WO2012093881A2

WO2012093881A2 - Method for manufacturing a multi-layer oriented polyolefin film and multi-layer oriented polyolefin film manufactured thereby

Info

Publication number: WO2012093881A2
Application number: PCT/KR2012/000140
Authority: WO
Inventors: Jong Cheol Kim; Jong Ha Kum; Sung Woo Park
Original assignee: Youl Chon Chemical Co., Ltd.
Priority date: 2011-01-06
Filing date: 2012-01-06
Publication date: 2012-07-12
Also published as: CN103298600A; KR101243463B1; KR20120080027A; IN2013MN01283A; CN103298600B; JP2015155202A; JP2014506208A; JP5807070B2; WO2012093881A3

Abstract

This disclosure is directed to a method for manufacturing a multi-layer oriented polyolefin film, and a multi-layer oriented polyolefin film obtained thereby. In the method, a machine direction orientation after an extrusion is followed by an additional extrusion, wherein the additional extrusion allows lamination of a resin layer so that even a low-melting point resin may be laminated via the continuous extrusion. Accordingly, the method allows a simple process, thereby reducing time and cost.

Description

METHOD FOR MANUFACTURING A MULTI-LAYER ORIENTED POLYOLEFIN FILM AND MULTI-LAYER ORIENTED POLYOLEFIN FILM MANUFACTURED THEREBY

This disclosure relates to a method for manufacturing a multi-layer oriented polyolefin film, and a multi-layer oriented polyolefin film manufactured thereby.

In general, multi-layer oriented polyolefin films, such as polypropylene (PP) or polyethylene (PE) films, have been widely used in packaging materials or lamination coating (laminated sheets). In addition to the PP and PE films, there have been used polyvinyl chloride (PVC) films or polyethylene terephthalate (PET) films. However, PVC films may emit harmful materials, such as dioxin, upon incineration, and PET films may not be cost-efficient and have a difficulty in recycling.

Therefore, multi-layer oriented polyolefin films advantageous in terms of cost-efficiency and recyclability, particularly multi-layer biaxially oriented polypropylene (BOPP) films have been used more frequently. Such BOPP films are advantageous in terms of cost-efficiency and recyclability, and also have an excellece in mechanical properties such as tensile strength, rigidity, surface hardness and impact resistance, optical properties such as gloss and transparency, and food hygiene characteristics such as non-toxicity and odorless characteristics. Thus, they are useful for packaging materials (food packaging, etc.) or lamination coating (laminated sheets).

Fig. 1 is a schematic structural view of a conventional general BOPP film, and Fig. 2 is a schematic view illustrating a method for manufacturing a BOPP film according to the related art.

Referring to Fig. 1, a BOPP film generally includes a PP layer as a core layer 3, and a skin outer layer 1 and a skin inner layer 2 stacked on one side and the other side of the core layer 3, respectively. Herein, the skin outer layer 1 comprises PP, while the skin inner layer 2 comprises PP or PE. In addition, a functional resin layer 4 may be stacked on the skin outer layer 1 and/or skin inner layer 2.

For example, when such a BOPP film is used for lamination coating (laminated sheets), particularly as a film for lamination coating (laminated sheets) wherein an identification matter such as a photograph, ID document, printed matter or menu board etc. are inserted between two sheets of BOPP films and then hot-melted, or as a packaging film (e.g. food packaging), the functional layer 4 may include a low-melting point adhesive resin such as ethylene vinyl acetate (EVA) or polyethylene (PE) capable of hot-melting (heat sealing).

In addition, referring to Fig. 2, when manufacturing the BOPP film having the above-described structure according to the related art, the skin outer layer 1, core layer 3 and the skin inner layer 2 are co-extruded through an extruder 5 so that the three

layers

1, 2, 3 are laminated at extrusion dies. In this manner, it is possible to form a multi-layer film. Then, the extruded multi-layer film is passed through a cooling roll 6 so that it is cooled, and then is subjected to biaxial orientation, i.e., the machine direction orientation (MDO) and successive transverse direction orientation (TDO). In other words, as shown in Fig. 2, the extruded multi-layer film is passed through an machine direction orientation device 7 having multiple roll combinations R to carry out the orientation along the machine direction (i.e., longditudinal direction). Then, the machine direction oriented film is passed continuously to a transverse direction orientation device 8 to carry out the orientation along the transverse direction by way of a rail pattern. After that, the machine direction and transverse direction oriented film is wound at a winding roll 9.

As described above, a method for manufacturing a multi-layer BOPP film according to the related art includes extrusion, cooling, MD orientation and TD orientation so as to provide a multi-layer film having a structure of PP layer/PP layer/PP (or PE) layer as shown, for example, in Fig. 1.

