KR101921697B1 - Flexible polylactic acid resin composition - Google Patents

Abstract

The present invention relates to a poly (lactic acid) resin composition which exhibits excellent hydrolysis resistance and exhibits excellent flexibility such as mechanical properties, transparency, heat resistance, blocking resistance and bleeding-out properties, . The poly (lactic acid) resin composition comprises a block copolymer and a catalyst, wherein the block copolymer comprises a hard segment containing a predetermined poly (lactic acid) repeating unit and a polyether polyol repeating unit Wherein the catalyst comprises a metal and the content of the catalyst relative to the weight of the polyol acid resin composition is less than 50 ppm on a metal basis.

Description

FLEXIBLE POLYLACTIC ACID RESIN COMPOSITION [0001]

The present invention relates to a novel poly (lactic acid) resin composition. More specifically, the present invention relates to a polyolefin resin composition which exhibits excellent hydrolysis resistance and exhibits excellent flexibility, such as excellent mechanical properties such as mechanical properties, transparency, heat resistance, blocking resistance and anti-bleed out properties, The present invention relates to a poly (lactic acid) resin composition which can be usefully used.

Crude oil-based resins such as polyethylene terephthalate (PET), nylon, polyolefin, or flexible polyvinyl chloride (PVC) are still widely used as materials for various applications such as packaging materials. However, such a crude oil-based resin has no biodegradability and thus has a problem of causing environmental pollution such as discharging a large amount of carbon dioxide, which is a global warming gas, during disposal. In addition, as petroleum resources gradually become depleted, the use of biomass-based resins, typically polylactic acid resins, has been widely studied.

However, since such a poly (lactic acid) resin is insufficient in mechanical properties compared to a crude oil-based resin, there is a limit to the field or application to which it can be applied. Particularly, attempts have been made to apply poly (lactic acid) resin as a packaging material for packaging films and the like, but such applications are limited due to the low flexibility of the poly (lactic acid) resin.

In order to overcome the limitation of the poly (lactic acid) resin, a method of adding a low molecular weight softener or plasticizer to a poly (lactic acid resin), or introducing a plasticizer obtained by addition polymerization of a polyether or aliphatic polyester- .

However, even if a packaging film or the like containing a poly (lactic acid) resin is obtained by these methods, it is a fact that there is a limit in improving the flexibility in most cases. In addition, the plasticizer or the like not only bleeds out over time, but also has a disadvantage that haze of the packaging film is increased and transparency is lowered.

In recent years, a method of obtaining a block copolymer by introducing a polyurethane polyol repeating unit into a poly (lactic acid) resin has been proposed in order to solve the above problems (Korean Patent Registration Nos. 1191966, 1191967, 1191968 and 1191961, and Korean Patent Publication Nos. 2012-0068552, 2012-0068550, 2012-0094552, 2012-0086118, and 2012-0086117).

On the other hand, poly (lactic acid) resins are generally very susceptible to hydrolysis, mainly due to the back-biting reaction of the catalyst remaining in the resin after polymerization, and as a result, And the molecular weight is lowered.

Furthermore, the resulting monomers and oligomers volatilize during the molding process of the resin, leading to contamination and corrosion of the machine and also to quality problems of the molded product. Specifically, in the case of sheet production by extrusion molding, the residual monomers and oligomers in the resin are volatilized during sheet extrusion, resulting in a variation in thickness of the sheet to be produced. In the case of injection molded articles, And mechanical properties may be deteriorated.

Accordingly, the development of films for packaging on polylactic acid resin, which shows excellent flexibility and exhibits excellent hydrolysis resistance and excellent physical properties such as mechanical properties, transparency, heat resistance, blocking resistance, and bleeding-out characteristics, .

Korean Registered Patent No. 1191966 (SK Chemicals Co., Ltd.) Oct. 17, Korean Registered Patent No. 1191967 (SK Chemicals Co., Ltd.) Oct. 17, Korean Registered Patent No. 1191968 (SK Chemicals Co., Ltd.) Oct. 17, Korean Registered Patent No. 1191961 (SK Chemicals Co., Ltd.) Oct. 17, Korea Patent Publication No. 2012-0068552 (Eskay Chemical Co., Ltd.) 2012.06.27. Korea Patent Publication No. 2012-0068550 (Eskay Chemical Co., Ltd.) 2012.06.27. Korea Patent Publication No. 2012-0094552 (Eskay Chemical Co., Ltd.) 2012.08.27. Korea Patent Publication No. 2012-0086118 (Eskay Chemical Co., Ltd.) 2012.08.02. Korea Patent Publication No. 2012-0086117 (Eskay Chemical Co., Ltd.) 2012.08.02.

Therefore, an object of the present invention is to provide a polyolefin composition which exhibits excellent hydrolysis resistance and exhibits excellent flexibility such as excellent mechanical properties, transparency, heat resistance, blocking resistance and bleeding-out property, And to provide a lactic acid resin composition.

According to the above object, the present invention provides a poly (lactic acid) resin composition comprising a block copolymer and a catalyst, wherein the block copolymer comprises a hard segment containing a poly (lactic acid) repeating unit represented by the following formula (1) Wherein the catalyst comprises a metal and the content of the catalyst relative to the weight of the polyol acid resin composition is less than or equal to the metal standard < RTI ID = 0.0 > Of less than 50 ppm. ≪ RTI ID = 0.0 >

[Chemical Formula 1]

(2)

In the general formulas (1) and (2), 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 poly (lactic acid) resin composition according to the present invention exhibits biodegradability peculiar to poly (lactic acid) resin, exhibits improved flexibility and excellent mechanical properties, heat resistance, transparency, anti-blocking property and anti-bleeding property. In addition, since the hydrolysis resistance is excellent and the physical properties are stable over time and the thickness of the sheet is very uniform during molding, it can be suitably applied as a packaging material in various fields to replace the packaging film obtained from crude oil- It can contribute to prevention of environmental pollution.

