HK1185091B - Polylactic acid resin composition and packaging film - Google Patents

Abstract

The present invention relates to a polylactic acid resin composition which has optimized flexibility and excellent appearance, and can be effectively used as a packaging film due to the superior physical properties thereof, such as the mechanical properties thereof, transparency, heat resistance, an anti-blocking property, and film processability; and also relates to a packaging film including the polylactic acid resin composition. The polylactic acid resin composition comprises: a hard segment including a predetermined polylactic acid repeating unit; a polylactic acid resin including a polyurethane polyol repeating unit in which polyether polyol repeating units are linearly bound regularly by urethane bonding; and a predetermined amount of anti-oxidant.

Description

Polylactic acid resin composition and packaging film

Technical Field

The present invention relates to a polylactic acid resin composition and a packaging film. More particularly, the present invention relates to a polylactic acid resin composition useful as a packaging material, which has not only improved flexibility but also excellent appearance and excellent properties such as mechanical properties, transparency, heat resistance, anti-blocking property, film processability and the like, and a packaging film comprising the same.

This application claims the benefit of korean patent application No. 10-2010-0130224, filed on 17/12/2010, the entire disclosure of which is hereby incorporated by reference in its entirety.

Technical Field

Most conventional polymers derived from petroleum resources, such as polyethylene terephthalate (PET), nylon, polyolefin, and polyvinyl chloride (PVC) resins, have been used in materials for various applications, such as packaging materials. However, these polymers resist biodegradation and involve environmental problems in the waste treatment process, such as carbon dioxide gas, which causes global warming. In addition, there has been extensive research on the use of biomass-based resins including polylactic acid after depletion of petroleum resources.

However, since plant-derived polylactic acid is lower in mechanical properties and the like than petroleum-based resins, its applicable fields and applications are limited. In particular, efforts have been made to use polylactic acid resins as packaging materials, such as packaging films, but they have failed due to poor flexibility of polylactic acid resins.

In order to overcome the problems of the polylactic acid resin, it has been proposed to add a low molecular weight toughening agent or plasticizer to the polylactic acid resin, or to apply a plasticizer produced by addition polymerization of polyether-based or aliphatic polyester-based polyol to the polylactic acid resin.

However, there is only little improvement in flexibility in most packaging films containing polylactic acid resins produced according to these methods. Furthermore, the packaging films exhibit poor stability, since the plasticizers bleed out over time and have the disadvantage of an increase in haze (haze) coupled with a decrease in low transparency. In most cases of the conventional methods, the plasticizer causes a reduction in mechanical properties of the packaging film, and in particular, it is hardly suggested that a polylactic acid resin having excellent mechanical properties can be easily processed by extrusion and the like. In addition, many cases of adding a plasticizer cause yellowing of the polylactic acid resin and deteriorate the appearance of the packaging film.

Accordingly, there is a continuous need for a polylactic acid resin film having improved flexibility and excellent appearance, and exhibiting excellent properties including mechanical properties, transparency, heat resistance, anti-blocking property, processability of the film, and the like.

Detailed Description

Technical purpose

Accordingly, it is an object to provide a polylactic acid resin composition useful as a packaging material, which exhibits favorable appearance and excellent properties such as mechanical properties, transparency, heat resistance, anti-blocking property, film processability and the like, and optimized flexibility.

Another object of the present invention is to provide a packaging film comprising the polylactic acid resin composition.

Technical solution

The present invention provides a polylactic acid resin composition comprising:

a polylactic acid resin including a hard segment (hard segment) including polylactic acid repeating units of the following chemical formula 1 and a soft segment (soft segment) including polyurethane polyol repeating units in which polyether polyol repeating units of the following chemical formula 2 are linearly connected via urethane bonds; and

antioxidant, which is 100-1500ppmw, based on the amount of monomers used to form the polylactic acid repeat units:

[ chemical formula 1]

[ chemical formula 2]

Wherein A is a linear or branched alkylene group of 2 to 5 carbon atoms, m is an integer of 10 to 100, and n is an integer of 700 to 5000.

The invention also provides a packaging film comprising the polylactic acid resin composition.

Hereinafter, the polylactic acid resin composition according to the specific embodiment and the packaging film including the same will be explained in detail.

According to an embodiment of the present invention, there is provided a polylactic acid resin composition including: a polylactic acid resin including a hard segment including a polylactic acid repeating unit of the following chemical formula 1 and a soft segment including a polyurethane polyol repeating unit in which a polyether polyol repeating unit of the following chemical formula 2 is linearly connected via a urethane bond; and 100-1500ppmw antioxidant, depending on the amount of monomers used to form the polylactic acid repeat units:

[ chemical formula 1]

[ chemical formula 2]

Wherein A is a linear or branched alkylene group of 2 to 5 carbon atoms, m is an integer of 10 to 100, and n is an integer of 700 to 5000.

Such a polylactic acid resin composition includes a specified polylactic acid resin and a specific amount of an antioxidant, and the polylactic acid resin includes a polylactic acid repeating unit represented by chemical formula 1 substantially as a hard segment. And, the polylactic acid includes a polyurethane polyol repeating unit as a soft segment in which a polyether polyol repeating unit of chemical formula 2 is linearly connected via a urethane bond (-C (═ O) -NH-).

The polylactic acid resin has biodegradability that is a characteristic of a biomass-based resin because it includes a polylactic acid repeating unit as a hard segment. Further, according to experimental data obtained by the present inventors, it was shown that the polylactic acid resin exhibits improved flexibility (e.g., relatively low total young's modulus measured in the machine direction and the transverse direction) due to the inclusion of the polyurethane polyol repeating unit as a soft segment, and allows the production of a film having high transparency and low haze.

Further, the present inventors revealed that it is possible to suppress yellowing of the polylactic acid resin, and by providing a polylactic acid resin composition containing an amount of an antioxidant together with the polylactic acid resin, a resin composition and a film having excellent appearance can be obtained, and completed the present invention. Thus, the resin composition of an embodiment of the present invention may comprise about 100-1500ppmw, preferably about 500-1500ppmw and more preferably about 1000-1500ppmw of antioxidant, depending on the amount of monomer (e.g., lactic acid or lactide) used to form the polylactic acid repeat units of the polylactic acid resin. If the content of the antioxidant is too low, yellowing of the polylactic acid resin may be caused by oxidation of the flexible component such as the soft segment, and the appearance of the resin composition and the film may be poor. On the other hand, if the content of the antioxidant is too high, the antioxidant may decrease the polymerization rate of lactide, and thus a hard segment including the polylactic acid repeating unit may not be properly formed, and the mechanical properties of the polylactic acid resin may be deteriorated.

In contrast, in the case of using the resin composition of one embodiment of the present invention including the antioxidant having the optimized content, more specifically, in the case of obtaining the polylactic acid resin and the resin composition of one embodiment by adding the antioxidant having the optimized content during the polymerization of the polylactic acid resin, the polymerization conversion rate (polymerization) and the polymerization degree of the polylactic acid resin may be increased, and the productivity may be increased. Also, since the resin composition can exhibit excellent thermal stability during film formation exceeding 180 ℃, it is possible to suppress the formation of monomers such as lactide or lactic acid or low molecular weight materials such as cyclic oligomer chains. Therefore, as a result of suppressing the decrease in molecular weight and the color change (yellowing) of the film, it becomes possible to provide a packaging film having not only excellent appearance but also improved flexibility and excellent general properties such as mechanical properties, heat resistance, anti-blocking properties and the like.

Meanwhile, in the polylactic acid resin composition of the one embodiment, the polylactic acid repeating unit of chemical formula 1 included in the hard segment of the polylactic acid resin may refer to a polylactic acid homopolymer or a repeating unit of the homopolymer. Such polylactic acid repeating units can be obtained according to a typical method for preparing a polylactic acid homopolymer. For example, it can be obtained by a method of forming L-lactide or D-lactide, a cyclic diester of lactic acid from L-lactic acid or D-lactic acid and performing ring-opening polymerization of L-lactide or D-lactide, a cyclic diester of lactic acid, or a method of direct polycondensation of L-lactic acid or D-lactic acid. Among them, the ring-opening polymerization method is preferable because it can provide a polylactic acid repeating unit having a higher polymerization degree. Further, the polylactic acid repeating unit may be prepared by copolymerizing L-lactide and D-lactide at a certain ratio such that the copolymer is amorphous, but the polylactic acid repeating unit is preferably prepared by homopolymerization of L-lactide or D-lactide to improve heat resistance of the film comprising the polylactic acid resin. More specifically, L-lactide or D-lactide material having an optical purity of about 98% or more may undergo ring-opening polymerization to produce polylactic acid repeating units. Lower optical purity can reduce the melting temperature (Tm) of the polylactic acid resin.