In addition, after providing a multi-layer film through the above-described continuous process, a functional resin layer 4 is further laminated on the skin outer layer 1 and/or skin inner layer 2, as mentioned above. That is, in the method according to the related art, the functional resin layer 4 such as ethylene vinyl acetate (EVA), etc. is laminated through additional processes such as coating, lamination (hot-melting), etc. However, such additional processes are complicated and take much time and cost.

Herein, in order to carry out the lamination of the functional resin layer 4, a co-extrusion method including introducing the functional resin into the skin extrusion section upon the multi-layer extrusion coating may be contemplated. However, when there is a significant difference in physicochemical properties between the functional resin and polyolefin (e.g. PP), such co-extrusion may be difficult. That is, low-melting point resins or resins other than polyolefin resins are not amenable to the co-extrusion. For example, in the case of a low-melting point resin such as EVA, its melting point difference from PP causes degradation of interlayer adhesion strength (adhesive force). In addition, while the multi-layer film is passed through the rolls R of the MD orientation device 7, the resin layer 4 may be scratched, resulting in degradation of an appearance of the resultant product. Further, the resin layer 4 may be stuck to the rolls R, thereby making it difficult to carry out the co-extrusion.

To this end, the method for laminating a functional resin layer 4 according to the related art requires additional processes such as coating or lamination (hot-melting) which require a relatively long time and high cost, and as a result, cause an increase in manufacturing cost.

This disclosure is directed to providing a method for manufacturing a multi-layer oriented polyolefin film, which allows even a low-melting point functional resin to be laminated through a continuous process and allows a simple and time-efficient process to reduce a manufacturing cost of products. This disclosure is also directed to providing a multi-layer oriented polyolefin film obtained by the method.

In embodiments of the invention, provided ia a method for manufacturing a multi-layer oriented polyolefin film, including: carrying out a first extrusion molding of a multi-layer polyolefin film; first cooling the first extrusion molded film; machine direction orienting the first cooled film along the longditudinal direction; carrying out a second extrusion molding in order to laminate at least one resin layer on the machine direction oriented film; second cooling the film laminated with the resin layer; and transverse direction orienting the second cooled film along the transverse direction.

In an example embodiment, the second cooling of the film laminated with the resin layer may be carried out by using a cooling roll having an uneven structure on its surface to form air flow grooves on the resin layer.

In another embodiments of the invention, provided is a multi-layer oriented polyolefin film obtained by the above-described method.

According to embodiments of the method for manufacturing a multi-layer oriented polyolefin film, a machine direction orientation is followed by an additional extrusion/cooling (i.e., second extrusion/second cooling), wherein a resin layer is laminated through the additional extrusion. Thus, even a low-melting point resin may be laminated through the extrusion. In this manner, multiple layers, including a resin layer, may be laminated through such continuous extrusion to provide a multi-layer oriented polyolefin film. Accordingly, the method has a simple process, is time-efficient, and reduces the manufacture cost of products.

The above and other aspects, features and advantages of the disclosed embodiments will be more apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

Fig. 1 is a schematic structural view of a general conventional biaxially oriented polypropylene (BOPP) film.

Fig. 2 is a schematic view of manufacturing apparatus illustrating a conventional method for manufacturing a BOPP film according to the related art;

Figs. 3 and 4 are schematic structural views illustrating the multi-layer oriented polyolefin films according to embodiments; and

Fig. 5 is a schematic view of manufacturing apparatus illustrating a method for manufacturing a multi-layer oriented polyolefin film according to an embodiment.

1: skin outer layer 2: skin inner layer

3: core layer 4: functional resin layer

5: extruder 6: cooling roll

7: machine direction orientation device

8: transverse direction orientation device

9: winding roll

10: skin outer layer 20: skin inner layer

30: core layer 40: resin layer

100-1: first extruder 100-2: second extruder

150: resin feed section 200: first cooling roll

300: machine direction orientation device

400: second cooling roll

500: transverse direction orientation device

600: winder

Example embodiments now will be described more fully hereinafter with reference to the accompanying drawings, in which example embodiments are shown. The present disclosure may, however, be embodied in many different forms and should not be construed as limited to the example embodiments set forth therein. Rather, these example embodiments are provided so that the present disclosure will be thorough and complete, and will fully convey the scope of the present disclosure to those skilled in the art. In the description, details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the presented embodiments.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. As used herein, the singular forms "a", "an, "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. Furthermore, the use of the terms a, an, etc. does not denote a limitation of quantity, but rather denotes the presence of at least one of the referenced item.

It will be further understood that the terms "comprises" and/or "comprising" or "includes" and/or "including" when used in this specification, specify the presence of stated features, regions, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and/or groups thereof.

The multi-layer oriented polyolefin film (hereinafter also referred to as "oriented film" in brief) according to embodiments will be explained. Then, the method for manufacturing the multi-layer oriented polyolefin according to the embodiments will be explained.

Figs. 3 and 4 are schematic structural views illustrating the multi-layer oriented polyolefin films according to embodiments.

