of the present invention provides a molded article including the packaging material.

In one embodiment of the present invention, the molded product is an ice pack, frozen food packaging bag, frozen food container, refrigerated food packaging bag, refrigerated food container, shrink film, heavy packaging film, automatic packaging film, stretch wrap, and bag. It may be any one selected from among.

In one embodiment of the present invention, the molded product is a packaging material for packaging liquid, powder, and solid contents, and is used in fields that require strength against internal or external impact during manufacturing, distribution, and sales. It may be a molded product.

The polyethylene multilayer film and the packaging material containing the same according to an aspect of the present invention are multilayer films containing polyethylene as the main component. In addition to polyethylene, polyolefin-based resins can be used, and more preferably, all layers are made of polyethylene-based resin, so that they can be used as a single layer. It is made of materials that are easy to recycle and does not cause environmental pollution.

In addition, the polyethylene multilayer film and the packaging material containing the same according to an aspect of the present invention do not significantly deteriorate in mechanical and thermal properties compared to the existing composite film of different materials and the packaging material manufactured therefrom, thereby preventing damage during processing and commercialization. It can be minimized.

In addition, the polyethylene multilayer film and the packaging material containing the same according to an aspect of the present invention have excellent falling ball impact strength and puncture strength and are excellent in durability at low temperatures, so they can be used in ice packs, frozen food packaging bags, frozen food containers, and refrigerated food packaging bags. It may be suitable for use in molded products used at low temperatures, such as refrigerated food containers.

In addition, the polyethylene multilayer film and packaging material containing the same according to an aspect of the present invention can have excellent heat sealability and high-speed bundling processability even within a low temperature range where the film is not damaged or its physical properties are not deteriorated.

In addition, the polyethylene multilayer film and the packaging material containing the same according to an aspect of the present invention are packaging materials for packaging liquid, powder, and solid contents, and require strength against internal or external impacts during the manufacturing, distribution, and sales process. It can be applied in a variety of fields.

Hereinafter, the present invention will be described in more detail. However, the following specific examples or examples are only a reference for explaining the present invention in detail, and the present invention is not limited thereto, and may be implemented in various forms.

Also, unless otherwise defined, all technical and scientific terms have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention pertains. The terminology used in the description herein is merely to effectively describe specific embodiments and is not intended to limit the invention.

Additionally, as used in the specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to also include the plural forms, unless the context clearly dictates otherwise.

Additionally, when a part is said to “include” a certain component, this means that it may further include other components, rather than excluding other components, unless specifically stated to the contrary.

In addition, the terms “about”, “substantially”, etc. used in this specification are used at or close to the numerical value when manufacturing and material tolerances inherent in the mentioned meaning are presented, and are used to aid understanding of the present invention. It is used to prevent unscrupulous infringers from unfairly using disclosures that contain precise or absolute figures.

In this specification, the term “as a main ingredient” means used as a main ingredient compared to other ingredients, specifically, for example, 50% by weight or more, more specifically 55% by weight or more, 60% by weight or more, 65% by weight or more. , which means using more than 70% by weight, more than 75% by weight, and more than 80% by weight.

In this specification, a multilayer film containing polyethylene as a main component means that polyethylene is the main component, that is, 50% by weight or more, 50 to 100% by weight, among the components of all layers of a multilayer film in which at least two or more layers are laminated, In addition to polyethylene, it may contain polyolefin-based resin from the viewpoint of recycling, and more preferably, all layers may be made of polyethylene-based resin.

In this specification, the term “surface layer” refers to the outermost layer of a multi-layer laminated film, and when two or more layers are laminated, each outermost layer is divided into a first surface layer (outer layer) and a second surface layer (inner layer). That is, the outermost layer at the highest level and the outermost layer at the lowest level are divided into a first surface layer (outer layer) and a second surface layer (inner layer), respectively. For example, when two layers are stacked, each layer can be the first surface layer (outer layer) and the second surface layer (inner layer), and when three layers are stacked, the outermost layer excluding the middle layer is the first surface layer (outer layer). and the second surface layer (inner layer).

As used herein, the term “metallocene-polyethylene” refers to a polyethylene resin produced using a metallocene catalyst.

In this specification, “weight average molecular weight” can be measured by methods well known in the art, and is, for example, polystyrene equivalent molecular weight analyzed by GPC (gel permeation chromatograph).

In this specification, “Cross fractionation chromatography (CFC) is a method that combines Temperature Rising Elution Fractionation (TREF) and Gel Filtration Chromatography (GPC), and is a method that combines olefinic resin, Specifically, it is a method that can simultaneously determine the crystallinity distribution and molecular weight distribution of polyethylene resin.

In this specification, “lamination” of a multilayer film includes both co-extrusion and physical stacking, or lamination using a separate adhesive, etc. Even better, it can be co-extruded and laminated from the viewpoint of recycling.

The unit of additives not specifically described in this specification may be weight percent.

