KR102620810B1 - Biaxially Oriented High-density Polyethylene Film with an Excellent Heat-Sealable and Method for Manufacturing by Thereof - Google Patents

Abstract

It is a base film for industrial coating, printing, lamination, and sealables. It uses an adhesion promoter to improve adhesive strength, minimizes heat shrinkage to improve heat resistance, and uses masterchip, an anti-blocking masterbatch, to make it easy to process. A biaxially stretched high-density polyethylene film and its manufacturing method are disclosed. The disclosed biaxially stretched high-density polyethylene film with improved thermal adhesiveness includes a thermal adhesive layer including linear low-density polyethylene, polyolefin elastomer, and a master chip; A bonding layer containing polyolefin elastomer and ethylene vinyl acetate on the upper surface of the heat sealing layer; A first core layer containing 100 wt% of high-density polyethylene on the upper surface of the bonding layer; A second core layer containing 100 wt% of high-density polyethylene on the upper surface of the first core layer; and a surface layer including high-density polyethylene and a master chip on the upper surface of the second core layer.

Description

Biaxially oriented high-density polyethylene film with improved heat sealability and method for manufacturing the same {Biaxially Oriented High-density Polyethylene Film with an Excellent Heat-Sealable and Method for Manufacturing by Thereof}

The present invention relates to a biaxially stretched high-density polyethylene film with improved thermal adhesion and a manufacturing method thereof. Specifically, it is a base film that can be applied to industrial coatings, flexible packaging printing and laminating, and sealables, and has improved thermal adhesion. It relates to a biaxially stretched high-density polyethylene film and a method of manufacturing the same.

Recently, as society has changed, a variety of packaging materials such as industrial packaging materials and flexible packaging materials have been developed, ranging from electrical and electronic products to daily necessities.

Polyolefin, a single material, is light and hard, and has excellent physical properties such as heat resistance and chemical resistance, so it is widely used in packaging materials. In particular, polyolefin is becoming a widespread issue as an eco-friendly packaging material as the possibility of recycling after product use is emphasized.

Biaxially stretched polyethylene, one of the polyolefins, has superior tensile strength compared to non-stretched polyethylene, is eco-friendly as it does not emit harmful substances, and has excellent moisture barrier performance compared to other materials, so it has the potential to be used as a flexible packaging material. high.

In particular, low-density polyethylene not only has low density and crystallinity, but also has excellent flexibility and toughness, so it is widely used as a sealant film for packaging materials. However, even if the film is manufactured by biaxially stretching low-density polyethylene, it can be used for industrial coating, flexible packaging printing, and lamination. There are shortcomings in its use in terms of processability, heat resistance, and thermal adhesiveness.

In order to improve the thermal adhesiveness of the film during the manufacturing process of flexible packaging, adhesives or other resins are coated or laminated on the polyolefin film to provide thermal adhesiveness. However, there is a problem in that it is difficult to maintain the desired level of adhesion of the film only by coating with adhesives or other resins. In addition, the lamination method improves thermal adhesiveness, but is economically inefficient because the cost of the final film increases due to the complicated process.

Even if adhesion is improved by coating or laminate, the surface friction coefficient of the base film increases, making processing difficult.

Therefore, there is a need to develop packaging materials that are eco-friendly and recyclable by minimizing additives, and have excellent processability, heat resistance, and thermal adhesiveness.

Public Patent Publication 10-2011-0077864 (Published on July 7, 2011)

The present invention was created in consideration of the above-mentioned points, and includes a heat sealing layer including linear low-density polyethylene, polyolefin elastomer, and a master chip; A bonding layer containing polyolefin elastomer and ethylene vinyl acetate on the upper surface of the heat sealing layer; A first core layer containing 100 wt% of high-density polyethylene on the upper surface of the bonding layer; a second core layer containing 100 wt% of high-density polyethylene on the upper surface of the first core layer; and a surface layer containing high-density polyethylene and a master chip on the upper surface of the second core. It is a multi-layered film that is based on high-density polyethylene, minimizes additives, etc., is environmentally friendly and recyclable, improves thermal bonding strength, and improves heat bonding strength at high temperatures. The purpose is to provide a biaxially stretched high-density polyethylene film that can minimize thermal contraction rate and a method for manufacturing the same.

In order to achieve the above object, the biaxially stretched high-density polyethylene film with improved thermal adhesiveness according to the present invention includes a thermal adhesive layer containing linear low-density polyethylene, polyolefin elastomer, and a master chip; A bonding layer containing polyolefin elastomer and ethylene vinyl acetate on the upper surface of the heat sealing layer; A first core layer containing 100 wt% of high-density polyethylene on the upper surface of the bonding layer; a second core layer containing 100 wt% of high-density polyethylene on the upper surface of the first core layer; and a surface layer including high-density polyethylene and a master chip on the upper surface of the second core layer.

The thermal bonding layer is characterized in that it contains 30 to 50 wt% of linear low density polyethylene, 45 to 65 wt% of polyolefin elastomer, and 3 to 10 wt% of master chip based on the total weight percent.

The bonding layer is characterized in that it contains 50 to 70 wt% of polyolefin elastomer and 30 to 50 wt% of ethylene vinyl acetate based on the total weight percent.

The ethylene vinyl acetate has a density of 0.93 to 0.95 g/cm3, a melt index (MI) of 1 to 6, and the ethylene vinyl acetate contains 12 to 18 wt% of vinyl acetate based on the total weight%.

The surface layer is characterized in that it contains 95 to 99 wt% of high-density polyethylene and 1 to 5 wt% of master chip based on the total weight percent.

The master chip is characterized in that it contains 5 to 10 wt% of at least one selected from silica, synthetic silica, zeolite, calcium carbonate, and PMMA.

The thickness of the heat sealing layer is 1 to 2 ㎛, the thickness of the bonding layer is 2 to 4 ㎛, the thickness of the second core layer is 2 to 3 ㎛, and the thickness of the surface layer is 1 to 2 ㎛. Do it as

The biaxially stretched high-density polyethylene film is manufactured by stretching 4 to 5 times in the longitudinal direction and 9 to 11 times in the transverse direction.

The biaxially stretched high-density polyethylene film is characterized by a sealing start temperature of 90°C or lower.

The biaxially stretched high-density polyethylene film is characterized by an adhesive strength of 5.0 or more.

The biaxially stretched high-density polyethylene film is characterized in that the heat shrinkage rate is 3% or less in both the longitudinal and transverse directions after heating with hot air at 100 ° C. to 120 ° C. for 5 to 15 minutes.

The biaxially stretched high-density polyethylene film is used as a base film for industrial coating, printing and lamination of flexible packaging materials, and sealables.

In the method of manufacturing a biaxially stretched high-density polyethylene film, at least one of high-density polyethylene, linear low-density polyethylene, polyolefin elastomer, and master chip is melt-extruded at 210 to 250°C, and then formed into a multilayer of at least three layers through T-Die. Discharging and rapidly cooling to 70°C or lower using a casting roll to produce an unstretched sheet; First stretching the unstretched sheet 4 to 5 times in the longitudinal direction at 120 to 125°C; Secondary stretching the first stretched film 9 to 11 times in the transverse direction at 125 to 130°C; and heat-treating the secondarily stretched film at 125 to 135° C. in a heat treatment zone.

