HK1185094B - Polylactic acid resin film - Google Patents

Description

Polylactic acid resin film

Technical Field

The present invention relates to a polylactic acid resin film. More particularly, the present invention relates to a polylactic acid resin film having not only biodegradability as a polylactic acid resin but also excellent flexibility, mechanical properties, stability and transparency as a packaging material.

The disclosures of korean patent application nos. 10-2011-.

Technical Field

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

However, since plant-derived polylactic acid is lower in heat resistance, 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. Moreover, films are unsuitable as packaging materials because they exhibit poor stability as the plasticizer bleeds out over time (bleedout) and contaminates the contents of the package. Also, the packaging film has disadvantages of increased haze and decreased transparency. In the case of most conventional processes, films are unsuitable as packaging materials because an improvement in the flexibility of the film results in a great reduction in the mechanical properties or antiblocking properties.

Therefore, there is a continuing need for packaging films having optimized properties such as good flexibility, mechanical properties, stability and clarity and biodegradability.

Detailed Description

Technical purpose

Accordingly, an object of the present invention is to provide a polylactic acid resin film having not only biodegradability as a polylactic acid resin but also optimized properties such as excellent flexibility, mechanical properties, stability, transparency, and the like.

Technical solution

The present invention provides a polylactic acid resin film comprising a polylactic acid resin, the polylactic acid resin comprising a hard segment comprising polylactic acid repeating units having the following chemical formula 1 and a soft segment comprising polyurethane polyol repeating units in which polyether polyol repeating units having the following chemical formula 2 are linearly connected via a urethane bond, wherein a total young's modulus in both longitudinal and transverse directions of the film is 350 to 750kgf/mm²And the total initial tensile strength of both the longitudinal and transverse directions of the film is 20kgf/mm²Or greater:

[ chemical formula 1]

[ chemical formula 2]

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

Hereinafter, a polylactic acid resin film according to a specific embodiment of the present invention will be explained in detail.

According to one embodiment, the present invention provides a polylactic acid resin film comprising a polylactic acid resin comprising a hard segment comprising polylactic acid repeating units of the following chemical formula 1 and a soft segment comprising polyurethane polyol repeating units in which polyether polyol repeating units of the following chemical formula 2 are linearly connected via a urethane bond, wherein a total young's modulus in both longitudinal and transverse directions of the film is about 350-750kgf/mm²The total initial tensile strength of the film in both the machine and transverse directions is about 20kgf/mm²Or greater:

[ chemical formula 1]

[ chemical formula 2]

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

The polylactic acid resin, which is a main component of the film, contains a polylactic acid repeating unit represented by chemical formula 1 mainly as a hard segment. Also, the polylactic acid resin includes a polyurethane polyol repeating unit as a soft segment, in which a polyether polyol repeating unit having chemical formula 2 is linearly connected via a urethane bond (-C (= O) -NH-).

The polylactic acid resin and the film described above have biodegradability characterized as a biomass-based resin because they contain polylactic acid repeating units as hard segments. Further, according to experimental data obtained by the present inventors, it was shown that the polylactic acid resin exhibits improved flexibility and allows the production of a film having high transparency, low haze and improved stability by including the polyurethane polyol repeating unit as a soft segment.

Moreover, when a film having dimensions of 10mm width and 150mm length was 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, at a distance between grips (grip) of 100mm, a film made of polylactic acid resin could exhibit a value of about 350-750kgf/mm²Preferably about 450-²And more preferably about 500-²And a total Young's modulus in both the longitudinal and transverse directions of about 20kgf/mm²Or greater, and preferably about 20 to 60kgf/mm²The total initial tensile strength in both the longitudinal and transverse directions. Such properties of the film may be caused by the structural features of the polylactic acid resin disclosed above.

Specifically, the polylactic acid resin may include a block copolymer prepared by copolymerizing a polylactic acid repeating unit with a polyurethane polyol repeating unit in which a polyether polyol repeating unit is linearly connected via a urethane bond due to a reaction with a diisocyanate compound. Since the polylactic acid resin contains the block copolymer obtained by such as, the film containing the resin can exhibit optimized characteristics not only in terms of flexibility but also in terms of general properties such as mechanical properties. For example, it may satisfy the total young's modulus range and total initial tensile strength range disclosed above. Moreover, such superior properties of the film may be attributed to an optimized production process or the form of the film discussed below (e.g., the form of a biaxially oriented film). Also, since the polylactic acid resin contains a block copolymer, the soft segment component or the residual monomer is less exuded. Therefore, the film may exhibit excellent stability and relatively low weight loss even after high temperature heat treatment. Also, the film may exhibit excellent transparency and low haze due to the reduction of bleeding.