Unless otherwise specified herein, the term 'resin' or 'polymer' may refer to a polymerizable compound prepared by polymerizing monomers. Specifically, it may include homopolymers, copolymers, terpolymers, and interpolymers. The term 'interpolymer' refers to a polymer prepared by polymerizing two or more different monomers. Therefore, the general term interpolymer may include not only copolymers but also terpolymers. The copolymer refers to a polymer prepared from two different monomers, and the terpolymer refers to a polymer prepared from three different monomers.

Hereinafter, unless otherwise specified herein, when a part such as a layer, film, thin film, region, plate, etc. is said to be “on” or “on” another part, this refers not only to the case where it is “right on” the other part, but also to the case where it is “right on” the other part. It may also include cases where there is another part in the middle.

One embodiment of the present invention uses polyethylene as the main ingredient and all components forming the multi-layer film are polyolefin resins, specifically polyethylene, as a single material to enable recycling, so that it is recyclable without causing environmental pollution and existing heterogeneous films. Damage during processing and commercialization can be minimized as the mechanical and thermal properties are not significantly reduced compared to the composite film and the packaging materials manufactured from it. In particular, the durability of the surface area and the heat bonding boundary area at low temperatures is excellent, and the low temperature is low. Polyethylene with a multi-layer structure is suitable for use in molded products used at low temperatures, such as ice packs, frozen food packaging bags, frozen food containers, refrigerated food packaging bags, and refrigerated food containers, as its high-speed bundling processability is significantly improved due to excellent heat sealing properties at low temperatures. Films and packaging materials manufactured therefrom can be provided.

At this time, the polyolefin-based resin includes polyethylene-based resin and polypropylene-based resin, and specifically refers to low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE), and polypropylene (PP).

The present invention will be described in detail as follows.

The polyethylene multilayer film according to one aspect of the present invention includes polyethylene A satisfying the following physical properties (1) to (2) in at least one layer, and the melt temperature of the first surface layer (outer layer) and the second surface layer (inner layer) The difference may be 20°C or more, more specifically 20 to 100°C, more specifically 30 to 80°C, and more specifically 35 to 70°C.

(1) On cross fractionation chromatography (CFC), at least one peak exists between 88 and 100 °C, at least one peak exists between 40 and 75 °C, and the weight ranges from 40 to 75 °C. Average molecular weight is over 90,000 g/mol

(2) The melt index measured at 190°C and 2.16kg according to ASTM D1238 is 0.2 to 10 g/10min.

In one aspect, the polyethylene A may satisfy the physical properties of (3) a density of 0.890 to 0.925 g/cm3 according to ASTM D1505. For example, it may be 0.895 to 0.920 g/cm3 or 0.900 to 0.920 g/cm3, but is not limited thereto.

In one aspect, the melt index of polyethylene A may be 0.2 to 10 g/10min, for example, 0.3 to 8 g/10min, 0.5 to 3g/10min, but is not limited thereto.

In one aspect, at least one layer of the multilayer film may include polyethylene A alone or a resin mixture of polyethylene A and metallocene-polyethylene, and may include polyethylene A alone or polyethylene A and metal. It may contain more than 70% by weight, 70 to 100% by weight, of a resin mixture mixed with polyethylene. The mixing ratio is not limited, but polyethylene A and metallocene-polyethylene can be mixed and used in a weight ratio of 1 to 9:9 to 1, and a higher content of polyethylene A can be used. For example, polyethylene A and metallocene-polyethylene can be mixed and used at a weight ratio of 6 to 9:4 to 1. The metallocene-polyethylene is a polyethylene resin polymerized using a metallocene catalyst, and may be low-density polyethylene, linear low-density polyethylene, high-density polyethylene, etc., and may be a homopolymer or copolymer.

In one aspect, the multilayer film may be a lamination of two or more layers, one or both of which include the polyethylene A, and the melt temperature difference between the first surface layer (outer layer) and the second surface layer (inner layer) is It may be 20°C or higher. More specifically, when the multilayer film has two layers and the layer for providing sealing when applied to a packaging material is referred to as the inner layer, it may be more preferable to include the polyethylene A in the outer layer rather than the inner layer to achieve the desired impact strength. However, it is not limited to this.

In one aspect, the multilayer film may be a stack of three or more layers, and at least one or all of the layers include polyethylene A, and the outermost layer is divided into a first surface layer (outer layer) and a second surface layer. When referred to as (inner layer) and the other intermediate layers as intermediate layers, the difference in melting temperature between the first surface layer (outer layer) and the second surface layer (inner layer) may be 20°C or more. In addition, when the layer for providing sealing when applied to a packaging material is referred to as the inner layer, it may be more preferable to include the polyethylene A in the middle or outer layer rather than the inner layer in order to develop the desired impact strength, but is not limited thereto. .

As described above, the sealing properties are excellent in the range where the difference in melting temperature (melting point) between the outer layer and the inner layer is 20°C or more, and the sealing properties are excellent at low temperatures, preventing bursting of the sealing portion in frozen and low temperature conditions. there is. In addition, since high-speed processing is possible when manufacturing packaging materials, productivity can be further improved.