In the step of manufacturing the unstretched sheet, the multilayer includes a heat adhesive layer containing 30 to 50 wt% of linear low-density polyethylene, 45 to 65 wt% of polyolefin elastomer, and 3 to 10 wt% of master chip; A bonding layer containing 50 to 70 wt% of polyolefin elastomer and 30 to 50 wt% of ethylene vinyl acetate on the upper surface of the heat sealing layer; A first core layer containing 100 wt% of high-density polyethylene on the upper surface of the bonding layer; a second core layer containing 100 wt% of high-density polyethylene on the upper surface of the first core layer; And a surface layer containing 95 to 99 wt% of high-density polyethylene and 1 to 5 wt% of a master chip on the upper surface of the second core layer.

In the first stretching step, the heat-sealing layer is stretched in the longitudinal direction at 110 to 115°C, which is 10°C lower than the stretching temperature of the surface layer.

In the primary stretching step, the longitudinal primary stretching uses a coated stretching roll, and the arrangement of the coated stretching roll maximizes contact while the unstretched sheet wraps around the coated stretching roll. , characterized in that a wrap angle of 180°C or more is maintained to prevent the unstretched sheet from slipping.

In the coated stretching roll, the coating material includes polytetrafluoroethylene, and the density of the polytetrafluoroethylene is 2.13 to 2.20 g/cc.

The biaxially stretched high-density polyethylene film manufacturing method is characterized by minimizing contamination and enabling long-term production.

The biaxially stretched high-density polyethylene film with improved thermal adhesiveness according to the present invention includes a thermal adhesive layer containing linear low-density polyethylene, polyolefin elastomer, and a master chip; A bonding layer containing polyolefin elastomer and ethylene vinyl acetate on the upper surface of the heat sealing layer; A first core layer containing 100 wt% of high-density polyethylene on the upper surface of the bonding layer; a second core layer containing 100 wt% of high-density polyethylene on the upper surface of the first core layer; and a surface layer containing high-density polyethylene and a master chip on the upper surface of the second core, making it environmentally friendly and recyclable by minimizing additives, and lowering the coefficient of friction to reduce surface roughness and prevent sticking. It is easy to process, has excellent heat resistance by minimizing heat shrinkage at high temperatures, and provides significantly improved heat adhesiveness.

The method for manufacturing a biaxially stretched high-density polyethylene film according to the present invention includes at least one of high-density polyethylene, linear low-density polyethylene, polyolefin elastomer, ethylene vinyl acetate, and master chip, and is melt-extruded at 210 to 250°C and then extruded through T-Die. Manufacturing an unstretched sheet by discharging it in at least 4 or more layers and rapidly cooling it to 70°C or lower using a casting roll; First stretching the unstretched sheet 4 to 5 times in the longitudinal direction at 120 to 125°C; Secondary stretching the first stretched film 9 to 11 times in the transverse direction at 125 to 130°C; and heat-treating the secondarily stretched film at 125 to 135° C. in a heat treatment zone, thereby providing good productivity and excellent thickness deviation and smoothness.

Figure 1 is a flowchart of a biaxially stretched high-density polyethylene film manufacturing process according to an embodiment of the present invention.
Figure 2 shows a biaxially stretched high-density polyethylene film manufacturing process according to an embodiment of the present invention.
Figure 3 shows a coated roll arrangement during longitudinal stretching according to an embodiment of the present invention.
Figure 4 shows the stress of a biaxially stretched high-density polyethylene film according to an embodiment of the present invention.
Figure 5 shows a biaxially stretched high-density polyethylene film according to an embodiment of the present invention.

All terms described in this specification are general terms that are currently widely used in consideration of the functions of the present invention, but these may vary depending on the intention of a person skilled in the art, custom, or the emergence of new technology. Additionally, if the inventor specifies any term in the present invention, its meaning will be described in the description of the invention. Therefore, the terms used in the present invention should not be interpreted simply as the names of the terms, but should be interpreted based on the actual meaning of the term and the overall content described in the description of the present invention.

Hereinafter, a biaxially stretched high-density polyethylene film with improved thermal adhesiveness according to an embodiment of the present invention and a method for manufacturing the same will be described in detail with reference to the attached drawings. In order to clearly explain the present invention in the drawings, parts not related to the description are omitted, and the same reference numerals are used for identical or similar components throughout the specification.

The present invention provides a biaxially stretched high-density polyethylene film with improved thermal adhesiveness.

The biaxially stretched high-density polyethylene film with improved thermal adhesiveness according to an embodiment of the present invention includes a thermal adhesive layer containing linear low-density polyethylene, polyolefin elastomer, and a master chip; A bonding layer containing polyolefin elastomer and ethylene vinyl acetate on the upper surface of the heat sealing layer; A first core layer containing 100 wt% of high-density polyethylene on the upper surface of the bonding layer; a second core layer containing 100 wt% of high-density polyethylene on the upper surface of the first core layer; and a surface layer including high-density polyethylene and a master chip on the upper surface of the second core layer. That is, the biaxially stretched high-density polyethylene film may be a multilayer film in which three or more layers are stacked. Therefore, the layers of the biaxially stretched high-density polyethylene film may be composed of various layers, such as 3 to 7 layers. In the present invention, 'upper surface' means the upper surface.

The biaxially stretched high-density polyethylene film of the present invention includes a heat sealing layer. The heat sealing layer may act as a sealing surface. The thermal adhesive layer may include linear low-density polyethylene, polyolefin elastomer, and master chip to improve thermal adhesive strength and processability. Therefore, the heat sealing layer may include 30 to 50 wt% of linear low-density polyethylene, 45 to 65 wt% of polyolefin elastomer, and 3 to 10 wt% of master chip based on the total weight percent. As another example, the heat sealing layer may include 35 to 45 wt% of linear low-density polyethylene, 50 to 60 wt% of polyolefin elastomer, and 5 to 7 wt% of master chip based on the total weight percent.

Additionally, the thickness of the heat sealing layer may be 1 to 2 ㎛ relative to the total thickness of the film, but may be more preferably 1.5 ㎛. Therefore, when the thickness of the thermal adhesive layer is less than 1㎛, thermal adhesive strength can be reduced. In addition, when the thickness of the heat sealing layer exceeds 2㎛, the physical properties such as strength and heat resistance of the film of the present invention can be reduced by reducing the thickness of the core layer.

The linear low-density polyethylene may be included in the heat sealing layer. Polyethylene is a lightweight and durable thermoplastic resin with a variety of crystal structures. Therefore, polyethylene can be used in various fields such as films, tubes, plastic parts, and laminates. In addition, the polyethylene is a polyolefin-based polymer and is classified into low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE), ultra-high molecular weight polyethylene (UHMWPE), and cross-linked polyethylene (PEX or XPLE) depending on density and branching. can be classified.

Additionally, the linear low-density polyethylene can be produced by polymerizing ethylene, 1-butene, and a small amount of 1-hexene and 1-octene using a metallocene catalyst. The linear low-density polyethylene has a linear skeleton with short and uniform branches, unlike the long branches of low-density polyethylene. Therefore, the linear low-density polyethylene has similar strength to high-density polyethylene, but has high impact strength, is very flexible, and can improve chemical resistance. Additionally, the linear low-density polyethylene can be used as an adhesion promoter. Adhesion promoters can promote adhesion between laminated layers under stress treatment conditions required for biaxial orientation as a film. Another advantage of adhesion promoters is that they allow longitudinal stretching (MD) at low temperatures without stress-induced separation of the laminated layers. Specifically, because stretching the film at a low temperature causes greater orientation than stretching it at a high temperature, the orientation of the film can be increased at a low longitudinal stretching (MD) temperature by using linear low-density polyethylene, an adhesion promoter, and thus energy It can be efficient in some respects.