At the same time, the film may exhibit flexibility and stiffness optimized to the packaging film, since the film meets a specific range of overall young's modulus. 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, resulting in poor appearance, or too high film rigidity causes large noise. Moreover, the film is too hard to take a shape according to the shape of the food.

Also, when the tensile test is performed under the same conditions as in the young's modulus test, the film satisfies the specific total initial tensile strength range disclosed above. When the initial tensile strength is outside the range, the handling properties of the film may be deteriorated, and the film may be easily torn and cause damage to the contents. In contrast, the film of one embodiment satisfies a specific total initial tensile strength range, and thus may exhibit excellent mechanical properties that may be preferable for packaging.

Therefore, the polylactic acid resin film of one embodiment exhibits not only biodegradability but also optimized properties such as excellent flexibility, mechanical properties, stability, transparency, and the like, and thus can be very preferably used for packaging and the like.

Hereinafter, the membrane of one embodiment is explained in more detail. First, a polylactic acid resin, which is a main component of the film, is explained in detail, and then, a film including the polylactic acid resin is explained in detail.

In the polylactic acid resin included in the film, the polylactic acid repeating unit of chemical formula 1 included in the hard segment 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 a cyclic diester of lactic acid, L-lactide or D-lactide, from L-lactic acid or D-lactic acid, and performing ring-opening polymerization of the L-lactide or D-lactide, or a method by 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 in such a ratio as to make a copolymer amorphous, but the polylactic acid repeating unit is preferably prepared by homopolymerization of L-lactide or D-lactide to increase heat resistance of a film comprising the polylactic acid resin. More specifically, an L-lactide or D-lactide material having an optical purity of about 98% or more may be subjected to ring-opening polymerization to provide polylactic acid repeating units. Lower optical purity can reduce the melting temperature (Tm) of the polylactic acid resin.

Also, the polyurethane polyol repeating units in the soft segment have a structure in which the polyether polyol repeating units of chemical formula 2 are linearly connected via 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 the 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 connected 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. In addition, the polyurethane polyol repeating unit makes it possible to provide a film having excellent properties without deteriorating heat resistance, anti-blocking property, mechanical properties or transparency of the polylactic acid resin or the film comprising the polylactic acid resin.

On the other hand, polylactic acid copolymers comprising soft segments in which polyester polyol repeating units are linked via urethane bonds have 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. Since such polylactic acid copolymer has a wide molecular weight distribution and an extremely low glass transition temperature, the conditions for film extrusion are not good, and thus the resulting film has insufficient mechanical properties, heat resistance and anti-blocking properties.

Furthermore, it is already known that: a polylactic acid copolymer in which a tri-or higher-functional isocyanate compound is used to copolymerize a polyether polyol repeating unit and a polylactic acid repeating unit in a branched form, 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. However, they also have problems: since the block size of the polylactic acid repeating unit as the hard segment is too small and the glass transition temperature of the polylactic acid copolymer is too low, the heat resistance, mechanical properties and anti-blocking property of the film are insufficient. Also, the conditions of the operating conditions of the film extrusion process are not good due to the broad molecular weight distribution and poor melting characteristics of the polylactic acid copolymer.

Also, since an excessive amount of catalyst is used in the polymerization process of the polylactic acid copolymer, degradation of the polylactic acid copolymer seems to occur during the preparation or use of the film. Moreover, it is recognized that this problem leads to low stability, high haze and poor clarity, pinhole formation, and the like.

In contrast, the polylactic acid resin included in the film of an embodiment includes a polyurethane polyol repeating unit in which a plurality of polyether polyol repeating units are linearly connected via a urethane bond. Thus, it has an optimized glass transition temperature and a narrow molecular weight distribution. Also, since it has a large segment of a polylactic acid repeating unit and a polyurethane polyol repeating unit, it can provide a film having excellent mechanical properties, heat resistance, anti-blocking property, and the like, and excellent flexibility. Accordingly, it was found that the polylactic acid resin included in the film of one embodiment overcomes the problem of the previous retention of the copolymer resin, and can be made into a film exhibiting excellent properties, including excellent transparency and stability and greatly improved flexibility.