In one aspect, when the multilayer film is composed of three layers, the layer for providing sealing when applied to a packaging material is referred to as the inner layer, and the layer for providing functionality such as a printing layer is referred to as the outer layer, with an outer layer (A) and a middle layer. (B) and the inner layer (C) may be sequentially laminated, and the outer layer, middle layer, and inner layer may each be laminated in at least one layer, and the outermost layer of the outer layer and the inner layer is the first surface layer. (outer layer) and second surface layer (inner layer), and the other layers in between are called middle layers, and the polyethylene A is included in the remaining layers except for the first surface layer (outer layer) and the second surface layer (inner layer). It may be more desirable to achieve the desired impact strength, but is not limited thereto.

In one aspect of the present invention, the multilayer film may be a sequential lamination of an outer layer (A), a middle layer (B), and an inner layer (C), and the outer layer, the middle layer, and the inner layer may each be laminated in at least one layer. there is. Among these, at least one layer may contain polyethylene A alone or a resin mixture of polyethylene A and metallocene-polyethylene, and the other layers may be made of polyolefin-based resin, or better, polyethylene-based resin. there is. Although it is not limited to this, it may contain more than 70% by weight of polyethylene A alone or a resin mixture, and less than 30% by weight is polyolefin-based resin, for example, a type different from the polyethylene A and metallocene-polyethylene. It can be used by mixing polyethylene resins or polyethylene resins with different physical properties.

In one aspect, the resin mixture may have a content of polyethylene A of 10% by weight or more and less than 100% by weight, for example, 10 to 99% by weight, but is not limited thereto. It is even better because it can achieve an impact strength of .

In one aspect, the polyethylene A and metallocene-polyethylene may be a polymerization of ethylene and a C3-C18 α-olefin comonomer. The metallocene-polyethylene refers to polyethylene polymerized using a metallocene catalyst. Specifically, the α-olefin comonomer may be any one or a mixture of two or more selected from 1-propylene, 1-butene, 1-hexene, 1-heptene, and 1-octene.

In one aspect of the present invention, the polyethylene multilayer film may include a functional layer on the surface layer, and the surface layer may refer to an outer surface layer rather than an inner layer used as a sealing layer. The functional layer refers to any one or two or more layers selected from a barrier coating layer, a top coating layer, and a printing layer, but is not limited thereto.

In one aspect, the polyethylene multilayer film may have a total thickness of 30 to 300 ㎛, 40 to 250 ㎛, or 45 to 200 ㎛, but is not limited thereto.

Hereinafter, a more specific aspect of the polyethylene multilayer film according to one aspect of the present invention will be described in more detail by exemplifying a configuration in which three layers are stacked. This is an example to explain the present invention in more detail and is not limited to this laminated structure. Alternatively, the outer layer, middle layer, and inner layer described later may each be composed of at least one layer laminated, and including the first ethylene polymer means included in any one of the laminated configurations of at least one layer or more.

In a more specific embodiment, the polyethylene multilayer film (hereinafter referred to as “multilayer polyethylene film”) includes an outer layer (A) containing a first ethylene polymer; an intermediate layer (B) comprising a second ethylene polymer; and an inner layer (C) comprising a third ethylene polymer; It may be stacked in the order (A)/(B)/(C).

At this time, the intermediate layer includes the polyethylene A, and the polyethylene film of the multilayer structure may have densities of the first ethylene polymer, the second ethylene polymer, and the third ethylene polymer satisfying the following equations 1 to 3.

[Equation 1]

0.935 ≤ M ₁ ≤ 0.968

[Equation 2]

0.890 ≤ M ₂ ≤ 0.925

[Equation 3]

0.850 ≤ M ₃ ≤ 0.910

(In Equations 1 to 3, M ₁ is the density of the first ethylene polymer, M ₂ is the density of the second ethylene polymer, and M ₃ is the density of the third ethylene polymer, and the density is ASTM D 792 It is measured according to , and the unit of density is g/cm ^3. )

Among them, the intermediate layer (B) may be polyethylene A that satisfies the physical properties (1) to (3) described above.

In addition, in addition to the middle layer, when the outer layer and the inner layer are composed of at least two or more layers, polyethylene A satisfying the above physical properties (1) to (3) may be included in any layer except the outermost layer.

In one aspect, the polyethylene multilayer film may have a falling ball impact strength per unit thickness of 15 gf/㎛, 15 to 50 gf/㎛, or 20 to 50 gf/㎛ according to ASTM D1709. In addition, the puncture strength per unit thickness is 0.2 to 0.4 N/㎛, and the melting point difference between the outer layer (A) and the inner layer (C) is 20 ℃ or more, for example, 20 to 100 ℃. It may simultaneously satisfy the physical properties. . By satisfying these physical properties at the same time, it is desirable because it can prevent tearing or bursting of the packaging material due to internal or external impact when applied to packaging materials, and even better, it is desirable because it exhibits excellent impact strength even in a frozen state. The puncture strength refers to the maximum strength measured when the film is broken by a pin with a diameter of 6.5 mm piercing the inner surface of the film at a speed of 500 mm/min, and the falling ball impact strength and puncture strength per unit thickness are as above. It refers to the value obtained when the falling ball impact strength and puncture strength values measured in the same way are divided by the total thickness of the film.