And, the repeating unit of the polyurethane polyol contained in the soft segment of the polylactic acid resin has the structure: in this structure, the polyether polyol repeating units of chemical formula 2 are linearly linked through a urethane bond (-C (═ O) -NH-). More specifically, the polyether polyol repeating unit means a polymer prepared from a monomer such as an alkylene oxide by ring-opening (co) polymerization, or a repeating unit of a polymer, and it may have a hydroxyl group at its terminal. Such terminal hydroxyl groups may react with the diisocyanate compound to form urethane bonds (-C (═ O) -NH-), and thus the polyether polyol repeating units are linearly linked to each other to provide polyurethane polyol repeating units. By including such a polyurethane polyol repeating unit as the soft segment, the flexibility of the film including the polylactic acid resin can be greatly improved. Further, the polyurethane polyol repeating unit makes it possible to provide a film having excellent properties without deteriorating the heat resistance, anti-blocking property, mechanical properties or transparency of the polylactic acid resin or film comprising the polyurethane polyol repeating unit.

On the other hand, a polylactic acid copolymer containing a soft segment in which polyester polyol repeating units are linked via urethane bonds, or a resin composition or film including the polylactic acid copolymer has been known. However, there are some problems: the film comprising the polylactic acid copolymer has low transparency and high haze due to low compatibility between the polyester polyol and the polylactic acid. In addition, since such polylactic acid copolymer has a wide molecular weight distribution and poor melting characteristics, the conditions for film extrusion are not good, and thus the resulting film has insufficient mechanical properties, heat resistance, and anti-blocking properties.

Further, a polylactic acid copolymer in which a trifunctional or higher-functional isocyanate compound is used to copolymerize a polyether polyol repeating unit with a polylactic acid repeating unit in a branched manner, or a polylactic acid copolymer in which a copolymer of a polyether polyol repeating unit and a polylactic acid repeating unit is extended by a urethane reaction has been known. However, they also have problems: since the block size of the polylactic acid repeating unit corresponding to the hard segment is also small, and due to the wide molecular weight distribution and poor melting characteristics of the polylactic acid copolymer, the conditions for film extrusion are not good, and the heat resistance, mechanical properties and anti-blocking properties of the film are insufficient.

In contrast, since the polylactic acid resin comprising a polylactic acid repeating unit and a polyurethane polyol repeating unit in which a plurality of polyether polyol repeating units are linearly connected via a urethane bond, and the resin composition comprising the same have a high molecular weight and a narrow molecular weight distribution, it is possible to provide a film having excellent mechanical properties, heat resistance, anti-blocking properties, and the like, and excellent flexibility due to the polyurethane polyol repeating unit. Therefore, it was found that the polylactic acid resin and the resin composition comprising the same according to one embodiment of the present invention overcome the problem of the previous copolymer retention, and can produce a film exhibiting excellent properties and greatly improved flexibility.

The polyether polyol repeat units and the diisocyanate compound may be present in an amount of about 1:0.50 to 1:0.99 of the terminal hydroxyl groups of the polyether polyol repeat units: the molar ratios of the isocyanate groups of the diisocyanate compound react with each other to form polyurethane polyol repeat units. The reaction molar ratio of the terminal hydroxyl groups of the polyether polyol repeating units to the isocyanate groups of the diisocyanate compound may preferably be in the range of about 1: 0.60 to 1: 0.90, and more preferably about 1: 0.70 to 1: 0.85.

As will be explained hereinafter, the polyurethane polyol repeating unit refers to a polymer in which polyether polyol repeating units are linearly connected through a urethane bond, or a repeating unit of the polymer, and may have a hydroxyl group at a terminal thereof. Thus, the polyurethane polyol repeat units can be used as an initiator in the formation of polylactic acid repeat units during polymerization. When the terminal hydroxyl group: when the molar ratio of the isocyanate groups exceeds about 0.99, the number of terminal hydroxyl groups of the repeating units of the polyurethane polyol is insufficient (OHV < 3), so that the repeating units of the polyurethane polyol cannot be suitably used as an initiator. On the other hand, when the hydroxyl group: when the molar ratio of the isocyanate group is too low, the terminal hydroxyl group of the repeating unit of the polyurethane polyol becomes excessive (OHV > 21) so that a repeating unit of polylactic acid and a polylactic acid resin having a high molecular weight cannot be obtained.

Meanwhile, for example, the polyether polyol repeating unit may be a polyether polyol (co) polymer prepared by ring-opening (co) polymerization of one or more alkylene oxide monomers, or a repeating unit thereof. Examples of the oxyalkylene monomer include ethylene oxide, propylene oxide, butylene oxide and tetrahydrofuran. The polyether polyol repeat units prepared from the monomers can be exemplified by: a repeating unit of polyethylene glycol (PEG); repeating units of poly (1, 2-propanediol); repeating units of poly (1, 3-propanediol); a repeating unit of polytetramethylene glycol; a repeating unit of polytetramethylene glycol; repeating units of a polyol copolymerized from propylene oxide and tetrahydrofuran; repeating units of a polyol copolymerized from ethylene oxide and tetrahydrofuran; and repeating units of a polyol copolymerized from ethylene oxide and propylene oxide. In view of the ability to impart flexibility to the polylactic acid resin film, affinity for the polylactic acid repeating units, and water content properties, the repeating units of poly (1, 3-propanediol) or polytetramethylene glycol may be preferably used as the polyether polyol.

Further, the polyether polyol repeat units may have a number average molecular weight of about 450-. If the molecular weight of the polyether polyol repeating unit is too high or too low, the flexibility or mechanical properties of a film obtained from the polylactic acid resin and the resin composition of one embodiment may be insufficient. In addition, the productivity of the resin composition may be reduced, or the flexibility or mechanical properties of the film may be reduced.

Also, the diisocyanate compound may be any compound having two isocyanate groups as long as it can form a urethane bond with the terminal hydroxyl group of the polyether polyol repeating unit. Examples of the diisocyanate compound include 1, 6-hexamethylene diisocyanate, 2, 4-toluene diisocyanate, 2, 6-toluene diisocyanate, 1, 3-xylene diisocyanate, 1, 4-xylene diisocyanate, 1, 5-naphthalene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, 3' -dimethyl-4, 4' -diphenylmethane diisocyanate, 4' -biphenylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, and hydrogenated diphenylmethane diisocyanate. In addition, various other diisocyanate compounds known to those skilled in the art may be used without particular limitation. In view of the ability to impart flexibility to the polylactic acid resin, 1, 6-hexamethylene diisocyanate is preferable.

Meanwhile, the polylactic acid resin included in the resin composition of an embodiment may include a block compound in which the polylactic acid repeating unit hard segment is copolymerized with the polyurethane polyol repeating unit soft segment. More specifically, the terminal carboxyl group of the polylactic acid repeating unit may be connected to the terminal hydroxyl group of the polyurethane polyol repeating unit via an ester bond in the block copolymer. For example, the chemical structure of the block copolymer may be represented by the following formula 1:

[ general formula 1]

Polylactic acid repeating unit (L) -Ester polyol repeating unit (E-U-E-U-E) -Ester-polylactic acid repeating unit (L)

Wherein E is a polyether polyol repeat unit, U is a urethane linkage, and Ester is an Ester linkage.

Since the resin includes a block copolymer in which a polylactic acid repeating unit and a polyurethane polyol repeating unit are copolymerized, the film thus produced may have excellent transparency, mechanical properties, heat resistance, or anti-blocking properties while suppressing bleeding of the polyurethane polyol repeating unit for providing flexibility. In addition, since at least some of the polylactic acid repeating units and the polyurethane polyol repeating units form a block copolymer, the molecular weight distribution, glass transition temperature (Tg), and melting temperature (Tm) of the polylactic acid resin may be optimized, and mechanical properties, flexibility, heat resistance, and the like of the film may be improved.

However, not all of the polylactic acid repeating units contained in the polylactic acid resin and the resin composition must be in the form of a block copolymer having a polyurethane polyol repeating unit, and at least some of the polylactic acid repeating units may not be bonded to the polyurethane polyol repeating unit, but may take the form of a polylactic acid homopolymer. In this case, the polylactic acid resin takes a mixed form in which the block copolymer is present together with a polymer of polylactic acid repeating units that remains uncoupled from the polyurethane repeating units, i.e., a polylactic acid homopolymer.

Meanwhile, the polylactic acid resin may include about 80 to 95 parts by weight of the hard segment and about 5 to 20 parts by weight of the soft segment, preferably about 82 to 92 parts by weight of the hard segment and about 8 to 18 parts by weight of the soft segment, and most preferably about 85 to 90 parts by weight of the hard segment and about 10 to 15 parts by weight of the soft segment, per 100 parts by weight of the total polylactic acid resin (when a polylactic acid homopolymer is optionally included, 100 parts by weight of the total block copolymer and homopolymer).