Therefore, the linear low-density polyethylene may contain 30 to 50 wt% based on the total weight% of the heat sealing layer. As another example, the linear low-density polyethylene may contain 35 to 45 wt % based on the total weight % of the heat sealing layer. If the content of the linear low-density polyethylene is less than 30 wt%, the processability and workability of the heat sealing layer may be reduced, and it may be difficult to increase the orientation of the film at a low longitudinal stretching temperature. In addition, when the content of the linear low-density polyethylene exceeds 50 wt%, the heat adhesive strength may be reduced by reducing the content of other components.

Additionally, the density of the linear low-density polyethylene may be 0.91 g/cm3 to 0.94 cm3. In addition, when the density of the linear low-density polyethylene is less than 0.91 g/cm3, the processability and workability of the heat sealing layer may be reduced. In addition, even when the density of the linear low-density polyethylene is more than 0.94 cm3, longitudinal stretching may be difficult at low temperatures, and flexibility may also be reduced. In addition, as an adhesion promoter, it may be preferable that the density of the linear low-density polyethylene is lower than the density of the high-density polyethylene, which is the core layer. In addition, the linear low-density polyethylene may preferably have higher flexibility and lower crystallinity than the high-density polyethylene that is the core layer.

The polyolefin elastomer may be included in the heat sealing layer. The polyolefin elastomer can improve the thermal adhesiveness of the film of the present invention. The polyolefin elastomer is a type of very low density polyethylene (VLDPE) and can be manufactured by polymerizing ethylene, 1-butene, and small amounts of 1-hexene and 1-octene using a metallocene catalyst. The polyolefin elastomer has high impact strength, is very flexible, and can improve chemical resistance. Additionally, the polyolefin elastomer can be used as an adhesion promoter. That is, the adhesion promoter can promote adhesion and thermal bonding between laminated layers under stress treatment conditions required for biaxial orientation such as a film.

Therefore, the polyolefin elastomer may contain 45 to 65 wt% based on the total weight% of the heat sealing layer. As another example, the polyolefin elastomer may contain 50 to 60 wt % based on the total weight % of the heat sealing layer. If the content of the polyolefin elastomer is less than 45 wt%, thermal adhesive strength may be reduced, and it may be difficult to increase the orientation of the film at a low longitudinal stretching temperature. In addition, if the content of the polyolefin elastomer exceeds 65 wt%, the content of other components may be reduced, thereby reducing the workability and processability of the heat sealing layer.

Additionally, the polyolefin elastomer may have a density of less than 0.90 g/cm3. Additionally, as an adhesion promoter, it may be preferable that the density of the polyolefin elastomer is lower than the density of high-density polyethylene, which is the core layer. Additionally, it may be desirable for the polyolefin elastomer to have higher flexibility and lower crystallinity than high-density polyethylene, which is the core layer.

The master chip may be included in a thermal adhesive layer. The master chip can improve the processability of the film of the present invention. In other words, the master chip can lower the coefficient of friction and smooth the surface of the film, making it easier to process. In addition, the master chip is an anti-blocking masterbatch, which prevents the film of the present invention from sticking or twisting and makes it easy to process.

The master chip, which is a polyethylene masterbatch chip, may include inorganic particles or organic particles. That is, the master chip is a resin obtained by adding the inorganic particles or organic particles to polyethylene resin and dispersing the compound. The master chip may contain 5 to 10 wt% of at least one of silica, synthetic silica, zeolite, calcium carbonate, and PMMA (Methyl Methacrylate) as inorganic particles and/or organic particles. When the inorganic particles are silica-based, the average particle diameter may be 10㎛ or less, but more preferably 5㎛ or less, which makes it easier to process the film. The zeolite is a microporous aluminum silicate mineral that is mainly used as an adsorbent or catalyst. Using the very regularly arranged micropores present in the zeolite structure, small gas or liquid molecules can be selectively separated according to size and shape. The PMMA is an acrylic cross-linked resin that is made in the form of a bead and has good transparency and weather resistance, so it can be easily adhered and printed.

Therefore, the master chip may contain 3 to 10 wt% of the total weight% of the heat sealing layer. As another example, the master chip may contain 5 to 7 wt% of the total weight of the heat sealing layer. If the content of the master chip is less than 3wt%, the friction coefficient is high, making it difficult to process the film of the present invention. In addition, if the content of the master chip exceeds 10 wt%, processing may be easy, but it may cause a decrease in the content of other components and reduce transparency, etc.

The biaxially stretched high-density polyethylene film of the present invention includes a bonding layer on the upper surface of the heat sealing layer. The bonding layer may include polyolefin elastomer and ethylene vinyl acetate. The bonding layer may include 50 to 70 wt% of polyolefin elastomer and 30 to 50 wt% of ethylene vinyl acetate based on the total weight percent. Hereinafter, detailed descriptions of overlapping components will be omitted.

Additionally, the thickness of the bonding layer may be 2 to 4 ㎛ relative to the total thickness of the film, but may be more preferably 2.5 to 3 ㎛. Therefore, when the thickness of the bonding layer is less than 2㎛, adhesion between laminated layers can be reduced. In addition, when the thickness of the heat sealing layer is more than 4㎛, the physical properties such as strength and heat resistance of the film of the present invention can be reduced by reducing the thickness of other layers.

The polyolefin elastomer may be included in the bonding layer. The polyolefin elastomer has high impact strength, is very flexible, and can improve chemical resistance. Additionally, the polyolefin elastomer can improve the thermal adhesiveness of the film of the present invention. That is, the polyolefin elastomer can be used as an adhesion promoter. Adhesion promoters can promote adhesion and thermal bonding between laminated layers under stress treatment conditions required for biaxial orientation as a film.

Therefore, the polyolefin elastomer may contain 50 to 70 wt% based on the total weight% of the bonding layer. If the content of the polyolefin elastomer is less than 50wt%, thermal adhesive strength and flexibility for high impact strength may be reduced, and it may be difficult to increase the orientation of the film at a low longitudinal stretching temperature. In addition, when the content of the polyolefin elastomer exceeds 70 wt%, the content of other components may be reduced, thereby reducing the adhesion between laminated layers.

Additionally, the polyolefin elastomer may have a density of 0.90 g/cm3 or less. Additionally, it may be desirable for the polyolefin elastomer to have higher flexibility and lower crystallinity than high-density polyethylene, which is the core layer.

The ethylene vinyl acetate may be included in the bonding layer. That is, when the polyolefin elastomer, which is a low melting point polyethylene resin, is co-extruded on the heat sealing layer, which is one side of the biaxially stretched high-density polyethylene film of the present invention, the compatibility between the high-density polyethylene, which is the core layer described below, and the polyolefin elastomer is low, and when co-extruded Adhesion between layers is incomplete, so desirable thermal adhesive strength cannot be obtained. Therefore, in order to improve adhesion between these layers, ethylene vinyl acetate may be included in the bonding layer.