Referring to Fig. 3 and Fig. 4, the oriented film according to an embodiment may include at least two layers of multi-layer polyolefin film (F, also referred to as "multi-layer film" in brief), and a resin layer 40 laminated on the multi-layer film F.

Herein, the multi-layer film F is obtained by laminating two or more layers via extrusion at the same time, wherein each layer includes at least polyolefin resin as a base resin (main material). For example, the multi-layer film F may have a stack of 2 to 5 layers, more particularly 3 to 4 layers. In an examplel embodiment, the multi-layer film F may include a core layer 30, a skin outer layer 10 laminated on one side of the core layer 30, and a skin inner layer 20 laminated on the other side of the core layer 30.

In an example embodiment, the multi-layer film F may have a tri-layer structure having the three layers, i.e., the skin outer layer 10, the core layer 30 and the skin inner layer 20, stacked successively, as shown in Figs. 3 and 4. Herein, each

layer

10, 20, 30 may include, as a base resin (main material), at least one resin selected from the group consisting of polypropylene (PP) and polyethylene (PE). More particularly, the skin outer layer 10 and the core layer 30 may be a PP layer having PP as a base resin. In addition, the skin inner layer 20 may be formed of PP layer, PE layer or PP-PE composite layer, each having PP, PE, or PP-PE composite as a base resin.

In addition, the oriented film includes a resin layer 40 laminated on the multi-layer film F. The resin layer 40 may be formed as one layer or two layers and be laminated on at least one of the skin outer layer 10 and the skin inner layer 20. Fig. 3 shows that the resin layer 40 is laminated on the skin inner layer 20, while Fig. 4 shows that the resin layers 40 are laminated on both the skin outer layer 10 and the skin inner layer 20.

As described below, the resin layer 40 is not formed by an additional coating process or a lamination process using hot-melting, but is laminated on the multi-layer film F through an extrusion process subsequent to machine direction orientation according to an embodiment. The method for manufacturing a multi-layer oriented polyolefin film will be explained in detail.

Fig. 5 is a schematic view showing an apparatus for carrying out the method according to an embodiment. Fig. 5 is for illustrative purpose only, and various embodiments other than Fig. 5 may be made.

Referring to Fig. 5, the apparatus includes several devices of a first extruder 100-1, a first cooling roll 200, a machine direction orientation device 300, a second extruder 100-2, a second cooling roll 400, a transverse direction orientation device 500 and a winder 600. These devices are arranged so that a continuous process may be carried out. There is no particular limitation in particular structure of each devices. For example, the machine direction orientation device 300 may include a combination of multiple rolls R as shown in Fig. 5. In Fig. 5, the reference numbers R1 and R2 represent guide rolls R1, R2 adjacent to the first cooling roll 200 and the second cooling roll 400, respectively.

The method for manufacturing a multi-layer oriented polyolefin film according to an embodiment includes carrying out a first extrusion molding to form a multi-layer polyolefin film F, first cooling the first extrusion molded film F, machine direction orienting the first cooled film F along the machine direction (i.e., longditudinal direction), carrying out a second extrusion molding to laminate at least one resin layer 40 on the machine direction oriented film F, second cooling the film F laminated with the resin layer 40, and transverse direction orienting the second cooled film F along the transverse direction. These steps of the method are carried out in a continuous manner.

In the first extrusion molding, the multi-layer film F is extrusion-molded through a first extruder 100-1. Particularly, the extrusion is carried out in such a manner that two or more layers are co-laminated, thereby providing the multi-layer film F. Herein, the first extruder 100-1 has extrusion sections in a number corresponding to the number of layers forming the multi-layer film F, and the layers are laminated at extrusion dies. For example, when a multi-layer film F having a tri-layer structure of a skin outer layer 10, core layer 30 and a skin inner layer 20 is to be formed, the first extruder 100-1 may have three extrusion sections corresponding to the tri-layer structure.

In addition, to perform the extrusion molding of the multi-layer film F, a polyolefin-based resin composition may be introduced to the first extruder 100-1. The polyolefin-based resin composition may include, as a base resin (main material), at least one polyolefin resin. There is no particular limitation on the polyolefin resin. Preferably, at least one resin selected from PP and PE may be used. In addition, as the polyolefin resin, copolymer of at least one of ethylene and propylene, particularly ethylene-methacrylic acid binary copolymer or ethylene-methacrylic acid-ester ternary copolymer, etc. may be used but not limited thereto.

Meanwhile, the polyolefin-based resin composition includes at least polyolefin resin and may further include other resins or additives if necessary. In a non-limiting example mbodiment, the polyolefin-based resin composition may include other resins or additives in an amount of 0 to 40 parts by weight, specifically 5 to 20 parts by weight based on 100 parts by weight of polyolefin resin. The additives are those generally used in the art and preferably examples thereof may include at least one selected from the group consisting of slip agents, anti-blocking agents, antistatic agents, etc. Particlur types of such additives will be described in detal hereinafter.