Hereinafter, the present invention will be described in more detail.

Composition and properties of poly (lactic acid) resin composition

According to one embodiment of the present invention, there is provided a poly (lactic acid) resin composition comprising a block copolymer and a catalyst, wherein the block copolymer comprises (i) a hard segment comprising a poly (lactic acid) And a soft segment comprising a polyurethane polyol repeat unit wherein the polyether polyol repeat units of the formula (2) are linearly linked, the catalyst comprising a metal, and wherein the weight ratio of the catalyst to the weight of the poly Is less than 50 ppm on a metal basis.

Such a poly (lactic acid) resin composition basically contains the poly (lactic acid) repeating unit represented by the above formula (1) as a hard segment. Also, the poly (lactic acid) resin composition contains a polyurethane polyol repeating unit as a soft segment, wherein the polyether polyol repeating units represented by the above formula (2) are urethane bonds (-C (= O) -NH -). ≪ / RTI >

Such a poly (lactic acid) resin composition basically exhibits biodegradability specific to a biomass-based resin as it contains a poly (lactic acid) repeating unit as a hard segment. Further, as a result of the experiments conducted by the inventors of the present invention, it is possible to provide a film exhibiting greatly improved flexibility (for example, low Young's modulus) as well as excellent transparency and low haze value by including the polyurethane polyol repeating unit as a soft segment Do.

Generally, polylactic acid resins are most susceptible to hydrolysis among polyester resins. Various causes affect the hydrolysis, but fundamentally, the back-biting reaction by the residual catalyst is the basic mechanism. The backbiting reaction is divided into an intermolecular reaction (Scheme 1) and an intramolecular reaction (Scheme 2) depending on where it occurs:

[Reaction Scheme 1]

[Reaction Scheme 2]

In the intermolecular reaction, it is known that the middle of the linear alkyl chain is cleaved to generate an oligomer, and in the intramolecular reaction, the linear alkyl chain terminal is cleaved to generate lactide, which is a monomer, and the rate is accelerated at high temperature. As a result, the poly (lactic acid) resin has a considerable decrease in molecular weight after processing such as injection or extrusion, and the physical properties are not stabilized. In addition, the lactide or oligomers generated during decomposition are volatile, which causes contamination of the machine during molding and corrosion of the machine in the long term. Further, a sheet or film which requires uniform thickness may cause a thickness variation during molding. Conventionally, a catalytic deactivator has been applied to reduce the activity of the catalyst to improve the water-solubility, which is a problem of the poly (lactic acid) resin. However, such a catalyst deactivator plays a role of slowing down the back- It does not fundamentally prevent deterioration of properties due to long-term storage. Furthermore, since the flexible poly (lactic acid) resin has a lower glass transition temperature (Tg) than that of the conventional poly (lactic acid) resin, the mobility of the polymer chain is relatively large and the hydrolysis resistance at the use temperature of the molded article may be low.

Accordingly, the polylactic acid resin composition of the present invention contains a specific range of the catalyst.

The poly (lactic acid) resin composition according to one embodiment may have a content of the catalyst relative to the total weight of the composition of less than 50 ppm, for example, in the range of 5 to 35 ppm, based on the metal contained in the catalyst. Alternatively, the content may be from 0.1 to 50 ppm, or from 5 to 15 ppm, from 15 to 35 ppm, from 1 to 20 ppm, from 20 to 40 ppm, from 5 to 45 ppm, or from 5 to 30 ppm.

Preferable examples of the catalyst may be selected from the group consisting of an alkaline earth metal catalyst, a rare earth metal catalyst, a transition metal catalyst, an aluminum catalyst, a germanium catalyst, a tin catalyst, an antimony catalyst, These may include tin-based catalysts. More specific examples of the catalyst include stannous octoate (tin (II) 2-ethylhexanoate), dibutyltin dilaurate, dioctyltin dilaurate, titanium tetraisopropoxide , Aluminum triisopropoxide, and the like, but are not limited thereto.

The polylactic acid resin composition of the present invention having the above-specified range of the catalyst has a very low content of residual monomers in the composition.

The polylactic acid resin composition according to one embodiment may have a residual monomer (i.e., lactide) content of less than 0.5% by weight based on the total weight of the composition, for example, 0.1% by weight or less and 0.5% By weight, less than 0.5% by weight, or from 0.3% by weight to less than 0.5% by weight. Or from 0.1 to 0.4% by weight, from 0.2 to 0.4% by weight, or from 0.3 to 0.4% by weight. In addition, the poly (lactic acid) resin composition according to one embodiment hardly increases the residual monomer content even under hydrolysis conditions. For example, the residual monomer content may be 1.0% by weight or less, for example, 0.1 to 1.0% by weight, 0.1 to 0.9% by weight, 0.1 to 0.8% by weight, 0.1 to 0.7% by weight, 0.2 to 1.0% by weight, 0.3 to 1.0% by weight, 0.4 to 1.0% by weight, or 0.5 to 1.0% by weight.

In addition, the polylactic acid resin composition according to one embodiment has a very small decrease in molecular weight even under the conditions of thermal melt extrusion (thermal hydrolysis). (Initial Mw-Mw after hydrolysis) / initial Mw) may be 20% or less, for example, 1 to 20%, and more preferably 1 to 20%, when the melt- 1 to 15%, 1 to 13%, 5 to 20%, 5 to 15%, 5 to 13%, 7 to 20%, 7 to 15%, or 7 to 13%.