Additionally, the structure of ethylene vinyl acetate (EVA) is as follows.

[Formula 1: Ethylene vinyl acetate (EVA)]

Ethylene vinyl acetate (EVA) is a copolymer of ethylene and vinyl acetate, and is an extremely elastic and tough thermoplastic resin with excellent transparency and gloss, almost no odor, and may contain 12 to 18 wt% of vinyl acetate. The ethylene vinyl acetate (EVA) has the following characteristics: low cost, excellent adhesion to many polar and non-porous substrates, excellent bending resistance and puncture resistance, and excellent waterproofing effect. Therefore, the ethylene vinyl acetate (EVA) can be copolymerized with other resins such as low-density polyethylene, linear low-density polyethylene, etc. or can be used as part of a multilayer film.

Therefore, the ethylene vinyl acetate may contain 30 to 50 wt% based on the total weight% of the bonding layer. If the content of ethylene vinyl acetate is less than 30 wt%, adhesion between laminated layers may be reduced. If the content of ethylene vinyl acetate is more than 50 wt%, the content of polyolefin elastomer may be reduced, thereby reducing heat adhesive strength.

Additionally, the density of the ethylene vinyl acetate may be 0.93 to 0.95 g/cm3, and the melt index may be 1 to 6. If the density is less than 0.93 g/cm3, adhesion between laminated layers may be reduced, and even if it is more than 0.95 g/cm3, stretchability may be reduced due to high density. If the melt index is less than 1, the extrusion load may increase, and if it is more than 6, it may cause insufficient extensibility.

The biaxially stretched high-density polyethylene film of the present invention includes a first core layer on the upper surface of the bonding layer. Polyethylene is a thermoplastic resin that is lightweight and has excellent durability with a variety of crystal structures. Therefore, polyethylene can be used in various fields such as films, tubes, plastic parts, and laminates. In addition, the polyethylene is a polyolefin-based polymer and is classified into low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE), ultra-high molecular weight polyethylene (UHMWPE), and cross-linked polyethylene (PEX or XPLE) depending on density and branching. can be classified.

The high-density polyethylene may be included in the first core layer at 100 wt%. Additionally, the thickness of the first core layer may be 14 μm to 49 μm or 20 to 24 μm relative to the entire thickness of the film. If the thickness of the first core layer is less than 14㎛, the physical properties such as heat resistance and transparency of the film of the present invention may be reduced. In addition, if the thickness of the first core layer exceeds 49㎛, the thickness of other layers may be reduced, which may reduce the thermal adhesive strength and processability of the film of the present invention.

In addition, the high-density polyethylene is a thermoplastic resin with a linear structure or a low level of short branches, and can improve heat resistance and chemical resistance by preventing heat shrinkage of the film of the present invention. In addition, the high-density polyethylene has a relatively low impact strength compared to low-density polyethylene, but has low elongation and excellent tensile strength, so it can be easily processed. That is, the high-density polyethylene has a good modulus and the surface of the film is stiff, making it easy to process.

In addition, the density of the high-density polyethylene may be 0.94 to 0.96 g/cm3, and the melt index (MI) may be 0.5 to 6, preferably 0.5 to 2, and more preferably 1 to 1.5. In the present invention, the melt index is expressed as g/10 min. If the density of the high-density polyethylene is less than 0.94 g/cm3, heat resistance may be insufficient, and if the density is greater than 0.96 g/cm, the extensibility may be insufficient. In addition, if the melt index of the high-density polyethylene is less than 0.5, it may cause extrusion load and may be difficult to work with, and if the melt index is more than 6, it may be difficult to form a film due to insufficient extensibility due to high fluidity.

The biaxially stretched high-density polyethylene film of the present invention includes a second core layer on the upper surface of the first core layer. The second core layer may include 100wt% high-density polyethylene. The thickness of the second core layer may be 2 to 3 ㎛ relative to the total thickness of the film, but may be more preferably 2.5 ㎛. If the thickness of the second core layer is less than 2㎛, the thermal adhesive strength and processability of the film of the present invention may be reduced. Additionally, if the thickness of the second core layer is more than 3㎛, physical properties such as heat resistance of the film may be reduced.

The biaxially stretched high-density polyethylene film of the present invention includes a surface layer on the upper surface of the second core layer. The surface layer can act as a printing surface. The surface layer may include high-density polyethylene and a master chip. The surface layer may include 95 to 99 wt% of high-density polyethylene and 1 to 5 wt% of master chip based on the total weight. Additionally, the thickness of the surface layer may be 1 to 2㎛ relative to the total thickness of the film, but may be more preferably 1.5. If the thickness of the surface layer is less than 1㎛, the thermal adhesive force and adhesive strength of the film of the present invention may be reduced. Additionally, if the thickness of the surface layer exceeds 2㎛, heat resistance, etc. may be reduced.

The high-density polyethylene may be included in the surface layer. The high-density polyethylene may contain 95 to 99 wt % based on the total weight % of the surface layer. As another example, the high-density polyethylene may contain 97 to 98 wt % based on the total weight % of the surface layer. Therefore, if the content of high-density polyethylene is less than 95%, heat resistance, etc. may be reduced. Additionally, if the content of the high-density polyethylene exceeds 99 wt%, the content of the master chip, which is an anti-blocking masterbatch, may be reduced, making processing difficult.

In addition, the density of the high-density polyethylene may be 0.94 to 0.96 g/cm3, and the melt index (MI) may be 0.5 to 6, preferably 0.5 to 2, and more preferably 1 to 1.5. If the density of the high-density polyethylene is less than 0.94 g/cm3, heat resistance may be insufficient, and if the density is greater than 0.96 g/cm, the extensibility may be insufficient. In addition, if the melt index of the high-density polyethylene is less than 0.5, it may cause extrusion load and may be difficult to work with, and if the melt index is more than 6, it may be difficult to form a film due to insufficient extensibility due to high fluidity.

The master chip may be included in the surface layer. The master chip can improve the processability of the film of the present invention. In other words, the master chip can lower the coefficient of friction and smooth the surface of the film, making it easier to process. In addition, the master chip is an anti-blocking masterbatch, which prevents the film of the present invention from sticking or twisting and makes it easy to process.

The master chip, which is a polyethylene masterbatch chip, may include inorganic particles or organic particles. That is, the master chip is a resin obtained by adding the inorganic particles or organic particles to polyethylene resin and dispersing the compound. The master chip may contain 5 to 10 wt% of at least one of silica, synthetic silica, zeolite, calcium carbonate, and PMMA (Methyl Methacrylate) as inorganic particles and/or organic particles.

Accordingly, the master chip may contain 1 to 5 wt% based on the total weight% of the heat sealing layer. As another example, the master chip may contain 2 to 3 wt% of the total weight of the heat sealing layer. If the content of the master chip is less than 1 wt%, the friction coefficient is high, making it difficult to process the film of the present invention. In addition, if the content of the master chip exceeds 5wt%, processing may be easy, but it may cause a decrease in the content of other components, thereby reducing transparency, etc.

As such, the thickness of the biaxially oriented high-density polyethylene film of the present invention, which is laminated in multiple layers, may be 20 to 60 μm or 25 to 35 μm, and more preferably 30 μm. In this group, the thickness of the heat sealing layer is 1 to 2 ㎛, the thickness of the bonding layer is 2 to 4 ㎛, the thickness of the second core layer is 2 to 3 ㎛, and the thickness of the surface layer is 1 to 2 ㎛. It can be. Within the above range, the biaxially stretched high-density polyethylene film of the present invention can be suitably used as a base film for industrial coatings, printing and lamination of flexible packaging materials, and sealables.