When providing the multi-layer film F through the first extrusion, the layers may be formed of the same or different materials. For example, as shown in Figs. 3 and 4, the skin outer layer 10 and the core layer 30 may be formed to be a PP layer, respectively by using PP as a base resin (main material). The skin inner layer 20 may be a PP layer, PE layer or a PP-PE composite layer by using PP, PE or PP-PE composite as a base resin (main material). It is prefreably that the skin inner layer 20 is a PE layer. Since PE layers have higher compatibility with a low-melting point resin such as ethylene vinyl acetate (EVA), etc. as compared to PP layers, PE layers may be preferable in preventing an interlayer separation.

In addition, when first extruding the multi-layer film F, it is preferable to extrude the outermost layer (skin outer layer 10) of the multi-layer film F to include at least one additive selected from slip agents and anti-blocking agents. Particularly, when the skin outer layer 10 has no resin layer 40 thereon and become the outermost layer of the final product (oriented film) as shown in Fig. 3, it is preferable for the materials forming the skin outer layer 10 to further include at least one additive selected from slip agents and anti-blocking agents.

The slip agents are those capable of imparting slip property (or release property). Examples of such slip agents may include at least one selected from the group consisting of silicone, siloxane, silane, wax and oleic amide, etc. In addition to above-mentioned slip agents, any slip agents capable of imparting lubricability to the surface of the oriented film and reducing the frictional coefficient may be used. The slip agents may be used in, but not limited to, an amount of 0.1 to 20 parts by weight, specifically 2 to 12 parts by weight based on 100 parts by weight of polyolefin resin.

The anti-blocking agents are those capable of preventing adhesion between two adjacent films by forming a small space at the interface of the adjacent films. Examples of the anti-blocking agents may include at least one selected from the group consisting of inorganic particles such as silica, diatomaceous earth, kaolin, talc, etc. The anti-blocking agents may be used in, but not limited to, the same amount as the slip agents, particularly in an amount of 0.1 to 20 parts by weight, specifically 2 to 12 parts by weight based on 100 parts by weight of polyolefin resin.

When providing the multi-layer film F through the first extrusion, it is preferable to control a thickness of each layer. For example, referring to Fig. 3, the multi-layer film F has a tri-layer structure of the skin outer layer 10, core layer 30 and the skin inner layer 20, wherein the skin outer layer 10 may have a thickness T10 corresponding to 1~10% of the total thickness T of the oriented film, the core layer 30 may have a thickness T30 corresponding to 30~70% of the total thickness T of the oriented film, and the skin inner layer 20 may have a thickness T20 corresponding to 1~10% of the total thickness T of the oriented film. In addition, the first extrusion may be carried out at a various range of temperatures depending on the materials used for the first extrusion. For example, the first extrusion may be carried out at a temperature of 140~320℃.

Referring to Fig. 5, the extrusion molded multi-layer film F through the first extrusion molding is then passed through a first cooling roll 200 so that it may be cooled (first coolng). Although Fig. 5 shows one cooling roll 200 in the manufacturing apparatus, one, two or more cooling rolls 200 may be arranged continuously in the appratus. The cooling temperature, i.e., the temperature of the first cooling roll 200 may be, but not limited to, 5~80℃.

Then, the first cooled multi-layer film F is transferred to a machine direction orientation device 300 along a guide roll R1 so that it is oriented along the machine direction (i.e., longitudinal direction). For example, as shown in Fig. 5, the machine direction orientation (MDO) may be carried out through a plurality of rolls R. The orientation temperature of this mchine direction orientation step, i.e., the temperature of the rolls R installed in the machine direction orientation device 300 may be, but not limited to, 80~160℃. In addition, the machine direction orientation may be carried out at an orientation ratio of 1.5 to 10 times, particularly 3 to 7 times, and more particularly 4 to 5 times. The ratio of the machine direction orientation may be realized by the speed of rolls R.

After the machine direction orientation, the multi-layer film F is further subjected to additional extrusion (second extrusion) and cooling (second cooling) continuously. During the second extrusion, a resin layer 40 is laminated on the multi-layer film F. Particularly, as shown in Fig. 5, the machine direction oriented multi-layer film F is supplied to a second extruder 100-2. Herein, the second extruder 100-2 may have a resin feed section 150 from which materials forming the resin layer 40 are supplied. The multi-layer film F is passed through the second extruder 100-2, and the materials forming the resin layer are supplied from the resin feed section 150 at the same time. In this manner, while the resin layer 40 is extruded, the resin layer 40 is laminated on the multi-layer film F at the dies.