In the polylactic acid resin according to one embodiment of the present invention, the polylactic acid repeating unit represented by formula (1) contained in the hard segment is a repeating unit constituting a poly (lactic acid) homopolymer. Such polylactic acid repeating units can be obtained by a method for producing polylactic acid homopolymers well known to those skilled in the art. For example, a method of producing cyclic L-lactide or D-lactide from L-lactic acid or D-lactic acid and ring-opening polymerization thereof, or a method of direct dehydration condensation polymerization of L-lactic acid or D- , And a polylactic acid repeating unit having a higher degree of polymerization can be obtained through ring-opening polymerization. The poly (lactic acid) repeating unit may be prepared by copolymerizing L-lactide and D-lactide at a certain ratio so as to exhibit noncrystallinity. In order to further improve the heat resistance of the film containing the polylactic acid resin, L-lactide, or D-lactide. More specifically, the polylactic acid repeating unit can be obtained by ring-opening polymerization using an L-lactide or D-lactide raw material having an optical purity of 98% or more, and if the optical purity is less than the above range, the melt temperature and heat resistance Can be lowered.

In addition, the polyurethane polyol repeating units included in the soft segment have a structure in which the polyether polyol repeating units of Formula 2 are linearly connected via a urethane bond (-C (= O) -NH-). More specifically, the polyether polyol repeating units are obtained by ring-opening (co) polymerization of a monomer such as an alkylene oxide and have a hydroxyl group at the terminal. The terminal hydroxyl group reacts with the diisocyanate compound to form the urethane bond (- C (= O) -NH-), and the polyether polyol repeating units are linearly connected to each other via the urethane bond to form the polyurethane polyol repeating unit. By including such a polyurethane polyol repeating unit in a soft segment, the flexibility of the film containing the polylactic acid resin can be greatly improved. Such a polyurethane polyol repeating unit makes it possible to provide a film exhibiting excellent physical properties without lowering the heat resistance, blocking resistance, mechanical properties or transparency of the poly (lactic acid) resin or the film containing the poly (lactic acid) resin.

As described above, the poly (lactic acid) resin composition according to one embodiment of the present invention is characterized in that a plurality of polyether polyol repeating units include a polyurethane polyol repeating unit and a poly (lactic acid) repeating unit linearly connected via a urethane bond, It is possible to provide a film showing excellent flexibility while satisfying excellent molecular weight characteristics due to a small molecular weight distribution and containing a polylactic acid repeating unit in a large segment size so that the film can exhibit excellent mechanical properties, heat resistance and blocking resistance . On the other hand, conventional poly (lactic acid) copolymers have problems such as low transparency of film and high haze value due to low compatibility of polyester polyol and poly (lactic acid), and also have problems in that the molecular weight distribution is wide, So that the film extruded state is not good and the mechanical properties, heat resistance and blocking resistance of the film are insufficient. Further, conventionally, polyether polyol repeating units are copolymerized with polyol repeating units in a branched form using a trifunctional or higher isocyanate compound, or after the polyether polyol repeating units and poly (lactic acid) repeating units are copolymerized, The polylactic acid copolymer in the form of a polylactic acid has a small block size of the polylactic acid repeating unit corresponding to the hard segment so that the heat resistance, mechanical properties and blocking resistance of the film are not sufficient, and the molecular weight distribution is wide, And the film extrusion state is poor.

The polyether polyol repeating unit and the diisocyanate compound are reacted so that the molar ratio of the terminal hydroxyl group of the polyether polyol repeating units and the isocyanate group of the diisocyanate compound is 1: 0.50 to 1: 0.99, Units can be formed. Preferably, the molar ratio may be from 1: 0.60 to 1: 0.90, more preferably from 1: 0.70 to 1: 0.85.

As described in more detail below, the polyurethane polyol repeating unit has a hydroxyl group at the end thereof, and therefore can act as an initiator in the polymerization process for the formation of the polylactic acid repeating unit. However, if the reaction molar ratio of the hydroxyl group: isocyanate group is excessively high, the number of terminal hydroxyl groups of the polyurethane polyol repeating unit becomes insufficient (OHV < 3) and may not function properly as an initiator. This makes it difficult to produce a polylactic acid resin having excellent molecular weight characteristics and the like, and the polymerization yield can also be greatly lowered. On the contrary, if the molar ratio of the hydroxyl group to the isocyanate group is too low, the number of terminal hydroxyl groups of the polyurethane polyol repeating unit becomes excessively large (OHV > 21) and a polylactic acid repeating unit having a high molecular weight and a polylactic acid resin Can be difficult to obtain.

On the other hand, the polyether polyol repeating unit may be, for example, a repeating unit of a polyether polyol (co) polymer obtained by ring-opening (co) polymerization of at least one alkylene oxide. Examples of the alkylene oxide include ethylene oxide, propylene oxide, butylene oxide, and tetrahydrofuran. Examples of the polyether polyol repeating unit obtained by the reaction include repeating units of polyethylene glycol (PEG); Repeating units of poly (1,2-propylene glycol); Repeating units of poly (1,3-propanediol); Repeating units of polytetramethylene glycol; Repeating units of polybutylene glycol; A repeating unit of a polyol which is a copolymer of propylene oxide and tetrahydrofuran; A repeating unit of a polyol which is a copolymer of ethylene oxide and tetrahydrofuran; Or a repeating unit of a polyol which is a copolymer of ethylene oxide and propylene oxide. Considering flexibility imparted to the poly (lactic acid) resin film, affinity with the poly (lactic acid) repeating unit and humidifying property, the polyether polyol repeating unit may be a repeating unit of poly (1,3-propanediol) or polytetramethylene glycol Is preferably used.

