WO2012023779A2 - Environmentally friendly multilayer barrier film and preparation method thereof - Google Patents

Environmentally friendly multilayer barrier film and preparation method thereof Download PDF

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Publication number
WO2012023779A2
WO2012023779A2 PCT/KR2011/005999 KR2011005999W WO2012023779A2 WO 2012023779 A2 WO2012023779 A2 WO 2012023779A2 KR 2011005999 W KR2011005999 W KR 2011005999W WO 2012023779 A2 WO2012023779 A2 WO 2012023779A2
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resin
layer
film
resin layer
layers
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WO2012023779A3 (en
Inventor
Hojin Yu
Sang Il Kim
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SKC Co Ltd
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SKC Co Ltd
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/06—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material
    • B32B27/08—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/30—Layered products comprising a layer of synthetic resin comprising vinyl (co)polymers; comprising acrylic (co)polymers
    • B32B27/306—Layered products comprising a layer of synthetic resin comprising vinyl (co)polymers; comprising acrylic (co)polymers comprising vinyl acetate or vinyl alcohol (co)polymers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/36—Layered products comprising a layer of synthetic resin comprising polyesters
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/40—Layered products comprising a layer of synthetic resin comprising polyurethanes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B7/00—Layered products characterised by the relation between layers; Layered products characterised by the relative orientation of features between layers, or by the relative values of a measurable parameter between layers, i.e. products comprising layers having different physical, chemical or physicochemical properties; Layered products characterised by the interconnection of layers
    • B32B7/04—Interconnection of layers
    • B32B7/12—Interconnection of layers using interposed adhesives or interposed materials with bonding properties
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B38/00—Ancillary operations in connection with laminating processes
    • B32B38/0012—Mechanical treatment, e.g. roughening, deforming, stretching
    • B32B2038/0028—Stretching, elongating
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2250/00—Layers arrangement
    • B32B2250/03—3 layers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2250/00—Layers arrangement
    • B32B2250/05—5 or more layers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2250/00—Layers arrangement
    • B32B2250/24—All layers being polymeric
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2250/00—Layers arrangement
    • B32B2250/40—Symmetrical or sandwich layers, e.g. ABA, ABCBA, ABCCBA
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2307/00—Properties of the layers or laminate
    • B32B2307/70—Other properties
    • B32B2307/716—Degradable
    • B32B2307/7163—Biodegradable
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2329/00—Polyvinylalcohols, polyvinylethers, polyvinylaldehydes, polyvinylketones or polyvinylketals
    • B32B2329/04—Polyvinylalcohol
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B37/00—Methods or apparatus for laminating, e.g. by curing or by ultrasonic bonding
    • B32B37/14—Methods or apparatus for laminating, e.g. by curing or by ultrasonic bonding characterised by the properties of the layers
    • B32B37/15—Methods or apparatus for laminating, e.g. by curing or by ultrasonic bonding characterised by the properties of the layers with at least one layer being manufactured and immediately laminated before reaching its stable state, e.g. in which a layer is extruded and laminated while in semi-molten state
    • B32B37/153—Methods or apparatus for laminating, e.g. by curing or by ultrasonic bonding characterised by the properties of the layers with at least one layer being manufactured and immediately laminated before reaching its stable state, e.g. in which a layer is extruded and laminated while in semi-molten state at least one layer is extruded and immediately laminated while in semi-molten state

Definitions

  • the present invention relates to an environmentally friendly multilayer film with improved gas-barrier property which is useful for wrapping material, and a preparation method thereof.
  • Petroleum-based thermoplastic resin films such as polypropylene films and polyethylene terephthalate films have been widely used for wrapping material due to its high mechanical strength and good processability.
  • thermoplastic resin films have low gas-barrier property which is not appropriate for safekeeping of the contents from external gases, particularly oxygen gas in the atmosphere, or maintaining a constant gaseous composition inside the packaging.
  • thermoplastic resin films with gas-barrier property by coating with a gas-barrier layer comprising a polyvinyl alcohol (PVOH)-based resin.
  • PVOH polyvinyl alcohol
  • Korean Patent Laid-open Publication No. 2001-21633 discloses a composite polyester film comprising a polyester base film and a coating layer formed on one surface of the base film, the coating layer comprising PVOH and a water dispersed copolyester resin having sulfonyloxy residue.
  • the composite polyester film has a thickness of 5 to 50 ⁇ and exhibits good transparency, barrier property and resistance to mechanical stress.
  • Korean Patent Laid-open Publication No. 2004-37065 discloses a gas-barrier film comprising a base layer of a thermoplastic resin and a gas-barrier layer coated on the base layer, containing silicon alkoxide hydrolysate, phyllosilicate containing silicon alkoxide and a PVOH-based resin, which exhibits good gas-barrier property even under high humidity more than 90 % R.H.
  • Korean Patent Laid-open Publication No. 2002-92812 discloses a gas-barrier film consisting of a base layer of a thermoplastic resin, and a gas-barrier layer coated on one side of the base layer, the gas-barrier layer comprising a PVOH-based resin, silicon alkoxide hydrolysate and polyethylene oxide; and a sealing layer coated on the other side of the base layer.
  • the gas-barrier film has good appearance and exhibits good gas-barrier property even under high humidity.