If the content of the soft segment is too high, it is difficult to provide a high molecular weight polylactic acid resin and a resin composition comprising the high molecular weight polylactic acid resin, and mechanical properties of the film such as strength may be reduced. Further, due to the lowered glass transition temperature, sliding properties, processability, or dimensional stability during packaging using the film may be poor. On the other hand, if the soft segment content is too small, it is difficult to improve the flexibility of the polylactic acid resin and the film. In particular, the glass transition temperature of the polylactic acid resin is excessively increased and the flexibility of the film may be deteriorated, and the polyurethane polyol repeating unit of the soft segment is difficult to properly function as an initiator, which results in a decreased polymerization conversion rate or hinders the formation of a high molecular weight polylactic acid resin.

The polylactic acid resin composition of one embodiment disclosed above includes a specific content of an antioxidant together with the polylactic acid resin. Such an antioxidant contained with a specific content can suppress yellowing of the polylactic acid resin and can make the appearance of the resin composition and film good, as disclosed above. Also, the antioxidant can suppress oxidation or thermal degradation of the soft segment.

As the antioxidant, one or more antioxidants selected from hindered phenol-based antioxidants, amine-based antioxidants, sulfur-based antioxidants, phosphite-based antioxidants, and the like may be used, and other various known antioxidants applicable to the polylactic acid resin composition may also be used.

Since the resin composition of one embodiment has polyether polyol repeating units, it tends to be easily oxidized or thermally degraded in a high-temperature polymerization reaction or a high-temperature extrusion or setting process. Therefore, a heat stabilizer, a polymerization stabilizer or the above-disclosed antioxidant is preferably used as the antioxidant. Specific examples of the antioxidant include phosphoric acid-based heat stabilizers such as phosphoric acid, trimethyl phosphate, or triethyl phosphate; hindered phenol-based primary antioxidants such as 2, 6-di-tert-butyl-p-cresol, octadecyl 3- (4-hydroxy-3, 5-di-tert-butylphenyl) propionate, tetrakis [ methylene-3- (3, 5-di-tert-butyl-4-hydroxyphenyl) propionate ] methane, 1,3, 5-trimethyl-2, 4, 6-tris (3, 5-di-tert-butyl-4-hydroxybenzyl) benzene, diethyl 3, 5-di-tert-butyl-4-hydroxybenzyl phosphite, 4 '-butylidene-bis (3-methyl-6-tert-butylphenol), 4' -mercaptobis (3-methyl-6-tert-butylphenyl) or bis [3 ], 3-bis- (4 '-hydroxy-3' -tert-butyl-phenyl) butanoic acid ] ethylene glycol ester; amine-based secondary antioxidants such as phenyl-alpha-naphthylamine, phenyl-beta-naphthylamine, N '-diphenyl-p-phenylenediamine or N, N' -di-beta-naphthyl-p-phenylenediamine; sulfur-based secondary antioxidants such as dilauryl disulfide, dilauryl thiopropionate, distearyl thiopropionate, mercaptobenzothiazole, or tetramethylthiuram disulfide, tetrakis [ methylene-3- (laurylthio) propionate ] methane; or secondary phosphite-based antioxidants, such as triphenyl phosphite, tris (nonylphenyl) phosphite, triisodecyl phosphite, di (2, 4-di-tert-butylphenyl) pentaerythritol diphosphite or tetrakis [2, 4-bis (1, 1-dimethylethyl) phenyl ] 2, 4' -diyl diphosphonite. Among them, phosphite-based antioxidants are most preferably used together with other antioxidants.

As disclosed above, the antioxidant may be included in the resin composition in an amount of about 100-1500ppmw, preferably about 500-1500ppmw, and more preferably about 1000-1500ppmw, based on the amount of the monomer used to form the polylactic acid repeating unit in the resin composition. If the content of the antioxidant is excessively low, yellowing of the oxidized polylactic acid resin due to a flexible component such as the soft segment may occur, and the appearance of the resin composition and the film may be poor. On the other hand, if the content of the antioxidant is too high, the antioxidant may reduce the polymerization rate of lactide and may not properly form a hard segment including the polylactic acid repeating unit, and may deteriorate the mechanical properties of the polylactic acid resin.

In addition to the antioxidant disclosed above, the polylactic acid resin may contain various well-known additives such as a plasticizer, a UV stabilizer, a color blocking agent (color blocking agent), an anti-gloss agent, a deodorant, a flame retardant, a weather resistant agent, an antistatic agent, an anti-blocking agent, an antioxidant, an ion exchanger, a coloring pigment, and inorganic or organic particles in such an amount that the physical properties of the resin are not adversely affected.

Examples of the plasticizer include phthalate plasticizers such as diethyl phthalate, dioctyl phthalate and dicyclohexyl phthalate; aliphatic dibasic acid ester plasticizers, such as di-1-butyl adipate, di-n-octyl adipate, di-n-butyl sebacate and di-2-ethylhexyl azelate; phosphate plasticizers such as diphenyl-2-ethylhexyl phosphate and diphenyl octyl phosphate; polyhydroxy carboxylic acid ester plasticizers such as acetyl tributyl citrate, acetyl tri 2-ethylhexyl citrate, and tributyl citrate; aliphatic ester plasticizers such as methyl acetylricinoleate and amyl stearate; polyol ester plasticizers, such as triacetin; and epoxy plasticizers such as epoxidized soybean oil, epoxidized linseed oil, fatty acid butyl ester, and epoxidized octyl stearate. And examples of the coloring pigment may be inorganic pigments such as carbon black, titanium oxide and zinc oxide; and organic pigments such as cyanines, phosphorus, quinines, violanthrones, isoindolinones, and thioindigoids. Inorganic or organic particles may be used to improve the film in anti-blocking properties, and examples are silica, colloidal silica, alumina sol, talc, mica, calcium carbonate, polystyrene, polymethyl methacrylate, and silicon examples. In addition, various additives suitable for the polylactic acid resin or the film thereof may be employed, and their types and routes of acquisition are well known to those skilled in the art.

The polylactic acid resin in the resin composition, for example, the block copolymer contained therein, may have a number average molecular weight of about 50,000 to 200,000 and preferably about 50,000 to 150,000. Also, the polylactic acid resin may have a weight average molecular weight of about 100,000 to 400,000 and preferably about 100,000 to 320,000. The molecular weight may affect the mechanical properties of the polylactic acid resin. When the molecular weight is too small, the polylactic acid resin may be poorly processed into a film after a melting process such as extrusion because its melt viscosity is too low, and the film, although obtained, has poor mechanical properties such as strength. On the other hand, when the molecular weight is too high, the resin may be processed into a film having a poor yield point (yield) during melting because its melt viscosity is too high.

The polylactic acid resin, for example, a block copolymer contained therein, may have a molecular weight distribution (Mw/Mn), defined as a ratio of weight average molecular weight (Mw) to number average molecular weight (Mn), of about 1.60 to 2.20 and preferably about 1.80 to 2.15. In view of such a narrow molecular weight distribution, the polylactic acid resin has suitable melt viscosity and melt properties so that it can be processed and extruded into a film in a melt process. In addition, high physical properties, such as strength, can be found in films made from polylactic acid resins. In contrast, when the molecular weight distribution is too narrow (too small), the polylactic acid resin may be difficult to process into a film because its melt viscosity is too high at the processing temperature of extrusion. On the other hand, when the molecular weight distribution is too broad (too large), the film may be deteriorated in physical properties such as strength, and the resin may be difficult to produce into a film or may be poorly extruded into a film because its melt viscosity is too small.

Also, the polylactic acid resin may have a melting temperature (Tm) of about 160-. If the melting temperature is too low, a film made of the polylactic acid resin may be poor in heat resistance, and if the melting temperature is too high, the polylactic acid resin requires high temperature for melting process such as extrusion or increases viscosity, thereby making it difficult to extrude the resin into a film.

In addition, the polylactic acid resin, for example, the block copolymer contained therein, has a glass transition temperature (Tg) of about 25 to 55 ℃, and preferably about 30 to 55 ℃. Since the polylactic acid resin has the above glass transition temperature range, a film including the resin composition of one embodiment of the present invention may have optimized flexibility and rigidity, and it may be preferably used as a packaging film. If the glass transition temperature of the polylactic acid resin is too low, the film exhibits too low rigidity, even though it may have improved flexibility, and thus it may be poor in sliding property, processability, dimensional stability, heat resistance, or anti-blocking property during a packaging process using the film and is not suitable for application to a packaging film. On the other hand, a film having an excessively high glass transition temperature provides low flexibility and excessively high rigidity so that it can be easily folded and thus wrinkles do not easily disappear, or it can exhibit poor adhesive strength of an adhesive interface to a target to be wrapped. Further, when it is used for packaging, it may cause a large noise, and is difficult to be used as a packaging film.

