WO2012067388A2

WO2012067388A2 - Environmentally friendly heat-shrinkable film

Info

Publication number: WO2012067388A2
Application number: PCT/KR2011/008663
Authority: WO
Inventors: Kyung Youn Kim; Deuk-Young Lee; Sang Il Kim; Don Chul Lee
Original assignee: Skc Co., Ltd.
Priority date: 2010-11-15
Filing date: 2011-11-14
Publication date: 2012-05-24
Also published as: WO2012067388A3; KR20120052088A

Abstract

An environmentally friendly heat-shrinkable film comprising a polymer blend of a first polymer containing an aliphatic polycarbonate and a second polymer containing a biodegradable aliphatic polyester, which has improved properties in terms of heat-shrinkability, thermal resistance, biodegradability, shrinkage stress, frictional coefficient and haze, and thus useful as a heat-shrinkable label or wrapping material for food products.

Description

ENVIRONMENTALLY FRIENDLY HEAT-SHRINKABLE FILM

FIELD OF THE INVENTION The present invention relates to an environmentally friendly heat-shrinkable film which is useful as a label for food/beverage container or wrapping material for food products.

BACKGROUND OF THE INVENTION

Conventional plastics such as polyethylene (PE) and polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), polyester (PET) are not completely satisfactory in terms of their performance characteristics. These petroleum-derived films require high energy-consumption, emit a large amount of carbon dioxide, and generate environmentally hazardous pollutants when disposed or incinerated.

For example, PVC films have recently become disfavored because they emit toxic pollutants such as dioxin on combustion due to their chlorine, plasticizer and other additive components. Further, PP, PS, and PET films are chemically and biologically very stable so that they are not biodegradable and accumulate in the soil when disposed, which shortens landfill's life and causes soil pollution.

In order to solve such problems, there have been employed environmentally friendly polymers such as biodegradable polylactic acid (PLA) or aliphatic polycarbonates (PC) which is derived from carbon dioxide.

However, PLA films have unacceptably low shrinkage stress and high shrinkage rate due to its high crystallinity, which results in poor appearance after shrink and thus are not appropriate for a label. Meanwhile, aliphatic PC films cannot exhibit satisfactory properties in terms of thermal resistance and other mechanical properties since aliphatic PC is amorphous polymer having low glass transition temperature (Tg).

Further, PET films exhibit good mechanical properties due to the stable molecular structure, while they have high shrinkage stress and thus PET films are not appropriate for using as a label for flexible PE/PP bottles.

Therefore, there is a need for developing a novel heat-shrinkable film which can solve the problems of conventional heat-shrinkable films. SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide an environmentally friendly film having improved heat-shrinkability and high thermal resistance useful as a label or wrapping material.

In accordance with an aspect of the present invention, there is provided an environmentally friendly heat-shrinkable film comprising a polymer blend of a first polymer containing an aliphatic polycarbonate and a second polymer containing a biodegradable aliphatic polyester, wherein the film is uniaxially or biaxially oriented, and exhibits a heat-shrinkage of at least 30% in at least one direction when treated in hot water at 90 °C for 10 seconds.

Further, the present invention provides a heat-shrinkable label or wrapping material comprising the environmentally friendly heat-shrinkable film.

The heat-shrinkable film of the present invention has good properties in terms of heat-shrinkability, thermal resistance, biodegradability, shrinkage stress, frictional coefficient and haze, and thus can be used as a label for food/beverage containers or wrapping material for food products. Further, the inventive film using aliphatic polycarbonates reduces carbon dioxide and hardly emits environmentally harmful pollutants when disposed or incinerated. DETAILED DESCRIPTION OF THE INVENTION

The heat-shrinkable film of the present invention is characterized in that the film comprises a polymer blend of a first polymer containing an aliphatic polycarbonate and a second polymer containing a biodegradable aliphatic polyester, wherein the film is uniaxially or biaxially oriented, and exhibits a heat-shrinkage of at least 30% in at least one direction when treated in hot water at 90 °C for 10 seconds, and the film is drawn in at least one direction.

The aliphatic polycarbonate of the first polymer may be prepared by copolymerization of carbon dioxide and an epoxide compound, the epoxide compound being selected from the group consisting of an alkylene oxide, a cycloalkene oxide and a mixture thereof. The copolymerization is preferably alternating copolymerization. Examples of catalysts for copolymerization include Zn precursors such as diethyl zinc (US Patent No. 3,585,168), a coordination complex containing onium salts (Korean Patent No. 10-0853358), and cobalt catalysts.