  • a multilayer barrier film comprising at least one first resin layer and at least two second resin layers, both outermost layers of the film being the second resin layers, wherein the first resin layer comprises a polyvinyl alcohol (PVOH) resin having a melting temperature (Tm) of 170 to 220 °C and the second resin layer comprises a polylactic acid (PLA) resin or a polyethylene terephthalate (PET) resin having a melting temperature of 205°C or less.
  • PVOH polyvinyl alcohol
  • Tm melting temperature
  • PVA polylactic acid
  • PET polyethylene terephthalate
  • a method for preparing a multilayer barrier film comprising the steps of a) melt-extruding a first resin comprising a polyvinyl alcohol (PVOH) resin having a melting temperature (Tm) of 170 to 220 °C to obtain at least one first resin layer and melt-extruding a second resin comprising a polylactic acid (PLA) resin or a polyethylene terephthalate (PET) resin having a melting temperature of 205°C or less to obtain at least two second resin layers; and b) combining the first and the second resin layers so as to prepare a laminate comprising at least one first resin layer and at least two second resin layers, both outermost layers of the film being the second resin layers.
  • PVOH polyvinyl alcohol
  • Tm melting temperature
  • the multilayer barrier film of the present invention employing environmentally friendly resins exhibits good biodegradability and improved gas-barrier property, and physical properties of the film hardly deteriorates due to the protective layer.
  • the gas-barrier property can be enhanced by adjusting the thickness of the PVOH layer.
  • FIG. 1 oxygen permeabilities over time for the gas-barrier films obtained in Examples and Comparative Examples.
  • a barrier layer (a first resin layer) consists of a polyvinyl alcohol (PVOH) resin which is not a biomass but a biodegradable resin.
  • PVH polyvinyl alcohol
  • a typical PVOH resin can not be melt-extruded into a film sheet, since its melting temperature (Tm) is similar to the initial decomposition temperature (Td). Therefore, a coating process is usually employed to form a PVOH barrier layer.
  • Tm melting temperature
  • Td initial decomposition temperature
  • the inventive film uses a modified PVOH resin having a melting temperature (Tm) of 170 to 220 °C so as to employ an extrusion process to form a PVOH layer.
  • the PVOH resin used in the present invention has a melting temperature of 180 to 200 °C and an initial decomposition temperature higher than the melting temperature by 10 °C or more.
  • the polymerization degree of the PVOH resin is preferably in the range of from 300 to 3,000.
  • a PVOH resin layer of the inventive film can be adjusted to have various thicknesses so that the barrier property can be more enhanced.
  • the barrier layer (a first resin layer) has a thickness ranging from 100 nm to 100 ⁇ , whereas that of a PVOH barrier layer prepared by a conventional coating process is only 1 ⁇ or less.
  • the inventive film shows improved gas-barrier property, particularly an oxygen-permeability of 10 cc/m -day or less according to ASTM D3985.
  • the inventive film comprises at least three layers in which a protective layer (a second resin layer) is placed on both surfaces of a PVOH barrier layer (a first resin layer), and thus, the PVOH layer can be prevented from external environment, thereby maintaining the barrier property.
  • a protective layer a second resin layer
  • PVOH barrier layer a first resin layer
  • the protective layer (a second resin layer) comprises polylactic acid (PLA) resin or a polyethylene terephthalate (PET) resin.
  • PLA polylactic acid
  • PET polyethylene terephthalate
  • the inventive film uses a modified PET resin having a melting temperature lower than an initial decomposition temperature of a PVOH resin.
  • the PET resin used in the inventive film has a melting temperature ranging from 170 to 205 °C.
  • a PLA resin used in the present invention preferably has a weight-average molecular weight (Mw) ranging from 50,000 to 300,000, and a PET resin preferably has a weight-average molecular weight ranging from 10,000 to 60,000.
  • inventive film In case the inventive film consists of three layers, it may be composed of [ protective layer / barrier layer / protective layer ], and in case the inventive film comprises more than three layers it may be composed of [ protective layer / barrier layer / barrier layer / protective layer ] or [ protective layer / barrier layer / protective layer / barrier layer / protective layer ].
  • Adhesive strength between the layers may become weak as thickness of the layers increase. Accordingly, an adhesive layer may be further formed between the layers.
  • the inventive film may be composed of [ protective layer / adhesive layer / barrier layer / adhesive layer / protective layer ].
  • the adhesive layer may be formed by using a resin selected from a polyethyleneimine resin and a polyurethane resin.
  • a thickness of the protective layer is in the range of from 1 to 150 ⁇ , and a thickness of the entire multilayer barrier film is in the range of from 5 to 200 ⁇ .
  • the thickness of layer can be adjusted even in nanoscale in order to enhance the adhesion between the layers.
  • the inventive film may be a coextrusion film or a lamination film.
  • the multilayer barrier film of the present invention is prepared by a method comprising: a) melt-extruding a first resin comprising a polyvinyl alcohol (PVOH) resin having a melting temperature (Tm) of 170 to 220 °C into at least one first resin layer and melt-extruding a second resin comprising a polylactic acid (PLA) resin or a polyethylene terephthalate (PET) resin having a melting temperature of 205°C or less into at least two second resin layers; and b) combining the first and the second resin layers so as to prepare a laminate comprising at least one first resin layer and at least two second resin layers, both outermost layers of the film being the second resin layers.