In addition, such a polyether polyol repeating unit may have a number average molecular weight of 450 to 9,000, preferably 1,000 to 3,000. If the molecular weight of such a polyether polyol repeating unit is excessively large or small, the flexibility and mechanical properties of the film obtained from the polylactic acid resin of one embodiment may become insufficient. In addition, the molecular weight characteristics of the polylactic acid resin, for example, the weight average molecular weight and the molecular weight distribution in a predetermined range can not be realized, so that the processability of the polylactic acid resin may be deteriorated or the mechanical properties of the film may be deteriorated.

The diisocyanate compound capable of bonding with the terminal hydroxyl group of the polyether polyol repeating unit to form a urethane bond can be any compound having two isocyanate groups in the molecule. Examples of such diisocyanate compounds include 1,6-hexamethylene diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 1,3-xylene diisocyanate, 1,4-xylene diisocyanate, , 5-naphthalene diisocyanate, m-phenylenediisocyanate, p-phenylenediisocyanate, 3,3'-dimethyl-4,4'-diphenylmethane diisocyanate, 4,4'- bisphenylenediisocyanate, hexamethylene di Isocyanate, isophorone diisocyanate, or hydrophenylmethane diisocyanate. In addition, various diisocyanate compounds well known to those skilled in the art can be used without limitation. However, it is preferable to use 1,6-hexamethylene diisocyanate in view of imparting flexibility to the poly (lactic acid) resin film.

Meanwhile, the poly (lactic acid) resin composition according to an embodiment of the present invention may include a block copolymer in which the poly (lactic acid) repeating unit of the hard segment described above is combined with the polyurethane polyol repeating unit of the soft segment. More specifically, in such a block copolymer, the terminal carboxyl group of the polylactic acid repeating unit may form an ester bond with the terminal hydroxy group of the polyurethane polyol repeating unit. For example, the chemical structure of such a block copolymer can be represented by the following general formula 1:

[Formula 1]

Polyester repeating unit (L) -Ester-polyurethane polyol repeating unit (E-U-E-U-E) -Ester-

In the general formula 1, E represents a polyether polyol repeating unit, U represents a urethane bond, and Ester represents an ester bond.

Since the poly (lactic acid) resin composition includes a block copolymer in which a poly (lactic acid) repeating unit and a polyurethane polyol repeating unit are combined, it is possible to inhibit the polyurethane polyol repeating units and the like for imparting flexibility from being bleed out, The film formed of the lactic acid resin may have excellent physical properties such as transparency, mechanical properties, heat resistance, blocking resistance, and the like.

However, it is not necessary that all of the polylactic acid repeating units contained in the polylactic acid resin have a form of a block copolymer bonded with the polyurethane polyol repeating units, and at least a part of the polylactic acid repeating units But may be in the form of a poly (lactic acid) homopolymer. In this case, the poly (lactic acid) resin composition may be in the form of a mixture comprising the above-described block copolymer and a poly (lactic acid) homopolymer, which is not bonded to the polyurethane polyol repeating unit.

On the other hand, the poly (lactic acid) resin composition has the above-mentioned hard segment 65 to 95 (based on the total weight thereof (the weight of the block copolymer and the weight of the homopolymer when the poly (lactic acid homopolymer) And 5 to 35% by weight of soft segment, preferably 80 to 95% by weight hard segment and 5 to 20% by weight soft segment, more preferably 82 to 92% by weight hard segment and soft segment 8 To 18% by weight. When the content of the soft segment is too high, it may become difficult to provide a poly (lactic acid) resin having molecular weight characteristics (for example, a relatively high molecular weight and a narrow molecular weight distribution) of one embodiment, The physical properties may be deteriorated. On the other hand, if the content of the soft segment is too low, there is a limit to improve the flexibility of the poly (lactic acid) resin and the film thereof, and it is difficult for the soft segment polyurethane polyol repeating unit to act as an initiator. It may be difficult to provide the resin.

The poly (lactic acid) resin composition may further contain a phosphorus stabilizer and / or an antioxidant to inhibit oxidation or pyrolysis of the soft segment or the like during its production. Examples of the antioxidant include a hindered phenol antioxidant, an amine antioxidant, a thio antioxidant, and a phosphite antioxidant. The kinds of each of these stabilizers and antioxidants are well known to those skilled in the art.

In addition to these stabilizers and antioxidants, the polylactic acid resin composition may contain various known plasticizers, ultraviolet stabilizers, coloring inhibitors, matting agents, deodorants, flame retardants, endurance agents, antistatic agents, release agents, antioxidants , Ion exchangers, coloring pigments, inorganic or organic particles, and the like.

Examples of the plasticizer include phthalate ester plasticizers such as diethyl phthalate, dioctyl phthalate and dicyclohexyl phthalate; Aliphatic dibasic acid ester plasticizers such as di-n-butyl adipate, di-n-octyl adipate, di-n-butyl sebacate and di-2-ethylhexyl azelate; Phosphate ester plasticizers such as diphenyl 2-ethylhexyl phosphate and diphenyloctyl phosphate; Tributyl acetyl citrate, tri-2-ethylhexyl acetyl citrate, tributyl citrate, and other hydroxycarboxylic acid ester plasticizers; Fatty acid ester plasticizers such as methyl acetyl ricinoleate and amyl stearate; Polyhydric alcohol ester plasticizers such as glycerin triacetate; Epoxidized soybean oil, epoxylated amami-oil fatty acid butyl ester, and epoxy-based stearyl epoxy stearate. Examples of the coloring pigment include inorganic pigments such as carbon black, titanium oxide, zinc oxide and iron oxide; Organic pigments such as cyanine pigments, phosphorus pigments, quinone pigments, lineron pigments, isoindolinone pigments, and thioindigo pigments. Inorganic or organic particles may be further added to improve the anti-blocking property of other films. Examples of the inorganic or organic particles include silica, colloidal silica, alumina, alumina sol, talc, mica, calcium carbonate, polystyrene, polymethylmethacrylate, Silicon, and the like. In addition, various additives known to be usable in the polylactic acid resin or the film thereof can be included, and the specific kind and the method of obtaining it are known to those skilled in the art.