The polyether polyol repeating unit and the diisocyanate compound may be used with each other for the terminal hydroxyl groups of the polyether polyol repeating unit: the diisocyanate compound has a molar ratio of isocyanate groups of about 1:0.50 to 1:0.99 reacted to form polyurethane polyol repeating 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 unit of the polyurethane polyol is insufficient (OHV < 3), so that the repeating unit 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 groups is too low, the terminal hydroxyl groups of the repeating units of the polyurethane polyol become 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 alkylene oxide 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 preferably be used as the polyether polyol, and the polyether polyol repeating units may have a number average molecular weight of about 400-.

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 film of an embodiment may include a block copolymer in which a hard segment-the polylactic acid repeating unit is copolymerized with a soft segment-the polyurethane polyol repeating unit. 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 particular, since the polylactic acid repeating unit and the polyurethane polyol repeating unit form a block copolymer, the glass transition temperature (Tg) and the melting temperature (Tm) of the polylactic acid resin can be optimized, and it is possible to improve the flexibility, the anti-blocking property, the heat resistance, and the like of the film.

However, not all of the polylactic acid repeating units contained in the polylactic acid resin 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 95wt% of the hard segment and about 5 to 20wt% of the soft segment, preferably about 82 to 92wt% of the hard segment and about 8 to 18wt% of the soft segment, and most preferably about 85 to 90wt% of the hard segment and about 10 to 15wt% of the soft segment, based on the total weight of the polylactic acid resin (when a polylactic acid homopolymer is optionally included, the total weight of the block copolymer and the homopolymer).

If the soft segment content is too high, it is difficult to provide a high molecular weight polylactic acid resin, and mechanical properties of the film such as strength may be reduced. In addition, the lowered glass transition temperature of the polylactic acid resin causes poor sliding properties, workability, anti-blocking properties, or dimensional stability during packaging. 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 excessively increases and may deteriorate the flexibility of the film. Also, it is difficult for the polyurethane polyol repeating unit of the soft segment 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 may further include a phosphite-based stabilizer and/or an antioxidant to prevent oxidation or thermal degradation of the soft segment during the preparation process. As the antioxidant, a hindered phenol-based antioxidant, an amine-based antioxidant, a sulfur-based antioxidant, a phosphite-based antioxidant, and the like may be used. These types of stabilizers and antioxidants are well known to those skilled in the art.

In addition to these stabilizers and antioxidants, the polylactic acid resin may contain various known additives such as plasticizers, UV stabilizers, color blockers (colorblocking agents), anti-gloss agents, deodorants, flame retardants, weather resistant agents, antistatic agents, antiblocking agents, antioxidants, ion exchangers, coloring pigments, 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. Also, examples of the coloring pigment may be inorganic pigments such as carbon black, titanium oxide and zinc oxide; and organic pigments such as cyanines, phosphors, 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. Further, 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, for example, a 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. Meanwhile, 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, the 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 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 of 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 for 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.

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, the film containing the polylactic acid resin 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.

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 a melting process such as extrusion or increases viscosity, thereby making it difficult to extrude the resin into a film. However, since the polylactic acid resin disclosed above has an optimized glass transition temperature and such a melting temperature, it is excellent in melt processability, and makes it possible to provide a film having excellent general properties including heat resistance and optimized flexibility.

And, the polylactic acid resin 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 a (co) polymer having a polyurethane polyol repeating unit.

In particular, the polylactic acid resin having the excellent properties disclosed above and the block copolymer contained therein may be prepared by: reacting a (co) polymer having a polyether polyol repeating unit with a diisocyanate compound to prepare a (co) polymer having a polyurethane polyol repeating unit in which the polyether polyol repeating unit is linearly linked via a urethane bond, and reacting the prepared (co) polymer with lactic acid or lactide. However, when polyester polyol repeating units are introduced into a polymer instead of polyether polyol repeating units, or urethane reaction is performed after polymerization of polyether polyol and lactic acid by changing the order of copolymerization, it is difficult to prepare a block copolymer having the excellent properties disclosed above and a polylactic acid resin comprising the block copolymer.

Also, it may be a main factor enabling the preparation of the polylactic acid resin having the above-disclosed properties to properly control the molecular weight of the entire polylactic acid resin, the molecular weight of the polyether polyol (co) polymer, or the amount of the (co) polymer having the repeating unit of the polyurethane polyol corresponding to the soft segment used. Suitable ranges for the molecular weight and the content of the soft link of the polylactic acid resin have been disclosed above, and therefore, a more detailed explanation is skipped herein.