  • PVOH polyvinyl alcohol
  • PET polyethylene terephthalate
  • steps a) and b) may be conducted by a coextrusion process, i.e., the first and the second resin layers are extruded simultaneously and then combined together so as to prepare a laminate comprising at least one first resin layer and at least two second resin layers, both outermost layers of the film being the second resin layers.
  • the resulting laminate further drawn in at least one direction and then heat-treated.
  • the first and/or the second resin layers obtained in step a) may be further coated with an adhesive layer and the first and the second resin layers are combined by the adhesive layer in step b).
  • the laminate comprises at least one first resin layer, at least two second resin layers, and adhesive layers therebetween, both outermost layers being the second resin layers.
  • the first and the second resin layers obtained in step a) are further drawn and then heat-treated before the coating process.
  • the melt-extrusion temperature of the first resin is preferably 170 to 250 °C, more preferably 170 to 220 °C.
  • the multilayer barrier film according to the present invention has an improved gas-barrier property.
  • the gas-barrier property can be further enhanced by adjusting the thickness of the PVOH barrier layer, and physical properties of the inventive barrier film hardly deteriorates owing to a protective layer.
  • the inventive film exhibits environmentally friendly property, even shows a biodegradability of 100 % when a PLA resin is used as the protective layer resin. Accordingly, the multilayer barrier film of the present invention is useful in the fields requiring environmentally friendly property and gas-barrier property, e.g., food packaging.
  • Feedstock resins used in Examples 1 to 3 were as below.
  • Example 1 Preparation of multilayer film [ PLA / PVOH / PLA ]
  • a polyvinyl alcohol resin (G-Polymer, Nippon Gohsei) having a melting temperature of 180 °C was used as a first resin, and a polylactic acid resin (4032D, Nature Works) having a melting temperature of 170 °C was used as a second resin.
  • the first resin and the second resin were melt-extruded by a coextrusion process using three extruders and then combined in a feed block so as to form a three layer laminate having a structure of second resin layer / first resin layer / second resin layer.
  • the melt-extrusion temperatures of the first resin and the second resin were 220 °C and the thickness ratio between the first resin layer and the second resin layer was 1 : 5.
  • the laminate was cooled using a casting roll at 15°C and drawn 3.0 times in the longitudinal direction at 80 °C and then drawn 3.8 times in the transverse direction at 90 °C.
  • the drawn film was heat-treated at 100 °C to obtain a three layer film having a total thickness of 20 ⁇ ⁇ .
  • G-Polymer Nippon Gohsei
  • XTP10 polyethylene terephthalate resin
  • the first resin and the second resin were melt-extruded by a coextrusion process using three extruders and then combined in a feed block so as to form a three layer laminate having a structure of second resin layer / first resin layer / second resin layer.
  • the melt-extrusion temperatures of the first resin and the second resin were 220 °C and 240 °C, respectively, and the thickness ratio between the first resin layer and the second resin layer was 1 : 5.
  • the laminate was cooled by a casting roll at 15°C and drawn 3.0 times in the longitudinal direction at 80 °C and then drawn 3.8 times in the transverse direction at 90 °C.
  • the drawn film was heat-treated at 100 °C to obtain a three layer film having a total thickness of 20 ⁇ .
  • Example 3 Preparation of multilayer film [ PLA / adhesive resin / PVOH / adhesive resin / PLA ]
  • a polyvinyl alcohol resin (G-Polymer, Nippon Gohsei) having a melting temperature of 180°C was used as a first resin
  • a polylactic acid resin (4032D, Nature Works) having a melting temperature of 170°C was used as a second resin
  • a polyurethane resin having a melting temperature of 205°C was used as an adhesive resin.
  • the first resin and the second resin were melt-extruded into a first resin layer and a second resin layer, respectively.
  • the melt-extrusion temperatures of the first resin and the second resin were 220 °C and 240 °C, respectively, and the thickness ratio between the first resin layer and the second resin layer was 1 : 5.
  • the first and the second resin layers were cooled by a casting roll at 15°C and drawn 3.0 times in the longitudinal direction at 80°C and then drawn 3.8 times in the transverse direction at 90°C, followed by heat-treatment at 100°C.
  • the drawn layers were coated with the adhesive resin and then combined together so as to form a laminate having a structure of second resin layer / adhesive layer / first resin layer / adhesive layer / second resin layer, having a total thickness of 20 ⁇ .
  • Feedstock resins used in Comparative Examples 1 to 5 were as below.
  • Table 2 PVOH PLA PET EVOH PVdC
  • a polylactic acid resin (4032D, NatureWorks) having a melting temperature of 170°C was melt-extruded at 220°C and then cooled by casting roll at 15°C and drawn 3.0 times in the longitudinal direction at 80°C.
  • a solution comprising 3 wt% of a polyvinyl alcohol resin (POLINOL, OCI) having a melting temperature of 225-230°C was coated thereon using Mayer rod #6 in a wet-thickness of 16.4 ⁇ . The resulting film was drawn 3.8 times in the transverse direction at 130°C and then heat-treated at 230°C to obtain a coating film having a total thickness of 20 ⁇ .