In one aspect of the present invention, more specifically, the density of the first ethylene polymer may be 0.950 to 0.968 g/cm ³ , or 0.955 to 0.965 g/cm ³ , and the density of the second ethylene polymer may be 0.890 to 0.925 g. /cm ³ , 0.895 to 0.920 g/cm 3 , or 0.900 to 0.920 g/cm 3 , and the density of the third ethylene polymer may be 0.860 to 0.905 g/cm ³ , or 0.860 to 0.890 g/cm ³ , but must be It is not limited to this.

An outer layer (A) comprising a first ethylene polymer satisfying the above physical properties; an intermediate layer (B) comprising a second ethylene polymer; and an inner layer (C) comprising a third ethylene polymer; This multi-layered polyethylene film laminated in the (A)/(B)/(C) order and the packaging material manufactured from it are made of a single polyethylene material, so they are easy to recycle, and have higher impact resistance and tensile strength compared to conventional composite films of different materials. Mechanical properties such as strength do not deteriorate, and the printing processability and durability are excellent, so the possibility of defects occurring during the printing process is very low. The packaging material is not easily damaged during use, such as transportation and storage, making commercialization easy. there is.

In particular, it exhibits excellent physical properties such as durability of the film surface at low temperatures and bursting strength of the heat bonding boundary at the same time, so its utility value is very high in a variety of temperature ranges, including low temperatures.

In addition, any ethylene polymer that satisfies the above physical properties can be used regardless of its type, so the influence of the type of functional group contained in the ethylene polymer and the molecular structure of the ethylene polymer can be minimized, and it can be used as an inexpensive product that is easier to commercialize. Even if ethylene polymer products in the price range are used, a multi-layer polyethylene film with excellent physical properties targeted by the present invention can be obtained, and versatility can be significantly improved.

In particular, a polyethylene film with a multi-layer structure whose falling ball impact strength and puncture strength per unit thickness simultaneously satisfies the above range and packaging materials manufactured therefrom can have excellent mechanical and thermal properties, and durability and heat resistance on the film surface even at low temperatures. Since it exhibits excellent physical properties such as bursting strength at the adhesive boundary area, it has very high utility value within a variety of temperature ranges, including low temperatures. Therefore, it can be very suitable for use in molded products that are manufactured at high or room temperature and distributed and used at low temperatures, such as ice packs, frozen food packaging bags, frozen food containers, refrigerated food packaging bags, and refrigerated food packaging containers. It can become wider.

In one aspect of the present invention, more specifically, the melting point difference between the outer layer (A) and the inner layer (C) may be 20°C or more, 20 to 100°C, 50 to 90°C, or 55 to 90°C. It is not necessarily limited to this.

Since the melting point difference between the outer layer (A) and the inner layer (C) satisfies the above range, the polyethylene film with a multilayer structure according to an aspect of the present invention does not damage the outer layer (A) and the middle layer (B) or deteriorate its physical properties. The heat sealing process can be carried out even in a sufficiently low temperature range, and the outer layer (A) and middle layer (B) according to one aspect of the present invention are relatively thin compared to polyester, polyamide, etc., which are mainly used in conventional laminated films of different materials. Even though it has a low melting point, there is no problem of damage to the film or deterioration of its physical properties, and excellent heat sealability and high-speed bundling processability of the film can be achieved.

In particular, when high-speed bundling processability is reduced, this immediately leads to an increase in the unit cost of the packaging material produced, thereby greatly reducing the productivity and economic feasibility of the film and packaging material. The polyethylene film with a multilayer structure according to one aspect of the present invention has the outer layer (A ) and the inner layer (C) are maintained at a large melting point difference, thereby improving the processability of the film and resulting economic effects.

Additionally, in one aspect of the present invention, the melting point of the inner layer (C) may be 90°C or lower and 85°C or lower, for example, 40 to 90°C or 40 to 85°C, but is not necessarily limited thereto.

In addition, in one aspect of the present invention, the heat bonding initiation temperature for heat bonding the inner layer (C) may be 40 to 120 ℃, 50 to 110 ℃, or 50 to 100 ℃, but is not necessarily limited thereto. no.

At this time, the thermal bonding initiation temperature refers to the temperature at which the adhesive strength of the inner layer (C) measured according to ASTM F2029 and ASTM F88 is 1000 gf or more.

Since the melting point and heat bonding start temperature of the inner layer (C) satisfy the above range, the multi-layer polyethylene film according to the present invention and the packaging material manufactured therefrom are protected from damage or damage to the outer layer (A) and middle layer (B) of the film. Even in a sufficiently low temperature range where the problem of deterioration of the physical properties does not occur, the effects of excellent heat sealability and high-speed bundling processability of the film can be realized to a higher degree.

In one aspect of the present invention, the thickness ratio of the outer layer (A), middle layer (B), and inner layer (C) may be 1: 1 to 10: 0.2 to 2. For example, it may be 1: 1 to 8: 0.3 to 1, or 1: 4 to 8: 0.5 to 1, but is not necessarily limited thereto.