Hereinafter, the preparation method of the polylactic acid resin 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 by a typical polymerization method according to the polyether polyol (co) polymer.

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, the polylactic acid resin included in the film of one embodiment, particularly the block copolymer included in the polylactic acid resin, may be prepared by: in the presence of a (co) polymer having a polyurethane polyol repeating unit, 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 ring-opening polymerization. That is, according to this polymerization, a polylactic acid repeating unit included as a hard segment is formed and a polylactic acid resin is prepared. At this time, the polyurethane polyol repeating unit is bonded to at least some of the terminal groups of the polylactic acid repeating unit, and a block copolymer may be generated.

Thus, a block copolymer (included in the film of one embodiment) can be obtained which is very different in structure and properties from a conventional polylactic acid copolymer or a branched copolymer prepared from a prepolymer composed of a polyether polyol and polylactic acid by chain extension using a diisocyanate compound or by reaction with a trifunctional isocyanate compound, respectively. In particular, such a block copolymer 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 a 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) and polyether polyol repeating units are alternately and randomly distributed, a film obtained therefrom cannot satisfy the aforementioned properties, such as glass transition temperature, and has poor mechanical properties or heat resistance.

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 specific hard and soft segments are combined, it may exhibit more improved flexibility while showing biodegradability of the polylactic acid resin. Also, 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.

Also, since the polylactic acid resin is made to have a specific glass transition temperature and optionally a specific melting temperature, the film made of the polylactic acid resin may exhibit not only optimized flexibility and rigidity as a packaging material, but also excellent processability for a melting process, anti-blocking property, and heat resistance. Therefore, the polylactic acid resin can be preferably applied to a packaging material such as a packaging film.

Hereinafter, a film including one embodiment of the polylactic acid resin will be explained in more detail.

Since the film comprises the polylactic acid resin, the 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 the like and may exhibit optimized flexibility and rigidity since it comprises the polylactic acid resin composition.

The packaging film may have various thicknesses 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.

Also, the film may exhibit a weight loss of about 3wt% or less, preferably about 0.01 to 3.0wt%, and more preferably about 0.05 to 1.0wt%, after being 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 3wt%, the film may have poor dimensional stability, and the plasticizer, residual monomer or additive may permeate out of the film, contaminate the contents packaged by the film, and it may be difficult to use as a food packaging material.

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 film can be provided with properties necessary for food packaging materials, such as heat sealability, a gas barrier layer against water vapor, oxygen or carbonic acid gas, releasability, printability and the like as required for packaging films, as long as the advantages of the packaging film are not deteriorated. For this reason, a polymer having such properties may be mixed with 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, for example, the above-disclosed film may be obtained by: the polylactic acid resin is formed into a biaxially stretched film (biaxially oriented film) using a sequential biaxial stretching process or a parallel biaxial stretching process, and then heat-set. In this regard, the oriented film may be formed by melt-extruding the 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 longitudinal and transverse directions.

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 stretch ratio may be set to about 1.5 to 10 times for each direction, or may be different between the longitudinal 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. Further, the film may have biodegradability that is characteristic of the polylactic acid resin. Therefore, the packaging film can be preferably applied to various packaging fields. For example, the packaging film 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 cooling/freezing food, shrinkable outer wrapping films, bundling films, sanitary films such as sanitary napkins or diapers, laminated 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, processability of film, 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 (KOHmg/g): measured by: dissolving the polyurethane polyol repeat units (or (co) polymers) in dichloromethane, acetylating the repeat units, hydrolyzing the acetylated repeat units to produce acetic acid, and titrating the acetic acid using 0.1NKOH in methanol. Which corresponds to the number of terminal hydroxyl groups of the repeat unit (or (co) polymer) 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: ShodexLF804 by 2 ea) 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 TAInstruments) 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 TAInstruments) 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) 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.

(7) 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-shaped 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.

(8) 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 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.

(9) 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 (8). The average of five measurements is shown. MD and TD represent the machine and transverse directions of the film, respectively.

（10）F5（kgf/mm²) MD and TD: in the stress-strain curve obtained in the tensile strength test of (8), 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.

（11）F100（kgf/mm²) MD: in the stress-strain curve obtained in the tensile strength test of (8), 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.

(12) 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 (8) was measured at a pulling speed of 300mm/min and a distance between grips of 100mm according to astm d638 using UTM (manufactured by INSTRON). The average of five measurements is shown. Since the young's modulus, in particular the sum of the young's modulus values measured in the longitudinal and transverse directions, 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.