Meanwhile, the resin composition of one embodiment of the present invention may include less than about 1 wt%, preferably about 0.01 to 0.5 wt%, of residual monomers (e.g., lactide monomers for forming a polylactic acid repeating unit) according to the weight of the polylactic acid resin contained therein. Since the resin composition includes the block copolymer having the specific structural characteristics and the polylactic acid resin including the block copolymer having the specific structural characteristics, and the antioxidant in a specific content, most of lactide monomers used in the preparation process participate in polymerization and form polylactic acid repeating units. On the other hand, depolymerization or degradation of the polylactic acid resin does not substantially occur. Accordingly, the polylactic acid resin composition of an embodiment can keep residual monomers, such as residual lactide monomers, to a minimum.

If the content of the residual monomer exceeds about 1 wt%, there may be an odor problem in the film forming process using the resin composition, and a decrease in the strength of the final film may be caused due to a decrease in the molecular weight of the polylactic acid resin during the film forming process, and particularly, the monomer may bleed out and it may cause a safety problem when it is applied to food packaging.

Meanwhile, in the pellet product, the polylactic acid resin may have a color b value of less than 6, and preferably 5 or less. Since yellowing of the polylactic acid resin may be suppressed by the antioxidant contained in the resin composition of an embodiment at an optimized content, it may have a color b value of less than 6. If the color b value of the resin composition becomes 6 or more, the appearance of the film becomes poor and the product value is lowered when the resin composition is used for the film.

Meanwhile, the polylactic acid resin composition may be prepared by a method comprising the steps of: ring-opening (co) polymerizing one or more monomers, such as alkylene oxides, to form a (co) polymer having polyether polyol repeat units; reacting the (co) polymer with a diisocyanate compound in the presence of a catalyst to form a (co) polymer having a polyurethane polyol repeating unit; and polycondensing lactic acid (D-lactic acid or L-lactic acid) or ring-opening polymerizing lactide (D-lactide or L-lactide) in the presence of the antioxidant and a (co) polymer having a polyurethane polyol repeating unit.

In particular, polylactic acid having the excellent properties disclosed above and a block copolymer contained therein can be prepared by: reacting a (co) polymer having a polyether polyol repeating unit and a diisocyanate compound to prepare a (co) polymer having a polyurethane polyol repeating unit in which the polyether polyol repeating unit is linearly connected via a urethane bond, and reacting the resulting (co) polymer with lactic acid or lactide. Also, the polylactic acid resin composition of an embodiment includes a specific content of an antioxidant so that it may have a property of inhibiting yellowing. Such a resin composition exhibits greatly improved flexibility due to the repeat units of the polyurethane polyol, and makes it possible to provide a film that exhibits excellent mechanical properties, heat resistance, anti-blocking properties, and the like, and has a good appearance due to inhibited yellowing.

Meanwhile, when polyester polyol repeating units are introduced into a polymer instead of polyether polyol repeating units, or chain extension (or chain extension) is performed after polymerization of polyether polyol and lactic acid or lactide by changing the order, it is difficult to prepare a block copolymer having the excellent properties disclosed above and a polylactic acid resin comprising the block copolymer, and it goes without saying that the resin composition of one embodiment of the present invention cannot be obtained.

Hereinafter, the preparation method of the polylactic acid resin composition will be explained in more detail.

First, a (co) polymer having a polyether polyol repeating unit is prepared by ring-opening polymerization of one or more monomers such as alkylene oxide, and this can be obtained according to a typical polymerization method of polyether polyol (co) polymers.

Then, the (co) polymer having a polyether polyol repeating unit, the diisocyanate compound and the urethane reaction catalyst are loaded into a reactor and subjected to urethane reaction while being heated and stirred. By this reaction, two isocyanate groups of the diisocyanate compound and the terminal hydroxyl group of the (co) polymer can be combined to form a urethane bond. Therefore, a (co) polymer having a polyurethane polyol repeating unit in which polyether polyol repeating units are linearly connected through a urethane bond may be formed and serve as a soft segment in the polylactic acid resin. In this context, the polyurethane polyol (co) polymer may be in the form of E-U-E, wherein the polyether polyol repeating units (E) are linearly connected by urethane bonds (U) and have polyether polyol repeating units at both ends.

The carbamate reaction can be obtained in the presence of a tin catalyst, such as stannous octoate, dibutyltin dilaurate, or dioctyltin dilaurate. In addition, the urethane reaction can be obtained under typical reaction conditions for the preparation of polyurethane resins. For example, the diisocyanate compound and the polyether polyol (co) polymer may be reacted in a nitrogen atmosphere in the presence of a urethane reaction catalyst at 70 to 80 ℃ for 1 to 5 hours to produce a (co) polymer having a polyurethane polyol repeating unit.

Next, a polylactic acid resin composition of an embodiment including a block copolymer (or a polylactic acid resin including a block copolymer) and a specific content of an antioxidant may be prepared by: in the presence of a (co) polymer having a polyurethane polyol repeating unit and a specific content of an antioxidant, lactic acid (D-lactic acid or L-lactic acid) is subjected to a polycondensation reaction, or lactide (D-lactide or L-lactide) is subjected to a ring-opening polymerization. That is, according to these polymerizations, polylactic acid repeating units containing as hard segments are formed to prepare a polylactic acid resin while yellowing due to oxidation of the soft segments is suppressed by an antioxidant. At this time, the polyurethane polyol repeating unit is bonded to at least some of the terminal groups of the polylactic acid repeating unit to prepare a block copolymer.

Thus, a block copolymer and a resin composition which are very different in structure and characteristics from conventional polylactic acid copolymers or branched copolymers prepared from prepolymers consisting of polyether polyol and polylactic acid by chain extension using a diisocyanate compound or by reaction with a trifunctional isocyanate compound, respectively, can be obtained. In particular, the block copolymer according to the embodiment may contain blocks (hard segments) in which polylactic acid repeating units are linked to each other in relatively large mass (molecular weight) units, so that a film made of the polylactic acid resin containing the block copolymer may have a narrow molecular weight distribution and a suitable Tg, and thus may exhibit excellent mechanical properties and heat resistance. In contrast, since the conventional copolymer should have a structure in which polylactic acid repeating units having a small mass (molecular weight) are alternately and randomly distributed together with polyether polyol repeating units, a film obtained therefrom cannot satisfy the above-mentioned properties, such as glass transition temperature, and has poor mechanical properties or heat resistance. Further, since the block copolymer can be prepared while suppressing yellowing by an antioxidant during polymerization, the resin composition and the film including the resin composition can also exhibit excellent appearance properties.

The ring-opening polymerization of lactide can be carried out in the presence of a metal catalyst, such as an alkaline earth metal, a rare earth metal, a transition metal, aluminum, germanium, tin, or antimony. More specifically, the metal catalyst may be in the form of a carbonate, alkoxide, halide, oxide, or titanium tetraisopropoxide carbonate. Preferably, stannous octoate, titanium tetraisopropoxide or aluminum triisopropoxide can be used as the metal catalyst.

Since the polylactic acid resin composition includes a block copolymer (polylactic acid resin) in which a specific hard segment and a soft segment are combined, it can exhibit more improved flexibility while showing biodegradability of the polylactic acid resin. Further, such a structure can minimize the bleeding of the soft segment responsible for flexibility, and can greatly prevent the soft segment from causing a decrease in mechanical properties, heat resistance, transparency, or haze properties of the film.

Further, the polylactic acid resin contains a specific content of an antioxidant and can exhibit suppressed yellowing during production or use, and the resin composition containing these components makes it possible to provide a packaging film having excellent properties such as greatly improved flexibility and excellent mechanical properties while exhibiting excellent appearance and quality.

Thus, according to another embodiment of the present invention, a packaging film comprising a polylactic acid resin is provided. Since the packaging film includes the polylactic acid resin composition, the packaging film may be preferably used as a packaging material in various fields because the film is excellent in mechanical properties, heat resistance, anti-blocking property, transparency, and processability, and may exhibit optimized flexibility and rigidity and a good appearance without yellowing.

The packaging film may have varying thickness and a thickness of 5 to 500 μm depending on its use. For example, when the packaging film is used as a wrapping film or envelope, it may preferably have a thickness of 5 to 100 μm, more preferably 7 to 50 μm and still more preferably 7 to 30 μm in terms of flexibility, workability and strength.

And, when the packaging film having dimensions of 10mm width and 150mm length is subjected to a tensile test using an Instron1123UTM at a temperature of 20 ℃, a relative humidity of 65% and a pulling speed of 300mm/min and a distance between grip portions (grip) of 100mm, the packaging film may exhibit about 350 to 750kgf/mm²Preferably about 450 to 650kgf/mm²And more preferably about 500 to 600kgf/mm²The total young's modulus in both the machine direction and the transverse direction. This range of total young's modulus may reflect the optimized flexibility and rigidity of the packaging film, which seems to be due to the structural properties and glass transition temperature satisfied in polylactic acid resin.