  • POLINOL polyvinyl alcohol resin
  • a polyethylene terephthalate resin (CTF41, SKC) having a melting temperature of 255°C was melt-extruded at 285°C and then cooled by casting roll at 15°C and drawn 3.0 times in the longitudinal direction at 80°C.
  • a solution comprising 3 wt% of a polyvinyl alcohol resin (POLINOL, OCI) having a melting temperature of 225 ⁇ 230°C was coated thereon using Mayer rod #6 in a wet-thickness of 16.4 ⁇ . The resulting film was drawn 3.8 times in the transverse direction at 130°C and then heat-treated at 230°C to obtain a coating film having a total thickness of 20 ⁇ .
  • POLINOL polyvinyl alcohol resin
  • a polylactic acid resin (4032D, NatureWorks) having a melting temperature of 170°C was melt-extruded at 220°C.
  • the extrudate was cooled by a casting roll at 15°C and drawn 3.0 times in the longitudinal direction at 80°C and drawn 3.8 times in the transverse direction at 90°C.
  • the drawn film was heat-treated at 100°C to obtain a mono-layer film having a thickness of 20 ⁇ .
  • Comparative Example 4 Preparation of multilayer film [ EVOH / PLA / EVOH ]
  • An EVOH (EVAL, uraray) having a melting temperature of 160°C was used as a first resin, and a polylactic acid resin (4032D, NatureWorks) having a melting temperature of 170°C was used as a second resin.
  • the first resin and the second resin were melt-extruded by a coextrusion process using three extruders and then combined together in a feed block to form a three layer laminate having a structure of second resin layer / first resin layer / second resin layer.
  • the melt-extrusion temperatures of the first resin and the second resin were 220 °C and the thickness ratio between the first resin layer and the second resin layer was 1 : 5.
  • the laminate was cooled using a casting roll at 15°C and drawn 3.0 times in the longitudinal direction at 70°C and drawn 3.8 times in the transverse direction at 90°C.
  • the drawn film was heat-treated at 100°C to obtain a three layer film having a total thickness of 20 ⁇ .
  • a polyethylene terephthalate resin (CTF41, SKC) having a melting temperature of 255°C was melt-extruded at 285°C and then cooled by casting roll at 15°C and drawn 3.0 times in the longitudinal direction at 105°C.
  • a solution comprising 50 wt% of a PVdC resin (PVDC LATEX, Asahi Kasei) having a melting temperature of 200°C was coated thereon using Mayer rod #8 in a wet-thickness of 16.4 ⁇ . The resulting film was drawn 3.8 times in the transverse direction at 130°C and then heat-treated at 230°C to obtain a coating film having a thickness of 20 ⁇ .
  • Test 1 Evaluation of gas permeability
  • the oxygen-permeability of the films obtained in Examples 1 to 3 and Comparative Examples 1 to 5 were measured using a gas permeability meter (OX-TRAN, MOCON) according to ASTM D3985 under atmospheric condition. Next, the each film was subjected to a printing process and then oxygen-permeability was measured along the same manner.
  • OX-TRAN gas permeability meter
  • the inventive barrier films obtained in Examples 1 to 3 have more improved oxygen-barrier property than the conventional barrier films obtained in Comparative Examples 1 to 5. Moreover, the barrier films obtained in Examples 1 to 3 maintained low gas permeability even after printing, while the barrier films obtained in Comparative Examples 1 to 5 show high gas permeability after printing.
  • Test 2 Evaluation of gas permeability under humid condition
  • the oxygen-permeability of the films obtained in Examples 1 to 3 and Comparative Examples 1 to 5 were measured using a gas permeability meter (OX-TRAN, MOCON) at 25°C under 1 atm and 50 % R.H. according to ASTM D1434. The results are shown in Table 4.
  • the inventive barrier films obtained in Examples 1 to 3 have more improved oxygen-barrier property under 50 % R.H. than the conventional barrier films obtained in Comparative Examples 1 to 5. Meanwhile, the film of Comparative Example 1 exhibits a gas permeability similar to the film of Comparative Example 3 under 50% R.H. since the PVOH coating layer demolished under high humidity.
  • Test 3 Evaluation of gas permeability over time
  • the oxygen-permeability of the films obtained in Examples 1 to 3 and Comparative Examples 1 to 5 were measured once a day using a gas permeability measuring instrument (OX-TRAN, MOCON) according to ASTM D3985 under atmospheric condition. The results are shown in FIG. 1.

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Abstract

A multilayer barrier film comprising at least one first resin layer and at least two second resin layer, both outermost layers being the second resin layers, wherein the first resin layer comprising PVOH having Tm 170~220 degrees Celsius and the second resin layer comprising PLA or PET having Tm 205 degrees Celsius or less, can enhance gas-barrier property by adjusting a thickness of the PVOH layer and exhibits good biodegradability since it employs environmentally friendly resins.

Description

ENVIRONMENTALLY FRIENDLY MULTILAYER BARRIER FILM AND PREPARATION METHOD THEREOF
FIELD OF THE INVENTION
The present invention relates to an environmentally friendly multilayer film with improved gas-barrier property which is useful for wrapping material, and a preparation method thereof. BACKGROUND OF THE INVENTION
Petroleum-based thermoplastic resin films such as polypropylene films and polyethylene terephthalate films have been widely used for wrapping material due to its high mechanical strength and good processability.