In addition, the biaxially stretched high-density polyethylene film of the present invention has a heat shrinkage rate of 3% or less in both the longitudinal and transverse directions after heating with hot air at 100 to 120 ° C. for 5 to 15 minutes. In addition, the haze of the biaxially stretched high-density polyethylene film of the present invention is 4.5% or less, and the film adhesive strength is 5.0 or more.

Therefore, the biaxially stretched high-density polyethylene film improves heat resistance by minimizing heat shrinkage, is easy to process by lowering the coefficient of friction, and is an industrial coating composed of multiple layers with excellent heat adhesion by using low-density polyolefin elastomer and ethylene vinyl acetate. , It is a base film for printing and lamination of flexible packaging materials and sealables. In addition, it is a film with improved thermal adhesiveness that minimizes additives and is eco-friendly and recyclable.

The present invention provides a method for producing a biaxially stretched high-density polyethylene film with improved heat resistance and transparency.

Figure 1 is a flowchart of a manufacturing process for a biaxially stretched high-density polyethylene film according to an embodiment of the present invention, Figure 2 shows a manufacturing process for a biaxially stretched high-density polyethylene film according to an embodiment of the present invention, and Figure 3 is a flow chart according to an embodiment of the present invention. Shows the coated roll arrangement during longitudinal stretching.

Referring to Figures 1 and 2, a biaxially stretched high-density polyethylene film with improved thermal adhesiveness according to an embodiment of the present invention can be manufactured in three processes. That is, at least one of high-density polyethylene, linear low-density polyethylene, polyolefin elastomer, ethylene vinyl acetate, and master chip is melt-extruded at 210 to 250°C, and then discharged as a multi-layer of at least three layers through a T-Die, and then cast. Manufacturing an unstretched sheet by rapidly cooling it to 70°C or lower using a roll; First stretching the unstretched sheet 4 to 5 times in the longitudinal direction at 120 to 125°C; Secondary stretching the first stretched film 9 to 11 times in the transverse direction at 125 to 130°C; and heat-treating the secondarily stretched film at 125 to 135° C. in a heat treatment zone.

The step of manufacturing the unstretched sheet includes at least one of high-density polyethylene, linear low-density polyethylene, polyolefin elastomer, ethylene vinyl acetate, and master chip, and melt-extruding the sheet at 210 to 250°C, then forming at least three layers through T-Die. Discharge in the above multiple layers and rapidly cool to 70°C or lower using a casting roll.

That is, a heat sealing layer containing 30 to 50 wt% of the linear low-density polyethylene, 45 to 65 wt% of the polyolefin elastomer, and 3 to 10 wt% of the master chip; A bonding layer containing 50 to 70 wt% of the polyolefin elastomer and 30 to 50 wt% of the ethylene vinyl acetate on the upper surface of the heat sealing layer; A first core layer made solely of the high-density polyethylene on the upper surface of the bonding layer; a second core layer made solely of the high-density polyethylene on the upper surface of the first core layer; and a surface layer containing 95 to 99 wt% of the high-density polyethylene and 1 to 5 wt% of the master chip on the upper surface of the second core layer; are sequentially placed into the hopper of the coextruder and melt-extruded. The melt-extruded resin can be discharged in a plate-shaped form with at least 3 or more layers through a T-Die, and cooled to 70°C or lower and solidified using a casting roll.

During the melt extrusion, the molding material is generally heated and melted using an extrusion molding machine, but the molding resin may be molded in a softened state without heating and melting. The extrusion molding machine used at this time can be any of a single-axis compression molding machine, a twin-axis co-directional or a bi-directional extrusion molding machine, and there is no need to install a ventilation hole, but a single-axis serial random type may be more preferable for uniformity of physical properties. there is. Extrusion conditions are not particularly limited and can be selected depending on each situation. Preferably, the temperature is about 50°C higher than the melting point and decomposition temperature of the resin. Therefore, the extrusion temperature is within the range of 210 ~ 250℃. If it is lower than 210℃, complete melting is impossible and the pressure may increase during extrusion. If it is higher than 250℃, decomposition phenomenon becomes noticeable, sulfurization occurs, and deterioration occurs in the extruder. It may cause foaming, etc.

Additionally, the cooling/solidification can be performed using a metal roll to uniform the thickness of the sheet or improve surface properties. The cooling temperature may be 70°C or lower, preferably 60 to 70°C, and more preferably 65°C. If the cooling temperature exceeds 70°C, the degree of crystallinity of the solidified molding may increase and the stretching suitability may decrease. The cooling rate can be determined within the range of 3 to 200 degrees Celsius.

In the step of first stretching in the machine direction, the unstretched sheet may be stretched 4 to 5 times in the machine direction at 120 to 125°C.

In the first stretching step in the longitudinal direction, longitudinal stretching using the speed difference of rolls is the most common method and is widely used due to its excellent productivity. In other words, longitudinal stretching can be achieved by using the speed difference between the two nip rolls while heating the film, which is fixed and running between at least two nip rolls and guide rolls, in the pressure process of the nip rolls or in the rolls themselves. The stretching temperature is within the range of 120 to 125℃. If the stretching temperature is less than 120℃, stretching may be poor due to insufficient softening. If it exceeds 125℃, crystallization progresses too much and uniform mechanical properties cannot be obtained. . Additionally, if the stretching ratio is less than 4 times, the stretching effect cannot be obtained, and if it is more than 5 times, transverse stretching may become difficult.

Additionally, in the first stretching step in the longitudinal direction, the heat-adhesive layer can be stretched in the longitudinal direction at 110 to 115 °C, which is 10°C lower than the stretching temperature of the surface layer. That is, the thermal bonding layer contains linear low-density polyethylene and polyolefin elastomer as an adhesion promoter, so that longitudinal stretching (MD) can be performed at a low temperature without separation of the laminated layers induced by stress. Specifically, because stretching the film at a low temperature causes greater orientation than stretching it at a high temperature, the orientation of the film can be increased at a low longitudinal stretching (MD) temperature by using linear low-density polyethylene and polyolefin elastomer as adhesion promoters. , it can be efficient in terms of energy.

In addition, as the working time elapses during longitudinal stretching, the degree of contamination of the stretching roll increases, and the gloss of the roll surface decreases and becomes cloudy, which can lead not only to contamination of the film but also to a decrease in productivity. Therefore, one of the ways to solve this problem may be the arrangement of the stretching roll and the coating material of the stretching roll.

That is, referring to FIG. 3, in the primary stretching step, a coated stretching roll is used for the longitudinal primary stretching, and the arrangement of the coated stretching roll is such that the unstretched sheet surrounds the coated stretching roll. While maximizing contact, it is possible to maintain a wrap angle of 180°C or more to prevent the unstretched sheet from slipping. Two nip rolls can be attached to each stretching roll, and stretching is performed between rolls 1 and 2, rolls 3 and 4, and rolls 5 and 6, giving a total of three stretching sections. In the three stretching sections, longitudinal stretching may be performed 4 to 5 times. Additionally, in the coated stretching roll, the coating material is made of polytetrafluoroethylene, and the density of the polytetrafluoroethylene is 2.13-2.20 g/cc. Therefore, due to the arrangement of the stretching roll and the coating material, it is possible to produce a long film with minimal contamination of the film.