When the thickness of each layer satisfies the ratio of the above range, excellent characteristics such as falling ball impact strength and puncture strength per unit thickness can be realized to a higher degree, and durability at low temperatures can be further improved.

In addition, in one aspect of the present invention, the tensile strength of the multilayer polyethylene film may be 350 kg/cm ² or more, 380 kg/cm ² or more, for example, 350 to 600 kg/cm ² , but is necessarily limited thereto. It's not like that. When the tensile strength satisfies the above range, the polyethylene film with a multilayer structure according to an aspect of the present invention has superior mechanical properties, and damage to the film can be further minimized during the commercialization process.

In one aspect of the present invention, the melt index of the first ethylene polymer, second ethylene polymer, and third ethylene polymer may be 0.2 to 10 g/10 min. Specifically, it may be 0.2 to 9 g/10min, more specifically 0.3 to 8 g/10min, and more specifically 0.5 to 3g/10min, but is not necessarily limited thereto. At this time, the melt index means the value measured at 190°C and 2.16 kg according to ASTM D 1238.

In addition, in one aspect of the present invention, the molecular weight distribution of the first ethylene polymer may be 3 to 10, preferably 5 to 9, and the molecular weight distribution of the second and third ethylene polymers may be 1 to 5, Preferably it may be 2 to 4, but is not necessarily limited thereto.

As the first ethylene polymer, the second ethylene polymer, and the third ethylene polymer satisfy the melt index and molecular weight distribution ranges, the polyethylene film with a multilayer structure according to an aspect of the present invention can further improve its processability and mechanical properties. .

In one aspect of the present invention, the total thickness of the multilayer polyethylene film may be 30 to 300 μm. Specifically, it may be 40 to 250 ㎛, more specifically 45 to 200 ㎛, but is not necessarily limited thereto. When the total thickness satisfies the above range, the durability of the multilayer polyethylene film according to one aspect of the present invention can be further improved.

In one aspect of the present invention, the first ethylene polymer, the second ethylene polymer, and the third ethylene polymer may be an ethylene copolymer obtained by polymerizing ethylene and a C3-C18 α-olefin comonomer.

Specifically, the α-olefin comonomer is propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, It may be any one selected from 1-hexadecene and 1-octadecene, or a mixture of two or more thereof. More specifically, the α-olefin comonomer is 1-propylene, 1-butene, 1-hexene, and 1-heptene. and 1-octene, or a mixture of two or more thereof is more preferable in deriving the effect according to the present invention, but is not necessarily limited thereto. Through the use of the above-mentioned α-olefin comonomer, it is possible to produce a high molecular weight ethylene copolymer while imparting fluidity to the ethylene homopolymer, so the multilayer polyethylene film containing it has mechanical properties such as impact resistance and tensile strength. This can be further improved.

In one aspect of the present invention, the content of the α-olefin comonomer contained in 100 parts by weight of the ethylene copolymer may be 1 to 40 parts by weight, preferably 1 to 30 parts by weight, and more preferably 1 to 20 parts by weight. However, it is not necessarily limited to this. When the content of the α-olefin comonomer satisfies the above range, the rigidity and impact resistance of the ethylene polymer can be further improved, and it can be more easily applied alone to molded products such as films, injection, compound, sheet, and blow molding. It can be easy.

In one aspect of the present invention, the first ethylene polymer, the second ethylene polymer, and the third ethylene polymer can be obtained by appropriately selecting a polymerization method. For example, single-polymerization by any one selected from gas-phase polymerization, slurry polymerization, solution polymerization, and high-pressure ionic polymerization using a multi-site catalyst such as a Ziegler-Natta catalyst or a single-site catalyst such as a metallocene-based catalyst as a polymerization catalyst, or these. It may be carried out as a multi-stage polymerization by a combination of, but this is only a non-limiting example and is not necessarily limited thereto.

The above single site catalyst is a catalyst capable of forming uniform active species, and is generally obtained by contacting a compound selected from metallocene-based transition metal compounds and non-metallocene-based transition metal compounds with an activation cocatalyst. Lose.

At this time, single-site catalysts have a more uniform active site structure than multi-site catalysts, allowing polymerization of polymers with high molecular weight and high uniformity, so polymerization using single-site catalysts is preferable, and among single-site catalysts, metallocene-based catalysts are preferred. Polymerization using is more preferable, but is not necessarily limited thereto.

In particular, it is more preferable to obtain the effect according to the present invention that at least one selected from the first ethylene polymer, the second ethylene polymer, and the third ethylene polymer is formed through polymerization using a metallocene catalyst, but it is necessarily limited thereto. It's not like that.

The method for producing a polyethylene film with a multilayer structure according to an aspect of the present invention using the first ethylene polymer, the second ethylene polymer, and the third ethylene polymer is a method that can produce the effect desired by the present invention. is not limited. For example, injection molding method, extrusion molding method, inflation method, T-die method, calendar method, blow molding method, vacuum molding method, pressure molding method, etc. can be used to derive the effect according to the present invention. It is more desirable to use the inflation method, but this is only a non-limiting example and is not necessarily limited to this.