In an embodiment, the materials forming the resin layer 40, i.e. the materials supplied from the resin feed section 150 to the second extruder 100-2 are not particularly limited. In the second extrusion, examples of the materials of the resin layer 40 may include at least one selected from the group consisting of polyolefin resins, silicone resins, urethane resins, acrylic resins, polyamide resins, metallocene resins, nylon resins, ethylene vinyl acetate (EVA), ethylene methyl acetate (EMA), ethylene methyl acrylic acid (EMAA), ethylene glycol (EG), ethylene acid terpolymer and rubber.

According to an embodiment, the transverse direction orientation is not carried out right after the machine direction orientation. Rather, the resin layer 40 is laminated through the additional extrusion, i.e., the second extrusion. Accodrdingly, it is possible to use materials having physicochemical properties different from those of the base resin forming the multi-layer film F as for the resin layer 40 (e.g. materials having a lower or higher melting point than polyolefin, etc.).

Particularly, in an embodiment, it is possible to use resins other than polyolefin, more particularly functional resins having a lower or higher melting point than polyolefin, as for the resin layer 40. Preferably, in the second extrusion, materials including a resin having a lower melting point than the materials used for the first extrusion may be used as materials for the resin layer 40. For example, low-temperature adhesive resins capable of hot-melting (heat sealing) at low temperature may be used. Particularly, resins having a low melting point and high sealability, such as EVA, EMA, EMMA, low-temperature metallocene resins and ethylene acid terpolymer may be used as for the low-temperature adhesive resins. Herein, the ethylene acid terpolymer may be useful when the oriented film is applied to in-mold labels, and examples of the ethylene acid terpolymer may include ethylene/propylene/butadiene terpolymer, etc. In addition, examples of commercially available terpolymer products include appeel® 52009 available from DuPont Co. The low-melting point resins as materials for the resin layer 40 are not limited to the above listed resins, and PE may also be used. For example, when PP is used as the base resin of the skin outer layer 10 and/or skin inner layer 20, PE having a lower melting point than PP may be used as the resin forming the resin layer 40.

As described above, according to an embodiment, the resin layer 40 is laminated through the second extrusion. Thus, there is no limitation in materials forming the resin layer 40, and the resin layer may have various functionalities. Preferably, in an embodiment, the resin layer 40 may include materials containing an antistatic agent. Herein, the resin layer 40 becomes an antistatic layer. There is no limitation in the antistatic agent as long as it has an antistatic property. Preferably, the antistatic agent may be a permanent antistatic agent with no change in antistatic quality as time goes. In addition, it is more preferable that the antistatic agent may provide the oriented film with a surface resistance of 10¹⁰ Ω/㎠ or less.

For example, the antistatic agent may include polyamide resin or ethylene glycol (EG), and commercial product such as IRAGASTT® P18 (Ciba, Germany) may be used as the antistatic agent. In addition, the antistatic agent may be selected from conductive polymers. Examples of the conductive polymers may include at least one selected from the group consisting of polyacetylene, poly(p-phenylene vinylene), poly(p-phenylene), poly(thienylene vinylene), polythiophene, polyaniline, polyethylene dioxythiophene, polyisothianaphthene, polypyrrole and poly(p-phenylene sulfide).

The antistatic agent may be used in the materials of the resin layer 40 to impart the antistatic property. Otherwise, a master batch containing the antistatic agents may be used for the resin layer 40. For example, a master batch based on PP or PE and further containing an adequate amount of antistatic agent may be used for the resin layer 40. When the resin layer 40 is provided with the antistatic property by having the antistatic agent in the resin layer 40, the oriented film may be useful as a packaging material for electronic appliances, etc. In order to make the oriented film more useful as a packaging material for electronic appliances, etc., it is preferable that the oriented film have a surface resistance of 10¹⁰ Ω/㎠ or less by using the resin layer 40 containing the antistatic agents.

Meanwhile, when imparting static electricity-preventing property (antistatic property) to the oriented film, a method for containing (adding) an antistatic agent to the multi-layer film F, for example, to the skin outer layer 10 or skin inner layer 20 may be contemplated. However, such a method has the problems as follows.

Since the antistatic agent is a resin having a low molecular weight and low melting point, it may be exuded toward the surface of the film F as time goes. Herein, when the multi-layer film F includes an antistatic agent, the antistatic agent may be exuded during the machine direction orientation, resulting in contamination of the surface of the rolls R. As a result, the surface of the film F may also be contaminated (whitening). In addition, due to the loss of antistatic agent (i.e., loss of antistatic agent attached to the surface of rolls R or film F), antistatic property may also be degraded.

However, according to an embodiment, an antistatic agent is contained in the resin layer 40 during the second extrusion (in-line extrusion) subsequent to the machine direction orientation, and thus it becomes possible to overcome the above-mentioned problems. That is, according to an embodiment, an antistatic agent is contatined in the resin layer 40 through the second additional extrusion after the machine direction orientation, and thus may not cause the contamination of the surface of rolls R of the machine direction orientation device 300 or the surface of the film F. Therefore, it is possible to realize stable antistatic property without the loss of the antistatic agent.