The poly (lactic acid) resin composition has a weight average molecular weight of, for example, 100,000 to 400,000, preferably 100,000 to 320,000, and has a molecular weight defined as a ratio of a number average molecular weight (Mn) to a weight average molecular weight The distribution (Mw / Mn) has a value of, for example, 1.60 to 2.20, preferably 1.80 to 2.15. As described above, the poly (lactic acid) resin composition is produced by reacting a polyether polyol repeating unit with a diisocyanate compound to form a polyurethane polyol repeating unit in which a plurality of polyether polyol repeating units are linearly linked to a urethane bond, &Lt; RTI ID = 0.0 &gt; and / or &lt; / RTI &gt; As the polylactic acid resin comprises the block copolymer thus obtained, it can have a significantly narrow molecular weight distribution as compared with previously known similar polylactic acid copolymers with relatively large molecular weights.

In addition, the polylactic acid resin, for example, the block copolymer contained therein, may have a number average molecular weight of 50,000 to 200,000, preferably a number average molecular weight of 50,000 to 150,000. The number average molecular weight may affect the workability or mechanical properties of the resin as well as the weight average molecular weight and the molecular weight distribution. As the number average molecular weight has the above-mentioned range, the processability of the poly (lactic acid) resin as a film can be maintained to be excellent, and mechanical properties such as strength of the resin and film can be kept excellent.

As the poly (lactic acid) resin has properties such as a large molecular weight and a narrow molecular weight distribution, it exhibits an appropriate melt viscosity and melting property when it is melt processed by a method such as extrusion, and exhibits excellent film extrusion state and processability. In addition, due to such molecular weight characteristics, the film comprising the poly (lactic acid) resin can exhibit excellent mechanical properties such as strength. In contrast, when the molecular weight is too large or the molecular weight distribution becomes too narrow (small), the melt viscosity at the processing temperature for extrusion and the like may be excessively large and the processing as a film may be difficult. On the other hand, When it is widened (enlarged), the mechanical properties such as the strength of the film are lowered or the melt viscosity is too small, so that the melt property is poor and the molding itself into a film may be difficult or the film extrusion state may not be good.

As described above, the poly (lactic acid) resin composition is not only excellent in processability due to its optimized molecular weight characteristics, but also excellent in mechanical properties such as strength and heat resistance and blocking resistance of the film obtained therefrom. And the like.

In addition, the poly (lactic acid) resin composition may have a melting temperature (Tm) of 160 to 178 ° C, preferably 165 to 175 ° C. If the melting temperature is too low, the heat resistance of the film containing the polylactic acid resin may be deteriorated, and if the melting temperature is excessively high, the processing property to a film or the like may deteriorate.

And, the polylactic acid resin, for example, the block copolymer contained therein, may have a glass transition temperature (Tg) of 25 to 55 DEG C, preferably a glass transition temperature (Tg) of 30 to 55 DEG C. As the glass transition temperature range is indicated, the flexibility and stiffness of the film containing the poly (lactic acid) resin are optimized and can be used as a film for packaging. If the glass transition temperature of the poly (lactic acid) resin is excessively low, the flexibility of the film may be improved. However, as the stiffness becomes too low, the slipping, handling, Blocking property may be deteriorated, and therefore, application to a packaging film may be undesirable. On the other hand, if the glass transition temperature is too high, the flexibility of the film is low and the stiffness is too high, so that the film is easily folded and the mark is not lost or the adhesion to the product is poor when wrapped. Further, noise may be generated severely during packaging of the film, which may limit its application to packaging films.

Method for producing poly (lactic acid) resin composition

On the other hand, the above-mentioned poly (lactic acid) resin composition can be obtained by ring-opening (co) polymerization of a monomer such as at least one alkylene oxide to form a (co) polymer having a polyether polyol repeating unit; 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; (D- or L-lactic acid), or ring-opening polymerization of lactide (D- or L-lactide) in the presence of a (co) polymer having a polyurethane polyol repeating unit And can be produced by a production method. In this case, the catalyst is a metal-based catalyst. In particular, the amount of the catalyst to be used may be less than 50 ppm, preferably 5 to 35 ppm based on the metal contained in the catalyst. Preferred examples of the catalyst to be used are as described above.

According to a preferred example, a (co) polymer having a polyether polyol repeating unit and a diisocyanate compound are subjected to a urethane reaction in the presence of a catalyst, whereby the polyether polyol repeating units are reacted with a polyurethane polyol (Co) polymer having a repeating unit is obtained and then polymerized with lactic acid or lactide in the presence of a catalyst to obtain a polylactic acid resin of one embodiment having excellent physical properties such as the above-mentioned molecular weight characteristics and a block copolymer . On the other hand, in the case of introducing a polyester-based polyol repeating unit other than the polyether-based polyol repeating unit or by first polymerizing the polyether-based polyol with lactic acid or the like in a different sequence of reaction and then extending the chain, It may be difficult to produce a block copolymer having the same excellent properties and a polylactic acid resin of one embodiment including the block copolymer.

Further, it is also possible to use polyurethane polyol having a polyurethane polyol repeating unit corresponding to the reaction molar ratio of the (co) polymer having a polyether polyol repeating unit and the diisocyanate compound, the molecular weight of the polyether polyol (co) polymer, or the content of the soft segment The amount of the (co) polymer to be used, and the like are also a major factor enabling the poly (lactic acid) resin of one embodiment to be produced. The appropriate range of the reaction molar ratio, the molecular weight of the polyether polyol (co) polymer, and the like are as described above.