At this time, the multilayer structure can be implemented by laminating once or twice or more, and can also be implemented by co-extrusion using a plurality of extruders, but is not necessarily limited to this. At this time, in the case of co-extrusion, various physical properties of the film can be realized to a higher degree by controlling the number of extruders.

In one aspect of the present invention, a functional layer may be additionally laminated on the outer layer (A).

At this time, the functional layer may include one or two or more layers selected from a barrier coating layer, a top coating layer, and a printing layer, and more specifically, a printing layer, an aluminum deposition layer, an oxygen blocking layer, an impact-reinforcement layer, It may include a heat-resistant reinforcing layer, etc., and specifically, the oxygen blocking layer may be made of ethylene vinyl alcohol (EVOH), etc., and the impact-resistant reinforcing layer may be made of polyamide (PA), polyester, etc., but it is not necessarily limited thereto.

Another aspect of the present invention provides a packaging material manufactured from the above-described multi-layer polyethylene film and a molded article including the same. At this time, the molded products may include ice packs, frozen food packaging bags, frozen food containers, refrigerated food packaging bags, refrigerated food containers, shrink film, heavy packaging film, automatic packaging film, stretch wrap, and bags. .

The packaging material according to one aspect of the present invention has excellent durability and mechanical properties over a wide temperature range, including low temperature, despite continuous temperature changes during the manufacturing process at room temperature, the heat sealing process at high temperature, and the distribution and storage process at low temperature. It can be maintained. Therefore, considering the effects according to the present invention, it is more preferable that the packaging material is applied to molded products used at low temperatures such as ice packs, frozen food packaging bags, frozen food containers, refrigerated food packaging bags, and refrigerated food containers, but this is not limited. This is only an example and is not necessarily limited to this.

The present invention will be described in more detail below based on examples and comparative examples. However, the following Examples and Comparative Examples are only one example to explain the present invention in more detail, and the present invention is not limited by the following Examples and Comparative Examples.

[Physical property measurement method]

(1) Density

Measurements were made according to ASTM D1505 and ASTM D 792. The unit is g/cm3.

(2) Melt Index

Measured at 190°C and 2.16 kg according to ASTM D 1238. The unit is g/10min.

(3) Falling ball impact strength

Measurements were made according to ASTM D 1709.

(4) Tensile strength

Measurements were made according to ASTM D 882. The unit of tensile strength is kg/cm ² .

(5) Cross fractionation chromatography (CFC)

It was measured using a combination of Temperature Rising Elution Fractionation (TREF) and Gel Filtration Chromatography (GPC).

This measurement equipment combines Temperature Rising Elution Fractionation (TREF) and Gel Filtration Chromatography (GPC) to simultaneously analyze the density and molecular weight distribution of polymers according to temperature. The sample extracted through the autosampler was stabilized at 100°C for 60 min and then crystallized at a rate of 0.5min/°C up to 30°C. The temperature for fractionation was raised at 3 ℃ intervals up to 120 ℃, and the analysis was conducted by measuring the density distribution and molecular weight distribution for the injection amount at each temperature increase section and synthesizing the data up to the final temperature. In the calculated two-dimensional graph, continuous linear behavior and discontinuous point distribution mean the density and molecular weight distribution at the corresponding temperature, respectively. The peak position was derived and utilized from the density data of the multilayer resin, and the weight average molecular weight was derived and utilized from the molecular weight data.

(6) Weight average molecular weight

This is the molecular weight equivalent to polystyrene analyzed by GPC (gel permeation chromatograph).

It was measured using gel filtration chromatography (GPC) in the cross-fraction chromatography measurement device.

- Column: Graphite column

- Solvent: TCB (Trichlorobenzene)

- Flow rate: 1.0 ml/min

- Sample concentration: 1.0 mg/ml

- Injection volume: 200 ㎕

- Column temperature: 160 ℃

- Detector: IR5 detector

- Standard: Polystyrene (corrected with cubic function)

(7) Melting point

Using a differential scanning calorimeter (DSC, Q20, TA instrument), the melting point was measured while increasing the temperature from -50°C to 200°C at a rate of 10°C/min in a N ₂ environment.

[Example 1]

As the resin for the outer layer (A), the first ethylene polymer [density: 0.957 g/cm ³ , melting point 131 ℃, melt index: 1.0 g/10 min (190 ℃, 2.16 kg), YUZEX 7302, SK geo centric] was used. And, as the resin for the middle layer (B), a second ethylene polymer [density: 0.913 g/cm ³ , melting point 119°C, MI: 0.8 g/10 min (190°C, 2.16kg), BO1401, DL Chemicals] was used. , a third ethylene polymer [density: 0.885 g/cm ³ , melting point 74°C, MI: 1.0 g/10 min (190°C, 2.16kg), Supreme 891, SK geo centric] was used as the resin for the inner layer (C). did. The above resin was co-extruded through blown film molding while controlling the processing temperature for each layer from 165 ℃ to 195 ℃ using a total of 3 extruders with a screw size of 24 pi, so that the layer composition of the film was (A)/(B)/( C) A polyethylene film with a three-layer structure was formed. At this time, the die diameter was 50 mm, the die gap was 0.7 mm, the bubble expansion ratio during film production was 2.6:1, and the cooling line cooled by air was 12 cm high based on the die. The cooled and solidified film was pulled by a nip roller and wound into a film roll. The thickness of each layer and the total thickness of the film were 17㎛/68㎛/17㎛ (total 102㎛).