However, when the overall young's modulus is excessively low, the film may undergo a stretching or relaxation phenomenon during the film forming process, and exhibit poor processability, gas permeability, crack formation, or dimensional stability. In addition, insufficient slip properties result in poor release properties or make it difficult to use the film as a wrapping film because the film is deformed before wrapping goods such as containers or food. On the other hand, when the total young's modulus is too high, the fold line may be maintained once it is formed in the film during packaging, resulting in a poor appearance, or the film may become difficult to package because the film is not easily folded following the shape of the object to be packaged.

Also, the packaging film may have 10kgf/mm in the machine direction and the transverse direction²Or higher initial tensile strength, preferably about 12kgf/mm²Or higher initial tensile strength, and more preferably about 15kgf/mm²To about 30kgf/mm²As measured under the same conditions as those for young's modulus. If the initial tensile strength does not reach a lower limit, the film may exhibit poor processability and be prone to tearing, resulting in a high risk of damaging the contents packaged therefrom.

And, the packaging film may exhibit a weight loss of about 3 wt% or less, preferably about 0.01 to 3.0 wt% and more preferably about 0.05 to 1.0 wt%, when it is treated in a hot air oven at 100 ℃ for 1 hour. This property may indicate that the packaging film may have excellent heat resistance and bleed-out resistance properties. If the weight loss is more than 3 wt%, the film may have poor dimensional stability, and the plasticizer, remaining monomers, or additives may permeate out of the film, contaminating the contents packaged by the film.

The packaging film can exhibit a haze of about 3% or less and a light transmission of about 85% or more. Preferably, it may have a haze of about 2% or less and a light transmittance of about 90% or more, and more preferably a haze of about 1% or less and a light transmittance of about 92% or more. If the haze is too high or the light transmittance is too low, the film may make it difficult to easily identify the contents packaged therefrom, and a vivid appearance of a printed image may not be obtained when it is applied to a multilayer film having a printed layer.

The properties necessary for the food packaging material, such as heat sealability, a gas barrier layer against water vapor, oxygen or carbon dioxide gas, releasability, printability and the like as required for the packaging film may be provided to the packaging film as long as the advantages of the packaging film are not deteriorated. For this purpose, a polymer responsible for such properties may be mixed with the film, or a thermoplastic resin such as an acrylic resin, a polyester resin, or a silicone resin, or an antistatic agent, a surfactant, a releasing agent, or the like may be applied to at least one surface of the packaging film. Also, the packaging film may be formed into a multilayer film by coextrusion of other films, such as polyolefin sealants. The packaging film may also be formed into a multilayer film by adhesion or lamination.

Meanwhile, a typical method may be used to manufacture the above-described packaging film. For example, the polylactic acid resin may be formed into an oriented film (stretched film) by an inflation process, a sequential biaxial stretching process, or a concurrent biaxial stretching process, followed by heat setting. In this regard, the formation of an oriented film can be achieved by melt-extruding a polylactic acid resin into a sheet-like structure using an extruder equipped with a T-shaped die, thereafter cooling and solidifying the sheet-like extrudate to form a non-oriented film (non-stretched film), and stretching the non-oriented film in both the machine direction and the transverse direction.

The stretching conditions of the film may be appropriately adjusted depending on the heat shrinkability, dimensional stability, strength and young's modulus. For example, the stretching temperature may preferably be adjusted to a point exceeding the glass transition temperature of the polylactic acid resin and lower than the crystallization temperature in consideration of the strength and flexibility of the final product. Further, the stretching ratio may be set to about 1.5 to 10 times for each direction, or may be different between the machine direction and the transverse direction.

After formation of the oriented film, the packaging film may be finally realized by heat-setting, and for the strength and dimensional stability of the film, the heat-setting is preferably performed at 100 ℃ or more for about 10 seconds.

The packaging film can have not only excellent flexibility and transparency but also sufficient mechanical properties such as strength and anti-bleeding properties even after being stored for a long time. In addition, the film may have biodegradability that is a characteristic of polylactic acid resin. Therefore, the packaging film can be preferably applied to various packaging fields. For example, packaging films may be applied to industrial packaging materials, including agricultural multilayer films, sheets for protecting paint on automobiles, trash and fertilizer enclosures, in addition to being used as, for example, wraps and enclosures for daily consumer goods or food, packaging films for chilling/freezing food, shrinkable outer wrapping films, bundling films, hygiene films such as sanitary napkins or diapers, laminating films, shrinkable label packaging films, and cushion films for packaging candies.

Advantageous effects of the invention

As described above, the present invention provides a polylactic acid resin and a packaging film having optimized flexibility and rigidity, excellent mechanical properties, heat resistance, transparency, anti-blocking property, film processability, and the like, while exhibiting biodegradability due to the properties of the polylactic acid resin. Therefore, polylactic acid resins and packaging films can be applied to various fields as packaging materials, replacing packaging films made of petroleum-based resins and making a great contribution to the prevention of environmental pollution.

Details for practicing the invention

The present invention will be explained in detail with reference to the following examples. However, these examples merely illustrate the present invention, and the scope of the present invention is not limited thereto.

Method for definition and measurement of physical properties: the physical properties set forth in the following examples are defined and measured as follows.

(1) NCO/OH: the molar ratio of "isocyanate groups of diisocyanate compound (e.g., hexamethylene diisocyanate)/terminal hydroxyl groups of polyether polyol repeat units (or (co) polymer)" used in the reaction to form the polyurethane polyol repeat units.

(2) OHV (KOH mg/g): measured by: the polyurethane polyol repeat units (or (co) polymers) are dissolved in dichloromethane, the repeat units are acetylated, the acetylated repeat units are hydrolyzed to produce acetic acid, and the acetic acid is titrated using 0.1N KOH in methanol. Which corresponds to the number of terminal hydroxyl groups of the repeat units (or (co) polymers) of the polyurethane polyol.

(3) Mw and Mn (g/mol) and molecular weight distribution (Mw/Mn): measured by: a0.25 wt% solution of polylactic acid resin in chloroform and gel permeation chromatography (manufactured by ViscotekTDA305, column: Shodex LF804 by 2ea) were applied. Polystyrene was used as a standard material for determining the weight average molecular weight (Mw) and number average molecular weight (Mn). The molecular weight distribution was calculated from Mw and Mn.

(4) Tg (glass transition temperature, deg.c): the measurement was performed using a differential scanning calorimeter (manufactured by TA Instruments) while quenching the molten sample and then raising the temperature of the sample at a rate of 10 ℃/min. Tg was determined from the median and baseline of the tangents to the endothermic curve.

(5) Tm (melting temperature, deg.c): measured using a differential scanning colorimeter (manufactured by TA Instruments) while quenching the molten sample and then raising the temperature of the sample at a rate of 10 ℃/minute. The Tm is determined from the maximum value of the melting endothermic peak of the crystal.

(6) Residual monomer (lactide) content (wt%): after 0.1g of the resin was dissolved in 4ml of chloroform, 10ml of hexane was added thereto and filtered, it was measured by GC analysis.

(7) Content of repeating units of polyurethane polyol (wt%): the content of the repeating unit of the polyurethane polyol in the prepared polylactic acid resin was measured using a 600MHz Nuclear Magnetic Resonance (NMR) spectrometer.

(8) Color of pellet b: the color b value of the resin chips (pellets) was measured by using a colorimeter CR-410 manufactured by Konica Minolta Sensing co. and represents an average value of 5 measurement results.

(9) And (3) extrusion state: the polylactic acid resin was extruded at 200-250 ℃ into a sheet phase using a30 mm single screw extruder equipped with a T-die, and the extruded sheet was electrostatically deposited on a casting drum cooled to 5 ℃ to prepare an unstretched sheet. At this time, the melt viscosity of the extruded sheet was measured using a Physica rheometer (Physica, usa). In detail, while maintaining the initial temperature of the extrudate, a shear force was applied thereto at a shear rate of 1 (1/s) by a 25mm parallel plate type instrument, during which the complex viscosity (Pa · s) of the molten resin was measured using the Physica rheometer. The state of melt viscosity (extrusion state) was evaluated according to the following criteria.

Very good: melt viscosity good enough to perform winding around a cooling drum, o: the melt viscosity was slightly low and entanglement was possible, but difficult, x: the melt viscosity is too low to be entangled.