Hereinafter, a method for producing such a polylactic acid resin will be described in more detail.

First, monomers such as one or more alkylene oxides are ring-opened (co) polymerized to form a (co) polymer having a polyether polyol repeat unit. This is a method for producing a polyether polyol You can proceed accordingly.

Thereafter, the (co) polymer having the polyether polyol repeating unit, the diisocyanate compound and the urethane reaction catalyst are charged in the reactor, heated and stirred to perform the urethane reaction. By this reaction, two isocyanate groups of the diisocyanate compound and a terminal hydroxyl group of the (co) polymer are bonded to each other to form a urethane bond. As a result, a (co) polymer in which polyether polyol repeating units have polyurethane polyol repeating units in a linearly linked form via the urethane bond can be formed, which is included as a soft segment of the above-mentioned poly (lactic acid resin composition) . At this time, the polyurethane polyol (co) polymer is formed in such a manner that the polyether polyol repeating units (E) are linearly bonded in the EUEUE form via a urethane bond (U) and have polyether polyol repeating units at both ends .

The urethane reaction may be carried out using conventional tin (Sn) based catalysts such as stannous octoate (II) 2-ethylhexanoate, dibutyltin dilaurate, dioctyltin dilaurate dioctyltin dilaurate, and the like. In addition, the urethane reaction can be carried out under the reaction conditions for the production of a conventional polyurethane resin. For example, after a diisocyanate compound and a polyether polyol (co) polymer are added in a nitrogen atmosphere, the urethane reaction catalyst is added thereto and reacted at a reaction temperature of 70 to 80 ° C for 1 to 5 hours to obtain a polyurethane polyol (Co) polymer can be produced.

Next, polycondensation of lactic acid (D- or L-lactic acid) or ring-opening polymerization of lactide (D- or L-lactide) in the presence of the (co) polymer having the polyurethane polyol repeating unit The polylactic acid resin composition according to the embodiment, particularly the block copolymer contained therein, can be produced. That is, when such a polymerization reaction is carried out, a poly (lactic acid) repeating unit contained as a hard segment is formed, and the poly (lactic acid) resin is produced, wherein at least a part of the poly A copolymer may be formed. As a result, it has been found that a polylactic acid copolymer in which a prepolymer prepared by previously bonding a polyether polyol and a poly (lactic acid) to each other has been prepared, followed by chain extension of the prepolymers with a diisocyanate compound, A block copolymer of one embodiment exhibiting a structure and molecular weight characteristics different from those of the branched copolymer obtained by reacting with the isocyanate compound described above may be formed. In particular, the block copolymer of this embodiment may include a block (hard segment) in which the polylactic acid repeating units are bonded to each other in a relatively large unit (molecular weight), so that the film formed of the polylactic acid resin composition containing the block copolymer has a narrow molecular weight distribution and An appropriate Tg, and therefore excellent mechanical properties and heat resistance.

On the other hand, the above-mentioned lactide ring-opening polymerization reaction may be carried out in the presence of an alkaline earth metal, a rare earth metal, a transition metal, aluminum, germanium, tin or antimony, In the presence of a metal catalyst. More specifically, such metal catalysts may be in the form of the carboxylates, alkoxides, halides, oxides or carbonates of these metals. Preferably, as the metal catalyst, tin octoate, titanium tetraisopropoxide or aluminum triisopropoxide may be used.

The above-mentioned poly (lactic acid) resin composition can exhibit improved flexibility while exhibiting biodegradability of the poly (lactic acid) resin by including a block copolymer having a specific hard segment and a soft segment bonded thereto. Also, the soft segment for imparting flexibility can be minimized to be bleed out, and the degradation of mechanical properties, heat resistance, transparency or haze characteristics of the film can be greatly reduced by the addition of such a soft segment.

In addition, since the poly (lactic acid) resin composition is produced to have a predetermined molecular weight characteristic, that is, a specific weight average molecular weight and a molecular weight distribution range, it exhibits excellent processability that can be easily formed into a film by a melt processing method such as extrusion, The mechanical properties such as the strength of the resin can be maintained excellent. For example, the poly (lactic acid) resin composition can be melt-processed by a method such as extrusion at a processing temperature of 200 to 250 ° C, and is preferably 500 to 3000 Pa.s, preferably 800 to 2000 Pa.s Of the melt viscosity. Accordingly, the poly (lactic acid) resin composition can be easily processed into a film having excellent film extruded state and excellent physical properties, and its productivity can be greatly improved.

In particular, the poly (lactic acid) resin composition is excellent in hydrolysis resistance due to the inclusion of a proper amount of catalyst, and therefore has a stable physical property over time, and is very uniform in thickness during molding into a sheet, It is possible to replace the packaging film obtained from the base resin and contribute to prevention of environmental pollution.

Embodiments of the Invention

Best Mode for Carrying Out the Invention Hereinafter, the function and effect of the present invention will be described in more detail through specific examples of the present invention. It is to be understood, however, that these embodiments are merely illustrative of the invention and are not intended to limit the scope of the invention.

* Property Definition and Measurement Method : Definition and measurement method of each property in the following embodiments are as summarized below.

(1) NCO / OH: terminal hydroxyl group of an isocyanate group of a diisocyanate compound (for example, hexamethylene diisocyanate) / polyether polyol repeating unit (or (co) polymer) for formation of polyurethane polyol repeating unit "

(2) OHV (KOH mg / g): The polyurethane polyol repeating unit (or (co) polymer) was dissolved in dichloromethane and acetylated, and acetic acid produced by hydrolysis thereof was titrated with 0.1N KOH methanol solution . This corresponds to the number of hydroxyl groups present at the end of the polyurethane polyol repeat unit (or (co) polymer).