Examples of the epoxide compound include ethylene oxide, propylene oxide, butene oxide, pentene oxide, hexene oxide, octene oxide, decene oxide, dodecene oxide, tetradecene oxide, hexadecene oxide, octadecene oxide, butadiene monooxide, l,2-epoxide-7-octene, cyclopentene oxide, cyclohexene oxide, cyclooctene oxide, cyclododecene oxide, 2,3-epoxide norbornene, limonene oxide, and a mixture thereof.

The copolymerization in preparation of the aliphatic polycarbonate may be conducted under C0₂ pressure of 1 to 100 atm, preferably 5 to 30 atm. Further, the copolymerization may proceed at a temperature of 20 °C to 120 °C, preferably 50 °C to 90 °C. The copolymerization process may be conducted through a batch or semibatch process, or a continuous process. In case of batch or semibatch process, a reaction time for copolymerization may be 1 to 24 hours, preferably 1.5 to 4 hours. In case of continuous process, an average retention time of catalysts may be adjusted to 1.5 to 4 hours.

The examples of the aliphatic polycarbonate include polyethylene carbonate, polypropylene carbonate, and a polymer blend thereof.

The aliphatic polycarbonate used in the inventive film preferably has a number-average molecular weight (Mn) ranging from 50,000 to 500,000, wherein the Mn is measured by gel-permeation chromatography (GPC) using polystyrene having a uniform distribution of molecular weight, as a standard material for calibration.

Aromatic polycarbonates are very dangerous even in the preparation process because toxic bisphenol-A and phosgene are used as starting materials. In contrast, aliphatic polycarbonates prepared by using carbon dioxide are very safe and can contribute to reduction of carbon dioxide emission. Further, aromatic polycarbonates are not decomposed in soil when disposed and they generate toxic pollutants when incinerated. However, aliphatic polycarbonates can be degraded into carbon dioxide and water by incineration.

The inventive film comprising such amorphous aliphatic polycarbonate can attain good shrinkability sufficient for a label.

In order to improve thermal resistance and post-processability, the first polymer containing the aliphatic polycarbonate is blended with a second polymer containing a biodegradable aliphatic polyester.

Examples of the biodegradable aliphatic polyester include poly lactic acid, polylactic acid copolymers, polycaprolactone, polyhydroxyalkanoates, polyglycolic acid, polybutylene succinate, poly(butylene adipate-co-terephthalate), and a polymer blend thereof. The biodegradable aliphatic polyester is preferably a crystalline polymer having a melting temperature of 60 °C or more.

Preferably, the biodegradable aliphatic polyester has a number-average molecular weight (Mn) ranging from 1,000 to 500,000.

In the inventive film, the crystalline biodegradable aliphatic polyester of the second polymer protects the amorphous aliphatic polycarbonate of the first polymer, resulting in improvement of the thermal resistance, post-processability, and biodegradability. At the same time, the biodegradable aliphatic polyester of the second polymer having poor shrinkage property can be also complemented by the amorphous aliphatic polycarbonate of the first polymer.

The inventive film may further comprise other additives such as electrostatic generator, anti-static agent, anti-oxidant, heat stabilizer, compatibilizer, UV blocking agent, anti-blocking agent and inorganic lubricant to the extent they do not adversely affect the film properties. Preferably, the additives are comprised in an amount of 0.01 to 10 wt% based on the total weight of the film.

In the inventive film, a weight ratio of the first polymer to the second polymer in the polymer blend preferably ranges from 1 : 0.25 to 1 : 99.

Further, the inventive film may have a thickness of 5 to 500 μηι.

The heat-shrinkable film of the present invention can be prepared by the steps comprising blending a first polymer containing an aliphatic polycarbonate with a second polymer containing a biodegradable aliphatic polyester and optionally mixing with additives, melt-extruding the blend polymer to obtain a undrawn sheet and then drawing the undrawn sheet, followed by heat-setting.

In the preparation, the undrawn sheet may be drawn in both the longitudinal and the transverse directions to obtain a biaxially oriented film, or may be drawn in one of the longitudinal and the transverse directions to obtain a uniaxially oriented film.

The melt-extrusion temperature is preferably 150 to 280 °C, the drawing temperature is preferably 50 to 100 °C, and the drawing ratio is preferably from 1.5 to 10.0 times, more preferably 2.5 to 5.0 times. Further, the heat-setting is preferably conducted at a temperature ranging from 50 to 150 °C. When the conditions of process falls within the above ranges, the desired heat-shrinkage property can be easily achieved.

In preparation of biaxially oriented film, relaxation may be subjected to the film in the range of 0.01 to 5 % after heat-setting so as to adjust the shrinkage balance. Otherwise, relaxation to the film may be subjected in the range from -0.01% to -5.0%, in order to give a proper shrinkage stress to the film.

The heat-shrinkable film of the present invention has good properties in terms of heat-shrinkable, shrinkage stress, frictional coefficient, thermal resistance, haze and biodegradability.