However, such thermoplastic resin films have low gas-barrier property which is not appropriate for safekeeping of the contents from external gases, particularly oxygen gas in the atmosphere, or maintaining a constant gaseous composition inside the packaging.
In order to solve such problems, there have been developed techniques to provide thermoplastic resin films with gas-barrier property by coating with a gas-barrier layer comprising a polyvinyl alcohol (PVOH)-based resin.
Korean Patent Laid-open Publication No. 2001-21633 discloses a composite polyester film comprising a polyester base film and a coating layer formed on one surface of the base film, the coating layer comprising PVOH and a water dispersed copolyester resin having sulfonyloxy residue. The composite polyester film has a thickness of 5 to 50 μπι and exhibits good transparency, barrier property and resistance to mechanical stress.
Further, Korean Patent Laid-open Publication No. 2004-37065 discloses a gas-barrier film comprising a base layer of a thermoplastic resin and a gas-barrier layer coated on the base layer, containing silicon alkoxide hydrolysate, phyllosilicate containing silicon alkoxide and a PVOH-based resin, which exhibits good gas-barrier property even under high humidity more than 90 % R.H.
Further, Korean Patent Laid-open Publication No. 2002-92812 discloses a gas-barrier film consisting of a base layer of a thermoplastic resin, and a gas-barrier layer coated on one side of the base layer, the gas-barrier layer comprising a PVOH-based resin, silicon alkoxide hydrolysate and polyethylene oxide; and a sealing layer coated on the other side of the base layer. The gas-barrier film has good appearance and exhibits good gas-barrier property even under high humidity.
However, such conventional gas-barrier films, prepared by coating a PVOH resin, have problems in that it is difficult to form a coating layer having a thickness over a certain level, and its adhesive strength easily becomes weak as the thickness increases. Moreover, forming a protective layer requires an additional lamination process which lowers production efficiency.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a novel multilayer barrier film having improved gas-barrier property and a preparation method thereof.
In accordance with an aspect of the present invention, there is provided a multilayer barrier film comprising at least one first resin layer and at least two second resin layers, both outermost layers of the film being the second resin layers, wherein the first resin layer comprises a polyvinyl alcohol (PVOH) resin having a melting temperature (Tm) of 170 to 220 °C and the second resin layer comprises a polylactic acid (PLA) resin or a polyethylene terephthalate (PET) resin having a melting temperature of 205°C or less.
In accordance with another aspect of the present invention, there is provided a method for preparing a multilayer barrier film, comprising the steps of a) melt-extruding a first resin comprising a polyvinyl alcohol (PVOH) resin having a melting temperature (Tm) of 170 to 220 °C to obtain at least one first resin layer and melt-extruding a second resin comprising a polylactic acid (PLA) resin or a polyethylene terephthalate (PET) resin having a melting temperature of 205°C or less to obtain at least two second resin layers; and b) combining the first and the second resin layers so as to prepare a laminate comprising at least one first resin layer and at least two second resin layers, both outermost layers of the film being the second resin layers.
The multilayer barrier film of the present invention employing environmentally friendly resins exhibits good biodegradability and improved gas-barrier property, and physical properties of the film hardly deteriorates due to the protective layer. The gas-barrier property can be enhanced by adjusting the thickness of the PVOH layer. BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects and features of the present invention will become apparent from the following description of the invention, when taken in conjunction with the accompanying drawing, which shows:
FIG. 1 : oxygen permeabilities over time for the gas-barrier films obtained in Examples and Comparative Examples.
DETAILED DESCRIPTION OF THE INVENTION In the film of the present invention, a barrier layer (a first resin layer) consists of a polyvinyl alcohol (PVOH) resin which is not a biomass but a biodegradable resin.
A typical PVOH resin can not be melt-extruded into a film sheet, since its melting temperature (Tm) is similar to the initial decomposition temperature (Td). Therefore, a coating process is usually employed to form a PVOH barrier layer. However, such coated PVOH barrier layer has the problems that its adhesive strength easily becomes weak as the thickness increases and even it is difficult to form a coating layer having a thickness over a certain level. Accordingly, the inventive film uses a modified PVOH resin having a melting temperature (Tm) of 170 to 220 °C so as to employ an extrusion process to form a PVOH layer.
Preferably, the PVOH resin used in the present invention has a melting temperature of 180 to 200 °C and an initial decomposition temperature higher than the melting temperature by 10 °C or more. Further, the polymerization degree of the PVOH resin is preferably in the range of from 300 to 3,000.
A PVOH resin layer of the inventive film can be adjusted to have various thicknesses so that the barrier property can be more enhanced. Preferably, the barrier layer (a first resin layer) has a thickness ranging from 100 nm to 100 μιτι, whereas that of a PVOH barrier layer prepared by a conventional coating process is only 1 μηι or less. As a result, the inventive film shows improved gas-barrier property, particularly an oxygen-permeability of 10 cc/m -day or less according to ASTM D3985.