According to another embodiment, the materials of the resin layer 40 may include a nylon resin. In other words, the resin layer 40 may be a nylon resin layer containing a nylon resin as a main material. When the resin layer 40 includes a nylon resin, the oriented film may be useful as a packaging material for food by virtue of excellent gas barrier property of nylon resin. In addition, nylon resins have an excellent low-temperature resistance, and thus may be useful for packaging of frozen food. Any nylon resin having an amide bond (-CONH) in its molecule may be used herein. Examples of the nylon resin may include any one selected from the group consisting of Nylon 6, Nylon 66 and Nylon 12, or a combination thereof (e.g. Nylon 6 + Nylon 66, Nylon 6 + Nylon 12, Nylon 6 + Nylon 66 + Nylon 12).

Further, a resin composition having the above-mentioned resin as a main material and further containing other additives may be used for the resin layer 40. In an example embodiment, used for the resin layer 40 is a resin composition containing at least one base resin selected from the group consisting of low-melting point adhesive resins, such as ethylene vinyl acetate (EVA), ethylene methyl acetate (EMA), ethylene methyl acrylic acid (EMAA), low-temperature metallocene resin and ethylene acid terpolymer; antistatic resins (antistatic agents) such as polyamide resins, ethylene glycol (EG) and conductive polymers; and resins having gas-barrier property and low-temperature resistace, such as nylon resins; optionally further in combination with at least one additive selected from the group consisting of slip agent, anti-blocking agent, etc.

Particular types of the slip agent and anti-blocking agent are the same as described above. For example, the slip agent may be used in an amount of 0.1 to 20 parts by weight, specifically 2 to 12 parts by weight based on 100 parts by weight of the base resin. The anti-blocking agent may be used in an amount of 0.1 to 20 parts by weight, specifically 2 to 12 parts by weight based on 100 parts by weight of the base resin.

In addition, during the second extrusion, the resin layer 40 may be formed to have a thickness T40 corresponding to 1~50% of the total thickness T of the oriented film. Further, the extrusion temperature in the second extrusion may be decided considering the materials of the resin layer 40, i.e., the particular type and melting point of the base resin forming the resin layer 40. For example, the second extrusion temperature may be 150~330℃. When the second extrusion temperature is lower than 150℃, it may be difficult to perform the second extrusion. When the second extrusion temperature is higher than 330℃, it may cause undesirably high flowability. For example, when using a low-melting point resin, it is advantageous to carry out the second extrusion at 180~250℃.

Referring to Fig. 5, the multi-layer film F laminated with the resin layer 40 via the second extrusion is passed continuously through a second cooling roll 400 so that it undergoes the second cooling. When the multi-layer film F is passed through the second cooling roll 400, it is advantageous that the second cooling is carried out in such a manner that the resin layer 40 is in close contact with the roll surface of the second cooling roll 400. Although Fig. 5 shows only one cooling roll 400 in the apparatus, one or more cooling rolls 400 may be disposed continuously in the apparatus. The cooling temperature in the second cooling, i.e., the temperature of the second cooling roll 400 may be set as, but not limited to, 5~80℃.

In an embodiment, it is preferabe that air flow grooves be formed on the resin layer 40 when the resin layer 40 is cooled in the second cooling. Such air flow grooves may improve the winding quality of the film. As described below, when the transverse direction oriented film is wound at a winder 600, it may be wrinkled during the winding and may not be restored with ease. Since the resin layer 40 is not formed by the conventional coating process as used in the related art but is laminated through the continuous second extrusion after the machine direction orientation, it may be wrinkled during winding. When a low-melting point material is used for the resin layer 40, more wrinkling may occur.

The air flow grooves may provide air flow paths to prevent such wrinkling effectively during winding. That is, the air flow grooves may effectively prevent the wrinkling by allowing air present between two adjacent films to be discharged through the air flow grooves. Multiple air flow grooves may be formed and there is no particular limitation in the shapes of the air flow grooves. The air flow grooves may be formed on the surface of the resin layer 40 along the longitudinal direction or widthwise direction, for example, in a linear pattern or lattice-like pattern, or in an embossed pattern, in a regular or irregular manner.

In an example embodiment, the air flow grooves are formed during the second cooling. Herein, a second cooling roll 400 having an uneven structure (engraved structure) on the surface thereof may be used to form the air flow grooves. Particularly, as shown in Fig. 5, a cooling roll engraved to have an embossed surface 450 is used as the second cooling roll 400 so that air flow grooves may be formed on the resin layer 40. In other words, when the multi-layer film F laminated with the resin layer 40 from the second extrusion is passed and cooled through the second cooling roll 400, the resin layer 40 is allowed to be in close contact with the second cooling roll 400 having the embossed surface 450 so that air flow grooves are formed on the resin layer 40. There is no particular limitation in shapes and structures of the uneven structure formed on the second cooling roll as long as the uneven structure may form the air flow grooves, and various designs may be used. For example, the uneven structure may be formed in a linear or lattice-like pattern parallel or perpendicular to the axial direction of the second cooling roll 400. In an example, the uneven structure may be formed in a regular or irregular embossed pattern protruding from the surface of the second cooling roll 400.