(3) Mw and Mn (g / mol): The poly lactic acid resin was dissolved in chloroform at a concentration of 0.25 wt% and measured by gel permeation chromatography (Viscotek TDA 305, Column: Shodex LF804 x 2ea) The weight average molecular weight (Mw) and the number average molecular weight (Mn) were respectively calculated as polystyrene as a standard material.

(4) PDI (Mw / Mn): The molecular weight distribution value (PDI) was calculated from Mw and Mn measured in (3) above.

(5) Tg (glass transition temperature, 占 폚): Using a differential scanning calorimeter (TA Instruments), the sample was subjected to melt quenching and then heated to 10 占 폚 / min. The midline value of the tangent line and the baseline near the endothermic curve was defined as Tg.

(6) Tm (melting temperature, 占 폚): Using a differential scanning calorimeter (manufactured by TA Instruments), the samples were melt-quenched and then heated at a rate of 10 占 폚 / min. The maximum value of the melting endothermic peak of the crystal was defined as Tm.

(7) Content (% by weight) of polyurethane polyol repeating units: The content of the polyurethane polyol repeating units contained in each produced poly (lactic acid) resin was quantified using a 600 MHz nuclear magnetic resonance (NMR) spectrometer.

(8) Residual monomer (lactide) content (wt%): 0.1 g of the resin was dissolved in 4 mL of chloroform, and then 10 mL of hexane was added thereto.

Materials used : The raw materials used in the following examples and comparative examples are as follows:

(1) a polyether-based polyol repeating unit (or (co) polymer) or a corresponding substance

- PPDO 2.4: poly (1,3-propanediol); Number average molecular weight 2,400

(2) Diisocyanate compound (or trifunctional or higher isocyanate)

- HDI: hexamethylene diisocyanate

(3) Lactide monomers

- L-lactide or D-lactide: Optical purity of 99.5% or more from Purac

(4) Antioxidants, etc.

- U626: bis (2,4-di-t-butylphenyl) pentaerythritol diphosphite

(5) Catalyst

- urethane reaction catalyst: dibutyltin dilaurate (Dabco T-12, manufactured by Air products)

- lactide ring opening polymerization catalyst: stannous octoate (tin (II) 2-ethylhexanoate, Dabco T-9, manufactured by Air Products)

Examples 1 and 2 and Comparative Examples 1 to 3: Preparation of poly (lactic acid) resin composition

Components and contents of the reactants as shown in Table 1 below were charged together with the catalyst in an 8 L reactor equipped with a nitrogen gas inlet tube, a stirrer, a catalyst inlet, an outlet condenser and a vacuum system. As the catalyst, dibutyltin dilaurate in the amount shown in Table 1 below was used in relation to the weight of the total reactants. The urethane reaction was carried out under a nitrogen stream at 70 ° C for 2 hours, and 4 kg of L- (or D-) lactide was added to perform nitrogen flushing five times. Thereafter, the temperature was raised to 150 ° C to completely dissolve the L- (or D-) lactide, and the amount of the reactant as a catalyst as a catalyst through the catalyst inlet Tin octoate was diluted with 100 mL of toluene and added to the reaction vessel. The reaction was carried out at 185 DEG C under a pressure of 1 kg of nitrogen for 2 hours, 200 ppm of phosphoric acid was added to the catalyst inlet and mixed for 15 minutes to inactivate the residual catalyst. Unreacted L- (or D-) lactide (about 5 wt.% Of the initial charge) was then removed through a vacuum reaction until it reached 0.5 Torr. The molecular weight, Tg and Tm of the obtained resin, the residual monomer content and the like were measured and are shown in Table 1 below.

Thermal hydrolysis (thermal melt extrusion) Test example

The resin compositions of the above Examples and Comparative Examples were dried under reduced pressure at 80 캜 for 6 hours under a vacuum of 1 Torr, and then the weight average molecular weight (Mw) was measured. Then, the melt-extruded product was extruded into a sheet at an extrusion temperature of 190 DEG C in a 30 mm single screw Haake extruder equipped with a T-die, and then the weight average molecular weight (Mw) was measured. The results are shown in Table 2 below.

Example of lactide regeneration test

The resin compositions of the above examples and comparative examples were each dried under reduced pressure at 80 ° C for 6 hours under a vacuum of 1 Torr and extruded into a sheet on an extruder (30 mm single screw Haake extruder) equipped with a T- Extruded, and cast on a drum cooled to 5 캜 by electrostatic casting to prepare a poly (lactic acid) sheet. Each polylactic acid sheet thus prepared was placed in a convection oven and stored at 180 ° C for 10 hours. At this time, the content of monomers remaining in the sheet was measured at the initial stage, one hour, three hours, five hours and ten hours. The results are shown in Table 3 below.

Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Monomer / catalyst usage ratio 30000 10000 6000 1800 450 Dibutyl tin dilaurate (ppm) 100 100 100 100 100 Tin octoate (ppm) 35 100 170 340 675 Total Sn content (ppm) 10 30 50 100 200 PPDO 2.4 (g) 378.8 378.8 378.8 378.8 378.8 HDI (g) 21.2 21.2 21.2 21.2 21.2 NCO / OH 0.8 0.8 0.8 0.8 0.8 OHV (KOH mg / g) 6 6 6 6 6 U626 (g) 3 3 3 3 3 L-lactide (g) 4000 4000 4000 4000 4000 Polyurethane polyol
Repeated unit content (% by weight) 10 10 10 10 10 Polymerization time (min) 120 90 80 60 50 Tg (占 폚) 42 42 42 42 42 Tm (占 폚) 168 168 168 168 168 Mw (x 1000 g / mol) 220 240 230 190 170 PDI 1.97 2.10 2.01 2.10 2.10 Residual monomer content (% by weight) 0.4 0.4 0.5 0.5 0.7

division Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Mw
(x 1000 g / mol) Before extrusion 220 240 230 190 170 After extrusion 195 210 180 120 100 Mw reduction rate (%) 11.4 12.5 21.7 36.8 41.2