The physical properties of the obtained polyethylene multilayer film are shown in Table 1 below.

[Example 2]

In Example 1, polyethylene (Yuzex 8300, SK geocentric) with a density of 0.963 g/cm ³ , melting point of 132°C, and MI: 0.7 g/10 min (190°C, 2.16kg) was used as the resin for the outer layer (A). And, as the resin for the inner layer (C), polyethylene (Supreme 894, SK geocentric) with a density of 0.890 g/cm ³ , melting point of 85°C, and MI: 3.5 g/10 min (190°C, 2.16kg) was used. The thickness of each layer and the total thickness were 16 ㎛/43 ㎛/16 ㎛ (total 75 ㎛), and except for this, it was manufactured in the same manner as in Example 1. The physical properties of the obtained polyethylene multilayer film are shown in Table 1 below.

[Example 3]

In Example 1, the resin for the intermediate layer (B) was polyethylene (BO1401, DL Chemicals) with a density of 0.913 g/cm ³ , a melting point of 119°C, and an MI: 0.8 g/10 min (190°C, 2.16kg) and metal. It was prepared in the same manner as in Example 1, except that a resin mixture of Rosen-polyethylene (Dow, INNATE™ TH60) at a weight ratio of 9:1 was used. As a result, it was confirmed that it exhibited similar physical properties to Example 1.

[Comparative Example 1]

In Example 1, polyethylene (Smart 151S, SK geo centric) with a density of 0.915 g/cm ³ , melting point of 116°C, and MI: 1.0 g/10 min (190°C, 2.16kg) was used as the resin for the middle layer (B). It was prepared in the same manner as Example 1 except for what was used.

The physical properties of the obtained polyethylene multilayer film are shown in Table 1 below.

[Comparative Example 2]

In Example 1, polyethylene (Yuzex 8300, SK geocentric) with a density of 0.963 g/cm ³ , melting point of 132°C, and MI: 0.7 g/10 min (190°C, 2.16kg) was used as the resin for the outer layer (A). And, as the resin for the middle layer (B), polyethylene (Yuclair FN435, SK geocentric) with a density of 0.919 g/cm ³ , melting point of 121°C, and MI: 1.2 g/10 min (190°C, 2.16kg) was used. The thickness of each layer and the total thickness were 20 ㎛/52 ㎛/20 ㎛ (total 92 ㎛), and except for this, it was manufactured in the same manner as in Example 1.

The physical properties of the obtained polyethylene multilayer film are shown in Table 1 below.

[Comparative Example 3]

In Example 1, polyethylene (Smart 151, SK geocentric) with a density of 0.915 g/cm ³ , melting point of 114°C, and MI: 1.0 g/10 min (190°C, 2.16kg) was used as the resin for the inner layer (C). It was prepared in the same manner as Comparative Example 1 except that.

The physical properties of the obtained polyethylene multilayer film are shown in Table 1 below.

	Example 1	Example 2	Comparative Example 1	Comparative example 2	Comparative Example 3
Outer layer (A) density/melt index (thickness)	0.957/1.0 (17㎛)	0.963/0.7 (16㎛)	0.957/1.0 (17㎛)	0.963/0.7 (20㎛)	0.957/1.0 (17㎛)
Middle layer (B) density/melt index (thickness)	0.913/0.8 (68㎛)	0.913/0.8 (43㎛)	0.915/1.0 (68㎛)	0.919/1.2 (52㎛)	0.915/1.0 (68㎛)
Inner layer (C) density/melt index (thickness)	0.885/1.0 (17㎛)	0.890/3.5 (16㎛))	0.885/1.0 (17㎛)	0.885/1.0 (20㎛)	0.915/1.0 (17㎛)
Inner layer melting point (℃)	74	85	74	74	114
Melting point difference between outer/inner layers (℃)	57	47	57	58	17
Peak position between 88 and 100 ℃ on CFC of middle layer resin (℃)	91	91	-	92	-
Peak position between 40 and 75 ℃ on CFC of middle layer resin (℃)	63	63	69	-	69
Weight average molecular weight (Mw, g/mol) between 40 and 75 ℃ on CFC of middle layer resin	134,000	134,000	78,000	76,000	78,000
Falling ball impact strength per unit thickness (gf/㎛)	23	26	7	2	10
Tensile StrengthMD/TD (kg/cm 2 )	473/477	473/437	530/523	381/293	392/299

As shown in Table 1, the multilayer film of the example according to the present invention satisfies a specific range of physical properties measured from cross-fraction chromatography when compared to the comparative example using a polyethylene resin with similar density and melt index. , it was confirmed that the falling ball impact strength was significantly improved. In addition, it was confirmed that in the physical property range where the falling ball impact strength is 15 gf/㎛ or more, it is suitable for use as a packaging material, as almost no damage occurs in frozen or low temperature conditions, such as ice packs. In addition, it was found that the multilayer film had excellent mechanical properties due to its excellent tensile strength, and that its sealing properties were also excellent at low temperatures.