The air flow grooves may be removed easily when the oriented film is converted into a commercial product or is used. Particularly, the oriented film wound at a winder 600 may be cut into a desired size to be a product. Herein, an application of heat to the oriented film allow an easy removal of the air flow grooves. In other words, when the oriented film is heated to a desired temperature, the air flow grooves may be removed and the oriented film may maintain its smoothness. In addition, the air flow grooves may be removed easily while the oriented film is used. For example, the oriented film may be used for packaging, labels and lamination coating (laminated sheets). Herein, when the oriented film is heated for sealing or coating adhesion, the air flow grooves may be removed with ease by the heat.

Referring to Fig. 5, the second cooled film is transferred to a transverse direction orientation device 500 along guide rolls R2 so that it is oriented along the widthwise direction (TDO). Herein, any conventional transverse direction orientation device may be used for the purose. The transverse direction orientation may be carried out by setting the temperature of the transverse direction orientation device 500 at 100~200℃, but is not limited thereto. In addition, the transverse direction orientation may be carried out at an orientation ratio of 2~15 times, particularly 5~12 times, and more particularly 5~10 times. Such a transverse direction orientation ratio may be realized by a rail pattern.

As mentioned above, the transverse direction oriented film is wound at the winder 600 and then is made as a product. After the transverse direction orientation, the film is subjected to trimming as usual before it is wound. Particularly, when both ends of the film have a difference in thickness after the film is passed through the transverse direction orientation device 500, trimming may be carried out to remove the both ends, and then the film is wound at the winder 600.

According to the embodiments described above, the transverse direction orientation is not carried out right after the machine direction orientation. Rather, the second extrusion and second cooling are included between the transverse direction orientation and the machine direction orientation. The resin layer 40 is laminated through the second extrusion so that even a resin having a low melting point may be extruded and laminated. A multi-layer oriented film having a resin layer 40 may be obtained through the continuous extrusion. In this manner, it is possible to simplify the manufacturing process, and thereby reducing time and cost. Further, when using a second cooling roll 400 having an uneven structure on its surface 450 during the second cooling, it is possible to prevent wrinkling by virtue of the air flow grooves formed on the resin layer 40, and thus to improve the appearance of the multi-layer film. In addition, the resin layer 40 has excellent interlayer adhesion strength to the film F, and particularly has adhesion strength equal to or higher than the strength that may be obtained by the conventional coating process.

The oriented film according to the embodiments may be useful for various packaging materials, labels, lamination coating (laminated sheets), or the like. For example, the oriented film may be used as a packaging material for food, electronic appliances and medical products, as lamination coating (laminated sheets) for ID documents, printed matters, menu boards, etc., and as a label adhesion.

In an embodiment, provided is a multi-layer oriented polyolefin film obtained by the above-described method. The multi-layer oriented polyolefin film has the same structure and layers as described above.

The examples and comparative examples will now be described. Test about the interlayer adhesion strength (adhesive force) of the extruded film according to the examples as compared to a conventional coating film will be described. The test is provided to evaluate the interlayer adhesion strength (adhesive force) between the resin layer 40 and the skin inner layer 20.

[Examples 1 and 2]

The apparatus as shown in Fig. 5 is used to form a skin outer layer 10/core layer 30/skin inner layer 20 via extrusion, followed by cooling and machine direction orientation at an orientation ratio of 4 times. After the machine direction orientation, an EVA layer as a resin layer 40 is laminated on the skin inner layer 20 through an in-line process of continuous extrusion, followed by cooling and transverse direction orientation at an orientation ratio of 8 times. In this manner, a tetra-layer structured oriented film as shown in Fig. 3 is prepared. Herein, the skin outer layer 10 and the core layer 30 are PP layers and the skin inner layer 20 is a PE layer (Example 1). In Example 2, a paper is thermally laminated on the EVA layer.

[Comparative Examples 1 and 2]

A commercially available thermally laminated EVA product is used as a sample for Comparative Examples 1 and 2. Particularly, a skin outer layer (PP layer)/core layer (PP layer)/skin inner layer (PE layer) is formed via extrusion and cooled, followed by machine direction orientation at an orientation ratio of 4 tiems and transverse direction orientation at an orientation ratio of 8 times. The machine direction orientation and transverse direction orientation are carried out continuously. Then, an EVA layer is thermally laminated on the skin inner layer (PE layer) through an off-line process, and the resultant multi-layer film is used as Comparative Example 1. Meanwhile, a paper is thermally laminated on the EVA layer, and the resultant multi-layer film is used as Comparative Example 2.