In the second stretching step in the transverse direction, the first stretched film may be stretched 9 to 11 times in the transverse direction at 120 to 125°C.

In the step of secondary stretching in the transverse direction, stretching may be carried out not only by conventional methods but also by other methods without limitation, but tenter transverse stretching is the most common. Transverse stretching can be achieved by fixing both ends of the running film with continuously running clips, and gradually increasing the distance between the clips at both ends at an appropriate temperature. The stretching temperature is within the range of 125 to 130°C. If the stretching temperature is less than 125°C, stretching may be difficult due to insufficient softening, and if it is higher than 130°C, the surface may partially dissolve and a uniform thickness cannot be obtained. Additionally, if the stretching ratio is less than 9 times, the transverse mechanical strength is not sufficient, and conversely, if it exceeds 11 times, fracture may occur.

In the heat treatment step, the secondary stretched film can be heat treated at 125 to 135° C. in a heat treatment zone to produce the biaxially stretched high-density polyethylene film of the present invention. The film of the present invention can be heat treated for uniformity such as dimensional stability, heat resistance, and strength. The heat treatment is a common method, but it may be preferable to perform it for 0.5 to 120 seconds at a temperature in the range of 125 to 135°C under the tension, relaxation or limited contraction of the film.

In addition, the heat treatment can be carried out two or more times by changing the conditions within the above range, and the atmosphere can be carried out under general air, argon gas, nitrogen gas, or a mixture of these gases. If this heat treatment step is not performed, it is prone to deformation, especially near the glass transition temperature, and may limit post-processing or customer use. The most suitable heat treatment temperature for the film can be determined based on the speed of the film passing through the atmosphere, that is, the processing time. Processing time is determined depending on various conditions, but generally it may be better to set it to 3 minutes or less. If the heat treatment time is long, deformation such as stretching of the film may occur during molding.

Referring to Figure 5, the biaxially stretched high-density polyethylene film manufactured through the above three processes can produce a multilayer film with a five-layer structure.

Therefore, the biaxially stretched high-density polyethylene film of the present invention can be manufactured by stretching 4 to 5 times in the longitudinal direction and 9 to 11 times in the transverse direction. In addition, after heating the first and second stretched films with hot air at 100°C to 120°C for 5 to 15 minutes, the heat shrinkage rate is 3% or less in both the longitudinal and transverse directions. Additionally, the haze of the film is 4.5% or less and the adhesive strength is 5.0 or more. In addition, the sealing start temperature of the biaxially stretched high-density polyethylene film of the present invention is 90°C or lower. In other words, it is a biaxially stretched high-density polyethylene film with excellent adhesive strength (sealing strength) even at low temperatures with a sealing start temperature of 90°C or lower.

As such, the method for manufacturing a biaxially stretched high-density polyethylene film according to an embodiment of the present invention provides a process with high productivity by minimizing contamination and excellent thickness deviation and smoothness.

Hereinafter, preparation examples and examples will be illustrated. The following preparation examples and examples are provided only to aid understanding of the present invention.

<Manufacture of biaxially stretched high-density polyethylene film>

[Example 1] - Preparation of biaxially stretched high-density polyethylene film

The thermal bonding layer uses 40wt% linear low-density polyethylene containing inorganic particles, 55wt% polyolefin elastomer, and 5wt% master chip (containing 5wt% synthetic silica) granules, and the bonding layer uses 60wt% polyolefin elastomer and 40wt% ethylene vinyl acetate granules. The first core layer uses 100wt% high-density polyethylene granules, the second core layer also uses 100wt% high-density polyethylene granules, and the surface layer contains 98wt% high-density polyethylene and 2wt% master chip (containing 5wt% synthetic silica) granules. Using a , each layer is extruded by another extruder, melted and bonded with a roll, and extruded into a 5-layer film laminated as a heat sealing layer, a bonding layer, a first core layer, a second core layer, and a surface layer, and the casting roll is heated to 65°C. An unstretched sheet was produced by cooling and solidifying. The unstretched sheet was stretched 4 times in the longitudinal direction, then stretched 9 times in the transverse direction, and then stepwise heat treated at 135°C in a heat treatment zone composed of multiple zones to produce a 30㎛ thick film.

[Example 2] - Preparation of biaxially stretched high-density polyethylene film

The thermal bonding layer uses 30wt% linear low-density polyethylene containing inorganic particles, 60wt% polyolefin elastomer, and 10wt% master chip (containing 5wt% synthetic silica) granules, and the bonding layer uses 70wt% polyolefin elastomer and 30wt% ethylene vinyl acetate granules. The surface layer was prepared in the same manner as in Example 1, except that a 30.4㎛ thick film was prepared using 95wt% high-density polyethylene and 5wt% master chip (containing 5wt% synthetic silica) granules.

[Example 3] - Preparation of biaxially stretched high-density polyethylene film

The thermal bonding layer uses 50wt% linear low-density polyethylene containing inorganic particles, 47wt% polyolefin elastomer, and 3wt% master chip (containing 5wt% synthetic silica) granules, and the bonding layer uses 50wt% polyolefin elastomer and 50wt% ethylene vinyl acetate granules. The surface layer was prepared in the same manner as in Example 1, except that a 30.0㎛ thick film was prepared using 99wt% high-density polyethylene and 1wt% master chip (containing 5wt% synthetic silica) granules.

[Comparative Example 1] - Production of biaxially stretched high-density polyethylene film

The thermal bonding layer uses 55wt% linear low-density polyethylene containing inorganic particles, 43wt% polyolefin elastomer, and 2wt% master chip (containing 5wt% synthetic silica) granules, and the bonding layer uses 45wt% polyethylene elastomer and 55wt% ethylene vinyl acetate granules. The surface layer is a three-layer film laminated as a heat sealing layer, bonding layer, and surface layer using 99.5 wt% high-density polyethylene and 0.5 wt% master chip (containing 5 wt% synthetic silica) granules, except that the thickness is 30.1 ㎛. A film was prepared in the same manner as in 1.

[Comparative Example 2] - Production of biaxially stretched high-density polyethylene film

The thermal bonding layer uses 73wt% linear low-density polyethylene and 27wt% polyolefin elastomer granules that do not contain inorganic particles, the bonding layer uses 72wt% polyolefin elastomer and 28wt% ethylene vinyl acetate granules, and the surface layer uses 100wt% high-density polyethylene granules. A film was prepared in the same manner as in Example 1, except that a film with a thickness of 31.2 μm was prepared.

[Comparative Example 3] - Production of biaxially stretched high-density polyethylene film

The thermal bonding layer uses 65wt% linear low-density polyethylene containing inorganic particles, 23wt% polyolefin elastomer, and 12wt% master chip (containing 5wt% synthetic silica) granules, and the bonding layer uses 20wt% polyolefin elastomer and 80wt% ethylene vinyl acetate granules. A film was prepared in the same manner as in Example 1, except that the surface layer was made of 93 wt% high-density polyethylene and 7 wt% master chip (containing 5 wt% synthetic silica) granules, and a 30.0 μm thick film was prepared.