(13) 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).

(14) 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.

(15) Pinhole and bleed resistance: after the heat treatment of (12), 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.

(16) 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 dh 2000) according to jis k 7136.

(17) Anti-adhesion property: the antistatic surface of the film sample was matched to the printing surface by COLORITP type hot stamping using foil (Kurz) and left standing at 40 ℃ under a pressure of 1kg/cm2 for 24 hours, after which blocking between the antistatic layer and the printing 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.

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

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

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: aliphatic polyester polyols 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: bis (2, 4-di-tert-butylphenyl) pentaerythritol diphosphite

-S412: tetrakis [ methane-3- (laurylthio) 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: bis [3, 3-bis- (4 '-hydroxy-3' -tert-butyl-phenyl) butanoic acid ] ethylene glycol ester

A. Preparation of polylactic acid resins A to H

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 130ppm 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 increased to 150 ℃ to completely dissolve L-lactide (or D-lactide), and 120ppm 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 200ppm was supplied 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). 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. Then, the temperature was raised to 150 ℃ to completely dissolve the L-lactide, and a 120ppm 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 in an amount of 200ppm was fed through the catalyst inlet and blended with the reaction mixture for 15 minutes to deactivate the catalyst. Until 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. Then, the temperature was raised to 150 ℃ to completely dissolve the L-lactide, and a 120ppm 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 in an amount of 200ppm was fed through the catalyst inlet and blended with the reaction mixture for 15 minutes to deactivate the catalyst. Until 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 130ppm 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 120ppm and 1000ppm, respectively, based on the total weight of the reactants, and charged into a reactor. The reaction was carried out at 190 ℃ for 2 hours under a nitrogen pressure of 1kg, and then phosphoric acid in an amount of 200ppm was fed through the catalyst inlet and blended with the reaction mixture for 15 minutes to deactivate the catalyst. Until 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.

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. Then, the temperature was raised to 150 ℃ to completely dissolve the lactide, and a 120ppm 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 in an amount of 200ppm was fed through the catalyst inlet and blended with the reaction mixture for 15 minutes to deactivate the catalyst. Until the pressure reached 0.5 torr, vacuum was applied to remove unreacted L-lactide. Then, HDI and a 120ppm dilution of the catalyst dibutyltin dilaurate in 500ml toluene were introduced into the reactor through the catalyst inlet 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. Then, the temperature was raised to 150 ℃ to completely dissolve the lactide, and a 120ppm 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 in an amount of 200ppm was fed through the catalyst inlet and blended with the reaction mixture for 15 minutes to deactivate the catalyst. Until the pressure reached 0.5 torr, vacuum was applied to remove unreacted L-lactide. Then, D-L75 was introduced into the reactor through the catalyst inlet along with a 120ppm dilution of the catalyst dibutyltin dilaurate in 500mL of 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-. Further, the polylactic acid resin contains a soft segment of a repeating unit of polyurethane polyol in an appropriate content of 5 to 20% by weight.

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.

In contrast, it is recognized that the resin H in which the soft segment of the polyurethane polyol repeating unit (or (co) polymer) is used in an amount of less than 5% by weight exhibits a Tg of more than 55 ℃. Moreover, since resin J contains the polyurethane polyol repeating unit (or (co) polymer) in an amount exceeding 20% by weight (this amount is considerably high), the resulting polylactic acid resin has a weight average molecular weight of less than 100,000 and a glass transition temperature of less than 25 ℃.

Also, the resin L is a polylactic acid resin prepared by directly using polyethylene glycol having a molecular weight of 8000 as an initiator for 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 the resin L exhibits a Tg of only 15 ℃ and has a low polymerization conversion rate, and the melt viscosity of the resin is too low to be separately made into a film at a film extrusion temperature of 200 ℃ or more.

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. Such 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.

Finally, the resins P and R are polylactic acid copolymers (P) or branched copolymers (R) prepared by addition polymerization of polyether polyol repeat 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 R), respectively. Resins P and R have molecular weight distributions as broad as 2.50 and 3.91 and their Tg are extremely low compared to the present invention and their Tm is also relatively low.

[ Table 2]

As shown in Table 2, the films of examples 1 to 5 were prepared from the polylactic acid resin of the present invention, which contained the soft segment (polyurethane polyol repeating unit) in an amount of 5 to 20wt% and had 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 ℃. Also, the film of example 6 was prepared by using the polylactic acid resin (resin E) and the general polylactic acid resin (resin M) falling within the scope of the present invention.