Accordingly, it was confirmed that by using polyethylene as a single material, recycling is not only easy, but also its utility can be expanded by maintaining or further improving mechanical properties such as impact resistance.

On the other hand, as shown in Comparative Examples 1 and 2, there is no peak between 88 and 100 ° C and no peak between 40 and 75 ° C on cross fractionation chromatography (CFC) of the polyethylene resin used in the middle layer. In cases where the weight average molecular weight in the range of 40 to 75 ℃ does not meet the range of 90,000 g/mol or more, it was confirmed that the falling ball impact strength per unit thickness was significantly reduced.

In addition, as shown in Comparative Example 3, if the difference in melting point (melt temperature) between the inner layer and the outer layer does not satisfy the range of 20 ℃ or more, sealing is not good when manufacturing a multilayer film, and sealing is not maintained at low temperatures and bursting occurs. It was confirmed that problems such as

The polyethylene multilayer film according to one aspect of the present invention is a packaging material for packaging liquid, powder, and solid contents, and can be applied to fields that require strength against internal or external impacts during manufacturing, distribution, and sales. Specifically, it can be applied to ice packs, frozen food packaging bags, frozen food containers, refrigerated food packaging bags, refrigerated food containers, shrink film, heavy packaging film, automatic packaging film, stretch wrap, and bags.

As described above, the present invention has been described with specific details and limited embodiments, but these are provided only to facilitate a more general understanding of the present invention, and the present invention is not limited to the above embodiments, and the field to which the present invention pertains is not limited to the above embodiments. Those skilled in the art can make various modifications and variations from this description.

Accordingly, the spirit of the present invention should not be limited to the described embodiments, and the scope of the patent claims described later as well as all things that are equivalent or equivalent to the scope of this patent claim shall fall within the scope of the spirit of the present invention. .

Claims (17)

1. As a multilayer film containing polyethylene as its main ingredient,

   A polyethylene multilayer film comprising polyethylene A satisfying the following physical properties (1) to (2) in at least one layer, and having a melt temperature difference of 20° C. or more between the first surface layer (outer layer) and the second surface layer (inner layer).

   (1) On cross fractionation chromatography (CFC), at least one peak exists between 88 and 100 °C, at least one peak exists between 40 and 75 °C, and the weight ranges from 40 to 75 °C. Average molecular weight is over 90,000 g/mol

   (2) The melt index measured at 190°C and 2.16kg according to ASTM D1238 is 0.2 to 10 g/10min.
2. According to clause 1,

   The polyethylene A is a polyethylene multilayer film that satisfies the following physical properties (3).

   (3) Density according to ASTM D1505 of 0.890 to 0.925 g/cm3
3. According to clause 1,

   A polyethylene multilayer film comprising the polyethylene A alone or a resin mixture of polyethylene A and metallocene-polyethylene in the at least one layer.
4. According to clause 3,

   A polyethylene multilayer film comprising more than 70% by weight of polyethylene A alone or the resin mixture.
5. According to clause 3,

   The resin mixture is a polyethylene multilayer film having a content of polyethylene A of 10 or more to less than 100% by weight.
6. According to clause 1,

   The polyethylene multilayer film is a polyethylene multilayer film having a falling ball impact strength per unit thickness of 15 gf/㎛ or more according to ASTM D1709.
7. According to clause 1,

   The polyethylene multilayer film is a polyethylene multilayer film with a total thickness of 30 to 300 ㎛.
8. According to clause 3,

   The polyethylene A and metallocene-polyethylene are polyethylene multilayer films that are ethylene copolymers obtained by polymerizing ethylene and C3-C18 α-olefin comonomers.
9. According to clause 8,

   A polyethylene multilayer film wherein the α-olefin comonomer is one or a mixture of two or more selected from 1-propylene, 1-butene, 1-hexene, 1-heptene, and 1-octene.
10. According to clause 1,

    The polyethylene multilayer film is a polyethylene multilayer film that is laminated at least two layers including a layer containing the polyethylene A.
11. According to clause 1,

    The polyethylene multilayer film is a polyethylene multilayer film in which at least three layers are laminated, including a layer containing the polyethylene A.
12. According to clause 1,

    A polyethylene multilayer film comprising a functional layer on the surface layer of the polyethylene multilayer film.
13. According to clause 12,

    The functional layer is a polyethylene multilayer film comprising one or two or more layers selected from a barrier coating layer, a top coating layer, and a printing layer.
14. A packaging material comprising the polyethylene multilayer film of any one of claims 1 to 13.
15. Molded article comprising packaging material according to claim 14.
16. According to clause 15,

    The molded product is any one selected from ice packs, frozen food packaging bags, frozen food containers, refrigerated food packaging bags, refrigerated food containers, shrink film, heavy packaging film, automatic packaging film, stretch wrap, and bags. .
17. According to clause 15,

    The molded product is a packaging material for packaging liquid, powder, and solid contents, and is used in fields that require strength against internal or external impacts during manufacturing, distribution, and sales.