The inventive film comprises at least three layers in which a protective layer (a second resin layer) is placed on both surfaces of a PVOH barrier layer (a first resin layer), and thus, the PVOH layer can be prevented from external environment, thereby maintaining the barrier property. The barrier property of conventional barrier films, on the other hand, without protective layer easily deteriorates when the PVOH layer directly exposed to a printing process.
In the inventive film, the protective layer (a second resin layer) comprises polylactic acid (PLA) resin or a polyethylene terephthalate (PET) resin. Since a typical PET resin has a melting temperature higher than an initial decomposition temperature of a PVOH resin, whereby it is difficult to use coextrusion process, the inventive film uses a modified PET resin having a melting temperature lower than an initial decomposition temperature of a PVOH resin. Preferably, the PET resin used in the inventive film has a melting temperature ranging from 170 to 205 °C.
A PLA resin used in the present invention preferably has a weight-average molecular weight (Mw) ranging from 50,000 to 300,000, and a PET resin preferably has a weight-average molecular weight ranging from 10,000 to 60,000.
In case the inventive film consists of three layers, it may be composed of [ protective layer / barrier layer / protective layer ], and in case the inventive film comprises more than three layers it may be composed of [ protective layer / barrier layer / barrier layer / protective layer ] or [ protective layer / barrier layer / protective layer / barrier layer / protective layer ].
Adhesive strength between the layers may become weak as thickness of the layers increase. Accordingly, an adhesive layer may be further formed between the layers. For example, the inventive film may be composed of [ protective layer / adhesive layer / barrier layer / adhesive layer / protective layer ]. The adhesive layer may be formed by using a resin selected from a polyethyleneimine resin and a polyurethane resin.
Preferably, a thickness of the protective layer (a second resin layer) is in the range of from 1 to 150 μηι, and a thickness of the entire multilayer barrier film is in the range of from 5 to 200 μιιι. The thickness of layer can be adjusted even in nanoscale in order to enhance the adhesion between the layers.
Thus, the inventive film may be a coextrusion film or a lamination film.
The multilayer barrier film of the present invention is prepared by a method comprising: a) melt-extruding a first resin comprising a polyvinyl alcohol (PVOH) resin having a melting temperature (Tm) of 170 to 220 °C into at least one first resin layer and melt-extruding a second resin comprising a polylactic acid (PLA) resin or a polyethylene terephthalate (PET) resin having a melting temperature of 205°C or less into at least two second resin layers; and b) combining the first and the second resin layers so as to prepare a laminate comprising at least one first resin layer and at least two second resin layers, both outermost layers of the film being the second resin layers. In the inventive method, steps a) and b) may be conducted by a coextrusion process, i.e., the first and the second resin layers are extruded simultaneously and then combined together so as to prepare a laminate comprising at least one first resin layer and at least two second resin layers, both outermost layers of the film being the second resin layers. Preferably, the resulting laminate further drawn in at least one direction and then heat-treated.
Otherwise, in the inventive method, the first and/or the second resin layers obtained in step a) may be further coated with an adhesive layer and the first and the second resin layers are combined by the adhesive layer in step b). Thus, the laminate comprises at least one first resin layer, at least two second resin layers, and adhesive layers therebetween, both outermost layers being the second resin layers. Preferably, the first and the second resin layers obtained in step a) are further drawn and then heat-treated before the coating process.
In the inventive method, the melt-extrusion temperature of the first resin is preferably 170 to 250 °C, more preferably 170 to 220 °C.
The multilayer barrier film according to the present invention has an improved gas-barrier property. The gas-barrier property can be further enhanced by adjusting the thickness of the PVOH barrier layer, and physical properties of the inventive barrier film hardly deteriorates owing to a protective layer. Moreover, the inventive film exhibits environmentally friendly property, even shows a biodegradability of 100 % when a PLA resin is used as the protective layer resin. Accordingly, the multilayer barrier film of the present invention is useful in the fields requiring environmentally friendly property and gas-barrier property, e.g., food packaging.
Hereinafter, the present invention is described more specifically by the following examples but these are provided only for illustrations and the present invention is not limited thereto.
Feedstock resins used in Examples 1 to 3 were as below.
Table 1
Figure imgf000010_0001
Example 1: Preparation of multilayer film [ PLA / PVOH / PLA ]
A polyvinyl alcohol resin (G-Polymer, Nippon Gohsei) having a melting temperature of 180 °C was used as a first resin, and a polylactic acid resin (4032D, Nature Works) having a melting temperature of 170 °C was used as a second resin.
The first resin and the second resin were melt-extruded by a coextrusion process using three extruders and then combined in a feed block so as to form a three layer laminate having a structure of second resin layer / first resin layer / second resin layer. The melt-extrusion temperatures of the first resin and the second resin were 220 °C and the thickness ratio between the first resin layer and the second resin layer was 1 : 5.
The laminate was cooled using a casting roll at 15°C and drawn 3.0 times in the longitudinal direction at 80 °C and then drawn 3.8 times in the transverse direction at 90 °C. The drawn film was heat-treated at 100 °C to obtain a three layer film having a total thickness of 20 μ ι.
Example 2: Preparation of multilayer film [ PET / PVOH / PET ]
A polyvinyl alcohol resin (G-Polymer, Nippon Gohsei) having a melting temperature of 180 °C was used as a first resin, and a polyethylene terephthalate resin (XTP10, SKC) having a melting temperature of 205 °C was used as a second resin.