(10) Initial tensile Strength (kgf/mm)²) MDMD, TD: a film sample having a length of 150mm and a width of 10mm was conditioned at a temperature of 20 ℃ and a humidity of 65% RH for 24 hours, and the tensile strength was measured at a pulling speed of 300mm/min at a distance between the grips of 100mm according to ASTM D638 using a universal tester (manufactured by INSTRON). The average of five measurements is shown. MD and TD represent the machine and transverse directions of the film, respectively.

(11) Elongation (%) MD, TD: the elongation is determined at the point when the film is torn under the same conditions as in the tensile strength test of (10). The average of five measurements is shown. MD and TD represent the machine and transverse directions of the film, respectively.

(12)F5(kgf/mm²) MD and TD: in the stress-strain curve obtained in the tensile strength test of (10), the tangent value at the stress point of 5% strain is determined, and the stress value at 5% elongation is obtained from the tangent slope. The average of five measurements is shown. MD and TD represent the machine and transverse directions of the film, respectively.

(13)F100(kgf/mm²) MD: in the stress-strain curve obtained in the tensile strength test of (10), the tangent value at the stress point of 100% strain is determined, and the stress value at 100% elongation is obtained from the tangent slope. The average of five measurements is shown. MD and TD represent the machine and transverse directions of the film, respectively.

(14) Young's modulus (kgf/mm)²) MD and TD: the Young's modulus of the same film sample as in the tensile strength test of (10) was measured according to ASTM D638 using UTM (manufactured by INSTRON) at a pulling speed of 300mm/min and a distance between the grip portions of 100 mm. The average of five measurements is shown. Because the young's modulus, in particular, the sum of the young's modulus values measured in the machine direction and the transverse direction, corresponds to the flexibility of the film, a lower young's modulus value may indicate a higher flexibility. MD and TD represent the machine and transverse directions of the film, respectively.

(15) Wave pattern (horizontal line): the wave form degree due to the difference in melt viscosity when two resins having different molecular weights or a resin and a plasticizer were mixed and extruded into a film was evaluated on a 4-sized film samples according to the following criteria.

Very good: no wave pattern (horizontal line), o: up to 3 modes (horizontal line), x: 5 or more modes (horizontal lines).

(16) Weight loss rate (%) at 100 ℃: the film samples were conditioned at 23 ℃ and 65% RH for 24 hours and weighed, then heat treated. Then, it was treated in a hot air oven at 100 ℃ for 60 minutes and conditioned again under the same conditions as in the preheating treatment, and weighed. The percent change in pretreatment weight between pretreatment and post-treatment processes was calculated.

(17) Pinhole and bleed resistance: after the heat treatment of (15), the surface of the film sample was observed to check the generation of pin holes. Further, the bleeding of the low molecular weight plasticizer on the film surface was evaluated on a4 size film sample using the tactile sense according to the following criteria.

Very good: no pin holes and no bleeding, o: up to 5 pinholes or ooze were observed, but not severe, x: 5 or more pinholes or severe bleeding.

(18) Haze (%) and light transmittance (%): the film samples were conditioned at 23 ℃ and 65% RH for 24 hours and the average haze values were measured at three different points using a haze meter (Model Japan NDH2000) according to JIS K7136.

(19) Anti-adhesion property: the antistatic surface of the film sample was matched to the printing surface by COLORIT P-type hot stamping using foil (Kurz) and at 40 ℃ at 1kg/cm²Was left standing for 24 hours under pressure, after which adhesion between the antistatic layer and the printed surface was observed. Based on the observation, the blocking resistance property of the film between the antistatic layer (layer a) and the printed surface of the in-mold transfer foil was evaluated according to the following criteria. The actual performance is guaranteed to be at least o.

Very good: no change, o: slight surface change (less than 5%), ×: foil removal 5% or higher.

(20) Yellowing and coloring of the film: after the film sample was pulverized with a pulverizer, and subjected to moisture absorption drying and crystallization at 120 ℃, the sample was melted at about 200 ℃ and again made into chips by a small single screw extruder (Haake co., Rheomics600 extruder). The difference in color b value before/after the film formation process was measured, and yellowing coloration was evaluated according to the following criteria.

Very good: 2 or less, substantially no yellowing,. smallcircle: 5 or less, slightly yellow, x: above 5, severe yellowing occurs.

The materials used in the following examples and comparative examples are given below:

1. polyether polyol repeating units (or (co) polymers) or equivalents thereof (coreesponds)

PPDO 2.4: poly (1, 3-propanediol); number average molecular weight 2400

PPDO 2.0: poly (1, 3-propanediol); number average molecular weight 2000

PPDO 1.0: poly (1, 3-propanediol); number average molecular weight 1000

-PTMEG 3.0: polytetramethylene glycol; number average molecular weight 3000

-PTMEG 2.0: polytetramethylene glycol; number average molecular weight 2000

-PTMEG 1.0: polytetramethylene glycol; number average molecular weight 1000

-PEG 8.0: polyethylene glycol; number average molecular weight 8000

-PBSA 11.0: an aliphatic polyester polyol prepared by polycondensation of 1, 4-butanediol, succinic acid and adipic acid; number average molecular weight of 11,000

2. Diisocyanate compound (or trifunctional or higher isocyanate)

-HDI: hexamethylene diisocyanate

-D-L75: bayer, Desmodur L75 (trimethylolpropane +3 toluene diisocyanate)

3. Lactide monomer

-L-lactide or D-lactide: the product made from Purac has an optical purity of 99.5% or more

4. Antioxidants, etc

-TNPP: phosphorous acid tris (nonylphenyl) ester

-U626: diphosphorous acid di (2, 4-di-tert-butylphenyl) pentaerythritol ester

-S412: tetrakis [ methane-3- (lauroylthio) propionate ] methane

-PEPQ: tetrakis [2, 4-bis (1, 1-dimethylethyl) phenyl ] diphosphonite (1,1 '-diphenyl) -4,4' -diyl

-I-1076: octadecyl 3- (3, 5-di-tert-butyl-4-hydroxyphenyl) propionate

-O3: ethylene glycol bis [3, 3-bis- (4 '-hydroxy-3' -tert-butyl-phenyl) butyrate ]

A.Preparation of polylactic acid resins A to J

The reactants and catalyst were fed to an 8L reactor equipped with a nitrogen line, an agitator, a catalyst inlet, an effluent condenser and a vacuum system according to the instructions shown in table 1 below. As catalyst, dibutyltin dilaurate was used in an amount of 130ppmw based on the total weight of the reactants. The carbamate reaction was performed at 70 ℃ for 2 hours under a nitrogen atmosphere, and then 4kg of L-lactide (or D-lactide) was fed into the reactor, followed by five nitrogen flushes.

Subsequently, the temperature was raised to 150 ℃ to completely dissolve the L-lactide (or D-lactide), and 120ppmw of tin 2-ethylhexanoate catalyst based on the total content of the reactants was diluted in 500ml of toluene, and the diluted solution was fed into the reactor through the catalyst inlet. The reaction was carried out at 185 ℃ for 2 hours under a nitrogen pressure of 1kg, and then phosphoric acid in an amount of 200ppmw was fed through the catalyst inlet and blended with the reaction mixture for 15 minutes to deactivate the catalyst. After catalyst deactivation, vacuum was applied until the pressure reached 0.5 torr to remove extraneous L-lactide (or D-lactide) (about 5 wt% of the initially charged weight). The molecular weight, Tg, Tm, and the like of the resulting resin were measured, and are given in table 1.

B.Preparation of polylactic acid resin L

According to the instructions shown in table 1 below, polyol and 4kg of L-lactide were fed into an 8L reactor equipped with a nitrogen line, stirrer, catalyst inlet, effluent condenser and vacuum system, followed by five nitrogen flushes. The temperature was then raised to 150 ℃ to completely dissolve the L-lactide and a 120ppmw dilution of the catalyst tin 2-ethylhexanoate in 500ml of toluene was introduced into the reactor through the catalyst inlet. The reaction was carried out at 185 ℃ for 2 hours under a nitrogen pressure of 1kg, and then phosphoric acid was fed in an amount of 200ppmw through the catalyst inlet and blended with the reaction mixture for 15 minutes to deactivate the catalyst. Before the pressure reached 0.5 torr, vacuum was applied to remove unreacted L-lactide. The molecular weight, Tg, Tm, and the like of the resulting resin were measured, and are given in table 1.

C.Preparation of polylactic acid resin M

According to the instructions shown in table 1 below, 6g of 1-dodecanol and 4kg of L-lactide were fed into an 8L reactor equipped with a nitrogen line, stirrer, catalyst inlet, effluent condenser and vacuum system, followed by five nitrogen flushes. The temperature was then raised to 150 ℃ to completely dissolve the L-lactide and a 120ppmw dilution of the catalyst tin 2-ethylhexanoate in 500ml of toluene was introduced into the reactor through the catalyst inlet. The reaction was carried out at 185 ℃ for 2 hours under a nitrogen pressure of 1kg, and then phosphoric acid was fed in an amount of 200ppmw through the catalyst inlet and blended with the reaction mixture for 15 minutes to deactivate the catalyst. Before the pressure reached 0.5 torr, vacuum was applied to remove unreacted L-lactide. The molecular weight, Tg, Tm, and the like of the resulting resin were measured, and are given in table 1.