Each sample according to Example 1 and Comparative Example 1 is evaluated in terms of interlayer adhesion strength, and the results are shown in the following Table 1.

Interlayer Adhesion Strength (Peel Strength)

(1) Each sample is cut into a size of 15 mm X 150 mm (width X length) by using a cutter bar.

(2) The resin layer (EVA layer) and the skin inner layer (PE layer) of the sample cut into a predetermined size are subjected to interlayer separation within a predetermined length by using a blade.

(3) The sample that has been subjected to interlayer separation within a predetermined length is dipped into a container in which a standard electrolyte is contained, followed by sealing (electrolyte: 1M LiPF₆ solution).

(4) The electrolyte container having the sample is stored in a drying oven at 85℃ for 1 day.

(5) After 1 day, the sample is removed from the container and the interlayer adhesion strength (peel strength) is determined by using a tensile strength tester at an angle of 180˚.

(6) The samples according to Example 2 and Comparative Example 2 are evaluated in terms of the interlayer adhesion strength (peel strength) between the resin layer (EVA layer) and paper using the above-mentioned method. The results are also shown in the following Table 1.

Table 1

Results of Interlayer Adhesion Strength

Results	Ex.1	Comp. Ex.1	Ex.2	Comp. Ex.2
Layered structure of the oriented film	PP/PP/PE/EVA	PP/PP/PE/EVA	PP/PP/PE/EVA/paper	PP/PP/PE/EVA/paper
Method for forming EVA layer	In-line extrusion	Off-line thermal lamination	In-line extrusion	Off-line thermal lamination
Interlayer adhesion strength (after 1 day)	2.0 kgf	1.5 kgf	0.4 kgf	0.4 kgf

As shown in Table 1, when the resin layer (EVA layer) is laminated through the in-line extrusion according to the embodinents, the multi-layer oriented film has an interlayer adhesion strength equal to or higher than that of the conventional thermally laminated film (Comparative Examples 1 and 2). In addition, when evaluated by the naked eye, each of the multi-layer oriented films of Examples 1 and 2 has excellent surface appearance. Further, the paper-laminated multi-layer oriented film shows no coming off, when the paper-laminated multi-layer oriented film is folded. This suggests that the paper-laminated multi-layer oriented film has a good adhesion to the paper.

While the embodiments have been shown and described, it will be understood by those skilled in the art that various changes in form and details may be made thereto without departing from the spirit and scope of the present disclosure as defined by the appended claims. In addition, many modifications can be made to adapt a particular situation or material to the teachings of the present disclosure without departing from the essential scope thereof.

This disclosure is directed to a method for manufacturing a multi-layer oriented polyolefin film, and a multi-layer oriented polyolefin film manufactured thereby. The method allows a simple process, thereby reducing time and cost.

Claims

A method for manufacturing a multi-layer oriented polyolefin film, comprising:

carrying out a first extrusion molding of a multi-layer polyolefin film;

first cooling the first extrusion molded film;

machine direction orienting the first cooled film along the longditudinal direction;

carrying out a second extrusion molding in order to laminate at least one resin layer on the machine direction oriented film;

second cooling the film laminated with the resin layer; and

transverse direction orienting the second cooled film along the transverse direction.
The method according to claim 1, wherein the second cooling of the film laminated with the resin layer is carried out by using a cooling roll having an uneven structure on its surface to form air flow grooves on the resin layer.
The method according to claim 1 or 2, wherein the first extrusion molding is carried out in such a manner that the film comprises a skin outer layer, a core layer and a skin inner layer, and the second extrusion molding is carried out in such a manner that a resin layer is laminated on at least one selected from the group consisting of the skin outer layer and the skin inner layer.
The method according to claim 1 or 2, wherein a material comprising at least one selected from the group consisting of polyolefin resins, silicone resins, urethane resins, acrylic resins, polyamide resins, metallocene resins, nylon resins, ethylene vinyl acetate, ethylene methyl acetate, ethylene methyl acrylic acid, ethylene glycol, ethylene acid terpolymer and rubber is used for the resin layer in the second extrusion molding.
The method according to claim 1 or 2, wherein a material comprising a resin having a lower melting point than a material used for the first extrusion molding is used for the resin layer in the second extrusion molding.
The method according to claim 1 or 2, wherein a material comprising an antistatic agent is used for the resin layer in the second extrusion molding.
The method according to claim 1 or 2, wherein a material comprising a nylon resin is used for the resin layer in the second extrusion molding.
The method according to claim 3, wherein the first extrusion molding is carried out in such a manner that the skin outer layer comprises at least one selected from the group consisting of slip agent and anti-blocking agent.
A multi-layer oriented polyolefin film manufactured by the method according to claim 1 or 2.