The first resin and the second resin were melt-extruded by a coextrusion process using three extruders and then combined in a feed block so as to form a three layer laminate having a structure of second resin layer / first resin layer / second resin layer. The melt-extrusion temperatures of the first resin and the second resin were 220 °C and 240 °C, respectively, and the thickness ratio between the first resin layer and the second resin layer was 1 : 5.
The laminate was cooled by a casting roll at 15°C and drawn 3.0 times in the longitudinal direction at 80 °C and then drawn 3.8 times in the transverse direction at 90 °C. The drawn film was heat-treated at 100 °C to obtain a three layer film having a total thickness of 20 μπι.
Example 3: Preparation of multilayer film [ PLA / adhesive resin / PVOH / adhesive resin / PLA ]
A polyvinyl alcohol resin (G-Polymer, Nippon Gohsei) having a melting temperature of 180°C was used as a first resin, a polylactic acid resin (4032D, Nature Works) having a melting temperature of 170°C was used as a second resin, and a polyurethane resin having a melting temperature of 205°C was used as an adhesive resin.
The first resin and the second resin were melt-extruded into a first resin layer and a second resin layer, respectively. The melt-extrusion temperatures of the first resin and the second resin were 220 °C and 240 °C, respectively, and the thickness ratio between the first resin layer and the second resin layer was 1 : 5.
The first and the second resin layers were cooled by a casting roll at 15°C and drawn 3.0 times in the longitudinal direction at 80°C and then drawn 3.8 times in the transverse direction at 90°C, followed by heat-treatment at 100°C.
The drawn layers were coated with the adhesive resin and then combined together so as to form a laminate having a structure of second resin layer / adhesive layer / first resin layer / adhesive layer / second resin layer, having a total thickness of 20 μηι.
Feedstock resins used in Comparative Examples 1 to 5 were as below. Table 2 PVOH PLA PET EVOH PVdC
Nature
Manufacturer OCI SKC Kuraray Asahi Kasei
Works
PVDC
Product POLINOL 4032D CTF41 EVAL
LATEX
Tg (°c) 85 60 80 48 -17
Tc (°C) 110 130
Tm (°C) 230 170 255 160 200
Td (°C) 200† 240† 300† 220† 200†
20,000- 150,000- 35,000- 15,000- 50,000-
Mw
80,000 200,000 40,000 30,000 100,000
Comparative Example 1: Preparation of PVOH mono-layer coating film (base film-PLA)
A polylactic acid resin (4032D, NatureWorks) having a melting temperature of 170°C was melt-extruded at 220°C and then cooled by casting roll at 15°C and drawn 3.0 times in the longitudinal direction at 80°C. A solution comprising 3 wt% of a polyvinyl alcohol resin (POLINOL, OCI) having a melting temperature of 225-230°C was coated thereon using Mayer rod #6 in a wet-thickness of 16.4 μηι. The resulting film was drawn 3.8 times in the transverse direction at 130°C and then heat-treated at 230°C to obtain a coating film having a total thickness of 20 μπι.
Comparative Example 2: Preparation of PVOH mono-layer coating film (base film-PET)
A polyethylene terephthalate resin (CTF41, SKC) having a melting temperature of 255°C was melt-extruded at 285°C and then cooled by casting roll at 15°C and drawn 3.0 times in the longitudinal direction at 80°C. A solution comprising 3 wt% of a polyvinyl alcohol resin (POLINOL, OCI) having a melting temperature of 225~230°C was coated thereon using Mayer rod #6 in a wet-thickness of 16.4 μηι. The resulting film was drawn 3.8 times in the transverse direction at 130°C and then heat-treated at 230°C to obtain a coating film having a total thickness of 20 μηι.
Comparative Example 3: Preparation of PL A mono-layer film
A polylactic acid resin (4032D, NatureWorks) having a melting temperature of 170°C was melt-extruded at 220°C. The extrudate was cooled by a casting roll at 15°C and drawn 3.0 times in the longitudinal direction at 80°C and drawn 3.8 times in the transverse direction at 90°C. The drawn film was heat-treated at 100°C to obtain a mono-layer film having a thickness of 20 μηι.
Comparative Example 4: Preparation of multilayer film [ EVOH / PLA / EVOH ] An EVOH (EVAL, uraray) having a melting temperature of 160°C was used as a first resin, and a polylactic acid resin (4032D, NatureWorks) having a melting temperature of 170°C was used as a second resin.
The first resin and the second resin were melt-extruded by a coextrusion process using three extruders and then combined together in a feed block to form a three layer laminate having a structure of second resin layer / first resin layer / second resin layer. The melt-extrusion temperatures of the first resin and the second resin were 220 °C and the thickness ratio between the first resin layer and the second resin layer was 1 : 5.
Then, the laminate was cooled using a casting roll at 15°C and drawn 3.0 times in the longitudinal direction at 70°C and drawn 3.8 times in the transverse direction at 90°C. The drawn film was heat-treated at 100°C to obtain a three layer film having a total thickness of 20 μηι.