D. Preparation of polylactic acid resin O

PBSA polyol (polyester polyol) and HDI were fed into an 8L reactor equipped with a nitrogen line, stirrer, catalyst inlet, effluent condenser and vacuum system, followed by five nitrogen flushes, according to the instructions shown in table 1 below. As catalyst, dibutyltin dilaurate was used in an amount of 130ppmw based on the total weight of the reactants. The carbamate reaction was performed at 190 ℃ for 2 hours under a nitrogen atmosphere, and then 4kg of L-lactide was fed into the reactor and completely dissolved at 190 ℃ in a nitrogen atmosphere. Tin 2-ethylhexanoate as an addition polymerization catalyst and dibutyltin dilaurate as an ester and/or ester amide exchange catalyst were diluted in 500ml of toluene in amounts of 120ppmw and 1000ppmw, respectively, based on the total weight of the reactants, and charged to the reactor. The reaction was carried out at 190 ℃ for 2 hours under a nitrogen pressure of 1kg, and then phosphoric acid was fed in an amount of 200ppmw through the catalyst inlet and blended with the reaction mixture for 15 minutes to deactivate the catalyst. Before the pressure reached 0.5 torr, vacuum was applied to remove unreacted L-lactide (about 5 wt% of the initial amount). The molecular weight, Tg, Tm, and the like of the resulting resin were measured, and are given in table 1.

E. Preparation of polylactic acid resin P

PEG, 3.6kg of L-lactide and 0.4kg of D-lactide were fed into an 8L reactor equipped with a nitrogen line, stirrer, catalyst inlet, effluent condenser and vacuum system, followed by five nitrogen flushes, according to the instructions shown in table 1 below. The temperature was then raised to 150 ℃ to completely dissolve the lactide and a 120ppmw dilution of the catalyst tin 2-ethylhexanoate in 500ml of toluene was fed into the reactor through the catalyst inlet. The reaction was carried out at 185 ℃ for 2 hours under a nitrogen pressure of 1kg, and then phosphoric acid was fed in an amount of 200ppmw through the catalyst inlet and blended with the reaction mixture for 15 minutes to deactivate the catalyst. Before the pressure reached 0.5 torr, vacuum was applied to remove unreacted L-lactide (about 5 wt% of the initial amount). Then, HDI was introduced into the reactor through the catalyst inlet along with a 120ppmw dilution of the catalyst dibutyltin dilaurate in 500ml toluene, as shown in Table 1. The polymerization was carried out at 190 ℃ for 1 hour under a nitrogen atmosphere. The molecular weight, Tg, Tm, and the like of the resulting resin were measured, and are given in table 1.

F. Preparation of polylactic acid resin Q

PEG, 3.6kg of L-lactide and 0.4kg of D-lactide were fed into an 8L reactor equipped with a nitrogen line, stirrer, catalyst inlet, effluent condenser and vacuum system, followed by five nitrogen flushes, according to the instructions shown in table 1 below. The temperature was then raised to 150 ℃ to completely dissolve the lactide and a 120ppmw dilution of the catalyst tin 2-ethylhexanoate in 500ml of toluene was introduced into the reactor through the catalyst inlet. The reaction was carried out at 185 ℃ for 2 hours under a nitrogen pressure of 1kg, and then phosphoric acid was fed in an amount of 200ppmw through the catalyst inlet and blended with the reaction mixture for 15 minutes to deactivate the catalyst. Before the pressure reached 0.5 torr, vacuum was applied to remove unreacted L-lactide (about 5 wt% of the initial amount). Then, D-L75 was introduced into the reactor through the catalyst inlet along with a 120ppmw dilution of the catalyst dibutyltin dilaurate in 500ml toluene, as shown in Table 1. The polymerization was carried out at 190 ℃ for 1 hour under a nitrogen atmosphere. The molecular weight, Tg, Tm, and the like of the resulting resin were measured, and are given in table 1.

G. Examples 1-5 and comparative example 1, and comparative examples 6-8: film formation

The polylactic acid resins prepared in a to F were dried at 80 ℃ under reduced pressure of 1 torr for 6 hours, and then extruded into a sheet-like structure under the temperature conditions shown in table 2 using a30 mm single screw extruder equipped with a T-shaped die. The extruded sheet was electrostatically deposited on a casting drum cooled to 5 ℃ to produce a non-oriented film (non-stretched film). They were elongated to 3 times in the machine direction between heated rolls under the stretching conditions shown in table 2. Then, the film was fixed using clips, then stretched to 4 times in a tenter, and fixed again in the transverse direction, followed by heat treatment at 120 ℃ for 60 seconds to produce a biaxially oriented polylactic acid resin 20 μm thick. The evaluation results of the film are summarized in table 2.

H. Example 6 and comparative examples 2 to 5: film formation

The resin compositions or polyols shown in table 2 were dried at 80 ℃ under reduced pressure of 1 torr for 6 hours, and melt-kneaded in a twin-screw kneader at 190 ℃ to produce chips of the compositions. They were dried at 80 ℃ under reduced pressure of 1 torr for 6 hours, and a biaxially oriented polylactic acid resin film 20 μm thick was produced in the same manner as in G. The evaluation results of the film are summarized in table 2.

[ Table 1]

As shown in table 1, resins a to E are polylactic acid resins (block copolymers) prepared by: poly (1, 3-propanediol) having a molecular weight of 1000-. Also, the polylactic acid resin is polymerized in the presence of a specific content of an antioxidant, and it is recognized that the resin exhibits a low color b value due to inhibited yellowing and the residual monomer content is low.

In polylactic acid resins, it has been found that polyurethane polyol repeating units (or (co) polymers) have OHVs of 3 to 20 so that they can function as initiators of polymerization of polylactic acid repeating units. Further, the final polylactic acid resin A-E has a weight average molecular weight of 100,000 to 400,000, a molecular weight distribution of 1.80 to 2.15, a Tg of 25 to 55 ℃ and a Tm of 160 to 178 ℃. In view of these thermal parameters, the resins can be prepared as chips, and they individually can be produced into films because the resins exhibit suitable melt viscosities at film extrusion temperatures of, for example, 200 ℃ or higher. Moreover, it is recognized that little yellowing is observed due to the low residual lactide content of less than 1 wt% and the low color b value of less than 6 in the resin.

In contrast, it is recognized that the color b value of resin F is relatively high because the antioxidant content, which is insufficient in molecular weight and 25ppmw, is lower than the amount of monomer (lactide) used to form the polylactic acid repeating units.

And, the resin L is a polylactic acid resin prepared by directly using poly (1, 3-propanediol) having a molecular weight of 2000 and polyethylene glycol having a molecular weight of 8000 as initiators of ring-opening polymerization of L-lactide without through a urethane reaction. However, in this case, OHV of the initiator is too high to obtain a polylactic acid resin having a desired weight average molecular weight. Furthermore, it is recognized that since the resin L does not contain an antioxidant, the resin L contains much residual lactide, and its Tg is only 15 ℃ and has a low polymerization conversion rate. Further, it is recognized that the melt viscosity of the resin is too low to be separately made into a film at a film extrusion temperature of 200 ℃ or higher.

The resin M is a polylactic acid resin prepared by ring-opening polymerization of L-lactide with a small amount of 1-dodecanol as an initiator without introducing a soft segment (polyurethane polyol repeating unit) according to a conventional preparation method of a polylactic acid resin. The polylactic acid resin alone can be produced into a film at a film extrusion temperature of 200 ℃ or higher. However, it was found to have a molecular weight distribution as large as 2.30, which is very broad.

And, the resin O is a polylactic acid copolymer prepared by using a polyurethane formed from a polyester polyol repeating unit such as PBSA instead of a polyether polyol repeating unit as a soft segment while copolymerizing the polyurethane with lactide in the presence of a ring-opening polymerization catalyst, a transesterification catalyst and/or a transesterification catalyst. In the polylactic acid copolymer, polyurethane is randomly introduced in a small segment size and copolymerized with a polylactic acid repeating unit during an ester and/or ester amide exchange reaction. Resin O has a molecular weight distribution as broad as 2.85 and its Tg is low and its Tm is also relatively low. Furthermore, resin O contains no antioxidant and it is therefore recognised that the residual lactide content is relatively high and the colour b value is rather high.