All of the membranes of examples 1 to 6 were foundHaving a length of 20kgf/mm in both longitudinal and transverse directions²Or higher total initial tensile strength, which indicates good mechanical properties. In addition, they retained 350-²The total young's modulus in both the longitudinal and transverse directions, which reflects excellent flexibility. This optimized range of total young's modulus is helpful in maintaining a suitable level of stiffness. And, 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 3wt% 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 contrast, the film of comparative example 1 prepared from the conventional polylactic acid resin M exhibited more than 750kgf/mm²The total young's modulus in both the longitudinal and transverse directions of (a) is such that the flexibility is insufficient to use the film as a packaging film. Further, the extrusion state of the film of comparative example 3 made of the resins M and L together was poor because of the large difference in melt viscosity between the two resins. The modes are also found in the final membrane. Further, the appearance of the film is poor due to the vacuum generated on the film, and the extremely low Tg of the resin L poses a problem with respect to the anti-blocking property.

The initial tensile strength and light transmittance were 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 have high haze due to incomplete dispersion of the plasticizing component in the resin, and it is recognized that the plasticizing component bleeds out from the surface of the film over time.

Furthermore, the resin H of comparative example 2 hadHas a relatively high Tg. For this reason, it was recognized that the film obtained from the resin H had insufficient flexibility and was difficult to use for packaging because it had more than 750kgf/mm²The total young's modulus in both the longitudinal and transverse directions.

Also, the film of comparative example 6 was formed of a copolymer that did not satisfy the characteristics of the present invention because it contained a polyester polyol repeating unit and had a low Tg. Such films exhibit relatively good flexibility because the polyurethane component responsible for flexibility is randomly incorporated as small segment units. 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 example 7 and comparative example 8 were formed of 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 do not satisfy the structural characteristics of the polylactic acid resin of the present invention or the characteristics of the film of the present invention. It was also found that these films exhibited non-uniform melt viscosity and poor mechanical properties. Also, since the blocking characteristics of the hard and soft segments 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.

Also, since an excessive amount of catalyst is used in the preparation of the film, the polylactic acid resin is degraded during the preparation or use of the films of comparative examples 6 to 8. Therefore, it generates pin holes and significant weight change at high temperature, exhibiting poor stability.

Claims (11)

1. A polylactic acid resin film comprising a polylactic acid resin containing:

a hard segment comprising a polylactic acid repeating unit having the following chemical formula 1; and

a soft segment comprising polyurethane polyol repeating units in which polyether polyol repeating units having the following chemical formula 2 are linearly connected via a urethane bond,

wherein the total Young's of the film in both the longitudinal and transverse directionsModulus of 350 to 750kgf/mm²And the total initial tensile strength of the film in both the longitudinal and transverse directions is 20kgf/mm²Or greater:

[ chemical formula 1]

[ chemical formula 2]

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

wherein the polyether polyol repeating units are linearly connected via a urethane bond to form the polyurethane polyol repeating unit, the urethane bond being formed by reacting a terminal hydroxyl group of the polyether polyol repeating unit and a diisocyanate compound in a molar ratio of the terminal hydroxyl group of the polyether polyol repeating unit to an isocyanate group of the diisocyanate compound of 1:0.60 to 1: 0.90.

2. The film of claim 1, exhibiting a haze of 3% or less and a light transmission of 85% or more.

3. The film as claimed in claim 1, wherein the polylactic acid resin has a melting temperature (Tm) of 160-.

4. The film of claim 1 having a weight loss rate of 0.01 to 3.0wt% after being treated at 100 ℃ for 60 minutes.

5. The film according to claim 1, 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 contained in the hard segment are connected via an ester bond.

6. The film of claim 5, wherein the polylactic acid resin comprises the block copolymer; and the polylactic acid repeating unit remains unconnected to the polyurethane polyol repeating unit.

7. The film of claim 1, wherein the polylactic acid resin has a weight average molecular weight of 100,000-400,000.

8. The film of claim 1, wherein the polylactic acid resin comprises 80-95wt% of the hard segment and 5-20wt% of the soft segment.

9. The film of claim 1, which is used for packaging.

10. The film of claim 1, which is a biaxially oriented film.

11. The film of claim 1, having a thickness of 5-500 μ ι η.