Lactide regeneration test - Residual monomer content (wt.%) Elapsed time Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 0 hr 0.4 0.4 0.5 0.5 0.7 1 hr 0.4 0.4 0.6 0.6 1.1 3 hr 0.5 0.5 0.8 1.2 1.7 5 hr 0.6 0.5 0.9 2.1 2.9 10 hr 0.7 0.7 1.1 2.9 3.7

Referring to Table 1, the resin compositions of Examples and Comparative Examples were prepared by mixing poly (1,3-propanediol) (PPDO) having a molecular weight of 2,400 with 1,6-hexamethylene diisocyanate (NCO / OHV) (Or co-polymer) in which polyether polyol repeating units such as poly (1,3-propanediol), etc., are linearly linked and reacted with a polyisocyanate (HDI) to obtain a polyurethane polyol repeating unit Polylactic acid resin (block copolymer).

In the poly (lactic acid) resin, the polyurethane polyol repeating unit (or (co) polymer) has a value of OHV of 3 to 20, and can preferably serve as an initiator in the polymerization process for the formation of the poly . The resin compositions of the final prepared examples and comparative examples had 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 DEG C, a Tm of 160 to 178 DEG C, and a softening component (polyurethane polyol repeat unit) Is 5 to 20% by weight, and is a resin composition which can be made into a chip.

In particular, as shown in Table 1 above, the polylactic acid resin compositions of Examples 1 and 2 according to the present invention are characterized in that the amount of tin-based catalyst remaining in the composition is less than 50 ppm based on Sn, Melt extrusion), the effect of the back-binding reaction by the residual catalyst is small and the residual monomer content is small. On the other hand, in the case of the polylactic acid resin compositions of Comparative Examples 1 to 3 in which the amount of the tin-based catalyst was 50 ppm or more on the basis of Sn, the residual monomer content was higher than in the Examples.

Further, as shown in Table 2 above, the poly (lactic acid) resin compositions of Examples 1 and 2 according to the present invention had little effect on the back-binding reaction due to the residual catalyst even under high temperature thermal hydrolysis (thermal melt extrusion) On the other hand, the poly (lactic acid) resin compositions of Comparative Examples 1 to 3 show a very low molecular weight reduction rate under high temperature thermal hydrolysis conditions.

In addition, as shown in Table 3, the sheet extruded using the polylactic acid resin compositions of Examples 1 and 2 according to the present invention showed very little increase in the residual monomer content over time, while Comparative Examples 1 to 3 Of the polylactic acid resin composition, the content of the residual monomer is gradually increased with the elapse of time.

Claims (14)

A polylactic acid resin composition comprising a block copolymer and a catalyst,
Wherein the block copolymer comprises a) a hard segment comprising a polylactic acid repeat unit of the following formula (1), and b) a polyether polyol repeat unit of the following formula (2), wherein the diisocyanate compound having two terminal hydroxyl groups and two isocyanate groups in the molecule And a soft segment comprising a polyurethane polyol repeat unit linearly connected via a urethane bond formed by the reaction of the urethane bond,
Wherein the catalyst comprises a metal and the content of the catalyst relative to the weight of the polylactic acid resin composition is less than 50 ppm on a metal basis.
[Chemical Formula 1]

(2)

In the general formulas (1) and (2), 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 method according to claim 1,
Wherein the content of the catalyst relative to the weight of the poly (lactic acid) resin composition is 5 to 35 ppm on a metal basis.
The method according to claim 1,
Wherein the catalyst is selected from the group consisting of an alkaline earth metal catalyst, a rare earth metal catalyst, a transition metal catalyst, an aluminum catalyst, a germanium catalyst, a tin catalyst, an antimony catalyst and a mixture thereof.
The method of claim 3,
Wherein the catalyst comprises a tin-based catalyst.
The method according to claim 1,
Wherein the content of residual monomers in the composition is less than 0.5% by weight based on the weight of the polylactic acid resin composition.
6. The method of claim 5,
Wherein the poly (lactic acid) resin composition has a residual monomer content of 1.0% by weight or less after being stored at 180 DEG C for 10 hours.
The method according to claim 1,
Wherein the polylactic acid resin composition has an initial reduction ratio of weight average molecular weight of 20% or less upon thermal melt extrusion at 170 to 200 캜.
The method according to claim 1,
Wherein the diisocyanate compound is 1,6-hexamethylene diisocyanate (HDI).
The method according to claim 1,
In the polylactic acid resin composition, the molar ratio of the terminal hydroxyl group of the polyether polyol repeating units to the isocyanate group of the diisocyanate compound is 1: 0.50 to 1: 0.99.
The method according to claim 1,
Wherein the polylactic acid resin composition comprises a block copolymer in which a terminal carboxyl group of a polylactic acid repeating unit contained in the hard segment and an end hydroxyl group of the polyurethane polyol repeating unit are linked by an ester bond.
11. The method of claim 10,
Wherein the polylactic acid resin composition comprises the block copolymer and a polylactic acid repeating unit not bonded to the polyurethane polyol repeating unit.
The method according to claim 1,
Wherein the polylactic acid resin composition has a weight average molecular weight of 100,000 to 400,000.
The method according to claim 1,
And 65 to 95% by weight of the hard segment and 5 to 35% by weight of the soft segment based on the weight of the poly (lactic acid) resin composition.
The method according to claim 1,
Wherein the polyether polyol repeating unit has a number average molecular weight of 450 to 9,000.