Finally, the resins P and Q are polylactic acid copolymers (P) or branched copolymers (Q) prepared by addition polymerization of polyether polyol repeating units with lactide to form a prepolymer and then by subjecting the prepolymer to chain extension with a diisocyanate compound (copolymer P) or to reaction with a trifunctional isocyanate compound (copolymer Q), respectively. Resins P and Q have molecular weight distributions as broad as 2.50 and 3.91 and their Tg is low and their Tm is also relatively low. Furthermore, resins P and Q do not contain antioxidants and it is therefore recognized that the residual lactide content is relatively high and the color b value is rather high.

[ Table 2]

As shown in Table 2, the films of examples 1 to 5 were prepared from the polylactic acid resin composition of the present invention, which contained a specific content of an antioxidant and a polylactic acid resin, which contained a soft segment (polyurethane polyol repeating unit) in an amount of 5 to 20 wt%, and had the properties of a low color b value, a weight average molecular weight of 100,000-400,000, a molecular weight distribution of 1.80 to 2.15, and a Tm of 160-178 ℃. Further, the film of example 6 was prepared by using a composition in which the polylactic acid resin of the present invention (resin E), the general polylactic acid resin (resin M), and an antioxidant were mixed together.

All of the films of examples 1 to 6 were found to have 10kgf/mm in both the machine direction and the transverse direction²Or higher initial tensile strength, which indicates good mechanical properties. Furthermore, they exhibit a kgf/mm of 750kgf/mm²Or less, in both the machine and transverse directions, which reflects an advantageGood flexibility. This optimized range of total young's modulus is helpful in maintaining a suitable level of stiffness. Further, they were found to be excellent in various physical properties including transparency, haze, anti-blocking property and heat resistance, as indicated by a weight loss rate of 3 wt% or less, haze of 5% or less and light transmittance of 90% or more after treatment in a hot air oven at 100 ℃ for 1 hour. In addition, the films of examples 1 to 6 had good appearance and were excellent in thermal stability, and even after the film extrusion process, the color b change (yellow coloration) was not severe.

In contrast, the film of comparative example 1 prepared from the general polylactic acid resin M exhibited more than 750kgf/mm²The total young's modulus in both the machine direction and the cross direction, so that the flexibility is too insufficient to use the film as a packaging film. Further, the extruded state of the film of comparative example 3 made of resins M and L together was poor due to the large difference in melt viscosity between the two resins. The modes are also found in the final membrane. In addition, the appearance of the film is poor due to pinholes on the film generated by a high content of residual lactide, and an excessively low Tg of the resin L causes a problem with respect to the anti-blocking property. Initial tensile strength, clarity and yellowing are also poor.

Also, in comparative example 4 and comparative example 5, a film was formed only by mixing poly (1, 3-propanediol) having a number average molecular weight of 2400 and an aliphatic polyester polyol having a number average molecular weight of 11,000, the aliphatic polyester polyol was prepared by polycondensation of 1, 4-butanediol, succinic acid, and adipic acid, and the resin M was used as a plasticizing component without using a soft segment polyurethane polyol repeating unit of the resin. The films of comparative example 4 and comparative example 5 had high haze and were poor in yellowing coloration due to incomplete dispersion of the plasticizing component in the resin, and it was recognized that the plasticizing component bleeds out from the surface of the film over time.

Further, the resin F of comparative example 2 has a low molecular weight and therefore it cannot be extruded into a film. However, by mixing the resin F with the general polylactic acid resin M having no soft segment, film extrusion is possible, but due to a large difference in melt viscosity between the two resins, the extruded state is poor and a wave pattern is also found in the final film. Due to this, the initial tensile strength and light transmittance of the film are also poor. Furthermore, it is recognized that due to the low antioxidant content, partial yellowing coloration occurs during film formation.

Also, the film of comparative example 6 was formed of a copolymer including a polyester polyol repeating unit and having a broad molecular weight distribution. Such films exhibit relatively good flexibility, since the polyurethane component responsible for flexibility is randomly incorporated as small segment units. However, it is difficult to form a film because it exhibits blocking problems and poor heat resistance due to low Tg and Tm because polylactic acid repeating units are also introduced in a relatively small size. Furthermore, the films are high in haze and have low transparency due to low compatibility between the polyester polyol and the polylactic acid, both responsible for flexibility. A broad molecular weight distribution occurs during the preparation of the resin due to ester and/or ester amide exchange reactions, resulting in non-uniform melt properties and deterioration in film extrusion state and mechanical properties.

The films of comparative examples 7 and 8 were formed from a resin prepared by addition polymerization of a polyether polyol with lactide to form a prepolymer and then by subjecting the prepolymer to a urethane reaction with a diisocyanate or a trifunctional or higher-functional compound. These resins also have a broad molecular weight distribution, and the polyether polyol repeating units in the resins are linearly linked via urethane bonds, but in addition, they do not satisfy the structural features of the present invention comprising a polylactic acid repeating unit of a relatively high molecular weight as a hard segment. It was also found that these films exhibited non-uniform melt viscosity and poor mechanical properties. In addition, since blocking characteristics of the hard segment and the soft segment of the resin are deteriorated and the resin has low Tm and Tg, the resin has low heat resistance, so that it is difficult to form a film due to the blocking problem.

Furthermore, due to the high residual lactide content and the relatively high color b value, the films of comparative examples 6 to 8 exhibited rather poor appearance in the film state, and the weight loss rate of 100 ℃ was not commercially suitable. In addition, since the films of comparative examples 6 to 8 required the use of an excessive amount of catalyst during the preparation of the resin, the degradation of the polylactic acid resin was caused in the film formation or use. Therefore, they are poor in yellowing coloration of the film and cause pinholes and significant weight change at high temperature, exhibiting poor stability.

Claims (13)

1. A polylactic acid resin composition comprising:

a polylactic acid resin including a hard segment including a polylactic acid repeating unit of the following chemical formula 1 and a soft segment including a polyurethane polyol repeating unit in which a polyether polyol repeating unit of the following chemical formula 2 is linearly connected via a urethane bond; and

an antioxidant in the range of 100-1500ppmw based on the amount of said monomer used to form said polylactic acid repeat unit,

wherein the urethane bond is formed by a reaction between a terminal hydroxyl group of the polyether polyol repeating unit and a diisocyanate compound, and the polyether polyol repeating unit is linearly connected via the urethane bond to form the polyurethane polyol repeating unit, and

wherein the polylactic acid resin comprises a block copolymer in which a terminal carboxyl group of the polylactic acid repeating unit and a terminal hydroxyl group of the polyurethane polyol repeating unit are connected via an ester bond,

[ chemical formula 1]

[ chemical formula 2]

Wherein A is a linear or branched alkylene group of 2 to 5 carbon atoms, m is an integer of 10 to 100, and n is an integer of 700 to 5000.

2. The polylactic acid resin composition according to claim 1, wherein the polylactic acid resin has a number average molecular weight of 50,000-200,000 and a weight average molecular weight of 100,000-400,000.

3. The polylactic acid resin composition according to claim 1, wherein the polylactic acid resin has a glass transition temperature (Tg) of 25-55 ℃ and a melting temperature (Tm) of 160-178 ℃.

4. The polylactic acid resin composition according to claim 1, wherein the polylactic acid resin comprises the block copolymer; and a polylactic acid repeating unit that remains unattached to the polyurethane polyol repeating unit.

5. The polylactic acid resin composition according to claim 1, wherein the polyether polyol repeating unit has a number average molecular weight of 450-9000.

6. The polylactic acid resin composition according to claim 1, wherein the molar ratio of the terminal hydroxyl group of the polyether polyol repeating unit to the isocyanate group of the diisocyanate compound is from 1:0.50 to 1: 0.99.

7. The polylactic acid resin composition according to claim 1, wherein said polylactic acid resin comprises 80 to 95 parts by weight of said hard segment and 5 to 20 parts by weight of said soft segment per 100 parts by weight of said polylactic acid resin.

8. The polylactic acid resin composition according to claim 1, having a color b value of less than 6.

9. The polylactic acid resin composition according to claim 1, wherein the residual monomer content is less than 1 wt% based on the weight of the polylactic acid resin.

10. The polylactic acid resin composition according to claim 1, wherein the antioxidant is at least one selected from the group consisting of a hindered phenol-based antioxidant, an amine-based antioxidant, a sulfur-based antioxidant and a phosphite-based antioxidant.

11. A packaging film comprising the polylactic acid resin composition according to claim 1.

12. The packaging film of claim 11, having a thickness of 5-500 μ ι η.

13. The packaging film as claimed in claim 11, having 350-750kgf/mm²In the general machine and cross directionsYoung's modulus in the direction of 10kgf/mm²Or higher initial tensile strength, 0.01 to 3.0 wt% weight loss after treatment in a hot air oven at 100 ℃ for 1 hour, haze of 3% or less, and light transmittance of 85% or more.