[Comparative Example 4] - Production of biaxially stretched high-density polyethylene film

The unstretched sheet was stretched 6 times in the longitudinal direction and then stretched 12 times in the transverse direction, and was prepared in the same manner as in Example 1, except that the film thickness was 20.2 ㎛.

[Comparative Example 5] - Production of biaxially stretched high-density polyethylene film

The unstretched sheet was stretched 3 times in the longitudinal direction and then stretched 8 times in the transverse direction, and was prepared in the same manner as in Example 1, except that the film thickness was 41.0 ㎛.

[Comparative Example 6] - Production of biaxially stretched high-density polyethylene film

The unstretched sheet was stretched 6 times in the longitudinal direction and then 8 times in the transverse direction, and was prepared in the same manner as in Example 1, except that the film thickness was 28.0 ㎛.

Table 1 below shows the components and contents of the examples and comparative examples of the present invention.

Example or
Comparative example Floor classification Ingredients and content (wt%) Extension ratio (pear) film full
Thickness (㎛) HDPE LLDPE POE EVA master chip longitudinal transverse Example 1 Heat adhesive layer - 40 55 - 5 4 9 30.0 bonding layer - - 60 40 - 1st core layer 100 - - - - 2nd core layer 100 - - - - surface layer 98 - - - 2 Example 2 Heat adhesive layer - 30 60 - 10 4 9 30.4 bonding layer - - 70 30 - 1st core layer 100 - - - - 2nd core layer 100 - - - - surface layer 95 - - - 5 Example 3 Heat adhesive layer - 50 47 - 3 4 9 30.0 bonding layer - - 50 50 - 1st core layer 100 - - - - 2nd core layer 100 - - - - surface layer 99 - - - One Comparative Example 1 Heat adhesive layer - 55 43 - 2 4 9 30.1 bonding layer - - 45 55 - surface layer 99.5 - - - 0.5 Comparative Example 2 Heat adhesive layer - 73 27 - - 4 9 31.2 bonding layer - - 72 28 - 1st core layer 100 - - - - 2nd core layer 100 - - - - surface layer 100 - - - - Comparative Example 3 Heat adhesive layer - 65 23 - 12 4 9 30.0 bonding layer - - 20 80 - 1st core layer 100 - - - - 2nd core layer 100 - - - - surface layer 93 - - - 7 Comparative Example 4 Same ingredients and content as Example 1 6 12 20.2 Comparative Example 5 Same ingredients and content as Example 1 3 8 41.0 Comparative Example 6 Same ingredients and content as Example 1 6 8 28.0

<Test example>

[Test Example 1] - Adhesion strength test

The films prepared according to Examples to Comparative Examples were measured according to the KS F 3101 method using a universal testing machine.

[Test Example 2] - Transparency test

The films prepared according to Examples to Comparative Examples were measured according to the ASTM D-1003 method using a haze meter from NIPPON DENSHOKU (Japan, Model NDH-7000).

[Test Example 3] - Heat shrinkage (MD/TD) test

The films prepared according to Examples and Comparative Examples were cut into 10 cm

Heat shrinkage rate (%) = (length before heat treatment - length after heat treatment)/(length before heat treatment) × 100

[Test Example 4] - Tensile strength and elongation at break test

The films prepared according to Examples to Comparative Examples were cut to 10 cm × 10 cm, mounted so that the spacing between chucks was 50 mm, and measured using ASTM D-882.

[Test Example 5] - Friction coefficient test

The films prepared according to Examples to Comparative Examples were measured according to the ASTM D-1894 measurement method.

Table 2 below shows the results for the above test examples.

Test Items Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Film thickness (㎛) 30.0 30.4 30.0 30.1 31.2 30.0 20.2 41.0 28.0 Adhesive strength
(kgf/15mm) 5.3 5.6 5.1 3.7 4.3 4.1 4.3 4.3 3.9 Haze (%) 4.0 4.4 3.8 6.5 7.1 6.2 5.1 5.8 5.3 thermal water
reduction rate
(%) M.D. 3.00 3.00 2.75 4.75 2.70 2.75 4.50 4.25 3.25 TD 1.25 1.50 1.00 4.50 1.00 2.70 2.50 2.25 1.25 Seal
robbery
(MPa) M.D. 78.0 81.8 86.8 62.8 75.4 71.8 63.0 70.3 72.2 TD 257.1 280.3 296.9 169.2 237.4 210.5 171.2 248.5 194.2 fracture
elongation M.D. 313.5 321.1 331.4 241.2 270.3 252.2 252.1 271.0 301.2 TD 44.5 45.2 47.2 37.9 35.7 33.2 33.1 37.7 40.2 friction
Coefficient IN/IN 0.32 0.26 0.35 0.35 0.41 0.30 0.33 0.40 0.31 OUT/OUT 1.15 1.20 1.29 1.43 1.52 1.26 1.26 1.75 1.32

Referring to Table 2, the biaxially stretched high-density polyethylene film manufactured according to the examples of the present invention has an adhesive strength of 5.0 to 6.0 kgf/15mm, a heat shrinkage rate of 3.0% or less, a haze of 4.5 or less, and a coefficient of friction of 0.35 (IN). It was found that it is not only suitable for printing and lamination as it is less than /1.30(OUT), but also is a base film for sealables with excellent adhesive strength, and is also easy to process due to the low coefficient of friction.

In particular, the heat sealing layer and the bonding layer of the multi-layered film contain at least one of polyolefin elastomer or ethylene vinyl acetate, and the adhesive strength is 5.0 to 6.0 kgf/mm in all examples, which is an acceptable adhesive strength level for sealables. It was confirmed that it was more than 3.5kgf/15mm. It was found that this was the result of including appropriate amounts of polyolefin elastomer and ethylene vinyl acetate as adhesion promoters. On the other hand, in the case of the comparative example in which the content of polyolefin elastomer was relatively small, it was found that the adhesive strength was lowered compared to all examples. In addition, it was confirmed that the adhesive strength showed the lowest value in the case of Comparative Example 5, where the longitudinal and transverse stretch ratios were excessively small. Therefore, it was confirmed that the adhesive strength is affected by the presence or absence of the adhesive promoter, the appropriate content, and the stretching ratio.

In addition, it was confirmed that all examples showed a heat shrinkage rate of 3% or less. It was found that this was the result of using high-density polyethylene, which has good heat resistance, in two or more layers. On the other hand, in the case of Comparative Example 1, which had a small content of high-density polyethylene and consisted of three layers, and Comparative Example 4, where the longitudinal and transverse direction stretching ratios were larger than those of all examples, it was found that the thermal contraction rate significantly increased. Therefore, it was confirmed that not only the type and content of the resin, but also the stretching ratio in the longitudinal and transverse directions affected the thermal contraction rate of the film of the present invention.

Additionally, transparency of 4.5% or less was obtained in all examples. On the other hand, Comparative Example 1, Comparative Example 2, and Comparative Example 3, which were composed of three layers, showed transparency exceeding 6%, and Example 1 and Comparative Examples 4 to 6 only had lower draw ratio turbidity than all examples. It was found that the increase, that is, the transparency decreased. Therefore, it was confirmed that not only the type and content of resin, but also the stretching ratio affects the physical properties, that is, transparency, of the film of the present invention.