The inventive film exhibits a heat-shrinkage of at least 30% in at least one direction when treated in hot water at 90 °C for 10 seconds. When the heat-shrinkage ratio falls within the above range, the film can be applied for various shapes of containers or bottles.

Further, the inventive film preferably exhibits the maximum shrinkage stress ranging from 1 to 9 N when treated in hot water at 90 °C for 10 seconds. When the maximum shrinkage stress falls within the above range, appearance quality of the film after shrinkage can be more improved and even can be applied to flexible PE/PP bottles.

Further, the inventive film preferably exhibits a dynamic frictional coefficient of less than 0.70 and a static frictional coefficient of less than 0.65. When the frictional coefficient falls within the above range, the films are effectively prevented to adhere together during drawing or hot-filling process. Further, the inventive film preferably exhibits a haze of 30% or less, which is appropriate for various wrapping uses, and exhibits a biodegradability of 20% or more and thus is environmentally friendly. The inventive heat-shrinkable film can be used as a heat-shrinkable label or wrapping material. For example, a uniaxially oriented heat-shrinkable film of the present invention may be used as a heat-shrinkable label, and a biaxially oriented heat-shrinkable film of the present invention may be used as wrapping material. The heat-shrinkable label can be used as a label for food/beverage containers, and the wrapping material can be used for wrapping food products.

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.

The compositions and processes for preparing films according to the present invention and conventional process are summarized in Table 1.

Example 1: Preparation of PPC/PLA blend film

A polypropylene carbonate resin (QPAC40, Empower Materials Inc.) which is prepared by alternating copolymerization of carbon dioxide and propylene oxide, was used as a first polymer. A polylactic acid resin (m.p.145 °C, 4042D, Nature Works LLC) was used as a second polymer.

The first and the second polymers are blended at a weight ratio of 70 : 30, and then 1.0 parts by weight of tris(2,4-di-t-butylphenyl) phosphite (RICHFOS 168, Young's Corporation) as a heat stabilizer and 3.0 parts by weight of polylactic acid whose terminal group is substituted by maleic anhydride (S C Co., Ltd.) as a compatibilizer were added thereto, based on 100 parts by weight of the polymer blend.

The polymer blend was melt-extruded at 190 °C and then cooled by a casting roll at 10 °C to obtain a sheet. The sheet was drawn at a draw ratio of 5.0 in the transverse direction at 65 °C, and then heat-set at 60 °C to obtain a film having a thickness of 50μηι.

Example 2: Preparation of PPC/PBS blend film A polypropylene carbonate resin (QPAC40, Empower Materials Inc.) which is prepared by alternating copolymerization of carbon dioxide and propylene oxide, was used as a first polymer. A polybutylene succinate resin

(m.p. 105 °C, G4560, Irechem Co., Ltd.) was used a second polymer.

The first and the second polymers are blended at a weight ratio of 70 : 30, and then 3.0 parts by weight of tris(2,4-di-t-butylphenyl) phospite (RICHFOS

168, Young's Corporation) as heat stabilizer was added thereto based on 100 parts by weight of the polymer blend.

The polymer blend was melt-extruded at 190 °C and then cooled by a casting roll at 15 °C to obtain a sheet. The sheet was drawn at a draw ratio of 3.0 in the longitudinal direction at 65 °C and then drawn at a draw ratio of 4.0 in the transverse direction at 80 °C, followed by heat-setting at 60 °C to obtain a film having a thickness of 20μηι.

Comparative Example 1: Preparation of PPC film

A polypropylene carbonate resin (QPAC40, Empower Materials Inc.) which is prepared by alternating copolymerization of carbon dioxide and propylene oxide, was melt-extruded at 170 °C and then cooled by a casting roll at 10 °C to obtain a sheet. The sheet was drawn at a draw ratio of 1.5 in the longitudinal direction at 70 °C and then drawn at a draw ratio of 4.0 in the transverse direction at 100 °C, followed by heat-setting at 50 °C to obtain a film having a thickness of 20μπι.

Comparative Example 2: Preparation of PPC/PET blend film

A polypropylene carbonate resin (QPAC40, Empower Materials Inc.) which is prepared by alternating copolymerization of carbon dioxide and propylene oxide, was used as a first polymer. A polyethylene terephthalate resin (m.p. 250 °C, S C Co., Ltd.) was used a second polymer. The first and the second polymers are blended at a weight ratio of 50 : 50

The polymer blend was melt-extruded at 240 °C and then cooled by a casting roll at 20 °C to obtain a sheet. The sheet was drawn at a draw ratio of 3.0 in the transverse direction at 85 °C, and then heat-set at 120 °C to obtain a film having a thickness of 50μπι.