Comparative Example 5: Preparation of PVdC coating film (base film-PET)
A polyethylene terephthalate resin (CTF41, SKC) having a melting temperature of 255°C was melt-extruded at 285°C and then cooled by casting roll at 15°C and drawn 3.0 times in the longitudinal direction at 105°C. A solution comprising 50 wt% of a PVdC resin (PVDC LATEX, Asahi Kasei) having a melting temperature of 200°C was coated thereon using Mayer rod #8 in a wet-thickness of 16.4 μπι. The resulting film was drawn 3.8 times in the transverse direction at 130°C and then heat-treated at 230°C to obtain a coating film having a thickness of 20 μπι. Test 1: Evaluation of gas permeability
The oxygen-permeability of the films obtained in Examples 1 to 3 and Comparative Examples 1 to 5 were measured using a gas permeability meter (OX-TRAN, MOCON) according to ASTM D3985 under atmospheric condition. Next, the each film was subjected to a printing process and then oxygen-permeability was measured along the same manner.
Table 3
Figure imgf000016_0001
As shown in Table 3, it is found that the inventive barrier films obtained in Examples 1 to 3 have more improved oxygen-barrier property than the conventional barrier films obtained in Comparative Examples 1 to 5. Moreover, the barrier films obtained in Examples 1 to 3 maintained low gas permeability even after printing, while the barrier films obtained in Comparative Examples 1 to 5 show high gas permeability after printing.
Test 2: Evaluation of gas permeability under humid condition
The oxygen-permeability of the films obtained in Examples 1 to 3 and Comparative Examples 1 to 5 were measured using a gas permeability meter (OX-TRAN, MOCON) at 25°C under 1 atm and 50 % R.H. according to ASTM D1434. The results are shown in Table 4.
Table 4
Figure imgf000016_0002
Figure imgf000017_0001
As shown in Table 4, it is found that the inventive barrier films obtained in Examples 1 to 3 have more improved oxygen-barrier property under 50 % R.H. than the conventional barrier films obtained in Comparative Examples 1 to 5. Meanwhile, the film of Comparative Example 1 exhibits a gas permeability similar to the film of Comparative Example 3 under 50% R.H. since the PVOH coating layer demolished under high humidity.
Test 3: Evaluation of gas permeability over time
The oxygen-permeability of the films obtained in Examples 1 to 3 and Comparative Examples 1 to 5 were measured once a day using a gas permeability measuring instrument (OX-TRAN, MOCON) according to ASTM D3985 under atmospheric condition. The results are shown in FIG. 1.
As shown in FIG. 1, the inventive barrier films obtained in Examples 1 to
3 exhibited better oxygen-barrier property than the conventional barrier films obtained in Comparative Examples 1 to 5 throughout the test period. Meanwhile, the films obtained in Comparative Examples 1 and 3 exhibited too high gas permeability (about 1,000 cc/m2 day) in compared with other films and therefore they could not be shown on the graph.

Claims

WHAT IS CLAIMED IS:
1. A multilayer barrier film comprising at least one first resin layer and at least two second resin layers, both outermost layers of the film being the second resin layers, wherein the first resin layer comprises a polyvinyl alcohol (PVOH) resin having a melting temperature (Tm) of 170 to 220 °C and the second resin layer comprises a polylactic acid (PLA) resin or a polyethylene terephthalate (PET) resin having a melting temperature of 205°C or less.
2. The multilayer barrier film of claim 1, which is a coextrusion film or a lamination film.
3. The multilayer barrier film of claim 1, wherein the first resin layer has a thickness ranging from 100 nm to 100 μιη.
4. The multilayer barrier film of claim 1, wherein an oxygen-permeability according to ASTM D3985 of the multilayer barrier film is 10 cc/m2-day or less.
5. The multilayer barrier film of claim 1, which has a multilayer structure of the second resin layer / the first resin layer / the second resin layer;
the second resin layer / the first resin layer / the first resin layer / the second resin layer; or
the second resin layer / the first resin layer / the second resin layer / the first resin layer / the second resin layer.
6. The multilayer barrier film of claim 1, wherein an adhesive layer is further added between the first and the second resin layers.
7. The multilayer barrier film of claim 6, wherein the adhesive layer comprises a polyethyleneimine resin or a polyurethane resin.
8. A method for preparing a multilayer barrier film, comprising the steps of: a) melt-extruding a first resin comprising a polyvinyl alcohol (PVOH) resin having a melting temperature (Tm) of 170 to 220 °C to obtain at least one first resin layer and melt-extruding a second resin comprising a polylactic acid (PLA) resin or a polyethylene terephthalate (PET) resin having a melting temperature of 205°C or less to obtain at least two second resin layers; and
b) combining the first and the second resin layers so as to prepare a laminate comprising at least one first resin layer and at least two second resin layers, both outermost layers of the film being the second resin layers.
9. The method of claim 8, wherein steps a) and b) are conducted by a coextrusion process and the method further comprises the steps of drawing the resulting laminate in at least one direction and then heat-treating.
10. The method of claim 8, wherein the method further comprises the steps of drawing and heat-treating the first and the second resin layers obtained in step a) and coating an adhesive layer on the first and/or the second resin layers and the first and the second resin layers are combined by the adhesive layer in step b). 1. The method of claim 8, wherein the melt-extrusion temperature of the first resin is 170 to 250 °C.
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