In addition, it was confirmed that the friction coefficient was 0.35 or less in all examples of the present invention. This prevented the improvement of the friction coefficient of the film of the present invention by adding a small amount of master chip, an anti-blocking masterbatch, to all examples. As a result, it was found that the surface of the film of the present invention was smooth and was not twisted or stuck, making it suitable for processing as a base film for printing and lamination. On the other hand, Comparative Example 2, which did not contain the master chip, which was an inorganic particle, had the highest friction coefficient of over 0.40, Comparative Example 1, which contained a very small amount, ranked next, and Comparative Example 3 ranked lowest. In Comparative Example 3, a large amount of master chips were added, but the content of high-density polyethylene was small, so it was confirmed that it had a higher coefficient of friction compared to the Example. In addition, Comparative Examples 4 to 6, which had the same components and contents as Example 1 but different stretching ratios, were found to have higher friction coefficients than all Examples. Therefore, it was confirmed that the friction coefficient was also affected by the presence and content of anti-blocking masterbatch, the content of high-density polyethylene, and the longitudinal and transverse stretching ratios.

It was confirmed that the tensile strength and elongation at break of the example based on high-density polyethylene and appropriately containing linear low-density polyethylene, polyolefin elastomer, ethylene vinyl acetate, and master chip were higher than the comparative example.

The embodiments described above are merely illustrative, and various modifications and equivalent embodiments can be made by those skilled in the art. Therefore, the true scope of technical protection of the present invention must be determined by the technical spirit of the invention described in the claims.

Claims (18)

In the biaxially stretched high-density polyethylene film,
A thermal adhesive layer containing linear low-density polyethylene, polyolefin elastomer, and a master chip;
A bonding layer containing polyolefin elastomer and ethylene vinyl acetate on the upper surface of the heat sealing layer;
A first core layer containing 100 wt% of high-density polyethylene on the upper surface of the bonding layer;
a second core layer containing 100 wt% of high-density polyethylene on the upper surface of the first core layer; and
It includes a surface layer containing high-density polyethylene and a master chip on the upper surface of the second core layer,
The heat sealing layer contains 30 to 50 wt% of linear low-density polyethylene, 45 to 65 wt% of polyolefin elastomer, and 3 to 10 wt% of master chip, based on the total weight percent,
The bonding layer contains 50 to 70 wt% of polyolefin elastomer and 30 to 50 wt% of ethylene vinyl acetate based on the total weight%,
The ethylene vinyl acetate has a density of 0.93 to 0.95 g/cm3 and a melt index (MI) of 1 to 6,
The ethylene vinyl acetate is a biaxially stretched high-density polyethylene film with improved thermal adhesiveness, characterized in that it contains 12 to 18 wt% of vinyl acetate based on the total weight%.
delete delete delete According to paragraph 1,
The surface layer is a biaxially stretched high-density polyethylene film with improved thermal adhesiveness, characterized in that it contains 95 to 99 wt% of high-density polyethylene and 1 to 5 wt% of master chip based on the total weight percent.
According to clause 5,
The master chip is a biaxially stretched high-density polyethylene film with improved thermal adhesiveness, characterized in that it contains 5 to 10 wt% of at least one selected from silica, synthetic silica, zeolite, calcium carbonate, and PMMA.
According to paragraph 1,
The thickness of the heat sealing layer is 1 to 2 ㎛, the thickness of the bonding layer is 2 to 4 ㎛, the thickness of the second core layer is 2 to 3 ㎛, and the thickness of the surface layer is 1 to 2 ㎛. A biaxially stretched high-density polyethylene film with improved heat resistance and transparency.
According to paragraph 1,
The biaxially stretched high-density polyethylene film is manufactured by stretching 4 to 5 times in the longitudinal direction and 9 to 11 times in the transverse direction.
According to paragraph 1,
The biaxially stretched high-density polyethylene film is a biaxially stretched high-density polyethylene film with improved thermal adhesion, characterized in that the sealing start temperature is 90 ° C. or lower.
According to paragraph 1,
The biaxially stretched high-density polyethylene film is a biaxially stretched high-density polyethylene film with improved thermal adhesiveness, characterized in that the adhesive strength is 5.0 or more.
According to paragraph 1,
The biaxially stretched high-density polyethylene film is a biaxially stretched high-density polyethylene film with improved thermal adhesion, characterized in that the heat shrinkage rate is 3% or less in both the longitudinal and transverse directions after heating with hot air at 100 ° C. to 120 ° C. for 5 to 15 minutes.
According to paragraph 1,
The biaxially stretched high-density polyethylene film is a biaxially stretched high-density polyethylene film with improved thermal adhesiveness, characterized in that it is used as a base film for industrial coating, printing and lamination of flexible packaging materials, and sealables.
In the method of manufacturing a biaxially stretched high-density polyethylene film,
At least one of high-density polyethylene, linear low-density polyethylene, polyolefin elastomer, ethylene vinyl acetate, and master chip is melt-extruded at 210 to 250°C, and then discharged in at least three layers through a T-Die, and a casting roll is used. manufacturing an unstretched sheet by rapidly cooling it to 70°C or lower;
First stretching the unstretched sheet 4 to 5 times in the longitudinal direction at 120 to 125°C;
Secondary stretching the first stretched film 9 to 11 times in the transverse direction at 125 to 130°C; and
A method for producing a biaxially stretched high-density polyethylene film with improved thermal adhesion, comprising the step of heat-treating the secondarily stretched film at 125 to 135° C. in a heat treatment zone.
According to clause 13,
In the step of manufacturing the unstretched sheet,
The multilayer is,
A heat sealing layer containing 30 to 50 wt% of linear low-density polyethylene, 45 to 65 wt% of polyolefin elastomer, and 3 to 10 wt% of master chip;
A bonding layer containing 50 to 70 wt% of polyolefin elastomer and 30 to 50 wt% of ethylene vinyl acetate on the upper surface of the heat sealing layer;
A first core layer containing 100 wt% of high-density polyethylene on the upper surface of the bonding layer;
a second core layer containing 100 wt% of high-density polyethylene on the upper surface of the first core layer; and
A method for producing a biaxially stretched high-density polyethylene film with improved thermal adhesion, comprising a surface layer containing 95 to 99 wt% of high-density polyethylene and 1 to 5 wt% of a master chip on the upper surface of the second core layer.
According to clause 14,
In the first stretching step,
A method for manufacturing a biaxially stretched high-density polyethylene film with improved thermal adhesiveness, characterized in that the thermal adhesive layer is stretched in the longitudinal direction at 110 to 115 ° C, which is 10 ° C lower than the stretching temperature of the surface layer.
According to clause 13,
In the first stretching step,
The longitudinal primary stretching uses a coated stretching roll, and the arrangement of the coated stretching roll is such that the unstretched sheet maximizes contact while wrapping and exiting the coated stretching roll and prevents the unstretched sheet from slipping. A method of manufacturing a biaxially stretched high-density polyethylene film with improved thermal adhesiveness, characterized in that a wrap angle of 180°C or higher is maintained.
According to clause 16,
In the coated stretching roll,
The coating material includes polytetrafluoroethylene,
A method for producing a biaxially stretched high-density polyethylene film with improved thermal adhesiveness, characterized in that the density of the polytetrafluoroethylene is 2.13-2.20 g/cc.
According to any one of claims 13 to 17,
A method for manufacturing a biaxially stretched high-density polyethylene film with improved thermal adhesion, characterized in that it minimizes contamination and enables long-term production.