Comparative Example 3: Preparation of PLA resin film A polylactic acid resin (m.p.170 °C, 4032D, Nature Works LLC) was melt-extruded at 230 °C and then cooled by casting roll at 20 °C to obtain a sheet. The sheet was drawn at a draw ratio of 3.0 in the transverse direction at 105 °C, and then heat-set at 165 °C to obtain a film having a thickness of 50μπι. The films obtained in Examples 1 and 2 and Comparative Examples 1 to

3 were evaluated for the following properties. The results are shown in Table 1.

(1) Heat-shrinkage A film sample was cut into 200mm (length) x 15mm (width) pieces, maintained at 90 °C in a water bath for 10 seconds, and the length of the pieces were measured. Using the following equation, the degrees of shrinkage in each of the longitudinal and the transverse directions were calculated:

Heat shrinkage (%) = [ ( length before heat treatment - length after heat treatment ) / length before heat treatment ] x 100

(2) Maximum shrinkage stress

The maximum shrinkage stress of a film sample was measured by using stress analyzer (QM150S, Qmesys Co., Ltd.) equipped with a load cell, after being dipped in 90 °C water bath for 10 seconds.

(3) Thermal resistance

Bottles were labeled with a film sample, filled with 70 °C liquid and tested whether blocking with each other is caused. The results are evaluated in the following criteria:

Good: The bottles did not adhere at all.

Decent: The bottles adhered slightly, but could be separated by cooling. Poor: The bottles adhered, and could not be separated.

(4) Haze

The haze of a film sample was measured according to ASTM D1003 by using a hazemeter (SEP-H, Nihon Semitsu Kogaku Co., Ltd.). (5) Biodegradability

The biodegradability of a film sample was measured according to ASTM

D5338. Table 1

As shown in Table 1, the inventive films obtained in Examples 1 and 2 exhibited higher heat-shrinkage in at least one direction than the conventional films obtained in Comparative Examples 1 to 3, and shrinkage stresses of the inventive films were adequate for a heat-shrinkable film.

Further, the inventive films exhibit high thermal resistance, good biodegradability and relatively low haze, which are useful as a label for food containers or wrapping material for food products.

While the invention has been described with respect to the above specific embodiments, it should be recognized that various modifications and changes may be made to the invention by those skilled in the art which also fall within the scope of the invention as defined by the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A heat-shrinkable film comprising a polymer blend of a first polymer containing an aliphatic polycarbonate and a second polymer containing a biodegradable aliphatic polyester, wherein the film is uniaxially or biaxially oriented, and exhibits a heat-shrinkage of at least 30% in at least one direction when treated in hot water at 90 °C for 10 seconds.

2. The heat-shrinkable film of claim 1, wherein the aliphatic polycarbonate is prepared by copolymerization of carbon dioxide and an epoxide compound, the epoxide compound being selected from the group consisting of an alkylene oxide, a cycloalkene oxide, and a mixture thereof.

3. The heat-shrinkable film of claim 1, wherein the aliphatic polycarbonate is selected from the group consisting of polyethylene carbonate, polypropylene carbonate, and a polymer blend thereof.

4. The heat-shrinkable film of claim 1, wherein the aliphatic polycarbonate has a number-average molecular weight (Mn) ranging from 50,000 to 500,000.

5. The heat-shrinkable film of claim 1, wherein the biodegradable aliphatic polyester is selected from the group consisting of polylactic acid, polylactic acid copolymers, polycaprolactone, polyhydroxyalkanoates, polyglycolic acid, polybutylene succinate, poly(butylene adipate-co-terephthalate), and a polymer blend thereof.

6. The heat-shrinkable film of claim 1, wherein the film further comprises additives selected from the group consisting of electrostatic generator, anti-static agent, anti-oxidant, heat stabilizer, compatibilizer, UV blocking agent, anti-blocking agent, inorganic lubricant, and a mixture thereof, in an amount of 0.01 to 10 weght% based on the total weight of the film.

7. The heat-shrinkable film of claim 1, wherein the polymer blend comprises the first and second polymers at a weight ratio ranging from 1 : 0.25 to 1 : 99.

8. The heat-shrinkable film of claim 1, wherein the film is drawn at a ratio of 1.5 to 10 times in at least one direction of the longitudinal and the transverse directions and is heat-set at a temperature of 50 °C to 100 °C.

9. The heat-shrinkable film of claim 1, wherein the film has a maximum shrinkage stress of 1 to 9 N when treated in hot water at 90 °C for 10 seconds, a haze of 30% or less, and a biodegradability of 20% or more.

10. A heat-shrinkable label comprising the heat-shrinkable film according to any one of claims 1 to 9.

1 1. A wrapping material comprising the heat-shrinkable film according to any one of claims 1 to 9.